Post-orogenic evolution of the central Tyrrhenian margin: insights from high penetration and high resolution seismic reflection profiles

Abstract

The Tyrrhenian side of the central southern Apennines transition zone have experienced extensional processes since Late Miocene, occurring mainly along NE-SW and NW-SE main discontinuities (Liotta, 1991; Faccenna et al., 1994; De Rita & Giordano, 1996; Orsi et al., 1996; Acocella & Funiciello, 1999). NE-trending systems, cutting and interrupting the continuity of the main NW–SE striking planes, have been interpreted by several authors as transfer faults (Liotta, 1991; Faccenna et al., 1994), presumably related to the second order belt curvature (Oldow et al., 1993). Volcanic activity, aligned on a NW-SE direction, have been controlled by the same orthogonal systems of deformations (De Rita et al., 1994a; De Rita et al., 1994b; Faccenna et al., 1994; Acocella et al., 1996; De Rita & Giordano, 1996), predating and triggering magma rise (Acocella & Funiciello, 2002). The importance of NE-SW oriented transverse structures, has been also revealed by the seismic zonation of Italy (Meletti et al., 2000), individuating a NNE-SSW oriented discontinuity, representing, according to Di Bucci (2002), a barrier in the propagation of NW-SE trending active fault systems. Seismotectonic studies on this boundary sectors, within the Apennines, demonstrated the presence of NW–SE and NNE–SSW seismogenic structures, the latter still acting as transfer faults (De Luca et al., 2000; Pace et al., 2002; Milano et al., 2002, 2005). Records of strike-slip activity on NW-SE planes have been also reported by several authors in Plio-Quaternary times (Moussat et al., 1986; Sartori, 1990; Hyppolite et al, 1994; Cinque et al., 1993; Caiazzo et al., 2006; Cinque et al., 1993). The strike-slip activity on such planes has been ascribed to a broader geodynamical setting, related to the tectonic disjunction between Southern Apennines and a Calabrian arc retreating towards SE (Knott & Turco, 1991; Cinque et al., 1993; Doglioni et al., 1996). Transverse structures acted as tear faults in compression, as transfer fault in extension, triggered volcanic activity and controlled earthquakes distribution. The occurrence from Early Pleistocene of a NW-SE directed extension, furtherly rearranged and complicated the structural pattern. The aim of this PhD thesis is to unravel the tectono-sedimentary evolution of the sector and to better understand the kinematic history of the main tectonic contacts, from Late Miocene to Holocene times. A seismostratigraphical approach is here proposed. The identification of structural styles by seismic reflection profiles is a difficult procedure that may lead to mistakes in the interpretation. Map distributions of seismically detected structures represents a fundamental tool in order to directly observe the geometric pattern of the main faults and establish the regional stress field distribution. Three different seismic grids, located in the Gaeta Gulf, enabled structural and stratigraphical observations on the postorogenic evolution of the central Tyrrhenian margin, both on the onshore and on the offshore sectors. High penetration and high resolution seismic profiles provided different details of investigations, enabling us to better comprehend the structural pattern and the geometrical relationships between major tectonic discontinuities, merging in the study area in a complex accommodation zone. This PhD thesis is built up as a collection of three scientific papers, presented in the next chapters, that are the result of the work done in the last three years. These complementary papers form a coherent work, pointing out relevant implications on the Neogene evolution of the central Tyrrhenian margin. In the first of these papers data from high penetration seismic lines have been used to reconstruct the geometry and structural setting of the offshore sectors of the Latium and Campanian Tyrrhenian margin from Late Miocene to Quaternary times. The 3D modelling of the base of the Plio-Pleistocene seismic units revealed the occurrence of NNE-SSW and WNW-ESE right and left-lateral shear zones. Tulip, palm tree flower structures and other structural features have been seismically detected an mapped, in order to create a synthetic structural maps and a kinematic model of a relatively unexplored sector. In the second paper, high penetration seismic reflection profiles, kindly provided by ENI s.p.a, enabled the reconstruction of the deep structural architecture of the Volturno Plain, where deep wells reported at least 3km of Pleistocene continental and marine deposits. Releasing bends, structural inversions and normal listric faults have been displayed by seismic profiles, enabling the reconstruction of the main principal displacement zones (PDZs) active in Pleistocene times. In the third and last paper, the Late Quaternary-to Holocene evolution of the northern Campania continental shelf has been investigated by the interpretation of a grid of high resolution Sparker and Chirp sub-bottom profiles. Morphobathymetric maps were reconstructed by the interpolation of seismically detected horizons, enabling in this way structural observations. Igneous intrusions, degassing features and minor faulting have been seismically detected and interpreted in a more comprehensive regional framework.