Provenance and tectonic setting of Upper Devonian sandstones from Ilanqareh Formation ... ·...

Provenance and tectonic setting of Upper Devonian sandstones from Ilanqareh Formation (NW Iran) 545

ProvenanceandtectonicsettingofUpperDevoniansandstonesfromIlanqarehFormation(NWIran)

Adel Najafzadeh1, Mahdi Jafarzadeh2,*, and Reza Moussavi-Harami2

1 Islamic Azad University, Tabriz branch, Iran.2 Faculty of Sciences, Geology Department, Ferdowsi University of Mashhad, Iran.

* [email protected]

ABSTRACT

Provenance and tectonic setting of the Upper Devonian sandstones in NW Iran have been interpreted on the basis of petrography and trace-element analysis of samples from two different stratigraphic sections. Modal analysis data of 27 samples with medium sand size and well-sorted properties from Ilanlu section and 23 samples from Ilanqareh section reveal that monocrystalline and polycrystalline (average 6% for Ilanlu section and 3% for Ilanqareh section) quartz grains with inclusions, such as rutile needle and apatite, can be derived from felsic igneous rocks of a craton interior setting. Geochemically, trace-element concentrations, such as La, Th, Sc and Zr, and ratios, such as La/Sc, Th/Sc, La/Co, and Th/Co, of sandstones from Ilanqareh Formation at both localities indicate felsic igneous source rocks and a passive continental margin setting for the source area. Furthermore, the evidence of recycling (for example, well rounded zircons) in the studied samples indicates that recycled sedimentary rocks should also be considered as one of the major source rocks. Enrichment in Zr, negative Sr anomalies and Th/U ratios higher than 3.8 for these sandstones are further evidence for recycled sources, which can be related to the effect of the Hercynian orogeny in NW Iran.

Key words: provenance, geochemistry, tectonic setting, Devonian, Ilanqareh Formation, Azarbaijan, Iran.

RESUMEN

La proveniencia y el ambiente tectónico de areniscas del Devoniano Superior del SW de Irán se interpretan en este trabajo con base en análisis petrográficos y de elementos traza de muestras de dos secciones estratigráficas. Los datos del análisis modal de 27 muestras de la sección Ilanlu, con tamaño de grano de arena media y buena clasificación, y de 23 muestras de la sección Ilanqareh, revelan que granos de cuarzo monocristalino y policristalino, los cuales contienen inclusiones, tales como agujas de rutilo y apatito, pudieron haberse derivado de rocas ígneas félsicas del interior de un cratón. La abundancia de elementos traza como La, Th, Sc y Zr y las relaciones La/Sc, Th/Sc, La/Co, and Th/Co en areniscas de la Formación Ilanqareh en las dos localidades indican rocas fuente de tipo ígneo félsico y un ambiente de margen continental pasivo para el área fuente. Además, la evidencia de reciclaje (por ejemplo, circones bien redondeados) en las muestras estudiadas indica que rocas sedimentarias recicladas deben ser también consideradas como una de las principales rocas funete. El enriquecimiento de Zr, anomalías negativas de Sr y valores de Th/U mayores que 3.8 en esas areniscas son evidencia adicional de fuentes recicladas, las cuales pueden estar relacionadas al efecto de la orogenia Herciniana en el NE de Irán.

Palabras clave: proveniencia, geoquímica, ambiente tectónico, Devoniano, Ilanqareh Formation, Azarbaijan, Iran.

Revista Mexicana de Ciencias Geológicas, v. 27, núm. 3, 2010, p. 545-561

Najafzadeh,A.,Jafarzadeh,M.,Moussavi-Harami,R.,2010,ProvenanceandtectonicsettingofUpperDevoniansandstonesfromIlanqarehFormation(NWIran):RevistaMexicanadeCienciasGeológicas,v.27,núm.3,p.545-561.

Najafzadeh et al.546

INTRODUCTION

Several models are commonly used to deduceprovenanceparameters(sourcerocklithology,climate,weathering, transport, andgeotectonic setting) frompetrographicanalysisonsandstone framework (e.g.,Dickinson,1985;LePeraandArribas,2004).Also,duringthe last twodecades, theuseofgeochemicaldataforprovenance inferences has been significantly developed (see,e.g.,McLennan,2001;Armstrong-Altrinet al.,2004;Gaboet al.,2009).Recentinvestigationsongeochemicalcharacteristicsofancientandmoderndetritussedimentshavebeencarriedoutinordertoinferthesourcerocks,provenanceandtectonicsetting(Guet al.,2002;NesbittandYoung,1996;Whitmoreet al.,2004;Bhatia,1983;Roseret al.,2002;Yanet al.,2006),althoughcautionisrequiredintheirindiscriminateuse(Armstrong-AltrinandVerma,2005).Traceelements(e.g.,Nb,Ni,V,Co,Y,La,Th,ScandZr)inclasticsedimentaryrocksareconsideredtobeimmobileunderconditionsofweathering,diagenesisandmoderatelevelsofmetamorphism,andarecommonlypreservedinsedimentaryrocks(BhatiaandCrook,1986;McLennanet al.,1993).Therefore,suchtraceelementsmightconstitutewell-establishedprovenanceandtectonic

settingindicators(e.g.,BhatiaandCrook,1986,Armstrong-Altrin,2009).

SincemostofpetroleumreservoirsinIranarehost-edincarbonaterocks(Vaziri-Moghaddamet al.,2010;Kavoosiet al.,2009)lessattentionhasbeenpaidtothesiliciclasticsediments,especiallyinrelationtoprovenancestudies.Afewprovenancestudies,basedonpetrographyandgeochemistryofsandstones,havebeencarriedout.Forexample,JafarzadehandHosseini-Barzi(2008)usedpetrographyandmajor-elementgeochemistrytoevaluateprovenance,tectonicsettingandpaleoweatheringconditionsofAhwazSandstoneMemberoftheAsmariFormation(Oligo-Miocene)insouthwestIran.Inthepresentstudy,weusedthepetrographicandgeochemical(trace-element)methodstointerprettheprovenanceandtectonicsettingoftheUpperDevoniansandstonesfromIlanqarehFormationatIlanluandIlanqarehsectionsinAzarbaijanProvince,NWIran(Figure1).

REGIONAL GEOLOGIC SETTING

In 1853, Grewingk, for the first time, reported the presenceofPalaeozoicrocksinnorthwesternIran.He

Jolfa

Persian Gulf

ARAS RIVER

0 5 10 15 km

AZERBAIJAN

45° 30'

45° 30'45° 15'

45° 15'

TehranTabriz

Mashhad

CaspianSea

Aras Dam

IlanluSection

NIlanqarehsection

Poldasht

Yula galdi

IRAN

45° 00'

39° 30'45° 00'

Ilanqareh section

Hasun-e-bozorg

Ilanqareh

Aras DamHasanKand Ilanlu

Section

KUH-E-ALIBASHI

RESHTEYE GECHENDAGH

P

D

Divankhaneh

Ddl

PLQc

Dc

Pr

Pd

Dc

DDc

Pd

P

Ddl

Pr

LEGEND

Sandstone and limestone (Ilanqareh Formation)

Dark grey limestone, red marly limestone (equivalent of Ruteh Formation)Dark red, violet sandstone

Dolomite, grey gypsum, quartz sandstone

Grey, thin-bedded to massive conglomerate

Intermediate volcanic rocks including tuff

Dark grey, medium bedded dolomitic rocks

Pale grey, medium to thick bedded dolomitic limestone (Muli Formation)

RoadBorder line (Aras River)

Measur d sectionePLQc

Hasun-e-bozorg

39°

sv

Hasan Kand

Figure 1. Location map of Ilanlu and Ilanqareh sections in the northwest Iran. The study area is located in the Azarbaijan Province of Iran, modified from BolourchiandSaidi(1989).


