The neoproterozoic Mantiqueira Province and its Africanconnections: a zircon-based U–Pb geochronologic subdivision
for the Brasiliano/Pan-African systems of orogens
Luiz Carlos da Silvaa,∗, Neal J. McNaughtonb, Richard Armstrongc,Leo Afraneo Hartmannd, Ian R. Fletcherb
a Geological Survey of Brazil—CPRM/Associated Researcher at the University of Bras´ılia—UnB/SGAN 603,CONJ. J, 1o. Andar, DF 70830-030 Brasilia, Brazil
b Centre for Global Metallogeny, School of Earth and Geographical Sciences,The University of Western Australia, Nedlands 6009, Australia
c Research School of Earth Sciences, Australian National University, ANU, Canberra, Australiad Federal University of Rio Grande do Sul, UFRGS, Porto Alegre, Brazil
Received 15 April 2003; accepted 12 October 2004
Abstract
The Mantiqueira Province (MPV) is a large, complex structural province deformed by the Neoproterozoic/Early Paleozoicometrictectono-l tool for, totallinguccession
III. New, which
ngllisionalRio Pi
ion. Thellisionalecycling
Brasiliano Orogenic event in South America. Its evolution is herein detailed on the basis of the geological and gecharacterisation, structural and thermal overlapping of the distinct phases of the orogenic collage. In addition to thestructural analysis, some 50 new zircon U–Pb SHRIMP data from a large number of selected units provided a powerfuunderstanding the granitic chronostratigraphy and the orogenic evolution. We also integrated existing U–Pb analysessome 240 determinations, which also furnished important constraints to delineate the precise tectono-magmatic s(orogenic episodes).
The study delineated a highly complex evolution, comprising three successive systems of orogens: Brasiliano I, II andcrustal growth including juvenile intraoceanic volcano-plutonic arcs characterises the earlier Brasiliano I orogenic systempresents collisional climaxes at ca. 790 Ma (Embu Domain) and 730–700 Ma (Sao Gabriel Orogen). On the other hand, recycliof pre-existing crustal sources are the dominant processes operating within the systems Brasiliano II and III. The coclimaxes within the Brasiliano II are recorded at 640–620 Ma (Dom Feliciano Orogen) and 600 Ma (Paranapiacaba andenorogens), whereas the Brasiliano III climaxes are bracketed between 590–560 Ma (Arac¸uaı Orogen) and 520–500 Ma (BuziosOrogen).
The available geochronological data from the Pan-African literature suggests temporally similar orogenic successprotracted, dominantly accretionary, Pan-African I system lasts from 850 to 700 Ma, whereas the Pan-African II (copeak at 650–600 Ma) and the Pan-African III (collisional peak at 590–540 Ma) are characterised dominantly by crustal r
204 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
processes. The study reinforced previous attempts to correlate the northernmost Arac¸uaı Orogen and the West Congo Orogen(AWCO), both belonging to the system Brasiliano/Pan-African III. Additionally, our study does not confirm models for a directlinkage between the south-eastern orogens from Ribeira and Dom Feliciano belts (Brasiliano II) and the south-western Africanorogens, i.e. Kaoko, Damara, Gariep, and Saldania (Pan-African III).
Keywords:Neoproterozoic Brasiliano/Pan-African systems of orogens; Mantiqueira Province; U–Pb SHRIMP ages
1. Introduction
The Mantiqueira Province (MPV) ofAlmeida et al.(1981)is a major (ca. 700,000 km2) and highly complexstructural province deformed by the Brasiliano “Oro-genic Cycle” in South America, during the Neoprotero-zoic/Early Paleozoic (900–480 Ma). It extends from33◦ S in Uruguay to the southern border of Bahia State,Brazil (15◦ S). It is nearly 3000 km long, averaging200 km wide, and it is parallel to the South AmericanAtlantic coast along the eastern margins of the Rio deLa Plata and Sao Francisco Cratons (Fig. 1). Owing toits geographical location, flanking south-eastern SouthAmerican and facing Africa, the province is a key el-ement for unravelling connections between Brasilianoand Pan-African orogens during the amalgamation ofthe W Gondwana Supercontinent (Fig. 1).
Structural studies since the early 1980s suggestedthe MPV evolved as a Himalayan-type diachronicoblique continent-continent collision between SouthAmerican and African cratons. Early E-W, WNW-ESE or NW-SE syn-collisional tectonics, followed bydevelopment of NE-SW, NNE-SSW transpressional(dextral) shear zones, accommodated the orogenicstresses (e.g.Figueiredo and Campos Neto, 1993;Fernandes et al., 1992; Heilborn et al., 1995; Machado,1997; Ebert and Hasui, 1998; Pedrosa-Soares andWiedmann-Leonardos, 2000; Campos Neto, 2000;Trouw et al., 2000). Hence, the evolution of the dis-tinct orogens is a response to continental collision pro-c belt-p t ofe e syst dis-t andm the
distinct terranes, during the Neoproterozoic collage,giving rise to the present intricate NE-trending mosaic,characterises the main tectonic pattern of the province(Figs. 1 and 2a, b). Additionally, the transpressive sys-tems control the opening of the volcanic-sedimentarybasins, the generation of syn-transcurrent crustal plu-tons, and the terminal intrusion of the post-orogenicbatholiths.
The present study is based on two decades of sys-tematic field and laboratory research on the MPV ge-ology by the senior author, at the Geological Surveyof Brazil (CPRM). It was supported also by systematicexchange of information with researchers from severalBrazilian universities, from the South African Coun-cil for Geoscience and from the University of Stellen-bosch. These studies included field and laboratory workon both continents, with results published elsewhere(Chemale et al., 1995; Babinski et al., 1996, 1997;Gresse et al., 1996; Silva et al., 1999, 2000a, 2000b;Hartmann et al., 2000a). The synthesis of these studieswas integrated into a Ph.D. Thesis (Silva, 1999) anda (GIS)-based geological and geochronological com-pilation of the entire MPV, at 1:2,500,000.000 scale(Silva et al., 2003b).
The integration of some 50 new zircon U–PbSHRIMP analyses, partly complemented by Sm–Nddata from the southern, central-north and northdomains of the province, provide the main geochrono-logical support for this study. New U–Pb SHRIMPanalyses (Table 2) were obtained in cooperativep ndt
ingU ntedb ts nic
esses, by means of transpressional late-orogenicarallel tectonics, responsible for the developmenxtended deep shear systems. In most cases, thems are the limits of distinct terranes and separateinct records of orogenic magmatism, deformationetamorphism. Accordingly, the re-articulation of
-
rojects with the Australian National University ahe University of Western Australia.
The critical analysis and integration of the exist–Pb ages from the province literature, complemey the analyses shown inTable 2furnished consistenupport for the overall interpretation of the oroge
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 205
Fig. 1. Simplified tectonic map of the Mantiqueira Province’s orogens and terranes, modified from Siva et al. (2002e, 2002f) andDelgado et al.(2004). The inset displays the probable Mantiqueira Province position, during the assembly of the SW Gondwanaland, at ca. 560 Ma (system ofOrogens Brasiliano/Pan-African III) (Digital topography of South American from the USGS).
206 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Fig. 2. Geological map simplified (and modified) from the (GIS)-based (a) “Geological Map of the Mantiqueira Province”, Scale 1:2,500,000(Silva et al., 2002d) (Arcview edition by Joseneusa Brilhante Rodrigues) and (b) “Geological Map of the Mantiqueira Province”, Scale 1:2,500,000(Silva et al., 2002d) and the “Geological Map of Minas Gerais State, Scale 1:1,000,000 (Silva et al., 2002e) (Arcview edition by JoseneusaBrilhante Rodrigues).
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 207
Fig. 2. (Continued).
208 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
evolution. Readers interested in this complete synthe-sis, totalling some 220 analyses, should access the “Ta-ble A (Supplementary data)”, archived in the electronicdata depository from the Precambrian Research Web-site.
2. Geological setting: the polycyclic MPV
The MPV is a mosaic of distinct Neoprotero-zoic terranes that, collectively, comprise several sys-tems of orogens, preserving important infracrustaland supracrustal paleotectonic remnants ascribedto Archean, Paleoproterozoic and Mesoproterozoicmegacycles. The Brasiliano systems includes (Figs. 1and 2a, b):
(i) Neoproterozoic rifted continental margin succes-sions, locally (in the northern segment) contain-ing representatives of two Neoproterozoic, pre-Sturtian glaciogenic events. These successionswere metamorphosed under greenschist to gran-ulite facies conditions during the Neoproterozoiccollage and represent overthrusted, metasedimen-tary thrust-fold basins;
(ii) widespread Neoproterozoic-Cambrian granitoidsincluding pre-syn- to post-tectonic I-type, S-types, A-types, and alkaline associations. In thenorthern domain, the post-tectonic granitoidsare dominantly polydiapiric, zoned, I-Caledonian
x-pre-
( insem-
( antso-
ry
( zoicun-en-
al/m( o-
cesses within an orogenic zone, spanning from 880to 500 Ma.
2.1. Review of MPV geotectonic and geographicalappellations
Orogen-parallel tectonic events represented by threemajor orogenic belts were responsible by the presentextended NE-SW-trending (south domain) and theNNE-SSW-trending inflexion at the north domain.The major orogenic belts, Dom Feliciano, Ribeira andAracuaı, comprise seven orogens, discontinuously ex-posed and with some poorly constrained limits. As aconsequence, some segments of the province have re-ceived a large number of tectonic and regional des-ignations, often with conflicting significance. One ofthe most controversial issues on the tectonic evolutionis the definition of the boundary between the Arac¸uaıOrogen and the Ribeira Belt. The internal organisa-tion of the Ribeira Belt, especially its northernmosttermination is another matter of dispute in the litera-ture. Some authors (Brito-Neves et al., 1999; CamposNeto, 2000; Vlach, 2001; Cordani et al., 2002) suggestthat Embu Complex constitutes a displaced terrane, at-tached to the north-east domain of the Ribeira Belt(Paranapiacaba Orogen), during the late Brasiliano col-lage. Other authors (Wernick et al., 1993; Topner, 1996,1997; Dantas et al., 2000), based on the similar agesof syn- and post-tectonic magmatism (630–590 Ma)and similar (Paleoproterozoic) Nd model-ages from theb theys atice atede olvet arel ar-t diesb ajorc ent,s mi-n sedb )C t,ta -m do-m pia-c the
plutons; minor pre-collisional, juvenile epanded calc-alkaline associations are also resented;
iii) syn-orogenic arc-related sedimentary basand volcanic-sedimentary back arc assblages;
iv) dismembered ophiolite and ocean floor remnassociated with juvenile, pre-collisional, intraceanic arcs;
(v) late- to post-collisional volcanic-sedimentabasins;
vi) Archean, Paleoproterozoic and Mesoproteroremnants of partially reactivated terranes thatderwent Neoproterozoic overprint under greschist to granulite-facies conditions.
The study characterised distinct collisionagmatic/metamorphic peaks, followingSengor’s
1990) observations of multiple collisional pr
asement of all tectonic domains, concluded thathared (at least a final) common tectonic-magmvolution, and hence could not represent amalgamxotic terranes. Presently, we are unable to reshese crucial controversies, and we believe theyikely to remain controversial, until new detailed cographic, geophysical, structural, and isotopic stuecome available. These uncertainties are not a moncern for a descriptive review study like the preso for the purpose of this paper we adopted, withor modifications, the tectonic organisation propoy Brito-Neves et al. (1999), Campos Neto (2000,ordani et al. (2002). Accordingly, in the present tex
he north domain of the MPV comprises the Arac¸uaınd Buzos orogens (Arac¸uaı Belt, and the northernost segment of the Ribeira Belt). The centralain of the province is composed of the Parana
aba and Rio Pien orogens, the Embu Terrane and
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 209
Table 1Main geotectonic and geographical appellations for the major orogenic units and events within Mantiqueira Province
210 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Costeiro Granitic Belt (a minor domain of uncertaintectonic significance), all ascribed to the main seg-ment of the Ribeira Belt. Finally, the Dom FelicianoOrogen (Dom Feliciano Belt) and Sao Gabriel Oro-gen (Vila Nova Belt) constitute the southernmost tip ofthe province.Table 1summarises the main evolution-ary models for the orogenic/tectonic evolution and theconsequent intricate and, at some extent, conflictingnomenclature.
2.2. Reactivated Archean, Atlantican andRodinian remnants in MPV
Archean and Paleoproterozoic “basement”gneisses, are almost continuously exposed at the northdomain of the province, the Arac¸uaı Orogen. Thenorth-west and north limits of the orogen are thewest continental margin of the Sao Francisco Craton/Plate (Fig. 2b; Table 2), whereas the opposite (eastern)continental margin, probably corresponding to asegment of the Congo Craton (e.g.Pedrosa-Soares etal., 2001), is not so well defined.
In central and southern domains of the province, ow-ing to the extended exposure of the Phanerozoic coverof the Parana basin, which conceals most of the west-ern margin of the Paranapiacaba, Sao Gabriel and DomFeliciano Orogens, there are only minor segments ofexposed basement units, mostly as small basement in-liers (Fig. 2a and b;Table 2). Accordingly, the role thatthese severed basement segments played from break-u ternG
hatr aP notw , sof i,2 lec en-t ncesf cana sentr s ana es-p sials re-w -t
3. Mantiqueira multi-episodic orogenic collageand the systems of orogens Brasiliano I, II, andIII
The present correlation study based on the tectonic-magmatic and isotopic signatures of the orogenic mag-matism within the entire province is based on some180 U–Pb crystallisation ages obtained in some 160key pre-, syn- and post-orogenic units. This updateddatabase was crucial for this first attempt to the dis-crimination the precise time intervals for all pre-, syn-and post-orogenic metamorphic and magmatic stagesfrom the entire province. Complementary to the radio-metric ages, the chemical and tectonic-magmatic clas-sification of each pluton were also tabulated, respect-ing wherever possible, the original authors’ classifica-tions. The complete crystallisation and metamorphicage record is tabulated inTable 2and A. The latter (A),includes the complete references of the sources of theages and is organised accordingly to the seven orogenswhich constitute the province; within each orogen itis internally organised, accordingly to the successivepre-, syn- and post-orogenic phase. Table A (Supple-mentary data) can be accessed in the electronic datadepository with Precambrian Research Website.
