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Experimental studies of metal-silicate partitioning of Sb: Implications for the terrestrial and lunar mantles |
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| Authors: | K Righter M Humayun AJ Campbell L Danielson MJ Drake |
| Institution: | a Mailcode KT, NASA-JSC, 2101 NASA Parkway, Houston, TX 77058, USA b Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA c Dept. of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA d National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310-3706, USA e Dept. of Geology, University of Maryland, College Park, MD 20742, USA |
| Abstract: | The terrestrial mantle has a well defined Sb depletion of ∼7 ± 1 (Jochum and Hofmann, 1997), and the lunar mantle is depleted relative to the Earth by a factor of ∼50 ± 5 (Wolf and Anders, 1980). Despite these well defined depletions, there are few data upon which to evaluate their origin—whether due to volatility or core formation. We have carried out a series of experiments to isolate several variables such as oxygen fugacity, temperature, pressure, and silicate and metallic melt compositions, on the magnitude of  . The activity of Sb in FeNi metal is strongly composition dependent such that solubility of Sb as a function of fO2 must be corrected for the metal composition. When the correction is applied, Sb solubility is consistent with 3+ valence. Temperature series (at 1.5 GPa) shows that  decreases by a factor of 100 over 400 °C, and a pressure series exhibits an additional decrease between ambient pressure (100 MPa) and 13 GPa. A strong dependence upon silicate melt composition is evident from a factor of 100 decrease in  between nbo/t values of 0.3 and 1.7. Consideration of all these variables indicates that the small Sb depletion for the Earth’s mantle can be explained by high PT equilibrium partitioning between metal and silicate melt  . The relatively large lunar Sb depletion can also be explained by segregation of a small metallic core, at lower pressure conditions where  is much higher (2500). |
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