Early–Middle Pleistocene eastward migration of the Abruzzi Apennine (central Italy) extensional domain

Abstract

The evolution of the Apennine arc is related to the flexural retreat of the Adriatic lithosphere plate, the NE migration of the compressive front and the contemporaneous rifting of the Tyrrhenian basin. Evidence of the NE migration of the orogen can also be inferred from the analysis of the intra-Apennine Quaternary extensional tectonics. Stratigraphic and structural data collected along NE–SW transects in the Abruzzi Apennines (central Italy), indeed, indicate that the westernmost normal faults (activated during the Pliocene) have to be considered inactive since the Early Pleistocene (Turano valley fault) or the beginning of the Middle Pleistocene (Salto valley and Liri valley faults). In contrast, the easternmost faults (Campo Imperatore and Mt. Morrone faults) were activated during the Early Pleistocene and are still active, as demonstrated by the displacement of Late Pleistocene–Holocene deposits and landforms. Within the innermost portion of the extensional domain, the Fucino and upper Aterno valley fault systems show persistent activity since the Pliocene. Besides the evidence of a progressively NE-shifted intra-Apennine extension, available data suggest that a period of co-existing activity of the presently inactive and newly activated faults (e.g. Liri valley and Mt. Morrone faults, respectively) occurred during the Early Pleistocene. This indicates that for a few hundred thousand years active faults in the central Apennines were more numerous than in the period of the present tectonic regime. This may have resulted in a reduced activity per fault (lower slip rates) or an increased intra-Apennine extension rate. Quaternary faults in the Abruzzi Apennines generally coincide with pre-existing discontinuities such as old thrust ramps or syn-orogenic normal faults. Based on a simple geometric criteria, i.e. direction, dip, length of the pre-existing discontinuities located east of the investigated area, and assuming a still active NE-migration of the extensional domain, it is possible to hypothesize that the old and presently inactive normal faults of the Maiella and Montagna dei Fiori anticlines may accomodate active extension of the future. The NE-ward shifting of the extensional domain would be, instead, locked if the process of lithospheric flexural retreat which drove the Neogene-Quaternary p.p. structural evolution of the Apennine chain has ended during the Early Pleistocene.