Appalachian-Caledonian Orogenic system: a chronologically ordered listing of publications concerning the eastern Gondwanan margin (Gander-Avalon tectonic belts) of Newfoundland, the Canadian Maritimes, New England, and Anglesey (Wales)
The Google Earth files Avalon_Nashoba.kmz and New England.kmz located at http://instruct.uwo.ca/earth-sci/fieldlog/Google_Earth/ contain a random set of waypoints and map overlays relevant to this topic.
New England 1842-1957
Percival, J. G., 1842, Report on the geology of the of the state of Connecticut: New Haven, Osborn and Baldwin, 495 p., map.
Rice, W. N., and Gregory, H. E., 1906, Manual of the geology of Connecticut: State Geological and Natural History Survey of Connecticut, Bulletin 6, 273 p.
Foye, W. G., 1949, The geology of eastern Connecticut: State Geological and Natural History Survey of Connecticut. Bulletin 74, 100 p
Nichols, D. R., 1956, Bedrock geology of Narragansett Pier quadrangle, Rhode Island: U. S. Geological Survey Geologic Quadrangle Map GQ-0091, scale 1:24,000.
Jenness, S. 1957. Gander Lake (East Half), Newfoundland. Geol. Surv. Canada Map 3-1957 - referenced by Kennedy and McGonigle (have a copy of his thesis)
Jenness, S. 1958. Geology of the Lower Gander River ultrabasic belt, Newfoundland. Geol. Surv. Canada Report 12, 58 p. + 3 maps (have) - Map shows all units included in the Gander Lake Group as unit 5. However a unit composed of interbedded pyroclastics and basic lavas was differentiated as 5a; Pyroxenite (2); serpentinite (3, 3a) and gabbro (4) - units considered to be intrusive were not restricted to unit 5a.
Jenness, S. 1963. Terra Nova and Bonavista Map-areas Newfoundland (2D (E1/2) and 2C). Geol. Surv. Canada Memoir 327, 184 p. - referenced by Kennedy and McGonigle.
Williams, H. 1964. Botwood, Newfoundland. Geol. Surv. Canada Map 60-1963 - the Botwood map shows the Gander Lake Group divided into three units : unit 3 (Lower Gander Lake) - sheared micaceous grey quartzose greywacke and siltstone; unit 4 - altered basic to silicic volcanic rocks, and conglomerate; interlayered with unit 5 - grey to black slate and siltstone, greywacke and minor volcanic rocks. Unit 4 occurs as elongated lenses within unit 5,and both units are intruded by pyroxenites, gabbros, and (quartz-) diorites (9), and serpentinite (10).
Church, W.R. 1972. Ophiolite : its definition, origin as oceanic crust, and mode of emplacement in orogenic belts, with special reference to the Appalachians. Canada Dept. Energy, Mines, Resources, Earth Physics Branch Pub., 42, 71-85. - Fig 1 showing a "Gander Lake Ellsworth clastic zone", but commented that "The Gander Lake belt...represent Cordilleran-type ultramafic-mafic rocks related to Acadian (mid-Devonian) igneous and tectonic activity (cf. Chapman, 1968)". This comment was based on Chapmans conclusions concerning the intrusive nature of the coastal gabbro bodies of Maine and New Brunswick (St Stephen).
Kennedy, M.J. and McGonigal 1972. The Gander Lake and Davidsville
Groups of Northeastern Newfoundland: new data and geotectonic implications. CJES
9, 4, 452-459. - Map Fig 2 is very similar to that of Jeness (1957). They
subdivided the Gander Lake Group of Jeness into a lower Gander Lake Group unconformably overlain by a Davidsville group - also referred to as the
Sedimentary and Volcanic terrane (with a single steep penetrative slaty cleavage
or foliation) - which included the middle and upper units of Jeness's Gander
In the supposedly older Gander Lake Group (Metasedimentary terrane) "Mafic intrusive rocks, rare amphibolite and small serpentinite bodies also occur in this terrane". "Granitic intrusions are also present, together with deformed mafic and ultramafic rocks."
"On the northern shore of Gander Lake coarse greywackes of the Middle Ordovician sequence contain schistose clasts up to 1in across ... composed of psammite and mafic schist similar to rocks of the metasedimentary terane..." . They also recognised the existence of melange with large pieces of metamorphic rock up to 200 ft across, and large fragment of schistose garnetiferous leucocratic muscovite granite, and one schistose serpentinite fragment. The fragments exhibit pre-melange polyphase deformation."
"The melange zone" appears to be the basal member of the Davidsville Group in the north of the area, but it is absent further south." It may be tectonic and represent a zone of gravity sliding, indicating that the Davidsville Group is locally allochthonous or it may be an olistostrome."
"It seems possible the gneissic rocks underlie and form a sialic basement to the Avalon Platform sequence..."
"The significance of the melange zone overlying the Gander Lake Group is presently obscure. It appears to be the basal member of the of the Davidsville Group in the north of the area, but it is absent farther south. It may be tectonic and represent a zone of gravity sliding, indicating that the Davidsville is locally allochthonous or it may be an olistostrome." (Later Pajari and Currie 1978 would show this melange to be a continuous but relatively narrow unit within the upper Davidsville, but also present on Green Island, and at Rocky Bay and Aspen Cove.)
"Similar rocks with pre-Devonian structures may occur in southern New Brunswick (A.A. Ruitenberg, pers comm 1971)"
"The pre-lower Ordovician metasedimentary sequence of the west flank of the Mobile Belt (Fleur de Lys Supergroup) shows close structural and metamorphic similarities (Kennedy 1971) to the pre-Middle Ordovician metasedimentary Gander Lake Group of the east flank. Both metasedimentary terranes may have once formed part of a continuous terrane." "The Gander Lake Group could be interpreted as the western part of an analogous continental rise prism which thins eastwards on to the Avalon Platform." "resolution of the problem of Gander Lake - Fleur de Lys correlation will provide evidence for or against the presence of a pre-Ordovician ocean basin in Central Newfoundland."
Jenness 1972. CJES 9, 12, 1779-1781 - discussion
Kennedy and McGonigal 1972. CJES 9, 12, 1781-1783 - reply to Jeness - "Garnetiferous leucocratic granites on the south shore of Gander lake are intrusive into our Gander Lake Group but do not intrude the Davidsville Group." The granites are "clearly cut by the second schistosity of our Gander Lake Group."
"If there is only one age of mafic rocks and one age of ultramafic rocks in the area, Jeness' interpretations are correct." "The amphibolites of the metasedimentary terrane occur as polydeformed fragments in the basal Davidsville melange and in the graywackes of the Davidsville Group." "Ultramafic rocks intrude the greywackes of the Davidsville Group on the north shore of Gander Lake, but schistose serpentinite .... occurs as small bodies within our Gander Lake Group, which have clearly been deformed with the surrounding metasediments. Thus two separate suites of ultramafic rocks are present. The earlier, deformed with the metasedimentary terrane occurs as a large schistose serpentinite inclusion in the Davidsville melange between Musgrave Harbour and Carmanville... , and should not be confused with the serpentinites that intrude the overlying Davidsville Group..."
Berger, A. - 1972 discussion - It seems clear to me that the Aspen Cove Pluton (garnetiferous leucocratic granite) intrudes and is not unconformably overlain by the Middle Gander Lake Group..." " The ragged Harbour and Aspen Cove Plutons cannot, therefore, be pre-Middle Ordovician in age..."
Bruckner, J. 1972. CJES 9, p. 1778-1779 - discussion of Kennedy and McGonigal 1972.
Church, W.R. 1972. Ophiolite: its definition, origin as oceanic crust, and mode of emplacement in orogenic belts, with special reference to the Appalachians. The Ancient Oceanic Lithosphere. Canadian Contribution no 6 to the Geodynamics Project, v. 42, no. 3, 71-85.
Church, W. R., and Gayer, R. A. 1973. The Ballantrae ophiolite. Geol. Mag., 110, 497-510 - Exploits and Gander zones shown located on the SE side of Iapetus as Exploits-Tetagouche and Ellsworth-Gander zones, respectively.
Stevens, R.K., Strong, D. and Kean, B. 1974. - eastern Appalachian ultramafic rocks as mantle diapirs
Strong, D., Dickinson, O'Driscoll, and Kean, B. 1974. - east dipping Appalachian subduction zone
Malpas, J. and Strong, D. 1975. - the ophiolites represent mantle diapirs
Blair, R. 1975. The Shoal Pond ultramafic complex, Newfoundland. B.Sc. thesis, University of Western Ontario.
Church 1976. CJES Ages of zircons from the Bay of Islands ophiolite complex, western Newfoundland: Comment. Geology 4 623-625 - "the Cole Hill trondjhemite body within the Shoal Pond melange of the Gander Lake belt is associated with ophiolitic olistoliths which also are lithologically and chemically similar to units of the Betts Cove ophiolite." the ultramafic and mafic rocks of the Middle Gander Lake Group between Gander and Carmanville are present as chaotically distributed olistoliths (slide blocks) rather than as intrusive bodies ."
Rast, N., Kennedy, M.J., and Blackwood, R.F., 1976. Comparison of some tectonographic zones in the Appalachians of Newfoundland and New Brunswick. CJES, 13, 6, p. 868-875. "the Gander/Avalon Zone boundary in New Brunswick ...controlled the development of subsequent basin, which have been deformed by Taconic and Acadian movements." "In Newfoundland the same boundary has remained essentially inactive in Paleozoic times."
Bell, K., Blenkinsop, and Strong, D. 1977. The geochronology of some granitic bodies from eastern Newfoundland and its bearing on Appalachian evolution CJES 14, 456-476. - Fig 1, Gander zone, Botwood zone, Exploits zone, Fleur de Lys zone
Church, W.R. 1977. The ophiolites of southern Quebec: oceanic crust of Betts Cove type. CJES, 14, 1668-1673. - Fig 1 shows "Ellsworth-Gander Lake zone with a reference to the Shoal Pond ophiolite"
McKerrow and Cocks 1977. The location of the Iapetus Ocean suture in Newfoundland. Canadian Jour. Earth. Sci., 14, 488-495 - claim the Reach fault as the location of the Iapetus Ocean suture in Newfoundland
Church, W.R. 1977. Ophiolites of the Appalachian System. Association Mafiques ultra-mafiques dans les orogenes. Colloque Internationaux de C.N.R.S., Grenoble 1977, no. 272, 35-38. "The ophiolitic rocks of the eastern belt occur as blocks in the Shoal Pond ophiolitic melange.... Pyroxenes in gabbroic units, however, have very low Ti contents and in this respect resemble the Betts Cove ophiolite. It seems likely that the ophiolitic material was emplaced from the north-west into an exogeosynclinal basin developed with the eastern margin of the Appalachian system." Fig 1 - The ophiolitic melange is located within the Ellsworth-Gander Lake zone. "the clinopyroxenites ...are characterised by very low Ti contents. In this respect the Rhyd Y Bont complex closely resembles the Betts Cove and Gander Lake (Shoal Pond) ophiolites of Newfoundland, and the Asbestos - Thetford ophiolite of the Quebec..", "The Rhyd Y Bont complex could represent a section of dismembered oceanic lithosphere which following obduction was emplaced by gravity sliding into a marginal deep water basin accumulating muds, cherts and submarine volcanic rocks."
Church, W.R. 1977. Late Proterozoic Ophiolites. Association Mafiques ultra-mafiques dans les orogenes. Colloque Internationaux de C.N.R.S., Grenoble 1977, no. 272, p. 105-118.
Pajari, G.E. and Currie, K.L. 1978. The Gander Lake and Davidsville Groups of northeastern Newfoundland: a re-examination CJES 15, 708-714. - abst:"the ocean floor sequence of ultramafites, mafic volcanic rocks with minor plagiogranites and turbidites of the Davidsville Group proper were disturbed by olistostromes and tectonic slides beginning in late Ordovician time." "final tectonic emplacement occurred in the Devonian." "Southeast of the fault, the gneiss complex was metamorphosed to sillimanite grade before deposition of the Gander Lake Group."The Gander Lake Group may be time equivalent to the Davidsville Group." " The observed relations are compatible with obduction of oceanic material in late Ordovician time."
"we agree that the term (Davidsville Group) is a useful one to designate the assemblage of of black, greenish and maroon shale, slate, greywacke and siltstone with basal volcanic rocks, which seems to rest on an ultramafic base." "This association strongly resembles the ocean floor sequences of Notre Dame Bay to the west,.." " The two groups belong to quite different geological settings whose contacts are everywhere faulted." "or the ultramafic basement." "Blackwood (1977) has observed the Gander Lake Group resting unconformably on the gneiss complex." "The presence of ultramafic fragments within the Davidsville Group shows that the latter is younger than the ultramafic belt, and in some sense rests upon it." " these fact... strongly suggest an oceanic floor origin for the Davidsville Group and a mantle origin for its presumed ultramafic base" "Stratigraphic evidence on the age of the olistostromes shows that transport may have commenced as early as Arenig time." "Assuming that the Davidsville Group and the underlying ultramafic rocks represent oceanic material, this configuration is consistent with obduction of oceanic plate over continental crust." "Since the age is indeterminate, the evidence for the "Ganderian orogeny" (Kennedy 1975) evaporates." "The observed relations are compatible with obduction of oceanic material during Ordovician time."
Church, W.R. 1978. correspondance - The Gander ultramafic rocks are olistoliths within a fore-land basin olistostromal melange at the base of the Davidsville, the obduction complex from where it was derived is located further west.. It does not represent an in-situ obduction complex.
Pajari, G.E. and Currie, K.L., S.P. 1978. reply - "The Shoal Pond complex does not map as an "olistolith within shales "" "The Shoal Pond and Weir's Pond complexes consist of mafic volcanic and ultrabasic rocks which were topographic highs that shed their debris during Llanvirn time." "an unconformity.... has been observed at their top. These easterly obducted slabs were involved in a major olistostromal event which involved Caradocian sediments, and was therefore distinctly younger....."
"field evidence ... clearly proves that the Davidsville Group is autochthonous, and not transported."
"The Gander Lake and Davidsville Groups have been shown... to be a single sequence of sedimentation." "the ultramafic and volcanic rocks are allochthonous, and were thrust into this sequence in Llandeilo-Llanvirn time."
"we wish to apologise to the pioneers of plate tectonic models in Newfoundland for suggesting that the eastern margin of the mobile belt had not been explained. It was our intention to suggest that detailed models for the eastern side, such as those of Strong et al (1974), Malpas and Strong (1975) and Stevens et al (1974) were clearly inadequate to explain the observations."
Church, W.R. (1979). reply to reply "the Shoal Pond complex could be an olistolith since internally the sequence youngs westwards whereas ..... isolated blocks of leucogabbro within shales occur to the east of the basal ultramafic cumulate unit of the complex." "according to Jeness' thesis, and from a telephone conversation with Jeness himself, my understanding is that the locality from which McKerrow .....(McKerow and Cocks, 1977).... collected the Arenig fossils is located within rocks which contain blocks of pyroxenite and serpentinite. ......If the Arenig fossil locality is within the ophiolitic olistostrome unit, it implies that emplacement was Arenig, and that younger exogeosynclinal units 5 and 6 entirely post-date emplacement." "I can even conceive that the younger olistostrome units 9, 10 were derived from the east." "why is a Tremadocian age for the ophiolite erroneous"
Bruckner 1978. Curr. Res. Part C, Geol. Surv.Canada Paper 78-1C, p. 127-129 - discussion of Pickerill 1978
Blackwood, R.F. 1978. Rpt Activities 78-1
Currie, K., Pajari, G. and Pickerill, R. 1979. - Fig 14.1 Obduction model : Gander River Group = unit 4; oceanic floor is unit 1, unit 3 and the unit 2 volcanic assemblage; unit 5 (Davidsville) is now post-obduction and unconformable on the obducted ophiolite and on unit 4; unit 6 is coarse debris laterally equivalent to unit 5 deposited locally in the vicinity of the obducted slab. The upper olistostromal units are derived from the east.
Blackwood, R.F. 1979. Rpt Activities 79-1 -
Blackwood, R.F. 1979. - map 7929. Gander River SW 55E,49N; NE 54 30'E, 49 15'N
Currie, K., Pajari, G., and Pickerill, R. 1980. - "...the base of the Davidsville Group can be established by choosing the stratigraphically lowest occurrence of clastic rocks containing ultramafic or plagiogranite debris." "conodont assemblages from limestone immediately overlying ultrabasic rocks (Blackwood 1978),.."
Colman-Sadd, S.P. 1980. Geology of south-central Newfoundland and evolution of the eastern margin of Iapetus Am Jour Sci 280, 991-1017 - evolution of the eastern margin of Iapetus.
Pajari, G.E., Pickerill, R.K., and Currie, K.L. 1980. discussion Am Jour Sci 280, 934-935 - "Gander River Ultrbasic Belt slabs were emplaced during Davidsville Group time and specifically just prior to deposition of the of the Upper Llanvirn - Lower Llandeilo limestones ... and not during the Acadian deformation. The provenance of the sedimentary succession changed from a quart-rich terrain (Gander Group) to include a significant mafic, ultramafic, plagiogranite, and albite-porphyry component immediately following emplacement of the Gander River Ultrabasic belt slabs.."
Colman-Sadd, S.P. 1980. reply Am Jour Sci 280, 936-938. "I have proposed that it was not until the Silurian-Devonian Acadian orogeny that ultrabasic rocks of the Gander River belt came into tectonic contact (as opposed to sedimentary contact) with the Gander Group, and it was not until this orogeny that the Davidsville and Gander Groups were deformed." "(This view) is supported by recent mapping (Blackwood, 1980, and in press), which shows ultramafic rocks in fault contact with the Davidsville Group and completely surrounded by it. Emplacement of some ultramafic rocks must, therefore have post dated the sub-Davidsville unconformity."
Blackwood, R.F. 1980. - map of the Gander Lake area (Gander West) Rpt 80-1- detailed copy of Jenness's map
Blackwood, R.F. 1981 - map 81-100 West Gander Rivers and Dead Wolf Pond
(Geology of Anglesey)
New England 1958-1981Mikami, H. M., and Digman, R. E., 1957, The bedrock geology of the Guilford 15-minute quadrangle and a portion of the New Haven quadrangle: State Geological and Natural History Survey of Connecticut, Bulletin 86, 99 p.
Lundgren, L., Jr., Goldsmith, R., and Synder, G. L., 1958, Major thrust fault in southeastern Connecticut: Geological Society of America Bulletin, v. 69, n. 12, p. 1606.
Rodgers, J., Gates, R. M., and Rosenfeld, J. L., 1959, Explanatory Text for Preliminary Geological Map of Connecticut, 1956: State Geological and Natural History Survey of Connecticut Bulletin 84, 64 p.
Snyder, G. L., 1959, Bedrock geology of the Norwich Quadrangle, Connecticut: United States Geological Survey Quadrangle Report GQ-144, scale 1:24,000.
Goldsmith, R., 1959, Axial-plane folding in southeastern Connecticut; Article 169, U. S.: Geological Survey Professional Paper P-0424-C, p. C54-C57.
Feininger, T. G., 1963, Westerly Granite and related rocks of the Westerly-Bradford area: New England Intercollegiate Geological Conference Guidebook, 55th Annual Meeting, Providence, Rhode Island,55 p.
Lundgren, L., Jr., 1963, The bedrock geology of the Deep River quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report n. 13, 40 p.
Dixon, H. R., 1964, The Putnam Group of Eastern Connecticut: U. S. Geological Survey Bulletin, v. 1194-C, p. C1-C12.
Lundgren, L., 1964, The bedrock geology of the Essex quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report n. 15, 36 p.
Snyder, G.L., 1964, Petrochemistry and bedrock geology of the Fitchville Quadrangle, Connecticut: United States Geological Survey, Bulletin 1161-I, 63 p., with map, scale 1:24,000.
Feininger, T. G., 1965, Bedrock geologic map of the Ashaway quadrangle, Connecticut-Rhode Island: U. S. Geological Survey Geologic Quadrangle Map GQ-403, scale 1:24000.
Dixon, H. R., and Pessl, F., Jr., 1966, Geologic map of the Hampton Quadrangle, Windham County, Connecticut: U. S. Geological Survey Report, GQ-0468, scale: 1:24,000.
Lundgren, L., 1966a, Muscovite reactions and partial melting in southeastern Connecticut: Journal of Petrology,v. 7, p. 421–453.
Lundgren, L., Jr., 1966b, The bedrock geology of the Hamburg quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report N. 19, scale 1:24,000.
Lundgren, L., Jr., 1967, The bedrock geology of the Old Lyme quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report N. 21, scale 1:24,000.
Goldsmith, R., 1967a, Bedrock geologic map of the New London quadrangle: U. S. Geological Survey Geologic Quadrangle Map GQ-574, scale 1:24,000.
Goldsmith, R., 1967b, Bedrock geologic map of the Niantic quadrangle, New London County: U. S. Geological Survey Geologic Quadrangle Map GQ-575, scale 1:24,000.
Goldsmith, R., 1967c, Bedrock geologic map of the Montville quadrangle, New London County: U. S. Geological Survey Geologic Quadrangle Map GQ-609, scale 1:24,000.
Dixon, H. R., and Lundgren, L. W., 1968, Structure of eastern Connecticut, in Zen, E., White, W. S., Hadley, J. B., and Thompson, J. B., Jr., editors, Studies of Appalachian geology, northern and maritime: NewYork, Wiley Interscience Publishers, p. 219–229.
Feininger, T. G., 1968, The up dip termination of a large dike of Westerly Granite and the regional distribution of the Westerly and Narragansett Pier granites in Rhode Island and Connecticut: U. S. Geological Survey Professional Paper P-0600, p. D181–D185.
Osberg, P. H., 1968, Stratigraphy, structural geology, and metamorphism of the Waterville – Vassalboro area, Maine: Maine Geological Survey, Bulletin 20, 64 p.
Rickard, L. V., 1969. Stratigraphy of the Upper Silurian Salina Group, New York, Pennsylvania, Ohio, and Ontario: New York State Museum and Science Service Map and Chart Series 12, 57 p.
Rodgers, J., 1970, The tectonics of the Appalachians: New York, Wiley-Interscience, 271 p.
Buma, G., Frey, F. A., and Wones, D. R., 1971, New England granites: trace element evidence regarding their origin and differentiation: Contributions to Mineralogy and Petrology, v. 31, n. 4, p. 300–320.
Lundgren, L., Jr., and Ebblin, C., 1972, Honey Hill Fault in Eastern Connecticut - Regional Relations: Geological Society of America Bulletin, v. 83, n. 9, p. 2773–2794.
Tera, F., and Wasserburg, G. J., 1972, U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks: Earth and Planetary Science Letters, v. 14, p. 281–304.
Lundgren, L., Jr., and Thurrell, R. F., 1973, Bedrock geology of the Clinton quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report 29, 22 p.
Rickard, L.V., 1973. Stratigraphy and structure of the subsurface Cambrian and Ordovician carbonates of New York: New York State Museum and Science Service Map and Chart Series 18, 26 p.
Zietz, I., Kirby, J. R., Jr., and Gilbert, F. P., 1974, Aeromagnetic map of Connecticut: U. S. Geological Survey Geophysical Investigations Map GP-897, scale 1:125,000.
Bernold, S., 1976, Preliminary bedrock geologic map of the Guilford quadrangle, Connecticut: State Geological and Natural History Survey of Connecticut, Open File Report OF-76-1, scale 1:24,000.
Pankiwskyj, K. A., Ludman, A., Griffin, J. R., and Berry, W. B. N., 1976, Stratigraphic relationships on the southeast limb of the Merrimack synclinorium in Central and West-Central Maine, in Lyons, P. C., andBrownlow, A. H., editors, Studies in New England Geology: Geological Society of America Memoir, v. 146, p. 263–280.
Shride, A. F., 1976, Stratigraphy and correlation of the Newbury volcanic complex, northeastern Massachusetts, in Lyons, P. C., and Brownlow, A. H., editors, Contributions to the stratigraphy of New England:Geological Society of America Memoir, v. 148, p. 147–177.
Osberg, P. H., 1978, Synthesis of the geology of the Northern Appalachians, U.S.A.: Geological Survey of Canada Paper 78-13, p. 137–147.
Williams, H., 1978, Tectonic lithofacies map of the Appalachian orogen: Newfoundland, Canada, St. Johns, Memorial University of Newfoundland Map No. 1, scale 1:1,000,000.
Lundgren,L., 1979, The bedrock geology of the Haddam quadrangle: State Geological and Natural History Survey of Connecticut Quadrangle Report n. 37, 44 p.
Watson, E. B., 1979, Zircon saturation in felsic liquids: Experimental results and applications to trace element geochemistry: Contributions to Mineralogy and Petrology, v. 79, p. 407–419.
Wintsch, R. P., 1979, The Willimantic fault: A ductile fault in eastern Connecticut: American Journal of Science, v. 279, p. 367–393.
Pignolet, S., Grant, N. K., and Hickman, M. H., 1980, Rb-Sr geochronology of the Honey Hill Fault area, eastern Connecticut: Geological Society of America, Abstracts with Programs, v. 12, p. 77–78.
Zietz, I., Gilbert, F. P., and Kirby, J. R., 1980, Aeromagnetic map of Connecticut, Massachusetts, New Hampshire, Rhode Island, Vermont, and part of New York: U. S. Geological Survey GeophysicalInvestigations Map GP-928, scale 1:1,000,000
Gaudette, H. E., Vitrac-Michard, A., and Allegre, C. J., 1981, North American Precambrian history recorded in a single sample; high-resolution U-Pb systematics of the Potsdam Sandstone detrital zircons, New York State: Earth and Planetary Science Letters, v. 54, p. 248–260.
Pignolet, S., ms, 1981,
Rb-Sr geochronology of the Honey Hill Fault area, eastern Connecticut: Oxford,
Ohio, Miami University, Master’s thesis, 71 p.
Rodgers, J., 1981, The Merrimack synclinorium in northeastern Connecticut: American Journal of Science, v. 281,p. 176–186.
Newfoundland-Canadian Maritimes-New England 1982-present ( Geology of Anglesey )
Bellini, F. X., Corkum, D. H., and Stewart, A. J., 1982, Geology of foundation excavations at Seabrook Station, Seabrook, New Hampshire, in Farquhar, O. C., editor, Geotechnology in MassachusettsConference Proceedings 1980: Amherst, University of Massachusetts, Graduate School, p. 109–117.
