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The Appalachian System

    The Appalachian system is located along the eastern margin of continental North America, and in this respect appears to be a mirror image of the Cordilleran system. The resemblance is however only coincidental, the marginal position of the Appalachian system being a reflection of the fact that during the Mesozoic break-up of Pangea, North America separated from Europe along approximately the same line as that marking its earlier collision with Avalonia and Baltica during the Taconic/Acadian/Caledonian closure of the Iapetus ocean. The Iapetan system extends from Norway/Greenland through Great Britain, Ireland, Newfoundland, Maritime Canada, Quebec/New England, and the southeastern states of the U.S., to perhaps as far south as southern Chili and Argentina in South America. In the area of the North Sea it connected with the North German-Polish ocean that at one time separated Avalonia from Baltica. The closure boundary of this ocean is commonly referred to as the Tornquist line.

    The Proto-Atlantic and present-day Atlantic lines of closing and opening, respectively - napatlaniap1.jpg

    The Iapetus (Proto-Atlantic) ocean of the Appalachian - Caledonian system - napchurch1.jpg

    In the Maritime, New England, and southern Appalachian sections of the Appalachian system however, the geology not only reflects events related to the closure of the Iapetus Ocean during the Ordovician/Siluro-Devonian Taconic-Acadian orogeny but also events related to the closure of a more southerly Rheic/Saxothuringian ocean - the ocean separating the newly formed Laurentia-Avalonia-Baltica supercontinent from the Gondwana continent (North Africa) - during the Carboniferous Alleghanian orogeny. In reality therefore, the Appalachian orogen is composed of two northeasterly diverging oceanic belts (Iapetan and Rheic ocean crust and arc material) accreted to the continental margins of Laurentia to the west, Avalonia and Baltica to the east, and Gondwana (Africa and South America) even further to the east.

    Paleogeographic reconstructions for Laurentian, Avalonian, Baltic, and Gondwana during the Paleozoic - napmag1.jpg

    The most complete and best exposed section across the Iapetan segment of the Appalachian system is found in Newfoundland/New Brunswick and the British Isles. In Newfoundland the Iapetus system is composed of eight structural zones arranged from West to East as follows:

    1) the Laurentian continental crust: - Grenvillian basement rocks overlain by autochthonous Late Proterozoic - Cambro-Ordovician shelf sediments; allochthonous ophiolites and associated olistostromal melanges; and autochthonous sediments laid down in a foreland basin developed in front of the advancing early Ordovician ophiolitic nappe.

    2) the Fleur de Lys (orthotectonic) terrane: - composed of a western subzone of marble-bearing psammitic (arenaceous) and pelitic (argillitic) metasediments, likely deep water equivalents of the shelf sediments of the Laurentian margin; a core subzone of psammitic metasediments and mafic intrusive rocks metamorphosed to eclogite and amphibolite; and the eastern Mings Bight subzone of psammitic metasediments imbricated with shear pods and lenticular units of ultramafic\clinopyroxenite\gabbro material of ophiolitic affinity.

    3) the Notre Dame Bay (paratectonic) terrane: - allochthonous boninitic (ophiolitic) rocks of early Ordovician age, obducted from east to west over the Fleur de Lys zone, and overlain by more mature (calc-alkaline felsic) autochthonous arc volcanic and plutonic rocks likely formed above a westerly dipping subduction zone (subduction polarity reversal).

    4) The Iapetus ocean suture zone (Lukes Arm - Red Indian Line).

    5) The Exploits terrane of volcanic arc rocks , possibly underthrust by psammitic rocks of the Gander Lake zone.  Paleomagnetic data indicates that the rocks of the Exploits terrane formed at high latitudes in the  southern Iapetus ocean.

    6) The Davidsville terrane of deep water deposits and melanges laid down coeval with the west to east obduction of the GRUB line ophiolites.

    7) The GRUB terrane of oceanic rocks (ophiolite) thrust to the south over rocks of the Gander Lake zone.

    8) The Gander Lake terrane of Gondwana continental margin psammitic metasediments.

    9) The Avalonia terrane of late Proterozoic volcanic rocks overlain by Cambrian sediments, Ordovician iron formations (Belle Isle), and some Silurian mafic intrusive rocks(?).

