Correlation of ignimbrites in the central Anatolian volcanic province using zircon and plagioclase

15 Pages·2011·2.57 MB·English

by  Erkan Aydar

JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
ContentslistsavailableatSciVerseScienceDirect
Journal of Volcanology and Geothermal Research
journal homepage: www.elsevier.com/locate/jvolgeores
Correlation of ignimbrites in the central Anatolian volcanic province using zircon and
plagioclase ages and zircon compositions
Erkan Aydar a,⁎, Axel K. Schmitt b,⁎⁎, H. Evren Çubukçu a, Lutfiye Akin a, Orkun Ersoy c, Erdal Sen a,
Robert A. Duncan d, Gokhan Atici e
aHacettepeUniversityDepartmentofGeologicalEngineering,Beytepe,Ankara,06800,Turkey
bDepartmentofEarthandSpaceSciences,UniversityofCalifornia,LosAngeles,595CharlesYoungDr.,LosAngeles,CA,90095-1567,USA
cNigdeUniversity,DepartmentofGeologicalEngineering,51245Nigde,Turkey
dCollegeofOceanicandAtmosphericSciences,OregonStateUniversity,Corvallis,OR97331,USA
eGeneralDirectorateofMTA,DepartmentofGeology,DumlupinarBulvari,No:139,06800,Ankara,Turkey
a r t i c l e i n f o a b s t r a c t
Articlehistory: Episodesofhigheruptivefluxes(>10−3km3/year)incontinentalenvironmentsareassociatedwithmagma-
Received26June2011 tismrelatedtosubduction,post-orogeniccollapse,intra-platehotspots,orrifting.Duringsuchepisodes,
Accepted10November2011 voluminousignimbritedepositsareproducedwhichcoverlandscapesover104–105km2.Insuchsequences,
Availableonline30November2011
brieferuptiverecurrenceandchemicalsimilaritylimittheapplicabilityofgeochronologicalandgeochemical
correlationmethods.Here,wepresentcomplementarygeochronologicaldata(40Ar/39Arplagioclaseeruption
Keywords:
and 206Pb/238Uzirconcrystallizationages)forignimbrites fromtheMiocene–Holocene Central Anatolian
Tephrostratigraphy
Volcanic Province (CAVP). In addition, we successfully employed zircon geochemistry (trace elements,
Pyroclasticdeposits
Geochronology oxygenisotopes)asanalteration-resistantindicatortocorrelaterhyodacitictorhyoliticignimbriteswhose
Miocene eruptionagedifferencesaretoobrieftoberesolvedby40Ar/39Argeochronology.Byapplyingthismethod,
Continentalplateau we dismiss previous correlations between stratigraphic members (i.e., Sofular and Gördeles, Sofular and
Sarımadentepe),butdemonstratecloserelationshipsforotherCAVPignimbrites(i.e.,Kavakunits1to4;
Cemilköyignimbriteandoverlyingfalloutdeposits).Ourchronostratigraphyrevealstwopreviouslyunrecog-
nizederuptivepulsesat~9–8Maand7–5Mawhicharecharacterizedbyincreasingmagmatictemperatures
(~75–100°Cwithineachcycle).Despitealong-term(10Ma)eruptiveproductivitythatisaboutoneorderof
magnitudesmallerthaninothermagmaticallyactivecontinentalplateaus,theCAVPachievedhigheruptive
fluxesduringbrief(1–2Ma)intervals.
©2011ElsevierB.V.Allrightsreserved.
1.Introduction DeSilva,1989;Perryetal.,1993;McCullochetal.,1994;Temeletal.,
1998;Ferrarietal.,2002;BryanandErnst,2008).Intheseprovinces,py-
Extensivepyroclasticflowdeposits(ignimbrites)aregeneratedby roclasticfalloutdepositscanbewidelyandcoherentlydispersedform-
ground-huggingpyroclasticdensitycurrentsthatresultfromeruption ingprominentmarkerbeds(e.g.,Wilsonetal.,1995),andindividual
of volatile-rich dacitic to rhyolitic magmas at high discharge rates pyroclastic flows can travel large distances (~100km; Wörner et al.,
(Smith,1960;Wilsonetal.,1980).Theresultingdeposits,frequently 2000).Becauseofflowchannelization,thicknessanddistributionofig-
eruptedfromcalderas,formextensivevolcanicprovincesinmanyloca- nimbritesvarylocallywhichimpedeslateralcorrelationbymapping,
tionsworldwide(e.g.,Western NorthAmerica; Central Andes,North especially in older, more eroded sequences. Moreover, mineralogical
Island of New Zealand, Central Anatolia) where subduction (fluid- andchemicalhomogeneityofignimbriteswithinindividualprovinces,
fluxed)andpost-collisional,hot-spot,orrift-related(decompression) alterationofpoorlyinduratedglassyrocks,andanabundanceofacci-
mantle-derived magmatism has imprintedon continental crust (e.g., dentallithicandcrystalcomponentscanfrustratecorrelationusingcon-
ventional geochronological and geochemical tools (e.g., Hildrethand
Mahood,1985;Glazneretal.,1986;DeSilva,1989;Shane,1998).
⁎ Correspondingauthor.Tel.:[phone];fax:[phone]. IntheCentralAnatolianVolcanicProvince(CAVP),Miocene–Pliocene
⁎⁎ Correspondingauthor.Tel.:[phone];fax:[phone]. ignimbritescollectivelycover20,000km2(LePennecetal.,1994).This
E-mailaddresses:[email protected](E.Aydar),[email protected] estimateextrapolatesoverinpartdeeplyincisederosionalremnantsof
(A.K.Schmitt),[email protected](H.E.Çubukçu),
theseignimbrites.Thesedeposits,intercalatedwithterrestrialsediments
lutfi[email protected](L.Akin),[email protected](O.Ersoy),
[email protected](E.Sen),[email protected](R.A.Duncan), and local lava flows, form a bizarre badlands-type landscape. Despite
[email protected](G.Atici). multi-decadal research, the stratigraphic relations within the CAVP
0377-0273/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.
