Geophysical data along the northern Italian sector of the European Geotraverse

Abstract

Magnetic, gravimetric and seismic reflection data were obtained in the area between Genoa and Pontremoli northwards from the Ligurian coast to the Lombardy South-Alpine sector. Data and interpretation provide evidence on geometry, depth and nature of the subsurface down to the magnetic basement (superficial crust). From these factors we attempt a structural outline of the southern Alps-Po Basin-northern Apennine system. By filtering the Bouguer anomalies, the gravimetric data reveal residual anomalies relative to the “Milan High” and a band of translated structures on the southern Alpine and northern Apennine rims. Magnetic data indicate the presence of a substratum with high susceptibility and magnetic bodies having various natures and origins. These bodies can be ascribed to ophiolites, volcanites and tectonically disrupted basement slabs beneath the southern Alps and northern Apennines. Seismic reflection data provide structural evidence of the sedimentary sequence. By integrating seismic interpretations with borehole and surface geological data, we depicted the structural geometries as well as the chronological evolution of the area. The study area consists of a rigid zone acting as a foreland and two orogenic zones, having Tertiary compressive structures, which overthrust the central zone to the north and south. The central zone was affected by Permian extensional tectonics coupled with volcanism, uplifted in the Triassic-Lias and dislocated by synsedimentary faults during the Mesozoic. Beginning in the Tertiary the area was subjected to gradual sinking. The fault zones are characterized by large-scale Paleogene-Neogene overthrusting involving the pre-Mesozoic basement. On the Apennine side, the panorama is complicated by the presence of localized thick ophiolitic bodies.