黄河硫同位素组成与青藏高原隆起

SULFUR ISOTOPIC COMPOSITION OF YELLOW RIVER WATER AND UPLIFT OF THE QINGHAI-XIZANG PLATEAU

黄河水的平均δ３＋ＳＯ值为＋８．４‰，是世界主要大河中硫同位素组成最重的河流；从上游至下游，河水的矿δ３＋ＳＯ值规律性地逐渐增重，在龙门—三门峡河段达最大值。这反映了由于青藏高原隆起而引起的中国西北地区气候干燥趋势及随后出现的沙漠化、古盐湖蒸发岩的形成和黄土堆积环境对黄河水硫同位素组成的控制性影响。

In the last ten-days of September of 1993 we carried out an environmental geology-geochemical investigation along the main channel of the Yellow River. At that time the Yellow River had an ordinary runoff. Water specimens were collected in 15 river sections from the upper to the lower reaches. Each water sample is 10 L and was sampled in the water layer of the surface to 50 cm deep. The water samples were filtered by a fiberglass filter film with 0.45 am bore diameter, and their concentration of SO was determined by means of the chemical gravimetric method.The sulfur isotopic ratio of sulfate was determined by a MAT-252 mass spectrometer after the preparation for the isotopic analysis. All the data given in this paper are expressed in the international conventional “δ” notation. For comparison, at the same time, we took water samples in 13 river sections from the upper to the lower reaches of the Yangtze River and carried out the same determination works for them.From the figure of δ34SO values against SO concentrations we can see that from the upper to the lower reaches of the Yellow River the concentration of SOvaries from 7.5 mg/L to 108mg/L with an average of 81.0mg/L. The δ34SO also shows a wide range. However all δ34SO values of the Yellow River are within a positive range, +3.57-+11.1‰, with a mean value of +8.4‰. There is a nearly positive linear correlation between δ34SO and SO. As contrasted with the Yellow River, the Yangtze River shows a more narrow range of sulphate concentration,16.7-28.4mg/L, with a mean value of 20.5mg/L. The δ34SO ranges from -3.47 to +5.94‰ with the mean value of +2.3‰. No correlation between δ34SO and sulphate concentrations can be found in the Yangtze River water.Comparing the δ34SO of the Yellow and the Yangtze River water to that of water of major rivers in the world it can be seen that the Yellow River water may be the richest in sulfur isotopic composition possibly besides some of rivers in Australia. In contrast the Yangtze River water may be the poorest in δ34SO value. It reveals that these two great rivers, located in the north and the south of China,respectively and flowing through the hinterland of China continent from west to east, are obviously different in the two indexes of δ34SO and sulphate concentration. The Yellow River water is characterized by enriching of 345 with a high sulphate concentration, while the Yangtze River water is characterized by deficit of 34S with a lower sulphate concentration.The characteristics of sulfur isotopic composition of the Yellow River water may be mainly attributed to its unique occurring environment and its sources of sulfur besides the effect of low precipitation lasting for recent more than 10 years and the effect of low water level in 1993. In this paper the variation of δ34SO of the Yellow River water with the change of the environmental condition from the upper to the lower reaches of the river is described in detail.To summarize, owing to the great uplift of the Qinghai-Xizang Plateau the climate in the northwest area of China tends gradually to drying. Accompanied wnh this uplift other important geological processes, such as desertification, loess deposition and the formation of the Yellow River with a tremendous sand content. occurred in succession. The Yellow River water with a high sulphate concentration and a richer sulfur isotopic composition seems to be related to these processes, especially the uplift of the Qinghai-Xizang Plateau. As to the remarkable geochemical difference in sulfur isotope and sulphate concentration between the Yellow River and the Yangtze River can possibly be interpreted by separation of the Qiuling mountains.