Tracing serpentinite recycling through heavy molybdenum isotopes in intraplate basalts

Direct evidence for serpentinite recycling in the mantle source of intraplate basalts is scarce. Fortunately, slab serpentinites and their dehydrated products exhibit distinct Mo systematics compared to subducted oceanic crust, providing a powerful tracer of their recycling. Here, we present new Mo contents and isotope ratios for intraplate alkali basalts from the eastern North China Block since 100 Ma to investigate the potential contribution of subducted Izanagi-Pacific slab serpentinite to their mantle source. Our results document that many basalts exhibit heavy Mo isotopes (δ^98/95Mo_NIST3134 values range from -0.41‰ to -0.06‰). Combined with whole-rock radiogenic Sr-Nd and olivine O isotope systematics, the heavy Mo isotopic signature can be interpreted to represent a signal from deeply subducted Izanagi-Pacific slab serpentinite. Heavy Mo isotopes in intraplate basalts can thus serve as a reliable indicator for tracing recycled serpentinites. Continental crust growth and oceanic crust subduction are compensated by deeply subducted slab serpentinite with heavy Mo, producing a nearly constant Mo isotopic composition of the mantle since 3.5 Ga. Moreover, subducted Izanagi-Pacific slab serpentinites transfer significant amounts of H₂O to the deep mantle, contributing to the destruction of the North China Craton, the high H₂O contents of intraplate basalts in eastern China, and the high electrical conductivity of the mantle beneath eastern China. This study provides direct evidence for serpentinite recycling and improves our understanding of global Mo cycling.