Continental growth spurts were all before 1 Ga This plus ophiolites, kimberlites, komatiites, TTG,UHPT…suggest that modern plate tectonics was not occurring.

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?

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!

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)

Modes of advectionTUBES

CIRCUITS,

BOUNDARY

LAYERS

ELEVATOR

HEAT EXCHANGER

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

According to Stern, deep subduction started at 1 Ga

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

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

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

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

dense roots fall off warm up in

ambient mantle rise

possible mechanism for Atlantic & Indian ocean plateaus & DUPAL anomaly

Delamination cycle