Timing of crust formation, deposition of supracrustal sequences, … · 2007-12-13 · Timing of...

Precambrian Research 149 (2006) 197–216

Timing of crust formation, deposition of supracrustal sequences,and Transamazonian and Brasiliano metamorphism in the East

Pernambuco belt (Borborema Province, NE Brazil):Implications for western Gondwana assembly

Sergio P. Neves a,∗, Olivier Bruguier b, Alain Vauchez c, 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

Received 21 July 2005; received in revised form 10 January 2006; accepted 21 June 2006

Abstract

The main structural feature of the central domain of Borborema Province (NE Brazil) is a network of dextral and sinistralshear zones. These shear zones rework an older, regionally developed, flat-lying foliation in orthogneisses and supracrustal belts,which in the East Pernambuco belt was formed under amphibolite facies conditions. This study reports LA-ICP-MS U–Pb zirconages of metaigneous and metasedimentary rocks aiming to constraint the pre-transcurrent tectonothermal evolution in the EasternPernambuco domain. Ages of 2125 ± 7 and 2044 ± 5 Ma in a mafic layer of banded orthogneiss are interpreted as the age of theprotolith of the orthogneiss and of high-grade Transamazonian metamorphism, respectively. The latter age is consistent with theoccurrence of low Th/U, metamorphic zircon xenocrysts, dated at 2041 ± 15 Ma, in the leucosome of a migmatitic paragneiss. Agranitic orthogneiss dated at 1991 ± 5 Ma reflects late to post-Transamazonian magmatic event. A similar age (1972 ± 8 Ma) wasfound in rounded zircon grains from a leucocratic layer of banded orthogneiss. Ages of detrital zircons in a paragneiss sample indicatederivation from sources with ages varying from the Archean to Neoproterozoic, with peak ages at ca. 2220, 2060–1940, 1200–1150and 870–760 Ma. Detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665 Ma. Magmaticzircons with the age of 626 ± 15 Ma are found in the leucosome of a migmatitic paragneiss and constrain the age of the Brasilianohigh-temperature metamorphism. A lower intercept age of 619 ± 36 Ma from a deformed granodiorite dated at 2097 ± 5 Ma and thecrystallization age of 625 ± 24 Ma of the felsic layer of banded orthogneiss also confirm the late Neoproterozoic metamorphism.These results show that the present fabric in basement and supracrustal rocks was produced during the Brasiliano orogeny.

Paleoproterozoic ages reported in this study are similar to those found in other sectors of the Borborema Province, the Cameroonand Nigeria provinces, and the Sao Francisco/Congo craton. They show the importance of the Transamazonian/Eburnean eventand suggest that these tectonic units may have been part of a larger, single continental landmass. Likewise, similarities in post-Transamazonian metamorphic and magmatic events in the Borborema, Nigeria and Cameroon provinces suggest that they shared a
common evolution and remained in close proximity until the opening of the Atlantic Ocean.© 2006 Elsevier B.V. All rights reserved.
Keywords: Laser ablation ICP-MS; Zircon U–Pb geochronology; Neoproterozoic belts; Transamazonian orogeny; Brasiliano orogeny

∗ Corresponding author. Tel.: +55 81 2126 8240; fax: +55 81 2126 8236.E-mail address: [email protected] (S.P. Neves).

0301-9268/$ – see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.precamres.2006.06.005

mailto:[email protected]

dx.doi.org/10.1016/j.precamres.2006.06.005

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198 S.P. Neves et al. / Precambr
1. Introduction

There is broad consensus that most of westernGondwana was already formed by 600 Ma. Continen-tal reconstructions for this period (e.g., Caby et al.,1991; Castaing et al., 1994; Trompette, 1997) show thatthe Brasiliano/Pan-African Borborema, Cameroon andNigeria provinces occupied a central position in relationto the Amazonian and West Africa cratons, to the west,the Sao Francisco/Congo craton, to the south, and theSaharan metacraton (Abdelsalam et al., 2002), to the east(Fig. 1). In the lack of paleomagnetic data, understand-ing how and when this configuration was reached rely ongeological and geochronological grounds. Knowledgeof the tectonothermal history of the late Neoproterozoicbelts is thus essential to evaluate possible correlationsbetween adjacent (within individual provinces) and dis-tant (transcontinental) units and, therefore, to provideinsights into the dynamics of amalgamation of westernGondwana.

The Precambrian crustal evolution of the BorboremaProvince has been much debated in recent years. Resolv-ing some critical pending issues is necessary to elabo-rate continental reconstructions for the Neoproterozoic.In the central domain, comprised between the Patosand Pernambuco shear zone systems (Fig. 1), the mostcontroversial issues are (1) the existence of a contrac-tional event in the early Neoproterozoic (Cariris Vel-hos orogeny, ∼1 Ga; Brito Neves et al., 1995), and(2) whether or not terranes accretion took place dur-ing this proposed orogeny. The suggestion of an earlyNeoproterozoic orogeny resulted from the discovery of1000–900 Ma-old intermediate to felsic metavolcanicrocks and orthogneisses in the Alto Pajeu belt (Fig. 1;Brito Neves et al., 1995; Van Schmus et al., 1995;Kozuch et al., 1997; Brito Neves et al., 2000, 2001a;Kozuch, 2003). Peraluminous orthogneisses intercalatedin the supracrustal sequence were interpreted as syncol-lisional granites. Santos and Medeiros (1999) proposedthat the Alto Pajeu belt is one of four tectonostrati-graphic terranes that amalgamated during the CaririsVelhos and Brasiliano orogenies to constitute the cen-tral domain. Several authors (Mariano et al., 2001;Guimaraes and Brito Neves, 2004; Neves, 2003 and ref-erences therein) have, however, questioned the existenceof the Cariris Velhos orogeny and the terrane accre-tion model, suggesting, instead, continuity between theproposed terranes since the Paleoproterozoic Transama-
zonian orogeny. Therefore, in this paper, the followingnon-genetic terms will be used to describe supracrustalsuccessions and orthogneisses occurring from west toeast in the central domain: Cachoeirinha belt, Alto
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Pajeu belt, Alto Moxoto belt and East Pernambuco belt(Fig. 1).

To improve knowledge and address the controversialpoints above, zircon grains from samples from the EastPernambuco belt were dated by laser ablation inductivelycoupled plasma-mass spectrometry (LA-ICP-MS). Theaim of this study is threefold: (1) constrain the timingof magmatic and metamorphic events and of depositionof supracrustal sequences, (2) compare its geologicalevolution with other regions in northeastern Brazil andwith the Pan-African belts of Nigeria and Cameroon, and(3) assess how these domains and surrounding cratonspulled together to make up western Gondwana.

2. Geological setting

2.1. Regional geology

The Borborema Province is characterized by a com-plex network of large transcurrent shear zones (Vauchezet al., 1995; Fig. 1). In the central domain, a linked systemof E–W- to ENE–WSW-striking dextral and NNE–SSW-to NE–SW-striking sinistral shear zones is spatiallyassociated with abundant granitic and syenitic plutons(Fig. 1B; Vauchez and Egydio-Silva, 1992; Guimaraesand Da Silva Filho, 1998; Ferreira et al., 1998; Neves andMariano, 1999; Neves et al., 2000; Silva and Mariano,2000). A former shallow-dipping regional foliation ispreserved in orthogneisses and metasediments outcrop-ping between the strike slip-related steeply dipping tovertical mylonitic zones. The metamorphic grade underwhich this foliation was developed differs between theCachoeirinha belt and the Alto Pajeu, Alto Moxoto andEast Pernambuco belts. The Cachoeirinha belt consistsof greenschist facies metapelites, metagreywackes andbimodal metavolcanics (Bittar and Campos Neto, 2000;Kozuch, 2003; Medeiros, 2004) deformed at relativelyhigh pressures (6–9 kbar; Sial, 1993; Caby and Sial,1997). Its low metamorphic grade stands in contrast withthat of the other three belts, which were regionally heatedabove 500 ◦C under low- to medium-pressures metamor-phic conditions (Vauchez and Egydio-Silva, 1992; Bittarand Campos Neto, 2000; Leite et al., 2000a; Neves et al.,2000).

