Navegando por Assunto "Sanukitoide"

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Acesso aberto (Open Access)
Afinidades petrológicas e geocronologia U-Pb em zircão de ortognaisses do Complexo Gnáissico-Migmatítico Água Azul, Terreno Sapucaia, Província Carajás.
(Universidade Federal do Pará, 2024-10-09) PINTO, Eliziane de Souza; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Água Azul do Norte area is part of the geological context of the Carajás Province, precisely in the Sapucaia Terrain, according to the recent tectonic compartmentalization proposals presented by the Granitoid Petrology Research Group (GPPG/UFPA). This region is formed by a mesoarchean orthognathic basement with TTG affinity (Água Azul GneissicMigmatitic Complex; 2.93 Ga) associated with late Mesoarchean intrusions with sanukitoid signatures (Água Azul and Água Limpa Granodiorites; 2.88-2.87 Ga), high-Ba-Sr sodic (Nova Canadá Granodiorite; 2.89-2.87 Ga) and high-K calc-alkaline (Boa Sorte Granite; 2.89- 2.85 Ga) signatures. The review of geological and petrographic data indicated that the TTG crust of Água Azul do Norte is compositionally heterogeneous and records strong evidence of progressive metamorphism and migmatization. Therefore, this work reclassifies this TTG basement as being formed by orthogneisses, which occasionally present variations to tonalitic to quartz dioritic compositions that resemble fragments of a more primitive, intensely deformed and gneissified crust. These varieties show compositional banding in an E-W direction, often disturbed by shear bands and drag folds. Considering the classification of migmatites, they have an orthognathic paleosome and leucosomes rich in Qz+Pl±Bt parallel to the banding (stromatic metatexite) and frequentely outlined by mafic aggregates (melanosome rich in biotite and hornblende). They form four compositional varieties: i) hornblende±biotite tonalitic orthogneiss (HBTnl), ii) clinopyroxene-hornblende tonalitic orthogneiss (CHTnl), iii) epidote-biotite orthogneiss quartz diorite (EBQzD) and iv) hornblende-biotite orthogneiss quartz diorite (HBQzD). They present a large proportion of mafic minerals (M'> 15%), especially biotite and hornblende, which can occur slightly stretched along the foliation plane. Plagioclase and secondary quartz are abundant and occur in the matrix or, in the case of plagioclase, as phenocrysts, while alkali-feldspar and primary quartz are practically insignificant. Whole rock geochemical analysis indicated that samples MED-120A (EBQzD) and MEP-53B (HBQzD) present moderately magnesian character, medium-K calcium-alkaline signature, relative depletion in K2O, MgO, Ba, Ni and Cr and enrichment in Na2O, Al2O3, TiO2, Fe2O3 and Zr, reflecting a certain affinity with traditional tonalite-trondhjemitic associations. The presence of many zircon crystals with igneous features preserved in these samples marks the crystallization age of the protolith at 3.06 Ga, suggesting that they are crustal fragments approximately 100 Ma older than the underlying crust (Água Azul Orthognathic Complex). MED-144 (HBTnl) exhibited a strongly magnesian character, high-K calcium-alkaline signature, high K2O/Na2O ratio and enrichment in MgO, Ba, Ni and Cr, very similar to the composition observed in sanukitoids. The U-Pb data obtained for this sample indicated a crystallization age of 2.92 Ga, similar to that observed in sanukitoids described in the Ourilândia do Norte region (Arraias Granodiorite). The other samples showed significant contents of compatible elements (e.g. Fe, Mg, Ni, Cr) and moderate contents of incompatible elements (e.g. K, Rb, Ba, Sr, Zr, Ti) and revealed an intermediate behavior between TTGs and granitoids enriched in Mg, as well as a strong affinity with the São Carlos Orthogneiss (2.93 Ga) described in the same terrain. Concordant U-Pb ages obtained for samples MED-95A (HBTnl) and EDC-28B (CHTnl) indicated acrystallization at 2.95-2.93 Ga contemporaneous with the emplacement of the Água Azul TTGs and the São Carlos Orthogneiss. The textural behavior of the quartz and mafic minerals indicates dynamic recrystallization mechanisms at intermediate to high temperatures (~500-650ºC), while the morphology observed in the migmatites (stromatic metatexitic and leucosomes with hydrated minerals) suggests that there was a low amount of melt produced and fluids participation in the partial melting process. Combined with the mineral paragenesis (Pl+Qz+Bt±Hbl±Ep), these factors point to a granitic protolith metamorphosed under amphibolite facies conditions, with the migmatization being strongly contemporaneous with the deformation and peak of the regional metamorphism described in the Carajás region (2.89 Ga; MED-95A).
