Géochronologie U-Pb par ablation laser et ICP-MS (LA-ICP-MS ...

Journal of South American Earth Sciences 25 (2008) 285–297
www.elsevier.com/locate/jsames
U–Pb ages of plutonic and metaplutonic rocks in southern
Borborema Province (NE Brazil): Timing of Brasiliano
deformation and magmatism
Sérgio P. Neves a, *, Olivier Bruguier b , Delphine Bosch c ,
José Maurício Rangel da Silva a , Gorki Mariano a
a Departamento de Geologia, Universidade Federal de Pernambuco, 50740-530 Recife, Brazil
b ISTEEM, Service ICP-MS, Université de Montpellier II, 34095 Montpellier, France
c Laboratoire de Tectonophysique, Université de Montpellier II, 34095 Montpellier, France
Abstract
The Borborema Province of northeastern Brazil is divided into three main domains: northern, central, and southern. Several U–Pb zircon
ages of plutons and orthogneisses became available in the recent years in the central and northern domains, but similar results are scarce
in the southern domain. This study reports U–Pb dates for single zircon grains from one orthogneiss (Jupi orthogneiss) and two plutons
(Cachoeirinha syenitic pluton and Cabanas granite) south of the East Pernambuco shear zone system (EPSZ). The results provide geochronological
constraints on the timing of deformation and magmatism in this part of the southern domain and allow correlations with
the central domain. The Jupi orthogneiss was emplaced and deformed during development of the regional flat-lying foliation. A
206 Pb/ 238 U weighted apparent mean age of 606 ± 8 Ma is interpreted as the crystallization age of the protolith of the orthogneiss and
consequently the age of high-grade Brasiliano metamorphism. The NNE-trending Cachoeirinha pluton is only locally affected by
strike-slip deformation, whereas the ENE-trending Cabanas granite is intensely affected by deformation related to the EPSZ. The
587 ± 8 Ma and 573 ± 4 Ma ages of the Cachoeirinha pluton and Cabanas granite, respectively, bracket the main period of activity
of the EPSZ. Tectonomagmatic activity in the study area is similar to the age of Brasiliano events in the central domain, north of
the EPSZ. In addition, xenocrystic zircons in the Jupi orthogneiss and Cabanas granite are interpreted as inherited from Paleoproterozoic
source rocks, suggesting the presence of widespread reworked old crust in the southern domain, similar to the central domain. These
results support the idea that the central and southern domains belonged to the same crustal block before the onset of the Brasiliano
orogeny.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Laser ablation ICP-MS; Zircon U–Pb geochronology; Neoproterozoic plutons; Brasiliano orogeny
Resumo
A Província Borborema (Nordeste do Brasil) é dividida em três grandes domínios: norte, central e sul. Várias datações U–Pb em zircão
foram adquiridas nos últimos anos nos domínios norte e central, mas são escassas no domínio sul. Neste estudo são apresentadas idades
U–Pb de zircões de um ortognaisse (ortognaisse Jupi) e de dois plutons (Cachoeirinha, de composição sienítica, e Cabanas, de composição
granítica) localizados ao sul da zona de cisalhamento Pernambuco leste (ZCPE). Estes resultados são os primeiros a serem reportados
para eventos deformacionais e magmáticos nesta parte do domínio sul e permitem estabelecer correlações com o domínio central ao
norte da ZCPE. O ortognaisse Jupi foi alojado e deformado durante o desenvolvimento da foliação regional de baixo ângulo. Uma idade
media 206 Pb/ 238 U de 606 ± 8 Ma é interpretada como a idade de cristalização do protólito do ortognaisse e, consequentemente, do
* Corresponding author. Tel.: +55 081 327 18240; fax: +55 081 327 18 234.
E-mail address: serpane@hotlink.com.br (S.P. Neves).
0895-9811/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jsames.2007.06.003