内蒙古东乌旗瓦窑地区奥陶纪铜山组沉积时代及构造环境判别

铜山组作为内蒙古北疆兴安地层区早古生代的沉积记录,其沉积环境、成岩时代及构造环境的研究是认识兴蒙造山系早期构造演化的理想窗口。对出露于内蒙古东乌旗瓦窑地区的奥陶纪铜山组进行沉积序列、沉积相及沉积物特征研究,结果显示铜山组为一套陆源碎屑浊积岩。首次获得铜山组中夹层凝灰岩LA-ICP-MS锆石U-Pb年龄为458.5±2.6Ma,显示其沉积时代为中奥陶世—晚奥陶世早期。碎屑岩地球化学分析揭示,铜山组物源区主要具活动大陆边缘和大陆岛弧特征。结合区域地质资料,推测其为活动大陆边缘环境下浊积扇沉积的产物。

Tectonic background and deposition epoch of the Tongshan Formation in Wayao area of Dong Ujimqin Banner, Inner Mongolia

The sedimentary environment, deposition epoch and tectonic environment type of Tongshan Formation as well as the early Paleozoic sedimentary records of Xing''an stratigraphic region constitute an important window to study the early stage tectonic evolu-tion of Xing-Meng orogenic belt. The authors studied Ordovician Tongshan Formation exposed in the Wayao area of Dong Ujimqin Banner in Inner Mongolia. Sedimentary sequence, sedimentary facies and features of sediments indicate that Tongshan Formation is ter-rigenous clastic turbidite. LA-ICP-MS zircon U-Pb dating of volcanic tuff sampled from Tongshan Formation yielded the deposition-al age of 458.5±2.6Ma for the first time in Inner Mongolia and restricted its age between late Middle Ordovician and early Late Ordovi-cian. Geochemistry of the detrital rocks shows that the tectonic setting of the provenance for the Tongshan Formation is mainly charac-terized by the Active Continental Margin (ACM) and Continental Island Arc (CIA). Combined with the regional geological data, the authors infer that the Tongshan Formation was formed by the turbidite fan in a active continental margin tectonic environment.