LA-ICP-MS Zircon U-Pb Dating of the Volcanic Rocks from Yamansu Formation in the Eastern Tianshan,and Its Geological Significance

This paper presents the geochemical characteristics and isotope chronology of volcanics from Yamansu Formation,occurring in Jueluotage tectonic belt in the eastern Tianshan of China.Petrological,isotope chronology and geochemical features of these volcanic rocks show that:(1)Yamansu Formation is composed of basite-mesite-acidic volcanic rock,pyroclastic rocks and pyroclastic sedimentary rocks.And it is mainly of calc-alkaline series.The geochemical characteristics demonstrated and inherited zircon age suggests that Yamansu volcanic rocks were formed at arc settings with continental basement.(2)In situ zircon U-Pb LA-ICP-MS dating on the zircon of Yamansu Formation yielded an age of 348.0±1.7Ma(MSWD=1.15)in the eastern section,335.9±2.4Ma(MSWD=1.03)in the middle and 334.0±2.5Ma(MSWD=1.02)in the western section,which stands for volcanic age.(3)The magmatic activity started from the east and then developed to the middle and western sections,like the close of scissors.