Upload
lykiet
View
215
Download
0
Embed Size (px)
Citation preview
Abstract Volume8th Swiss Geoscience MeetingFribourg, 19th – 20th November 2010
Department ofGeosciences
2. Mineralogy-Petrology-Geochemistry
58Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2. Mineralogy-Petrology-Geochemistry
Eric Reusser
Swiss Society of Mineralogy and Petrology (SSMP)
2.0 AbidiR.,Slim-ShimiN.,HatiraN.,MarignacCh.,GasquetD.,MejriZ.:Approchemicrothermométriquepourladéterminationdel’originehydrothermaldef luideminéralisateurdugisementàPb-(Zn)-Sr-Bad’ElAguiba(Tunisieseptentrional)
2.1 BaderT.,FranzL.,deCapitaniC.,RatschbacherL.,HackerB.R.,WeiseC.,PoppM.:TectonometamorphicevolutionoftheWudangComplex(centralChina)
2.2 BauerK.,VennemannT.,MulchA.:ReconstructionofNeogenepaleoelevationandpaleoclimaticconditionsoftheEuropeanAlpsandthecircum-Alpineregionbystableisotopeanalyses
2.3 Cavargna-Sani M., Epard J-L., Bussy F., Ulianov A.: Zircon U/Pb dating of the Late Carboniferous ZervreilaOrthogneiss,AdulaNappe.
2.4 Diamond L.W., Tarantola A., Stünitz H.: Effects of deviatoric stress on natural f luid inclusions in quartz: anexperimentalstudy
2.5 ElKorhA.,SchmidtS.Th.,BallèvreM.,BruguierO.:U–PbgeochronologyofanorthogneissdiscoveredwithintheHP–LTmetamorphicrocksoftheIledeGroix,ArmoricanMassif,France
2.6 HermannJ.,RubattoD.:Pre-AlpinemetamorphismintheclassicalAlpinestaurolite-garnetschistofCampolungo
2.7 Huber C., BachmannO., Dufek J.: Thermo-mechanical reactivation of locked crystalmushes:melting-inducedinternalfracturationandassimilationprocessesinmagmas
2.8 HunzikerD.,CaddickM.,ReusserE.,BurgJ-P.,MüllerE.: Theinfluenceofferric/ferrousironratiosinbulkandmineralsofblueschistsfromtheInnerMakran(SEIran)onthermobarometricrecalculations
2.9 HürlimannN.,MüntenerO.,UlmerP.:Subvolcanicmafictointermediatedike-systems:contraintsonpost-plutonicactivity(S-Adamello,N-Italy)
2.10 Katona I., SerneelsV.: Thepigmentsof themedievalpainters inFribourg: Investigationofa topqualitymuralpaintingfromtheCordeliersChurchinFribourg.
2.11 KayaniS:Combustionanalysisofameteoritedebris
2.12 KhozyemH.M.,AdatteT.,TantawyA.A.,Spangenberg J.E.,KellerG.,FöllmiK.: NatureandTempoof thePETM(Paleocene-Eocenethermalmaximum)events,newinsightsfromtheGSSPDababyiasection(Luxor,Egypt).
2.13 KocsisL.,OunisA.,ChaabaniF.,NailiS.M.:NewisotopedatafromtheLateCretaceousandPaleogenephosphatebedsoftheGafsaBasin,Tunisia
2.14 KönigD.,SerneelsV.:GeochemicalandmineralogicalexaminationsofromancruciblesfromAutun(France)
2.15 LambrechtG.,DiamondL.W.:FluidboilingandmixingduringlateststageorogenicgoldmineralizationatBrusson,NWItalianAlps
2.16 MaggettiM.,MorinD.,SerneelsV.,NeururerC.:KilnfurnituresfromthefaiencemanufactureofGranges-le-Bourg(HauteSaône,France):contrastingrecipes
2.17 MaggettiM.,RosenJ.,SerneelsV.,NeururerC.:ThefaiencemanufactureLeBoisd’Épense(North-easternFrance,18/19thcentury)
2.18 MarolfA.R.,VennemannT.W.,BonzonJ.:Forensicgeology:characterisationoflightelementstableisotopesinsoilsamplesoftheSwissPlateau
2.19 Martin L.H.J., SchmidtM.W., Hametner K., Günther D.: Element partitioning between immiscible silicate andcarbonatitemeltsbycentrifugeexperiments
2.20 Mattsson H.B., Bosshard S.A., Hetényi G., Almqvist B.S.G., Hirt A.M., Caricchi L., Caddick M.: Internal f lowstructuresincolumnarjointedbasaltfromHrepphólar,Iceland
2.21 Mavris C., Egli M., PlötzeM., Götze J., Mirabella A., Giaccai D., HaeberliW.: Mineral weathering along a soilchronosequenceinahighAlpineproglacialarea:amultipleapproach
59
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.22 MeierM.F.,GrobétyB.:FumarolicaerosolsfromElChichónvolcano,Mexico
2.23 Monsef R., Emami M. H., Rashidnejad Omran N., Monsef I.: Petrogenetic evolution of Neogene volcanism innorthernUromieh-DokhtarMagmaticBelt:Insightsontheoriginofpost-collisionmagmatism
2.24 Moulas E., Connolly J., Burg J.-P., KostopoulosD.: Refining the granulite-faciesmetamorphism in theRhodopemetamorphiccomplex-Greece
2.25 OrtelliM.,MoritzR.,VoudourisP.,CoscaM.,SpangenbergJ.:TertiaryPorphyryandEpithermalAssociationoftheSapes-KassiteresDistrict,EasternRhodopes,Greece
2.26 ParmigianiA.,HuberC.,BachmannO.,ChopardB.:Reactivemultiphasef lowatthepore-scale:themeltingofacrystallineframeworkduringtheinjectionofbuoyanthotvolatiles.
2.27 PretetC.,FelisT.,SamankassouE.:Constrainingcalciumisotopefractionationincorals
2.28 RegisD.,EngiM.,RubattoD.,DarlingJ.: ComplexdynamicsintheSesiaZonesubductionsystemdeducedfrommultiplegenerationsofwhitemicaandallanite:thepowerofmicrotexturalanalysiscombinedwithpetrochronology
2.29 SerneelsV.:ThousandYearsofmassiveIronProductionintheDogonCountry(Mali,WestAfrica):Technology–Economy-Environment
2.30 SkopelitisA., SchalteggerU.,UlianovA.,BrackP.: TheAdamellobatholith (Italy): a fossilmagmachamberoraccumulationofmagmapulses?
2.31 SoulignacR.:MineralogicaltechniquesandethnoarchaeologyappliedtothestudyofsmithingslagsinMali(Africa)
2.32 TămasC.G.,MunteanuG.,CauuetB.,MutG.:MiningarchaeologicalstudiesinEasternPyrenees,France:Baillestavyironminingarea
2.33 Thierrin-MichaelG.:FossiliferouspotteryinAjoie(NWSwitzerland)andadjacentregionsfromLaTèneandGallo-romansites:Informationonproductionanddistributionthroughmicroscopicandchemicalanalyses
2.34 TrittschackR.,GrobétyB.:Insightsintothedehydroxylationkineticsoflizarditeandchrysotile
2.35 VerberneR.,UlmerP.,MüntenerO.:Calculatingrheologicpropertiesofmagmasfromfieldobservationscombinedwithexperimentaldata.
2.36 VilsF.,ElliottT., Smith-DuqueC.E.,AltJ.C.,TeagleD.:Howlongdoesseawaterandoceaniccrustinteract?
2.37 von Allmen K., Böttcher M.E., Samankassou E., Nägler T.F.: Barium isotope fractionation in natural bariummineralsandprecipitationexperiments:Afirstglimpseattheglobalbariumcycle
2.38 WestermannS.,SteinM.,MateraV.,FietN.,AdatteT.,FöllmiK.B.:PalaeoredoxchangeduringOAE1a:newinsightsfromphosphorusandredox-sensitivetraceelements
2.39 WongfunN.,FurrerG.,BrandlH.,PlötzeM.:InfluenceofextrinsicweatheringfactorsonmineraldissolutioninDammaglacierforefield
2.40 ZurfluhF.J.,HofmannB.A.,GnosE.,EggenbergerU.:Water-solublesaltsandtemperaturevariationinmeteoritesrecoveredinthehotdesertofOman
60Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.0
Approchemicrothermométriquepourladéterminationdel’originehyd-rothermaldefluideminéralisateurdugisementàPb-(Zn)-Sr-Bad’ElAguiba(Tunisieseptentrional)
RiadhABIDI1,NajetSLIM-SHIMI2,NouriHATIRA3,ChrisitianMARIGNAC4,DominiqueGASQUET5,ZouhairMEJRI1
1 Faculté des sciences de Bizerte, département de géologie, Jarzouna-Bizerte.7021. Tunisie. ([email protected])2 Faculté des sciences mathématiques, physiques naturelles de Tunis. Campus Universitaire. 1060 Tunis. Tunisie.3 Faculté des sciences de Gabes (Faculté des Sciences de Gabès, Cité Riadh, Zirig 6072 Gabès)4 Ecole Nationale Supérieure des Mines de Nancy, Parc de Saurupt, 54042 Nancy, France.5 Université de Savoie – CISM Laboratoire EDYTEM Bâtiment Belledonne Campus de Technolac 73370 LE BOURGET DU LACLegîted’ElAguibareprésentel’undesplusimportantsgîtesdelazonedesf lyschs.IlestsituésurlabordureorientaledumassiftriasiqueduJebelHamra.CeTriasfaitpartiedeslamestriasiquesextrusiveslelongdel’accidentGhardimaou–CapSerrat(DécrochementsenestreorientéNE-SW),etformeavecdesterrainsargilocarbonatésd’âgecrétacés-paléocène(UnitéEdiss),unefenêtretectoniquedansl’unitéNumidienne(argilo-gréseused’âgeoligocènesupérieur-miocèneinférieur).
Lecorpsminéralisé,constituéd’unebrècheargilo-dolomitique,estsituédanslazonedebroyageentreleTriasquirepré-senteletoitdugîteetlepaléocènequireprésentelemurdugîte.Laminéralisationestdiscordanteparapportàlarocheencaissanteetseprésentesousplusieursformes:cimentdesbrèchesdedissolution,remplissagedesfracturesetdesca-vitésdedissolutiondanslesbancsdedolomienoired’âgetriasiqueetremplacementdelarocheencaissante(dolomied’âgetriasique).Cegisementprésenteuneparagenèsesimplecomposéeparlagalène,lasphalérite,lamarcasiteetlapyritequisontaccessoirementprésentsavecuneganguereprésentéeparlacélestite(gangueprincipale),labarytine,lacalciteetlequartz.
Lesmesuresmicrothermométriques,réaliséesessentiellementdansdesinclusionsprimairesetsecondairesbiphasées(li-quide+vapeur)danslacélestiteetlacalcitedugîted’ElAguiba,ontétéeffectuéessuruneplatinechauffanteréfrigéran-tedetype«LinkamMDS-600®»
1.CélestiteLasalinitéduf luidecontenudanslesinclusionsf luidesprimairesbiphasées,estcompriseentre5.41-10.36%poidséq.NaClavecunemoyennede8.13%poidséq.NaCl.Pourlesinclusionsf luidessecondairesbiphaséeslasalinitévarieentre5.56et15.96%poidséq.NaClavecunmaximumdefréquencevers8à9%poidséq.NaCl.Lacompositionduf luideenCaCl2contenudanslesinclusionsprimairesetsecondairesbiphaséesvarieentre0et3.4Wt%.CaCl2;tandisquelacompositionduf luideenNaClcontenudans les inclusionsprimairesetsecondairesvarieentre5et12Wt.%NaCl.Latempératured’homogénéisationduf luidecontenudanslesinclusionsprimairesbiphaséesvarieentre149et230°Cavecunemoyennede184°C.Pourlesinclusionssecondairesbiphasées,latempératured’homogénéisationvarieentre130et230°Cavecunetempératuremoyennede174°C.Lef luideaunedensitémoyennede1.03etunepressionmoyennede190.71bars.Lavari-ationduchangementd’étatdesphasesd’uneinclusionbiphaséedanslacélestiteestrésuméedanslafigure.1.
2.CalciteLesinclusionsf luidesprimairesbiphaséesmontrentunesalinitéquivarieentre4.03%et10.36%poidséq.NaClavecunemoyenne de 6.7 % poids éq. NaC, une composition moyenne en CaCl2 de 2.6 wt. % CaCl2 et une températured’homogénéisationquivarieentre151°et225.7°Cavecunemoyennede178°C.Danslesinclusionssecondaires,lasalinitémoyenneestde7.4%poidséq.NaCletlatempératured’homogénéisationvarieentre130.7°et240.1°Cavecunemoyennede177°C.Lef luideaunedensitémoyennede1.03etunepressionmoyennede200.34bars
Lef luideminéralisateurdugîted’ElAguibacorrespondraitdoncaunmélangeàtendanceadiabatiquedeplusieursf luideschaudsdedifférentesorigineshydrothermalesoùlatempératurerésulteseulementdumélangedef luidessanséchangedechaleuraveclarocheauxalentours.Lef luidecontenudanslacélestiteetlacalcitemontreunesalinitémoyenneàfaibleetunetempératureélevéeetvariable.Cef luideseraitunmélangedesaumuresdubassinavecunf luidemagma-tique-météorique.
Figure1.Evolutionduchangementd’étatd’unel’inclusionf luideprimairebiphasée(L+V)danslecélestitedugîted’ElAguibaaucours
ducycledecongélation.(Tctempératuredecongélation,TitempératurededébutdefusiondelaglaceetTmtemperaturedefindefu-
siondelaglace).
61
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.1
TectonometamorphicevolutionoftheWudangComplex(centralChina)
BaderThomas1,FranzLeander1,deCapitaniChristian1,RatschbacherLothar2,HackerBradleyR.3,WeiseCarsten2,PoppMichael2
1 Mineralogisch-Petrographisches Institut, Universität Basel, CH-4056 Basel ([email protected])2 Institut für Geologie, Technische Universität Bergakademie Freiberg, D-09599 Freiberg3 Geological Sciences, University of California, Santa Barbara, CA-93106
Located in the Paleozoic-Mesozoic Qinling-Dabie-Sulu-belt in central China, the Wudang Complex is composed ofNeoproterozoicsiliciclasticmeta-sedimentsandmarbleswithintercalatedacidicandbasicmeta-volcanicsandisoverlainbyCambrian-Ordovicianlimestonesanddolomites.DuringtheTriassiccollisionoftheYangtzeandtheSino-Coreanplates,theWudangComplex,whichbelongstothesubductedYangtzeplate,underwentahighpressuremetamorphism.Thisstudy investigates thismetamorphic overprint combining thermodynamicmodelingusing theDOMINO-THERIAKpro-grams(deCapitani&Petrakakis2010)withconventionalgeothermobarometry.
Felsicgneisssample76017AfromthecentralpartoftheWudangComplex,displaysthepeakmetamorphicassemblagegarnet–albite–phengite–biotite–quartz–rutile.BasedongarnetcorecompositionandtheSi-contentofphengite,DOMINOmodeling (MnTNCKFMASHsystem,excessH2O)yields510°Cat1.2GPamost likelyrepresenting thepressurepeakofthePTpath.Identicalresultswereobtainedfromgarnetgneiss76032Ctaken~30kmfurthernorth.Thematrixofanothergarnetgneissfromthesameoutcropshowsaretrograderecrystallizationtostilpnomelane,albite,quartz,andminorclinozoisitepointingtoalateoverprintat~320°Cand>0.3GPa.
SeveralmetabasicschistsfromWudang’snorthernpartdisplaytheassemblagechlorite–phengite–amphibole–epidote–albite–quartz–titanite.Amphibolesarebluishmagnesioriebeckite/winchiteorpalegreenactinolite.PhengitehashighSi-contentsof3.4-3.5p.f.u.Basedonchlorite-phengite-quartzequilibria(Vidaletal.2005;Dubacqetal.2009)metamorphicconditionsof280-330°Cat0.5-0.8GPawerederived.Phengite’sSip.f.u.-isoplethscalculatedwithDOMINOpointtopres-sures of 0.7-0.8GPa at these temperatures.Discretedomains of stilpnomelane– calcite –phengite – chlorite – schist753011Apreservedrecordsofanearlymetamorphic stageat250-320°Cat0.5-0.9GPawhileotherdomainspoint toasubsequentoverprintat400-420°Cand0.5GPa.
Thesepetrologicaldatahighlightthehigh-pressureblueschisttogreenschistfaciesmetamorphicoverprintoftheWudangComplexduringthesubductionoftheleadingedgeoftheYangtzeplate.Thecentralpartwasburiedtogreaterdepthsalthoughthesamegeothermalgradientof~12°C/kmis,withinerrorsofgeobarometry,alsoappropriateforthelow-grademetamorphicnorthernpart.Ar/ArdatingofamphibolesandKwhitemicas(Mattaueretal.1985;Ratschbacheretal.2003)demonstratethatthishappenedintheLateTriassic.Duringsubduction,theWudangformedacontinuousportionofthedowngoing slab and, during exhumation,was delaminated and imbricated along south-directed thrust faults (Huang,1993).
Thecriticalassemblagestilpnomelane–albite–clinozoisiteinsample76032Dindicates,thattheexhumationofthecen-tralpartoccurredratherfast,asthestabilityofstilpnomelaneisindicativeforelevatedpressuresattemperaturesbelow~320°Cwhilethenorthernpart,atleastlocally,underwentamedium-pressureoverprintat~400°Cand0.5GPa.
REFERENCESDeCapitani, C.& Petrakakis, C. 2010: The computation of equilibrium assemblage diagramswith Theriak/Domino
software.Am.Mineral.95,1006-1016.Dubacq, B.,Vidal,O.&DeAndrade,V. 2009:Dehydrationof dioctahedral aluminousphyllosilicates: thermodynamic
modellingandimplicationsforthermobarometricestimates.Contrib.Mineral.Petrol.159,159-174.Huang,W.1993:Multiphasedeformation anddisplacementwithin abasement complexon a continentalmargin: the
WudangComplexintheQinlingOrogen,China.Tectonophysics224,305-326.Mattauer,M.,Matte,P.,Malavieille,J.,Tapponnier,P.,Maluski,H.,Xu,Z.Q.,Lu,Y.L.&Tang,Y.Q.1985:Tectonicsofthe
Qinlingbelt:build-upandevolutionofeasternAsia.Nature317,496–500.Ratschbacher,L.,Hacker,B.R.,Calvert,A.,Webb,L.E.,Grimmer,J.C.,McWilliams,M.,Ireland,T.,Dong,S.&Hu,J.2003:
Tectonics of the Qinling Belt (Central China): Tectonostratigraphy, geochronology, and deformation history.Tectonophysics366,1-53.
Vidal,O., Parra, T.&Vieillard, P. 2005: Thermodynamic properties of the Tschermak solid solution in Fe-chlorites:applicationtonaturalexamplesandpossibleroleofoxidation.Am.Mineral.90,347-358.
62Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Figure1.SummaryofthemetamorphicevolutionoftheWudangComplex
2.2
ReconstructionofNeogenepaleoelevationandpaleoclimaticconditionsoftheEuropeanAlpsandthecircum-Alpineregionbystableisotopeanalyses
BauerKerstin1,2,VennemannTorsten1,MulchAndreas2
1 Institut de Minéralogie et Géochimie, Anthropôle, Université de Lausanne, CH-1015 Lausanne, Switzerland ([email protected]) 2 Institut für Geologie, Leibniz Universität Hannover, Callinstr. 30, 30167 Hannover, Germany
Thestableisotopecompositionofoxygenandhydrogeninrainwatercorrelateswiththeairtemperatureandwiththealtitudeofprecipitation.Ifmeteoricwateristakenupintothestructureofmineralswithaknownwater-mineralfractio-nationfactor,itispossibletodetermineitsoriginald18OanddDvaluesandtherebytheformeraltitudeofprecipitationfrommeasurementsoftheisotopiccompositionofthehostmineralandknowledgeoftheambienttemperaturecondi-tions(e.g.Mulchetal.2004).
ThisstudywillapplythisapproachtoMioceneprecipitationinthecircum-Alpineregionviatheanalysesofhydrousclayminerals (e. g.Mulch& Chamberlain 2007). Previous paleontological and geochemical analyses of fossils (e.g. Janz&Vennemann2005,Kocsisetal.2009),fromthesamesamplestobeusedfortheclaymineralanalysiswillhelptoconstrainthepaleoclimaticconditionsthatexistedduringtheformationoftheclaysduringtheMiocene.ThecombinationofthemarinepaleoclimaticaswellasotherterrestrialfossilrecordswiththedetritalrecordoftheclaysmayallowestimatesonthechangesinelevationoftheAlpineregionduringorogenesis.
Measuredd18Ovaluesofbetween15.4and21.2‰,suggestthattheclayswereformedinthepresenceofmeteoricwaterthathadacomparableisotopiccompositiontothatofmodernwaterintheAlpineregionandattemperaturesofforma-tionthatcorrespondtotypicalsurfacetemperatures.
