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Plate Tectonics

Plate Tectonics. ISCI 2001 Chapters 22-24. Plate Activities – Divergent Plate Boundaries. (1). Plates may ‘ diverge ’ Plates move apart Lava fills spaces in between (2). What types of structures are produced? Volcanic mountains Rift valleys (3). Examples Mid-Atlantic Ridge

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Plate Tectonics

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  1. Plate Tectonics ISCI 2001 Chapters 22-24

  2. Plate Activities – Divergent Plate Boundaries • (1). Plates may ‘diverge’ • Plates move apart • Lava fills spaces in between • (2). What types of structures are produced? • Volcanic mountains • Rift valleys • (3). Examples • Mid-Atlantic Ridge • Great Rift Valley (Africa near Nairobi Kenya)

  3. Rift Valley in Kenya

  4. Mid-Atlantic Ridge

  5. Convergent Boundaries • (1). When two plates collide • One plate usually subducts • Most dense or oldest plates • (2). Types of convergence • Oceanic – Oceanic • Trench formation (Marianas Trench) • 11,000 m or 7.0 miles deep • Pacific and Phillipine Plates collide • Formation of volcanic islands or arcs • Subduction plate mantle rock melts comes to the surface and cools • Oceanic – Continental • Oceanic basaltic plate (more dense) subducts under granitic continental plate • Mantle rock melts, magma rises and cools forms island chains • Volcanic Arcs (Peru) • Continental – Continental • Massive plate collisions (both granitic) • No subduction, why? • Both have same density • Massive mountains are formed • Himalayas

  6. Marianas Trench

  7. Oceanic – Continental The convergence of the Nazca and SouthAmericanPlates has deformed and pushed up limestone strata to form the towering peaks of the Andes, as seen here in the Pachapaqui mining area in Peru.

  8. Continental – Continental

  9. Transform Plate Boundaries • (1). ‘Sliding Plate’ Boundaries • Slipping of plates causes ‘faults’ • (2). Slipping causes plate movements • Boundaries move in opposite directions against each other • (3). Where are they normally found? • Mostly ocean basins • Continental plate: San Andreas Fault

  10. San Andreas Fault

  11. Types of Faults • (1). Dip-Slip (See figure 24.5) • Hanging wall and vertical wall move vertically along the fault plane • Movement is vertical • (2). Strike-Slip • Movement is horizontal • San Andreas Fault motion • (3). Oblique • Move horizontally and vertically

  12. Slip-Dip Conjugate Normal faults, Canyonlands National Park, Utah

  13. Fault Types

  14. Folding • (1). Bending in Rock layers • Caused by compression • (2). Results • Anticlines or synclines

  15. Mountain Formation • (1). Folded Mountains • During formation continental crust thickens and wrinkles into vertical folds from compression • Appalachians, Rockies and Himalayas • (2). Unwarped • Domed shaped • Single anticline (crust is heaved upwards; no folds produced) • Adirondack mountains NY • (3). Fault-Block • Land is ‘uplifted’ , stretched and elongated • Very steep profile • Tetons (Wyoming); Sierra Nevada (California)

  16. Mountain Formation Folded Mountain – Antarctica

  17. Mountain Formation Adirondack Mountains – unwarped

  18. Mountain Formation- (Fault-Block)

  19. Consequences of Plate Movements • (1). Earthquakes • Transform faults • Compression and tension caused by stress of plate movements -- Slipping • Focus location • Rock is snapped or broken releasing ‘elastic’ energy • (2). Types • Intraplate (10%) • Away from plate boundaries • New Madrid, Missouri • Interplate (90%) • Plate boundaries • Transform plates (mild Eqs) • Subduction zones (strong)

  20. Earthquakes

  21. Subduction Zones – Ring of Fire! 80% of all interplate EQs occur here

  22. Powerful Interplate EQs and Tsunamis • (1). Coast of Sumatra • Indian and Burma Plate collision • Megathrust quake • 100 billion tons of TNT • (2). Production of a Tsunami • Quake took place in the Indian ocean • As subduction occurred • The seafloor bent as the other plate sank • Stress caused rock to snap and thrust upwards • Force caused water to creat large wave • 30m +/- above sea level

  23. Earthquakes – San Francisco 1906

  24. Magnitude of Earthquakes –Richter Scale • (1). Logarithmic scale • Each point represents a 10-fold increase in quake shaking strength • Measures shaking • Also indicates 30 fold increase in energy output • 1 thru 10 • Examples • 1906 San Francisco (8.2) • Sumatran 2004 (9.0)

  25. Richter Scale

  26. Sumatra EQ and Tsunami 184,000 People died

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