Brasiliano (Pan-African) granitic magmatism in the Pajeú-Paraíba belt, Northeast Brazil: an isotopic and geochronological approach

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1 Precambrian Research 135 (2004) Brasiliano (Pan-African) granitic magmatism in the Pajeú-Paraíba belt, Northeast Brazil: an isotopic and geochronological approach Ignez P. Guimarães a,, Adejardo F. Da Silva Filho a,cícera Neysi Almeida b, W.R. Van Schmus c,joão M.M. Araújo a, Silvana C. Melo a, Evenildo B. Melo d a Departament of Geology, Pernambuco Federal University, Recife, Brazil b CNPq DCR-Research, Brazil c Department of Geology, 1475 Jayhawk Blvd.-Room 120, University Kansas, Lawrence, KS 66045, USA d Department of Mine Engineering, Pernambuco Federal University, Recife, Brazil Received 9 December 2003; accepted 7 July 2004 Abstract The Neoproterozoic Brasiliano/Pan-African Orogeny in the Borborema Province (BP) NE Brazil, is characterized by intense granitic magmatism spatially associated with continental scale shear zones and metamorphism under high temperature conditions. U/Pb zircon and Rb Sr whole rock data for 14 granite intrusions from the Pajeú-Paraíba Belt have ages that suggest more than 100 Ma of intrusive magmatism, which can be divided in four events: the oldest granites (between 620 and 600 Ma) are medium-to-slightly high-k calc-alkaline I-type granitoids, intruded into metagreywackes and gneiss-granites of Ga; they are related to the peak of metamorphism and to the development of a flat lying foliation. The youngest intrusions ( Ma) have geochemical signature of A-type, post-orogenic, extension-related granites, and are associated with sub-volcanic bimodal magmatism, probably contemporaneous with deposition of small sedimentary basins in the North (Iara, Jaibaras graben and Saíri) and Central (Fatima, Betânia and Carnaúbeira) Tectonic Domains of the Borborema Province; they reflect post-tectonic relaxation of the Brasiliano Orogeny. Between these episodes, two other intrusive events were identified: (1) high-k calc-alkaline granitoids and shoshonitic granitoids associated with mafic syenites, meladiorites and hornblende biotite diorites, intruded between 590 and 581 Ma, associated with a transcurrent deformation event, and (2) alkaline post-collisional granitoids having U/Pb zircon ages of ca. 570 Ma, marking the final stage of the Brasiliano Orogeny. In the South Domain of the Borborema Province, migmatization took place between 610 and 600 Ma. Although similar ages were not found in the granitoids of the Central Tectonic Domain, field evidence suggest that migmatization followed the intrusions of the oldest ( Ma) granitoids Elsevier B.V. All rights reserved. Keywords: Neoproterozoic; Granitoids; Crustal evolution; Borborema Province Corresponding author. address: ignez@ufpe.br (I.P. Guimarães) /$ see front matter 2004 Elsevier B.V. All rights reserved. doi: /j.precamres

2 24 I.P. Guimarães et al. / Precambrian Research 135 (2004) Introduction The Borborema Province (BP) comprises a large region in northeastern Brazil, north of the São Francisco Craton (Fig. 1A). In pre-drift reconstructions, this province is adjacent to similar Pan-African belts and cratonic terranes in western Africa (Caby et al., 1981; Caby, 1989; Jardim de Sá, 1984; Toteu et al., 1990, 1994, 2001; Brito Neves and Cordani, 1991; Castaing et al., 1993; Trompette, 1997; Brito Neves et al., 2002; Neves, 2003). The BP represents the western part of a belt that occupies northern Gondwana (Van Schmus et al., 1995). The late Neoproterozoic (Brasiliano = Pan-African) evolution of the Borborema Province, northeast Brazil, was marked by a great abundance of granitic intrusions, the majority of them, associated with NE SW shear zones (Vauchez et al., 1995; Neves and Vauchez, 1995; Archanjo, 1993; Jardim de Sá, 1994). Almeida et al. (1967), based on petrography, recognized four granite types within the Borborema Province: (1) Conceição type medium to fine grained granodiorites and tonalites; (2) Itaporanga type granodiorites with large K-feldspar phenocrysts; (3) Itapetim type fine grained biotite granites, associated with the Itaporanga type, and (4) Catingueira type peralkaline granites, syenites and quartz syenites. Sial (1986) characterized geochemically the granitoids of the Piancó Alto Brígida Fold Belt in the Central Tectonic Domain of the Borborema Province (=Cachoeirinha Salgueiro Belt) and correlated them with the granitoids described by Almeida et al. (1967), i.e.: (1) Calc-alkalic (Conceição type); (2) Potassic calc-alkalic (Itaporanga type); (3) Peralkalic (Catingueira type) and (4) Trondhjemitic (Serrita type). Brito Neves et al. (2000), based on previous studies, divided the Brasiliano granitoids into three super suites: (I) Composed of hybrid and crustal granitoids (calcalkaline, high-k calc-alkaline, trondhjemitic and peraluminous suites) intruded since the contractional tectonics, up to the late phase of strike-slip displacements. (II) Enriched-mantle derived suite. This includes high-k calc-alkaline, shoshonitic and ultrapotassic, and alkaline suites, syn- and late kinematic intrusives of the major stike-slip events. (III) Within-Plate hybrid suites, related to post-closure uplift and the collapse phase of the orogenic structures. We report here the results of our petrologic, geochemical and isotopic study of 14 Neoproterozoic granitic intrusions from the central part of the BP, and discuss their origin in terms of magmatic and tectonic processes. 2. Geological setting The BP consists of gneissic and migmatitic basement complexes, mostly formed during the Paleoproterozoic (Transamazonian tectonic cycle Ga), and are partially covered by Mesoproterozoic to Neoproterozoic metasedimentary and metavolcanic rocks (Van Schmus et al., 1995; Dantas et al., 1998; Fetter, 1999; Brito Neves et al., 2001; Kozuch, 2003). In addition to the Transamazonian orogenic cycle, the BP was affected by the Cariris Velhos ( 1.0 Ga) and Brasiliano (0.6 Ga) events. The Cariris Velhos event is represented by muscovite biotite gneisses, garnet-biotite schists, and metavolcanic rocks intruded by granitic plutons (now augen-gneisses) of early Neoproterozoic age (Santos, 1995; Brito Neves et al., 2001; Kozuch, 2003); it is mainly distributed in the Central Tectonic Domain of the BP (Fig. 1B). The Brasiliano event affected the entire province and was responsible Fig. 1. (A) The mainly shear zones and the tectonostratigraphic terranes proposed by Santos et al. (1999): AMT, Alto Moxotó; APT, Alto Pajeú; RCT, Rio Capibaribe; PABB, Piancó Alto Brígida belt; SB, Sergipano belt; PAT, Pernambuco Alagoas; GJT, Grajeiro; SED, Seridó belt; JC, São José do Campestre; RP, Rio Piranhas; JG, Jaguaribeano; CE, Ceara; MC, Medio Coreaú; RP, Riacho do Pontal. WPSZ and EPSZ are the two branches (west and east) of the Pernambuco lineament as proposed by Neves and Mariano (1997). PSZ, Patos shear zone. The occurrences of eclogite core from Beurlen et al. (1992). (B) Sketch geological map of the Central Tectonic Domain of the Borborema Province emphasizing the studied granitoids (1 = Timbaúba; 2 = Bom Jardim; 3 = Toritama; 4 = Fazenda Nova; 5 = Itapetim; 6 = Tabira; 7 = Pajeú; 8 = Solidão; 9 = Campina Grande; 10 = Queimadas; 11 = Serra Branca; 12 = Prata; 13 = Plutons along the Afogados da Ingazeira Shear Zone (AISZ) Pereiro, Serra do Velho Zuza). CCSZ = Campina Grande shear zone; SSZ = Solidão shear zone; JBSZ = Juru Belém shear zone.

