Sedimentary provenance constraints on drainage evolution models for SE Tibet: Evidence from detrital K‐feldspar

Abstract

The unusual drainage pattern of the Jinsha River (upper Yangtze) is closely linked to the uplift of the Tibetan Plateau, but when this pattern became established is controversial. In this study we compare the Pb isotopic composition of detrital K‐feldspars from the modern Jinsha River with those from the Plio‐Pleistocene Xigeda Formation, a sequence of fluvial and lacustrine deposits widely distributed along the major rivers draining the Tibetan Plateau, to investigate their relationship and to constrain the drainage evolution of the region. Our results demonstrate that the Jinsha River had achieved its current sediment‐transport pattern by the late Pliocene, indicating a drainage character similar to that operating at present. Our findings not only suggest an upper age limit for formation of the Jinsha River but also shed new light on the evolution of the whole Yangtze system. K‐feldspar grains from the Jinsha River have less radiogenic Pb than those in the Red, Mekong, and Salween Rivers, providing a key test as to whether the Jinsha River was previously connected to the paleo‐Red River. Comparison with published Pb isotopic data shows that these characteristically unradiogenic feldspars are absent in the onshore Cenozoic archive from the Hanoi Basin, suggesting that there has been no connection between the lower Jinsha River and the Red River since the Eocene.

Provenance and Drainage Evolution of the Red River Revealed by Pb Isotopic Analysis of Detrital K‐Feldspar

“…This mineral is unlikely to survive more than one erosion-transport-deposition cycle (Tyrrell et al, 2006;Zhang, Tyrrell, et al, 2014). These characteristics allow accurate Pb isotopic measurements (Clift et al, 2008) and make the K-feldspar wellsuited for the provenance study of first-cycle sediment (Tyrrell et al, 2006;Zhang et al, 2017).…”

“…The yellow dotted lines denote possible paths of the paleo-Red River as proposed by Clark et al (2004). The red dots indicate the Cenozoic sediments in the Hanoi Basin and Panzhihua area studied by Clift et al (2008) and Zhang et al (2017), respectively. The gray dots denote the sand samples from the Jinsha, Red, Mekong, and Salween Rivers by Bodet and Schärer (2001), Clift et al (2008), and Zhang et al (2017).…”

“…The depositional environments of the clastic sediments in the region of this borehole vary over time from coastal plain, littoral and neritic ( Figure 2). Neritic Zhang et al (2017). Neritic Zhang et al (2017).…”

“…Neritic Zhang et al (2017). The gray dots denote the sand samples from the Jinsha, Red, Mekong, and Salween Rivers by Bodet and Schärer (2001), Clift et al (2008), and Zhang et al (2017). The white dotted lines represent the boundary of the Yinggehai-Song Hong Basin.…”

“…, 2008;Flowerdew et al, 2012;Tyrrell et al, 2009;Zhang, Tyrrell, et al, 2014). The heterogeneous Pb isotopic composition in detrital K-feldspars allows us to investigate the sediment provenance of the Red River system (Bodet & Schärer, 2001;Clift et al, 2008;Zhang et al, 2017). In this study, we present a detailed investigation of the Pb isotopic composition of detrital K-feldspar from marine core samples in the Y-SH Basin in order to investigate the provenance variation with implications for the drainage evolution of the Red River since the Oligocene.…”