However,thetreatmentofthesamplematerialischallengingduetoitsextremelysmallgrainsizeandhygroscopicbeha-vior,whichmakesthedDvaluesdifficulttointerpret.Atrendtolowervaluesforsmallergrainsizefractionshintstopossiblecontaminationoramixof several components.XRDanalyses showthat the separatesdonotconsistofpuresmectite,butavaryingmixtureofsmectiteandilliteandalsomixed-layerminerals,whichmayalsofalsifythevaluesobtained.Furthertestsandexperimentstoinvestigatethesepossibilitiesareinprogress.
Furthermore,newsamplematerialwillbecollectedtofillthegapsbetweentheexistingdata.Drillcoresormoredetailedprofileswouldgivebetterconstraintsonthetemporalandspatialdistributionoftheresults.Inaddition,samplesfrom
100 200 300 400 500 600Temperature [°C]
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Pres
sure
[GPa
]
Central + North-central Wudang
NorthernWudang
76032C76071A
76022B
76053A
76057A
760210A753011A
753011A
63
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
alteredvolcanicmaterialsuchasbentonitesmayprovidebetterabsoluteageconstraintscomparedtothepresentapproachofusingbiostratigraphyofindividuallyplacedsamplelocalities.Materialwithahighercontentofclaywillbeofadvantagetoachieveahigheryieldforthesamplepreparationandwillpossiblylimitsomeofthecontaminatingeffects.
AnotheraspectoftheresearchprojectwillinvolvetheinvestigationofrecentlyformedAlpinesoilsatdifferentaltitudes.The isotopecompositionof theclaysize fractionwillbe investigated incombinationwithprecipitationandsoilwaterisotopecompositioninordertostudythedirectinteractionofmeteoricwaterwiththemineralsduringsoilformation.
REFERENCESJanz,H.&Vennemann,T.W., 2005: Isotopic composition (O,C, Sr andNd) and trace element ratios (Sr/Ca,Mg/Ca) of
MiocenemarineandbrackishostracodsfromNorthAlpineforelanddeposits(GermanyandAustria)asindicatorsforpaleoclimate.Palaeogeography,Palaeoclimatology,Palaeoecology225(2005),216-247.
Kocsis, L.,Vennemann,T.W.,Hegner,E., Fontignie,D.,&Tütken,T., 2009:ConstraintsonMioceneoceanographyandclimate in theWestern andCentral Paratethys:O-, Sr-, andNd-isotope compositions ofmarine fish andmammalremains.
Palaeogeography,Palaeoclimatology,Palaeoecology271(2009),117-129.Mulch,A., Teyssier, C., Cosca,M.A.,Vanderhaeghe,O.,&Vennemann, T.W., 2004:Reconstructingpaleoelevation in
erodedorogens.Geology32,6(2004),525-528.Mulch,A.&ChamberlainC.P.,2007:StableIsotopePaleoaltimetryinOrogenicBelts–TheSilicateRecordinSurfaceand
CrustalGeologicalArchives.ReviewsinMineralogy&Geochemistry66(2007),89-118.
2.3
ZirconU/PbdatingoftheLateCarboniferousZervreilaOrthogneiss,AdulaNappe.
MattiaCavargna-Sani1,Jean-LucEpard1,FrançoisBussy2&AlexeyUlianov2
1 Institut de Géologie et Paléontologie, Université de Lausanne, Bâtiment Anthropole, 1015 Lausanne ([email protected])2 Institut de Minéralogie et Géochimie, Université de Lausanne, Bâtiment Anthropole, 1015 Lausanne
TheZervreilaOrthogneissisoneofthedominantlithologiesofthenorthernAdulaNappe(Jennyetal.1923).However,theageofmagmaticemplacementofthisrockwasneverdeterminedprecisely.Thisageisimportanttobetterunderstandthelithologies(lithostatigraphy)andthegeometryoftheAdulaNappe.
GeochemicaldatashowthattheprotolithoftheZervreilaOrthogneissisaSi-richgranite.Zirconsfromthisorthogneissformaveryhomogeneouspopulation. Inheritedcoresandevidencesofmetamorphicgrowthareabsent.AccordingtoPupinclassification(1980),thesearemainlyP-typezirconssimilartozirconsfoundinalkalinegranitesfromextensionaltectonicenvironments.WehavedatedthezirconsfromtheZervreilaOrthogneissbyLA-ICPMSusinganElementXRsec-tor-field instrument interfacedtoanUP-193excimerablationsystem.A5Hzrepetitionrateandanon-sampleenergydensityof2-2.4J/cm2wereappliedtominimisethelaserinducedfractionation.AGJ-1zirconwasusedasaprimarystan-dard.Analyseswereperformedonoscillatorymagmaticgrowthzonesrecognisableincathodoluminescenceimages.
SamplesdatedcomefromfourlocalitiesinthenorthernAdulaNappe:ValScaradra,Zervreila,andtwocloselysituatedoutcropsfromZapport.TheU/Pbagesofthesesamplesarelargelyconcordant;the206/238agevaluesare296.10(+2.90-1.80)Ma,291.20(+8.10-3.00)Ma,288.65(+3.25-4.75)and293.60(+3.90-2.00)Ma,respectively.Withintheanalyticalerror,thesefouragesareinterpretedtoresultfromthesamemagmaticeventandtocorrespondtotheintrusiontimeofagra-niticbody,probablyemplacedwithintheAdulaparagneissesinthelateVariscanpost-orogeniccontext.
REFERENCESJenny,H.,Frischknecht,G.&Kopp,J.1923:GeologiederAdula.Beitr.Geol.KarteSchweiz(N.F.)51,1-123.Pupin,J.P.1980:Zirconandgranitepetrology.ContributionstoMineralogyandPetrology73,207-220.
64Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.4
Effectsofdeviatoricstressonnaturalfluidinclusionsinquartz:anexpe-rimentalstudy
DiamondLarrynW.,1TarantolaAlexandre1,StünitzHolger
1 Rock–Water Interaction Group, Institute of Geological Sciences, University of Bern, Baltzerstrasse 3, CH-3012 Bern, Switzerland ([email protected])2 Department of Geology, University of Tromsø, Dramsveien 201, 9037 Tromsø, Norway
Fluidinclusionsinquartzareknowntomodifytheirshapes,texturesanddensitiesduringsheardeformation.Modificationsofchemicalcompositionarealsosuspected.However,suchchangeshavenotbeenexperimentallydemonstrated, theirmechanismsremainunexplained,andnocriteriaareavailabletoassesswhetherdeformedinclusionspreserveinformati-ononpaleofluidpropertiesandpaleostressconditions.
Toaddresstheseissues,quartzcrystalscontainingnaturalCO2-H2O-NaClf luidinclusionshavebeenexperimentallysub-jectedtodeviatoricstressesof90–250MPaat700°Cand~600MPaconfiningpressure.Strainsofupto1%causethein-clusionstodevelopirregularshapes(Fig.1,2a)andtogeneratemicrocracksincrystallographicplanesorientedsubperpen-dicular to themajor compression axis,s1. The uniform alignment of themicrocracks imparts a planar fabric to thesamples(Fig.1b).Inclusionexpansionduetomicrocrackingreaches20%,producinglowfluiddensitiesthatbearnorela-tiontophysicalconditionsoutsidethesample.Nevertheless,thecompositionoftheprecursorinclusionsispreserved(Fig.2b).Themicrocrackshealandformswarmsoftinysatelliteinclusionswithawiderangeofdensities,thehighestreflec-tingthestressvalueofs1.Thesenewinclusions loseH2Oviadiffusion,therebypassively increasingtheirsaltandgascontents,andtriggeringplasticdeformationofthesurroundingquartzviaH2O-weakening.Consequently,thequartzsam-plesdeformplasticallyonlyindomainsoriginallyrichininclusions.
Thisstudyshowsthatf luidinclusionsdeformedbydeviatoricstressesmayrecordinformationonpaleostressesandonpre-deformationf luidcomposition,andthattheyplayakeyroleinfacilitatingcrystal-plasticdeformationofquartz.
Figure1.Summaryandnomenclatureofshapechangesaccompanying~1%plasticstrain.Viewlookingdowns1.
a
Figure2a.Shapechangesaccompanying~1%plasticstrain:Exampleviewlookingdowns1
65
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
b
Figure2b.Shapechangesaccompanying~1%plasticstrain:Exampleviewlookingperpendiculartos1.
Figure3.Compositionalchangesaccompanying~1%plasticstrain.
REFERENCESDiamond, L.W., Tarantola,A.& Stünitz,H., 2010:Modification of f luid inclusions in quartz by deviatoric stress II:
Experimentally induced changes in inclusion volumeand composition.Contributions toMineralogy andPetrologyDOI10.1007/s00410-010-0510-6.
Tarantola,A.,Diamond, L.W.& Stünitz,H., 2010:Modification of f luid inclusions in quartz by deviatoric stress. I:Experimentallyinducedchangesininclusionshapesandmicrostructures.ContributionstoMineralogyandPetrologyDOI10.1007/s00410-010-0509-z.
2.5
U–PbgeochronologyofanorthogneissdiscoveredwithintheHP–LTmetamorphicrocksoftheIledeGroix,ArmoricanMassif,France
ElKorhAfifé1,SchmidtSusanneTh.1,BallèvreMichel2&BruguierOlivier3
Département de Minéralogie, Université de Genève, Rue des Maraîchers 13, CH-1205 Genève, Suisse ([email protected], [email protected])2 Géosciences Rennes (UMR CNRS 6118), Université de Rennes 1, Campus de Beaulieu, F-35042 Rennes Cedex, France ([email protected])3 Géosciences Montpellier (UMR CNRS 6250), Université de Montpellier 2, Place Eugène Bataillon, F-34095 Montpellier Cedex 05, France ([email protected])
Forthefirsttime,analbiticorthogneisshasbeenrecognisedanddatedwithintheHP–LTblueschistfaciesmetabasitesandmetapelitesoftheIledeGroix.Itispartoftheremnantsofanaccretionarycomplexformedaftersubductionandexhumationofanoceaniccrustand itssedimentarycover (Bernard-Griffithsetal.,1986).TheHP–LTevent (blueschist
66Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
facies)isdatedat358–365Mawiththe40Ar/39Ar(phengite)andRb–Sr(wholerock,phengiteandepidote)methods(Bosseetal.,2005).Thealbiticorthogneissoccursas40cmthicklayerswithinHP-LTmetapelitesandiscomposedofanassemblageofalbiticplagioclase, perthitic porphyroclasts of K-feldspars, quartz, phengite, epidote rimmingmetamict allanite, and garnet.Accessorymineralsconsistoftitanite,apatiteandzircon.Themajorelementcompositioncorrespondstothatofperalu-minousleucogranites,characterisedbyveryhighcontentsofSiO2(75.5wt%),lowCaOcontents(1.7wt%)andhighA/CNKratios(1.5).The[FeOt/(FeOt+MgO)]ratioishigh(0.8).ThetraceelementcompositionoftheorthogneissdisplayshighLILE,ThandUcontents,MORB-likeHREEabundancesandmoderateNbandYvalues.Despitetheperaluminousorogenicsignature,thechemicalcompositionofthestudiedorthogneiss,aswellasthepresenceofaccessoryallanite,apatite,tita-niteandzirconindicateawithin-plateanorogenicoravolcanicarcorigin.TitaniteandzirconweredatedbyLA-ICPMS,attheUniversitiesofMontpellierandLausanne,respectively,bothusinganElementXRspectrometer.Titanite(40to200μm)wasanalysedin-situinthinsections.Zircons(25to100μmlong)wereextractedandseparatedfollowingtheconventionalmineralseparationproceduresusinggravimetricandmagneticme-thods.TitaniteandzirconU–PbdataarerepresentedtogetherinaTera-Wasserburgdiagram(Fig.1).Nocommonleadcorrectionwasapplied.ThedatadefineaConcordiainterceptat480.9±3.1Ma,withaMSWDof12,interpretedastheageofthemagmaticemplacementduringtheearlyOrdovician.Additionalzircongrainsyield lateNeoproterozoic (i.e.Cadomian)206Pb–238Uages[546.6–606.0Ma]. TitaniteandzirconU–PbagesindicatethatthefelsicmagmatismfromtheIledeGroixiscontemporaneouswiththegranitictorhyolitic,pre-orogenicplutonismwidelyrecognizedintheinternalzonesoftheVariscanbelt,relatedtotheOrdoviciancontinentalrifting.ThiseventledtotheopeningoftheRheicandGalicia-SouthernBrittanyoceans,andtothedetachmentofthemicrocontinentArmoricafromGondwana.Themagmaticprotolithprobablyinheriteditsspecificchemicalcompositionfromacombinationoforogenicandanoro-genicsignaturesduetopartialmeltingoftheCadomianbasementduringgraniteemplacementinacontinentalriftingenvironment.
Figure1.Tera–WasserburgplotsfortitaniteandzircongrainsfromorthogneissGROA115a.(a)Alldata,(b)titanites,(c)zircons.
REFERENCESBernard-Griffiths, J., Carpenter,M.S.N., Peucat, J.-J.& Jahn, B.M. (1986).Geochemical and isotopic characteristics of
blueschistfaciesrocksfromtheIledeGroix,ArmoricanMassif(northwestFrance).Lithos19,235–253.Bosse,V.,Feraud,G.,Ballèvre,M.,Peucat, J.-J.&Corsini,M. (2005).Rb-Srand 40Ar/39Arages inblueschists fromthe Ilede
Groix(ArmoricanMassif,France):Implicationsforclosuremechanismsinisotopicsystems.ChemicalGeology220,21–45.
67
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.6
Pre-AlpinemetamorphismintheclassicalAlpinestaurolite-garnetschistofCampolungo
JörgHermann1,2&DanielaRubatto1,2
1 Research School of Earth Sciences, The Australian National University, AU-0200 Canberra ([email protected])2 Present Address: Institute of Mineralogy and Geochemistry, Université de Lausanne, Anthropole, CH-1015 Lausanne
TheCampolungoarea,Ticino,representsoneoftheclassicalareaswhereAlpinemetamorphism,structureandtectonicshavebeeninvestigated.Theareaexposesawell-preservedMesozoicstratigraphy(Bianconi,1971)rangingfrombasalquart-zitestodolomites(presumedTriassicdepositionage)toBündnerschiefer(presumedJurassicdepositionage).ThissequenceshowsaseriesofoverprintingAlpinestructures(Gruijc&Mancktelow,1996)andassociatedmetamorphismreachesam-phibolitefaciespeakconditions(~6.5kbaratthethermalpeakof~600°C;Todd&Engi,1997).,Staurolite-garnetschistsoutcropstratigraphicallybelowthequartzites.TheschistsdisplayacomparablestructuralandmetamorphicevolutiontotheMesozoicrocksandthushavebeeninterpretedaslatePaleozoicclasticsedimentsthatweremetamorphosedduringtheAlpineorogeny.
We investigated indetail staurolite-garnetschists inthevicinityof theCapannaLeit.Thesamplesconsistofphengite,quartzandfine-grainedgraphite,markingapenetrativefoliationthatisalsorefolded.Asecondgenerationofphengiteispresentintheaxialplanecleavageofthecrenulation.Garnetoccursasporphyroblasts,partlyovergrowingthefoliation.Staurolitealsoformspostkinematicporphyroblasts.Latebiotitef lakesoverprintthemainfoliation.Rutilecoresareover-grownbyilmenite,andaccessorytourmaline,monaziteandzirconaredispersedthroughoutthesamples.Especiallyingraphiterichrocks,monazitecontainsorientedgraphiteinclusionsprovidingevidencethatmonaziteformedsyntopost-kinematictothemainfoliation(Fig.1).
MonazitegrainswereseparatedforSHRIMPdatingfromtwostaurolite-garnetschists.Despiteitstexturalposition,mona-ziteconsistentlyyieldedpre-Alpineagesof~330Ma,correspondingtotheknownVariscanmetamorphism.NotraceofAlpine(~30Ma)metamorphismwasfoundinmonaziteinthesesamples.ThisindicatesthatatleastpartofthefoliationintherocksisnotofAlpineageandthatthestaurolite-garnetschistsrepresentacrystallinebasementtotheMesozoicsediments.
Amultistageevolutionisalsopreservedinthegarnet.WhereasMn,FeandMgelementalmapsdonotshowanyzoning,theCa-mapdisplaysastrongdiscontinuityseparatingalarge,zonedgarnetcorefromasmall,homogenousrim.Thetran-sitionischaracterizedbyahighlyirregularsurfacethatcrosscutpreviouszoningandisenrichedinCa.ItisimportanttonotethatgarnetinthenearbyBündnerschiefer(thatexperiencedonlyAlpinemetamorphism)donotshowanyofthesefeatures.
TraceelementprofilesacrossthegarnetdisplayaYandHREErichcorewithmarkedtraceelementdepletiontowardstheintermediategarnetzone,typicalofprogradegrowthzoning.Phosphorousincreasessteadilyfromcoretotheintermedi-atezone.Atthediscontinuity,visibleintheCamaps,YandHREEincreasebyafactorof5,indicatingresorptionofpre-existinggarnet.Intherim,YandHREEdecreasedrasticallyagain,whileP,aftershowingasignificantdropattheinter-face,increasestovaluesobservedintheintermediategarnetzone.WeinterprettheseobservationsastheAlpineprogadegrowthofagarnetrimonapreviously,partlyresorbed,Variscangarnet.Thegarnetcorecontainsinclusionsofchloritoidandstaurolite,whereasonlystaurolitewasfoundinthegarnetrim.Therefore,thepetrographicobservations,majorele-mentmappingandtraceelementprofilesingarnetcombinedwiththedatingofmonaziteindicatethattheinvestigatedmica-schistsatCampolungoexperiencedstaurolite-garnetgrademetamorphismduringVariscanaswellasduringAlpinemetamorphism.
REFERENCESBianconi, F.,1971.Geologiaepetrografiadella regionadelCampolungo.BeiträgezurGeologischenKartederSchweiz,
vol.142.Kümmerly&Frey,Bern.Grujic,D.,&Mancktelow,N.S.,1996.StructureofthenorthernMaggiaandLebendunNappes,CentralAlps,Switzerland.
EclogaeGeologicaeHelveticae89,461–504.Todd,C.S.,&Engi,M.1997.MetamorphicfieldgradientsintheCentralAlps.JournalofMetamorphicGeology,15,513-
530.
68Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Figure1.Monazitecrystal(200µmlong)withinternalgraphitefoliationfromastaurolite-garnetschist.Theageofmonazitesinthis
sampleis~330Ma,indicatingthatpre-AlpinemetamorphismanddeformationispresentintheCampolungoarea.
2.7
Thermo-mechanicalreactivationoflockedcrystalmushes:melting-indu-cedinternalfracturationandassimilationprocessesinmagmas
HuberChristian1,BachmannOlivier2&DufekJosef1
1 School of Earth and Atmospheric Sciences, Georgia Institute Technology, Ferst drive 311, Atlanta, GA, USA ([email protected])2 Department of Earth and Space Science, University of Washington, Seattlle,
Thermalreactivationoflockedcrystalmushesintheuppercrustisafundamentalsteptowardstriggeringvolcanicerup-tionsofcrystal-richmagmas.Modelsofsuchreactivationeventsindicatethatpartialmeltingofthecrystallineframeworkisenergeticallycostlyandleadtoaveragecrystallinitiesthatarelowerthanthoseobservedinmanyeruptedcrystalmus-hes.Here,weshowthatinternaloverpressurizationofthemushinducedbysmallamountsofmelting(10-20%)breaksthecrystallineframeworkbymicrofracturationandallowsforefficientunlocking.Hence,thismelting-inducedoverpres-surization,enhancedbyadditionofgasinwetmagmaticsystems,playsanimportantroleingeneratingvolcanicdepositswithcrystal contents close to the rheological lock-up (~50vol%crystals)byaccelerating the incorporationofhighlycrystallinepartsofthemagmachamber(self-assimilation).Itcanalsoparticipateindisintegratingpiecesofcountryrockthatarecommonlyscavengedinmagmas,leadingtobulkassimilationofcrustallithologiesinshallowreservoirs.
69
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.8
Theinfluenceofferric/ferrousironratiosinbulkandmineralsofblue-schistsfromtheInnerMakran(SEIran)onthermobarometricrecalculations
HunzikerDaniela1,CaddickMark2,ReusserEric2,BurgJean-Pierre&MüllerElisabeth3
1 Geological Institute, Structural Geology and Tectonics, ETH Zurich, Sonneggstrasse 5, NO E69, CH-8092 Zurich ([email protected])2 Institute for Mineralogy and Petrology, ETH Zurich, Clausiusstrasse 25, CH-8092 Zurich3 Electron Microscopy ETH Zurich (EMEZ), HP D11, CH-8093 Zurich
Toreconstructsubductionparameterslikedepthofburialandsubsequentexhumationthethermobarometricconditionsofrecrystallizationofblueschistfaciesrockshastobewellconstrained.Calculations andmodels involve charge balance-based assumptions concerning the Fe3+/Fe2+ ratio ofmineral phases.However,theseratiosarepoorlyknownformostminerals,especiallyforsodicamphiboles.
