Attempt to Date Pleistocene Normal Faults of the Corinth-Patras Rift

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Attempt to date Pleistocene normal faults of the Corinth-Patras Rift (Greece) by U/Th Method, and tectonic implications Nicolas Flotté, Valérie Plagnes, Denis Sorel, Antonio Benedicto

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Nicolas Flotté, Valérie Plagnes, Denis Sorel, Antonio Benedicto. Attempt to date Pleistocene normal faults of the Corinth-Patras Rift (Greece) by U/Th Method, and tectonic implications. Geophysical Research Letters, American Geophysical Union, 2001, 28 (19), pp.3769-3772. 10.1029/2001GL012964. hal-03124803

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HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 19, PAGES 3769-3772, OCTOBER 1, 2001

Attempt to date Pleistocene normal faults of the Corinth- Patras Rift (Greece) by U/Th method, and tectonic implications NicolasFlott6 •, Va16riePlagnes a, Denis Sorel •, AntonioBenedicto •

Abstract. The Rift of Corinth is a major intra-continentalrill calculatedthe upliti rate of the terraces.Assuming that the controlledby a Pleistoceneand still active detachmentfault. uplift rate was similar lot the oldest,more uplitted lacustrine Its hangingwallcontains normal faults which have migrated synrift deposits,sedimentation in the early rill may have as evidenced by geomorphologic studies and by the startedroughly lMyr ago (Sorei, 2000). The age of the rift geometrical relations of the sedimentaryseries that they can be estimated in an other way: the total throw on the controlled successively.However, becauseof the lack of detachment is the sum of the throws on the successive normal paleontologicaldata in the continentalsynrift sediments,the faults, such as on the cross-sectionof fig.2. If the mean timing of this migrationis unknown.Theret0re, we attempted extensionrate duringthe rifting was similarto the presentday to date directly the faults using the U/Th methodon calcite rate determinedby GPS measurements(e.g. Billiris, 1991; crystallizations.Preliminary results reveal that this method Clarkeet al., 1998), this alsoindicates that the filling initiated may be a usefultool in neotectonics.In this first attempt,we 1Myr ago. studiedthe Xylokastro-Loutrofault and the Valimi fault. The In order to date more accuratelythe migrationof the normal age obtainedon post-tectoniccalcite of the first fault shows faults,we attemptedto usethe U/Th methoddirectly on fault- that it lockedat least 112.4 + 0.4ka ago. Syntectoniccalcite of relatedcalcites. It is assumedthat fluids commonlycirculate the Valimi fault yields an age of 382.0 + 31. I ka, showingthat and calcitecrystallises within faultsduring their activity(syn- the fault was still active at that time. Tectonicimplications of tectonic calcite) or after fault death (post-tectoniccalcite). these results are discussed. Measuring the U/Th isotopesin these calcites may give respectivelyan absoluteprecise age of activityor a minimum age of fault death.This approachappears to be moredirect .•_ _ _!• ..... L ß 1. Introduction than other geochronk,glcal •iudic• on ICI,LIIL• •LIL,,ii •,3 Co3•i•,- ray exposuredating (rOBe, 26A1, 36C!) of morphological The geometryof a rill can usuallybe preciselydescribed on featuresdisplaced by the faults (e.g. Ritz et al., 1995), U- the basis of field observationsand subsurthcegeophysical seriesnuclides adsorbed by detrital materialsin fault (Szabo data. But the reconstruction of its structural evolution is more and Rosholt, 1989) or K/At dating of synkinematicillite in problematic:one needsto know preciselythe geometricaland fault gouge(Zwingmann et ai., 2001). Here, we presentthe chronologicalrelationships of the rill sedimentaryinfiil, and first results obtained on two faults, and their tectonic an accuratepalaeontological timing of thesedeposits. In the implications. Corinth-Patrasrill, most of the older synritt series,which are Faultsare usuallymore or lessthick zonescontaining several now uplitied in the northernPeloponnesus, are untOrtunately slip surfaces,which are not necessarilysynchronous. In the lacustrineand devoid of significant stratigraphictOssils. studiedarea, the sampledfaults are thin zones,often limited TheretOre,most authorsspeculated that rifting might have to one major slip surface;they .juxtapose relatively competent startedduring the P!ioceneor eventhe Miocene(e.g. Dufaure, Mesozoic limestones and much weaker Pleistocene sediments 1975; OFF,1989). Seismologicalstudies in the westernrill with a visible throw of several hundred meters to more than showthat the major activestructure is a low angledetachment one kilometer. TheretOre, most of the detOrmation occurred fault (Rigo, 1994). The outcrop of this detachmentin the on the major fault planewhich hasbeen sampled, and the age northern Peloponnesushas been recognized(Sorel, 2000). obtainedis likely representativeof the fault zone. During its evolution, steeper normal faults successively To datea smallsample t?om such a zoneand compareits age branched on the detachment t¾om the south to the north, to the age of cessationof motionseems to be themore direct localizingprogressively more-northern basins. In the younger way to approachthe absolutetiming of the structural part of the series,marine intercalations occur. These marine evolutionin continentalsettings. ingressionshave built a spectacularflight of steppedmarine terraces(fig. l), which reach highs of up to 700m between Corinth and Xylokastro (e.g. S0btier, 1977; Dufaure and 2. Descriptionof the sampledfaults Zamanis, 1980). Using the altitudesof the marine terraces Followinga detailedfieldwork and structuralmapping, we shorelinesand their ages, Keraudren and Sorel (1987) sampledthe Xylokastro-Loutrofault that we presumerecent andthat couldbe still activeaccording to Armijo et al. (1996), and the Valimi fault locatedmore to the southand likely older (fig.•). IUMR8616, Universit6 ParisXI-Orsay, France The footwall of the Xylokastro-Loutrofault is a c.a. 1,000 m 2LaboratoireSciencesdu elimat etde l'environnement, CNRS,F- high Mesozoiclimestones mountain. Between the fault and 91198 GiftYvette,France. the shorelineof the gulf, its hangingwallconsists of a thick Copyright2001 by the AmericanGeophysical Union. seriesof Pleistocenewhite sandymarls, which accumulated duringthe subsidence of thehangingwall. This series has been Papernumber 2001GL012964. later uplifted, and is notchedby three regressivestepped 0094-8276/01/2001GL012964505.00 marine terraces.The sampled segment(along the Loutro-

