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Lithium isotopic systematics of hydrothermal vent fluids at the Main Endeavour Field, Northern Juan de Fuca Ridge

Foustoukos, D. I.; James, R. H.; Berndt, M. E. and Seyfried, W. E . (2004). Lithium isotopic systematics of hydrothermal vent fluids at the Main Endeavour Field, Northern Juan de Fuca Ridge. Chemical Geology, 212(1-2) pp. 17–26.

DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1016/j.chemgeo.2004.08.003
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Abstract

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.
ISSN: 0009-2541
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)
Item ID: 10488
Depositing User: Rachael James
Date Deposited: 31 Mar 2008
Last Modified: 20 Jul 2011 11:11
URI: http://oro.open.ac.uk/id/eprint/10488
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