-
ric
Geo
Keywords:PaleoproterozoicSouth-American platformCrustal
evolutionSiderianOrosirian
ks a
Brasiliano (Neoproterozoic) structural provinces (Tocantins,
Bor-borema, Mantiqueira, Pampean), according to Almeida et al.
(1981).Many basement inliers of these Brasiliano provinces e of
variedgeotectonic/or structural origins e are also depicting
records of thePaleoproterozoc rock asemblages and events.
Furhtermore, that importance of Paleoproterozoic rock
units,blocks and terranes can also be inferred for the basement of
the
preliminarily attested and identied: Siderian, Rhyacian,
Orosirianand Statherian (thus following and respecting the
Paleoproterozoicsubdivision proposed by IUGS/UNESCO 2004). In fact,
this groups ofevents and super-events that led to the crustal
growth of the South-American continent ts naturally and quite
properly the division(periods) of the Paleoproterozoic Era.
Additionally, the stages hereproposed to the South-American
continent can be characterized asclose to or complying with Condies
(2000) conception of episodiccontinental growth, encompassing
groups of events and super-
Contents lists availab
e
els
Journal of South American Earth Sciences 32 (2011) 270e286E-mail
address: [email protected] geologic map of the South-American
continent, whenanalyzed under the point of view of the composition
and aggluti-nation of the Rodinia supercontinent (e.g. Fuck et al.,
2008) (Fig. 1),is a very useful document to evaluate the importance
of theparticipation of Paleoproterozoic rocks, terranes and
differentblocks in the constitution of that supercontinent.
Firstly, thatimportance should be emphasized for the basement
framework ofthemain cratonic nuclei (Amazonian, So Luis, So
Francisco, Rio dela Plata) of the South-American Platform.
Additionally, importancecan also be pointed out for the basement
framework of the main
block, As discussed below).In the last 25 years, the advance in
the geologic knowledge of
the South-American continent has been notable, thanks to
newsystematic geological and geophyxical mapping (carried out
byuniversities, private and statal companies) and acquisition of
newgeochronological data (mainly by UePb and SmeNd
methods),obtained from laboratories of various parts of Brazil
andworldwide.
Regarding the Paleoproterozoic, the collection of
substantialdata has revealed a vast diversity of rock-forming
processes, vari-able through the geologic time, so that its four
major stages can beStatherianBrazilian cycle
1. Introduction0895-9811/$ e see front matter 2011 Elsevier
Ltd.doi:10.1016/j.jsames.2011.02.004representing therefore examples
of Wilson Cycles. In other cases, the records of extensional
processesand those of convergent interaction of lithospheric plates
(orogenies) are either concurrent in time (withdifcult
discrimination between them) or concurrent in the
geographic-geologic space (they occur indifferent and separated
domains), privileging different regions. The four periods of
rock-forming eventsdiscussed here (Siderian, Rhyacian, Orosirian,
Statherian) are mainly recorded and recognizable for mostof the
cratonic domains of the continent, but they are gradually being
identied within the Paleo-proterozoic basement blocks (inliers) in
the large Neoproterozoic (Brasiliano) provinces of the conti-nent.
In the latter, such discrimination is much more difcult due to the
overprint of the Brasilianothermo-dynamic processes. For many years
(in the recent past), the word Transamazonian (event,orogeny,
cycle) had been used to cover indiscriminately all these many
different Paleoproterozoic events,of the four different periods.
With the present discrimination of the four major stages (periods)
on timeof rock-forming processes (igneous, metamorphic and
sedimentary assemblages) the term Trans-amazonian has naturally
become obsolete, and its usage is no longer advisable.
2011 Elsevier Ltd. All rights reserved.
major Phnerozoic syneclises (Amazonas, Paranaiba, Paran) andeven
for some terranes docked in the Andean Chain (e.g. Arequipaby the
International Stratigraphic Chart (IUGS/UNESCO 2004). There are
some particular cases for whichrifting and drifting events precede
the processes of convergent interaction between lithospheric
plates,Received 20 July 2010Accepted 14 February 2011
register rock-forming events (orogeny and taphrogeny) clustered
in the four different periods as denedThe Paleoproterozoic in the
South-Amein the geologic time
Benjamim Bley de Brito NevesInstituto de Geocincias da
Universidade de So Paulo, Departamento de Mineralogia e
a r t i c l e i n f o
Article history:
a b s t r a c t
The Paleoproterozoic bloc
Journal of South Am
journal homepage: www.All rights reserved.an continent:
Diversity
tectnica, Rua do Lago 562, Cidade Universitria, 05508-080 So
Paulo-SP, Brazil
nd terranes that constiture of the South-American continent
basement
le at ScienceDirect
rican Earth Sciences
evier .com/locate/ jsames
-
meriB.B. de Brito Neves / Journal of South Aevents responsible
for peaks of continental crust production withthe duration of some
hundred million years.
In some of these proposed time intervals (periods), one
maydistinguish taphrogenetic (distensional events) from
orogeneticevents (convergent plate interactions), sometimes in a
sequencesimilar to the complete or incomplete Wilson Cycles,
sometimes asactivities concurrent in time (same time interval) but
taking placein different regions.
Up to now, there has been a relatively complete representationof
all the above-mentioned stages in the Amazonian, the largestand
most complete Rodinias descendant (Fuck et al., 2008), SoFrancisco
and Rio de la Plata cratons. Some of these stages/periodsvery
represented, but some other still are demanding additionalresearchs
and discussion. In other Paleoproterozoic terranes andblocks of the
continent, either cratons or parts of the basement ofmobile belts,
this representation is assigned to one, two or three ofthese
events/super-events. In general, the four time intervalmentioned
assembled tectonic processes that played an importantand
well-orchestrated role in building the continent by (lateral
and
Fig. 1. The Rodiniass descendants in South America (modied from
Fuck et al., 2008). Thblocks. See other gure (Figs. 2, 3 and 4), as
complement.can Earth Sciences 32 (2011) 270e286 271vertical) growth
of its several continental tracts. These were lateroverprinted by
Mesoproterozoic and Neoproterozoic thermal-tectonic events. The
data available so far not sufcient to denewhich of these
periods/super-events was the most conspicuous interms of the
crustal growth. Up to now, apparently the Rhyacian(represented by
orogenic cycles in all cratons, terranes and base-ment blocks) and
the Statherian (territorial extension of the events,products and
sub-products) are good candidates.
It is worth mentioning occurrences of high-grade ortho
derivedrocks (and to a lesser extent, some volcanic sedimentary
rockassemblages) in the time interval 2.5e2.3 Ga (Siderian), which
isa new fact in the geology of South America to be distinguished.
Inmost of the cases, these data present the support of very good
litho-structural and isotopic data. This notable fact counteracts
modelsanddataof continental crustal growthasproposedbyCondie
(2000),which has already been reiterated by several researchers.
Forexample, according to Windley (1995), the Siderian was a kind
oflull in the continental crust growth process. Besides attesting
tothis fact, there is a large perspective of other Siderian events
to be
e main Paleoproterozoic domains are distinguished in different
cratons, terranes and
-
meriidentied and/or better characterized. Mostly the Siderian
rockassemblages are strongly reworked continental tracts, which
wereincluded as inliers in Rhyacian belts and even within
youngerProterozoic cycles.
In the geological literature concerning South-American
conti-nent, there has been a tendency to include all these
differentPaleoproterozoic super-events/events (ages and areas) in
the so-called Transamazonian Cycle as proposed by Hurley et al.
(1967)and Almeida et al. (1973), as a response to the rst
geochronologicaldata, obtained by low resolution characteristics
methods, such asKeAr and RbeSr. These studies were valid and
important at theirtime, but this broad and non-discriminating name
(Trans-amazonian event, cycle, orogeny) is totally out-of-date, in
variousways, with the advent of new geologic, tectonic and
geochrono-logical data. This generic name should be abandoned,
because evena redenition (which could cover part of the Rhyacian
events) couldbe hazardous for the progress of knowledge.
2. The Siderian period
The conrmation of rock-forming events during the Siderian
ofSouth America is a relatively new discovery/fact and has
beentreated with caution. These occurrences have been registered
indifferent structural provinces of the continent, thanks to
invest-ments in geologic cartography and precise and accurate
isotopicstudies (run by the Brazilian Geological Survey and
researchers ofdifferent universities).
Nonetheless, these occurrences have helped to overcome
somepreconceived ideas. Therstwas the excessive coverage given to
theso-called Transamazonian Cycle (throughout the whole
Paleo-proterozoic). The second was the false dillema
Transamazonian(designation misused throughout the whole
Paleoproterozoic)versus Brasiliano (designation misused for most of
the of post-Paleoproterozoic rock assemblages).
For descriptive purposes, the occurrences of Siderian
rockassemblage are divide into two main groups: i)
expressivegeographic-geologic occurrences (Bacajs, Granja, Luiz
Alves) andii) punctual/local presence within older (Archean,
Rhyacian)tectonic domains (see Figs. 1 and 2). These groups and
other indi-cations suggest that many Siderian occurrences will be
revealedwith the progress of the studies.