We approach the problemby studying the petrography, geochemistry and thermobarometry of scarcely studied blue-schistsintheInnerMakranofSoutheastIran.Comparingmetamorphicpressureandtemperatureconditionscalculatedwithdifferentferric/ferrousironratiosofbulkandmineralsillustratesthestronginfluenceofthisratio.RecalculationsusingthetruebulkFe3+/Fe2+ratiooftheMakranblueschistsmeasuredbycolorimetrictitrationandanestimatedvaluefrommineralparagenesesdifferlargely.Thisisprobablyduetoinaccurateamphibolemodels,whichtendtoconsideratoo lowferric/ferrous ironratio.Usingelectronenergy-lossspectroscopy (EELS)quantitativeanalysesofallparageneticmineralphaseswillbeanalyzedandcross-checkedwithmicro-X-rayabsorptionnear-edgestructure(XANES)analysisandMössbauerspectroscopy.
Theresultsenteredintoamphibolemodelswillimprovepressure/temperaturerecalculationsofblueschist-faciesandotheramphibole-bearingmetamorphicrocks.
2.9
Subvolcanicmafictointermediatedike-systems:contraintsonpost-plu-tonicactivity(S-Adamello,N-Italy)
HürlimannNiklaus1,MüntenerOthmar1&UlmerPeter2
1 Institute of Mineralogy and Geochemistry, Anthropole, CH-1015 Lausanne, Switzerland ([email protected])2 Institute of Geochemistry and Petrology, Clausiusstrasse 25, CH-8092 Zurich, Switzerland
Variousscalesofdikegeometriesprovidearecordofstrainduringtheiremplacement.Distinctdikegenerationsmightrecordstrain-evolutionthroughtime.Inaddition,dikerocksaregenerallyclosetoliquidcompositions,inparticularma-ficcompositions,relativetoplutonicrocks.Herewepresentfieldevidenceofstructuralrelationshipsandfirstpetrologi-calandgeochemicaldatathatcharacterizetheevolutionofpost-batholithsubvolcanicmagmaticactivityduringcoolingofaplutonic-suiteintheSouthernAdamellomassif(Italy).
At least threedifferentgenerationsofmafic to intermediatedikesofpicrobasaltic toandesiticcompositionpostdateasuccessionoflargevolumeplutonemplacement(Schalteggeretal.2009,HansmannandOberli1991,DelMoroetal.1985).Early,partiallydeformeddikegenerationsappeartoreflectmorelocalstrainwhereaslateronesreflectamuchmorere-gionalstrainpatternthatappearstobeindependentofinterplutonicandwallrockcontacts.Subverticaldikesarecharac-terizedbycomposite,multiplestagetexturesandareoftenphenocryst/xenocryst-richwhereassubhorizontal typesarerelatedtosimpleronestageorpulseemplacement.
Subhorizontaltypesshowawiderangeofphenocrystphasessuchasolivine,clinopyroxene,amphiboleandplagioclase.Evolvedphasessuchasallanite-epidote,titanite,apatiteandzirconaremainlyassociatedwithmorefelsiczonesorbandswithinthedikes.Plagioclaseinthesefelsiczonesshowsalargerangeofcompositionalvariation.Suchfelsiczonesappeartorepresentevolvedliquidsegregationsfromratherclosedsystemfractionation(equilibriumcrystallization).
70Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Bulkrockgeochemistryandpetrographyindicateanevolutiontomoreevolvedmagmastowardsyoungergenerationsandpulses.Particularlythelaterdikegenerationscarryvariableproportionsofxenocrysticmaterial.Majorandtraceelementconcentrationsofbulkrocksindicatethataphyricdikemarginsinsinglepulsesystemsdisplayamoreevolved‘hydraulichead’followedbyatrailingthatismoreprimitiveindicatedbyincreasingcontentsofMgO,Fe2O3,CrandNifromthedikemargintowardsthecenter.
Wewillpresentmajorandtraceelementsoftheaphyric-matrixobtainedbyLaser-Ablation-ICP-MS,todetermineactualliquidcompositionsandtotestequilibriumwithrespecttozonedphenocrysts.Wewillprovideconstraintsoncontamina-tionanditssourceswithquantitativeestimatesonxenocrystcontentinindividualsampleswithregardtodikesormagmapulsesthatshowlessornocontamination.Particularwellestablishedcompositionalzoningpatternsinclinopyroxene-phenocrystswillfurtherallowapplicationofrespectivegeospeedometerstoconstrainreservoirresidencetimeswithre-gardtocationinterdiffusion(Chakrabortyetal.2008).
REFERENCESChakraborty, S., Dohmen, R.,Mueller, T., Beaker,H.W.& TerHeege, J. 2008: Fe-Mg interdiffusion coefficients in
clinopyroxene:experimentaldeterminationsusingnanoscalefilms.AGU,FallMeeting2008,abstract#MR21C-04.DelMoro,A.,Pardini,G.,Quercioli,C.,Villa,I.M.&Callegari,E.1985:Rb/SrandK/ArchronologyofAdamellogranitoids,
SouthernAlps.MemoriedellaSocietàGeologicaItaliana,26,261-284.Hansmann,W.& Oberli F. 1991: Zircon inheritance in an igneous rock suite from the southernAdamello batholith
(ItalianAlps).ContributionstoMineralogyandPetrology,107,501-518.Schaltegger, U.,Brack,P.,Ovtcharova,M.,Peytcheva,I.,Schoene,B.,Stracke,A.&BargossiG.2009:Zirconandtitanite
recording1.5millionyearsofmagmaaccretion,crystallizationand initialcooling inacompositepluton (southernAdamellobatholith,northernItaly).EarthPlanetaryScienceLetters,286,108-218.
2.10
ThepigmentsofthemedievalpaintersinFribourg:InvestigationofatopqualitymuralpaintingfromtheCordeliersChurchinFribourg.
IldikoKatona&VincentSerneels
Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg ([email protected])
Duringthe80’s,thousandsoffragmentsofmuralpaintingdatingbacktothelatemedievalperiod(15thcenturyAD)werefoundduringrestorationworksinthechurchoftheCordeliersinFribourg.For25years,theyremainunexploitedattheArchaeologicalServiceofFribourguntiltheirextraordinaryestheticqualitywasrecognized.
Since2009,aninterdisciplinaryteamofresearchershasbeensetupandtheprojecthasbeensupportedbytheSNF.Itincludesthereconstructionoftheentirescene-20’000fragments-(S.Garnerie),thearthistorical(B.Pradervand,J.Bujard)andthetechnicalstudies(J.James,V.Serneels,I.Katona).Theaimofthisstudyistheidentificationofthematerials(pig-ments,binders,supports)andthedescriptionofthepaintingtechnique.
Chemical (XRF)andmineralogical (XRD)analysesareusedtogetherwithmicroscopicalobservationsofthesurfaceanddispersedpowdermicroscopyfortheidentificationofcomponents.Asthismajorworkofart isalreadyfragmented, itoffersonexceptionnalopportunityforthesystematicalsamplingofthewholepaintedlayerandtheproductionofnu-meroussmallpolishedsections.ThismakespossibletheuseofSEMasamajormethodofinvestigation.Ontheotherhand,theburialofthefragmentsunderthegroundinsidethechurchallowsaverygoodpreservationofthefragilepaintedlayer.
Themedievalartist,stillunidentified,wasusingalargevarietyofmineralpigments,includinghighqualityones,likeredcinnabar,blueazurite,artificialSn-Pbyellowandevengold.Histechniquewashighlysophisticatedwithpigmentsmix-turesfortheproductionofspecificshadesandsuperpositionoflayerstoobtaincomplexvisualeffects.Firstmineralogicalresultsonthismaterialwillbepresented.
71
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.11
Combustionanalysisofameteoritedebris
KayaniSaheeb-Ahmed
National University of Sciences and Technology, H-12, Islamabad-44000, Pakistan ([email protected])
AmeteoriteablationdebrishasbeenidentifiednearvillageLehri(33°09’09”N;73°33’35”E)indistrictJhelum,PakistanbyKayani(2009).Inthisresearchstudy,totalcarboncontentofthemeteoritedebrishasbeendeterminedandthisabundancehasbeencomparedwithvaluesreportedinliteraturetoidentifytheoriginsoftheparentbodyofthismeteoritedebris.
Carbonisoneofthemostimportantelementsinnature.Itcanexistinmanystableformsandthechemicalstructureofcarbonaceousmatterdependsuponavailable environmental conditions.Theabundance, compositionand structureofcarboncanbeanalyzedtogatherinformationabouttheinitialformationprocessandfollowingenvironmentalchangestothecarbonaceousmatter(Muraeetal.1993).Incarbonrichchondrites(stonymeteorites),carbonaceousmatterhasbeenidentifiedasgraphite,amorphous,kerogen-like,insomecasesdiamond,andmostlyasastructurallyunclearinsolublehighmolecularorganiccompound.Inironandstony-ironmeteorites,carbonisfoundasgraphiteorlessorderedgraphiticmatter(Muraeetal.1993;Swartetal.1983;Amarietal.1990).
In lightoftheabove, itseemsthatcarbonabundancecanserveasausefulclueto identifythenatureandoriginofaparticularmeteorite.Furthermoreitcanalsobeusedtodetectalterationsinthestructureoftheoriginalmatter(ofthemeteorite)dueto impactsorcollisionsetc.Forthemeteoritedebrisunderstudy,throughXRDanalysismagnetiteandwustitehavebeendetectedaspredominantironphases(Kayani2009).Presenceofwustiteshowsareducingenvironmentwhichmayhaveexistedeitherduetocollisionoftheparentbodywithanothercelestialobjectorduetohighpressureandtemperaturecausedbyresistancefromtheatmosphereofearth.Asthemeteoritedebrishasbeenfoundlyingoverthesiteinformofsmallstones,itseemsonentryintoearth’satmosphere,theparentmeteoroidsuccumbedtoincreasin-glyhighpressureandtemperatureandatacertainheightexplodedintoinnumerablesmallpiecesthatcametorestonthisparticularsite.Thiskindofbehavioristypicallyobservedwithchondritesastheyaremorevulnerabletohighpres-sureandtemperatureeffectsduetotheircompositionandstructure.
Inordertodeterminetheabundanceofcarbonandsulphurinthemeteoritedebris,aspecimenwastestedthroughcom-bustion analysis using the facilities at Petroleum Geochemistry Laboratory of Hydrocarbon Development Institute ofPakistaninIslamabad.Incombustionanalysisofmeteorites,carbonisreleasedoverthreedifferentheatingranges.Recentcontaminantsaredetectedbelow500°Cwhileweatheringproducts(i.e.carbonates)decomposearound1000°C.Thespal-logeniccomponents(frommetalsandsilicates)areidentifiedduringmelting.Heatingupto1000°Cisusedtodeterminetheweatheringagewhereasthemeltisanalyzedtoestablishaterrestrialorresidenceageforthemeteorite.Thetestingresultsare:Carbon0.43wt%andSulphur0.04wt%.
Thecarbonabundanceforthismeteoritedebrisisinconformitywithmediancarbonabundancevalueforenstatitechon-drites(i.e.0.4wt%)asreportedbyMooreandLewis(1965).ThiscarbonvalueandtheelementalcompositiondeterminedthroughXRFanalysisbyKayani(2009)supportstheideathattheparentmeteoroidbodyofthisdebrismayhavebeenanenstatitechondrite.Enstatitechondriteshaveahighironcontent(upto30wt%)andcontainamagnesium-siliconmineralenstatite(Mg2Si2O6).ThesiliconandmagnesiumabundancevaluesdetectedthroughXRFanalysisare3.93wt%and0.342wt%respectively(Kayani2009).Theincreasedrelativeabundanceofiron(56.28wt%)inthemeteoritedebrisisattributedtoablationeffectsexperiencedbytheparentmeteoroidbodyonitsentryintoearth’satmosphereanditssubsequentex-plosivedisintegrationintosmallmeteorites.Thismeteoroidmayberelatedtoaprimitiveundifferentiatedparentbodyoranasteroid.Suchasteroidsrepresenttheearliestrockybodiesthatoriginatedwithinthesolarsystem.Mostoftheseas-teroidsf loataroundthesunwithintheorbitsofMarsandJupiter(thesocalledasteroidbelt).
Onthebasisoftheanalysisincludedabove,themeteoritedebrisisidentifiedasthatofanenstatitechondrite.Theparentbodyofthismeteoritedebrismayhaveoriginatedfromtheasteroidbelt.Itmayhavebeenhurled(asaresultofacollisi-onwithaneighboringcelestialobject)intoatrajectorythatultimatelybroughtitintocloseproximityofearthandwasfinallypulleddownbyearth’sgravitycausingittocrashonthisparticularsite.
REFERENCESAmari,S.,Anders,E.,Virag,A.&Zinner,E.1990:Interstellargraphiteinmeteorites.Nature,345,238-240.Kayani, SA. 2009:Using combinedXRD-XRF analysis to identifymeteorite ablation debris. In: Proceedings of IEEE
InternationalConferenceonEmergingTechnologies,Islamabad,October19-20,219-220.Moore,C.&Lewis,C.1965:Carbonabundancesinchondriticmeteorites.Science,149,317-317.Murae,T.,Kagi,H.&Masuda,A.1993:Structureandchemistryofcarboninmeteorites.In:PrimitiveSolarNebulaand
OriginofPlanets(Ed.byOya,H.).Tokyo:TerraScientificPublishingCompany.Swart,P.,Grady,M.,Pillinger,C.,Lewis,R.&Anders,E.1983:Interstellarcarboninmeteorites.Science,220,406-410.
72Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.12
NatureandTempoofthePETM(Paleocene-Eocenethermalmaximum)events,newinsightsfromtheGSSPDababyiasection(Luxor,Egypt).
HassanM.Khozyem1,ThierryAdatte1,AbdelAzizTantawy2,JorgeE.Spangenberg3,GertaKeller4&KarlFöllmi1
1 Institut de Géologie et de Paléontologie (IGP), Université de Lausanne. [email protected] Department of Geology, South Valley University, Aswan 81528, Egypt.3 Institut de Minéralogie et Géochimie (IMG), Université de Lausanne.4 Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544, USA
ThePaleocene-EoceneThermalMaximumGSSPhavebeen carefully selectedbyThe InternationalUnionofGeologicalSciences(IUGS)locatedatthebaseofacharacteristiclithologicsuccession(theDababiyaQuarryBeds)thatoccursinthelowerpartoftheEsnaShale,awellknownformationthatoutcropsextensivelythroughoutEgypt.Thisselectionwasbasedon: (1) theorganiccarbon isotopeexcursion (CIE) , locatedat thebaseofBed1of theDababyiaQuarryBedsof theElMahmiyaMemberintheEsnaFormation.(2)themassextinctionofabyssalandbathyalbenthicforaminifera(Stensioinabeccariiformismicrofauna),whichisreflectedatshallowerdepthsbyaminorevent;(3)thetransientoccurrenceoftaxaamongtheplanktonicforaminifera(Acarininaafricana,A.sibaiyaensis,Morozovellaallisonensis)duringthe∂13Cexcur-sion;(4)thetransientoccurrenceoftheRhomboasterspp.–Discoasteraraneus(RD)assemblage;and(5)anacmeofthedinoflagellateApectodiniumcomplex.TheGSSP-definedPaleocene/Eoceneboundaryisapproximately0.8myolderthanthebaseofthestandardEoceneSeriesasdefinedbytheYpresianStageinepicontinentalnorthwesternEurope(Aubry,M.-Petal.,2007).
High-resolutionsamplinghasbeenachievedfromtwosectionslocatedattheleftandrightsideoftheoriginalDababiyaGSSP.62samplesfromtheleftsidesectionand42samplesfromtherightsidesectionhavebeensubjectedtomicropale-ontological(nannofossils),sedimentological,mineralogicalandgeochemicalanalysisinordertoreconstructthepaleoen-vironmentalconditionsandclimaticchangesoccurringduringthePETM.Preliminaryfieldwork,sedimentologicalandstableisotopesdatasuggestthattheDababiyaGSSPsectionhasbeendepositedinasmallchannelstructurewhichcanbetracedover200m,withthebasalunitsaandb(Aubryetal.,2005)thinningtowardstheedgesoftheoutcropandfinallydisappearing. ThePaleocene-EoceneGSSP isconsequentlyonlycompleteovera2-3meterswidth, inthecenterof theoutcrop.Geochemically,(1)bothorganicandbulkrockcarbonisotopesshowalong-termgradualdecreasingandreachmaximumnegativevaluesatthemidofbed.2,(2)asevereandpersistentdecreaseind15Norgto~0‰,(3)SharpdecreaseinproductivityattheCIEintervalfollowedbyasignificant increaseuptotheendofthePETM, (4)AchangeinredoxconditionfromoxicbelowthePETMtoanoxicconditionsinthelowermostPETM,followedbynormaloxicconditions,(5)Amaximumhumidity(kaolinitepeak)coincidingwiththebaseofthePETM.Despite,thelackoflateralcontinuity,theDababiyaGSSPisoneofthemostcompletePETMsectionandrevealsinterestinganduniquefeaturesthatmaybecrucialforabetterunderstandingofthePETMevents.
2.13
NewisotopedatafromtheLateCretaceousandPaleogenephosphatebedsoftheGafsaBasin,Tunisia
KocsisLászló1,OunisAnouar2,ChaabaniFredj2&NailiSalahMohamed3
1 Institut de Minéralogie et Géochimie, Faculté des Géosciences et Environnement, Université de Lausanne, Switzerland2 Laboratoire des Ressources Minérales et Environnement, Faculté des Sciences de Tunis, Université de Tunis El Manar, Tunisia3 Compagnie de Phosphate de Gafsa, Direction de Géologie, Métlaoui, Tunisia
DuringtheLateCretaceousandPaleogeneTunisiawaslocatedinthesouthernmarginofTethysanditwasapartofthemainTethyangiantphosphoritebelt.AtthisperiodTethyanwaterscoveredmostoftheTunisianlandmassandonlysomeareasliketheDjeffaraandKasserineislandsemerged.BetweentheseislandslocatedtheintracratonicGafsaBasinthatwasconnectedtotheopenseawestwardandsometimeswaterexchangeoccurredintheeastthroughtheChamsiPass(Fig.1).SedimentationintheGafsaBasinwasconductedinasemi-closedsea,whereinnerneriticandcoastalenvironmentalter-nated(e.g.Chaabani,1995,Zaïeretal.,1998).PhosphatebedsoccurredfirstontheHardGroundoftheAbiodFormationintheEarlyMaastrichtian,wherethelayerscanreachlocallyonemeterinthickness,whilelater,duringthePaleocene-EarlyEocenemoremassiveandeconomicallyimportantphosphoritesweredepositedinthearea(ChouabineFormation).
73
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Thefirstdetailedstable isotopestudyof thephosphateremains (sharkteethandcoprolites) fromtheGafsaBasinwasconductedbyOunisetal.(2008).Thecarbonisotopeanalysesresultedinapronouncednegativecarbonisotopeexcursion(CIE)of3-4‰atthelimitofUnit-CandUnit-DoftheChouabineFormation,whichwasidentifiedintwodifferentsectionsandintwodifferentarchives(Fig.1).Initially,thereforethisCIEwasproposedtomarkthePaleocene-Eocene(P/E)bound-aryinthephosphateseries.
Theoxygenisotopiccompositionsofthefossilsindicateastablewarm,tropicalclimateduringthedepositionofthephos-phatelayers.AttheP/Eboundary,howeveraglobalhyperthermalevent(PETM–PaleoceneEoceneThermalEvent)occur-redreflectedbyanegativeoxygenisotopeshiftinbenthicforaminiferarecord(e.g.Zachosetal.2001).TheabsenceofanythermalanomalyatthePETMintheGafsasectionswasexplainedbythetropicalpositionandtheshallow,semi-closedconditionoftheGafsaBasin(Ounisetal.,2008).Howeverwhetherthisprecedingresultisonlyduetothisspeciallocalconditionorratheraglobalphenomenonatlowlatitudesisnotutterlyclear.
Further investigation, therefore isnecessary focusingon theconnectionof theGafsaBasinwith theglobalocean, thepossibleeffectsofdiageneticalprocessesandtheverificationofwideroccurrenceofCIEintheregion.Henceotherisoto-pesystemssuchasSrandNdhavebeeninvolvedandappliedforthesamesamplesuitspreviouslyinvestigatedintheAlima and Bliji Mountains (Ounis et al., 2008). In addition, shark teeth from the different phosphate layers of theChouabineandMétlaouiFormationsintheKefEddourregion(Métlaoui)werecollectedandanalyzedforSrisotopicratios.
The87Sr/86SrratiosarewidelyintheexpectedrangeoftheLateCretaceousandPaleocene-Eoceneopenseawaterhowevertheyounger samples showmorepronounceddeviations from theglobal Sr-evolution curve.TheeNd valuesof the fewsampleanalyzedarequitevariableandtheyvaryfrom-8.8to-10.7.Thesepreliminarydataindicateeitherenhancedcon-tinentalreworkingorincreasedinfluenceofearlydiageneticf luidonthesampleswhichismostpossiblyrelatingtothegradualclosuringofthebasinduringthePaleogene.
Forfurtherinvestigatingthesubject,intheKefEddourregionadetailedsectionoftheChouabineFormationweresamp-ledfocusingnotonlythephosphatebuttheintercalatedmarlsandcarbonatelayersespeciallyacrossthesupposedP/Eboundary.Bulksediment,totalorganicmatter,phosphateremainsandforaminifersaretheinitialtargetsforstableisoto-peanalysescriticaltotheP/Eboundary.
