Experimental Investigation of Lithium Partitioning among Plagioclase, Rhyolitic Melt, and H2O Vapor

Volcanic eruptions are unpredictable and present a significant challenge for volcanic crisis management, primarily due to the variety of eruptive styles, ranging from effusive to explosive. By elucidating the dynamics of magma ascent, with a focus on degassing, we can better understand of the interconnections between petrological characteristics, geochemical and geophysical signals, volcanic hazards, and volcano monitoring. To this aim, lithium (Li), which has a high mobility in both silicate melts and crystals, has been used as a geospeedometer to monitor short-time processes, such as syn-eruptive magma ascent and degassing and post-eruptive processes (cooling). Yet, to appropriately interpret Li data in crystals from volcanic deposits, a clear understanding of the Li behavior and partitioning between the crystal-melt-fluid phases during an eruption is essential. Most of the Li partitioning data rely on glass inclusions and their host minerals, which do not always guarantee equilibrium conditions. Experimental data are largely missing, especially in the case of silica-rich hydrated magmas. Therefore, we provide Li contents and partitioning via phase-equilibrium experiments for analyzable-sized plagioclases crystallized from Li-bearing H2O-saturated rhyolitic melts at pressures from 50 to 150 MPa and temperatures of 800 and 875 °C. In addition to its applications in volcanology, this research could yield valuable information for assessing the economic viability of lithium in felsic deposits, specifically those with rhyolitic/granitic compositions (as highlighted by Benson et al., 2017), and in magmatic fluids. Moreover, it holds futuristic potential for extracting lithium directly from these fluids.