Other
Scientific paper
Feb 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.114..517m&link_type=abstract
Earth and Planetary Science Letters, Volume 114, Issue 4, p. 517-528.
Other
17
Scientific paper
DSRV Alvin dives in the Northern Mariana island arc recovered warm hydrothermal fluids from the summit areas of seamounts Kasuga 2 and Kasuga 3, as well as hydrothermal deposits of elemental sulfur, Fe- and Mn-oxides, and nontronite. The composition of a gas-rich ~ 39°C vent fluid sampled from Kasuga 2 Seamount is unusual compared to other submarine hydrothermal fluids in that it is enriched by 27% in Mg2+ and 17% in SO42-, and depleted by 64% in Ca2+, relative to ambient seawater. The elevated concentrations of dissolved CO2 (calculated from pH and ArmT), HCO3- and SO42+, and near absence of H2S, suggest that the unusual composition of this sample may result from the sub-seafloor addition of volcanic CO2 and SO2 to a seawater-derived hydrothermal fluid, resulting in: (1) `chemical weathering' reactions, whereby igneous minerals or alteration phases are attacked by CO2, adding Mg2+ and other cations, Si, and HCO3- into solution; and (2) hydrolysis of SO2 to SO42- and S(0), adding excess SO42- with a light δ34S signature to the fluid and causing deposition of elemental sulfur at the seafloor vents. Saturation-state calculations suggest that the concentrations of Si and Ca2+ in the fluid may be controlled at saturation with amorphous silica and dolomite respectively. The origin of the 9.3°C fluid collected from Kasuga 3 is difficult to determine because it is compositionally close to ambient seawater and shows possible evidence of both high- and low-temperature seawater-rock reaction. Banded and interlayered deposits of nontronite and Fe- and Mn-oxides were recovered from the Kasuga 3 summit, with oxygen-isotope geothermometry suggesting a formation temperature of ~ 22°C for the nontronite.
Fryer Patricia
McMurtry Gary M.
Sedwick Peter N.
Vonderhaar D. L.
Yeh Hsueh-Wen
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