Acesso aberto (Open Access)
Granodiorito Rio Maria e rochas associadas de Ourilândia do Norte – Província Carajás: geologia e afinidades petrológicas
(Universidade Federal do Pará, 2015-07-22) SANTOS, Maria Nattania Sampaio dos; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
The granitoids of sanukitoid affinity of the Ourilândia do Norte area, located near the Rio Maria-Carajás domain boundary, are associated with Rio Maria sanukitoid suite from the Mesoarchean age. In this area dioritic, quartz-monzodioritic, tonalitic and granodioritic rocks with variable proportions of amphibole and biotite were described. Contrary to what is observed in the sanukitoid rocks of the Rio Maria area, those of Ourilândia do Norte are constantly affected by deformational processes, relating to the installation of the Itacaiúnas Shear Zones. They exhibit pervasive foliation and microstructures developed under three dynamic recrystallization regimes: (1) Bulging recrystallization (300-400°C); (2) Subgrain rotation recrystallization (<500°C); (3) Grain boundary migration recrystallization (<600°C). Granitoids with sanukitoid affinities are magnesian and metaluminous and belong to medium to high potassium calc-alkaline series. They display non-collinear trends from (quartz) diorite toward granodiorite and exhibit a negative correlation for compatible elements (CaO, Fe2O3 t, MgO, TiO2, Zr, Ni, Cr and #Mg) and inverse behavior for incompatible ones (Ba, Sr), as well as Rb/Sr and Sr/Ba ratios. Moreover, they show amphibole, clinopyroxene and subordinate biotite and plagioclase fractionation. The clinopyroxene-bearing monzogranite shows trends parallel to those of sanukitoids and has a lower Sr/Ba ratio and #Mg content, due to its ferrous character, and probably does not belong to the sanukitoid series. The REE pattern of granodiorite shows a slight or absent Eu anomaly (Eu/Eu*=0.76-0.97) and moderate (La/Yb)N ratio, indicating garnet, amphibole or pyroxene fractionation. Tonalites are less depleted in HREE and have little Eu anomaly (Eu/Eu*=~0.95). Enclaves, (quartz) diorite and quartzmonzodiorite exhibit negative to positive Eu anomalies (Eu/Eu*=0.56-1.71) and a low (La/Yb)N ratio, whose horizontal pattern is similar to that of intermediate rocks from the Rio Maria area. Clinopyroxene-bearing monzogranite shows affinities for the tholeiitic series, following slightly different trends from granitoids, with a negative Eu anomaly (Eu/Eu*= 0.63-0.98) and (La/Yb)N slightly fractionated ratios. Negative Nb-Ta-Ti anomalies, associated with high (La/Yb)N and Y/Nb ratios suggest that these rocks were generated in a subduction zone from a depleted source mantle which was contaminated by fluids or melt. Analysis of the metassomatic agent nature revealed that less evolved rocks were contaminated by fluids, while granodiorites and related rocks were contaminated by melt, whose composition is similar to that of tonalite-trondhjemite-granodiorite (TTG). Enclaves, (quartz) diorite and clinopyroxene-bearing monzogranite were produced by relatively low pressures (La/Yb<1.0 GPa) and depths (<33.6 Km), with little or no residual garnet, while the other granitoids could ix have been generated under superior geothermal conditions (La/Yb=1.0-1.5 GPa; 33.6-50.5 Km) with variable proportions of residual garnet. Furthermore, these granitoids started to crystallize at depths between 30.3 and 20.2 Km and ended between 10.1 and 6.7 Km. Ourilândia do Norte sanukitoid rocks and the other analoguous intrusions of the Carajás Province show geochemical and petrogenetic affinities with high-SiO2 adakites and low-TiO2 sanukitoids. They may have originated through a one-stage process, by direct hybridization between the mantle and TTG-melt. Nevertheless, the modeling performed on Rio Maria and Karelian sanukitoids indicates that they were produced by a two-stage process, from meltmetasomatized peridotite remelting.