Gondwana Research 17 (2010) 676–687
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Gondwana Research
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g r
Ediacaran Águas Belas pluton, Northeastern Brazil: Evidence on age, emplacement
and magma sources during Gondwana amalgamation
Adejardo F. da Silva Filho a,⁎, Ignez P. Guimarães a, Valderez P. Ferreira a,
Richard Armstrong b, Alcides N. Sial a
a
b
Departamento de Geologia—CTG, Universidade Federal de Pernambuco, Rua Acadêmico Helio Ramos S/N Cidade Universitária, Recife, Pernambuco, 50740-530, Brazil
Research School of Earth Sciences, the Australian National University, Canberra, Australia
a r t i c l e
i n f o
Article history:
Received 12 January 2009
Received in revised form 29 September 2009
Accepted 6 October 2009
Available online 17 October 2009
Keywords:
Ediacaran
Syenogranite
Geochemistry
U–Pb SHRIMP geochronology
Oxygen isotopes
a b s t r a c t
Ediacaran syenogranites from the Águas Belas pluton, Borborema Province, Northeastern Brazil were investigated
in this work. The studied granitoids show high SiO2, Fe# [FeO/ (FeO+ MgO)], total alkalis (K2O + Na2O) and BaO
contents and medium Sr and low Nb contents. They show gentle fractionated rare earth patterns with discrete Eu
negative anomalies. Major and trace element data point to chemical features of transitional high-K calc-alkaline
to alkaline post-collisional magmatism. Structural data coupled with geochronological data suggest that NNE–
SSW-trending sinistral movements at shear zones were initiated at ca. 590 Ma and have activated E–W preexisting structures at the current crustal level. The synchronism of these shear zones allowed the dilation to
generate the necessary space for the emplacement of the Águas Belas pluton.
U–Pb SHRIMP zircon data show a cluster of ages around 588 ± 4 Ma which is interpreted as the crystallization age.
Some zircon grain cores yielded ages within 2060–1860 Ma and 1670–1570 Ma intervals. Oxygen isotope
compositions of zircon grains with distinct ages were measured using SHRIMP techniques. Twenty three analyses
in the same zircon spots previously analyzed for U–Pb show δ18O values ranging from 5.79‰ to 10.30‰ SMOW.
This large range of values results from variations both between grains and within grains (core–mantle/rim), and
is interpreted as the result of mixing of components with distinct oxygen isotope compositions. The U–Pb zircon
ages and the δ18O values associated with Paleoproterozoic Nd TDM model ages suggest that the protolith of these
granitoids involved a mantle component (Paleoproterozoic lithospheric mantle), Paleoproterozoic and
Mesoproterozoic igneous rocks. Interactions with Mesoproterozoic or Neoproterozoic supracrustal rocks, may
have occurred during the intrusion. The resulting magma evolved through biotite and K-feldspar fractionation.
© 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
1. Introduction
The Brasiliano orogeny (650–550 Ma) in the Borborema Province,
northeastern Brazil, is marked by a large number of granitoid
intrusions associated with either low- or high-angle large scale
shear zones (e.g. McReath et al., 2002; Guimarães et al., 2005; Bueno
et al., 2009). Geochronological data of these granitoids can constitute
an important tool in dating these tectonic events.
The post-collisional tectonic setting is characterized by large
intrusion of high-K calc-alkaline magmas. This tectonic setting usually
ends with minor amounts of highly evolved high-K calc-alkaline or
alkaline magmatism, which mark the end of the orogeny. Highly
evolved high-K calc-alkaline magmatism generally shows some
⁎ Corresponding author. Tel.: +55 81 21268240; fax: + 55 81 21262834.
E-mail address: [email protected] (A.F. da Silva Filho).
similarities with A-type granites (Liegéois et al., 1998). As pointed
out by Pearce (1996), the post-collisional granites are the most
difficult to classify, since some of them have subduction-like mantle
sources with many characteristics of volcanic-arc granites while
others show within plate character. According to Eby (1992), A-type
granitoids can be divided into A1- and A2-types. The A1-type occurs in
a true anorogenic setting and it has OIB signatures, while the A2-type
occurs in post-collisional or post-tectonic setting, usually shortly (10–
20 million years) after compressional tectonics, is rarely, or not
associated with silica-undersaturated alkaline rocks, have trace
element signatures similar to sub-continental lithosphere and crust,
and never have OIB signature.
Oxygen isotope ratios of magmas reflect their source and
contaminants. According to Eiler (2001) the mantle is a homogeneous
reservoir. Igneous zircons in high temperature equilibrium with
mantle magmas have an average of δ18O = 5.5 ± 0.3‰ (Valley et al.,
1998). This value remains approximately constant during fractionation processes, and change can only be achieved by adding a material
of a distinct oxygen isotope composition to the magma (Valley, 2003).
1342-937X/$ – see front matter © 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.gr.2009.10.002
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
Significant deviations from the mantle value are the result of magma
interactions with low temperature rocks (supracrustal rocks) and
rocks from near the surface associated with large oxygen isotope
fractionation.
Granites are classically considered by various authors to probe the
crust, giving important clues to the understanding of the crustal
evolution. The Pernambuco–Alagoas domain, which is among the
major crustal domains of the Borborema Province, was shown by Silva
Filho et al. (2002) to be comprised by various crustal sections of very
different Nd TDM ages. The Águas Belas pluton shows Paleoproterozoic
Nd TDM (Silva Filho et al., 2002) but is surrounded by supracrustals
and volcanics of Mesoproterozoic Nd TDM age (Van Schmus et al.,
2008), and then has been considered among the main metaluminous
granitic intrusion from the Pernambuco–Alagoas domain, with some
A-type petrographic and geochemical signature (Silva Filho et al.,
1996). The aim of this paper is to present geochemical, U–Pb SHRIMP
zircon and oxygen isotopic data for discussing the age, the sources and
the tectonic setting of a large granite intrusion, the Águas Belas pluton,
located in the Pernambuco–Alagoas domain of the Borborema
Province, which altogether could shed light on the last stages of the
Gondwana amalgamation.
2. Regional geology
The Borborema Province (Almeida et al., 1977) is located in northeastern Brazil, north of the São Francisco craton (Fig. 1a). Although the
region was highly deformed and metamorphosed during the Brasiliano
orogeny, many features of pre-Brasiliano geology can still be recognized
from the rocks, including isotopic signatures. In a pre-drift reconstruction (De Wit et al., 1988), the Borborema Province lies adjacent to coeval
Pan-African and cratonic terranes from western Africa (Toteu et al.,
2001).
