Petrogenesis of Jurassic granitoids from the Yanshan orogenic belt: Implications for crustal evolution in the northern North China Craton

Abstract

This study presents new geochronological and geochemical data for the Wangpingshi granite (WG) and Yuerya granite (YG) from the Yanshan orogenic belt, aiming to reveal their petrogenesis and source characteristics. Zircon U–Pb dating of the WG and YG plutons indicates formation ages of 171 Ma and 168 Ma, respectively. These granites are high-K calc-alkaline I-type granites, characterized by high SiO₂ and low P₂O₅ contents, enrichment in Rb, Th, U, and Pb, depletion in Nb, Ta, Ti, and P, with low Nb/U, Nb/Ta, and Zr/Hf ratios. They exhibit initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7045–0.7063, ε_Nd(t) values of −12.28 to −11.36, and zircon ε_Hf(t) values of −14.65 to −9.19. These geochemical and isotopic characteristics suggest that the granites originated from partial melting of a modified crustal source comprising both juvenile and ancient crustal components. Petrogenetic modeling indicates that the WG magma formed under pressures of 12.5–13 kbar with a garnet-bearing amphibolite residue, while the YG magma formed under pressures of 9–10 kbar with a plagioclase-dominated amphibolite residue. The source characteristics of the granites indicate that the lower crust underwent significant modification through magma underplating before the Jurassic, which likely weakened the crust and facilitated subsequent tectonic deformation. This research provides a lower age limit of 170–168 Ma for constraining the initiation of episode A of the Yanshanian Movement.