The Sicilian Orogenic Belt: a critical tapered wedge?

In Sicily the Africa-Europe convergence is testified by the timespace migration of a complex Chain-Foredeep system. The convergence took place from the Oligocene to the Pleistocene, involving several paleogeographic domains: the Sicilide Units, characterised by oceanic crust, which represents part of the Tethys, the continental crust Panormide domain, the thinned and oceanic-type crust Imerese-Sicanian (Ionian) domain, and the Ibleo-Saccense African margin. Recent interpretation of off-shore seismic lines shows that the advance of the frontal part of the chain stopped during the Early Pleistocene; on the other hand new onshore geological data indicate an accretionary wedge under sub-critical conditions affected by internal deformation due to the activation of deep transpressive crustal structures. The recognition of wide sub-horizontal overthrusts truncated by out-of sequence thrust systems permits the deformational events related to a thin skinned-type tectonic context to be distinguished from more recent thick skinned-type tectonics which involves the crustal levels. An interpretative model is proposed which takes in account the structural evolution, the times and the modalities of the orogenic advancement, passing from Messinian-Early Pliocene critical wedge to Late Pliocene-Early Pleistocene sub-critical conditions.