Geochemistry, geochronology, and origin of the Neoarchean Planalto Granite suite, Carajás, Amazonian craton: A-type or hydrated charnockitic granites?

New whole-rock geochemistry and LA-MC-ICPMS and Pb-evaporation geochronological data were obtained on zircon from the Neoarchean Planalto suite granites and associated charnockitic rocks of the Canaã area of the Carajás province, eastern Amazonian craton, Brazil. The Pb-evaporation ages of three samples from the Planalto suite are around 2730 Ma (2733 ± 2 Ma, 2731 ± 1 Ma and 2736 ± 4 Ma), whereas U–Pb LA-MC-ICPMS concordia ages obtained for these samples are 2729 ± 17 Ma, 2710 ± 10 Ma, and 2706 ± 5 Ma, respectively. An orthopyroxene quartz gabbro associated with the Pium complex and Planalto suite yielded a U–Pb concordia age of 2735 ± 5 Ma, interpreted as its crystallization age. The Planalto suite granites and the charnockitic rocks associated with the Mesoarchean Pium complex were probably crystallized at 2730 ± 10 Ma. The Planalto granites have ferroan character and are similar geochemically to reduced A-type granites. In previous studies, they have been classified as such, despite the fact that they are syntectonic. The tectonic setting and the association between the Planalto suite and charnockitic series led us to classify these biotite–hornblende granites as hydrated granites of the charnockitic series. The Planalto suite and the Neoarchean charnockitic magmas were more probably derived by partial melting of mafic to intermediate tholeiitic orthopyroxene-bearing rocks similar to those of the Pium complex. At 2.76 Ga, upwelling of asthenospheric mantle in an extensional setting propitiated the formation of the Carajás basin. Later on, at ca. 2.73 Ga, heat input associated with underplate of mafic magma induced partial melting of mafic to intermediate lower crustal rocks, originating the Planalto and charnockitic magmas. The emplacement of these magmas occurred under active regional stress and resultant major shear zones found in the Canaã dos Carajás area. The close association between the Planalto suite and charnockitic rocks suggests that they are similar to the high temperature granite magmatism found near the borders of Precambrian domains with different ages and tectonic evolution or in their zone of interaction.

► 2.73 Ga syntectonic granites of the Carajás province, Amazonian craton are discussed.
► They are associated with charnockitic rocks and similar to ferroan, A-type granites.
► Are these rocks A-type granites or hydrated facies of charnockitic series?
► They were derived by high temperature partial melting of Mesoarchean granulites.
► The granites were emplaced under active regional stress and differ from A-type.