Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/185
Comunicações Geológicas (2014) 101, Especial I, 325-329
IX CNG/2º CoGePLiP, Porto 2014
ISSN: 0873-948X; e-ISSN: 1647-581X
Geochemistry and gechronology of syn-collision to syntranscurrence Ediacaran transalkaline granites from the PEAL
domain, Borborema Province, NE Brazil
Geoquímica e geocronologia de granitos transalcalinos
Ediacaranos sin-colisionais a sin-transcorrentes do domínio
PEAL, Província Borborema, NE Brasil
A. F. da Silva Filho1*, I. P. Guimarães1, E. Dantas2, L. M. Cocentino1, D. R. Lima1,
E. Rufino1
Artigo Curto
Short Article
© 2014 LNEG – Laboratório Nacional de Geologia e Energia IP
Abstract: The Borborema Province is the western part of a major
late Neoproterozoic mobile belt that extends from Brazil through NW
Africa in pre-drift reconstructions. It has been divided into four
tectonic domains. The Pernambuco-Alagoas (PEAL) domain occurs
along the SE part of the Borborema Province. It contains the largest
granitic batholiths of the Borborema Province. Syn-collision, late to
post-collision and syn-transcurence suites occur within the northern
part of the PEAL domain. Their geochemical signatures show that
the studied suites can be divided into; (1) I-type, magnesian series,
cordilleran granitoids and (2) A2-type ferroan series granitoids.
Geochemical signatures associated to the Nd isotopic signature,
points to a Paleoproterozoic crust/mantle component within these
rocks, reworked during the Ediacaran amalgamation of West
Gondwana. The whole set of data suggest that the studied suites were
emplaced during different stages of the Brasiliano orogeny, a
transition between active margin and within-plate tectonic setting,
which commonly occur at the final stages of an orogenesis.
Keywords: Transalkaline, Granites, Neoproterozoic, Gondwana.
Resumo: A Província Borborema é a parte oeste de um cinturão
móvel que se extende do Brasil até o NW da África em reconstruções
pré-drift. Foi dividida em quatro domínios tectônicos. O domínio
Pernambuco-Alagoas (PEAL) está localizado na parte sudeste desta
província e contém os maiores batólitos graníticos da mesma. Suites
sin- e tardi- a pós-colisionais, e suítes sin-transcorrência ocorrem na
parte norte do domínio PEAL. Elas apresentam assinaturas
geoquímicas que nos permite dividi-las em granitos tipo-I, série
magnesiana e cordillerano, e em granitos tipo-A2, da série ferrosa.
Assinatura geoquímica associada a assinatura de Nd sugere a
existência
de
componente
crustal/mantélica
de
idade
Paleoproterozóica, retrabalhado durante o amalgamento de
Gondwana Oeste durante o Ediacarano. O conjunto de dados sugere
que as suítes estudadas foram posicionadas durante diferentes
estágios da orogênese Brasiliana, numa transição entre ambientes
tectônicos de margem ativa para intra-placas.
Palavras-chave: Trans-alcalino, Granitos, Neoproterozoicos,
Gondwana.
1
Departamento de Geologia, UFPE, 50739 Recife, Brazil.
Instituto de Geociências, UnB, Brasília, Brasil.
*
Corresponding author / Autor correspondente: [email protected]
2
1. Introduction
The Borborema Province (Fig. 1a) is the western part of a
major late Neoproterozoic mobile belt that extends from
Brazil through NW Africa in pre-drift reconstructions. This
province resulted from convergence and collision among the
West African, Congo-São Francisco, and Amazonia land
masses about 600 Ma (Van Schmus et al., 2008). It has been
divided into four tectonic domains (Van Schmus et al.,
2008); Northern, Transverse Zone, Pernambuco-Alagoas
(PEAL) and Sergipano domains The PEAL domain occurs
along the SE part of the Borborema Province. It contains the
largest granitic batholiths of the Borborema Province. The
PEAL is comprised by a collage of various units with ages,
within the interval 0.52 to 2.40 Ga. The Nd TDM model
ages identified within the PEAL domain (Fig. 1b) requires
that part of their units protoliths should have a
Mesoproterozoic or younger component, although many
gneisses also show a Paleoproterozoic or Arquean
component. The PEAL domain is an area comprised by
three sub-crustal domains (Silva Filho et al., 2014),
Garanhuns, Água Branca and Palmares. This paper deals
with the geochronological and geochemical characterization
of Ediacaran granitic suites (Fig. 1c) from the Garanhuns
sub-domain.
2. Geological setting
The Garanhuns sub-domain (Fig. 1b) comprises (Silva Filho
et al., 2008) Rio Una sequence (garnet-sillimanite-gneisses,
migmatized greywackes, quartz-feldspar gneisses and calcsilicates), orthogneisses, tholleiitic metamafics, and granitic
plutons. These units show Nd TDM model age between 1.8
Ga and 2.7 Ga. The Garanhuns sub-domain is cut by the
sinistral strike-slip shear zones: Capoeiras, Limitão-Caetés
and Rio da Chata, and they bounded by Itaíba and Palmares
shear zones. Rio da Chata and Palmares shear zones show
magnetometric geophysical anomalies. Dioritic plutons also
occur along these shear zones.
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collision stage show a weak flat-lying foliation. Those
emplaced during D3 are called syn-transcurrence, and they
crosscut D2 structures in the country rocks and does not
show planar or linear structures related to D2. We have
classified the studied suites into the following groups.
3.1. Syn-collision suites (610-630 Ma)
This group is represented by São Pedro and Jurema suites.
The Jurema suite shows elongate shape. It is comprised by
tonalites and quartz-diorites, coarse-grained, bearing quartz,
plagioclase, alkaline feldspar, biotite and garnet. The São
Pedro suite is comprised by stocks, sills and sheets of
equigranular tonalites, diorites, sienogranites and quartzdiorites. They are equigranular, medium to fine grained,
diorites, quartz-diorites, monzodiorites and tonalites. The
mineralogy is comprised by biotite, amphibole, pyroxene,
magnetite, sphene, K-feldspar, plagioclase, apatite and
quartz. They follow the contact between orthogneisses and
Rio Una sequence, but they also occur intruded into the Rio
da Chata shear zone, coinciding with a strong
magnetometric anomaly, suggesting limit between crustal
blocks. Both diorites and sienogranites are intruded within
orthogneisses, following a flat-lying S3 foliation. SHRIMP
U-Pb in zircon data for these diorites yielded an age of ca.
610 Ma (Brito Neves, personal communication).
3.2. Late to post-collision suites (590-580 Ma)
Fig. 1. a) The tectonic domains of the Borborema Province, according to
Van Schmus et al. (1995). 1- Cenozoic Sedimentary Covers. .b) PE-AL
crustal sub-domains according to Silva Filho et al. 2014. c) Simplified
geologic map of the studied area (Fig.1a). 1 - Studied granitoids; 2 Brasiliano migmatites (Ferreira costa); 3 - Peraluminous granites; 4 High-K calc-alkaline granitoids; 5 - Supracrustal rocks; 6 Paleoproterozoic orthogneisses and migmatites; 7 - Shear zones (SZ) and
8- Thrust faults.
Fig. 1. a) Os domínios tectônicos da Província Borborema, segundo Van
Schmus et al. (1995). 1= Coberturas sedimentares cenozoicas. b)
Domínios crustais do PE-A, de Silva Filho et al. (2014). c) Mapa
geológico simplificado da área estudada (Fig. 1a). 1 - Granitóides
estudados; 2 – Migmatitos Brasilianos; 3 - Granitos Brasilianos
Peraluminosos; 4 - Ganitóides cálcio alcalinos de alto-K; 5 –
Metassedimentos; 6 - Ortognaisses e migmatitos Paleoproterozóicos; 7 –
Zonas de Cisalhamentos e 8 - Falhas de empurrão.
3. Field relationship and petrography
Regional surveys within PEAL and Sergipano domains
have shown that Brasiliano orogeny is characterized by
three stages of deformations, where the main
compressional stage (D2) which is related to a flat-lying
foliation (S2), was transposed by D3 deformation that
generated a high-angle foliation (S3) and related
transcurrence. The study suites, emplaced during operation
of the D2, are called syn-collisional, and they show very
penetrative S2, while those emplaced during late- to post-
This group is represented by Alagoinhas and
Cachoeirinha suites. The Alagoinhas suite crops out over
an area of 80 km2, bounded by shear zones, and intruded
into Paleoproterozoic orthogneisses, and Neoproterozoic
metassediments. It shows three main facies, porphyritic
granodiorite, porphyritic sienogranite and equigranular
sienogranite. The K- feldspar phenocrysts from the
porphyritic sienogranite show length up to 5 cm. The
matrix is comprised by amphibole, biotite, quartz and
plagioclase. Mafic enclaves reach up to dozens meters
long and are quite common. They show granodioritic
composition and magmatic flow structure. Neves et al.