The orogenic evolution of the MPV is herein anal-ysed according toSengor (1990)by which orogenicbelts are the result of the activity of a large numberof convergent (in space and in time) plate boundaries,i.e. orogenies. The amalgamation of the convergentp theN di-a oro-g osN lti-p cog-n ar-l Ma)D hasbe g-l st-i ort-l Ma.Ae yclei ear-l ry
p to reconstruction of this sector of the south-wesondwana remains uncertain.The original configurations of the continents t
ifted and drifted away (Sao Francisco, Rio de Llata, Parana, Congo and Kalahari plates?) areell-defined and the ones that took their place are
ar, speculative. Recent research (Kroner and Cordan003; Pisarevsky et al., 2003) suggests new possibonfigurations for the Rodinian assembly and fragmation. Both studies delineate important consequeor the intracontinental adjustment of South Amerind South African Neoproterozoic belts. The pree-interpretation of a large number of U–Pb ages ittempt to minimise these uncertainties in Brazil,ecially with respect to one of the most controverubjects from the Brazilian literature, the highlyorked south-eastern limits of the Sao Francisco Cra
on (Fig. 2b).
late boundaries products (orogens) gave rise toeoproterozoic orogenic collage, by means of achronous, long lasted succession (systems) ofens (Brito-Neves et al., 1999; Silva, 1999; Campeto, 2000). Within the Pan-African belts these mule orogenic collage systems have long been reised.Porada (1989)discriminates between an e
ier (900–750 Ma) Katangan, and a later (750–500amarian orogenic ‘episodes’. This major divisioneen confirmed by other studies, includingTrompettet al. (1993), who distinguished an older, lon
ived and more ubiquitous orogenic ‘episode’, lang from ca. 1000 to 600 Ma, and a younger, shived ‘episode’, bracketed between ca. 600 and 540t the same time,Black and Liegeois (1993)delin-ated a polyphase evolution for the Pan-African C
n the Saharan African domain, represented byier (730–650 Ma) juvenile, Pan-African ‘accretiona
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 211
Table 2Zircon U–Pb SHRIMP, U–Pb conventional, Pb–Pb evaporation and Sm–Nd data on granitoids, orthogneisses and felsic volcanics related to thesystems of orogens from the Mantiqueira Province (southeastern Brazil) and from the Saldania Belt (south-western Africa)
Dated unit Crystallisationage (Ma)
Metamorphicoverprinting age(Ma)
ModelTDM age(Ma)
εNd (t) Reference
System of orogens Pan-African III (Saldania Orogen)Syn-collisional plutons (South Africa)
System of orogens Brasiliano III (Arac¸uaı Orogen)Post-collisional plutons from the northern domain (ES and MG)
Younger facies of Nanuque Batholith 532± 10 n.a. L.C. da Silva (unpub-lished data) (* )
Younger facies of Muniz Freire Batholith 500± 4 n.a. L.C. da Silva (unpub-lished data) (* )
Syn-collisional plutons from the southern domain (RJ)Rio de Janeiro Suite (Pao de Acucar
granite)559± 4 n.a. Silva et al. (2003a)
Rio de Janeiro Suite (Corcovado granite)(RJ)
560± 7 n.a. Silva et al. (2003a)
Syn-collisional plutons from the northern domain (MG)Nanuque Suite 573± 5 508± 8 (1σ) n.a. Silva et al. (2002a)Manhuac¸u Charnockite 584± 5 n.a. Silva et al. (2002a)Governador Valadares I gneissic granite 565± 31 n.a. Silva et al. (2002a)Governador Valadares II gneissic granite 561± 7 n.a. Silva et al. (2002a)
Pre- to syn-collisional pluton from the southern domain (RJ)Serra doOrgaos Batholith (RJ) 569± 6 n.a. Silva et al. (1999)(Early) pre-collisional plutons from the
Anorogenic plutons ascribed to the break up of the pre-Arac¸uaı continental crust: northern domain (BA)Salto da Divisa anorogenic bimodal
granitic suite875± 9 n.a. Silva et al. (2002a)
Western basement of the Arac¸uaı Orogen: reworked Sao Francisco Craton/plate margin (MG)Guanhaes TTG gneissic complex
N of Coluna Town 2867± 10 n.a. Silva et al. (2002a)Sao Joao Evangelista quarry 2711± 11 519± 5 (1σ) Silva et al. (2002a)Sao Pedro do Suac¸uı granite 2710± 6 497± 68 (li) Silva et al. (2002a)
Archean units of uncertain tectonic significance (MG)Juiz de Fora Complex ? 2985± 17 2856± 44 M1 Silva et al. (2002a)
McNaughton (2004)Ponta do Cabec¸o foliated anatecticGranite 868± 330 (li)# Silva et al. (2002c)
Syn-collisional magmatism from the southern Domain (RS)Pinheiro Machado Suite 609± 17 2239 −8.4 (t= 800) Silva et al. (1999)
Reworked (migmatitised) basement remnants from the northern domain of Pelotas Orogen (SC)Inherited core population from theAguas
Mornas banded anatectic granite2175± 13 Silva et al. (2003b)
Camboriu granitic migmatitic complexInherited core population from the
Caseca quarry banded anatectic granite2006± 3 Silva and
McNaughton (2004)
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 213
Table 2 (Continued)
Dated unit Crystallisationage (Ma)
Metamorphicoverprinting age(Ma)
ModelTDM age(Ma)
εNd (t) Reference
Inherited core population from the Pontado Cabec¸o foliated anatectic granite
2174± 22 Silva et al. (2002c)
Amphibolite from the Caseca quarry 2167± 20 Silva et al. (2000b)
Northern basement of Dom Feliciano Orogen (SC)Presidente Nereu Tonalite basement
window2201± 7 3022 −7.76 (t= 2200) Silva et al. (2000b)
Reworked basement remnants from southern domain of Dom Feliciano Orogen (SC)Arroio dos Ratos Gneiss Tonalite >2000 631± 13 2062 +2 (t= 2000) Silva et al. (1999)
System of orogens Brasiliano ICryogenian tonalitic gneisses within the ca. 610 Ma syn-collisional granitoids from the Pelotas Orogen
Tonalitic xenoliths 781± 5 Silva et al. (1999)
Acronyms BA, ES, MG, RJ, RS, SC stand for: Bahia, Espırito Santo, Minas Gerais, Rio de Janeiro, Rio Grande do Sul and Santa Catarina States.#: low precise minimum ages obtained on thin, high-U rims; (li): lower intercept; M1: 1st metamorphic recrystallisation; M2: 2nd metamorphicrecrystallisation. Age based on a single concordant analysis, with precision of (1σ). With exception of four samples signalized with (* ) dated byconvention U–Pb systematics (at the CPGeo-IG.USP) and one (** ) dated by Pb–Pb evaporation, all the others crystallisation and overprintingages are zircon U–Pb SHRIMP results. (* ) Data obtained.
terranes’ and younger (ca. 600 Ma) ‘reactivated base-ment terranes’. Finally,Caby (1998) presented athreefold subdivision for the Pan-African tectono-metamorphic events, in northern Africa: an Early Pan-African tectonic-metamorphic ‘Event’ (750–700 Ma);a Main Pan-African ‘Episode’ (630–580 Ma); and aLate Pan-African ‘Episode’ (580–520 Ma).
The lack of an integrated analysis and the scarcity ofrobust, zircon-based ages blurred the diachronic evolu-tion, and hindered a fully exploration of their peculiar-ities in the Brazilian literature. In the central domainof the province,Figueiredo and Campos Neto (1993),andCampos Neto and Figueiredo (1995)discriminatedfor the first time in the “Costeiro Domain” of the Riode Janeiro State, an earlier “Brasiliano I Orogeny”(670–600 Ma), i.e. the Ribeira “Belt”, and a later “RioDoce Orogeny” (590–490 Ma). The authors charac-terised the “Brasiliano I Orogen” on the basis of itsmajor ca. 630 Ma thrust-related granitoid phase, inter-preted as a pre-collisional component, succeeded bywidespread ca. 590 Ma, post-collisional granitic mag-matism. The late development of a pre-collisional stageat ca. 590 Ma, post-dating by approximately 40 m.y.the main tectonic phase recorded in the “BrasilianoI Orogeny” (Table 1), supported the recognition ofthe younger, “Rio Doce Orogeny”. In southern Brazil,there are also references to an E-W temporal orogenicpolarity (e.g.Fragoso-Cesar, 1991; Basei et al., 2000).
More recently,Trouw et al. (2000)also proposeda threefold subdivision for the central MPV in three‘stages’ (Table 1). The oldest stage (670–600 Ma) wasrelated to the evolution of the Tocantins Province(Brasılia Belt) ascribed to the E-W closure of the so-called Brazilides Ocean, west of the Sao Francisco Cra-ton. The second “stage” (630–520 Ma) developed inresponse to the closure of the “Ribeira extension ofthe Adamastor Ocean”, whereas the youngest ‘stage’(520–480 Ma) represents the Buzios Orogeny fromSchmitt (2000).
The present integration of the new U–Pb SHRIMPdata (Table 2) and the compiled conventional U–Pbdata highlights the ‘episodicity’ in the orogenic evo-lution and extinction of orogenic collages, as notedin other Precambrian and Phanerozoic areas (Sengor,1990). It reinforces the assumption of the superpo-sition or diachronic evolution of orogens with sim-ilar timing and significance, as previously charac-terised in northern Africa (Caby, 1998). Accordingly, asub-division of the Brasiliano collage into three sys-tems of orogens is delineated (Brasiliano I, II, andIII). Each one of these systems is characterised bydistinct orogenic paroxysms (collisional peak), pre-cisely dated at ca. 790 Ma and 730–700 Ma (Brasil-iano I); ca. 640–620 Ma and ca. 600 Ma (Brasiliano II)and, ca. 595–560 Ma and 520–500 Ma (Brasiliano III)(Table 3; Fig. 3). They have counterparts presenting
214 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Table 3U–Pb zircon-based tectonic-magmatic repartition of the granitic magmatism from the Mantiqueira Province
similar paroxysmal timing in the adjacent western To-cantins Province (southern Brasılia Belt) and in thePan-African orogens (Table 4). The temporally equiva-lent Pan-African orogenic stages (collage) are, respec-
tively, the Early Pan-African tectonic-metamorphic‘Event’; the Main Pan-African ‘Episode’, and the LatePan-African ‘Episode’ fromCaby (1998)(discussedbelow).
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 215
Table 4Tectonic-magmatic subdivision for the Pan-African systems of orogens
Belt/Orogen Dated event Age (Ma) References
Late Pan-African/Pan-African III (climaxes at ca. 590–540 Ma)Saldania Belt D1/syn-collisional granitoids 550–540 Silva et al. (2000a)West Congo Belt D1 565 Tack and
Fernandes-Alonso (1998)Kaoko Belt D2/D3 syn-collisional granites 550 Seth et al. (1998)Sri Lanka D1/syn-collisional granulites ∼550 Kroner et al. (1994, 2001)Southern India D1 high-grade metamorphic peak ∼550 Bartelett et al. (1998),
Kroner et al. (2001)East Atarctica D1 high-grade metamorphic peak
and syn-collisional granitoidsM2 530–515 Jacobs et al. (1998)
M1 570–550
Damara BeltCentral and North branches D2/D3 syn-collisional granitoids 580–560 Porada (1989), Hofmann
(1994)South Branch D1 550 Porada (1989)Mozambique Belt Tanzania D1 550 Meert et al. (1995)Mozambique Belt, S Malawi D1 metamorphic peak 570–550 Kroner et al. (2001)
Mountains Terrane (Australia)D1 540 Rozendaal et al. (1999)
Pan-African II (climaxes at ca. 650–590 Ma)Mozambique Belt E and S Tanzania D1 metamorphic granulitic peak 640–625 Muhongo et al. (2001),
Moeller et al. (2000)Pre-collisional gneissic granitoids 800–630
Central Madagascar D1 syn-collisional stratoids granitesand gabbroic intrusions
D2 530–515 Collins et al. (2003)
D1 630–615 Kroner et al. (2001)Damara Belt Intracratonic Branch D1 syn-collisional granitoids 650 Frimmel and Frank (1998)West African Ghana-Togo-Benin Province D1 syn-collisional anatexites and
anatexis and charnockite intrusion600–800 Castaing et al. (1993)
Eclogites protoliths
(Early) Pan-African I (climaxes at ca. 800–650 Ma)Arabian-Nubian Shield
Kenya D1/syn-collisional granitoids ∼830–730 Mosley (1993),Kroner andCordani (2003)
S and E Ethiopia–Sudan–Eritrea D1 granulite metamorphic peak 740–710 Unrug (1996)Pre-collisional TGG 880–700 Teklay et al. (1998)
Ophiolite 720–680 Johnson and Kattan (2001),Black and Liegeois (1993)
850–820Katanga Orogeny/Zambezi Belt/Lufilian Arc
(Zimbabwe-Zambia)D1 syn-collisional granitoids 820 Hanson et al. (1994)
216 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Fig. 3. Brasiliano branched systems of o
rogens from the Mantiqueira Province.
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 217
4. (Early) system of orogens Brasiliano I(collisional climaxes at ca. 790 and 730–700 Ma)
The record of this system is restricted to the south-western domain of the MPV in Rio Grande do SulState at the Vila Nova Belt (Chemale, 2000), the SaoGabriel Orogeny, sensuHartmann et al. (2000a)andthe Embu Terrane (sensuCampos Neto, 2000; Cordaniet al., 2002) (Figs. 1, 2a, b and 3).
