Late Oligocene - Miocene morpho-tectonic evolution of the central Gangdese batholith constrained by low-temperature thermochronology

Abstract

The morpho-tectonic evolution of the Tibetan Plateau is controlled by complicated interactions between tectonic uplift and surface erosion. The Gangdese batholith in the southern Lhasa terrane is a key orogenic belt for exploring the complicated morpho-tectonic evolution of the Tibetan Plateau. In this contribution, we apply apatite fission track (AFT) thermochronology to constrain the thermo-tectonic evolution of the central segment of the Gangdese batholith. Twenty-four granitoid samples were collected from both river valleys (e.g., the Yarlung and Xiang Rivers) and from the internal batholith areas located farther from river drainage (and/or local faults) networks. All samples exhibit Miocene AFT ages between ~19.9 and ~ 6.1 Ma. Inverse thermal history modeling results reveal that the central Gangdese batholith underwent a two-stage accelerated basement cooling in the Miocene. The first cooling stage took place during the late Oligocene to middle Miocene (~25–15 Ma), this period of moderate to rapid basement cooling coincides with activity along the Gangdese thrust and Great Counter thrust system, and the Oligocene-Miocene delamination of the Lhasa lithosphere and concomitant asthenosphere upwelling. These tectonic processes acted as first-order control on regional basement uplift, denudation and exhumation. Second, a middle-late Miocene (~14–5 Ma) rapid cooling is widely recognized in the whole Gangdese batholith. We suggest that this middle-late Miocene cooling is due to exhumation in response to tectonic and surface erosion processes such as N-S normal faults and enhanced river incision induced by the intensification of Asian monsoon. Finally, in combination with published low-temperature thermochronological and paleoaltimetry data, it is deduced that the present-day low-relief landscape of the southern Lhasa terrane resulted from a long-term balance between intense regional tectonic activity and surface erosion.