Influence of Mg²⁺, Fe²⁺ and Zn²⁺ Cations on ¹³C-¹⁸O Bonds in Precipitated Aragonite, Calcite and Dolomite: An <i>ab Initio</i> Study

Abstract

The influence of metal cations on 13 C- 18 O bonds in carbonates is still under debate. This paper used ab initio method to investigate this kind of influence of Mg 2+ , Fe 2+ and Zn 2+ cations on 13 C- 18 O bonds in precipitated aragonite, calcite and dolomite. The polynomials of Δ 47 and reduced partition function ratios (RPFRs) for 13/12 C, 14/12 C and 18/16 O of these minerals were given within temperatures ranging from 260 to 1500 K. We found that these cations significantly decreased the Δ 47 values at the level of 10 -3 - 10 -2 per mil , comparing with pure crystals; and that if the Δ 47 values were used to reconstruct the temperatures T s, the deviation of T was about 7.2 ° C for, for instance, zinc-enriched aragonite, as discussed in our paper. It was suggested that due to such influence, researchers would better use a proper thermometer according to the main impurity metal cations in carbonates. We also found that according to the probability theory, the theoretical value of the influence of phosphoric acid on Δ 47 of CO 2 degassed from different carbonates was zero.