4.1. Sao Gabriel Orogen (climax at 730–700Ma)
The unit constitutes the western domain of the Sul-rio-grandense Shield, the Vila Nova Belt, in the south-ern MPV. Owing to the Neoproterozoic/Eopaleozoicand Phanerozoic deposits laid down on its eastern andnorthern domains, respectively, the exposed area ofthe orogen is restricted to some 5000 km2. The east-ern Neoproterozoic/Eopaleozoic (Camaqua) basin wascharacterised as a post-collisional foreland basin andrelated alkaline granites from the adjacent Dom Feli-ciano Orogen (Gresse et al., 1996). A NW-trendingtranspressive shear zone (Ibare) marks the southernlimit of the terrane, whereas the eastern limit wouldcorrespond to a NE-SW fault (Cac¸apava) (Chemale,2000) (Fig. 2a). South of the NW-trending shear zoneboundary (Ibare), in addition to the foreland depositsand associated granitoids, fragments of Archean TTGhigh-grade gneisses, ascribed to the Rio de La PlataCraton/Plate are also exposed.
em-n liticf ).
4fic-
u ter-l fic-u antso ,1u esians in-t an-t em-b , area ,2
There are no U–Pb data on the plutonic peridotiticassociation, but (Leite et al., 1998) obtained a crystalli-sation age of ca. 733 Ma on a late metabasaltic unit. Mi-nor remnants of an early Tonian mafic plutonic (diorite)was also recognised and yielded a crystallisation ageof ca. 890 Ma and a metamorphic age of ca. 850 Ma(Leite et al., 1998, Fig. 3), but its tectonic significanceis not well established. Nd isotopic data fromChemale(2000) on the mafic-ultramafic assemblage, indicatea juvenile nature (positiveεNd values) and short-livecrustal residence (TDM model age of ca. 1000 Ma) fort= 750 Ma. The prediction of the existence of a pre-Adamastor oceanic arm, between the western Rio deLa Plata Craton and the eastern Kalahari Craton, des-ignated as the Charrua Ocean, was made on the basisof these juvenile Cryogenian ophiolitic assemblages byFragoso-Cesar (1991).
4.1.2. Syn-orogenic magmatism (760–730Ma)The syn-orogenic magmatism comprises a suc-
cession of plutonic-volcanic arc associations meta-morphosed in the amphibolite facies. The volcanicarc (Vacacaı Supergroup) comprises a wide range ofvolcanic-sedimentary units, namely: intermediate calc-alkaline flows and pyroclastic assemblages, tholei-itic mafic-ultramafic rocks, amphibolites, pillowedmetabasalts, magnesian schists, serpentinites, marble,metapelites. Slices of the ophiolitic association tec-tonically interleaved with the arc are also reported.The calc-alkaline volcanics yielded crystallisation ageso Ma( t al.,1 cka
sa ion,w fic-u liticr ssesy 0 to7e rd ofc itica e in-t na-t atet itive
The exposed fraction of the orogen comprises rants of a volcanic-plutonic arc, possible ophio
ragments and a back arc basin (discussed below
.1.1. Pre-orogenic units (? 900–800Ma)Pre-orogenic units include remnants of metama
ltramafic plutonic and volcanic assemblages, ineaved with the plutonic and volcanic arc. The maltramafic slivers are interpreted as scattered remnf a supposed obducted ophiolite (e.g.Fragoso-Cesar991; Fernandes et al., 1992; Leite et al., 1998). Thenit comprises serpentinised harzburgites, magnchists, and amphibolites with tholeiitic affinityruded by the plutonic arc granitoids (Cerro Miqueira unit). Other occurrences of similar asslages, interleaved with the volcanic arc sequencelso ascribed to the ophiolitic assemblage (Chemale000).
f ca. 760 Ma and metamorphic ages of ca. 700Machado et al., 1990; Leite et al., 1998; Remus e999). At least two sub-basins show affinities with barc and accretionary prism environments.
The plutonic arc (Cambaı Group), in turn, comprisen amphibolite facies calc-alkaline TTG associatith minor interleaved supracrustals and maltramafic plutonics xenoliths interpreted as ophioemnants. The metatonalitic and metadioritic gneiielded crystallisation ages spanning from ca. 7530 Ma, and metamorphic ages of ca. 700 Ma (Leitet al., 1998). Babinski et al. (1996)dated a youngeioritic gneissic phase obtaining a crystallisationa. 700 Ma. Slivers of the mafic-ultramafic ophiolssemblages are tectonically intercalated and ar
ruded by the arc granitoids. The Nd isotopic sigures of the plutonic-volcanic arc from intermedionalitic and dacitic rocks is characterised by pos
218 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
εNd values (fort= 750 Ma) and modelTDM ages closeto 1000 Ma (Babinski et al., 1996; Chemale, 2000),indicating relatively short-lived crustal residence forthe magma sources. There is only one K-rich gran-odioritic pluton associated with the TTG gneisses. Itfurnished a Nd-model age of 820 Ma and positiveεNdvalues (Babinski et al., 1996), and is interpreted as amore evolved phase of the arc, but its crystallisationage is not well constrained.
Accordingly, the Sao Gabriel Orogen currently rep-resents best example of a subduction-related orogen(sensuSengor, 1990) within the MPV. The (main) oro-genic magmatic phases within the accreted arc-terrane,evolved in a subduction-related accretionary setting,related to an intraocenic environment (Machado et al.,1990; Fragoso-Cesar, 1991; Babinski et al., 1996; Leiteet al., 1998; Remus et al., 1999; Chemale, 2000).
4.1.3. The reworked basementOwing to the possible intraoceanic development,
there is only local record of reworked basement rockswithin the arc-accretionary complex. These occur-rences are exposed within the easternmost ca. 870 Maback arc sub-basin (Passo Feio unit) (Remus et al.,1998). One of the basement rocks is a tholeiiticamphibolite, with an imprecise Paleoproterozoic age(Hartmann et al., 2000a) and a (quasi) Archean or-thogneissic sliver with crystallisation zircon U–PbSHRIMP age of ca. 2450 Ma and metamorphic over-printing age of ca. 560 Ma (Remus et al., 1996, in:R er-p withtg ifi-c(
4.2. Embu Terrane (collisional climax at ca.790Ma?)
The Embu Complex is a major tectonic unity inthe central segment of the MPV (Figs. 1–3). It is ex-posed within the eastern Sao Paulo State (Fig. 2b)and comprises mainly amphibolite facies interleavedortho and paragneisses, locally bearing metavolcanicsuccession. The pelitic/psammitic paragneisses showwidespread in situ partial melting and granitic genera-tion, giving rise to extended S-type granitic-migmatiticdomains. The basement consists of orthogneisses witha crystallisation age of ca. 2000 Ma and Archean her-itage (Babinski et al., 2001). The NE-trending ter-rane is flanked to the south-east by the CosteiroGranitic Belt, by means of an NE-trending shearzone (Cubatao). This shear zone is a segment of themain component of the Paraıba do Sul shear sys-tems, and is interpreted as the surface trace of amajor terrane boundary. On the north-eastern flank,another transpressive NE-trending shear zone (Tax-aquara) separates the Embu Terrane from the gran-itoids ascribed to the Paranapiacaba Orogen andfrom the Mesopeoterozoic Serra do Itaberaba basin(Figs. 1 and 2b).
In the southern segment of the domain, located some50 km south-west of Sao Paulo city, an early Neo-p tionw ting.T( ofa be-t efi ob-t tiono ie ageo ting(
46
m,s og-n ges
emus et al., 2000b). The authors ascribed the ovrinting age to a metamorphic event synchronous
he intrusion of the adjacent syn-tectonic Cac¸apavaranite, a plutonic unit of uncertain tectonic signance, temporally equivalent to the Arac¸uaı Orogenysystem Brasiliano III).
Only some 80 km E of the intraoceanic arc, reants of reworked basement tonalitic and granitic
hogneisses (Encantadas Complex) are recognisedomain is interpreted as a microcontinetal setting
he Sao Gabriel Orogeny evolution (Chemale, 2000)Fig. 2a). Tonalitic and granitic orthogneisses recrystallisation ages from ca. 2360 to 2260 Ma and aetamorphic overprinting age of ca. 2021 Ma (Corcher, in:Chemale, 2000). The latter author dated ather orthogneiss, obtaining similar Paleoproterorystallisation ages and early Brasiliano metamorge of ca. 800 Ma.
roterozoic (Cryogenian) tonalitic gneissic associaas recognised, by means of U–Pb SHRIMP dahe gneiss reveals a crystallisation age of 811± 13
Cordani et al., 2002), whereas an approximate age(first) metamorphic overprinting was bracketed
ween 700 and 650 Ma (M1). Another estimate for thrst metamorphic overprinting (ca. 790 Ma) wasained by means of a chemical isochron determinan primary monazites (Vlach, 2001). Finally (Cordant al., 2002) based on Rb–Sr data, also estimated anf ca. 560 Ma for a second metamorphic overprinM2).
.2.2. Syn- to post-collisional magmatism (ca.50–580Ma)
In addition to the early pre-collisional magmatiseveral syn- to post-collisional plutons were recised within the domain presenting crystallisation a
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 219
from ca. 630 to 590 Ma (Tassinari and Campos Neto,1988;Passarelli, 2001; Filipov and Janasi, 2001). Thesespan the syn- to post-collisional magmatism and sug-gest that the Embu Terrane shared a common evolu-tion, relative to the adjacent Paranapiacaba Orogen (seebelow).
4.3. Juxtaposition and collage of the Brasiliano Iorogenic components
The reduced dimensions of the exposed Sao Gabrielorogenic units make it difficult to reconstruct the re-gional orogenic evolution. The volcanic arc shows a re-gional NNE-trending foliation and records kinematicsstructures pointing to a WSW-directed thrusting overa supposed (concealed) eastern margin of the Rio deLa Plata Craton. The west-directed overthrusting ofthe accreted arc, would have occurred in response toan E-directed subduction of the Tonian Charrua Oceanlithosphere (Chemale, 2000) at ca. 700 Ma, as deducedfrom the metamorphic ages obtained on the volcanicassemblages (Remus et al., 1999). This early collagestage, pre-dated by some 70 m.y. the collage (colli-sional peak) of the adjacent Dom Feliciano Orogen,which occurred at ca. 630 Ma (Silva et al., 1999, Table2).
As far as the Embu Terrane is related, the re-constitution of the orogenic history is a more diffi-cult task because of the scarcity of robust ages onthe metamorphic overprinting, and complex field re-l ;C al.,2 tesa t do-m dur-i sede pro-d 0 to5 monfi entP niticB pha-s )D edw ds estedt oics
Outside the Sao Gabriel Orogen and Embu Ter-rane the Brasiliano I magmatism record is, sofar, meagre. It is restricted to minor, ca. 790 Matonalitic orthogneisses occurring as remnants withinthe (650–630 Ma) Dom Feliciano Orogen (Silva et al.,1999, Table 2) and in the ca. 630 Ma Rio Negro Arc,within the south-eastern domain of the Arac¸uaı Oro-gen (Heilbron and Machado, 2003). Despite the scantavailable geological and isotopic data for both occur-rences, they are of paramount importance as markers ofthe onset of the accretion of the early Brasiliano Cryo-genian continental crust, outside the Sao Gabriel andEmbu domains.
The former occurrence is exposed about 80 kmsouth-east of the plutonic arc from the Sao Gabriel Oro-gen and is characterised as tonalitic gneiss, yielding acrystallisation age of 781± 5 Ma. The gneisses occuras disrupted xenoliths, intruded by a syn-collisionalgranitic phase of the Dom Feliciano Orogen, at ca.610 Ma (Silva et al., 1999, Table 2), resulting inwidespread partial melting and anatexis of the tonalilicxenoliths. The tectonic significance of these remnantsrelative to the regional evolution of the Dom FelicianoOrogen is still poorly constrained. On one hand, theycould represent an eastern, extra-orogen, intracontinen-tal arc phase, temporally associated with the onset ofthe western Sao Gabriel Orogeny, lately reworked byt theya gen,s Fe-l itso eg-a fortd ro-t isses,e
a ant Riod MaR of7 tinga d-d the
ationships. Some authors (Brito-Neves et al., 1999ampos Neto, 2000; Vlach, 2001; Cordani et002) suggest that the Embu Complex constitudisplaced terrane, attached to the north-easain of the Ribeira Belt (Paranapiacaba Orogen)
ng the late Brasiliano collage. Despite its suppoxotic nature, a widespread anatectic graniticuction phase with ages spanning from ca. 6390 Ma, suggest that it shared at least a comnal tectonic-magmatic evolution with the adjacaranapiacaba Orogen, and with the Costeiro Graelt. This common evolution has already been emised byWernick et al. (1993), Topner (1996, 1997,antas et al. (2000), among others. The last mentionork (Dantas et al., 2000), by means of a Sm–Ntudy on the basement of both terranes, sugghat both were derived from similar Paleoproterozources.
he Dom Feliciano Orogeny. On the other hand,lso could be remnants of an eastern, distinct oroubsequently severed by the accretion of the Domiciano Orogeny magmatic arc. Independently ofrigin, Nd isotopic studies furnished moderately ntive εNd values and model Nd age of 2240 Ma= 800 Ma (Silva et al., 1999, Table 2), implying theerivation of the tonalite from continental Paleop
erozoic sources, coeval with the Encantadas gnexposed some 60 km W.
Conventional zircon U–Pb studies byHeilbronnd Machado (2003)recognised other Cryogeni
onalitic remnant exposed at a western suburb ofe Janeiro city. It is associated with the ca. 630io Negro Arc, and furnished a crystallisation age92± 12 Ma, whereas the metamorphic overpringe was 493± 6 Ma. The authors do not furnished aitional comments on the tectonic meaning and
220 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
geographical distribution of these remnants. The ageis approximately coeval with the ca. 810 Ma mag-matic arc from the adjacent Embu Terrane. Despitetheir approximately coeval nature, no evidence of pos-sible links between the evolution of both Cryogeniantonalites were discussed and, in a like manner as thesouthern occurrence, its regional tectonic significanceis still uncertain.
