Appalachian
AppalachianThe Appalachian Mountains
The Appalachian mountain system dominates the Eastern United States and seperates the Eastern seaboard from the interior with a belt of uplands that extends nearly 1,500 miles from northeastern Alabama to the Canadian border.; They are old, complex mountains, eroded from much older and greater ranges. The present topography is a result of erosion that has carved the weak rocks away, leaving a skeleton of resistant rocks behind as highlands. Because of this weathering, geologic differences are refelected in topography. In the Appalachians these differences are sharply demarcated and neatly arranged, so that all the major subdivisions except for New England lie in strips parallel to the Atlantic and to one another.
The Appalachian mountains were formed due to several collisions between the African, Eurasian and North American Plates. Africa and North America were joined into one super continent. The collision of these land masses over 1 billion years ago metamorphosed the original rock producing the Pedler gneiss and Old Rag granite which can be observed in the Shenandoah National Park. In late Precambrian time this super continent began to rift apart under the tensional forces producing the Catoctin rift basalts that can be observed in the Shenandoah. As they rifted apart, they created a growing ocean called the proto-Atlantic or Iapetus after the father of Atlas, for whom the Atlantic Ocean is named. Towards the end of the Precambrian, the tensional forces changed to compression and subduction began. Volcanic islands grew as a result of andesitic volcanism associated with the subduction.
With continued subduction and convergence, volcanic islands collided with North America and those rocks were thrust up on the continental margin. Deformation, metamorphism and magmatism accompanied this collision and gave rise to the Taconic Orogeny. Rocks metamorphosed and deformed in this event are seen in the Blue Ridge and Piedmont provinces. This all occured during the Ordovician time, about 425 million years ago. As North American, African, and Europe convergence continued, a small microplate known as the Avalon terrane, collided with North America producing a second phase of deformation, metamorphism and magmatism known as the Acadian Orogeny. This event had the largest effects in the Northern Appalachians and it's effects are very visiblein the Acadia National Park in Maine, but not easily seen in the Shenandoah and Great Smoky Mountain National Park to the south. This all occured during the Devonian time, about 380 million years ago.
With continued subduction, finally collision of the African continent with North America occured causing intense folding , which is most pronounced in the Valley and Ridge province, andmetamorphism. The European and South American plates were also converging with North America at this time to form a super continent called Pangea. Thiss all occured during the Alleghenian Orogeny furing the Pennsylvanian time. Pangea began to break up in Jurassic time about 200 million years ago as the present Atlantic Ocean opened...
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