    Geological map of Newfoundland

    Geology of Western Newfoundland I (Cooper, Weissenberger et al. 1998)

     Geology of Western Newfoundland II (Cooper, Weissenberger et al. 1998)

      Rocks west of the Iapetus suture are characterized by the presence of fossils of North American affinity (e.g. Olenellus), whereas those east of the suture invariably contain fossils of Gondwanan or European affinity (e.g. Paradoxides). During the early Ordovician a 'Celtic' shelly fauna occupied the arc environment of the southern Iapetus ocean from Norway to Argentina. The Iapetus ocean likely opened in later Proterozoic to Cambrian times, began to close in late Cambrian to Early Ordovician times - an event marked by the obduction of ophiolites over both the western and eastern continental margins - and was closed by a mid-Silurian (early Acadian) collision, an event marked by folding of Silurian and older rocks throughout the Appalachians. The closure was also marked by extensive felsic volcanism and plutonism, and in the southern part of Newfoundland the Avalonian continental margin virtually came into contact with the Laurentian margin, cutting out all the central volcanic zones.

    Most of the tectonic zones and faunal patterns found in Newfoundland are represented in the Caledonides of Ireland and Great Britain, and in the Appalachians of the Canadian Maritimes and Quebec/New England, and although equivalents of the overthrust ophiolite sheets of Western Newfoundland are absent from the Quebec and New England Appalachians, their prior existence is marked by the presence of detrital chromite in Ordovician foreland sediments of the Taconic allochthons. The Acadian orogeny in central New England however appears to be younger (Middle Devonian) compared to this event in Newfoundland, and to the Silurian deformation and metamorphism of terranes in eastern Maine (St. Croix, Islesboro, Ellsworth terranes).

    There is also reasonable evidence that the eastern Avalonian teranes of the New England region have underthrust the central 'Acadian' terranes of New England during the Pennsylvanian/Permian Alleghanian collisional orogeny so well represented in the Southern Appalachians. The thrust boundary is a ductile shear zone, the Putnam-Nashoba belt, bounded on either side by the Lake Char (East) and Clinton - Newbury (West) faults. Alleghanian metamorphism caused kyanite to replace Acadian age Sillimanite, and Alleghanian plutonism is evident in the intrusion of, for example, the Late Mississipian Pinewood Adamellite. In contrast the Alleghanian collision in the Southern Appalachians caused east over west thrusting of the already accreted Avalonian - Laurentian margin terranes.

    The Hercynian (Alleghanian) of Europe

    The Hercynian system (Rheic ocean) of Western Europe extends westwards from its intersection with the Polish Caledonides through southern Germany, Central France, Brittany, Spain and Portugal, and possibly northwest Africa. Collision of the Gondwana realm with Avalonia took place from Late Devonian time to the Permian. The deformation front passes through South Wales and the South of Ireland but is not seen in Newfoundland. The leading edge of the deformation front may be present in New Brunswick and also in the western part (Boston, Rhode Island) of the New England Appalachians, beyond which however it becomes prominent as the western boundary of the Valley and Ridge Structural Province of the Southern Appalachians. The southern edge is located in the Montagne Noire region of the south of France, the Pyrennees, and eastern Central Spain. If the belt crosses the Mediterranean it would have to turn back on itself and pass through Morocco and south to Senegal. The collision of Gondwana with Avalonia/Laurentia completed the assembly of the Permo-Triassic Pangean supercontinent.

        The Late Paleozoic Hercynian-Variscan system of Europe -  naphercyn1.jpg

    Nd Isotopes

    The Epsilon Nd values of Grenvillian crust and Late Proterozoic to early Cambrian rift facies sediments ranges from -3.1 to -6.6 at 450 Ma. For example, the Cambrian Dalton Fm has values of about -3.2. Sedimentary rocks representing the drift phase of the Appalachian system and the early stages of formation of the foreland basin are more negative ranging from -11.7 to -13.3. The Ordovician Walloomsac has a higher negative value of -11.7, the Austin Glen of the Taconic foreland basin sediments has values of about -8.4, and the Utica Shale ranges from -7.5 to -13.7. As suggested by Bock et al., the rift facies sediments of the Appalachians were likely derived from local Grenville basement source, whereas the younger drift facies sediments had a source in a much wider area of Laurentian rocks older than the Grenville. In this respect, the early rift history of the Western margin of the Appalachians would be similar to that of the Red Sea region which is currently fed by sediments from the topographically elevated Red Sea Hills bordering the Red Sea. East of the obduction zone, Middle to Late Ordovician and Permian plutonic rocks from southwestern Connecticut have values of -2 to -5, but juvenile values are exhibited by igneous rocks of the Hawley Formation of Massachusetts (+6 to -0.6) and the Maltby Lake volcanics of southwestern Connecticut (+8). The Wepawaug Schist overlying the Maltby Lakes exhibits values of -7.1 to -8.9, and the Bronson Hill belt rocks east of the Iapetus ocean, values of -2 to -5. Similarly, in the Ouachita section of the Appalachian system, sedimentary rocks older than 450 Ma display Epsilon Nd values more negative than -12 whereas younger rocks have values of -5 to -10, indicating the presence in these sediments of a detrital component derived from newly exhumed oceanic material accreted to the Laurentian margin during the early Ordovician.