The Pernambuco–Alagoas crustal domain (PEAL) is one among the
six crustal domains identified by Van Schmus et al. (2008) in the
Borborema Province. It is limited to the north with the Transverse
Zone domain, to the south with the Sergipano domain, and its eastern
part is cut by large granitic batholiths (Fig. 1b).
Medeiros and Santos (1998) recognized some metamorphic
sequences in the Pernambuco–Alagoas domain: (i) The Cabrobó
complex is a dominantly supracrustal unit comprised of biotite garnet
gneisses, locally migmatized, intercalated with quartzite, schist, calcsilicate and amphibolite, orthogneisses and migmatite; (ii) The Belém
do São Francisco complex is an infra-crustal segment composed of
migmatites, biotite-gneisses, tonalitic orthogneisses, and leuco-granodiorites to leuco-monzogranites. The occurrence of a low-angle
foliation and a swarm of small granitic intrusions, controlled by a
transpressive deformation, suggest that thrusting has operated in the
area (Silva Filho et al., 2002). Geological and geochronological data
collected in the past few years showed that the PEAL domain geology is
comprised by a Paleoproterozoic basement complex (Osako, 2005;
Neves et al., 2005a,b), supracrustal sequences, and Neoproterozoic
granitic batholiths.
Silva Filho et al. (1996, 1997, 2002) have identified various latetectonic granitic intrusions and suites in the eastern part of the PEAL
domain, with compositions ranging from high-K to calc-alkaline,
shoshonitic, mildly alkaline or peraluminous (± garnet-bearing)
granites. These intrusions were grouped into four granitic batholiths:
Buique–Paulo Afonso, Águas Belas–Canindé, Marimbondo–Correntes,
and Ipojuca–Atalaia. The Águas Belas granitoids are part of the Águas
Belas–Canindé batholith.
The Águas Belas–Canindé batholith is limited to the south by the
Sergipano domain, to the north and to the east by migmatites from the
Belem do São Francisco complex, and to the west by the supracrustal
Inhapi sequence (Fig. 2). It comprises biotite, amphibole syenogranites and amphibole–pyroxene bearing syenogranites cutting metatexites and diatexites of tonalitic composition. The metatexites grade
677
to diatexites from the margin to the centre of the western part of the
batholith.
The ages of the PEAL domain units are still poorly constrained. It is
probable that grouping units based primarily on rock-type has
lumped together units having primary depositional or plutonic ages
ranging from Paleoproterozoic (or older) to Brasiliano (Neoproterozoic). Brito Neves et al. (1995) presented Rb–Sr isochron ages
ranging between 1.13 Ga (diatexites) and 0.96 Ga for rocks assigned
to the Cabrobó and Belém do São Francisco complexes (Santos, 1995)
in western PEAL domain. The TDM model ages for rocks of these
complexes range between 1.50 Ga to 1.30 Ga (Santos, 1995).
Very few U–Pb (zircon) ages are available for the PEAL domain.
Van Schmus et al. (1995) reported a zircon upper-intercept apparent
age of 1577 ± 73 Ma for garnet-bearing migmatite, west of Palmeira
dos Indios town. A single U–Pb age in zircon obtained by LA-ICPMS
from migmatized tonalitic orthogneisses in the Jupi area, NE of
Garanhuns, yields an age of 2000 Ma (Neves et al., 2005a,b). The early
interpretations of a Paleoproterozoic to Archean age for most of the
PEAL domain have not been confirmed by the few new zircon ages.
U–Pb zircon ages in granitoids of the PEAL domain show an
interval from 570 Ma to 625 Ma (Silva Filho et al., 1997, 2008; Silva
Filho and Guimaraes, 2000) and Nd TDM model ages range from 1200
to 2000 Ma (Silva Filho et al., 2006). A larger data set reported by Silva
Filho et al. (2002, 2006) expanded the range of TDM ages from 900 to
2800 Ma and the data show a bimodal distribution, indicating that
most of the Nd formation ages are either Neoproterozoic or
Paleoproterozoic. The low frequency of samples with TDM ages from
1500 to l800 Ma may indicate that Cariris Velhos (980–920 Ma)
igneous rocks, which commonly have TDM ages in this range (Van
Schmus et al., 1995; Brito Neves et al., 2001), are scarce or not found in
the PEAL domain. Silva Filho et al. (2002) evaluated the evolution of
the PEAL domain based on Sm–Nd isotopic data from the Neoproterozoic granitoids, and defined two crustal sub-domains: Garanhuns
and Água Branca sub-domain.
Silva Filho et al. (2006) based on new Nd isotopic data from
granitoids, orthogneisses and supracrustal rocks proposed three crustal
sub-domains for the PEAL domain: (i) Garanhuns with TDM model ages
in the interval 1600 to 2600 Ma, (ii) Água Branca with TDM model ages
ranging from 900 to 1590 Ma and (iii) Palmares—TDM model ages
around 1110 Ma. The Àguas Belas pluton is intruded into rocks from
the Agua Branca sub-domain (Fig. 1b). This sub-domain is comprised by
the Águas Belas–Caninde batholith (Silva Filho et al., 2002) and by the
Inhapi Sequence (Van Schmus et al., 2008). It has been shown that the
Agua Branca sub-domain is comprised mainly by rocks of TDM model
ages from 900 Ma and 1590 Ma, and various granitic plutons and
orthogneisses of TDM ca. 2000 Ma, among them the Águas Belas pluton.
These data point to a setting where tectonic blocks of different ages have
been put in contact during a collisional process. Collisional process has
been constrained at 628 ± 12 Ma in the adjoining Sergipano Terrane
(Oliveira et al., 2006). Previous geological and geochemical reconnaissance of the Àguas Belas pluton (Silva Filho et al., 1996) showed that it is
comprised by late-tectonic metaluminous and high-K calc-alkaline
rocks. Metaluminous and amphibole ± pyroxene suites are classically
extracted from the lower crust or from the upper mantle. This pluton
was selected to study because it would bear inheritance from lower
crust or upper mantle, and, as it shows high and restricted SiO2 contents,
which is typical of crustal-derived granites, it would bear as well an
inheritance from the middle to the upper crust. So, the whole set of data
could shed light into the Brasiliano collisional process. This paper tries to
approach some complexities of the crustal evolution of this crustal
domain of the Borborema Province, using SHRIMP U–Pb zircon, oxygen
isotopes and trace elements geochemistry from the Águas Belas pluton.
