Effusive history of the Grande Decouverte Volcanic Complex, southern Basse-Terre (Guadeloupe, French West Indies) from new K-Ar Cassignol-Gillot ages

摘要

The Grande Decouverte Volcanic Complex (GDVC), active since at least 0.2 Ma, is the most recent volcanic complex of the Basse-Terre Island (Guadeloupe, Lesser Antilles Arc). A detailed geochronological study using the K-Ar Cassignol-Gillot technique has been undertaken in order to reconstruct the history of effusive activity of this long-lived volcanic system. Twenty new ages permit to suggest that the GDVC experienced at least six main effusive stages, from 200 ka to present time. To the north of the GDVC, the GDS (Grande Decouverte-Soufriere volcano) has been active since at least 200 ka, and to the south, the TRMF (Trois-Rivieres-Madeleine Field), started to be emplaced 100 ka. Morphological investigations suggest that the whole TRMF volcanism was emitted from vents distinct from the GDS, most probably a large E-W fissure network linked to the Marie-Galante rift. The mean age of 62 ± 5 ka, obtained for the E-W Madeleine-Le Palmiste alignment suggests that a fissure-opening event occurred at that time. However, whole-rock major and trace element signatures are similar for both systems, suggesting that a common complex magma-plumbing system has fed the overall GDVC. We report very young ages for lava flows from the TRMF, which implies that <10ka volcanic activity is now identified for both massifs. Although hazards associated with such effusive volcanism are much lower than those associated with potential flank-collapse of the Soufriere lava dome or a magmatic dome eruption with explosive phases within the GDS, the emplacement of relatively large Holocene age lava flows (3-1 × 10~8 m~3) suggests that a revised integrated volcanic hazard assessment for Southern Basse-Terre should now consider the potential for renewed future activity from two Holocene volcanic centers including the TRMF.