Timing and role of the Maranhão River Thrust in the evolution of the Neoproterozoic Brasília Belt and Tocantins Province, central Brazil Luiz J.H. D’el-Rey Silva ⁎ , Marcos A.R. de Vasconcelos, Dângelo V.G. Silva Universidade de Brasília, Instituto de Geociências, Campus Darcy Ribeiro, Asa Norte, CEP 70910-900, Brasília-DF, Brazil Received 5 May 2007; received in revised form 11 July 2007; accepted 29 September 2007 Available online 13 October 2007 Abstract A low-angle thrust fault places high-PT granulites (hangingwall) of the Internal Zone of the Neoproterozoic Brasília Belt (Tocantins Province, central Brazil) in contact with a lower-grade footwall (External Zone) comprised of nappes of distal passive margin- and back-arc basin-related supracrustals. The footwall units were emplaced at ∼ 750 Ma onto proximal sedimentary rocks (Paranoá Group) of the São Francisco paleo- continent passive margin. The high-PT belt is comprised of 645–630 Ma granulite-facies paragneiss and orthogneiss, and mafic–ultramafic complexes that include three major layered intrusions and metavolcanic rocks granulitized at ∼ 750 Ma. These complexes occur within lower- grade metasedimentary rocks in the hangingwall of the Maranhão River Thrust, which forms the Internal Zone–External Zone boundary fault to the north of the Pirineus Zone of High Strain. Detailed lithostructural studies carried out in Maranhão River Thrust hangingwall and footwall metasedimentary rocks between the Niquelândia and Barro Alto complexes, and also to the east of these, indicate the same lithotypes and Sm–Nd isotopic signatures, and the same D 1 –D 2 progressive deformation and greenschist-facies metamorphism. Additionally, footwall metasedimentary rocks exclusively display a post-D 2 deformation indicating that the Maranhão River Thrust propagated through upper crustal rocks of the Paranoá Group relatively late during the tectonic evolution of the belt. Fault propagation was a consequence of intraplate underthrusting during granulite exhumation. The results allow for a better tectonic understanding of the Brasília Belt and the Tocantins Province, as well as explaining the presence of the Pirineus Zone of High Strain. © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Structural analysis; Sm–Nd isotopes; Rio Maranhão Thrust; Underthrusting; Brasília Belt; Tocantins Province; Brazil 1. Introduction Regional-scale faults and shear zones play key roles in the tectonic evolution of orogenic belts. These structures, com- monly also terrane boundaries, facilitate exhumation of high-PT rocks. Examples associated with Gondwanan high metamor- phic grade terranes are abundant (e.g., the Tenmalai shear zone, India; Ishii et al., 2006). However, most commonly the specific role of a major fault in the tectonic evolution of an area re- mains unclear until detailed field studies provide a satisfactory understanding (e.g. Ishii et al., 2006; Searle, 2006; Searle and Phillips, 2007). Types of information required to develop such an under- standing vary according to each geological situation. For exam- ple, the kinematics of regional shear zones linked to exhumed granulites in India have been re-assessed through detailed studies of pseudotachylites and fissure veins (Sarkar and Biswal, 2005), or also through the nature of felsic magmas emplaced during collision-related extensional episodes during amalgamation of Gondwana (Santosh et al., 2005). Contrasting isotopic signatures of rocks on opposite sides of a regional fault suggest the existence of a suture, such as what was described by Park et al. (2005) in Korea. Further examples of detailed studies on major faults and/or shear zones can be found in Acharyya (2003), Chetty et al. (2003), Rajesh and Chetty (2006), and Vijaya Rao and Rajendra Prasad (2006). In this study, we look at the characteristics of a low-angle regional fault (the Maranhão River Thrust) to better understand the Neoproterozoic evolution of the Tocantins Province in central Brazil. Available online at www.sciencedirect.com Gondwana Research 13 (2008) 352 – 374 www.elsevier.com/locate/gr ⁎ Corresponding author. Fax: +55 61 33474062. E-mail addresses: ldel-rey@unb.br, luizhomemsilva@yahoo.com.br (L.J.H. D’el-Rey Silva). 1342-937X/$ - see front matter © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2007.09.004