Abstract: The No.2 Geobrigade of Tibet Geological Prospecting Bureau has disintegrated a set of volcanic rocks in the 1:50 thousand regional geological survey of the chubb area of Xietongmen county. It composed dominantly of andesite, rhyolite, volcanic breccia and tuff. The total thickness of the rock strata decreases from east to west in the study area. The U-Pb isotopes of zircons from rhyolite and andesite samples were determined by LA-ICP-MS. The weighted average ages of ²⁰⁶Pb/²³⁸U were 15.12±0.29Ma (MSWD=1.8, n=8), 45.39 ±0.56Ma (MSWD=0.93, n=14) in rhyolite and 15.29 ±0.16Ma (MSWD=1.4, n=59), 51.9 ±2.3Ma (MSWD=3.5, n=7), 45.2±1.4Ma (MSWD=3.8, n=10), 38.5±0.93Ma (MSWD=1.08, n=5) in andesite. Based on this, the eruption time limit of this suite of volcanic rocks is determined to be 15Ma or so, and it belongs to the Bugasi Group.