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Precambrian Research
journal homepage: www.elsevier.com/locate/precamres
Paleoarchean to Paleoproterozoic crustal evolution in the Guanambi-
Correntina block (GCB), north São Francisco Craton, Brazil, unraveled by U-
Pb Geochronology, Nd-Sr isotopes and geochemical constraints
N. Barbosaa,⁎, A.B. Menezes Leala, D. Debruyneb, L.R. Bastos Leala, N.S. Barbosaa, M. Marinhoa,
L. Mercêsa, J.S. Barbosaa, L.M. Koproskia
aGeoscience Institute, Federal University of Bahia, Salvador, BA, Brazil
bGeological Engineering, Center for Engineering, Federal University of Pelotas, Pelotas, RS, Brazil
A R T I C L E I N F O
Keywords:
São Francisco Craton
Guanambi-Correntina block
Archean-Paleoproterozoic rocks
U-Pb ages
Nd-Sr constraints
Geochemistry
A B S T R A C T
The north-central part of the São Francisco Craton (SFC) is one of the oldest terranes in the South American
platform and experienced three regional magmatic events at 3.4–3.3, 3.1–2.7, and 2.1 Ga. Our new SHRIMP U-
Pb data place the origin of Guanambi-Correntina block (GCB) in the Paleoarchean, contemporaneous with the
Gavião block in central north SFC. Lithological, geochemical, and isotopic evidence indicate that the 3.4–3.3 Ga
rocks of the Favelândia complex are derived from partial melting of E-MORB sources during flat subduction. The
3.1–2.7 Ga K-granitoids in the Santa Izabel complex are derived from a mixture of crustal and mafic sources, as
evidenced by the slightly negative to positive ƐNd(T) and Sr/Sri between 0.700 and 0.706. The 3.1–2.7 Ga event is
responsible for the recycling of the Paleoarchean TTG crust, generation of low- to high-K evolved crust, and
juxtaposition of the Favelândia and Santa Izabel complexes. The youngest magmatic event at ca. 2.1 Ga pro-
duced felsic plutons, derived from anatexis of Archean felsic rocks and mantle components. The collisional
process tectonically juxtaposed the Riacho de Santana greenstone belt and Archean felsic rocks at 2.1–2.0 Ga,
determining the region’s current configuration. Based on the data reported in this study and previously pub-
lished data, we suggest that the Guanambi-Correntina block was formed as an independent unit in the northern
SFC.
1. Introduction
The Eo- and Paleoarchean (4.0–3.2 Ga) eras mark the complex
history of the primitive continental crust and are the predominant
periods wherein TTG (tonalite, trondhjemite, and granite) and green-
stone belts have formed. Nevertheless, much of their geologic record
remains uncertain due to difficulties in finding preserved outcrops from
these eras (Armstrong and Harmon, 1981; Condie and Kröner (2013);
Dhuime et al., 2012; Condie, 2007; Hawkesworth et al., 2010, 2013;
Sanchez-Garrido et al., 2011; Smithies et al., 2007; Taylor and
McLennan, 1985, 1995). The evolution and tectonic setting of Eo- and
Paleoarchean felsic rocks remains controversial, and the excellently
preserved outcrops in the north-central portion of the São Francisco
Craton provide unique opportunities for understanding the formation of
primitive continental crust.
The spatial distribution of geochronological and isotopic data in
conjunction with field relationships suggests that crustal reworking
played an important role during the evolution of the São Francisco
Craton (e.g., Barbosa and Sabaté, 2004; Barbosa et al., 2012; Heilbron
et al., 2017). The north São Francisco Craton (SFC) preserves important
segments of 3.4–3.3 Ga rocks, such as the Gavião and Guanambi-Cor-
rentina blocks (Barbosa and Dominguez, 1996) (e.g., 3.4 Ga – Sete
Voltas massif; Martin, 1994). The Favelândia complex (Silveira and
Garrido, 2000) is located in the Guanambi-Correntina block (GCB) and
forms the focus of our study, as it contains the oldest known rocks in
this area (3.3 Ga; Rosa, 1999). The GCB contains fragments of Pa-
leoarchean to Paleoproterozoic rocks (U-Pb zircon: 3.3–2.1 Ga; Barbosa
et al., 2013; Medeiros et al., 2017; Rosa, 1999) that highlight the
continuous generation of the continental crust while preserving at least
one metamorphic stage from 2.0 to 1.9 Ga (Barbosa et al., 2012; Rosa
et al., 2000). The crustal growth of the SFC predominantly occurred in
the Neoarchean and Paleoproterozoic eras (e.g., Barbosa et al., 2012;
Heilbron et al., 2017), contemporaneous with the established world-
wide peak of crustal growth (Armstrong, 1991; Condie, 1998; O’Nions
https://doi.org/10.1016/j.precamres.2020.105614
Received 26 August 2018; Received in revised form 29 December 2019; Accepted 6 January 2020
⁎ Corresponding author.
E-mail address: ndsbarbosa@ufba.br (N. Barbosa).
Precambrian Research 340 (2020) 105614
Available online 13 January 2020
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and McKenzie, 1988; Taylor and McLennan, 1985).
This global peak with abundant accretionary orogenies is attributed
to periods of crustal thickening and supercontinents cycles. High
magma volumes are defined by crystallization ages in the geological
record linked to the orogenic setting (~2.9 and ~2.1 Ga). Examples of
~2.9 Ga and ~2.1 Ga rocks are found in several cratons, such as the São
Francisco, Amazonian, Yilgarn, Rio de la Plata, Pilbara, North China,
and Congo cratons, among others (Hawkesworth et al., 2019;
Kranendonk et al., 2019).
Much like other contemporary continents, the Early Archean rocks
in the South American platform are mainly remnants of TTGs sur-
rounded by orogenic calc-alkaline rocks and metasedimentary se-
quences. The presence of such primitive crust in the Favelândia com-
plex in the SFC provides an opportunity to improve our understanding
of the petrogenetic processes that generated their parental magmas,
which is essential to unravel Archean crustal dynamics. There is cur-
rently an extensive debate about the nature of the GCB, where two
different tectonic models have been proposed. The first model considers
the GCB as an originally independent tectonic unit related to the Gavião
block, based on geochronological and isotopic constraints
(Mascarenhas and Garcia, 1989; Brito Neves et al., 1980; Rosa et al.,
2000). The second model posits that the Guanambi-Correntina block
could be part of the Gavião block, as indicated by metamorphic and
structural records, classifying it as Gavião Oeste (Barbosa and Sabaté,
2004; Barbosa et al., 2012).
Unraveling the tectonic history and dynamics of Archean cratons
generally requires a multidisciplinary approach. Therefore, we report
new U-Pb SHRIMP zircon ages, in conjunction with isotopic (Nd-Sr) and
geochemical data for the Favelândia complex and the adjoining felsic
rocks. To test the conflicting models proposed for this crustal segment,
we will compare these rocks with their contemporary counterparts in
northern SFC and evaluate the chemical and isotopic data in an in-
tegrated way. Finally, we will also reassess published data of the Santa
Izabel complex and the Guanambi batholith to define the importance of
crustal contribution during generation of those rocks.
2. Geological setting
The north-central portion of the SFC, the GCB, is composed of
Paleoarchean to Neoarchean rocks that are intruded by the
Paleoproterozoic Guanambi batholith and coeval rocks (Arcanjo et al
2005; Barbosa et al., 2013; Brito Neves et al., 1980; Cordani et al.,
1985; Fernandes et al., 1982; Jardim de Sá et al., 1976; Mascarenhas,
1979; Mascarenhas and Garcia, 1989; Mascarenhas et al., 1985; Rosa
et al., 2000; Silveira and Garrido, 2000; Távora et al., 1967). According
to Rosa et al. (2000), the GCB was accreted to the Gavião block along
the N–S trending Igaporã lineament in the Paleoproterozoic. The GCB is
subdivided into four tectonic units basedon lithotypes, age, meta-
morphic conditions, and genesis (e.g., Silveira and Garrido, 2000): (i)
the Favelândia complex; (ii) the Santa Izabel complex; (iii) the Riacho
de Santana greenstone belt; and (iv) the Guanambi batholith (Fig. 1).