Orthogneiss complexes underlie large areas of theAlto Pajeu, Alto Moxoto and East Pernambuco belts.They yielded U–Pb and Pb–Pb evaporation ages mostlyvarying from 2.2 to 2.0 Ga (Santos, 1995; Van Schmus
et al., 1995; Leite et al., 2000b; Brito Neves et al.,2001b; Melo et al., 2002; Kozuch, 2003; Neves et al.,2004; Santos et al., 2004a), and Sm–Nd data indicate theexistence of Archean protoliths for some of these Pale-

S.P. Neves et al. / Precambrian Research 149 (2006) 197–216 199

Fig. 1. (A) South America–Africa fit showing cratons and Neoproterozoic provinces of western Gondwana, and sketch highlighting main shear zonesin Borborema Province. (B) Schematic geological map of eastern Borborema Province showing location of the studied area in the East Pernambucob een theA r ZoneP

oBnaMtm

z(K2rit

elt (EPB) of central domain. Dashed lines highlight boundaries betwlto Pajeu (APB) and Alto Moxoto (AMB) belts. PaSZ, Patos Sheaernambuco Shear Zone system.

proterozoic orthogneisses (Van Schmus et al., 1995;rito Neves et al., 2001b; Melo et al., 2002). Domi-ance of Paleoproterozoic to Archean Sm–Nd modelges in granitic and syenitic plutons (Ferreira et al., 1998;ariano et al., 2001; Guimaraes et al., 2004) suggests

hat Paleoproterozoic to Archean basement constituteost of the central domain.In the Alto Pajeu belt, metavolcanic rocks have U–Pb

ircon ages mainly comprised between 1000 and 970 MaBrito Neves et al., 1995; Van Schmus et al., 1995;ozuch et al., 1997; Brito Neves et al., 2000; Kozuch,
003). Van Schmus et al. (1995) and Kozuch et al. (1997)eport U–Pb ages for metavolcanic rocks in the Cachoeir-nha belt in the interval 810–720 Ma. Refinement ofhese data due to the presence of inherited zircons and
central and northern domains, and between the Cachoeirinha (CB),system; EPSZ, East Pernambuco Shear Zone system; WPSZ, West

new age determinations indicate a younger depositionalage (660–620 Ma; Kozuch, 2003; Medeiros, 2004). Inthese two belts, Sm–Nd ages range from 1.8 to 1.2 Ga(Brito Neves et al., 2001a; Kozuch, 2003; Archanjo andFetter, 2004). The oldest Nd model ages suggest thatPaleoproterozoic or older sources provided importantcontribution for detritus that filled their precursor sed-imentary basins. In the Cachoeirinha belt, this inferenceis further supported by the occurrence of zircons withages up to 3278 Ma in a quartzite sample (Silva et al.,1997) and of Paleoproterozoic zircons in a metarhyolite
(Kozuch, 2003). The Sertania metasedimentary complexin the Alto Moxoto belt yielded zircon grains with agesaround 2.0 Ga (Santos et al., 2004a) and Sm–Nd agesvarying from 2.0 to 3.0 Ga (Brito Neves et al., 2001b).

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These data indicate its provenance mainly from Pale-oproterozoic and Archean sources, but only places anupper bound on the age of deposition. The age of depo-sition of supracrustal sequences in the East Pernambucobelt is still unknown.

2.2. Study area

The study area is located in the northwestern partof the East Pernambuco belt (Fig. 1). It comprisesbanded orthogneisses, granitic augen gneisses, metased-imentary rocks and igneous intrusions (Fig. 2). Bandedorthogneisses are characterized by alternating bands ofdioritic and granitic compositions. Zircon U–Pb dat-ing from a monzodioritic orthogneiss and a graniticaugen gneiss (Taquaritinga orthogneiss) in the southernpart of the study area yielded ages of 1974 ± 32 and1521 ± 6 Ma, respectively (Sa et al., 2002).

In the geological map of the state of Pernambuco(Gomes, 2001), Surubim and Vertentes complexes arerecognized as two distinct supracrustal units, mainlybased on the occurrence of metavolcanic rocks in thelatter. Metavolcanic rocks were not identified by us inthe study area nor in other localities of the East Pernam-buco belt. Metasedimentary rocks are indistinguishablein terms of rock association, structure or metamorphicgrade between the Surubim and Vertentes complexes.Furthermore, our mapping shows that basement gneisseswere misinterpreted as belonging to the Vertentes com-plex. Therefore, this complex is not considered hereas a valid tectonostratigraphic unit. In consequence,metasedimentary rocks in the study are attributed to theSurubim complex. The main lithotypes are biotite gneiss,biotite schist, quartz-feldspar paragneiss, quartzite andmarble, locally with small lenses of para-amphiboliteand calc-silicate rock. Sillimanite and garnet are ubiqui-tous accessory phases, which together with local migma-tization attest high-temperature metamorphism.

From the structural point of view, the study areais characterized by flat-lying gneissic foliation inorthogneisses and supracrustal rocks. This early fabric isdeformed by recumbent to upright folds and transcurrentshear zones (Neves et al., 2005). Stretching lineationsassociated with the flat-lying foliation have ESE–WNWtrend in supracrustal rocks and NE–SW trend inbanded orthogneiss and Taquaritinga orthogneiss. In themetasedimentary sequence, numerous kinematic indica-tors showing a top-to-the-west/northwest sense of shear
denote a well-developed non-coaxial deformation. Theseoblique lineations were interpreted (Neves et al., 2005) asthe result of extension oblique to the transport directionin the deeper orthogneisses during progressive defor-
earch 149 (2006) 197–216

mation. A deformed epidote-bearing biotite granodior-ite (Alcantil pluton; Fig. 2) displays a flat-lying mag-matic/gneissic foliation crosscut by subvertical shearbands. This pluton was previously regarded as a Neo-proterozoic intrusion emplaced during the top-to-the-northwest tectonics (Neves et al., 2005). However, dataacquired in the present study favor its intrusion duringthe Paleoproterozoic, followed by solid-state deforma-tion during the Brasiliano orogeny (see below). Twoplutons partially outcrop in the southern part of the studyarea (Fig. 2). The ca. 585 Ma-old, syenitic Toritama plu-ton (Guimaraes and Da Silva Filho, 1998) is interpretedas early kinematic with respect to strike-slip shearing(Neves et al., 2000). The Santa Cruz do Capibaribe plu-ton is a composite intrusion containing gabbronoritesand diorites in the core and monzonites at the margins,displaying only local solid-state deformation.

3. Studied samples

Samples for this study represent the main lithologicalunits and key relations between age and deformation inthe study area. Six samples weighting 8–12 kg each werecollected from four localities (Fig. 2B). Samples SCC1Aand SCC1B are, respectively, mafic and felsic layersof banded orthogneiss. SCC1A is a medium-grained,dark-colored biotite amphibole gneiss with quartz mon-zodioritic composition. SCC1B is a medium-grained,leucocratic granitic gneiss containing less than 10%biotite. The gneissic banding dips 36◦ towards N104◦Eand a strong stretching lineation plunging gently tonortheast (21◦, N47◦E) is present in both lithologies.Sample SCC9 is a medium to coarse-grained sillimanitebiotite paragneiss containing garnet porphyroblasts upto 1 cm in diameter. Sample SCC12 is the leucosome ofa migmatitic paragneiss, and SCC2 is a granitic gneiss.Since contact relationships are not exposed, it is not pos-sible to determine whether the granitic gneiss is a sheetintercalated in metasedimentary sequence or whether itunderlies it. Quartz ribbons in sample SCC2 attest strongsolid-state deformation and define a lineation plunging7◦, N150◦E. Sample SSC5 is from the Alcantil pluton,showing foliation dipping 36◦ towards N24◦E.

4. Analytical techniques

Zircons were separated using conventional tech-niques. After crushing and sieving of the powdered sam-
ples, heavy minerals were concentrated by panning andthen by heavy liquids. The heavy mineral concentrateswere subsequently processed by magnetic separationusing a Frantz separator. Zircon grains were hand picked


F howingN udied aa 02).

fo(Sa

ig. 2. (A) Simplified geological map of the East Pernambuco belt seves et al. (2000) and Gomes (2001). (B) Geological map of the st

nalysed by LA-ICP-MS, and existing TIMS U–Pb ages (Sa et al., 20

rom the non-magnetic fraction at 1.5 A intensity and 1◦
r 2◦ side tilt (Samples SCC1A and SCC9), 2◦ side tiltsamples SCC1B and SCC2), and 4◦ side tilt (samplesCC5 and SCC12). The grains were then mounted ondhesive tape, enclosed in epoxy resin with chips of a
location of studied area. Modified from Neves and Mariano (1999),rea (modified from Neves et al., 2005) showing location of samples

standard material (G91500; Wiedenbeck et al., 1995)
and polished to about half of their thickness. Internalstructure and morphology were subsequently observedby Scanning Electron Microscopy (SEM) using a JEOL1200 EX II operating at 120 kV. After BSE imaging, car-

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bon coating was removed by using alcohol and the resingrain mount was subsequently slightly repolished to getrid of any residual carbon which can potentially con-tain significant amount of 204Pb (see Hirata and Nesbitt,1995). The mount was then cleaned in ultra-pure MQwater and dried before its introduction in the ablationcell.

Data were acquired at the University of Montpel-lier II using a 1991 vintage VG Plasmaquad II turboICP-MS coupled with a Geolas (Microlas) automatedplatform housing a 193 nm Compex 102 laser fromLambdaPhysik. Analyses were conducted using an in-house modified ablation cell of ca. 5 cm3 which resultedin a shorter washout time and an improved sensitivitycompared to the initial larger ablation cell (ca. 30 cm3).Ablation experiments were conducted in a He atmo-sphere to enhance sensitivity and reduce inter-elementfractionation (Gunther and Heinrich, 1999). Data wereacquired in the peak jumping mode in a series of fiverepeats of 10 s each, measuring the 202Hg, 204(Pb + Hg),206Pb, 207Pb, 208Pb and 238U isotopes similarly to theprocedure described in Bruguier et al. (2001). Signal wasacquired after a 10 s period of pre-ablation to allow forcrater stabilization and to remove surface contaminationas well as fall-out from previous analyses. The laser wasfired using an energy density of 20 J cm−2 at a frequencyof 3 or 4 Hz. The laser spot size was of 52 and 26 �m insamples SCC1A, SCC1B and SCC9, and 26 �m in sam-ples SCC2, SCC5 and SCC12. Some additional analysesusing a spot size of 15 �m were further made in the rimsof zircon grains from sample SCC1A.

