Aragonite (U-Th)/He geochronology: Full retentivity across geologic timescales (104-107 yr)

In this study we explore aragonite retentivity to helium by comparing (U-Th)/He ages to independent age constraints provided by U/Th and U-Pb dating. We utilize aragonite speleothems from Botovskaya cave in Siberia and Soreq cave in Israel where the current temperature is-1 degrees C and-20 degrees C, respectively and is almost fluctuations-free. We then explore the retentivity of the dated aragonite samples using data from petrographic thin sections and thermal models.The obtained (U-Th)/He ages are statistically identical to independent age constraints extending backwards 6 Ma. This demonstrates that aragonite with relatively common grain size (20-500 mu m) is retentive to helium at surface temperatures of 0-20 degrees C for millions of years. Moreover, its retentivity is higher than expected using currently available helium diffusion kinetics data for aragonite. Our results indicate that aragonite (U-Th)/He geochronology is feasible for aragonite held at near surface temperatures even when the sample grain size is relatively small. Aragonite samples that experienced post-depositional heating may lose helium. (U-Th)/He ages of such samples can be used to constrain paleo surface temperatures and the timing of tectonic and thermal events.

Automated summary

In this study, the retentivity of aragonite to helium is explored by comparing (U-Th)/He ages to independent age constraints provided by U/Th and U-Pb dating. Aragonite speleothems from Botovskaya cave in Siberia and Soreq cave in Israel are utilized, and the retentivity of the samples is examined using petrographic thin sections and thermal models. The obtained (U-Th)/He ages are found to be statistically identical to independent age constraints, indicating that aragonite can retain helium for millions of years at surface temperatures of 0-20 degrees C. The results suggest the feasibility of aragonite (U-Th)/He geochronology for samples held at near surface temperatures, even with small grain sizes.