Tectonic framework of Uccellina Mounts

Abstract

Geological mapping and macro and microstructural analyses led to reconstruct the structural setting and the tectonic evolution of Monti dell’Uccellina area (Southern Tuscany). A polyphase tectonic history, characterized by three main tectonic events linked to the development of folds and cleavages has been recognized. During the fi rst tectonic phase east verging F1 folds with axial plane foliation developed under very low grade metamorphic conditions, as highlighted by illite and chlorite cristallinity data. The main stacking of the nappe pile occurred during the fi rst tectonic phase. The further tectonic evolution is characterized by the development of thrusts, associated with East verging shear zones, that led to the emplacement of three tectonic complexes, each one made by the superposition of three different tectonic units that from top to bottom are “Collelungo Unit”, “Vacchereccia Unit” and “Monti dell’Uccellina Unit”. During the second tectonic phase, the nappe pile is deformed by a kilometric scale upright antiform gently plunging toward the North. The last tectonic phase, related to post-collisional extensional tectonics, is characterized by the development of folds and low angle detachment faults. The new data pointed out for the assignment of “Pseudoverrucano” Auctt. formation, recognized by previous Authors in the north-western part of the study area, to the Triassic Verrucano group. The reconstruction of the geological setting of the different tectonic units led to recognize that the Triassic Verrucano formation occurs in two different tectonic units: the Vacchereccia Unit, made up only by a slice of Verrucano, and at the bottom of the Monti dell’Uccellina Unit where it constitutes the base of a post-triassic continental margin sequence