Basedonstratigraphiccharacteristics,Alavi-NainiandBolourchi(1973)dividedthisformationintofourpartsinascendingorder:PartA:mainlycomposedofdolomitewithinterbedsoflimestoneandshale.PartB:consistsoffossilbearingthin-beddedlimestoneandshale.PartC:mainlyshaleandsandstone.PartD:composedoftheLowerCarboniferouslimestones.

AmuchbetterandalmostcompletesectionthroughtheupperpartoftheMuliandtheentireIlanqarehFormationsisexposednearthevillageofIllanlu(BolourchiandSaidi,1989). Thestudyarea(TheIlanluandIlanqarehsections)islocatedinthenorthwestIran,AzarbaijanProvince. TheIlanlusectionislocatedatsouthoftheArasDam(NorthernIlanluvillage)withthicknessof510mandtheIlanqarehsec-tionislocatedinnorthwestofPoldasht(westernIlanqarehvillage)(Figure1),andalsotheIlanqarehFormationisabout320matthislocality.

ANALYTICAL METHODS

Asstatedabove,twostratigraphicsectionsoftheIlanqarehFormationweremeasuredandsampledatIlanluandIlanqarehlocations(Figures2and3).Fiftyrepresenta-tivefreshoutcropsampleswereselectedforpetrographicstudies.

Theselectedsamplesweremainlywell-sortedandun-weathered, fine- to medium grained, sand-size. Framework mineral composition (modal analysis) was quantified using thepoint-countingmethodofGazzi-DickinsonasdescribedbyIngersollet al. (1984). Classification of grain types was doneusingtheDickinson(1985)method(Table1).

Frameworkgrainswerecountedfor250to300countsperthinsection.ModalanalysisdatafrompointcountingoftheframeworkgrainsandtherecalculatedsandstonecompositionsoftheIlanqarehsandstonesareshownin

statedthatthesesedimentaryrocks,suchassandstones,conglomeratesandfossiliferouslimestones,areDevonianinageandtransgressedoveracrystallinebasement.MoreinformationcanbefoundinFrechandArthaber(1900)report on the same region. The first biostratigraphic data weregivenbyRieben(1935)aboutthegeologyoftheIran-Azerbaijanborderland.

Alavi-NainiandBolourchi(1973)reportedthatintheareanorthofTabriz,sedimentaryrocksarepresum-ablyofEarlytoLateDevonianinage(MuliandIlanqarehFormations)thathavetransgressedonaPrecambrianbase-mentoronLowerPaleozoicsandstonesanddolomitesoftheLalunandMilaFormationsandareinturnoverlainbyPermianplatformdolomitesoftheRutehFormation.TheIlanqarehFormationinthestudyareaconformablyoverliestheMuliFormationandunderliesJeirud(Devonian)orRuteh(Permian)Formations.

PaleogeographicinvestigationsindicatethatatthetimeofdepositionofIlanqarehFormation(Devonianage),thenorthwestIranwasapartofthelongandwidenorthernpassivemarginofGondwanalandborderingthePaleo-TethysOcean(Sengor,1990;Beydoun,1991). Stumpet al.,(1995)indicatedthattheLateDevoniantoEarlyCarboniferoussedimentsarenotuniformlydistrib-utedacrosstheArabianPeninsuladuetoupliftanderosionassociatedwiththeHercynianOrogenyduringtheendofDevoniantoCarboniferous.Also,regionalcomparisonbetweenIlanqarehFormationofnorthwestIranwiththeUpperPaleozoicformationsinSyria,Iraq,TurkeyandSaudiArabiabyHusseini(1991)indicatesthatduringthePaleozoictimes,NorthAfricaandArabiawerepartofabroadcontinentalshelfmarginand,furthermore,theseareasweresubjectedtomajorintra-continentalextensionfromLateDevoniantopossiblyEarlyCarboniferousandtheArabianandadjacentplateswerestructurallyaffectedbyaregionalHercyniantectonicevent(Figure2).

Figure2.CorrelationchartoftheDevonianrockunitsinNWIran,SaudiArabia,Turkey,IraqandSyria,compiledfromHusseini(1991).


SeriesThick

ness (m

)

Lithology

Upp

er D

evon

ian

500

400

300

200

100

0

Ilanq

areh

For

mat

ion

ShaleFine-grained sandstone

Coarse-grained sandstone

Ferruginous sandstone

Thin-bedded Limestone

Tuff

Thick-bedded Limestone

Medium-bedded Limestone

Thin-bedded Sandy Limestone

LEGEND

300

200

100

0

Lateral distance 80 km

Covered

Formatio

n

IL IQ

98

273032, 333435, 37

58,5756

60, 616264

66, 6768, 6970, 71, 7273, 74, 75, 76

303233

35, 37

48, 4947

50

51

52, 53

41

54, 56

29

34

38, 39

43444546

55

65

Figure3.LithostratigraphiccolumnarsectionsoftheUpperDevonianSandstonesatIlanluandIlanqareh.IL:IlanlusectionandIQ:Ilanqarehsection(seeFigure1forlocationofthesections).

Tables1and2.Trace-elementanalysis (12samplesfromIlanlu

sectionand10samplesfromIlanqarehsection)wasdonebyICP-AESatthelaboratoriesoftheGeologicalSurveyofIran(Table3).Accuracyandprecisionwereestimatedandmonitoredfromthecontrolsamples.Detectionlimits(DL)fortheelementswere(inppm):10forBa,1forRb,

Co,Zr,Hf,Sr,PbandV,0.1forNbandSc,0.8forCr,0.3forLaandTh,0.4forY,0.5forU,2forNiandZnand100forTi.Theprecisionofreplicateanalysisisbetterthan5%forallanalyzedtraceelementsexceptZrandV,whichhaveprecisionsof5-8%.ItisimportanttomentionthatalthoughtherecommendationsofVermaandSantoyo(2005)andVermaet al.(2009)werenotfullyfollowedin


