Magmatic system are dominated by volatiles H2O, CO2, F, CL and S (the igneous quintet). Multiple studies have partitioning of 4 out of these 5 volatiles (H2O, CO2, F and Cl) between nominally volatile-free minerals and melts, whereas the partitioning of the sulfur is poorly known. To better contstrain the behavior of sulfur in igneous system we measured the partitioning of sulfur between clinopyroxene and silicate melts over a range of pressure, temperature, and melt composition from 0.8 to 1.2 GPa, 1000 to 1240 °C, and 49 to 66 wt%SiO2 (13 measurements), orthopyroxene (2 measurements), amphibole (2 measurements) and olivine (1 measurement) in some of the same run products. experiments were performed at high and low oxygen fugacities, where sulfur in the melt is expected to be dominantly present as S6+ or a S2- species, respectivelly.When the partition coefficient is calculated as the total sulfur in the crystal divided by the total sulfur in the melt, the partition coefficient varies from 0.017 to 0.075 for clinopyroxene, from 0.036 to 0.229 for plagioclase, and is a maximum of 0.001 for olivine and of 0.003 for orthopyroxene. The variation in the total sulfur partition coefficient positivelly correlates with cation-oxygen bond lenghts in the crystals; the measured partition coefficients for total sulfur are only approximatekly one-third of those measured in low oxygen fugacitiy, anhydrous experiments. However when the partition coefficient is calculated as total sulfur in the crystal divided by S2- in the melt, the clinopyroxene partition coefficients for experiments with melt between ̴ 51 wt% and 66 wt% SiO2 can be described by a single mean value of 0.063 ± 0.010 (1 sigma standard deviatin about the mean). These two observations support the hypothesis that sulfur, as S2-, replaces oxygen in the crystal structure. The results of hydrous experimentsat low oxygen fugacity and anhydrous experiments at high oxygen fugacity suggest that oxygen fugacity has a greater effect on sulfur partitioning than water. Althought the total sulfur clinopyroxene-melt partition coefficients are affected by the Mg/(Mg+Fe) ratio of the crystal, partition coefficients calculated using S2- partition coefficient appear unaffected by IVAl in the clinopyroxene structure. No effect of anorthite content nor of iron concentration in the crystal was seen in the data for plagioclase-melt partitioning. The data obtained for orthopyroxene and olivine were too few to establish any trend. the partition coefficient of total sulfur and S2- between the crystal studied and silicate melts are typically lower than those of fluorine, higher than those of carbon, and similar to those of chlorine and hydrogen. these sulfur partition coefficients can be combined with analyses of volatiles in nominally volatile-free minerals and in previously published partition coefficients of H2O, C, F, and Cl to constrain the concentration of the igneous quintet, the five major volatiles in magmatic systems.

The quintet completed: the partitioning of sulfur between nominally volatile-free minerals and silicate melts

A. De Min;
2020-01-01

Abstract

Magmatic system are dominated by volatiles H2O, CO2, F, CL and S (the igneous quintet). Multiple studies have partitioning of 4 out of these 5 volatiles (H2O, CO2, F and Cl) between nominally volatile-free minerals and melts, whereas the partitioning of the sulfur is poorly known. To better contstrain the behavior of sulfur in igneous system we measured the partitioning of sulfur between clinopyroxene and silicate melts over a range of pressure, temperature, and melt composition from 0.8 to 1.2 GPa, 1000 to 1240 °C, and 49 to 66 wt%SiO2 (13 measurements), orthopyroxene (2 measurements), amphibole (2 measurements) and olivine (1 measurement) in some of the same run products. experiments were performed at high and low oxygen fugacities, where sulfur in the melt is expected to be dominantly present as S6+ or a S2- species, respectivelly.When the partition coefficient is calculated as the total sulfur in the crystal divided by the total sulfur in the melt, the partition coefficient varies from 0.017 to 0.075 for clinopyroxene, from 0.036 to 0.229 for plagioclase, and is a maximum of 0.001 for olivine and of 0.003 for orthopyroxene. The variation in the total sulfur partition coefficient positivelly correlates with cation-oxygen bond lenghts in the crystals; the measured partition coefficients for total sulfur are only approximatekly one-third of those measured in low oxygen fugacitiy, anhydrous experiments. However when the partition coefficient is calculated as total sulfur in the crystal divided by S2- in the melt, the clinopyroxene partition coefficients for experiments with melt between ̴ 51 wt% and 66 wt% SiO2 can be described by a single mean value of 0.063 ± 0.010 (1 sigma standard deviatin about the mean). These two observations support the hypothesis that sulfur, as S2-, replaces oxygen in the crystal structure. The results of hydrous experimentsat low oxygen fugacity and anhydrous experiments at high oxygen fugacity suggest that oxygen fugacity has a greater effect on sulfur partitioning than water. Althought the total sulfur clinopyroxene-melt partition coefficients are affected by the Mg/(Mg+Fe) ratio of the crystal, partition coefficients calculated using S2- partition coefficient appear unaffected by IVAl in the clinopyroxene structure. No effect of anorthite content nor of iron concentration in the crystal was seen in the data for plagioclase-melt partitioning. The data obtained for orthopyroxene and olivine were too few to establish any trend. the partition coefficient of total sulfur and S2- between the crystal studied and silicate melts are typically lower than those of fluorine, higher than those of carbon, and similar to those of chlorine and hydrogen. these sulfur partition coefficients can be combined with analyses of volatiles in nominally volatile-free minerals and in previously published partition coefficients of H2O, C, F, and Cl to constrain the concentration of the igneous quintet, the five major volatiles in magmatic systems.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/2957246
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