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Journal of South American Earth Sciences 25 (2008) 285–297

U–Pb ages of plutonic and metaplutonic rocks in southernBorborema Province (NE Brazil): Timing of Brasiliano

deformation and magmatism

Sergio P. Neves a,*, Olivier Bruguier b, Delphine Bosch c,Jose Maurıcio Rangel da Silva a, Gorki Mariano a

a Departamento de Geologia, Universidade Federal de Pernambuco, 50740-530 Recife, Brazilb ISTEEM, Service ICP-MS, Universite de Montpellier II, 34095 Montpellier, France

c Laboratoire de Tectonophysique, Universite de Montpellier II, 34095 Montpellier, France

Abstract

The Borborema Province of northeastern Brazil is divided into three main domains: northern, central, and southern. Several U–Pb zirconages of plutons and orthogneisses became available in the recent years in the central and northern domains, but similar results are scarcein the southern domain. This study reports U–Pb dates for single zircon grains from one orthogneiss (Jupi orthogneiss) and two plutons(Cachoeirinha syenitic pluton and Cabanas granite) south of the East Pernambuco shear zone system (EPSZ). The results provide geo-chronological constraints on the timing of deformation and magmatism in this part of the southern domain and allow correlations withthe central domain. The Jupi orthogneiss was emplaced and deformed during development of the regional flat-lying foliation. A206Pb/238U weighted apparent mean age of 606 ± 8 Ma is interpreted as the crystallization age of the protolith of the orthogneiss andconsequently the age of high-grade Brasiliano metamorphism. The NNE-trending Cachoeirinha pluton is only locally affected bystrike-slip deformation, whereas the ENE-trending Cabanas granite is intensely affected by deformation related to the EPSZ. The587 ± 8 Ma and 573 ± 4 Ma ages of the Cachoeirinha pluton and Cabanas granite, respectively, bracket the main period of activityof the EPSZ. Tectonomagmatic activity in the study area is similar to the age of Brasiliano events in the central domain, north ofthe EPSZ. In addition, xenocrystic zircons in the Jupi orthogneiss and Cabanas granite are interpreted as inherited from Paleoprotero-zoic source rocks, suggesting the presence of widespread reworked old crust in the southern domain, similar to the central domain. Theseresults support the idea that the central and southern domains belonged to the same crustal block before the onset of the Brasilianoorogeny.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Laser ablation ICP-MS; Zircon U–Pb geochronology; Neoproterozoic plutons; Brasiliano orogeny

Resumo

A Provıncia Borborema (Nordeste do Brasil) e dividida em tres grandes domınios: norte, central e sul. Varias datacoes U–Pb em zircaoforam adquiridas nos ultimos anos nos domınios norte e central, mas sao escassas no domınio sul. Neste estudo sao apresentadas idadesU–Pb de zircoes de um ortognaisse (ortognaisse Jupi) e de dois plutons (Cachoeirinha, de composicao sienıtica, e Cabanas, de compos-icao granıtica) localizados ao sul da zona de cisalhamento Pernambuco leste (ZCPE). Estes resultados sao os primeiros a serem reporta-dos para eventos deformacionais e magmaticos nesta parte do domınio sul e permitem estabelecer correlacoes com o domınio central aonorte da ZCPE. O ortognaisse Jupi foi alojado e deformado durante o desenvolvimento da foliacao regional de baixo angulo. Uma idademedia 206Pb/238U de 606 ± 8 Ma e interpretada como a idade de cristalizacao do protolito do ortognaisse e, consequentemente, do

0895-9811/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jsames.2007.06.003

* Corresponding author. Tel.: +55 081 327 18240; fax: +55 081 327 18 234.E-mail address: serpane@hotlink.com.br (S.P. Neves).

286 S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297

metamorfismo Brasiliano. O pluton Cachoeirinha, de direcao NNE-SSW, e afetado por deformacao nao-coaxial apenas localmente,enquanto o Granito Cabanas, de direcao ENE-WNW, e fortemente deformado na sua porcao norte pela ZCPE. As idades de587 ± 8 Ma e 573 ± 4 Ma destes dois plutons limitam o perıodo principal de funcionamento da ZCPE. A atividade termotectonicana area estudada e similar a idade de eventos brasilianos no domınio central ao norte da ZCPE. Adicionalmente, populacoes de xenoc-ristais de zircao no ortognaisse Jupi e no Granito Cabanas herdadas de fontes Paleoproterozoicas sugerem a presenca no domınio sul deextensas areas antigas retrabalhadas, similarmente ao observado no domınio central. Estes resultados indicam que os domınios central esul pertenciam ao mesmo bloco crustal antes do inıcio da orogenese Brasiliana.� 2007 Elsevier Ltd. All rights reserved.

Palavras-chave: ICP-MS; Geocronologia U–Pb; Zircao; Plutons neoproterozoicos; Orogenese Brasiliana

1. Introduction

The Neoproterozoic evolution of Borborema Province(NE Brazil) is still a contentious issue, with contrastingmodels for the tectonic setting in which magmatic anddeformational events occurred. In particular, the signifi-cance of the Cariris Velhos event and whether the Brasil-iano orogeny took place in an intracontinental settinghave been debated. The Cariris Velhos event was definedin the central domain of the Borborema Province follow-ing the recognition of a metavolcanosedimentary belt withintercalated orthogneisses of early Neoproterozoic age(Brito Neves et al., 1995). For a group of workers, thisbelt formed as a consequence of a complete orogeniccycle. They also suggested the possibility that this oro-genic event affected other portions of the BorboremaProvince, mainly in its southern domain (Brito Neveset al., 1995, 2000; Kozuch, 2003). Conversely, others con-sider that the belt where the Cariris Velhos event has beenrecorded was a continental rift intruded by intraplategranites, with deformation and metamorphism only occur-ring during the Brasiliano orogeny (Neves, 2003; Gui-maraes and Brito Neves, 2004; Neves et al., 2004).Regarding the geodynamic evolution of the BorboremaProvince during the Neoproterozoic, again two opposingviews compete. In one model, the Borborema Province isregarded as an accretionary orogen whose evolutioninvolved a collage of allochtonous terranes (Santos andMedeiros, 1999; Brito Neves et al., 2000; Santos et al.,2004). The other model proposes that intraplate tectonismdriven by far-field stresses reworked preexisting Archean–Paleoproterozoic crust and younger sedimentary succes-sions deposited dominantly in continental basin settings(Neves, 2003; Neves et al., 2004, 2006).

