二连盆地马尼特坳陷中新生代构造演化与沉积充填响应及差异隆升与砂岩型铀成矿的关系探讨

马尼特坳陷是发育在二连盆地中东部的一个伸展性坳陷。晚三叠世和晚侏罗世期间,马尼特坳陷及邻区在多板块近十字交叉挤压应力的作用下发生造山运动,造山运动使造山带区域地壳加厚,造成下地壳发生拆沉作用,从而引发地壳伸展垮塌,在地壳上部发育众多的伸展性盆地,马尼特坳陷就是在这样的背景下形成的。在伸展力的作用下盆地基底经历快速沉降、缓慢沉降、停止沉降阶段。其中快速沉降阶段促使坳陷发育烃源层,为坳陷产出能源打下良好的基础,也为砂岩型铀成矿提供还原剂创造条件。缓慢沉降和停止沉降这2个时期造成坳陷的沉积速度大于沉降速度,主要发育以河流相为主的沉积体系,为盆地内河流相砂体的发育打下良好的基础。在差异隆升作用的影响下,被活化的马尼特坳陷盆缘和盆中深大断裂成为深部油田水上涌至目的层段砂体内的通道,携带CH4、H2S等还原剂的油田水与地表溶滤渗入水中的碳酸铀酰反应,将碳酸铀酰中的六价铀还原成四价铀在适当部位从水中沉淀析出堆积成矿。

Manite depression is an extensional depression developed in the central and eastern part of Erlian basin.During the late Triassic and late Jurassic,orogeny occurred in Manite depression and its adjacent area under the action of nearly cross compression stress of multiple plates,which thickened the crust of the orogenic belt and caused the dismantling and subsidence of the lower crust,which led to crustal extension and collapse,and a large number of extensional basins were developed in the upper crust.Manite depression was formed under this background.Under the action of extensional force,the basement of the basin experienced rapid subsidence,slow subsidence and stop subsidence.Among them,the rapid subsidence stage promotes the development of hydrocarbon source beds in the depression,which lays a good foundation for producing energy in the depression and creates conditions for providing reducing agents for sandstone-type uranium mineralization.During the two periods of slow subsidence and stopping subsidence,the sedimentary velocity of the depression is greater than that of subsidence,and the sedimentary system dominated by fluvial facies is mainly developed,which lays a good foundation for the development of fluvial sand bodies in the basin.Under the influence of differential uplift,the activated basin margin and deep faults in the Manite depression become the channels from the water of the deep oil field to the sand body of the target formation,and the oilfield water carrying reductants such as CH4 and H2S reacts with uranyl carbonate leached into the water,reducing the hexavalent uranium in uranyl carbonate to tetravalent uranium and precipitating and accumulating in the water.