603-pp3 - UNIVERSITY OF SOUTH ALABAMA Last Time A Seismic...

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1 MAS 603: Geological Oceanography MAS 603: Geological Oceanography Lecture 3: Divergent Plate Lecture 3: Divergent Plate Boundaries and Evolution of Oceans Boundaries and Evolution of Oceans UNIVERSITY OF SOUTH ALABAMA Last Time Last Time A) Seismic waves and the Earth's interior B) Seismic Tomography C) Mineral phase changes, inner core nuclear reactors, and outer core magnetism (weird stuff) Seismic Waves But wave refraction results in the formation of “shadow zones” where P or S-waves do not occur. The S-wave shadow zone is wider than the P-wave shadow zone P-wave shadow zones Deep Seismic The speed that S- and P- waves travel through the Earth varies an many places. The most dramatic changes are associated with the 4 major layers… … but 5-50 km down, you get sharp drop in wave speed. Polymorphs of SiO 2 Quartz has 6 polymorphs related to pressure and temperature α -quartz β -quartz Deep Seismic Really impressive. COCORP lines are being run all around the world these days
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2 Seismic Tomography Seismic tomography is a method of using seismic waves from earthquakes (plus some other data) to create 3D images of the mantle. These studies pick out areas of fast or slow mantle, which correspond to areas of high and low temperature. Seismic Tomography and descending lithospheric plates Today Today’ s Agenda Today Today’ s Agenda s Agenda A) Composition of Oceanic crust B) Origin of magma in divergent plate boundaries C) Evolution of oceans (the Wilson Cycle) Oceanic Crust Oceanic Crust Oceanic crust is approximately 5 km thick. Oceanic Crust Oceanic Crust Oceanic crust is approximately 5 km thick. 1) We can easily get samples of the upper crust.
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3 Oceanic Crust Oceanic Crust Oceanic crust is approximately 5 km thick.
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