Recebido em 14 de setembro de 2015; aceito em 29 de abril de 2016Resumo O Domínio Iriri-Xingu, sul da Província Amazônia Central, é uma das regiões geologicamente menos conhecidas do Cráton Amazônico. Nela predominam rochas vulcânicas e granitóides paleoproterozoicos e o embasamento regional raramente aflora. Estudos petrográficos e feições de campo possibilitaram identificar três conjuntos de rochas: Granitos Tipo A (sienogranitos e quartzo-sienitos), Granitos Tipo I (monzogranitos, quartzo-monzodioritos, quartzo-monzonitos e granodioritos) e rochas vulcânicas e vulcanoclásticas do Grupo Iriri (riolitos e dacitos, e ignimbritos dacíticos, respectivamente). As idades Pb-Pb em zircão confirmam a ocorrência de pelo menos dois eventos magmáticos orosirianos nessa região: 1992-1986 Ma e 1889 Ma. Dados isotópicos Sm-Nd das rochas estudadas forneceram idades-modelo Nd T DM de 2,43 a 3,13 Ga com ε Nd(t) de -10 a -3, o que permitiu confirmar uma fonte crustal antiga para esses magmas, típica da Província Amazônia Central. Esses resultados indicam que os eventos magmáticos de 1,99 Ga e 1,89 Ga, que são comuns no Domínio Tapajós, também ocorrem no Domínio Iriri-Xingu. Contudo, apresentam fontes crustais arqueanas contrastantes com as fontes paleoproterozoicas características do Domínio Tapajós. Além disso, as idades obtidas em cristais de zircão das rochas vulcânicas do Domínio Iriri-Xingu são mais antigas que ca. 1880 Ma, habitualmente correlatas ao Grupo Iriri. Assim, este trabalho propõe uma redefinição litoestratigráfica dessa unidade, com base na ocorrência de rochas vulcânicas de ca. 1988 Ma na sua área-tipo. Palavras-chave:Província Amazônia Central; Rochas paleoproterozoicas; Grupo Iriri. AbstractThe Iriri-Xingu Domain, located in the southern Central Amazonian Province, is one of the less geologically known regions in the Amazonian Craton. It is dominated by Paleoproterozoic volcanic rocks and granitoids, and the regional basement rarely crops out. Petrographic and field data allowed distinguishing three rocks groups: A-type Granites (syenogranites and quartz-syenites), I-type Granites (monzogranites, quartz-monzodiorites, quartz-monzonites and granodiorites) and Iriri Group volcanic and volcaniclastic rocks (rhyolites and dacites, and dacitic ignimbrites, respectively). Pb-Pb zircon ages indicate at least two Orosirian magmatic events in this region: 1992-1986 Ma and 1889 Ma. Sm-Nd isotopic data provided Nd T DM from 2.43 to 3.13 Ga, and ε Nd(t) from -10 to -3, which confirm an old crustal source for these magmas, typical of the Central Amazonian Province. These results show that the 1.99 and 1.89 Ga magmatic events, which are common in the Tapajós Domain, also occur in the Iriri-Xingu Domain. However, their Archean crustal sources contrast with the Paleoproterozoic sources characteristic of the Tapajós Domain. Additionally, the zircon ages obtained in this study for the volcanic rocks of the Iriri-Xingu Domain are older than ca. 1880 Ma, which typically correlate with the Iriri Group. Thus, we propose a lithost...

ABSTRACT:The Tapajós Domain, located in the southern portion of the Amazonian Craton, is a tectonic domain of the Tapajós-Parima Province, a Paleoproterozoic orogenic belt adjacent to a reworked Archean crust, the Central Amazonian Province. This domain has been interpreted as the product of an assemblage of successive magmatic arcs followed by post-orogenic A-type magmatism formed ca. 1880 Ma-old granites of the Maloquinha Intrusive Suite. The study presented here was carried out in four granitic bodies of this suite (Igarapé Tabuleiro, Dalpaiz, Mamoal and Serra Alta) from the eastern part of the Tapajós Domain, as well as an I-type granite (Igarapé Salustiano) related to the Parauari Intrusive Suite. The A-type granites are syenogranites and monzogranites, and alkali feldspar granites and quartz syenites occur subordinately. These rocks are ferroan, alkalic-calcic to alkalic and dominantly peraluminous, with negative anomalies of Ba, Sr, P and Ti and high rare earth elements (REE) contents with pronounced negative Eu anomaly. This set of features is typical of A-type granites. The Igarapé Salustiano granite encompasses monzogranites and quartz monzonites, which are magnesian, calcic to calc-alkalic, high-K and mainly metaluminous, with high Ba and Sr contents and depleted pattern in high field strength elements (HFSE) and heavy rare earth elements (HREE), characteristic of I-type granites. The source of magma of these A-type granites is similar to post-collisional granites, while the I-type granite keeps syn-collisional signature. Most of the studied granites have ε Nd (-3.85 to -0.76) and Nd T DM model ages (2.22 to 2.46 Ga) compatible with the Paleoproterozoic crust of the Tapajós Domain. We conclude that the Archean crust source (ε Nd of -5.01 and Nd T DM of 2.6 Ga) was local for these A-type granites. KEYWORDS: