Structural and metamorphic history of a segment of the Sesia-Lanzo zone, and its bearing on the kinematics of Alpine deformation in the western Alps

Abstract

Summary The Sesia-Lanzo zone of the western Alps is a zone of heterogeneous crystalline basement that was reworked and remobilised during the Alpine orogeny, partly under eclogite-facies metamorphic conditions. Reworking took place in three separable phases of deformation, each under different metamorphic conditions and each localised predominantly within a particular zone in the crust. The structures and fabrics produced by the phase of deformation post-dating the early eclogite-facies event, and associated with glaucophane-albite parageneses, suggest a strike-slip tectonic setting. Within the Sesia-Lanzo zone, up to a few tens of kilometres of N-S strike-slip movement is inferred for the late Cretaceous-early Tertiary. Movement within a strike-slip system may have been responsible for much of the uplift of the eclogitic rocks from 60 km depth.