Lithium isotope geochemistry of marine pore waters: Insights from cold seep fluids.

Scholz, Florian, Hensen, Christian, De Lange, G. J., Haeckel, Matthias, Liebetrau, Volker, Meixner, A., Reitz, Anja and Romer, R. L. (2010) Lithium isotope geochemistry of marine pore waters: Insights from cold seep fluids. Geochimica et Cosmochimica Acta, 74 . pp. 3459-3475. DOI 10.1016/j.gca.2010.03.026.

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Abstract

Lithium concentration and isotope data (δ7Li) are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments, a sediment-hosted hydrothermal system and two Mediterranean brine basins. The new reference data and literature data of hydrothermal fluids and pore fluids from the Ocean Drilling Program follow an empirical relationship between Li concentration and δ7Li (δ7Li = −6.0(±0.3) · ln[Li] + 51(±1.2)) reflecting Li release from sediment or rocks and/or uptake of Li during mineral authigenesis. Cold seep fluids display δ7Li values between +7.5‰ and +45.7‰, mostly in agreement with this general relationship. Ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite–illite is the major sink for light pore water Li in deeply buried continental margin sediments. Deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport-related fractionation trends. Pore fluids on passive margins receive disproportionally high amounts of Li from intensely weathered and transported terrigenous matter. By contrast, on convergent margins and in other settings with strong volcanogenic input, Li concentrations in pore water are lower because of intense Li uptake by alteration minerals and, most notably, adsorption of Li onto smectite. The latter process is not accompanied by isotope fractionation, as revealed from a separate study on shallow sediments. A numerical transport-reaction model was applied to simulate Li isotope fractionation during upwelling of pore fluids. It is demonstrated that slow pore water advection (order of mm a−1) suffices to convey much of the deep-seated diagenetic Li signal into shallow sediments. If carefully applied, Li isotope systematics may, thus, provide a valuable record of fluid/mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure.

Document Type: Article
Keywords: Hydrology; Geochemistry
Research affiliation: OceanRep > SFB 574 > B6
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574
OceanRep > SFB 574 > B5
GFZ
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gca.2010.03.026
ISSN: 0016-7037
Projects: West Nile Delta, SFB574
Contribution Number:
ProjectNumber
SFB 574185
Expeditions/Models/Experiments:
Date Deposited: 03 Jun 2010 09:46
Last Modified: 27 Sep 2017 13:34
URI: http://oceanrep.geomar.de/id/eprint/8454

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