Pre-orogenic extensional deformations within Permian-Triassic rocks of Southern Tuscany: structural record of an episode of Early Mesozoic continental rifting?

The advances in the field of inversion tectonics have shown that many thrust belts were originated at the expenses of pre-orogenic rift basins with complex extensional architectures. Pre-orogenic extensional deformations have been widely documented across the northern Apennines of southern Tuscany by the recognition of syn- sedimentary normal faults within the Mesozoic carbonate sequences of both metamorphic and non-metamorphic tectonic units. In local- ity «I Canaloni», in the heart of southern Tuscany, a detailed struc- tural analysis of the shallow marine deposits belonging to the Arenarie di Poggio al Carpino Formation reveals that inherited extensional structures also occur within Permian-Triassic meta-sedi- mentary deposits. The extensional structures recognized in this locality played a key role on nucleation and development of Tertiary contractional structures. Thrusts splays of a composite duplex, that we indicate as Canaloni Duplex, constantly located at boudin necks which represent mechanical perturbations within the sequence. The restoration of contractional structures highlights the nature and extent of the extensional deformation within the Permian-Triassic sequence. The observation of pre-orogenic extensional structures within the Arenarie di Poggio al Carpino Formation together with syn-sedimentary normal faults within the overlying Upper Triassic strata of the Verrucano Group, may be interpreted as evidence for an episode of Early Mesozoic continental rifting.