Journal of South American Earth Sciences 12 (1999) 453±470 - PDF

Journal of South American Earth Sciences 12 (1999) 453±470 Basin in lling in the southern-central part of the Sergipano Belt (NE Brazil) and implications for the evolution of Pan-African/ Brasiliano cratons

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Journal of South American Earth Sciences 12 (1999) 453±470 Basin in lling in the southern-central part of the Sergipano Belt (NE Brazil) and implications for the evolution of Pan-African/ Brasiliano cratons and Neoproterozoic sedimentary cover Luiz J.H. D'el-Rey Silva* Universidade de BrasõÂlia-Instituto de GeocieÃncias, Campus UniversitaÂrio Darcy Ribeiro, Asa Norte, CEP , BrasõÂlia-DF, Brazil Abstract The Neoproterozoic sedimentary cover deposited across the interface of several Pan-African/Brasiliano fold-thrust belts with their respective cratons is strongly similar and has been widely correlated throughout Gondwana. In particular, the upper part of the cratonic cover of the SaÄ o Francisco Craton has been interpreted as a ring of foreland basin sediments. However, detailed studies carried out around the southern-central part of the Sergipano Belt (NE Brazil) and its interface with the northern margin of the SaÄ o Francisco Craton demonstrate that: (1) sedimentation records the evolution of a passive continental margin and is divided into two cycles (I and II), each one comprising a basal siliciclastic megasequence overlain by a carbonate megasequence; (2) the cratonic cover comprises cycle I and part of the basal megasequence of cycle II; (3) all of these rocks spread continuously across the craton margin into the Sergipano Belt, where they occur around basement domes and are overlain by a metadiamictite formation and a metacarbonate formation that complete cycle II; and (4) basement and cover underwent the same Brasiliano (670±600 Ma) compressive deformation under sub-greenschist metamorphic conditions. These data deny the foreland basin model for the cratonic sediments to the south of the Sergipano Belt and, coupled with recent data on the evolution of other margins of the craton, indicate that the Neoproterozoic sedimentary cover derives from highs existing close to the centre of the ancient SaÄ o Francisco Plate. This sedimentary cover was also in uenced by highs of an Andean-type margin that evolved ca 900±640 Ma along the western side of the plate. Such evolution also applies to the Neoproterozoic cover of other cratons of the Pan-African/Brasiliano orogeny. # 1999 Elsevier Science Ltd. All rights reserved. Resumo A cobertura sedimentar Neoproterozo ica da interface entre as vaâ rias faixas dobradas Pan-Africanas/Brasilianas e seus respectivos craâ tons guarda similaridades muito fortes e tem sido amplamente correlacionada e, particularmente a parte superior da cobertura que circunda o Cra ton SaÄ o Francisco tem sido suposta ou interpretada como detritos oriundos da erosaä o das faixas dobradas, depositados em bacias tipo foreland. Contudo, estudos realizados na parte centro-sul da Faixa Sergipana (NE do Brasil) e sua interface com o Cra ton SaÄ o Francisco demonstram que: (1) A sedimentac aä o registra a evoluc aä o de margem continental passiva e eâ dividida em dois ciclos (I e II) cada um formado por megasequeã ncia basal siliciclaâ stica sobreposta por megasequeã ncia carbonaâ tica; (2) A cobertura cratoã nica compreende os sedimentos do Ciclo I e a megasequeã ncia siliciclaâ stica do ciclo II; (3) Todas essas rochas espalham-se continuamente do craâ ton para a faixa, onde ocorrem em torno de domos do embasamento e saä o sotopostas a metadiamictitos e metacarbonatos que completam o Ciclo II; e (4) Embasamento e cobertura registram a mesma deformac aä o compressiva Brasiliana, sob metamor smo maâ ximo do faâ cies xisto verde (670±600 Ma atraâ s). Esses dados negam o modelo foreland para a cobertura cratoã nica a sul da Faixa Sergipana e, combinados com outros recentemente publicados para outras margens do