Isotope compositions of dissolved lithium in the rivers Jinshajiang, Lancangjiang, and Nujiang: Implications for weathering in Qinghai-Tibet Plateau

Abstract The Li isotope geochemistry of the Jinshajiang (upper reach of the Changjiang), Lancangjiang (Meckong) and the Nujiang (Salween) rivers have been studied to better understanding the weathering of continental crust. The three rivers show different water geochemistry, the Jinshajiang followed by the Lancangjiang contains much solute from dissolution of evaporites; the Jinshajiang has the highest average Li content and δ 7 Li values. The relatively low δ 7 Li values (+4.74∼+12.9‰) of the river waters, compared to those of large rivers in the world, probably reflect less weathering intensity in this arid and cold region. The Jinshajiang water has relatively high and constant δ 7 Li values, and is considered to be affected by evaporite dissolution and the high δ 7 Li values indicating that precipitation of salt minerals might have resulted in enrichment of 7 Li in the remaining water. It is thought that H 2 SO 4 has been involved in crustal weathering in the region, especially in the Nujiang basin.