Rhyacian magmatism at the southern Bacajá Domain: implications for the crustal evolution of the SE Amazonian Craton and Columbia assembly

Collisional orogenesis represents one of the most complex geodynamic processes, leading to the formation of diverse granitoids, including charnockites and strongly peraluminous granites. The coexistence of I-A and S-type granites in these settings reflects crustal thickening and the extreme thermal conditions of orogenic belts. However, the nature, timing, and tectonic setting of the Rhyacian magmatism in the SE Amazonian Craton remain poorly understood. This study addresses this gap by integrating geological mapping, petrography, whole-rock geochemistry, U-Pb geochronology, and Nd-Hf isotopic studies conducted in the southern portion of the Bacajá Domain, a Paleoproterozoic collisional orogen in the SE Amazonian Craton. Our results identify previously unrecognized Rhyacian granitic and charnockitic rocks, formerly assigned to the Mesoarchean Cajazeiras Complex: (i) 2.12 Ga high-K calc-alkaline Bandeirante Granite (εHf_(t) = -6.5 to -4.6, εNd_(t) = -3.40); (ii) 2.10 Ga to 2.07 Ga calc-alkaline to high-K calc-alkaline Alto Rio Preto Granite (εHf_(t) = -10.2 to -6.3, εNd_(t) = -8.96 to -2.84); (iii) 2.09 Ga ferroan Maravilha Charnockite (εHf_(t) = -9.2 to -8.2, εNd_(t) = -3.01 to -1.91); (iv) 2.06 Ga magnesian Serra Azul Charnockite (εHf_(t) = -8.8 to -5.8_, εNd_(t) = -6.41 to -4.71); and (v) 2.05 Ga strongly peraluminous Bernardino Granite (εNd_(t) = -6.71). Overlapping ages suggest a prolonged magmatic activity (∼70 Ma). These rocks are mostly calc-alkaline and magnesian but vary to calcic or alkali-calcic and ferroan. Whole-rock geochemistry, zircon U–Pb–Hf, and whole-rock Nd isotopes point to a collisional origin for the magmatic rocks with extensive reworking of Archean sources and limited mantle contribution. We propose a two-stage geodynamic model: (1) collision between the Archean Bacajá basement and pre-collisional island arcs with the Carajás Province (∼2.12–2.10 Ga), leading to significant crustal thickening and the generation of small syn-collisional plutons; (2) the thickened crust becomes unstable, leading to crustal delamination and the generation of late- to post-collisional magmas (2.09–2.05 Ga). Compiled zircon U–Pb–Hf data reveals crustal reworking and juvenile input patterns similar to the Guiana Shield and West African Craton, supporting the hypothesis of their juxtaposition during the Columbia assembly.