_6-PlateTectonics_11Sept08

_6-PlateTectonics_11Sept08 - QuickTimeª and a...

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Unformatted text preview: QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Road Map Sept. 11 - Chap. 3 (cont) Sept. 16 - Chap. 3 - “finished” Sept. 18 - Hour test #1 QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Global Tectonics: Plates and Plumes What is the evidence that plates are rigid? Earthquakes: 1960–2000 Most of the world's active volcanoes (triangles) are along the edges of tectonic plates (the lines). QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Evidence from location of volcanoes Earth’s volcanic activity over the past 10,000 years Fig 11.12 SUBDUCTION ZONE EARTHQUAKES QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. The "WADATi-BENIOFF" ZONE: The dipping plane of earthquakes beneath a subduction zone QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. At 8:32 Sunday morning, May 18, 1980, Mount St. Helens erupted. May 18, 1980 eruption USGS photograph by Austin Post QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Boiling away even today QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. The "Wadati-Benioff" Zone What is the evidence that plates are rigid? What the location of volcanoes reveals: What – Volcanic activity reveals a pattern very similar to Volcanic that of earthquakes. that Divergent boundary data is sparse and doesn’t truly Divergent indicate a lack of activity, but rather a lack of ability to collect such data. collect – Recall from Section 4.6 how magma is generated Recall in subduction areas and rises. in – What is not explained by plate tectonics are What intraplate hot spots such as those in Hawaii, Africa, and Yellowstone. While few, they do not fit the model well. model What is the evidence that plates are rigid? Distribution of mountain belts Distribution – In similar fashion, deformation should reveal In mountains along boundaries. Is this the case? mountains By and large, yes – Some mountain belts have little/no earthquake Some activity and no active volcanism. activity E.g., Appalachian Mts. have fold features that indicate E.g., that perhaps they were former subduction systems. that Evidence from location of mountain ranges Earth’s major mountain chains Fig 11.12 QuickTimeª and a QuickTimeª and a TIFF (Uncompressed) decompressor TIFF (Uncompressed) picture. decompressor are needed to see this are needed to see this picture. QuickTimeª and QuickTimeªand a a TIFF (Uncompressed) decompressor QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this decompressor TIFF (Uncompressed)picture. QuickTimeª and picture. are needed to seesee thispicture. are needed to this a TIFF (Uncompressed) decompressor are needed to see this picture. 12.2 What is the evidence that plates are rigid? plates Plate tectonics theory states that lithospheric plates Plate are rigid, concentrating deformation at their boundaries with little occurring in the interiors. boundaries Most earthquakes and volcanoes concentrate in Most narrow zones along plate boundaries, so deformation is restricted to the margins of plates. Plate tectonics does not explain hot spot volcanoes, but they are few enough not to discount the theory. but Young, still-growing mountain belts coincide with Young, deforming plate boundaries. Ancient mountain belts mark the location of former plate boundaries. mark So, how did Pangea break up? TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor QuickTimeª and a are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. What is the evidence that plates move apart at divergent plate boundaries? at Freshly-cooled submarine lava flows and pillow basalts along ocean ridges QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. What is the evidence that plates move apart What at divergent plate boundaries? at Geologist’s sketch of the seafloor along the mid-Atlantic ridge east of Florida. Normal faults form escarpments several hundred meters high. Fig 12.11 The mid-ocean ridge (shown in red) winds its way between the continents much like the seam on a baseball. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. What is the evidence that plates move apart at divergent plate boundaries? at Iceland is unique in that the mid-ocean ridge (MidAtlantic Ridge) is present above sea level. The island is widening at the rate of ~4 mm/year. Fig 12.11 QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Oceanic lithosphere Upper Mantle ...
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