Geochronological data together with conventional fieldand petrologic studies are required to tackle these contro-versies. Numerous U–Pb ages of plutons and orthogneis-ses became available in recent years in the central andnorthern domains (see reviews by Brito Neves et al.,2000; Neves, 2003; Neves et al., 2006). Similar resultsare scarce in the southern domain, and their acquisitionis essential to compare tectonomagmatic events at a prov-ince-wide scale. In this paper, we report laser ablationinductively coupled plasma-mass spectrometry (LA-ICP-

MS) zircon U–Pb ages of two plutons and one orthogneisssouth of the East Pernambuco shear zone system (EPSZ),which is conventionally taken as the limit between thecentral and southern domains in the eastern part of theBorborema Province. These are the first U–Pb zircon agesreported so far for this portion of the southern domain.Along with available structural information (Neveset al., 2003, 2005), they provide well-constrained agelimits for the main period of tectonic activity related tothe Brasiliano orogeny and shed new light on the age ofbasement rocks underlying the study area. In addition,we compare our new data with recently published datapertaining to north of the EPSZ (Brito Neves et al.,2001; Guimaraes et al., 2004; Neves et al., 2006) to evalu-ate possible correlations between the central and southerndomains.

2. Geological setting

2.1. Previous geochronological work

The geology of the southern domain south of the EPSZ(Fig. 1) is dominated by high-grade, commonly migmatiticorthogneisses and metasedimentary rocks and numerouslarge igneous intrusions. Orthogneisses and supracrustalrocks are grouped, respectively, in the Belem do Sao Fran-cisco and Cabrobo complexes (Medeiros, 1998; Gomes,2001). Only a few geochronological data are available forthese units. Zircons from two samples of orthogneisseswrapped by mylonites of the EPSZ, but still preserving aflat-lying foliation, have been dated by the Pb-evaporationmethod (Neves et al., 2004). One sample, a medium-grained quartz dioritic gneiss, yields an age of2075 ± 7 Ma, interpreted as the crystallization age of theprotolith of the orthogneiss during the Transamazonianevent. The other, a coarse-grained granitic gneiss (Caruaruorthogneiss; Fig. 1), yields a Neoproterozoic age of629 ± 9 Ma, indicating the existence of a flat-lying, folia-tion-forming event during the Brasiliano orogeny.40Ar/39Ar biotite ages around 560 Ma were obtained forone pluton and a peraluminous orthogneiss (Osako,2005). These ages are older than 40Ar/39Ar biotite agesfrom granitic mylonites in the EPSZ and in plutons andcountry rocks north of the EPSZ (545–533 Ma; Neves

Fig. 1. Sketch map of Borborema Province showing the main transcurrent shear zones and its division into northern (ND), central (CD), and southern(SD) domains, with location of study area south of the East Pernambuco shear zone system (EPSZ). The main map shows the main geological units of thestudy area and location of dated samples.

S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297 287

et al., 2000), which indicates that regional cooling toaround 300–350� (approximate closure temperature forAr diffusion in biotite; e.g., Dahl, 1996) in the southerndomain was reached 15–25 Ma earlier than in the centraldomain.

Nd isotope data also provide some time constraints forthe southern domain. Nd model ages of supracrustal andmigmatitic rocks yield mostly Paleoproterozoic–Archeanages (2.0–2.6 Ga; Da Silva Filho et al., 2002; Osako,2005), but one Mesoproterozoic age (1.09 Ga) wasobtained for a sample of biotite gneiss (Da Silva Filhoet al., 2002). Most plutons also have PaleoproterozoicTDM ages, mainly between 1.8 and 2.2 Ga. However, onegroup of plutons yields distinctly younger Nd model ages,mainly between 1.5 and 1.0 Ga (Da Silva Filho et al.,2002). These data suggest that a large part of the southerndomain formed during the Paleoproterozoic but the addi-

tion of juvenile material occurred during Mesoproterozoicand/or Neoproterozoic times.

2.2. Study area

The study area comprises ortho- and paragneisses ofvariable composition and several large igneous intrusions,two of which are considered herein: the Cachoeirinha plu-ton and the Cabanas granite (Fig. 1). Grey gneisses andmigmatitic orthogneisses with mafic/intermediate proto-liths, interpreted as basement complexes, dominate in theeast. The small Caruaru orthogneiss, a biotite amphibolegranitic gneiss, occurs south of the homonymous city andis distinguished from the grey gneisses by its coarse grainsize, granitic composition, and usually lower strain. Thesouthern part of the study area is dominated by a graniticorthogneiss, here named the Jupi orthogneiss, which is

Fig. 2. (A) Field and (B,C) microstructural aspects in crossed polars of the Jupi orthogneiss. (A) Subhorizontal foliation containing a xenolith of flattenedpelitic paragneiss. (B) Foliation defined by mica flakes and an elongate K-feldspar grain (left upper side) that probably represents a magmatic crystal thatdid not fully recrystallize during synmagmatic deformation. (C) Dominant granoblastic microstructure with polygonal aggregates of quartz, K-feldspar,and plagioclase typical of high-temperature recrystallization.

