The transition from Alboran to Algerian basins (Western Mediterranean Sea)

20 Pages·2014·16.4 MB·English

by  Mourad Medaouri

JournalofGeodynamics77(2014)186–205

ContentslistsavailableatScienceDirect

Journal of Geodynamics

journal homepage: http://www.elsevier.com/locate/jog

The transition from Alboran to Algerian basins (Western

Mediterranean Sea): Chronostratigraphy, deep crustal structure

and tectonic evolution at the rear of a narrow slab rollback system

MouradMedaouria,JacquesDéverchèreb,∗,DavidGraindorgeb,RabahBracenea,

RabieBadjia,AziouzOuabadic,KarimYelles-Chaouched,FethiBendiabe

aSONATRACHExploration,Boumerdes,Algeria
bUniversitéde Brest(UBO) ,CNRSUMR 6538DomainesOcéaniques,InstitutUniversitaireEuropéendelaMer,29280Plouzané,France
cDéparteme nt deGé ologie, FSTGA T,Lab.LGG IP,USTHB ,Algiers,Alge ria
dC.R.A.A.G.(Ce ntr edeRech ercheen Astro nomie ,Astrop hysique etGéophysique),Bouzareah,Algiers,Algeria
eEntreprise Nationa le deGéophy siq ue(ENAGEO) ,Avenuedu1e rN ovembre,BP6 8,Boumerde s,Alger ia

a r t i c l e i n f o a b s t r a c t

Articlehistory: TheeasternAlboranbasinanditstransitiontotheAlgerianbasinisakeyareaintheMediterranean
Receiv ed19April2013 real mwher econtrov ersial kine ma ticandge od ynam icalmo delsa re pr opo sed. Mo dels implystriking
R21ecDeeivceedm ibne r re2v0is1e 3d form differe nces re garding the n ature of th e cr ust, the preval ence of britt le faulting and du ctile sh ear, the
originofmagmatism,thestyleofMiocenedeformationandthedrivingmechanismsoftheAlboranplate
Accepted3January2014
kinematics.CombininganewchronostratigraphicchartoftheAlboranandAlgerianbasinsbasedonthe
Availableonline27January2014
Habibas(HBB-1)coredrill,deepseismicsectionsstrikingWSW-ENEandSSE-NNW,andpotentialfield

data,were-assessthetectonicevolutionthatcontrolledthesedimentationandbasementdeformation
Keywords:
ofthewesternmostlimitoftheAlgerianbasinanditstransitionwiththeAlborandomain.AWSW-
Alboransea
TMeicotcoennice s kinematics daliorencgte∼d1 0ex0tkemnsfioronmal Bteucrtdoingaicl iapnhatsoeT hoartso snhiaanpetdim ae sst,rwethcihcehdi scaosnstuinmeendtatlo crreussutl twfirtohm tytphiecaWl StiWlte-dd ibreloctcekds

Crustalstructure migrationoftheAlboranblockdrivenbyanarrowslabrollback.IntheAlgerianbasin,thiseventwas

Seismicreflection followedbytheemplacementofanoceanic-typecrust.Potentialfieldsignaturesofthedeepbasinas
Potentia lfielddata wellasge om etri calcorrelation sw ith onlandoutcr opsof innerzone ssug gestamini mu mW SW- direct ed
SSTlaEbP rfoalulbl tamckar gin displ ac ement of the Alboran terr ane o f ∼200 k m. At the so uther n foot of the Al ge rian basin , the continent-
oceantransitionissharpandmayresultfromthewestwardpropagationofaslabtearatdepth,forming

twosegmentsofSTEP(Subduction-TransformEdgePropagator)margins.Ourresultssupportmodelsof

intensesheartractionsatthebaseofanoverridingplategovernedbyslabrollback-inducedmantleflow.

Finally,Messiniansalttectonicsaffectedoverlyingdepositsuntiltoday.AlateTortoniantoQuaternary

dominantlytranspressivetectonicepisodelinkedtotheAfrica-Iberiaconvergencepost-datesprevious

events,deformingthewholemargin.

©2014ElsevierLtd.Allrightsreserved.

1. Introduction Jolivet and Faccenna, 2000; Faccenna et al., 2004; Bezada et al.,

2013), a process which would have favored late (post-orogenic)

The Alboran and Algerian basins are two domains of the lithosphericandcrustalthinning(PlattandVissers,1989;Comas

westernmost Mediterranean Sea that formed within the zone of et al., 1992, 1999; García-Duen˜as et al., 1992; Maldonado et al.,

convergence between the African and Eurasian plates. The Alb- 1992;Wattsetal.,1993)coevalwithwidespreadmagmatismand

oran domain locates at the center of the Gibraltar Arc System, volcanism(Duggenet al., 2004, andreferencestherein)and also

an arcuate Alpine range comprising the Betic and Rif mountains with thrusting and shortening of the external zones of the Betic

(Fig.1).BothbasinsareoftenassumedtohavedevelopeduntilEarly andRifbelts(e.g.,García-Duen˜asetal.,1992;Comasetal.,1992)

Miocene time in response to a westward slab rollback (Réhault (Fig.1).SinceLateMiocene,extensionhasbeenfollowedbyNW-SE

et al., 1985; Lonergan and White, 1997; Gueguen et al., 1998; shorteningresponsibleforbasininversion,foldingandreverseor

strike-slipfaulting,mainlyexpressedintheAlborandomainand

still active today (Comas et al., 1992, 1999; Watts et al., 1993;

∗ Chalouan et al., 1997; Fernandez-Ibanez et al., 2007; Martínez-
Correspondingauthor.Tel.:[phone].
E-mailaddress: jacdev@ univ -bre st.fr(J.Déverchère). García et al., 2011, 2013). Further eastwards, the Algerian basin