4.5. Tocantins Province connections
The early history of the Brasiliano I is followed inthe adjacent Tocantins Province/South Brasılia Belt bya similar, but not coeval, evolution (Fig. 2b). The ac-cretion of the Passinho diorites in MPV at ca. 880 Ma,took place simultaneously in the Tocantins Provincewith the accretionary phase of the Goias Magmatic Arc(950–750 Ma) (Pimentel and Fuck, 1992; Pimentel etal., 1997, 2000). Nevertheless, the temporal equiva-lence and the restricted occurrence of the ca. 880 Mametadiorite in the Sao Gabriel Orogen does not en-courage any further comparison between both domains,otherwise separated by some 2000 km distance. On theother hand, there is a good temporal equivalence be-tween the Sao Gabriel Orogen arc (760–730 Ma) andthe ca. 750 Ma Anapolis-Ituac¸u Arc, a late componentof the Goias Magmatic Arc (Pimentel et al., 2000).
When it comes to the Embu Terrane, there issynchroneity between the major accretionary events,despite the distinct scales of the volume of newly ac-c romt .y.)tf ca.8 eM2G
4
or-r ic-m eo th-w ara,K tiono to
the intraoceanic arc complex) was under way in south-western Africa, the break up and rifting of the Kibarancontinental crust, followed by the extrusion of the localbranch of the Adamastor Ocean, was just beginning (ca.750 Ma) (Frimmel and Frank, 1998; Chemale, 2000).
In other areas of the African continent, the Pan-African I accretionary phase developed coevally withthe Brasiliano I, with large scale production of Tonianand Cryogenian magmatic arcs (Table 4, and refer-ences therein). In the north-eastern and eastern partsof Africa (North Cameroon, Trans-Saharan, Mozam-bique belt, Katangan Orogeny and the Arabian-NubianShield, West African Ghana-Togo-Benin Province), thePan-African events in response to ocean-floor spread-ing and consumption were dominated by widespreadnew crustal TTG growth. The Arabian-Nubian Shieldrecords an earlier (ca. 880–700 Ma) TTG accretionaryphase, followed by a later ca. 700–650 Ma collisionalpeak. The North Cameroon belts record an early ac-cretionary phase with ages spanning from ca. 800 to700 Ma. The Katangan Orogen/Lufilia Arc, in turn,yielded accretion ages from ca. 950 to 820 Ma anda second accretionary stage at ca. 700 Ma. Finally,within the Mozambique Belt, the high-grade metamor-phic peak was dyachronous spanning from ca. 800 Ma(Northern Mozambique) to 640 Ma (E and S. Tanzania)and ca. 550 Ma Tanzania and S Malawi (Table 4).
5. System of orogens Brasiliano II (collisionalc
ro-g y,t nsa DomF elt)( ys-t iticB
ca.6 xesr ianoI theA
nctc uringt ins
retion crust in both domains. The ca. 810 Ma arc fhe Embu Terrane is discretely younger (some 20 mhan a late manifestation of the Goias Magmatic Arcrom the Brasılia Belt (Tocantins Province), dated at30 Ma (Pimentel et al., 2000). The ca. 790 Ma for th1, metamorphic peak on the Embu Terrane (Vlach,
001) is coeval with the age of the M1 event from theoias Magmatic Arc (Pimentel et al., 2000).
.6. Brasiliano/Pan-African connections
The Brasiliano/Pan-African I system of orogens cespond (in part) to the “Early Pan-African tectonetamorphic Event” ofCaby (1998). This early stagf juvenile crustal addition is not recorded in the souestern African belts (i.e. Saldania, Gariep, Damaoko and West Congo). By the time the subducf southern Brazilian Charrua Ocean (giving rise
limaxes at ca. 640–620 Ma and ca. 600 Ma)
The system Brasiliano II is ascribed to three oens, extending from 35◦ S, close to Montevideo cit
o 22◦ S, northeast of Sao Paulo city. The orogere designated from south to north as Pelotas/eliciano, Rio Pien and Paranapiacaba (Ribeira B
Figs. 1, 2a, b and 3). Besides the three orogens, the sem Brasiliano II also comprises the Costeiro Granelt (Basei et al., 2000).The orogenic climaxes (ca. 640–620 Ma, and
00 Ma) post-date by ca. 130 and 70 m.y. the climaecorded by the orogens from the system Brasil, and pre-dates by ca. 40 m.y. the climax fromracuaı Orogen (ca. 560 Ma, Brasiliano III) (Fig. 3).The evolution of the system took a very disti
ourse as compared to the orogens evolved dhe Brasiliano I. The three distinct orogenic doma
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 221
are typically collisional-related orogens, characterisedby pre- to syn-collisional magmatism with strong in-fluence of Paleo and Mesoproterozoic enriched litho-spheric mantle and crust. Additionally, they showwidespread post-orogenic magmatism and forelandbasin development, associated with the tectonic col-lapse of the orogen (Fig. 3; Table 3).
5.1. Dom Feliciano Orogen (climax at ca.640–620Ma)
The Dom Feliciano Orogen (Dom Feliciano Belt)extends some 1100 km from Montevideo (Uruguay) tothe northeast of Santa Catarina State (Figs. 1 and 2a).The main orogenic component is an eastern mag-matic arc (Florianopolis, Pelotas and Aygua), and awestern metamorphosed continental margin sequence(Brusque, Porongos and Lavalleja units) (Fig. 2a). Mostof the orogen limits are concealed by the PhanerozoicParana Basin to the west and by the Atlantic Oceanto the east. Hence, the tectonic relationships and itslimits with the western Rio de La Plata and Paranaplates are unknown. Only its northern tip, characterisedby the NNW-thrusting of the passive margin depositsonto the Luıs Alves Microplate, is well established(Basei, 1985, 2000). An extended, transpressive shearbelt (Major Gercino-Dorsal de Canguc¸u-Sierra Bal-lena) separates a magmatic arc from the continentalmargin deposits in Santa Catarina, Rio Grande do Suland Uruguay (Basei et al., 2000) (Figs. 1 and 2a). Thesea e su-t s, thee belt.I pre-t n in-t (thea gleo
re-l lka-l thew Pa-l weent
5ain
p con-
tinental margin (Jost and Bittencourt, 1980). The unitis exposed between the eastern border of the Rio deLa Plata Plate and the western border of the magmaticarc (Fig. 2a). The sequence was metamorphosed un-der greenschist to lower amphibolite facies and de-formed during the main collisional phase and dockedonto the eastern margin of the Rio de La Plata andParana plates (Basei, 1985; Basei et al., 2000). Lo-cally the metasedimentary succession includes inter-leaved metamafic-ultramafic slices (Jost and Bitten-court, 1980), of uncertain tectonic significance. In ad-dition to the ultramafic bodies, felsic volcanic horizonswith a crystallisation age of ca. 780 Ma (C.C. Porcher,in: Chemale, 2000a) are intercalated with the metased-imentary package. The tectonic significance of the fel-sic volcanism is still open to speculations, but the ca.780 Ma crystallisation age may be a first estimate forthe age of the opening stage for the continental marginbasin. Reworked interleaved basement orthogneissesfurnished zircon U–Pb SHRIMP metamorphic ages ofca. 630 Ma constraining the inversion and metamor-phic peak overprinting age within the Pelotas Batholith.In Santa Catarina State the passive margin basin hasrecords of undated minor ocean floor realms (Silva,1991). Interleaved anatectic felsic volcanics yield acrystallisation age of ca. 640 Ma (Table 2), which rep-resents a preliminary estimate for the age of the waningstages of the sedimentation: the basin opening age isstill undetermined. If future studies confirm this ca.640 Ma age for the depositional sequence, the data willb atesf cur-r le-o ,2m orth-e ed asa e nog eta-t
5m-
p SulS post-c ento -i is
uthors consider the shear belt as a major terranure, separating two supposedly unrelated terraneastern granitic arc and the western thrust and fold
n the present work we adopted an alternative interation by which the shear zone would represent aracontinental shear belt, separating two domainsrc and the thrust fold belt), that evolved during a sinrogenic episode (Dom Feliciano Orogen).
In Rio Grande do Sul State, post-collisional (foand) volcanic-sedimentary deposits and coeval aine granites overlapped the thrust and fold belt inestern border. At the north-western tip of the arc,
eoproterozoic basement inliers are exposed bethe arc and the post-tectonic western deposits.
.1.1. Pre-orogenic unitsIn Uruguay and Rio Grande do Sul State, the m
re-orogenic unit consists of an extended passive
e in disagreement with almost all previous estimor the age of sedimentation and volcanism. Theseent estimate for the basin infilling varies from Paproterozoic (Silva, 1991), Mesoproterozoic (Basei000), or even Archean (Hartmann et al., 2000a). Ainor segment of the sequence, exposed in the nastern tip of the Brusque basin, may be considerprobable Mesoproterozoic remnant, but there arood geochronological constraints for this interpr
ions.
.1.2. Pre- to syn-collisional magmatismPre- to syn-collisional granitoids are the main co
onent of the Pelotas Batholith in Rio Grande dotate and Uruguay, whereas in Santa Catarina, theollisional granitic magmatism is the main componf the Florianopolis Batholith (Fig. 2a). From the chem
cal and isotopic points of view, the magmatism
222 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
characterised by the predominance of granites s.s, witha narrow compositional range. They have dominantlyhigh-K calc-alkaline (HKCA) signatures, suggestive oftheir evolution as a mature continental arc. The crys-tallisation is bracketed between ca. 640 and 620 Ma(Basei, 1985, 2000; Chemale et al., 1995; Babinski etal., 1997; Silva et al., 1999, 2002c; Silva, 1999). Theisotopic signatures point to important Mesoproterozoiccrustal inheritance for the magmatism from the northsegment of the arc (Mantovani et al., 1987; Basei et al.,2000; Silva, 1999; Table 2). Some plutons, occurringoutside the main batholith area, are intrusive into thethrust and fold belt, and show older (Paleoproterozoicand Archean) inheritance (Basei, 2000; Silva, 1999;Table 2).
5.1.3. Post-collisional unitsThe post-collisional, extensional magmatism is also
characterised by abundant high-K calc-alkaline, A-type sub alkaline, alkaline with rare peralkaline andshoshonitic plutons (Bittencourt and Nardi, 1993;Basei, 2000; Basei et al., 2000; Chemale et al., 2003;Silva et al., 2002c, 2003b, 2004; Figs. 2a, b and 3;Table 2). The plutonic events are related to the infillingof the late-tectonic Camaqua and Itajaı basins. The for-mer (Camaqua), is located at the south-western marginof the orogen, covering part of the adjacent Sao GabrielOrogen. The latter (Itajaı), is exposed over the adjacentArchean basement (Luıs Alves Microplate) (Fig. 2a).Both units were interpreted as foreland basins (Gressee ol-c ca.6 a( in-fi romt alticl yr set oft
5zoic
P omF ag-m TGo zoicoa ther
occurrences of reworked basement are situated at thenorth-western tip of the Pelotas Arc, and are comprisedof orthogneisses (Arroio dos Ratos unit) and associatedhigh-grade supracrustals and meta-anorthositic rocks(Fig. 2a). A metatonalitic gneiss yielded a metamorphic(SHRIMP) age of ca. 631 Ma and Sm–Nd model-ageof ca. 2000 Ma, indicating Paleoproterozoic crystallisa-tion and Brasiliano reworking (Silva et al., 1999, Table2). A crystallisation age of ca. 2070 was obtained bymeans of the U–Pb SHRIMP systematics on associ-ated granodioritic gneiss (J. Leite, in:Chemale, 2000).The Paleoproterozoic ages indicate a temporally equiv-alence between this complex and the Encantadas gneissfrom the basement of the adjacent Sao Gabriel Orogen(Fig. 2a).
Minor expositions of Paleoproterozoic rocks inSanta Catarina State are restricted to partially melted(migmatised) tonalitic and amphibolitic remnantswithin the syn-collisional Neoproterozoic anatecticgranites and migmatites from the batholith (Fig. 2a).Additionally to this restitic material, two major Pa-leoproterozoic protolithic sources, with crystallisationages of 2175± 13 Ma and 2006± 3 Ma where dated oninherited zircon cores from anatectic syn-collisionalgranitoids (Silva et al., 2002c, 2004, Table 2).Basei(2000) obtained on one of these anatectic granites,through U–Pb conventional systematics, an age of ca.600 Ma, interpreted as the crystallisation age. The re-assessment of the sample by means of zircon U–PbSHRIMP systematics, the ca. 600 Ma age was as-c in-t f ther et utiono ry-r and-i norP atedn dowi na
entd ternflp Ma( r-p rianb hern
t al., 1996) but their true nature is in debate. The vanism associated to the basin infilling lasted from10 Ma (Silva et al., 2002c, Table 2) to ca. 560 MBasei, 2000). In Rio Grande do Sul State, the basinlling phase lasted until ca. 470 Ma, as deduced fhe zircon U–Pb SHRIMP age obtained on a basava flow (Hartmann et al., 2000a). This later phase maepresent a taphrogenic event precursor to the onhe Phanerozoic Parana basin infilling.
.1.4. The reworked basementIn the Rio Grande do Sul State, the Phanero
arana Basin and the foreland deposits from the Deliciano Orogen cover minor Archean cratonic frents. They comprise mainly granulite-facies Trthogneisses (ca. 2550 Ma) and Paleoproteroverprinting age (ca. 2020 Ma) (Hartmann et al., 1999)nd are ascribed to the Rio de la Plata Craton. O
ribed to melt-precipitated zircon overgrowths, anderpreted as the (anatectic) crystallisation age oock (Silva and McNaughton, 2004, Table 2). Despithese isotopic advances, the geographical distribf the partially melted migmatitic and their countocks remnants are still poorly constrained, demng additional field and isotopic studies. Another mialeoproterozoic gneiss (Presidente Nereu), situorth of the orogen is exposed as a basement win
n an area of a few km2 and yielded a crystallisatioge of 2201± 17 Ma (Silva et al., 2000b, Table 2).
In Uruguay, another recently recognized basemomain is exposed in Uruguay on the south-easank of the Dom Feliciano Orogen (Fig. 2a). It com-rises migmatitic orthogneiss, dated at ca. 1000Preciozzi et al., 1999; Basei, 2000). The authors intereted the domain as a possible fragment of Kibaasement from the Pan-African orogens of sout
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 223
Africa. The discovery of this paleotectonic unit is sig-nificant with respect to correlation between the south-ern MPV orogens and Gariep/Damara counterparts insouthern Africa. The possibility exists that this terranecould be a major continental block, concealed by theAtlantic platform sediments.
