The University of Southampton
University of Southampton Institutional Repository

Isotopic fractionation during congruent dissolution, precipitation and at equilibrium: Evidence from Mg isotopes

Pearce, Christopher R., Saldi, Giuseppe D., Schott, Jacques and Oelkers, Eric H. (2012) Isotopic fractionation during congruent dissolution, precipitation and at equilibrium: Evidence from Mg isotopes Geochimica et Cosmochimica Acta, 92, pp. 170-183. (doi:10.1016/j.gca.2012.05.045).

Record type: Article

Abstract

This study provides direct experimental evidence of magnesium (Mg) isotope fractionation between an aqueous fluid and magnesite during its congruent dissolution, precipitation and at equilibrium. Closed-system batch reactor experiments were performed at temperatures from 120 to 200 °C and at 15 or 30 bar CO2 pressure. During congruent magnesite dissolution the fluid became enriched in isotopically heavy Mg, with a steady-state ?26Mgfluid composition that was 0.4‰ higher than the dissolving magnesite at 15 bar of CO2 pressure and 0.15‰ higher at 30 bar of CO2 pressure. Magnesite precipitation was provoked by increasing the reactor temperature after equilibrium had been attained via dissolution. Rayleigh isotope fractionation effects were observed immediately after the reactor temperature was increased and rapid magnesite precipitation occurred. However, isotopic exchange continued as the system equilibrated, eradicating this Rayleigh signal. The equilibrium 26Mg/24Mg fractionation factors (?eqm) for the magnesite-fluid system were found to be 0.99881 at 150 °C and 0.99912 at 200 °C. Taken together, these observations (1) support the theoretical hypothesis that mineral-fluid equilibrium is dynamic (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium), and (2) indicate that isotopes will continue to exchange and equilibrate even if the mineral surfaces and co-existing fluids are in chemical equilibrium. The fact that isotopes continue to exchange at chemical equilibrium will tend to eradicate both kinetic and paleo-environmental isotopic signatures, and the degree to which such signatures are completely eradicated depends on how deep into the surface the isotopic exchange process penetrates

PDF Pearce_et_al_(2012).pdf - Version of Record
Restricted to Repository staff only
Download (847kB)

More information

Published date: 1 September 2012
Organisations: Geochemistry

Identifiers

Local EPrints ID: 342522
URI: http://eprints.soton.ac.uk/id/eprint/342522
ISSN: 0016-7037
PURE UUID: 4f996553-8014-4d65-8620-1cc9b331cf69

Catalogue record

Date deposited: 07 Sep 2012 13:31
Last modified: 18 Jul 2017 05:28

Export record

Altmetrics

Contributors

Author: Christopher R. Pearce
Author: Giuseppe D. Saldi
Author: Jacques Schott
Author: Eric H. Oelkers

University divisions

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.

×