Cap XII

Resumo:

O magmatismo granítico no domínio da Zona

Transversal da Província Borborema, NE do Brasil,ocorreu em três intervalos de tempo principais: 650-

620 Ma, 590-570 Ma e 545-520 Ma. O intervalo mais

antigo é caracterizado por intrusões de granitóides sin-cinemáticos cálcio-alcalinos de alto K com epidoto

magmático, cálcio-alcalinos e shoshoníticos. O segun -

do intervalo de tempo é marcado por intrusões abun -dantes de magmas cálcio-alcalinos de alto K sem epi -

doto magmático, além de magmas sieníticos peral -

calinos, metaluminosos de alto K, ultrapotássicos eraros shoshoníticos. Magmas peralcalinos e do tipo A

marcam o final do ciclo Brasiliano na região. Os gra -

nitóides mais antigos apresentam valores de TDM maisjovens (< 2.0 Ga) e valores menos negativos de εNd(cerca de -2 a -14) comparados com aqueles para os

granitóides de 590-570 Ma, para os quais os valores deTDM variam de cerca de ca 1,5 a 2,5 Ga, e os de εNdde cerca de -8 a -20. Os valores mais altos e variáveis

das razões iniciais 87Sr/86Sr são observados nos grani -tóides de 650-620 Ma. Esses dados indicam uma

mudança importante da fonte do magma com o tempo

geológico. Os granitóides mais antigos parecem repre -sentar uma mistura de magma derivado do manto juve-

nil, neoproterozóico, com magma derivado de fusão de

crosta continental paleoproterozóica, o que produziriaidades modelo Nd intermediárias, de cerca de 1,2 a 1,4

Ga. Isto é compatível com a mistura de magmas deriva -

dos do manto e crosta, como indicado por relações decampo que indicam um forte relacionamento entre mag -

mas granitíticos e dioríticos. Os plútons de 590-570 Ma

apresentam valores isotópicos de Sr e Nd compatíveiscom magmas formados por refusão de crosta continen -

tal inferior paleoproterozóica, o único reservatório

geoquímico com aquelas características. A únicaexceção entre as rochas dessa idade são os sienitos

peralcalinos ultrapotássicos, que apresentam razões

iniciais de Sr alta e valores muito negativos de εNd“values”, interpretados como derivados de uma fonte

no manto enriquecida em elementos incompatíveis. O

grupo mais antigo de rochas apresenta assinaturas geo -químicas típicas de granitos sin-tectônicos, enquanto

que o grupo de 590-570 Ma mostra assinaturas típicas

de magmas tardi-a pós-tectônicos.

Palavras-chave: Granitos, Granitos Cálcio-Alcalinos,

Sienitos Peralcalinos, Granitos Shoshoníticos, Epidoto

INTERMEDIATE TO ACIDIC MAGMATISM AND CRUSTAL EVOLUTION IN THE TRANSVERSAL

ZONE, NORTHEASTERN BRAZIL

Valderez P. FerreiraNEG-LABISE, Departamento de Geologia, UFPE, Recife, PE

valderez@ufpe.br

Alcides N. SialNEG-LABISE, Departamento de Geologia, UFPE, Recife, PE

ans@ufpe.br

Márcio M. Pimentel

Instituto de Geociências, UnB, Brasília, DF

marcio@unb.br

Cândido A.V. MouraCentro de Geociênciss, UFPA, Campus do Guamá, Belém, PA

c_moura@ufpa.br

Magmático, Evolução Crustal, Zona Transversal,

Província Borborema.

Abstract:

Granitic magmatism in the Transversal Zone domain of

the Borborema province, NE Brazil, occurred in three maintime intervals: 650-620 Ma, 590-570 Ma and 545-520 Ma.

The oldest is characterized by intrusions of syn-kinematic

magmatic-epidote bearing high-K calc-alkalic, calc-alkalicand shoshonitic granitoids. The second time interval is

marked by abundant intrusions of magmatic epidote-free

high-K calc-alkalic magmas, as well as peralkalic, metalumi-nous high-K syenitic, unique ultrapotassic, and rare

shoshonitic magmas. Peralkalic and rare A-type magmas

mark the end of the Brasiliano cycle in the region. The oldestgranitoids present younger TDM (< 2.0 Ga) and less negative

εNd (ca. -2 to -14) compared with the 590-570 Ma granitoids,

for which TDM varies from ca 1.5 to 2.5 Ga, and εNd fromca. -8 to -20. The highest and more variable initial 87Sr/86Sr

values are observed in the 650-620 Ma granitoids. These data

indicate an important change in the magma source with time.The oldest granitoids seem to represent a mixture of

Neoproterozoic, juvenile, mantle-derived material with

magma derived from the melting of Paleoproterozoic conti-nental crust, which yielded intermediate Nd model ages, of

ca. 1.2-1.4 Ga. This is compatible with the mixture of mantle-

derived and crustal magmas, as indicated by field relation-ships that show close relationships between host granitoid

and K-dioritic magmas. The 590-570 Ma plutons have Sr and

Nd isotopic values compatible with magmas formed byremelting of Paleoproterozoic lower continental crust, the

only geochemical reservoir with these characteristics. The

only exception among these rocks are the ultrapotassic peral-kalic syenitoids, which present high initial Sr ratios and very

negative εNd values, interpreted as derived from an incom-

patible element enriched mantle source. The oldest group ofrocks has signatures typical of syn-tectonic granites, while

the 590-570 Ma group has signatures typical of late- to post-

tectonic magmas.

Keywords: Granites, Calc-Alkalic Granites, Peralkalic

Syenites, Shoshonitic Granites, Transversal Zone, MagmaticEpidote, Crustal Evolution, Borborema Province.

Resumen:Magmatismo granítico en la Zona Transversa de la

Província estructural de Borborema, en el nordeste de Brasil,

se produjo en tres intervalos de tiempo: 650-620 Ma, 590-570Ma y 545-520 Ma. El grupo más viejo está caracterizado por

intrusiones de rocas graníticas calco-alcalinas con alto pota-

sio, calco-alcalinas y shoshoníticas, sin a tardi-cinemáticas,con epidota magmática. El segundo intervalo de tiempo de

intrusiones está marcado por abundantes magmas calco-

alcalinos de alto potasio sin epidota magmática, sienitas per-alcalinas o metaluminosas de alto potasio, magmas ultra-

potásicos y, raramente, shoshoníticos. Magmas peralcalinos

y escasos magmas del tipo-A marcan el final del cicloBrasiliano en esta región. Los granitos más viejos presentan

TDM más joven (< 2.0 Ga) y valores menos negativo εNd(desde -2 hasta -14) comparados con los granitos con 590-570 Ma para los cuales TDM varía desde 1.5 hasta 2.5 Ga, y

εNd desde ca. -8 hasta -20. Valores más altos y más variables

de razones iniciales 87Sr/86Sr son observados en el grupo degranitoides con 650-620 Ma. Estos datos indican un impor-

tante cambio de fuente de magma con el tiempo. Los grani-

toides más viejos parecen representar una mezcla de materialjoven derivado del manto, en el Neoproterozoico, con magma

derivado de la fusión de la corteza continental Paleoproterozoica

que ha generado edades modelos intermediarias desde 1.2

hasta 1.4 Ga. Esto es compatible con un proceso de mezcla de

magmas derivados de la corteza, como lo indican las rela-ciones de campo que muestran íntima relación entre magmas

graníticos y magmas dioríticos potásicos. Los plutones con

590-570 Ma tienen valores isotópicos de Sr y Nd compatiblescon magmas formados por refusión de la corteza continental

Paleoproterozoica inferior, el único reservatorio con estas

características. La excepción entre estas rocas correspondena las sienitas peralcalinas ultrapotásicas que presentan alta

razón isotópica inicial de Sr y valores de εNd muy negativos,

interpretados como derivados de una fuente en el manto muyrica en elementos incompatibles. El grupo de rocas graníti-

cas más viejas posee signaturas geoquímicas típicas de gra-

nitos sintectónicos, mientras los granitos más jóvenes pre-sentan signaturas típicas de magmas tardías pos-tectónicos.

