LA-ICP-MS zircon U-Pb geochronology of the eastern part of the Xiaomaoling composite intrusives in Zhashui area, Shaanxi, China

The eastern part of the Xiaomaoling composite intrusives in the Qinling Mountains is considered to consist mainly of the early Songjiawuchang altered proterobase or bojite, the late Mihunzhen altered diorite, Mogouxia altered quartz diorite and Yejiawan altered monzodiorite. The LA-ICP-MS U-Pb isotope dating for zircons from the rock masses above yields four ages: 864.4Ma±1.7Ma from Songjiawuchang, 846.7Ma±2.7Ma from Mihunzhen, 859.4Ma±1.7Ma from Mogouxia and 861.1Ma±1.8Ma from Yejiawan. All the data suggest that the eastern part of the Xiaomaoling composite intrusives belongs to the Neoprotozoic in age. The metamorphic age obtained from the early Precambrian metamorphic rocks of the Xiaomaoling-Douling uplift belt is close to the age of the North Qinling orogenic event(1000Ma～848Ma) based on the previous materials and combining with the intrusives' own character, the authors infer that the eastern part of the Xiaomaoling composite intrusives forms in the post-collisional stress relaxation environment.