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        Geological Time Chart, Paleozoic, GSC-1999
        Terrane map of the Canadian Cordillera - cord2terr1.jpg

        Terranes of the northern Cordillera  include:

        1) a) Nisutlin, upper - Devonian - Mississippian silici-clastic sediments, felsic to mafic volcanics, carbonates;
            b) Nisutlin, lower - Lake George - Devonian-Mississippian amphibolite facies augen gneiss, pelitic schist, quartzite and minor amphibolite; amphibolites are within-plate (Barkerville?);
            c) Dorsey -   lower unit, which is intruded by the top of the Ram Stock, of  greenschist to amphibolite facies
    siliciclastic rocks and interleaved metaplutonic rocks;  middle unit, in part Pennsylvanian, greenschist to sub-greenschist facies phyllite, chert, tuff, siliciclastic, volcanic and carbonate rocks; upper unit of sub-greenschist facies epiclastic, tuffaceous, siliciclastic, carbonate, and volcanic rocks.
        2) Taylor Mountain - high-P amphibolites (blue schists), schist, marble, meta-chert (Oceanic protoliths), intruded by post-kinematic mid-Triassic granitoids;
        3) Slide Mountain/Seventy Mile - Mississippian to Permian oceanic crust; includes eclogites (early Mississippian? Stewart Lake and Simpson Range - arc; mid-Permian Faro, Ross River, Last Peak - MORB/WP);

    Current debate on the plate tectonic history of the Yukon-Tanana terranes of the Northern Cordillera:
    Mihanlynuk, M.G., et al., discussion, and Hansen, V.L. and Oliver, D.H., reply, 1999, BGSA, 111, 1416-1422, of paper by Hansen, V.L., and Dusel-Bacon, C. 1998.

Map of the Northern Cordillera according to Hansen and Dusel-Bacon, 1998 - cord3hansen1.jpg
        versus
Map of the Northern Cordillera according to Mihanlynuk et al. 1999 - cord3mihal1.jpg

    Southeast Alaska region
Geological map Southeast Alaska, showing sample locations, Ducel-Bacon and Cooper, 1999 - cord3dusel4.jpg
What is the relationship between the Lake George and Nisutlin assemblages?
What is the Taylor Mountain terrane composed of?
What does the Seventy Mile terrane likely represent?
What is the structural succession of the supposed terranes?
 
    The Teslin Zone
Geological map of the Teslin zone, Stevens et al. 1996 - cord3stevens1.jpg
Lithotectonic assemblage correlation diagram, Teslin tectonic zone, Stevens et al. 1996 - cord3stevens2.jpg
Model for the Paleozoic evolution of the Teslin tectonic zone, Stevens et al. 1996 - cord3stevens3.jpg

    Western Tagish Lakes region
Map of the western Northern Cordillera, Currie and Parrish, 1997 - cord3currie1.jpg
Map of the western Northern Cordillera, Currie and Parrish, 1997 - cord3currie3.jpg
Composite sections of the rocks of the Tagish Lakes region, western Northern Cordillera, Currie and Parrish, 1997 - cord3currie2.jpg

Map of the western margin of Stikinia, Coast Range,  Brew et al. 1994  - cord3brew1.jpg

   Protoliths of mafic rocks of the Lake George, Taylor Mountain and Seventy Mile/Slide Mountain terranes
Map of the Northern Coordillera, Ducel-Bacon and Cooper, 1999 - cord3dusel1.jpg
Spidergrams for rocks of the Lake George, Taylor Mountain and Seventy Mile assemblages/terranes,  Ducel-Bacon and Cooper, 1999 - cord3dusel2.jpg
Ti/100-Zr-3*Y and Nb*2-Zr/4-Y diagrams for Lake George, Taylor Mountain and Seventy Mile volcanic rocks, Ducel-Bacon and Cooper, 1999 - cord3dusel3.jpg

    Models
Devonian-Mississippian evolution of the Yukon-Tanana, Creaser et al. 1999 - cord3eclo4.jpg
The Hansen - Dusel-Bacon model, Hansen and Dusel-Bacon, 1998. - cord3hansen2_1.htm
The oroclinal model, Nelson and Mihalynuk., 1993 - cord3nelson2_1.jpg

Aleinikoff, J. N., Dusel-Bacon, C., Foster, H. L., 1981, Proterozoic zircon from augen gneiss, Yukon-Tanana Upland, east-central Alaska. Geol., 9, 469-473

Anderson-R., 1984.  Late Triassic and Jurassic magmatism along the Stikine Arch  and the geology of the Stikine Batholith, north-central British Columbia. Geological Survey of Canada. 84-1A; Pages 67-73.

Erdmer, P. , 1985, An examination of the cataclastic fabrics and structures of parts of Nisutlin, Anvil and Simpson allochtons, central Yukon: test of the arc-continent collision model. Jour. Struct. Geol., v. 7, p. 57-72. Cordillera.

Dusel-Bacon, C. and Aleinikoff, J.N. , 1985, Petrology and tectonic significance of augen gneiss from a belt of Mississippian granitoids in the Yukon-Tanana terrane, east-central Alaska. Geol. Soc. America Bull., v. 96, p. 411-425.

Mortensen, J.K., and Jilson, G.A., 1985. Evolution of the Yukon-Tanana terrane: evidence from southeastern Yukon Territory. Geology, 13, 806-810.
Map of the Finlayson Lake region, Mortensen and Jilson, 1985  - cord3mort1.jpg

Comment - scan figures 1, cord3mort1.jpg, fig

Aleinikoff, J.N., Dusel-Bacon, C. , et al. 1986, Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska. BGSA, v. 97, no. 5, p. 626-637.

Erdmer, P. , 1987, Blueschist and eclogite in mylonitic allochthons, Ross River and Watson Lake areas, southeastern Yukon: CJES, 24, 7, 1439-1449.

Comment- in glauc bear. qtz rich schist and assoc. w. peridotite; met. is Triassic or older, 1988 Cordilleran tectonics: Abst. w. pgms, Denver, 20, 7, A109.

Ford-A-B; Brew-D-A, 1988. The Douglas Island volcanics; basaltic-rift--not andesitic-arc--volcanism of the "Gravina-Nutzotin Belt", northern southeastern Alaska. Abstracts with Programs - Geological Society of America. 20;  7, p. 111.

Comment- back arc basin closure; Yukon-Tanana; Gravina-Nutzotin; Douglas Island volcanics; Duke

Anderson, P.G. and Hodgson, C.J., 1989. The structure and geological development of the Erickson gold mine, Cassiar District, British Columbia, with implications for the origin of mother-lode-type gold deposits. CJES, 26, 2645-2660.

Comment - Sylvester allochthon emplaced in mid-Jurassic as a result of collision with Quesnel arc.

Samson, S.D., et al., 1989. Evidence from neodymium isotopes for mantle contributions to Phanerozoic crustal genesis in the Canadian Cordillera. Nature, 337, 705-709.

Comment - Both Alexander (560 - 90 Ma) and Stikinia (400-6m Ma) have epsilon Nd values between CHUR and DM; (figures scanned for 300B); Stikine samples before 200 Ma are close to DM where from c. 200 to c. 150 the data points trend down from DM to CHUR which could imply contamination of DM magmas by small amounts of very epsilonNd crustal sediment.

Hansen, V. L. Armstrong, R.L. and Mortensen, J.L., 1989, U-Pb, Rb-Sr, and K-Ar isotopic constraints for ductile deformation and related metamorphism in the Teslin suture zone, Yukon-Tanana terrane, south-central Yukon: CJES, 26, 11, 2224-2235.

Comment- Triassic? age for the Teslin suture

Hansen, V.L. , 1989, Structural and kinematic evolution of the Teslin suture zone, Yukon: record of an ancient transpressional margin: Jour. Struct. Geol., 11, 6, 717-736.

Aleinikoff, J.N. et al., 1990, A summary of constraints on the history of the Yukon-Tanana terrane, east central Alaska: GAC Abst. w. Prog., Vancouver, A1.

Comment- felsic meta-igneous rocks = 375 zircon; 2-2.3 inherited components; only dated Precambrian rock is an orthogneiss 130 km east of Fairbanks= 671+34; Augen gneiss = 341+4 extends NW-SE forms the core of a Mississipian arc; unfoliated Taylor Mountain batholith is 212 late Triassic; underthrust Jurr-Cret flysch derived from the Gravina arc underthrust the Y-T and provided a low 207Pb/204Pb component mixed with lead from the Devonian terrain for the Cret granites

Box, S.E. et al., 1990, Kilbuck terrane: oldest known rocks in Alaska: Geology, 18, 12, 1219-1222.

Comment- argues that basement of various Alaska basement terranes including the Yukon Tanana is 2-2.1 Ma and lacks 1.8 ages; therefore related to Australian, Baltic, Guiana, Siberian? or West African Shields.

Currie, L.D. , 1990, Is the Nisling terrane a composite terrane? Evidence from the Florence Range, Northern Coast Mountains, Northwestern B.C.: GAC Abst. w. Prog., Vancouver, , A29.

Comment- Florence range includes Nisling south of Whitehorse; boundary with the Stikine is the Llewellyn fault;from north to south - Boudary ranges volcanic and deep water seds = oceanic crust; foliated Hale Mountain Granite; Wann River metamorphosed interm. volc; Florence Range is metamorphosed Nisling; units separated by shear zones related to northeasterly compression; unconformably overlain by middle to late Mesozoic volcanic rocks - are these Stikine?

Dusel-Bacon, C and Douglas, S.L., 1990, New thermobarometric evidence for high pressure medium temperature metamorphism of two subterranes of the Yukon Tanana composite terrane (YTT) in easternmost Alaska: GAC Abst. w. Prog., Vancouver, , A35.

Comment- southern terrane referred to as the Augen Gneiss terrane exhibit early Cret cooling ages and were met at 8-12.5 kb; Talor Mountain was metamorphosed at 6-12.5 kb; suggestst that booth the AGS and Taylor participated in the same Late Triassic early Jurassic event involving plate convergence; early Cret ages related to extension

Gehrels, G.E. et al. 1990. Ancient continental margin assemblage in the northern Coast Mountains, southeast Alaska and northwest Canada. Geology, 18, 208-211.

Comment - quart-rich terrane is structurally imbircated between the Stikine and the Taku

Hansen, V.L., 1990, Yukon-Tanana terrane: a partial acquittal: Geology, 18, 4, 365-369.

