Boletim IG. Instituto de Geociências, USP. V. 7: 45 - 80, 1976

THE UPPER PRECAMBRIAN OF SOUTH AMERICA

by Fernando F M de Almeida * Yociteru Hasui * Benjamim Bley de Brito Neves **

1. INTRODUCTION

A great deal of stratigraphic, petrogra­ events and units are more easily recognized. phic, structural, tectonic and geochronological The avajlable data on the Middle and l.ower data, as well as geological maps have been Precambrian are still insufficient for an ade­ published in the past decade on the Precam­ quate reconstruction of their geological his­ brian in South America. Some synthesis has tory. been made and the most important ones guided the elaboration of the Tectonic Maps of Brazil (Ferreira, 1972) and of South America (in This paper presents an approach of the print). structural framework and tectonic evolution of the South American Continent during The Upper Precamhrian (1) is the best the Precambrian, with emphasis on the Upper known time interval because its geological Precambrian time intervalo

2. THE SOUTH AMERICAN PLATFORM (2)

The South American Platform is the merged under the Atlantic Oceano The Patago­ ancient platform of South America and oc­ nian Platform, consolidated in the Upper Paleo­ rupies the ml90r part of the continent. Its zoic, is at the southern Iimit of the South Ame­ western border was reworked by tecto-oroge­ rican Platform. The sedimentary cover over this nic processes of the Andean Chain, and its boundary difficults to trace its exact delinea­ boundary is covered by sediments. To the tion, but it should be located south of the north and east, the platform's borders are sub- Sierras Australes and east of the Sierras Trans-

* Instituto de Geociências, Universidade de São Paulo - Caixa Postal, 20899 - São Paulo, SP - Brazil

.. Departamento de Geociências, Universidade Federal de Pernambuco - Caixa Postal, 1538 - Recife, PE - Brazil.

(1) The division of the Precambrian adopted in South America is the one proposed by Almeida (1971) : Upper Precambrian, 570 - 1800 m.V., Middle Precambrian, 1800-2600 m.V. and Lower Precambrian, more than 2600 m.V. (2) South American Platform (Almeida, 1971) substitutes the name Brazilian Platform (Almeida, 1967).

-45 - +0

o

o

u.. , rnm1 2 3 4 t7ZZJ ~ ~ 5 6 7 « ~~ - Ld~ c..

500 1000 - km

Figure 1 - THE MAJOR GEOTECTONIC UNITS OF SOUTH AMERICA 1 - South American Platform. 2 - Patagonian Platform. 3 - Andean Chain. 4 - Sub-Andean Fore­ deep. 5 - Brasiliano and older exposed basement, remobilized in the Patagonian Platform and the Andean Chain; in the South American Platform: Guiana Shield (I), Central Brazil Shield (11), Atlantic Shield (111) 6 - Phanerozoic sedimentary and volcano-sedimentary covers. 7 - Southern limit of the South American Platform.

-46- pampeanas, in Argentina (Fig.l). The Uruaçu Belt (Fig. 2) presumably The basement of the &:luth Americau developed between 1300 and 1000 m.y. in the Platform is exposed in various massifs and Uruaçuano Cycle (3). in three shields. The massifs are found in the north of Argentina, in Eastern Paraguay and The regenerations of the Upper Precam­ the central north of Brazil. The shields are brian saved large areas of the formely conso­ the Guiana, Central Brazil and Atlantic lidated platform, which acted as the forelands ~ields . In the last one is included the ex­ with relation to the geosynclinal belts and posed area of Uruguay and &:luthern Brazil regions evolved since then. These cratons (4) (Fig. I) are shown in Fig. 2, as well as the fold belts and regions. The sedirnentary or volcano-sedirnentary covers were formed during the Silurian-Juras­ The several indicated units will be decri­ sic in orthoplatformal condition s. and since bed in the next chapters. the Upper J urassic they were formed during a tectono-magmatic reactivation of the plat­ 3. THE CRATONIC AREAS AT THE BEGIN­ formo The Cisandean Dalle was formed on the NING OF UPPER PRECAMBRIAN AND Andean edge of the platform, during the THEIR EVOLUTION IN THIS TIME INTER­ Cenozoic. The evolution during Phanero­ VAL zoic times of the South American Platform was analysed by Almeida (1969) and will 3.1. AMAZONIC CRATON not be discussed here. The Amazonic Craton (Amazonic Plat­ In addition to these covers, there are form of Suszcynski, 1970) is the largest unit those formed in the Upper Precambrian over of the &:luth American Platform. hs eastern the oldest are as. border touches on the Paraguay-Araguaia Belt and the western border on the Andean Belt. Its basement is exposed on the Guiana The South American Platform consoli­ ~ield as well as on a large part of the Central dated as a result of the geosynclinal and tecto­ Brazil ~ield, where it was called Guaporé -orogenic processes which began ca. 1000 m. y. Craton (Almeida, 1964). Fig. 3 and ceased between the end of the Precambrian and the Cambro-Ordovician, included in the Brasiliano Cycle (Almeida, 1967) The Amazonic Craton is stilllittle known, mainly as a result of the dense forests and Fig. 2 shows the major geotectonic units deep weathering. &:lme studies were realized of South America. along rivers and in areas of economic interest,

(3) This cycle was originally called Minas-Uruaçuano by Almeida (1968), but the Minas Supergroup showed to be older than 1300 m .y.

(4) Craton in the used sense means platforms with basement consolidated during pre-Brasiliano times; generally the geosynclinal development finished with the Trans-Amazonic foldings (ca·1800 - 1700 m.y.). This meaning is in accord with that one adopted for the second edition of the Tectonic Map of Europe and adjacent countries (1 :2.500.000), as noticed in the Explanatory Note (UNESCO and Academy of Sciences of the USSR, 1973), and for the International Tectonic Map of the World in compilation by the Subcom­ mission for the Tectonic Map of the World.

- 47 - 80 I

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11 111 u 40 - ...-

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500 1000

- KM

Figure 2 - THE MAJOR PRECAMBRIAN GEOTECTONIC UNITS OF SOUTH AME RICA: 1 - Craton basement expositions: Amazonic Craton in Guiana Shield (1), in western Central Brazil Shield (2) and in Eastern Paraguay (3); São Luis Craton (4); São Francisco Craton (5); Rio de La Plata Craton in Uruguay (6), Tandilia (7) and Sierras Australes (8). II - Major massifs: Goiás Central Massif (9), Pernambuco-Alagoas Massif (10), Guaxupé Massif (11) . III - Precambrian massifs remobilized in the Andean Chain and Patagonian Platform. IV - Uruaçu and E.spinhaço Fold Belts. V - Fold belts and regions of the Brasil iano Cycle: Paraguay-Araguaia Belt (12), Brasilia Belt (13), Sergipano Belt (14), Araçuai Belt (15), Northeastern Region (16), Southeastern Region (17). V I - Sierras Pam­ peanas Massifs. V II - Sedimentary covers correlative of the Brasil iano Cycle. VIII - Phanerozoic sedimentary and volcano-sedimentary covers. I X - Southern I imit of the South American Platform. X - Craton limit. o

...... ':' 4 5 6 ...~~+ ... .. ~~~ ..~ ===-__ ===-~500 .!I!DB KM

Figure 3 - THE AMAZONIC CRATON 1 - Guriense and Jequié units: Imataca (1) , Kanuku (lI) , Coeroeni-Fallawatra (111), Ile de Cayenne (IV) Rio Falsino (V) and basement of the Grão Pará Group (VI). 2 - Trans-Amazonic areas. 3 - Un­ differentiated Pré-Brasiliano areas. 4 - Goiás Central Massif. 5 - Pa·raguay-Araguaia Fold Belt. 6 - Se­ dimentary and volcano-sedimentary covers related to Upper Precambrian reactivations. 7 - Sedimen­ tary covers relafed to the Brasiliano Cycle. 8 - Sedimentary covers correlativa of the adjacent Brasilia­ no geosyncline. 9 - Phanerozoic sedimentary covers. 10 - Craton border. Arrows indicate vergeces. with descril"tions 'of stratigraphic sequences The Trans-Amazonic rocks show ages of and radiometric analyses by K-Ar and Rb-Sr 2000 ± 200 m,y. for the metamorphism and methods, Many synthesis papers are published, many granitoid intrusi0ns. This was followed the most recent of which are those of Choubert by the deposition of molassic sediments (Rio (1974), Singh (1974), Amaral (1974), lssler Fresco Formation, Brazil; Muruwa Formation, (1974), Montalvão (1974) and Almeida Republic of Guiana~ Orapu and Bonidoro, (1974 a) , There are flumerous and profoumd French Guiana; Cinaruco Formation, Venezue­ controversies over the stratigraphic correla­ la), acid to intermediary volcanism (Surumu, tions and geological interpretations. Cuchivero and Iwokrama Formations in the Guianas and northern Roraima, Brazil) and The oIdest roch are metasedimentary the intrusion of granitoid rocks dated ca. and metabasic rocks metamorphosed in amphi­ 1800 m.y. bolite and granulite facies, frequent1y migma­ tized and penetrated by granitoid rocks. Their In the Upper Precambrian, the Amazonic age oorresponds to the Guriense (5) and Jequié Craton underwent reactivations between 1700 and form the Coeroeni - Fallawatra (Suriname), and 900 m.y. With the resultant paraplatform Kanuku (Republic of Guiana), lle de Cayenne conditions molassoid sediments were deposited along with associated acid and intermediate (French Guiana) and lmataca Complexes, as well as the basement of the Grão Pará Group volcanism and granitic intrusions. The sedi­ mentary and volcanic COvers have been eroded (Serra dos Carajás, Brazil) and the granulitic and are not continuous, nor are observable rocks of Rio FaIsino (Brazil), complete seetions, making difficult the stra­ tigraphic study and correlations.

Large areu of this regi0n were subjeeted to geosynclinaI evolution in the Middle Preeam­ The radiometric datings of these vo1canic brian, during the Trans-Amazonic, Sedimen­ and intrusive roGks are not yet sufficient. tary and vo1canic rocks may be found there, Nevertheless, an examination of the datings which were folded, metamorphosed and pene­ shows that at Ieast in the Amazonic Craton trated by abundant acidic intrusions, Among exposed in the Central Brazil Shield, the 01- the various stratigraphic units, the Grão Pará der ages are concentrated in east, while the (BeisiegeI et al" 1973) and Amapá Groups younger are in the west. There have been (Brazil), Orapu-Bonidoro (French Guiana) some attempts to distinguish the reactivation and Armina-Rosebel (Suri~ame) Series, should eventc; in the Platform, and several were be mentioned, The Pastora Group (Venezuela) proposed, thought not always convincing1y. and Barama-Mazaruni Complex (Republic of Guiana) were correlated to the above, but The stratigraphic sequences suggest that the data of Hurley et aI. (1973) seem to indi­ two major events may be considered, with cate that they are pre-Trans-Amazonic materi­ approximate ages of 1700-1400 m.y . and 1300· ais, -900 m.y .

