The Qinghai-Xizang Plateau is an area where a large number of salt lakes are distributed .We have collected several hundred samples of natural waters over the Plateau since 1976 and carried out researches on their hydrogen and oxygen isotopes.The results indicate that thd &D and &^18O values of the salt lake waters over the Plateau range from -64.1 to +12.4‰ and from -11.19 to +8.62‰,respectively.From the different types of surfaces,ground and lake waters of various salinities it is inferred that the compositions of H and O isotopes in the initial water of Qinghai Lake are &D=55.0‰ and δ^18O=-10.0‰,and those in the original water from the lakes in northern Xizang are δD=-116.0‰ and δ^18O=-16.2‰.Brines in the salt lakes are derived from rain water through prolonged cir-culation.Oilfield water also makes some contribution to the salt lakes in the Qaidam Basin.Similar slopes of evaporation lines of water isotopes are noticed for the Qinghai Lake area and northern Xizang.This is attributed to the evolution of the isotopes in these water bodies in an environment of middle latitude and high elevation.
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