Sample Rock Type Qpq Qm Qm un Qm non Qp Qt Q F Lt L Rf

27IL quartzarenite 3 216 78 138 3 219 219 4 3 0 030IL quartzarenite 5 227 82 145 10 237 232 3 12 2 732IL quartzarenite 3 228 89 139 5 233 231 4 5 0 233IL quartzarenite 4 206 79 127 7 213 210 5 9 2 534IL quartzarenite 4 233 91 142 7 240 237 3 7 0 335IL quartzarenite 2 220 85 135 2 222 222 2 3 1 137IL quartzarenite 3 234 93 141 3 237 237 8* 3 0 055IL Subarkose 5 231 83 148 7 238 236 9* 9 2 456IL quartzarenite 1 218 87 131 3 221 219 3 3 0 257IL quartzarenite 5 216 82 134 5 221 221 4 5 0 060IL Subarkose 5 216 88 128 10 226 221 6 11 1 661IL quartzarenite 7 231 92 139 10 241 238 5 11 1 462IL quartzarenite 9* 224 82 142 9 233 233 3 9 0 064IL quartzarenite 10* 226 83 143 12 238 236 7 12 0 265IL quartzarenite 8 245 91 154 11 256 253 2 11 0 366IL quartzarenite 10* 229 89 140 13 242 239 4 13 0 367IL quartzarenite 9* 253 98 155 12 265 262 3 12 0 368IL quartzarenite 7 235 89 146 9 244 242 5 10 1 369IL quartzarenite 9* 238 90 148 11 249 247 4 13 2 470IL quartzarenite 5 230 90 140 8 238 235 3 8 0 371IL quartzarenite 5 235 91 144 8 243 240 5 9 1 472IL quartzarenite 7 256 101 155 7 263 263 4 7 0 073IL quartzarenite 9 223 87 136 14 237 232 7 14 0 574IL quartzarenite 4 237 99 138 6 243 241 6 6 0 275IL quartzarenite 5 237 96 141 8 245 242 3 10 2 576IL quartzarenite 7 237 95 142 10 247 244 3 10 0 398IL quartzarenite 4 243 101 142 6 249 247 6 8 2 429IQ quartzarenite 4 236 92 144 5 241 240 4 5 0 130IQ quartzarenite 2 230 91 139 4 234 232 3 6 2 432IQ quartzarenite 4 245 103 142 6 251 249 4 6 0 233IQ quartzarenite 2 243 99 144 3 246 245 2 4 1 234IQ quartzarenite 2 249 98 151 5 254 251 2 5 0 335IQ quartzarenite 4 241 93 148 5 246 245 4 5 0 137IQ quartzarenite 2 245 101 144 5 250 247 3 5 0 338IQ quartzarenite 4 247 99 148 7 254 251 3 7 0 339IQ quartzarenite 4 257 102 155 5 262 261 4 7 2 341IQ quartzarenite 3 228 89 139 5 233 231 4 6 1 343IQ quartzarenite 2 234 91 143 5 239 236 3 5 0 344IQ quartzarenite 5 256 105 151 7 263 261 3 7 0 245IQ quartzarenite 3 231 89 142 3 234 234 3 5 2 246IQ quartzarenite 4 238 96 142 4 242 242 4 4 0 047IQ quartzarenite 3 238 92 146 5 243 241 3 5 0 248IQ quartzarenite 3 249 98 151 5 254 252 5 5 0 249IQ quartzarenite 3 231 87 144 3 234 234 2 5 2 250IQ quartzarenite 2 236 91 145 2 238 238 4 2 0 051IQ quartzarenite 1 241 94 147 1 242 242 4 2 1 152IQ quartzarenite 3 241 103 138 3 244 244 3 4 1 153IQ quartzarenite 2 234 97 137 4 238 236 5 5 1 354IQ quartzarenite 4 226 88 138 5 231 230 4 7 2 356IQ quartzarenite 3 232 91 141 5 237 235 4 5 0 2n 45 50 50 50 50 50 50 47 50 50 50Mean 3.9 235 92 143 6.4 241 239 3.8 7.0 0.6 2.5Stdev 1.8 11 7 6 3.1 11 11 1.2 3.1 0.8 1.6

Table1.DetritalmodesfromUpperDevoniansandstonesoftheIlanqarehFormation.Qmmonocrystallinequartz;QmnonNon-undulousemonocrystal-linequartz;QmunUndulousemonocrystallinequartz;Qpqpolycrystallinequartz;QpPolycrystallinequartzose;QtTotalquartzosegrains;QTotalQmandQpq;FTotalfeldspargrains;LUnstablelithicfragments;LtTotalsiliciclasticlithicfragments;RfTotalunstablerockfragmentsandchert.

* Unusual compositions were identified from single-outlier type discordancy tests (Verma, 1997; Verma et al.,2008).MeanandstandarddeviationvalueswerereportedasroundedvaluesafterDODESYSapplicationassuggestedbyBevingtonandRobinson(2003)andVerma(2005).


thiswork,theDLdatadoshowthesystematicrelationshipputforthbytheseauthorsforqualitycontrolofchemicalanalysis,correspondingtoseveralodd-evenelementpairsorsequences,suchasCo-Ni(odd-evenpairwiththeDLof1ppm(low)and2ppm(high),respectively)La-Ba(DL0.3-10),Sc-Ti-V(DL0.1-100-1),andSr-Y-Zr-Nb(DL1-0.4-1-0.1).

For the identification and elimination or separation of unusualcompositions,thecomputerprogramDODESYS(byS.P.VermaandL.Díaz-González,manuscriptinprepa-ration)wasused.Thisprogramuseshighlypreciseandaccuratecriticalvalues(Vermaet al.,2008;VermaandQuiroz-Ruiz,2008)forthediscordancytestmethodinitiallyproposed by Verma (1997). The final statistical parameters (meanandstandarddeviationvalues)werereportedafterDODESYSapplicationasroundedvalues(BevingtonandRobinson,2003;Verma,2005).

RESULTS

Petrography and modal analysis

Texturally,thesandstonesfromIlanqarehFormationare medium to fine-grained, with rounded to subrounded grainsthataremoderatelytowell-sorted.Notethatthesamples from the Ilanqareh section are finer than Ilanlu section.ManyquartzgrainsatIlanluandIlanqarehsec-tionshaveincipientsilicaovergrowthsandsomesamplesespeciallyatIlanqarehsectionhavecarbonatecement,withminoramountsofclaymineralascement.Thesesilicaover-growthsmaybetheresultofpressuredissolutionatthegraincontacts,whenthegrainswereburiedunderthepressureoftheoverlyingrocks.Straight,concavo-convexandsuturedgraincontactsarepresentwhereframeworkgrainshavelowcementcontentinsandstonesfrombothsections.

Theframeworkgrainsofsandstonesatbothlocalitiesaremainlyquartzandlessfrequentlyoffeldsparandrockfragments(Table1).

Mostofthequartzgrainsaremonocrystalline,whileafewpercentofpolycrystallinequartzarepresent inbothsectionsespeciallyat Ilanlusection(Figure4a).Monocrystallinequartzgrainsexhibitunitextinctionratherthanunduloseextinction(Figures4aand4b).

Compositionally,themostabundantlithicfragmentismicrocrystallinechertespeciallyatIlanlusection(Figure4b).Allstudiedthinsectionsinbothstratigraphicsectionscontainsmallamountsofpotassiumfeldspar(K)andpla-gioclase(Figure4c).Althoughfeldsparsarerareinmanysamplesfrombothsections,butwhenpresent,theyarecloudy,whichisrelatedtoalteration.

