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Continental growth spurts were all before 1 Ga

Continental growth spurts were all before 1 Ga. This plus ophiolites, kimberlites, komatiites, TTG,UHPT…suggest that modern plate tectonics was not occurring before Late Precambrian Today, delamination equals arc and plateau addition. Can we bridge geophysics,geochemistry & geodynamics?.

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Continental growth spurts were all before 1 Ga

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  1. Continental growth spurts were all before 1 Ga This plus ophiolites, kimberlites, komatiites, TTG,UHPT…suggest that modern plate tectonics was not occurring before Late Precambrian Today, delamination equals arc and plateau addition

  2. 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 Mantle convection controlled from the top; episodicity is plate reorganization, not mantle avalanches!

  3. TRI-CYCLING THROUGH THE EARTH • RIDGE-TRENCH ‘CYCLE’ (the escalator) • SUPERCONTINENT CYCLE (the trolley) • SLAB-PLUME ‘CYCLE’ (the tube) • SUBTERRANEAN CYCLE (delamination, orogenic cycle; the elevator)

  4. Modes of advection TUBES ELEVATOR CIRCUITS, BOUNDARY LAYERS HEAT EXCHANGER

  5. According to Stern, deep subduction started at 1 Ga 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

  6. Ringwood& Green, 1966

  7. New parameters • Scale (size) • Homologous temperature • Stress • Buoyancy parameter • Architecture • Fertility • Entrainability

  8. What triggered this new understanding? The upper crust paradox Recognition of true arc growth rates The need to get rid of enormous amounts of lower crust Appreciation of role of Eclogite Appreciation of SCALE

  9. Recent workers who are, or are almost onto this, once they leave the crust or MORB Bob & Suzanne Kay Roberta Rudnick Sobolov, Green, Scholl, Elliott, Natland, Presnall, Cin-Ty Lee

  10. MASS BALANCE • km3/yr • TOTAL MIDPLATE MAGMA VOLUMES 3-6 • Growth rate of arc garnet pyroxenite cumulates 1.5-6 • Underside erosion & delamination of continents 4-6 • Production rate of magmas in arcs 4-5 • LOWER CRUSTAL LOSS = ‘HOTSPOT’ MAGMATISM • CYCLE TIME 40-80 MYR • 10-30 KM CHUNKS

  11. Delamination cycle • dense roots • fall off • warm up in ambient mantle • rise • possible mechanism for Atlantic & Indian ocean plateaus & DUPAL anomaly

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