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

Lithium isotopic systematics of hydrothermal vent fluids at the Main Endeavour Field, Northern Juan de Fuca Ridge
Lithium isotopic systematics of hydrothermal vent fluids at the Main Endeavour Field, Northern Juan de Fuca Ridge
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.
Lithium isotopes, Juan de Fuca Ridge, submarine hydrothermal systems, phase separation, hydrothermal alteration
0009-2541
17-26
Foustoukos, D.I.
20471030-c262-4327-928e-24b2fe260ff1
James, R.H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Berndt, M.E.
6dc66197-4e95-46b0-8a2d-f08ba31bd6d5
Seyfried, W.E.
706792e4-fce2-4349-bfb2-55e8ed9f5556
Foustoukos, D.I.
20471030-c262-4327-928e-24b2fe260ff1
James, R.H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Berndt, M.E.
6dc66197-4e95-46b0-8a2d-f08ba31bd6d5
Seyfried, W.E.
706792e4-fce2-4349-bfb2-55e8ed9f5556

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), 17-26. (doi:10.1016/j.chemgeo.2004.08.003).

Record type: Article

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.

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More information

Published date: 2004
Keywords: Lithium isotopes, Juan de Fuca Ridge, submarine hydrothermal systems, phase separation, hydrothermal alteration
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 210107
URI: http://eprints.soton.ac.uk/id/eprint/210107
ISSN: 0009-2541
PURE UUID: dac4e62b-f41c-4a4c-b6b7-bfc68d078501
ORCID for R.H. James: ORCID iD orcid.org/0000-0001-7402-2315

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Date deposited: 06 Feb 2012 13:30
Last modified: 15 Mar 2024 03:30

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Contributors

Author: D.I. Foustoukos
Author: R.H. James ORCID iD
Author: M.E. Berndt
Author: W.E. Seyfried

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