Gondwana Research 15 (2009) 454–470

Contents lists available at ScienceDirect

Gondwana Research

j ourna l homepage: www.e lsev ie r.com/ locate /gr

Relics of eclogite facies assemblages in the Ceará Central Domain, NW BorboremaProvince, NE Brazil: Implications for the assembly of West Gondwana

Ticiano J. Saraiva dos Santos a,⁎, Maria da Glória M. Garcia b, Wagner Silva Amaral a, Renauld Caby c,Eberhard Wernick d, Michel H. Arthaud e, Elton L. Dantas f, M. Santosh g

a Institute of Geosciences, P.O. Box 6152, University of Campinas—UNICAMP, 13083-970, Campinas, SP, Brazilb IGc-Universidade de São Paulo (USP), Rua do Lago, 562, CEP 05508-900, São Paulo, SP, Brazilc Laboratoire de Tectonophysique, Univ. de Montpellier II, Sciences et Techniques, 34095 Montpellier Cedex 05, Franced IGCE-Universidade Estadual Paulista (UNESP), Av 24A, CEP 13506-900, Rio Claro, SP, Brazile Universidade Federal do Ceará, Dep. de Geologia, Campus do Pici, CEP 60455-760 Fortaleza, CE, Brazilf Instituto de Geociências, Universidade de Brasília (UnB), CEP 70910-900 Brasília, DF, Brazilg Faculty of Science, Kochi University, Akebono-cho 2-5-1, Kochi 780-8520, Japan

⁎ Corresponding author. Fax: +55 19 35214552.E-mail address: ticiano@ige.unicamp.br (T.J. Saraiva

1342-937X/$ – see front matter © 2009 International Adoi:10.1016/j.gr.2009.01.003

a b s t r a c t

a r t i c l e i n f o

Article history:

The Borborema Province, in Received 2 July 2008Received in revised form 23 December 2008Accepted 6 January 2009Available online 18 January 2009

Keywords:Borborema ProvinceGeochemistryRetrograded eclogitesSubductionWest Gondwana

the NE of Brazil, is a rather complex piece in the Brazil–Africa puzzle as itrepresents the junction of the Dahomeyide/Pharusian, Central African, Araçuai and Brasilia fold belts locatedbetween the West-African/São Luis, Congo/São Francisco and Amazonas craton. The correlation between theDahomeyides from W-Africa (Ghana, Benin, Togo, and Mali) and the Borborema Province involves the MédioCoreaú and Central Ceará domains. The inferred continuation of the main oceanic suture zone exposed in theDahomeyides of WAfrica is buried beneath the Phanerozoic Parnaíba Basin in Brazil (northwest of the MédioCoreaú domain) where some high density gravity anomalies may represent hidden remnants of an oceanicsuture. In addition to this major suture a narrow, nearly continuous strip composed of mainly mafic podscontaining relics of eclogite-facies assemblages associated with partially migmatized granulite-faciesmetapelitic gneisses has been found further east in the NW Borborema Province. These high pressure maficrocks, interpreted as retrograded eclogites, are located between the Transbrasiliano Lineament and the SantaQuitéria continental arc and comprise primitive to evolved arc-related rocks with either arc- or MORB-typeimprints that can indicate either deep subduction of oceanic lithosphere or roots of continental and oceanicmagmatic arcs. Average peak P–T conditions under eclogite-facies metamorphism (T=770 °C andP=17.3 kbar) were estimated using garnet–clinopyroxene thermometry and Jd content in clinopyroxene.Transition to granulite-facies conditions, as well as later widespread re-equilibration under amphibolitefacies, were registered both in the basic and the metapelitic rocks and suggest a clockwise P–T pathcharacterized by an increase in temperature followed by strong decompression. A phenomenon possiblyrelated to the exhumation of a highly thickened crust associated with the suturing of the Médio Coreaú andCentral Ceará domains, two distinct crustal blocks separated by the Transbrasiliano Lineament.

© 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction

Sutures which represent probable zones of ocean closure are key-features for the understanding of the Gondwana geodynamicassembly and modern transoceanic geological correlations. Suturezones are identified mainly by continental and oceanic magmatic arcs,accretionary complexes, subduction complexes including ophiolites,thrust belts and geophysical data (Lesquer et al., 1984; El-Hadj Tidjaniet al., 1997; Pimentel et al., 2000). Of particular importance in thiscontext are high-pressure (HP) granulitic/eclogitic belts which

dos Santos).

ssociation for Gondwana Research.

indicate deep subduction of oceanic lithosphere or underplatedroots of continental and oceanic magmatic arcs (Black et al., 1994;Caby, 2003; Attoh and Morgan, 2004; Agbossoumondé et al., 2004).The ocean-closure or craton-convergence picture resulting from theidentification of several Gondwana sutures is blurred by extensiveshear tectonics which developed during and shortly after the mainBrasiliano/Pan-African collision phase. Thus, the main shear zonesalso became an important reference in trancontinental Gondwana-correlations (Caby, 1989; Caby et al., 1995; Trompette, 1994; BritoNeves et al., 1999; Santos et al., 2008).

The Borborema Province developed as a result of convergence ofWest African–São Luis and São Francisco Cratons during theamalgamation of West Gondwana (Brito Neves and Cordani, 1991;Brito Neves et al., 2000) (Fig. 1) and comprises at least seven distinct

Published by Elsevier B.V. All rights reserved.

Fig. 1. A) Pre-drift reconstruction of the NE Brazil and NW Africa during late Neoproterozoic and early Paleozoic (adapted from Caby, 1989); B) Simplified geological map of theBorborema Province showing the main domains and Brasiliano granitic plutons. Details in the text.

455T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

456 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

geological/geotectonic domains (Brito Neves et al., 2000; Van Schmuset al., 2008). The correlations of the Dahomeyides from W-Africa(Ghana, Benin, Togo, and Mali) with the Borborema Province, NEBrazil, principally involve the Médio Coreaú and Central Cearádomains (Ceará State). Main correlation pieces are passive marginhigh pressure metasediments surrounding the W-African/São Luiscraton, affected by a thrust belt with vergence against the craton,magmatic arc belts, an old (Archaean/Early Proterozoic) basementreactivated and migmatized during the Brasiliano/Pan-African oro-geny, molassic sedimentary/volcanic basins and the expressive 4°50′,Kandi and Transbrasiliano lineaments (Caby, 1989; Trompette, 1994;Monié et al., 1997; Santos et al., 2008).

The key missing link in this W-Africa–Brazil correlation is the stripof suture mélange, including granulitic and eclogitic mafic/ultramaficrocks, well defined in the Dahomeyides, but not yet found in theBorborema Province (Santos et al., 2008). The inferred continuation ofthemain oceanic suture zone exposed in the Dahomeyides ofWAfricais buried beneath the Phanerozoic Parnaíba Basin in Brazil (northwestof the Médio Coreaú domain) where some high density gravityanomalies may represent hidden remnants of an oceanic suture. Thepresence of an oceanic realm in this regionwas supported by Fetter etal. (2003) to explain the growth of the Santa Quitéria magmatic arcfarther to the southeast. Nonetheless, the join of two major distinctcrustal blocks, the Médio Coreaú and Central Ceará domains, mayrepresent a subordinate suture in the region. In this work we providedetailed petrographic and mineral chemistry data regarding maficrocks showing relics of eclogite-facies assemblages found nearForquilha, Ceará State, at the western border of the Santa Quitériamagmatic arc in the Central Ceará Domain. We also presentthermobarometric data used in order to obtain information regardingthe metamorphic P–T path of the retrogressed eclogites andsurrounding rocks. The data are then discussed in the light of theMédio Coreaú/Dahomeyides correlation and the Gondwana geody-namic scenario.

2. Regional setting

The northwestern portion of the Borborema Province is composedof two crustal domains, the Médio Coreaú and Ceará Central, whoselimit is marked by the Transbrasiliano Lineament, which continuesinto Africa as the 4°50′-Kandi Fault Lineament (Fig. 1). The contactbetween the Médio Coreaú domain and the São Luis craton to thenorthwest is hidden beneath the Phanerozoic sediments of theParnaíba Basin.

The Médio Coreaú domain is mainly composed of basementorthogneisses with tonalite–trondhjemite–granodiorite (TTG) affi-nities, as well as amphibolite facies gneisses, amphibolites, leuco-granites, mafic granulites, enderbites, leptynites, kinzigites, andmigmatites. U–Pb and Sm–Nd studies of these rocks (Fetter et al.,2000) show the gneisses are of early Paleoproterozoic age (2.36–2.30 Ga) and yield Nd crustal residence (TDM) ages between 2.61and 2.38 Ga. The supracrustal sequence of the Médio CoreaúDomain is represented by the Martinópole Group and comprisesmainly of fine-grained metasedimentary rocks: metapelitic rock,metagraywackes and quartzites with minor intercalations of calc-silicate, metacarbonates, and felsic metavolcanic rocks. Although thetectonic environment responsible for their deposition remainsunclear, some authors proposed that quartzites belong to a nappethat may represent the southern extension of the Atacora quartzitenappe in Benin-Togo (Caby et al., 1991). Fetter et al. (2003)suggested that the Martinópole Group might represent a forearcbasin that developed during the late Neoproterozoic growth of theSanta Quitéria continental arc complex located to the southeast inthe Ceará Central Domain.

The depositional age of the Martinópole Group has beenestablished by U–Pb zircon data from a metarhyolite (777±11 Ma)

concordantly intercalated with clastic sediments (Fetter et al., 2003).The Nd model ages for the basal unit of this group, between 1.24and 1.32 Ga (Fetter, 1999), suggest a significant contribution ofNeoproterozoic juvenile volcanic material. The upper unit displaysNd model ages between 1.61 and 2.69 Ga, which represents amixture between Neoproterozoic juvenile material and Paleoproter-ozoic basement gneisses (Fetter et al., 2003). The NeoproterozoicUbajara basin is a greenschist facies, proximal, platformal sedimen-tary sequence comprising slate, siltstone, sandstone, carbonate, andgreywacke.

