Facies variations and permeability of ignimbrites in active geothermal systems; case study of the Xáltipan ignimbrite at Los Humeros Volcanic Complex

Ignimbrites’ facies are key for interpreting the dynamics of explosive eruptions. Furthermore, they provide evidence of the physicochemical processes that acted during and after their deposition. Nevertheless, ignimbrites commonly present complex facies associations that require an integrative analytical methodology over a robust stratigraphic framework for their proper characterization. This work presents a facies characterization of the caldera-forming Xáltipan ignimbrite at Los Humeros Volcanic Complex, by integrating a combination of petrophysical and geochemical analyses aimed at its outflows (exposed) and intracaldera (buried) deposits. Based on the petrophysical properties, a three-facies association is identified controlled by welding and secondary mineralization effects: (1) The basal facies, characterized in the outflows by highly welded deposits (ranks V-VI), with low porosity (~4–8%), and practically impermeable conditions ( 400 m thick, the entire facies association is observed, while when the thickness is