Résumé
The Lesser Antilles arc, still active nowadays, results from the westward subduction of the North and South American plate beneath the Caribbean plate. Along the Lesser Antilles trench, the volcanic arc regionally shows a north-south dichotomy. To the south the arc emplaced and stayed in a rather steady-state position since the Late Oligocene-Early Miocene period whereas, to the north, remnants of a Eocene-Miocene arc crop out in the forearc location of the present-day active volcanoes. This has been interpreted as a migration of the volcanism (e.g. Legendre et al., 2018). While magmatic products of the three main periods of activity are still present in the southern part of the arc, to the northern part they display on two distinct arc. Petro-geochemical study of the magmatic products from the different volcanic islands can be used as a powerful tool to discuss the geodynamical evolution of the Lesser Antilles arc through time and space. Saint-Barthelemy Island belongs to the northern part of the Lesser Antilles arc, corresponding to the oldest period of the arc activity. Major and trace elements and Sr, Nd, Pb and Hf isotopes have been measured on 24 representative lavas from the Saint Barthelemy island selected in order to cover the variability of differentiation degree and age. Studied samples, ranging from basalt to rhyolite with a majority of andesite, mostly belong to the calc-alkaline series. All samples show significant LREE/HREE enriched patterns normalized to CHUR with an increase of the enrichment factor through time. Middle-Eocene samples exhibit the smallest LREE/HREE enrichment factor combined to the lowest REE content. Extended trace element patterns, normalized to Depleted Mantle, show a marked enrichment in large ion lithophile elements (LILE) and Pb combined to significant negative anomalies in high-field strength elements (HFSE). Such features arc typical of samples formed in subduction zone and support various participation degree of dehydration fluids. Sr-Nd-Pb-Hfinitial isotopes from all studied samples are located in the worldwide arc domain in Nd-Sr, Nd-Hf and Pb-Pb diagrams but yield significant variation which can be interpreted in terms of variations in source components and percentage of fluid participation. At last, comparing Saint Barthelemy samples with synchronous magmatic products of Saint-Martin and Martinique islands outlines the similarity between Saint Barthelemy and Saint-Martin supporting a decoupled evolution of the northern part of the Lesser Antilles arc relative to its southern segment.