2.1. Amazonian Craton
2.1.1. Bacajs block and Central AmapAlthough extensional events
were to be expected after the
Archean fusion (as is the case of the So Francisco Craton
describedbelow), in the Amazonian Craton, the Siderian period was
markedby orogenic formation of high- and low-grade metamorphic
rocks.
The most notorious cases are the Bacajs domain, located in
thesouth easternmost part of the Rhyacian Maroni-Itacaiunas
Belt(Tassinari and Macambira, 2004), to the north of the Archean
Car-ajs-Rio Maria blocks, south of the Amazonas River. In this
domain,between reworked Arcehan rock units extensively crosscut
by(Rhyacian and Orosirian) granitic intrusions, Vasquez et al.
(2008)identied 2.36e2.34 Ga granite-greenstone-type terraness
cros-scut by 2.31 Ga granitoid intrusions. In reality, these
Siderian rockassemblages are true relicts present in the interior
of a youngergranitic domain (of 2.21e1.86 Ga of age), situated
along the Bacajsriver (Trs Palmeiras greenstone) and of
supracrustal rocks in theXingu-Iriri mesopotamia. Banded
porphyroclastic meta-tonalitesare recognized with boudins of mac
igneous rocks (trendingNEeSW) juxtaposed to the supracrustal rocks
yielding UePb agesof 2338 5 Ma, interpreted as representing igneous
zircon
B.B. de Brito Neves / Journal of South A272crystallization. The
supracrustal rocks are metamac, intermediatemetavolcanic
(andesites, dacites), volcaniclastic, and some BIFs, allshowing
geochemical afnities with island-arc settings. The
meta-volcaniclastic and intermediatemetavolcanic rocks yield UePb
agesof ca. 2.45 Ga and of 2.36e2.34 Ga respectively.
There is also unpublished information by CPRM (the
BrazilianGeological Survey) of other similar occurrences east of
the Bacajsdomain, which are true relicts inside a younger
(Rhyacian) mobilebelt (Rosa-Costa et al., 2006).
North of the Amazonas River, within the context of the
Maroni-Itacainas Belt and in its important Archean basement inlier,
incentral Central Amap, Rosa-Costa et al. (2006, 2008) obtaineda
large number of UePb and PbePb ages (specially by the evapo-ration
method) in the 2.4e2.3 Ga interval. These age values weredetected
at specic points within an Archean nuclei, but thepetrographic and
isotopic data indicate true Siderian crustal growth.
Even if all these cases demand additional geologic and
isotopicinvestigation, they are a valuable discovery for several
reasons. Asthe Maroni-Itacainas Belt as a whole characteristically
containsmany pre-Rhyacian remains, the discovery of new Siderian
crustalgrowth records are to be expected. Isolated citations exist
in theliterature of the occurrence of zircons of Siderian age in
the abovementioned areas and in many others (Almeida et al., 2007),
thusconstituting a theme that deserves attention and systematic
revi-sion for the future.
2.2. The So Francisco Craton (the Siderian Taphrogenesis)
2.2.1. Basement of the Itabuna-Salvador-Juazeiro (Bahia)
andMineiro Belts (Minas Gerais)
Several relatively isolated tectono-magmatic events took placein
the So Francisco Craton, resulting in the formation of mac(dike
swarms), mac-ultramac complexes and various graniticrocks of
immediately post-Neoarchean ages. Due to their impor-tance and
nature, these rocks were referred to as representative ofa Siderian
Taphrogenesis by Delgado et al. (2003).
Mac dike swarms are known in the southern (QuadrilteroFerrfero)
and in the northern (Serrinha bock) parts the craton. It isalso
worth mentioning the Contenda-Jacobina Fault Zone
(strikingapproximately NeS), which hosts the important Jacar River
mac-ultramac layered complex (ca. 2475 Ma age). Several
sub-alkalinegranitic and syenitic bodies are also recognized in
southern Bahia,considered to be an intraplate-type magmatic event
intrusive intoArchean TTG complexes. These are clearly post-Archean
rock units(ages between 2.56 and 2.4 Ga), some of which are
relatively verylarge (up to 200 km long).
In the northeast of the craton (Serrinha Block, Fig. 3),
Oliveiraet al. (2004) pointed out the intrusion of monzonitic and
mon-zodioritic rocks of alkaline nature and of Siderian age, and
they havea discussed the presence of tonalitic rocks of this age in
the ItapicuruRiver Greenstone. These authors have also suggested
the possibilitythat part of the greenstone volcanism (reaching
back-arc conditionsin the Rhyacian) might started earlier, in the
Siderian (Fig. 4).
Despite the need of more detailed studied, events and
rockssimilar to those found in Bahia have briey been reported
withinthe basement of the southern part of the craton in Minas
Gerais.
Togetherwith intraplatemagmatism,which can be considered tobe
isolated or taphrogeny-related process, it is necessary to stress
outthe evolution process of the Atlantic-type continental margin
thatpreceded the opening of an ocean and the development of the
so-called Mineiro Belt (predating the Rhyacian orogenies). The
litho-stratigraphic development of the Minas Supergroup
sedimentsconstitutes a notable sedimentary record of the
development of apassive continental margin (somehow comparable to
that of theCretaceous Atlantic-type margins of South America). This
taphroge-
can Earth Sciences 32 (2011) 270e286netic process (riftedrift
transition) still has a poor geochronological
-
meriB.B. de Brito Neves / Journal of South Acontrol, based on a
few PbePb data for carbonaceous sediments, aswell as some detrital
zircons from clastic sediments, which are well-understood in the
regional geologic context. These events took placebetween 2.25e2.40
Ga, preceding the orogenic evolution of theMineiro Belt, according
to vila et al. (2010).
Basedon these andother similardata for the So
FranciscoCraton(e.g. evolution of the Colomi Group, northern part
of the craton) and
Fig. 2. The main paleoproterozoic domains for the central and
northern part of south AmeriConceio; 4 e Luis Alves Craton.can
Earth Sciences 32 (2011) 270e286 273other cratonic nuclei, the
expectation is open for new records anddata related to this
taphrogenesis that resulted and succeeded therst expressive
agglutinations of continental masses by the end ofthe Neoarchean.
Particularly for this craton, the dominant idea isthat the
extensional events following the Neoarchean fusion wereimportant.
The discrimination of such events (overprinted by theRhyacian
orogenic events) should be urgently pursued.
ca, with emphasis for the Siderian domains: 1e Granja Massif; 2e
Bacajs; 3 e Almas-
-
meriB.B. de Brito Neves / Journal of South A2742.3. The Rio de
la Plata Craton
2.3.1. Taquaremb blockThe incontestable majority of
geochronological information for
thedifferent terranes that constitute theRiode la Plata
Cratonpointsto its consolidation in the Rhyacian, with localized
later remobili-zations during Orosirian (late deformation?) and
Statherian events(magmatism). The consolidation in the Rhyacian and
the extremelyuniform character of the chrono-tectonic history of
this craton isrmly based on the recent synthesis, by Rapela et al.
(2007).
On the other hand, there are (up to now) some isolated
obser-vations, such as those in Tickyj et al. (2004) and Hartmann
et al.
Fig. 3. Sketch tectonic map of the main Archean blocks
(paleoplates) and the mobile belts (So Francisco Craton and
surroundings (modied of Barbosa and Sabat, 2004).can Earth Sciences
32 (2011) 270e286(2008) referring to the presence of pre-Rhyacian
rocks, which areworth mentioning. In the northernmost of the
craton, in the so-called Taquaremb block, west of the
exposurewindow of the RioGrande do Sul basement, in the Santa Maria
Chico Complex gran-ulitic rocks (polycyclic, with partial
retrograde metamorphism tothe amphibolite facies) of granodioritic
composition, presentedUePb (SHRIMP) ages of 2.35 Ga, obtained from
zircon cores.
These rocks are admittedly relicts inside a
Paleoproterozoicdomain, as already recorded in the literature.
Additionally, someother zircon nuclei from granulitic rocks of
trondhjemitic natureyielded Archean ages (Hartmann et al., 2008 and
Tickyj et al., 2004),which indicates the possibility of
pre-Rhyacian protoliths, whose
Rhyacian and Orosirian) that were developed among them, in the
eastern domain of the
-
Rio N
meriFig. 4. The principal Statherian occurrences in South
America: Orogenic development (sedimentary, volcano-sedimentary,
volcanic and plutonic activities).
B.B. de Brito Neves / Journal of South Anature and extension are
open research themes for the future.Possible metamorphic reworking
of these rock in the Orisirian willbe discussed later in this
paper.
