La primavera caldera (Mexico): Structure and geothermal system inferred from gravity

Abstract

Rsxico possesses, in different gsologic environ ments, a large geothermal potential. The installed caz pacity for generating electricity from high enthalpy hydrothermal systems amounts to 645 AW. It is expected to increase this capacity at short term by bringing -into production geothermal systems located in the TPVB (Trans-Mexican Volcanic Belt). The TRVR hosts most of the developed or promising geothermal areas (Alonso et al., 1985), which can be related to the historic and present day volcanism featuring this province. To the W of the TMWB, next to Guadalajara City, is located -the geothermal field of la Primavera. This field is -associated to a Pleistocenic rhyolitic caldera. The feasibility for generating electricity from this field has been well established through different geological geochemical, and geophysical studies, and by the explo ratory wells. Current studies are aimed to assist its development, i.e. to characterize the geothermal sys-tern and to define its extension, In this context, a -gravity study was conducted to obtain information on the structure of this silicic caldera. Oata of a gra-vity survey were processed (regional-residual separa-tion, upward and downward continuations, vertical derivatives, and filtering). Gravity modelling (Z-D in-version, 2-D and 3-D forward modelling) was also done. The caldera is featured by a complex structure. A se-ries of structural highs and lows were observed inside the caldera. The major structural trends affecting --these structures belong to the regional structural fabric. A correlation with geochemical and hydrological data enabled to establish a geologic framework for the prevailing conceptual hydrogeological model.