Figure1.PalaeogeographicalmapofthestudiedGafsaBasininTunisiaandtheobtainedoxygenandcarbonisotopedistributionsalong
twoPaleocene–EocenesequencesintheChouabineFormation(Ounisetal.,2008).NotethenegativeCIEatthelimitofUnit-Cand
Unit-D,butnovariationintheoxygenisotoperecord.
REFERENCESChaabani,F.,1995.DynamiquedelapartieorientaledubassindeGafsaauCrétacéetauPaléogène:Etudeminéralogique
etgéochimiquedelasériephosphatéeEocène,Tunisieméridionale.ThèseDoc.Etat.Univ.TunisII.Tunisie.Ounis,A.,Kocsis, L.,Chaabani, F.&PfeiferH.-R. 2008:Rare earthelementand stable isotopegeochemistry (d13Cand
d18O)ofphosphoritedepositsintheGafsaBasin,Tunisia.Palaeogeogr.Palaeoclimatol.Palaeoecol.,268,1–18.Zachos,J.,Pagani,M.,Sloan,L.,Thomas,E.&Billups,K.2001:Trends,rhythms,andaberrationsinglobalclimate65Ma
topresent.Science292,686–693.Zaïer,A., Beji-Sassi,A., Sassi, S.&Moody, R.T.J. 1998: Basin evolution anddeposition during the Early Paleocene in
Tunisia.In:Macgregor,D.S.,Moody,R.T.J.andClark-Lowes,D.D.(Eds.),1998.PetroleumGeologyofNorthAfrica.Geol.Soc.LondonSpec.Publ.132,pp.375–393.
74Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.14
GeochemicalandmineralogicalexaminationsofromancruciblesfromAutun(France)
DanielaKönig&VincentSerneels
Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg ([email protected])
TheinvestigatedcruciblefragmentsarisefromanarchaeologicalexcavationofthesiteoftheLycéemilitaireinAutun(France).DuringtheexcavationofalargecraftsmanquarterattheRomantownofAutun,severalhundredkilosofcru-ciblefragmentshavebeencollected.Thereareobviousevidencesforfoundryworkbuttheproductionofcopper-basedalloys(Zn,Sn,Pb)isalsosupposable.ThearchaeologicalsiteisdatedtotheGallo-Romanperiod(Chardron-Picault&Pernot,1999).
Thisstudyaimstospecifythestructureoftheceramicstoidentifytherawmaterialanddescribethetechnologyofpro-duction.Forthis,usedanalyticalmethodscompriseopticalmicroscopy,SEMandSEM-EDXanalysesonwallcross-sections,X-raydiffractionanalyses(XRD)fromdifferentiablepartsoftheinnerwalllayeraswellasX-rayf luorescencespectroscopy(XRF)onthedifferentlayersofthecrucibles.
Ingeneral,thecruciblesshowamultilayeredwallstructure,whicharemadeupoftwotothreelayersofdifferentceramicmaterials.Eachlayerpossessesdistinctthicknessesandfabriccharacteristics.Thefirst(outer)andthesecond(inner)lay-er,whicharepresentinallcruciblesareopticallydistinguishablebythedifferingcolourandtheglass-matrixcomposition.Thesefeaturessupposemajormineralogicalheterogeneitiesbetweensinglelayersandindividualfragments.Aninnermost(third)layer,whichismissinginsomeoftheinvestigatedfragments,isprobableakindofinnerprotectinglayer.Thefa-bricisinfluencedbytwomoreimportantfactors.Firstly,thestronggradientoftemperaturebetweentheinnerandtheouterpartarebasedonthehighexternalfieriness.Secondly,thefabricisinfluencedbyinteractionbetweentheinnermetalliccharge,theceramicandthecontributiongasesfromoutside.
Thefirstresultsshowremarkabledifferencesbetweenthetwomainlayers.The inner layer ischaracterisedbyahighcontentofmullite,low-cristobalite,quartzandinsomecasesorthoclase,whereasthelow-cristobaliteisoftenillcrystal-lised.Therefore,firingtemperaturesareproposedtohavereachedapproximately1100°Cto1300°C.Incontrasttheouterlayerisdominatedbyahighercontentofmullitebearingglass.Additionally,somesamplescontainsecondaryanalcimeinthefirstlayer,whichwasformedduringtheburialstage.XRFanalysisdocumentsatentimeshigherCaOconcentrati-oninthefirst(outer)layerasinthesecond(inner)one.ThesporadicallyoccurringthirdlayerhasalsoadifferingCaOconcentration,whichishigherthantheconcentrationinthesecond(inner)one.Thisfeaturecouldbeafirsthintofdif-ferentsourcematerialsforthesinglelayers.
REFERENCESChardron-Picault, P.& Pernot,M. (1999): Un quartier antique d’artisanatmétallurgique àAutun - Le site du Lycée
militaire.Paris:MSH,320p.
2.15
FluidboilingandmixingduringlateststageorogenicgoldmineralizationatBrusson,NWItalianAlps
LambrechtGlenn1,DiamondLarryn1
1 Rock–Water Interaction Group, Institute of Geological Sciences, University of Bern, Switzerland ([email protected])
Weareinvestigatingf luidinclusionsinhydrothermalquartz-carbonate-sulphideveinsfromtheabandonedFeniliaMineatBrusson,northwesternItalianAlps.StudiedquartzsamplescontainearlyprimaryandpseudosecondaryinclusionsthatcanbeapproximatedbytheCO2–H2O–NaClsystem.Twotypesareobserved(Fig.1):first,abundantlow–XCO2LaqLcarVin-clusionsthathomogenizetoliquidat~230°Candhaveanaqueoussalinityof3.7mass%NaClequiv.;second,high–XCO2LaqLcarinclusionswithsimilarhomogenizationbehaviourandanaqueoussalinityof2.2mass%NaClequiv.Thetwocontras-
75
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
tinginclusiontypesweredescribedbyDiamond(1990)andinterpretedtohaveformedduringboiling(phaseseparationinto“vapour”and“liquid”)ofthelow–XCO2-typeore-bearingsolution.Newcharge-contrastimaginghasrevealedfineovergrowthsofquartzonthemain-stagecrystals(quartzzone3inFig.2c).Thesehostlate-primaryinclusionassemblages,whichconsistofrarelow–XCO2LaqLcarVinclusions(identicaltothosede-scribedabove)coexistingwithabundantLaqVinclusions.Thelatterwerepreviouslyunknownatthisdeposit.Theircarbo-nicphaseshavevariablevolumefractions[j(car)]rangingfrom0.075to0.47(±4%)(Fig.1a),which,alongwithelementpartitioningdata,isdiagnosticofboiling.Theseinclusionshomogenizeat³180°CviathetransitionLaqV→Laq.
RamananalysisrevealedCO2,CH4andN2withinthecarbo-nicphasesofallLaqVinclusions,butthemolarratiosofthegasesvarysystematically.InFig.1btheseanalysesrevealalineararraystretchingfromcompositionsclosetothoseoflow–XCO2 LaqLcarV and high–XCO2 LaqLcar inclusions (end-memberno.1inFig.1)tocompositionsofabout4.4mol.%CO2,91.4mol.%N2and4.2mol.%CH4(end-memberno.2inFig.1).
Figure1.(a)Relationshipbetweenvolumefractionofthecarbonic
phase [j (car)] and mole fraction of N2 in the carbonic phase
[XN2(car)]and(b)molarcompositionofthecarbonicphaseinLaqV,
low–XCO2 LaqLcarV, and high–XCO2 LaqLcar inclusions from quartz-
veinsampleshostedbydifferenttypesofwallrock.
Theliquidend-members1,2and2baremutuallymiscibleattheentrapmenttemperatureofthelow–XCO2liquid,230°C.Therefore,thelinearcompositionaltrendofthelateprimaryLaqVinclusionsinFig.1bcanbeinterpretedasamixingline.Thus,itappearsthatboilingandmixingoccurredsimultaneouslyintheveinsystemduringprecipitationofquartzzone3(Fig.2c).
Figure2.(a)Photographofquartzcrystalwithfreegolddepositedonthesurface.(b)SEMcharge-contrastimageofapolishedsection
throughthiscrystal.(c)Schematicinterpretationofthecharge-contrastimageinb.Seetextforfurtherdetails.
ThequartzsampleinFig.2exhibitstwogenerationsofgold:smallinclusionswithinalategrowthzone(Earlygoldinzone2,Fig.2c);andfreegoldmostlyoverlyingtheoutercrystalsurface(Lategold,Fig.2c).Charge-contrastimagingrevealsthatthislategoldisyoungerthanthefinecrystalgrowthzone3(Fig.2c)thathoststhelateprimaryLaqVinclusionassembla-ges.Thelategoldisalsoindirectcontact,andthereforecoeval,withhealedfractures(zoneno.4inFig.2c)thathostasecondaryassemblageofvariable–XCO2inclusions(includingbothlow–XCO2LaqLcarVandhigh–XCO2LaqLcartypes).These
76Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
newtemporalandcompositionaldeductionsareusedtoreconstructthehistoryofquartzgrowthintheFeniliavein:First,alow–XCO2-typecarbonicliquidformsmain-stagequartz(zone1inFig.2c)andalterstheadjacentwallrock.Subsequentsimultaneousprecipitationofgoldandquartzispresumablytriggeredbycoolingorbywall-rockreactions.Progressivecoolingandreductioninf luidpressureowingtoon-goingupliftoftheWesternAlpsinducesboilingofthemain-stagef luid(Diamond,1990).Poref luidfromthewallrockssimultaneouslyseepsintotheopenvein,whereitmixeswithboilingcarbonicf luid.AtthismomentthelateprimaryLaqVinclusionsaretrapped (zone3 inFig.2c).Finally,anewpulseofboiling,ore-bearingcarbonicf luidenterstheminelevel,fracturingtheexistingquartzcrystalsanddepositingthelategoldontopofthem(zone4inFig.2c).Withoutanyevidenceforwall-rockporewatersatthisstage,itseemsmostlikelythatpartitioningofgold-complexingligands (aqueousHS–andH2S)fromtheliquidintothecarbonicvapourtriggereddepositionofthelategold.
REFERENCESDiamond,L.W.1990:FluidinclusionevidenceforP-V-T-Xevolutionofhydrothermalsolutionsinlate-alpinegold-quartz
veinsatBrusson,Val-d’Ayas,NorthwestItalianAlps.AmericanJournalofScience,290,912-958.
2.16
KilnfurnituresfromthefaiencemanufactureofGranges-le-Bourg(HauteSaône,France):contrastingrecipes
MaggettiMarino1,MorinDenis2,SerneelsVincent1,NeururerChristoph1
1 Department of Geosciences, Mineralogy and Petrography, University of Fribourg, CH-1700 Fribourg ([email protected])2 CNRS, TRACES - UMR 5608, Université de Toulouse, F-31058 Tolouse
Duringarchaeologicalexcavationsofthebrickworks(16th-19thc.)fromGranges-le-Bourg(Morin&Morin-Hamon2004),faiencewastewasfoundfromanunknownlate18th/early19thc.production.InGranges-le-Bourg,coarse,aswellasfineceramicwasthereforeproducedsimultaneously.Archaeometricanalysisincluded35samplesofkilnfurnitureortechnicalceramic(firingplates,saggars,spacers,props,wads),5bricksandtilesand7claysinordertostudythechemical-mine-ralogicalcompositionoftheseobjects.Analyticaltechniqueswereopticalmicroscopy,X-rayf luorescence,X-raydiffractionandscanningelectronmicroscopy,coupledtoanenergy-dispersiveX-rayspectrometer.
Afirstgroupofkilnfurniture(firingplates,saggarsandprops)is,astobeexpected,calcium-andmagnesium-poor,wellsuitedtosupporthighfiringtemperaturesaswellasseveralfiringcycles.Thecoarseceramic(bricks&tiles)hasaniden-ticalchemicalcomposition.Saggarsandbricksaregrog-tempered.Thesecondgroupofspacersandwadsiscalcium-andmagnesium-rich(beween5-10wt.%CaOresp.MgO),matchingthechemicalcompositionofthefaienceproduction.Theancientpottersobviouslyusedtworecipesforthekilnfurniture:thebrick&tilerecipeandthefaiencepasterecipe.Theuseofanonrefractorypasteforthespacersandwadsispuzzling.Ceramicobjectswithsuchhighf lux(CaO,MgO)willmeltaround1100oC-theyarenotverywellsuitedtoresisthighfiringtemperaturesofafaiencekiln,nortosupportmanyfiringcycles.Weretheseobjectsusedonlyonce?LocalTriassic(Anisian)marlscontainmuchdolomiteandarechemicallysimilartotheHigh-Mggroup.Asshownbyverticalprofilesoftworawmaterialsoutcrops,thereisadecarbonatisationtowardsthesurface.ThetoplayerscorrespondchemicallywelltotheMgO-poorobjects.Thepottersusedsuchlocalrawmaterialandnotimported,specificrefractoryclays.Acoatingofeithertinglaze(withsignificantlylesstinoxidethanthefaiencepieces)orleadglazehasbeenappliedtotheinteriorofthesaggars.Fortheseobjects,asmallglaze-ceramicbodyinterfacehasbeenobservedonlyfortheleadglaze.Theabsenceofanysignificantreactionzoneindicatesthattheglazesuspensionwasappliedonalready(biscuit)firedsaggars.
REFERENCEMorin,D.,& Morin-HamonH. J. 2004: La tuilerie-faïencerie deGranges-le-Bourg, Bulletin de la sociöté d’Histoire et
d’Archéologiedel’ArrondissementdeLure,23,94-104.
77
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.17
ThefaiencemanufactureLeBoisd’Épense(North-easternFrance,18/19thcentury)
MaggettiMarino1,RosenJean2,SerneelsVincent1,NeururerChristoph1
1 Department of Geosciences, Mineralogy and Petrography, University of Fribourg, CH-1700 Fribourg ([email protected])2 DR CNRS, UMR 5594, Faculté des Sciences, Université de Dijon, F-21000 Dijon
TheFrenchfactoryLeBoisd’Epensewasanimportanttin-glazepotteryproductionsiteintheyears1735-1742and1764-1848,withalmost200workersatthetopofitsactivity.Wepresenttheanalyticalresultsfor56faiences(=tin-opacifiedleadglazedearthenware),28samplesoftechnicalceramic(saggarsandspacers)and6localclays.Analyticaltechniqueswereopticalmicroscopy,X-rayf luorescence(XRF),X-raydiffraction(XRD)andscanningelectronmicroscopy,coupledtoanenergy-dispersiveX-rayspectrometer(EDS).
AsshownbyXRFanalysis,thefaienceisveryhomogeneousandhasatypicalcalcareousfaiencebody(16-24wt.%CaO).Nochemicaldifferencecanbeevidencedbetweenthebiscuitsandthefaienceswitha“grandfeu”oranenameldecorati-on.TheproductsfromthissitecaneasilybedistinguishedfromtheactuallyknownFrenchfaiencereferencegroups.Thespacersweremadefromthesamepasteasthefaience,butthesaggarswithaimportedrefractoryclay,richinAl2O3.Forthe faience body, amixing of two local clays has been reported in a paper from1877.However, the prospected localCretaceous(MiddleAlbian)claysneverexceed12wt.%CaO.AnadditionofaCaO-richmaterialisundoubtedlynecessaryto reach the 16-24wt.%CaO of the faience. This is not a localmarl, butmost probably a very pure chalk from theChampagne.FiringtemperatureswereinferredbyXRDandlie<950°Cforthebiscuitsandbetween950-1050°Cfortheglazedpieces, indicatinga twochamberedkiln.Thequalityof the tinglaze is ingeneralgood, showingrare roundedquartzcrystals,very fewnewlycrystallizedphases (K-feldspars,cristobalite?)andbubbles.Contrasting, thecassiteritecrystalsareheterogeneouslydispersed,formingclusters.Theabsenceofanyglaze-bodyinterfaceisconsistentwiththeapplicationoftheliquidglazetoanalreadyfiredbody.Areameasurementsshowthatalltinopacifiedglazescanbeclas-sifiedasSiO2-PbOglazes(~80wt.%)containingabout9wt.%SnO2,withotheroxidesinconcentrations<5wt.%.Spotanalysesoftheglassmatrixindicateamuchlowertinoxideamountofabout2wt.%ascomparedtotheareameasurements.
2.18
Forensicgeology:characterisationoflightelementstableisotopesinsoilsamplesoftheSwissPlateau
MarolfAndré1,VennemannTorsten1&BonzonJeanne2
1 Institut de minéralogie et géochimie, Université de Lausanne, Bâtiment Anthropole, CH-1015 Lausanne ([email protected])2 Musée cantonal de géologie, Université de Lausanne, Bâtiment Anthropole, CH-1015 Lausanne
ThepurposeofthisworkistocharacterisesoilsamplesfromtheSwissPlateaufortheirstablecarbonandoxygenisotopecompositionsasabasisforforensicandgeologicalresearch.FivesamplinglocationswerechoseninthecantonsofGeneva,Vaud,FribourgandValais,andsixinthecantonofZurich.Thecoordinatesofthelatterlocationshavebeentakenfromrealcrimescenes (anonymised).Fourteensamplesperlocationwerecollectedforall localitiesexceptforthecantonofZurichwheresixsamplesperlocationwerechosen,followingaregularpatternforalllocalities.AllthesoilsampleswerecharacterisedfortheircarbonandoxygenisotopiccompositionviaIsotopeRatioMassSpectrometry(IRMS).Organiccom-poundshavebeenremovedandcarbonatesandsilicatesanalysedseparatelywithaGasBenchII,respectivelyaCO2-laserbasedextractionline,bothlinkedtoanIRMS.
TheresultsindicatethatcarbonandoxygenisotopesareapromisingtooltoinvestigatevariationsinsoilsfromtheSwissPlateau,butdistinguishingbetweenlocationsinthesameregionisstillchallenging.Despitethesedifficulties,threemajordomainscanbeclearlydistinguishedandthedatashowsthatisotopescanbeanadditional,newfingerprintofsoils.ThedomainsofValais(Martigny),theRomandie(Lausanne,Genève,Yverdon)andtheZürichregion(Gockhausen,Hausen-am-Albis, Kindhausen, Oetwil-an-der-Limmat, Wallisellen and Wiesendangen) can be distinguished. A fourth domain(Fribourg),however,slightlyoverlapstheZürichregionandtheRomandiedomainandhenceremainsambiguous.
78Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Thefactthatothersamplesofcarbonate,quartzandclaymineralsthathavebeenanalysedfromtheMolasseshowsimilarvaluestothesoilsanalysedhere,couldindicatethattheMolasseandthecorrespondingreworkedQuaternarydepositsarethemainsourcesofinorganicsoilmaterial.Eveniftheformationandevolutionofsoilsarestillnotwellunderstoodindetail,biologicalactivity isunlikely to influence themineralogyof soilsanalysedhere inamajorway,although localdifferencesrelatedtoorganicacidsmaybepresent.Thedataprovidenewinsightintochemicalandphysicalprocessesofsoilformationandmaythusbeofhelpforinterpretationsofthegeology,pedology,andforforensics.Moreanalysesofsoilswillcertainlyhelptoprovidefurtherandadditionalconstraintsonsoilprovenanceintimeandspace.
2.19
Elementpartitioningbetweenimmisciblesilicateandcarbonatitemeltsbycentrifugeexperiments
MartinLukasH.J.1,SchmidtMaxW.1,HametnerKathrin2&GüntherDetlef2
1 Institute of Geochemistry and Petrology, ETH, Clausiusstrasse 25, CH-8092 Zürich ([email protected]) 2 Laboratory of Inorganic Chemistry, ETH, Wolfgang-Paulistr. 10, CH-8093 Zürich
Carbonatiteareknownfortheireconomicimportanceastheyareenrichedinrareincompatibleelements,whichareex-ploitedfortechnicalindustry.Themechanismswhichcanformcarbonatitesare:(a)verysmalldegreeofpartialmeltingofaCO2-richmantle,(b)extremedifferentiationofaCO2-richundersilicifiedmagma,(c)bysilicate-carbonatiteliquidim-miscibility.
Thisstudyisfocusedonliquidimmiscibilityanditaimstodeterminetraceelementpartitioncoefficients(KD)betweencarbonatiteandsilicatemeltsinexperiments.TheKDvalueswillthanbeappliedtonaturalconjugatemeltpairsoccurringinvolcanoeseruptingbothsilicateandcarbonatitemagmas.
Thestrategyofthisstudyistoobtainliquidimmiscibilitybyexperiments,segregatethecoexistingliquidsbycentrifuginganddetermineelementpartitioncoefficientsforhighlysodicandhighlypotassiccarbonatite-silicatemeltsystems.Thesepartitioncoefficientsarethenappliedtotestwheatherliquidimmiscibilitywastheprocessformingkamafugite–carbona-titepairs. IncomparisonwiththeonlyexistingpreviouscentrifugestudyfromVeksleretal. (1998),westudyclose-to-natural systemsanddetermine≥40elementpartitioncoefficients.The investigated sodic system is fromLee&Wyllie(1997),thepotassicsystemsimulatestheItalianintra-appeninickamafugite-carbonatitesuite.Kamafugitesarehighlysi-licaundersaturated,haveextremeK2OcontentsandK2O/Na2O>5,crystallizingphologopite,olivine,leucite,melilite,andalsokalsilite.Theyareassociatedwithcarbonatites,whichatsomelocalitiescarrymantlexenolithsindicatingthattheyoriginatefromdepths>45km.
