Trace element partitioning between majoritic garnet and silicate melt at 10–17 GPa: Implications for deep mantle processes

• DOI: 10.1016/j.lithos.2012.06.013
• Publication Date: 2012-06-18T14:16:29Z
• Authors: Alexandre Corgne; Lora S. Armstrong; Shantanu Keshav; Yingwei Fei; William F. McDonough; William G. Minarik; Karen Moreno
• Keywords: Peridotite; Ionic radius; Trace element

article i nfo Melting experiments were performed on a silica-rich peridotite composition at 10-17 GPa to determine majoritic garnet-melt partition coefficients (D) for major and trace elements. Our results show that D for many elements, including Na, Sc, Y and rare earth elements (REE), varies significantly with increasing pres- sure or proportion of majorite component. Lu and Sc become incompatible at 17 GPa, with D decreasing from 1.5 at 10 GPa to 0.9 at 17 GPa. As predicted from lattice strain, log D for isovalent cations entering the large site of majoritic garnet exhibits a near-parabolic dependence on ionic radius. Our data are used to refine a previously published predictive model for garnet-melt partitioning of trivalent cations, which suffered from a lack of calibration in the 10-20 GPa range. Our results suggest that Archean Al-depleted komatiites from Barberton (South Africa) may have been generated by partial melting of dry peridotite at depths be- tween 200 and 400 km. We also speculate that transition zone diamonds from Kankan (Guinea), which con- tain inclusions of majoritic garnet, may have formed from the partial reduction of CO2-rich magmas that subsequently transported them to the surface. This hypothesis would provide an explanation for the REE pat- terns of majoritic garnet trapped within these diamonds, including Eu anomalies. Finally, we show that seg- regation of majoritic garnet-bearing cumulates during crystallisation of a deep Martian magma ocean could lead to a variety of Lu/Hf and Sm/Nd ratios depending on pressure, leading to a range of e 143