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ProterozoichistoryoftheBorboremaProvince(NEBrazil):CorrelationswithneighboringcratonsandPan-AfricanbeltsandimplicationsfortheevolutionofwesternGondwana

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SérgioP.Neves

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Proterozoic history of the Borborema province (NE Brazil):

Correlations with neighboring cratons and Pan-African belts

and implications for the evolution of western Gondwana

Sergio Pacheco Neves

Departamento de Geologia, Universidade Federal de Pernambuco, Recife, Brazil

Received 18 December 2001; revised 31 December 2002; accepted 5 March 2003; published 9 July 2003.

[1] Geological and geochronological correlationsbetween Borborema province (NE Brazil) andneighboring cratons and Brasiliano/Pan-African beltsindicate that the Amazonian, West African, and SaoFrancisco/Congo cratons and the basement of theAraguaia, Borborema, Nigerian, and Cameroonprovinces were part of the Atlantica supercontinent.This continent was established at the end of theTransamazonian/Eburnean cycle (�2.0 Ga) and, apartfrom ubiquitous taphrogenesis in the 1.8–1.7 Gainterval, remained largely unaffected for the following1 Ga. Around 1 Ga an important magmatic event inBorborema province correlates with rifting episodesand anorogenic magmatism in the Sao Francisco,Congo, and Amazonian cratons. These events areinterpreted as failed attempts to break up Atlantica,which at this time may have been part of the largerRodinia supercontinent. Renewed extensionalconditions in Borborema province during the middleand late Neoproterozoic are attributed to far-fieldstresses transmitted to the interior of Atlantica byoutwardly dipping subduction zones that encircled itsnorthern (present day coordinates) portion. The rarityof petrotectonic assemblages typical of subductionzone environments indicates that extension did notevolve enough to form large oceans basins and thusthat the Borborema province essentially includesreworked intracontinental domains. Regionaldeformation and metamorphism, starting at 650–640Ma, and shear zone development, beginning at 590–595 Ma, were continuously developed through timeand were synchronous throughout most of theBorborema, Araguaia, Cameroon, and Nigerianprovinces. Postorogenic conditions were reached540–530 Myr ago, while active deformation wasstill occurring in other belts that accreted aroundAtlantica to form western Gondwana. INDEX TERMS:

1035 Geochemistry: Geochronology; 9619 Information Related to

Geologic Time: Precambrian; 8110 Tectonophysics: Continental

tectonics—general (0905); KEYWORDS: Atlantica supercontinent,

Neoproterozoic belts, western Gondwana. Citation: Neves, S. P.,

Proterozoic history of the Borborema province (NE Brazil):

Correlations with neighboring cratons and Pan-African belts and

implications for the evolution of western Gondwana, Tectonics,

22(4), 1031, doi:10.1029/2001TC001352, 2003.

1. Introduction

[2] The Borborema province, northeastern Brazil, is sur-rounded in paleogeographical reconstructions of the westernGondwana supercontinent by the Neoproterozoic Brasi-liano/Pan-African Araguaia, Nigerian, and Cameroon beltsand by the Amazonian, West African, and Sao Francisco/Congo cratons (Figure 1). This strategic position impliesthat understanding the Proterozoic evolution of the Borbor-ema province would place important constraints on howwestern Gondwana formed. In the last 10 years a hugeamount of data from several fields bearing on the geology ofthe Borborema province has accumulated. Together with asteady increase in basic geological knowledge, these dataallow the proposition of new models, or the testing ofexisting ones, for the tectonic evolution of the Borboremaprovince, as well as its correlation with adjoining terranes.In particular, three major advances occurred. The firstconsisted in the availability of geochronological and isoto-pic data, obtained through several different systematics(U-Pb, Pb-Pb, Sm-Nd, 40Ar/39Ar), which were very few innumber until the early 1990s. The second was the wide-spread use of kinematic analysis in tectonic studies, whichreplaced the purely geometrical analysis that prevailed inthe preceding decades. Finally, detailed structural, petrolog-ic, and geochronologic studies of granitoid plutons allowedthe correlation of magmatic and tectonic processes. Thispaper presents a synthesis of these data and interprets themin the larger context of western Gondwana evolution. It isconcluded that there is strong evidence for formation of theAtlantica continent [Rogers, 1996] during the Paleoproter-ozoic and for its permanence during the remainder of theProterozoic. In turn, this implies that the orogenic belts thatoccur between the Sao Francisco/Congo, Amazonian, andWest African cratons formed dominantly in an intraconti-nental setting.

2. General Geology and Geochronology

[3] The Borborema province is traditionally subdivided indomains separated by major shear zones. For descriptivepurposes and following previous authors [e.g., Brito Neveset al., 2000], fivemain domains will be considered (Figure 2):

TECTONICS, VOL. 22, NO. 4, 1031, doi:10.1029/2001TC001352, 2003

Copyright 2003 by the American Geophysical Union.0278-7407/03/2001TC001352$12.00

5 - 1

a northern domain, to the north of the Patos-Campina-Grande shear zone system, further subdivided, from south-east to northwest, into the Rio Grande do Norte, centralCeara, and Medio-Coreau domains; a central domain,between the Patos-Campina Grande and the Pernambucoshear zone systems; and a southern domain to the south ofthe Pernambuco shear zone system.[4] The geology of the Borborema province is dominated

by large areas of gneissic/migmatitic rocks, representing thebasement of the region, semicontinuous belts of metamor-phosed supracrustal rocks, numerous Brasiliano intrusions,and a network of transcurrent shear zones (Figure 2). Acomprehensive description of the main geological character-istics of the province is given by Caby et al. [1991].[5] Basement rocks are dominantly orthogneisses, rang-

ing in composition from quartz diorite to granite, butmetaultramafics, metagabbros, amphibolites and metasedi-mentary rocks are locally important. Much geochronologi-cal work has been conducted in the northern domain. There,two large Archean nuclei have been identified (Figure 2),one cropping out in the northeastern portion of the RioGrande do Norte domain, where U-Pb zircon ages up to 3.4Ga were obtained [Dantas et al., 1998, 2000], and other inthe central Ceara domain [Fetter et al., 2000]. Paleoproter-