3769 3770

Inactive normal j fault ion GULFCORINTH • Activenormalfault f Detachmentfault l'l'l-l-l.l.l.l.l. Xylokastroterraces marine

Xyloimstro-Loutrofault

fault

0 30km , I ,, i , ,i

22ø00,E

Fig I. Structuralsketch map of northernPeloponnese. Thick half

Korfiotissaroad) is about 5km long; the offset is more than indicatingthat the fault was locked when the karsticconduit I km and can be consideredas one of the mostrepresentative. formed. Thus this calcite seals and post-datesthe fault A largeexhumed fault plane,several hundred meters in size activity.Two sampleswere collectedR)r U/Th analyses. (fig. l), is exposednear a lacustrinetravertine limestones The Valimi fault is an inactive t3.ult, located farther south quarry. Large grooves and corrugationsindicate a N-S (fig. I). Its footwall consistsof Mesozoic limestones.In its trendingextension. On a nearby outcrop,a karstic conduit hangingwallhave accumulated more than I km of syntectonic filled with a 3cm thick crystallinecalcite mat crossesthe fault seriesof freshwatersandy marls and conglomerates.To the plane.This mat is characterisedby fibrousundeformed calcite north, this series is offset by younger faults, likely crystals perpendicularto the conduit's surface (Fig.3-a), synchronouswith the Xylokastro-Loutrofault. Moreover,the

s N Valimi fault GULF Helike OF CORINTH

5 km

Fig 2. Syntheticcross-section in the Krathis valley (localisation A-B on Fig 1). Samelegend as Fig 1. . 3771

