Equilibrated Gas and Carbonate Standard-Derived Dual (Δ47 and Δ48) Clumped Isotope Values

Abstract

Carbonate clumped isotope geochemistry has primarily focused on mass spectrometric determination of m/z 47 CO₂ for geothermometry, but theoretical calculations and recent experiments indicate paired analysis of the m/z 47 (¹³C¹⁸O¹⁶O) and m/z 48 (¹²C¹⁸O¹⁸O) isotopologues (referred to as ${\text{Δ}}_{47}$ and ${\text{Δ}}_{48}$) can be used to study non-equilibrium isotope fractionations and refine temperature estimates. We utilize 5,448 ${\text{Δ}}_{47}$ and 3,400 ${\text{Δ}}_{48}$ replicate measurements of carbonate samples and standards, and 183 ${\text{Δ}}_{47}$ and 195 ${\text{Δ}}_{48}$ replicate measurements of gas standards from 2015 to 2021 from a multi-year and multi-instrument data set to constrain ${\text{Δ}}_{47}$ and ${\text{Δ}}_{48}$ values for 27 samples and standards, including Devils Hole cave calcite, and study equilibrium ${\text{Δ}}_{47}$-${\text{Δ}}_{48}$, ${\text{Δ}}_{47}$-temperature, and ${\text{Δ}}_{48}$-temperature relationships. We compare results to previously published findings and calculate equilibrium regressions based on data from multiple laboratories. We report acid digestion fractionation factors, $\text{Δ}{*}_{63-47}$ and $\text{Δ}{*}_{64-48}$, and account for their dependence on the initial clumped isotope values of the mineral.