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

Abstract

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 (F1, F2 and F3) and related tectonic foliations (S1 and S2) 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 F1 folds was accompanied by metamorphism which produced a sin-kinematic mineralogical assemblage developed on the S1 tectonic foliation. This paragenesis, consisting of calcite + quartz ± muscovite ± Fe- and Ti-oxides, is indicative for a temperature of about 200-300°C according to the T values estimated for the F1 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