Precambrian Research 149 (2006) 197–216 Timing of crust formation, deposition of supracrustal sequences, and Transamazonian and Brasiliano metamorphism in the East Pernambuco belt (Borborema Province, NE Brazil): Implications for western Gondwana assembly Sergio´ P. Neves a,∗, Olivier Bruguier b, Alain Vauchez c, Delphine Bosch c, Jose´ Maur´ıcio Rangel da Silva a, Gorki Mariano a a Departamento de Geologia, Universidade Federal de Pernambuco, 50740-530 Recife, Brazil b ISTEEM, Service ICP-MS, Universit´e de Montpellier II, 34095 Montpellier, France c Laboratoire de Tectonophysique, Universit´e de Montpellier II, 34095 Montpellier, France Received 21 July 2005; received in revised form 10 January 2006; accepted 21 June 2006 Abstract The main structural feature of the central domain of Borborema Province (NE Brazil) is a network of dextral and sinistral shear zones. These shear zones rework an older, regionally developed, flat-lying foliation in orthogneisses and supracrustal belts, which in the East Pernambuco belt was formed under amphibolite facies conditions. This study reports LA-ICP-MS U–Pb zircon ages of metaigneous and metasedimentary rocks aiming to constraint the pre-transcurrent tectonothermal evolution in the Eastern Pernambuco domain. Ages of 2125 ± 7 and 2044 ± 5 Ma in a mafic layer of banded orthogneiss are interpreted as the age of the protolith of the orthogneiss and of high-grade Transamazonian metamorphism, respectively. The latter age is consistent with the occurrence of low Th/U, metamorphic zircon xenocrysts, dated at 2041 ± 15 Ma, in the leucosome of a migmatitic paragneiss. A granitic orthogneiss dated at 1991 ± 5 Ma reflects late to post-Transamazonian magmatic event. A similar age (1972 ± 8 Ma) was found in rounded zircon grains from a leucocratic layer of banded orthogneiss. Ages of detrital zircons in a paragneiss sample indicate derivation from sources with ages varying from the Archean to Neoproterozoic, with peak ages at ca. 2220, 2060–1940, 1200–1150 and 870–760 Ma. Detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665 Ma. Magmatic zircons with the age of 626 ± 15 Ma are found in the leucosome of a migmatitic paragneiss and constrain the age of the Brasiliano high-temperature metamorphism. A lower intercept age of 619 ± 36 Ma from a deformed granodiorite dated at 2097 ± 5 Ma and the crystallization age of 625 ± 24 Ma of the felsic layer of banded orthogneiss also confirm the late Neoproterozoic metamorphism. These results show that the present fabric in basement and supracrustal rocks was produced during the Brasiliano orogeny. Paleoproterozoic ages reported in this study are similar to those found in other sectors of the Borborema Province, the Cameroon and Nigeria provinces, and the Sao˜ Francisco/Congo craton. They show the importance of the Transamazonian/Eburnean event and suggest that these tectonic units may have been part of a larger, single continental landmass. Likewise, similarities in post- Transamazonian metamorphic and magmatic events in the Borborema, Nigeria and Cameroon provinces suggest that they shared a common evolution and remained in close proximity until the opening of the Atlantic Ocean. © 2006 Elsevier B.V. All rights reserved. Keywords: Laser ablation ICP-MS; Zircon U–Pb geochronology; Neoproterozoic belts; Transamazonian orogeny; Brasiliano orogeny ∗ Corresponding author. Tel.: +55 81 2126 8240; fax: +55 81 2126 8236. E-mail address: [email protected] (S.P. Neves). 0301-9268/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2006.06.005 198 S.P. Neves et al. / Precambrian Research 149 (2006) 197–216 1. Introduction Pajeu´ belt, Alto Moxoto´ belt and East Pernambuco belt (Fig. 1). There is broad consensus that most of western To improve knowledge and address the controversial Gondwana was already formed by 600 Ma. Continen- points above, zircon grains from samples from the East tal reconstructions for this period (e.g., Caby et al., Pernambuco belt were dated by laser ablation inductively 1991; Castaing et al., 1994; Trompette, 1997) show that coupled plasma-mass spectrometry (LA-ICP-MS). The the Brasiliano/Pan-African Borborema, Cameroon and aim of this study is threefold: (1) constrain the timing Nigeria provinces occupied a central position in relation of magmatic and metamorphic events and of deposition to the Amazonian and West Africa cratons, to the west, of supracrustal sequences, (2) compare its geological the Sao˜ Francisco/Congo craton, to the south, and the evolution with other regions in northeastern Brazil and Saharan metacraton (Abdelsalam et al., 2002), to the east with the Pan-African belts of Nigeria and Cameroon, and (Fig. 1). In the lack of paleomagnetic data, understand- (3) assess how these