Palabras llave: Granitos, Granitos Calco-Alcalinos,Sienitas Peralcalinas, Granitos Shoshoníticos, Epidota

Magmática, Magmas Ultrapotásicos, Zona Transversa,

Evolución Cortical, Província Borborema.

Introduction

The Borborema structural province, northeastern

Brazil, is a mosaic of metasedimentary fold belts and massifs

separated by a complex system of continental-scale strike-slipshear zones (Almeida et al., 1981), which together with the

voluminous granitic magmatism, are the most outstanding

features of this province (Caby et al., 1991). The tectonic evolution of the province has been

explained by models involving the accretion of tectonostrati-

graphic terranes as the major mechanism of crustal growth(eg. Brito Neves et al., 1995; Santos, 1996; Santos et al.,

1997, Santos & Medeiros, 1999; Brito Neves et al., 2000).

Mafic to ultramafic complexes, some of them interpreted asoceanic crust remnants (Beurlen et al., 1992), occur nearby

suspect terrane boundaries, and were used by Santos et al.

(1997) as argument to reinforce the hypothesis of collision ofcontinental blocks. Juxtaposition of blocks during the

Brasiliano cycle has been invoked by many authors, on the

basis of structural geology (eg. Bittar & Campos Neto, 2000),U-Pb zircon ages and Sm-Nd isotopic data from orthogneisses

(e.g. Fetter et al., 2000), as well as from undeformed granitic

rocks (eg. Sampaio et al., 2000; Silva Filho et al., 2000).This process of terrane collage took place during

assembly of the western Gondwana (Santos & Brito Neves,

1993; Brito Neves et al., 2000). Some authors, however, pres-ent alternative hypothesis to the generally accepted model of

terrane accretion, based on geochemical signatures of high-K

calc-alkalic and associated dioritic rocks (e.g. Mariano et al.,2000; Neves et al., 2000), as well as on the lack of some

parameters indicative of continental margin, such as ophio-

lites (Neves, et al., 2000; who proposed an intracontinentalorogen for the whole province).

In the present study, the geochemical and isotopic char-

acteristics of the intermediate to acidic magmatism intrusiveduring the Brasiliano orogeny in the Transversal zone domain

of the Borborema Province, will be reviewed and discussed,

aiming to understand their meaning in the scenario of crustalevolution of the region.

Geological setting

The Borborema province is characterized by a gently-

dipping regional foliation observed in both supracrustal andbasement rocks (Caby et al., 1995), and by a network of con-

tinental scale transcurrent ductile shear zones (Vauchez et al.,

190

alkalic, and shoshonitic granitoids at 650-620 Ma. (2) a late to post-collisional period (590-570 Ma),

marked by relative movements of terranes partially amalga-

mated, and migration of terranes along E-W Pernambuco andPatos mega shear zones, as well as along the narrower NE-

trending shear zones connecting these major shear zones, as

indicated by the synkinematic crystallization of several plu-tons emplaced along these shear zones. This period is charac-

terized by intrusions of voluminous magmatic epidote-free

high-K calc-alkalic magmas, peralkalic, metaluminous high-K syenitic, and rare shoshonitic magmas, as well as unique

ultrapotassic magmas, until most movements along shear

zones stopped. Peralkalic and rare A-type magmas mark the end of the

Brasiliano cycle in the region.

The Transversal Zone domain

The Transversal Zone domain of the Borboremaprovince has been interpreted as a superterrane (Santos, 1996;

Santos et al., 1997) assembled after a collage of several ter-

ranes and belts, which are from east to west: Granjeiro,Cachoeirinha (Brasiliano age), and the pre-Brasiliano ter-

ranes Riacho Gravatá, Alto Pajeú, Alto Moxotó and Rio

Capibaribe (Fig. 1). The consolidation of the pre-Brasilianoterranes is related to the Transamazonian and Cariris Velhos

cycles, but they have been reworked during the Brasiliano

cycle (Santos et al., 2003). A complete picture of the tectonic setting and crustal

evolution of the Transversal Zone is still far from being solved

and consensual, but geochronological data, including Rb-Sr,zircon TIMS and SHRIMP U-Pb on a significantly large num-

ber of granitic plutons, led Brito Neves et al. (2003) to propose

three main stages of granitic magmatism in the province: 650-625 Ma, 580-570 Ma e 545-520 Ma.

Almeida et al. (1967) were pioneers in the study of gran-

ite types in this part of the Borborema province. They describedin the Granjeiro and Cachoeirinha terranes, on the basis of pet-

rography, the granitoids of the so-called Itaporanga and

Conceição types, terminology that is still used in the region.Eight petrogenetic suites were described in the

Transversal Zone by Sial (1987) and Ferreira et al. (1998),

including the two types recognized by Almeida et al (op cit.),on the basis of petrography and mineralogy, chemistry, and

1995). These Neoproterozoic shear zones are believed to havedeveloped within a continental plate to accommodate the

deformation imposed by oblique collision active at the mar-

gin (Vauchez et al., op cit.). The structural characteristics and rock types of the

Borborema province were developed mainly during the late

Mesoproterozoic to early Neoproterozoic (Cariris Velhosevent) and late Neoproterozoic-Cambrian (Brasiliano/Pan

African orogeny) (Brito Neves et al., 2000; 2003). The

Brasiliano cycle (670-570 Ma) promoted reworking of thecrust formed during the earlier Cariris Velhos event and was

the major tectonothermal event in the Borborema province.

This is attested by the structures and by a large volume ofgranitic magmatism (~30% of the exposed rocks) that was

added to the crust during this event. The Cariris Velhos-age

rocks have been observed only in the Transversal Zonedomain of the Borborema province (Brito Neves et al., 2000).

Two of the shear zones in the province, the E-W-trend-

ing dextral Pernambuco and Patos shear zones, stand out fortheir large dimensions, which reach over 500 km and 2 km in

width, linked with narrower (typically 1 km) N- NE-trending

shear zones (Neves, 1996). They subdivide the province intothree major domains (Fig. 1): (a) setentrional domain, north

of the Patos shear zone, (b) Transversal zone domain,

between the two shear zones and (c) the meridional domain,south of the Pernambuco shear zone. These domains are inter-

preted as representing a collage of smaller lithotectonic

domains (Brito Neves et al., 2000). Spatial association ofgranitic plutons and shear zones, as well as peralkalic syenitic

dike sets parallel to or slightly oblique to the shear zone, has

led many authors to believe that shear zones have controlledthe magma ascent and emplacement (eg. Ferreira & Sial,

1986; Neves, 1991; Jardim de Sá, 1993; Archanjo et al., 1994;

Neves & Vauchez, 1995; Araújo et al., 1995; Hollanda et al.,1998). However, regional deformation, magma emplacement

and shear zone development are interpreted as successive

events in the Transversal Zone (Neves & Vauchez, 1995).