Someofthenon-undulatorymonocrystallinequartzcontainsinclusionsofapatiteandrutileneedles,whichshowthatthattheymayhavebeenderivedfromplutonicsourcerocksorsedimentaryrecycling(Figure4d).Accessorymineralsinascendingorderofdecreasingarewell-rounded

zirconandapatite,aswellasmuscoviteandbiotiteinbothsections(Figures4eand4f).

Theevidenceofrecycling(e.g.,roundedzircon)inthestudiedsandstonesamplesatbothlocalitiesindicatesthatoldersedimentaryrocksmaybeconsideredasoneofthemajorsourcerocks(e.g.,HartleyandOtava,2001).

Modalanalysisfrompoint-countingoftheframeworkgrainsarepresentedinTable1.Monocrystallinequartz(Qm),polycrystallinequartz(Qp),totalfeldspar(F)andtotallithic fragments (L) are identified. Varieties of monocrystal-linequartzextinctiontypes(unduloseandnon-undulose)arealsorecognized(Table1).

Petrographicstudiesofsamplesshowthat,accordingto Folk (1980) classification, these sandstones are mainly quartzarenites(Figure5),excepttwosamplesfromIlanlusection that they are classified as subarkose.

Trace elements geochemistry

TraceelementconcentrationsofsandstonesfromIlanqarehFormationatIlanluandIlanqarehsectionsarereportedinTables3and4.Likewise,averagedataoftheuppercontinentalcrustcomposition(UCC)(TaylorandMcLennan,1985)areincludedasareference.

Large-ion lithophile elements (LILE): Rb, Ba, Sr, Th, U Comparedwithaverageuppercontinentalcrust(UCC)

(TaylorandMcLennan,1985),analyzedsandstonesatIlanluandIlanqarehsectionshaverelativelylowconcentrationsinlargeionlithophileelements(LILE),suchasRb,Th,UanddistinctdepletionespeciallyinSrandBa(Figures6aand6b).TheaverageabundancesofRb(21ppm),Th(5.5ppm),U(0.53ppm),Sr(2ppm)andBa(50ppm)fromIlanlusectionandRb(50.8ppm),Th(9.7ppm),U(1.3ppm),Sr(98.9ppm)andBa(285.7ppm)fromIlanqarehsectionarerelativelylowconcentrations(Tables3and4).

Thegeneralpaucityofclaymineralsinthesesand-stonesfromIlanqarehFormationatIlanluandIlanqarhsections probably influenced the depletions of these ele-ments,suchasBa,ThandU,astheymaybeoftenhostedascationsinthephyllosilicatemineralstructures(e.g.,Caraccioloet al.,2009).

High field-strength elements (HFSE): Zr, Hf, Nb and YZr,Nb,HfandYarepreferentiallypartitionedinto

meltsduringcrystallizationandanatexis(FengandKerrich,1990;Torres-Alvaradoet al.,2003),andasaresult,theseelementsareenriched infelsicrather inmaficrocks.Additionally, they are thought to reflect provenance compo-sitionsasaconsequenceoftheirimmobilebehavior(TaylorandMcLennan,1985).

Ingeneral, theconcentrationsofsomehighfieldstrengthelements,suchasNbandY,arelowerinsandstonesfromIlanlusectioncomparedwiththoseoftheUCC(Figure6a),butatIlanqarehsectionarenearthenormalizationvalue


Sample Qt F L (%) Qm F Lt (%) Q F Rf(%) Qm u Qm nu Qp(%)

Qt F L Qm F Lt Q F Rf Qp Qmu Qmnu

27 IL 98.2 1.8 0.0 96.9 1.8 1.3 98.2 1.8 0.0 1 36 6330 IL 97.9 1.2 0.8 93.8 1.2 5.0 95.9 1.2 2.9 2 35 6332 IL 98.3 1.7 0.0 96.2 1.7 2.1 97.5 1.7 0.8 1 39 6033 IL 96.8 2.3 0.9 93.6 2.3 4.1 95.5 2.3 2.3 2 38 6034 IL 98.8 1.2 0.0 95.9 1.2 2.9 97.5 1.2 1.2 2 38 6035 IL 98.7 0.9 0.4 97.8 0.9 1.3 98.7 0.9 0.4 1 38 6137 IL 96.7 3.3 0.0 95.5 3.3 1.2 96.7 3.3 0.0 1 39 5955 IL 95.6 3.6 0.8 92.8 3.6 3.6 94.8 3.6 1.6 2 35 6356 IL 98.7 1.3 0.0 97.3 1.3 1.3 97.8 1.3 0.9 0 40 6057 IL 98.2 1.8 0.0 96.0 1.8 2.2 98.2 1.8 0.0 2 37 6160 IL 97.0 2.6 0.4 92.7 2.6 4.7 94.8 2.6 2.6 2 40 5861 IL 97.6 2.0 0.4 93.5 2.0 4.5 96.4 2.0 1.6 3 39 5862 IL 98.7 1.3 0.0 94.9 1.3 3.8 98.7 1.3 0.0 4 35 6164 IL 97.1 2.9 0.0 92.2 2.9 4.9 96.3 2.9 0.8 4 35 6165 IL 99.2 0.8 0.0 95.0 0.8 4.3 98.1 0.8 1.2 3 36 6166 IL 98.4 1.6 0.0 93.1 1.6 5.3 97.2 1.6 1.2 4 37 5967 IL 98.9 1.1 0.0 94.4 1.1 4.5 97.8 1.1 1.1 3 37 5968 IL 97.6 2.0 0.4 94.0 2.0 4.0 96.8 2.0 1.2 3 37 6069 IL 97.6 1.6 0.8 93.3 1.6 5.1 96.9 1.6 1.6 4 36 6070 IL 98.8 1.2 0.0 95.4 1.2 3.3 97.5 1.2 1.2 2 38 6071 IL 97.6 2.0 0.4 94.4 2.0 3.6 96.4 2.0 1.6 2 38 6072 IL 98.5 1.5 0.0 95.9 1.5 2.6 98.5 1.5 0.0 3 38 5973 IL 97.1 2.9 0.0 91.4 2.9 5.7 95.1 2.9 2.0 4 38 5974 IL 97.6 2.4 0.0 95.2 2.4 2.4 96.8 2.4 0.8 2 41 5775 IL 98.0 1.2 0.8 94.8 1.2 4.0 96.8 1.2 2.0 2 40 5876 IL 98.8 1.2 0.0 94.8 1.2 4.0 97.6 1.2 1.2 3 39 5898 IL 96.9 2.3 0.8 94.6 2.3 3.1 96.1 2.3 1.6 2 41 5729 IQ 98.4 1.6 0.0 96.3 1.6 2.0 98.0 1.6 0.4 2 38 6030 IQ 97.9 1.3 0.8 96.2 1.3 2.5 97.1 1.3 1.7 1 39 6032 IQ 98.4 1.6 0.0 96.1 1.6 2.4 97.6 1.6 0.8 2 41 5733 IQ 98.8 0.8 0.4 97.6 0.8 1.6 98.4 0.8 0.8 1 40 5934 IQ 99.2 0.8 0.0 97.3 0.8 2.0 98.0 0.8 1.2 1 39 6035 IQ 98.4 1.6 0.0 96.4 1.6 2.0 98.0 1.6 0.4 2 38 6037 IQ 98.8 1.2 0.0 96.8 1.2 2.0 97.6 1.2 1.2 1 41 5838 IQ 98.8 1.2 0.0 96.1 1.2 2.7 97.7 1.2 1.2 2 39 5939 IQ 97.8 1.5 0.7 95.9 1.5 2.6 97.4 1.5 1.1 2 39 5941 IQ 97.9 1.7 0.4 95.8 1.7 2.5 97.1 1.7 1.3 1 39 6043 IQ 98.8 1.2 0.0 96.7 1.2 2.1 97.5 1.2 1.2 1 39 6144 IQ 98.9 1.1 0.0 96.2 1.1 2.6 98.1 1.1 0.8 2 40 5845 IQ 97.9 1.3 0.8 96.7 1.3 2.1 97.9 1.3 0.8 1 38 6146 IQ 98.4 1.6 0.0 96.7 1.6 1.6 98.4 1.6 0.0 2 40 5947 IQ 98.8 1.2 0.0 96.7 1.2 2.0 98.0 1.2 0.8 1 38 6148 IQ 98.1 1.9 0.0 96.1 1.9 1.9 97.3 1.9 0.8 1 39 6049 IQ 98.3 0.8 0.8 97.1 0.8 2.1 98.3 0.8 0.8 1 37 6250 IQ 98.3 1.7 0.0 97.5 1.7 0.8 98.3 1.7 0.0 1 38 6151 IQ 98.0 1.6 0.4 97.6 1.6 0.8 98.0 1.6 0.4 0 39 6152 IQ 98.4 1.2 0.4 97.2 1.2 1.6 98.4 1.2 0.4 1 42 5753 IQ 97.5 2.0 0.4 95.9 2.0 2.0 96.7 2.0 1.2 1 41 5854 IQ 97.5 1.7 0.8 95.4 1.7 3.0 97.0 1.7 1.3 2 38 6056 IQ 98.3 1.7 0.0 96.3 1.7 2.1 97.5 1.7 0.8 1 39 60