A brief evaluation on the emplacement of this pluton has been done in
order to position it in relation to the chronology of the adjoining shear
zones and to the flat-lying foliation from the adjoining supracrustal
sequences.
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Fig. 1. a) Sketch geological map of the Borborema Province. The main tectonic domains are from Van Schmus et al. (1995) and Van Schmus et al. (2008). PESZ = Pernambuco shear zone; PSZ = Patos shear zone. 1—Palaeozoic sedimentary
basin. b) Schematic map for the crustal sub-domains of the PEAL domain.
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
679
Fig. 2. a) Simplified geological map of the PEAL Domain, showing the location of the studied area. 1—Palaeozoic sedimentary cover; 2—Brasiliano granitoids; 3—Ipojuca–Atalaia Batholith;
4—Buique–Paulo Afonso Batholith; 5—Águas Belas–Canindé Batholith; 6—Garanhuns Batholith; 7—Palmares Sequence; 8—Venturosa Sequence; 9—Garanhuns Quartzites; 10—Inhapi
Sequence; 11—Alagoana Sub-belt; 12—Belém do São Francisco Complex; 13—Archean block; 14—Transcurrent Shear zones (PESZ—Pernambuco; RCSZ—Rio da Chata; PSZ—Palmares;
LCSZ—Limitão–Caetés; ISZ—Itaíba; SBUSZ—São Bento do Una); 15—Transpressive shear zones (GSZ—Garanhuns; MSZ—Maravilha shear zone). b) Simplified geological map of the studied
area. 1—The Águas Belas pluton (c—pyroxene syenogranites, d—amphibole, biotite syenogranite); 2—Garnet-two micas bearing granites from the Serrote dos Macacos (580 Ma);
3—Águas Bela—Canindé batholith; 4—Metasediments from the Inhapi Sequence; 5—Belem do São Francisco Complex; 6—Transpressive Maravilha shear zone; 7—Limitão–Caetés
transcurrent shear zone; 8—Fractures; 9—Photo structural lineaments; 10—Milonitic foliation; 11—Location of the sample AB-08, analyzed for U–Pb and Sm–Nd.
3. Geology and petrography
The Águas Belas pluton constitutes an elongated intrusion with an
18 km long E–W-trending major axis (Fig. 2b). It is intruded along the
contact between the Inhapi supracrustal sequence and the Águas
Belas–Canindé batholith, being part of the Água Branca crustal subdomain (Silva Filho et al., 2006). Northwards and very close to the
pluton the Venturosa Sequence crops out. This sequence is comprised
by metasedimentary rocks and orthogneisses. Structural analysis of
this sequence shows a main Sp low-angle foliation with SE–NW
stretching lineations (Silva Filho et al., 2007). Another main feature of
this sequence is a high-angle foliation related to NE–SW shear zones,
which are younger than the Sp low-angle foliation and spatially
related to various high-K calc-alkaline granitoids. The country rocks to
the north are sillimanite–garnet–biotite-gneisses, to the west biotite–
muscovite–garnet gneisses both from the Inhapi Sequence, and to the
south are other Neoproterozoic granitic plutons from the Águas
Belas–Canindé Batholith. The contacts of the pluton are sharp with
both gneisses and granitoids. An E–W-trending mylonitic foliation has
been identified in the northern contact. Xenoliths of migmatized
gneisses are observed along the northern outer contact. The Águas
Belas pluton truncates the Maravilha ductile low-angle shear zone
which runs NE–SW (Fig. 2b). The NE–SW Limitão–Caetés ductile shear
zone cuts the Venturosa Sequence and terminates at the NE tip of the
Águas Belas pluton. This shear zone shows low-angle foliation (Osako,
2005) dipping eastward. The Águas Belas pluton cuts the Inhapi
Sequence foliation at a high angle. Within the pluton an E–W weak
lineation, parallel to its main axis has been recognized. Remote
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A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
sensing imagery (Osako, 2005) shows internal E–W and NE–SW
brittle foliations as well.
A geophysical discontinuity has been identified a few kilometres
to the north of the Águas Belas pluton (Silva Filho et al., 2007). It runs
from the E–W Pernambuco shear zone, the northern limit of the
Pernambuco–Alagoas domain, with trends ranging from NE–SW to
E–W, suggesting that the Águas Belas pluton is intruded close to an
important E–W-trending crustal discontinuity. Syn- to late-tectonic
granitoid intrusions, with ages ranging from 580 to 590 Ma have
been mapped along NE–SW shear zones (Neves et al., 2006; Silva
Filho et al., 2007).
The data available suggest that intrusion of the Águas Belas
occurred after the peak of the Brasiliano metamorphism, which was
probably associated with the flat-lying foliation in both Venturosa
(Limitão–Caetés shear zone) and Inhapi Sequences (Maravilha shear
zone). The E–W-trending lineation recorded within the Águas Belas
pluton and lack of large mylonitic zone within it suggest that the
intrusion took place at the beginning of the operation of a discrete
ductile E–W shear zone. The pluton was later cut by brittle faults,
which were the channels for the ascent of bimodal volcanic rocks that
include pyroclastic rhyolites and basalts. These brittle faults are
associated with the initial stage evolution of the interior sedimentary
basins of Gondwana break-up.
The Limitão–Caetés high-angle shear zone is a splay of the
Pernambuco shear zone, and it terminates at the east contact of the
Águas Belas pluton. A two-mica granite, the Serrote dos Macacos
pluton, intruded a few kilometres north of the Águas Belas pluton,
within the Limitão–Caetés shear zone (Fig. 2), yielded U–Pb monazite
age of 580 ± 3 Ma (Osako, 2005).
Two main petrographic facies were recorded in the Águas Belas
pluton (Fig. 2b): amphibole ± biotite syenogranite to quartz syenite and
pyroxene ± amphibole syenogranite. They are coarse to medium
grained rocks with low concentration of modal mafic minerals (less
than 6%). Evidence of deformation under low temperature was recorded
in the northern and southern border of the Águas Belas pluton. The low
temperature deformation is characterized by recrystallized quartz as
micro grains and elongated quartz grain showing undulose extinction.
