内蒙古四子王旗小文公乡古元古代基性岩墙锆石测年及其构造意义

Zircon LA-ICP-MS U-Pb dating and the tectonic significance of Paleoproterozoic basic dyke in Xiaowengong township,Siziwangqi banner,Inner Mongolia

通过对内蒙古中部四子王旗小文公乡地区侵入华北克拉通结晶基底的辉长辉绿岩墙样品开展锆石LA-ICP-MS U-Pb定年,共获得3组年龄数据,结合锆石CL图像特征分析认为:第一组位于锆石核部的测点获得207 Pb/206 Pb年龄为1925~1934 Ma,应为捕获锆石,揭示出与华北克拉通北缘基底一致的1930 Ma左右的年龄信息;第二组6个测点位于锆石幔部,207 Pb/206 Pb年龄分布在1798~1865 Ma之间,加权平均年龄为1838 Ma±30 Ma(MSWD=8.0),代表该岩墙的辉绿岩墙侵位年龄,与华北克拉通早期非造山岩浆岩、结晶基底广泛经历的1850~1800 Ma的麻粒岩相-高角闪岩相变质作用以及裂谷沉积时代相对应,暗示华北克拉通在古元古代末已经成为前罗迪尼亚大陆的一部分,此后进入相对稳定时期,于1830Ma左右开始经历伸展作用;第三组年龄为变质年龄,4个测点的206 Pb/238 U加权平均年龄为281.0 Ma±7.8 Ma(MSWD=6.0),可能是兴蒙造山带碰撞造山事件的响应。本文所揭示的三期热事件,对华北克拉通构造演化历史的对比研究工作具有重要意义。

For LA-ICP-MS U-Pb dating,zircons are collected from the basic dike that intruded in the crystal basement of the North China Craton(NCC)and three groups of age obtained.The first is 1925 Ma~1934 Ma that should be from the captured zircon corresponding to 1930 Ma of age of basement of north margin of the north China craton.Combined with characteristics of zircon CL image the second is 1798 Ma~1865 Ma,the weighted average 1838 Ma±30 Ma(MSWD=8.0)from six points at mantle of zircon sample representing emplacement age of the dyke and corresponding to 1850 Ma~1800 Ma of granulite-high amphiblite metamorphism and rift sedimentation that non-orogenic magmatic rocks and the crystalline basement experienced during early period of the China craton implying that the north China craton was merged into pre-Rodinia continent and became stable since then and was exposed to stretching about 1830 Ma.The third is the weighted average age 281.0 Ma±7.8 Ma(MSWD=6.0),may be response to Xingmeng orogenic collision event.Three heat events revealed in this paper are of significance to correlation of tectonic evolution history of the north China craton.