craâ ton, indicam que a sedimentac aä o da cobertura Neoproterozo ica como um todo foi controlada por altos proâ ximos ao centro da antiga placa SaÄ o Francisco e, particularmente ao longo da borda oeste da * Fax: or address: (L.J.H. D'el-Rey Silva) /99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S (99) 454 L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453±470 placa, tambeâ m por altos da margem continental andina ali desenvolvida entre 900 e 640 Ma atraâ s. Tal evoluc aä o aplica-se tambeâ m aá cobertura Neoproterozo ica de outros craâ tons do sistema orogeã nico Pan-Africano/Brasiliano. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction The Sergipano Belt of NE Brazil (Fig. 1) is a triangle-shaped, ESE±WNW trending orogenic belt lying between the SaÄ o Francisco Craton to the south, and the Pernambuco-Alagoas Massif, which is part of the Borborema Province, to the north (Fig. 1; Almeida et al., 1981; Santos and Brito Neves, 1984). The belt occupies the central part of the e2000 km long megaorogen (Fig. 2) connecting the Oubanguides Belt (or North Equatorial Belt) of Africa, with the Riacho do Pontal and Rio Preto belts of Brazil (Davison and Santos, 1989; Jardim de Sa et al., 1992; Jardim de SaÂ, 1994; Trompette, 1994). Because the SaÄ o Francisco Craton is surrounded by several Pan-African/ Brasiliano deformation belts (Fig. 2) and because the Sergipano Belt contains basement domes mantled by metasediments with well preserved sedimentary features, lying less than 5 km away from the craton margin (the Itaporanga Fault, as will be seen ahead), understanding the tectonic evolution of the craton and Fig. 1. Major tectonic elements of northeastern Brazil: in (a) the SaÄ o Francisco Craton (SFC) and the Borborema Province (BP), and in (b) the Riacho do Pontal (RP) and Sergipano (S) belts, the latter one lying to the south of the Pernambuco-Alagoas Massif (Pe-Al). The SaÄ o Luiz Craton is also shown. PaSZ = Patos Shear Zone, PeSZ = Pernambuco Shear Zone. Based on Almeida et al. (1981) and Mascarenhas et al. (1984). See text. Fig. 2. Simpli ed map showing the main lithotectonic units around the SaÄ o Francisco-Congo and Kalahari cratons, based on Trompette (1994) and Germs (1995). Lithostratigraphy legend: (cratons) 1 = Basement, 2 = Paleo-Mesoproterozoic cover rocks, 3 = Neoproterozoic cover rocks, 4 = Late Neoproterozoic-Cambrian cover rocks; (belts) 5 = Polycyclic basement, 6 = Paleo- Mesoproterozoic metasediments, 7 = Neoproterozoic metasediments with ma c-ultrama c intercalations and indication of thrusting movement. B = Brasõ lia, C = Arac uaõâ, D = West Congo, E = Kaoko, F = Damara, G = Gariep, H = Malmesbury (or Vanrhynsdorp) belts. See text. L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453± Fig. 3. Simpli ed geological map of the Sergipano Belt. Modi ed from D'el-Rey Silva (1992). The Belo Monte-Jeremoabo fault (BMJF) stretches up to the border of the Sergipe-Alagoas basin, and separates the internal zone (to the north) from the intermediate, external and cratonic zones (to the south). The internal zone stands for a Meso-Neoproterozoic Andean-type margin. The other zones stand for a deformed passive continental margin. See text. the belt may provide answers to questions concerning the evolution of Proterozoic supercontinents. The interface between the fold-thrust belts and the SaÄ o Francisco-Congo and Kalahari cratons (Fig. 2) is covered by generally at-lying continental to shallow marine siliciclastic and carbonate Neoproterozoic sediments which are su ciently similar to encourage several authors (e.g. Teixeira and Figueredo, 1991; Trompette, 1994, and many references therein) to postulate their stratigraphic correlation across the cratons and into the external units of the marginal belts. The upper section of the Neoproterozoic cover around the SaÄ o Francisco Craton has been interpreted as foreland basin deposits recording the erosion of the belts themselves, implying a late-post tectonic radial sedimentary