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.Earth-Science Reviews 50 2000 77111

www.elsevier.comrlocaterearscirev

The origin and evolution of the South American Platform

Fernando Flavio Marques de Almeida a, Benjamim Bley de Brito Neves b,1,Celso Dal Re Carneiro c,)

aDepartment of Mining, Escola Politecnica, Uniersidade de Sao Paulo; Alameda Franca 432, Apart. 9, 01422-000, Sao Paulo SP, Brazil

bDepartment of Geology, Instituto de Geociencias, Uniersidade de Sao Paulo, P.O. Box 11 348, 05422-970, Sao Paulo SP, Brazil

cDepartment of Geosciences Applied to Teaching, Instituto de Geociencias, Uniersidade Estadual de Campinas, P.O. Box 6152,

13083-970, Campinas SP, Brazil

Received 9 March 1998; accepted 14 November 1999

Abstract

The South American Platform is defined as the stable continental portion of the South American plate not affected by the

Phanerozoic Caribbean and Andean orogenic zones. It is surrounded by these orogenic zones and extends to the

marginal Atlantic coast. The basement of the platform consists of Archean and Proterozoic continental crusts arranged . . . .during three main sets of orogenic events: 1 Trans-Amazonian Paleoproterozoic , 2 Late Mesoproterozoic and 3

BrasilianorPan African. The latter resulted in the consolidation of the youngest mobile belts of the platform basement. It is, .by far, the main phenomenon responsible for the overall pattern of tectonic components cratonic nuclei and fold belts and

the formation of the general structural framework at the time when the platform was a portion of the Gondwana

supercontinent. During the Phanerozoic Eon, different cover stages were developed through six main sedimentary cratonic

sequences, of which the last one is exclusive to the South American continent. The final individualization stages and theirrespective post-Paleozoic sequences were accompanied by a series of specific intracratonic processes, both tectonic rift

. .basins, overprint of new structural styles in previous basins and magmatic basaltic and alkaline . The activation processes

have generally been attributed to the opening of the Atlantic Ocean on the east and the Andean orogeneses on the north andwest. Nevertheless, a minor part of these events may have been caused by sublithospheric actions mantle-activated

.processes beneath the interior of the platform. q2000 Elsevier Science B.V. All rights reserved.

Keywords:tectonics; South America; platform; basement; platform covers; Archean, Proterozoic; Phanerozoic

1. Introduction

This paper aims to synthesize the present state-of-

the-art of the geological knowledge on the origin and

)

Corresponding author. Fax: q55-19-289-1562. .E-mail addresses: [email protected] F.F.M. de Almeida ,

[email protected] B.B. de Brito Neves , [email protected] .C. Dal Re Carneiro .

1Fax: q55-11-210-4958.

evolution of the South American Platform, the oldest

part of the South American Plate. .Two of the present authors BBBN and CDRC

think that it is time to update the most quoted paperon Brazilian tectonics: the classical 36-page Brazil-

ian National Department for Mineral Resources Pro- .duction DNPM Bulletin 241, Origin and Evolution

of the Brazilian Platform Origem e Eolucao da. Plataforma Brasileira , by Almeida, 1967 following

.Almeida, 1966 : this broad synthesis on the Brazilian

0012-8252r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. .P I I : S 0 0 1 2 - 8 2 5 2 9 9 0 0 0 7 2 - 0


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( )F.F.M. de Almeida et al.rEarth-Science Reiews 50 2000 7711178

Geology was written before the development of the

new global tectonics, with emphasis on the Precam-

brian basement, as well as delineating the most

promising research lines to be followed. We try to

consider as much as possible all the produced geo-

logical information since the appearance of the two .papers of Almeida 1966, 1967 . All zones of the

entire continent have been investigated under differ-

ent detail levels and at present the overall picture is

better known. The present progress on Braziliangeology may be evaluated in books Almeida and

.Hasui, 1984; Schobbenhaus et al., 1984 , continen-tal-scale geological maps of Brazil 1984, scale

1:2,500,000, published by DNPM researchers and

colaborators; Delgado and Pedreira, 1995, scale. 1:7,000,000 and South America DNPM, 1997,

.1:5,000,000, unpublished , although many maps and

reports still remain unpublished. Most of the pub-

lished material is in Portuguese, a fact that highlights

the interest of such an essay. Facing the progress of

the geological knowledge on other better-studied

continents, the authors believe that such a synthetic

picture may help comparisons. .In its modern concept, a platform or craton

represents a stable continental part of a plate, i.e., a

stable portion of the Earths crust adjoining one ormore active mobile belts Sengor, 1990; Park and

.Jaroszewski, 1994 . For South America, it means the

relatively undeformed portion of the continental

landmass during Mesozoic and Cenozoic times, not .strongly affected by the Andean and Caribbean

orogenic processes from Venezuela in the north to

. . .Fig. 1. Situation map of: 1 the South American Platform; 2 Phanerozoic covers; 3 Andean fold belt.


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( )F.F.M. de Almeida et al.rEarth-Science Reiews 50 2000 77111 79

Argentina in the south at the northern border of the

Sierra de La Ventana fold belt.

Our major objective is to update the paper of .Almeida 1967 and to evaluate if the available data

support the initial definition of such platform. Some

research needs seem to have been overcome, some

remain, and new ones have naturally appeared. Eventhe expression, South American Almeida et al.,

.1978 instead of Brazilian Platform, has been

changed, because the former fits the geological limits

of the stable portion of the continental plate better .Fig. 1 . In fact, the limits are surely not confined

within any geographical political boundaries.

The reader should keep in mind that such an

exercise involving 3.5 Ga of geological development

and more than 10,000,000 km2 requires some preten-

tiousness. So, naturally such an intention faces some

risks, as well as imperfections. All criticism is wel-

come as a profitable tool for the improvement of afuture version.

During more than three decades, the Brazilian

tectonic and geological knowledge has experienced a

great progress. Some models have guided such re-

search since the middle of the 60s. The former

influence of the geosynclinal theory was slowly re-

placed by the original Plate Tectonics towards thenew Global Tectonics see, among others, Moores

.and Twiss, 1995, Kearey and Vine, 1996 . In Brazil,

basic nationwide mappings have been conducted by

the DNPMCPRM2

system, the RadamBrasil Pro-ject, and state-owned mining and research institu-

tions, as well as by private mineral companies and

public universities. These latter have received mod-

ern equipment for isotopic and geochemical analy-

ses, geophysical prospecting, etc., and have gradu-

ated hundreds of MS and PhD students. A large

amount of new data has been generated by state

institutions and by working agreements between uni-

versities and foreign research centers. The growth in

geological research was recorded in 20 national geo- .logical congresses since 1967 with annals , a count-

less regional symposia, and also in a series of papers

in international periodicals.

2CPRM the Brazilian Company of Mineral Resources,

aiming to operate as the Brazilian Geological Surey.

2. Geology

Relatie stability is one defining characteristic of

a platform. The main stabilization phase of the South

American Platform was achieved by the transition

CambrianOrdovician. The concept of platform sta-

bility has been strengthened in the general scope ofnew global tectonics Brito Neves and Alkmim, 1993;

.Park and Jaroszewski, 1994 , resulting in objective .e.g., absence of orogenic diastrophism and subjec-

tive implications of the concept. For a given platform

some additional geological attributes have been rec-

ognized within well-defined time limits in

relation to a previously defined mobile belt:

- Antiquity is the first one, for the common fact

that Archean and Proterozoic rocks usually domi-

nate such basement domains.

- Transitority is an essential characteristic, as itinvolves a long history of evolutionary tectonic

phases.

- Diersity of structural associations in the frame-

work of the basement and of some well-defined .cover sequences Phanerozoic or older .

Local occurrences of Precambrian cratonic sub- .lithospheric processes mantle-activated as well as

records of cratonic tectonic activation lithosphere-.activated are common; these are promoted by defor-

mation associated with surrounding younger mobile

belts. Besides all these qualitative criteria are often-

quoted geophysical characteristics, such as largelithosphere thickness, low seismicity rates, moderate

to low heat-flow conditions and geothermal gradi- .ents, etc. Park and Jaroszewski, 1994 . All of them

are rather well recorded in this platform.

The records of the evolution of the platform .basement began in the Archean Table 1 . Most

radiometric ages belong to the Neo-Archean 2.82.5.Ga but there is also an important number of values

.of Meso-Archean times 3.22.8 Ga and a few ofPalaeo-Archean ages 3.63.2 Ga, chiefly younger

.than 3.4 Ga . The group of older ages tends to beenlarged with the increasing sophistication of iso-

topic analyses see Table 1 and Brito Neves and.Sato, 1998 . Fig. 2 is a situation map of the quoted

geographical names, rivers, states, the principal cities

and localities, but the reader is addressed to available

detailed maps for a precise location.


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Table 1

The main tectonic events in the basement of the South American Platform, from the younger ones to the oldest: . .10 Orogenic events of the Brasiliano collage, diachronous from a structural province to another. The last time interval 0.540.50 Ga is

characterized by escape tectonics and fissural magmatism. . .9 SunsasAguape belt, southwestern part of the Amazonian region BrazilBolivia , low-grade volcano-sedimentary assemblages.

