Chapter 2 The Pleistocene extension of the Campania Plain in the framework of the southern Tyrrhenian tectonic evolution: morphotectonic analysis, kinematic model and implications for volcanism

Abstract

Abstract The Tyrrhenian margin of the Apennine chain (TMAC) experienced widespread extensional tectonics characterized by volcanism and the formation of several marine and intermontane troughs and basins in Pleistocene times. The Campania Plain is part of this extensional system, which encompasses an area from southern Tuscany to the northern margin of Calabria. Extensional tectonics affecting these continental areas is likely to be related with the final stages of the opening of the southern Tyrrhenian Sea, which developed since Middle Tortonian times. This work presents a quantitative kinematic model explaining the relationships between extension in the Tyrrhenian Sea, basin formation in the TMAC, migration of the Apenninic arcs and geotectonic setting of the volcanism. A synthesis of the volcanic, structural and geophysical data available in the literature, coupled with a detailed morphotectonic analysis of the study areas were used in computer-aided reconstruction techniques based on interactive modelling of rigid block rotations to realistically assemble in a unique kinematic framework the first-order structures that are observed in the Apennines area and in the Tyrrhenian basin. Once established, the extension directions in the various sectors of the Apennine chain, by comparing the results of the morpho-structural analysis with data collected from the abundant geological literature, we identified two distinct kinematic elements characterizing the Apennine chain that, from Plio-Pleistocene times, moved independently with respect to the Eurasian reference plate: the Northern Apennines Arc (NAA) and the Southern Apennines Arc (SAA). On the basis of the first-order geological and goephysical constraints, as well as on trial and error experiments, we identified two distinct rotation stages for the Apennine chain. During the first stage, from 3.5 to 0.78 Ma, the NAA and the SAA migrated independently. In the second stage, from 0.78 Ma to the present, the NAA stopped migrating, while the SAA continued migrating towards SE. Thus, N-S extension in the Campania Plain is the result of the relative motion of the NAA with respect to the SAA during the first stage only, whereas the present-day NW-SE extension in this area, which is characterized by intense volcanism (e.g. Ignimbrites, Somma-Vesuvio, Ischia, Campi Flegrei), is related to the migration towards the SE of the SAA with respect to the NAA. The simplifying assumption of rigidity of the two arcs does not substantially affect the model presented, which only aims at describing the process of extension and associated magmatic activity in the TMAC. Furthermore, the model presented above could not take into account many aspects of the complex tectonic evolution of the TMCA. Nevertheless, it realistically assembles in a unique kinematic framework the first-order structures that are observed in the Apennine area and in the Tyrrhenian basin.