Relations of Hercynian metamorphism with magmatism and deformation in the Eastern Pyrenees. Implications for Hercynian evolution

Abstract

The Hercynian metamorphic evolution at different crustal levels of the Roc de Frausa Massif has been constrained relative to the deformation and intrusion of igneous rocks. The main deformation phase is considered to have been synchronous throughout the whole crustal section exposed. Intrusion of igneous bodies took place subsequently to deformation and overprinted the previously foliated texture of the country rocks. At shallow levels two metamorphic peaks are distinguished, viz. a regional one, synchronous with the main deformation, and a contact-metamorphic peak. At deeper levels and away from the intrusives the regional metamorphic climax is post-kinematic. Near the intrusives, the contact-metamorphic episode constituted the latest and highest temperature stage of a continuous prograde metamorphic evolution. The crustal evolution is characterized by a first compressive event at intermediate-pressure metamorphic conditions, followed by a post-tectonic event characterized by low-pressure - high-temperature metamorphism and ubiquitous magmatism. The first event is registered at shallow levels of the crust, whilst the second event is only recorded in exposures representing deeper crustal levels. The high-temperature metamorphism and magmatism could be a result of either the incorporation of mantle material into the lower crust subsequent to a thickening episode, or a subcrustal collapse of a previously thickened lithosphere.