Precambrian Research 175 (2009) 187–205
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Precambrian Research 175 (2009) 187–205 Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres The age distributions of detrital zircons in metasedimentary sequences in eastern Borborema Province (NE Brazil): Evidence for intracontinental sedimentation and orogenesis? Sérgio P. Neves a,∗, Olivier Bruguier b, José Maurício Rangel da Silva a, Delphine Bosch b, Vanja Coelho Alcantara a, Cristiane Marques Lima a a Departamento de Geologia, Universidade Federal de Pernambuco, 50740-530 Recife, Brazil b Géosciences Montpellier, Université de Montpellier II, 34095 Montpellier, France article info abstract Article history: Detrital zircons in metasedimentary rocks attributed to three different complexes in the Central and Received 14 April 2009 Pernambuco-Alagoas domains of the Borborema Province, northeastern Brazil, were dated by LA-ICP- Received in revised form 4 September 2009 MS. Two samples from each of the following complexes were analyzed: Sertânia and Surubim, in the Accepted 20 September 2009 Central Domain, and Rio Una, in the Pernambuco-Alagoas Domain. One sample of the Sertânia Complex yielded only Paleoproterozoic zircons, whereas Neoproterozoic zircons predominate in the other, with the Keywords: youngest zircon indicating deposition after 642 Ma. One of the samples of the Surubim Complex yielded, Laser ablation ICP-MS again, only Paleoproterozoic concordant zircon ages. In the other sample, although Paleoproterozoic Detrital zircon geochronology Metasedimentary belts zircons predominate, ages vary from the Mesoarchean to the Neoproterozoic. The age of the youngest Provenance zircon in this latter sample indicates deposition after 850 Ma and an overgrowth on an Archean grain Brasiliano orogeny yielded an age of 623 ± 6Ma(2), interpreted as the age of peak metamorphism. The two samples of the Continental reconstructions Rio Una Complex yielded predominantly detrital zircons with ages in the ranges 2.2–2.1 Ga and 1.7–1.6 Ga. In this complex, the youngest detrital zircon suggests deposition after 917 Ma and metamorphic zircons indicate peak metamorphic conditions between 600 Ma and 617 Ma. The results of this study, together with available data from the literature, allow the following conclu- sions: (a) The Sertânia Complex is a Neoproterozoic sequence, and not Paleoproterozoic, as previously thought; (b) The similarity in lithological associations, detrital zircon populations and C isotope signature between the Sertânia and Surubim complexes suggest that they belong to the same lithostratigraphic unit; (c) Although the Rio Una Complex can be older than the Sertânia/Surubim Complex, the lack of zir- cons younger than 900 Ma can also result from insufficient sampling or absence of young rocks alongside the drainage system that collected detritus to this complex; (d) The regional metamorphism related to the Brasiliano Orogeny attained its climax at 630–600 Ma; (e) The age spectra of detrital zircons require their derivation from erosion of rocks formed not only during known geological events in the Borborema Province and in the nearby São Francisco/Congo Craton, but also from the Amazonian Craton, suggest- ing accumulation in an intracratonic setting within a preexisting large continent; (f) The short timespan between deposition and orogenic deformation may explain the overall medium- to high-temperature metamorphism due to maintenance, in the subsequent compressional event, of the elevated geothermal gradients produced during broad-scale lithosphere extension. © 2009 Elsevier B.V. All rights reserved. 1. Introduction age(s), provenance and metamorphism of its diverse supracrustal belts. These data will allow comparisons and correlations to be The Borborema Province, northeastern Brazil, occupies a cen- made both across the province and with other Neoproterozoic tral place in western Gondwana (Fig. 1). Therefore, understanding provinces and cratons in western Gondwana, and will place more its tectonic evolution is crucial to place constraints on conti- robust constraints on geodynamic models of tectonic evolution. nental reconstructions, which requires knowledge of deposition For instance, did western Gondwana grow by amalgamation of several disparate crustal fragments or did it result from rework- ing of a previous continent? In the latter case, was this continent ∗ Corresponding author. Tel.: +55 81 21268240; fax: +55 81 212618234. part of the Columbia and/or Rodinia supercontinents? Answers to E-mail address: [email protected] (S.P. Neves). these questions require consideration of the large tracts of Archean 0301-9268/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2009.09.009 188 S.P. Neves et al. / Precambrian