The University of Southampton
University of Southampton Institutional Repository

An experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures (51 to 350°C): insights as to chemical processes in near-shore ridge-flank hydrothermal systems

An experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures (51 to 350°C): insights as to chemical processes in near-shore ridge-flank hydrothermal systems
An experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures (51 to 350°C): insights as to chemical processes in near-shore ridge-flank hydrothermal systems
Studies of hydrothermal circulation within partly buried basement on the eastern flank of the Juan de Fuca Ridge (JFR) have shown that ridge-flank geochemical fluxes are potentially important for the global budgets of some elements. There are major uncertainties in these flux calculations, however, because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments, either by diffusive exchange with basement or during upwelling to the seafloor. To better understand the nature and temperature control of basalt-fluid and sediment-fluid reactions at the JFR flank, we have conducted laboratory experiments between 51 and 350°C and at 400 bars pressure. K, Rb, and Si are leached from basalt between 150 and 351°C, and Sr and U are taken up. The direction of exchange of Li and Ca with basalt varies with temperature. Li and Sr are removed from fluid at 150°C, but isotope studies show that there is simultaneous release of both elements from basalt, indicating that uptake is controlled by the formation of secondary minerals. Moreover, our experiments confirm that Sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high-temperature axial hydrothermal systems. Our data and field data from the JDR flank indicate that uptake of U into basalt at moderate temperature could remove between 9.9 and 15 × 106 mol U yr?1 from the oceans. This is higher than a recent estimate based on measurements of U in altered ocean crust (5.7 ± 3.3 × 106 mol yr?1), which concords with arguments that the ?element/heat ratios of JDR flank fluids are too large to be representative of average global flank fluids. K, Ca, Sr, Ba, Li, Si, and B are leached from terrigenous sediments between 51 and 350°C, and U is taken up. Cs and Rb are removed from the fluid below 100°C and leached from the sediment at higher temperature. Sr isotope data show that Sr is preferentially mobilised from volcanic components within terrigenous sediments, which may lead to an overestimation of the ridge-flank Sr isotope flux at the JDR if there is exchange of sediment pore fluids with basement.
0016-7037
681-691
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Allen, Doug E.
43da5fe2-63b9-41fb-b0ab-e4154aa69c5b
Seyfried, W.E.
706792e4-fce2-4349-bfb2-55e8ed9f5556
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Allen, Doug E.
43da5fe2-63b9-41fb-b0ab-e4154aa69c5b
Seyfried, W.E.
706792e4-fce2-4349-bfb2-55e8ed9f5556

James, Rachael H., Allen, Doug E. and Seyfried, W.E. (2003) An experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures (51 to 350°C): insights as to chemical processes in near-shore ridge-flank hydrothermal systems. Geochimica et Cosmochimica Acta, 67 (4), 681-691. (doi:10.1016/S0016-7037(02)01113-4).

Record type: Article

Abstract

Studies of hydrothermal circulation within partly buried basement on the eastern flank of the Juan de Fuca Ridge (JFR) have shown that ridge-flank geochemical fluxes are potentially important for the global budgets of some elements. There are major uncertainties in these flux calculations, however, because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments, either by diffusive exchange with basement or during upwelling to the seafloor. To better understand the nature and temperature control of basalt-fluid and sediment-fluid reactions at the JFR flank, we have conducted laboratory experiments between 51 and 350°C and at 400 bars pressure. K, Rb, and Si are leached from basalt between 150 and 351°C, and Sr and U are taken up. The direction of exchange of Li and Ca with basalt varies with temperature. Li and Sr are removed from fluid at 150°C, but isotope studies show that there is simultaneous release of both elements from basalt, indicating that uptake is controlled by the formation of secondary minerals. Moreover, our experiments confirm that Sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high-temperature axial hydrothermal systems. Our data and field data from the JDR flank indicate that uptake of U into basalt at moderate temperature could remove between 9.9 and 15 × 106 mol U yr?1 from the oceans. This is higher than a recent estimate based on measurements of U in altered ocean crust (5.7 ± 3.3 × 106 mol yr?1), which concords with arguments that the ?element/heat ratios of JDR flank fluids are too large to be representative of average global flank fluids. K, Ca, Sr, Ba, Li, Si, and B are leached from terrigenous sediments between 51 and 350°C, and U is taken up. Cs and Rb are removed from the fluid below 100°C and leached from the sediment at higher temperature. Sr isotope data show that Sr is preferentially mobilised from volcanic components within terrigenous sediments, which may lead to an overestimation of the ridge-flank Sr isotope flux at the JDR if there is exchange of sediment pore fluids with basement.

This record has no associated files available for download.

More information

Published date: 2003
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 210115
URI: http://eprints.soton.ac.uk/id/eprint/210115
ISSN: 0016-7037
PURE UUID: f29aa5fb-5e7a-4ccf-9c30-5f9e515e70e2
ORCID for Rachael H. James: ORCID iD orcid.org/0000-0001-7402-2315

Catalogue record

Date deposited: 06 Feb 2012 14:00
Last modified: 15 Mar 2024 03:30

Export record

Altmetrics

Contributors

Author: Doug E. Allen
Author: W.E. Seyfried

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×