Elsevier Encyclopedia of Geology

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of the region is limited. The cratonic basement is

composed of an Archaean core, a large Palaeoproter-

ozoic orogenic domain, and a Mesoproterozoic oro-

genic zone to the south-west.

The Archaean core, or Central Amazonian geo-

chronological province, is the portion of the craton

not affected by the Palaeoproterozoic orogenies. It

consists of granite–greenstone and high-grade ter-

ranes, overlain by Archaean volcanosedimentary se-

quences and very thick packages of undeformed

Palaeoproterozoic to Mesoproterozoic sedimentary

and volcanic units. The Caraja

s mining district, lo-

cated in the north-western portion of the province,

contains the largest high-grade iron-ore reserves in

Brazil as well as important copper, manganese, gold,

and nickel deposits.

According to recent estimates, approximately 70%

of the Amazon Craton consists of Palaeoprotero-

zoic juvenile crust, which forms the basement of

three geochronological provinces: Maroni-Itacaiunas,

Ventuari-Tapajo

s, and Rio Negro-Juruena (Figure 6).

The Maroni-Itacaiunas Province encompasses a seg-

ment of a Palaeoproterozoic accretionary Orogen,

which is the main manifestation of the 2200–1950 Ma

Transamazonian event. The Ventuari-Tapajo

s and Rio

Negro-Juruena provinces are also collages of juvenile

terranes generated in the intervals 1950–1800 Ma and

1800–1550 Ma, respectively.

The south-western part of the Amazon Craton,

along the border with Bolivia, comprises parts of a

Mesoproterozoic Orogen developed between 1500 Ma

and 1300 Ma. It involves a Palaeoproterozoic base-

ment, a juvenile terrane, and late to post-tectonic

granites.

o Luis and Rio de la Plata Cratons

The existence of the Sa

o Luis and Rio de la Plata

cratons has been inferred from structural features of

the various Brasiliano belts together with geochrono-

logical and geophysical data.

Figure 7 Neoproterozoic suture zones of Brazil, and the plates that collided to form the South American portion of western

Gondwana. Note that the internal parts of the plates correspond to the cratons.

312 BRAZIL

Figure 8 Geological map of the Mantiqueira orogenic system, showing the Arac¸ uaı

Orogen and the Ribeira and Dom Feliciano belts.

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The Sa

o Luis Craton on the northern coast has only

small exposures of a granite–greenstone-belt associ-

ation, which yield potassium–argon cooling ages of

around 2100 Ma. Potassium–argon dates obtained

from the exposures of adjacent areas fall in the inter-

val between 660 Ma and 500 Ma, indicating that they

were formed during the Brasiliano event. This led to

the interpretation that a small piece of the West Afri-

can Craton, represented by the Sa

o Luis Block,

was left in South America during the opening of the

Atlantic (Figures 2 and 3).

The Rio de la Plata Craton underlies the Palaeozoic

Parana

Basin in southern Brazil (Figure 2). The pres-

ence of a cratonic block that underlies the Parana

Basin, originally inferred from the tectonic polarity

of the Neoproterozoic orogenic belts exposed in the

region, was confirmed by gravity and teleseismic

travel-time studies. Furthermore, exposures of

Palaeoproterozoic crust unaffected by the Brasiliano

event in Uruguay and Argentina are now viewed as

extensions of the cratonic block that underlies the

Parana

Basin.

Neoproterozoic Orogenic Domains

The Neoproterozoic orogenic domains form a

complex network of interacting orogens and were

generated by the collisions that led to the assem-

bly of western Gondwana between 640 Ma and

520 Ma.

Figure 9 Geological map of the Tocantins orogenic system, showing the Araguaia, Paraguay, and Brası

lia belts.

314 BRAZIL

Accretion of juvenile crust played a minor role in

the Brasiliano orogenies; recycling of the pre-existing

continental lithosphere was the dominant process.

Besides wide zones of deformation and metamorph-

ism, the Brasiliano orogenic domains contain a rela-

tively large volume of syn- and post-collisional

granites. Furthermore, a substantial part of the oro-

genic zone is either transpressional in origin or has at

least been modified by strike-slip movement in the

late stages of development.

Neoproterozoic suture zones have been directly

mapped or inferred with the help of geophysics in

almost all the orogenic domains, so that the plates

involved in the creation of the Brazilian portion of

western Gondwana can be delineated as shown in

Figure 7.

Mantiqueira Orogenic System

The Mantiqueira orogenic system extends over a zone

2500 km long and 200 km wide along the south-east

coast of Brazil, and comprises the Arac¸uaı

Orogen

and the Ribeira and Dom Feliciano belts (Figure 8);

the West Congolian, Kaoko, and Gariep belts are

their African counterparts. The Mantiqueira system

overprints a branch of the Tocantins system in the

area to the south of the Sa

o Francisco Craton and

continues further south, reaching the Uruguayan

shield beyond the Brazilian border.

