Polydeformed structures of the central Apuane Alps between Arni and Mt. Corchia: Historical knowledges, structural data and open problems [La struttura polideformata delle Alpi apuane centrali tra Arni e M. Corchia: conoscenze storiche, dati attuali e problemi aperti]

This contribution concerns the puzzling polydeformed structure cropping out in the Arni-Mt Corchia area and surroundings, in the central-eastern Apuane Alps Metamorphic Complex (AMC). The main point is the presence of thick and long belts of principally Mesozoic and Tertiary paraschists (Apuane Unit) exhibiting widespread milonitic and/or cataclastic-milonitic meso- to microfabrics. In the frame of the AMC large-scale structure, characterised by a general Apennine strike of all the tectonic lineaments, these belts are persistent mainly along a 5-6 km wide, WSW-ENE trending length from the high Frigido valley (Massa) up to E of Isola Santa village, in the Turrite Secca valley, a transversal setting well known since the work of GIGLIA (1967). These structures resulted from extreme development of localised shear deformation during the last stages of the compressive tectonic phase of the Tertiary orogenesis, being clearly involved in polystage D 2 deformations. The recognition and detailed mapping of such shear pattern allows to highlight further aspects in the progressive deformation of the compression tectonics (D 1) and the following uplift-related extension (D 2) in the lowermost metamorphic unit directly visible in the Apennine chain.