Dallmeyer, R. D., 1982, 40Ar/39Ar ages from the Narragansett Basin and southern Rhode Island basement terrane; their bearing on the extent and timing of Alleghenian tectonothermal events in New England:Geological Society of America Bulletin, v. 93, n. 11, p. 1118–1130.
Goldstein, A. G., 1982, Geometry and kinematics of ductile faulting in a portion of the Lake Char mylonite zone, Massachusetts and Connecticut: American Journal of Science, v. 282, p. 1378–1405.
Lyons, J. B., Boudette, E. L., and Aleinikoff, J. N., 1982, The Avalonian and Gander zones in central eastern new England in St-Julien, P., and Beland, J., editors, Major Structural zones and faults of the Northern Appalachians: Geological Association of Canada Special Paper 24, p. 43–66.
O’Hara, K. D., and Gromet, L. P., 1983, Textural and Rb-Sr isotopic evidence for late Paleozoic mylonitization within the Honey Hill fault zone, southeastern Connecticut: American Journal of Science, v. 283,p. 762–779.
Watson, E. B., and Harrison, T. M., 1983, Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types: Earth and Planetary Science Letters, v. 64, p. 295–304.
Williams, H., and Hatcher, R. D., Jr., 1983, Appalachian suspect terranes, in Hatcher, R. D., Jr., Williams, H., and Zietx, I., editors, Contributions to the tectonics and geophysics of mountain chains: Geological Society of America Memoir, v. 158, p. 33–53.
Zen, E., Goldsmith, R., Ratcliffe, N. M., Robinson, P., and Stanley, R. S., compilers, 1983, Bedrock geologic map of Massachusetts: United States Geological Survey, Special Geologic Map, 3 sheets, Scale 1:
Bothner, W. A., Boudette, E. L., Fagan, T. J., Gaudette, H. E., Laird, J., and Olszewski, W. J., 1984, Geologic framework of the Massabesic Anticlinorium and the Merrimack Trough, southeastern New Hampshire,in Hanson, L. S., editor, Geology of the Coastal Lowlands; Boston, MA to Kennebunk, ME: Salem, Massachusetts, Department of Geological Sciences, Salem State College, New England Intercollegiate Geological Conference, Guidebook, v. 76, p. 186–206.
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Losh, S., and Bradbury, H. J., 1984, Late Paleozoic deformation within the Honey Hill-Lake Char fault zone, southern New England: Geological Society of America Abstracts with Programs, v. 16, n. 1, p. 48.Ludwig, K. R., 2002, Squid, version 1.05, A user’s manual: Berkeley Geochronology Center Special Publication, N. 2, 16 p.
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Zartman, R. E., and Naylor, R. S., 1984, Structural implications of some radiometric ages of igneous rocks in southeastern New England: Geological Society of America Bulletin, v. 95, p. 522–539.
Wonderley, P.F., and Neuman, R.B. 1984. The Indian Bay Formation: fossiliferous Early Ordovician volcanogenic rocks in the northern Gander Terrane, Newfoundland, and their regional significance. Canadian Journal of Earth Sciences, 21: 525-532.
Goldsmith, R., 1985a, Honey Hill fault and Hunts Brook syncline, in Tracy, R. J., editor, Guidebook for fieldtrips in Connecticut and adjacent areas of New York and Rhode Island, New Haven, Connecticut: New England Intercollegiate Geological Conference, 77th annual meeting, State Geological and Natural HistorySurvey of Connecticut, Guidebook n. 6, p. 491–507.
Goldsmith, R., 1985b, Bedrock geologic map of the Old Mystic and part of the Mystic quadrangles, Connecticut, New York, and Rhode Island: U. S. Geological Survey Miscellaneous Investigations Series Map I-1524, scale1:24,000.
Hermes, O. D., and Zartman, R. E., 1985, Late Proterozoic and Devonian plutonic terrane within the Avalon Zone of Rhode Island: Geological Society of America Bulletin, v. 96, n. 2, p. 272–282.
McLellan, E. L., and Stockman, S., 1985, Age and structural relations of granites, Stony Creek area, Connecticut, in Tracy, R. J., editor, Guidebook for fieldtrips in Connecticut and adjacent areas of NewYork and Rhode Island, New Haven, Connecticut: New England Intercollegiate Geological Conference,77th annual meeting, State Geological and Natural History Survey of Connecticut, Guidebook n. 6,p. 61–114.
Rodgers, J., 1985, Bedrock geological map of Connecticut: Hartford, Connecticut Geological and Natural History Survey, Department of Environmental Protection, scale 1:125,000.
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Wintsch, R. P., and Sutter, J. F., 1986, A tectonic model for the late Paleozoic of southern New England: Journal of Geology, v. 94, p. 459–472.
Webster, J. R., and Wintsch, R. P., 1987, Petrochemistry and origin of the Killingworth dome rocks, Bronson Hill anticlinorium, south-central Connecticut: Geological Society of America Bulletin, v. 98, p. 465–474.
Wintsch, R. P., and Aleinikoff, J. N., 1987, U-Pb isotopic and geologic evidence for late Paleozoic anatexis, deformation, and accretion of the late Proterozoic Avalon Terrane, southcentral Connecticut: AmericanJournal of Science, v. 287, p. 107–126.
Zartman, R. E., and Hermes, O. D., 1987, Archean inheritance in zircon from late Paleozoic granites from the Avalon Zone of southeastern New England; an African connection: Earth and Planetary ScienceLetters, v. 82, n. 3–4, p. 305–315.
Barosh, P. J., and Moore, G. E., Jr., 1988, The Paxton Group of southeastern New England: United States Geological Survey Bulletin, v. 1814, 18 p
Elbert, D. C., Harris, A. G., and Denkler, K. E., 1988, Earliest Devonian conodonts from marbles of the Fitch Formation, Bernardston Nappe, north-central Massachusetts: American Journal of Science, v. 288,p. 684–700.
Eusden, J. D., and Barreiro, B., 1988, The timing of peak high-grade metamorphism in central-eastern New England: Maritime Sediments and Atlantic Geology, v. 24, p. 241–255.
Goldsmith, R., 1988, Tectonic significance of dikes of Westerly Granite, southeastern Connecticut and southwestern Rhode Island: Northeastern Geology, v. 10, n. 3, p. 195–201.
Hozik, M. J., 1988, Tectonic implications of the brittle fracture history of the Permian Narragansett Pier Granite, Rhode Island, in Bartholomew, M. J., Hyndman, D. W., Mogk, D. W., and Mason, R., editors,Basement Tectonics 8: Characterization and comparison of ancient and Mesozoic continental margins:Proceedings of the Eighth International Conference on Basement Tectonics, v. 8, p. 503–525.
Smith, I. E. M., Brothers, R. N., Muiruri, R. G., and Browne, P. R. L., 1988, The geochemistry of rock and water samples from Curtis Island volcano, Kermadec group, southwest Pacific: Journal of Volcanologyand Geothermal Research, v. 34, p. 233–240.
Williams, H., Coleman-Saad, S. P., and Swinden, H. S., 1988, Tectonic-stratigraphic subdivisions of central Newfoundland: Current Research, Part B, Geological Survey of Canada Paper 88-1B, p. 91–98.
Zartman, R. E., and Haines, S. M., 1988, The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs—A case for bi-directional transport: Geochimica et Cosmochimica Acta, v. 52,p. 1327–1339.
Zartman, R. E., Hermes, O. D., and Pease, M. H., Jr., 1988, Zircon crystallization ages and subsequent isotopic disturbance events in gneissic rocks of eastern Connecticut and western Rhode Island:American Journal of Science, v. 288, p. 376–402.
Goldstein, A. G., 1989, Tectonic significance of multiple motions on terrane-bounding faults in the Northern Appalachians: Geological Society of America Bulletin, v. 101, p. 927–938.
Gromet, L. P., 1989, Avalonian terranes and late Paleozoic tectonism in southeastern New England; constraints and problems, in Dallmeyer, R. D., editor, Terranes in the Circum-Atlantic Paleozoicorogens: Geological Society of America Special Paper N. 230, p. 193–211.
Hogan, J. P., and Sinha, A. K., 1989, Compositional variation of plutonism in the coastal Maine magmatic province; mode of origin and tectonic setting: Augusta, Maine, Maine Geological Survey, Studies inMaine Geology, v. 4, p. 1–33.
Lyons, J. B., Bothner, W. A., Doolan, B. L., Hatch, N. L., Jr., Moench, R. H., and Stanley, R. S., 1989, Metamorphism and tectonics of eastern and central North America; v. 2, A transect through the NewEngland Appalachians: Washington, D. C., American Geophysical Union, 64 p.
Pease, M. H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: United States Geological Survey Bulletin no. 1796, 26 p., 1sheet.
Spear, F. S., and Harrison, T. M., 1989, Geochronologic studies in central New England; I, Evidence for pre-Acadian metamorphism in eastern Vermont: Geology, v. 18, p. 181–184.
Dipple, G. M., Wintsch, R. P., and Andrews, M. S., 1990, Identification of the scales of differential element mobility in a ductile fault zone: Journal of Metamorphic Geology, v. 8, n. 6, p. 645–661.
Skehan, J. W., and Rast, N., 1990, Pre-Mesozoic evolution of Avalon terranes of southern New England, in Socci, A. D., Skehan, J. W., and Smith, G. W., editors, Geology of the Composite Avalon Terrane ofSouthern New England: Geological Society of America Special Paper, v. 245, p. 13–53.
Tucker, R. D., and Robinson, P., 1990, Age and setting of the Bronson Hill magmatic arc; a re-evaluation based on U-Pb zircon ages in southern New England: Geological Society of America Bulletin, v. 102,p. 1404–1419.
Wintsch, R. P., Andrews, M. S., and Ambers, C. P., 1990, Thrust napping versus fold napping in the Avalon terrane of southeastern Connecticut, in Socci, A. D., Skehan, J. W., and Smith, G. W., editors, Geology ofthe composite Avalon terrane of southern New England: Geological Society of America Special Paper,v. 145, p. 209–233.
Wintsch, R. P., Webster, J. R., Bernitz, J. A., and Fout, J. S., 1990, Geochemical and geological criteria for the discrimination of high grade gneisses of intrusive and extrusive origin, southern Connecticut, in Socci,A. D., Skehan, J. W., and Smith, G. W., editors, Geology of the composite Avalon terrane of southernNew England: Geological Society of America Special Paper, v. 245, p. 187–208.
Ayuso, R. A., and Bevier, M. L., 1991, Regional differences in Pb isotopic compositions of feldspars in plutonic rocks of the northern Appalachian Mountains, U.S.A., and Canada: A geochemical method ofterrane correlation: Tectonics, v. 10, p. 191–212.
Goldsmith, R., 1991a, Structural and metamorphic history of eastern Massachusetts: United States Geological Survey Professional Paper 1366-H, p. H1–H63.
Goldsmith, R., 1991b, Stratigraphy of the Nashoba zone, eastern Massachusetts: an enigmatic terrane: United States Geological Survey Professional Paper 1366-F, p. F1–F22.
Ratcliffe, N. M., Aleinikoff, J. N., Burton, W. C., and Karabinos, P. A., 1991, Trondhjemitic, 1.35-1.31 Ga gneisses of the Mount Holly Complex of Vermont; evidence for an Elzevirian event in the Grenvillebasement of the United States Appalachians: Canadian Journal of Earth Sciences, v. 28, p. 77–93.
Robinson, P., and Goldsmith, R., 1991, Stratigraphy of the Merrimack Belt, central Massachusetts: United States Geological Survey Professional Paper 1366-E-J, p. G1–G37.
Zartman, R. E., and Marvin, R. F., 1991, Radiometric ages of rocks in Massachusetts, in Hatch, N. L., Jr., editor, The bedrock geology of Massachusetts: United States Geological Survey Professional Paper1366J, p. J1–J19.
Barr, S. M., and Hegner, E., 1992, Nd isotopic compositions of felsic igneous rocks in Cape Breton, Nova Scotia: Canadian Journal of Earth Sciences, v. 29, p. 650–657.
Church, W.R. 1992. Intra-Iapetus brachiopods from the Ordovician of eastern Ireland: implications for Caledonide correlation CJES, 29, 4, p. 830-832, p. 833-834 - "faunas with supposed 'Celtic' affinities were subsequently found south of the Reach Fault in Arenig sediments (Jenness 1963; McKerrow and Cocks 1977; Neuman 1984) overlying GRUB line ophiolites (high-Cr low-Ti primitive arc type material) obducted onto rocks of the Gander Group; in rocks of the Baie d'Espoir Group (cf. Orthambonites cf. Productorthis, Colman-Sadd 1976) of southeast Newfoundland; in tuff associated with pillow lava of the Indian Bay Formation within the Gander zone (Wonderly and Neuman 1984); and more recently (Colman-Sadd and Swinden 1984; Dec and Colman-Sadd 1990), in ophiolite debris-bearing limestone conglomerates above the Spruce Brook Formation (Mount Cormack window of Gander Terrane rocks?). "
Church, W.R. 1992. Discussion on the trace of the Iapetus suture in Ireland and Britain CJES 149, 1048-1049 - "If the GRUB line ophiolites of Newfoundland to the south of the amalgamated oceanic arcs of the Exploits zone are not remnants of Iapetan oceanic crust, what do they represent? Petrographically and chemically they are more similar to primitive arc ophiolites than to oceanic crust, and could have formed above a northwesterly dipping subduction zone within the southernmost part of Iapetus. In this respect they are the mirror image of the Betts Cove - Ballantrae - Highland Border ophiolites of the northern Iapetan margin. In the British Caledonides, a possible analogue to the GRUB ophiolites is the Rhyd Bont ophiolitic fragment within the New Harbour fore-deep succession of Anglesey." Geology of Anglesey
Getty, S. R., and Gromet, L. P., 1992, Geochronological constraints on ductile deformation, crustal extension, and doming about a basement-cover boundary, New England Appalachians: American Journal of Science, v. 292, p. 359–397.
Goldstein, A. G., 1992, Motion on the Clinton-Newbury and related faults and multiple deformation of the Merrimack Group in eastern Massachusetts; aspects of the Alleghanian Orogeny in southeastern New England, inRobinson, P., and Brady, J. B., editors, Guidebook for fieldtrips in the Connecticut Valley region ofMassachusetts and adjacent states: New England Intercollegiate Geological Conference 84th annual meeting, University of Massachusetts Geology Department Contribution, v. 66–1, p. 120–131.
Soper, N.J., Strachan, R.A., Holdsworth, R.E., Gayer, R.A., and Greiling, R.O. , 1992. Sinistral transpression and the Silurian closure of Iapetus. JGS, v. 149, p. 871-880. - place the suture along the Solway line in Scotland and Ireland but along the Dover Fault separating the Gander and Avalon zones in Newfoundland.
West, D. P., Jr., Ludman, A., and Lux, D. R., 1992, Silurian age for the Pocomoonshine Gabbro-Diorite, southeastern Maine and its regional tectonic implications: American Journal of Science, v. 292,p. 253–273.
Wintsch, R. P., Sutter, J. F., Kunk, M. J., Aleinikoff, J. N., and Dorais, M. J., 1992, Contrasting P-T-t paths: Thermochronologic evidence for a Late Paleozoic final assembly of the Avalon composite terrane in theNew England Appalachians: Tectonics, v. 11, n. 3, p. 672–689.
Bothner, W.A., Gaudette, H. E., Fargo, T. G., Bowring, S. A., and Isachsen, C. E., 1993, Zircon and sphene U/Pb ages of the Exeter Pluton: constraints on the Merrimack Group and part of the Avalon composite terrane: Geological Society of America, Abstracts with Programs, v. 25, p. 485.
Holdaway, M. J., and Mukhopadhyay, B., 1993, A re-evaluation of the stability relations of andalusite: Thermochemical data and phase diagram for the aluminum silicates: American Mineralogist, v. 78,p. 298–315.
Hussey, A. M, II, Aleinikoff, J. N., and Marvinney, R. G., 1993, Reinterpretation of age and correlation between tectonostratigraphic units, southwestern Maine: Geological Society of America, Abstracts withPrograms, v. 25, p. 25.
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Sevigny, J. H., and Hanson, G. N., 1993, Orogenic evolution of the New England Appalachians of southwestern Connecticut: Geological Society of America Bulletin, v. 105, p. 1591–1605.
Wintsch, R. P., Sutter, J. F., Kunk, M. J., Aleinikoff, J. N., and Boyd, J. L., 1993, Alleghanian assembly of Proterozoic and Paleozoic lithotectonic terranes in south central New England: New constraints fromgeochronology and petrology, in Cheney, J. T., and Hepburn, T. C., editors, Field Trip Guidebook for the Northeastern United States, 1993, Boston GSA: University of Massachusetts, Geology Department, Contribution No. 67, v. 1, p. H1–H30.
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Goldstein, A. G., 1994, A shear zone origin for Alleghanian (Permian) multiple deformation in eastern Massachusetts: Tectonics, v. 13, p. 62–72.
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Lin, S., van Staal, C. R., and Dube, B., 1994, Promontory-promontory collision in the Canadian Appalachians: Geology, v. 22, p. 897–900.
Moecher, D. P., and Wintsch, R. P., 1994, Deformation-induced reconstitution and local resetting of mineral equilibria in polymetamorphic gneisses; tectonic and metamorphic implications: Journal of Metamorphic Geology, v. 12, p. 523–538.
Rankin, D. W., 1994, Continental margin of the Eastern United States; past and present, in Speed, R. C.,editor, Phanerozoic evolution of North American continent-ocean transitions, Boulder, CO: Geological Society of America, DNAG Continent-ocean transect volume, p. 129–218.
van Staal, C. R., 1994, Brunswick subduction complex in the Canadian Appalachians: record of Late Ordovician to Silurian collision between Laurentia and the Gander margin of Avalon: Tectonics, v. 13,p. 946–962.
Whalen, J. B., Jenner, G. A., Currie, K. L., Barr, S. M., Longstaffe, F. J., and Hegner, E., 1994, Geochemical and isotopic characteristics of granitoids of the Avalon Zone, New Brunswick: Possible evidence for repeated delamination events: Journal of Geology, v. 102, p. 269–282.
Wintsch, R. P., 1994, Bedrock geologic map of the Deep River area, Connecticut with explanatory text: State Geological and Natural History Survey of Connecticut, Open File Report OF-94-1, scale 1:24,000.
Drummond, M. S., Bordelon, M., De Boer, J. Z., Defant, M. J., Bellon, H., and Feigenson, M. D., 1995,Igneous petrogenesis and tectonic setting of plutonic and volcanic rocks of the Cordillera de Talamanca, Costa Rica–Panama, Central American arc: American Journal of Science, v. 295, p. 875–919.
Fargo, T. R., and Bothner, W. A., 1995, Polydeformation in the Merrimack Group, southeastern New Hampshire and southwestern Maine: Geological Society of America, Abstracts with Programs, v. 27,p. 42.
Hepburn, J. C., Dunning, G. R., and Hon, R., 1995, Geochronology and regional tectonic implications of Silurian deformation in the Nashoba Terrane, southeastern New England, U.S.A., in Hibbard, J. P., van Staal, C. R., and Cawood, P. A., editors, Current perspectives in the Appalachian-Caledonian Orogen: Geological Association of Canada, Special Paper 41, p. 349–365.
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Ortega-Gutierrez, F., Ruiz, J., and Centeno-Garcia, E., 1995, Oaxaquuia, a Proterozoic microcontinent accreted to North America during the late Paleozoic: Geology, v. 23, p. 1127–1130.
Sevigny, J. H., 1995, Late-Taconian and pre-Acadian history of the New England Appalachians of southwestern Connecticut: Geological Society of America Bulletin, v. 107, p. 487–498.
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Stewart, D. B., Tucker, R. D., and West, D. P., Jr., 1995, Genesis of Silurian composite terrane in northern Penobscot Bay, in Hussey, A. M., II, and Johnston, R. A., editors, Guidebook to field trips in southern Maine and adjacent New Hampshire: Augusta, Maine, Maine Geological Survey, New England Intercollegiate Geological Conference, Guidebook 87, p. 29–49.
Stewart, D.B., Unger, J.D., and Hutchinson, D.R., 1995, Silurian tectonic history of Penobscot Bay region, Maine: Atlantic Geology, v. 31, no. 2, p. 67 79.
West, D. P., Jr., Guidotti, C. V., and Lux, D. R., 1995, Silurian orogenesis in the western Penobscot Bay region, Maine: Canadian Journal of Earth Sciences, v. 32, p. 1845–1858.
Barr, S. M., and White, C. E., 1996, Contrasts in late Precambrian-early Paleozoic tectonothermal history between Avalon composite terrane sensu stricto and other possible peri-Gondwanan terranes in southernNew Brunswick and Cape Breton Island, Canada, in Nance, R. D., and Thompson, M. D., editors, Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic: Boulder, Colorado, Geological Society of America Special Paper 304, p. 95–108.
Harper, D. A., Mac Niocaill, C., and Williams, S. H., 1996, The palaeogeography of Early Ordovician Iapetus terranes: An integration of faunal and palaeomagnetic constraints: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 121, p. 297–312.
Lathrop, A. S., Blum, J. D., and Chamberlain, C. P., 1996, Nd, Sr, and O isotopic study of the petrogenesis of two syntectonic members of the New Hampshire Plutonic Series: Contributions to Mineralogy and Petrology, v. 124, p. 126–138.
Nance, R. D., and Murphy, J. B., 1996, Basement isotopic signatures and Neoproterozoic paleogeography of Avalonian-Cadomian and related terranes in the circum-North Atlantic, in Nance, R. D., and Thompson,M. D., editors, Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic: Boulder, Colorado, Geological Society of America Special Paper 304, p. 333–346.
O’Brien, S. J., O’Brien, B. H., Dunning, G. R., and Tucker, R. D., 1996, Late Neoproterozoic Avalonian and related peri-Gondwanan rocks of the Newfoundland Appalachians, in Nance, R. D., and Thompson,M. D., editors, Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic: Boulder, Colorado, Geological Society of America Special Paper 304, p. 9–28.
van Staal, C. R., Sullivan, R. W., and Whalen, J. B., 1996, Provenance and tectonic origin of the Gander Zone in the Caledonian/Appalachian orogen: Implications for the origin and assembly of Avalon, in Nance,R. D., and Thompson, M. D., editors, Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic: Boulder, Colorado, Geological Society of America Special Paper 304, p. 347–367.
Whalen, J. B., Fyffe, L. R., Longstaffe, F. J., and Jenner, G. A., 1996, The position and nature of the Gander-Avalon boundary, southern New Brunswick, based on geochemical and isotopic data from granitoid rocks: Canadian Journal of Earth Sciences, v. 33, p. 129–139.
Coleman, M. E., Pulver, M., Byrne, T. B., Kiyokawa, S., Wintsch, R., David, K. L., and Martin, M., 1997, Late Paleozoic shortening and metamorphism within the Bronson Hill Terrain, central Connecticut: Geological Society of America Abstracts with Programs, v. 29, n. 6, p. 231.
Donohue, C. L., Laird, J., and Bothner, W. A., 1997, Prograde metamorphism in the Berwick Fm. calc-silicates, Merrimack Group, southeastern New Hampshire: Geological Society of America, Abstracts with Programs. v. 29, p. 41–42.
Forster, H. J., Tischendorf, G., and Trumbull, R. B., 1997, An evaluation of the Rb vs. (Y _ Nb) discrimination diagram to infer tectonic setting of silicic igneous rocks: Lithos, v. 40, p. 261–293.
Kerr, A., 1997, Space-time composition relationships among Appalachian-cycle plutonic suites in Newfoundland, in Sinha, A. K., Whalen, J. B., and Hogan, J. P., editors, The Nature of Magmatism in theAppalachian Orogen: Boulder, Colorado, Geological Society of America Memoir 191, p. 193–220.
Lyons, J. B., Bothner, W. A., Moench, R. H., and Thompson, J. B., Jr., 1997, Bedrock Geologic Map of New Hampshire: United States Geological Survey Map Series, scales 1:250,000 and 1:500,000.
MacNiocaill, C., van der Pluijm, B. A., and Van der Voo, R., 1997, Ordovician paleogeography and the evolution of the Iapetus ocean: Geology, v. 25, p. 159–162.
Joanne K. Prigmore, Andrew J. Butler, and Nigel H. Woodcock 1997. Rifting during separation of eastern Avalonia from Gondwana; evidence from subsidence analysis Geology; v. 25; no. 3 March, p. 203-206.
Pulver, M. H., Coleman, M. E., Byrne, T., Wintsch, R. P., Kunk, M. J., Boyd, J. L., and Dunnigan, J., 1997,Structure and chronology of a section of the Bronson Hill Terrane; significance for late Paleozoic to early Mesozoic exhumation in south-central New England: Geological Society of America Abstracts with Programs, v. 29, n. 6, p. 231.
Ratcliffe, N. M., Walsh, G. J., and Aleinikoff, J., 1997, Basement, metasedimentary and tectonic cover of the Green Mountain massif and western flank of the Chester dome, in Grover, T. W., Mango, H. N., andHasenohr, E. J., editors, New England Intercollegiate Geological Conference: Castleton, Vermont, Guidebook to Field Trips in Vermont and adjacent New Hampshire and New York, 89th Annual Meeting, p. C6: 1–54.
Whalen, J. B., van Staal, C. R., Longstaffe, F. J., Gariepy, C., and Jenner, G. A., 1997, Insights into tectonostratigraphic zone identification in southwestern Newfoundland based on isotopic (Nd, O, Pb)and geochemical data: Atlantic Geology, v. 33, p. 231–241.
Goldstein, A. G., 1998, Lake Char-Honey Hill-Clinton Newbury fault system from southern Massachusetts to southern Connecticut; low-angle normal faults in the Northern Appalachians and their tectonic significance, in Murray, D. P., editor, Guidebook for fieldtrips in Rhode Island and adjacent regions of Connecticut and Massachusetts, Kingston, RI: New England Intercollegiate Geological Conference, 90th annual meeting, p. A1.1-A1.20.
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Karabinos, P., Samson, S. D., Hepburn, J. C., and Stoll, H. M., 1998, Taconian orogeny in the New England Appalachians: Collision between Laurentia and the Shelburne Falls arc: Geology, v. 26, p. 215–218.