Arac¸uaı´ Orogen The Arac¸uaı

–West Congo Orogen

(Figure 8) encompasses the terrane between the Sa

Francisco Craton and the east coast of Brazil, as well

as the West Congolian Belt of Africa. This orogen is

the northern termination of the Mantiqueira system

and its African counterpart, and it displays the un-

usual shape of a tongue, being surrounded on all

sides, except the south, by cratonic areas. The Brazil-

ian or Arac¸uaı

portion of the orogen is made up of the

Arac¸uaı

fold–thrust belt to the west and a wide zone

of high-grade and granitic rocks to the east, which

represents its crystalline core. This internal zone is

also known as the northern Ribeira, Atlantic, or

Coastal Mobile Belt.

The Arac¸uaı

fold–thrust belt verges towards the ad-

jacent craton and involves a basement older than

Figure 10 Geological map of the Borborema Strike-slip System.

BRAZIL 315

1800 Ma, a 1750 Ma ensialic rift assemblage, Neopro-

terozoic passive margin to foreland strata, and other

correlative units. The crystalline core, dominated by an

array of north-north-east–south-south-west-striking

dextral transpressional zones, comprises a Palaeo-

proterozoic basement, amphibolite or granulite facies

Neoproterozoic sedimentary units, and a batholithic

body of Brasiliano granites (625–530 Ma).

The Arac¸uaı

–West Congo Orogen is currently

viewed as the product of the closure of a Red Sea type

ocean, whose development started with rift formation

in the Tonian between 900 Ma and 800 Ma.

Figure 11 Locations of the most important Brazilian Phanerozoic sedimentary basins. Maps and isopachytes (in metres) of

Palaeozoic sags, modified from Milani E and Thomaz-Filho A (2000) Sedimentary basins of South America. In: Cordani UG, Milani

EJ, Thomaz FA, Campos DA (eds.) Tectonic Evolution of South America, pp. 389–449. 31st International Geological Congress, Rio de

Janeiro. Offshore Bouguer anomaly map from Mohriak (2003) Rift architecture and salt tectonics in South Atlantic sedimentary basins.

In: Mohriak WU

Rifted Sedimentary Basins of South Atlantic: Turbidite Reservoirs, Sedimentary and Tectonic Processes. 41st Brazilian

Geological Congress and 1st International Conference of the Geophysical Society of Angola, Short Course Notes, CD-ROM, Socı

edade

Brasiliera de Geologı

a, Joa

o Pessoa, Brazil.

316 BRAZIL

Figure 12 Stratigraphical chart of Brazilian Palaeozoic sag basins. Modified from the Brazilian Petroleum Agency (Age

ncia Nacional do Petroleo,ANP)homepageatwww.anp.gov.br

BRAZIL 317

Ribeira and Dom Feliciano belts Together, the

north-east–south-west orientated Ribeira and Dom

Feliciano belts occupy a strip approximately 200 km

wide and 1600 km long along the south-east coast

of Brazil. The northern boundary with the Arac¸uaı

Orogen is artificially taken to be where the fabric

elements bend slightly to become north-north-east–

south-south-west. The Ribeira Belt truncates the

easternmost portion of the Tocantins orogenic

system, represented by the southern Brası

lia Belt,

and is overlain by the Parana

-Basin strata to the

south, where the Luis Alves basement block separates

it from the Dom Feliciano Belt.

A Palaeoproterozoic basement with some Archaean

inliers, Mesoproterozoic to Neoproterozoic metase-

dimentary units, Eocambrian foreland deposits, and

Figure 13 Schematic geological sections of (A) Solimo

es, (B) Parnaı

ba, and (C) Parana

sag basins. Modified from the Brazilian

Petroleum Agency (Age

ncia Nacional do Petroleo,ANP)homepageatwww.anp.gov.br

318 BRAZIL

voluminous granites emplaced in the pre-collisional

to post-collisional stages are the main components of

the Ribeira and Dom Feliciano belts. Various terranes

and three magmatic arcs have been characterized

along these belts.

The overall architecture of both the Ribeira and

Dom Feliciano belts is a system of north-west-verging

thrusts and nappes, which pass to the south-east and

south into a transpressional zone. In the Ribeira Belt

the internal transpressional zone is right lateral,

whereas left lateral displacements dominate the

Dom Feliciano Belt. This tectonic picture can be in-

terpreted in two basic conflicting ways. It is portrayed

either as a result of a late transpressional modification

of a pre-existing frontal collisional orogen or as a

product of an oblique plate convergence that led to

the development of a transpressional orogen. Regard-

less of which hypothesis is correct, the evolution of

the Ribeira and Dom Feliciano belts is associated

with the interaction of three continental masses (the

o Francisco–Congo, Rio de la Plata, and Kalahari

cratons), which were separated by an ocean that con-

tained magmatic arcs and microcontinents. The whole

convergence stage lasted from 600 Ma to 520 Ma.

Tocantins Orogenic System

The Tocantins system comprises the orogens de-

veloped between the Amazon, Rio de la Plata, and

o Francisco cratons, and occupies a large area in

northern and central Brazil. The Tocantins System,

together with the Borborema strike-slip province of

north-eastern Brazil (see next section), resembles the

present-day Himalayan system in architecture. The

Araguaia, Paraguay, and Brası

lia belts are the ex-

posed components of the Tocantins System (Figure 9).

