Isotopic Footprint of Mexican Geothermal Fluids: Constraining the Tectonic Settings

Abstract

The geothermal fluids (water and gases) of all four major reservoirs currently exploited in Mexico by the CFE – Cerro Prieto, Las Tres Vírgenes, Los Azufres, and Los Humeros – were the focus of an extensive isotopic investigation between 2014 and 2018. This project – led by CeMIEGeo (Centro Mexicano de Innovación en Energía Geotérmica) and CONACYT-SENER (Fondo Sectorial Conacyt-Secretaría de Energía-Sustentabilidad Energética) – led to the acquisition of a very large isotopic database of geothermal fluids. The database includes all stable noble gas contents (He, Ne, Ar, Kr, and Xe) and their isotopes, stable isotopes of water (d2H and d18O), CO2 (d13C and d18O), S (d34S), Cl, and Br (d37Cl and d81Br), and radiogenic isotopes of Sr in water (87Sr/86Sr), together with the major and trace element chemistry of water. Here, we report the results of our He, C, and Sr investigation, emphasizing in particular the distinct isotopic signatures among these geothermal fields, a reflection of their specific tectonic settings.