Continental growth spurts were all before 1 Ga

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Continental growth spurts were all before 1 Ga

• This plus ophiolites, kimberlites, komatiites,
  TTG,UHPTsuggest that modern plate tectonics was
  not occurring before Late Precambrian
• Today, delamination equals arc and plateau
  addition

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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

Mantle convection controlled from the top
episodicity is plate reorganization, not mantle
avalanches!
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(No Transcript)
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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)

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Modes of advection
TUBES
ELEVATOR
CIRCUITS, BOUNDARY LAYERS
HEAT EXCHANGER
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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 subduction70 km of
eclogite
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Ringwood Green, 1966
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New parameters

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

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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

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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

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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

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Delamination cycle

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