Test 3-11/12-Next Thursday Applications of plate tectonics model to intraplate features: -Coral reefs associated with subsiding seafloor. -Fringing-coral adhering to side of active volcano, right at the sea-level. -Barrier-volcano is no longer active and is eroding away to the wave depth. However, the coral continues to protect the land it?s on, forming a ring around a volcano. -Atoll-Volcano has eroded to wave depth, mostly, but the coral has continued to protect the land it?s on. -Coral needs to adhere to something, which is in many cases rock. -Sea-mount: land formed by magma breaking through to the surface at a subduction zone/hot-spot, eventually becoming an island-good place for coral, right at the rim. -Tablemount (guyot): A sea-mount that?s no longer active and has eroded to the wave-depth. WILSON CYCLE-Know an ocean?s life cycle, but don?t focus too much on terms: -John Tuzo Wilson -Life cycle of ocean basins -Formation -Growth -Destruction -Embryonic: Motion: Uplift, forming complex systems of rift valleys, such as the East African rift valleys. -Juvenile: Motion: Divergence (things start spreading now, forming narrow seas with matching coasts, such as the Red Sea). -Mature: Divergence (spreading)-Ocean basin with continental margins (ex. Atlantic and Arctic Oceans). -Declining: Convergence (subduction): Island arcs and trenches around basin edge (ex. Pacific Ocean). Sentiment starts to pile up. -Terminal: Convergence (collision and uplift): Narrow, irregular seas with young mountains (ex. Mediterranean Sea) -Suturing ?A description of the aggregation and break-up of supercontinents. Initially, a HYPERLINK "http://www.answers.com/topic/hot-spot-2" \t "_top" hot spot rises up under a HYPERLINK "http://www.answers.com/topic/craton" \t "_top" craton , heating it, causing it to swell upward, stretch and thin, and finally split into two pieces. This process not only splits a continent in two, it also creates a new divergent plate boundary. Next, a new ocean basin comparable to today's Red Sea is generated between the two new continents. As the ocean basin widens, the stretched edges, where the two continents used to be joined, cool, become denser, and sink below sea level. Wedges of divergent continental margins sediments accumulate on both new continental edges. The ocean basin may widen to thousands of miles. All of the above is the opening phase of the Wilson cycle. The closing phase of the cycle begins when a new HYPERLINK "http://www.answers.com/topic/subduction" \t "_top" subduction zone forms at the margin of one of the continents. This may form anywhere in the ocean basin, and may face in any direction. Once this zone is active, the ocean basin begins to disappear, forming a remnant ocean basin. When most of the remnant basin has subducted, the two continents are about to collide. Magma is generated deep in the subduction zone, rising to the surface to form volcanoes, which build into a cordillera. This is accompanied by HYPERLINK "http://www.answers.com/topic/aureole" \t "_top" metamorphism , folding, and faulting. When the two continents finally collide, the closing phase of the Wilson cycle is technically over. Because the subduction zone acts as a ramp, the continent with the subduction zone slides up over the edge of the continent without it. After the collision has occurred, this cordillera will be eroded down to a HYPERLINK "http://www.answers.com/topic/peneplain" \t "_top" peneplain . With the collision, the continental thickness doubles, and since continental crust is less dense than oceanic, the reunited sections will rise with erosion, through HYPERLINK "http://www.answers.com/topic/isostasy" \t "_top" isostasy . Thus, most of the upper continent will be eroded away, and the lower continent will eventually return to the earth's surface.? ? INCLUDEPICTURE "http://www.earth.northwestern.edu/people/seth/202/new_2004/seth_images/5_6_01.jpg" \* MERGEFORMATINET Schematic illustrations of the Wilson cycle, the fundamental geological processes controlling the evolution of the continents a-b) A continent rifts, such that the crust stretches, faults and subsides. c) Seafloor spreading begins, forming a new ocean basin. d) The ocean widens and is flanked by sedimented passive margins. e) Subduction of oceanic lithosphere begins on one of the passive margins, closing the ocean basin (f) and starting