Almeida 98

Ž .Earth-Science Reviews 50 2000 77–111
www.elsevier.comrlocaterearscirev
The origin and evolution of the South American Platform
Fernando Flavio Marques de Almeidaa
, Benjamim Bley de Brito Neves b,1
,´
Celso Dal Re Carneiro c,)
´
a
Department of Mining, Escola Politecnica, UniÕersidade de Sao Paulo; Alameda Franca 432, Apart. 9, 01422-000, Sao Paulo SP, Brazil´ ˜ ˜
b
Department of Geology, Instituto de Geociencias, UniÕersidade de Sao Paulo, P.O. Box 11 348, 05422-970, Sao Paulo SP, Brazilˆ ˜ ˜
c
Department of Geosciences Applied to Teaching, Instituto de Geociencias, UniÕersidade Estadual de Campinas, P.O. Box 6152,ˆ
13083-970, Campinas SP, Brazil
Received 9 March 1998; accepted 14 November 1999
Abstract
The South American Platform is defined as the stable continental portion of the South American plate not affected by the
Phanerozoic — Caribbean and Andean — orogenic zones. It is surrounded by these orogenic zones and extends to the
marginal Atlantic coast. The basement of the platform consists of Archean and Proterozoic continental crusts arranged
Ž . Ž . Ž . Ž .during three main sets of orogenic events: 1 Trans-Amazonian Paleoproterozoic , 2 Late Mesoproterozoic and 3
BrasilianorPan African. The latter resulted in the consolidation of the youngest mobile belts of the platform basement. It is,
Ž .by far, the main phenomenon responsible for the overall pattern of tectonic components cratonic nuclei and fold belts and
the formation of the general structural framework at the time when the platform was a portion of the Gondwana
supercontinent. During the Phanerozoic Eon, different cover stages were developed through six main sedimentary cratonic
sequences, of which the last one is exclusive to the South American continent. The final individualization stages and their
Žrespective post-Paleozoic sequences were accompanied by a series of specific intracratonic processes, both tectonic rift
. Ž .basins, overprint of new structural styles in previous basins and magmatic basaltic and alkaline . The activation processes
have generally been attributed to the opening of the Atlantic Ocean on the east and the Andean orogeneses on the north and
Žwest. Nevertheless, a minor part of these events may have been caused by sublithospheric actions mantle-activated
.processes beneath the interior of the platform. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: tectonics; South America; platform; basement; platform covers; Archean, Proterozoic; Phanerozoic
1. Introduction
This paper aims to synthesize the present state-of-
the-art of the geological knowledge on the origin and
)
Corresponding author. Fax: q55-19-289-1562.
Ž .E-mail addresses: ffma@vol.com.br F.F.M. de Almeida ,
Ž .bbleybn@usp.br B.B. de Brito Neves , cedrec@ige.unicamp.br
Ž .C. Dal Re Carneiro .´
1
Fax: q55-11-210-4958.
evolution of the South American Platform, the oldest
part of the South American Plate.
Ž .Two of the present authors BBBN and CDRC
think that it is time to update the most quoted paper
on Brazilian tectonics: the classical 36-page Brazil-
ian National Department for Mineral Resources Pro-
Ž .duction DNPM Bulletin 241, Origin and Evolution
Žof the Brazilian Platform Origem e EÕoluc¸ao da˜
. ŽPlataforma Brasileira , by Almeida, 1967 following
.Almeida, 1966 : this broad synthesis on the Brazilian
0012-8252r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
Ž .PII: S0012-8252 99 00072-0

( )F.F.M. de Almeida et al.rEarth-Science ReÕiews 50 2000 77–11178
Geology was written before the development of the
new global tectonics, with emphasis on the Precam-
brian basement, as well as delineating the most
promising research lines to be followed. We try to
consider as much as possible all the produced geo-
logical information since the appearance of the two
Ž .papers of Almeida 1966, 1967 . All zones of the
entire continent have been investigated under differ-
ent detail levels and at present the overall picture is
better known. The present progress on Brazilian
Žgeology may be evaluated in books Almeida and
.Hasui, 1984; Schobbenhaus et al., 1984 , continen-
Žtal-scale geological maps of Brazil 1984, scale
1:2,500,000, published by DNPM researchers and
colaborators; Delgado and Pedreira, 1995, scale
. Ž1:7,000,000 and South America DNPM, 1997,
.1:5,000,000, unpublished , although many maps and
reports still remain unpublished. Most of the pub-
lished material is in Portuguese, a fact that highlights
the interest of such an essay. Facing the progress of
the geological knowledge on other better-studied
continents, the authors believe that such a synthetic
picture may help comparisons.
Ž .In its modern concept, a platform or craton
represents a stable continental part of a plate, i.e., a
stable portion of the Earth’s crust adjoining one or
Žmore active mobile belts Sengor, 1990; Park and¨
.Jaroszewski, 1994 . For South America, it means the
relatively undeformed portion of the continental
landmass during Mesozoic and Cenozoic times, not
Ž .strongly affected by the Andean and Caribbean
orogenic processes from Venezuela in the north to
Ž . Ž . Ž .Fig. 1. Situation map of: 1 the South American Platform; 2 Phanerozoic covers; 3 Andean fold belt.

( )F.F.M. de Almeida et al.rEarth-Science ReÕiews 50 2000 77–111 79
Argentina in the south at the northern border of the
Sierra de La Ventana fold belt.
Our major objective is to update the paper of
Ž .Almeida 1967 and to evaluate if the available data
support the initial definition of such platform. Some
research needs seem to have been overcome, some
remain, and new ones have naturally appeared. Even
Žthe expression, South American Almeida et al.,
.1978 instead of Brazilian Platform, has been
changed, because the former fits the geological limits
of the stable portion of the continental plate better
Ž .Fig. 1 . In fact, the limits are surely not confined
within any geographical–political boundaries.
The reader should keep in mind that such an
exercise involving 3.5 Ga of geological development
and more than 10,000,000 km2
requires some preten-
tiousness. So, naturally such an intention faces some
risks, as well as imperfections. All criticism is wel-
come as a profitable tool for the improvement of a
future version.
During more than three decades, the Brazilian
tectonic and geological knowledge has experienced a
great progress. Some models have guided such re-
search since the middle of the 60’s. The former
influence of the geosynclinal theory was slowly re-
placed by the original Plate Tectonics towards the
Žnew Global Tectonics see, among others, Moores
.and Twiss, 1995, Kearey and Vine, 1996 . In Brazil,
basic nationwide mappings have been conducted by
the DNPM–CPRM2
system, the RadamBrasil Pro-
ject, and state-owned mining and research institu-
tions, as well as by private mineral companies and
public universities. These latter have received mod-
ern equipment for isotopic and geochemical analy-
ses, geophysical prospecting, etc., and have gradu-
ated hundreds of MS and PhD students. A large
amount of new data has been generated by state
institutions and by working agreements between uni-
versities and foreign research centers. The growth in
geological research was recorded in 20 national geo-
Ž .logical congresses since 1967 with annals , a count-
less regional symposia, and also in a series of papers
in international periodicals.
2
CPRM — the Brazilian Company of Mineral Resources,
aiming to operate as the Brazilian Geological SurÕey.
2. Geology
RelatiÕe stability is one defining characteristic of
a platform. The main stabilization phase of the South
American Platform was achieved by the transition
Cambrian–Ordovician. The concept of platform sta-
bility has been strengthened in the general scope of
Žnew global tectonics Brito Neves and Alkmim, 1993;
.Park and Jaroszewski, 1994 , resulting in objective
Ž .e.g., absence of orogenic diastrophism and subjec-
tive implications of the concept. For a given platform
some additional geological attributes have been rec-
ognized — within well-defined time limits — in
relation to a previously defined mobile belt:
- Antiquity is the first one, for the common fact
that Archean and Proterozoic rocks usually domi-
nate such basement domains.
- Transitority is an essential characteristic, as it
involves a long history of evolutionary tectonic
phases.
- DiÕersity of structural associations in the frame-
work of the basement and of some well-defined
Ž .cover sequences Phanerozoic or older .
Local occurrences of Precambrian cratonic sub-
Ž .lithospheric processes mantle-activated as well as
Žrecords of cratonic tectonic activation lithosphere-
.activated are common; these are promoted by defor-
mation associated with surrounding younger mobile
belts. Besides all these qualitative criteria are often-
quoted geophysical characteristics, such as large
lithosphere thickness, low seismicity rates, moderate
to low heat-flow conditions and geothermal gradi-
Ž .ents, etc. Park and Jaroszewski, 1994 . All of them
are rather well recorded in this platform.
The records of the evolution of the platform
Ž .basement began in the Archean Table 1 . Most
Žradiometric ages belong to the Neo-Archean 2.8–2.5
.Ga but there is also an important number of values
Ž .of Meso-Archean times 3.2–2.8 Ga and a few of
ŽPalaeo-Archean ages 3.6–3.2 Ga, chiefly younger
.than 3.4 Ga . The group of older ages tends to be
enlarged with the increasing sophistication of iso-
Žtopic analyses see Table 1 and Brito Neves and
.Sato, 1998 . Fig. 2 is a situation map of the quoted
geographical names, rivers, states, the principal cities
and localities, but the reader is addressed to available
detailed maps for a precise location.

Table 1
The main tectonic events in the basement of the South American Platform, from the younger ones to the oldest:
Ž . Ž .10 Orogenic events of the Brasiliano collage, diachronous from a structural province to another. The last time interval 0.54–0.50 Ga is
characterized by escape tectonics and fissural magmatism.
Ž . Ž .9 Sunsas–Aguapeı belt, southwestern part of the Amazonian region Brazil–Bolivia , low-grade volcano-sedimentary assemblages.´
Ž .- Cariris Velhos orogenic event a Wilsonian Cycle along the central part of the Borborema Province.
Ž .8 Orogenic events in the southwestern part of the Amazonian region:
Ž .- GuaporerRondonianrSan Ignacio 1.45–1.30 Ga .´
Ž .- Disputable orogenic events in the southwestern part of the Central Goias Massif ‘‘Uruac¸uano Belt’’, high-grade rocks and along the´
Ž .Espinhac¸o range Central Bahia and Minas Gerais, low-grade assemblages .
Ž . Ž .7 Widespread events of extensional tectonics Statherian Taphrogenesis .
Ž .- The Rio Negro–Juruena Orogenesis arc plutonism in the central-western Amazonian region is the unique evidence for plate
interactions.
Ž .6 Trans-Amazonian Orogeneses: main deformational events of Paleoproterozoic mobile belts. Granitic plutonism.
Ž .5 Some occurrences of metamorphic events, high-grade gneisses. Local juvenile rock-formation event.
Ž .4 Local occurrences of metamorphic events and granite plutonism.
Ž . Ž .3 High diversity of rock assemblages: orthogneisses Trondhjemites, tonalites, granodiorites, monzogranite and granites, TTG suites ,
Ž .gneissic granulites of both igneous and sedimentary origins , mafic–ultramafic complexes, noritic dikes; volcano-sedimentary piles
Ž .Grao-Para Group , greenstone belt associations, etc.˜ ´
Ž . Ž .2 Widespread occurrences of high-grade terranes, mainly orthogneisses, and the oldest known occurrences of granite-greenstone LTG
assemblages.
Ž .1 Sparse occurrences of high-grade complexes.

