The Wyoming Province exposes one of the most isotopically evolved Archean cratons. The Wyoming Province forms an early part of the north American Precambrian shield, to which younger terranes were accreted. However, the origin of the province is unclear, with some isotopic data suggesting that it was derived from an older reservoir that must have been older than 4.0 Ga if it U/Pb ratio was comparable to average crust. Determining the age and composition of this older reservoir is crucial for understanding the processes that lead to the transformation of this craton from an older, relatively high U/Pb system to a low U/Pb system by the end of the Archean. The work involves a detailed geologic and geochemical investigation, including SHRIMP U-Pb geochronology, of the Middle to Early Archean crust in the Beartooth Mountains where the evolved isotopic signature is best documented. Results will be important in constraining the processes involved in Earth's early geochemical differentiation.
