Abstract: The rocks of the Kangbutiebao Formation suffered greenschist low amphibolite facies metamorphism. The isotope ages reported are all metamorphic ones. According to the colors, crystal shapes and U Pb isotopic composition of zircons, the zircons in acid volcanic rocks of the formation may be divided into inherited zircon, magmatic zircon, mixed zircon (containing a small core of inherited zircon) and metamorphic zircon. The volcanic rocks of the formation were determined using the single grain zircon U Pb method to have an age of 407.3±9.2 Ma, assigned to the Early Devonian age. Meanwhile the ages of two phases of metamorphism and reference age of the source region of volcanic rocks have been obtained.