The Pb/Pb and U/Pb isotopic ratios of unknowns werecalibrated against the G91500 zircon crystal as an exter-nal ablation standard, which was measured four timeseach five unknowns using the bracketing technique. Datawere reduced using a calculation spreadsheet, whichallows correction for instrumental mass bias and inter-element fractionation. Accurate common lead correctionin zircon is difficult to achieve, mainly because of theisobaric interference of 204Hg on 204Pb. The contribu-tion of 204Hg on 204Pb was estimated by measuring the202Hg and assuming a 204Hg/202Hg natural isotopic com-position of 0.2298. This allows to monitor the commonlead content of the analysed grain, but corrections oftenresult in spurious ages. Analyses yielding 204Pb closeto, or above the limit of detection were then rejected.Table 1 thus presents only analyses for which 204Pb wasbelow detection limit. For instrumental mass bias, all
measured standards were averaged to give a mean massbias factor and its associated error. This mass bias fac-tor and associated error were then propagated with themeasured analytical errors of each individual sample.
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Inter-element fractionation for Pb and U are much moresensitive to analytical conditions and a bias factor wasthus calculated using the four standard measurementsbracketing each five unknowns. These four measure-ments were then averaged to calculate a U–Pb bias factorand its associated error, which were added in quadra-ture to the individual error measured on each 206Pb/238Uunknown. This typically resulted in a 2–5% precision(1σ R.S.D.%) after all corrections have been made (seeTable 1). Ages quoted below were calculated using theIsoplot program of Ludwig (2000).

5. Zircon morphology and internal structure

Zircon grains from the mafic and felsic layers ofbanded orthogneiss have distinct morphologies andinternal structures. In sample SCC1A (mafic band), mostgrains are elongated (aspect ratios varying from 2:1 to4:1), ranging from 150 to 400 �m in length. In spiteof rounded terminations, the original euhedral to sub-hedral shape can still be recognized in many grains.Oscillatory zoning, typical of magmatic growth, is com-mon (Fig. 3A) although it is faint and partially obliter-ated in many grains, suggesting local redistribution ofelements during metamorphism. Dissolution and repre-cipitation in some grains is indicated by embaymentscutting the concentric zoning (Fig. 3B). Overgrowthrims, where present, are usually thin (<20 �m), andsome grains exhibit structureless domains (Fig. 3B). Allthese features are interpreted as representing a mag-matic zircon population affected by a metamorphicevent. Inherited cores were not observed in the analyzedgrains.

In contrast with zircon grains from Sample SCC1A,those from sample SCC1B have aspect ratio normallybetween 1:1 and 2:1 and are shorter (less than 300 �mlong). Their main characteristic is the presence of over-growths with thin oscillatory zoning, suggesting mag-matic growth over preexisting crystals (Fig. 3C). Somecrystals have subhedral to euhedral shapes (Fig. 3D) andoscillatory zoning typical of magmatic zircons.

In sample SCC2 (granitic orthogneiss) the dominantzircon population consists of clear, subhedral to euhe-dral grains with faint oscillatory or no apparent zoning,sometimes with inherited cores (Fig. 3E and F).

The most common population of zircons in theparagneiss sample SCC9 comprises rounded to slightlyelongated (aspect ratios up to 2.5:1) grains with clear
oscillatory zoning (Fig. 4A). Some grains also havebright, high-U, overgrowth rims (Fig. 4A), preferentiallylocated at the terminations of the crystals and responsi-ble for rounding of the original euhedral shape. A few

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203Table 1LA-ICP-MS U–Th–Pb results for zircons from rocks of the Borborema Province (Brazil)

Sample Pb* (ppm) U (ppm) Th (ppm) Th/U 204Pb/206Pb 208Pb/206Pb 207Pb/206Pb ±1σ 207Pb/235U ±1σ 206Pb/238U ±1σ ρ Apparent Ages (Ma) Disc (%)

206Pb/238U ±1σ 207Pb/206Pb ±1σ

SCC1A#1 156 580 110 0.19 3.66E−06 – 0.1192 0.0006 4.6583 0.2623 0.2834 0.0159 1.00 1608 79 1945 8 17.3#2* 99 274 85 0.31 4.87E−06 – 0.1325 0.0019 6.8423 0.2023 0.3745 0.0097 0.88 2050 45 2132 25 3.8#3* 92 241 68 0.28 4.70E−06 – 0.1268 0.0005 6.5162 0.2461 0.3728 0.0140 0.99 2042 65 2054 7 0.5#4* 103 274 118 0.43 4.41E−06 – 0.1297 0.0005 6.5833 0.1586 0.3681 0.0087 0.99 2020 41 2094 7 3.5#5* 83 215 61 0.29 6.63E−06 – 0.1259 0.0005 6.5767 0.1872 0.3788 0.0107 0.99 2071 50 2042 6 −1.4#6 89 259 70 0.27 6.55E−06 – 0.1302 0.0013 6.1569 0.1260 0.3429 0.0062 0.88 1901 30 2101 17 9.5#7* 131 419 158 0.38 4.19E−06 – 0.1268 0.0004 6.4644 0.1580 0.3695 0.0089 0.99 2027 42 2054 6 1.3#8* 104 271 50 0.19 4.78E−06 – 0.1264 0.0010 6.5018 0.2790 0.3730 0.0157 0.98 2044 73 2049 14 0.2#9* 37 110 59 0.53 1.51E−05 – 0.1261 0.0005 6.1478 0.0812 0.3536 0.0044 0.95 1952 21 2044 8 4.5#10 194 723 475 0.66 3.00E−06 – 0.1231 0.0009 4.7008 0.0492 0.2770 0.0022 0.75 1576 11 2001 12 21.3#11 216 672 472 0.70 2.67E−06 – 0.1240 0.0008 5.7877 0.0604 0.3384 0.0028 0.79 1879 13 2015 11 6.8#12 87 281 60 0.21 6.57E−06 – 0.1223 0.0005 5.5101 0.2605 0.3267 0.0154 1.00 1822 74 1991 7 8.5#13 287 795 639 0.80 2.16E−06 – 0.1269 0.0004 5.4198 0.1006 0.3099 0.0057 0.98 1740 28 2056 6 15.3#14* 138 394 188 0.48 3.94E−06 – 0.1310 0.0007 6.8117 0.1324 0.3771 0.0070 0.96 2063 33 2111 10 2.3#15 137 477 131 0.27 4.37E−06 – 0.1201 0.0008 4.8532 0.0830 0.2931 0.0046 0.91 1657 23 1957 12 15.3#16* 87 230 105 0.46 6.18E−06 – 0.1320 0.0010 7.0809 0.0903 0.3892 0.0040 0.80 2119 19 2124 13 0.2#17* 76 205 178 0.87 9.50E−06 – 0.1322 0.0005 6.8481 0.1425 0.3756 0.0077 0.98 2056 36 2128 7 3.4#18* 96 311 114 0.36 5.23E−06 – 0.1253 0.0004 6.1540 0.2326 0.3562 0.0134 1.00 1964 63 2033 6 3.4#19 135 525 247 0.47 3.91E−06 – 0.1319 0.0010 4.6341 0.0921 0.2549 0.0047 0.93 1464 24 2123 13 31.1#20* 97 281 103 0.37 5.51E−06 – 0.1266 0.0006 6.2522 0.2710 0.3582 0.0154 0.99 1974 73 2051 8 3.8#21 152 754 258 0.34 4.36E−06 – 0.1252 0.0004 3.4946 0.0773 0.2025 0.0044 0.99 1189 24 2031 6 41.5#22* 155 352 201 0.57 4.70E−06 0.170 0.1315 0.0011 7.3206 0.2538 0.4037 0.0136 0.97 2186 62 2118 15 −3.2#23* 169 257 80 0.31 5.45E−06 0.118 0.1317 0.0020 7.1134 0.2963 0.3917 0.0151 0.93 2130 70 2121 27 −0.4#24* 269 507 298 0.59 3.20E−06 0.178 0.1315 0.0010 6.7704 0.2441 0.3735 0.0132 0.98 2046 61 2118 14 3.4#25 236 587 330 0.56 3.89E−06 0.147 0.1310 0.0011 6.4622 0.1260 0.3579 0.0062 0.89 1972 30 2111 15 6.6#26 277 654 408 0.62 2.95E−06 0.185 0.1319 0.0011 6.4648 0.0618 0.3554 0.0014 0.42 1960 7 2124 15 7.7#27 61 136 76 0.56 6.14E−06 0.192 0.1337 0.0010 6.8295 0.1082 0.3705 0.0052 0.89 2032 25 2147 13 5.4#28* 106 258 71 0.27 7.25E−06 0.076 0.1257 0.0009 6.4235 0.1082 0.3707 0.0057 0.91 2033 27 2038 13 0.3#29* 130 278 108 0.39 6.81E−06 0.122 0.1317 0.0014 7.1760 0.1942 0.3952 0.0098 0.91 2147 45 2121 19 −1.2#30* 258 631 281 0.45 3.28E−06 0.105 0.1255 0.0009 6.1352 0.2052 0.3545 0.0116 0.98 1956 55 2036 13 3.9#31* 288 489 231 0.47 3.44E−06 0.172 0.1314 0.0016 6.7414 0.1936 0.3721 0.0096 0.90 2039 45 2117 22 3.7#32* 147 323 118 0.37 5.18E−06 0.103 0.1259 0.0011 6.2179 0.1529 0.3583 0.0083 0.94 1974 39 2041 15 3.3#33 240 717 225 0.31 3.51E−06 0.107 0.1259 0.0012 5.9811 0.1053 0.3446 0.0051 0.84 1909 24 2041 17 6.5#34 61 249 30 0.12 9.82E−06 0.053 0.1221 0.0014 4.5698 0.0872 0.2715 0.0041 0.80 1548 21 1987 21 22.1#35* 207 619 75 0.12 3.82E−06 0.054 0.1325 0.0013 6.7513 0.1612 0.3740 0.0081 0.92 2048 38 2132 17 3.9#36* 144 436 209 0.48 5.34E−06 0.096 0.1263 0.0007 6.1788 0.1137 0.3549 0.0062 0.96 1958 30 2047 9 4.3#37* 101 285 95 0.33 6.62E−06 0.098 0.1314 0.0011 6.7888 0.0749 0.3747 0.0028 0.69 2052 13 2117 14 3.1#38 122 340 101 0.30 5.13E−06 0.080 0.1255 0.0013 5.7987 0.1460 0.3352 0.0077 0.92 1863 37 2036 18 8.5#39 189 540 142 0.26 3.19E−06 0.078 0.1255 0.0019 5.7908 0.1221 0.3346 0.0049 0.69 1861 23 2036 27 8.6#40 184 473 269 0.57 3.73E−06 0.158 0.1313 0.0007 6.3251 0.0620 0.3495 0.0028 0.81 1932 13 2115 10 8.6#41* 199 472 351 0.74 3.46E−06 0.193 0.1312 0.0017 6.6435 0.0893 0.3674 0.0013 0.26 2017 6 2114 23 4.6#42* 135 335 127 0.38 4.43E−06 0.117 0.1251 0.0009 6.3293 0.1032 0.3670 0.0054 0.90 2015 25 2030 12 0.7#43* 188 459 208 0.45 3.64E−06 0.129 0.1319 0.0017 6.8990 0.1266 0.3793 0.0049 0.71 2073 23 2124 23 2.4#44* 228 566 271 0.48 2.59E−06 0.153 0.1320 0.0014 6.7767 0.1754 0.3769 0.0088 0.91 2062 41 2124 19 2.9

