马达加斯加Maevatanana金矿区花岗岩锆石U-Pb年龄、Hf同位素特征及其地质意义  

Zircon U-Pb ages and Hf isotopic characteristics of granites in the Maevatanana gold field,Madagascar and geological significance

作　　者：李鹏[1,2] 刘善宝[2] 施光海[1] 张树德 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质科学院,北京100037 [3]崇义章源钨业股份有限公司,赣州341300

出　　处：《岩石学报》2015年第4期1153-1170,共18页Acta Petrologica Sinica

基　　金：中国地质调查局项目(12120113102100)资助

摘　　要：马达加斯加中部Maevatanana、Andriamena和Beforona三条绿岩带共有上百处铬、镍、铁、金等金属矿点。对位于马达加斯加中北部绿岩带的Maevatanana西南部花岗岩体进行主量元素、微量元素、锆石LA-MC-ICP-MS U-Pb定年及Lu-Hf同位素分析。岩体主要由黑云母二长花岗岩构成,为准铝质到弱过铝质的高钾钙碱性系列花岗岩,富集Rb、Ba、K等大离子亲石元素（LILE）,亏损Nb、Ta、Ti等高场强元素（HFSE）,其稀土元素总量为∑REE=92.02×10^-6,A/CNK=1.01。其内锆石LA-MCICP-MS U-Pb的年龄为739-767Ma,即中新元古代,其εHf（t）均为负值,揭示该矿区花岗岩体源区为陆壳。其中岩浆锆石和继承锆石的Hf同位素二阶段模式年龄相近,表明花岗岩源岩的形成时期和基底黑云角闪斜长片麻岩的原岩一致。地球化学性质显示花岗岩体为I型花岗岩,与埃达克岩类似。综合数据认为岩体形成于中-新元古代（824-720Ma）Rodinia超大陆裂解,伴随Mozambique洋闭合Tanzanian克拉通与印度Dharwar克拉通汇聚背景下的陆缘弧岩浆活动。There are more than one handred metal deposits（ chromium,nickle,iron,gold etc.） distributed in three greenstone belts（ Maevatanana,Andriamena and Beforona） from Central Madagascar. In this investigation,we reported major and trace element compositions,LA-MC-ICP-MS zircon U-Pb ages and Lu-Hf isotopic compositions of granites in the greenstone belt from the southwestern Maevatanana,Central-North Madagascar. The granites,mainly composed of biotite and adamellite,belong to aluminous to slight peraluminous K-rich calc-alkaline series and are characterized by high LILE contents（ e. g. Rb,Ba,K）,low HFSE contents（ e. g. Nb,Ta,Ti）,with ∑REE = 92. 02 × 10^- 6and A / CNK = 1. 01. The ages of the granite range between 739 - 767 Ma. AllεHf（ t） values are negative,suggesting that their magma sources were from continental basement. Two-stage Hf modle ages of the overgrown and inherited zircons are similar,suggesting that forming age of protolith of the granite was the same as the biotite-amphiboleplagioclase gneiss,and the granite formed by partial melting of the basement. Geochemical features of the granite show similarity to type-I granite,resembling characterstics of the adakite. It is suggested that the granite was associated with arc magmatism of continental convergence margin between the Tanzanian craton and Dharwar craton,India,during Meso-Neoproterozoic（ 824 - 720Ma） when Rodinia supercontinent broke up with close of the Mozambique Ocean.

关 键 词：花岗岩 锆石U-PB定年 LU-HF同位素 中-新元古代 马达加斯加 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]