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Robinson, P., Tucker, R. D., Bradley, D., Berry, H. N., IV., and Osberg, P. H., 1998, Paleozoic orogens in New England, USA: GFF, v. 120, p. 119–148.
van Staal, C. R., Dewey, J. F., Mac Niocaill, C., and McKerrow, W. S., 1998, The Cambrian-Silurian tectonic evolution of the northern Appalachians and British Caledonides: History of a complex, west and southwest Pacific-type segment of Iapetus, in Blundell, D. J., and Scott, A. C., editors, Lyell: the Past is the Key to the Present: London, Geological Society Special Publication, v. 143, p. 199–242.
Whalen, J. B., Rogers, N., van Staal, C. R., Longstaffe, F. J., Jenner, G. A., and Winchester, J. A., 1998,Geochemical and isotopic (Nd, O) data from Ordovician felsic plutonic and volcanic rocks of the Miramichi Highlands: petrogenetic and metallogenetic implications for the Bathurst Mining Camp: Canadian Journal of Earth Sciences, v. 35, p. 237–252.
Wintsch, R. P., Coleman, M., Pulver, M., Byrne, T., Aleinikoff, J., Kunk, M., and Roden-Tice, M., 1998, Late Paleozoic deformation, metamorphism, and exhumation in central Connecticut, in Murray, D. P.,editor, Guidebook for field trips in Rhode Island and adjacent regions of Connecticut and Massachusetts, Kingston, Rhode Island: New England Intercollegiate Geological Conference, 90th annual meeting, p. C2.1-C2.21.
Acaster, M., and Bickford, M. E., 1999, Geochronology and geochemistry of Putnam-Nashoba Terrane metavolcanic and plutonic rocks, eastern Massachusetts; constraints on the early Paleozoic evolution of eastern North America: Geological Society of America Bulletin, v. 111, p. 240–253.
Fyffe, L. R., Pickerill, R. K., and Stringer, P., 1999, Stratigraphy, sedimentology and structure of the Oak Bay and Waweig formations, Mascarene Basin: implications for the paleotectonic evolution of southwestern New Brunswick: Atlantic Geology. v. 35, p. 59–84.
Goldstein, A., and Hepburn, J. C., 1999, Possible correlations of the Norumbega fault system with faults in southeastern New England, in Ludman, A., and West, D. P., Jr., editors, Norumbega fault system of the Northern Appalachians: Geological Society of America Special Paper, v. 331, p. 73–83.
Greenough, John D., Krogh, Tom E., Kamo, Sandra L., Owen, J. Victor, and Ruffman, Alan, 1999. Precise U–Pb dating of Meguma basement xenoliths: new evidence for Avalonian underthrusting1 . CJES, v, 36, p. 15-22 Slightly discordant (1.6%), “facetted” zircons from a mafic granulite indicate a minimum crystallization age of 629 Ma, with near concordant (0.7%) rounded zircons suggesting a maximum age for the last metamorphic event affecting the zircons at 575 Ma. Two near concordant (–0.9 to 0.4%) monazite fractions from a pelitic granulite indicate a major metamorphic disturbance at 378 ± 1 Ma, 10 Ma prior to dyke entrainment and coincident with Meguma regional metamorphism. Projections from 378 Ma through four highly discordant (15–42%) metapelite zircon fractions give provenance ages between 880 and 1050 Ma and two others project to maximum ages of 1530 Ma. Unlike Meguma sediments which lack Grenvillian age ( 1 Ga) detrital zircons and are dominated by 2000 Ma detrital zircons, these dates indicate a dominantly Grenvillian age provenance for the pelitic xenoliths. The “Avalonian” igneous, metamorphic, and provenance ages from the xenoliths suggest the Meguma rests on Avalonian basement. Because Avalonian sediments need a Grenvillian provenance and Meguma sediments lack such a source but require a ³2.0 Ga component missing in the xenoliths, it seems unlikely the Meguma was deposited on Avalonian crust. Thus the dating places on firmer footing the suggestion from earlier structural, seismic, and geochemical work that the Meguma structurally overlies Avalonian terrane. Thrusting occurred between the time of earliest Meguma deformation ( 400 Ma) and intrusion of the xenolith bearing dyke ( 370 Ma).
Hussey, A. M., II, Ludman, A., Bothner, W. A., and West, D. P., Jr., 1999. Fredericton and Merrimack troughs;once one or always two?: Geological Society of America, Abstracts with Programs, v. 31, p. 25.
Spear, F. S., Kohn, M. J., and Cheney, J. T., 1999, P-T paths from anatectic pelites: Contributions to Mineralogy and Petrology, v. 134, p. 17–32.
Tassinari, C. C. G., and Macambira, M. J. B., 1999, Geochronological provinces of the Amazonian Craton:Episodes, v. 22, p. 174–182.
Bradley, D. C., Tucker, R. D., Lux, D. R., Harris, A. G., and McGregor, D. C., 2000, Migration of the Acadian Orogen and foreland basin across the Northern Appalachians of Maine and adjacent areas: United States Geological Survey, Professional Paper, v. 1624, 55 p.
Dorais, M. J., and Paige, M. L., 2000, Regional geochemical and isotopic variations of northern New England plutons: Implications for magma sources and for Grenville and Avalon basement-terrane boundaries: Geological Society of America Bulletin, v. 112, p. 900–914
Eusden, J. Dykstra,
Jr., Guzofski, Chris A., Robinson, Alexander C.
and Tucker, Robert D. 2000.
Timing of the Acadian Orogeny in
Northern New Hampshire. The Journal of Geology, v.
108, p. 219 232 .
The out of sequence thrust nappe propagation proposed in figure 4 could have been created by a tectonic buttress (dashed vertical line within Avalon composite in fig 4B 4C) that formed in Pre Ludlovian times along the Maine coast as the St. Croix and Ellsworth terranes accreted (Rankin 1994; Stewart et al. 1995). This orogenic belt, formed just prior to and flanking the southeast margin of the Acadian Orogeny, may have served as a barrier precluding southeast migration of the Acadian orogenic front. This northwest subduction along the Laurentian margin in figure 4 is consistent with the recent tectonic interpretations of Karabinos et al. (1998) for the Bronson Hill Arc in Vermont and New Hampshire and van Staal (1994) for the Brunswick subduction complex in New Brunswick.
Developed principally to illustrate the complexities of Taconian orogenic effects in the Ordovician, both models show a west dipping slab geometry and B type subduction during the latest Ordovician and earliest Silurian along the Bronson Hill. If this slab geometry persisted throughout at least some of the Acadian, one would expect east vergent, syncollisional, thrust nappe structures and olistostromal facies along the Bronson Hill, as Eusden et al. (1996a) have previously reported for the Presidential Range. Though it is not within the scope of this article to explain the west vergent structures seen 100 km along strike in the Connecticut Valley region (Robinson et al. 1991), we suggest that the New Zealand plate boundary can again be used as an analog. Pettinga and Wise (1994) suggest a flower structure exists due to transfer along the Alpine Fault from the Puysegur trench with east dipping subduction to the Hikurangi trench with west dipping subduction. In this model, both east and west verging structures exist, separated by approximately only 100 km along strike, close to the geometry of thrust nappes observed in the CMT of New Hampshire.
Samson, S. D., Barr, S. M., and White, C. E., 2000, Nd isotopic characteristics of terranes within the Avalon Zone, southern New Brunswick: Canadian Journal of Earth Sciences, v. 37, p. 1039–1052.
Tassinari, C. C. G., Betterncourt, J. S., Geraldes, M. C., Macambira, M. J. B., and Lafon, J. M., 2000, The Amazonian Craton, in Cordani, U. G., Milani, E. J., Thomaz Filho, A., editors, Grafica e Programacao Visual: Rio de Janeiro, Brazil (BRA), p. 41–95.
Thompson, M. D., and Bowring, S. A., 2000, Age of the Squantum ?Tillite? Boston basin, Massachusetts: U-Pbzircon constraints on terminal Neoproterozic glaciation: American Journal of Science, v. 300, p. 630–655.
Williams, I. S., and Hergt, J. M., 2000, U-Pb dating of Tasmanian dolerites: A cautionary tale of SHRIMP analysis of high-U zircon, in Woodhead, J. D., and others, editors, Beyond 2000: New frontiers in isotope research, Lorne, Australia, abstracts and proceedings: Melbourne, Australia, University of Melbourne, p. 185–188.
Cawood, P. A., McCausland, P. J. A., and Dunning, G. R., 2001, Opening Iapetus; constraints from the Laurentian margin in Newfoundland: Geological Society of America Bulletin, v. 113, p. 443–453.
Dorais, M. J., and Wintsch, R. P., 2001, A Laurentian provenance of the Merrimack Belt, New England Appalachians: Geological Society of America, Abstracts with Programs, v. 33, p. 261.
McLennan, S. M., Bock, B., Compston, W., Hemming, S. R., and McDaniel, D. K., 2001, Detrital zircon geochronology of Taconian and Acadian foreland sedimentary rocks in New England: Journal of Sedimentary Research, v. 71, p. 305–317.
Tucker, R. D., Osberg, P. H., and Berry, H. N., IV, 2001, The geology of a part of Acadia and the nature of the Acadian orogeny across central and eastern Maine: American Journal of Science, v. 301, p. 205–260.
Winter, J. D., 2001, An Introduction to Igneous and Metamorphic Petrology: Upper Saddle River, New Jersey, Prentice Hall, 697 p.
Wintsch, R. P., Kelsheimer, K. L., Kunk, M. J., and Aleinikoff, J. N., 2001, A new look at the Alleghanian overprint of Acadian metamorphic rocks in southern New England: Evidence from structure, petrology and thermochronology, in West, D. P., and Bailey, R. H., editors, Guidebook for geological field trips in New England: Boston, Geological Society of America Annual Meeting, p. V1–V26.
Aleinikoff, J. N., Wintsch, R. P., Fanning, C. M., and Dorais, M. J., 2002, U-Pb geochronology of zircon and polygenetic titanite from the Glastonbury Complex, Connecticut, USA: An integrated SEM, EMPA,TIMS, and SHRIMP study: Chemical Geology, v. 188, n. 1–2, p. 125–147.
Barr, S. M., White, C. E., and Miller, B. V., 2002, The Kingston Terrane, southern New Brunswick, Canada; evidence for an Early Silurian volcanic arc: Geological Society of America Bulletin, v. 114, p. 964–982.
Barr, S. M., White, C. E., Miller, B. V., and van Staal, C. R., 2002, The myth of “Avalonia”: Did it constitute a single terrane or several different terranes in the early Paleozoic: Geological Society of America Abstracts with Programs, v. 34, n. 1, p. A28.
Bradley, D. C., and Tucker, R., 2002, Emsian synorogenic paleogeography of the Maine Appalachians: Journal of Geology, v. 110, p. 483–492.
Hussey, A. M., II, and Berry, H. N., IV, 2002, Bedrock geology of the Bath 1:100,000 map sheet, coastal Maine: Maine Geological Survey, Bulletin 42, 50 p.
Hussey, A. M., II, and Marvinney, R. G., 2002,
Bedrock geology of the Bath 1:100,000 quadrangle, Maine: Maine Geological
Survey, Open-File Map 02-152, scale 1:100,000.
Miller, B. V., and Fyffe, L. R., 2002, Geochronology of the Letete and Waweig Formations, Mascarene Group, southwestern New Brunswick: Atlantic Geology, v. 38, p. 29–36.
Taggart, J. E., and Siems, D. F., 2002, Major element analysis by wavelength dispersive X-ray fluorescence spectrometry: U.S. Geological Survey Open-File Report OF-02-0223, p. T1–T9.
Teyssier, C., and Whitney, D. L., 2002, Gneiss domes and orogeny: Geology, v. 30, p. 1139–1142.
Barr, S. M., Davis, D. W., Kamo, S., and White, C. E., 2003, Significance of U-Pb detrital ages in quartzite from peri-Gondwanan terranes, New Brunswick and Nova Scotia, Canada: Precambrian Research, v. 126,p. 123–145.
Fortey, R. A., Cocks, L., and Robin, M., 2003, Palaeontological evidence bearing on global Ordovician-Silurian continental reconstructions: Earth-Science Reviews, v. 61, p. 245–307.
Ludman, A., and Berry, H. N., IV,
Bedrock geology of the Calais quadrangle, Maine: Maine Geological Survey,
Open-file report 03-97, scale: 1:100,000.
McLaughlin, K. J., Barr, S. M., Hill, M. D., Thompson, M. D., Ramezani, J., and Reynolds, P. H., 2003, The Moosehorn Plutonic Suite, southeastern Maine and southwestern New Brunswick: age, petrochemistry, and tectonic setting: Atlantic Geology, v. 39, p. 123–146.
McNicoll, V. J., Whalen, J. B., and Stern, R. A., 2003, U-Pb geochronology of Ordovician plutonism, Bathurst mining camp, New Brunswick, in Goodfellow, W. D., McCutcheon, S. R., and Peter, J. M., editors, Massive sulfide deposits of the Bathurst mining camp, New Brunswick, and northern Maine: Economic Geology Monographs, v. 11, p. 203–218.
Moench, R. H., and Aleinikoff, J. N., 2003. Stratigraphy, geochronology. and accretionary terrane settings of two Bronson Hill arc sequences, northern New England: Physics and Chemistry of the Earth, v. 28,p. 113–160.
van Staal, C. R., Wilson, R. A., Rogers, N., Fyffe, L. R., Langton, J. P., McCutcheon, S. R., McNicoll, V., and Ravenhurst, C. E., 2003, Geology and tectonic history of the Bathurst Supergroup, Bathurst mining camp, and its relationships to coeval rocks in southwestern New Brunswick and adjacent mine; a synthesis: Economic Geology Monograph, v. 11, p. 37–60.
Van Wagoner, N. A., and Dadd, K. A., 2003. A Silurian age for the Passamaquoddy Bay volcanic sequence in southwestern New Brunswick; implications for regional correlations: Geological Society of America,Abstracts with Programs, v. 35, p. 79.
David P. West, Jr., Heather M. Beal, and Timothy W. Grove, 2003. Silurian deformation and metamorphism of Ordovician arc rocks of the Casco Bay Group, south-central Maine. CJES 40 887-905.
The Casco Bay Group in south-central Maine consists of a sequence of Late Cambrian to Early Ordovician interlayered quartzofeldspathic granofels and pelite (Cape Elizabeth Formation) overlain by Early to Late Ordovician back-arc volcanic (Spring Point Formation) and volcanogenic sedimentary rocks (Diamond Island and Scarboro formations). These rocks were tightly folded and subjected to low-pressure amphibolite-facies metamorphism in the Late Silurian.This phase of deformation and metamorphism was followed by the development of a variety of structures consistent with a period of dextral transpression in Middle Devonian – Early Carboniferous time. Previously dated plutons within the sequence range in age from 422–389 Ma and record a period of prolonged intrusive activity in the region. Similarities in age, volcanic rock geochemistry, and lithologic characteristics argue strongly for a correlation between rocks of the Casco Bay Group and those in the Miramichi belt of eastern Maine and northern New Brunswick. The Cape Elizabeth Formation correlates with Late Cambrian to Early Ordovician sediments of the Miramichi Group (Gander Zone) and the Spring Point through Scarboro formations correlate with Early to Late Ordovician back-arc basin volcanics and volcanogenic sediments of the Bathurst Supergroup. The folding and low-pressure metamorphism of the Casco Bay Group is attributed to Late Silurian to Early Devonian terrane convergence and possible lithospheric delamination that would have resulted in a prolonged period of intrusive activity and elevated temperatures at low pressures. Continued convergence and likely plate reconfigurations in the Middle Devonian to Carboniferous led to widespread dextral transpression in the region.
Discussion: Upper Casco Bay Group correlatives
Past efforts to correlate rocks of the Casco Bay Group with other rocks in the northern Appalachians have been hindered by a lack of information on depositional ages and information on tectonic setting. However, recent isotopic age determinations (Aleinikoff et al. 1993; Tucker et al. 2001), geochemical analysis of metamorphosed volcanic rocks (Lawrence and Beane 2001; West et al. 2003), and detailed mapping (Pankiwskyj 1996; Hussey and Berry 2002; West 2002) have provided new insight into the tectonic setting of the Casco Bay Group. Previously suggested Casco Bay Group correlatives to the south (e.g., Massabesic Gneiss Complex in New Hampshire and Nashoba Terrane in Massachusetts) would seem to be untenable given large age differences (in the case of the Massabesic: Aleinikoff et al. 1995) and basic lithologic differences (in the case of the Nashoba: Hepburn et al. 1995). Correlations with Avalonian and Peri Gondwanan terranes to the east (e.g., St. Croix belt, Ellsworth Terrane, coastal New Brunswick terranes) are also unlikely for similar reasons (Berry and Osberg 1989; Rankin 1994; Stewart 1998; White and Barr 1996; Johnson and McLeod 1996).The most likely correlatives with the upper part of the Casco Bay Group are found along strike to the northeast in the Miramichi belt (see Fig. 1) of eastern Maine (Ludman 1991; Ludman et al. 1993) and northern New Brunswick (van Staal 1987, 1994; van Staal and Fyffe 1995). Although comparisons of these rocks are hindered by differences in regional metamorphic grade (amphibolite facies in the Casco Bay Group versus largely greenschist facies in the Miramichi) and the effects of severe tectonic thinning in the Casco Bay Group, close similarities are seen and will be discussed in detail later in the text.
Interlayered quartzofeldspathic granofels and pelites of the Cape Elizabeth Formation are lithologically very similar to a thick sequence of interbedded quartzofeldspathic wackes and pelites in the Miramichi belt (Baskahegan Lake Formation in Maine (Ludman 1991) and the Miramichi Group in New Brunswick (van Staal and Fyffe 1995)). These rocks are Late Cambrian to Early Ordovician in age based on the presence of trace fossils (Pickerill and Fyffe 1999) and radiometric ages from overlying units. As discussed earlier in the text, the only constraint on the age of the Cape Elizabeth Formation is that it is older than the overlying 469 ± 3 Ma Spring Point Formation. Thus a Late Cambrian to Early Ordovician age for the Cape Elizabeth Formation is plausible. Rocks of the Miramichi Group (including the Baskahegan Lake Formation) have been interpreted by van Staal et al. (1996) to represent a Late Cambrian to Early Ordovician passive margin sequence deposited on the eastern margin of the Iapetus Ocean (i.e., Gander Zone of Williams 1979). Metamorphosed late Arenig to Llanvirn (time scale of Tucker and McKerrow 1995) volcanic rocks of the Spring
Point Formation overlie the Cape Elizabeth Formation and these rocks are likely correlatives to volcanic rocks of similar age in the Bathurst Supergroup (van Staal et al. in press) that overlies the Miramichi Group in the Miramichi belt. Geochemistry from volcanic rocks of the Bathurst Supergroup (Rogers et al. in press; Rogers and van Staal in press) suggests a back arc basin tectonic setting (Tetagouche–Exploits back arc basin of van Staal et al. 1991), which is similar to the geochemical signature for rocks of the Spring Point Formation in Casco Bay (Lawrence and Beane 2001) and south central Maine (West et al. 2003). Recent work in the Miramichi belt, summarized by van Staal et al. (in press), has revealed a more complex tectonic history for the Bathurst Supergroup and necessitated a four fold subdivision of these rocks. Although the Spring Point Formation is most similar in age and lithologic characteristics to the California Lake Group (as described in Rogers et al. in press), van Staal et al. (in press) suggest that the Tetagouche–Exploits back arc basin contained a number of widely separated distinct blocks that were later juxtaposed during theLate Ordovician to Early Silurian closure of the basin. Given the complexity of this tectonic setting, the Spring Point volcanic rocks may not correlate directly with any of the newly defined members of recognized units in the Bathurst Supergroup of the Miramichi belt, but similarities in age, lithology, geochemical characteristics, and structural position within the orogen argue for a general correlation with these rocks.
It is important to note that the Miramichi Group (Cape Elizabeth equivalent) and the Bathurst Supergroup (Spring Point equivalent) are separated by a disconformity in New Brunswick (van Staal and Fyffe 1995). Similarly, the Cape Elizabeth equivalent (Baskahegan Lake Formation) in the Miramichi belt of eastern Maine is unconformably overlain by Ordovician volcanic rocks (Bowers Mountain Formation: Ludman et al. 1993), which have been correlated with theBathurst Supergroup. To date, no unconformity has been recognized between the Cape Elizabeth and Spring Point formations in Maine. However, this Ordovician unconformity is quite subtle and has only been recognized relatively recently in the Miramichi belt, thus its recognition, if it exists, would be very difficult in Maine where amphibolite facies metamorphism and ductile shearing are ubiquitous. Metavolcanic rocks of the Spring Point Formation are overlain by thin but distinctive black, graphitic quartzite and quartz–mica schist (Diamond Island Formation), followed by a thicker sequence of predominantly pelitic schist (Scarboro Formation). In the southern Miramichi belt in New Brunswick, Oak Mountain Formation volcanic rocks are overlain by Caradocian shale and feldspathic wacke of the Belle Lake Formation (Fyffe et al. 1983; Pickerill and Fyffe 1999). Similarly, in the Bathurst Supergroup of the northern Miramichi belt, volcanic rocks are overlain by Llanvirn–Caradoc sedimentary assemblages (van Staal et al. in press). Thus, Late Arenig to Llanvirn volcanic rocks overlain by dominantly sedimentary sequences are common to both the Casco Bay and Miramichi belts. In summary, Ordovician rocks of the upper Casco Bay Group correlate most favorably with rocks of similar age in the Miramichi belt of eastern Maine and adjacent New Brunswick. These rocks have been interpreted by van Staal et al. (1991, 1996) to represent a Late Cambrian to Early Ordovician passive margin sequence (Miramichi Group) unconformably overlain by Middle to Late Ordovician back arc volcanic rocks and associated volcanogenic sedimentary rocks (Bathurst Supergroup). A similar interpretation is favored for the upper part of the Casco Bay Group in Maine with the extensive Cape Elizabeth Formation representing the passive margin sequence, the Spring Point Formation representing the back arc volcanics, and the Diamond Island and Scarboro formations representing overlying back arc basin sediments.
Implications for middle Paleozoic orogenesis
Tectonic models of middle Paleozoic (Acadian) orogenesis in northern New England and adjacent Canada have evolved through the years as progressively more data has become available (e.g., Bradley 1983; Osberg et al. 1989; Ludman et al. 1993; Eusden et al. 1996; van Staal and de Roo 1995; Bradley et al. 2000; Tucker et al. 2001). While many of the earlier models attributed all middle Paleozoic tectonism to the Devonian Acadian orogeny, recent work (e.g., Bevier and Whalen 1990; West et al. 1992; 1995; van Staal and de Roo 1995: Bradley et al. 2000; Tucker et al. 2001) suggests a prolonged period of Early Silurian to Late Devonian deformation, metamorphism, and intrusive activity. Because the region lacks ophiolitic sutures that are important aspects of most tectonic reconstructions, deciphering the temporaland spatial distribution of deformation and metamorphism is critical to unraveling the tectonic history of the region. Upright isoclinal folding and an associated pervasive schistosity (D1 deformation) are the dominant deformational features preserved in rocks of the upper Casco Bay Group in south central Maine. Microstructural analysis indicates that an episode of low pressure amphibolite facies metamorphism was synchronous with this deformational event. Porphyritic shonkinite of the 418 Ma Lincoln Sill cuts the map scale D1 fold in the Casco Bay Group (Fig. 3) and thus the folding and associated metamorphism must be pre Devonian. However, both 40Ar/39Ar hornblende (West et al. 1995) and U–Pb sphene ages (Tucker et al. 2001) from the area range from 390 to 380 Ma and suggest this deformation and metamorphism is significantly younger. The following two models are proposed to explain this apparent contradiction:
(1) Rocks of the Casco Bay Group in south central Maine are polymetamorphic having been initially metamorphosed during folding prior to the intrusion of the 418 Ma Lincoln Sill and then re metamorphosed in the Middle Devonian.Although obvious textural evidence (e.g., pseudomorphs) for polymetamorphism in the field area is not widespread, polymetamorphism is prevalent in much of coastal, south central, and western Maine (Novak and Holdaway 1981; Berry 1987; Guidotti 1989; Guidotti and Holdaway 1993; Grover and Lang 1995), and it is somewhat unusual to not find it here. There are suggestions of multiple stages of garnet growth in some areas (e.g., Fig. 9e) and obvious pseudomorphs of earlier minerals might not be expected if the pressure–temperature conditions of a second metamorphic event were similar to an earlier metamorphic episode (see the “transition zone” of Guidotti and Johnson 2002).
(2) The rocks were folded and metamorphosed in the Late Silurian prior to intrusion of the Lincoln Sill and remained hot for a period of nearly 40 million years, when they finally cooled below hornblende and sphene blocking temperatures (500–550°C). This would seem unlikely given the low pressure nature of the metamorphism in this region, however, numerous plutons in the area span this age range (Haskell Hill = 408 Ma; Mixer Pond = 400 Ma; North Searsmont = 389 Ma) and an episode of lithospheric delamination proposed by Tucker et al. (2001) would likely result in a prolonged period of elevated heat flow in the region. At present, each of these models is plausible and further detailed geochronological investigations (e.g., in situ monazite dating) will be needed to distinguish between these and other possibilities.
North trending, asymmetric Z folds characterize D2 deformation in the upper Casco Bay Group and these features have been attributed to a significant period of regional dextral transpression in Middle Devonian to Early Carboniferous time (West and Hubbard 1997). Dextral transpression during this time interval is well documented throughout the northern Appalachians (e.g., Kirkwood 1995;
van Staal and de Roo 1995; Ludman and West 1999) and likely reflects changing plate configurations following Silurian– Devonian collisions along the eastern margin of Laurentia. 40Ar/39Ar muscovite cooling ages from the study area indicate the region cooled below 350°C in the Early Carboniferous (West et al. 1995) and regional penetrative deformation following this time period is unlikely. Localized D3 dextral shear bands and asymmetric boudinage are likely a later manifestation of the dextral transpression discussed earlier in the text and may be a precursor to the development of the Norumbega fault system in the Carboniferous (West and Hubbard 1997; Ludman and West 1999).
