Approximately 350 million to 300 million years ago, the combined continents of Europe and Africa (Gondwana) collided with North America, to form the super-continent Pangaea. This collision exerted massive pressure on what is today the eastern seaboard of North America. This pressure resulted in an enormous uplift of the entire region, called the Appalachian orogeny. Pressure and heat over millions of years "cooked" the rock, folding, twisting and faulting it. Farther west the collision was gentler and resulted in less faulting and more wrinkling, creating ridges and valleys which became the Appalachian mountains.
Closer to the point of impact, the immense pressure turned igneous and sedimentary rock into metamorphic rock and broke it in numerous places, creating faults which were very susceptible to being worn away by wind and water. Over time these erosive forces wore the landscape down to nearly sea level. This worn_down landscape is now the Piedmont.
Evidence for the Appalachian orogeny stretches for many hundreds of miles on the surface from Alabama to New Jersey and can be traced further subsurface to the southwest. In the north it enters a region of confused topography associated with earlier orogenies, but clearly the Applachian deformation extends north to Labrador and Newfoundland.
The Appalachian orogeny is also called the Alleghenian orogeny, due to the formation of the Allegheny Mountains at the time.
External links
Geology of Manassas National Battlefield Park (http://www.nps.gov/mana/pphtml/subenvironmentalfactors13.html) (public domain source)
Alleghenian orogeny page at SUNY Stonybrook (http://www.ic.sunysb.edu/Stu/ckramer/AlleghenianOrogeny.htm)
Orogeny (Greek for "mountain generating") is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within a time frame.
Orogenic events occur solely as a result of the processes of plate tectonics; the problems which were investigated and resolved by the study of orogenesis contributed greatly to the theory of plate tectonics, coupled with study of flora and fauna, geography and mid ocean ridges in the 1950s and 1960s.
It was, in the context of orogeny, contested hotly by proponents of vertical movements in the crust (similar to tephrotectonics), or convection within the asthenosphere or mantle (geology).
Appalachianorogeny (Appalachian Mountains,) is a well studied orogenic belt resulting from a late paleozoic collision between North America and Africa.
Himalayan orogeny (Himalaya Mountains) is a result of the ongoing collision of the Indian Plate with the Eurasian Plate.
Ouachita orogeny (Ouachita Mountains) of Arkansas and Oklahoma is an orogenic belt that dates from the late Paleozoic and is most likely a continuation of the Appalachianorogeny west across the Mississippi embayment rift zone.
Feeds |
Contact