Immisciblecarbonatite-silicatemeltsdevoidofcrystalsareproducedat1GPa,1230°Cand1.7GPa,1220-1250°Cforthesodicandultrapotassicsystems,respectively.Thetraceelementspikedstartingmaterialswerefirstequilibratedinstaticexperiments,reloadedinasinglestagepistoncylindermountedonacentrifugeasdescribedbySchmidtetal.(2006),andrerunatidenticalP-Tconditionsat700gfor3-5hourstophysicallyseparatetheliquids.LA-ICPMSanalyseswereperfor-medonsevencentrifugedexperimentsrepresentingthetwosystems.
Theresultsindicatethatthepartitioncoefficientsareclosetounity.ThealkaliandalkaliearthelementshaveaaffinitytopartitionintothecarbonatitemeltaswellasPandMowhereastheHFSEhaveastrongaffinityforthesilicatemelt.TheLREEelementspartitionweaklyintothecarbonatitemeltwhereastheHREEpreferthesilicatemelt.Theweakparti-tioningoftheLREEintothecarbonatitemeltindicatesthatliquidimmiscibilityisnottheprocessenrichingthecarbona-titesinREE.
REFERENCESLee,W.J.&Wyllie,P. J.1997:Liquid immiscibilitybetweennepheliniteandcarbonatitefrom1.0to2.5GPacompared
withmantlemeltcomposition.ContributionstoMineralogyandPetrology,127,1-16.Schmidt,M.W.,Connolly,J.A.D.,Gunther,D.&Bogaerts,M.2006:Elementpartitioning:Theroleofmeltstructureand
composition.Science,312,1646-1650.Veksler,I.V.,Petibon,C.,Jenner,G.A.,Dorfman,A.M.&Dingwell,D.B.1998:Traceelementpartitioninginimmiscilble
silicate-carbonatite liquid systems:an initial experimental studyusingacentrifugeautoclave. JournalofPetrology,39,2095-2104.
79
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.20
InternalflowstructuresincolumnarjointedbasaltfromHrepphólar,Iceland
MattssonHannesB.1,BosshardSonjaA.1,HetényiG1,AlmqvistBjarneS.G.2,HirtAnnM.2,CaricchiLuca3&CaddickMark1
1 Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8003 Zurich ([email protected])2 Institute of Geophysics, ETH Zürich3 Department of Earth Sciences, University of Bristol, U.K.
Columnar jointedbasalt fromHrepphólar in southern Icelanddisplay spectacular internal structureswhencut.Thesestructuresfollowtheoverallorientationofthecolumnsanddisplaysemi-circulartocircularfeatureswhencross-cut.Itwaspreviouslybelievedthattheseinternalstructuresformedasaresultofalterationduetocirculationofmeteoricwaterwithinthecolumn-boundingfracturesafteremplacement.However,newfieldobservationsofviscousfingeringwithinthecolumnsandthefactthatapproximately80%ofthesemi-circularfeaturesarefoundwithinthecolumnwhereastheremaining20%arecutbythecolumn-boundingfracturesclearlyshowsthattheseinternalstructuresmusthaveformedpriortocrack-propagation(andarethusprimaryfeatures).
Herewepresenttheresultsoftexturalandpetrologicalanalysesthroughacross-sectionofacolumn,incombinationwithmagneticsusceptibilityandanisotropymeasurementsofthesamesamples.Thevariationintexturesandgeochemistrycanbeattributedtothepresenceofdiffusebandingcausedbyvariationsinthemodalproportionsofthemainphenocrystphases(i.e.,plagioclase,clinopyroxene,olivineandtitanomagnetite/ilmenite).Orientationofplagioclaselathsandtitano-magnetitecrystals (basedonmeasurements in thinsectionsandAMS-measurements)areconsistentwithvertical f lowalignment.Nowhereinthecolumncanevidencefordownwardsf lowbefound(excludingthepossibilityofsmall-scaleconvectioncellsgeneratingthesefeatures).
Itisproposedhere,thatthevolumedecreaseassociatedwithsolidification(typically10-15vol.%forbasalticsystems)andtheincreasingweightoftheoverlyingcrustresultsinupwellingofpartiallycrystallizedmaterialintothecentreofthecolumns.Preliminarynumericalmodelingindicatesthattheisothermswithinindividualcolumnsbecomesteeperwithincreasingdepthinalavaf low(allowingforlargerdisplacementdistances).Weproposethatthisupwellingcanbearathercommonphenomenoninnature,butwithoutthepresenceofchemicallydistinctcompositions(ortexturalbanding)itcanbedifficulttorecognizesuchfeaturesinthefield.
80Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.21
MINERALWEATHERINGALONGASOILCHRONOSEQUENCEINAHIGHALPINEPROGLACIALAREA:AMULTIPLEAPPROACH
ChristianMavris1,MarkusEgli1,MichaelPlötze2,JensGötze3,AldoMirabella4,DanieleGiaccai4,WilfredHaeberli1
1 Department of Geography, University of Zurich, Zurich, 8057, Switzerland ([email protected])2 ETH Zurich, Institute for Geotechnical Engineering, Zurich, 8093, Switzerland3 Institute of Mineralogy, TU Bergakademie Freiberg, Freiberg, D-09596, Germany4 Istituto Sperimentale per lo Studio e la Difesa del Suolo, Centro di ricerca per l’Agrobiologia e la Pedologia, Firenze, Italy
Climatechangeandglaciermeltingfeedtheneedforunderstandingtheprocessesrelatedtoweatheringofrecentlyexpo-sedareas.PaststudiesinhighAlpineenvironmentsshowthatclaymineralformationratesarehigherinyoungersoils(<1000yr)thaninoldersoils(>10000yr).However,investigationsofprocessesthatoccurinthefirstdecadesofsoilfor-mationarerare.
InthepresentstudyweinvestigatedthemineralweatheringinarecentlyexposedhighAlpinechronosequence.ThestudywasundertakenintheMorteratschglacierforefield,locatedinSESwitzerland.Theprogressivelyexposedproglacialareaoffersafulltimesequencefrom0to150yroldsurfaces.TherockbasementistheBerninacrystallineunit,mostlycons-titutedofVariscangranitoidrocks(Büchi,1994).Previousmineralogicalstudiescarriedoutinthesoilsoftheproglacialforefield(Mavrisetal.,2010)showadecreaseofbiotiteandepidoteasafunctionoftimeinthefineearthfraction(<2 mm).Mineralogicalmeasurementsoftheclayfraction(<2 µm)werenowcarriedoutusingXRDandDRIFT.Furthermore,ana-lysisinthed(060)rangewerecarriedout.Thedecreasingcontentoftrioctahedralphaseswithtimeintheclayfractionconfirmsactivechemicalweatheringandformationandtransformationofparentrockmineralogy.Measurementoflayerchargesallowedthedetectionofsmectiteandvermiculiteandtheattributionoftheparentphases.Alongtheselectedchronosequence,thesmectitecontentincreasedsteadily.Furthermore,thecombinationofcathodoluminescence(CL)andNomarskiDICmicroscopyfortheobservationofthefineearthfraction(<2mm)allowedtheobservationofcompositionalandweatheringfeaturesinboththeparentmaterialandthesoils.Themineralformationandtransformationprocessesdetectedwithintheconsideredtimespanconfirmthehighreactivityoffreshlyexposedsediments.
Fig.1.Smectitecontentasafunctionofpedogenesis.Squaredot=glacialtill,dot=topsoilsalongtheproglacialarea.
REFERENCESBüchi H. 1994: Der variskischeMagmatismus in der östlichen Bernina (Graubünden, Schweiz). Schweizerische
MineralogischeundPetrographischeMitteilungen,74,359-371Mavris,C.,Egli,M.,Plötze,M.,Blum,J.D.,Mirabella,A.,Giaccai,D.,Haeberli,W.(2010)–Initialstagesofweatheringand
soilformationintheMorteratschproglacialarea(UpperEngadine,Switzerland).Geoderma,155,3-4,359-371.
81
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.22
FumarolicaerosolsfromElChichónvolcano,Mexico
MeierMarioFederico1,GrobétyBernard1,2
1 Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg ([email protected], [email protected])2 Fribourg Center for Nanomaterials (FriMat), University of Fribourg, CH-1700 Fribourg
Quiescentvolcanoesareemittingcontinuouslyaerosolparticlesbyfumarolicanddiffusedegassingintothetroposphere.Theimpactoftheseparticlesontheenvironment,e.g.ontheradiationbudget,maybeconsiderably.However,onlyscarceinformationaboutthenatureandtheevolutionofsuchparticlesisavailable(e.g:Matheretal.2003;Pfefferetal.2006).TheaimofthisstudyistocharacterizechemicallyandmorphologicallyfumarolicparticulatematterfromElChichónvolcano(Chiapas,SouthMexico,1150m.a.s.l.).
ForthatpurposeaerosolparticlesweresampledactivelyontopolycarbonateNucleporefiltersandTransmissionElectronMicroscopy(TEM)gridsin2009.Thesamplingdevices,anactivePM10andacorrosionresistantelectrostaticsampler,wereusedatthecraterrim(CR)andclosetothefumarolesinsidethecrater.ThesampleswereanalyzedbyTEMandComputerControlled Scanning ElectronMicroscopy (CCSEM), both combinedwith simultaneous EnergyDispersive Spectroscopyanalysis(EDX).
Severalthousandsofparticlesinthesizefraction0.4–10µmhavebeenanalyzedandclassifiedbyCCSEM.Thesolidparticleconcentrationinsidethecraterwasaround3000particles/liter,whereasontherimtheconcentrationwashalfashigh.Atboth sitesmostof theparticleswerecontaining sulfur.Thedominant fumarolicparticle specieswere sulfur/sulfuricacidparticlesandNa-,K-,Na-K-respectivelyCa-sulfates.Totalsulfurcontainingparticlef luxisestimatedtobe0.1kgs-1.Alkalichloridescouldalsobedetected.Claysareconsideredtohaveanon-fumarolicorigin.Theirabundanceisthesameatbothsamplingsites.Aluminumcontainingparticles (Al-oxides)areclearlymoreabundantattheCR.Thatpointstoahigherinfluenceofsoilparticlesonthetotalparticleconcentrationoutsidethecrater.Manyparticlessampledinside the craterare compositeparticles. Someof themcontainNa-sulfateneedlesandpseudo-hexagonalNa-K-sulfatecrystals.OthercompositeparticlesarecontainingP,S,K,Na,K,(Mg),(Al),(Zn)and(Pb).Thephosphoruspointstoanonmagmaticsource(Obenholzeretal.2003).Mostofthecompositeparticles,includingthePrichparticles,arenolongerpresentattheCR.
ThefumarolesatElChichónemithydrothermalsteamrichinCO2andloweramountsofH2S,acidicspeciessuchasSO2andHClarenearlyabsent(Rouwetetal.2009).Duringthesamplingperiod,thegasemissionswereaccompaniedbygeyseractivitywith increaseddischargeofNa-Cl-SO2waters. Sulfateparticles canbederived fromboth typesof activity.Thepresenceofthedifferentsulfatescanbepartiallyinterpretedasprecipitationproductsresultingfromtheevaporationofgeyserderivedliquiddroplets.Theprecipitationsequenceforsodiumdominatedneutral(Ca)-Na-K-SO4wateris(arcanite)-aphtitalitefollowedbyaNa-sulfatephase,asobserved.Moredataaboutfumarolicaerosolsarecrucialforabetterunder-standingofformationprocessesandtheirimpactontheenvironment.
REFERENCESMather,T.A.,Pyle,D.M.&Oppenheimer,C.,2003:Troposphericvolcanicaerosol.InRobock,A.&Oppenheimer,C.,eds.:
VolcanismandtheEarth’satmosphere.GeophysicalMonograph139,WashingtonD.C.,AGU,189-212.Obenholzer,J.H.,Schroettner,H.,Golob,P.&Delgado,H.,2003:ParticlesfromtheplumeofPopocatépetlvolcano,Mexico
—theFESEM/EDSapproach.InOppenheimer,C.,Pyle,D.M.&Barclay,J.,eds.:Volcanicdegassing.GeologicalSociety,London,SpecialPublications,213,123-148.
Pfeffer,M.A.,Rietmeijer,F.J.M.,Brearley,A.J.&Fischer,T.P.,2006:Electronmicrobeamanalysesofaerosolparticlesfromtheplumeof PoásVolcano,CostaRica and comparisonwith equilibriumplume chemistrymodelling. Journal ofVolcanologyandGeothermalResearch,152,1-2,174-188.
Rouwet,D.,Bellomo,S.,Brusca,L.,Inguaggiato,S.,Jutzeler,M.,Mora,R.,Mazot,A.,Bernard,M.,Cassidy,M.&Taran,Y.,2009:MajorandtraceelementgeochemistryofElChichónvolcano-hydrothermalsystem(Chiapas,Mexico).Geofísicainternational,48(1),55-72.
82Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.23
PetrogeneticevolutionofNeogenevolcanisminnorthernUromieh-DokhtarMagmaticBelt:Insightsontheoriginofpost-collisionmagmatism
MonsefReza1,EmamiMohamadHashem2,RashidnejadOmranNematallah3&MonsefIman4
1 Islamic Azad University, Estahban Branch, Iran ([email protected])2 Islamic Azad University, Islamshahr Branch, Iran3 Geology Department Basic Science Faculty, Tarbiyat Modares University, Tehran, Iran4 Shahid Beheshti University, Faculty of Earth Sciences, Tehran, Iran
TheNeogenevolcanicrockswereexposednorthernpartoftheUromieh-DokhtarMagmaticBelt,alongwhichtheNeo-TethyanoceaniclithospherewasclosedduringaperiodbetweenEoceneandOligocene.
Thecollision-relatedvolcanicrocks,whichweremostevidentduringtheEarlyMiocenetoEarlyPliocene,spanthewholecompositionalrangefromandesiticbasalttopargasiticandesiteanddisplaycalc-alkalinecharacter.Theseactivitiesfor-medinrelationtolocalizedextensionalbasinsandweredominatedbypargasiticandesitetoandesiticbasaltlavaf lowsandandesiticbasaltdykes.
MajorandtraceelementsgeochemistrydataexhibitenrichmentinLILEandLREErelativetoHFSE(La(N)/Yb(N)=3-9.7andLa(N)/Nb(N)=2.5-4.5),depletioninNb,TaandTi,andalsohighTh/YbandCe/NbratiosrelativetoMantlearray.TheHFSEdatademonstratethatvolcaniclavashavehighabundancesofNb/YbandNb/Taratios.
Ourgeochemicaldataindicatethatcalc-alkalinevolcanicrockswerederivedfromthemantlemetasomatizedenrichedsourcewitheffectiveofliquidandsedimentf luxcomponentsinheritedfromapre-collisionsubductionslab.
AftercollisionbetweenArabianplateandCentralIranBlockinEarlyCenozoic,thisregionhasexperiencedoflithosphericthinning and volcanismactivity formed in relation to localized extensional regimeduring theEarlyMiocene toEarlyPliocene.Thevolcanismpostdatescontinentalcollision,occurringintranstensionaltectonicenvironment.
Fig1:P-mantlenormalizedREEandtraceelementpatterns
forselectedNeogenepost-collisionvolcanicrocksin
Uromih-DokhtarMagmaticBelt.TheP-mantlenormalizing
valuesarefromSun&McDonough1989.
REFERENCESMcCulloch,M.T.&Gamble,J.A.,1991:Geochemicalandgeodynamicalconstraintsonsubductionzonemagmatism.Earth
andPlanetaryScienceLetters,102,358-375.Sun, S.S. andMcDonough,W.F., 1989:Chemical and isotopic systematics of oceanic basalts: implications formantle
compositionandprocesses.In:Saunders,A.D.andNorry,M.J.(Eds.):MagmatisminOceanBasins.GeologicalSocietySpecialPublicationLondon,313–345.
83
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.24
Refiningthegranulite-faciesmetamorphismintheRhodopemetamorphiccomplex–Greece
MoulasEvangelos1,ConnollyJames1,BurgJean-Pierre1&KostopoulosDimitrios2
1 Department of Earth Sciences – ETH-Zurich, Sonneggstrasse 5, CH-8092 Zurich ([email protected])2 Department of Mineralogy and Petrology, Panepistimioupoli Zographou, 15784 Athens, Greece
TheRhodopemetamorphiccomplex(RMC)innorthernGreece-southernBulgariaisastackofsynmetamorphicnappesthrust mostly during Mesozoic times and having experienced extension coeval with magmatic activity during theCenozoic,inparticularduringtheOligocene.Thehigh-pressure(HP)metamorphicrocksofthecentralRhodopeareover-printedbygranuliteandamphibolite-faciesmetamorphism.Thegranulite-faciesmetamorphismhaspreviouslybeenin-terpretedtorecordhigh-pressure,weshowherethatthepressureofgranulitemetamorphismwasunexceptional.
Aretrogressedkyanite-eclogitefromtheintermediatethrustsheetsoftheRMC(outcropnearThermesvillage-northernGreece)wasinvestigatedtoestablishthemetamorphicconditionsduringdecompressionfromeclogite-facies.
Texturesindicatingkyanitereplacementbysymplectitesofcorundum+plagioclase(An40-60)andspinel(Sp50-Hc50)+plagio-clase(An40-60)revealmicro-scalemetasomaticprocesses.Weusedfreeenergyminimizationandcompositionalphasedia-grams(X-Xsections)fortheNa2O-CaO-FeO-MgO-Al2O3-SiO2(NCFMAS)systemtodefinethepressureandtemperature(PT)spaceinwhichthesesymplectiteshaveformed.Thethermodynamicmodellingrevealsthatthegranulite-faciesoverprintoccurredatapressure<ca1.0GPa.ThePTconditionsofthekyanitebreakdownareboundedbytheunivariantphasefields:
garnet=plagioclase+sillimanite+spinelandsapphirine+sillimanite=spinel+cordierite
Our results show thatmodelling of the symplectiticmineralogy in the simplifiedMASH system is inappropriate forNCFMASsymplectites.
2.25
TertiaryPorphyryandEpithermalAssociationoftheSapes-KassiteresDistrict,EasternRhodopes,Greece
MelissaOrtelli1,RobertMoritz1,PanagiotisVoudouris2,MichaelCosca3andJorgeSpangenberg4
1 Départment de Minéralogie, Rue de Maraîchaire 13, CH-1205 Genève ([email protected])2 University of Athens, 15784 Athens, Greece 3 US Geological Survey, Denver Federal Center, Denver 80225, USA4 Institut de Minéralogie et de Géochimie, Anthropole, CH-1015 Lausanne
TheSapes-KassiteresdistrictbelongstotheEasternRhodopesandislocated20kmnorthwestofAlexandroupoli,Thrace,Greece.TertiarymagmatismassociatedwithvarioustypesofmineralizationinnortheasternGreeceandBulgariaisrelatedtopost-orogenicextension(Voudourisetal.2003,Marchevetal.2005).ThisextensionalcontextresultedintheformationofN-orientedfaultsystemscontrollingtheascentofmagmaandtheemplacementoforedeposits.TheSapes-KassiteresdistrictcontainstheSt-Demetrios,ViperandtheSt-Barbaraprospectsandisdescribedasanassociationofporphyryandepithermalgolddepositshostedbyvolcano-sedimentaryrocks(Voudourisetal.2003,Michael2004).Ourstudyarea,to-getherwiththewell-knownPeramaHillproject,ispartofazoneintheEasternRhodopesstraddlingGreeceandBulgaria,whichisthefocusofcontinuousexplorationinterestforgoldbyminingcompaniesoverthelastdecade.
TheearliestmineralizingeventistheKonosMo(-Cu)porphyryhostedbyagranodiorite-tonaliteandcontainingmainlydisseminatedpyriteandsomeCu-mineralizationinsericiticalteredhostrocks,whichiscrosscutbymolybdenite-pyrite
84Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
veins,dark-greybandedquartzveins(B-veins)andsulfide-richgypsumveins.Epithermaleventsformthepredominantmineralizationofthedistrict,startingwithhigh-sulfidationmineralizationatSt-Demetrioswithhydrothermalvuggysi-licabrecciaandnativegoldassociatedwithtellurides,sulfidesandsulfosalts,followedbytwodifferentlow/intermediate-sulfidationeventscharacterizedbyamethyst-chalcedonyveinsrelatedtoquartzadulariaalterationandmilkyquartzbasemetalveinsrelatedtosericiticalteration.
Fluidinclusionmicrothermometricdatawerecollectedfromquartz,calcite,sphaleriteofthemineralizedveinsfromtheSapes-Kassiteresdistrict,andshowanevolutionofhomogenizationtemperatures(withoutpressurecorrection)rangingfrom560°C, corresponding to thehigh-temperature porphyry system, to 160°C, related to a superficial or epithermalenvironment.Anearlyboilingassemblagearound500 °C iscrosscutbybrine inclusiontrailsyieldinghomogenizationtemperaturesaround240°Cwithsalinitiesbetween30and50wt.%NaClequiv.Fluidinclusionsrelatedtotheepithermalveins(Viperamethyst-chalcedonyveins,andmilkyquartz-calciteveins)yieldhomogenizationtemperaturesbetween170to315°Candsalinitiesbelow6wt.%NaClequiv.
