The Planalto Suite is located in the Canaã dos Carajás Domain of the Carajás Province in the southeastern part of the Amazonian Craton. The suite has Neoarchean age (~2.73 Ga), ferroan character and affinity with A-type granites. Magnetic petrology studies allowed the distinction of two groups: (1) Ilmenite granites devoid of magnetite and showing low magnetic susceptibility (MS) values (MS between 0.6247x10-3 and 0.0102x10-3 SI; average of 0.1522x10-3); (2) Magnetite-ilmenite-bearing granites which display comparatively higher but still moderate MS values (between 15.700x10-3 and 0.8036x10-3 SI; average of 5.1717x10-3). Textural evidence indicates that amphibole, ilmenite, titanite, and, in the rocks of Group 2, also magnetite formed during magmatic crystallization. However, titanite chemical composition suggests that it was re-equilibrated by subsolidus processes. The amphibole varies from potassian-hastingsite to chloro-potassian-hastingsite and shows Fe/(Fe+Mg) >0.8. Biotite also shows high Fe/(Fe+Mg) ratios and is classified as annite although relatively enriched in Al compared to the annite end member. Plagioclase porphyroclasts are oligoclase (An25-10) and the grains of the recrystallized matrix display oligoclasic or albitic composition (An9-2). Mineral chemistry, magnetic petrology and whole rock geochemistry indicate that the dominant group 1 granites of the Planalto Suite were formed under reduced conditions below the FMQ buffer. The group 2 granites crystallized under more oxidizing conditions on or slightly above the FMQ buffer. Pressures of 900-700 MPa for the origin and of 500-300 MPa for the emplacement were estimated for the Planalto magmas. Geothermometers suggest initial crystallization temperatures between 900 °C and 830 °C and water content in the magma higher than 4 wt %. The mineralogical comparison between the Planalto Suite and the Archean subalkaline Estrela Granitic Complex of the Carajás Province reveals strong compositional analogies indicating that they were probably formed under similar conditions. The amphibole and biotite compositions of Planalto and Estrela granites are relatively enriched in Al being comparable with those of the Neoarchean Matok Pluton of the Limpopo Belt. They differ using the same criteria of the Proterozoic rapakivi A-type granites. On the other hand, in terms of Fe/(Fe+Mg) ratio, the Planalto and Estrela granites approach the reduced Mesoproterozoic rapakivi granites and the reduced to moderately oxidized Paleoproterozoic granites of, respectively, the Velho Guilherme and Serra dos Carajás suites and differ from the oxidized granites (Jamon Suite) of the Carajás province and also of Matok pluton. It is concluded that the Planalto Suite and similar Neoarchean granites of the Carajás Province differ in mineralogical characteristics and crystallization parameters of some classic examples of A-type granites and, except for its reduced character, they are akin to the Neoarchean Fe-K and Mg-K granitoids of the Limpopo Belt, as exemplified by the Matok granitoids. This indicates that the collisional setting of Carajás and Limpopo exerted strong influence in the nature of the Neoarchean granitoid magmas.
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