| Citation: | WANG Yu，NIMA Ciren，LIU Haiyong，et al. Thermochronologic study on initiation timing of north–south rift systems in Qinghai-Xizang Plateau: A case study of western Lhasa terrane[J]. Bulletin of Geological Science and Technology，2026，45（6）：1-9 doi: 10.19509/j.cnki.dzkq.tb20250377
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The Miocene north–south rift systems within the Qinghai-Xizang Plateau represent a key expression of intracontinental east–west extension following the India–Eurasia collision, and investigating their initiation mechanism and along-strike propagation patterns is critical for deciphering deep lithospheric geodynamic processes. Two competing end-member hypotheses have been proposed for these rifts. One advocates north-to-south rift propagation, whereas the other supports south-to-north unidirectional expansion, and this controversy remains unresolved. This study focuses on the Lunggar Rift and the Dangre Yongcuo–Xuru Co Rift in the western Lhasa terrane. It aims to constrain the timing of tectonic activity along the southern segments of these two major rifts, compare the new results with published thermochronological datasets from their northern segments, discriminate the along-strike propagation behaviour, and further unravel the deep geodynamic driving forces.
Zircon and apatite fission-track low-temperature thermochronology was applied to Gangdese granite and Miocene clastic sandstone samples collected from the southern segments of the two rifts. Monte Carlo thermal-history inversion was implemented via the HeFTy software package to reconstruct the cooling-exhumation evolutionary paths of rocks and provide chronological constraints on the activation timing of normal faults.
Zircon fission-track dating on granite samples yielded an early-Miocene cooling age of (25.9 ± 2.7) Ma. Apatite fission-track ages were predominantly clustered within 12-10 Ma. Thermal-history modeling identified a prominent rapid-cooling episode during 10-8 Ma, with an estimated cooling rate of ～50 ℃/Ma and a corresponding vertical uplift rate of ～2 km/Ma. When integrated with previously published thermochronological results from northern rift segments, data from this study demonstrated roughly synchronous rift-related exhumation along strike. Detrital apatite fission-track analyses resolved two distinct exhumation age peaks at (13.7 ± 2.0) Ma and (8.0 ± 2.9) Ma, documenting multiphase tectonic exhumation of source terranes. No northward-only or southward-only unidirectional rift propagation was observed.
The initiation of north–south rifts in the Qinghai-Xizang Plateau is predominantly driven by asthenospheric upwelling induced by Indian lithospheric slab tearing, together with vertical buoyancy stresses generated by middle-lower crustal flow. There is no one-to-one spatial correspondence between the surface distribution of rifts and deep slab-tear windows. The development of these rifts marks a critical tectonic transition from mechanical coupling to decoupling between the upper crust and the underthrust Indian lithosphere. Therefore, classical unidirectional rift-propagation models should be reconsidered. This study provides new thermochronological constraints for understanding continental extensional deformation within collisional orogens of the Xizang-Himalayan system.
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