    Chart indicating the distribution of epsilonNd values for New England Appalachian rocks at 450 Ma - napbock1.jpg

    On the Avalonian continental margin, most of the late Proterozic (c. 600 Ma) granites have Epsilon values from 0.1 to + 6.9 (the Louil Hills peralkaline rocks are 5.3 to 6.9). The exceptions are the Simmons Brook Granodiorite and Sea Cove Pluton located to the southwest and on the Avalon side of the Dover Fault where it records strong negative values of -6.3 to -8.2. These values are also decidely more negative that of the 680 - 570 Ma old plutonics rocks on the northwest side of the Dover Fault, which tend to have either slightly negative (> -2.8) or slightly positive values (<1.6). The elevated Simmons Brook values may reflect the presence of a Precambrian continental source terrane underlying the Dover falt region to its southwest. Silurian plutonic rocks to the south of the fault have values of 4.8, whereas Devonian plutons have values of 0.8 to 4.0.  In contrast plutonic rocks northwest of the Dover fault have generally negative values, with some Cambro-Ordovician rocks recording values as low as -8.0.

    Radiometric ages

Long Range dikes - 614 Ma mark the initial rift phase of the Northern Appalachians

Catoctin - 564 Ma (Hoffman 1997, GSA ANN Meet. p. A-280)

Sept Isle Intrusion - 564 Ma (Hoffman 1997, GSA ANN Meet. p. A-280)

Maximum base of the Cambrian - 551 Ma

Skinner Cove - 550 Ma (Hoffman 1997, GSA ANN Meet. p. A-280)

Lake Ambrose volcanic rocks, Exploits zone - 513+2 Ma

Thetford Mines ophiolite - 504 Ma

Twillingate Trondjhemite, NDB - 507+3 Ma

Betts Cove ophiolite - 489 Ma; Snooks Arm is lower Middle Arenig

Wild Bight late Tremadoc - early Arenig north subduction and southernly obduction, Maclachlan, K. and Dunning, 1998 GSA NE p. 59 -489+3-486+4

Lithostratigraphy and geochemistry of the Cottrels Cove Group, Buchans - Roberts Arm volcanic belt: new constraints for the paleotectonic setting of the Notre Dame subzone, Newfoundland Appalachians

Dec, T, Swinden, H.S., and Dunning, 1997, CJES, 34, 86-103, R.G Cottrels Cove is the eastern extension of the Roberts Arm and correlates with the Chanceport Group on New World Island. composed of the Fortune Harbour formation with calc alkaline lavas and volcaniclastic deposits with tuff at 484+2 (= Tremadocian?) with inheritance at 2517+26. Epsilon Nd = -10.2

Mansfield Cove - 479+3 = Annieopscotch ophiolite??;

Dunning, G.R, U/Pb geochronology of the Coney Head Complex, Newfoundland p. 1072-1075, ophiolite Newfoundland Burlington White Bay; allochthonous plutonic rocks, tonalite at 474 Ma

(=Buchans, Roberts Arm); autochthonous microgranite at 432 (Silurian) cuts the tonalite, has inherited Proterozoic zircon.

