西藏北羌塘盆地友谊泉水化学特征及成盐指示

Hydrochemical characteristics and evaporate-generating indicators of Youyiquan area in North Qiangtang Basin,Tibet

羌塘盆地是侏罗系海相找钾工作的目标区域。对该盆地泉水的水化学进行研究可对其找钾前景做出有效评价。羌塘盆地友谊泉地区发育有一系列地表泉水,在野外采集了11个泉眼的水体样品,在室内对这些水样进行了化学成分、氢和氧及锶同位素测定。泉水的Cl-含量分别与Na+、矿化度呈正相关关系,钠氯系数接近于1,溴氯系数较低,显示出泉水具有溶滤特征;钾盐系数和钾氯系数较大,指示出较为明显的含钾异常。泉水的氢、氧同位素数据点落在全球大气降水线和区域降水线附近,表明泉水受大气降水所补给;锶同位素数据指示泉水中的矿物质可能来源于夏里组和/或索瓦组。此外,古地理、古气候资料显示,羌塘盆地在侏罗纪期间长期处于干旱气候条件,并于夏里期在北羌塘出现了一个相对封闭的潮坪-泻湖环境。这些证据表明,羌塘盆地内的侏罗系具备较为有利的成盐成钾条件,而夏里组的条件相对较好。

The Oiangtang Basin is an objective area for exploration of Jurassic marine potash deposits. The potashprospecting perspective can be estimated effectively according to research on hydrochemistry of springs in the basin. There is a series of springs in the Youyiquan area in North Qiangtang Basin. In this study water of 11 springs was sampled, and chemical components, δD and δ18O, 87Sr/86Sr were measured in laboratory. Content of Cl- has positive correlation with content of Na＋ and mineralization. Also, n （Na＋ ）/n （Cl-） is close to 1 and Br- ·10^3/Cl- is lower than 1. All of these data indicate that spring water is from leaching water in the strata. Hydrogen and oxygen isotopic data of spring water fall near lines of the global atmospheric precipitation and regional precipitation, which indicates that spring water is supplied by atmospheric precipitation. Strontium isotopic data of spring water suggest further that mineral components of water may come from Xiali Formation and/ or Suowa Formation. Moreover, paleogeographic and paleoclimatic data imply that the Qiangtang Basin was under arid climatic conditions in Jurassic and a relatively closed lagoon existed in North Qiangtang Basin during the Xiali Stage. These data indicate that Jurassic strata of the Qiangtang Basin have favorable conditions for the for mation of evaporite and Xiali Formation seems to be the most favorable strata for evaporite formation.