Experimental Constraints on the Pressure Dependence of Sulfur Solubility in Hydrous Oxidized Silicic Melts.

Abstract : Understanding the sulfur cycle in subduction zones is of crucial importance to quantify element fluxes in this context and also to assess the potential atmospheric impact of sulfur-rich gas emissions during major volcanic eruptions. Significant amounts of sulfur are present in subducting basaltic oceanic crust and its overlying sediments. Recent experimental studies suggest that geochemical specificities of arc magmas require sediment melting in the subduction zone (e.g., Johnson \& Plank, 1999). On the same way, numerous petrological or geochemical studies suggest that the basaltic oceanic crust could melt in certain circumstances (young and hot slab), producing silicic melts termed adakites. The silicic melts produced by sediment or basalt melting at high pressure are both potential carrier of sulfur in the mantle wedge. However, experimental studies of sulfur solubilities in silicic melts have been mainly carried out at low pressures, i.e. below 400 MPa, most of the experimental data so far available being acquired at 200 MPa (e.g. Carroll and Rutherford, 1985, 1987, 1988; Luhr, 1990; Baker and Rutherford, 1996, Scaillet et al., 1998; Clemente et al., 1998). We have therefore started an experimental program to constrain the pressure dependence of sulfur solubility in hydrous silicate melts. Experiments have been performed in the pressure range 400-3000 MPa on a variety of melt compositions including the Pinatubo dacite (a representative example of natural Cenozoic adakites), a high silica rhyolite, a representative mid-ocean ridge basalt from the Juan de Fuca Ridge, a trondhjemitic melt produced by MORB melting at 3000 MPa and a pelitic sediment from the Barbados accretionary prism, Lesser Antilles. All experiments were hydrous (4 to 10 wt % H$_{2}$O in the system) with 1 wt % added elemental sulfur. Experiments at 400-1000 MPa were performed in internally heated vessels pressurized with Ar and the 2000-3000 MPa runs were carried out in a piston-cylinder apparatus using talc- Pyrex-graphite furnace assemblies. The experiments were performed between 750$\deg$ C and 1000\deg C. At 400 MPa and 1000\deg C, results show that, at near - H$_{2}$O saturation, both dacite and rhyolite compositions achieve S content in the range 2500-3000 ppm for H$_{2}$O content of 8-9 wt %. Decreasing H$_{2}$O induces a significant decrease of S in Pinatubo (to 1100 ppm), while in rhyolite the effect is much less marqued owing to the lack of anhydrite crystallization. For the Pinatubo dacite at 1000 MPa and 750$\deg$ C, with 6 wt % H$_{2}$O, the sulfur content is near the detection limit of 50 ppm while at 1000\deg C it reaches 650 ppm. These results suggest the important effect of water content of melt on the sulfur solubility at high pressure.
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Conference papers

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Submitted on : Wednesday, June 7, 2006 - 9:49:48 AM
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• HAL Id : hal-00078661, version 1

Citation

Gaëlle Prouteau, Bruno Scaillet. Experimental Constraints on the Pressure Dependence of Sulfur Solubility in Hydrous Oxidized Silicic Melts.. AGU, 2006, Baltimore, United States. ⟨hal-00078661⟩

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