1. AESC 2010, Perth, July 7th DYNAMIC EARTH: Restless Earth and Earth structure The role of lower crustal flow in the formation of subaqueous Archaean continental flood basalts NicolasFlamenta, b,PatriceRey a, NicolasColticeb, GillesDromartb & Nicolas Olivierb a The University of Sydney – bUniversité de Lyon
2. 2 Subaqueous Archaean flood basalts Flament et al. Archaean pillow basalts in 5 to 15 thick Archaean Large Igneous Provinces In the Pilbara, WA, at ~ 3.5 Ga Photo P. Rey In Isua, Greenland, at ~ 3.8 Ga Photo M. Boyet
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4. rare to absent in the Phanerozoic3 Subaqueous Archaean flood basalts Flament et al. Arndt (1999) Kump & Barley (2007)
5. What was different in the Archaean?The radioactive heat production was 2 to 3.5 times greater 4 Subaqueous Archaean flood basalts Flament et al. Heat production from Th, K and U
6. Abundant mafic and ultramafic rocks indicate high eruption temperatures 5 Subaqueous Archaean flood basalts Flament et al. What was different in the Archaean?The mantle was ~ 200 ± 100°C hotter
7. 6 Subaqueous Archaean flood basalts Flament et al. What was different in the Archaean?The volume of the continents was between 20 and 80% of present
8. 7 Subaqueous Archaean flood basalts Flament et al. Higher sea levels in the Archaean Present-day configuration Flament, Coltice & Rey (2008)
9. 8 Subaqueous Archaean flood basalts Flament et al. Higher sea levels in the Archaean Possible late-Archaeanconfiguration Flament, Coltice & Rey (2008) Continents flooded by ~ 1km of water does not fully explain subaqueous CFBs 5 to 15 km thick
10. Flament et al. Subaqueous Archaean flood basalts 9 Continental geotherms: the Archaean paradox Hot continental crust? Or not? England & Bickle (1984) Nisbet (1984) Cold lithosphere? Archaean diamonds? Richardson et al. (1984)
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16. Scaling laws for τ as a function of TMoho 14 Subaqueous Archaean flood basalts Flament et al. Estimate τ from the subsidence history of a CFB to estimate TMoho
27. Conclusions The subsidence history of CFBs can be used to constrain the Archaeangeotherm The Maddina Formation basalts constrain the secular cooling of the East Pilbara crust as ≥ 150ºC The flow of hot, ductile lower continental crust was a key process that maintained ArchaeanCFBs below sea level Flament et al. Subaqueous Archaean flood basalts 21