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4 26 I.P. Guimarães et al. / Precambrian Research 135 (2004) for low-to-high grade metamorphism, abundant magmatism, and development of continental-scale transcurrent shear zones. The most important shear zones are represented by the Patos and Pernambuco systems (Vauchez et al., 1995) and the Afogados da Ingazeira- Galante-Mari shear zone (Brito Neves et al., 2001) (Fig. 1B). The E-W shear zones divide the BP into three segments, referred to as North, Central and South Tectonic Domain by Van Schmus et al. (1995). The studied area is located in the Central Tectonic Domain, which was previously named the Transversal Zone by Ebert (1970). It is limited by the Patos shear zone to the north, Pernambuco shear zone to the south, Afogados da Ingazeira shear zone to the west, and the coastal area to the east (Fig. 1B). Trompette (1994) suggests continuation of the Central Tectonic Domain to the African side of West Gondwana, between the Adamaoua and Garoua shear zones in Cameroun. However, structural data of Neves and Mariano (1999) indicate that the Pernambuco lineament is not a transcontinental structure. It is segmented into two branches and its tectonic role during the Brasiliano was secondary. In the past few years, many authors (Santos, 1995; Santos et al., 1997; Ferreira et al., 1998; Santos and Medeiros, 1999) suggested that the Brasiliano evolution of the BP was controlled by accretion of exotic terranes (Fig. 1A). Each domain was segmented into many terranes. Brito Neves et al. (2000, 2001) kept the terrane model only for the Central Tectonic Domain. The South Tectonic Domain was divided into Southern Domain and Pernambuco Alagoas Massif. The later has been called the Pernambuco-Alagoas complex by Da Silva Filho et al. (2002). In the Southern Domain, Brito Neves et al. (2000) kept the tectonic model of Brito Neves (1983), dividing it into: Sergipano fold belt, Rio Preto fold belt, and Riacho do Pontal fold belt. The North Tectonic Domain was subdivided into: Rio Grande do Norte domain, encompassing two-fold belts (Jaguaribeano-Encanto and Seridó), two massifs (São José do Campestre and Rio Piranhas), Central Ceará domain, and Médio Coreau domain. The Central Tectonic Domain encompasses: Piancó-Alto Brigída (Piancó Alto Brígida Belt), the Alto Moxotó (AMT), Alto Pajeú (APT), and Rio Capibaribe (RCT) terranes. According to this terrane accretion model, the studied granitoids are located in the APT, AMT and RCT (Fig. 1A and B), which are terranes in the former Pajeú- Paraíba fold belt (Brito Neves, 1983). The APT comprises muscovite biotite gneisses, garnet-biotite schists, and metavolcanic rocks intruded by early Neoproterozoic granitic plutons (now augengneisses). These rocks were deformed during the Brasiliano cycle, initially by a transcurrent episode, and later by extension (Santos et al., 1997; Brito Neves et al., 2001; Neves, 2003). The AMT is composed of metavolcanometasedimentary sequences, including a calc-alkaline volcanic sequence of arc affinity and Paleoproterozoic blocks ( Ga) of tonalitic to granodioritic composition (Santos, 1995). The RCT is constituted by early Neoproterozoic sequences of schist and gneiss with intercalations of marble and calc-silicate rocks plus Mesoproterozoic orthogneiss of granitic composition as well as anorthositic intrusions. Some authors (Neves and Mariano, 1997; Mariano et al., 2001), based on geochemical and structural data, concluded that the Pernambuco shear zone can not be considered as the limit between distinct terranes as proposed by Santos (1995) and Brito Neves et al. (2001); in addition, the distinct terranes forming the BP are underlain by lithospheric mantle blocks, with similar geochemical and isotopic signature. According to these authors, these are strong arguments against the evolution of the BP based on the terrane accretion model. On the other hand, structural, geophysical and isotopic data suggest that the Patos shear zone is the limit between the APT and the Rio Grande do Norte Domain (Brito Neves et al., 2001). Beurlen et al. (1992) described two occurrences of ophiolites (Fig. 1B) within Paleoproterozoic gneisses, close to their tectonic contact with early Neoproterozoic metasedimentary rocks of the Piancó Alto Brígida belt. These occurrences have been cited as evidence of oceanic closure during either the Brasiliano (Bittar and Campos Neto, 2000; Beurlen et al., 1992) or the Cariris Velhos (Santos et al., 1997) orogeny. In this work, we will follow the tectonic model of Brito Neves (1983), in which the studied area is part of the Pajeú-Paraíba belt, without further discussion on this always controversial subject of terrane nomenclature. Bittar (1999) estimated Brasiliano metamorphic peak conditions for the west part of the APT (São Cae-

