Tectonics North Pakistan Pogue 1992

8/3/2019 Tectonics North Pakistan Pogue 1992

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TECTONICS, VOL. 11, NO. 4, PAGES 871-883, AUGUST 1992LATE PALEOZOIC RIFTING INNORTItERN PAKISTANKevinR. Pogue, ,2Joseph . DiPietro, ,3 SaidRahimKhan, Scott . Hughes,John . Dilles, Robert .Lawrence 1

Abstract.Metasedimentaryocks xposedn theeasternPeshawar asinand he southern wat egionof northernPakistanrovide videnceor atePaleozoicontinentalifting.The onsetof extensionalectonicsn theEarlyCarboniferousis ndicated y northderived lastsn theJafarKandaoFormation roded rom hermallynduced pliftsof partsof theformerly assive argin f Gondwana.ift highlandsereeroded ntil heywere nundateduringheMiddleCarboniferous.enewed pliftaccompaniedheeruption fbasalticava flows during heEarly Permian.Uplift alongsouth ipping, ortheasttriking ormalaults uringheCarboniferousasaccompaniedy alkalinemagmatismrepresentedy theShewa-ShahbazgarhindWarsak orphyriesandKogasyenite. eochemistryf basalticlows nowamphibolites)nd ntrusionsssociatedithPermian plift ssimilar o the coevalPanjalvolcanics f northwesternndiaand ndicatesift zonemagmatism.ostriftinghermalsubsidenceed to thedepositionf UpperTriassicmarinecarbonateockswhichunconformablyverlie he iff basalts.A similar ectonic istory n centralAfghanistanuggestscontinuityetweenhe wo egions rior o theopening f theNeo-Tethys.INTRODUCTION

The Cenozoic ompressionaltructuresreated y thecollisionof India with Eurasiahave been he focusof manygeologicalnvestigationsf theHimalaya. y comparison,heearlier ectonic istory f theHimalayanegion asbeenpoorly ocumented.hedetailedtratigraphyndpaleontologyof sedimentaryndmetasedimentaryocks nd adiometricatesandgeochemicalnalyses f igneousocks hatarenecessaryto decipherhisearlier istory reonlynowbecomingavailable.One areawhere hesupply f new nformationasbeen speciallyich s theHimalaya f northern akistan,where relatively omplete aleozoicndearlyMesozoicstratigraphyasbeendescribedPogue t al., 1992].Theexcellent xposures,ccessibility,ndpaleontologicalontrolof thePakistan ection rovide n unparallelediewof pre-

!'DepartmenifGeosciences,regontateniversity,Corvallis.2 Nowat Departmentf Geology, hitman ollege,WallaWalla, Washington.3 Nowat Geology epartment,niversity f SouthernIndiana, Evansville.4 Geologicalurvey f Pakistan,slamabad,akistan.5 Departmentf Geology,daho tate niversity,ocatello.Copyright1992 by the AmericanGeophysical nion.Papernumber 2TC00335.0278-7407/92/92TC-00335 $10.00

Himalayansedimentationn the northernmarginofGondwana. his stratigraphicnformation,whencombinedwith new geochemical nalyses nd adiometric ateson theigneousocksof theregion,permits herecognition f a majorphaseof late Paleozoic ifting.PREVIOUS INVESTIGATIONS

In Pakistan,ndianplateexposures f middlePaleozoicmetasedimentsre confined o theregionnorthof theKhairabad hrustand southof the Main Mantle thrust MMT),the suture between the Indian continent and the Kohistan islandarc (Figure 1). These ockscrop out extensivelyn themountains urroundinghe eastern eshawar asinand n theHimalayan oothillsof Swatdistrict o the north Figure2).The metamorphic rade anges rom owergreenschistacies nthe southern eshawar asin o middleamphibolite acies ncentral Swat.

The initial reconnaissancetudyof theareacoverednFigure2, performed y Martin et al. [1962], outlined hestratigraphyndmade mportant bservationsoncerningintrusive elationships. owever, hehigher-grademetamorphismndmoreextensive eformationargelyerasedthe macrofossilecordof the northern ocks, hereby imitingMartin et al. [ 1962] to a description f the rock units.The firstfirm paleontological ontrol n the Peshawar asinwasprovided y Stauffer 1968],whodescribed Devonianeef nthe southern asinand documentedhepresence f poorlypreserved ossils n the more northern ocalities.Talent andMawson 1979] added o thepa!eontologicalatasetasdidPogueandHussain 1986],whorevised hestratigraphyfStauffer 1968] andextendedts application s ar northasSwabi.Bulk samples f carbonateocks rom henorthernPeshawar asinand southern wat yieldedconodonts, nablingPogueet al. [ 1992] to revise he stratigraphyf Martin et al.[ 1962] andconstructocalandregional orrelations.ogue tal. [1992] describedeveral onodont-bearingorizons riticalto the presentstudy rom outcrops earRustam,wherePeshawar asinstratigraphy anbe traced round he westernend of the Ambela ntrusive omplex Figure2). Conodontsrecoveredrom the mostnortherly f theseoutcrops10 kmNNW of Rustam)are strained y ductile low andhaveaconodont oloralterationndexof 7 indicating ost ocktemperaturesf approximately 00C [Pogue t al., 1992].The first studyof the gneousocksof the areaby Coulson[1936a], ncluded hemical nalyses n "soda-granite"rom theKhyberareanearWarsakandon "porphyries"romnearShahbazgarhiFigure3). Coulson 1936a]concludedhat herocks rom the wo areasweregeochemicallyery similarandpossibly onsanguineous.n a separate tudy,Coulson[ 1936b,p. 340, 1937], noted hepresence f numerous"epidiorite" ikesand sills hatwere "similar ndpossibly fPanjalTrap age" ntrudingmarblenorthof Swabi Figure2).The metamorphismf marblemidwaybetween wabiandRustamwasattributedo dikesof "epidioritic ndamphibolitic" ock. Coulson 1937,p. 228] also nvoked heproximityof the "Bunergranite," escribed sa "biotite-granitewith 74.30% silica,"as a contributingactor n themetamorphism.The igneousocksof Swatand heeastern eshawar asinwere e-examined y Martin et al. [1962]whonamed nddescribedhe Swat granites nd granitegneisses,he AmbelaGranite Bunergraniteof Coulson 1937]), and he Shewa


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872 Pogue t al.: LatePaleozoic ifling n Northern akistanS. R.