Table2.RecalculatedmodalpointcountsoftheUpperDevoniansandstonesoftheIlanqarehFormation.SeeTable1fordetailsofthecolumnheadingabbreviations.


(Figure6b).TheaverageabundancesofHFSE forIlanlusectionare:Zr(600pm),Hf(12.9ppm),Nb(4.4ppm)andY(7.2ppm)andforIlanqarehsectionare:Zr(239.3ppm),Hf(9.5ppm),Nb(9.1ppm)andY(17.9ppm)(Tables3and4).

SamplesfromtheIlanlusectionaredistinctlyenrichedinZr(average600ppm),butsamplesfromtheIlanlusec-tionareslightlyenrichedinZr(239ppm)andbothsectionsaredistinctlyenrichedinHf(average12.9ppmforIlanluand9.5ppmforIlanqarehsection)(Figure6aand6b).Zirconiumisgenerallyconsideredtobetheleastmobileele-ments during chemical weathering. Significant amounts of Zr are typically fixed in resistant minerals such as zircon.

Ferromagnesian trace elements: Co, Cr, Ni, Sc, VAlthoughtheaverageabundancesofCo(7.8ppm),

Sc(2ppm),andV(15ppm)fromIlanlusectionandCo(3.3ppm),Sc(7.3ppm),andV(35.2ppm)fromIlanqarehsectionarerelativelylow(Tables3and4)incomparisontotheaverageuppercontinentalcrust(UCC),Crisdistinctlyenrichedinbothsections(average328ppmforIlanluandaverage100ppmforIlanqarehsection)andNiisnearthenormalizationvaluetorelativelyenrichedinsamplesfromIlanlusectionandisnearthenormalizationvalueinIlanqarehsection(Figure6aand6b).

ThisenrichmentinCrandNimaysuggestsomeinputof mafic and ultramafic materials from the source area as a minorsource;however,thevariationsinCo,CrandVvaluesmayalsobeduetochangesintheoxidationstate,thereforenot reflecting source area composition. Thus, they must be usedwithcaution(Bauluzet al.,2000).

DISCUSSION

Provenance

Petrography Becauseofthescarcityoffeldsparsandrockfrag-

mentsinourstudiedsamples,provenancewasestablishedmainlyfromtheinterpretationofquartzgraintypes.ToevaluatetherelativeimportanceofquartzgraintypesfordeterminingtheprovenanceoftheUpperDevoniansand-stonesfromIlanqarehFormation,weplottedpolycrystalline(compositegrains)quartzversusundulatory(strained)tonon-undulatory(unstrained)monocrystallinequartz(Figure7),followingthetechniqueofTortosaet al.(1991).ThisplotsuggeststhatquartzgrainsoftheIlanqarehsandstonesatIlanluandIlanqarehsectionsareofplutonicorigin.Therelatively high proportion of fine to medium-grain mono-crystallinequartzinsandstonesmaybeattributedtothedisaggregationoforiginalpolycrystallinequartzduringhighenergyand/orlongdistancetransportfromthesourcearea(DabbaghandRogers,1983).

The polycrystalline quartz grains are composed of five ormorecrystalswithstraighttoslightlycurvedintercrystalboundaries(Figure4a).Thistypesuggestsanoriginfromplutonicigneousrocks(Folk,1980).

Thepetrographiccharactersareconsistentwithsand-stonesderivedfromanareaoflowreliefonastableshelfmargin(e.g.,Amireh,1991).Suchcharactersmayalsoindicatethatthesandstoneswerederivedfromacratonicinterior(BurnettandQuirk,2001)andweredepositedonapassivemargin(EmiliaandArribas,2004).

Sampleno.

27IL

30IL

34IL

35IL

37IL

60IL

62IL

69IL

70IL

72IL

73IL

74IL Mean Sd.Dev UCC

Ba 70 26 83 54 39 56 107 14 91 19 22 19 50 32 550Rb 36.6 22.8 20 33.9 19.2 8.8 25.9 24.4 18.6 14 25 5.9 21 9 112Zr 1136 234 909 862 819 183 468 273 743 885 226 426 600 330 190Hf 16.6 8.38 11.6 14 18.9 10.5 8.79 12.5 19.1 13.78 11.9 8.23 12.9 3.8 5.8Nb 7.3 1.67 4.7 9.72 4.17 1.16 5.24 1.01 6.42 6.9 2.2 2.2 4.4 2.8 12Co 1.76 1.26 2.9 0.75 2.85 0.75 4.1 0.75 1.01 1.8 1.75 1.7 1.78 1 17Cr 238 374 226 242 392 335 282 358 417 328 372 372.6 328 65 83La 35.2 18.4 23.5 33.5 29.0 12.7 17.0 10.4 32.3 31.6 20.1 11.7 23 9 30Y 14.8 4.4 11.3 6.9 8.8 7.4 7.06 3.6 7.3 7.5 3.3 3.9 7.2 3.4 22Th 11.1 3.2 7.3 5.02 5.7 2.3 6.2 3.45 5.9 6.9 3.1 5.3 5.5 2.4 10.7Sr 109 93.2 82 88.5 83.1 72 51.3 24.7 77.4 81.9 47.3 21.2 2 0.7 350U 0.5 0.63 0.65 0.53 0.5 0.44 0.74 0.5 0.6 0.45 0.5 0.4 0.53 0.09 2.8Sc *4.75 1.23 2.73 2.42 1.98 0.9 2.73 1.06 2.61 2.57 1.85 1.42 2 0.7 13.6Ni 6.6 43.5 11 10.5 50.3 3.4 12.4 4.34 41.7 66 59.8 167* 28 24 44Pb 23.6 11.3 13.6 33.9 19.1 19 12.6 14.2 17.9 16.9 15 14.7 13.60 6.13 17V 28.2 13.3 13.5 30.8 15.3 6.1 15.9 8.9 14.1 17.1 8.7 11.3 15 7 107Zn 91 54 31.7 49.7 43.7 34.4 71.6 65.1 42.3 46 51 190 91 42.9 71Ti 5198 681 4550 4466 3361 487 1983 459 1315 3277 845 1021 2303 1767

Table3.WholerocktraceelementcompositionofrepresentativeUpperDevoniansandstonesoftheIlanqarehFormationatIlanlusection.Elementalconcentrationsarepartspermillion.

