115 Petrology, Volcanology, and Mantle Plumes across the Solar System (Posters)

This session focuses on recent advances in characterizing and quantifying volcanic processes throughout the Solar System in light of recent and upcoming missions to volcanically active worlds and resurgence in volcano science.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

The Effect of Sulfur on Hydrous Partial Melting in the Mantle Wedge

Paper number: 115-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Oceanic crust carries volatile elements such as water (H2O) and sulfur (S) into the mantle as it subducts. As oceanic crust experiences increasing pressures and temperatures, volatile-bearing minerals are destabilized, releasing H2O and S into the mantle. Previous experimental studies have demonstrated that the presence of H2O decreases the solidus of mantle rocks, but the role of S on magma formation in the mantle wedge is less understood. Under different redox conditions, sulfur can exist as either S2- or S6+, affecting the stability of minerals and partial melts in different ways. However, the effect of sulfur valence on mantle melting has yet to be tested experimentally. We studied the effects of S valence on primary arc magma formation with piston cylinder experiments at 1250 °C and 1 GPa in gold-palladium (Au90Pd10) capsules. Our starting compositions consisted of peridotite (KLB-1) with added H2O and S. Two different experimental designs were employed to induce reducing and oxidizing conditions to fix the presence of S as either S2- or S6+. Additionally, control experiments were run with the same amount of H2O, but no S. All experiments were analyzed using an electron microprobe. Under oxidizing conditions, where S is present as sulfate (S6+), higher melt fractions were produced relative to reducing conditions (S as S2-) at identical pressure and temperature. Relative to the sulfur free experiments, the addition of sulfide (S2-) and sulfate (S6+) to hydrous peridotite decreases and increases melt fractions, respectively. These results suggest that sulfate is acting as a flux in the mantle to promote melting, while sulfide is not, likely due to the greater stability of sulfide minerals relative to sulfate minerals at high temperatures. More broadly, our experiments imply that the melt fraction is influenced by the oxidation state of the mantle wedge.

 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413640

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