东秦岭东段五垛山花岗岩基白草垛花岗伟晶岩微量元素富集型锆石特征及岩浆热液过程  

Trace element enriched zircon and magmatic hydrothermal process of Baicaoduogranitic pegmatite in Wuduoshan batholith in the eastern part of East Qinling

作　　者：陈国超[1,2,3,4] 张晓飞 裴先治 李瑞保[2] 李佐臣[2] 魏均启[4] 陈孝珍 季宪军[1] 张勇[3] CHEN Guochao;ZHANG Xiaofei;PEI Xianzhi;LI Ruibao;LI Zuochen;WEI Junqi;CHEN Xiaozhen;JI Xianjun;ZHANG Yong(Nanyang Institute of Technology,Nanyang,Henan 473000,China;Key Laboratory of Western China’s Mineral Resources and Geological Engineering,Ministry of Education,Xi’an,Shaanxi 710054,China;Key Laboratory of Metallogeny and Mineral Assessment,Ministry of Natural Resources,Beijing 100037,China;Hubei Key Laboratory of Resources and Eco-Environment Geology,Hubei Geological Bureau,Wuhan,Hubei 430034,China;Development and Research Centre,China Geological Survey,Beijing 100037,China)

机构地区：[1]南阳理工学院,河南南阳473000 [2]长安大学西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [3]自然资源部成矿作用与资源评价重点实验室,北京100037 [4]资源与生态环境地质湖北省重点实验室,湖北省地质局,湖北武汉430034 [5]中国地质调查局发展研究中心,北京100037

出　　处：《地质学报》2023年第3期688-704,共17页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42172236、41872233、41872235);河南省重点研发与推广专项项目(编号212102310030);自然资源部成矿作用与资源评价重点实验室开放基金项目(编号ZS006);资源与生态环境地质湖北省重点实验室开放基金项目(编号KJ2022-35);长安大学西部矿产资源与地质工程教育部重点实验室开发基金项目(编号300102261505);南阳理工学院交叉科学研究项目联合资助的成果。

摘　　要：锆石是岩石中常见的副矿物,锆石晶体结构和地球化学特征的变化可以记录热液蚀变过程。东秦岭东段白草垛花岗伟晶岩中识别出三种类型锆石。类型一锆石具有明显的振荡环带,部分锆石边部有少量裂隙,微量元素含量相对较低,重稀土元素(HREE)富集,具明显Ce的正异常和Eu的负异常,指示其为岩浆锆石。类型二锆石具核-幔-边结构,边部裂隙发育,核部与类型一锆石具有相似的CL和微量元素特征,为岩浆锆石;幔部呈深色海绵状,内部结构不均匀,偶见环带锆石残留,微量元素含量较高,具有较高的U和Th含量,Ce异常不明显,具热液锆石特征,为热液沿着裂隙进入锆石内部不完全热液改造的结果。类型三锆石的结构特征和微量元素含量与类型二锆石的幔部相似,具有异常高U和Th含量以及较高的Dα值,为类型二锆石近完全热液改造的结果。花岗伟晶岩作为岩浆演化晚期的产物,经过结晶分异,残留的岩浆热液富集微量元素,岩浆热液沿着锆石的裂隙进入晶体内部对锆石经过不同程度热液改造,形成了花岗伟晶岩中不同类型的锆石。Zircon is an accessory mineral in igneous rocks and can provide a record of hydrothermal alteration through variations in crystal structures,and geochemical properties.In samples of altered granitic pegmatite from the Baicaoduo region in the eastern part of East Qinling,three different forms of zircon were found.Type 1 zircons feature pronounced oscillatory zones,low trace element levels,and are concentrated in the heavy rare earth elements(HREE).Some Type 1 zircons also have a modest number of fractures near the rim.They are magmatic zircons because the Ce exhibits clear positive anomalies and significant negative Eu anomalies.Type 2 zircons have developed rim fractures and a core-mantle-rim structure.The core has similar CL and trace element characteristics to Type 1 zircon,which is magmatic zircon.Type 2 zircon mantle has dark spongy,uneven internal structure,occasionally contains zircon residue,a high trace element content,and inconspicuous Ce anomaly.It has hydrothermal zircon characteristics due to incomplete reworking of hydrothermal solution into zircon along the fracture.The Type 3 and Type 2 zircon mantles have comparable structural characteristics and trace element content,with abnormally high U and Th content and high Dαvalue,which is the result of complete hydrothermal reworking of Type 2 zircon.As a byproduct of later magmatic development known as granitic pegmatite,leftover magmatic hydrothermal enhances trace elements by crystallization differentiation.In granitic pegmatite,the zircon is reworked to varied degrees by the magmatic hydrothermal that penetrates the crystal via the zircon's fracture.

关 键 词：东秦岭 花岗伟晶岩 锆石LA-ICP-MS定年 黑云母原位Rb-Sr定年 热液锆石 

分 类 号：P597.3[天文地球—地球化学] P588.131[天文地球—地质学]