The Ceará Central Domain (Figs. 1B and 2) is a composite crustalblock composed of vast tracts of juvenile middle Paleoproterozoic(2.1–2.0 Ga, Fetter, 1999; Martins et al., 2009) high-grade felsicorthogneisses and migmatites, an inlier of Archean crust, aNeoproterozoic supracrustal sequences (Ceará Group) and, theroots of a Neoproterozoic continental arc called the Santa Quitériabatholith (Figs. 1B and 2). Both the basement complex andsupracrustal rocks are intruded by numerous syn- to late- andpost Brasiliano granitoids. As the construction of a continental arcrequires the subduction of oceanic lithosphere, this implies that asubstantial oceanic domain existed to the northwest of theBorborema Province prior to the amalgamation of West Gondwana,presumably the Pharusian Ocean. The southeastern limit of thisdomain is the Senador Pompeu Lineament, which is a major tectonicboundary between the Central Ceará domain and the Rio Grande doNorte domain to the east (Fig. 1B).

The plutonic rocks of the Santa Quitéria magmatic arc enclose alarge variety of dioritic to granitic lithologies and is flanked byvolcanic, volcanoclastic and calc-silicate rocks, gneiss and migmatites,schists, quartzites, marble and, turbidites, generally named CearáGroup and interpreted as a passive margin-type sedimentary unit(Arthaud et al., 2008). The U–Pb ages obtained so far from thebatholith inmetagabbro and granitic gneiss, range from 665 to 620Marespectively, although the outlying remnants of supracrustal rockssuggest that the development of this arc could have begun as early as775 Ma (Fetter et al., 2003). Nd isotopic signatures are consistent withvariable mixtures between juvenile Neoproterozoic magmas and thesurrounding Paleoproterozoic gneisses (or lithosphere), indicatingthat the complex represents neither a juvenile arc nor a suite of crustalmelts, but probably the remnants of a pre-collisional early Brasilianocontinental arc (Fetter et al., 2003).

The western portion of the Santa Quitéria batholith comprises asequence of biotite gneiss, sillimanite–garnet gneiss, muscovite–sillimanite quartzite, quartz–muscovite schist, amphibole gneiss,granitic augen gneiss, garnet-bearing leucogranite and mafic rocks(Fig. 2). These rocks display a predominant N–S low-angle E-dippingfoliation and low-medium (around 30°) E or SE-plunging stretchinglineation defined by sillimanite, quartz, biotite and muscovite.Towards west, the thrusting event evolves progressively to thestrike-slip event, the main manifestation of which is a pervasiveNE–SW to NS-trending and steeply dipping foliation with NE–SW toN–S oriented stretching lineation. The orientation of the foliations andlineations and kinematic features (S–C structures, asymmetricfeldspar and, mica-fish) indicate an evolutionary history with west-northwestward thrusting progressively changing to an overall dextralstrike-slip motion along NESW-trending shear zones.

Small bodies of metamorphosed mafic rocks, ranging from 0.5 to100 m in width and 0.2 to 6 km in length, are present frequentlyadjacent to shear zones and are represented by garnet–clinopyrox-enites, garnet–amphibolites, and incipient metagabbro–norite rockswith relicts of porphyritic or gabbro-ophitic texture. These rocks occuras enclaves, boudins, dismembered blocks, and sheets, withinmigmatite-greygranitic gneiss, granitic to ultramylonitic augen gneiss,amphibolites andmetasedimentary rocks. These rockswere submittedto amphibolite- to granulite-facies metamorphic conditions similar tothe surrounding metasediments.

Fig. 2. Simplified geological map of the Médio Coreaú Domain. Explanations in the text.

457T.J.Saraiva

dosSantos

etal./

Gondw

anaResearch

15(2009)

454–470

Table 1Representative analyses of garnet from the Ceará Central high-pressure mafic and metapelitic rocks.

Sample TJFC302 TJFC302 TJFC306 TJFC306 vc57a vc57a vc57 g vc57 g vc60 vc60 WT8-17a WT8-17a WT8-17b WT8-17b

Core Rim Core Rim Core Rim Core Rim Core Rim Core Rim Core Rim

SiO2 39.36 38.99 38.03 38.55 38.08 37.67 37.93 37.81 38.22 38.20 38.12 37.59 37.20 38.42TiO2 0.06 0.03 0.07 0.11 0.04 0.05 0.14 0.03 0.24 0.06 0.05 0.01 0.49 0.02Al2O3 22.55 22.66 22.12 22.08 21.82 21.76 21.60 21.75 21.92 21.97 22.10 22.13 22.08 22.12Cr2O3 0.10 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00FeO 19.92 21.49 23.52 24.01 28.53 27.51 25.48 27.84 22.57 25.10 30.15 33.18 31.99 32.52MnO 0.35 0.55 0.36 0.51 0.74 0.93 0.36 0.51 0.37 0.60 0.61 0.58 0.92 0.70MgO 9.06 8.26 3.79 4.88 5.09 4.85 3.66 3.41 5.69 4.94 4.56 5.32 3.40 5.81CaO 9.17 8.42 12.22 10.37 6.73 6.38 11.17 9.22 10.51 9.15 4.69 1.85 4.04 2.40Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Total 100.57 100.57 100.10 100.51 101.03 99.16 100.33 100.56 99.53 100.01 100.28 100.66 100.12 101.98Si 2.96 2.95 2.96 2.98 2.96 2.98 2.96 2.96 2.96 2.97 3.00 2.95 2.96 2.97AlIV 0.04 0.05 0.04 0.02 0.05 0.02 0.04 0.04 0.04 0.03 0.00 0.05 0.04 0.03AlVI 1.96 1.98 1.99 1.99 1.95 2.00 1.95 1.97 1.97 1.99 2.05 2.00 2.03 1.98Ti 0.00 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.03 0.00Cr 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Fe2+ 1.25 1.36 1.53 1.55 1.85 1.82 1.66 1.82 1.46 1.63 1.98 2.18 2.13 2.10Mg 1.02 0.93 0.44 0.56 0.59 0.57 0.43 0.40 0.66 0.57 0.53 0.62 0.40 0.67Mn 0.02 0.04 0.02 0.03 0.05 0.06 0.02 0.03 0.02 0.04 0.04 0.04 0.06 0.05Ca 0.74 0.68 1.02 0.86 0.56 0.54 0.93 0.77 0.87 0.76 0.40 0.16 0.35 0.20Na 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Alm 41 45 51 52 61 61 55 60 48 54 67 73 72 70Grs 24 22 34 29 18 18 31 26 29 25 13 5 12 7Prp 34 31 15 19 19 19 14 13 22 19 18 21 14 22Sps 1 1 1 1 2 2 1 1 1 1 1 1 2 2

Total cations calculated for 12 oxygens.

458 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

Dehydration melting in metapelites has been observed east of theForquilha city where sillimanite metapelites are invaded by severalquartzo-feldspathic veinlets and veins containing garnet as thedominant ferro-magnesian mineral (+rutile+sillimanite+graphite).In such cases, the related country rocks show a prograde replacement ofbiotite by garnet along the vein margins. Both patches and layers of

Table 2Representative analyses of clinopyroxene from the Ceará Central high-pressure mafic and m

Sample VC-302 VC-302 TJF6-306 TJF6-306

SiO2 53.36 56.66 52.63 52.50TiO2 0.05 0.10 0.07 0.19Al2O3 1.89 17.12 1.25 2.76FeO 6.18 2.29 8.24 8.21Cr2O3 0.18 0.00 0.08 0.03MnO 0.04 0.04 0.13 0.10MgO 14.76 5.59 13.81 12.98CaO 23.32 13.19 23.57 23.20Na2O 0.55 4.80 0.36 0.61K2O 0.00 0.02 0.01 0.01Total 100.35 99.80 100.14 100.58Si 1.96 2.05 1.95 1.94Al 0.08 0.73 0.05 0.12Ti 0.00 0.00 0.00 0.01Fe 0.19 0.07 0.26 0.25Cr 0.01 0.00 0.00 0.00Mg 0.81 0.30 0.76 0.72Mn 0.00 0.00 0.00 0.00Ca 0.92 0.51 0.94 0.92Na 0.04 0.34 0.03 0.04K 0.00 0.00 0.00 0.00WO 48 58 48 49EN 42 34 39 38FS 10 8 13 14JD 4 43 3 4Mg/(Mg+Fe) 0.81 0.81 0.75 0.74Na/(Ca+Na) 0.04 0.40 0.03 0.05

Total cations calculated for 6 oxygens.

garnet-bearing leptynites (=khondalites) considered as neosomes areinterlayered with sillimanite–biotite micaschists. The end-member ofthis assemblage is represented by lenses of a typical kinzigite/khondalite association. Fine-grained layers and lenses of pyrigarnite toretrograded eclogite are enclosed within the metapelitic granulites.Some stocks of garnet-bearing porphyritic granite (=charnockitic

etapelitic rocks.

