基于海相石盐流体包裹体的古海水演化热力学模拟
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The Rmodynamic Simulation of Paleoseawater Evolution Based on Halite Fluid Inclusions
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    摘要:

    传统观点认为地质时期海水成分一成不变,然而包裹体测试技术的迅速发展,揭示出显生宙以来海水成分至少发生过两次大的旋回变化。本文基于世界多个海相沉积盆地的原生石盐包裹体实测数据,探讨了显生宙以来古海水地球化学、水化学类型、蒸发岩矿物组合特征的显著变化,并结合EQL/EVP卤水蒸发平衡模型,定量模拟了两种典型海水的蒸发演化过程、析盐规律和矿物组合特征,分析和探讨了中国海相沉积盆地的成钾前景。应用Spencer相图,揭示出在过去的600 Ma期间,古海水成分点在Cl SO4和Ca Cl两个相区内随时间发生周期性的震荡变化,志留纪、泥盆纪、侏罗纪和白垩纪的海水类型与现代海水迥然不同,为典型的Ca Cl型水。Mg 2K SO4 / Mg Ca 2K Jnecke相图分析结果显示,这些时期的石盐包裹体成分,位于富CaCl2、贫MgSO4的Mg Ca 2K相图中光卤石、钾石盐稳定相区,指示原始海水相对于现代海水具有富Ca、贫Mg的特征,其析出的典型矿物组合主要有石盐、钾石盐、光卤石和溢晶石等。而新元古代、二叠纪和第三纪大部分石盐包裹体成分,都落到了Mg 2K SO4相图上的钾盐镁矾和钾石盐相区,和现代海水成分较为类似,具有富Mg2+、SO2-4的特征,其析出的典型矿物组合包括石盐、钾盐镁矾、硫镁矾、钾石盐和光卤石等。EQL/EVP 定量模拟结果显示,富SO4 Mg型的海水和富Ca Cl型的古海水,蒸发演化路径和矿物析出序列截然不同,Ca Cl型的海水更易形成优质钾盐矿床,有利的成钾时段为寒武纪 早石炭世、侏罗世 新生代早中期。

    Abstract:

    The traditional view is that the composition of sea water is invariable during the geological period. However, with the rapid development of the testing technology of fluid inclusion, more and more measured data of fluid inclusion reveal that the seawater composition occurred at least two cyclic changes during the Phanerozoic period. Based on measured data of primary halite fluid inclusions from multiple marine basins in the world, this paper discusses the paleoseawater geochemistry, water chemistry type, significant change of evaporite mineral assemblages since Phanerozoic period. Combined with the brine evaporation balance model of EQL/EVP, this study simulates quantitatively the evaporation process of two typical seawater, analyses the salt precipitation law and mineral assemblages characteristics during evolution process, and evaluates the prospect of potash deposits in marine sedimentary basin in China. The Spencer diagram reveals that the paleoseawaters composition occurs cyclical shift between Cl SO4 and Ca Cl phase zone during the past 600 Ma, the seawater type of Silurian, Devonian, Jurassic and Cretaceous is typical Ca Cl type, which is significantly different from modern seawater. The Mg 2k SO4 / Mg Ca 2k Jnecke diagram show that the halite inclusions composition of Silurian, Devonian, Jurassic and Cretaceous are located in Mg Ca 2K phase zone of CaCl2 rich and MgSO4 poor, Sylvite, carnallite stable phase zone, which indicate the original seawater has the feature of Ca rich and Mg poor in comparison with modern seawater, and the corresponding typical mineral assemblages are halite, sylvite, carnallite and tachyhydrite. But most of halite inclusions composition of Late Proterozoic, Permian and Tertiary, located in sylvite and kainite phase zone of Mg 2K SO4 diagram, is similar to modern seawater composition characterized by Mg rich and SO4 rich, and the typical mineral assemblages is halite, kainite, kieserite, sylvite and carnallitite. The quantitative model results of EQL/EVP show that the SO4 Mg rich and CaCl2 rich seawater have obviously different evaporation evolution path and mineral precipitation sequence, the CaCl2 rich paleoseawater is conducive to quality potash deposits, and the favorable metallogenic epoch is from Cambrian to Early carboniferous, and from Jurassic to early middle cenozoic.

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马黎春,刘成林,马建强,韩继秋,牛磊,孙明光,商雯君.2015.基于海相石盐流体包裹体的古海水演化热力学模拟[J].地质学报,89(11):1962-1969.
MA Lichun, LIU Chenglin, MA Jianqiang, HAN Jiqiu, NIU Lei, SUN Mingguang, SHANG Wenjun.2015. The Rmodynamic Simulation of Paleoseawater Evolution Based on Halite Fluid Inclusions[J]. Acta Geologica Sinica,89(11):1962-1969.

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  • 在线发布日期: 2015-11-02
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