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Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas

  • Ruifang Huang and Hans Keppler EMAIL logo
Published/Copyright: January 10, 2015
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American Mineralogist
From the journal American Mineralogist Volume 100 Issue 1

Abstract

The distribution of sulfur in the system Na2O-K2O-CaO-Al2O3-SiO2-H2O-S was investigated at 2 kbar, 750-950 °C, and oxygen fugacities ranging from the Co-CoO to the Re-ReO2 buffer. Anhydrite (CaSO4) crystallized in all the experiments conducted at oxidizing conditions (Ni-NiO + 0.5 to 1 and above). Under otherwise equal conditions, an inverse relationship between sulfur and CaO concentration was observed in melts coexisting with anhydrite, with the solubility product K = [CaO][SO3] being constant, where [CaO] and [SO3] are the molar fraction of CaO and SO3 in the quenched glasses. This suggests that anhydrite dissociates upon dissolution in the melt according to CaSO4anhydrite = Ca2+melt + SO42-melt. The solubility product strongly depends on temperature, with lnK = - (28 573 ± 917)/T + (11.26 ± 0.80). This corresponds to an enthalpy of dissolution of ΔHR = 237.5 ± 7.6 kJ/mol. Under reducing conditions (Co-CoO and Ni-NiO buffer), CaO has no effect on the fluid/melt partition coefficient of sulfur Dsfluid/melt. At 850 °C, 2 kbar partition coefficients were 519 ± 30 at the Ni-NiO buffer and 516 ± 11 at the Co-CoO buffer, for CaO contents in the melt up to 1 wt%. These data are virtually identical to those measured in the CaO-free haplogranite system under reducing conditions. However, under more oxidizing conditions, the fluid/melt partition coefficient of sulfur appeared to have increased somewhat in the presence of CaO. This increase may, however, also be related to the fact that the final melt compositions in these runs were distinctly peraluminous. Our data show that calcium has no effect on the degassing of sulfur at reducing conditions, but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite.

Keywords: Anhydrite; sulfur; haplogranite; solubility; partitioning; oxygen fugacity
Received: 2014-3-3
Accepted: 2014-8-6
Published Online: 2015-1-10
Published in Print: 2015-1-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2015-4959
Keywords for this article
Anhydrite; sulfur; haplogranite; solubility; partitioning; oxygen fugacity

Articles in the same Issue

  1. The American Mineralogist at 100 years, and a mineralogy renaissance
  2. At the blurry edge of mineralogy
  3. Mineral evolution and Earth history
  4. Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex
  5. The rapid expansion of environmental mineralogy in unconventional ways: Beyond the accepted definition of a mineral, the latest technology, and using nature as our guide
  6. Microelectronic junctions in arsenian pyrite due to impurity and mixed sulfide heterogeneity
  7. The structure of water-saturated carbonate melts
  8. In-situ measurements of fluorine and chlorine speciation and partitioning between melts and aqueous fluids in the Na2O-Al2O3-SiO2-H2O system
  9. High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultrahigh-pressure chromitites in ophiolites
  10. Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate minerals
  11. Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland)
  12. Tourmaline as a petrogenetic monitor of the origin and evolution of the Berry-Havey pegmatite (Maine, U.S.A.)
  13. Applications of Hirshfeld surfaces to mineralogy: An example of alumohydrocalcite, and the classification of the dundasite group minerals
  14. Optical absorption anisotropy of high-density, wide-gap, high-hardness SiO2 polymorphs seifertite, stishovite, and coesite
  15. The system Na2CO3-FeCO3 at 6 GPa and its relation to the system Na2CO3-FeCO3-MgCO3
  16. Chlorine-hydroxyl diffusion in pargasitic amphibole
  17. The use of cation-cation and anion-anion bonds to augment the bond-valence model
  18. AIM analysis and the form of the bond-valence equation
  19. Atomistic simulation on mixing thermodynamics of calcite-smithsonite solid solutions
  20. Combined geochemistry and geochronology constrains coupled subduction of oceanic and continental crust in the Huwan shear zone, central China
  21. Near-infrared investigation of folding sepiolite
  22. First-principles study of sulfur isotope fractionation in pyrite-type disulfides
  23. Tetrataenite in terrestrial rock
  24. Thermo-compression of pyrope-grossular garnet solid solutions: Non-linear compositional dependence
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  27. Synthetic and natural ammonium-bearing tourmaline
  28. Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas
  29. Nuragheite, Th(MoO4)2·H2O, The Second Natural Thorium Molybdate And Its Relationships To Ichnusaite And Synthetic Th(MoO4)2†
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