No unusual compositions were identified from single-outlier type discordancy tests (Verma, 1997; Verma et al.,2008).MeanandstandarddeviationvalueswerereportedasroundedvaluesafterDODESYSapplicationassuggestedbyBevingtonandRobinson(2003)andVerma(2005).


a) b)

c) d)

e) f)

GeochemistryInordertodeterminethesourceofsedimentsusing

trace-elements(forexample,Th,Co,Ni,Sc,Zr,HfandNb),itisnecessarytoascertainthattheelementisrelativelyim-mobileinthesedimentarycycle(BhatiaandCrook,1986;McLennan,2001;Shao et al.,2001).

Th aboundances are higher in felsic than in mafic igne-oussourcerocksandintheirweatheredproducts,whereasCo, Sc and Cr are more concentrated in mafic than felsic igneous rocks and in their weathered products. Mafic and felsic source rocks differ significantly in the ratios such of La/Sc,Th/Sc,La/Co,Th/CoandCr/Thandhenceprovideusefulinformationabouttheprovenanceofsedimentaryrocks(e.g.,Cullerset al.,1988;Cullers,2000;CullersandPodkovyrov,2000).Inthisstudy,La/Sc,Th/Sc,La/CoandTh/CovaluesoftheUpperDevoniansandstonesaremore

similartovaluesforsedimentsderivedfromfelsicsourcerocks than to those for mafic source rocks, thus suggesting felsicsourcerocks.However,Cr/Thissimilartovaluesfrom mafic source rocks because of the enrichment of Cr (Table5).

FloydandLeveridge(1987)statedthattheelementalratioofLa/Thplottedversustheconcentrationofhafniumdemonstratesthedegreeofrecyclinginsandstonesanditalsoprovidesinformationabouttheprovenance.ALa/ThversusHfplotfortheUpperDevoniansandstonesatbothsectionsshowsanintenserecyclingandsedimentarysourceandapassivemargintectonicsettingforthesesandstones(Figure8a).

Th/Uinsedimentaryrocksisofinterest,asweather-ingandrecyclingtypicallyresultinlossofU,leadingtoanelevationintheTh/Uratio.TheTh/Uratioinmostup-

Figure4.a)Photomicrographshowingquartzgrainsconsistingmainlyofmonocrystallinequartzgrainswithunduloseextinction(blackarrow)andpolycrystallinequartzgrain(whitearrow);b)Feldspargrainwithafewalterationc)chertgrain(whitearrow)andmonocrystallinequartzgrainswithnonunduloseextinction(blackarrow);d)quartzgrainincludinginclusionsofrutileneedles;e)roundedgrainofzirconasindicatorofrecycling(whitearrows);andf)whitearrowshowsmuscovitegrain.


F R

Q

95

75

samples from Ilanqareh section

samples from Ilanlu section

RF

Q

95

75

Q

F R

litharenite

feldspaticlitharenite

lithicarkose

arkos

e

sublitharenitesubarkose

quartzarenite95

75

1:13:1 1:3F/RF

percrustalrocksistypicallybetween3.5and4andTh/Uvalueshigherthan4mayindicateintenseweatheringinsourceareasorsedimentrecycling(McLennanet al.,1993).Th/UratiosinthesandstonesfromIlanqarehFormationatIlanlusectionrangefrom5.2to22andforIlanqarehsectionrangefrom3.7to11.8,indicatingthederivationofthesesandstonesfromrecyclingofthecrust.

Th/Sc ratio commonly reflects the average composi-

tionofthesourcerocks.ScandiumandTharetransferredquantitativelyfromsourcetosediment;hence,theratioisused todeduce thecompositionof thesourcerock(McLennanet al.,1993).WhenTh/ScisplottedonthediagramofZr/Sc–Th/Sc(Figure8b),therecycledsourcerocksfortheallsandstonesamplesfromtheIlanlusec-tionandmostsamplesfromIlanqarehsectionarefurthersupportedbytheirhighZr/Scratio.StronglyenrichedZr

Figure 5. QFR triangular classification plot (Folk, 1980) of Sandstones from Ilanqareh Formation.

Sampleno.

30IQ

34IQ

38IQ

40IQ

43IQ

46IQ

50IQ

52IQ

54IQ

56IQ Mean Sd. Dev UCC

Ba 380 206.2 223 282 352 395 221 252.5 319.8 224 285.7 71.1 550Rb 54 43 63 91 36 33.4 48 42 52 46 50.8 16.6 112Zr 256 224 229 269 235 221 241 260 215 243 239.3 17.9 190Hf 8.7 9.2 10.4 9.4 8.2 8.3 11.1 10.1 9.1 8.5 9.5 0.9 5.8Nb 9.2 8.5 10.7 9.3 7.6 6.6 11.2 6.8 6.9 14.1 9.1 2.4 12Co 4.8 3.9 5.1 2.9 3.2 3.8 2.9 1.8 1.8 2.5 3.3 1.1 17Cr 170.5 95 114 104 163 53 61 86 77 83 100.7 39.3 83La 41 35 37.6 43.2 24 29 20.64 19.99 18.23 30.13 29.9 9.1 30Y 21 19.2 24.3 23.2 18.2 13.1 10.3 14.3 16 19.68 17.9 4.5 22Th 10.8 8.7 10.3 10.6 9.2 9.12 9.8 9 10.4 8.6 9.7 0.8 10.7Sr 92 81 108 109 121 96 104.5 102 79.9 95.4 98.9 12.8 350U 1.5 1.02 1.38 0.9 0.84 1.56 0.84 0.9 1.33 2.3 1.3 0.5 2.8Sc 7 5.2 9 10 5.1 6 6 5.4 6 13 7.3 2.6 13.6Ni 21 26 31 43.5 35 51 28 21 23 18 29.8 10.7 44Pb 13.5 10.8 10.7 10.2 8.5 9.3 8.9 9.5 10.7 9.7 10.2 1.4 17V 43 38 29 24 52 60 23 32 28 23 35.2 12.9 107Zn 33 42 55 61 29.8 25 34 28 44.1 28.8 38.1 12.2 71Ti 1235 842 1696 1510 753 1907 2246 819 2515 2501 1602.4 684.2

Table4.WholerocktraceelementcompositionofrepresentativeUpperDevoniansandstonesoftheIlanqarehFormationatIlanqarehsection.Elementalconcentrationsarepartspermillion(ppm).


