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

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±5Ma 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±15Ma, in the leucosome of a migmatitic paragneiss. A granitic orthogneiss dated at 1991±5Ma reflects late to post-Transamazonian magmatic event. A similar age (1972±8Ma) 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 870–760Ma. Detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665Ma. Magmatic zircons with the age of 626±15Ma 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±36Ma from a deformed granodiorite dated at 2097±5Ma and the crystallization age of 625±24Ma 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.