HR: 10:25h
AN: V42B-01    [Abstracts]
TI: A Model to Predict Changes in S Solubility in Silicate Melts with Changes in Oxygen Fugacity
AU: * Jugo, P J
EM: pjugo@Laurentian.ca
AF: Earth Sci., Laurentian Univ., Sudbury, ON P3E 2C6, Canada
AU: * Jugo, P J
EM: pjugo@Laurentian.ca
AF: Geowissenschaften, Univ. Frankfurt, Frankfurt, D-60054, Germany
AU: Wilke, M
EM: max@geo.uni-potsdam.de
AF: Geowissenschaften, Univ. Potsdam, Golm, D-14476, Germany
AU: Woodland, A
EM: woodland@em.uni-frankfurt.de
AF: Geowissenschaften, Univ. Frankfurt, Frankfurt, D-60054, Germany
AB: The behavior if S in magmatic systems is of interest because of the impact of high-S explosive volcanism on climate, the controlling role of sulfides on the behavior of base and precious metals, and the potential use of S speciation as an indicator of the oxidation state of magmas. In silicate melts S can be present as sulfide (S^2- ), sulfate (S⁶⁺) or a combination of both species. Significant differences exist in the amounts of S that can be dissolved in sulfide-saturated melts (e.g. melts coexisting with pyrrhotite or coexisting with an immiscible sulfide liquid) and sulfate-saturated melts (e.g. melts coexisting with anhydrite): sulfate-saturated melts typically containing several times more S than sulfide-saturated melts. The transition from sulfide-dominated to sulfate- dominated systems occur at fO₂ in the range FMQ < fO₂ < FMQ+2. In this interval both sulfide and sulfate species coexist; however, we know very little about the total amount of S that can be dissolved in silicate melts when S is present both as sulfide and sulfate. We derived a model for the total S content in silicate melts as a function of fO₂ that accounts for the contribution of each species in the melt. For basaltic melts, the resulting equation is: {S}_T = [S^2-](1 + exp(2.23ΔFMQ-2.89)) where {S}_T is the total mount of S that can be dissolved in the melt; [S^2-] is the S content at sulfide saturation, and the factor [exp(2.23ΔFMQ-2.89)] accounts for the contribution to {S}_T from S dissolved as (S⁶⁺). The model: (a) predicts an exponential increase in the total S content of sulfide- saturated silicate melts with increasing fO₂, starting at about FMQ and up to the fO₂ at which the melt reaches sulfate saturation; (b) explains the high S content found in some basaltic melt inclusions in olivine; (c) predicts low degrees of partial melting for the generation of S-rich, sulfide-undersaturated magmas at fO₂ within the range of magma generation in supra-subduction zones and other metasomatized magma sources.
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3619 Magma genesis and partial melting (1037)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly