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CU-Boulder GEOL 1010 - Earth’s Interior

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1Earth’s InteriorChapter 21Earth’sInteriorMajor 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 - PericlaseCore•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 mantle2How 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•ExperimentsSeismology•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 regionsSeismologyP-waves S-wavesVelocity Structure and Earthquakes at N. Tonga(VanderHilst, Nature (1995)Red = slow = hot green = fast = coldXenoliths•Xenolithsare ‘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 lithosphericmantle Xenoliths3XenolithsXenolith-PeridotiteMeteorites•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 Meteorites4Experiments•Multi-Anvil Press–Synthesis experiments to 1000 km depth–Samples 1-5 mm3•Diamond Anvil Cell–Spectroscopy–Ultrasound–X-ray diffractionMulti-anvil Press 5000 ton(BayerischesGeoinstitut)Multi-anvil Press Sample AssemblyMulti-anvil Press Octahedral Assembly: After and BeforeMulti-Anvil Press OctahedronDiamond-anvil Cell5DAC on DiffractometerMica Crystal with Quartz @ 5GPa Ringwoodite Crystal with Quartz6410km:Olivine Wadsleyite525 kmWadsleyite Ringwoodite660 kmRingwoodite Perovskite + MgO660 kmRingwoodite Perovskite + MgOTetrahedral Si Octahedral SiConvection 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?Convection in solid mantle7Convection:One Cell or Two?Magnetic Field•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 ReversalsMagnetic Field Reversals8Interior Terms•Crust–Oceanic–Continental•Mantle–Upper–Transition–Lower•Core–Outer–Inner•Peridotite•Eclogite•Spinel•Perovskite•Xenolith•Discontinuity•Phase Change•Tomography•KimberliteInterior Terms•Basalt•Chondrule•Multi-anvil press•Diamond anvil cell•Convection•Magnetic reversal•Dynamo•Magnetic fieldRingwoodite Crystal with


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CU-Boulder GEOL 1010 - Earth’s Interior

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