Amphibole-rich clots are frequently recorded. In the pyroxene ±
amphibole syenogranite, the amphibole is green, bluish, and Fe-rich,
formed by the reaction of light green pyroxene and the magma. Na-rich
amphibole (afverdsonite) is recorded as a later crystallized phase in the
amphibole ± biotite syenogranite to quartz syenite. Anti-rapakivi
texture was recorded in both petrographic units reflecting later
crystallization of K-feldspar. Biotite occurs in very small modal amounts
(<1%) always as inclusions in amphiboles or, as a later phase, replacing
amphiboles. Sphene is the main accessory phase. It occurs as subidiomorphic to idiomorphic orange crystals reflecting high LREE
concentrations (Guimarães et al., 1993). Zircon, opaque minerals,
allanite and apatite are the other accessory minerals recorded in the
Águas Belas granitoids.
4. Geochemistry and Sm–Nd data
Representative samples from the Águas Belas pluton were analyzed
for major elements by ICP-AES and for trace elements by ICPMS at
ACME Laboratories in Canada. The results are shown in Table 1.
The Águas Belas granitoids range from metaluminous to slightly
peraluminous, straddling the boundary with the peralkaline field
(Fig. 3a). They plot in the fields of alkaline to highly fractionated calcalkaline granites (Fig. 3c) in the scheme proposed by Sylvester (1989).
The plutonic TAS diagram (Fig. 3b), with fields after Middlemost
(1997), emphasizes the trans-alkaline character of the Águas Belas
granitoids. They have high SiO2 (69.1–73.1 wt.%) and total alkalis,
with Na2O + K2O ranging from 8.3 to 10.5 wt.% and K2O/Na2O ratios
ranging from 1.2 to 1.9. One sample analyzed from the southern
border of the batholith shows higher K2O/Na2O ratio (2.2). They have
high Fe# [FeOt / (FeOt + MgO)] values (0.8 to 0.92, Fig. 3d), which
classify them as belonging to the ferroan series granitoids (Frost et al.,
2001). All the analyzed samples fall within the shoshonitic field in the
K2O vs. SiO2 diagram (Fig. 3e).
The Águas Belas granitoids show high Ba contents (1300–2650 ppm),
medium Sr contents (430–690 ppm) and low to medium Rb contents
(203–258 ppm). The contents of the high field-strength elements
(HFSE) are relatively low (Nb = 8–14 ppm; Ta = 0.2–2.0 ppm;
Zr = 81–189 ppm). One sample from the southern border of the
batholith shows high Ba (6155 ppm) and Sr contents (1660 ppm) and
have high K2O/Na2O ratio (2.2).
The REE patterns (Fig. 4) normalized to chondrite values of
Nakamura (1974) are characterized by gentle fractionated pattern,
with CeN/YbN ranging from 8.7 to 3.3, with only one sample showing
higher value (19.5), without substantial negative Eu anomalies (0.98
to 0.86).
Bivariate plots between elements that readily enter rock-forming
minerals may be used to test the fractional crystallization hypothesis
by comparing model mineral fractionation vectors with observed data
arrays. Ba versus Sr correlations can provide information particularly
on the feldspars and biotite fractionation. The Ba versus Sr data for the
Águas Belas granitoids define a trend compatible with K-feldspar and
biotite fractionation (Fig. 5a), which agrees with the negative Eu
anomalies recorded in the REE patterns. The lack of correlation
between Ba and Sr with Eu/Eu* (Fig. 5b, c) does not support plagioclase
fractionation during the evolution of the Águas Belas granitoids. On the
other hand, the positive correlation between Na2O and SiO2 reflects
the later crystallization of Na-rich amphiboles, as observed in the
petrographic studies.
Nd isotopic analysis for one sample was carried out at the Isotope
Geochemistry Laboratories—Kansas University. It shows negative εNd
(600 Ma) values (− 12.4) with Paleoproterozoic TDM (2130 Ma)
model age.
5. Geochemical signature
In spite of their high Ba contents, the studied granitoids do not
meet the criteria established by Tarney and Jones (1994) for high Ba–
Sr (HiBaSr) granitoids, due to their medium Sr contents and low LREE
and high HREE contents. The REE patterns of the studied granitoids
are distinct from either HiBaSr granites, which have highly fractionated patterns and from A-type granites, which have gentle fractionated patterns but with substantial negative Eu anomalies.
Multi-element diagrams normalized to the values suggested by
Thompson (1982) for the studied granitoids and the average element
concentration of I-type S-type and HiBaSr granites (Fowler et al., 2008)
are shown in Fig. 6a and b. The studied granite patterns are characterized
by troughs at Nb, Ti, P and either peak or troughs at Sr. Compared to the
average of I-type and HiBaSr granites (Tarney and Jones, 1994) the
studied granitoids have lower Sr, P and Ti concentrations.
Morrison (1980) pointed out the main characteristics of the
shoshonitic association: high total alkalis (K2O + Na2O > 5), low TiO2
(<1.3 wt.%), no Fe enrichment in the AFM diagram and high contents
of LILE (Ba, Sr, Rb), low Nb, and steep REE patterns. The Águas Belas
granitoids show some distinctions when compared to granitoids of
the shoshonitic association because they have low Sr contents and
have REE patterns characterized by lower (Ce/Yb)N ratios.
The Águas Belas granitoids exhibit a trans-alkaline and ferropotassic character. These features are common to most alkaline
granite suites. However, the studied granitoids show high Ba and low
Nb and Y contents, whereas the alkaline granites have low Ba and high
Nb and Y contents. According to Liegéois et al. (1998), alkaline
granites, not peralkaline granites, show K-feldspar always dominating
over plagioclase, i.e. they are alkali-feldspar granite and syenogranite
in composition. The alkaline granites show petrography very similar
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
681
Table 1
Representative geochemical and isotopic data for granites from the Águas Belas Pluton.