Fig. 2. Situation map of the quoted geographical names, rivers, main cities, states and localities.
Ž . Ž .All known up to now Archean nuclei Fig. 3
have in some way been involved in the structural
framework of the mobile belts of the three major
subsequent Precambrian orogenic events: Transama-
Ž .zonianrEburnean mainly in Paleoproterozoic times,
2.2–1.8 Ga; ‘‘Late Mesoproterozoic’’, 1.3–0.95 Ga;
and BrasilianorPan African, 0.9–0.5 Ga. During
such collages, plate interactions reached their cli-
maxes, thus forming and successively reworking a
series of accretionary, collisional or transpressional
mobile belts, which formed different supercontinen-
tal domains. A high diversity of mineral deposits as,
Ž .for instance, gold Martini 1998 was formed due to
these processes. The existing names for such super-

Fig. 3. Archean nuclei and Paleoproterozoic mobile belts of the South American Platform.
Žcontinental collage domains are Atlantica Ledru et
.al., 1994; Rogers, 1996 in the Paleoproterozoic,
Ž .Rodinia Hoffman, 1991; Unrug, 1996 at the time of
the Mesoproterozoic–Neoproterozoic boundary, and
ŽWestern Gondwana e.g., Unrug, 1996, among oth-
.ers , from the end of the Neoproterozoic to the
beginning of the Phanerozoic. There is a clear una-
nimity among Brazilian Earth scientists on the con-

cept of this later supercontinental accretion as well
as on a younger one, the Late PaleozoicrTriassic
Pangea.
After the formation of each of these major col-
lages, there were phases of taphrogenic processes
Žwith widespread continental break-up rifting, disper-
.sion, occasionally fission , thus providing the just-
Žaccreted supercontinental landmass of which the
.South American Platform was part with important
sites of intracratonic sedimentation and anorogenic
Žmagmatism Almeida and Hasui, 1984; Schobben-
.haus et al., 1984 . The records of lithological assem-
blages and other structural patterns for these kinds of
intracratonic Proterozoic events after the Trans-
Amazonian collage are well represented in the Ama-
Ž .zonian northern part and Sao Francisco regions˜
Ž . Žcentral to eastern part of the platform Brito Neves
.et al. 1995 .
During the Late Paleozoic, the collage made by
the Hercynian cycle was responsible for the forma-
tion of a new supercontinent, Pangea. The South
American Platform area remained relatively stable
during the subsequent break-up of Pangea, from the
end of the Triassic, and during the different Creta-
ceous stages of the Atlantic opening and related
events. The same is true in the development of the
Pacific and Caribbean active and transform margins,
from that same time span up to now. This continental
portion has been persistently stable even if one con-
siders the tectonic and magmatic processes that oc-
curred in its interior, as natural cratonic responses to
the peripheral orogenies and continental break-up at
the surrounding borders.
The Patagonian block, south of the Hercynian
Ž .Sierra de la Ventana northeast Argentina was not
part of the stable platform area. The Patagonian
block was diversely involved in orogenic processes
during the Phanerozoic, as can be seen by its present
shape, dimensions and position among three active
Ž .margins only one passive margin, on the east , and
because of the relatively young thermal age of its
Žbasement mainly Mesoproterozoic and Neoprotero-
.zoic .
It is not an easy task to define a western limit
Ž . Ž .Figs. 1 and 3 between the platform the stable area
and the activatedrregenerated zones related to the
Andean and Caribbean orogens for two main rea-
sons. The lack of reliable geological and geophysical
data does not allow a good definition of the entire
boundary zone. Moreover, any limit made at this
stage would be arbitrary. Generally, this western
boundary of the stable area is parallel to the western
Ž .Brazilian to western Uruguay and Paraguay border,
but it is not a straight line. Actually, parts of the
ŽBrazilian territory Acre, Solimoes Basin, Pantanal˜
. Žarea, etc. show some tectonic influence folding,
.shearing etc. from the Andean Chain.
As mentioned before, in the basement of the
South American Platform, the BrasilianorPan-Afri-
can collage succeeds two previous ones of similar
extent and importance. The succession of intercon-
nected Brasiliano orogeneses formed the last funda-
mental tectonic and structural arrangements for the
basement of this platform. Therefore, all rocks and
structures of the Precambrian Eon, of the Neopro-
terozoic and older eras, are somehow subordinated to
the framework of the Brasiliano collage.
All the orogenic phases of the Brasiliano collage
are not precisely known and one should not expect
that they have been synchronic from one structural
Ž .province to another Table 1 . Some modern
Žgeochronological data Chemale, 1998; Brito Neves
.and Sato, 1998 have preliminarily indicated the
main events of plate interactions are ca. 750 and 600
Ma, for most of the Brazilian structural provinces
Ž .Almeida and Hasui, 1984 . Younger accretionary
Ž .events ca. 580–550 Ma have been detected only in
Žthe southeastern part of the Platform at the Man-
tiqueira Province, Fig. 2, from Rio de Janeiro to
.Espırito Santo — the Rio Doce Orogeny — and in´
Žthe southwestern part of the Platform Pampean
.Province, in Argentina , but all these records need
Žadditional data. From the Neoproterozoic III ca. 590
. ŽMa up to the beginning of the Ordovician ca. 500
.Ma , an important group of tectonic events have
Žbeen recognized wich are connected to the latest
.phases of the Brasiliano collage : collisional im-
pactogenesis, extrusion or escape tectonics, post-oro-
genic collapse, etc. Many of these intracratonic post-
collisional events of some provinces were coeval to
the above-mentioned youngest accretionary oroge-
Ž .nies Pampean and Rio Doce of other provinces.
Stabilization of the basement structures and full
platformal conditions only appeared at the beginning
of the Ordovician Period but the age for the final
individualization of this platform is the Mesozoic

Ž .Era after continental drift . During the Phanerozoic,
pre-Ordovician Brasiliano structures provided differ-
ent types of tectonic heritage for the development of
the sedimentary platform cover in all types of basins.
This is the case of the precursor Cambrian–Early
Ordovician rifts of the Paleozoic syneclises, the ar-
rangement of isopach lines in the syneclises, the
internal and external shapes of all sedimentary basins
and specially the particular case of the Mesozoic–
Cenozoic rift-basins. These effects are common for
all Paleozoic basins, but they are conspicuous in
Žpost-Triassic taphrogenic basins Cordani et al.,
.1984 linked to the Atlantic opening.
3. The Archean
The available isotopic data for this eon can be
placed more specifically in three time intervals: 3.4–
3.2, 3.0–2.8, and 2.7–2.5 Ga from the Paleo-Archean
to the Neo-Archean. The frequency order of ages is
inverted due to a small critical number of isotopic
data. The values obtained up to now are not enough
to discriminate evolutionary stages for any Archean
nuclei in South American. The present geographi-
cal–geological areas for the Archean nuclei them-
selves are relatively modest in size, even though
there is evidence that they were more extensive,
shown by the common occurrence of reworked pro-
toliths in the interior of Paleoproterozoic mobile
Ž .belts Cordani and Brito Neves, 1982 . Also, it is
plausible to expect greater former extents, because of
the embryonic stage of geochronological research in
Žthis continent RbrSr and KrAr are still are the
.predominating methodologies of analyses . This sce-
nario may change in the future, with progress in
isotopic research and through the use of more power-
ful methods.
The Archean lithostructural types, regardless of
the above-mentioned comments and age intervals,
fully confirm the classical pair of terranes of the
Ž .platform basement of the world: 1 high-grade or-
thogneisses of TTG-suite, granulitic orthogneisses,
Ž .mafic–ultramafic bodies; and 2 low-grade green-
stone belts and similar volcano-sedimentary associa-
tions. Besides these granite–greenstone terranes,
other less common lithotypes have been identified in
both marine and continental environments. Among
the less common lithotypes are: volcano-sedimentary
sequences of mantle-activated rifts such as the Grao˜
Para Group, Serra dos Carajas mineral province´ ´
Ž .Macambira and Lafon, 1995 ; diversified sedimen-
Žtary and volcano-sedimentary sequences quartzitic,
peraluminous, calc-silicate-rich, manganese and
.iron-rich rock assemblages ; as paragneisses and or-
thogneisses possessing crustal affiliation, important
migmatization processes, local mafic–ultramafic dike
swarms, etc. References for these Archean types may
be found in the Extended Abstracts of a symposium
held in Brasilia by the Sociedade Brasileira de Ge-
Ž .ologia 1996 .
Usually, larger Archean nuclei occur as central
core areas bound by Paleoproterozoic mobile belts.
The size of these nuclei is variable but only a few,
like the Xingu block, in the Amazonian craton, are
Ž .of large dimensions Fig. 3 . The Archean lithotypes
are mainly preserved and best represented — in
Ž .order of importance — in the Amazonia Fig. 4 ,ˆ
Ž .Sao Francisco Fig. 5 , Goias–Tocantins, Luıs˜ ´ ´
Ž .Alves–Rio de La Plata blocks Fig. 6 . These blocks
are only continental fractions of Neoproterozoic
plates that played the role of cratonic areas during
the Brasiliano collage. It is not advisable to assign
full cratonic characteristics even to these larger blocks
as is usual in other continents, because of the
widespread processes of structural reworking, mag-
matism and heating from the surrounding mobile
belts, specially those produced by the Trans-
Amazonian collage.
Smaller occurrences of Archean rock assemblages
are almost completely masked in the remote interior
Ž .of Trans-Amazonian belts Ledru et al. 1994 . They
Žare defined as basement inliers Cordani and Brito
.Neves, 1982 , where rejuvenating processes are con-
spicuous and previous tectonic behavior is difficult
to decipher.
There are minor occurrences of Archean rocks in
the interior of all Brasiliano provinces outside the
ŽPaleoproterozoic structural domains including both
the above described ‘‘Archean nuclei’’ and the
.Trans-Amazonian mobile belts of the Neoprotero-
Ž .zoic plates Brasiliano cratons or large ‘‘massifs’’
and other large lithospheric segments. These minor
Ž .occurrences used to play two special roles: a
‘‘tectonic highs’’ or local uplifted basement blocks,

Ž . Ž .Fig. 4. A general sketch-map for the northern part of the South American Platform — 1 Guyanas and 2 Guapore shields — with´
Ž .emphasis on the Archean nuclei and the surrounding Paleoproterozoic Maroni–ItacaiunasqVentuari–Tapajos, Rio Negro–Juruena mobile´
Ž .belts. The westernmost part of this Brasiliano Amazonian craton is composed of the Mesoproterozoic to Early Neoproterozoic fold belts of
Ž .San Ignacio and Sunsas–Aguapeı, in the Brazilian–Bolivian territories based on Tassinari et al., 1996 .´ ´

Ž .Fig. 5. The central and central-eastern part of the South American Platform. The main Paleoproterozoic Trans-Amazonian mobile belts of
ŽEastern Bahia and Western Bahia surround the Archean cratonic nuclei. Links among the Western Bahia Belt, Mineiro belt south of the Sao˜
. Ž .Francisco craton and the Ticunzal and Eastern Goias Paleoproterozoic occurrences have been sketched. An outline for the Neoproterozoic´
Sao Francisco craton is drawn only for reference.˜

ŽFig. 6. The ‘‘Joinville Massif’’, positioned between three Brasiliano areasrfold belts. The main central area north of Blumenau ‘‘Luıs´
.Alves craton’’ is formed by high-grade Archean rocks reworked during the Trans-Amazonian collage. The Curitiba area, marginal to the
Ž .Ribeira belt ‘‘marginal massif’’ is part of the same Trans-Amazonian collage but reworked at deeper crustal levels during the Brasiliano
Ž .events based on Basei et al., 1998 .