Geochronological data revealed distinct Archean complexes in the
study area, namely, the Favelândia and the Santa Izabel complexes
(Mascarenhas, 1979). Both underwent a complex metamorphic evolu-
tion highlighted by granulite facies rocks (Barbosa et al., 2013;
Medeiros et al., 2017; Mascarenhas, 1979; Rosa et al., 2000). Below, we
present the geological-geochronological aspects of the Archean units
that constitute the Guanambi-Correntina block, as well as the younger
rocks represented by the Guanambi batholith and an associated mafi-
c–ultramafic sequence known as the Riacho de Santana greenstone belt
(Silveira and Garrido, 2000) (Fig. 1).
2.1. The Favelândia complex
The Favelândia complex (Arcanjo et al., 2000), the focus of this
study, comprises tonalitic to granodioritic gneisses, migmatites and
granulites outcropping between younger rocks of the Santa Izabel
complex (Silveira and Garrido, 2000; Fig. 1). In the outcrops, gray or-
thogneisses with plagioclase, quartz,±microcline and biotite are
dominant. Common secondary and accessory minerals are zircon,
apatite, titanite, epidote, sericite, and opaque minerals. Their textures
are granoblastic and lepidoblastic (Rosa, 1999), and these rocks have
experienced amphibolite to granulite facies metamorphism (Portela
et al., 1976; Rosa, 1999). They show a strong deformation that is
commonly cataclastic, mylonitic or homogeneous, and xenoliths are
folded together with the host rocks. Enclaves of mafic rocks and felsic
veins occur interfolded or crosscutting the gneisses, respectively, in
addition to pods of mafic rocks.
The Favelândia complex was affected by variable migmatization
and K-feldspatization processes during the Paleoproterozoic
(Mascarenhas and Garcia, 1989; Moutinho da Costa and Silva, 1980).
The U-Pb zircon age of one orthogneiss is 3.3 Ga and the Rb-Sr age is
3.2 Ga, indicating that these rocks are Paleoarchean (Rosa et al., 2000;
Barbosa et al., 2013). These same orthogneisses have ƐNd(t) values of
−3.5 and 87Sr/86Sr(i) values of 0.701 (Barbosa et al., 2013).
2.2. The Santa Izabel complex
The Santa Izabel complex constitutes the southeastern portion of the
Guanambi-Correntina block (Fig. 1), and contains major exposures of
lithologically diverse Archean rocks. This complex is a N-S trending
structure with a width of 36 km and a length of approximately 180 km
(Fernandes et al., 1982; Portela et al., 1976). The rocks display a
transitional contact between orthogneisses, granulites, and migmatites
(Medeiros, 2013). The composition of orthoderived lithotypes ranges
from tonalites, granodiorites, and granites to monzodiorites, while the
kinzigites are paraderived. Minor lithotypes include norites, diorites,
amphibolites, calc-silicates, and pyroxenites (e.g., Arcanjo et al., 2005).
The main minerals in the granitoids are plagioclase, quartz, biotite ±
K-feldspar and hornblende; epidote, zoisite and calcite occur as sec-
ondary minerals, and the accessories include zircon, titanite, magnetite,
and apatite. Textures are granoblastic, nematoblastic, porfiroclastic and
lepidoblastic. The rocks experienced saussuritization and sericitization,
and contain amphibolite enclaves (Arcanjo et al., 2000; Medeiros,
2013). Multiple amphibolite and granulite facies metamorphic events
were recognized, generating gneissic, migmatitic, granulitic, and my-
lonitic structures (Arcanjo et al., 2005; Portela et al., 1976). The geo-
chemical characteristics of the orthoderived rocks are as follows: me-
taluminous to peraluminous, high Al contents, TTG compositions, low
to high-K calc-alkaline granitoids, enriched in LREE and depleted in
HREE (Arcanjo et al., 2000). Before the 2.2 Ga U-Pb age obtained by
Rodrigues et al. (2012; see below), this complex was interpreted as a
product of the same subduction event that generated the Riacho de
Santana greenstone belt (Varela and Teixeira, 1999). The Santa Izabel
complex hosts 3.1–2.9 to 2.7 Ga felsic rocks (Barbosa et al., 2013;
Medeiros, 2013) and reveals migmatization and granulitization at
2.1–2.0 Ga (Arcanjo et al., 2005; Medeiros et al., 2017; Silveira and
Garrido, 2000). The isotopic data reveal crustal reworking in these
rocks, as the ƐNd(t) and 87Sr/86Sr(i) range from −4.7 to +0.3 (Barbosa
et al., 2013; Rosa, 1999) and from 0.704 to 0.707, respectively (Brito
Neves et al., 1980; Fernandes et al., 1982; Jardim de Sá et al., 1976;
Mascarenhas and Garcia, 1989). The complex is considered to be re-
presentative of the Paleoproterozoic reworking that generated the
coeval orogenic belt (Mascarenhas, 1979).
2.3. The Riacho de Santana greenstone belt
The Riacho de Santana greenstone belt is a narrow N–S-oriented
structure between Archean and Paleoproterozoic felsic rocks. It was
amalgamated with the Favelândia and Santa Izabel complexes to the
east during the Paleoproterozoic (Rosa et al., 2000). The rocks are
largely covered by Quaternary and Tertiary deposits (Fig. 1). According
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
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Fig. 1. Geologic framework of the Guanambi-Correntina block in the northern São Francisco Craton – SFC (adapted from Rosa, 1999). Inset shows the SFC and the
study area, dark gray: basement rocks; light gray and white: cover rocks. Bold (uppercase) names refer to the plutons and supracrustal sequences.
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
3
to Silveira and Garrido (2000), the sequences comprise three major
associations: (i) a Lower Unit, consisting of komatiitic rocks with thin
intercalations of metabasalts and metagabbros, associated with BIFs,
quartzites, metacherts, calc-silicate rocks, aluminous shales, meta-
carbonates, and metagraywackes; (ii) an Intermediate Unit, consisting
of metabasalts and metagabbros, intermediate to felsic metatuffs, alu-
minous schists, graphite schist, actinolite schist and metacherts; and
(iii) an Upper Unit, consisting of a sequence of quartzites and meta-
carbonates with minor metabasalts, metatuffs, and chlorite/sericite
schists. The greenschist metamorphic grade is characteristic of the belt
(Menezes Leal et al., 2008; Silveira and Garrido, 2000). Geochemically,
the metabasalts are classified as high-iron-tholeiites; they have flat
HREE patterns, low LREE/HREE contents, and high Ba/Zr, Ba/Nb, Ti/Y,
Nb/Y, Nb/Th, and Zr/Y ratios. These data indicate an enriched mantle
source (Menezes Leal et al., 2008), which is corroborated by Nd isotopic
data showing ƐNd(T) values of +2.8 and +2.1 (Barbosa et al., 2013).
2.4. Guanambi batholith
This igneous domain extends geographically along the central-south
part of the Guanambi-Correntina block (Fig. 1), where it covers an
extensive area of approximately 6000 km2 (Rosa et al., 2000). This
Paleoproterozoic igneous province was generated by multiple intru-
sions with a mean U-Pb age of 2050 ± 4 Ma (Rosa et al., 2000). The
batholith intrudes into the Favelândia and Santa Izabel complexes and
in the Riacho de Santana greenstone belt. The main aspects of the
Guanambi batholith were reported by Rosa (1999) and will be sum-
marized here. The dominant lithologies are syenites and monzonites,
with minor monzodiorites. The batholith was divided into multiple
phases, including late leucocratic and porphyritic intrusions. The var-
ious phases show a similar mineralogy dominated by plagioclase, K-
feldspar, quartz, amphibole, and biotite, with zircon, apatite, monazite,
and opaque minerals as the main accessories. Mafic and felsic xenoliths
occur next to the contact with the host rocks. The silica content in these
rocks ranges from 50.70 to 77.20 wt%, they are metaluminous, ultra-
potassic (K2O/Na2O > 1), and show enrichment in Ba, Sr, and Rb,
along with a prominent LREE fractionation. Their 87Sr/86Sr(i) compo-
sition ranges from 0.703 to 0.707while their ƐNd(2.0Ga) ranges from
−10.6 to −7.4 (Rosa et al., 2000). Based on these data, the Guanambi
batholith has been interpreted as derived from a process involving
fractional crystallization of a lamprophyric magma derived from a Pa-
leoproterozoic enriched mantle source (Rosa, 1999).