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intruded by several small bodies of diorite and leucogra-nite. In contrast with the grey gneisses, the Jupi orthogneissis a leucocratic, generally muscovite-bearing biotite gneissthat locally contains a large amount of xenoliths of peliticparagneiss (Fig. 2A). These xenoliths are petrographicallysimilar to micaschists and paragneisses that dominate thewestern part of the study area and display the assemblagebiotite ± muscovite ± sillimanite + garnet + plagioclase +quartz. The Jupi orthogneiss presents a dominantly flat-lying foliation that is cross-cut by a subvertical sinistral shearzone in its western portion (Fig. 1). A flat-lying foliation isalso dominant in the other metasedimentary and metaig-neous units, away from shear zones and Brasiliano plutons.

The biotite–muscovite-bearing Cabanas granite, whichcrops out at the southern side of the EPSZ (Fig. 1), con-tains xenoliths of high-T granitic mylonites. These xeno-liths are similar to those that resulted from deformationof granitoids of the Caruaru–Arcoverde batholith in thenorthern branch of the EPSZ, indicating intrusion afterthe onset of the activity in the EPSZ (Neves et al., 2003).The ENE-trending shape of the Cabanas granite, togetherwith the parallelism between magnetic foliations and linea-tions, obtained by anisotropy of magnetic susceptibility(AMS), inside the pluton and the mylonitic fabric of theEPSZ, indicates crystallization under the influence of thedextral transcurrent regime (Neves et al., 2003). The

contact between the Cabanas granite and the Cachoeirinhapluton was not directly observed in the field. However, (1)dikes of biotite granite and muscovite-bearing pegmatite,which might be genetically related to the Cabanas granite,locally intrude the Cachoeirinha pluton and (2) the Caba-nas granite intrudes a granitic pluton that shows concor-dant contacts with the Cachoerinha pluton. Theseobservations suggest the Cachoeirinha pluton is older thanthe Cabanas granite.

The Cachoeirinha pluton contains two main petro-graphic facies: inequigranular to porphyritic biotite amphi-bole syenite and medium-grained biotite amphibole quartzsyenite. The biotite amphibole syenite is the most abundantfacies and constitutes most of the northern and easternparts of the pluton. The biotite amphibole quartz syeniteis mostly found in the central and southern parts of the plu-ton. Magmatic foliation defined by the shape-preferred ori-entation of K-feldspar is visible in most outcrops of thebiotite amphibole syenite, especially close to the margins,with steep dips dominantly to ESE. Solid-state deforma-tion overprinting of the magmatic foliation is restricted inmost places to weak deformation at high temperatures, asshown by chessboard extinction in quartz and developmentof myrmekitic intergrowths around K-feldspar. Strongersolid-state deformation occurs along meters to tens ofmeters long sinistral and dextral shear zones. Dextral and

Fig. 3. SEM images of selected dated zircon grains of the Jupi orthogneisssample showing position of the LA-ICP-MS spots (spot size �25 lm) andcorresponding ages (errors quoted at the 2r level). (A) Euhedral zirconwith faint oscillatory zoning representative of the dominant population.(B) Elongate zircon with rounded corners. (C) Equidimensional anhedralzircon.

S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297 289

sinistral shear zones are consistently oriented NNE andENE, respectively. These observations, in association withan AMS survey, are evidence that intrusion of the Cach-oeirinha pluton occurred during bulk NW–SE shortening,with zones of non-coaxial shear developing locally (Neveset al., 2005).

3. Studied samples

The Jupi orthogneiss sample presents, in thin section, afoliation defined mainly by biotite together with thinmuscovite and subordinately by elongate grains of K-feld-spar and plagioclase (Fig. 2B and C). These elongate feld-spar grains indicate the igneous origin of the rock, butmetamorphic recrystallization is extensive. A polygonalmicrostructure in which most feldspar and quartz grainsmeet at triple junctions dominates, indicating that solid-state recrystallization occurred at high temperature(Fig. 2C). Apart from zircon, apatite is the only prominentaccessory, occurring as short prismatic crystals included orpartially included in biotite and feldspars. Zirconsextracted from this sample cluster in two distinct groupson the basis of their morphology, as observed by scanningelectronic microscopy (SEM; Fig. 3). One population con-sists of euhedral to suhedral grains with preserved crystalfaces and oscillatory zoning, typical of igneous crystalliza-tion (Fig. 3A). The other comprises equidimensionalrounded grains and elongated grains with rounded corners,which are characteristics of detrital grains transported dur-ing sedimentary processes (Fig. 3B and C).

The sample of the Cachoeirinha pluton chosen for geo-chronological work came from the biotite amphibole sye-nite facies. It contains large grains of amphibole and K-feldspar in an equigranular matrix composed of microcline,plagioclase, biotite, and minor quartz. Magnetite, sphene,zircon, and apatite occur as accessory phases. The zirconsare elongated and present bipyramidal terminations typicalof a magmatic growth (Fig. 4). The sample of the Cabanasgranite was deformed by strike-slip shearing and displaysmicrostructural features typical of mylonites deformed atintermediate temperature conditions, with porphyroclastsof K-feldspar and plagioclase wrapped by quartz, musco-vite and biotite. Zircon and apatite are the only accessoryphases. No SEM images are available for zircons of thissample.

4. Analytical techniques

Zircons were separated using conventional techniques.After crushing and sieving of the powdered samples, heavyminerals were concentrated by panning and then by heavyliquids. The heavy mineral concentrates were subsequentlyprocessed by magnetic separation on a Frantz separator.Zircon grains were hand picked from the non-magneticfraction at 1.5 A intensity and 2� side tilt. The grains werethen mounted on adhesive tape, enclosed in epoxy resinwith chips of a standard material (G91500; Wiedenbeck

et al., 1995), and polished to about half of their thickness.U–Pb data were acquired at the University of MontpellierII using a 1991 vintage VG Plasmaquad II turbo ICP-MScoupled with a Geolas (Microlas) automated platform

Fig. 4. SEM images of selected dated zircon grains of the Cachoeirinhapluton sample showing position of the LA-ICP-MS spot (spot size �25 l)and corresponding age (errors quoted at the 2r level).

