摘要
笔者等在野外调查的基础上,对出露于滇西临沧岩浆弧北部凤庆箐头山地区原1∶25万凤庆县幅划分的二叠纪糜棱岩化黑云二长花岗岩进行了系统的年代学、岩石学和地球化学研究。该花岗岩体中,锆石具典型的振荡环带,Th/U值均大于0.2,为岩浆成因,其LA-ICP-MS U-Pb年龄为213±5 Ma,应当为岩浆结晶年龄,表明该岩体形成于晚三叠世,而非前人认为的二叠纪。全岩主微量元素分析结果显示,箐头山花岗岩Na_(2)O/K_(2)O值低,富Al_(2)O_(3),铝饱和指数(A/NCK值)平均为1.18,属过铝质高钾钙碱性系列。稀土配分曲线右倾,具有轻稀土富集、重稀土弱亏损、负铕异常明显的特征(δEu=0.36~0.50);富集大离子亲石元素Rb和K,亏损高场强元素Zr。在Rb—(Y+Nb)判别图解中,箐头山花岗岩投影点落入后碰撞花岗岩区,并具有明显向板内花岗岩转换的特征。结合区域地质资料,笔者等认为获得的213 Ma可能代表昌宁—孟连古特提斯洋闭合之后地壳由碰撞后造山向构造伸展转换的时限,为昌宁—孟连古特提斯洋碰撞后造山作用的结束提供时代约束。
Objectives:Geologists at home and abroad have done a lot of research on the evolution of the Paleo-Tethyan ocean in the Changning—Menglian suture zone,but there is still lack of precise chronological constraints on the end time of post-collisional orogeny after its closure.We study the emplacement age,genetic type and material source of Qingtoushan granite,located in the northern part of Lincang magmatic arc,in Fengqing area,western Yunnan Province,so as to constrain the post collisional orogeny after the closure of Changning—Menglian ocean basin.Methods:Combined with the results of 1∶50000 and 1∶250000 Regional Geological and Mineral Survey Projects in recent years,we studied the petrology,geochemistry and LA-ICP-MS zircon U-Pb dating of mylonitized biotite monzogranite exposed in the Qingtoushan area,providing evidences for the tectonic evolution of the Changning—Menglian suture zone.Results:The LA-ICP-MS zircon U-Pb dating of the Qingtoushan granite yields a magma crystallization age of213±5 Ma (MSWD=3.4,n=14),which is attribute to characteristics of typical oscillatory zoning,and Th/U ratios greater than 0.2.The granite belongs to peraluminous high-K calc-alkaline series,with low Na2O/K2O ratio,rich in Al_(2)O_(3),and the average Al saturation index A/NCK is 1.18.The REE distribution curves have the characteristics of right deviation LREE enrichment,weak depletion on HREE,and obviously negative anomacies of Eu (δEu=0.36~0.50).The granites are enriched in lithophile elements Rb,K;and are depleted in the high field strength elements,such as Zr.In the Rb—(Y+Nb) discrimination diagrams of trace elements,the projection points fall into the post-COLG,which have the characteristics of obviously transformed to intraplate granite.Conclusions:The crystallization age of 213±5 Ma indicates that the Qingtoushan granite was formed in the Late Triassic rather than the Permian.It is the youngest acid magma with the dual properties of post-collisional granite and intraplate granite discovered in the Lincang mag
作者
田素梅
刘军平
范振华
包佳凤
孙柏东
俞赛赢
吴嘉林
朱勋早
宋冬虎
TIAN Sumei;LIU Junping;FAN Zhenhua;BAO Jiafeng;SUN Baidong;YU Saiying;WU Jialin;ZHU Xunzao;SONG Domghu;无(Yunnan Institute of Geological Survey,Kunming,650216;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,MNR,Kunming,650051;Institute of Geology and Mineral Resources of Shandong Province,Jinan,250100;Yunnan Institute of Land and Resources Planning and Design,Kunming,650216)
出处
《地质论评》
CAS
CSCD
北大核心
2021年第5期1280-1296,共17页
Geological Review
基金
国家自然科学基金地区基金资助项目(编号:420602005)
国家自然科学基金特提斯重大研究计划重点项目(编号:92055207)
西南三江有色金属资源基地调查项目(编号:DD20160016)
子项目云南省1∶5万诗礼、犀牛街、大河、老家库、哨街幅区域地质矿产调查项目的成果。
关键词
锆石U-PB测年
地球化学
昌宁—孟连结合带
弧—陆碰撞
箐头山花岗岩
云南凤庆
zircon U-Pb dating
geochemistry
Changning—Menglian suture zone
arc—continent collision
Qingtoushan granite
Fengqing
western Yunnan