2.4. The Luiz Alves Craton/terrane
The Luiz Alves cratonic segment (Figs. 1, 2, and 5) is a
terranesituated in the southern coast of Brazil (from south of So
Paulo toSanta Catarina), between two Brasiliano belts: the Ribeira
belt (thePien magmatic arc) to the north and the Dom Feliciano
(Brusque-Tijucas belt) to the south. This terrane has behaved as
stablenucleous during the Brasiliano orogeny, and so it is an
importanttectonic element responsible for the segmentation of the
broadMantiqueira Province. In despite of the modest size of this
stablenucleous (10,000 km2), it is the most concise and complete
andwell-documented representation of the Siderian crustal
growthamong all the cratons of the continent (Basei et al., 1998,
2008).Actually, this terrane has worked out as a microplate during
theBrasiliano tectonic scheme of plate interactions.
The so-called Santa Catarina Granulite Complex is composedof; i)
various high-grade, hyperstene-bearing tonalitic-granodio-ritic
orthogneisses showing conspicuous gneissic foliation andcontaining
enclaves, fragments and boudins of mac-ultramacrocks and ii)
migmatitic gneisses. Components of metasedimentaryorigin are
minority. There is also an intrusive mac-ultramaccomplex (Barra
Velha) composed of gabbros, gabbro-norites andwebsterites, all
affected by high-grade metamorphism. To thenorth, TTG-type felsic
and leucocratic orthogneisses predominate,with several charnockite
intercalations.
The Brasiliano deformation is limited to the vicinity of
shearzones, being accompanied by granitic intrusions (to the
north)and several internal (e.g. Campo Alegre) and foreland (e.g.
Itajai)volcano-sedimentary basins.egro Juruena accretionary belt)
and the anorogenic processes and records (diversied
can Earth Sciences 32 (2011) 270e286 275Two high-grade
metamorphic episodes are clearly identied inthe basement complexes
based on excellent control by geochro-nological data: the rst and
more important at ca. 2.35 Ga (ageobtained from various rock types,
in most domains); the secondevent at ca. 2.15 Ga is (superposed to
the rst one) is represented bydeformed granitoids, some felsic
granulites and paragneisses. Mostprobably, these events are
separated by a signicant time intervalduring which erosion and
deposition of sedimentary rocks musttook place. Sm/Nd model ages
are of ca. 2.8e2.7 Ga.
2.5. Basement inliers of the (Brasiliano) Borborema province
2.5.1. The Granja massif (NW Cear/NE Piau)This massif is exposed
only in the north-western most part of
the Borborema Province and also constitutes part of the
basementParnaba Syneclise basement, which covers at least two
thirds ofthe original original size of the massif, leaving exposed
an area ofapproximately 6.000 km2. The basement of this relatively
stablenucleus (within the mobile belt) is constituted by high-grade
rocks,mainly TTG orthogneisses, amphibolitic gneisses and
garnet-amphibolites inter-layered with kinzigitic rocks, some mac
gran-ulites and locally migmatites, trending NEeSW and obeyinga
striking fabric of Brasiliano shear, which additionally
separatesthese nuclei from the Neoproterozoic supracrustal domains
(MdioCorea Belt). Thermo-barometric data indicate granulite
meta-morphism for these rocks around 750 C and pressures of 7e8
kbar(Santos et al., 2008). The rocks of this massif are intruded by
Bra-siliano granites and it is deeply affected by Neoproterozoic
shearzones.
Despite Neoproterozoic reworking events (granites, shearing),the
geochronological data (summarized by Santos et al., 2008) arevery
good, which discriminates this massif as one of the mostconcrete
and expressive record of the Siderian events in the
-
meriB.B. de Brito Neves / Journal of South A276continent. UePb,
with data for different rock types that showpredominant ages
between 2,30 and 2,36 Ma. TDM model ages aremostly between 2.38 and
2.48 Ga (only two values above 2.54 Ga),and with weakly positive
eNd, values between 0.4 and1.9,indicating the juvenile nature of
this Siderian magmatic (andmetamorphic) event.
Similarly to the Luiz Alves Craton, the Granja Massif
representsan interesting tectonic high within the Brasiliano
domains, the
Fig. 5. An outline for the main tectonic elements of the
southeast of South America (cent(Curitiba block or microplate) and
the Siderian (Luis Alves craton) blocks, that have workecan Earth
Sciences 32 (2011) 270e286latter one presenting very clear Siderian
signature. Additionally, itis necessary to stress that the Granja
Massif is a context verydifferent (composition, structure and age)
from that of So LuisCraton situated further in Maranho state
(composed of Rhyacianrock assemblages). Several authors correlated
both areas or sug-gested a continuation of Granja (Cear State) in
Maranho (SoLuis), which is not supported by the available
geological andgeochronological data.
ral and southern part of the Mantiqueira province). Special
remarks for the Rhyaciand out as foreland for the adjacent
Brasiliano belts.
-
meri2.5.2. Rio Piranhas Massif (Rio Grande do Norte Terrane)In
the eastern portion of the Rio Grande do Norte terrane (the
northern segment of the Borborema Province), in the Rio
Piranhasmassif, which is an extensive Rhyacian basement inlier
(naturallimit) for the Brasiliano Belt from Serid to the west).
Dantas et al.(2008) have recently pointed out the presence of some
supracrustalrocks (Santa Luzia sequence) that yielded Siderian ages
(mainlybetween the cities of Lages and Angico). These are
amphiboliticrocks (meta-andesites and metabasalts) and intercalated
withbanded iron formations and calc-silicatic units, exposed
withina domain of Rhyacian calc-alkaline orthogneisses (Caic
complex).
The supracrustal rocks and associated gneisses present
SiderianUePb ages (ca. 2.33 Ga), ca. 150 Ma older than those of the
classicRhyacian Caic Complex basement, which underlies these
Side-rian rock units.
2.6. The basement of the Tocantins Province
2.6.1. Almas-Conceio block (northeastern portion of the
GoisCentral Massif)
In the Tocantins Province, in the ample portion of the
basementwest of the northern segment of the Neoproterozoic Braslia
Belt, aninteresting occurrence of Siderian rocks was identied
withina Rhyacian orthogneissic domain (Fuck et al., 2001). These
rocks arepart of the western basement of the Braslia Belt
(Brasiliano) andprobably extend to the north-western portion of the
So FranciscoCraton.
In the domain between Almas and Conceio (parallels 11 S and13
S), and part of the basement of the Arai and Natividade
sedi-mentary groups, Statherian in ages, rocks of calc-alkaline
nature of2346 16 Ma, interpreted as the crystallization age.
Similarly,a granite-gneiss north of Conceio do Tocantins yielded
the age of2375 6Ma, which is equally interpreted as of the
formation age ofthe igneous protolith. SmeNd model ages falling in
the 2.6e2.5 Gainterval and positive eNd values (between zero and
1.0) arereported for these rocks.
Although preliminary, these results (because of the place
theyoccupying) (Fig. 2) trigger the discussion whether a
(tectonic,paleogeographic) relationship exists with those rocks and
the rockunits and values found in the Granja (north-western part of
Bor-borema Province) and those of in the Bacajs massifs (south
east-ernmost part of the Amazonian Craton). The distribution of
theGranja and Almas-Conceio occurrences (present position asresult
of the last Brasiliano events), in both sides of the
Trans-brasiliano Lineament deserves special attention.
2.7. The Mantiqueira Province basement
2.7.1. The Quirino Complex/unitIn the structurally complex
northern part of the Mantiqueira
Province (eastern Araua Central and Northern Ribeira),
localexposures (structural and erosional windows) of
Paleoproterozoicrocks are attributed to the Statherian and older
periods (Heilbronet al., 2004, synthesis work). In general,
high-grade rocks of theRhyacian cycles are more commonly found in
the whole basementof this northern part of this province.
The Quirino Complex occurs as an intensely reworked base-ment at
the central part of theNeoproterozoicmobile belt (along thebasement
of the Paraba do Sul klippe), that is placed along an axialzone of
structural divergence, composed of high-grade rocks, horn-blende
meta-tonalites andmetagranodiorites with enclaves of calc-silicate,
mac and ultramac rocks. Two groups of rock units wererecently
identied and described in this Quirino Complex (Vianaet al., 2008),
representing solid proof of the existence of two crus-
B.B. de Brito Neves / Journal of South Atal growthpulses. Therst
consists of high-potassiumrocks, yieldingUePb zircon ages of ca.
2308Ma, and the second ofmedium- to low-potassium rocks with
Rhyacian ages (2169e2137 Ma).
3. The Rhyacian period
The Rhyacian events and super-events (in the sense of
Condie,2000) of continental crust formation and growth represent
themost abundant records of the sialic basement in the
continent(cratons, Proterozoic belts and so on), in terms of number
andquality of geologic and isotopic data as well as of the
diversity ofstyles of occurrences. These events are concretely
recorded withinthe cratons and the reworked massifs of the
basement, as well aswithin the smaller exposures (several types) of
the basement of theMeso- and Neoproterozoic mobile belts. In all
cases with plenty andincreasing literature. Additionally, as
complementing this fact, theincidence of Rhyacian ages is quite
overwhelming in the detritalzircon studies of supracrustal rocks of
(Meso- and Neoproterozoic)mobile belts.
