High-Temperature and High-Pressure Experimental Study on the Thermal Conductivity and Thermal Diffusivity of Gneiss

As a representative rock type of the ancient continental crustal basement, gneiss plays a crucial role in understanding the thermal structure and tectonic evolution of the lithosphere due to its thermal transport properties. In this study, the thermal conductivity (κ) and thermal diffusivity (D) of precambrian metamorphic basement gneiss from Dali, Yunnan, located at the southeastern margin of the Tibetan Plateau, were simultaneously measured for the first time under high-temperature (300–1073 K) and high-pressure (1.0–3.0 GPa) conditions using the transient plane source technique. Experimental results demonstrate that both κ and D decrease with increasing temperature, indicating that the heat transfer mechanism of gneiss is phonon thermal conduction, where phonon scattering is the primary mechanism leading to the decrease in κ and D. When the temperature exceeds 950 K, the saturation effect of phonon scattering causes κ and D of gneiss to no longer decrease but tend to stabilize. Empirical fitting reveals a significant positive linear correlation between pressure and the thermal transport properties of gneiss, suggesting that pressure enhances thermal transport. Based on these results, we infer that the middle to lower continental crust may exhibit relatively uniform thermal conductivity ((2.0±0.3) W/(m·K)). A lithospheric thermal structure model derived from the experimental data indicates that the Moho temperature range of 1030–1210 K at 44 km depth and the lithospheric thickness range of 65–95 km in the study area, demonstrating a pronounced thermal gradient. Furthermore, by integrating the temperature-depth relationship of the brittle-ductile transition zone, the focal depths of large earthquakes in this region are constrained to 11–23 km. These findings provide novel thermodynamic constraints for understanding tectonic deformation mechanisms and seismic hazard assessment in the southeastern Tibetan Plateau.