13_tectonics_10_post

13_tectonics_10_post - 13: Plate Tectonics Divergent...

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e tectonics: 1 Divergent boundaries & continental rifting Convergent boundaries & mountain-building Hot spots and absolute plate motions Causes of plate motion 13: Plate Tectonics
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e tectonics: 2 Features of divergent plate boundaries Mid-ocean ridge / spreading center Mid-ocean ridge / spreading center : broad, faulted, elevated feature : broad, faulted, elevated feature with axial depression that marks a divergent plate boundary in the with axial depression that marks a divergent plate boundary in the oceans Fig. 2.8 Map Side view Side view
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e tectonics: 3 Volcanic / magmatic activity At surface: small shield volcanoes, pillow basalts At depth: intrusion of dikes & mafic rocks (gabbro) Fig. 4.8 Features of divergent plate boundaries Block diagram
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e tectonics: 4 Deformation: Fissures (gaping cracks) & normal faults due to stretching Fig. 9.21 Photo: G.E. Sigvaldason Map Map Features of divergent plate boundaries
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e tectonics: 5 arthquake activity: Spreading centers (ridges): normal faulting (shallow depth) Transform faults: strike-slip faulting (shallow depth) Fig. 3.8 Block diagram Features of divergent plate boundaries
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e tectonics: 6 Fig. 4.12 Graph Age vs. depth Surface of Surface of sea floor sea floor Q1. How old is the seafloor present at a depth of 4000 m? A. ~10 million years B. ~20 million years C. ~30 million years D. ~40 million years
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e tectonics: 7 Seafloor depth increases exponentially with increasing age. Fig. 4.12 Graph Age vs. depth Surface of Surface of sea floor sea floor
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e tectonics: 8 Age vs. depth New oceanic crust forms at spreading centers. Contracts & subsides as it cools. Fig. 4.12 Side view Side view Q2. The mid-ocean ridges are elevated above the surrounding seafloor because _________. A. ridge rocks are hot and therefore of relatively low density B. the lithospheric plates are thickest at the ridges so they stand up taller C. rising ocean currents leave a vacuum above the ridge D. ridge rocks are mafic, whereas the ocean basin crust consists of ultramafic rock
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e tectonics: 9 Age vs. depth Fig. 4.12 Side view Side view Q3. Oceanic lithosphere thickens away from the mid-ocean ridge primarily due to ______. A. the addition of new crust due to hot-spot volcanism B. the addition of new crust due to sedimentation C. the addition of new lithospheric mantle as a result of cooling New oceanic crust forms at spreading centers. Contracts & subsides as it cools.
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e tectonics: 10 Fast-spreading ridges are wider than slow-spreading because more young, hot crust is present Side view Side view Age vs. depth & sea level
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e tectonics: 11 Sea level Fig. 13.17 Graph Global spreading rates increase --> fast-spreading ridges displace more water --> sea level ____ Global spreading rate is one of the main influences on sea level; glacial ice volume is also important
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e tectonics: 12 Continental rifting Continental rifts Continental rifts : : elongate depressions that form when new that form when new divergent boundaries divergent boundaries develop in continental develop in continental crust.
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13_tectonics_10_post - 13: Plate Tectonics Divergent...

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