Résumé
Located in the southeastern Caribbean, the Grenada Basin is bounded to the east by the modern Lesser Antillesisland arc, to the west by the Aves Ridge, commonly interpreted as a Cretaceous-Paleocene extinct volcanic arc,and to the south by the transpressive plate boundary with South America. The Grenada Basin has long beenregarded as a classical back-arc basin until recent studies suggest alternative models, such as forearc openingor Wernicke-type simple shear. The genetic relations between the Grenada Basin and its adjacent arcs remaintherefore controversial. Our analysis of seismic reflection and refraction data acquired during the GARANTIcruise (May-June 2017 onboard R/V L’Atalante) sheds light on basement nature and topography, depositionalhistory and deformation of the sedimentary infill, including vertical motions, of the Lesser Antilles back-arc area.Correlations with well logs located on the northern Venezuelan shelf, DSDP sites on the Aves Ridge, and IODPsites off the west coast of Martinique Island, also provide chronostratigraphic constraints.Seismic lines across the Grenada Basin reveal a significant asymmetry: the basement deepens from 5 to 10km southeastwards while flat-lying sediment units thicken from 2 to 7 km. A 6.5 to 7 km thick oceanic crustunderlies the southeastern half of the basin over a width of about 80 km. The Grenada Basin comprises threemajor depositional sequences defined by unconformities and/or changes in the seismic facies, from bottom to top:- Sequence 1: undifferentiated Eocene sediments represented by strong reflectors that drape the acoustic basement,as well as syntectonic deposits.- Sequence 2: Oligocene to Middle Miocene distal turbidites, probably originating from the Orinoco River thatflowed from the south into the Grenada Basin at that time. Sequence 2 lies unconformably over Sequence 1.- Sequence 3: Late Miocene to Recent arc-derived turbidites and pelagic sedimentation, with little detri-tal input from South America, due to the emplacement of the eastward drainage of the Orinoco River southof the northern Venezuelan coastal range during Middle Miocene. Sequence 3 lies unconformably over Sequence 2.Since the oldest syntectonic sediments date from the Eocene, the last tectonic event that shaped the present-daybasement topography dates back from the Eocene. Given the horizontality of Sequences 2 and 3 within the basinand along the Aves Ridge, no differential vertical motions occurred between the Grenada Basin and the AvesRidge since then. This raises questions about the subsidence mechanisms that led to the current depth of theoceanic crust in the southeastern Grenada Basin. By contrast, reflectors in Sequences 2 and 3 are bent upwardsalong the Lesser Antilles slope, reflecting the uplift of the Neogene Lesser Antilles arc. These observations will beintegrated in a future model for the evolution of the Lesser Antilles back-arc area, as part of the ANR GAARAntiproject.