204S.P.N

evesetal./P

recambrian

Research

149(2006)

197–216

Table 1 (Continued )


206Pb/238U ±1σ 207Pb/206Pb ±1σ

#45* 230 548 267 0.49 2.87E−06 0.156 0.1317 0.0017 6.7659 0.1210 0.3727 0.0046 0.69 2042 22 2120 23 3.7#46* 73 169 77 0.46 8.04E−06 0.136 0.1339 0.0008 7.1834 0.0931 0.3892 0.0045 0.90 2119 21 2149 10 1.4#47 145 370 162 0.44 3.58E−06 0.137 0.1318 0.0015 6.4289 0.0827 0.3539 0.0020 0.45 1953 10 2121 20 7.9#48* 193 468 114 0.24 2.67E−05 0.076 0.1318 0.0029 7.1683 0.3275 0.3944 0.0158 0.88 2143 73 2122 39 −1.0#49* 211 625 190 0.30 2.06E−05 0.087 0.1319 0.0019 6.9519 0.2354 0.3823 0.0117 0.91 2087 55 2123 25 1.7#50* 111 306 97 0.32 4.29E−05 0.092 0.1313 0.0029 7.0291 0.2867 0.3882 0.0133 0.84 2114 61 2116 39 0.1#51 114 313 62 0.20 3.97E−05 0.071 0.1257 0.0020 5.9734 0.1163 0.3447 0.0040 0.60 1909 19 2038 28 6.3#52 201 573 178 0.31 2.93E−05 0.104 0.1259 0.0026 5.8183 0.1714 0.3352 0.0070 0.71 1864 34 2041 37 8.7#53* 282 725 258 0.36 1.98E−05 0.104 0.1263 0.0020 6.2292 0.1175 0.3577 0.0038 0.56 1971 18 2047 27 3.7

SCC1B#1* 119 330 90 0.27 4.95E−06 – 0.1217 0.0013 5.8986 0.3450 0.3515 0.0202 0.98 1942 96 1981 19 2.0#2* 123 368 83 0.23 4.39E−06 – 0.1217 0.0019 5.7713 0.1889 0.3439 0.0099 0.88 1906 47 1981 28 3.8#3* 80 231 148 0.64 6.20E−06 – 0.1200 0.0010 5.8375 0.1012 0.3527 0.0053 0.87 1948 25 1957 15 0.5#4 52 136 73 0.53 1.19E−05 – 0.1298 0.0005 7.1566 0.3326 0.3997 0.0185 1.00 2168 85 2096 7 −3.4#5 55 563 376 0.67 1.02E−05 – 0.0658 0.0013 0.9231 0.0268 0.1018 0.0021 0.72 625 12 800 42 21.9#6* 79 225 122 0.54 7.05E−06 – 0.1200 0.0012 6.0305 0.1294 0.3645 0.0069 0.89 2003 33 1956 18 −2.4#7* 61 177 60 0.34 1.04E−05 – 0.1209 0.0016 5.8620 0.3088 0.3517 0.0179 0.97 1943 85 1969 24 1.3#8* 145 425 117 0.27 3.34E−06 – 0.1216 0.0005 5.6962 0.0993 0.3397 0.0058 0.98 1885 28 1980 7 4.8#9* 115 346 117 0.34 5.55E−06 – 0.1204 0.0007 5.6963 0.1392 0.3430 0.0081 0.97 1901 39 1963 11 3.1#10* 154 463 135 0.29 3.15E−06 – 0.1219 0.0009 5.7435 0.0860 0.3417 0.0044 0.85 1895 21 1984 14 4.5#11* 143 424 225 0.53 4.13E−06 – 0.1204 0.0007 5.7924 0.1409 0.3489 0.0083 0.97 1929 39 1963 10 1.7#12* 112 325 86 0.26 6.10E−06 – 0.1213 0.0007 5.9861 0.2552 0.3579 0.0151 0.99 1972 71 1976 11 0.2

SCC2#1* 37 106 24.38 0.23 5.14E−06 – 0.1213 0.0008 6.1294 0.1257 0.3664 0.0072 0.95 2012 34 1976 11 −1.8#2* 36 109 27.31 0.25 5.37E−06 – 0.1215 0.0007 5.8041 0.0725 0.3466 0.0038 0.88 1918 18 1978 10 3.0#3 82 227 48.23 0.21 2.55E−06 – 0.1319 0.0009 6.7873 0.1094 0.3733 0.0055 0.91 2045 26 2123 12 3.7#4 107 363 30.69 0.08 2.12E−06 – 0.1190 0.0004 5.0373 0.0602 0.3070 0.0035 0.95 1726 17 1941 6 11.1#5* 66 192 29.91 0.16 3.05E−06 – 0.1214 0.0007 5.9431 0.1193 0.3551 0.0068 0.96 1959 32 1977 10 0.9#6* 35 95 19.36 0.20 5.92E−06 – 0.1228 0.0017 6.2670 0.0937 0.3702 0.0022 0.40 2030 10 1997 24 −1.7#7* 28 81 16.59 0.20 8.61E−06 – 0.1217 0.0008 5.9290 0.1596 0.3533 0.0092 0.97 1951 44 1981 12 1.6#8* 36 100 17.84 0.18 5.44E−06 – 0.1233 0.0007 6.2643 0.0721 0.3686 0.0036 0.85 2023 17 2004 11 −0.9#9* 36 98 15.85 0.16 5.46E−06 – 0.1236 0.0009 6.3046 0.0935 0.3700 0.0048 0.88 2029 23 2009 12 −1.0#10* 37 99 43.57 0.44 6.15E−06 – 0.1233 0.0014 6.2831 0.1439 0.3696 0.0073 0.86 2027 34 2005 21 −1.1#11 54 175 47.22 0.27 4.25E−06 – 0.1265 0.0008 5.7264 0.2653 0.3283 0.0151 0.99 1830 73 2050 11 10.7#12* 51 141 25.59 0.18 4.31E−06 – 0.1220 0.0008 6.0819 0.1097 0.3614 0.0061 0.94 1989 29 1986 11 −0.1#13 35 89 40.13 0.45 5.28E−06 – 0.1375 0.0006 7.6026 0.0691 0.4009 0.0032 0.89 2173 15 2196 7 1.0#14* 59 193 39.36 0.20 4.51E−06 – 0.1228 0.0008 6.0807 0.0679 0.3592 0.0035 0.87 1978 17 1997 11 1.0#15* 28 83 21.82 0.26 9.70E−06 – 0.1222 0.0011 6.0280 0.1212 0.3577 0.0065 0.90 1971 31 1989 16 0.9#16* 49 144 17.45 0.12 5.48E−06 – 0.1232 0.0012 6.1414 0.3689 0.3615 0.0205 0.94 1989 96 2003 18 0.7#17* 14 38 5.61 0.15 1.32E−05 – 0.1233 0.0014 6.1371 0.0988 0.3611 0.0036 0.63 1987 17 2004 20 0.8#18* 41 118 21.83 0.19 4.91E−06 – 0.1223 0.0003 6.0817 0.1179 0.3606 0.0069 0.99 1985 33 1990 5 0.3#19* 130 373 79.56 0.21 1.77E−06 – 0.1219 0.0005 6.0312 0.0604 0.3618 0.0033 0.90 1990 15 1985 8 −0.3#20* 32 92 21.63 0.23 8.13E−06 – 0.1236 0.0007 6.0503 0.2258 0.3551 0.0131 0.99 1959 62 2008 10 2.5#21 59 162 24.23 0.15 3.47E−06 – 0.1282 0.0007 6.7044 0.0816 0.3792 0.0041 0.88 2073 19 2074 10 0.1