5 I.P. Guimarães et al. / Precambrian Research 135 (2004) tano Complex) at P = (4.4 ± 1.0) kbar (geobarometer of Hodges and Spear, 1982) and T = 700 C (geothermometer of Spear, 1981). These data are similar to those obtained by Coutinho (1994) for the garnetbiotite gneisses from the São Caetano Complex, based on the equilibrium of the metamorphic assemblage, and using the Thermocalc program (P = (4.7 ± 1.6) kbar, T = (703 ± 101) C) and those obtained by Leite et al. (2000) for the APT in the Monteiro-Sumé area. It is important to establish the timing of the peak of the metamorphism in order to assess its possible relationship with the plutonism. However, this has not been done systematically in the Central Tectonic Domain of the Borborema Province. Leite et al. (2000) reported an upper intercept U Pb zircon age of 972 ± 4 Ma for orthogneisses intruded by the Brasiliano Tabira pluton and a concordant sphene fraction from the same sample giving the age of metamorphism at 612 ± 9 Ma. In north-central Cameroon the peak of granulite facies metamorphism, associated with flat-lying foliation, has ages in the range of Ma (Toteu et al., 1987, 1994). The ages can also represent the age of the metamorphic peak in the studied area, if a pre- Gondwana reconstruction is considered. Because the major Brasiliano granitic intrusions are associated with shear zones, their study is important to understand the evolution of the BP during the Brasiliano. In the western part of the Pajeú-Paraíba Belt, Sales (1997) identified two distinct levels of crustal blocks separated by the Afogados da Ingazeira shear zone (AISZ Fig. 1). In the south, the present level of exposure reflects metamorphism under lower pressure and temperature conditions (4 kbar and 600 C) when compared to the north (6.4 kbar and 670 C). Vertical movement of blocks along the AISZ is also supported by structural data (Sales, 1997; Araújo, 1997). Distinct crustal blocks are also recorded in the northeastern part of the Pajeú-Paraíba belt: the block located south of the Campina Grande shear zone (which is part of the Patos Lineament), shows intense migmatization and metamorphic conditions under pressure higher than 6 kbar and temperature of ca. 700 C(Almeida et al., 1997). Sm Nd TDM model ages in rocks of this block are ca. 2.0 Ga. The block to the north of the Campina Grande shear zone is composed of well foliated biotite ± muscovite orthogneisses, metamorphosed under amphibolite facies conditions, with Sm Nd model ages in the Ga range (Brito Neves et al., 2001). Narrow and elongated deposits of detrital sediments, sandstones, arkoses and conglomerates occur to the west of the AISZ. These sediments have been interpreted as part of the Tacaratu Formation of the Jatobá Basin, of Upper Silurian age (Veiga and Ferreira, 1990). However, elongated and narrow basins are rift-related, and the Jatobá Basin is interpreted as a syncline from the Paleozoic. Other small Paleozoic basins occur in the Central Tectonic Domain (Betânia, Fátima, Carnaúbeira, Mirandiba, São José do Belmonte Veiga and Ferreira, 1990). The sediments cropping out in all of these small basins have been interpreted as chrono-correlated to the Tacaratu Formation. The absence of fossils in these sediments makes it difficult to date them. The Upper Silurian age was estimated from lithologic correlation. Several Cambrian pullapart basins (Iara, Jaibaras graben and Saíri), consisting of extension-related molassic deposits, have been described further northwest in Ceará State (Fetter, 1999). The Mocambo granite that flanks the Jaibaras Graben, the largest of these extensional basins, yields a U/Pb zircon crystallization age of 532 ± 6Ma(Fetter, 1999). Bimodal sub-volcanic rocks occur as dyke swarms, in the Monteiro Sumé area, oriented in a general N-S direction. They are dacite and rhyolite with subordinate alkaline diabase and are co-magmatic with the Cambrian Prata Granitic Complex (Guimarães et al., 2000). 3. The granite intrusions Twelve large granitoid intrusions (Queimadas pluton, Bom Jardim complex, Toritama complex, Timbaúba pluton, Tabira pluton, Itapetim complex, Fazenda Nova complex, Campina Grande Pluton; Serra Branca pluton, Solidão pluton, Pajeú pluton, Prata complex) and two small plutons intruded along the Afogados da Ingazeira shear zone (Pereiro and Serra do Velho Zuza plutons) were investigated for their main field, petrographic geochemical and isotopic characteristics. The geochemical data from Fazenda Nova are from Neves and Vauchez (1995). Except for the Bom Jardim and Toritama complexes, which are syenites, all the other intrusions are granite or granodiorite to tonalite in composition. Most have K-rich dioritic enclaves. The Tabira and Timbaúba plutons comprise E- W elongated intrusions of porphyritic to equigran-

