Crustal structure of the South American–Caribbean plate boundary at 67°W from controlled source seismic data

Abstract

We present the results of new seismic reflection and wide‐angle data across the SE Caribbean plate boundary. The 550 km long N–S profile crosses the structures involved in the active 55 Ma long continent‐arc oblique collision between the Caribbean (CAR) and the South American (SA) plate. From the north to the south these structures include the accretionary prism, the extinct volcanic arc (Leeward Antilles arc), the Tertiary Bonaire basin, the continental‐size dextral strike‐slip fault system (San Sebastián–El Pilar fault), the allochthonous exhumed terranes, and the authocthonous fold and thrust belt (Caribbean Mountain system) and foreland basin. The wide‐angle data show that these elements are characterized by different velocity structures and that they are separated by sharp lateral velocity variations. The Leeward Antilles arc exhibits a velocity structure similar to that of the Lesser Antilles active volcanic arc, indicating that the extinct arc has not been modified by the collision with the SA plate. The data show a ∼20 km change in crustal thickness across the San Sebastián fault, suggesting that the dextral strike‐slip fault is a crustal feature that likely continues in the mantle as a primary strand of the plate boundary between the South American and the Caribbean plates. South of the strike‐slip fault and beneath the exhumed eclogitic terranes, the data image a north dipping, high‐velocity (>6.5 km/s) anomaly in the upper crust (3–11 km), indicating that high‐pressure/low‐temperature rocks are the likely lithologies responsible for the high seismic velocities and suggesting that exhumation of these assemblages is enabled by the strike‐slip fault.