When stressing out that in the 250 Ma time interval (between2300
and 2050 Ma) crustal growth was conspicuous, it is worthmentioning
that:
i) The exact gographical-geological location of these
cratonicnuclei, massifs, terranes and blocks of Rhyacian age
areunknown, and theymight have been apart from each other
bythousands of kilometers
ii) Certainly several rock-forming cycles (Wilson-type or
not)must have taken place at the same time or in series,competing
mutually or not. Therefore, misleading simpli-cations (same cycle,
undue continuities) should be ruled out.
As expressed above, the data on Rhyacian events and super-events
are abundantly registered in the literature, a substantial partof
which is referenced in this text. For each area/case, it must
beimplicit here that there are very good published studies
(whichreading is advisable).
This incontestable wealth of data on the Rhyacian crustalgrowth
in different crustal and geotectonic types is a fact worth
ofvarious developments. Considering the abundande of Rhyaciandata
their pattern similar to those in other continents, all leads
thatthese crustal growth peaks are indicators of a global
phenomenon(e.g. Condie, 2000, among others). On the other hand, the
existenceof large continental masses (supercontinents) in the
Rhyacian issupported by many authors and studies (supercontinents
Atlantica,NENA, Hudsonia, Columbia, NUNA, Capricornia etc.), on the
basis ofdata relative to the Paleoproterozoic as a whole and to the
Rhyacianperiod in particular.
Regarding South America, the main records relative to
theRhyacian are illustrated in Figs.1 and 3 theywill be described
as vemain types of records.
a) Relatively complete and linear mobile belts involving
andpartially reworking preexisting, Archean nuclei. They
usuallypresent some clearly juvenile (accretionary) portionse
includingvolcano-sedimentary, granite-greenstone and similar
contexts,TTG associations etc. e and others that clearly represent
(bygeologic and isotopic means) the reworking of preexisting
Pale-oproterozoic and Archean terranes, which now gure asauthentic
basement inliers in these belts.
The best examples are in the Eastern Mobile Belt of Bahia or
theItabuna-Salvador-Juazeiro belt (Fig. 3), according to Delgado et
al.(2003), Barbosa and Sabat (2004); in the Mineiro Belt (vilaet
al., 2010); and in the Maroni-Itacainas Belt, in the eastern
can Earth Sciences 32 (2011) 270e286 277portion of the Amazonian
Craton (or the so-called Transamazonas
-
meriBelt of Santos, 2003), according to Rosa-Costa et al. (2006,
2008).One may also include in this context the western portion of
BahiaState (Western Mobile Belt of Bahia, part of the So
FranciscoCraton) and part of eastern Gois ( Dianpolis e Silvnia
Belt),which present several discontinuous Rhyacian basement
windows,underneath Proterozoic and Phanerozoic covers. An
additionalexample of these Rhyacian events and mobile belts is
recorded insome the large massifs, such as the Gois Central Massif
(clus-tering granite-greenstone terrains), Pernambuco-Alagoas, and
SoJos do Campestre, to be commented (See Delgado et al.,
2003;Dantas et al., 2008; Della Giustina et al., 2008).
As a result of these cycles of continental mass agglutination
inthe Rhyacian, important (epi-Rhyacian) cratonic nuclei wereformed
and acted as forelands to Orosirian and subsequent mobilebelts and
on which expressive sedimentary and volcano-sedi-mentary sequences
developed.
In general, the Rhyacian mobile belts include large Meso-
andNeo-Archean cratonic nuclei (and also some smaller nuclei
andblocks) and rework others, through complex paleogeographicand
tectonic histories, with succeeding accretionary and
collisionalprocesses, which sometimes exceed the formal limit for
the Oro-sirian (2.05 Ga).
In the cases of the So Luis and Rio de La Plata cratons
(andprobably in the case of Paranapanema craton) as well as of
theCuritiba terrane (microplate), the data of the basement are
alsoindicating Rhyacian ages, but they do not present Archean
nuclei,and they are dealt as separated cases below.
b) Segments of previous Rhyacian mobile belts which are not
cir-cumscribing Archean nuclei. Regarding their tectonic
rolesduring the evolution of the Brasiliano structural
provinces,these segments use to present two kinds of behavior: i)
Stable(cratonic) segments (e.g. So Luis, Rio de la Plata); ii)
reworkedsegments (descratonised or regenerated) due the overprintof
new thermal and tectonic conditions (so-called massifs).So, these
latter have worked out as basement inliers (differenttypes) into
the Brasiliano frame (e.g. Rio Piranhas, Gois Central,Curitiba
etc.). Sometimes, in some erosional windows of theMeso and
Neoproterozoic mobile belts, these massifs (struc-tural highs,
hinterlands etc.) use to play an important role.
As already mentioned, the incontestable majority of UePb datafor
the Rio de la Plata Craton granitic-migmatitic and
granite-greenstone basement point to crustal growth events in the
Rhya-cian (see Rapela et al., 2007), with the majority of the ages
fallingbetween 2,2 and 2,05 Ga. There are only a few relic tracts
thatpresent indication of local old Archean and Siderian rock
units.
The So Lus Craton, is a small fraction of the Western
AfricanCraton that remained in South America after the Pangea ssion
andis exposed complying with Cretaceous tectonic injunctions.
Kleinand Moura (2008) identied three distinct events of rock
forma-tion, all showing characteristics of juvenile origin. The
older event,ca. 2240 Ma, is characterized by the formation of
supracrustal rocks(sedimentary and volcano-sedimentary). This was
followed byevent of 2168e2147 Ma, marked by the deposition of
supracrustalrocks and the emplacedment of granitoids of
calc-alkaline char-acter (quartz-diorites, tonalites and
granodiorites of island arcs).The nal event, ca. 2090e2086 Ma is
represented by two mica-bearing, peraluminous (S-type) granitoids,
interpreted as repre-sentatives of a collisional events.
The Curitiba terrane/massif (microplate during the
Brasilianoorogenic processes) in central-eastern Paran (exposure
area ca.8000 km2) is a segment of a Rhyacian mobile belt separating
twoBrasiliano contexts (the Apia Belt to the north and the Pien
B.B. de Brito Neves / Journal of South A278Magmatic Arc to the
south), according to Siga et al. (1995). Thissmall high-grade
massif presents complex and special historicand isotopic
characteristics, being essentially composed by bandedgneisses,
migmatites (tonalitic leucosome), amphibolites andcharno-enderbites
etc. This is known as the Atuba Complex,exposed in a marked NE
structural trend of the Brasiliano ductileshearing. According to
geologic and isotopic data (Siga et al., 1995;Sato et al., 2003)
protoliths of these rocks are Archean in age (TDMagesw 3.1e2.7 Ga)
and underwent important metamorphism andmigmatization processes
around 2100 Ma (2086e2130 Ma). It isinteresting to add that
differently from So Luis Craton, almost alleNd data for this
segment (of a Rhyacian mobile belt) presentnegative to strongly
negative values. Besides, this segment wasreworked in various ways
in the late Paleoproterozoic (StatherianTaphrogenesis, granitic
plutonism), in the Mesoproterozoic (Caly-minian volcanism) and
mainly in the Neoproterozoic (during theBrasiliano events).
c) Segments, various mobile belts fractions as those above
des-cribed, occur as regenerated basement highs (massifs,inliers)
to several ofMeso- andNeoproterozoicmobile belts. Sotheyare
responsible for thebranchingof these belts aswell as
forcontributing to their structural and geometric complexity.
Thesebasement exposures in Borborema Province (Central Cear,
RioPiranhas, So Jos do Campestre, Pernambuco-Alagoas
etc),Mantiqueira Province (Quirino, Guanhes etc.) and
TocantinsProvince (Gois Central massif) as well as
Paleoproterozoicbelts further to the east (Cavalcante-Almas area)
present ingeneral characteristics which are similar to those
described inthe previous items. However, their integrity and
continuity wasbroken by younger geological events during the Meso-
andNeoproterozoic cycles, especially due to the Brasiliano cycle.
Inpractically all Meso- and Neoproterozoic mobile belts there
arereal records (local windows) and other indications of
Paleo-proterozoic tracts, mainly Rhyacian in age.
d) Sedimentary and volcano-sedimentary sequences belonging
togranite-greenstone terranes, occupyingmore or less sparse
andrestrict domains. There are several references in the
literatureof Rhyacian sedimentation (outside the classic domains
ofcrustal growth during this period). The best documentedexample is
that of the cover sequences of the Archean green-stone belts from
Gois, described by Jost et al. (2008), whichleads to several other
possibilities of new discoveries in thefuture.
In Central Brazil there is an Archean block of ca. 25,000
km2,forming a major part of the so-called Gois Central Massif ,
whichhave acted as backland for the Braslia Belt in the
Brasilianodevelopment. In this block, several greenstone belts are
welldocumented. The upper portions of these sequences are
formedmetasedimentary piles, including carbonaceous phyllites,
gray-wackes and dolomites (in Crixs), iron formations of
differentfacies, phyllites, volcanic ashes and graywackes (in
Guarinos), calc-silicate rocks, metacherts (in Pilar de Gois) etc.
