%0 Conference Paper %F Oral %T Strain localization in shear zones during exhumation: a graphicalapproach to facies interpretation %+ Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO) %A Cardello, Giovanni Luca %A Augier, Romain %A Laurent, Valentin %A Roche, Vincent %A Jolivet, Laurent %< avec comité de lecture %B EGU General Assembly 2015 %C Vienne, Austria %I COPERNICUS %S Geophysical Research Abstracts %V 17 %N EGU2015-7578 %8 2015-04-12 %D 2015 %Z Sciences of the Universe [physics] %Z Sciences of the Universe [physics]/Earth SciencesConference papers %X Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shearzones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailedcharacterization and processes comprehension are far to be fully addressed. In this work, a graphic approach totectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), whichis mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite.Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, fromsyn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphicreactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frameof smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved withinlarge boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetricboudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed bychlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture isprogressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequenceof stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage.In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formedglaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tensiongashes that gradually evolve to blueschist shear bands. This process determinates the formation of smaller asymmetricsyn-blueschist boudins and is associated with epidote grain-size reduction, synonym of more intense strainlocalization. In the latest stage (3), newly formed chlorite-rich shear bands bound new boudins of the previouslyproduced terms having blueschist fine-grained heritage. Sense of shear is consistently top-to-the-ENE through theentire localization process. Greenschist-related boudinage is associated with quartz precipitation along the mainshear bands and at the necks of boudins, places of strain localization. Metamorphic reactions and transpositionsgradually obliterate the former texture, being progressively more active towards the top, where minor shear zoneshave been deforming at the expenses of similar folds and epidote-rich levels. The resulting qualitative analysismeans to be a proxy for further numerical models and a comparison to similar field-study areas. %G English %L insu-01291521 %U https://insu.hal.science/insu-01291521 %~ OBSPM %~ INSU %~ BRGM %~ CNRS %~ UNIV-ORLEANS %~ ISTO %~ OSUC %~ VOLTAIRE %~ PSL %~ OBSPM-PSL %~ ANR