Revista Mexicana de Ciencias

Geológicas

ISSN: 1026-8774

rmcg@geociencias.unam.mx

Universidad Nacional Autónoma de

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México

Leal, Pablo Rodrigo; Vattuone, María Elena; Latorre, Carlos Oscar

Zeolite assemblages from Northern Patagonian Andes, Argentina: A review

Revista Mexicana de Ciencias Geológicas, vol. 28, núm. 2, 2011, pp. 212-225

Universidad Nacional Autónoma de México

Querétaro, México

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Leal et al.212

ZeoliteassemblagesfromNorthernPatagonianAndes,Argentina:Areview

Pablo Rodrigo Leal*, María Elena Vattuone,and Carlos Oscar Latorre

Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, C.P. C1428EHA, Ciudad Autónoma de Buenos Aires, Argentina.

* leal@gl.fcen.uba.ar

Revista Mexicana de Ciencias Geológicas, v.28, núm. 2, 2011, p. 212-225

Leal,P.R.,Vattuone,M.E.,Latorre,C.O.,2011,ZeoliteassemblagesfromnorthernPatagonianAndes,Argentina:Areview:RevistaMexicanadeCienciasGeológicas,v.28,núm.2,p.212-225.

ABSTRACT

In this work very low-grade metamorphic assemblages found in the Northern Patagonian Andes (Argentina) are summarized. On the basis of previous studies, several occurrences of zeolites have been delimited. According to their mineralogy, textures and structures, three different alteration stages that evidence a progressive decrease in temperature have been established. The first one (stage I) was the consequence of an event of regional metamorphism that reached the greenschist facies (350 °C and 2 kbar). During this stage, pyroxene, amphibole and feldspar primary phenocrysts broke down to produce an assemblage of actinolite, grossular-andradite, chlorite, albite, prehnite, titanite, clinozoisite, epidote and calcite. In the subsequent stages, direct hydrothermal precipitation took place as the temperature decreased. Thus, zeolites, calc-silicates, calcite, quartz and cristobalite started to precipitate as cavity fillings. During stage II, temperature decreased below 220 °C and wairakite, yugawaralite, laumontite, pectolite, dachiardite, celadonite, thomsonite, pumpellyite and interstratified chlorite/smectite crystallized. Prehnite, adularia, titanite and albite were also deposited but only as minor species. These minerals mainly alter feldspar phenocrysts and fill amygdules of basalts and andesites. Stage III is characterized by a temperature drop (below 180 °C) and by the crystallization of hydrothermal secondary minerals within open spaces. Most of the alkaline zeolites were deposited during this last event of alteration, filling joints in metabasites and granitoids. Although Ca-stilbite is the most abundant alteration mineral, analcime, natrolite, barrerite, offretite, chabazite, stellerite, heulandite, mordenite, scolecite, mesolite, quartz, calcite, cristobalite and smectites were also produced.

Key words: zeolites, low-grade metamorphism, metabasites, hydrothermal alteration, Northern Patagonian Andes, Argentina.

RESUMEN

En esta contribución se compilan las paragénesis de bajo grado metamórfico que se hallaron en los Andes Patagónicos Septentrionales (Argentina). Sobre la base de estudios previos, se delimitaron numerosas localidades caracterizadas por la abundancia de zeolitas. De acuerdo con sus composiciones mineralógicas, sus texturas y sus estructuras se reconocen tres estadios diferentes de alteración que reflejan un progresivo decrecimiento de la temperatura. El primero de ellos fue consecuencia de un metamorfismo regional que alcanzó condiciones de esquistos verdes (350 °C y 2 kbar). Durante este evento, la alteración de fenocristales primarios de feldespatos, piroxenos y anfíboles produjo actinolita, grosularia-andradita, clorita, albita, prehnita, titanita, clinozoisita-epidoto y calcita. En los estadios sucesivos, se incrementa la precipitación directa de minerales a partir de soluciones hidrotermales a medida que la temperatura

Zeolite assemblages from Northern Patagonian Andes 213

disminuye. Así, comenzaron a precipitar zeolitas, calcosilicatos, calcita, cuarzo y cristobalita rellenando cavidades. Durante un segundo evento, la temperatura descendió por debajo de 220 °C, ocasionando la cristalización de wairakita, yugawaralita, laumontita, pectolita, dachiardita, celadonita, thomsonita, pumpellyíta y estratificados de clorita/esmectita. Sólo en cantidades subordinadas se formaron prehnita, adularia, titanita y albita. Estos minerales alteran fenocristales de feldespato y rellenan vesículas en basaltos y andesitas. El último evento tuvo lugar cuando la temperatura descendió por debajo de 180 °C y se caracteriza por la cristalización tardía de minerales secundarios de baja temperatura dentro de cavidades. Durante este período precipitó el mayor número de zeolitas alcalinas, rellenando cavidades en metabaltos y granitoides. Si bien la estilbita-Ca es el mineral más abundante del tercer evento de alteración, también se encuentran analcima, natrolita, barrerita, offretita, chabazita, estellerita, heulandita, mordenita, escolecita, mesolita, cuarzo, calcita, cristobalita y esmectitas.

Palabras clave: zeolitas, bajo grado metamórfico, metabasita, alteración hidrotermal, Andes Patagónicos Septentrionales.

INTRODUCTION

Verylowgrademetamorphismisawidespreadphe-nomenonassociatedwithmajorprocessesthattakeplaceintheshallowerlevelsoftheEarth’scrust(FreyandRobinson,1999).Temperaturesandpressuresupto400ºCand4kbarproducechangesinthetextures,chemistryandmineralogyoftherocks.Aszeolitescanbeproducednotonlybymeta-morphismbutalsobyhydrothermalalterationprocesses,theybecomeoneofthemostimportantgroupofmineralstounderstandtherecordofchangesimprintedinalteredrocks.Ontheotherhand,overthepast40years,somezeo-liteshavebeenusedinagriculture,wastewatertreatment,gasseparation,buildingconstructions,ascatalysts,energystoragecollectorsandinmedicine(Deeret al.,2004).EventhoughtheyhavebeendescribedindifferentprovincesofArgentina,PatagonianAndesofferthegreatestvarietiesandsome areas where they can become a profitable resource.

Ithaslongbeenrecognizedthat theupliftoftheNorthernPatagonianAndesistheresultofthesubductionofoceaniccrustbeneaththeSouthAmericanwesternmargin,fromtheLatePaleozoictopresenttimes.Changesintherateofplateconvergenceandridgecollisionsproducedthemainstructuralandpetrologicalcharacteristics,whichledtoadivisionintotwodifferentsectors(Figure1a):Anorth-ernone(Lat38°-43°S),wherethestudyareaislocated,ischaracterizedbyasetofPaleogeneigneousrockswithsuperimposedverylowgrademetamorphicassemblages,andasouthernonedominatedbyCretaceousvolcanism(Ramos,1999).

Inthenorthernsector,severalstudieshavebeencarriedoutbydifferentauthorstodeterminethethermalanomaly and the hydrothermal fluids associated with meta-morphism.Thestudyofthesecondaryassemblagesallowstodeterminethetemperatureandpressureoftheprocessthataffectedtherocksofthisarea.Thesedataareusefultounderstandthegeologicalevolutionoftheregion,aswellastodeterminezoneswherezeolitesmaybeavaluablere-sourcenotonlyfortheindustry,butalsoforfurtherstudiesonmineralogyandpetrology.

Inlightofthereasonspresentedabove,duringthelast

fifteen years, secondary minerals present in the Northern PatagonianAndeshavebeenthefocusofnumerousresearchstudies.Previoussurveysallowedustocharacterizeeachassemblage,theirmineralogy(speciallythezeolitesspe-cies)andtheP-Tconditions.Duetothefactthatenoughinformationaboutthesecondaryassemblagesofmanydifferentoccurrenceshavebeenalreadyobtained,theaimof the present study is to make the first review of the sub-greenschistmetamorphismbetweenLat38°30’and44°00’S.Thus,allthesecondaryminerals,theirtextures,structuresandassemblages,aswellasthecharacteristicsoftheirwallrock,areheresummarized.Byanalysingthesedata,changesinthetemperatureandpressureandintheamountof hydrothermal fluids over the time are estimated.

