Signification des âges ⁴⁰Ar/³⁹ Ar le long de détachements crustaux : exemples de l'île d'Ikaria (Cyclades, Grèce) et du massif du Tende (Corse alpine, France)

Abstract : Numerous studies have shown the impact of deformation on the K-Ar system, and therefore ⁴⁰Ar/³⁹ Ar ages. These studies often do not provide data characterizing deformation and are limited to a comparison of the ages obtained indeformed rocks and an undeformed protolith. The first part of this study thus consisted in studying the strain distribution at different scales and finely describing strain intensity gradients. The study focused on two granitic protoliths, associated respectively with a difference in age between the formation of the protolith and the age of the tectonometamorphic events that is low (<1 Ma ; Ikaria Island) or inversely high (> 240 Ma ; Tenda massif). In the firstcase study, deformation results in a 40Ar loss in K-bearing phases, interpreted as resulting from the reduction of diffusion domains sizes which is not accentuated by an increasing strain intensity. In the second case study, the 40Arinheritance of the protolith results in fluids and extraneous 40Ar circulation through the actively deforming structures,ages in phengite being increasingly older approaching the most localizing structures in some sections, while others behave in an opposite way, more in line with the progressive strain localization in time. For both cases, interpretation of ages obtained in the newly formed phases during deformation is ambiguous between cooling, crystallization and mixing, and requires a detailed examination of the data confronted with the possible closing temperatures.Interpretations indicate for the Ikaria case study a strain localization in less than 1-3 Ma along a second order gradient of about ten meters in thickness. Strain localization at the scale of a shear zone occurs more rapidly in the case of a post-orogenic exhumation of a MCC (~ 7 Ma) than in the case of the exhumation of continental material involved in a subduction prism (~ 14-10 Ma).
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Alexandre Beaudoin. Signification des âges ⁴⁰Ar/³⁹ Ar le long de détachements crustaux : exemples de l'île d'Ikaria (Cyclades, Grèce) et du massif du Tende (Corse alpine, France). Sciences de la Terre. Université d'Orléans, 2017. Français. ⟨NNT : 2017ORLE2027⟩. ⟨tel-01887525⟩



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