J. metamorphic Geol., 2013, 31, 165–186

doi:10.1111/jmg.12008

Three steps of serpentinization in an eclogitized oceanic serpentinization front (Lanzo Massif – Western Alps) B. DEBRET,1,2,3 C. NICOLLET,1,2,3 M. ANDREANI,4 S. SCHWARTZ5 AND M. GODARD6 1 Clermont Universite´, Universite´ Blaise Pascal, Laboratoire Magmas et Volcans, Clermont-Ferrand, France ([email protected]) 2 CNRS, UMR6524, LMV, Clermont-Ferrand, France 3 IRD, R163, LMV, Clermont-Ferrand, France 4 Laboratoire de Ge´ologie de Lyon, ENS – Universite´ Lyon 1, Villeurbanne, France 5 Institut des Sciences de la Terre, Universite´ Grenoble I, Grenoble, France 6 Ge´osciences Montpellier, Universite´ Montpellier 2, Montpellier, France

ABSTRACT

The Lanzo peridotite massif is a fragment of oceanic lithosphere generated in an ocean–continent transition context and eclogitized during alpine collision. Despite the subduction history, the massif has preserved its sedimentary oceanic cover, suggesting that it may have preserved its oceanic structure. It is an exceptional case for studying the evolution of a fragment of the lithosphere from its oceanization to its subduction and then exhumation. We present a field and petrological study retracing the different serpentinization episodes and their impact on the massif structure. The Lanzo massif is composed of slightly serpentinized peridotites (