Details
| Original language | English |
|---|---|
| Pages (from-to) | 1-16 |
| Number of pages | 16 |
| Journal | Geochimica et cosmochimica acta |
| Volume | 326 |
| Early online date | 4 Apr 2022 |
| Publication status | Published - 1 Jun 2022 |
Abstract
Sulfur is a key element in terrestrial magmatic processes yet its geochemical behavior remains one of the most difficult to model due to its heterovalent chemistry. The maximum amount of sulfur a silicate melt can dissolve before saturating with sulfide (e.g., pyrrhotite) or sulfate (e.g., anhydrite) changes with the redox state of the system and has important implications for the sulfur budget of a magmatic system. Several empirical models have been developed to predict the sulfur content of a silicate melt at either sulfide (under reducing conditions) or sulfate (under oxidizing conditions) saturation, but only one model existed that systematically assessed how the sulfur content of a basaltic melt changes as a function of oxygen fugacity (fO2) across the transition from sulfide- to sulfate-dominated conditions. The applicability of that model to intermediate and felsic melts rests on the assumption that changes in melt composition do not affect how sulfide or sulfate dissolves in the melt. Here, we report new experimental data that constrain the sulfur concentration at sulfide saturation (SCSS) and the sulfur concentration at anhydrite saturation (SCAS) in a dacitic melt as a function of fO2. The experiments were conducted using a H2O-saturated natural dacitic melt at 1000 °C, 300 MPa, and at log fO2 varying over four orders of magnitude encompassing the sulfide-sulfate transition (log fO2 = ΔFMQ−0.7, ΔFMQ+0, ΔFMQ+0.5, ΔFMQ+1, ΔFMQ+1.48, ΔFMQ+1.54, ΔFMQ+1.75, ΔFMQ+2.08 and ΔFMQ+3.3). New SCSS and SCAS data and modeling for dacitic melts reveals that the sulfide-sulfate transition occurs at ΔFMQ+1.81 ± 0.56, defined by the following equations to predict the sulfur content of intermediate to evolved silicate melts as a function of fO2:SCSSdacitic = [S2−] (1 + 10(2.00ΔFMQ – 3.05))SCASdacitic = [S6+] (1 + e(1.26 – 2.00ΔFMQ))The results presented here demonstrate that the basaltic-derived SCSS-SCAS model is not appropriate for dacitic melts and that the sulfide-sulfate transition is shifted to higher fO2 in more evolved silicate melts. Implications include the stability of sulfides to higher fO2 in more evolved silicate melts and the potential for a narrower transition from a sulfide- to a sulfate-dominated melt than that predicted by thermodynamics.
Keywords
- Dacitic melts, SCAS, SCSS, Sulfate saturation, Sulfide saturation
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Geochimica et cosmochimica acta, Vol. 326, 01.06.2022, p. 1-16.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Sulfide and sulfate saturation of dacitic melts as a function of oxygen fugacity
AU - Kleinsasser, Jackie M.
AU - Simon, Adam C.
AU - Konecke, Brian A.
AU - Kleinsasser, Michael J.
AU - Beckmann, Philipp
AU - Holtz, François
N1 - Funding Information: Financial support in the form of an International Institute Grant, a Department of Earth and Environmental Sciences Turner Award, and Rackham Graduate Student Research Grant from the University of Michigan are gratefully acknowledged as well as a National Science Foundation Graduate Research Fellowship and Society of Economic Geologists Fellowship awarded to J.M.K. The experimental work was supported by DFG (German Science Foundation) project HO 1337/43 to F.H. A.C.S acknowledges support from NSF EAR 1524394. Funding Information: We thank Dr. Owen Neill and Dr. Eric Hetland at the University of Michigan for expertise and assistance using the EPMA and fruitful conversations about modeling the SCSS and SCAS, respectively; Sarah Haselbach, Stefan Linsler, and Harald Behrens at Leibniz Universität for experimental support. The authors thank Dr. Matteo Masotta, Dr. Pedro Jugo, and three anonymous reviewers for their careful reading and comments to make the study and manuscript better. Discussions with Dr. Jugo in particular were key to understanding the results. We are also incredibly grateful for the handling and comments from AE Dr. Zoltan Zajacz and his insistence on improving key aspects of this manuscript. Financial support in the form of an International Institute Grant, a Department of Earth and Environmental Sciences Turner Award, and Rackham Graduate Student Research Grant from the University of Michigan are gratefully acknowledged as well as a National Science Foundation Graduate Research Fellowship and Society of Economic Geologists Fellowship awarded to J.M.K. The experimental work was supported by DFG (German Science Foundation) project HO 1337/43 to F.H. A.C.S acknowledges support from NSF EAR 1524394.
