Zircon U-Pb ages and Hf isotopic characteristics of the Dehe biotite monzonitic gneiss pluton in the North Qinling orogen and their geological significance

摘要

The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt (NQOB). It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet. LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton. Most of the ɛHf(t) values are negative, and the two-stage model ages are consistent with the age of the Qinling Group. The isotope data show that the Dehe granite was formed in the following geological setting: in the syn-collision setting of the NQOB in the Neoproterozoic, crustal thickening induced partial melting of materials derived from the Qinling complex, and then the maga upwelled and intruded into the Xiahe Group. The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.