察尔汗盐湖石盐的流质包裹体氢氧稳定同位素分析及其地球化学意义

HYDROGEN AND OXYGEN STABLE ISOTOPE ANALYSES OF FLUID INCLUSIONS IN HALITE IN CHARHAN SALT LAKE WITH GEOCHEMICAL IMPLICATIONS

本文是在建立了盐酸胍法制备样品用于氧同位素分析方法研究的基础上,测定了察尔汗湖区各类天然水及ZK88—01占孔岩心的原生石盐流质包裹体氢氧稳定同位素组成。该方法适用于高盐度卤水微量δ^(18)O分析,具有成本低、操作简便和定量转化的优点,值得在国内推广。 根据原生石盐包体水δD、δ^(18)O的分布特征,论述了察尔汗盐湖距今5万年来湖水的演化历程。划分出三种不同成盐环境下的演化期,各期中古湖水体具有波动的继承性,各期间可能存在成盐环境的突变.根据天然水δD、δ^(18)O关系初步获得该区蒸发线为:δD=2.5δ^(18)O-45.3;证实了剖面上部淤泥水与达布逊湖水下渗有关;下部明显地有侧向水补给.

The stalble isotope composition of primary fluid inclusions in a crystal represents the isotopic composition of the liquid in which that crystal formed. By studying the isotope composition of the primary fluid inclusions in evaporite minerals from ancient lake deposits, we can explore the history of ancient salt lakes. An analysis of the hydrogen and oxygen isotopic ratios of primary halite fluid inclusions was conducted in a long core, (about 47m) on the north shore of Dabusun Lake, Charhan saline pan, Qaidem basin, China.Brine samples were also collected in the vicinity of Dabusun lake. An analytical method suitable for micro-water samples, including fluid inclusions (typically less than 8 mg) has been established.The method involves reaction of water with zinc to produce H2and water with guanidinc hydrochloride to produce CO2. The standard deviation of the guanidine hydrochloride method is ± 0.15- ± 0.30‰ in water samples and ± 0.61‰ in samples from fluid inclusions.The standard deviation of the zinc method for fluid inclusion samples is ± 4.8‰. The texture of halite and the stable isotopic relationships of primary halite fluid inclusions in a long core show that the history of Charhan Lake (from about 50, 000 years ago to now) can be divided into 3 evolution periods with different salt- forming environments: the relatively stable desiccation period (50, 000-30, 000a.B.P), the fluctuation desiccation period with low temperature (30, 000-15, 000 a.B.P.) and the fluctuation desiccation period with temperture increasing (from 15, 000 a.B.P. to now) For all three periods there appear to have been minor fluctuations between fresh and saline water , the lake never became dried, but there appear to have been sudden changes on salt-florming environment between these periods. Modern Dabusun Lake originated as a dissolution lake, like the newborn (1967) West Dabusun Lake, however, Dabusun Lake is concentrataed enough to form potash salts on its northern shore.The water supply to the modern Charhan saline pan is dominated by meteoric water (mainly from the Kunlun Mountains to the south), however, smaller amounts of oil field brines do flow to the surface along the north edge of the Charhan saline pan.