Evolution of polycyclic basement complexes in the Aracuay Orogen, based on U–Pb SHRIMP

Abstract

Paleoproterozoic basement of the Arac¸ua´ı Orogen is composed of amphibolite and granulite facies orthogneiss units known as Mantiqueira and Juiz de Fora complexes. Six U–Pb SHRIMP crystallization ages for the Mantiqueira Complex range from 2137±19 to 2041±7 Ma. Studied samples are characterized by the abundance of inherited Archean zircon grains, TDM model ages ranging from 2.9 to 3.2 Ga, and strongly negative εNd(t) (−9 to −13). Gneiss protholits were mainly generated by partial melting of older continental material, and the Mantiqueira Complex is related to active margin and syn-collisional magmatism. High-grade gneiss samples of the Juiz de Fora Complex yields crystallization ages of 2119±16 and 2084±13, and inherited zircon grains are absent. This plutonic unit much probably evolved within an oceanic magmatic arc setting, or on a very stretched continental crust. The Mantiqueira and Juiz de Fora complexes, together with the Kimezian basement of the West Congo Belt, were parts of a Paleoproterozoic orogenic system disrupted and deeply reworked during the evolution of the Arac¸ua´ı–West Congo Orogen. Neoproterozoic metamorphic overprint is dated at ca. 590–574 Ma.