Petrogenesis of the Early Cretaceous volcanic-intrusive complex in northern North China Craton: Implications for crustal magma system evolution

Abstract

Identifying the origin and evolution of silicic magma is crucial for elucidating the transcrustal magmatic system and the evolution of continental crust. The Early Cretaceous volcanic-intrusive complex in the Kulongshan area provides an important insight into the evolution of silicic magma. Zircon UPb dating indicates that these spatially associated rocks formed between 140 and 131 Ma. The volcanic and subvolcanic rocks and alkali feldspar–alkaline granites are high silica (SiO₂ = 75.79–77.89 wt%) and alkali-rich and demonstrate strong negative Eu anomalies (Eu/Eu* = 0.02–0.06), as is typical of A-type rocks. Significant geochemical discontinuities were found between the potassium (K)-feldspar granite porphyry (SiO₂ = 67.86–70.80 wt%, Eu/Eu* = 0.20–0.44) and the high-silica rocks. These rocks exhibit ε_Hf(t) and T_DM2 values ranging from −18.1 to −9.2 and 2.34 to 1.84 Ga, respectively, indicating that the magmas originated from partial melting of the Paleoproterozoic continental crust. The geochemical characteristics show that the high-silica volcanic and subvolcanic rocks, along with the alkali-feldspar–alkaline granites, display a distinct trend of fractional crystallization. The K-feldspar granite porphyry exhibits distinct characteristics of feldspar accumulation. The consistent material source of the Kulongshan volcanic-intrusive complex suggests that the magma may have ascended from the source area, leading to magma interaction in the deep magma reservoir, followed by fractional crystallization in the shallow magma reservoir. The results indicate that Early Cretaceous high-silica rocks were formed via the extraction and coalescence of interstitial melts within the magma reservoir, with the K-feldspar granite porphyry representing residual crystal accumulation.