domains and surrounding cratons ing how and when this configuration was reached rely on pulled together to make up western Gondwana. geological and geochronological grounds. Knowledge of the tectonothermal history of the late Neoproterozoic 2. Geological setting belts is thus essential to evaluate possible correlations between adjacent (within individual provinces) and dis- 2.1. Regional geology tant (transcontinental) units and, therefore, to provide insights into the dynamics of amalgamation of western The Borborema Province is characterized by a com- Gondwana. plex network of large transcurrent shear zones (Vauchez The Precambrian crustal evolution of the Borborema et al., 1995; Fig. 1). In the central domain, a linked system Province has been much debated in recent years. Resolv- of E–W- to ENE–WSW-striking dextral and NNE–SSW- ing some critical pending issues is necessary to elabo- to NE–SW-striking sinistral shear zones is spatially rate continental reconstructions for the Neoproterozoic. associated with abundant granitic and syenitic plutons In the central domain, comprised between the Patos (Fig. 1B; Vauchez and Egydio-Silva, 1992; Guimaraes˜ and Pernambuco shear zone systems (Fig. 1), the most and Da Silva Filho, 1998; Ferreira et al., 1998; Neves and controversial issues are (1) the existence of a contrac- Mariano, 1999; Neves et al., 2000; Silva and Mariano, tional event in the early Neoproterozoic (Cariris Vel- 2000). A former shallow-dipping regional foliation is hos orogeny, ∼1 Ga; Brito Neves et al., 1995), and preserved in orthogneisses and metasediments outcrop- (2) whether or not terranes accretion took place dur- ping between the strike slip-related steeply dipping to ing this proposed orogeny. The suggestion of an early vertical mylonitic zones. The metamorphic grade under Neoproterozoic orogeny resulted from the discovery of which this foliation was developed differs between the 1000–900 Ma-old intermediate to felsic metavolcanic Cachoeirinha belt and the Alto Pajeu,´ Alto Moxoto´ and rocks and orthogneisses in the Alto Pajeu´ belt (Fig. 1; East Pernambuco belts. The Cachoeirinha belt consists Brito Neves et al., 1995; Van Schmus et al., 1995; of greenschist facies metapelites, metagreywackes and Kozuch et al., 1997; Brito Neves et al., 2000, 2001a; bimodal metavolcanics (Bittar and Campos Neto, 2000; Kozuch, 2003). Peraluminous orthogneisses intercalated Kozuch, 2003; Medeiros, 2004) deformed at relatively in the supracrustal sequence were interpreted as syncol- high pressures (6–9 kbar; Sial, 1993; Caby and Sial, lisional granites. Santos and Medeiros (1999) proposed 1997). Its low metamorphic grade stands in contrast with that the Alto Pajeu´ belt is one of four tectonostrati- that of the other three belts, which were regionally heated graphic terranes that amalgamated during the Cariris above 500 ◦C under low- to medium-pressures metamor- Velhos and Brasiliano orogenies to constitute the cen- phic conditions (Vauchez and Egydio-Silva, 1992; Bittar tral domain. Several authors (Mariano et al., 2001; and Campos Neto, 2000; Leite et al., 2000a; Neves et al., Guimaraes˜ and Brito Neves, 2004; Neves, 2003 and ref- 2000). erences therein) have, however, questioned the existence Orthogneiss complexes underlie large areas of the of the Cariris Velhos orogeny and the terrane accre- Alto Pajeu,´ Alto Moxoto´ and East Pernambuco belts. tion model, suggesting, instead, continuity between the They yielded U–Pb and Pb–Pb evaporation ages mostly proposed terranes since the Paleoproterozoic Transama- varying from 2.2 to 2.0 Ga (Santos, 1995; Van Schmus zonian orogeny. Therefore, in this paper, the following et al., 1995; Leite et al., 2000b; Brito Neves et al., non-genetic terms will be used to describe supracrustal 2001b; Melo et al., 2002; Kozuch, 2003; Neves et al., successions and orthogneisses occurring from west to 2004; Santos et al., 2004a), and Sm–Nd data indicate the east in the central domain: Cachoeirinha belt, Alto existence of Archean protoliths for some of these Pale- S.P. Neves et al. / Precambrian Research 149 (2006) 197–216 199 Fig. 1. (A) South America–Africa fit showing cratons and Neoproterozoic provinces of western Gondwana, and sketch highlighting main shear zones in Borborema Province. (B) Schematic geological map of eastern Borborema Province showing location of the studied area in the East Pernambuco belt (EPB) of central domain. Dashed lines highlight boundaries between the central and northern domains, and between the Cachoeirinha (CB), Alto Pajeu´ (APB) and Alto Moxoto´ (AMB) belts. PaSZ, Patos Shear Zone system; EPSZ, East Pernambuco Shear Zone system; WPSZ, West Pernambuco Shear Zone system. oproterozoic orthogneisses (Van Schmus et al., 1995;