PakistanIndia

Jalalabad basin ;shawlar

IslamabadAttock-CheratPotwarRangePlateau

0 5O 100i I IkilometersI70 E 72 E 74 E

N

Fig. 1. Locationmapof thePeshawarasin ndvicinityshowing elected ajor aults.B is Besham; Pis KhyberPass.Smallopencircles re geochemicalampleocalities. ocations f faultsare fromGansser 1981], YeatsandLawrence 1984],Lawrence t al., [1989], andBaig [1990].

36 N

34 N

32 N

Formation.Martin et al. [1962] also irst noted he presence,in Swat, of a stratigraphicallyersistent mphibolite orizonthat was nterpreted y King [1964] as a metamorphosedill.The Ambela Graniteof Martin et al. [1962] was he subject fa petrographicnalysis y Siddiqui 1965, 1967]whorecognized varietyof intrusiveocks, ncluding yenite ndtheNaranjiKandaoCarbonatite.heBabajiSyenite, ogaSyenite, ndChingalaiGranodiorite neisswerenamed sconstituents f the "AmbelaGraniticComplex" n a furtherstudyby Siddiqui t al. [1968]which ncluded etrologic ndgeochemicalnalyses f feldspathoidalyenitesndassociatedrocks.The similaritybetween he ntrusiveocksat WarsakandShewa-Shahbazgarhiirst notedby Coulson 1936a,b],togetherwith a new ocalityof similar"alkalinemicrogranites"ear heTarbeladamsiteFigure ), ledKempeandJan 1970] o propose n extensive lkaline gneousprovince ncompassinghenorthem eshawar asin. heysuggestedhat he alkaline ockswere ntrudedn two stagesduring he Tertiary.On thebasisof petrographicndgeochemicalnalyses f alkaline ntmsivesromWarsak ndShewa-Shahbazgarhiompared ith heKogasyenite nalyzedby Si. diquiet al. [ 1968],Kempe 1973,p. 399] concluded,"therecanbe little doubt hat the Warsak-Shewa roups f

granite nd herocks t Kogaarepetrogeneticallyelated."K/At dates, nterpreted sageof emplacement, erealsoreportedor theWarsakalkalinegranite 41 Ma) and heKoganephaline yenite 50 Ma) [Kempe,1973].The mafic ocksassociated ith theporphyriticmicrogranitest Warsakwerethe subject f a petrographicndgeochemicalnvestigationyKempe [1978, p. M35], who concludedhatamphiboliticmetagabbrondmetadiabasereviouslynterpreteds ntrusive[Ahmadet al., 1969; Kempe, 1973] weremetamorphosedmarie uffs or lava flows nterlayered ith Paleozoicmetasediments.t wassuggestedhat heassociatedorphyriticmicrogranites ightalsohavean extrusive riginandrepresent metamorphosedighlyporphyritic lkaline hyoliticlavas."

A detailed tudyby Janet al. [ 1981a]of thegeology ndpetrographyf the "alkaline omplex" earTarbela amrevealed widevarietyof rocks ncluding iabase,lbitite,sodicgranite,andcarbonatite ithin a fault zone nPrecambrianmetasediments.anet al. [1981a,p. 3] cited he"close etrographicesemblance"f theTarbelaalkalinegraniteswith thoseof Shewa-ShahbazgarhindWarsakasevidence or including hese ocks n a "LateCretaceous-EarlyTertiaryalkaline gneous rovince". hepetrographyndgeochemistry f all igneous ocks nterpreted spart of a


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-F-F

-F 4-

-F-F

-F-F

4-

-FMain Mantle thrust zone

3445' N I+1Kohistan island arc terrane

I Ipost-riffmetasedimentsPermian?and younger

Daggar:)DP-7-10F

Rustam

KP-121 ShewaShahbazgarhieshawarMardan

34o15 ' N

Karapagreenschist ndamphiboliteequivalent

Shewa porphyry

Ambela ntrusive omplexK= Koga syenite

pre- and syn-riftPaleozoic metasediments

Swat gneiss

Basin .-,N ?'

I km5 10 5 0 Swabi- "L--':.-'ij.:0 5 10 15 o "b' faulti72 E 7230' EI I

Precambrianmetasediments

Fig.2. Tectonic ap f thenortheasterneshawarasin nd outhentral wat. mall pen irclesregeochemical ample ocalities.

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:::::::::::::::::::::::::::::::::::::::::::::::::::::/ / / / / q/ ,,_ / / I:::::::::::::::::::::::::::::::: .::::::::::::::::::::::::::::::::::::::::::::.:. % % % % %..:::;:i:::i:i:i:i:i:'":' .:: ...:.:.::::::-:.:'.'....... '.:-::::::::: ::::::::: / / / / /I t r z ::::::::.:.:.:.....:.:.::. .:::: .:::::, ,, ,, ,, ,, ,,.:::::::::::::::-: : :::: ::::::::::::.... ,,, ,,, ,,, ,,,"::::ii:i:!:.i.!.!.!.i.i.i.i.i.;.i.ii!i!i!.iiiiii:i!!!i!;i!;i:i;i!::' ...:..iii::::" :11. '.! :'/",/",/",/",", z::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::'"" :::::::':': "'/"'/"'Mansehra, ================ii!!!!!!!i!i!i!!!i.!!i!!iii!i!i!i:;!!i!!ii!i::ii!ii?;;ii!!i;Shahbaz .::::.::::::::."'"'"':'"'::..:.......j:'..,.:__ ........ ......--:Cad3on,erousoq3h,; ;) _ . % v,,., -'"T?:::,. AmbelaGraniticCom

34o00N 72 0'E I'.',' ' granitend raniteneissFig. 3. Major gneousntrusionsn thevicinity f thePeshawarasin. is carbonatite;is Tarbelaintrusions.mall pen ircles regeochemicalampleocalities.