VC-57A VC-57A VC-57g VC-57g VC-60 VC-60

51.69 51.01 51.84 51.10 52.30 52.380.28 0.15 0.10 0.35 0.22 0.232.22 2.12 1.34 2.18 1.82 2.0111.84 13.70 12.21 11.86 9.06 9.030.08 0.06 0.05 0.00 0.00 0.000.12 0.14 0.06 0.08 0.06 0.1012.02 11.09 11.33 11.18 13.18 13.1821.04 20.85 22.49 22.35 22.56 22.500.82 0.85 0.51 0.60 0.49 0.610.04 0.03 0.01 0.02 0.00 0.00100.14 99.99 99.93 99.72 99.70 100.031.94 1.93 1.96 1.93 1.96 1.950.10 0.09 0.06 0.10 0.08 0.090.01 0.00 0.00 0.01 0.01 0.010.37 0.43 0.39 0.38 0.28 0.280.00 0.00 0.00 0.00 0.00 0.000.67 0.63 0.64 0.63 0.74 0.730.00 0.01 0.00 0.00 0.00 0.000.85 0.85 0.91 0.91 0.90 0.900.06 0.06 0.04 0.04 0.04 0.040.00 0.00 0.00 0.00 0.00 0.0045 44 47 47 47 4736 33 33 33 38 3820 23 20 20 15 156 6 4 4 4 40.64 0.59 0.62 0.63 0.72 0.720.07 0.07 0.04 0.05 0.04 0.05

Table 3Representative analyses of plagioclase from the Ceará Central high-pressure mafic and metapelitic rocks.

Sample TJF5-302 TJF5-302 TJF5-306 TJF5-306 Vc-57a vc-57a VC-57g VC-57g VC-60 VC-60 WT8-17a WT8-17a WT8-17b

Position Corona Symp Corona Symp Corona Symp Core Rim Corona Symp Inc Matrix Matrix

SiO2 59.72 60.23 59.13 61.13 64.43 61.98 62.22 62.81 61.90 62.33 62.68 62.05 61.96TiO2 0.03 0.01 0.00 0.00 0.00 0.06 0.01 0.00 0.00 0.04 0.02 0.00 0.00Al2O3 25.51 24.83 26.07 24.31 22.74 24.02 23.67 23.83 24.07 23.61 24.09 23.77 23.94Fe2O3 0.29 0.26 0.15 0.11 0.11 0.19 0.18 0.11 0.11 0.12 0.06 0.02 0.06MnO 0.01 0.01 0.00 0.00 0.00 0.00 0.03 0.00 0.04 0.00 0.00 0.01 0.00MgO 0.01 0.01 0.01 0.01 0.03 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.05CaO 7.58 6.33 7.85 5.99 3.93 5.34 5.53 4.73 5.72 4.93 5.72 4.74 4.68Na2O 7.57 8.25 7.05 8.16 9.25 8.51 8.43 8.82 8.35 8.76 6.69 8.27 8.53K2O 0.05 0.01 0.11 0.17 0.10 0.11 0.23 0.24 0.11 0.10 0.17 0.45 0.13Total 100.77 99.94 100.36 99.86 100.59 100.21 100.30 100.55 100.31 99.89 99.42 99.41 99.36Si 4.14 4.20 4.11 4.25 4.41 4.29 4.30 4.32 4.28 4.32 3.80 3.68 3.81Al 2.08 2.04 2.13 1.99 1.84 1.96 1.93 1.93 1.96 1.93 1.13 0.00 1.11Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.66 0.00Fe3+ 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Mg 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01Ca 0.56 0.47 0.59 0.45 0.29 0.40 0.41 0.35 0.42 0.37 0.38 0.30 0.31Na 1.02 1.11 0.95 1.10 1.23 1.14 1.13 1.18 1.12 1.18 0.81 0.95 1.02K 0.00 0.00 0.01 0.02 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.03 0.01Ab 64 70 62 71 81 74 72 76 72 76 67 74 76An 36 30 38 29 19 26 26 23 27 24 32 23 23Or 0 0 1 1 1 1 1 1 1 1 1 3 1

Total cations calculated for 8 oxygens.

459T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

granite with euhedral K-feldspar megacrysts) have also been observedin the same unit. They are preserved as boudins within common Kfeldspar strongly foliated to mylonitic orthogneiss that represents aretrograded end-member coeval with the sillimanite-bearing mineralassemblages.

3. Petrography and mineral chemistry

Five samples of garnet–clinopyroxene amphibolites collected fromthe western part of the Santa Quitéria magmatic arc were selected fordetailed petrographic studies, mineral chemical analyses, and ther-mobarometric computations). Mineral analyses were carried out atthe Electron Microprobe Laboratory at the University of São Paulo

Table 4Representative analyses of amphibole from the Ceará Central high-pressure mafic and meta

Sample TJF302 TJF302 TJF306 TJF306 VC5

SiO2 44.58 45.29 45.11 45.83 43.3TiO2 0.90 1.08 1.18 0.97 1.47Al2O3 13.03 13.43 12.35 11.63 12.0FeO 10.81 9.79 13.73 14.08 17.6MnO 0.03 0.07 0.12 0.12 0.10MgO 13.65 14.41 11.92 12.46 10.3CaO 11.74 12.09 11.81 12.12 11.13Na2O 2.29 2.19 1.61 1.51 2.40K2O 0.13 0.08 0.47 0.41 0.39F 0.00 0.00 0.00 0.00 0.00Cl 0.00 0.00 0.00 0.00 0.00Total 97.17 98.42 98.30 99.13 98.9Si 6.44 6.43 6.52 6.57 6.33AlIV 1.56 1.58 1.48 1.43 1.67AlVI 0.65 0.67 0.63 0.53 0.41Ti 0.10 0.12 0.13 0.11 0.16Fe3+ 0.42 0.38 0.40 0.48 0.70Fe2+ 0.89 0.78 1.26 1.21 1.46Mn 0.00 0.01 0.02 0.01 0.01Mg 2.94 3.05 2.57 2.66 2.26Ca 1.82 1.84 1.83 1.86 1.74Na 0.64 0.60 0.45 0.42 0.68K 0.02 0.02 0.09 0.07 0.07

Structural formulae calculated to 13 cations excluding Ca, Na, and K. Total cations calculate

Institute of Geosciences using a JEOL/JXA-8600 electron microprobemicroanalyser with five spectrometers, operating in EDS (energydisperse system) and WDS (wavelength disperse system) modes. TheTracor Northern/Noran Instrument (1990) analysis system operatedunder the following routine conditions: a) Beam current: 20 nA; b)Beam diameter: 5 µ; c) Accelerating potential: 15 kV. Representativemineral analyses are given in Tables 1–4. Fe 3+calculations accordingto Droop (1987). Mineral abbreviations follow Kretz (1983).

The basic bodies occur as lenses and/or boudins in differentdegrees of amphibolitization interlayered within banded, granulite-facies partially migmatized gneisses. The cores of these bodies arenormally massive, whilst towards their borders the rock is foliated oreven mylonitized. When present, the foliation is defined by elongated

pelitic rocks.

7A VC57A VC57G VC57G VC60 VC60

7 43.41 43.43 42.99 44.53 45.331.31 1.87 1.88 1.83 1.63

5 10.62 11.78 11.65 11.31 10.415 19.41 16.84 17.98 14.22 13.92

0.10 0.07 0.05 0.07 0.079 9.42 9.50 9.37 12.14 12.56

11.02 11.26 11.35 11.39 11.182.08 1.96 1.91 2.03 1.860.35 0.55 0.52 0.19 0.200.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00

7 97.72 97.25 97.70 97.69 97.146.47 6.49 6.41 6.49 6.601.53 1.51 1.59 1.52 1.400.33 0.56 0.46 0.43 0.390.15 0.21 0.21 0.20 0.180.72 0.25 0.43 0.53 0.601.70 1.85 1.81 1.20 1.100.01 0.01 0.01 0.01 0.012.09 2.12 2.08 2.64 2.731.76 1.80 1.81 1.78 1.750.60 0.57 0.55 0.57 0.520.07 0.10 0.10 0.04 0.04

d for 23 oxygens.

460 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

garnet crystals and symplectitic aggregates, as well as retrogradedamphibole porphyroblasts. The essential mineral phases are garnet,clinopyroxene, amphibole, plagioclase, and quartz, with minor rutile,ilmenite, titanite, and apatite.

The main textural features common to all the samples aresymplectites or aggregates formed after Na-rich clinopyroxenebreakdown and reaction coronas surrounding garnet (Fig. 3A). Themost common symplectites are represented by clinopyroxene+plagioclase±amphibole intergrowths (Fig. 3C), but two other types ofsymplectites have also been observed: ilmenite+clinopyroxene andilmenite+plagioclase (Fig. 3E), probably after titanite and/or rutile,which occur locally as an important phase. The coronas around garnet

Fig. 3. A) Plagioclase coronas around garnet and Pl+Cpx±Amp symplectites. VC-60; B) Pclinopyroxene pseudomorphs and plagioclase coronas. VC-60; D) Cpx–Pl symplectites showinfoliated sample. TJF6-302; E) Ilm+Pl symplectites indicating retrograded stages in the meretrogressed sample showing transition to actinolitic compositions. VC-57a.

are normally granoblastic, consisting of a plagioclase inner rim and aclinopyroxene and/or amphibole outer rim of variable thickness. Ingeneral, the thinner plagioclase coronas are associated with clinopyr-oxene-rich rims. Additionally, two samples of coarse-grained, foliatedgarnet–kyanite–biotite–K-feldspar gneisses that represent the countryrock for the basic bodies were also analysed. In these rocks an early,granulite-facies peak assemblage composed of Ky+Bt1+K-fsp+Grt+Rut+Qtz in preserved in pods. Evidence of partial melting is theproduction of leucocratic veins and k-feldspar+kyanite assemblages.Biotite occur both as inclusions in the rims of the garnet and in kyaniteand in pressure shadows and matrix. Rutile is an important phase thatappears as common inclusion in kyanite and in garnet, as well as in the

l+Qtz+Cal+Tnt granoblastic inclusions in garnet. VC-306; C) Symplectitic high-Nag optical discontinuity possibly related to pseudomorphs after Na-rich clinopyroxene intabasic rock. VC-57g; and F) Plagioclase+amphibole coronas around garnet in more

461T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

matrix. Other accessory minerals include ilmenite, apatite, monazite,and zircon.