doi:10.1016/j.jvolgeores.2011.11.005
84 E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
haveremainedcontroversialbecauseofdifficultiesinlaterallytracingin- Quaternarystratovolcanoes(suchasErciyesDag,HasanDag)andnu-
dividualignimbrites,andgeochronologicaldata(mostlybasedonK–Ar merousmonogeneticvents(cindercones,maars,domes)exist(Aydar
whole-rockanalyses,duetotheabsenceofsanidine)thatfrequentlyis and Gourgaud, 1998). Stratigraphically, the Ürgüp formation
problematicbecauseofunconstrainedparent–daughterisotopicdistur- (Pasquarè,1968)isthemajorlithostratigraphicunitwhichwasoriginal-
bance(Pasquarè,1968;LePennecetal.,1994;Mues-Schumacherand lysubdividedintonineignimbritesmembers(lentilsortonguesifdis-
Schumacher,1996;LePennecetal.,2005;Viereck-Götteetal.,2010). continuous; Fig. 2; Table 1): Akkoy, Kavak, Sarimaden Tepe Tongue,
Similarcomplications,suchasthescarcityorabsenceofsanidine,affect Cemilköy,Tahar,Gördeles,IncesuMember,SofularLentil,andValibaba-
stratigraphic correlations in other continental ignimbrite provinces tepe, so named after type localities (villages and hills, for which the
such as the Altiplano Puna and the Sierra Madre Occidental (e.g., Turkishnamesare“köy”and“tepe”,respectively).Thevoluminousrhy-
McDowell,2007;Salisburyetal.,2011). olitic–daciticignimbritesareseparatedbyfluvio-lacustrinesediments,
Toovercometheselimitations,weemployzirconasarobustchro- soil,orlavaflows(Fig.3).Besidesmammalianbiostratigraphyandmag-
nometer and indicator mineral that is unaffected by alteration, and netostratigraphy(Pasquarè,1968;LePennecetal.,2005),onlylimited
combineitwith40Ar/39Arstepwise-heatingofplagioclase.Thispermits radiometric (K/Ar) data has been available for the CAVP (e.g.,
aconsistencycheckfordisturbanceoftheparent–daughterrelationsin Innocentietal.,1975;Mues-SchumacherandSchumacher,1996).
theK–Ardecaysystembecausezirconreliablydatescrystallizationina
magmaandisunaffectedbypost-magmaticheatingoralteration.How- 2.2.Comparativestratigraphies
ever, zircon frequently displays significant pre-eruptive residence or
recycling.Suchcrystalshavebeentermedantecrysts(seereviewsin Cretaceousgraniticandgabbroicrocksconstitutethepre-volcanic
Simon et al., 2008; Schmitt, 2011), and because of their ubiquity in basementofCappadociawithoutcropsmainlyintheAcıgöl,Tilköy,
silicicmagmas,zirconstrictlyprovidesamaximumagefortheeruption. andKeslikarea.Thisisconfirmedbyagesforagraniticsamplefrom
40Ar/39Ardating,bycontrast,canyieldreliableeruptionages,butthe theAcıgölarea(40Ar/39Arage:78.4±0.4Ma;206Pb/238Uzirconage:
K–ArdecaysysteminmaterialsavailablefordatinginCAVPignimbrites 77.8±4.4Ma; Tables 1 and 2). Outside the CAVP, the substratum
(e.g., plagioclase, biotite, glass) can be more readily disturbed than comprises metamorphic rocks of the Central Anatolian Crystalline
zircon (e.g., by excess 40Ar, or K mobility; Cerling et al., 1985; Hora Complex (Dilek and Sandvol, 2009). Pre-volcanic rocks such as the
etal.,2010),oraffectedbyxenocryticcontamination(e.g.,Spelletal., Yesilhisar conglomerates frequently form xenolithic fragments in
2001).Itisthereforeadvantageoustocombinezirconandplagioclase, CAVPpyroclasticrocks.
ageswhich–ifconcordant–cancollectivelyestablisharobustchrono- Inourstratigraphicre-evaluationoftheCAVP(Table1;Figs.2and
stratigraphicframework.ForkeyCAVPignimbritesdatedhere,onlya 3;seealsomapinelectronicAppendix1),wefollowtheterminology
fewcasesrevealedcomplexcrystaloriginsforzircon.Traceelements outlinedinLePennecetal.(1994),identifying10ignimbritemem-
and oxygen isotopes in zircon further allow for correlation between bers(instratigraphicorderfromoldtoyoung):Kavak,Zelve,Sarıma-
units where eruption and crystallization age uncertainties overlap. dentepe,Sofular,Cemilköy,Tahar,Gördeles,Kızılkaya,Valibabatepe,
This highlights the potential of zircon asa reliable indicator mineral andKumtepe(Table1).
forthecorrelationofignimbrites.
2.3.Kavakignimbrite
2.Geologicalbackground
TheKavakignimbritesrepresenttheoldestpyroclasticdepositsin
2.1.OutlinesofCentralAnatolianVolcanism theCAVP.Theyareinterbeddedwithfluvio-lacustrinesedimentsin-
dicatingmultipleeruptiveepisodes(stratigraphiccolumninelectron-
CentralAnatoliaconstitutesahighplateauat1400–1500meleva- icAppendix2).Collectively,theKavakignimbriteshaveavolumeof
tion which hosts a continental volcanic province with eruptions of ~80km3distributedovera~2600km2area(LePennecetal.,1994).
MiocenetoUpperHoloceneage(heretermedCentralAnatolianVol- Mues-Schumacher and Schumacher (1996) and Le Pennec et al.
canicProvinceCAVP;Fig.1).Thisprovinceisalsoknownunderitsre- (2005)subdividedtheKavakignimbritesintomultiplesub-unitssep-
gional name Cappadocia (etymologically: “the land of beautiful arated by sediments (e.g., Upper and Lower Göreme ignimbrites;
horses”), and several other names have been used in the literature Table1).Lately,Viereck-Götteetal.(2010)proposedtwonewignim-
(Central or Centro-Anatolian Plateau, Anatolian Highland, Ürgüp brite members underlying the Lower Göreme: Guvercinlik and
plateau, Neogene plateau in Pasquarè, 1968, or Nevsehir Plateau in Eneski.Here,wemaintainacollectivetermforallKavakignimbrites
LePennecetal.,1994).TopographicallyagentlyN-dippingdepres- because of their temporal and lithological similarity, and a lack of
sion,itisboundedbytheTaurusMountainrangeinthesouth,and mappablemarkerhorizons.
