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Plate tectonics

Plate tectonics. 1. Intro-important concepts 2. Kinematics-plane view & on a sphere 3. Extensional tectonics 4. Compressional tectonics 5. Transform boundaries. Today’s lecture: 1. Earth Structure 2. What is lithosphere, asthenosphere?

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Plate tectonics

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  1. Plate tectonics 1. Intro-important concepts 2. Kinematics-plane view & on a sphere 3. Extensional tectonics 4. Compressional tectonics 5. Transform boundaries

  2. Today’s lecture: 1. Earth Structure 2. What is lithosphere, asthenosphere? 3. Describe the fundamental observations that led to PT 4. Continents in motion 5.The oceanic crust and lithosphere 6.Transform faults 7. Convergent margins, subduction and collision 8. Making it all work.

  3. Chondrites- bulk Earth Iron meteorites=core-like

  4. Heat engine- very efficient Earth differentiation- primarily by magmatism Mantle convection- Mostly solid state Melting shallow by adiabatic decompression Lithosphere- the cold lid at the top

  5. Earth Io

  6. Convection hypotheses: two layers vs one layer

  7. Gravity highs (continents) and lows (oceans) Earthquales and magmatism- highly localized atcontinental margins and within oceans

  8. Oceanic lithosphere- different from continental: Basaltic crust, relatively thin (5-7 km), leads to topographic lows Mid-ocean ridges, transform faults

  9. Young------- Old

  10. CRUST REPLACEMENT Growth rate of 2 - 4 cm per year and a length of 60,000 km means that new crust is created at a rate of Crust - (2-4 cm per year) x 60,000 km = (2-3x10**[-5] km) x 60,000 km = 1.2-1.8 square kilometers per year How long does it take to replace all of the oceanic crust? The total surface area of the Earth is Area = 4 x pi x R**2 = 4 x pi x (6,400 km)**2 ===> Area = 5.1x10**8 square km. The oceans cover 55 % of the Earth's crust and so the time required to replace all of the oceanic crust is time = 0.55 x 5.1 x 10**8 sq km / 1.2-1.8 sq km per year ===> time = 160,000,000-240,000,000 years That is, the entire oceanic crust of the Earth is replaced every few hundred million years.

  11. Is this prediction correct?

  12. Spreading at mid-ocean ridges must be compensated by subduction. In addition,there are transform faults in the oceans.

  13. Transform faults accommodate obliqueness of spreading-that is spreading is perpendicular to the ridge axis and any curvature is taken up by transforms.

  14. Oceanic transform faults are similar to lithospheric-scale strike-slip fault on continents, such as the San Andreas. There is a major difference- key to understanding plate tectonics.

  15. Paleogeography

  16. Convergent margins- what happens there? There are two types- subduction and collision

  17. Continents carry the record of convergent margin events of the past

  18. Continents also break- to form new oceans

  19. IMPORTANT CONCEPTS: Lithosphere-asthenosphere, mantle convection Oceanic lithosphere, Mid-ocean ridges Transform faults, magnetic anomalies,magmatism Paleogeography,, convergent margins- subduction and collision,

  20. How does the future look like?

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