Petrography, geochemistry and zircon U-Pb geochronology of the Siderian-Rhyacian granitoids of NW Bacajá Domain, Amazonian Craton

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 southeastern Amazonian Craton. Understanding the diversity of these rocks in the geological record is essential to improve the evolution of knowledge of the Amazonian Craton. Thus, this work presents petrographic, geochemical, and geochronological (U-Pb LA-ICP-MS in zircon) data on granitoids of the São José Complex, Canaã Granite, Sant’Ana Granodiorite and Uirapuru Granite, that occur in the northwestern of the Bacajá Domain. São José Complex is composed of biotite tonalites and granodiorites slightly peraluminous from 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 environment prior to the Transamazonian Orogeny, formed from the melt of Archean crustal sources and amphibolitic rocks. The granitoids like Canaã Granite, Sant’Ana Granodiorite and Uirapuru Granite are composed of weakly metaluminous to peraluminous monzogranites, granodiorites with subordinate tonalites and syenogranites, with high SiO2 and K2O contents and high-K calc-alkaline to shoshonitic affinities, of ferroan I-type and A-type. The age of 2124 ± 7 Ma was obtained for the Sant’Ana Granodiorite, which may indicate its formation in syn- to post-collisional environments related to magmatic episodes of the Transamazonian Orogeny. The granodiorite was crystallized from partial melt of crustal sources derived from intermediate rocks such as tonalites and psammitic gneisses that occur in the region.

Keywords

• U-Pb Geochronology
• Granitois
• Petrogenesis
• Transamazonian orogeny