Integration of geochronological, geochemical and field

data, on both granitic and regional metamorphic rocks, sug-gest two major episodes in the Brasiliano cycle:

(1) collisional period (670-620 Ma), characterized by

low-angle foliation, and by intrusion of abundant syn-kine-matic magmatic-epidote bearing high-K calc-alkalic, calc-

191Cap XII

Fig. 1. Transversal Zone of the Borborema structural province, northeastern Brazil, emphasizing Neoproterozoic granitic andsyenitic plutons. Terranes are named after Santos et al.(1997)

- Zona Transversal da província estrutural da Borborema, Nordeste do Brasil, enfatizando os plútons neoproterozóicos graníticose sieníticos. Os terrenos são nomeados de acordo com Santos et al.(1997)

isotopic characteristics, four of which are magmatic epidote-

bearing (mEp). These are: mEp metaluminous high-K calc

alkalic, metaluminous high-K calc alkalic epidote-free, mEptrondhjemitic, mEp metaluminous calc-alkalic, mEp

shoshonitic, peralkalic, peralkalic ultrapotassic, and metalu-

minous high-K syenitoids. Further work focussing the AltoPajeú terrane, confirmed this grouping (eg. Guimarães et al.,

1998). One A-type calc-alkalic anorogenic complex is

described in the Alto Moxotó terrane (Melo et al., 1996).Large areas of the Granjeiro terrane are covered by

Mesozoic sediments of the Araripe Basin and are not well

known. Only a few plutons are described in this terrane.Among them are the 580 Ma magmatic epidote-free high-K

calc-alkalic granitoids (Itaporanga, Bodocó and Serra da

Lagoinha granitoids) and peralkalic syenitic, foliated plutons,emplaced next to the boundary with the Cachoeirinha terrane.

The Cachoeirinha terrane corresponds to a late

Neoproterozoic foldbelt that contains low-grade psammitic andpelitic rhythmite beds with a few intercalations of mafic to fel-

sic volcanic rocks (Brito Neves et al., 2000). This terrane used

to be described together with the Riacho Gravatá terrane as asingle belt, and known as the Piancó-Alto Brígida (Brito

Neves, 1983) or as the Cachoeirinha-Salgueiro foldbelt (Sial,

1984). The Brasiliano magmatism during the 650-620 Mainterval, in this terrane, is mainly calc-alkalic (e.g. the plutons

regionally known as Conceição-type granitoids), with subordi-

nate throndhjemite (e.g. Serrita pluton), whereas during the590-570 Ma interval rocks are more K-enriched, shoshonitic to

peralkalic in composition (e.g. Serrote dos Cavalos stock).

The Riacho Gravatá belt comprises volcanic rocks(mainly felsic, with subordinate mafic and intermediate) with

minor sedimentary rocks, metamorphosed in greenschist

facies. Brasiliano granitoids are rare in this domain.

The Alto Pajeú terrane is a metavolcano-sedimentary

domain with peak metamorphic age around 960 Ma, during

the contractional Cariris Velhos event (Santos et al., 2003).This terrane was deformed once more during the Brasiliano

cycle, which in this domain is characterized by voluminous

magmatism in three time intervals, beginning with high-Kcalc-alkalic and shoshonitic magmas, intruded during the

650-620 Ma interval (e.g. Tavares batholith, Pessôa, 2001;

Conceição das Creoulas batholith, Brasilino et al., 1998).Magmatism in the 590-570 Ma interval began with high-K

calc-alkalic series followed by unique ultrapotassic magmas

(eg. Triunfo syenite, Ferreira et al., 1994) so far not found inany other domain of the Borborema province. Peralkalic

dikes cutting across the boundary between this and the

Cachoeirinha and Rio Capibaribe terranes (Silva Filho et al.,1993; Ferreira & Sial, 1997; 2002) register the end of the

Brasiliano cycle (520 Ma) in the Borborema province.

The Rio Capibaribe terrane consists of Transamazonian(2.2-1.8 Ga) basement covered by two major complexes. The

oldest is the Vertentes complex that encompasses a migma-

tized volcano-sedimentary sequence probably related to theCariris Velhos event (Brito Neves et al., 2000). The younger

sequence (Surubim complex) is mainly composed of

metapelites and metacarbonates of probable Neoproterozoicage. Mesoproterozoic anorogenic magmatism (gabbro,

anorthosite, mafic dikes and A-type granites) is a characteris-

tic of this terrane (Brito Neves et al., op cit.). Neoproterozoicgranitic magmatism in this terrane started with high-K calc-

alkalic magmas at ca. 690 Ma (Bezerros pluton; Silva et al.,

1996). The peak of magmatism at 580 Ma was mostly of met-aluminous high-K (eg. Bom Jardim syenite; Guimarães and

Silva Filho, 1997) to high-K calc-alkalic rocks (e.g. Fazenda

Nova and Serra da Japecanga complexes, Neves & Vauchez,1995). Post-kinematic magmatism is characterized by silica-

oversaturated peralkalic intrusions (e.g. Moderna pluton,

Ferreira & Sial, 2002).The Alto Moxotó terrane consists of large areas of

Paleoproterozoic basement, including some Archean rem-

nants, and some early Neoproterozoic supracrustal sequences(Lagoa das Contendas, Sertânia, Caroalina complexes; Brito

Neves et al, 2000). Brasiliano granitic magmatism is rare in

this terrane compared to other terranes, but it contains one ofthe two A-type granitic complexes described in the

Transversal Zone (Prata complex, Melo et al., 1996).

192

Fig. 2. QAP diagram for neoproterozoic granitic and syenitic plutons ofthe Transversal Zone. The magma series trends are from Lameyre andBowden (1982). TH = trondhjemite, LKCA = low-K calc-alkalic,MKCA = medium-K calc-alkalic. Shaded areas represent modal com-positions for the studied granitoids and syenitoids, classified accordingto one of these series

- Diagrama QAP para plutons Neoproterozócios graníticos e sieníticosda Zona Transversal. As séries de magmas são de Lameyre e Bowden(1982). TH = trondhjemito, LKCA = cálcio-alcalino de baixo K, MKCA= cálcio-alcalino de médio K. As áreas sombreadas representam ascomposições modais dos granitóides e sienitóides estudados, classifica-dos de acordo com uma dessas séries

Fig. 3. Amphibole-rich clots hosted by diorite enclave, which isin turn hosted by 650-620 Ma magmatic epidote-bearing gran-

odiorites, in the Cachoeirinha-Salgueiro terrane, TransversalZone

- Agregados ricos em anfibólios inclusos em enclave diorítico,que por sua vez está incluso em granodioritos com epidoto

magmático de 650-620 Ma, no terreno Cachoeirinha-Salgueiro,Zona Transversal

bole, biotite, microcline, epidote, and sphene, a mineral com-position typical of I-type granitoids, as defined by Chappell &

White (2001). Unlike the high-K calc-alkalic (HKCA) grani-

toids in the Transversal Zone, megacrysts in these CA plutonsare plagioclase. Two plutons, Santo Antonio and Angico

Torto, exhibit kyanite-bearing black-spotted aureoles a few

meters from the contact with these plutons, characterized byfine-grained mica foliation, and the assemblage garnet, kyan-

ite, staurolite, muscovite with Si < 3.1, biotite, plagioclase

and quartz. Quartz and rutile inclusions in garnet suggestpeak P9 kbar during garnet growth (Caby & Sial, 1996)

Amphibole-rich clots are common and widespread in

all plutons of this kind in the Cachoeirinha terrane (Fig. 3).They consist of deep green calcic amphibole aggregates frac-

tionated from host magma, or as fine-grained, angular amphi-

bolite containing calcic plagioclase that is regarded as frag-ments from the source rock for the tonalite-granodiorite mag-

Fig. 4. Photomicrographs ofmagmatic epidote in 650-620 Ma

granitoid from the TransversalZone: (a) euhedral, 1 mm long,

partially enclosed by biotite(nicols crossed). (b) subhedral

(ca. 1.2 mm long) with allanitecore, partially enclosed bybiotite (nicols not crossed)

- Fotomicrografias de epidotomagmático em granitóides de

650-620 Ma da ZonaTransversal: (a) euédrico, 1 mm

de comprimento, parcialmenteenglobado por biotita (nicóis

cruzados); (b) subédrico (ca de1.2 mm de comprimento) com

núcleo de allanita, parcialmenteenglobado por biotita (nicóis

paralelos)

193Cap XII

a

b

Field relationships and petrography

650-620 Ma-old, syn-kinematic magmatism:Magmatic epidote-bearing granitoids

Magmatic epidote (mEp)-bearing calc-alkalic (CA)granitoids in the Cachoeirinha terrane are metaluminous to

slightly peraluminous tonalites to granodiorites, forming

batholiths and stocks that constitute the so-called Conceição-type granitoids, as described by Almeida et al. (1967). They

intruded low-grade metaturbidites and metapelites (Sial,

1993; Sial et al., 1999). All intrusions have crystallizationages around 630 Ma. They form a compositional trend in the

QAP diagram following the low-K calc-alkalic trend of

Lameyre & Bowden (1982) (Fig. 2). They usually formequigranular, medium- to coarse-grained, round to elongate

plutons composed of zoned plagioclase, quartz, calcic amphi-

194

ning and inclusions of zircon that display inherited cores.