Comment- Permo-Triassic subduction of the Teslin beneath the Slide Mountain; Slide Mountain represents sediments laid down on oceanic crust; Hansen equates the Slide Mountain with the Sylvester allochthon; initiation of obduction in the Triassic; Jurassic obduction of amalgamated Slide Mountain on Teslin over the Nisling; Triassic? age for the Teslin suture; considers Nisling to be continental North America, but Box et al. Geology, 1990, 12, 1219, argue that Nisling and other Alaskan terranes are not North American

McClelland, W.C. et al., 1990, Geologic and structural relations along the Western flank of the Coast Mountains batholith: Stikine River to Cape Fanshaw, Central SE Alaska: GAC Abst. w. Prog., Vancouver, A86.

Comment- the Gravina consists of Upper Jurassic and lower Cret argillite, volcanoclastic turbidites, and basalts that depositionally overlie the Alexander; the Taku includes metapelite wwith minor interlayers of marble and basalt of uncertain age ( but see Samson); both are structurally overlain by the Ruth terrane which is the equivalent of the Nisling Pelly gneiss, and includes metapelite, quartzose metaclastic strata, quartzite , marble , mafic metavolcanics and felsic metatuff; orthogneis in the Ruth is Devonian (zircon). Early southwest verging structures in the Gravina are overprinted by ductile fabrics asscoiated with east dipping thrust faults that bring the Taku over the Gravina, and the Ruth over the Taku and Gravian; these structures deform Albian Gravina and are cut by mid-Cret plutons; they record underthrusting of the Alexander and Taku beneath the Y-T and Stikine; the Leconte Bay shear zone is late Paleocene-Eocene, and accomodates overthickening of crust during mid-Cretaceous collision

Mihalynuk , 1990, : GAC Abst. w. Prog., Vancouver,  A88.

Comment- Stikine in the Tagish Lakes area; oldest Stikine are late Triassic sheared pyroxene phyric basalts. Paleozoic carbonates are absent. 100 km of dextral movement on the Llewellyn fault, west side up component. Nisling detritus shed onto the Stikine. Likely the Nisling is the dominant basement since late Triassic Stikine cong. contain abundant Nisling clasts but no clasts of the Cache Creek.

Mortensen, J.K. , 1990, Significance of U-Pb ages for inherited and detrital zircons from Yukon-Tanana terrane, Yukon and Alaska: GAC Abst. w. Prog., Vancouver,  A91.

Comment- older multgrain zircon ages of 2.1-2.3 are in good agreement with Nd model ages for Miss peraluminous granitoids, but new analyses of morphologically distinct small fractions and single grains of zircon indicate a more complex source. zircons from meta-igneous rocks have sources from 3.1-1.7; eighteen single zircons from the Cleary sequence quartzites north of Fairbanks have ages of 1.2, 1.3-1.4, 1.8-1.9, 2.5, 3.4; eight single zircons from the Nasina quartzite west of Dawson are 1.8-2.1 and 2.6-2.8.; the previously determined 2.1-2.3 are average ages;

Nokleberg, W.J. et al., 1990, Structure and tectonics of the Yukon-Tanana, southern Wickersham, and Seventymile terranes along the Trans-Alaskan crustal transect (TACT), East-Central Alaska: GAC Abst. w. Prog., Vancouver,  A97.

Comment- The YTT is structurally over and underlies the Wickersham miogeoclinal rocks; amphib-eclogite (Teslin) overlie greenschist of the core; early to mid-Cretaceous compressive deformation related to underplating of the Gravina and Kahiltna Mesozoic flysch during collision of Wrangellia/Alexander? (Magnetotelluric data); imbrication of the Y-K with the Wickersham and overthrusting of the Slide Mountain and Stikine took place during the same compressional event; regional extension was late Cretaceous

Beaudoin, 1991, A thin low-velocity crust beneath the Yukon - Tanana terrane: GSA Abst. w. Prog., San Francisco, 23, 2, 5.

Brew, D.A., Karl, S.M., Barnes, D.F., Jachens, R.C., Ford, A.B. and Horner, R., 1991. A northern Cordilleran ocean-continent transect: Sitka Sound to Atlin Lake, British Columbia. CJES, 28, 840-853.

Comment -

Gehrels, G.E. McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, UPb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: CJES, 28, 8, 1285-1300.

Comment- Upper Proterozoic to upper Paleozoic continental margin assemblage interpreted to belong to the Yukon-Tanana; single zircons, 495, 750, 1.05-1.4, 2-1.75, 2.3, 2.7-2.5, 3.0

Labson, 1991: GSA Abst. w. Prog., San Francisco, 23, 2, 43.

Comment- deep crustal geoelectic structure near the Tintina fault zone; thick Pal and Mesozoic seds have been overridden by a several km thick veneer of Yukon - Tanana

Miller, M.M. and Saleeby, J.B., 1991, Continental detrital zircon in Carboniferous ensimatic arc rocks, Bragdon Formation, eastern Klamath terrane, northern California: BGSA, 103, 2, 268-276.

Comment- Precambrian continental source for zircons in Upper Devonian and lower Carboniferous; discusses problem of sourec of 2.1-2.0 zircons

Gehrels, G.E., McClelland, W.C., Samson, S.D., Patchett, P.J. and Orchard, M.J., 1992. Geology of the Western flank of the Coast Mountains between Cape Fanshaw and Taku inlet, southeastern Alaska. Tectonics, 11, 567-585.