(5) Three major geotectonlc cvcles and complexes are considered for the evolution of South America during the time preceding the Upper Precambrian. The corresponding metamorphism and granitization epochs have been approximatelv dated and thev was considered for the division of the South American Precam· bian. TheV are: Guriense, of more than 3000 m,v.; Jequié, of more than 2600 ± 100 m .V. and Trans-Ama­ zonic . of more than 1800 ± 100 m .V. As their beginning ages are unknown, these denominations are ' also emploVed to name the time intervals between the metamorphism and granitization epochs.

- 50- The fust event is characterized by acid Prainha, Riozinho do AfrÍsio and Prosperança to intermediary lava flows, inc1uding restrict formations would be of this type. molassic intercalations and co-magmatic intru­ Marginal basins of the Paraguay-Araguaia sions. The Sobreiro, Uatumã and Iriri forma­ geosyncline were formed at the edge of the tions in Brazil, seem to have deposited during Amazonic Craton, south of the 130 S parallel, this period. The molassic continental or ma­ until the end of the Brasiliano CycIe. The up­ rine sediments that cover these units have per miogeosynclinal sequences extended to diverse local designations, lik.e Gorotire, Be­ these basins, with less thicknesses, and has neficente, Dardanelos, Mutum-Paraná and Ro­ been idiomorphically folded and fauIted. raima Formations. The latter presents in some These basins extend up to 150 km within locations basic intrusions of 1500-1700 m.y. the interior of the craton. The oldest deposits At times they have been taken as indicators of some basins incIude typical tillites related of the end of a reactivation process, but some to the Late Precambrian glaciation that ex­ granites covered by the Roraima Formation tended over a great region of Brazil and Eastern seem to be as young as 1490 m.y. (Bellizzia, Paraguay. 1975). Granitic intrusions also exist in that formation (Colvée et aI., 1975). As is evident, the oldest events in the Amazonic Craton are not c1ear, and the se­ The second event is called Rondoniense dimentary and volcano-sedimentary covers Event on the western side of the Central Bra­ present problems of interpretation and cor­ zilian Shield (Amaral, 1974), J ari-Falsino relation. Geochronologica1 datings have been on the Brazilian side of the Guiana Shield of great value, though many are controversial (Montalváo, 1974), K'mudku in the Republic and others have not always been accompanied of Guiana (Barron, 1969), Orinoquense in by an adequate geologica1 study of the analysed Venezuela (Martin Bellizzia, 1968) and Nicke­ samples. rie in Surinam (priem et al., 1971). During this event, molassoid sediments were depo­ Table 1 tentatively outlines the described sited together with acid to basic effusives evolution of the Amazonic craton. and granitic intrusives, many of which are tin-bearing. The Cadiueus, Cubencranquén. In eastern Paraguay, the Amazonic Palmeiral, Acari and Amoguijá formations, Craton's basement is exposed in two small among others, could be attributed to this massifs (Fig. 5). They are formed of meta­ evento Catac1astic zones developed in vast sediments and metabasites of amphibolite regions of the Guiana Shield with formation facies, with intruded granitoids. The age of of breccia and mylonites (the K 'mudku Event), these rocks were obtained by the K-Ar method as well as regional reheating, responsible for the (Comte and Hasui, 1971), and although not isotopic rejuvenation which reflects on the decisive, they indicate that the rocks are of radiometric ages. pre-Brasiliano age and the Amazonic Craton extends to the south at least until 270 S la­ titude. Rhyolites whose ages correspond At the end of the Upper Precambrian, ar to the end of the Brasiliano Cycle (Cambro­ perhaps already in the Cambro-Ordovician, - Ordovician) are located over the cratonic . molassoid sediments were again deposited. rocks, in the Caapucu region. These Caapucu They are interpreted as platform correlatives of volcanics are associated with granitic intrusions the Brasiliano Cyc1e, which covered that and represent a valcano-plutonism in the Ama­ area of the interior of the Amazonic Craton zonic ératon next to the limit of the Paraguay­ exposed in the Central Brazil Shield. The Araguaia BeIt.

- 51 - TABLE 1

Tentative oulline of the evolution of the Amazonic Craton

Age m. y. Events Lithostratigraphic units

Prosperança, Prainha and Riozinho d'ü Afrisio formations (molassoids). Alto Paraguay Group (molasse). 500 - 1000 Brasiliano I- Jangada, Escobar, Araras, Corumbá, Bo- doquena, ltapocumi Groups (marginal basins correlative to the Paraguay-Ara- guaia miogeosyncline).

Cubencraquém, Cadiueus, Palmeiral, Aca- ri, Amoguijá formations (acidic-intenne- 900 - 1300 Reactivation diary effusives and molassoids).

Gorotire, Beneficente, Dardanelos, Mu- 1400 - 1700 Reactivation tum-Paraná, Roraima formations (molas- soids).

Uatumã, Sobreiro, Iriri formations (acid- -intermediary effusives).

Surumu. Kuyuwimi, Iwokrama, Cuchive- ro, Rio Fresco. Muruwa, Orapu, Bonido- ro and Cinaruco Formations (molasses and acid to intermediary effusives) 1800 - 2600 Trans-Amazonic Amapá and Grão Pará Groups, Armina- -Rosebel. Paramaca, Paramaka and Mo- rowijne Series.

more J.equié Barama-Mazaruni, Coeroeni-Fallawatra, than and Kanuku, Imataca Complexes, the base- 2600 Guriense ment of the Grão-Pará Group and other nuelei

3.2. SÃO FRANCISCO CRATON The Caraiba and Jequié Complexes appear on the northeastern part of the craton. The São Francisco Craton (according The Caraiba Complex (Barbosa, 1970) is to Almeida, 1967) is a unit that has been formed .of granulites, basic rocks and migmati­ intensely studied, but the data reflect above tes with basic paleosome. Its structures are ali the disperse are as of economic interest. complexes, generally trending N-S. Associated granitoids have given ages of 2500-2700 m.y . lt was the foreland of the fold belts of At approximately the l3°S parallel, the Ca­ the Brasiliano Cycle, located on its borders. raiba Complex gradually passes to the Jequié Fig.4. Complex (Cordani, 1973). The later extends

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VII ~ \ \ \ ~:.. ~. 'g~~ 1

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--22 300 KM

Figure 4 - SÃO FRANCISCO CRATON 1 - Pre-Trans-Amazonic and Trans-Amazonic undifferentiated areas. Caraiba Complex (I) Jacobina Group (11), Jequié Complex (111), Quadrilatero Ferrifero (IV). 2 - Uruaçu Folded Belt and Guaxupé Massif (V). 3 - Espinhaço Belt and related covers on the Diamantina Plateau (VI).4 - Trans-Amazonic areas rejuvenated during the Brasiliano Cycle. 5 - Brasiliano units: Brasilia Fold Belt (VII), Northeas­ tern Fold Region (VIII), Sergipano Fold Belt (IX), Araçuai Fold Belt (X). 6 - Sedimentary covers cor­ rei ative of the Brasiliano Cycle-: Bámbui Group in the São Francisco Basin (XI) and in the Salitre-Jaca­ ré Basin (XII) Rio Pardo (XIII). 7 - Phanerozoic sedimentary covers. 8 - Major faults. 9 - Craton li­ mito Arrows indicate vergences. to the 160 S parallel (Mascarenhas, 1973) The situation is more complex in the and its granulites have ages around 2700 southeastern region of the São Francisco m.y. and were migrnatized at the end of the Craton. There, the Uruaçu and Brasilia Belt Trans-Amazonic Cyc1e (ca. 1800 m.y.). end, as well as the Southeastern Folded Region. The lithology was described by Rosier (1965) and Ebert (1968) as represented by gneisses, Irregular bands of schists, quartzites and migmatites, granulites and granites, attributed gneisses, which seem to be the segments saved to the Mantiqueira, Paraiba, Juiz de Fora by the migmatization, appear in these comple­ and Serra dO$ Órgaos Séries. The datings xes. Only the narrow N-S Jacobina belt almost of Cordani et al . (1973) showed that the rocks 220 km long seems to be Trans-Amazonic. are aged 2780 m.y. (Mantiqueira Séries) and lt is composed of quartzites and schists of 1980 m.y. (paraiba and Juiz de Fora Series); amphibolite facies, with isoc1inal folding, they were remobilized in the Brasiliano Cyc1e, faults and overthrusts toward west over the and have been migrnatized and intruded of Caraiba Complex. granites and pegmatites. The remobilized area seems to correspond to the infrastructure Migmatites and granitoids of minimum of the Southeastern Folded Region (Hasui age of 2800 m.y. of the Bação Complex are et aI., 1975a). found in the southern part of the São Fran­ cisco Craton (Quadrilátero Ferrífero). This Dykes of non-metamorphosed diabase complex is covered by detritic metasediments, and pyroxenite exist in the northeastern itabirites and dolomites, metamorphosed in region of the craton; tpey are intrusives in greenschist and amphibolite facies of the Rio granulites and with K-Ar ages of 1300 to 1700 das Velhas Supergroup. Granitoid and basic­ m.y . In the eastern region, more than a dozen -ultrabasic rocks are associated to it. Datings stocks of alkaline rocks occur (pedreira et aI., for these rocks show age around 2700 m.y. 1969) with K-Ar ages of ca. 760 m.y. (Corda­ ni, 1973). There is a special undelineated The Minas Supergroup covers the Rio belt with one or two hundred kilometers das Velhas, unconformably. The former is wid;, extending f TOm the region at 160 S oonstituted of a sequence containing banded and 420 W coordinates to the southeastern bor­ ironstones over and underneath detritic sequen­ der of the Parnaiba Synec1ise. Along this belt, ces. The Minas Supergroup is observed in there were isotopic rejuvenation in the Brasilia­ overtuned and faÚlted sync1inoria (Dorr, 1969); no Cyc1e and K-Ar ages of 500-600 m.y . the superposed deformations can be attributed were obtained systematically on rocks with to several phases (Barbosa, 1968). The meta­ higher Rb-Sr age. It seems to have been simply morphism was of greenschist and amphibolite a termo-tectonic reactivation along the belt, facies. The minimum age obtained by Herz and that it is not an extension of the infras­ (1970) was 1300 m.y., and recent datings tructure of the Southeastern Folded Region. (Cordani, umpublished) furnished Trans-Ama­ zonic ages. The most important feature, however, is The Minas Supergroup is locally covered the Espinhaço Belt, a N-S one in the central byfolded metasediments of greenschist facies part of the .São Francisco Craton, extending (essentially quartzites) whose geotectonic signi­ over than 2200 km. Detritic metasediments, a­ finance is not known (Itacolomi Group). Possi­ bove all quartzites and phyllites, are found the­ bly they may be correlated to the Espinhaço re with hundreds of meters in eastern part and Group. thousands meters in western partoThe sedimen-

