Extensional tectonics in the Hercynian Armorican belt (France). An overview

Denis Gapais (1) , Jean-Pierre Brun (1) , Charles Gumiaux (2) , Florence Cagnard (3) , Gilles Ruffet (1) , Christian Le Carlier de Veslud (1)

1 GR - Géosciences Rennes
2 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

A synthesis of existing geological, structural and geophysical data shows that the south Armorican Hercynian belt was marked by syn-convergence crustal thinning and dextral wrenching that were in part coeval in late Carboniferous times. Our kinematic model is further supported by new structural data and 40Ar/39Ar ages on synkinematic leucogranites. Extension and strike-slip followed earlier crustal thickening and exhumation of high-pressure metamorphic units in late Devonian-early Carboniferous times. Crustal extension led to the development of core complexes cored by migmatites and crust-derived granite laccoliths. At this time, the South Armorican shear zone acted as a transfer zone separating the extending domain of South Brittany from the non-extending domain of Central Brittany submitted to dextral wrenching. The overall structural pattern and attached kinematics are compared with recent numerical models and illustrated by a 3D interpretative model that integrates geological and deep seismic reflection data (ARMOR 2 profile).

Mots clés: Strike-slip; Armorican massif; Convergence; Tectonics; Hercynian belt

Domaines: Planète et Univers [physics]; Sciences de la Terre; Tectonique

Denis Gapais, Jean-Pierre Brun, Charles Gumiaux, Florence Cagnard, Gilles Ruffet, et al.. Extensional tectonics in the Hercynian Armorican belt (France). An overview. Bulletin de la Société Géologique de France, 2015, 186 (2-3), pp.117-129. ⟨10.2113/gssgfbull.186.2-3.117⟩. ⟨insu-01140598⟩