DECIPHERING ZIRCON (U-TH)/HE THERMOCHRONOLOGY DATA SCATTER IN ARCHEAN GRAINS FROM THE BEARTOOTH RANGE, MONTANA

The Beartooth Range in southwestern Montana is a basement uplift of similar structural style and timing to other “Laramide” uplifts. Exhumation timing and rates for the Beartooth Range have previously been constrained with Apatite fission track and sedimentary analysis of adjacent basins. Here, we present zircon (U-Th)/He thermochronology data from the Beartooth Mountains to better extend these constraints to deeper times and explore potential pre-Laramide phases of exhumation. We collected several samples along an elevation transect in the southwest corner of the Beartooth Mountains to achieve this goal. Dates range from 16 to 620 Ma and are roughly correlated with effective uranium (eU) concentrations, which suggest some amount of the date dispersion is a consequence of radiation damage effects. In order to further investigate additional sources of date variation in our data, we also examined U/Th and radiation damage zonation profiles in zircon grains collected from the same Beartooth samples. We used Electron Microscopy techniques, including Cathode Luminescence and Back Scattered Electron imaging, and Laser Ablation Inductively Coupled Plasma Mass Spectrometry to investigate U/Th zonation, and Raman spectroscopy maps to investigate damage zonation. These measurements were used as inputs to thermal history forward modeling to investigate the magnitude of zonation induced scatter, and whether it is sufficient to explain our observed dispersion.