LA-ICPMS Zircon U-Pb Dating of Tangzang Quartz-diorite Pluton in the West Segment of North Qinling Mountains and Its Tectonic Significance

The Tangzang quartz-diorite pluton which has the characteristics of Adakite was founded in a geological survey in Baoji,Shaanxi.Zircons from the quartz-diorite pluton are generally colorless and long columnar with obvious magmatic zone.The LA-ICPMS zircon U-Pb geochronology of 29 samples from the pluton with Th/U ratios from 0.33 to 1.10,yielded a weighted mean 206Pb/238U age of(454.0±1.7)Ma as the magmatic crystalline age of the protolith of the quartz diorite.Integrated the formation age of the Guanzizhen and Yanwan ophiolites in the west segment of north Qinling orogenic belt,it is indicated that the subduction process of Danfeng ocean along the Shangdan belt had existed,and the age of(454.0±1.7)Ma is the early period of the subduction process.The result provides an important evidence on the research of orogenic process,mantle crust interaction,and continental dynamics of north Qinling mountains.