METHODOLOGY

Althoughdifferentinstrumentswereusedforeachoneofthecontributionsconsideredinthisreview,themethodologyemployedwasthesame.Preparationofthinandpolishedsections,X-raydiffractionanalysisandmi-croanalyseswereaccomplishedinordertoidentifyeachmineralspecies.X-raydiffractionpatternswerecollectedbetween 2θ = 4°–70° in 0.05 steps using Cu-Kα radiation (50kV,30mA).Mostoftheanalyzedsampleshadtobeconcentrated,separatingmineralsbyhand-pickingunderabinocularmicroscope.Specialcarewastakentoobtainpuresamplestoavoidmineralmixtures.Microanalysesweremainlycarriedoutwithascanningelectronmicroscope(SEM-Phillips9100),at20kV,coupledtoanenergy-dis-persiveX-rayspectrometer(EDS),whichallowedtoobtainqualitativechemicalanalysis.

GEOLOGICAL SETTING

Themainmorphotectonicunits exposed in thePatagonianAndesaretheconsequenceoftwomainperiodsofsubductionalongthewesternmarginofGondwana.The

Leal et al.214

Figure1.Outlinemapofthestudyareashowingitsdifferentgeologicalunits,themajorstructuresandthemostimportantlocalitieswherethesecondaryassemblagesdescribedinthispaperweresampled(indicatedbynumberedrectangles);localitiesarelistedinTable1.

Zeolite assemblages from Northern Patagonian Andes 215

oldestone,knownasGondwanicMagmaticCycle,affectedthecentralpartofnorthernPatagonia(easternmoststudyarea),whereastheyoungestonewasdevelopedalongthewesternmarginofSouthAmericaproducingthepresentcordillera,wherethestudyareaisincluded.TheAndeanOrogeny(asthislasttectono-magmaticcycleisknown)couldhavestartedaroundtheLatePaleozoicaccordingtotheoldestmagmaticrocksrelatedtothesubductionofproto-Pacific oceanic crust below the South American western margin(Hervéet al.1998).

Igneousrocksformedbyarcvolcanismwerewidelydistributedandemplacedonametamorphicbasementcomposedofgneisses,schists,migmatites,amphibolitesandtonalites(DallaSaldaet al.,1999).ThesemetamorphicrocksaregroupedintotheColohuinculComplex,whoseagesareconstrainedintotheLateProterozoic(Turner,1965;Linareset al.,1988;DallaSaldaet al.,1999).AsthismetamorphicbasementandtheoverlyingPhanerozoicsedimentarycoverarenotassociatedwiththemineralogystudiedinthispaper,theirdetailedcharacteristicsarenotgoingtobedescribedinthiswork.Inthefollowingsec-tion, we will focus on the most significant features related tovolcanicandintrusiveunitswhichareassociatedwithverylowgrademetamorphicassemblages.

Volcanic units

FromLatePermiantoMiddleTriassic,extensionalprocessesinthecentralpartofSouthAmericaproducedbimodalmagmatism,whichisrepresentedbytheChoiyoiGroup (Groeber, 1946; Kay et al.,1989;Llambias,1999).Despitethefactthatthisunitcoversapproximately200,000km2oftheArgentinianterritory,inthestudyareaitonlyappearsassmalloutcropssurroundedbymetamorphicandigneousrocks.InthePatagonianAndes,theChoiyoiGroupisrestrictedtothenorthernsector(Figure1b),whereitmainlyconsistsofandesiticplateausandvolcanicbreccias(Turner, 1976).

Jurassicvolcanicrocks(ChonAike,LoncoTrapial,Huemul,MontesdeOca,Piltriquitrón,LagolaPlata,ElQuemadoformationsandequivalents)mainlyoccurinthesouthernandcentralpartofthePatagonianAndes(Figure1b).AccordingtoUlianaet al.(1985),thisvolcanismwasaconsequenceofthesteepeningofthesubductingoceaniccrustthatproducedextensionthroughouttheouterpartoftheplate,coetaneouslytoarcvolcanism,alongthewesternborderofSouthAmerica.Thus,basaltsandandesiteslocatedattheeasternslopeoftheAndes,alongthestudyarea,wereproducedduringthisperiod.

Cretaceousandesitesand rhyolites (Divisaderoformation)overlie thepreviousunitsfromLat44°33’Stowardsthesouth(Figure1b).Thesevolcanicrocksare locallyseparatedfromtheJurassicvolcanismbysedimentaryrocksoftheRioMayobasin,whichrepresentaback-arcbasinformedduringregionalextension(Ramos

et al.,1982;Franzeseet al.,2003).JurassicandCretaceousvolcanismbelongtothesamemagmaticarc,andhenceboth units have calc-alkaline affinities (Ramos et al.,1982;Ulianaet al.,1985).

Andesites,basalts,dacitesandignimbrites(AucaPan,Ventana,NahuelHuapiandHuitreraformations),groupedintheSerieAndesítica,wereformedfromthePaleocenetotheOligocene.Thisunitmainlycropsoutinthenorthernsectorofthestudyarea(Figure1),withmorethan1,500mthickness, and has calc-alcaline affinity (Dalla Salda et al.,1981;Rapelaet al.,1984).AccordingtoRapelaet al.(1984),twodifferentunitsarecomprisedinthisgroup:AndeanSerieAndesítica,composedofandesitesgeneratedduringtheEocene,andextra-AndeanSerieAndesíticawhichis200mthickandismainlycomposedofPaleoceneignimbrites.TheirgeochemicalsignaturesevidencethattheyarerelatedtothemagmaticarcformedbythesubductionoftheNazcaPlatebeneaththeSouthAmericawesternmargin(DallaSaldaet al.,1981).

InMiocenetimes,themagmaticarcmovedtowardsthewest,producingignimbritesandtuffs(CollónCuráFormation)asaconsequenceofrepeatedfelsicexplo-siveevents(MazzoniandBenvenuto,1990).DuringthePliocene,themagmaticarcmigratedwestwardfromtheNorthernPatagonianAndes(Rapelaet al.,1984).Today,theQuaternaryvolcanicfrontisassociatedwiththeLiquiñe-OfquifaultsystemlocatedinChile(MuñozandStern,1989;Laraet al.2001).Inthestudyarea,Quaternarybasaltsonlyoccurassmallbasalticplateausplacedatthetopoftheranges.

Intrusive units

Carboniferousgranitoids(Huechulafquencomplex)appearassmalloutcropsinthenorthernsectorofthestudyarea(Figure1b).Thesegranitoidsmightindicatethebegin-ningoftsubductioninthewesternmarginofthePatagonianAndes,orcouldbeconsideredastheconsequenceofthesubduction-collisioninthePatagonia-Gondwanaproto-margin(Ramos1984;DallaSaldaet al.,1991).

DuringJurassicandCretaceoustimes,meanwhileandesites,dacitesandrhyoliteshadbeeneruptedontothesurface,plutonicrockswerebeingemplacedbeneaththem(HallerandLapido,1982).TheAndeanPatagonianBatholith,composedofgranitoidsandminordioritesandgabbros,wastheresultofthisigneousactivity(Ramoset al.,1982;Bruceet al.,1991;Pankhurstet al.,1999,Lizuain,1999).Althoughtheagesofthebatholithvarybetween160and 8 Ma, Rapela and Kay (1988) recognized five major pulsesthattendtobeyoungerwestwards(González-Díaz,1982).Accordingtotheirages,compositionsandgeographicposition,GordonandOrt(1993)recognizedtwodiffer-entbatholiths:Sub-CordilleranBatholithandCordilleranBatholith(Figure1b).TheformerpresentsJurassicages,smallersizesandmainlyoccurstowardstheeastofthe

Leal et al.216

foothillaxis.Conversely,thelatterpresentsCretaceousagesandcomprisesthecoreofthePatagonianfoothillsthroughout2,200kilometers.However,despitetheirdif-ferences,bothbatholithspresentsimilarmagmaticarcsignatures(GordonandOrt,1993;Pankhurstet al.1999;Rapela and Kay, 1988).

