Muscovite recrystallization and saddle-shaped Ar/Ar age spectra: example from the Blond granite (Massif Central, France) |
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| Authors: | Pavel Alexandrov Gilles Ruffet Alain Cheilletz |
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| Institution: | 1 CRPG-CNRS, BP 20, 54501 Vandoeuvre Cedex, France
2 Géosciences Rennes, UMR CNRS 6118, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France |
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| Abstract: | Muscovites from the Blond granite (West French Massif Central) were dated by the 40Ar/39Ar single-grain method. The 40Ar/39Ar ages obtained vary from 305.5 ± 0.3 Ma to 311.3 ± 0.5 Ma, and most of the age spectra are slightly saddle-shaped. The analyzed muscovites show phengitic recrystallization under optical microscope observations, SEM images, and electron microprobe chemical analyses. It is proposed that the saddle-shaped age spectra result from a partial recrystallization, which produced three different isotopic reservoirs in the analyzed white mica single grains: domains of early muscovite, domains of neocrystallized muscovite formed by phengitic and Al-Fe substitutions, and “low-activation energy sites.” |
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