Navegando por Assunto "Granulitos"

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Caracterização petrográfica, geoquímica e geocronológica U-PB das rochas de alto grau metamórfico do Complexo Tartarugal Grande, sudeste do Escudo das Guianas, Amapá
(Universidade Federal do Pará, 2016-10-26) PAIVA, Hanna Paula Sales; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
The Tartarugal Grande Complex is represented by a high rock metamorphic association degree of Paleoproterozoic with Archean relics, which occurs on the northern edge of the Amapá Block, in the context of Maroni-Itacaiúnas Province, southeast of the Guyana Shield. In this region, the Tartarugal Grande Complex meets gneiss and granulite rocks, dominated enderbitic and charnockitics types, forming elongated rocks and marked by lineament NW-SE direction, characterized as transcurrent and thrust shear zones. This unit is formed by an intricate combination of high-grade metamorphic rocks and this study aimed to characterize these rocks petrographically, geochemically and geochronology discussing the processes in this metamorphic terrain. Petrographic analyzes identified five types of rocks classified as charnockitic granulite, charnoenderbitic granulite, enderbitic granulite, mafic granulite and leucogneisses Migmatization features as neossomes also present in felsic granulites (charnockitics, enderbitics and charnoenderbitics) and gneisses. The felsic granulites are the dominant rocks in the area, while the mafic granulites occur as smaller rocks, metric dimensions, embedded in other granulites and gneisses. The leucognaisses are commonly associated with enderbitic/charnockitic granulites, showing sudden contacts with these rock types. The lithogeochemical studies in these rocks indicated that the Tartarugal Grande Complex predominance of acid rock with silica content between 61 and 75%, and peraluminous, due to the presence of minerals such as biotite, garnet and cordierite. The mafic granulites are dominantly basic types (SiO2 between 48 and 55%) with high Fe2O3 levels (12 to 26%), MgO (5 to 19%) and CaO (2 to 12%). In geochemical classification diagrams felsic granulites and leucognaisses are located in granite field, while the mafic granulites plots in gabbro field. In AFM diagram, the felsic granulites have characteristics of collisional calc-alkaline suite and mafic granulites are basaltic types of tholeiitic suite. In the multi-element diagrams felsic granulites out more significant anomalies of Ti and P, in addition to the strong negative anomaly of Nb, characteristic of subduction environments. The mafic granulites shows, mostly signed with sub-horizontal pattern. For the rare earth elements (REEs), felsic granulites at moderate enrichment of light REEs, for heavy REEs with low Eu anomalies (ratio Eu/Eu* = 0.19 to 5.51). The mafic granulites had a lower degree of fractionation and recorded insignificant Eu anomalies (ratio Eu/Eu* = 0.44 to 1.07). The leucogneisses shows very similar to the felsic granulites signature, but have different genesis. In the discrimination diagrams of tectonic environments, it was established magmatic arc environment related to the subduction zone. U-Pb geochronological analyses in situ zircon crystals by LA-ICP-MS done in charnoenderbitic granulite, enderbitic granulite, garnet–biotite leucogneisse and charnockitic granulite, provided average ages of 2045 ± 14 Ma, 2084 ± 7.9 Ma, 2617 ± 25 Ma and 2671 ± 10 Ma respectively. These results represent the formation age of the protoliths of these rocks. Ages obtained by other studies by Sm-Nd whole rock-garnet between 2.02 and 1.98 Ga indicate a high grade metamorphic event near the age placement of plutons. The parageneses characteristics of the rocks found in the search area are represented by: mesopertitic Mc + Qtz + Pl + Opx + Bt (charnockitic granulite); Pl + Qtz + mesopertitic Mc + Opx ± Bt (charnoenderbitic granulite); Pl + Qtz + mesopertitic Mc + Opx + Bt ± Cpx ± Hbl (enderbitic granulite); Pl (An60) + Opx + Cpx + Hbl (mafic granulite) and; Qtz + Mc + Pl ± Bt ± Grt ± Crd (leucogneisses) and these associations indicate that the rocks was subjected to conditions of regional metamorphic granulite facies in temperature conditions between 780 and 850°C and pressure between 5 and 7 kbar. Not extensive meltings (anatexis) are also common in the area where masses of sienogranitics compositions originated under high temperature conditions from granulites and gneisses. In addition, characteristics indicative of cooling were found in these rocks, such as partial or total replacement of pyroxene by biotite and/or hornblende, garnet by biotite and cordierite by pinit. Thus, in accordance with results of studies already developed in the area and indicated by datings performed in this present study, it was concluded that the Tartarugal Grande Complex comprises rocks that were involved during magmatic events in Neoarchean and Rhyacian, followed by high-grade metamorphism in Paleoproterozoic end and related thermo-tectonic Transamazonian event. This event deformed pre-existing types and rebalanced minerals rocks, resulting in a complex association of granulites and gneisses with different ages, origins and deformation intensities.