contiinental mountain building. g) The ocean basin is destroyed by a continental collision, which completes the mountain buliding process. At some later time continental rifting begins again.? CONTINENTAL CRUST: Granite Ocean crust: Basalt. -Break point: The end of the continental shelf. -Continental slope: the sharp slope at the end of the shelf, dropping down to the ocean. -Sediments: Near shore, on shelf: clay, salt, sand, cobbles, boulders?the stuff from land?terrogenic (lithogenic) bits of rocks that have eroded from the land. -These terrogenic materials get from the land to the ocean by several means. The number one way is RIVERS. Flood and storms also work, but they?re not typical. -Wind work well for moving stuff too?typically very small particles, like clay. -Glaciers also work. Because they?re like bulldozers, what they deposit is a mix bagged. -Settling time for clay: About 50 years, because it?s so small and light. -Longshore current: moves sand, so it?s not just at one point. -At break: Sand can just go down one particle at a time, but typically just gets stuck until a large amount falls all at once. This is called a turbidity current?a large amount of sand falling down to the ocean crust. -The pile of sand at the end of continental slope, on the ocean: Continental Rise. -After continental rise: No more sand?clay starts. -After the continental rise, there?s the abyssal plain, which is ?the flattest place on Earth.? The abyssal plain has something called abyssal clay. The plain was originally sharp, jagged, and uneven, but it was mostly covered by clay, except for the abyssal hill. -Biogenic sediment: Not dead whales, since those will be eaten. Only good strong teeth might be found there. Two types of plankton: -Phytoplankton (photosynthetic). -Zoaplankton-eat the plants of the ocean. -Planktons have shells, which are called tests. These tests can be made out of silica (SI)2, or SIO2.nH2O), or CaCO3 (Calcium Carbonate, like Muscle shells). -Plankton are small, so they stay suspended and don?t just fall to the bottom. -Plankton: Don?t sink, because they?re too light. Get to bottom through waste. -You have to have at least like 30% biogenic components to be called a biogenic sediment. Called an ooze because it oozes out. -Form rad ooze: Called that, because it?s an ooze made because it?s made out of foraminifera (calcareous) and radiolari (siliceous). -We use diotamaceous earth (basically glass) to feed cows (doesn?t hurt, because it?s too small), because it kills the parasistes. It also is used to filter beer and wine (because it?s a really good filter), and dentist toothpasted. Silica: -DIATOMS (algae) -Photosynthetic -Diatomaceous earth?makes great filters, because of all the tiny holes, which they use for nutrients -Radiolarians (protozoans) -Use external food -Siliceous ooze ----------------------------------------- Calcium Carbonate: -Coccolithophores (algae) -Photosynthetic -Coccoliths (nano-plankton) -Rock chalk -Foraminifera (protozoans) -Use external food You need nutrients/upwelling to have phytoplankton. When you have them, you can have zoa. When you have zoas, you have fish. Upwelling-one place-diverging currents, where deep water can come up. Biogenic sediment: has to be at least 30% biological components. -Continental Shelf: Gets nutrients from land, and thus tons of phytoplankton there. It?s not biogenic sediment though, because it doesn?t reach 30%, due to all of the sand and clay, etc. -After Abyall plain, you get to a mid-ocean ridge, where the ocean is splitting in both directions. Then you get back to an abyssal plain, a continental rise, a continental slope, and a continental shelf. -Measuring the Sea Floor (less than 5% of it has been mapped): -Soundings -Sea-beam. -Satellites used to measure the sea-floor. -Satellite altimetry: Seafloor interpreted by gravitational anomalies. Remove tides, wind, waves, gyre hills, etc, and everything else, until just a bump is left that is just gravity. The satellites measure the undulations in sea surface that result from gravitational differences, and thus we get an idea for what the sea-floor looks like. -Turbidity currents (current of sand at continental break down the slope)?creates submarine canyons, due to the strong erosional force. Near canyons-fans of sand. -NEXT: Hydrothermal vents.
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