Geochemistry of seafloor hydrothermal vent fluids at EPR 9°50'N: Time series data from 2004-2016
Abstract
Hydrothermal fluids were collected from vent sites along the East Pacific Rise (EPR) at 9°50'N in 2004, 2008 and 2016 in isobaric gas-tight titanium samplers. These dates bracket the seafloor eruption that occurred at EPR 9°50'N between 2005 and 2006. The reported data focus on P vent and Bio9, as these vents were active during all three sampling periods. The concentration of aqueous volatiles reached maxima at both vents in 2008. At P vent, CO2, H2, and H2S were 124 mM/kg, 0.55 mM/kg and 12.2 mM/kg, respectively. The concentrations at Bio9 in 2008 were, 106 mM/kg CO2, 1.1 mM/kg H2, and 12.6 mM/kg H2S. Fe and Mn concentrations were the highest at both vent sites in 2004, and then decreased in 2008 and again in 2016. The range at P vent was 1.5-6.3 mM/kg Fe and 315-1212 uM/kg Mn, while at Bio9 the concentrations were 1.6-3.7 mM/kg Fe and 301-650 uM/kg Mn. The trends in CO2, H2, and H2S at P vent (2008 and 2016) and Bio9 (all years) are consistent with changes in subsurface pressure and temperature as a result of the eruption that alter the conditions at which dissolved components partition between vapor and liquid phases in the NaCl-H2O system. The trend in Fe and Mn concentrations is surprising and highlights the complex partitioning behavior of these elements in systems in which the concentrations are controlled by fluid-mineral equilibria as well as phase separation. Between 2004 and 2008, fluids at P vent transitioned from single-phase (535 mM/kg Cl) to a low-density vapor (370 mM/kg). Upon phase separation, the concentrations of H2S and H2 increased, while Fe and Mn concentrations decreased considerably. These changes highlight the importance of phase separation on controlling mass transfer from the crust to overlying ocean. In contrast to the other aqueous volatiles, CH4 concentrations in 2008 (47 µM) were lower or equal to concentrations in 2004 or 2016, 50-100 µM. CH4 is decoupled from the effects of phase separation, and is likely extracted from fluid inclusions in the host rock by circulating fluids. Li and CH4 concentrations follow similar patterns over time, supporting a rock-based source for CH4. That CO2 concentrations are elevated (relative to pre-eruption and 2016 values) up to two years after the eruption informs our understanding of the rates of heat and mass transfer in MOR hydrothermal systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.V14A..03S
- Keywords:
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- 1009 Geochemical modeling;
- GEOCHEMISTRY;
- 1032 Mid-oceanic ridge processes;
- GEOCHEMISTRY;
- 1034 Hydrothermal systems;
- GEOCHEMISTRY;
- 1832 Groundwater transport;
- HYDROLOGY