Conclusions : (1) Similarities in age, volcanic rock geochemistry, and lithologic characteristics argue strongly for a correlation between rocks of the upper Casco Bay Group in south central Maine and rocks exposed in the Miramichi belt of eastern Maine and northern New Brunswick. In this model, interlayered quartzofeldspathic granofels and pelites of the Cape Elizabeth Formation correlate with Late Cambrian – Early Ordovician passive margin sediments of the Miramichi Group (Gander zone). Overlying volcanic rocks of the Spring Point Formation and sedimentary rocks of the Diamond Island and Scarboro formations correlate with Arenig to Caradoc back arc basin lithologies of the Bathurst Supergroup. (2) Late Silurian deformation and low pressure amphibolite facies metamorphism of the upper Casco Bay Group in south central Maine can be attributed to convergence and associated terrane accretion. A model of lithospheric delamination proposed by Tucker et al. (2001) could explain a prolonged period of intrusive activity coincident with a period of elevated temperatures at low pressures. (3) Structures consistent with dextral shear deformation are pervasive and are correlated with a period of regional dextral transpression in Middle Devonian to Early Carboniferous time in the northern Appalachians.
Wintsch, R. P., Kunk, M. J., Boyd, J. L., and Aleinikoff, J. N., 2003, P-T-t paths and differential Alleghanian loading and uplift of the Bronson Hill terrane, south-central New England: American Journal of Science, v. 303, p. 410–446.
39th Ann. GSA Northeastern Meeting, T25, 2004
BARR, S.M., WHITE, C. E., KING, M.S., and BLACK, R. S., 2004. PERI-GONDWANAN TERRANES OF SOUTHERN NEW BRUNSWICK, CANADA: NEW INSIGHTS AND ENIGMAS. 39th Ann. GSA Northeastern Meeting, T25.
Southern New Brunswick consists of fault-bounded belts of rocks which show both similarities and contrasts in Late Proterozoic - Early Paleozoic evolution. The number of distinct terranes represented by these belts, and their affinity to the classical Avalon and Gander zones of the northern Appalachian orogen, remain controversial, in spite of a large body of accumulated field, petrochemical, and geochronological data. Myriad Carboniferous and younger faults in the area obscure the original nature of boundaries between rock packages, and it is likely that many of the original components are missing. Remnants of high-pressure metamorphic belts provide evidence for the presence of former terrane boundaries. P-T estimates for the Hammondvale metamorphic suite (HMS) on the northwestern margin of Caledonia terrane indicate peak metamorphic conditions at 9.5-12 kbar and 580-420°C. The HMS is interpreted to represent a remnant of an accretionary complex formed in association with ca. 620 Ma subduction in Caledonia terrane, and its presence confirms that the now-adjacent Brookville terrane was not part of the Caledonia (Avalon) terrane at that time. The Pocologan metamorphic suite at the boundary between the Brookville and Kingston terranes had peak P-T conditions of 9.5 kbars and 550°C, probably at ca. 420 Ma. A complex later history is indicated by40Ar/39Ar cooling ages as young as ca. 320 Ma. Modelling of magnetic and gravity data, constrained by magnetic susceptibility and density measurements from surface samples, indicates that present fault boundaries are sub-vertical or dip slightly to the southeast, although more shallow structures indicative of northwesterly thrusting are evident in some areas. The models require geophysically distinct bodies at depth (ca. 6 km or more) that are interpreted to correspond to Avalon, Brookville (Bras d'Or???), and Ganderia basements. Tracing terranes of southern New Brunswick into Maine is complicated by abundant Silurian and Devonian igneous units, and by apparent offset to the southeast to Grand Manan Island, where rock types and ages show elements of Avalon, Brookville, New River, and/or St. Croix terranes, in fault-bounded packages. Correlation with the mainland of New Brunswick or Nova Scotia is not yet resolved.
MATARAGIO, J.P. HOGAN, J. P., and WALKER, J. D., 2004. INITIAL ND-SR ISOTOPIC COMPOSITION OF GRANITE PLUTONS FROM EASTERN AND CENTRAL MAINE: IMPLICATIONS FOR TERRANE ACCRETION. 39th Ann. GSA Northeastern Meeting, T25.
Initial Nd and Sr isotopic composition of Paleozoic granites from the Medial New England Terrane (MNET) and the Composite Avalon Terrane (CAT) in Maine indicate the basement beneath these terranes changed dramatically after the Silurian. Two major episodes of Paleozoic magmatism are documented in this area. "Silurian" magmatism is bimodal, and characterized by distinctive epizonal plutonic and volcanic igneous complexes (e.g., Vinalhaven, South Penobscot).Silurian magmatism is known southeast of the Norumbega Fault Zone (NFZ). Silurian granites exhibit a large variation in eNd values (2.5 to -8) and 87Sr/86Sr)i ratios (0.703 to 0.713).
"Devonian to Carboniferous" magmatism is dominantly granitic and includes stocks of (1) peraluminous granite (e.g., Waldoboro); 2) metaluminous granite (e.g., Deer Isle, Mt. Waldo); and (3) Large batholiths of weakly peraluminous to metaluminous granite with megacrystic alkali feldspar (e.g., Lucerne).Devonian magmatism is wide spread throughout the area and is found on both sides of the NFZ. Devonian granites exhibit a narrow range in eNd (0.8 to -2) and a large range in 87Sr/86Sr)i ratios (0.701-0.710). On a Nd-Sr isotopic correlation diagram the fields for Silurian and Devonian granites partially overlap, however, they exhibit distinctly different slopes. Silurian granites define the field with the steeper slope. The most radiogenic Silurian granite yields a TDM age of 1.8 Ma. Devonian granites define the field with a shallow slope. The most radiogenic Devonian granite yields a TDM age of 1.4 Ma. This is compatible with Silurian and Devonian granites being derived from partial melting of distinct basement source regions. Silurian granites and Devonian granites intrude both MNET and CAT. This suggests 1) "terrane-bounding" faults in coastal Maine juxtapose distinct upper crustal terranes but not distinct basement terranes and that the upper crustal terranes were assembled prior to the Silurian melting event. 2) The source region for Silurian granites was not "tapped" during the Devonian melting event, either because of its refractory nature, or because the Silurian granites and their (GANDER??) host terranes are both allochthonous and were displaced over the MNET (AVALON???) basement source region prior to the Devonian melting event.
POLLOCK, J., MCNICOLL, V., VAN STAAL, C.R., and WILTON, D., 2004. GEOLOGY OF THE TALLY POND GROUP, NEWFOUNDLAND: NEW GEOCHRONOLOGY AND GEOCHEMICAL DATA FROM THE EXPLOITS SUBZONE, DUNNAGE ZONE. 39th Ann. GSA Northeastern Meeting, T25.
The (Tally Pond) group comprises Cambrian island-arc felsic pyroclastic rocks with intercalated mafic volcanic rocks and epiclastic volcanic and sedimentary rocks. ...arc plutonic rocks of the Crippleback Lake Quartz Monzonite form the basement to the Tally Pond group. A sequence of dominantly pillowed mafic volcanic rocks, mafic to andesitic volcaniclastics, and intercalated felsic volcanic rocks are nonconformable on the Crippleback Lake Quartz Monzonite. U-Pb zircon geochronology indicates that the felsic volcanic rocks were erupted at 509 ± 1 Ma. Dykes and stocks of medium-grained gabbro-diorite intrude all of the rocks of the Tally Pond group. These mafic intrusions yielded a U-Pb zircon age of 465 ± 2 Ma. Major, trace and rare earth element geochemistry indicates that the volcanic rocks have geochemical affinities consistent with a volcanic arc paleotectonic environment. Mafic intrusive rocks show no evidence of arc-related volcanism. Pb isotope data from VMS occurrences in the Tally Pond group contrast with those from the Notre Dame Subzone and are comparable to data from the Exploits subzone. Theyoungest rocks in the study area are conglomerates and coarse-grained sandstones of the Silurian Rogerson Lake Conglomerate which unconformably overlies rocks of the Tally Pond group; the conglomerate is dominated by volcanic clasts derived from the underlying Exploits subzone sequences. The Early Cambrian rocks of the Tally Pond group are analogous to rocks of the Brookville and Bras d’Or terranes in New Brunswick and Nova Scotia. Previous workers have suggested that the Brookville and Bras d’Or terranes represent the eastern margin of the Central Mobile Belt of the Appalachians (Gander Zone). Correlation of the Tally Pond group with these terranes, suggests that the Tally Pond group formed along the peri-Gondwanan margin of Iapetus. The Silurian Rogerson Lake Conglomerate that unconformably overlies the Tally Pond group indirectly indicates that these terranes were accreted to Laurentia by Late Ordovician.
REUSCH, D.N., VAN STAAL, C.R., and MCNICOLL, V.J., 2004. DETRITAL ZIRCONS AND GANDERIA'S SOUTHERN MARGIN, COASTAL MAINE. 39th Ann. GSA Northeastern Meeting, T25.
In central Newfoundland, a large, Upper Cambrian (~494 Ma) ophiolitic thrust sheet, the Gander River Ultrabasic Belt (GRUB), constitutes one of the most striking features of the northern Appalachian orogen. Gander Zone arenites and shales of Cambro-Tremadoc age occupy the footwall southeast of the GRUB line and the Cormacks window. Arenig strata that unconformably overlie both the ophiolite and Gander Zone sediments, combined with a 474 Ma stitching pluton, demand a Tremadoc/early Arenig age of emplacement (Penobscot orogeny). In the simplest scenario, the ophiolite formed in a back-arc setting southeast of the Cambrian Victoria arc; Gander Zone arenites accumulated along the southeasterly passive margin; and hot ophiolite was obducted shortly after its formation.
In New Brunswick and Maine, a thousand kilometers southeast (length of Java), discontinuousCambrian marine igneous rocks (509 Ma Ellsworth, 502 Ma Castine, 497 Ma Lawson Brook, 493 Ma East Scotch) of the Ellsworth and Annidale terranes (EAT) comprise bimodal assemblages largely devoid of arc or continental signature. Rare arc-like rocks, however, suggest an ensimatic back-arc setting. The structurally lower St. Croix terrane comprises, in downward order, Caradocian shales and orthoquartzites (Kendall Mountain), quartzofeldspathic wackes (Woodland), and Tremadocian black shales and basalts (Calais-Penobscot). Both assemblages display top-to-NW sense-of-shear in early structures that must be post-Tremadoc and possibly post-Caradoc. A white-weathering, pin-striped arenite from Ellsworth Falls, close to highly sheared rocks at the northwestern limit of the Ellsworth terrane, yielded dominantly 545±4Ma (n=28; 73%) and lesser younger (507±6 Ma) and older Neo- (ca. 630 Ma, 680 Ma), Meso- (1.21 Ma, 1.50 Ma), and Paleoproterozoic (1.97-2.09 Ma) zircons, an age distribution typical of Gander Zone arenites.
The Ellsworth-Annidale terranes and GRUB share similar rock assemblages, ages, and contact relationships with the Gander Zone but their emplacement histories may differ. Paleo-position of EAT and its age of emplacement remain important questions.
VAN STAAL, C. R., MCNICOLL, V., VALVERDE-VAQUERO, P., BARR, S. M., FYFFE, L. R., and REUSCH, D. N., 2004. GANDERIA, AVALONIA, AND THE SALINIC AND ACADIAN OROGENIES. 39th Ann. GSA Northeastern Meeting, T25.
New SHRIMP-analyses of zircon grains from Cambrian arenites in New Brunswick and Maine constrain the location of the Gander-Avalon terrane boundary, which is critical to understanding the Early Silurian Salinic and Early Devonian Acadian orogenies. Whereasperi-Gondwanan Ganderia and Avalonia have similar arc-dominated Neoproterozoic basements, their Lower Paleozoic rocks and tectonic evolutions differ significantly. In Ganderia, Middle Cambrian through Tremadoc arenites and shales overlie Lower Cambrian arc rocks, which were locally accompanied by coeval tectonism. In Avalonia, however, shale-dominated Lower Cambrian to Ordovician strata indicate a stable platform. Arenite samples collected from the Baskahegan Lake, Calais, Ellsworth, and Matthews Lake Formations contain abundant Early Cambrian and Late Neoproterozoic detrital zircon grains derived, probably, from local basement as well as important populations of Mesoproterozoic (1.2 -1.6 Ga) and Early Paleoproterozoic (2.0 - 2.3 Ga) zircon grains, which suggest an Amazonian provenance. We propose that the Gander-Avalon zone boundary coincides with the Caledonia Fault in New Brunswick, lies southeast of Grand Manan Island (Stanley Brook granite is c. 535 Ma), which is due to sinistral offset along the Oak Bay fault, and emerges southeastward from the Gulf of Maine as the Bloody Bluff Fault.
At~430 Ma, the bulk of Ganderia accreted to Laurentia along its northern margin due to closure of the Middle Ordovician Tetagouche backarc basin, which caused the Salinic orogeny. Around this time (440-425 Ma), the coastal volcanic/Mascarene arc/backarc complex developed on its southern margin above a northwest-subducting Avalonian plate. Inversion of the Mascarene backarc basin at ~ 420 Ma signals the start of the Avalonia-Ganderia collision, which caused the Acadian orogeny.
Aleinikoff, J. N., Horton, J. W., Jr., Drake, A. A., Jr, Wintsch, R. P., Fanning, C. M., and Yi, K., 2004,Deciphering multiple Mesoproterozoic and Paleozoic events recorded in zircon and titanite from theBaltimore Gneiss, Maryland; SEM imaging, SHRIMP U-Pb geochronology, and EMP analysis, in Tollo,R. P., Corriveau, L., McLelland, J., and Bartholomew, M. J., editors, Proterozoic tectonic evolution of theGrenville Orogen in North America: Geological Society of America Memoir, v. 197, p. 411–434.
Black, L. P., Kamo, S. L., Allen, C. M., Davis, D. W., Aleinikoff, J. N., Valley, J. W., Mundil, R., Campbell, I. H.,Korsuch, R. J., Williams, I. S., and Foudoulis, C., 2004, Improved 206Pb/238U microprobe geochronologyby the monitoring of a trace-element-related matrix effect; SHRIMP, ID–TIMS, ELA–ICP–MS andoxygen isotope documentation for a series of zircon standards: Chemical Geology, v. 205, p. 115–140.
Bothner, W. A., Laird, J., Escamilla, C. J., Kerwin, C. W., Schulz, J., and Loveless, J. P., 2004, EDMAPS/newmaps in southeastern New Hampshire: Geological Society of America, Abstracts with Programs,v. 36, p. 57.
Bream, B. R., Hatcher, R. D., Jr., Miller, C. F., and Fullagar, P. D., 2004, Detrital zircon ages and Nd isotopic data from the Southern Appalachian crystalline core, Georgia, South Carolina, North Carolina, and Tennessee; new provenance constraints for part of the Laurentian margin: Geological Society of America, Memoir, v. 197, p. 459–475.
Burg, J. P., Kaus, B. J. P., and Podladchikov, Y.
Y., 2004, Dome structures in collision orogens: Mechanical investigation of the gravity/compression interplay, in
Whitney, D. L., Teyssier, C., and Siddoway, C. S.,editors, Gneiss domes in
Orogeny: Geological Society of America Special Paper, v. 380, p. 47–66.
Churchill-Dickson, L., 2004, A late Silurian (Pridolian) age for the Eastport Formation, Maine; a review of the fossil, stratigraphic, and radiometric age data: Atlantic Geology, v. 40, p. 189–195.
Daniels, D. L., and Snyder, S. L., 2004, New England states aeromagnetic and gravity maps and data: A website for distribution of data: U.S. Geological Survey Open-File Report 2004–1258, http://pubs.usgs.gov/of/2004/1258/index.htm.
Ericksson, K. A., Campbell, I. H., Palin, J. M., Allen, C. M., and Bock, B., 2004, Evidence for multiple recycling in Neoproterozoic through Pennsylvanian sedimentary rocks of the central AppalachianBasin: Journal of Geology, v. 112, p. 261–276.
Fayon, A. K., Whitney, D. L., and Teyssier, C., 2004, Exhumation of orogenic crust: Diapiric ascent versus low-angle normal faulting, in Whitney, D. L., Teyssier, C., and Siddoway, C. S., editors, Gneiss domes in Orogeny: Geological Society of America Special Paper, v. 380, p. 129–139.
Karabinos, P., Morris, D., and Rayner, N., 2004, Silurian tectonism in the western New England Appalachians: Geological Society of America, Abstracts with Programs, v. 36, n. 2, p. 91.
Reusch, D. N., van Staal, C. R., and McNicoll, V. J., 2004, Detrital zircons and Ganderia’s southern margin, coastal Maine: Geological Society of America Abstracts with Programs, v. 36, n. 2, p. 129
Thomas, W. A., Becker, T. P., Samson, S. D., and Hamilton, M. A., 2004, Detrital zircon evidence of a recycled orogenic foreland provenance for Alleghanian clastic-wedge sandstones: Journal of Geology, v. 112,p. 23–37.
Tohver, E., Bettencourt, J. S., Tosdal, R., Mezger, K., Leite, W. B., and Payolla, B. L., 2004, Terrane transfer during the Grenville orogeny: tracing the Amazonian ancestry of southern Appalachian basementthrough Pb abd Nd isotopes: Earth and Planetary Science Letters, v. 228, p. 161–176.
Tollo, R. P., Aleinikoff, J. N., Borduas, E. A., Hackley, P., and Fanning, C. M., 2004, Petrologic andgeochronologic evolution of the Grenville Orogen, northern Blue Ridge Province, Virginia, in Tollo,R. P., Corriveau, L., McLelland, J., and Bartholomew, M. J., editors, Proterozoic tectonic evolution of theGrenville Orogen in North America: Geological Society of America Memoir, v. 197, p. 411–434.
van der Velden, A. J., van Staal, C. R., and Cook, F. A., 2004, Crustal structure, fossil subduction, and the tectonic evolution of the Newfoundland Appalachians; evidence from a reprocessed seismic reflection survey: Geological Society of America Bulletin, v. 116, p. 1485–1498.
van Staal, C. R., McNicoll, V. J., Valverde-Vaquero, P., Barr, S. M., Fyffe, L. R., and Reusch, D. N., 2004, Ganderia, Avalonia, and the Salinic and Acadian orogenies: Geological Society of America Abstractswith Programs, v. 36, n. 2, p. 128.
Vermeesch, P., 2004, How many grains are needed for a provenance study?: Earth and Planetary ScienceLetters, v. 224, p. 441–451.
Walsh, G. J., Aleinikoff, J. N., and Fanning, C. M, 2004, U-Pb geochronology and evolution of Mesoproterozoic basement rocks, western Connecticut, in Tollo, R. P., Corriveau, L., McLelland, J., and Bartholomew,M. J., editors, Proterozoic tectonic evolution of the Grenville Orogen in North America:Geological Society of America Memoir, v. 197, p. 729–753.
West, D.P., Jr, Coish, R.A. and Tomascak, P.B. 2004. Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine: evidence from trace element and isotope geochemistry Geol. Mag. 141, 125–140.
p. 136 "This suggests that Early to Middle Ordovician Tetagouche-Exploits basin (van Staal,Winchester & Bedard, 1991;vanStaal et al.1998) can be traced well into southern Maine."
p. 138 the following tectonic model is proposed for the Casco Bay Group in Maine. (1)Arc volcanism along the Gander continental margin begins in Early Ordovician time and the Cape Elizabeth Formation represents volcanogenic sediment shed from this growing volcanic arc. (2) Crustal thinning and rifting of this continental arc begins about 470 Ma and bimodal volcanic rocks of the Spring Point Formation are erupted during the early stages of this rifting episode. Rocks of the Cushing Formation and Falmouth-Brunswick sequence may represent continued arc magmatism on the trench side of the back-arc basin. (3)Metasedimentary rocks of the Diamond Island and Scarboro formations (above the Spring Point Formation) reflect sedimentation within the back-arc basin. Late Ordovician (?) or Silurian compressional tectonic events subsequently closed the back-arc basin and juxtaposed the various elements of the arc–back-arc basin complex.
Whitney, D. L., Teyssier, C., and Vanderhaeghe, O., 2004, Gneiss domes and crustal flow, in Whitney, D. L.,Teyssier, C., and Siddoway, C. S., editors, Gneiss domes in Orogeny: Geological Society of America Special Paper, v. 380, p. 15–33.
Yin, A., 2004, Gneiss domes and gneiss dome systems, in Whitney, D. L., Teyssier, C., and Siddoway, C. S.,editors, Gneiss domes in Orogeny: Geological Society of America Special Paper, v. 380, p. 1–14.
Becker, T. P., Thomas, W. A., Samson, S. D., and Gehrels, G. E., 2005, Detrital zircon evidence of Laurentian crustal dominance in the Lower Pennsylvanian deposits of the Alleghanian clastic wedge in easternNorth America: Sedimentary Geology, v. 182, p. 59–86.
Dorais, M. J., Nelson, W. R., and Tubrett, M. N., 2005, What caused the Acadian Orogeny, New England Appalachians? A provenance study of the Carrabassett Formation, Central Maine Basin: GeologicalSociety of America, Abstracts with Programs, v. 37, n. 1, p. 31.
Karabinos, P., 2005, Age and style of emplacement of basement uplifts in the northern Appalachians: Geological Society of America, Abstracts with Programs, v. 37, p 20.
Tomascak, P. B., Brown, M., Solar, G. S., Becker, H. J., Centorbi, T. L., and Tian, J., 2005, Source contributions to Devonian granite magmatism near the Laurentian border, New Hampshire and Western Maine, USA: Lithos, v. 80, p. 75–99.
Tremblay, A., and Pinet, N., 2005, Diachronous supracrustal extension in an intraplate setting and the origin of the Connecticut Valley-Gaspe´ and Merrimack Troughs, Northern Appalachians: Geological Magazine,v. 142, p. 7–22.
van Staal, C. R., 2005, The Northern Appalachians, in Selley, R. C., Robin, L., Cocks, M., and Plimer, I. R., editors, Encyclopedia of Geology: Oxford, Elsevier, v. 4, p. 81–91.
Wintsch, R. P., Aleinikoff, J. N., Dorais, M. J., Unruh, D. M., and Walsh, G. J., 2005c, Melt weakening in crustal-scale tectonic wedging, southern New England: EOS Transactions, v. 86, n. 52, p. V21A-0591.
Wintsch, R. P., Aleinikoff, J. N., Unruh, D. M., and Walsh, G., 2005a, Evidence for tectonic wedging of Avalon terrane rocks into the Gander zone, southern New England: Geological Society of America Abstractswith Programs, v. 37, p. 31.
Wintsch, R. P., Aleinikoff, J. N., Webster, J. R., and Unruh, D. M., 2005b, The Killingworth complex: A Middle and Late Paleozoic magmatic and structural dome, in McHone, N. W., and Petersone, M. J.,editors, Guidebook for fieldtrips in Connecticut, New Haven, CT: New England Intercollegiate Geological Conference, 97th annual meeting, State Geological and Natural History Survey of Connecticut,Guidebook n. 8, p. 305–324.
Valverde-Vaquero, P., van Staal, C. R., McNicoll, V., and Dunning, G. R., 2006, Mid-Late Ordovician magmatism and metamorphism along the Gander margin in central Newfoundland: London, Journal of the Geological Society, v. 163, p. 347–362.
Walsh, G. J., Scott, R. B., Aleinikoff, J. N., and Armstrong, T. R., 2006, Preliminary Bedrock geologic map of the Old Lyme quadrangle, New London and Middlesex Counties, Connecticut: U.S. Geological SurveyOpen File Report 2006-1296, scale 1:24:000.
Zagorevski, A., Rogers, N., van Staal, C. R., McNicoll, V., Lissenberg, C. J., and Valverde-Vaquero, P., 2006, Lower to Middle Ordovician evolution of peri-Laurentian arc and backarc complexes in Iapetus; constraints from the Annieopsquotch accretionary tract, central Newfoundland: Geological Society of America Bulletin, v. 118, p. 324–342.
American Journal of Science 2007 v. 307, January
JOHN N. ALEINIKOFF, ROBERT P. WINTSCH, RICHARD P. TOLLO, DANIEL M. UNRUH, C. MARK FANNING, and MARK D. SCHMITZ. 2007. AGES AND ORIGINS OF ROCKS OF THE KILLINGWORTH DOME, SOUTH-CENTRAL CONNECTICUT: IMPLICATIONS FOR THE TECTONIC EVOLUTION OF SOUTHERN NEW ENGLAND. American Journal of Science, v. 307, 1, p. 63–118.
The Killingworth dome of south-central Connecticut occurs at the southern
end of the Bronson Hill belt. It is composed of tonalitic and trondhjemitic
orthogneisses (Killingworth complex) and bimodal metavolcanic rocks (Middletown
complex) that display calc-alkaline affinities. Orthogneisses of the
Killingworth complex (Boulder Lake gneiss, 456 6 Ma; Pond Meadow gneiss, 460 Ma)
were emplaced at about the same time as eruption and deposition of
volcanic-sedimentary rocks of the Middletown complex (Middletown Formation, 449
4 Ma; Higganum gneiss, 459 4Ma). Hidden Lake gneiss (339 3Ma) occurs as a pluton
in the core of the Killingworth dome, and, on the basis of geochemical and
isotopic data, is included
in the Killingworth complex.
Pb and Nd isotopic data suggest that the Pond Meadow, Boulder Lake, and Hidden Lake gneisses (Killingworth complex) resulted from mixing of Neoproterozoic Gander terrane sources (high 207Pb/204Pb and intermediate Nd) and less radiogenic (low 207Pb/204Pb and low Nd) components, whereas Middletown Formation and Higganum gneiss (Middletown complex) were derived from mixtures of Gander basement and primitive (low 207Pb/204Pb and high Nd) sources. The less radiogenic component for the Killingworth complex is similar in isotopic composition to material from Laurentian (Grenville) crust. However, because published paleomagnetic and paleontologic data indicate that the Gander terrane is peri-Gondwanan in origin, the isotopic signature of Killingworth complex rocks probably was derived from Gander basement that contained detritus from non-Laurentian sources such as Amazonia, Baltica, or Oaxaquia. We suggest that the Killingworth complex formed above an east-dipping subduction zone on the west margin of the Gander terrane, whereas the Middletown complex formed to the east in a back-arc rift environment. Subsequent shortening, associated with the assembly of Pangea in the Carboniferous, resulted in Gander cover terranes over the Avalon terrane in the west; and in the Middletown complex over the Killingworth complex in the east. Despite similarities of emplacement age, structural setting, and geographic continuity of the Killingworth dome with Oliverian domes in central and northern New England, new and published isotopic data suggest that the Killingworth and Middletown complexes were derived from Gander crust, and are not part of the Bronson Hill arc that was derived from Laurentian crust. The trace of the Ordovician Iapetan suture (the Red Indian line) between rocks of Laurentian and Ganderian origin probably extends from Southwestern New Hampshire west of the Pelham dome of northcentral Massachusetts and is coverd by Mesozoic rocks of the Hartford basin.
