华南印支期花岗岩成因再探——以湘西紫云山和桂东北石板弯复式花岗岩体为例  

Re-exploration of Indosinian granites in South China——A case study from the Ziyunshan granitic complex in western Hunan and the Shibanwan complex granites in northeastern Guangxi

作　　者：马鑫 汪相[1] MA Xin;WANG Xiang(School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023)

机构地区：[1]南京大学地球科学与工程学院,南京210023

出　　处：《地质论评》2023年第6期2047-2081,共35页Geological Review

基　　金：国家自然科学基金资助项目(编号:41872047)的成果。

摘　　要：华南印支期花岗岩主要分布在湘、赣、桂及其邻区,其岩体数量之多、出露面积之广使得它们成为华南花岗岩研究的重要组成部分,但是,对于它们的构造属性及其与成矿作用的关系仍众说纷纭。笔者等选取湘西双峰县紫云山和桂东北资源县石板弯两个印支期复式花岗岩体,对它们的主体相和补体相分别开展了岩相学、岩石化学和锆石学的系统研究,从而确定:①这两个复式花岗岩体的主体相的岩性分别为(紫云山)花岗闪长岩和(石板弯)黑云母二长花岗岩,具有正常的花岗岩岩石化学成分(如:SiO_(2)含量为67.23%~71.94%、FeO^(T)含量为2.03%~3.73%),富相容的微量元素(如:Ba、Sr、Zr等),不明显的Eu负异常(Eu/Eu*平均值为0.49);它们的岩浆锆石U-Pb年龄和ε_(Hf)(t)值分别为239.6±2.3 Ma和-4.9~-1.0(紫云山花岗闪长岩)、239.7±3.3 Ma和-8.8~-1.1(石板弯黑云母二长花岗岩);因此,它们属于印支早期的同造山花岗岩。②这两个复式花岗岩体补体相的岩性分别为(紫云山)白云母碱长花岗岩和(石板弯)二云母碱长花岗岩,具有较高的SiO_(2)含量(73.92%~76.55%)和较低的FeO^(T)含量(0.71%~1.21%),富不相容的微量元素(如:Rb、Ta、U等),强烈的Eu负异常(Eu/Eu*平均值为0.14);它们的热液锆石U-Pb年龄和ε_(Hf)(t)值分别为217.4±2.8 Ma和-7.3~-1.3(紫云山白云母碱长花岗岩)、217.4±2.2 Ma和-10.3~-3.1(石板弯二云母碱长花岗岩)。因此,它们属于印支晚期的造山后花岗岩。另外,石板弯复式花岗岩体中云头界钨矿石中的热液锆石U-Pb年龄和ε_(Hf)(t)值分别为217.7±2.8 Ma和-10.5~-3.7,与石板弯二云母碱长花岗岩中的热液锆石U-Pb年龄和Hf同位素组成完全一致,说明两者具有密切的成因联系。笔者等认为:在早三叠世,华南板块受到印支板块、华北板块、太平洋板块等多个构造单元的挤压作用,造成华南地块地壳加厚和深熔作用;在~239 Ma,该区的挤压作�Objectives:The Indosinian granites in South China are mainly distributed in Hunan,Jiangxi,Guangxi Provinces and their adjacent areas.The large scale of these granites makes them an important research objective in granite petrology of South China.However,there are still questions on their tectonic implication and their relationship with mineralization.Methods:This paper takes the Ziyunshan granitic complex in Shuangfeng County,western Hunan Province,and the Shibanwan granitic complex in Ziyuan County,northeastern Guangxi Zhuang Autonomous Region,as investigated samples,and carries out petrographic,geochemical and zirconological researches on their main intrusive phases and subsequent intrusive phases.Results and Conclusions:(1)The main intrusive phases of the two granitic complexes are a granodiorite for the Ziyunshan complex and a biotite monzogranite for the Shibanwan complex.They show whole-rock compositions of normal granite(e.g.,67.23%~71.94%SiO_(2)and 2.03%~3.73%FeO^(T)),and are enriched in compatible trace elements(e.g.,Ba,Sr,Zr,etc.),with negative Eu anomalies(average Eu/Eu∗ratio is 0.49).Their zircon U-Pb ages andε_(Hf)(t)values are 239.6±2.3 Ma and-4.9~-1.0 for the Ziyunshan granodiorite,and 239.7±3.3 Ma and-8.8~-1.1 for the Shibanwan biotite monzogranite,respectively.Therefore,this paper concludes that they belong to the early Indosinian syn-orogenic granites.(2)The subsequent intrusive phases of the two granitic complexes are a muscovite alkali-feldspar granite for the Ziyunshan complex and a two-mica alkali-feldspar granite for the Shibanwan complex,with high SiO_(2)content(73.92%~76.55%),low FeO^(T)content(0.71%~1.21%),enriched in compatible trace elements(e.g.Rb,Ta,U,etc.),with strong negative Eu anomalies(average Eu/Eu∗ratio is 0.14);Their zircon U-Pb ages andε_(Hf)(t)values are 217.4±2.8 Ma and-7.3~-1.3 for the Ziyunshan muscovite alkali-feldspar granite,and 217.4±2.2 Ma and-10.3~-3.1 for the Shibanwan two-mica alkali-feldspar granite,respectively.Therefore,this paper concludes that they

关 键 词：复式花岗岩体 地球化学 锆石U-Pb年龄 印支运动 岩浆热液矿床 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学] P612