Geologia e petrografia do Complexo São José, Região Sul de Uruará, Porção Oeste do Domínio Bacajà, Província Transamazonas

Abstract

Based on field data and petrographic analyses, integrated with a review of previous studies, this study re-evaluates the spatial distribution, internal structure, and contact relationships of the São José Complex, whose protolith is dated at 2.50 Ga, and reinterprets the petrological and tectonic context of this unit, located in the southern portion of Uruará, Pará State, geologically situated in the northwesternmost sector of the Bacajá Domain, within the south-central part of the Transamazonian Province, Amazonian Craton. The São José Complex, previously interpreted as a preserved igneous unit, is composed mainly of biotite tonalites and biotite granodiorites, with subordinate granites commonly crosscut by aplitic dikes, the São José Complex is here reinterpreted and a new geological map is proposed. Nine petrographic varieties of metagranitoids have been identified: (i) hornblende-bearing metatonalites, including biotite-hornblende metatonalite (BHTn) and hornblende-biotite metatonalite (HBTn); (ii) biotite-bearing metagranitoids, including biotite metatonalite (BTn), biotite metagranodiorite (BGd), and biotite metamonzogranite (BMzG); (iii) garnet-bearing granitoids, represented by garnet-biotite metatonalite (GBTn) and garnet-biotite metagranodiorite (GBGd); and (iv) muscovite-bearing metagranodiorites, including biotite-muscovite metagranodiorite (BMGd) and muscovite-biotite metagranodiorite (MBGd). Additionally, amphibolite lenses and BIF xenoliths were described. Structurally, the São José Complex shows low-strain domains with weak deformation and high-strain zones close to major shear zones, which are characterized by NW–SE trending mylonitic foliation dipping 60–80° / NE. The foliation trajectory transects the unit, suggesting structural continuity with adjacent lithostratigraphic units. Aerogeophysical imagery reveals a prominent NE–SW-trending lineament (interpreted as a shear zone) that crosscuts the São José Complex and truncating the regional NW–SE shear zones. The geological context and available data, particularly the protolith age of 2.50 Ga, support the interpretation that these rocks are metamorphic rather than preserved igneous bodies, as initially proposed. The mineral assemblage of the metagranitoids, plagioclase +quartz +biotite ±alkali feldspar ±hornblende ±garnet ±muscovite, supports a metamorphic origin under amphibolite-facies conditions. However, in QAP diagrams, the metagranitoids plot along a trend consistent with fractional crystallization, suggesting that their tonalitic protoliths evolved through a calc-alkaline granodioritic series. This interpretation is supported by the presence of hornblende in several varieties and implies hornblende±plagioclase fractionation. The garnet-bearing tonalites and muscovite-bearing granodiorites may have originated from more evolved protoliths, possibly involving sedimentary contributions. In terms of tectonic setting, the protoliths of this unit were likely formed in an Archean island-arc environment (~2.50 Ga), analogous to the rocks of the Uruará Orthogneiss, and were later metamorphosed during the collisional peak of the Transamazonian Orogeny (~2.10 Ga), i.e., ~400 Ma after the formation of their protoliths. Due to regional-scale similarities, it is proposed that the São José Complex be grouped within the same tectonic association as the Uruará Orthogneiss