Precise measurements of highly siderophile elements in ancient lunar impact rocks

• Antragsteller: Professor Dr. Harry Becker
• Fachliche Zuordnung: Mineralogie, Petrologie und Geochemie
• Förderung: Förderung von 2008 bis 2010
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 86586546

Excess abundances and proportions of the highly siderophile ( iron-loving ) elements (HSE; Ir, Rh, Ru, Pd, Pt, Os, Re, Au) in the Earth s mantle are commonly explained by late accretion of large planetesimals after formation of the Earth s core. New HSE abundance data for samples from the Earth s mantle show unique proportions of these elements that are unlike those found in known primitive meteorites. Possible explanations include the occurrence of ancient primitive meteorites with somewhat different compositions, the presence of a residual HSE fractionation originating from core formation, or poorly understood processes that would fractionate the HSE in the mantle. In contrast to Earth where recycling has returned pre-3.8 Ga old meteorite-contaminated crust back into the mantle, the lunar crust still maintains a record of late accretion since its formation 4.5 billion years ago. Precise abundance data on some Apollo 17 and 14 impact melt rocks indeed yielded HSE compositions for lunar impactors that are very similar to compositions found in the Earth s mantle. Because of the scarcity of complete HSE data sets on such rocks, it is necessary to better constrain the distribution of impactors with distinct HSE abundance patterns on the Moon. We propose to obtain complete HSE abundance patterns and Osmium isotopic data on Apollo 14 and Apollo 16 impact melt rocks and on granulitic breccias. The results will have major implications for the interpretation of the HSE composition of the Earth s mantle.

• DFG-Verfahren: Sachbeihilfen