Finally,Miocenegraniticstocks(Colucounit)werefoundtothewestoftheNorthernPatagonianAndes.TheserocksrepresentthelastintrusionsgeneratedbytheTertiaryAndeanarcmagmatism,andareemplacedalongtheaxisoftheLiquiñeOfquifaultsystem(González-Díaz,1982;LavenuandCembrano,1999)(Figure1b).

DISTRIBUTION AND GENERAL ASPECTS OF ZEOLITES OCCURRENCES

AlongtheNorthernPatagonianAndesthealterationprocessesthatproducedzeolite-richassemblagesseemtobeconcentratedinsomerestrictedareas(Figure1b).Duringthelastyears,severalstudieswerecarriedoutintheselocali-tiesinordertodeterminethemineralassemblagesandthecrystallizationsequences.Table1summarizesthenamesofthelocalitiesaffected,theirgeographiccoordinates,the

compositionofthehostrocksandthemaincontributionspublishedabouteachones.Theaimofthissectionistoestablishthecommonfeaturespresentedbythesecondaryassemblagesinalltheseareas.

Thereisaclearrelationshipbetweenthecompositionofthehostrockandthemineralizationthattookplaceineachoccurrence(VattuoneandLatorre,1990).Granitoidsonlypresentsomejointslinedbyalterationmineralsof1to5mmwide.Thebreakdownofplagioclaseoriginatedalbiteandcalcium-richzeolites,whereaschlorite,epidoteandprehnitewereproducedbythealterationofprimaryamphiboleandbiotite.Onthecontrary,inbasicandinter-mediatevolcanicrocks,thesecondarymineralscompletelyfill cavities and replace primary minerals (Figure 2). The groundmass,aswellasphenocrysts,arepervasivelyal-teredtoalbite,Ca-zeolites,pumpellyite,phyllosilicates,quartzandcristobalite.Nevertheless,inthesevolcanicrocks,secondarymineralsmostlyoccurconcentratedinjoints(formingveinsoffewcentimeterswidebyseveralcentimeterslong;Figures2c-2e),invesicles(Figure2f,2g),orincavitiesthatcanreachmorethan10centimeters(Figure2a,2b).

EventhoughallJurassic,CretacicandTertiaryvol-canicrockspresentalterationassemblages,Paleogene

Localities Lat S Long W Wall Rocks Main References

1 AlumineRucachoroi

39º14’14’’39º13’41’’

70º55’03’’71º10’36’’

JurassicandCretaceousvolcanites(AluminéFormation)andMiocenebasalts(RancahueFormation)

Lagorioet al.(2001);LatorreandVattuone(1996);Vattuone (1990); Vattuone and Latorre (1990);Vattuone et al. (1996b); Martínez Dopico et al.(2004);Gallegoset al.,(2008)

2 PiloLilJuníndelosAndes

39º38’28’’39º56’36’’

70º56’49’’71º04’28’’

Miocenebasaltandandesites(ChimehuinFormationandequivalents)

Vattuone et al. (1999); Vattuone et al. (2005b;2008)

3 CollónCura 40º23’44’’ 70º38’31’’ Oligocenebasalts(CollónCuraFormation)

LatorreandVattuone(1994a)

4 PioProtoSanMartíndelosAndesChapelco

40º06’50’’40º09’10’’40º18’25’’

71º10’36’’71º21’17’’71º23’11’’

Paleogenebasalts(SerieAndesiticaFormation)

VattuoneandLatorre(1994,1996a);Vattuoneet al.(1997; 1999; 2001b); Tourn and Vattuone (2002); VattuoneandTourn(2002)

5 MeliquinaPasoCórdoba

40º19’18’’40º36’50’’

71º21’01’’71º10’18’’

Paleogeneandesitesandtuffs(SerieAndesíticaFormation)

Latorre and Vattuome (1995); Vattuone et al.(1996a)

6 VillaLaAngostura 40º38’42’’ 71º37’35’’ Jurassicbasalts(MontesdeOcaFormation),Paleogeneandesites(SerieAndesítica)andCretaceousgranitoids(LosMachisFormation)

Depine et al. (2003); Leal (1999); Latorre andVattuone(1994b)

7 Confluencia 40º54’13’’ 71º01’20’’ Tertiarybasaltsandandesites(SerieAndesíticaFormation)

Vattuoneet al.(2001a,2001c)

8 Huemul 40º57’49’’ 71º19’19’’ MetabasitesofJurassicage(MontesdeOcaFormation)andPaleogenebasalts(Ventanaformation)

Gargiulo(2006);GargiuloyVattuone(2008)

9 FutalaufquenCholilaNahuelPan

42º49’18’’42º29’55’’42º57’20’’

71º36’41’’71º30’01’’71º12’43’’

Cretaceousvolcanites(DivisaderoFormation)

Vattuoneet al.(2000b,2002,2005a,2006);VattuoneandLatorre(2002a,b)

10 ElMolle 43º43’50’’ 70º02’06’’ Cretaceousbasalts(TresPicosFormation)

Vattuone et al. (2000a); Vattuone and Latorre(1999)

Table1.Characteristicfeaturesofthestudiedlocalities.Geographiccoordinates,wallrockcompositionsandcontributionsforeachoneofthelocalitiesindicatedintheFigure1.

Zeolite assemblages from Northern Patagonian Andes 217

Figure 2. Photographies of the most common secondary textures. a, b: Basalt outcroups from localities 1 and 7 with advanced alteration to low grade minerals; c-e: veins filled with zeolite assemblages, from localities 1 and 10; f, g: vesicles filled with secondary minerals from locality 2.

Leal et al.218

andtheirtexturesallowustorecognizethreemaindiffer-entstages(Figure4).Itisworthemphasizingthateventhough each one of these stages represents a specific range ofP-TconditionsitdoesnotmeanthatallthemineralslistedineachcolumnoftheFigure4areinequilibrium.Thesestagesonlyrepresentgroupsofmineralsformedbythesamegeologicalprocessthatproducedsimilar,butnotequal,conditionsalongthestudyarea,andthereforemorethanoneassemblageconstituteeachcolumn,accordingtothe wall-rock composition and the chemistry of the fluids (PO2,PCO2,pH,etc.)ineachlocality.Inthissection,theseassemblages,theirtextures,structuresandreactionswillbedescribed.

Stage I

Regional metamorphism was the first process that affectedtheigneousrocksofthestudyarea(Figure4,stageI).Thiseventaffectedallrocks,butindifferentwaysaccordingtotheirchemicalcomposition.Mineralsgener-atedduringthisstageonlyoccurreplacingfewphenocrystsandrepresenttheoldestsecondaryassemblages.Itisworthemphasizingthatalthoughthevarietyofmineralspeciesproducedbythemetamorphismisbroad,theirnumberisscarce. The assemblages associated with this first stage evidenceagradualtemperaturedecreasefromundergreen-schistconditionstozeolitesfacies.

VattuoneandLatorre(1990)andLagorioet al.(2001)describedhedenbergite-diopside,granditegarnetandortho-claseasthehighestmetamorphicassemblagesgeneratedbybreakdownofprimarymineralsunderamphibolitefaciesconditions(Figure3b).Thesemineralsoccurinfewlocali-tiesandwereonlyrecognizedinJurassicvolcanicrocks.

Epidote+chlorite+albite+quartz+magnetite+titanite + grandite garnet + K-feldspar assemblages suggest thatthemetamorphicgradedecreasedtogreenschistfacies.AssociationsliketheseweredeterminedbyVattuoneandLatorre(1990)andVattuoneet al.(2005a)inCretaceousvolcanicrocksaroundthelocalities1and9(Figure1).AccordingtoDeeret al.(1986)anassociationofgranditegarnet,magnetiteandepidoteallowedustoestimatetem-peraturesbelow325°Candpressuresabove2kbar.

