IN PHU HOẠT STRUCTURAL ZONE AND ITS GEOLOGICAL IMPLICATION
Bùi Đ́nh Công1, Nguyễn Thị Bích Thủy2, Nguyễn Chiến Đông1, Tạ Đ́nh Tùng1
1Vietnam Institute of Geosciences and Mineral Resources, No 67 Chiến Thắng, Hà Đông, Hà Nội
2General Department of Geology and Minerals, No 6 Phạm Ngũ Lăo, Hà Nội
Abstract: Granitoid rocks of the Bản Chiềng complex exposed in the Phu Hoạt structural zone. The rocks are granosyenite, less granodiorite and granite in composition. They exhibit porphyritic texture with phenocryst of K-feldspar. Major rock forming minerals are K- feldspar, plagioclase, quartz, less biotite and hornblende. Zircon and monazite crystals are accessory minerals. Zircon separated from the three granite samples are long and prismatic in shape, usually white and brownish in color. Size of zircon grains ranging from 150 to 300 μm with the length/width ratios of 3:1÷2:1. Cathodoluminescence images of analyzed zircon grains showing fine oscillatory internal structure that indicated magmatic origin of zircon. Emplacement age of granitoid was determined by SHRIMP zircon U-Pb isotope method and yielded average 206Pb/238U age of 27.4-29.5 Ma. These age values of the Bản Chiềng granitoids demonstrate the existence of the magmatic activity and formation of continental crust took place during early late Paleogene.
Keywords: SHRIMP zircon U-Pb age, Bản Chiềng granitoid, Phu Hoạt structural zone.
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