.- Cariris Velhos orogenic event a Wilsonian Cycle along the central part of the Borborema Province. .8 Orogenic events in the southwestern part of the Amazonian region:

.- GuaporerRondonianrSan Ignacio 1.451.30 Ga .

.- Disputable orogenic events in the southwestern part of the Central Goias Massif Uruacuano Belt, high-grade rocks and along the .Espinhaco range Central Bahia and Minas Gerais, low-grade assemblages .

. .7 Widespread events of extensional tectonics Statherian Taphrogenesis . .- The Rio NegroJuruena Orogenesis arc plutonism in the central-western Amazonian region is the unique evidence for plate

interactions. .6 Trans-Amazonian Orogeneses: main deformational events of Paleoproterozoic mobile belts. Granitic plutonism. .5 Some occurrences of metamorphic events, high-grade gneisses. Local juvenile rock-formation event. .4 Local occurrences of metamorphic events and granite plutonism. . .3 High diversity of rock assemblages: orthogneisses Trondhjemites, tonalites, granodiorites, monzogranite and granites, TTG suites ,

.gneissic granulites of both igneous and sedimentary origins , mafic ultramafic complexes, noritic dikes; volcano-sedimentary piles .Grao-Para Group , greenstone belt associations, etc.

. .2 Widespread occurrences of high-grade terranes, mainly orthogneisses, and the oldest known occurrences of granite-greenstone LTG

assemblages. .1 Sparse occurrences of high-grade complexes.


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Fig. 2. Situation map of the quoted geographical names, rivers, main cities, states and localities.

. .All known up to now Archean nuclei Fig. 3

have in some way been involved in the structural

framework of the mobile belts of the three major

subsequent Precambrian orogenic events: Transama- .zonianrEburnean mainly in Paleoproterozoic times,

2.21.8 Ga; Late Mesoproterozoic, 1.30.95 Ga;

and BrasilianorPan African, 0.90.5 Ga. During

such collages, plate interactions reached their cli-

maxes, thus forming and successively reworking a

series of accretionary, collisional or transpressional

mobile belts, which formed different supercontinen-

tal domains. A high diversity of mineral deposits as, .for instance, gold Martini 1998 was formed due to

these processes. The existing names for such super-


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Fig. 3. Archean nuclei and Paleoproterozoic mobile belts of the South American Platform.

continental collage domains are Atlantica Ledru et.al., 1994; Rogers, 1996 in the Paleoproterozoic,

.Rodinia Hoffman, 1991; Unrug, 1996 at the time of

the MesoproterozoicNeoproterozoic boundary, and

Western Gondwana e.g., Unrug, 1996, among oth-.ers , from the end of the Neoproterozoic to the

beginning of the Phanerozoic. There is a clear una-

nimity among Brazilian Earth scientists on the con-


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cept of this later supercontinental accretion as well

as on a younger one, the Late PaleozoicrTriassic

Pangea.

After the formation of each of these major col-

lages, there were phases of taphrogenic processeswith widespread continental break-up rifting, disper-

.sion, occasionally fission , thus providing the just-accreted supercontinental landmass of which the

.South American Platform was part with important

sites of intracratonic sedimentation and anorogenicmagmatism Almeida and Hasui, 1984; Schobben-

.haus et al., 1984 . The records of lithological assem-

blages and other structural patterns for these kinds of

intracratonic Proterozoic events after the Trans-

Amazonian collage are well represented in the Ama- .zonian northern part and Sao Francisco regions

. central to eastern part of the platform Brito Neves.et al. 1995 .

During the Late Paleozoic, the collage made bythe Hercynian cycle was responsible for the forma-

tion of a new supercontinent, Pangea. The South

American Platform area remained relatively stable

during the subsequent break-up of Pangea, from the

end of the Triassic, and during the different Creta-

ceous stages of the Atlantic opening and related

events. The same is true in the development of the

Pacific and Caribbean active and transform margins,

from that same time span up to now. This continental

portion has been persistently stable even if one con-

siders the tectonic and magmatic processes that oc-curred in its interior, as natural cratonic responses to

the peripheral orogenies and continental break-up at

the surrounding borders.

The Patagonian block, south of the Hercynian .Sierra de la Ventana northeast Argentina was not

part of the stable platform area. The Patagonian

block was diversely involved in orogenic processes

during the Phanerozoic, as can be seen by its present

shape, dimensions and position among three active .margins only one passive margin, on the east , and

because of the relatively young thermal age of itsbasement mainly Mesoproterozoic and Neoprotero-

.zoic .

It is not an easy task to define a western limit . .Figs. 1 and 3 between the platform the stable area

and the activatedrregenerated zones related to the

Andean and Caribbean orogens for two main rea-

sons. The lack of reliable geological and geophysical

data does not allow a good definition of the entire

boundary zone. Moreover, any limit made at this

stage would be arbitrary. Generally, this western

boundary of the stable area is parallel to the western .Brazilian to western Uruguay and Paraguay border,

but it is not a straight line. Actually, parts of theBrazilian territory Acre, Solimoes Basin, Pantanal

. area, etc. show some tectonic influence folding,.shearing etc. from the Andean Chain.

As mentioned before, in the basement of the

South American Platform, the BrasilianorPan-Afri-

can collage succeeds two previous ones of similar

extent and importance. The succession of intercon-

nected Brasiliano orogeneses formed the last funda-

mental tectonic and structural arrangements for the

basement of this platform. Therefore, all rocks and

structures of the Precambrian Eon, of the Neopro-

terozoic and older eras, are somehow subordinated to

the framework of the Brasiliano collage.All the orogenic phases of the Brasiliano collage

are not precisely known and one should not expect

that they have been synchronic from one structural .province to another Table 1 . Some modern

geochronological data Chemale, 1998; Brito Neves.and Sato, 1998 have preliminarily indicated the

main events of plate interactions are ca. 750 and 600

Ma, for most of the Brazilian structural provinces .Almeida and Hasui, 1984 . Younger accretionary

.events ca. 580 550 Ma have been detected only in

the southeastern part of the Platform at the Man-tiqueira Province, Fig. 2, from Rio de Janeiro to

.Esprito Santo the Rio Doce Orogeny and inthe southwestern part of the Platform Pampean

.Province, in Argentina , but all these records needadditional data. From the Neoproterozoic III ca. 590

. Ma up to the beginning of the Ordovician ca. 500

.Ma , an important group of tectonic events havebeen recognized wich are connected to the latest

.phases of the Brasiliano collage : collisional im-

pactogenesis, extrusion or escape tectonics, post-oro-

genic collapse, etc. Many of these intracratonic post-collisional events of some provinces were coeval to

the above-mentioned youngest accretionary oroge- .nies Pampean and Rio Doce of other provinces.

Stabilization of the basement structures and full

platformal conditions only appeared at the beginning

of the Ordovician Period but the age for the final

individualization of this platform is the Mesozoic


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. .Fig. 4. A general sketch-map for the northern part of the South American Platform 1 Guyanas and 2 Guapore shields with .emphasis on the Archean nuclei and the surrounding Paleoproterozoic MaroniItacaiunasqVentuariTapajos, Rio NegroJuruena mobile

.belts. The westernmost part of this Brasiliano Amazonian craton is composed of the Mesoproterozoic to Early Neoproterozoic fold belts of .San Ignacio and SunsasAguape, in the BrazilianBolivian territories based on Tassinari et al., 1996 .


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.Fig. 5. The central and central-eastern part of the South American Platform. The main Paleoproterozoic Trans-Amazonian mobile belts ofEastern Bahia and Western Bahia surround the Archean cratonic nuclei. Links among the Western Bahia Belt, Mineiro belt south of the Sao

. .Francisco craton and the Ticunzal and Eastern Goias Paleoproterozoic occurrences have been sketched. An outline for the NeoproterozoicSao Francisco craton is drawn only for reference.


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Fig. 6. The Joinville Massif, positioned between three Brasiliano areasrfold belts. The main central area north of Blumenau Lus.Alves craton is formed by high-grade Archean rocks reworked during the Trans-Amazonian collage. The Curitiba area, marginal to the

.Ribeira belt marginal massif is part of the same Trans-Amazonian collage but reworked at deeper crustal levels during the Brasiliano .events based on Basei et al., 1998 .


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with formation of volcano-sedimentary basins, maficdike-swarms, acid to intermediate volcanism extru-

.sive, explosive, subvolcanic , maficultramafic plu-

tonism, etc. It is possible that the extensional pro-

cesses locally led to the formation of oceanic floor .Pimentel et al., 1998a,b as in the western part of

GoiasTocantins massif the Juscelandia, Indianopo- .lis and Palmeiropolis sequences and in the central-

western part of the Amazonian region, previous sites

for the Rio NegroJuruena belt. For the latter, there

is strong evidence for a complete evolution of an

accretionary orogen, since the formation of an

oceanic floor up to a final coalescence of magmatic .arcs during this period Tassinari et al., 1996 .

In the northern part of the platform the Amazo-.nian region, Fig. 4 , the Trans-Amazonian mobile

belts surround the Xingu Macambira and Lafon,. 1995 and Pakaraima Archean blocks Cordani and

.Brito Neves, 1982 . These belts include a series ofminor Archean crustal fragments as basement inliers.

