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 δ7Li values. The relatively low δ7Li 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 δ7Li values, and is considered to be affected by evaporite dissolution and the high δ7Li values indicating that precipitation of salt minerals might have resulted in enrichment of 7Li in the remaining water. It is thought that H2SO4 has been involved in crustal weathering in the region, especially in the Nujiang basin.