Characterization of recent deformational sequences in some areas of the Abruzzi Apennines (central Italy): implications and problems

Abstract

Recent integrated studies of structural geology, geomorphology and stratigraphy have made it possible to reconstruct the Quaternary kinematic evolution of two key-areas for the study of the recent tectonics of the Abruzzi Apennines. Pleistocene continental deposits were studied in the Upper Sangro River Valley. These deposits, conglomerate and boulder beds, were displaced by NW-SE faults which have a left-lateral behaviour, with an almost negligible vertical component. The left-lateral strike-slip deformation occurred after the deformation connected to extensional tectonics. For the second area, between the little towns of Barisciano and Calascio, near the Gran Sasso chain, the structural analysis and, to a minor extent, observations made on Pleistocene continental deposits have made it possible to define the existence of a strike-slip deformation, of Pleistocene age, which occurred after the deformation related to the extensional tectonics. It is reasonable to believe that the change in deformational regime did not precede the Lower Pleistocene on the basis of geomorphological and stratigraphic considerations. In addition this paper also provides bibliographic references of works presenting evidence of transcurrent movements on NW-SE faults in the Abruzzi Apennines. The finding of recent transcurrent movements along NW-SE faults raises some interpretationsl problems. Such problems derive from the fact that the deformational event underway at the regional scale in the Abruzzi Apennines is generally believed to be related to extensional tectonics, which is responsible for the major vertical displacements assumed to have occurred mainly along NW-SE faults. Perhaps a single deformational mechanism can explain the co-existence of normal and strike-slip movements. Such a model is very difficult to infer, because the causes of the strike-slip movements at the NW-SE faults during the Quaternary are not clear. An alternative view is represented by a model according to which extensional and strike-slip deformations alternate. The interpretational problems can be summarized into four basic points: 1) role of the transcurrent deformations; 2) possible influence of the movements of lower order structures; 3) relationship with the origin of intra-mountain basins; 4) relationship with seismic activity. Beyond the problems themselves, the discussion on these four points shows how many difficulties can arise when seeking to work out neotectonic models for areas characterized by structurally and kinematically complex orogens, especially when passing from considerations at the regional scale to considerations at the local scale.