Ž . Žand b places where Proterozoic supracrustals Meso
.and Neoproterozoic in age have been locally van-
ished through drastic erosion and the basement may
crop out.
It is not yet possible to discriminate Archean
cycles for the basement of the South American Plat-
form due to the small number of isotopic data, and
the common reworking during later events. The
Archean terranes rarely may be considered to be
autonomous structures during Paleoproterozoic at a
regional scale of analysis. These terranes had short
Žperiods of stability because they were reworked at
.different degrees during the successive Paleopro-
terozoic accretionary and collisional events. Among
the available geochronological and geological data
the most important group seems to be the final
Ž .events of the Archean 2.7–2.5 Ga , ‘‘Jequie Cycle’’´
and ‘‘Rio das Velhas event’’, as they have been
informally named. At this time many continental
landmasses were consolidated, with repercussions to
the further general geological conditions of the Paleo-
proterozoic.
4. The Paleoproterozoic
4.1. Distribution
Paleoproterozoic terranes predominate in most of
the platform lithospheric blocks, with only rare ex-
Žceptions, like Pampia and Rio Apa which have
.provided only Mesoproterozoic age data up to now .
Moreover, many portions of the primary extension of
the Paleoproterozoic units and terranes have fre-
quently been masked due to the tectono-magmatic
reworking resulting from subsequent Proterozoic
Ž .orogenic processes such as Rio Negro–Juruena and
collages.
Palinspastic Paleoproterozoic reconstructions must
take into account different types of volcano-sedimen-
tary and sedimentary basins — ‘‘dalas’’, intracra-
tonic syneclises, rifts, continental margins, small
oceanic basins and arc-related basins — which de-
veloped on and around the rigid substratum of the
Archean landmasses. Subsequently, such basins
gradually underwent further plate interaction pro-
Ž .cesses and were reworked at different crustal levels ,
reflecting a series of accretionary and collisional
orogens between 2.2 and 1.8 Ga.
There are few radiometric ages between 2.5 and
Ž .2.1 Ga Machado et al. 1996 for those early Paleo-
proterozoic volcano-sedimentary basin fills, ancient
restructured contexts being even rarer. A significant
number of nonsynchronous ages are available for the
main subsequent orogenic phases from one orogenic
Žzone to another Sabate et al., 1990, Ledru et al.,´
.1994 : the data are distributed from 2.2 up to 1.8 Ga,
Ž .i.e., from the end of the Rhyacian 2.30–2.05 Ga up
Ž .to the end of the Orosirian 2.05–1.80 Ga periods.
ŽThe development of the Trans-Amazonian belts from
.northern Amazonia to Argentina is therefore as-
sumed to be a result of a series of continuous and
Žinterrelated orogenic processes accretionary and col-
.lisional , or a collage, which lasted until the end of
Orosirian time. For the ‘‘stable’’ surrounding areas
Ž . Ž .Archean blocks a series of coeval and later
tectonic events of continental scale took place as
anorogenic and post-orogenic granitic plutonism,
subvolcanic, intermediate extrusive and explosive
Žvolcanism of acid character Surumu and equivalent
.groups in Guyanas and Venezuela , shearing tecton-
Ž .ics escape tectonics? accompanied by syenitic in-
trusives, etc. Even thick detritical sedimentary se-
quences of platform type were developed locally
Ž . Ž .Roraima group in the same time span pre-1.8 Ga ,
Žwhile elsewhere surrounding the Amazonian blocks
.and others , many orogenic belts of the same collage
were active.
The above described records are widespread all
over the South American Platform, offering some
kind of obstacles for the acceptance of the new
Ž .IUGS time-scale Plumb, 1991 , which prescribes
1.6 Ga for the end of the Paleoproterozoic. Many
ŽBrazilian geologists have suggested 1.8 Ga end of
.the Orosirian period to be the end of this Protero-
zoic Era, because of the continental importance of
the Trans-Amazonian collage.
Ž .In the Statherian period 1.80–1.60 Ga , after the
Trans-Amazonian collage, widespread phenomena of
Žepeirogenesis subsequent to crustal thickening and
. Žgranitogenesis and taphrogenesis Brito Neves et al.,
. Ž .1995 took place in this new super continental land-
mass. Such intracratonic tectonic events — an insep-
arable feature of the Paleoproterozoic platform —
were characterized by extensional processes, rifting

with formation of volcano-sedimentary basins, mafic
Ždike-swarms, acid to intermediate volcanism extru-
.sive, explosive, subvolcanic , mafic–ultramafic plu-
tonism, etc. It is possible that the extensional pro-
cesses locally led to the formation of oceanic floor
Ž .Pimentel et al., 1998a,b as in the western part of
ŽGoias–Tocantins massif the Juscelandia, Indianopo-´ ˆ ´
.lis and Palmeiropolis sequences and in the central-´
western part of the Amazonian region, previous sites
for the Rio Negro–Juruena belt. For the latter, there
is strong evidence for a complete evolution of an
accretionary orogen, since the formation of an
oceanic floor up to a final coalescence of magmatic
Ž .arcs during this period Tassinari et al., 1996 .
ŽIn the northern part of the platform the Amazo-
.nian region, Fig. 4 , the Trans-Amazonian mobile
Žbelts surround the Xingu Macambira and Lafon,
. Ž1995 and Pakaraima Archean blocks Cordani and
.Brito Neves, 1982 . These belts include a series of
minor Archean crustal fragments as basement inliers.
Some of them received classical names in geological
literature such as Adampada, Imataca, Kanuku, etc.
Ž .Schobbenhaus et al. 1984 . To the west, fragments
of the Trans-Amazonian collage are still present as
Ž .interior remnants isotopically detected in the whole
Ž .Rio Negro–Juruena belt Sato and Tassinari, 1996 ;
and even further to the west of this belt, these
fragments are being found in the basement of the
Mesoproterozoic belts on the Brazil–Bolivia bound-
Žary zone Lomas Maneche Group, Litherland et al.,
.1986 .
These facts confirm that Trans-Amazonian col-
lages have dominated the whole northern part of this
platform. In the central and eastern-central part of
the continent, the Trans-Amazonian mobile belts
Ž .Fig. 5 also include some internal reworked Archean
Žfragments the basement of Rio ItapicururSerrinha
greenstone belt, Jequie block, Santa Izabel gneiss-´
.granulitic ‘‘belt’’, etc. and circumscribe very large
Ž .Archean blocks, like Gaviao–Lenc¸ois central Bahia ,˜ ´
ŽCampo Belo–Claudio south of Minas Gerais, Fig.´
.3 and that in the central part of the Goias–Tocantins´
Ž .massif granite–greenstone terranes domain . All of
these Archean blocks present some kind of Paleopro-
terozoic reworking.
Ž .The Eastern Bahia mobile belt III in Fig. 5 ,
which is sometimes called ‘‘Atlantico’’ or ‘‘Salva-ˆ
dor-Juazeiro’’, probably continued northwards into
Žthe basement of Borborema Province Pernambuco–
.Alagoas, Caldas Brandao and Rio Piranhas massifs ,˜
where it was deeply and diversely reworked by
Brasiliano and other events. The Western Bahia mo-
Ž .bile belt II in Fig. 5 crops out in small areas,
because of the extensive Mesoproterozoic and Neo-
proterozoic platform covers, but there are probably
southern links with the so-called ‘‘Mineiro belt’’
Ž .Teixeira et al., 1996 of the Quadrilatero Ferrıfero´ ´
area in Minas Gerais. It may also extend farther west
to the eastern Goias State, where some lithostructural´
Žunits of similar nature and age occur Ticunzal
.Group .
For the southeastern and southern Brazilian states,
Trans-Amazonian terranes often occur as part of the
infrastructure of the Brasiliano belts. They are di-
versely reworked and usually difficult to be recog-
nized. Many occurrences of Trans-Amazonian rock
units have been detected in the basement of the
ŽArac¸uaı belt Guanhaes, Itacambira-Barrocao,´ ˜ ˜
.Gouvea, blocks or rock units , Paraıba do Sul beltˆ ´
ŽJuiz de Fora, Quirino-Dorania and Cabo Frio groups,ˆ
. Žblocks or rock units , in the Ribeira belt Embu
.terrane . These Paleoproterozoic occurrences are
Žnoteworthy in the ‘‘Joinville Massif’’ Hasui et al.
.1975 between the Brasiliano Ribeira and Dom Feli-
Ž .ciano belts, in two different domains Fig. 6 . They
are found not only in the southern marginal zone of
Ž .the Ribeira belt Curitiba Domain, Siga, 1995 , where
Trans-Amazonian orthogneisses occur as paleosomes
of Brasiliano migmatites, but also all over the do-
Žmain of gneissic–granulitic rocks with mafic–ultra-
.mafic bodies included of the region of Luıs Alves–´
Ž .Barra Velha Luıs Alves Craton , in Santa Catarina´
Ž .state, of primary Archean ages Fig. 6 . For these
Ž .Archean domains there is evidence Siga, 1995 of
Žmesozonal Trans-Amazonian reworking isotopic re-
.setting included .
Important Trans-Amazonian structures occur once
again in the southern portion of the platform, as a
dominant part of the Rio de La Plata Craton base-
ment in central Uruguay and northern Argentina
Ž . Ž .Fig. 7 . High-grade rocks some greenstone belts
are dominant with typical east–west structural trends,
orthogonal to the bordering Brasiliano belts of the
ŽPampean province, Cordoban to the west, Ar-
. Žgentina and Dom Feliciano to the east, Brazil and
.Uruguay .

Ž .Fig. 7. The Neoproterozoic blocks large, intermediate and small
and the different types of Neoproterozoic fold belts surrounding
and among them. The informal classification used for these belts
is that of Condie, 1989, with some minor modifications. The
Neoproterozoic blocks of the southwest part of the figure were
Ž .diversely reworked partially regenerated by Hercynian and An-
Ž .dean orogeneses AA, PA, RP , and they are out of the platform
domains. CA — Amazonian; PR — Parnaıba; SL–WA — Sao´ ˜
ŽLuıs–West Africa; RN — Rio Grande do Norte Caldas Brandao´ ˜
.qRio Piranhas massifsqbasement of Serido belt ; SFCKA —´
Sao Francisco–Congo–Kasai–Angola; AA — )
Arequipa–Anto-˜
falla; PA — Pampia; RP — Rio de La Plata; PP — Parana-
panema; KAL — Kalahari.
Therefore, for most of the central, southeastern
and southern parts of the platform, the original fea-
tures and structures of the Trans-Amazonian mobile
belts have been diversely fragmented; they play dif-
ferent roles as pieces of the basement of younger
mobile belts, each of them within a particular level
of crustal reworking. Trans-Amazonian structures are
Žwell preserved only in Rio de La Plata Craton Dalla
.Salda et al., 1998 .
Common geological features of the Paleoprotero-
zoic mobile belts as final results of wide plate tec-
tonic interactions may be summarized as follows:
Ž .a Supracrustal sequences of extensional basins
Žof continental basement rifts, syneclises, passive
. Žmargins, etc , with predominating clastic quartzites,
.U- and Au-bearing conglomerates and chemical-
Ž .clastic composition Fe- and Mn-bearing schists ,
partially to strongly involved in the Trans-Amazonian
deformation such as Parima, Kwitaro, Coeroeni, Ja-
cobina, Colomi, Areiao, Minas, Ticunzal, Cantagalo˜
Ž .Groups or Supergroups , etc.
Ž .b Volcano-sedimentary supracrustal sequences
of oceanic affiliation, back-arc type and similar basins
Ž .active rifts , generally attributed to greenstone belts,
like those of the Barama–Mazaruni Supergroup s. l.
Ž .from Venezuela to Amapa , Contendas–Mirante,´
Ž .SerrinharRio Itapicuru Bahia , etc. These
supracrustal rocks occur in independent basins
Ž .parallel or longitudinal to the former ones and they
may also underlie the abovementioned extensional
sequences.
Ž .c Gneissic-granulitic orthogneisses, diversely
Ž .sorted rocks, of basic tholeiitic , intermediate to
Žacid tonalitic, trondhjemitic, granodioritic and¨
. Ž .granitic , from low- to high-potassium shoshonitic
content, usually strongly deformed rocks, which
originated during Paleoproterozoic subduction pro-
cesses of oceanic realms and later collisional events.
Ž .d Basement inliers of gneiss-migmatitic and
gneiss-granulitic compositions of original Archaen
ages entirely enclosed and submitted to the Trans-
Amazonian trends, which formed microplates, ter-
ranes, etc. during the evolutionary history of the
mobile belt.
Ž . Že Some long and linear shear zones Sadowski,
.1983 , some of them accompanied by late orogenic
syenitic and granitic plutons.
The Trans-Amazonian collage, as postulated here,
was responsible for the widespread agglutination of
Ž .all continental and microcontinental nuclei which
were consolidated at the end of the Archean by
means of the Paleoproterozoic mobile belts. Larger