UePb dataobtained from the detrital zircons of Crixs graywackes
indicateArchean (3.35 Ga, 2.8 Ga) and Rhyacian (2222 Ma, 2229 Ma)
ages.Guarinos banded iron formations yielded Archean (2.6 Ga),
Side-rian (ca. 2453 Ma) and also Rhyacian (2232 Ma) ages
(detritalzircons). A SmeNd isochron indicates the age of T 2189 36
Ma,and negative eNd (6.89) for the Pilar de Gois calc-silicate
rocksand metacherts. Based on these data and on other
stratigraphicevidences, the authors (Jost et al. 2008) concluded
that the threeupper sequences of the sedimentary unit/group of the
greenstonesare coeval, probably lateral facies variations, and they
must havebeen constrained to the same Rhyacian
tectonic-sedimentary
can Earth Sciences 32 (2011) 270e286processes.
-
the domain of the Serrinha and Uau blocks (Fig. 3), the ages
forthese supracrustal rocks (felsic andmac metavolcanic rocks) fall
in
(north of Manaus) a magmatic arc suite followed by
collisionalgranitoids of ages between 1975 and 1968 Ma. Further
south,
merithe 2.2e2.15 Ga time interval, according to Oliveira et al.
(2004).This is a similar situation as that of Gois, above
described. ThisRhyacian age records can be further identied in
other similarcrustal types in this craton and in others, even in
cases where theinfrastructure yielded Archean ages.
e) Within the GoisCentralMassif, to thewestof
theNiquelndiacomplex, a small exposure of the Serra
daMesaGroupbasement(between Uruau and Mara Rosa) occurs. There is
the record ofmeta-volcano-sedimentary sequence, crosscut by
granites,which is worth mentioning. The Campinorte Sequence
(ex-posed due to the erosion of the Serra da Mesa) is composed
ofmetapsammites and metapelites (being quartz-micaschists themost
common rocks), with gondite andmetachert lenses (DellaGiustina et
al., 2008) and subordinate meta-rhyolites andpyroclastic rocks.
Ortho derived metamorphic rocks (tonalitesand granodiorites) are
intrusive into this sequence, and theyyieldUePb ages of
2.18e2.16Ga. SmeNddeterminations lead topositive or slightly
negative eNd values, indicating the juvenilenature of these rocks,
thatwere strongly reworked by Brasilianoevents. Most probably,
similar rocks/contexts of larger surcialexpression can occur in
this massif, west of the large bodiesmac-ultramac bodies underlying
Statherian and youngermetasediments.
f) The recognition of Paleoproterozoic (mostly Rhyacian)
gneissicand migmatitic rock types within the basement (erosional
orstructural windows) of all Brasiliano structural provinces
haswidely been described in the literature. Most of these
indica-tion were based on RbeSr and KeAr methods. This
hascontributed to the spreading of the generic term Trans-amazonian
basement. This mean Transamazonian as syno-nimous of
Paleoproterozoic (geological time), what deserves tobe rened. For
the basement of the major Paleozoic syneclises(Parnaba, Amazonas
and Paran), such generalization has alsobeen common, from scarce
data (RbeSr and KeAr) obtainedfrom deep well cores. In all cases,
proper revision of suchinformation is necessary by means of methods
of more robustgeochronological methods. These indications should
not bepromptly ruled out, but they have to be subject of
isotopicstudies for the future.
g) Detrital zircons of Rhyacian age are very common in
Meso-proterozoic and Neoproterozoic rocks of the mobile belts. It
isnecessary to stress out beforehand that in the study of
detritalzircons of these mobile belts variable quantities of grains
ofOrosirian and Statherian (and even of younger periods) agesare
found, showing that the expositions/source areas for thesebelts
were very much varied.
4. Orosirian period
In the Orosirian, the forms of crustal evolution of the
South-American platform were very diversied, with important,
accret-ionary and collisional orogenic events, with their own
characteristicmarks, distinct from the preceding and succeeding
periods. Besidesthat, there is also a diversied range of records of
anorogenic tectonicIn the So Francisco Craton, eastern Bahia, there
is a series ofgreenstone belts with supracrustal rocks related to
oceanic envi-ronments, so including many back-arc basins (Delgado
et al., 2003).The geochronological control of all these occurrences
is stillpreliminary. At least for the Rio Itapicuru and Rio Capim
green-stones northern segment of the Itabuna-Salvador-Cura Belt,
in
B.B. de Brito Neves / Journal of South Aprocesses, plutonism
above all.Valrio et al. (2009) identied magmatic arc associations
(I-typegranites) and volcanic and granitic associations of
collisional naturewith ages between 1.9 Ga and 1.88 Ga. In turn,
Fraga et al. (2009)described to the northeast (Brazil-Guianas
border) a suite of sub-alkaline charnockitic rocks, monzogranitic
to leucogranodioriticcomposition, named Serra da Prata suite, with
ages between 1943and 1933 Ma, to which the authors attributed a
post-collisionalnature. All these data show the importance of the
Orosirian mag-matism in the Amazonian region, despite their
integration is stilllacking.
This important accretionary belt (in which collisional
eventsAdditionally to the events and super-events
discriminatedbelow, there are many reconnaissance geochronological
determi-nations throughout the basement of the Brasiliano provinces
thatyielded ages between 2.0 and 1.8 Ga and that were
almostcompulsively alluded to the Transamazonian Cycle. These
deter-minations possibly have their own geologic meaning, such as
tec-tono-magmatic reworking, metamorphism, uplift and cooling(which
is the case of many KeAr values of ca. 1.8 Ga) etc., whichshould be
properly checked in the future and then, correctly inte-grated to
the Orosirian context.
4.1. Accretionary orogenies/terranes
4.1.1. The Ventuari-Tapajs (or Tapajs-Parima) BeltAs an
accretionary province, the Ventuari-Tapajs (Tassinari and
Macambira, 2004; Cordani and Teixeira, 2007) or
Tapajs-Parima(Santos, 2003) is particularly outstanding in the
Amazonian craton.It is localized the central-western part of the
Craton, presentingNNW-SSW structural trends, about 3000 km long
(from Venezuelato the basement of the Alto Xing basin, in Mato
Grosso, Brazil) andup to 450 kmwide. This orogenic belt was
accreted to the west sideof the so-called Central Amazonian Craton
(composed of Archaennuclei and Rhyacian belts). The present degree
of knowledge of thisaccretionary belt is still pretty low due to
various regional condi-tions (lack of detailed geological maps,
rain forest, indian territoriesetc.). There is a strong demand for
the completion of the studiesbecause of different mineral resources
there present (e. g. Goldoccurrences).
In this province, a notable succession of magmatic arcs
isrecognized by the authors cited above (Jacareacanga, Cur,
Cre-porizo, Tropas, Parauari etc., in chronological order)
developedbetween 2.03 and 1.87 Ga. Some secondary sedimentation
events(arc-related basins) and other minor collisional events have
beenidentied locally. Isotopic data indicate a juvenile nature of
theoriginal rocks, with eNd values ranging from positives (up to
2.1)and weakly negatives (1.6). This seems to be consensual
amongresearchers. The presence of supracrustal rocks of
sedimentaryorigin (from the greenschist to the amphibolite facies)
is subordi-nate in the Province.
There are some minor divergences regarding the limits
andevolution mode of this accretionary belt (the same is valid for
theprovinces that delimit it). This is fully understandable and
expec-ted, having in mind the Amazonian region is still poorly
known. Aparticular focus of divergences is the delimitation of this
provincefrom the younger accretionary Statherian Rio
Negro-Juruenaprovince, to the west and from the Rhyacian
Maroni-Itacainasprovince, to the east (see Fig. 2).
Regarding the transition zone between the areas mapped
asMaroni-Itacainas and Ventuari Tapajs, there is a series of
newcontributions to be considered. Almeida et al. (2007)
identied
can Earth Sciences 32 (2011) 270e286 279have been identied, so
far) has no similar in the South-American
-
assigned from the Paleoproterozoic to the beginning of the
Paleo-
mericontinentet, and it is characterized for being for many
years animportant source of primary and secondary (alluvial)
gold.
4.1.2. The Cabo Frio TerraneThe easternmost part of the Ribeira
Belt (northern Mantiqueira
Province, northern sector) was recognized as a
tectono-strati-graphic terrane (in the sense of Howell, 1995) by
Heilbron et al.(2004), due to its litho-structural characteristics
and geologicevolution. This Orosirian terrane (Schmitt et al.,
2008) of unknownprovenance (Africa?) played the role of a backland
that dockedalong the easternmost part of the Ribeira orogen, at the
end of theCambrian (ca. 520 Ma).
The so-called Regio dos Lagos Complex encompasses tonaliticto
granitic orthogneisses with dioritic enclaves and
amphiboliticlenses (representing old dismembered mac dikes). The
UePb ageof the order of 1.9 Ga (admitted as of accretionary
origin), what isan unusual fact in this continent (out of the
Amazonian Craton)and unknown in the African counterpart. Some rare,
high-grademetasedimentary aluminous bands (Bzios-Palmital
metasedi-mentary association) with calc-silicate intercalations are
associ-ated with the development of the Brasiliano orogeny (during
itslatest phases in this continent).
