Open AccessChemistry of hydrothermal vent fluids from the Main Endeavour Field, northern Juan de Fuca Ridge: Geochemical controls in the aftermath of June 1999 seismic events
Author(s) -
Seyfried W. E.,
Seewald J. S.,
Berndt M. E.,
Ding Kang,
Foustoukos D. I.
Publication year - 2003
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002jb001957
Subject(s) - hydrothermal vent , hydrothermal circulation , chloride , seawater , geology , brine , supercritical fluid , ridge , boron , mid ocean ridge , mineralogy , geochemistry , chemistry , oceanography , paleontology , organic chemistry
In June 1999, an intense swarm of earthquakes occurred on the Endeavour segment of the Juan de Fuca Ridge influencing hydrothermal activity in and around the Main Endeavour Field (MEF). Here we report the dissolved concentrations of 31 species from five high‐temperature vents sampled 3 months after the seismic event. The spatial variability of vent fluid chemistry is extreme. Vapor‐dominated vent fluids at Cantilever and Sully sites have high measured temperatures (375°–379°C), high dissolved gas and boron concentrations, but low SiO 2 . Modeling results indicate that these fluids can be accounted for by supercritical phase separation and brine condensation. Other vent fluids have moderate temperatures (340°–366°C) and chloride concentrations (208–426 mmol/kg), and may result from mixing of supercritical, vapor‐rich fluids with evolved seawater. Phase equilibria calculations indicate that in addition to chloride, redox, temperature, and especially pressure play key roles in accounting for compositional variability of vent fluids at MEF. In comparison with earlier (1988) data, the 1999 data set reveals significantly lower chloride concentrations and higher boron, whereas alkali and alkaline earth cations are lower by 10–20% in keeping with chloride decrease. That dissolved chloride, boron, and other elements returned to preevent levels when again sampled in 2000 provide additional data documenting the inherently dynamic nature of hydrothermal systems at mid‐ocean ridges.