Fig 3. Picturesof thedated samples. 3a: post-tectoniccalcite of Xylokastro-Loutrofault. Stalagmite- like elongatedcalcite crystals perpendicular to the conduitsurface. Sub•amples were collected in the lesscoloured parts in orderto avoiddetrital contamination. S l-a is closeto the wall. Its ageshould be closerto the fault lock. S I-b is locatedhigher and thus shouldbe youngerthan SI-a. This is confirmedby U/Th dating.3b: syn-tectoniccalcite sampled on the Valimi fault. It is mixed with brecciated limestones of the •)otwall.

series is discordantlyoverlain by conglomeratesrelated to The two sub-samplesof post-tectoniccalcites ti'om the theseyounger faults. The Valimi fault is theretbreolder than Xylokastro-Loutrothult (SI-a and S l-b) give homogeneousU the Xylokastro-Loutrolhult. It is a major simple thult contents(0.55-0.89 ppm) and 234U?38U activity ratios (2.12- characterisedby a fault brecciasmade of clastsof substratum 2.13). Respectivecalculated ages are: ! ! 2.4 + 0.4 ka and cementedby white isometriccalcite (tbllowing the definition 108.2 + !.0 ka. Sl-a is older than Sl-b, these ages being of Ramseyand Huber, 1983) (Fig.3-b). The limestonesof the consistentwith the growth of the calcite mat (Fig.3a). tbotwallare devoidof calciteveins, so thatthe crystallisations Consistencyof these resultssuggests a geochemicalU-Th are clearly associatedwith the damagezone. A microscopic system remainedclosed t?om the time of crysta!lisation. study indicatesthat the calcite is twinned and a slightly Therefore, calculated ages may be consideredto be of broken, indicating that the t•ult was still active atier the geologicalsignificance. crystallisationof the calcite. Thus the sampledcalcite is Syn-tectoniccalcite t¾om the Valimi fault (S2) yields an age synchronous with the fault activity. Patches of this of 382.0 + 31. ! ka. In the lack of a secondsample, we cannot syntectoniccalcite stuck on the t•ult planehave been sampled ascertainthat the geochemicalsystem remained closed. and calcitegrains have been carefullysorted t¾om Mesozoic limestonesclasts for U/Th analysis. 4. Tectonic implications

3. U/Th method & results Our resultssuggest that the Xylokastro-Loutrothult is locked sinceat least! 12 ka. This is in agreementwith geologicaland The U/Th datingmethod, described in Ivanovichand Harmon geomorphologicalobservations along this t•ult system.For (1992), is usually applied on middle and upper Pleistocene instance,above Kamaresvillage, the c.a. 200m strandlineof corals(Barnes et al., 1956), mollusksshells (Kaut•nan et al., the highestmarine terrace notches the fault planeand cuts into 1971), or speleothems(Rosholt and Antal, 1962). A detailed the footwall limestones. This terrace, which seals the fault descripti•)nof theanalytical process used in thiswork is given activity, is laterallyequivalent to one of the steppedterraces in Part 6. eastof Xylokastrothat has beenattributed to the 5.5 marine Isotopicratios were measuredusing a Finnigan262 Thermo- isotopicstage (125 ka) by Keraudrenand Sorel(1987). IonisationMass Spectrometer(TIMS) in the Laboratoiredes Seismologyand field observationsindicate that the normal Sciences du Climat et de l'Environnement of the CEA/CNRS faults located south of the Xylokastro-Loutrot•ult are (Gif-sur-Yvette, France).Analytical resultsare presentedin inactive. The recent and active extension across the Corinth Table I. rill, at a rateof 1-1.5cm.yr '• (Clarkeet al., 1998),should

Table1. TIMS U-Thresults and age estimates from calcite samples. & is theapparent 23øTh/234U age. Errors are calculatedbyerror propagation andgiven at 20 level.23øTh/234U ratiosare activity ratios calibrated toHU! assumedtobe atsecular equilibrium. Ages Ao have been corrected ibr2•0' Th-excessdueto detrital material mixed with calci'te, even if all2_t -øTh/ 232 Th activity ratios are higher than 100. A• are corrected ages,us•ing thehypothesis ofan initial 230-' Th/- 232 Th = I (Causseand Vincent, 1989). Decay constants used: * 230Th=9.1953 , 10,•/-6 34 U=2.8338 , 10-6 ,*' 238 U=!.55125 , 10-10 .

