Timing of Variscan mid-crustal shearing and batholith intrusion in the Central Pyrenees (Ariege, France)

Abstract

A gneiss body in the Variscan Aston massif is overlain by Cambro-Ordovician metasediments that have been intruded by a granite batholith. At the gneiss-cover contact a 1.2 km-thick zone of highly strained medium-grade metasediments occurs. The batholith is surrounded by a zone where metasediments are strained and metamorphosed due to intrusion of the pluton. This contact aureole overprints the shear zone at the gneiss-cover contact, showing deformation and retrogression of the medium-grade metasediments. This relationship reveals a younger age for batholith intrusion with respect to the formation of the shear zone at the gneiss-cover contact. This observation together with regional correlation indicates that formation of the shear zone occurred between 292 and280Ma ago.