- 54:" tation had frequent repetitions of environ­ The São Francisco Craton presents mental conditions, and the stratigraphic subdi­ sedirnentary covers of the Bambui Group, visions and correlations are diffjcult. and of Mesozoic and Cenozoic ages. The Jequitaí Formation of Minas Gerais State and A sequence at the meridional end of the Bebedouro Formation of Bahia State are the belt (Espinhaço Group) shows folding homologous and have typical tillites, wich of intermediate-type and a low-degree meta­ represent deposits of continental glaciers morphism. These characteristics are also obser­ related to the Upper Precambrian glaciation. ved in Diamantina Plateau (Chapada Diaman­ At least two tillite leveIs was recognized. A tina Group), which is located in the central­ thin varvite deposit is known between them -northern region of the craton. The same in the Brumadinho quarry (Cabral Ridge , sequence in the central and northern portions Minas Gerais) and pavements with striations of the belt (Santo Onofre Group), shows and grooves produced by the ice exist at isocIinal linear folding and intense faulting Agua Fria Ridge (South of Jequitaí, Isotta and its metamorphism is more inten~ .toward et ai., 1969; Ponçano and Paiva, 1975) and the west, reaching greenschist . facies parage­ at Cabral Ridge. nesis. Acid volcanic rocks occur in the se­ quence, and basic dykes are common as welI. The Bambui Group which extends Vergences seem to turn towards the west , over the craton, is an extension of the Brasília, but in the region of western Diamantina Pla­ Sergipano and Northeastern upper geosyncIi­ teau, it turns to east. nal units. It covers a vast area to the west of the Espinhaço Ridge, where it was not ap­ These units cover the Caraiba Complex propriately attributed to the "São Francisco and are covered in turn by the Bambui Group, Basin". To the east from Espinhaço Ridge, with angular unconformities. They was initial­ it covers the Chapada Diamantina Group ly related to an Espinhaço CycIe (1800 - 1300 and was attributed to the "Salitre-Jacaré m.y. Ferreira, 1972). However, the Chapada Basin". The minirnum extension of that cover Diamantina Group (Brito Neves, 1968) is is 420.000 km2 in both "basins". The thick­ correlated to the Santo Onofre Group (Schob­ ness does not exceed 1000 m, and almost benhaus, 1972) which metasedirnents and alI of the Brasília miogeosyncIinal formations volcanic rocks gave a metamorfism age of are present, with less thickness and some 1000 .± 100 m.y. (Rb-Sr isochron, Brito faciological variations. The deformations of Neves, to be published). This dating may be this cover are idiomorphic. The only linear attributed to the Uruaçuano CycIe, and, so, folding are as are located on the borders of the possibílity of an extension of the Uruaçu the craton tumed towards the Brasília' mio­ Belt to the Espinhaço Belt would not be geosyncIine, and in the region bordering the . rejected. Espinhaço Ridge. To the east of the ESpinha­ ço, there are even isoclinal folds, with E-W The Espinhaço Ridge was aSSociated trending, and axial planes dipping ~owards to a miogeosyncIine by Pflug et aI. (I 969r the north. This occurs in narrow belts, separa­ In the northem region, this miogeosyncIine ted by undeforined zones. The general meta­ should contour a presumed massif at Diamanti­ morphism is null or of very low degree, but in na Plateau (Lençois Craton). Moreover, they folded zones it reaches greenchist facies. considered the Quadrílatero Ferrífero as an extension of the Esp~ço miogeosyncIine and, in the eastem region, they supposed the Table 2 outlines the discribed evolution existence of an eugeosyncliiie. of the São Francisco Craton.

- 55- TABLE 2.

Tentative outline of the evolution of the São Francisco Craton

Age m.y. Events Uthostratigraphic units

500 - 1000 Brasiliano Três Marias Formation (molasse) Bambui Group (platform cover cor- rei ative to the geosynclinal units)

500 - 800 Reactivations Alkaline intrusions (ca. 680 m.y.) Isotopical rejuvenated belt (500-600 m.y.)

1300 - 1000 Uruaçuano Espinhaço, Chapada Diamantina, San- to Onofre Groups (metamorphism ca. 1000 m. y.) Itacolomi Group (?)

1300 - 1700 Reactivations Basic and ultrabasic intrusions.

1800-2600 Trans-Amazonic Minas Supergroup, Paraiba and Juiz de Fora Séries (?) and Jacobina Group.

2600 - 3000 Jequié Mantiqueira Series, Rio das Velhas Supergroup and Jequié-Caraiba Com- plexes more than Guriense Bação Complex and other nuc1ei 3000

3.3. SÃO LUIS CRA TON 3.4. RIO DE LA PLAT A CRATON

The São Luis Craton (Almeida, 1967; Th~ Rio de La Plata Craton (Almeida Hurley et al ., 1967) is located at the central et al., 1971) is almost entirely covered of northern border of the South American Plat­ sedirnents of the Paraná Syneclise and post­ formo lt is almost entirely covered by the -Paleozoic basins. lts basement is exposed in sediments of the Parnaiba Syneclise and small three regions: southeastern Uruguay. Tandilia meso-cenozoic basins. The basement is expo­ and Sierras Australes in Argentina. Fig. 5. sed in small massifs and seems to be formed In Uruguay, Ferrando and Fernandez of metasediments of amphibolite facies, with (1971) distinguished three belts of meta­ migmatization and intrusion of granites. The sediments of greenschist and amphibolite fa­ eastern massif (Granja Massif, Brito Neves, cies. These were separated by migmatitic 1975) represents the craton's border neighbo­ belts with granitic intrusions. The structures ring the Northeastern Fold Region. The avail­ trend E-W with variations to N70E. The lable datings are of 1850-2470 m.y. (K-Ar). ages obtained for them are 2000 + 200 Although 2000 ± 200 m. y. figures predomina­ m.y . Only one granite intrusion at north te, it is not excluded the possibility of pre­ of Montevideo shows 560 m.y. and it is attri­ ·Trans-Amazonic age. buted to the influence of the Brasiliano Cycle

- 56- 55 2 +20 I /~ I

5 6 7 8 [ill]]] ~EJ EJ

9 B .' : :·~II .'. · . .~ .

.. ' . .. ' . .. ' ,' + . , . ':":: -.

Figure 5 - SOUTHERN REGION OF THE SOUTH AMERICAN PLATFORM 1 - Craton basement expositions.Amazonic craton: Apa River (I) and Eastern Paraguay massifs (11) Rio de La Plata craton: Uruguay (111). Tandilia (IV), Si erras Australes (V) and Rio Grande do Sul (7) (VI). 2 - Fold belt and region of the Brasiliano Cycle : Paraguay-Araguaia Belt (V 11), Southeastern Region (VIII). 3 - Sierras Pampeanas massifs. 4 - Patagonian Platform. 5 - Andean Chain. 6 - Sedimentary covers correlative of the Brasiliano Cycle. 7 - Phanerozoic sedimentary and volcano-sedimentary covers. 8 - Southern limit of South American Platform. 9 - Craton border,

- 57- at the border of the.craton. sintectonic aml post-tectonic acid magmatism The relation between the Rio de La Pla­ was very discrete, forming small bodies along ta and Amazonic Cratons is hidden under the the inner zone of the belt. sedimentary cover, though they may possibly be parts of only one large unit. Certain problems arise with no solutions at momento The fust one is with respect to the borders of the Uruaçu BeU. Traditionally, it was considered to be formed essentially by The mountains th"t stand out in the micaschists; gneisses and migmatites are thou­ Tandilia region's quaternary plain are formed ght to be pre-Uruaçuano. However, these by gneisst\S, migmatites and granitoids whose rocks show gradual transitions. Angular uncon­ age is 2160 ± 60 m.y. (Halpern, 1972). Amos formities were identified locally, between the et aI. (1971) described sandstones and stroma­ two types of lithology, but this is not rule tolitic limestones (La Tinta Group), covering even in the Araxá Group type-area. Thus, the plutono-metamorphic basement. These it is sometimes difficult to delineate the hor­ rocks represent a platform cover of the Brasi­ der between the Uruaçu BeU and the Goiás liano Cycle, similar to the Bambui Group. Central Massif without a carefull mapping.

Granites and associated rhyolites occur The eastern limit would . be a thrust at the Sierras Australes, with Brasiliano and fault that carried the Araxá Group over the. pre-Brasiliano ages (Amos et al., 1971; Halpern, Brasília Belt's units. The existence of that 1972). These are the most meridional of the fault has not been proved, althought there Rio de La Plata Craton's basement. may be local thrusts. The Araxa Grouplooks like to pass gradually to the metarnorphites of the Brasilia BeU; as a result, the border between the two units is not easely marked. 4. UPPER PRECAMBRIAN FOLO BELTS

4.1. URUAÇU BELT The available datings of the Uruaçu Belt (Hasui and Almeida, 1970) are not conclusive. The Uruaçu Belt developed between the The K-Ar figures indicate that the Brasiliano Amazonic and the São Francisco Cratons Cycle rejuvenated the Uruaçuano rocks, but (Fig. 6). It is formed of metasediments and there are significant results of 1000 m.y. metabasites of high greenschist and amphibo­ which would correspond to a minimum age lite facies of high pressure type of meta­ for the metamorphism. From the other side, morphism. These rocks are included in the some intrusive granites in the Central Massif Araxá Group, with thicknesses exceeding of Goiás furnish a reference Rb-Sr isochron 1500 m. The folding is of linear type, trending of 1400 m.y., which would indicate a magmatic paralle1 to the axis of the belt. The vergence event in the massif immediately preceeding turns towards the São Francisco Craton. The the Uruaçuan regeneration. Thus, the apro­ pre-tectonic magrnatism occurred in the inner ximate figures of 1300 and 1000 m.y. could part of the belt, generating several small basic­ corresponde to the limits of the regeneration -ultrabasic intrusions. This peridotitic belt and tecto-orogenic evolution of the Uruaçua• shows Cr, Ni and asbestos mineralisations. The no Cycle (6).

161 Recent Rb-Sr isochron age determinations confirm the 1000 m.y. age for the metamorphism of the Araxá Group 'Hasui and Almeida, in pressl.