i...-. :..:.... : :-' -.. ' ...... :•?.Si•-...... :"'•_ .... 1.• '0'.•6•)•.00062,!227•-0.•39 0.69•/•"0022 112,907 1.40 . 1•2•? 0,412 ';•4.;•.•....:'8•)5•:•;' l.$, •0.5485+/-0,0007...2.1312+/-0.0085...0.6½88+/-0.0052!08.535208 .... 1•17:•, 0.979 .se .10.]00]+/-0.0002. 3].]4 3772 FLOTTI• ET AL.' ATTEMPT TO DATE PLEISTOCENE NORMAL FAULTS OF THE CORINTH-PATRAS RIFT

therefore be accommodated on an active thult located thrther AcknowledgmentsWe thank C. Caussefor her activecontribution north (eventuallythe ofl•;horeeastward prolongation of the to the analysisand to the ideasdeveloped in thiswork. Helike thult). This is also supportedby the uplitt of the Kamaresand Xylokastroterraces for the last 125 ka at least, References duringwhich they are locatedin the tbotwallof this active normal fault. Armijo, R., B. Meyer, G.C.P. King, A. Rigo, D. Papanastassiou, Quaternaryevolution of theCorinth Rift and its implicationsfor The 382.0 + 31.1 ka age obtainedon the Valimi fault agrees the late Cenozoic evolution of the Aegean,Geophy.J. lnt., 126, with the data indicatinga Pleistoceneage of the Corinth- ! !-53, 1996. Patras rill recalled above, rather than with older ages Barnes,J.W., E.J. Lang, H.A. Potratz,Ratio of ionium to uranium proposedtbr the initiationof titling by differentauthors (e.g. coral limestones,Science, 124, 175-176, 1956. Billiris, H., D. Paradissis,G. Veis, P. England,W. Featherstone,B. Dut3,ure,1975; Ori, 1989,Armijo et al., 1996). Parson,P. Cross,P. Rands,M. Rayson,P. Sellers,V. Ashkenazi, M. Davison,J. Jackson,N. Ambraseys,Geodetic determination of 5. Discussion tectonic deformation in central Greece from 1900 to 1988,Nature, 350, 124-129, 1991. The preliminaryresults presented here suggest that the dating Causse,C., J.S. Vincent,Th/U disequilibriumdating of middleand late Pleistocenewood and shelf from Banks and Victoria islands, of Pleistocenefaults by TIMS basedon the U-seriescan be a Arctic Canada,Canadian journal of Earth Sciences,26, 2718- strong useful tool in neotectonicsanalysis, especially in 2723, 1989. continentalsettings where paleontologicaldata are scarce. Clarke, P.J., R.R. Davies, P.C. England, B. Parsons,H. Bi!!iris, D. However, care must be taken in using ages obtainedfor the Paradissis,G. Veis, P.A. Cross, P.H. Denys, V. Ashkenazi,R. syntectoniccalcite as absolutetracers of the fault activity or Bingley, H.G. Kahle, M.V. Muller, P. Briole, Crustal strain in death becausesyntectonic calcite may have /brmed at any central Greece from repeatedGPS measurementsin the interval 1989-1997,Geophys. ,1. lnt., 135, 195-214, 1998. time between the initiation and the lock of the thult. The Dufaure, J.J., Le relief du P61oponn•se,Thesis, Universit6Paris IV, throws on the faults of the Corinth-Patras rift can reach l km 1422 pp, 1975. or more. But calcite which formed early during the thult Dufaure, J.J., A. Zamanis, Styles n6otectoniqueset 6tagementsde activity may be deslroyedduring the later slip. It is more niveaux matins sur un segmentd'arc insulaire, !e P61oponn•se, likely that the syntectoniccalcite patchessamples tbrmed Proc. Colloquiumon Niveaux matins et tectoniquequaternaire dans!'aire mdditerran6enne,University of Paris1,1980. lately duringthe fault activity. If we assumethat'(l) the 1.5 Kaufman, A., W.S. Broecker, T.L. Ku, D.L. Thurber, The status of cm/yr extensionrate