Nitrogen Partitioning Between Reduced Silicate Melts and Metallic Iron Alloys
Friday, 19 December 2014
Solubility and partitioning of elements during early planetary history is critical in understanding element concentrations and distribution in the terrestrial planets. Nitrogen is the most depleted element in the bulk silicate Earth relative to CI chondrites , which may be explained by its high pressure behavior under reduced conditions relevant to planetary accretion and differentiation. Under oxidized conditions N dissolves in silicate melts as N2, but as fO2 decreases N-H species become the dominant form of dissolved N and the solubility increases [2-7]. DNmetal/melt (the N partition coefficient between metal and melt) is affected by pressure, fO2, fH2, and metal composition [3-5] but with less than 20 published experiments over a wide pressure range, these dependencies have been poorly constrained. Here we present new N-bearing experiments on graphite-saturated silicate melts in equilibrium with Fe-rich metallic melts. Experiments were performed at 1.2 GPa and 1400 ˚C in a piston cylinder apparatus, with N added as Si3N4, FexN, and urea [(NH2)2CO] to basaltic starting compositions. Glassy and metallic run products were gold coated and analyzed by EMPA. Detection limits and standard errors in N concentrations were improved (e.g. better than 1% for > 0.4 wt% N) relative to previous studies [2-5] by fitting non-linear backgrounds to wavelength-scans on standards and unknowns. Preliminary experiments with fO2 of IW-2 to IW-4 produced glasses with a maximum of 0.6 wt% N and metals with a maximum of 1.1 wt% N. DNmetal/melt are comparable to values at a similar pressure determined in the LH-DAC . Further experiments will explore the effects of fO2 and H content on DN and N solubility. References:  Halliday (2013) GCA 105, 146-171.  Libourel et al. (2003) GCA 67, 4123-4135.  Kadik et al. (2011) Geochem. Int. 49, 429-438.  Kadik et al. (2013) PEPI 214, 14-24.  Roskosz et al. (2013) GCA 121, 15-28.  Stanley et al. (2014) GCA 129, 54-76.  Falksen et al. (in prep).