Apatite U-Th/He Evidence for Late Oligocene or Earliest Miocene Initiation of Exhumation in the Gobi Altai, Mongolia

Far-field influences of the India-Asia collision have often been cited as a general cause for the still-active transpressional deformation evident in the Gobi Altai range of south-central Mongolia as well as elsewhere in the region. The timing of initiation for deformation is a potentially important component in understanding the broader geodynamic evolution of Central Asia. However, it has been difficult to determine this timing in detail, with past studies suggesting a latest Miocene or younger age. We report apatite U-Th/He data from the Gobi Altai's Ikh Bogd block, showing a clear systematic relationship of age with depth below a range-capping low-relief erosion surface. Older higher-elevation ages are more dispersed and consistent with very slow Mesozoic to earlier Cenozoic cooling, whereas the lowest samples give ages of 25 to 35 Ma showing much lower internal dispersion. Additional work on other ranges as well as pending 4He/3He data will help confirm this result but we currently interpret this age-elevation pattern as a partial retention zone that began to be exhumed at about 30 Ma. This earlier timing for initial exhumation is a better fit to available geological evidence and is more consistent with the timing of events within the India-Asia collision and Central Asia.