Foustoukos, D. I.; James, R. H.; Berndt, M. E. and Seyfried, W. E .
|DOI (Digital Object Identifier) Link:||http://doi.org/10.1016/j.chemgeo.2004.08.003|
|Google Scholar:||Look up in Google Scholar|
Vent fluids issuing from the Main Endeavour Field (MEF), Juan de Fuca Ridge, were analyzed for δ7Li to help constrain subseafloor hydrothermal alteration and phase separation processes. Magmatic activity prior to sampling of the fluids in 1999 enhanced heat and mass transfer, as indicated by the large scale, but temporary, changes in vent fluid chemistry. In particular, dissolved chloride concentrations indicate formation of supercritical Cl-poor vapors, which affected alteration throughout the MEF system. δ7Li of fluids, however, ranges from +7.2 to +8.9‰ and reveals no significant correlation with dissolved chloride, being consistent with results of hydrothermal experiments that show no lithium isotope fractionation during supercritical phase separation. On a chloride-normalized basis, Li concentration data indicate relatively short residence times or high fluid/rock mass ratios of vent fluids most impacted by phase separation effects. Reaction path models involving Li isotope data also show elevated fluid/rock mass ratios. Boron data, in contrast, suggest direct input from degassing magma. Enhanced heat flow associated with magmatic injection at depth inhibits penetration of seawater-derived hydrothermal fluid into fresh basalt, particularly in those systems where magmatic volatile input is most active. The inverse correlation between Li/Cl and B/Cl in vapor-rich vent fluids may be a useful indicator of recent subseafloor magmatic activity.
|Item Type:||Journal Article|
|Copyright Holders:||2004 Elsevier B.V.|
|Keywords:||Lithium isotopes; Juan de Fuca Ridge; submarine hydrothermal systems; phase separation; hydrothermal alteration|
|Academic Unit/Department:||Science > Environment, Earth and Ecosystems
|Interdisciplinary Research Centre:||Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)|
|Depositing User:||Rachael James|
|Date Deposited:||31 Mar 2008|
|Last Modified:||14 Jan 2016 16:53|
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