The Erro-Tobbio peridotite (western Alps) is a slice of subcontinental
mantle that underwent pre-Jurassic passive rifting, followed by
sea-floor hydration and Cretaceous (Alpine) subduction. Analysis of its
extension- and subduction-related structures and metamorphism suggest
the dip below the Adria plate of both the extensional detachments and
the subduction plane. High-pressure boudinage structures of rigid
metarodingite within ductile antigorite serpentinite prove that
antigorite survived subduction and remained stable at eclogite facies
conditions. Subduction of serpentinized peridotites from ophiolite
slabs is here considered the most effective mechanism of bringing water
to great depth within the mantle.