Some primary epidote grains have allanite core. The HKCA plutons in this terrane are porphyritic monzodi-

orites to granodiorites characterized by K-feldspar

megacrysts, up to 15 cm long. Magmatic epidote in these plu-tons occupies up to 5% per volume and is included in plagio-

clase or rimmed by biotite, sometimes with allanite core.

They present magmatic structures indicative of highfluid dynamics and minor mingling with K-dioritic magmas.

These structures are observed in all plutons of this type in this

terrane, but the Tavares and Brejinho plutons, in particular,are the ones where magmatic structures are very well devel-

oped and preserved. Among the structures (Fig. 5) are

(Pessôa, 2001): (a) elliptical and circular structures character-ized by rythmic, concentric banding, in which mafic and fel-

sic bands alternate, in a pattern observed in vertical and hori-

zontal expositions, indicating a tridimensional nature; (b)Ladder dikes, and up a 1 m long snail structures, in which

magma flow is at a high angle to the magmatic foliation. They

are characterized by concave mafic-rich bands that alternatewith felsic-rich bands, and mineral composition similar to the

host granite, and in many of them K-feldspar cumulates occur

in the nucleus; (c) “channel” composed of pillow-like K dior-ites sitting in a felsic matrix. These structures are indicative of

convection during the formation of the magma chamber due

to intermittent heat input from external source. These fea-tures are interpreted to be due to convective currents origi-

nated by underplating of mafic magma (Weinberg et al.,

2001), implying in contrast of temperatures within the

mas (Sial, 1993; Sial et al., 1999). High δ18O (zircon) values

(11.1‰-11.8‰) are found in the Emas granitoid, one pluton

of this type in this terrane (Ferreira et al., 2003). These highmagmatic values are compatible with altered seafloor basalt,

which has suffered oxygen exchange with low-temperature

oceanic water, as protolith. Amphibole-rich clots showinghigh δ18O (whole-rock) values (9.9‰-11.5‰), usually 1.5‰

lower than in corresponding host granitic rocks (Sial et al.,

1998) support this hypothesis. Several plutons in the Alto Pajeú terrane contain mag-

matic epidote (Sial et al., 1999) (Fig. 4): Teixeira granitoid

(shoshonitic), Brejinho, Tavares, Conceição das Creoulas,Murici, and Riacho do Icó plutons (metaluminous high-K

calc alkalic).

The E-W-trending Teixeira composite batholith isformed by three intrusions: (a) shoshonitic monzonite (cen-

tral-eastern part), (b) throndhjemitic tonalite (western por-

tion), and (c) peralkalic syenite (a small eastern intrusion).The shoshonitic granitoids predominate over the other types.

They are mostly equigranular, fine- to medium-grained pera-

luminous quartz monzonites to monzogranites, forming atrend between that of the high-K and medium-K calc alkalic

series in the QAP diagram (Fig. 2). In these rocks, perthitic

microcline (flake and veined perthite) predominates over pla-gioclase and quartz. Plagioclase in contact with microcline

usually exhibits drop-like quartz inclusions, and myrmekite,

and is often deformed with bent twinning plane and wavyextinction. Among the mafic phases, ferro edenite is the most

common, sometimes forming agglomerates, showing twin-

Fig. 5. Magmatic structures in high-K calc-alkalic granitoids of the Transversal Zone: (a) snail structure; (b) ladder dike; (c) channel ofpillow-like K-diorite in a more felsic matrix; (d) snapshot of a structure in a vertical section across a thermal plume head

- Estruturas magmáticas em granitóides cálcio-alcalinos de alto K da Zona Transversal: (a) estrutura em caracol; (b) diques em escada;(c) canal de K-dioritos com estrutura em almofada em matriz mais félsica; (d) estrutura de uma seção vertical do topo de uma pluma tér-mica

a

b

c

d

that is 580-570 Ma old and another one that is 520 Ma old,

and will be discussed in the next section.

The older group consists of ultrapotassic syenitoidsthat occur within the southwestern region of the terrane (Serra

do Man batholith, Ferreira et al., 2002), or are part of the

syenitoid line recognized by Ferreira & Sial (1986), whichoccur along the boundary between the Alto Pajeú and

Cachoeirinha terrane (Triunfo, Serra do Casé, Serra do

Livramento, Serrote das Duas Irmãs, Serrote do Paulo, andBom Nome plutons). The ultrapotassic alkali feldspar syeni-

toids are mineralogically very simple, consisting of perthitic

microcline and aegirine-augite as main phases, and sphene,apatite, quartz, and rare magnetite and richterite after pyrox-

ene, as accessory phases. Alkalic pyroxenites are found as co-

magmatic inclusions, syn-plutonic, and late-stage dikes in theplutons along the syenitoid line, and have the same mineral

phases as the host syenite, although in different proportions

(Fig. 6). Host syenite and alkalic pyroxenite inclusions areinterpreted as formed after liquid immiscibility process from

a single mafic syenite magma (Ferreira et al., 1994).

Mica-pyroxenite xenoliths found in the Triunfo syeniteare interpreted as derived from the lithospheric mantle source

of the syenite (Ferreira et al., 1995). They are composed of

diopside-salite (80% of the bulk rock), with subordinate (andin variable amounts) F-rich phlogopite, which shows chem-

istry comparable with that observed in kimberlites and high

195Cap XII

magma chamber at short distances. The concentric struc-

tures represent magma flow in conduits and a frozen snap-

shot of thermal plume. Mafic-intermediate syn-plutonicdikes, indicative of mingling of magmas, are also present.

Ages of plutons of this type range from 651 ± 15 Ma

(TIMS zircon U-Pb, Tavares pluton, Brito Neves et al.,2003) to 638 ± 5 Ma (TIMS zircon U-Pb, Brejinho pluton;

Guimarães & Silva Filho, 2000). A Rb-Sr isochron yields an

age of 638 ± 29 Ma for the Conceição das Creoulas pluton(Brasilino et al., 1998). Pb-Pb zircon evaporation method

indicates an age of 643 ± 2 Ma for the Remédios pluton.

The plutons in the Alto Pajeú terranes are interpreted,on the basis of geochemistry, as emplaced in an early- to

syn-orogenic event in a collisional setting (e.g.Guimarães et

al., 1998; Brasilino et al., 1998; Brito Neves et al., 2003).The plutons in the Cachoeirinha terrane are interpreted as

emplaced syn-tectonically in a contractional event (Sial,

1993).