6 28 I.P. Guimarães et al. / Precambrian Research 135 (2004) ular epidote-bearing biotite-hornblende granodiorites to monzogranites, deformed under high-t conditions. Rounded to elliptical microgranular enclaves are common. Amphibole-rich clots, surrounded by coarsegrained amphibole and biotite are hosted by the granodiorite-monzogranite. chunks of quartz, up to 30 cm long, were also observed enclosed by the granitoids of the Timbaúba Pluton. Amphibole-rich clots and chunks of quartz are features shared by many granitoid intrusions of similar ages and compositions in other belts of the Borborema Province (Guimarães and Da Silva Filho, 2003; McReath et al., 1993; Sial et al., 1998). The Timbaúba pluton is intruded into the contact between Cariris Velhos ( Ga) orthogneissmetagreywacke and Neoproterozoic metasedimentary sequences (Gomes, 2001); the latter include garnetbearing biotite gneiss and limestone with Nd model ages (TDM) between 1.5 and 1.4 Ga range. The Tabira pluton intrudes ca Ga orthogneiss (Leite et al., 2000) with Nd model ages in the Ga range (Kozuch et al., 1997). Flat-lying foliation cut by late, high-angle foliation is recorded in the plutons and in their country rocks, suggesting that the emplacement of these granitoids is related to the peak of regional metamorphism and associated with the flat-lying event. Evidence of deformation under high-t conditions recorded within the Timbaúba pluton, dikes of dioritc composition associated with the Timbaúba pluton showing migmatization, and the intrusion of the Timbaúba Pluton during a plastic stage of the country rocks (Fig. 2) suggest that the Timbaúba intrusion was pre- to syn-migmatization. The Itapetim complex cuts Cariris Velhos orthogneisses ( 950 Ma; Kozuch et al., 1997) and metassediments with T DM 1.4 Ga. The ca. 1.0 Ga orthogneisses have flat-lying foliation and are locally migmatized. The Itapetim complex is constituted by epidote-bearing porphyritic monzogranites, with large perthite and plagioclase phenocrysts (up to 7 cm long) in a matrix of biotite, hornblende, microcline plagioclase, and quartz. Swarms of diorite enclaves are quite common. Late dikes of granodioritic composition, showing magmatic foliation and layering, cut the complex. The Bom Jardim complex intrudes migmatite with Sm Nd model ages (TDM) of ca. 2.2 Ga, close to the contact with Mesoproterozoic supracrustal rocks. The Toritama complex intrudes 1.5 Ga orthogneissic migmatites (Sá et al., 2002) and Neoproterozoic paragneisses. Plutons of the complexes range in composition from hornblende-biotite ± clinopyroxene monzonite to syenite. They are very coarse to medium grained, and range in texture from porphyritic to equigranular. Enclaves of mafic syenite and hornblende-biotite diorite are common. The dominant facies is a mafic porphyritic monzonite to syenite, with phenocrysts of perthitic microcline in a medium-grained matrix composed of hornblende and locally contain relicts of clinopyroxene, biotite, microcline, plagioclase, small amounts of quartz, sphene, zircon, apatite, allanite, and monazite. Both intrusions show low-to-moderate inward dipping magmatic foliations. The Fazenda Nova complex, which is part of the Fazenda Nova Serra da Japecanga Batholith (Neves et al., 2000), and the Campina Grande complexes are composed of coarse-grained porphyritic granites intimately associated with hornblende-biotite diorites. The porphyritic granite consists of megacrysts of perthitic microcline up to 10 cm long in a medium-grained matrix of plagioclase, quartz, microcline, hornblende, biotite; the accessory phases are sphene, allanite, zircon, apatite, and magnetite. Primary epidote was recorded in the coarse grained granites from the Campina Grande complex. The mafic facies occur as enclaves with a wide range of sizes. They are dioritic to granodioritic, varying in texture from fine-grained equigranular to porphyritic. The Fazenda Nova complex is mainly intruded into the contact zone between a 2.0 Ga sequence of orthogneisses and migmatized paragneisses and 1.5 Ga orthogneisses (Sá et al., 2002). The Campina Grande complex is intruded into the contact zone between migmatites with T DM 2.0 Ga in the south and early Neoproterozoic (0.95 Ga) orthogneisses in the north. The Pajeú complex intrudes early Neoproterozoic supracrustal rocks (Santos, 1995) and it is comprised of biotite-hornblende bearing, medium-grained Fig. 2. (A) Deformation under high temperature and localized migmatization within the Timbaúba granites; (B) Diorite dyke associated to the Timbaúba intrusion, partially migmatized intruded during a plastic stage of the country rock; (C) Migmatized and folded diorite within the northern border of the Timbaúba intrusion; (D) Apophysis of the Timbaúba granites intruded during a plastic stage of the country rocks.

