Coexisting Depleted and Enriched Mantle-derived Magmatic Rocks in the Liaodong Peninsula: Implications for the Destruction of the North China Craton

Abstract

The North China Craton (NCC) experienced significant lithospheric thinning of over 100 km during the Mesozoic, accompanied by extensive magmatic activity and extensional tectonics. However, the timing and mechanism of this thinning remain the subjects of debate. This study presents zircon U-Pb ages, Hf isotopic data and whole-rock elemental and Sr-Nd isotopic compositions of the Guanshui monzonites and diorites in the eastern NCC. Zircon U-Pb dating reveals that both rock types formed at ca. 130 Ma. The monzonites, characterized by high Mg^# (50.9–57.9), low Nb/U ratios (2.53–3.89) and depleted isotopic compositions, suggest derivation from asthenospheric mantle modified by slab-derived fluids. The diorites, distinguished by low SiO₂ (49.5–50.8), high Mg^# (66.7–68.5) and an EM2-type enriched mantle isotopic signature, point to a lithospheric mantle source modified by subducted sediment melts. The coexistence of monzonites and diorites suggests a transition in magma source from lithospheric to asthenospheric mantle, implying that lithospheric thinning may have commenced around 130 Ma. The destruction of the NCC was likely driven by localized, small-scale drip-style detachment processes, rather than wholesale lithospheric removal.