590-570 Ma-old, late-kinematic magmatism

The magmatic epidote-free high-K calc alkalic granitoids

Plutons of this type are intruded in the Granjeiro ter-

rane (Bodocó, Itaporanga and Serra da Lagoinha plutonsthat constitute the so-called Itaporanga-type granitoids as

described by Almeida et al., 1967), and in the Alto Pajeú ter-

rane (e.g. Fazenda Nova, Serra da Japecanga, Brejo daMadre de Deus, Campina Grande, Esperança batholiths).

They have been emplaced near terrane boundaries, and have

peak emplacement age around 580 Ma, except for theBezerros batholith, which is the oldest (687 Ma), and the

only one that presents solid-state foliation (Silva et al.,

1996).Similarly to the mEp-bearing calc-alkalic granitoids,

these plutons are characterized by porphyritic textures, with

up to 8 cm long K-feldspar megacrysts. They range in com-position from quartz monzonite, quartz syenite to monzo-

granite, forming a trend in the QAP diagram in the field of

high-K calc alkalic granitoids (Fig. 2). As in the case of thethe mEp-bearing HKCA granitoids, these plutons feature

magma mingling with dioritic magma, and among these, a

mixing of magmas of contrasting compositions, which wasan important petrogenetic process (e.g. Mariano, 1989,

McMurry, 2001, Neves and Vauchez, 1995, Sial et al.,

1989). Evidence of successive mafic magma supplies,which continued at a declining rate, can be observed in the

Fazenda Nova/Serra da Japecanga complex. This led to the

production of stromatic-like structures, followed by theintrusion of contorted syn-plutonic dikes, and of late-stage

dikes, some of which have chilled finer-grained margins

(Neves and Vauchez, 1995).Mixing of granitic and dioritic magma was more

intense in some plutons (e.g. Itaporanga and Bodocó) and

favoured the expressive development of hybrid granodior-ites showing field and petrographic evidence of mingling,

such as pillow-like and net-veined structures, and mantled

feldspar megacrysts captured from the host quartz mon-zonite. Large mixed zones can be mapped in these plutons at

small scales (e.g. Mariano, 1989; McMurry, 2001).

The Itaporanga pluton in the Granjeiro terrane had itsemplacement in a transpressive shear zone system, with the

ascent of magma facilitated by pre-existing steep fault zone

that bounds crustal discontinuities (Archanjo et al., 1999).

The peralkalic potassic to ultrapotassic syenitoids

The Transversal Zone is the domain in the Borboremaprovince that presents the largest and more widespread peral-

kalic syenitoid and granitoid plutons. Syenitoids form a group

Fig. 6. Field relationships between the 570 Ma Triunfo ultrapotassicsyenites and coexisting alkalic pyroxenite, formed by a liquid immisci-bility process (a) co-magmatic alkalic pyroxenite enclaves; (b) syn-plu-

tonic dike of alkalic pyroxenite

- Relações de campo entre os sienitos ultrapotássicos de Triunfo de 570Ma e piroxenitos alcalinos coexistentes, relacionados por um processode imiscibilidade de líquidos: (a) enclaves co-magmáticos de piroxeni-

to alcalino; (b) dique sin-plutônico de piroxenito alcalino

a

b

pressure xenoliths in kimberlites, calcite, hyalophane, sphene,

apatite, and traces of barite.

A gravimetric study performed on the Triunfo batholith(Motta, 2000), the largest known peralkalic ultrapotassic

body in the Borborema province, confirms the existence of a

denser layer, below the syenite, with a density compatiblewith that of alkalic pyroxenite. The gravimetric modeling

suggests a proportion of 97.5/2.5 (syenite/pyroxenite), a lat-

eral extension of 20 km and maximum thickness of 8.5 km,the pyroxenite being only 200 m thick, and a structure inter-

mediate between a lacolith and a lapolith (Motta op cit.).

Magnetic fabrics and microstructures in the Triunfobatholith suggest that it has a tabular shape, and that magma

emplacement occurred by lateral migration along a flat-lying

crustal structure after fracture propagation and ascension ofmagma, during a crustal extension event with a minimum

compressive stress (Archanjo & Bouchez, 1997).

Peralkalic potassic granitoids are quartz alkali syen-ites to alkali feldspar granites that occur as ring dikes around

mEp-bearing trondhjemites in ring structures (Serrita and SW

Serrita stocks; Neves; 1987; Ferreira & Sial, 1987); as a dikeset near Catingueira town, and as small stocks (Guandu,

Cavalos, Bernardo Vieira, and Cana Brava) (Ferreira & Sial,

op cit). Only one pluton of this type has been dated (U-Pb zir-con age of 573 ± 45 Ma for the Catingueira pluton; Brito

Neves et al., 2003). These rocks contain aegirine-augite and

alkalic amphibole as major mafic phases, with magnetite andapatite as main accessory phases. Fluorite and cassiterite are

locally present at amounts < 0.5%, and albitization is locally

an important phenomenon (e.g. ring dikes at Serrita stocks;Ferreira & Sial, op cit.).

The metaluminous high-K syenitic plutonsPlutons with these characteristics are found in the

Cachoeirinha (Terra Nova pluton), Alto Pajeú (Pajeú) and Rio

Capibaribe (Toritama and Bom Jardim plutons) terranes. The 150 km2 Terra Nova pluton is mainly composed

of porphyritic syenite and quartz syenite in which hornblende

and feldspars are up to 2 cm long phenocrysts in a matrixcomposed of hornblende, plagioclase, quartz, sphene, biotite,

epidote, and ferro-augite (Silva Filho et al., 1987). The

emplacement of this pluton, at 556 ± 79 Ma (Rb-Sr; Silva

196

Fig. 7. Photomicrographs of 545-520 Ma peralkalic dikes of theTransversal Zone: (a) richterite-bearing syenite (largest crystal is c. 0.5mm long) (nicols not crossed); (b) aegirine-augite syenite (pyroxenecrystal is ca. 0.4 mm across) (nicols crossed)

- Fotomicrografia de diques peralcalinos de 545-520 Ma da ZonaTransversal: (a) sienito com richterita (cristal maior tem cerca de 0,5mm de comprimento) (nicóis paralelos); (b) aegirina-augita sienito(cristal de piroxênio tem cerca de 0,4 mm de comprimento (nicóiscruzados)

Fig. 8. SiO2 vs. K2O diagramfor Transversal Zone grani-toids and syenitoids. Fieldsare from Peccerillo andTaylor (1976). SH= shoshon-ite, HK = high-K calc-alkalic,MK = medium-K calc-alka-lic, Low-K = low-K calc alka-lic fields.Epi = epidote;HKCA = high-K calc-alkalic;SH = shoshonitic; MHK =metaluminous high-K;Trondh = trndhjemite; CA =calc-alkalic

Fig. 8. Diagrama SiO2 vs.K2O para granitóides e sieni-tóides da Zona Transversal.Os campos são de Peccerilloand Taylor (1976). SH=shoshonito, HK = cálcio-alcalino de alto K, MK = cál-cio-alcalino de médio K,Low-K = cálcio-alcalino debaixo K. Epi = epidoto;HKCA = cálcio alcalino dealto K; SH = shoshonito;MHK = metaluminoso dealto K; Trondh = trond-hjemito; CA = cálcio alcalino

b

a

migmatites of the Alto Pajeú terrane. They comprise mafic

syenite-monzonites, mesocratic syenites and leucosyenites in

which mafic syenites occur as enclaves and synplutonic dikes(Guimarães & Silva Filho, op cit.). These authors interpreted

the complex as intrusive into the later stage of the Brasiliano

cycle and magmas generated in a metasomatized lithosphericmantle.