R. P. WINTSCH, J. N. ALEINIKOFF, G. J. WALSH, W. A. BOTHNER, A. M. HUSSEY, II, and C. M. FANNING. 2007. SHRIMP U-Pb EVIDENCE FOR A LATE SILURIAN AGE OF METASEDIMENTARY ROCKS IN THE MERRIMACK AND PUTNAM-NASHOBA TERRANES, EASTERN NEW ENGLAND. American Journal of Science, n. 307, 1, p. 119–167.
U-Pb ages of detrital, metamorphic, and magmatic zircon and metamorphic
monazite and titanite ..... from the Merrimack and Putnam-Nashoba terranes of
eastern New England. ....deposited in the middle Paleozoic above Neoproterozoic
basement of the Gander terrane and juxtaposed by Late Paleozoic thrusting in
thin, fault-bounded slices. The correlative Hebron and Berwick formations
(Merrimack terrane) and Tatnic
Hill Formation (Putnam-Nashoba terrane), contain detrital zircons with
Mesoproterozoic, Ordovician, and Silurian age populations. On the basis of the
age of the youngest detrital zircon population ( 425 Ma), the Hebron, Berwick
and Tatnic Hill formations are no older than Late Silurian (Wenlockian). The
minimum deposition ages of the Hebron and Berwick are constrained by ages of
cross-cutting plutons (414 3 and 418 2 Ma, respectively). The Tatnic Hill
Formation must be older than the oldest metamorphic monazite and zircon ( 407
Ma). Thus, all three of these units were deposited between 425 and 418 Ma,
probably in the Ludlovian. Age populations of detrital zircons suggest
Laurentian and Ordovician arc provenance to the west. High grade metamorphism of
the Tatnic Hill Formation soon after deposition probably requires that
sedimentation and burial occurred in a fore-arc environment, whereas
time-equivalent calcareous sediments of the Hebron and Berwick formations
originated in a back-arc setting. In contrast to age data from the Berwick Formation, the Kittery Formation contains primarily Mesoproterozoic detrital zircons; only 2 younger grains were identified. The absence of a significant Ordovician population, in addition to paleocurrent directions from the east and structural data indicating thrusting, suggest that the Kittery was derived from peri-Gondwanan sources and deposited in the Fredericton Sea. Thus, the Kittery should not be considered part of the Laurentian-derived Merrimack terrane; it more likely correlates with the early Silurian Fredericton terrane of northeastern New England and Maritime Canada.
GREGORY J. WALSH, JOHN N. ALEINIKOFF, and ROBERT P. WINTSCH. 2007. ORIGIN OF THE LYME DOME AND IMPLICATIONS FOR THE TIMING OF MULTIPLE ALLEGHANIAN DEFORMATIONAL AND INTRUSIVE EVENTS IN SOUTHERN CONNECTICUT. American Journal of Science, v. 307, 1, p. 168–215.
.... the Lyme dome, southern Connecticut ...... Detrital zircon geochronology in combination with ages on intrusive rocks brackets the deposition of quartzite in the core of the dome sometime between ca. 925 and 620 Ma. Granite and granodiorite intruded the Neoproteorozic metasedimentary rocks in the core of the dome at ca. 620 to 610 Ma. Four major early Permian events associated with the Alleghanian orogeny affected the rocks in the Lyme dome area. Syn-tectonic migmatization and widespread penetrative deformation (D1, ca. 300 – 290 Ma) included emplacement of alaskite at 290 +/- 4 Ma during regional foliation development and aluminosilicate-orthoclase metamorphic conditions. Rocks of the Avalon terrane may have wedged between Gander cover rocks and Gander basement in the core of the Lyme during D1. Limited structural evidence for diapiric uplift of the Lyme dome indicates that diapirism started late in D1 and was completed by D2 (ca. 290 – 280 Ma) when horizontal WNW contractional stresses dominated over vertical stresses. Second sillimanite metamorphism continued and syn-tectonic D2 granite pegmatite (288 +/-4 Ma) and the Joshua Rock Granite Gniess (284 +/-3 Ma) intruded at this time. North-northwest extension during D3 (ca. 280 – 275 Ma) led to granitic pegmatite intrusion along S3 cleavage planes and in extensional zones in boudin necks during hydraulic failure and decompression melting. Intrusion of a Westerly Granite dike at 275 +/-4 Ma suggests that D3 extension was active, and perhaps concluding, by ca. 275 Ma. Late randomly oriented but gently dipping pegmatite dikes record a final stage of intrusion during D4 (ca. 275 – 260 Ma), and a switch from NNW extension to vertical unloading and exhumation. Monazite and metamorphic zircon rim ages record this event at ca. 259 Ma. The evolution of the Lyme dome involved D1 mylonitization, intrusion, and migmatization during north-directed contraction, limited late D1 diapirism, D2 migmatization during WNW contraction with associated flexural flow and fold interference, D3 NNW horizontal extension and decompression melting, and final D4 vertical extension and rapid exhumation. Late regional uplift, extension, and normal faulting at higher crustal levels may have been caused by diapiric rise of the lower crust, below the structural level of the Lyme dome. The rocks record no evidence of Acadian metamorphism or deformation, suggesting that the Gander zone here was not tectonically juxtaposed with Avalon until the Alleghanian orogeny.
Lin, SHOUFA; DONALD W. DAVIS, SANDRA M. BARR, CEES R. VAN STAAL YADONG CHEN, and MARC CONSTANTIN 2007. U-Pb GEOCHRONOLOGICAL CONSTRAINTS ON THE EVOLUTION OF THE ASPY TERRANE, CAPE BRETON ISLAND: IMPLICATIONS FOR RELATIONSHIPS BETWEEN ASPY AND BRAS D’OR TERRANES AND GANDERIA IN THE CANADIAN APPALACHIANS: American Journal of Science, v. 307, p. 371-398.
"New U-Pb zircon ages from nine samples of igneous and sedimentary rocks in the Aspy terrane, Cape Breton Island, show that Neoproterozoic rocks form major part of the terrane and confirm that the terrane was affected by a major Silurian-Devonian tectonothermal event. A rhyolitic crystal tuff, a leucotonalite pluton and a felsic sheet yield ages of 618.8+/- 0.6 Ma, 619.7 +/- 0.9 Ma and 573.5 +/- 2.7 Ma, respectively. A metasedimentary unit contains zircon ranging in age from ca. 546 to ca. 1520 Ma. A diorite has an age of 428.6 +/- 1.9 Ma, and another diorite unit and a quartz porphyry also have probable Late Silurian ages. A third diorite yields an age of 373.0 +/- 0.5 Ma, part of a widespread bimodal igneous event represented by both volcanic and plutonic rocks throughout the Aspy region. Geochronological results and field relationships indicate that the Neoproterozoic rocks are similar to those in the Bras d’Or terrane and form the basement to the (Ordovician-) Silurian rocks in the Aspy terrane, and that the Aspy terrane is probably correlative with rocks in the Hermitage flexure of southern Newfoundland where Silurian metasedimentary and metavolcanic rocks lie unconformably on similar Neoproterozoic rocks. Likely correlative rocks also occur in the Kingston terrane of southern New Brunswick. The results of this study support the idea that the Aspy-Kingston terrane is part of Ganderia and that Neoproterozoic rocks in the Bras d’Or terrane and correlative rocks in southwestern Newfoundland and elsewhere represent exposed basement to Ganderia in the Canadian Appalachians."
Rankin, D. W., Coish, R. A., Tucker, R. D., Peng, Z. X., Wilson, S. A., and Rouff, A. A., 2007. Silurian extension in the upper Connecticut Valley, United States and the origin of middle Paleozoic basins in the Quebec Embayment: American Journal of Science, v. 307, p. 216–264.
Zagorevski, A., van Staal, C. R., McNicoll, V., and Rogers, N., 2007. Upper Cambrian to upper Ordovician island arc activity in the Victoria Lake supergroup, central Newfoundland: tectonic development of the northern Ganderian Margin: American Journal of Science, v. 307, p. 339–370.
"The Exploits Subzone of the Newfoundland Appalachians comprises remnants of Cambro-Ordovician peri-Gondwanan arc and back-arc
complexes that formed within the Iapetus Ocean. The Exploits Subzone
experienced at least two accretionary events as a result of the rapid closure of the main
portion of the Iapetus tract: the Penobscot orogeny (c. 480 Ma), which juxtaposed the
Penobscot Arc (c. 513 – 486 Ma) with the Gander margin, and c. 450 Ma collision of the
Victoria Arc (c. 473 – 454 Ma) with the Annieopsquotch Accretionary Tract that
juxtaposed the peri-Laurentian and peri-Gondwanan elements along the Red Indian
Line. The newly recognized Pats Pond Group forms a temporal equivalent to other
Lower Ordovician intra-oceanic complexes of the Penobscot Arc. The Pats Pond
Group (c. 487 Ma) has a geochemical stratigraphy that is consistent with rifting
of a volcanic arc. An ensialic setting is indicated by low
0.3 to -0.5) near the stratigraphic base and its abundant zircon inheritance (c.
560 Ma and 0.9 – 1.2 Ga). The spatial distribution of Tremadocian arc –
back-arc complexes indicates that the Penobscot arc is best explained in terms
of a single east-dipping subduction zone. This model is favored over west
dipping models, in that it explains the distribution of the Penobscot arc
elements, continental arc magmatism, and the obduction of back-arc Penobscot
ophiolites without requiring subduction of the Gander margin or subduction
Pollack, J. C., Wilton, D. H. C., van Staal, C. R., and Morrissey, K. D., 2007. U-Pb zircon geochronological constraints on the Late Ordovician-Early Silurian collision of Ganderia and Laurentia along the Dog Bay Line: The terminal Iapetan suture in the Newfoundland Appalachians: American Journal of Science, v. 307, p. 399–433.
"The Dog Bay Line is a major Silurian terrane boundary in the
Exploits Subzone of the Newfoundland Appalachians. Late Ordovician-Early
Silurian rocks northwest of the Dog Bay Line, the Badger and Botwood groups,
contain detritus sourced exclusively from Laurentia. These rocks were deposited
upon peri-Gondwanan volcanic arc terranes that were accreted to Laurentia in the
Middle Ordovician. The Davidsville and Indian Islands groups southeast of the
Dog Bay Line have stratigraphic links to peri-Gondwanan terranes and were
deposited during the Late Ordovician-Early Silurian upon the peri- Gondwanan
margin of Iapetus and were then accreted to Laurentia in the Early Silurian. A
change from Paleozoic-dominated (Badger Group) to Meso- and
Neoproterozoicdominated (Botwood Group) detritus in sequences northwest of the
Dog Bay Line is attributed to the Middle Ordovician collision and exhumation of
peri-Laurentian arc terranes of the Notre Dame Subzone with Laurentia. Unroofing
and erosion of these accreted arc terranes re-exposed Laurentian basement and
deposited detritus from the latter into the Botwood Group. Salinic orogenesis
resulting from the collision of Ganderia with Laurentia resulted in obduction
and erosion of the accreted Victoria and Exploits arcs and deposition of the
detritus into a forearc basin on Laurentia.
Strachan, R.A.; Collins, A.S.; Buchan, C.; Nance, R.D.; Murphy, J.B.; D'Lemos, R.S. 2007. Terrane analysis along a
Neoproterozoic active margin of Gondwana: insights from U-Pb zircon
geochronology. Journal of the Geological Society, Volume 164, Number 1, 2007,
The tectonic affinities of terranes in accretionary orogens can be evaluated using geochronological techniques. U-Pb zircon data obtained from paragneisses of the Coedana Complex (Anglesey) and the Malverns Complex, southern Britain, indicate that they were deposited during the mid- to late Neoproterozoic and have a comparable Amazonian provenance. Metamorphism of the Coedana gneisses occurred at 666 ± 7 Ma, similar to the age of metamorphism in the Malverns Complex. Anglesey therefore probably evolved in proximity to the Avalonian basement of mainland southern Britain during the mid- to late Neoproterozoic and is not a `suspect terrane' relative to the remainder of Avalonia.
Van Staal. C. R., 2007, Pre-Carboniferous metallogeny of the Canadian Appalachians, in Goodfellow, W. D., editor, Mineral Resources of Canada: A Synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods, Jointly by the Mineral Deposit Division of the Geological Association of Canada and the Geological Survey of Canada.
Geological Society of America, Northeast section meeting, Durham, NH, 2007 - http://gsa.confex.com/gsa/2007NE/finalprogram/ - link to program
Monday, 12 March 2007
Rev. James W. Skehan, S.J. — Geologist, Teacher, Mentor, Priest: A Jesuit Journey I
GEOLOGICAL CASE FOR AVALON OFF NORTH AFRICA AT 595 MA: THOMPSON, M.D.,
Avalon terranes have commonly been pictured as originating along the Amazonian margin of Gondwana based on Nd isotopic signatures of crystalline rocks and 1.0-1.3 Ga detrital zircons that could have derived from South American source belts. We suggest that the geological evidence can also be reconciled with the peri-Gondwanan African position implied by our paleopole from ca. 595 Ma Lynn-Mattapan volcanic rocks in the Southeastern New England Avalon Zone.
Source rocks that could have generated positive initial ?Nd values observed in Avalonian igneous rocks of maritime Canada were first pointed out in the Tocantins Province of central Brazil. Comparable results are also published, however, for Pan African belts closer to our paleomagnetically preferred site. These include the Anti-Atlas orogen that was active along the northern margin of the west African craton during Gondwana assembly, as well as the Trans-Saharan suture between the West African craton and the Saharan paleocontinent on the east.
Mesoproterozoic-age detrital zircons for which there are no source belts in the West African craton might be longitudinally derived from other terranes along the Gondwanan margin, or even from a terrane separating Avalonia from West Gondwana. Possible candidates are Middle American terranes like Ouaxaquia (eastern Mexico) where igneous and metamorphic basement rocks have yielded U-Pb zircon dates between ca. 1.1 Ga and 0.9 Ga. A second aspect of detrital zircon suites deposited in proximity to West Africa is the expected presence of grains in the ca. 2.27-2.05 Ga interval marking events loosely known as the Eburnean orogeny. Zircons of this age are rare in Avalonian-cycle sandstones, but they have been identified in quartzite of the Blackstone Group which predates Avalonian arc magmatism in southeastern New England. High concentrations of detrital zircon ages around 2.0 Ga are also reported from quartzite clasts in conglomerates from the Caledonia and Mira terranes in New Brunswick and Nova Scotia, respectively. It appears from these examples that older Avalonian sedimentary sequences could have been supplied in part by source areas of Eburnean age, but that transport patterns changed with the onset of Avalonian tectonism so that ca. 2.0 Ga Paleoproterozoic zircons are present only locally as recycled grains.
METAMORPHISM AND FAULT ZONE ACTIVITY IN THE NASHOBA TERRANE, EASTERN MASSACHUSETTS:MARKWORT, Ross J.
2-6 10:15 AM MONAZITE AGES FOR METAMORPHISM AND FAULT ZONE ACTIVITY IN THE NASHOBA TERRANE, EASTERN MASSACHUSETTS: MARKWORT, Ross J., new evidence for the tectonic history of the Nashoba terrane.
The oldest monazite core age encountered, ~ 450 Ma (Late Caradoc), is from a grain within a garnet porphyroblast in a mylonitic schist that may represent a detrital grain. A second core age of 438 Ma (early Llandovery) in a now mylonitized granite likely represents an original igneous crystallization age. The first regional metamorphism (M1) affecting the terrane occurred in the interval ~ 430-420 Ma [Wenlock-Ludlow). A second metamorphic event (M2), associated with widespread migmatization, occurred between ~ 410 Ma and 390 Ma (L Dev.) and may be separable into two phases, the older coincident with the youngest phase of the Andover Granite. Sinistral ductile shearing accompanied both the M1 and M2 events. Following M1 and M2, peak metamorphic assemblages in the shear zones were overprinted during several intervals from ~ 375-340 Ma (Late Dev - Early Carb) and the shearing style shifted from ductile to more brittle-ductile conditions.
Rev. James W. Skehan SJ — Geologist, Teacher, Mentor, Priest: A Jesuit Journey II
1:05 PM CONSTRAINTS ON THE EVOLUTION OF THE AVALONIAN MANTLE AND TECTONIC IMPLICATIONS: MURPHY, J. Brendan,
12-2 1:25 PM A REVIEW OF COASTAL MAINE STRATIGRAPHY: BERRY, Henry N. IV, The following stratigraphic columns are used, from east to west. (1) coastal volcanics, (2) Ellsworth, (3) Islesboro, (4) Rockport, (5) St. Croix, (6) Benner Hill, (7) Fredericton, (8) Casco Bay, (9) East Harpswell, (10) Falmouth-Brunswick, (11) central Maine, (12) Merrimack, and (13) Shapleigh.
I. Progress since the 1985 State map: (1) may lack Devonian strata entirely; includes coeval volcanic-plutonic complexes; sub-Bar Harbor unconformity at West Gouldsboro. (2) Ellsworth is Cambrian; Lamoine Granite Gneiss carries Ellsworth foliation; Castine unconformity is within the Cambrian. (5) Battie may = Matthews Lake; Jam Brook is fault-related; Clarry Hill schist is west of Sennebec Pond fault. (6) Formations are defined; Prison Farm in thrust contact. (7) Appleton Ridge = Digdeguash. (8) is M. Ord. (9) is Late Ord, exposed in window through Boothbay thrust. (10) is separate from 8. (11) Hutchins Corner Fm defined, may rest on 10; Waterville/Vassalboro thrust on Sangerville. (12) is Sil., may rest on 8; may be partly equivalent to 11. (13) equivalent to Rangeley sequence; east-bounding thrust in question.
II. Remaining questions (for me): (1) Relationship to 2? (2) Deer Isle ultramafic? Calderwood Fm? (3) Islesboro Fm age? (4) Ogier Point = Islesboro? Rockport ls congl = Ashburn? (5) Rhyolites at Owls Head? Origin of Battie congl? (6) Pillow basalts at Friendship? (7) Cross River Fm? (8) Sheepscot Pond Gn? Passagassawakeag Gn? Kingdom Bog mem. of Scarboro? (9) Relationship to 7? (10) Mt. Ararat Fm? (11) Relationship to 10? Vassalboro vs. Hutchins Corner SW of Augusta? Rocks near Sebago pluton, in Standish? (12) Berwick Fm? (13) Relationship to 11?
Assignment of these sections to various terranes by workers from away remains unsatisfying because of so many loose ends and mis-matched stratigraphy. Diagnostic Avalon faunas (Acado-Baltic) lie to the east. Celtic faunas lie to the northwest. A peri-Gondwanan origin in eastern Iapetus seems likely, with accretion by late Silurian and significant modification by Devonian thrusting.
12-3 1:45 PM 40 YEARS OF MAPPING AND STILL WE DON'T KNOW: LUDMAN, Allan,
12-5 2:25 PM METAMORPHIC EVOLUTION OF HP-LT TECTONITES IN THE BRUNSWICK SUBDUCTION COMPLEX, NEW BRUNSWICK AND ITS IMPLICATIONS FOR THE SALINIC OROGENY IN NEW ENGLAND: VAN STAAL, Cees,
The Silurian Salinic orogeny, dynamically distinct from the Early Devonian Acadian orogeny, is still contentious in New England, although the name and hypothesis of such an event derives from an unconformity recognised by Boucot in the Central Maine belt of northern Maine during the 1960's. The Brunswick complex comprises a well preserved association of latest Ordovician-Early Silurian forearc terranes, an association that is only partially preserved elsewhere. Its metamorphic core is represented by exhumed slices of underplated backarc oceanic and continental rocks. Underplating was sequential and started at c. 447 Ma with underplating of a seamount at epidote-blueschist depth (400oC-7Kb). Mineral zonation (act-bar-gln-act) suggests an anticlockwise hairpin P-T-t path reflecting subduction initiation beneath the c. 460 Ma Fournier ophiolite and subsequent subduction-related refrigeration. Accretion of the Spruce Lake block at c. 442 Ma imbricated the overlying Fournier ophiolite and partially extruded the intervening blueschists. The ophiolite slices above the blueschists were metamorphosed to greenschist conditions (360oC-4.8 Kb). Underplating of the Spruce lake block beneath the blueschist, led to metamorphism characterised by winchite ± Na-augite (350oC-6.2 Kb) or actinolite ± pumpellyite (350oC-5.5 Kb), but zonation (Ep & Am) and microstructures suggest a clockwise P-T path, which is also shown by the structurally underlying greenschist nappes of the Tetagouche block (380oC-5.7 Kb), which were underplated between 435-430 Ma. Both blocks are characterised by late-D1 biotite or stilpnomelane porphyroblasts, which are ascribed to Salinic collision with the Gander margin at c. 430 Ma. Tectonism in the accretionary wedge is directly linked to tectonism in the Matapedia forearc and the Fredericton foredeep. Llandovery exhumation of the Fournier ophiolite and its late Llandovery reburial beneath the onlapping Matapedia forearc relates to underplating of the Tetagouche block and subduction hinge-retreat. The blueschists and Spruce Lake nappes were exhumed during the Salinic Wenlock collision, but reburied beneath a latest Silurian/Early Devonian clastic wedge shortly thereafter. The latter represents the northwards advancing Acadian orogenic wedge.
2:45 PM Break
12-6 3:00 PM FORMATION OF NEW ENGLAND GNEISS DOMES: KARABINOS, Paul,
Northward extrusion of quartz-feldspar-rich core gneisses beneath mica-rich Silurian units during Acadian shortening explains many of the critical observations. The domes are surrounded by high-strain zones (HSZ), which decoupled deformation in the core gneisses from that in the overlying nappes of Silurian metasediments. Units were dramatically thinned or omitted in the HSZ. Sense of shear indicators suggest that rocks above the HSZ were displaced southwest relative to rocks below it. P-T paths of rocks from below the HSZ in the Chester dome indicate decompression of several kbars during metamorphism, whereas rocks above the HSZ record nearly isobaric conditions. These observations are consistent with normal-sense displacement between the core of the domes and the mantling sequence during Acadian deformation. During extrusion, the core gneisses cut upsection into the nappes of Silurian rocks and the thickness of the intervening Lower Paleozoic section was dramatically reduced.
12-7 3:20 PM POST-ORDOVICIAN CONTRASTS IN THE GEOLOGICAL EVOLUTION OF THE NORTHERN AND SOUTHERN APPALACHIAN OROGEN: HIBBARD, James,
The New York promontory serves as the divide between the northern and southern segments of the Appalachians. The first order character of the pre-Silurian crustal building blocks of the orogen is essentially uniform along the length of the orogen. Following Late Ordovician-Silurian sinistral oblique accretion of Carolinia and Ganderia along the Appalachian margin, the northern and southern segments of the orogen appear to record distinctly different histories. The northern Appalachians contain a robust middle to late Paleozoic lithotectonic record of Silurian to Early Devonian tectonism with an extensional component followed by Acadian, Neoacadian, and Alleghanian events across most of the orogen. Although the tectonic details of this record are controversial, e.g. subduction polarity and bulk kinematics, it is generally agreed that this record relates to the accretion of the peri-Gondwanan tracts of Avalonia and Meguma and the culminating interaction of Gondwana with Laurentia.
The southern Appalachian
middle to late Paleozoic lithotectonic record is sparse, with relevant strata
preserved as clastic basins and wedges along the western margin of the orogen
and magmatic rocks of ambiguous origin in the hinterland; this meager record
reflects Neoacadian and Alleghanian events. The Alleghanian event is explicitly
tied to the collision of Gondwana with Laurentia, but the nature of the
Neoacadian event is unknown, as no counterpart to either Avalonia or Meguma is
recognized in the southern orogen. The contrast in lithotectonic evolution
between the northern and southern segments of the orogen during the middle to
late Paleozoic appears to be related mainly to the limited distribution of
Avalonia and Meguma. This difference implies that the oceanic tract trailing
Carolinia and Ganderia, i.e. the Rheic Ocean, was more complex than the older
Iapetus Ocean in that it harbored first-order lateral variations.
12-9 4:00 PM SUMMARY OF ORIGIN AND ACCRETION OF THE ARGENTINE PRECORDILLERA TERRANE: THOMAS, William A.,
13-7 3:20 PM NORTHERN APPALACHIAN ACCRETION OF AVALONIA: EVIDENCE FROM CHEMOSTRATIGRAPHY AND K/AR DATING OF ILLITIZATION IN THE SILURIAN ARISAIG GROUP, NOVA SCOTIA: BURGREEN, Blair N.
Tuesday, 13 March 2007
The Neo-Acadian Orogeny and Implications for Tectonic and Depositional Setting of Devonian–Carboniferous Rocks in the Appalachian Orogen
26-3 9:00 AM THE BOUNDARY BETWEEN THE VERMONT AND NEW HAMPSHIRE TERRANES: AN ACADIAN CONUNDRUM: CHENEY, John T.
A long recognized conundrum of New England geology is the enigmatic relationship between the Acadian orogeny in Vermont and New Hampshire. The difference is manifest in seemingly synchronous yet different metamorphic styles of different Siluro-Devonian stratigraphies. The Buchan style metamorphism of New Hampshire, with counterclockwise P-T paths and regional high-T, low-P metamorphism contrasts markedly with the Barrovian metamorphism of Vermont, with its clockwise P-T paths culminating in maximum burial depths of ca 30-35 km.
The VT & NH terranes meet in the vicinity of the Chicken Yard line - the traditional stratigraphic boundary - forming the Connecticut Valley Metamorphic Low (CVML). In the CVS of Vermont and along strike in Massachusetts, the array of accumulated ion microprobe 208Pb/232Th spot ages from matrix and inclusion monazite grains is largely confined to 350-390 Ma. 40Ar/39Ar cooling ages from muscovite in these same rocks range from 330 Ma to 350 Ma. In Massachusetts, Cambro - Ordovician rocks have temperature-time histories that are identical to Siluro-Devonian units. The age signature of the VT metamorphism continues east across the CVML into the garnet zone in the NH stratigraphic sequence.
