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Plate Tectonics Prof. Voss Page 1 Continental Drift match continent shapes fossils rock types image: pangea pangea-r-anim 200 million years ago single continent Pangea image: cdrift cdrift-a 150 million years ago Laurasia in north Gondwana in south image: cdrift cdrift-b image: pangea pangea-anim 70 million years ago current continents different positions image: cdrift cdrift-c image: cdrift cdrift-d Seafloor Spreading - explained how continents could move ocean floor young compared to land little sediment - igneous rock Midocean Ridge mountain range in center of oceans molten rock from mantle rises through crack spreads outward and hardens carries continents along record of Earth's magnetic field image: midocean midocean-ridgeridge-mag Plate Tectonics - movement of large sections of Earth's crust plate section of crust tectonics Greek for "builder" image: 06 06-03 plates move because mantle is highly plastic just below surface convection current rise from center, break crust slide at rates of a few cm/yr midocean rise and rift - where new crust is formed subduction zone - old crust destroyed, deepest part of oceans melts, lowlow-density magma rises, volcanos, mountains image: 06 06-04 Continental 11/18/2001 Plate Tectonics Prof. Voss Drift continued motion of plates Earthquakes along plate boundaries Page 2 image: platemove image: 06 06-06 PLATE BOUNDARIES A. Divergent new crust created plates move apart midmid-Atlantic ridge image: plateboundaries B. Convergent plates pushed together one plate pushed back to mantle high mountains over continents deep trenches in oceans C. Transform or Transcurrent plate slide laterally past each other San Andreas fault image: contcont image: oceanocean image: SAtransform image: PLateboundary Erosion - Earth sculpting removal of parts of crust to new locations Weathering reduces rocks to loose debris that can be moved chemical water, oxygen, carbonic acid forms new materials mechanical image: erosion image: 11/18/2001 Plate Tectonics Prof. Voss water, waves, freezing roots mass-wasting movement to lower ground streams, hydraulic action Page 3 bryce 11/18/2001