(2005) have identified textures typical of deformation
along both borders, east and west, and have related the
emplacement of this pluton to the activity of the
neighbouring shear zones. TIMS U-Pb in zircon data
have been obtained for this suite yielding an age of 581 ±
3 Ma. The Cachoerinha pluton is located in the northern
limit of the Garanhuns sub-domain, intruded also into
Paleoproterozoic orthogneisses and metassediments.
Neves et al. (2005) have showed that it was intruded
during shortening, directed to NW. They show
composition ranging from quartz-syenites, sienogranites,
charnoquites and diorites, slightly porphyritic and
isotropic, with perthitic microcline as phenocrysts. Field
relationships between syenites and the diorites suggest
magma mixing during its evolution. The matrix from the
syenites and from the diorites are comprised by biotites,
pyroxenes, quartz, opaque, sphene, microcline, zircon,
plagioclase, perthite, apatite, epidote and allanite. TIMS
U-Pb in zircon data have been obtained for this suite
yielding an age of 587 ± 1 Ma.
Syn-collision to syn-transcurrence granitoids
3.3. Syn-transcurrence suites (570-560 ma)
The Panelas pluton (Fig. 1c) is intruded into orthogneisses
and granites, between Canhotinho and Ribeirão shear
zones, both of them sinistral. It is comprised by very
coarse grained porphyritic granodiorites, and dioritic
enclaves. The granodiorites are comprised by plagioclase
phenocrystals, and the matrix is comprised by microcline,
quartz, biotite, sphene, plagioclase, epidote, opaque,
apatite and zircon. LA-ICPMS U-Pb in zircon data have
been obtained for this Panelas pluton yielding an age of
560 ± 4 Ma. Santa Luzia pluton is emplaced close to the
Rio da Chata shear zone, and is comprised by biotiteamphibole quartz-monzonites, containing high content of
sphene. TIMS U-Pb in zircon data have been obtained,
yielding an age of 573 ± 5 Ma.
4. Whole-rock geochemistry
Syn-collision suites – They are mainly transalkaline
suites (Middlemost, 1997) (Fig. 2a), and are ferroan series
granites (A-type granites) (Frost et al., 2001) (Fig. 2b).
They are K2O-rich and most of them fall in the field for
shoshonitic suites in the diagram of Peccerillo & Taylor
(1976) (Fig. 2c). The samples plot into the field for WPG
granites and into the field for VAG + Syn-COLG in the
diagrams of Pearce et al. (1984) (Figs. 3a and 3b).The syncollisional suites are very rich in REE, and show a deep Eu
anomaly (Fig. 4a). They show a spidergram with a quite
flat slope pattern, and troughs at Nb, Ta, Sr, P and Ti (Fig.
4b).
327
Late to post-collision suites – They are transalkaline
suites according to Middlemost (1997) (Fig. 2a), and are
split into the field of ferroan series (A-type granite) and
into the field of magnesian series (Cordilleran granites),
FeO(FeO+MgO) vs. SiO2 diagram (Frost et al. ,2001)
(Figs.2b). They are K2O-rich and plot into the field for
shoshonitic suites of the Peccerillo & Taylor (1976) (Fig.
2c). They plot into the field for VAG + Syn-COLG in the
diagrams of Pearce et al. (1984) (Figs. 3a and 3b).Their
REE patterns are characterized by negative Eu anomalies
(Fig. 4a). Their spidergrams patterns show a weak
fractionation of LILE related to the HREE (Fig. 4b).
Syn-transcurrence suites – The samples are
transalkaline suites in the Middlemost (1997) diagram
(Fig. 2a), and plot into the field for A-type granites and
into the field for cordilleran granites in the Frost et al.
