Partition coefficient of phosphorus between liquid metal and silicate melt with implications for the Martian magma ocean

摘要

Phosphorus in Martian mantle is believed to be five to ten times more abundant than in Earth's mantle, and the distribution of this essential ingredient for life between different deep reservoirs is critical for understanding the habitability of the red planet. In this study, we investigated the behavior of phosphorus in a Martian magma ocean scenario, and measured the partition coefficient of phosphorus (D-p) between liquid metal and silicate melt within the pressure range of 3-8 GPa, temperatures between 1973 and 2173 K and oxygen fugacity ranging from -1.5 to similar to -2.5 as normalized to the iron-wustite oxygen buffer. Our results show D-p increasing with pressure but decreasing with temperature. A decrease of oxygen fugacity has a negative effect on D-p. The moderately siderophile character of phosphorus indicates that the Martian core might be an important reservoir of phosphorous. Based on our experimental results and phosphorus abundance in Martian mantle and bulk Mars, a minimum pressure of 5.8-10.4 GPa is estimated at the base of Martian magma ocean or during the impact melting if a contribution from the late accretion scenario is taken into account. The shallow Martian magma ocean would avail the preservation of volatiles after the rapid solidification of the planet.