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• We have been talking about minerals primarily in the earth’s crust • What About the rest?? Mantle composition (rheology) dicontinuities Harzburgite (80%olv 20%OPX) lithosphereLherzolite (60%olv 40%OPX, grt) MOHO asthenosphere Pyrolite (lherzolite-like) Upper mantle Olivine b-spinel 410 Pyroxene b-spinel + stishovite 660 Spinel Lower mantle perovskite + periclase Upper Mantle Minerals • Olivine (60%), Pyroxene (30%), Garnet (10%) • Rest is compositionally homogeneous discontinuities • What’s different?? 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 Lower mantle Spinel perovskite + periclase 660 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. 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 Lower Mantle Minerals • Perovskite ((Mg, Fe)SiO3, Magnesiowüstite: ((Mg,Fe)O), and Stishovite (SiO2) • ~80% Perovskite, ~20% Magnesiowustite, minor stishovite (which doesn’t form if Mg or Fe are around) • At these high pressures, all Si is 6coordinate (SiO6 subunits; Octahedral coordination) 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… Meteorite types • Stony, stony-iron, and iron • Stony: Chondritic or Achondritic – Chondrules – spherical bits of olive or pyroxene condensed from the hot soar nebula over 4 ½ billion years ago • Stony-iron: Composed of nickel-iron metal and stony components (mafic minerals) • Iron: Nickel-iron alloys Kamosite and Taenite Perovskite • (Mg, Fe)SiO3 • As the major mineral in the lower mantle, possibly the most abundant earth material! Core 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 Earth • Image taken by Voyager I in 1990 • Photos taken 4 billion miles away from earth • A mosaic image, filtered and magnified • • • We succeeded in taking that picture and, if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam. The earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity -- in all this vastness -- there is no hint that help will come from elsewhere to save us from ourselves. It is up to us. It's been said that astronomy is a humbling, and I might add, a character-building experience. To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we've ever known. Formation of the Universe • Courtesy JPL http://cougar.jpl.nasa.gov/HR4796/anim.html Formation of the Universe • Courtesy JPL http://cougar.jpl.nasa.gov/HR4796/anim.html Planetary Geology • How can we know anything about the geology of another planet? Venus • • • • Clouds Magnetic field Geology? Have we ever been there? • Data shows that most of the rocks are mafic – basalts with seemingly little soil development… make sense??