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Stable and radiogenic strontium isotope fractionation during hydrothermal seawater-basalt interaction

Stable and radiogenic strontium isotope fractionation during hydrothermal seawater-basalt interaction
Stable and radiogenic strontium isotope fractionation during hydrothermal seawater-basalt interaction

The fluid-rock interactions occurring in hydrothermal systems at or near mid-oceanic ridges (MOR) were studied experimentally by reacting crystalline and glassy basalt with seawater at 250 °C and 290 °C while monitoring the liquid phase Sr isotopic evolution (87Sr/86Sr and δ88/86Sr). The results indicate that seawater Sr was incorporated into anhydrite during the early stages of seawater-basalt interaction. Liquid 87Sr/86Sr values trend towards the basaltic signature as non-stoichiometric basalt dissolution became the dominant process. This suggests that the interplay between fast Sr incorporation into secondary sulfates versus slow and continuous Sr liberation due to basalt dissolution at intermediate temperatures could partly explain previously identified discrepancies between MOR heat budget constraints and the marine 87Sr/86Sr budget. Late-stage anhydrite re-dissolution, likely caused by the liquid phase becoming more reducing through further basalt dissolution, as well as by quenching of the experiments, represents a potential explanation for the low amounts of anhydrite found in naturally altered oceanic basalt samples. Relatively strong decreases in liquid δ88/86Sr values in experiments with crystalline basalt suggest that isotopically light Sr was preferentially released due to non-stoichiometric dissolution. A slight preference of anhydrite for isotopically heavy Sr (εAnhydrite-Liquid 88/86=0.034±0.019‰) is indicated by the data, suggesting that changes in MOR spreading rates and Sr removal could be recorded in the isotope compositions of authigenic, sedimentary Sr phases. Such insights will help to constrain the influence of hydrothermal systems on the oceanic stable Sr cycle.

Hydrothermal activity, Isotopes, Mid-oceanic ridges, Seawater, Strontium
0016-7037
131-151
Voigt, Martin
adb0895a-d4f6-49bc-9461-ef390ef9595c
Pearce, Christopher R.
c83b6228-0b64-4f5a-a8ad-e5cd33a11de3
Baldermann, Andre
adfadac2-a657-4f1e-9dc8-66d2e8589f63
Oelkers, Eric H.
3cf51d71-be44-4bed-803e-3b240bdb147b
Voigt, Martin
adb0895a-d4f6-49bc-9461-ef390ef9595c
Pearce, Christopher R.
c83b6228-0b64-4f5a-a8ad-e5cd33a11de3
Baldermann, Andre
adfadac2-a657-4f1e-9dc8-66d2e8589f63
Oelkers, Eric H.
3cf51d71-be44-4bed-803e-3b240bdb147b

Voigt, Martin, Pearce, Christopher R., Baldermann, Andre and Oelkers, Eric H. (2018) Stable and radiogenic strontium isotope fractionation during hydrothermal seawater-basalt interaction. Geochimica et Cosmochimica Acta, 240, 131-151. (doi:10.1016/j.gca.2018.08.018).

Record type: Article

Abstract

The fluid-rock interactions occurring in hydrothermal systems at or near mid-oceanic ridges (MOR) were studied experimentally by reacting crystalline and glassy basalt with seawater at 250 °C and 290 °C while monitoring the liquid phase Sr isotopic evolution (87Sr/86Sr and δ88/86Sr). The results indicate that seawater Sr was incorporated into anhydrite during the early stages of seawater-basalt interaction. Liquid 87Sr/86Sr values trend towards the basaltic signature as non-stoichiometric basalt dissolution became the dominant process. This suggests that the interplay between fast Sr incorporation into secondary sulfates versus slow and continuous Sr liberation due to basalt dissolution at intermediate temperatures could partly explain previously identified discrepancies between MOR heat budget constraints and the marine 87Sr/86Sr budget. Late-stage anhydrite re-dissolution, likely caused by the liquid phase becoming more reducing through further basalt dissolution, as well as by quenching of the experiments, represents a potential explanation for the low amounts of anhydrite found in naturally altered oceanic basalt samples. Relatively strong decreases in liquid δ88/86Sr values in experiments with crystalline basalt suggest that isotopically light Sr was preferentially released due to non-stoichiometric dissolution. A slight preference of anhydrite for isotopically heavy Sr (εAnhydrite-Liquid 88/86=0.034±0.019‰) is indicated by the data, suggesting that changes in MOR spreading rates and Sr removal could be recorded in the isotope compositions of authigenic, sedimentary Sr phases. Such insights will help to constrain the influence of hydrothermal systems on the oceanic stable Sr cycle.

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More information

Accepted/In Press date: 11 August 2018
e-pub ahead of print date: 22 August 2018
Published date: 1 November 2018
Keywords: Hydrothermal activity, Isotopes, Mid-oceanic ridges, Seawater, Strontium

Identifiers

Local EPrints ID: 424182
URI: http://eprints.soton.ac.uk/id/eprint/424182
ISSN: 0016-7037
PURE UUID: ed840c78-047c-44ac-af06-d5cb8a945b23

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Date deposited: 05 Oct 2018 11:33
Last modified: 08 Jan 2022 11:26

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Contributors

Author: Martin Voigt
Author: Christopher R. Pearce
Author: Andre Baldermann
Author: Eric H. Oelkers

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