The tectonic evolution of the Neoproterozoic Brasília Belt, central Brazil: a geochronological and isotopic approach

Abstract

ABSTRACT:The Brasília Belt is one of the most complete Neoproterozoic orogens in western Gondwana. Rapid progress on the understanding of the tectonic evolution of the belt was achieved due to new U-Pb data, combined with Sm-Nd and Lu-Hf analyses. The evolution of the Brasília orogen happened over a long period of time (900 -600 Ma) involving subduction, magmatism and terrain accretion, as a result of the consumption of the Goiás oceanic lithosphere. Provenance studies, based on U-Pb zircon data, indicate that the sedimentary rock units record different tectonic settings and stages of the evolution of the orogen. The Paranoá and Canastra groups represent passive margin sequences derived from the erosion of the São Francisco Craton. The Araxá and Ibiá groups, however, have dominant Neoproterozoic detrital zircon populations, as young as 650 Ma, suggesting derivation from the Goiás Magmatic Arc. The Goiás Magmatic Arc represents a composite arc terrain, formed by the accretion of older (ca. 0.9 -0.8 Ga) intraoceanic island arc(s), followed by more evolved continental arcs. It extends for several thousand kilometers, from SW Goiás, through NE Brazil and into Africa. Metamorphism took place between 650 -630 Ma reflecting final closure of the Goiás Ocean and continental collision. KEYWORDS: Brasília Belt; Neoproterozoic; U-Pb geochronology; Sediment provenance. RESUMO: A Faixa Brasília é um dos mais completos orógenos Neoproterozoicos no Gondwana Ocidental. Durante os últimos dez anos, o rápido progresso no entendimento da evolução tectônica desse orógeno foi proporcionado pela produção de novos dados geocronológicos U-Pb SHRIMP e LA-ICPMS, combinados com análises Sm-Nd e Lu-Hf. Os dados demonstraram que a evolução da Faixa Brasília acontenceu ao longo de um prolongado intervalo de tempo (900 -600 Ma), envolvendo subducção, atividade ígnea e acreção de terrenos, como resultado do consumo da litosfera do oceano Goiás. Estudos de proveniência de sedimentos baseados em geocronologia U-Pb de minerais detríticos indicam que as unidades sedimentares da Faixa

Sedimentary provenance in the southern sector of the São Francisco Basin, SE Brazil

“…However, tracking whether these sources are located in the Brasília or in the Araçuaí Belt is not just a single task. The T DM ages between 1.3 and 2.1 Ga and ε Nd(550 Ma) values between -9.53 to -4.09 are compatible with the Sm-Nd signatures of igneous rocks from both the western Brasília (Pimentel et al 1999, Pimentel 2016) and the eastern Araçuaí belt (Pedrosa-Soares et al 2011). Our exclusively negative ε Hf(t) values do not help solve the question as they mainly point to sources with a long crustal residence time.…”

“…1.4 Ga and volcanoclastic rocks (Chaves et al 2013) with ages close to 1.2 Ga occur in the Espinhaço Supergroup. Detrital zircon populations within this interval age were also obtained in the Macaúbas Group (Babinski et al 2012) and in the Espinhaço Supergroup , Valeriano et al 2004, Chemale Jr. et al 2012, both of which are located in the eastern belt, and in the Paranoá, Canastra, Araxá and Ibiá groups of the western belt (Pimentel et al 2011, Pimentel 2016. These units could have been reworked and they possibly provided sediments to the São Francisco Basin.…”

“…Sources in the 1400-1050 Ma interval occur in the Mesoproterozoic basement of the Brasília Belt (Pimentel et al 1999, Pimentel 2016 and in the Araçuaí Belt. Zircon grains from crystal-tuff (Guadagnin et al 2015) were dated at ca.…”

“…1). Intriguingly, the timing of the deposition of most of the sediments is constrained to be younger than 560 Ma (Warren et al 2014, Paula-Santos et al 2015, which is much younger than the orogen's metamorphic peak (~630 Pimentel et al 1999, Pimentel 2016. As such, this represents early stages of subsidence in the basin.…”

“…Although the Brasília Belt has a wide range of magmatic rocks spanning through the Ediacaran, the plutonism dated at ca. 540 Ma is considered anorogenic (Pimentel 2016), meaning that refinements in the timing regarding the subsidence and filling of the São Francisco Basin still need to be done. Also, by ca.…”