V33A-3085
Solubility and Partitioning of Carbon and Sulfur in Fe-rich Alloy and Silicate Melt Systems at High Pressures and Temperatures: Implications for Earth’s Heterogeneous Accretion

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Yuan Li1, Rajdeep Dasgupta1, Kyusei Tsuno1, Brian Monteleone2 and Nobu Shimizu3, (1)Rice University, Houston, TX, United States, (2)3Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)WHOI, Department of Geology and Geophysics, Woods Hole, MA, United States
Abstract:
The partitioning of C and S between Fe-rich alloy and silicate melt are critical to understand the origin and distribution of these two volatile elements in terrestrial planets. Thirty-five experiments in graphite capsule have been performed at 2-8 GPa and 1600-2200 °C to investigate the effects of P, T, fO2, H2O, and melt composition on C and S partitioning in Fe-Ni±S±Si alloy and silicate melt systems. The results show that C-solubility in Si-free alloy melt is ~5.5 wt% and is little affected by P, T, or the presence of 0-5 wt.% S [1]. However, C-solubility in Si-bearing alloy decreases from ~5.5 to ~1.8 wt% with increasing Si content to 10 wt.%. C-solubility in silicate melt is mainly controlled by fO2 and the bulk H2O content. At fO2 from IW-0.6 to IW-1.5, C-solubility drops from ~90 to ~10 ppm. However, at fO2 below IW-1.5, C-solubility increases up to 240 ppm with decreasing fO2 if the melt H2O content is 0.3-0.8 wt.%; whereas C-solubility decreases or only slightly increases if melt H2O is <0.2 wt.%. Raman and FTIR spectra show that the silicate glass with fO2 around IW-0.6 contained ~10-30 ppm carbon as CO32-; however, at fO2<IW-1 CO32- peak was undetectable in IR-spectra and a strong correlation between Raman peak intensities of H2 and CH4 was observed. varied from 130 to 4600 and is mainly controlled by fO2 and melt H2O content, as in the case for C-solubility in silicate melt but in an opposite way. varied from 0.4 to 38, mainly controlled by fO2, P, and T. Our new results along with previous data suggest that in a magma ocean, in particular at dry conditions, much more C than S would have segregated in the core. To satisfy the C/S ratios currently estimated for Earth’s core and silicate mantle [2], a C-rich but S-poor material needs to be delivered to the silicate Earth after complete core formation. Alternatively, a C- and S-rich material was delivered to the Earth during the late stage of core formation, but with S preferentially segregated in the core in the form of sulfide. [1] Li et al. (2015), EPSL. [2]McDonough (2014), Treatise Geochem.