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We have been talking about minerals primarily in the earth’s crust What About the rest??

We have been talking about minerals primarily in the earth’s crust What About the rest??. dicontinuities. Harzburgite (80%olv 20%OPX). lithosphere. Lherzolite (60%olv 40%OPX, grt). MOHO. asthenosphere. Pyrolite (lherzolite-like). Upper mantle. Olivine  b -spinel. 410. Pyroxene 

shelby-singleton
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We have been talking about minerals primarily in the earth’s crust What About the rest??

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  1. We have been talking about minerals primarily in the earth’s crust • What About the rest??

  2. dicontinuities Harzburgite (80%olv 20%OPX) lithosphere Lherzolite (60%olv 40%OPX, grt) MOHO asthenosphere Pyrolite (lherzolite-like) Upper mantle Olivine  b-spinel 410 Pyroxene  b-spinel + stishovite 660 Spinel  perovskite + periclase Lower mantle Mantle composition (rheology)

  3. discontinuities Harzburgite (80%olv 20%OPX) lithosphere Lherzolite (60%olv 40%OPX, grt) MOHO asthenosphere Pyrolite (lherzolite-like) Upper mantle Olivine  b-spinel 410 Pyroxene  b-spinel + stishovite 660 Spinel  perovskite + periclase Lower mantle Upper Mantle Minerals • Olivine (60%), Pyroxene (30%), Garnet (10%) • Rest is compositionally homogeneous • What’s different??

  4. Upper Mantle Olivine • Olivine – Thought to be about 10-12% Fe in upper mantle • At pressures around the 410-km discontinuity, Fo-rich olivine transforms to a ccp structure called wadsleyite. • Iron rich olivines do not undergo this transformation. At higher pressures, both the Fa-rich olivine and wadsleyite transform to a spinel structure, (Mg,Fe)2SiO4, called ringwoodite. • This occurs when the pressure forces the structure to become as closest-packed as it can get  in order to become more dense it must transform to a new phase.

  5. Garnet, Pyroxene • As pressure increases  Pyroxene  Garnet (primarily pyrope) • Increases from 50 to 520 km • Past 520 km, Garnet Ca-perovskite • Past 720 km, more Mg rich Garnets begin to form Mg-perovskite

  6. Lower Mantle Minerals • Perovskite ((Mg, Fe)SiO3, Magnesio-wüstite: ((Mg,Fe)O), and Stishovite (SiO2) • ~80% Perovskite, ~20% Magnesio-wustite, minor stishovite (which doesn’t form if Mg or Fe are around) • At these high pressures, all Si is 6-coordinate (SiO6 subunits; Octahedral coordination)

  7. Perovskite • (Mg, Fe)SiO3 • As the major mineral in the lower mantle, possibly the most abundant earth material!

  8. Do we have any Lower Mantle Minerals?? • NO • How do we know they are there? • METEORITES!?!?!?! • P-S waves tell us something about composition • Nuclear chemistry also tells us something about composition • EXPERIMENTS – simulate P-T  see what you get…

  9. Core

  10. Core • Outer Core • Liquid – made of Iron (Fe) and Nickel (Ni) (about 4%) and some S, Si, and O (enough to make the density less than Fe and Ni alone) • Movement of this liquid is responsible for earth’s magnetic field • Inner Core • Solid, Hexagonally-closest packed Fe and Ni

  11. Geodynamo • The inner core spins – what happens when a solid is spun inside a liquid containing ions?? • Generate an electromagnetic field! • The polarity of that field has flopped many times in earth’s history Model of a magnetic reversal taking ~1,000 years… http://www.es.ucsc.edu/~glatz/geodynamo.html

  12. The electromagnetic field also protects the planet from solar sourced ionic particles (solar wind) • The geodynamo is additionally responsible for the position of magnetic north

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