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874 Pogue t aI.:LatePaleozoic ifting n Northern akistan

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Pogue t al.:LatePaleozoic ifting n Northern akistan 875Table b. DescriptionsndPetrology f AmphibolitesndDiabase ikesFrom heEastern eshawarBasin,Swat, and the BeshamArea, NorthernPakistan

Sample Description PetrologyDP-2-3B foliated nd ineated pidote mphibolite Hb + Ep + Qtz+ Olig+ Sph+ Aphorizon n Marghazar ormationfoliated and lineatedepidoteamphibolitehorizon n Marghazar ormationvesiculardiabase ill intrudingOrdovicianMisri BandaQuartzitediabase ikecuttingAmbelagranite

DP-7-10F

KP-12JD-10JD-12JD-120JD-121JD-122

JD-125

foliatedand lineatedepidoteamphibolitehorizonn Marghazar ormationfoliatedand lineareal pidoteamphibolitehorizon n Marghazar ormationfoliated epidote amphibolite sill infeldspathicuartziteweakly foliated garnetamphibolitewithinGar-Musc chist,Marghazar ormation(?)foliated and !ineatedgarnet amphibolitewithinquartzite,eldspathicuartzite, ndmarbleof Marghazar ormation(?)fo!iated and lineareal mphibolitewithinGar-Musc-Biot schist of MarghazarFormation(?)

ActinoliticHbl + Qtz + Alb(?) + Ep +Sph + ApHbl + Chl + Alb + Ep + Calc +Augire+ Mag + Qtz + Sph + ApHbl + Alb(?) + Ep + Clz + Sph+ Ksp+ Hem + Ap(detailed etrology navailable)(detailed etrology navailable)Hbl + Qtz + Olig + Biot + Ep + Clz +Sph + PyHbl + Olig(?) + Gar + Qtz + Sph +

IlmHbl + Olig(?) + Qtz + Clz + Gar +Sph + ApHbl + Qtz + Andesine I!m(?) + Sph+ Clz + Ap

Abbreviationsreactino!iteAct),albite Alb),apatiteAp),biotiteBiot), laciteCalc), hloriteChl),clinozoisiteClz),epidoteEp),garnetGar),hematiteHem), omblendeHbl), lmeniteIlm),K-feldspar(Ksp),magnetiteMag),muscoviteMusc), ligoclaseOlig), yritePy),quartzQtz), nd pheneSph).

0.70.60.50.40.30.20.1

AA A

I ' I ' I I I0 1 2 3 4 5

wt.% TiO2 amphibolites nd diabasedikes - this studyx PanjalolcanicsfZanskarHoneggerand others 1982)

AmphibolitesfHazara-KashmirsyntaxisPapritzand Rey (1989)Fig. 4. Covariafion f P205 andTiO2 illustratinghe angefromsubalkaliclow P andTi) to alkaliccompositionshighP andTi) of mafic units rom the Peshawar asin,Swat,Hazara-Kashmir yntaxis, ndLadakh.

"Peshawarlain gneous rovince" assummarizedy KempeandJan 1980] andagainby Kempe 1983]. n addition o thealkaline ocks rom heWarsak,Shewa-Shahbazgarhi,mbela,andTarbelaoutcrops,arbonatiterom heKhyberarea Janetal., 198 b] andgranite ndcarbonatitexposed earMalakand[Chaudhry t al., 1974, 1976;Ashraf ndChaudhry, 977]werecitedaspossibleurthermanifestationsf thealkalineigneous rovince.The common ssociation f alkalineigneousockswith extensionalectonicsedKempeandJan[ 1980] to propose rift origin or theprovince. hey furtherconcluded that the Peshawar basin is the eroded remnant of aTertiary ift valley.KempeandJan 1980,p. 76] invoked"reboundelief ension" r "compressioneleaseollowing heinitial plate collision"as a tectonic nvironment.The irstarge-scalepplicationf39Ar/40Aratingtechniqueso themetamorphicnd gneousocksof northernPakistan y MaluskiandMatte 1984]provided newsetofradiometric geson the ntrusionsf thePeshawarlainalkaline gneous rovince. eterminationsn amphiboletwosamples) ndbiotite onesample) rom heWarsak alkalinegranitegneiss"yielded gesof 43.5, 40, and42 Ma,respectively. heseages,as well as he 41 Ma K/Ar dateofKempe 1973],were nterpretedsmetamorphicather hanemplacementges.An ageof 23 Ma on muscoviterom heMalakandGranitewasviewed sanemplacementge,sincethe ocks ampled howed oeffects f Himalayanmetamorphismnd ntrusive ontacts rosscutoliations fHimalayan Tertiary)age.Syenitic neiss f theAmbelaGraniticComplex ielded 47.5 Ma agewhichwasinterpreted,longwith the50 Ma K/Ar dateof Kempe 1973],


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876 Pogue t al.:LatePaleozoic ifting n Northern akistanas "the minimumage of the climax of the metamorphism"[MaluskindMatte, 984, . 12].The 9Ar/40Arges fMaluski and Matte [ 1984], togetherwith K/Ar andRb/Sr ageslaterpublished y Le Baset al. [ 1987]plus wo additionalK/Ar dates, ed Kempe 1986] to a reassessmentf theemplacementhronology f thePeshawar lainalkalineigneous rovince.Kempe 1986]acceptedheMaluskiandMatte1984]nterpretationf he 9Ar/40Argessrepresentingmetamorphicvent;however, e speculatedhatemplacementmmediately recededhemetamorphism.The Rb/Sr agesof 297 _+ and 315 _+15 Ma on the KogaSyeniteby Le Baset al. [ 1987] anda K/Ar age rom theTarbela ntrusivecomplexof 350 _+15 Ma [Kempe, 1986]forcedKempe 1986] to abandonheconcept f coevalmagmatismelated o a single iftingevent or thePeshawarplain alkaline gneous rovince nd o suggestepetition falkalinemagmatism ververy ongperiodsnstead. ertiaryrifting wasretainedby Kempe [1986] as he tectonicenvironment of the alkaline intrusions at Warsak and for thebulk of the Ambela ntrusive omplex.On the basisof K/Arageson biotite,Le Bas et al. [1987] nterpretedsolatedcarbonatitesxposed 0 km NW and60 km northof Peshawar(Figure3) to havebeen ntruded long hrust aultsat 31 + 2Ma and ater deformed y the hrusts t 24 _+ Ma. WhileKempe [1986] consideredhese arbonatiteso representhefinal stages f rift-relatedmagmatism,he association f theintrusionswith faults nterpreted s thrusts rompted e Basetal. [1987] to reject he Tertiaryrifting hypothesis.Rafiq's [1987] investigation f the AmbelaGraniticComplexyielded he mostcomprehensiveeochemicalndpetrological atasetyet obtained rom these ocks.On thebasisof their geochemical imilaritieswith granites f the eastAfrican ift, Rafiq [ 1987] suggestedwithin-plateift settingfor the bulk of the intrusions near Ambela.MAGMATISM