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8 30 I.P. Guimarães et al. / Precambrian Research 135 (2004) syenogranite and coarse-grained porphyritic monzogranites. Diorite occurs as enclaves within the coarsegrained monzogranite. The Queimadas and Solidão intrusions are comprised of, respectively, biotite-hornblende monzogranites and clinopyroxene-hornblende monzogranites to granodiorites; they also contain rare mafic enclaves. Both plutons had their emplacement controlled by shear zones and show magmatic fabrics overprinted by solid-state deformational fabrics. The Queimadas Pluton intrudes Paleoproterozoic migmatized sillimanite gneisses, with T DM 2.1 Ga (Van Schmus et al., 1995). It is a very large E-W trending dyke, cut by a later NEtrending ductile brittle fault system (Almeida, 1999), that gave the body a mega-boudin shape. Its emplacement is considered to be syn-tectonic to the dextral Campina Grande shear zone. The Solidão pluton intrudes early Neoproterozoic orthogneisses and supracrustal rocks. Its emplacement was initially connected to the kinematics and geometry of the dextral EW-trending Solidão shear zone, which forms a conjugate pair with the sinistral NE-trending Afogados da Ingazeira shear zone. The conjugate shear zones created an extensional zone that allowed the emplacement of the Solidão Pluton (Araújo, 1997). The Serra Branca Pluton is composed of biotite granodiorites to monzogranites. Magmatic foliation is common as well as cross-bedding. The pluton appears to have evolved through distinct magma pulses, associated with the movement of the E-trending, dextral Coxixola shear zone. It is enclosed by Paleoproterozoic gneiss-migmatites with a Sm Nd TDM model age of ca. 2.7 Ga (Guimarães and Da Silva Filho, 1997). The Prata complex comprises two segments separated by a body of norite, which occurs as enclaves in the complex. The southern segment is composed of locally garnet-bearing, undeformed, equigranular to porphyritic biotite syenogranites, showing mixing and comingling with diabase and dacite (Melo et al., 1995). Allanite is the most abundant accessory phase; the crystals can reach up to 2 mm in length. Granitoids in the northern segment have a ubiquitous magmatic foliation. They are medium-to-coarse-grained hornblendebiotite monzogranites. Mafic enclave swarms are common. Rapakivi texture occurs locally. The whole complex cuts Paleoproterozoic migmatites. The Pereiro and Serra do Velho Zuza plutons show roughly rounded shapes and intrude migmatites with the age of 2.0 Ga. The plutons consist of biotite syenogranites which contain some mafic enclaves. Biotites from Pereiro and Serra do Velho Zuza Plutons as well as those from the granites of the Prata Complex are rich in annite, suggesting crystallization under low f O2 conditions. 4. Geochronological data U/Pb zircon analyses were performed at the Isotopic Geochemistry Laboratories, Geology Department, Kansas University, USA. U Pb zircon data were obtained from three or four multicrystal (at least four crystals) magnetic fractions from each intrusion. The procedures are described in Appendix A. The zircon grains were abraded for 2 h and then washed with HNO 3. Those grains clear of inclusions were picked to be analyzed. At least two distinct zircon populations were recorded in the Itapetim complex, Timbaúba and Tabira plutons. The analyzed zircon population consists of euhedral, internally clear zircon grains free of inclusions. The results are shown in Table 1 and Fig. 3A C. The discordia yield upper intercept ages ranging from 645 ± 4.8 Ma (Timbaúba), 638 ± 4.9 Ma (Itapetim), to 624 ± 2.1 Ma (Tabira), when forced to zero. Kozuch (2003) obtained concordant zircon fraction from one sample of the Tabira granodiorite, with the age of 611 ± 9 Ma, and an average of three age determinations of 604 ± 15 Ma, which could be considered identical within error to the regressed age presented here. Ages in the same time span, have been obtained by Kozuch (2003) in other granitoids with similar petrographic and geochemical features (Olho D agua granodiorite with an age of 607 ± 7.7 Ma) and gabbros (Alto Vermelho, age of 619 ± 9 Ma) in the Alto Brígida fold belt and gabbros from the Pajeú-Paraíba belt (Jabitacá, age of 626 ± 3 Ma). The age of 612 ± 9 Ma obtained by Leite et al. (2000) for the metamorphism of the Tabira pluton country rocks is similar to the crystallization age of the Tabira granodiorites, suggesting a chronologic correlation between the intrusion of the Tabira granodiorites and the metamorphism. Only one zircon population was recorded so far within the Bom Jardim, Pajeú and Campina Grande complexes. The zircons are euhedral, pink, clear grains and gave upper intercept ages of 592 ± 7.4 Ma (Bom Jardim pluton), 586 ± 21 Ma (Pajeú Pluton) and 581

9 Table 1 U Pb zircon data from the studied granitoids Sample fraction Weight (mg) U (ppm) Pb (ppm) 206 Pb/ 204 Pb (observed) 206 Pb/ 238 U ±2σ (%) 207 Pb/ 235 U ±2σ (%) 207 Pb/ 206 Pb ±2σ (%) 206 Pb/ 238 U ±2σ (Ma) 207 Pb/ 235 U ±2σ (Ma) 207 Pb/ 206 Pb ±2σ (Ma) Timbaúba M( 1) M(0) NM( 1) Tabira M( 1) M(0) NM( 1) Itapetim complex (see Guimarães and Da Silva Filho, 2000 for data) Bom Jardim complex (sample BJ-275) M(6) a M(1) a M(0) a M(0) b M( 1) a Pajeú complex (PJ-09) M(2) M(0) M(1) Fazenda Nova complex (FN-01) M(1) M(0) M( 1) I.P. Guimarães et al. / Precambrian Research 135 (2004)

