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Download Quick Quiz Plate Tectonics Introduction to Plate Tectonics
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Quick Quiz Magnetic stripes along the seafloor are evidence for a) Earth’s electric reversals b) Seafloor spreading c) Convection currents in the mantle d) Magnetite's ability to orient with a magnetic field 1 Plate Tectonics Mechanism Divergent Boundaries oceanic rifts continental rifts Convergent Boundaries island arcs continental/ocean plate boundaries fold mountain belts (suture zone) Transform Faults Hot Spots 2 Introduction to Plate Tectonics Plates are moving from 1-12 cm per year India: 12 cm per year, Africa: abt. 1 cm/year Distance between North America and Europe increasing about 2 cm/year What could possibly move these massive plates? Nuclear forces? Long range electromagnetic forces? Gravitational forces? Contact forces? 3 1 Convection (Plate Motion) Plates consist of lithosphere (solid), and rest on asthenosphere (semi-liquid) Convection takes place in asthenosphere Forces Ridge Push Slab Pull Basal Drive (negligible?) Energy source: heat from radioactivity in the rocks under the mantle 4 2 Features of Plate Tectonics Divergent plate boundaries In ocean On land Convergent plate boundaries Ocean to ocean Ocean to continent Continent to continent Transform boundaries Hot spots 9 3 Divergent Plate Boundaries Oceanic Rifts Mid-Atlantic Ridge Earthquakes: shallow, frequent, mild Features: central rift valley, abyssal hills, abyssal plains Iceland 10 4 Divergent Plate Boundaries Continental Rifts Pangea (about 200 m.y.a.) East Africa Baja Peninsula Red Sea 14 5 Convergent Plate Boundaries Ocean – Ocean Convergent Boundary Subduction Zones Ocean Trenches Island Arcs (Japan, Philippines) • Volcanoes - violent Earthquakes: frequent, shallow/medium/deep, severe • Benioff Zone 16 6 Convergent Plate Boundaries Ocean – Continent Convergent Boundary Subduction Zone Ocean trench Continental Margins (Andes, Cascade Mtns.) Earthquakes: frequent, shallow/medium/deep, severe • Benioff Zone Violent volcanic mountain chain 20 7 8 Convergent Plate Boundaries Continent – Continent Convergent Boundary Continental Collisions: fold mountain belts Suture zones Severe frequent earthquakes that are shallow and intermediate in depth Examples • Himalayas • Appalachians 26 9 Transform Faults Common along spreading centers Link segments of the spreading areas Where two plates slide against each other Strong, frequent, shallow earthquakes Most dramatic example is the San Andreas Fault in California 1989 Loma Prieta Earthquake 1994 Northridge Earthquake 30 10 11 12 Hot Spots Hawaii, Yellowstone, and others exist far from plate boundaries Hot Spots are mantle plumes Plates move over hot spots Hawaii an example of a linear island chain Seamounts 37 13 Continental Evolution Dating of basement rocks in N. America show varying age N. America originated as a small landmass Continental accretion added mass to N. America Convergent boundaries make new continental material East N. America much older than west 41 14 Summary Plate Tectonics explains what is observed rift valleys, island arcs, fold mount belts, etc. Continents rest on large plates moved by ridge push and slab pull Gravitation and electromagnetic Fueled by radioactivity in earth’s core Features Convergent Plate Boundaries Divergent Boundaries Transform Faults Hot Spots 43 15