Eventhoughpumpellyite-actinolitefaciesarelesscommon, tremolite-actinolite+epidote-clinozoisite+pumpellyite+chloriteassemblageoccursinthelocality9(Figure1)(Vattuoneet al.,2005a).Temperaturesandpres-suresformineralassociationslikethesewereestablishedbySchiffmanandLiou(1980)ataround250°Cand1.5kbar,respectively.

Prehnite-pumpellyitefaciesoccursinthelocalitynumber4,indicatingatemperaturedecrease.Underthiscondition,prehnite+pectolite+chlorite+laumontite+pumpellyite+albitecrystallizedinsideJurassicandPaleogenevolcanites(Figures3c,3d).

Finally,zeolitesfaciescharacterizestheendofthe

tuffs,basaltsandandesitesarethemostalteredunitsintheNorthern Patagonian Andes (Figure 1b, localities 5 and 7). These volcanic rocks present interestratified smectite/chlo-rite (s/c) produced by olivine alteration, whereas albite, zeolitesandepidoteweregeneratedbythebreakdownofplagioclase(VattuoneandLatorre,1990).Thus,thegreatestconcentrationsofzeolitesandothersecondarymineralsareassociatedwithvolcanicrocks,whichhavehigherperme-abilitythanthegranitoids.

Therelationshipbetweentheseverylowgrademeta-morphicassemblagesandoredepositsintheNorthernPatagonianAndeshasnotbeenclearlyestablished.Orede-positsthatoccurinthissectoroftheAndeshavebeenobjectsoffewstudies.GarridoandDomínguez(1999)studiedLaVoluntadporphyrycopper(ainFigure1b),whichisrelatedtoPermianstocks(281±4Ma).AccordingtoAmetranoet al.(1979) and Pezzutti and Genini (1999), the Condorcanqui depositrepresentsanothercopperanomalyandconsistsofquartzveinswithbornite,chalcopyrite,chalcocite,digen-iteandpyritehostedbyCretaceousandesites(cinFigure1b).Nearthislastdeposit,aMo-Cu-Auporphyryoccurshostedinthemetamorphicbasement(Genini,1999)(binFigure1b).Towardsthesouth,aPaleogeneporphyrycopper(Huemulesdeposit)composedofpyrite,galena,sphalerite,chalcopyrite,covellite,pirrhotiteandborniteassociatedwithgoldandsilveroccurs(VieraandHughes,1999)(einFigure1b).Additionally,goldandsilveranomaliesassoci-ated with sulfide mineralization, hosted in andesitic rocks of Jurassicage,constituteanhydrothermaldepositnamedElDesquite(Soechting,2002)(finFigure1b).Finally,Pesce(1978) reported hydrothermal mineralization rich in pyrite, chalcopyriteandgalenahostedinvolcanicrocksbutlinkedtoCretaceousgranitoids(ginFigure1b).

Itisworthemphasizingthatzeoliteassemblagesareassociatedwithoremineralizationonlyinsomerestrictedlocalities (number 6, 7 and 8, see Figure 1b). In these areas, nativecopper,pyriteandchalcopyriteappeardisseminatedinthevolcanicrocksorliningjoints.Besides,closetolocality4,zeolitescoatedbynativecopperandcupritewerefound(Figure3a,Vattuoneet al.,1996b;TournandVattuone,2002).FurtherstudiesfocusingontheagesoforedepositsandtheirsecondarymineralswouldbenecessarytoconcludeaboutanypossiblelinkagebetweenzeoliteprecipitationandthemetalmineralizationsoftheNorthernPatagonianAndes.

ZEOLITES ASSEMBLAGES

Asfarasweknow,nearly20differentzeolitesandmanyothersecondarymineralsoccurinseveraloccurrencesoftheNorthernPatagonianAndes.Duetothefactthatitsevolutionstartedasregionalmetamorphismandendedupassmallthermalanomalies,secondarymineralswereproducedbymetamorphicreactionsorbydirectprecipita-tion from hydrothermal fluids. Their mineral assemblages

Zeolite assemblages from Northern Patagonian Andes 219

metamorphicprocess.Epidote+albite+chlorite+inter-estratified c/s + laumontite and, to a lesser extent, adularia +pumpellyite+prehnite+heulandite+mordeniteoccuraffecting the same volcanic units (localities 4, 7 and 9, Figure1).

Thus,regionalmetamorphismcouldhavereachedtemperaturesofapproximately350°Candpressuresbelow2kbar.Scarceaggregatesofzeolitesandphyllo-silicates, which fill cavities in the groundmass of basalts andandesites,suggestthatattheendofthismetamorphicevent small amounts of fluids could have taken part of this first process.

Stage II

Superimposedtoregionalmetamorphism,hydrother-malprocessesproducedverylowgradeassemblagesrichinzeolitesalteringthewallrocks.Theseprocessesgeneratedmostofthesecondaryminerals(mainlyzeolites;Figure4,stageII),buttheyonlyaffectedrestrictedareasassociatedwith the rise of fluids. Localities 5, 7 and 10 (see Figure 1b) showthebestoutcropsofhydrothermallyalteredCretaceousandTertiaryvolcanicrocks(VattuoneandLatorre,1996a,

1999;Vattuoneet al.1996b,2005a).Stage II is mainly found as amygdule filling and as

veinletsinbasaltsandandesites.Epidote,wairakite,yuga-waralite,laumontite,pectolite,prehnite,pumpellyite,da-chiardite, thomsonite, interestratified c/s, celadonite, quartz, albiteandadulariawereprecipitatedwhenhydrothermalfluids reached temperatures within zeolites facies (Vattuone andLatorre,1994,1996b;Vattuoneet al.,2001b,2006;Figures5a-5e).Asaresult,alargenumberofCa-zeolitesweregenerated,beinglaumontitethemostabundant(Figure5a).Thegreatestdiversityofalterationmineralsoccursinbasaltsandandesites,whereasingraniticrocksactinolite,prehnite,epidoteandchloriteonlyappearspseudomorphi-callyalteringbiotitecrystals(VattuoneandLatorre,1990).Duringthisstagethewall-rockalterationmusthavebeenless abundant because the fluids were mainly in contact with previoussecondarymineralsformedinstageI.

Theupperlimitoflaumontite-wairakite-yugawaralitestability field allows us to estimate pressures around 0.6 kbar andtemperaturesbetween220and250°C(MiyashiroandShido, 1970; Zeng and Liou, 1982; Frey et al.1991)(Figure6a).Whereas,calc-silicatemineralsinequilibriumwiththezeolitesgeneratedinthisstagesuggesttemperaturesbelow230°C(Vattuoneet al.1999).

Figure3.Microphotographiesofthemostcharacteristicassemblages.a:Basaltwithnativecooper,sericiteandzeolitesfoundinlocality1;b:diopsideandgarnetcrystalsinametabasitefromlocality1;c:twinedcrystalofpumpelleyíte;d:prehniteandchloriteformedbycompletealterationofaprimarybiotite.

Leal et al.220

Stage III

Duringthelaststage(Figure4,stageIII)mineralsofvery low temperature precipitated from hydrothermal fluids. Thesehydrothermalassemblagesvaryfromtheedgetothecentre of the cavities evidencing an evolution in fluid condi-tionsovertime.Insomelocalities,thisassemblageisnotprecededbyanyothersecondaryminerals,whichsuggeststhat hydrothermal fluids affected a larger area during the laststage(Figure5f).Themostcharacteristicassemblagesgeneratedduringthisstagecanbefoundinlocalities1,4,6 and 7 (Figure 1b).

These secondary minerals fill cavities in basalts and andesitesaswellasjointsingraniticrocks,whichsuggeststhat the chemistry of the hydrothermal fluids was not primar-ilyaffectedbythecompositionofthewallrocks.Howeveritisworthemphasizingthatthehighestconcentrationsofzeoliteswerealwaysobservedinvolcanicrocks,wherethey appear as thin coatings, filling amygdules and joints ofseveralcentimeterswide,orreplacingprimaryigneousminerals.

