SHRIMP ZIRCON U-PB ISOTOPE AGE OF BẢN CHIỀNG GRANITOID

IN PHU HOẠT STRUCTURAL ZONE AND ITS GEOLOGICAL IMPLICATION

Bùi Đình Công¹, Nguyễn Thị Bích Thủy², Nguyễn Chiến Đông¹, Tạ Đình 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 Lão, 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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