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

The influence of metal cations on 13C-18O bonds in carbonates is still under debate. This paper used ab initio method to investigate this kind of influence of Mg2+, Fe2+ and Zn2+ cations on 13C-18O bonds in precipitated aragonite, calcite and dolomite. The polynomials of ∆47 and reduced partition function ratios (RPFRs) for 13/12C, 14/12C and 18/16O of these minerals were given within temperatures ranging from 260 to 1500 K. We found that these cations significantly decreased the ∆47 values at the level of 10−3 10−2 per mil, comparing with pure crystals; and that if the ∆47 values were used to reconstruct the temperatures Ts, 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 ∆47 of CO2 degassed from different carbonates was zero.