Žnuclei like Pakaraima, Xingu, Gaviao-Lençois, Cen-˜ ´
.tral Goias, etc., Fig. 3 and smaller ones were sub-´
mitted to different styles of tectonic activation during
the Paleoproterozoic orogenic stages and were as-
sembled together by mobile belts to compose a large
Žcontinental landmass around 1.8 Ga ‘‘Atlantica’’, as
.suggested by Rogers, 1996 . The importance of this
supercontinent, which is very well documented in the
basement of South American and African platforms,
transcends the present geographical limits of both
continents. The connection of orogenic events, acting
together to build a final supercontinental landmass is
the reason for the use of the term collage.
4.2. Tectonic and sedimentary enÕironments postdat-
ing the Trans-Amazonian collage
Different types of tectonic and sedimentary envi-
ronments have diachronously succeeded the Paleo-
proterozoic collage, as a physical and natural conse-
quence to lithospheric thickening and growth. There
is a remarkable set of continental-scale linked fault
Ž .system mostly normal faults and related cratogenic
Ž .basins rift systems, volcanic traps, minor syneclises ,
mafic dike-swarms and, even, some continental pas-
sive margins. The breaking processes of that conti-
Žnental landmass and their related sedimentary mostly
. Ždetritical types , volcanic acid, intermediate, mafic
.and bimodal groups, dike swarms , volcano-sedimen-
Žtary, plutonic granites, anorthosites, mafic–ultra-
.mafic bodies lithological records play a special role
in this platform. These post-Trans-Amazonian crato-
genic processes are part of a global phenomenon,
Ž .and a group of their earlier events 1.8 to 1.6 Ga
have recently been described as being of special
magnitude, starting the ‘‘Statherian Taphrogenesis’’,
Ž .according to a synthesis by Brito Neves et al. 1995 .
It is difficult to estimate precise time intervals for the
many cratogenic tectonic events — paraplatformal
and orthoplataformal — which have activated the
post-Trans-Amazonian supercontinental landmass
Žduring a large time span of about 0.9 Ga from 1.8
.up to 0.95 Ga of which the Statherian period seems
to have been only the first remarkable step.
In the present central and western central part of
the Amazonian block and in the western part of the
Goias–Tocantins block, the extensional events seem´
to have gone beyond the usual limits of a simple
cratogenic tectonics. There are reliable indications,
in the first area, and still disputed data for the second
Ž .area due to the lack of accurate geochronology that
these post-Trans-Amazonian processes evolved, from
rift to drift, and then to the formation of true oceanic
basins, and from these to orogenic belts, first in the
Ž .Upper Paleoproterozoic case of Rio Negro–Juruena
Žand later on during Mesoproterozoic times probable
.case of the ‘‘Uruaçuano’’ belt .
During Mesoproterozoic times, many of the Up-
per Paleoproterozoic linked fault systems and inte-
rior basins such as Espinhaço–Chapada Diamantina
and the Araı ‘‘belt’’ were submitted to tectonic´
inversion. These included a considerable amount of
crustal shortening and formation of elevated oro-
graphic features when they were transformed into
special types of ‘‘ensialic’’ orogens, with characteris-
tic lateral transitions to weakly deformed cratonic
covers.
The sedimentary, volcano-sedimentary and mag-
matic rock assemblages developed by the Statherian
Taphrogenesis are present from Venezuela
Ž .Avanavero, Pedras Pretas mafic magmatism in the
north of the continent to the northern part of Ar-
Ž .gentina Tandilia dike-swarm . Only a minor part of
the assemblages has remained without any tectonic
overprint, such as a flat-lying cover of the litho-
spheric portions that became Brasiliano cratons. Most
of the Statherian assemblages, as already mentioned,
were partially or totally reactivated in the subsequent
ŽProterozoic orogenic cycles, in Mesoproterozoic like
.Espinhaço–Chapada Diamantina, Uruaçuano, etc. as
Žwell as in Neoproterozoic times as part of the
.Brasiliano belts . There is a special case of Stathe-
rian rock associations that were only deformed dur-
Ž .ing the last Brasiliano group of events, ca. 0.6 Ga
i.e., about 1.1 Ga after their primary formation, like
in the Jaguaribeano fold belt, Ceara State, Northeast´
Brazil.
4.3. Rio Negro–Juruena belt
The Rio Negro–Juruena belt, where a complete
evolution of an accretionary fold belt is recorded for
Žthe Statherian period, seems to be unique Tassinari
.et al., 1996 . It occupies a wide space of the central
Žpart of the Amazonian block from the north Vene-

.zuela and Brazil to the south at the small Rio Apa
Ž .block Brazil–Paraguay boundary . Its lateral limits
Žare still poorly defined, both to the east Trans-
.AmazonianrPaleoproterozoic belts and to the west
Ž .Mesoproterozoic belts . It is mainly composed of
gneissic and migmatitic rocks of granitic, granodi-
oritic and tonalitic nature, with occasional preserved
supracrustal assemblages, which follow a dominant
NW–SW trend. Granitization, migmatization phe-
Žnomena and high-grade metamorphism upper am-
.phibolite facies predominate along the entire belt;
granulitic rocks are local.
Important series of anorogenic plutonic rocks and
some other volcano-sedimentary assemblages of
cover rocks characterize this granitic–migmatitic belt
as a result of younger Paleoproterozoic to Mesopro-
Žterozoic cratogenic episodes namely Parguazense,
.Madeira, etc. . The general knowledge of this belt is
not yet satisfactory; problems still remain unsolved
as the concept of the Rio Negro–Juruena belt is
derived from geochonological reconaissances rather
than from geological fieldwork. From Tassinari
Ž . Ž .1981 to Tassinari et al. 1996 , the amount of
geochonological data have increased considerably.
With the abovementioned circumstances, where
the coherence of various geochronological data are
Ždoubtless remarkable including Sm–Nd investiga-
.tions, Sato and Tassinari, 1996 this belt has been
interpreted as a product of the coalescence of mag-
matic arcs between 1.75–1.55 Ga, following subduc-
tion processes of oceanic realms and adding juvenile
components to the continental lithosphere. The above
described anorogenic plutonic rocks and platform
covers display ages varying from 1.6 up to 1.0 Ga
and most of them postdate the main belt develop-
ment.
5. The Mesoproterozoic
5.1. Distribution
The geological information on the Mesoprotero-
zoic in South America is largely heterogeneous both
in quality and quantity. In many aspects, the crato-
genic events show some degree of similarity with
those of the upper part of Paleoproterozoic
Ž .Statherian .
The exuberance of such preserved occurrences
should be emphasized — areas of millions of square
Ž .kilometers Schobbenhaus et al. 1984 — without
Žany similar good expositions in the world Brito
.Neves et al., 1995 , even though some of them are
found in the Amazonian rain forest. Sedimentary and
volcano-sedimentary basins of different nature and
types, diversified anorogenic plutonism, etc., have
privileged large portions of this supercontinent joined
Žby the Trans-Amazonian collage before and after
.Rio Negro–Juruena Orogeny whose most represen-
tative areas are in the Amazonas region and in the
Ž .central-eastern part east of meridian 508W Gr. of
the continent. The pre-Neoproterozoic occurrences
were certainly larger than the present known records.
Although geological knowledge is far from com-
plete, it is possible to describe a series of cratogenic
basins, characterized by different degrees of tectonic
stability which display sedimentary sequences
Ž .mostly detritical rocks , volcano-sedimentary flood
basalts and anorogenic volcano-plutonism. Strati-
graphic systematizations is difficult because of the
lost original lateral dimensions, erosional descontinu-
ities, partial or total younger tectonic overprints
Ž .Mesoproterozoic and Neoproterozoic . Additionally,
there is a natural problem to be faced: hundreds of
local informal names were introduced by different
geologists working at reconaissance scales. This suc-
cession of cratogenic events ranges in time from the
Late Paleoproterozoic up to the beginning of the
Ž .Neoproterozoic from 1.9–1.8 up to 0.95 Ga .
Part of these events should represent tectonic
responses of the interior of the continental plate to
Žplate interactions at their margins like Rio Negro–
.Juruena, San Ignacio, Sunsas–Aguapeı, etc. . There´ ´
is another series of cratogenic events displaying evi-
dence of autonomous processes of sublithospheric
Ž .activation mantle-activated areas and rifts such as
‘‘Cachoeira Seca’’, ‘‘Quarenta Ilhas’’, ‘‘Nova Flo-
Ž .resta’’ all of them in the Amazonian region ,
‘‘Salvador-Ilheus’’ and similar mafic magmatism´
Ž .post-Espinhac¸o belt Bahia , etc., which have pro-
vided important tholeiitic basic and alkaline magma-
tism.
In the interior of some Brasiliano fold belts, away
from the cratonic domains for this cycle, part of the
Žsame Paleo and Mesoproterozoic rock units of a
.previous cratogenic nature are present; some of

Žthem have already been mapped in Riacho do Pon-
.tal, Araçuaı, Brasilia belts, etc. . Many others may´
occur, but the discrimination is difficult due to the
tectonic overprint of the Neoproterozoic orogeneses.
5.2. The Mesoproterozoic collage
Mesoproterozoic fold belts are a minority in areal
extent among the tectonic realms of the South Amer-
ican Platform. With quite few exceptions, the Meso-
proterozoic mobile belts were the place and target of
strong restructuration as basements of the Neopro-
terozoic orogens, which have preferred younger
Ž .structural sites younger thermal age zones for their
development. Only Mesoproterozoic mobile belts lo-
cated in the interior of Brasiliano cratonic domains
could be preserved from the widespread Neoprotero-
zoic regeneration.
The Mesoproterozoic collage, as first assumed
here, seems to have been completed in two main
Žorogenic phases, ca. 1.3 Ga San IgnaciorGuapore,´ ´
.‘‘Uruaçuano’’, ‘‘Espinhaço’’ and ca. 0.95 Ga
ŽSunsas–Aguapeı, Cariris Velhos and possibly the´
.‘‘Grenvillian’’, to be mentioned . Even described as
minor in areal extent, such Mesoproterozoic mobile
belts were responsible for the agglutination of a very
Žlarge supercontinent, Rodinia according to Hoff-
.man, 1991 . The Paleoproterozoic orogeneses have
already prepared wide stable cratonic areas in order
to assemble such a supercontinent, to which the
Mesoproterozoic mobile belts contributed as comple-
mentary and final agents of agglutination.
Ž .a The westernmost remnants of the worldwide
net of Mesoproterozoic mobile belts are now found
in the basement of the Andean Chain, in the north
Ž . Ž‘‘Garzon-Santa Marta’’ belt and in the south ‘‘Oc-
.cidentalia Terranes’’ , therefore they are not part of
the South American Platform basement. Part of these
western belts may eventually reach the basement of
the South American Platform in the area of the
Pampia block, but such discrimination is beyond the
presently available data. Probably, such belts are
remnants of a greater and longer Mesoproterozoic
Ž .orogenic development the Grenvillian best repre-
sented and preserved in the northern platforms.
In the South American Platform, Litherland et al.
Ž .1986 have distinguished in the common Brazilian
and Bolivian area in the western Amazonian block
two very well-preserved Mesoproterozoic orogenic
developments. The older is the San Ignacio belt,´
composed of schists, meta-arkoses and paragneisses
Ž .ca. 1340 Ma , pierced by a considerable amount of
Ž .granite ca. 1310 Ma and characterized by migmati-
zation processes; it is a kind of central nucleus. The
Sunsas–Aguapei belts surround the previous central
nucleus of San Ignacio structures and are mostly´
Žcomposed of clastic metasedimentary sequences of
.rifts and passive margin settings , mature and imma-
ture rocks, with some mafic–ultramafic magmatic
contributions. The ages of the igneous rocks, related
Žto the closing orogenic events pegmatites, alkaline
.rocks , are about 950 Ma. All the eastern lateral
Žportions of these belts in Brazil western portion of
.the Amazonian craton is marked by anorogenic
rapakivi granites, Sn-bearing, with the same age
Ž .range from 1.5 to 0.95 Ga , which seems to charac-
terize impactogenic processes on the foreland do-
main. A clearer discrimination, both in area and age
records, between the westernmost Mesoproterozoic
belts of the Amazonia and the older one of Rioˆ
Negro–Juruena domain is an objective for further
research.
Ž .b In the central part of Brazil, along the eastern
border of the Goias–Tocantins massif there is a´
Ž .group of structural features rifts and rock units
Ž .clastics, acid to intermediate volcanics of continen-
tal character, generated during the Statherian Taphro-
genesis. Probably, the same cratogenic extensional
tectonic processes occur west of these rifts where
Žlarge mafic–ultramafic bodies are known Barro Alto,
.Niquelandia, Canabrava as well as rock units of
Ž .oceanic affiliation Juscelandia and correlatives . All
these structures and assemblages were submitted to
Žorogenic processes, from low- the first group, in the
. Žeast to high-metamorphic grade the second group,
.in the west during Mesoproterozoic times, around
1.3 Ga, probably following strong events of colli-
sional interaction. These orogenic processes have
been a common source of debate, especially because
of the masking overprint of the Brasiliano structural
and metamorphic features. Actually, this Mesopro-
terozoic belt further became part of the internal
Ž .domain thick skin of the thrust-and-fold belt of
Brasilia, during Neoproterozoic times. So, the identi-
Ž .fication of the Mesoproterozoic ‘‘Uruaçuano’’ di-
astrophic records is generally full of obstacles and is

