Pb isotope compositions of detrital K‐feldspar grains in the upper‐middle Yangtze River system: Implications for sediment provenance and drainage evolution

Abstract

The upper-middle Yangtze River drains the Qiangtang Block, the Songpan-Ganzi, the Yangtze Craton, and the Qinling-Dabie orogenic belt. These tectonic units have been shown to have heterogeneous Pb isotopic compositions, which allow this isotope system to be used as a sediment provenance tool. In this study we have employed laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) to measure Pb isotope compositions of sand-sized K-feldspar grains from the upper-middle Yangtze River. Data are presented from four major tributaries: Yalongjiang, Minjiang, Jialingjiang, and Hanjiang, as well as from the main Yangtze River near Yichang. A portion of K-feldspar grains in the Yalongjiang shows an ultraradiogenic character ( 206 Pb/ 204 Pb > 20), which is unique in the upper-middle Yangtze. Moreover, these ultraradiogenic grains were transported as far as Yichang, just downstream from the Three Gorges, suggesting that the Pb-in-K-feldspar method could be applied to the sediments within the Jianghan Basin to date the formation of the Three Gorges. Pb isotopic data from Yichang indicate that erosion in the Longmen Shan and neighboring regions is more important than the Jinshajiang in supplying sediment. The grains in Hanoi Basin have little overlap with the Songpan-Ganzi, but show a good match with the Yangtze Craton in its range of lower 206 Pb/ 204 Pb ratios. These observations support the idea that the ''Middle Yangtze'' used to be a tributary of the paleo-Red River and that there has been no drainage linking the SongpanGanzi and the Red River since the Eocene.

Erosion patterns in the Changjiang (Yangtze River) catchment revealed by bulk-sample versus single-mineral provenance budgets

“…The major contribution from the Jialingjiang revealed by mineralogical and stream-profile analyses is not evident. More consistent results were obtained by the analysis of K-feldspar grains (Zhang et al, 2014).…”

“…Broadly concordant erosion patterns were inferred from Pb isotopic compositions of K-feldspar (Zhang et al, 2014), representing 10 ± 2% of Yangtze sand. Amphibole represents 1.4 ± 0.7% of Yangtze sand, and provenance budgets based on the distribution of diverse blue/green amphibole groups in major tributaries provided unrobust and partly discordant information.…”

“…Single-mineral budgets: detrital K-feldspar Zhang et al (2014) used the Pb isotopic signatures of K-feldspars to characterize different sources of sand and found that they overlap widely in the Yalongjiang, Minjiang, and Jialingjiang but are more radiogenic (higher 206 Pb/ 204 Pb) in the Jinshajiang and ultra-radiogenic (highest 206 Pb/ 204 Pb) in the Yalongjiang. Their data set allowed them to conclude that sediment supply is dominated by the Yalongjiang, Minjiang, and Jialingjiang, which drain the eastern flank of the Tibetan plateau and Amphibole-chemistry data set and relative abundance of amphibole types in different rivers are provided in Supplementary Tables S6 and S7. cut across the Longmen Shan with an impressive topographic gradient.…”

“…Diverse methods have been applied to quantify denudation rates, including landscape morphometry, heavy-mineral analyses, bulk-sediment geochemistry, isotope fingerprints of detrital K-feldspar, cosmogenic isotopic tracers, and detrital-zircon geochronology (Chappell et al, 2006;Jie et al, 2007;Yang et al, 2009Yang et al, , 2012Jia et al, 2010b;He et al, 2013aHe et al, , 2014Zhang et al, 2014). Erosion patterns inferred from these different approaches, however, diverge widely.…”

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

“…Published Pb isotopic data from detrital K-feldspar show that sands in the modern Jinsha and Yalong Rivers have distinctive Pb isotopic signals [Clift et al, 2008;Zhang et al, 2014], implying that this method [Tyrrell et al, 2006] might be appropriate for tracing the sediment source(s). In this study, based on detailed field investigation, we have used detrital K-feldspar Pb isotopic data from the Xigeda Formation and modern rivers draining SE Tibet to constrain their provenance.…”