in ux towards the centre of the craton (e.g. Dominguez, 1993). However, based on detailed studies carried out in the area surrounding the Itabaiana and SimaÄ o Dias domes (Fig. 3), coupled with the results of detailed sedimentology studies performed in a locality about 50 km to the south, within the SaÄ o Francisco Craton (Saes, 1984), this model has been ruled out in the southern part of the Sergipano Belt and an alternative explanation has been required for the cratonic sediments (D'el-Rey Silva, 1992, 1995a,b; D'el-Rey Silva and McClay, 1995). To reach this alternative, the results of these studies (summarised here) are combined with other data published more recently for other margins of the SaÄ o Francisco Craton, allowing to discuss the correlation of the Neoproterozoic cratonic cover and its origin considering the evidence for mantle plume-controlled uplift of the ancient SaÄ o Francisco Plate simultaneously with two oceanic margins, one active and the other passive, that existed respectively along its western and northern edges, between 11.0 and 0.65 Ga, as discussed below. Such events are coeval with the initial and nal break-up of the Rodinia supercontinent (11000±700 Ma, as in Unrug, 1997) and are applicable to other cratons and belts of western Gondwana as well. 456 L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453±470 Fig. 4. Summary stratigraphy of the Itabaiana-Carira dome area, based on D'el-Rey Silva (1992, 1995b), D'el-Rey Silva and McClay (1995). Sedimentation lasted from E1.0 Ga (U±Pb zircon data in metavolcanics of the Maranco domain (Brito Neves et al., 1993)) to possibly 0.65 Ga (see text). New U±Pb data from zircons in volcaniclastics indicate an older age of 810 Ma for the Ribeiro polis Formation (personal communication Van Schmus, February 1999). 2. The Sergipano belt: An overview 2.1. Structural/metamorphic zones and lithotectonic domains The Sergipano Belt (Fig. 3) is cross-cut by the Phanerozoic Sergipe-Alagoas and Tucano-Jatoba sedimentary basins and, according to its structural and metamorphic features, may be divided longitudinally, from north to south, into an internal, an intermediate, an external and a cratonic zone, whereas its lithotypes have been grouped by Santos et al. (1988), Davison and Santos (1989) and Silva Filho (1998) in seven lithotectonic domains named Sul-Alagoas, CanindeÂ, Poc o Redondo, MarancoÂ, MacurureÂ, Vaza Barris and Estaà ncia. These domains are all bounded by highangle thrusts associated with sinistral and dextral sense strike-parallel movement, respectively, to the east and west of the Tucano±Jatoba basin (Jardim de Sa et al., 1986; D'el-Rey Silva, 1992, 1995a). The crystalline basement crops out in the Itabaiana, SimaÄ o Dias and Jirau do Ponciano gneiss domes, within the belt, or in the craton itself (Fig. 3). Near the belt, the cratonic basement consists of Archean-Paleoproterozoic granulite-gneiss terrains, and Paleoproterozoic greenstone sequences (Mascarenhas et al., 1984; Teixeira and Figueiredo, 1991; Barbosa, 1996; Silva, 1996). The Jirau do Ponciano and SimaÄ o Dias domes display gneisses with Rb±Sr whole rock and isochron ages around 2500 Ma (Amorim et al., 1993; Humphrey and Allard, 1969). The internal zone comprises the domains to the north of the Belo Monte±Jeremoabo fault (BMJF). It exhibits a Neoproterozoic polyphase compressive deformation with north/northeast verging F 2 folds/ thrusts, fold axis parallel to a northwest-trending stretching lineation (Amorim, 1995), amphibolite-granulite metamorphism (greenschist is retrogressive), and L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453± Fig. 5. Simpli ed geological map of the Itabaiana-Carira area. Combining data in D'el-Rey Silva (1992, 1995a,b) and in Santos et al. (1988). The line section AB (see Fig. 6) and the rectangle area of Fig. 7 are both indicated. See text. kyanite-bearing assemblages of intermediate pressure in areas close to the basement dome (Jardim de Sa et al., 1981; Silva, 