ozoic ages between 2.27 and 2.35 Ga were obtained in theMedio Coreau domain [Fetter et al., 2000; T. J. S. Santos etal., 2000]. However, most dated basement samples in thenorthern domain yielded middle Paleoproterozoic ages, withmany of them clustering in the time interval 2.10–2.24 Ga[Hackspacher et al., 1990; Legrand et al., 1991, 1997;Souza et al., 1993; Dantas et al., 1998; Fetter et al., 2000].Sm-Nd data indicate that part of the Paleoproterozoicbasement represents reworked Archean crust in the RioGrande do Norte domain, while juvenile crust dominates inthe central Ceara domain [Fetter et al., 2000].[6] U-Pb and Pb-Pb zircon ages on basement rocks in the

central domain are more scarce than in the northern domain,but they also point out the preponderance of 2.2–2.0 GaPaleoproterozoic crust, with Archean domains being locallyfound [Santos, 1995; Van Schmus et al., 1995; Silva et al.,1996; Melo, 1998; Melo et al., 2000; Brito Neves et al.,2001a; Sa et al., 2002]. The same apparently applies to thesouthern domain, judging from Rb-Sr ages in orthogneisses[Brito Neves et al., 2000, and references therein] and Ndmodel ages of Brasiliano granitoids [Da Silva Filho et al.,1999, 2002; Neves et al., 2000a; Mariano et al., 2001].Thus formation of new crust and reworking of older crustalsegments in the interval 2.2–2.0 Ga is a main feature of theBorborema province as a whole. This major period ofcrustal accretion, known as the Transamazonian OrogenyCycle [Cordani and Sato, 1999], probably involved severalorogenic episodes and corresponds to the Eburnean orogenyin Africa [Ledru et al., 1994].[7] In the Rio Grande do Norte domain the Transamazo-

nian event was followed by intracrustal rifting and deposi-tion of volcanosedimentary sequences, together withintrusion of anorogenic granites. These sequences nowconstitute the NNE-trending Oros and Jaguaribe belts(Figure 2). In the Oros belt, deposition of supracrustalrocks is constrained by U-Pb zircon age from a metarhyo-lite to have occurred at 1.79 Ga and pre-dates graniteintrusion at 1.67 Ga [Sa et al., 1991, 1995]. In the Jaguaribebelt, sediment deposition postdates granite emplacement,which occurred 1.77 Gyr ago, indicating that basin devel-opment was not entirely synchronous in this region [Sa etal., 1997]. Rifting and deposition of supracrustal rocks inthe Medio-Coreau domain also occurred during the latePaleoproterozoic, as indicated by an U-Pb zircon age of1.78 Ga in felsic metavolcanic rocks tectonically intercalat-ed with Neoproterozoic rocks [T. J. S. Santos et al., 2000].In the central and southern domains, Paleoproterozoicsupracrustal rocks have not yet been identified, but anoro-genic magmatism of Paleoproterozoic to Mesoproterozoicage is recorded. It is represented by two occurrences ofA-type granites (now orthogneisses), dated at 1.52 Ga [Sa etal., 2002] and 1.68–1.58 Ga [Accioly et al., 2000] and bymetagabbroic-anorthositic complexes of 1.72 Ga [Accioly etal., 2000] (Figure 2). These data indicate that the Borbor-ema province achieved stable cratonic conditions 200–300Myr after the Transamazonian event.[8] The central domain was the locus of an important

magmatic event in the latest Mesoproterozoic/earliest Neo-proterozoic, for which the name Cariris Velhos was coined

Figure 1. Generalized geological map of western Gond-wana showing the distribution of main cratons and Pan-African/Brasiliano belts. Dashed lines are approximatecontours of cratons discussed in text. Cratons are asfollows: AM, Amazonian; CC, Congo; SF, Sao Francisco;and WA, West African. Belts are as follows: AB, Araguaiabelt; BB, Brasılia belt. Provinces are as follows: BP,Borborema province; CA, Cameroon province; EN, EastNigerian province; and WN, West Nigerian province. TS isTuareg shield. See color version of this figure in the HTML.

5 - 2 NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE

Figure 2. Sketch map showing the main geological units, plutons, and shear zones of Borboremaprovince. Inset depicts geographical subdivisions of the Borborema province. SFC is Sao Franciscocraton. Legend definitions are as follows: 1, Sao Francisco craton; 2, craton cover sequences; 3, Archeanbasement; 4, Transamazonian and undifferentiated basement; 5, supracrustal belts; 6, 1.7–1.5 Gaorthogneiss and meta-anorthosite; 7, Cariris Velhos orthogneisses; 8, Brasiliano plutons; 9, molassicgrabens; 10, Phanerozoic cover; and 11, main transcurrent shear zones, which are CGSZ, CampinaGrande; PaSZ, Patos; EPSZ and WPSZ, East Pernambuco and West Pernambuco, respectively; GSZ,Granja; SPSZ, Senador Pompeu; and SSZ, Sobral. See color version of this figure in the HTML.

NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE 5 - 3

[Brito Neves et al., 1995]. It is well documented by U-Pbzircon dating of metavolcanics (1.12–0.93 Ga) [VanSchmus et al., 1995; Kozuch et al., 1997] and metagrani-toids (980–920 Ma) (Figure 2) [Van Schmus et al., 1995;Kozuch et al., 1997; Leite et al., 2000; Brito Neves et al.,2001b]. Occurrence of the Cariris Velhos event in thesouthern domain is suggested by Sm-Nd data from Brasi-liano granitoids. In this region some plutons yielded TDMmodel ages between 1.5 and 1.0 Ga, which may either resultfrom mixed sources with Paleoproterozoic and Brasilianoages or from juvenile sources of Cariris Velhos age [DaSilva Filho et al., 2000, 2002]. It has been proposed that theCariris Velhos event represents a true orogeny [Brito Neveset al., 1995; Santos, 1995; Santos and Medeiros, 1999;Brito Neves et al., 2000, 2001b]. According to this view thecentral domain would differ from the northern one, whereonly the Brasiliano/Pan-African orogeny of the late Neo-proterozoic is recorded.[9] With the exception of metasediments in the Oros and

Jaguaribe belts and in part of the Medio-Coreau domain,and metasediments associated with Cariris Velhos metavol-canics, most supracrustal rocks were deposited during theNeoproterozoic. This has been conclusively proved byzircon U-Pb dating and Sm-Nd model ages of metasedi-ments of the Serido (<650 Ma) [Van Schmus et al., 2000]and Ceara (750–800 Ma) belts [Fetter, 1999] in thenorthern domain. Although preliminary, available Sm-Ndand U-Pb isotopic data in the central domain also indicatethat deposition of most supracrustal rocks occurred inmiddle to late Neoproterozoic times [Van Schmus et al.,1995; Kozuch et al., 1997; Bittar and Campos Neto, 2000].Finally, carbon isotope fluctuations in metasedimentarycarbonates from the Medio-Coreau and southern domainsare compatible with Neoproterozoic deposition [Sial et al.,2000]. The Brasiliano orogeny of the late Neoproterozoicaffected all the preexisting units and was responsible for anintense magmatic activity and is considered in section 3.