290 S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297

housing a 193 nm Compex 102 laser from LambdaPhysik.Details of the analytical procedures and data reduction aredescribed in Neves et al. (2006).

5. Results

Table 1 shows the results of the analytical data for thestudied samples. Ages of zircons are expressed in termsof either their 207Pb/206Pb ratios (grains older than 1 Ga)or their 206Pb/238U ratios (grains with Neoproterozoicages). Errors for single analysis and mean ages are quotedat the 2r level.

5.1. Jupi orthogneiss

Analyses of zircons from the studied sample of the Jupiorthogneiss cluster into two age groups (Fig. 5a). Seventeenof the analyzed grains plot close to the concordia and yielda 206Pb/238U weighted apparent mean age of 606 ± 8 Ma(MSWD = 0.64; Fig. 5b). These grains are euhedral, con-tain oscillatory magmatic zoning, and have high Th/U

ratio (0.54–2.5; Table 1). Therefore, the weighted meanage is interpreted as the age of zircon crystallization froma melt (magmatic age) and, consequently, of the igneousprotolith of the orthogneiss.

Other analyses indicate old, Paleoproterozoic ages(Fig. 5c), among which six cluster close to concordia andyield a weighted 207Pb/206Pb mean age of 1980 ± 13(MSWD = 1.5). The oldest grain analysed exhibits a207Pb/206Pb age of 2108 ± 36 Ma. These ages wereobtained on rounded zircon grains or elongated zircongrains with rounded corners. In both cases, the zirconshave high Th/U ratios similar to magmatic ones. Theyare interpreted as xenocrysts inherited from the parent rockthat melted to produce the protolith of the Jupiorthogneiss.

5.2. Cachoeirinha pluton and Cabanas granite

Analysed zircons from the sample of the Cachoeirinhapluton yield a weighted 206Pb/228U mean age of587 ± 8 Ma (MSWD = 0.49; Fig. 6). The euhedral shapeand high Th/U ratio (0.48–1.55; Table 1) of the grains indi-cate that this age must correspond to the zircon crystalliza-tion age and thus to the date of emplacement of theCachoeirinha pluton.

Analyses of zircon grains from the Cabanas granite lieon a discordia with an upper intercept of 2192 ± 14 Maand a lower intercept of 570 ± 7 Ma (MSWD = 1.06;Fig. 7a). The lower intercept is anchored by 16 concordantanalyses that yield a weighted 206Pb/228U mean age of573 ± 4 (MSWD = 1.07; Fig. 7b), which is considered thebest estimate for the emplacement age of the intrusion.The upper intercept is interpreted as the average age of axenocrystic component derived from deep-seated sourcerock. One analysis at 3383 ± 30 Ma and another at1560 ± 16 Ma suggest that the parent rock also includedArchean and Mesoproterozoic components.

6. Discussion

6.1. Brasiliano-age events

The 606 ± 8 Ma age of the Jupi orthogneiss is consid-ered to represent the crystallization of its granitic proto-lith. Together with the high-temperature gneissic fabric,this age is taken as evidence that the Jupi orthogneisswas a synkinematic intrusion emplaced during a high-grade tectonic event. Likewise, the 629 ± 9 Ma age ofthe Caruaru orthogneiss (Neves et al., 2004) is interpretedas dating the emplacement of its granitic protolith. Intru-sion of the protoliths of both the Caruaru orthogneissand the Jupi orthogneiss clearly predates the developmentof transcurrent shear zones, because strike–slip-relatedmylonitic belts truncate their subhorizontal fabric (Neveset al., 2004). Considering that the structure in these tworock units parallels that present in migmatized metasedi-mentary rocks and grey orthogneisses, we propose that

Table 1U–Th–Pb LA-ICP-MS results for zircon grains from plutonic bodies of the southern domain of Borborema Province (Brazil)

Sample Pb (ppm) U (ppm) Th (ppm) Th/U 208Pb/206Pb 207Pb/206Pb ± (1s) 207Pb/235U ± (1s) 206Pb/238U ± (1s) Rho Apparent ages (Ma)

206Pb/238U ± (1s) 207Pb/206Pb ± (1s)

Cachoeirinha pluton

sc4* 23 185 200 1.08 0.375 0.0623 0.0030 0.7985 0.0531 0.0929 0.0043 0.70 573 25 686 102sc33* 52 540 257 0.48 0.165 0.0619 0.0016 0.7957 0.0258 0.0932 0.0019 0.64 574 11 672 54sc15* 60 575 425 0.74 0.227 0.0608 0.0006 0.7822 0.0243 0.0933 0.0028 0.95 575 16 631 20sc40* 43 415 232 0.56 0.218 0.0642 0.0034 0.8272 0.0462 0.0934 0.0017 0.32 575 10 750 112sc32* 19 138 133 0.97 0.465 0.0652 0.0024 0.8544 0.0882 0.0950 0.0092 0.94 585 54 782 76sc31* 22 184 200 1.08 0.357 0.0594 0.0012 0.7789 0.0301 0.0951 0.0032 0.86 586 19 581 43sc36* 36 250 156 0.62 0.444 0.0617 0.0038 0.8100 0.0578 0.0951 0.0035 0.52 586 21 665 131sc18* 58 528 465 0.88 0.251 0.0630 0.0015 0.8288 0.0416 0.0954 0.0042 0.88 587 25 710 51sc3* 26 196 304 1.55 0.448 0.0656 0.0011 0.8688 0.0609 0.0960 0.0066 0.97 591 38 795 34sc9* 23 187 286 1.53 0.442 0.0618 0.0012 0.8226 0.0289 0.0966 0.0028 0.83 594 16 666 42sc8* 60 518 376 0.73 0.234 0.0607 0.0019 0.8131 0.0302 0.0971 0.0020 0.56 597 12 630 66sc19* 65 599 555 0.93 0.252 0.0617 0.0030 0.8281 0.0535 0.0974 0.0041 0.65 599 24 663 106sc38* 53 482 357 0.74 0.251 0.0610 0.0027 0.8195 0.0622 0.0974 0.0060 0.81 599 35 639 95sc6* 27 221 199 0.90 0.297 0.0621 0.0026 0.8376 0.0412 0.0977 0.0025 0.51 601 14 679 90sc24* 44 406 235 0.58 0.184 0.0641 0.0013 0.8663 0.0288 0.0980 0.0025 0.78 603 15 745 44sc10 10 85 76 0.88 0.244 0.0624 0.0006 0.8922 0.0177 0.1037 0.0018 0.89 636 11 688 19

