秦岭杂岩东枣园榴闪岩多期变质及地质意义  

The multi-stage metamorphism of the Dongzaoyuan garnet amphibolite in the Qinling Complex and its geological significance

作　　者：王一鸣 宫相宽 吴慧芸 吴学谦 杨浩东 WANG Yiming;GONG Xiangkuan;WU Huiyun;WU Xueqian;YANG Haodong(Xinjiang Key Laboratory of Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt,College of Geology and Mining Engineering,Xinjiang University,Urumqi Xinjiang Uygur Autonomous Region 830017,China)

机构地区：[1]新疆中亚造山带大陆动力学与成矿预测自治区重点实验室新疆大学地质与矿业工程学院,新疆维吾尔自治区乌鲁木齐830017

出　　处：《矿物学报》2024年第2期226-241,共16页Acta Mineralogica Sinica

基　　金：新疆维吾尔自治区自然科学基金项目(2022D01C660);国家自然科学基金项目(42302059)。

摘　　要：北秦岭构造带秦岭杂岩是一条高压-超高压变质带,经历过早古生代期间巨量陆壳物质的俯冲-深俯冲和折返,带内出露的榴闪岩保留了变质时代和温压条件的重要信息,可以为北秦岭早古生代变质演化历史的恢复提供重要限定。本项研究对陕西省丹凤县东枣园一带出露于秦岭杂岩混合岩化长英质片麻岩中的榴闪岩进行了详细的锆石U-Pb年代学、岩石地球化学和矿物化学研究。结果表明,该榴闪岩中存在两种成分的角闪石(Amp_(1)和Amp_(2))和斜长石(Pl_(1)和Pl_(2)),石榴子石无明显成分环带,以保留了角闪石(Amp_(1))+斜长石(Pl_(1))+石英+钛铁矿/榍石、石榴子石+角闪石(Amp_(2))+斜长石(Pl_(2))+石英+钛铁矿两期变质矿物组合为特征。锆石记录了(497±3)、(450±3)、(419±5)和(399±5)Ma四期变质年龄,根据锆石不同年龄微区的稀土元素组成特征和矿物包裹体组合,认为它们分别对应于榴辉岩相、麻粒岩相以及两期角闪岩相变质时代。结合该岩石具有与秦岭杂岩中榴辉岩一致的岩石地球化学特征,表明该岩石是退变的榴辉岩,其在经历~500 Ma的榴辉岩相变质和~450 Ma、~420 Ma两期退变质后,在~400 Ma叠加了一期高角闪岩相进变质作用,该期进变质可能与拆离自俯冲陆壳的岩片在折返过程中发生旋转有关。The Qinling Complex in the North Qinling Belt is a high-pressure-ultra-high-pressure metamorphic zone which had experienced subduction-deep subduction and exhumation processes of massive continental crust materials in the early Paleozoic.The garnet amphibolite exposed in the Qinling Complex had recorded important information of multi-stage metamorphic ages and P-T conditions,which can provide important constraints for the reconstruction of the early Paleozoic metamorphic evolution history of the North Qinling Belt.In this paper,detailed zircon U-Pb geochronology,geochemistry,and mineral chemistry of garnet amphibolite samples collected from the migmatized felsic gneiss in the Qinling Complex in the Dongzaoyuan area,Danfeng County,Shaanxi Province have been studied.The results show that there are two kinds of amphibole(Amp_(1) and Amp_(2))and plagioclase(Pl_(1) and Pl_(2))in the garnet amphibolite.There is no obvious compositional zoning in garnet.The garnet amphibolite is characterized with two sets of metamorphic mineral assemblages including(1)amphibole(Amp_(1))+plagioclase(Pl_(1))+quartz+ilmenite/sphene and(2)garnet+amphibole(Amp_(2))+plagioclase(Pl_(2))+quartz+ilmenite.The LA-ICP-MS zircon U-Pb dating yielded four metamorphic ages of 497±3 Ma,450±3 Ma,419±5 Ma,and 399±5 Ma,respectively.According to the REE compositions and mineral inclusion assemblages of zircons,it is considered that the four metamorphic ages correspond to those of eclogite facies,granulite facies,and two amphibolite facies,respectively.In addition,the garnet amphibolite has similar geochemical characteristics of the eclogite in the Qinling Complex.It is suggested that the garnet amphibolite was formed by the multi-stgae retrograde metamorphism of original eclogite which underwent eclogite facies metamorphism at~500 Ma,and retrograde metamorphism of two stages at~450 Ma,and~420 Ma,respectively.The garnet amphibolite finally experienced a prograde metamorphism of high amphibolite facies at~400 Ma,which may be related to the rotation of sl

关 键 词：秦岭杂岩 榴闪岩 多期变质 矿物化学 

分 类 号：P588.3[天文地球—岩石学]