Paleogene V-shaped basins and Neogene subsidence of the Northern Lesser
Antilles Forearc
Abstract
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 >450-km-long 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 faults-bounded Basins-and-Spurs System. High-resolution
bathymetric and deep multichannel seismic data acquired during cruises
ANTITHESIS1-3, reveal a drastically different tectonic evolution of the
NLA forearc.
During Eocene-Oligocene time, the NLA margin accommodated the Bahamas
Bank collision and the consecutive margin convex bending by
trench-parallel extension along N40-90°-trending normal faults, opening
V-shaped valleys in the forearc. Backarc spreading in the Kalinago Basin
and block rotations 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 is partly accommodated along the newly-imaged
N300°-trending, 200-km-long Tintamarre Normal 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 first deep
seismic images in the NLA forearc show that the NE-SW faulting and the
prominent V-Shaped valleys result from a past and sealed tectonic phase
related to the margin bending and consecutive blocks rotation.