even denied by some geologists. This orogeny is a
fact supported by a large amount of geological and
isotopic data.
Ž .c Drawing a parallel arc with the Uruaçuano
belt, hundreds of kilometers to the east, the Stathe-
rian linked fault system of Espinhaço and Western
Chapada Diamantina — from Piauı to Minas Gerais´
state — was subject to tectonic inversion, with
important crustal shortening, producing a long linear
fold belt by the interaction of ancient rifted basement
blocks. It is characterized by a discontinuous folding
style, whose intensity increases from east to west,
usually low-level regional metamorphism, rare
granitic magmatism and basement reworking, and a
Žproblable age within the Ectasian Period -1.4 Ga;
.)1.2 Ga . Between 1.1 and 0.9 Ga an important
Ž .event of regional mafic magmatism sills and dikes
took place in previously deformed rock units, indi-
cating post-tectonic extensional activity of the Meso-
proterozoic tectogenesis, partially masked by the
strong overprint of Brasiliano structures mainly in
the southern parts, Minas Gerais State. For both the
‘‘Uruaçuano’’ and Espinhaço belts, additional data
— geological and isotopic — are necessary to re-
solve the remaining problems.
Ž .d In the northeastern part of the platform, in the
basement of a typical Brasiliano Province, Bor-
borema, south of Patos lineament, there are notewor-
thy records of accretionary orogenic processes, which
have only recently been identified. From the south-
western border of the Parnaıba Basin up to the´
Atlantic coast, the lithological and structural evi-
dence for this belt occupy a large WSW–ESE area
about 800 km long and over 200 km wide. Its
northern segment, the Pianco-Alto Brıgida beltrter-´ ´
rane, displays records of bimodal and subordinate
MORB magmatism and the volcano-sedimentary as-
sociation of a probable forearc basin, of ca. 1.1–1.05
Ga. Southwards, the segment of the Pajeu–Paraiba´
fold beltrterrane is characterized by hundreds of
calc-alkaline sheet-like bodies, stocks, batholiths and
arc-related volcano-sedimentary associations, all of
them indicating subduction and collisional processes
around 1.0–0.95 Ga. Although still the object of
Ž .ongoing investigations Van Schmus et al., 1995 ,
these are the best records for an accretionary Meso-
proterozoic orogeny — Cariris Velhos events — in
Žthe continent. The Brasiliano overprint folding,
metamorphism, shearing, granite plutonism, etc.,
.younger than 0.9 Ga is strong. Nevertheless, previ-
ous Mesoproterozoic processes could be recognized
and differentiated with the use of SmrNd and UrPb
geochronological methods.
In general, the information rescue and the recog-
nizing degree of Mesoproterozoic structures is al-
ways in inverse proportion to the level of reworking
by Brasiliano structures. It also depends on the qual-
ity of the available geochronological data. In the
South American Platform basement such work is still
being carried out, but it is time to consider the
importance of the Mesoproterozoic collage and its
structures, developed during two different orogenic
stages. Nowadays, when the collage and fusion of a
Ž .Mesoproterozoic supercontinent Rodinia is often
discussed, we realize that the improving knowledge
of this platform tends to increase its importance.
6. The Neoproterozoic
The early beginning of Neoproterozoic first wit-
nessed the last orogenies of the previous era and the
Žconsequent fusion of continental landmasses prior to
.950 Ma . The subsequent scenery, still in the Tonian
period, all over Western Gondwana, was character-
ized by diachronous taphrogenic processes gradually
completing the fission of the Mesoproterozoic super-
Ž .continent diachronously up to 750 Ma that installed
a new cycle of global tectonics, the Brasiliano itself.
Two major groups of tectonic components then
started to interact.
Ž .a Neoproterozoic blocks, large, intermediate and
small lithospheric fragments derived from the break-
out of the previous supercontinent, which start to
work out as rigid domains, such as plates, mi-
Ž .croplates, microcontinents, ‘‘terrranes’’, etc. Fig. 7 .
Ž .b Different evolutionary stages of the Brasiliano
Ž .fold belts or the Neoproterozoic basins , positioned
inter and intra these Neoproterozoic blocks. A practi-
Ž .cal and elementary way to represent and to classify
such ‘‘basins’’rorogenic belts is based on their pre-
inversion lithostratigraphic records. These tools are
capable of showing original paleogeographic envi-
ronments and tectonic settings. Some of these pri-
mary ‘‘basins’’ — syneclises, rifts, rift systems,
aulacogens, gulfs, oceanic branchs, small oceanic

Žand oceanic basins which display several informal
names as ‘‘Adamastor’’, ‘‘ANEKT’’, ‘‘Brasilides’’,
.‘‘Goiano’’, ‘‘Ribeirao da Folha’’, etc. could only˜
preserve some of their original characteristics, even
after the many stages that have gradually trans-
formed them into fold belt segments. Naturally, some
other ‘‘basins’’ or part of ‘‘basins’’ offer more
difficulties to identify their original characteristics.
(6.1. The Neoproterozoic blocks ‘‘the probable sons
)of Rodinia’’
The major fragments of the Upper Mesoprotero-
zoic supercontinent fission have worked out as plates
Ž .or ‘‘subplates’’ , whose remaining continental por-
tions were transformed into the so-called Brasiliano
Žcratons Amazonian, Sao Luıs–West Africa, Sao˜ ´ ˜
.Francisco–Congo, Rio de la Plata, etc. , as tenta-
tively shown in Fig. 7, outlining the end of the
Neoproterozoic collage. All these fragments were
somewhat reworked during the Brasiliano events,
and these phenomena were especially more relevant
for the small blocks, with variable intensity from
shallow to deep crustal levels. Besides the ample
exposition of basement rocks usually defined as cra-
tons, ‘‘massifs’’, basement ‘‘highs’’, etc., there is in
the infrastructure of the Brasiliano belts other direct
Ž .and indirect evidence including isotopic data of
important portions of the pre-Neoproterozoic base-
ment, which were severely reworked and are now
part of gneissic–migmatitic complexes.
Ž .In fact, when these blocks are figured out Fig. 7
there is a certain amount of implicit subjectivity in
aspects such as number, size and shape. For instance,
along the periphery of the major blocks it was not
Žpossible to represent all the parcels involved and
.reworked as basement of the circumscribing fold
belts, under both thin-skin and thick-skin structural
conditions.
As fractions of the Mesoproterozoic superconti-
nent fission, these blocks are composed of segments
of the Trans-Amazonian and Upper Mesoproterozoic
collages, especially of the former one. It is necessary
to consider that some blocks were substantially mod-
ified and that some others have increased in area by
Neoproterozoic granitogenesis, like Goias–Tocantins´
Ž .whose western border is a Brasiliano magmatic arc ,
Pernambuco–Alagoas, Rio Piranhas, etc. These new
features may give the false impression that they are
generally larger than their previous dimensions, and
once again this brings problems to their correct
graphic representations.
The segments of pre-Neoproterozoic collage oc-
curring in the internides of the Brasiliano fold belts
generally present evidence of regeneration: tectonic,
thermal-metamorphic, compositional, etc. and some-
times all of them together. When these lithological
units became ductile they may be mixed up with
Neoproterozoic gneissic–migmatitic domains. Some-
times, when mostly submitted to brittle tectonics
Žthey may appear as remarkable rigid flakes, slivers,
.overthrusted fractions, etc. local structural features.
The discrimination of the whole pre-Neoproterozoic
lithostratigraphic contexts in the interior of the many
Brasiliano fold belts is an open question. This is
clear as much as these contexts are positioned far
from the cratonic domains, at distal sites.
The behavior of the Neoproterozoic blocks during
the orogenic Brasiliano processes varied to some
extent, as Neoproterozoic plates and microplates
Ž .subplates , as microcontinents, as internal structural
‘‘highs’’ of fold belts, etc. Besides, they were the
basement for ensialic sedimentary basins, both in
interior and continental margins. It is necessary to
add the role of ‘‘terranes’’, for some of these smaller
blocks, in the sense of erratic blocks considerably
Ždisplaced from their original positions Troia–Taua,´
.Guanhaes, probably Luıs Alves block, etc. . Marginal˜ ´
parts of some major blocks were occupied by Brasil-
Žiano continental magmatic arcs - like west of
Goias–Tocantins, south of Pernambuco–Alagoas,´
.east and west of Pampia, etc. and thrust-and-fold
Žbelts Sao Francisco Peninsula as a whole, southeast-˜
.ern part of Amazonia, etc. . Therefore, the placing ofˆ
Ž .Neoproterozoic blocks Fig. 4 , as descendants of a
supercontinental fission, has natural deficiencies and
uncertainties.
There is evidence that the interaction of some
Neoproterozoic blocks involved consumption of
oceanic realms positioned among them, thus generat-
ing accretionary orogenies and subsequently colli-
sional and transpressional orogenic types. When an
oceanic basin was not present, the interactions of the
blocks caused deformation of the continental sedi-
mentary or volcano-sedimentary piles between them
with deep reworking of the basement underlying