Comment - Endicott

Mortensen, J.K., 1992. Pre-mid-Mesozoic tectonic evolution of the Yukon-Tanana terrane, Yukon and Alaska. Tectonics, 11, 4, 836-853.

Currie, L. and Parrish, R.R., 1993, Jurassic accretion of Nisling terrane along the western margin of Stikinia,Coast Mountains, northwestern British Columbia: Geology, 21, 3, 235-238.

Comment-

Nelson, J. and Mihalynuk, M.G., 1993. Cache Creek ocean: closure or enclosure. Geology, 21, 173-176.1

Beaudoin, C. et al., 1994, Crustal velocity structure northern Yukon - Tanana upland, central Alaska: BGSA, 106, 8, 981-1001.

Comment-

Brew, D.A., et al., discussion, and Currie, L. and Parrish, R.R. reply, 1994, Jurassic accretion of Nisling terrane along the western margin of Stikinia, Coast Mountains, northwestern British Columbia: Geology, 22, 1, 89-90.
Map of the western margin of Stikinia, Coast Range,  Brew et al. 1994  - cord3brew1.jpg

Comment- unmetamorphosed Triassic volcanic and carbonate rocks of the Stuhini Group west of the Nisling; further west are amphibolites, gaabros and ultramafic rocks, and in the bottom corner of the map are shown what appear to be more Nisling, see Brew et al, 1985a, 1985b, 1991 (CJES, 1991, 28, 840-853).  Currie comments that metamorphic fragments in Upper Triassic conglomerate (described by Souther, J.G. Geology and minerals deposits of Tulsequah map-area, British Columbia: Geol. Surv. Canada Memoir 362, 84p) were likely derived from pre-Triassic metamorphic rocks of Stikinia, and that inherited Precambrian zircons found in the circa 205 Ma Zippa Mountain syenite complex (Bevier and Anderson, 1991) could have been dervied from within Stikinia. They also suggest that the Nisling could form a klippe above Stikinia.

Foster, H.L. Keith, T.E.C., and Menzie, W.D, 1994, Geology of the Yukon - Tanana area of east-central Alaska: In Plafker, G. and Berg, H., eds., The geology of Alaska: the geology of North America volume G-1, Geol. soc. America, Boulder, G-1, 205-240.

Comment-

Mihalynuk, M.G., Nelson, J, and Diakow, L.J., 1994. Cache Creek terrane entrapment: oroclinal paradox within the Canadian Cordillera, Tectonics, 13, 2, 575-595.

Cui, Y., and Russell, J.K., 1995. Nd-Sr-Pb isotopic studies of the southern Coast Plutonic Complex, southwestern British Columbia. BGSA, 107, 2, 127-138.

Comment - Coast Plutonic complex has epsilonNd values of 4.2-8.9 and low SR/Sr. consist mainly of mantle derived material; no variation with rock type or age; Wrangellia is an isotopically juvenile terrane.

Johnston, S.T. and Erdmer, P., 1995, Hot-side-up aureole in southwest Yukon and limits on terrane assembly of the northern Canadian Cordillera: Geology, 23, 5, 419-422.

Comment- Lower Jurassic Aishihik batholith is intrusive into Nisling, Stikinia, and Yukon-Tanana.

Stevens, R.A., Erdmer, P., Creaser, R.A., and Grant, S.L., 1995. Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon - Tanana terrane of south-central Yukon. CJES, 33, 103-116.

Stevens, R. A. and Harms, T.A., 1995. Investigations in the Dorsey terrane; Part 1, Stratigraphy, structure, and metamorphism in the Dorsey Range, southern Yukon Territory and northern British Columbia. Current Research - Geological Survey of Canada,  117-127.
    Abstract: In the Dorsey Range, the informally named Dorsey assemblage and the mid-Permian Ram Stock characterize the Dorsey terrane. The Dorsey assemblage can be subdivided into three units. The structurally lowest unit, which is intruded by the top of the Ram Stock, consists of greenschist to amphibolite facies siliciclastic rocks and interleaved metaplutonic rocks. The middle unit, in part Pennsylvanian, consists of greenschist to sub-greenschist facies phyllite, chert, tuff, siliciclastic, volcanic and carbonate rocks. The upper unit consists of sub-greenschist facies epiclastic, tuffaceous, siliciclastic, carbonate, and volcanic rocks. Penetrative ductile deformation in the lower unit grades to localized and more brittle deformation in the upper unit. The base of the Ram Stock is in thrust-shear contact with an underlying   package of rocks referred to as the imbricate assemblage. Tectonic fabrics in the Ram Stock and imbricate assemblage are cut by an Early Jurassic(?) pluton.

Plint, Heather E. and Gordon, Terence, 1996.  Structural evolution and rock types of the Slide Mountain and Yukon-Tanana terranes in the Campbell Range, southeastern  Yukon Territory.    In: Cordillera and Pacific margin--Cordillere et marge du Pacifique.  Current Research - Geological Survey of Canada. Pages 19-28.

