SHRIMP ZIRCON
U-PB ISOTOPE AGE OF BẢN CHIỀNG GRANITOID
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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