Slide 1Slide 2Slide 3Mantle composition (rheology)Upper Mantle MineralsUpper Mantle OlivineGarnet, PyroxeneLower Mantle MineralsPerovskiteCoreSlide 11Do we have any Lower Mantle Minerals??•We have been talking about minerals primarily in the earth’s crust•What About the rest??Mantle composition (rheology)Lherzolite (60%olv 40%OPX, grt)Harzburgite (80%olv 20%OPX)Pyrolite (lherzolite-like)Olivine -spinelPyroxene -spinel + stishoviteSpinel perovskite + periclaselithosphereasthenosphereUppermantle410660MOHOdicontinuitiesLower mantleUpper Mantle Minerals•Olivine (60%), Pyroxene (30%), Garnet (10%)•Rest is compositionally homogeneous•What’s different??Lherzolite (60%olv 40%OPX, grt)Harzburgite (80%olv 20%OPX)Pyrolite (lherzolite-like)Olivine -spinelPyroxene -spinel + stishoviteSpinel perovskite + periclaselithosphereasthenosphereUppermantle410660MOHOdiscontinuitiesLower mantleUpper 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.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-perovskiteLower 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)Perovskite•(Mg, Fe)SiO3•As the major mineral in the lower mantle, possibly the most abundant earth material!CoreCore•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 NiDo 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
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