Some of them received classical names in geological

literature such as Adampada, Imataca, Kanuku, etc. .Schobbenhaus et al. 1984 . To the west, fragments

of the Trans-Amazonian collage are still present as .interior remnants isotopically detected in the whole

.Rio NegroJuruena belt Sato and Tassinari, 1996 ;

and even further to the west of this belt, these

fragments are being found in the basement of the

Mesoproterozoic belts on the BrazilBolivia bound-

ary zone Lomas Maneche Group, Litherland et al.,.1986 .

These facts confirm that Trans-Amazonian col-

lages have dominated the whole northern part of this

platform. In the central and eastern-central part of

the continent, the Trans-Amazonian mobile belts .Fig. 5 also include some internal reworked Archean

fragments the basement of Rio ItapicururSerrinha

greenstone belt, Jequie block, Santa Izabel gneiss-.granulitic belt, etc. and circumscribe very large

.Archean blocks, like GaviaoLencois central Bahia , Campo BeloClaudio south of Minas Gerais, Fig.

.3 and that in the central part of the Goias Tocantins .massif granitegreenstone terranes domain . All of

these Archean blocks present some kind of Paleopro-

terozoic reworking. .The Eastern Bahia mobile belt III in Fig. 5 ,

which is sometimes called Atlantico or Salva-dor-Juazeiro, probably continued northwards into

the basement of Borborema Province Pernambuco.Alagoas, Caldas Brandao and Rio Piranhas massifs ,

where it was deeply and diversely reworked by

Brasiliano and other events. The Western Bahia mo- .bile belt II in Fig. 5 crops out in small areas,

because of the extensive Mesoproterozoic and Neo-

proterozoic platform covers, but there are probably

southern links with the so-called Mineiro belt .Teixeira et al., 1996 of the Quadrilatero Ferrfero area in Minas Gerais. It may also extend farther west

to the eastern Goias State, where some lithostructuralunits of similar nature and age occur Ticunzal

.Group .

For the southeastern and southern Brazilian states,

Trans-Amazonian terranes often occur as part of the

infrastructure of the Brasiliano belts. They are di-

versely reworked and usually difficult to be recog-

nized. Many occurrences of Trans-Amazonian rock

units have been detected in the basement of theAracua belt Guanhaes, Itacambira-Barrocao,

.Gouvea, blocks or rock units , Paraba do Sul belt Juiz de Fora, Quirino-Dorania and Cabo Frio groups,

. blocks or rock units , in the Ribeira belt Embu.terrane . These Paleoproterozoic occurrences are

noteworthy in the Joinville Massif Hasui et al..1975 between the Brasiliano Ribeira and Dom Feli-

.ciano belts, in two different domains Fig. 6 . They

are found not only in the southern marginal zone of .the Ribeira belt Curitiba Domain, Siga, 1995 , where

Trans-Amazonian orthogneisses occur as paleosomesof Brasiliano migmatites, but also all over the do-

main of gneissic granulitic rocks with mafic ultra-.mafic bodies included of the region of Lus Alves

.Barra Velha Lus Alves Craton , in Santa Catarina .state, of primary Archean ages Fig. 6 . For these

.Archean domains there is evidence Siga, 1995 ofmesozonal Trans-Amazonian reworking isotopic re-

.setting included .

Important Trans-Amazonian structures occur once

again in the southern portion of the platform, as a

dominant part of the Rio de La Plata Craton base-ment in central Uruguay and northern Argentina . .Fig. 7 . High-grade rocks some greenstone belts

are dominant with typical eastwest structural trends,

orthogonal to the bordering Brasiliano belts of thePampean province, Cordoban to the west, Ar-

. gentina and Dom Feliciano to the east, Brazil and.Uruguay .


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.Fig. 7. The Neoproterozoic blocks large, intermediate and small

and the different types of Neoproterozoic fold belts surrounding

and among them. The informal classification used for these belts

is that of Condie, 1989, with some minor modifications. The

Neoproterozoic blocks of the southwest part of the figure were .diversely reworked partially regenerated by Hercynian and An-

.dean orogeneses AA, PA, RP , and they are out of the platform

domains. CA Amazonian; PR Parnaba; SLWA Sao LusWest Africa; RN Rio Grande do Norte Caldas Brandao

.qRio Piranhas massifsqbasement of Serido belt ; SFCKA Sao FranciscoCongoKasaiAngola; AA ) ArequipaAnto-falla; PA Pampia; RP Rio de La Plata; PP Parana-

panema; KAL Kalahari.

Therefore, for most of the central, southeastern

and southern parts of the platform, the original fea-

tures and structures of the Trans-Amazonian mobile

belts have been diversely fragmented; they play dif-

ferent roles as pieces of the basement of younger

mobile belts, each of them within a particular level

of crustal reworking. Trans-Amazonian structures arewell preserved only in Rio de La Plata Craton Dalla

.Salda et al., 1998 .

Common geological features of the Paleoprotero-

zoic mobile belts as final results of wide plate tec-

tonic interactions may be summarized as follows: .a Supracrustal sequences of extensional basins

of continental basement rifts, syneclises, passive. margins, etc , with predominating clastic quartzites,

.U- and Au-bearing conglomerates and chemical- .clastic composition Fe- and Mn-bearing schists ,

partially to strongly involved in the Trans-Amazonian

deformation such as Parima, Kwitaro, Coeroeni, Ja-

cobina, Colomi, Areiao, Minas, Ticunzal, Cantagalo .Groups or Supergroups , etc.

.b Volcano-sedimentary supracrustal sequences

of oceanic affiliation, back-arc type and similar basins .active rifts , generally attributed to greenstone belts,

like those of the BaramaMazaruni Supergroup s. l. .from Venezuela to Amapa , ContendasMirante,

.SerrinharR io Itapic uru B ahia , etc . T he se

supracrustal rocks occur in independent basins .parallel or longitudinal to the former ones and they

may also underlie the abovementioned extensional

sequences. .c Gneissic-granulitic orthogneisses, diversely

.sorted rocks, of basic tholeiitic , intermediate to

acid tonalitic, trondhjemitic, granodioritic and. .granitic , from low- to high-potassium shoshoniticcontent, usually strongly deformed rocks, which

originated during Paleoproterozoic subduction pro-

cesses of oceanic realms and later collisional events. .d Basement inliers of gneiss-migmatitic and

gneiss-granulitic compositions of original Archaen

ages entirely enclosed and submitted to the Trans-

Amazonian trends, which formed microplates, ter-

ranes, etc. during the evolutionary history of the

mobile belt. . e Some long and linear shear zones Sadowski,

.1983 , some of them accompanied by late orogenic

syenitic and granitic plutons.

The Trans-Amazonian collage, as postulated here,

was responsible for the widespread agglutination of .all continental and microcontinental nuclei which

were consolidated at the end of the Archean by

means of the Paleoproterozoic mobile belts. Larger


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nuclei like Pakaraima, Xingu, Gaviao-Lencois, Cen- .tral Goias, etc., Fig. 3 and smaller ones were sub-

mitted to different styles of tectonic activation during

the Paleoproterozoic orogenic stages and were as-

sembled together by mobile belts to compose a largecontinental landmass around 1.8 Ga Atlantica, as

.suggested by Rogers, 1996 . The importance of this

supercontinent, which is very well documented in the

basement of South American and African platforms,

transcends the present geographical limits of both

continents. The connection of orogenic events, acting

together to build a final supercontinental landmass is

the reason for the use of the term collage.

4.2. Tectonic and sedimentary enironments postdat-

ing the Trans-Amazonian collage

Different types of tectonic and sedimentary envi-ronments have diachronously succeeded the Paleo-

proterozoic collage, as a physical and natural conse-

quence to lithospheric thickening and growth. There

is a remarkable set of continental-scale linked fault .system mostly normal faults and related cratogenic

.basins rift systems, volcanic traps, minor syneclises ,

mafic dike-swarms and, even, some continental pas-

sive margins. The breaking processes of that conti-nental landmass and their related sedimentary mostly

. detritical types , volcanic acid, intermediate, mafic

.and bimodal groups, dike swarms , volcano-sedimen-tary, plutonic granites, anorthosites, maficultra-

.mafic bodies lithological records play a special role

in this platform. These post-Trans-Amazonian crato-

genic processes are part of a global phenomenon, .and a group of their earlier events 1.8 to 1.6 Ga

have recently been described as being of special

magnitude, starting the Statherian Taphrogenesis, .according to a synthesis by Brito Neves et al. 1995 .

It is difficult to estimate precise time intervals for the

many cratogenic tectonic events paraplatformal

and orthoplataformal which have activated the

post-Trans-Amazonian supercontinental landmassduring a large time span of about 0.9 Ga from 1.8

.up to 0.95 Ga of which the Statherian period seems

to have been only the first remarkable step.

