Sulfur and the redox evolution of arc magmas

Petrologists have observed for long time that arc magmas are commonly oxidized relative to mid-ocean ridge basalts, but the processes that drive this difference are still debated. The transport of sulfur in and out of arc magmas during subducting slab dehydration, magma degassing, and sulfide mineral precipitation can influence the redox state of magmas. Conversely, the solubility of sulfur in magmas is closely tied to oxidation state, and sulfur can act as a valuable tracer of magma redox evolution. These projects use the geochemistry of primitive melt inclusions to tease apart these processes, yielding valuable insights in magma evolution that have implications for things like volcano gas monitoring, ore deposit formation, and arc magma petrogenesis.

• Sulfate cycling in the southern Cascade Arc

• Global sulfur cycling

Iron and sulfur redox state during the cooling of basaltic melts

Measuring the relative concentrations of redox-senstitive elements like sulfur (present at S⁶⁺ and S^2- in basaltic melts) and iron (present as Fe³⁺ and Fe²⁺ in basaltic melts) in volcanic glass is an incredibly precise and powerful means to study melt redox state. However, this is only true if volcanic glass accurately records the conditions of the melt at higher temperature. In this work, we use the rapidly quenched rims of seafloor pillows to test whether sulfur and iron valence state in basaltic melts undergo changes during the processes of cooling and quenching to volcanic glass.

• Submarine Pillows as Natural Experiments for S and Fe cooling behavior

Micro-analysis of volcanic glass

The chemistry of volcanic glass is an incredibly useful record of magmatic system. As part of our work, we are interesting in pushing the boundaries of what we can learn from seafloor glasses and crystal-hosted glass inclusions. We use techniques like XANES, SIMS, LA-ICPMS, and EPMA to study the structure, isotopic chemistry (e.g. σ³⁴S), and trace element geochemistry (including metals such as Cu, Zn, W, Mo, etc.) of basaltic melts.

• Methods development for the analysis of S and Fe via XANES in beam-sensitve glasses

• An example application of in-situ sulfur isotope analyses in the Cascade arc