Sample
AB-02
AB-08
AB-10
AB-11
SiO2
Al2O3
MnO
MgO
Fe2O3
CaO
Na2O
K2O
TiO2
P2O5
Total
70.36
14.22
0.06
0.38
1.07
3.73
6.75
0.27
0.06
2.33
100.15
69.14
14.39
0.07
0.42
2.99
1.15
3.55
6.92
0.25
0.07
99.7
70.4
15
0.05
0.32
2.24
0.67
3.53
6.20
0.18
0.06
99.8
71.16
14.88
0.04
0.33
1.99
0.76
3.73
6.03
0.16
0.08
99.89
70.55
14.69
0.04
0.31
2.16
0.7
3.76
6.64
0.16
0.09
99.1
70.64
14.5
0.06
0.34
2.28
0.96
3.78
6.47
0.18
0.08
99.65
72.4
14.8
0.04
0.26
1.51
0.84
4.12
4.88
0.13
0.08
99.9
73.12
14.2
0.04
0.22
1.63
0.87
4.22
5.23
0.11
0.04
99.91
72.39
14.23
0.05
0.27
1.77
0.85
4.2
5.25
0.13
0.05
99.47
72.12
14.26
0.06
0.19
2.12
0.88
4.15
5.44
0.11
0.04
99.66
71.09
14.41
0.05
0.34
2.19
1.0
3.77
6.23
0.17
0.07
99.66
71.44
14.16
0.06
0.33
1.6
0.87
4.08
5.51
0.12
0.06
98.49
2566
nd
nd
3.6
nd
203
710
0.2
11.1
1.5
159
19
31
59
nd
23.1
4.09
1.11
nd
nd
nd
nd
nd
nd
1.73
0.26
0.877
0.1171
− 18.50
− 12.41
2139
1968
nd
nd
4.2
nd
211
592
0.7
11.1
6.0
121
28
78.4
205
nd
56.2
8.94
2.15
nd
0.9
nd
nd
nd
nd
2.67
0.37
0.875
1893
nd
nd
3.1
nd
29
613
1.0
2.7
0.8
106
13
16.5
36
nd
18.0
3.95
1.31
nd
0.7
nd
nd
nd
nd
2.75
0.41
0.858
1983
7.1
19.3
4.4
8.9
243
569
0.7
14.1
1.9
143
19.5
44.7
80.8
8.1
30.2
4.6
1.02
3.74
0.6
3.45
0.6
1.61
0.27
1.59
0.27
0.874
1848
5.0
19.3
3.8
9.8
236
542
0.7
16.7
2.4
127
17.6
25.3
45.9
4.67
18.4
3.2
0.61
2.78
0.45
2.66
0.53
1.56
0.28
1.84
0.28
0.870
1500
nd
nd
nd
nd
nd
490
nd
nd
nd
89
10
9.49
22
nd
7.0
1.58
0.5
nd
0.3
nd
nd
nd
nd
0.94
0.15
0.853
1335
5.8
19.4
3.1
9.4
231
460
0.8
12.3
2.7
87
13.9
16.4
29.3
3.22
12.1
2.3
0.5
2.28
0.36
2.36
0.44
1.38
0.24
1.42
0.24
0.881
1297
4.1
19.3
3.3
10.4
224
458
1.0
19
3.5
92
13
15.7
29.9
3.08
12.3
2.3
0.5
2.03
0.32
2.06
0.4
1.26
0.22
1.6
0.27
0.868
1384
5.6
19.5
3.4
10.5
257
429
1.3
22.9
4
101
18.4
20.4
33.4
4.04
16
2.6
0.59
2.73
0.46
2.8
0.54
1.61
0.28
1.95
0.34
0.918
1757
4.2
18.9
3.5
12.1
258
558
0.9
14.3
3.6
111
17.1
22.7
40.7
4.25
17.7
2.9
0.53
2.7
0.46
2.8
0.55
1.53
0.26
1.75
0.31
0.866
1323
4.9
19.9
3.9
14.4
262
427
2.0
20
5.1
93
14.1
20.8
34.8
3.68
13.8
2.4
0.37
1.86
0.38
2.12
0.39
1.23
0.2
1.67
0.29
0.829
Trace elements in ppm
Ba
2427
Cs
nd
Ga
nd
Hf
nd
Nb
nd
Rb
nd
Sr
664
Ta
nd
Th
nd
U
nd
Zr
nd
Y
nd
La
189
Ce
17
Pr
nd
Nd
nd
Sm
nd
Eu
nd
Gd
nd
Tb
nd
Dy
nd
Ho
nd
Er
nd
Tm
nd
Yb
nd
Lu
nd
Fe#
0.860
147
Sm/144Nd
0.1211
(0)
εNd
− 18.29
εNd(0.6 Ga)
− 12.50
TDM (Ma)
2214
AB-12
AB-13
AB-14
AB-15
AB-17
AB-20
AB-21
AB-22
Nd = not determined. Fe2O3 = Total iron. Fe# = FeOt / (FeOt + MgO).
to evolved calc-alkaline granitoids, and the distinction can be attained
on geochemical grounds.
The Águas Belas granitoids are mainly syenogranite in composition and, plot (Fig. 7) within the post-collisional field in the Rb versus
(Y + Nb) diagram (Pearce, 1996). They have high values of Fe#
(> 0.8), Fe-rich and Na-rich amphiboles, REE patterns characterized
by low (Ce/Yb)N values and high total alkalis, with Al2O3 / (Na2O +
K2O) molecular ratios ~ 1.0. In the Yb/Ta versus Y/Nb diagram (Fig. 8)
the Águas Belas granitoids plot along a trend between the OIB and IAB
average fields, showing trace element signature distinct from OIBlike signature (Fig. 9). In spite of the many similarities with A2-type
granites, the studied granitoids have much lower contents of Y and
Zr, and higher Sr concentrations, when compared to those for
alkaline granites. The geochemical signature of the Águas Belas
granitoids favours their classification as a transitional high-K calcalkaline to alkaline post-collisional magmatism.
6. SHRIMP U–Pb and oxygen isotope zircon data
6.1. Analytical methods
SHRIMP U–Pb dating was used to determine the age of zircons
from the studied granitoids. Zircon grains were separated from the
total rock sample (AB-08) using standard crushing, washing and
heavy liquid. Hand-picked selected zircons were placed onto doublesided tape and mounted together with chips of the reference zircons
(FC1and SL13) in epoxy resin, ground to half thickness, and polished
with 3 µm and 1 µm diamond paste. A conductive gold-coating was
applied just prior to analysis. The grains were photographed in
reflected and transmitted lights, and cathodoluminescence (CL)
images were produced in a scanning electron microscope in order
to investigate the internal structures of the zircon crystals, to
characterize different populations, and to ensure that the spot was
wholly within a single age component within the sectioned grains.