In the present central and western central part of

the Amazonian block and in the western part of the

GoiasTocantins block, the extensional events seem

to have gone beyond the usual limits of a simple

cratogenic tectonics. There are reliable indications,

in the first area, and still disputed data for the second .area due to the lack of accurate geochronology that

these post-Trans-Amazonian processes evolved, from

rift to drift, and then to the formation of true oceanic

basins, and from these to orogenic belts, first in the .Upper Paleoproterozoic case of Rio Negro Juruena

and later on during Mesoproterozoic times probable.case of the Uruacuano belt .

During Mesoproterozoic times, many of the Up-

per Paleoproterozoic linked fault systems and inte-

rior basins such as EspinhacoChapada Diamantina

and the Ara belt were submitted to tectonicinversion. These included a considerable amount of

crustal shortening and formation of elevated oro-

graphic features when they were transformed into

special types of ensialic orogens, with characteris-

tic lateral transitions to weakly deformed cratoniccovers.

The sedimentary, volcano-sedimentary and mag-

matic rock assemblages developed by the Statherian

Taphrogenesis are present from Venezuela .Avanavero, Pedras Pretas mafic magmatism in the

north of the continent to the northern part of Ar- .gentina Tandilia dike-swarm . Only a minor part of

the assemblages has remained without any tectonic

overprint, such as a flat-lying cover of the litho-

spheric portions that became Brasiliano cratons. Most

of the Statherian assemblages, as already mentioned,were partially or totally reactivated in the subsequent

Proterozoic orogenic cycles, in Mesoproterozoic like.Espinhaco Chapada Diamantina, Uruacuano, etc. as

well as in Neoproterozoic times as part of the.Brasiliano belts . There is a special case of Stathe-

rian rock associations that were only deformed dur- .ing the last Brasiliano group of events, ca. 0.6 Ga

i.e., about 1.1 Ga after their primary formation, like

in the Jaguaribeano fold belt, Ceara State, NortheastBrazil.

4.3. Rio NegroJuruena belt

The Rio NegroJuruena belt, where a complete

evolution of an accretionary fold belt is recorded forthe Statherian period, seems to be unique Tassinari

.et al., 1996 . It occupies a wide space of the centralpart of the Amazonian block from the north Vene-


16/35


.zuela and Brazil to the south at the small Rio Apa .block BrazilParaguay boundary . Its lateral limits

are still poorly defined, both to the east Trans-.AmazonianrPaleoproterozoic belts and to the west

.Mesoproterozoic belts . It is mainly composed of

gneissic and migmatitic rocks of granitic, granodi-

oritic and tonalitic nature, with occasional preserved

supracrustal assemblages, which follow a dominant

NWSW trend. Granitization, migmatization phe-nomena and high-grade metamorphism upper am-

.phibolite facies predominate along the entire belt;

granulitic rocks are local.

Important series of anorogenic plutonic rocks and

some other volcano-sedimentary assemblages of

cover rocks characterize this graniticmigmatitic belt

as a result of younger Paleoproterozoic to Mesopro-terozoic cratogenic episodes namely Parguazense,

.Madeira, etc. . The general knowledge of this belt is

not yet satisfactory; problems still remain unsolvedas the concept of the Rio NegroJuruena belt is

derived from geochonological reconaissances rather

than from geological fieldwork. From Tassinari . .1981 to Tassinari et al. 1996 , the amount of

geochonological data have increased considerably.

With the abovementioned circumstances, where

the coherence of various geochronological data aredoubtless remarkable including Sm Nd investiga-

.tions, Sato and Tassinari, 1996 this belt has been

interpreted as a product of the coalescence of mag-

matic arcs between 1.751.55 Ga, following subduc-tion processes of oceanic realms and adding juvenile

components to the continental lithosphere. The above

described anorogenic plutonic rocks and platform

covers display ages varying from 1.6 up to 1.0 Ga

and most of them postdate the main belt develop-

ment.

5. The Mesoproterozoic

5.1. Distribution

The geological information on the Mesoprotero-

zoic in South America is largely heterogeneous both

in quality and quantity. In many aspects, the crato-

genic events show some degree of similarity with

those of the upper part of Paleoproterozoic .Statherian .

The exuberance of such preserved occurrences

should be emphasized areas of millions of square .kilometers Schobbenhaus et al. 1984 without

any similar good expositions in the world Brito.Neves et al., 1995 , even though some of them are

found in the Amazonian rain forest. Sedimentary and

volcano-sedimentary basins of different nature and

types, diversified anorogenic plutonism, etc., have

privileged large portions of this supercontinent joinedby the Trans-Amazonian collage before and after

.Rio Negro Juruena Orogeny whose most represen-

tative areas are in the Amazonas region and in the .central-eastern part east of meridian 508W Gr. of

the continent. The pre-Neoproterozoic occurrences

were certainly larger than the present known records.

Although geological knowledge is far from com-

plete, it is possible to describe a series of cratogenic

basins, characterized by different degrees of tectonic

stability which display sedimentary sequences .mostly detritical rocks , volcano-sedimentary flood

basalts and anorogenic volcano-plutonism. Strati-

graphic systematizations is difficult because of the

lost original lateral dimensions, erosional descontinu-

ities, partial or total younger tectonic overprints .Mesoproterozoic and Neoproterozoic . Additionally,

there is a natural problem to be faced: hundreds of

local informal names were introduced by different

geologists working at reconaissance scales. This suc-

cession of cratogenic events ranges in time from the

Late Paleoproterozoic up to the beginning of the .Neoproterozoic from 1.91.8 up to 0.95 Ga .

Part of these events should represent tectonic

responses of the interior of the continental plate toplate interactions at their margins like Rio Negro

.Juruena, San Ignacio, SunsasAguape, etc. . There is another series of cratogenic events displaying evi-

dence of autonomous processes of sublithospheric .activation mantle-activated areas and rifts such as

Cachoeira Seca, Quarenta Ilhas, Nova Flo- .resta all of them in the Amazonian region ,

Salvador-Ilheus and similar mafic magmatism .post-Espinhaco belt Bahia , etc., which have pro-vided important tholeiitic basic and alkaline magma-

tism.

In the interior of some Brasiliano fold belts, away

from the cratonic domains for this cycle, part of thesame Paleo and Mesoproterozoic rock units of a

.previous cratogenic nature are present; some of


17/35


them have already been mapped in Riacho do Pon-.tal, Aracua, Brasilia belts, etc. . Many others may

occur, but the discrimination is difficult due to the

tectonic overprint of the Neoproterozoic orogeneses.

5.2. The Mesoproterozoic collage

Mesoproterozoic fold belts are a minority in areal

extent among the tectonic realms of the South Amer-

ican Platform. With quite few exceptions, the Meso-

proterozoic mobile belts were the place and target of

strong restructuration as basements of the Neopro-

terozoic orogens, which have preferred younger .structural sites younger thermal age zones for their

development. Only Mesoproterozoic mobile belts lo-

cated in the interior of Brasiliano cratonic domains

could be preserved from the widespread Neoprotero-

zoic regeneration.

The Mesoproterozoic collage, as first assumedhere, seems to have been completed in two main

orogenic phases, ca. 1.3 Ga San IgnaciorGuapore, .Uruacuano, Espinhaco and ca. 0.95 Ga

SunsasAguape, Cariris Velhos and possibly the.Grenvillian, to be mentioned . Even described as

minor in areal extent, such Mesoproterozoic mobile

belts were responsible for the agglutination of a verylarge supercontinent, Rodinia according to Hoff-

.man, 1991 . The Paleoproterozoic orogeneses have

already prepared wide stable cratonic areas in order

to assemble such a supercontinent, to which theMesoproterozoic mobile belts contributed as comple-

mentary and final agents of agglutination. .a The westernmost remnants of the worldwide

net of Mesoproterozoic mobile belts are now found

in the basement of the Andean Chain, in the north . Garzon-Santa Marta belt and in the south Oc-

.cidentalia Terranes , therefore they are not part of

the South American Platform basement. Part of these

western belts may eventually reach the basement of

the South American Platform in the area of the

Pampia block, but such discrimination is beyond the

presently available data. Probably, such belts are

remnants of a greater and longer Mesoproterozoic .orogenic development the Grenvillian best repre-

sented and preserved in the northern platforms.

