The Goiás Massif: Implications for a pre-Columbia 2.2–2.0 Ga continentwide amalgamation cycle in central Brazil

Abstract

The Goiás Massif is a collage of Archean-Paleoproterozoic terranes that crop out in the central Brazil Northern Brasília Belt and acted as the continental margin onto which Neoproterozoic Brasiliano orogenic events took place. Most belts in the massif formed from 2.2 to 2.0 Ga, a widespread age bracket in the São Francisco-Congo Craton, pericratonic areas and other terranes associated with the formation of the “Atlantica Supercontinent”. However, the genesis of the Goiás Massif has always been a matter of debate due to a sharp crustal thickness contrast marked on surface by the trace of the Rio Maranhão Thrust and widely hypothesized as a suture zone. The hypothesis that this suture would have been formed when a microcontinent was accreted to the rest of the massif during the Neoproterozoic Brasiliano Orogeny is tested in this paper through mapping and zircongeochronology of rocks along the Rio Maranhão Thrust. Our study indicates that units contain Paleoproterozoic ages, have similar geological features to other Goiás Massif 2.2–2.0 Ga terranes and show no evidence of syn-collisional Neoproterozoic magmatism. We therefore reinterpret the available data to propose instead, that the amalgamation of the massif occurred fully in the Paleoproterozoic. First, the gravimetric contrast marked by the Rio Maranhão Thrust represents in fact a Neoproterozoic lower crust delamination event that affected both the Brasiliano Orogen and the terrane it was accreted against, the Campinorte Arc. Second, Serra da Mesa Suite Mesoproterozoic granites intruded both sides of the Rio Maranhão Thrust and thus, indicate the two domains were amalgamated prior to the Mesoproterozoic. Finally, Mesoproterozoic volcanic and plutonic rocks follow the trace of the Rio Maranhão Thrust, suggesting a reactivated intracontinental structure rather than an original product of Brasiliano collision. The Goiás Massif also show important similarities to the São Francisco Craton: a) orogen building and magmatism from 2.2 to 2.0 Ga; b) metamorphic peaks from 2.11 to 2.08 Ga; c) zircon age peaks at ∼1.76 Ga, ∼1.58 Ga and ∼1.2 Ga largely attributed to crustal extension events and d) contiguous seismic signature from massif to craton. These common features allied to our reassessment of central Brazil geochronology and the nature of central Brazil sharp crustal thickness contrast indicate that the Goiás Massif was fully assembled during a 2.2–2.0 Ga Orogeny as part of the western border of the São Francisco(-Congo) paleocontinent. A comprehensive understanding of this orogeny is vital to test the validity of Atlantica and to infer the landmasses later involved in the assembly of Columbia.