10 Table 1 (Continued ) Sample fraction Weight (mg) U (ppm) Pb (ppm) 206 Pb/ 204 Pb (observed) 206 Pb/ 238 U ±2σ (%) 207 Pb/ 235 U ±2σ (%) 207 Pb/ 206 Pb ±2σ (%) 206 Pb/ 238 U ±2σ (Ma) 207 Pb/ 235 U ±2σ (Ma) 207 Pb/ 206 Pb ±2σ (Ma) Campina Grande complex (CG-26A) M(3) a M(1) a M(0) a M( 1) c Queimadas Pluton (see Almeida et al., 2002 for data) Serra Branca (SB-03) M(2) M(1) M(0) M( 1) Solidão Pluton (CS-07) M(1) M(0) M( 1) NM( 1) Serra do Velho Zuza Pluton (SVZ-250) M(2) M(1) M(0) M( 1) Pereiro Pluton (PE-01) M(3) M(0) M( 1) a Abraded for 2 h. b Abraded for 10 h. c Abraded for 15 h. 32 I.P. Guimarães et al. / Precambrian Research 135 (2004) 23 53

11 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 3. U Pb Concordia diagram for the Timbaúba, Itapetim and Tabira intrusions. ± 2 Ma (Campina Grande Pluton) when forced to zero (Table 1; Fig. 4A and B). These data agree with Rb Sr isochron ages of 592 ± 49 Ma for the Pajeú pluton (Guimarães et al., 1999) and of 585 ± 38 Ma for the Bom Jardim and Toritama complexes (Guimarães and Da Silva Filho, 1998). The Fazenda Nova complex, which constitutes the eastern part of the Caruaru Arcoverde batholith (Melo et al., 2000), shows at least two distinct zircon populations. The euhedral, pink, clear zircon population defines an upper intercept age of 588 ± 12 Ma (Table 1, Fig. 4C). This age is similar, within error, to those obtained by Pb Pb zircon evaporation (Melo et al., 2000) in the central part of the Caruaru Arcoverde batholith (591 ± 5 Ma). The Queimadas, Serra Branca, and Solidão Plutons have similar ages, at ca. 570 Ma (Table 1 and Fig. 5A C). The Queimadas and Serra Branca granitoids show at least two zircon populations. The younger populations have ages of 570 ± 24 Ma and 575 ± 16 Ma, respectively, when forced to zero. The Solidão granitoid has a minimum age of 570 ± 21 Ma. This age

12 34 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 4. U Pb Concordia diagram for the Bom Jardim, Campina Grande, Fazenda Nova, Pajeú plutons. is similar to that (1991 ± 61 Ma, U.I.; 574 ± 74 Ma, L.I.) obtained by Kozuch (2003). There is a large inherited component in the rock that has an upper intercept of 2050 ± 62 Ma (Fig. 5C), which is similar to the Sm Nd TDM model ages ( Ga, Guimarães et al., 1998). This suggests that the zircon grains in these granitoids best represent xenocrystic components inherited from the source rocks of the Solidão granitoids. The Serra do Velho Zuza and Pereiro plutons show at least two zircon populations. The light pink, euhedral one gave ages of 538 ± 23 Ma (four fractions) and 544 ± 6.7 Ma (three fractions), respectively (Fig. 6A and B; Table 1). The southern segment of the Prata Complex shows a Rb Sr isochron age of 512 ± 30 Ma (Melo et al., 1995). These crystallization ages allow the studied granitoids to be divided into four groups. Group 1 has ages in the Ma range (Tabira, Timbaúba, Itapetim). Group 2 has ages of Ma (Bom Jardim, Toritama, Pajeú, Fazenda Nova, Campina Grande). Group 3 has ages of ca. 570 Ma (Queimadas, Solidão, Serra Branca). Group 4 has ages in the Ma range (Prata, Pereiro, Serra do Velho Zuza).

13 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 5. U Pb Concordia diagram for the Queimadas, Serra Branca, Solidão plutons. 5. Geochemistry Major and trace element data of representative samples are given in Table 2. The granitoids of Groups 2 4 are K-rich rocks (Fig. 7) with K 2 O/Na 2 O ratios > 1, while granitoids from Group 1 show Na 2 O K 2 O. The dioritic enclaves hosted by granitoids of Group 1 are clearly less K-rich than the diorites hosted by granitoids of Group 2 (Guimarães et al., 2001). All granitoids studied are metaluminous to slightly peraluminous with A/CNK 1.1 (Fig. 8). The granitoids from Group 2 are high-k calc-alkaline (Fazenda Nova and Campina Grande) and shoshonitic (Bom Jardim, Toritama and Pajeú Guimarães and Da Silva Filho, 1998). They show the lowest FeO tot /(FeO tot + MgO) ratios (Table 2) among the granitoids studied ( 0.60). Group 3 granitoids have high FeO tot /(FeO tot + MgO) ratios (Table 2). They are geochemically similar to the postcollisional ferro-potassic granitoids of Nigeria (Ferré et al., 1998). The granitoids of Group 4, the youngest, are SiO 2 -rich (>70 wt.%) and show more alkalic character, with higher contents of alkalis, Rb, Zr, Nb, Y, and lower contents of Ba and Sr compared to granitoids of the other groups; they also have high FeO tot /(FeO tot + MgO) ratios, similar to those recorded in granitoids of Group 3. The granitoids of Groups 3 and 4 fall within the ferroan plutons field (Fig. 9) in the FeO tot /(FeO tot + MgO) versus SiO 2 diagram of Frost et al. (2001), reflecting a close affinity to relatively anhydrous and reduced magmas, which are common conditions in exten-

