Thermal Conductivity and Thermal Diffusivity of Leucogranites at High Temperature and Pressure: Implications for the Thermal Structure of the Himalayan Orogenic Belt

Abstract The thermal conductivity ( κ ) and thermal diffusivity ( D ) of two types of Himalayan leucogranite were measured using a transient plane‐source method in a temperatures range of 298–1173 K and pressures of 0.5–1.5 GPa. Both the κ and D of leucogranites have a positive correlation with pressure. With increasing temperature, D initially decreases rapidly and then stabilizes. At temperatures below 973 K, κ decreases with temperature, after which it increases with temperature. The biotite in the recovered samples underwent dehydration‐melting reaction. The increase of κ at high temperatures (>973 K) may be attributed to the aqueous melt produced by the reaction, which correlates positively with the content of biotite. Lithosphere thermal modeling in the Himalayan orogenic belt indicates that the Himalayan crust exhibits a high geothermal gradient. The dehydration of muscovite may be the primary mechanism resulting in partial melting of the upper and middle crust to produce leucogranite melts. During the decompression process, dehydration of amphibole may provide deep water sources.