Fluid circulation in a complex volcano-tectonic setting, inferred from self-potential and soil CO2 flux surveys: The Santa María–Cerro Quemado–Zunil volcanoes and Xela caldera (Northwestern Guatemala)

Abstract

International audienceThe region encompassing Santa María, Cerro Quemado, and Zunil volcanoes, close to Quetzaltenango, the second largest city of Guatemala, is volcanically and tectonically complex. In addition, the huge Xela caldera, about 20 km in diameter, crosses this area and links up to the important Zunil fault zone located between the three volcanoes. Two highly active geothermal sites, named Zunil-I and Zunil-II, are also located between these three volcanic edifices at the southeastern boundary of Xela caldera. In order to determine the permeability variations and the main structural discontinuities within this complex volcano-tectonic setting, self-potential and soil CO2 flux measurements have been coupled, with a step of 20 m, along a 16.880 km-long profile crossing the entire area. Two shallow hydrothermal systems, with maximum lateral extensions of 1.5 km in diameter, are indicated by positive self-potential/elevation gradients below Santa María and Cerro Quemado volcanoes. Such small hydrothermal systems cannot explain the intense geothermal manifestations at Zunil-I and Zunil-II. Another minor hydrothermal system is indicated by self-potential measurements on the flank of Santa María along the edge of the Xela caldera. CO2 flux measurements display slight variations inside the caldera and decreasing values crossing outside the caldera boundary. We hypothesize the presence of a magmatic body, inside the southeastern border of Xela caldera, to explain the deeper and more intense hydrothermal system manifested by the Zunil-I and the Zunil-II geothermal fields. This magmatic system may be independent from Santa María and Cerro Quemado volcanoes. Alternatively, the hypothesized Xela magmatic system could have a common magmatic origin with the Cerro Quemado dome complex, consistent with previous findings on regional gas emissions. Sectors bordering the Cerro Quemado dome complex also have high amplitude minima-short wavelength anomalies in self-potential, interpreted as preferential rain water infiltration along faults of major permeability, probably related with the most recent stages of Cerro Quemado dome growth

An assessment of hydrothermal alteration in the Santiaguito lava dome complex, Guatemala: implications for dome collapse hazards

“…We are not currently aware, however, of the existence of active fumaroles associated with the summit or eruption scar of Santa María. A self-potential and soil CO 2 survey conducted by Bennati et al (2011) of the area around Santa María (but not extending to the Santiaguito dome complex) was interpreted to indicate the potential presence of a hydrothermal system, related to a residual magmatic body from the 1902 eruption, extending radially about 800 m from the summit of Santa María. Additional kaolinite-mapped pixels within the Santa María scar and downslope of the domes may be due to small debris flows, alluvium, and colluvium originating from the kaolinite-rich source areas exposed along the headwall summit scarp of Santa María.…”

Textural Insights Into the Evolving Lava Dome Cycles at Santiaguito Lava Dome, Guatemala

“…Santa Maria is located on the southern edge of the Xela Caldera and is part of the Central American Volcanic Arc which extends from Mexico to El Salvador (Figure 2; Duffield et al, 1993;Bennati et al, 2011). Eruptive activity at Santa Maria began around 103 ka, and the edifice was constructed in four stages before a 25 thousand-year period of quiescence prior to 1902 (Rose et al, 1977;Rose, 1987a;Conway et al, 2013).…”

Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island)

“…Many recent studies used soil CO 2 diffuse emissions as a useful and unambiguous tracer of volcanic and tectonic structures ( Azzaro et al, 1998;Giammanco et al, 1998;Finizola et al, 2003Finizola et al, , 2004Revil et al, 2008Revil et al, , 2011Bennati et al , 2011;Bonforte et al, 2013). In this study of the NWRZ of Piton de la Fournaise, we adopted a multidisciplinary approach combining (1) soil CO 2 flux and isotopic data, (2) seismic events spanning from 1996 to 2015, (3) a photogrammetric model to quantify the dyke distribution and orientation and, finally, (4) the spatial density of the cinder cones in the area investigated, with the aim of identifying and better constraining potentially active structures within this rift zone.…”