Navegando por Autor "OLIVEIRA, Marcelo Augusto de"

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Caracterização geológica, petrográfica e geoquímica do Trondhjemito Mogno e Tonalito Mariazinha, Terreno Granito-Greenstone mesoarqueano de Rio Maria, SE do Pará
(2010-06) GUIMARÃES, Fabriciana Vieira; DALL'AGNOL, Roberto; ALMEIDA, José de Arimatéia Costa de; OLIVEIRA, Marcelo Augusto de
The Mogno Trondhjemite is one of the largest TTG units of the Rio Maria Granite-Greenstone Terrane (RMGGT). It was considered as representative of a second generation of Archean TTG in that terrane. However, field, petrographical, geochemical, and geochronological studies demonstrate the existence of two distinct TTG units in its main area of occurrence. For the dominant TTG unit, showing NW-SE to EW foliation and distributed in the eastern and western domains of the mapped area, the term Mogno Trondhjemite was maintained. The new TTG unit, which occurs in the center-western domain and displays a NE-SW to NS dominant trend, is named as Mariazinha Tonalite. Hence, the original area of occurrence of the Mogno Trondhjemite was significantly reduced. Moreover, Pb-Pb zircon ages indicate that the Mogno Trondhjemite and the Mariazinha Tonalite are neither coeval, nor related to the second generation of TTGs of the RMGGT. The two TTG studied units are composed of epidote-biotite tonalites and trondhjemites of the high Al2O3 type, with geochemical characteristics similar to those of the typical Archean TTG granitoids. Compared with the Archean TTG units of the Xinguara region, the Mogno Trondhjemite geochemical characteristics are transitional between those of the Caracol Tonalitic Complex and the Água Fria Trondhjemite, while those of the Mariazinha Tonalite approaches those of the Caracol Tonalitic Complex. The studies undertaken in the Mogno Trondhjemite and associated Archean granitoids demonstrated that the TTG series of the RMGGT are more diversified and complex than previously admitted. The domain of the second Archean generation of TTG of the RMGGT was drastically reduced and a new Archean TTG association, the Mariazinha Tonalite, was identified and characterized.
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Geologia, petrografia e geoquímica do Granodiorito Sanukitoide Arqueano Rio Maria e rochas máficas associadas, leste de Bannach-PA
(Universidade Federal do Pará, 2005) OLIVEIRA, Marcelo Augusto de; ALTHOFF, Fernando Jacques; http://lattes.cnpq.br/1004206862799097; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
New occurrences of the Archean Rio Maria Granodiorite (RMGD) situated to the east of Bannach town, immediately to the west of it’s type-area, in the Rio Maria Granite-Greenstone Terrain (RMGGT), southeastern Amazonian craton, were studied. The typical granodiorites, wich are dominant in the RMGD, include systematically mafic enclaves, as observed in other areas. However, in the studied area there are also mafic and intermediate rocks (IMR) with the RMGD. The Rio Maria Granodiorite is intrusive in the greenstone belts of the Andorinhas Supergroup. Field relationships between the RMGD and Archeans tonalites and trondhjemites (TTGs) are not conclusive being admitted that both have similar ages. Leucogranites correlated with the Xinguara and Mata Surrão Archean granites and the Paleoproterozoics Musa and Bannach granites of the Jamon Suite are intrusive in the RMGD. The dominant rocks of the RMGD are quite uniform, with, medium-to coarse-evengrained texture, and granodioritic or subordinate monzogranitic composition. The GDrm shows generally a gray color with greenish shades due to it’s strongly saussuritized plagioclase, white the monzogranites displays a rose gray color. The Rio Maria Granodiorite display generally a weak or striking WNW-ESE foliation due to mafic minerals and, sometimes, enclaves orientation. Two domains of IMR were identified: In the main domain, located near Bannach town, are exposed mostly quartz diorites and quartz monzodiorites; in the second domain situated in the center of the area, a minor occurrence of layered rocks was described. The dominant rocks in the larger body are mesocratic, dark-green, sometimes with rose tones rocks, with fine-to coarseevengrained texture. The layered rocks, interpreted as cumulatic rocks are inequigranular with a remarkable concentration of generally quadratic or short prismatic coarse amphibole crystals, enveloped by leucocratic intercumulus material. The RMGD and IMR rocks show similar textural and mineralogical aspects. The RMGD is formed dominantly by epidote-biotite-hornblende granodiorite (EpBtHbGd) with subordinate epidote-hornblende-biotite granodiorite (EpHbBtGd), and epidote-biotite-hornblende monzogranite (EpBtHbMzG). The mafic enclaves included in the RMGD are epidote-biotitehornblende diorites (EpBtHbDr) transitioning to monzodiorities. In the main mafic body epidotebiotite-hornblende quartz diorite (EpBtHbQzD) varying to epidote-biotite-hornblende quartz monzodiorite (EpBtHbQzMzD) are dominant. The layered rocks are enriched in mafic minerals, mostly amphibole, compared to monzodiorites and granodiorites. The RMGD and IMR follow the calc-alkaline series trend in some diagrams. However, they display lower Al2O3 and CaO and larger MgO, Cr and Ni contents compared to calc-alkaline series, approaching geochemically the sanukitoids series. The patterns of rare earth elements of different rocks are similar, with pronounced enrichment in light rare earth elements (LREE) and strong to moderate fractionation of heavy rare earth elements (HREE) (La/Ybn=11,92 a 44,38). However, the (La/Yb)n ratio is lower in the EpBtHbQzD and EpBtHbQzMzD (La/Ybn=17,20 a 22,81), compared to the RMGD (La/Ybn=15,52 a 44,38). Compared to the RMGD and IMR, the layered rocks are relatively enriched in HREE (La/Ybn=11,92 a 14,37), probably in response to amphibole accumulation. The RMGD and IMR display some geochemical affinities, but also significant difference, and are interpreted as cogenetic but not comagmatic rocks. Geochemical data show that there is a ompositional gap between both the RMGD and IMR and the layered rocks and mafic enclaves, suggesting distinct processes for the origin of the latter group of rocks. Field aspects and petrographic and geochemical caracteristics denote that the RMGD and IMR are cogenetic rocks. However, geochemical data suggest that the intermediate rocks and the RMGD are not related by a fractional cristalization process. The wide distribution of granodiorities and relatively local occurrence of do not also favor this hypothesis. It is concluded that the intermediate rocks derived from similar sources than those of RMGD, but probably result of a higher degree of melting, being both cogenetic, but not comagmatic rocks. The layered rocks are genetically related to the sanukitoid association, but they had a particular magmatic evolved involving participation of crystal accumulation processes.
