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Wednesday July 11 • Plate tectonics (pp 339-343) • Plate boundaries (pp 343-348) • Earthquakes (pp 375-384) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Free floating magnetite particles align following a well defined pattern around a magnet. If support is frozen, and magnet is moved, magnetite particles keep trace of the old position of the magnet Magnetic poles drift? Yes, but not possible to have two north poles!!! Plate tectonics is the explanation!! Evidences of plate tectonics 1) 2) 3) 4) 5) Shape of continents Magnetic pole drift Hot spots Magnetic striping and age of seabed Similarities in fauna and flora Evidences of plate tectonics 1) 2) 3) 4) 5) Shape of continents Magnetic pole drift Hot spots Magnetic striping and age of seabed Similarities in fauna and flora Evidences of plate tectonics 1) 2) 3) 4) 5) Shape of continents Magnetic pole drift Hot spots Magnetic striping and age of seabed Similarities in fauna and flora Plate motion and boundaries Why do plates move?? QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. PLATE MOTION Three types of plate boundary Divergent boundary Animation 1 QuickTime™ and a Cinepak decompressor are needed to see this picture. Example: Mid-Atlantic Ridge •a topographically high area near the middle of the Atlantic Ocean •splits nearly the entire Atlantic Ocean north to south, Divergent: Atlantic Ridge LAVA FOUNTAINS KRAFLA VOLCANO ICELAND Rio Grande Rift Convergent boundary I: oceanic -continental plate involved -> Subduction Animation 2 QuickTime™ and a Video decompressor are needed to see this picture. OCEANIC-CONTINENTAL COLLISONS SUSTAIN MOST VOLCANIC ACTIVITY AROUND THE PACIFIC OCEAN Convergent boundary II: oceanic -oceanic plates involved -> Subduction Subduction processes in oceanicoceanic plate convergence result in the formation of volcanic arc islands Convergent boundary III: NO oceanic plate(s) involved -> Mountain chains Animation 3 QuickTime™ and a Cinepak decompressor are needed to see this picture. Convergent boundary III: NO oceanic plate(s) involved -> Mountain chains Example: Andes Mtns West margin of the South American continent •oceanic Nazca Plate is pushed toward and beneath the continental portion of the South American Plate •typical example of a convergent plate boundary Nazca - S.America plate collision Transform boundary Transform boundary Animation 4 QuickTime™ and a Cinepak decompressor are needed to see this picture. Example: San Andreas fault in California Pacific Plate slides past the North American Plate. Transform boundary Plate Motion Summary Earthquakes • Are due to the release of strain in the lithosphere • They propagate as waves of two types: • Compression (or longitudinal or Pmode) waves • Deformation (or transversal or S-mode) waves