PRELIMINAR STUDY OF THE FIRST GAS COMPOSITIONS FROM THE ACTIVE CRATER FUMAROLES OF COPAHUE VOLCANO

AGUSTO M.; TASSI F; CASELLI A; VASELLI O; CAPACCIONI B; CALIRO S; CHIODINI G; LAMBERTI M C; LICCIOLI C

COPIAPÓ

Workshop; 12TH GAS WORKSHOP - CCVG - IAVCEI; 2014

SERNAGEOMIN - CEGA -

Copahue volcano (37º45?S-71º10?W, 2977 m a.s.l.) is part of Copahue-Caviahue Volcanic Complex (CCVC)(Argentina-Chile), located at the Southern Andean Volcanic Zone. The summit of this stratovolcano, consists of nine NE-oriented craters. Eruptive activity during the last 250 years, occurring from the easternmost crater that hosts a hot acidic lake (30-60°C, pH~0) with a diameter of~200 m, was characterized by at least 13 low-magnitude phreatic and phreato-magmatic events, affecting the nearby villages.  The crater lake acted as a direct condenser gases from the volcanic conduit, for this reason it was not possible to make direct sampling of the fumaroles of the crater and the composition of the gases emitted from the active crater of the volcano was unknown. Since November-December 2011 the discharge rate of fluids from the Copahue summit has significantly increased up to December 22nd 2012, when a new phreatomagmatic eruption occurred and is still ongoing. Before the latest eruption the only gas composition data were from fumaroles located in geothermal areas surrounding the volcano. Since the disappearance of the lake during the last eruptive event, numerous fumaroles were exposed in the active crater of the volcano allowing to obtain the first direct data of geochemical gas samples between January and March 2013. During these samplings were recorded the highest temperatures measured for fumarolic emissions in the region, with values ​​up to 300 ° C in emissions disposed on the upper part of the crater wall and temperatures above 450 ° C in fumaroles associated with the main conduit sampled at the bottom of the crater. In this work a preliminary study of the first geochemical and isotopic (δ13C of CO2 and CH4, dD of CH4 and H2O, d18O of H2O, δ15N, 3He/4He and 40Ar/36Ar) data gases of the active crater  Copahue volcano is presented, as well as data from manifestations from the thermal areas surrounding the building.