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

Abstract. Determining subducted processes is very important for understanding lithological heterogeneity because Substantial quantities of slabs are recycled into the mantle. Molybdenum isotope have been used to distinguish the addition of crustal materials since the significant Mo isotopic differences of reservoirs. Here we undertake a systematic Mo isotopic investigation on a suite of well-characterized continental basalts from Keluo and Halaha-Chaoer, located at Northeast China. The δ⁹⁸Mo varied from -0.41 to -0.23 ‰ with an average of -0.34 ‰ for Keluo samples and from -0.18 to -0.12 ‰ with an average of -0.15 ‰. The former is lighter than fresh oceanic basalts (-0.21 ‰) while the latter is similar to oceanic basalts. The Mo isotopic variations, combine with other geochemical indications (LOI, Ce/Pb, La/Yb and so on), cannot be interrupted to chemical weathering, continental crust contamination or partial melting, but are explained by the addition of various oceanic crustal materials in magma sources. The relationships between δ⁹⁸Mo and Ba/Th, Th/U, ¹⁴³Nd/¹⁴⁴Nd for the samples suggest sediment, fresh and altered oceanic crust have contributed to the large variations in these samples. The study here indicates the great potential of Mo isotopes to distinguish different types of recycled oceanic crust materials in the mantle.