Sulfide saturation and resorption modulates sulfur and metal availability during the 2014–15 Holuhraun eruption, Iceland

Abstract

Mafic magmas may experience multiple stages of sulfide saturation and resorption during ascent and differentiation. Quenched tephra erupted during the 2014–15 Holuhraun eruption preserve abundant evidence for sulfide resorption, offering a rare opportunity to explore the sulfide life cycle from nucleation to resorption. Specifically, we combine detailed textural and chemical analyses of sulfides and silicate melts with geochemical models of sulfide saturation and degassing. This integrative approach demonstrates that sulfides began nucleating in melts with ~8 wt% MgO, persisted during fractionation to 6.5 wt% MgO, before resorbing heterogeneously in response to sulfur degassing. Sulfides are preserved preferentially in confined geometries within and between crystals, suggesting that kinetic effects impeded sulfur loss from the melt and maintained local sulfide saturation on eruption. The proportion of sulfides exhibiting breakdown textures increases throughout the eruption, coincident with decreasing magma discharge, indicating that sulfide resorption and degassing are kinetically limited. Sulfides likely modulate the emission of sulfur and chalcophile elements to the atmosphere and surface environment, with implications for assessing the environmental impacts and societal hazards of basaltic fissure eruptions.