湘西南苗儿山岩体北段加里东期花岗岩成因:来自岩石学、地球化学和锆石U-Pb年代学的证据  

Petrogenesis of the Caledonian granites in the northern part of Miaoershan pluton,southwestern Hunan Province:Evidence from petrology,geochemistry and zircon U-Pb age

作　　者：杜云 郭爱民 卢友月[2] 田磊 王敬元 周立同 樊晖 罗小亚 DU Yun;GUO Aimin;LU Youyue;TIAN Lei;WANG Jingyuan;ZHOU Litong;FAN Hui;LUO Xiaoya(Hunan Institute of Geological Survey,Changsha 410116,Hunan,China;Wuhan Center of China Geological Survey,Wuhan 430205,Hubei,China)

机构地区：[1]湖南省地质调查院,湖南长沙410116 [2]中国地质调查局武汉地质调查中心,湖北武汉430205

出　　处：《中国地质》2021年第5期1540-1561,共22页Geology in China

基　　金：中国地质调查局项目(121201009000150002)资助。

摘　　要：苗儿山岩体位于湘西南与桂北交界处,为由晋宁期、加里东期、印支期和燕山期花岗岩组成的复式岩体。其中,加里东期花岗岩构成该复式岩体的主体,可划分为六个侵入次。本次通过锆石LA-ICP-MS测年,获得第一、第二、第六侵入次的年龄分别为(428.1±3.6)Ma、(420.3±3.4)~(421.3±3.2)Ma和(408.3±3.5)Ma。加里东期花岗岩的(^(87)Sr/^(86)Sr)_(i)为0.71765,ε_(Nd)(t)为-9.7,δ^(18)O值为9.8‰,总体属壳源弱过铝-强过铝质花岗岩,形成于碰撞挤压峰期之后挤压减弱、应力松弛的后碰撞构造环境,其早期和晚期的源区岩石类型和形成温度有所区别:早期花岗岩的上地壳源区成分较为复杂,不仅存在泥岩,还有砂屑岩和/或变质火成岩,其形成温度较高(>875℃);晚期花岗岩的源岩为上地壳泥岩,属典型的S型花岗岩,其形成温度较低(<875℃)。The Miaoershan pluton,located at the junction of southwestern Hunan and Northern Guangxi,is a composite batholith composed of Jinningian,Caledonian,Indosinian and Yanshanian granites.Among them,Caledonian granites constitute the main body of the composite batholith,which can be divided into six intruding episodes.Through zircon LA-ICP-MS dating,the ages of the first,second and sixth episodic granites were measured at(428.1±3.6)Ma,(420.3±3.4)-(421.3±3.2)Ma and(408.3±3.5)Ma,respectively.The average(^(87)Sr/^(86)Sr)_(i),ε_(Nd)(t)and theδ^(18)O values of the Caledonian granites are 0.71765,-9.7,and 9.8,respectively Caledonian granites are generally crust derived weak peraluminous-strong peraluminous granites,formed in post-collisional tectonic environment characterized by weakened compression and relaxed stress after the peak period of collision and extrusion.Their material and heat sources are different in the early and late stages.The early stage granites were derived from upper crustal metamorphic mudstone,psammite and/or metamorphic igneous rocks,and their formation temperature is relatively high(>875℃).The late stage granites were derived from upper crustal metamorphic mudstone with lower formation temperature(<875℃),showing the characteristics of typical S-type granites.

关 键 词：锆石U-PB测年 地球化学 岩石成因 加里东期 苗儿山岩体 湘西南 地质调查工程 江西省 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]