The U–Th–Pb analyses were made using the SHRIMP II of the
Research School of Earth Sciences, The Australian National University,
Canberra, Australia. Each analysis consisted of 6 scans through the
mass range. SHRIMP analytical procedures followed the methods
described in Williams (1998, and references therein). The standard
zircon SL13 (Claue-Long et al., 1995) was used to determine U
concentration and the Pb/U ratios were normalized relative to a value
equivalent to an age of 1099 for the FC1 reference zircon (Paces and
Miller, 1993). Raw isotopic data were reduced using the Squid
program (Ludwig, 2001), and age calculations and Concordia plots
were done using both Squid and Isoplot/Ex software (Ludwig, 2003).
The results are listed in Table 2.
682
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
Fig. 3. a) Shand's Index for the granitoids of the Águas Belas granitoids. Fields after Maniar and Piccoli (1989); b) the studied granitoids in the TAS diagram with fields after Middlemost
(1997); c) The studied granitoids are projected in the Sylvester (1989) diagram. d) The composition range of the studied granitoids in the FeOtot / (FeOtot + MgO) versus SiO2 diagram.
Fields of ferroan and magnesian granitoids are from Frost et al. (2001). The fields of RRG+ CEUG (anorogenic granitoids); POG (post-orogenic granitoids) and IAG + CAG + CCG (orogenic
granitoids) after Pearce et al. (1984). e) The studied granitoids plotted in the K2O versus SiO2 diagram with fields after Peccerillo and Taylor (1976). Open triangle—syenogranites; closed
triangle—enclave.
6.2. Zircon description and results
The analyzed zircon crystals are pale yellow, with rare inclusions.
They are usually elongate, prismatic, length/width ratio ranging from
4:1 to 4:2 (Fig. 10), with length ranging from 100 µm up to 270 µm. All
of them, except the core of crystal 4 (Fig. 10), show oscillatory zoning
and many show a clear overgrowth. The contact core-overgrowth is
irregular and sharp, and the core usually shows elongate shape. The
analyzed zircons show Th/U ratios ranging from 0.2 to 0.7, which is
typical of magmatic zircons (Williams and Claesson, 1987).
Twenty three zircon grains were analyzed, totalling 26 analyzed
spots. A cluster of 14 concordant analyses yields a 206Pb/228U age of
588 ± 4 Ma (Fig. 11). The euhedral shape and the high Th/U ratio of
the grains suggest that this age must correspond to a best estimation
for the emplacement age of the Águas Belas pluton.
The analyzed sample also shows inherited zircon cores that yield
slightly discordant 207Pb/206Pb ages (Table 2). The zircon cores yield
ages of 1594 ± 13 Ma, 1895 ± 14 Ma, and 2060 ± 23 Ma. The core of the
crystal 4 (Fig. 10) yielded an age of 1594 ± 13 Ma while the rim shows
an age of 613 ± 6 Ma. The core shows no oscillatory zoning, but the rim
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
683
Fig. 4. Chondrite-normalized REE patterns (Nakamura, 1974) of the Águas Belas
granitoids.
does show. Both of them show high Th/U ratios, suggesting that at least
the zircon rim has igneous origin.
6.3. Oxygen isotopes
The oxygen isotope analyses were conducted using the SHRIMP II
in 23 spots in the same zircon spots analyzed previously for U–Pb
(Fig. 11), and results are reported in the SMOW scale. The δ18O values
lie between 6.35‰ and 10.30‰. Only spot 23.2 (Table 2), with 207Pb/
206
Pb age = 1315 ± 300 Ma, shows a significantly lower δ 18 O
value = 5.79‰. Due to being highly discordant (66%) and large age
error, this analyzed spot is not going to be taken under further
consideration.
Grain 4 shows the lowest δ18O values, 6.69‰ and 6.35‰, for core
and rim respectively. Grain 11 shows 18O/16O values of 8.19‰ and
10.01‰ for the rim and core respectively. The core of zircons, spots
11.2 and 22.1, show rounded shape and high values of 18O/16O. The
δ18O values for rims of Neoproterozoic age range from 6.69 to 10.30‰,
with average value of 8.26 ± 0.71‰. This > 2‰ variation is large and
not compatible with cogenetic rocks crystallized in a closed system.
Average δ18O (zircon) value is lower (8.23 ± 0.46‰) when the highest
(10.30‰) and the lowest (6.69‰) values are not considered. In this
case, considering whole rock silica contents, calculated average whole
rock δ18O values, following Valley et al. (1994), vary from 10.06 ±
0.46‰ to 10.30 ± 0.46‰ for SiO2 contents of 69.14% and 73.12%,
respectively, the silica range observed for the Águas Belas rocks. These
average values are consistent and compatible with high δ18O crustalderived magmas crystallized in a closed system. The highest δ18O
(zircon) values (10.01 and 11.01‰) from the Paleoproterozoic cores
are 2–3‰ higher than the δ18O (zircon) values observed for zircons of
this age studied by Valley et al. (2005), who reported that during the
Proterozoic the range of δ18O (zircon) gradually increases in a secular
change that documents maturation of the crust. The high δ18O values
of Proterozoic zircon cores of this study are compatible with high δ18O
values of (meta) sedimentary rocks.
The δ18O (zircon) values of Mesoproterozoic cores are lower (6.35‰
and 6.89‰) and can be interpreted as resulting from the exchange of
protoliths with surface waters at low temperature followed by melting
or contamination, as suggested by Valley et al. (2005) for Archaen
zircons that show δ18O values in the range 6.5–7.5‰.
7. The granitoid source and tectonic setting
Values of δ18O (zircon) lower than 7‰ recorded in the 592 ± 7 Ma
zircon grain from the studied granitoids reflect interactions between
Fig. 5. Bivariate trace element diagrams monitoring feldspar involvement in the
evolution of the Águas Belas granitoids. The fractionated vectors were built using the
partition coefficients from Villemant et al. (1981).
crustal rocks and lithospheric mantle magmas. The involvement of a
crustal component in the Águas Belas granitoids protolith is
supported by the presence of zircon grains with Paleoproterozoic
and Mesoproterozoic age and their Nd isotopic data. However, this
crustal component could be incorporated to the magma, during its
ascent through the crust.
Mesoproterozoic zircon grains with low δ18O values were probably
inherited from igneous rock originated from a protolith involving
mantle and minor crustal components. Mesoproterozoic igneous
684
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
Fig. 8. The Yb/Ta versus Y/Nb plot showing the Águas Belas granitoids plotting in
between the OIB and AIB fields.
