Geochemical, geochronological, and Sr-Nd-Hf isotopic constraints on the petrogenesis of the Qicun intrusive complex from the Handan-Xingtai district: Implications for the mechanism of lithospheric thinning of the North China Craton

摘要

The Qicun intrusive complex is one of the major ore-related intrusions in the Handan-Xingtai district, eastern North China Craton. It consists of four intrusive bodies dominated by monzonite, quartz monzonitic diorite, quartz monzonite, and biotite diorite, respectively. The biotite diorite has a LA-ICP-MS zircon U-Pb age of 128.9 ± 0.93 Ma, indicating its emplacement in the early Cretaceous when the North China Craton was extensively reactivated. Rocks of the Qicun complex have high MgO (1.69-9.50 wt.%), high La_N/Yb_N (5.32-17.59) and Sr/Y (18.05-101.10) ratios, with low Y (8.17-20.43 ppm) and Yb (0.86-1.85 ppm) contents. They are enriched in light rare earth elements (LREE) but depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE) with weak or no positive Eu anomalies, features assembling adakites. In addition, whole-rock samples have initial ~(87)Sr/~(86)Sr ratios ranging from 0.70663 to 0.70767 and ε_(Nd)(t =130 Ma) between -16.5 and -14.3, which are consistent with zircon ~(176)Hf/~(177)Hf ratios of 0.281739 to 0.282083 and ε_(Hf)(t) values of - 33.8 to -21.7. The isotopic signatures, when combined with existing geological and geochemical data, indicate that the Qicun complex, and by inference other contemporaneous intrusions in the Handan-Xingtai district, formed by mixing of mantle-derived magmas with partial melts of delaminated lower continental crust under a lithospheric extensional setting related to the destruction of the North China Craton. Widespread presence of inherited zircon grains of ca. 2.5-2.4 Ga in the intrusions is consistent with a contribution of delaminated lower crust in the formation of the Qicun complex.