A DIGITAL GEOLOGIC MAP OF THE GREATER ANTILLES AND VIRGIN ISLANDS – A TOOL FOR ANALYSIS

As part of a resource and environmental assessment, the first fully digital geologic map and database of the Greater Antilles and Virgin Islands (GAVI) has been compiled. Existing data from each of the islands was integrated across the region to provide a uniform view of the geology. As part of the compilation, new U/Pb dates were obtained, and a database of available radiometric ages compiled. A series of tectonostratigraphic terranes were defined for the region on the basis of unique lithologies, geologic histories, and distinct mineral deposit types.

The system we developed to make the digital geologic map of Alaska an analytical tool was adapted for GAVI. This adaptation uses many of the same attribute tables and a similar coding scheme for map units. For example, granite of Tertiary-Cretaceous boundary age is coded the same whether in Alaska or GAVI. This facilitates using the same tools or algorithms used for analysis and assessment in Alaska to be applied to GAVI.

In the schema, a numeric attribute named GAclass is assigned to each map unit based on lithology, setting, and age. This attribute is structured such that ranges of values are hierarchical based on age and lithology. Once assigned, the GAclass attribute automatically links to additional attributes that define maximum and minimum age, geologic setting, and a one-to-many relationship of hierarchically defined lithology. Using this schema, map units can be “correlated” from island to island, facilitating analysis.

Data for the geologic map was provided by Cuban Ministry of Energy and Mines in 57 1:100,000-scale sheets and from the Dominican Republic Ministry of Industry and Commerce, Department of Mining, at a scale of 1:250,000 (both in Spanish). Haitian data was published by their Ministry of Mines and Energy Resources (in French) and Jamaican data was from their Mines and Geology Division, Ministry of Mining and Natural Resources, both at a scale of 1:250,000. Puerto Rico was in 64 USGS 1:20,000-scale geologic maps. We used several maps from dissertations for the U.S. and British Virgin Islands at scales varying between 1:24,000 and approximately 1:60,000. We digitized these sources and built translations of their unit descriptions into a common database. Every polygon is coded tied to its original source map unit and every arc to its original source map.