Timing of effusive volcanism and collapse events within an oceanic arc island: Basse-Terre, Guadeloupe archipelago (Lesser Antilles Arc)

Timing of effusive volcanism has been investigated at the scale of an active volcanic island within the Lesser Antilles outer arc. Thirty-two new accurate K–Ar ages were obtained throughout the island of Basse-Terre, Guadeloupe, by the use of the K–Ar Cassignol–Gillot technique. Coupled with geomorphological and geochemical data, this study provides a general evolution model for Basse–Terre. Where available, paleomagnetic data are in agreement with the geomagnetic polarity time scale. Time scales of volcanic processes for the three northernmost massifs of the island have been constrained between 2.79 ± 0.04 and 0.435 ± 0.008 Ma. Whereas the Basal Complex lasted only 110 kyr (2.79 ± 0.04 – 2.68 ± 0.04 Ma), the Septentrional and the Axial Chains spread each over about 600 kyr, from 1.81 ± 0.03 to 1.15 ± 0.02 Ma, and from 1.02 ± 0.03 to 0.435 ± 0.008 Ma respectively. This geochronological study demonstrates the temporal North to South migration of volcanism throughout the whole island, at a rate of 18 km/Myr over the last 2.8 Myr, and 25 km/Myr for the last 1.8 Myr. The Basal Complex and Septentrional Chain illustrate the occurrence of fissural volcanism over one third of the island along a NNW–SSE striking axis, whereas the Axial Chain is composed of imbricate composite volcanoes aligned along a NW–SE direction. The southern part of the Axial Chain has been affected by two huge flank-collapses, the first event (640 ka; 5 to 10 km3) was SW oriented while the second (550 ka; 20 to 25 km3) was SE oriented. Erosion of the collapse areas reaches 84 km3/Myr (1250 t/km2/yr) within the last 650 kyr, and 30 km3/Myr (5250 t/km2/yr) during about 200 kyr, before the Sans Toucher volcano grew within the collapse structures. Northern Basse-Terre volcanics are mostly basaltic andesites and andesites, and geochemical characteristics belong to a typical Lesser Antilles Central Islands range, representative of non-primitive magmas. Finally, Basse-Terre volcanic massifs emplacement is sequentially related to both regional active faulting around Guadeloupe archipelago along a main NW-SE striking direction, and the westwards propagation of the Désirade, and then Marie-Galante rift systems.