Evolução tectono-metamórfica e petrogênese de gnaisses migmatíticos e granitoides mesoarqueanos do Subdomínio Sapucaia (Província Carajás): uma abordagem geocronólogica, isotópica e estrutural

Abstract

The Sapucaia Subdomain, located between the Rio Maria Domain and the Canaã dos Carajás Subdomain, exhibits a Mesoarchean lithostratigraphy that includes greenstone belts, TTG suites, migmatized gneisses, sanukitoids, potassic granites, and "hybrids." This study presents a description of the main migmatitic structures of the basement within this subdomain and proposes the individualization of the Caracol, Colorado, Água Azul and São Carlos orthogneisses, grouping them into the Caracol Gneiss-Migmatitic Complex. Intruding this complex and the Sapucaia greenstone belt sequence, the Água Fria Trondhjemite represents a second generation of sodic magmatism, along with the Mg-rich granodiorites of the Água Limpa Sanukitoid Suite and the Xinguara Potassic Granite. The migmatites exhibit features indicative of in situ and in-source syn-anatectic melting, characterized by stromatic metatexites, net-structured metatexites, schollen, schlieren diatexites, and rare occurrences of patch metatexites. The paleosome is composed of orthogneiss and amphibolite, while the leucosome is quartz-feldspathic and the melanosome is biotite-rich. The unsegregated neosome is represented by a fine-grained granodiorite. Anatexis occurred under upper amphibolite-facies conditions (~650–700°C). The orthogneisses of the Caracol Complex are metagranitoids with high SiO2 and Na2O contents, low MgO, and strong REE fractionation. The sanukitoids of the Água Limpa Suite follow a calc-alkaline trend, enriched in Mg, Ni, Cr, and LILEs. Despite being younger, the Água Fria Trondhjemite exhibits geochemical affinity with the gneisses but with higher K2O content. The Xinguara Granite is calc-alkaline, rich in SiO2 and K2O, with pronounced negative Eu anomalies, indicating a crustal origin. Geochronological data indicate protolith crystallization of the gneisses between 2.95–2.93 Ga, with regional metamorphism between 2.89–2.84 Ga, coeval with the granulites of the Carajás Province. The sanukitoids of the Água Limpa Suite and the Água Fria Trondhjemite date to 2.87 Ga, followed by the Xinguara Granite at 2.86 Ga. Isotopic data from the orthogneisses reveal positive ƐHf(t) and ƐNd(t) values (+0.65 to +3.9), with Hf-TDM C and Nd-TDM model ages between 3.21 to 2.98 Ga, suggesting a juvenile source. The sanukitoids show ƐHf(t) and ƐNd(t) values ranging from –3.31 to +1.76, model ages from 3.28 to 2.91 Ga, δ18O values between 5.0 and 7.6‰, and feldspar Pb compositions with μ > 10, indicating a mantle source contaminated by crustal material. The Água Fria Trondhjemite exhibits ƐHf(t) and ƐNd(t) values ranging from +1.14 to +3.59, with Hf-TDM C model ages of 3.05 to 3.21 Ga. The Xinguara Granite has a Nd-TDM model age of 2.94 to 2.86 Ga, with ƐNd(t) values between +1.32 and +2.55. The temporal proximity between mantle extraction and the crystallization age of these granitoids suggests a rapid crustal growth process in the region. Geochemical data indicate that the melt responsible for the high (La/Yb)N ratio gneiss group derived from the melting of non-enriched metabasalts, previously transformed into garnet-amphibolite. Sources compositionally similar to the average Archean metabasalts from the Sapucaia and Identidade Greenstone Belts could generate such melts, though at different degrees of partial melting (25–30% or 10–15%). The low (La/Yb)N ratio gneiss-forming melt could also be derived from a similar source but without garnet. The sanukitoid melt resulted from 19–20% partial melting of a mantle source enriched by 32% of a TTG-like melt within the garnet stability field. The Água Fria Trondhjemite formed from 5–10% partial melting of metabasalts, whereas the Xinguara Granite resulted from different degrees of melting of sources similar to the older gneisses. Experimental petrology suggests that the sanukitoids crystallized at 1000–970°C in the liquidus stage and 700°C in the solidus stage, with crystallization pressures of 900–600 MPa and emplacement pressures of 200–100 MPa. These rocks exhibit mineralogy indicative of crystallization under oxidizing conditions (NNO +0.3 to +2.5) and high-water content (H₂Omelt > 6–7%). The Mesoarchean evolution of the Sapucaia Subdomain occurred in three main phases: (1) >3.0 Ga, formation of the primitive felsic crust; (2) between 2.95–2.92 Ga, formation of the Caracol Complex gneisses; (3) 2.89–2.84 Ga, crustal thickening during sinistral transpressive tectonic associated with exhumation and metamorphism of the TTG basement. Crustal stabilization allowed for the formation of younger sanukitoid and TTG magmas (Água Fria Trondhjemite). The ascent of these magmas supplied heat for the melting of regional basement metagranitoids, leading to the formation of anatectic granites. During this stage, gneissic foliation was obliterated by deformation and intrusion of younger granitoids. The integration of the data suggests that tectonic processes facilitated the generation of both crustal and mantle-derived magmas at the end of the Mesoarchean in the Sapucaia Subdomain. It can be inferred that crustal growth in the Sapucaia Subdomain was initially controlled by mantle plumes associated with vertical tectonics, similar to observations in the Pilbara and Dharwar cratons. However, unlike the Rio Maria Domain, the dome-like structuring of the gneissic basement in this subdomain was intensely obliterated by the action of sinistral transpressive tectonics (non-coaxial deformation), forming sigmoidal bodies with an E-W orientation.