The on shore sized of the Cabo Frio Terrane is modest,
estimatedto be a little less than 3000 km2, but its presence,
characteristicsand age are extremely important. In fact, it must
have acted as anexotic terrane, such as a microplate or a fraction
of an Orosirian arc(coming from African?) docked/incorporated to
the MantiqueiraProvince, at the end of the Ribeira Belt development
(east of theBzios back-arc), in the northernmost portion of the
Province (inthe Rio de Janeiro State).
4.2. Orogens and other collisional events
4.2.1. The Jacobina-Areio (Jacobina e Contendas) BeltThe
Contendas (Areio)-Jacobina Fold System in the central part
of the So Francisco Craton (Fig. 3) stretches out from north
tosouth for ca. 500 km, being less than 30 km in width and
altitudesabove 1000 m last century. The literature is
extensive.
The sedimentation environment of the Jacobina Group wasa
relatively stable platform (foreland basin?; post-Rhyacian
trans-tractional rift?), due to the maturity of most of its
metasediments.These rocks were folded andmetamorphosed between 2.0
and 1.96Ga, according regional inferences, since there are no
direct deter-minations. Characteristically, this narrow and linear
belt delineatedthe eastern border of the Archean Gavio-Lenois
cratonic nucleus,and the collision of this nucleus with other
segments (Archeanmicrocontinents and Rhyacian belt) to the east.
South of this belt,this hilly structure overlies the
volcano-sedimentary deposits of theContendas Mirante Complex, and
is affected by this latest defor-mation phase registered there,
most probably the collisional eventthat marked the end of the
Itabuna-Salvador-Juazeiro Belt accre-tionary history.
In general, the litho-stratigraphic context of the Jacobina
Ridgeconsists composed of siliciclastic rocks (monomictic
conglomer-ates, quartzites, schists) intercalated with metabasic
rocks, meta-tuffs and iron- and manganese-rich jaspilites. The
Campo Formosomac-ultramac complex and several internal ultramac
bodiesrepresent Orosirian mantle manifestations (Delgado et al.,
2003).Folding is intense, close to isoclinal folds present, with
rupture ofanks, and clear vergence toward the Archean block in the
west.The geochronological data point to Rhyacian sources (the
youngestdetrital zircons yield ages ca. 2.08 Ga) and the nal
deformationphase, based on data obtained from intrusive granites,
occurredbetween 1.94 and 1.91Ga (RbeSr data). The constraint of
this
B.B. de Brito Neves / Journal of South A280collisional belt to
the Orosirian is practically consensual, probablyzoic. This block,
derived from Laurentia, has a controversial tectonichistory, but
Grenvillian ages (end of the Mesoroterozoic) undoubt-edly
predominate.
There is a region in the Arequipa Massif where
high-grademetamorphic rocks are exposed (Mollendo, San Juan, Beln).
Oro-sirian ages from 1910 Ma to 1811 Ma, obtained by
reconnaissancemethods (Tosdal, 1996), were attributed to these
rocks and theirsignicance with respect to the general context of
the massif is stilldebatable. There are some preliminary
indications that other coevalprotoliths were rejuvenated during the
Grenvillian, under high-grade metamorphic conditions.
Anyway, the record of Orosirian events (probably of
collisionalnature) in the Arequipa Massif must be considered and
furtherinvestigated.
4.2.3. The Orosirian reworking4.2.3.1. The Taquaremb block
(basement of the Dom FelicianoBelt). There is a considerable amount
of geochronological data, notyet properly synthesized, on tectonic
processes already occurring inthe Orosirian, which are interpreted
as the nal processes of theRhyacian belts. The formal time limit
(2.05 Ga) between the end ofthe Rhyacian and the beginning of the
Orosirian is not always welldened well constrained in the Amazonian
and So Franciscocratons.
In the Rio de la Plata Craton a similar example is found in
theTaquaremb block (alreadymentioned above, when referring to
theSiderian), which is a marginal exposure of the craton, lateral
tothe Brasiliano domain, at the westernmost of Rio Grande do
SulState. The basement of the Rio de La Plata craton and adjacent
areashas already been described in detail as part of the history of
theRhyacian crustal evolution (Rapela et al., 2007, among others).
Inthe Santa Maria Chico Granulitic Complex e garnet-rich
granuliticrocks (pyroxenites and lherzolites) e isolated
metamorphicevents of 2.35 Ga (considered as the rst regional
metamorphicevent) have already been identied and described as
Siderianremnants within a real Rhyacian domain.
Recently, Tickyj et al. (2004), dating monazites of this
complexusing UePb methods, identied important Orosirian reworking
inthese high-grade rocks. From a total of half a hundred
determina-tions, 30% of the data (obtained at garnet rims) are
indicating agesbetween 1844 and 2014 Ma. The context of these
isotopic deter-minations (SHRIMP UePb) is substantial and valuable
and must beconsidered and properly discriminated, although the real
signi-cance in regional tectonic terms is still an open
problem.
4.3. Orosirian anorogenic volcanism and plutonism
One of the most striking characteristics of the Orosirian
periodin the continent was the intraplatemagmatism that
affectedmainlyall the central and eastern portions of the Amazonian
regionbetween 2000Ma and 1860Ma. These processes are also
importantas a mark of the stable regime that succeeded the Rhyacian
orog-enies and as an eastward intracratonic equivlent of coeval
accre-tionary processes (Ventuari-Tapajs, to the west). But, this
belt wascomposing a group of collisional events occurring to the
east,following the long accretionary history of the
Itabuna-Salvador-Cura belt. It is worth adding that the
geochronological knowledgeis still indirect and other types of
investigation are required.
4.2.2. The Arequipa MassifThe Arequipa Massif is a basement
inlier of the Andean
cordillera stretchingout fromthe Peruvian coast tonorthernChile.
Itunderwent a notorious plycyclic evolution, with isotopic ages
can Earth Sciences 32 (2011) 270e286also affected by part of
this magmatism.
-
part explosive (ignimbrites and common breccias), which
privi-
merileged the areas consolidated in the Rhyacian (small
extension overthe recently-consolidated Ventuari-Tapajs). The
original extensionexceeded 700,000 km2, which makes it comparable
to several LIPsof the world, always intercalated with the
anorogenic plutonismand more locally and restrictedly with some
sedimentary contexts.The ages come from various sources and methods
and spreadbetween 1900 Ma and 1870 Ma (maximum values up to 2000
Ma).Good recent reviews and syntheses are in Santos (2003)
andTassinari and Macambira (2004).
The associated anorogenic plutonism is notable, closely
relatedin time and space to the volcanism, privileging the Archean
blocksfrom Carajs (Serra dos Carajs, Cigano, Seringa, Estrela,
Para-upebas, Pojuca granites) and Rio Maria (Jamon, Musa,
Redeno,Bannach, Gradas granites etc., felsic dikes). Generally
these areA-type granitoids, with ample compositional variation.
Syenitesand monzogranites the dominant rock types (see DallAgnol et
al.(2006) for an updated synthesis). The ages for these
graniticrocks are very close to one other, ranging in the interval
between1.9e1.8 Ga (1.88 Ga is considered the most frequent
value).
The conjunction of these magmatic events between 2.0 and 1.86Ga,
their vast extension, the context of the succeeding ample
cra-tonization (epi-Rhyacian) justied the proposal of a LIP in
thisregion. These magmatic events preceded (in time and in terms
ofcratonic tectonics) the establishment of the Roraima
ortho-platformal basin (to be discussed).
Out of the Amazonian region, a few anorogenic magmatismevents of
this period are pointed out in the So Francisco Craton. Inthe
Paramirim block, a fraction of the Archean-Paleoproterozoicbasement
between the Espinhao and ChapadaDiamantina, there isan important
occurrence of syenitic magmatism hosting the mostexpressive
uraniferousmineralization of Brazil. The syenites (rich inalbite
and titanite) of Lagoa Real present (crystallization) ages of
ca.1904 44 Ma (Chaves et al., 2007, zircon ages by
LA-ICPMS),following an intense metamorphic recrystallization
around1860 69Ma (with uraninite precipitation). This is not a
completelysolved problem and other obstacles exist due to later
tectonicreworking (Espinhao?, Brasiliano?); nonetheless, the
Orosirianages must be taken into account.
In northwest of Bahia, south-southeastern margin of the Par-naba
Basin, the Angico Dias carbonatitic complex yielded an age of2.01
Ga (UePb in zircon and baddeleyite), and therefore must
beconsidered as the rst occurrence of this type of rock in all
thePaleoproterozoic of South America. Pyroxenites, alkaline
dunites,syenites, carbonatites and lamprophyres are found in the
complex,which is inserted in a context of alkaline basaltic
magmatism in anintraplate environment (Delgado et al., 2003).