To the east, the Bronson Hill terrane consists of a sequence of nappes, each with a unique P-T path, that are stacked in an inverted metamorphic sequence and punctuated by late gneiss domes. Each of the domains of the Bronson Hill is separated by a post metamorphic fault that records a significant break in peak P and/or T and each unit has its own characteristic monazite age array. The lowest and western most unit, the big staurolite domain, contains monazite as old as ca 360 Ma, similar to the Vermont monazite ages, and, most significantly, 320 Ma monazite as inclusions in staurolite and 280 Ma matrix monazite grains. Muscovite 40Ar/39Ar ages along and east of the BHT range from 335 Ma at Fall Mtn. to around 250-290 Ma over much of central NH. Accordingly, the rocks of the big staurolite domain underwent metamorphism after the VT rocks cooled through the muscovite closure temperature and after the peak of metamorphism in the overlying NH nappes, presumably during juxtaposition of the two terranes during the Alleghanian and certainly not during the Acadian.
26-4 9:20 AM THE NEOACADIAN OROGENY IN THE SOUTHERN AND CENTRAL APPALACHIANS: A KINEMATIC MODEL LINKING MIDDLE DEVONIAN–EARLY MISSISSIPPIAN ACCRETION OF THE CAROLINA SUPERTERRANE, OROGENIC CHANNEL FLOW, AND FORELAND SEDIMENTATION: MERSCHAT, Arthur J.
The Neoacadian orogeny in the southern and central Appalachians (SCA) is characterized by 380-340 Ma metamorphism, deformation, and plutonism in the Blue Ridge and Inner Piedmont (IP). The IP is the core of the Neoacadian orogen in the SCA and records Late Dev.-Miss. closure of the Rheic remnant ocean basin, and high-grade metamorphism (sillimanite I and II) of Siluro-Dev. pelite and psammite. The IP is a large, composite, sillimanite-grade terrane that extends from near the VA-NC border, to central AL and consists of the eastern Tugaloo, Milton, and Cat Square (CSt) terranes. The IP is bounded to the west by the Brevard fault zone and the east by the central Piedmont suture. The CSt is bounded by the younger-over-older Brindle Creek fault to the west and the central Piedmont suture to the east. It consists of a unique sequence of Siluro-Dev. metapsammite and pelitic schist intruded by Dev. anatectic granitoids (Toluca Granite, ~378 Ma, and Walker Top Granite, ~366 and ~407 Ma). Rare mafic and ultramafic rocks occur in the eastern CSt and may represent relict oceanic lithosphere on which CSt sediments were deposited. Minimum sediment thickness is estimated at 4 km (13,000 ft). Detrital zircons indicate CSt rocks have a maximum age of ~430 Ma, with both Laurentian (1.1, 1.4, 1.8, 2.8 Ga) and peri-Gondwanan Carolina superterrane (Ct) (500, 600 Ma) provenance. Intrusion of the Concord and Salisbury plutonic suites into the Ct and position of the Smith River allochthon above the IP support Dev. subduction of the CSt and Tugaloo terranes beneath the Ct. Thus, the CSt was a Siluro-Devonian remnant ocean basin between Laurentia and the approaching Ct. Net estimates of SW-directed dextral strike-slip displacements of the Brevard fault zone range from 250 to 450 km. Palinspastic restoration of the IP delimits the location of the CSt basin to the Pennsylvania embayment, and links the mid-Dev. to Miss. deformation in the Neoacadian core with SW-migrating pulses of the diachronous Acadian-Neoacadian clastic wedge. Location and SW-migration of the clastic wedge in concert with structural patterns in the IP support transpressive NW-directed collision of the Ct with the New York promontory and zippered closing of the basin from NE to SW. Subduction of the CSt and parts of the Tugaloo terranes beneath the Ct resulted in a SW-directed orogenic channel.
26-5 9:40 AM EVALUATION OF THE GEOCHRONOLOGIC EVIDENCE FOR THE TIMING OF PALEOZOIC OROGENIC EVENTS ALONG THE WESTERN FLANK OF THE SOUTHERN APPALACHIANS: MILLER, Brent,
A comprehensive database was constructed from 528 journal articles, abstracts, and other sources (1959 to 2006) providing 454 Ar/Ar, EPMA, K-Ar, Rb-Sr, Sm-Nd, and U-Pb, ages. All ages taken together at face value show a distinct Taconian maximum at 460-480 Ma, an asymmetric Alleghanian peak at ~340 Ma tailing off to 250 Ma, and between the two lies a broad swath of Acadian or Neoacadian ages. This general pattern is retained through a stepwise quality control process that yields a surprisingly small subset of highly robust ages. The Ar/Ar dataset reveals virtually no Taconian cooling ages, little distinction between Acadian and Neoacadian cooling ages, and an Alleghanian 335 Ma spike. Only 18 U-Pb zircon ages have bearing on the distinction between Neoacadian vs. Acadian plutonism and metamorphism. Ion-microprobe ages from two Acadian granites (one of which, Rabun, is now known to be Alleghanian) are questionable. Two Spruce Pine intrusions have high-precision Acadian ages of ca. 377 Ma. Fourteen reported ages, evenly divided between Acadian and Neoacadian, await publication before their significance can be evaluated.
Although there are many potential biases in this type of evaluation, it does highlight historical trends in thinking about the timing of tectonothermal events and it potentially points the way to future progress in better deciphering the history of southern Appalachian orogenic effects. The database is available in spreadsheet format from the author's website.
26-6 10:15 AM PALEOMAGNETIC OVERPRINTING AS EVIDENCE OF NEO-ACADIAN TECTONISM IN NORTHERN APPALACHIAN PERI-GONDWANAN TERRANES: THOMPSON, M.D.,
26-7 10:35 AM NEOACADIAN DEFORMATION WITHIN THE MEGUMA TERRANE: HORNE, Richard J. The Early Devonian Torbrook Formation provides a minimum age on fold development and 40Ar/39Ar ages generally support a middle Devonian (ca 380-390 Ma) age. The Late Devonian (ca. 375 Ma) South Mountain Batholith (SMB) postdates the main folding event, it however records subtle internal strain consistent with folding accompanying transpression on the terrane-bounding fault. Flexural slip locally deforms porphyroblasts within the contact aureole of the SMB and 40Ar/39Ar ages for some auriferous saddle reef veins coincide with igneous ages. Shear zones parallel to the regional fold axial trend accompanied and may have played a role in granite emplacement. Rapid uplift following granite emplacement may explain the change to the late, brittle, flexural-slip folding.
26-8 10:55 AM THE NEOACADIAN OROGENY IN THE MEGUMA TERRANE, NOVA SCOTIA, CANADA: WHITE, Chris E.
The ca. 380 Ma and 376-372 Ma plutons and high-temperature/low-pressure metamorphism may have been related to delamination of a shallow-dipping Rheic Ocean lithosphere following accretion of Meguma to Avalonia. Rapid uplift and erosion in the Meguma terrane between 370 and 360 Ma resulted in deposition of the Upper Devonian to Lower Carboniferous Horton Group in the northern parts of the terrane. Uplift coincided with intrusion of the younger (ca. 363 and 357 Ma) plutons in southern Meguma terrane and reflects continued northwestward subduction of Rheic Ocean lithosphere under the Meguma terrane as Gondwana approached from the southeast. Widespread ca. 320 Ma deformation in southern Nova Scotia maybe related to the final juxtaposition of Gondwana.
26-9 11:15 AM NEOACADIAN PLUTONISM IN THE NEWFOUNDLAND APPALACHIANS: A POORLY CONSTRAINED BUT ECONOMICALLY IMPORTANT MAGMATIC EVENT: KERR, Andrew
As currently understood, "NeoAcadian" plutonism in Newfoundland is largely confined to an arcuate belt within the eastern Gander Zone and adjacent Avalon Zone. It appears to be spatially associated with this boundary, although it postdates juxtaposition of the two zones. Compared to extensive Silurian and early Devonian magmatism in the Dunnage and Gander zones, this late plutonism is spatially displaced towards the southeast, i.e., outboard with respect to Laurentia. The compositional spectrum of late plutonism is bimodal but felsic-dominated. Granites are typically silica-rich, strongly potassic, and metaluminous to variably peralkaline in character, showing strong regional enrichments in U, Th and F. The Nd isotopic signatures of late granites provide a striking illustration of the fundamental (crustal-scale) importance of the Gander-Avalon boundary, which here demarcates discrete lower crustal blocks.
26-10 11:35 AM WHAT IS THE ACADIAN OROGENY?: MURPHY, J. Brendan
We suggest that collision of all peri-Gondwanan terranes be referred to as the Salinic orogeny, with Ganderian, Avalonian and Carolinian stages for those who interpret these terranes to have collided independently. We suggest that the term Acadian orogeny be reserved for events related to subduction of the Rheic Ocean, with Meguma and Carolinian stages for those who believe that these terranes collided independently from within that ocean. In this scheme a separate Neo-Acadian orogeny would be unnecessary.
Structural Geology and Tectonics
30-8 19 TIMING OF METAMORPHISM AND DEFORMATION IN SOUTHEASTERN PENNSYLVANIA AND NORTHERN DELAWARE: BLACKMER, Gale C.,
New 40Ar/39Ar age data from southeastern Pennsylvania and northern Delaware, together with published monazite data, suggest that development of the dominant regional fabrics and cooling from metamorphic conditions happened in the Devonian, with only localized, minor white mica growth during the Pennsylvanian. The study area is a portion of the central Appalachian Piedmont consisting of greenschist to granulite facies metamorphic rocks, including three provisional divisions of the Wissahickon Formation, separated into structural blocks by major NE-trending faults. Units were sampled as follows, from SE to NW: type Wissahickon Fm SE of the Rosemont Fault (Block 1); Baltimore Gneiss, Mt. Cuba Wissahickon fm, and Setters Fm between the Rosemont and Street Road faults (Block 2); Glenarm Wissahickon fm between the Street Road and Embreeville faults (Block 3); Peters Creek Schist and Octoraro Fm between the Embreeville and Martic faults (Block 4); and Antietam and Harpers formations, undivided, NW of the Martic Fault (Block 5). Amphiboles from amphibolite to granulite facies rocks in Block 2 yield 40Ar/39Ar ages indicating cooling through the ~500ºC isotherm at ~400-375 Ma, suggesting that the Baltimore Gneiss (basement) and the Mt. Cuba Wissahickon fm were at roughly the same structural level at about this time. In comparison, monazite that grew during formation of the regional fabric in garnet-grade rocks in Block 3 yields microprobe ages of ~400 Ma. White mica from lowermost greenschist facies rocks in Block 5 yields a growth age similar to the amphibole cooling and monazite growth ages. This may indicate a time of thrusting on the Martic Fault. White micas from Blocks 1-4 yield 40Ar/39Ar cooling ages of about 365 Ma in all units. We interpret these ages to represent cooling through ~350ºC. No regional patterns are apparent. Age spectra of white micas from the vicinity of the Pleasant Grove-Huntingdon Valley shear zone, within Block 4, are more complex and suggest minor recrystallization during Alleghanian shearing. Regionally, white mica ages from Block 4 are comparable with results from correlative units in the Potomac Terrane of Virginia and Maryland. The amphibole cooling ages from Block 2 are similar to amphibole ages from the Sykesville and Laurel formations of the Potomac Terrane.
30-11 22 TRACE ELEMENT EVIDENCE FOR LATE ORDOVICIAN TO EARLY SILURIAN CRUSTAL THICKENING, SOUTHWEST CONNECTICUT: PROCTOR, Brooks P.1, WINTSCH, Robert
The Beardsley orthogneiss is .....zircon yield 446 ± 2 Ma (Sevigny and Hanson, 1993)......the Pumpkin Ground (PG) orthogneiss is .... zircon yield 428 ± 2 Ma (Sevigny and Hanson, 1993). ......These results suggest that the Beardsley orthogneiss developed in a Late Ordovician volcanic arc setting, which from plate tectonic reconstructions was likely on the eastern margin of Laurentia. About 20 m.y. later, the S-type PG orthogniess developed over a transitional crust from VAG to WPG. This is consistent with merging of the Gander and Laurentian lower crusts, and may reflect tectonic activity during the Salinic orogeny.
30-12 23 ASTHENOSPHERIC UPWELLING AND SLAB ROLL-BACK OF THE SUBDUCTING AVALON PLATE: GEOCHEMICAL EVIDENCE FROM THE LEBANON GABBRO, EAST-CENTRAL CONNECTICUT: BOWMAN, Jeffrey D.
Wednesday, 14 March 2007
Isotopic and Other Indicators of Sediment Provenance and Basement Character
45-2 9:00 AM SM-ND ISOTOPIC AND WHOLE-ROCK CHEMICAL COMPOSITIONS OF LATE NEOPROTEROZOIC AND CAMBRIAN SEDIMENTARY AND METASEDIMENTARY ROCKS OF THE CALEDONIAN HIGHLANDS (AVALONIA), SOUTHERN NEW BRUNSWICK: SATKOSKI, Aaron Preliminary Nd isotopic results from this study combined with previously published data show that the Hammondvale Metamorphic Suite and metasedimentary rocks of the Broad River Group have negative eNd values, whereas the sedimentary rocks of the Coldbrook and Saint John groups show more positive eNd values. The Broad River Group and Hammondvale Metamorphic Suite samples fall well outside the Avalonian igneous isotopic window, suggesting a non-Avalonian source. In contrast, Coldbrook Group and Saint John Group samples fall within the main Avalonian isotopic window, suggesting a substantial Avalonian crustal component. Previously published Nd isotopic data from igneous units in the Broad River and Coldbrook groups have mostly positive eNd values, consistent with the Coldbrook and Saint John group sediments being derived from those rocks. The positive values from the igneous units, however, are not consistent with the more negative values for the Broad River and Hammondvale metasedimentary rocks. These sediments must have had a large, isotopically mature source, presumably outside Avalonia.
45-3 9:20 AM PROVENANCE STUDIES IN THE MEGUMA TERRANE, SOUTHERN NOVA SCOTIA, CANADA: BARR, Sandra M. Petrographic and chemical data suggest that the source area included calc-alkalic tonalitic and granodioritic rocks; the derived sediment experienced little transport and was poorly sorted during rapid deposition in an active continental margin environment. Previously reported detrital zircon ages cluster at 700-550 Ma and 2150-2000 Ma, compatible with African or Amazonian sources. Available epsilon Nd data are highly negative, and more compatible with an Amazonian source. The source of detrital muscovite is not yet resolved but preliminary data indicate ages of 600-560 Ma. Similarities in age and isotopic compositions suggest some links between sediment provenance in the Meguma terrane and now-adjacent Avalonia.
45-4 9:40 AM REINTERPRETING THE PROVENANCE OF EASTERN LAURENTIAN LATE PROTEROZOIC RIFT FILL: NEW WHOLE-ROCK PB ISOTOPIC CONTRAINTS: BREAM, Brendan R. Recent work demonstrates that some cratons have distinct whole-rock Pb isotopic signatures. New whole-rock Pb isotopic data were obtained for 20 samples from a previous detrital zircon and Nd isotopic study. Of these samples, 17 have 207Pb/204Pb values > 15.65 and most 206Pb/204Pb values are between 18.2 and 20.2. The metasedimentary rocks have higher 207Pb/204Pb values for given 206Pb/204Pb values relative to rocks from the mid-continent ~1.4 Ga Granite-Rhyolite and 1.0-1.3 Ga Grenville terranes of New York and Texas. This distinct Pb isotopic signature of the metasedimentary rocks precludes incorporation of significant components of Laurentian material and necessitates an alternate source.
Amazonia is the southeastern Laurentia conjugate rift margin in most Rodinia reconstruction and it contains rocks with similar U/Pb ages and Nd and Pb isotopic signatures to samples from the southern Appalachians. The U/Pb detrital ages and Nd and Pb isotopic signatures of the metasedimentary sequence are also strikingly similar to those of the underlying southern and central Appalachian basement (scAB). Distinct scAB signatures were used to argue that it was an exotic block that was transferred from Amazonia to Laurentia during the Grenville Orogeny. Thus, Blue Ridge and western Inner Piedmont metasedimentary sequences were mostly derived from: (1) a post-Rodinian Laurentian margin that included accreted Amazonian material (scAB); (2) the Amazonian conjugate margin; or (3) both margins. All three scenarios imply that during Rodinia breakup Laurentia included a rifted margin dominated by extended Amazonian blocks and possibly a continental interior that was submerged, topographically subdued, or isolated in terms of its drainage pattern.
45-5 10:15 AM GRAPTOLITE BIOSTRATIGRAPHY AND K-BENTONITE TEPHROCHRONOLOGY FROM A CORE SECTION THROUGH THE UTICA, TRENTON, AND BLACK RIVER GROUPS NEAR BALSTON SPA, NEW YORK: ROLOSON, Melissa. These relations indicate that the base of the Utica here is substantially older than it is farther west in the central Mohawk Valley..........
45-6 10:35 AM AVALONIA: A NEOPROTEROZOIC LOW-18O TERRANE: POTTER, Joanna. ...... We attribute this 18O-depletion to pervasive, post-magmatic hydrothermal alteration. This alteration likely occurred during the last stages of Neoproterozoic igneous activity, and was related to rifting as Avalonia separated from the Gondwanan supercontinent at ca. 560-550 Ma. The development of rift-wrench extensional basins allowed large-scale fluid infiltration and hydrothermal alteration of the Avalonian crust. As this systematic 18O-depletion is not observed in the Neoproterozoic igneous rocks of the other peri-Gondwanan terranes, its occurrence implies that Avalonia remained separate from Ganderia until at least ~550 Ma.
45-7 10:55 AM MAGMA SOURCE CHARACTERISTICS OF CAMBRIAN VOLCANIC ROCKS IN THE ELLSWORTH TERRANE, PENOBSCOT BAY AREA, MAINE: SCHULZ, Klaus J. The Ellsworth terrane in the Penobscot Bay area of Maine consists of Cambrian bimodal volcanic rocks of the Castine Volcanics (~502 Ma), Ellsworth Schist (~509 Ma), and North Haven Greenstone. The volcanic rocks are divided into four geochemical types based on data for immobile trace elements: two types of tholeiitic basalt (Tb-1a, Tb-1b) and two types of rhyolite (Rhy-1, Rhy-2). Here we report Nd isotope data that provide further constraints on the source characteristics of these bimodal volcanics.
Tb-1a basalts, present in all units of the Ellsworth terrane, have compositions transitional between N-MORB and E-MORB, including slightly depleted LREE and primitive mantle-normalized trace element patterns (PMNP) with no Th or Ta anomalies. They have large positive εNd500 values of +7.9 to +8.6 (mean +8.2; n = 6) indicating a long-term depleted mantle source and no crustal contamination. Tb-1b basalts, present only in the Castine Volcanics, are compositionally similar to E-MORB, including enriched LREE and PMNP with no Th or Ta anomalies. They have lower positive εNd500 values of +5.6 and +7.0 (mean +6.3; n = 2) and TDM model ages of 452 and 718 Ma. Rhy-1 rhyolites, present mainly in the Castine Volcanics, have tholeiitic compositions with immobile trace element ratios overlapping those of the Tb-1b basalts. Their positive epsilonNd500 values (mean +6.5; n = 3) also overlap those of the Tb-1b basalts, supporting a genetic relationship. Rhy-2 rhyolites, present mainly in the older Ellsworth Schist, are calc-alkaline with enriched LREE and PMNP with positive Th and negative Ta and Ti anomalies. Relatively low epsilonNd500 values near zero (-0.9 to +0.5) and TDM model ages ranging from 1067 to 1130 Ma indicate an evolved crustal component in the source area of the Rhy-2 rhyolites.
The geochemical and Nd isotope data support a non-arc setting for the Ellsworth terrane. Further, the compositional similarity of the Ellsworth basalts to those found in rift basins in the present Gulf of California suggests that the Ellsworth evolved in a similar tectonic regime. The older Rhy-2 rhyolites may reflect crustal contamination/ melting during initial crustal rifting. Such a rift setting is compatible with the Baja rift model proposed for the Neoproterozoic-Cambrian evolution of peri-Gondwanan terranes (Keppie et al., 2003, Tectonophysics 365: 195-219).
45-8 11:15 AM U-PB DETRITAL ZIRCON GEOCHRONOLOGY OF AVALONIA: CONSTRAINTS ON THE OPENING OF THE RHEIC OCEAN: POLLOCK, Jeff Avalonia comprises Neoproterozoic-early Palaeozoic magmatic arc terranes that extend from eastern Massachusetts to the type area in eastern Newfoundland. Most of Avalonia is at low metamorphic grade, generally mildly deformed, and consists of volcanic, plutonic and sedimentary rocks that record at least five distinct groupings of pre-Iapetan tectonomagmatic and depositional events at ca. 760 and 730 Ma, 685-670 Ma, 635-590 Ma, and 590-545 Ma. The Neoproterozoic rocks are overlain by a terminal Neoproterozoic-Early Ordovician cover of fine-grained siliciclastic rocks containing Acado-Baltic faunas.
U-Pb geochronology on detrital zircons from seven samples from the major lithotectonic elements in Avalonia was completed in order to address multiple first-order questions concerning the evolution of both Avalonia and the Rheic Ocean. The data from Neoproterozoic-Early Cambrian strata (Conception, Musgravetown, and Signal Hill groups and Random Formation) are dominated by Ediacaran (c. 580 Ma) ages and suggest derivation from the underlying arc-volcanic sequences. Although the Arenig Bell Island Group comprises mostly Ediacaran and Cambrian zircons, it also contains significant quantities of Mesoproterozoic and Palaeoproterozic zircons. This change in provenance may be related to the rifting and isolation of Avalonia from Gondwana in the Early Ordovician.
45-9 11:35 AM ANCIENT LAURENTIAN DETRITAL ZIRCON IN THE SOUTHERN UPLANDS TERRANE, BRITISH CALEDONIDES: WALDRON, John W.F. Zircons from a sample deposited early in the depositional history (Kirkcolm Fm.) display a range of U-Pb ages from Paleoarchean to late Ordovician, including the oldest such grain yet recorded from the British Isles. Neoarchean (2.8 - 2.5 Ga), Paleoproterozoic (2.0 - 1.7 Ga), and Mesoproterozoic (1.5 - 1.0 Ga) age populations suggest sources in Laurentia, such as the Grenville and Trans-Hudson orogens. The overall age distribution is comparable to metasedimentary rocks of the Laurentian margin of Iapetus in the Taconian orogen of W. Newfoundland. Samples with younger depositional ages show increasing amounts of Grenville-age zircon (ca. 1.0 Ga) and a general trend of reduced Archean input. Several analyses from the Glenlee Fm. plot on a discordia line suggesting overprinting of Archean zircon in the Early Paleozoic, consistent with tectonothermal reworking of Laurentian detritus in the Grampian orogen.
Field Guides - NEGSA 2007, Durham, NH.
Hon, R. , Hepburn, J.C. & Lair, Jo. 2007. Siluro-Devonian igneous rocks of the easternmost three terranes in southeastern New England: examples from NE Massachusetts and SE New Hampshire.Guidbook to field trips in New Hampshire, adjacent Maine and Massachusetts, 42nd Ann Meet. NEGSA, March 11 2007, p. 23-43 (20). http://instruct.uwo.ca/earth-sci/fieldlog/cal_napp/napp/new_eng_maritimes/Nashoba_Avalon/NEGSAFT_F4.pdf
Swanson, M.T., 2007. Structure of Late Paleozoic brittle dextral strike-slip faults in Coastal Maine exposures. Guidbook to field trips in New Hampshire, adjacent Maine and Massachusetts, 42nd Ann Meet. NEGSA, March 11 2007, p. 3-18 (16).
Ulf Linnemann, R. Damian Nance, Petr Kraft, Gernold Zulauf. 2007. The Evolution of the Rheic Ocean: From Avalonian-Cadomian Active Margin to Alleghenian-Variscan Collision. GSA Spec paper, 592 p. ISBN: 9780813724232.
Ribeiro, António; Munhá, José; Dias, Rui; Mateus, António; Pereira, Eurico; Ribeiro, Luísa; Fonseca, Paulo; Araújo, Alexandre; Oliveira, Tomás; Romão, José; Chaminé, Hélder; Coke, Carlos; Pedro, Jorge, 2007. Geodynamic evolution of the SW Europe Variscides. Tectonics, Vol. 26, No. 6, 14 December 2007 The place of Avalonia in the Variscides of SW Europe. http://instruct.uwo.ca/earth-sci/fieldlog/Variscan_Hercynian/Ribeiro07/Rib07_f10.jpg http://instruct.uwo.ca/earth-sci/fieldlog/Google_Earth/ Variscides.kmz
Potter, J. et al., 2008. Altering Avalonia: oxygen isotopes and terrane distinction in the Appalachian peri-Gondwanan realm. Can.. Earth Sci., 45., p. 815-825.
Boston - -3.1; Mira/Caledonia - -1.2; Newfoundland Avalon - +2.8; Antigonish - +5.3; low values not observed in Paleozoic felsic intrusive rocks in Avalonia or in Ganderia; low values produced during transtensional events in Avalonia, preluding Cambrian submergence of Avalonia; Avalonia was a separate terrain from Ganderia.
Potter, J. et al. 2008. Regional 18O-depletion of Neoproterozoic igneous rocks from Avalonia, Cape Breton Island and southern New Brunswick, Canada. BGSA, 120, 3/4, p. 347-367
"Neoproterozoic igneous rocks of the Avalonian Mira terrane, Cape Breton Island, and Caledonia terrane, southern New Brunswick, have experienced regional 18O-depletion. The majority of these rocks have delta18OWR values between –1 and +6‰, markedly different from igneous rocks of the inboard Ganderian terranes, which have normal-high delta18OWR values of +7 to +12‰. The 18O-depletion of these Avalonian terranes resulted from pervasive hydrothermal alteration."
"The hydrothermal alteration occurred at ca. 560–550 Ma during initial transcurrent rifting of Avalonia at the Gondwanan margin."
"within Mira and Caledonia terrane crust before its submergence in the early Cambrian (ca. 540–530 Ma)."
"The almost ubiquitous 18O-depletion exhibited by the Neoproterozoic rocks in these Avalonian terranes is absent in the associated Ganderian terranes, suggesting that Avalonia remained separate from Ganderia until at least the Cambrian-Ordovician."