twoprominentQuaternary stratovolcanoes (Hasan Dagand Erciyes Kavakignimbritesarewellexposedintheeasternandnortheast-
Dag) in the west and east, respectively. Neogene continental sedi- ernpartsoftheÇardakdepressionwhichistheirprobablesourcearea
ments,mostlyendorheicfluviatileandlacustrinedeposits,andlate- (Froger et al., 1998). The sequence (electronic Appendix 2) starts
orogenic volcanic deposits (Pasquarè, 1968) fill this depression. with a whitish ashy fallout deposit followed by a reversely graded
Structurally,thewesternandeasternlimitsoftheplateauaredefined pumice-richflow(Kavak-1).Ash-richlacustrinesedimentsseparate
bytheTuzgölüandEcemisfaults,respectively(Fig.1). the Kavak-1 subunit from overlying Kavak-2. The Kavak-2 subunit
Numerousstudieshaveaddressedvariousvolcanological,petrologi- hasabaserichinandesiticlithics,whichdiminishinabundanceup-
cal, geochemical, and tectonical aspects of the CAVP (e.g., Beekman, sectionandgradeintoash-richflowdepositsnearthetop.Character-
1966; Pasquarè, 1968; Innocenti et al., 1975; Besang et al., 1977; isticaccretionarylapilliarepresentnorth-northeastofKavakvillage
Pasquarèetal.,1988;Schumacheretal.,1990;Temel,1992;LePennec andintheNarvalley.Carbonaceousfluvio-lacustrineconglomerates
etal.,1994;Topraketal.,1994;Aydaretal.,1995;Druittetal.,1995; withasmallintercalatedpumiceousfalloutdepositseparateKavak-
Notsuetal.,1995;Mues-SchumacherandSchumacher,1996;Schuma- 2 from Kavak-3. Kavak-3 is consolidated to moderately indurated
cher and Mues-Schumacher, 1996; Schumacher and Mues- withseveralpumice-richhorizonsinanashmatrixandoverlainby
Schumacher,1997;AydarandGourgaud,1998;Temeletal.,1998;Şen ~50cmofyellowish-beigepumiceousfalloutofKavak-4.Thisunitis
etal.,2003;LePennecetal.,2005;Viereck-Götteetal.,2010;Schmitt characteristically pale pinkish in color and its overlying pyroclastic
etal.,2011).Apartfromitslandmarkignimbrites,theCAVPcomprises flowdepositcontainsfewlithicandpumiceclastsinanash-richma-
eroded Miocene andesitic volcanic complexes, as well as lava fields trix.Thetopofthesequencecomprisesintenselyweatheredashfall-
and flows (e.g., Aydar and Gourgaud, 1998). In addition, several outdepositswithdark-graytoblackalteredpumice.
E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97 85
Fig.1.(a)OverviewmapoftheCentralAnatolianVolcanicProvince(CAVP)includingprominenttectonicstructuresinAnatolia.(b)Digitalelevationmodelofthestudyarea
(insetinpanela)showingmajoreruptivecentersforCAVPignimbrites.
AllKavakignimbritescontaincrystal-richpumicewithlarge(3to conditionsareindicatedbyourdiscoveryofwell-preservedrhinocer-
5mm)phenocrystsofbiotite,plagioclase,andquartz.Alkalifeldspar otidaeskullandbones(upperandlowerjaws,femurs;S.Sen,pers.
isabsent(cf.LePennecetal.,1994).Intensedevitrificationandalter- comm.)intheKavak-4depositnearKaracaşar(north-easternAcıgöl).
ationarecommon.Wecouldnotconfirmthepresenceofcarbonized The good preservation of the bones implies low-temperature em-
plants (cf. Le Pennec et al., 1994) but subaerial emplacement placementinasubaerialenvironment.
86 E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
Fig.2.GeneralizedgeologicmapoftheCAVPwithdistributionsofMiocene(Kavak,Zelve,Sofular,Sarımadentepe,Cemilköy,Tahar,andGördeles),Pliocene(KızılkayaandValibabatepe)
andQuaternary(Kumtepe)ignimbriteunitsandmajorvolcaniccenters.Forclarity,unitsareundifferentiatedwithineachagegroup,andinterbeddedfluvio-lacustrinesedimentshave
beenomitted.
2.4.Zelveignimbrite and Mues-Schumacher (1997) and us that accretionary lapilli also
occur within in the basal fall-out as well as the overlying flow
Zelve ignimbrite is one of the most spectacular ignimbrites of deposits,indicatingwater–magmainteractionthroughouttheeruption
Cappadocia where it is frequently quarried as masonry stone. It sequence.
shows a snow-white basal pyroclastic fallout deposit overlain by a Themainignimbritebodyistypicallybeigetopink,withgradation
singlecoolingunitofinduratedpinkignimbrite(stratigraphiccolumn frompumice-rich to ash-richand lithic-poorin the middleparts of
inelectronicAppendix3).Itlikelyoriginatedfromasourcenearto the section. Rhythmic inverse grading of pumice exists in multiple
thatoftheKavakignimbritesandcovers~4200km2aroundÜrgüp, flow units towards the top of the section, with interspersed lithic-
Avanos, and Nevşehir with a total volume of ~120km3 (Le Pennec rich horizons and occasional accretionary or armored lapilli (Le
etal.,1994). Pennecetal.,1994;SchumacherandMues-Schumacher,1997).Local-
In detail, the Zelve ignimbrite consists of two distinct eruptive ly,sub-sphericalbariteconcretionsexistwhoseabundanceappearsto
deposits: rhyolitic pumice fallout up to 10m thick and partly inter- berelatedtofaults,indicativeoflocalizedhydrothermalactivity.The
beddedwith pyroclastic surges(SchumacherandMues-Schumacher, Zelveignimbritealsoexhibitssecondaryalterationofvolcanicglass
1997)andanoverlyingsingle-cooling-unitignimbrite.Pumiceinthe into erionite-, clinoptilolite-, and chabasite-type zeolites around
basalfalloutisglassyandtubularwithscarcephenocrystsofplagioclase, Sarıhıdır and Tuzköy villages where the ignimbrite potentially en-
biotite,andquartz.Devitrificationandalterationoccasionallyreplace teredalake.
