Precise measurements of highly siderophile elements in ancient lunar impact rocks
Final Report Abstract
In the course of the project different planetary materials have been studied in order to evaluate the origin of the excess HSE abundances of the Earth’s mantle and lunar crustal rocks. Concentrations of HSE and 187Os/188Os have been determined for chondritic meteorites, terrestrial peridotites and lunar impact melt rocks. In the case of chondrites the data reveal differences in the HSE abundance patterns and ratios such as Re/Os, 187Os/188Os, Pd/Ir, Rh/Ir and Au/Ir among chondrite classes. Good to excellent linear correlations of HSE for bulk rocks of some chondrite classes are explained by binary mixing and possibly dilution by silicates. Relative abundances of Rh and Au for the primitive mantle HSE model composition were deduced from the study on terrestrial peridotites. In combination with the results of previous studies, the inferred HSE composition of the primitive mantle (HSE) does not match with the HSE abundance patterns of chondritic meteorites, and thus, HSE abundances in the Earth’s mantle may have originated from a mixture of different meteoritic materials recorded in lunar impact melt rocks. The new HSE data on peridotites yields a compatibility sequence of Re ≤ Au < Pd < Pt ≤ Rh < Ir < Ru ≤ Os during magmatic processes in the mantle, consistent with previous results on peridotites, komatiites and basalts. HSE abundances and 187Os/188Os in lunar impact melt rocks serve as important tracers to place constraints on the late accreted meteoritic material during the late accretion period in the Earth-Moon system. Some of the impactor end-member compositions identified in lunar impact melts are similar to chondrites, while others show slightly suprachondritic HSE ratios. Excess HSE abundances of the Earth’s mantle and suprachondritic Pd/Ir and Ru/Ir inferred for the primitive mantle may be explained by binary mixing of two different meteoritic end-member compositions similar to those recorded in lunar impact melt rocks.
Publications
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(2008): Chondrites do not Match the Highly Siderophile Element Composition of the Earth´s Mantle – Constraints From new Rh/Ir and Au/Ir Data on Peridotites. Jahrestagung der Deutschen Mineralogischen Gesellschaft, Berlin, Germany.
Fischer-Gödde, M., Becker, H., Wombacher, F., Gao, S. and Lorand, J.P.
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(2008): Fractionation of refractory highly siderophile elements in the early solar system. Paneth Kolloquium, Nördlingen, Germany
Fischer-Gödde, M., Becker, H. and Wombacher, F.
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(2009): Highly siderophile element Abundances and 187Os/188Os in lunar impact melt rocks: Implications for late accretion processes in the Earth-Moon system. “Earth Control on Planetary Life and Environment”
99th Annual Meeting of the Geologische Vereinigung e.V. (GV), Göttingen, Germany.
Fischer-Gödde, M., Becker, H. and Wombacher, F.
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(2010): Highly siderophile element
abundances and 187Os/188Os in lunar impact melt rocks: Implications for late accretion
processes in the Earth-Moon system. 41st Lunar and Planetary Science Conference,
2262.
Fischer-Gödde, M., Becker, H. and Wombacher, F.
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(2010): Rhodium, gold and other highly
siderophile element abundances in chondritic meteorites. Geochimica et Cosmochimica
Acta, 74, 356-379
Fischer-Gödde, M., Becker, H. and Wombacher, F.
