Thermal Conductivity of Basalt‐Olivine Aggregates: Implications for Heat Transfer in Partially Molten Rocks

Abstract We measured the thermal conductivity of composites consisting of mid‐ocean ridge basalt (MORB) and polycrystalline olivine, as an analog for partially molten systems, to investigate the influence of low degree melting on heat transport. Experiments were conducted at 1 GPa and temperatures up to 1,600 K, with MORB fractions ranging from 0.1 to 10 vol.%. Adding MORB to the olivine matrix significantly altered the composite's thermal conductivity. Prior to melting, composites containing 0.1 and 10 vol.% MORB showed the most pronounced increase in conductivity relative to pure olivine, while intermediate fractions (∼1–5 vol.%) exhibited a decrease, followed by a rise at higher MORB contents. We attribute this non‐monotonic behavior to impurity–lattice interactions within the MORB‐bearing olivine, which reduce lattice disorder and enhance heat transport. Upon melting MORB, the thermal conductivity of the composites decreased, with the largest reductions (∼35%) observed in the 0.1 and 10 vol.% MORB samples, indicating that the melt acts as a thermal insulator. Applied to planetary interiors, these results suggest that lateral variations in melt fraction within thermal boundary layers could generate heterogeneities in heat flow, potentially affecting mantle convection patterns and the formation or evolution of thermal plumes.