such basins. The available geochronological data
indicate important interactions, general convergence
activities with subduction, first in the Criogenian
Ž . Žperiod ca. 750 Ma , in the Neoproterozoic III ca.
.600 ma , and in some particular cases, from the end
of Neoproterozoic III to the early beginning of the
ŽCambrian 580–540 Ma. From one province to an-
other, such interactions and their orogenic events are
not synchronous.
Centripetal convergence of the Neoproterozoic
blocks may be assumed for the orogenic processes
and tectonic consolidation of most of the provinces,
like Borborema, Tocantins, etc. In all provinces the
Ž .arrrangement of blocks, as figured out Fig. 7 , after
the Brasiliano orogeny, had a last component of
Žlateral displacement along linear shear zones linea-
.ments , which seems to be connected with collisional
Ž . Žimpactogenesis and late-collisional escape tecton-
.ics events. These shear zones, present in all Brasil-
iano provinces, are additionally responsible for
Žseveral varied volcano-sedimentary post-tectonic,
. Žpull-apart basins and intrusions alkaline granites,
.granodiorites diachronously formed from one
province to another, from ca. 590 up to ca. 500 Ma.
ŽThese associated events of sedimentation immature
.continental clastic plus varied volcanism and anoro-
Žgenic plutonism are considered together Alpha se-
.quence as representative of an important tectonic
transition stage, preceding the general conditions of
tectonic stability of the Ordovician period, during
which the platform started to achieve striking stabil-
Ž .ity and to develop their first real cratonic mature
cover sequences.
6.2. Origin, classification and arrangement of the
Brasiliano fold belts
The early origin of the Brasiliano fold belts is
related to the formation of sedimentary and
volcano-sedimentary sites led up by the Tonian
Taphrogenesis, which broke up the Mesoproterozoic
Ž .supercontinent Rodinia . Subsequent convergent ac-
tivities started to take place and led to the subduction
of oceanic realms and the tectonic inversion of the
Ž .different systems of original Tonian and younger
basins, continental rifts systems, interior syneclises,
proto-oceanic basins, etc. The final picture was the
collision and transpressional movements conducted
by the convergence of the Neoproterozoic blocks.
All these combined processes developed a complete
Ž .new global cycle Brasiliano , whose consequence
was the agglutination of a newer supercontinental
Ž .landmass Western Gondwana , Neoproterozoic to
Cambrian in age, which joined together only some of
the many descendantsrfragments of Rodinia.
To cover some important aspects of the Brasiliano
Ž .cycle the classification scheme of Condie 1989 was
choosen, because lithostratigraphic composition and
tectonic mobility are prevailing factors among a
series of variables which allow good inferences about
the earlier tectonic settings of these Neoproterozoic
Ž .fold belts Fig. 7 . First, the two remarkable main
kinds of Proterozoic rock associations, QPCs
diamictite–quartzite–pelite–carbonate association
Žsyneclises, continental margins, miogeosynclines,
.etc., of proximal domains of the fold belts and
Žvolcano-sedimentary association latu sensu litho-
sphere-activated and mantle-activated rifts, forearc
and backarc basins, of distal domains of the fold
.belts are present in the far interior of most fold
belts. For this second more general case, three differ-
ent subtypes of rock associations are distinguished
here: BVAC s bimodal volcanic–arkose-con-
glomerate, turbidites; ‘‘Greenstone’’slarge propor-
tions of volcanic with both calc-alkaline and tholei-
itic affinities, absence of komatiites; and also special
and local associations with remnants of oceanic floor
Žand subduction complexes ‘‘ophiolites and related
.deep-sea sediments’’ . Another subsidiary type of
fold belts included here are those which constitute
magmatic arcs, which are usually situated on
marginal parts of the Neoproterozoic blocks, as pre-
viously mentioned.
The present distribution of the Brasiliano fold
belts, post-collage and post-Mesozoic continental
drift, may be described as forming four main struc-
Žtural provinces: Borborema northeast of the
. Ž .platform , Tocantins central part , Mantiqueira
Ž . Žsoutheast and south and Pampean southwest of the
.platform , which have already been named and dis-
Ž .cussed by Almeida et al. 1981 . This is a kind of
preliminary and useful geographical–geological clas-
sification, even with recognized paleogeographic and
tectonic connections among these provinces.
Another possible approach for the arrangements
of these belts is attractive, as that emphasizing the

chelogenic character of the belts surrounding the
Žmajor Neoproterozoic blocks which have acted as
.seed-nuclei , namely: Peri-Amazonian, Peri-West
Africa, Peri-Franciscan, Peri-Rio de la Plata, Peri-
Kalahari, etc. Regarding such classification and dis-
tribution, it is necessary to remark that generally the
Ž .rock assemblages as above discussed are arrranged
displaying lateral gradations from the Neoprotero-
zoic blocks themselves to the interior of the fold
belts. This means, from more stable types, miogeo-
Žclines and similar proximal environments QPC rock
.associations to more unstable types, distal environ-
Ž .ments BVAC, ‘‘Greenstone’’, ‘‘Ophiolites’’ , with
the rock associations increasing volcanic components
to the more distal parts. The regional metamorphism
and folding phases also usually displays the same
polarity, with the gradual intensification of both
features towards the distal domains, far from the
Neoproterozoic blocks.
The informal names used to designate fold belts
may lead to problems and deserve comments, be-
cause sometimes the influence of a geographical
point of view may be hiding some important geolog-
ical facts about close relationships and previous con-
tinuities among the fold belts. For instance, there are
fold belts positioned among different blocks that
may be up to 5000 km long, with no fundamental
discontinuities to be discussed, like that from the
Ž .Rockelides lateral to the West Africa block up to
ŽCordoba in Argentina western part of Rio de La´
.Plata . Different names have been used along this
Žbelt Araguaia, Tocantins, Paraguay, Cordoban or
.East Pampean, etc. in order to cover the many
different geographic segments rather than to state
true different geological aspects themselves. Another
Žexample is the case of the fold belt or group of fold
. Žbelts surrounding the S. Francisco peninsula just a
part of the Sao Francisco–Congo–Kasai–Angola˜
.Craton which exihibits a litho-stratigraphical and
structural coherence along thousands of kilometers.
First, with proximal facies of ancient continental
Ž .passive margins QPC assemblages and their lateral
passage to distal and deeper proto-oceanic and
oceanic sites, up to some local ophiolitic remnants.
Second, this peri-continental paleogeographic con-
text was transformed into a more or less continuous
arrangement of centripetally convergent thrust-and-
Ž .fold belts, with thin-skin domains proximal areas
Ž .laterally giving way to to thick-skin distal area
domains. Nevertheless, instead of a general unique
Ž .name like peri-Sao Francisco, for example many˜
local geographical names based mostly on physio-
Žgraphic aspects Rio Preto, Brasılia, Rio Grande,´
.Araçuaı, Rio Pardo, Sergipano, etc. were used to´
designate the same long peripheral belt, hiding the
importance of such mutual and global relationships.
The initial tectonic settings for these fold belts
were rather variable, as a function of the nature of
Žthe basement, the extension factor of the Tonian
.event , the relative position to the Neoproterozoic
blocks, sedimentary sources and volcanism, etc. The
same is true for inversion tectonic conditions, in
many different interactive conditions, obliquity of
Ž .the convergence, intensity and type B or A of
subduction, aspects of crustal shortening, etc. Some
fold belts show evidence of tectonic inheritance from
the previous Mesoproterozoic and Paleoproterozoic
Žframeworks, like in the Borborema province from
. ŽCariris Velhos trends , Araçuaı from Espinhaço and´
.Trans-Amazonian trends , the northern part of Man-
Ž .tiqueira from Trans-Amazonian trends and so on.
Conversely, some fold belts seem to have originated
straight from the first structural lines of the Tonian
rifting, without any apparent influence of basement
Ž .trends such as those of Araguaia east of Amazoniaˆ
and Rockelides, the western part of Sergipano belt,
Rio Pardo belt, etc. The natural diversity of fold
belts resulting from the Brasiliano collage is still
challenging a synthesis.
Moreover, different kinds of granitization pro-
cesses have accompanied all the phases of evolution
of the Brasiliano fold belts up to the completion of
Ž .this collage and postdating it Cambrian period .
Examples are the many gneissic–migmatitic com-
plexes and products of migmatization processes that
can be seen in Borborema and Mantiqueira provinces,
which mostly include basement rocks and Neopro-
terozoic supracrustals and which open a series of
problems for stratigraphic classification. These show
Žspecial geodynamic conditions high isothermal gra-
.dients for the Brasiliano, which is in agreement with
Žwidespread isotopic rejuvenating phenomena Rb–Sr
.and K–Ar systems, mainly for most of the pre-
Neoproterozoic rock associations.
The general structural trends of the South Ameri-
can Platform and its final geographical–geological

shape, still as part of the Western Gondwana, were
dominated by the network of shear zones, as already
mentioned, which was followed by a series of other
Žlithogenetic activities sedimentary, volcanic and plu-
.tonic , which lasted until the end of the Cambrian.
Among these shear belts, the position, role and be-
Žhavior of the Transbrasiliano Lineament Schob-
.benhaus et al., 1984 , which transversely intersects
the entire platform, from NNE to SSW and in so
doing practically divides two distinct arrangements
for Neoproterozoic blocks and fold belts, should be
mentioned. To the west, the large Amazonian block
with its peripheral belts is the dominating feature. To
Žthe east of it, the number of blocks of different
.sizes and types of fold belts is greater, and the array
Žof the Brasiliano collage is much more complex see
.Fig. 7 . There is considerable evidence for the poly-
cyclical movements along this continental shear zone,
from Precambrian to Recent times, and the same is
true for many others lineaments.
The primary displacements promoted along the
shear zones is not known well enough because most
of the studies have offered more qualitative than
quantitative results, mainly of reconnaissance map-
ping. Some authors estimate hundreds of kilometers
Žfor strike–slip movement for the case of Trans-
.brasiliano and Patos lineament, for instance have
partially been confirmed by structural, isotopic and
geophysical studies of the adjacent domains. During
all the Phanerozoic Eon, but especially in the Meso-
zoic and Cenozoic eras, these shear belts behaved
like polycyclical sites or zones of tectonic move-
Žments huge vertical displacements have been con-
.firmed , as preferential sites of the tectonic heritage
as shown by the analysis of all sedimentary basins
Ž .see Cordani et al., 1984 .
7. The Phanerozoic platform cover
The stages of the litho-structural development of
the cratonic cover of South American Platform vary
Ž .considerably and are well recorded Fig. 8 . From
the Cambrian period onwards they comprise count-
less volcano-sedimentary and sedimentary covers
Ž .some of them associated with plutonic suites stages.
ŽThe first of these or the transition stage Almeida,
.1967 corresponds to the Alpha sequence, which will
be described below. When tectonic stabilization was
reached, after the Cambrian Period, volcanism was
almost completely absent during the calmer and
longer post-Cambrian stabilization stage. During this
second major stage, since the first half of the Ordovi-
Žcian period, true cratonic sequences the concept of
.Sloss, 1988 , composed of marine and continental
sediments, started to develop successively until Tri-
assic and Jurassic times.
The best representation for these sequences are
now in the larger Gondwana or Paleozoic syneclises:
Ž 2 . Ž 2 .Solimoes 600,000 km , Amazonas 400,000 km ,˜
Ž 2 . Ž 2 .Parnaıba 700,000 km , 1,100,000 km and´
Ž 2 .Chaco–Parana 600,000 km , this last mostly in´
ŽArgentina. The stratigraphy of these basins as well
.as the coastal younger ones have been revised a few
Ž .years ago, as follows: Solimoes Eiras et al., 1994 ,˜
Ž . ŽAmazonas Cunha et al., 1994 , Parnaıba Goes and´ ´
. Ž .Feijo, 1994 , Acre Feijo and de Souza, 1994 , Parana´ ´ ´
Ž .and Chaco–Parana Milani et al., 1994 . The range´
of thicknesses varies from 3000 to 5000 m from one
depocenter to another. The sedimentary fill of Acre
Ž 2 .basin 200,000 km , to the west of the Solimoes˜
syneclise, includes equivalents of these sequences,
but its evolution presents some similarities to those
of the subandean basins. The sequences are also
present in the bottom of many interior and coastal
Mesozoic–Cenozoic rifts such as ParecisrAlto Xingu
Ž 2 .500,000 km Araripe, Tucano–Jatoba, Barreiri-´
Ž .nhas, Sergipe–Alagoas, etc. Fig. 8 .
The cratonic sequences are separated from each
other by interregional unconformities; they go
Žthrough five major tectono-sedimentary cycles six,
.if the Alpha sequence is also included , agreeing
Ž .with Soares et al. 1974, 1978 . These sequences
correspond to successive major events of the plat-
form surface lowering below the regional base level
Žand its subsequent uplift. Each of these cycles des-
.ignated by a Greek letter from alpha to zeta is an
assembly of stratigraphic groups and formations, even
of isolated beds, in some cases, between regional
unconformities. Many problems and obstacles are
Žcommon for thickness estimates after previous ero-
.sional events of the former sedimentary column, as
changes of thickness due to compacting, post-deposi-
tional geometric modifications, poorly defined
andror insufficient chronological data, etc. Never-
theless, this approach seems to be the most practical

