塔里木盆地西南部南华纪-震旦纪裂谷分布及原型盆地演化

Distribution of Nanhua-Sinian rifts and proto-type basin evolution in southwestern Tarim Basin,NW China

利用野外露头、地震、钻井及区域航磁资料,对塔里木盆地西南部(下文简称塔西南)南华纪-震旦纪裂谷分布进行分析,在新元古代-寒武纪不同时期岩相古地理恢复基础上,探讨了研究区原型裂谷盆地演化模式。研究发现,新元古代Rodinia超大陆裂解事件在塔西南克拉通边缘和内部形成三叉裂谷系并分布在昆仑山前和麦盖提斜坡。昆仑山前裂谷呈近东西向展布,是三叉裂谷系发展为大洋的裂谷。麦盖提斜坡发育呈北东向展布的罗南和玉北衰退型裂谷,裂谷内部表现为多个地垒、地堑组成的复合堑-垒结构特征。塔西南新元古代-寒武代原型盆地演化可划分出南华纪裂谷、震旦纪初始被动大陆边缘、寒武纪稳定被动大陆边缘3个阶段。经历了南华纪末、震旦纪末区域性构造运动,但塔西南地区构造格局未发生明显改变,南华纪裂谷期沉积中心在震旦纪-早寒武世表现出继承性特征。其中昆仑山前南华纪裂谷在震旦纪-早古生代演化为克拉通边缘坳陷,麦盖提斜坡中段罗南衰退型裂谷在早寒武世成为台内凹陷,与斜坡东、西段古隆起构成“两隆一凹”的古地理格局。麦盖提斜坡中段罗南衰退型裂谷的后期演化形成了震旦系和下寒武统两套成藏组合,是该区今后重要的勘探方向。

Based on seismic data,outcrop evidence,logging data and regional aeromagnetic data,the distribution of Nanhua–Sinian rifts in the southwestern Tarim Basin was analyzed,and on the basis of restoration of lithofacies paleogeography in different periods of Neoproterozoic–Cambrian,the evolution model of the proto-type rift basin was discussed.The Neoproterozoic Rodinia supercontinent split event formed the trigeminal rift system at the edge and inside of the craton in the southwestern Tarim Basin located in the Kunlun piedmont and Maigaiti slope.The rift in Kunlun piedmont zone was distributed along the E-W direction and was the oceanic rift in the trigeminal rift system.Two decadent rifts in N-E strike developed in the Luonan and Yubei areas of Maigaiti slope,and the interior of the rifts were characterized by a composite graben-horst structure composed of multiple grabens and horsts.The Neoproterozoic–Cambrian proto-type basin evolution in the southwestern Tarim Basin can be divided into three stages:rift in the Nanhua,embryonic passive continental margin in the Sinian,and stable passive continental margin in the Cambrian.Despite the regional tectonic movements in the end of Nanhua and Sinian,the tectonic framework of the southwestern Tarim Basin had not changed significantly,the sedimentary center of Nanhua rift basin showed the characteristics of succession in the Sinian–Early Cambrian.The Nanhua rift in Kunlun piedmont evolved into a craton marginal depression during the Sinian–Early Paleozoic,while the Luonan decadent rift in the midsection of Maigaiti slope evolved into a sag inside platform in Early Cambrian,constituting the paleogeographic framework of“two paleouplifts and one sag”with the paleouplifts in east and west sides of the slope.The later evolution of the Luonan decadent rift in the midsection of the Maigaiti slope formed two sets of reservoir-forming assemblages,the Sinian and the Lower Cambrian ones,which are important exploration targets in future.