New U-Pb zircon and Ar/Ar muscovite age constraints on the emplacement of the Lizio syn-tectonic granite (Armorican Massif, France) |
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Authors: | Romain Tartèse Marc Poujol Gilles Ruffet Philippe Boulvais Philippe Yamato Jan Košler |
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Institution: | aUMR CNRS 6118 géosciences, université de Rennes 1, 35042 Rennes cedex, France;bCNRS (CNRS/INSU), UMR 6118, géosciences Rennes, 35042 Rennes cedex, France;cDepartment of Earth Science and Centre for Geobiology, University of Bergen, 5007 Bergen, Norway |
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Abstract: | LA-ICP-MS U-Pb analyses performed on zircon grains from the Lizio granite yielded an emplacement age of 316 ± 6 Ma. Typical S-C structures show that the Lizio granite was emplaced contemporaneously with dextral shearing along the northern branch of the South Armorican Shear Zone and that it was therefore active at that time. 40Ar/39Ar analyses performed on muscovite grains yielded plateau dates ranging between 311.5 and 308.2 Ma. Muscovite chemistry is typical of primary magmatic muscovite, which precludes a late fluids-induced resetting of the K-Ar isotopic system. 40Ar/39Ar dates thus likely correspond to the cooling ages below the argon closure temperature. Considering the uncertainties on the measured ages, we can propose that either the Lizio granite cooled down quickly in less than a million of years or that it remained in a hot environment for several millions of years after its emplacement. This latter scenario could have been sustained by shear heating during dextral shearing along the northern branch of the South Armorican Shear Zone. |
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Keywords: | 40Ar/39Ar dating Armorican Massif Lizio granite South Armorican Shear Zone U-Pb dating France |
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