3. Results
3.1. Sampling and petrographical aspects
Representative samples from the Archean Favelândia and Santa
Izabel complexes and from the Paleoproterozoic Guanambi batholith
were selected for geochronological, geochemical, and isotopic studies.
We collected samples from the Favelândia and Santa Izabel complexes
ca. 0–40 km northwards of the city Riacho de Santana (Fig. 1). The
outcrops are characterized by gneisses that show variable stages of
deformation, including mylonitization (Fig. 2) and experienced at least
amphibolite facies conditions. The tectonic structures are related to the
regional stress-field (160°/60° dip direction) resulting from successive
collisional processes. Field observations indicate that the Favelândia
complex contains mafic xenoliths (Fig. 2; Silveira and Garrido 2000).
Pegmatites and aplites intrude the orthogneisses and are themselves
crosscut by local shear zones and faults. The main rock types are
granodiorites and granites, all rocks are medium- to fine-grained and
leucocratic, and the outcrops present variable colors between pink and
gray. The classification of the samples was based on the QAPF diagram
using the calculated normative compositions (Supplementary material).
Samples for petrographical analysis were collected from different
regions in the study area; most of them show a gneissic structure while
one sample has a mylonitic structure. The studied rocks were separated
into groups based on the geochronological data (see below). The major
phases in Group 1, the Favelândia complex, are plagioclase, quartz,
biotite,± hornblende1, and microcline1, hornblende2, epidote, apatite,
allanite, zircon, and opaque minerals are accessory minerals. Common
secondary phases are muscovite as biotite alteration, epidote2 over
plagioclase, microcline2, zoizite. In general, the minerals show inter-
lobate or serrated grain boundaries. Biotite1 generally occurs as elon-
gate subhedral to anhedral crystals and forms tabular flakes that define
the foliation. Plagioclase occurs as euhedral prismatic to anhedral
grains and is sericitized and saussuritizated. Quartz is anhedral and
forms aggregates of ribbons or sigmoidal shapes, they form polygonal
grains and show undulatory extinction. The metasomatism is marked by
thin epidote veins and K-feldspatization. Chlorite is present in a few
places as a secondary mineral forming substitution rims on biotite. A
protomylonitic texture is characteristic, alongside inequigranular, sub-
idiomorphic, blastoporphyritic, nematoblastic, lepidoblastic, and lo-
cally granoblastic textures. Most rocks are classified as granodiorite
gneisses.
Similar petrographic features are observed in Group 2, the Santa
Izabel complex. The major phases are plagioclase, quartz, biotite1, and
microcline1 ± muscovite. Titanite, epidote, hornblende, zircon, apa-
tite and opaque minerals are accessory minerals. Common secondary
phases are sericite, epidote2, microcline2, apatite, zoizite,± calcite,
muscovite, and chlorite. The biotite1 generally occurs as elongate sub-
hedral to anhedral crystals and forms tabular flakes that define the
foliation. Plagioclase and K-feldspar occurs as euhedral prismatic to
anhedral grains and is sericitized and saussuritizated. Quartz is anhe-
dral and forms aggregates of ribbons or sigmoidal shapes, polygonal
grains, and undulatory extinction. Microcline shows straight and curved
contacts with quartz and plagioclase. Their textures are equi- to in-
equigranular, hypidiomorphic, nematoblastic, lepidoblastic, and these
rocks are fine- to coarse-grained, and in one case, porphyritic. The rock
compositions range from quartz monzonitic to syenogranitic.
3.2. Geochemistry
The whole-rock compositions of 7 samples (including 5 from
Arcanjo et al., 2005) from Favelândia and 6 from the Santa Izabel
complexes are listed in the Supplementary material. Geochronological
(see Section 3.3) and geochemical data reveal two groups of rocks with
distinct major and trace element compositions. Group 1 comprises
samples from the Paleoarchean Favelândia complex and has SiO2 con-
tents between 65.57 and 72.02 wt%, while silica contents in Group 2
(Mesoarchean Santa Izabel complex) range from 62.66 to 77.99 wt%. In
general, the samples are metaluminous to weakly peraluminous (A/
CNK = 1.0–1.08; Fig. 3A). Group 1 shows TTG affinities, indicated by a
total alkali content (Na2O + K2O) that ranges between 5.73 and 8.20,
K2O/Na2O values between 0.24 and 0.88 (Supplementary material),
low FeOt/(FeOt + MgO) values between 0.60 and 0.86 (Fig. 3B), and
Fe2O3 + MgO + MnO + TiO2 < 5. Group 2 shows a calc-alkaline
affinity (Fig. 3C), with Na2O + K2O of 7.77–12.01, K2O/Na2O values of
0.88–1.90 (Supplementary material), FeOt/(FeOt + MgO) values be-
tween 0.81 and 0.98, and Fe2O3 + MgO + MnO + TiO2 < 4.
The samples can be separated into two groups based on their major
element variation: Group 1 has the following major elemental abun-
dances: CaO = 1.50–3.73; TiO2 = 0.25–0.50; P2O5 = 0.02–0.27;
MgO = 0.39–1.65; Fe2O3 = 2.31–3.94; Al2O3 = 14.68–15.77 wt%.
Group 2 is characterized by: CaO = 0.69–1.57; TiO2 = 0.04–0.45;
P2O5 = 0.01–0.14; MgO = 0.01–0.65; Fe2O3 = 0.36–3.37 and
Al2O3 = 11.54–15.98 wt%.
The trace elements also show irregular distributions in Harker dia-
grams (not shown). Interestingly, the high Co, Ni, Cr, and Mg contents
in Group 1 indicate an ultramafic source or limited fractionation, while
Group 2 contains lower concentrations of these elements. The Nb/Th
ratios in both groups are also distinct, with Nb/Th values between 0.88
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
4
and 0.46 in Group 1 and between 0.42 and 0.24 in Group 2. The Sr
content of the studied rocks decreases from Group 1 to Group 2,
pointing to increasing plagioclase fractionation during magmatic dif-
ferentiation. Ba and Rb also increase from Group 1 to Group 2.
All samples are characterized by enrichments in large ion lithophile
elements (LILEs) and light rare earth elements (LREE) and depletions in
some high field strength elements – HFSEs (e.g., Nb, Ta, Ti; Fig. 4B) and
heavy rare earth elements – HREE (Fig. 4A and B). These data and the
negative Nb, Ta, and Ti anomalies suggest that subduction process-re-
lated changes affected both groups. In Group 1, the heavy rare earth
elements (HREE) contents are variable (Yb: 0.471–1.4 ppm; Lu:
0.06–0.19 ppm), the Sr/Y values range between 11.34 and 54.40, while
Fig. 2. Field aspects of some studied outcrops of the Guanambi-Correntina felsic rocks. (A) Santa Izabel complex: Pink gneiss. (B) Favelândia complex: Medium-
grained facies. (C) Santa Izabel complex: Enclaves isoclinally folded with the host rocks. (D and E) Meta quartz-Monzonite of the Santa Izabel complex and
Monzodiorite gneiss of the Guanambi batholith: The rocks are interspersed in a N-S-oriented shear zone. Codes indicate the studied samples. (F) Favelândia complex:
Granodiorite gneiss with equigranular texture. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)
Fig. 3. (A) A/NK vs. A/CNK (after Shand, 1943). (B) FeOt/(FeOt + MgO) vs. SiO2 (Frost et al., 2001); (C) Na2O + K2O + CaO vs. SiO2.
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
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the Lan/Ybn values of 17.68–40.43. Group 2 shows higher HREE con-
tents (Yb: 0.2–9.1), Sr/Y values ranging between 0.36 and 30.15, and
Lan/Ybn values of 24.82–119.00. The positive Eu anomaly (Eu/
Eu* = 2.85), in sample RS-07B, is most likely related to Eu-rich pla-
gioclase. Conversely, the negative anomaly (Eu/Eu* = 0.13) in sample
RS- 314 indicates Eu-depleted plagioclase or fractional crystallization of
plagioclase (Fig. 4A).
