Map of deformation partitioning in the polydeformed and polymetamorphic Austroalpine basement in Valtellina and Val Camonica, (Central Alps)

Foliation trajectories, superposed to classical lithological information, have been used in this essay to represent the tectonometamorphic evolution of metamorphic rocks at the map scale. Each trajectory is characterized by a chronological connotation (dot pattern) and by a metamorphic connotation (colour); the relative timing of tectonic imprints has been reconstructed by means of the superposition of structures, while the metamorphic terms have been attributed on the basis of a meso- and microstructural-petrographic analysis of the metamorphic assemblages supporting all fabric elements (e.g. foliations, lineations). In addition, fabric gradients have been reported where pre-existing, quasi-isotropic rocks could be utilised (e.g. igneous rocks); these have been represented as colour gradients: from light colours (low strain domains = coronitic fabrics) to full colours (high strain domains = mylonitic fabrics). This new mapping approach, applied to a section of the Austroalpine domain of the Central Alps (Passo Mortirolo, Alta Val Camonica - Valtellina, Italy), which is characterized by polyphasic pre-Alpine and Alpine tectonometamorphic cycles, made the complete representation of lithostratigraphic and tectonometamorphic evolutions possible; therefore, this map is an example of a new method of representation of the full tectono-metamorphic history of a continental crust that underwent two superposed tectonic cycles (Variscan andAlpine) and successive structural stages related to a sequence of metamorphic re-equilibrations. Besides, this approach can be successfully applied in all tectonic and metamorphic settings generally recorded by metamorphic basements.