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Relation entre magmatisme et métamorphisme Haute-Température Basse-Pression. Réexamen du massif de l'Agly (Pyrénées Orientales)

Abstract : The Agly massif undergone a high temperature - low pressure metamorphism which shows an apparent thermal gradient comparable to that of present-day volcanic zones (120°C.km-1). Such abnormal thermal gradients have given way to various hypotheses, including structural deformations (crustal thinning, delamination), or heat input due to a magmatic activity.The outcrops through the Agly massif allow the study of an apparently hiatus-free succession of metamorphic facies ranging from greenschists to granulites. The massif is composed of a basement of precambrian gneisses and cambrian orthogneisses. The basement is unconformably overlain by a paleozoïc sedimentary cover. The late-Carboniferous granitoïds, associated to mafic intrusions, are observed at all levels.We have used thermodynamic modelling and thermobarometric calibrations to revisited the thermobarometric data for both cover and basement rocks. Both methods provide consistent barometric results, 4,5 ± 0,5 kbar for the deepest parts of the massif and a hiatus in the range of 1,5 kbar between the basement and the cover. Post-peak reactions correspond to a decompression. A conductive thermal modelling of sills injection allow us to test the influence of various parameters on the heat flow through the crust modeled : thermal conductivity and heat capacity ; initial geotherm ; crust thickness ; metamorphic reactions ; timing, geometry, temperature and depth of sill injection. Crustal delamination, thinning or magma emplacement in the lower crust cannot reproduce the observed HT-LP metamorphic conditions, unless associated with magma injection at the depth corresponding to the one of the top of the Agly basement.
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Baptiste Tournaire Guille. Relation entre magmatisme et métamorphisme Haute-Température Basse-Pression. Réexamen du massif de l'Agly (Pyrénées Orientales). Sciences de la Terre. Université Pierre et Marie Curie - Paris VI, 2017. Français. ⟨NNT : 2017PA066476⟩. ⟨tel-01901258⟩

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