29801 - Eclogite Engine Don L. Anderson Caltech Can we...

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Unformatted text preview: Eclogite Engine Don L. Anderson Caltech Can we bridge geophysics,geochemistry & geodynamics? Continents; the missing link The lower crust is transient It is recycled 6 times faster than upper crust Recent arc growth estimates are 5X previous estimates! Therefore, a huge previously unaccounted for flux THE UPPER MANTLE ECLOGITE CYCLE All the components of so-called hotspot or plume magmas originate in crust, lithosphere, cumulates or mantle wedge The Isotope Zoo EM1, EM2, HIMU, DUPAL, LONU, High 3He/4He, C-, FOZO, Os Mantle is a Top-Down System QuickT ime and a TIFF (Uncompressed) decompressor are needed to see this picture. Sources of dissipation The top boundary condition is not simple delamination Many ways to get big chunks of mafic matter into upper mantle Subduction of seamount chains, aseismic ridges Delamination of island arcs Delamination of compressional mountain belts Estimating mantle sources & sinks, continental addition & loss, through time, depends critically on when deep subduction, got underway David Scholl 1 Gyr of oceanic crust subduction=70 km of eclogite But lots of other things get put into the mantle OIB ~2 Km 3 /yr 20 km 3 /yr Piles up @ 70 km/Gyr MASS BALANCE Recycling rate of oceanic crust (basaltic + gabbroic) ~20 km 3 /yr Midplate extrusive magmatism 1-2 km 3 /yr (4 to 8 current Hawaiis; 10x more average Hawaiis) (Factor of 10 to 20 mismatch for Hofmann & White recycling mechanism) Underside erosion of continents at marine margins 2.5 km 3 /yr Erosion plus delamination at continental collisions 2-3 km 3 /yr Production rate of magmas in arcs 3-9 km 3 /yr [Scholl (2006) gives 4-5 km3/yr] Growth rate of arc garnet pyroxenite cumulates 1.5-6 km 3 /yr Island arcs and oceanic plateaus (and Hawaiis) can also delaminate Midplate volcanisms & arcs can be upper mantle recycling RIDGE-TRENCH ANNIHILATION Abandonment of young oceanic crust and mantle wedge BAB Mantle wedge Trapped crust Future suture EM1 EM2 HIM U FOZO LOMU HI 3 HE/U All of the isotope and trace element signatures of OIB are manufactured in the subduction factory, wedge & crust dense roots fall off warm up in ambient mantle rise possible mechanism for Atlantic & Indian ocean plateaus & DUPAL...
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This note was uploaded on 02/22/2012 for the course HIST 312 taught by Professor Staff during the Fall '10 term at Rutgers.

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29801 - Eclogite Engine Don L. Anderson Caltech Can we...

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