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Master Thesis

Évolution tectonique avant-arc de la subduction à la transition Petites et Grandes Antilles, le passage d'Anegada et le bassin de Sombrero : utilisation des nouvelles données de la campagne Antithesis

Abstract : The Caribbean and Americas plate convergence causes an heterogenic deformation of the arc and the Lesser Antilles forarc. Along the complete arc, an apparent and relative seismic quiescence is observed and particularly a gap exists at the transition zone between the Great and Lesser Antilles, at the south of the Anegada Passage, where the arc shows a stronger oblique curvature. Imaging the structure of the subduction zone and particularly the forearc deformation is an important approach to know the local seismicity. The origin and the tectonic activity in the Anegada passage, connected at its ends by two major basins (Virgin Islands basin and Sombrero basin) are still controversial. In December 2013, during the Antithesis cruise, 4 wide-angle seismic lines, and 10 reflection seismic lines were acquired together with extensive bathymetric data on the North Lesser Antilles margin. These data allow to propose the tectonic evolution and the seismology activity of this area. The roughnesses of the oceanic crust with an only small amount of trench sedimentation have an influence on the deformation front of the margin and the accretionary wedge. The wedge is bordered by a strike-slip fault accommodating the obliquity of the subduction. The Sombrero basin is strongly asymmetric and the nature of the crust is identical on both sides. The study of the basin sedimentation allows to identify two different phases affected by old and vertical extensive crust events. The third phase of deposits is relatively calm confirmed by current tectonic and seismic activity reduced in the transition of the Anegada passage. Our main results suggest that the partitioning of the accretionary wedge and the forearc seems to be not influenced by the convergence obliquity. This result can be confirmed and is consistent with recent geodetic data which indicate a decoupled interplate. The older tectonic activity of the north of the Anegada passage seems calm and this major fault disappears in the Sombrero passage thereby ruling out the existence of the Porto - Rico/ Virgin Island micro-plate.
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Master Thesis
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Muriel Laurencin. Évolution tectonique avant-arc de la subduction à la transition Petites et Grandes Antilles, le passage d'Anegada et le bassin de Sombrero : utilisation des nouvelles données de la campagne Antithesis. Océanographie. 2014. ⟨dumas-01059695⟩

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