pumice glass with yellowish zeolitic aggregates. Overlying the basal
falloutisaseriesofpyroclasticunitswhichdisplaylaminated,plane- 2.5.Sarımadentepeignimbrite
parallel,orlow-anglecrossbedding.Thethreemajordivisionsare(in
stratigraphic order): the lower surge series, the upper pumice beds, The Sarımadentepe ignimbrite has scattered exposures in the
and the upper surge series (Schumacher and Mues-Schumacher, NevşehirPlateauwithvaryingestimatesforarea(3900and5200km2)
1997). Accretionary lapilli are abundant in these deposits and were andvolume(80and110km3)inLePennecetal.(1994)andViereck-
characterized as both, rim-type (Schumacher and Schmincke, 1991; Götteetal.(2010),respectively.Ourfieldworksupportedbywhole-
SchumacherandMues-Schumacher,1997)andcore-typeinapumice rock geochemical correlation suggests a much smaller size of the
layerintheuppersurgeseries(SchumacherandSchmincke,1991).At Sarımadentepeignimbrite.Itisexclusivelylocalizedintheeasternto
variancewithLePennecetal.(1994)areobservationsbySchumacher southeastern part of the Çardak depression (Mustafapaşa and Ayvalı
E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97 87
238206/PbUZircon Age 5.11±0.37 6.33±0.23 6.07±0.67 6.66±0.40 8.32±0.37 8.59±0.51 9. 13±0.40 9.43±0.38 AFD:10.0±0.5 9.13±0.51
Ar/Ar Age 2.52±0.49 5.19±0.07 6.34±0.07 6.14±0.22 7.20±0.09 8.17±0.O8 8.44±0.12 9.19±0.15 9.20±0.10 AFD:9.08±0.06 9.12±0.O9
This study Kumtepe Ign. Valibabatepe Ign. Kızılkaya Ign. Gördeles Ign. Tahar Ign. Cemilköy Ign. Sofular Ign. Sarımaden TepeIgn. Zelve Ign. 4. .3Kavak Ign.2. .1
Viereck-Goette et al., 2010 Incesu member Kizilkaya member Gordeles member Tahar member Cemilkoy member Sarimaden Tepe member Zelve member Kavak member Lower and Upper Goreme BedLower and Upper Uchisar Beds Güvercinlik member Eneski member
2005 Most probableage range 2.6-3.0 4.5-5.5 6.8-7.6 7.2-7.8 7.6-8.4 8.03-8.7 8.5-9.0 9.0-14
Le Pennec et al., Valibabatepe Kizilkaya Gordeles Tahar Cemilkoy Sarimadentepe Zelve Kavak
Age 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
K/Ar 1.1± 2.8± 4.3+4.3+4.5+ 4.0± 6.5±6.8± 7.5±7.7±6.9±7.3±8.7±9.2+
Schumacher and Schumacher, 1996 Valibabatepe-Sofular Incesu Kizilkaya Gordeles Tahar Cemilkoy Sarimadentepe Akdag-Zelve Upper Goreme Lower Goreme
Schumacheret al., 1990 Valibabatepe Incesu Kizilkaya Sarimadentepe Akdag Upper Gorcme Lower Goreme
Le Pennec et al.1994 Valibabatepe Kizilkaya Sofular Gordeles Tahar Cemilkoy Sarimadentepe Zelve Kavak
Temel, 1992 K/Ar Age Kavak 11.2±2.5
nimbrites. Besang et al., 1977 4.9±0.2 Kizilkaya5.5±0.2
CAVPig 975 K/Ar Age 2.7±0.1 2.8±0.1 3.0+0.1 4.4±0.1 5.4±1.I 6.8±1.4 7.8±1.6 8.0±1.6 8.2±1.6 8.6±1.7 8.5±0.2
ewstratigraphicrelationsfor Pasquarè, 1968 Innocenti et aI., 1 Valibabatepe Valibabatepe Andesite (5Ma) Karahoyuk Sofular Incesu Baskoy Sofular Gordeles Gordeles Tahar Tahar Cemilkoy Cemilkoy Sarimdentepe Sanmadentepe Kavak Kavak Akkoy Akkoy
able1ublishedandn Beekman, 1966 Kizilkaya Gelveri Selime Tuff Gostuk
TP
88 E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
Fig.3.CompositestratigraphiccolumnandnewcrystallizationanderuptionagesfortheCAVP.AFD=Air-falldeposit.
areas;Fig.2)andinthevicinityoftheEcemişfault(Figs.1and2).Inthe underlying~2–3cmthickhorizonofdark-brownandlithic-richash.It
Kurşunluteperegion,Sarımadentepeignimbriteoverliesapalaeosolde- isstronglyweldedanddisplayscolumnarjointingandup-sectioncolor
velopedaboveZelveignimbrite.Abasalfalloutdepositwithamaxi- variationsfrompaleyellowtobrownish-scarlet.PumiceofSarımaden-
mumthicknessof~1.5mintheÇardakregionisweldedanddisplays tepeignimbriteareeutaxitic,low-vesicularitywithplagioclase,biotite,
inverse grading (details of field relations in electronic Appendix 4). clinopyroxene, and oxide phenocrysts in pale to dark yellowish and
The overlying main flow deposit is in gradational contact with an brownishmatrix.
E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97 89
Table2
40Ar/39ArradiometricagesforCAVPignimbrites.
Sample Unit UTM UTM Material Totalfusion 2σ Plateau 2σ N MSWD Isochron 2σ 40Ar/36Ar 2σ J
easting northing age error age error age error initial error
(Ma) (Ma) (Ma)
KPD-08-009 Kavak 659645 4276775 Feldspar 9.11 0.12 9.12 0.09 11/11 0.29 9.13 0.15 285 42 0.001810
KPD-08-016 Kavak 659645 4276775 Feldspar 9.22 0.11 9.20 0.10 9/11 0.39 9.16 0.24 296 73 0.001795
KPD-08-018 Sarımadentepe 662381 4265700 Feldspar 8.37 0.09 8.44 0.12 10/11 1.98 8.54 0.20 138 114 0.001690
KPD-08-021 Gördeles 661557 4262949 Feldspar 6.34 0.07 6.34 0.07 10/11 0.65 6.24 0.18 332 75 0.001762
KPD-08-023 Cemilköy 658734 4261370 Feldspar 7.08 0.09 7.20 0.09 8/11 0.88 7.37 0.25 126 182 0.001734
KPD-08-025 Kızılkaya 661493 4260438 Feldspar 5.07 0.09 5.19 0.07 8/10 0.92 5.20 0.08 294 3 0.001749
KPD-08-031 Tahar 673454 4268634 Feldspar 6.11 0.28 6.14 0.22 10/11 0.21 6.10 0.23 299 8 0.001673
KPD-08-034 Zelve 658675 4280901 Feldspar 9.07 0.08 9.08 0.06 9/11 0.34 9.03 0.13 302 13 0.001780
KPD-08-035 Kavak 659439 4285471 Feldspar 9.18 0.17 9.19 0.15 11/11 0.25 9.13 0.17 294 15 0.001707
KPD-08-039 Sofular 672489 4286122 Feldspar 8.16 0.10 8.17 0.08 11/11 0.14 8.16 0.10 297 23 0.001656
KPD-08-050 Valibabatepe 728262 4282640 Feldspar 2.39 1.13 2.52 0.49 9/9 0.69 2.42 0.60 295 7 0.001719
K-015 Acıgölgranite 632344 4267719 Feldspar 78.37 0.29 78.44 0.29 10/13 0.28 78.37 0.44 299 18 0.001992
AgescalculatedusingbiotitemonitorFCT-3(28.04Ma)andthetotaldecayconstantλ=5.530E−10/yr.Nisthenumberofheatingsteps(definingplateau/total);MSWDisanF-statistic
thatcomparesthevariancewithinstepageswiththevarianceabouttheplateauage.Jcombinestheneutronfluencewiththemonitorage.Bold:agesusedinTable1andFig.3.
