The passira anorthositic complex and associated granites: an example of the anorogenic magmatism (calymmian/statherian) event in the Eastern Borborema Province, NE Brazil

Abstract

The Passira Anorthositic Complex (PAC) is situated in Pernambuco State, Northeastern Brazil, within the Rio Capibaribe Terrain of the Borborema Province. Host rocks are rhiacian migmatitic gneisses. The PAC is a massif-type complex of batholithic proportions composed mainly of metamorphosed anorthosite, gabbro, norite, diorite and ultramafic lenses mineralized in Fe-Ti oxide minerals. A dyke swarm formed by apatite-rich ferro-diorite enriched in Zr, Ba and LREE, occurs around the complex. A multicrystal U-Pb zircon age of 1.70+0.02 Ga was obtained for the anorthosite, which is interpreted as|the age of crystallization. The associated granites (now orthogneisses) include metaluminous alkaline; sub-alkaline garnet-bearing and peraluminous types having anorogenic geochemical characteristics. They have U-Pb ages between 1.58±0.09 Ga and 1.68±0.09 Ga, obtained in zircon and monazite monocrystals by laser ablation mass spectrometry. The PAC and associated granites behaved as a tectonic unit during the Brasiliano-age deformations. The association was formed in Rio Capibaribe Terrain during an extensional event occurred at the Statherian-Callymian transition