Journal of the Geological Survey of Brazil (Sep 2022)
Petrography, geochemistry and zircon U-Pb geochronology of the Siderian-Rhyacian granitoids of NW Bacajá domain, Amazonian Craton, Brazil
Abstract
Archean and Paleoproterozoic granitoids with different geochemical affinities are widely distributed in the basement of high-grade metamorphic rocks of the Bacajá Domain, which consists of Rhyacian granite-greenstone terrain with Archean-Siderian fragments, one of which is in the southeast Amazonian Craton. Understanding the diversity of these rocks in the geological record is essential to improve the evolution of knowledge in the context of the Amazonian Craton. Thus, this work presents petrographic, geochemical and geochronological data (U-Pb method in zircon) of granitoids of the São José Complex, Canaã Granite, Sant’Ana Granodiorite and Uirapuru Granite that occur in the northwest of the Bacajá Domain. São José Complex is composed of biotite tonalites and granodiorites slightly peraluminous of medium to high-K, magnesian and I-type affinities, one U-Pb zircon age was obtained at 2502 ±6 Ma which may represent a subduction magmatism in pre-collisional stage arc environments prior to the Transamazonian Orogenesis, formed from the melt of Archean crustal sources and amphibolitic rocks. The granitoids like Canãa Granite, Sant’Ana Granodiorite and Uirapuru Granite are composed of monzogranites, granodiorites slightly meta to peraluminous with subordinate tonalites and syenogranites, with high SiO2 and K2O content and high-K calc-alkaline to shoshonitic affinities, are ferroan I-type and A-type. One age of 2124±7 Ma was obtained for the Sant’Ana Granodiorite and may indicate its formation in syn- to post-collisional environments related to magmatic episodes of the Transamazonian Orogeny, were crystallized from partial melt of crustal sources derived from intermediate rocks such as tonalites and psammitic gneisses that occur in the region.
