湘东南东风岩体锆石U-Pb年代学、Hf同位素组成及稀土矿床特征  

Zircon U-Pb chronology,Hf isotopes and REE deposit characteristics of Dongfeng granitic pluton in southeastern Hunan Province

作　　者：张锦煦 林碧海 廖凤初 孙骥 谭仕敏 何艳林 周超 朱继华 熊雄 李超 陈剑锋 ZHANG JinXu;LIN BiHai;LIAO FengChu;SUN Ji;TAN ShiMin;HE YanLin;ZHOU Chao;ZHU JiHua;XIONG Xiong;LI Chao;CHEN JianFeng(Geological Survey Institute of Hunan Peovince,Changsha 410116,Hunan,China;Geophysical and Geochemical Survey Institute of Hunan,Changsha 410116,Hunan,China;Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,Central South University,Changsha 410083,Hunan,China)

机构地区：[1]湖南省地质调查所,湖南长沙410116 [2]湖南省地球物理地球化学调查所,湖南长沙410116 [3]中南大学有色金属成矿预测与地质环境监测教育部重点实验室,湖南长沙410083

出　　处：《矿床地质》2023年第6期1101-1120,共20页Mineral Deposits

基　　金：中国地质调查局二级项目(编号:DD20230055、12120115029301);湖南省地质院科研项目(编号:HNGSTP202306);湖南省自然资源厅科研项目(编号:2023-02)联合资助。

摘　　要：文章对湘东南地区的东风岩体进行了锆石LA-ICPMS U-Pb年龄、Hf同位素以及岩石地球化学分析,以研究岩石成因及形成构造背景,并对东风风化壳离子吸附型重稀土矿的成因进行了探讨。东风岩体2件二长花岗岩的锆石U-Pb年龄为(433.5±2.6)Ma和(432.0±2.5)Ma,显示为加里东晚期。东风岩体锆石ε_(Hf)(t)值介于-5.12~-7.45,计算得到二阶段地幔亏损模式年龄(T_(DM2))介于1714~1882 Ma,显示其成岩物质为壳源的特征。东风岩体的地球化学特征显示其为高钾钙碱性、强过铝质的花岗岩,在成因类型判别图解中显示为S型花岗岩,构造背景判别图解显示为后碰撞构造环境。综合东风岩体花岗岩的地球化学特征和Hf同位素特征,笔者认为,东风岩体形成于扬子板块与华夏板块陆内汇聚的后碰撞伸展环境,为增厚地壳减压熔融和软流圈地幔上涌诱发古老地壳物质重熔形成的S型花岗岩。东风稀土矿床为一个由富轻稀土元素的母岩经风化后形成的大型重稀土矿床,富含稀土元素的高Y型花岗岩母岩为矿床的形成提供了重要物质基础,气候及地形地貌条件为稀土元素发生淋滤迁移和吸附富集提供了重要保证。This paper presents new zircon LA-ICP-MS U-Pb ages,Lu-Hf isotope and geochemical data of the Dongfeng granitic pluton in southeastern part of Hunan Province,aiming to constrain its petrogenesis and tectonic implication,and to explore the metallogenic mechanism of the Dongfeng ion adsorption type heavy rare-earth deposit.The LA-ICP-MS zircon U-Pb analysis of two biotite monzogranite yielded ^(206)Pb/^(238)U ages of(433.5±2.6)Ma and (432.0±2.5)Ma,respectively,suggesting that the Dongfeng granitic pluton formed in Late Caledonian.The granites contain high K_(2)O and belong to calc-alkali,strongly peraluminous(A/CNK=1.12~1.43),and geochemically classified as S-type granite.The primitive mantle-normalized trace element spider diagram shows that the Dongfeng monzogranite is relatively depleted in Ba,Nb,Sr,P,Ti and relatively enriched in Rb,(Th+U),Nd,(Zr+Hf)as well as zirconε_(Hf)(t)(-5.12 to-7.45)and ^(176)Hf/^(177)Hf(0.282300 to 0.282374)values indicating that this pluton is mostly product of crust melting.Tectonic setting discrimination diagrams show characteristics of monzogranite produced in post-collisional extensional environment.Hf isotopic and geochemical analyses indicate that the Dongfeng monzogranite belongs to S-type granite,derived from the partial melting of old crustal materials,when asthenosphere mantle upwelling,causing remelting of crustal materials under the geodynamical background of extensional environment after intraplate convergence between Yangtze Plate and Cathaysia Plate.The Dongfeng deposit is a newly discovered,large-sized ion adsorption type heavy rare-earth deposit,with an averaging grade of 0.050%~0.099%of REO,which formed from weathering of biotite monzogranite enriched in LREE,the high content of Y in parent granite provides the major sources in the formation of the deposit.Topographic features and climatic characteristics in the Dongfeng area are the key conditions for eluviation and sorption inducing the formation of ion adsorption type rare-earth deposit.

关 键 词：东风花岗岩体 加里东期 锆石U-Pb定年和Hf同位素 离子吸附型稀土矿 矿床成因 湘东南 

分 类 号：P618.7[天文地球—矿床学]