Pattern of orogenic rotations in central-eastern Sicily: implications for the timing of spreading in the Tyrrhenian Sea

New palaeomagnetic data from upper Triassic to Pliocene sediments reveal that in eastern Sicily a major 70degrees clockwise (CW) rotation took place between Oligocene and late Tortonian time, followed by a further 30degrees CW rotation. Results from central Sicily are less coherent. They show 44-83degrees post-Oligocene CW rotation, local 14degrees post-late Tortonian counterclockwise (CCW) rotation, and 25 post-mid-Pliocene CW rotation. We interpret the larger CW rotation observed in eastern Sicily as related to a more internal palaeogeographical position with respect to central Sicily. Our results complement pre-existing data from the northwestern Sicily carbonates, and indicate that all the internal carbonate nappes coherently rotated by c. 100degrees CW during tectonic emplacement, implying a west-to-east increase of shortening in the Sicilian Maghrebian belt. In Sicily, compressive deformation started during the Langhian, i.e. just after the deposition of the upper Oligocene-upper Burdigalian Numidian Flysch turbidites. Therefore the age of the older 70degrees palaeomagnetic rotation (synchronous to the thrusting) is constrained to occur between the Langhian and late Tortonian. Furthermore, by considering a maximum possible rotation rate of 20degrees Ma(-1), we infer that CW rotation started in Sicily in Langhian-Serravallian times, between 15-16 and 11-12 Ma ago. The 100degrees CW rotation observed in pre-orogenic strata from the whole of Sicily is mirrored by 80degrees orogen-scale CCW rotations characterizing the internal southern Apennines. Palaeomagnetism therefore shows that during orogenesis, the southern Apennines and the Sicilian Maghrebides rotated in a `saloon-door' fashion, synchronous to back-arc spreading of the southern Tyrrhenian Sea. Consequently, our palaeomagnetic data suggest that the southern Tyrrhenian back-arc basin started to spread during Langhian-Serravallian times (from 15-16 to 11-12 Ma), significantly earlier than the late Tortonian age (8 Ma) suggested so far by oceanic drilling data.