-58- The structures of the Uruaçu Belt 4.2. PARAGUAY-ARAGUAIA BELT show deviations in the central region, adap­ ted to the Pirenópolis structural feature. The Paraguay-Araguaia Belt evolved on Trus is a N60W trending lineament, with the eastern edge of the Amazonic Craton structural meaning not yet understood. In the (Fig. 6). It has a curved form and extends northern block, the structures have a general over 3200 km, disappearing under the Paraná SSW trend, but they deviate gradually to and Amazon Syneclises sediments. N60W near the Pirenopolis feature. In the southern block the structures have a N45W In the central region of Brazil the belt trend and also show a deflection to N60W. is covered by modern sediments (Bananal Is­ land). This resulted in the independent develop­ ment of studies on the southern and northern In the southern part of the São Francisco segments of the belt. Craton, the Andrelândia Series (Ebert, 1956) represents the extension of the Uruaçu Belt. Almeida (1968) distinguished two phases It is formed of detritic sediments, arkosic at the of miogeosynclinal evolution in the meridional base, with some associated limestones. The segment. The first one produced flyschoid se­ metamorphism of high pressure type was diments of the Cuiabá Group, which were of greenschist and amphibolite facies and folded and metamorphosed. The second cor­ its intensity increases from N to S and W responds to the sedirnentation of a marine to E. Folding was intense with vergence regression conglomerate and glacial-marine towards the N. deposits, which total over 1000 m of thickness (Jangada and Escobar Groups). The upper unit is a carbonate sequence with more than The Andrelândia Series seems to branch 2000 m of thickness (Araras, Corumbá, Bodo­ off, with one branch extending towards SW quena and Itapocumi Groups), with 1000 m (ltapira Group). The two branches are separa­ of pelitic rocks at the topo Stromatolitic struc­ ted by the triangular Guaxupé Massif. Its tures are present in the Corumbá limestones. western border is covered by the Paraná Syne­ c1ise sediments. This massif is constituted These units exhibit metamorphism of by granulites, migmatized and intruded by greenschist facies and folding of holo~orphic­ granites. The structures have NW trends, and -type trending parallel to the belt axis. The a superposed NE trend exists in part (Olivei­ vergence turns towards the Amazonic Craton. ra and Alves, 1974, Oliveira, 1973). The nor­ The known magmatic intrusions are restricted theastern border of the massif is concordant to the inner part of the belt; they are granitic with the structures of the Uruaçu Belt, but in post-tectonic stocks aged of 500 m.y. the southeastern edge their NW structures are truncaded at right angle by the Jacutinga transcurrent fauU (Ebert, 1974), through The fmaI stratigraphic unit corresponds which the massif contact the SW trending to molasse deposits (Alto Paraguay Group), ac­ Uruaçu branch (ltapira Group). cumulated in a foredeep 800 km long. It Iies over the Amazonic Craton 's cover and partly extends to the fold belt in its curved area. In this fault zone, it has been recognized The sediments possibily reach 5000 m of a molassic deposit (Eleutério Group, Ebert, thickness and are of c1astic nature accumu­ 1974) which seems to be related to the Brasi­ Iated in a transitionaI environrnent. At the liano Cycle. top they are continental. (Almeida, 1974b).The

- 59- 500

Figure 6 - CENTRAL BRASILlAN REGION OF THE SOUTH AMERICAN PLATFORM 1 - Cratons: São Francisco ('I) and Amazonic (11). 2 - Massifs: Goiás (111) and Guaxupé (IV). 3 - U­ ruaçu Fold Belt. 4 - Fold belts and region of the Brasiliano Cycle: Brasilia (V), Paraguay-Araguaia (VI), Southeastern (VII). 5 - Sedimentary covers correlative of the Brasiliano Cycle. 6 - Phanerozoic sedimentary and volcano-sedimentary covers. 7 - Craton border. 8 - Piren6polis structural feature. Arrows indicate vergences.

-60- Alto Paraguay Group shows holomorphic Estrondo Group extends to the South, borde­ folding only in the farthest area from the ring the Bananal Island (Fig. 6), but its conti­ cratonie border, as well as very low grade nuation under the Paraná Syneclise is not of metamorphism. known.

The units of second phase of geosy ncli­ 4.3. BRASILIA RE LT nal sedimentation and the molassic deposits partially covers the Amazonic Craton. One The Brasília Belt was formed at the occurrence should be mentioned: the depo­ western and southern border of the São Fran­ sition of the Jacadigo Group occurred in a ba­ cisco Craton in the Brasiliano Cycle, and ex­ sin on the edge of the craton at the end of the tends over 1100 km (Fig. 6). Brasiliano orogenesis, at the Corumbá (Brazil) and Mutum (Bolivia) regions. This unit is Miogeosynclinal conditions with deposi­ formed of arkoses at the base, and of alterna­ tion of medium and fine-grained detrie sedi­ ting layers of ferruginous jaspilite, hematite ments occurred with the regeneration (Canas­ and cryptomelane, with intercalations of clas­ tra and Araí Groups). This was foUowed by the tic sediments. accumulation of the BambuÍ Group, which is formed of psammites at the base (para­ In the northern segment, Almeida noá Formation), limestones, dolomites and (J 974c) described the Tocantins-Araguaia geo­ pelites (paraopeba Formation), at the topo suture. The Brasiliano regeneration permitted These units, more than 3000 m thick, show the intrusion of several basic and ultrabasic linear folding and thrust faults. The vergen­ bodies, as well as a volcanism of basic compo­ ce is turned towards the São Francisco Craton. sition. These magrnatic rocks <>ccur in a N-S The metamorphism was weak, not exceeding belt of tens kilometers of width and 500 km the low greenschist facies. No evidences of of extension. The geosuture also allowed magmatism are known in connection with the arrival of geosynclinal conditions to the the evolutlon of the Brasilia Belt. east. To the south of the craton, Ebert (J 968) gave the narne São João dei Rei Group to the The Tocantins Group accumulated in this clastic sediments and limestones, metarnorpho­ regenerated zone, beeing constituted of peli­ sed in greenschist facies. It shows linear folding tic sediments transformed in greenschist facies. and vergence towards the north. This unit It shows linear folding, trending N-S and with represents the extension of the Brasilia Belt vergence towards the Amazonic Craton. The and, around the 449 W meridian, it disappears. Tocantins Group is correlated to the Cuiabá The Barnbui Group is trangressive over the Group. craton, as described above . Near Sete Lagoas, Marchese (1974) described stromatolites of the Eastward, the Tocantins Group shows Gymnosolenida Supergroup and Cloud and gradual transition to rocks of high greenschist Dardenne (1973) recognized Conophyton of and arnphibolite facies, which was not appro­ Vazante region. priately correlated to the Araxá Group. It was named Estrondo Group (Hasui et aI., 1975b), The upper sedimentary unit is represen­ and would corresponds to the filling of the ted by molasses of the Tres Marias Formation inner zone of the geosyncline. Its folding is which fiUed the marginal Pirapora basin, of linear type, trending N-S, and the vergence partially over the craton 's cover (BarnbuÍ is towards W. Migrnatization and granitoid Group) and partially over the folded zone in intrusions occurred in the eastern parto The the west Minas Gerais.

- 61 - The evolu·tion of the Brasilia Belt compa­ Massif, at Serra Dourada, Danni et alo (J 973) red to that of the Paraguay-Araguaia Belt shows recognized two stratigraphic units over the Goi­ perfect analogy (Almeida, 1968). .ano Basal Complex. The frrst one is composed of metasediments of greenschist facies (quartzi­ The mineral resources of the Brasilia tes, schists and phyllites), with about 300m Belt are in the Bambui Group, with the mar­ thickness. It is gently folded and covers uncon­ ked presence of sedimentary phosphates, formably the second unit, which inc1udes and Pb-Zn deposits of singenetic origin and schists, gneisses and migmatites and is correla­ remobilized towards fault zones. ted with the Araxá Group. lt shows many Iittle basic-ultrabasic intrusions. It seems The Brasilia and Uruaçu Belts are separa­ that the Araxá Group has had extension till ted from the Paraguay-Araguaia Belt by the the Serra Dourada region . The upper unit may Goiás Central Massif (Fig. 6). This unit has be interpreted as a cover correlative of the heterogeneous composition. Basic gneisses, Brasiliano Cyc1e, constituted over the central kinsigites, charnockites and granulites appear massif. on the eastern part, with ages exceeding 2600 m.y. On the rest of the massif there are intensi­ The Goiás Central Massif was part of the Iy migmatized metasediments of amphibolite Amazonic Craton during the Uruaçuano Cyc1e. fades, with apparent Trans-Amazonic age During the Brasiliano Cyc1e, it became an axial (Hasui and Almeida, 1970). All these Iithologies zone of the divergent polarities of Paraguay­ are grouped on the name Goiano Basal Com­ -Araguaia and BrasÍlia Belts. plex (Almeida, 1968). 4.4. SERGIPANO BELT Three large basic-ultrabasic massifs stand out in the eastern part of the complex: the The regeneration of the northeastern Cana Brava, Tocantins and Barro Alto massifs. part of the São Francisco Craton allowed They are elongated, with up to 3000 km 2, and the development of the Sergipano Belt. (Fig7) are characterized by a petrographic zoning, lts limits are the craton and the Pernambuco­ with the zones parallel to each other and de­ -Alagoas massif (Brito Neves, 1975). The cen­ eping westward. Ni, Cr, Cu and asbestos minera­ tral and eastern portions of the belt are covered lizations have been described there (Berbert, by meso-cenozoic sediments. 1970). Their K-Ar ages vary from over 3000 During the geosynclinal stage (Propriá to 600 m.y., indicating that they are very an­ Geosync1ine, Humphrey and Allard, 1969), cient massifs, rejuvenated in subsequent events. an outer and an inner zones developed, separa­ ted by a geantic1ine (Brito Neves. 1975). The Goaiano Basal Complex was affected In the outer zone, adjacent to the São by the younger tecto-orogenic cyc1es, under­ Francisco Craton, the sedimentation had a going fracturing, diaphtoresis, isotopic rejuve­ miogeosync1inal character, and inc1udes a lower nation and some granitic intrusions (Ferreira, terrigenous (Itabaiana, Jacarecica, Capitão 1972). and Palestina Forrnations), a carbenate (Jaco­ ca, Olho d'Água forrnations), an upper terrige­ The Goiano Basal Complex structures nous and a molassic sequences. The latter ap­ trend generally N30E, and show some influen­ pears in a graben over the geantic1inal zone ce of the Pirenopolis feature. The Barro Alto (Juá Forrnation), as well as in a foredeep (Es­ massif is inflected and has a boomerang shape. tância Formation) inserted in part over the cratonic area and in part over the folded In the central southern part of the zone.

-62- In the inner zone, the sedimentary se­ 4.5 . ARAÇUAI BELT quence is more complex, with quartzites (Santa Cruz Formation), followed by medium and Almeida (in preparation) proposes the fine immature clastics, with some intercalations name Araçuaí for the fold belt at the ~uthe­ of limestones. astern edge of the 810 Franci~o Craton, Fig. 4. It has an extension of more than 500 Metamorphism in these sediments was km and is related to the Brasiliano Cycle. of greenschist facies in the outer zone and of amphibolite facies in the inner one. It was After the con~lidation of the Espinha­ of low-pressure type. Migmatites are found ço Belt at about 1000 m.y., new miogeosyn­ in the inner zone, adjacent to the Pernambuco­ dinal conditions develloped in the region and -Alagoas Massif. the deposit ion of the Macaubas Group detritic sedirnents occurred probably with more than In the geanticline some basement seg­ 2000 m thickness. In the best known zone, ments are exposed, more or less reworked, at the southern part of the belt, this group as well as in the nucleus of domic structures has quartzites and conglomerates of the Calí• found in the outer and inner zones. 'forme Formation (Karfunkel and Karfunkel, 1975) at the bottom and conglomeratic meta­ The linear folding developed during the greywackes of the Terra Branca Formation at Brasiliano Cycle trends NW -SE and the ver­ the upper part. These metagreywackes with ma­ gences are towards SW in the outer zone and ximium thickness of 250 m represent glacial­ towards NE in the inner zone, the geanticline -marine deposits (Hettich, 1975) related to the beeing the axial zone af divergence. In the Late Precambrian glaciation. The marine drifts western part of the Sergipano belt, this diver­ correspond to the tillites of the Jequitaí gence is not observed; in both zones, the ver­ Formation, known over the 810 Francisco gence turns to S W. Craton. The BambuÍ Group, which covers the foreland located to the west from the The basic-ultrabasic as well as the acid fold belt, probably has a synchronous sedimen­ sintectonic magmatism was very discrete in tary equivalent in the upper part of the Macau­ the belt, restricted to the inner part. basGroup.

