Deformation of the Crust PANGAEA Pangaea was assembled 290 m.y. Continental collision produced the interior mountains -- Appalachian - Caledonian, Hercynian, and Urals Features preserved in these uplifted areas allow the geologist to "see" the ancient oceans that were destroyed in the process Continental Crust Structure of continents exhibits a pattern: eroded remnants of very old deformed rocks in the interior - Shields more recent deformation in mountain systems closer to the margins oceans open and close and mountains are uplited and reduced by erosion The Stable Interior Cratons - extensive, flat, tectonically stable interior of the continents Shields - parts of the craton consisting of crystalline basement rocks - composition, structure, and textures indicate periods of intense metamorphism, partial melting and the intrustion of magmas into the older rocks OROGENIC BELTS Most geologists believe that mountains form by plate collisions Subduction when one plate is more dense that the other Continent collision when two pieces of continental lithosphere collide The Himalayan Orogeny Subduction of India under the Eurasian Plate - 60 my The main central thrust forms when India collided with Tibet - 40my A second thrust formed about 20 my - the main boundary thrust The Himalayas are "carved" from these two great stacks The Appalachians Valley and Ridge - Deformation in the Ordovician, Devonian and Permian Blue Ridge - pC crystalline rocks - thrust over the Valley and Ridge Piedmont - pC and Paleozoic metamorphosed rocks thrust over the Blue Ridge Coastal Plain - relatively young rocks The Cordillera Complex of different types of orogenic zones Volcanic Action - Cascades Upwarped - Reverse Faults - The Front Range Fault Block Mountains - Basin and Range Folded Mountains - Appalachian Stacking of thrust faults - Himalayas and Appalachian Coastal Plain and Shelf The Atlantic Coastal Plain began to form during the Triassic when the rifting that preceded the opening the Atlantic Immature sedimentary rocks accumulated in the graben and were intruded by basaltic dikes and sills Regional Vertical Movement Epeirogeny - gradual upward and downward movements without significant deformation Michigan Basin and the Black Hills are two prime examples Cooling and contraction can produce basins and heating and expansion can produce domes