HR: 0830h
AN: V41C-0316    [PDF]
TI: Experimental Study of the Effects of Dissolved Sulfur on Olivine-Liquid Ni Partitioning Behavior
AU: * Brophy, J G
EM: brophy@indiana.edu
AF: Dept. of Geological Sciences, Indiana University, Bloomington, IN 47401
AU: Li, C
EM: cli@indiana.edu
AF: Dept. of Geological Sciences, Indiana University, Bloomington, IN 47401
AB: The partitioning of Ni between olivine and a silicate melt is best described in terms of the Nernst partition coefficient, D$_{Ni}$ which is equal to (wt % Ni)$^{oliv}$ / (wt % Ni)$^{melt}$. Ni in a silicate melt may partition into olivine according to the following reaction NiO$^{melt}$+ Fe$_{2}$Si$_{0.5}$O$_{2}$$^{oliv}$ = Ni$_{2}$Si$_{0.5}$O$_{2}$$^{oliv}$ + FeO$^{melt}$. In the presence of dissolved S, the oxide species in the melt may react via the following reactions FeO$^{melt}$ + 0.5 S$_{2}$$^{melt}$ = FeS$^{melt}$ + 0.5 O$_{2}$$^{melt}$ NiO$^{melt}$ + 0.5 S$_{2}$$^{melt}$ = NiS$^{melt}$ + 0.5 O$_{2}$$^{melt}$ Thus the abundances of FeO and NiO in the melt and, therefore, the value of D$_{Ni}$ between olivine and a silicate melt are a function of both fS$_{2}$ and fO$_{2}$ in the melt. Because natural magmas may contain significant amounts of dissolved S, those values of D$_{Ni}$ determined in sulfur-free systems may not be applicable to natural magmas. To address the extent to which D$_{Ni}$ may be a function of dissolved S content, a series of one-atmosphere crystallization experiments were conducted on a moderately evolved MORB lava to which was added 10 % (by weight) powdered San Carlos olivine (MgO = 10.9 wt. %, Ni $\sim$ 300 ppm). All experiments were conducted at 1245$^{o}$ C where approximately 5-10 volume % olivine (Fo$_{88}$) coexisted with melt. fO$_{2}$ was maintained at a constant value of 10$^{-9.5}$. fS$_{2}$ was varied from 0 to 10$^{-1.9}$, the latter being well below the theoretical sulfide saturation point. Over this range of fS$_{2}$, the dissolved S content in the melt increased from 0 to 480 ppm and the value of D$_{Ni}$ decreased from ~8 to ~2.4. These results confirm a strong dependence of D$_{Ni}$ on the amount of dissolved S in the melt and suggest that experimentally determined D$_{Ni}$ values in sulfur-free systems should be used with caution.
DE: 3630 Experimental mineralogy and petrology
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting