远源地下水入侵阿拉善高原沙漠:酸溶物Sr同位素证据

The Invasion of Remote Groundwater into Deserts on the Alxa Plateau: Acid Soluble Sr Isotopic Evidence

  • 摘要: 选取北方西-东向气候剖面上物质组成相似的四个沙漠(塔克拉玛干、巴丹吉林、腾格里和毛乌素),测定其地表沙酸溶物87Sr/86Sr比值、Ca2+和Sr2+浓度。Ca2+和Sr2+浓度相关性极好,在降雨量低的塔克拉玛干沙漠中最高,向东逐渐降低,在降雨量多的毛乌素沙漠中最低。降雨量是控制阳离子浓度变化的主导因素。酸溶物87Sr/86Sr比值在四个沙漠中有不同于阳离子变化的区域特征。塔克拉玛干沙漠酸溶物87Sr/86Sr比值在0.71以下,巴丹吉林和腾格里沙漠的大于0.7112,而毛乌素沙漠的在0.71-0.7112之间变化。塔克拉玛干和毛乌素沙漠地表沙酸溶物87Sr/86Sr比值仅受气候变化的制约。巴丹吉林和腾格里沙漠除了受气候因素影响外还受其它因素的制约,最可能的就是远源地下水。经计算,远源地下水对巴丹吉林沙漠的影响份额为47%,对腾格里沙漠为44%,接近气候因素的影响。

     

    Abstract: 87Sr/86Sr ratios and Ca2+, Sr2+ concentrations of acid soluble fractions of surface sands are measured for four deserts (Taklimakan, Badain Jaran, Tengger and Mu Us) with similar mineral and geochemical compositions in the W-E direction over North China. Ca2+ and Sr2+ concentrations have an excellent correlation, are the highest in the Taklimakan Desert with the low rainfall, decreasing Eastwards, and the lowest in the Mu Us sandy land with the high rainfall. The rainfall is the main factor controlling cationic concentration. Acid soluble 87Sr/86Sr ratios have regional characteristics different from cationic change in the four deserts. Acid soluble 87Sr/86Sr ratios are lower than 0.71 for the Taklimakan desert, more than 0.7112 for the Badain Jaran and Tengger deserts, and change between 0.71 and 0.7112 in the Mu Us sandy land. Acid soluble 87Sr/86Sr ratios of surface sands in the Taklimakan desert and the Mu Us sandy land are only affected by climate factors. The Badain Jaran and Tengger deserts were affected not only by climate factors but also by additional factors, e.g. remote groundwater. By calculation, the effects of remote groundwater presents 47% on the Badain Jaran desert, 44% on the Tengger desert, respectively, approaching the impact of climate factors.

     

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