2.6.Sofularignimbrite andSchumacher(1996),however,suggestedthattheSofularignimbrite
isthedistalfaciesoftheValibabatepeignimbrite,whereasLePennec
Sofularignimbritecomprisesa~1mthickfine-grainedpumiceous etal.(2005)arguedforSofularbeingthedistalfaciesoftheGördeles
fallout deposit overlain by ~25m of a single flow unit. The flow ignimbrite. More recently, Viereck-Götte et al. (2010) used geo-
deposit is indurated, ash-supported lithic- and pumice-poor with chemical and mineralogical data to correlate the “Sofular lentil”
maximumpumicesizetypicallyb4cm.Phenocrystsinpumicecom- with the “Sarımadentepe member” of Pasquarè (1968). Here, we
priseplagioclase,biotite,andoxides. proposethatSofularunitisaseparateignimbriteunitasconstrained
Becauseofverylimitedexposureinthevicinityofitstypelocality byradiometricdatingandgeochemicalidentity.
(Sofular village; Fig. 2), the stratigraphic placement of the Sofular
ignimbrite has been most contentious in the CAVP. Originally pro-
2.7.Cemilköyignimbrite
posed as a “lentil” between Valibabatepe and İncesu members
(Pasquarè,1968),itwassubsequentlyplacedbetweentheGördeles
Thismemberrepresentsanextensiveandvoluminousunitwith
andKızılkayaignimbrites(LePennecetal.,1994).Mues-Schumacher
an estimated volume of 300km3, covering 8600km2 (Le Pennec
etal.,1994).Thisignimbritewassufficientlyvoluminoustoregionally
fillinthepaleomorphology,creatingavolcanicpeneplain.Itcharac-
A teristically forms smooth surfaces with prominent erosion features
(“fairychimneys”)duetoitsunweldednature.
OnlyinSoğanlıvalley,aroundCemilköy,Yüksekli(NorthofKızılır-
makvalley),KeşlikvillagesandatKolkoluTepe(SoutheastofAyvalı)
(Fig. 2), a thin, slightly altered pre-ignimbrite fallout deposit with
lapilli-sized pumice is observed beneath the main ignimbrite flow.
Themainignimbritebodyispale-gray,containingwhite-palepumice
in prismatic shapes with strongly flattened and elongate vesicles
(“slatyfabric”inLePennecetal.,1994).Pumiceintheflowoccursin-
versely graded with a maximum pumice size of 70cm. The lithic
clastscomprisevolcanicclastsinDamsavalley,andophioliticrocks
in Ayvalı region (Fig. 2), depending on locally exposed basement.
B
Phenocrystsareplagioclase,biotite,amphibole,andoxides.
2.8.Localfalloutdeposits
In the Güzelöz, Tilköy, and Karain regions, fallout deposits, not
evidentlyassociatedwithanyignimbrites,areexposed(Fig.2).Stra-
tigraphically, these pumice layers have been variably placed be-
tweenKızılkaya andCemilköyignimbrites(LePennec et al.,1994;
Topraketal.,1994;Viereck-Götteetal.,2010).IntheGüzelözregion,
twopumiceousfallouts,separatedby~2mofpaleosol,areinterca-
lated between Cemilköy and Gördeles ignimbrites. In vicinity of
Tilköy,bothfalloutdepositsaredirectlyoverlainbyKızılkayaignim-
brite.Viereck-Götteetal.(2010),basedontheregionallithological,
Fig.4.Zirconsaturation(a)andU/Y(b)vs.Ti-in-zircontemperatureinCAVPignim- mineralogical,andgeochemicalsimilaritiesofpumicefromdifferent
brites(closedcircles).Basementgranite(sampleK-015)valuesshownforcomparison deposits,proposedthattheyareallstratigraphicallyequivalent.The
(opencircle).Notethathatchedregioninlowerrightofthediagramis“forbidden”
eruption center may be located to the west of Tilköy/Derinkuyu
becausethiswouldimplyzirconcrystallizationatsuper-saturationtemperatures.All
(Viereck-Götte et al., 2010). We propose that they are correlative
data(withinuncertainty)areconsistentwithcrystallizationattemperaturenearor
belowthesaturationtemperature. totheunderlyingCemilköyignimbrite(seebelow).
90 E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
2.9.Taharignimbrite
A
ThisignimbriteisrestrictedtotheeasternpartoftheCAVP.Itis
distributedover1000km2withanestimatedvolumeof25km3(Le
Pennec et al., 1994). It is generally pale-pink to scarlet-brown and
mostly unwelded, but welding and columnar jointing is prominent
around Sofular village. Its type locality is Tahar (Yeşilöz) village
whereitis~120mthick(Fig.2;electronicAppendix5).Thethickness
of the Tahar ignimbrite decreases in all directions from Hodul Dag,
correlatingwithdecreasingmaximumlithicclastsize.Thisimpliesa B
sourcelocationnearHodulDag(LePennecetal.,1994).Thesequence
starts with alternating lapilli and ashy fallout deposits (~4m thick
nearYeşilöz)whicharedirectlyoverlainbyatleastthreesuccessively
emplaced flow deposits, separated by thin fallout deposits. Overall,
Taharignimbriteis veryrichin lithics,especiallyat thebase ofthe
flow.Glassy,beigetopinkishpumicewithincipientlyflattenedvesi-
cles is typical for the main flow deposit. It contains phenocrysts C
of plagioclase, amphibole, clinopyroxene, and orthopyroxene. At
Yeşilöz, the Tahar ignimbrite is deposited on lacustrine sediments
andoverlainbylavaflows.
2.10.Gördelesignimbrite
This member has an estimated extent of ~3600km2 and a total
volume of 110km3 (Le Pennec et al., 1994). In the field, Gördeles
canbeconfusedwithKızılkayaorSarımadentepeignimbriteswhich
allareincipientlytomoderatelyweldedandpalegraytolightbrown-
Fig.6.ZircontraceelementvariationdiagramsforKavakandZelveignimbrites.
ish in color. We distinguish two different units of Gördeles (Lower
andUpper)whichareseparatedbyapaleosol(stratigraphicdetails
inelectronicAppendix6).Alagbreccialayerwithgasescapepipes Gördeles, which mainly extends toward to east of the plateau. The
is present at the base of the Lower Gördeles around Kayırlı village main flow unit contains pumice with textural differences (fibrous
(SWpartofmapinFig.2).Nearby,atŞahinkalesitepe,thepresence vs. sub-spherically vesiculated) and color variations ranging from
oflithic-richlagbrecciaswithpumices>60cmindicatesproximity pale-brown to bright-white which are, however, compositionally
tothevent(LePennecetal.,1994).TheUpperGördeleshasathinpu- identical. Phenocrysts are plagioclase, biotite, clinopyroxene, and
miceous fallout deposit directly overlain by ground surge deposits. oxides.
