Mid ocean ridges - e Entirely basalt f Depressurization...

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Mid ocean ridges 1. Fast-spreading ridge a. Magma chambers feed fissure eruptions b. Magma chamber small, only 0.5 to 1 km below ocean floor c. ASC is axial volcano summit caldera d. Layer 2a made of lava flows sand intrusions e. Gabbro is coarsely crystalline rock f. 14cm/yr, 140km/my 2. Slow spreading ridge a. Dikes transport magma from chamber to floor b. Pillow basalt and sheet flows erupt on bottom c. As crust moves away from intrusions rift collapses along faults d. Spreading rate ~5cm/yr, 50km/my 3. Fast vs Slow spreading a. Topographic contrast i. Axial high with narrow valley (fast) vs wide axial valley ii. Smooth topography (FSR) vs rough iii. Detectable melt lens at FSR, not at SSR 4. Making magma at a mid-ocean ridge a. Upwelling solid mantle is focused at the ridge b. As mantle rock decompresses it melts c. Melt is relatively buoyant and rises to surface d. As crust separates more melt intrudes and solidifies to replace it
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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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Mid ocean ridges - e Entirely basalt f Depressurization...

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