内蒙古商都地区白云鄂博群尖山组碎屑锆石u-Pb年代学和Hf同位素研究:对华北克拉通西部陆块北缘前寒武纪地壳演化的制约  

Geochronological and Lu-Hf isotopic study on detrital zircons of the Jianshan Formation, Bayan Obo Group in Shangdu area, Inner Mongolia: Constraints on Precambrian crustal evolution of the Western Block,North China Craton

作　　者：李长海 刘正宏[1] 赵庆英[1] 徐仲元[1] 石强[1] 王师捷 陈煜嵩 LI ChangHai;lIU ZhengHong;ZHAO QingYing;XU ZhongYuan;SHI Qiang;WANG Shi Jie;CHEN YuSong(College of Earth Sciences,Jilin University,Changchun 130061,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]吉林大学自然资源部东北亚矿产资源评价重点实验室,长春130061

出　　处：《岩石学报》2020年第9期2815-2833,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41872203、41872194)资助.

摘　　要：华北克拉通前寒武纪地壳生长过程是地质学的研究热点。本文对华北克拉通西部陆块北缘的白云鄂博群尖山组进行了碎屑锆石U-Pb定年和Hf同位素分析,并在此基础上对尖山组的沉积时限、物源及西部陆块北缘的前寒武纪地壳生长过程进行了探讨。样品TM33中碎屑锆石年龄主要集中在1872~2100Ma (n=64),并有~1960Ma的主年龄峰值和~2000Ma的次年龄峰值,Hf同位素分析结果显示锆石的εHf(t)值在-2.6~7.9之间(除1个测点为-17.6),Hf同位素二阶段模式年龄(tDM2)变化范围在2240~4386Ma之间。样品Z1724中碎屑锆石年龄分布于1784~2200Ma(n=44),并有~1965Ma的主年龄峰值和~2080Ma次年龄峰值。谐和线上最年轻一组锆石的加权平均年龄为1794±73Ma(n=2),εHf(t)在-5.4~3.2之间,Hf同位素二阶段模式年龄(tDM2)变化范围在2584~3203Ma之间。基于以上数据,结合侵入白云鄂博群底部1670Ma的辉长岩以及白云鄂博群底部全岩207Pb-206Pb等时线年龄为1649Ma的沉积碳酸盐岩,尖山组的沉积时间被限定在1800~1650Ma。尖山组的物源主要来自固阳、西乌兰不浪地区新太古代基底以及大青山和卓资地区古元古代晚期孔兹岩带。综合前人对研究区及邻区中新元古代沉积地层中碎屑锆石的Hf同位素研究结果,认为华北克拉通西部陆块北缘可能存在2600~2750Ma、~2500Ma和2000~2100Ma三期主要的地壳生长事件,且最后一次规模可能小于前两次。The Precambrian crustal growth of North China Craton( NCC) has been a hot topic for geologists for a long time. This paper presents LA-ICP-MS U-Pb dating and in-suit Lu-Hf isotopic analysis results of detrital zircons from Jianshan Formation,Bayan Obo Group in the northern western block of North China Craton to illustrate its depositional time and provenance as well as the Precambrian crustal growth in this area. The ages of detrital zircons from Sample TM33 cluster at 1872 ~ 2100 Ma( n = 64),with a major age peak at ~ 1960 Ma and a minor peak at ~ 2000 Ma. The in-suit Lu-Hf isotopic analysis of the zircons indicate their εHf( t)values vary from-2. 6 to 7. 9( except one of-17. 6),with two-stage Hf model ages( tDM2) varying between 2240 Ma and 4386 Ma( averaged at 2749 Ma). The ages of detrital zircons from Sample Z1724 are mainly between 1784 ~ 2200 Ma( n = 44),with a major age peak at ~ 1965 Ma and a minor peak at ~ 2080 Ma. The weighted average age of the youngest concordia ages is 1794 ± 73 Ma( n = 2).In-suit zircon Lu-Hf isotopic analysis indicate their εHf( t) values vary from-5. 4 to 3. 2,with two-stage Hf model ages( tDM2)between 2584 ~ 3203 Ma. Based on the above data and combined with the 1670 Ma gabbro intruding into Bayan Obo Group and the carbonatite with whole rock207 Pb-206 Pb age at 1649 Ma,the depositional age for Jianshan Formation is between 1800 Ma and 1650 Ma.The main provenances for Jianshan Formation are the Neo-Archean basement in Guyang,Xiwulanbulang and Kondalite Belt in Daqingshan,Zhuozi. There might exist three crustal growth events in the northern western block of NCC at 2600 ~ 2750 Ma、~ 2500 Ma and 2000 ~ 2100 Ma respectively,and the scale of the last one might be much smaller than the other two.

关 键 词：白云鄂博群 碎屑锆石 前寒武纪地壳生长 华北克拉通 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]