3. Timing and Duration of the Brasiliano

Event

3.1. Medio-Coreau and Central Ceara Domains

[10] Duration of Brasiliano events in the central Cearaand Medio-Coreau domains is well constrained by isotopicdata on metamorphic rocks, plutons, and shear zones. Peakmetamorphic conditions, culminating with the production ofmigmatites and granulites, occurred at 590–630 Ma, asindicated by U-Pb zircon and monazite ages [Fetter, 1999;Vlach and Nogueira Neto, 1999]. A contractional strainregime is indicated by NW thrusting in the Medio-Coreaudomain [T. J. S. Santos et al., 2000], and nappe emplace-ment toward the SSW in the central Ceara domain [Cabyand Arthaud, 1986; Caby et al., 1995]. A 580 Ma U-Pbzircon age of a late transcurrent granite [Fetter, 1999] and40Ar/39Ar amphibole ages in the Granja and SenadorPompeu shear zones (Figure 2) [Monie et al., 1997] indi-cates that strike-slip motion started before 580 Ma. The40Ar/39Ar hornblende ages [Monie et al., 1997] and U-Pbsphene and garnet ages [Fetter, 1999] show that regional

cooling below 500�C occurred 555–545 Myr ago. This wasfollowed by rapid unroofing, deposition of supracrustalsequences in extensional basins [Brito Neves, 1998], andintrusion of posttectonic granites, one of which yielded aU-Pb zircon age of 532 Ma [Fetter, 1999].

3.2. Rio Grande do Norte Domain

[11] Transpressional deformation under low-pressure(low-P), high-temperature (high-T) conditions characterizesthe Serido belt [Archanjo and Bouchez, 1991; Jardim de Sa,1994]. Three syntranscurrent plutons in this domain weredated by the zircon U-Pb method [Leterrier et al., 1994;Trindade et al., 1999] and yielded ages between 576 and579 Ga (Figure 3). These ages are similar to those of othershear zone-related plutons in the Borborema province.However, in contrast with other sectors of the province,40Ar/39Ar amphibole and mica ages in the intervals 545–540 Ma and around 500 Ma, respectively [Corsini et al.,1998; Souza et al., 1998], indicate that regional temper-atures remained elevated well within the Cambrian.

3.3. Central Domain

[12] Some granites in the central domain have U-Pb zirconages between 620 and 645 Ma [Guimaraes et al., 1998;Guimaraes and Da Silva Filho, 2000] (Figure 3) and arelocally deformed and migmatized, indicating that the Brasi-liano activity started synchronously with that in the Medio-Coreau and central Ceara domains. In this area the gneissicfoliation on basement and supracrustal rocks has dominantlygentle to moderate dips and strikes NE-SW. This fabric,whose age of development is under dispute (see nextsection), is reworked by EW dextral and NE-SW sinistralstrike-slip shear zones (Figure 3). Kinematic and micro-structural work show that the shear zones developed initiallyat high-T conditions, with deformation concentrating innarrow belts when temperatures declined [Vauchez andEgydio-Silva, 1992; Neves and Vauchez, 1995; Vauchez etal., 1995; Neves and Mariano, 1999; Silva and Mariano,2000]. Most plutons in the central domain are early to latekinematic with respect to the shear zones [Neves andVauchez, 1995; Archanjo and Bouchez, 1997; Neves andMariano, 1999; Guimaraes et al., 2000]. The ages of theoldest shear zone-related plutons (581–592Ma) [Guimaraeset al., 1998; Melo et al., 2000] constrain the start of motionon the shear zones at 595–590 Ma. The 40Ar/39Ar mineralages indicate that regional cooling to around 500�C occurredrelatively early (585 Ma) in the eastern portion of the centraldomain, but temperatures remained elevated until 545–533 Ma, when they finally fell below 300�C [Neves et al.,2000b]. This finding is consistent with microstructuralevidence indicating deformation at lower metamorphic con-ditions in plutons dated at 570 Ma [Araujo et al., 1996;Guimaraes et al., 2000; Almeida et al., 2002] than in thosewith ages around 590 Ma [Neves and Mariano, 1999].Unlike other areas in the central domain, which were region-ally heated above 500�C at low- to medium-P conditions(<6–7 kbar) [Vauchez and Egydio-Silva, 1992; Leite, 1997;Bittar and Campos Neto, 2000; Neves et al., 2000b], primarystructures are often preserved in the Cachoeirinha/Salgueiro

5 - 4 NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE

belt (Figure 2). Metamorphic conditions in this belt aremostly at the greenschist facies, and pressure estimates fromplutons and their thermal aureoles vary from 6 to 9 kbar [Sial,1993; Caby et al., 2003]. The plutons must be early tectonicsince undisturbed bedding is preserved in their thermalaureole [Caby et al., 2003]. The 40Ar/39Ar amphibole ageof 625 Ma for one of them [Dallmeyer et al., 1987] isprobably close to the emplacement age.

3.4. Southern Domain

[13] Kinematic and geophysical studies conducted in thesouthern, EW- to SE-trending belts of the Borboremaprovince (Riacho do Pontal and Sergipano, Figure 2) concurthat the Brasiliano deformation was dominated by thrust andnappe emplacement toward the south, with partial meltingconditions being reached during peak metamorphism [Davi-

son and Santos, 1989; Jardim de Sa et al., 1992; D’El-ReySilva, 1995; Oliveira, 1998]. Although it is widely agreedthat this evolution started before 600 Ma, precise geochro-nological data are lacking. To the north of the Sergipanobelt, three granitoid plutons interpreted as late tectonic haveyielded zircon U-Pb ages between 624 and 592 Ma [DaSilva Filho and Guimaraes, 2000]. This suggests thatregional cooling may have occurred earlier than in thecentral and northwestern domains. An U/Pb zircon age of528 Ma in a postorogenic pluton [Da Silva Filho et al.,1999] marks the end of the Brasiliano orogeny in this part ofthe Borborema province.

