GNGTS 2017 - 36° Convegno Nazionale

716 GNGTS 2017 S essione 3.3 results in a decrease in the sub-crustal heat flow, while a constant sub-crustal heat flow requires thermally thinner (i.e. warmer) lithosphere. This process is observed even when the temperature dependence of thermal conductivity -an inverse relationship- is not accounted for. We can also observe the distortion of the surface heat flow footprints produced by heat sources at different depths caused by lateral and vertical inhomogeneities in thermal conductivity and the thermal refraction phenomena involved. The known limitations of the linear model, even in an ideal case, are shown in Fig. 1, which is an example output for a 2D section. Line a and b are the true relationships for a constant 40 and 50 km crust, respectively: by imposing a constant lithospheric thickness, (the intercept) Fig. 1 - Crustal thickening under ideal conditions: a standard crustal column (Wedepohl, 1995) is scaled from 40 km to 50 km, with a smooth lateral transition occurring over 150 km. Top left: the model section (SED: sediments, UCC: upper continental crust, LCC: lower continental crust, SCL: sub-continental lithospheric mantle). Top right: the depth-wise distribution of radioactive heat production ( A ), thermal conductivity ( k ) and temperature ( T ). The green and red lines refer to two crustal columns, far from the lateral transition (see markers on the section), while the blue line represent the temperature difference between the two. Bottom left: gravity anomaly against the reference crust at the green marker, surface heat flow Q(SFC) , basal heat flow Q(CMB) . Bottom right: crustal thickness and surface heat flow. Linear relationships: a) true condition for the 40 km crust; b) true condition for the 50 km crust; c) result of fitting with data at the two markers; d) result of fitting in the transition zone. Fit parameters: see Tab. 1.