Contrasting Mo Isotopic Signatures in Basalts linked to Distinct Subduction Processes in the North China Craton

Subduction is a fundamental process driving mantle evolution and material recycling, yet distinguishing the contributions of oceanic versus continental subduction to mantle heterogeneity remains a challenge. This study examines Mo isotopes, combined with elemental and Sr-Nd-Pb isotopic data, of Early Cretaceous basalts in Sihetun (western Liaoning) and Feixian (western Shandong) in the North China Craton (NCC), regions influenced by distinct subduction processes. Sihetun basalts, exhibit light Mo isotope (δ^98/95Mo = -0.97 ~ -0.60‰), low Mo contents (0.32~0.41 ppm), high Ce/Mo ratios (292~426), and EMI-like Sr-Nd isotopic compositions. These characteristics suggest a mantle source containing dehydrated oceanic crust and pelagic sediments, possibly related to the oceanic subduction of the Paleo-Pacific plate. In contrast, Feixian basalts show heavier Mo isotope signatures (δ^98/95Mo = -0.09 ~ 0.07‰), higher Mo content (1.1~1.4 ppm), lower Ce/Mo ratios (137~197), and EMII-like Sr-Nd isotopic compositions. These features point to the contribution of recycled continental crust and terrigenous sediments in their mantle sources, suggesting that their source were effected by both the deep subduction of the Yangtze continent and oceanic subduction of the Paleo-Pacific plate. These distinct Mo isotopic variations across the NCC reveal that oceanic subduction typically leads to lighter Mo signatures, while continental subduction introduces heavier Mo isotopic signature to the overlying lithospheric mantle. This study highlights Mo isotopes as a powerful tracer for subduction-related processes and provides new insights into how oceanic and continental subduction regimes drive mantle enrichment and global geochemical cycles.