Oxygen isotope values combinedwith f luid inclusiondata reveal thepresenceof amagmatic source formineralizingf luidsrelatedtotheporphyrysystemandtheepithermalveins,withmeteoricwatercontributingtotheoxygenisotopiccompositionoftheepithermalveins.
Accordingtothe40Ar/39Ardata,theSapes-Kassiteresdistrictincludesmagmaticandmineralizingevents,whichtookplacebetween31.3and33.1Ma.ThisstudyrevealsthattheSapes-Kassiteresmagmatismandmineralizationwerecontempo-raneousatabout32MawithotherEasternRhodopesoredistrictsinBulgaria,likeMadjarovoandZvezdel.Atthedistrictscale,the40Ar/39Aragestendtoconfirmthechronologyofthemagmatismandmineralizationeventsobservedinthefield(Figure1).Theporphyrymineralization(biotitecoolingage:32.6±0.5Ma)precedesthebiotiteageofthepotassicaltera-tionat32.0±0.5Ma.Adulariafromthelow/intermediatesulfidationsystemyieldedanageof31.5±0.2Ma.Onesetofthemagmaticsteamaluniteshasaplateauagesof31.9±0.2Maoverlappingwiththebiotiteandadulariaages.Anothermagmaticsteamaluniteyieldsaslightlyyoungerageof31.2±0.4Ma.
Figure1.ModifiedgeneticmodelbyVoudouris(1993).Thecoloreditemshighlightthenewcontributionsofthisstudy.
REFERENCESMarchev, P., Kaiser-Rohrmeier,M.,Heinrich,C.,Ovtcharova,M., vonQuadt,A., Raicheva,R., 2005,Hydrothermal ore
deposits related to post-orogenic extensionalmagmatism and core complex formation: The RhodopeMassif ofBulgariaandGreece:OreGeologyReviews27,p.53-89.
Michael, C., 2004, Epithermal systems and goldmineralization inwestern Thrace (NorthGreece) : Bulletin of theGeologicalSocietyofGreecevol.XXXVI,p.416-423
Voudouris,P.,1993,Mineralogische,mikrothermometrischeundgeochemischeUntersuchungenanepithermalenAu-AgGangmineralisationenbeiKassiteres/Sape(Nordostgriechenland).PhDThesisatHambourgUniversity.
Voudouris,P.,Melfos,V.,Vavelidis,M.,Arikas,K.,2003,GeneticrelationbetweentheTertiaryporphyryCu(-Mo)andtheepithermalAu(-Ag)depositsintheRhodopesmetallogenicprovince,Thraceregion,NorthernGreece:Eliopoulosetal.(eds)MineralExplorationandSustainableDevelopment,SGAmeetingAthensAugust2003,p.542-544.
85
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.26
Reactivemultiphaseflowatthepore-scale:themeltingofacrystallineframeworkduringtheinjectionofbuoyanthotvolatiles.
ParmigianiAndrea1,HuberChristian2,BachmannOlivier3&ChopardBastien1
1 Computer Science Department, University of Geneva, CH-1211 Geneva 4, Switzerla(anderea.parmigiani @unige.ch)2 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, GA 30332, USA.3 Department of Earth and Space Sciences, University of Washington, WA, USA.
Multiphasereactivef lowsoccurnaturallyinvariousenvironmentsintheshallowsubsurface,e.g.CO2injectionsinsatu-ratedreservoirs,exsolvedmethanef luxinshallowsedimentsandH20-CO2volatilesinmagmaticsystems.Becauseoftheirmultiphasenaturetogetherwiththenonlinearfeedbacksbetweenreactions(dissolution/meltingorprecipitation)andthef lowfieldatthepore-scale,thestudyofthesedynamicalprocessesremainsagreatchallenge.Inthisstudywefocusontheinjectionofbuoyanthotvolatilesexsolvedfromamagmaticintrusionunderplatingacrystal-rich magma (porous medium). We use some simple theoretical models and a pore-scale multiphase reactive latticeBoltzmannmodeltoinvestigatehowtheheatcarriedbythevolatilephaseaffectstheevolutionoftheporousmediumspatiallyandtemporally.Wefindthatwhenthereactionrateisrelativelyslowandwhentheinjectionrateofvolatilesislarge(highinjectionCapillarynumber),thedissolutionoftheporousmediumcanbedescribedbyalocalPecletnumber(ratioofadvectivetodiffusivef luxofheat/reactantinthemaingaschannel).Whentheinjectionrateofvolatileisreduced,orwhenthereactionrateislarge,thedynamicstransitiontomorecomplexregimes,wheresubverticalgaschannelsarenolongerstableandcanbreakintodisconnectedgasslugs.
Forthecaseoftheinjectionofhotvolatilesincrystal-richmagmaticsystems,wefindthattheexcessenthalpyadvectedbybuoyantvolatilespenetrates theporousmediumoverdistances~rPe,where r is theaverage radiusof thevolatilechannel(~poresize).Thetransportofheatbybuoyantgasesthroughacrystalmushisthereforeinmostcaseslimitedtodistances<meters.Ourresultsalsosuggestthatbuoyantvolatilescancarrychemicalspecies(Li,F,Cl)farintoamushastheir corresponding localPecletnumber is severalordersofmagnitudegreater than that forheat,owing to their lowdiffusioncoefficients.
86Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.27
Constrainingcalciumisotopefractionationincorals
PretetChloé1,FelisThomas2&SamankassouElias1
1 Département de géologie et paléontologie, rue des maraîchers 13, CH-1205 Genève, Switzerland ([email protected])2 MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
Basedonamulti-proxydatasetconsistingofd44Ca,d18OandSr/Ca,thispreliminaryreportdiscussestheparametersthatcontrolthecalciumisotopefractionationintropicalcorals.Potentialfactorsthatcontrolthecalciumisotoperatioincoralskeletonincludebiologicalfactors(vitaleffects),tempera-tureandsalinity.Currentlythecalciumpathwayandisotopicfractionationincoralsisnotfullyconstrained.Therefore,detailedmeasurementsandamulti-proxyapproachappearfundamentalfortheunderstandingofparametersthatinflu-encethefractionation.
OurdatasetisbasedonfossillastdeglacialcoralsamplesfromTahiti,coredduringtheIODPExpedition310(Camoinetal.,2007).Foranaccuraterecord,thecoralskeletonwasmicro-drilledatsubseasonalresolution.CaandOisotopiccom-positionaswellastheSr/Caratioweremeasured,usingthesamesample.ForCa,weusedaTIMSFinniganTritonT1,followingthemethoddescribedinHeuseretal.(2002).
Ourpreliminaryresultsshowthatthefractionationisalmostconstantwithinerrorbars.Norelationshipbetweenpreci-pitationrateandcorald44Caisrecognized.
Subseasonaltemperaturesvariationsreconstructedfromcorald18OsignalandSr/Caratioarenotmirroredincorald44Ca.TheweaktemperaturedependencereportedbyBöhmetal.(2006)ispossiblynottheonlyparameterthatisresponsibleforthefractionation.
Removingsea-surfacetemperaturecomponentfromthecorald18Osignal(d18Oseawater)resultsinacorald44Carecordthat
revealssomesimilaritytothereconstructedd18Oseawaterrecord,pointingtosalinityasapotentialfactorthataffectscorald44Ca.However,wenotethatinmoderncoralstheseasonalcycleofsalinityatTahiticannotberesolved(Cahyarinietal.,2008).Thesepreliminaryresultsrequirefurtherinvestigation,includingmeasurementsofskeletonoriginatingfromcoralsculturedunderwell-monitoredenvironmentalconditions.
Furthermore,weplantomeasuretheisotopiccompositionofdifferentmicrostructuralpartsofcorals(e.g.,calcificationcenterversusfibers)inordertobetterconstrainthecalciumisotopefractionationprocesses.
REFERENCESBöhm,F.,Gussone,N.,Eisenhauer,A.,Dullo,W.,Reynaud,S.,&Paytan,A.2006:Calciumisotopefractionationinmodern
scleractiniancorals.GeochimicaetCosmochimicaActa,70(17),4452-4462.CahyariniS.Y.,PfeifferM.,TimmO.,DulloW.,&SchönbergD.G.2008:Reconstructingseawaterd18Ofrompairedcoral
d18OandSr/Caratios:Methods,erroranalysisandproblems,withexamplesfromTahiti(FrenchPolynesia)andTimor(Indonesia).GeochimicaetCosmochimicaActa,72,2841-2853.
Camoin,G.F., Iryu,Y.,McInroy,D.&theIODPExpedition310Scientists2007:ProceedingsoftheIODP310. IntegratedOceanDrillingProgramManagementInternational,Inc,Washington,DC.
Heuser,A.,Eisenhauer,A.,Gussone,N.,Bock,B.,Hansen,B.T.,Nägler,T.F.2002:Measurementofcalciumisotopes(d44Ca)usingamulticollectorTIMStechnique.InternationalJournalofMassSpectrometry,220,385–397.
87
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.28
ComplexdynamicsintheSesiaZonesubductionsystemdeducedfrommultiplegenerationsofwhitemicaandallanite:thepowerofmicrotex-turalanalysiscombinedwithpetrochronology
DanieleRegis1,MartinEngi1,DanielaRubatto2,JamesDarling1
1 Institut für Geologie, Universität Bern, Baltzerstrasse 3, CH-3012 Bern ([email protected])2 Research School of Earth Sciences, Australian National University, Canberra
Researchworldwideontheevolutionofterrainswithhigh-pressure(HP)rocksaimstoelucidatethegeodynamicallyfun-damentalprocessesatconvergentmargins.TheWesternAlps,notablytheirinternalparts(Sesia-LanzoZone,DentBlanchenappe,andsmallerklippenunits),havelongbeenrecognizedasaclassicHPterrane:asubstantialareaofpredominantlycontinental,polycyclicbasementtransformedtoblueschistoreclogitefaciesintheAlpineorogeny.However,recentregi-onalwork(Babistetal.,2006)hasindicatedsubstantialgapsandinconsistenciesintheclassicviewoftheWesternAlps,andnewmodelsemphasizingthesequenceofregionalpoly-deformationandpoly-metamorphismhavebeenproposed.Toretracethestepsofthiscomplexevolution,itisessentialtolinkthedetailedpetrographyandmicrochemicalanalysisofthemajorandaccessoryphaseswiththeirmicrotexturalrelationsandsubgrain-scalegeochronology,usingaretentiveisotopicsystem.
Wepresentacasestudyonasinglepoly-deformedeclogitefaciessamplefromtheSesiaZone(ItalianWesternAlps),whichcontainsphengiteandallanitecrystalswithmultiplemetamorphicdomains.
Thesample,collectedintheScalarovalley,consistsofquartz(60%),phengite(20%),allanite/epidote(10%),detritalfeldspar(2%)andalbite (5%)withaccessorymonazite,apatite, titaniteandzircon.Twofoliationsaremarkedbywhitemicaofdifferentcomposition:Phengite(Wm2-Phe2)markingthemainfoliation(S3)containslargerelicf lakes(Wm1-Phe1,pre-S3).Texturallyoldphengitecores(Phe1)arerimmedbymuscovite(Wm1),thecompositionofwhichisidenticaltothatofwhitemicacoresinS3(Wm2).Thelatterareinturnsurroundedbyphengiterims(Phe2).Occasionally,Phe1formsreliccoresinthemicaalignedalongS3.
InthesamequartziteREE-richallanitecoreshaveafirstrimofREE-poorallaniteandanexternalrimofepidote.Corrodedrelicsofmonaziteareoccasionallypresentintheallanitecore.Theallanitecontentsdecreasefromcore(Alncore:REE+Y0.5-0.44a.p.f.u.)torim(Alnrim:REE+Y0.3-0.24a.p.f.u)totheepidoterim(Ep:REE+Y<0.05a.p.f.u.).Bothtypesofallani-teareCe-dominated,incorporatingonlysmallamountsofLaandNd.ThezoningseeninBSEimagesisduetodifferencesinREE,ThandUcontents,whichgenerallydecreasefromcoretorim.TheepidoterimisFe-andSr-rich.
Allanitecoresandrimscontainminutephengiteinclusions.ThesewereanalyzedbyEMPtocomparetheircompositionwiththatofmicamarkingtheS3foliation.Abundantmicainclusionsintheallanitecoresareidenticalincompositiontothetexturallyoldestphengitepreservedinthesample(Phe1).Allaniterimscontaininclusionsofmicas,thecompositionofwhichareindistinguishablefromthoseofthelowpressuremicas(Wm1/Wm2).
ThetwogenerationsofallaniteweredatedbyionmicroprobeusingtheTh-Pbsystem.TheepidoterimwastoorichincommonPbtoobtainreliableagedata.TheREE-richallanitecoresyieldconsistent208Pb/232Thageswithweightedmeanof75.6±0.8Ma(10analyses,MSWD1.02).TheREE-poorallanitemantleissystematicallyyoungerat69.8±0.8Ma(11analyses,MSWD1.8).Thetwoallanitepopulationsarethusindicativeoftwometamorphicstagesthatpre-datethe~65MaHPas-semblagethathasgenerallybeenacceptedastheageoftheeclogitefaciesmetamorphismintheSesiaZone(Ingeretal.1996,Duchêneetal.1997,Rubattoetal.1999).ThelatterislikelyrepresentedbythetexturallylateHPfoliation(Phe2)preserved inthesample.ThismayexplaintheremarkablediversityofAr-AragedatareportedbyVenturini (1995) forsamplesfrommanylocalitiesintheSesiaZone,includingtheCimaBonzearea,wherethepresentsamplewastaken.
Thisstudyrevealsthatthesubduction-collisionhistoryhasproducedacomplexrecordinsinglerocksamples,inthiscaseanimpurequartzite.Combiningmicrotexturalanalysisandpetrochronology,specifiedstagesofthemetamorphicevolu-tionandpolyphasedeformationwerediscerned;SHRIMPdatingofselectgrowthdomainsofallaniteyieldeda(minimum)durationof~6MafortheagedifferencebetweentwostagesoftheHP-evolution.Itisnotclearwhytheeclogitestageat65Masimplyleftnoimprintinthistypeofsample,whereasearlierstagesdid.Accordingtotheregionaltectonicframe-work(Babistetal.2006),thetwomainbasementblocksoftheSesiaZone(i.e.theBardandMombaroneunits)wereamal-gamatedwiththetrailofBonzemetasedimentsbetweenthematHP-conditions,priortothecomplexexhumationhistory.
88Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
REFERENCESBabistJ.,HandyM.R.,HammerschmidtK.&Konrad-Schmolke,M.,2006.Multi-stageexhumationofhighpressurerocks
fromasliverofcontinentalcrust:anexamplefromtheSesiazone,ItalianWesternAlps.Tectonics,26:25.DuchêneS.,Blichert-ToftJ.,LuaisB.,TéloukP.,LardeauxJ.-M.,AlbarèdeF.1997.TheLu-Hfdatingofgarnetsandtheages
oftheAlpinehigh-pressuremetamorphism.Nature387,586.IngerS.,RamsbothamW.,CliffR.A.,&RexD.C.,1996.MetamorphicevolutionoftheSesia-LanzoZone,WesternAlps:
timeconstraintsfrommulti-systemgeochronology.Contrib.Mineral.Petrol.126,152.RubattoD.,GebauerD.&CompagnoniR.,1999.Datingofeclogite-facieszircons:theageofAlpinemetamorphisminthe
Sesia-LanzoZone(WesternAlps).EarthPlanet.Sci.Lett.167,141.Venturini,G., 1995.Geology, geochemistry and geochronology of the inner central Sesia Zone (WesternAlps, Italy).
MémoiresdeGéologie(Lausanne),25:148p.
2.29
ThousandYearsofmassiveIronProductionintheDogonCountry(Mali,WesternAfrica):Technology–Economy-Environment
SerneelsVincent1
1 Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg ([email protected])
Inpre-industrialsocieties,irontoolsareessentialforagricultureandironweaponsforwarfareandpoliticalpower.IronproductiontookplaceeverywhereinAfrica,longtimeago(atleast2’500years)andwelbeforethecolonisation.Thepro-ductiontechniqueisalwaysbasedonthe“bloomeryprocess”:solidstatereductionofironoxidesintometalbyreactionwiththecarbonmonoxidefromthecombustionofcharcoal.AlloverAfrica,societiesdevelopedanincrediblyhighnum-berofdifferentproductionlinestoobtainironfromahugherangeoforesusingverydifferentfurnaces(verysmalltovery large,windorbellowsdriven, free standingor sunked,etc).Thereason for this technologicalvariability remainsunexplained.
Fortenyears,theancientironproductioninthedogonCountry(centralMali,WestAfrica)isinvestigatedonthefieldandinthelaboratory.Theaimofthestudyistheunderstandingofthetechnologiesandthemeasureoftheimpactofthisproductiononthesocietiesandtheenvironment.
Inthestudiedarea(15’000km2),about150productionsiteshavebeenlocated.Sevendifferenttechnologicaltraditionshavebeencharacterisedindifferentareas.Averyremarkableconcentrationofremainshasbeenidentifiedinarestrictedarea(500km2),aroundthevillageofFiko.
Thesystematicsurveyoftheproductionsitesrevealedabout15largecomplexes,characterisedbyhugheheapsofslagandfurnaceremains.Theslagheapsaremappedindetailduringfieldworkandthevolumesofwastearecalculated.Furnaceremainsareexcavatedandstratigraphictrenchesarecuttedintotheheaps.Slags,ores,liningsandcharcoalaresystema-ticallysampledforlaboratorystudies(XRF,XRD,SEM-EDS).Datesareobtainedby14Concharcoal.
Thetechnologyisalwaysthesame,basedonverylargefurnace(3-4m3)usingcharcoalandnaturaldraftandnobellows(lowtemperatures1100°c/longtimes>24h).Lateriticores,minedinseveralpointsalloverthearea,areused.Gradesarelowinthenaturalore(Fe2O355–65%)butenrichmentbyhandsortingallowstoincreaseitsignificantly.Tappedslagscontainingfayaliteandfewfreewüstitearethetypicalwastes(FeO45–50%).
Thesizesoftheheapsrangefrom5’000to40’000tons.ThetotalamountofslagfromthetechnologicaltraditionofFikocanbeevaluatedto300’000tons.Thequantityof ironcanbeestimatedonthebasisofachemicalbalancecalculatedbetweentheoreandslag.Thetotalquantityofironmusthavebeenover100’000tons.
Theproductionstartedprobablyaround500ADbutdevelopedmainlybetween1000and1750ADatthetimeoftheriseoftheMaliEmpire.Theproductionriseduptoaquasiindustriallevel(100tons/year),involvingalargepartofthelocalpopulationandwithasignificantimpactonthewoodressources(2000tonswood/year).
This study is part of the global interdisciplinary project “Human Population and Paleoclimatic Evolution in West Africa” leaded by prof. E. Huysecom (Geneva) and funded by the SNF, the SLSA and several additional sources. The various aspects of the archaeometallurgical studies involved several european and african researchers: V. Serneels, S. Perret, M. Mauvilly, I. Katona, R. Soulignac (Fribourg), C. Brunner (Geneva – Toulouse), B. Eichhorn (Frankfurt), B. Traoré (Bamako – Paris), A. Dembélé (Bandiagara).
89
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.30
TheAdamellobatholith(Italy):afossilmagmachamberoraccumulationofmagmapulses?
SkopelitisAlexandra1,SchalteggerUrs1,UlianovAlexey2&BrackPeter3
1 Département de Minéralogie, Rue de Maraîchers 13, CH-1211 Genève 4 ([email protected], [email protected])2 Institut de minéralogie et géochimie, Anthropole, CH-1015 Lausanne ([email protected])3 Departement Erdwissenschaften, ETH Zürich, CH-8092 Zürich ([email protected])
Wewanttostudyplutonsandbatholithsindetailtoelucidatetheirmodesofformation,andinparticular,toreconstructthetimerequiredfortheiremplacement.Thislatterinformationislinkedtotheoverallthermalbudgetoftheintrudedareaandthecoolingrateoftheintrudedmagmaticbodies.Itisimportanttoknowhowthetimescalesofsolidificationrelatetothetimeelapsingbetweentheemplacementoftwoconsecutivemagmabatches.Inotherwords,wewanttoknowtowhatextentwhichpartsofaplutonwerepresentina,atleastpartially,moltenstate.
ThisstudyfocusesonthetimeneededtobuildtheAdamellobatholithintheItalianAlps,mainlyinthenorthernpart,whichcomprisestheRédiCastello(RdC),theAdamello,theAvioandthePresanellasuperunits(Fig.1).Previousagedeter-minationsfromtheAdamellorocksshowayoungingtowardsthenorth,basedonU-PbzircondataandK-ArandRb-Srresults(summariesinCallegari&Brack,2002;Schalteggeretal.,2009).Thesouthofthebatholithischaracterizedbymoremaficcompositionsrangingfromgabbroictotonalitic,whereasthenorthiscomposedprincipallyoftonalite,leucotona-liteandtrondhjemiterocks(Brack,1983).Moreover,previousisotopestudiesacrosstheAdamelloshowedanincreaseofthe87Sr/86Srand18O/16Oratiosfromsouthtonorth,indicatinganincreasingcrustalcontaminationtowardsthenorth(DelMoroetal.,1983;Dupuyetal.,1982),confirmedbypetrographicalchangesinthetonalites,suchasincreasingabundanceofbiotitecomparedtoamphiboleinthesamedirection.Inthisproject,geochronologyandwholerockaswellasmineralchemistrywillbeusedtounderstandtheformationofthetonalites.Weattemptunderstandinganddistinctionofinheri-tedgeochemicalcharacteristicsfromthesourceandthoseacquiredduringfractionationandcrystallisation.