Due to the dearthof paleontologicalontrol, hemetasedimentaryountry ockhas,until ecently, rovidedewconstraints n the timing of Peshawar asinmagmatism. hissituationwas argely emedied y conodontonation f themetasedimentsf the eastern eshawar asinby Pogue t al.[1992]. Conodonts ecovered rom metasediments orth ofRustambracketedhe ageof the Swatamphibolite orizonfirst mappedby Martin et al. [1962]. Westphalian conodontsfromphyllitic imestones0 m below he amphibolitendCarnian conodonts from marbles 500 m above restrict theemplacement f the amphibolite rotolith o MiddleCarboniferouso Late Triassic, time span hatcoincides iththe ange f ages educedor thePanjal olcanicsf theKashmirbasin Gansser, 964].The Panjalvolcanics onsistof basaltic nd elsicpyroclasticsthe "agglomeraticlates")overlainby up to 2500 m of basaltic ocks thePanjal"traps")whichwere nterpreted y Bhatet al. [1981],on thebasis ftheirgeochemistry,o havebeenerupted uring ontinentalrifting hatclimaxedn thePermian.Geochemicalnalysesfthe Swatamphibolite y Ahmad 1986]alsosuggestedprotolithof continental asalt.The amphibolite orizonwasmapped hroughout watby Lawrence t al. [1989]asanintrusionwithin he AlpuraiGroup.On thebasis f contactrelationshipsnd ts consistent ositionwithin hestratigraphicequence,heprotolith f the Swatamphibolitewasreinterpreted y DiPietro [1990] to be basalticlows atherthan he sill first proposed y King [1964].

An equally mportant iscoverymadeduring ecentmapping n Swat [DiPietro, 1990] and he Peshawar asin[Pogue t al., 1992] is that he diabase ikesandsills irstnotedby Coulson 1937] are restrictedo rocksstratigraphicallynderlyinghe amphibolite orizon. heseintrusions re widespreadn the pre-Permian ection etweenthe Main Mantle and Khairabad hrustsbut have no/beenobservedn Mesozoicor younger ocks.The relationshipssuggesthat he diabasewas ntrudedn oneepisode fPermianmagmatism, nd urtherobservationsf dikesterminatingn the Swat amphibolite orizon DiPietro,1990]supporthe notion hat he ntrusions erved s eedersorbasalticvolcanism.An investigation f similarmaficintrusions nd amphibolite xposedn theHazara-Kashmirsyntaxismidway between he Peshawar ndKashmirbasins yPapritzandRey [1989]revealedhat he ntrusionsndamphiboliteesemble neanother eochemicallyndaregeochemically imilar o thePanjalvolcanics. apritzandRey[1989] alsoobservedhatmafic ntrusionsn the syntaxisregionwere absentn rocksyounger hana stratigraphicallypersistent mphibolite orizon.Mafic dikes ntrudingMansehraranitenHazaraielded9Ar/40Arlateauatesf284 + 4 Ma and262 + 1 Ma confirming Permianage orbasalticmagmatismn this area [Baig, 1990].The 262 + 1 Madate s especiallynoteworthy s t falls within a 10 Ma"window" or Panjal volcanism sbracketed y fossils n theZanskar reaof northernndia (Figure1)[Gaetani t al., 1990].The geochemistry f Swat amphibolites, mphibolitesfrom the Hazara-Kashmir yntaxis, ndPanjalvolcanicssupportsheirderivationromcoevalor at east quivalentprotoliths roduced y rift zonemagmatism. he majorelement hemistry, btained y wavelength ispersive rayfluorescenceXRF) analysis, f eightamphibolitesnd wodiabases asprovided y theU.S. Geological urvey tDenver,Colorado Table 1). Traceelement nalysesTable 1)wereobtained y instrumentaleutron ctivation nalysis(INAA) at OregonStateUniversity.Covariationsn P205 andTiO2 (Figure4) exhibit6X rangesn bothelementswithoutsignificantdistinction etween he three ypes.Overall elemental ariationsn Swatamphibolites re moresuitable or assessmentf the tectonomagmaticegime.Thesearedepicted s multielementspidergram)lots Figures and6), shownnormalized o primordialmantlevalues TaylorandMcClennan,1985]. A widerangeexists mong ncompatibleelementse.g. Th = 0.4-17 ppm,La = 4.4-72 ppm,andBa =43-640 ppm), whichcoincides ith thevariation bservednmajorelement nd ransitionmetalabundances.he overalluniformityamongpattern hapes, specially mong he essmobile elements Ta to Yb), reflectsa similarmagmaticorigin.An exception o thisuniformity s displayed y acontrastn Th/Ta ratios,which orms he basis or separatingthe compositionsnto two types.RelativelyhighTh/Ta andespeciallyepleted a (andNb) abundancesre ypical fvolcanic ocksderivedby subductiononeprocessese.g.,Pearce,1982]. However,suchcompositionslsoexhibitdepleted andTi values, nd heirpatternsypically ieldnegative nomalies f Ta (Nb), P, andTi. RelativelyhighThandU values n the Swatunitsare ikely derived rom crustalcontaminationy Th-richgranitic ocksor possible lterationduring he magmatic tage. his s also eflectedn the mobileelementsK to Th in all patterns lthough he observedvariation s more ikely related o metamorphismnd heensuing ffectsof water-induced obility Pearce, 982].


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Pogueet al.: Late PaleozoicRifting n NorthernPakistan 877

200SwatmphibolitesDiabasesO0_ 10o

I [] KP-21 JD-,101 I JD-125i i i i i i i i i i i iK Rb BaTh Ta La CeSr P Zr HfSmTi Tb Yb

Fig. 5. Multielementplotsof SwatandPeshawar asinamphibolites nddiabases aving ow Th/Ta ratios,shownnormalized o EarthmantleabundancesTaylorandMcClennan, 1985].