In the South American Platform, Litherland et al. .1986 have distinguished in the common Brazilian

and Bolivian area in the western Amazonian block

two very well-preserved Mesoproterozoic orogenic

developments. The older is the San Ignacio belt,composed of schists, meta-arkoses and paragneisses .ca. 1340 Ma , pierced by a considerable amount of

.granite ca. 1310 Ma and characterized by migmati-

zation processes; it is a kind of central nucleus. The

SunsasAguapei belts surround the previous central

nucleus of San Ignacio structures and are mostlycomposed of clastic metasedimentary sequences of

.rifts and passive margin settings , mature and imma-

ture rocks, with some maficultramafic magmatic

contributions. The ages of the igneous rocks, relatedto the closing orogenic events pegmatites, alkaline

.rocks , are about 950 Ma. All the eastern lateralportions of these belts in Brazil western portion of

.the Amazonian craton is marked by anorogenic

rapakivi granites, Sn-bearing, with the same age .range from 1.5 to 0.95 Ga , which seems to charac-

terize impactogenic processes on the foreland do-main. A clearer discrimination, both in area and age

records, between the westernmost Mesoproterozoic

belts of the Amazonia and the older one of RioNegroJuruena domain is an objective for further

research. .b In the central part of Brazil, along the eastern

border of the GoiasTocantins massif there is a .group of structural features rifts and rock units

.clastics, acid to intermediate volcanics of continen-

tal character, generated during the Statherian Taphro-

genesis. Probably, the same cratogenic extensionaltectonic processes occur west of these rifts where

large maficultramafic bodies are known Barro Alto,.Niquelandia, Canabrava as well as rock units of

.oceanic affiliation Juscelandia and correlatives . All

these structures and assemblages were submitted toorogenic processes, from low- the first group, in the

. east to high-metamorphic grade the second group,.in the west during Mesoproterozoic times, around

1.3 Ga, probably following strong events of colli-

sional interaction. These orogenic processes have

been a common source of debate, especially becauseof the masking overprint of the Brasiliano structural

and metamorphic features. Actually, this Mesopro-

terozoic belt further became part of the internal .domain thick skin of the thrust-and-fold belt of

Brasilia, during Neoproterozoic times. So, the identi- .fication of the Mesoproterozoic Uruacuano di-

astrophic records is generally full of obstacles and is


18/35


even denied by some geologists. This orogeny is a

fact supported by a large amount of geological and

isotopic data. .c Drawing a parallel arc with the Uruacuano

belt, hundreds of kilometers to the east, the Stathe-

rian linked fault system of Espinhaco and Western

Chapada Diamantina from Piau to Minas Geraisstate was subject to tectonic inversion, with

important crustal shortening, producing a long linear

fold belt by the interaction of ancient rifted basement

blocks. It is characterized by a discontinuous folding

style, whose intensity increases from east to west,

usually low-level regional metamorphism, rare

granitic magmatism and basement reworking, and aproblable age within the Ectasian Period -1.4 Ga;

.)1.2 Ga . Between 1.1 and 0.9 Ga an important .event of regional mafic magmatism sills and dikes

took place in previously deformed rock units, indi-

cating post-tectonic extensional activity of the Meso-proterozoic tectogenesis, partially masked by the

strong overprint of Brasiliano structures mainly in

the southern parts, Minas Gerais State. For both the

Uruacuano and Espinhaco belts, additional data

geological and isotopic are necessary to re-

solve the remaining problems. .d In the northeastern part of the platform, in the

basement of a typical Brasiliano Province, Bor-

borema, south of Patos lineament, there are notewor-

thy records of accretionary orogenic processes, which

have only recently been identified. From the south-western border of the Parnaba Basin up to theAtlantic coast, the lithological and structural evi-

dence for this belt occupy a large WSWESE area

about 800 km long and over 200 km wide. Its

northern segment, the Pianco-Alto Brgida beltrterrane, displays records of bimodal and subordinate

MORB magmatism and the volcano-sedimentary as-

sociation of a probable forearc basin, of ca. 1.11.05

Ga. Southwards, the segment of the PajeuParaibafold beltrterrane is characterized by hundreds of

calc-alkaline sheet-like bodies, stocks, batholiths and

arc-related volcano-sedimentary associations, all of

them indicating subduction and collisional processes

around 1.00.95 Ga. Although still the object of .ongoing investigations Van Schmus et al., 1995 ,

these are the best records for an accretionary Meso-

proterozoic orogeny Cariris Velhos events inthe continent. The Brasiliano overprint folding,

metamorphism, shearing, granite plutonism, etc.,.younger than 0.9 Ga is strong. Nevertheless, previ-

ous Mesoproterozoic processes could be recognized

and differentiated with the use of SmrNd and UrPb

geochronological methods.

In general, the information rescue and the recog-

nizing degree of Mesoproterozoic structures is al-

ways in inverse proportion to the level of reworking

by Brasiliano structures. It also depends on the qual-

ity of the available geochronological data. In the

South American Platform basement such work is still

being carried out, but it is time to consider the

importance of the Mesoproterozoic collage and its

structures, developed during two different orogenic

stages. Nowadays, when the collage and fusion of a .Mesoproterozoic supercontinent Rodinia is often

discussed, we realize that the improving knowledge

of this platform tends to increase its importance.

6. The Neoproterozoic

The early beginning of Neoproterozoic first wit-

nessed the last orogenies of the previous era and theconsequent fusion of continental landmasses prior to

.950 Ma . The subsequent scenery, still in the Tonian

period, all over Western Gondwana, was character-

ized by diachronous taphrogenic processes gradually

completing the fission of the Mesoproterozoic super-

.continent diachronously up to 750 Ma that installeda new cycle of global tectonics, the Brasiliano itself.

Two major groups of tectonic components then

started to interact. .a Neoproterozoic blocks, large, intermediate and

small lithospheric fragments derived from the break-

out of the previous supercontinent, which start to

work out as rigid domains, such as plates, mi- .croplates, microcontinents, terrranes, etc. Fig. 7 .

.b Different evolutionary stages of the Brasiliano .fold belts or the Neoproterozoic basins , positioned

inter and intra these Neoproterozoic blocks. A practi- .cal and elementary way to represent and to classify

such basinsrorogenic belts is based on their pre-

inversion lithostratigraphic records. These tools are

capable of showing original paleogeographic envi-

ronments and tectonic settings. Some of these pri-

mary basins syneclises, rifts, rift systems,

aulacogens, gulfs, oceanic branchs, small oceanic


19/35


and oceanic basins which display several informal

names as Adamastor, ANEKT, Brasilides,.Goiano, Ribeirao da Folha, etc. could only

preserve some of their original characteristics, even

after the many stages that have gradually trans-

formed them into fold belt segments. Naturally, some

other basins or part of basins offer more

difficulties to identify their original characteristics.

(6.1. The Neoproterozoic blocks the probable sons)of Rodinia

The major fragments of the Upper Mesoprotero-

zoic supercontinent fission have worked out as plates .or subplates , whose remaining continental por-

tions were transformed into the so-called Brasilianocratons Amazonian, Sao LusWest Africa, Sao

.FranciscoCongo, Rio de la Plata, etc. , as tenta-

tively shown in Fig. 7, outlining the end of theNeoproterozoic collage. All these fragments were

somewhat reworked during the Brasiliano events,

and these phenomena were especially more relevant

for the small blocks, with variable intensity from

shallow to deep crustal levels. Besides the ample

exposition of basement rocks usually defined as cra-

tons, massifs, basement highs, etc., there is in

the infrastructure of the Brasiliano belts other direct .and indirect evidence including isotopic data of

important portions of the pre-Neoproterozoic base-

ment, which were severely reworked and are nowpart of gneissicmigmatitic complexes.

.In fact, when these blocks are figured out Fig. 7

there is a certain amount of implicit subjectivity in

aspects such as number, size and shape. For instance,

along the periphery of the major blocks it was notpossible to represent all the parcels involved and

.reworked as basement of the circumscribing fold

belts, under both thin-skin and thick-skin structural

conditions.

As fractions of the Mesoproterozoic superconti-

nent fission, these blocks are composed of segments

of the Trans-Amazonian and Upper Mesoproterozoic

collages, especially of the former one. It is necessary

to consider that some blocks were substantially mod-

ified and that some others have increased in area by

Neoproterozoic granitogenesis, like GoiasTocantins .whose western border is a Brasiliano magmatic arc ,

PernambucoAlagoas, Rio Piranhas, etc. These new

features may give the false impression that they are

generally larger than their previous dimensions, and

once again this brings problems to their correct

graphic representations.

The segments of pre-Neoproterozoic collage oc-

curring in the internides of the Brasiliano fold belts

generally present evidence of regeneration: tectonic,

thermal-metamorphic, compositional, etc. and some-

times all of them together. When these lithological

units became ductile they may be mixed up with

Neoproterozoic gneissic migmatitic domains. Some-

times, when mostly submitted to brittle tectonicsthey may appear as remarkable rigid flakes, slivers,

.overthrusted fractions, etc. local structural features.

The discrimination of the whole pre-Neoproterozoic

lithostratigraphic contexts in the interior of the many

Brasiliano fold belts is an open question. This is

clear as much as these contexts are positioned far

from the cratonic domains, at distal sites.The behavior of the Neoproterozoic blocks during

the orogenic Brasiliano processes varied to some

extent, as Neoproterozoic plates and microplates .subplates , as microcontinents, as internal structural

highs of fold belts, etc. Besides, they were the

basement for ensialic sedimentary basins, both in

interior and continental margins. It is necessary to

add the role of terranes, for some of these smaller

blocks, in the sense of erratic blocks considerablydisplaced from their original positions TroiaTaua,

.Guanhaes, probably Lus Alves block, etc. . Marginal parts of some major blocks were occupied by Brasil-iano continental magmatic arcs - like west of

GoiasTocantins, south of PernambucoAlagoas,.east and west of Pampia, etc. and thrust-and-fold

belts Sao Francisco Peninsula as a whole, southeast-.ern part of Amazonia, etc. . Therefore, the placing of

.Neoproterozoic blocks Fig. 4 , as descendants of a

supercontinental fission, has natural deficiencies and

uncertainties.

