Thermal and rheological properties of granodioritic rocks from the Central Andes, North Chile

Abstract

The thermal and elastic behavior of three granodioritic rocks from the North Chilean Coastal Cordillera has been studied at atmospheric pressure and at temperatures from 25°–1000°C. Properties investigated are thermal conductivity, thermal diffusivity, heat capacity, thermal expansion and elastic properties as a function of pressure as well as textural and structural changes during heating. Using the thermophysical data the thermal conductivities as a function of temperature and pressure are presented. Thermal conductivity decreases from 2.71 W/(m K) at surface conditions to 1.66 W/(m K) at 1 GPa and 800°C. Using the thermal conductivity as a function of temperature and pressure, temperature-depth distributions are calculated for different surface heat flow values. It is shown that conductive heat transport alone is not sufficient to explain a heat flow of > 100 mW/m 2 often observed in magmatic arcs. It is thus concluded that convective heat transport plays an important role. Models of the temperature distribution and of rheologic patterns with depth in the Andean crust have been constructed. It is suggested that the brittle-ductile transition occurs at depths less than 20 km.