The Appalachian Orogen

Abstract

The Paleozoic Appalachians formed during a complete Wilson cycle along the eastern Laurentian margin between the breakup of supercontinent Rodinia and the amalgamation of all continents to form supercontinent Pangea. The Appalachian Wilson cycle began by breakup of Rodinia and formation of a Neoproterozoic to early Paleozoic rifted margin and platform succession on the eastern margin of Laurentia. Three orogenies produced the Appalachians: the Ordovician Taconic orogeny, which involved arc accretion; the Acadian–Neoacadian orogeny, which involved north-to-south, transpressional, zippered, Late Devonian–early Mississippian collision of the Carolina superterrane in the southern central Appalachians, the Avalon and Gander superterranes in the New England Appalachians, and Silurian collision in the Maritime Appalachians and Newfoundland; and the Alleghanian orogeny, which involved late Mississippian to Permian collision of all previously formed Appalachian crust with Gondwana to form supercontinent Pangea. The Alleghanian orogeny also involved zippered, north-to-south, transpressional, then head-on collision. All orogenies were diachronous. Similar coeval orogenies affected western and central Europe (Variscan events), eastern Europe and western Siberia (Uralian events), and southern Britain and Ireland; only the Caledonide (Grampian–Finnmarkian; Caledonian–Scandian) events affected the rest of Britain and the Scandinavian Caledonides. These different events, coupled with the irregular rifted margin of Laurentia, produced an orogen that contains numerous contrasts and non-through going elements, but it also contains components, such as the platform margin and peri-Gondwanan elements, that are traceable throughout the orogen. Present-day topography is very young, and probably related to uplift during the late Miocene to early Pliocene.