Northeastern Section - 43rd Annual Meeting (27-29 March 2008) - http://gsa.confex.com/gsa/2008NE/finalprogram/session_20193.htm
T4. Evidence for Provenance of Peri-Gondwanan Terranes
10-1 1:05 PM GEOCHEMISTRY AND SM-ND ISOTOPIC SIGNATURE OF THE 0.76 GA BURIN GROUP: A COMPOSITIONAL EQUIVALENT OF THE BASEMENT FOR LATE NEOPROTEROZOIC AVALONIAN MAGMATISM?: MURPHY, J. Brendan, Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada, bmurphystfx.ca, MCCAUSLAND, Phil J.A., Earth Sciences, University of Western Ontario, Biology and Geology building, 1151 Richmond St, London, ON N6A 5B7, Canada, O'BRIEN, Sean J., Geological Survey of Newfoundland and Labrador, Newfoundland and Labrador Department of Natural Resources, St. John's, NF A1B, Canada, PISAREVSKY, Sergei, University of Edinburgh, School of Geosciences, Edinburgh, EH9 3JW, United Kingdom, and HAMILTON, Michael, Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, ON M5S 3B1, Canada
"760 Ma Burin Group..... consists of low grade massive and pillowed basalts, abundant dykes and sills, with minor mafic pyroclastic rocks and limestone. "
"its tectonic evolution and its relationship to the voluminous 635-570 Ma arc-related magmatism "
"most basalts have juvenile compositions, with eNd values similar to contemporaneous depleted mantle"
"Other basalts have lower eNd values, and the negative correlation of eNd with La/Sm, together with a positive correlation of eNd with 147Sm/144Nd suggest that their isotopic signatures have been modified by a Mesoproterozoic or older crust or sub-continental lithospheric mantle into which Burin Group mafic volcanics were emplaced. "
"The isotopic signature of the Burin mafic rocks is similar to that inferred for the source of the main phase of Avalonian magmatism. These data, together with paleocontinental reconstructions for ca. 760 Ma, suggest that the Burin Group is a local representative of a ensimatic arcs within the peri-Rodinian ocean, possibly as a far-field response to the breakup of Rodinia. Vestiges of these arcs were accreted to the northern Gondwanan margin at about 650 Ma, and then recycled by subduction beneath that margin during the main ca. 635-570 Ma Avalonian event. "
10-2 1:25 PM AVALONIA'S FOUNDATION? PRELIMINARY PALEOMAGNETISM AND U-PB ZIRCON GEOCHRONOLOGY OF THE MID-NEOPROTEROZOIC BURIN GROUP, NEWFOUNDLAND: MCCAUSLAND, Phil J.A., Earth Sciences, University of Western Ontario, Biology and Geology building, 1151 Richmond St, London, ON N6A 5B7, Canada, pmccausluwo.ca, MURPHY, J. Brendan, Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada, HAMILTON, Michael A., Geology, Univ of Toronto, Toronto, ON M5S 3B1, Canada, PISAREVSKY, Sergei, University of Edinburgh, School of Geosciences, Edinburgh, EH9 3JW, United Kingdom, and O'BRIEN, Sean J., ?Geological Survey of Newfoundland and Labrador, ? Newfoundland and Labrador Department of Natural Resources, St. John's, NF ?A1B, Canada
"single published U-Pb zircon age of 763 +/- 2 Ma on a gabbro sill (Wandsworth), "
"moderately SW-dipping mafic dykes intrude gabbro which has a preliminary U-Pb zircon age of 764.5 +/- 2.1 Ma, "
"The low paleolatitudes in both cases are consistent with the low paleolatitudes found for Avalonia from mid- to Late Neoproterozoic time."
10-3 1:45 PM THE PENOBSCOTTIAN ARC SYSTEM OF COASTAL MAINE AND SOUTHERN NEW BRUNSWICK: FYFFE, Leslie R.1, JOHNSON, Susan C.2, and MCLEOD, Malcolm J.2, (1) New Brunswick Natural Resources, Geological Surveys Branch, PO Box 6000, Fredericton, NB E3B 5H1, Canada, les.fyffegnb.ca, (2) New Brunswick Natural Resources, Geological Surveys Branch, PO Box 5040, 207 Picadilly Road, Sussex, NB E4E 5L2, Canada
"This Penobscottian arc is bordered to the southeast by the New River terrane and to the northwest by the Miramichi terrane.
The oldest arc volcanics occur in the Mosquito Lake Road Formation (~ 514 Ma) of southwestern New Brunswick. Detrital zircons from underlying sandstone of the Matthews Lake Formation are dominated by a population (537-567 Ma) derived from exposed Late Neoproterozoic New River basement. Smaller populations include Neoproterozoic (644 - 807 Ma) and Mesoproterozoic (1.20 -1.51 Ga) ages.
Cambrian volcanics in Maine include felsic tuffs of the Ellsworth Formation (~509 Ma) and domal volcanics of the Castine Formation (~502 Ma). Detrital zircons from Ellsworth sandstone are dominated by a population (530-569 Ma) likely derived from unexposed New River basement. Smaller populations include Cambrian (493-515 Ma), Neoproterozoic (630 to 679 Ma), Mesoproterozoic (1.21 - 1.50 Ga), and Paleoproterozoic (1.97-2.09 Ga) ages.
Felsic tuffs and domal volcanics of the Lawson Brook Formation in the Annidale area of New Brunswick were erupted between ~ 497 Ma and ~ 493 Ma. Zircons from the tuffs contain an inherited component of ~ 940 Ma. Lateral facies equivalents to the Lawson Brook Formation have been intruded by high-level felsic intrusions ranging in age from ~ 478 to ~ 469 Ma.
Ages of detrital zircons and inherited xenocrysts are consistent with formation of the Penobscottian arc on continental crust proximal to Amazonia. Along-strike variations in stratigraphy, volcanic geochemistry, and ages of eruption indicate that the tectonic setting of the arc changed from compressional in the Middle Cambrian to extensional in Late Cambrian. Arc magmatism ceased following collision with the Miramichi terrane in the Early Ordovician. Post-orogenic felsic magmatism (478-469 Ma) in the Penoscottian arc was generated contemporaneously with development of the Ordovician Meductic arc and Tetagouche back-arc basin."
10-4 2:05 PM REFINED AGES OF PALEOZOIC PLUTONS AS CONSTRAINTS ON AVALONIAN ACCRETION IN SOUTHEASTERN NEW ENGLAND: THOMPSON, Margaret D., Geosciences Department, Wellesley College, 106 Central Street, Wellesley, MA 02481, mthompsonwellesley.edu and RAMEZANI, Jahandar, Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139
" CA-TIMS single-zircon U-Pb (weighted mean 206Pb/238U) dates of 425.97 ± 0.64 Ma for the Cape Ann Granite and 378.08 ± 0.62 Ma for the Peabody Granite represent significant refinements in both precision and accuracy over previous multi-grain results (450 ± 25 Ma and 380 ± 15 Ma, respectively). "
" The Silurian age of the Cape Ann Granite and work in progress on the Quincy Granite, along with re-calibration of the geologic time scale cast doubt on Ordovician magmatism in southeastern New England. Rather, these developments strengthen the pattern of Siluro-Devonian igneous activity known from previous geochronology (427 ± 2 Ma Lexington pluton; 417 ± 6 Ma Franklin pluton, 392 ± 4 Ma Salem gabbro-diorite), as well as fossiliferous Newbury volcanic rocks. This magmatic episode coincides with deformation, metamorphism and plutonism in the Nashoba terrane that has been interpreted in terms of the amalgamation of Ganderian and Avalonian elements prior to docking with Laurentia."
" Coastal Maine experienced similar activity as composite Avalon converged with and ultimately overthrust inboard sequences of the Fredericton Trough and Central Maine Basin (Acadian orogeny of some workers). Geochemical dissimilarities between Newbury and coastal Maine volcanic rocks have suggested that Siluro-Devonian convergence involved subduction with both frontal arc and extensional back-arc components, and the alkalic characteristics of the plutons in the Southeastern New England Avalon Zone may reveal a deeper level of the latter.
The Peabody Granite falls with other Late Devonian igneous rocks in southeastern New England (378 ± 3 Ma diorite at Waltham, 370 ± 7 Ma Scituate plutonic suite, 373 ± 2 Ma Wamsutta rhyolite). Bodies of comparable age seal the Avalonian terrane boundary in coastal Maine. "
10-5 2:25 PM ZIRCON-BASED PROVENANCE STUDIES: GOING ALL THE WAY REQUIRES MORE THAN JUST A DATE: HIETPAS, Jack1, SAMSON, Scott1, CHAKRABORTY, Suvankar2, and MOECHER, David2, (1) Department of Earth Sciences, Syracuse University, 204 Heroy Laboratory, Syracuse, NY 13244, jhietpassyr.edu, (2) Department of Earth and Environmental Sciences, University Of Kentucky, Lexington, KY 40506
10-6 3:05 PM PRESSURE-TEMPERATURE-TIME CONDITIONS, ND AND PB ISOTOPIC COMPOSITIONS AND DETRIAL ZIRCON GEOCHRONOLOGY OF THE MASSABESIC GNEISS COMPLEX, NEW HAMPSHIRE: DORAIS, Michael J.1, WINTSCH, Robert P.2, KUNK, Michael J.3, ALEINIKOFF, John4, UNDERDOWN, Christine1, and KERWIN, Charles M.5, (1) Geological Sciences, Brigham Young University, Provo, UT 84602, doraisbyu.edu, (2) Geological Sciences, Indiana University, Bloomington, IN 47405, (3) U.S. Geological Survey, 926A National Center, Reston, VA 20192, (4) U.S. Geol Survey, Denver, CO 80225, (5) Dept. of Earth Sciences, Univ of New Hampshire, 56 College Rd, Durham, NH 03824-3589 10-7 3:25 PM
" The Massabesic Gneiss Complex of southeastern New Hampshire is a peri-Gondwanan inlier with either Ganderian or Avalonian affinities. To help determine the relationship of the complex to these peri-Gondwanan terranes, we dated amphibole, muscovite, and biotite in Massabesic amphibolites and paragneisses by the 40Ar/39Ar method, determined bulk-rock Nd and Pb isotopes of Massabesic orthogneisses, and determined the ages of detrital zircons in a Massabesic quartzite by SHRIMP.
The 40Ar/39Ar analyses yielded uniform ages of ~255-260, ~240, and ~238 Ma for amphibole, muscovite, and biotite respectively, showing cooling from the Permian at ~9°C/m.y. Metamorphic pressures and temperatures calculated using standard mineral thermobarometers yield peak anatectic metamorphic conditions of ~9 Kb and ~700°C, and conditions in overprinting schistosities of 7 Kbars at the same 700°C temperatures. Compared to Avalonia of southern Connecticut, one-dimensional thermal modeling shows that the slightly younger ages and the slightly slower cooling rate is explained by a 2-3 km deeper level of Permian metamorphism. These results are consistent with P-T-t paths in all exposed Avalonian rocks in New England, and confirm a Permian clockwise P-T path.
The majority of Avalonian rocks have positive bulk-rock eNd compared to more negative values for Ganderian plutons, however there is considerable overlap in eNd between the two terranes. Massabesic orthogneiss eNd and 207Pb/204Pb values are inconclusive for terrane determination because they plot in the overlapping fields of Ganderia and Avalonia. However, detrital zircons from a Massabesic quartzite are similar to inherited zircons from Ganderian plutons and those in the Lyme dome of southern Connecticut. Mismatches in zircon ages and abundances between Avalonian supracrustals and the Massabesic quartzite make an Avalonian correlation doubtful. Thus while the detrital zircon data suggest a Massabesic – Ganderia correlation, the P-T-t data indicate that the Massabesic was coupled with Avalonia of southern New England during the Alleghanian. "
10-7 3:25 PM SIGNIFICANCE OF DETRITAL ZIRCON AGES FROM THE WESTBORO QUARTZITE, AVALON TERRANE, EASTERN MASSACHUSETTS: HEPBURN, J. Christopher, Department of Geology and Geophysics, Boston College, Chestnut Hill, MA 02467-3809, hepburnbc.edu, FERNÁNDEZ-SUÁREZ, Javier, Departmento de Petrologia y Geoquímica, Universidad Complutense, Madrid, 28040, JENNER, George A., Dept. of Earth Sciences, Memorial University of Newfoundland, St. John’s, NF A1B3X5, Canada, and BELOUSOVA, Elena A., GEMOC, Dept. of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia
"Quartzites are found in much of the Avalon terrane (sensu stricto) in SE New England (SENE), where they form scattered exposures within intrusive and volcanic rocks associated with the ~ 600 Ma Avalonian arc magmatism. These quartzites, assigned to the Westboro Fm. in MA, the Plainfield Fm. in RI and CT and the Blackstone Group in RI, have been interpreted to pre-date the Avalonian arc magmatism based largely on the assumed age of cross-cutting granites supported by previous studies of detrital zircons where the youngest grain found was ~ 1Ga. We analyzed 95 detrital zircon grains from an orthoquartzite from the Westboro Fm. type locality, Westborough, MA by U-Pb (LA-ICP-MS), but 15 were rejected due to their high discordance. Thirteen zircons lie in the 590-650 Ma age range. The age distribution from the remaining analyses includes age peaks at ~1200, 1500 and 1900 Ma; the oldest zircon is 2688 Ma. Based on the pooled concordia age of the six youngest (concordant and overlapping) analyses, the maximum sedimentation age deduced from this sample is 600±3 Ma (Ediacaran).
Lack of ~ 600 Ma detrital zircons in previous studies of quartzites from SENE (except for one grain in the Plainfield Quartzite in CT; Karabinos and Gromet, 1993) indicates either that this population of zircons was missed due to sample bias or, more likely, that quartzites of more than one age are present in this terrane. We think that at least the belt of quartzite along the western edge of the Avalon terrane from Westborough southward into the Plainfield Fm. of W. RI and E. CT is part of a younger succession that formed post 600 Ma, whereas field evidence suggests the Blackstone Group likely predates the Avalonian magmatism. Quartzites mapped as the Westboro in other areas of E. MA may fall into either group. The younger quartzites must lie unconformably on the ~ 600 Ma Avalonian magmatic rocks and may be as young as Cambrian, when the Boston area was in a stable shelf environment.
The Mesoproterozoic and Paleoproterozoic age populations are consistent with previous detrital zircon studies in SENE and elsewhere in the Avalon composite terrane of the N. Appalachians, strengthening ties of the Boston area to other Avalonian fragments. They also support a non-West African craton connection for western Avalonia and are entirely consistent with an Amazonian craton derivation. "
10-8 3:45 PM PROVENANCE OF THE MEGUMA TERRANE, NOVA SCOTIA: WHITE, Chris E.1, WALDRON, John W.F.2, BARR, Sandra M.3, SIMONETTI, Antonio4, and HEAMAN, Larry M.4, (1) Nova Scotia Department of Natural Resources, PO Box 698, Halifax, NS B3J 2T9, whitecegov.ns.ca, (2) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G2E3, Canada, (3) Geology, Acadia Univ, Wolfville, NS B4P 2R6, Canada, (4) Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada
"Quartzites are found in much of the Avalon terrane (sensu stricto) in SE New England (SENE), where they form scattered exposures within intrusive and volcanic rocks associated with the ~ 600 Ma Avalonian arc magmatism. These quartzites, assigned to the Westboro Fm. in MA, the Plainfield Fm. in RI and CT and the Blackstone Group in RI, have been interpreted to pre-date the Avalonian arc magmatism based largely on the assumed age of cross-cutting granites supported by previous studies of detrital zircons where the youngest grain found was ~ 1Ga. We analyzed 95 detrital zircon grains from an orthoquartzite from the Westboro Fm. type locality, Westborough, MA by U-Pb (LA-ICP-MS), but 15 were rejected due to their high discordance. Thirteen zircons lie in the 590-650 Ma age range. The age distribution from the remaining analyses includes age peaks at ~1200, 1500 and 1900 Ma; the oldest zircon is 2688 Ma. Based on the pooled concordia age of the six youngest (concordant and overlapping) analyses, the maximum sedimentation age deduced from this sample is 600±3 Ma (Ediacaran).
Lack of ~ 600 Ma detrital zircons in previous studies of quartzites from SENE (except for one grain in the Plainfield Quartzite in CT; Karabinos and Gromet, 1993) indicates either that this population of zircons was missed due to sample bias or, more likely, that quartzites of more than one age are present in this terrane. We think that at least the belt of quartzite along the western edge of the Avalon terrane from Westborough southward into the Plainfield Fm. of W. RI and E. CT is part of a younger succession that formed post 600 Ma, whereas field evidence suggests the Blackstone Group likely predates the Avalonian magmatism. Quartzites mapped as the Westboro in other areas of E. MA may fall into either group. The younger quartzites must lie unconformably on the ~ 600 Ma Avalonian magmatic rocks and may be as young as Cambrian, when the Boston area was in a stable shelf environment.
The Mesoproterozoic and Paleoproterozoic age populations are consistent with previous detrital zircon studies in SENE and elsewhere in the Avalon composite terrane of the N. Appalachians, strengthening ties of the Boston area to other Avalonian fragments. They also support a non-West African craton connection for western Avalonia and are entirely consistent with an Amazonian craton derivation."
10-9 4:05 PM PROVENANCE AND TECTONIC SETTING OF LATE NEOPROTEROZOIC AND CAMBRIAN SEDIMENTARY AND METASEDIMENTARY ROCKS IN AVALONIA OF SOUTHERN NEW BRUNSWICK: SATKOSKI, Aaron M.1, BARR, Sandra M.1, and SAMSON, Scott D.2, (1) Earth and Environmental Science, Acadia Univ, Wolfville, NS B4P 2R6, Canada, aaron.satkoskiacadiau.ca, (2) Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse Univeristy, Syracuse, NY 13244
" Neoproterozoic though Cambrian clastic sedimentary and/or metasedimentary rocks occur in the Hammondvale Metamorphic Suite (> ca. 620 <680 Ma) and Broad River (ca. 620 Ma), Coldbrook (ca. 560-542 Ma) and Saint John (ca. 540-490 Ma) groups in the Avalonian Caledonia terrane of southern New Brunswick. The lithological, major and trace element chemical, and Nd isotopic compositions of the sedimentary rocks provide new constraints on the provenance and environment of deposition of these units and hence on the tectonic evolution of this typical part of Avalonia. Nd isotopic and whole-rock chemical data show that the Hammondvale Metamorphic Suite and metasedimentary rocks of the Broad River Group have negative eNd values, were derived from recycled sedimentary and mafic igneous sources, and were deposited in intra-arc basins as part of the ca. 620 volcanic-arc complex. In contrast, sedimentary rocks of the Coldbrook Group show generally positive eNd values and likely were derived from Avalonian felsic to intermediate igneous sources and deposited in rift basins associated with 560-550 Ma arc extension. Samples from the overlying Saint John Group have felsic to mafic igneous sources, but are characterized by negative eNd values and likely were deposited as part of a newly forming passive margin sequence.
Many metasedimentary and sedimentary samples from the Hammondvale Metamorphic Suite, Broad River Group, and Saint John Group fall outside the normal range for Avalonian igneous rocks, whereas Coldbrook Group samples fall mainly in the typical Avalonian igneous range, suggesting a substantially larger Avalonian crustal component in their evolution. Based on their mostly positive eNd values, the sedimentary units in the Coldbrook Group were derived from associated volcanic units as well as the older Broad River Group igneous units. The more negative eNd values for samples from the Hammondvale Metamorphic Suite and Broad River Group indicate a large, isotopically mature source from more interior locations in Gondwana. Based on overlapping detrital muscovite ages and similar Nd isotopic values, the lower Saint John Group units were derived from the Hammondvale Metamorphic Suite, whereas the middle to upper units, which have more evolved Nd isotopic values, appear to require a source outside of the Caledonia terrane. "
10-10 4:25 PM PROVENANCE STUDIES OF CAMBRIAN SEDIMENTARY ROCKS IN AVALONIA, SOUTHERN NEW BRUNSWICK AND CAPE BRETON ISLAND, NOVA SCOTIA, CANADA: BARR, Sandra M.1, WHITE, Chris E.2, HAMILTON, Michael A.3, REYNOLDS, Peter H.4, and SATKOSKI, Aaron M.1, (1) Department of Earth and Environmental Science, Acadia University, Wolfville, NS B4P 2R6, Canada, sandra.barracadiau.ca, (2) Natural Resources, P.O. Box 698, Halifax, NS B3J 2T9, Canada, (3) Jack Satterly Geochronology Lab, Dept. of Geology, Univ of Toronto, Toronto, ON M5S 3B1, (4) Earth Sciences, Dalhousie Univ, Halifax, NS B3H 3J5, Canada
"Cambrian sedimentary rocks typical of Avalonia occur in the Caledonia terrane of southern New Brunswick and the Mira terrane of Cape Breton Island, Nova Scotia. The lowermost unit in the Saint John area, the Ratcliffe Brook Formation, is the age-equivalent of the Chapel Island Formation in the type area of eastern Newfoundland and likely extends into the Ediacaran Period of the Late Neoproterozoic. The Ratcliffe Brook Formation differs from similar lithologies in the underlying Seeley Beach Formation of the Coldbrook Group (equivalent to the Rencontre Formation of eastern Newfoundland) in containing abundant detrital muscovite and less abundant pyroclastic material. New 40Ar/39Ar data for detrital muscovite from the Ratcliffe Brook Formation has a maximum age of ca. 620 Ma, and a minimum age of 550 Ma. The overlying Glen Falls Formation consists of grey to white quartz arenite, equivalent to the Random Formation of eastern Newfoundland, and is overlain by the Hanford Brook Formation, age of which is constrained to late Early Cambrian by fossils and a previously published U-Pb (zircon) age of ca. 511 Ma from an ash horizon. Overlying units extend through the Middle and Late Cambrian and into the Early Ordovician.
Laser ablation MC-ICPMS analysis of 100 detrital zircons from the Glen Falls Formation yield a nearly unimodal age population with a peak at ~540 Ma. Subordinate age clusters occur between 600-665 Ma and 1850-2100 Ma, with spot ages also at 750, 1540, 2900, and 3100 Ma. The dominant population age is similar to the previously published U-Pb zircon age of 531 Ma from ash in the upper part of the underlying Ratcliffe Brook Formation. Nd isotopic data indicate that the provenance changed during deposition from more juvenile sources (positive to moderately negative eNdt values in the Seeley Beach, Ratcliffe Brook, and Glen Falls formations) to more evolved sources (eNdt values as low as -8.5 from the Late Cambrian part of the sequence). Work is in progress to obtain detrital muscovite and zircon ages from equivalent units in the Mira terrane of Cape Breton Island, and in lithologically similar units in adjacent Ganderian terranes. Although the age and eNdt data have broad similarities to those from units of the same age in the Meguma terrane, they differ in detail, and a linkage between the two terranes at that time is unlikely. "
10-11 4:45 PM DETRITAL ZIRCON CONSTRAINTS ON THE PALEOZOIC PROVENANCE OF PERI-GONDWANAN TERRANES IN SOUTHERN MEXICO: NANCE, R. Damian, Department of Geological Sciences, Ohio University, Athens, OH 45701, nanceohiou.edu, MILLER, Brent V., Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, KEPPIE, J. Duncan, Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, México, DF 04510, Mexico, MURPHY, J. Brendan, Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada, and DOSTAL, Jaroslav, Department of Geology, St. Mary's University, Halifax, NS B3H 3C3, Canada
"Several terranes of peri-Gondwanan affinity are exposed in central and southern Mexico. They include: (1) the Oaxaquia terrane, a ~1 Ga crustal block that underlies much of central Mexico and is overlain by a veneer of unmetamorphosed latest Cambrian-Ordovician and Silurian strata containing Gondwanan fauna, and (2) the Mixteca and Sierra Madre terranes, which mainly comprise metamorphosed Paleozoic siliciclastic and oceanic rocks juxtaposed against the Oaxaquia terrane along major, N-S dextral faults of Permian age. Detrital zircon age populations from: (1) the latest Cambrian-Pennsylvanian cover of the Oaxacan Complex (Oaxaquia terrane), (2) the Paleozoic Acatlán Complex (Mixteca terrane), and (3) the ?Silurian Granjeno Schist (Sierra Madre terrane), are dominated by Mesoproterozoic (~950-1300 Ma), late Neoproterozoic-Cambrian (~500-700 Ma), Ordovician (~440-480 Ma), and Permo-Carboniferous (~290 Ma) ages, with additional early Neoproterozoic (~800-950 Ma) and mid-Proterozoic and older (~1300-2200 Ma) signatures. These ages suggest Precambrian provenances in: (1) the Oaxaquia terrane or other ~1 Ga basement complexes of the northern Andes, (2) the ~500-600 Ma Brasiliano orogens and ~600-950 Ma Goias magmatic arc of South America, and the Pan-African Maya terrane of the Yucatan Peninsula, and (3) ~1.4-3.0 Ga cratonic provinces that most closely match those of Amazonia. Exhumation of ~440-480 Ma and ~290 Ma granitoids within the Acatlán Complex likely provided additional sources in the Paleozoic.
These data collectively suggest palinspastic linkages to the northwest margin of Amazonia during the late Proterozoic-Paleozoic and support continental reconstructions that place the Oaxaquia terrane adjacent to Amazonia throughout the Paleozoic rather than those that either accrete Oaxaquia to Laurentia in the late Ordovician-early Silurian or advocate more complex Paleozoic Oaxaquia-Laurentia-Gondwana relationships. They also support a broad correlation between the Paleozoic strata in the Sierra Madre terrane (Granjeno Schist) and similar Paleozoic rocks (e.g. Cosoltepec Farmation) in the Mixteca terrane, and suggest that both were deposited along the southern, Gondwanan (Oaxaquia) margin of the Rheic Ocean in the ?Siluro-Devonian and were accreted to Laurentia with the closure of this ocean during the late Paleozoic amalgamation of Pangea."