These two basal layers are reliable field indicators for the Upper
2.11.Kızılkayaignimbrite
A ThisisthemostwidespreadignimbriteunitintheCAVPwhereit
formsflatsurfacesoveranareaof~8500–10600km2withavolume
of 180km3 (Le Pennec et al., 1994; Schumacher and Mues-
Schumacher,1996).Itisincipientlytostronglyweldedwithoccasion-
al columnar jointing. Its average thickness varies between 13 and
15m, classifying it as a low aspect ratio ignimbrite (Schumacher
and Mues-Schumacher, 1996). Locally, thicknesses reaches
>40–50m (e.g., the Derinkuyu underground city) and peak at
B
~80m(Ihlaravalley).
Kızılkayaignimbriteconsistsofabasalpre-ignimbritePlinianfall-
outdepositandtwomainflowunitsseparatedbyaflowdiscontinu-
ity.Pumiceglassinthelowerflowunitisalsomorestronglyvapor-
phasealteredcomparedtotheupperflow.Texturally,Kızılkayapum-
iceresemblesGördelesignimbritepumice,withsimilarphenocrysts
ofplagioclase,biotite,orthopyroxene,andoxides.
C
2.12.Valibabatepeignimbrite
This is another low-aspect ratio (5200km2, 100km3; Le Pennec
etal.,1994)ignimbriteintheCAVP.Itisdark,stronglywelded,anddis-
playseutaxitictexturesandwell-developedfiamme.Outcropsareex-
tensiveintheeasternpartsoftheCAVPwhereitreachesamaximum
thicknessof40maroundTalas,atthebaseofMt.Erciyesfromwhich
it originated (Şen et al., 2003). Basal Plinian fallout deposits contain
daciticpumicewithamodalmineralassemblageofplagioclase,amphi-
bole,andclinopyroxene.Theabsenceofbiotiteisoneofthemainfield
Fig.5.ZircontraceelementvariationdiagramsforCemilköyandGördelesignimbrites
incomparisontozirconfromfalloutdepositsoverlyingCemilköy(“?fallout”). characteristicsoftheValibabatepeignimbrite.ThedesignationIncesu
E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97 91
isalsousedintheliteratureforthisignimbrite,butweprefertheorig- respectively(ACMELabs).Thin-sectionsofallsampleswereprepared
inalnameValibabatepe(Pasquarè,1968). atHacettepeUniversity,DepartmentofGeologicalEngineering,where
mineralchemistrywasanalyzedon45selectedsamplesusingaCarl-
2.13.Kumtepeignimbrite ZeissEVO-50EPScanningElectronMicroscope(SEM)equippedwith
Bruker-AxsXFlash3001SDD-EDS.Publicationoftheentiregeochemical
TheyoungestignimbriteintheCAVPeruptedfromtheQuaternary datasetisanticipatedinaseparatestudy.Here,weonlydrawonafew
Acıgöl Volcanic Complex located in its western part (Druitt et al., sub-aspectsoftheseresultsastheypertaintoourgeochronologialdata
1995;Schmittetal.,2011).Itwasformedbytwoconsecutiveerup- (Tables2and3).
tions whose deposits are locally separated by paleosol and cinder
conedeposits(Druittetal.,1995).TheLowerAcıgölTuff(=Lower 3.Methods
Kumtepe) comprises lapilli-sized fallout interbedded with multiple
ash layers and a single flow deposit. The Upper Acıgöl Tuff (Upper 3.1.U–Pb,traceelement,andoxygenisotopesinzircon
Kumtepe) has a basal lapilli fallout deposit which differs from
theLowerAcıgölTuffbyabundantobsidianlithicclasts.Itisoverlain Zircon was extracted from composite pumice samples following
byapalepinkishtobeigeflowunit.Althoughgeochemicallynearly crushing and dissolution with cold 40% HF. Crystals were hand-
identical,marginaldifferencesincrystalabundanceexist:thelower picked from the HF indigestible residue, placed on adhesive tape,
tuffcontainsglassy,aphyric,and moderatelyvesicularpumicewith and cast in Buehler Epoxicure resin. Polishing was conducted with
very rare plagioclase and biotite microphenocrysts, whereas crystal SiCcoated-paperand1μmdiamondsuspension.Zirconswereimaged
content (plagioclase, biotite, oxides) is slightly higher in the upper using backscatter-electron and cathodoluminesence (CL) detectors
tuff. The names Upper and Lower Acıgol Tuffs were introduced be- ontheUniversityofCaliforniaLosAngeles(UCLA)LeoVP1430SEM.
cause they originated from the Acıgöl caldera (Druitt et al., 1995; Aftercleaning(1NHCl,deionizedwater),aconductiveAulayer
Fig. 2), withwidely dispersed falloutdeposits over Cappadociaand was applied. Secondary ionization mass spectrometry (SIMS, ion
flow deposits to the north and east. To the south, flows onlap the microprobe)analyseswereperformedusingaCAMECAims1270at
pre-existing Erdaş Massif (Fig. 2). Henceforth, we subsume the UCLA.Thesequenceandprotocolswefollowedweretoanalyzeoxy-
Upper and Lower Acıgöl Tuffs under the term Kumtepe Ignimbrite genisotopesfirst(Trailetal.,2007),followedbyU–Pbandtraceele-
(Pasquarè,1968). ments(Schmittetal.,2003).Thissequenceavoidscontaminationof
oxygeninzirconby16Oimplantedunderprimaryionbeambombard-
2.14.Samplingstrategy mentduringU–Pbanalysis.AllU–Pbageswerecorrectedforcommon
Pbusing 207Pband 230Thdisequilibriumfollowingproceduressum-
Duringmultiplefieldcampaignsbetween2008and2010,unaltered marizedinSchmittetal.(2003).
freshrocksampleswerecollectedformineralogical,geochemical,and Oneimportantanalyticalmodificationwasthatwealsoincluded
geochronologicalanalyses(samplinglocationsinTables2and3;elec- traceelementsatmass/chargestations49(49Ti+),57(57Fe+),88.5
tronic Appendix 1). Sampling targeted pumice from key ignimbrite (177Hf++) 89 (89Y+), and 196 (180HfO+) in addition to the Zr, Pb,
unitsthroughouttheexposedsectionsincludingfalloutandflowde- Th,andUspeciesroutinelyanalyzed.A30eVoffsetwasappliedto
posits,aswellasepiclasticsedimentarydeposits.Isopachsandisopleth 177Hf++ and 89Y+ to suppress potential molecular interferences,
maps for juvenile and accidental clast components were generated. and the mass/charge=89 peak was corrected for a minor interfer-
GeophysicalinvestigationsincludedAnisotropyofMagneticSuscepti- enceof178Hf++usingmeasured177Hf++.Traceelementconcentra-
bility(AMS)analysistoconstrainflowdirectionsfromignimbritedrill tions were calculated using sensitivity factors relative to 94Zr O+
2
cores. We obtained a total of 554 whole-rock geochemical analyses from analysis of 91500 standard zircon using Zr-internal-standard
obtained byinductively coupled plasma(ICP) emission spectroscopy valuesexceptforHfforwhichanelectronprobemicroanalysiswork-
(ES) and mass spectrometry (MS) for major and trace elements, ingvaluewasused(Table2inLiuetal.,2010).Analysisof57Fe+aids
Table3
U–Pbzirconages,traceelementcompositions,andoxygenisotopiccompositionsofCAVPignimbrites.
