ALBERT

Description: The dataset contains B, Li, Mg and Sr concentrations and isotopic compositions of black-smoker, acid-sulfate fluids and "hybrid-types" as well as of fresh and altered rocks from different vent fields (DESMOS and North Su) within the Manus Basin, Papua New Guinea. The data is used to understand the controls of their compositional variability. In particular, the formation of acid-sulfate and hybrid smoker fluids is still poorly understood, and their high Mg concentrations are explained either by dissolution of Mg-bearing minerals in the basement or by mixing between unmodified seawater and magmatic fluids. Mg isotope ratios of the acid-sulfate fluids from Manus Basin are seawater-like, which supports the idea that acid-sulfate fluids in this study area predominantly form by mixing between unmodified seawater and a Mg-free magmatic fluid. Changes in the B, Li, and Sr isotope ratios relative to seawater indicate water-rock interaction in all acid-sulfate fluids. Further, the combination of δ7Li with B concentrations of the same fluids links changes in δ7Li to changes in (1) basement alteration, (2) water-to-rock ratios during water-rock interaction and/or (3) the reaction temperature. These isotope systems, thus, allow tracing of basement composition and acid-sulfate driven alteration of the backarc crust, and help increase our understanding of hydrothermal fluid-rock interactions and the behavior of fluid-mobile elements.

Description: The dataset contains boron (B) concentrations and isotope ratios of hydrothermal vent fluids and volcanic rocks from different vent fields within the Manus Basin, Papua New Guinea, and Nifonea volcano, New Hebrides back-arc. The fluids from these settings show a range of salinities, gas contents, acidities, and host rock compositions; many of them are influenced by phase separation and by addition of magmatic volatiles (both CO2 and SO2). Previous studies of hydrothermal vents in arc/back-arc settings suggest that B contents and isotopic composition of vent fluids are controlled by interactions between seawater, basement and sediments, and propose that phase separation and magmatic fluids play only a subordinate role. In our study, we demonstrate that vent fluids with minor magmatic input indeed reflect the interaction between seawater and oceanic crust. In contrast, the low-salinity Nifonea fluids and some of the acid-sulfate fluids from the Manus Basin have higher B contents as expected, whereas other volatile-rich fluids from the Manus Basin show B depletions. The lack of correlation between B contents and the intensity of magmatic fluid influx (CO2 and SO2) may indicate that magma degassing is not responsible for the B enrichments or depletions in these vent fluids. B enrichments might be related to preferential partitioning of B into the vapour phase during phase separation under PT-conditions well above the two-phase curve and critical line (i.e. T 〉〉 Tcritical, P 〉〉 Pcritical). However, this cannot explain the low B concentrations in the vapour-rich vent fluids from the Manus Basin and the low B isotope ratios in the Nifonea fluids. Instead, we propose that B concentrations and isotope ratios in submarine vent fluids largely depend on the residence and reaction time of the vent fluid in the subsurface. In general, all vent fluids are still influenced by water-rock interaction during hydrothermal circulation. However, vent fluids with short residence times define a trend towards lower B concentrations and isotope ratios, which can be explained by mixing between hydrothermal and magmatic fluid, which is similar to the composition of the host rock. In contrast, the B signature of the magmatic fluid can be overprinted due to preferential mobilization of B from the oceanic crust into vapour-rich fluids at longer reaction times. Thus, B may provide a tool for estimating the extent of B leaching and hence hydrothermal alteration in the subseafloor.

Description: Calculated pure hydrothermal end-member Li and B isotope compositions in high-temperature fluids from Brothers volcano, Kermadec Arc, Western Pacific collected during SO-253 cruise. Boron and Li isotope compositions of the high-temperature vent fluids from Brothers Volcano are in the range of other black smoker fluids from the Western Pacific and imply water-rock interaction at low water/rock ratios.

Description: Lithium, boron and magnesium isotope compositions in high-temperature and acid-sulfate fluids from Brothers and Macauley volcano, Kermadec Arc, Western Pacific collected during SO-253 cruise. The acid-sulfate fluids exceed Mg concentrations of seawater and differ from previously known acid-sulfate fluids with seawater-like Mg concentrations. Based on our data, we explain the Mg enrichments with venting of a brine phase (Macauley volcano) and dissolution of caminite and Mg leaching from the ocean crust (Lower Cone, Brothers Volcano).

Description: We obtained altered basaltic upper basement from the modern Nankai Trough seaward of the trench, recovered by drilling on IODP Expedition 333. We performed laboratory friction experiments on bare surfaces and gouge powders of this material, in addition to and in combination with other materials for comparison. Based our friction data, we suggest that in addition to creep the altered Nankai basalts may also allow the possibility of slow slip events.