CARIBBEAN PLATE BOUNDARIES—EOCENE SUBDUCTION, COLLISION AND SUTURING IN PUERTO RICO: SIGNIFICANCE OF THE GREAT SOUTHERN PUERTO RICO FAULT ZONE

The northern margin of the Caribbean plate is distinguished by the southeastward curving Greater Antillean (GA) arc. Volcanism above the south-facing subduction zone ceased after the western Cuba segment of the arc collided with the Bahamas platform between 66 and 44 Ma. In eastern Cuba, Hispaniola and attached islands to the south collisional structures are less prominent because of the southeastward curvature of the GA arc away from the Bahamas Platform. South of the Cauto fault in Oriente Province, Eocene igneous rocks crop out as they do in Hispaniola and Puerto Rico. In Puerto Rico, Eocene lavas and plutons are most common among northwesterly striking faults that distinguish the Great Southern Puerto Rico fault zone (GSPRFZ). Tertiary strata include lavas, volcaniclastic and other sedimentary units some of which are fine-grained and cherty and may be pelagic. Well layered strata may contain olistoliths and commonly record faults and folds some of which may be penecontemporaneous. Older, Late Cretaceous rocks covering the oceanic crust southwest of the GSPRFZ may have been offscraped and deformed as they were carried toward the trench. Subduction related Eocene volcanism was areally limited and short-lived. Convergence waned during Oligocene time perhaps in response to the arrival and collision of thick oceanic terrains (eg. Cayman Ridge, Nicaraguan Rise, Beata Ridge) with the overriding plate. During collision, volcanic units at the edge of the overriding crust were uplifted and destabilized sufficiently so that masses calved off and collapsed southwestward forming an apron of debris (Sabana Grande Formation). We propose that the Eocene volcanic rocks record renewed subduction, although the subduction was north-facing and involved the consumption of the Caribbean plate along a zone roughly coincident with the back arc of the Cretaceous belt.