Polymetamorphism in the Alpujarride Complex, Betic Cordillera, South Spain.

The pre-Alpine metamorphic history of basement rocks of the Alpine Betic-Rif orogen is still uncertain as a result of intense Miocene reworking. Reaction sequences and textures recorded in pre-Mesozoic quartz-K-feldspar-plagioclasebiotite-muscovite anatectic gneisses of the Upper Alpujarride units underwent a complex polymetamorphic history. U-Pb SHRIMP dating of magmatic zircons from coarse-grained porphyritic gneisses indicates an anatectic event at 286±11 Ma. Refractory pelitic enclaves (kyanite-rutile-andalusite-ilmenite-biotite-muscovite±staurolite, devoid of quartz and feldspars) included in the gneisses formed after partial melting of pre-Permian metasediments at relatively high pressure (P). This was followed by late Variscan decompression, producing andalusite at low P in the enclaves and the granitic gneiss. During the Alpine Orogeny, the enclaves were affected by diverse local reactions: (1) andalusite was transformed to Alpine kyanite from reactions catalyzed bymuscovite and biotite; (2) garnet coronas formed close to the gneiss, together with phengitic muscovite; and (3) Variscan biotite in contact with garnet reequilibrated under high/ medium-P and medium-temperature metamorphic conditions. This reaction sequence occurring in polymetamorphic rocks allows the unraveling of their polyorogenic history and the assignment of relative ages to minerals and mineral assemblages through integrated field, mineralogical, petrological, and geochronological analyses. [ABSTRACT FROM AUTHOR]