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 To cite this version: 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 implica- tions. Geophysical Research Letters, American Geophysical Union, 2001, 28 (19), pp.3769-3772. 10.1029/2001GL012964. hal-03124803 HAL Id: hal-03124803 https://hal.archives-ouvertes.fr/hal-03124803 Submitted on 1 Feb 2021 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 N E S 0 30km , I ,, i , ,i 22ø00,E Fig I. Structuralsketch map of northernPeloponnese. Thick half<lottedline: emergenceof the Gulf of Corinth detachmentfault. Hatchedlines: normal faults branching on the detachment.Grey areas:synrifi sediments;from dark to light grey:older to recentdeposits; dashed area: undivided synrifi series. White: mainly holocenealluvial fans.Dotted stripebetween Loutro and Corinth: middle and upperPleistocene stepped marine terraces. 1: XylokastroLoutrofault. 2: Valimi fault.A-B: sectionof Fig 2. 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 S I-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