1993). The intermediate, external and cratonic zones comprise respectively the MacurureÂ, Vaza Barris and Estaà ncia domains and are separated by the SaÄ o Miguel do Aleixo and the Itaporanga faults (Fig. 3). The rst two zones display a D 1 ±D 3 polyphase deformation, with F 2 folds/thrusts verging mostly to the south/southwest, fold axis parallel to a west/northwest trending and shallowly plunging stretching lineation, and a north±south amphibolite to greenschist facies range of metamorphism. In contrast, 458 L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453±470 the cratonic zone displays much less deformation and almost no metamorphism, so the sediments are generally at-lying (D'el-Rey Silva 1992, 1995a). Based on age determinations in Brito Neves et al. (1993) and Van Schmus et al. (1995), and on his own eld and geochemical studies, mainly REE, Silva Filho (1998) states: (1) the Maranco and Caninde domains are intraoceanic arcs consisting respectively of metasediments and metavolcanics displaying zircon U±Pb ages of Ma and Ma, along with a 1940 Ma suite of juvenile gabbros and associated metasediments/metavolcanics. Both domains exhibit deformed S-type granites with 1715 Ma U±Pb zircon ages; (2) the Poc o Redondo domain consists of tonalitic migmatites and paragneisses; and (3) The Sul- Alagoas domain comprises lithotypes typical of an accretionary prism, as well as the Jirau do Ponciano basement dome that is overlain by a sillimanite-bearing quartzite formation (not shown in Fig. 3; Silva Filho et al., 1978a; Amorim, 1995), all intruded by tonalitic granitoids displaying Rb±Sr age of Ma. As detailed by D'el-Rey Silva (1992, 1995b) the Estaà ncia, Vaza Barris and Macurure domains form a craton-platform-basinal continuous wedge developed on a continental margin (Fig. 4). The Macurure Domain is a 13 km-thick wedge comprising the Macurure Group (siliciclastic and carbonate metasediments and metavolcanics of eugeoclinal a nities), a suite of syn- to post-tectonic calc-alkaline granites (only partially displayed in Fig. 3), also found in the internal zone, as well as in the Pernambuco-Alagoas Massif (Giuliani and Santos, 1988; Fujimori, 1989; Silva Filho et al., 1992), and the Jua Formation: undeformed psephites derived from rocks of the Maranco domain and in lling a small graben (Silva Filho et al., 1978a; Santos et al., 1988). The Vaza Barris domain is a 1 to e4 km-thick wedge of platformal (miogeoclinal), shallow marine siliciclastic and carbonate metasediments and minor volcanic rocks occurring around basement domes and divided into the Miaba, SimaÄ o Dias, and Vaza Barris groups. The Estaà ncia domain is a 1±3 km-thick blanket of continental to shallow marine siliciclastic and carbonate sediments resting unconformably on the SaÄ o Francisco Craton and divided into the Estaà ncia and SimaÄ o Dias groups Summary tectonic evolution D'el-Rey Silva (1992, 1995a) interpreted the Sergipano Belt in terms of an oblique collision of the Pernambuco-Alagoas Massif and the ancient SaÄ o Francisco-Congo Plate, after subduction of an ocean to the north, being the MarancoÂ, Poc o Redondo and Caninde domains allochtonous terrains or not. Rotation of kinematics vectors due to the northwest trend of the continental margin accounts for the dextral slip of the faults in the western side of the belt (Fig. 3) and the Jua Formation graben records late- to post-tectonic belt-parallel stretching. Silva Filho (1998) shows that the subduction zone existed since around 1045 Ma, with formation of intraoceanic arcs up to 1940 Ma, and accretion around 715 Ma to an Andean-type margin developed along the southern border of the Pernambuco-Alagoas Massif. The collision of the SaÄ o Francisco-Congo plate resulted in the polyphase deformation and regional metamorphism dated 1670±600 Ma, according to Rb±Sr data on phyllites of the external zone (Brito Neves and Cordani, 1973) and in syn- to late-tectonic granites within the intermediate and internal zones (Chaves, 1991; McReath