3.5. Synthesis

[14] From a review of available data it seems thatregional deformation and metamorphism was synchronous

Figure 3. Sketch geological map of central and Rio Grande do Norte domains of the Borborema provinceshowing the subdivision of the Patos and Pernambuco lineaments in two branches, the Patos and CampinaGrande shear zones (PASZ and CGSZ) and theWest Pernambuco and East Pernambuco shear zones (WPSZand EPSZ). Numbers are U-Pb and Pb-Pb zircon ages (in Myr) of Brasiliano plutons and orthogneisses, andnumbers preceded by an A are 40Ar/39Ar amphibole ages in shear zones (in Myr). Circled numbers areplutons referred to in Figures 5 and 6. Also shown is the occurrence of eclogite to the west of theCachoeirinha belt. See text for sources of data. Inset depicts the proposed division of the Borboremaprovince in tectonostratigraphic terranes [Santos et al., 1999]: SFC, Sao Francisco craton; terranes: AM,Alto Moxoto; AP, Alto Pajeu; CE, Ceara; JC, Sao Jose do Campestre; JG, Jaguaribe; MC, Medio-Coreau;PA, Pernambuco-Alagoas; PB, Pianco-Alto Brıgida; PO, Riacho do Pontal; RC, Rio Capibaribe; RP, RioPiranhas; SD, Serido; and SE, Sergipano. See color version of this figure in the HTML.

NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE 5 - 5

throughout most of the Borborema province, starting before630–640 Myr ago. The tectonic regime varied from place toplace. It is characterized by rather classical medium pressureregional metamorphism in the central Ceara domain; bythin-skinned tectonics in the Sergipano and Riacho doPontal belts; by dominantly low-P, high-T metamorphismin the eastern portion of the central domain and in the RioGrande do Norte domain; and by medium-P, low-T con-ditions in the Cachoeirinha belt. Absence of large shearzones and of syntectonic granites younger than 590 Ma inthe northern part of the southern domain suggest that themain period of tectonic activity in this sector ended whenthe strike-slip regime was starting in the central and north-ern domains about 590 ± 10 Myr ago.

4. Significance of the Cariris Velhos and

Brasiliano Events

[15] The main structural feature of the Borborema prov-ince is a network of strike-slip shear zones that reworks aflat-lying gneissic foliation [Vauchez et al., 1995]. While itis generally agreed that transcurrent motion records defor-mation associated with the Brasiliano orogeny, someauthors have claimed development of the flat-lying foliationduring an early tectonic episode of Paleoprotrerozoic age[Jardim de Sa, 1984, 1994, and references therein]. In thisscenario the Brasiliano event is seen as only responsible forregional heating, granite intrusion, and shear zone develop-ment. In view of the Neoproterozoic age of the central Cearaand Serido belts [Fetter et al., 2000; Van Schmus et al.,2000] and structural evidence pointing to coeval develop-ment of the flat-lying foliation in basement and cover rocks[Caby et al., 1995], it is now clear that the flat-lyingfoliation in the northern domain developed during theBrasiliano orogeny. However, many authors [Brito Neveset al., 1995, 2000; Santos, 1995; Santos and Medeiros,1999; Santos et al., 1999] have recently assigned develop-ment of the flat-flying foliation in the central and southerndomains to the Cariris Velhos event, which is interpreted asan orogenic episode. Some go a step further and proposethat the Borborema province is an accretionary orogenformed by amalgamation of several disparate terranes dur-ing the Cariris Velhos and Brasiliano events [Santos andMedeiros, 1999; Santos et al., 1999] (Figure 3). Evidencefor two Neoproterozoic orogenies and for terrane accretionin the Borborema province are critically evaluated below.[16] The main piece of evidence used to argue for Cariris

Velhos contractional deformation is sheets of augengneisses and muscovite-bearing migmatites derived fromtwo-mica leucogranites that yielded ages in the 980–920 Ma interval [Brito Neves et al., 2000, 2001b]. Theserocks are interpreted as crustal collisional granites [Santos,1995; Santos and Medeiros, 1999; Brito Neves et al., 2000]because they are peraluminous and show negative Ba, Nb,Sr, and Ti anomalies in spidergrams of trace elements,which, according to these authors, is similar to the patterndisplayed by Himalayan leucogranites. However, theserocks have relatively low abundances of Al2O3 (11.4–14.6 wt %) [Santos, 1995], and their ocean ridge granite-

normalized patterns [Pearce et al., 1984] are more similar tointraplate than to collisional granites (Figure 4). Further-more, Nd model ages for these rocks have yielded valuesbetween 1900 and 1400 Ma [Brito Neves et al., 1995,2001b], suggesting involvement of substantial amounts ofPaleoproterozoic sources in their genesis and thus existenceof widespread preexisting basement. These characteristicsare more akin to A-type granites emplaced during conti-nental rifting. In addition, metavolcanics with which theorthogneisses are associated belong to bimodal sequences,with metarhyolites � metabasalts [Van Schmus et al., 1995;Bittar et al., 2001; I. P. Guimaraes, personal communica-tion, 2001], and the metabasites have geochemical signa-tures and negative epsilon Nd values suggestive ofemplacement in an intraplate setting [Bittar et al., 2001].Therefore the possibility that the foliation in Cariris Velhosplutonic rocks developed only during the Brasiliano eventcannot be excluded.[17] Assuming that the regional fabric records deforma-

tion related to the Cariris Velhos event, late Neoproterozoicages would not be expected in orthogneisses bearing a flat-lying foliation. This supposition was not confirmed in twocases. Leite et al. [2000] dated a foliated granitic sheetconcordant with the low-angle foliation in metasedimentsby the U/Pb zircon method (Figure 3). In spite of the largeerror the dated sample yielded an undoubtedly Brasilianoage (560 ± 118 Ma). Although the possibility remains thatthe sheet intruded an older foliation, the straightforwardinterpretation is that the regional foliation was developedonly during the Brasiliano orogeny. Another evidence for atangential tectonic event of Brasiliano age is provided by anorthogneiss located just to the south of the East Pernambucoshear zone (Figure 3), which was dated at 630 Ma by thePb-Pb method [Neves and Mariano, 2001]. Additionally,

Figure 4. Ocean ridge granite-normalized trace elementconcentrations of Cariris Velhos orthogneisses [Santos,1995] compared with Phanerozoic collisional and anoro-genic granites [Pearce et al., 1984]. See color version of thisfigure in the HTML.

