活动陆块背景下蒸发盆地后生阶段富钾区的演变

Evolution of the Potash-Rich Areas in Evaporation Basin during the Epigenetic Stage with Continental Block Being Active

在分析四川盆地成钾地质背景的基础上,提出"成盐源控论"的思想,"成盐源"为早期符合成盐条件下的沉降中心。指出富钾区并不一定在最利成盐的沉降中心,可能经过卤水的运移沉积在凹陷边缘压力相对较低的地带。在成岩阶段,随着沉积凹陷的不断埋深,沉积厚度不断增厚,储卤层剩余压力持续增加,温度不断上升,钾盐的溶解度升高,以至于钾盐在深盆中只会不断地溶解而不会沉积,在压实作用下,压实卤水从凹陷中心流向凹陷边缘。富含钾的地下水运移至压力相对较低的位置,在一定的条件下得以析出或富集。以四川三叠系南充盐盆杂卤石和平落坝富钾卤水成矿特点为例作进一步详细说明。

Based on analysis of potash-forming background in the Sichuan Basin, the theory of ＂source con- trol＂ for potash is proposed. The so-called source areas are referred to those sinking centers meeting the conditions of forming potash early while the potassium-rich areas are probably not the early potassium＇ s sedimentary centers and after migrating along with brine potassium possibly would deposit in the edge of the depression where formation＇ s pressure is relatively low. During the diagenesis stage, the sedimentary center increasingly subsided, resulting in larger depositional thickness, greater remaining pressure of potassium reservoir and higher temperature of formation. Under such conditions, the potash＇ s solubility increases so much that potash＇ s solution is prior to its accumulation in the deep depression＇ s center. Drived by the compaction force, the potassium-rich water in the sedimentary rock would flow from the center to the edge of depression. At last, the potassium-rich water would migrate to those areas with lower pressure, then precipitate and accumulate so as to develop potash deposit. In this paper, the ore-forming characteristics of both the Triassic Nanchong salt basin polyhalite and the Pingluo Dam potassium-rich brine in Si- chuan Basin are taken as examples for further detailed discussion.