四川盆地三叠纪古盐湖已达钾石盐析出阶段——来自石盐流体包裹体化学组成的约束

Argument that brine of salty lake in Sichuan Basin had reached crystallizing point of potash minerals during Triassic: Evidence from chemical composition of fluid inclusions in halite

石盐的流体包裹体成分可提供古流体组成的物理化学信息,用以探查卤水组成变化及环境演化规律等。四川盆地位于上扬子地台,其中的早-中三叠纪沉积建造是中国海相找钾的有利层位之一。获取石盐沉积时期的卤水成分信息,是深刻认识四川盆地古海水蒸发浓缩程度的重要途径。文章利用激光剥蚀电感耦合等离子体质谱法,对采自川东地区长平3井嘉陵江组的石盐流体包裹体开展了化学组成分析,结果显示古卤水化学类型为Mg_SO4型;流体包裹体中的ρ(K^+)与现代海水浓缩到钾石盐析出阶段的ρ(K^+)基本一致,可能揭示了盆地三叠纪时期古卤水已达到钾石盐析出阶段,对四川盆地沉积环境演化及钾盐成矿规律研究等具有重要的理论意义。

The chemistry of primary fluid inclusions in halite can be used to study brine composition change and envi- ronment evolution of the salt lake. Sichuan Basin is located in the northwest of the Yangtze Platform, and its early-middle Triassic sedimentary formation is one of the favorable stratigraphic horizons for marine potash ex- ploration in China. The obtaining of the brine composition during halite deposition is an important way for un- derstanding evaporation degree of the ancient seawater in Sichuan Basin. In this paper, the chemical compositionof fluid inclusions in the halite in the fourth member of Jialingjiang Formation wastested by laser ablation induc- tively coupled plasma mass spectrometry （LA-ICP-MS）. The results show that the brine in fluid inclusions has less Ca2 ＋ but abundant SO4-, which suggests the ancient brine chemistry belongs to Mg-SO4 type. Potassium concentration in fluid inclusions is basically consistent with that in modern seawater when it is concentrated to the sylvite precipitation stage. It is revealed that Triassic brine of Sichuan Basin had reached the crystallizing point of potash minerals. The conclusion reached by the authors will be of important theoretical significance for studying sedimentary environmental evolution and metallogenic regularity of potash reurces in Sichuan Basin.