Geodynamic Controls on Mantle Differentiation and Preservation of Long‐Term Geochemical Heterogeneity: Focus on the Primitive Undegassed Mantle

Abstract The compositional evolution of the Earth's mantle is the result of mantle differentiation and thermal evolution. Partial melting of mantle materials produces geochemical heterogeneities, allows for degassing and depends on the thermal state of the mantle, itself governed by convection. Helium and argon constraints suggest that the Earth's mantle is not fully degassed, implying the preservation of long‐term heterogeneities, including the primitive undegassed mantle. While previous research has shown that the preservation of old heterogeneities can be improved by increasing the material's density or viscosity, the role of mantle dynamics in controlling mantle differentiation remains unclear. Therefore, using 3D spherical mantle convection simulations tracking bulk composition and degassing, we investigate the influence of mantle viscosity, heat‐producing elements (HPEs) enrichment and initial temperature on mantle differentiation. The resulting preservation of primitive undegassed material is systematically analyzed. Results show that thermal evolution (i.e., the cooling history of the mantle) is the main control of the processing history. The ability of the mantle to release its heat, also determined by shallow conditions, governs the processing rates and the types of material processed within melting zones. Models testing the influence of HPEs concentration and initial temperature all reach Earth's current processing rate estimates but primitive undegassed material preservation varies between after . Therefore, the processing history is crucial when studying preservation of long‐term heterogeneities. The dispersal of the unsampled primitive material by convection allows its temperature to converge to that of the average mantle, promoting its preservation.