Fold and fault interactions during the development of an elongated narrow basin.docx
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Fold and fault interactions during the development of an elongated narrow basin.docx
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Foldandfaultinteractionsduringthedevelopmentofanelongatednarrowbasin
Foldandfaultinteractionsduringthedevelopmentofanelongatednarrowbasin:
TheAlmanzoraNeogene-QuaternaryCorridor(SEBeticCordillera,Spain)
AntonioPedreraandJesúsGalindo-Zaldívar
DepartamentodeGeodinámica,UniversidaddeGranada,
Granada,Spain
CarlosSanzdeGaldeanoandÁngelCarlosLópez-Garrido
InstitutoAndaluzdeCienciasdelaTierra,CSIC,FacultaddeCiencias,UniversidaddeGranada,
Granada,Spain
Abstract
[1] Elongatedcorridorsgrowindifferenttectonicsettings,mainlyinareasdeformedbyfoldandfaultsetsparalleltotheborders.TheAlmanzoraCorridor,however,isagoodexampleofanE-Welongatedasymmetricalnarrowbasindevelopedinachangingstressscenario,generatedbytheinteractionoffoldandfaultsetsorientedparallelandobliquetothecorridorborders.TheinitialcrustalthickeningprocesswasmainlyrelatedtothedevelopmentoftheE-WorientedSierradeLosFilabreslargeantiform,whichconstitutesamajorheterogeneity.DuringtheTortonian,aNW-SEconvergenttectonicsetting,obliquetothisalreadyemergedantiform,givesrisetoalargedextralsimpleshearbandthatdetermines:
thedevelopmentofamajorfold(LasEstanciasantiform),theasymmetricallocationofminortectonicstructures(faultsandminorfolds),andthedistributionofsedimentation/denudationareasthatfinallyconfiguretheAlmanzoraCorridorsynform.Furthermore,developmentofNW-SEorientednormalfaultspointstoNE-SWorthogonalextensioninanewstressfieldobliquetothecorridorborders.Thisregionillustratesthattheelongatedcharacterofthecorridorsmaypersist,inheritedfromtheorientationofpreviouscrustalrheologicalheterogeneities.Inaddition,marinetransgressionmaybeproducedincompressionalsettings,favoredbythesynformdevelopmentduringinitialstagesofcrustalthickening,finallyledtothereliefuplift.
Received2April2007;revised26July2007;accepted20August2007;published9November2007.
Keywords:
folddevelopment,paleostressevolution,marinetransgression.
IndexTerms:
5475PlanetarySciences:
SolidSurfacePlanets:
Tectonics(8149);8005StructuralGeology:
Foldsandfolding;8004StructuralGeology:
Dynamicsandmechanicsoffaulting(8118);8031StructuralGeology:
Rheology:
crustandlithosphere(8159);8164Tectonophysics:
Stresses:
crustandlithosphere.
1.Introduction
[2] Longelongatedvalleysarecommonindifferenttectonicframeworks,wherefaultsorfoldswithdominanttrendsoccur.Fold-and-thrustbeltsdeveloporthogonaltothetrendofcompressionandproduceasuccessionofhighsandvalleys[e.g.,ClarkeandCarver,1992;Ferrièreetal.,2004].Thedepressedareascorrespondtothesynforms,andaregenerallyfilledbysediments.Inextensionalcontexts,thegeometryoftheelongateddepressionsisusuallycontrolledbynormalfaultsetsthatgrowperpendiculartotheminimumstressaxis,asintheBasinandRangeprovince[e.g.,Vargaetal.,2004],theAfricanriftzone[e.g.,Ebinger,1989;Chorowicz,2005]andtheAegeanregion[e.g.,Armijoetal.,1996;Pavlidesetal.,2006].Inareasdeformedbytranscurrentfaults,elongatedvalleysareorientedparalleltothefaulttracesthatconstitutethebasinboundaries,forinstanceintheCaliforniaregion[e.g.,Howelletal.,1980].Inareasofoverprintedfaultsandfoldswithdifferenttrends,however,thebasinsbecomediscontinuousandirregularlyshaped[e.g.,MatencoandSchmid,1999;Pedreraetal.,2006].Thedevelopmentoflargefoldsduringtheinitialstagesofcrustalthickeningmaypointtorheologicaldiscontinuitiesthatdeterminethegeometryofthelatertectonicdeformations.Whenstressesrotate,faultswilloccurpreferentiallysubparalleltothepreviouselongatedreliefsowingtotheinheritedanisotropy;yetotherstructuralassociationstakeplaceaswell,determiningthedevelopmentofcomplexelongatedcorridors.
Figure1. GeologicalmapofthecentraleasternBeticCordillera,showingdifferentdomainsandthemainfoldsandfaultsdevelopedsinceTortoniantimes.NotethatthesynformscoincidewiththeNeogene-Quaternarybasinposition.ThepositionofthetopographicprofileFigure7aismarked.
[3] ThereliefoftheBeticCordillera,locatedinthewesternmostpartoftheAlpineChain,isproducedbytheinteractionoffoldsandfaultsthataccommodatetheN-StoNW-SEconvergencebetweentheEurasianandAfricanplates[DeMetsetal.,1990](Figure1).SeveraldomainscanbedistinguishedintheCordilleraonthebasisoflithologicalandtectonometamorphicfeatures:
theInternalZones,mainlyformedbythreemajorcomplexesthatincludemetamorphicrocks,someofthemofPaleozoicage:
theNevado-Filábride,AlpujárrideandMaláguidecomplexes(generallynotaffectedbyAlpinemetamorphism);theFlyschUnits,whichareTertiarydetriticsedimentaryrocks,mainlyrepresentedinthewesternBetics[Egeler,1963;EgelerandSimon,1969];andtheExternalZones,essentiallymadeupofMesozoicandCenozoicsedimentaryrocks.
