Crustal structures in the central-eastern Alpine sector: A revision of the available DSS data

Abstract

In the Alpine sector east of the Giudicarie line the investigation of crustal structure is less developed than in the western and central sectors because seismic Near Vertical Reflection (NVR) profiles are not yet available. However, it is felt that a revision, by a complete, homogeneous reinterpretation of several refraction wide-angle reflection profiles or Deep Seismic Soundings (DSS), recorded during different phases of the early exploration, will help in defining a model of the deep crust and of the Moho boundary in the whole area from the central to the eastern Alps. Six interpretative cross sections are proposed as the final output of the seismic modelling as well as a map of the crust-mantle boundary. The main results of this investigation are the following: • - The lower crust and the Moho beneath the northern Alps show a fairly homogeneous structure; the seismic velocity of the European lower crust is anomalously low. While in the north the southward dip of the bottom of the European crust is of about 12°, in the center of the investigated area its dip is reduced to about 6°. In this zone of flatter Moho a complex crust-mantle transition is observed. • - The northern strip of the Adriatic crust appears highly fragmented into small blocks, each block dipping in different directions (N, NE, NW). • - As far as the relationship between the surface tectonic features and the deep crustal structure is concerned, it is found that, while the edge of the Adriatic Moho is fairly coincident with the Periadriatic lineament in its western sector (Tonale line), it appears to be strongly displaced in the eastern one (Pustertal line). • - Also in the eastern Alps, in agreement with the interpretation of the European Geotraverse (crossing eastern Swiss Alps and Lombardian southern Alps), a wedge of the Adriatic lower crust overrides the more ductile European crust, protruding northwards beyond the edge of the Adriatic Moho. These results can help to better investigate the complex interactions between the European and Adriatic plates, as well as to study the relationships between deep and surface structures.