520 Ma-old, post-orogenic magmatism

The A-type plutons

Two calc-alkalic A-type plutonic complexes have beenrecognized in the Transversal Zone. One of which is the 570

Ma Queimadas foliated pluton (Almeida et al., 1997). The

other one, which is better known, is the 520 Ma-old Pratacomplex that constitutes a 250 km2 composite intrusion in

gneisses and migmatites (Melo et al., 1996), Alto Moxotó ter-

rane, next to the boundary with the Alto Pajeú terrane. It com-prises several granitic intrusions, and dioritic dikes. The main

pluton consists of porphyritic coarse-grained biotite horn-

blende monzonites and medium-grained equigranular biotitesienogranites, in which rapakivi texture occurs locally.

Fluorite is a common accessory phase, a typical mineral of A-

Filho et al., 1993) is interpreted to have occurred during late-

collisional stage of the Brasiliano cycle, controlled by move-

ments of the Pernambuco shear zone, in a compressiveregime (Silva Filho et al., 1993).

The Pajeú syenite is a large (40 km vs. 20 km) elon-

gate pluton intrusive into gneisses and migmatites of thewesten part of the Alto Pajeú terrane, presenting two major

facies: porphyritic syenite, the major facies, characterized by

2-8 cm K-feldspar megacrysts, and fine-grained syenite. Mineralphases are the same in the two facies (microcline, orthoclase,

quartz, minor plagioclase, calcic amphibole, sphene, epidote,

allanite, apatite, zircon, magnetite) (Reyes et al., 1996).Melanocratic syenitic enclaves, which present acicular

apatite, and net-veined structures, and synplutonic dikes, are

indicative of mingling, and locally mixing of magmas.Enclaves are aligned following the magmatic foliation. TIMS

U-Pb zircon age of 586 ± 21 Ma is reported by Guimarães &

Silva Filho (1998). Reyes et al. (op cit.), on the basis of geo-chemical data, interpret that the emplacement of this pluton

took place in a late to post-collisional setting.

The Bom Jardim (Rb-Sr age of 585 ± 38 Ma; Guimarãesand Silva Filho, 1997) and Toritama complexes are elongate

multiple-injected magmas intrusive into gneisses and

197Cap XII

Terrane

Rio Capibaribe

Rio Capibaribe

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Cachoeirinha

Cachoeirinha

Granjeiro

Granjeiro

Rio Capibaribe

Rio Capibaribe

Rio Capibaribe

Rio Capibaribe

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Alto Pajeú

Cachoeirinha

Cachoeirinha

Cachoeirinha

Cachoeirinha

Alto Pajeú-

Cachoeirinha

Pajeú boundary

Alto Pajeú-

Cachoeirinha

Pajeú boundary

Alto Pajeú-

Cachoeirinha

Pajeú boundary

Alto Pajeú-

Cachoeirinha

Pajeú boundary

Alto Pajeú-

Cachoeirinha

Pajeú boundary

Magma

series

HKCA

HKCA

HKCA

SH

HKCA

HKCA

SH

HKCA

CA

CA

HKCA

HKCA

MHKS

HKCA

PER/SH

PER

HKCA

SH

HKCA

MHKS

UP

UP

A-type

TROND

CA

SH

MHKS

PER

PER

PER

UP

Pluton

Bezerros

Timbaúba

Tavares

Teixeira

Brejinho

Conceição das Creoulas

Serra do Arapuá

Remédios

Conceição

Emas

Itaporanga

Bodocó

Bom Jardim

Fazenda Nova

Pinheiro

Moderna

S-Caldeirão Encantado

Betânia

Campina Grande

Pajeú

Serra do Man

Triunfo

Prata

Palmeira

Angico Torto

Salgueiro

Terra Nova pluton

Catingueira

Terra Nova dikes

Princesa Isabel dikes

Serra do Livramento

Serrote de Duas Irmãs

Bom Nome

Age Ma

687 ± 34

644 ± 5

651 ± 15

645

638 ± 5

638 ± 29

612 ± 24

643 + 2

635 ± 9 / 633 ± 9

627 ± 19

585 ± 2

559 - 593

592 ± 7 / 585 ± 38

588 ± 12

581 ± 1.6

586 ± 21 592 ± 49

581 ± 28

572

512 ±30

505 ± 4

557 ± 71

556 ± 79

573 ± 45

515 ± 20

Method

Pb-Pb

U-Pb

U-Pb

U-Pb

U-Pb

Rb-Sr

Rb-Sr

Pb-Pb

U-Pb / Rb-Sr

U-Pb

U-Pb

Rb-Sr

U-Pb

U-Pb

U-Pb

U-Pb Rb-Sr

Rb-Sr

Rb-Sr

Rb-Sr

U-Pb

Rb-Sr

Rb-Sr

U-Pb

Rb-Sr

(87Sr/86Sr)i

0.70526

0.7115-0.7080

0.7093

0.71054

0.70598

0.70911

0.7058

0.7057- 0.7063

0.70714

0.70839

0.70903

0.71087

0.710

0.7132

0.71062

0.7047

0.0761

0.71071 / 0.70978

0.7098

0.7088

0.7106

εNd(0.60)

-4.2 to -5.4

-3.4

-13.9

-3.6 to -10.1

- 2.8

-16.6

-1.2

-2.0

-9.0

-19

-12.4

-7.1 -7.6

-13.6

-5.0

-11.9

-16.5

-18.6 -16.0

-17.3

-16.1

-14.2

-3.8

-13.5

-15.6

-17.5

-3.6

T DM

1.4

1.4

2.1

1.84 -1.421.31

2.14

1.23

1.30

1.65

1.9

1.92

1.92

2.14

1.5

1.87

2.10

2.07 2.17

2.47

2.4

2.17

1.40

1.86

2.39

2.37

1.38

reference

Silva et al ., 1996

Guimarães et al., 2001

Brito Neves et al ., 2003*, this work#BBBN oral commu.*; Ferreira, 1991#, this work**

Guimarães e Silva Filho, 2000*, Torres, 2000#Brasilino et al .,**, Brasilino 2003#

This work

This work##, Lins, 2000#

Brito Neves et al ., 2003*, Sial, 1993*#

Van Schmus et al., 1995#, This work*/**

Brito Neves et al ., 2003*, Sial 1987**, Van Schmus

et al., 1995#

McMurry, 2001

Guimarães and Silva Filho, 1997

Van Schmus et al., 1995

This work

This work

This work

Lins, 2000

Almeida et al ., 1997*, Guimarães et al ., 1998#

Guimarães and Silva Filho, 1998

Ferreira et al

Ferreira et al, 1995

Melo et al., 1996

Kozuch et al., 1997

This work

Silva Filho, et al., 1990**, Van Schmus et al., 1995#

Silva Filho et al., 1993**, Van Schmus et al ., 1995#

Brito Neves et al ., 2003*, Van Schmus et al ., 1995#

Silva Filho and Guimarães, 1990**; Ferreira and

Sial, 2002

Ferreira and Sial

Ferreira, 1991

Ferreira, 1991

Ferreira, 1991

Table 1. Radiogenic isotope data for granitoids from the Transversal Zone, Borborema Province, NE Brazil. On the references: * U-Pb data, ** Rb-Sr, data # Sm-Nd, Data## Pb-Pb, data. Group of granitoids: HKCA = high-K calc alkalic; MHKS = metaluminous high-K syenitoids,

PER = peralkalic, SH = shoshonitic, UP = ultrapotassic

type granitoids emplaced at high levels into the crust. Field

evidence for mingling with dioritic magmas, such as syn-plu-

tonic dikes, and net-veined and pillow-like structures, areobserved in most part of the pluton. This complex is inter-

preted by Melo et al. (op cit.) as the result of an extension-

related crustal anorogenic magmatism.

