40Ar-39Ar Dating for Muscovite in Garnet Muscovite-Felsic Schists of the Dahongshan Group in Southwestern Yangtze Block and Its Geological Significance
详细信息
- 责任者：Yang Hong (Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Liu Fulai
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(6)
- 关键词：白云母 ; muscovite ; 片岩 ; schist ; 氩—氩计时 ; Ar-Ar dating ; 扬子地台 ; Yangtze Platform
- 页码：p.2161-2170
- 图表：illus., 1 table, 53 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
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.