甘孜-理塘俯冲增生杂岩带中二叠世构造演化——来自龙蟠蛇绿岩年龄、地球化学的证据  

The tectonic evolution of the Garze-Litang subduction-accretionary complex in the Middle Permian: Evidence from geochronology and geochemistry of the Longpan ophiolite

作　　者：任飞[1] 尹福光[1] 孙洁[1] 徐长昊[2] 张璋[1] 陈波 REN Fei;YIN Fuguang;SUN Jie;XU Changhao;ZHANG Zhang;CHEN Bo(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China;Chengdu University of Technology,Chengdu 610080,Sichuan,China;Hainan Geology Co.,Ltd.,Haikou 570000,Hainan,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]成都理工大学,四川成都610080 [3]海南地质有限公司,海南海口570000

出　　处：《地质通报》2021年第6期942-954,共13页Geological Bulletin of China

基　　金：国家自然科学基金项目《特提斯构造域地质编图及区域对比研究》(批准号:92055314);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(成都中心)》(编号:DD20190375);《地质调查综合智能编图系统与应用》(编号:DD20190415);《三江造山带昌都—澜沧地区区域地质调查》(编号:DD20190053)。

摘　　要：龙蟠蛇绿岩位于甘孜-理塘俯冲增生杂岩带南段,以蛇绿混杂岩中的辉绿岩、玄武岩作为研究对象,开展地球化学及年代学研究。结果显示,岩石具有较低的SiO_(2)、TiO_(2)、Na_(2)O,低的K2O,高的Al_(2)O_(3)、CaO和MgO,具亚碱性玄武质岩石特征。稀土元素总体含量较低,平均为59.08×10^(-6);(La/Yb)N值为1.93~2.96,(La/Sm)N值为1.41~1.77,轻稀土元素微弱富集,轻、重稀土元素分馏不明显,Eu异常不明显,表明岩石经历了以斜长石为主的分离结晶作用,且形成于还原环境,与富集型洋脊玄武岩类似。强不相容微量元素相对富集,玄武岩相对亏损Sr、Nb,Nd相对富集;辉绿岩Ba、Nb亏损,Sr富集,有明显的富集型洋脊玄武岩特征。在辉绿岩中获得一组LA-ICP-MS锆石U-Pb年龄262.3±1.5 Ma,表明龙蟠蛇绿混杂岩形成于中二叠世。结合研究区已有的研究成果,表明至少在中二叠世中期甘孜-理塘洋盆还在持续扩张,为甘孜-理塘洋盆中二叠世构造演化提供直接证据。Longpan ophiolite is located in the southern part of the Garze-Litang subduction-accretionary complex.It was selected as a research object for detailed geochemistry and chronology studies.The petrogeochemistry study shows that it is characterized by relatively low SiO_(2),TiO_(2),Na_(2)O and K2O,and high Al_(2)O_(3),CaO and MgO,revealing a feature of sub-alkaline basaltic rocks.Its signature of rare earth elements shows an affinity to enriched mid-ocean ridge basalts( E-MORB) with relatively low REE content,slight enrichment of LREE,indistinctive REE fractionation(( La/Yb)N= 1.93 ~ 2.96,( La/Sm)N= 1.41 ~ 1.77),without obvious Eu negative anomaly.Basalts are depleted in Sr and Nb,enriched in Nd,while diabases are depleted in Ba and Nb,enriched in Sr.Both rocks are enriched in highly incompatible elements,which shows obvious characteristics of enriched mid-ocean ridge basalts. The LA-ICP-MS U-Pb dating of zircon from the diabase yielded an age of 262.3±1.5 Ma,which indicates that the Longpan ophiolite mélange was formed in the Middle Permian.Combined with the previous achievements,it is suggested that the Garze-Litang Ocean was still in the process of continuous expansion in the Middle Permian.The discovery can enrich the research content of the Garze-Litang ophiolite mélange belt and provide direct evidence for the tectonic evolution of the Garze-Litang in Middle Permian.

关 键 词：甘孜-理塘俯冲增生杂岩带 U-PB年龄 E-MORB 大地构造 蛇绿岩 地球化学 

分 类 号：P534.46[天文地球—古生物学与地层学] P542[天文地球—地质学]