中国地台区张裂盆地沉积

本文着重讨论中国地台区某些张裂盆地的沉积与演化特征。张裂盆地可分为陆内断陷和裂谷、克拉通边缘裂陷槽和被动大陆边缘。裂谷在发展过程中依次形成玄武岩-红层-蒸发盐组合或玄武岩-红层-煤系组合→深湖相组合→红层组合。中小型断陷的岩石组合类似但多不完整。豫陕裂陷槽的岩石组合为下部硅碎屑岩组合,以钾玄岩系为主体的火山岩组合,上部硅碎屑岩-碳酸盐组合,以及较深水相泥硅质岩组合。地处被动大陆边缘的扬子地台南部早寒武世海是以波浪作用为主的陆架,其东南边缘的石煤可能是远洋、半远洋沉积。本文还扼要讨论了张裂盆地在控制某些矿产资源的形成与分布方面的一些问题。

SEDIMENTATION OF EXTENSIONAL BASINS IN PLATFORM REGIONS OF CHINA

Extensional basins in platform regions of China can be divided into three types; intracontinental faulted basin and rift, aulacogen, and passive continental margin. Intra continental faulted basin and rift are predominated by nonmarine deposits, with some exceptions of marine transgression in paralic basins. During the processes of rifting, basalt-red bed-evaporite association or basalt-red bed-coal bearing series association→deep water lacustrine association→red bed association could be formed successively. Rock associations in medium to small faulted basins are similar but mostly incomplete, also with differences in volcanic rock types. The strike of depositional facies belt is controlled to some extent by characteristic tectoienic-morphologic configuration of faulted basin and rift. Differences of aulacogen from rift lies in: long period of development, connected with geosyncline at a high angle and marine environment dominated in whole evolution. In the Henan-Shaanxi Aulacogen, rock associations formed during the processes of basin development are in the sequence of lower siliciclastics association, volcanic rock (dominated by potassic basalt) association, upper siliciclastics-carbonate association, as well as relatively deep water facies mud silicalite, which is basically similar to other aulacogens. Deep water association should be further investigated, however. Distribution of sedimentary facies belt is also controlled to a certain extent by tectonic-morphologic configuration. Tidal dominated environment is quite similar to modern analogues The early Cambrian sea in the southern part of Yangtze Platform where once was a passive margin was a wave-dominated shelf environment, with little differences to modern analogues. Early Paleozoic stone coals developed in the southeastern margin of the Yangtze Platform and its adjacent area probably are pel agic and hemipelagic deposits. The anoxic event relatedto a warm ocean with high sea level possibly occurred during the Sinian and early Paleozoic. The formation and distribution of some mineral resources are also controlled by ext ensional basins, such as turbidite and burial hill oil reservoirs in the Tertiary rift, phosphorite and nickel-molybdenum polymetal ore deposits in shelf region of the passive continental margin. It is rare in the world that anoxic event of oceans had made stone coal widely distributed, stone coal should be considered as an important hydrocarbon source rock. Many reports have shown that some mineral resources are closely related to aulacogen, such as Precambrian syndeposi-tional layered and massive sulfide deposits and uranium-vanadium-copper stratabo-und deposits, even the Witwaterstrand type gold-uranium pyrite ore deposits in South Africa. Therefore, it is necessary to treat extensional basins including aulacogen with a due concern.