Paleogene V-Shaped Basins and Neogene Subsidence of the Northern Lesser Antilles Forearc

摘要

Oblique collision of buoyant provinces against subduction zones frequently results in individualizing and rotating regional-scale blocks. In contrast, the collision of the Bahamas Bank against the Northeastern Caribbean Plate increased the margin convexity triggering forearc fragmentation into small-scale blocks. This deformation results in a prominent sequence of V-shaped basins that widens trenchward separated by elevated spurs, in the Northern Lesser Antilles (NLA, i.e., Guadeloupe to Virgin Island). In absence of deep structure imaging, various competing models were proposed to account for this Basins-and-Spurs System. However, high-resolution bathymetric and deep multichannel seismic data acquired during cruises ANTITHESIS 1-3, reveal a drastically different tectonic evolution of the NLA Forearc.During Eocene-Oligocene time, the Caribbean Northeastern Boundary accommodated the Bahamas Bank collision and the subsequent margin convex bending by major left-lateral strike-slip faults systems in the Greater Antilles and by trench-parallel extension along N40 degrees-90 degrees-trending normal faults in the NLA. Block rotations, forearc fracturing, and V-shaped valleys opening went along with this tectonic phase, which ends up with tectonic uplifts and an earliest-middle Miocene regional emersion phase. Post middle Miocene regional subsidence and tectonic extension in the forearc are partly accommodated along the newly imaged N300 degrees-trending, 200-km-long normal Tintamarre Faults Zone. This drastic subsidence phase reveals vigorous margin basal erosion, which likely generated the synchronous westward migration of the volcanic arc. Thus, unlike widely accepted previous theoretical models, the NE-SW faulting and the prominent V-shaped valleys result from a past and sealed tectonic phase related to the margin bending and subsequent blocks rotation.