Acesso aberto (Open Access)
Petrogênese e evolução magmática da Suíte Sanukitóide Rio Maria, Terreno Granito – Greenstone de Rio Maria, Cráton Amazônico
(Universidade Federal do Pará, 2009-08-25) OLIVEIRA, Marcelo Augusto de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; 2158196443144675
The Archean sanukitoid Rio Maria suite yielded zircon ages of ~2.87 Ga and is exposed in large domains of the Rio Maria Granite-Greenstone Terrane, southeastern Amazonian craton. It is intrusive in the greenstone belts of the Andorinhas Supergroup, in the Arco Verde, Mariazinha, and Caracol tonalite, and Mogno trondhjemite. Archean potassic leucogranites, Água Fria trondhjemite, and the Paleoproterozoic granites of Jamon Suite are intrusive in the rocks of the Rio Maria suite. The dominant rocks have granodiorite to subordinate monzogranitic compositions, with minor proportions of intermediate quartz-diorites or quartz-monzodiorites rocks, in addition to mafic end members occurring as layered rocks or as enclaves. The Rio Maria suite has clear geochemical characteristics of Sanukitoids rocks (high Mg#, elevated Cr and Ni contents, LREE enrichment, and high Ba and Sr contents relative to typical calc-alkaline series). The significant geochemical contrasts between the occurrences of the granodiorites in different areas suggest that this unit corresponds in fact to a granodioritic suite of rocks derived from similar but distinct magmas. In spite of their broad geochemical similarities, granodiorites, intermediate rocks, and mafic enclaves show some significant differences in their REE patterns and in the behavior of Rb, Ba, Sr, and Y. The granodiorites and intermediate rocks are not related by fractional crystallization and the internal evolution of intermediate rocks were leaded by fractionation of amphibole + biotite ± apatite, whereas granodiorites evolved by fractionation of plagioclase + amphibole ± biotite. The layered rocks should have been derived from the granodiorite magma by accumulation of 50% of amphibole (dark layer) and 30% of amphibole ± plagioclase accumulation (gray layer). Modeling and geochemical data suggest that mafic enclave and granodiorite magmas were originated at different depths and should have mingled during their ascent and final emplacement and a limited interaction would explain the relatively uniform geochemical behavior of each rock variety and the distinct trends displayed by their rocks in different modal and geochemical diagrams. These contrasts between granodiorites and mafic enclaves are reflected in the behavior of the Sr and Y, which are generally seen as good indicators of the pressure of melt formation. The behavior of these elements, observed in different sanukitoid rocks from Archean terranes worldwide, indicates that the geochemical and modal contrasts observed between the granodioritic (granodiorites) and monzonitic (mafic enclaves) sanukitoid series are a general feature of these rocks and their origin is strongly dependent of the pressure of magma generation and, as a consequence, that the nature of the series could indicate the approximate depth of formation of its magma. The petrogenesis of the Rio Maria suite requires melting of a modified mantle extensively metasomatized by addition of about 30% TTG-like melt to generate the granodiorite (21% of melt) and intermediate magmas (24% of melt), and ~20% TTG-like melt in the case of mafic enclave magma (9% of melt). Our modeling results indicate that an active subduction tectonic setting was present in the Rio Maria terrane in between 2.98 to 2.92 Ga to generate the TTG magmas and the proposed metasomatism of the mantle by these magmas, before the melting process responsible for the origin of the sanukitoid magmas. A tectonothermal event at ~2.87 Ga, possibly related to a mantle plume, causing the partial melting of the metasomatized mantle and generating the Rio Maria sanukitoid magmas. In the rocks of the Rio Maria suite, the mineral assemblage is dominated by amphiboleplagioclase-biotite and epidote minerals, all of inferred magmatic origin, pyroxenes being notably absent. Textural and compositional criteria indicate that amphibole is a principal mineral on the liquidus of all the Rio Maria rocks. To derive crystallisation conditions, the phase assemblages, proportions and compositions of the natural rocks were compared with experimental works carried out on similar magma compositions. The comparison shows that the parental magmas were water-rich, with more than 7 wt% dissolved H2O near liquidus, with crystallisation temperature in the range 950-680°C. The Mg/(Mg+Fe) ratios of both amphibole and biotite indicate fO2 conditions in the range NNO + 0.5 up to NNO + 2.5, therefore pointing to both water-rich and oxidizing conditions for sanukitoid magmas. Analyses of amphibole aluminium content in cumulate rocks, indicate in addition a high pressure crystallisation stage, around 700-1000 MPa, prior to emplacement in the upper crust at around 200 MPa. Sanukitoid magmas share therefore two of the principal characteristics of modern arc magmas, elevated redox sate and volatile contents, which suggest that they may have formed in a geodynamic environment broadly similar to present-day subduction zones.