科研之友
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摘要
The abundances and distribution of incompatible trace elements in low-Ca pyroxene are important to the interpretation of the thermal and chemical evolution of the lunar magma ocean and cumulate mantle. We conducted high pressure (2 GPa) and high temperature (1340-1450 degrees C) experiments to constrain trace elements partitioning between low-Ca pyroxene and a wide range of lunar picritic melt compositions (TiO2 = 1.6-16.6 wt%) under reducing conditions imposed by graphite-lined molybdenum capsules. We show that addition of TiO2 in the melt decreases rare earth element (REE) and Y partition coefficients in low-Ca pyroxene and quantified this effect through a parameterized lattice strain model. Together with published high quality partitioning data of tetravalent high field strength elements (HFSEs) in the literature, we also developed a parameterized lattice strain model for Ti, Hf and Zr partitioning in low-Ca pyroxene. Partition coefficients of REE and HFSE are positively correlated with Al and Ca abundances in low-Ca pyroxene and negatively correlated with temperature. HFSE partition coefficients show an inverse correlation with Fe content in low-Ca pyroxene. As examples of lunar applications, we estimated REE and HFSE partition coefficients in low-Ca pyroxene close to the multiple saturation points of lunar picritic melts, and found small variations of these partition coefficients in low-Ca pyroxene from individual lunar picritic melts. Constant REE and HFSE partition coefficients can be used in melting models exploring the petrogenesis of individual picritic melts. On the other hand, large variations in estimated REE and HFSE partition coefficients for low-Ca pyroxene are expected during lunar magma ocean crystallization, underscoring the significance of temperature-composition dependent REE and HFSE partition coefficients for understanding lunar magma ocean evolution.
- 出版日期2013-10-15