5 - 6 NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE

structural and petrologic studies in the central domain showthat the same deformational event affected Neoproterozoicformations and older supracrustal sequences and orthog-neisses [Leite, 1997; Bittar and Campos Neto, 2000;Medeiros et al., 2001], which do not support the contentionthat the flat-lying regional fabric was formed during theCariris Velhos event. Finally, while lower intercept agesobserved on several U-Pb concordia diagrams of basementorthogneisses suggest metamorphism during the Brasilianoorogeny, a metamorphic imprint of early Neoproterozoicage has not yet been reported.[18] More integrated petrological, structural, and geo-

chronological studies are needed to better characterize theCariris Velhos event, but mounting evidence argues againstthe possibility that it represents a major orogenic phase. Theabsence (or lack of recognition so far due to deficientgeochronology) of an orogenic event of early Neoproter-ozoic age in Brasiliano/Pan-African belts correlatable withthe Borborema province (Araguaia, Cameroon, and Nigeria)strengthens the alternative possibility that the Cariris Velhoswas a rifting episode, with basin inversion only occurringduring the Brasiliano.[19] If the Borborema province grew by amalgamation of

terranes, evidence for oceanic closure and arc magmatismshould be preserved in the geological record. One occurrenceof eclogite [Beurlen et al., 1992] has been described in thecentral domain (Figure 3) and cited as evidence for oceanclosure during either the Cariris Velhos [Santos et al., 1997]or the Brasiliano [Bittar and Campos Neto, 2000;Caby et al.,2003] events. So far, this is the only direct evidence indicativeof an oceanic setting in the Borborema province. In thenorthern part of the Sergipano belt, juvenile gabbros andassociated metasedimentary/metavolcanic rocks have beeninterpreted as an island arc [Jardim de Sa et al., 1992], butthis view is questionable because the gabbros have geochem-ical signatures similar to continental basalts [Oliveira andTarney, 1990]. In the central Ceara domain a large (�40,000km2) plutonic complex was suggested to represent a mag-matic arc [Fetter, 1999], but its negative eNd value and thelack of associated calc-alkalic metavolcanics weaken thisinterpretation. So absence of unambiguous evidence foractive margins suggests that large oceans did not separatethe proposed terranes of the Borborema province.[20] Other lines of evidence used in support to the

hypothesis of terrane accretion are the geochemistry andpetrology of Brasiliano plutons in the different domains andthe existence of large shear zones that could representsuture zones [Santos and Medeiros, 1999]. In a review ofthe petrology of Brasiliano plutons, Ferreira et al. [1998]concluded that, although contrasts exist between plutons inthe northern, central, and southern domains, the petrolog-ical and geochemical characteristics of granitoids do notallow the individualization of different terranes. Lookingonly at plutons of the high-K calc-alkalic association, themost extensive plutonic suite in the Borborema province,Neves and Mariano [1997] pointed out that granitoidsresemble each other in terms of major and trace elementcharacteristics in different sectors (Figure 5). Similarly,calc-alkalic granitoids in the Cachoeirinha/Salgueiro and

Sergipano belts share many petrographic, geochemical, andisotopic characteristics [Sial et al., 1998]. Furthermore, oneof the most distinctive features of the Brasiliano magma-tism is that diorites of the high-K calc-alkalic association[Neves et al., 2000a; Mariano et al., 2001], metaluminoussyenites [Guimaraes and Silva Filho, 1998], and ultra-potassic syenites [Ferreira and Sial, 1993; Ferreira et al.,1994] have enriched isotopic and geochemical signatures(Figure 6) pointing to an origin by partial melting of anancient (>2 Ga), metasomatized continental mantle litho-sphere. Such a peculiar composition of the lithosphericmantle in different sectors of the Borborema provincewould not be expected if it had grown by amalgamationof disparate terranes. The data from granitoids and mantle-derived rocks thus indicate the existence of a relativelyhomogeneous continental lithosphere (=single terrane)formed during the Paleoproterozoic Transamazonian cycleextending throughout a large part of the province.[21] The major transcurrent shear zones that crosscut the

Borborema province are natural candidates as suture zonesbetween the proposed terranes. In particular, the Patos andPernambuco lineaments are often interpreted as first orderboundaries [e.g., Santos et al., 1999], and so the descriptivedivision of the Borborema province in northern, central, andsouthern domains would also be a genetic one. Detailedstructural work carried out in many shear zones [Vauchez etal., 1995; Corsini et al., 1996; Neves and Mariano, 1999,and references therein], and the geochronological datadiscussed in the last section, however, show that they are

Figure 5. Representative rare earth element patterns forgranitoids of the high-K calc-alkalic association in the RioGrande do Norte domain (pluton numbered 5 in Figure 3), atthe boundary of the Cachoeirinha/Salgueiro belt withbasement rocks (plutons numbered 3 and 4 in Figure 3),and in the Rio Capibaribe terrane (pluton numbered 1 inFigure 3) [from Neves and Mariano, 1997]. See colorversion of this figure in the HTML.

NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE 5 - 7

late Brasiliano features which rework the regional flat-lyingfoliation. Both the Patos and Pernambuco lineaments aredivided into two main branches, the first in the Patos andCampina Grande shear zones and the latter in the WestPernambuco and East Pernambuco shear zones (Figure 3).The Patos shear zone is in structural continuity with theSerido belt; strike-slip shearing along the shear zone oc-curred simultaneously with tranpressional deformation inthe belt [Corsini et al., 1991]. The presence of zirconsderived from Cariris Velhos and late Neoproterozoic crust inthe Serido belt [Van Schmus et al., 2000] indicates thenearby location of the northern and central domains in thelate Neoproterozoic and, incidentally, provides evidenceagainst large displacements across the Patos shear zone.The East Pernambuco shear zone is subdivided into high-temperature (amphibolite facies) and low-temperature(greenschist facies) belts and postdates emplacement ofthe �590 Myr old Caruaru-Arcoverde batholith [Nevesand Mariano, 1999]. Therefore the Patos and East Pernam-buco shear zones are not, and have not reworked, terraneboundaries.[22] Taking into account the above discussion and (1) the

nature of metamorphic rocks in the supracrustal beltsthroughout the Borborema province (dominantly para-gneisses and micaschists, with subordinate quartzite andmarble), suggesting deposition in continental settings occa-sionally subjected to marine ingressions rather than deposi-tion in open oceanic environments; (2) the restrictedoccurrence of petrotectonic assemblages characteristic ofsubduction zone environments (high-pressure rocks, mag-matic arcs, melanges, etc.); (3) the fact that the Borboremaprovince mainly consists of reworked Paleoproterozoiccrust and not from juvenile oceanic blocks, it is concluded

that the Brasiliano orogeny took place dominantly in anintracontinental setting.

