Geology Ch 19: Plate Tectonics
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brantlyduncan on December 11, 2011
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34 terms
Terms | Definitions |
|---|---|
 absolute motion | motion relative to an external reference frame |
| relative motion | absolute motions of plates leads to their motion relative to each |
| Continental Drift: Alfred Wegner | -idea that continents move freely over earth's surface, changing their positions relative to one another. |
| Evidence Supporting Continental Drift | o Fit of continents o Fossil distribution o Glacial deposits and striae orientation o Climate zones |
| Paleomagnetism | -study of ancient magnetic fields |
| Curie Point | the temperature below which a material becomes magnetized |
| Sea Floor Spreading: Harry Hayes | -hypothesis that the sea floor forms at the crest of the mid ocean ridge then moves horizontally away from the ridge crest toward an oceanic trench. |
| Plate | large mobile slab of rock that is part of the earth's surface. |
| Convection | circulation pattern driven by the rising of hot material and/or the sinking of cold material |
| • Evidence supporting Sea Floor Spreading | o Heat flow variation between ridges and trenches • Existence of ridge and its high heat flow • Existence of oceanic trenches and their low heat flow o Deep vs Shallow earthquakes o Young age of ocean basin rocks and sediments • Explains the young age of the rock of the sea floor as caused by the loss of old sea floor through subduction into the mantle |
| Marine Magnetic Anomalies (Vine and Matthews hypothesis) | o Symmetrical anomaly pattern relative to the ridge crest (mirror image |
| • Pattern of magnetic anomalies at sea matches the pattern of magnetic reversals | o Relationship of marine magnetic anomalies to polarity reversals in continental basalts. |
| older | seafloor is _____farther from ridge |
| Fracture Zones & Transform Faults | -cores from deep sea drilling tested plate motion by allowing us to compare the actual age of the sea floor with the age predicted from magnetic anomalies. -another test of plate motion has been made by studying the seismicity of fracture zones. |
| Transform Fault | the portion of a fracture zone between two offset portions of a ridge crest. |
| Divergent Plate Boundaries | -marked by rift valleys, shallow focus earthquakes, high heat flow, and basaltic volcanism |
| East African Rift | is an example of early stage of divergence |
| Red Sea | is an example of intermediate stage of divergence |
| Atlantic Ocean Basin | is example of mature stage of divergence |
| Transform Boundaries | -marked by strike-slip faults and shallow focused earthquakes |
| Ocean-Ocean Convergence | • The subducting plate bends downward forming the outer wall of an oceanic trench, which usually forms a broad curve convex to the subducting plate. |
| island arc | a curved line of volcanoes that form a string of islands parallel to the oceanic trench |
| accretionary wedge | sediments that accumulated on subducting plate as it traveled from ridge are scraped off and accreted (added) to overriding plate |
| forearc | • The trench side of an arc is the ____ |
| backarc | and the other side of the arc is the ____ |
| Ocean-Continent Convergence | EX: Andes, Cascades |
| Magmatic Arc | a broad term used both for island arcs at sea and for belts of igneous activity on the edges of continents |
| backarc thrust belt | : thrust faults form behind arc in response to convergence; "stickiness" between plates |
| Continent-Continent Convergence | EX: Himalaya, Appalachians |
| Surture Zone | • The two continents are welded together along a dipping ______ that marks the old site if subduction |
| Mantle Convection | o The slow overturning of Earth's hot ductile interior as heated rock wells up from below, cools near surface and sinks back down again |
| Ridge Push | o Plates near the mid oceanic ridge also slide down the sloping lithosphere-asthenosphere boundary at the ridge. o As a plate moves away from a divergent boundary, it cools and thickens. o Cooling sea floor subsides as it moves and this subsidence forms the broad side slopes of the mid-oceanic ridge. |
| Slab Pull | o Cold, dense, leading edge of a subducting plate pulling the rest of the plate along with it. o Cold lithosphere sinking at a steep angle through hot mantle should pull the surface part of the plate away from the ridge crest and then down into mantle as it cools. |
| Mantle Plumes | narrow columns of hot mantle rock that rise through the mantle, much like smoke rising in a chimney. -thought to have large, spherical or mushroom shaped heads above a narrow, rising tail. |
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