Navegando por Assunto "Granitoids"

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Origem e evolução do complexo granitoide neoarqueano de vila Jussara: implicações para a evolução crustal da província Carajás
(Universidade Federal do Pará, 2022-07-15) SILVA, Fernando Fernandes da; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
New information on the geology, combined with the acquisition of geochemical and isotopic data (U-Pb, Hf and Nd) from the Vila Jussara Suite, are presented in order to discuss a petrogenetic model for the Neoarchean granitoids of the Carajás Province. This suite appears as a series of coalescing plutons with sigmoidal and elongated shapes, in the E-W direction, which follow the regional trend. The central areas of the plutons are slightly deformed, while the marginal portions have a mylonitic appearance and are delimited by sinistral shear zones belonging to the transcurrent system of the Itacaiúnas Shear Belt. These granitoids present a broad compositional spectrum, with four individualized lithotypes: (i) biotite-hornblende serial monzogranite, which is subdivided into oxidized and reduced types; (ii) biotitehornblende tonalite; (iii) biotite monzogranite; and (iv) porphyritic granite (hornblende biotite monzogranite/granodiorite). The geochronological data U-Pb and Pb-Pb in zircon provided an age of crystallization of 2.74 Ga for the granitic and porphyritic granite varieties, and for the biotite-hornblende tonalite variety, an age of 2.76 Ga. The isotopic data of Nd and Hf suggest that the magmas of the Vila Jussara suite are not juveniles [εNd (-3.5 to 1.5) and εHf (-1.2 to 3.5)] and were derived from rocks of Mesoarchean age (TDM > 3.0 Ga). The petrogenetic model adopted to generate the primary magmas of this suite admits as source rock the Mesoarchean granulites from the Ouro Verde area of the Canaã dos Carajás subdomain. Field relationships, geochemical and isotopic data suggest that the granitoids that make up the Vila Jussara Suite are not formed from a single parental magma, but by multiple magma injections generating extensive hybridization. Its magmas were placed along pre-existing structures under a transtensional tectonic regime dominated by pure shear in a post-collisional syntectonic context.
Acesso aberto (Open Access)
Petrografia e evolução crustal da porção sul do Domínio Pacajá, Cráton Amazônico: evolução policíclica do Mesoarqueano ao Riaciano
(Universidade Federal do Pará, 2025-08-13) NERI, Arthur Santos da Silva; DALL’ AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The integration of field, petrographic, mineralogical, geochemical, geochronological (U-Pb in zircon, monazite, and titanite), and isotopic data (Sm-Nd in whole rock and Lu-Hf in zircon) undertaken in the southern portion of the Bacajá Domain enabled the identification and characterization of new granitoid and charnockitic units previously encompassed within the Cajazeiras Complex. These discoveries allowed a redefinition of the regional stratigraphy and advancing the understanding of the crystallization conditions, origin, and evolution of magmatic and metamorphic orthoderived rocks. A long-lived Rhyacian magmatic event (~70 Ma) was recognized, beginning around 2.12 Ga and lasting until 2.05 Ga. During this interval, the following units were identified: Bandeirante (2.12 Ga, εHf(t) = -6.5 to -4.6, εNd(t) = -3.40); and Alto Rio Preto (2.10-2.06 Ga, εHf(t) = -10.2 to -6.3, εNd(t) = -8.96 -2.80) granites; Maravilha (2.09 Ga, εHf(t) = - 9.2 to -8.2, εNd(t) = -3.01 to -1.91) and Serra Azul (2.07 Ga, εHf(t) = -8.8 to -5.8, εNd(t) = -6.44 to -4.71) charnockites; Bernardino granite (2.05 Ga, εNd(t) = -6.71). Geochemically, the units are mostly high-K calc-alkaline and magnesian (Alto Rio Preto and Bernardino granites, Serra Azul charnockite), transitioning to calcic or alkali-calcic and ferroan (Bandeirante granite and Maravilha charnockite, respectively). They range from metaluminous to weakly peraluminous, except the Bernardino granite, which is strongly peraluminous. The Nd-Hf isotopic integration indicates a crustal source with strongly negative epsilon values and Archean model ages, with a marked contrast to crystallization ages, pointing to long crustal residence