Peralkalic syenitic dikes

The second group of peralkalic rocks as referred to insection “The peralkalic potassic to ultrapotassic syenitoids”

consists of potassic, silica-saturated syenitoids intrusive into

low-metamorphic grade metapelites of the Cachoeirinha ter-rane (Riacho de Santo Antônio dikes, Ferreira & Sial, 2002),

at the Rio Capibaribe terrane (Moderna and associated dike,

Ferreira & Sial, op cit) or forms two dike sets, intrusive at the

southernmost Cachoeirinha terrane, next to the boundary with

the Alto Pajeú terrane (Terra Nova dikes) or across the bound-ary of the two terranes (Princesa Izabel dikes) (Silva Filho et

al., 1993, Ferreira & Sial, 1997). Each dike set is composed

of about 50 dikes each, and are texturally and mineralogical-ly similar.

They are silica saturated to slightly oversaturated

alkali feldspar trachyte/syenite, presenting large textural vari-ation, including aphanitic, fine- to medium-grained types,

which have equigranular, inequigranular or microporphyritic

textures. Main phases in both dike sets are zoned orthoclase,aegirine-augite to aegirine and amphibole (early crystallized

pargasite to Fe-pargasite or late-crystallized ferro-richerite)

198

Fig. 9. Shand index diagram for Transversal Zone granitoids and syenitoids. Symbols are the same as for Fig. 8

- Diagrama de índice de Shand para granitóides e sienitóides da Zona Transversal. Os símbolos são os mesmos da Fig. 8

Fig. 10. R1 vs. R2 diagram (Batchelor and Bowden, 1985) for Transversal Zone granitoids and syenitoids. Symbols are the same as forFig. 8

- Diagrama R1 vs. R2 (Batchelor & Bowden, 1985) para granitóides e sienitóides da Zona Transversal. Os símbolos são os mesmos daFig. 8

tallization as major petrogenetic process, in spite of the field

evidence for an important mixing and assimilation process ofmore mafic magma in the high-K calc alkalic plutons. The

metaluminous character of these two suites is compatible

with generation from anatexis of a hornblende-rich source(eg. Whitney, 1988), probably in the lower crust. Higher Rb

and Sr contents, and higher Rb/Sr ratios for the HKCA gran-

itoids than for other suites are compatible with the presenceof coexisting, although volumetrically small, mafic magmas.

The mEp-bearing shoshonitic rocks (SH) are metalu-

minous in composition (Fig. 9), exhibit a relatively wide rangeof SiO2 (from ca. 60 up to 75% SiO2), and are characterized

by lower MgO, TiO2, Fe2O3T, and P2O5 contents, higher

Al2O3 and Na2O, and higher Ba/Rb and Sr/Rb ratios than theother groups. They present decreasing Na2O and Al2O3 with

increasing silica contents, in contrast with the other series in

which these oxides have positive correlation (Na2O) orremain constant (Al2O3) with increasing silica.

The potassic and ultrapotassic (UP) plutons are peralka-

lic (Fig. 9), characterized by enrichment in incompatible ele-ments (K, Sr, Ba, P, REE), have low Zr and Nb concentrations,

and present Nb and Ti negative anomalies in MORB-normal-

ized diagrams (Ferreira, 1991). Enrichment in these elementsin the ultrapotassic syenites, as well as in their alkalic pyroxen-

ite co-magmatic inclusions are interpreted as inherited from a

metasomatized-mantle source. This hypothesis is reinforced bythe chemistry of the mica-pyroxenite xenoliths that show also

high K and Ba contents (K2O = 1-5wt%; Ba = 1400-1500ppm),

variable Cr (21-3000 ppm) and Ni (20-280ppm), very low Nb(6 ppm), and high F (0.4-1.8 wt%) contents, being LREE-

enriched (Ferreira et al., 1995).

The trondhjemitic granitoids are all peraluminous, havea major chemistry similar to that of continental trondhjemites,

with high Al2O3 contents (usually > 16%), low MgO (0.10 to

0.53%) and CaO (0.33 to 1.7%), and predominance of Na2Oover K2O (Na2O/K2O varies from 1.19 to 2.6) (Neves, 1986).

Alumina contents decrease with increasing silica contents,

and together with very high Sr (1800-3700 ppm) and Ba(1800 to 7400 ppm) contents, indicate early crystallization of

(Fig. 7). Amphibole in the Terra Nova dikes has more variable

compositions, and has crystallized straight from the magma,while in the Princesa Isabel dikes, amphibole was largely pro-

duced after pyroxene, with few exceptions. Larger textural

variation is observed in the Terra Nova dikes, which cut,among other rocks, the peralkalic ultrapotassic Serra do Casé

and Serra do Livramento plutons (570 Ma), attesting their

younger ages (Rb-Sr age of 515 ± 20 Ma; Silva Filho et al.,1993).

On the basis of marked differences in magnetic suscep-

tibility, O and Nd isotopic data for the two dike sets, Ferreira& Sial (1997) concluded that they are derived from different

mantle sources. The Princesa Izabel dike set is interpreted as

emplaced in a post-orogenic, extensional setting, and marksthe amalgamation after collision between the Cachoeirinha

and Alto Pajeú terranes. The emplacement of the Terra Nova

dike set is interpreted as controlled by the strike-slip regimeof the Pernambuco shear zone in the Early Cambrian (Silva

Filho et al., 1993).

Geochemistry and tectonic setting

Magmatic epidote-bearing granitoids from all seriesgroup close to each other in a SiO2 vs. K2O diagram, in the

HKCA field of Peccerilo & Taylor (1976), with a few samples

lying in the calc-alkalic and shoshonitic fields (Fig. 8).Samples from the other series plot in the shoshonitic field in

this diagram. Trondhjemitic plutons are medium- to high-K

calc-alkalic, peraluminous in composition.The high-K calc alkalic (HKCA), both magmatic epi-

dote bearing and free, and calc alkalic (CA) granitoids are

metaluminous to peraluminous (Fig. 9), being undistinguish-able from each other on the basis of major and minor ele-

ments, as they form overlapping trends in most variation dia-

grams. They show negative correlations between SiO2 andTiO2, CaO, MgO, MnO, and Fe2O3, the opposite behavior

being observed with Na2O and K2O, while Al2O3 remains

constant with increasing silica. Positive correlations betweenBa/Rb vs. Zr/Rb, and Zr/Rb vs. Sr/Rb attest to fractional crys-

199Cap XII

Fig. 11. log Rb vs. Log (Y + Nb) diagram of Pearce et al. (1984) for Transversal Zone granitoids and syenitoids. Syn-colg = syn-collisionalgranites; WPG = within-plate granites; VAG = volcanic-arc granitoids. Symbols are the same as for Fig. 8

Diagrama log Rb vs. Log (Y + Nb) de Pearce et al . (1984) para granitóides e sienitóides da Zona Transversal. Syn-colg = granites sin-col-isionais, WPG = granites intra-placas, VAG = granites de arco vulcânico. Os símbolos são os mesmos da Fig. 8

plagioclase, which is reflected in the peraluminous nature of

the granitoids. Low Rb/Sr precludes the use of the Rb-Sr sys-

tematics for dating (Neves, op cit.). This author proposed thatthe Serrita stock was generated through partial melting of

altered basaltic rocks, where amphibole and garnet remain in

the residue, and subsequent crystallization at pressures above6 kbar.

The high-K syenitoids are metaluminous to slightly

peraluminous (Fig. 9), have SiO2 contents varying from ca.55 to 65wt%, plotting in the field of ultrapotassic rocks in the

SiO2 vs. K2O% diagram (Fig. 8). Likewise the peralkalic plu-

tons, these syenitoids do not show Eu anomaly in REE chon-drite-normalized diagrams. Guimarães & Silva Filho (1990)

found high Ba (2000-4500 ppm) and very high Sr (1000-2200

ppm) contents, as well as high Cr (up to 470 ppm) and Ni (30-250 ppm) in the Bom Jardim complex, compatible with man-

tle-derived magmas, with minor crustal contamination.

