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Mantle Convection

Mantle Convection. Geochemical Reservoirs . Primitive mantle composition Is inferred from chondrites Continental crust, EM1, HIMU enriched in incompatibles; MORB depleted MORB shows inverse pattern from Cont. Crust suggesting crust forms by extraction from MORB

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Mantle Convection

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  1. Mantle Convection

  2. Geochemical Reservoirs Primitive mantle composition Is inferred from chondrites Continental crust, EM1, HIMU enriched in incompatibles; MORB depleted MORB shows inverse pattern from Cont. Crust suggesting crust forms by extraction from MORB Ocean Islands (OIB)enriched but Show MORB pattern of Pb, Nb Significant differences between OIBs Hoffman [1997]

  3. Isotope Geochemistry Rb87 Sr87 Very long half life Rb incompatible – goes into melt So high Sr87/86 identifies early differentiation

  4. Radiogenic elements HIMU – recycled oceanic crust? EM2 – oceanic crust with sediment EM1 – continental lithosphere? FOZO – “focus zone” – lower mantle? Hoffman [1997]

  5. Seismic Tomography - Mid-mantle Anomalies 1300 km S velocity 1300 km P velocity

  6. Seismic Tomography – slabs extending into the lower mantle

  7. Basic question: How does the interior of the earth work? Why does it work that way?: He3 – primordial He4 – produced by U, Th decay OIB usually have high He3/4 Does high He3/4 result from Primordial He3 or from low U, Th? Tackley [2000]

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