Fig. 6. a) Multi-element chondrite-normalized plots (normalizing values from
Thompson, 1982) to demonstrate the essential differences between the Águas Belas
granitoids (a) and the average of I-type, S-type and High Ba–Sr granites (b). I-type, Stype and High Ba–Sr granites are from Tarney and Jones (1994).
rocks have not been identified so far within the PEAL Domain. Neves
et al. (2008) have determined U–Pb zircon age of 1560 ± 16 Ma for the
Cabanas pluton in the Garanhuns sub-domain, but with no clear
indication of an igneous origin for it. Van Schmus et al. (1995) had
found migmatitic garnet-gneiss with similar age near Palmeira dos
Indios, yielding an upper intercept of 1577 ± 73 Ma and lower
Fig. 7. The studied granitoids in the tectonic discriminant diagram of Pearce (1996).
WPG = within plate granite; ORG = oceanic ridge granite; Syn-COLG = syn-collisional
granite; Post-COLG = post-collisional granite.
intercept of 538 ± 34 Ma. The presence of zircons of Mesoproterozoic
age within the Pernambuco–Alagoas Domain suggests that part of its
crust should contain rocks with this age. The only well documented
Mesoproterozoic igneous suite within the Borborema Province is the
Taquaritinga orthogneisses (Sá et al., 2002), which occur within the
Transverse Domain. They show a clear A-type granite character and
yielded U–Pb zircon age of 1521 ± 6 Ma. The presence of zircon with
1560 Ma and mantle oxygen isotope value within the Águas Belas
granitoids favours the presence of juvenile Mesoproterozoic rocks in
the PEAL Domain. This hypothesis should be further investigated
because there is no oscillatory zoning in this zircon.
The Paleoproterozoic Nd TDM model age recorded in the studied
granitoids cannot support the presence of juvenile lithospheric
mantle in the Águas Belas granitoids protolith. The involved
lithosphere should have a Paleoproterozoic age otherwise. If a
juvenile Neoproterozoic lithosphere had been involved, the εNd
(0.60 Ga) value showed by the Águas Belas pluton would be much less
positive than − 12.4.
Fig. 9. Multi-element OIB-normalized plots show the geochemical distinct signatures
between the Águas Belas granitoids and the OIB.
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
685
Table 2
U–Pb and oxygen isotopic data of the sample AB-08 from the Águas Belas Pluton.
Grain.
spot
206
%
1.1
2.1
3.1
4.1
4.2
5.1
6.1
7.1
8.1
9.1
10.1
11.1
11.2
12.1
13.1
14.1
16.1
16.2
17.1
18.1
19.1
20.1
21.1
22.1
23.1
23.2
0.10
0.40
–
0.24
0.00
0.12
0.00
12.16
0.42
0.30
0.81
0.29
0.04
0.05
2.06
0.20
0.22
0.38
0.49
0.04
0.10
0.12
0.14
0.15
3.54
6.53
U ppp
Pbc
608
691
496
431
149
597
671
1136
805
654
778
390
388
560
816
694
679
528
761
692
330
597
745
241
905
250
Th
ppm
232
118
234
128
138
104
203
227
335
345
176
331
102
10
152
243
298
199
210
267
365
101
186
225
6
280
115
0.20
0.35
0.27
0.33
0.72
0.35
0.35
0.30
0.44
0.28
0.44
0.27
0.03
0.28
0.31
0.44
0.30
0.41
0.36
0.55
0.32
0.32
0.31
0.03
0.32
0.47
238
Th/
U
ppm
206
Pb⁎
(1)206Pb/238
U age
(1)207Pb/206
Pb age
% Dis
49.6
56.5
41.3
37.0
35.2
49.3
56.1
93.3
63.9
47.7
65.7
31.7
99.0
46.6
59.0
57.3
55.3
42.8
61.4
57.8
27.0
49.2
73.3
73.6
73.3
30.1
583.7 ± 5.9
584.2 ± 5.9
596 ± 6.1
613 ± 6.4
1565 ± 16
591.7 ± 7.5
598.9 ± 6.1
520.1 ± 6.8
567.5 ± 5.7
524 ± 14.0
600.2 ± 6.2
582 ± 10
1675 ± 25
595.7 ± 6.1
510.8 ± 5.3
590.8 ± 60
582.9 ± 5.9
579.9 ± 60
576 ± 5.8
598.2 ± 7.1
586.5 ± 6.3
590.6 ± 6.7
697.8 ± 7.1
1956 ± 19
561.2 ± 6.6
794 ± 14
577 ± 18
575 ± 29
597 ± 16
548 ± 27
1594 ± 13
595 ± 19
572 ± 16
671 ± 170
593 ± 24
584 ± 23
608 ± 59
585 ± 29
1895 ± 14
592 ± 17
618 ± 63
588 ± 19
606 ± 21
611 ± 29
598 ± 25
572 ± 16
604 ± 26
589 ± 19
1041 ± 29
2060 ± 23
616 ± 99
1315 ± 300
−1
−2
0
– 11
2
1
−5
29
4
12
1
1
13
−1
21
0
4
5
4
−4
3
0
49
5
10
66
(1)207Pb⁎ /
Pb⁎
±%
0.0593
0.0592
0.0598
0.0585
0.0984
0.0598
0.0591
0.0619
0.0597
0.0595
0.0601
0.0595
0.1160
0.0597
0.0604
0.0596
0.0601
0.0602
0.0599
0.0591
0.0600
0.0596
0.0740
0.1272
0.0603
0.0850
0.83
1.3
0.75
1.2
0.7
0.89
0.74
8.0
1.1
1.1
2.7
1.3
0.76
0.77
2.9
0.9
0.96
1.3
1.2
0.74
1.2
0.9
1.4
1.3
4.6
15
206
(1)207Pb⁎/
235
U
±%
0.774
0.774
0.799
0.804
3.727
0.792
0.794
0.717
0.758
0.694
0.809
0.775
4.747
0.796
0.687
0.788
0.784
0.781
0.771
0.793
0.788
0.788
1.166
6.220
0.757
1.540
1.3
1.7
1.3
1.7
1.4
1.6
1.3
8.1
1.5
2.9
2.9
2.3
1.8
1.3
3.1
1.4
1.4
1.7
1.6
1.4
1.6
1.5
1.8
1.7
4.7
16
(1)206Pb⁎/
U
±%
Err
corr
δ18
O‰
0.0948
0.0948
0.0969
0.0998
0.2747
0.0961
0.0974
0.084
0.09203
0.0847
0.0976
0.0945
0.2968
0.0968
0.08246
0.096
0.0946
0.0941
0.09347
0.0972
0.0953
0.0959
0.1143
0.3545
0.091
0.1311
1.1
1.1
1.2
1.3
1.1
1.4
1.1
2.7
1.1
1.8
1.7
1.1
1.1
1.1
1.1
1.1
1.1
1.2
1.1
1.2
1.1
1.1
1.2
1.8
1.1
1.1
.789
.618
.820
.657
.859
.832
.820
.168
.683
.930
.368
.804
.911
.811
.347
.765
.741
.634
.671
.860
.690
.796
.598
.649
.258
.116
8.04
8.72
10.30
6.69
6.35
8.56
8.35
7.45
7.04
8.61
8.44
8.19
10.01
8.67
8.41
8.55
8.74
8.67
8.26
8.07
7.81
8.27
6.89
11.01
7.57
5.79
238
Errors are 1-sigma; Pbc and Pb⁎ indicate the common and radiogenic portions, respectively. Error in standard calibration was 0.24% (not included in above errors but required when
comparing data from different mounts). (1) Common Pb corrected using measured 204Pb. % Dis = % discordant.
