Late Cenozoic deformation and glacial imprint on the Terskey Range, Kyrgyzstan

It is widely recognized that the topography of the Earth's surface records coupling between tectonics, climate and surface processes. However, the relative contributions of tectonic and climatic drivers to the observed topography, rates and patterns of erosion remain poorly constrained in many mountain regions. The Terskey Range, located in the Kyrgyz Tian Shan, is an ideal natural laboratory to investigate this question because of its well-documented structure, kinematics and denudation history. Cenozoic deformation of the Terskey Range is mainly characterised by southward tilting associated with thrusting along the Main Terskey Fault; this fault delimits the mountain range to the north. Tilting can be reconstructed using relict low-relief surfaces that have undergone minimal Cenozoic erosion. Slip along the Main Terskey Fault initiated in the early Miocene and accelerated at around 10 Ma. A comparison between short- and long-term denudation rates suggests a significant increase during the Quaternary, which has been linked to glaciation of the range. The geomorphology of the range, with deeply incised, highly concave main valleys contrasting to less incised and concave minor valleys, suggests significant but variable ice dynamics.

We focus here on the reanalysis of published low-temperature thermochronology data (apatite fission-track, apatite and zircon (U-Th-Sm)/He) of two elevation transects from the glacially affected Barskoon Valley, one of the main valleys draining the Terskey Range to the north. We collected three new valley-bottom samples from the Barskoon Valley to better constrain differential erosion along the valley, with the aim to discriminate between tectonic, fluvial and glacial drivers of valley incision. Inverse thermal-history modelling of the elevation profiles, combining new and existing data, indicates a significant increase in exhumation rate since around 3 Ma in the northern transect. We suggest that this signal records the initiation of efficient glacial erosion in Terskey Range. Future studies will include higher resolution 4He/3He thermochronology of the valley-bottom samples and inversion of the preglacial topographic relief using thermal-kinematic Pecube.