MineralsgeneratedduringthisstagearesummarizedinFigure4.Althoughstilbiteisthemostabundant,Ca-heulandite,mordenite,scolecite,mesolite,chabazite,Ca-K-Na phillipsite, analcime, natrolite, barrerite, offretite, stellerite, quartz, calcite, fluorite, cristobalite and smectites were also found as late fillings in some cavities (Vattuone andLatorre,2002a;VattuoneandTourn2002;Vattuoneet al.2001a,2002,2008;MontenegroandVattuone2008;Figures5f-5i).Beidellyitecompositionofthesmectiteswas found in the aggregates that fill the cavities of the groundmass,whereassaponitecompositionoccurswhentheyaretheresultofolivinephenocrystsalteration(Vattuoneet al., 1997). It is important to emphasizing that alkaline zeolitesbecamemoreabundantduringthis laststage.Offretite, barrerite and chabazite, together with fluorite and fluorapatite suggest an increase of alkaline elements in the hydrothermal fluids.

Inthelocalities5and6somestilbitesandheulanditesalsocouldhavebeengeneratedafterlaumontitewhentemperature decreased. According to Liou (1971) and Miyashiro and Shido (1970) laumontite breaks down to formstilbiteorheulanditeattemperaturesbelow200°C.Therefore,theassemblagesfoundinthestudiedareamusthavebeenproducedatlowertemperaturesandpressuresbelow2kbar.

Magnetite,sphalerite,pyrite,chalcopyrite,nativecopperandcupriteprobablyprecipitatedfromthesamehydrothermal fluids that formed the very low grade meta-morphicassemblages(Figure4)(Vattuoneet al.,1996a;TournandVattuone,2002).Theseoremineralsoccurasdisseminatedspecksoflessthantwomillimeters(localities6 and 8; Figure 1b), or filling thin veinlets and amygdules associatedwithquartz(localities1,2and4;Figure1b).Eventhoughallthesemineralsoccurscatteredintheentirestudy area, sulfides are concentrated in localities 6 and 8,

whereasnativecopperandcupriteweremainlyfoundinlocality4(seeFigure1b).

Finally,asitwasassumedthatthestagesIIandIIIrepresenttheevolutionofthefirstmetamorphicevent,changesinpressureandtemperatureovertimecanbeschematized.OnthebasisofZengandLiou(1982),Liouet al.(1985)andFreyet al.(1991),whoestablishedthemost

Figure 4. Paragenetic sequence scheme. Wall-rock composition (B=bas-andesites, G=granitoids) and localitiy number ([x]) are indicated inside eacharea.

Zeolite assemblages from Northern Patagonian Andes 221

Figure5.MicrophotographiesofthemostcommonsecondarymineralsgeneratedduringstagesIIandIII.a,B:Laumontiteandcalciteassemblagesinmetavolcanites;c:dachiarditeagregates;d:albite,epidote,chlorite,smectiteandpumpelleyiteassemblages;e:calcite,heulanditeandyugawaralite;f:basalt cavities filled by stilbite and calcite (locality 6); g: small crystals of analcime covering joint planes; h: analcime and barrerite; i: vesicles filled by barreriteandgonardite.

Leal et al.222

ZEO

PP

PrA

PA

GS

4

6

5

3

1

2

200 400150 250 450300 500350 55050 1000

Temperature (°C)

Pressure(Kbar)

StageI

Stage IIStage III

Wairakite

Laumontite

Yugawaralite

Temperature (°C)

Pressure(Kbar)

250200 300100 150

1

1.5

0.5

0

a)

b)

commonP-Tdiagramsforlow-grademetamorphisminmetabasites,Figure6bshowstheevolutionoftemperatureandpressurededucedformthealterationassemblagesofthestudyareas.

DISCUSSION AND CONCLUSIONS

Assecondaryassemblageshavenotbeendated,thegeologicsettingassociatedwiththemisstillsubjectofcontroversy.However,therearetwofeaturesthatenableustosuggestsomegeneralconditionsforthezeolitemin-eralizationstudiedinthispaper.

InregardtothetectonicsettingassociatedwiththezeolitemineralizationinNorthernPatagonianAndes,ifathermalanomalytriggeringhydrothermalactivitywastheresultoftheCretaceousorMiocenegraniticintrusions,sec-ondary assemblages should define a zonning increasing their temperatureofformationtowardstheseunits.However,thegeographicdistributionofsecondarymineralsdoesnotvary following a specific trend. On the contrary, the thermal anomalythatproducedthesealterationsdoesnotseemtoberestrictedtotheplutonicbodies,whichsuggeststhatthe

mineralizationwasmainlycontrolledbythedevelopmentofthevolcanismandthelineamentsoftheuppermostsectorofthelithosphere.

Ontheotherhand,therelationshipbetweenthesec-ondary assemblages and rocks of specific ages suggests that thesemineralizationsmusthavebeengeneratedfromtheJurassictotheMiocene.Theassemblagesproducedduringthe first stage mainly occur in volcanic rocks of Jurassic age and,subordinately,intheTertiaryvolcanites(Depineet al.,2003).Thus,thisregionalmetamorphismshouldhavetakenplaceaftertheJurassic;perhapsduringtheCretaceous,whentherelativemotionbetweenNazcaplateandSouthAmericaincreased,producingahighthermalanomalyandafterwardshydrothermalactivity(Rapelaet al.,1983,1984).Ontheotherhand,Quaternarybasaltsdonotpresentsecondaryassemblages,whichsuggeststhatthesealterationprocessesmust have finished before this period. Hence, the P-Tcondi-tionsofthealterationprocessesaccordswiththeperiodinwhichthevolcanicarcwasmoreactiveinthestudyarea.ThisfactallowsustoexplainwhytheMesozoicvolcanicrockspresenthighermetamorphicgradethantheTertiarybasalts.Inaregionalstudyoflow-grademetamorphismontheCentralAndes(northwardsthestudyarea)Leviet al.(1989)suggestthatthegradeofmetamorphismishigherintheoldestrocks.Accordingtoallthedatacompiledforthiscontribution,wesuggestthatthesamesituationoccurssouthwards,alongthestudyarea.

Onthebasisofthesefacts,wesuggestthattheal-terationprocesseswererelatedtothethermalanomalythatproducedtheCretaceous-Miocenevolcanicarcde-velopment.Thecoincidencebetweenthemostimportantmagmaticperiodandthemineralizationeventsupportsthishypothesis.

Finally,asaresultofthepresentstudy,thefollowingconclusionscanbedrawn:

1.Therocksfoundinthestudyareapresentthreemainassemblagesthatweregeneratedduringthreedif-ferentstagesofalteration.TheoldestonewastheresultofaCretaceousregionalmetamorphism,whereasduringthelasttwostagesthehydrothermalalterationwasmorepervasive.Althoughthelasthydrothermalprocesseswerespatiallyrestrictedincomparisontothepreviousregionalmetamorphism(duetothefactthatitwasconstrainedbyfluid circulation) the major concentration of zeolites is as-sociatedwiththeselastprocesses.

2.Theoldestmetamorphicassemblagecouldhavestartedunderamphibolitefaciesconditions,buttemperaturegraduallydecreasedtothegreenschistfacies.Themineral-ogicalassemblagesassociatedwithgranditegarnetssuggestthat this first event reached temperatures of about 350 °C andpressuresnear2kbar.Astemperaturedecreased,mostofthehighgrademetamorphicmineralssufferedretrogrademetamorphismuntiltheyturnedintothesecondaryassem-blagesthatnowadayscanbefound.

3. Hydrothermal precipitates filled cavities of the volcanicrockswithzeolites,phyllosilicates,cristobaliteand

Figure6.a)P-Tdiagramshowingthestabilityrelationshipamongyuga-waralite,laumontiteandwairakiteafterZengandLiou(1982),Liouet al.(1985)andFreyet al.(1991);b)SchematicdiagramoftheP-Tconditionsofeachstage.P-T fields for low grade metamorphic facies are from Frey et al.(1991);ZEO:zeolitesfacies,PP:prehnite-pumpellyitefacies,PA:pumpellyite-actinolitefacies,PrA:prehnite-actinolitefaciesandGS:greenschistfacies.

