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NORTH AMERICA/Southern and Central Appalachians 77 no Palaeozoic components All are dominated by zircons derived from Grenvillian and older Laurentian sources, suggesting provenance from exhumed and cannibalized platform, and rifted margin sedimentary and volcanic rocks Clasts in Llanvirn polymictic conglomerates in the Sevier Basin sample platform carbonate and older lithologies, but none are derived from sources in the Taconian Orogen Detrital zircon suites from the rifted margin succession (Ocoee Supergroup, Ashe Formation, and equivalents) across the southern Appalachian Blue Ridge and western Inner Piedmont (Tugaloo Terrane) are all dominated by zircons from $1.1 Ga, with smaller components of zircons from 1.3–1.5 Ga Dahlonega gold belt detrital zircons, though also dominated by 1.1- to 1.4-Gy-old components, contain components from 2.7–2.9 Ga, 1.9–2.2 Ga, and 650–700 Ma These rocks were traditionally considered only a more distal facies of the Ocoee Supergroup, but detrital zircons suggest they may be more exotic In addition, the Dahlonega gold belt contains an arc complex from 460 and 480 Ma Goochland Terrane, the Tugaloo Terrane west of the Brevard fault zone in the Carolinas and north-eastern Georgia, and possibly in the Pine Mountain window in Georgia and Alabama were remobilized, although remobilization of basement in the latter may be younger (see later) A suite of thrust sheets carrying deep-water sedimentary rocks was emplaced onto the New England and Canadian Maritimes margin at this time, locally carrying oceanic crust and mantle in ophiolite sheets (Quebec and Newfoundland) These extend into the central Appalachians as the Hamburg Klippe in New Jersey and the south-eastern Pennsylvania Piedmont None has been identified farther south Other premetamorphic thrusts formed at this time from the Pennsylvania Piedmont southward Amalgamation of old and new crust generated during the Taconian events formed a superterrane along the south-eastern Laurentian margin Taconic Events Deposition continued until post-430 Ma in the stillopen remnant of the Theic Ocean that lay between south-eastern Laurentia and the approaching Carolina Superterrane Here a sequence of immature deepwater sandstones (subgreywacke to greywacke) and pelites that today consist of aluminous schist and biotite gneiss were probably deposited on oceanic(?) crust Detrital zircons include the usual prominent 1.1- to 1.4-Ga suite, but with the addition of major components of zircons from 600, 500, and 430 Ma, along with small populations of zircons from 1.9–2.2 and 2.7–2.9 Ga This diverse population suggests sediment was derived from both Laurentia and Carolina Presence of younger zircons precludes docking of the Carolina Superterrane before the Late Devonian or Early Carboniferous The Taconic Orogeny is clearly diachronous in the southern and central Appalachians, with earlier pulses beginning in the Late Arenig in the southern Appalachians and the younger event—the type Taconic Orogeny—beginning sometime in the Llandeilo or Caradoc in the central Appalachians Corresponding suites of plutons, penetrative deformation, and metamorphism to conditions as high as granulite facies were a product of subduction, obduction, and arc accretion The 455- to 460-My-old plutonic–volcanic suite (Hillabee, Ropes Creek, Poor Mountain, Chopawamsic, Baltimore) in the southern and central Appalachians has a mid-oceanic ridge basalt (MORB) to arc affinity At that time, the Neoproterozoic to Cambrian rifted margin assemblage was A-subducted beneath the arc, penetratively deformed, and metamorphosed to mid-crustal metamorphic assemblages During the Taconic events, the Laurentian margin underwent A-subduction and several oceanic and arc assemblages were obducted onto the margin, with accompanying emplacement of the Cowrock, Cartoogechaye, and Tugaloo Terranes in the southern Appalachians, and the Chopawamsic, Potomac, and Baltimore Terranes in the central Appalachians (Figure 3) In New Jersey and eastern Pennsylvania, Grenvillian basement was remobilized in the core of the recumbent Musconnectong Nappe Basement was also remobilized to the north-east (Hudson–New Jersey Highlands) and south-west, forming external massifs in the core of the Blue Ridge from Virginia to Georgia Internal massifs in the eastern Virginia Cat Square Terrane Pine Mountain Terrane The Pine Mountain Terrane in west-central Georgia and eastern Alabama is a complex window exposing 1.1-Gy-old Grenvillian basement and a thin cover sequence of Early Palaeozoic(?) schist, quartzite– dolomite, and a higher schist The window is framed by the dextral Towaliga and Goat Rock and Dean Creek faults to the north and south, respectively, but is closed by the Box Ankle Thrust at the east end All of these faults yield Alleghanian ages, but the Box Ankle Fault was emplaced at sillimanite-grade pressure and temperature (P–T) conditions, whereas the Towaliga and Goat Rock(?) faults moved during garnet-grade conditions, and the Dean Creek Fault moved under chlorite-grade conditions (the same as the Modoc, farther east) Detrital zircons from the
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