K-Ar Geochronology and geochemistry of underwater lava samples from the Subsaintes cruise offshore Les Saintes (Guadeloupe): Insights for the Lesser Antilles arc magmatism

Abstract

Dating of submarine volcanic systems is key to understand the history of tectonic and volcanic interactions within the Lesser Antilles volcanic arc. In this study, we investigate the radioisotopic dating of submarine volcanic systems located between Les Saintes (Guadeloupe) and Dominica islands in an intra-arc graben bounded to the west by the active Roseau fault. Submarine lava flows and domes have been sampled with the remotely operated vehicle (ROV) Victor6000 controlled onboard the Ifremer's N/O L'Atalante during the 2017 Subsaintes cruise. We sampled distinct volcanic edifices or sets of edifices in the area, in the previously identified Agoucha and Roseau volcanic complexes, and the Coche and Crawen seamounts, in addition to the basement exposed along the Roseau fault scarp. Pre-degassing of these samples before K-Ar dating has been mandatory to strongly limit their atmospheric argon contamination. Based on twelve new K-Ar ages, we find that the earliest volcanism in the area corresponds to the Agoucha volcanic complex with coeval ages of 4.23 ± 0.06 and 4.17 ± 0.06 Ma. These are also the oldest ages obtained for the recent Lesser Antilles arc to the north of Martinique Island. A lava flow sampled along the Roseau fault scarp yielded an age of 4.12 ± 0.06 Ma, further attesting that early phase of submarine volcanism occurred in the area about 1 Ma earlier than the emergence of Les Saintes Islands, which has been dated onland at ~3 Ma. The Roseau volcanic complex was constructed during a relatively long duration of at least 600 kyr, between 3.13 ± 0.05 and 2.52 ± 0.04 Ma, while a much shorter duration is observed for the smaller Coche and Crawen volcanoes, with ages at about 2.2 and 2.0 Ma, respectively. Together with ages of subaerial lavas from Terre-de-Haut in Les Saintes archipelago, these ages suggest that an intense volcanic activity occurred between 3 and 2 Ma in this part of the recent Lesser Antilles arc. The much younger age of 0.274 ± 0.009 Ma obtained here to the north of Colibri volcano, might be related with the northward magmatism of Dominica Island which displays similar timing and geochemistry. Overall, trace elements data show that Crawen, Coche, Agoucha, and, to a lesser extent, Roseau lavas have strong similarities with Basse-Terre, while pyroclastic units, Colibri and some Roseau lavas, are similar to those from Dominica and Les Saintes islands. Finally, this study shows that dating the submarine volcanic activity, which remains mostly unknown and undated, is a key component to understand the formation of volcanic arcs such as the Lesser Antilles arc.