Margaree mafic-silicic intusive gneiss, Port aux Basques, west of the Cape Ray separating the peri-Laurentian Dashwoods subzone from the Hermitage Avalonian, Valverde-Vaquero & Dunning 1998 GSA NE, p. 82 - 474+14, 472+2.5, 465+3

Buchans and Roberts Arm volcanics - 473+2 Ma U/Pb upper intercept (Late Arenig-Llanvirn conodonts);

latest Arenig - Llanvirn Buchan rhyolite = 473+3 upper intercept

Oughterard Granite, Western Ireland, and D3, Tanner et al., 1997 (Geol. Jour.) - 473 Ma

South Lake, Wild Bight, Nfland SE subduction, Maclachlan, K. amd Dunning 1998 GSA NE p. 59 - 472+3

Late tectonic Aberdeen granite, Scotland - 470 Ma

early to middle Llanvirn Cutwell Oil Islands rhyolite = 469+5 upper intercept

Joslin Turn tonalite, intr. Ammonoosac V. (Rankin, 1996, GSA NE, p. 92 & 1998 NE p. 68) - 469 Ma

Hungry Mountain - 467 Ma

Burlington Granodiorite, Notre Dame Bay - 463+6 Ma; p. 1182 467+8 by Whalen for tonalite (w. ultramafic xenoliths) thrust over Buchans from the west (= Burlington granodiorite).

Tulks Hill rhyolite = 462+4-2, has limestone with Llanvirn-Llandeilo;

Ascot - Weedon volcanics, Quebec - 460 - 441 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; basal Llandeilo ash = 460 Ma

Southwest Brook complex, south of southern terminus of Grand Lake (correlated with the Burlington granodiorite) - 456+3 = age of Swedish bentonites eg. Big Bed of Kinnekulle and N. American bentonites, also = Burlington 463+6 and Hungry Mountain 467+8, Whalen 1987, average age of inherited zircon = 1430+18;

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; basal Caradoc = 456+2 Ma

Bronson Hill volcanics - 454 - 442 Ma

Staurolite growth in the Walloomsac, NY (Lanzirotti, unpub; Bock et al 1996) - 454 Ma

Brookfield Pluton, Connecticut (S andH, 1995) - 453 Ma

Beardsley Orthogneiss, SW Connecticut VS, (Sevighy 1993) - 446 Ma

Crawton clasts, Scotland, (Haughton and Halliday 1991) - 443 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; base of Silurian = 443 Ma

Ordovician/ Silurian Boundary - 438 Ma

Cape St. Mary sills, Avalon (Greenough et al., 1993) - 441+2

[Cape St John, Burlington Pen - 441+50; 353+15 Ma]

Newton Gneiss, Connecticut (Sevigny and Hanson, 1995) - 446-438 Ma

Fintona Granite. Ireland (Thirlwall, 1988) 437+6

Boogie Lake Monzonite, post-dates def. in Ord. ophiolite and arc rocks - 435 Ma

Crawton clasts, Scotland (Haughton and Halliday, 1991) - 433 Ma

Main Gut Gabbro - 431 Ma

Tuff Bands, Tonalee Fm., below Lettergesh (Williams et al., 1992) - 431 Ma

Southern New Brunswick granites (Whalen et al 1994) - 430 - 422 Ma

Lettergesh, Ireland - 430 - 425 Ma

Calc-alkaline granite in the Putnam (Hepburn 1994, GSA NE p. 53) - 430 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; latest Llandovery = 430+2.4 Ma

Springdale/Bottwood/Topsails (Chandler) - 429+6

La Poile Garabal Hill Bear Pond rhyolite w. Boogie Lake clasts (Chandler) - 429 Ma

Burgeo Intrusive Suite Western Head, deformed - 429 Ma

    Llandovery/Wenlock boundary - 428 Ma

Pumpkin Ground Orthogneiss, SW Connecticut VS (Sevigny and Hanson, 1993) - 428+2

Money Point, NB - 427.5 Ma

Arrochaor, Scotland - 427 Ma

Strontian and Ratagain Granites, Scotland - 425 Ma

Formation of eclogites in Norwegian Caledonian eclogites - 425 Ma

Stony Lake volcanics, unconformable on folded Bottwood - 423 Ma

    Wenlock/Ludlow boundary - 421

    Acadian (Salinian) deformation in Newfoundland

Gaultis Granite, Newfoundland, syn-D1 def. - 421+2 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; latest Ludlow = 420+4 Ma

La Poile is 420+8 lower intercept, Silurian, and contains inherited 1376+120 Proterozoic zircons

    Peak early 'Acadian' (Salinian) Met., Strait Schist, southern CV (Lanzirotti and Hanson, 1995) - 420-400 Ma

