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How the formation of the Appalachian Mountains controlled the formation of the United States Formation of the Appalachians: Proto N. America Taconic Orogeny 1st island arc ‘docked’ against eastern North America Formation of the Appalachians Acadia Orogeny (after Taconic) Alleghanian Orogeny: Final closure of ocean basin Taconic Orogeny (first) Alignment of Appalachians and Caledonides during Pangea Initial doming & upwarping Pangea begins to break up, just east of the Appalachians Triple Junction A series of triple junctions form east of the Appalachians Rift Valley Appalachians over here somewhere North America Future Atlantic Ocean Europe/Africa Active rift zones of triple junctions align to form long rift valley Failed rift arms (aulacogens) form major continental drainages Aulacogen Lacustrine deposits at top Basalts & dikes at bottom East African Rift Zone Similar to aulacogen Linear sea North America Europe/Africa New Atlantic Ocean Mature mid-Atlantic ridge North America Europe/Africa Present-day Atlantic Ocean Widening of the Atlantic has taken about 200 million years. In the meantime, the Appalachians -- originally about 30,000 feet tall -- have been eroding… … in the meantime Continental Shelf Debris from weathering and erosion of Appalachian Mountains. Distributed downslope by mass wasting and streams/rivers. Starts here, not at the present-day location of the beach 10,000 - 15,000 feet thick Atlantic aulacogens Failed rift basins (aulacogens) in North America Still seismically active (1906 Charleston ‘quake, numerous earthquakes in New York) Hard rocks (folded & faulted continental shelf rocks - lots of marine fossils) Hard rocks (island arc rocks, all volcanic) Fall Line (escarpment separating volcanics from coastal plain sediments Coastal Plain (sediment) Fall Line Columbia, SC Rapids Broad River 1.2Ga rocks (that’s billion years) Taconics (600 million years old) Acadian Rocks Major drainage systems are aulacogens Putting it all together Coarse material Rock fall Rock slide Talus Creep Fine material Stream transport -> Debris flows Fall Line Mechanical weathering Chemical weathering Beach sand & sedimentation on continental shelf Yes, these are the Appalachians…
