Petrogenesis and tectonic implications of the Silurian adakitic granitoids in the eastern segment of the Qilian Orogenic Belt, Northwest China

Jiao-Long Zhao1, Xiao-Jun Huang2, Pei-Qing Hu1, Zhen-Xi Yang3, Ying Fan3, Er-Teng Wang1, Fu-Bo Yang1, Jing-Yu Zhang1
1School of Earth Sciences, Key Laboratory of Mineral Resources in Western China (Gansu Province), Lanzhou University, Lanzhou, China
2Nuclear Industry 247 Brigade, Tianjin North China Geological Survey Bureau, Tianjin, China
3Fourth Institute of Geological and Mineral Exploration of Gansu Provincial Bureau of Geology and Mineral Resources, Jiuquan, China

Tóm tắt

Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at 423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series. Both are peraluminous in composition and have relatively depleted Nd isotopic [εNd(t) = (− 3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Post-collisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.

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