Sample Unit UTM UTM 206Pb/238U 2σ N MSWD δ18O 2σ U/Y Ti Timin Ti T(Ti) T(Ti) T(Ti) T(Sat)
easting northing age error (‰) error average average (ppm) max average min max (°C)
(Ma) (ppm) (ppm) (°C) (°C) (°C)
K-287 ?fallout 668597 4251465 6.90 0.34 10 1.45 5.70 0.27 0.44 6.6 3.3 11 772 −63 53 757
K-372 ?fallout 669989 4261766 6.76 0.30 10 0.46 5.49 0.21 0.52 5.4 3.5 8.8 753 −39 48 762
KL-17 Kavak 659575 4276850 9.43 0.38 9 0.39 6.82 0.40 0.82 3.4 2.5 5.0 711 −28 33 -
KPD-08-004 ?fallout 658460 4253373 6.96 0.28 10 0.59 5.41 0.40 0.54 4.7 3.4 5.7 741 −30 17 789
KPD-08-009 Kavak 659645 4276775 9.95 0.49 8 0.25 6.09 0.18 0.81 4.5 2.9 6.3 736 −39 31 779
KPD-08-034 Kavak 658675 4280901 10.0 0.5 8 0.52 7.06 0.17 0.87 3.1 2.2 4.6 702 −26 37 744
KL-01 Sarımadentepe 662886 4265561 8.59 0.51 10 0.47 5.04 0.33 0.21 9.6 6.7 16 811 −37 53 794
KL-02A Gördelesrhyolite 661605 4263615 6.33 0.23 19 0.48 7.76 0.49 0.28 9.2 6.4 12 806 −37 29 802
KL-02B Gördelescumulate " " " " " " 6.66 0.77 0.28 9.1 6.4 17 805 −35 69 645
KL-03 Cemilköy 658718 4261333 6.66 0.40 10 1.51 5.87 1.21 0.48 4.6 2.4 7.2 739 −58 42 722
KL-05 Kızılkaya 668363 4261396 5.11 0.37 10 0.31 5.31 1.02 0.53 6.1 4.7 9.8 765 −25 48 767
KL-10 Kavak 659680 4276796 9.13 0.51 10 1.08 6.86 0.37 0.46 4.8 3.4 5.7 741 −30 16 816
KL-18 Zelve 659432 4285492 9.13 0.40 15 0.90 6.34 0.99 0.48 5.2 3.7 7.3 749 −31 33 753
KL-19 Sofular 672502 4286351 8.32 0.37 16 0.36 6.41 0.28 0.24 9.3 7.3 16 807 −24 61 826
KPD-08-031 Tahar 673454 4268634 6.07 0.67 1 – 4.54 0.52 0.31 6.3 – – 768 – – 776
K-015 AcıgölGranite 632344 4267719 77.8 4.4 7 1.06 7.15 0.34 1.18 1.3 0.9 1.6 632 −23 16 779
AllagesrelativetoAS3zircon(1099.1Ma)aftercorrectionforcommonPbandinitialdisequilibrium.Bold:agesusedinTable1andFig.3.
?Fallout:previouslyuncorrelateddepositsoverlyingCemilköyignimbrite.
δ18OzirconinSMOWrelativetoAS3zircon(5.34‰).
Tiaverages,minima,andmaximavaluesexcludinghighFe/Zranalysesresultingfrombeamoverlapontocrystalimperfections.
T(Ti)=Ti-in-zircontemperaturescalculatedforTiO2activity=0.5usingcalibrationinFerryandWatson(2007).
T(Sat)=zirconsaturationtemperaturesfromwhole-rockpumicecompositionsusingcalibrationinWatsonandHarrison(1983).
92 E.Aydaretal./JournalofVolcanologyandGeothermalResearch213-214(2012)83–97
inmonitoringbeam-overlapontoinclusions(e.g.,glass,Fe–Tioxides) 4.Results
in zircon, but because reliable Fe concentration data for 91500 are
unavailable,weonlyreportFe/ZrrelativetothemaximumFe/Zrin 4.1.40Ar/39Areruptionages
91500(electronicAppendix7).Fe/Zrsignificantlyelevatedrelative
to91500(i.e.,>1+10%estimateduncertainty),indicatespotential Plagioclase40Ar/39Arplateauandisochronageswereobtainedfrom
beam overlap onto glass or Fe–Ti oxide inclusions in zircon, and 8 to 11 heating steps, after excluding low temperature steps that
we consequently discarded the corresponding Ti values. Replicate yieldedloweragesindicatingminor40Arloss.Becauseofthebetteran-
analysis of zircon AS3 (Duluth gabbro; Paces and Miller, 1993) alytical precision, we focus in this report on 40Ar/39Ar plateau ages,
yieldedconcentrationsofTi=29.6±5.9ppm,Y=2374±874ppm, emphasizingthatplateauandisochronagesareconsistent(Table2).
andHfO =1.25±0.24wt.%relativetothe91500standard. Initial40Ar/36Ar,determinedfromtheisochronintercept,isgenerally
2
indistinguishablefromtheairvalue,butcomparativelyimpreciseinter-
3.2.40Ar/39Argeochronology cepts result from clustering of the step isotopic compositions for
Sarımadentepe (KPD-08-018) and Cemilköy (KPD-08-023) samples.
