老挝万象平原重力异常及其地质体特征

老挝万象平原盐类矿层赋存于古近纪古新统塔贡组中,含钾矿物以光卤石为主,少量钾石盐。老挝万象平原全区重力为负值,重力场总趋势为西高东(北)低。重力负异常及重力低是由于新生界厚度大、特别是岩盐厚度大,且白垩系基底埋藏深引起。重力高区域与上述相反,是由于古近纪岩盐厚度小、埋藏浅引起;重力高与重力低之间的梯度带多数是由于岩盐及钾盐层埋深及厚度在重力高到重力低之间埋深迅速变浅,厚度快速增大引起。在万象平原东利用重力异常进行钾盐勘查布置钻孔时,应选择重力负异常区及剩余重力异常图上的重力低或以重力低为主的区域,首批钻孔应布在重力负异常及剩余重力异常图上的重力低的中心附近的梯度带上。即布置在靠近盐背斜中心附近的斜坡上。

GRAVITY ANOMALY AND GEOLOGIC BODY CHARACTERISTICS OF VIENTIANE PLAIN OF LAOS

The saline ledge were hosting in the paleocene series Paleogene period Tagong group, most K-bearing minerals are carnallites but few k-halite. The gravity value of Vientiane Plain of Laos is negative, the general trend of gravity field is higher at westem area but lower at easter（northern） area. The gravity negative anomaly and gravity low are cause by the thicker Cenozoic erathern ledge especially the thicker halite ledge and Cretaceous basement embedding deeply. The gravity high area are opposite with it, which were caused by the thin Paleogene halite ledge and shallow embedding. The thickness varying caused the gradient. The area could be choosed while laying bores for potash exploration with gravity anomaly at the weastern Vientiane plain, where gravity low area and the area at gravity negative anomaly zone and residual gravity anomaly figure, so the first group of bores should laying at the gradient near the centre of gravity low at the gravity negative anomaly area and the residual gravity anomaly figure, that is on the slope near salt anticline center.