5. Comparisons With Neighboring Cratons

and Neoproterozoic Belts

[23] The pre-Brasiliano events recorded in the Borboremaprovince match similar ones in the adjoining Sao Francisco/Congo, West African, and Amazonian cratons and in otherBrasiliano/Pan-African belts. In the following, only themost recent overviews of the geology of these regions willbe referred. Additional references are to be found in thecited works.[24] Figure 7 compares zircon U-Pb and Pb-Pb ages of

pre-Brasiliano orthogneisses in the Borborema province andin the Araguaia, Cameroon, and Nigerian provinces withages of plutonic and metaplutonic rocks (TTG orthog-neisses, calc-alkalic gneisses, undeformed plutons, andanorogenic granites) in the Sao Francisco/Congo, Amazo-nian, and West African cratons. Considering the Archean/Paleoproterozoic history of the cratons, (1) Archean agespresent in the northern domain of the Borborema province[Dantas et al., 1998; Fetter et al., 2000] correlate withperiods of crustal growth at 3.5–3.4 Ga, 3.2–3.0 Ga, 2.8–2.7 Ga, and �2.5 Ga in the three cratonic areas [Potrel etal., 1998; Cordani and Sato, 1999; Tassinari and Macam-bira, 1999; Teixeira et al., 2000; Egal et al., 2002]; (2)basement ages in the Medio-Coreau domain [Fetter et al.,2000; T. J. S. Santos et al., 2000] are similar to an earlyPaleoproterozoic orogeny at 2.3 Ga recorded in the Congocraton [Feybesse et al., 1998]; and (3) reworking of Arche-an crustal rocks and formation of juvenile crust in theinterval 2.2–2.0 Ga in the Borborema province agree withthe age of the great Eburnean (in Africa) or Transamazonian(in Brazil) orogeny in the Sao Francisco [Teixeira et al.,2000], Congo [Feybesse et al., 1998], West African [Boheret al., 1992; Doumbia et al., 1998; Egal et al., 2002; Hirdesand Davis, 2002], and Amazonian [Cordani and Sato,1999; Tassinari and Macambira, 1999; Norcross et al.,2000] cratons. Orogenic deformation ceased in the SaoFrancisco/Congo and West African cratons after 2.0 Ga,but crustal accretion and deformation continued in south-western Amazonian craton until circa 1.0 Ga [Tassinari andMacambira, 1999].[25] Concerning the basement of Brasiliano/Pan-African

belts, (1) rocks with Archean ages are found in the northernportion of the Araguaia belt [Alvarenga et al., 2000], whichborders the eastern edge of the Amazonian craton and mayrepresent its continuation to the east, and in the westernNigerian province [Dada, 1998], which may be the contin-uation of the Rio Grande do Norte domain, and (2) juvenilePaleoproterozoic crust dominates in the eastern Nigerianprovince [Ferre et al., 1996] and in Cameroon [Toteu et al.,1994, 2001], which correlates with the central and southerndomains of the Borborema province.[26] Considering Paleo/Mesoproterozoic intraplate events,

the ages of metavolcanic rocks in the Oros and Jaquaribebelts (1.79–1.77 Ga) [Sa et al., 1995, 1997] and in theMedio-Coreau domain [T. J. S. Santos et al., 2000] coincide

Figure 6. Chondrite-normalized La concentrations (LaN)versus eNd (600 Ma) values for diorites of the high-Kassociation from plutons numbered 1, 2, 4, and 5 in Figure 3and for metaluminous syenites and ultrapotassic syenitesfrom plutons numbered 6 and 7, respectively, in Figure 3.Sources of data are Jardim de Sa [1994],Neves et al. [2000a],and Mariano et al. [2001] for diorites; Guimaraes and DaSilva Filho [1998] for metaluminous syenites; and Ferreiraand Sial [1993] and Ferreira et al. [1994] for ultrapotassicsyenites. See color version of this figure in the HTML.

5 - 8 NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE

with (1) the initial phase of rifting leading to deposition ofvolcanosedimentary sequences of the Espinhaco Group andintrusion of anorogenic granites in the Sao Francisco craton(1.75 Ga) [Schobbenhaus, 1996; Uhlein et al., 1998],(2) intrusion of gabbroic dikes in the Guyana portion ofthe Amazonian craton (1.79 Ga) [Norcross et al., 2000],(3) intrusion of anorogenic granites in the central and easternportions of the Amazonian craton (1.88 – 1.83 Ga)[Dall’Agnol et al., 1999], and (4) 1.9–1.8 Ga anorogenicmagmatism reported in southwestern Nigeria [Rahaman etal., 1983]. Likewise, anorogenic rocks of the central domainof the Borborema province have late Paleoproterozoic toearly Mesoproterozoic ages (1.7–1.5 Ga) [Accioly et al.,2000; Sa et al., 2002] similar to those of rapakivi granitesand associated mafic and ultramafic rocks in the northwest-ern (1.54 Ga) [Dall’Agnol et al., 1999] and southwestern(1.61–1.55 Ga) [Bettencourt et al., 1999] portions of theAmazonian craton.[27] Episodes that temporally correlate with the Cariris

Velhos event include: (1) intrusion of felsic alkaline plutonsassociated with crustal rifting in the Araguaia belt [Alvar-enga et al., 2000]; (2) a new rifting episode in the area ofthe Espinhaco Supergroup [Schobbenhaus, 1996; Uhlein etal., 1998]; (3) intrusion of mafic dike swarms in thesoutheastern part of the Sao Francisco craton [Renne etal., 1990]; and (4) emplacement of peralkalic granites andrhyolites followed by voluminous continental flood basaltsand rhyolites in the western edge of the Congo craton [Tacket al., 2001].

