南澜沧江构造带景洪怕冷岩体锆石U-Pb年龄、Lu-Hf同位素特征及其对古特提斯构造演化的约束  

Zircon U-Pb geochronology and Lu-Hf isotope of the Jinghong Paleng pluton in southern Lancangjiang tectonic belt,and its constraints on the tectonic evolution of the Paleo-Tethys

作　　者：王伟 孙载波 周坤 刘和松[3] 吴嘉林 丛峰[4] 赵江泰 刘卫东 李小军 刘梦琼 WANG Wei;SUN Zaibo;ZHOU Kun;LIU Hesong;WU Jialin;CONG Feng;ZHAO Jiangtai;LIU Weidong;LI Xiaojun;LIU Mengqiong(Yunnan Institute of Geological Survey,Kunming 650216,Yunnan,China;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Ministry of Natural Resources,Kunming 650061,Yunnan,China;School of Earth Sciences,Yunnan University,Kunming 650500,Yunnan,China;Chengdu Center of China Geological Survey,Chengdu 610081,Sichuan,China;Yunnan Archtectural Engineering Design Compang Limited,Kunming 650217,Yunnan,China)

机构地区：[1]云南省地质调查院,云南昆明650216 [2]自然资源部三江成矿作用及资源勘查利用重点实验室,云南昆明650061 [3]云南大学地球科学学院,云南昆明650500 [4]中国地质调查局成都地质调查中心,四川成都610081 [5]云南省建筑工程设计院有限公司,云南昆明650217

出　　处：《地质通报》2021年第7期1068-1083,共16页Geological Bulletin of China

基　　金：中国地质调查局项目《全国陆域及海区地质图件更新与共享》子项目《云南省系列地质图件数据处理与洋板块地质研究》(编号:DD20190370);国家自然科学基金项目《三江南段景洪大勐龙地区高压变质岩p-T-t轨迹及其对原-古特提斯构造演化的制约》(批准号:42062005);云南省自然资源厅地勘基金项目《云南1∶5万曼各、小街、曼班、大勐龙、万纳兰、勐宋坝六幅区域地质调查》(编号:D2017014)

摘　　要：景洪怕冷岩体位于景洪市大勐龙镇西侧,该岩体以闪长岩为主,内部包裹了辉长岩、角闪岩、辉石岩、角闪橄榄岩等小型岩体。利用LA-ICP-MS锆石U-Pb法对怕冷岩体中的辉长岩、黑云英云闪长岩和斜长角闪岩进行精确定年,获得其结晶年龄分别为252.5±1.6 Ma、264.3±2.0 Ma和273.6±1.9 Ma,表明该岩体的形成时代为中—晚二叠世。与该构造带上的其他岩体相比,形成时代较晚,可能为洋盆俯冲晚期岩浆流动分异作用较弱形成。全岩主量和微量元素研究表明,闪长岩和辉长岩均具有典型岛弧岩浆岩的地球化学特征,指示该岩体形成于与板块俯冲有关的大洋岛弧环境。斜长角闪岩锆石初始(^(176)Hf/^(177)Hf)_(i)值为0.282833~0.282858,对应的ε_(Hf)(t)变化范围在8.8~13.2之间,单阶段亏损地幔Hf模式年龄t_(DM1)为370~549 Ma(平均值为470 Ma),明显老于原岩结晶时代。结合区域地质资料分析,滇西地区古特提斯洋(昌宁-孟连洋)的俯冲于晚石炭世开始,直到晚二叠世末期洋盆才闭合进入弧陆碰撞造山阶段。Outcropped in the western Damenglong Town of Jinghong City,the Paleng pluton is lithologically dominated by diorite in which several small gabbro,amphibolite,pyroxenite and hornblende peridotite plutons are emplaced.By means of LA-ICP-MS zircon U-Pb method,gabbro,tonalite and amphibolite in the Paleng pluton were dated,and yielded crystallization age of 252.5±1.6 Ma,264.3±2.0 Ma and 273.6±1.9 Ma,respectively,which indicates that the Paleng pluton was emplaced in Middle-Late Permian.Compared with other plutons along this tectonic belt,it was emplaced relatively late,and might be formed from weaker differentiation in the late stage of ocean basin subduction.The study of whole rock major and trace elements shows that both the diorite and gabbro have the geochemical characteristics of typical island-arc magmatism,indicating that the pluton was formed in the oceanic island arc environment related to plate subduction.The initial Hf isotope ratios (^(176)Hf/^(177)Hf)_(i) of the zircons from amphibolites range from 0.282833 to 0.282858,with correspondingε_(Hf)(t) values of 8.8~13.2.These zircons have depleted mantle Hf model ages (t_(DM1)) of 416~499 Ma,with an average of 470 Ma,obviously older than the crystallization of the original rocks(273.6 Ma).Combined with the analysis of regional geological data,the subduction of the ancient Tethys Ocean(Changning-Menglian Ocean)in western Yunnan began in the Late Carboniferous,and the ocean basin closed and entered the arc-continent collision orogenic stage until the end of the Late Permian.

关 键 词：岛弧 晚古生代 古特提斯洋 锆石U-Pb定年 景洪怕冷岩体 

分 类 号：P597[天文地球—地球化学]