0264-3707/$–seefrontmatter©2014ElsevierLtd.Allrightsreserved.

http://dx.doi.org/10.1016/j.jog.2014.01.003
M.Medaourietal./JournalofGeodynamics77(2014)186–205 187

Fig.1. GeologicalmapoftheAlboranSeaandmajortectonicfeaturesoftheGibraltararcformedbytheBeticRifandTellmountainbelts(modifiedfromComasetal.,

1992).WAB=WestAlboranBasin;EAB=EastAlboranBasin;SAB=SouthAlboranBasin;AB=AlgerianBasin;YR=YusufRidge;YB=YusufBasin;HE=HabibasEscarpment;

HB=HabibasBasin;CB=ChellifBasin.Somedrillingsitescorrespondtothe1995OceanDrillingProgramproposal(holes976,977,978and979);otheronesareHBB-1

(Habibas-1Sonatrachcommercialwell)andARZ-1(Arzew-1Sonatrachcoredrill).ESCI-Alb2b-2cistheSpanishAlboranexperimentmultichannelseismicreflectionline

(Comasetal.,1995;Booth-Reaetal.,2007).Spi02isthewide-angleseismiclineofSPIRALproject(“SismiqueProfondeetInvestigationRégionaledelamargeALgériennne).

S1,S2andS3areSonatrachseismicsections(2002Survey)showninthisstudy.Othersections(blacklines)wereusedforinterpretation.

correspondstoanabyssalplaingenerallyassumedtobeflooredby (2) the Tertiary kinematics of the Alboran block (timing and

anoceanic-typecrustformedduringtheMiddletoLateMiocene amount of westward displacement, see e.g. Gueguen et al.,

as the result of crustal backarc extension (Réhault et al., 1985; 1998;JolivetandFaccenna,2000;Mauffretetal.,2004,2007;

Deweyetal.,1989;Mauffretetal.,2004;Booth-Reaetal.,2007; Duggenetal.,2004;Plattetal.,2006);

Leprêtreetal.,2013).BothareasdepictPlio-Quaternarywitnesses (3) theamount,timingandnatureofthemagmaticandvolcanic

ofshorteningorupliftofthebasinmarginsandalsocontrasting activitywhichhasconsiderably(andextensively)modifiedand

imprintsinthepresent-dayseafloorphysiography(Woodsideand alteredthecrustalstructures(e.g.Duggenetal.,2004;Booth-

Maldonado, 1992; Campos et al., 1992; Déverchère et al., 2005; Rea et al., 2007) and may mask the importance of tectonic

Graciaetal.,2006;Ballesterosetal.,2008;Mauffretetal.,2007; featuresandthenatureofthebasement.

Fernandez-Ibanez et al., 2007; Domzig et al., 2009; Yelles et al.,

2009;Strzerzynskietal.,2010;Martínez-Garcíaetal.,2011).The
floor o f the Albora n sea is mo rphologically co mp lex , with iso- Therefore,theAlboranSeaandtheAlgerianbasinconstitutea
lated hi ghs or seamo unts o f volcanic origin a nd locally eme rged nice example of a backarc do main wh ere comp eting hypothese s
ridge s mor e t han 100km lo ng (e.g. the Alb oran Ridge and the ond rivingpro ces se scanbe investig ated.Ho wever,ma nyhypothe-
Habiba s Esca rpme nt), whe reas the Alge rian basi n is fla t, m uch ses arepoo rlysuppo rted by data,especia llyregard ingex tensional
deeper ( ∼2800m) and surroun ded by relati vely s tee p m argins, stru ctu res, kin ematic ind ica tors and timing of deform ation. One
except atthejun cti onw iththeAlbor and omain(Ca merlen ghietal., ofthemain interestso ftheAlbo ran-A lgerian of fshoretransiti onal
2009;M a rtín ez-Garcí aeta l.,2 011). do mai nisth atitoffe rs the opportunitytoide ntifyint ensecrustal
Alt houghnumerous da tas etsareavailable(seee.g.Comasetal., thinning a ndsh e arings upp osedtohave oc curredin anarro wslab
1992,1995; Booth-Rea etal .,20 07; Martínez -Gar cía etal.,2 01 3), backarc( rollb ack)setti ngusings tra tigrap hiccontr ols ,o riginals eis-
theco mplex ityofthee vo luti onoft heAlborandoma in res ultsin micdata andpote ntialfie lddat a.
sev eraldebates foc usin gon: T he p oint s we addr ess i n this study aims at: (1) re-assessing
thechr onostra tigr aphyoft he Albo rando main and dis cussthetim-

ingofsedimentationandofdeformationphasesversustheones
(1) thegeodynamicprocessesresponsiblefortheopeningofthe occ urr ingintheAlger ianb as in;(2)clarify ingthe issuesr ega rding
Alge rian-Alboran deep ba sins: subduc tion ro llback, d eta ch- thenature of the crustand thesty lea ndamoun tof thinnin g,bybet-
ment and/or STE P (Su bduction -Transform Edge Pro pagator) terd escrib ing the 3Da rchi tect ureo fthe basinan d deepcrus tat the
tearin g slab and d elamination, convective remo val, mantle tran sitionofth eA lbo ranandAlge ria ndo main s;an d(3) exam in ing
diapiris m, d ouble vergence sub duction zo nes, poloi dal and kinematic an d g eodynam ic i mplicatio ns (disme mb erin g and dis-
toroidalm antleflo ws,etc.(se ee.g.summ ariesin Micharde tal., placement ofth eAlboranm icroplate;rol lbackeffectson thes tyle,
2002;Sp akman andW ort el,2 004 ;Goversan d Wortel,2 00 5; distribution a nda mounto fcrustalthin ningoft heover rid ing plate;
Valera etal.,200 8;V ergèsan dFern andez, 2012 ;Duarte etal., timingofth edif ferentst ep softec tonicevo lu tion andcomp arison
2013;S ch ella rtand Moresi ,201 3;Meyera ndSch ellart,2 01 3); withm od els ofnarrow slabr ol lbackand STEPpro paga tion).
188 M.Medaourietal./JournalofGeodynamics77(2014)186–205