There is evidence that the interaction of some

Neoproterozoic blocks involved consumption ofoceanic realms positioned among them, thus generat-

ing accretionary orogenies and subsequently colli-

sional and transpressional orogenic types. When an

oceanic basin was not present, the interactions of the

blocks caused deformation of the continental sedi-

mentary or volcano-sedimentary piles between them

with deep reworking of the basement underlying


20/35


such basins. The available geochronological data

indicate important interactions, general convergence

activities with subduction, first in the Criogenian . period ca. 750 Ma , in the Neoproterozoic III ca..600 ma , and in some particular cases, from the end

of Neoproterozoic III to the early beginning of theCambrian 580540 Ma. From one province to an-

other, such interactions and their orogenic events are

not synchronous.

Centripetal convergence of the Neoproterozoic

blocks may be assumed for the orogenic processes

and tectonic consolidation of most of the provinces,

like Borborema, Tocantins, etc. In all provinces the .arrrangement of blocks, as figured out Fig. 7 , after

the Brasiliano orogeny, had a last component oflateral displacement along linear shear zones linea-

.ments , which seems to be connected with collisional . impactogenesis and late-collisional escape tecton-

.ics events. These shear zones, present in all Brasil-iano provinces, are additionally responsible for

several varied volcano-sedimentary post-tectonic,. pull-apart basins and intrusions alkaline granites,

.granodiorites diachronously formed from one

province to another, from ca. 590 up to ca. 500 Ma.These associated events of sedimentation immature

.continental clastic plus varied volcanism and anoro-genic plutonism are considered together Alpha se-

.quence as representative of an important tectonic

transition stage, preceding the general conditions of

tectonic stability of the Ordovician period, duringwhich the platform started to achieve striking stabil-

.ity and to develop their first real cratonic mature

cover sequences.

6.2. Origin, classification and arrangement of the

Brasiliano fold belts

The early origin of the Brasiliano fold belts is

related to the formation of sedimentary and

volcano-sedimentary sites led up by the Tonian

Taphrogenesis, which broke up the Mesoproterozoic .supercontinent Rodinia . Subsequent convergent ac-

tivities started to take place and led to the subduction

of oceanic realms and the tectonic inversion of the .different systems of original Tonian and younger

basins, continental rifts systems, interior syneclises,

proto-oceanic basins, etc. The final picture was the

collision and transpressional movements conducted

by the convergence of the Neoproterozoic blocks.

All these combined processes developed a complete .new global cycle Brasiliano , whose consequence

was the agglutination of a newer supercontinental .landmass Western Gondwana , Neoproterozoic to

Cambrian in age, which joined together only some of

the many descendantsrfragments of Rodinia.

To cover some important aspects of the Brasiliano .cycle the classification scheme of Condie 1989 was

choosen, because lithostratigraphic composition and

tectonic mobility are prevailing factors among a

series of variables which allow good inferences about

the earlier tectonic settings of these Neoproterozoic .fold belts Fig. 7 . First, the two remarkable main

kinds of Proterozoic rock associations, QPCs

diamictitequartzitepelite carbonate associationsyneclises, continental margins, miogeosynclines,

.etc., of proximal domains of the fold belts and

volcano-sedimentary association latu sensu litho-sphere-activated and mantle-activated rifts, forearc

and backarc basins, of distal domains of the fold.belts are present in the far interior of most fold

belts. For this second more general case, three differ-

ent subtypes of rock associations are distinguished

here: BVAC s bimodal volcanicarkose-con-

glomerate, turbidites; Greenstones large propor-

tions of volcanic with both calc-alkaline and tholei-

itic affinities, absence of komatiites; and also special

and local associations with remnants of oceanic floor

and subduction complexes ophiolites and related.deep-sea sediments . Another subsidiary type of

fold belts included here are those which constitute

magmatic arcs, which are usually situated on

marginal parts of the Neoproterozoic blocks, as pre-

viously mentioned.

The present distribution of the Brasiliano fold

belts, post-collage and post-Mesozoic continental

drift, may be described as forming four main struc-tural provinces: Borborema northeast of the

. .platform , Tocantins central part , Mantiqueira . southeast and south and Pampean southwest of the.platform , which have already been named and dis-

.cussed by Almeida et al. 1981 . This is a kind of

preliminary and useful geographicalgeological clas-

sification, even with recognized paleogeographic and

tectonic connections among these provinces.

Another possible approach for the arrangements

of these belts is attractive, as that emphasizing the


21/35


chelogenic character of the belts surrounding themajor Neoproterozoic blocks which have acted as

.seed-nuclei , namely: Peri-Amazonian, Peri-West

Africa, Peri-Franciscan, Peri-Rio de la Plata, Peri-

Kalahari, etc. Regarding such classification and dis-

tribution, it is necessary to remark that generally the .rock assemblages as above discussed are arrranged

displaying lateral gradations from the Neoprotero-

zoic blocks themselves to the interior of the fold

belts. This means, from more stable types, miogeo-clines and similar proximal environments QPC rock

.associations to more unstable types, distal environ- .ments BVAC, Greenstone, Ophiolites , with

the rock associations increasing volcanic components

to the more distal parts. The regional metamorphism

and folding phases also usually displays the same

polarity, with the gradual intensification of both

features towards the distal domains, far from the

Neoproterozoic blocks.The informal names used to designate fold belts

may lead to problems and deserve comments, be-

cause sometimes the influence of a geographical

point of view may be hiding some important geolog-

ical facts about close relationships and previous con-

tinuities among the fold belts. For instance, there are

fold belts positioned among different blocks that

may be up to 5000 km long, with no fundamental

discontinuities to be discussed, like that from the .Rockelides lateral to the West Africa block up to

Cordoba in Argentina western part of Rio de La .Plata . Different names have been used along thisbelt Araguaia, Tocantins, Paraguay, Cordoban or

.East Pampean, etc. in order to cover the many

different geographic segments rather than to state

true different geological aspects themselves. Anotherexample is the case of the fold belt or group of fold

. belts surrounding the S. Francisco peninsula just a

part of the Sao FranciscoCongoKasaiAngola.Craton which exihibits a litho-stratigraphical and

structural coherence along thousands of kilometers.

First, with proximal facies of ancient continental .passive margins QPC assemblages and their lateral

passage to distal and deeper proto-oceanic and

oceanic sites, up to some local ophiolitic remnants.

Second, this peri-continental paleogeographic con-

text was transformed into a more or less continuous

arrangement of centripetally convergent thrust-and- .fold belts, with thin-skin domains proximal areas

.laterally giving way to to thick-skin distal area

domains. Nevertheless, instead of a general unique .name like peri-Sao Francisco, for example many

local geographical names based mostly on physio-graphic aspects Rio Preto, Braslia, Rio Grande,

.Aracua, Rio Pardo, Sergipano, etc. were used todesignate the same long peripheral belt, hiding the

importance of such mutual and global relationships.

The initial tectonic settings for these fold belts

were rather variable, as a function of the nature ofthe basement, the extension factor of the Tonian

.event , the relative position to the Neoproterozoic

blocks, sedimentary sources and volcanism, etc. The

same is true for inversion tectonic conditions, in

many different interactive conditions, obliquity of .the convergence, intensity and type B or A of

subduction, aspects of crustal shortening, etc. Some

fold belts show evidence of tectonic inheritance from

the previous Mesoproterozoic and Paleoproterozoicframeworks, like in the Borborema province from

. Cariris Velhos trends , Aracua from Espinhaco and.Trans-Amazonian trends , the northern part of Man-

.tiqueira from Trans-Amazonian trends and so on.

Conversely, some fold belts seem to have originated

straight from the first structural lines of the Tonian

rifting, without any apparent influence of basement .trends such as those of Araguaia east of Amazonia

and Rockelides, the western part of Sergipano belt,

Rio Pardo belt, etc. The natural diversity of fold

belts resulting from the Brasiliano collage is stillchallenging a synthesis.

Moreover, different kinds of granitization pro-

cesses have accompanied all the phases of evolution

of the Brasiliano fold belts up to the completion of .this collage and postdating it Cambrian period .

Examples are the many gneissicmigmatitic com-

plexes and products of migmatization processes that

can be seen in Borborema and Mantiqueira provinces,

which mostly include basement rocks and Neopro-

terozoic supracrustals and which open a series of

problems for stratigraphic classification. These showspecial geodynamic conditions high isothermal gra-.dients for the Brasiliano, which is in agreement with

widespread isotopic rejuvenating phenomena RbSr.and KAr systems, mainly for most of the pre-

Neoproterozoic rock associations.

The general structural trends of the South Ameri-

can Platform and its final geographicalgeological


22/35


shape, still as part of the Western Gondwana, were

dominated by the network of shear zones, as already

mentioned, which was followed by a series of otherlithogenetic activities sedimentary, volcanic and plu-

.tonic , which lasted until the end of the Cambrian.

Among these shear belts, the position, role and be-havior of the Transbrasiliano Lineament Schob-

.benhaus et al., 1984 , which transversely intersects

the entire platform, from NNE to SSW and in so

doing practically divides two distinct arrangements

for Neoproterozoic blocks and fold belts, should be

mentioned. To the west, the large Amazonian block

with its peripheral belts is the dominating feature. Tothe east of it, the number of blocks of different

.sizes and types of fold belts is greater, and the arrayof the Brasiliano collage is much more complex see

.Fig. 7 . There is considerable evidence for the poly-

cyclical movements along this continental shear zone,

from Precambrian to Recent times, and the same istrue for many others lineaments.

