Petro-structural map of the Dent Blanche tectonic system between Valpelline and Valtournenche valleys, Western Italian Alps

Abstract

Please click here to download the map associated with this article. The mountain ridge between Valpelline and Valtournenche valleys (Western Italian Alps) consists of a high-strain zone, several kilometres wide, in which basement and cover of the Dent Blanche and Mont Mary tectonic units (nappes of the Austroalpine domain) show complex interrelations. New detailed petro-structural maps across the ridge help to update the structural and metamorphic evolution of these Austroalpine units. The Alpine imprint, under blueschist facies onditions, is evident only locally, notably in shear zones. Such high-strain zones developed in the basement, and in a post-Permian cover (Roisan metasedimentary Zone) where the polyphase Alpine overprint is strong. The pre-Alpine structural and metamorphic evolution is commonly well-preserved in many domains with little Alpine strain. The presented maps from 1:2,500 to 1:20,000 scales, and cross sections, are the primitive data source of this work. They synthesize the geological and structural setting of this area and improve knowledge of the Western Alpine evolution by attributing tectonic structures to the evolving Alpine metamorphic stages.