Molybdenum isotopic constraints on temporal variations in slab inputs to arc magmas within the Mongol-Okhotsk tectonic regime

This study documents temporal variations in slab inputs to arc magmas within the Mongol-Okhotsk tectonic regime by investigating molybdenum isotopic compositions of the Mesozoic mafic−intermediate igneous rocks in the Erguna Massif in NE China. The early Mesozoic rocks, formed in an active continental margin setting, exhibit higher δ98/95Mo values and Ce/Mo ratios, more enriched Sr-Nd isotopes than those of depleted mantle, along with positive Mo-Pb isotope correlations. These features suggest that their primary magmas were derived from partial melting of a mantle wedge modified by altered oceanic crust-derived aqueous fluids and sediment-derived melts. Conversely, the late Mesozoic igneous rocks, formed in an extensional setting, show lower δ98/95Mo values, higher Th/La ratios, and more radiogenic 87Sr/86Sr and 207Pb/204Pb ratios than mantle values. When integrated with higher Hf/Nd ratios compared to early Mesozoic counterparts, their magma sources are interpreted as the early Mesozoic mantle domains subsequently modified by residual sediment-derived melts. Additionally, early Mesozoic magmatism with heavy Mo isotopes is primarily associated with porphyry Cu-Mo deposits, whereas late Mesozoic magmatism with light Mo isotopes is linked to porphyry-type Mo and epithermal deposits. These findings reveal that temporal variations in slab inputs directly control the diversity of arc magmas and regional mineralization.