The northwest-directed "Bretonian phase" in the French Variscan Belt (Massif Central and Massif Armoricain): A consequence of the Early Carboniferous Gondwana-Laurussia collision

Michel Faure (1, 2) , Xian-Hua Li (3) , Wei Lin (3)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Géodynamique - UMR7327
3 State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics

In the Variscan French Massif Central and Armorican Massif, the tectonic significance of a widespread NW–SE-trending stretching lineation, coeval with medium pressure–medium temperature metamorphism, is an open question. Based on a structural analysis in the southern part of the Massif Central, we show that this top-to-the-NW shearing is a deformation event, referred to as D2, which followed a D1 top-to-the-south shearing Devonian phase, and was itself re-deformed by a Late D3 Visean–Serpukhovian southward-thrusting event. We date the D2 phase at 360 Ma (Famennian–Tournaisian boundary). In the Armorican Massif, D2 is the “Bretonian phase” recorded in the metamorphic series and sedimentary basins. Geodynamically, D2 is related to a general northwestward shearing during the Laurussia–Gondwana collision, which occurred after the closure of the Rheic Ocean, as indicated by the emplacement of the Lizard ophiolitic nappe in Britain. The left-lateral Nort-sur-Erdre fault accommodated the absence of ductile shearing in Central Armorica.

Keywords: Bretonian phase; French Massif Central; Armorican Massif; Variscan belt

Domains: Sciences of the Universe [physics]; Earth Sciences

Michel Faure, Xian-Hua Li, Wei Lin. The northwest-directed "Bretonian phase" in the French Variscan Belt (Massif Central and Massif Armoricain): A consequence of the Early Carboniferous Gondwana-Laurussia collision. Comptes Rendus Géoscience, 2017, 349, pp.126-136. ⟨10.1016/j.crte.2017.05.002⟩. ⟨insu-01540215⟩