5.2. Paranapiacaba Orogen (climax at ca.610–600Ma)
The NE-trending Paranapiacaba Orogen (Figs. 1and 2a, b) extends ca. 500 km from south-easternParana State to northeast of Sao Paulo city. Its maxi-mum wide is reached at the south-western domain (ca.100 km). The northern tip is bounded to the north-westby the Socorro-Guaxupe nappe terrane (TocantinsProvince) and on north-east by the Embu Terrane. Onthe south-eastern flank the orogen is flanked by Meso-proterozoic Perau-Votuverava volcanic-sedimentary(back arc) assemblages (Basei et al., 2003). On thecentral-eastern segment, the Curitiba Microplateflanks the orogen by means of an inferred suturezone (Lancinha Shear Zone) (Basei et al., 2000;Campos Neto, 2000). Finally, the Phanerozoic ParanaBasin covers the western and south-western orogenflanks.
5.2.1. Pre-orogenic unitsIn the south domain of the orogen, pre-orogenic
units from the Paranapiacaba Orogen are well exposed.T argid d bl i-t ion( ert itics ,2 tot erea nale
56
di-m rani nalv sed
mainly in the north domain in Sao Paulo State.They are a volcanic-sedimentary association with lim-ited oceanic floor extrusion, and are interpreted asback arc basins (Sao Roque Group) (Hackspacker etal., 2000; Juliani et al., 2000; Campos Neto, 2000)(Figs. 2a, b and 3). The oceanic floor spreading oc-curred at 630–620 Ma, the age of the E-MORB lavasand gabbroic intrusions (Hackspacker et al., 2000). Thedating of a felsic sequence, coeval with the gabbroicplutonism, yielded a crystallisation age of ca. 620 Ma(Juliani et al., 2000). The basin magmatism precededthe accretion of the syn-collisional granitic arc by ca.20 m.y. (discussed below).
The continental margin deposits host the orogenicgranitic units, which are distributed alongside the ca.500 km NE-trending extension of the domain (Fig. 2aand b). It consists mainly of high-K calc-alkaline plu-tons with chemical and isotopic signatures akin tothe mature continental arcs and showing a strong Pa-leoproterozoic influence (e.g.Gimenez Filho et al.,2000; Janasi et al., 2001). The crystallisation ages arebracketed between ca. 630 and 600 Ma (Topner, 1996;Gimenez Filho et al., 2000; Prazeres Filho, 2000; Janasiet al., 2001).
The syn-collisional metamorphism of the grani-toids and volcanic-sedimentary assemblages achievedlow-grade conditions (greenschist facies), but presentlythere is no geochronological data on this event.
hey are characterised by passive continental meposits, occurring as irregular remnants separate
arge orogenic granitic batholiths (Fig. 2a). The deposion was dominated by carbonate platform successItaiacoca, Lajeado andAgua Clara units), deep waturbidites (Votuverava unit) and carbonate-psammequences (Capiru and Setuva units) (Campos Neto000). The last mentioned units are thrusted
he south-east over the Curitiba Microplate. Thre no gechronological data on this depositiopisode.
.2.2. Pre- to syn-collisional units (ca.30–605Ma)
Pre-collisional units include metavolcanic-seentary sequences and pre- to syn-collisional g
toids (Fig. 2a and b). The former are extensioolcanic-sedimentary rift-like successions, expo
ny
s
-
Extensional magmatic from ca. 610 to 540 Malowed the cessation of the main contractional epis(Figs. 2a, b and 3and Table 7). This event is ascribto the waning stages of the orogenic episode thatacterises the tectonic collapse of the orogens. Thtrusions are mainly high-K calc-alkaline, with A-tyand silica-oversaturated alkaline signatures, relatdistinct juvenile and reworked Paleo and Mesoprotzoic crustal sources and enriched lithospheric ma(Janasi and Ulbrich, 1991; Prazeres Filho, 2000; Jaet al., 2001). Minor juvenile shoshonitic phases arecally recognised in association with post-collisiona590 Ma rapakivi plutons (Wernick, 2000).
In addition to the granitic plutonism, the latectonic post-tectonic phase also comprises devment of volcanic-sedimentary basins, located atsouth-western flank of the orogen and classified asland basins byCampos Neto (2000).
224 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Atuba Complex and associated low-grade passive mar-gin successions, designated as the Curitiba Terrane(Siga, 1995; Harara et al., 1997; Basei et al., 2000;Campos Neto, 2000) is the main basement of the oro-gen. The terrane is considered by these authors as aMicroplate setting for the Neoproterozoic evolution.It is a polycyclic domain showing U–Pb conventionalages of ca. 2160 Ma (Siga, 1995; Harara et al., 1997),interpreted as crystallisation ages. In addition to theearly Paleoproterozoic ages,Kaulfuss (2001)obtainedca. 1750 Ma for the crystallisation of units previouslyattributed to the Atuba Complex.
Only recently, by means of U–Pb SHRIMP system-atics, Paleoproterozoic ages as ascribed to a first meta-morphic/migmatic event (M1), and a crystallisation ageof ca. 3040 Ma was obtained (Sato et al., 2003). Thesame study also revealed the Neoproterozoic migmati-sation age of ca. 560–590 Ma (M2).
The terrane is in tectonic contact through trans-pressive transcurrent shear zones with Mesoprotero-zoic metavolcanic-sedimentary successions (SW), theParanapiacaba Orogen (NW), and the Rio Pien Orogen(SSE). The northern tip of the domain is in tectoniccontact with the Neoproterozoic granitic/supracrustalbelt (Costeiro Granitic Belt) and the Embu Terrane.The Lancinha Shear Zone separates he last men-tioned (Embu Terrane) from the Curitiba Microplate
nicpia-
gein-ond
es
seaasack
f theed
assu
Sengor, 1990) which, in Neproterozoic times, gave riseto the Sao Roque back arc basins, in response to theParanapiacaba orogenic evolution (Fig. 2b).
5.3. Rio Pien Orogen (climax at ca. 605–595Ma)
The third component of the system Brasiliano IIis represented by a narrow (ca. 250 km long× 25 kmwide), wedge shaped, NE-trending syn- to post-orogenic granitic belt. The belt, interpreted as asubduction-related arc (Basei et al., 2000; Harara,2001), is overthrusted to the south-east onto the LuısAlves Craton/Plate, through the Pien-Tijucas transpres-sive shear zone, and to the north-west it is flanked bythe Curitiba Microplate (Figs. 1 and 2a). Relative tothe other major orogens from system Brasilano II, theRio Pien collisional peak had a later evolution with acollisional climax dated at ca. 605–595 Ma (Harara etal., 1997; Harara, 2001; Figs. 1, 2a, b and 3; Table 3).
5.3.1. Pre-orogenic units (ca. 630Ma)Rio Pien Orogen records the best evidence for the
presence of ophiolitic remnants in the central MPV(Fig. 3), consisting of meta-mafic-ultramafic plutonicassemblages (Harara et al., 1997; Harara, 2001). Atholeiitic gabbro from this association was dated bymeans of zircon U–Pb SHRIMP systematics, yieldinga crystallisation age of ca. 630 Ma (Harara, 2001), iden-tical, within error, to the age of the ocean floor remnantsfrom the Paranapiacaba Orogen back arc assemblage.
56
a-j thes ,r pics arcs,wTS Ma,w s of6
5the
m ,2 er
.3.2. Pre- to syn-collisional magmatism (ca.20–600Ma)
Syn-collisional magmatism from the other two mors orogens from the system Brasiliano II, andyn-collisional plutonism from the Rio Pien Orogenepresent chemical (high-K calc-alkaline) and isotoignature characteristics of the mature continentalith Paleoproterozoic crustal influence (Harara, 2001).he pre-collisional phase of the Pien-Mandiritubauite, yielded crystallisation ages of 620–610hereas the syn-collisional phase, furnished age05–595 Ma (Harara et al., 1997; Harara, 2001).
.3.3. Post-collisional units (ca. 600–560Ma)The post-collisional plutonism occurs along
ain NE-trending Pien-Tijucas Suture Zone (Harara001) (Fig. 2a). It shows chemical alkaline and p
(Figs. 1 and 2a, b).The southern and south-central pre-oroge
volcano-sedimentary sequences from the Paranacaba Orogen in Parana and Sao Paulo States (Fig. 2b)experienced a polycyclic evolution. The initial staof basin development began in the Calymnian asdicated by a U–Pb age of ca. 1480 Ma, obtainedpaleo sills with amphibolitic composition intercalateinto a metavolcanic-sedimentary basin in Parana State(Basei et al., 2003). In Sao Paulo State, meta-andesityielded crystallisation ages of ca. 1400 Ma (Juliani etal., 2000). The basin assemblages record incipientfloor extrusion as indicated by tholeiitic basaltic lavand intermediate derivatives characteristic of a barc environment (Juliani et al., 2000). The evolution ofthese Mesoproterozoic basins lasted until the end oBrasiliano collage when they became sites of renewcrustal stretching and infilling. The unit evolveda polycyclic Mesoproterozoic ‘resurrect’ basin (sen
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 225
alkaline signatures (Kaul and Cordani, 2000; Harara,2001) and yielded crystallisation ages from ca. 600 to560 Ma (Siga, 1995; Basei et al., 2000; Harara, 2001).The coeval volcanic-sedimentary basins are locatedon the southern Archean basement (Luıs Alves Mi-croplate), in Parana and Santa Catarina States (Fig. 2a).
5.3.4. Reworked basementThe orogen is overthrusted onto its south-eastern
basement, the Santa Catarina Granulitic Complex(Fig. 2a), which is interpreted a microcontinental platesetting for the orogenic evolution (Basei et al., 2000).The domain comprises chiefly high-grade TTG or-thogneisses and plutonic mafic-ultramafic rocks, andis intruded by ca. 2000 Ma granitoids and Neopro-teozoic/Cambrian alkaline granites and volcanics, andvolcanic-sedimentary foreland basins related to thepost-orogenic phase of the Rio Pien Orogen (Baseiet al., 2000; Harara, 2001). The gneiss complex ex-hibits chemical signatures suggesting its evolution asan intraoceanic arc (Figueiredo et al., 1996; Hart-mann et al., 2000b). The crystallisation age of theTTG association was a matter of dispute in the lit-erature. Only recently, a trondhjemitic orthogneissyielded, through zircon U–Pb SHIRIMP systematics,the Neoarchean crystallisation age (ca. 2710 Ma) and aPaleoproterozoic (ca. 2170 Ma) overprint was demon-strated (Hartmann et al., 2000b). The unit is a cra-tonic fragment (Luıs Alves Microcontinent) relativeto the southern Dom Feliciano and to the northernR etai ting,t ing.T onald enice g-m l.,2
5
i (ca.1 di-v eis-s ciess
The belt is bounded to the south-east by the ArcheanLuıs Alves cratonic fragment, separated by the CosteiroTranscurrent Shear Zone, interpreted a major suture(Basei, 2000). The north-eastern domain of the belt, lo-cated between the Atlantic Ocean coast and the EmbuTerrane, is in tectonic contact with the latter throughthe transpressive Cubatao Shear Zone, another sup-posedly major terrane boundary. In both domains, thegranitic belt is overthrusted to the north-west ontothe Luıs Alves Craton and onto the Embu Terrane(Figs. 1 and 2a, b). There are few radiometric agesfrom the unit, the pre- to syn-collisional calc-alkalinebatholiths (Paranagua) yielded a crystallisation age ofca. 615 Ma (Basei, 2000).
5.5. Juxtaposition and collage of the Brasiliano IIorogenic components
As far as the orogenic polarities are referred, there isnot a consensus on the evolution of the system Brasil-iano II. Within the Dom Feliciano Orogen, the ex-trusion vector of the collisional structures (flat-lyingW-NW-vergent foliation) and the apparent eastwardzonation of the post-collisional granitoids, ledCamposNeto (2000)and Basei et al. (2000)to postulate anE-dipping subduction of the Adamastor Ocean litho-sphere underneath the Kalahari Craton. This polaritypattern is in disagreement with models adopted in mostprevious works, which inferred a westward subduc-tion of the Kalahari plate under the Rio de La PlataC ,1o
io Pien orogens (Basei et al., 2000; Brito-Nevesl., 1999; Campos Neto, 2000). In addition to the
ntense metamorphic Paleoproterozoic overprinhe unit also shows minor Neoproterozoic reworkhis later episode is restricted mainly to transtensieformation, associated to post-tectonic, taphrogxtra-orogen rifting, basin filling, and alkaline maatism at ca. 600–560 Ma (Siga, 1995; Basei et a000).
.4. Costeiro Granitic Belt (climax at ca. 615Ma)
The Costeiro Granitic Belt (sensuBasei et al., 2000)s a narrow (up to 30 km wide) and extended00 km long) NE-trending belt, comprising a greatersity of calc-alkaline metagranitic and orthognic plutons, as well as remnants of amphibolite faupracrustal sequences.
The Paranapiacaba Orogen (sensuCampos Neto000) also represents a complicated and poorlytrained jig-saw comprising: (i) two evolved coinental arc granitoids accreted onto the wesargin of the Curitiba Microplate; (ii) two preoproterozoic terranes (Curitiba and Luıs Alvesicroplates); (iii) Mesoproterozoic and Neoprote
oic resurrected basins (Ac¸ungui Supergroup anerra do Itaberaba Group); and (iv) late- and pollisional volcano-sedimentary basins. Scenariosodelling this intricate orogenic evolution may
ound elsewhere (Hackspacker et al., 2000; Caos Neto, 2000), but a generalised model of orenic juxtaposition for this complicated jig-sawo far, incomplete and mostly speculative, deser
226 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
more additional systematic isotopic and structuralstudies.
The Rio Pien Orogen/arc (Figs. 1 and 2a), in turn,represents a narrow wedge shaped unit, comprisinga syn-orogenic calc-alkaline suite (Pien-MandiritubaArc) ascribed to a NW-directed subduction of a lo-cal arm of the Adamastor Ocean (Machiavelli et al.,1993; Basei et al., 2000; Harara, 2001). The south-eastern flank of the arc is overthrusted to the SE ontoits basement (Luıs Alves Microplate), by means ofa transpressive shear zone. This tectonic limit wouldcorrespond to a major Neoproterozoic suture, the so-called Pien Suture Zone (Basei et al., 2000; Harara,2001).