Several other occurrences of mac and ultramac bodies inBahia,
showing discordant relationship with the structures of thedomains
of Rhyacian mobile belts and they have been pointed outas
candidates of Orosirian intraplate magmatism, lacking geologicand
geochronological support.
4.4. The Roraima plateau e Roraima Supergroup
The Roraima Supergroup (Reis et al., 1990) covers a large
regionof northern Brazil and neighboring countries (more
than160,000 km2) and is characterized by plateaus supported by
sub-This large plutonic and volcanic province has generally
beenreferred to as Uatum (group, complex, magmatism) and includesa
diversied suite of multiple designations
Iriri-Iricoum-Surumu-Cuchivero-Iwokrama in northern Brazil and
neighboring countries.Special emphasis is given to the intermediate
and acid volcanism, in
B.B. de Brito Neves / Journal of South Ahorizontal (weakly and
locally deformed) siliciclastic units. Itoverlies and characterizes
the large orthoplatformal domain con-structed after the end of the
Uatum volcanism-plutonism.
The supergroup is composed essentially of various
siliciclasticrocks (conglomerates, sandstones, arkosean sandstones,
shales)intercalated with tuffs and volcanic ashes (Santos et al.,
2003a, b).There are several peculiar characteristics in the Roraima
plateau: itselevated altitudes, its notable geographic scenarios of
a thick sedi-mentary plateau submitted to dissecation, the limit of
countries(Venezuela, Brazil, Guianas), the locus of the rst, oldest
(pre-1873Ma), great stable area in the evolution of the Amazonian
Craton(Amazonian-Laurentian block), and the source of detrital
diamonds.The original Roraima extension can be estimated as a much
biggerarea, such is the amount of its remnants widespread around
it.
This unit overlies the (LIP) Uatum and it has been recentlydated
by means of UePb analyses of zircons from tuffaceousintercalations,
which indicated an age of 1873 3 Ma (Santos et al.,2003a, b). This
determination is very well constrained by the age ofthe underlying
basement and also by the ages obtained for macdikes (Statherian
Avanavero or Pedras Pretas magmatism, ca. 1782Ma) that crosscut the
supergroup. It is worth adding that in the SoFrancisco Craton (and
adjacent zones) similar stability conditionswould only took place
ca. 100 million years later (ca. 1.76e1.78 Ga),with the development
of vast and thick siliciclastic covers (ChapadaDiamantina and
similar areas, to be discussed).
5. The Statherian period
In the crustal evolution of the South-American continent,
theStatherian period is represented by two distinct and very
wellcharacterized sets of tectonic events and super-events,
withexceptional geologic and geochronological records. Exclusively
inthe central-western portion of the Amazonian region,
accretionaryprocesses were dominant, along the so-called Rio
Negro-Juruenabelt. This belt was placed following a chelogenic
scheme of crustalgrowth (typical for the Amazonian craton), from
NNE to SSW, so itwas adjusted to the western side of the
Ventuari-Tapajs (Orosirianin age). On the other hand, in the rest
of the continent (even in theAmazonian Craton), taprhrogenic
processes were by far predomi-nant, either sparsely or concentrated
in area, constituting excep-tional basin-forming processes
associated to magmatism, fromVenezuela to Uruguay.
For the Rio Negro-Juruena accretionary system there are
rela-tively recent evolutionary syntheses by Santos et al.
(2003a,b),Tassinari and Macambira (2004), Cordani and Teixeira
(2007) thatgather much geologic and geochronological information.
For thetaphrogenic processes, marked by several ssural
intrusives,granitic and explosive volcanism, and extensional
events, there isa previous synthesis by Brito Neves et al. (1995),
presentlydemanding robust updating, in view of the substantial
scienticadvances in last years.
These sets of Statherian crustal growth events must be
viewedunder an optics that transcends the South-American continent.
Inthe case of the accretionary belt, the Rio Negro-Juruena is only
partof a much wider orogenic development (Rio Negro
Juruena-Transcontinental-Labrador-Gothian-Kongsbergian)
encompassing,to the north, the Laurentian and Baltic blocks, where
it is beststudied and known (Brito Neves, 2004).
In the case of the taphrogenesis, it occurs in a similar way
andpractically in all Paleoproterozoic blocks (which were
certainlyseparated from each other) of this and other continents
(speciallyNorth America and Africa). It is certainly represents a
globalphenomenon.
In both cases (accretionary and taphrogenic processes) there
areproblems with the heterogeneity of the data. In particularly,
the
can Earth Sciences 32 (2011) 270e286 281recognition of
accretionary processes in South America is far from
-
formation of basins during taphrogenesis, the coverage of
the
meriTeixeira, 2007). From the reconnaissance methods used
initially(RbeSr and KeAr), gradually passing to methods such as
UePband SmeNd and some systematic mapping, the predominance
ofStatherian orogenic activity has been conrmed. According
toseveral researchers, the data fully attest the presence of a
juvenile(or little affected by crustal contamination) accretionary
crustalprovince for the Rio Negro Juruena Belt. The eNd(t) values
arepredominantly positive (up to 4), side-by-side with
slightlynegative values (down to 2.0).
5.2. Intraplate basic magmatism
As said above, the Statherian taphrogenic events affected all
thePaleoproterozoic blocks of the South-American continent,
practi-cally with no exceptions, and a vast literature is
available. Amongtheme is vast, and an extensive (though
heterogeneously detailed)literature exists (e.g. see Brito Neves et
al., 1995; Delgado et al.,2003; Danderfer et al., 2009). The number
and variety of casesare large and easily extrapolates any attempt
of synthesis, oncethere are signicant occurrences (and
corresponding literature) inthe Guyanas Shield (Brazil and
neighboring countries) to the north,down to fractions in the Rio de
la Plata Craton and the basement ofthe Dom Feliciano Belt (in
Uruguay) to the south.
5.1. Accretionary events e Rio Negro Juruena Belt
The Rio Negro Juruena accretionary processes succeeded in
timethe Orosirian Ventuari-Tapajs system, according to a long
evolu-tion cycle, between 1780 and 1550 Ma (entering the
Calymmianperiod) and sense of younging from NE to SE. The time
interval isvery long even for a multiple accretionary process. The
territorialdomain is also very large, as opposed to a
non-satisfactory generalgeologic and isotopic knowledge. There are
very few areas studiedin detail.
The orogenic belt roughly trends NW-SE in the
central-westernportion of the Amazonian region, from Venezuela (Mit
Complex)and Colombia (Casiquiare Domain) to the upper Juruena
river, northof Mato Grosso (basement of the Parecis Basin), with a
possibility ofan extension southwards into the Rio Apa massif,
totaling morethan2600km. Thewidthusually proposed for theProvince
is around400 km, but there are records of rocks of the same nature
to thewestin the basement of the Rondonian Province, in Bolivia,
within theso-called Paragua Craton (Bittencourt et al., 2010).
The Province is constituted by (granodioritic, tonalitic
andgranitic) gneisses and migmatitic rocks, with a few
metamacintercalations, forming a general scenario of calc-alkaline
rockassemblagesof magmatic arc afnity, but as already said, ata
reconnaissance level. The supracrustal units are more
restrictedthroughout the Province, being recognized
volcano-sedimentarycontexts (greenstone belt-type associations),
some of them ofintermediate and felsic nature (rhyolites,
rhyodacites, tuffs). Somesubvolcanic granites (1.65e1.55 Ga) are
known, which record lateintraplate activities.
As mentioned before, the identication of this accretionarydomain
(in Brazil) was mainly based on radar images andgeochronological
data, resulting in several publications, inte-grated in the
syntheses mentioned above (e.g. Cordani andideal, since it is
located in a rain forest domain where detailedgeological maps are
not available. The continuity of this beltnorthwards into Laurentia
and Baltica is also an open questiondemanding further
investigation.
When it comes to diversied intraplate magmatism and
B.B. de Brito Neves / Journal of South A282these intraplate
extensional phenomena the basic magmatismdeserves attention, and it
is here discussed separately only fordescriptive reasons:
a) In the Amazonian Craton, crosscutting the Roraima
Supergroupand its basement (Brazil and neighboring countries), the
so-called Avanavero or Pedras Pretas magmatism; this conistsof a
series of thick sills, dikes and small plugs of gabbroid/basaltic
composition. This magmatism is one of the mostimportant
andexpressive events inSouth-America, and it canbeobserved in
the1/5,000,000 geologicmap. Large sills, up to1 kmthick, basic
igneous rocks of composition varying from tholeiiticto
andesi-basalts were identied (Menezes Leal et al., 2006).
Recent determinations by the UePb method using zircon
andbaddeleyite (Santos et al., 2003a, b) indicated an age of 1782
3Mafor this magmatism, which also constitutes a mark of
age(maximum) for the Roraima Group.