Inordertoachievethesegoals,webenefitfromoriginalindus- relatively shallow water with mainly shaly to marly sediments

trial deep-reflection seismic sections striking WSW and NNW passing to evaporite sediments at the top of the Messinian. No

(Fig.1)overalargeareauncoveredbypreviousstudiesandless MessiniansaltisfoundintheHabibasBasinandthetopofthisunit

disturbedbyTertiarymagmatismthanfurthernorthorwest.We waspartiallyerodedbythePlioceneunconformity.ThePliocene

alsocorrelatethesedimentarysequencesoftheAlboranSeabasin represents a period of renewed deepening of the basin with

with coeval sequences in the Algerian Neogene basin by using sediments deposited initially in the bathyal regime, shallowing

detailedchronostratigraphyfromanadditionalwellintheSouth upwardintoouterneritic.Thelithologiesaremainlyshaleswith

Alboranbasin(HBB-1,Fig.1)whichispreciselytiedtoseismicsec- acoupleofsandstones(turbidites)withinthepackagerestingon

tions,allowingforconstructionofaregionalagemodelbetween thePlioceneunconformity.

sub-basins. Crustal types and kinematics are also discussed by

examiningthegravity,magneticandseismicreflectiondatafrom

differentpartsoftheAlboranandAlgeriantransitionzone.Finally, 2.1.2. AlgeriandomainandtransitiontoeasternAlboranbasin

weattempttocomparetherelativeimportanceofpost-Messinian Miocene-Quaternary deposits overlay a Mesozoic basement

transpressiondescribedintheAlboransea(Fernandez-Ibanezetal., formedbythrustsheetsinthewesternonshoreAlgerianmargin

2007;Martínez-Garcíaetal.,2013)andlessknownpre-Messinian (Thomas, 1985; Perrodon, 1957). However, the offshore distri-

deformationsinordertobetterassesstheNeogenekinematicand bution of this Mesozoic deformed terrane is unknown. The base

geodynamicalevolutionintheeasternandsouthernAlboransea. of the Cenozoic basin fill is represented by uppermost Burdi-

galiantoSerravallianmarlsandsandstones.Overlyingthelatter,

theTortonianstrataaremadeupoflimestones,marlsandsand-

2. Geologicalandgeodynamicalsettings stones.TheMessiniansequenceonlanddepictsmarlsalternating

withdiatomitesandplatformlimestones(Thomas,1985;Neurdin-

2.1. DepositionalpatternintheAlboranandAlgeriandomains Trescartes, 1992). On top of the Messinian deposits, there are

massivegypsumbedswithmarlandsandstoneintercalations.

2.1.1. Alborandomain The shelf setting of the Algerian-south Balearic margin was

The center of the Alboran domain is a large Neogene basin explored by the Arzew well (ARZ-1, Fig. 1) drilled on a seismi-

locatedintheinnerpartoftheRif-Betic-Maghrebianorogenicbelt. callydefinedMiocene-Pliocenenose(Burolletetal.,1978).Onthis

Several sub-basins have developed and depict significant thick- shelf, in contrast to the Habibas well (Section 2.1.1 and Fig. 2),
nessva riations:the Wes tAlboranB asin (WAB) ,theEastA lboran amas siv e,∼130m t hick Messinia ngy psumbed has been fou nd,

Basin(EAB)andtheSouthAlboranBasin(SAB),separatedbyseveral overlain by 540m of Pliocene-Quaternary marls and limestones.

ridges,seamounts,andtroughs(Fig.1).Themaximumthicknesses ThelowerMessinian(145mthick)iscomposedofgraymarlsand

locateintheWAB,wherethesedimentarypileisupto8kmthick clayswithsomegypsumintercalations.TheupperTortonianunit

anddisplaysacurveddepocentrethatmimicstheorogenicfront (204mthick)ismadeofgraymarlswithintercalationsofpyroclas-

oftheGibraltarArcSystem(Comasetal.,1992;Sotoetal.,1996, ticmaterial.

2012;Chalouanetal.,1997).TowardtheEast,thethicknessofthe The offshore Yusuf basin (YB, Fig. 1), located at the junction

sedimentaryfillingdecreasesto2–3kmintheEAB,atthetransition betweenSABandAB(Algerianbasin),containsupperMioceneto

towardtheAlgerianbasin,whereasintheSAB,maximumsediment Plio-Quaternarysedimentsupto2000mthick,partofthemdrilled

accumulationreaches4km(Comasetal.,1995;Booth-Reaetal., atODPsites977and978(Alvarez-Marrón,1999;Medaourietal.,

2007;Mauffretetal.,2007;Medaourietal.,2012;Martínez-García 2012).

etal.,2013). Finally, the deepest sedimentary sequence of the Algerian

AttemptsofcorrelationsofsedimentarysequencesoftheBetic Basin (AB) depicts a succession of units typical of the western