3.3.Zircon SHRIMP U-Pb age
3.3.1. Granodiorite gneiss (sample RS-310)
Zircon grains from this sample are translucent to opaque, brown to
dark brown, subrounded, and present short to long prismatic shapes
with sizes ranging from 130 to 276 µm. Their morphology is highly
variable, with elongation ratios that vary between 6.3 and 1.5. The
cathodoluminescent images (CL) revealed variable textures such as
oscillatory zoning that varies in intensity or sector zoning.
Recrystallization and resorption are also observed and are mirrored in
some rims, and metamict grains are also present. Zircon fractions
consisting of 9 grains were analyzed. The Th/U values range from 0.13
to 0.76 (Supplementary material), but two core analyses yielded low
ratios of 0.01 and 0.07 (RS-310–11.1 and −1.1, respectively) and were
not used in the age calculation. The discordant analyses defined a re-
gression line with an upper intercept at 3320 ± 19 Ma, and
MSWD = 5.8 (Fig. 5A).
3.3.2. Hornblende granodiorite gneiss (sample RS-307)
Zircon grains in this rock are prismatic, subhedral, translucent,
brown, and range in size between 161 and 308 µm. They are stubby to
elongate and their elongation values vary between 1.7 and 3.8, with an
average of 2.8. The crystals display oscillatory zoning or structureless
CL textures; homogeneous portions indicate recrystallization, while
subrounded terminations indicate resorption. Most grains show high U
contents in cores (dark-colored grains). Eight analyses in cores of ig-
neous zircon crystals have Th/U ratios ranging from 0.13 to 0.41. The
regression line through these data generates an upper intercept age at
3303 ± 14 Ma and MSWD = 4.7 (Fig. 5B). The analyses of the rims
(n = 5) are discordant, revealing a Paleoproterozoic age. However, one
analysis (RS-307–6.2) presents a 207Pb/206Pb age of 2676 ± 19 Ma
and a discordance of 7% (Supplementary Material).
3.3.3. Granite gneiss (sample RS-07A)
The zircon grains in this sample are subhedral, transparent and
translucent, and colorless, yellow to light brown. They have grain sizes
ranging from 155 to 364 µm, with an average elongation of 2. A few
grains have length/width ratios of 2.8, which corresponds to a long
prismatic habit. The CL images dominantly show oscillatory zoning
textures with sector zoning, fine-scaled, some are structureless in-
dicating recrystallization and resorption. The cores of 8 grains were
analyzed, and gave a discordant age of 2679 ± 17 Ma and
MSWD = 4.6 (Supplementary Material). However, three selected spots
(Th/U = 0.25–1.39) were highly concordant (± 1%), yielding an age
of 2683 ± 5 Ma and MSWD = 0.0034 (Fig. 5C).
3.3.4. Meta-quartz monzonite (sample RS-302A)
The zircon population in this sample is translucent to opaque,
brown to dark brown, and subrounded. Most are short prisms with sizes
between 140 and 325 µm and elongation ratios between 1.2 and 2.4. CL
images show highly metamict internal textures, with high-U contents.
Some grains are homogeneous, with sector zoning, fine-scaled- or
pronounced oscillatory zoning. Other grains may present resorption,
recrystallization, and metamictization. Twelve analyses were used to
calculate an upper intercept age. Their Th/U ratios ranged from 0.26 to
1.86, except in one zircon (3.44) (Supplementary Material), and they
yielded an age of 2669 ± 22 Ma (MSWD = 8.6). Three data points in
zircon cores revealed a concordant age at 2681 ± 5 Ma and
MSWD = 0.093 (Fig. 5D).
3.3.5. Granite gneiss (sample RS-301)
Zircon grains in this rock are euhedral to subhedral, translucent, and
brown-colored, with sizes ranging from 160 to 285 µm, and short
prismatic shapes with a length/width ratio of 1.5. The crystals generally
display homogeneous textures on CL images. The grains are structure-
less, with subrounded terminations indicating recrystallization and re-
sorption, and show large recrystallized rims. The grains contain high U-
contents defining a dark-luminescence. Thirteen analyses in the cores of
igneous zircon grains have Th/U ratios between 0.11 and 2.35
(Supplementary material). The regression line through these spots
yields an upper intercept age at 2675 ± 26 Ma and MSWD = 3.8
(Fig. 5E).
3.3.6. Monzodiorite gneiss (sample RS-302B)
Zircon grains from this sample are translucent, yellow and pale
brown, subrounded, elongated prisms with sizes ranging from 145 to
217 µm. Several igneous textures and post-magmatic characteristics can
be observed on CL images, such as resorption, recrystallization, and
oscillatory zoning, while other grains show homogeneous textures.
Zircon fractions consisting of 4 grains with Th/U ratios ranging from
Fig. 4. (A) Chondrite-normalized REE plot; (B) Primitive mantle-normalized spidergram for the studied rocks. Normalized values are from (A) Nakamura (1974); and
(B) McDonough and Sun (1995). Red and blue lines: data from Santos Pinto et al., 2012. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
6
0.11 to 1.83 (Supplementary material) were analyzed. The spot RS-
302B-5.1 presents a minor discordance, and the 207Pb/206Pb age is
2044 ± 11 Ma. The discordant analyses defined a regression line with
an upper intercept at 2054 ± 15 Ma and MSWD = 1.6 (Fig. 5F), si-
milar to the age of the Guanambi batholith.
3.4. Nd and Sr isotopes
The Archean samples from the Guanambi-Correntina block exhibit
bimodal Nd isotopic data, which are generally consistent with the new
Paleoarchean and Neoarchean zircon U-Pb ages. The older rocks have
fSm/Nd values between −0.37 and −0.44, while younger rocks have
fSm/Nd values between −0.48 and −0.61 (Table 1). The TDM ages are
approximately 3.6 Ga, with ƐNd(3.3 Ga) between −3.5 and −1.7
(Table 1), implying derivation from a more primitive protolith. The
ƐNd(T) values of the 2.7 Ga rocks (6 samples) range from +2.5 to −4.5
while their TDM ages range from 2.9 to 3.1 Ga.
The 3.3 Ga old samples yielded unrealistically low 87Sr/86Sr(3.3 Ga)
values of ca.< 0.700 (Table 1). On the other hand, previous studies
have shown that the younger samples show variable 87Sr/86Sr(2.7 Ga)
values ranging from 0.703 to 0.707 (Jardim de Sá et al., 1976; Rosa,
1999), indicating a contribution of crustal sources. In the 87Sr/86Sr vs.
ƐNd(T) diagram (Fig. 7A), the Group 1 samples plot close to BSE (Bulk
Silicate Earth), while the Group 2 samples show more radiogenic
compositions. The samples with higher 87Sr/86Sr and lower Ɛ Nd(T)
correspond to the younger rocks. Group 1 samples show slightly posi-
tive ƐNd(T)values, whereas Group 2 samples show more negative ƐNd(T)
values.
Fig. 5. Concordia diagrams (Wetherill, 1956) showing analytical data from granitoid gneisses of the Favelândia complex (samples RS-310, 307), Santa Izabel
complex (samples RS-07A, 302A, 301) and Guanambi batholith (sample RS-302B).
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
7
4. Discussion
4.1. Petrogenesis: Genetic interpretation of the granitoids bodies from GCB
and related rocks
The approaches used to estimate the source of the oldest GCB rocks
and related rocks (Sete Voltas, Aracatu, Bernarda, Boa Vista-Mata
Verde, Contendas-Mirante massifs – Gavião block) are based on whole-
rock geochemical and Sr-Nd isotopic constraints. The discussions of
Paleoarchean rocks are based on comparisons of data between rocks of
the GCB and Gavião block. Two stages of felsic magma emplacement
are identified during the Archean. The first magmatism of Paleoarchean
age is represented mainly by tonalite and granodiorite gneisses (e.g.,
Santos Pinto et al., 2012). Fig. 6 compares the composition of
3.4–3.3 Ga granitoids in the north central SFC, showing that these rocks
have similar compositions and can be classified as TTG. Geochemical
analyses from the Sete Voltas, Bernarda, Boa Vista-Mata Verde, and
Favelândia rocks (Group 1) display high Na2O and low K2O/Na2O
contents (Fig. 6). Such features, along with high La/YbN and Sr/Yva-
lues (Supplementary material), highlight the important role of garnet
during magma genesis. In chondrite-normalized REE plots, the Pa-
leoarchean samples do not show significant Eu and Sr anomalies (Fig. 4
A and B). Interestingly, some Favelândia samples show slightly negative
Eu anomalies, which reflects plagioclase segregation by fractional
crystallization. However, our data differs from an Icelandic source type,
which is characterized by negative Eu anomalies, unfractionated REE
patterns, and Fe enrichment (Reimink et al., 2014 and references
therein).
