四川米易垭口地区前震旦纪五马箐组与其侵入岩体的锆石U-Pb年代学、Lu-Hf同位素特征及其地质意义  

Zircon U-Pb chronology and Lu-Hfisotopic characteristics of the Pre-Sinian Wumaqing Formation and its intrusions in Yakou area, Miyi County,Sichuan Province, and their geological significance

作　　者：殷桂芹 陈友良[1] 张宝玲 顾孟娟 王勤[1] 姚建 尹观 YIN GuiQin;CHEN YouLiang;ZHANG BaoLing;GU MengJuan;WANG Qin;YAO Jian;YIN Guan(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;280 Institute of Nuclear Industry,Guanghan 618300,China)

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]核工业二八〇研究所,广汉618300

出　　处：《岩石学报》2022年第4期1126-1148,共23页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42072096);中国核工业地质局重点科研项目(202137-3);成都理工大学珠峰科技计划(2021ZF11413)联合资助.

摘　　要：在扬子板块西缘断续分布有多套变质沉积岩系,厘定区内不同岩石单元的时代对于探讨扬子西缘的构造演化具有重要意义。本文对出露于扬子板块西缘米易垭口地区的五马箐组变沉积岩以及侵入其中的片麻状黑云二长花岗岩体进行了锆石LA-ICP-MS U-Pb定年和Lu-Hf同位素分析。结果表明:区内五马箐组的沉积时代介于1.19~1.01Ga,其地层归属为会理群而非康定群,位于五马箐组之下的“冷竹关组”并非变沉积地层而是一套片麻状黑云二长花岗岩体。五马箐组碎屑锆石年龄存在~1.56Ga、~2.50Ga两个主要峰值以及~1.43Ga、~1.68Ga、~1.87Ga、~2.32Ga、~2.68Ga五个次要峰值,推断其物质来源主要为扬子板块西南缘的撮科杂岩、隐伏的或还暂未发现的太古代基底岩石、同时期岩浆岩和早期变沉积岩的再循环。碎屑锆石的ε_(Hf)(t)值在~1.7Ga发生了显著变化,暗示扬子板块西缘的构造体制由陆壳汇聚向裂谷活动转变,且在~1.56Ga处于裂谷岩浆活动的峰期。花岗岩体正的ε_(Hf)(t)值反映出扬子板块西缘在~1.0Ga有一次新生陆壳生长事件,可能是格林威尔造山后的伸展塌陷构造背景下裂谷岩浆活动的产物。There are several sets of metasedimentary rock series distributed intermittently in the western margin of Yangtze Block,it is of great significance to determine the ages of different rock units in the area for discussing the tectonic evolution.This study has conducted zircon LA-ICP-MS U-Pb dating and Lu-Hf isotopic analysis of the metasedimentary rocks from the Wumaqing Formation as well as its intrusive gneissose biotite adamellite in Yakou area,western margin of Yangtze Block.The results indicate that the sedimentary age of Wumaqing Formation in the area is between 1.19~1.01Ga,and the strata belongs to Huili Group rather than Kangding Group.The“Lengzhuguan Formation”under the Wumaqing Formation is not a metasedimentary stratum but a set of gneissose biotite adamellite.The detrital zircon dating of the Wumaqing Formation have two main peaks of~1.56Ga and~2.50Ga,five minor peaks of~1.43Ga,~1.68Ga,~1.87Ga,~2.32Ga and~2.68Ga,it is speculated that its sedimentary material sources are mainly from Cuoke complex,buried or undiscovered Archean basement,contemporaneous magmatic rocks and the recycled of early metasedimentary rocks in the southwestern margin of Yangtze Block.Theε_(Hf)(t)values of detrital zircons has changed significantly at~1.7Ga,suggesting that the tectonic regime in the western margin of Yangtze Block has shifted from continental crust convergence to rift activities,and the rift magmatism has peaked at~1.56Ga.The positiveε_(Hf)(t)values of granitic pluton implies that there was a new continental crust growth event at~1.0Ga in the western margin of Yangtze Block,possibly is the product of rift magmatism under the extensional collapse tectonic setting after the Grenvillian Orogeny.

关 键 词：垭口地区 五马箐组 锆石U-Pb-Lu-Hf同位素 沉积时代 构造意义 

分 类 号：P588.121[天文地球—岩石学] P588.344[天文地球—地质学]