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USGS CMG InfoBank: Ophiolites

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Comment: 10:05 - 11:09 (01:04)
Source: Annenberg/CPB Resources - Earth Revealed - 3. Earth's Interior
Keywords: ophiolite, mantle, "Scott Bogue", gabbro, iron, magnesium, sediment, "sea floor"

Our transcription: In other places, huge slices of mantle rock have been brought to the surface by tectonic activity attached to pieces of sea floor crust.
These unusual rock slices are called "ophiolites".
An ophiolite is a sequence of rocks that geologists interpret as being a cross section through the oceanic crust, the part of the Earth's crust that underlies the oceans.
It's a sequence of rocks that might be three to five kilometers thick, the bottom most layers consist of rocks like these behind us, which are rocks of the Earth's mantle composed of minerals rich in iron and magnesium.
Moving up through the three to four kilometer thick section, you move into rocks called "gabbros" which are richer in silica than these, and then, finally, to rocks, which are thought to be the rocks that form the actual floor of the ocean, rocks that were either erupted volcanically or deposited as sediments on the ocean floor.

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