THERMAL AND RHEOLOGICAL PROPERTIES OF GRANODIORITIC ROCKS FROM THE CENTRAL ANDES, NORTH CHILE

The thermal and elastic behavior of three granodioritic rocks from the North Chilean Coastal Cordillera has been studied at atmospheric pres sure and at temperatures from 25 degrees-1000 degrees C. Properties in vestigated are thermal conductivity, thermal diffusivity, heat capacit y, thermal expansion and elastic properties as a function of pressure as well as textural and structural changes during heating. Using the t hermophysical data the thermal conductivities as a function of tempera ture 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 deg rees C. Using the thermal conductivity as a function of temperature an d pressure, temperature-depth distributions are calculated for differe nt surface heat flow values. It is shown that conductive heat transpor t alone is not sufficient to explain a heat flow of > 100 mW/m(2) ofte n observed in magmatic arcs. It is thus concluded that convective heat transport plays an important role. Models of the temperature distribu tion and of theologic patterns with depth in the Andean crust have bee n constructed. It is suggested that the brittle-ductile transition occ urs at depths less than 20 km.