Zeolite assemblages from Northern Patagonian Andes 223

calcite.Thisassemblageindicatesadecreaseintemperature,andhighconcentrationsofalkalineelements,SiO2andCO2in the fluids (Vattuone and Latorre, 1990). At the beginning, the fluids must have had high temperature and therefore their compositioncouldhavebeencontrolledbythewallrock.During this stage the fluids could have leached Ca, Fe and Mgfrombasaltsandandesites.Thus,smectitesandzeoliteswithhighCaandlowSiO2musthavebeenproducedduringthesecondstageandseemtobestronglylinkedtothewallrockcomposition.Overtime,secondarymineralslinedthewalls of cavities (isolating the fluids from the wall-rocks), meanwhilethetemperatureofthesystemdecreased.Asaresult, the last fluids (stage III) could have produced minor wall-rockalteration,andzeoliteswithalkalineelementsandhigherSiO2formed.

4.Zeoliteassemblagesgeneratedbyhydrothermalprecipitation (during the last stages) occur in specific locali-ties.Eventhoughmanyspecieswererecognized,laumon-titeandstilbitearethemostcommon.Thesemineralsaremainly found as open space fillings in the most permeable rocks.Basalts,andesitesandignimbriteshostzeolitesindifferentamountsaccordingtotheirpermeability.Inthestudyarea,thehighestabundanceofzeoliteswasfoundinlocality 7, where they fill veins and amygdules of a Tertiary ignimbrite.

ACKNOWLEDGMENT

Theauthorswishtoacknowledgethesupportpro-videdbyBuenosAiresUniversity(UBACyTX238)andCONICET(Pip02244).Theauthorsareverygratefultothereferees(Dr.LibertodePabloandDr.CarlesCanet)andtheeditorsfortheirhelpfulsuggestionsanddiscussions.

REFERENCES

Ametrano, S., Coira, B., Donnari, E., Pezzutti, N., 1979, Mineralización decobreasociadaalplutonismoTerciarioenlazonadelaminaCondorcanqui,provinciadeChubut:ServicioGeológicoMinero,unpublishedreport,40.

Bruce,R.M.,Nelson,E.,Weaver,S.,Lux,D,1991,TemporalandspatialvariationintheSouthernPatagonianbatholith.Constraintsonmagmaticarcdevelopment,inHarmon,R.S.,Rapela,C.W.(eds.),AndeanMagmatismanditsTectonicSetting:GeologicalSocietyofAmerica,Specialpaper,265,1-12.

DallaSalda,L.,Leguizamon,M.,Mazzoni,M.,Merodio,J.,Rapela,C.W.,Spalletti,L.,1981,CaracterísticasdelvulcanismoPaleogenoenlaCordilleraNordpatagónicaentrelaslatitudes39°30’y41°20’S,in 8 Congreso Geológico Argentino, San Luis, 3, 629-657.

DallaSalda,L.,Herve,F.,Munizaga,F.,Pankhurst,R.J.,Parada,M.A.,Rapela,C.W.,1991,ThemagmaticevolutionofnorthernPatagonia;Newimpressionsofpre-AndeanandAndeantectonics:GeologicalSocietyofAmerica,SpecialPaper265,29-43.

DallaSalda,L.,Varela,R.,Cingolani,C.,1999,ElbasamentoPrecámbrico-PaleozoicoinferiordelaPatagonia,IslasMalvinasyAntártica, inCaminos, R. (ed.), Geología Argentina, 29(5), 107-112.

Deer,W.,Howie,R.,Zussman,J.,1986,Rock-FormingMinerals;DisilicatesandRingSilicates:Essex,England,LongmannScientific and Technical, volume 1B, 45-134.

Deer,W.,Howie,R.,Zussman,J.,Wise,W.,2004,RockFormingMinerals;4B-FrameworkSilicates:Londres,GranBretaña,TheGeologicalSociety,2ndEdition,982pp.

Depine,G.,Gargiulo,M.F.,Leal,P.R.,Scaricabarozzi,N.,Spagnuolo,C.,Vattuone,M.E.,2003,Paragénesisdeceolitasenrocasvolcánicasde laCordilleraPatagónicaNorthern,VillaLaAngostura,Neuquen,Argentina,in10CongresoGeológicoChileno,Concepción,Chile:11pages(CD).

Franzese,J.,Spalletti,L.,GómezPérez,I.,Macdonald,D.,2003,TectonicandpaleoenvironmentalevolutionofMesozoicsedimentarybasinsalongtheAndeanfoothillsofArgentina(32°-54°S):JournalofSouthAmericanEarthSciences,16,81-90.

Frey,M.,deCapitani,C.,Liou,J.G.,1991,Anewpetrogeneticgridforlow-grademetabasites:JournalofMetamorphicGeology,9,497-509.

Frey,M.,RobinsonD.,1999,Low-gradeMetamorphism:Wiley-BlackwellEd.,313pp.

Gallegos,E.,MartínezDopicoC.,CrostaS.,BerbegliaY.,VattuoneM.E.,2008,MineralogíadeFaujasita-Caacompañadadeescolecitaythomsonitaenvolcanitasmiocenas,CordilleraPatagónicaSeptentrional,in9CongresodeMineralogíayMetalogenia,SanSalvadordeJujuy:31-38.

Gargiulo, M.F., 2006, Facies metamórficas y edades relativas de las rocas delextremoorientaldelBrazoHuemul,provinciadeNeuquén:RevistadelaAsociaciónGeológicaArgentina,61,218-230.

Gargiulo,M.F.,Vattuone,M.E.,2008,ZeoliteassemblagesinpaleogenebasaltsofMallínAhogado,NorthernPatagonianAndes,Neuquén,Argentina,in4thInternationalConferenceoftheFederationofEuropeanZeoliteAssociations(FEZA),Paris,Francia:2pp.

Garrido, M., Domínguez, E., 1999, El yacimiento de pórfiro cuprífero La Voluntad,Neuquén,inZappettiniE.(ed.),RecursosMineralesdelaRepúblicaArgentina,35,809-818.

Genini,A.D.,1999,Prospectodecobre-molibdeno,cerroCoihue,Chubut,inZappettiniE.(ed.),RecursosMineralesde laRepúblicaArgentina,35,1289-1290.

González-Díaz,E.F.,1982,ChronologicalzonationofgraniticplutonisminthenorthernPatagonianAndesofArgentina:themigrationoftheintrusivecycles:EarthScienceReviews,18(3-4),365-393.

Gordon,A.,Ort,M.H.,1993,EdadycorrelacióndelplutonismosubcordilleranoenlasprovinciasdeRioNegroyChubut(41°-42°30’LS),in12CongresoGeológicoArgentinoy2CongresodeExploracióndeHidrocarburos,Mendoza,Argentina:4,120-127.

Groeber, P., 1946, Observaciones geológicas a lo largo del meridiano 70. HojaChosMalal:RevistadelaAsociaciónGeológicaArgentina,1(3), 177-208.

Haller,M.J.,Lapido,O.R.,1982,TheJurassic-CretaceousVolcanismintheNorthernPatagonianAndes:EarthScienceReviews,18,395-410.

Hervé,F.,Aguirre,L.,Godoy,E.,Massone,H.,Morata,D.,Pankhurst,R.,Ramírez,E.,Sepulveda,V.,Willner,A.,1998,NuevosantecedentesacercadelaedadylascondicionesP-TdeloscomplejosmetamórficosdeAysén,Chile, in10CongresoLatinoamericano de Geología, Buenos Aires: 2, 134-137.

Kay, S.M., Ramos, V.A., Mpodozis, C., Sruoga, P., 1989, Late Paleozoic JurassicsilicicmagmatismattheGondwanalandmargin:analogyto the middle Proterozoic in North America?: Geology, 17, 324-328.