The outer belt's units extend over the The metamorphism of the Araçuaí Belt São Francisco Craton, where they show dis­ shows polarity, increasing from the crafon continuous folding and metamorphism restric­ border and reach ing the amphibolite facies, ted to the folded areas. The covers have been with kyanite. Granite intrusions are present, referred as BambuÍ, Miaba and Canudos Forma­ and volcanic rocks are known in the upper part tions. of the Macaubas Group (Gorlt, 1972).

Mineral resources are scarce in the Sergi­ The Araçuaí Belt shows holomorphic pano Belt, limited to the internaI zone. They folding trending parallel to the craton edge, may be summarized as asbestos related to car­ w ith vergence turned towards it. South of 18QS bonated intercalations, magnetite and vanadium latitude, a great system of thrust faults raised perhaps associated with ultrabasic rocks, and a portion of the basement setting it overthe mineraIs of complex pegmatites (beril, colum­ craton cover (Bambuí Group). So, in this re­ bite, lepidolite, lithiophillite). gion the Macaubas Group has been eroded.

- 63- Towards the Atlantic coast, the inner 5. UPPER PRECAMBRIAN FOLO REGIONS tectonofacies of the Brasiliano geosyncline are exposed. They are not yet well studied and 5.1. NORTHEASTERN FOLO REGION the relat lonsh ips w ith the &:>utheastern Fold Region are nOI known. The Northeastern Fold Region is the name here given to the unit formerly known fhe structures of the Araçuaí Belt at as the Caririana or Eastern Northeast Fold Region. It is limited by the Parnaíba Synecli­ 16ºS lat itude turn to ESE. Although deeply se, the São Francisco Craton, the Luis eroded and greatly covered by cenozoic sed i­ S10 Cratori (Granja Massif, Brito Neves, 1975) ments, they are recognized in windows lill and Pernambuco-Alagoas Massif. (Fig. 7). the coastal region . In this region they form the Salobro Formation of the Rio Pardo Group \t s observable structure is more complex (pedreira et aI., 1969). The upper portion than that of the &:>utheastern Region, because of thls group is formed by detritic carbonate it is composed of severaI fold systems separated beds, accumulated in a basin next to the craton by median massifs and geanticlines, which edge ; these beds are equivaIent of the Bambuí show part s of the pre-Brasiliano basement. Group. Radiometric datings (Cordani, 1974) in­ dicate age of 630 + 170 m.y. for them. The entire fold region is fragmented by enormous deep and ancient faults, reacti­ vated in the Brasiliano Cycle, mostly with trans­ current character. The fault movements marke­ 4.6. GURUPI BELT dly influenced the design of the Brasiliano structures. Some of the faults border the fold Metased irnents of greenschist facies are systems and others lie within the geotectonic exposed along the Gurupi and Guamá rivers units of the fold regions. The most important 10 the north central region of Brazil. Outside are the Pernambuco and Paraiba Faults, tren­ tbese valleys, they are covered by sediments of ding E-W. They had mainly dextral transcurrent the Parnaiba Syneelise. movements and Iimit the so-called Transversal Zone (Ebert, 1967).

They show NW trending structures and The median massifs generally have the contact with the migmatites of the São polig.onaI shapes, elongated parallel to the fold Luiz Craton is by faults. system. They are formed of gneisses, migmati­ tes and granitoid rocks, whose complicated Hurley et aI. () 967) obtained K-Ar structures are due to the policyclic evolution. ages of 600 t 60 m.y. and associated these Brasiliano migmatites of early consolidation rocks to the Gurupi BeIt, developed around appear in some median massifs. Oatings show the São Luis Craton 10 the Brasiliano Cyele. Trans-Amazonic and J equié ages for the older Actually, the sign ificance of those ages is not nuelei. yet ele ar , because similar figures were obtained from the migmatites atributed to the craton_ The geantielines are structural highs of lesser importance. and like the median If the existence of this belt is still uncer­ massifs show an important incidence of gra­ t:.lin, so are the correlatlons with the Paraguay­ nitoid intrusions. -Araguaia Belt or with the Northeastern Fold Region. The folded systems have oval, rhombic

-64- I -1 r- ( -1 A B "'r- I CO ~ 4 ~ • ~~ .. ",:,,- m~

- ·····,',." O. -,. ", B J a ", . '

200 km

Figure 7 - NORTHEASTERN REGION OF THE SOUTH AMERICAN PLATFORM A - são Francisco (11 and São Luis (2) Cratons. B - Pernambuco-Alagoas Massif (3). C - Sergipano Fold Belt: inner zone (4), geanticline (5) and outer zone (6). 0- Northeastern Fold Region Median massifs: TeiKeira (7), Rio Piranhas (S), Troia (9), Santa Quitéria (10). Geanticlines: Camalau (11), Nova Floresta (121. Acari (13). E- Northeastern Region Fold Systems: Riacho do Pontal (14), Pajeu­ -Paraiba (15), Pianc6-Alto Brigida (16), Serid6 (17), Jaguaribe (1S), Curu-Independência (19), Médio Coreau (20). F - Molasse basins of the Brasiliano Cycle. G - Sedimentary covers correlative of the Brasiliano Cycle. H - Phanerozoic sedimentary covers. I - Craton limit. J - Major faults. Arrows indicate vergences.

- 65- and linear shapes, always more or less sigmoi­ framite and molybdenite, are also found in dai, reflecting transcurrent fault movements. the Seridó Fold System and in Rio Piranhas Massif. The sedimentary fillings of the geosyn­ dinal region ineluded: a lower terrigenous 5.2. SOlJfHEASTERN FOLD REGION sequence, mainly psammitic (Caicó, Equador, Cabrobó, Parelhas and other groups), an inter­ The Southeastern Fold Region is located mediary carbonate sequence with fine detri­ on the Atlantic edge of the continent, from tics assoc'iated (Quixaba Formation), and an Uruguay to the 160 S approximately (Fig. 8). upper terrigenous pelitic sequence, essentially The name is proposed to substitute the designa­ pelitic, with some associated psammites and tion Ribeira Fold Belt. limestones (Salgueiro, Seridó, Cachoeirinha The fold region, at south of the 21 Os Groups). parallel, is largely covered by the Paraná Syne­ c\ise sediments. However, in the exposed The regional metamorphism is of gre­ basement three fold systems separated by two enschist and amphibolite facies of low to median massifs are identified (Hasui et aI. , medium pressure-type. Migmatization occur­ 1975a). red in the lower stratigraphic leveI.

The fold systems are constituted of Linear foldings are observed in the geosynclinal sequences, diversely named in folded systems, with undefined vergences. different regions (Açungui Group in the Apiaí The direction of the structures vary greatly, System, the Brusque, Porongos and Lavalleja with sinuosities introduced by fault displa· Groups in the Tijucas System and Rocha Group cements. Nevertheless, the &eneral trend is NE . in the Eastern Uruguay System). In the best studied areas, it has been distinguished a lower Basic magmatism occurred in ali the terrigenous unit, with pelites, psammites and phases of the fold region evolution, always limestones at the topo and a upper terrigenous very poorly. The acid magmatism is the most unit. These rocks show metamorphism in gre­ notable; Almeida et aI. (1967) and Brito Neves enschist and amphibolite facies, of low to and Pessoa (1974) described and elassified intermediate pressure type seOes. ineluding the various types of bodies. The most abun­ the devellopment of migmatization processo dant are the sintectonic batoliths aged of 650 ± 30 m.y . There are also late-tectonic The folding was intense, with axis trending bodies of 540 ± 25 m.y. and post-tectonic N30E. The vergence is not elearly defined, of 460 - 5 10m.y. These values are furnished turning to both senses. The pre-tectonic mag­ by numerous K·Ar and Rb-Sr datings. matism was basic and very poorly developed. Molasse deposits occur in small fault­ The sintectonic magmatism, by the other -basins, with associated effusive acid and hand, formed great number of large granitoid basic rocks. The sequences reach 3000 m batholits, with age af ca. 600 m .y . and high thickness. affinity for the median massifs.

W ith respect to mineral resources, the The median massifs are formed af ancient deposits are associated to the pegmatite pro­ nuelei af Middle and Lower Precambrian ages, vinces of Seridó and Jaguaribe, with beryl, like thase dated by Girardi et aI. (1974) and spodumene amblygonite, tantalite-columbite Miniali (1972). They are constituted of granu­ and cassiterite. Scheelite, associated to wol- lites, migmatites and basic-ultrabasic rocks.

- 66- These nuelei are contoured by migmatites, Granitic intrusions are formed during generated in the Brasiliano Cycle. In the Pelo­ the orogenesis or the stage of transition. They tas Massif only this kind of rocks has been are small, post-tectonic bodies with age 500 recognized tiU now. ± 50 m.y., as inferred from the ·results of Cordani et alo (1974) and Cordani and Kawashi­ ta (1971). Several small molas se basins have been ~rmed in the final stage of evolution. They are Between the parallelsof21 and 240 S, the located on the folded systems and at their bor­ Southeastern Fold Region is characterized by a ders and received molassic sediments and acid block structure , with several deep and ancient to intermediate flows, with thickness up to faults. The system of faults is only partially 5000 m. The lower molasses are folded (Maricá known, but is was reactivated in the Brasiliano and Camarinha Formations), while the upper 0- Cycle, mainly in the Cambro-Ordovician, nes show only block-tilting due to faults (Al­ with transcurrent movements with a regional meida, 1969). dextral slip. The Apiaí System and the Joinvile

<." O

3

li 7 .. • ; . . . 0' • 0", ...... KM

Figure 8 - SOUTHEASTERN FOLO REGION 1 - Rio de Lá Plata Craton: Uruguay (I) and RiO Grande do Sul (7) (11) . 2 - Pré-Uruaçuano areas, remobilized during the Brasiliano Cycle. 3 - Uruaçu Fold Belt. 4 - Southeastern Region Median Massifs: Joinvile (111) and Pelotas (IV). 5 - Southeastern Region Fold Systems: Apiai (V). Tijucas (Vil and Eastern Uruguay (VII). 6 - Molasse basins of the Brasiliano Cycle. 7 - Phanerozoic sedimen­ tary and volcano-sedimentary covers. 8 - Major faults.

