Constraining thrust-belt thermal histories from partially reset zircon (U-Th)/He datasets: An “inheritance envelope” approach with examples from the Sevier belt of central Utah

Abstract:

Low-temperature thermochronology has become an established tool for deciphering the time-temperature (t-T) histories of sedimentary units involved in basin burial and thrust-belt exhumation. However, thermochronologic datasets from detrital samples can be complex and difficult to interpret if these samples contain grains with different pre-depositional t-T histories that are only partially reset. Here, we present an approach for interpreting complex detrital zircon (U-TH)/He datasets to constrain the maximum foreland basin burial temperatures and timing of thrust-belt related exhumation in the Sevier belt of central Utah. Using forward modeling of t-T paths, we combine the radiation-damage based kinetic model for He diffusion in zircon with a series of pre-depositional He ages to construct “inheritance envelopes” that encompass a wide range of age variation. A forward model is successful if an inheritance envelope captures or bounds the observed age variation in a given dataset. We highlight this approach with two datasets collected from sedimentary units in the Oquirrh Mountains and Wasatch Range near Provo, UT. For the Oquirrh Mtns. dataset, large observed age variation is modeled using a maximum burial temperature of ~173 °C, and an initial Sevier-belt related exhumation event at 110 Ma. The Wasatch Range samples are more straight-forward, with a lack of partially reset ages but some observed variation caused by radiation damage effects. For these samples, our model results constrain a maximum burial temperature of ~230 °C, with a subsequent exhumation event at 100 Ma. Combined, these results suggest a steady eastward migration of exhumation in the Sevier belt during the Late Cretaceous and demonstrate that our inheritance envelope approach is most sensitive to maximum burial temperatures and the timing of initial exhumation.