粤北笋洞和岩庄花岗岩SHRIMP锆石U-Pb年龄及其地质意义  

ZIRCON SHRIMP U-Pb AGES AND GEOLOGICAL SIGNIFICANCE OF THE SUNDONG AND YANZHUANG GRANITES,NORTHERN GUANGDONG PROVINCE

作　　者：吴佳[1,2] 巫建华[1,2] 刘晓东[1,2] 王凯兴[1,2] 刘帅 WU Jia;WU Jjanhua;LIU Xiaodong;WANG Kaixing;LIU Shuai(School of Earth Science,East China University of Technology,Nanchang,Jiangxi 330013,China;State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang,Jiangxi 330013,China)

机构地区：[1]东华理工大学地球科学学院,江西南昌330013 [2]东华理工大学核资源与环境国家重点实验室,江西南昌330013

出　　处：《矿物岩石》2023年第2期27-38,共12页Mineralogy and Petrology

基　　金：中国核工业地质局项目(编号:201475)。

摘　　要：粤北下庄铀矿田是我国确定的第一个花岗岩型铀矿田,矿田内的岩浆活动具有加里东、印支和燕山多期、多阶段的特点,并以印支期为主体,但部分花岗岩体的划分、命名和时代归属仍需进一步研究。现有资料显示,矿田中部的笋洞岩体又被归入中南部的高栋岩体,但笋洞岩体的单颗粒锆石稀释法年龄为189 Ma、而高栋岩体的LA-ICP-MS锆石U-Pb年龄为236~232 Ma,二者分别属于燕山期和印支期岩浆活动的产物;矿田中西部的岩庄岩体又被视为笋洞岩体的一部分,但岩庄岩体的LA-ICP-MS锆石U-Pb年龄为161 Ma,小于笋洞和高栋岩体年龄。针对这些问题,本次研究在深入研究笋洞岩体、岩庄岩体岩相学特征的基础上,采用SHRIMP锆石U-Pb法测定了它们的锆石U-Th-Pb的含量,发现笋洞和岩庄花岗岩不仅含有捕获锆石,而且笋洞岩体还含有高铀锆石。剔除这些捕获锆石和高铀锆石的年龄数据后,笋洞中粗粒二云母花岗岩和岩庄细粒二云母花岗岩的锆石^(206)Pb/^(238)U加权平均年龄分别为240.0±2.4 Ma(N=15、MSWD=0.98)和234.4±2.4 Ma(N=13、MSWD=0.94),指示两者均属印支期岩浆活动的产物。笋洞岩体与高栋岩体的岩性特征一致,且年龄在误差范围内也一致,支持笋洞岩体与高栋岩体属同一岩体,并与鲁溪岩体、下庄岩体构成下庄铀矿田花岗岩岩基;岩庄岩体侵入笋洞岩体,且SHRIMP锆石U-Pb年龄小于笋洞岩体,支持岩庄岩体是侵入花岗岩岩基的晚期小岩体。Xiazhuang uranium ore field in northern Guangdong Province is the first granite type uranium ore field identified in China.The ore field is dominated by Indosinian magmatic rocks,and is characterized by multi-stage magmatic events of Caledonian,Indosinian and Yanshanian magmatic activities.However,there are still problems on the classification,naming and age attribution of some granite bodies,which need to be solved by further research.For instance,the available data show that the Sundong rock mass in the central ore field was once classified to the Gaodong rock mass in the central part of the ore field.However,the geochronological analysis shows that the single-grain zircon dilution age of Sundong rock mass is 189 Ma,while the LA-ICP-MS zircon U-Pb age of Gaodong rock mass is 236 to 232 Ma.The former is the product of Yanshanian magmatic activity,while the latter is the product of Indosinian magmatic activity.The Yanzhuang pluton in the central and western part of the ore field is regarded as a part of the Sundong pluton,but the LA-ICP-MS zircon U-Pb age of the Yanzhuang pluton is 161 Ma which is younger than the ages of Sundong and Gaodong pluton.In order to solve the problems of age and naming,the U-Th-Pb content of zircon from the granite pluton in the ore field is measured by SHRIMP zircon U-Pb method on the basis of in-depth study of the petrographic characteristics of Sundong and Yanzhuang pluton.The results show that the Sundong and Yanzhuang granites not only contain trapped zircons,but also include high uranium zircons.After stripping out the ages of captured zircons and high-uranium zircons,the zircon ^(206)Pb/^(238)U weighted mean ages of the middle-coarse grained granites from Sundong and fine grained granites from Yanzhuang are 240.0±2.4 Ma(N=15,MSWD=0.98)and 234.4±2.4 Ma(N=13,MSWD=0.94),respectively,which indicates the magmatic emplacement in Indosinian period.Because both the lithologic characteristics of Sundong pluton and Gaodong pluton and the age within the error range of the two rock masses

关 键 词：花岗岩 高铀锆石 SHRIMP锆石U-PB年龄 地质意义 下庄铀矿田 

分 类 号：P597[天文地球—地球化学]