Figures 10 and 11 show tectonic discrimination dia-grams for the studied suites of rocks. The oldest (650-620

Ma) plutons display signatures typical of syn-tectonic mag-

matism (destructive plate margins and volcanic-arc granites).On the other hand, the 590-570 and 545-520 Ma plutons are

similar to late to post-tectonic granites (late orogenic and vol-

canic arc granites transitional to within plate granites).

Sr and Nd isotopes

Sr and Nd isotopic data for plutons of the Transversal

Zone compiled from literature and from this work are listed

in Table 1.The initial (87Sr/86Sr) ratios of the shoshonitic grani-

toids are the lowest among the studied granitoids, varying

from 0.7047 (Salgueiro pluton) to 0.70526 (Teixeira grani-toid), compatible with limited crustal contribution. Initial Sr

ratios for the mEp-bearing CA granitoids are variable, rang-

ing from 0.70598 to 0.710621. These values are lower,

although partially overlapping, than the values for the mEp-

bearing HKCA group (0.70839-0.71002). Low initial Sr

ratios are observed for the epidote-free HKCA granitoids,around 0.706, in spite of field evidence for local mixing

between crustal and mantle-derived magmas. The A-type

granitoid presents high initial 87Sr/86Sr (0.71320; Melo et al.,1996), which suggests an important crustal component

involved in their source.

The peralkalic potassic and ultrapotassic syenitoidshave high initial Sr ratios, 0.710, which together with strong-

ly negative εNd values (ca. -19) are interpreted as inherited

from a contaminated upper mantle source (Ferreira et al.,1997).

The values of εNd (0.6 Ga) for all groups are negative,

and there is a tendency for younger suites to have more neg-ative values, compatible with interaction with a thicker crust.

Magmatic epidote-bearing CA granitoids from the

Cachoeirinha terrane display εNd (0.6Ga) in the -1 to -2range, and TDM model ages between 1.2 and 1.4 Ga (Sial

et al., 1999). These data, together with the low initial Sr ratios

and widespread presence of amphibole-rich clots, are com-patible with the hypothesis of generation of these tonalites

and granodiorites by partial melting of a metabasalt.

Values of εNd for these mEp-bearing CA granitoids arelower and with a restricted range compared to the values for

the mEp-bearing HKCA granitoids that occur in the Alto

Pajeú terrane (-2.8 to - 10.1). The values of εNd are morevariable also in a single pluton (e.g. from -3.6 to -10 in the

Brejinho granitoid) and are compatible with variable degrees

of interaction of mantle-derived magma with crustal material. The peralkalic syenite dikes present two distinct εNd

and TDM values: less negative εNd (-3.6) and younger TDM(1.38 Ga) for the Princesa Izabel dikes, that occur across andin both sides of the Cachoeirinha and Alto Pajeú terrane

boundary, at the northernmost part of the syenitoid line, and

more negative εNd (-17) and older TDM (2.37 Ga) for the

200

Fig. 12. Nd vs. Nd model age plot for Transversal Zone granitoids and syenitoids. Symbols are the same as for Fig. 8

- Diagrama Nd vs. idade modelo Nd para granitóides e sienitóides da Zona Transversal. Os símbolos são os mesmos da Fig. 8

ships that show close relationships between the host granitoid

with K-dioritic magmas. An alternative hypothesis is that the

oldest granitoids are the product of remelting ofMesoproterozoic continental crust.

Most works on the Borborema province have conclud-

ed studies that during the Brasiliano cycle no juvenile materi-al was added to the crust, although mantle material is very

common and presence of two magmas is observed in most

suites of the region (Sial et al, 1992). A tectono-thermal evo-lution with intralithospheric differentiation is interpreted for

the Brasiliano cycle at this part of the Borborema province

(Neves et al., 2000). Positive εNd isotopic data determinedon calc-alkalic granodiorites emplaced at the easternmost

extension of the Patos shear zone (B.B. de Brito Neves, writ-

ten communication, 2003), however, suggest presence ofjuvenile material. This evidence, although observed so far in

only one Neoproterozoic pluton, coupled with the possibility

that juvenile Neoproterozoic mantle-derived magma wasinvolved in the production of the 650-620 Ma granitoids,

must be taken into account in the models for the tectonic

model for the evolution of the province.The 590-570 Ma plutons have Sr and Nd isotopic

values of magmas formed by remelting of Paleoproterozoic

lower continental crust, the only geochemical reservoir withthese characteristics. The only exception among these

younger rocks are the ultrapotassic peralkalic syenitoids,

which present high initial Sr ratios and very negative εNdvalues, interpreted as derived from an incompatible element

enriched-mantle source.

The 545-520 Ma peralkalic dikes present PaleoproterozoicNd model ages, but the less negative εNd values for the

Manaíra-Princesa Izabel dikes suggest smaller degree of con-

tamination, probably during ascent and emplacement at lowpressure, as also suggested by oxygen isotope values ( δ18O

from +8 to +9‰ SMOW; Ferreira & Sial, 1997) for these

rocks. Strongly negative εNd value for the Terra Nova dikessuggest an incompatible element enriched mantle source,

similar to that for the syenites along the syenitoid line.

Acknowledgments

Part of the field and laboratory work was made pos-sible by means of a grant from CNPq to VPF process n.

463029/00-3.

Terra Nova dikes, that occur in the Cachoeirinha terrane, next

to the boundary with Alto Pajeú terrane, at the southernmost

syenitoid line.Depleted mantle Nd model ages tend to be older in

the younger suites. The mEp-bearing CA and HKCA grani-

toids from the Cachoeirinha and Alto Pajeú terranes havesource of Mesoproterozoic age, while the other suites, includ-

ing the mEp shoshonitic granitoids have Paleoproterozoic

model ages (Fig. 12).

Discussion and conclusion

Predominance of magmatic epidote-bearing granitoids

(solidification pressures around 6 kbar) in the 650-620 Ma

interval in contrast with the presence of magmatic epidote-free (solidification pressure around 3-4 kbar) in the 590-570

Ma time interval for magmas of similar composition is prob-

ably due to contrasting oxidation state of the magma, andmode of emplacement to different stages of tectonic evolu-

tion. Late collision is characterized by a gradual change of

motion from perpendicular to the collision zone to transcur-rent motion, which is initially achieved by ductile deforma-

tion, while the collision is still hot, and is superseded by brit-

tle fracturing (Shackleton, 1986). Hot crust and ductile defor-mation would allow magma to have a rather fast emplace-

ment and solidification rate, which prevented epidote dissolu-

tion (e.g. Sial et al., 1999), as compared with epidote-freesimilar suites emplaced later in the Brasiliano cycle (ca. 580

Ma), in a post-collisional, extensional setting, in brittle con-

ditions, and in which thicker crust was formed.The 650-620 Ma old granitoids present younger εNd

model ages (< 2.0 Ga) and less negative Nd (ca. -2 to -14)

than the 590-570 Ma granitoids, for which TDM varies fromca 1.5 to 2.5 Ga, and εNd from ca. -8 to -20. The highest and

more variable initial 87Sr/86Sr values, on the other hand, are

observed in the oldest granitoids, while lower initial Sr ratiosare found in the 590-570 Ma magmas. These data indicate an

important change of type of magma source with time. The

oldest granitoids could represent a mixture ofNeoproterozoic, juvenile, mantle-derived material with

magma derived from melting of Paleoproterozoic continental

crust, which would yield intermediate Nd model age, of ca.1.2-1.4 Ga. This is compatible with mixture of mantle-

derived and crustal magmas, as indicated by field relation-

201Cap XII