Experimental determination of crystal/melt partitioning of Ga and Ge in the system forsterite-anorthite-diopside

The crystal/liquid partitioning of Ga and Ge has been measured experimentally between forsterite, diopside, anorthite and spinel and melts in the pseudoternary system forsterite-anorthite-diopside at one atmosphere pressure and 1300°C. Gallium is incompatible with forsterite and diopside [ D ( Ga) = 0.024 and 0.19, respectively], is only slightly incompatible in anorthite [ D ( Ga) = 0.86] and is highly compatible in spinel [ D ( Ga) = 4.6]. The partition coefficient for Ge is within a factor of two of unity for forsterite, diopside and anorthite [ D ( Ge) = 0.62, 1.4 and 0.51, respectively], but Ge is incompatible in spinel [ D ( Ge) = 0.1]. The coefficients for the exchange of Ga and Al and the exchange of Ge and Si between minerals and melts generally are within a factor of two of unity, as is expected from the geochemical coherence of these element pairs in natural samples. The application of our results to the interpretation of natural basaltic and mantle samples from the Earth and basalts from the Moon and the Shergottite Parent Body demonstrates that it is possible to discriminate between different mantle source compositions using Ga/Al and Ge/Si ratios. The Ge variation among lunar mare basalts may be indicative of a heterogeneous lunar mantle. The substantial depletion of Ge in Chassigny relative to the other SNC meteorites may be evidence of either a heterogeneous Shergottite Parent Body (SPB) mantle, or of different geochemical behavior for Ge in the SPB.