Swat/Peshawarasincompositionsielding ow Th/Ta ratios(Figure5) are moreappropriateor defining ourceegions swell as the tectonomagmaticegime.The nearly lat patternand ow alkali element bundancesf JD-125 suggestderivation rom nonenriched r depletedMORB-like) mantle,possibly btained y largerdegrees f melting n a riftenvironment o produce tholeiiticcomponent f the series.By contrast, he high Ti diabase, P-2, yieldsa pattem whichcompares ell with KP-12) probably erived rom owerdegrees f meltingand ypifying healkalicmembers f thesequence. lthoughsomemobility s expectedn alkalielementsK andRb), these elations re supported y theP205 versus iO2 relations xemplified y subalkalicJD-125andJD-122) andalkalic KP-2 andKP-12) signatures.hepresence f thoeliiticmembershatdisplay omewhatprimitive,normalMORB-like, pattems f traceelementsJD-122 andJD-125, Figure5) arguesor an extensionalystemthatproducedmagmashateruptedwithout ignificantrystalfractionation.

If the maficdikesandamphibolitesf thePeshawar asinand Swat are the product f Permian ifting,as suggestedytheir geochemistrysoutlined bove, henalkaline gneousrocksof the Peshawar asin ntruded y thesedikesarepre-Permian.The alkalineporphyry f Shewa-Shahbazgarhi2OO100

Swat Amphibolites & Diabases

A DP-2-3BJD-12DP-7-1 [] JD-121O KP-12 [] JD-120, , ......b BaT Ta La r P Zr Hf SmTi Tb YbFig. 6. Multielementplotsof SwatandPeshawar asinamphibolites nddiabases avinghighTh/Ta ratios,shownnormalizedo EarthmantleabundancesTaylorandMcClennan, 1985].

contains nusuallyargediabase ikesand ntrudes pperDevonian-Lower arboniferous etasedimentslowerpartofthe JafarKandaoFormationofPogueet al., [1992]) 5 kmsoutheast f Rustam.A Carboniferousmplacementge stherefore uggestedor the Shewa-Shahbazgarhiocks. Thischronologys supported y Carboniferousb/Sr ageson theKoga Syenite Le Baset al., 1987] whichshares closepetrogeneticelationship ith theShewa-Shahbazgarhiporphyry Kempe, 1973].The interpretationf Kempe 1978],that he porphyriticmicrogranitesnd homblende chists tWarsakare metamorphosedolcanicsnterlayered ithPaleozoicmetasediments,upports oth heemplacementchronology educedo theeastand heclose elationshipbetween healkalineporphyry ndmafic gneousocks.Thehornblende chists xposed t Warsakarealmost ertainly heequivalentof the Swat amphibolite.A similarassociation fmetamorphosedorphyry ndmaficvolcanics asbeendescribedrom he Kashmir asin,wheresheared orphyriticrhyolite, ithologicallydentical o cataclasticorphyryromthe Shewa-Shahbazgarhirea,underlieshebasalt lowsof thePanjalvolcanics Davies,1956].The relationshipsetweenhealkaline gneousocksand hemetasedimentaryountryockoutlined bovesupportMaluskiandMattds [1984]interpretationf Eocene adiometric ges s epresentativefmetamorphismather hanemplacement. lkalinemagmatismin the Peshawar basin is thus viewed as a Carboniferousevent,whichprecededhePermian mplacementf diabasentrusionsanderuptionof basalt lows.The presence f numerous iabase ikes ndicateshatmuchof the AmbelaGraniticComplexwasemplaced rior to thePermian.Rafiq [1987] concludedhat heentirecomplexwasemplaced uring hemiddle o latePaleozoic; isconclusionwasbasedon theLate Carboniferous b-Sragedetermined yLe Bas et al. [1987] for the Koga Syenite,whichwasinterpretedo have ntruded uring he waningphases fAmbelamagmatism. owever, he eastern alf of the AmbelaComplex s largelymegacrystic ranite hatstronglyresembleshe MansehraGraniteof Hazara,aswell aspartsofthe Swat granite o the north.The eastern dgeof theAmbelamegacrystic ranite s separatedrom similarMansehraGraniteby less han 20 km across he gorgeof the ndusRiver (Figure3). In the walls of the gorge,basal ntrusive ontacts f boththe AmbelaandMansehra ranites reconcordant ithquartzite ndphylliteof the TanawalFormation uggestingthaterosion y the river hasbreached formerlycontinuoussheet-like ntrusion.An emplacementgeof Late Cambrianand/orEarly Ordovician or theMansehraGranite s based n a516 + 16 Ma Rb/Sr isochron [Le Fort et al., 1980], a 500 MaU/Pb zircondate R. ZartmanandP. Zeitler, personalcommunication,986) nd n39Ar/40Arate f493 1Ma[Baig, 1990]. A similarage or Ambelamegacrystic ranite sin agreementwith Rafiq's 1987] conclusionhat hese ocksconstitutehe oldestsuite n the complex.The SwatGraniteGneiss,exposed15 km northof the AmbelaGraniticComplex(Figures and3), wasconsideredy DiPietro 1990] o beanotherMansehra-correlativelutonbased n texturalsimilaritiesand intrusive elationships.The western alf of theAmbelacomplex onsistsrimarilyof syenite ndalkalinegranite Rafiq, 1987] hat ntrudemetasedimentaryountry ock as youngas Carboniferous.Most of these ocksare petrogeneticallyelated o theKogaSyenite Rafiq, 1987]. However,southof Daggar,part of theAmbela ntrudesmetasedimentaryocksof thebasalKashala


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878 Poguetal.'LatePaleozoiciftingn NorthernakistanFormation,whosemiddlehorizons aveyielded arlyLateTriassicconodontsPogue t al., 1992]. The granitic ocks nthisareaare tourmaline eating nddevoidof diabaseintrusions, uggesting correlationwith tourmaline ranitegneiss escribed y DiPietro 1990] as ntruding he Swatamphibolite 5 km northwest f Daggar.The presence f post-Permian,Carboniferous,ndprobableCambrianntmsivesindicate hat heAmbelaGraniticComplexwasamplacedduringat least hreedistinct pisodes f magmatism.The interpretationsf contact nd ntrusive elationshipsand adiometric gesdescribedbove ontradictheassociationof Pashawar asinmagmatismwith Himalayancollisionaltectonicsirstproposed y KempeandJan 1970].However,the absence f deformation nddiabase ikessupportheTertiary 23 Ma) agederived y MaluskiandMatte [1984] orthe Malakand Granite.STRATIGRAPHYEastern Pashawar Basin

Lithologies nd acies elations f latePrecambrian-Devonianmetasedimentsxposedn the eastern ashawarbasin ndicate epositionn a northward eepening,epicontinental,hallowmarineenvironmentFigure7). Late