Harker diagrams (not shown) of the Paleoarchean rocks from
Guanambi-Correntina and Gavião blocks suggest that the TTG suites did
not evolve by fractional crystallization of single parental magma;
however, they show similar isotopic and trace element compositions,
indicating that they formed through similar magmatic processes.
However, post-crystallization processes can also remobilize major and
minor elements and modify the primary composition of the rocks.
Isotopic features indicate a slightly negative ƐNd(3.3Ga) (−4.47 to
−1.73) and low Sr/Sri values (0.700–0.701; Barbosa et al., 2013) for
the Favelândia complex. Some samples display anomalously low Sr/Sri
(< 0.6989) values that are accompanied by high Rb/Sr ratios, this in-
crease can be associated with K-feldspatization and sericitization pro-
cesses. The Sete Voltas massif (Gavião block) presents ƐNd(3.4Ga) of +3.7
to −5.6 and Sr/Sri values of 0.700 (Martin, 1994). Fig. 7 shows that the
Favelândia and Sete Voltas rocks have similar Sr-Nd isotopic signatures.
Thus, we can assume that the rocks in these two regions were derived
from magmatic sources with similar isotopic characteristics. Interest-
ingly, their respective geographic positions and field relationships in-
dicate that these rocks were formed in different tectonic compartments
and cannot be considered as a part of the same tectonomagmatic event.
The initial Sr-Nd isotopic composition of the Paleoarchean rocks
shows a large variation (Fig. 7A). The Bernada massif shows ƐNd(3.3Ga)
(+3.1) and Sr/Sri values (< 0.699) (Santos Pinto et al., 2012). In the
Boa Vista and Mata Verde massifs, the ƐNd(3.3Ga) and Sr/Sri values range
from +3.59 to −2.06 and 0.700 to 0.712, respectively (Marinho, 1991;
Marinho et al., 1994a,b). The Mariana massif displays ƐNd(3.3Ga) va-
lues ranging from +0.7 to −1.1 and Sr/Sri values between 0.719 and
0.710 (Santos Pinto, 1996). The Aracatu massif presents Sr/Sri values of
0.702 and ƐNd(3.2Ga) of −1.8 to −1.1 (Santos Pinto, 1996). Most Sr/Sri
values in these Paleoarchean rocks are higher than BSE at 3.4–3.3 Ga.
Fig. 6. (A) Normative An-Ab-Or triangle showing the trondhjemite, tonalite, granodiorite and granite fields (O’Connor, 1965); (B) K-N-Ca diagram showing the TTG
field and calk-alkaline trend (Martin, 1994). Dashed line and gray area are data from Marinho et al. (1994a,b) and Santos Pinto et al. (2012).
Table 1
Sm-Nd and Rb-Sr whole rock data for selected rocks of the Guanambi-Correntina block.
Sample 147Sm/144Nd 143Nd/144Nd ε(0) fSm/Nd TDM (Ga) T1 ε(T1) 87Sr/86Sr 87Rb/86Sr Sr/Sri
(Ma)
RS-301 0.0893 0.510533 −41.06 −0.55 3.1 2700 −4.06 0.737676 0.987956 0.699
RS-302A 0.0827 0.510450 −42.69 −0.58 3.0 2700 −3.44 0.792123 4.503560 0.616
RS-314 0.1031 0.510935 −33.23 −0.48 2.9 2700 −1.00 1.137880 24.20377 0.192
RS-308 0.0763 0.510640 −38.97 −0.61 2.9 2700 +2.49 0.804529 3.579526 0.665
RS-07b 0.1099 0.510877 −34.35 −0.44 3.2 3300 −4.47 0.792240 3.02232 0.674
RS-310 0.1247 0.510996 −32.04 −0.37 3.6 3300 −1.73 0.762518 1.675219 0.682
RS-307b 0.1122 0.510666 −38.47 −0.43 3.6 3300 −2.88 0.717892 0.416127 0.698
BR-WP-12B* 0.0950 0.5100607 −50.3 −0.52 3.9 3300 −3.5 – – –
BR-WP-12A* 0.0796 0.510430 −43.07 0.60 3.0 – – – – –
RS-07a 0.0886 0.510622 −39.33 −0.55 3.0 2700 −1.9 0.782796 2.554623 0.683
* Previous data.
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
8
The early Archean mantle was probably more enriched in incompatible
elements than the post-Archean mantle (Herzberg et al., 2010 and re-
ferences therein), thus negative ƐNd(T) values can be expected. There-
fore, the broad isotopic range that includes slightly negative to positive
ƐNd(T) values and low Sr/Sri values indicates that the Paleoarchean
rocks were produced by E-MORB sources or mixtures between enriched
and depleted MORB sources, likely with some crustal contamination. In
addition, some trace element ratios (e.g., Nb/Th) indicate a juvenile
source for the Favelândia complex, similar to other Paleoarchean
complexes, and the spider diagram (Fig. 4A) shows a pattern similar to
the E-MORB series. The higher Nb/Th values indicate a more mafic
source. The concordance between U-Pb ages, Nd-Sr isotopes, and geo-
chemical data from the north-central portion of SFC supports the idea
that these rocks were formed in a coeval magmatic event at 3.4–3.3 Ga.
On the other hand, Fig. 7B shows that the Paleoarchean Favelândia
complex displays different Nd isotope evolutionary trends than the
rocks of the Gavião block, indicating that both complexes are unrelated.
Unlike most TTGs, the 3.1–2.7 Ga metagranitoids of the Santa Izabel
complex in the GCB show LREE-enrichment, variable negative Eu
anomalies, and K-enrichment. They display variable ƐNd(2.7Ga) values
(+2.49 to −4.47) that are lower than those in the 3.3 Ga rocks, while
their Sr/Sri values range from 0.703 to 0.707 (Jardim de Sá et al., 1976;
Rosa, 1999). These combined data suggest a heterogeneous mafic
source and/or addition of crustal material. Accreted 3.3 Ga TTG gneiss
sources are indicated in the diagram of ƐNd(T) vs. Sr/Sri (Fig. 7A), and
these isotopic values demonstrate that this complex was generated
through reworking of Paleoarchean materials.
The Paleoproterozoic Guanambi batholith is dominated by syenites
and granites that preserve igneous features. Geochronological data
compiled from Rosa (1999) indicate a crystallization age of
2054 ± 6 Ma, and the intrusive body dated here shows a similar age of
2054 ± 15 Ma (Fig. 5). The chemical results indicate a metaluminous
composition, with enrichment in LILEs (Ba, Sr, Rb) and LREE (Rosa,
1999; Rosa et al., 2000). Based on the current data, the model for
Guanambi Batholith sources involves crustal remelting of Neoarchean
sources, as indicated by their TDM ages of 2.7 Ga and crustal Sr-Nd
isotopic features. Based on isotopic data, we hypothesize that the Santa
Izabel complex is the main precursor to the high silica components of
the Guanambi batholith and minor mantle contributions. According to
Rosa et al. (2000), a partial melt of enriched mantle contributed to the
magma’s genesis. These felsic rocks can be created through variable
melting degrees of thickened continental crust.
4.2. Geodynamic environment of crustal accretion and regional implications
The Guanambi-Correntina block is the traditional name for the
tectonic unit that comprises the Favelândia and Santa Izabel complexes,
the Riacho de Santana greenstone belt and Guanambi batholith (Fig. 1).