Comment - Mapping at 1:50 000 scale in the Campbell Range, Yukon  Territory examined the Finlayson Lake fault zone and the Slide  Mountain and Yukon-Tanana terranes. Map units identified are:  (a) Yukon-Tanana terrane: DTp chlorite-actinolite phyllite,  DTa  argillite, DTc  metachert and slate; (b) Slide  Mountain terrane: DPsc and DPsp metachert,  argillite, and phyllite, DPsg  greenstone, breccia, gabbro,  and metasedimentary rocks, DPslg leucogabbro, and DPss serpentinite; and (c) Earn Group: DMec metachert  and argillite, and DMes sandstone, siltstone, and shale. Unit DPsg (Slide Mountain ophiolite) is thrust over DTp  and DTa  in the west and DPsc in the east. The map pattern of DTc suggests a klippe preserved from erosion by normal faulting along its southern boundary. These structures may represent a flower  structure or an originally east-directed thrust sequence disrupted  by west-directed back thrusts with continued shortening.

Stevens, R.A. et al., 1996. Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon - Tanana terrane of south-central Yukon: CJES, 33, 1, 103-116.
Geological map of the Teslin zone, Stevens et al. 1996 - cord3stevens1.jpg
Lithotectonic assemblage correlation diagram, Teslin tectonic zone, Stevens et al. 1996 - cord3stevens2.jpg
Model for the Paleozoic evolution of the Teslin tectonic zone, Stevens et al. 1996 - cord3stevens3.jpg
 

Butler, R.F., Gehrels, G.E., and Bazard, D.R., 1997. Paleomagnetism of Paleozoic strata of the Alexander terrane, southeastern Alaska. BGSA, 109, 10, 1372-1388.

Creaser, R.A., Erdmer, P.E., Stevens, R.A., and Grant, S.G., 1997. Tectonic affinity of Nisutlin and Anvil assemblages strata from the Telsin tectonic zone, northern Canadian Cordillera: contraints from neodymium isotope and geochemical evidence. Tectonics, 6, 107-121.

Currie, L.D. and Parrish, R.R., 1997. Paleozoic and Mesozoic rocks of Stikinia exposed in northwestern British columbia: implications for correlations in the northern Cordillera. BGSA, 109, 1402-1420.
Stikinia is a tectonostratigraphic terrane in the Canadian Cordillera that formed in a volcanic arc environment during
    Paleozoic and Mesozoic time. Until now, the Paleozoic rocks that form a semicontinuous belt along its western margin (STikine asemblage) were only recognized in a restricted area in northern British Columbia, between the Stikine and Taku river areas. In contrast, Mesozoic Stikinia rocks form an almost continuous belt that extends much farther to the north, leading some authors to question the nature of the unexposed Paleozoic basement north of the Taku River area. The following correlations have significant implications for tectonic reconstructions of the northern Cordillera because they suggest that Stikinia's Paleozoic volcanic-sedimentary basement is more widespread than previously thought. On the basis of similar rock types and lithologic associations, six new U-Pb zircon dates, and the common intrusive relationship with 184-195 Ma plutons, the Stikine assemblage is correlated with the Boundary Ranges suite, a metamorphosed Paleozoic volcanic assemblage exposed in the Tagish Lake area, north of the Taku River and south of the Yukon-British Columbia border. The recognition of the Boundary Ranges suite and the Jurassic plutons that intruded it (Tagish Lake
    suite) as part of Stikinia has implications for the age and character of the Stikinia-Tracy Arm terrane boundary because the Boundary Ranges and Tagish Lake suites from the footwall of a major Middle Jurassic shear zone that carried the continental margin-like rocks of the Tracy Arm terrane in its hanging wall. This correlation also implies that the late Paleozoic basement to the Mesozoic Stikinia arc is not a continental margin assemblage, at least as far north as the British Columbia-Yukon border, and possibly farther. The Boundary Ranges suite, and therefore the Stikine assemblage, are also tenatively correlated with parts of the Yukon-Tanana terrane in Yukon (Aishibik Lake area), parts of the Taku terrane in southeast Alaska, and undivided metamorphic rocks in west-central British Columbia. Differences in the isotopic signatures of these rocks may reflect along-strike changes in the character of the basement rocks of the late Paleozoic Stikinia volcanic arc.

Map of the western Northern Cordillera, Currie and Parrish, 1997 - cord3currie1.jpg
Map of the Tagish Lakes region, western Northern Cordillera, Currie and Parrish, 1997 - cord3currie2.jpg
Map of the western Northern Cordillera, Currie and Parrish, 1997 - cord3currie3.jpg

Grant, Steven Lloyd, 1997. Geochemical, radiogenic tracer isotopic, and U-Pb geochronological studies of Yukon Tanana Terrane rocks from the  Money Klippe, southeastern Yukon, Canada. MSc, University of Alberta. Edmonton, AB, Canada. 177 p.

