BOLIVAR and GULFREX MCS Data Constrain Closure of the Grenada Backarc Basin During Oblique Collision Between the Lesser Antilles Arc System and Northern South America

The Lesser Antilles evolved from the mid-Cretaceous as an extensional arc system formed above a steeply dipping slab of Atlantic oceanic crust. The arc became extensional during the Paleocene - early Eocene along normal faults at the eastern edge of the basin as the present-day Lesser Antilles chain rifted away from the Aves Ridge. Backarc rifting ceased during the early Eocene, leaving the 140 km wide 3 km deep Grenada backarc basin. Sediment accumulation reached nearly 8 km during the Paleogene with another 1.5 km of sediments accumulating during the Neogene. In this presentation, we combine newly acquired MCS lines from the BOLIVAR study with existing GULFREX data collected in 1975 to document the structural and stratigraphic effects of closure of the Grenada backarc basin because of the progressive, oblique collision between the Lesser Antilles arc system and northern South America. The southern end of the Grenada basin has been narrowed from an undeformed width of approximately 100 km to a deformed width of 30 km, and rotated nearly 90 degrees to the west as the arc system obliquely collides with the South American margin. Shortening of the colliding backarc basin is mainly accommodated by inversion of Paleogene normal faults on the eastern edge of the basin, folding, low-angle thrust faults, and possibly shale diapirism. We propose that this closure in the area is a backthrusting response during Oligocene - late Miocene closure along the leading edge of the oblique arc-continent collision in the Eastern Venezuelan basin.