Capecchiacci Downstream composition of acidic volcanic waters discharged from Copahue crater lake (Argentina): the chemical evolution of Rio Agrio watershed..

.- F. TASSI, A. CASELLI, O. VASELLI, M. AGUSTO AND F. CAPECCHIACCI

Sienna

Congreso; Congresso Federazione Italiana della Scienze della Tierra; 2007

FIST

TheCopahue-Agrio-CaviahueComplex,iscomposedbytheCopahuepolygenicfissural-stratovolcanoandtheAgriosquarecaldera.ItislocatedonthewestborderofArgentina,intheNeuquénprovince,ontheAndesRangenearbytheboundarywithChile.ThisareabelongstotheSouthernAndeanVolcanicZone(SVZ:33.3º-46ºS).Copahuevolcano(37º45’S-71º10.2’W,2977ma.s.l.)isanactiveandesitictobasaltic-andesiticstratovolcano,nestedonthewesternrimoftheLatePlioceneAgriocaldera(Linaresetal.,1999).TheCopahue-AgrioComplexislocatedwithinafirst-ordermorphotectonictransitionzonebetweenthehighandbroadCentralAndes(-3-4kmmeanelevation,upto800kmwide)andthenarrowandlow(~1kmmeanelevation,300kmwide)PatagonianAndes(Groeber,1921).Thiszonehasbothrathernormalcrustalthickness(~40km)oftheSouthAmericanplateandsubductionangle(30º)oftheNazcaplate(Bohmetal.,2002;Lüthetal.,2003).Duringthelast250years,thisvolcanohasexperiencedatleast12low-magnitudephreaticandphreato-magmaticeruptions(Martinietal.,1997;NaranjoandPolanco,2004).Thelasteruptivecycletookplacefromtheeasternmostcrater(ithasnineNE-orientedcraters)inJuly1992,August1992,September1995andJuly-October2000(DelpinoandBermúdez,1993and2002;GVP,2000a,b),beingatpresentinafumarolicstage(GlobalVolcanismNetwork,2000a,b;DelpinoyBermúdez,2002).