塔里木盆地西北缘震旦系沉积物源分析及对盆地属性的制约

Provenance analysis of Sinian sediments on the northwestern margin of Tarim Basin and its restriction on basin types

新元古代是全球大地构造演化中一个十分重要的阶段,经历了罗迪尼亚(Rodinia)超大陆聚合和裂解的过程。作为我国三个最主要的克拉通盆地之一的塔里木盆地,其发育的新元古界南华系和震旦系沉积体系纪录了大量新元古代盆地构造属性和板块动力学信息,同时也是塔里木克拉通盆地深层油气勘探的重点层系。以塔里木盆地西北缘什艾日克剖面震旦系为对象,在野外调查和沉积学特征研究的基础上,开展碎屑锆石U-Pb定年和物源示踪研究。震旦系苏盖特布拉克组碎屑锆石存在约2600,2300,2000~1800,790~730和620 Ma等5个年龄峰值,其中2600,2300和2000~1800 Ma年龄峰值的碎屑锆石来自于塔里木克拉通内部新太古代-中元古代基底;790~730 Ma年龄峰值的碎屑锆石可能来源于塔里木盆地新元古代晚期的裂谷岩浆作用形成的岩浆岩;而620 Ma年龄峰值的锆石直接来自地层沉积时的岩浆作用,表明碎屑物质可能来源于塔里木盆地本身。结合地震剖面所具有断陷-坳陷的结构特征、南华系快速充填的浊积岩沉积建造、震旦系由碎屑岩建造转变为海相碳酸盐岩建造、震旦系苏盖特布拉克组沉积同期的岩浆作用,认为塔里木盆地西北缘震旦系经历了裂谷性盆地的断-坳转换阶段和坳陷阶段。

The Neoproterozoic is a very important stage in the global tectonic evolution,which experienced the amalgamation and break-up of the Rodinia.The Nanhua and Sinian strata in the Tarim Basin,which is one of the three major craton basins,have recorded a great deal of information about the tectonic attributes and plate dynamics of the basin in the Neoproterozoic.These are also the key strata for deep oil and gas exploration in the Tarim Craton Basin.Based on field investigations and studies of sedimentary characteristics,this paper studies the U-Pb dating of detrital zircons and provenance of sediments from the Sinian strata outcropped on the northwestern margin of the Tarim Basin.The age distribution of detrital zircons from the Sugetebrak Formation have five peaks in age of about 2600,2300,2000-1800,790-730 and 620 Ma.The detrital zircons with peak ages of 2600,2300 and 2000-1800 Ma are from the Neoarchean-Mesoproterozoic basement within the Tarim Craton,the detrital zircons with peak ages of 790-730 Ma may be derived from magmatic rocks formed by rifting during the late Neoproterozoic in the Tarim Basin,and the zircons with a peak age of 620 Ma were directly derived from magmatism at the time of formation deposition.These results suggest that the clastic material may have originated in the Tarim Basin itself.In view of the fault depression to depression structure on seismic profile,the rapidly filled turbidite sedimentary construction in the Nanhua strata,the transformation of Sinian strata from a clastic rock sequence to a marine carbonate sequence,and the magmatism during the sedimentary period of the Sinian Sugetebrak Formation,it is concluded that the northwestern margin of the Tarim Basin experienced the transition from fault-depression to rift subsidence during the Sinian.