Geometrie di deformazione nell'alta valle di Colonnata; un esempio di strutturazione polifasica e composita nelle Alpi Apuane

Within the frame of a meso- and microstructural investigation on the metamorphic rocks of the Alpi Apuane, this contribution deals with an area located northeast of Carrara, the upper Colonnata valley. This area provides a wide range of structures and strain-related features formed during the compressive (D1) and the later (D2) events of the Tertiary tectono-metamorphic evolution of the Alpi Apuane complex, in the general frame proposed by Carmignani & Kligfield (1990, and references). Studies of the geometry of folds and related foliations, have been combined with a detailed microfabric analysis on the different types of marble tectonites. The analyses allowed to recognize structures related to the transition between the late stages of compressive phase and beginning of D2 evolution. The structures (two generations of successive folds and shear zones) we have focussed our attention on, appear to be related with a large scale strain partitioning that involves a component of coaxial deformation leading to a shortening in vertical direction. Thanks to microstructural evidence, we have been able to refer such deformational features to a retrograde thermal path in conjuction with the late development of the antiformal stack and at the beginning of D2 deformation.