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Evidence of multi-stage faulting by clay mineral analysis: Example in a normal fault zone affecting arkosic sandstones (Annot sandstones)

dc.rights.licenseopenen_US
hal.structure.identifierLaboratoire Chrono-environnement (UMR 6249) [LCE]
dc.contributor.authorBUATIER, M.
hal.structure.identifierEnvironnements et Paléoenvironnements OCéaniques [EPOC]
dc.contributor.authorCAVAILHES, Thibault
hal.structure.identifierLaboratoire Chrono-environnement (UMR 6249) [LCE]
dc.contributor.authorCHARPENTIER, Delphine
hal.structure.identifierLaboratoire Chrono-environnement (UMR 6249) [LCE]
dc.contributor.authorLERAT, Jeremy
hal.structure.identifierLaboratoire Chrono-environnement (UMR 6249) [LCE]
dc.contributor.authorSIZUN, Jean Pierre
hal.structure.identifierGéosciences Montpellier
hal.structure.identifierBassins
dc.contributor.authorLABAUME, Pierre
hal.structure.identifierCentre scientifique et Technique Jean Feger [CSTJF]
dc.contributor.authorGOUT, Claude
dc.date.accessioned2024-05-07T10:25:15Z
dc.date.available2024-05-07T10:25:15Z
dc.date.issued2015-06
dc.identifier.issn0191-8141en_US
dc.identifier.urihttps://oskar-bordeaux.fr/handle/20.500.12278/199698
dc.description.abstractEnFault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation
dc.language.isoENen_US
dc.subject.enFault
dc.subject.enArkosic sandstones
dc.subject.enClay minerals
dc.subject.enFoliation
dc.subject.enGouge
dc.title.enEvidence of multi-stage faulting by clay mineral analysis: Example in a normal fault zone affecting arkosic sandstones (Annot sandstones)
dc.typeArticle de revueen_US
dc.identifier.doi10.1016/j.jsg.2015.03.012en_US
dc.subject.halPlanète et Univers [physics]/Sciences de la Terre/Tectoniqueen_US
dc.subject.halSciences de l'environnement/Milieux et Changements globauxen_US
bordeaux.journalJournal of Structural Geologyen_US
bordeaux.page101-117en_US
bordeaux.volume75en_US
bordeaux.hal.laboratoriesEPOC : Environnements et Paléoenvironnements Océaniques et Continentaux - UMR 5805en_US
bordeaux.institutionUniversité de Bordeauxen_US
bordeaux.institutionCNRSen_US
bordeaux.peerReviewedouien_US
bordeaux.inpressnonen_US
bordeaux.import.sourcehal
hal.identifierhal-01172423
hal.version1
hal.popularnonen_US
hal.audienceInternationaleen_US
hal.exportfalse
workflow.import.sourcehal
dc.rights.ccPas de Licence CCen_US
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