Northeastern Section - 44th Annual Meeting (22–24 March 2009)- http://gsa.confex.com/gsa/2009NE/finalprogram/session_23366.htm
S7. Provenance and Orogenic History of Ganderia: Key Element in the Mid-Paleozoic Accretionary History of the Appalachian Orogen
47-1 8:00 AM GEOCHRONOLOGY AND GEOCHEMISTRY OF THE ANNIDALE GROUP, SOUTHERN NEW BRUNSWICK, CANADA: CAMBRO-ORDOVICIAN ARC-RELATED MAGMATISM ALONG THE MARGIN OF GANDERIA: JOHNSON, Susan C.1, MCLEOD, Malcolm J.1, FYFFE, Les R.2, and DUNNING, Greg R.3, (1) Geological Surveys Branch, New Brunswick Department of Natural Resources, P.O. Box 5040, Sussex, NB E4E 5L2, Canada, susan.johnsongnb.ca, (2) Geological Surveys Branch, New Brunswick Department of Natural Resources, P.O. Box 6000, Fredericton, NB E3B 5H1, Canada, (3) Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NF A1B 3X5, Canada
"Late Cambrian - Early Ordovician rocks of the Annidale Group are preserved within a northeast-trending, fold-thrust belt along the northwestern margin of the peri-Gondwanan New River terrane in southern New Brunswick. The group comprises a complex assemblage of marine mafic-intermediate volcanic and sedimentary rocks, rhyolite flows and domes, gabbro and plagiogranite. New U/Pb data indicates that tectonic interleaving of the c. 497 – 489 Ma Annidale Group and its juxtaposition with New River basement occurred prior to c. 476 Ma, the age of the Stewarton gabbro that stitches the faulted contact. Younger (c.478-472 Ma) felsic volcanic rocks and associated rhyolite domes are interpreted to lie unconformably on the Annidale Group.
Geochemical signatures of the Annidale Group are indicative of supra-subduction zone magmatism. Mafic-intermediate volcanic rocks are subalkaline, mostly tholeiitic to transitional basaltic andesites that exhibit both arc and non-arc geochemical signatures. Most samples show weak to strong negative Nb and Ta and positive Th anomalies on extended rare earth plots and fall clearly within volcanic-arc fields on trace-element discrimination diagrams. One exception is a group of extreme LREE-depleted basalts associated with plagiogranite intrusions, which display concave-upwards REE patterns typical of N-MORB affinity, but with uncharacteristically low TiO2 (0.48-0.54%) more typical of arc tholeiites. These basalts are also magnesian-rich (13.7 – 17.2% MgO) and strongly enriched in Cr (1180-4910 ppm) and Ni (390-880ppm).
These new data bearing on the age and tectonic setting of the Annidale Group are in accord with recent models for the tectonic development of the Exploits Subzone in Newfoundland and confirm that Latest Cambrian – Early Ordovician magmatism in the Annidale Group can be related to the development of the Penobscot arc along the Gander margin. Latest Arenig to Middle Ordovician (post-Penobscottian) magmatism, possibly related to the initiation of the Victoria arc, affected both the Annidale Group and adjacent Neoproterozoic – Early Cambrian New River terrane. A recent 40Ar/39Ar age of 444 +/- 5 Ma for metamorphic muscovite in schistose felsic tuff of the Annidale Group indicates that unroofing of the arc volcanics was coincident with the final closure of Iapetus."
47-2 8:20 AM DETRITAL ZIRCON AGES FROM CONGLOMERATE AND SANDSTONE UNITS OF NEW BRUNSWICK AND COASTAL MAINE: PALEOGEOGRAPHIC IMPLICATIONS FOR GANDERIA AND THE CONTINENTAL MARGIN OF WESTERN GONDWANA: FYFFE, Les R., New Brunswick Department of Natural Resources, Geological Surveys, PO Box 6000, Fredericton, NB E3B 5H1, Canada, Les.Fyffegnb.ca, BARR, Sandra M., Geology, Acadia Univ, Wolfville, NS B4P 2R6, Canada, MCLEOD, Malcolm J., Geological Surveys Branch, New Brunswick Department of Natural Resources, P.O. Box 5040, Sussex, NB E4E 5L2, Canada, MCNICOLL, Vicki J., Geological Survey of Canada, 601 Booth Street, Otawa, ON K1A 0E8, Canada, VALVERDE-VAQUERO, Pablo, Instituto Geológico y Minero de España (IGME), La Calera 1, Tres Cantos (Madrid), 28760, Spain, VAN STAAL, Cees R., Geological Survey of Canada, 625 Robson Street, Vancouver, BC V6B 5J3, Canada, and WHITE, Chris E., Natural Resources, P.O. Box 698, Halifax, NS B3J 2T9, Canada
"Detrital zircon ages were determined from conglomerate and sandstone samples from six fault-bounded belts in New Brunswick and coastal Maine. Formations sampled included Martinon (Brookville belt), Flagg Cove (Grand Manan Island belt), Matthews Lake (New River belt), Ellsworth (Ellsworth belt), Calais (St. Croix belt), and Baskahegan Lake (Miramichi belt). Their range of depositional ages based on the youngest detrital zircon population and stratigraphic, paleontological, and cross-cutting intrusive relationships are: Martinon between 602 ± 8 and 546 ± 2 Ma; Flagg Cove between 574 ± 7 and 535 ± 3 Ma; Matthews Lake between 539 ± 5 and 514 ± 2 Ma; Ellsworth between 507 ± 6 and 504 ± 3 Ma; Calais between 510 ± 8 and 479 ± 2 Ma; and Baskahegan Lake between 525 ± 6 and 488 ± 2 Ma.
All of the samples are dominated by Neoproterozoic (pan-African) zircon populations. The Paleozoic Matthews Lake, Ellsworth, and Calais formations contain main population peaks at 539 ± 5 Ma, 545 ± 4 Ma, and 556 ± 7 Ma, respectively, consistent with derivation mainly from magmatic rocks of the Brookville, Grand Manan Island, and/or New River belts, previously dated at 553 to 528 Ma. In contrast, the main peak in the Paleozoic Baskahegan Lake Formation is older at 585 ± 5 Ma. The main peak in the Neoproterozoic to Early Cambrian Flagg Cove Formation is at 611 ± 7 Ma with a secondary peak at 574 ± 7 Ma; the former was likely derived from locally exposed igneous units dated at ~618 to ~611 Ma. The Neoproterozoic Martinon Formation exhibits dominant peaks at 674 ± 8 Ma and 635 ± 4 Ma. Ganderian basement gneiss dated at ~675 Ma and intruded by plutonic rocks dated at ~584 Ma in the Hermitage Flexure of Newfoundland are possible sources for these older zircon components in the Martinon and Baskahegan Lake formations. Plutonic rocks in the New River belt dated at ~629 to ~622 Ma may be the source of the younger component in the Martinon Formation.
The samples also contain a small number of Mesoproterozoic, Paleoproterozoic, and Archean zircon grains, the latter as old as 3.23 Ga. The presence of zircons in the range 1.07 to 1.61 Ga is consistent with an origin along the peri-Gondwanan margin of Amazonia rather than West Africa. The general similarity of zircon provenance for samples from New Brunswick and coastal Maine suggests that all the Ganderian belts were part of a single microcontinent. "
47-3 8:40 AM MIDDLE CAMBRIAN TO EARLY ORDOVICIAN ARC – BACK-ARC DEVELOPMENT ON THE LEADING EDGE OF GANDERIA, NEWFOUNDLAND APPALACHIANS: ZAGOREVSKI, Alexandre1, VAN STAAL, Cees R.2, ROGERS, Neil1, and MCNICOLL, Vicki1, (1) Geological Survey of Canada, 601 Booth St, Ottawa, ON K1A 0E8, Canada, azagorevnrcan.gc.ca, (2) Geological Survey of Canada, 625 Robson Street, Vancouver, BC V6B 5J3, Canada
"Evolution of many modern intra-oceanic and continental arc systems is exemplified by cycles of arc construction, rifting and separation of remnant and active arcs by a back-arc basin cored by oceanic crust. Synthesis of recently obtained geochronological, geochemical, isotopic and stratigraphic data is enabling detailed resolution of the evolution of the Cambro-Ordovician Penobscot arc system that developed on the leading edge of Ganderia, a peri-Gondwanan microcontinent. The Cambrian to Lower Ordovician Penobscot arc is characterized by continuous migration of the magmatic front, and the development of multiple volcanically active rift basins and multiple phases of polymetallic VMS formation (c. 513, 505, 496, 491 and 487 Ma). The rift basins display a variety of characteristics ranging from bimodal calc-alkaline magmatism to felsic-dominated incipient rift magmatism to tholeiitic/boninitic supra-subduction zone ophiolites. Zircon inheritance, Sm/Nd isotopic evidence and limited exposure of Ediacaran basement indicate that the Ganderian crust was highly attenuated and/or fragmented but formed the basement to the Penobscot arc throughout its history. Comparison to modern analogues suggests that part of the Penobscot arc developed in a similar tectonic setting as the volcanically active Havre Trough and Taupo Volcanic Zone. The Penobscot arc magmatism was terminated by an orogenic episode marked by the obduction of back-arc ophiolites onto the Ganderian passive margin."
47-4 9:00 AM GEOCHRONOLOGICAL AND ISOTOPIC EVIDENCE FOR PROGRESSIVE RECYCLING OF OLDER CRUST IN ARC SYSTEMS LINKED TO GANDERIA IN CENTRAL NEWFOUNDLAND: VICKI, McNicoll, Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada, VmcnicolNRCan.gc.ca, HINCHEY, John, Geological Survey of Newfoundland and Labrador, PO Box 8700, St. John's, NF A1B 4J6, Canada, KERR, Andrew, Geological Survey of Newfoundland and Labrador, Department of Natural Resources, PO Box 8700, St. John's, NF A1B 4J6, Canada, andykerrgov.nl.ca, and SQUIRES, Gerry, Teck-Cominco Ltd, PO Box 9, Millertown, NF A0H 1V0
"Recent U-Pb geochronological and Sm-Nd isotopic studies in central Newfoundland are aimed primarily at defining the age of important volcanogenic massive sulphide (VMS) deposits within the Victoria Lake Supergroup, a collage of Cambrian and Ordovician rocks representing peri-Gondwanan arc systems within the Iapetus Ocean. However, these data also have interesting implications for the extent and influence of Precambrian crust in the region, and for the progressive accretion of Paleozoic arcs in the region now termed "Ganderia".
An age of ca. 565 Ma from felsic tuffs associated with the Burnt Pond VMS prospect adds to the extent of late Precambrian rocks of both plutonic and volcanic affinity, and indicates that the latter have significant mineral potential. The discrimination of these Precambrian and Paleozoic volcanic sequences is difficult on the basis of their geochemistry, although Sm-Nd data may provide some distinction. Two ages from felsic rocks closely associated with the Duck Pond VMS deposit confirm that it and its host rocks (Tally Pond Group) are of Cambrian age (ca. 514 - 509 Ma). U-Pb SHRIMP data indicate the presence of inherited zircons with ages of ca. 573 Ma and 563 Ma in these rocks. These ages match those obtained directly from late Precambrian rocks in the area, and indicate that the Tally Pond Group likely developed upon this older substrate. Sm-Nd model ages for Tally Pond Group samples are considerably older than ca. 570 Ma, suggesting that the incorporated Precambrian crust had a significantly older heritage. Two ages from the Boomerang VMS deposit indicate that its host rocks form part of a younger (ca. 491 Ma) Ordovician sequence within the Victoria Lake Supergroup. U-Pb SHRIMP data from these samples indicate the presence of inherited zircons with ages of ca. 514 Ma and 510 Ma. These ages closely match those obtained from the Tally Pond Group. Collectively, such patterns support a wider model in which Paleozoic peri-Gondwanan island arcs in central Newfoundland were progressively accreted to a Precambrian crustal fragment, and in which the older arcs provided the foundations for progressively younger sequences."
47-5 9:20 AM ND ISOTOPIC CONSTRAINTS ON THE ORIGIN OF THE NASHOBA TERRANE, EASTERN MASSACHUSETTS: KAY, Andrew, Geology and Geophysics, Boston College, Devlin Hall 213, 140 Commonwealth Avenue, Chestnut Hill, MA 02467, kayanbc.edu, HEPBURN, J. Christopher, Department of Geology and Geophysics, Boston College, Chestnut Hill, MA 02467-3809, KUIPER, Yvette D., Geology and Geophysics, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467, and INGLIS, Jeremy, Department of Earth Sciences, Boston University, 685 Commonwealth Avenue, Boston, MA 02215 9:40 AM Break
"The Nashoba Terrane is a highly metamorphosed (to upper amphibolite facies) terrane in eastern Massachusetts located between the Avalon Terrane (sensu stricto) to the east and the Merrimack Belt to the west. It is interpreted as a tectonized remnant of an early Paleozoic or Late Neoproterozoic volcanic arc/backarc complex. Its origin has long been debated. New Nd isotopic data on three of the older units in the terrane were obtained to better constrain the tectonic origin of the terrane and its possible correlation with Ganderia. The Marlboro Fm. consists of amphibolites interpreted as metamorphosed tholeiitic to calc-alkaline basalts. Two hornblende amphibolites have positive eNd values of 3.55 ± 0.22 and 7.15 ± 0.12. An amphibolite from the Boxford Mbr. of the Nashoba Fm., a sequence of largely metamorphosed mafic rocks, also has a high positive eNd value of 8.36 ± 0.15. The Fish Brook Gneiss is a 499 +6/-3 Ma felsic gneiss with SiO2 values of 66%-78% and plots largely in the volcanic arc granite field on tectonic discrimination diagrams. Two samples from the Fish Brook Gneiss have negative eNd values of -3.31 ± 0.17 and -1.36 ± 0.15.
The positive eNd values from the amphibolites of the Marlboro Fm. and the Boxford Mbr. are consistent with an oceanic island arc/backarc origin. The negative eNd values from the Fish Brook Gneiss likely indicate incorporation of older continental material or sediments from an unknown source. These values overlap with those found in Ganderia. Avalonian rocks generally have higher eNd values, so it is unlikely that Avalonian crust or detritus is involved in the generation of the Fish Brook Gneiss. Thus, these preliminary data suggest that the Nashoba terrane may have formed as an independent oceanic arc/backarc complex and that by ~500 Ma the terrane incorporated continental crustal material, most likely from Ganderia."
47-6 10:00 AM GANDERIA, NEW CALEDONIA, THE CARBONATOR, AND LARGE POINT SINKS: REUSCH, Douglas N., Natural Sciences, Univ of Maine at Farmington, 173 High Street, Farmington, ME 04938, reuschmaine.edu and MAASCH, Kirk Allen, Climate Change Institute and Department of Earth Sciences, University of Maine, 5790 Bryand Global Sciences Center, Orono, ME 04469-5790
"Ganderia, during its transfer from Gondwana to Laurentia, must have perturbed the global carbon cycle at least twice, first when it underthrust seafloor in the earliest Ordovician (Penobscot orogeny) and second as a side effect of late Ordovician arc-arc collision along the Hurricane Mountain suture (Red Indian Line). Ganderia's modern cousin, the Norfolk Ridge ribbon continent east of Australia, jammed the subduction zone of the Loyalty arc during the latest Eocene; the obducted New Caledonian seafloor is a viable candidate for precipitating growth, via pCO2 drawdown, of the Antarctic ice sheet. The "carbonator" refers to a scenario such as would result if a large mass of seafloor was translated through present-day Mt. Cook: surprisingly large factors, including volume of eroded material (for New Caledonia, <600,000 km3), exhumation rate, high acid-neutralizing capacity of peridotites (<9 mol CO2 kg-1), hydrothermally-enhanced carbonation rate (>1000-fold increase at 185 vs. 25ºC), and fraction dissolved, combine to produce surprisingly large flux (>0.1 Tmol yr-1). The last factor is most uncertain, and ferruginous, dolomitic carbonates in foreland basin sequences that occur beneath chromite-bearing sandstones should be examined as candidates for the actual carbon sequestered by the dissolution of the adjacent seafloor. The emplacement of single large igneous provinces has been linked to CO2-forced global warming. Conversely, seafloor exhumation, such as took place in New Caledonia and along the GRUB line, may create "point CO2 sinks" large enough to cool the globe. "
47-7 10:20 AM TECTONIC HISTORY OF THE AVALON AND NASHOBA TERRANES ALONG THE WESTERN FLANK OF THE MILFORD ANTIFORM, MASSACHUSETTS: WALSH, Gregory J., U.S. Geological Survey, Box 628, Montpelier, VT 05602, gwalshusgs.gov, ALEINIKOFF, John N., U.S. Geological Survey, MS 963, DFC, Denver, CO 80225, and DORAIS, Michael J., Department of Geology, Brigham Young Univ, Provo, UT 84602
"The Bloody Bluff fault zone (BBfz) juxtaposes the peri-Gondwanan Nashoba and Avalon terranes in Massachusetts. Cambrian to Silurian rocks in the Nashoba terrane include intrusive rocks of the Grafton Gneiss, metavolcanic rocks of the Marlboro Formation, and metasedimentary and metavolcanic rocks of the Nashoba Formation. A SHRIMP U-Pb zircon age of 515 ± 4 Ma from the cross-cutting Grafton Gneiss constrains the Marlboro Formation to Early Cambrian or older. Neoproterozoic rocks in the Avalon terrane include metasedimentary rocks intruded by arc-related plutonic rocks. New SHRIMP U-Pb zircon ages exist for the Ponagansett Gneiss, a megacrystic biotite granite gneiss (612 ± 5 Ma), Northbridge Granite Gneiss, a coarse grained biotite granite gneiss (607 ± 5 Ma), and the Hope Valley Alaskite Gneiss (606 ± 5 Ma). These newly dated rocks in the Nashoba and Avalon terranes are calc-alkaline continental arc granites with age-corrected Epsilon Nd and Pb isotope values that overlap the fields for Gander and Avalon basement.
In the Nashoba terrane, dominant deformation is associated with upper amphibolite facies metamorphism. Metamorphic zircons from amphibolite in the Marlboro Formation are 355 ± 4 Ma, and record no evidence of an earlier Silurian event reported elsewhere by others. Major structural features are not continuous across the BBfz. In the Avalon terrane, the age of relict D1 deformation in the metasedimentary rocks may be Neoproterozoic. Late Paleozoic Alleghanian deformation (D2) produced a regional dominant foliation with associated mylonites that increase in intensity towards the BBfz. Subsequent Alleghanian D3 folding produced the NE-trending Milford antiform and NW-trending Oxford anticline. Thin, steeply dipping, NE-trending D3 mylonitic shear zones increase towards the southwestern part of the Milford antiform. The shear zones may be splays of the Hope Valley shear zone (HVsz), and may represent the structural termination of the HVsz northward into the Milford antiform within the Avalon terrane. Here, the HVsz is not a terrane boundary. Extensional veins, shear bands, and thin mylonitic fault zones indicate west-side-down normal displacement and show that the Milford antiform is truncated by late movement along the BBfz. "
47-8 10:40 AM LATE SILURIAN DEPOSITION AND LATE DEVONIAN METAMORPHISM OF GANDER COVER AT THE SOUTHERN END OF THE CENTRAL MAINE TERRANE: EVIDENCE FROM SHRIMP ANALYSIS OF DETRITAL ZIRCONS: WINTSCH, R.P., Department of Geological Scineces, Indiana University, 1001 E 10th Str, Bloomington, 47405, wintschindiana.edu, ALEINIKOFF, John N., U.S. Geol. Survey, Denver, CO 80225, and WALSH, Gregory J., U.S. Geological Survey, Box 628, Montpelier, VT 05602
"New SHRIMP U-Pb ages of cores and rims of detrital zircons from samples historically assigned to the Ordovician Brimfield Schist show that the depositional age of the metasedimentary rocks can be no older than late Silurian. Seven analyzed samples of rocks called Brimfield on the Bedrock Geological Map of Connecticut include five samples from between the Killingworth and Lyme domes in southern Connecticut, one sample from the eastern margin of the Hopyard basin, and one sample from the Hamilton Reservoir Formation (HRF) in the Westford quadrangle adjacent to the intrusive dioritic gneiss at Hedgehog Hill (HHG). The age of deposition of these rocks is constrained to be younger than the youngest detrital zircons, which in most samples is about 420 Ma, with a few samples containing grains as young as ~410 Ma. A late Silurian age for the HRF sample is constrained by the 416 ± 3 Ma age of the cross-cutting HHG. All samples contain a large fraction of Ordovician and early Silurian grains, and one sample from the eastern margin of the Killingworth dome is entirely composed of grains younger than ~480 Ma. This age population suggests a provenance area proximal to an emerging Ordovician volcanic arc (presumably to the west in current coordinates). Six of seven samples show moderate to large concentrations of Mesoproterozoic zircons, confirming an eastward (current coordinates) transport direction from Grenvillian provenances. Four of the seven samples show a small component of Ediacaran age (630-542 Ma), consistent with these sediments being deposited upon Gander basement rocks. Rims on zircons from five samples were wide enough to analyze, and show overgrowth events from Middle Devonian through the Carboniferous. Rims as old as ~390 Ma suggest rapid deposition and metamorphism of these sediments.
Based on our new data and previously published results, all metasedimentary rocks west of the Quinebaug Formation and east of the Ordovician intrusive rocks on the west side of the Hartford basin, including the Tatnic Hill, Hebron, Southbridge, and Brimfield formations are probably late Silurian in age. This suite of rocks, now at least 15 km thick, suggests an accretionary wedge of sediments accumulated on the eastern margin of the Gander terrane, and metamorphosed during the arrival of the Avalon terrane in the early Devonian. "
47-9 11:00 AM PROVENANCE OF THE LAKESMAN TERRANE: DETRITAL ZIRCON GEOCHRONOLOGY OF THE SKIDDAW GROUP IN THE LAKE DISTRICT OF NORTHERN ENGLAND: WALDRON, John W.F., Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G2E3, Canada, john.waldronualberta.ca and HEAMAN, Larry, Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada
"Accordingly, the Lake District rocks, together with similar rocks from the Isle of Man, have been placed by some researchers in a separate Lakesman Terrane, correlated with Appalachian Ganderia.
The Skiddaw group is divided into several slices by probable Acadian thrusts. In the Northern Fells thrust slices, the stratigraphy is relatively simple; basinal mudstones are interleaved with lenticular units of turbiditic sandstone of Early Ordovician age, which were sampled for detrital zircon geochronology. Preliminary results suggest that Late Neoproterozoic sources contributed the largest proportion of grains. Early Mesoproterozoic zircon is next in abundance. Paleoproterozoic grains with ages > 2000 Ma are consistent with sources in the West African or Amazonia cratons of Gondwana. Zircons between 2.5 and 3.0 Ga indicate Archean cratonic sources. These preliminary results confirm a peri-Gondwanan provenance for the Lakesman Terrane and have implications for the relationship between Ganderia and Avalonia in the Early Paleozoic. "
47-10 11:20 AM EVOLUTION OF THE PERI-GONDWANAN MARGIN OF SOUTHERN BRITAIN: SCHOFIELD, D.I.1, DAVIES, J. R.2, and WILSON, D.1, (1) British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom, disbgs.ac.uk, (2) British Geological Survey, Tongwnlais, Cardiff, CF15 7NE, United Kingdom
"The Cambrian to Tremadocian succession is marked by subsidence in a number of discrete basins and formation of a Tremadoc arc (<489 to >478 Ma) illustrating attenuation of the Gondwanan margin in response to both the onset of Iapetan subduction and opening of the Rheic ocean. Palaeogeographic affinities of these basins are poorly understood although inversion in the Harlech Dome (<489 to >466 Ma), low grade metamorphism within the Arfon Basin (490 Ma) and folding in the Monian Supergroup attest to tectonism analogous to Penobscottian accretionary events on the Gander margin of the northern Appalachians.
Renewed subsidence recorded in the Ordovician record of the Welsh Basin is interrupted by intrabasinal uplift during Sandbian times (460 Ma) associated with development of volcanic edifices in the north and margins of the basin. Following a Katian highstand (>445 Ma), glacioeustatic regression that reached its acme during Hirnantian times is interrupted by localised deformation in the basin margin (‘Shelvian Orogeny') that may record the distant effects of Avalonia/Baltica collision.
Good preservation of Silurian strata within the Welsh Basin and adjacent shelf area has enabled more detailed sequence stratigraphic analysis in which anomalous high frequency lowstands can be interpreted with respect to intrabasinal tectonics. Events include an intra-Telychian event (<436 to >428 Ma), an Early Wenlock event (<428 to >426 Ma), enhanced subsidence during Pridoli times (<418 to >416 Ma) and final, Early Devonian penetrative deformation (400 Ma) that together record closure of Iapetus and the possible influence of Rheic ocean subduction. "
Late Proterozoic Age Framework:
Carolina (1) 633 -----------------------------------------------------547
Cadomia (1) 615-600 585-570 540
Avalonia (1) 630-------------600 570---------550
Anti-Atlas (5) 762 650 580
Terrane Carolina (1) Cadomia (1)(2) Avalonia(1) Meguma(4) Meguma Basement(4) Arisaig (Silurian)(3)
Age 633-547 615-600, 585-570, 540 630-600, 570-550 629-575
Nd Juvenile Evolved ->less so Intermediate Nd comp Underthrust 400-370 Ma epNd -4.8 - -9.3
Det zirc1 MesoProt in NeoProt >2.5;2.4; 2.2-2.0 (2) 1.65-1.5; 1.25-1.15 2.0 .88;1.05;1.5 620-520,1.2-.9; (1.4-1.0), 2.2-1.5; Few Archean
Det zirc2 2.3-2.0 in Cambrian 650-600 (2)
Source of data: (1) Samson et al., 2004; (2) Samson et al., 2005; (3) Murphy et al, 2004; (4) Greenough et al. 1999; see http://instruct.uwo.ca/earth-sci/fieldlog/cal_napp/napp/new_eng_maritimes/gander.htm for references; (5) see http://instruct.uwo.ca/earth-sci/fieldlog/pan_african/maroc/maroc.htm
Terrane Ganderia (Ellsworth)(6) Anglesey(7) Avalonia Newfoundland(9)
666 Coedana(8); <501South Stack 760-545
Det zircon 2.09-1.97; 1.50, 1.21; 680-630; 545; 507 >2.5; 2.2-1.95; 1.5; 1.3-1.25; (800); 627-543 580 in L. Prot and Cambrian
(6) REUSCH, D.N., VAN STAAL, C.R., and MCNICOLL, V.J., 2004. ; (7) Collins, A.S., 2004; (8) Strachan et al., 2007; (9) Pollock, J., 2007