Experimental quantification of the effect of Mg on calcite–aqueous fluid oxygen isotope fractionation.

Mavromatis, Vasileios, Schmidt, Mark , Botz, Reiner, Comas-Bru, Laia and Oelkers, Eric H. (2012) Experimental quantification of the effect of Mg on calcite–aqueous fluid oxygen isotope fractionation. Chemical Geology, 310-311 . pp. 97-105. DOI 10.1016/j.chemgeo.2012.03.027.

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Abstract

Magnesium calcites were synthesized from aqueous solutions supersaturated with respect to calcite at 25, 40, 60, and 80 °C in gas tight batch reactors for up to 35 days. Any amorphous material still present in the precipitates was removed using a partial dissolution treatment. Resulting purified Mg-calcite had Mg contents ranging from 6 to 32 mol% MgCO3. An isotopic steady-state was attained between the fluid and the precipitated solids within two weeks at 25 °C. δ18O values derived from the experiments at steady-state, depend on both temperature and the Mg content of the calcite in accord with:
1000lnαMg-calcite–H2O=18,030/T−32.42+(6×108/T3–5.47×106/T2+16,780/T−17.21)×CMg
where αMg-calcite–H2O represents the calcite–water oxygen isotope fractionation factor, T refers to the temperature in °K and CMg denotes the mole percent of MgCO3 in the calcite. These results indicate that the addition of 5 mol% MgCO3 into the calcite increases 1000lnαMg-calcite–H2O by 0.88 as compared to that of pure calcite at 25 °C. This difference could lead to a 4.2 °C decrease in estimated formation temperature estimates. These results demonstrate that the accurate interpretation of oxygen isotope fractionation in magnesium calcites requires explicit provision for the effect of magnesium on oxygen isotope fractionation factors.

Highlights
► The effect of Mg on calcite–aqueous fluid oxygen isotope fractionation was investigated. ► Mg incorporation is increasing the calcite–aqueous fluid oxygen isotope fractionation. ► This effect is reduced at higher temperatures. ► Obtained results are important for paleo-temperature estimation.
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Document Type: Article
Additional Information: WOS:000305307800008
Keywords: AUTHIGENIC CARBONATES; MAGNESIUM CARBONATES; Mg-calcite; Oxygen isotope fractionation; Paleo-temperature estimation; SYNTHETIC ARAGONITE; WATER; PRECIPITATION; 25-DEGREES-C; TRANSFORMATION; SUBSTITUTION; EQUILIBRIUM; TEMPERATURE
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > SFB 574 > B5
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.chemgeo.2012.03.027
ISSN: 0009-2541
Projects: Future Ocean, SFB574
Contribution Number:
ProjectNumber
SFB 574169
Date Deposited: 15 Mar 2013 10:38
Last Modified: 07 Dec 2017 13:31
URI: http://oceanrep.geomar.de/id/eprint/20749

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