accumulation_of_them_all 2 - Planet Earth September 5...

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Planet Earth September 5, 2007 “The present is the key to the past” is an example of a a) hypothesis b) theory c) model d) guiding principle in the interpretation of the rock record PLATE TECTONICS II Topics covered in this lecture 1. Geologic evidence for plate tectonics 2. Divergent plate boundaries 3. convergent plate boundaries 4. something 5. something The Geologic Evidence for Plate Tectonics a) Geometrical fits of the continents a. Alfred Wegener - 1904 b) Geologic match-ups between the continents c) Similar fossils on now widely separate continents d) The distribution of earthquakes and volcanoes a. Alfred Wegener discovered all these Continental Drift 1. The theory of continental drift was based on a. The fit of continents around the Atlantic b. Geologic match-ups between the continents c. Similar fossils on now widely separate continents 2. Alfred Wegener had no mechanism, but he understood that it happened 3. There were matching ancient rock assemblages amongst continents 4. Fossils of the freshwater reptile Mesosaurus have been found in South America and Africa Distribution of Earthquakes and Volcanoes a) Earthquakes in the Atlantic define a very narrow boundary between the North American and Eurasian plates a. The crest of the Mid-Atlantic Ridge has had a great amount of earthquake action. b) Earthquakes and volcanoes in the Pacific outline the boundaries between the plates AKA ring of fire Plate Boundaries a) Three types of plate boundary are required to accommodate plate motion a. Divergent i. The plates move apart, and the deeper mantle wells up and cools to form new lithosphere ERGO there is no gap. As it rises, it melts
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partially (bouts 5%), kinda like BUTTA ON A HOT DAY. The little bit of liquid magma that comes off of it forms on the top, it’s called the Oceanic Crust. LAVA. ii. Lithosphere = cold mantle. b. Convergent i. One plate slides beneath the other, and is recycled in the deep mantle ii. The lithosphere goes down into the deep earth, it warms up, and stops being lithosphere! It’s called subduction. iii. Only one plate subducts, the other does not. c. Transform i. The plates slide horizontally past each other ii. San Andreas Fault 1. Transform boundaries are commonly marked by linear fault traces that offset rivers, highways, etc. 2. Offset streams along the San Andreas Fault 3. Most transform boundaries are found on the ocean floor where they offset divergent boundaries Atlantic Ocean Floor a) Divergent plate boundaries are often marked by giant submarine mountain ranges on the ocean floor (mid-ocean ridges) Iceland a) has ocean crust on LAND…SNAP Africa and Arabia are breaking apart along a divergent plate boundary in the Red Sea and the Gulf of Aden. The Red Sea is only a BABY…bout a million years of age a) Continental rifting East African Rift a) The African continent is being ripped apart along the East African Rift Seismicity beneath Japan Mantle Structure Beaneath the Tonga Arc a) Velocities of seismic waves help image the cold subducting slab beneath the Tonga arc
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