Program > Browse abstracts by speaker > Secchiari Arianna

Among volatile elements, sulfur plays a pivotal role in deep Earth geochemical cycling, influencing the redox state of the mantle, metal transport, and ore formation. In subduction zones, fluid-mediated reactions drive the transfer of elements from the subducting slab to the mantle wedge. However, the mechanisms governing sulfur mobility and speciation in these fluids remain poorly constrained due to the experimental challenges of measuring sulfur-bearing volatiles. These primarily stem from the analysis of ultra-low fluid amounts in experimental capsules and the high reactivity of sulfur species, which can alter the composition of high-pressure and high-temperature (HP-HT) fluid during and after synthesis.

To address this knowledge gap, we have developed a novel analytical protocol that enables accurate, high-precision measurement of sulfur-bearing volatile species (H₂S, SO₂) in experimental HP–HT fluids.

A series of experiments was conducted under geologically relevant conditions (P = 3 GPa, T = 700°C) simulating subarc environments, with controlled oxygen fugacity and runtimes ranging from six hours to one week. The resulting volatiles were analyzed using a capsule-piercing device coupled to a quadrupole mass spectrometer (Tiraboschi et al., 2016) calibrated with gas mixtures of known composition.

Our findings confirm that the bulk fluid composition was preserved throughout synthesis and quenching, validating thermodynamic predictions. Moreover, we demonstrate for the first time that chemical equilibrium between the solid and fluid phase is achieved within five hours and that the sulfide phase remains inert, even under relatively oxidizing conditions.

This methodology marks a major step forward, providing a robust tool for investigating sulfur volatiles' behavior in subduction zone fluids. Future applications include extending the protocol to more chemically complex systems and exploring sulfur's interactions with other volatile species in deep Earth environments. These advancements will enhance our understanding of sulfur cycling in subduction zones and its broader implications for metallogenic processes.