Geological Interpretation of Combined Seabeam, Gloria and Seismic Data from Anegada Passage (Virgin Islands, North Caribbean)

I. Jany¹, K.M. Scanlon², and A. Mauffret¹

¹ Department de Geologie Oceanique, Universite Pierre et Marie Curie, 4 Place Jussieu,  75252 Paris Cedex 05, France
² U.S. Geological Survey, Branch of Atlantic Geology,  Woods Hole, MA 02543, U.S.A.

Marine Geophysical Researches 12: 173-196, 1990

The Anegada Passage (sensu lato) includes several basins and ridges from the Southeast of Puerto Rico to the corner of the Virgin Islands Platform. Seabeam (Seacarib 1) and Gloria long-range sidescan sonar surveys were carried out in this area. These new data allow us to propose an interpretation of the Anegada Passage.

Most of the features described are related to wrench faulting:

1. St. Croix and Virgin Islands Basins are pull-apart basins created in a right-lateral strike-slip environment based on their rhomboidal shape and seismic data (e.g. the flower structure). These two pull-aparts are divided into two sub-basins by a curvilinear normal fault in the Virgin Islands Basin and a right-lateral strike-slip fault in the St. Croix Basin.
2. Tortola Ridge and a "dog’s leg" shaped structure are inferred to be restraining bends between two right-lateral strike-slip faults.
3. We identified two ENE-WSW volcanic lineaments in the eastern area and one volcano lying between Virgin Islands and St Croix Basins.
4. As shown by the seismic activity main wrench motion occurs along the north slope of Virgin Islands Basin and through Anegada Passage. A branching of the main fault transmits the transtensional motion to St Croix Basin.

A two-stage story is proposed for the creation of the basins. A first extensional event during Eocene (?)- Oligocene-lower Miocene time created Virgin Islands, St Croix Basins and the tilted blocks of St Croix Ridge. A second transtensional event from Pliocene to Recent gave the present day pattern to this area. However, the displacement along the strike-slip faults is no more than 15 km long.

The proposed geodynamic model is based in the separation of the northeastern Caribbean boundary into two blocks. In the West, the indenter of Beata Ridge gives a northeastern motion to Hispaniola Block. In the East, as a result of Hispaniola Block’s motion, the Puerto-Rico-Virgin Islands Block could escape in an east-northeast direction.