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29801 - Eclogite Engine DonL.Anderson Caltech Canwebridge...

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Eclogite  Engine Don L. Anderson Caltech
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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
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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…
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Mantle is a Top-Down System QuickTime  and a TIFF (Uncompressed) decompressor are needed to see this picture. Sources of dissipation The top boundary condition is not simple delamination
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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
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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
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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 Hawaii’s; 10x more average Hawaii’s) (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 Hawaii’s) can also delaminate Midplate volcanisms & arcs can be upper mantle recycling
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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
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dense roots fall off warm up in ambient  mantle rise possible mechanism for  Atlantic & Indian ocean  plateaus & DUPAL 
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