Soil CO2 fluxes in Chichinautzin Volcanic Field, Mexico

Monogenetic volcanism is one of the most widespread volcanic manifestations on Earth, yet its timing and location remain difficult to predict. In monogenetic volcanic fields, tectonic structures may provide important pathways for magma ascent and help identify zones of enhanced volcanic activity; however, these structures are often difficult to recognize because they can be concealed beneath lava flows and pyroclastic deposits from previous eruptions. Diffuse soil CO 2 emissions provide a useful geochemical tool for identifying active or permeable structures that may facilitate the transport of deep fluids toward the surface. Here, we present the first systematic assessment of diffuse soil CO 2 emissions in the Chichinautzin Volcanic Field (CVF), the monogenetic volcanic field closest to Mexico City. We quantified and spatially analyzed soil CO 2 fluxes measured during four campaigns conducted in 2011, 2012, 2013, and 2015 using sequential Gaussian simulation (sGs). CO 2 fluxes were generally within the range expected for soil respiration, from 0 to 67.4 g m -2 d -1 , with a mean value of approximately 30 g m -2 d -1 . The spatial distribution of diffuse CO 2 emissions revealed a correspondence between relatively high fluxes and mapped faults located in the northern and northeastern sectors of the CVF, suggesting that these structures may act as preferential pathways for deep-fluid migration. Although the measured fluxes do not indicate anomalous volcanic degassing at the regional scale, the spatial association between CO 2 anomalies and tectonic structures highlights the potential of diffuse gas measurements to complement geological and geophysical approaches to characterize active permeability in monogenetic volcanic fields. Denser and spatially targeted surveys across the northern and northeastern sectors are therefore needed to better constrain the distribution and dynamics of diffuse degassing, particularly because these areas encompass highly populated regions in the vicinity of Mexico City. This study establishes a baseline for diffuse CO 2 emissions in the CVF and provides a reference for future monitoring of a volcanic field located in close proximity to one of the world's largest urban centers.