Is "V" shaped Basins and Spurs system in Northern Lesser Antilles Forearc related to transition from Subduction to Collision?

Description

Forearc sedimentary basins record changes in tectonic regime and are thus key area to investigate the tectonic history of a subduction zone through time.Since Cretaceous, The Lesser Antilles subduction zone has undergone a multiphase tectonic history resulting in its present-day complex architecture. One peculiar aspect for this subduction is the trench / arc convexity from Martinique, in the South, where the subduction is frontal, to Anguilla, to the North, where the convergence obliquity is greater than 50°. The forearc of this convex margin shows varying and complex tectonic structures including poorly documented prominent "V" shaped deep sedimentary basins and spurs that trend perpendicular to the trench.High resolution Bathymetric, Low Frequency Multi-Channel-Seismic (MCS) and Wide-Angle-Seismic (WAS) data recorded during ANTITHESIS 1 and 3 Oceanographic campaigns, provide a pseudo-3D insight into shallow to deep margin structure. Correlating our offshore data and field geological data we decipher the initiation and evolution of the offshore Basins and Spurs system east of the Anguilla bank. These data suggest a 3-steps margin tectonic history since early Eocene.1-Frontal subduction along a straight trench (Cretaceous sup. - Paleocene): Parallel to the trench extensional faults system resulted from subduction-related margin basal erosion.2-Margin convex bending (Eocene - Oligocene): Extension parallel to the trench triggered N40° - N50° V-shaped fracturing, which structured the Basins-and-Spurs system. The margin bending and this resulting deformation are possibly related to Bahamas Bank collision.3-North-westward increase in convergence obliquity (Miocene - Present-day): In the Northern and highly oblique Puerto Rico - Virgin Island (PRVI) margin segment, left-lateral strike-slip systems, as the Anegada passage and the Bunce fault for instance, are likely to result from strain partitioning. In contrast, in the Northern Lesser Antilles (NLA) margin segment, to the south of the Anegada Passage, tectonic deformation is dominated by N100° - N110° active extensional faults system, sub-parallel to the trench. These faults cut through the Basins-and-Spurs system. We thus discuss the role of subduction of recent topographic ridges and dip variation of the down-going plate in normal faults reactivation.This study sheds a new light onto the V-shaped Basins-and-Spurs system, its origin, structure and tectonic evolution through time. We finally propose a tectonic model for the whole NLA forearc, which is a case study of along strike transition from collision (Greater Antilles) to subduction with southward decreasing obliquity (Lesser Antilles).

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