印支运动在鄂尔多斯盆地和四川盆地启动时间的讨论：来自生长地层的证据

Discussion on the initial timing of the Indosinian movement in the Ordos basin and the Sichuan basin: Constraints from growth strata evidence

造山带的形成、演化与周缘盆地受统一构造事件影响,“盆”与“山”在构造和沉积方面相互耦合,沉积盆地存在造山事件的响应,如生长地层、包卷层理等。生长地层为同构造或同变形阶段沉积,其沉积时代可以有效约束构造事件时代。中央造山带近东西向展布,北侧为鄂尔多斯地块,南侧为扬子地块。中央造山带的形成主要源于原—古特提斯洋的闭合,原特提斯洋在早古生代闭合,古特提斯洋在中生代闭合,后者改造前者并响应全球印支运动。印支运动的启动,一方面促使现今中国大陆雏形的形成,另一方面响应Pangea超大陆的最终汇聚,具有重要的大地构造意义。古特提斯洋闭合,华南地块和华北地块汇聚拼贴,并在鄂尔多斯盆地和四川盆地沉积地层中保留了很好的记录。笔者在鄂尔多斯盆地南缘上三叠统识别出一套生长地层,通过最年轻碎屑锆石与区内相同地层凝灰岩锆石对比,限定印支运动启动时间为233 Ma左右;在四川盆地北缘上三叠统须家河组识别出一套生长地层,通过对比分析,推测印支运动启动时间为216 Ma左右。

The formation and evolution of the orogenic belt and the peripheral basin were controlled by some genetic tectonic events.The"basin"and"range"are coupled to some extent both in structure and sedimentation.Sedimentary structures can always respond to related orogenic events,such as growth strata and convolute bedding.Growth strata are sedimentary records of the tectonic events,and the analysis of their deposit age can effectively constrain the timing of the tectonic events.The Central China Orogen is distributed in the east-west direction.The north side of the central segment is the Ordos block,and the south side is the Yangtze block.The Central China Orogen mainly resulted from the closure of the Pro-Paleo Tethys Ocean,the extinction of Pro-Tethys Ocean happened in the Paleozoic and the Paleo-Tethys Ocean was closed in the Mesozoic.Notably,the latter modified the orogen resulting from the former and responded to the global Indosinian movement.The Indosinian movement not only facilitated the final assembly of supercontinent Pangea,but also was of great significance in the formation of the rudimentary sketch of China’s mainland today.In the process of the Indosinian movement,the South China block and the North China block were collaged,and the Indosinian movement was initiated.The Ordos Basin and the Sichuan Basin recorded the orogenic events well in sedimentary strata.In this paper,the authors identified growth strata in the Upper Triassic on the south margin of the Ordos Basin.The starting time of the Indosinian movement in the Ordos Basin is about 233 Ma.A sets of growth strata were identified in the Upper Triassic on the north margin of the Sichuan Basin and the start time was about 216 Ma.