Neogene basins with deposits in the Alboran sea have been Mediterraneanbasins(Alvarez-Marrón,1999;Mauffretetal.,2007;

performedsincealongtime,asbothareasincludemarinetocon- Booth-Reaetal.,2007;Estradaetal.,2011;Fig.3BandC),i.e.,from

tinentalsedimentarysequencesfromEarlyMiocenetoHolocene top to bottom: Plio-Quaternary sequence, Upper Messinian Unit

age,includingfrequentvolcanism(Hernandezetal.,1987;Comas (UU),MessiniansaltorMobileUnit(MU),LowerUnit(LU),Torto-

etal.,1996,1999;Lustrinoetal.,2011).IntheWAB,thissequence nian(T)andSerravalian(S)Units.However,pre-saltandMessinian

hasbeendrilledatSite976duringOceanDrillingProgramLeg161 unitsareoftenpoorlyidentifiedinage,thicknessandnature,since

(Comasetal.,1996).Moreover,thesedimentaryunitsbeneaththe theyhaveneverbeendrilledintheabyssalplainandalsobecause

AlboranSeabasinarewelldocumentedfromseismicdata(Campillo no continuous correlation is possible from the upper margins or

etal.,1992;Maldonadoetal.,1992;Comasetal.,1992;Wattsetal., intermediatebasinstowardthedeepAlgerianbasin.

1993;Booth-Reaetal.,2007,andreferencestherein).Byextrap-

olationofcommercialdrillingresultsfromthenorthernAlboran

Sea and using volcanic deposits, Jurado and Comas (1992) have 2.2. UncertaintiesonthenatureofAlboran/Algeriandomainsand

proposed to distinguish six seismic stratigraphic units (VI to I), onthekinematicevolution

boundedbyunconformities,representingagesrangingfromEarly

MiocenetoQuaternarytimes. Two main episodes of extension are generally proposed for

In the deepest part of the SAB, the Habibas basin contains theAlborandomain:Burdigalian–Langhian(about17–15Ma)and

3.5km of sediments drilled in the Habibas (HBB-1) well (Fig. 2; Serravallian–earlyTortonian(about14–9Ma).Themiddletoearly-

see also Medaouri et al., 2012, and references therein). The lateMiocenevolcanismandmuddiapirsinthebasinarethought

metamorphic basement (4496m deep) is covered by 1263m of to be related to these extensional episodes (Comas et al., 1992,

Langhian–Serravallian, 563m of Tortonian, 613m of Messinian 1996,1999;Wattsetal.,1993;Chalouanetal.,1997;Pérez-Belzuz

marine deposits, including some gypsum and halite on the top, etal.,1997;Sotoetal.,2012).Seismicimagessuggestthatrifting

and 1044m of Plio-Quaternary deposits. The Langhian and Ser- wascompletedinthelateTortoniantime;afterthat,acompres-

ravalian sediments are all deposited in relative deep water, in sional/contractional regime has affected the whole basin and its

lowerslopefantoabyssalplainsettings.AtthebottomoftheSer- surroundings (Mauffret et al., 1987, 1992; Bourgois et al., 1992;

ravalliansequence,abasinfloorfan(BFF)isrecognized(Medaouri Maldonadoetal.,1992;Comasetal.,1992;Camposetal.,1992;

etal.,2012).TheTortonianandMessinianunitsaredepositedin Watts et al., 1993; Morel and Meghraoui, 1996; Chalouan et al.,
M.Medaourietal./JournalofGeodynamics77(2014)186–205 189

Fig.2. ChronostratigraphicchartdeterminedintheHabibasBasin.(1)Habibaswellformationstage,lithologyanddepth;(2)Habibaswellbiostratigraphyagesissuedfrom

planktonicandforaminiferaanalysis;(3)Sub-unitchartproposedinthisstudyforHabibasandSouthAlboranbasins;(4)ChronostratigraphyandfaciesunitsfortheSouth

Alboranbasin;(5)AlboranBasinseismicunitfromJuradoandComas(1992);(6)Habibasbasinmainstratigraphicsequences.

1997). Here, we briefly report on the state of knowledge on the drilledsitesHBB-1,ODP976,ALG-1andDSDP121,Fig.1),whereas

basementandonthestructuralevolutioninspaceandtime. itsnatureandoriginremainuncleartotheeast,wherenumerous

basementhighsarevolcanic(Galindo-Zalvidaretal.,1998;Booth-

2.2.1. Basementofthebasins Reaetal.,2007,andreferencestherein).Thetransitionbetweenthe
Th ebasemen t oft heAlboranBasinisgenerallyconsideredas Alge ria n basin and theeastA lboranba sin depictsa gentlewe st-
similar tothosef oun din theRif -Betic an dTellCor dilleras,i.e. of warddec rease inc rust althi ckness( Sotoe tal.,200 8 ),inco ntrast
metam orp hictyp e(Com as eta l.,1992,1 996, 1999 ;Plattetal., 199 8; witht hepronou nc edgrad ientsfoun donth en ort hernan ds outhern

Fig.3. ChronostratigraphicandseismostratigraphiccorrelationsfromtheAlboranBasinandnorthernmargintotheAlgeriandeepbasin.(A)SouthAlboranBasin:main

chronostratigraphicunits;(B)SouthernAlgerianbasin:seismicandchronostratigraphicunitsdefinedinthisstudy;(C)NorthAlgerian(SouthBalearic)basin:seismicand

chronostratigraphicunitsdefinedbyBooth-Reaetal.(2007);(D)OnshoresouthernBeticmargin(Nijar-Verabasins):stratigraphyages,formationnameandlithology,

modifiedafterBooth-Reaetal.(2007).MBS=MessinianBottomSalt.
190 M.Medaourietal./JournalofGeodynamics77(2014)186–205