Mean = 586.6 ± 8.4 [1.4%] 95% conf. Wtd bydata-pt errs only, 1 of 16 rej. MSWD = 0.49,probability = 0.94

Jupi orthogneiss

sb15 9 90 202 2.25 0.394 0.0590 0.0010 0.6430 0.0115 0.0790 0.0004 0.30 490 3 567 37sb11* 5 40 48 1.19 0.354 0.0631 0.0014 0.8355 0.0288 0.0961 0.0026 0.78 591 15 711 46sb20* 6 61 33 0.54 0.254 0.0593 0.0011 0.7902 0.0295 0.0966 0.0031 0.87 595 18 578 40sb29* 8 61 96 1.57 0.481 0.0590 0.0022 0.8345 0.0438 0.1025 0.0038 0.7 629 22 568 82sb18* 5 42 41 0.98 0.323 0.0640 0.0028 0.8030 0.0505 0.0910 0.0042 0.73 561 25 742 91sb6* 3 25 38 1.49 0.378 0.0582 0.0025 0.7917 0.0423 0.0987 0.0032 0.61 607 19 536 92sb13* 3 26 31 1.18 0.371 0.0607 0.0025 0.8234 0.0429 0.0984 0.0032 0.62 605 19 629 88sb7* 4 30 51 1.71 0.394 0.0622 0.0002 0.8104 0.0298 0.0945 0.0035 1.00 582 20 680 7sb23* 3 27 26 0.97 0.343 0.0611 0.0015 0.8493 0.0332 0.1007 0.0031 0.78 619 18 644 53sb10* 6 55 62 1.14 0.335 0.0609 0.0021 0.8295 0.037 0.0989 0.0029 0.65 608 17 634 73sb16* 7 63 78 1.24 0.412 0.0618 0.0013 0.8157 0.0381 0.0957 0.0040 0.88 589 23 668 46sb5* 5 46 45 0.97 0.252 0.0596 0.0023 0.8159 0.042 0.0993 0.0034 0.67 610 20 589 82sb8* 10 79 122 1.53 0.431 0.0640 0.0014 0.8400 0.0504 0.0953 0.0053 0.93 587 31 740 45sb12* 16 118 213 1.81 0.532 0.0606 0.0010 0.8298 0.0226 0.0993 0.0022 0.82 610 13 625 34sb24* 3 24 25 1.08 0.341 0.0642 0.0017 0.8842 0.0265 0.0999 0.0015 0.51 614 9 748 55sb17* 4 34 50 1.44 0.433 0.0642 0.0022 0.9215 0.0657 0.1040 0.0065 0.87 638 38 750 73sb14* 9 71 112 1.57 0.414 0.0601 0.0011 0.8171 0.0267 0.0986 0.0027 0.84 606 16 608 38sb45* 42 315 520 1.65 0.576 0.0613 0.0011 0.8488 0.0542 0.1005 0.0062 0.96 617 36 649 38sb19 15 106 185 1.74 0.508 0.0624 0.0017 0.9275 0.0318 0.1078 0.0023 0.61 660 13 688 58

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Table 1 (continued)

Sample Pb (ppm) U (ppm) Th (ppm) Th/U 208Pb/206Pb 207Pb/206Pb ± (1s) 207Pb/235U ± (1s) 206Pb/238U ± (1s) Rho Apparent ages (Ma)

206Pb/238U ± (1s) 207Pb/206Pb ± (1s)

Mean = 605.7 ± 8.3 [1.4%] 95% conf. Wtd bydata-pt errs only, 2 of 19 rej. MSWD = 0.64,probability = 0.85

sb32 22 71 63 0.88 0.287 0.1206 0.0014 4.2668 0.0714 0.2566 0.0032 0.73 1472 16 1965 20sb22 60 186 103 0.56 0.163 0.1208 0.0009 4.8631 0.1584 0.2919 0.0093 0.98 1651 46 1968 13sb31 157 438 230 0.52 0.154 0.1178 0.0006 5.2940 0.0759 0.3258 0.0044 0.94 1818 21 1924 9sb21 150 370 318 0.86 0.244 0.1223 0.0008 5.7271 0.2520 0.3396 0.0148 0.99 1885 71 1990 11sb9# 171 389 416 1.07 0.301 0.1209 0.0005 5.7316 0.1800 0.3440 0.0107 0.99 1906 51 1969 7sb33# 66 172 103 0.60 0.190 0.1232 0.0008 5.9513 0.1774 0.3503 0.0102 0.97 1936 48 2003 12sb2# 189 453 409 0.90 0.258 0.1217 0.0006 5.9896 0.2679 0.3571 0.0159 0.99 1968 75 1981 8sb30# 158 364 265 0.73 0.231 0.1212 0.0013 6.0052 0.1175 0.3594 0.0059 0.84 1979 28 1974 19sb42 101 250 159 0.63 0.093 0.1307 0.0014 6.5551 0.3149 0.3637 0.0170 0.98 1999 80 2108 18sb36# 182 465 118 0.25 0.094 0.1232 0.0015 6.1800 0.0903 0.3638 0.0028 0.54 2000 13 2003 22sb1# 214 475 431 0.91 0.282 0.1218 0.0008 6.2267 0.2792 0.3708 0.0165 0.99 2033 77 1983 11

