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ANATOMY OF CONTINENTS: Shields, Stable Platforms, Young Mt. Belts Isostacy Extra load cause depression of bottom Mountain Building by Continental Rifting Wilson Cycle: First few phases are visible in east Africa and adjacent regions. Wilson Cycle: Doming and Fragmentation East African Rift Wilson Cycle: Continental Rifting Rift Valley with Volcano - Tanzania Wilson Cycle: Narrow Ocean Basin Red Sea from space Wilson Cycle: Wide Ocean Basin Wilson Cycle: Destruction of Ocean Basin through Subduction, beginning of the Orogeny Japan: A volcanic arc formed as the Pacific Plate is subducted Accretion of the Island Arc – Now an Exotic Terrane Accreted (Exotic) Terranes of Western North America Wilson Cycle: Final closing of the Ocean Basin, Culmination of the Orogeny; Continent – Continent Collision Himalayas from space. Mountains are snow covered, India is to the left and Tibet to the right. Isostatic Rebound: As mountain erodes roots rises. •For every 1 km of mountain eroded, only 2/3 of a km of elevation is lost. • Shield – deep interior of mountain root exposed at surface, high grade metamorphic and intrusive igneous rock. •Stable Platform – sediments from erosion of mountain are deposited surrounding the shield. High Grade Metamorphic Rocks with Igneous Instrusions Orogenic events that created North America Another round of the Wilson Cycle then splits the old mountain belts apart Pangaea 250 mya