Araguaia Belt The north–south trending Araguaia

Belt on the eastern margin of the Amazon Craton

comprises a west-verging basement-involved fold–

thrust belt, which is 1200 km long and 150 km

Figure 14 Palaeogeographical reconstruction of western Gondwana in the Late Palaeozoic, showing the location of the Parana

Basin in the foreland domain of accretionary processes on the Gondwanan margin. Modified from Milani EJ (1992) Intraplate tectonics

and the evolution of the Parana

Basin, SE Brazil. In: De Wit MJ, Ransome IGD (eds.)

Inversion tectonics of the Cape Fold Belt, Karoo and

Cretaceous Basins of Southern Africa

. Rotterdam, Balkema, pp. 101–108.

BRAZIL 319

wide. To the south it is separated from the Brası

´lia

Belt by a basement block, which is affected by the

north-east–south-west-trending Transbrasiliano Fault

Zone; to the east and to the north it is covered by

the sediments of the Palaeozoic Parnaı

ba Basin

(Figure 9). The Archaean and Palaeoproterozoic

basement is overlain by Neoproterozoic metasedi-

ments, which are the best exposed in the belt.

A 720 Ma ophiolite occurs within thrust sheets in

the central portion of the belt.

Paraguay Belt The Paraguay Belt, the youngest

member of the Tocantins orogenic system, is a pro-

nounced salient on the south-eastern border of

the Amazon Craton (Figure 9). Vendian glaciomarine

deposits overlain by carbonates containing an

Ediacaran fauna, together with continental foreland

deposits, are the main units exposed in the belt. Its

overall architecture is characterized by a system of

open to tight upright folds in the culmination zone

of the large salient, which grade into two cratonward-

verging systems of folds and thrusts at its north-

eastern and southern ends. The deformation and

metamorphism in the Paraguay Belt is estimated to

have occurred between 550 Ma and 500 Ma and

probably represents the last steps towards the final

assembly of western Gondwana.

Brasilia Belt The Brası

´lia

Belt is an east-verging

fold–thrust belt (1200 km long and up to 300 km

wide) that fringes the Sa

o Francisco Craton to the

west and south-west (Figure 9). The basement is an

extension of the Archaean–Palaeoproterozoic sub-

stratum of the adjacent Sa

o Francisco Craton. In the

internal zone, the Palaeoproterozoic basement re-

ceived two Neoproterozoic accretions: an Archaean

granite–greenstone terrane and a large magmatic arc

(Figure 9). A suture zone juxtaposes the Rio de la

Plata and Sa

o Francisco plates in the southern portion

of the belt.

A 1770 Ma ensialic rift sequence, a thick Neo-

proterozoic passive-margin package, and deep-

marine and probably ocean-floor assemblages are

the main cover units. Mesoproterozoic layered

mafic–ultramafic complexes and foreland-basin

sediments are also involved.

From a structural standpoint the Brası

lia Belt con-

sists of two distinct compartments that join along

the pronounced east–west-trending Pirineus syntaxis:

an east–south-east-verging basement-involved fold–

thrust belt to the north, and a system of spoon-shaped

east–south-east-verging nappes to the south. The

Transbrasiliano Lineament, a north-east–south-west-

orientated dextral strike-slip fault zone, overprints

the internal portions of both the Brası

lia and

Figure 15 Stratigraphical chart of the Parana

Basin showing the evolutionary stages and their genetic controls. Note the corres-

pondence between depositional stages/unconformities and orogenic events in the Andean chain during the foreland stage. Based on:

(1) Zalan PV, Wolff S, Astolfi MA,

et al. (1990) The Parana

Basin, Brazil. In: Leighton MW, Kolata DR, Oltz DF, and Eidel JJ (eds.) Interior

Cratonic Basins

, pp. 681–708. AAPG Memoir 51. Tulsa: American Association of Petroleum Geologists; (2) Milani EJ (1992) Intraplate

tectonics and the evolution of the Parana

Basin, SE Brazil. In: De Wit MJ, Ransome IGD (eds.)

Inversion tectonics of the Cape Fold Belt,

Karoo and Cretaceous Basins of Southern Africa

. Rotterdam, Balkema, pp. 101–108.

320 BRAZIL

Araguaia belts and seems to continue further north

beneath the Phanerozoic cover, merging with the

Borborema Strike-slip System (see next section).

The evolution of the Tocantins System proba-

bly started with an interaction between Sa

Francisco–Congo and the Rio de la Plata at around

790 Ma. Arc magmatism took place between 900 Ma

and 630 Ma, reflecting subduction and progressive

closure of a large ocean separating Sa

o Francisco–

Congo from Amazonia. After accretion of the arcs

Figure 16 SchematicgeologicalsectionsofBrazilianeasternmargin(A)EspiritoSanto,(B)Campos,and(C)Santosbasins.

Modifiedfrom theBrazilianPetroleum Agency(Age

nciaNationaldoPetroleo,ANP)homepageatwww.anp.gov.br

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