Cenozoic basin evolution of the Virgin Islands basin and Anegada Passage, northeastern Caribbean

The Virgin Islands basin (VIB) is a 1 to 4.5 km¬‐deep, fault‐bounded marine passage that forms the southwestern and deepest segment of the Anegada Passage connecting the Atlantic and Caribbean Seas. A variety of models have been proposed to explain the tectonic origin of the VIB that range from right‐ and left¬‐lateral pull-apart basins, a rotational-type basin, and a rift basin formed orthogonally to the direction of the North America plate beneath the Caribbean plate This study integrates several geological and marine geophysical data types to better understand the Miocene to recent kinematics of a VIB opening and its present-day tectonics. A grid consisting of 400 km’s of 2D seismic lines, provided courtesy of the 2006 Danish Galathea 3 expedition, reveals the geometry of faults underlying the VIB to a depth of 7.5 seconds two-way time (~8 km), and a 68 km-long deep-penetration line from Shell shows the basin structure to a depth of 15 km.

The VIB is an asymmetrical half-graben with greater throw along its southeastern bounding normal fault than along the normal fault on its northwestern edge. The elongate, 40-km-long island of St. Croix is the uplifted footwall of the southeastern, larger-throw normal fault, while the elongate island of Vieques, Puerto Rico, is the uplifted footwall of the normal fault bounding the northwestern edge of the basin. A linear, active, oblique-¬slip fault system can be traced for a distance of 80 km along the axis of the basin. High-resolution bathymetric data reveals a previously unrecognized linear, fault scarp offsetting the deep basinal sediments and seafloor of the VIB and extending 66 km to the west into the whiting basin southeast of Puerto Rico. Gravity and magnetic transects across the Virgin Islands basin and Anegada Passage constrain the depth to basement, ranging from 8.5 km below sea level in the VIB to 3.5 km below sea level in the Anegada Passage to the northeast. I present a tectonic model for the VIB involving: 1) Early Miocene opening of the basin as part of the Kallinago intra-arc basin; 2) Middle Miocene oblique collision of the Bahama carbonate platform and early left-lateral shear, basin opening, and offset of the Kallinago basin; and 3) counterclockwise rotation and right-lateral shear along the Virgin Islands strike-slip fault system through the VIB.