Comerford Dam Silurian intrusive suite (Rankin 1998 GSA NE p. 68) - 419+6

Crawton SE derived clasts (Haughton and Halliday, 1991) - 419-417 Ma

La Poile (K-feldspar phenocrysts) and Otter Point - 418

Hawks Nest, post-D1, syn D2 - 418 Ma

North River Igneous suite in Mississqoi-Barnard volcanics (GSA NE 1994, p. 3) - 418 Ma

Southern Uplands Lamprophyres - 418-413 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; base of Devonian estimated to be 417

Linstraten ignimbrite on both sides of the HBF - 416 Ma

Burgeo intrusive suite, Newfoundland, undeformed - 415 Ma

    Pridoli/Ludlow boundary - 414 Ma

Cape North metamorphism and intrusion, NB - 414 Ma

Midland Valley Distinkhorn (Haughton and Halliday, 1991) - 413 Ma

Crawston NE derived clasts (Haugton and Halliday, 1991) - 412 Ma

Port aux Basques metamorphism - 412 Ma

Unfoliated granite in the Putnam (Hepburn 1994 GSA NE, p. 53) - 412 and 349.

Loon Bay Suite - 408 Ma

Spaulding Tonalite (Robinson, GSA NE, 1996, p. 94) - 408+2 Ma

Kinsman Granite (Robinson, GSA NE, 1996, p. 94) - 403+3 Ma

    Lower Devonian/Pridoli boundary - 408 Ma (but 417 Ma according to Tucker and McKerrow 1995)

Ansonia lecuogranite SW Connecticut VS (Sevigny and Hanson, 1993) - 406+13

Southern Uplands Lamprophyres - 400 Ma

Dike, post-upright isoc. folding, pre-shear, Central Maine belt - 399 Ma

North Bay Granite, post-tectonic - 396 Ma

Chetwynd - 390 Ma

New Hampshire met high, cooling ages (Robinson, gsa NE, 1996, p. 94) - 398 - 392 Ma

Tucker, R.D and McKerrow, W.S. CJES 1995 32, 368-379 Early Paleozoic chronology: a review in light of new U-Pb zircon ages from Newfoundland and Britain; base mid Devonian = 391 Ma

Donegal Granite, sheared - 388 Ma

Central Maine low temp hornblende reg. met - 381-368 Ma

Cheviot and Criffel - 388 Ma

    Middle Devonian/Lower Devonian - 387 Ma (but 391 Ma according to Tucker and McKerrow 1995)

    New England Acadian Deformation - 380 - 375 (Sevigny and Hanson, 1993)

Belchertown Tonalite cuts mid Acdian backfolds, Pelham (Robinson, GSA NE, 1996, p. 94) - 380 Ma

    Upper Devonian/Middle Devonian - 374 Ma

Monazite in xen. in Belchertown (Robinson, GSA NE, 1996, p. 94) - 374 Ma

Met monaz. cent. Mass. (Robinson, GSA NE, 1996, p. 94) - 367 to 355 Ma

Peg in Monson Gneiss, zir, cuts isoc. & back, but is cut by mylon. which is folded
by 3rd stage dome folds (Robinson, GSA NE, 1996, p. 94) - 366+1 Ma

Hardwick pluton???

    Mississipian/Upper Devonian - 360 Ma, strongly deformed, Robinson, GSA NE, 1996, p. 94) - 360+1 Ma

Monaz. in retrog Sill bearing Acadian rocks, central MA, sphene, Mon., peg zirc.,

with N-S linear fabrics (Robinson, GSA NE, 1996, p. 94) - 359-356 Ma

Fitzwilliam granite, post tectonic (Robinson, GSA NE, 1996, p. 94) - 354+1 Ma

    Pennsylvanian/Mississipian - 320 Ma

    Classic prograde Ky bearing younger 'Acadian' (Alleghanian), central MA, sphene, Mon., peg zirc., N-S
linear fabrics (Robinson, GSA NE, 1996, p. 94) - 300-295 Ma

Pinewood Adamellite (Sevigny & Hanson, 1993) - 290 Ma

    Permian/Pennsylvanian - 286 Ma

Younger met. of 623 Ma Massabessic (Putnam-N. window) (Wintsch, GSA NE, p. 92) - 280 - 275 Ma

Chemical remag. sed. rocks of the central Appalach during folding (Stamatakos, 1996) - 275-255 Ma

    Triassic/Permian - 245 Ma

Youngest age of cooling of lowest part of west dipping thrust stack ??

(Wintsch GSA NE, 1994 p. 92) - 240 Ma


Structural Provinces of North America.


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