Lithium isotope signatures of weathering in the hyper-arid climate of the western Tibetan Plateau

•Low δ7Li sediments and streams on the western and southern Tibetan Plateau.•δ7Li variations of river sediments correspond to weathering intensity.•Low δ7Li values of major lake inflows reflects limited formation of clay minerals under a hyper-arid climate.•δ7Li differences across the Tibetan Plateau follow the precipitation gradient.