S.P.Neves

etal./Precam

brianR

esearch149

(2006)197–216

205Table 1 (Continued )


206Pb/238U ±1σ 207Pb/206Pb ±1σ

SCC5#1 47 134 74 0.55 1.15E−05 – 0.1283 0.0006 5.8296 0.2949 0.3295 0.0156 0.94 1836 75 2075 8 11.5#2 62 188 168 0.89 8.33E−06 – 0.1267 0.0006 5.9225 0.1740 0.3389 0.0099 0.99 1881 48 2053 8 8.4#3 47 171 129 0.76 1.16E−05 – 0.1219 0.0015 4.9253 0.2436 0.2930 0.0132 0.91 1657 65 1984 22 16.5#4 3 31 1 0.04 2.44E−04 – 0.0615 0.0009 0.8451 0.0713 0.0996 0.0046 0.94 612 27 658 30 7.1#5* 44 124 84 0.68 1.14E−05 – 0.1300 0.0010 6.5989 0.1624 0.3680 0.0081 0.90 2020 38 2099 14 3.7#6* 42 115 78 0.68 1.48E−05 – 0.1295 0.0005 6.6790 0.3127 0.3741 0.0173 0.99 2048 81 2091 6 2.0#7 120 341 383 1.12 8.01E−06 – 0.1291 0.0007 6.2820 0.3132 0.3529 0.0172 0.98 1949 81 2086 10 6.6#8 69 291 295 1.01 1.32E−05 – 0.1219 0.0004 4.3412 0.2316 0.2583 0.0136 0.98 1481 69 1984 6 25.4#9* 33 91 58 0.63 2.38E−05 – 0.1299 0.0005 6.5389 0.1601 0.3651 0.0088 0.99 2006 42 2097 7 4.3#10 62 205 156 0.76 1.51E−05 – 0.1235 0.0014 5.3041 0.2700 0.3116 0.0155 0.98 1748 76 2007 20 12.9#11 55 326 125 0.39 1.40E−05 – 0.1004 0.0008 2.5316 0.1016 0.1829 0.0072 0.98 1083 39 1631 15 33.6#12* 66 173 99 0.57 1.93E−05 – 0.1299 0.0004 6.8323 0.3240 0.3814 0.0179 0.99 2083 83 2097 6 0.7#13 33 103 64 0.62 2.57E−05 – 0.1294 0.0011 6.3456 0.1257 0.3557 0.0065 0.92 1962 31 2090 15 6.1#14* 70 186 146 0.78 1.30E−05 – 0.1304 0.0006 7.0925 0.3184 0.3945 0.0174 0.98 2144 80 2103 8 −1.9#15 46 136 84 0.62 2.26E−05 – 0.1246 0.0015 5.5176 0.1346 0.3245 0.0065 0.83 1812 32 2023 21 10.4#16 59 231 98 0.42 1.59E−05 – 0.1196 0.0012 4.3837 0.2096 0.2658 0.0124 0.98 1519 63 1950 18 22.1#17 62 163 118 0.72 1.11E−05 – 0.1278 0.0003 6.4429 0.3484 0.3657 0.0196 0.99 2009 92 2068 4 2.8#18* 63 183 125 0.68 1.45E−05 – 0.1300 0.0005 6.6770 0.3456 0.3725 0.0188 0.92 2041 88 2098 6 2.7#19 28 348 205 0.59 3.09E−05 – 0.0762 0.0024 1.1706 0.2002 0.1114 0.0077 0.98 681 45 1101 61 38.2#20* 52 149 127 0.85 1.48E−05 – 0.1305 0.0010 6.9160 0.1202 0.3843 0.0058 0.81 2096 27 2105 13 0.4#21* 36 102 86 0.85 2.31E−05 – 0.1297 0.0006 6.7763 0.2768 0.3790 0.0148 0.96 2072 69 2094 9 1.0#22 67 221 121 0.55 1.21E−05 – 0.1243 0.0004 5.5019 0.1117 0.3209 0.0065 0.99 1794 31 2020 6 11.2

SCC9#1 45 226 75 0.33 2.21E−05 0.136 0.0828 0.0014 2.1517 0.0465 0.1885 0.0026 0.65 1113 14 1264 32 11.9#2 53 309 28 0.09 1.57E−05 0.096 0.0789 0.0011 1.8376 0.0329 0.1688 0.0024 0.80 1006 13 1171 27 14.1#3 62 150 110 0.73 1.47E−05 0.219 0.1191 0.0002 5.9187 0.2116 0.3603 0.0117 0.91 1984 55 1943 4 −2.1#4 74 556 365 0.66 1.04E−05 0.208 0.0646 0.0001 1.1037 0.0340 0.1238 0.0038 1.00 753 22 763 5 1.3#5 83 566 162 0.29 8.74E−06 0.142 0.0798 0.0012 1.5553 0.0482 0.1414 0.0038 0.86 853 21 1191 31 28.4#6 21 104 78 0.74 3.12E−05 0.239 0.0786 0.0011 1.9876 0.0737 0.1835 0.0063 0.92 1086 34 1161 28 6.5#7 34 92 52 0.57 2.21E−05 0.198 0.1322 0.0018 5.9414 0.2243 0.3259 0.0115 0.93 1818 56 2128 24 14.5#8 292 764 298 0.39 4.39E−06 0.117 0.1234 0.0002 6.2161 0.2047 0.3653 0.0105 0.94 2007 49 2006 3 −0.1#9 29 229 72 0.31 1.74E−05 0.089 0.0658 0.0003 1.1328 0.0484 0.1249 0.0053 0.99 759 30 799 11 5.0#10 56 139 60 0.44 1.47E−05 0.110 0.1273 0.0009 6.7126 0.2754 0.3826 0.0154 0.98 2088 72 2060 13 −1.3#11 18 115 87 0.75 3.09E−05 0.265 0.0669 0.0004 1.2097 0.0333 0.1311 0.0035 0.98 794 20 835 12 4.9#12 20 149 2 0.01 3.40E−05 0.261 0.0678 0.0006 1.0954 0.0308 0.1171 0.0032 0.96 714 18 863 17 17.3#13 38 267 71 0.27 1.94E−05 0.098 0.0719 0.0007 1.3831 0.0179 0.1394 0.0011 0.63 842 6 984 21 14.5#14 27 220 167 0.76 3.00E−05 0.225 0.0677 0.0010 1.1012 0.0319 0.1180 0.0032 0.93 719 18 859 29 16.3#15 22 162 109 0.67 4.12E−05 0.203 0.1086 0.0016 1.7673 0.0339 0.1181 0.0015 0.65 719 8 1776 27 59.5#16 16 135 69 0.51 3.52E−05 0.112 0.0643 0.0010 1.0284 0.0266 0.1159 0.0024 0.80 707 14 752 33 6.0#17 64 181 59 0.32 1.40E−05 0.129 0.1202 0.0004 5.7776 0.2325 0.3487 0.0131 0.93 1928 62 1959 6 1.6#18 58 265 136 0.51 1.17E−05 0.160 0.0803 0.0006 2.1497 0.0673 0.1943 0.0059 0.97 1144 32 1203 16 4.9#19 13 99 65 0.66 5.95E−05 0.203 0.0647 0.0020 1.0637 0.0546 0.1193 0.0048 0.79 727 28 763 67 4.8#20 131 394 67 0.17 5.95E−06 0.087 0.1183 0.0003 5.0870 0.1057 0.3118 0.0064 0.99 1750 31 1931 5 9.4#21 43 349 100 0.29 1.51E−05 0.123 0.0718 0.0005 1.1083 0.0480 0.1120 0.0048 0.99 684 28 980 14 30.2#22 13 75 35 0.46 4.34E−05 0.201 0.0677 0.0005 1.3235 0.0516 0.1418 0.0054 0.98 855 30 860 17 0.6#23 14 90 39 0.43 3.41E−05 0.145 0.0710 0.0010 1.3802 0.0252 0.1411 0.0016 0.62 851 9 956 29 11.1#24 26 131 45 0.34 2.61E−05 0.342 0.1220 0.0010 2.5433 0.0257 0.1512 0.0009 0.62 908 5 1986 14 54.3

206S.P.N

evesetal./P

recambrian

Research

149(2006)

197–216

Table 1 (Continued )


