Experimental investigation of the partitioning of phosphorus between metal and silicate phases: implications for the Earth,Moon and Eucrite Parent Body |
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| Authors: | Horton E Newsom Michael J Drake |
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| Institution: | Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 U.S.A. |
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| Abstract: | The solid metal/silicate melt partition coefficient for P, D(P), has been determined experimentally at 1190°C and 1300°C. The dependence of the partition coefficient on oxygen fugacity has been investigated, and is consistent with a valence state of 5 for P in the silicate melt. The experimental partition coefficients are given by: The experimentally determined partition coefficients may be used to interpret the low ratios of the Earth, Moon and eucrites relative to C1 chondrites. The low ratios in the eucrites may be explained by partitioning of P into 5% to 25% of a sulfur-bearing metallic liquid assuming equilibration and separation of the liquid metal from the silicates at low degrees of partial melting of the silicates. The low ratios in the eucrites compared to C1 chondrites require the separation of an additional 2% to 10% solid metal.The lowering of both and ratios in the Moon may be explained by partitioning of P and W into metal during formation of a small core by separation of liquid metal from silicate at low degrees of partial melting of the silicates. The ratios in the Earth and Moon are virtually indistinguishable, while ratios differ by a factor of two. The concentrations of FeO also appear to be different. These observations are difficult to reconcile with the hypothesis of a terrestrial origin of the Moon following formation of the Earth's core, but are consistent with independent formation of the Earth and Moon. |
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