RocksfromthecenterandthenorthoftheAdamelloshowarestrictedrangeincomposition(diorite-granodiorite,63-70%wtSiO2)althoughtherockshavedifferentmineralogy,grainsizeandtexture.Indeed,thetexturesobservedinrocksfromthenorth-easternborderareasarespecificbecauseoftheirfoliation,probablyduetodeformationinconnectionwiththeadjacentTonaleLine.ThepreliminarygeochemicaldatahighlightthattheRdChasametaluminouscomposition,where-astheothersunits-youngerandsituatednorthwards-aremoreperaluminous.Laserablation-ICP-MSU-Pbagedetermi-nationsonzirconfromtonalitesoriginatingfromthecentralandnorthernpartsofthebatholithhavebeencarriedouttodeterminetheageofcrystallizationandreconstructtheintrusionsequence.FirstresultsconfirmthatthecenterandnorthernpartoftheAdamelloemplacedbetween43and34Ma(Fig.1).Withourpresentanalyticalprecisionof0.4-1%(N=8-32)of the 206Pb/238Uagewecandemonstrateourability toresolvesuchagedifferencesandhavearguments that theAdamellobatholithformedincrementallybyseveralpulsesyoungingtowardsthenorthandshowingdifferentcomposi-tion.TheCLimagingperformedbeforeLA-ICP-MSanalysisrevealedwellcrystallizedmagmaticzonationsandxenocrysticcoresinparticularfornorthernunits.Finally,theseresultsclearlyfavouranamalgamationofdistinctmagmaticpulsesovermillionsofyearsthatpreviouslydifferentiatedinadeepermagmaticsystemastheprocessformingtheAdamellobatholith.
We acknowledge funding of FNS in the frame of ProDoc project Adamello 4-D.
REFERENCESBrack, P. 1983:Multiple intrusions examples from the Adamello batholith (Italy) and their significance on the
mechanismsofintrusions.Mem.Soc.Geol.It.26,145-157Callegari,E.&Brack,P.2002:GeologicalmapoftheTertiaryAdamellobatholith(NorthernItaly)explanatorynotesand
legend.Mem.Sci.Geol.54,19-49DelMoro,A., Ferrara,G., Tonarini, S.&Callegari, E. 1983: Rb-Sr systematics on rocks from theAdamelloBatholith
(SouthernAlps).Mem.Soc.Geol.It.26,261-284Dupuy,C.,Dostal,J.&Fratta,M.1982:GeochemistryoftheAdamelloMassif(NorthernItaly).Contrib.Min.Pet.80,41-48Schaltegger,U.,Brack,P.,Ovtcharova,M.,Peytcheva,I.,Schoene,B.,Stracke,A.&Bargossi,G.2009:Zirconandtitanite
recording1.5millionyearsofmagmaaccretion,crystallizationand initialcooling inacompositepluton (southernAdamellobatholith,northernItaly).EarthPlanet.Sci.Lett.186,108-218
90Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Figure1.GeologicalmapoftheAdamellobatholith,indicatingournewLA-ICP-MSU-Pbagesonzircon(ModifiedafterBracketal.,un-
published)
2.31
MineralogicaltechniquesandethnoarchaeologyappliedtothestudyofsmithingslagsinMali(Africa)
SoulignacRaphaëlle1
1 Department of Geosciences, Chemin du Musée 6, CH – 1700 Fribourg ([email protected])
Archaeologicalexcavationsoftenrevealhemisphericalpiecesofslagthatarethewasteresultingofthesmithingofironinahearth.Theyareformedbytheaccumulationofseveralfusedmaterialsatthebaseofthehearth,betweenthelight-ingandtheextinctionofthefire.Smithingslagsshowahighvariability(size,weight,shape,internalstructure,materialstheyaremadeof)ref lectingthecomplexityofthesmithingwork:variabilityofstartingmaterials,thermomecanictreat-ments,skillsofthesmith,economicpressure.
Withthisintentiontounderstandinmoredetailsthoseslags,weundertookanethnoarchaeologicalapproachwithtra-ditionalsmithsoftheDogongroupinMali.Thisethnoarchaeologicalapproachisbasedontheobservationandtherecordoftheproductionof126traditionalhoesofironor“daba”in4villagesof2ethnicalgroupswithseveralsmiths.Theyweregiveneachtimevariousstartingmaterialswithdifferentcomposition(%C:0.17,0.35,0.45)orshape(barsof4x4cm,2x2cm,1x1cmetc).Thewastes(slagsandhammerscales)havebeencollectedafteronesingleforgingorafteroneworkingday.Theyareunderstudyinthelab,usingmineralogicaltechniques:XRF,XRD,SEM-EDXS.Thefirstresultswillbediscussed.
Itappearsthatforonesinglepieceofiron,thequantityofironlostduringtheoperationvariesfrom7to25%.Ifthesmithhastoweldtogether2piecesofiron,thenthelengthoftheoperationincreasesandalsotheamountofironlost,upto60%.
91
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.32
MiningarchaeologicalstudiesinEasternPyrenees,France:Baillestavyironminingarea
CălinG.Tămaş1,2,GabrielMunteanu3,BéatriceCauuet3&GérardMut3
1 Department of Geosciences, University of Fribourg, 6, chemin du Musée, CH-1700 Fribourg ([email protected])2 Faculty of Biology and Geology, University Babeş-Bolyai, 1, M. Kogălniceanu str., 400084, Cluj-Napoca, Romania3 Laboratoire des Travaux et Recherches Archéologiques sur les Cultures, les Espaces et les Sociétés (TRACES), Université Toulouse 2 Le Mirail, CNRS UMR 5608, Maison de la Recherche, 5 allées Antonio-Machado, 31 058 Toulouse Cedex 09, France
SeveralirondepositshostedinLowerCambrianlimestonesanddolomites(CanaveillesFormation)areknowninthenort-hernpartofCanigouMassif,EasternPyrenees,France(Guitardetal.,1998).Accordingtotheabovementionauthorsse-veraldepositslikeBatère,Escaro-Escoums,Aytua-Torrent,Casteil-Falguerosa,Sahorre,Fillols-Taurinya,leLlech,laCoumehavebeenmineduntilmid20thcenturywhentheminingactivityfinallystopped.
BaillestavyisasmallvillagesituatedclosetolaCoumedeposit.Thislocalityrepresentsaminingsitebutinthesametimeitisknownduetothelargeamountofironslags.Archaeologicaldiggingscarriedoutwithintheslagdepositofthechur-chSt.AndrewfromBaillestavy(Mut,2001)pointedoutametallurgicactivitybacktoGaulandRomantimes(2ndcenturyBC–1stcenturyAD).InsteadofthepresenceofAncientslagwastedumpsinBaillestavy,accordingtoFinot(1902)theironexploitationstartedonlyin1830.
MiningarchaeologicalstudiesstartedrecentlyinBaillestavyareahavingseveralaims:
-tomakeanuptodatereviewoftheaccessibleminingvestigesandtheirconservationstate;-toidentifydifferentperiodsofminingbasedonpeculiaritiesofdiggingtechniques;-datingoftheoldestminingactivity.
Thestudydevelopedduringthreefieldworkcampaignsbeingfocusedonsurfaceandundergroundexploration,identifi-cationofallaccessibleminingworks,topographyoftheworks,archaeologicalobservations,geologicalmapping,andar-chaeologicaldiggings.FourminingsiteshavebeeninvestigatedinthevicinityofBaillestavy:MasMorer,PeñaBlanca,laCoumeandMasBourasse.
Takingintoaccountthediggingtechnique,atleastthreeperiodsofactivityhavebeenobserved:
1–handtoolswithnarrowtraces;2–Catalantypechisel;3–blastholes(twotypes).
Theorebodiesandtheirhostrockshavebeenmappedforalltheidentifiedminingsites.Thegeologicalstudyoftheun-dergroundworksgavemoreinformationsconcerningthegenesisoftheorebodiesandhelpedtobetterunderstandthedevelopmentofthemines.
ThearchaeologicaldiggingsconductedintheundergroundworksfromMasBourasseminingsector,situatednorth-westoflaCoumedeposit,allowedMunteanu(2010)tocertifythattheironoreswereminedduring1stcenturyAD.
REFERENCESGuitard,G.,Laumonier,B.,Autran,A.,Bandet,Y.&Berger,G.M.1998:CartegéologiquesdelaFranceà1/50.000.Notice
explicativedelafeuillePrades,198p.Finot,M.1902:Procès-verbaldevisitedesrecherchesdeminesdeferde laSociétédePauillacàBaillestavyetEstoher.
MinistèredesTravauxPubliques,ServicedesMines,Dépt.desPyrénéesOrientales,Prades,no.1246,8p.Munteanu,G.2010:LedistrictminierdeBaillestavy(PyrénéesOrientales).Laproductionduferdel’Antiquitéàl’époque
moderne–exploration,topographie,chronologieetgéologiedesminessouterraines.MasterII,UniversitéToulouseleMirail(unpubl.).
Mut,G.2001:LesforgesdeBaillestavy,inSablayrolles,R.(ed.),LesressourcesnaturellesdesPyrénées.Leurexploitationdurantl’Antiquité,Entretiensd’archéologieetd’histoire,St-Bertrand-de-Comminges,2001,p.141-153.
92Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.33
FossiliferouspotteryinAjoie(NWSwitzerland)andadjacentregionsfromLaTèneandGallo-romansites:Informationonproductionanddis-tributionthroughmicroscopicandchemicalanalyses
Thierrin-MichaelGisela
Department of Geosciences, University of Fribourg, ch. du musée 6, 1700 Fribourg et Section archéologie et paléontologie, Office de la cul-ture du Canton du Jura, 2900 Porrentruy
Fossiliferous,alsocalled“shell-tempered”,potteryispresentedasaphenomenoninlateLaTèneandGallo-romanperiodsinseveralregions–likeNormandy,BelgiumandSouthEngland.Inmostcasestheseceramicproductionsarelinkedtoclayoutcropsinthesameregion.Insomeinstances,however,thesewaresarethoughttohavebeenwidelydistributedfromoneproductionarea.
FossiliferouspotteryisthemostimportantfabricgroupatmidtolateLaTènesitesinAjoieandremainssignificantamongGallo-romanmaterial(7sitesconsidered).Hand-formedbowlsofdifferentdimensionarethemostfrequentform.Thesefindingsallowedadiachronicstudyofthispottery,spanningover300yearsansweringfollowingquestions:whichrawmaterialswereused?,thesameclay(s)throughout?,sameordifferingpreparationintime?
ThepresenceoffossiliferouspotteryisalsowelldocumentedoncontemporarysitesinthenearbyBaselregion,amongthemthekiln-siteofSissach-Brühl(Basel-Landschaft,Switzerland).WhileverycoarsepiecesfromAjoiearedistinctiveandseemtooccuronlythere,afinerfabricispresentonallsites.Macroscopically,thematerialfromdifferentsitesisundis-tinguishable.Werethereonlyfewproductionsitesandexchange,ormanyproductions?Inordertodeterminethis,piecesfromSissach-BrühlandthreeLaTènesettlements(mostlyhand-formedbowls),aswellassherdsofhand-formedcookingpotsfromtheRomantownAugustaRauricorum(Basel-Landschaft,Switzerland)andsurroundingvillae,werecomparedtothefindsfromAjoie.
Macroscopic,microscopicandchemical(XRF-WDS)comparisontovirgulamarlfromtheupperJurassic(Kimmeridgian)provedthisparticularclaytobeusedinAjoie–eitherpureorcrushedandmixedwithnon-calcareousquarternaryclays.Outcropsofthemarlylayerareeasilyaccessiblefromallthesites.Somegallo-romanpiecesrevealedanotherpreparation:crushedspathiclimestone,locallyavailable,mixedwithnon-calcarousclay.
ThesherdsfromtheBaselregionallshowfossilassemblagesdifferentfromtheAjoiepottery.FossiliferousmarlylayersfromtheDoggercertainlyprovidedtherawmaterialsforsomeofthem,whileothersappeartobemixtures(naturalorintentional)ofdifferentnotyet identifiedclays (the identification isdifficultalso,becausethinsectionsfromceramicsherdsdonotalwaysshowdiagnosticfossilfragmentsandassemblages).Thisdiversityinrawmaterialsupportstheas-sumptionthatthiswarerarelytravelledfarfromtheproductionsiteinthediscussedregionofNWSwitzerland.DuringtheLaTèneperiodatleast,thereisnoevidenceofdistributionfrommoreimportantproductionsites,inspiteofacertainpopularitysuggestedbythehighpercentagesoffossiliferouspotteryamongtheceramicmaterialinthesettlements.
2.34
Insightsintothedehydroxylationkineticsoflizarditeandchrysotile
TrittschackRoy&GrobétyBernard
University of Fribourg, Department of Geosciences, Chemin du Musée 6, CH-1700 Fribourg ([email protected])
Lizardite and chrysotile represent two prominent trioctahedral 1:1 phyllosilicates of the serpentine mineral group.Lizardite(Mg3Si2O5(OH)4)hasaconventionalsheetsilicatestructure,whereasinchrysotilethesameTO-layersarerolledtocylinders.Thechrysotile structurehas thusnota classical3D-symmetry,butonly rotational andno radial symmetry.Physicalpropertiesare,therefore,expectedtoreflectalsothisnon-conventionalsymmetry.
Theaimofthisstudyistounderstandtheinfluenceofspecialsymmetryofchrysotileonthemechanismandtheratedeterminingstepsofthedehydroxylationreaction.Thedehydroxylationkineticsoflizarditeserves,thereby,asreference.
93
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Theoretical deprotonation andwater forming schemeswere comparedwith results of in-situHigh-TemperatureX-raydiffraction,in-situIR-spectroscopy,FTIRandDifferentialThermogravimetryexperimentsonwellcharacterizedchrysotileandlizarditesamples.In-situIRandHT-XRDexperimentsunderambientpressuregavestartingtemperaturesforthede-hydroxylationoflizaditebetween500°Cand550°Cwhichliesintherangeofformerinvestigations(Franketal.2005).
Chrysotiledehydroxylationdependonstructuralfeaturesliketheinnerandoutertubediameterwhichitselfdictatethephysicalproperties.Thedehydroxylationstartsattheoutermostlayersataround450°Cand500°C,whereasinnermostlayers breakdownabout600°C (Metraux et al. 2002). The initial dehydroxylationproduct of bothpolymorphs isX-rayamorphous,butcrystallizesafteracertain timeto forsterite.Thesephase transformationswerealso followedbyFTIRanalyses,whichofferadetailedinsightintothestructuralrecombinationduringthedehydroxylation.
Kineticdatawerecalculatedfromtwoindependentmethods,in-situHigh-TemperatureX-raydiffractionandDifferentialThermogravimetrytechniquesfordifferentatmospheres(N2,O2,air,etc.).Assumingproportionalitybetweentheintegralintensityofdiffractionpeaksandtheamountofserpentinepresent,thereactionratecanbeextractedfromtherateofintensitydecrease.Data from isothermal runshavebeen treatedwith theconventionalAvramimethodaswellas the“timetoagivenfraction”(TGF)method.LatteroneoffersthepossibilitytodiscoverchangesintheactivationenergyEaduringthecourseofdehydroxylation(Putnis1992).ThesamereactionprogressdependencyofEacanalsobeobtainedbytheisoconversionalFriedmananalysisfromaseriesofdynamicDTGdata.
IsothermalHT-XRDexperimentsonlizarditeyieldedEaofaround340kJmol-1(Avramimethod).DatatreatedwiththeTGFmethodshowedaprogressiveincreaseoftheEawiththefractiontransformedfromaround200kJmol-1(α=0.1)to340kJmol-1(α=0.9).Non-isothermalDTGanalysesonlizarditewithdifferentheatingratesandunderacontrollednitrogenat-mosphere confirmed the TGF results and enabled amuchmore detailed resolution of the Ea during the dehydrationprogress.Apreliminarymechanisticinterpretationoftheseresultswillbegiven.
REFERENCESFrank,M.R.,Earnest,D.J.,Candela,P.A.,Wylie,A.G.,Wilmot,M.S.&Maglio,S.J.2005(abstract):Experimentalstudyof
thethermaldecompositionoflizarditeupto973K,SaltLakeCityAnnualMeeting2005Metraux,C.,Grobéty,B.&Ulmer,P.2002:Fillingofchrysotilenanotubeswithmetals,JorunalofMaterialResearch,17,
1129-1135.Putnis,A.1992:IntroductiontoMineralSciences,CampridgeUniversityPress,457p.
2.35
Calculatingrheologicpropertiesofmagmasfromfieldobservationscom-binedwithexperimentaldata.
VerberneRoel1,UlmerPeter2,MüntenerOthmar1
1 Institut de Minéralogie et Géochimie, batiment Anthropole, CH-1015 Lausanne ([email protected]) 2 Institut für Geochemie und Petrologie, Clausiusstrasse 25, CH-8092 Zürich
Inordertoinvestigatetheemplacementprocessesthatoccurinshallowlevelplutonicmagmareservoirs,wetrytorelatephaseassemblagesandmineralcompositiontotheemplacementhistoryofaparticularrocksuitebycombiningfieldandexperimentalapproachestounderstandthephysical,rheologicalandtemporalevolutionofcrystallizingbatholiths.
HerewepresentacasestudyoftheListinoRingStructureoftheAdamelloBatholith,N-Italy,whereprocessesofinterac-tionbetweenfelsicandmaficmagmas,suchasmaficdikeinjectioninpartlycrystallizedsilicicmagmas,dikedisaggrega-tion,enclaveformation,andnear-solidusshearingwerestudiedinglacier-polishedoutcrops.Mostofthesephenomenaaregenerallyassignedtof luiddynamicprocessesoperatinginamagmareservoir(Turner&Campbell,1986),whererheolo-gicalbarriers(e.g.viscositycontrast)inhibitchemicalmixingofmaficmagmaswithcrystal-richsilicicmagmas(Sparks&Marshall,1986;Blundy&Sparks,1992).
Ourapproachcentersaroundthedeterminationofmineralassemblagesandcrystalfractionspresentatthetimeoftheprocessunderinvestigation.Themineralassemblageatthetimeofinjectionofmaficmagmas,canbedeterminedfromtheobservationthatmineralsfromthehostmagmaarebeingmechanicallyincorporatedasphenocrystsintothe
94Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
maficenclavesbeforequenchingoccurs.Inthecaseofsynmagmaticdeformation,thecrystalspresentduringdeformationcanpossiblybeidentifiedbydeterminingthecrystalfractiondisplayingplasticdeformation.
Havingdeterminedthemodalmineralogyandcompositionofphases,combiningwithwholerockchemistryofbothmag-masandapressureestimateobtainedfromAl-in-HornblendebarometrybyBlundy&Caddick(unpublished),allowsustoconstrainthetemperatureandH2O-contentofthehostmagma.Themeltfractionandcompositionofthehostmagmacanthenbecalculatedfromavailableexperimentaldata,andthemeltcompositioncanbefurtherconstrainedbythechemicalanalysisofassemblagesfoundin(back)veins,whicharethoughttorepresentthemeltcomponentofthesystem.
Observedcrosscuttingrelationshipsbetweenthedifferentmagmaticphasescombinedwiththeirrespectiveoffsetalongsynmagmaticshearzonescanbeusedtodeterminestrainandpossiblystrainratesthroughdatingofthevariousphases.Havingdeterminedthecomposition,pressure,temperatureandcrystallinityofthehostmagma,itsrelativeviscositycanbecalculatedusingtheexperimentallycalibratedrelationshipbetweenrelativeviscosityandtheparticlevolumefraction(Costaetal.,2009andreferencestherein).
REFERENCESBlundy,J.D.andSparks,R.J.S.,1992.PetrogenesisofmaficinclusionsingranitoidsoftheAdamelloMassif,Italy.Journal
ofPetrology,33:1039-1104.Costa,A et al., 2009.Amodel for the rheologyof particle-bearing suspensions andpartiallymolten rocks.Geochem.
Geophys.Geosyst.,10,Q03010,doi:10.1029/2008GC002138.Sparks, R.S.J. andMarshall, L.A., 1986. Thermal andmechanical constraints onmixing betweenmafic and silicic
magmas.J.volc.geotherm.res.,29:99-124.Turner,J.S.andCampbell,I.H.,1986.Convectionandmixinginmagmachambers.Earth.Sci.Rev.,23:255-352.
2.36
Howlongdoesseawaterandoceaniccrustinteract?
FlurinVils1,TimElliott1,ChristopherE.Smith-Duque2,JeffreyC.Alt3&DamonTeagle2
1 University of Bristol, BS8 1RJ Bristol, United Kingdom (1 correspondence: [email protected])2 National Oceanography Centre, SO14 3ZH Southampton, United Kingdom3 University of Michigan, MI 48109-1005, USA
Afterhavingbeenformedatmid-oceanridges,oceanicplatescoolastheymoveawayfromtheridgesandbecomeolder.Muchofthiscoolingisrelatedtohydrothermalalterationbyseawaterinfiltratingtheplates.Duringseawater-rockinter-action,primarymineralsaretransformedintosecondaryminerals.Thistransformationcanmobilizeelements,whichareleachedoforenrichedintheoceaniccrustandisthereforeinfluencingthebulkrockcomposition.
