Petrogenesis and tectonic settings of the Neoarchean A-type granitoid complex from the Carajas Province, Amazonian craton: constraints from geochemistry, SHRIMP U-Pb zircon geochronology and Hf-Nd isotopes

The Neoarchean granitoids of the Vila Jussara complex are located in the Sapucaia domain in Caraj & aacute;s Province, where they appear as a series of coalescing, sigmoidal-shaped plutons with high-angle foliations (75-85 degrees) that follow a regional east-west trend. These plutons are mainly formed of seriated biotite-hornblende monzogranite, although subordinate varieties include biotite-hornblende tonalite, biotite granite and hornblende-biotite granite. The granitoids are distinguished by their Fe* index [FeOt/(FeOt/MgO) ratio]. The biotite-hornblende monzogranites present moderate to high values of this ratio and can be characterized as oxidized and reduced ferroan A-type granites. The biotite granites and hornblende-biotite granites are porphyritic granitoids and are transitional between oxidized granites and slightly magnesian granites. By contrast, the biotite-hornblende tonalites have lower and restricted Fe* indices and magnesian characteristics. Sensitive high-resolution ion microprobe U-Pb dating gives ages of 2743 +/- 11 Ma for the oxidized biotite-hornblende monzogranites, 2745 +/- 20 Ma for the reduced biotite-hornblende monzogranites, 2742 +/- 14 Ma for the hornblende-biotite granites and 2766 +/- 9.6 Ma for the biotite-hornblende tonalites. The Nd and Hf isotopic data suggest that the magmas of the Vila Jussara suite present a slight crustal contribution with or without contamination and were derived from rocks of Meso- to Paleoarchean age (2.82 < T-DM < 3.45 Ga); the epsilon(Nd)(t) values are mostly between -3.62 and +1.55 and the epsilon(Hf)(t) values are between -4.77 and +1.78. The petrogenetic model that was used to determine the primary magmas of this suite suggests that the source rocks were geochemically similar to Mesoarchean granulites from the Cana & atilde; dos Caraj & aacute;s domain. The emplacement of Neoarchean granites occurred by multiple injections of magma, generating extensive hybridization under a transpressional/transtensional tectonic regime dominated by pure shear and resulting in a syntectonic post-collisional setting for these rocks.