Mean = 1980 ± 13 [0.68%] 95% conf. Wtd bydata-pt errs only, 0 of 6 rej. MSWD = 1.5,probability = 0.19

Cabanas granite

yb13* 20 218 104 0.47 0.131 0.0591 0.0005 0.7297 0.012 0.0896 0.0013 0.85 553 7 570 19yb4* 19 194 116 0.60 0.164 0.0582 0.0007 0.7350 0.0128 0.0915 0.0012 0.73 565 7 539 26yb6* 16 161 77 0.48 0.136 0.0607 0.0013 0.7681 0.0187 0.0917 0.0011 0.48 566 6 629 46yb25* 33 370 61 0.16 0.067 0.0614 0.0039 0.7812 0.0582 0.0923 0.0036 0.53 569 21 652 136yb29* 87 711 1253 1.76 0.511 0.0621 0.0011 0.7949 0.0425 0.0929 0.0047 0.94 573 28 676 38yb26* 17 177 85 0.48 0.151 0.0623 0.0033 0.7981 0.0422 0.0930 0.0007 0.13 573 4 683 112yb10* 19 187 80 0.43 0.189 0.0597 0.0018 0.7696 0.0256 0.0936 0.0012 0.38 577 7 591 67yb3* 19 192 68 0.36 0.137 0.0579 0.0004 0.7484 0.0121 0.0937 0.0014 0.9 578 8 526 15yb23* 27 274 125 0.46 0.144 0.0591 0.0012 0.7651 0.0285 0.0938 0.0029 0.84 578 17 572 44yb5* 39 435 77 0.18 0.049 0.0595 0.0005 0.7701 0.0204 0.0939 0.0024 0.94 579 14 585 19yb27* 17 164 111 0.68 0.189 0.0630 0.0012 0.8179 0.0211 0.0941 0.0016 0.66 580 9 710 41yb20* 21 212 133 0.63 0.187 0.0610 0.0006 0.7939 0.0158 0.0944 0.0016 0.87 581 10 639 21yb22* 20 200 86 0.43 0.127 0.0590 0.0005 0.7679 0.0163 0.0944 0.0019 0.92 582 11 566 18yb24* 36 385 71 0.18 0.054 0.0587 0.0003 0.7673 0.0173 0.0947 0.0021 0.97 583 12 558 12yb21* 24 246 111 0.45 0.143 0.0600 0.0004 0.7887 0.0161 0.0954 0.0018 0.93 587 11 603 16yb28* 64 614 137 0.22 0.166 0.0628 0.0016 0.8346 0.0385 0.0964 0.0037 0.83 593 22 701 54yb9 21 60 78 1.30 0.352 0.0966 0.0004 3.6300 0.0988 0.2725 0.0073 0.99 1553 37 1560 8yb8 99 290 393 1.36 0.386 0.1230 0.0013 4.4349 0.0495 0.2614 0.0010 0.36 1497 5 2001 19yb11 54 161 16 0.10 0.051 0.1326 0.0006 6.0751 0.0669 0.3323 0.0033 0.92 1849 16 2133 8yb1 72 190 48 0.25 0.082 0.1345 0.0006 6.6649 0.1332 0.3594 0.007 0.98 1979 33 2158 7yb2 64 160 40 0.25 0.092 0.1338 0.0012 6.8821 0.1262 0.3731 0.0059 0.87 2044 28 2148 16yb30 45 110 31 0.28 0.167 0.1547 0.0027 7.6944 0.1647 0.3608 0.0045 0.58 1986 21 2398 30yb7 132 161 65 0.40 0.120 0.2836 0.0028 26.3895 0.4727 0.6749 0.0101 0.83 3325 39 3383 15

Mean = 572.7 ± 4.1 [0.72%] 95% conf. Wtd bydata-pt errs only, 0 of 16 rej. MSWD = 1.07,probability = 0.37

Note: For each rock, ages have been calculated on the basis of 206Pb/238U weighted averages from data labelled *. For the Jupi orthogneiss, the Paleoproterozoic age has been calculated on the basis of207Pb/206Pb weighted averages from data labeled #.

292S

.P.

Neves

eta

l./

Jo

urn

al

of

So

uth

Am

erican

Ea

rthS

ciences

25

(2

00

8)

28

5–

29

7

Fig. 5. (a) U–Pb concordia diagram for zircons from Jupi orthogneisssample (b) Zoom showing the weighted mean age of 17 Neoproterozoiczircon analyses. (c) Zoom of Paleoproterozoic zircons showing theweighted mean age of 6 zircon analyses.

520

560

600

640

680

720

0.08

0.09

0.10

0.11

0.12

0.65 0.75 0.85 0.95 1.05

207Pb/235U

206 Pb

/238 U

206Pb/238U weighted mean:587±8 Ma (n = 15)

MSWD=0.49

Cachoeirinha pluton(Borborema Province, Brazil)

Fig. 6. U–Pb concordia diagram for zircons from the Cachoeirinhapluton.

S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297 293

the extensive migmatization is coeval with the develop-ment of the regional flat-lying fabrics in orthogneissesand supracrustal rocks, formed during the Brasilianoorogeny. Therefore, these data allow the timing of thistectonic phase of the Brasiliano orogeny to be broadlyconstrained to the time span 630–600 Ma.

The 587 ± 8 Ma and 573 ± 4 Ma ages of the Cachoeir-inha pluton and Cabanas granite, respectively, are consis-tent with field relationship and internal structures in theseintrusions, which suggest that the Cachoeirinha pluton isolder than the Cabanas granite (Neves et al., 2005). Thelack of large mylonitic zones in the Cachoeirinha plutonand its NNE-trending orientation indicate that it wasnot intensely affected by strike–slip-related deformation.This indication suggests that its intrusion occurred atthe beginning of the transcurrent regime that producedthe dextral EPSZ and associated sinistral shear zones.In contrast, the presence of mylonitic xenoliths and exten-sive mylonitization of the Cabanas granite along itsnorthern side indicate that its intrusion took place whenthe transcurrent regime was fully established (Neveset al., 2003).

