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The Léon Domain (French Massif Armoricain): a westward extension of the Mid-German Crystalline Rise? Structural and geochronological insights

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Abstract

The Léon Domain in the NW part of the French Massif Armoricain is a stack of synmetamorphic nappes displaced from south to north in ductile conditions. From bottom to top, an orthogneissic basement is overthrusted successively by (1) a Lower Nappe of gneiss including mafic eclogites, (2) an Intermediate Nappe of biotite–garnet–staurolite micaschists with mafic blocks, and (3) an upper nappe made up of Neoproterozoic phyllites covered by unmetamorphosed Paleozoic sedimentary series. This microstructural study documents a polyphase evolution with firstly a top-to-the-N shearing, secondly followed by upright folding of the stack of nappes coeval with migmatization, and lastly, a dextral wrenching along the North Armorican Shear Zone associated with emplacement of synkinematic plutons. New U–Th/Pb chemical dating of monazites from biotite–garnet–staurolite micaschists, migmatites, and granitoids argue for 340–335 Ma, 335–327 Ma, and about 320 Ma ages for synthrusting metamorphism, anatexis, and wrenching, respectively. A metagabbro from Le Conquet yields a zircon LA-ICP-MS age of 478 ± 4 Ma, which corresponds to magma emplacement time. The Léon Domain is interpreted as a microcontinent separated from Armorica by the Le Conquet-Penzé suture to the south and east, and from Laurussia by the Rheic suture to the north. A possible correlation with the Mid-German Crystalline Rise of Central Europe is discussed.

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Acknowledgments

LA ICP MS analyses have been supported by the program “Cartographie géologique de la France au 1/50000” directed by P. Rossi in BRGM (Orléans, France). Constructive reviews by G. Eisbacher, M. Sintubin, and R. Greiling are greatly acknowledged.

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  1. ISTO Campus Géosciences, Orléans University, 1A Rue de la Férollerie, 45071, Orléans Cedex 2, France

    Michel Faure, Claire Sommers, Jérémie Melleton & Olivier Lautout

  2. BRGM, Av. Claude-Guillemin, 45060, Orléans Cedex 2, France

    Jérémie Melleton & Alain Cocherie

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  1. Michel Faure
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  2. Claire Sommers
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Correspondence to Michel Faure.

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Faure, M., Sommers, C., Melleton, J. et al. The Léon Domain (French Massif Armoricain): a westward extension of the Mid-German Crystalline Rise? Structural and geochronological insights. Int J Earth Sci (Geol Rundsch) 99, 65–81 (2010). https://doi.org/10.1007/s00531-008-0360-x

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