| 崆岭杂岩中角闪岩类的年代学和地球化学 |
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| 引用本文： | 魏君奇,景明明.崆岭杂岩中角闪岩类的年代学和地球化学[J].地质科学,2013,48(4):970-983. |
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| 作者姓名： | 魏君奇 景明明 |
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| 作者单位： | 1. 大陆动力学国家重点实验室, 西北大学地质学系 西安 710069;
2. 边防学院 西安 710108 |
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| 摘 要： | 通过崆岭杂岩中角闪岩类的年代学和地球化学研究,以揭示黄陵结晶基底的形成及演化。崆岭杂岩主要由太古代的TTG片麻岩和角闪岩类岩石,以及早元古代孔兹岩系组成,角闪岩类以围岩或包体的形式存在于TTG片麻岩的周围和内部。角闪岩类围岩的全岩Sm-Nd等时线年龄为2 998.9 Ma,原生岩浆锆石的U-Pb年龄为3 013 Ma,均代表角闪岩类原岩的形成时间,且与包体状斜长角闪岩原岩的年龄(3.0 Ga)相同。说明以围岩或包体存在的角闪岩类,其原岩的形成年龄均为3.0 Ga。微量元素和Nd同位素地球化学特征指示,角闪岩类原岩形成的构造环境为大陆初始裂谷环境。角闪岩类岩石中变质新生锆石的U-Pb年龄为2 043 Ma,指示黄陵地区存在第Ⅲ期(2.1～1.9 Ga)角闪岩相热变质事件,且该期热变质作用将松散的陆源碎屑岩等变质为孔兹岩系,从而构成早元古代结晶基底,并与晚太古代稳定陆块焊结在一起,最终完成整个黄陵结晶基底的形成。
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| 关 键 词： | 崆岭杂岩 角闪岩类 锆石U-Pb年龄 Sm-Nd同位素 |
| 收稿时间： | 2013-05-10 |
| 修稿时间： | 2013-05-10; |
Chronology and geochemistry of amphibolites from the Kongling complex |
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| Wei Junqi
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Jing Mingming.Chronology and geochemistry of amphibolites from the Kongling complex[J].Chinese Journal of Geology,2013,48(4):970-983. |
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| Authors: | Wei Junqi Jing Mingming |
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| Institution: | 1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069;
2. PLA Border Defense Academy, Xi'an 710108 |
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| Abstract: | The Kongling complex,an important part of the basement block for the Yangtze Craton,is exposed in the northern of the Huangling anticline in western Hubei province.It mainly consists of TTG gneisses,amphibolites and khondalite series.The amphibolites were derived from ultramafic-mafic volcanic rocks,and the TTG gneisses were derived from TTG granites.The amphibolites are occurred surrounding TTG gneisses as adjoining rocks,and inside TTG gneisses as enclaves.This study focuses on the amphibolites as adjoining rocks.The whole-rock Sm-Nd isochron age of 2 998.9 Ma on the amphibolites,this age are interpreted as eruption time of ultramafic-mafic volcanic rocks.According to CL images and Th/U ratios,all zircons from amphibolites can be divided into two types:Protolith igneous zircon and metamorphic growth zircon.The protolith igneous zircons show a core-rim structure,and the cores have well-developed magmatic oscillatory zoning,and the rims are thin and bright.Their U-Pb spot analysis were done on cores,and the results form a discordia with the upper intercept at 3 013±23 Ma,MSWD=0.38,this age are same interpreted as eruption time of ultramafic-mafic volcanic rocks.In addition,the protolith igneous zircons U-Pb age is 3.0 Ga for the amphibolites as enclaves.Therefore,both of the amphibolites as adjoining rocks or enclave,their protolith rocks were formed in the same time of 3.0 Ga.After this,the ultramafic-mafic volcanic rocks belt was intruded by TTG granites so that the Archean granite-greenstone terrain formed.Experienced the first and second metamorphic event,the Archean granite-greenstone terrain was transformed to Neoarchean stable landmass.Based on trace elements and isotope geochemical data,it is inferred that the ultramafic-mafic volcanic rocks is formed continental initial rift.The metamorphic growth zircons have such internal structure as cloudy zoning,sector zoning,planar zoning,indicating they were formed in amphibolite-facies.These zircon U-Pb analysis results form a discordia with the upper intercept at 2 043±51 Ma,MSWD=50,this age is interpreted as the timing of the third thermal metamorphic event,which may be related to the assemblage of Columbia supercontinent.During the third metamorphic event,the detrital sedimentary rock was transformed to Khondalite,which was tied to Neoarchean stable landmass,so that the Huangling crystalline basement was formed in Early Proterozoic. |
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| Keywords: | Kongling complex Amphibolites Zircon U-Pb age Sm-Nd isotopes |
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