Several previous works have speculated on the origin and evolution of
the Guanambi-Correntina block (Arcanjo et al., 2005; Barbosa and
Sabaté, 2004; Barbosa et al., 2013; Brito Neves et al., 1980; Cordani
et al., 1985; Fernandes et al., 1982; Jardim de Sá et al., 1976;
Mascarenhas, 1979; Mascarenhas and Garcia, 1989; Rosa et al., 2000;
Silveira and Garrido, 2000). Initially, it was considered an independent
tectonic unit related to the adjacent Gavião block. These interpretations
were based on the discontinuity of Paleoproterozoic rocks of similar
composition from the Guanambi batholith to the East (Fig. 8) and the
presence of a regional shear zone along the Riacho de Santana and
Urandi cities. In contrast, more recent interpretations considered the
GCB as a Precambrian shield that was integrated in the north-central
SFC and subjected to a common geologic evolution, as it was recently
referred to as ‘West Gavião’ by Barbosa et al. (2012). On the other hand,
the field mappingfrom that study did not allow dating the regional
suture between the Guanambi-Correntina and the Gavião blocks, the
Santo Onofre shear zone.
Based on the lithological, geochemical, and radiometric data pre-
sented in this study, we suggest that the Guanambi-Correntina and the
Gavião blocks represent two Archean terranes that collided during a
Paleoproterozoic collisional event. The following evidence supports this
model: (i) Granulitic rocks in the western portion of the Santo Onofre
shear zone give U-Pb ages of 2.0 Ga (Fig. 8; Barbosa et al., 2013) and
are found alongside post-tectonic coeval rocks (Rosa, 1999); (ii) Mig-
matites of the Santa Izabel complex with 3.14 Ga paleosomes and
2.23 Ga neosomes (Medeiros et al., 2017) indicate a regional event
imposed on the Archean basement; (iii) Metabasalts dated at 2.2 Ga, of
the Riacho de Santana greenstone belt with MORB affinities, near the
Santo Onofre shear zone and restites of this belt are found to the north
and south; (iv) Metasedimentary rocks of Riacho de Santana Greenstone
belt containing graphite schists are typical of an oceanic basin succes-
sion; (v) Crustal reworking between 2.7 and 2.1 Ga affected both
blocks, however, Paleoproterozoic magmatism is much more prominent
in the Gaunambi-Correntina block (Fig. 9B); (vi) the Nd isotopic evo-
lution (Fig. 7B) shows different Paleoarchean trends in the Gavião and
Guanambi-Correntina rocks.
Our new U-Pb zircon ages enable to constrain the tectono-magmatic
events in the Guanambi-Correntina block: magmatic expressions
Fig. 7. (A) ƐNd(T) vs. Sr/Sri diagram; (B) εNd(0) vs. Time diagram for the Archean studied samples. Both diagrams compare the isotopic composition and evolution of
Paleoarchean felsic rocks (Favelândia, Sete Voltas, Aracatu, Bernarda, Boa Vista Mata-Verde rocks), (Data from Marinho et al., 1994a,b, Depleted mantle after Dickin,
2005).
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
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Fig. 8. Geologic map from central north São Francisco Craton, highlighting the 3.4–3.3 Ga primitive crust. Guanambi-Correntina block to the west, Gavião block to
the east (Barbosa et al., 2012).
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
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occurred episodically at 3.3 Ga, 3.1– 2.7 Ga, and 2.1 Ga, eventually this
Paleoproterozoic magmatism occurred prior to 2.1 Ga, as in other SFC
regions. Early Archean to Paleoproterozoic rocks constitute the con-
tinental segment in the GCB, similar to the Gavião block. The crust
records two main episodes, which generated most of the felsic rocks,
one in the Neoarchean and a second event in the Paleoproterozoic. In
the Paleo to Mesoproterozoic, the suture zone between Gavião and GCB
block was scenario of the drift and makeup of the basin, named
Espinhaço (see below). The detailed tectonic evolution of the
Guanambi-Correntina block will be presented chronologically in the
following sections.
4.2.1. 3.4 – 3.3 Ga TTG magmatism
The Paleoarchean magmatism has been recorded in the GCB and
Gavião block and seems to be much more widespread than previously
thought (Fig. 8). The 3.4–3.3 Ga ages were documented initially in the
Sete Voltas massif and afterwards in the Boa Vista-Mata Verde, Ber-
nada, and Aracatu massifs (Martin et al., 1991, 1997; Nutman and
Cordani, 1993). Thus, we propose that these ancient terranes that are
typically dominated by TTG suites were generated mainly by partial
melting of juvenile sources (see Section 4.1; Fig. 9A), based on their
lithology, positive to negative ƐNd(T) and low Sr/Sri values, and geo-
chemical compositions. The slightly negative ƐNd(T) values indicate the
possibility for reworking of older crust. While> 3.5 Ga dated crust is
not currently known, crustal reworking could be confirmed in future
studies analyzing detrital zircon grains.
The formation of the Archean TTG and early continental crust
(Martin et al., 2014 and references therein) have been related to the
subduction of an enriched MORB source (Condie and Kröner (2013);
Hastie et al., 2016 and references therein; Moyen and Martin, 2012).
The key features discussed in Section 4.1 indicate a juvenile source for
the Paleoarchean magmatism in the north-central SFC. Therefore, our
data indicate that the first crust in the GCB was generated from the
partial melt of a subducted oceanic crust (Fig. 9A and 10a), similar to
the oceanic-plateau material, in a flat subduction setting (oceanic arc),
as proposed by Martin et al. (2014).
Multiple generations of Paleoarchean granitoids are occasionally
associated with greenstone belts; the north-central part of the SFC
contains the primitive continental nuclei of this region (Fig. 8). After
the establishment of the SFC, these rocks crop out as small blocks or
xenoliths in gray gneisses (Martin, 1994; Figs. 8 and 9B) as a result of
erosion and reworking by superimposed events (Fig. 9A). Indeed, the
early Archean continental record does not support high net crust-pro-
duction at this time (Fig. 9B) (Spencer et al., 2018 and references
therein), although it remains possible that intense crustal reworking
consumed much of this crust to generate the K-rich granitoids (e.g.,
Liégeois et al., 1998; Nabatian et al., 2014). Fig. 9B highlights the
generation of crustal rocks from 3.4 to 2.1 Ga, showing that Gavião
block experienced more crustal production than the GCB between 3.4
and 2.7 Ga, while the Guanambi-Correntina shows a larger crustal
Fig. 9. (A) Time line showing the main magmatic and metamorphic events in Guanambi-Correntina block; (B) Histogram shows crustal growth based on U-Pb and
TDM ages in the Gavião block (GB) and GCB; Adapted from Allen (2007).
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
11
production in the Paleoproterozoic.
Published U-Pb zircon ages and Sr-Nd isotopes in the north-central
SFC craton reveal TTG accretion at 3.4–3.3 Ga and episodes of re-
mobilization and crustal reworking at 2.7 Ga, and ~2.0 Ga. Thus, the
Archean to Paleoproterozoic tectonothermal events in the region can be
divided into three stages at 3.3, 3.1–2.7 and 2.1–2.0 Ga (Fig. 9A and B).
For instance, the Favelândia complex, originated at 3.3 Ga, was sub-
sequently metamorphosed at 2.7 and 2.1 Ga (Fig. 9A). These data in-
dicate the polyphasic evolution of the SFC in this period, and a similar
cyclicity can be observed in the Gavião block (Barbosa et al., 2012). The
small portion of surviving meta-TTGs are overprinted by Paleoproter-
ozoic events, and comprise granulites, migmatites, and orthogneisses.
The Archean rocks underwent Paleoproterozoic metamorphism at
medium to high pressures.
4.2.2. 3.1–2.7 Ga Archean crustal growth and reworking
From 3.3 Ga onward, the newly formed crust was intensely re-
worked, with multiple episodes of magmatism and metamorphism
generating the granulite facies rocks. The available data highlight that
Meso- to Neoarchean rocks are widely exposed in the GCB, much like in
Gavião block (Figs. 1 and 8). U-Pb analyses reveal that the Santa Izabel
complex records a prominent peak of crustal growth during the
Neoarchean (Fig. 9A and B). The Santa Izabel complex is a key region
for deciphering the history of the GCB, as it represents an important
magmatic event between the oldest and younger magmatism in the
GCB. The isotopic and geochemical data indicate at least one magmatic
arc setting for the 3.1–2.7 rocks, or multiple series of accretionary arcs.
