Geo101.13.Volcanoes

Geo101.13.Volcanoes - Where do Volcanoes occur? 1)...

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1 Volcanoes … the venting of the Earth … vents or fissures through which magma (molten rock) and gasses reach Earth’s surface. Where do Volcanoes occur? 1) Mid-Ocean Ridges (MORs), Rifts, Spreading Centers, Divergent plate margins 2) Convergent margins, Subduction zones 3) Hotspots Where do Volcanoes occur? Where do Volcanoes occur? Plate tectonics is a particularly efFcient mechanism for eliminating heat through the planets surface… Tectonic Activity Map of the Earth How / where do igneous rocks originate ?
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2 Mantle Tomography 1) The global Mid-Ocean Rift (MOR) System MOR Mid-Ocean Rift Lithosphere Asthenosphere 1400 C The 1400°C isotherm bends up under the upwelling mid ocean ridge and bends down at the downwelling limbs of the convection cell. The upwelling increases the geothermal gradient in a localized region. Decompression Melting at MOR Mantle rising under the ridge decompresses (purple line) and begins to melt when it reaches the dry solidus. Localized movement of the geothermal gradient 0 1000 2000 C 100 200 300 km DEPTH TEMPERATURE he geot rmal gradient 0 1000 2000 C 0 d r y s o l i u melt begins more and more melt Spreading Centers (MOR) Decompression Melting - process involves the upward movement of the earth's mantle to an area of lower pressure. The reduction in overlying pressure enables the rock to melt, leading to magma formation. Oceanic crust Moho Mantle Pillow lava Newer, thinner sediments Older, thicker sediments Peridotite layer Hot mantle rises, decompresses, and melts. Sheeted dikes in basalt Gabbro Magma Chamber Rift on the mid-Atlantic ridge, showing a graben or negative feature: SLOW SPREADING
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3 Fast Spreading…East Pacific Rift with ridges and large transform faults Divergent boundaries, a Mid-Ocean Ridge Eruptions along rifts Rifting Volcanism Krafla, Iceland: “curtain of fire” a fountaining eruptive fissure with lava flows Lava Fountains
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4 Lava Fountains Eruptions under water… Pillow lavas Pillow lavas: Iceland Rift vent…a Black Smoker Very hot water, 380 °C, bringing minerals (Fe and Cu ores) and bizarre life forms based on hydrogen sulfide-oxidizing bacteria, Chemosynthesis rather than photosynthesis! 2) Convergent Margin Volcanoes …lines of red dots on this map Convergent Margin (Arc) Water is released Water causes melt Lithosphere Crust Asthenosphere L i th o s p h e r Melts occur because water, taken down by the subducted plate, escapes into the mantle and drasticly lowers the melting point (i.e. move the solidus) Oceanic crust Continental crust
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Geo101.13.Volcanoes - Where do Volcanoes occur? 1)...

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