Cambrian o Early Ordovician ectonism, oincidental ithintrusion f theMansehra nd elatedgranites, reatedhighlands orthof the depositionalasin rom whichCambrianstratawere eroded Pogue t al., 1992]. Shallowmarine sedimentation resumed in the Ordovician and continuedrelativelyuninterruptedntil near hecloseof theDevonian.An abruptchange rom carbonate-o clastic-dominatedsedimentation at the contact between the Nowshera and JafarKandao ormations eraldshedemise f passive picontinentalsedimentation. The basal 30 cm of the Jafar KandaoFormation, xposed km northof Swabi, s calcareoussandstoneontainingarbonateebbles erived rom heunderlying owshem ormation. imestonesrom heupperNowshera ormation m below hiscontact ieldedUpperDevonian Frasnian) onodonts.hecarbonateebble eds reoverlainby 50+ m of pebblyargilliteandconglomerateithclast ithologiesndicative f derivationrom hepre-NowsheraPaleozoic ection. imilar ithologies reexposed kmsoutheastf Rustam,wherea limestoneenswithinargilliteyieldeduppermost evonian lateFamennian)o LowerCarboniferousToumaisian) onodonts. 300+ m intervalofargilliteoverlying heconodont orizon ontains everalchannel-filling obble onglomeratesith well-roundedlasts,up to 40 cm in diameter, f quartzite ndgranitic ock.The

PeshawarBasin

Swat

Ambela ourmaline ranitediabase dikes and sills

Ambela lkaline ranite,syenite

Shewa-Shahbazgarhiorphyry

gramtegneissdiabase dikes and sills

Swat Granitic Gneiss

limestone/-- calcareousarblel dolomite argillaceous/chistose argillite/ sandy/hyllite quartzitic:l quartzite fossils conglomerate breakupnconformity metabasalt

highest l]'atigraphicnterval bservedo be intrudedAmbelamegacrystic ranite

Fig. 7. Correlation f generalized tratigraphicolumnsor Swat [DiPietro,1990] and he easternPashawar asin Pogue t al., 1992].Numbersn pm'enthesesiveapproximateormationhicknessesnmeters.


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Pogueet al.: Late PaleozoicRifting in NorthernPakistan 879

clast ithologiesndicate orthward erivation, ecause raniticrocksof a suitableprovenance re absent o the south.Lithologies f thegranitic lasts losely esemblendianplatePrecambrianranitic asement escribedy Baig [1990] n thegorgeof the ndusRiver 100 km to thenortheast. he upperonehalf of theJafarKandaoFormation isplays reathorizontal ariability.Pogueet al. [ 1992]recovered owerCarboniferousVisean) conodontsrom oneof severaldiscontinuousntervals f quartziticimestonehatareinterbeddedith hedominant rgillite ndquartzite,ndminorconglomerate. thin ntervalof argillaceousimestone 0 mbelow hecontactwith metamorphosedasalts f theKarapaGreenschistieldedMiddleCarboniferousWestphalian)conodontsPogue t al., 1992].The KarapaGreenschist, itha mineral ssemblagef chlorite-quartz-ilmenite-albite-sphene,hasa sharpcontactwith the uppermost rgillitebedof theJafarKandaoFormation.No relict low structuresr ointinghavebeenobservedhatwould ndicate ubaerialr subaqueouseruption.However, he majorityof thebasalt lowsof thecorrelative anjalvolcanics ereerupted ubaeriallyBhatandZainuddin, 978].The KarapaGreenschists overlain y 50 mof argilliteand thin-beddedimestonehat orm the baseof theKashala Formation. The remainder of the Kashala Formationconsists f thin ntervals f phyllite nterbedded ith thick-bedded rownmarble hatcontains ateTriassic Camian)conodontsPogueet al., 1992]. No Permianstratahavebeenrecognized,ut heTriassicossiliferousorizonsreseparatedfrom the KarapaGreenschist y over 500 m of strata hatcouldbe, in part, Permian.Massivewhite marbleof the NikanaiGharFormation orms he top of the Peshawar asinsection.Swat

The oldestunit exposedn Swat s theManglaurFormation, probable orrelativeo thePrecambriannd

Cambrian? Tanawal Formation which forms the base of thePaleozoicsection n the Peshawar asin Kazmi et al., 1984;Lawrenceet al., 1989]. The ManglaurFormation s intrudedby severalargesheet-like odies f UpperCambrian watGraniticGneiss nd s overlain y theMarghazar ormation,the oldest nitof theAlpuraiGroupof DiPietro 1990](Figure7). An unconformityt theManglaur/Marghazarcontacts ndicated y thepresencef pebbles ndK-feldsparclasts, erived rom he SwatGraniticGneiss,n Marghazarpsammitic chist. he MarghazarFormation aries rom 1000 m in thickness nd consists f peliticschist,hornblende chist, sammitic chist, nd schistose arble.A20- 50-m-thick ntervalof amphiboliteorms he opat allexposuresn centralSwat, and otherdiscontinuousamphibolite odiesoccur hroughouthe unit. n areaswherethe MarghazarFormation s thin, t is composed lmostentirelyof the upperamphibolite orizon. hemetasedimentaryartof theMarghazar ormationscorrelativewith the upper afarKandao ormation ased nlithologic imilarities nd he stratigraphicosition elow heKarapaGreenschist-correlativemphibolite orizon. heKashalaFormationoverlies he Marghazar ormation nd sthe oldest unit common to Swat and the Peshawar basin. Theprincipal ithologiesn the wo areas re similar, lthoughheunit gradually hinsandbecomesmoreschistoseo the north.In Swat, he KashalaFormation s overlainby marbleof theNikanai Ghar Formation n the regionsouth f theLoe Sargneiss ome,andby graphitic hylliteof the SaiduFormationelsewhere.Interpretation

The conglomeratentervals n the owerJafarKandaoFormation ecord heprogressiveenudationf a tectonichighland orthof thedepositionalasin.The upliftof this

Fig. 8. (a) Geologicmapof theLewanaiGharareaof southern watorientedo facilitate own-structureviewing. atterns re hesame s orFigure ; tg s tourmalineraniteTertiary). b) nterpretationfpre-Himalayanstructure f the LewanaiGhar area.


