四川盆地三叠系杂卤石形成条件的实验研究

四川盆地三叠系杂卤石有很大一部分产于硬石膏层中,与硬石膏互层。在许多杂卤石产出层位,缺失钾镁盐甚至石盐等易溶盐类。上述现象用已有的研究资料难以解释。本文通过100多个实验点的平衡实验,研究了35℃ K—Na—Mg—Ca—SO_4—Cl—H_2O六元海水体系中,NaCl及K、Mg盐均不饱和条件下杂卤石形成的可能性。与饱和溶液相比,不饱和溶液中杂卤石稳定区收缩。但在饱和溶液被稀释将近1倍时,杂卤石仍有一定的稳定范围。 在实验研究的基础上分析了四川盆地三叠系含杂卤石剖面的成因。由于成盐期卤水频繁地被淡化,形成“石膏——石盐+钾镁盐——石膏”沉积韵律。成岩作用中盐层遭受来自石膏层的水的溶滤。在石膏层较厚,盐层较薄的层段,石盐和钾镁盐可被全部溶掉,形成对NaCl及K、Mg盐均不饱和的液体。当这种对易溶盐类不饱和的液体进入膏层,部分K、Mg组分就能与CaSO_4结合生成杂卤石被保留下来,形成现在所看到的“硬石膏一杂卤石——硬石膏”剖面。

AN EXPERIMENTAL STUDY ON THE FORMATIVE CONDITIONS OF POLYHALITE IN TRIASSIC SYSTEM IN SICHUAN BASIN

This thesis deals with the existence possibility of polyhalite in the six-component sea -water system K+, Na+, Mg2+, Ca2~/Cl~, SO42-2O at 35C by equilibria experiment, on the condition that NaCl and K, Mg salts are unsaturated. The stable existence area of polyhalite in unsaturated solutions becomes contractive,It maintains proper range although solutions were diluted from saturated ones to about half concentrations.On the basis of the experimental data, the origin of polyhalite - bearing sections (Triassic System) in Sichuan Basin has been discussed. Becauce of frequent desalinations of the brine in salt - precipitation stage,"gypsum-halite + K, Mg salts-gypsum" sequences have been deposited. In the course of diage-nesis.the salt bed was dissolved and leached by the solution from gypsum beds. In the localities where gypsum bed was thick and salts bed was thin, halite and K, Mg salts would be dissolved thoroughly. In the above solution, K, Mg components combine with CaSO4 to produce polyhalite. Then, "anhydrite -polyhali te - anhydrite" sequnces have been formed.