![]() For instance, mafic rocks have been found along the Fries Fault in the central Blue Ridge area of Montgomery County, VA. Evidence of subsurface activity, dikes and sills intruding into the overlying rock, is present in the Blue Ridge as well. Mount Rogers, Whitetop Mountain, and Pine Mountain are all the result of volcanic activity that occurred around this time. There is evidence of this activity in today's Blue Ridge Mountains. ĭuring this continental break-up, around 600 million to 560 million years ago, volcanic activity was present along the tectonic margins. The weathering of limestone, now exposed at the land surface, produces the lime-rich soils that are so prevalent in the fertile farmland of the Valley and Ridge province. ![]() This is the same process by which limestone forms in modern oceans. Shells and other hard parts of ancient marine plants and animals accumulated to form limey deposits that later became limestone. The rocks of the Valley and Ridge province formed over millions of years, in the Iapetus. This was called the Iapetus Ocean and was the precursor of the modern Atlantic Ocean. Eventually, the tectonic forces pulling the two continents apart became so strong that an ocean formed off the eastern coast of the Laurentian margin. The basin continued to subside, and over a long period of time, probably millions of years, a great thickness of sediment accumulated. The sediment spread out in layers on the basin floor. Rivers from the surrounding countryside carried clay, silt, sand, and gravel to the basin, much as rivers today carry sediment from the midcontinent region to the Gulf of Mexico. For example, in the what is now the southern United States, the Ococee Basin was formed. The eroded sediments from these mountains contributed to the formation of sedimentary basins and valleys. The mountains formed during the Grenvillian era underwent erosion due to weathering, glaciation, and other natural processes, resulting in the leveling of the landscape. Īfter the Grenville orogeny, the direction of the continental drift reversed, and the single supercontinent Rodinia began to break up. While the rift edge is shown lower than, and parallel to, the equator at the time of the Rodinian formation and drift, subsequently, there was a counter-clockwise drift of Laurentia and the early Blue Ridge. Breakup of Rodinia and formation of the Iapetus Ocean Proposed reconstruction of Rodinia for 750 Million years ago (0.75 Ga), with orogenic belts of 1.1 billion years ago (1.1 Ga) highlighted in green. The present Appalachian Mountains have at least two areas which are made from rock formations that were formed during this orogeny - the Blue Ridge Mountains and the Adirondacks. Mountain-building referred to as the Grenville Orogeny occurred along the boundaries of the cratons. All the other cratons of the earth also collided at about this time to form the supercontinent Rodinia and were surrounded by one single ocean. The first mountain-building tectonic plate collision that initiated the construction of what are today the Appalachians occurred during the Mesoproterozoic period at least one billion years ago when the pre-North American craton called Laurentia collided with other continental segments, notably Amazonia. Geological history Proterozoic Era Grenville Orogeny and formation of Supercontinent Rodinia Land added to Laurentia during the Grenville orogeny. ![]() These mountain ranges likely once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded. The birth of the Appalachian ranges marks the first of several mountain building plate collisions that culminated in the construction of the supercontinent Pangea with the Appalachians and neighboring Anti-Atlas mountains (now in Morocco) near the center. The rocks exposed in today's Appalachian Mountains reveal elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor – strong evidence that these rocks were deformed during plate collision. The geology of the Appalachians dates back more than 1.1 billion years to the Mesoproterozoic era when two continental cratons collided to form the supercontinent Rodinia, 500 million years prior to the later development of the range during the formation of the supercontinent Pangea. This includes the Canadian classification of the Appalachian Uplands and the US classification of the Appalachian Highlands. The Appalachian Mountains, as defined by physiographic classification. Geologic description of the Appalachian Mountains
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