Navegando por Autor "NASCIMENTO, Aline Costa do"

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Acesso aberto (Open Access)
Evolução tectono-metamórfica e petrogênese de gnaisses migmatíticos e granitoides mesoarqueanos do Subdomínio Sapucaia (Província Carajás): uma abordagem geocronólogica, isotópica e estrutural
(Universidade Federal do Pará, 2025-05-09) NASCIMENTO, Aline Costa do; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
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.
Acesso aberto (Open Access)
Petrologia magnética e química mineral dos granitoides mesoarqueanos de Ourilândia do Norte (PA)
(Universidade Federal do Pará, 2020-06-29) NASCIMENTO, Aline Costa do; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Ourilândia do Norte area is located in the midwestern portion of the Carajás province, whose tectonic segment is comprised between the Rio Maria (RMD) and Carajás domains (CD), where outcrop three main Mesoarchean (2.92-2.88 Ga) granitoids: (i) leucogranite and associated high-Ti granodiorite – are constituted by equi- to heterogranular monzogranites and associated granodiorite with high titanite contents. Both of them have biotite as an essential mafic phase, lack amphibole and host TTG basement; (ii) sanukitoids – are represented by granodiorites (equigranular, heterogranular and porphyritic), with subordinate tonalite, quartz monzodiorite and quartz diorites occurrences. These rocks are characterized by the presence of hornblende as an essential mineral and associated mafic enclaves; and (iii) trondhjemite – represented by porphyritic granitoids with fine-grained mafic enclaves. Based on magnetic susceptibility (MS) studies these granitoids were distinguished into three magnetic populations: (i) lowest magnetic values (A; MS ranging from 0.05x10-3 to 0.57x10-3 SI) – characterized by rare opaques phases, predominant sanukitoids and trondhjemite; (ii) moderate magnetic values (B; MS 0.59x10-3 to 2.35x10-3 SI) – the modal ilmenite contents prevails over magnetite, with variable proportions of sanukitoids and leucogranites; and (iii) high magnetic values (C; MS 2.35x10-3 to 17.0x10-3 SI) – characterized by the highest magnetite contents, with subordinate ilmenite occurrence as trellis and composite textural types. The leucogranites and associated high-Ti granodiorite predominate over porphyritic sanukitoid. Amphiboles classify as magnesio-hornblende, characterized by Mg/(Mg+Fe+2) ratio ≥ 0.70, and minor occurrence of ferropargasite e actinolite-hornblende. For the trondhjemite, amphibole occurs as an acessory mineral and corresponds to magnesio- hornblende and tschermakite. Biotite crystals have Fe+2/(Mg + Fe+2) ratio down 0.6 in leucogranites and associated high-Ti granodiorite, and lower values (≤ 0.4) in sanukitoids and trondhjemite. Plagioclase crystals are predominantly oligoclase, without significant compositional variations between phenocrysts and matrix, and are frequently replaced by sericite. Although there are four distinct textural types of epidote and titanite, were investigated two main textural types: the former has magmatic origin and the latter indicate late-magmatic origin. In terms of the pistacite molecule contents in epidote {Ps = [Fe+3/(Fe+3 + Al)]*100}, Ps values of 25 to 36 %, 26 to 36 % and 22 to 30 % were estimated for the leucogranites, sanukitoids and trondhjemite, respectively, along with TiO2 contents ≤ 0.137, suggesting magmatic origin. Temperature estimative based on zircon (TZr) and apatite saturations (TAp) are in the range TZr 841-990 °C and TAp 884-979 °C (leucogranite and associated high-Ti granodiorite), TZr 826-972 °C and TAp 864-886 °C (sanukitoids) and, finally, TZr 853-977 °C and TAp 909 °C (trondhjemite), which all of them are interpreted as close to liquidus, with pressure estimates in general between 100 and 280 MPa, akin to upper crust conditions. Geothermometers and barometers based on aluminium contents in amphibole indicate temperature around 738-811 °C (sanukitoids) and 779-892 °C (trondhjemite). The lower temperatures(< 800 °C) is assumed as resulted of opening magmatic system related to deformation, and denote that dynamic recrystallization may have occurred at temperatures close to solidus, indicative of a syntectonic nature. Although the leucogranites and associated high-Ti granodiorite present relative enrichment of #Fe in whole- rock, are calc-alkaline affinity granitoids, overlapping the Cordilleran granites with SiO2 > 70%, low HFSE (high field strength elements) abundances, magmatic magnetite and high MS, pointing to oxidized crystallization conditions (problably at ∆NNO+2.8). Sanukitoids varieties have FeOt/(FeOt + MgO) < 0.7 in whole-rock, amphibole and biotite, low MS, indicating less oxidized crystallization conditions (∆NNO+1.0); however, the equigranular varieties and trondhjemite probably are formed in conditions relatively close to the ΔFMQ+0.5. The lower MS and lower magnetite contents reported for the sanukitoids and trondhjemite can also be attributed to the earlier epidote formation and to the late magmatic processes, which are responsible by the magnetite instability. It is concluded that the precursor magma of the sanukitoids are hydrated (H2O > 4-7 %), whereas lower water contents in melt (H2O < 4-7 %) are suggested for the leucogranites and associated high-Ti granodiorite; and trondhjemite, as indicated by their amphibole absence and acessory amphibole contents, respectively, along with low contents of hydrated mineralogy. These results are compared to those estimated for calc-alkaline rocks of the Rio Maria suite from the Carajás province and oxidized members from other Archean to Paleoproterozoic terrains such as Baltic Belt, Sarmatian orogen (Western Europe), Closepet-type granites and high-Mg granodiorites of the Matok pluton (Limpopo Belt – South Africa).