Arc parallel extension and localization of volcanic complexes in Guadeloupe, Lesser Antilles

Abstract

Subduction of Atlantic seafloor under the Caribbean plate causes shallow earthquakes within the Lesser Antilles volcanic arc. Such earthquakes, above the subduction interface, show strike‐slip or normal fault plane solutions, the latter with ∼E‐W striking nodal planes. To better assess seismic hazard and the coupling between volcanism and tectonics, we investigated faulting related to overriding‐plate deformation in the Guadeloupe archipelago. Using aerial photographs, satellite SPOT images, and topographic maps (1/25000 scale), we mapped active and middle to late Pleistocene fissures and normal fault systems that cut the uplifted coral platforms Grande‐Terre and Marie‐Galante and the volcanic rocks of Basse‐Terre. The available marine geophysical data show that the faults extend offshore to bound submarine rifts. The E‐W striking, 1500 m deep, V‐shaped Marie‐Galante rift separates the two islands of Marie‐Galante and Grande‐Terre. Normal faults in the north of Grande‐Terre appear to mark the similarly V‐shaped, western termination of the 5000 m deep, N°50E to N130°E striking Desirade graben. Three shallow, M ∼ 5.5 earthquakes (6 May 1851, 29 April 1897, 3 August 1992) appear to have ruptured segments of the Marie‐Galante rift boundary faults. The young “La Grande Découverte” volcanic complex of Basse‐Terre, including the 1440 A.D. Soufrière dome, lies within the western termination of the Marie‐Galante rift. The ancient volcanic shoulders of the rift buttress the active dome to the north and south, which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the Caribbean Sea, or southeastward into the Atlantic Ocean. The Marie‐Galante rift is typical of other troughs transverse to the northeastern edge of the Caribbean plate. We interpret such troughs, which are roughly orthogonal to the arc, to result from slip‐partitioning and extension perpendicular to plate convergence. That they disappear southward implies that they result from interaction between the Caribbean and North American plates.