The discovery of Late Triassic hypabyssal mafic dykes in the Huozhou complex and their geological significance: Evidence from petrology, geochemistry, and geochronology

Abstract

The Huozhou complex in the Trans-North China Orogen exhibits two events of mafic magmatism (separated by ca. 700 Ma): Neoproterozoic (920 ± 15 Ma) Shimenyu diabase and Late Triassic (217 ± 2.5 Ma) Xingtangsi diabase. Investigations have focused on systematic petrology, zircon U-Pb dating, Lu-Hf isotopes, and lithogeochemistry. The research findings indicate that the Late Triassic Xingtangsi diabase of the Huozhou complex can be classified as a transitional type between intermediate and mafic rocks based on their SiO₂ content. This classification is supported by an average SiO₂ content of 53.94%, ranging from 53.33% to 54.28%. In the Zr/TiO₂ vs. Ce diagram, all samples lie within the range of basalt. The zircons from the Late Triassic Xingtangsi diabase have low ε_Hf(t) values ranging from –12.7 to –8.7, with an average of –11.1. Additionally, the single-stage model age T_DM1 is estimated to be between 1207 and 1701 Ma. These findings suggest that the magma responsible for the dyke originated from either partial melting or an enriched mantle source inside the Meso-Proterozoic lithospheric mantle. The elevated concentrations of Th (thorium) and LREEs (light rare earth elements), as well as the Th/Yb and Th/Nb ratios, suggest the potential incorporation of subducted sediments within the magma source region. The rock displays negative Nb, Ta, Zr, Hf, and Ti anomalies. These geochemical attributes align with the distinctive traits observed in volcanic rocks found within island arcs. The formation of the Late Triassic Xingtangsi diabase is likely associated with the geological context of an arc setting, which arises from the collision between the Yangtze plate and the North China Craton.