GNGTS 2014 - Atti del 33° Convegno Nazionale

Then the analytic signal and the field moduli methods have been applied to the aeromagnetic data at different levels. The dipolar shape disappears and the maxima are positioned nicely on the different geological structures. The results obtained by applying the two methods are coincident in most of the areas of anomaly. In particular, the map at 5 km shows the complexity of the distribution of sources in the upper part of the crust, thanks to the positioning of the maximum of the amplitudes at small scales. With increasing altitudes the amplitudes decrease and the maximum was moving, so localizing the position of deeper crustal structures (Fig. 2c). Even at higher altitudes (5-10 km), after calculating the modules of the field and of the analytic signal, the dipolar aspect of the anomalies disappears, and the maximum amplitudes of | F | and | A | are positioned above the anomaly sources, such as the anomaly of the center Adriatic. In addition to these types of anomalies with a “standard” behavior at our latitudes, we also recognized anomalies with reverse dipolar aspect. An example could be the magnetic field in the area close to the Pyrenees orogens, where the anomalies have the lows positioned exactly on top of the mountain range. Rising to an altitude of 100-150 km this area is characterized by a single large minimum which extends for several hundred kilometers (Fig. 2b). This could be interpreted as being due to a negative magnetic contrast caused by the deep roots of the Pyrenees mountain chain. These results are useful for giving a valid interpretation of the EML above the TESZ. The maps shown in Fig. 2c describe a strong amplitude difference between the central-western and the central-eastern Europe, near the suture between the two platforms. The shape and extent of the maximum amplitudes in the maps seem to give a more complex explanation than that proposed in the previous works. On the one hand, the extension of the maximum amplitude of | F | and | A | along the NW-SE direction can be interpreted by a source localization exactly occurring along the TESZ, which represents an area of ​separation between two platforms of different nature and depths. In literature there are many geological and geophysical studies that describe the difference in thickness between the Precambrian and Paleozoic platforms and, probably, this different depth could be the cause of the reverse dipolar aspects of many anomaly. To demonstrate this type of interpretation a simple test was performed in which, considering a discontinuity that puts two bodies in contact, K1 and K2, with different thickness (Fig. 3a), were calculated the values ​of the total-intensity magnetic field T , by considering a inclination of magnetization of 65° and the analytic signal | A |. It can show a low above the shallow body K1 and a high at NE of the fault, where the thick body K2 is greater, while the analytic signal is positioned exactly above the main discontinuity. The profile obtained from this test seems to be plausible than a profile extracted from real data at 200 km of altitude and passing through the fault line. In Fig. 3b we see that the maximum amplitude of | A | is slightly shifted towards the high of the anomaly, probably due to the inclination of the fault plane. The amplitudes of | F | and | A |, however, are positioned not only along the suture zone, but they have an extension which also occupies a large part of central Europe, in which is located the magnetic low EML (Fig. 3c). This shows that the sources are not placed exclusively along the fault line, but also within the Paleozoic platform. From these results it appears that the contributions responsible for the nature of this anomaly are to be reconnected to both the presence of the fault of Teisseyre-Tornquist, which puts in contact two different platforms with different depths and thicknesses and both to the presence of bodies with a strong remanent component, which characterize large part of the Central European crust, as argued by Taylor and Ravat (1995). Moreover, also from the combined effect of these two types of different sources derive the large extent and the reverse dipolar aspect of the anomaly. Among the main anomalies that give a contribution to this kind of phenomenon, there is one placed above the Bohemian Massif (Czech Republic). Observing the total magnetic field, we note that this anomaly continues to be visible even at higher altitudes, (Fig. 3c). In addition, the analysis of the analytic signal of this anomaly showed the positioning of the maximum just above its magnetic low, indicating the source position. 170 GNGTS 2014 S essione 3.2