老挝他曲盆地钾盐矿床蒸发岩硫同位素特征及成钾指示意义

Characteristics of Evaporites Sulfur Isotope from Potash Deposit in Thakhek Basin,Laos,and Its Implication for Potash Formation

老挝含盐盆地白垩纪时期位于新特提斯域东南部,晚白垩世沉积了巨型钾盐矿床.其中,万象东南部的他曲盆地钻孔含盐系中硬石膏δ34SV-CDT值集中分布在13.8‰～ 15.3‰,与同期海相蒸发岩δ34S值近似,表明石膏为海相成因.据此,也进一步证实老挝含盐盆地成钾物质大多来自于同时期的古海水,但同时也受到大陆水的掺杂.依据老挝含盐盆地与思茅盆地钾盐矿床沉积时代相近,同时结合勐野井组石膏硫同位素组成,笔者初步认为两盆地在硫同位素组成上具有相近的海源特征,推断它们在海侵期可能曾连通.

The Laos＇s salt-bearing Basin was located in the southeast of new Tethys domain during Cretaceous and hosted huge potash deposit during late Cretaceous.δ34Sv-cDT of anhydrite from borehole of Thakhek basin located in the southeastern Vientiane with value of 13.8‰ ～ 15.3‰ is similar to that of contemporaneous marine evaporites that indicated these anhydrites were with marine origin.These evidences further prove that the potassium materials in both the Laos＇ s salt-bearing basin sourced from Cretaceous seawater with the mixture of fresh water from land.Combining with the update data that the time of potash deposition in both the Laos＇ s salt-bearing basin and Simao basin was approximated and sulfur isotopic composition of Mengyejing Formation,we inferred that the sulfur isotopic composition in both the Laos＇ s salt-bearing basin and Simao basin were consistent with that of contemporaneous sea water and proposed a preliminary scenario that the two basins were possibly connected when marine transgression happened.