et al., 1998; Silva Filho, 1998). Such evolution implies a suture zone that includes the Macurure fault and the BMJF (Fig. 3), close to which metamorphism attained the highest pressures in the belt (Silva Filho, 1998). The Riacho do Pontal Belt (the western continuity of the Sergipano Belt, Fig. 2) displays very similar features, including the continuity of the suture line (Jardim de Sa et al., 1992; Jardim de SaÂ, 1994; Torres et al., 1994), so Angelim (1998) has suggested the same tectonic evolution as portrayed here. 3. Basin evolution in the southern-central part of the belt 3.1. Main geological features A large area stretching over the Estaà ncia, Vaza Barris and Macurure domains (the Itabaiana-Carira area, Fig. 5) has been studied in detail. The Itaporanga fault separates the Estaà ncia domain (to the south) from gneiss domes and the (meta)sedimentary/ volcanic cover of the two other domains. The Itabaiana and SimaÄ o Dias domes are granite-granodiorite, amphibolite-grade gneiss bodies intruded by basic-ultrabasic rocks and granites, all partially retrometamorphosed to the greenschist facies. The crystalline basement for the Macurure domain has been proven by geophysical studies and by small slices of gneisses that occur in the hangingwall of thrust faults (D'el-Rey Silva, 1992, 1995b). The basement-cover contact dips at low-angles along the northern, eastern, and western margins of the Itabaiana dome, as well as along the western side of the SimaÄ o Dias dome. Elsewhere, the contact dips at high-angles. Rocks on both sides of the contact are generally sheared, except in one part of the eastern margin of the Itabaiana dome and one part of the western margin of the SimaÄ o Dias dome, where undeformed conglomerate rests upon an erosive unconformity on well banded and mylonitic gneiss. L.J.H. D'el-Rey Silva / Journal of South American Earth Sciences 12 (1999) 453± Fig. 6. Simpli ed geological cross-section along line AB shown in Fig. 5. From D'el-Rey Silva (1992, 1995a). Details in the text. The basement's metamorphic banding (S n ) and the cover's original layering (S o ) record similar D 1 ±D 3 deformational evolution, during which mappable structures developed in the area. These include the Itaporanga, Escarpa, Pelada, Mocambo, Ribeiro polis, SaÄ o Miguel do Aleixo and Dores faults, which are sub-vertical, WNW±ESE trending thrusts (interpreted as inverted normal faults Ð see ahead) associated with sinistral strike-slip and with F 2 folds. The larger ones are seen in the western sides of both basement domes. Beyond S n and S o, these structures also a ect layerparallel foliation (S 1 ), small- to mesoscopic-scale recumbent F 1 folds, and a stratigraphic inversion mapped in the southwestern side of the area (Fig. 5) and ascribed to D 1 nappes. The structural pattern in vertical cross-sections (Fig. 6) is that of a generally at lying cratonic zone, where deformation is mostly characterised by gentle-open F 2 folds that a ect S o, but a gradual increase in the intensity of the axial planar foliation (S 2 ) and in the aspect ratio of these folds is observed close to and across the Itaporanga fault, towards the north. Within the external and intermediate zones, small- to large-scale F 1 folds and nappes are a ected by F 2 folds to form a classical type 3 interference pattern (Ramsay, 1967) subsequently disrupted and uplifted by the high angle thrust/strike-slip faults, interpreted as such because they merge at the same basal extensional detachment of the basin opening (Fig. 6; D'el-Rey Silva, 1992, 1995a). The intense D 2 attening imprinted numerous mesoscopic, tight F 2 folds with a penetrative WNW± ESE trending S 2 foliation that is sub-parallel to S n,s o, and S 1, except in the F 2 hinges, and that dips steeply to NNE. The F 2 fold axes are parallel to a penetrative stretching lineation well documented by several strain markers in most of the rock types. Strike-slip faults, such a
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