Architecture and kinematics of forearc basins and intra-caldera resurgences: new insight from the Paola Basin (western offshore Calabria region) and the Campi Flegrei caldera (Campania region)

This thesis deals with the patterns of tectonic deformation at different time and spatial scales ranging from tens to millions of years and from one to tens of kilometers, respectively. The study areas are the Campi Flegrei (Campania region, Italy) and Paola Basin (western offshore Calabria region, Italy). The Campi Flegrei and its offshore prolongation, the Pozzuoli Bay, are a laboratory for investigating volcano-tectonic deformations at 1yr-1kyr timescale and 1km spatial scale related to the dynamics of the Neapolitan Yellow Tuff (NYT) caldera and its intra-caldera resurgence. Resurgence is the late stage, long-term uplift of a collapse caldera floor to form a dome-like structure. The comprehension of its development and structural pattern is crucial for predicting the caldera behaviour during periods of unrest. This work investigates the resurgent activity of the NYT caldera using an integrated analysis of high-resolution swath bathymetry, reflection seismic profiles and interferometric synthetic-aperture radar (InSAR) data. The interpretation of the data shows that resurgence affects a ~ 50 km2 wide almost circular area centred in the Pozzuoli harbor. The resurgent area is surrounded by a ~ 3-4 km wide structural discontinuity corresponding to the Ring Fault Zone (RFZ) that formed during the NYT caldera collapse (~15 ka BP). The uplift of the caldera resurgence occurs along a series of inward-dipping reverse faults of the RFZ characterized by a decreasing-upward inclination of fault planes from ~70° to ~15°. The development of these structures is controlled by the reactivation and deformation of pre-exiting normal faults associated with the NYT caldera collapse. Deformation of reactivated faults often results in folding of overlying and/or juxtaposed strata, in the style of ~ 500 m wide antiformal folds, mostly located along the periphery of the resurgent area. The structural pattern of the resurgence consists of disjoint uplifted blocks of the caldera floor. Two main structural elements are detected inside the resurgent area both off- and onshore, separated by a NNE-SSW trending high-angle normal fault. The most uplifted block comprises the area from Mt Nuovo to La Pietra, whereas the adjacent uplifted sector extends eastwards to include Mt Spina. The morpho-bathymetric expression of the two uplifted blocks is represented by a ~5 km wide antiformal structure, encircled by Bagnoli and Epitaffio valleys. In the hinge zone of the resurgent dome a series of high-angle normal faults form a small apical graben. In order to analyze long term deformations (Myr timescale) occurring at a tens of kilometers spatial scale, this study focuses on the Paola Basin, a segment of the forearc region of the Tyrrhenian-Ionian subduction system. Fore-arc basins are parts of fore-arc region that form structurally in response to a variety of subduction zone processes. The sedimentary infill records the complex tectono-stratigraphic evolution of basin associated with subduction system, and thus, allows deciphering the formation mechanisms of basins developed in compressional intraplate settings. We analyse these processes in the Paola Basin using reflection seismic profiles and bathymetric data. The Paola Basin is a NNW-SSE trending asymmetric syncline, bounded by the offshore sector of the Coastal Chain to the East and by the regional-scale Paola Anticline to the West. It hosts up to 5.5 km thick Plio-Quaternary deposits, most of them showing eastward-dipping clinoforms. These latter are associated to shelfal progradation, supplied from the north via longshore currents, dispersing sediments from unknown Apenninic/Sila entry points. A local circulation of longshore currents flowed southwards and dispersed sediments from unknown Apenninic/Sila entry points. An aggradational internal geometry characterizes the uppermost part of the sedimentary infill with a thickness decreasing westwards, suggesting a sediment supply from the Coastal Chain. In the Early Pliocene, the proto Paola Basin extended from the Paola Anticline up to the western flank of the Sila Massif. Since ∼ 3.5 Ma, the uplift of the Coastal Chain shortened the proto Paola Basin, leading to the separation of the basin from the Crati basin. Short wavelength (∼ 80 km) lithospheric buckling, caused by a ENE-WSW oriented, arc-normal paleo-stress field, is the most likely mechanism that explains the pattern of tectonic subsidence of the Paola Basin, the uplift of the Paola Anticline and part of the uplift experienced by Sila Massif during the Plio-Quaternary. Kilometre-scale, strike-slip restraining and releasing bends are widely spread over the hinge zone of the Paola Anticline, defining the Paola Ridge. Their formation is compatible with an NW-SE oriented maximum stress axis meanwhile strike-slip fault accommodates the arc-parallel component of the plate motion. The change in direction from ENE-WSW to NW-SE of the maximum stress axis in the fore-arc region is a consequence of the transition from orthogonal to oblique subduction, associated to the bending of the Northern Calabria Arc. Regional uplift and folding of the Northern Calabrian Arc induced tensile stress resulting in the formation of N-S trending normal faults in the extrados of the Sila Massif anticline. In this context, the Paola Basin can be defined as a “Neutral Accretionary-type” forearc basin.