扬子地块西南缘大红山群石榴白云母-长石石英片岩的白云母^(40)Ar-^(39)Ar定年及其地质意义  

^(40)Ar-^(39) Ardating for muscovite in garnet muscovite-felsic schists of the Dahongshan Group in southwestern Yangtze Block and itsgeological significance

作　　者：杨红[1] 刘福来[1] 刘平华[1] 王舫[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2013年第6期2161-2170,共10页Acta Petrologica Sinica

基　　金：创新研究群体科学基金项目(40921001);中国地质调查局地质调查工作项(1212011121276);国家杰出青年科学基金项目(40725007)联合资助

摘　　要：大红山群是扬子地块西南缘出露的古元古代结晶基底,主要经历了绿片岩相-低角闪岩相变质作用。本研究对大红山群老厂河组变质中酸性岩和变质沉积岩——石榴白云母-长石石英片岩中的白云母进行了40Ar-39Ar测年,得到三个样品的坪年龄和40Ar/39Ar等时线年龄结果较统一,坪年龄代表的变质年龄分别为837.7±4.2Ma、839.6±4.2Ma和844.2±4.2Ma。变质沉积岩和变质中酸性岩的变质时代类似,均介于837～845Ma。大红山群变质基性岩中变质锆石的U-Pb定年年龄为849±12Ma(杨红等,2012),40Ar-39Ar测年数据与锆石定年数据相结合,说明大红山群古元古代结晶基底中的火山岩和沉积岩均在新元古代经历了同期变质作用,其主期低角闪岩相变质作用发生于新元古代837～850Ma。结合前人发表的扬子西缘～750Ma的变质年龄,扬子西缘从北向南的区域变质作用时限可扩展到750～850Ma。此外,扬子西缘存在750～850Ma的岩浆事件,本文研究结果说明,扬子地块西缘在新元古代不仅发生了大规模岩浆作用,也发生了750～850Ma的区域变质作用,扬子西缘存在新元古代的岩浆-变质事件。岩浆事件与变质事件之间可能存在相关性,即新元古代岩浆作用引起了扬子西缘的区域动力热流变质作用。Dahongshan Group is a stratigraphic unit of Paleoproterozoic crystalline basement in SW Yangtze Block,which experienced greenschist-lower amphibolite facies metamorphism. This study focused on metamorphic geochronology of the Dahongshan Group by40 Ar-39 Ardating for muscovite in garnet muscovite-felsic schists which are meta-sedimentary and meta-intermediate-acidic rocks from the Laochanghe Formation. The plateau and isochron ages of the three samples are very similar. The three plateau ages for muscovite which represent the metamorphic ages are 837. 7 ±4.2Ma,839. 6 ±4.2Ma and 844.2 ±4.2Ma,respectively. The metamorphic ages of meta-sedimentary rocks and meta-intermediate-acidic rock are similar,ranging from 837Ma to 845Ma. Zircon U- Pbdating age of garnet hornblende gneiss interbedding with the schists is 849 ± 12Ma （ Yang et al. ,2012 ） .40 Ar-39 Ardating correlating with zircon U-Pbdating give an age range of 837～850Ma,which represents the low-amphibolite facies metamorphic time of the metasedimentary,meta-intermediate-acidic and meta-basic rocks in the Dahongshan Group. Then the regional metamorphic time of western Yangtze block from north to south could be expanded to 750～850Ma. Correlating with the Neoproterozoic large-scale magmatism of 750～850Ma in western Yangtze,this study demonstrates that not only magmatism but regional metamorphism happened in Neoproterozoic Era. There must be relativity between the two events： Magmatism caused the regionaldynamo thermal flow metamorphism in Neoproterozoic Era.

关 键 词：扬子西缘 大红山群 白云母Ar-Ar定年 新远古代变质事件 

分 类 号：P588.344[天文地球—岩石学] P597.3[天文地球—地质学]