Beneath mid-ocean ridges, mantle upwelling and decompression melting are fundamental processes contributing to the formation of oceanic crust. Previous geodynamic models have suggested that mantle upwelling driven by separating plates can be intensified by thermochemical buoyancy and the thickening of aging lithosphere, resulting in thicker crust. However, the relative contributions of these factors to crustal accretion remain uncertain. We conducted numerical modeling in three scenarios to investigate this: (1) buoyant flow models incorporating age-dependent lithospheric thickening as a reference; (2) passive flow models incorporating age-dependent lithospheric thickening to isolate the effect of buoyancy; and (3) passive flow models that neglect age-dependent lithospheric thickening to isolate its effect. Models are performed under varying potential mantle temperatures (Tp), viscosity structures, and spreading rates. Variations in the model-predicted crustal thickness among these models provide estimates for the relative contributions of buoyancy and thickening of aging lithosphere to crustal production. The results suggest that both buoyancy and thickening of aging lithosphere increasingly contribute to crustal production as spreading rate decreases. However, except in ultraslow spreading rates with lower viscosity and warmer Tp, the impact of the thickening of aging lithosphere predominates over buoyancy. Furthermore, the relative importance of buoyancy-induced crustal production increases as spreading rates decrease. The observed more variable crustal thickness at ultraslow spreading ridges can be attributed to the fact that, for a given Tp contrast, buoyancy-induced crustal production at ultraslow spreading rates amplifies the variability in crustal thickness compared to that in fast spreading rates where passive upwelling dominates.

mantle upwelling, melting, mid-ocean ridge