Geochemistry of Yarlung Zangbo River Sediments in the Upper, Middle and Lower Reaches, Southern Tibet: Comparisons on Provenance, Weathering and Climate Change

Abstract

Sediment geochemistry serves as a powerful proxy for understanding Earth‐surface dynamics. This study presents the first comprehensive analysis of major and trace elements alongside weathering indices (Chemical Index of Alteration—CIA, Compositional Variability—ICV) from fluvial sediments to characterise spatial variations in provenance, weathering, and climate history from the upper to the lower reaches in the Yarlung Zangbo River (YZR). High ICV in the middle reaches suggests limited compositional modification during transport. Low CIA values (avg. 55 ± 8) indicate weak chemical weathering under a cold‐arid regime, peaking in the middle reaches. Significant differences in calculated temperatures reveal the coldest conditions in the upper reaches and the warmest in the middle, consistent with modern temperatures. Abnormally weathered materials across all YZR regions are likely attributed to extreme climates and diverse landforms, especially in the upper and lower reaches. Physical weathering dominates sediment production in the YZR, which is derived from the Lhasa Terrane and Himalayan regions. The midstream displays the most diverse range of materials, whereas upstream and downstream sediments are primarily felsic, likely sourced from Paleogene Linzizong volcanic rocks and the Great Himalayan Crystalline (GHC). Complex lithologies contribute to spatial differences in geochemical provenance. These results reveal the interactions among provenance, weathering, and climate, highlighting the impact of diverse climates and active tectonics on geochemical processes.