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Transcript
This is Planet Earth / Earth Story Lecture 5 PLATE TECTONICS II Drifting Continents, Oceans That Open And Close, Mountains and Basins Alfred Wegener’s evidence for Continental Drift Continental fit Correlation of rocks and climate Crustal structure Distribution of fossil plants and animals Direct measurements of changing distance between the continents Best to use continental margins rather than coastlines Arthur Holmes (1931) – Sub-crustal convection causes continental and oceanic crust to move together Exploration of the Ocean Floor – Oceanic Ridges Oceanic ridges (shown in red) wind their way between the continents Sea Floor Spreading Trench Oceanic ridge Magnetic stripes on the sea floor Continental Drift + Sea Floor Spreading = PLATE TECTONICS (Tuzo Wilson, 1965) Oceanic Ridge (Constructive Boundary) The Mid-Atlantic Ridge The ridge was central in the breakup of Pangaea that began some 180 million years ago. Subduction Zones (Destructive Boundary) Ocean-Continent Destructive/ Convergent Boundary (e.g. West coast of South America – subduction of Nazca Plate ) Ocean-Ocean Destructive/ Convergent Boundary (e.g. Japan) The Pacific ‘Ring of Fire’ The Island arcs and oceanic trenches the encircle the whole of the Pacific plate are referred to as the ‘Ring of Fire’ Collisional Boundary Leads to formation of a mountain / orogenic belt The Himalayas - example of a collisional boundary The Himalayas and the Tibetan Plateau The collision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau. The cross-sections show the meeting of these two plates before and after their collision. The reference points (small squares) show the amount of uplift of an imaginary point in the Earth's crust during this mountain-building process. Conservative Boundary Transform faults are also referred to as STRIKE-SLIP or WRENCH faults Conservative / Transform Boundary Examples San Andreas fault J. Tuzo Wilson is credited with the concept of transform faults. He proposed that these large faults or fracture zones connect two spreading centres or occur on land Summary of Plate Boundaries Hawaiian Islands Hots Spots Convection in the Asthenosphere Thermal convection in fluids was first described by Lord Rayleigh Plate Tectonic Driving Mechanisms Ridge Push Slab Pull Convection Currents Mantle Drag Present day relative movements of plates Recommended Reading Press, F. and Siever, R. 2000. Understanding Earth (3rd Edition). Freeman (ISBN 0-71674-117-2). Chapter 20 Skinner, B.J., Porter, S.C. and Park, J. 2004. Dynamic Earth: An Introduction to Physical Geology (5 th Edition). Wiley (ISBN 0-471-45157-6). Chapter 2