GNGTS 2014 - Atti del 33° Convegno Nazionale

related to structures located in the Variscan orogen or older continental lithospheric basements, such as dioritic bodies and calc-alkaline volcanics (Thébault, 2006). In northern Spain, we may observe the magnetic anomaly located in the southern part of the Cameros Basin. This anomaly, with a 26 nT maximum and a weak minimum to the north (14 nT), could be caused by Triassic intrusions placed along the northern margin of the Cameros Basin (Del Río et al. , 2013). At higher altitudes, the European magnetic field is defined mainly by an intense and extended magnetic low placed above the Central Europe with an intense magnetic high northeast of it. Such anomaly of Europe has been studied and interpreted by many authors in the last decades (Von Frese et al. , 1981; Ravat, 1989; Ravat et al., 1993; Taylor and Ravat, 1995; Pucher, 1994). From a geological point of view, the European magnetic low (EML) is placed exactly above the Trans-European Suture Zone (TESZ) (Fig. 1b), which is the most prominent geological boundary in Europe, separating mobile Phanerozoic units in the south and west from the Precambrian East European Craton. TESZ is oriented NW-SE from the North Sea to the Black Sea, along a distance exceeding 2000 km, and, in the northern part, the most important feature of this fan zone is the Teisseyre-Tornquist fault. Moho depths increase across the TESZ from 30 km, beneath Phanerozoic Europe, to 45 km, beneath the craton (Guterch et al. , 1986). A relatively high heat flow characterizes the Palaeozoic western Europe, in contrast with the thick, relatively cold, Precambrian eastern craton. Thus, this important fan zone separates the “cold” western lithosphere with a low heat flow of 30-40 mW/m 2 from the “hot” Eastern lithosphere that is characterized by a higher heat flow of 40-70 mW/m 2 (Majorowicz and Plewa, 1979; Cermák et al. , 1989; Cermák and Bodri, 1998; Plewa, 1998; Majorowicz et al. , 2003; Królikowski, 2006). The Palaeozoic structures are largely obscured by Mesozoic and younger strata of the North Sea-Danish-North German-Polish Basin. A detailed analysis of this basin complex and its partial inversion is required to unravel the enigmatic early Phanerozoic history of this major suture zone. Many authors tried to interpret the EML using different approaches. Von Frese et al. (1981) and Ravat (1989) considered a prismatic blocks modeling with three-dimensional spherical coordinates, while Nolte and Hahn (1992) used a three-dimensional block consisting of smaller prisms extended one degree in latitude and three degrees in longitude. Nolte and Hahn (1992) also noted that the component of residual magnetization is much smaller than that induced (low Q) for the source rocks. Ravat et al. (1993) interpreted this anomaly as an effect of the structural features and of changes in the thickness of the crust, assuming a non-magnetic upper mantle. Taylor and Ravat (1995) added an alternative explanation for the origin of this anomaly, based on the effect of crustal sources with reverse magnetization at medium and shallow depths of the Paleozoic European platform. The regional directions of magnetization were chosen in relation to those found by palaeomagnetic studies of the sedimentary basins of Germany. Thus, it would be the direction of the remanent magnetization vector to determine the shape of some of the magnetic anomaly. Pucher (1994) inferred a model that causes the effect of the magnetic anomalies generated by the orientation of metamorphic pyrrhotite rocks of Paleozoic age. The results indicated directions of reverse magnetization, probably due to re-magnetization, with a wide minimum to the South and maximum to north. Taylor and Ravat (1995) have thus interpreted the EML as a result of the coalescence of the magnetic field, measured at satellite altitudes, of a large number of reversely magnetized bodies. Application methods and interpretation. We first studied the error related to | F | method (eq.1), by considering magnetic inclination changes. In the large area of study, the magnetic field inclination varies from 50° to 70° and the influence of the variation anomalies positioned at different latitudes, has been calculated by taking as an example the anomaly of the central Adriatic, for which two synthetic-sources maps of | F |, were generated by considering, respectively, the average value of inclination Europe ( I =65°) and its local value ( I =60°) (see Fig. 2a). Then we calculated their difference, which ranges from -11 to 6 nT. This implies that the amplitude variation in the area concerned is equal to only 3.3% of the signal amplitude. 168 GNGTS 2014 S essione 3.2