Evolution of the Yangtze River network, southeastern Tibet: Insights from thermochronology and sedimentology

Abstract

We performed apatite and zircon (U-Th)/He dating on a granitic pluton that has been offset by ~10 km by motion on the sinistral strikeslip Xiangcheng fault in SW Sichuan, SE Tibetan plateau, where the Shuoqu River incises a deep valley before joining the upper Yangtze River. Mean ZHe cooling ages range from 49.5 ± 2.2 Ma to 68.6 ± 6.0 Ma. Samples located above 3870 m yield mean apatite (U-Th)/He ages ranging from 30.6 ± 1.4 Ma to 40.6 ± 2.7 Ma, whereas samples at lower elevations range from 9.8 ± 1.3 Ma to 14.6 ± 2.7 Ma. In the same region, Cenozoic continental sediments are exposed on the flanks of deep valleys. They consist of unsorted conglomerates and sandstones that partly fill a paleotopography. The sediments were deposited during an episode of rapid sedimentation, followed by incision that varies between 0.5 and 1.2 km. Thermal and exhumational modeling of the granite thermochronometric data indicates rapid cooling during the middle Miocene that was likely related to fluvial incision. Our findings suggest that the upper Yangtze River and its tributary (Shuoqu) were connected by the middle Miocene. Our modeling also supports the idea that the exhumation pattern during the Cenozoic in the southeastern margin of the Tibetan Plateau is spatially and temporally heterogeneous.

Two Stages of Accelerated Exhumation in the Middle Reach of the Yarlung River, Southern Tibet Since the Mid‐Miocene

“…Major drainage settings in the southern and eastern Tibetan Plateau. Topographic map of southern and eastern Tibetan Plateau, showing AHe and AFT ages(Carrapa et al, 2014(Carrapa et al, , 2017Dai et al, 2013;Ge et al, 2017Ge et al, , 2018Ge et al, , 2020Gourbet et al, 2019;Ingalls et al, 2018;Lee et al, 2000, Lee & Whitehouse, 2007Li et al, 2015Li et al, , 2016Li et al, , 2017Nie et al, 2018;Orme, 2019;Ouimet et al, 2010;Replumaz et al, 2020;Rohrmann et al, 2012;Schmidt et al, 2015;Seward & Burg, 2008;Tremblay et al, 2015;Tu et al, 2015;Wang et al, 2007;Yang et al, 2018;Yu et al, 2011;Yuan et al, 2002Yuan et al, , 2009Zeitler et al, 2014). Locations of measured sections of Siwalik Group are fromLang and Huntington (2014).…”

Formation of the Yangtze Three Gorges: Insights from detrital apatite fission‐track dating of sediments from the Jianghan Basin

“…In addition, the endemic East Asian cyprinids which dispersed from the Pearl River and Red River drainages (location in Figure 1) to the Yangtze River suggest that the Three Gorges had been formed at the late Oligocene-early Miocene (Chen et al, 2021). Our AFT data do not reflect a major contribution from the Tibetan Plateau which should be well recognized by a Cenozoic exhumation signal (Cao et al, 2019;Gourbet et al, 2020;Wang et al, 2011). This can be related to dilution along the Yangtze drainage (Sun et al, 2020) because the eastern margin of the Tibetan Plateau is thousands of kilometres away from the Jianghan Basin.…”

Contrasting exhumation histories and relief development within the Three Rivers Region (south-east Tibet)

“…1). Glacial erosion and vigorous periglacial processes have been shown to be efficient in smoothing high-elevation regions above the glacial equilibrium line altitude (ELA) (Brozovic et al, 1997;Egholm et al, 2009Egholm et al, , 2017Hales and Roering, 2009). Zhang et al (2016) have proposed that these processes could be active in south-eastern Tibet and could lead to seemingly continuous low-relief high-elevation surfaces despite spatially differential and diachronous tectonic exhumation of 2-4 km between the surfaces.…”