-67- Massif structures show deflections from the 6. THE PRECAMBRIAN IN THE ANDEAN regional N30E to N60E as they approach CHAIN AND IN THE PATOGONlAN PLAT­ the block-structured zone. FORM

The Southeastern Fold Region borders the Rio de La Pia ta Craton in Uruguay and di­ The western blocks are formed by meta­ sappears under the Atlantic Oceano As will sediments of greenschist and amphibolite be shown below, it presumably returns and facies (São Roq.ue Group), with many sintec­ penetrates the continent through the Colorado tonic granitoid intrusions. The eastern and River valIey (Argentina). northern blocks are constituted by rocks of amplúbolite and graJ . lite facies, with In Sierras Austra1es, post-tectonic granites certainly pre-Uruaçuano ages, migmatizéd and occur (Quartino and Villar-Fabre, 1967), intruded by granitoids during the Brasiliano with a K-Ar age of 575 ± 10 m.y. (Halpern CycIe. These lithologies .has been described et aI., 1972). The granites are intrusive in a by Wemick (1967) and Ebert (1968) and metamorphic basement in which occur rhyoli­ incIuded in the Amparo and Paraiba Groups. tes recently dated by Rb-Sr with 671 ± 35 m .y . So, the blocks show Brasiliano units as well (Varela and Cingolani, 1975). This p1utono­ as remobilized older rocks. The structures in -volcanic magmatism may be compared to that the blocks show various directions, predomina­ of Caapucu in Eastern Paraguay. These rocks ting a N60-70E trend. These units extend till at Sierras Australes are covered by folded the southern borde r of the Uruaçu Belt and Pa1eozoic sediments, considered as a platform the limits are at least in part by faults. At cover, possibly filling an aulacogene (Har­ the J acutinga F ault Zone there is the molassic rington, 1970), and deformed in the Mesozoic. Eleutério Formation, related to the Brasiliano The Pre-Cordillera and the Cordillera CycIe. Frontal (province of Mendonza, NW Argentina) expose part of the Sierra Pintada System, formed by the San Rafael Block and by the 0 To the north of 21 S parallel, the Mendocino-Pampeano Belt (Criado Roque, exposed rocks are of Trans-Amazonic and 1972a,b). In the San Rafael Block, the presence older ages, remobilized during the Brasiliano of Precambrian or Cambrian metasediments CycIe (Cordani et al., 1973; Cordani, 1973). and eruptives is highly probable (La Ventana That area seems to correspond to the exposed Formation). These rocks are covered uncon­ infrastructure of the Southeastern Fold formably by Cambro-Oidovician limestones. Region. The structures generalIy trend NNE, Towards the southeast, in the Province of La except in the part near the faulted-block Pampa, the existence of Precambrian rocks region, where they inflect to N60E. The limit presumed by Criado Roque needs to be confir­ of remobilized area is not yet defined. medo The dated occurrences are PaleozOlc : Lihuel-Calel is Upper Permian (Halpern et aI., 1971) and Pichi Mahuida has 550 ± 35 m.y. With respect to mineral resources, the (Halpern et al ., 1972). The Mendocino-Pam­ Southeastern Fold Region has Pb-Zn deposits peano Belt seems to have developed after in the Apiai System, Au and Cu in the molas­ the regeneration of the structures related to se basins and in the Apiai System, and complex the Brasiliano Cycle. These structures follow pegrnatites with Sn, W, and Li-bearing mine­ the southern edge of the Rio de La Plata rais. Craton and are exposed in small nuclei on the

- 68- north-Pampean Plain . The geosynclinal evo­ sifs are constituted by a crystalline basement , lution took place in Eo- and Meso-Paleozoic. which shows metasedimentary rocks meta­ morphosed in greenschist and amphibolite facies, partially migmatized and intruded Farther south, in the Provinces of Rio by granitoids. Its age was determined by Negro , Neuquén and Chubut, the exposed RbjSr isochrons corresponding to the Upper ba se ment is constit uted of metasediments Precambrian; the results point out effects considered of Precambrian age . They are of the Brasiliano Cycle and remobilization penetrated by granites of Paleozoic age, til! of older, probably Upper Precanlbrian , rocks Pennian (Halpern, 1968). The possibility that (Cingolani and Varela, 1975). the metasedimentary complex is older, should not be overlooked; this would confirm the Several granitoid rocks of the Sierras existence of an Upper Precambrian-Cambrian Pampeanas have been dated. There are granites folded belt around the southern border of related to the Brasiliano Cycle and others the South American Platform, regenerated in related to a tectono-magmatic reactivation the Paleozoic. This belt would coincide with with intense acid and intennediate plutono­ the 500-600 m.y . geochronological province -volcanic magmatism (Stepanicic and Linares, that Halpern et a!. (1972) suggested to cross 1969, Halpern et aI., 1970, Gonzalez and the Argentina territory . Toselli, 1974). This process affccted a zone extending at least between the Provinces of The Sierras Pampeanas, the Pre-Cordil­ Sàn Luis and Catamarca. lt seems to be a lera, the Eastem Cordil!cra and the Puna, reflected reactivat ion const ituting an effect in NW Argentina, and neighboring regioos of on the platfonn of the tectonic and magmatic Chile and Bolivia, show clear evidences of a processes which took place in the Paleozoic geosynclinal evolution related to the Brasi­ geosynclines at its border. Thus, the Sierras liano Cycle. Borello (1969) distinguished a Pampeanas must be considered a reactivated monoliminal geosynclinal evolution in that re­ area of the South American Platform. gion, including an eastern miogeosyncline and a western eugeosyncline with ophiolites. The Sierras Transpampeanas shall be This evolution took place in the Upper Precam­ excluded from the South American Platform; brian and Lower Cambrian, with deposition they present Ordovician metased iments of a of flysch in both zones and limestones in Paleozoic geosyncline. the miogeosyncline. Molasses constituted at the end of the cycle in the Provinces of Catamarca The problem of the Precambrian-Canl­ and Cordoba (Ambato Group). The flysch is brian limit surges in considering the stratigra­ intensely folded and re-folded, having been phic relations, which in northwestern region of generally metamorphosed in greenschist and Argentina are the closest to that limit in South amphibolite facies, with intensity growing America. In the Sierra Villicun and the Sierra from E to W. Migmatization and granite intru­ Chica de Zonda (province of San Juan) there sions took place in the inner zone; some of the­ are non-metamorphic limestones, of Lower se rocks provided pebbles for the Cambrian Cambrian, containing fossils of the Ol/enelus and Lower Tremadocian conglomerates. Am­ fauna (Borello, 1964). The basement of these phibolite facies is observed in the Puna, Eastern 1ayers, thought not in direct contact with Cordillera and Sierras Pampeanas (Caminos, them, is exposed in the area. It is constituted 1972, Gordillo and Lencinas, 1972). by intensily metamorphosed and even migma­ tized rocks (Sierra Pie de PaIo, 35 km E of Almost ali of the Sierras Pampeanas mas- Villicun).

-69 - In the Eastern Cordillera (province of Precambrian rocks occur: Sierra de Santa Mar­ Salta) the Puncoviscana Formation is of Infra­ ta, Guajira Peninsula, Central and Eastern cambrian age. It has flysch character, is Jittle Cordillera. The presence of Cambrian and Or­ or non-metamorphosed and contains fossil dovician fossils and the low-medium degree remains with no stratigraphic value (Oldhamia, of metamorphism in the Paleozo ic rocks bilobites). lt is penetrated by the Quesera facilitate the distinction between them and granodiorite, dated of 530 ± 20 m.y. The the Precambrian rocks. The latter are schists, Puncoviscana Formation and the intrusion gneisses, migmatites and granites. In the Sierra are covered unconformably by the Mesón de Santa Marta (Radelli, 1962), the Precam­ Group (Ramos,' 1973), of probable Upper brian complex is formed of Iithologies of Cambrian age. This group is under the fossiJi­ high amphibolite to granulite facies, with ferous Lower Tremadocian beds. acid intrusions dated of 1400 m.y. (Rb/Sr isochron) and 753 m.y . (pinson et. aI., 1962; In Peru, Precambrian rocks are exposed Irving, 1971 ; MacDonald and Hurley , 1969). in the south (Cordillera de la Costa and Western The Iithologic nature and the radiometric Cordillera) and in the center and north (Eastern values suggest the existence of an ancient Cordillera and the Maranhão River valley). nucleus, perharps even older than 1400 m.y ., In the south, schists, gneisses and migmatites which seems to have been rejuvenated in the are exposed and were dated at 600 m.y. (Wes­ Upper Precanlbrian. The Eastern Cordillera tern Cordillera, Stewart et aI., 1974), seeming in Colombia forks of into two branches that to testify that Brasiliano episodes occured in penetrate Venezuela. Upper Precambriall"rocks the region. In the center and north, the exposed exist in both. Precambrian rocks are very extensive. They are diverse metased iments of geosynclinal The oldest rocks of Venezuelan Andes origin, including locaI basic eruptives, Showing are included . in the 19lesias Group (Kunding, superposed folding and metamorphism of 1938) of Upper Precambrian age. They are low pressure, even of amphibolite facies (Au­ schists, gneisses, migmatites and amphibolites, debaud et aI., 1971) with migmatization very well develloped in the Barinas State, and granitization. These rocks form elevated, where they have been described by Schubert faulted nuclei, and are covered unconformably (1968). The Bela Vista Formation shows a by the fossiliferous Ordovician beds (Dalmay­ lower degree of metamorphism than that rac, 1970). Group and isolder than 660.! 30m.y.,which is the minimum age of the migmatitic gneisses In Equador, the basement of the Andean associated to it (Martin Bellizzia, 1968). Rocks Belt seems to be exposed in a small area in the of the Yumare Complex occur in the western south, next to the coast, and in the axial region Caribe Range, similar to those of the Sar:ta of the Eastern Cordillera. This is a Iittle known Marta Massif of Colombia. These rocks show are a where elevated fault blocks, tilted towards metamorphism of amphiboJite and granulite east, expose metamorphic rocks of greenschist facies and have associated anorthosites in the and amphibolite facies, showing local migma­ San QuentinMassif (Bellizziá, 1973). Age of tization and granitization. These rocks are 1250 m .y. has been obtained for the Precam­ considered to be Precambrian aIthough there brian rocks from Guajira Arch (Bellizzia, 1973). are no stratigraphic and radiometric datings to prove it. There are doubts with respect to the existence of Precambrian rocks in Chile. There In Colombia, there are various regions are metamorphic rocks attributed to a crystal­ in the Andean Cordillera where the Upper line basement in the coastal region between

-70- Valparaiso and the Taitas Peninsula, as well rials as well as rupt ural phenomena and re­ as other locations in the north and south. -heating also took place on these cratonic Bonorino (1971) considered them Neo-Paleo­ areas. zoic, while other authors suppose them to be The Brasiliano fold belts have several Eo-Paleozoic or Precambrian (Miller, 1973). characteristic features in comparison with This would be the case for the occurrences north of the Santiago parallel (Miller, 1973) the fold regions. which are noted in Fig. I. The fold belts occupied a marginal po­ 7. CONCLUSIONS sition in relation to the cratons and show nar­ row, elongated forms, simple structure and rare The South American Platform consolida­ expositions of the basement within them. ted at the end of the Brasiliano Cycle, attaining The fold regions are located among different orthoplatform conditions after the Cambro­ cratons, occupying extensive poligonal areas of -Ordovician.lts southern and western borders, thousands of square kilometers; they show a respectively adjacent to the Patagonian Plat­ complex structural organization, involving va- form and the Andean Chain, are hidden under "rious geosynclinal or fold systems, separated by the sedimentary cover. To the north, and east, "several median massifs and geanticlines; within its borders fonn a continental margin of Atlan­ them, the pre-Brasiliano basement is frequently tic type. exposed.