(2001) diagrams (Figs. 2b). They plot only into the field
for shoshonitic suites of the Peccerillo & Taylor (1976)
(Fig. 2c). The samples plot into the field for WPG granites
and into the field for VAG + Syn-COLG in the diagrams
of Pearce et al. (1984) (Figs. 2-A and 2-B), suggesting that
their syn-collisional geochemical signatures were inherited
from their protolith, or that the shear zones to which they
are related had also transpressional kynematics. They show
a wide REE pattern envelope suggesting that the REE
were fractionated during the magmas evolution (Fig. 4a).
They show similar spidergrams, which are characterized
by high enrichment in LILE, and troughs in the elements
Nb, Ta, Sr, P and Ti, and fractionation between LILE and
HREE Tb, Tm and Yb (Fig. 4b).
Fig. 2. A) The studied granitoids plot in TAS diagram, with fields after Middlemost (1997); B) The composition range of the studied granitoids in the
FeOt/(FeOt+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 Maniar & Piccoli (1989); C- The studied granitoids in the
K2O vs SiO2 diagram, with fields after Piccerilo & Taylor (1976).
Fig. 2. A) Os granitoides estudados plotados no diagrama TAS, com os campos de Middlemost (1997); B) A variação composicional dos granitoides
estudados no diagrama FeOt/(FeOt+MgO) versus SiO2. Os campos dos granitoides ferrosos e magnesianos são de Frost et al. (2001). Os campos de
RRG+CEUG (granitoides anorogênicos), POG (granitoides pós-orogênicos) e IAG+CAG+CCG (granitoides orogênicos) de Maniar & Piccoli (1989); COs granitoides estudados no diagrama K2O vs SiO2, com os campos de Piccerilo & Taylor (1976).
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A. F. da Silva Filho et al. / Comunicações Geológicas (2014) 101, Especial I, 325-329
Fig. 3. Trace elements for the study granitoids in the tectonic discriminant diagrams of (A) Pearce (1996) and (B) Pearce et al. (1984). Syn-COLG = syncollisional granites; VAG = volcanic-arc granites; WPG = within-plate granites; ORG = oceanic ridge granites; Post-COLG = post-collisional granites.
Symbols as in Figure 1.
Fig. 3. Elementos traços para os granitoides estudados nos diagramas discriminantes de (A) Pearce (1996) e (B) Pearce et al. (1984). Syn-COLG =
granitos sin-colisionais; VAG = granitos de arco vulcânico; WPG = granitos intra-placa; ORG = granitos de cadeias oceânicas; Post-COLG = granitos
pós-colisionais. Símbolos como na figura 1.
within these rocks, reworked during the Ediacaran
amalgamation of Gondwana; 2) Part of the samples from the
syn-collision and syn-transcurrence suites, and the whole set
of samples from late to post-collision suites, plot into the
field for VAG + Syn-COLG, which has been interpreted as
that for granites associated to island arc or to continental arc.
However, a WPG signature/component has been identified
so far in some studied suites, suggesting they have a
component related to an extensional tectonic setting, a
component which was inherited from a stage of basin
formation. This stage has been described by Silva Filho et
al. (2014). The whole set of data, suggest that the studied
suites were intruded during the transition between active
margin and within-plate tectonic setting of the Brasiliano
orogeny. It commonly occurs at the final stages of an
orogeny. We recorded a rough correspondence between age
of the plutons and chemical signature, where the majority of
the younger plutons plots into the A-type field.
Acknowledgments
We are indebted to the Brazilian Geological Survey, which
supported part of this work, to the CNPq that funded the
lab work through various grants, and to Randy Van
Schmus for two decades of proficuous cooperation.
Fig. 4. A- Chondrite normalized REE plots for the studied granitoids.
Chondrite values from Sun (1980). B- Spidergram patterns normalized to
the values suggested by Thompson (1982) for the studied granitoids.
Fig. 4. A- Os ETR normalizados pelo condrito para os granitoides
estudados. Valores de condrito de Sun (1980). B- Padrões Spidergram
normalizados para os valores sugeridos por Thompson (1982) para os
granitoides estudados.
5. Discussion and conclusions
The geochemical signatures divided the studied suites into:
(1) I-type, magnesian series, cordilleran granitoids and (2)
A2-type ferroan series granitoids. Geochemical data
associated to the Nd isotopic signatures (Silva Filho et al.,
2002) suggest: 1) Paleoproterozoic crust/mantle component
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