In the mafic rock garnet occurs as 1- to 3-mm porphyroblastsforming either clusters or individual grains sometimes concentratedwithin foliation-parallel layers or randomly distributed in the matrix.Inclusions are rare or absent, and the most frequent ones being mono-to polymineralic rutile and quartz. In some samples garnet showsinclusion-free rims and cloudy, dusty cores with both tiny mineralinclusions and granoblastic Cal+Pl+Rt+Qtz or Tnt+Pl+Ilmassemblages taken as a possible pre-eclogite stage (Fig. 3B). In themetapelitic samples, garnet occur as pre- to syn-kynematic crystals aslarge as 1–2 cm that may contain normally oriented quartz, ilmenite,and rutile inclusions. Biotite inclusions were found near the rims.Garnet compositions for both lithotypes are shown in Fig. 4 and onlyslight variations in compositional zoning were detected in theanalysed garnet grains. The grains from the metabasites show ageneral increase in Fe and a decrease in Mg and Ca from core to rim. Inall the samples except one, the Fe contents range between 50 and60 wt.% and MgbCa. Late retrogressive effects in these types probablyinclude an increase in the average Fe contents and a gradual change inMg and Ca values, from MgbCa (TJF6-306, VC-57g—related to thepresence of titanite) to similar values toward the rims (VC-60). In themost retrogressed sample, Mg and Ca contents are very similar (VC-57a). Sample TJF6-302 shows an opposite behavior, with almandinecontentsb50% and MgNCa. Most of the samples plot in the high-pressure eclogite field (C-type), except for sample TJF6-302, whichplots mostly in the B-type, medium-pressure eclogite field (Fig. 4). Inthe metapelitic gneisses the garnet is almandine-rich with nearly flatpatterns in which grossular and pyrope end members have comple-mentary distribution. Mg/Fe ratios increase abruptly towards theoutermost rim. In all the rock types, spessartite contents are negligible.

Pyroxene occurs mainly as granoblastic clinopyroxene aroundgarnet and as pseudomorphs formed by plagioclase-diopsidic

Fig. 4. Compositional ranges of garnet from the Ceará Central high-pressuremafic andmetapecompositions from rims to cores in each sample. Eclogite classification fields follow Colemangneissic terranes (Medium Pressure); and C) eclogitic lenses in alpine-type metamorphic r

clinopyroxene-(and subordinate amphibole) symplectites in opticalcontinuity either in massive or foliated rocks (Fig. 3C, D). In somesamples, the former ferromagnesian minerals are clearly replaced byfine grained secondary clinopyroxene plus plagioclase. Developmentof narrow rings of pyroxene between quartz and plagioclase is alsocommon. These symplectitic agglomerates are locally rimmed bynarrow, discontinuous amphibole strings that were interpreted asthe original boundaries of the former Na-rich clinopyroxene grains.No pyroxene was found as inclusions in garnet. These mineralreactions point to progressive retrogression from eclogite to garnetamphibolite. In the least retrogressed samples, garnet grains arerimmed solely by thin plagioclase+pyroxene association. In all therocks analysed, the primary Jd-rich clinopyroxene was replaced bycalcic types, mainly diopside, except for sample VC-57a, in whichaugitic compositions were detected (Fig. 5A). The chemical composi-tions of clinopyroxene vary significantly among the samples, al-though no marked zonation was observed from rims to cores in thepyroxenes, as well as from granoblastic grains to symplectites. Mg/(Mg+Fe) ratios vary from 0.59 to 0.81 and the most retrogressedsamples present the lowest values. Plots of Mg/(Mg+Fe) vs. Na/(Ca+Na) ratios show chemical internal variations that were probablygenerated by exhumation processes (Fig. 5B). More diopsidiccompositions are shown by most of the samples (XMg=0.71–0.81), but in samples VC-57a and VC-57b these values are in the rangeof 0.59–0.64. Average compositions of the clinopyroxenes showdiopsidic values (EN32–44; WO42–48), attaining 43% of jadeite contentin sample TJF6-302, near the core of an Na-rich clinopyroxenepseudomorph formed by pyroxene+plagioclase symplectites.Augite-rich compositions were detected in sample VC-57a, both inrims and symplectites.

Dark green amphibole commonly occurs as large, partiallyoriented grains in the matrix or as a minor component ofplagioclase+clinopyroxene symplectites. Depending on the degree

litic rocks shown in a Alm+Sps–Grs–Prp diagram. The arrows senses indicate changinget al. (1965): A) eclogite inclusions in mantelic rocks; B) eclogite lenses in migmatitic

ocks (High Pressure).

Fig. 5. A) Chemical classification of clinopyroxene from the Ceará Central high-pressure mafic rocks; and B) Mg/(Fe+Mg)–Na/(Ca+Na) plot.

462 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

of retrogression, this mineral appears in lighter colors. Nearly all theamphiboles analysed are calcic types varying from tschermakitichornblende to magnesium hornblende, with minor pargasitichornblende (Fig. 6A). In general, the less retrogressed samplesshow higher Al contents in comparison to those showing actinoliticcompositions (Fig. 6B). In sample VC-57a, the amphibole composi-tions plotting near actinolitic hornblende field show retrogradeeffects (Fig. 3F).

Plagioclase in the metabasites occurs mainly as recrystallizedgrains in coronas around garnet and also as granoblastic in-

clusions in garnet. The composition of the plagioclase varies fromoligoclase to andesine (An19-38) (Fig. 7). No compositional var-iations were observed from cores to rims. In the metapeliticsamples recrystallized and relic plagioclase is oligoclase to ande-sine (An23-32), whilst those found as exsolutions in K-feldspar arealbite.

Rutile and ilmenite are ubiquitous accessory phases. The formerappears as well-formed to globular grains included in garnet andwithin amphibole, or associated with the symplectites, possiblyrepresenting former inclusions in the Na-rich clinopyroxene. Ilmenite

Fig. 6. A) Chemical classification of amphibole from the Ceará Central high-pressure mafic; and B) concentration of Al in four- and six-fold coordinates sites for amphiboles.

463T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

is restricted to the matrix and also occurs as symplectitic phasetogether with plagioclase and clinopyroxene.

4. P–T conditions

In order to estimate the metamorphic conditions, we employedboth conventional thermobarometry based on local mineral equili-brium and the average P–T calculations based on Thermocalc (Powellet al., 1998) with its internally consistent thermodynamic dataset(Powell and Holland, 1988). Wherever possible, P–T calculations weredone using the core and rim compositions or garnet, but the absenceof garnet in some of the retrograde stages precluded the computation

of temperature and pressure for these stages. For Thermocalc, the 2σerrors are automatically calculated. For the conventional thermo-barometers, errors were estimated on the basis of their upper andlower limits based on compositional variations. As pre-peak meta-morphic conditions were not found in any of the samples analysedonly the retrograde path could be delineated.

4.1. Eclogite stage

In the samples analysed, the high-pressure eclogite assemblagesare represented by Na-rich clinopyroxene+pyrope-rich garnet+rutile+quartz. It is to be noted here that we could not get any relict

Fig. 7. Chemical classification of plagioclase from the Ceará Central high-pressure mafic and metapelitic rocks.

464 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

omphacite, and the calculations are based on the jadeite-richclinopyroxene. Temperatures for this stage were estimated usingdifferent calibrations based on Fe–Mg exchange between garnet andclinopyroxene (Ellis and Green, 1979; Powell, 1985; Krogh, 1988),calculated using the PTMAFIC software (Soto and Soto, 1995).Equilibration pressures for the eclogite-facies assemblage werecalculated on the basis of the jadeite content in clinopyroxene basedon the albite breakdown reaction: Ab=Jd+Qtz. For XJd=0.43 at770 °C the calibration of Holland (1980) gives a pressure of 16.8 kbar,whilst the ternary solid solutionmodel of Meyre et al. (1997) indicatesa value of 17.8 kbar. As only secondary plagioclase was found in themineral assemblage, forXAb in plagioclase=1.these values are taken asminimum pressures. These P–T conditions possibly represent meta-morphism at depth either from a represent deep highly thickenedcrust or through deep subduction.

4.2. Granulite stage

This early retrograde stage in the granulite field is represented bythe appearance of plagioclase+augite coronas around garnet and byplagioclase+augite symplectites as a result of the breakdown of Na-rich clinopyroxene possibly according to the reaction Omph+Qtz=Na−Pl+Cpx. These reaction textures are normally taken asrepresentative of eclogite- to granulite facies-transition and have beenidentified in many similar terranes (O'Brien, 1989; Oh and Liou, 1988;Ni et al., 2006; Zhang et al., 2006). The geometric organization of thisvermicular texture suggests replacement along cleavage planes andfractures. To calibrate this first retrograde stage, we used augiticcompositions found in well-defined former Na-rich clinopyroxenepseudomorphs from sample VC-57a associated with Pl (An19–26),garnet coronas and domains of garnet core to inner rim compositions(Alm58-60-Grs18-19-Prp19-21), as well as diopside+plagioclase(An24-36)+amphibole from samples TJF6-302 and VC-60. Averagevalues of 870±40 °C for 14.5±1.5 kbar were calculated using theinternally consistent data of Thermocalc.

