Geology of the Susa Shear Zone (Susa Valley, Western Alps)

Abstract

The 1:10,000 scale geological map of the Susa Shear Zone (SSZ) in the inner sector of the Western Alps, aims to describe the geological setting and tectonic evolution of a first-order Alpine shear zone, which drove exhumation and juxtaposition of different oceanic and continental margin units (i.e. the blueschist-facies External Piedmont Zone in its hanging wall and the eclogite-facies Internal Piedmont Zone and Dora Maira Massif in its footwall). The SSZ corresponds to a tectonic mélange showing a block-in-matrix structure, wherein mylonitic calcschists embed blocks of different rock units. Geological mapping and structural analysis investigated overprinting relationships among shear planes and structures related to different deformation phases: they show that the SSZ evolved through two tectonic events, during which apparent reverse top-to-E shear planes were superposed by extensional top-to-W ones.