Neogene exhumation of the Greater Himalaya Slab in Gyirong area, Tibet, constrained by fission track geochronology

Constituting the material majority and high topography of the Himalaya, the Greater Himalayan Slab (GHS) occurs as the best scientific media for revealing the deformation, surface uplift and topographic evolution of the Himalayan Orogenic Belt. This paper focuses on the field of the Gyirong area in central Himalaya and relies on fission track (FT) thermochronology in revealing the cooling and exhumation and further related tectonic and topographic information of the GHS. Fission track thermochronology yields zircon FT ages between 13 and 2.4Ma and apatite FT ages between 1.9 and 0.6Ma across a 30km north-south GHS section. Spatially, the FT ages show positive correlation with both elevation and latitude position. In combination with regional thermochronologies, these FT ages suggest three episodes of cooling and exhumation of the GHS. ① Middle Miocene, to ~13Ma, regional syntectonic rock cooling by large scale extension of the Southern Tibet Detachment System (STDS); ② Late Miocene slowed cooling by the ceasing of ductile extension of the STDS; ③ approximately since Pliocene, from ~5.8-2.7Ma, rapid and accelerated cooling. Combined with tectonic landform analysis of the Gyirong drainage, the FT thermochronological spatial pattern suggests that the Pliocene rapid cooling was driven by surface processes dominated by river incision. The regional transition from tectonic to climatic exhumation of the Himalaya may probably imply that the Himalaya had accomplished a significant elevation before Late Miocene, and further drove a significant change in local and even global climate, which in turn established the base for climate exhumation of the Himalaya since Pliocene.