Mineralogical and bulk compositional records of an advective fluid flux event near the Variscan HT-LP metamorphic climax. Catalonian Coastal Ranges, NE Iberian Peninsula

Metamorphic rocks of the Osor complex (NE Iberian peninsula) show quartz-rich gneissic semi-pelitic, and quartz-absent, mica-rich, schistose domains that have been related to the effects of infiltration of a magmatic fluid evolved during cooling of syntectonic peraluminous leucogranites and pegmatites. The infiltrating fluid became progressively alkali-rich through leaching of these elements from the enclosing metamorphic rocks as it became progressively focused in developing micaceous, high-strain domains subparallel to the main crenulation cleavage. The flux took place around the peak of the HT-LP metamorphism during nearly isobaric heating followed by initially nearly isobaric cooling evolving towards decompressional cooling. Channels of focused flow became the loci of late- to post-tectonic Na-rich plagioclase, muscovite and biotite growth. The growth of the alkali-rich phases promoted further weakening of the domains that continued to be zones of high-strain during a late extension coeval with cooling and decompression.