206Pb/238U ±1σ 207Pb/206Pb ±1σ

#25 47 340 77 0.23 1.43E−05 0.139 0.0669 0.0012 1.1766 0.0228 0.1275 0.0009 0.35 774 5 835 38 7.4#26 27 187 69 0.37 2.23E−05 0.174 0.0780 0.0002 1.4617 0.0354 0.1359 0.0033 1.00 821 19 1147 4 28.4#27 28 201 203 1.01 2.70E−05 0.353 0.0617 0.0005 0.9321 0.0143 0.1095 0.0014 0.86 670 8 665 17 −3.3#28 22 149 42 0.28 2.39E−05 0.119 0.0659 0.0014 1.2907 0.0294 0.1420 0.0012 0.37 856 7 804 44 −6.5#29 21 122 72 0.59 3.85E−05 0.180 0.0734 0.0007 1.5632 0.0481 0.1545 0.0046 0.96 926 26 1025 19 9.6#30 91 725 171 0.24 7.39E−06 0.088 0.0703 0.0004 1.2421 0.0274 0.1282 0.0027 0.97 778 16 936 11 17.0#31 63 301 214 0.71 1.17E−05 0.238 0.0780 0.0005 2.0370 0.0388 0.1894 0.0034 0.94 1118 18 1147 13 2.5#32 87 442 333 0.75 9.36E−06 0.215 0.0787 0.0004 1.9194 0.0303 0.1768 0.0026 0.93 1049 14 1166 11 10.0#33 17 128 70 0.55 3.21E−05 0.178 0.0744 0.0016 1.2313 0.0417 0.1201 0.0031 0.77 731 18 1052 44 30.5#34 74 160 112 0.70 1.16E−05 0.203 0.1387 0.0006 7.5496 0.1135 0.3947 0.0057 0.96 2145 26 2211 7 3.0#35 36 240 110 0.46 1.56E−05 0.173 0.0741 0.0006 1.4389 0.0325 0.1408 0.0029 0.93 849 17 1045 17 18.8#36 44 312 112 0.36 1.90E−05 0.138 0.0682 0.0005 1.2866 0.0258 0.1369 0.0026 0.93 827 14 874 15 5.4#37 121 176 74 0.42 3.78E−06 0.127 0.2721 0.0020 20.9677 0.7087 0.5589 0.0184 0.98 2862 76 3318 11 13.7#38 44 333 156 0.47 1.79E−05 0.207 0.0685 0.0009 1.1344 0.0242 0.1202 0.0020 0.76 731 11 883 28 17.1

SCC12#1* 25 242 13 0.05 2.16E−05 – 0.0625 0.0008 0.8913 0.0227 0.1035 0.0023 0.87 635 13 690 26 7.9#2* 12 133 274 2.06 4.15E−05 – 0.0619 0.0006 0.8332 0.0305 0.0976 0.0034 0.96 600 20 671 22 10.5#3* 3 32 26 0.80 1.42E−04 – 0.0609 0.0018 0.8968 0.0314 0.1067 0.0020 0.55 654 12 637 62 −2.6#4* 4 42 60 1.44 1.35E−04 – 0.0601 0.0010 0.8720 0.0214 0.1053 0.0018 0.71 645 11 605 37 −6.6#5* 68 817 67 0.08 1.10E−05 – 0.0602 0.0004 0.8269 0.0673 0.0996 0.0081 1.00 612 47 611 15 −0.2#6* 20 218 307 1.41 1.77E−05 – 0.0604 0.0012 0.8145 0.0272 0.0978 0.0026 0.81 601 16 619 41 2.8#7 101 315 13 0.04 5.88E−06 – 0.1190 0.0008 5.3509 0.1082 0.3261 0.0062 0.94 1819 30 1942 12 6.3#8* 47 484 52 0.11 2.34E−05 – 0.0603 0.0006 0.8247 0.0275 0.0992 0.0031 0.95 610 18 613 23 0.5#9 57 185 18 0.10 1.22E−05 – 0.1225 0.0010 5.4307 0.0908 0.3214 0.0047 0.88 1797 23 1994 14 9.9#10 137 441 26 0.06 5.25E−06 – 0.1216 0.0010 5.3739 0.0755 0.3204 0.0037 0.81 1792 18 1980 15 9.5#11 125 360 28 0.08 5.56E−06 – 0.1229 0.0005 5.7922 0.2003 0.3418 0.0117 0.99 1895 56 1999 7 5.2#12 117 313 13 0.04 4.51E−06 – 0.1252 0.0011 6.4045 0.0931 0.3710 0.0044 0.81 2034 21 2032 15 −0.1#13* 6 59 20 0.34 1.07E−04 – 0.0607 0.0007 0.8585 0.0278 0.1026 0.0031 0.93 630 18 628 25 −0.3#14 119 355 12 0.03 6.08E−06 – 0.1237 0.0006 5.7574 0.0909 0.3376 0.0051 0.96 1875 24 2010 8 6.7

Errors are 1σ and refer to last digits. The right hand column is percentage discordance assuming recent lead losses. For each studied rock, analyses labelled * were included in the age calculation,whereas others were omitted.


Fig. 3. SEM images of selected dated zircon grains in orthogneiss samples showing position of the LA-ICP-MS spot and corresponding age (errosquoted at the 1σ level). (A, B) Sample SCC1A (mafic layer of banded orthogneiss). (A) Oscillatory-zoned zircon with rim overgrowth at the rightside. (B) Rounded grain with irregular zoning. (C, D) Sample SCC1B (felsic layer of banded orthogneiss). (C) Fragment of zircon grain containingl rowth ro SCC2 (g m that

emt

Stetswzl

toe

arge elliptical core with coarse oscillatory zoning surrounded by overgscillatory-zoned overgrowth at upper and right side. (E, F) Samplerain with oscillatory-zoned core. (F) Grain with broadly elliptical for

longated grains preserve subhedral shapes typical ofagmatic zircon, suggesting transport over short dis-

ances (Fig. 4B).Two zircon populations are observed in sample

CC12 (migmatitic paragneiss leucosome). One con-ains elongated (aspect ratio up to 4:1), subhedral touhedral zircon grains with faint oscillatory zoning andhin or absent overgrowth rims (Fig. 4C). The other con-ists of rounded (Fig. 4D) to slightly elongated grainsith overgrowths that may truncate internal oscillatory

oning. Inherited cores are present in some grains of theatter population.

Finally, the deformed granodiorite sample SCC5 fromhe Alcantil pluton contains a homogeneous populationf small (∼100 �m long), subhedral to anhedral, slightlylongated grains.

im with thin oscillatory zoning. (D). Euhedral zircon grain with thinlygranitic orthogneiss). (E) Fragment of large, homogeneous euhedralyielded the oldest age of all analyzed zircons in orthogneiss samples.

6. U–Pb zircon data

Table 1 shows the results of analytical data for thestudied samples. In the following, ages of zircons areexpressed in terms of either their 207Pb/206Pb ratios(grains older than 1 Ga) or their 206Pb/238U ratios (grainswith Neoproterozoic ages). Errors for single analysis andmean ages are quoted at the 2σ level.

6.1. Sample SCC1 (1A and 1B)

Analyses of zircons from sample SCC1A (mafic layer
of banded orthogneiss) fall into two age groups thatdefine two Pb loss trends in the concordia diagram(Fig. 5a). For each population, analyses showing dis-cordance smaller than 5% can be pooled together to

208 S.P. Neves et al. / Precambrian Research 149 (2006) 197–216

Fig. 4. (A, B) SEM images of selected zircon grains in sample SCC9 (pelitic gneiss). (A) Rounded zircon grain with overgrowth rims at upper leftzircon

wing pounded

and lower right sides truncating oscillatory-zoned core. (B) Elongatedgrains in sample SSC12 (leucosome from migmatitic paragneiss) shoat the 1σ level). (C) Subhedral grain with thin overgrowth rim. (D) Ro

define 207Pb/206Pb weighted means of 2125 ± 7 and2044 ± 5 Ma (Fig. 5b). The clear distinction of these twoage groups strongly suggests that they correspond to twodifferent events. The lack of inherited cores in most zir-con grains suggests that the group with the older agerepresents igneous crystallization of the protolith. Thisis consistent with well preserved oscillatory zoning in thegrains where ca. 2125 Ma ages were obtained (Fig. 3A).Truncation of oscillatory zoning, recrystallized zones orregions with fading oscillatory zoning observed in somegrains (Figs. 3A and B) are typical of magmatic zir-cons modified by high-grade metamorphism (e.g. Corfuet al., 2003). The youngest age of ca. 2044 Ma is thusinterpreted as representing the Transamazonian meta-morphic event. Because there is no discernable differ-ence in the Th/U ratios between zircons of the two agegroups (Table 1), local redistribution by recrystalliza-tion processes without new metamorphic growth is themost likely explanation for the igneous-like high Th/U(>0.1; Williams and Claesson, 1987) ratio of the zir-con domains with ca. 2044 Ma ages. Overgrowth rimsthat clearly represent new zircon growth revealed tobe too thin to be accurately dated. Analyses showing
high discordance indicate Pb losses that could be relatedeither to a young (e.g. Brasiliano) event or to recent,zero age, disturbances, or even a combination of both(Fig. 5a).
grain with no apparent zoning. (C, D) SEM images of selected zirconsition of the LA-ICP-MS spot and corresponding age (errors quoted

grain with thin overgrowth rims at the left and right sides.

Analyses of zircons from the leucocratic band SCC1Bdisplay a very different distribution when compared withsample SCC1A. Most grains plot close to Concordia(see Fig. 6a) at about 1.98 Ga, and, together with anal-ysis #5 (Table 1), define a discordia line with upperand lower intercepts of 1985 ± 12 and 578 ± 37 Ma(MSWD = 1.2). The upper intercept is well constrainedby concordant analyses and ten highly concordant grainsgive a 207Pb/206Pb weighted mean of 1972 ± 8 Ma(Fig. 6b), in agreement with the upper intercept age.The Th/U ratio of these grains (ranging from 0.2 to 0.7;Table 1) is typical of magmatic zircons (Williams andClaesson, 1987), which suggests that the 1972 Ma agecorresponds to crystallization of the zircons. Since theseanalyses were obtained from large rounded cores sur-rounded by a thin oscillatory zoned rim (see Fig. 3C), itis concluded that the age of 1972 Ma corresponds to thatof the source rocks that underwent anatexis to producethe leucocratic band. It is probably noteworthy that thisage is similar to the U–Pb age of 1974 Ma obtained by Saet al. (2002) from an orthogneiss some kilometers to thesoutheast (Fig. 2), suggesting that the orthogneiss wasthe main source component for the melt. One grain is
concordant at 2096 ± 14 Ma, indicating the source alsoincluded a ca. 2.1 Ga old component. One euhedral zir-con grain (see Fig. 3D) yielded a 206Pb/238U apparent ageof 625 ± 24 Ma (Fig. 6a). The high Th/U ratio (0.67) of


F(w

toptttfm

6

fc1eTa

ig. 5. (a) U–Pb concordia diagram for zircons from sample SCC1Amafic layer of banded orthogneiss). (b) Zoom showing the twoeighted mean ages of Paeloproterozoic zircons.

his grain (Table 1), its euhedral shape and the magmaticscillatory zoning of overgrowths (Fig. 3D) are inter-reted as indicating growth from a magma. Therefore,his age most likely corresponds to the crystallization ofhe leucocratic band, implying that the mesoscopic struc-ure of the banded orthogneiss is a late Neoproterozoiceature, resulting from intrusion of syntectonic graniticelts in a preexisting protolith.

