Molybdenum isotope composition of the upper mantle and its origin: insight from mid-ocean ridge basalt

The molybdenum (Mo) isotope system is pivotal in reconstructing marine redox changes throughout Earth’s history and has emerged as a promising tracer for igneous and metamorphic processes. Understanding its composition and variation across major geochemical reservoirs is essential for its application in investigating high-temperature processes. However, there is debate regarding the δ^98/95 Mo value of the Earth’s mantle, with estimates ranging from sub-chondritic to super-chondritic values. Recent analyses of global mid-ocean ridge basalt (MORB) glasses revealed significant δ^98/95Mo variations attributed to mantle heterogeneity, proposing a two-component mixing model to explain the observed variation. Complementary studies confirmed the sub-chondritic δ^98/95Mo of the depleted upper mantle, suggesting remixing of subduction-modified oceanic crust as a plausible mechanism. These findings underscore the role of Mo isotopes as effective tracers for understanding dynamic processes associated with mantle-crustal recycling.