A very extensive cratonic area was conso­ Regarding the sedimentary filling, the lidated after the Trans-Amazonic. During the belts include essentially detritic-chemical se­ Upper Precambrian, regeneration and geosyn­ quences, with few volcanic contributions; some c1inal evolution occurred, along marginal stratigraphic units are transgressives over the belts and regions between the not regenerated cratons. In fold regions, terrigenous sediments portions. These acted as forelands during the predominate, limestones being rare, and the Uruaçuano and Brasiliano Cycles. Some por­ total thicknesses are smaller. tions also constitute median massifs, geanti­ c1ines and fauIt-blocks; they were remobilized The belts present holomorphic folding with intensity in inverse relation to their size. trending parallel to the cratonic border, to­ wards which the polarities are directed. The The Pre-Uruaçuano structures are scarcely metamorphism is of greenshist facies, seemly known, thought they seem to have been remo­ of low-intermediary pressure type. The pre-tec­ bilized through tectonic, magmatic and thennal tonic magmatism was practically absent; processes of the Trans-Amazonic. The oldest acid magmatism generated only some post­ rocks are metasediments of high amphibolite -tectonic stocks restricted to the inner zones. and granulite facies, with associated ultrabasi­ In the fold regions, each system shows holo­ teso The Trans-Amazonic processes affected vast morphic folding with longitudinal trend, but areas; they seem to include belts of geosyncli­ the polarities are indefined or badly defined. nal evolution and other" areas only isotopically Reactivations of deep and ancient fauIts where rejuvenated. important in the devolopment of the regions and their tectogenesis. Metamorphisms was The cratons became the settings for ex­ of greenschist and amphibolite facies, of low­ tensive tectonic-magmatic reactivation proces­ medium pressure type. Migmatization was fre­ ses, with the formation of vplcano-sedimentary quent. The pre-tectonic magmatism was POQrly covers. Intrusions of acid and alkaline mate- developed, but the sintectonic was extremely

- 71 - active and shows affinity to the geanticlines Platform, relat~d to the Brasiliano Cyc1e, and median massifs. show linear folding and metamorphism of greenschist-amphibolite facies of low-medium In the fold belts, molassic sediments fill pressure type, inc1uding migmatization and foredeeps, intradeeps and marginal troughs. active anatexis. These characteristics are si­ Subsequent vo1canism did not occur. Molasse milar to those of other Brasiliano fold regions, deformations become less intense as they go contrasting notably with those of Uruaçu from the futerior of the belt towards the crato­ Belt. The latter is characterized by a scarcity nic areas. In fold regions, intradeeps are supe­ of migmatites and granites, high pressure rimposed to the folded systems and their bor­ metamorphism and the development of basic­ ders. The molasses show different structural ultrabasic bodies. and stratigraphic stages; to the intermediary stage are associated acid-intermediate and su­ The fold belts and regions developed bordinate basic vo1canic rocks, with important at the east of Amazonic-Rio de La Plata cra­ mineralizations. Molasse deformations are much tons finished their evolution in Cambro-Ordo­ more intense in the lower units than in the vician times. After the consolidation, it upper. followed a typical platformal evolution, charac­ terized by the development of the large Paleo­ In the regions and belts, the analysis of zoic Paraná and Parnalba Synec1ises, which the lithology of the orogenic period reveals may be · figured as frustrated geosync1ines. that the Brasiliano Cyc1e produced only mode­ rate reliefs. Phanerozoic sedimentary areas show a marked influence of Precambrian structural The mineral resources of the folded framework, particularly that of the Upper belts are singenetic, stratiform and remobi­ Precambrian. Generally, the belts and regions lized ones. In the folded regions they are more consolidated as a result of ihe Brasiliano varied, with lithophile and siderophile ele­ Cyc1e show subsidence tendencies, while ments of granitic affinity associated to peg­ the cratonic nuc1ei, geantic1ines and median matites, skarnites and greisens. In addition, massifs show a tendency for positive move­ there are metais in vein deposits, concentra­ ments. ted from the sediments. SUMMARY The facts and inferences presented for the Patagonian Platform and Andean Chain, seem to indicate that the succeeding fold This paper deals with the structural belts developed in Phanerozoic times, along organization and tectonic evolution of South the southern and western border of the South American Continent basement during the Up­ American Platform, were stablished over an per Precambrian. extensive Upper Precambrian folded unit a­ round the Amazonic-Rio de La Plata cratons. The South American Platform is the old There is not sufficient informations on the platform of South America. It has more than number of Precambrian tectono-magmatic half of this extension covered by sediments and cyc1es, but the youngest one certainly can be volcanic rocks of Phanerozoic age; the base­ correlated to the Brasiliano . ment is exposed in three vast shields andseveral little massifs. The rocks of the Andean Chain and of the southern border of the South American In the exposed basement some cratonic

-72- nuclei have been distinguished, with structu­ sition and the fold regions are between cratonic res developed in the Middle Precambrian areas: both show different characteristic of (Trans-Amazonic) and Lower Precambrian organization, sedimentation, structures, tecto­ (Jequié and Guriense). The Lower Precambrian nism, metamorphism, magmatism and me tal­ structures are described in small scaHered nu­ logenesis. clei, alI the rest seeming to have been remobi­ lized by tectonic, magmatic and thermal pro­ In the southern borde r of the South cesses of Trans-Amazonic age . These processes American Platform a fold region developed, affected large areas but are still insufficiently which possibly represents the extension of understood. the Southeastem Fold Region, and continues to the Andean Belt . In the Upper Precambrian, these cratonic . nuclei underwent intense process of reacti­ The South American Platform consolida­ vation, in large areas, with formation of volca­ ted during Cambro-Ordovician time. Its wes­ no-sedimentary covers, acid, basic and alkaline tern and southern adjacent areas were places intrusive rocks, cataclastic zones and thermally of geosynclinal evolution up to the Devonian affected zones. in the Patagonian Platform and up to the Cenozoic in the Andean Chain. The eastern During the Upper Precambrian, geosyn­ half of the South American Platform had a clinal evolution processes developed at the platformal evolution since the Silurian. borders and between the cratons, generating foId belts and regions. The frr st1y deveIoped AKNOWLEDCEMENTS belt is Iocated in Central Brazil, related to the pruaçuano Cycle (ca. 1300-1000 m.a.). The Es­ The Authors are grateful to the Funda­ pinhaço and Uruaçu Belts are attributed to this ção de Amparo à Pesquisa do Estado de São cycle. Paulo, the Conselho Nacional de Desenvol­ vimento Científico e Tecnológico and the The other units are related to the Brasi­ Superitendência de Desenvolvimento do Nor­ liano Cycle ( 1000 m.y. to Cambro-Ordovician deste, for the support in the field investigations time). The fold belts are located in marginal po- at many opportunities.

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-75 ~ Rev. Bras. Geoc. 3 (I): 1-22, DANNI, J .G.M.; DARDENNE, M.A.; FUCK, São Paulo. R.A .; RIBEIRO, MJ. - 1973 - Geologia da extremidade sudoeste CORDANI, U.G.; HALPERN, M.; BERE­ da Serra Dourada. Rev. Bras. NHOLC, M. - 1974 - Comentários Geoc. 3 (3): 160-180, Soc. Bras. sobre as determinações geocrono­ Geol., São Paulo. lógicas da Folha de Porto Alegre. Texto Explicativo das Folhas de DOR R 11, J.v.N. - 1969 - Physiographic, Stra­ Porto Alegre e Lagoa Mirim, tigraphic and Structural Deve­ 70-77. Dep. Nac.Prod. Min ., Rio lopment of the Quadrilatero Fer­ de Janeiro. rífero, Minas Gerais, Brazil. Geol. Surv. Prof. P. 641 - A. CORDANI, U.G .; KAWASHITA, K. - 1971 Estudo geocronológico pelo mé­ EBERT, H. - 1956 - in Relatório anual do Di­ todo Rb - Sr de rochas graníticas retor de 1955, Div. Geol. Min ., intrusivas no Grupo Açungui. A­ p. 62-81. Dep. Nac. Prod . Min., nais XXV Congr. Bras. Geol., 1: Rio de Janeiro. 105-110, Soc. Bras. Geol., São Paulo. EBERT, H. - 1968 - Ocorrências da fácies CRIADO ROQUE, P. - 1972a - Bloque de San granulítica no sul de Minas Ge­ Rafael. Geologia Regional Argen­ rais e em áreas adjacentes, em tina. Acad . Nac. Ciencias, pp. 288- dependência da estrutura oro­ -295. Cordoba. gênica: hipóteses sobre sua ori­ gem. An . Acad. Brasil. Ciênc. CaIADO ROQUE, P. - 1972b - Cinturon mo­ 40 (supl.): 215-219, Rio de Ja­ vil Mendocino-Pampeano. Geolo­ neiro. gia Regional Argentina, Acad. Nac. Ciencias, p. 297 -303. Cordo­ EBERT, H. - 1974 - O Grupo Eleutério e a ba. Falha J acutinga (Nordeste de SP). XXVIII Congr. Bras. Geol. CUERDA, AJ.; CINGOLANI, C.A. and BAR­ I: 726-730, Soc. Bras. Geol., RANQUERO, H.R. - 1975 - Estra­ Porto Alegre. tigrafia deI basamento precambri­ co en la comarca de los Cerros FERRANDO, L.A.; FERNANDEZ, A.N . - Pan de Azúcar-Del Corral, Sier­ -1972 - Esquema tectônico-crono• ras Australes (Província de Bue­ estratigrafico dei Predevoniano dei nos Aires) li Cong. ibero-Ameri­ Uruguay. An. XXV Congr. Bras. cano de Geologia Economica, Geol.,l: 199-210, Soc. Bras. tomo I, p. 57 -63 . Geol., São Paulo. DALMA YRAC, B. - 1970 - Mise en évidence FERREIRA, E. O. - 1972 - Explanatory note d'une chaine anté-ordovicienne et of the Tectonic Map of Brazil. problablement précambrienne Dep. Nac. Prod . Min., BoI. I . dans la Cordillere orientale du Rio de Janeiro. Pérou Central (région de Huanu­ (0). C.R. Acad. Se. Paris, 270: GlRARDI, V.A.V.; CORDANI, U.G.; CANDI­ 1088-1091. DIDO, A.; MELFI, AJ .; KAWA-