The samples analyzed by 40Ar/39Ar incremental heating experi- In both these cases, however, we have no indication for significant
ments were plagioclase separates prepared from whole rock pieces excess 40Ar. Ages decrease up-section, with overlapping ages of
fromthepyroclasticunits.Visiblyobviousalterationwasfirstremoved 9.11±0.04Ma(weightedmeanofthreeanalyses)and9.08±0.06Ma
usingarocksaw.Thiswasfollowedbycrushingthesamplesusinga (MSWD=0.34)forKavakandZelve,respectively.Resolvablyyounger
porcelain jaw crusher, until approximately 25% of the grains were agesareobtainedforSarımadentepe(8.44±0.12Ma;MSWD=1.98)
sievedintothe210–300μmfraction.Thissizefractionwasrinsedsever- andSofularignimbrites(8.17±0.08;MSWD=0.14).40Ar/39Arplagio-
altimesusingultra-purede-ionizedwaterandsetina40°Coventodry clase ages for overlying Cemilköy (7.20±0.09Ma; MSWD=0.88),
overnight.ThesampleswerefurtherprocessedusingaFrantzmagnetic Tahar (6.14±0.22Ma; MSWD=0.21), and Gördeles ignimbrites
separatortoconcentratethenon-magneticfeldsparfractionfromthe (6.34±0.07Ma;MSWD=0.65)aresignificantlyolderthantheageof
remaining phases. All samples were cleaned by acid leaching in 1N the capping and wide-spread Kızılkaya ignimbrite (5.19±0.07;
HCl (60min), 6N HCl (60min), 1N HNO (60min) and ultra-pure MSWD=0.92), but age differences are irresolvable between Tahar
3
de-ionizedwater(60min)inanultrasonicbathheatedto~50°C.Be- andGördeles.Theyoungestpre-Quaternaryignimbriteunitisthelocal-
foreirradiationapproximately100mgofeachplagioclaseconcentrate lydistributedValibabatepe(2.52±0.49Ma;MSWD=0.69).Wecon-
washand-pickedusingabinocularmicroscopetoremoveanygrains sider the significance of these ages as eruption ages in the light of
containing(remaining)alterationorotherphases.Finally,theseplagio- complementary206Pb/238Uzircongeochronology.
claseseparateswereacidleachedwith5%HF(15min)togentlyetch
awaythe(altered)rimsofthecrystals. 4.2.206Pb/238Uzirconcrystallizationages
Approximately50mgofplagioclasewasirradiatedfor6hinthe
TRIGACLICITnuclearreactoratOregonStateUniversity,alongwith Typically,10–15spotanalyseswereconductedpersample,target-
the FCT-3 biotite (28.03±0.18Ma, 1σ) flux monitor (Renne et al., ingU-richdomainsinthezirconcrystalsusingCLdarkregionsasa
1998).IndividualJ-valuesforeachsamplewerecalculatedbyparabol- proxy(e.g.,MillerandWooden,2004).Individualsamplesgenerally
ic extrapolation of the measured flux gradient against irradiation yieldeduniform206Pb/238Uagesfromwhichweightedaveragezircon
heightandtypicallygive0.3–0.5%uncertainties(1σ).The 40Ar/39Ar crystallizationagesarecalculated(Table3).Theexceptionsaresam-
incrementalheatingagedeterminationswereperformedusingacon- pleKL-03(Cemilköy)andKPD08-031(Tahar)whichyieldedhetero-
tinuous 10W CO laserprobe combined with a MAP-215/50 mass geneous 206Pb/238U ages (discussed below), and only the youngest
2
spectrometer at Oregon State University. Irradiated samples were crystal(orcoherentcrystalpopulation)wasusedforcalculatingcrys-
loadedintoCu-planchettesinanultrahighvacuumsamplechamber tallizationages.Thelateeruptedandleastsilicicunit(Valibabatepe
andincrementallyheatedbyscanningadefocusedCO laserbeamin ignimbrite) lacks zircon. This is in contrast to Viereck-Götte et al.
2
preset patterns across the sample in order to evenly release the (2010) who described accessory zircon in Valibabatepe (Incesu in
argon gas. After heating, reactive gases were cleaned up using an theirterminology),whereasmanyotherignimbritesforwhichTable
SAES Zr–Al ST101 GP50 getter operated at 400°C for ~15min and 4 in Viereck-Götte et al. (2010) does not list zircon have in fact
twoSAESFe–V–ZrST172gettersoperatedat200°Candroomtemper- yielded abundant zircon crystals (including Kızılkaya, Gördeles,
ature,respectively.Beforeanalyzingasample,andaftereverythree Tahar,andCemilköy).
heating steps, system blanks were measured. Data peak intensities CAVPignimbritezirconcrystallizationagesdecreaseupwardwith
werereducedusinglinear orexponential curve fits withrespectto stratigraphicalpositionand40Ar/39Areruptionage.206Pb/238Uzircon
theinlettimeofthegassampleintothemassspectrometer.Allages ages range between 9.63±0.40Ma (MSWD=4.2; average of four
werecalculatedusingthecorrected(SteigerandJäger,1977)decay samples)forKavakand5.11±0.37Ma(MSWD=0.31)forKızılkaya.
constantof5.530±0.097×10−101/a(2σ)asreportedby(Minetal., Differencesbetweencrystallizationanderuptionagesarewithinan-
2000).Foradetaileddescriptionoftheanalyticalfacilityandthecon- alyticaluncertaintyformostsamples,but fortwoKavakignimbrite
stantsusedintheagecalculationswerefertoTable2inKoppersetal. samples (KPD-08-009 and KPD-08-034) pre-eruptive zircon resi-
(2003). denceover~0.9±0.4Macanberesolved.InthecaseofCemilköyig-
Wecalculatedplateauagesandisochronagesasweightedmeans nimbrite (KL-03), the average 206Pb/238U zircon age is significantly
with1/σ2asweightingfactorandasYORK2least-squarefitswithcor- youngerthanthe40Ar/39Arage(−0.54±0.37Ma).KL-03isalsoun-
relatederrorsusingtheArArCALCv2.5softwarethatisavailablefrom usual in that a comparatively large fraction (~25%) of the analyzed
the http://earthref.org/tools/ararcalc.htm website (Koppers, 2002, zirconcrystalsyieldedolderages:oneoutof14crystalsanalyzedis
and references therein).Plateau agesandisochronswithvaluesfor aCretaceousxenocryst(106±6Ma),andthreecrystalsyieldedages
the mean square of weighted deviates (MSWD) higher than unity around ~9±1Ma, similar in age to zircon from underlying Kavak
weretakentoindicateanincreasedscatterduetogeologicaluncer- andZelveignimbrites.Thethreeantecrystsareunlikelytobemag-
tainties beyond the precision of the increment ages themselves. In matic because of the geographically separated eruption centers
these cases the reported analytical errors are multiplied by the forCemilköyandKavak/Zelve(Frogeretal.,1998).Wethereforesus-
square-rootoftheMSWD.Inthispaper(seealsosummaryinelec- pectthatcrystalsbecameentrainedduringtheeruption,andthatpla-
tronicAppendix8), allerrors onthe 40Ar/39Aragesare reportedat gioclase may also be in part xenocrystic, which could contribute
the95%confidencelevel(2σ). excess40Arifdegassingwasincomplete(e.g.,Spelletal.,2001).We