Slightly lower values were obtained for the metapelitic gneisses, inwhich pressure estimates were made with the GASP-GPAQ barometeraccording to the Hodges and Crowley (1985), Koziol and Newton(1988) and Koziol (1989) calibrations, using the GPT spreadsheet(Reche and Martinez, 1996). For a minimum reference temperature of700 °C values of 11.7 to 13.2 kbar were obtained. Lack of biotiteinclusions in the innermost part of the garnet and the spuriouschemical results obtained from the rutile and/or ilmenite analysesprecluded the use of garnet–biotite Fe–Mg exchange or ilmenite–garnet association for thermometric calculations using core composi-tions. Temperature estimations were then obtained from phaseequilibrium considerations. The kyanite+K-feldspar assemblage,typical of high-pressure granulite-facies metapelites and formed bythe reaction Ms+Qtz=Als+K−Fsp+Melt was used to set thelower temperature limit, whilst the upper limit was determined by thereaction Bt+Grt=Opx+Als+Melt, which marks the appearance oforthopyroxene in metapelitic rock compositions, since this mineralwas not observed in the samples. Temperature estimations lie in the720–840 °C range, which are in good agreement with those foundfrom mafic assemblages.

The eclogite- to granulite-facies transition conditions suggest aclockwise path and similar results were found by Affaton et al. (2000)for the Dahomeyide suture in Togo. On the other hand, anticlockwisepaths were obtained by Agbossoumondé et al. (2004) for coroniticmetanorites from the Agou Massif and recent studies in metanoriticrocks east of the Santa Quitéria magmatic arc reveal a nearly-isothermal pressure increase related to the replacing of opx-bearing,cpx-free assemblages by typical HP granulite-facies, cpx+grt assem-blages. It is then possible that the two types of rocks register distinctP–T conditions, probably associated with their position in relation tothe respective sutures. Also, similar HP metamorphism followed by atemperature increase to high-temperature conditions during retro-grade evolution was recently recorded from the collisional suture insouthern India during the assembly of Gondwana (Shimpo et al.,2006).

465T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

4.3. Amphibolite stage

This stage is marked by the formation of mainly small amphibolecrystals around the clinopyroxene+plagioclase symplectites andaround garnet coronas formed by plagioclase, possibly by partialhydration of the previous assemblage. Replacement of rutile and/orilmenite by titanite occurred probably in this stage. For thedetermination of symplectite equilibria we used the Holland andBlundy (1994) plagioclase–hornblende geothermometer, whichpoints to P–T ranges between 5–7.5 kbar and 530–700 °C for theformation of the symplectites (Fig. 8). Average calculations usingThermocalc equilibria in two samples (TJF6-302 andVC-57g) gave741±93 °C and 12.2±1.7 kbar. Textural andmineralogical observations showthat the formation of the symplectites continued until the amphibolite–

Fig. 8. Plots of hornblende–plagioclase thermo

epidote transition. The thermobarometer based on the total Al contentin amphibole vs. An content in plagioclase (Plyusnina, 1982) was usedfor the calibration (Fig. 9A). The error estimate for this geothermometerdepends on the analytical uncertainties in mineral compositions.Considering an average error of 1.0 mole% for both Al in amphiboleand Ca in plagioclase, the standard deviation would be ±1.0 kbarand ±10–15 °C. Jd contents of 7–8% are consistent with minimalpressures of 6.7 kbar for the retrograde assemblages. Evidence for thisstage was found in all the samples analysed, which attained relativelyhigh temperatures. Hornblende-bearing retrograded eclogites arenormally taken as representative of hot types, formed under relativelyhigh geothermal gradients, with P/T ratios similar to that of theamphibolite facies (Heinrich,1986; Liu et al.,1996; Aoya, 2001). Plots onthe formula proportion diagrams of Laird and Albee (1981) in the study

barometer of Holland and Blundy (1994).

Fig. 9. A) Diagram showing the results for the experimental hornblende–plagioclasethermobarometer of Plyusnina (1982); and B) diagram for temperature based onhornblende–plagioclase equilibria of Spear (1980).

466 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

of amphibole chemical variations in the metamorphic series of theregion of Vermont showing compositional sense arrows for high-,medium-, and low-pressure mafic schists indicate that, indeed, all theamphibole was formed under medium- to low-pressure conditions(Fig. 10).

4.4. Epidote amphibolite stage

The formation of titanite coronas around ilmenite and thetransformation from andesine to oligoclase, as well as a markeddecrease in the Al, Ti, and Na contents in amphibole, were taken as

evidence for the transition from amphibolite to epidote–amphibolitefacies. This retrogressed stage was calibrated in all samples usingconventional thermobarometric techniques using thermobarometersof Holland and Blundy (1994) and Plyusnina (1982), together with thethermometer of Spear (1980)—(Fig. 9A–B). The experimental work ofMoody et al. (1983) was used to constrain the lower limits ofamphibolite to epidote–amphibolite-facies (following Bücher andFrey, 1994). Average values of 595±87 °C for 5.1±1.3 kbar wereobtained for the epidote–amphibolite assemblages.

4.5. Greenschist stage

A final retrograde phase, probably related to the last stages ofunroofing, was reported locally as the formation of Mg-rich chlorite andbiotite after garnet along fractures and by the replacement of calcichornblende by actinolite along borders and cleavage planes. Approx-imate P–T conditions (460±40 °C for 4.1±1.0 kbar) were estimatedusing actinolitic compositions of hornblende vs. Ca content inplagioclase in sample VC-57g according to the diagram of Plyusnina(1982)—Fig. 9A.

5. Discussion and conclusions

Recent concepts on the assembly of the supercontinent Gondwana(e.g., Meert and Lieberman, 2008, and references therein) hasprovided increasing focus for correlation between the geology of W/NW Africa and E/NE Brazil. A large number of studies during the last20 years have addressed the geologic, tectonic, metamorphic,magmatic and isotopic aspects from the Borborema Province, NEBrazil, and the Dahomeyides/Pharusian Foldbelt in Ghana, Nigeria,Togo, Benin, Mali and Algeria and the Central African Foldbelt inNigeria, Cameroon, Chad and Central African republic (Caby, 1989;Castaing et al., 1994; Trompette, 1997; Arthaud et al., 2008; VanSchmus et al., 2008; Santos et al., 2008; Klein and Moura, 2008;Goscombe andGray, 2008; Vaughan and Pankhurst, 2008; Bueno et al.,2009). Many of the correlations faced a hard challenge due thecomplex structure of the Borborema Province, the junction of severalBrasiliano/Pan-African foldbelts between the W-African/São Luis andthe W-Congo/São Francisco cratons. Such complexity becomes clearby the characterization of at least seven major geological domains inthe Borborema Province (e.g., Brito Neves et al., 2000). Northwardfrom the São Francisco craton they are: (1) the Sergipano domain; (2)the Pernambuco–Alagoas domain; (3) the Riacho do Pontal domain;(4) the Transverse domain with a bundle of expressive E–W trendingshear zones; (5) theRioGrandedoNorte domain; (6) the Central Cearádomain in central and eastern Ceará state and (7) the Médio Coreaúdomain, W to the Sobral fault (a local name for the Transbrasilianolineament) in NW Ceará state.

The Dahomeyides in western Africa is a Brasiliano/Pan-Africancollision foldbelt between the passive continental margin of the W-African Craton (WAC) and the Saharan Metacraton (SMC) whose activemargin is represented by the Nigerian–Togo–Benin Province (Affaton etal., 1991; Abdelsalam et al., 2002). An important piece in this model is astrip of mafic–ultramafic bodies (amphibolites, garnet amphibolites,eclogites, and granulites) which occurs mainly in the intermediatenappes of the foldbelt, an imbricated monocyclic succession of mainlymuscovite or kyanite metaquartzites, garnet–chloritoid micaschists,leucocratic gneisses, amphibolites and albite–kyanite–sillimanitegneisses. Their protoliths are mainly picritic basalts and basalts as wellas their fractionated and accumulated derivates. The strip of basic–ultrabasic rocks and some of their enclosing rocks, with positive gravityand magnetic anomalies, is interpreted as the suture of the chain (Bayerand Lesquer, 1978). The main mafic/ultramafic high-grade bodies of thesuture stripe are Seméré, Djabatou, Toutouto, Kabyé, Shai, Sotoubua, Lato,Agou, Dérouvarou, Amalaoulaou, among many others and the mafic/ultramafic rocks are generally retrograded; the granulitic and eclogitic

Fig. 10. Formula proportion diagrams for amphiboles. Arrows indicate the compositional limits of metamorphic mafic schists of Vermont (Laird and Albee, 1981). Endmemberamphibole compositions are shown as ●.

467T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

rocks back to the amphibolite and greenschist facies (Attoh, 1990;Griffiths et al.,1991; Attoh et al.,1997; Jahn et al., 2001; Agboumoussondeet al., 2001, 2004; Attoh and Morgan, 2004). There are still doubtswhether some of themafic/ultramafic rocks belong to the suture zone orto a western adjacent intraoceanic island arc comprising a volcano-volcanoclastic sequence and subducted arc roots represented by mafic–ultramafic to tonalitic rocks.

Farther to the north, in the Pharusian Foldbelt of Algeria, theoccurrence of eclogitic rocks is more diversified as they are either

Table 5Summary of the P–T results from the Ceará Central high-pressure mafic and metapelitic roc

Garnet–clinopyroxene amphibolites

Sample/stages TJFC-302 TFJC-306 VC-57a V

T (°C) P (kbar) T (°C) P (kbar) T (°C) P (kbar) T

Eclogite 770±30 17.3±0.4Granulite 898±123 15.7±1.9 873±135 14.3±2.0

874±115 12.8±2.0829±103 13.8±1.9

Amphibolite 701±110 12.4±1.7 7777

Epidote–amphibolite 610±90 6.2±1.4 597±67 4.2±1.8 620±105 6.3±1.2 6525±5 2±1

Greenschist 4

located at the 4°50′ shear zone and the W-UGI suture (Caby, 2003).The 4°50′ fault is a reactivation of a crypto-suture which marks a W-dipping 690–650 Ma subduction of the passive LATEA plate marginunder the Iskel basement generated by a 900 Ma. W-dippingsubduction. The W- and E-UGI sutures are, respectively, east- andwest-dipping 680–610 Ma. subduction zones bordering the granuliticIOGU and IGU belt considered an Archean/Paleoproterozoic micro-continent (Peucat et al., 1996; Caby, 2003). In this geological frame,the Eastern Saharan Craton is an E-Hoggar geotectonic unit which

ks using distinct thermobarometric techniques (explanations in the text).

