Shaping of the Appalachian orogen by the breakup of Rodinia and middle-to-late Paleozoic, zippered, transpressional processes: Geologic and geophysical evidence

English Abstract:

The Paleozoic Appalachian orogen formed on the Laurentian margin via three orogenies that affected the entire orogen. The Ordovician Taconic orogeny involved arc accretion; the Late Devonian-Early Carboniferous Acadian-Neoacadian orogeny involved accretion of peri-Gondwanan terranes (Gander, Avalon, Meguma); and collison of Gondwana in the Late Carboniferous-Permian Alleghanian orogeny formed supercontinent Pangea. A fourth orogeny, the Late Ordovician to Early Devonian Salinic event, has been documented in the Maritime Appalachians with hints in the central Appalachians. The promontory-embayment shape of the western part of the Appalachian orogen was dictated by the irregular Neoproterozoic margin of Laurentia that formed during supercontinent Rodinia breakup. Much of the Appalachians remain buried beneath sedimentary cover of the Atlantic continental margin, but geologic and geophysical (magnetic and gravity) data locate tectonic boundaries and provide insights into terrane and pluton compositions. These data reveal that the interior (eastern and southern) parts of the orogen were shaped by middle-to-late Paleozoic accretionary-collisional transpressional, rotational processes (zippered), and that peri-Gondwanan terranes make up at least half of the orogen. Middle and late Paleozoic events were dominated by dextral strike-slip as Gondwana collided with Laurentia forming Pangea. Pangea breakup left the Suwanee terrane as a Gondwana remnant. Appalachian structure is truncated to the east by the East Coast magnetic anomaly, which may mark the original suture with Gondwana reactivated as the boundary of Pangea breakup. Despite the dominance of early (north) and late (southern-central) Paleozoic thrusting on the western margin of the Appalachians, strike-slip processes dominate interior parts of the orogen, and non-Laurentian, exotic terranes make up more than half of the orogen.