Comment - This study presents geochemical and isotopic analyses of supracrustal and igneous rock from the Money klippe in southeastern Yukon in order to constrain the tectonic evolution of the pericratonic Yukon Tanana terrane. Samples from the supracrustal Nisutlin assemblage have epsilon Nd0 ranges of -20.4 to +4.9, indicating that while some Nisutlin assemblage rocks are similar to the North American miogeocline, juvenile material (uncommon in the miogeocline) also contributed to the Nisutlin provenance. These data support models indicating that the Nisutlin assemblage formed as a distal portion of the miogeocline. Some of the samples from the mafic Anvil assemblage have geochemical characteristics of calc-alkalic basalt, which does not support the correlation of the Anvil assemblage to the ocean floor-dominated Slide Mountain terrane. Geochemistry indicates  that the Simpson Range plutonic suite (SRPS) is the product of calc-alkalic continental arc magmatism. U-Pb dating of zircons shows that all SRPS rocks were formed between 344 and 360 MA. Inherited zircon of broadly Proterozoic age, ND model ages (TDM) = 1.67 to 2.10 Ga), initial Sr ratios 87Sr/86Sr = 0.7074 to 0.7099, and 207 Pb/204 Pb, 206Pb/204 Pb, and 208Pb/204 Pb ratios in excess of those of the uniform reservoir all show that older crust has contributed significantly to the petrogenesis of the SRPS, although to varying amounts, perhaps depending on the thickness of the intruded crust. These studies are compatible with a model which suggests that the Yukon Tanana terrane consists in part of a Devonian-Mississippian fringing arc built on the distal portion of the North American miogeocline.

Erdmer, Philippe; Ghent, Edward-D; Archibald, Douglas-A; Stout, Mavis, 1998.  Paleozoic and Mesozoic high-pressure metamorphism at the  margin of ancestral North America in central Yukon. Geological Society of America Bulletin. 110, 5, 615-629.

Comment -  Eclogite and blueschist in the Yukon-Tanana and Slide Mountain terranes in the Yukon and Alaska preserve a partial  record of middle Paleozoic, late Paleozoic, and early Mesozoic subduction and subsequent unroofing. Near Faro, eclogites are commonly mylonitized and partially retrogressed. The analysis of Fe-Mg exchange between garnet and clinopyroxene suggests    temperatures (T) in the 400-500 degrees C range for eclogite, and    jadeite ( approximately 40 mol%)+quartz suggest minimum    pressures (P) of 11-13 kilobar at that temperature range; clinopyroxene - garnet - epidote - quartz suggest pressure near 15    kilobar (P (sub H2O) = P (sub S) ). Eclogite near Last Peak, which contains brown hornblende, late-stage oligoclase, and    biotite, yielded P-T estimates up to 625 degrees C at a minimum pressure of 14 kilobar. Eclogite near Ross River yielded   temperatures near 525 degrees C and a minimum pressure near 13 kilobar. The previously proposed Permian-Triassic age of high-pressure tectonism for the entire Yukon-Tanana terrane in the Yukon was inferred from isotopic dating of one eclogite and one blueschist in separate localities. In this study, isotopic (super 40)Ar/ (super 39) Ar analysis of white mica from eclogite in the Simpson range yielded a date of 344+ or -1 Ma. Eclogite and    blueschist from Ross River yielded white mica (super 40) Ar/ (super 39) Ar dates of 267+ or -3 Ma and 273+ or -3 Ma, respectively. White mica in eclogite from Faro was dated at 260+ or -3 Ma. White mica in two eclogites from Stewart Lake, about 2 km apart, yielded (super 40) Ar/ (super 39) Ar dates of 228+ or -1 Ma and 346+ or -3 Ma. White mica in Last Peak eclogite, for which a concordant U-Pb zircon date is 269 Ma, yielded an integrated date of 236+ or -1 Ma. Overprinting in the blueschist facies and final cooling in some localities predated eclogite metamorphism in others. The cooling ages indicate significant plate convergence as early as Carboniferous time and either the existence of more than one subduction zone or continuous convergence and episodic exhumation above a single zone. When this is considered together with the range of ages of other high-pressure occurrences, the North American Cordillera is seen to be characterized by multiepisodic and diachronous high-pressure metamorphism.

Soja, C.M., and Antoshkina, A.I., 1997. Coeval development of Silurian stromatolite reefs in Alaska and the Ural Mountains: implications for paleogeography of the Alexander terrane. Geology, 25, 539-542, and discussion by deFreitas, T.A., and reply by Soja, C.M., and Antoshkina, A.I., 1998, Geology, 26, 382-384.

Kapp, Paul A and Gehrels, George, 1998. Detrital zircon constraints on the tectonic evolution of the Gravina Belt, Southeastern Alaska. Canadian Journal of Earth Sciences, 35, 3, 253-268.

    Comment - Upper Jurassic-Lower Cretaceous marine clastic strata and mafic to intermediate volcanic rocks of the Gravina belt are part of a complex suture zone separating the Alexander and Wrangellia terranes on the west from the Yukon-Tanana and Stikine terranes to the east. U-Pb ages have been determined on 118 single detrital zircon grains from Gravina strata in an effort to determine the tectonic setting of the Gravina belt and the paleoposition of outboard terranes prior to their Late Cretaceous juxtaposition against inboard terranes. Samples from five stratigraphic units yield ages of 105-120 (n = 5), 140-165 (n = 56), 310-380 (n = 17), 400-450 (n = 19), 520-560 (n = 5), and 1755-1955 Ma(n = 5). The 105-120 and 140-165 Ma grains were shed primarily  from arc-related plutons that lie outboard of the Gravina belt. The lack of 120-140 Ma ages coincides with a lull in magmatism in  the outboard arc and in the western United States, which suggests that Gravina strata accumulated during major changes in plate  motion along the Cordilleran margin. The 400-560 Ma zircons  were derived from rocks of the Alexander terrane which also lie to the west. In contrast, the 310-380 and >900 Ma grains were  apparently shed from inboard regions. Likely sources include the Yukon - Tanana and Stikine terranes in the northern Cordillera and assemblages in the northern California region which contain igneous rocks and detrital zircons of the appropriate ages. Our data accordingly support models in which the Gravina basin  formed in narrow rift or transtensional basins, whereas the outboard Alexander and Wrangellia terranes were located along  the California-Oregon- Washington-British Columbia-Alaska margin. Our data are less supportive of models in which the Gravina strata and underlying Alexander and Wrangellia terranes were separated from western North America by a large ocean basin, or were located along the coast of Mexico.

