Late Cenozoic Denudation and Topographic Evolution History of the Lhasa River Drainage in Southern Tibetan Plateau: Insights From Inverse Thermal History Modeling

Abstract

The interaction of surface erosion (e.g., fluvial incision) and tectonic uplift shapes the landform in the Tibetan Plateau. The Lhasa River flows toward the southwest across the central Gangdese Mountains in the southern Tibetan Plateau, characterized by a low-relief and high-elevation landscape. However, the evolution of low-relief topography and the establishment of the Lhasa River remain highly under debate. Here, we collected thermochronological ages reported in the Lhasa River drainage, using a 3D thermokinematic model to invert both late Cenozoic denudation and relief history of the Lhasa River drainage. Our results show that the Lhasa River drainage underwent four-phase denudation history, including two-stage rapid denudation at ∼25–16 Ma (with a rate of ∼0.42 km/Ma) and ∼16–12 Ma (with a rate of ∼0.72 km/Ma). In the latest Oligocene–early Miocene, uplift of the Gangdese Mountains triggered the rapid denudation and the formation of the current main drainage of the Lhasa River. In the middle Miocene, the second stage of the rapid denudation and the high relief were associated with intense incision of the Lhasa River, which is probably due to the enhanced Asian summer monsoon precipitation. This later rapid episode was consistent with the records of regional main drainage systems. After ∼12 Ma, the denudation rate decreases rapidly, and the relief of topography in the central Gangdese region was gradually subdued. This indicates that the fluvial erosion resulting from Asian monsoon precipitation increase significantly impacts on the topographic evolution in the central Gangdese region.

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

“…The highly-elevated Gangdese belt in the southern Tibetan Plateau may have facilitated the formation of the Asian monsoon by forming an orographic barrier (mechanical blocking) or surface sensible heating (Sun and Wang, 2005;Liu and Dong, 2013;Tang et al, 2013) during the late Oligocene-Miocene. During the middle Miocene to late Miocene (~14-5 Ma), the enhanced Asian monsoon increased the precipitation rates and erosion rates of the Yarlung River and its tributaries (Dai et al, 2021;Cai et al, 2021). At the same time, the Indian plate continuously subducted underneath the southern Lhasa Terrane and fragmented into several pieces, resulting in slab-tear with consequential asthenosphere upwelling and formation of N-S normal faults in the shallow crust as discussed above (Fig.…”

“…Therein, tectonic factors include the activity of the Gangdese thrust (GT) and the Great Counter thrust (GCT) (e.g., Yin et al, 1994Yin et al, , 1999Laskowski et al, 2018), the movement of ~N-S trending normal faults due to syn-convergent extension (e.g., Styron et al, 2013;Sundell et al, 2013), and delamination of the Lhasa lithospheric root (e.g., Chung et al, 2003Chung et al, , 2005Zhao et al, 2009). Climatic and erosion processes that might have played a role are the intensified monsoonal precipitation and incision of the Yarlung River and its major tributaries (e.g., Sun and Wang, 2005;An et al, 2006;Cai et al, 2021).…”

“…et al, 2013, 2021). The Lhasa River drainage underwent rapid denudation at ~16-12 Ma with a rate of ~720 m/Ma (Cai et al, 2021). The Nimu River, another tributary of the Yarlung River, experienced intense incision at ~12-8 Ma (Yuan et al, 2009).…”

“…1; Pan et al, 2006;Ji et al, 2009). Tectonically, the southern Lhasa terrane experienced crustal thickening and continuous deformation throughout the Cenozoic, accompanied by extensive magmatic and fault activity (Harrison et al, 1992;Yin et al, 1994Yin et al, , 1999Zhu et al, 2015;Cao et al, 2020). Whereas topographically, the highelevation low-relief landscape of the Gangdese region is being actively incised by the Yarlung River and its tributaries (Dai et al, 2013(Dai et al, , 2021Cai et al, 2021).…”

“…A substantial amount of thermochronological data have been obtained from the Lhasa terrane, particularly from its southern part, and various mechanisms have been proposed to interpret these cooling events based on their localities. For example, along the Lhasa River, thermal history models reveal enhanced basement cooling and denudation in the early Miocene, and were interpreted as a result of the incision of the ancestral Yarlung River system (Li et al, 2016;Cai et al, 2021). While fast exhumation along the midstream Yarlung River in the mid-Miocene and Pliocene-Pleistocene were considered to be related with the combined effect of enhanced precipitation and normal fault activity (Dai et al, 2021).…”