Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics |
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Authors: | Münker Carsten Pfänder Jörg A Weyer Stefan Büchl Anette Kleine Thorsten Mezger Klaus |
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Institution: | Institut für Mineralogie, Corrensstrasse 24, Universit?t Münster, 48149 Münster, Germany. muenker@nwz.uni-muenster.de |
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Abstract: | It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago. |
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