The existing data reveal that the main phase of tec-tonomagmatic activity in the study area lasted from 630to 570 Ma, with a first phase of low-angle tectonics, fol-lowed by strike–slip shearing. The ages of the Cachoeirin-ha pluton and Cabanas granite can be interpreted asindicating that deformation associated with the EPSZ is20–30 Ma younger than that responsible for the regionalflat-lying foliation. However, at the present time, it isnot yet unequivocal whether there was a progressivechange from one regime to the other or if they are discrete

620

600

580

560

540

5200.084

0.088

0.092

0.096

0.100

0.104

0.60 0.70 0.80 0.90 1.00 1.10

207Pb/235U

206 Pb

/238 U

206Pb/238U weighted mean:573±4 Ma (n = 16)

MSWD = 1.07

Cabanas Granite

400

800

1200

1600

2000

0.0

0.1

0.2

0.3

0.4

0 2 4 6 8

207Pb/235U

206 Pb

/238 U

1560±16 Ma

One analysis at3383±30 Ma

Cabanas Granite

Discordia line withUpper intercept: 2192±14 Ma

Lower intercept: 570±7 Ma(MSWD = 1.06)

Fig. 7. (a) U–Pb concordia diagram for zircons from the Cabanas granite.(b) Zoom showing the weighted mean age of 16 Neoproterozoic zirconanalyses.

294 S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297

episodes temporarily separated. Lack of ages in the timeinterval 605–590 Ma may be due simply to the absenceof suitable lithologies (paucity of magmatism) or deficientknowledge.

6.2. Evidence for Paleoproterozoic basement

The mineralogy, presence of xenoliths of pelitic parag-neiss, and a xenocrystic zircon population in the Jupiorthogneiss suggest that its protolith was produced by par-tial melting of metasedimentary rocks. The Paleoprotero-zoic xenocrystic zircon population consists of roundedgrains, whose abundance makes it unlikely they werederived through assimilation of country rocks. The highTh/U ratio (0.25–1.07; Table 1) of grains that yield a meanage of approximately 1.98 Ga suggests that the source sed-

imentary rock itself had a strong inflow of sedimentsderived from an igneous source with this age.

Similar to the Jupi orthogneiss, the two-mica Cabanasgranite also contains a xenocrystic population of zircons,most likely inherited from its source rock. However, in thiscase, the parent rock was derived predominantly from anolder source, as is indicated by the upper intercept age ofapproximately 2.2 Ga. The data do not allow us to con-clude whether the Cabanas granite and Jupi orthogneisswere derived from anatexis of different sedimentarysequences or formed by partial melting from different crus-tal levels within the same rock package. In any case, theysubstantiate the presence of a Paleoproterozoic basementsouth of the EPSZ.

6.3. Correlations with the central domain

The occurrence of Transamazonian basement (�2.2–2.0 Ga) is well documented in the central domain northof the EPSZ (Brito Neves et al., 2001; Neves et al., 2004,2006) (Fig. 8 and Table 2). It is also suggested in the south-ern domain by Sm–Nd isotopic data from plutons andcountry rocks (Da Silva Filho et al., 2002; Osako, 2005)and now confirmed by the age of inherited zircons in theJupi orthogneiss and Cabanas granite. Orthogneisses haveages mostly in the range 1.97–2.13 Ga and are consideredthe basement for younger igneous, metaigneous, andmetasedimentary rocks (Sa et al., 2002; Neves et al.,2004, 2006). The 1.7–1.5 Ga granitic gneisses and meta-anorthosites (Fig. 8 and Table 2) that are also found inthe central domain and interpreted as anorogenic intru-sions emplaced after the Transamazonian orogeny (Acciolyet al., 2000; Sa et al., 2002). It is perhaps significant thatone zircon grain in the Cabanas granite yielded an age of1560 ± 16 Ma, which opens up the possibility that rocksof this age can also be identified in the southern domain.

Suggestions that an early Neoproterozoic orogeny (Car-iris Velhos event) affected the southern portion of the Bor-borema province (Brito Neves et al., 1995, 2000; Kozuch,2003) are not supported by this study. Also, in the centraldomain, lower intercept ages in concordia diagrams fromseveral samples of orthogneisses only point to an importanttectonothermal event during the late Neoproterozoic Bra-siliano orogeny (Brito Neves et al., 2001; Santos et al.,2004; Neves et al., 2006). Dating of magmatic and meta-morphic zircons north of the EPSZ yields ages in the range630–610 Ma (Neves et al., 2006), indicating that high-grademetamorphism was roughly synchronous with that in thesouthern domain.

Brasiliano intrusive rocks can be classified according totheir relationships with transcurrent shear zones thattransect this region as prekinematic, early-kinematic, andsyn- to late-kinematic. In the southern domain, they corre-spond, respectively, to the Caruaru and Jupi orthogneisses,the Cachoeirinha pluton, and the Cabanas granite. Theages of these three groups of rocks closely agree with equiv-alent groups in the central domain. An increasing number

Fig. 8. Simplified geological map of eastern Borborema Province showing available geochronological U–Pb and Pb–Pb ages for igneous and metaigneousrocks. All ages are U–Pb zircon ages in Ma except that labeled 1.58–168 Ga (Mo), which corresponds to monazite ages in Ga. Sources of data: Acciolyet al. (2000), Sa et al. (2002), Guimaraes et al. (2004), Neves et al. (2004), Neves et al. (2006), this work.

