Soil CO2 Degassing Path along Volcano-Tectonic Structures in the Pico-Faial-São Jorge Islands (Azores Archipelago, Portugal)

Abstract

The Azores archipelago is composed of nine volcanic islands located at the triple junction between the North American, Eurasian, and Nubian plates. Nowadays the volcanic activity in the archipelago is characterized by the presence of secondary manifestations of volcanism, such as hydrothermal fumaroles, thermal and cold CO 2 -rich springs as well as soil diffuse degassing areas, and low magnitude seismicity. Soil CO 2 degassing (concentration and flux) surveys have been performed at Pico, Faial, and São Jorge islands to identify possible diffuse degassing structures. Since the settlement of the Azores in the fifteenth Century these three islands were affected by seven onshore volcanic eruptions and at least six destructive earthquakes. These islands are crossed by numerous active tectonic structures with dominant WNW-ESE direction, and less abundant conjugate NNW-SSE trending faults. A total of 2,855 soil CO 2 concentration measurements have been carried out with values varying from 0 to 20.7 vol.%. Soil CO 2 flux measurements, using the accumulation chamber method, have also been performed at Pico and Faial islands in the summer of 2011 and values varied from absence of CO 2 to 339 g m −2 d −1 . The highest CO 2 emissions were recorded at Faial Island and were associated with the Pedro Miguel graben faults, which seem to control the CO 2 diffuse degassing and were interpreted as the pathways for the CO 2 ascending from deep reservoirs to the surface. At São Jorge Island, four main degassing zones have been identified at the intersection of faults or associated to WNW-ESE tectonic structures. Four diffuse degassing structures were identified at Pico Island essentially where different faults intersect. Pico geomorphology is dominated by a 2,351 m high central volcano that presents several steam emissions at its summit. These emissions are located along a NW-SE fault and the highest measured soil CO 2 concentration reached 7.6 vol.% with a maximum temperature of 77 • C. The diffuse degassing maps show that anomalous CO 2 degassing areas are controlled essentially by the tectonic structures and the lithology of the sites since the youngest volcanic systems are characterized by very low CO 2 emissions.

CO2 Flux from Volcanic Lakes in the Western Group of the Azores Archipelago (Portugal)

“…Two statistical analysis procedures were applied to the CO 2 flux data, namely the graphical statistical approach (GSA) (e.g., [51]) and sequential Gaussian simulation (sGs) [56]. The GSA procedure is based on cumulative probability plots, leading to the identification of different populations in the geochemical data [57], which afterwards may be associated with diverse CO 2 sources, such as biogenic processes or volcanic-hydrothermal input (e.g., [24,35,36,51,56,58,59]).…”

Relationship between soil CO2 flux and tectonic structures in SW Sicily

“…In this context, the study of the spatial distribution of geochemical anomalies represents a valid additional tool to define and identify active buried structures and areas of active deformation as well. Actually, many studies showed as faults and fractures play a key role in the localization and evolution of geochemical anomalies at the surface [De Gregorio et al, 2002;Finizola et al, 2004;Finizola et al, 2006;Granieri et al, 2006;Werner and Cardellini 2006;Rowland and Simmons, 2012;Brothelande et al, 2014;Cellura et al, 2014;Viveiros et al, 2017]. This is because the migration of fluids through the crust occurs mainly through channels of high permeability generally represented by regional active faults or in sectors under active deformation [Sibson and Rowland, 2003;Fairley and Hinds, 2004;Dogan et al, 2007;Faulkner et al, 2010;Fossen and Rotevatn, 2016].…”

Soil gas CO2 emissions from active faults: a case study from the Anninghe—Zemuhe fault, Southeastern Tibetan Plateau, China

“…Therefore, a great interest has been focused on studying of CO 2 Earth degassing. There are many targets for such research, such as the relationships between the CO 2 flux and the tectonic structures (Etiope et al, 1999;Jolie et al, 2015), the researches of volcanic degassing (Inguaggiato et al, 2012;Chen et al, 2019;Fischer and Aiuppa, 2020), and the quantification of deeply derived CO 2 discharging into the atmosphere (Lee et al, 2016;Viveiros et al, 2017;Jacome-Paz et al, 2020;Bekaert et al, 2021;Rahilly and Fischer, 2021).…”