Fig.4. (a)LinedrawingoftheESCI-Alb-2b-2cprofile(Booth-Reaetal.,2007)locatednorthofSectionS2(Fig.1)andshowingtheirandourinterpretationofcrustalsegments;

(b)UninterpretedSonatrachWSW-ENEseismiclineS2,fromSouthAlboranBasin(SAB)totheAlgerianbasin;(c)InterpretedSonatrachWSW-ENEseismiclineS2,from

SouthAlboranBasin(SAB)totheAlgerianbasin.LP+Q=LatePliocenetoQuaternaryUnit;EP=EarlyPlioceneUnit;UU2=MessinianUpperEvaporiteSub-Unit2;UU1=Upper

EvaporiteSub-Unit1;MU=MessinianMobileUnit(SaltUnit);LU=MessinianLowerEvaporiteUnit;T=TortonianUnit;S=SerravallianUnit;L=LanghianUnit;LB=Late

BurdigalianUnit;MCR=MiddleCrustReflectors;NF1toNF4=NormalFaults;Spi02=Wide-angleseismicrefraction(Spiralproject).CC=ContinentalCrust.Seetextfor

details.
marginsoftheAlboransea.Usingdeepseismicimagesinthenorth- thicknesses,theypropose3typesofcrust:(1)athinnedcontinen-

ern part of the transition between both basins (Section ESCI-Alb tal crust intruded by arc magmatism below the SAB; (2) a new

2b2c, Fig. 1 and Fig. 4a), Booth-Rea et al. (2007) report a sim- magmaticarc-typecrustbelowtheEABastheresultofthewest-
ilar cr ustal W -E t hinn ing from ∼15 t o ∼ 6k m, wit h no ap p arent wardmigr ationof subdu ction, coev alw ith sho rtenin ga nd thrust

faulting,scarcetiltedblocksandwidespreadvolcanics.Fromseis- emplacementintheGibraltararcforelanddomain;and(3)anew

micsignatures,geochemistryofvolcanicrockssampledandcrustal oceaniccrustbelowtheAB,asearlierproposed(Comasetal.,1995;
M.Medaourietal./JournalofGeodynamics77(2014)186–205 191

Mauffretetal.,2004).However,theexactnatureandextentofcrust etal.,1996;Calvertetal.,2000;Valeraetal.,2008),implyingeither

typesatthetransitionbetweentheeasternAlboranregionandthe aneastwardoranwestwardmigrationoftheeasternAlboranplate,

Algerianbasinremainquestionable. dependingonthesenseofdelaminationinferred.

Allthreetypesofmodelsarebasedonideasandassumptions

2.2.2. Structuralevolutionandtimingofextension about the mechanical behavior of the lithosphere, however they

Comas et al. (1992) and Watts et al. (1993) propose 3 main areuntilnowdifficulttodiscriminatebecausetheypredictsome-

stages of tectonic evolution in the Alboran Sea: (1) initial rifting times relatively similar structures at a broad spatial scale, and

during Aquitanian–Burdigalian, (2) major rifting lasting through becauseourknowledgeofthedeepcrustalandmantlestructures

Langhian-Tortonian,and(3)basinshorteningintheupperTorto- issparseandinaccurate.Acombinationofslabmigration,mantle

nian/Messiniantorecent.However,thepreciseperiodwhenthe removalanddelaminationisalsooftenhypothesized(Plattetal.,

mainriftingeventintheAlboranSeabasintookplaceisdebated 2006; Booth-Rea et al., 2007; Roure et al., 2012). Recent quanti-

(Wattsetal.,1993;Booth-Reaetal.,2007).Awesttoeastmigra- tative geodynamic modeling (Meyer and Schellart, 2013; Duarte

tioninextensionisobservedatleastfortheEarlytoLateMiocene etal.,2013;SchellartandMoresi,2013)showsthatnarrowslabroll-

evolutionoftheAlboranandAlgerianbasins(Comasetal.,1995, backinducesanintenseuppermantleflowandcanexplaincoeval

1999;Plattetal.,1998;Mauffretetal.,2004):thischronologyis extensioninbackarcdomainandshorteninginthefore-arcandarc

opposite to the one expected in a westward-migrating orogenic region.WhethertheseresultsapplytotheAlborancaseisworth

wedge,whichhasledsomeauthorstoproposeaneastwardmigra- to check, and major questions remain unresolved regarding the

tion driven by mantle delamination (Docherty and Banda, 1995; dynamicevolution,thenatureoftheslab(s)imagedbeneathAlbo-

Maldonadoetal.,1999).Thistimingofformationandevolutionof ran(Bezadaetal.,2013),thepositionandevolutionofslabwindows

Alboranseasub-basinsalsodiffersfromthetimingatthetransi- andslabtears(Faccennaetal.,2004;Duggenetal.,2004;Govers

tionfromtheAlborantotheAlgerianbasinsproposedbyBooth-Rea and Wortel, 2005; Bezada et al., 2013), and finally the origin of

etal.(2007):usingageofsedimentonlapsonthecrust,theyargue theextensionhavingformedtheAlboranbasinintheAfrica-Iberia

foranoceanicandmagmaticarccrustformationmigratingwest- collisionframework.