5.6. Tocantins Province connections
The system Brasiliano II followed a similar evo-lution in the adjacent Southern Brasılia Belt fromthe Tocantins Province, with a coeval collisional cli-max M1 at ca. 630 Ma within the Soccorro-GuaxupeNappe/Orogen. This event, resulting from the west-ward subduction of the Sao Fransico Plate under theParana Plate, corresponds to the “first orogenic stage”(Trouw et al., 2000; Campos Neto, 2000). Subse-quently, this Nappe system was overprinted by thewestward collage of the Arac¸uaı Orogen, against thesouthern margin of the Sao Francisco Plate, at ca.560 Ma (Trouw et al., 2000; Fig. 2a). This “secondorogenic stage” (M2), resulting from the subductions heA pat-t onict
5
o-g canE -l andt anG eltc onicb att d col-la
A broad correlation between the south-western Pan-African orogens, i.e. Damara, Saldania, Gariep andKaoko belts, and the southern Brazilian Dom Feli-ciano, Paranapiacaba and Rio Pien orogens (Brasil-iano II), has long been accepted (e.g.Porada, 1979,1989; Fragoso-Cesar 1991; Trompette, 1994; Gresse etal., 1996, among others). Despite this consensus, newU–Pb ages obtained on the Saldanian syn-collisionalgranitoids of ca. 550 Ma (Silva et al., 2000a, Table 2)and of ca. 565 Ma on the Kaoko Belt granitoids fur-nished new insight to the debate. Ages from the Pan-African collisional magmatism, some 70 m.y. youngerthan their Brazilian counterparts led (Silva et al., 1997a,2000a; Frimmel and Frank, 1998) to argue against thecurrent correlation models.
6. Brasiliano III system of orogens (climaxes at595–560 Ma and 530–500 Ma)
This later orogenic system embraces the Arac¸uaıOrogen (collisional climax at 595–560 Ma) and theyoungest collisional event within the province, ascribedto the 530–500 Ma Buzios Orogeny (Figs. 1 and 2b;Table 2, and references therein).
The Aracuaı Orogen embraces the entire northerndomain of the province from southern Bahia State to thevicinities of the Rio de Janeiro city, some 950 km south(Figs. 1 and 2b). A large pre- to syn-collisional graniticbelt, hosted into huge metamorphosed metasedimen-t t andf terna ndedb onicm thee rm.T dt con-n ed.S ce oft dtbi c-t the2 tab-l on-s nitic
outhern margin of the Sao Francisco plate under tracuaı Orogen arc, caused a complex interference
ern on the nappe system with a late NW-direct tectransport (Trouw et al., 2000; Fig. 2b).
.7. Pan-African connections
The Brasiliano/Pan-African II system of orens broadly corresponds to the “Main Pan-Afripisode” from Caby (1998). The temporal equiva
ence between the Brasiliano II system of orogenshe Pan-African II includes mainly the West Africhana-Togo-Benin Province; the Mozambique Blosure at the S and W Tanzania; the intracratranch of the Damara Belt; the D1 metamorphic peak
he Central Madagascar orogens, and to the seconisional stage within the North Cameroon belts (Table 4,nd references therein).
ary and volcanic-sedimentary successions (thrusold belt), are the main orogenic units. On its wesnd northern tectonic domains, the orogen is bouy the reworked Archean/Paleoproterozoic cratargin of the Sao Francisco Craton, whereas toast, it is concealed by the Atlantic Ocean platfohe manner in which the Arac¸uaı Orogen terminate
o the south remains unresolved as its southernections with the Ribeira Belt units are poorly definome authors are very cautious about the presen
he orogen south of the 21◦ S parallel and are inclineo use this parallel reference as the Arac¸uaı-Ribeiraoundary (e.g.Wiedmann-Leonardos et al., 2000). The
nflection to NNE of the regional NE-trending direion of the southernmost segment (in the vicinity of1◦ S parallel) may have some influence on the es
ishment of this limit. Despite these opinions, we cider the southern tip of the ca. 590–560 Ma gra
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 227
belt, the south-eastern termination of the orogen, tobe located in the vicinity of the Rio de Janeiro city,more than 200 km southern of the reference parallel(Figs. 1 and 2a). Accordingly, this configuration for theAracuaı Orogen embraces at its southern boundary, theRio Doce and Rio Negro orogens fromFigueiredo andCampos Neto (1993)andCampos Neto (2000).
Outside the Arac¸uaı Belt, in Rio Grande do SulState, an isolated minor (40 km× 10 km) syn-tectonicgranitic intrusion (Cac¸apava do Sul Batholith), geo-graphically associated to the Dom Feliciano Orogen,was dated at ca. 560 Ma (Remus et al., 2000a). Thesame age (ca. 560 Ma) was obtained on the reworkedca. 2450 Ma basement of the syn-orogen pluton (Re-mus et al., 1996, in:Remus et al., 1999). Both agessuggest a local event developed temporally with theAracuaı Orogen collisional peak. Owing to the smallexposed area, it is not possible to evaluate the re-gional significance and the orogenic context from theseunits.
6.1. Pre-orogenic units from the Ara¸cuaı Orogen(?1000–840Ma)
The orogen is characterised by a large continen-tal margin depositional assemblage represented by theMacaubas Group and correlatives, laid down in thenorth-western (external) domain (Fig. 2b). There arefew isotopic data to place constraints on the sedi-mentation age of the continental margin associationsb tioni cio-m thed ca.9 dos,2
Marine metasedimentary and metavolcanic-sedimentary successions are also the dominant units atthe eastern (internal) domain of the orogen (Rio Doce,Paraıba do Sul groups and correlatives) (Fig. 2a). Theyare poorly constrained from the depositional point ofview, owing to metamorphic overprinting under higherconditions (amphibolite and granulite). Accordingly,their internal organisation, depositional environments,and the timing relatively to the basins and orogenicevolution, are not well established. Consequently,some of these successions may correspond to pre- andsyn-orogenic sub-basins, whereas others, to passivemargins. Oceanic successions, like those describedby Pedrosa-Soares et al. (1998)at the NW segment,seem to be absent from the eastern (internal domain).At the southeasternmost extension of the internaldomain, MORB-type amphibolites interleaved withthe marine succession were recognised, and yieldeda (conventional U–Pb) crystallisation age of ca.850 Ma (Heilbron and Machado, 2003). The datedamphibolites were interpreted by the authors assyn-depositional dykes constraining the maximum agelimit for the basin infilling.
The onset of the break-up of the continental crust,precursor to the rifting and drifting phase, was onlyrecently recognised through the dating of a felsic-alkaline bimodal pluton, intrusive into the basementof the northern tip of the orogen (Salto da Divisa foli-ated granite). The pluton, affected by the Arac¸uaı maindeformation phase, yielded a magmatic zircon U–PbS ,2 gens s ofc f theeF nicbi enicm
66
aseo eis-s uth-e Mi-c o
ut at the northwesternmost extremity, the associancludes extensive record of pre-Sturtian (?) gla
arine metadiamictites. The maximum age forepositional phase obtained on detrital zircon is50 Ma (Pedrosa-Soares and Wiedmann-Leonar000).
Some 50 km south-east of the glacio-marine (pral) deposit, the continental margin succession shrecord of an ocean formation stage comprising deep sea deposits (Ribeirao da Folha unit), contai
ng mafic-ultramafic plutonics, tholeiitic amphiboliteelitic and chemical-exhalative rocks, interpretedispersed and metamorphosed oceanic floor andlitic remnants (Pedrosa-Soares et al., 1998). One of
he amphibolitic occurrences was dated (whole-rm–Nd isochron systematics) and furnished an apnt age of ca. 820 Ma, interpreted by the authors, axtrusion age of the oceanic floor realms.
HRIMP crystallisation age of 875± 9 Ma (Silva et al.002a, Table 2). In the western basement of the oroome mafic tholeiitic dykes, with crystallisation agea. 900 Ma is another indirect estimate for the age oxtensional pre-orogenic stage (Machado et al., 1989).inally, an alkaline intrusion into the northern cratoasement, dated at ca. 675 Ma (Teixeira et al., 1997),
s the youngest record of the extensional pre-orogagmatism.
.2. (Early) pre-collisional magmatism (ca.30Ma)
The pre-collisional (ca. 630 Ma) magmatic phf the orogen is represented by two tonalitic gnic complexes. The main unit is exposed at the sornmost segment of the orogen (Serra do Marroplate ofCampos Neto, 2000), in Rio de Janeir
228 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
State (Rio Negro Complex). Some 600 km north-eastof this major complex, in Minas Gerais State, anothercoeval tonalitic association (Chapada Bueno TonaliticGneiss), still poorly constrained from the cartographi-cal point of view, crops out.
The former (main) association, is exposed as a long(ca. 200 km long) and very narrow (ca. 3 km wide)terrane comprising an expanded (sensuPitcher, 1983)dioritic to granodioritic, mainly tonalitic gneissic as-sociation (Tupinamba, 1999; Tupinamba et al., 2000).The unit is intruded and locally severed by a late pre-collisional phase (Serra dosOrgaos unit) intruded atca. 570 Ma (Silva et al., 2003a, Table 2). A tonaliticgneiss from the complex yielded a U–Pb conventionalzircon age of ca. 634 Ma, interpreted as the crystallisa-tion age of the pluton (Tupinamba et al., 2000). Basedon isotopic (Nd and Sr) data, the unit was ascribedto a juvenile intraoceanic pre-collisional magmatic arc(Tupinamba, 1999; Tupinamba et al., 2000; Heilbronand Machado, 2003). In addition to the juvenile, dom-inant tonalitic association, the arc also includes S-type leucogranites and gneisses, dated at ca. 600 Ma(Tupinamba et al., 2000).
Besides this major exposition, other remnants of co-eval tonalitic gneiss (Chapada Bueno Tonalitic Gneiss)are known further north, in Minas Gerais State (Paes,1999). A tonalitic gneiss from this unit, was datedthrough Pb–Pb evaporation and U–Pb conventionalmethods and yielded respectively ca. 625 Ma (Paes,1999) and 630 Ma (L.C. Silva, unpublished data, Ta-b RioN aterp atc toj nceh Arc,o ver-t f thisc thei ismw
6
n-i sed-i plu-t at
quantity of isolated plutons and major batholiths, whichdo not define a continuum, but are internally organisedaccording to major E-W compositional zoning (Fig. 3;Tables 2 and 3). The western plutons comprise mainlypre- to syn-collisional, high-K calc-alkaline continen-tal arc-association, whereas the easternmost plutons arecomposed mainly of S-type anatectic granites typicalof a syn-collisional continental arc-associations.
The former (western arc) includes three ma-jor batholiths (Serra dosOrgaos, Moniz Freire andGalileia) characterised by discrete post-magmaticsolid-state metamorphic overprinting. The crystalli-sation ages record a North-South age-span from ca.595 to 585 Ma (Galileia Batholith); ca. 580 Ma (Mo-niz Freire Batholith), and ca. 570 Ma (Serra dosOrgaos Batholith) (Sollner et al., 1989; Nalini, 1997;Tupinamba, 1999; Noce et al., 2000; Silva et al.,2003a). They represent chemical and isotopic affinitieswith the Cordilleran I-type, K-rich calk-alkaline series(sensuPitcher, 1983). Their Nd isotopic signature isakin to the mature continental arcs, with contributionfrom enriched Paleoproterozoic mantle lithosphere andcrustal sources (Nalini, 1997; Tupinamba, 1999). Ac-cordingly, the extended association corresponds to a(late) pre-collisional phase from the Arac¸uaı Orogen(Serra dosOrgaos-Galileia Arc).
The latter (eastern arc) is composed of numerous(discontinuously exposed) syn-collisional peralumi-nous leucograntic/charnockitic S-type plutons, exhibit-ing moderate to strong solid-state overprinting, andc lumi-n pet-r ites)i re-d rgestg dis-ca ch-i tes.T romn ith)t ,2 ecy-c
theB hep ne-b ack
le 2). In a like manner as that observed in theegro Arc, the tonalitic gneiss is also intrude by a lre-collisional association (Galileia Tonalite), dateda. 590 Ma (Nalini, 1997). Presently, we are unableudge whether the northern early tonalitic occurreas a direct geotectonic relation to the Rio Negror whether it represents a distinct tectonic unit. Ne
heless, these uncertainties and the recognition ooeval tonalitic association further north highlightsmportance of the earlier pre-collisional magmatithin the Aracuaı Orogen evolution.
.3. Pre-to syn-collisional units (580–560Ma)
A discontinuous 900 km long NNE-trending gratic belt, hosted into the pre- and syn-orogenic metamentary belt, represents the pre- to syn-collisionalonic stage (Fig. 2b). The belt is composed of a gre
onstitute the eastern anatectic association. Peraous granitic augengneisses, with chemical andographic crustal signatures (S-type gneissic granncluding C-type foliated granites (charnockites), pominate in the south-eastern extension. It is the laranitic association within the orogen, extendingontinuously from Rio de Janeiro city (Pao de Acucarnd Corcovado hills) for some 900 km north, rea
ng the limit between Minas Gerais and Bahia Stahe syn-collisional crystallisation ages also varies forth to south from ca. 580 Ma (Nanuque Bathol
o ca. 560 Ma (Rio de Janeiro Batholith) (Silva et al.003a, Table 2) and characterises a continentally rled magmatic arc (Rio de Janeiro-Nanuque).
