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.
Xue et al. (Mon,) studied this question.