[28] As is the case of most supracrustal sequences in theBorborema province, Sm-Nd model ages and some U-Pbzircon ages of paragneisses and schists from Cameroonindicate that their protoliths were deposited during the ageinterval 1000–700 Ma [Toteu et al., 2001]. These sequencesmay be, in part, the metamorphosed equivalents of theextensive sedimentary units that cover a large part of theSao Francisco and West African cratons, which weredeposited in epicontinental and platformal environmentsduring the Neoproterozoic [Villeneuve and Cornee, 1994;R. V. Santos et al., 2000; Sial et al., 2000]. Noteworthy isthe rarity of petrotectonic assemblages typical of subductionzone environments in the Brasiliano/Pan-African belts inbetween the Amazonian, West African, and Sao Francisco/Congo cratons. Metamafic/ultramafic bodies, which repre-sent remnants of ophiolitic complexes, have been reportedin the Araguaia belt [Alvarenga et al., 2000] and in theGhana and Oubanguides belts [Castaing et al., 1994] butnot in the more internal portions of the Nigerian andCameroon provinces, and high-pressure rocks are rare.Additionally, positive eNd values in granitoids, typical ofcontinental magmatic arcs, have not been described. In-stead, in the Nigerian and Cameroon provinces, likewise theBorborema province, eNd values are extremely negative,indicating that the granites formed from Paleoproterozoic oreven older sources [Dada, 1998; Toteu et al., 2001]. Thissituation contrasts with the cases of the Brasilia belt andTuareg shield (Figure 1), where a long Neoproterozoictectonic history involving subduction, terrane accretion,

Figure 7. Histograms of U-Pb and Pb-Pb zircon ages of pre-Brasiliano orthogneisses in the (a)Borborema, (b) Araguaia, and (c) Nigerian and Cameroon provinces and plutonic andmetaplutonic rocks inthe (d) Sao Francisco/Congo, (e) Amazonian, and (f) West African cratons. The large peak centered at 1.4Ga in Figure 7e reflects the greater number of ages available for the southwestern Amazonian craton ascompared with its central and eastern portions and not superproduction of crust at that time. Here n is totalnumber of age determinations. See text for sources of data. See color version of this figure in the HTML.

NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE 5 - 9

formation of magmatic arcs, and arc-continent and conti-nent-continent collisions is well documented [Caby et al.,1989; Black et al., 1994; Liegeois et al., 1994; Dardenne,2000; Pimentel et al., 2000].

6. Discussion

[29] Ledru et al. [1994], based on the similarity of circa2.1 Gyr old fluviodeltaic deposits in the Amazonian, SaoFrancisco/Congo, and West African cratons, proposed thatthese three cratonic provinces formed a single continent atthe end of the Transamazonian/Eburnean orogeny. Subse-quently, Bossiere et al. [1996] and Norcross et al. [2000]highlighted the similarities in geology and gold mineraliza-tion between the northern part of the Amazonian craton andthe West African craton, further supporting the hypothesisof a Paleoproterozoic supercontinent. Rogers [1996] pro-posed the name Atlantica for this supercontinent andincluded the Rio de la Plata craton on it. Dominance ofPaleoproterozoic crust and existence of 1.7 Ga dike swarmsand rapakivi granites in the Rio de la Plata craton [Teixeiraet al., 1999] support this proposition. From the correlationsdescribed in the latter section, the general picture thatemerges is that there is strong evidence for the existenceof Atlantica and that it also included the basement of theBorborema, Araguaia, Nigerian, and Cameroon provinces.The proposed post-Transamazonian history of Atlantica isoutlined below.[30] Apart from ubiquitous continental rifting in the

1.8–1.5 Ga interval, Atlantica remained largely unaffectedby tectonic events for about 1 Gyr following its formation.The exception was the southwestern portion of the Amazo-nian craton, where several episodes of terrane accretion andarc magmatism occurred between 1.8 and 1.3 Ga, culmi-nating with a final collision, probably with Laurentia,around 1.0 Ga [Tassinari and Macambira, 1999; Geraldeset al., 2001]. Recently acquired paleomagnetic poles formafic rocks in SW Amazonia suggests that initial collisionoccurred around 1.2 Ga and took place with the LhanoUplift of west central Texas, the southernmost portion ofLaurentia [Tohver et al., 2002]. It is possible that theseevents led to the suturing of Atlantica with Laurentia/Balticaand thus that Atlantica was part of the larger Rodiniasupercontinent at the late Mesoproterozoic.[31] Because a long history of arc magmatism between

900 and 630 Ma in the Brasılia belt evidences the existenceof a large ocean to the south and west of the Sao Franciscocraton [Pimentel et al., 2000], the Rio de la Plata cratonmust have rifted and drifted away from Atlantica soon afteraggregation of Rodinia. Viewed from this larger perspec-tive, the Cariris Velhos event in the Borborema provinceand related extensional events in the Sao Francisco/Congocraton [Renne et al., 1990; Schobbenhaus, 1996; Uhlein etal., 1998; Tack et al., 2001] and in the Araguaia belt[Alvarenga et al., 2000] are interpreted as failed attemptsto further fragment the Paleoproterozoic continent. Forreasons discussed in previous sections, it is unlikely that alarge ocean developed during the Cariris Velhos event.However, TDM ages between 1.9 and 1.4 Ga for Cariris

Velhos plutonic rocks [Van Schmus et al., 1995; Brito Neveset al., 2001b] and the presence of Brasiliano plutons withTDM ages around 1 Ga at the northern border of theSergipano belt [Da Silva Filho et al., 2000] indicateaccretion of some juvenile material to the continentallithosphere during this event, suggesting either formationof oceanic crust or underplating of mafic magmas duringactive rifting.[32] Following the Cariris Velhos event, stable conditions

resumed in the Borborema province, and sedimentationtook place in epicontinental and platformal environmentscoevally with the extensive cover units preserved in the SaoFrancisco and West African cratons [Villeneuve and Cornee,1994; R. V. Santos et al., 2000; Sial et al., 2000]. Duringmiddle to late Neoproterozoic, ocean basins encircled thenorthern margin of the West African craton, with subductionzones dipping away from it [Black et al., 1994; Hefferan etal., 2000]. As a result, far-field tensional stresses transmit-ted to the interior of Atlantica may have promoted extensionand development of continental rift basins (Figure 8a).Some of these basins evolved to a protooceanic stage, withsubsequent subduction and oceanic closure leading to thelocal occurrence of eclogites in the central domain of theBorborema province [Beurlen et al., 1992], and obductionof ultramafic rocks and pillow basalts in the Araguaia belt[Alvarenga et al., 2000]. Subduction of oceanic lithosphereexplains the low-temperature and medium- to high-pressuremetamorphism in the Cachoeirinha belt, which stands incontrast with the general high-temperature metamorphismof other sectors of the Borborema province. The virtualabsence of a juvenile component in granitoids and lack ofassociated calc-alkalic metavolcanic sequences, however,suggest that the volume of subducted oceanic lithospherewas not enough to allow development of continental mag-matic arcs.[33] By around 650Ma, subduction had consumedmost of

