Heat flow in the Western Po Basin and the surrounding orogenic belts

On the basis of lithostratigraphic data from petroleum wells, geophysical logs and laboratory measurements, we revised surface heat-flow values from previous studies and obtained new data for the western sector of the Po Basin (Italy). The available bottom-hole temperatures were corrected for mud circulation. The in situ thermal conductivity was estimated by taking into account the combined effects of mineral composition, anisotropy, temperature and porosity. The radiogenic heat of the basin rocks was evaluated from natural gamma-ray logs and with laboratory ?-ray spectrometry. After correction for sedimentation and palaeoclimate influences, the inferred surface heat flow of the basin is 73 +/- 4 mW m-2 in the undeformed Po foredeep and decreases to 64 +/- 6 mW m-2 in the Alps and Apennines buried units, affected by active thrust. Numerical and analytical calculations indicate that such a decrease is likely caused by thrusting. Local heat flow minima (<60 mW m-2) may be related to groundwater movement. These data together with those available for the surrounding orogenic belts allow redrawing the heat-flow pattern of northwestern Italy.