The 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...
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