Structure, age and mode of emplacement of the Hercynian Bordères-Louron pluton (Central Pyrenees, France) |
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Authors: | Gérard Gleizes Gérard Crevon Asfawossen Asrat Pierre Barbey |
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Institution: | (1) CNRS-UMR 5563 LMTG, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France;(2) Department of Earth Sciences, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia;(3) CRPG-CNRS, B.P. 20, 54501 Vandoeuvre-les-Nancy Cedex, France |
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Abstract: | The Hercynian Bordères-Louron pluton (20 km2) in the Central Pyrenees intrudes Devonian and Carboniferous metasediments. It shows a concentric zoning and consists of a significant proportion of (quartz) gabbros in its periphery, and of granodiorites, biotite monzogranites and biotite-muscovite monzogranites in its core. AMS study shows that the pluton corresponds to an elongated dome with a N100°E-trending axis. The anisotropy intensity Ppara% is high in the south and in the core of the pluton, whereas it is low in the north. The shape parameter T indicates that the fabric is strongly planar in a large central band oriented NW-SE, whereas it is strongly linear in the western and eastern tips of the pluton. These characteristics suggest that the Bordères-Louron pluton emplaced in two episodes: (1) intrusion of mafic magmas along a N100°E sill parallel to the regional foliation of the host metasediments; and (2) injection of three successive silicic batches (granodiorite, biotite monzogranite, two-micas monzogranite) which pushed aside the early mafic injections. In situ U-Pb dating of zircon grains indicates that the emplacement age of the biotite monzogranite is 309 ± 4 Ma, synchronous with the D
2 dextral transpressive event and close to the ages of the eastern Pyrenean plutons, may be slightly older. |
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Keywords: | Granite emplacement Variscan Pyrenees Zircon U-Pb age Anisotropy of magnetic susceptibility Bordères-Louron |
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