Tectono-metamorphic evolution of the Alpi Apuane Metamorphyc Complex: new data and constraints for geodynamic model

New data on the tectono-metamorphic history of the Alpi Apuane Metamorphic Complex have been collected in the northwest part of the complex, in an area straddle at the tectonic contact between the Massa and the Apuane units. Our petrologic data, showing that the peak of metamorphism in the Massa Unit occurred in the magnesiochloritoid and kyanite stability field (temperature between 400 and 500C and pressure higher than 0,8 GPa), and the results of meso- and microstructural analysis allowed us to propose exhumation paths for the major metamorphic units. The exumation history we suggest implies that the overthrusting of the more deeply buried (chloritoid + kyanite) Massa Unit on the top of the less deeply buried (chloritoid + pyrophyllite) Apuane Unit occured during the late stage of the D1 deformation, the contact between the two units being deformed by syn-metamorphic D2 structures (15-8 Ma old). The tectonic evolution and the proposed PT- t-d paths suggest a continuum of exhumation from the syn-compressional (late-D1) to the late/post-compressional (D2) stages of the Tertiary orogenesis. During the exhumation history of the lowermost units, the upper parts of the nappe pile (Liguride and Subliguride units plus Tuscan Nappe) suffered tectonic extension and thinning producing the present day geometry of nappe system.