Mechanisms of subduction accretion as implied from the broken formations in the Apennines, Italy

Mesoscale structural analysis of the Ligurian broken formations of the Northern Apennines and the regional occurrence of subduction-related structures indicate polyphase folding as the mechanism responsible for progressive disruption. The evidence for direct correlation between regionally extensive noncylindrical folds and tectonic disruption has a strong bearing on determining how the Ligurian accretionary prism evolved. For example, the block-in-matrix structure of the Ligurian tectonic melanges is produced through extension developed along fold limbs in a compressive stress field, as expected from offscraping and intraprism deformation. The model implied by the mesoscale and macroscale analyses of the Ligurian tectonic melanges provides one mechanism of accretion reconciling two deformation styles, i.e., stratal disruption and folding, commonly seen in ancient accretionary prisms. Furthermore, this model could be relevant in active accretionary prisms, especially in the intraprism part, where the seismic and drilling data are sparse.