the oceans that existed to the north and south of Atlantica,bringing the Tuareg shield and the Brasılia belt in closeproximity to it (Figure 8b). In consequence, contractionaldeformation began to prevail in the interior of Atlantica.Extensional conditions, however, persisted locally and led toformation of rift basins, from which the Serido belt is the bestrepresentative. Infilling of the Serido basin by materialderived from erosion of the Cachoeirinha belt [Van Schmuset al., 2000] may have resulted from extrusion of the thickand rheologically weak pile of volcanics and sediments thataccumulated during the repeated episodes of Neoproterozoicsedimentation and magmatism.[34] Ages of early Brasiliano granitic plutons and orthog-

neisses in the central Ceara [Fetter, 1999] central [Guimaraeset al., 1998; Guimaraes and Da Silva Filho, 2000] andsouthern [Da Silva Filho and Guimaraes, 2000; Neves andMariano, 2001] domains of the Borborema province, typi-cally in the 640–620 Ma interval, constrain the age of a firstdeformation event characterized by development of a flat-lying foliation. After 600 Ma a second deformation eventresulted in strain partitioning between an anastomosingnetwork of transcurrent shear zones, folded domains, andless deformed areas that preserved the previously formed flat-

5 - 10 NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE

lying foliation [Caby et al., 1995; Vauchez et al., 1995;Nevesand Mariano, 1999]. This stage of orogenic evolution wasaccompanied by the intrusion of huge volumes of mantle-and crustal-derived magmas [Ferreira et al., 1998; Neves etal., 2000a, and references therein], which peaked in the 590–570 Ma interval [Guimaraes et al., 1998, 2000; Melo et al.,2000]. The two Brasiliano deformational events were prob-ably continuous in time because some plutons record the twofinite strain patterns [Neves et al., 1996, 2000b]. Two finitestrain fields with similar ages and structures to those in theBorborema province are recognized in Cameroon [Toteu etal., 1990, 1994] and Nigeria [Ferre et al., 2002], indicatingthat the main period of the Brasiliano/Pan-African orogeny inthese belts lasted 70–80 Myr. Postorogenic, 540–530 Ma

granites mark the end of the Brasiliano/Pan-Africanevent in these provinces, while active deformation wasstill taking place in other Brasiliano/Pan-African belts[Trompette, 1997].

7. Conclusions

[35] The model proposed for the development of theBorborema province has several implications for the evo-lution of western Gondwana. Geological correlations sug-gest that the Amazonian, West African, and Sao Francisco/Congo cratons and the basement of the Araguaia, Borbor-ema, Nigerian, and Cameroon provinces formed a singleunit after the Transamazonian/Eburnean orogeny. If the

Figure 8. Model aiming to explain the tectonic evolution of the Borborema province. (a) During themiddle Neoproterozoic the West African craton was surround by outwardly dipping subduction zonesthat may have induced an extensional strain regime in the interior of Atlantica. (b) Basins formed duringthis period were deformed together with older cover successions and preexisting units when oceanclosure occurred at the late Neoproterozoic, but local extensional conditions still persisted locally. (Notethat no attempt was made to show area increase and reduction in these successive stages because of thelarge uncertainties involved). See color version of this figure in the HTML.

NEVES: PROTEROZOIC HISTORY OF THE BORBOREMA PROVINCE 5 - 11

interpretation that large oceans did not develop at any timeduring the Mesoproterozoic and Neoproterozoic holds true,this Paleoproterozoic continent remained relatively coherentfor most of the Proterozoic, yielding the core around whichwestern Gondwana grew. It is also implied that the Borbor-ema, Nigerian, and Cameroon provinces underwent a tec-tonic history substantially different from other Brasiliano/Pan-African belts. Their orogenic evolution spanned around100 Myr and took place essentially in an intracratonicsetting; differences in surface geology were inherited eitherfrom earlier Archean and Paleoproterozoic events, frompost-Transamazonian intraplate events, or from differentamounts of extension in precursor rift basins of supracrustalbelts. On the other hand, orogenic belts that developed

marginally to the Atlantica continent, as, for example, theBrasılia belt and the Tuareg shield, record a much longerand complex orogenic history. While in the former theBrasiliano/Pan-African orogeny mainly involved reworkingof preexisting units, the latter added primitive material towestern Gondwana through accretion of juvenile crust.

[36] Acknowledgments. The ideas presented in this paper evolvedthrough time by stimulating discussions with several colleagues. I amespecially indebted to Gorki Mariano with whom I have worked in closecollaboration for the last 10 years. Research support has been provided bygrants of the Conselho Nacional de Desenvolvimento Cientıfico e Tecno-logico (CNPq) of Brazil. Constructive reviews by D. Evans and R. Caby areacknowledged.

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Vauchez, A., and M. Egydio-Silva, Termination of acontinental-scale strike-slip fault in partially meltedcrust: The West Pernambuco shear zone, northeastBrazil, Geology, 20, 1007–1010, 1992.

Vauchez, A., S. P. Neves, R. Caby, M. Corsini,M. Egydio-Silva, M. H. Arthaud, and V. Amaro,The Borborema shear zone system, NE Brazil,J. South Am. Earth Sci., 8, 247–266, 1995.

Villeneuve, M., and J. J. Cornee, Structure, evolutionand paleogeography of the West African craton andbordering belts during the Neoproterozoic, Precam-brian Res., 69, 307–326, 1994.

Vlach, S. R. F., and J. A. Nogueira Neto, Sistematica(Th/U)-Pb de datacao de monazita em microssondaeletronica: Estudo de rochas metamorficas policıcli-cas da regiao de Granja, CE, paper presented at VIICongresso Brasileiro de Geoquımica, Soc. Bras. deGeol., Porto Seguro, Brazil, 1999.

���������S. P. Neves, Departamento de Geologia, Universi-

dade Federal de Pernambuco, Recife, Pernambuco50740, Brazil. (serpane@hotlink.com.br)

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