今天是2019年04月19日

东秦岭南召县五朵山岩体二云母花岗岩地球化学、锆石U-Pb年代学及地质意义

DOI:10.3799/dqkx.2018.306

作者:李开文,方怀宾,郭君功,刘 坤 ,赵 焕 ,王小娟

联系地址:河南省地质调查院,河南郑州 450001

摘要:秦岭造山带地处华北板块与扬子板块结合带,经历了复杂的构造演化过程,其板块拼合机制及碰撞时限一直备受争议.对东秦岭南召县五朵山岩体二云母花岗岩进行岩石地球化学和LA-ICP-MS锆石U-Pb年代学研究,结果表明岩石具有高硅(SiO2=69.32%~74.28%)、高铝(Al2O3=14.14~17.28)、高碱含量(Na2O+K2O=7.68%~9.03%)等特征,且相对富钾贫钠,在岩石类型上属于强过铝质“S”型花岗岩类.岩石具有中等的稀土元素含量,呈现轻稀土富集、重稀土亏损的右倾配分模式,中等的负Eu异常,富集K、Rb、Th等大离子亲石元素,亏损Ba、Nb、Sr、P、Ti等元素,表明南召县二云母花岗岩可能形成于陆陆碰撞所导致的陆壳加厚环境.LA-ICP-MS锆石U-Pb分析结果表明,二云母花岗岩锆石均具有明显的韵律环带,Th/U比值均大于0.4,暗示岩浆成因特征,206Pb/238U加权平均年龄为433±2 Ma;结合构造环境特征,表明东秦岭南召地区在早志留世末期由俯冲环境转换为陆陆碰撞环境.

关键字:二云母花岗岩;岩石学;地球化学;LA-ICP-MS锆石U-Pb定年;南召县;东秦岭

Petrogeochemistry, Zircon U-Pb Dating and Geological Significance of Two-Mica Granites from Wuduoshan Granite in Nanzhao County, Eastern Qinling Mountains

Author:Li Kaiwen, Fang Huaibin , Guo Jungong , Liu Kun , Zhao Huan , Wang Xiaojuan

Author Address:Henan Institute of Geological Survey, Zhengzhou 450001, China

Abstract:The Qinling orogenic belt, located in the suture zone of the North China Plate and the Yangtze Plate, has undergone a complicated tectonic evolution process however, its plate combination mechanism and collision time limit have been controversial. In this study, petrogeochemistry analyses and LA-ICP-MS zircon U-Pb dating are undertaken for the two-mica granites from Wuduoshan in Nanzhao County, eastern Qinling mountains. Results show that the two-mica granites have SiO2=69.32%-74.28%, Al2O3=14.14%-17.28%, Na2O+K2O=7.68%-9.03%, and belong chemically to peraluminous series of S type. Meanwhile, the two-mica granites have a moderate amount of rare earth elements, with medium fractionation characteristics between light rare earth elements and heavy rare earth elements and medium negative Eu anomalies. The trace elements diagram shows enrichment of large ion lithophile elements (LILEs) and depletion of Ba, Nb, Sr, P and Ti, indicating that the two-mica granites may have been formed in the thickened crust caused by the collision between continents. Zircons from the two-mica granites in this study display fine-scale oscillatory growth and high ratios of Th/U (>0.4), indicating a magmatic origin. The dating of the two-mica granites yields a LA-ICP-MS zircon U-Pb age of 433±2 Ma. Combined with constructional environment, it is concluded that it was transformed from plate subduction to continental collision in the Nanzhao County at late of Early Silurian.

Keyword:two-mica granites; petrology; geochemistry; LA-ICP-MS zircon U-Pb dating; Nanzhao County; eastern Qinling mountains

 

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作者简介:李开文(1984-),男,工程师,主要从事区域地质矿产调查工作.ORCID: 0000-0003-2354-5778. E-mal: likaiwen0502@163.com

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