0.01

0.1

1

10

Sam

ple/

UCC

Rb Sr Ba Pb Th U Hf Zr Nb Y Sc V Cr Co Ni Zn

0.1

1

10

Rb Sr Ba Pb Th U Hf Zr Nb Y Sc V Cr Co Ni Zn

Sam

ple/

UCC

a)

b)

inzirconcanbeeasilyrecycledandScispresentinlabilephases.Therefore,theZr/Scratioisconsideredasoneoftheproxytoevaluatethepresenceorabsenceofrecycling(McLennanet al.,1993).ButthreesamplesfromIlanqarehsection fallow the trend of first order sediments and show a simplepositivecorrelationbetweentheseratios.

Tectonic setting

Petrography Sandstonesfromdifferent tectonicsettingshave

differentdetritalcomponentsandgeochemicalcomposi-tion(Dickinsonet al.,1983;Bhatia,1983;Kroonenberg,1994;CritelliandNilsen,2000;Roseret al.,2002;Yanet al.,2006).Inthefollowingsections,wewilldiscusshowthedetritalandchemicalcompositionsoftheUpperDevonianSandstonesmaybeusedtodeterminetheirtec-tonicsetting.

Platetectonicprocessescontrolthecharacteristicsof

thedetritalgrainsofsandstones(Dickinsonet al.,1983;Marsaglia,2004).PlottingdatafromthemodalanalysisoftheIlanqarehSandstonesintheternaryQt-F-LandQm-F-LtdiagramsofDickinsonet al.(1983)showsthattheUpperDevoniansandstonesatbothlocalitiesfallsentirelyinthecratonicinteriorandclosetotherecycledorogenfield (Figure 9).

AspointedoutbyDickinsonet al.(1983),sandstonesplotting in the cratonic field are mature sandstones derived fromrelativelylow-lyinggranitoidandgneissicsources,supplementedbyrecycledsandsfromassociatedplatformorpassivemarginbasins.However,processofdiagenesismaychangetheoriginalcompositionoftherocks,whichinturnaffecttheresultsofQ-F-Lplot(McBride,1985).Hence,suchprovenancedeterminationhastobeconsideredwithcaution.

GeochemistryTraceelementsaregenerallythoughttobequanti-

tativelytransportedintoclasticsedimentaryrocksafter

Figure6.Multi-elementnormalizeddiagramsforsandstonesofIlanqarehFormationnormalizedagainstaverageuppercontinentalcrust(TaylorandMcLennan,1985).


Qp >3 Crys units per grain> %25 of total

polycrystalline quartz

>%75 of totalpolycrystalline quartz

Qm unQm non

Slates &schistes

Mid and upper rank GNEISSESLowrank

GRANITES

Qp >3 Crys units per grain> %25 of total

polycrystalline quartz

>%75 of totalpolycrystalline quartz

Qm unQm non

Slates &schistes

Mid and upper rankGNEISSES

Lowrank

GRANITES

Qp 2–3 Crystal units per grain Qp 2–3 Crystal units per grain

weathering, and thus, they may reflect the signature of parent materialsandtheseelementscanbeusedinsedimentaryrockstodeterminetheirprovenanceandtectonicsetting(e.g.,McLennanet al.,1993;Bahlburg,1998;BurnettandQuirk,2001;ZimmermannandBahlburg,2003;Cingolaniet al.,2003;Liet al.,2005).

ThestronglynegativeSr-anomaly,whichissuggestingtheolderrecycledenvironments/passivemarginsetting,is common inallof the sandstone samplesat IlanluandIlanqarehsections(Figure6).SmallpositiveHf-Zr

anomalies at both sections suggest a slight influence of maturesedimentarydetritus(zircon,rutile)ofapassivecontinentalmargin(e.g.,MaderandNeubauer,2004).Furthermore,weusedthetrianglediagrams(La–Th–ScandTh–Sc–Zr/10andTh–Co–Zr/10)anddiscriminationdiagramofLa/ScversusTi/Zr(BhatiaandCrook,1986),tounderstandthetectonicsettingofstudiedsamplesbasedontheseplots.MostoftheIlanqarehsandstonesatbothsectionsclusterwithinorclosetothepassivecontinentalmargin field (Figure 10); therefore, they may have been

Figure7.Varietalquartzdiamondplotcurrentlyusedtodiscriminatesandssourcedbydifferenttypesofcrystallinerocks,onthebasisoftheextinctionpatternandpolycrystallinityofquartzgrains.Qmnon:low-undulositymonocrystallinequartzgrains;Qmun=high-undulositymonocrystallinequartzgrains; Qp2–3 = coarse-grained polycrystalline quartz grains; Qp > 3 = fi ne-grained polycrystalline quartz grains. Upper Devonian sandstones are com-pared with granites provenance fields after Tortosa et al.(1991).SymbolsasFigure5.

Elementalratio

Uppercontinental crust2

Range of sedimentfrom mafic sources1

Range of sedimentfrom felsic sources1

Range of sandstonesfrom Ilanqareh section

n = 10

Range of sandstonesfrom Ilanlu section

n = 12

La/Sc 2.21 0.43–0.86 2.50–16.3 2.3–6.7 6.2-15Th/Sc 0.79 0.05–0.22 0.84–20.5 0.7–1.8 1.7–3.7La/Co 1.76 0.14–0.38 1.80–13.8 7.1–14.9 4.1–44.7Th/Co 0.63 0.04–1.40 0.67–19.4 2–5.8 1.5–6.7Cr/Th 7.76 25–500 4.00–15.0 5.8–17.7 21.4–145.7

Table5.RangeofelementalratiosfromUpperDevoniansandstonesoftheIlanqarehFormationatIlanluandIlanqarehsectionscomparedtoelementalratios in sedimens derived from felsic rocks, mafic rocks and in the Upper Continental Crust.

1Cullers(2000);CullersandPodkovyrov(2000);Cullerset al.(1988).2McLennan(2001);TaylorandMcLennan(1985).


derivedfromsuchtectonicsetting,althoughsomesamplesplotincontinentalislandarc.Thisinterpretationmustbe made cautiously, because specific tectonic settings do notnecessarilyproducerockswithuniquegeochemicalsignatures(Bahlburg,1998).

Probebale source rocks (regional perspective)

ApaleogeographicmapoftheLateOrdoviciantoLateDevonianofnorthernArabiasuggeststhatNorthAfricaandArabiaformedabroadstablecontinentalshelfonthenorthernmarginoftheGondwanasupercontinent(Beydoun,1991;Al-JubouryandAL-Hadidy,2009)borderingthePaleo-TethysOcean(Figure11).

StudiesoftheLateOrdoviciantoLateDevonianrocksinthenorthofArabianplateshowthattheyweredepositedineitherterrestrialorshallowmarineenvironments(Al-HarbiandKhan,2008)(Figure11).

