LIU Rui1, CHEN Mi2, TIAN Xiang-sheng3, HU Heng1, YANG De-pin4
(1. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;
2. Hubei Geological Survey, Wuhan 430034, China;
3. Third Institute Geological and Mineral Exploration of Gansu Provincial Bureau of Geology and Mineral Resources, Lanzhou 730050, China;
4. Puding City Land and Resources Bureau, Anshun 562100, China)
Abstract: Both Lantian and Muhuguan granitoid plutons are located in the western part of the East Qinling Orogen and are separated by the Luonan-Luanchuan regional fault. The former consists mainly of porphyritic and intermediate-fine grained monzogranite, while the latter is composed of monzogranite, granodiorite and biotite granite. Zircons extracted from the two plutons are characterized by oscillatory zoning and Th/U ratios higher than 0.1 suggesting the igneous origin. They yield U-Pb ages of 147±2 Ma and 149±1 Ma for Lantian and Muhuguan plutons, respectively, indicating that they are formed in the Late Jurassic. The εHf(t) values for the two plutions range from -16.9 to -7.2 and from -9.3 to -6.8, with Hf modal ages of 1.7―2.3 Ga and 1.6―1.8 Ga, respectively, suggesting that they were likely formed by reworking of Paleo- to Meso-Proterozoic crust. Petro-geochemistry data indicate the formation of the two plutons lived through a complex process involving melting of ancient crust, wall-rock contamination, magma mixing and crystallization differentiation. The ca.150 Ma magma in the East Qinling Orogen may be representative of the lithospheric extension during the Late Jurassic to the Early Cretaceous, which was related to the Late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.
Key words: petro-geochemistry; U-Pb age; Hf isotope; lithospheric extension; East Qinling
ACTA MINERALOGICA SINICA Vol. 34, No. 4, 2014, Page 469-480