Gehrels, G. E and Kapp, P. 1998. Detrital zircon geochronology and regional correlation of metasedimentary rocks in the Coast Mountains, Southeastern Alaska. Canadian Journal of Earth Sciences. 35, 3, 269-279.

  Comment -  U-Pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the Coast Mountains in southeastern Alaska. These rocks belong to the Port Houghton assemblage, which consists of upper Paleozoic pelitic and psammitic schist, metaconglomerate, metabasalt, and marble. The Port Houghton assemblage rests unconformably(?) on metamorphosed and deformed mid-Paleozoic arc-type volcanics
(Endicott Arm assemblage), which gradationally overlie upper Proterozoic(?)-lower Paleozoic continental margin strata (Tracy Arm assemblage). Three main clusters of ages are present: 330-365 Ma (19 grains), 1710-2000 Ma (27 grains), and 2450-2680 Ma (6 grains). Additional grains are approximately 2334, 2364, and 3324 Ma. Comparison of these ages with detrital zircon ages in other Cordilleran assemblages supports previous interpretations that metasedimentary rocks in the Coast Mountains (i) form a southwestern continuation of the Yukon-Tanana terrane
of eastern Alaska and Yukon, (ii) are not correlative with strata of the Alexander terrane, and (iii) contain detritus that was probably shed from cratonal rocks in the Canadian Shield to the east. Several scenarios exist to explain the occurrence of these continental margin rocks west (outboard) of arc-type and ocean-floor assemblages such as the Stikine, Cache Creek, Quesnel, and Slide Mountain terranes.

Hansen, V.L., and Dusel-Bacon, C. 1998. Structural and kinematic evolution of the Yukon-Tanana upland tectonites, east-central Alaska: a record of late Paleozoic to Mesozoic crustal assembly. BGSA, 110, 211-230.
Map of the Northern Cordillera according to Hansen and Dusel-Bacon, 1998 - cord3hansen1.jpg

Ross, G. M and Harms, T. A., 1998. Detrital zircon geochronology of sequence "C" grits, Dorsey Terrane (Thirtymile Range, southern Yukon); provenance and stratigraphic correlation. In: Radiogenic age and isotopic studies, Report 11. Current Research - Geological Survey of Canada, 107-115.

de Keijzer, M., Williams, P.F., and Brown, R.L., 1999.  Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America. CJES, 36, 3, 479-494.

Creaser, R.A., Goodwin-Bell, J-A. S., and Erdmer, P. 1999. Geochemical and Nd isotopic constraints for the origin of eclogite protoliths, northern Cordillera: implications for the Paleozoic tectonic evolution of the Yukon-Tanana terrane. CJES, 36, 10, 1697-1709.
Tectonic map of the Teslin-Finlayson Lake region showing eclogite localities, Creaser et al. 1999 - cord3eclo1.jpg
Spidergrams for Steward Lake and Simpson Range eclogites, Creaser et al. 1999 - cord3eclo2.jpg
Spidergrams for Faro, Ross Lake, and Last Peak eclogites, Creaser et al. 1999 - cord3eclo3.jpg
Devonian-Mississippian evolution of the Yukon-Tanana, Creaser et al. 1999 - cord3eclo4.jpg

Dostal, J., Gale, V., Church, B.N., 1999. Upper Triassic Takla Group volcanic rocks, Stikine Terrane, north-central British Columbia: geochemistry, petrogenesis, and tectonic implications. CJES, 36, 1483-1494.

Erdmer, P., Thompson, R. I. and Daughtry, K. L., 1999. Pericratonic Paleozoic succession in Vernon and Ashcroft
    map areas, British Columbia. In: Cordillera and Pacific margin/ Interior Plains and Arctic Canada. Current Research - Geological Survey of Canada. 205-213.

    Comment:  Ductilely deformed and metamorphosed pericratonic rocks of inferred Early Paleozoic age overlie the
    Neoproterozoic-Eocambrian Silver Creek schist in the Vernon map area along an apparent stratigraphic contact. Permian (Harper Ranch Group) and Triassic (Nicola Group and Slocan Formation) strata overlie the pericratonic succession along an unconformable depositional contact. The pericratonic succession, long  recognized to include amphibolitic schist, marble, and quartzite,  includes in addition to these a distinctive metaconglomerate, and  forms a robust regional marker. The tripartite regional stratigraphy and its inferred Proterozoic or older depositional basement cross the Okanagan Valley without apparent offset, and persist for at least 100 km westward, as far as the Nicola horst.  The pericratonic succession underlies rocks presently assigned to the Quesnellia terrane at this latitude.

