TY - JOUR

T1 - Sulfur isotope fractionation between fluid and andesitic melt

T2 - An experimental study

AU - Fiege, Adrian

AU - Holtz, François

AU - Shimizu, Nobumichi

AU - Mandeville, Charles W.

AU - Behrens, Harald

AU - Knipping, Jaayke L.

N1 - Funding Information: This project was supported by the German Science Foundation ( BE1720/25-1 to H. Behrens), by the German National Academic Foundation , and by Collaborative Research Grants from the U.S. National Science Foundation ( EAR-0838482 to C.W. Mandeville, EAR-0838436 to N. Shimizu, and EAR-0838328 to K.A. Kelley). We acknowledge Don Lindsley, Bruce Watson, Jay Thomas, Antonio Buono, for assistance with synthesis of S standard glasses, and Bruce Taylor, Minoru Kusakabe, Shuhei Ono, and Nicole Keller for assistance with sulfur isotopic analyses of synthesized glasses. Special thanks go to Alain Burgisser for providing the DCompress model and to O. Dietrich for samples preparation. We acknowledge the Synchroton Light Source ANKA for provision of instruments at their beamlines and we would like to thank J. Göttlicher and R. Steininger for assistance in using beamline SUL-X. We are grateful for the constructive reviews and helpful suggestions of the J.C.M. De Hoog, N. Métrich, T. Sisson, J.B. Lowenstern and an anonymous reviewer as well as for the editorial work of P. King. Publisher Copyright: © 2014 Elsevier Ltd. Copyright: Copyright 2014 Elsevier B.V., All rights reserved.

PY - 2014/10/1

Y1 - 2014/10/1

N2 - Glasses produced from decompression experiments conducted by Fiege et al. (2014a) were used to investigate the fractionation of sulfur isotopes between fluid and andesitic melt upon magma degassing. Starting materials were synthetic glasses with a composition close to a Krakatau dacitic andesite. The glasses contained 4.55-7.95wt% H2O, ~140 to 2700ppm sulfur (S), and 0-1000ppm chlorine (Cl). The experiments were carried out in internally heated pressure vessels (IHPV) at 1030°C and oxygen fugacities (fO2) ranging from QFM+0.8 log units up to QFM+4.2 log units (QFM: quartz-fayalite-magnetite buffer). The decompression experiments were conducted by releasing pressure (P) continuously from ~400MPa to final P of 150, 100, 70 and 30MPa. The decompression rate (r) ranged from 0.01 to 0.17MPa/s. The samples were annealed for 0-72h (annealing time, tA) at the final P and quenched rapidly from 1030°C to room temperature (T).The decompression led to the formation of a S-bearing aqueous fluid phase due to the relatively large fluid-melt partitioning coefficients of S. Secondary ion mass spectrometry (SIMS) was used to determine the isotopic composition of the glasses before and after decompression. Mass balance calculations were applied to estimate the gas-melt S isotope fractionation factor αg-m.No detectable effect of r and tA on αg-m was observed. However, SIMS data revealed a remarkable increase of αg-m from ~0.9985±0.0007 at >QFM+3 to ~1.0042±0.0042 at ~QFM+1. Noteworthy, the isotopic fractionation at reducing conditions was about an order of magnitude larger than predicted by previous works. Based on our experimental results and on previous findings for S speciation in fluid and silicate melt a new model predicting the effect of fO2 on αg-m (or δ34Sg-m) in andesitic systems at 1030°C is proposed. Our experimental results as well as our modeling are of high importance for the interpretation of S isotope signatures in natural samples (e.g., melt inclusions or volcanic gases).

AB - Glasses produced from decompression experiments conducted by Fiege et al. (2014a) were used to investigate the fractionation of sulfur isotopes between fluid and andesitic melt upon magma degassing. Starting materials were synthetic glasses with a composition close to a Krakatau dacitic andesite. The glasses contained 4.55-7.95wt% H2O, ~140 to 2700ppm sulfur (S), and 0-1000ppm chlorine (Cl). The experiments were carried out in internally heated pressure vessels (IHPV) at 1030°C and oxygen fugacities (fO2) ranging from QFM+0.8 log units up to QFM+4.2 log units (QFM: quartz-fayalite-magnetite buffer). The decompression experiments were conducted by releasing pressure (P) continuously from ~400MPa to final P of 150, 100, 70 and 30MPa. The decompression rate (r) ranged from 0.01 to 0.17MPa/s. The samples were annealed for 0-72h (annealing time, tA) at the final P and quenched rapidly from 1030°C to room temperature (T).The decompression led to the formation of a S-bearing aqueous fluid phase due to the relatively large fluid-melt partitioning coefficients of S. Secondary ion mass spectrometry (SIMS) was used to determine the isotopic composition of the glasses before and after decompression. Mass balance calculations were applied to estimate the gas-melt S isotope fractionation factor αg-m.No detectable effect of r and tA on αg-m was observed. However, SIMS data revealed a remarkable increase of αg-m from ~0.9985±0.0007 at >QFM+3 to ~1.0042±0.0042 at ~QFM+1. Noteworthy, the isotopic fractionation at reducing conditions was about an order of magnitude larger than predicted by previous works. Based on our experimental results and on previous findings for S speciation in fluid and silicate melt a new model predicting the effect of fO2 on αg-m (or δ34Sg-m) in andesitic systems at 1030°C is proposed. Our experimental results as well as our modeling are of high importance for the interpretation of S isotope signatures in natural samples (e.g., melt inclusions or volcanic gases).

UR - http://www.scopus.com/inward/record.url?scp=84908049610&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2014.07.015

DO - 10.1016/j.gca.2014.07.015

M3 - Article

AN - SCOPUS:84908049610

VL - 142

SP - 501

EP - 521

JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

SN - 0016-7037

ER -