A Jurassic oceanic core complex in the high-pressure Monviso ophiolite (western Alps, NW Italy)

The eclogite-facies Monviso ophiolite (MO) in the Western Alps displays a complex record of Jurassic rift–drift, subduction zone and Cenozoic collision tectonics in its evolutionary history. Serpentinized lherzolites intruded by 163±2 Ma gabbros are exposed in the footwall of a thick shear zone (Baracun Shear Zone = BSZ), and are overlain by basaltic lava flows and syn-extensional sedimentary rocks in the hanging wall. Mylonitic serpentinites with sheared ophicarbonate veins and talc-, and-chlorite-schist rocks within the BSZ represent a rock assemblage that formed from seawater-derived hydrothermal fluids percolating through it during intra-oceanic extensional exhumation. Lower Cretaceous calcschist, marble and quartz-schist metasedimentary assemblage unconformably overlies the footwall – hanging wall units, representing a post-extensional sequence. The MO, BSZ and the associated structures and mineral phases represent a core complex formation (OCC) in an embryonic ocean (i.e., the Ligurian-Piedmont Ocean). The heterogeneous lithostratigraphy and the structural architecture of the MO documented here are the products of rift-drift processes that were subsequently overprinted by subduction zone tectonics, and may also be recognized in other (ultra)high-P-belts worldwide.