S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297 295

of pre-transcurrent plutons with ages between 620 and645 Ma have been recognized in the central domain (BritoNeves et al., 2003; Guimaraes et al., 2004), indicating thatthe thermal anomaly responsible for partial melting andgranite intrusion that affected this area is of approximatelythe same age as the intrusion of the protoliths of the Caru-

Table 2Summary of available geochronological data for igneous and metaigneous roc

Rock type or unit Mineral Age (Ma)

Banded orthogneiss Zircon 2125 ± 7Metagranodiorite Zircon 2097 ± 5Diotitic orthogneiss Zircon 2098 ± 15Diotitic orthogneiss Zircon 2075 ± 7Granitic gneiss Zircon 2072 ± 8Granitic gneiss Zircon 1991 ± 5Granodioritic orthogneiss Zircon 1974 ± 32Meta-anorthosite Zircon 1718 ± 19Granitic gneiss Monazite 1680 ± 100Granitic gneiss Monazite 1640 ± 90Granitic gneiss Zircon 1580 ± 90Augen gneiss Zircon 1521 ± 6Timbauba pluton Zircon 645 ± 5Caruaru orthogneiss Zircon 629 ± 9Migmatite leucosome Zircon 626 ± 15Jupi orthogneiss Zircon 606 ± 8Bom Jardim pluton Zircon 592 ± 7Caruaru–Arcoverde batholith Zircon 591 ± 5Caruaru–Arcoverde batholith Zircon 588 ± 12Caruaru–Arcoverde batholith Zircon 587 ± 5Cachoeirinha pluton Zircon 587 ± 8Cabanas Granite Zircon 573 ± 4Queimadas pluton Zircon 570 ± 24

aru and Jupi orthogneisses (629 Ma and 606 Ma, respec-tively) in the south. The most voluminous magmatism inthe central domain is represented by intrusions spatiallyassociated with strike-slip shear zones with ages mainly inthe range 592–585 Ma (Guimaraes and Da Silva Filho,1998; Brito Neves et al., 2003; Neves et al., 2004; Guimaraes

ks in eastern Borborema Province

Method Reference

U–Pb (LA-ICP-MS) Neves et al. (2006)U–Pb (LA-ICP-MS) Neves et al. (2006)Pb–Pb evaporation Neves et al. (2004)Pb–Pb evaporation Neves et al. (2004)Pb–Pb evaporation Neves et al. (2004)U–Pb (LA-ICP-MS) Neves et al. (2006)U–Pb (convencional) Sa et al. (2002)U–Pb (convencional) Accioly et al. (2000)U–Th–Pb (ion microprobe) Accioly et al. (2000)U–Th–Pb (ion microprobe) Accioly et al. (2000)U–Th–Pb (ion microprobe) Accioly et al. (2000)U–Pb (convencional) Sa et al. (2002)U–Pb (convencional) Guimaraes et al. (2004)Pb–Pb evaporation Neves et al. (2004)U–Pb (LA-ICP-MS) Neves et al. (2006)U–Pb (LA-ICP-MS) This studyU–Pb (convencional) Guimaraes et al. (2004)Pb–Pb evaporation Neves et al. (2004)U–Pb (convencional) Guimaraes et al. (2004)Pb–Pb evaporation Neves et al. (2004)U–Pb (LA-ICP-MS) This studyU–Pb (LA-ICP-MS) This studyU–Pb (convencional) Guimaraes et al. (2004)

296 S.P. Neves et al. / Journal of South American Earth Sciences 25 (2008) 285–297

et al., 2004), which overlap the age (587 Ma) of theCachoeirinha pluton. Plutons emplaced at the advancedstages of shear zone development in the central domain(Almeida et al., 2002; Guimaraes et al., 2004) are similarin age (575–570 Ma) to the Cabanas granite (Table 2).

Taken together, these results support the proposal thatthe central and southern domains underwent similar tec-tonothermal evolution during most of the Proterozoiceon. This finding weakens arguments in favor of an evolu-tion involving collage of allochtonous terranes (Santos andMedeiros, 1999; Brito Neves et al., 2000; Santos et al.,2004). Although it could be argued that previously sepa-rated blocks underwent similar geologic histories beforeconvergence and collision, it is unlikely. No evidence forpetrotectonic assemblages typical of subduction zone envi-ronments and suture zones have been documented, and theEPSZ is not a terrane boundary. Instead, detailed struc-tural study shows that the EPSZ is a relatively late Brasil-iano feature developed in an intracontinental setting(Neves et al., 1996, 2000). Therefore, the southern and cen-tral domains probably belonged to the same crustal blockbefore the onset of the Brasiliano orogeny.

7. Conclusions

This study presents the first U–Pb zircon results for thesouthern domain of the Borborema Province south of theEPSZ and places important age limits on the tectonomag-matic evolution of this region. The 606 ± 8 Ma age of theJupi orthogneiss dates the peak of high-grade Brasilianometamorphism and, consequently, the regional low-anglefoliation. Together with structural data obtained in previ-ous studies, the 587 ± 8 Ma and 573 ± 4 Ma crystalliza-tion ages of the Cachoeirinha pluton and Cabanasgranite, respectively, bracket the main period of activityof the EPSZ. The occurrence of inherited zircon compo-nents in the Jupi orthogneiss and Cabanas granite is evi-dence for a widespread Paleoproterozoic crust in thesouthern domain. These results are comparable to thosefound north of the EPSZ, which indicates these twodomains underwent similar tectonothermal evolutionduring most of the Proterozoic eon. The existence of anorogenic event of early Neoproterozoic age and thehypothesis of terrane accretion are therefore not sup-ported by the available data.

Acknowledgments

LA-ICP-MS analyses were conducted as part of post-doctoral studies by SPN, financed by the Brazilian agencyConselho Nacional de Desenvolvimento Cientıfico e Tec-

nologico (CNPq). Samples were collected during fieldworkfunded by the Fundacao de Amparo a Ciencia e Tecnologia

do Estado de Pernambuco (FACEPE).

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