North American Perspectives II: Appalachians (Paleozoic) Processes in Structural Geology & Tectonics Ben van der Pluijm © WW Norton+Authors, unless noted otherwise 4/25/2016 4:33 PM We Discuss … 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 Eastern N America ©PSG&T PA Salient, 19 Oroclines Tennessee Salient Marshak, 2004 Hnat, 2011 Eastern N America ©PSG&T 20 Paleogeography through Paleomagnetism Paleo-inclination: distance from pole: tan(I) = 2 cotan(L) Paleo-declination: rotation relative to (averaged) pole Note: reversal indeterminacy Eastern N America ©PSG&T 21 Oceanic Terranes and Collision (Paleomagnetic evidence) MacNiocaill et al., 1997 Eastern N America ©PSG&T 22 Pangea Family Tree Pangea Early Triassic, ~237 Ma (from www.scotese.com) Scotese, 2004 Eastern N America ©PSG&T 23 Opening and Closing of Proto-Atlantic (Iapetus) Ocean Chris Scotese Eastern N America ©PSG&T 24.