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880 Pogue t al.: Late Paleozoic ifting n Northern akistanhighland limaxedduring heEarly Carboniferous hengranitic obbles erived rom subaerially xposed recambrianbasement eredepositedn fluvial channels. he ateralvariabilityand conglomeratentervals f the upper afarKandao ndicate hat tectonic nstability ontinuednto theMiddle Carboniferous.The absence of strata in Swat correlative with the thick(3000 m) lower Paleozoicsectionof the Peshawar asinsuggests watas a source or theclastic ntervals f the owerJafar KandaoFormation.The sediments f thebasalMarghazarweredepositedn eroded recambrianocks s heMiddleCarboniferous eas artially nundated wat.Much of Swatremained xposed ntilburiedby thePermian(?) asalt lowswhich orm theprotolithof the upperMarghazar mphibolitehorizonandKarapaGreenschist.he absence f relictpillowstructuresn the amphibolite/greenschist,pparentackofPermianstrata, nd hepresence f reworkedowerPaleozoicPanderodus conodonts in the Lower Permian Amb Formationof the Salt Range B. Wardlaw, personal ommunication,1989) suggesthat eneweduplift and erosion ccompaniedsubaerial xtrusion f the basalt.A major ransgression,initiatedby thermalsubsidencef theriftedmargin,reestablishedhallowmarinesedimentationy the ateTriassic, when the fossiliferouscarbonate ocks of the KashalaFormationweredeposited.STRUCTURE

Over 2000 m of Cambrian hroughDevonianmetasedimentaryocksare exposedn theChingalaisynclinorium,whereas nly 30 km to the north,on thesouthernmarginof theLoe Sardome, owerPaleozoic ocksare absent Figure2). The intervening istancencreaseso 50-60 km when he shortening ffectsof Himalayan oldingareremoved.The proximityof these ontrastingections recludesa gradual ransition nd mplies nstead he existence f anintervening ault or seriesof faultsalongwhich uplift of thenorthern lock occurredelative o the southern lockduringthe Carboniferous. he precise ocation f theprincipalinferred ault(s)bounding he upliftedSwatblock s unknownbecause xposed edrock n the criticalarea s entirelypost-Lower Carboniferousn age.However,smaller-scaleaults npre-Carboniferousocks n Swatand hePeshawar asinareinterpreted srepresentativef thedeformationaltyle ngeneral.One such ault s suggestedy contact elationshipson the eastern flank of the Loe Sar dome, 13 km north ofDaggar,where he thickness f theMarghazar ormationsabruptlyquadrupled y the additionof an oldersection Figure2). A detailedmapof thearea,oriented o facilitate own-structure iewing, s presentedn Figure8a. Lithologiclayering,which parallels he contactwith older ormationsnthe youngersection, s truncated gainst he contactwith theManglaurFormationand Swat Gneiss n the older section.Figure 8b is an interpretation f the contact elationshipsncrosssection, rior to intrusion f tourmaline ranite tg) andprior to Himalayan oldingandmetamorphism.he truncationof layering n theolderMarghazars interpretedo haveresulted rom syndepositionalormal aulting.Two subparallel igh-angle aultswhichoffsetPrecambrian-Silurian formations north and east of Swabi(Figure2) may definea minorCarboniferous raben. henortheast trikeof these aults s oblique o theHimalayanstructural rendsbut is parallel o the strikeof diabase ikes n

the AmbelaGraniticComplex o the north Rafiq, 1987].Thesedikes,as well as thecontacts etweenndividual raniticintrusionshat comprise he AmbelaComplex,haveanortheasterntrike Rafiq, 1987], ndicating northwest-southeast rientationof maximumextension uringemplacement.Anothersuspectedaleozoic ormal aulthostshe"alkaline"gneous omplex xposed earTarbelaDam (Figure3)[Janet al., 1981a].This fault, expresseds a 300 m wideshear one n Precambrianmetasediments,as nterpreted yCalkinset al. [1975] as a segment f the dominantlyeft-lateralDarband ault,of Himalayan ge.The associationfmafic intrusionswith this fault, which are elsewhere estrictedto pre-Permianocks,suggestshat t originated san olderPaleozoicstructure.f the 350 + 15 Ma K/Ar date Kempe,1986]on an amphibole lbitite rom heTarbela omplexsaccepted s an emplacement ge, hen nitial motionmusthaveoccurred uring,or prior to, theLate Devonian.SUMMARY AND CONCLUSIONS

Stratigraphic,adiometric, tructural, ndgeochemicalevidencendicatesmajor ifting n northern akistan uring helate Paleozoic.Prerift sedimentaryocksweredepositeds ateas he Late Devonian Frasnian)n a northward eepeningepicontinentalea Figure9a). Thermally nduced pliftandemergence f the northern art of the epicontinentalasinbeganprior to the Early Carboniferousndwasaccompaniedby the development f major northeast trikingnormal aultsand the inceptionof alkalinemagmatism Figure9b). Alkalinemagmatism ontinued nto the Middle Carboniferous, hileerosioned to the eventual ubmergencef theEarlyCarboniferous ighlands Figure9c). Renewedupliftaccompaniedhe emplacement f porphyritic lkaline hyoliteflows,diabase ikesandsills,andbasalt lowsduring heLateCarboniferous-Permianlimax of rifting (Figure9d). Thermalsubsidenceubsequento riftingreestablished arinesedimentation y the Late Triassic Figure9e).The rift sequence utlined boveprovideshe irstdirectevidence rom Pakistan or the atePaleozoic ragmentationfnorthernGondwana.Stratigraphic vidence or latePaleozoicrifting hasbeendocumentedn Zanskar nd headjacent ahul-Spiti areaof northernndia wherePermianmarinesedimentsunconformablyverlieeroded ormal aultbounded ighlands[Baudet al., 1989; Gaetaniet al., 1990]. The timing andgeochemistryf Panjalvolcanismn KashmirandZanskaralsosupport n association ith late Paleozoic ifting [Bhatetal., 1981; Seng6r,1984; Baudet al., 1989; Gaetaniet al.,1990]. Seng6r 1984] proposedhat hePanjal"traps"weregenetically elated o rifting of the Cimmerianmicrocontinent(I, T, and A in Figure 10), a stripof the northemmarginofGondwanawhich detachedrom ndia during he atePaleozoicanddriftednorthward, losing hePaleo-Tethys ndopeningthe Neo-Tethys n its wake (Figure 10). Gaetaniet al. [1990]similarlyascribe edimentary vidence or rifting to theopening f the Neo-Tethys. he selection f Cimmeria s herifted fragment s supported y the similarstyleand imingofextensionalectonicsn continentalragmentsn Iran andAfghanistan I and A in Figure 10) [Seng6r,1990; Seng6r tal., 1988]. The openingof theNeo-Tethys s indicatedn Iranby a widespread nconformity t the baseof thePermiansectionwhich hasbeenattributedo uplift alongnormal aultsprior to rifting [St6cklin,1984].Evidenceof late Paleozoic


