Gneiss domes and granite emplacement in an obliquely convergent regime: New interpretation of the Variscan Agly Massif (Eastern Pyrenees, France)
Published:January 01, 2004
Ph. Olivier, G. Gleizes, J.L. Paquette, 2004. "Gneiss domes and granite emplacement in an obliquely convergent regime: New interpretation of the Variscan Agly Massif (Eastern Pyrenees, France)", Gneiss Domes in Orogeny, Donna L. Whitney, Christian Teyssier, Christine S. Siddoway
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Like the metamorphic core complexes of the Basin and Range (United States), the gneiss domes of the west European Variscan range have been associated with large-scale extension. In particular, the development of the Agly Massif, a gneiss and micaschist dome in the eastern Pyrenees (France), has been related to N-S–directed, late Variscan or Cretaceous extension. However, new microstructural and kinematic investigations in the Agly Massif demonstrate that (i) there is no major detachment, (ii) the pervasive deformation associated with the early metamorphism indicates a southward vergence, and (iii) the numerous mylonitic bands observed at different levels of the section acted as gently dipping normal faults and display opposite shear senses on both northern and southern flank of the dome. Shearing on these bands caused a multi-kilometer–scale thinning distributed across the whole lithologic column.
Two new U-Pb zircon analyses yielded an age of 317 ± 3 Ma for a deformed granite from the core of the dome, and an age of 307 ± 0.4 Ma for a deformed granite emplaced in the micaschist cover. This suggests that two phases of magmatism occurred in the Agly Massif, the first prior to doming and the second during doming and the emplacement of the main Pyrenean plutons associated with a dextral transpressive phase. Therefore, the Agly gneiss dome formed in a transpressive regime and not in a late Variscan or Cretaceous extensional regime related to the collapse of a previously thickened crust.