Calibration of the dolomite clumped isotope thermometer from 25 to 350 °C, and implications for a universal calibration for all (Ca, Mg, Fe)CO3 carbonates

Experimental calibration of clumped isotope reordering in dolomite

“…∆47 values of these 90 °C reactions were corrected to the canonical 25 °C scale by adding a 90 °C phosphoric acid fractionation factor of 0.092 ‰ (Henkes et al, 2013). This value is significantly lower than the dolomite ∆47 acid fractionation suggested by Murray et al (2016); however, as demonstrated by Bonifacie et al (2017), discussed in Lloyd et al (2017), and further supported by the high-temperature equilibration experiments of the present study (see below), it appears that dolomite and calcite have indistinguishable ∆47 acid fractionations on the carbonate clumped isotope systems at Caltech.…”

“…Thus, we report ∆47-derived temperatures, calculate equilibrium ∆47 values for heating experiments, and forward-model cooling dolomite marbles using three ∆47-T calibrations suitable for high temperature studies: briefly, a 2 nd -order polynomial fit to natural and experimental carbonate data from Bonifacie et al (2017) (hereafter, the 'Bonifacie calibration'), a 2 nd -order polynomial fit to calcite and dolomite ∆47 data generated solely at Caltech from Lloyd et al (2017) ('Lloyd calibration'), and an ab initio model for equilibrium 13 C-18 O clumping in carbonates calculated in Schauble et al (2016) and transferred into the CO2 reference frame in Bonifacie et al (2017) ('Schauble + Bonifacie calibration').…”

“…∆47 values of lab-grown dolomites are dependent on precipitation temperature, and thus ∆47 values in natural materials can be used to estimate the temperature of (re)crystallization (Bonifacie et al, 2017;Ghosh et al, 2006).…”

“…Regardless of calibration choice, dolomite ∆47 rate constants determined using both models are resolvably slower than those of calcite and apatite, and predict that high-grade dolomite crystals should preserve apparent equilibrium blocking temperatures of between ~210 and 300 °C during cooling on geologic timescales. Best agreement between model predictions and natural dolomite marbles was found when using the exchangediffusion model and the ab initio ∆63-T calibration of Schauble et al (2006), projected into the ∆47 reference frame by Bonifacie et al (2017). Therefore, we recommend modeling dolomite ∆47 reordering using the exchange-diffusion model and this parameter set.…”

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

“…The equation is  47 = 0.00173 x (10 6 /T 2 ) 2 + 0.0203 x 10 6 /T 2 + 0.261 where T is the temperature in Kelvin. Data used in this calibration comes only from measurement made at the Caltech laboratories Ghosh et al, 2007;Came et al, 2007;Guo et al, 2009;Tripati et al, 2010;Eagle et al, 2010;Thiagarajan et al, 2011;Dennis et al, 2011;Stolper and Eiler, 2015;Eagle et al, 2015;Spooner et al, 2016;Bonifacie et al, 2017). …”