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Poguetal.:LatePaleozoiciftingnNorthernakistan 881

Figure9a

Precambrian sediments

Precambrianbasement AMG

CarboniferousVisean

Figure9b

' Peshawar Basin ILower Paleozoic Lowerafar graniteKandao

Precambrian sediments

Precambrianbasement AMGInitiation of

alkalineintrusives

Swat

Precambrianbasement pre-riftthermalbulge

CarboniferousWestphalian B

Figure9c

' Peshawar Basin IUpper Jafar Kandaodeposition

SL

Precambrianediments ,,,('

Swat IMarghazardeposition

.,..,..,..,..,..,..,..,..,..,..,..,..,..,.

PrecambrianPrecambrian AUG basementbasement

Permian ' Peshawarasin I Swat.--Salt Range Karapa_asaltslo. Permian ........................................

TriassicCarnian I Peshawar Basin I Swat IKashaladepositionSL Jr

Fig. 9. Sequential chematic ross ectionsllustratinghe atePaleozoico early Mesozoic ectonicevolutionof part of the Gondwananmarginof northern akistan. G is Swatgranitegneiss,AMG isAmbelamegacrystic ranite,AAG is Ambelaalkalinegranite, ndSP is Shewaporphyry.SL isapproximate ea evel.


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882 Pogue t al.: Late PaleozoicRifting n NorthernPakistan

10S 110E

20 E 250 Ma Late Permian10S

60S

110E

60S20 E

10S300 Ma Late Carboniferous

110E

20 E 350 Ma60S

Early Carboniferous

rifting s alsopreservedn the Helmandblock zone)of centralAfghanistan, notherCimmerian ragment Figure 1). Thenorthern art of the Helmandblock Behsud ubzone fBoulin, [ 1988]) consists f Proterozoic asementntruded y496 + 11 Ma granodioritesverlainby upperPaleozoic ndTriassic trata.A relativelycomplete ndgreatly hickenedPaleozoic ectionwith shallow-water picratonic ffinitiescharacterizeshesouthern art Tezak-Nawar ubzone fBoulin, 1988]). Boulin 1988] nterpretedheabbreviatedPaleozoic section of the Behsud subzone to have resulted fromLate Devonian o Late Carboniferous plift accompanyingextension long southdippingnormal aults.The obvioussimilarityof the Behsud nd Tezak-Nawarsubzones ith Swatand he Peshawar asinsuggestsontinuity etween he woareas Figure 10, 350 and300 Ma) prior o opening f theNeo-Tethyan cean asin epresentedodayby theWaziristanophiolites Figure 10, 250 Ma).

Acknowledgments. his studywas supported y NationalScience oundation rants NT-81-18403, EAR-83-18194,INT-86-09914, EAR 86-17543, and NT 86-42445. Additionalfinancialsupportwasprovided y the Geological urveyofPakistan.The studybenefited rom discussionsnd/or ieldexcursionswith M. S. Baig, A. A. K. Ghauri, Anita Grunder,Ahmad Hussain, M. Qasim Jan, A. H. Kazmi, Kaleem urRahman Mirza, Lawrence Snee, R. A. K. Tahirkheli, andRobertYeats.Assistancen the field wasprovided y ImtiazAhmad,SajjadAhmad,GulzarAziz, andMohammed iaz ofPeshawarUniversity,by AhmadHussain, ahirKarim, andWali Ullah of the GeologicalSurveyof Pakistan, ndby ElisaWeinmanPogue. awrence neeprovided amplesorgeochemicalnalyses. hispaperwas mproved sa resultofmanuscripteviewsby JamesNatland,A.M. C. Seng0r, ndRobert Yeats.

Fig. 10. GeneralizedatePaleozoicectonic volution fnorthernPakistan nd surroundingegions Mercatorprojection; odifiedromScotesendDenham1990]).Shadedareas epresent ceanic rust, on-shadedreas, ontinentalcrust.Abbreviations re A, AfghanistanHelmandblock);Aft.Africa; Ant, Antarctica;Ara, Arabia; Aus, Austrailia; nd,India; , Iran; M, Madagascar; , Peshawar asin;T, Tibet(Lhasablock).SeeSeng0r 1990, igure6A] for a derailedinterpretationf Early Triassicectonics.

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Baud,A., J. Marcoux,andG. Stampfli,LatePermian Early TriassicTethyanmarginofIndia: Evolution from rifting to drifting (Salt-Range, Kashmir, Zanskar raverse),Proceedins of the 28th InternationalGeologic Congress, ol. 1, p. 103, 1989.Bhat, M.I., and S.M. Zainuddin, Environmentoferuptionof the Panjal raps,HimalayanGeol.,8, 728-737, 1978.Bhat, M.I., S.M. Zainuddin, and A. Rais, Panjaltrap chemistry nd he birth of Tethys,Geol.Mag., 118, 367-375, 1981.Boulin, J., Hercynianand Eocimmerian vents nAfghanistan and adjoining regions,Tectonophysics, 48, 253-278, 1988.Calkins, J.A., T.A. Offield, S.K.M. Abdullah,and S.T. All, Geology of the southern

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J. H. Dilles andR.D. Lawrence,Department fGeosciences,Oregon State University,Corvallis, OR 97331.J. A. DiPietro, GeologyDepartment,University of Southern ndiana, Evansville, N47712.S.S. Hughes,Department f Geology, dahoState University, Pocatello, D 83209.K. R. Pogue,Department f Geology,Whitman College, Walla Walla, WA 99362.S. R. Khan, GeologicalSurvey of Pakistan,Chak Shahzad, P.O. Box 1461, Islamabad,Pakistan.

(Received August 2, 1990;revisedJanuary9, 1992;accepted anuary23, 1992)

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Tectonics North Pakistan Pogue 1992