Soil CO2 flux baseline in Planchón – Peteroa Volcanic Complex, Southern Andes, Argentina - Chile

Abstract

The Planch´on – Peteroa Volcanic Complex exhibits two active degassing areas: Peteroa crater, PC, and peripheral hydrothermal areas, analyzed in three sampling sites, namely Valle Ba˜nos del Azufre, VBA, Valle del Pe˜n´on, VP and Valle Valenzuela, VZ. This prospective study was designed to investigate the soil diffuse emissions of CO2 at this volcanic complex. The survey consisted of 560 measurements of CO2 soil diffuse flux and temperature carried out at PC, VBA, VP. The results of this work show that diffuse CO2 is emitted at PC through two welldefined diffuse degassing structures and flux distribution that can be modeled by combining two log-normal populations. Here, the main source of soil CO2 is a shallow aquifer recharged by steam condensation and meteoric fluids that interact with rising magmatic gases. The carbon isotopic signature reveals that CO2 diffuse degassing is affected by secondary soil processes during its ascent. The total diffuse CO2 output at the surveyed area of PC, which covers ̴77,000 m2 around the crater fumarolic field, is 6.49 ± 0.32 t d􀀀 1. Soil diffuse emissions at the hydrothermal peripheral sites, VBA and VP, were studied covering a total area of 5̴ 90,000 m2. These emissions are characterized by poorly defined diffuse degassing structures and flux distributions that can be modeled by combining three log-normal populations, which suggest that multiple sources feed CO2 diffuse emissions. In concordance, the isotopic analysis also suggests a mixed source of CO2 and degassing affected by secondary processes that modify the original isotope composition. CO2 soil degassing at VZ shows a clear relation with the vegetated areas of the soil. The minimum endogenous CO2 output estimation here proposed for the Plancho´n – Peteroa Volcanic Complex is that of PC, 6̴ .5 t d􀀀 1. The thermal energy release was computed for PC, and the estimation is 2.57 ± 0.53 MW.