Plates & Regions

North American Perspectives II: Appalachians (Paleozoic)

Processes in Structural Geology & Tectonics Ben van der Pluijm

North American Perspectives II: Appalachians (Paleozoic)

• Opening and closing of Proto-Atlantic (Iapetus and Rheic Oceans) based on paleogeography and paleomagnetism. • Appalachians preserve Laurentian (N America) and Gondwanan (Africa) margins, separated by a belt with ocean remnants (ophiolites, arcs, islands/plateaus, subduction complexes), best preserved in the northern segment. • Southern Appalachians dominated by Late Paleozoic deformation from final ocean basin closure, resulting in large overthrusts that are exposed in tectonic windows. • Curved mountain belts (oroclines) and salients/recesses (irregular plate margins) are explored. • Paleogeographic reconstruction shows Appalachian history from late Precambrian ocean opening to closing.

Eastern N America ©PSG&T 2 Geologic Timescale (GSA, v.4, 2012)

Eastern N America ©PSG&T 3 US and Canadian Appalachians

Eastern N America ©PSG&T 5 The Appalachians and Caledonides: Birthplace of Past Plate Tectonics

Eastern N America ©PSG&T 6 Paleogeography: Fossil Biozones

Paleozoic Paleogeography: Paradoxides davidis intermedius • Fossil biomes (Specimen FMNH PE 28971-B, • Paleomagnetism 240mm or 9.25 inches long) • No ocean floor magnetic anomalies

Eastern N America ©PSG&T 7 History of Proto-Atlantic Oceans (Iapetus and Rheic Oceans)

Chris Scotese’s PaleoMap Project http://www.scotese.com/

Eastern N America ©PSG&T 8 Appalachian-Caledonian belt and US Appalachians

Eastern N America ©PSG&T 9 Zones of the Appalachian Collisional Orogen

N America Remnants of Proto-Atlantic (Arcs, Islands, Plateaus)

Africa (Gondwana)

Eastern N America ©PSG&T 10 Northern Appalachians (Lower and Middle Paleozoic)

N America Proto-Atlantic Remnants Africa (Gondwana)

Eastern N America ©PSG&T 11 Ophiolite Obduction (Ordovician)

Table Mountain peridotite (Gros Morne, Newfoundland)

Eastern N America ©PSG&T 12 Southern Appalachians (3D)

Eastern N America ©PSG&T 13 3D Geology: Seismic reflection profiling

See Chapter 15: Geophysical Imaging

Eastern N America ©PSG&T 14 COCORP in the S Appalachians

Geological map of southern Appalachians with locations of COCORP seismic reflection profiles.

Cook and Vasudevan, 2006

Eastern N America ©PSG&T 15 Alleghanian (Upper Paleozoic) Collision

S Appalachian detachment and Grandfather Mountain Window

Eastern N America ©PSG&T 16 Extra: Radiometric (Ar) Dating of Appalachian Faults

Hnat, 2014

Eastern N America ©PSG&T 17 Orogenic Curvature along the Appalachians

Eastern N America ©PSG&T 18 Curved Orogens (=Oroclines): the Pennsylvania Salient

From NASA Gray and Stamatakos, 1997

Valley and Ridge, PA • Origin and meaning of curved orogens (Carey’s “orocline”; 1955) • Primary vs. secondary curvature

Tennessee Salient

Marshak, 2004 Hnat, 2011

Paleo-inclination: distance from pole: tan(I) = 2 cotan(L) Paleo-declination: rotation relative to (averaged) pole Note: reversal indeterminacy

MacNiocaill et al., 1997

Pangea

Early Triassic, ~237 Ma (from www.scotese.com)

Scotese, 2004

Chris Scotese