Typicalshallow-marinedepositsarerecordedinsouthernTurkey(CaterandTunbridge,1992),northernSyria(Bestet al.,1993),northwestIran(Stocklinet al.,1964)andnorthernIraq(Wolfard,1981).Shallow-marinedepositsshowthattheseareashavebeenlocatedthesouth-ernmarginalshelfoftheLateOrdoviciantoLateDevonianPaleo-TethysOcean.Inaddition,mostofthesestudiesshowthatthesiliciclasticdepositsprogradedfromsouth(wheretheArabo-NubianShieldcropsoutatthepresenttime)tonorth,towardsthenorthernbordersofNorthAfricaandArabia(Figure11).Forexample,DevonianJaufsandstones(ofpassivemargintectonicsetting)ofSaudiArabiaarealsoreportedtobedepositedonalow-lyinglandmassformingthestablecontinentalmarginoftheArabian-NubianShield,flanking the southern margin of the Paleo-Tethys Ocean (Al-Ramadanet al.,2004).

Asstatedabove,Stumpet al.(1995)indicatedthattheLateDevoniantoEarlyCarboniferoussedimentsarenotuniformlydistributedacrosstheArabianPeninsuladuetoupliftanderosionassociatedwiththeHercynianOrogenyduringtheendofDevoniantoCarboniferous.ThistectoniceventisinterpretedtobethecrustalresponsetoregionalcompressioncausedbytheinitiationofsubductionofPaleo-TethyanoceaniccrustnearthemarginofGondwanaalongTurkeyandIran(McGilliveryandHusseini,1992).

ConsideringpaleogeographicdataduringtheLateDevonianandpetrographicandgeochemicalstudies,thesourceofsandstonesfortheIlanqarehFormationmightbeassignedtoArabianshield,buttheeffectofrecyclingduetoHercyniantectoniceventonthesesandstonesmightbeconsidered.Suchprovenanceinterpretationhastobeconsideredwithcautionbecausetheroleofsedimentaryenvironmentanddiagenesis.

CONCLUSIONS

TheprovenanceoftheUpperDevoniansandstonesofIlanqarehFormationatIlanluandIlanqarehsectionsinnorthwesternIranhasbeenassessedusingintegratedpetrographicandgeochemical(trace-elements)studies.Theresultsaregenerallyinagreement.Petrographically,mostofthesesandstonesareQuartzarenitesexcepttwosamplesfromIlanlusection.Thepetrographic(frameworkminer-alogyandquartztypes)andgeochemicalcharacteristicssuggestplutonicigneousrocksasmajorparentrocksforthemandareaffectedbyrecycling.RecyclingsourcesforthesesandstonescanberelatedtotheHercynianorogenyinNWIran.

Thisapproachhas revealed that the sandstonesof IlanqarehFormationwereprimarilyderived from

Zr/Sc

Th/S

c

0.1 1 10 100 10000.01

0.10

1.00

10.00

UCC

PHG Zirconaddition

Sedment recyclingFEL

AND

Magmaticevolution BAS

0 1 2 3 4 5 876 1211109 151413 16Hf (ppm)

La/T

h

012345

876

1110

9

felsic island arc source

mixed felsic and mafic source

andesitic island arc sourcea) b)

increasing older sediment component

passive marginsource

Figura8.a)SourcerockHf–La/Th—discriminationdiagramforthediscussionoftheclasticsedimentsandtheircompositions(FloydandLeveridge,1987)forUpperDevoniansandstonesfromIlanqarehFormationatIlanluandIlanqarehsections.SymbolsasFigure5.b)PlotofTh/ScversusZr/ScofUpper Devonian sandstones from Ilanqareh Formation (modified after McLennan et al.,1993).TheUpperDevoniansandstonesareenrichedinzircon,duetosedimentarysortingandrecycling.Legend:PHG=Phanerozoicgranite;FEL=felsicvolcanicrock;AND=andesite;BAS=basalt(igneousrockaveragesfromCondie,1993);UCC=UpperContinentalCrust(compositionafterTaylorandMcLennan,1985).Thelowerandintermediatearrows(compositional trend) define the trend expected in first-cycle sediments due to magmatic evolution from mafic to felsic; upper arrow shows the trend producedbytheadditionofzirconduringsedimentarysortingandrecycling.SymbolsasFigure5.


AB

C

D

Th

Co Zr/10

Th

Sc Zr/10A

B

C

D

La

Sc

A

B

D

Th

C

La/Sc

Ti/Z

r

2 4 6 8 10 12

10

20

30

40

50

60

70

80

A

B CD

F Lt

Cratoninterior

QuartzoserecycledTransitional

continental

Basementuplift

Transitionalarc

Mixed Transitionalrecycled

Qm

Dissectedarc

F L

Basementuplift

Transitionalcontinental

Cratoninterior

Recycledorogen

Transitionalarc Undissected

arc

Dissected arc

Qt

F

Qm

Lt

Qm

Qt Qt

F L

Lithicrecycled

Undissectedarc

Figure10.TraceelementcompositionofthesandstonesfromIlanqarehFormationonthetriangleandbivariatetectonicsettingdiscrimi-nationdiagramsofBhatiaandCrook(1986)..Seetextfordetails.Legend:A=oceanicislandarc;B=continentalislandarc;C=activecontinentalmargin;D=passivecontinentalmargin.SymbolsasFigure5.

Figure9.QtFLandQmFLtternarydiagramsfortheUpperDevoniansandstonesfromIlanqarehFormationbasedonDickinsonet al.(1983).SymbolsasFigure5.


AFRICAN PLATE ARABIAN PLATE IRANIAN PLATE

Passive marginBroad clastic shelfClastic supplyA B

Schematic Plate Cross-section

OCEANIC CRUST

UPPER MANTLE

PALAEO - TETHYS OCEAN

INDIA-PAKISTANPLATE

Tibet

FarahBlock

AfghanBlock

PASSIVE MARGIN

Alborz

NorthwestIran

Sanandaj-Sirjan ZoneTurkey

ContinentalClastic

ARABIAN PLATE

Deltaic andShallow marine clastic

LATE ORDOVICIAN TO LATE DEVONIAN

PALAEO - TETHYS OCEAN

445-364 Ma

AFRICAN PLATE

A

B

40° S 20° S

GONDWANA

LutBlock

CentralIran

sourcestypicalofacratonicinterior.Also,theprovenancecharacteristicsbasedonpetrographicandgeochemicalmethods suggest that the Ilanqareh sandstonesweredepositedonapassivemarginthatreceivedlargeamountsofmaturedetritusfromthesourceareas.Moreover,thedataareconsistentwithalongdistancetransport,possiblyovertheArabianshieldthatmighthavesuppliedsandstothedepositionalbasinalongthepassivemarginalcoastofthePaleo-Tethys.

ACKNOWLEDGEMENTS

WethankDr.S.P.Vermaforhishelpfuladviceandconstructivesuggestionsduringthereviewofthemanu-script. This article is benefited from thoughtful reviews andconstructivecommentsofDrs.J.Armstrong-Altrin,K.PandarinathandA.Varga.

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Manuscriptreceived:May10,2010Correctedmanuscriptreceived:August8,2010Manuscriptaccepted:August12,2010

Provenance and tectonic setting of Upper Devonian sandstones from Ilanqareh Formation ... ·...

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