chapter_19_powerpt.CM-11e - Plate Tectonics Physical...

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Steve Kadel, Glendale Community College Plate Tectonics Physical Geology 11/e, Chapter 19
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Plate Tectonics Basic idea of plate tectonics theory is that Earth’s surface is divided into a few large, thick plates that move slowly and change in size Intense geologic activity is concentrated at plate boundaries , where plates move away, toward or past each other Theory born in late 1960s by combining hypotheses of continental drift and seafloor spreading
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Early Case for Continental Drift Puzzle-piece fit of coastlines of Africa and South America has long been known In the early 1900s, Alfred Wegener noted that South America, Africa, India, Antarctica, and Australia have almost identical late Paleozoic rocks and fossils Glossopteris (plant), Lystrosaurus and Cynognathus (animals) fossils found on all five continents Mesosaurus (reptile) fossils found in Brazil and South Africa only
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Fig. 19.11 Fig. 19.11 Jigsaw puzzle fit and matching rock types between South America and Africa
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Fig. 19.3 Fig. 19.3 Distribution of plant and animal fossils that are found on the continents of South America, Africa, Antarctica, India, and Australia give evidence for the supercontinent of Gondwana.
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Wegener’s Matching of Mountain Ranges on Different Continents (From Tarbuck & Lutgens, 8e)
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Early Case for Continental Drift Wegener reassembled continents into the supercontinent Pangea Pangea initially separated into Laurasia and Gondwanaland (about 225-135 my ago) Laurasia - northern supercontinent containing North America and Asia, minus India Gondwanaland - southern supercontinent containing South America, Africa, India, Antarctica, and Australia Late Paleozoic glaciation patterns on southern continents best explained by their reconstruction into Gondwanaland
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Fig. 19.2 Pangaea breakup and continental drift
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Fig. 19.4 Distribution of late Paleozoic glaciation; arrows show direction of ice flow
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Early Case for Continental Drift Coal beds of North America and Europe support reconstruction into Laurasia Reconstructed paleoclimate belts suggested polar wandering, potential evidence for Continental Drift Continental Drift hypothesis initially rejected Wegener could not come up with viable driving force continents should not be able to “plow through” sea floor rocks while crumpling themselves but not the sea floor
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Fig. 19.5 Fig. 19.5A. & B. Two ways of interpreting the distribution of ancient climate belts
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Fig. 19.6 Fig. 19.6 Apparent wandering of the South Pole since the Cretaceous period as determined by Wegener from paleoclimatic evidence
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Fig. 19.7 Wegener’s concept of continental drift implied that the less-dense continents drifted through oceanic crust, crumpling up mountain ranges on the leading edges as they pushed against oceanic crust.
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Paleomagnetism and Continental Drift Revived Studies of rock magnetism allowed determination of magnetic pole locations (close to geographic poles) through time Paleomagnetism uses mineral magnetic alignment direction and dip angle to
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