U-Pb zircon age of granitoid from Bản Chiềng complex in the Phu Hoạt structural zone and its geological implication

Bi Đnh Cng, Nguyễn Thị Bch Thủy, Nguyễn Chiến Đng, Tạ Đnh Tng

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. The zircon grains separated from the three granite samples 00are 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 3:12:1. CL images of analyzed zircon grains showing fine oscillatory internal structure that indicated magmatic origin of zircon. 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 granitoid demonstrate the existence of the magmatic activity and formation of continental crust took place during late Paleogene.

Keywords: SHRIMP U-Pb zircon age, Bản Chiềng granitoid, Phu Hoạt structural zone