The collisional knot in Liguria

Abstract

A series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the Po plain into the northern Apennines and the Ligurian Alps. They help to more clearly define the subsurface structure of this intricate ‘Ligurian knot’. In particular, it has been possible to identify a number of high velocity bodies, and they may be correlated with such geological entities as the Adriatic Mesozoic, ophiolites of the Apenninic Liguride nappes, and ophiolites or Mesozoic carbonates underlying the Antola flysch in the Alpine part of the knot. When combining the refraction and reflection lines, these bodies appear to be bounded by important dislocation surfaces, such as the Padanide sole thrust (Plio-Pleistocene), the Villalvernia Varzi line (Oligo-Miocene), the Ottone-Levanto line (Oligo-Miocene), and the Volpedo-Valle Salimbene fault (Oligo-Miocene; reactivated as a transfer fault in the Plio-Pleistocene). The 3D geometry may be interpreted in terms of regional kinematics and is compatible with a model that envisages an Oligo-Early Miocene NW translation of the Adriatic indenter, coupled with collapse in the Provencal-Ligurian sea and rotation of the Sardinia-Liguria complex into the roll-back of the Adriatic subduction zone. The refraction interpretations, extending to a depth of 15 km, are supplemented by data on the Moho configuration obtained for the European Geotraverse. The Moho appears to be dissected into a series of patches which may be interpreted in terms of the shallow crustal configuration and its history. In particular, the deepest patch appears to be terminated by the Volpedo-Valle Salimbene fault, which consequently would displace the entire crust.