Thermal properties of garnet-bearing amphibolite at high temperature and pressure and its impact on the thermal structure of the lithosphere

     The thermal conductivity and thermal diffusivity of minerals and rocks under high temperature and pressure can provide data supporting for historical simulation of geological processes, and they are also necessary parameters for establishing the thermal structure of deep layer under a stable state.

     Amphibolite is a crucial component of the continental crust and subduction zone. The physical properties of amphibolite are of great significance for understanding the physical structure of the continental crust and subduction zones. In this study, using a thermal properties testing platform on a hinged cubic press, the thermophysical properties of two types of amphibolite were studied at 0.5-1.5 GPa and 300-973 K by the transient plane heat source method. The experimental results show thermal conductivity and thermal diffusivity decrease with the increasing of temperature and increase with the increasing of pressure. The influence of temperature on these parameters is much greater than that of pressure. Under fixed pressure, the thermal conductivity can vary up to 15.1% with temperature changes, while the thermal diffusivity can vary up to 40.0%. Under fixed temperature, the influence of pressure on the thermal conductivity can reach up to 23.4% and the influence on the thermal diffusion coefficient can reach up to 15.7%. The experimental data were successfully fitted using empirical formulas. The thermal conductivity and thermal diffusivity of garnet amphibolite in this study is notably higher than those of amphibolite without garnet and those reported in previous studies, so it is believed that the presence of garnet significantly enhances the thermal conductivity of amphibolite.

     Combining high-temperature and high-pressure data from previous studies as well as this study and the parameters of the thermal lithosphere model, the thickness of the thermal lithosphere in different regions of the North China Craton under different surface heat flows was calculated. The results reveal that within a surface heat flow range of 50-80 mWm^-2, the thermal lithosphere thickness of the Bohai Basin varies between 49.8 and 145.7 km, the thickness of the central orogenic varies belt between 53.3 and 201.5 km, and the thickness of the Ordos Basin varies between 54.4 and 231.2 km.