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

Le résumé fourni par la source

The Neoarchean granitoids of the Vila Jussara complex are located in the Sapucaia domain in Carajás Province, where they appear as a series of coalescing, sigmoidal-shaped plutons with high-angle foliations (75–85°) 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 [FeO t /(FeO t /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 ε Nd ( t ) values are mostly between −3.62 and +1.55 and the ε 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 Canaã dos Carajás 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.

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