From Serra do Carajs (north and south) to Rio Maria
(throughXiguara) some volcanic records of this age interval are
also known,consisting ofa basalt-and esite-rhyolite association
studied by e.g.Rivalente et al. (1998). The basalts occur as NE-
and NW-trendingdikes and are classied in two groups, of high- and
low-TiO2. Thebasaltic rocks are concentrated to the north of the
Serra dos Car-ajs. The geochronological data, resulting from the
RbeSr method,varies from 1720 Ma (rhyolites) to 1874 Ma (basalts),
with rela-tively low initial Sr87/Sr86 ratios, but relatively high
errors (of theorder of 8%).
b) In the south-southeastern domain of the So Francisco Cratonat
least three distinctgroups of mac dikes, according to
theircomposition, nature and age (Statherian, Tonian and
UpperCretaceous). There is a N-S-trending dike generation of
somecentimeters to decimeters in width associated with sills
andsmall basic stocks, partially deformed (superimposed Brasi-liano
deformation along the margins of the craton) andpartially
undeformed, marking the presence of the Statheriantaphrogenesis in
that region. The deformed rocks were trans-formed in
quartz-chlorite schists and chloritoid-sericite schists.The
undeformed part show gabbroic features and composition.
KeAr data indicate ages from the Statherian to the Calymmian.The
baddeleyte UePb dating of the Ibirit gabbro yielded the age of1714
5 Ma (with lower discordia intercept pointing to Brasilianovalues).
The predominant trend of these rocks, ages, position in thecontext
of the craton (of the So Francisco paleocontinent) areindications
of a post-Orosirian extensional event to which theevolution of the
Northern Espinhao rift system (basin).
c) The innermost portion of the Rio de la Plata Craton in
Uruguay(Pedra Alta Terrane) is marked by an important dike
swarm(called Florida) trending approximately EeW, which can
berecognized at various scales and has been the object ofnumerous
petrologic and isotopic works (e. g. Teixeira et al.,1999). To the
east, this swarm is suddenly truncated by theSarandi Del Yi fault
system (part of the Brasiliano events).
From the compositional point of view basic rocks of the
ande-sitic-tholeiitic and basaltic-andesitic types are recognized.
Theoriginal magmas display some degree of contamination with
theolder continental crust. The dikes are up to 50 m thick
(generally
-
meri5.3. Felsic magmatism
The following description and order follow expository
reasonsmainly, because it is recognized that there are several
concreteindications of causal relationships between the igneous
events andthe basin tectonism.
5.3.1. The Amazonian regionIn the northern part of the Amazonian
region (Guyanas Shield)
there are sparse records of Statherian granitic plutonism and
felsicvolcanism.
It is worth stressing out that there are plutonic and
volcano-sedimentary activities in the southern portion of the
Craton, in thenorthern portion of Mato Grosso, between the
Roosevelt and TelesPires rivers, covering an area of ca. 40,000
km2. This seems to bea kind of cratogenic tract, as an exotic
terrane in the interior of theRio Negro-Juruena Province (with
which the relationship has notyet been properly established).
Various felsic volcanic (from daciteto rhyolite) and volcaniclastic
rocks (ignimbrites, tuffs, ashes), andsubordinated basalts are
associated with anorogenic (A-type)granites (Leite et al., 2001).
The general characteristics of thismagmatism and of the associated
volcano-sedimentary rocksindicate intracratonic or intraplate
extensional environment.
5.3.2. Central BrazilIn the central-eastern part of the
continent, between meridians
40Wand 48Wand parallels 11S and 20S several occurrences
ofStatherian felsic activities are found. These occurrences
precededthe installation of the Brasiliano Cycle (differentiation
of cratons,terrains, massifs and mobile belts), acting as a part of
the substrateof this development, and because of that they exhibit
thereforedifferent grades of reworking. Only, in some local cases,
the rockunits are undeformed and they preserved igneous texture
andstructures.
Toward west, in Gois and the south of Tocantins, the Gois
TinProvince stands out, where several granitic rocks (some 15
smallbodies), and volcanic and sedimentary associations, including
sili-ciclastic and volcanic rocks (Arai and Natividade groups)
wereidentied two groups of ages: ca. 1.77 Ga (called Rio Paran
sub-province) and from 1.58 up to 1.77 Ga (Rio Tocantins
subprovince).From the litho-stratigraphic, tectonic and
metallogenetic points ofview (Dardenne and Schobbenhaus, 2001), all
these occurrencesare together indicative of intraplate activity and
display remarkableliterature.
In the eastern portion (and with attested subsupercial
con-nection), from Bahia (north) to Minas Gerais (south), a
complexsystem of Statherian sedimentary to volcano-sedimentary
basins(rifts and syneclises) developed and was later deformed in
the pre-Brasiliano and in theBrasiliano, constituting the so-called
EspinhaoFold System. It is attested by a vast and increasing
bibliography (seeDelgado et al., 2003 and Danderfer et al., 2009).
In Minas Gerais,betweenSerroand Itabira, adozenof small
tomedium-sizedgraniticbodies (Borrachudos Suite) described by
Dussin and Dussin (1995),are intruded in the
Archan-Paleoproterozoic basement (Guanhesblock) under an anorogenic
regime. Similar granites have beendescribed in the Paramirim
corridor, in central-western Bahia, alonga fraction of the
Paleoproterozoic basement, between two majorbeltsof the
volcano-sedimentary (Espinhao-Chapada Diamantina)groups.
5.3.3. Northeastern Brazil (Borborema Province)The basement of
the Borborema northern segment in Cear
(from the Mdio Corea to the Jaguaribeana belt) and in Rio
Grandedo Norte (So Jos Belt, northwest of the Rio Piranhas
Massif),
B.B. de Brito Neves / Journal of South Aseveral occurrences of
anorogenic (acid to intermediate) volcanicrocks and associated
granitic plutonism have been recognized. Allof them clearly cut the
older dominantly Rhyacian basement, aswell as they are reworked by
contractional and shearing events ofthe Brasiliano Cycle. This
reworking can be local, but can transformgranitic rocks in
augen-gneisses and volcano-sedimentary bandsinto true schist
belts.
The exact areal extension of this volcanism-plutonism
associa-tions is not yet known, because part of the
volcano-sedimentary(Ors Group etc.) sequences and the granitic
contexts (severalaugen-gneisses, Serra do Deserto Suite, suite G2
etc.) have beenstrongly involved together with the older basement
rocks by theBrasiliano deformations. The complete discrimination
still remainsto be done and evaluated.
In the Rio Grande do Norte Terrane, some granitic bodies
oftabular shape and alkaline nature (intrusive in the
Rhyaciangneissic-migmatitic substrate) have been identied and they
yiel-ded UePb ages ca. 1740 Ma. Other coeval granites are present
andeven some older ones, as intrusive (augen-gneisses) in this
base-ment (Caic Complex, Rhyacian in age) were subsequentlydeformed
and tansformed into gneisses by the Brasiliano events.These
granitoids are very common and usually referred to as G2-type (G1
would be the granites of the Rhyacian basementthemselves).
In several parts of the Paleoproterozoic (Rhyacian) basement
ofthe Transversal Zone (between Patos and Pernambuco EeW
line-aments) gabbro-anorthositic bodies, always deformed by the
Bra-siliano, have been identied Only in some of the many
cases,Statherian ages have been conrmed (Delgado et al., 2003;
Santoset al., 2010), and in many others are waiting age
determinations.
5.3.4. MantiqueiraIn the northern part of the Mantiqueira
Province, within the
domain of the Araua Belt basement, the presence of
supracrustalrocks (Espinhao) and associated anorogenic granites
(Borrachu-dos) has been debated. To the east, in the northern
portion of theRibeira Belt basement in Minas Gerais and Rio de
Janeiro, there aremany convergent ideas, which were reviewed by
Heilbron et al.(2004). In Minas Gerais, there are successions of
Statherian (andeven Mesoproterozoic) supracrustal rocks, as the So
Joo Del ReiGroup, which were reworked in the Brasiliano. In Rio de
Janeirothere are several references to granitic rocks
(orthogneisses) ofalkaline nature and Statherian ages, so that the
age value of 1.7 Gahas usually been used as the upper age limit for
the basement rocksof the belt.
To the south, in Paran, along the southern border of the
ApiaBelt and adjacent to the Lancinha Lineament (north-northeast
ofCuritiba) some intensely deformed (mylonitic and
ultra-mylonitic)granitoid bodies of alkaline afnity occur within
younger volcano-sedimentary supracrustal rocks. In the Betara
(close to thesouthern part of the fault) and Tigre (to the north)
nuclei, alongthe same structural trend, Statherian intraplate
granitoids(respectively 1748 and 1772 Ma old, Cury et al., 2002)
weredescribed, demonstrating the presence of the Statherian
taphro-genesis in the basement of the belt. Part of this Statherian
graniticrocks were transformed into mylonites by the Brasiliano
processesof extrusion.
Additionally inUruguay, in the central-westernportionof
theNicoPerezTerraneea regenerated fractionof theRiode laPlata
Cratoneimmediately east of the Sarandir Del Yi fault, there is an
interestingoccurrence of a small subvolcanic granitic body (
-
B.B. de Brito Neves / Journal of South American Earth Sciences
32 (2011) 270e286284
-
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