PY - 2022/6/1
Y1 - 2022/6/1
N2 - Sulfur is a key element in terrestrial magmatic processes yet its geochemical behavior remains one of the most difficult to model due to its heterovalent chemistry. The maximum amount of sulfur a silicate melt can dissolve before saturating with sulfide (e.g., pyrrhotite) or sulfate (e.g., anhydrite) changes with the redox state of the system and has important implications for the sulfur budget of a magmatic system. Several empirical models have been developed to predict the sulfur content of a silicate melt at either sulfide (under reducing conditions) or sulfate (under oxidizing conditions) saturation, but only one model existed that systematically assessed how the sulfur content of a basaltic melt changes as a function of oxygen fugacity (fO2) across the transition from sulfide- to sulfate-dominated conditions. The applicability of that model to intermediate and felsic melts rests on the assumption that changes in melt composition do not affect how sulfide or sulfate dissolves in the melt. Here, we report new experimental data that constrain the sulfur concentration at sulfide saturation (SCSS) and the sulfur concentration at anhydrite saturation (SCAS) in a dacitic melt as a function of fO2. The experiments were conducted using a H2O-saturated natural dacitic melt at 1000 °C, 300 MPa, and at log fO2 varying over four orders of magnitude encompassing the sulfide-sulfate transition (log fO2 = ΔFMQ−0.7, ΔFMQ+0, ΔFMQ+0.5, ΔFMQ+1, ΔFMQ+1.48, ΔFMQ+1.54, ΔFMQ+1.75, ΔFMQ+2.08 and ΔFMQ+3.3). New SCSS and SCAS data and modeling for dacitic melts reveals that the sulfide-sulfate transition occurs at ΔFMQ+1.81 ± 0.56, defined by the following equations to predict the sulfur content of intermediate to evolved silicate melts as a function of fO2:SCSSdacitic = [S2−] (1 + 10(2.00ΔFMQ – 3.05))SCASdacitic = [S6+] (1 + e(1.26 – 2.00ΔFMQ))The results presented here demonstrate that the basaltic-derived SCSS-SCAS model is not appropriate for dacitic melts and that the sulfide-sulfate transition is shifted to higher fO2 in more evolved silicate melts. Implications include the stability of sulfides to higher fO2 in more evolved silicate melts and the potential for a narrower transition from a sulfide- to a sulfate-dominated melt than that predicted by thermodynamics.
AB - Sulfur is a key element in terrestrial magmatic processes yet its geochemical behavior remains one of the most difficult to model due to its heterovalent chemistry. The maximum amount of sulfur a silicate melt can dissolve before saturating with sulfide (e.g., pyrrhotite) or sulfate (e.g., anhydrite) changes with the redox state of the system and has important implications for the sulfur budget of a magmatic system. Several empirical models have been developed to predict the sulfur content of a silicate melt at either sulfide (under reducing conditions) or sulfate (under oxidizing conditions) saturation, but only one model existed that systematically assessed how the sulfur content of a basaltic melt changes as a function of oxygen fugacity (fO2) across the transition from sulfide- to sulfate-dominated conditions. The applicability of that model to intermediate and felsic melts rests on the assumption that changes in melt composition do not affect how sulfide or sulfate dissolves in the melt. Here, we report new experimental data that constrain the sulfur concentration at sulfide saturation (SCSS) and the sulfur concentration at anhydrite saturation (SCAS) in a dacitic melt as a function of fO2. The experiments were conducted using a H2O-saturated natural dacitic melt at 1000 °C, 300 MPa, and at log fO2 varying over four orders of magnitude encompassing the sulfide-sulfate transition (log fO2 = ΔFMQ−0.7, ΔFMQ+0, ΔFMQ+0.5, ΔFMQ+1, ΔFMQ+1.48, ΔFMQ+1.54, ΔFMQ+1.75, ΔFMQ+2.08 and ΔFMQ+3.3). New SCSS and SCAS data and modeling for dacitic melts reveals that the sulfide-sulfate transition occurs at ΔFMQ+1.81 ± 0.56, defined by the following equations to predict the sulfur content of intermediate to evolved silicate melts as a function of fO2:SCSSdacitic = [S2−] (1 + 10(2.00ΔFMQ – 3.05))SCASdacitic = [S6+] (1 + e(1.26 – 2.00ΔFMQ))The results presented here demonstrate that the basaltic-derived SCSS-SCAS model is not appropriate for dacitic melts and that the sulfide-sulfate transition is shifted to higher fO2 in more evolved silicate melts. Implications include the stability of sulfides to higher fO2 in more evolved silicate melts and the potential for a narrower transition from a sulfide- to a sulfate-dominated melt than that predicted by thermodynamics.
KW - Dacitic melts
KW - SCAS
KW - SCSS
KW - Sulfate saturation
KW - Sulfide saturation
UR - http://www.scopus.com/inward/record.url?scp=85128311623&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2022.03.032
DO - 10.1016/j.gca.2022.03.032
M3 - Article
AN - SCOPUS:85128311623
VL - 326
SP - 1
EP - 16
JO - Geochimica et cosmochimica acta
JF - Geochimica et cosmochimica acta
SN - 0016-7037
ER -