INTERFERING PATHS OF DEFORMATION AND DEVELOPMENT OF ARCS IN THE FOLD-AND-THRUST BELT OF THE CENTRAL APENNINES (ITALY)

In the foreland fold-and-thrust belt of the central Apennines, the maj or thrust sheets design systems of arcs, interfering with noncoaxial t rends. Localization of shortening by thrusting and shearing appears to be controlled by the squeezing of low-competence, basinal units (Marc he, Gran Sasso-Monte Picca and Monte Genzana) in between the rigid blo cks of the Lazio-Abruzzi and Adriatic carbonate platforms. The geometr ical interlocking has been resolved by differential rotations of the s uperposed thrust sheets, as also substantiated by paleomagnetic data. The structural analysis and the age of the syntectonic siliciclastic d eposits suggest an irregular sequencing of superposed contractional an d extensional events during late Miocene-middle Pliocene times. Interf ering kinematic paths characterize the arcuate belts, where slip parti tioning has adjusted the coeval deformation of the noncoaxially arrang ed 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 nest ro tated blocks have resulted in the back and forth superposition of cont ractional and extensional structures in adjacent domains. Our kinemati c reconstruction of the central Apennines indicates that it is impossi ble to perform the retrodeformation of tectonic events by assuming a r egular outward progression of deformation pulses. In such a strongly a rcuate belt, the irregular trajectories of the displacement field and the complex overprinting relations between different sets of structure s reflect the kinematic accommodation of blocks with contrasting rigid ity and are not fitted easily within a regionally smoothed stress fiel d.