14 36 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 6. U Pb Concordia diagram for the Pereiro, Serra dovelho Zuza plutons. sional environments. In contrast, granitoids of Groups 1 and 2 plot within the magnesian plutons field (Fig. 9), reflecting hydrous, oxidizing magmas (Frost and Lindsley, 1991). The origin of magnesian granitoids has been interpreted as related to subduction (Frost et al., 2001). All four groups of the studied granitoids fall within the field of the Caledonian post-collisional granitoids from Ireland and Great Britain (Fig. 9). Chondrite normalized REE patterns (Fig. 10) show that the REE are comparatively lower in granitoids

15 Table 2 Representative major and trace element compositions of the studied granitoids Sample Intrusion Timbaúba Itapetim Tabira Pajeú Bom Jardim Toritama Campina Grande TI-33 TI-12 IG-01 IG-36 CT-22 CT-24 PJ-08 PJ-09 BJ-75 BJ-344 TO-03 TO-04 CG 23 CG 21 SiO TiO Al 2 O Fe 2 O MgO CaO Na 2 O K 2 O P 2 O MnO LOI Total ppm Ni < Cr < Zr Hf Y Nb Ta <0.5 < Ba Sr Rb Th La Ce Nd Sm Eu Gd Tb Ho Tm < Yb Lu Fe I.P. Guimarães et al. / Precambrian Research 135 (2004)

16 Table 2 (Continued ) Sample Intrusion Solidão Serra Branca Queimadas Serra do Zuza Pereiro Prata CS-14 CS-39 SB-05 SB-09 QM-91 QM-107 SZ-222 SZ-231 PE-54 PE-208 PRT-38 PRT-34 SiO TiO Al 2 O Fe 2 O MgO CaO Na 2 O K 2 O P 2 O MnO LOI Total ppm Ni <5 < <5 5 <5 Cr <10 <10 80 < < <10 Zr Hf Y Nb Ta <0.5 <5 < Ba Sr Rb Th La Ce Nd Sm Eu Gd Tb Dy= Ho Er=5.57 Er = 4.7 Tm < Yb Lu <0.2 < o nd 0.6 Fe Fe = Feot/(MgO+FeOt). 38 I.P. Guimarães et al. / Precambrian Research 135 (2004) 23 53

17 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 7. K 2 O vs. SiO 2 for the studied granitoids. Fields after Peccerillo and Taylor (1976). (A) Soshonitic series; (B) high-k calc-alkaline series; (C) calc-alkaline series; (D) tholeiitic series. with SiO 2 >69 wt.%. Significant Eu anomalies are not observed in the patterns of Groups 1 and 2, and both groups have fractionated patterns with (Ce/Yb) N > 30. The granitoids of Group 3, except for the Solidão pluton, show significant negative Eu anomalies (Eu * = ) and (Ce/Yb) N ratios in the range. The Solidão granitoids show small positive Eu anomalies and (Ce/Yb) N ratios ranging from 19 to 25 (Fig. 9C), suggesting that they originated from a distinct source. The Group 4 granitoids have higher HREE contents and their patterns are characterized by deep negative Eu anomalies (Eu * = ), and low (Ce/Yb) N ratios (10 25). Trace element distribution patterns (Fig. 11A D) show that all granitoids studied have Nb depletion, which decreases slightly from Group 1 to 4. Troughs are also observed at Ti and Sr and tend to increase in magnitude from Group 1 to 4. The Solidão pluton is an exception, showing small peaks at Sr, which in association with small positive Eu anomalies, suggests an evolution involving feldspar accumulation. All the granitoids studied are enriched in LILE (large ion lithophile elements) compared to HFSE (high field strength elements), which is a general characteristic of calc-alkaline granitoids. Larger negative anomalies in Sr and Ti and distinctively higher contents of Y and Yb are observed in the granitoids from Group 4, similar to those recorded in A-type granitoids (Whalen et al., 1987). The patterns of the granitoids from Groups 1 and 2 display no significant troughs at Sr, less pronounced Ti troughs, and lower Y, Yb, and Nb values, resulting in a trace element distribution pattern characteristic of calc-alkaline arc granitoids.

18 40 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 8. Shand s Index for the studied granitoids; fields after Maniar and Piccoli (1989). Discriminant diagrams of Pearce (1996); Pearce et al. (1984) are used here to summarize some of the geochemical trace element features of the granitoids (Fig. 12). Group 1 granitoids have trace element com- positions which plot within the volcanic arc granitoid field. Granitoids from Group 2 have compositions, which range from the volcanic arc granitoid field to the syn-collision granite field. Granitoids from Group 3 Fig. 9. The compositional range of the studied granitoids in the FeO tot /FeO tot + MgO) vs. weight percent SiO 2 diagram. Fields of Ferroan and Magnesian granitoids as well as the field (gray) of Caledonian post-collisional plutons from Ireland and Britain are from Frost et al. (2001).