Dusel Bacon, C., and Cooper, K.M., 1999. Trace-element geochemistry of metabasaltic rocks from the Yukon-Tanana upland and implications for the origin of tectonic assemblages in east-central Alaska. CJES, 36, 10, 1671-1695.

Map of the Northern Coordillera, Ducel-Bacon and Cooper, 1999 - cord3dusel1.jpg
Spidergrams for rocks of the Lake George, Taylor Mountain and Seventy Mile assemblages/terranes,  Ducel-Bacon and Cooper, 1999 - cord3dusel2.jpg
Ti/100-Zr-3*Y and Nb*2-Zr/4-Y diagrams for Lake George, Taylor Mountain and Seventy Mile volcanic rocks, Ducel-Bacon and Cooper, 1999 - cord3dusel3.jpg
Geological map Southeast Alaska, showing sample locations, Ducel-Bacon and Cooper, 1999 - cord3dusel4.jpg

Johnston, S.T. et al., discussion, and Currie, L.D. and Parrish, R.R., reply, 1999, BGSA, 111, 1103-1106, of paper by Currie, L.D. and Parrish, R.R., 1997.

Mihanlynuk, M.G., et al., discussion, and Hansen, V.L. and Oliver, D.H., reply, 1999, BGSA, 111, 1416-1422, of paper by Hansen, V.L., and Dusel-Bacon, C. 1998.
Map of the Northern Cordillera according to Mihanlynuk et al. 1999 - cord3mihal1.jpg

Selby, D., Creaser, R.A., and Nesbitt, B.E., 1999. Major and trace element compositions and Sr-Nd-Pb systematics of crystalline rocks from the Dawson Range, Yukon, Canada. CJES, 36, 1463-1481.

Comment - Geochemical (major, trace, and rare earth elements) and isotopic (Nd, Sr, and Pb) data of the Devono-Mississippian Wolverine Creek Metamorphic Suite, mid-Cretaceous Dawson Range batholith, mid-Cretaceous Casino Plutonic Suite, and Late Cretaceous plutons provide new information on the origin and
evolution of the rocks from the Dawson Range in west-central Yukon, northern Canadian Cordillera. Isotopic and other geochemical data for the Wolverine Creek Metamorphic Suite metasedimentary rocks indicate that the detrital components were derived from two distinct provenances: (1) the North America craton, which contributed evolved felsic, upper crustal material; and (2) a calc-alkaline arc, which shed juvenile mafic-intermediate material. The geochemical affinity of the metaigneous rocks indicates that the Yukon-Tanana terrane represented a continental arc during Devonian-Mississippian times, with magmas derived from geochemically primitive sources and partial melting of the Yukon-Tanana terrane supracrustal rocks. The Dawson Range batholith likely represents crustally derived magmas from the Yukon-Tanana terrane during the mid-Cretaceous, with the contemporaneous Casino Plutonic
Suite representing a late-stage fractionate of these magmas. The Late Cretaceous porphyry Cu mineralization is genetically related to plutons derived from mantle-source magmas related to active subduction.

Aleinikoff-John-N; Farmer-G-Lang; Rye-Robert-O; Nokleberg-Warren-J, 2000. Isotopic evidence for the sources of Cretaceous and Tertiary granitic rocks, East-Central Alaska; implications for the tectonic evolution of the Yukon-Tanana Terrane. Canadian Journal of Earth Sciences, 37, 6, 945-956.

Comment - Magnetotelluric traverses across the southern Yukon-Tanana terrane (YTT) reveal the presence of a thick conductive layer (or layers) beneath Paleozoic crystalline rocks. These rocks have been interpreted to be flysch of probable Mesozoic age, on the basis of the occurrence of Jurassic-Cretaceous flysch in the Kahiltna assemblage and Gravina-Nutzotin belt flanking the YTT to the southwest and southeast, respectively. The Pb, Nd, Sr, and
O isotopes in Cretaceous and Tertiary granitic rocks that crop out throughout the YTT were measured to determine if these rocks do in fact contain a component of flysch. Previous limited analyses indicated that the Pb isotopes of the granitic rocks could be a mixture of radiogenic Pb derived from Paleozoic crystalline rocks of the YTT with an increasing component of relatively nonradiogenic Pb with decreasing age. Our Nd, Sr, and O data,  along with additional Pb isotope data, eliminate flysch as a likely  source and strongly suggest that the nonradiogenic end-member  was derived from mafic rocks, either directly from mantle magma or by melting of mafic crust. The lack of a sedimentary component in the granitic plutons suggests either that the plutons did not incorporate significant amounts of flysch during intrusion or that the conductive layer beneath the YTT crystalline rocks is not flysch.

        Stevens, R.A., Erdmer, P., Creaser, R.A., and Grant, S.L., 1995. Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the teslin tectonic zone, part of the Yukon-Tanana terrane of south-central Yukon. CJES, 33, 103-116.

        Oliver, D.H. and Mortensen, J.K., 1998. Stratigraphic succession and U-Pb geochronology from the teslin suture zone, south-central Yukon, in Yukon exploration and Geology 1997: Exploration and Geological Services Division, Yukon Indian and Northern Affairs Canada, 69-75.
 
 

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Structural Provinces of North America.

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