Petrogenesis of Mesozoic Magmatic Suites in the Jiaodong Peninsula: Implications for Crust-Mantle Interactions and Decratonization

The North China Craton (NCC) has thick lithosphere in the Paleozoic (>200 km) but appears to be decratonized in the Mesozoic. However, the actual processes operated in the lower crust-deep mantle are still unclear. The Mesozoic granitic rocks can provide important clues to the NCC decratonization mechanism. Here, we conducted trace element modeling to check whether partial melting of the Archean lower crust can generate these Mesozoic magmatic suites. Meanwhile, zircon Hf isotope analysis was conducted to reveal crust-mantle interaction processes and further give constraints on the decratonization of the NCC. Zircon Hf isotope data of the Linglong, Guojialing, and Aishan suites, the mafic microgranular enclaves (MMEs) in the Guojialing suite, and mafic dykes display minor differences: the Linglong (160-150 Ma), Guojialing (similar to 130 Ma), and Aishan (118-116 Ma) suites have zircon epsilon Hf(t) = -25:4 to -14.5, -15.3 to -10.4, and -23.1 to -11.9, respectively. The Cretaceous mafic dyke (126 Ma) has a highly negative epsilon Hf(t) value (-22.8 to -17.7). Meanwhile, the MMEs (in the Guojialing granodiorite, DCW-2A, 129 Ma) have zircon epsilon Hf(t) = -13:0 to -8.9. Temperature-pressure conditions calculated using amphibole compositions for both the Guojialing granodiorite and its MMEs are basically identical, implying possible magma mixing. Our modeling results show that certain trace elements (e.g., Tb, Yb, and Y) have to be retained in the source to match the composition of the Linglong suite, which requires substantial garnet residues (high-pressure melting) in the Jurassic. The Early Cretaceous garnet-dominated lower crust is Yb-/Y-enriched but depleted in elements like Sr and La. Therefore, it could not form geochemical features like high Sr/Y and La/Yb ratios akin to the Guojialing suite. Integrating the modeling results and zircon Hf isotope data, we propose that the crust in the eastern NCC had thickened and partially melted by dehydration to produce an eclogitic residue containing a large amount of garnet (>50% by weight) during the Jurassic (Linglong granite), whereas upwelling of hot and hydrous mafic magma from the asthenospheric mantle induced fluxed melting of both the lower crust and lithospheric mantle in the Early Cretaceous, during which the lithospheric mantle and part of the lower crust in the Jiaodong were removed by the convective mantle. About 10 Mys later while the Aishan suite formed, the crust was not thick anymore, and melting occurred under moderate pressure which does not necessarily require abundant garnet as the residue phase.