GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.2 167 the field at level z =0 and z/ [ (x- ξ) 2 +(y- η) 2 +z 2 ] 3/2 is the upward continuation operator. It is known that, approaching or moving away from the Earth’s surface, we can see that the contributions of individual sources change considering being, those related to shallow sources, most visible at lower scales and viceversa. In fact, considering the aeromagnetic map of Europe at low altitude, we observe a complex magnetic field characterized by little and local high-frequency anomalies, that describe the presence of localized and shallow sources in the upper-crust (fig.1a). The complexity of the geological structures of Europe leaves many questions and interpretations related to the meaning and validity of the measurements of the magnetic field. In addition to magnetic anomalies with a “standard” behavior at our latitudes (the high south and the low north), in Europe there are other anomalies that do not meet these characteristics presenting a reverse dipolar aspect, due either to negative magnetic contrasts or to a reversed inducing field. These formations are made up of large deposits of the Permian quartz-Porfiry. Henkel (1994) has shown that the metasedimentary rocks containing pyrrhotite may have magnetic susceptibility greater than 2 x 10-3 (cgs), while the values ​of the Koenisberger Q ratio, between the residual component and that of induced magnetization, is around 100. In particular, a complex district of high-frequency magnetic anomalies dominates above the central Europe and especially the Czech-Polish area. In this area the magnetic field derives mainly from metamorphic rocks and deep basic and ultrabasic intrusions. In western Europe the most significant magnetic features are defined by the Paris basin anomaly, whose structures’ nature and composition are still unknown (Pham et al. , 2000), and, in general, by anomalies Fig. 1 – European magnetic field maps at 5 km (a) and 200 km (b) of altitude.