内蒙古乌拉特中旗色尔腾山岩群东五分子岩组锆石SHRIMP定年及其地质意义

色尔腾山岩群是华北克拉通中西部早前寒武纪变质结晶基底的主要组成部分，对研究华北克拉通基底演化具有十分重要的意义。色尔腾山岩群的形成时代是目前研究的热点之一，本文通过岩石学和锆石SHRIMP U-Pb定年研究，查明了内蒙古乌拉特中旗乌兰乡查干哈达地区色尔腾山岩群东五分子岩组的岩石组成和年代学特征。东五分子岩组遭受了后期岩浆和构造作用的强烈破坏，未见顶底，主要由中细粒斜长角闪岩、细粒黑云斜长片麻岩、眼球状细粒黑云斜长片麻岩、条带状细粒黑云斜长片麻岩和细粒黑云角闪片岩组成，矿物组合特征指示岩石经历了低绿片岩相-低角闪岩相变质。其中，眼球状细粒黑云斜长片麻岩出露相对较厚，与细粒黑云斜长片麻岩多呈互层状产出，局部偶夹细粒黑云斜长片麻岩。本次研究选取其中新鲜的细粒黑云斜长片麻岩进行了锆石SHRIMP U-Pb测年分析，其锆石多呈自形-半自形，发育震荡环带，主体为岩浆成因，锆石SHRIMP U-Pb定年结果为（1 930.7±9.6）Ma，代表原岩（中酸性火山岩）冷凝结晶年龄，表明东五分子岩组经历变质作用的时代应晚于1 930 Ma。

Zircon SHRIMP Dating and Its Geological Significance of Dongwufenzi Formation of Sertengshan Group in Urad Zhongqi,Inner Mongolia

The Sertengshan Group is an important component of the Early Precambrian metamorphic basement in the mid-west of the North China craton. It is of significance to study the tectonic evolution of the Early Precambrian North China craton. The formation age of the Sertengshan Group is one of the current research hotspots. In this paper, through the study of petrology and zircon SHRIMP U-Pb dating, the rock composition and chronological characteristics of Dongwufenzi Formation of the Sertengshan Group in the Chaganhada area of Urad Zhongqi were identified. The Dongwufenzi Formation suffered severe destruction of magmatism and tectonism in the later period, and has no an intact top and bottom. It is mainly composed of medium-fine amphibolites, fine-grained biotite plagioclase gneisses, augen fine-grained biotite plagioclase gneisses, banded fine-grained biotite plagioclase gneisses, and fine-grained biotite hornblende schists. The mineral assemblage characteristics indicate that it experienced low green schist facies-low amphibolite facies metamorphism. Most automorphic and semi-automorphic zircons with oscillatory zoning indicate its magmatic origin from the fine-bearing biotite plagioclase gneiss. The zircon SHRIMP U-Pb dating results (1 930.7±9.6 Ma) represent the formation age of basal rock, suggesting that the metamorphic age of the Dongwufenzi Formation should be later than 1 930 Ma.