Garnet–kyanite–biotite gneisses

C-57g VC-60 WT8-17a WT8-17b

(°C) P (kbar) T (°C) P (kbar) T (°C) P (kbar) T (°C) P (kbar)

896±114 15.8±2.1 825±25 10.2±0.6 825±25 12.1±0.4

78±109 13.2±2.2 706±74 8.7±0.6 710±70 9.8±0.556±104 12.2±2.044±102 11.7±1.925±40 11.1±0.705±90 5.7±0.7 612±82 5.9±1.7

60±40 4.1±1.0

Fig. 11. P–T paths for the high-pressure mafic (grey arrow) and metapelitic rocks (blackarrow) from Ceará Central based on thermobarometric calculations according to aseries of methods. Facies and Ky–Sil–And boundaries after Spear (1993). Jadeiteisopleths after Meyre et al. (1997) for quartz saturated systems; Al-in Hb isopleths afterPlyusnina (1982); Jd+Qtz=Ab reaction after Holland (1980, 1983); Opx-free reactionfield for mafic compositions after Pattison et al. (2003). The boxes represent P–Testimates based on compositional variations using conventional thermobarometry(empty boxes: mafic rocks; filled box: metapelites); symbols represent the centers oferror ellipses based on the 1σ uncertainties in the P–T space using Thermocalc (see textfor discussion). For reference (dashed lines and stars) are the PT paths for south Togo(Agboumoussonde, 2001).

468 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

resulted from the amalgamation of four terranes (Djounet, Edembo,Aouziquer, Borghat) prior to 700 Ma.; its contact with the centralLATEA unit is done by the 8°30′Shear Zone (Liégeois et al., 2003).

Among the many proposed links between Dahomeyides and theBorboremaProvincewhich include gravity andmagnetic data (Lesqueret al.,1984; Tohver et al., 2006), two are fundamental: (1) the proposedcontinuity between the 4°50′, Kandi and Transbrasiliano faults/lineaments and (2) the correlation of the Médio Coreaú Brasilianometasediments (NWCeará state, Brazil) with the external nappe zoneof the Dahomeyides in Ghana, Togo and Benin, which comprise theBuen, Kanté, Atacora and Kara units (Affaton,1990; Caby,1989; Caby etal., 1991; Castaing et al., 1993; Santos et al., 2008; Klein and Moura,2008). Themain suture zone for the Pharusian Ocean extends beneaththe Parnaíba Basin—this is consistent with Africa–South Americareconstructions and the TBL–Kandi lineaments (Fetter et al., 2003).This, however, does not preclude the presence of other smallersubordinate sutures within the BP. In this geological context, thedescription as well as the determination of the P–T metamorphicconditions of retrograded eclogites and garnet amphibolites from amafic/ultramafic horizon in the Central Ceará domain represents anew piece for understanding the correlation between the BorboremaProvince, NE Brazil, and theDahomeyides/Pharusides in Africa (Santoset al., 2008). The Central Ceará domain comprises a basement ofArchaean TTG association, juvenile Paleoproterozoic leucocraticgneisses and restricted granulites, all partially reworked during theBrasiliano/Pan-African orogeny. The overall geological characteristicsof the Central Ceará basement are quite similar to those of the internalnappes of the Dahomeyides. On the basement rests a sequence ofmedium-grade, high-pressure Brasiliano metasediments intruded bythe Santa Quitéria continental magmatic arc (Fetter, 1999; Fetter et al.,1997, 2000, 2003). The high-pressure mafic rocks occur as meter-thicklenses in garnet±sillimanite±kyanite-bearing schists and gneissesbuilding up an at least 10 km longNE–SW trending strip near Forquilhaat the western border of the magmatic arc. The horizon occurs in athrust belt reactivated or overprinted by an expressive younger shearfault bundle. These retrograded eclogites occurmainly as amphibolite-facies rocks in which former eclogite facies assemblages, whichincludes Na-rich clinopyroxene+pyrope-rich garnet+rutile+quartz, were found as preserved compositions. High-pressure meta-morphic peak conditions may represent very deep conditions in ahighly thickened crust and were followed by transition from eclogiticto granulitic conditions marked mainly by the appearance ofplagioclase+augite coronas around garnets and by plagioclase+clinopyroxene symplectites as a result of Na-rich clinopyroxenebreakdown. The generalized amphibolite facies stage is marked bythe crystallization of many small amphibole crystals around theclinopyroxene+plagioclase symplectites and plagioclase coronassurrounding garnets. The succeeding epidote amphibolite and greens-chist stages are registered by the formation of titanite coronas aroundilmenite and the change from andesine to oligoclase, aswell asmarkeddecrease in the Al, Ti and Na contents in the amphibole and garnetreplacement by Mg-rich chlorite and biotite and calcic hornblende byactinolite. P–T conditions for the Forquilha retrograded eclogites aresimilar to those found in the eastern side of the Santa Quitéria arc,where eclogitic peak conditions are ∼17 kb at ∼800 °C; the transitionto the granulite facies occurred at 12–15 kb and 750–850 °C and mainre-equilibration at 8.7 kb and700–800 °C (Garcia et al., 2006).The peakconditions are also about the same as for eclogites fromthe Dashomeyides and Pharusides: 690–750 °C and 25–27 kb fornorthern Mali (Jahn et al., 2001; Caby et al., 2008); 19±4 kb; 700±95 °C and 13±2 kb, 650±50 °C, respectively, for the upper and lowerLato assemblages, southern Togo (Mènot and Seddoh, 1985; Agbou-moussondé et al., 2001); 850±50 °C and 13–15 kb for the Kabyécomplex, northern Togo (Griffiths et al., 1991); 750 °C and 13–15 kb intheAleksoud area in the LATEAdomain, southernAlgeria (Barbeyet al.,1989). The metamorphic evolution of the Forquilha eclogites suggests

a clockwise P–T path, comparable to that established for theintermediate nappe zone of the Dahomeyides (Castaing et al., 1993),where evolution is related to an early HP-HT burial stage followed byoblique nappe stacking in SW direction and subsequent uplift. Asecond anticlockwise P–T path evolution as observed in the internalnappe zone is missing. The results of the P–T calculations are given inTable 5. A synthesis of the thermobarometric results is shown in Fig.11.

The occurrence of eclogites/retrograded eclogites and associatedgarnet amphibolites defining a disrupted but persistent horizon inhigh-grade schists and gneisses and bound by thrust fault reactivatedor overprinted by younger shear zones in the western neighborhoodof the Santa Quitéria magmatic arc in the Central Ceará domain of theBorborema Province is of great geological/geotectonic interest. Thishorizon, characterized in terms of metamorphism for the first time inthis work, after its discovery was tentatively correlated with theeclogites from theWest Ugi Suture Zone in the Pharusian belt, CentralHoggar, Algeria (Santos et al., 2008). More detailed studies clarifiedthat the Forquilha eclogites are rocks characterized by a clock-wise P–T path including distinct prograde and a retrograde evolutionarystages. The eclogites comprise primitive to evolved arc-related rocks;the associated amphibolites have an arc- or a MORB-imprint (Santoset al., 2007). The metamorphic P–T conditions, evolution, thegeochemical characteristics of the Forquilha rocks as well as their

469T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

thrust/shear zone bounded occurrence are quite similar to those fromthe Internal Nappes/Suture zone from the Dahomeyides in Gahna,Togo and Mali, but a direct geological correlation between the twooccurrences is inconsistent with other geological data. However, webelieve that the Forquilha horizon may be a crypto-suture in theCentral Ceará domain of the Borborema Province and an importantpiece in the Brasiliano–Pan-Afican correlation puzzle. Our study hasalso important bearing on the tectonic evolution of the Gondwanasupercontinent during its final phase of assembly in the lateNeoproterozoic–Cambrian times (cf. Meert and Lieberman, 2008). Inthis context, the high-pressure mafic-rock assemblages reported inthis study, as well as from other parts of Gondwana in recent studiesmay provide important clues to the understanding of the platetectonic architecture during the birth of Gondwana.

Acknowledgements

The authors are grateful to the FAPESP (Fundação de Amparo aPesquisa do Estado de São Paulo, grants 03/07663-3 and 07/58535)and CNPq/MCT (Conselho Nacional de (Desenvolvimento Científico eTecnológico) (millenium project proc. 42.0222/2005-7)) for thefinancial support of the field and laboratory work. We also thankAllen H. Fetter for his review and comments.

References

Abdelsalam, M.G., Liégeois, J.P., Stern, R.J., 2002. The Saharan Metacraton. Journal ofAfrican Earth Sciences 34, 119–136.

Affaton, P., 1990. Le Bassin des Volta (Afrique de l'Ouest): une marge passive, d'âgeprotérozoique supérieur, tectonisée au Panafricain (600 +50 Ma). Editions del'ORSTOM, Collection Etudes et Theses, Paris, 500 pp.

Affaton, P., Rahaman, M.A., Trompette, R., Sougy, J., 1991. The Dahomeyide orogen:tectonothermal evolution and relationships with the Volta Basin. In: Dallmeyer, D.,Lécorché, J.P. (Eds.), The West African Orogens and Circum-Atlantic Correlatives.Springer-Verlag, Berlin, pp. 107–122.

Affaton, P., Kröner, A., Seddoh, K.F., 2000. Pan-African granulite formation in the KabyeMassif of northern Togo (West Africa): Pb–Pb zircon ages. International Journal ofEarth Sciences 88, 778–790.

