Earth’s Surface and Tectonic Processes: Part 2

Continental Drift Wegener proposed the idea of supercontinent called Pangaea

Evidence of Pangaea 1) Coastline fit : Puzzle 2) Geologic fit: Rocks are same on matching coasts 3) Paleoclimatology: (past climates) - Coal formation in polar regions...coal only forms in tropical regions 4) Fossil Correlation: Matching fossils of dead animals on matching coast lines

Theory of Plate Tectonics Idea put forward by Alfred Wegener in 1912 For a long time scientists debated Wegener’s ideas. Nowadays they are generally considered to be correct Plates travelling on the asthenosphere Convection currents move these plates 2-3 cm per year

Plate Movement 1) Divergence Plates move apart due to convection in the asthenosphere Creates either: Mid Ocean Ridges / Rift Zones Examples: Mid-Atlantic Ridge or African Rift Valley Sea floor spreads, new magma rises and fills the crack Creates Transform Faults, as this does not happen in a straight line.

2) Convergence Plates come together and one goes under the other. a) Ocean plates are more dense, so they go under continental plates. Where this happens is called subduction zone Plate goes back to mantle

B) Two ocean plates come together, neither want to go down Eventually one does, and creating Shield Cone volcanoes and Island Arcs Philippines for example

Convergence c) Two continental plates. These plates “fold up”, creating fold mountains Himalayas, Rockies.

3) Horizontal Movement Plates sliding past each other Tear or Strike-slip fault or Transform Example: San Andreas fault in California AND Mid-Atlantic Ridge Sometimes the plates get stuck, tension builds, when released can cause earthquakes