The interaction of extensional and contractional deformations in the outer zones of the Central Apennines, Italy

Abstract

The relationships among normal faults and thrusts in the Apennines of Italy are often unclear, and the local absence of syn-tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures. The activity of normal faults has been variously regarded as due to pre-, syn- or post-orogenic extension, and the contrasting evidence from different sites has produced an ongoing debate on the normal fault–thrust interaction. The results of a kinematic analysis on selected composite structures of the outer zones of the Central Apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations. Detailed mapping, outcrop-scale observations and structural overprinting relationships support a positive inversion tectonic history, where normal faults and fault-controlled escarpments formed first, and were later deformed by thrusts and related folds. All normal faults control the distribution of foredeep deposits, thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the Apennine thrust belt. The systematic collection of structural data may help to unravel the evolution of adjacent sectors of the Apennine chain, as well as of other belt-foredeep–foreland systems whose extension–contraction relationships are poorly constrained.