Ocean - GEOL 114 The Earth's Dynamic Interior Lecture Notes...

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GEOL 114 The Earth's Dynamic Interior Lecture Notes (Copyright © 2006 by Jeffrey S. Barker) 12. Oceanic Crust and Plate Tectonics Before continuing to discuss the processes of the Mantle, we should take some time to discuss the Oceanic Crust, simply because one of the important processes taking place in the Mantle is the creation of Oceanic Crust. Later we will discuss Continental Crust, and we will see that in general, Oceanic Crust is more dense than Continental Crust. From our understanding of isostasy, it seems logical that the more dense Oceanic Crust will be less buoyant than the Continental Crust, and so will have lower overall elevation. Since there is enough liquid water to cover about 70% of the surface of the Earth, and since water will flow to reach the lowest point, these lower elevation areas are the ones covered with water. Oceanic Crust is not more dense because it is covered with water; Oceanic Crust is covered with water because it is more dense than Continental Crust . Notice in the map below that there are several areas of shallow seas on the edges of continents (pink color, e.g. north of Australia, east of South America, north of Scandinavia and Russia). These are areas where Continental Crust is covered with shallow seas. About 400 Million years ago, the interior portions of North America were also covered by shallow GEOL 114 1 12. Oceanic Crust and Plate Tectonics
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seas which deposited the fossil-rich sandstones and limestones we find; however our area was, and still is, Continental Crust. Morphology Let's look at the morphology (shape) of the ocean floor along a cross-section from South America to Africa (below). It is a little bit difficult to define where the Continental Crust ends and the Oceanic Crust begins. However, we might consider that the boundary is where the shallow Continental shelf changes to the steep Continental slope. Beyond this, large flat areas of the ocean floor called abyssal plains extend for a thousand kilometers or more. In the center of the Atlantic, a broad ridge occurs, with a valley located at the apex of the ridge. This is the Mid-Atlantic Ridge, and it actually reaches the surface at Iceland. In other areas, such as the western Pacific near Japan, or the eastern Pacific along the coast of Central and South America, deep ocean trenches occur. These are topographic features that are deeper (10 km below sea level) than the highest mountains are high (less than 9 GEOL 114 2 12. Oceanic Crust and Plate Tectonics
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km above sea level for Mt. Everest). Paralleling these deep trenches are arcs of volcanic islands (such as Japan, the Aleutians, Indonesia) or active volcanic areas on the continents (the Andes, the Cascades, the volcanoes of Central America and Mexico). Mid-Ocean Ridges
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This note was uploaded on 11/02/2010 for the course GEOLOGY 111 taught by Professor Howardr.naslund during the Spring '10 term at Binghamton University.

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Ocean - GEOL 114 The Earth's Dynamic Interior Lecture Notes...

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