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The Gela Nappe of south central Sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening. Synorogenic sediments allow the deformation to be dated. Two distinct structural styles are observed in the Gela Nappe: The central salient part of the nappe (Caltanissetta basin) consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe (Sciacca and Monte Judica) consist of a stack of several thrust sheets. These different structural styles correspond to the pretectonic Mesozoic stratigraphy of the foreland plate. Carbonate platforms exist on the Adventure bank and Hyblean Plateau ahead of Sciacca and Monte Judica, respectively, while the Caltanissetta basin region appears to have accumulated basinal clay facies. Where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front, deformation is taken up by imbrication on‐steep ramps through the carbonates generating a relatively thick orogenic wedge. In the basinal setting, where no strong rheology exists, the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip. Hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas, producing a nonlinear thrust front. In the basinal region, accretion of foreland material to the nappe by imbrication was only prominent during the Messinian when subaerial exposure prevented low‐friction transport of the nappe across the highest levels of the stratigraphy. A steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment, possibly due to progressive compaction of the clays.

New palaeomagnetic data from upper Triassic to Pliocene sediments reveal that in eastern Sicily a major 70° clockwise (CW) rotation took place between Oligocene and late Tortonian time, followed by a further 30° CW rotation. Results from central Sicily are less coherent. They show 44–83° post-Oligocene CW rotation, local 14° 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 . 100° 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 70° 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 20° Ma −1 , we infer that CW rotation started in Sicily in Langhian–Serravallian times, between 15–16 and 11–12 Ma ago. The 100° CW rotation observed in pre-orogenic strata from the whole of Sicily is mirrored by 80° 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.

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