Fluid Inclusion Evidence for Subseafloor Magmatic-Hydrothermal Processes at Brothers Volcano, Kermadec Arc, New Zealand

Abstract Brothers volcano is a submarine dacitic caldera located on the southern Kermadec arc. It is host to the NW Caldera vent field (Site U1530 and Hole U1530A), which locally discharges more focused, metal-rich fluids, and the Upper Cone hydrothermal vent field (Site U1528 and Hole U1528D), which discharges predominantly diffuse, acidic fluids (pH 1.9). These two active vent sites were drilled in 2018 by International Ocean Discovery Program (IODP) Expedition 376. Fluid inclusions hosted in anhydrite, quartz, barite, and alunite recovered from drill core samples were studied by microthermometry, Raman spectroscopy, and laser ablation-inductively coupled plasma-mass spectrometery (LA-ICP-MS) to obtain detailed depth profiles of temperature, salinity, and composition of the hydrothermal fluids. These analyses allow for a better understanding of complex hydrothermal processes such as ph…