Petrogenesis and tectonic implications of the Triassic granitoid plutons in west Qinling Mountains, China: insights from LA-ICP-MS zircon U-Pb ages, and Lu-Hf isotope of the Zhongchuan pluton

The Zhongchuan pluton is one of the most important acidic intermediate plutons in the western Qinling orogenic belt. The authors collected geochemical and geochronologycal data for the Triassic granitoid plutons of the west Qinling Mountains and found that nearly all plutons share the similar features with the Zhongchuan pluton. We present new LA-ICP-MS zircon U-Pb ages, major and trace element geochemistry, and zircon Hf isotope systematics for the granites of the Zhongchuan pluton to elucidate the evolution of granitoid plutons in the western Qinling Mountains during the Triassic. LA-ICP-MS zircon U-Pb dating indicates that the Xujiaba and Guandigou units formed at 220.1 +/- 1.2 Ma and 215.9 +/- 0.85 Ma, respectively, reflecting the time of the Late Triassic. The zircon Hf isotope dating indicates that the Xujiaba and Guandigou units have an inhomogeneous epsilon(Hf)(t) and two-stage Hf model ages. The isotopic data imply that the granites of each unit share the same origin, which probably derived from the partial melt of metagreywackes and then mixed with the mantle-derived magma. Based on the regional geological history, petrographic characteristics and new geochemical and isotopic data of the Zhongchuan pluton, we suggest that the Triassic magma was derived from the partial melts of metagreywackes and was influenced by the mantle-derived melt during the collision of the Yangtze and Qinling plates.