Abstract:

 Located in Xinglong County of Hebei Province, the northern margin of North China Craton, Wuling-shan complex is a batholith with an outcrop area of 230 km². The complex is mainly composed of porphyry-like alkali syenite, alkaline quartz-syenite and alkali feldspar syenite porphyry. The zircon U-Pb dating for 3 samples of the earliest emplaced porphyry-like alkali syenite in the complex yielded three weighted mean ages of (128.0±0.6) Ma, (127.3±1.2) Ma and (126.8±0.4) Ma, respectively. It shows that the complex was intruded in the Early Cretaceous. The in situ Hf isotopic analyses of the zircons gave the two-stage model ages ranging from 1.13 to 1.75 Ga, while the εHf(t) values from －7.8 to 1.7. The ε_Hf(t) value combined with the petrography of dark enclave of the porphyry-like alkali syenite indicates that the Wulingshan complex was formed by mixing of different magma from crust-, lithosphere enriched mantle-and depleted mantle-derived melts. By comparing the ε_Hf(t) values of different Early Cretaceous A-type granites occurring in the northern margin of North China Craton, we can conclude that these A-type granites were derived from different sources, with more contribution of depleted mantle composition as the time evolution. It suggests that the largescale lithospheric thinning almost finished at that time, while the depleted mantle materials started upwelling and were involved in the magmatic activity.

Key words: zircon U-Pb dating, Hf isotope, A-type granite, Wulingshan, Hebei