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Oxygen and clumped isotope fractionation during the formation of Mg calcite via an amorphous precursor

Dietzel, Martin; Purgstaller, Bettina; Kluge, Tobias; Leis, Albrecht; Mavromatis, Vasileios

Abstract:
The oxygen and clumped isotope signatures of Mg calcites are routinely used as environmental proxies in a broad range of surroundings, where Mg calcite forms either by classical nucleation or via an amorphous calcium magnesium carbonate (ACMC) precursor. Although the (trans)formation of ACMC to Mg calcite has been identified for an increasing number of settings, the behavior of both isotope proxies throughout this stage is still unexplored. In the present study ACMC (trans)formation experiments were carried out at constant pH (8.30 ± 0.03) and temperature (25.00 ± 0.03 °C) to yield high Mg calcite (up to 20 mol% Mg). The experimental data indicate that the oxygen isotope values of the amorphous and/or crystalline precipitate (δ$^{18}$O$_{prec}$, analyzed as Mg calcite) are affected by the (trans)formation pathway, whereas clumped isotopes (Δ$_{47prec}$ = Δ$_{47Mg-calcite}$) are not. The oxygen isotope evolution of the solid phase can be explained by the instantaneous trapping of the isotopic composition of the aqueous (bi)carbonate complexes. This entrapment results in remarkably high 10$^{3}$ln(α$_{prec-H2O}$) values of ∼33‰ at the initial ACMC formation stage. ... mehr

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Verlagsausgabe §
DOI: 10.5445/IR/1000117963
Veröffentlicht am 23.04.2020
Originalveröffentlichung
DOI: 10.1016/j.gca.2020.02.032
Scopus
Zitationen: 1
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Angewandte Geowissenschaften (AGW)
Publikationstyp Zeitschriftenaufsatz
Publikationsmonat/-jahr 05.2020
Sprache Englisch
Identifikator ISSN: 0016-7037
KITopen-ID: 1000117963
Erschienen in Geochimica et cosmochimica acta
Band 276
Seiten 258–273
Vorab online veröffentlicht am 04.03.2020
Schlagwörter Oxygen isotope fractionation, Clumped isotopes, Amorphous calcium magnesium carbonate, Mg calcite, Transformation
Nachgewiesen in Scopus
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