Characteristics and U-Pb ages of zircon in metavolcanics from the Kangbutiebao Formation in the Altay orogen, Xinjiang

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.