times. These granitoids were generated by the collision between the Bacajá and Carajás domains in a late- to post-collisional setting during the Transamazonian Orogeny. Crustal thickening and subsequent delamination are interpreted as the main mechanisms responsible for partial melting and generation of these magmas. The Nd-Hf isotopic signatures reveal a coherent crustal compartmentalization between the Bacajá, Carecuru and Lourenço (Amazonian Craton) and Bauolé-Mossi domains (West Africa Craton), suggesting that these segments were juxtaposed during the amalgamation of the Columbia supercontinent. The Alto Rio Preto granite is composed of epidote-bearing granites and granodiorites-tonalites. This granite was emplaced at pressures of 0.4-0.7 GPa and temperatures between 949 and ~640 ºC, evolved under oxidizing conditions (NNO±0.5 to ±1), with initial water contents of ~2-6 wt%. The preservation of magmatic epidote results of a complex interaction between generation and emplacement pressures, oxidizing conditions and water content in the magma, combined with low density and viscosity that facilitated rapid magma ascent (4-5 km/year) through the crust, preventing complete epidote dissolution. Field and petrographic data suggest that this granite represents a syntectonic intrusion, with geochemical affinities with high-K calc-alkaline series. The parental magma of the monzogranitic facies was derived from dehydration melting of a basaltic source at 0.99 GPa and 865 °C leaving an amphibolite residuum. These granitoids represent an example of crustal reworking of lower mafic crust and do not contribute to net crustal growth in the collisional zone between the Bacajá and Carajás domains. The Maravilha charnockite comprises two petrographic associations: (i) monzonite-granite-charnockite and (ii) granodiorite-monzogranite, with or without igneous orthopyroxene and fayalite + quartz. The (i) association crystallized at temperatures between 1052 and ~680 °C, and evolved under reducing (FMQ±0.5), with ≤3 wt% initial water contents. The (ii) crystallized at temperatures between 918 and ~680 °C and evolved under oxidizing conditions (NNO±0.5), with ~4 wt% initial water contents. Both associations were emplaced at pressures between 0.3 and 0.6 GPa The Serra Azul charnockite consists of tonalites, granodiorites, and rare granites, with or without igneous orthopyroxene. These rocks were emplaced at pressures 0.3-0.6 GPa, temperatures between 1078 and ~700 ºC, and evolved under oxidizing conditions (NNO±0.7 to ±2), with initial water contents ~ 2-3 wt%. Thermodynamic data indicate that fayalite is restricted to low pressures (≤0.3 GPa) and reduced conditions (FMQ -2 to -0.6), but it can crystallize under water-rich conditions (2.3 to 6.2 wt%, possibly up to 9 wt%). In contrast, orthopyroxene can crystallize over a wide pressures range (0.1-1 GPa), from reduced to oxidizing conditions (FMQ-2 to NNO+2.5), and under moderate water contents (~5.2 to 6.5 wt%). The Cajazeiras Complex comprises tonalitic to monzogranitic orthogneisses crystallized at 2.97-2.94 Ga, followed by Pb-loss/metamorphism at 2.80–2.81 Ga and Paleoproterozoic metamorphism 2.21-2.01 Ga. These rocks show geochemical affinities with sanukitoid s.l., representing the oldest sanukitoid magmatism in the Amazonian Craton and the second oldest worldwide. The Nd-Hf data (εNd(t) +0.65; εHf(t) +0.5 to +2.5) suggest a juvenile contribution and short crustal residence time, with model ages close to the crystallization age. The discovery of these rocks implies that the mantle was already metasomatized in the Mesoarchean and opens possibilities for the presence of other typical Archean rocks in the basement of the domain. These orthogneisses were metamorphosed under upper amphibolite to granulite facies. The metamorphic peak was marked by the assemblage clinopyroxene-amphibole-biotite-quartzmagnetite- ilmenite-melt, under conditions of ~0.52–0.55 GPa/760–790 °C at ~2.21 Ga. Cooling toward the solidus occurred at ~ 2.10-2.08 Ga, and retrograde metamorphism is represented by the amphibole-biotite-quartz-magnetite-ilmenite-H₂O assemblage, developed under ~0.40–0.48 GPa/600–650 °C at ~2.01 Ga.
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).