Efficient release of bromine by super-eruptions

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Waelkens, C. M., Stix, J., Monteleone, B., & Burckel, P. Efficient release of bromine by super-eruptions. Geology, 49(12), (2021): 1416–1420, https://doi.org/10.1130/G49114.1.Bromine is a key halogen element in the quantification of volcanic volatiles, but analytical difficulties in measuring its very low abundances have prevented progress in understanding its behavior and its role in volcanic emissions. We present a new data set of bromine, chlorine, and fluorine concentrations in melt inclusions and matrix glasses for two rhyolitic super-eruptions from the Toledo and Valles calderas, New Mexico, USA. We show that before eruption, Br and Cl were efficiently partitioned from the gas-saturated magma into a separate fluid phase, and we calculate the mass of halogens in the fluid phase. We further demonstrate that syn-eruptive magma degassing was negligible during the super-eruptions, so that the main source of halogen emissions must have been the fluid phase. If the fluid phase were erupted, the large mass of Br and Cl could have severely impacted the atmospheric chemistry upon eruption.This research was supported by a Geological Society of America grant (C. Waelkens), Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery and CREATE grants (J. Stix), and Institut de Physique du Globe de Paris multidisciplinary program PARI and Paris–IdF region SESAME grant 12015908 (P. Burckel). The Northeast National Ion Microprobe Facility is subsidized by U.S. National Science Foundation (NSF) facility support grant NSF-EAR-1664308