Interfering paths of deformation and development of arcs in the fold‐and‐thrust belt of the central Apennines (Italy)

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Abstract
In the foreland fold‐and‐thrust belt of the central Apennines, the major thrust sheets design systems of arcs, interfering with noncoaxial trends. Localization of shortening by thrusting and shearing appears to be controlled by the squeezing of low‐competence, basinal units (Marche, Gran Sasso‐Monte Picca and Monte Genzana) in between the rigid blocks of the Lazio‐Abruzzi and Adriatic carbonate platforms. The geometrical interlocking has been resolved by differential rotations of the superposed thrust sheets, as also substantiated by paleomagnetic data. The structural analysis and the age of the syntectonic siliciclastic deposits suggest an irregular sequencing of superposed contractional and extensional events during late Miocene‐middle Pliocene times. Interfering kinematic paths characterize the arcuate belts, where slip partitioning has adjusted the coeval deformation of the noncoaxially arranged tectonic units. In the arcuate Gran Sasso‐Monte Picca thrust belt, out‐of‐sequence thrusting, displacement transfer on high‐angle, strike‐slip faults and growth of high‐angle normal faults behind the most rotated blocks have resulted in the back and forth superposition of contractional and extensional structures in adjacent domains. Our kinematic reconstruction of the central Apennines indicates that it is impossible to perform the retrodeformation of tectonic events by assuming a regular outward progression of deformation pulses. In such a strongly arcuate belt, the irregular trajectories of the displacement field and the complex overprinting relations between different sets of structures reflect the kinematic accommodation of blocks with contrasting rigidity and are not fitted easily within a regionally smoothed stress field.