METAMORPHIC OPHIOLITES OF THE LIGURIAN ALPS: STATE OF THE ART ON AN EXHUMED SUBDUCTION INTERFACE

The metamorphic ophiolites of the central Ligurian Alps, primarily exposed in the Voltri Massif and the Sestri-Voltaggio Zone, preserve an extensive record of Jurassic oceanic lithosphere subducted to high-pressure (HP) and locally ultrahigh-pressure (UHP) conditions during Alpine orogenesis. This review synthesizes published structural, petrological, geochronological and geophysical data on the main tectono-metamorphic units of these metamorphic ophiolites. Their protoliths derived from the Ligurian-Piedmont Ocean, a branch of the western Tethys formed within a magma-poor margin and ocean-continent transi- tion setting characterized by mantle exhumation and MORB-type magmatism. The metamorphic evolution records a cold subduction regime, with peak conditions spanning from pumpellyite-actinolite to eclogite-facies. In the Voltri Unit, the best constrained in terms of P-T-t, peak eclogite-facies conditions reached ca. 1.8-2.5 GPa and 450-550 degrees C, whereas the recent discovery of coesite indicates localized UHP conditions of at least ca. 2.8 GPa. Geochronological data constrain the main eclogite-facies event between ca. 50 and 40 Ma, fol- lowed by exhumation-related cooling and a widespread greenschist-facies overprint at ca. 34-29 Ma. he regional structural architecture reflects a polyphase deformation history: early structures formed during subduction, composite fabrics developed during initial exhumation, and later transpressional reactivation accompanied Alps-Apennine interaction at the "Ligurian collisional knot". Current tectonic interpretations debate the relative role of serpentinite-hosted subduction channel processes versus the exhumation of large coherent slices. Available geologi- cal and geophysical evidence suggests that both mechanisms operated at different scales within a fossil plate interface marked at depth by a shallow Adriatic mantle wedge and a hydrated low-velocity zone. The Ligurian meta-ophiolites thus provide a key natural laboratory for investigating subduction-interface dynamics and tectonic reorganization at the Alps-Apennines junction.