Geology Plate Tectonics
Geology Plate Tectonics 20841
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This 4 page Class Notes was uploaded by Katie Thedford on Monday September 19, 2016. The Class Notes belongs to 20841 at Fort Lewis College taught by Allie Jackson in Fall 2016. Since its upload, it has received 4 views. For similar materials see Geol 113-2 in Geology at Fort Lewis College.
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Date Created: 09/19/16
Geology – Plate T ectonics Deep water injection causes earthquakes not fracking! Old Theories of continents and mountains o Mountains formed from compressional forces due to earth’s gradual cooling and contraction (like prunes) o Ocean basins and continents are permanent fixtures since the mantle is solid. The earth’s outer shell is incapable of movement. o “forces within the earth” caused foundering of the sea floor forming trenches, earthquakes, and volcanic activity. o Sediment building up over time builds island chains above sea level New Theory! Continental Drift o Alfred Wagner (1880-1930) The continents fit together to form one big one (Pangea) 1915 published “The Origin of Continents and Oceans” o His Proof: Matching fossils in south America and Africa whose living forms could not hat crossed the oceans Matching mountain ranges across oceans o Geologic structures o Rock types o Rock ages Evidence of glaciation in areas where there shouldn’t be glaciers. (paleoclimate matching) Puzzle piece fit of continents Mechanisms for continental Drift? o Continents plowing through ocean crust like a ship? o Caused by earth’s spin? o Tidal forces caused by moon and sun? All presented ideas had no supporting ideas and Wegner died in Greenland still looking for answers o Paleomagnetism Renewed interest in 1950’s came up with the idea of magnetized minerals in rocks 2 Minerals arrange themselves towards poles while molten and are locked into orientation when cooled Iron minerals archive the magnetic signal when cooled Apparent polar wandering offers clues that continents where not in the same place over time o Scientific revolution begins in the oceans 3 Different rocks are found in the oceanic crust compared to continental crust Oceanic crusts are mafic Heat flow is much greater at mid ocean ridges o Sea-Floor Spreading Hypothesis Proposed by Harry Hess in the 1960’s Geomagnetic Reversals Earth’s magnetic field periodically reverses polarity Dates when polarity of earth’s magnetism changed were determined from lava flows recorded in the ocean crust In 1963 Fred Vine and D. Matthews tied the discovery of magnetic stripes in the ocean crust near ridges to Hess’s concept of seafloor spreading 4
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