Abstract

The Voltri Group occurs along the western alpine arc, west of Genoa, Italy. In the Voltri Group slices from different lithospheric levels (continental mantle, mesozoic ophiolites, continental margin sediments) are coupled. Primary relationships between them are rarely preserved, because of the intense alpine tectonics. Structural mapping of the central-southern sector of the Voltri Group evidenced a regional transposition foliation (Fc = composite fabric) underlined by greenschist facies minerals, which is parallel to the lithologic surfaces (S <sub>o</sub> ) and to two older schistosities. Also the boundaries between different lithologic units are strongly overprinted by ductile and/or brittle/ductile structures, related to the development of the composite fabric. In spite of this very pervasive deformation and metamorphic reequilibration under greenschist facies conditions, relics of previous metamorphic episodes are preserved in all the lithologic units and correspond to lithospheric scale tectonic processes of: rifting (in the Erro-Tobbio and Beigua units), Upper Jurassic oceanic development (in the Erro-Tobbio, Beigua and Voltri-Rossiglione units), cretaceous subduction (in the Erro-Tobbio, Beigua and Voltri-Rossiglione units). Some of these units could therefore be coupled already during early stages of their evolution; subsequent deformative events (i.e. post-nappe folding and late thin-skinned thrusting episodes) masked the original nappe setting, producing the present-day overall geometry.

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