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Behavior of Li and its isotopes during serpentinization of oceanic peridotites

Behavior of Li and its isotopes during serpentinization of oceanic peridotites
Behavior of Li and its isotopes during serpentinization of oceanic peridotites
Analyses of Li and Li isotopes in serpentinized peridotites have been performed using Thermo-Ionisation Mass Spectrometry (TIMS) and Secondary Ion Mass Spectrometry (SIMS) techniques on samples collected from the southwest Indian Ridge (SWIR). In the bulk samples, Li concentrations range from 0.6 to 8.2 ppm, while whole rock δ6Li values range from -2.9 to -14‰. In situ analyses display a greater range in both Li concentration (0.1–19.5 ppm) and Li isotopic composition (-27 to +19‰), with the serpentinized portions having higher Li concentrations than the associated relict phases. These variations may reflect changes in Li partitioning and isotopic fractionation between serpentine and fluid with temperature and water/rock ratio. They may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization. As the serpentine forms by interaction with a circulating fluid, it preferentially removes 6Li, causing the Li in the fluid to become isotopically heavier. The isotopic composition of the initial hydrothermal fluid is dominated by basalt-derived Li, which easily overwhelms the very low Li content originally present in seawater. As this fluid circulates through ultramafic rocks, it induces the formation of serpentine that incorporates this mantle-derived Li. Hence, Li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves Li recycling within this crust. Consequently, Li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid. These results imply that serpentinized peridotites are probably only a minor sink of oceanic Li.
1525-2027
1007
Decitre, Sylvie
04b82ae2-4154-4850-aee0-3a4c881647be
Deloule, Etienne
5c3dc0e9-f223-4b29-9119-5af26e0974bd
Reisberg, Laurie
4e01cdfc-75c1-4943-8012-ef99b605e879
James, Rachael
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Agrinier, Pierre
cdf79a29-60ea-49e3-8ebd-3106cb4241d0
Mével, Catherine
8c55f020-7c37-403f-b4a9-149556462364
Decitre, Sylvie
04b82ae2-4154-4850-aee0-3a4c881647be
Deloule, Etienne
5c3dc0e9-f223-4b29-9119-5af26e0974bd
Reisberg, Laurie
4e01cdfc-75c1-4943-8012-ef99b605e879
James, Rachael
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Agrinier, Pierre
cdf79a29-60ea-49e3-8ebd-3106cb4241d0
Mével, Catherine
8c55f020-7c37-403f-b4a9-149556462364

Decitre, Sylvie, Deloule, Etienne, Reisberg, Laurie, James, Rachael, Agrinier, Pierre and Mével, Catherine (2002) Behavior of Li and its isotopes during serpentinization of oceanic peridotites. Geochemistry, Geophysics, Geosystems, 3 (1), 1007. (doi:10.1029/2001GC000178).

Record type: Article

Abstract

Analyses of Li and Li isotopes in serpentinized peridotites have been performed using Thermo-Ionisation Mass Spectrometry (TIMS) and Secondary Ion Mass Spectrometry (SIMS) techniques on samples collected from the southwest Indian Ridge (SWIR). In the bulk samples, Li concentrations range from 0.6 to 8.2 ppm, while whole rock δ6Li values range from -2.9 to -14‰. In situ analyses display a greater range in both Li concentration (0.1–19.5 ppm) and Li isotopic composition (-27 to +19‰), with the serpentinized portions having higher Li concentrations than the associated relict phases. These variations may reflect changes in Li partitioning and isotopic fractionation between serpentine and fluid with temperature and water/rock ratio. They may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization. As the serpentine forms by interaction with a circulating fluid, it preferentially removes 6Li, causing the Li in the fluid to become isotopically heavier. The isotopic composition of the initial hydrothermal fluid is dominated by basalt-derived Li, which easily overwhelms the very low Li content originally present in seawater. As this fluid circulates through ultramafic rocks, it induces the formation of serpentine that incorporates this mantle-derived Li. Hence, Li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves Li recycling within this crust. Consequently, Li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid. These results imply that serpentinized peridotites are probably only a minor sink of oceanic Li.

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Published date: 2002
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 210159
URI: http://eprints.soton.ac.uk/id/eprint/210159
ISSN: 1525-2027
PURE UUID: 72bcb57f-3d39-4ee9-b1a1-1b3044839dc6
ORCID for Rachael James: ORCID iD orcid.org/0000-0001-7402-2315

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Date deposited: 06 Feb 2012 17:08
Last modified: 23 Sep 2020 01:38

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Contributors

Author: Sylvie Decitre
Author: Etienne Deloule
Author: Laurie Reisberg
Author: Rachael James ORCID iD
Author: Pierre Agrinier
Author: Catherine Mével

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