Lagorio,S.,Massaferro,G.,Vattuone,M.E.,Latorre,C.,2001,MineralogíaymetamorfismodevulcanitasdeAluminé:Revistade laAsociaciónGeológicaArgentina,56(2),211-220.

Lara,L.,Rodríguez,C.,Moreno,H.,PérezdeArce,C.,2001,GeocronologíaK/Ar y geoquímica del volcanismo plioceno superior-pleistoceno delosAndesdelsur(39-42°S):RevistaGeológicadeChile,28(1), 67-90.

Latorre,C.O.,Vattuone,M.E.,1994a,Asociaciónesmectitas-calcosilicatosenmetabasaltoscercanosalríoCollónCura,Neuquen,Argentina,in 7 Congreso Geológico Chileno, Concepción, Chile: 2, 1085-1090.

Latorre,C.O.,Vattuone,M.E.,1994b,EstilbitayclinoptilolitaenlaSerie

Leal et al.224

Andesítica.LaAngostura,Neuquén,in2aReunióndeMineralogíayMetalogénesis,BuenosAires:183-189.

Latorre,C.,Vattuone,M.E.,1996,TiroditadeAluminé,ProvinciadelNeuquen,Argentina,in12CongresoGeológicoArgentinoy3deCongresodeExploracióndeHidrocarburos,BuenosAires:3,255-258.

Lavenu,A.,J.Cembrano,1999,CompressionalandtranpressionalstresspatternforPlioceneandQuaternarybrittledeformationinforearcandintraarczones(AndesofCentralandSouthernChile):JournalofStructuralGeology,21,1669-1691.

Leal,P.R.,1999,PetrologíadelasrocasígneasdelosalrededoresdellagoNahuelHuapi,Neuquén,in14CongresoGeológicoArgentino,Salta, Argentina: 2, 207-210.

Levi,B.,Aguirre,L.,Nystrom,L.O.,Padilla,H.,Vergara,M.,1989,Low-graderegionalmetamorphismintheMesozoic-CenozoicvolcanicsequencesoftheCentralAndes:JournalofMetamorphicGeology, 7, 487-495.

Linares,E.,Cagnoni,M.C.,DoCampo,M.,Ostera,H.A., 1988,GeochronologyofmetamorphicanderuptiverocksofsouthernNeuquénandNorthwesternRíoNegroprovinces,ArgentineRepublic:JournalofSouthAmericanEarthSciences,1(1),53-61.

Liou, J.G., 1971, P-T stabilities of laumontite, wairakite, lawsonite and relativemineralsinthesystemCaAl2Si2O8 – SiO2 – H2O:Journalof Petrology, 12, 379-411.

Liou,J.G.,Maruyama,S.,Cho,M.,1985,Phaseequilibriaandmineralparagenesesofmetabasites in low-grademetamorphism:MineralogicalMagazine,49,321-333.

Lizuain,A.,1999,ElJurásicoyCretácicodelaPatagoniayAntártica,inCaminos R. (ed.), Geología Argentina, 29(17), 433-443.

Latorre,C.O.,Vattuone,M.E.,1995,AsociacionesMineralesdelafaciesdeceolitasenelPasodelCórdoba,Neuquén,RepúblicaArgentina,in4.JornadasGeofísicasyGeofísicasBonaerenses,BuenosAires: 1, 287-294.

Llambias,E.J.,1999,ElmagmatismoGondwánicoduranteelPaleozoicosuperior-Triásico, inCaminosR.(ed.),GeologíaArgentina,29(14), 349-376.

MartínezDopico,C.,Gallegos,E.,Vattuone,M.E.,2004,Implicancesofthe activity of fluor-rich fluids on basalts affected by very low grademetamorphisminChapelcohills,Neuquen,Argentina:Bolletino di Geofisica. GeoSur, 45, 120-121.

Mazzoni,M.M.,Benvenuto,A.,1990,RadiometricagesofTertiaryignimbritesand theCollonCuraFormation,NorthwesternPatagonia,in10CongresoGeológicoArgentino,SanMigueldeTucumán: 1, 87-90.

Miyashiro, A., Shido, F., 1970, Progressive metamorphism in zeolite assemblages:Lithos,3,251-260.

Montenegro,T.,Vattuone,M.E.,2008,Asociacionesmineralesdemuybajogrado metamórfico vinculadas a alteración hidrotermal, sudoeste deTrevelin,Chubut,Argentina:RevistaMexicanadeCienciasGeológicas,25(2),302-312.

Muñoz,J.B.,Stern,C.R.,1989,Alkalinemagmatismwithinthesegment38°-39°SofthePlio-QuaternaryvolcanicbeltoftheSouthernSouthAmericanContinentalMargin:JournalofGeophysicalResearch,94(B4),4545-4560.

Pankhurst,R.J.,Weaver,S:D:,Hervé,F.,Larrondo,P.,1999,Mesozoic-CenozoicevolutionoftheNorthPatagonianBatholithinAysén,southernChile:JournaloftheGeologicalSociety,London,156,673-694.

Pesce, A.H., 1978, Estratigrafía de la cordillera patagónica entre los 43°30’ y44°delatitudsurysusáreasmineralizadas,in 7oCongresoGeológico Argentino, Buenos Aires: 1, 257-270.

Pezzutti,N.E.,Genini,A.,1999,ManifestacióncupríferaCondorcanqui,Chubut,inZappettini,E.(ed.),RecursosMineralesdelaRepúblicaArgentina,35,1249-1250.

Ramos,V.A.,1984,Patagonia:Uncontinentepaleozoicoaladeriva?,in9CongresoGeológicoArgentino,SanCarlosdeBariloche:BuenosAires,2,311-325.

Ramos,V.A.,1999,LasprovinciasGeológicasdelterritorioArgentino,inCaminosR.(ed.),GeologíaArgentina,29(3),41-96.

Ramos,V.A.,Niemeyer,H.,Skarmeta,J.,Muñoz,J.,1982,Magmaticevolutionof theAustralPatagonianAndes:EarthScienceReviews,18,411-443.

Rapela, C.W., Kay, S.M., 1988, Late paleozoic to recent magmatic evolution of Northern Patagonia: Episodes, 11(3), 175-182.

Rapela,C.W.,Spalletti,L.A.,Merodio,J.C.,1983,EvoluciónmagmáticaygeotectónicadelaSerieAndesíticaandina(Paleoceno-Eoceno)enlaCordilleraNorpatagónica:RevistadelaAsociaciónGeológicaArgentina,38(3-4),469-484.

Rapela,C.W.,Spalletti,L.A.,Merodio,J.C.,Aragon,1984,Elvulcanismopaleoceno-eocenodelaprovincavolcánicaAndino-Patagónica,in9ºCongresoGeológicoArgentino,SanCarlosdeBariloche:BuenosAires,1(8),189-213.

Schiffman,P.,Liou,J.,1980,SynthesisandstabilityrelationsofMg-AlpumpellyiteCa4Al5MgSi6O21(OH)7:JournalofPetrology,21,441-474.

Soechting,W.,2002,Controllitológicoyestructuralenelemplazamientodelsistemadevetasauríferasepitermalesdecuarzo-calcedoniaenelcordóndeEsquel,Chubut,Argentina,in15°CongresoGeológico Argentino, Calafate: Buenos Aires, 2, 272-277.

Tourn,S.,Vattuone,M.E.,2002,Cobrenativoycupritaenunaparagénesisceolíticaenamígdalasdelavasbasálticas,Chapelco,provinciadeNeuquén,in Brodtkorb, M., Kouharsky, M., Leal, P.R. (eds.), 6ºCongresodeMineralogíayMetalogenia2002,BuenosAires:425-432.

Turner,J.C.,1965,EstratigrafíadeAluminéyadyacencias(provinciadeNuequén):RevistadelaAsociaciónGeológicaArgentina,20(2),153-184.

