Uvá complex, the oldest orthogneisses of the Archean-Paleoproterozoic terrane of central Brazil

- We performed U-Pb zircon and whole-rock Sm-Nd dating of Uvá complex orthogneisses.
- The complex formed by two granitogenesis events lasting from ca. 3,1 to 2.9 Ga.
- Similar Nd model age (3.12-3.28 Ga) suggest similar mantle sources.
- The Uvá granitogenesis is ca. 150 m.y. older than any orthogneisses of the terrane.
- The Archean orthogneiss of Central Brazil are not coeval, but independent segments.

The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous part of the Tocantins Province, a large Brasiliano/Pan-African orogen of the South American Platform formed during the Brasiliano orogeny. The terrane amalgamated to the province during the late stages of the orogeny as a crustal segment consisting of six Archean orthogneiss complexes and five low-grade metamorphic, in part Paleoproterozoic (Rhyacian) greenstone belts. The Uvá complex is the southernmost orthogneiss association of the Archean-Paleoproterozoic terrane of central Brazil. New U-Pb LA-ICP-MS data from zircon crystals show that the complex formed at least during two magmatic stages. The older consists of polydeformed tonalite and granodiorite batholitic and diorite stock protoliths with igneous age of 3040 Ma to 2930 Ma. The youngest comprises tonalite, monzogranite and granodiorite tabular bodies formed between 2876 and 2846 Ma. As compared to the orthogneisses of the northern portion of the terrane, both the oldest and youngest granitogenesis stages of the Uvá complex are, in average, about 150 Ma older. This suggests that the northern and southern orthogneisses formed during different times as independent crustal segments, but when and why they amalgamated is still under investigation.