IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Understanding the eruptive dynamics of 2010-2011 Planchón-Peteroa unrest period through volcanic fluid sampling
Autor/es:
BENAVENTE O; PAONITA A; AGUSTO M; VASELLI O; TASSI F; CALIRO S; CAPACCIONI B; SALTORI O; AGUILERA F; CHIODINI G; GUTIERREZ F; CASELLI A
Lugar:
Puerto Varas
Reunión:
Congreso; Cities on Volcanoes 9; 2016
Institución organizadora:
IAVCEI
Resumen:
Planchón-Peteroa(35.240°S, 70.570°W, 3603 m a.s.l.) is a composite stratovolcano located in theTransitional Southern Volcanic Zone at the border between Argentina and Chile. FromJanuary 2010 up to July 2011, PP entered in an eruptive cycle characterized by phreaticand phreatomagmatic eruptions with a VEI ≤2. Even though different authorsreported geophysical, petrological and glaciovolcanic evidences about the2010-2011 unrest episode (e.g., Pritchard et al. 2013, Aguilera et al. 2012;Naranjo 2012, Liaudat et al 2013), no consensus on the mechanisms triggering thiseruptive cycle, the fluid sources involved, and the possible dynamicinteraction between those sources during the cycle have been achieved. In orderto unveil the dynamics of the 2010-2011 unrest period, this study presents chemicaland isotopic (δ18O?H2O,δD?H2O,δ13C?CO2, 3He/4He, 40Ar/36Arand δ15N?N2)data of gas discharges collectedduring five sampling campaigns (February 2010 to March 2015) from the fumaroleslocated at the PP summit.Our results shows that in2012, the acidic gas species contents of the fumaroles from the PP summitshowed a huge increase (SO2>CO2) with respect to the2010-2011 period, whereas the typical hydrothermal compounds (e.g. CH4and light hydrocarbons) decreases. This compositional change could beinterprated as a pulse of magmatic fluids, but the temporal evolution of the δ18O-H2O, δD-H2O, R/Ra and δ13C?CO2values suggest, in stead, anenhanced fluid contribution from a shallow source. In 2014-2015, the dominanthydrothermal signature characterizing the 2010-2011 samples was almostcompletely restored. The temporary decoupling of the chemical and isotopic parameterscan only be reconciled when two sources of magmatic fluids are proposed: abasaltic batch, controlling the fumarolic chemistry in 2010-2011 and 2014-2015,and a dacitic batch whose contribution to the fumarolic fluid emissionsachieved its maximum in 2012. Given this, we conclude that the eruptive period2010- 2011 of PP is related to the increasing of heat and mass transfer fromshallow hydrothermal-deep magmatic sources favoured by the formation and/orreactivation of cracks produced by the Maule earthquake (27th February 2010).The disturbance created by the volcanic events and the associated seismicactivity  (both related to the Mauleearthquake), could have reactivated a relatively ?old? (i.e., highly degassed)dacitic body that in 2012 imposed over that of basaltic composition.