鄂尔多斯盆地安塞地区三叠系延长组碎屑锆石U-Pb定年及其地质意义

通过统计前人对周缘岩浆岩、变质岩体的年代学成果,对比邻区碎屑锆石年龄结果,结合区域构造背景,运用LA-ICP-MS U-Pb年代学分析方法,对鄂尔多斯盆地安塞地区三叠系延长组上部砂岩中的碎屑锆石进行系统研究,以探讨延长组长2段地层物质来源。结果表明:1)安塞地区延长组长2段沉积时代不早于230±2 Ma;2)物源来自盆地北部、东北部;3)碎屑锆石中2 600~2 400 Ma的锆石来自于阴山和大青山—乌拉山地区,与2 500 Ma克拉通化形成大规模岩浆事件相对应;2 000~1 800 Ma的锆石来自于大青山—乌拉山、集宁以及阴山地区,与吕梁运动的两幕发生裂陷盆地闭合和非造山岩浆活动和基底抬升相关;显生宙中380~350 Ma、300~250 Ma、250~230 Ma的锆石来自于大青山—乌拉山、阴山地区,记录了古亚洲洋向华北板块北缘的快速俯冲事件,对应了海西期和印支期的岩浆事件。

Detrital zircon U-Pb dating of Triassic Yanchang Formation in Ansai area,Ordos Basin and its geological significance

According to the statistical data of the previous geochronology results of the magmatic and metamorphic rocks around the periphery, compared the result of detrital zircon age near area and combined with the regional tectonic background, using the method of LA-ICP-MS, systematic studied the detrital zircon age from the upper sandstones of Upper Triassic Yanchang Formation of Ansai area in Ordos Basin. This paper discussed the material provenances of Chang 2 in research area. The results show that：the age of Chang 2 of Upper Triassic Yanchang Formation in Ansai area is not earlier than 230±2 Ma. The provenance is from the northern and northeastern parts of Ordos Basin and the group of 2 600～2 400 Ma indicates that its material provenances may mainly come from Yinshan Mountain and Daqingshan-Wulashan region, which corresponds to 2 500 Ma cratonization and large-scale magmatic events, the group of 2 000～1 800 Ma indicates that its material provenances may mainly come from Yinshan Mountain, Daqingshan-Wulashan Mountain and Jining region, which corresponds to the Lüliang Movement of the two scene rift basin closure and related to anorogenic magmatism and basement uplift. The group of Phanerozoic 380～350 Ma, 300～250 Ma, 250～230 Ma indicates that its material provenances may mainly come from Yinshan Mountain and Daqingshan-Wulashan region, which records the paleo-Asian Ocean rapid subduction events in the northern margin of the North China plate, which corresponds to Hercynian and Indosinian magmatic events.