Neogene-Quaternary normal and transfer faults controlling deep-seated geothermal systems: The case of San Agustín del Maíz (central Trans-Mexican Volcanic Belt, México)

Abstract Investigating, from surface, deep-seated geothermal systems below hundreds to thousands of meters of thick clastic and unconsolidated sediments is always a timely theme for geothermal exploration. In this paper we describe a fieldwork and remote approach to the San Agustin del Maiz area, located in the central sector of the Trans-Mexican Volcanic Belt. Here, several geothermal manifestations are distributed in a broad basinal area, characterized by fluvio-lacustrine sediments unconformably resting on volcanic rocks. The tectonic control on the geothermal fluid circulation is highlighted by the alignment of thermal springs, by their temperature distribution and by the morphology of silica-sinter deposits, these latter aligned along the main trend of the regional faults, controlling dykes-feeding volcanoes, too. By integrating these data with structural and kinematic analyses collected in the fault-surfaces exposed in the volcanic bedrocks, it derives that permeable rock volumes, guarantying the arising of geothermal fluids from depth to the surface, are located at the intersection between WSW- striking normal faults and NNW- striking transfer faults, both framed in the current ∼NW-SE extension, active since Pliocene, at least. The proposed model offers new inputs for the geothermal exploration in Mexico, and, overall, for those areas worldwide with a similar tectonic setting.