• Late Eocene Uplift of the Al Hajar Mountains, Oman, Supported by Stratigraphy and Low-Temperature Thermochronology

      Hansman, Reuben J.; Ring, Uwe; Thomson, Stuart N.; den Brok, Bas; Stübner, Konstanze; Univ Arizona, Dept Geosci; Department of Geological Sciences; Stockholm University; Stockholm Sweden; Department of Geological Sciences; Stockholm University; Stockholm Sweden; Department of Geosciences; University of Arizona; Tucson AZ USA; Department of Applied Geosciences; German University of Technology; Muscat Oman; et al. (AMER GEOPHYSICAL UNION, 2017-12)
      Uplift of the Al Hajar Mountains in Oman has been related to either Late Cretaceous ophiolite obduction or the Neogene Zagros collision. To test these hypotheses, the cooling of the central Al Hajar Mountains is constrained by 10 apatite (U-Th)/He (AHe), 15 fission track (AFT), and four zircon (U-Th)/He (ZHe) sample ages. These data show differential cooling between the two major structural culminations of the mountains. In the 3km high Jabal Akhdar culmination AHe single-grain ages range between 392 Ma and 101 Ma (2 sigma errors), AFT ages range from 518 Ma to 324 Ma, and ZHe single-grain ages range from 62 +/- 3Ma to 39 +/- 2 Ma. In the 2 km high Saih Hatat culmination AHe ages range from 26 +/- 4 to 12 +/- 4 Ma, AFT ages from 73 +/- 19Ma to 57 +/- 8 Ma, and ZHe single-grain ages from 81 +/- 4 Ma to 58 +/- 3 Ma. Thermal modeling demonstrates that cooling associated with uplift and erosion initiated at 40 Ma, indicating that uplift occurred 30 Myr after ophiolite obduction and at least 10 Myr before the Zagros collision. Therefore, this uplift cannot be related to either event. We propose that crustal thickening supporting the topography of the Al Hajar Mountains was caused by a slowdown of Makran subduction and that north Oman took up the residual fraction of N-S convergence between Arabia and Eurasia.
    • Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

      McDermott, Robert G.; Ault, Alexis K.; Caine, Jonathan Saul; Thomson, Stuart N.; Univ Arizona, Dept Geosci (AMER GEOPHYSICAL UNION, 2019-08-15)
      Exhumation and landscape evolution along strike-slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U-Th)/He (He), zircon He, apatite fission-track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within similar to 26-4, similar to 110-12, similar to 94-28, and similar to 137-83 Ma, respectively. A new zircon U-Pb date of 113.9 +/- 1.7 Ma (2 sigma) complements existing geochronology and aids in interpretation of low-temperature thermochronometry data patterns. Samples <= 2 km southwest of the EDFZ trace yield the youngest thermochronometry dates. Multimethod thermochronometry, zircon He date-effective U patterns, and thermal history modeling reveal rapid cooling similar to 95-75 Ma, slow cooling similar to 75-30 Ma, and renewed rapid cooling similar to 30 Ma to present. The magnitude of net surface uplift constrained by published paleobotanical data, exhumation, and total surface uplift from similar to 30 Ma to present are similar to 1, similar to 2-6, and similar to 1-7 km, respectively. Exhumation is highest closest to the EDFZ trace but substantially lower than reported for the central Denali fault zone. We infer exhumation and elevation changes associated with similar to 95-75 Ma terrane accretion and EDFZ activity, relief degradation from similar to 75-30 Ma, and similar to 30 Ma to present exhumation and surface uplift as a response to flat-slab subduction and transpressional deformation. Integrated results reveal new constraints on landscape evolution within the Kluane Ranges directly tied to the EDFZ during the last similar to 100 Myr.