ALBERT

Description: This dataset contains the rawdata of a microthermometric study of fluid inclusions in hydrothermal precipitates and 87Sr/86Sr composition of their host sulfate minerals. The samples were recovered at Brothers volcano, originate from the NW Caldera and the Upper Caldera vent sites and were retrieved during RV Sonne cruise SO253 in December 2016/January 2017 and during RV Thompson cruise TN350 in March 2018. The fluid inclusion dataset contains 〉400 measurements of ice melting temperatures, 〉340 measurements of homogenization temperatures and includes a detailed descriptions of the measured fluid inclusions. The 87Sr/86Sr dataset contains Thermal Ionization Mass Spectrometry (TIMS) measurments of 5 single crystal and 6 bulk samples of the fluid inclusion (sulfate) samples or material taken in direct adjacency.

Description: Calculated end-member compositions of hydrothermal fluids (for samples that have at least ≥ 85 % end-member) from Haungaroa, Brothers Upper Caldera and NW Caldera Wall, Kermadec intraoceanic arc. Ambient background seawater concentrations are given for comparison.

Description: Rare Earth Element and yttrium (REY) concentrations measured with ICP-MS in hydrothermal fluids from the Kermadec intraoceanic arc. Seawater from 1000 m water depth, values for SW are * 100 (SW data from Alibo and Nozaki (1999; doi:10.1016/S0016-7037(98)00279-8)).

Description: Comparison of Brothers hydrothermal fluid composition collected by de Ronde et al. (2011; doi:10.1007/s00126-011-0345-8) with data collected during this study. In this study, only samples taken with IGT and Major samplers with end-member concentrations greater than 50% are shown. The three samples from the Upper Caldera Site are not included within this data set.

Description: Overview of all fluid samples collected during SO253 along the Kermadec intraoceanic arc together with parameters that were analyzed directly onboard.Fe were determined by a visual Fe CHEMets© field kit.

Description: Major, minor and trace element concentrations measured with ICP-OES, ICP-MS and data for SO42- in hydrothermal fluids from the Kermadec intraoceanic arc.

Description: This dataset provides the rawdata of an extensive microthermometric study of fluid inclusions in hydrothermal precipitates recovered at Brothers volcano. Samples originate from the NW Caldera and the Upper Caldera vent sites and were retrieved during RV Sonne cruise SO253 in December 2016/January 2017 and during RV Thompson cruise TN350 in March 2018. The dataset contains 〉400 single measurements of ice melting temperatures, 〉340 measurements of homogenization temperatures and includes a detailed descriptions of the measured fluid inclusions.

Description: This dataset provides 87Sr/86Sr in hydrothermal precipitates recovered at the Brothers volcano. Samples originate from the NW Caldera and the Upper Caldera vent sites and were retrieved during RV Sonne cruise SO253 in December 2016/January 2017 and during RV Thompson cruise TN350 in March 2018. All samples were analyzed using Thermal Ionization Mass Spectrometry (TIMS). The dataset contains measurements of 87Sr/86Sr in single crystals of anhydrite or barite and measurements of 87Sr/86Sr in sulfate bulk samples composing of anhydrite and/or barite.

Description: The northwestern caldera wall of Brothers volcano in the southern Kermadec arc features several clusters of hydrothermal venting in a large area that extends from near the caldera floor (~1700 mbsl) almost up to the crater rim (~1300 mbsl). Abundant black smoker-type hydrothermal chimneys and exposed stockwork mineralization in this area provide an excellent archive of hydrothermal processes that form seafloor massive sulfide deposits. Using sulfate precipitates from chimneys and stockwork recently recovered by remotely operated vehicles, we conducted fluid inclusion microthermometry and Sr isotope studies to determine the role of phase separation and mixing between vent fluid and seawater. The variability in the vast majority of fluid inclusion salinities (i.e., 0.1–5.25 wt.% NaCl eq.) and entrapment temperatures of up to 346°C are indicative of phase-separated hydrothermal fluids. Large salinity variations in samples with entrapment temperatures mostly below the boiling temperature for the sample’s depth show that the majority of fluids ascending below the NW Caldera are phase separating in the subsurface and cooling, prior to discharge. In several samples, entrapment temperatures of over 343°C suggest that phase-separating fluids have at least sporadically exited the seafloor at the NW Caldera site. Isobaric-isenthalpic mixing trends between coexisting phase-separated vapors and brines with seawater are consistent with phase-separated fluids at near-seafloor pressures of ~170 bar and suggest that the vast majority of the ascending fluids continue to phase separate to within tens to hundreds of meters below seafloor prior to mixing with seawater. A small subset of the most saline fluid inclusions (up to 18.6 wt.% NaCl eq.) is unlikely formed by near-seafloor phase separation and is considered to be produced either by supercritical phase separation or by the contribution of a magmatic brine from near the magmatic-hydrothermal interface. 87Sr/86Sr values of sulfate samples range from 0.7049 (i.e., near hydrothermal end-member) to 0.7090 (i.e., near seawater) and show that the crystals grew from vapor- and brine-derived fluids in a hydrothermally dominated mixing regime. Our work provides new insights into mineral growth conditions, mixing regimes, and in particular, the extent and character of subseafloor phase separation during the formation of hydrothermal vents and their underlying stockwork in seawater-dominated, arc-related hydrothermal systems.