Abstract
The granites of Núi Pháo Pluton belong to the Núi Điệng Complex, exposed in the Tam Đảo area, Đại Từ District, Thái Nguyên Province. Petrographically, they are two mica granites of medium to coarse grains. The rocks are relatively light in colour and have porphyric texture. Formerly, the emplacement age of these granites was thought to be Middle-Late Triassic on the basis of their relationship with the country rocks. In order to elucidate the emplacement age of this pluton and its geological implication, zircons separated from the Nui Phao granites were dated by LA-ICP-MS U-Pb method, giving an average 206Pb/238U age of 248±9.9 Ma. This dating result pointed out the exsistence of the Indosinian tectonothermal event in the study area . Inherited zircon with 206Pb/238U ages of 840 and 447 Ma are also present in the sample indicating that the continental crust in the study area also contains Neoproterozoic and Paleozoic materials.