LI Kuo, GONG Xiang-kuan*, SUN Min-jia, WANG Yi-ming, WU Hui-yun, ABDURSUL·Nijat

(Xinjiang Key Laboratory of Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Collaborative Innovation Center of Green Mining and Ecological Restoration for Xinjiang Mineral Resources, College of Geology and Mining Engineering, Xinjiang University, Urumqi 830017, China)

Abstract: The tectonic framework and tectonic evolution process of the North Qinling orogenic belt in the early Paleozoic have been widely concerned for a long time. Whether the Qinling Group had been experienced the overall continental crust subduction-deep subduction during the early Paleozoic is one of the big controversial issues. In this paper, the detailed LA-ICP-MS zircon U-Pb dating, geochemistry, mineral chemistry and zircon inclusion analysis of the amphibolite and felsic dykes outcropped in the felsic gneiss which is wallrock of the Zhaigen pluton in the Jiepai village, Zhaigen Township, Xixia County, Henan Province have been carried out in order to provide new constraints for discussing the above controversial issue better identify the early Paleozoic subduction history of the Qinling Group. The LA-ICP-MS U-Pb dating yielded the protolith age of ~820 Ma and metamorphic age of (422±5) Ma for the Jiepai amphibolite. Plagioclase and quartz inclusions were discovered in zircon grains. The amphibolite samples have similar geochemical characteristics with eclogites in the North Qinling. Two types of amphibole in the amphibolite have been identified. They should be formed during the amphibolite facies metamorphism and the subsequent retrograde metamorphism, respectively. Lots of inherited/captured zircons are preserved in the felsic dykes. Among them, the 1115-1576 Ma and 502-517 Ma aged zircons could be both inherited from the HP-UHP felsic gneiss of the Qinling Group, while the 908-935 Ma aged zircons could be sourced from the Zhaigen pluton. The felsic dyke was formed at (447±4) Ma and underwent metamorphic modification at ~420 Ma. In addition, the felsic dyke is characterized by relatively high contents of w(K2O), Rb and Ba, and relatively low contents of w(CaO), w(Fe2O3T), w(MgO) and w(TiO2), indicating that it could be the product of dehydration melting of phengite in the HP-UHP felsic gneiss of the Qinling Group. Combined with data of previous researches and this research, it is concluded that the Jiepai amphibolite had underwent amphibolite facies metamorphism only in the Early Paleozoic and it was not the retrograde metamorphic product of eclogite. This provides further evidence for the viewpoint that the Qinling Group had not been experienced the overall continental crust subduction-deep subduction in the early Paleozoic. During 420-460 Ma, the subducted-deep subducted continental crust was fractured and broken due to the upwelling of mantle-derived magma, its extensive partial melting and magmatic intrusion in its rollbacking and uplifting processes, and finally the melt of its partial melting was contaminated by unsubducted continental crust rocks. 

Keywords: amphibolite; felsic dyke; Qinling Group; petrogeochemistry; zircon U-Pb dating

ACTA MINERALOGICA SINICA Vol. 43, No. 5, 2023, Page 674