Chapter 21 Earth s Interior Earth s Interior Major Parts Crust Above the Moho Oceanic 8 to 10 km of basalt gabbro Continental 30 to 60 km of granite Mantle Moho to 2900 km Solid Rock Upper Moho to 410km Olivine pyroxene Transition Zone 410 670 km Silicate Spinels Lower 670 to 2900 km Perovskite periclase Core 2900 to 6367km Outer Core Liquid Metal Inner Core Solid Metal Crust Oceanic Crust Basalt and Gabbro Thin 8 10 km Dense 2 9 3 1 g cm3 Young 250 my Continental Crust Granite Diorite Seds Thick 30 60 km Light 2 7 2 8 g cm3 Old 250 4000 my Mantle Upper Mantle Moho to 410 km Peridotite Olivine pyroxene Eclogite Pyroxene Garnet Transition Zone 410 670 km Spinels and Spinelloids Lower Mantle 670 2900 km MgSiO3 Perovskite MgO Periclase Core Outer Core 2900 to 5150km Molten iron metal 10 lighter element No S wave transmission Inner Core 5150 6378 km Solid Iron Metal May slowly rotate relative to mantle 1 How do we know what s there Seismology S wave shadow P and S reflections and conversions Meteorites Earth formed from primitive meteorites Xenoliths from kimberlites basalts Experiments Seismology P waves S waves Xenoliths Seismology S wave shadow No S waves opposite side earthquakes Core outer must be molten P and S reflections Discontinuities at 410 and 670 km Phase Changes P and S travel time anomalies Tomography Hot and cold regions Velocity Structure and Earthquakes at N Tonga VanderHilst Nature 1995 Red slow hot green fast cold Xenoliths Xenoliths are strange rocks Xenoliths are inclusions in kimberlites and basalts Xenoliths provide natural high pressure rocks Kimberlites bring diamonds and other rock samples from as deep as 670 km Basalts are derived from the lithospheric mantle 2 Xenoliths Xenolith Peridotite Meteorites Meteorites tell us of Earth s bulk composition Chondrites are primitive meteorites Earth is chondritic Composition is similar to sun minus H He and other volatiles Meteorites Meteorites 3 Experiments Multi Anvil Press Synthesis experiments to 1000 km depth Samples 1 5 mm3 Diamond Anvil Cell Spectroscopy Ultrasound X ray diffraction Multi anvil Press Sample Assembly Multi Anvil Press Octahedron Multi anvil Press 5000 ton Bayerisches Geoinstitut Multi anvil Press Octahedral Assembly After and Before Diamond anvil Cell 4 DAC on Diffractometer Mica Crystal with Quartz 5GPa Ringwoodite Crystal with Quartz 5 410km Olivine Wadsleyite 660 km Ringwoodite Perovskite MgO Convection in solid mantle 525 km Wadsleyite Ringwoodite 660 km Ringwoodite Tetrahedral Si Perovskite MgO Octahedral Si Convection in solid mantle Driven by U Th K decay internal engine Moves about 2 cm yr Causes earthquakes Move plates Splits and rejoins continents One Cell or two 6 Magnetic Field Convection One Cell or Two Due to electrical currents from Earth s dynamo Convection in liquid metal outer core Convection is coupled to Earth s rotation Field is subject to sporadic reversals Last reversal was 30 000 years ago Field holds ozone layer UV shield in place Magnetic Field Reversals Magnetic Field Reversals 7 Interior Terms Crust Oceanic Continental Mantle Upper Transition Lower Core Outer Inner Peridotite Eclogite Spinel Perovskite Xenolith Discontinuity Phase Change Tomography Kimberlite Interior Terms Basalt Chondrule Multi anvil press Diamond anvil cell Convection Magnetic reversal Dynamo Magnetic field Ringwoodite Crystal with Quartz 8
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