ward,inagreementwithradiometricdatingofvolcanicrocksinthe

region(e.g.,Duggenetal.,2005).Finally,LateMioceneconjugate
3. Dataandmethods
shearandtectonicescape(DeLarouzièreetal.,1988;Maldonado

et al., 1992; Comas et al., 1999) linked to the Africa-Iberia colli-
3.1. Wellandcorrelations
sioncouldalsoexplain(atleastpartly)adiachronicityofextension

throughoutthebasin.
Synthetic seismograms were used to tie the well depths and
Therefore,manyuncertaintiesremain:(1)thetimingandthe
biostratigraphic data with the major seismic stratigraphic units
degreeofdiachronicitybetweensub-basinsareinaccurateoreven
andtheirlimitsusinglaboratoryphysicalpropertiesandwireline
questionable,becauseofthelackofprecisestratigraphiccorrela-
loggingsfromHabibas-1(HBB-1)well.Oncethisworkcomplete,
tions,andbecausetiltedblocksidentifiedinthenortherntransition
wewereabletocorrelatethesedimentaryunitsofAlgerianand
(EAB)areveryscarce(Booth-Reaetal.,2007);(2)theamountof
EastAlboranbasinsusingthesectionsstrikingWSW-ENE(Fig.1).
westwardmigrationattherearoftheAlboranblockdiffersstrongly
PreviousagesestimatedfromcommercialandODPboreholedata
betweenauthors,rangingbetweenlessthan200and700km(e.g.,
(Andalucia-A1, Site 976, Leg 161) in the Alboran basin (Comas
Lonergan and White, 1997; Michard et al., 2002; Duggen et al.,
etal.,1996)andfromcoevalsedimentsoutcroppingintheNeogene
2004;Mauffretetal.,2004,2007;Plattetal.,2003a,2006);(3)the
Beticbasins(JuradoandComas,1992;Booth-Reaetal.,2007)were
typeofmarginformedattheedgeofaretreatingnarrowslab(STEP
calibratedandoccasionallymodifiedonthebasisofthebiostrati-
type,GoversandWortel,2005)isyetpoorlydocumentedworld-
graphicagesobtainedbyexaminationofcalcareousnannofossils
wideandisnotclearlyassessedintheAlborandomain;and(4)no
andplanktonicforaminifermarkersincuttingsamplesfromwell
consensusisreachedonthedrivingmechanismstoexplaintime
HBB-1(Fig.1).Thenannofossilandplanktonicforaminiferascales
andspaceevolutionofextensionfromWestAlborantoAlgerian
fromBollietal.(1985)wereusedforagedeterminationsofrocks
basins.
recoveredfromwellHabibas-1andcorrelatedwiththeglobalcycle

chartfromHardenboletal.(1998).
2.3. ConflictingmodelsontheevolutionoftheAlboran/Algerian

basins
3.2. Seismicdata

A major feature of the Alboran Sea is the significant thinning

of the lithosphere and the crust (see Soto et al., 2008, and ref- The 3 seismic lines presented in this paper are part of a

erencestherein).Therearethreemainhypothesestoexplainthe SONATRACH seismic data set acquired offshore Algeria in 2002

AlboranseageodynamicevolutionduringMiocenetime:(1)exten- (Cope,2003).Thissurveywasdesignedtoimagewellbelowthe

siondrivenbythewestwardrollbackofasubductionzonebeneath widespreadMessiniansaltandtoexplorethehydrocarbonpoten-

theAlboranregion(e.g.,DeJong,1991;Zecketal.,1992;Royden, tial.OffshoreAlgeriamaybeverypromisingbutrequiresadeep

1993;Zeck,1996;LonerganandWhite,1997;Jolivetetal.,2008), understandingofthevariousbasins.

implyingstrikinglyvariablewestwardmigrationattherearofthe The presented lines image the domain corresponding to the

Alboran block (from ca. 200 to ca. 560km, see e.g. Maldonado westernlimitoftheAlgerianbasinandtheeasternlimitoftheAlb-

et al., 1999; Michard et al., 2002; Duggen et al., 2004; Mauffret orandomain.Notethatthesouthernhalfofthistransition(Fig.1)

et al., 2004, 2007; Platt et al., 2003a,b, 2006); (2) extension as a wasuntilnownotdescribedbelowtheMessiniansalt,contraryto

consequence of the sinking of the thickened lithospheric mantle thenorthernhalf(Comasetal.,1995;Booth-Reaetal.,2007).

andsubsequentextensionalcollapseoftheentiredomainbygrav- Themultichannelseismicreflectionprofileswereacquiredwith

ityprocessesand/orconvectiveremoval(PlattandVissers,1989; aseismicsourcemadeofatunedfirstpeakfromasleeveairgun

Zeck,1997;Plattetal.,2003b),implyingdiffuseanddiachronous array of 3000 CI shot at 2000 PSI and towed at 6m depth. The

deformationovertheAlborandomain;and(3)extensionlinkedto shotintervalis25m.Thereceiverisamultichannel6000m-long

delaminationofthelithosphericmantlebeneaththeAlborancrust streamercomposedof480groupsof12.5m-longtrackstowedat

(e.g.García-Duen˜asetal.,1992;DochertyandBanda,1995;Seber 8mdepth.Thisgeometryleadstoamaximumtheoreticalfoldof
192 M.Medaourietal./JournalofGeodynamics77(2014)186–205

Table1 filewhichwasusedfortherawdatapolereduction.Filteringwas
Multic hannel seismic data processing sequence. con ducted thro ughM AG MA Pm odule OAS ISMONTAJ software .

