Elementi per una valutazione della cinematica quaternaria della Piana del Fucino (Italia centrale): l'analisi delle deformazioni dei ciottoli delle Unità Plio-Pleistoceniche

Abstract

In order to better define the kinematics of the Quaternary tectonic structures of the Fucino Plain (Central Italy), a structural analysis has been carried out on deformed pebbles of Plio-Quaternary stratigraphic units. To this end, great importance has been attached to the attitude of the maximum shortening axes (Schrader 1988; Fig. 2). Through statistics it has been possible to infer indications on the local stress field responsible for the deformation. In the Fucino Plain recent neotectonic studies have made it possible to define the chronological framework of the recent tectonic activity as well as the kinematics of the major Quaternary structures (Galadini & Messina, 1993a; Fig. 1). The results obtained by means of structural analysis on deformed pebbles have been compared with those referring to the already mentioned neotectonic setting. Notably, three sites have been selected among the five surveyed (Fig. 1), for which most data are available. In these three sites (sites 1, 2 and 4 in Fig. 1), the local stress tensor, inferred from the deformed pebbles (Fig. 3; Table 1), approximate the attitude of the theoretical tensor obtained from the studies about the kinematics of the major structures. Around the Tre Monti fault zone (site 1 in Fig. 1) the almost vertical attitude of the maximum stress axes, derived from the pit-striae association, confirms that the kinematics of this structure are mainly extensional. In the Cupoli area (site 2 in Fig. 1), one of the preferential attitudes of the maximum shortening axes (about E-W, almost horizontal), confirmed by a large number of data, seems to be compatible with the deformations due to a N 115° main fault with left-lateral oblique kinematics. The geological evidence of movements with a left-lateral component in the La Mandrella area (site 4 in Fig. 1) is clearly confirmed by the attitude of the almost horizontal maximum shortening axes of the single pebbles, with two peaks at about NW-SE and E-W. The importance of these observations does not only lie in the fact that the mentioned data tend to confirm the already defined kinematic setting of the Fucino Plain, but it also proves the reliability of the structural analysis of the deformed pebbles to obtain indications on the recent local kinematics of a specific area. The available data highlights the complex Quaternary kinematics of the Fucino Plain, due to the presence of faults characterised by extensional movements and others mainly affected by transcurrent movements.