Navegando por Assunto "Archean"

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Acesso aberto (Open Access)
Petrogênese da Suíte Igarapé Gelado: implicações para o magmatismo neoarqueano da Província Carajás, Cráton Amazônico
(Universidade Federal do Pará, 2025-04-30) MESQUITA, Caio José Soares; DALL’ AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Igarapé Gelado suite (IGS) is located near the northern border of the Carajás Province, almost at its boundary with the Bacajá Domain, along the Cinzento lineament, and is intrusive in metavolcanic mafic rocks and banded iron formations. The central-eastern portion of the IGS comprises four rock varieties: tonalite to granodiorite with varying contents of biotite and amphibole, (1) with associated clinopyroxene and/or orthopyroxene (PBHTnGd) or (2) devoid of pyroxenes (BHTnGd); and monzogranites that exhibit variable biotite and amphibole content and can be (3) moderately (BHMzG) or (4) strongly (RBHMzG) reduced. The PBHTnGd shows ferrosilite and/or augite with subordinate hedenbergite. The amphiboles are K-hastingsite and, subordinately, Fe-Tschermakite in monzogranites. Biotites are ferroan, and in reduced granites show #Fe > 0.90. These micas are similar to those of alkaline to subalkaline rocks and compositionally akin of primary magmatic biotites. Plagioclase is oligoclase. The integration of thermineral chemistry;mobarometry results and thermodynamic modeling and their comparison with the paragenesis present in natural rocks improved the estimation of crystallization parameters (T, P, ƒO2, H2O), and allowed a better interpretation of magmatic evolution. The IGS granites crystallized at pressures of 550 ± 100 MPa, higher than those attributed to other Neoarchean granites in Carajás provinve. The estimated liquidus temperature for the IGS pyroxene variety is ~1000±50°C. BHTnGd and BHMzG formed within a similar temperature range to PBHTnGd, while RBHMzG had lower liquidus temperatures (≤900°C). Solidus temperatures of around ~660 °C were estimated for the four IGS varieties. The BHMzG magma evolved under conditions of low ƒO2, slightly above or below the FMQ buffer (FMQ±0.5), like those of the Planalto suite and the reduced granites of the Vila Jussara and Vila União suites of Carajás province. In the magmas of the PBHTnGd and BHTnGd varieties the oxygen fugacity attained FMQ+0.5. The RBHMzG crystallized under strongly reduced conditions equivalent to FMQ-0.5 to FMQ-1. The magmas of the monzogranitic varieties evolved with a H2O content of ≥4 wt%, attaining 7 wt% in the case of the reduced monzogranites. This is comparable to, or slightly exceeding, the levels typically attributed to the Neoarchean granites of Carajás province (≥ 4% wt%). In contrast, the variety with pyroxene has a water content (~4 wt%) like that of Café enderbite and Rio Seco charnockite from Carajás province, and Matok Pluton from Limpopo belt. Based on the chemical composition, the rocks from IGS are ferroan, reduced to oxidized A-type-like granites, akin to other Neoarchean granite suites from the Carajás province. The IGS are younger than the 2.76-2.73 Ga Neoarchean granites from the Carajás province. A crystallization concordia age of ~2.68 Ga was obtained by U-Pb SHRIMP in zircon for the RBHMzG variety, and similar upper intercept ages were furnished by the other IGS varieties, except for ages of ~2.5 Ga that resemble the ages of the IOCG Salobo deposits associated with reactivation of the Cinzento Lineament. Tmineral chemistry;he deformation of the IGS rocks was influenced by shear zones linked to that lineament, forming elongated bodies with varied foliation. These zones facilitated the migration and deformation of magmas from the final crystallization stages until their complete cooling, characterizing a syntectonic process. This syntectonicity is associated with the inversion of the Carajás Basin, and the younger crystallization age of these rocks indicates that the inversion occurred up to 2.68 Ga, extending the previously estimated interval (2.76– 2.73 Ga). The IGS displays negative to slightly positive values of εNd(t)(-2.86 to 0.18) and εHf(t)(-3.3 to 0.1), and Paleoarchean to Mesoarchean TDM ages [Nd-TDM(2.98-2.84) and Hf-TDM C (3.27-3.12)]. The positive values of εNd(t) and εHf(t) for the RBHMzG variety, suggest possible juvenile contribution or contamination in the source of its magma. The IGS rocks come from the melting of 19% (PBHTnGd) or 14% (BHTnGd) of contaminated mafic granulite, - and from melting of 9% (BHMzG) and 7% (RBHMzG) of a tholeiitic mafic granulite. The area of occurrence of the IGS is marked by hydrothermalism and mineralizations that locally modified the composition of rocks and minerals, allowing the leaching of REE and Y that changed the composition of some samples of BHMzG approaching them of (false) A1- subtype granites. In addition, these processes were responsible for zircon alteration, which resulted in grains showing enrichment of U, Th, and LREE, and massive textures, that furnished upper intercept U-Pb ages, contrarily to the zircon crystals of the RBHMzG variety that preserved primary characteristics and presented Concordia ages.
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).