Le Castillet syenites (Agly massif, Eastern Pyrenees, France): an unusual occurrence in the Pyrenees

Le Castillet syenites (Agly massif) are unusual rocks in the eastern Pyrene es made up of more than 95 % of potash feldspar and albite. These rocks are hosted in the Variscan Saint-Arnac granite and form small domes, the shape of which suggests an emplacement by magmatic stopping. Syenites and their closest host rocks suffered various hydrothermal alterations, the most obvi ous being transformation of biotite into muscovite + rutile. Discussion of the origin of these syenites is difficult because of those alterations: man y magmatic features :Ire well preserved but metasomatic transformation may have very much modified the primary rocks. (C) 1999 Academie des sciences.