Fig. 8. General records of the post-Paleozoic activation of the South American Platform, with emphasis on the following: 1. Archean and
Ž . Ž . Ž . Ž .Paleoproterozoic domains: 1, 2 Guyana and Guapore shields; 3 Sao Francisco craton; 4 Rio de la Plata Craton covered ; 2.´ ˜
Ž . Ž . Ž . Ž . Ž . Ž .Sedimentary coÕer, including A Subandean basins; B Solimoes basin; C Amazonas basin; D Parnaıba basin; E Parana basin; F˜ ´ ´
Ž . Ž .Chaco-Parana basin; G Parecis basin; H Alto Xingu basin; 3. Andean belt; 4. Exposed Upper Jurassic–Lower Jurassic Õolcanic rocks;´
(5. Main dike swarms; 6. Triassic alkaline rocks; 7. Upper Cretaceous alkaline rocks; 8. Lower Cretaceous alkaline granites and Õaried
)Õolcanism ; 9. Tertiary alkaline rocks; 10. Southernmost boundary of the platform.
way to synthesize all the cover stages of the platform
and its Phanerozoic tectonic history.
The paraplatformal Alpha sequence actually rep-
Ž .resents deposits late to post-tectonic and associated

magmatism of the then recently agglutinated Gond-
wana continent, rather than a real cratonic sequence.
After this stage of transition in the general gradual
and diachronous tectonic conditions, from mobile
belts to stable cratonic domains, the Paleozoic Gond-
wana basins from the Ordovician up to Jurassic
times received the deposition of four true cratonic
Ž .sequences Beta, Gamma, Delta and Delta-A , of
marine and continental environments, with their nat-
ural particuliarities from one basin to another. Dur-
ing these times, the closest plate border was the
Ž .Pacific margin Zalan, 1991 , and its complex his-´
tory of accretion and microcollision caused many
base-level changes and influenced these sedimentary
cratonic covers and their unconformities.
In post-Paleozoic times the interior of the plat-
form started to be intensively activated due to tec-
tonic processes of formation of the present active
and passive margins of the South American conti-
nent. This complex actiÕation stage and its corre-
sponding sedimentary and volcano-sedimentary
Ž .recording ‘‘Epsilon sequence’’ show important dif-
ferences and variations, both in physical space and in
Žtime, i.e., from the Upper Paleozoic first recordings
.in the northern part of the platform to Upper Creta-
ceous. In the Guyana shield, at the northern part of
the platform, Triassic rifts and mafic dike swarms
are synchronous to the opening of the North Atlantic.
In the southern part of the platform, important traps
Žof basaltic magmatism Serra Geral Group and rela-
. 2
tives , over 1,000,000 km , were mostly formed in
early Cretaceous times. Along the coastal Atlantic
area this stage of evolution presents first a series of
rifts with associated mafic magmatism, followed by
proto-oceanic domains, gulfs and the alike, near the
middle part of Cretaceous. Actually, Epsilon se-
quence does not strictly follow the general require-
ments for a cratonic sequence. However, this is a
practical and useful way to group a series of interre-
lated episodes and their lithogenetic products, at least
due to expositive reasons.
Ž .The last cover sequence Zeta mainly assembles
the sedimentary phases connected with the individu-
alization of the South American Platform, i.e. those
having the Atlantic shoreline as the regional base
level. It is indigenous and it was formed pari passu
with the last geomorphological evolution of this
platform. It is also representative of younger stages
Ž .of sedimentation and slight magmatism when tec-
Žtonic quietness started to be restored a gradual and
.diachronous restabilization , from the Upper Creta-
ceous to the Present, replacing the previous dramatic
events of the actiÕation stage.
7.1. Transition stage — Alpha sequence
ŽThis sequence includes sedimentary mostly im-
.mature continental clastic , volcano-sedimentary
Žacid to intermediate rocks and some mafic magma-
. Ž .tism are common with plutonic anorogenic rocks,
from the Neoproterozoic III up to the end of the
Cambrian, diachronous from one ‘‘basin’’ to an-
other, following the different steps and times of
consolidation of the four main structural Brasiliano
provinces. It is naturally complex and diversified
from place to place, and generally fills rifts and
pull-apart basins of modest sizes, which often crop
out on the periphery of the syneclises. A basal
unconformity to Neoproterozoic lithostructural rock
units is common and some of them reveal constraints
of a previous larger size, preceding the Phanerozoic
erosional phases. A generally well-marked upper
unconformity is defined with the Ordovician andror
ŽSilurian sediments Beta or Gamma sequence, the
.latter being the most common case .
In the northern part of the platform, representative
rock units for this sequence have not yet been recog-
nized. Alkaline ultramafic bodies occur along the
Ž .axis precursor rift system of the Amazonas
Ž .syneclise, Cambrian in age ca. 500 Ma , attributed
to late-Brasiliano impactogenesis led by the Araguaia
Ž .belt Peri-Amazonian .
The best representations of cratonic cover rocks
Žare found in the molassic foredeeps Alto Paraguai,
.Lagarto-Tobias Barreto, Itajaı, CamaquarGuaritas´ ˜
Ž .and some minor intradeeps Jua, part of Camarinha´
of the Brasiliano provinces. Similar deposits are also
Ž .present in post-collisional extrusion pull-apart
basins, always associated to extensional phases of
Žthe major shear belts Jaibaras, Cococi, Piranhas,
.Camarinha, etc. ‘‘basins’’ and ‘‘subbasins’’ , whose
previous larger size may be inferred from their lo-
cally preserved remnants. Volcano-sedimentary se-
quences filling these basins are hundreds to thou-
sands meters thick, mostly with immature clastic
Ž .deposits plus volcanic rocks and discontinuous

folding style. The brittle structures dominate. Granitic
plutonism is rare, except in the case of the ‘‘Joinville
Ž .Massif’’ the northern part of the Luıs Alves block ,´
where an important suite of alkaline to peralkaline
granites make the main elevations of the Serra do
Ž .Mar Almeida and Carneiro, 1998 , from Sao Paulo˜
to Santa Catarina states, in close association with
many occurrences of these ‘‘basins’’.
These types of ‘‘basins’’ are related to the pres-
Ž .ence of shear belts basin-forming tectonics and
they were protected against younger erosion episodes
due to the close presence of a Lower Paleozoic cover
mostly belonging to the Gamma sequence. The num-
ber and size of the ‘‘Eo-Paleozoic’’ occurrences
decreases sharply where these conditions are not
found.
Moreover, there is preliminary evidence of larger
and thicker areas of the occurrence of such basinal
rocks beneath the Parnaıba and Parana syneclises,´ ´
occupying the precursor triggering grabens for devel-
opment of these Paleozoic basins. Cambrian deposits
of this type have been found by deep wells along
their main depositional axes.
7.2. The Stability stage
The relative tectonic quietness from Ordovician
Žup to Upper Jurassic at some places, these tectonic
conditions stopped in Triassic times, and even before
. Žthem was defined as the stability stage Almeida,
.1966, 1967 . It was developed under orthoplatformal
conditions, when continuous and mature cover se-
Žquences of marine mostly, but not exclusively,
.Lower Paleozoic and continental provenances could
widely be formed, even beyond the present erosional
boundaries of the major syneclises and rifts.
Unconformities of an interregional character are
used to limit successive cratonic cover sequences:
Ž . Žthe Beta Ordovician–Silurian , Gamma Devo-
. Žnian–Lower Carboniferous , Delta Upper Carbonif-
. Ž .erous–Triassic and Delta-A Triassic–Jurassic are
composed of mature sediments. Magmatism was
Žpractically absent during this long stage over 350
.Ma in some basins , though its end is diachronous
and generally marked by Mesozoic basaltic magma-
tism, locally starting to appear at the end of the
Ž .Permian period Amazonas Basin .
7.2.1. The Beta sequence
The Beta sequence is formed by continental sedi-
ments presenting transitions to fossiliferous marine
deposits, thus characterizing the first important ma-
rine trangression on to the recently consolidated
Žplatform, from west to east Solimoes-Amazonas,˜
. ŽParana basin and from south to north Parnaıba´ ´
.basin . Its lower limit is very well marked by the
post-Cambrianrpre-Ordovician unconformity and its
upper surface limit is represented by the Eo-De-
vonian unconformity.
In the Solimoes basin, the Benjamin Constant˜
Formation is the oldest marine sedimentary record-
ing for this sequence and of all Brazilian basins
Ž .sandstones and black shales, at subsurface . All
Ž .syneclises and many interior some coastal rifts
present a fair representation for this sequence, with
continental and subsequent predominant marine sedi-
ments. Among the former can be mentioned some
minor occurrences of shallow marine and glacial
Ždeposits in Amazonas, Parnaıba and Parana Assine´ ´
.et al., 1994 syneclises. The sediments of this se-
quence often crop out in the periphery of the basins,
but most of them occur under subsurface conditions
Ž .as in the Parana basin Assine et al., 1998a,b .´
7.2.2. The Gamma sequence
This sequence is present in all Brazilian syneclises
as well as in the main paleozoic rift systems. It
corresponds to a complete transgressive–regressive
marine cycle, from the Early Devonian to the end of
the Lower Carboniferous, limited at the top and the
bottom by two important interregional unconformi-
ties.
In the Solimoes basin there are recordings of˜
marine and glacio-marine sediments. In the Ama-
zonas basin the recording of a complete sedimentary
cycle begins and ends with deltaic-fluvial sediments,
successively passing throughout neritic, euxinic,
glacio-marine and neritic facies. In the Parnaıba´
syneclise and in the Tucano–Jatoba rift system,´
recordings are also complete and similar to that of
Amazonas, but with remarkable erosional uncon-
formity and stratigraphical vacuity at its top. In the
Parana syneclise the recordings for the first phases of´
Ž .the transgressive cycle Parana Group , from con-´
glomerates and clear sandstones to black shales, are

