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

Precambrian Research 149 (2006) 197–216
Timing of crust formation, deposition of supracrustal sequences,
and Transamazonian and Brasiliano metamorphism in the East
Pernambuco belt (Borborema Province, NE Brazil):
Implications for western Gondwana assembly
Sérgio P. Neves a,∗ , Olivier Bruguier b , Alain Vauchez c , 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
Received 21 July 2005; received in revised form 10 January 2006; accepted 21 June 2006
Abstract
The main structural feature of the central domain of Borborema Province (NE Brazil) is a network of dextral and sinistral
shear zones. These shear zones rework an older, regionally developed, flat-lying foliation in orthogneisses and supracrustal belts,
which in the East Pernambuco belt was formed under amphibolite facies conditions. This study reports LA-ICP-MS U–Pb zircon
ages of metaigneous and metasedimentary rocks aiming to constraint the pre-transcurrent tectonothermal evolution in the Eastern
Pernambuco domain. Ages of 2125 ± 7 and 2044 ± 5 Ma in a mafic layer of banded orthogneiss are interpreted as the age of the
protolith of the orthogneiss and of high-grade Transamazonian metamorphism, respectively. The latter age is consistent with the
occurrence of low Th/U, metamorphic zircon xenocrysts, dated at 2041 ± 15 Ma, in the leucosome of a migmatitic paragneiss. A
granitic orthogneiss dated at 1991 ± 5 Ma reflects late to post-Transamazonian magmatic event. A similar age (1972 ± 8 Ma) was
found in rounded zircon grains from a leucocratic layer of banded orthogneiss. Ages of detrital zircons in a paragneiss sample indicate
derivation from sources with ages varying from the Archean to Neoproterozoic, with peak ages at ca. 2220, 2060–1940, 1200–1150
and 870–760 Ma. Detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665 Ma. Magmatic
zircons with the age of 626 ± 15 Ma are found in the leucosome of a migmatitic paragneiss and constrain the age of the Brasiliano
high-temperature metamorphism. A lower intercept age of 619 ± 36 Ma from a deformed granodiorite dated at 2097 ± 5 Ma and the
crystallization age of 625 ± 24 Ma of the felsic layer of banded orthogneiss also confirm the late Neoproterozoic metamorphism.
These results show that the present fabric in basement and supracrustal rocks was produced during the Brasiliano orogeny.
Paleoproterozoic ages reported in this study are similar to those found in other sectors of the Borborema Province, the Cameroon
and Nigeria provinces, and the São Francisco/Congo craton. They show the importance of the Transamazonian/Eburnean event
and suggest that these tectonic units may have been part of a larger, single continental landmass. Likewise, similarities in post-
Transamazonian metamorphic and magmatic events in the Borborema, Nigeria and Cameroon provinces suggest that they shared a
common evolution and remained in close proximity until the opening of the Atlantic Ocean.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Laser ablation ICP-MS; Zircon U–Pb geochronology; Neoproterozoic belts; Transamazonian orogeny; Brasiliano orogeny
∗ Corresponding author. Tel.: +55 81 2126 8240; fax: +55 81 2126 8236.
E-mail address: serpane@hotlink.com.br (S.P. Neves).
0301-9268/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.precamres.2006.06.005