Status and Geologic Setting of Geothermal Fields in Central America, Mexico, and the Caribbean

Abstract

The current installed geothermal capacity in Mexico, Central America, and the Caribbean is 869 MWe (Megawatts of electricity), of which 71 percent is in Cerro Prieto field, Mexico. The projected installed geothermal capacity of the region is 1,020 MWe in 1992, reflecting power plants to be brought on line in Costa Rica, El Salvador, Guatemala, St. Lucia, and Mexico.

With few exceptions, high enthalpy (heat content) geothermal fields in Mexico, Central America, and the Caribbean region are associated with active volcanic belts at plate boundaries. In Mexico, three high enthalpy fields occur within the 1,200 km-long Trans-Mexican Volcanic Belt (TMVB) along the western margin of the North American Plate. The 1,100 km-long Central American Volcanic Belt (CAVB) and TMVB result from subduction of the Cocos Plate beneath the western margins of the Caribbean and North American Plates, respectively. Several of the Central American and Mexican geothermal systems are related to young silicic volcanism, e.g., Los Humeros and La Primavera, Mexico, and Miravalles, Costa Rica. However, Momotombo (Nicaragua) and Ahuachapán (El Salvador) geothermal fields appear to be associated with mafic to intermediate composition volcanic centers.

In addition to magmatic heat sources, Central America hosts an extensive system of grabens in and behind the volcanic arc. The intersection of tensional structures and young volcanic centers yields highly favorable settings for exploitable geothermal systems. Several geothermal fields are being explored in Honduras, all of which are well to the east of young arc volcanism. These fields are related to graben faults and are thus similar to geothermal areas under development in the Basin and Range Province of Nevada and Utah in the United States.

In the eastern Caribbean, the density and volume of Quaternary volcanos is lower than in Central America and Mexico. The relative plate velocity at the convergent boundary between the Caribbean and the North and South American Plates is low. To date, one geothermal field is operating at La Bouillante, Guadeloupe (4 MWe), and a discovery well was drilled at Soufriere, St. Lucia.