Speaker: Daniel Stolper (Caltech)
The abundance of multiply substituted (‘clumped’) isotopologues (e.g., 13C16O218O2-) in carbonates is a thermodynamically controlled function of temperature for equilibrated systems. Measurement of clumped isotope abundances can thus be used under certain circumstances to measure carbonate formation temperatures. This technique represents a potentially powerful way to reconstruct past surface temperatures because unlike most isotope-based paleothermometers it does not require knowledge of the isotopic composition of the water with which the mineral equilibrated during formation. This opens up, in principle, temperature reconstructions for carbonate-bearing minerals from any time in Earth’s history. However, the effect of heating that all rocks experience during burial can modify these recorded ‘temperatures’ via diffusion and reordering of carbon and oxygen within the crystal. To gain insight into the importance of these processes in nature, I conducted high temperature and pressure experiments on calcites and carbonate-bearing apatites to quantify the kinetics of the resetting of the clumped-isotope thermometer. I will test models that fit the experimental data by comparing predicted to measured temperatures of natural samples with known thermal histories, including slowly cooled igneous calcites and apatites and surface-precipitated samples that have experienced elevated temperatures after burial. These results will demonstrate that thermal histories should generally be taken into account in interpreting the significance of clumped-isotope-based formation temperatures.