δ C and δ O heterogeneities in carbonates: Nonlinear mixing in the application of dual-carbonate-clumped isotope thermometer.

Rationale: Dual-carbonate-clumped isotope thermometry assumes any departure from Δ and Δ co-equilibrium is due to disequilibrium processes; however, the effects of endmember mixing have not been evaluated for Δ . We show that variations in δ C and δ O values within a sample can lead to offsets in Δ and Δ that can be mistaken for kinetic fractionation.

Methods: A numerical mixing model was developed to calculate the Δ and Δ values of samples with heterogeneous isotope compositions.

Effects of different constants and standards on the reproducibility of carbonate clumped isotope (Δ ) measurements: Insights from a long-term dataset.

Rationale: Carbonate clumped isotope (Δ ) thermometry examines the temperature-dependent excess abundance of the C- O bond in the carbonate lattice. Inconsistent temperature calibrations and standard values have been reported among laboratories, which has led to the use of equilibrated gases and carbonate standards for standardization. Furthermore, different acid fractionation factors and isotopic parameter sets have been proposed for improving inter-laboratory data comparability.

Analytical effects on clumped isotope thermometry: Comparison of a common sample set analyzed using multiple instruments, types of standards, and standardization windows.

Rationale: Carbonate clumped isotope geothermometry is being increasingly used in multiple disciplines in the geosciences. However, potential interlaboratory issues are arising from different standardization procedures that may contribute to the multiple Δ -temperature calibrations reported in the literature. We investigate this issue by comparing a common temperature calibration sample set across three different mass spectrometers, using multiple standardization methods.

Non-linear mixing effects on mass-47 CO2 clumped isotope thermometry: Patterns and implications.

Rationale: Mass-47 CO(2) clumped isotope thermometry requires relatively large (~20 mg) samples of carbonate minerals due to detection limits and shot noise in gas source isotope ratio mass spectrometry (IRMS). However, it is unreasonable to assume that natural geologic materials are homogenous on the scale required for sampling. We show that sample heterogeneities can cause offsets from equilibrium Δ(47) values that are controlled solely by end member mixing and are independent of equilibrium temperatures.