Research 175 (2009) 187–205 Fig. 1. (a) Sketch map of western Gondwana showing the distribution of the main cratons and Brasiliano/Pan-African belts. (b and c) Contrasting views on the late Neopro- terozoic paleogeography of western Gondwana. (b) Interpretation according to which extension within a preexisting continent (Atlantica) was followed by convergence and intracontinental reworking with minor or no consumption of oceanic lithosphere (Neves, 2003). (c) Interpretation according to which large oceans with intraoceanic volcanic arcs separating cratons and microcontinental fragments closed around 600 Ma (Cordani et al., 2003). Abbreviations: A, Amazonia; BNC, Borborema-Nigeria-Cameroon; CG, Central Goiás; K, Kalahari; LA, Luís Alves; PA, Paraná; RP, Rio de La Plata; SA, Sahara Metacraton; SCC, São Francisco/Congo; WA, West Africa. and Paleoproterozoic crust, and their supracrustal cover, present in mentary successions deposited in an extended continental domain, northeastern Brazil (Borborema Province) and central and northern perhaps with small intervening ocean basins (Neves, 2003; Neves Africa (Nigeria, Cameroon and Hoggar provinces). This is generally et al., 2004, 2006a; Van Schmus et al., 2008). In this latter case, not contemplated in the most recent paleogeographical reconstruc- a (para)autochthonous setting is implied. Until the nineties, ages tions for the Neoproterozoic (e.g., Meert and Torsvik, 2003; Pesonen of supracrustal belts in the Borborma Province were unknown, et al., 2003; Tohver et al., 2006; Rino et al., 2008). Where it is, rather although some of them were attributed, somewhat arbitrarily, to contrasting models are presented (Fig. 1). On one extreme, these the Paleoproterozoic, Mesoproterozoic or Neoproterozoic. Since provinces are shown as continental fragments in a large ocean sep- then, several geochronological works (reviewed below) were car- arating the São Francisco and Amazonian cratons (Cordani et al., ried out, but the amount of data is still meagre. In order to 2003), which was not yet completely closed by 550 Ma (Trindade et improve knowledge, we present in this contribution U–Pb ages of al., 2003, 2006). On the other extreme, an early assembly of western detrital zircons from metasedimentary rocks ascribed to three dif- Gondwana within a long-lived continent is envisaged (Castaing et ferent complexes in the eastern portion of the Borborema Province al., 1994; Rogers, 1996; Piper, 2000, 2007), with the Brasiliano/Pan- (Figs. 2 and 3). African orogen regarded as mainly intracontinental (Neves, 2003). In between these two models, Van Schmus et al. (2008) recently 2. Previous U–Pb studies suggested that separation of the Amazonian/West African craton from the São Francisco/Congo craton formed a large Neoprotero- The basement of the Borborema Province mainly consists of zoic ocean and that the Borborema Province and its counterparts Paleoproterozoic orthogneisses with U–Pb zircon ages comprised in central and northern Africa are extended portions of a larger con- between 2.2 Ga and 2.0 Ga (see reviews by Brito Neves et al., 2000; tinent from which the São Francisco/Congo Craton is the relatively Neves, 2003; Van Schmus et al., 2008), although exposures of undeformed remnant. Archean (Fetter et al., 2000; Dantas et al., 2004; Arthaud et al., 2008) The Borborema Province is frequently referred, by a group of and early Paleoproterozoic (ca. 2.3 Ga; Fetter et al., 2000; Melo workers, as a branched system of orogens (Brito Neves et al., et al., 2002; Santos et al., 2008a) crust are found in the northern 2000; Fuck et al., 2008), with the underlying assumption that and central domains. In the northern domain, the oldest exten- different metasedimentary units (and their gneissic basement) sive supracrustal units, with U–Pb ages of 1.75–1.80 Ga, are the are allochthonous and were amalgamated during Neoproterozoic Orós and Jaguaribe belts (Sá et al., 1995)(Fig. 2). They consist of accretionary orogenic events (Santos et al., 1999). Others, how- an association of metasedimentary and metavolcanic rocks domi- ever, infer that most supracrustal belts resulted from deformation nated by Al-rich schists and metarhyolites, interpreted as formed and metamorphism of Neoproterozoic sedimentary or volcanosedi- in a continental rift setting. The Saquinho Volcanic Sequence, in S.P. Neves et al. / Precambrian Research 175 (2009) 187–205 189 Fig. 2. Schematic map of the Borborema Province showing the main shear zones, plutons and supracrustal belts. Where available, ages of deposition, as inferred from the U–Pb age of the youngest detrital zircon grain (italics) or from interlayered metavolcanic rocks (normal type), are also shown. See text for sources of data. Abbreviations for main transcurrent