The scenario involves partial melting of juvenile material (MORB
sources), likely with a contribution of crustal sources, as indicated by
their high Sr/Sri ratios (0.703–0.707) and variable ƐNd(2.7Ga) (−4.1 to
+2.5) values. The available Rb-Sr isochron data indicates ages of
2748 ± 100 Ma, 2680 ± 83 Ma and 2685 ± 97 Ma with a Sr/Sri of
0.705 (Barbosa et al., 2013; Brito Neves et al., 1980; Mascarenhas and
Garcia, 1989), consistent with the new U-Pb ages provided in this study:
2683 ± 5 Ma, 2669 ± 22 Ma, and 2675 ± 26 Ma.
So far, evidence from field mapping has not been able to support a
subduction process for thiscomplex. However, considering that sub-
duction is the main mechanism for crustal growth, and based on our
new data discussed in Section 4.1, we infer that the rocks of the Santa
Izabel complex were generated in a series of oceanic and continental
accretionary arcs. The large age difference between the younger and
older rocks (~400 Ma) and the petrogenetic data may indicate chan-
ging tectonic settings. Some rocks show evidence of a continental arc
setting generated through mixture of two end-members, as suggested by
their contrasting ƐNd(2.7Ga) values. The main characteristics that support
this setting are: presence of felsic xenoliths, high K-contents, occasional
peraluminous compositions, variable Ta-Nb depletion, pronounced
LREE enrichment, TDM ages (3.3–3.1 Ga) similar to crustal sources in
the GCB, high Sr/Sri values (0.703–0.707), and negative ƐNd(2.7Ga) va-
lues. The most primitive isotopic and geochemistry data, and the pre-
sence of mafic xenoliths (Fig. 2C) can indicate an oceanic arc setting for
tonalitic rocks in this complex.
Interestingly, the continental crust in the GCB is dominantly
Neoarchean and Paleoproterozoic. The importance of Neoarchean
crustal growth in the GCB is highlighted by the substantial reworking of
Neoarchean material by the extensive Paleoproterozoic Guanambi
batholith. The production of 3.1–2.7 Ga felsic rocks was likely more
substantial than that of the 2.1 Ga event, since this Neoarchean event is
currently not widely exposed (Fig. 8). The continental growth event
that generated K-granitoids worldwide is also prominent in the GCB and
Gavião block. Thus, this tectonic event may be vital in explaining the
compositional change of (Paleo- to Neo-) Archean rocks through re-
melting of crustal components. From a metamorphic point of view, this
reworked crust is similar to the Favelândia complex, and experienced a
high-grade Paleoproterozoic orogenic event, as evidenced by the pre-
sence of high-grade metamorphic rocks including granulites, para- and
ortho-gneisses, and migmatites (Silveira and Garrido, 2000). Fragments
of greenstone belts occur as xenoliths in felsic bodies, indicating intense
crustal remobilization and reworking.
4.2.3. 2.1 Ga magmatic event – collisional orogen
The 2.1–2.0 Ga Guanambi batholith that extends across an area of
6000 km2 represents a major Paleoproterozoic stage of crustal growth
in the GCB (Figs. 1 and 9B) and involves significant additions of igneous
felsic material. The Guanambi batholith is interpreted as the product of
the amalgamation of microblocks and further cratonization (e.g., Rosa,
1999). Our Sr-Nd data reveals limited addition of juvenile material
during the 2.1–2.0 Ga magmatism, and point to reworking of
Neoarchean (2.7 Ga) crust during repeated crustal melting events. On
the other hand, the geochemical data (Rosa, 1999) indicate an im-
portant contribution of juvenile components.
Published data from the Riacho de Santana greenstone belt reveal a
U-Pb age of 2218 ± 18 Ma for the metabasalt (Rodrigues et al., 2012).
This age indicates that the emplacement of this unit precedes the
Guanambi batholith, but still in the Paleoproterozoic. The scenario for
the greenstone belt placement within the continent is related to the
subduction in Paleoproterozoic. The multiple granitoid intrusions
(Rosa, 1999) and the placement of the Riacho de Santana greenstone
belt are directly linked to a continental arc environment, superimposed
by collisional orogens. These Archean crusts are represented by the
Gavião block against the GCB, and probably by the basement of the
Phanerozoic sediments to the west (see Fig. 8). The GCB stabilized at
1.9 Ga, producing post-collisional bodies (Fig. 10; e.g., Cara Suja and
Ceraíma; Rosa, 1999).
The 2.0 Ga metamorphic event (granulites, gneisses, and migma-
tites) is contemporaneous with the magmatic emplacement of the
syntectonic Guanambi rocks. Lithological and field observations allow
to correlate this high-grade metamorphic overprint with a collisional
orogenic setting. Associated greenstone belts are adjoined by felsic
rocks, and most of these belts are derived from oceanic crust that was
obducted over the continent. The Paleoproterozoic crustal events re-
present the final major growth and cratonization stage of the GCB, and
the resulting block survived all superimposed events. This is distinct
from the Gavião block, wherein the most recent major crustal growth
events occur in the Meso- and Neoarchean (Fig. 9B).
4.2.4. Regional tectonic correlations
The Archean domain experienced the first tectonic processes in
Earth’s history (Condie and Kröner, 2013), and was characterized by
high convective flow and massive heat transfer to the atmosphere; high
devolatilization and chemical differentiation of the Earth (Ernst, 2009;
Nutman et al., 2015). The early Archean rocks in the South American
platform are predominantly TTGs, and most of them are thought to be
associated with oceanic arc settings (e.g., Favelândia, Sete Voltas
Massive, São José do Campestre/ Borborema Province), which is con-
sistent with tectonic models for the early Archean that advocate gen-
eration of continental crust in oceanic arc settings (Condie and Kröner,
2013); Nutman et al., 2015). These Paleoarchean rocks occur as small
bodies that were partially assimilated by younger rocks (Dantas et al.,
2013; Santos Pinto et al., 2012). The scarcity of preserved rocks with
this age indicates that few outcrops resisted overprinting by successive
events. The bulk Nd-Sr isotopic parameters of the Paleoarchean rocks
are compatible with a slightly depleted juvenile source (basaltic rocks),
enriched in LILE and LREE (Smithies et al., 2009). This early felsic crust
reflects an important new stage in the thermal and compositional
evolution of the mantle. For instance, the Paleoarchean rocks in
Yangtze Craton, South China, show ages from 3.31 to 3.29 Ga, they
have TTG compositions, enrichment of LREEs and LILEs, and their ƐHf(T)
range from +0.5 to −0.8; these features indicate a juvenile mafic
source in an arc setting (Guo et al., 2015). Similar features are observed
in the North SFC, where the discovery of a 3.4–3.3 Ga event is crucial
for the early history of this region, as it potentially allows a
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
12
compositional and tectonic link with contemporaneous rocks around
the world.
The crustal rocks in the northern SFC that form prominent preserved
units in several cratonic blocks originated in the Mesoarchean at
~3.0–2.7 Ga. They are calc-alkaline, with low- to high-K contents, and
their isotopic signatures indicate crustal components or enriched
mantle characteristics (e.g., Heilbron et al., 2017). The main tectonic
processes are orogenic, while evidence for generation of continental
arcs reflects the Mesoarchean emergence of modern-style subduction
(Smithies et al., 2007). Some Mesoarchean rocks show typical arc
signatures, such as decoupling of LILE and HFSE, resulting in negative
Nb-Ta-Ti anomalies and low Nb/Th ratios. The notable compositional
change in this period is related to the ascent of more potassic con-
tinental arc magmas and increased preservation potential during col-
lisional orogenesis (Johnson et al., 2019). The Santa Izabel complex and
the coeval felsic rocks in north SFC (e.g., Mairi, Paramirim, Ambrósio
and Santa Luz complexes) show these characteristics (Barbosa et al.,
2012). The SFC basement in the northern and the southern portions of
the craton is predominantly Meso- and Neoarchean in age. The nearby
Amazonian Craton lacks evidence of Paleoarchean rocks, but
Fig. 10. Schematic model illustrating the tectonic evolution of the Guanambi-Correntina block (Fv.: Favelândia, SV: Sete Voltas, Ar.: Aracatu, BV: Boa Vista, St. Iz.:
Santa Izabel).