very well documented, but a strong erosion event
removed the sediments of the regressive phase. The
same rock units of Parana are found in the bottom of´
the rift systems of the Parecis basin.
This is the most general stage of the Lower
Paleozoic covering in the South American Platform,
under stable tectonic conditions and strong marine
influence. The huge erosional unconformity of its top
is a platform milestone that was attributed to the
influences of the orogenic Hercynian events on the
Ž .western margin of the continent the Andean Chain .
7.2.3. The Delta sequence and the Delta-A ‘‘subse-
quence’’
The last Paleozoic tectonic-sedimentary cycle has
a complex evolution, limited by an Upper Permianr
Eo-Triassic unconformity. A climatic and paleogeo-
graphic differentiation can be observed in the sedi-
mentary recordings of this sequence, from the north-
Žern semi-arid conditions, fluvial and marine sedi-
. Ž .ments to the southern glacial, glacio-marine basins.
The Solimoes and Amazonas syneclises display˜
continental sediments with marine intercalations, with
typical and important evaporitic deposits. In the
Parnaıba basin, this sequence is characterized by low´
subsidence rates, shallow marine to continental sedi-
ments and progressive evidence for desertic environ-
ments from their basal beds to the top.
Permo-Carboniferous glacial deposits are widely
Ž .distributed in Gondwana Eyles, 1993; Smith, 1997 .
In the Parana syneclise the delta sequence is charac-´
terized by thick glacial deposits with marine interca-
Ž .lations five different horizons . Semi-arid to arid
conditions are recorded only near the top of the
sequence. The final phase of the tectono-sedimentary
cycle is composed of terrigenous sediments, from
litoral and shallow marine zones whose upper limit
reached the Triassic ages. Similar rock assemblages
are present in the Parecis basin, and there are also
some remnants of this sequence preserved in other
Ž .interior Tucano–Jatoba and even in some coastal´
Ž .rifts Sergipe–Alagoas .
ŽThe subsequence Delta-A was proposed Soares
.et al., 1974, 1978 to assemble the sediments of
desertic environments prevailing at the top of the
previous sequence, characterizing wide continental
Ž .conditions geocracy of Pangea , from the Early
Triassic period. Sometimes this subsequence is sepa-
Ž .rated from the lower main sequence Delta by local
unconformities. This subsequence represents one of
the largest deserts in the history of the Earth which
covered areas of the post-Hercynian supercontinent.
Ž .This post-Triassic part Delta A of the same general
Ž .development since the end of Lower Carboniferous
of the cycle has been separated as a subsequence, but
this is not a generally accepted concept. The end of
this subsequence is diachronous and it is related with
Žthe early breakout of the supercontinent from the
.Permian to Lower Cretaceous , marked by rifting
processes and basaltic magmatism. This new series
of tectonic-sedimentary realms then developed were
best defined as part of the Epsilon sequence.
7.3. The post-Paleozoic actiÕation — Epsilon and
Zeta sequences
As previously emphasized, the South American
Platform became individualized as the western part
Ž .of Pangea West Gondwana in the Cretaceous, and
since then it has been separated from the African
Ž .Platform. The initial taphrogenic rift systems, gulfs
processes preceding such a drift were generally initi-
ated in the Triassic period, even a little earlier, it had
Žits culminating in the Lower Cretaceous ca. 120–130
.Ma , with diachronic continental manifestations
Ž .tectonic and lithogenetic processes all over the
continent. These phenomena were first described as
Ž .‘‘Wealdean reactivation’’ Almeida, 1967 and later
Ž .on as ‘‘Mesozoic activation’’ Almeida, 1972 . Most
of the papers on such a complex subject considered
it as reflecting the continental drift, but it is neces-
sary also to add and to remember the influence of the
Žcoeval processes of orogenetic interactions subduc-
.tion, microcollision, faults on the Andean and
Caribbean margins of the plate.
A review of these processes will follow the differ-
Žent geographical–geological areas different struc-
.tural provinces , from north to south, which have
different behavior in terms of the most important
features.
7.3.1. The Guyana shield
This was the first region of the platform where the
processes of activation took place, especially that of
basic magmatism. Eo-Triassic up to Eo-Jurassic

Ž .ca. 225; ca. 180 Ma dike swarms, NNW–SSE
Ž .trending are common Cassipore diabases from´
Amapa up to the French Guyana territory, and from´
there to the continental boundary. Dikes of the same
nature and age are also common in the states of
Ž .Roraima, Para and Amazonas Brazil as well as in´
Suriname and Guyana. Such processes of magma-
tism and rifting are considered to be related to the
opening of the North Atlantic, which was effective
all over the Guyana Shield.
ŽThe Takutu rift attributed to the same tectonic
.cause is a NE–SW trending semi-graben about 3000
km long, 30–50 km wide, which developed from
Ž . Ž .Roraima Brazil to Guyana along older reactivated
Proterozoic structures of the Guyana Central Pre-
Ž .cambrian shear zone Costa et al., 1991 . The gen-
eral structure seems to be controlled by normal faults
— reactivated along the main trend of the shear zone
— and by some NW–SE trending transcurrent faults.
The preserved volcano-sedimentary pile exhibits
about 1500 m of basaltic flows, which dated from
180 up to 150 Ma — the Apoteri Formation —
Žcovered by 5500 m of clastic sediments minor
.clastic–evaporitic , mainly siltstone red-beds and
deltaic sandstones of the Late Jurassic to Lower
Cretaceous ages. Mesozoic alkaline plutonism is also
present, as the examples of Catrimani syenite of
Ž .Roraima Fig. 8 , with age ca. 100 Ma and the
alkaline ultramafic and carbonatitic province of Seis
Ž .Lagos, in Amazonas state Rio Negro valley , which
was tentatively attributed to the Upper TriassicrEo-
Cretaceous ages. A very thick Nb-bearing duricrust
characterizes the Seis Lagos region, from which
samples of the fresh bedrock have not yet been
obtained.
7.3.2. The Amazonas basin
The Amazonas syneclise itself is usually divided
into three major subbasins, as follows: Solimoes˜
Ž .Alto Amazonas , Medio Amazonas and Baixo Ama-´
zonas. All of them received continental sediments
Ž .Alter do Chao Formation from the Albian stage to˜
Ž .the Upper Cretaceous Turonian stage and several
Cenozoic covers. The same is true for the western
ŽAcre basin, at the boundary of the platform west-
.ward of Amazonas , under the Andean zone of influ-
ence.
Countless diabase sills and dikes intruded into the
Paleozoic lithostratigraphic pile, with a known maxi-
mum thickness of 809 m observed in the Solimoes˜
Ž . 3
subbasin. Aires 1983 estimated about 340,000 km
for the whole volume of intrusive magmatic material,
pointing out that the total thickness of the sills is
larger under two main general conditions: where the
basement of the basin is deeper and where the total
thickness of post-diabase beds is larger. Moreover,
these large thicknesses of basaltic magmatism are
generally situated where the major Precambrian shear
zones cross cut each other. The oldest known sills
Žare from the beginning of the Triassic period ca.
.250 Ma ; therefore, coeval to the above-mentioned
Cassipore diabase. A younger episode of sill and´
dike intrusion is known from the end of Jurassic to
the Neocomian stage.
The influence of the Andean orogenesis on this
region has been less investigated and is little known,
partially due to of the considerable extent and thick-
Ž .ness of the younger cover sequences Zeta . Influ-
ences and tectonic responses for these Andean
orogenesis are recognized in the Solimoes Basin,˜
Ž .situated between the structural arches of Purus east
Žand Iquitos this latter separating Solimoes from˜
.Acre-Pastaza, a sub-Andean basin and having as a
Precambrian basement rocks of the Rio Negro–
Juruena belt. Detected faults and folding systems of
Late-Jurassic and Eo-Cretaceous ages have affected
real Paleozoic cratonic sequences, and the sources
for such stress fields have their origin in the subduc-
tion processes of the Nazca plate. There is a very
important fault zone, the ‘‘megasuture of Solimoes’’˜
Ž .Caputo and Silva, 1991 , about 1000 km long,
developed by a system of faults N70–80E trending,
which is a good example of intraplate tectonics
derived from the active margin.
(7.3.3. The Guapore shield south of Amazonas-´
)Solimoes basin˜
Once again, the most conspicuous events of the
post-Paleozoic activation for this southern part of the
Amazonas basin are recorded by the occurrences of
diabase sills and dikes, also piercing rocks of the
basement and many others of Proterozoic and
Phanerozoic evolution. Basaltic flows are present in
both Mato Grosso and Rondonia states, with Jurassicˆ

and Cretaceous ages. The well-known basaltic flows
of the southwestern part of this shield, Tapirapua and˜
Anari, are the northernmost occurrences of magmatic
rocks affiliated with those of the Parana Basin´
Ž .Epsilon sequence . They are covered by Cretaceous
Ž .sandstones of the Parecis Formation Zeta sequence ,
which is correlated to the Bauru Group, to the south,
in the Parana Basin. Some kimberlite intrusions,´
Cretaceous in age, are present in this western part of
the shield, in the states of Mato Grosso and Rondonia.ˆ
7.3.4. The northeast region
During Late-Jurassic and Eo-Cretaeous two main
graben systems, SW–NE trending, were formed in
Žthis region, divided by basement tectonic highs Lima
.Filho et al., 1996, among others . The Afro-Brazilian
Ždepression Central Atlantic, with CaborPer-
nambuco, Sergipe–Alagoas, Reconcavo–Tucano–
.Jatoba basins and Bahia–Espirito Santo basins and´
ŽAraripe–Potiguar from west Pernambuco to the Rio
.Grande do Norte coastal area, Equatorial Atlantic ,
whose sedimentary remnants are trapped and pre-
served in the bottom of the deeper grabens, receiving
many informal names of basins and subbasins. They
Ž .present recordings for pre-rift Paleozoic sequences ,
Ž .rift and gulf stages Epsilon sequence before the
Žmarine sediments of Atlantic provenances Zeta se-
.quence , from different Upper Cretaceous stages
Ž .post-Albian .
In the interior of the Parnaıba syneclise, there are´
widespread continental sediments associated to rift-
Žing and basaltic magmatism ‘‘Alpercatas amphi-
.clise’’, after Goes and Coimbra, 1996 . Over 150 m´
Žof fluvial-lacustrine deposits Corda and Pastos Bons
.Formation were deposited at that time. Triassic and
Jurassic basaltic flows and diabase intrusions occur
Žon the western part of the basin ‘‘Mosquito’’ mag-
.matism , while younger Eo-Cretaceous sills, dikes
and minor basaltic flow are present in the eastern
Ž .part ‘‘Sardinha’’ magmatism , associated with some
clastic sedimentary rock units. The first Mesozoic
occurrence of marine-related or marine sedimenta-
tion is recorded in this area, as well as in the
previously mentioned rift system about the middle
Ž .part of Cretaceous after the Albian–Aptian stages .
The Brasiliano Borborema Province, part of the
shield to the east of the Parnaıba syneclise, presents´
many occurrences of basaltic magmatism, mainly
intrusions of tholeiitic nature. The relationship be-
tween the basaltic magmatism of the Borborema
ŽProvince and their ancient tectonic features activated
.in the Mesozoic time is not always clear. Occur-
rence of tholeiitic basalt magmatism generally coin-
cides with fault lines that formed the sedimentary
basins, a reality both for the interior and for the
continental margin areas.
There are several hypotheses for these occur-
rences of magmatism as that based on the clockwise
Žmovement of the South American plate Franc¸olin
. Žand Szatmari, 1987 , following a rotation pole about
.398W Gr., 78S which caused N–S extension stresses
in this part of the plate and E–W compression at the
Ž .same time Neocomian in the African counterpart
Ž . Žthe area around Cameroon . The so-generated or
.similar stress fields have thus reactivated many
Precambrian fault lines of the Borborema Province,
according to the different stages of the continental
drift. They initiated a series of Mesozoic grabens and
favored intrusion of diabase dikes around 120–130
Ma, especially from central and south Ceara to Rio´
Grande do Norte State, which present general E–W
trends, parallel to the southern border of Potiguar
ŽBasin Ceara MirimrCabugi magmatism and related´
.events .
ŽIn the coastal area, south of Recife CaborPer-
.nambuco basin it is necessary to mention the Ipo-
juca volcanism of probable Albian age, which com-
prises rhyolites, trachytes, basalts, different types of
tuffs, etc. of the same span of time as the alkaline
Ž .granite of Cabo Santo Agostinho ca. 100 Ma , the
unique Phanerozoic anorogenic granites of the plat-
form. In the domains of the Potiguar basin, there are
some local occurrences of alkaline basalts of
Ž .Oligocene to Miocene ages between 45 and 29 Ma ,
cutting across most of the sedimentary pile and
previous Mesozoic basaltic occurrences. During the
Oligocene some alkaline necks were positioned in
the surroundings of Fortaleza, in Ceara State.´
7.3.5. The Sao Francisco Craton and its eastern˜
Arac¸uaı Fold Belt´
The Sao Francisco Craton behaved as a very˜
stable area during the events of the post-Paleozoic
activation. Rifting and sedimentation processes are
Žpresent in its western part Eo-Cretaceous, connected
.with the Parnaıba Basin and along the Atlantic´

Almeida 98

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