The tectonono-metamorphic record of the Tuscan Nappe from the Colline Metallifere region (Northern Apennines, Italy)

This paper deals with a structural and petrographic study carried out on key outcrops belonging to the Tuscan Nappe exposed in the Colline Metallifere region (Montieri-Poggio Prugnoli). Here, the Tuscan Nappe was affected by polyphase deformation characterised by superposed folding events (F (sub 1) , F (sub 2) and F (sub 3) ) and related tectonic foliations (S (sub 1) and S (sub 2) ) in agreement with the structural setting described for the Tuscan Nappe exposed both in other places of southern Tuscany, and in the Alpi Apuane region. The development of F (sub 1) folds was accompanied by metamorphism which produced a sin-kinematic mineralogical assemblage developed on the S (sub 1) tectonic foliation. This paragenesis, consisting of calcite+quartz+ or -muscovite+ or -Fe- and Ti-oxides, is indicative for a temperature of about 200-300 degrees C according to the T values estimated for the F (sub 1) folding event documented for the Tuscan Nappe of the Apuan Alps, suggesting a very low grade metamorphism which affected the Tuscan Nappe during its stacking in the Northern Apennines collisional belt.