Banded amphibolites with lenses of amphibolite with garnet relics, metagabbro, pyroxemte and spinel pendotite with pyroxemte veins, occur in a continuous horizon m the Serie dei Laghi, a basement unit of the western Southern Alps, which shows a lower amphibolite facies Vanscan metamorphism. The chemical composition of the amphibolites is homogeneous, that of the associated metagabbros is variable; these rocks are quite similar to the MAR tholentic basalts and cumulitic gabbros The pyroxemtes

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... w a wide range of composition, as many ophiohtic pyroxenites do In the pendotites two groups are distinguished' upper mantle pendotites with restitic character (Mg# 90), peridodites with characteristics of a mantle contaminated by melts or fluids (Mg# less than 88).T and P estimates for the pyroxenites give T > 800 °C and P around 12 kb which suggests a lower crustal environment Amphibolites with Amph-Pl kelyphite around garnet and Di-Pl symplectite represent the products of transformation of an eclogitic assemblage and suggest even higher pressure conditions The amphibolite facies overprint appears related to the main regional Vanscan metamorphism (about 600 °C and 6-8 kb). The studied mafic and ultramafic rocks likely represent relics of an ophiolite belt. They were dispersed into turbiditic metasediments withm an accretionary prism in the early stages of the Vanscan cycle Keywords geochemistry, ophiolite, accretionary prism, Vanscan metamorphism, Serie dei Laghi, Southern Alps.