.2. Sample SCC2

Sixteen near concordant analyses of zircon grainsrom the orthogneiss sample SCC2 yielded a well-onstrained 207Pb/206Pb weighted mean age of
991 ± 5 Ma (Fig. 7). Some of these grains still preserveuhedral shapes (Fig. 3E), which together with highh/U ratios (see Table 1) indicates crystallization frommagma. The 1991 ± 5 Ma age is thus interpreted as
Fig. 6. (a) Concordia diagram showing discordia line for zircons fromsample SCC1B (felsic layer of banded orthogneiss). (b) Zoom showingthe 206Pb/207Pb weighted mean age of concordant Paleoproterozoiczircons.

corresponding to crystallization of the granitic pro-tolith. Three other grains yielded older ages indicatinginherited source components of 2196 ± 14 (Fig. 3F),2123 ± 24 and 2074 ± 20 Ma. The two latter roughlycorrespond to the two mean ages obtained in sampleSCC1A. These results are interpreted as indicatingthat the granitic orthogneiss is a late-Transamazonianintrusion containing a small proportion of inheritedzircon grains.

6.3. Sample SCC9

U–Pb data for detrital zircons from paragneiss sam-ple SCC9 exhibit ages ranging from more than 3320 toca. 665 Ma (Table 1). Data is reported in the concor-dia diagram (Fig. 8a) and in a cumulative probability

210 S.P. Neves et al. / Precambrian Research 149 (2006) 197–216

Fig. 8. (a) U–Pb concordia diagram for zircons from sample SCC9(pelitic gneiss). Inset: zoom at the Neoproterzoic showing the U–Pbage of the youngest grain in the zircon population. Green, concor-dant grains; red, discordant grains. (b) Histogram plot for 206Pb/207Pb

Fig. 7. U–Pb concordia diagram for zircons from sample SCC2(granitic orthogneiss).

plot (Fig. 8b). Most analysis fall on or near the con-cordia curve and those with less than 5% discordanceshow age peaks at ca. 2220, 2060–1940, 1200–1150,860–760 and 665 ± 34 Ma. Several discordant grainshave ages between 1100 and 900 Ma and a small peakis observed around 1690 Ma. Grains from all age groupshave high Th/U ratios. Together with the oscillatory zon-ing observed in most grains, this indicates provenance ofgrains from igneous protoliths (Williams and Claesson,1987), which constrain the deposition of the supracrustalsequence to be younger than the youngest grain (ca.665 Ma) in the zircon population.

6.4. Sample SCC12

On a concordia plot (Fig. 9A), analyses of zirconsfrom the leucosome of a paragneiss, except for one (#7;Table 1) define a discordia line (MSWD = 1.1) with upperand lower intercepts at 2041 ± 15 and 626 ± 15 Ma,respectively. Paleoproterozoic ages were obtained fromrounded zircons grains (Fig. 4D) that have low Th/Uratios (0.04–0.1; Table 5), typical of metamorphic zir-cons. These grains are interpreted as inherited froma protolith metamorphosed at ca. 2040 Ma. This is inagreement with analysis #12 (Table 1), which is concor-dant at 2032 ± 30 Ma and reinforces the interpretation ofthe data for sample SCC1A that the peak of Transamazo-nian metamorphism occurred around this time. Zirconswith Neoproterozoic ages plot near the concordia andhave a 206Pb/238U weighted mean age of 632 ± 17 Ma
(Fig. 9b) overlapping the lower intercept of the discordialine. These grains yield both high and low Th/U ratios(Table 1) typical of magmatic and metamorphic zircons,respectively. The high Th/U ratios of some grains (up
ages of the analyzed zircons. Green, concordant grains; red, discor-dant grains. (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of the article.)

to 2.06) suggest that the laser beam struck a Th-richinclusion, whereas the euhedral shape (Fig. 4C) and lowTh/U ratio of other grains is typical of zircons grownunder high grade conditions. The most precise lowerintercept age of 626 ± 15 Ma is therefore interpreted asdating crystallization of the leucosome, and is thus takenas our best estimate for the high-grade metamorphism ofthe supracrustal sequence during the Brasiliano orogeny.

6.5. Sample SCC5

Analyses of zircon from the Alcantil pluton (SCC5;Table 1) define a discordia line (Fig. 10a) with upperand lower intercepts of 2103 ± 11 and 619 ± 36 Ma,


Fig. 9. (a) Concordia diagram showing discordia line for zircons fromsiz

ry6gophemTnuT

Foa

ample SCC12 (leucosome of migmatitic paragneiss). (b) Zoom show-ng the 206Pb/238U weighted mean age of concordant Neoproterozoicircons.

espectively. The lower intercept is constrained by anal-sis #4 (Table 1), which yielded a 206Pb/238U age of12 ± 54 Ma and a low Th/U ratio of 0.04, typical ofrowth in the solid state. This indicates that the gran-diorite was metamorphosed at 619 ± 36 Ma, the morerecise lower intercept of the discordia line. Most grainsave older, mainly Paleoproterozoic ages, and a batch ofight concordant analyses yields a 207Pb/206Pb weightedean age of 2097 ± 5 Ma (Fig. 10b). One grain (#17;able 1) has a low discordance degree, but yields a sig-ificantly younger age (2068 ± 8 Ma) suggesting it hasndergone disturbances, possibly during the ca. 2044 Maransamazonian event.

The above results could be interpreted in two ways.irst, that intrusion occurred during the Brasilianorogeny and that temperature remained high enoughfter emplacement to allow growth of metamorphic zir-

Fig. 10. (a) Concordia diagram showing discordia line for zircons fromsample SCC5 (Alcantil pluton). (b) Zoom showing the 206Pb/207Pbweighted mean age of concordant Paleoproterozoic zircons.

con. In this hypothesis, the zircon population would con-sist almost entirely of xenocrystic grains inherited from ahomogeneous Paleoproterozoic source. Because this is arather unusual situation for granitic magmas, the secondpossibility, that emplacement took place at 2097 ± 5 Maduring the Transamazonian orogeny, is considered morelikely. The emplacement age of ca. 2100 Ma is youngerbut comparable to that of the older age found in theorthogneiss sample SCC1A (ca. 2125 Ma), suggestingthat the Alcantil pluton could represent less strained por-tions of basement orthogneisses in the region.

7. Discussion

7.1. Tectonothermal evolution of the study area

This work clearly reveals that two main tectonother-mal events affected the study area, one in the Pale-

ian Res
oproterozoic (Transamazonian orogeny) and the otherat the end of the Neoproterozoic (Brasiliano orogeny).The age pattern of sample SCC1A (mafic layer ofbanded orthogneiss) allows placing tight constraints onthe events associated with the Transamazonian orogeny.The lack of inherited cores, as revealed by SEMimages, suggests that the age cluster of 2125 ± 7 Macorresponds to the crystallization age of the bandedorthogneiss protolith. Six whole-rock samples of bandedorthogneiss display geochemical characteristics simi-lar to calc-alkaline magmas, suggesting generation ina volcanic arc setting (Sa et al., 2002). Consideringthis, the age reported here could correspond to juve-nile crustal accretion. The younger age (2044 ± 5 Ma)found in sample SCC1A is associated with metamor-phic features observed in the analyzed zircon grainsand is interpreted as dating the peak of Transamazo-nian metamorphism, possibly marking a major colli-sional event. This is corroborated by the occurrenceof metamorphic zircons with this age in the paragneissleucosome sample SCC12. The age of 1992 ± 7 Ma ofsample SCC2 (granitic orthogneiss), and the mean ageof 1972 ± 8 Ma for xenocrystic zircons from sampleSCC1B (felsic layer of banded orthogneiss) are inter-preted as reflecting a stage of late to post-orogenicmagmatism.

