Evidence of a shallow magma reservoir below Los Humeros volcanic complex: Insights from the geochemistry of silicate melt inclusions

Los Humeros volcanic complex (Eastern Trans Mexican Volcanic belt) is one of the three most important geo-thermal fields in Mexico and is currently producing electricity (ca. 90 MW). It-is therefore pertinent-to-coistrain the magma chamber characteristics, such as its depth, and the magmatic evolution of the complex in order to better define the superficial geothermal activity. In this paper we present the first geochemical data (major and trace elements) for 15 silicate melt inclusions and their five host rocks from Los Humeros volcanic complex. We constrained the evolution of the volcanic complex by coupling X-ray spectrometry, ICP-MS, microprobe, X-ray microtomography and NanoSIMS analyses together with thermodynamical modeling on both whole rocks and silicate melt inclusions. A ponding reservoir located within an interval betwwen 5 and 13 km at depth is evidenced by silicate melt inclusions entrapment pressures. This ponding depth's interval is in agreement with previous studies by thermal modeling, resistivity and geobaromatry done in the same area. The geothermal activity of Los Humeros volcanic area is expected to be the result of the cooling of the magma in the shallow chamber. A large geochemical variability, in less than 1 Ma, is demonstrated by trace and volatile element compositions evolution through time. Subduction contamination is expected into the mantle source with the highest contamination event at 69 Ka, during the second caldera event of Los Humeros volcanic complex.