-76- SHITA, K. - 1974 - Geocronolo­ -estroncio de rocas volcanicas e gia do complexo básico-uItrabási­ hipabisales (?) dei area norte de la co pré-brasilianano de Pien, Pr. Patagonia, Republica Argentina. Resumos das Comunicações, BoI. Rev. Asoc. Geol. Argentina, 1 :532-533,xxVIlI Congr. Bras. XXVII (2): 169-174. Geol., Porto Alegre . HALPERN, M.; URQUHART, M.U. and LINA­ GONZALEZ, R.R.; TOSELLI, AJ. - 1974 - RES, E. - 1972 - Radiometric Radiometric dating of igneous ages of crystalline rocks from rocks from Sierras Pampeanas, Southern South America as rela­ Argentina. Rev. Bras. Geoc. 4(3): ted to Gondwana and Andean 137-141, São Paulo. geologic provinces. Conf. on Solid Earth Problems, Com. Argentino GORDILLO, and LENCINAS, A.N. - 1972 - dei Manto Superior, 11: 245-256, Sierras Pampeanas de Cordoba Buenos Aires. y San Luis. Geologia Regional Argentina, Acad. Nac. Ciencias, p. 1-39, Cordoba. HARRINGTON, HJ. - 1970 - Las Sierras Aus­ trales de Buenos Aires, República GORLT, G. - 1972 - Fazieswechsel und Meta­ Argentina: cadena aulocogénica. morphose in der westlichen Ser­ Rev. Asoc. Geol. Argentina, XXV ra Negra (Espinhaço Zone, Minas (2): 151-181, Buenos Aires. Gerais, Brasilien). Geol. Rund., 61: 166 - 201, Stuttgart. HASUI, Y.; ALMEIDA, F.F.M. de - 1970 - Geo­ cronologia do Centro-Oeste brasi­ HALPERN, M. - 1968 - Ages of Antartic and leiro. BoI. Soc. Bras. Geol. 19: Argentine rocks bearing on con­ 5-26, São Paulo. tinental drift. Earth Planet. Se. Letters, 5: 159-167, Amsterdam. HASUI, Y.; CARNEIRO, C.D.R.; COIMBRA, A.M. - 1975a - The Ribeira Fol­ HALPERN, M. - 1972 - Geochronologic evo­ ded Belt. Rev. Bras. Geoc. 5 (4), lution of Southern South Ameri­ São Paulo. ca. An. Acad. Bras. Cienc. 44 (Supl.): 149-160, Rio de Janeiro. HASUI, Y.; HENNIES, W.T.; IWANUCH, W. - 1975b - Idades potassio-argo­ HALPERN, M.; LINARES, E. and LATORRE, nio do Precambriano da região C.O. - 1970 - Estudio preliminar centro-norte do Brasil. BoI. IG por el metodo estroncio-rubidio 6: 77-83, Inst. Geoc. Univ. São de rocas metamorficas y gra­ Paulo. niticas de la Provincia de San Luis, Republica Argentina. Rev. Asoc. Geol. Argentina, XXV (3): 293- 302. HASUI, Y. and ALMEIDA,F. F. M. de 1976 - A faixa de dobramentos Uruaçu no Brasil CentraI. IlI9 HALPERN, M.; LINARES, E. and LATORRE, Cong. Latinoamericaho de Geolo­ C.O. - 1971 - Edad rubudio- gia, AnaIs (in press). México

-77 - HERZ, N. - 1970 - Gneissic and igneous ISSLER, R.S. - 1974 - Esboço geológico-tec• rocks of the Quadrilátero Fer­ tônico do Craton do Guaporé. rífero, Minas Gerais, Brazil. US XXVIII Congr. Bras. Geol., BoI. Geol. Survey. Prof. Paper 641 -B. 1: 659-665 . (Resumos). Soc. Bras. Geol., Porto Alegre. HETTICH, M. - 1975 - Zur genese des Macaú­ bas und Geologie des Gebietes KÜNDING, E. - 1938 - Las rocas pre-Creta­ nordlich der Serra Negra (Minas ceas de los Andes Centrales de Gerais, Brasilien). Geol. Ih . B-14, Venezoela con algunas observacio­ s. 47-48, Hannover. nes sobre su tectônica. BoI. Geol. y Min. 2(2-4): 21-43, Ca­ HUMPHREY, F.L.; ALLARD, G.O. - 1969 - racas. Geologia da aÍea do Domo de Itabaiana e sua relação com a MARCHESE, H.G. - 1974 - Estromatolitos Geologia de Propriá. CENPES / Gymnosolenidos en el lado orien­ PETROBRÁS, Publ. Esp., Rio tai de Minas Gerais, Brazil. Rev. de Janeiro. Bras. Geo. 4 (4): 257-271, São Paulo. HURLEY, P.M.; ALMEIDA, F.F.M. de; MEL­ CHER, G.C.; CORDANI, U.G.; KARFUNKEL, B; KARFUNKEL,J,- 1975- RAND, Jr.; KAWASHITA, K.: Fazielle Entwicklung der mit­ VANDOROS, P.; PINSON, W.H . teleren Espinhaço Zone mit Jr.; FAIRBAIRN, H.W. - 1967 - besonder Berücksichtigung des Test of Continental drift by com­ Tillit Problems (Minas Gerais/ parison of radiometric ages. Brasilien). Unpublished thesis, Science 157 (3788): 495-500. Uni. Freiburg.

HURLEY, PM.; FAIRBAIRN, H.W.; GAU­ MARTIN-BELLIZZIA, C. - 1968 - Edades iso­ DETTE, H.E.; MENDONZA, V.; topicas de rocas venezollanas. MARTIN-BELLIZIA, C.; ESPE­ BoI. Geol. X (19): 356 - 380, JO, A. - 1973 - Progress report on Caracas. age dating in the Northem Guya­ na Shield. 11 Congr.Lat.Ama. MASCARENHAS, J.F. - 1973 - A geologia do Geol., 1 (Abstract). Centro-leste do Estado da Ba­ hia. Anais XXVII Congr. Bras. IRVING, E.M. - 1971 - La evolucion estructu­ Geol., 35-66, Soc. Bras. Geol., ral de los Andes mas septentrio­ Aracaju. nales de Colombia. Min. Minas y Petroleo, BoI. Geologico, XIX MACDONAW, D:W. and HURLEY, PM. - (2): 90 p. - 1969 - Precambrian gneisses from Northern South America. ISOTTA, C.L.; CAMPOS, A.C.R.; YOSHIDA, Buli. Geol. Soc. America, 80: R. - 1969 - Striated pavement 1867-1872. of the Upper Precambrian gla­ ciation in Brazil. Nature 222: MILLER, H. - 1973 - Caracteristicas estrutu­ 466-468, Londres. rales dei basamento geologico

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OLIVEIRA, MA.F. - 1973 - Petrologia das ro­ QUARTINO, BJ. and VILLAR-FABRE, J.F. chas metamórficas da região de - 1967 - Geologia y petrología São José do Rio Pardo, S P. Rev. deI basàrnento de Tandil y Bar­ Bras. Ceoe. 3 (4): 257-278, Soc. ker, provincia de Buenos Aires, Bras. Geol., São Paulo. a la luz deI estudio de localida­ des críticas. Rev . Asoc. Geol. OLIVEIRA, M.A.F .; ALVES, F.R. - 1974 - Argentina, XXII (1). Buenos Ai­ Geologia e Petrografia da Região res. de Caronde, 9>. XXVIII Congr. Bras. Geol., 1:431-433, SJc. Bras. Geol., Porto Alegre. RADELLI, L. - 1962 - Introducción ai estudio de la geologia y de la petrografia PEDREIRA, A.J .; OOUTO, P.G.; AZEVEDO, deI Macizo de Santa Marta. Geo­ H. - 1969 - Metassedimentos do logia de Colombia, Univ. Nacio­ Grupo Rio Pardo, Bahia. Anais nal de Colombia, 2: 41 - 155, XXIII Congr. Bras. Geol. 87-99. Bogotá. SJc. Bras. Geol., Sio Paulo. RAMOS, V.A. - 1973 - Estructura de los pri­ PFLUG, R.; SCHOBBENHAUS, C.; RENGER, mer~ contrafueres de la Puna F. - 1969 - Contribuição à geotec­ salto-jujeí'la y sus ' manifestaciones tônica do Brasil Oriental. Série Es­ volcanicas asociadas. Asoc. Geol. pecial n9 9, SUDENE, Recife. Argentina, Actas deI v9 Cong. Geol. Argentino, N : 159-202. PINOON, W.H., Jr.; HURLEY, P.M. ; MEL­ Buenos Aires. aIER, E. and F AIRBAIRN, H. - 1962 - K-Ar and Rb-& ages of ROSIER, G.F . - 1965 - Pe~uisas geológicas na biotites from Co 10mb ia, &>uth parte orÍental do Rio de Janeiro America. BuB. Geol. &>c. Ame­ e na parte vizinha do Estado de

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-79- SCHOBBENHAUS, C. - 1972 - Relatório Ge­ a reconnaissance survey. Buli. raI sobre a Geologia da região Geol. Soe. America, 85: 1107- setentrional da Serra do Espi­ -116. nhaço, Bahia Central. Série Geol. Reg. n9 19, &ip. Desenv. Nordes­ SUZSCZYNSKI, E. - 1970 - La géologie et la te, Recife_ tectonique de la Plateform Ama­ zonienne. Geol. Rund. 59 (3): ~HUBERT, C. - 1968 - Geologia de la region 1232-1253. de Barinitas - Santo Domingo, Andes Venezoelanos surorientales. TURNER, J.C.M. - 1972 - Cordil1era Oriental. Min. Minas Hidrocarb., Boletin Geologia Regional Argentina, A­ de Geologia, X (19): 183-261, cad. Nac. de Ciencias, p. 117-142, Caracas. Cordoba.

SINGH, S. - 1974 - The tectonic evolutio~ of UNESCO and ACADEMY OF SCTENf'ES OF that portion of the Guyana 91ield THE USSR - 1973 - Explanatory represented in Guyana - an evo­ note-Tectonic Map of Europe, lution of the present status of Paris. investigations and correlations a­ cross the Guyana 91ield. Rev. V ARELA, R. and CINGOLANI, C.A. - 1975 - Bras. Geoc. 4 (I): 41-49, ~o Nuevas edades radiométricas dei Paulo. basamento aflorante en el perfil dei Cerro Pan de Azúcar-Cerro SfEPANICIC, P.N. and LINARES, E. - 1969 - dei Corral y consideraciones sobre Edades radiometricas determina­ la evolucíon geocronológica de las das para la Republica Argentina rocas igneas de las Sierras Aus­ y su significado geologico. BoI. trales, Província de Buenos Aires. Acad. Nac. Ciencias, t. XLVII, pp. VI9 Cong. Geol. Argentino, Actas 51-96, Cordoba, Argentina. (in press).

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