Geochemistry of fluid discharges from Peteroa volcano (Argentina-Chile) in 2010?2015: Insights into compositional changes related to the fluid source region

TASSI F; PAONITA A; AGUSTO M; VASELLI O; AGUILERA F; BENAVENTE O; CHIODINI G; CALIRO S; GUTIERREZ F; CAPACCIONI B; CASELLI A; SALTORI O

CHEMICAL GEOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 432 p. 41 - 53

0009-2541

This study presents the first geochemical data of fluid discharges collected from February 2010 to March 2015from the Planchón?Peteroa?Azufre Volcanic Complex (PPAVC), located in the Transitional Southern VolcanicZone (TSVZ) at the border between Argentina and Chile. During the study period, from January 2010 to July2011, Peteroa volcano experienced phreatic to phreatomagmatic eruption possibly related to the devastatingMaule earthquake occurred on February 27, 2010. The compositional dataset includes low temperature (from43.2 to 102 °C) gas discharges from (i) the summit of Peteroa volcano and (ii) the SE flank of Azufre volcano,both marked by a significant magmatic fluid contribution, as well as bubbling gases located at the foothill ofthe Peteroa volcanic edifice, which showed a chemical signature typical of hydrothermal fluids. In 2012, strongcompositional changes affected the Peteroa gases fromthe summit area: the acidic gas species, especially SO2, increased,suggesting an input of fluids from magma degassing. Nevertheless, the R/Ra and δ13C?CO2 values decreased,which would imply an enhanced contribution from a meteoric-hydrothermal source. In 2014?2015,the chemical and isotopic compositions of the 2010?2011 gases were partially restored. The anomalousdecoupling between the chemical and the isotopic parameters was tentatively interpreted as produced bydegassing activity from a small batch of dacitic magma that in 2012 masked the compositional signature of themagmatic fluids released from a basalticmagma that dominated the gas chemistry in 2010?2011. This explanationreliably justifies the observed geochemical data, although the mechanisms leading to the change in time ofthe dominatingmagmatic fluid source are not clear. At this regard, a geophysical survey able to provide informationon the location of the two magma batches could be useful to clarify the possible relationships between thecompositional changes that affected the Peteroa fluid discharges and the 2010?2011 eruptive activity.