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
13
experienced extensive 3.0–2.7 Ga magmatic events, with compositional
characteristics similar to the SFC (e.g., Carajás and Rio Maria domains).
The TDMages and εNd(T) for 3.0–2.7 Ga range from 3.3 to 2.8 Ga and
+2.75 to −4.09, respectively (Feio et al., 2017), showing a similar
range as those in the Meso- and Neoarchean rocks of Santa Izabel
complex. Major crust formation occurs at 2.7 Ga in several cratons
across the globe, and fairly large areas are preserved in the Superior,
Yilgarn, and Belingwe cratons, amongst others (Roberts et al., 2015). In
the Yangtze Craton, the 3.0 to 2.7 Ga rocks range in composition from
TTG-type to S-type granitoids, similar to the Santa Izabel complex in
our study area. The εHf(T) data and inherited zircons suggest that, in the
Yangtze Craton, part of these rocks are derived from reworking of ~3.4
TTGs (Guo et al., 2015). The Meso- and Neoarchean ages in the North
Atlantic Craton range from 3.0 to 2.8 Ga, with subsequent polycyclic
events metamorphosing the rocks into granulites and migmatites
(Friend and Nutman, 2001), which is reminiscent of the reworking of
2.7 Ga source material that may be derived from the Santa Izabel
complex in the 2.05 Ga Guanambi batholith.
The Archean-Paleoproterozoic boundary marks the transition to-
wards modern plate tectonics (Condie and O’Neill, 2010; Gerya, 2014;
Lyons et al., 2014; Condie, 2015). The early Paleoproterozoic experi-
enced major environmental changes, including oxygenation of the at-
mosphere and oceans, and the 2.1 Ga period is thought to represent the
peak of crustal growth (e.g., Rogers and Santosh, 2009). This period
experienced large-scale orogenic events that consolidated the Archean
land masses through accretionary and collisional orogens. Each parti-
cular tectonic setting shows a geochemical style that reflects changes in
melt rate and magmatic processes. For example, oceanic arc settings
generated Paleoproterozoic rocks with TTG compositions (e.g., Barbosa
et al., 2019), especially during the early Paleoproterozoic. The tectonic
style evolved over time, and the resulting rocks correspondingly
changed their composition from low-K series to high-K series, and
eventually shoshonitic affinities. The Paleoproterozoic Guanambi
batholith shows crustal affinities that are interpreted as reworking of a
continental protolith, while some rocks show evidence for a juvenile
component (see Section 4.2.3). This batholith is contemporaneous to
the Paleoproterozoic Itabuna Salvador Curaçá belt in northeast SFC,
which is similar in terms of composition and tectonic setting. Both re-
gions are characterized by variable compositions and high-grade me-
tamorphism (Barbosa and Barbosa, 2017), and are thought to represent
successive magmatic arcs along the northern continental margin. The
Itabuna Salvador Curaçá and the Guanambi batholith have been cor-
related with the Eburnean belt in the Congo craton. The ages in this
belts range from 2140 Ma to 1900 Ma, with εNd(t) of −4.8 to − 6.2, and
Nd TDM ages of 3.0–2.6 Ga (Degler et al.,2018 and references therein).
This belt is composed of granitoids gneisses, granulites and migmatites
along N-S trending, recording evolved magmatic arc processes on a
continental margin (Cahen et al., 1979; Djama et al., 1992). The final
cratonization of the GCB at 2.0–1.9 Ga, coincides with the inferred age
of the SFC-Congo amalgamation, in both belts, the age range of the
orogenic cycle is constrained between 2.4 and 1.9 Ga with a peak of
tectono-metamorphic and plutonic activity between 2.1 and 2.0 Ga.
(Lerouge et al., 2006). The Mineiro belt represents the southern con-
tinental margin and comprises 2.4–2.1 Ga rocks in low- to medium-
grade terrane in an accretionary system (Barbosa et al., 2015; Barbosa
et al., 2019). The Mineiro Belt has a much larger age spectrum than the
Guanambi batholith, which demonstrates the need for more geochro-
nological studies to the Guanambi batholith. Additionally, the Paleo-
proterozoic orogens of the SFC have different tectonic styles, in the
northern portion was generate collision orogens, which reach the
granulite facies and in the southern portion there is an accretionary
orogeny in greenschist to amphibolite facies.
In the Amazonian Craton (Ventuari-Tapajós), the Paleoproterozoic
record ranges from 2.2 to 1.8 Ga (Santos et al., 2000). These rocks are
interpreted as products of partial melting of successive magmatic arcs
overprinted by low-grade metamorphism (Brito Neves, 2011), similar
to the Mineiro belt. Globally, the Paleoproterozoic evolution of the
north SFC has many similarities with other tectonic provinces in South
America and West Africa (e.g., São Luis, West Africa and Rio de la Plata
Cratons; e.g., Brito Neves, 2011), as well as with domains in Zimbabwe,
Slave, North China, Pilbara, and Yilgarn. The widespread high-grade
metamorphism in the Paleoproterozoic is the result of the super-
continent formation between 2.4 and 2.0 Ga, which resulted in the
joining of several continental masses, highlighted by propagation of
accretionary and collisional arcs (Salminen et al., 2009). Other cratons
such as the Yangtze craton show Paleoproterozoic ages from 2.08 to
1.85 Ga and formed in an arc-subduction environment, which affected
the Paleo- to Neoarchean rocks in high-grade metamorphism (Geng,
2015).
In summary, the integrated paleogeographic framework indicates
that the Favelândia complex is a 3.3 Ga continental nucleus of the
Guanambi-Correntina block that was formed in an oceanic arc setting,
and that other Paleoarchean rocks in north SFC were formed in a si-
milar tectonic setting. These primitive components were reworked into
extensive younger basement areas (e.g. Santa Izabel complex), to which
continental arcs accreted. Finally, greenstone belts and continental arc-
related igneous provinces such as the Guanambi batholith represent the
final magmatic stage of cratonization in the Northwest SFC.
5. Conclusions
• The oldest crust identified in the study area (Guanambi-Correntina
block) and in the Gavião block represents a 3.4–3.3 Ga magmatic
event with minor (preserved) spatial extent, and dominantly in-
volved juvenile sources.
• The Guanambi-Correntina block is dominated by two large mag-
matic events: K-granitoids at 3.1–2.7 Ga and a felsic igneous rocks at
2.1 Ga. The Neoarchean rocks are products of partial melting
oceanic crust (slab subduction) and reworking of older crustal rocks.
The Paleoproterozoic rocks in turn formed by partial melting
oceanic crust and reworking of these 2.7 Ga rocks; however, crustal
reworking is more important for these rocks, and the Santa Izabel
complex is the most probable source material.
• From a dynamic point of view, the 2.1 Ga event was the most im-
portant tectonothermal event in the Guanambi-Correntina block, as
it was responsible for the final consolidation of the Archean blocks.
• The GCB and Gavião block may represent different continental nu-
clei and were accreted during the Paleoproterozoic event. Thus, the
Precambrian basement in the GCB has a distinct geological history
but experienced a similar Paleoproterozoic metamorphic history as
the Gavião block.
• Based on our new data and reassessment of the available literature
data, we suggest that the GCB originated as an independent tectonic
unit that is coeval with the Gavião block.
Acknowledgments
N. S. Barbosa and co-authors acknowledge the Federal University of
Bahia (PROPG/PROPCI) for the financial support for Grammar revision.
A. B. M. Leal and co-authors thank the Brazilian Research Council –
CNPq (National Council for Scientific and Technological Development)
for the continuous financial support for the geologic research in the
north São Francisco Craton (grants 476901/2013-8). The Fundação de
Amparo à Pesquisa do Estado da Bahia – FAPESB for financial support is
greatly appreciated (grants 030/2016).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.precamres.2020.105614.
N. Barbosa, et al. Precambrian Research 340 (2020) 105614
14
https://doi.org/10.1016/j.precamres.2020.105614
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