NEW GEOLOGIC MAP OF THE GREATER ANTILLES AND VIRGIN ISLANDS

As part of a resource and environmental assessment, a new digital geologic map and database of the Greater Antilles has been compiled. Existing data derived from each of the islands was integrated across the region to provide a uniform view of the geology. Next a series of tectonostratigraphic terranes for the region were defined. These terranes display unique lithologies, geologic histories, and commonly distinct mineral deposit types. As part of the compilation, new zircon U/Pb dates were obtained, and a database of available radiometric ages was compiled.

The region includes multiple distinct geologic features. Cuba has the only unquestioned Jurassic, and perhaps older, rocks whereas on Hispaniola and Puerto Rico, Cretaceous metamorphic assemblages may contain Jurassic rocks. Cretaceous granitic rocks are present in Cuba, Dominican Republic, and Puerto Rico as are gabbro and trondhjemite of inferred Early Cretaceous age in the U.S. Virgin Islands. Cretaceous volcanic rocks are widespread in the region; they are of variable ages and do not reflect a single magmatic arc system. Early Cretaceous keratophyre and spilite in the Virgin Islands and northeast Puerto Rico are distinctive. Eocene volcanic rocks are prominent in southernmost Cuba, Puerto Rico, and the Virgin Islands and sparsely present in Haiti and eastern Jamaica. Volcanic rocks possibly as young as early Miocene are present in southern Hispaniola; the youngest volcanic rocks in the region are the Low Layton Lavas of Jamaica of late Miocene age and alkali basalt of Quaternary age on Hispaniola.

Carbonate rocks are widespread in the Greater Antilles, as old as Jurassic in Cuba and as young as Holocene in many areas. In Cuba, Early Cretaceous sedimentary rocks tend to be dominantly carbonates; volcanic clasts and debris are uncommon until Late Cretaceous. In contrast, Lower Cretaceous volcaniclastic sedimentary rocks are common in the Virgin Islands and Puerto Rico. Olistostromes are frequently described in uppermost Cretaceous and Eocene rocks; the Eocene deposits are commonly associated with mélange units. Sedimentary rocks that postdate the Eocene are dominantly carbonates or mixed clastic and carbonate rocks in which the clastic component reflects erosion of earlier volcanic units, as well as older carbonate rocks.