Is the Anegada Passage a sealed structure related to a past tectonic phase? A tectono-structure study of the Northern Lesser Antilles margin based on the Antithesis-1 cruise geophysical data

Abstract:

The Anegada Passage is a deep NE-SW-trending valley across the arcuate volcanic arc at the transition between the Greater and the Lesser Antilles. The passage includes a set of faults and basins connecting the Virgin Island Basin to the Sombrero Basin.

The geodynamic causes, the tectono-sedimentary evolution and the eastward extent of the Anegada passage are still unclear. Various models for the formation of the passage were published: (1) pure extension, (2) dextral or (3) sinsitral transtension.

During the geophysical cruise ANTITHESIS-1 (Nov.2013–Jan.2014), we acquired deep penetration multichannel seismic and wide-angle seismic data, high resolution seismic (3.5 khz) data and multibeam swath bathymetry in this poorly-investigated margin segment. These data shed new light on the extent and structure of the Anegada system as well as on its past and current tectonic activity.

The crustal thickness and velocity (Vp) structure are consistent with a previously-proposed oceanic origin under hotspot influence. The crustal Vp structure does not significantly vary astride the Anegada Passage suggesting similar nature of the rocks. Thus, the Anegada Passage does not correspond to a possible boundary between differing–origin basements in Greater and Lesser Antilles.

The Anegada system extends NE of the Sombrero Basin with a set of newly-observed basins and faults that all together draw an en echelon structure. This fault system widens eastward, with numerous short and shallow E-W-trending faults suggesting an anastomosing system near the accretionary prism.

Within the Sombrero Basin, the shallowest undeformed sedimentary unit overlays deformed and fan-shaped deeper units indicating a recently-sealed tectonic activity consistent with the seismic and geodetic records. This low current seismic and tectonic activity indicates that the Anegada Passage formed during a past tectonic phase possibly related to the Bahamas Platform docking against the Greater Antilles subduction zone.