Fluid infiltration and melt loss in a syntectonic contact metamorphic aureole from the Variscan Eastern Pyrenees

摘要: Granulite-facies migmatites were formed in the inner contact aureole and in xenoliths in the Ceret Variscan gabbro-dioritic intrusion (Roc de Frausa Massif, Eastern Pyrenees). The gabbro-diorite was emplaced synchronously to a late deformation phase (D3) folding the main Variscan cleavage (S2). Four types of migmatites can be distinguished according to the structures observed at meso-to micro-scale with varied mineral associations and chemical compositions.Migmatites range from metatexites (patchy to stromatic) to diatexites (schollen to melanosomes), the latter mainly cropping out as xenoliths. Metatexites and schollen migmatites show well-foliated paleosomes that preserve the oldest structures and granular or weakly foliated neosomes. Melanosome rocks have granoblastic textures and retain a weak foliation. Mineral associations range from the seven-phase assemblage: bi+ cd+ gt+ sil+ pl+ Kfs+ qz in metatexites and schollen migmatites to the five-phase assemblage bi+ cd+ gt+ pl+ qz in melanosome rocks, with sillimanite present locally as inclusions in garnet or cordierite. Whole-rock composition of metatexites and schollen migmatites is similar to that of non-migmatitic metapelites of the surrounding area, which we have interpreted to be their protoliths. Metatexitic migmatites contain up to 68% SiO2. Silica content in melanosomes decreases down to 40% SiO2, accompanied by an increase in Al2O3 and MgO+ FeO. Thermodynamic modeling in the NCKFMASHTO system for a patchy, a schollen and a melanosome rock with different mineral associations provides P conditions around 5.5 kbar. As a first approximation to the causes of …