Flat-lying foliation is dominant in the area, including metasedimentary (Inhapi) and metaigneous (Venturosa) sequences. This flatlying foliation is always cross-cut by subvertical sinistral shear zones.
Granulitic orthogneisses from the Venturosa Sequence have U–Pb
zircon (TIMS) age of 642 ± 15 Ma (Osako et al., 2006). An elongated
E–W-trending granitic intrusion mapped in the north part of the PEAL
Domain, shows flat-lying foliation and a 206Pb/238U weighted
apparent mean age of 606 ± 8 Ma (Neves et al., 2008). This age is
interpreted as the age of the high-grade Brasiliano metamorphism
and consequently the age of the flat-lying foliation. The age obtained
for the Águas Belas pluton is similar to the 40Ar/39Ar ages (581 ± 2 Ma
and 591 ± 3 Ma) recorded by Araújo et al. (2004) for the E–Wtrending Belo Monte–Jeremoabo shear zone, within the Sergipano
Domain, and to the U–Pb zircon age (587 ± 8 Ma) for the beginning of
the transcurrent regime that produced the dextral E–W-trending East
Pernambuco shear zone (Neves et al., 2008). Ages ranging from
630 Ma to 608 Ma determined in orthogneisses and granitoids have
been used to constrain the flat-lying foliation in the Pernambuco–
Alagoas domain and in the Transversal Zone Domain (Guimarães
et al., 2004; Neves et al., 2005a,b; Neves et al., 2008).
The lack of penetrative ductile deformation within the Águas Belas
Pluton, and the E–W-trending of its main axis, suggests that it was not
intensively affected by NNE strike–slip-related deformation. It also
suggests that the emplacement occurred during the early stage of the
transcurrent tectonic regime. A similar model has been proposed by
Neves et al. (2008) for the intrusion of the NE–SW-trending
Cachoeirinha Pluton, which shows similar age to the Águas Belas
pluton (587 ± 8 Ma). However, the Águas Belas pluton shows an E–
W-trending main axis, and, as pointed out by Guimarães et al. (2004,
2009) and Neves et al. (2008), plutons intruded along E–W
transcurrent shear zones in the Transversal Zone domain, in the
North Tectonic domain and in the northern part of the Pernambuco–
Alagoas domain show younger ages (~570 Ma). The presence of E–Wtrending flat-lying foliation within the Pernambuco–Alagoas domain,
in the Jupi orthogneisses and in quartzites from Venturosa Sequence,
which occur along the Garanhuns low-angle shear zone, suggest that
the Águas Belas pluton emplacement involved activation of E–W preexisting crustal structure by the NNE-trending Limitão–Caetés
sinistral shear zones. The E–W-trending structure acted as a
continental transform fault, and was reactivated during a high-angle
tectonic regime, creating the necessary space for the intrusion of the
Águas Belas pluton. A similar model has been proposed for the
Donegal Batholith (Stevenson et al., 2008). These arguments are
consistent with the post-collisional geochemical signature of the
Águas Belas granitoids, if it is taken into account that a high-angle
tectonic regime occurred after the collisional process.
8. Conclusions
All the chemical features suggest that the Águas Belas granitoids
correspond to a transitional high-K calc-alkaline to alkaline magmatism, emplaced during the late stage of the Brasiliano orogeny, under
the control of a set of shear zone, in between the Inhapi Sequence to
the north and Neoproterozoic granitoids to the south.
The structural and geochronological data suggest that NNE–SSWtrending sinistral shear zones were initiated at ca 590 Ma, and
activated E–W pre-existing structures at the current crustal level. The
synchronicity of these shear zones allowed the dilatation needed to
facilitate the space required to the emplacement of the Águas Belas
Pluton.
The magma evolved through K-feldspar and biotite fractionation,
but lack of plagioclase fractionation, which increased the Na2O
contents in the magma promoting the later crystallization of Na-rich
amphiboles.
The U–Pb SHRIMP age associated with oxygen isotopes in zircon,
geochemical and Nd isotopic data suggest that four intervening
components: Paleoproterozoic lithospheric mantle, Paleoproterozoic
crustal rocks, Neoproterozoic supracrustal sequences, and Mesoproterozoic igneous rock were involved in the studied granitoids
magmas. The necessary heating for promoting fusion was probably
the Paleoproterozoic lithospheric mantle magmas, which invaded the
crust through the deep-seated shear zones during the transition
686
A.F. da Silva Filho et al. / Gondwana Research 17 (2010) 676–687
Fig. 10. CL images of zircon crystals. Circles indicate the position of the U–Pb and oxygen isotope analysis listed in Table 2.
between compression and extension, during the final stage of the
Brasiliano orogeny. During its emplacement, the magma may have
interacted with Paleoproterozoic and/or Neoproterozoic supracrustal
rocks and, Mesoproterozoic igneous rocks.
Acknowledgments
AFSF thanks CAPES for a post-doctoral scholarship (BEX 3534/07-3).
A grant from the PRONEX/FACEPE program (APQ-0479-1.07/06) made
possible SHRIMP analyses at the ANU-Research School of Earth Sciences
at Canberra, Australia. We are thankful to Sam Mertens and Shane
Paxton for their assistance with the sample preparation. This manuscript
has been improved by the constructive review of William R. Van Schmus
and one anonymous reviewer from Gondwana Research.
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