[4] DuringtheMiddleMiocene,fission-trackdataindicatetheextensionalexhumationofthemetamorphiccomplexesrelatedtotheactivityoflow-anglenormalfaults[Johnson,1997;Johnsonetal.,1997].Ontheotherhand,thefirstsedimentaryevidenceofemergedInternalZonessubjectedtoimportantdenudationprocessesisaredconglomeratealluvialandfan-deltaunit[e.g.,Bragaetal.,2003].Later,duringtheTortonian,E-WandESE-WNWrangesandbasinsstartedtodevelop,coincidingwithlargeantiformsandsynforms[Weijermarsetal.,1985;Galindo-Zaldívaretal.,2003;SanzdeGaldeanoandAlfaro,2004;Augieretal.,2005].DuringthelateMiocene,faultsdevelopedcoevalwithfolds,thusinteractingduringthebasinformation[Estévezetal.,1982;Ottd'EstevouandMontenat,1985;Stapeletal.,1996;Booth-Reaetal.,2004;Marín-Lechadoetal.,2006].TheNeogene-QuaternarysedimentarybasinsgeneratedonthepreviouslystructuredmetamorphicbasementsaresituatedindifferenttectonicframeworkswithintheBeticCordillera:
theyaregenerallytranscurrentintheEasternBetics[BousquetandMontenat,1974;BousquetandPhilip,1976;Bousquet,1979;SanzdeGaldeano,1983;Montenatetal.,1987;Weijermars,1987;Huibregtseetal.,1998],whilerelatedtonormalfaultsandfoldsinthecentralandwesternBetics[Ruanoetal.,2004;Rodríguez-FernándezandSanzdeGaldeano,2006].
[5] TheAlmanzoraCorridorisanE-Welongateddepression(average35kmlongand6kmwide)situatedintheeasternpartoftheBeticCordillera.ThenorthernborderofthebasinistheSierradeLasEstanciasrange,consistingofAlpujárriderocks.ThesouthernborderistheSierradeLosFilabres,formedbyAlpujárrideandNevado-Filábriderocks(Figure1).ThebasinsedimentaryinfillischaracterizedbysiliciclasticsedimentsfromtheSerravallian–earlyTortonianuptoQuaternary,includingmarineandcontinentaldepositsthatarestronglycontrolledbydifferenttectoniceventsandhavebeenthesubjectofpreviousresearch[BragaandMartín,1988;Martínetal.,1989;Guerra-MerchánandSerrano,1993].
[6] IntheAlmanzoraCorridor,thefoldandfaultinteractionconfiguresthebasingeometryanddeformsthesedimentssinceSerravallian–earlyTortonian.Intheadjacentsedimentarybasins,suchasHuercal-Overa
2.GeneralFeaturesoftheSedimentaryandChronostratigraphicSetting
2.1.LithostratigraphicSequence
Figure2. (a)SimplifiedgeologicalmapshowingtheNeogeneinfillingoftheAlmanzoraCorridor.Therosediagramsshowflowdirectionsdeducedfromthedipofimbricateclasts.IngreydiagramsfromGuerra-Merchán[1992],onlythediagramswithmorethan10measurementsareplotted.(b)Lithostratigraphicsequencesandcorrelation,modifiedfromGuerra-MerchánandSerrano[1993]andbasedontheproposalofBragaandMartín[1988]andMartínetal.[1989],inagreementwithMontenatetal.[1987]fortheNeogeneoftheeasternBeticCordillera.Fieldexamplesofsedimentarystructures,(c)imbricateclastsand(d)crossbeddinglocatedinthenorthbasinboundary,whichindicateaflowdirectiontothenorth.BeddingistiltedbythegrowthoftheLasEstanciasantiform.
[8] TheNeogeneinfillingoftheAlmanzoraCorridorismadeupofseveralunitsseparatedbyunconformities.ThelithostratigraphicsequenceconsideredinthisstudyisbasedontheproposalofBragaandMartín[1988]andMartínetal.[1989],takingintoaccountchronostratigraphicdatafromGuerra-MerchánandSerrano[1993];anditagreeswiththeproposalofMontenatetal.[1987]regardingtheNeogenehistoryoftheeasternBeticCordillera(Figure2).
[9] Thefirstunitisathick,red,continentalconglomerateformation,whichliesunconformablyonthebasement,andiswellrepresentedinthesoutherncorridorborderandintheeasternandwesternterminations.ThisunitcanalsobeobservedinotherareasoftheCordilleraandconsistentlycontainscoarsegrainedconglomeratesfromthemetamorphiccomplexesgradingintosandstones.Theconglomeratesarepoorlysortedingeneral,butsometimesshowinvertedverticalclastdistribution,coarseningupward.IntheGranadabasin,somefossilssupportaSerravallianage[Martín-Suárezetal.,1993],althoughotherauthorssuggestanearlyTortonianage,atleastforpartsoftheunits[Guerra-MerchánandSerrano,1993;Doyleetal.,1996].IntheAlmanzoraCorridor,thisunitisinterpretedascontinentalalluvialfandepositsgeneratedbythedenudationofthemountainfront.
[10] ThecontinentalSerravallian-lowermostTortonianredsiliciclasticdepositsareoverlainbygreymarineclays[BragaandMartín,1988]withintercalatedpatchree
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