Architecture of the NYT caldera and inner resurgent dome (Pozzuoli Bay, Campi Flegrei): new insights from seismic reflection and DInSAR data

Abstract

The Campi Flegrei and its offshore prolongation (Pozzuoli Bay) are a volcanic area dominated by a collapse caldera associated with the Neapolitan Yellow Tuff (NYT) eruption, occurred at ~15 ka BP, and by an intra-caldera resurgent dome. We present new insights into: a) the geometry and kinematics of faults formed inside and at the edge of the caldera, b) the architecture of the caldera and the resurgent dome, and c) the relationship between the structural elements of the caldera and ground deformation. This work is based on the integration of single- and multi- channel seismic, swath bathymetry data and ground deformation maps. The main results highlight that the NYT caldera, offshore, is characterized by an ellipsoidal shape, elongated towards the ESE direction, with axes of ~8 km and ~7 km. It is bounded by a ~ 6 km long and 1–2 km wide ring fault zone (RFZ) mainly consisting of an inward-dipping normal fault system and antithetic, outward-dipping, faults. The sedimentary fill of the caldera is up to 60 m thick, and can be divided into six units, characterized by different seismic facies, composition and depositional process. The inner-caldera resurgent dome, ~ 5 km in diameter, is limited by inner boundary of RFZ and consists in a broad antiformal structure with brittle deformation localized in an apical graben. The base of the resurgence corresponds to the thalweg of the Epitaffio valley in the western sector of the Pozzuoli Bay and the Bagnoli valley to the east. The maximum cumulative uplift of the resurgent dome is ~180 m while its average uplift rate is ~ 9–12 mm/year, between 15.0–6.6 ka BP. A subsidence of ~10 m is suggested by the drowning of the infralittoral prograding wedge below the present-day storm wave base for the last 2 ka. The deformation velocity pattern of the Campi Flegrei displays a radial symmetry centered around the Pozzuoli harbor. It is possible to distinguish three almost-concentric sectors namely S1, S2, S3 with decreasing velocity from S1 (13-32 mm/year) to S3 (0.3-7.7 mm/year). The highest value (26-32 mm/year) is recorded at the Pozzuoli harbor. Sector S1 is bounded by a NE–SW-trending fault to the west and NW–SE faults to the east. The data suggest that this sector coincides with the resurgent dome of NYT caldera. The base of the latter corresponds to the faults bordering sector S1, and it can be correlated with the base of the resurgence recognized offshore. Sector S2 represents a narrow strip located between the base of the resurgence and the onland prolongation of the inner boundary of the RFZ. The results of our research allow to define the stratigraphic architecture and the shallow structure of the NYT collapse-caldera in the Pozzuoli Bay. Furthermore, they provide a base for the reconstruction of the resurgence geometry developed in the Campi Flegrei and its offshore prolongation and additional constraints on the dynamics of magma chamber.