A MAGNTEOTELLURIC DEEP-CRUSTAL STUDY IN SOUTH-CENTRAL PORTUGAL

A geothermal anomaly reported to exist in southern Portugal and with h eat flow density values as high as 160 mW/m2 was studied by the magnet o-telluric method. The results of the magneto-telluric survey indicate that the study area is divided into several high electrical resistivi ty, deep-rooted blocks separated by low electrical resistivity zones. Those latter zones coincide with the main trends of the faults that cr oss the region. The high heat flow density values reported for the are a are incompatible with the high electrical resistivities observed in the magneto-telluric survey. Furthermore, heat production values calcu lated for some of the rocks that crop out in the area of the geotherma l anomaly cannot explain the high heat flow density values. Since no h ydrothermal activity is known for the region and recent volcanism is a bsent, it is suggested that previous heat flow density calculations fo r the area covered by the magneto-telluric survey are overestimated.