The primary displacements promoted along the

shear zones is not known well enough because most

of the studies have offered more qualitative than

quantitative results, mainly of reconnaissance map-

ping. Some authors estimate hundreds of kilometersfor strikeslip movement for the case of Trans-

.brasiliano and Patos lineament, for instance have

partially been confirmed by structural, isotopic and

geophysical studies of the adjacent domains. During

all the Phanerozoic Eon, but especially in the Meso-zoic and Cenozoic eras, these shear belts behaved

like polycyclical sites or zones of tectonic move-ments huge vertical displacements have been con-.firmed , as preferential sites of the tectonic heritage

as shown by the analysis of all sedimentary basins .see Cordani et al., 1984 .

7. The Phanerozoic platform cover

The stages of the litho-structural development of

the cratonic cover of South American Platform vary .considerably and are well recorded Fig. 8 . From

the Cambrian period onwards they comprise count-

less volcano-sedimentary and sedimentary covers .some of them associated with plutonic suites stages.

The first of these or the transition stage Almeida,.1967 corresponds to the Alpha sequence, which will

be described below. When tectonic stabilization was

reached, after the Cambrian Period, volcanism was

almost completely absent during the calmer and

longer post-Cambrian stabilization stage. During this

second major stage, since the first half of the Ordovi-cian period, true cratonic sequences the concept of

.Sloss, 1988 , composed of marine and continental

sediments, started to develop successively until Tri-

assic and Jurassic times.

The best representation for these sequences are

now in the larger Gondwana or Paleozoic syneclises: 2 . 2 .Solimoes 600,000 km , Amazonas 400,000 km , 2 . 2 .Parnaba 700,000 km , 1,100,000 km and

2 .ChacoParana 600,000 km , this last mostly inArgentina. The stratigraphy of these basins as well

.as the coastal younger ones have been revised a few .years ago, as follows: Solimoes Eiras et al., 1994 ,

. Amazonas Cunha et al., 1994 , Parnaba Goes and . .Feijo, 1994 , Acre Feijo and de Souza, 1994 , Parana

.and ChacoParana Milani et al., 1994 . The rangeof thicknesses varies from 3000 to 5000 m from one

depocenter to another. The sedimentary fill of Acre 2 .basin 200,000 km , to the west of the Solimoes

syneclise, includes equivalents of these sequences,

but its evolution presents some similarities to those

of the subandean basins. The sequences are also

present in the bottom of many interior and coastal

MesozoicCenozoic rifts such as ParecisrAlto Xingu 2 .500,000 km Araripe, TucanoJatoba, Barreiri-

.nhas, SergipeAlagoas, etc. Fig. 8 .The cratonic sequences are separated from each

other by interregional unconformities; they gothrough five major tectono-sedimentary cycles six,

.if the Alpha sequence is also included , agreeing .with Soares et al. 1974, 1978 . These sequences

correspond to successive major events of the plat-

form surface lowering below the regional base leveland its subsequent uplift. Each of these cycles des-

.ignated by a Greek letter from alpha to zeta is an

assembly of stratigraphic groups and formations, even

of isolated beds, in some cases, between regionalunconformities. Many problems and obstacles arecommon for thickness estimates after previous ero-

.sional events of the former sedimentary column, as

changes of thickness due to compacting, post-deposi-

tional geometric modifications, poorly defined

andror insufficient chronological data, etc. Never-

theless, this approach seems to be the most practical


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Fig. 8. General records of the post-Paleozoic activation of the South American Platform, with emphasis on the following: 1. Archean and . . . .Paleoproterozoic domains: 1, 2 Guyana and Guapore shields; 3 Sao Francisco craton; 4 Rio de la Plata Craton covered ; 2.

. . . . . .Sedimentary coer, including A Subandean basins; B Solimoes basin; C Amazonas basin; D Parnaba basin; E Parana basin; F . .Chaco-Parana basin; G Parecis basin; H Alto Xingu basin; 3. Andean belt; 4. Exposed Upper JurassicLower Jurassic olcanic rocks;

(5. Main dike swarms; 6. Triassic alkaline rocks; 7. Upper Cretaceous alkaline rocks; 8. Lower Cretaceous alkaline granites and aried)olcanism; 9. Tertiary alkaline rocks; 10. Southernmost boundary of the platform.

way to synthesize all the cover stages of the platform

and its Phanerozoic tectonic history.

The paraplatformal Alpha sequence actually rep- .resents deposits late to post-tectonic and associated


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magmatism of the then recently agglutinated Gond-

wana continent, rather than a real cratonic sequence.

After this stage of transition in the general gradual

and diachronous tectonic conditions, from mobile

belts to stable cratonic domains, the Paleozoic Gond-

wana basins from the Ordovician up to Jurassic

times received the deposition of four true cratonic .sequences Beta, Gamma, Delta and Delta-A , of

marine and continental environments, with their nat-

ural particuliarities from one basin to another. Dur-

ing these times, the closest plate border was the .Pacific margin Zalan, 1991 , and its complex his-

tory of accretion and microcollision caused many

base-level changes and influenced these sedimentary

cratonic covers and their unconformities.

In post-Paleozoic times the interior of the plat-

form started to be intensively activated due to tec-

tonic processes of formation of the present active

and passive margins of the South American conti-nent. This complex actiation stage and its corre-

sponding sedimentary and volcano-sedimentary .recording Epsilon sequence show important dif-

ferences and variations, both in physical space and intime, i.e., from the Upper Paleozoic first recordings

.in the northern part of the platform to Upper Creta-

ceous. In the Guyana shield, at the northern part of

the platform, Triassic rifts and mafic dike swarms

are synchronous to the opening of the North Atlantic.

In the southern part of the platform, important traps

of basaltic magmatism Serra Geral Group and rela-. 2tives , over 1,000,000 km , were mostly formed in

early Cretaceous times. Along the coastal Atlantic

area this stage of evolution presents first a series of

rifts with associated mafic magmatism, followed by

proto-oceanic domains, gulfs and the alike, near the

middle part of Cretaceous. Actually, Epsilon se-

quence does not strictly follow the general require-

ments for a cratonic sequence. However, this is a

practical and useful way to group a series of interre-

lated episodes and their lithogenetic products, at least

due to expositive reasons. .The last cover sequence Zeta mainly assembles

the sedimentary phases connected with the individu-

alization of the South American Platform, i.e. those

having the Atlantic shoreline as the regional base

level. It is indigenous and it was formed pari passu

with the last geomorphological evolution of this

platform. It is also representative of younger stages

.of sedimentation and slight magmatism when tec-tonic quietness started to be restored a gradual and

.diachronous restabilization , from the Upper Creta-

ceous to the Present, replacing the previous dramatic

events of the actiation stage.

7.1. Transition stage Alpha sequence

This sequence includes sedimentary mostly im-.mature continental clastic , volcano-sedimentary

acid to intermediate rocks and some mafic magma-. .tism are common with plutonic anorogenic rocks,

from the Neoproterozoic III up to the end of the

Cambrian, diachronous from one basin to an-

other, following the different steps and times of

consolidation of the four main structural Brasiliano

provinces. It is naturally complex and diversified

from place to place, and generally fills rifts and

pull-apart basins of modest sizes, which often cropout on the periphery of the syneclises. A basal

unconformity to Neoproterozoic lithostructural rock

units is common and some of them reveal constraints

of a previous larger size, preceding the Phanerozoic

erosional phases. A generally well-marked upper

unconformity is defined with the Ordovician androrSilurian sediments Beta or Gamma sequence, the

.latter being the most common case .

In the northern part of the platform, representative

rock units for this sequence have not yet been recog-

nized. Alkaline ultramafic bodies occur along the .axis precursor rift system of the Amazonas

.syneclise, Cambrian in age ca. 500 Ma , attributed

to late-Brasiliano impactogenesis led by the Araguaia .belt Peri-Amazonian .

The best representations of cratonic cover rocksare found in the molassic foredeeps Alto Paraguai,

.Lagarto-Tobias Barreto, Itaja, CamaquarGuaritas .and some minor intradeeps Jua, part of Camarinha

of the Brasiliano provinces. Similar deposits are also .present in post-collisional extrusion pull-apart

basins, always associated to extensional phases ofthe major shear belts Jaibaras, Cococi, Piranhas,.Camarinha, etc. basins and subbasins , whose

previous larger size may be inferred from their lo-

cally preserved remnants. Volcano-sedimentary se-

quences filling these basins are hundreds to thou-

sands meters thick, mostly with immature clastic .deposits plus volcanic rocks and discontinuous


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folding style. The brittle structures dominate. Granitic

plutonism is rare, except in the case of the Joinville .Massif the northern part of the Lus Alves block ,

where an important suite of alkaline to peralkaline

granites make the main elevations of the Serra do .Mar Almeida and Carneiro, 1998 , from Sao Paulo

to Santa Catarina states, in close association with

many occurrences of these basins.