One of the most striking features, which makerasiliano III granitic magmatism unique within trovince, is the ubiquitous exposure of orthopyroxeearing granitoids (charnockites). Owing to the l
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 229
of detailed studies, and to the ubiquitous presence oforthopyroxene, these charnockites have been mistak-enly mapped and associated with the PaleoproterozoicJuiz de Fora orthogranulitic basement, which precludedtheir correct presentation on the available maps. Onlyin recent works has their magmatic nature and Neopro-terozoic age been recognised (Jord-Evangelista, 1996;Duarte, 1998; Silva et al., 2000c). At least the garnet-free members of these associations show affinities withthe magmatic (anatectic) charnockites, and the C-typegranitoids fromKillpatrick and Ellis (1992)andYounget al. (1997). One pluton, from the garnet-charnockiticassociation yielded a zircon U–Pb SHRIMP crystalli-sation age of ca. 580 Ma (Silva et al., 2002a, Table 2).
In addition to the orogenic magmatism, the pre-collisional stage of the orogen also records flysh-like, deep sea, metaturbiditic deposits, associated withthe continental margin deposits. The internal organ-isation of these assemblages is not well defined, ac-cordingly their relations with the orogenic zonationare not defined. At the western external tectonic do-main one of the sub-basins (Salinas unit) representsa maximum depositional age of ca. 570 Ma, obtainedon detrital zircons, and was ascribed to a late colli-sional deposition stage and the adjacent arc degradation(Lima et al., 2002). Another sub-basin from the north-western domain (Capelinha Formation) also presentssyn-collisional affinities, although there is no avail-able radiometric age (Pedrosa-Soares and Wiedmann-Leonardos, 2000).
thei andi int phicc thew do-m bo-l lowP
-t d at tern( nti-n asesf mw urn,c na-t nic-
sedimentary marine successions, is characterised by anorthern amphibolite-facies sub-domain and a south-ern granulite-facies sub-domain.
These higher metamorphic conditions gave rise tothe abundant ca. 580–560 Ma syn-peak S- and C-typemagmatism (Table 2). Accordingly, the eastern se-quence represents the roots (core) of the thrust andfold belt system, overthrusted onto the eastern mar-gin of the Sao Francisco Plate. At the north-western tipof the orogen, the metasedimentary belt shows a NNE-SSW-trend inflexion (Fig. 2b) as well as an inverted E-vergent tectonic transport. Accordingly, it represents apossible segment from the opposite continental marginof the Congo Craton (Pedrosa-Soares, personal com-munication).
6.4. Late- to post-collisional magmatism (ca.540–480Ma)
The remaining exposed granitic phases within theorogen (some 10% of the exposed arc) presents com-positional variations from gabbros to syenites, withfrequent charnockitic phases, and minor scattered,dominantly I-type and alkaline plutons (Wiedemann,1993; Figueiredo and Campos Neto, 1993; Cam-pos Neto and Figueiredo, 1995; Pedrosa-Soares andWiedmann-Leonardos, 2000) (Fig. 2b). They repre-sent the final collapse of the orogen and crop out asoccasionally zoned small batholiths, with mafic cores(Wiedemann, 1993; Pedrosa-Soares and Wiedmann-L n-t them a-t iso-t ,1 f theo of ano sion( isp Ma(
6
d byt erns x( has
The syn-collisional stage culminated withnversion and metamorphism of rifted basinss characterised by strong east-west variationhe metamorphic conditions. Low-grade metamorontinental margin sequences predominate withinestern (external) domain. The eastern (internal)ain, in turn, was affected dominantly by amphi
ite and granulite facies metamorphism, under and–high T (cordierite in/kyanite out).Pedrosa-Soares et al. (2001)delineated a major in
ernal organisation of the orogen, and highlighteransversal metamorphic polarity. Within the wesexernal) tectonic domain, comprising mainly coental margin deposits, metamorphic grade incre
rom low greenschist to low amphibolite facies froest to east. The eastern (internal) domain, in tomprising the magmatic granitic belt and the (aectic roots) of the metasedimentary and volca
eonardos, 2000). The tholeiitic phases present coaminated mantle signatures, when compared toodern arc-tholeiitic series. The high-K felsic magm
ism has been explained in terms of a chemical andopically “atypical” intracontinental arc (Wiedemann993). The arc was ascribed to the waning stages orogen, succeeding an east-directed subductionceanic lithosphere, and continent-continent colliWiedemann, 1993). The crystallisation ages of thost-collisional phase range from ca. 540 to 480Fig. 3; Tables 2 and 3).
.5. The reworked basement
The largest segment of Archean rocks reworkehe Brasiliano event within MPV is the north-westegment of the Arac¸uaı Orogen, the Guanhaes CompleFig. 2a). It comprises chiefly TTG orthogneiss, and
230 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
been interpreted as an alloctonous terrane, incorporatedinto the craton during the Brasiliano/Arac¸uaı collage.The SHRIMP results yielded crystallisation ages fromca. 2900 to 2700 Ma, and Neoproterozoic overprintingmetamorphic ages (Silva et al., 2002a, Table 2). As thedata are compatible with previous ages obtained in thecratonic basement from the south-east domain of thecraton (Carneiro et al., 1998; Noce et al., 1998; Teixeiraet al., 2000), it is presently reinterpreted as part of theArchean reworked basement of the craton, and not asa displaced terrane, juxtaposed during the Neoprotero-zoic collage. Together with the adjacent Paleoprotero-zoic orthogneiss complexes (see below), it correspondsto the western continental margin of the Arac¸uaı Oro-gen in Minas Gerais State (Fig. 2b; Table 2).
In Bahia State, the northern tip of the orogen isthrusted against a Archean/Paleoproterozoic gneissicbasement (Fig. 2b), but there is no reliable geochrono-logical data on this continental margin domain. Onlyabout 150 km north of this limit, a ca. 2710 Mahigh-grade charnockitic gneiss shows Neoproterozoicoverprinting, characterised by discrete zircon rims(overgrowths), imprecisely dated at ca. 710 Ma (1σ),by SHRIMP systematics (Silva et al., 2002c, Table 2).
In addition to the Archean cratonic margin, Pale-oproterozoic orthogneisses constitute most of the re-worked south-western basement of the orogen, at thesouth-easternmost margin of the Sao Francisco Cra-ton/Plate in Minas Gerais State (Fig. 2b;Table 2). Theyare severed TTG gneissic associations, interpreted ast arginoT ntlye my-l eiraC 200t ac-c e agea eg r-a igh,a olli-s eltsw Ma( thes arc,c dedi the
Mineiro Belt (Teixeira and Figueiredo, 1991). Togetherwith the adjacent western Archean TTG orthogneisses,they correspond to the easternmost continental marginof the Sao Francisco Craton/Plate. A second and bet-ter constrained metamorphic overprinting (M2) corre-sponding to the Neoproterozoic collage of the Arac¸uaıOrogen onto the eastern Sao Francisco cratonic margin,yielded an age of ca. 580–570 Ma (Silva et al., 2002a,Table 2).
South-east of this unit, another high-grade or-thogneissic domain (Juiz de Fora Complex) corre-sponding to the easternmost component of the SaoFrancisco Plate, the margin furnished crystallisationages on a charno-enderbitic gneisses from ca. 2200 to2140 Ma. The metamorphic granulite-grade overprint-ing, in turn, yielded ca. 580 Ma (Sollner et al., 1991;Machado et al., 1996).
Another Paleoproterozoic orthogneiss (CaparaoComplex,Fig. 2b) showing Brasiliano granulite-faciesoverprinting, crops out as a reworked basement inlierat the core of the orogen. A charnockitic leucogneissfurnished ca. 2195 and 590 Ma ages for the crys-tallisation and metamorphic overprinting events, re-spectively (Silva et al., 2002a, Table 2). The sameunit furnished similar ages through conventional U–Pbanalysis, but the crystallisation age was interpreted asthe age of the precursor of the rock (Sollner et al.,1991).
North of the Caparao Complex, in apparent conti-nuity is exposed in an amphibolite facies, reworkedb plex,F e-o isd pa-l wasd at-i MaaA nedo ectedf
eissf iss)( Ma( ind au-t ca.6
he roots of an arc accreted onto the eastern mf the Sao Francisco Craton/Plate (Silva et al., 2002a).he pre-collisional phase of the TTG arc, presexposed as amphibolite facies highly transposed
onitic orthogneisses (Piedade, formerly Mantiquomplex), furnished crystallisation ages from ca. 2
o 2100 Ma. The syn-collisional phase, in turn, wasreted between 2100 and 2050 Ma, the approximatlso of the first metamorphic event (M1) recorded on thneiss (Silva et al., 2002a). The metamorphic tempetures operating during the collisional peak were hnd the thermal flux remained elevated after the cional peak, giving rise to late-collisional crustal mith charnockitic composition, dated at ca. 2100
Table 2). The authors interpret these domains asevered roots of a reworked continental marginoeval with the Paleoproterozoic batholiths intrunto the southern tip of the craton and ascribed to
asement orthogneissic domain (Pocrane Comig. 2b). The unity is poorly constrained from the glogic and isotopic points of view, and until nowevoid of radiometric age. Only one amphibolitic
eodyke, intrusive into the regional orthogneissated by means of zircon U–Pb SHRIMP system
cs, and furnished a crystallisation age of ca. 1500nd metamorphic overprinting of ca. 600 Ma (Table 2).ccordingly, the 1500 Ma crystallisation age obtain the paleodyke, represents a minimum age exp
or the orthogneissic country-rock.West of Rio de Janeiro State, another orthogn
rom the basement of the orogen (Quirino OrthogneFig. 2b) yielded crystallisation ages of ca. 2185Valladares et al., 1996). The role of this minor domauring the orogenic evolution is not clear but the
hors also dated a metamorphic overprint yielding00 Ma.
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 231
Besides the orthogneissic units, other remnants ofthe Paleoproterozic megacycle are also present, espe-cially the rift-sag Espinhac¸o basin (Espinhac¸o Super-group) (Fig. 2b). The basin evolution started at ca.1700 Ma, as indicated by U–Pb ages obtained on ametarhyolite (Brito-Neves et al., 1979) and on bad-deleyite from mafic dykes, interpreted as related tothe extension of the basin (Silva et al., 1995). TheBorrachudos alkaline metagranite is another Paleo-proterozoic remnant of the taphrogenic phase, intru-sive into the Archean basement west of the orogen(Fig. 2b). The pluton was deformed and metamor-phosed in response to the Brasiliano overprinting onthe eastern Sao Francisco Cratonic margin. The rockpresents U–Pb crystallisation ages from ca. 1670 Ma(Chemale et al., 1998) to ca. 1740 Ma (Silva et al.,2002a, Table 2). It also shows evidence of Neopro-terozoic (undated) metamorphic overprinting on therims of the analysed zircon populations (Silva et al.,2002a).
6.6. Juxtaposition and collage of the orogeniccomponents: the Ara¸cuaı Orogen redefined
The precise characterization of these Late Pre-cambrian (ca. 595–560 Ma) pre- and syn-orogenicarcs (Table 2) reinforces the characterisation of ayounger orogenic stage predicted on the basis of re-gional studies on the north-eastern tip of the RibeiraBelt (Serra do Mar Microplate), i.e. the ‘Rio Doce’O m-p o-s nitics arM s as -a ocessi rcsa re-t a)c xisa cra-tT lga-m rrad e byt 01;H
The orogenic evolution of the early intraoceanic RioNegro and the Arac¸uaı Orogen is considered elsewhere(Campos Neto, 2000). The author discriminates anearly, ca. 630 Ma Rio Negro Arc/Orogen, from the ca.590 to 560 Ma Rio Doce Orogen (herein interpreted asa south-eastern extension of the Arac¸uaı Orogen). Therecent characterisation of ca. 630 Ma tonalitic gneisses,within the pre-collisional phase of the Arac¸uaı Oro-gen (Table 2), and coeval with the Rio Negro Arc,favours a continuous evolution for both associations,as part of a single orogen. Nevertheless, even with thenew isotopic constraints there is no robust evidence toplace firm constraints on these concurring evolutionalmodels, and much additional field and isotopic work isneeded to clarify the issue.
The assumed age of the ocean floor extrusion ofca. 820 Ma (Pedrosa-Soares et al., 1998) suggests itprobably represents a north-east extension of the To-nian Goianides and Charrua oceans, precursors to theAdamastor ocean proper. The former (Goianides), wassubducted beneath the south-western margin of the SaoFrancisco Plate (Pimentel et al., 1997; Campos Neto,2000) and the latter (Charrua), subducted under theeastern margin Rio de La Plata Plate further south(Chemale, 2000).
Recent Sm–Nd isotopic studies on the Arac¸uaıOrogen granitoids highlighted the role of a Meso toPaleoproterozoic remobilised continental crust, dur-ing the Late Brasiliano collision (e.g.Nalini, 1997;Tupinamba, 1999). We interpret these 1600 to 2000 MaT theSa ltingo ericm elts(
65
hes y( edo st-r est-v thes .5
rogeny (Figueiredo and Campos Neto, 1993; Caos Neto, 2000). Owing to the compatible tectontructural, chemical signatures, and orogenic gratages in the Arac¸uaı Orogen and in the Serra do Microplate, we considered the ‘Rio Doce’ Orogen a
outh-eastern extension of the Arac¸uaı Orogen. Actully, both segments share a common convergent pr
nitiated with the accretion of juvenile intraoceanic at ca. 630 Ma. This initial stage was followed by acc
ion of the cordilleran continental arc (ca. 595–570 Mulminating with widespread syn-collisional anatend the dockage of arc-terranes onto the eastern
onic margin (at ca. 580–560 Ma) (Table 2; Fig. 3).he E-directed subduction of the previously amaated Sao Francisco/Parana plates (beneath the Seo Mar Microplate) was the mechanism responsibl
his evolutionary process (Pedrosa-Soares et al., 20eilbron and Machado, 2003).
DM ages in the same context of the evolution ofouthern MPV granitoids, synthesised onTable 2, i.e.s mixed-source magmas, resulting from the mef a Paleoproterozoic continental crust and lithosphantle and mixing with newly accreted, juvenile m
e.g.Silva, 1999; Cordani et al., 2000).
