Exhumation of the Indus-Yarlung Tsangpo Suture Zone (NW India): New constraints from low-temperature thermochronology

Zhou, Renjie1, Aitchison, Jonathan C.1

1School of Earth and Environmental Sciences, The University of Queensland, St Lucia, QLD 4072, Australia

The Indus-Yarlung Tsangpo Suture Zone (IYTS) is the zone of original contact between two colliding masses of continental lithosphere, the Indian subcontinent and Eurasia. It extends for several thousand kilometres and is well exposed in NW India, southern Tibetan Plateau, and near the border between India and Myanmar. The rock record in the IYTS contains information regarding evolution of the now vanished Tethyan Ocean, its closure, and the on-going growth of the Himalaya. In the NW Himalaya, the IYTS zone is well exposed in the Zanskar River valley, and incorporates an array of sedimentary rock units collectively referred as the Indus Basin. On its northern side, the Indus Basin is in depositional contact with the Ladakh Batholith, the exhumed ‘root’ of the Trans-Himalayan continental arc that developed along the southern margin of Eurasia in association with subduction of Tethyan oceanic lithosphere. To the south, the Indus Basin contains rock units that are in faulted contact with rocks that represent the former margin of the Indian continent.

We present new low-temperature thermochronologic data produced by apatite U-Th/He, apatite fission-track and zircon fission-track methods. Samples were taken from the southern edge of the Ladakh Batholith where the depositional contact between the batholith and the Indus Basin (the Indus Molasse) is observed. A series of samples was also taken from the Indus Basin along river gorges that traverse the IYTS. Previous apatite fission track (AFT) ages from across the Ladakh Batholith are generally young along its northern flank (as young as ~5-6 Ma) while AFT ages from the south are older, spanning from ~22 to 35 Ma. We further constrain exhumation of the northern Indus Basin and southern Ladakh Batholith by applying geologic constraints to our thermal models, yielding evidence for two episodes of rapid exhumation in the late Eocene and Miocene. Preliminary AFT ages from the Indus Basin indicate exhumation at around 15 Ma, consistent with the second cooling episode observed along the southern Ladakh Batholith.


Biography

Dr Renjie Zhou holds the position of Lecturer in Tectonics at School of Earth and Environmental Sciences (SEES) at UQ. His research focuses on reconstructing the evolution of modern and past tectonic plate boundaries using a combination of field and laboratory (mostly geochronology and thermochronology) approaches.

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