TECTONIC SIGNIFICANCE OF A MAFIC MÉLANGE IN THE PANGEAN SUTURE ZONE, SW IBERIA

Pangea formed in the Late Paleozoic by the closure of the Rheic Ocean, which resulted in the collision between Gondwana and Laurussia and is expressed by the Appalachian (North America) and Variscan (western Europe) orogenies. The Pangean suture zone is exposed in southwestern Iberia, where the South Portuguese Zone, a fragment of Laurussia, is spatially juxtaposed against para-autochthonous Gondwana. The suture zone is characterized by fault-bounded units of oceanic meta-sedimentary rocks, mélanges and mafic complexes. Despite the tectono-stratigraphic sequence being well known, a number of key units exist whose origin and evolution remains poorly understood, including the Peramora mélange, the deepest structural unit exposed in the core of a regional anticline.

Detailed geologic mapping of the Peramora mélange (exposed in south-western Spain) reveals a complex pattern of imbricated tectonic and sedimentary mélanges. Petrographic examinations show muscovite, actinolite and minor biotite (greenschist facies) aligned with the tectonic fabric, S-C fabrics and crenulation cleavage, indicative of multi-phase deformation. These tectonic fabrics are likely related to the Late Paleozoic oblique collision between the South Portuguese Zone and the Gondwanan margin. Geochemical signatures of the sedimentary rocks display a range in TiO_2, and Fe₂O₃ + MgO, and are consistent with derivation from both continental and oceanic arcs. Detrital zircon analyses of key samples will constrain the age of deposition of the sedimentary derived matrix of the mélange. Ar-Ar dating of micas that define the tectonic foliation and of amphibole in post-tectonic igneous dykes will further constrain the timing of deformation events. These data will help to deduce the age, origin, evolution and provenance of this mélange within the suture zone and contribute to a better understanding the processes involved in the formation of Pangea.