Low abundances of highly siderophile elements in the lunar mantle: evidence for prolonged late accretion. Walker, Horan, Shearer and Papike EPSL, 2004. Sabine, Maureen, Scott and Karin. Lunar timeline. green glasses Mare basalt 3.4 Ga 15-19% MgO
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Walker, Horan, Shearer and Papike
Sabine, Maureen, Scott and Karin
green mantle: evidence for prolonged late accretionglasses
near primary precursors to very low TiO2 basalts.
near primary precursors to high TiO2 basalts.Apollo samples
→ cumulate from a pre-mare basaltic melt
→ melting of magma ocean cumulate assemblages @ >400 km depth, leaving behind ol and opx residuum
meteoritic contamination? mantle: evidence for prolonged late accretion
increased fractionation in residues
increased radiogenic Os in residues
orange mantle: evidence for prolonged late accretion glasses
Considered not relevant
green mantle: evidence for prolonged late accretion
Lunar glasses and dunite are depleted in Os relative to terrestrial rocks with similar MgO.
Possible reasons for low HSE abundances in the lunar mantle:
Possible reasons for high HSE abundances in the lunar mantle:
This suggests late accretion post 4.4 Ga
→ 75% HSE in crust
low HSE and high HSE/Pd mantle: evidence for prolonged late accretion→ no metal
Re/Os and relative abundances of the other HSE were not highly fractionated from chondritic in the mantle source of its parental melt