Abstract

Zircon crystals selected from granitoid Chieng Khuong Complex V0938 sample and V0821 have the LA-ICP-MS U-Pb analyses clustered at 263±8 Ma. Two sample zircon analyses give concordant ages concentrated at 263± 8 Ma (weighted mean). These results indicate the protolith of the granitoid Chieng Khuong Complex (primary magma crystallization age) to be late Paleozoic (ca. 263 Ma). The results Hf(t) of Chieng Khuong granitoid show that Hf isotopic ratio from -6.4 to-13.3, indicated granitoid was formed in a complicated environment and origin through partial melting of Proterozoic crust. Combine with Hf isotope and petrological probably indicating existence of the mixture between crust and mantle material during the formation of the magma. Thus, these rusults indicate the mixing crust – mantle model which is the main way to forming process of Chieng Khuong complex.