Abstract
Loki's Castle at 73°30′ N along the Arctic Mid-Ocean Ridge (AMOR) provides a natural laboratory to study the evolution of hydrothermal circulation in an ultraslow-spreading environment. In addition, a sedimentary input into the Loki's Castle hydrothermal circulation cell is indicated by vent fluid and gas chemistry. Here we present B and Sr isotope data to investigate interaction between fluid, MORB and sediment and to constrain mass transfer during hydrothermal circulation of a sediment-influenced, black smoker hydrothermal system. The high boron concentrations (1770–2170μmol/l) and the relatively low boron isotope composition of the vent fluids (δ11B values ranging from +11.6 to +15.2‰) reflect not only fluid/rock interaction with mafic crust but indicates a significant contribution from sediments, in agreement with other chemical and isotopic (87Sr/86Sr) analyses. We present a model of B extraction from sediments at a temperature of 300°C, which suggests a water/sediment ratio of approximately 2 to 3 at Loki's Castle. At these ratios, relative B extraction from sediment ranges from 35 to 55%.
Published Version
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