Biotite 40Ar/39Ar Isotopic Dating of the Biotite Plagiogneiss from Hongqiyingzi Group in Chicheng County, North Hebei Province, China and Its Geological Implication
摘要
This paper discusses whether the Hongqiyingzi Group in Chieheng County of North Hebei Province underwent the Indosinian tectonothermal event or not. Biotite 40Ar/39Ar isotopic dating of the biotite plagiogneiss sample from Hongqiyingzi Group in Chicheng County of North Hebei Province yields a well defined 40Ar/39Ar plateau age of (238.63±1.44) Ma and an isochron age of (238.77±1.71) Ma, respectively. This may be interpreted as the age of the later Indosinian tectonothermal event undergone by the biotite plagiogneiss after the Late Paleozoic regional amphibolite facies metamorphism. On the basis of the magmatic emplacement and its geochronological characteristics within North Hebei Province, this Indosinian tectonothermal event may be related to the regional acidic magmatie activity contemporaneously, and the latter provided hot sources for the former.