The Archean granulite-enderbite complex of the northern Carajás province, Amazonian craton (Brazil): Origin and implications for crustal growth and cratonization

Abstract

The central portion of the Canaã dos Carajás domain (Ouro Verde area) exhibits a peculiar scenario involving two units of orthopyroxene-bearing sodic rocks: (i) the Mesoarchean Ouro Verde felsic granulite with protolith crystallization and metamorphism ages of 3.05–2.93 Ga and 2.89–2.84 Ga, respectively, and (ii) the Neoarchean Café enderbite, composed of tonalites, trondhjemites and scarce quartz diorites that crystallized at 2.75–2.73 Ga and show syntectonic character. While the orthopyroxene in the felsic granulites was formed by breakdown of primary biotite during metamorphism, in the enderbitic rocks, this mineral was formed by crystallization of a hot water-poor magma at deep crustal levels. This terrane evolved in three important geodynamic stages: (1) at 3.05–2.93 Ga, TTG crust was generated by partial melting of LILE-enriched basalts in a N–S subduction setting; (2) from 2.89 to 2.84 Ga, in a collisional setting, large volumes of anatectic granites formed and contributed to crustal thickening, which triggered granulite-facies ultrahigh-temperature metamorphism in the TTG crust, forming the Ouro Verde felsic granulite; and (3) in the Neoarchean, at 2.75–2.73 Ga, the lowermost mafic crust was delaminated during crustal thickening, causing crustal underplating followed by partial melting of Mesoarchean mafic granulites, which was responsible for the origin of the enderbitic magma. This area was subjected to a transpressional tectonic regime, leading to the development of plutons (E–W-trending) amalgamated linearly and emplaced along ancient suture zones (ductile-brittle transition). Lu-Hf isotope data of magmatic zircon cores from the Mesoarchean felsic granulite show Hf-TDM2 values of 3.44–3.15 Ga and εHf(t) values between −1.7 and 3.0, which suggest juvenile sources. The Neoarchean enderbites present Hf-TDM2 ages of 3.46–3.29 Ga and lower εHf(t) values (between −4.8 and −1.9), which indicate a longer crustal residence time for these rocks. All these findings lead us to consider the central portion of the Canaã dos Carajás domain as exhumed lower crust, and the tectonic juxtaposition of anatectic granites, enderbites and high-grade metamorphic rocks suggests that the Ouro Verde area represents middle and deep exposure levels of the same crust.