Technical note: Disentangling pre- and post-depositional thermal histories in partially reset samples

Abstract. Interpreting thermochronological data of a partially reset detrital sample is challenging because its age distribution reflects a mixture of each grain’s individual pre-depositional and the shared post-depositional thermal history. A promising approach to meet this challenge is combined geo- and thermochronological dating on the same grains. We present an algorithm for disentangling the pre- and post-depositional thermal histories using data from zircon U/Pb-(U-Th)/He double-dating. It proceeds in three steps: (1) determining candidate post-depositional temperature-time paths by inverse thermal-history modeling of syn-depositional grains. (2) Calculating pre-depositional (U-Th)/He model ages for each candidate thermal history. (3) Evaluating the likelihood for each post-depositional history by testing if resulting pre-depositional model ages against the U-Pb crystallization ages of each grain and the timing of sediment deposition. We illustrate this strategy by applying it to a Devonian sandstone from the Northern Canadian Cordillera. The results show the general agreement of the modeled thermal histories and pre-depositional (U-Th)/He ages with existing thermochronological data. The temperature-time paths are also consistent with additional zircon-Raman thermochronological data from the same grains. We discuss the limitations of our approach imposed by the need for syn-depositional grains, its application to other thermochronometers, and how targeting rather than avoiding partially reset samples enhances our capability to extract thermal-history information from the detrital record.