These types of basins are related to the pres- .ence of shear belts basin-forming tectonics and

they were protected against younger erosion episodes

due to the close presence of a Lower Paleozoic cover

mostly belonging to the Gamma sequence. The num-

ber and size of the Eo-Paleozoic occurrences

decreases sharply where these conditions are not

found.

Moreover, there is preliminary evidence of larger

and thicker areas of the occurrence of such basinal

rocks beneath the Parnaba and Parana syneclises, occupying the precursor triggering grabens for devel-

opment of these Paleozoic basins. Cambrian deposits

of this type have been found by deep wells along

their main depositional axes.

7.2. The Stability stage

The relative tectonic quietness from Ordovicianup to Upper Jurassic at some places, these tectonic

conditions stopped in Triassic times, and even before. them was defined as the stability stage Almeida,

.1966, 1967 . It was developed under orthoplatformal

conditions, when continuous and mature cover se-quences of marine mostly, but not exclusively,

.Lower Paleozoic and continental provenances could

widely be formed, even beyond the present erosional

boundaries of the major syneclises and rifts.

Unconformities of an interregional character are

used to limit successive cratonic cover sequences: . the Beta OrdovicianSilurian , Gamma Devo-

. nianLower Carboniferous , Delta Upper Carbonif-. .erousTriassic and Delta-A TriassicJurassic are

composed of mature sediments. Magmatism waspractically absent during this long stage over 350

.Ma in some basins , though its end is diachronous

and generally marked by Mesozoic basaltic magma-

tism, locally starting to appear at the end of the .Permian period Amazonas Basin .

7.2.1. The Beta sequence

The Beta sequence is formed by continental sedi-

ments presenting transitions to fossiliferous marine

deposits, thus characterizing the first important ma-

rine trangression on to the recently consolidatedplatform, from west to east Solimoes-Amazonas,

. Parana basin and from south to north Parnaba .basin . Its lower limit is very well marked by the

post-Cambrianrpre-Ordovician unconformity and its

upper surface limit is represented by the Eo-De-

vonian unconformity.

In the Solimoes basin, the Benjamin ConstantFormation is the oldest marine sedimentary record-

ing for this sequence and of all Brazilian basins .sandstones and black shales, at subsurface . All

.syneclises and many interior some coastal rifts

present a fair representation for this sequence, with

continental and subsequent predominant marine sedi-

ments. Among the former can be mentioned someminor occurrences of shallow marine and glacial

deposits in Amazonas, Parnaba and Parana Assine .et al., 1994 syneclises. The sediments of this se-

quence often crop out in the periphery of the basins,

but most of them occur under subsurface conditions .as in the Parana basin Assine et al., 1998a,b .

7.2.2. The Gamma sequence

This sequence is present in all Brazilian syneclises

as well as in the main paleozoic rift systems. Itcorresponds to a complete transgressiveregressive

marine cycle, from the Early Devonian to the end of

the Lower Carboniferous, limited at the top and the

bottom by two important interregional unconformi-

ties.

In the Solimoes basin there are recordings ofmarine and glacio-marine sediments. In the Ama-

zonas basin the recording of a complete sedimentary

cycle begins and ends with deltaic-fluvial sediments,

successively passing throughout neritic, euxinic,

glacio-marine and neritic facies. In the Parnabasyneclise and in the TucanoJatoba rift system,

recordings are also complete and similar to that of

Amazonas, but with remarkable erosional uncon-

formity and stratigraphical vacuity at its top. In the

Parana syneclise the recordings for the first phases of .the transgressive cycle Parana Group , from con-

glomerates and clear sandstones to black shales, are


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very well documented, but a strong erosion event

removed the sediments of the regressive phase. The

same rock units of Parana are found in the bottom ofthe rift systems of the Parecis basin.

This is the most general stage of the Lower

Paleozoic covering in the South American Platform,

under stable tectonic conditions and strong marine

influence. The huge erosional unconformity of its top

is a platform milestone that was attributed to the

influences of the orogenic Hercynian events on the .western margin of the continent the Andean Chain .

7.2.3. The Delta sequence and the Delta-A subse-

quence

The last Paleozoic tectonic-sedimentary cycle has

a complex evolution, limited by an Upper Permianr

Eo-Triassic unconformity. A climatic and paleogeo-

graphic differentiation can be observed in the sedi-mentary recordings of this sequence, from the north-

ern semi-arid conditions, fluvial and marine sedi-. .ments to the southern glacial, glacio-marine basins.

The Solimoes and Amazonas syneclises displaycontinental sediments with marine intercalations, with

typical and important evaporitic deposits. In the

Parnaba basin, this sequence is characterized by lowsubsidence rates, shallow marine to continental sedi-

ments and progressive evidence for desertic environ-

ments from their basal beds to the top.

Permo-Carboniferous glacial deposits are widely .distributed in Gondwana Eyles, 1993; Smith, 1997 .

In the Parana syneclise the delta sequence is charac-terized by thick glacial deposits with marine interca-

.lations five different horizons . Semi-arid to arid

conditions are recorded only near the top of the

sequence. The final phase of the tectono-sedimentary

cycle is composed of terrigenous sediments, from

litoral and shallow marine zones whose upper limit

reached the Triassic ages. Similar rock assemblages

are present in the Parecis basin, and there are also

some remnants of this sequence preserved in other .interior TucanoJatoba and even in some coastal

.rifts SergipeAlagoas .The subsequence Delta-A was proposed Soares

.et al., 1974, 1978 to assemble the sediments of

desertic environments prevailing at the top of the

previous sequence, characterizing wide continental .conditions geocracy of Pangea , from the Early

Triassic period. Sometimes this subsequence is sepa- .rated from the lower main sequence Delta by local

unconformities. This subsequence represents one of

the largest deserts in the history of the Earth which

covered areas of the post-Hercynian supercontinent. .This post-Triassic part Delta A of the same general

.development since the end of Lower Carboniferous

of the cycle has been separated as a subsequence, but

this is not a generally accepted concept. The end of

this subsequence is diachronous and it is related withthe early breakout of the supercontinent from the

.Permian to Lower Cretaceous , marked by rifting

processes and basaltic magmatism. This new series

of tectonic-sedimentary realms then developed were

best defined as part of the Epsilon sequence.

7.3. The post-Paleozoic actiation Epsilon and

Zeta sequences

As previously emphasized, the South American

Platform became individualized as the western part .of Pangea West Gondwana in the Cretaceous, and

since then it has been separated from the African .Platform. The initial taphrogenic rift systems, gulfs

processes preceding such a drift were generally initi-

ated in the Triassic period, even a little earlier, it hadits culminating in the Lower Cretaceous ca. 120130

.Ma , with diachronic continental manifestations .tectonic and lithogenetic processes all over the

continent. These phenomena were first described as .Wealdean reactivation Almeida, 1967 and later

.on as Mesozoic activation Almeida, 1972 . Most

of the papers on such a complex subject considered

it as reflecting the continental drift, but it is neces-

sary also to add and to remember the influence of thecoeval processes of orogenetic interactions subduc-

.tion, microcollision, faults on the Andean and

Caribbean margins of the plate.

A review of these processes will follow the differ-ent geographicalgeological areas different struc-

.tural provinces , from north to south, which havedifferent behavior in terms of the most important

features.

7.3.1. The Guyana shield

This was the first region of the platform where the

processes of activation took place, especially that of

basic magmatism. Eo-Triassic up to Eo-Jurassic


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.ca. 225; ca. 180 Ma dike swarms, NNWSSE .trending are common Cassipore diabases from

Amapa up to the French Guyana territory, and fromthere to the continental boundary. Dikes of the same

nature and age are also common in the states of .Roraima, Para and Amazonas Brazil as well as in

Suriname and Guyana. Such processes of magma-

tism and rifting are considered to be related to the

opening of the North Atlantic, which was effective

all over the Guyana Shield.The Takutu rift attributed to the same tectonic

.cause is a NE SW trending semi-graben about 3000

km long, 3050 km wide, which developed from . .Roraima Brazil to Guyana along older reactivated

Proterozoic structures of the Guyana Central Pre- .cambrian shear zone Costa et al., 1991 . The gen-

eral structure seems to be controlled by normal faults

reactivated along the main trend of the shear zone

and by some NW SE trending transcurrent faults.The preserved volcano-sedimentary pile exhibits

about 1500 m of basaltic flows, which dated from

180 up to 150 Ma the Apoteri Formation covered by 5500 m of clastic sediments minor

.clasticevaporitic , mainly siltstone red-beds and

deltaic sandstones of the Late Jurassic to Lower

Cretaceous ages. Mesozoic alkaline plutonism is also

present, as the examples of Catrimani syenite of .Roraima Fig. 8 , with age ca. 100 Ma and the

alkaline ultramafic and carbonatitic province of Seis

.Lagos, in Amazonas state Rio Negro valley , whichwas tentatively attributed to the Upper TriassicrEo-

Cretaceous ages. A very thick Nb-bearing duricrust

characterizes the Seis Lagos region, from which

samples of the fresh bedrock have not yet been

obtained.

7.3.2. The Amazonas basin

The Amazonas syneclise itself is usually divided

into three major subbasins, as follo

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