.7. Buzios Orogen (collisional climax at30–500Ma)
Outside the Arac¸uaı Orogen, the latest stage of tystem Brasiliano III is ascribed to the Buzios OrogenSchmitt, 2000). This orogenic event was recognisn the basis of precise dating of “in situ” thruelated migmatitic veins, associated with the wergent thrusting of the Cabo Frio Terrane ontoouth-eastern extension of the Arac¸uaı Orogen, at ca30–500 Ma (Schmitt, 2000) (Figs. 2b and 3). A major
232 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
component of the Buzios Orogen is an amphibolitefacies volcanic-sedimentary rift-like succession, in-cluding N-MORB amphibolites and metaturbidites.The amphibolites yielded Sm–Nd model ages of ca.1000 Ma, whereas detrital zircons from the latter,yielded minimum ages spanning from ca. 1000 to700 Ma (Schmitt, 2000). Distinct from what is observedin the adjacent Neoproterozoic orogens, the BuziosOrogen collisional climax occurred under mediumto high P/T conditions, as deduced from the pres-ence of garnet-amphibolites and kyanite-sillimaniteand kyanite-K-feldspar assemblages, in high-grademetapelites (Schmitt, 2000).
The effect of this Cambrian convergent stage wasalso recognised by means of conventional zircon U–Pbgeochronology (Heilbron and Machado, 2003) ongneisses herein interpreted as a major component ofthe south-eastern tip of the Arac¸uaı Orogen. This lat-est Brasiliano collage episode is interpreted as a re-sult of the subduction of a possible promontory ofthe Congo Plate underneath the already welded south-eastern extension of the Arac¸uaı Orogen, implyinga north-west-directed subduction of the AdamastorOcean at 530–500 Ma (Schmitt, 2000; Campos Neto,2000; Heilbron and Machado, 2003).
Other Cambrian compressional magmatic episoderelated to a generation of syn-tectonic, amphibolite-facies anatectic mobilisates occur within the Mesopro-terozoic Punta del Este Terrane (Fig. 2a). It is datedat ca. 540–520 Ma (Preciozzi et al., 1999; Basei et al.,2 herne d ast aas ventw tot Oro-g astiw in-v rianI
6
O tate,t mento was
ca. 2000 Ma, with metamorphic overprinting ages ofca. 520 Ma (Schmitt, 2000). It represents a supposedwestern continental margin of the Cambrian BuziosOrogen (Schmitt, 2000; Heilbron and Machado, 2003).This easternmost and youngest segment is also inter-preted as an exotic fragment from the Congo Craton,amalgamated to the eastern MPV, during the waningstages of the Brasiliano collage (Fonseca et al., 1994,in: Schmitt, 2000).
6.8. Tocantins Province connections
The record of the Brasiliano III system of oro-gens within the Tocantins Province, is represented bythe Paraguay Belt, probably related to the ca. 520 MaPampean Orogen in Argentina (Trompette, 1994) andcoeval with the Buzios Orogen in MPV. In the south-eastern tip of the Tocantins Province, the interferenceof the Aracuaı Orogen (Brasiliano III) on the Socorro-Guaxupe Orogen (Brasiliano II) is well documented(Trouw et al., 2000; Campos Neto, 2000), particu-larly on the Andrelandia passive margin assemblage.This late collisional event is recognised by means ofthe north-west-directed ca. 560 Ma tectonic transport,overprinting an earlier east-directed ca. 630 Ma tec-tonic transport, giving rise to a highly complicated in-terference tectonic pattern (Trouw et al., 2000; CamposNeto, 2000).
The east-directed tectonic transport during theBrasiliano II orogen (Fig. 2) is attributed to the subduc-t ranP t, int hesepuat tiono romU mp-ta
6
ltsa :a out-l e.g.
000). The authors interpret this event as a soutxtension of the Rio Doce Orogeny (herein treatehe Aracuaı Orogeny). Owing to the younger 520 Mge, relative to the 560 Ma age of the Arac¸uaı colli-ional peak, we prefer to temporally correlate this eith the ca. 530–500 Ma Buzios Orogen. In addition
he Buzios Orogen, the ca. 540–520 Ma Pampeanen (Rapela, 2000), situated about 1000 km south-e
n Argentina and Paraguay (Rapela, 2000) took placeithin the same interval. But in this case, the oceanolved in the built up of the orogen was the Cambapetus Ocean and not the Adamastor proper.
.7.1. Reworked basementEast of the small exposed segment of the Buzios
rogen, at the coastal region of the Rio de Janeiro She reworked Paleoproterozoic orthogneissic basef the orogen crops out. The granitic orthogneiss
ion of the Sao Francisco Plate underneath the Paalate. The north-west-directed tectonic transpor
urn, was ascribed to the eastward subduction of treviously amalgamated Sao Francisco-Parana platesnder the Serra do Mar Microplate/Arac¸uaı Orogenrc (Trouw et al., 2000; Campos Neto, 2000). While
he first orogenic episode is related to the consumpf the Goianides Ocean (the Brazilides Ocean fnrug, 1997), the second is ascribed to the consu
ion of local branch of the Adamastor Ocean (Trouw etl., 2000; Campos Neto, 2000).
.9. Pan-African connections
The Aracuaı and West Congo Neoproterozoic bere counterparts of the Arac¸uaı-West-Congo Orogenconfined orogen developed in an embayment
ined by the Sao Francisco and Congo cratons (
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 233
Brito-Neves and Cordani, 1991; Trompette, 1994;Pedrosa-Soares et al., 1998). The collisional stage inthe West Congo Belt was dated at ca. 565 Ma (Tackand Fernandez-Alonso, 1998). The present integrationprovides a finer tuning for these correlations. The ca.565 Ma D1 syn-collisional peak age recorded from thesouth-western African side (Table 4) coincides, withinerror, with the ca. 580–560 Ma age range obtained forthe collisional peak from the Arac¸uaı Orogeny (Silvaet al., 2002a, 2003a).
The observation of east-vergent thrusting structuresin the eastern metasedimentary (internal) domain sug-gests the possibility of the correlation of these depositswith the Congo Craton continental margin, during theAWCO-Aracuaı-West Congo pre-orogenic extensionalphase (Pedrosa-Soares, personal communication).
Another important tool to this correlation attempt isfurnished by the crystallisation ages of ca. 924–912 Ma(U–Pb SHRIMP), obtained on the pre-orogenic rift-related, bimodal volcano-plutonic association of theWest Congo Belt (Tack et al., 2001). Additionally,the uppermost Mayumbiam rhyolitic lavas sequenceyielded a zircon U–Pb SHRIMP age of 912± 7 Ma.The difference between the ages of the anorogenic Saltoda Divisa granite (ca. 875 Ma) and the Mayumbiamlavas (ca. 912 Ma) suggest a migration of the ther-mal axis of the rift to the Brazilian side of the basinsome 40 m.y. after the onset of the rifting process. Be-sides the age difference, the great thickness of the bi-modal pile in the West Congo Orogen, compared tos int m-m ans
ast ernP stalB canb uth-e elt,t rianO inA heG Ro-d Ma( int ningf
Finally, the ca. 540–520 Pampean Orogen in Ar-gentina and Paraguay (Rapela, 2000), was also de-veloped synchronously with the waning stages of theBrasiliano III collage (Buzios Orogen). Nevertheless,this synchronism of the former (Pampean Orogeny),is related to the opening and consummation of theCambrian Iapetus Ocean, instead of the Neoprotero-zoic Adamastor Ocean.
7. Conclusions
The picture which emerged from this integratedgeochronological and field approach confirms and am-plifies the conclusions of recent review works on theSouth America Neoproterozoic (Brito-Neves et al.,1999; Campos Neto, 2000; Trouw et al., 2000). Thestudy also confirms the evolutionary path, through suc-cessive systems of orogens, marked by sequential anddiachronous ocean opening and closure, subduction,crustal melting and metamorphic overprinting. It cor-responds to successive and geographically diverse evo-lution of the Wilson’s Cycle, from ca. 880 to 500 Ma,which gave rise to the final Western GondwanalandSupercontinent amalgamation.
The Brasiliano Supercycle was characterised as acomposite orogen (nomenclature afterWilson, 1968;Sengor, 1990), with distinct convergent plate bound-aries, corresponding to the diachronic ‘branched sys-tem of orogens’ of (Brito-Neves et al., 1999; CamposN oro-g sest
ag-m cre-t anici asil-i thet n-c ro-g nceo theA tal-s yed am Pbg sug-g ariesb The
carce occurrences of the rift-related magmatismhe Aracuaı Orogen suggests that the rift was asyetric with a thermal axis located in the Afric
ide.Outside the AWC, the system Brasiliano III h
emporally equivalents in other short-lived, southan-African orogens. These include: Kaoko, Coaranch of Damara, Gariep, Saldania, West Afrielts; the Pan-African terranes from Sri Lanka, Sorn India, Madagascar, part of the Mozambique B
he Ross Orogeny (Antarctica) and the Delamarogeny/Ellsworth-Whitmore Mountains Terraneustralia (Table 4, and references therein). Within tariep and Damara orogen the breakup of theinia Supercontinent took place from ca. 780 to 740Frimmel and Frank, 1998), some 150 m.y. later thanhe West Congo, characterising a sequentially operom north to southwards.
eto, 2000). Its protracted, successive convergent (enic) evolution from ca. 880 to 500 Ma compri
hree major successive systems of orogens (Fig. 3a).The onset of the Neoproterozoic orogenic m
atism is attributable to an early Cryogenian acionary episode, which gave rise to an intraocesland arc, ascribed to the system of orogens Brano I (subduction-controlled orogen). Later on,ectonic evolution took place mainly as ‘collisioontrolled’ orogen giving rise to the systems of oens: Brasiliano II and III. The continuous convergef the Parana, Sao Francisco-Rio de La Plata andfrican Kalahari-Congo plates, triggering continencale compressional transpressive tectonics, plaajor role in this evolution. The integration of the U–eochronological updated database on the MPVests modifications to the accepted internal boundetween the distinct orogens forming the province.
234 L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240
Aracuaı Orogen had its geographic limits expanded onthe basis of the new U–Pb SHRIMP date obtained fromits pre- to syn-collisional arcs (ca. 590–560 Ma), in or-der to encompass the former Rio Doce Orogen.
In addition to the new design of the provincialinternal boundaries, the integrated analyses and re-interpretation of 180 zircon ages from 160 Neopro-terozoic plutons provided a new consistent provincialgranitic cronostratigraphy (Fig. 3; Table 3and A). Theintegrated analyses of the chemical, structural, andgeochronological data from the successive pre-, syn-and post-collisional magmatic pulses and metamor-phic peaks, furnished a first general and precise pic-ture of the orogenic evolution of the entire province.Accordingly, the study contributed to the general un-derstanding of the timing and nature of this highly com-plex and extended Brasiliano/Pan-African Supercycle(Table 4).
The study reinforces from the geochronologicalpoint of view previous reconstruction models delin-eating an Arac¸uaı-Western Congo integrated evolution(AWCO) (Pedrosa-Soares et al., 1998) from breakup(ca. 900 Ma) to reamalgamation stages (ca. 560 Ma).It also reinforces the criticism fromSilva et al. (1997,2000a)andFrimmel and Frank (1998), on previous cor-relations between the ca. 560–550 Ma southern Pan-African and the ca. 640–600 Ma southern Brazilianorogens. Accordingly, an alternative temporal corre-lation of the ca. 550 Ma Saldania Orogeny with Ross
he
Psil-nich-bslyor-
a
deshecants,theer-
ica, the known early juvenile crustal growth was veryrestricted, totalling perhaps less than 10% of the totalexposed Brasiliano crust. On the other hand, the Pan-African orogens, especially from the north-west andeast African continent, were much more efficient interms of generation of new crust. The >650 Ma (post-Brasiliano I) evolution, shared with other Pan-Africancontinental-collision orogens, show small-scale newcrustal growth and widespread crustal recycling. It de-lineates a major role for continental lithospheric man-tle delamination as has been demonstrated for thePan-African Trans-Saharan Belt (Black and Liegeois,1993). This is suggested in particular by: (i) extensivehigh-K calc alkaline and S-type magmatism; (ii) high-T/low-P metamorphism; (iii) major shear zones parallelto the cratonic limits; (iv) (scattered) thrust remnants ofobducted ophiolites; (v) post-collisional alkaline mag-matism; and (vi) marginal cratonic reactivation. Thesepeculiarities favour the current interpretations in theBrazilian literature as evidence of a Himalayan-typeevolution following a Cordilleran accretionary arc sys-tem.
Acknowledgements
The Brazilian Government’s “Conselho Nacional doDesenvolvimento Cientıfico e Tecnologico (CNPq)—Proc. 201.500.95-7” and Geological Survey of Brazil( s att geAb eo-l .W dM usaR ea oa d tog
A
ticlec .p
CPRM) supported the senior author’s investigationhe University of Western Australia. We acknowledntonio C. Pedrosa-Soares and Carlos Maurıcio Nocey the fruitful comments and observations on the g
ogical and tectonic evolution of the Arac¸uaı Orogene are also indebted to Inacio Medeiros Delgado anarcio Antonio da Silva and especially to Joseneodriguez for the ArcView edition of Figs. 1 and 2. Wre also grateful to the reviewers, Mario Campos Netnd Nuno Machado for their suggestions, which lereat improvement of the original version.
ppendix A. Supplementary data
Supplementary data associated with this aran be found, in the online version, atdoi:10.1016/jrecamres.2004.10.004.
Orogeny (in the Antarctic continent) and not with tsouthern Brazilian orogens was favoured.
The analysis of a large amount of U–Pb SHRIMdata allows a better definition of the extent of the Braiano overprinting over large basement paleotectopolycyclic units, mainly on the controversial souteastern limits of the Sao Francisco Craton. The U–Pages resetting and tectonic transposition (ubiquitourecorded into the Archean and Paleoproterozoicthogneisses), indicates that the designation of Sao Fran-cisco “Metacraton”, in the sense used byAbdelsalamet al. (2002)for the “Saharan Metacraton”, would bebest classification for this pre-Neoproterozoic unit.
A final assertion on the Neoproterozoic on both siof the Atlantic is that the crucial distinction between tNeoproterozoic evolution in South America and Afriis based neither on the timing of the successive evenor on the orogenic architecture, but on the scale ofearliest orogenic accretionary events. In South Am
L.C. da Silva et al. / Precambrian Research 136 (2005) 203–240 235
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