measuredby GPS method(Clarkeet al., U-seriesmethods of dating molluscs,Geoch. et Cosmoch.Acta, 1998) has been constant during the rifting, and (2) total 35, 1155-1183, 1971. horizontal extension calculated from cross-sections on the Keraudren, B., D. Sorel, The terracesof Corinth (Greece)- a detailed record of eustatic sea-level variations during the last 500,000 Valimi thult systemis 4km, then the Valimi thult shouldhave years,Marine Geology,77, 99-I 070, 1987. initiated670-700 ka ago. Ori, G.G., Geologichistory of the extensionalbasin of the Gulf of The results presentedhere are being completed by new Corinth (?Miocene-Pleistocene),Greece, Geology, 17, 918-921, datingson the Xylokastro-Loutrothult, on the Valimi thult 1989. and other faults. In parallel, a microstructuralanalysis and Ramsey,J.G., M.I. Huber, in The techniquesof modernstructural geology,Strain analysis, vol. 1, AcademicPress, London, 1983. fluid characterisationare being performed. Applying this Rigo, A., Etude sismotectoniqueet g6od6siquedu golfe de Corinthe method to several t•tults of the rill should enable us to (Gr•:ce), Ph.D. Thesis, Universityof Paris VII-IPGP, 281 pp, determinemore preciselythe timing of the thult migration, 1994. lateralthult propagations, and theretbre to betterunderstand Ritz, J.F., E.T. Brown, D.L. Bourl•:s,H. Philip, A. Schlupp,G.M. the rifting evolution. Raisbeck,F. Yiou, B. Enkhtuvshin,Slip rates along active faults estimatedwith cosmic-rayexposure dates: Application to tohe Bogdfault, Gobi-A!ta¾, Mongolia, Geology, 23, 1019-1022,1995. 6. Annex: Analytical U/Th procedure Rosholt, J.N., P.S. Antal, Evaluation of the 231Pa/U-230Th/U methodfor datingPleistocene carbonate rocks, US Geol. Survey Samplesof lessthan 2-gramswere combustedat 900øC for i ProfessionalPaper, 450-E, 108-11I, 1962. hour to oxydiseall organicand mineralcompounds present in S6brier,M., Tectoniquer6cente d'une transversale /• !arc6g6en. Le golfe de Corinthe et ses r6gions p6riph6riques,Ph.D. Thesis• the calcite.Next, the sampleswere dissolvedin HC! (6N) in Universit6Paris XI-Orsay, 137 pp, 1977. teflonbeakers containing a measured amount of mixed233U- Sorel, D., A Pleistocene and still-active detachment fault and the 236U-22øThspike already dried. The sample-spikemixture origin of the Corinth- Patr,asriff, Greece,Geology, 28, 83-86, (with a carrier FeCI3) was !eti on a hot plate overnight to 2000. Szabo, B.J., J.N. Rosholt, Uranium-series nuclides in the Golden ensurecomplete ionic equilibrationwith the spike solution. fault, Colorado, U.S.A.: dating latest thult displacementand Then, coprecipitationwith NH4OH (pH = 7) separatesU and measuringrecent uptake of radionuclidesby faultzonematerials, Th from mostof Ca. The developmentof the precipitateswas Appl. Geochem.,4, ! 77-182, 1989. ensured overnight. U and Th of these precipitateswere Zwingmann,H., W. Tanja, O. Robin, K/At dating of synkinematic separated using Dowex anion exchange resin (IX8) Illite in fault gouge,EUGXI, 2001. conditionedwith HC! 6N. Then, U andTh were purifiedusing Eichrom resins(Uteva and Teva respectively)conditioned by HNO3 3N. U and Th tYactionswere loadedonto pre-outgassed singlethenlure filaments with graphitecoating and the isotope (ReceivedFebruary 2, 2001' revisedMay 21, 2001' acceptedJune ratioswere measuredin the spectrometer. 27,2001.)