The age pattern of the paragneiss sample SCC9reveals provenance of its protolith mainly from Paleo-proterozoic and mid-Neoproterozoic sources, and con-strains the deposition of the supracrustal sequence tobe younger than 665 Ma (Fig. 8a and b). The Paleo-proterozoic ages correspond closely to the Transama-zonian event and may represent derivation of detritalgrains from nearby orthogneisses, although more dis-tal sources cannot be excluded. Proximal sources withArchean ages that could provide the oldest analyzedzircon grain (>3320 Ma) have not yet been directlydated in the central domain, but their existence issuggested by Sm–Nd model ages of Paleoproterozoicorthogneisses (Van Schmus et al., 1995; Brito Neveset al., 2001b). However, even the oldest Sm–Nd agesare generally younger than 3300 Ma, which favors amore distal source. This source may be located eitherwithin an Archean nucleus identified in the northeast-ernmost part of the Borborema Province (Dantas etal., 1998, 2004), ∼250 km to the north of the studyarea, or within the Sao Francisco craton. Grains withlate Paleoproterozoic ages of ca. 1690 Ma may have
their source in augen gneisses/meta-anorthositic com-plexes (Accioly et al., 2000), which occur to the eastof the study area (Fig. 2A). The abundance of zir-con grains with ages in the interval 1200–1150 Ma is
earch 149 (2006) 197–216

intriguing, as rocks with these ages have not yet beenidentified anywhere in the Borborema Province. It istentatively attributed to late Mesoproterozoic extensionand intraplate magmatism preceding the more exten-sive Cariris Velhos rifting event. Felsic volcanic rocksand granites related to the Cariris Velhos event (nowmetavolcanics and orthogneisses) in the Alto Pajeu beltconstitute the most likely source for zircons with ca.950–1050 Ma ages. A source for the abundant zircongrains with mid-Neoproterozoic ages might be relatedto magmatic episodes preceding and coeval with basinformation.

The Neoproterozoic age of one magmatic zircon inthe felsic layer of banded orthogneiss (625 ± 24 Ma),the maximum deposition age of the Surubim sequence(665 Ma), the crystallization age of the leucosome from amigmatitic paragneiss (626 ± 15 Ma), and the metamor-phic age of the Alcantil pluton (619 ± 36 Ma) show thathigh-temperature metamorphism was coeval with forma-tion of a flat-lying foliation in basement and supracrustalrocks. This metamorphism is clearly separated fromtranscurrent shear zone development because the oldestplutons deformed in the magmatic stage by strike-slipshearing are younger than 592 Ma (Guimaraes and DaSilva Filho, 1998; Neves et al., 2004). Although theimportance of the Transamazonian event in the studyarea is obvious, fieldwork (Neves et al., 2000, 2005) andthe geochronological results from this study indicate thatthe dominant mesoscopic ductile fabric in Paleoprotero-zoic orthogneisses was produced during the Brasilianoorogeny.

7.2. Regional correlations

7.2.1. Basement gneissesThe two age groups in sample SCC1A are similar

to those found in samples from the eastern portion ofthe Sao Francisco craton, where recent SHRIMP U–Pbdata indicate magmatic crystallization at 2.2–2.1 Ga andhigh-grade metamorphism at 2.08–2.05 Ga (Silva et al.,2002). In the Borborema Province, most zircon grainsthat yielded Paleoproterozoic U–Pb ages were analyzedby conventional methods (see Brito Neves et al., 2000,and Neves, 2003, for a review of available data). Thespread of ages, mainly from 2.25 to 2.0 Ga, may in partreflect mixed ages resulting from a combination of inher-ited zircon cores, primary igneous zircon crystalliza-tion, and metamorphic recrystallization. Nevertheless,
the existing data point out to an important period of crustgeneration at 2.2–2.1 Ga, followed by deformation andmetamorphism, and then by intrusion of late- to post-tectonic plutons.

ian Res

7

pCi(SpcamabfUi2s

cCsisttb(a

7

pce2dVbztbMtsPpp(bii

S.P. Neves et al. / Precambr

.2.2. Supracrustal sequencesThe maximum deposition age of the Surubim com-

lex is similar to that of the Cachoeirinha Group in theachoeirinha belt (Kozuch, 2003; Medeiros, 2004), and

ts zircon age pattern is remarkably similar to that foundVan Schmus et al., 2003) in the Serido belt (Fig. 1B).everal observations also suggest that the Surubim com-lex and the Sertania complex in the Alto Moxoto belt areorrelated. Both complexes consist of the same rock typessociation, have similar metamorphic grade (althoughigmatization is more frequent in the Sertania complex),

nd display comparable carbon isotope signature in mar-les (Santos et al., 2002). Although eight zircon grainsrom two samples of the Sertania complex had yielded–Pb SHRIMP ages around 2.0 Ga and interpreted as

ndicating Paleoproterozoic sedimentation (Santos et al.,004a), this only represents the maximum age of depo-ition.

The probable connection between supracrustal suc-essions in the East Pernambuco, Alto Moxoto,achoeirinha and Serido belts are consistent with depo-

ition in a regionally extensive basin formed dur-ng broad-scale lithospheric extension. The small timepan between deposition and deformation can explainhe overall high-temperature metamorphism, as highhermal gradients resulting from crustal thinning cane maintained in the subsequent contractional phaseThompson, 1989; De Yoreo et al., 1991; Thompson etl., 2001).

.2.3. Tectonothermal eventsEvidence for a metamorphic event in the early Neo-

roterozoic was not found in this study and in all studiesonducted so far in the central domain (Van Schmust al., 1995; Leite et al., 2000b; Brito Neves et al.,001a,b; Kozuch, 2003; Medeiros, 2004). Contractionaleformation of this age during the proposed Caririselhos orogeny (Brito Neves et al., 1995) has beenased on the interpretation that the early Neoprotero-oic metaigneous and metasedimentary succession ofhe Alto Pajeu belt represents a subduction arc assem-lage intruded by syncollisional granites (Santos andedeiros, 1999; Kozuch, 2003). However, the same

op-to-the-WNW/NW tectonic transport is found in theupracrustal succession and augen gneisses of the Altoajeu belt (Medeiros, 2004), and in the Surubim com-lex (Neves et al., 2005; this study), the Sertania com-lex (Santos et al., 2004a), and the Cachoeirinha Group
Medeiros, 2004). Identical kinematics in these fourelts strongly indicates deformation during the Brasil-ano orogeny. Furthermore, the geochemical character-stics of the metavolcanic and metaplutonic rocks of the
earch 149 (2006) 197–216 213

Alto Pajeu belt are typical of intraplate magmas, not ofsubduction-related ones (Bittar and Campos Neto, 2000;Bittar et al., 2001; Neves, 2003; Guimaraes and BritoNeves, 2004). These observations seriously cast in doubtthe existence of the Cariris Velhos event as an importantorogeny.

The Neoproterozoic age of deposition of supracrustalsequences and a common flat-lying foliation in basementgneiss and metasedimentary belts is observed throughoutthe Borborema Province (Caby and Arthaud, 1986; Cabyet al., 1995; Neves et al., 2000, 2005). It is no longerpossible to claim that the Brasiliano orogeny was onlyresponsible for granite intrusion and strike-slip shearing,as still advocated in several recent studies (Jardim de Saet al., 1995; Sa et al., 2002; Araujo et al., 2003; Santos etal., 2004b). The present architecture of the BorboremaProvince is a product of the Brasiliano orogeny, althoughit is clear the importance of the Transamazonian orogenyas a crust-forming event.

7.3. Implications for western Gondwana

The results of this study and the recent synthesisby Ferre et al. (2002) and Toteu et al. (2004) on thegeodynamic evolution of Nigeria and Cameroon, respec-tively, strengthen the earlier suggestion (Neves, 2003;Neves et al., 2004) that these belts shared a commonevolution throughout most of the Proterozoic. Commonfeatures include (1) extensive (ca. 2.1 Ga) Paleoprotero-zoic crust, (2) dominance of metasedimentary sequenceswith Neoproterozoic deposition ages, (3) ubiquitouspresence of flat-lying fabrics of late Neoproterozoicage (∼640–600 Ma), and (4) dominance of transcur-rent/transpressional deformation after 600 Ma. The lackof evidence for closure of large oceanic domains inall these regions does not support the interpretation ofthe Borborema Province as a series of amalgamatedterranes (e.g. Santos and Medeiros, 1999; Santos etal., 2004a,b). Destabilization of a preexisting conti-nent formed at the end of the Transamazonian/Eburneanorogeny (the Atlantica supercontinent of Rogers, 1996)provides the simplest explanation to the above find-ings. Several attempts to fragment this supercontinentare recorded by late Paleoproterozoic to Neoprotero-zoic intraplate extensional and magmatic events repre-sented by failed rifts and A-type granites and relatedrocks. A final period of plate-wide extension occurredin the mid/late Neoproterozoic. This was immediately
followed by convergence and contractional deformationmarking the beginning of the Brasiliano/Pan-Africanorogeny, which essentially occurred in an intracontinen-tal setting.

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7.4. Summary and conclusions

The main conclusions of this study concerning thePrecambrian tectonic and geochronological evolution ofthe study area in the East Pernambuco belt can be sum-marized as follows: (1) 2.15–2.10 Ga: generation of juve-nile crust, (2) 2.05–2.03 Ga: peak Transamazonian meta-morphism, (3) 1.99–1.97 Ga: intrusion of late orogenicmagmas, (4) after 665 Ma: deposition of supracrustalsequences and (5) 630–610 Ma: development of flat-lying fabrics and Brasiliano high-grade metamorphism.Available data from the literature, in addition, support theintrusion of anorogenic plutons at 1.7–1.5 Ga (Acciolyet al., 2000; Sa et al., 2002), and the development oftranscurrent shear zones and abundant magmatism at590–580 Ma (Neves et al., 2000, 2004). Most of thesefeatures are found in other sectors of the BorboremaProvince (Neves, 2003) and in the Nigeria and Cameroonprovinces (Ferre et al., 2002; Toteu et al., 2004; Njiosseuet al., 2005), suggesting a shared evolution during mostof the Proterorozoic.

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 field-work funded by the Fundacao de Amparo a Cienciae Tecnologia do Estado de Pernambuco (FACEPE).The comments from two anonymous reviewers helpedimproving the manuscript.

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