Low cut filter at 3 Hz

4. Results
Amplitude correction

4.1. Revisedchronostratigraphyandcorrelationbetweenbasins

First multiple attenuation ofAlboranandAlgeria

WehavecombinedthebiostratigraphicagesandNeogenefacies
Deconvolution before stack
providedbytheHBB-1well(Fig.2)withtheseismiccharacterofthe

units(Table2aandb)inordertobuildanewchronostratigraphic

First velocity analyses at 2 km intervals chartbasedonaseismicfaciescorrelationfromtheAlboranBasin

tothedeepAlgerianBasin(Fig.3).Weidentify3mainseismicunits

formedbymiddleMiocene(16.4Ma)toQuaternary(Figs.2and3)
S eco nd multiples atten uati on u sing Radon multiple modelling sedimen ts ,taking intoacco untp revio us worksinth eAlb or ans ea

(RyanandHsü,1973;JuradoandComas,1992;Maldonadoetal.,
Dip move-out 1992; Com aset al.,19 92,199 5;G autiere tal.,1 994;Alonso et al.,

1999;Comasetal.,1999;Alvarez-Marrón,1999;Booth-Reaetal.,

Second velocity analyses at 1 km intervals 2007;Sotoetal.,2012;Martínez-Garcíaetal.,2013)andrelyingon

theLofietal.(2011)’schartforMessiniandeposits.Table2aandb

depictstheseismicunitsuccessionsidentifiedintheAlgerian(AB)
Residual multiples attenuation
andsouthAlboran(SAB)basins,respectively.Thethreemainseis-

micunitsarebrieflydescribedasfollows:

Stack mutes for far traces and near traces

(1) pre-Messinianunits,madeoflateBurdigalian(LB),Langhian(L),
Final CMP stack of the 120 fold CMP gathers
Serravallian(S)andTortonian(T)sub-units,separatedeitherby

unconformitiesorbymajorsequenceboundaries.LBsub-unit

Migration with stack velocities limited to 3000 m/s isrecognizedbyanalogywiththeunitdrilledintheAlboran

sea (Jurado and Comas, 1992) and appears as a fan-shaped

depositionintheeastAB(Fig.4),whereasitisabsentinHB.L
Tau-P and time variant filters
sub-unitonlapsa21–16MyroldmetamorphicbasementinSAB

(Bellon,1976)andrepresentsaca.1km-thickdeposit(Table2b,

Final scaling: AGC gain Figs.2and5),whereasinAB,alargesyn-sedimentarydiapirism

isobserved(km55–110,Fig.4),inawaysimilartotheouter

WAB(Comasetal.,1992;Maldonadoetal.,1992;Sotoetal.,

120. The dataset has been processed according to the sequence 2012).TheSerravallian“S”sub-unitdepositedinashortstrati-

summarizedonTable1.Itallowstoclearlyimagethesedimentary graphictimeandcorrelateswithUnitIVofAB(Fig.3A–C).It

unitsdowntothebasement.Inthebasinwherethecrustisthin,the onlaps L sub-unit and depicts syn-rift tilting in western AB

seismiclinesalsoevidencethehighlyreflectivelowercrustdown (Fig.3BandC;km50–180,Fig.4).Finally,theTortonian“T”sub-

totheMoho. unitisawidespreadsequenceequivalenttoUnitIIIofJurado

andComas(1992)andBooth-Reaetal.(2007),depictingvari-

3.3. Gravityandmagneticdata ableseismicsignaturesandthicknessesinAB(Fig.4),witha

highlyreflectivelowerboundaryandanerosionaltruncation

Thestepsfollowedtoperformgravityandmagneticprocessing’s atitstop(Figs.2–6).

are those described in Talwani et al. (1959) and Asfirane and (2) Messinianunits,madeof3sub-units(LU,MU,UU)alreadywell

Galdeano (1995), respectively. The gravity data were acquired describedinthewesternMediterraneanrealm(Lofietal.,2011).

usingaLaCoste&Romberg(s/nS-39)gravimeterequippedwith LUismadeofabunchofstrongreflectorslocatedabovethetop

aSAGEupgradedacquisitionsystem.Dataprocessingwascarried of Tortonian reflector, MU is the plastic Messinian salt Unit,

outbyARKGeophysicsLimited.Aunitconversionof1.01983was andUUiscomposedofmarlsandevaporitesoftenformedof2

usedtoconvertcounterunitstomilligals.Theoreticalgravitywas sub-unitsUU1andUU2;

computedandsubtractedfromobservedgravityatallsurveypoints (3) post-Messinianunits,madeofPliocenetoQuaternarysediments

usingthe1967InternationalGravityformula.Acorrectiondensity drilledincommercialwellsinthewesternmostMediterranean

of 2.1mg/cc was selected to match that used during first phase basin,mainlycomposedoffine-graineddistalmarls,clays,and

ofprocessing.Adataqualityassessmentwasmadebyanalyzing scarce interbedded sandstones (Alonso et al., 1999). The EP1

the standard deviations of data wavelengths shorter than 4km. andEP2sequences(unitsP4andP3ofMartínez-Garcíaetal.,

A depth dependent along-line filter was finally applied in order 2013)onlaptheMessinianerosionalunconformityanddepict

to remove non-geological signal, short wavelength noise which strong lateral thickness variations and progressive internal

cannot derive from actual features at the seafloor. The residual unconformitiesonthelimbsofgrowinganticlines.Sequences

gravityanomaly(Fig.8)wasproducedfromahigh-passandcosine LP and Q, labeled “unit I” in Jurado and Comas (1992), Units

taperedfilteroftheBouguergravitygridusinga100kmcutoff.The IaandIbbyAlvarez-Marrón(1999),Unit“Ia+b”inBooth-Rea

magnetic data used in this study belong to acquisition recorded etal.(2007),orunitsP2-P1andQ3-Q2-Q1inMartínez-García

in 1979. The data were in the form of 1:100,000 scale maps etal.(2013),is400–800mthickanddepicthighfrequency,high

representingtherawmagneticanomalieswithaniso-lineinterval amplitude,highreflectivityreflectors.IntheAlborandomain,

of10nT.Digitalizationofthesemapsallowedusobtainingadigital numerous local basins and intrabasinal highs inherited from
Table2

Seismicunitsuccessionidentifiedinthe(a)Algerian(AB)and(b)SouthAlboran(SAB)Basins,respectively,withtheirmaincharacteristics.

