Deep structure of the Campanian–Lucanian Arc (Southern Apennine, Italy)

Abstract

Recent exploration activities and successful discovery of large oil fields in the upper Val d'Agri area (Southern Apennine, Italy) have encouraged the collection of large quantities of geological and geophysical data, and their integration into comprehensive geological models. Here we present a series of structural profiles based on several hundred kilometres of seismic lines (two- and three-dimensional) and the results of many deep wells. The best seismic lines have been extensively reprocessed, and also tied to magnetotelluric data. Geological interpretations of those lines have been interactively tested, and verified by gravity and magnetic modelling and structural balancing. The wells and seismic data demonstrate that the fundamental tracts of the deep architecture of the orogen, as it appears today, were developed only at the end of the Late Pliocene. The final closure of the ensialic shear-zone responsible for the subduction of at least 150 km of continental lithosphere originally underlying the Lagonegro Basin can be dated as Early Pliocene. The involvement of the Inner Apulian Platform in the core of the belt and the activation of a new and more external (left-lateral) oblique ensialic shear-zone can be constrained to the Late Pliocene–Pleistocene. The seismic profiles clearly show the underthrusting of the Outer Apulian Platform unit beneath the Inner Apulian Platform unit. The thick-skinned character of the Plio-Pleistocene contractional structures is evident from the structural profiles. This geometry is constrained by gravity–magnetic data and structural considerations, according to the relatively steep angle of dip (about 10°) of the Apulian foreland beneath the chain. The structural profiles depict the general architecture of the Campanian–Lucanian Arc: the Apennine Platform and Lagonegro Unit are largely allochthonous and a part of the Lagonegro basement could be buried below the Apennine Platform sole-thrust. The Neogene plastic successions of the Apennine Platform and Lagonegro Basin were detached and now outcrop in the Bradanic Foredeep. The Inner Apulian Platform constitutes a huge thrust-sheet, structured as a wide antiform in the core of the belt; its regional culmination roughly corresponds to the Val d'Agri area. Extensional and transtensional structures cross cut the pre-existing compressional structures as shown by the Quaternary valleys of Vallo di Diano and Val d'Agri. The profiles shown also highlight the existing contrast between the deep structures in the core of the belt and the tectonic style of the Lagonegro, Liguride and Sicilide Units. These units were in fact subjected to brittle–ductile deformation under metamorphic (part of Liguridi Units) and deep diagenetic to anchizonal conditions (Lagonegro Units) and were affected by a general overthrust-shear directed towards the NE. The Inner Apulian Platform was, on the contrary, involved in the thrust-belt together with its basement, whereas the Outer Apulian Platform, affected by A-subduction, underwent a regional bending with associated normal faulting.