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Evidences for a « hot » regional-scale Cretaceous Na-Ca metasomatic event in the Pyrenees

Marc Poujol 1 Philippe Boulvais 1
1 Terre, Temps, Traçage
GR - Géosciences Rennes
Abstract : In the Pyrenees, a Na-metasomatic event dated between 117 and 98 Ma has been recognized and was related to the hydrothermal system associated with the transtensive displacement of the Iberian plate relative to Europe. A set of geochemical and geochronological data has been acquired on five new occurrences of albitized rocks, sampled both to the north and to the south of the North Pyrenean fault (NPF). These albitized rocks are associated with ductile shear zones, faults, or undeformed zones and were developed at the expense of various protoliths (granite, migmatized metasediments or migmatites). None of these samples are pure albite, but their chemical and mineralogical evolutions demonstrate they have undergone dequartzification and albitization and even a slight carbonatation (CaO > 4%). The oxygen isotope compositions show that each of them developed under a peculiar regime of fluid-rock interaction, during which either the temperature or the fluid-rock ratio may have been different. The temperature of the Na-Ca metsomatism, based on the presence of newly formed andesine and sillimanite is estimated to be above 550°C. U-Pb dating on titanite show that albitization took place between 110 and 92 Ma, ie a period comparable with the known ages for the LP-HT North Pyrenean metamorphism (110-85 Ma). Na and Na-Ca metasomatisms are now recognized in the Northern Pyrenees, both sharing a common spatial and temporal distribution suggesting that they are two complementary records of the same long-lasting hydrothermal event. In further detail, the Na-metasomatism is restricted to the north of the NPF and is slightly older than the Na-Ca metasomatism located both to the north and to the south of the NPF. Both the time constraints and temperature estimates suggest that the Na-Ca metasomatism is related to the low-P high-T North Pyrenean metamorphism, whereas the Na-metasomatism might be related to the talc-
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-01080828
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Submitted on : Thursday, November 6, 2014 - 12:53:35 PM
Last modification on : Tuesday, December 3, 2019 - 1:32:19 PM

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Marc Poujol, Philippe Boulvais. Evidences for a « hot » regional-scale Cretaceous Na-Ca metasomatic event in the Pyrenees. 24 ème Réunion des sciences de la Terre 2014, Oct 2014, Pau, France. pp.229. ⟨insu-01080828⟩

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