Características geoquímicas de las rocas volcánicas del sistema geotérmico Los Humeros, Puebla y su relación con la mineralogía de alteración

Abstract

Volcanic rocks of the Los Humeros geothermal system range in composition from basaltic andesites to rhyolites and display different degrees of hydrothermal alteration. Petrographic examination, combined with x-ray diffraction, permitted the identification of different alteration minerals in paragenetic associations indicating temperatures from 150° to more than 300° C. This temperature range coincides with the current thermal gradient in the system. Major and trace elements from different lithological units suggest that the volcanic rocks from Los Humeros follow a calc-alkaline evolutionary trend with slight enrichment in potassium. The study of certain chemical elements (Zr, V, Ti o P), considered as relatively immobile in a hydrothermal environment, allow the estimation of mass transfer in volcanic rocks of the system. 87Srf86Sr ratios can be very useful as indicators for the source of certain chemical components (Ca and Sr). In the case of Los Humeros, volcanic rocks and hydrothermal calcites with similar isotopic values (averaging 0.70414) indicate that the chemical constituents were derived from similar magmatic sources. These isotopic values contrast with those found in the carbonate basement rocks (0.70730).