Siderophile geochemistry of Ga, Ge, and Sn: cationic oxidation states in silicate melts and the effect of composition in iron–nickel alloys

Evidence for high-pressure core-mantle differentiation from the metal–silicate partitioning of lithophile and weakly-siderophile elements

“…A1 indicate valences in the silicate melt of 5 + for Ta and Nb, 4 + for Si, 3 + for V and 2 + for Mn, Zn and Ga. Ga was previously found to be trivalent in 1 bar partitioning experiments (e.g. Schmitt et al, 1989;Capobianco et al, 1999). For In the data are in best agreement with a 1 + valence.…”

“…In the case of Ga, we included literature data at 10 and 25 GPa (Hillgren et al, 1996;Wade and Wood, 2001) for refining our trend (Fig. 5), however, most of the previous studies of Ga partitioning employed Ni-rich (>25 wt%; Capobianco et al, 1999;Righter and Drake, 2000) metals or MgO-poor silicates (<13 wt%; Jaeger and Drake, 2000), which are not comparable to our compositions. Fig.…”

Germanium isotopic variations in igneous rocks and marine sediments

“…Using the two extreme isotopic compositions of deep-sea clays and marine sponge for the d 74 Ge value of the fluid and a K D of 0.023 (Evans and Derry, 2002), a quartz-fluid would range between 0.9975 and 0.9995, which compares well with the size and the scale of the Si isotope fractionation during silica polymorphs transformations (Basile-Doelsch et al, 2005). In addition, Ge(IV) does not undergo reduction to Ge(II) under Earth surface conditions (Capobianco et al, 1999), so Ge isotope fractionation in cherts are certainly not associated with redox reactions but rather related to Ge(IV) incorporation into silica matrix. One important implication of this result is that, in addition to a sink of light isotopes of Ge associated with iron oxyhydroxide (Galy et al, 2002), the early diagenesis of silica provides an additional mechanism to explain the heavy d 74 Ge value of the ocean.…”

Group IVA irons: New constraints on the crystallization and cooling history of an asteroidal core with a complex history

“…There is a significant body of literature demonstrating that Ga can range from lithophile or siderophile depending on the P-T-Xi-fO 2 conditions (Schmidt et al, 1989;Kong and Ebihara, 1996;Capobianco et al, 1999;Jaeger and Drake, 2000;Righter and Drake, 2000;Holzapfel et al, 2001;Liu and Fleet, 2001), but the data for Ge present a less definitive perspective with most findings revealing that it behaves as a siderophile element under most conditions. Experimental investigations reveal that there is a strong bulk compositional dependency on the oxidation states of Ga and Ge in the silicate melts, with Jana and Walker (2003) and Anders and Grevesse (1989) for Au) in the parental melt to the IVA core.…”