Agboumoussonde, Y., Menot, R.P., Guillot, S., 2001. Metamorphic evolution ofNeoproterozoic eclogites from south Togo (West Africa). Journal of African EarthSciences 33, 227–244.

Agbossoumondé, Y., Guillot, S., Menot, R.P., 2004. Pan-African subduction—collisionevent evidenced by high-P coronas in metanorites from the Agou massif (southernTogo). Precambrian Research 135, 1–21.

Aoya,M., 2001.P–T–Dpathof eclogite from theSambagawaBelt deduced fromcombinationof petrological and microstructural analyses. Journal of Petrology 42, 1225–1248.

Arthaud, M.H., Caby, R., Fuck, R.A., Dantas, E.L., Parente, C.V., 2008. Geology of thenorthern Borborema Province, NE Brazil and its correlationwith Nigeria, NWAfrica.In: Pankhurst, R.J., Trouw, R.A.J., Brito Neves, B.B., de Wit, M.J. (Eds.), WestGondwana: Pre-Cenozoic Correlations Across the South Atlantic Region. GeologicalSociety, London, Special Publications, vol. 294, pp. 49–67.

Attoh, K., 1990. Dahomeyides of Southeastern Ghana: Evidence for Oceanic Closure andCrustal Imbrication in a Pan-African Orogen. Publication occasionnelle du C.I.F.E.G.,vol. 21. BRGM, Orleans, France.

Attoh, K., Morgan, J., 2004. Geochemistry of high-pressure granulites from the Pan-African Dahomeyide orogen, West Africa: constraints on the origin and composi-tion of the lower crust. Journal of African Earth Sciences 39, 201–208.

Attoh, K., Dallmeyer, R.D., Affaton, P., 1997. Chronology of nappe assembly in the Pan-African Dahomeyide orogen, West Africa: evidence from 40 Ar 39 Ar mineral ages.Precambrian Research 82, 153–171.

Barbey, P., Bertrand, J.M., Angoua, S., Dautel, D., 1989. Petrology and U/Pb geochronol-ogy of the Telohat migmatites, Aleksod, Central Hoggar, Algeria. Contributions toMineralogy and Petrology 101, 207–219.

Bayer, R., Lesquer, A., 1978. Les anomalies gravime'triques de la bordure orientale ducraton ouest africain: géométrie d'une suture panafricaine. Bulletin SociétéGéologique de France 20, 863–876.

Black, R., Latouche, L., Liegeóis, J.P., Caby, R., Bertrand, J.M., 1994. Pan African displacedterranes in the Tuareg shield (Central Sahara). Geology 22, 641–644.

Brito Neves, B.B., Cordani, U.G., 1991. Tectonic evolution of South America during theLate Proterozoic. In: Stern, R.J., Van Schmus, W.R. (Eds.), Crustal Evolution in theLate Proterozoic. Precambrian Research, vol. 53, pp. 23–40.

Brito Neves, B.B., Campos Neto, M.C., Fuck, R.A., 1999. From Rodinia to WesternGondwana: an approach to the Brasiliano–Pan African Cycle and orogenic collage.Episodes 22, 155–166.

Brito Neves, B.B., Santos, E.J., Van Schmus, W.R., 2000. Tectonic history of the BorboremaProvince, northeastern Brazil. In: Cordani, U., Milani, E.J., Thomaz Filho, A., Campos,D.A. (Eds.), Tectonic Evolution of South America, 31st International GeologicalCongress, Rio de Janeiro, Brazil, pp. 151–182.

Bücher, K., Frey, M., 1994. Petrologenesis of Metamorphic Rocks. Springer-Verlag. Ed.,318pp.

Bueno, J.F., Oliveira, E.P., McNaughton, N.J., Laux, J.H., 2009. U–Pb dating of granites inthe Neoproterozoic Sergipano Belt, NE-Brazil: implications for the timing andduration of continental collision and extrusion tectonics in the Borborema Province.Gondwana Research, 15, 86–97.

Caby, R., 1989. Precambrian terranes of Benin Nigeria and Northeast Brazil and the LateProterozoic SouthAtlantic. Geological Societyof America, Special Papers, 230,145–158.

Caby, R., 2003. Terrane assembly and geodynamic evolution of central–western Hoggar:a synthesis. Journal of African Earth Sciences 37, 133–159.

Caby, R., Sial, A.N., Arthaud, M.H., Vauchez, A., 1991. Crustal evolution and theBrasiliano orogeny in Northeast Brazil. In: Dallmeyer, R.D., Lécorché, J.C.P.L. (Eds.),The West African Orogens and Circum-Atlantic Correlatives. Springer Verlag,Berlin, pp. 373–397.

Caby, R., Arthaud, M.H., Archanjo, C.J., 1995. Lithostratigraphy and petrostructuralcharacterization of supracrustal units in the Brasiliano belt of Northeast Brazil:geodynamic implications. Journal of South American Earth Sciences 8, 235–246.

Caby, R., Buscail, F., Dembélé, D., Diakité, S., Sacko, S., Bal, M., 2008. Neoproterozoicgarnet–glaucofanites and eclogites: new insights for subduction metamorphism ofthe Gourma fold and thrust belt (eastern Mali). In: Ennih, N., Liégeois, J.P. (Eds.),The Boundaries of the West African Craton. Geological Society of London SpecialPublications, vol. 297, pp. 203–216.

Castaing, C., Triboulet, C., Feybesse, J.L., Chèvremont, P., 1993. Tectonometamorphicevolution of Ghana, Togo and Benin in the light of the Pan-African/Brasilianoorogeny. Tectonophysics 218, 323–342.

Castaing, C., Thiéblemont, C., Triboulet, C., Chevremont, P., 1994. Paleogeographicalreconstructions of the Pan-Africano/Brasiliano Orogen: closure of an oceanicdomain or intracontinental convergence between major blocks? PrecambrianResearch 69, 327–344.

Coleman, R.G., Lee, D.E., Beatty, L.B., Brannock, W.W., 1965. Eclogites and eclogites: theirdifferences and similarities. Geological Society of America Bulletim 76, 483–508.

Droop, G.T.R., 1987. A general equation for estimating Fe 3+concentrations inferromagnesian silicates and oxides from microprobe analyses, using stoichio-metric criteria. Mineralogical Magazine, 51, 431-437.

El-Hadj Tidjani, Affaton, P., Louis, P., Socohou, A., 1997. Gravity characteristics of the Pan-African Orogen in Ghana, Togo and Benin (West Africa). Journal of African EarthSciences 24, 241–258.

Ellis, D.J., Green, D.H., 1979. An experimental study of the effect of Ca upon garnet–clinopyroxene Fe–Mg exchange equilibria. Contributions to Mineralogy andPetrology. 71, 13–22.

Fetter, A.H., 1999. U–Pb and Sm–Nd Geochronological Constraints on the CrustalFramework and Geological History of Ceará State, NWBorborema Province, NE Brazil:Implications for the Assembly of Gondwana. University of Kansas, Ph.D. thesis,164 pp.

Fetter, A.H., Van Schmus, W.R., Santos, T.J.S., Arthaud, M.H., Nogueira Neto, J.A., 1997.Geologic history and framework of Ceará State: northwest Borborema Province, NEBrazil. Actas I South American Symposium on Isotope geology, Brazil, ExtendedAbstracts, pp. 112–114.

Fetter, A.H., Van Schmus, W.R., Santos, T.J.S., Arthaud, M.H., Nogueira Neto, J.A., 2000. U–Pb and Sm–Nd geochronological constraints on the crustal evolution and basementarchitecture of Ceará State, NW Borborema Province, NE Brazil: implications for theexistence of the Paleoproterozoic supercontinent “Atlantica”. Revista Brasileira deGeociências 30, 102–106.

Fetter, A.H., Santos, T.J.S., Van Schmus, W.R., Hackspacher, P.C., Brito Neves, B.B.,Arthaud, M.H., Nogueira Neto, J.A., Wernick, E., 2003. Evidence for Neoproterozoiccontinental arc magmatism in the Santa Quitéria batholith of Ceará State, NWBorborema Province, NE Brazil: implications for assembly of West Gondwana.Gondwana Research 6, 265–273.

Garcia, M.G.M., Arthaud, M.H., Nogueira Neto, J.A., Santos, T.J.S., 2006. High-pressuregranulites of Ceará Central Domain, Borborema Province, NE Brazil. Granulites &Granulites. Brasília. CD Rom Volume.

Goscombe, B.D., Gray, D.R., 2008. Structure and strain variation at mid-crustal levels in atranspressional orogen: a review of the Kaoko Belt structure and the character ofWest Gondwana amalgamation and dispersal. Gondwana Research 13, 45–85.

Griffiths, J.B., Peucat, J.J., Ménot, R.P., 1991. Isotopic (Rb–Sr, U–Pb and Sm–Nd) and traceelement geochemistry of eclogites from the pan-African Belt: a case study of REEfractionation during high-grade metamorphism. Lithos 27, 43–57.

Heinrich, C.A., 1986. Eclogite facies regional metamorphism of hydrous mafic rocks incentral Alpine Adula Nappe. Journal of Petrology 27, 123–154.

Hodges, K.V., Crowley, P.D., 1985. Error estimation and empirical geothermobarometryfor pelitic systems. American Mineralogist 70 (7–8), 702–709.

Holland, T.J.B., 1980. The reaction albite=jadeite+quartz determined experimentallyin the range 600–1200 °C. American Mineralogist 65, 129–134.

Holland, T.J.B., 1983. The experimental determination of activities in disordered andshort-range ordered jadeitic pyroxenes. Contributions to Mineralogy and Petrology82, 214–240.