Turner, J.C., 1976, Descripción Geológica de la Hoja 36a, Aluminé: Cartageológico-económicadelaRepúblicaArgentina,Boletín145, 77 pp.

Uliana, M.A., Biddle, K.T., Phelps, D.W., Gust, D.A., 1985, Significado del vulcanismoyextensiónmesojurásicosenelextremomeridionaldeSudamerica:RevistadelaAsociaciónGeológicaArgentina,40(3-4),231-253.

Vattuone, M.E., 1990, Paragénesis mineral del metamorfismo en el área deAluminé,CordilleraNeuquina:RevistadelaAsociaciónGeológica Argentina, 45(1),l07-ll9.

Vattuone,M.E.,Latorre,C.,1990,LowgrademetamorphismingranitoidsandvolcanicrocksofCordilleraNeuquina,Argentina:JournalofSouth American Earth Sciences, 3(4), 247 252.

Vattuone,M.E.,Latorre,C.,1994,Característicasmineralógicasygénesisde la laumontitadeChapelco,Neuquén, inBrodtkorb,M.,Schalamuk,I.(eds.),2aReunióndeMineralogíayMetalogénesis,LaPlata:429-435.

Vattuone, M.E., Latorre, C., 1996a, Metamorfismo de muy bajo grado enrocasvolcánicasdelaFormaciónVentana,SanMartíndelosAndes,Neuquen,Argentina:RevistaGeológicadeChile,23(2), 187-200.

Vattuone,M.E.,Latorre,C.,1996b,YugawaralitadeLagoMeliquina,Neuquén,inBrodtkorb,M.,Schalamuk,I.(eds.),3aReunióndeMineralogíayMetalogenia:LaPlata,InstitutodeRecursosMinerales,5,251-256.

Vattuone,M.E.,Latorre,C.,1999,CeolitascálcicasenvulcanitasdelCretácicoSuperior.Sugénesisenunpaleosistemageotermal.ElMolle,Chubut,RepúblicaArgentina:BoletíndelPrimerSimposiosobreelCretácicodeAméricadelSur,SerraNegra,Brasil,1,213-218.

Vattuone,M.E.,Latorre,C.,2002a,Na-MgoffretitefromFutalaufquen,PatagonianAndes,Argentina,inZeolite’02,6thInternationalConferenceontheOccurrence,PropertiesandUtilizationofnaturalZeolites:Thessaloniki,Greece,1,382-383.

Vattuone,M.E.,Latorre,C.,2002b,DachiarditacálcicaenmetandesitascretácicasdelCerroNahuelPan,Chubut.RepúblicaArgentina,in Brodtkorb, M., Kouharsky, M., Leal, P.R. (eds.), 6º Congreso deMineralogíayMetalogenia,BuenosAires:439-440.

Vattuone,M.E.,Tourn,S.,2002,Polimorfoortorrómbicodelaseriefluorapofilita/hidroxiapofilita asociado a chabacita y laumontita enamígdalasdebasaltos.Chapelco,Neuquén,inBrodtkorb,M.,Kouharsky, M., Leal, P.R. (eds.), 6º Congreso de Mineralogía y

Zeolite assemblages from Northern Patagonian Andes 225

Metalogenia,BuenosAires:441-446.Vattuone,M.E.,Latorre,C.O.,Viviani,R.,Borbolla,M.C.,1996a,

MineralogíadeceolitascálcicasyfilosilicatosmáficosquecaracterizanelmetamorfismohidrotermaldelasvolcanitaspaleógenasdesdeLagoHermosoaRíoTraful,Neuquén:Revistade la Asociación Geológica Argentina, 51(3), 235-247.

Vattuone,M.E.,Latorre,C.,Tourn,S.,1996b,AlteraciónhidrotermalconmanifestacionesdesulfurosrelacionadaaintrusionesmagmáticasdelbatolitoNordpatagónicoeneláreadeAluminé,Neuquén,inBrodtkorb,M.,Schalamuk,I.(eds.),3aReunióndeMineralogíayMetalogenia:LaPlata,InstitutodeRecursosMinerales,5,257-263.

Vattuone, M.E., Latorre, C., Leal, P.R., Martinez A., 1997, Asociaciones mineralesdebajogradoenPioProto,SanMartindelosAndes,Neuquen,RepúblicaArgentina, in8ºCongresoGeológicoChileno,Antofagasta,2,1561-1564.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,Martinez,A.,Viviani,R.,1999,Calcosilicatosy filosilicatosde faciesceolitayprehnita-pumpellyitaenPíoProto,Neuquen,PatagoniaArgentina:Boletínde la Sociedad Española de Mineralogía, 22, 185-197.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,2000a,Laprehnitadelasvolcanitasde“ElMolle”,Chubut, inSchalamuk, I.,Brodtkorb,M.,Etcheverry,R.(eds.),5ºCongresodeMineralogíayMetalogenia,LaPlata:6,480-494.

Vattuone, M.E., Latorre, C., Leal, P.R., 2000b, Metamorfismo de muy bajo gradoenvolcanitasmesozoicasdelaCordilleraPatagónica(42°-43°LS),Chubut,RepúblicaArgentina,in9ºCongresoGeológicoChileno, Puerto Varas, Chile: 2, 545-547.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,2001a,Barreritaenmetavolcanitasde Confluencia, Neuquen, Patagonia Argentina: Boletín de la SociedadEspañoladeMineralogía,24,23-32.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,2001b,Pectolitaenasociaciónconlaumontitayprehnita,enamigdalasdemetabasaltos,cerroChapelcoChico,Neuquén:RevistadelaAsociaciónGeológicaArgentina,56(2),240-243.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,2001c,Procesosdeformacióndeparagénesis ceolíticas en el metamorfismo de muy bajo grado de las volcanitas paleógenas al sur de Confluencia, Neuquen, Argentina:RevistaGeológicadeChile,28(2),3-22.

Vattuone,M.E.,Latorre,C.,Leal,P.R.,2002,Paragénesisdebarrerita,offretita,clinozoisita-esmectitaenamígdalasdebasaltos.RíoArrayanes.Chubut,in Brodtkorb, M., Kouharsky, M., Leal, P. (eds.),6ºCongresoNacionaldeMineralogíayMetalogenia,Buenos Aires: 447-452.

Vattuone, M., Latorre, C., Leal, P., 2005a, Polimetamorfismo de muy bajo a bajo grado en rocas volcánicas Jurásico/cretácicas al sur deCholila,Chubut,PatagoniaArgentina:RevistaMexicanadeCienciasGeológicas,22(3),315-328.

Vattuone,M.,Crosta,S.,MartínezDopico,C.,Gallegos,E.,Berbeglia,Y,Lagorio,S.,Latorre,C.O.,2005b,ZeolitasAlcalinasenbasaltosamigdaloidesdelascercaniasdeJunindelosAndes,Neuquén,in16ºCongresoGeológicoArgentino,LaPlata,2,601-602,.

Vattuone,M.E.,LatorreC.,LealP.R.,2006,Mineralogiayparagénesisdedachiarditacálcicaenvolcanitascretácicasceolitizadas.Esquel,Chubut,Patagoniaargentina:RevistaGeológicadeChile,33(1),161-176.

Vattuone,M.,LealP.R.,Crosta,S.,BerbegliaY.,GallegosE.,MartínezDopicoC.,2008,Paragénesisdezeolitas alcalinas enunafloramiento de basaltos olivínicos amigdaloides de Junín de los Andes,Neuquen,Patagonia,Argentina:RevistaMexicanadeCienciasGeológicas,25(3),483-493.

Viera,R.L.M.,Hughes,G.,1999,ElyacimientopolimetálicoauríferoHuemules,Chubut,inZappettiniE.(ed.),RecursosMineralesde la República Argentina, 35, 1369-1376.

Zeng,Y.,Liou,J.,1982,Experimentalinvestigationofyugawaralite-wairakite, equilibrium: American Mineralogist, 67, 937-943.

Manuscriptreceived:August2,2010Correctedmanuscriptreceived:January11,2011Manuscriptaccepted:February2,2011