Seismic Biostrati Thickness Seismicfacies Reflectionpatterns LithologyfromALG-1&ARZ-1wells

sub-units graphicage

(Ma)
TWT(s) m

(a)AlgerianBasin(AB)

Quaternary Q 0 0.4–0.6 400–700 Discontinuous,divergent,highfrequency, Shalewithinter-beddedsandylevelsatthe

1.9 highamplitude,highreflectivityreflectors. top

M
.M
e
d
a
o
u
rie
ta
l./Jo
u
rn
a
Pliocene early–late LP 13..91 aCmonptliintuudoeu,s h, pigahr arleleflle, chtiigvhit yfr ereqflueecntcoyr,s high LSiatnhdost haanmd nsaionnd yca mlcaarrlesu lmevels and lofGeo
EP 3.1 0.4 500 Discontinuous,lowreflectivity,low Compactgraymarlsandgypsumatthe d
UU UU2 55..3333 0.1 300 aCmonptliintuudoeu,s h,higigh h frferqe quuenencycy r,ehflieg chtors bUoUtt=oMmar lsand brittl ean hydrites ynam
MLoewsseirn –ia Mnobile – Upper 0.3 amplitude (D own laps and on laps) ((CDMUea =er p Cg ioBnna fgsolioon mt))er ates an d gypsum ics77(201
4
)1
8
6
CU UU1 5.6 0.2 200–400 Continuousreflectors,variableamplitude, –2
0
0.4 lowfrequency.CU=Chaotic. 5

(UU=Downlapsandonlaps)

MU 5.6 0.1 ≥600 Chaotictransparentfacies,lowamplitude Haliteanddirtysalt
5.96 ≥0.5 andlow frequency,o ccasio nally strong

reflections
LU 5.96 0.15 100–200 Setofcontinuouslowamplitudeandlow Plasticgraymarlsandgypsum

7.24 0.25 frequencyreflectors

1
9
3
1
9
4

Table2(Continued).

Seismic Biostrati Thickness Seismicfacies Reflectionpatterns LithologyfromALG-1&ARZ-1wells

sub-units graphicage

(Ma)
TWT(s) m

M
.M
e
d
Tortonian T 7.24 0.2 150–350 Paralleltodivergentreflectorsofhigh Graymarls,Sandswithpyroclasticintervals a
9.26 0.4 damiscpolinttui dneu ,o puassrseinflge ct too crhsaotic a nd ourie
ta
l./Jo
u
Serravallian S 9.26 0.1 100–200 Discontinuoushigh-amplitudereflectors, Plasticgraymarlsandlimestonelevels rn
a
11.7 0.2 tthraenbsoptatroemnt oinf stehqeu deenpcoecenters, oblique at lofG
e
o
d
y
n
Langhian L 11.7 0.2 ? Chaoticpattern Siltandsandyshalewithvolcaniclayers am
16.4 0.6? ics7
7
(2
0
1
4
Late Burdigalian LB ≥16.4 00..93 beDnaissecerogmnyet hinnitgubhol uoascm kdpsivlieturgdeen, to nrelaflpe cotno rtsil, theidgh gCeoonmgleotmrye rdaetpeos,s sitasn)ds and turbidities (fan )186–2
0
5
Basement B ? ? ? Chaoticpattern Unknown
Table2(Continued).

Thickness
Seismic Biostratigraphic TWT(s) m Seismicfacies Reflectionpatterns LithologyfromHBB-1well

Sub-Units age(Ma)

(b)SouthAlboranBasin(SAB)

Quaternary Q 0 0.3 470 Discontinuous,parallel,highfrequency, Shalewithinter-beddedsandylevelsatthe

1.9 0.5 highamplitude,highreflectivityreflectors top

LP 1.9 0.3 374 Continuous,parallel,lowfrequency,high Sandsandsandymarlsandlimestone
PlioceneEarly–Late
3.1 amplitude,lowreflectivityreflectors levels

M
EP 3.1 0.2 200 Shingledreflectorsoflowamplitudeand SandturbiditiesandMudMounded .M
5.42 low frequ ency onla p a cha otic facies Carbo nate Ramp on the M reflector edao
u
rie
ta
Messinian UU 5.42 0.3 370 Parallel and continuous of high frequency Marls and Gypsum beds intercalations l./Jo
5.73 andhighamplitudereflections u
Lower–Mobile–Upper rn
a
MU Absent lofG
e
o
d
y
LU 5.73 0.15 243 Parallel,continuous,highfrequency,high Marlsandshalewithoccasionallysand n
6.96 0.25 amplitud e beds am
ics7
7
(2
0
Tortonian T 69..9266 00..25 563 aCmonptliintuudoeusa npdarfarleleqlu reenflceyctors of high pShyarolec laansdti cMleavrlesl with sand intervals and 14)1
8
6
–
2
0
5

Serravallian S 9.26 0.1 107 Discontinuous,highamplitudewith ClaysandSiltclayswithsandyandmarl

11.7 chaotictransparentzones intervals

Langhian L 11.7 0.6 1156 Discontinuousreflectorsofhighamplitude, Undercompactedshale,inter-bedded

16.4 0.9 lowfrequency(foldedandfaulted) sandyandsandy–pebbleintervals

LateBurdigalian LB ≥16.4 Absent

Basement B 170 ? 90 Chaoticpattern Metamorphicrock(Schists)

220?
1
9
5