Holland, T.J.B., Blundy, J., 1994. Non-ideal interactions in calcic amphiboles and theirbearing on amphibole plagioclase thermometry. Contributions to Mineralogy andPetrology 116, 433–447.

Jahn, B.M., Caby, R., Monié, P., 2001. The oldest UHP eclogites of the world: age of UHPmetamorphism, nature of protoliths and tectonic implications. Chemical Geology178, 143–158.

Klein, E.L., Moura, C.A.V., 2008. São Luís Craton and Gurupi Belt (Brazil): possible linkswith theWest African Craton and surrounding Pan-African belts. In: Pankhurst, R.J.,Trouw, R.A.J., Brito Neves, B.B., de Wit, M.J. (Eds.), West Gondwana: Pre-CenozoicCorrelations Across the South Atlantic Region. Geological Society, London, SpecialPublications, vol. 294, pp. 137–151.

470 T.J. Saraiva dos Santos et al. / Gondwana Research 15 (2009) 454–470

Koziol, A.M., 1989. Recalibration of the garnet–plagioclase–Al2SiO5–quartz (GASP)geobarometer and application to natural parageneses. American Geophysical UnionSpring Meeting, Baltimore, Maryland. EOS, vol. 70, p. 493.

Koziol, A.M., Newton, R.C., 1988. Redetermination of the anorthite breakdown reactionand improvement of the plagioclase–garnet–Al2SiO5–quartz barometer. AmericanMineralogist, 73, 216–223.

Kretz, R., 1983. Symbols of rock-forming minerals. American Mineralogist 68, 277–279.Krogh, E.J., 1988. The garnet–clinopyroxene Fe–Mg geothermometer—a reinterpretation

of existing experimental data. Contributions toMineralogy and Petrology 99, 44–48.Laird, J., Albee, A.L., 1981. Pressure, temperature, and the time indicator in mafic schist:

their application to reconstructing the polymetamorphic history of Vermont.American Journal of Science 281, 127–175.

Lesquer, A., Beltrão, J.F., Abreu, F.A.M., 1984. Proterozoic links between northeasternBrazil andWest Africa: a plate tectonic model based on gravity data. Tectonophysics110, 9–26.

Liégeois, J.P., Latouche, P., Boughrara, M., Navez, J., Guiraud, M., 2003. The LATEAmetacraton (Central Hoggar, Tuareg shield, Algeria): behavior of an old passivemargin during the Pan-African orogeny. Journal of African Earth Sciences 37,161–190.

Liu, J., Bohlen, S.R., Ernst, W.G., 1996. Stability of hidrous phases in subducting oceaniccrust. Earth and Planetary Science Letters 143, 161–171.

Martins, G., Oliveira, E.P., Lafon, J.M., 2009. The Algodões amphibolite–tonalite gneisssequence, Borborema Province, NE Brazil: geochemical and geochronologicalevidence for Palaeoproterozoic accretion of oceanic plateau/back-arc basalts andadakitic plutons. Gondwana Research 15, 71–85.

Meert, J.G., Lieberman, B.S., 2008. The Neoproterozoic assembly of Gondwana and itsrelationship to the Ediacaran–Cambrian radiation. Gondwana Research 14, 5–21.

Mènot, R.P., Seddoh, K.F., 1985. The eclogites of the Lato hills, south Togo, West Africa:relics from the early tectono metamorphic evolution of the Pan-African orogeny.Chemical Geology 50, 313–330.

Meyre, C., De Capitani, D., Partzsch, J.H., 1997. A ternary solid solution model foromphacite and its application to geothermobarometry of eclogites from the MiddleAdula napppe (Central Alps, Switzerland). Journal of Metamorphic Geology 15,687–700.

Monié, P., Caby, R., Arthaud, M.H., 1997. The Neoproterozoic Brasiliano Orogeny inNortheast Brazil: 40Ar/39Ar and petrostructural data from Ceará. PrecambrianResearch 81, 241–264.

Moody, J.B., Meyer, D., Jenkins, J.E., 1983. Experimental characterization of thegreenschist/amphibolite boundary in mafic systems. American Journal of Science283, 48–92.

Ni, Z., Zhai, M., Wang, R., Tong, Y., 2006. Late Paleozoic retrograded eclogites fromwithinthe northern margin of the North China Craton: evidence forsubduction of thePaleo-Asian ocean. Gondwana Research 9, 209–224.

O'Brien, P.J., 1989. The petrology of retrograded eclogites of the Oberpfalz Forest,northeastern Bavaria, West Germany. Tectonophysics 157, 195–213.

Oh, C.W., Liou, J.G., 1988. A petrogenetic grid for eclogite and related facies under high-pressure metamorphism. The Island Arc 7, 36–51.

Pattison, D.R.M., Chacko, T., Farquhar, J., McFarlane, C.R.M., 2003. Temperatures ofgranulite-facies metamorphism: constraints from experimental phase equilibriaand thermobarometry corrected for retrograded exchange. Journal of Petrology 44,867–900.

Peucat, J.J., Capdevila, R., Choukroune, P., Fanning, C.M., Griffiths, J.B., Fourcade, S., 1996.Major and trace element geochemistry and isotope (Sr, Nd, Pb, O) systematics of anArchaean basement involved in a 2.0 Ga very high-temperature metamorphic(1000 °C) event: the In Ouzzal Massif, Hoggar, Algeria. Journal of MetamorphicGeology 14, 667–692.

Pimentel, M.M., Fuck, R.A., Jost, H., Ferreira Filho, C.F., Araújo, S.M., 2000. Geology of thecentral part of the Tocantins Province: implications for the geodynamic history ofthe Brasília belt. In: Cordani, U.G., Milani, E.J., Thomaz Filho, A., Campos, D.A. (Eds.),Tectonic Evolution of South America. 31st Int. Geological Congress, Rio de Janeiro,pp. 195–229.

Plyusnina, L.P., 1982. Geothermometry and geobarometry of plagioclase–hornblendebearing assemblages. Contributions to Mineralogy and Petrology 80, 140–146.

Powell, R., 1985. Regression diagnostics and robust regression in geothermometer/geobarometer calibration: the garnet–clinopyroxene geothermometer revisited.Journal of Metamorphic Geology 3, 231–243.

Powell, R., Holland, T.J.B., 1988. An internally consistent thermodynamic dataset withuncertainties and correlations: 3. Applications to geobarometry, worked examplesand a computer program. Journal of Metamorphic Geology 6, 173–204.

Powell, R., Holland, T., Worley, B., 1998. Calculating phase diagrams involving solidsolutions via non-linear equations, with examples using THERMOCALC. Journal ofMetamorphic Geology 16, 577–588.

Reche, J., Martinez, F.J., 1996. GPT: an excel spreadsheet for thermobarometriccalculations in metapelitic rocks. Computers and Geosciences 22 (7), 775–784.

Santos, T.J.S., Wernick, E., Amaral, W.S., 2007. Geochemical signatures for eclogite fromthe NW Borborema Province, Brazil. Ann. XI Congresso Brasileiro de Geoquímica.

Santos, T.J.S., Fetter, A.H., Nogueira Neto, J.A., 2008. Correlation of thewestmargin of theTransbrasiliano–Kandi Lineament in the Borborema Province (NE Brazil) andPharusian Belt (NWAfrica). In: Pankhurst, R.J., Trouw, R.A.J., BritoNeves, B.B., deWit,M.J. (Eds.), West Gondwana: Pre-Cenozoic Correlations Across the South AtlanticRegion. Geological Society, London, Special Publications, vol. 294, pp. 101–119.

Shimpo, M., Tsunogae, T., Santosh, M., 2006. First report of garnet–corundum rocks fromSouthern India: implications for prograde high-pressure (eclogite-facies?) meta-morphism. Earth and Planetary Science Letters 242, 111–129.

Soto, J.I., Soto, V.M., 1995. PTMAFIC: software package for thermometry, barometry, andactivity calculations in mafic rocks using an IBM-compatible computer. Computers& Geosciences 21 (5), 619–652.

Spear, F.S., 1980. NaSi–CaAl exchange equilibrium between plagioclase and amphibole.An empirical model. Contributions to Mineralogy and Petrology 72, 33–41.

Spear, F.S., 1993. Metamorphic Phase Equilibria and Pressure–Temperature–Time Paths,vol. 2. Mineralogical Society of America.

Tohver, E., D, Agrella-Filho, M.S., Trindade, R.I., 2006. Paleomagnetic record of Africa andSouth America for the 1200–500 Ma interval, and evaluation of Rodinia andGondwana assemblies. Precambrian Research 147, 193–222.

Trompette, R., 1994. Geology of Western Gondwana, Pan-African/Brasiliano Aggrega-tion of South America and Africa. A.A. Balkema, Rotterdam. 350 pp.

Trompette, R., 1997. Neoproterozoic (∼600 Ma) aggregation of Western Gondwana: atentative scenario. Precambrian Research 82, 101–112.

Van Schmus, W.R., Oliveira, E.P., Silva Filho, A.F., Toteu, S.F., Penaye, J., Guimarães, I.P.,2008. Proterozoic links between the Borborema Province, NE Brazil, and the CentralAfrican Fold Belt. In: Pankhurst, R.J., Trouw, R.A.J., Brito Neves, B.B., de Wit, M.J.(Eds.), West Gondwana: Pre-Cenozoic Correlations Across the South AtlanticRegion. Geological Society, London, Special Publications, vol. 294, pp. 69–99.

Vaughan, A.P.M., Pankhurst, R.J., 2008. Tectonic overview of the West Gondwanamargin. Gondwana Research 13, 150–162. doi:10.1016/j.gr.2007.07.004.

Zhang, J., Zhao, G., Sun, M., Wilde, S., Li, S., Liu, S., 2006. High pressuremafic granulites inthe Trans-North China Orogen: tectonic significance and age. Gondwana Research9, 349–362.