扬子地块西缘中元古代A型花岗岩的形成时代、地球化学特征及其大地构造意义  

Geochronological and Geochemical Characteristics of the Mesoproterozoic A-type Granite in the Western Yangtze Block and its Tectonic Implications

作　　者：赵锴 蔡永丰[1,2] 冯佐海 徐天德[3] 周云 刘风雷[1] 胡荣国 刘昊茹 ZHAO Kai;CAI Yongfeng;FENG Zuohai;XU Tiande;ZHOU Yun;LIU Fenglei;HU Rongguo;LIU Haoru(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,College of Earth Sciences,Guilin University of Technology,Guilin 541004,Guangxi,China;Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,Guilin University of Technology,Guilin 541004,Guangxi,China;Regional Geological Survey Party,Sichuan Bureau of Geology and Mineral Resources,Chengdu 610213,Sichuan,China)

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [2]桂林理工大学广西有色金属隐伏矿床勘查及材料开发协同创新中心,广西桂林541004 [3]四川省地质矿产勘查开发局区域地质调查队,四川成都610213

出　　处：《大地构造与成矿学》2021年第5期1007-1022,共16页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41502180);广西自然科学基金项目(2018GXNSFBA281069)联合资助

摘　　要：为阐明扬子地块西缘中元古代大地构造演化特征,本文对扬子地块西缘苴林地区花岗岩展开了系统的LA-ICP-MS锆石U-Pb年代学、全岩地球化学和Sr-Nd同位素研究。两个代表性花岗岩样品LA-ICP-MS锆石U-Pb年代学分析分别给出了1063±9 Ma和1064±6 Ma的年龄。全岩地球化学分析结果显示,苴林地区花岗岩具有高硅钾、贫镁钙、低磷钛特征,其A/CNK平均值为1.37,属于高钾钙碱性过铝质岩石;稀土元素配分曲线表现为右倾“海鸥”型,具负Eu异常,富集高场强元素Zr、Th、Hf和大离子亲石元素Rb、K,亏损Ba、Sr、P、Ti等元素;样品具有相对富集的Nd同位素组成,其εNd(t)值为−9.90~−4.53。综合研究表明,苴林地区花岗岩形成于中元古代晚期,表现出A型花岗岩的地球化学特征。结合前人研究认为,苴林地区花岗岩是古老地壳物质重熔的产物,形成于后碰撞或后造山的拉张环境,其形成与Rodinia超大陆的聚合密切相关。In order to elucidate the characteristics of the Mesoproterozoic tectonic evolution of the western margin of the Yangtze Block,this paper carried out systematic studies of zircon LA-ICP-MS U-Pb dating,whole rock geochemistry and Sr-Nd isotope analyses on the granite exposed in the Julin area of the western margin of the Yangtze Block.LA-ICP-MS zircon U-Pb geochronological results show that two representative granite samples give formation age of 1063±9 Ma and 1064±6 Ma,respectively.The whole-rock geochemical results show that the Julin granites are characterized by high Si and K,low Mg,Ca,P and Ti.The average A/CNK is 1.37,indicating a high-potassium calc-alkaline peraluminous series.The REE patterns show a right-leaning“seagull”type,with negative Eu anomalies.They are enriched in high field strength elements(e.g.,Zr,Th and Hf)and large ion lithophile elements(e.g.,Rb and K),and depleted in Ba,Sr,P and Ti.They show enriched Nd isotope compositions withεNd(t)values from−9.90 to−4.53.The above results indicate that the Julin granites were formed in the late Mesoproterozoic and exhibit geochemical characteristics similar to those of A-type granites.Comprehensive studies suggest that the Julin granites were derived from partial melting of old continental crust.They were formed in a post-collisional or post-orogenic extensional environment,which is closely related to the aggregation of the Rodinia supercontinent.

关 键 词：锆石U-PB定年 中元古代 A型花岗岩 RODINIA超大陆 苴林群 扬子地块 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]