Geodynamic implications of Pleistocene ultra-rapid vertical-axis rotations in the Southern Apennine (Italy)

Paleomagnetic analysis from lower Pleistocene (Sicilian) mudstones in the Sant’Arcangelo basin (Southern Apennines, Italy) shows no vertical-axis rotations. These results define the upper time constraint on the 238 counterclockwise rotations previously measured in the underlying lower Pleistocene (Santernian–Emilian) units of the Sant’Arcangelo basin. These rotations occurred before the Jaramillo subchron in a time span of ,0.5 m.y. Paleomagnetic rotations are coeval with the major phases of thrusting along the outer front of the Apennines, do not extend to the Adriatic foreland, and were limited to the hanging wall of the active thrust sheets along the outer front of the Apennines. Rapid counterclockwise rotations, coeval with thrusting and offset on left-lateral faults, represent the surface manifestation of the differential slab retreat and southwestward rollback of the trench in the Calabrian arc region. The unusually fast vertical-axis rotations indicate that the left-lateral component of deformation was particularly intense during the early Pleistocene in the Sant’Arcangelo region, located along the edge of the retreating subduction zone. These data suggest that the lateral breakoff of the African- Ionian-Adriatic subducting lithosphere, imaged by seismic tomography and deep seismicity, occurred in the Sant’Arcangelo region during the early Pleistocene.