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Unformatted text preview: e. Entirely basalt f. Depressurization creates magma 5. Structure of oceanic crust a. Oceanic crust forms at mid-ocean ridges b. Oceanic crust has a layered structure i. Sediment/hydrothermal deposits ii. Pillow lavas iii. Sheeted dikes iv. Magma chambers/gabbroic rocks v. Mantle c. Oceanic ridges have different forms and topography depending on spreading rate 6. Hydrothermal circulation system at a mid ocean ridge a. Cold seawater sinks down through cracks in the crust b. Hydrothermal fluid reacts with the crust and dissolve copper, zinc, iron, and sulfur c. Hot fluids carrying dissolved metals rise up through crust d. The hydrothermal fluids mix with cold seawater. Metals and sulfur combine to form black metal-sulfide minerals...
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- Spring '09