内蒙古霍林郭勒地区“宝音图群”锆石U-Pb年龄及其构造意义

Zircon U-Pb ages and tectonic significance of Buyant Group in Holingola area,Inner Mongolia

对内蒙古霍林郭勒地区出露的"宝音图群"砂岩进行了锆石LA-ICP-MS U-Pb同位素测年,样品112个分析点结果显示,具有主要峰值年龄257 Ma、283 Ma、313 Ma和少数老年龄(>1 700 Ma),且257 Ma的年龄表明该地层主体的沉积下限的时代为早三叠世,原定为下元古界的"宝音图群"实为早三叠世地层。该地层物源主要来自于大石寨组火山岩、苏尼特左旗—锡林浩特—西乌旗南岩浆弧和相邻地块的变质基底,并有少量华北板块北缘物源混入,说明在早三叠世初华北板块北缘与北侧地块已经开始碰撞。

The zircon LA-ICP-MS U-Pb isotopic dating of sandstones in Buyant Group in Holingola area of Inner Mongolia has been presented. The results from 112 sampling points show that the main peaks of yield ages are 257 Ma, 283 Ma, 313 Ma and some older ages （ 〉1 700 Ma）. The zircons with a peak age of 257 Ma indicate that the depositional age of the sedimentary rocks was Early Triassic, which means that Buyant Group should be as-signed into Lower Triassic, rather than Lower Proterozoic. The provenance of the sandstones are mainly the volcanic rocks of Dashizhai Formation, the Sunidzuoqi -Xilinhot - southern Xi Ujimqin volcanic arc and the metamorphic basement of the adjacent block, and partly from the northern margin of the North China Plate. It is indicated that the collision between the northern margin of North China Plate and the blocks to the north began in Early Triassic.