Tracing subducted oceanic slabs in the mantle by using molybdenum isotopes: A case study of intraplate basalts from Northeast China

Determining subduction-related processes is crucial for understanding lithological heterogeneity, as substantial quantities of slabs are recycled into the mantle. Molybdenum isotopes are valuable for distinguishing sources materials due to the significant isotope differences between the crust and the mantle. In this study, we systematically investigate Mo isotopes in a suite of well-characterized continental basalts from Keluo and Halaha-Chaoer, located in Northeast China. The δ⁹⁸Mo values of Keluo range from −0.41 to −0.23‰, with an average of −0.34‰, while Halaha-Chaoer samples ranged from −0.18 to −0.12‰, with an average of −0.15‰. The δ⁹⁸Mo values of Keluo basalts are lighter than the mean value of fresh oceanic basalts (−0.21‰), whereas those of Halaha-Chaoer basalts are similar to oceanic basalts. Combined with other geochemical indications (LOI, Ce/Pb, La/Yb and so on), the Mo isotopic variations cannot be attributed to chemical weathering, continental crust contamination or magmatic processes. Instead, the δ⁹⁸Mo variations in this study are explained by the incorporation of different oceanic crustal materials into the magma sources. Correlations of δ⁹⁸Mo with Ba/Th, Th/U, ¹⁴³Nd/¹⁴⁴Nd indicated that both sediment and altered oceanic crust have significantly influenced these variations. This study demonstrates the potential of Mo isotopes to distinguish different types of recycled oceanic crust materials.