Cenozoic collision of the Lesser Antilles Arc and continental South America and the origin of the El Pilar Fault

Abstract

It is proposed that the Cenozoic tectonic record of the southern Lesser Antilles arc and northeastern continental South America can be explained by ongoing right‐oblique collision between the arc and continent. The collision has proceeded by the transport of the leading edge of the arc across the slope and outer shelf of a former north facing passive margin of the South American continent. The overriding began in the study region near the Gulf of Cariaco in eastern Venezuela in late Eocene or Oligocene time and has migrated with a generally SE vector. Suturing has occurred between the arc and continent after the attainment of a critical distance of overlap; today's point of suturing lies in the Paria Peninsula. East of there, overriding continues. Major tectonic elements engaged in or created by the collision are the southern Lesser Antilles magmatic arc, forearc basin, the Araya‐Tobago terrane, a South American foreland thrust and fold belt, and a foreland basin. The Araya‐Tobago terrane is thought to consist of sediments of South American provenance that were accreted to the Lesser Antilles forearc during its transit of an ocean basin and the continental slope and outer shelf. The emplacement of the magmatic arc and the Araya‐Tobago terrane caused tectonic imbrication of shelf strata to propagate ahead of the arc front as a foreland thrust and fold belt. Tectonic loading of the shelf also caused subsidence of a major foreland basin on the continentward side of the thrust belt. It is proposed the El Pilar fault exists between the Gulf of Cariaco and the Paria Peninsula as an active right slip fault but not east of Paria. It is not a throughgoing transform fault between the South American and Caribbean plates. The El Pilar fault exists where the overlapping arc and the continent are sutured and takes up a suture‐parallel component of convergence between arc and continent. The eastern tip of the fault propagates east with the point of suturing. Reconstructions of the Cenozoic collision of the Lesser Antilles arc and the South American continent suggest that the arc lay somewhat north and west of its present position in the Eocene. This conclusion differs from that of plate reconstructions that assume that the arc was the leading edge of a Caribbean plate that has moved east from Pacific longitudes since the Eocene.