Twoprocessesmainlycontrolelementabundancesintheoceans:continentalweatheringandhydrothermalactivityintheoceanicplate.Thehydrothermalactivity is furtherdividedintohigh-T (nearridge)andlow-T (offtheridge)alteration.High-Talterationprocessescanbeeasilystudiedinhydrothermalventregions.Aslow-Talterationprocessesintheoceaniccrustareratherdiffuseandslow,therelimitsandconditions(time,temperature,etc.)arelargelyunknownandthusin-vestigationofoff-ridgealterationisimportant.Thisstudyinvestigatesthealterationprocessesofmid-oceanridgebasalts(MORB)inthelow-Tenvironmentsandconstructsatimeframeforseawater-rockinteractionintheseregions.
WeatheringofthecontinentalplateskeeptheU-seriesdecaychainintheocean(a234U/238U-ratioof~1.14)indisequilibri-um.Ontheotherhand,MORBformedattheridgeareinsecularequilibrium.ThusanyseawateralterationofMORBleadstoanenriched234U/238U-ratioandafter~5half-lifetimesofuraniumtheMORBareagaininsecularequilibrium.Preliminary234U/238U-dataonoldoceaniccrustfromODPSite1179(~129Ma)andODPSite843(~94Ma)showsthatalteredMORBaremostlyinsecularequilibrium.Nevertheless,higherUconcentrationsinthealteredMORBcomparedtofreshMORBonbothSitessuggeststhatseawateralterationoccurredearlier,butoutsidetheradiogenicdetectionwindowof~1.25Maforthe234U/238Udecaychain.AlteredMORBfromyoungerODPSites(e.g.ODPSite1301,~3.5Ma)showdisequilibrium,repre-sentingrecentseawater-rockinteractions.AdditionalU-seriesmeasurementsonODPSitesarecurrentlyproceedtofurtherconstrainthealterationtime-window.
95
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.37
Bariumisotopefractionationinnaturalbariummineralsandprecipitati-onexperiments:Afirstglimpseattheglobalbariumcycle
KatjavonAllmen(1,3),MichaelE.Böttcher(2),EliasSamankassou(1,3),andThomasF.Nägler(4)
(1 ) Department of Geosciences, Chemin du Musée 6, University of Fribourg, CH-1700 Fribourg, Switzerland ([email protected]),(2 ) Leibniz Institute for Baltic Sea Research (IOW), Geochemistry & Isotope Geochemistry Group, D-18119 Warnemünde, FGR ([email protected]),(3 ) present address: Section of Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland ([email protected]),(4 ) Institute of Geological Science, Baltzerstr. 3, University of Bern, CH-3012 Bern, Switzerland ([email protected])
Wepresentresultsfromanongoinginvestigationonthestablebarium(Ba)isotopefractionationinthenaturalBacycle.StableBaisotopesignaturesofinternationalIAEAreferencematerials(syntheticbariumsulfateandbariumcarbonate),naturalBamineralsandBaprecipitateshavebeenanalyzedtoevaluatepotentialdiscriminatingprocessesintheglobalgeochemicalbariumcycle.
Inthemodernocean,dissolvedBarium(Ba)showsavariableconcentrationandanutrient-typebehavior(Chanetal.,1976).Asanon-conservativeelement,Bahasarelativelyshortresidencetimeof11kyrs(Edmondetal.,1979).Baconcentrationsarereduced in theupperwatersof theopenoceanandenriched indeepwatersandareasofnutrientupwelling (e.g.,Church,1979).VariationsintheaccumulationrateofBaboundtocarbonateandsulfateinmarinesedimentsarethoughttobeindicativeofvariationsinmarinebiologicalproductivitythroughtime(e.g.,Church,1979;Paytan&Griffith,2007).DetritalsourcesofBafromcontinentalrunoff,hydrothermalalteration,anddiageneticBamobilityarehardtoconstrainwithBaconcentrationsalone.Thus,weproposethefractionationofstableBaisotopesasanewtooltoconstrainBabeha-viorintheglobalelementcycle.
Measurementswerecarriedoutonamulti-collectorICP-MSapplyinga130Ba/135Badoublespike.DataaregivenaspermildeviationsfromalaboratoryBanitratestandardsolutioninthed137/134Banotation(external2sstdev<0.1permil).Varioussyntheticsolidstandardsandthep.a.qualitysyntheticbariumchlorideusedfortheprecipitationexperimentsshowverysimilar isotoperesultsclosetothenitratestandardsolution.Theterrestrialbariumgangueminerals (fourbarites,onenorsethite[BaMg(CO3)2])weredepletedintheheavyisotope(d
137/134Baavaluesbetween0and-0.2permil).
AnaturalbaritefromanundisclosedChineselocalitygaveanisotopevalueof-0.4permil.High34S/32Sand18O/16Oratiosin this sample indicate that thisbaritehasbeenformedunder influenceofmicrobial sulfatereduction,probably inamarinediageneticenvironment.ThelargestBaisotopefractionationwith-0.5permilwasfoundinadiageneticbarite.Thisvalueisalsoaccompaniedbyhigh34S/32Sand18O/16Oratiosindicatingformationunderinfluenceofmicrobialsulfatereduction.Theobservednaturaldiscriminationsarebyfarlargerthantheanalyticaluncertaintyoftheisotopemeasure-ments,indicatingisotopediscriminationinthenaturalbariumcycle(vonAllmenetal.,2010).
Precipitationexperimentsfromaqueousbariumchloridesolutionsattemperaturesof20°and80°CindicatethatthelightBaisotopeisenrichedinpurebariumcarbonateorbariumsulfatecomparedtotheaqueoussolution.Amaximumisotopefractionationof-0.3permilisobserved,forbothbariumcarbonateandsulfate.Thisfractionationseemstobeinfluencedbyprecipitationrate(BaCO3)and/ortheaqueousspeciation,butlessbytemperature.
REFERENCES:Chan,L.H.,Edmond,J.M.,Stallard,R.F.,Broecker,W.S.,Chung,Y.C.,Weiss,R.F.&Ku,T.L.,1976:Radiumandbariumat
GEOSECSstationsintheAtlanticandPacific.EarthPlanet.Sci.Lett.,32,258-267.Church,T.M.,1979:Marinebarite,inBurns,R.G.(Editor),Marineminerals.MineralogicalSocietyofAmerica,Reviewsin
Mineralogy,6,175–209.Edmond,J.M.,Measures,C.,McDuff,R.E.,Chan,L.H.,Collier,R.,Grant,B.,Gordon,L.I.&Corliss,J.B.,1979:Ridgecrest
hydrothermalactivityandthebalancesofthemajorandminorelementsintheocean-Galapagosdata.EarthPlanet.Sci.Lett.,46,1-18.
Paytan,A.&Griffith,E.M.,2007:Marinebarite:Recorderofvariationsinoceanexportproductivity:Deep-SeaResearch:PartII,TopicalStudiesinOceanography,doi:10.1016/j.dsr2.2007.01.007.
vonAllmen,K.,Böttcher,M.E.,Samankassou,E.,&Nägler,T.F.,(2010):Bariumisotopefractionationintheglobalbariumcycle: First evidence frombariumminerals and precipitation experiments. Chem.Geol., (in press) doi:10.1016/j.chemgeo.2010.07.011
96Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.38
PalaeoredoxchangeduringOAE1a:newinsightsfromphosphorusandredox-sensitivetraceelements
StéphaneWestermann1,MelodyStein2,VirginieMatera3,NicolasFiet4,ThierryAdatte2&KarlB.Föllmi2
1 Department of Earth Sciences, University of Bristol, Wills Memorial, BS81RJ, Bristol, UK ([email protected])2 Institut de géologie et de paléontologie, Université de Lausanne, CH-1015, Lausanne, Switzerland3 I.N.R.S., Avenue de Bourgogne, 54500 Vandoeuvre-les-Nancy, France4 AREVA, 33 rue La Fayette, 75442 Paris, France
TheEarlyAptianrecordsanepisodeofsevereenvironmentalchangeincludinganoceanicanoxicevent(OAE),aplatformdrowningepisodeandabiocalcificationcrisis.Thisepisode,theso-calledOAE1a,correspondstooneofthemoststudiedanoxiceventsand ischaracterizedbyan increase inthed13Cvaluesprecededbyanegativespike.Here,weproposetotracechangesinoceanchemistryduringOAE1atoimproveourunderstandingofsuchphenomenaandtesttheproposedmodels.Thus,we investigatephosphorus (P) and redox-sensitive trace-element (RSTE)distributions in sections alongabasin-shelftransectinthewesternTethysthroughlowerAptiansediments.Wecomplementourgeochemicalanalysisbytheanalysisoforganic-mattercontents.
Weselectedthreerepresentativesections:GorgoaCerbara(centralItaly)intheUmbriaMarchebasin,Glaise(SEFrance)locatedintheVocontianTroughandCassis/LaBédoule(SEFrance)locatedalongtheProvencalplatform.
InthesectionsofGlaiseandCassis/LaBédoule,PcontentsshowfirstanincreaseattheonsetoftheEarlyAptianevent,justabovethed13Cnegativespike,andthen,duringtheOAE1a,followedbylowervalues.Asecondincreaseisobservedattheendofthecarbon-isotopicexcursion.Thissuggestsanincreaseinnutrientinput,whereasthereturntolowervaluesthroughthefirstpartoftheanoxiceventmayberelatedtoaweakenedcapacitytoretainPinthesedimentaryreservoirduetobottom-wateroxygendepletion.Thisgeneralpattern iscontrastedbythedataofGorgoaCerbara.Surprisinglyenough,thesedimentsdepositedduringtheOAE1a(theSellilevel)showsP-enrichments(mainlyauthigenicP)associatedwithmaximuminTOCvaluesandhighCorg:Ptotratios.ApartoftheremobilizedPappearstohavebeentrappedinthesedimentsandwasassuchpreventedfromreturningtothewatercolumn.
InthesectionofGorgoofCerbara,U,V,Mo,CoandAsdistributionspresentsimilarbehaviourwithalowbackgroundlevelalongthemainpartofthesection,contrastedbydifferentmaximainconcentrationswithintheSellilevel.IntheGlaisesection,aweakincreaseisobservedjustafterthenegativespikeind13CwhereasintheCassis/LaBédoulesection,nosignificantenrichmentshavebeenobservedinsedimentsequivalenttotheSellilevel.ThedifferentbehaviouroftheRSTEinthestudiedsectionsmayberelatedtothepalaeogeographicsettingofthestudiedsections.Ourdataseemtoin-dicatethedevelopmentofanoxicconditionsinbasinsettingsduringOAE1a.Inshallower-waterenvironments,conditionsmayhavebeenlessreducing.Moreover,inGorgoaCerbara,twodistinctenrichmentshavebeenobserved.Thisisinfavouroff luctuationsintheintensityofwater-columnanoxiaduringtheshiftind13C.
OurresultsshowthattheexpressionoftheOAE1aisdifferentfollowingthepalaeogeographicsettings.ThestratigraphicevolutionofPcontentssuggestsanincreaseinnutrientinputattheonsetoftheanoxicevent,justafterthenegativespikeind13C.RSTEandhighCorg:Ptotvaluesmayindicateanoxiaconditionsinthedeepenvironmentcharacterizedbyseveralanoxicphaseswithintermittentreturntolessoxygen-depletedconditions.Theserapidchangesinredoxconditionsmayberelatedtoaf luctuatingoxygen-minimumzoneandsuggestthatoceanicproductivityhasplayedakeyroleinbottom-wateroxygendepletionduringOAE1a.
97
Sym
po
siu
m 2
: M
iner
alo
gy-
Petr
olo
gy-
Geo
chem
istr
y
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
2.39
InfluenceofextrinsicweatheringfactorsonmineraldissolutioninDammaglacierforefield
WongfunNuttakan1,FurrerGerhard1,BrandlHelmut2&PlötzeMichael3
1 Inst. of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich ([email protected])2 Inst. of Evolutionary Biology and Environmental Studies, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich3 Inst. for Geotechnical Engineering, ETH Zürich, Schafmattstrasse 6, CH-8093 Zürich
Initialweatheringprocessesandsoilformationareofparticularinterestinalpinepostglacialareasduetotheircrucialroleonlifeunderharshconditions(Bernasconi&BigLinkprojectmembers2008).Atnear-neutralpHunderaerobiccon-ditions,theavailabilityofnutrientsinfine-grainedrockmaterialandsoilisusuallyverylow.Toovercomethislimitation,microorganismsandplantsmodifytheirlocalenvironmentbyvariousexudatesincludingorganicligands,siderophoresandalsocyanide.Cyanidecanbeaveryimportantagentduringtheinitialperiodofcolonizationandsoilformation.
Westudymechanismsofweatheringofprimaryrock-formingmineralsintermsofintrinsic(e.g.mineralogy,grain-size,surfacearea)andextrinsic (e.g.pH,Eh,concentrationsof ligands)weatheringfactors.RocksamplesandsamplesfromweatheredstreamsedimentswereobtainedfromtheDammaglacierforefieldarea(CentralAlps,Switzerland)atapproxi-mately2000ma.s.l.Thestreamsedimentsampleswerecollecteddistinguishingfourwaterregimesregardingthedistancefromthemainwaterstreamandtheaccessibilityofwater.
MineralogicalcompositionsdeterminedbyX-raydiffractionandRietveldanalysisshowsimilarityinmineralogicalhetero-geneityofthemetagraniticmaterialthroughouttheglacierforefield.Grain-sizedistributionandaccordinglytheminera-logicalcompositionareinfluencedbyhydrologicalfactorssuchastemporalavailabilityandf lowvelocityofwater.Inadditiontofieldobservations,weatheringofcrushedgraniteisinvestigatedincontrolledlabexperiments.At25 °C,theinfluencesofoxalate,citrateandcyanidearestudiedinbatchreactors.Theconcentrationofcyanideismaintainedbyaconstantpartialpressureofhydrogencyanidethroughgasbubbling.Thus, theconcentrationofcyanideanionstrictlydependsonpH.Preliminaryresultsshowthatcitrateexhibitsthemostdistincteffectandthepresenceofcyanidesup-pressedthemobilizationofiron.
REFERENCESBernasconi, S.M. andBigLinkprojectmembers. 2008:Weathering, soil formationand initial ecosystemevolutionona
glacierforefield:acasestudyfromtheDammaGlacier,Switzerland.MineralMag.72,19-22.
2.40
Water-solublesaltsandtemperaturevariationinmeteoritesrecoveredinthehotdesertofOman
ZurfluhFlorian1,HofmannBeda2,GnosEdwin3&EggenbergerUrs1
1 Institut für Geologie, Baltzerstrasse 1+3, CH-3012 Bern ([email protected])2 Naturhistorisches Museum Bern, Bernastrasse 15, CH-3005 Bern 3 Muséum d’Histoire naturelle, route de Malagnou 1, CP 6434, CH-1211 Genève
OneofthemajorgoalsofourlongstandingmeteoritesearchandresearchcollaborationbetweentheMinistryofCommerceandIndustry,SultanateofOmanandinstitutionsfromSwitzerlandistocollectastatisticalsignificantnumberofwelldocumentedmeteoritesamplestoperformstudiesonfinddensity(Gnosetal.2010),weatheringandcontamination(Al-Kathirietal.2005).Herewepresentanongoingstudyontheinteractionofordinarychondriteswiththedesertsoilwiththefocusonwater-solublesalts.
98Sy
mp
osi
um
2:
Min
eral
og
y-Pe
tro
log
y-G
eoch
emis
try
Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
Duringterrestrialresidencethecomponentsfirstattackedinanordinarymeteoritearetheironmineralskamaciteandtaeniteandthe ironsulfidetroilite (Wlotzka1993,Lee&Bland2004,Al-Kathirietal.2005).Besideoxygen,waterandmicrobes,saltsderivedfromthesoilaccelerateweatheringofthesemineralsinthemeteorite.Chlorineisanimportantconstituentinvolvedintheformationoftheironhydroxideakaganéite(Buchwald&Clarke1989).
Afirstsurveyofwater-solublesaltsinmeteoritesgaveinterestingresults:Aqueousleachingwasperformedon16small(3–6g)cubesfromtheinteriorof200–400gindividualstones.WedetectedMg2+,Ca2+,SO4
2-andCl-asthemajorions.Thesignalisdominatedbyeitherchlorineorsulphate.Chlorine,calciumandapartofthesulphatearederivedfromthesoil,whereasmagnesiumandsomeofthesulphateisofmeteoriticorigin.Thetotalconcentrationofwater-solubleionsvariesfrom1860ppmto10500ppminthesolid(Zurfluh2008).
Currentlyweperformadditionalteststooptimizetheexperimentalsetupofaqueousleaching.Multiplecubesfromonemeteoritepiecewereleachedduringvarioustimeperiodstogetanideaofsaltsolubilityasafunctionoftime.Additionally,theexperimentwasperformedunderN2atmospheretopreventoxidationofironduringleaching.UntilnowallextractiondataarecollectedfromsamplesofthelargeJaH091strewnfield,acommonL5S2W2-4ordinarychondrite(Russeletal.2004,Gnosetal.2006,Zurfluh2008,Gnosetal.2010).
Theprocessof contaminationwith these salts isnotunderstood indetail.One importantparametermaybe thedailytemperature f luctuation that causesapumpingeffect.Wesuppose thatdue to thedarkcolour,meteoritesundergoamuchlargertemperaturerangecomparedtothesurroundingsoil.
Toobtaindataontemperaturevariations insideameteorite,asamplefromJaH091strewnfieldwasequippedwithathermocoupleconnectedwithatemperaturedataloggerandplacedinthedesert.Asecondtemperaturesensorwasplacedinanaluminiumdiscandburiedatadepthof30cminthesoil.TheexperimentwasrunfromJune2009untilJanuary2010.Currentlyanewloggeriscollectingdataatthesamelocationtocoverthewholeyear.ThehighesttemperatureinthemeteoritewasmeasuredinmidJulyreaching66.3°Candthedailymin-maxtemperaturedifferencesinthemeteoriteaverages34.3°C. Incontrast, themaximumtemperaturerecordedinthesoil is54.8°Candthedailyvariationaverages21.6°C.Thistemperaturevariationinthemeteoriteismaybeenoughtoproduceapumpingeffectthattransportsionssolvedinwaterintotheporespaceofthemeteorite(averageporosityofordinarychondrites:8.9±4.9%;Consolmagnoetal.2008).Waterisavailablefrommorningdewandthelowannualprecipitation,typically<40mmthatoccursnormallybetweenJanuaryandMarch(Fisher1994).Duringhotperiodsthewaterevaporatesandthesaltsremainsinthemeteorite.Becauseofthelongresidencetimeofthemeteoriteandthelargenumberofthesecycleshighconcentrationsofsaltsre-sults.
REFERENCESAl-Kathiri, A.,HofmannB.A., JullA. J. T., andGnos E. 2005:Weathering ofmeteorites fromOman:Correlation of
chemical/mineralogicalweatheringproxieswith14Cterrestrialagesandtheinfluenceofsoilchemistry,Meteoritics&PlanetaryScience,40,1215-1239.
BuchwaldV.F.andClarkeR.S.1989:CorrosionofFe-NialloysbyCl-containingakaganeite(beta-FeOOH)-TheAntarcticmeteoritecase.AmericanMineralogist74,656-667.
ConsolmagnoG.J.,BrittD.T.andMackeR.J.2008:Thesignificanceofmeteoritedensityandporosity.ChemiederErde-Geochemistry68,1-29.
FisherM. 1994:Another look at the variability of desert climates, using examples fromOman.Global Ecology andBiogeographyLetters4,79-87.
Gnos, E., EggimannM.R.,Al-KathiriA. andHofmannB.A. 2006: The JaH091 strewn field,Meteoritics& PlanetaryScience41Suppl.,A64
Gnos,E.,Hofmann,B.,Walbrecker,J.,Zurfluh,F.,Eggenberger,U.,Greber,N.,Opitz,C.,Bretscher,A.andTrappitsch,R.2010:„The2010OmanmeteoritesearchcampaignwithamagneticsurveyofthemainimpactsiteoftheJaH091strewnfield,AbstractSwissGeoscienceMeeting2010,Fribourg.
LeeM.R.andBlandP.A.2004:Mechanismsofweatheringofmeteoritesrecovered fromhotandcolddesertsandtheformationofphyllosilicates.GeochimicaetCosmochimicaActa68,893-916.
Russell S. S., Folco L., GradyM.M., ZolenskyM. E., Jones R., Rigther K., Zipfel J. andGrossmann J. N. 2004: TheMeteoriticalBulletin,No.88,2004July.Meteoritics&PlanetaryScience39,A215-A272.
WlotzkaF.1993:AWeatheringscalefortheordinarychondrites(abstract).Meteoritics28,460.ZurfluhF.J.2008:MeteoritesintheSultanateofOman-EffectsofterrestrialweatheringintheJiddatalHarasis(JaH)091
Strewnfield.MSc-thesis,UniversityofBerne,138pp.