the mass of continental crust has not changed significantly since the early archean
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The mass of continental crust has not changed significantly since the early Archean. The mass of continental crust has not changed significantly since the early Archean. Proto-Archean. Formation of continental crust. Differenciation of primitive mantle. Enriched continental crust. - PowerPoint PPT PresentationTRANSCRIPT
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The mass of continental crust has not changed significantly since the early Archean
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The mass of continental crust has not changed significantly since the early Archean
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Undifferenciatedprimitive mantle
Enriched continental crust
Depleted mantle
Formation of continental crust
Differenciation of primitive mantle
Formation of the bulk of the continental crust in the Proto-Archean
Proto-Archean depleted mantle
Proto-Archean
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Nb/U
Both incompatible elements
U more incompatible than Nb
Differenciation higher Nb/U in continental crustlower Nb/U in depleted mantle
Nb/U ~30
Nb/U ~47
Nb/U ~10
Modern MORB
Continental crust
Primitive mantle
Archean basalts Nb/U ~ 30 - 47
Geochemical evidence
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Sylvester et al. (1997)
Late Archean basalts
Lunnon FormationYilgarn Craton
Depleted mantle source
Amount of continental crust extracted is the same as today
Crustal contamination curve
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3.5 Ga basalts and komatiites
Barberton Montain Land, South Africa
Campbell (2003)
Average Nb/U : 43
Suggest an early depleted mantle and and amount of continental crust extracted similar as today
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3.5 Ga Basalts from Pilbara Craton
Sylvester ()
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Isua 3.8 Ga
Porpoise Cove 3.8 Ga
Depleted mantle at 3.8 Ga
?Isotopic evidence
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Recycling
McCulloch and Bennett (1994)