19 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 10. Chondrite- normalized REE patterns (Sun, 1982) of the studied granitoids. plot within the fields of volcanic arc and within-plate granites. Group 4 granitoids are Nb- and Y-rich, plotting in the within-plate granite field. They are compositionally similar to A-type granites. All the granites studied plot within the post-collision granitoids field of Pearce (1996) diagram. However, as pointed out by Pearce (1996), the post-collision granites are the most difficult to classify, since some have subduction-like mantle sources with many characteristics of volcanic arc granites, and others show within-plate granite character. Interaction between mantle-derived sources and crust tends to move the granite composition towards the volcanic arc field. In the Central Tectonic Domain of the BP, evidence for subduction of oceanic lithosphere are very local (Beurlen et al., 1992), indicating that the Brasiliano Orogeny was mainly ensialic, as proposed by Jardim de Sá (1984), and the arc signature may be inherited from the source Sm Nd geochemical data Sm Nd isotopic analyses were made at the Isotope Geochemistry Laboratories, Kansas University, USA. The methodology is described in Appendix A. Results of representative samples are presented in Table 3. The older granitoids (Itapetim, Timbaúba and Tabira) show younger Sm Nd TDM model ages, similar to those recorded in the metagreywacke and metaigneous country rocks ( Ga), and higher ε Nd values (Fig. 13A). These are the only granitoids studied showing Mesoproterozoic TDM model ages. The granitoids of Group 2, including syenites monzogranites, mafic syenite and dioritic enclaves, show Sm Nd TDM model ages in the Ga range and ε Nd (at 590 Ma) ranging from 14 to 10. These data suggest that the sources of these granitoids could be a Transamazonian enriched lithospheric

20 42 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 11. Chondrite normalized, trace element abundance diagrams (spidergrams) for representative samples of the studied granitoids. Normalization factors are from Thompson (1982). mantle (diorites and syenites) and lower crust (granites). Because the syenites, diorites and granites have similar Sm Nd isotopic signature, the lower crust was probably extracted from a Paleoproterozoic lithospheric mantle, during the initial stage of the Brasiliano Orogeny. The 570 Ma granitoids show older TDM model ages ( Ga). The oldest TDM ages were recorded in the Serra Branca pluton, suggesting contribution of an Archean component in its source. The Queimadas magma probably originated by melting of granodiorite from lower crust (Almeida, 1999). Table 3 Summary of representative Sm/Nd isotopic results Intrusion Sample Nd (ppm) Sm (ppm) 147 Sm/ 143 Nd 143 Nd/ 144 Nd ± 2 ε Nd(0) ε Nd(t) T DM (Ga) Itapetim ITA ± Tabira CT ± Timbaúba TI ± Pajeú PJ ± Toritama TO ± Bom Jardim BJ ± Fazenda Nova FN ± Campina Grande CG ± Solidão CS ± Serra Branca SB ± Queimadas NA ± Prata PR-34D ± Pereiro PE ± Velho Zuza VZ ± Note: 143 Nd/ 144 Nd normalized to 146 Nd/ 144 Nd = ε Nd (0) calculated relative to CHUR(0) = Model ages (T DM ) were calculated according to the single-stage depleted-mantle model of DePaolo (1981). Ages used for ε Nd (t) are based on U/Pb ages or Rb/Sr age (Prata complex).

21 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 12. Studied granitoids in the tectonic discriminant diagrams of (A) Pearce et al. (1984) and (B) Pearce (1996). Granitoids from Group 4 have Sm Nd geochemistry signature similar to those recorded in granitoids of Group Discussion The granitoids studied record a long period of granitic magmatism ( 100 m.y.) during the Neoproterozoic in the Central Tectonic Domain of the BP. The oldest granitoids are associated with diorites and are low-to-slightly high-k calc-alkaline. However, the contents of K, even in the high-k case, are lower than those recorded in the granitoids of Group 2. To explain the Mesoproterozoic TDM ages recorded in these rocks it is necessary that isotopic interaction with the host monzogranites occurred. The geochemical and isotopic signature associated with the presence of quartz enclaves in the monzogranites are consistent with an origin by melting of metagreywackes, which originally formed from a mixture of Paleoproterozoic (2.0 Ga) ortho derived crust, Cariris Velhos (1.0 Ga) juvenile material, and small amount of metasediments. The origin of medium to slightly high-k granitoids of Group 1 (Itapetim complex) has been discussed in detail by Guimarães and Da Silva Filho (2000). Calc-alkaline granitoids with ages in the same time span Ma have also been recorded in the Piancó Alto Brígida belt and in the Sergipano belt of the Southern Domain (Table 4). The granitoids of Group 1 have most of the

22 44 I.P. Guimarães et al. / Precambrian Research 135 (2004) Fig. 13. Nd isotopic composition of the studied granitoids. Isotopic notations, model ages and reference mantle reservoirs are from De Paolo (1988). features of ACG granitoids of Barbarin (1999), which are the most abundant granitoids in volcanic island arcs and active continental margins associated with K-rich calc-alkaline granitoids. In Cameroon, ages of (630 ± 5) and (620 ± 10) Ma were recorded in recrystallized zircons from syntectonic granitoids and on metamorphic minerals, respectively (Toteu et al., 1990, 1994). In Cameroon this period was interpreted as a stage of convergence, during which a flat-lying foliation was developed under conditions of garnet-kyanite (northern Cameroon) or granulite facies (southern Cameroon) metamorphism and in association with calc-alkaline plutonism (Toteu et al., 2001). Granitoids of Group 1 were deformed under high-t conditions and were intruded parallel to the country rock foliation, during a flat-lying foliation forming event. This evidence, associated with the crystallization age of these granitoids, a U/Pb sphene age recorded by Leite et al. (2000) in early Neoproterozoic orthogneisses, and a possible correlation with the Cameroon Province, strongly suggests that Group 1 granitoids represent crust reworking during the peak of metamorphism. The stage of convergence ended in Cameroon with general anatexis at 620 Ma (Toteu et al., 2001). In the Central Tectonic Domain of the Borborema Province, rare geochronological data for the Ma period (Leite et al., 2000) is an exception. In the Timbaúba area, field relationships suggest that