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Geo101.10.MantleCrust1 - Earths Mantle to Crust and the...

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1 Earth’s Mantle to Crust… and the concept of Plate Tectonics… Egypt, Sinai, and the Arabian Peninsula - fundamental observations velocities increase downward increases are not smooth - velocity patterns define 4 primary layers LAYER VELOCITY, km/sec DEPTH, km crust 4-7 0-40 (cont) 0-5 (ocean) mantle 8-13 5/40 - 2900 outer core 7-10 2900-5200 inner core 11 5200-6371 …from these seismic waves, we know The velocity of P-waves in the mantle changes with depth The low velocity zone is the weak layer which we will see later is on which oceanic lithospheric plates move… Partial melt Upper Mantle Lower Mantle … characterization of Earth’s layers Seismic layers -based on earthquake wave speed) • Crust Upper mantle Lower mantle Outer core Inner core Flow layers - based on flow characteristics) • Lithosphere rigid shell cool temp • Asthenosphere soft, “plastic” warm temp Olivine (Mg,Fe) 2 SiO 4 Pyroxene (Mg,Fe,Ca) 2 Si 2 O 6 Peridotite contains less than 45% silica and is high in magnesium with appreciable iron. Peridotite is derived from the Earth's mantle , either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle The Mantle Peridotite Independent tetrahedra Olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4
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2 Dark mineral: pyroxene Pyroxene = XY(Si,Al) 2 O 6 (where X = Ca, Na, Fe +2 and Mg Single chain tetrahedra Pyroxene Green minerals: olivine …a mantle xenolith (Arizona) Quartz SiO 2 Granite K-feldspar KAlSI 3 O 8 or Rhyolite Plagioclase feldspar (Na,Ca)Al 2 Si 2 O 8 …plus accessory minerals such as Biotite K (Fe, Mg) 3 AlSi 3 O 10 (F,OH) 2 Pyroxene (Mg,Fe,Ca) 2 Si 2 O 6 Rhyolite contains more than 69% silica, low in iron and magnesium. Its mineral assemblage is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2). Biotite and pyroxene are common accessory minerals. Rhyolite is an extrusive or volcanic igneous rock more or less equivalent to granite, an intrusive igneous rock. The continental crust is primary of “granitic” composition The Crust Plagioclase Quartz (SiO 2 ) Microcline Feldspars (most common) Microcline KAlSi 3 O 8 Plagioclase (Na,Ca) Al 2 Si 2 O 8 Plagioclase Framework Silicates CRUST (1:2 ratio) The Crust Continental “granite” Oceanic basalt Oceanic and Continental Lithosphere Mantle “Peridotite -rich”
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