Acesso aberto (Open Access)
Geologia do setor nordeste da zona de cisalhamento de Granja - noroeste do Ceará
(Universidade Federal do Pará, 1992-03-20) GAMA JÚNIOR, Theodomiro; OLIVEIRA, Marcos Aurélio Farias de; http://lattes.cnpq.br/6704755061378988
This work is about the geology of the northeast part of the Granja Shear Zone, in the northwest portion of State of Ceará, Brazil. This part of shear zone consist of rocks from Gameleira and Granja complexes, and Martinópole Group. These units were individualized from geologic mapping, petrography, lithochemistry, tectonic regime and geocronology. The Gameleira Complex is present in the northern part of area, and in conventional air photos and image of radar shows a peneplanized relief Pattern. The lithological types are represented by kizingitic gneisses and ultramaficy mafic and enderbitic granulites. From lithochemistry study these rocks can be interpreted from and orthoderived origin. The milonitic foliation shows anastomosed pattern with trend NE - SW, with strong dips to SE, and the stretching lineations concentrated in poles around N 75 E, dipping not over than 25'. Radiometric ages obtained from Rb/Sr methods, Total Rock, were 1.915±19 Ma and 1.929+60 Ma. The Granja Complex is located in the center part of the area and shows either a peneplanized relief. The main lithological type is the tonalitic-granodioritic gneisses with trondhjemitic and monzo-granitic gneisses, and amphibolite lenses with subordinated ocurrence. Probably these rocks are derived from igneous rocks with calc-alkaline trend. The geometric pattern of milonitic foliation presents the same regional trend NE - SW, dipping to SE, with stretching lineations poles concentrated near those observed in Gameleira Complex. Radiometric ages obtained from Rb/Sr methods, Total Rock, were 2.40282 Ma, i.796±105 Ma, 1.791±141 Ma, 1.581±43 Ma and 498±31 Ma. The Martinópole Group occurs in southern part of the area, as elongated hills with trend NE - SW. The lithological type are represented by quartzites and calc-silicate gneisses, of paraderivated origin. The S milonitic foliation has NE SW trend, with strong to moderate dips to SE. The isotopic age of 2.4 Ga obtained from gneisses of Granja Complex, suggest that the Granja Shear Zone formation is related to a tectonic event of the end of Archaean, when rocks from lower crust upflit to higher level through an oblique sistem during the movement of Ceará Block to WSW overridding the São Luis Block. The goungest ages from rocks of Granja Complex are interpretated as due importants isotopft resetting related to sheary metamorphism and partial melting during the Lower Proterozoic and Upper Proterozoic thermal effects.
Acesso aberto (Open Access)
Petrologia e evolução crustal da porção central do Domínio Canaã dos Carajás, Província Carajás
(Universidade Federal do Pará, 2018-09-14) MARANGOANHA, Bhrenno; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; 0294264745783506
Geological mapping allied to microstructural, petrological, geochemical, geochronological (Pb-Pb and U-Pb) and isotopic (Nd and Hf) data performed in the central portion of the Canaã dos Carajás domain, Carajás province (Amazonian craton, Brazil) allowed the individualization of new geological units previously grouped into Xingu complex and Plaquê suite, besides the redefinition of the limits from the other units already mapped as well. Therefore, four main events have been described in this portion of the province as follows: (1) in the Mesoarchean, between 3.0 and 2.93 Ga, TTG crust was generated in an N–S subduction setting by partial melting of LILE-enriched basalts (formerly transformed in garnet amphibolite), similar to oceanic plateau basalts; (2) at 2.89–2.84 Ga, in collisional setting, large volume of anatectic granites was formed and contributed to crustal thickening, which triggered granulite-facies high-temperature metamorphism in the TTG crust, forming the felsic granulite from Ouro Verde area; and (3) in the Neoarchean, between 2.75 and 2.73 Ga, this portion of the crust underwent delamination process (detachment from the weak lower crust), promoting generation of enderbitic melt by partial melting of the lower crust (Mesoarchean mafic granulite). This event also promoted partial melting of the upper crust, which generated the Pium diopside-norite magma. The emplacement of this mafic melt into the Mesoarchean basement (felsic granulite) triggered their melting, and generates a leucogranitic melt, which both melts (mafic and felsic) mixed and mingled, then forming the Vila União hybrid granitoids. The emplacement of the mafic (Pium diopside-norite), felsic magmas (leucogranites), and their mixed products (Vila União hybrid granitoids), as well as the enderbitic magmas, was channeled into pre-existing Mesoarchean shear zones trending E– W in the crust (Itacaiúnas shear zone). The generation and consolidation of the Neoarchean magmas occurred in pure shear-dominated transpressional tectonic regime, giving rise to the syn-tectonic nature on these granitoids. This tectonic regime was responsible to the exhumation of the Mesoarchean granulitic crust in a regional imbricated system. Lu- Lu-Hf isotope data of magmatic cores of the zircons from the Mesoarchean felsic granulites from Ouro Verde area show Hf-TDM2 of 3.44–3.15 Ga and εHf(t) values between -1.7 and 3.0, which suggests juvenile source. The Neoarchean enderbite presents Hf-TDM2 of 3.46–3.29 Ga and lower εHf(t) values (between -4.8 and -1.9), and points to a longer crustal residence time to the enderbitic rocks. Hf-isotopic behavior for the Vila União granitoids [Hf-TDM2 between 3.46 and 3.29 Ga, and εHf(t) between -4.6 and -1.8] is quite similar to the enderbites, which the hybrid granitoids Hf-isotopic data are interpreted as being only the felsic end-member (leucogranitic magma) from the mixing system. Such statement is supported by the Ndisotopic data, which confirm the hybrid Neoarchean granitoids evolution from mixing at different proportions of juvenile (mafic end-member – Pium diopside-norite magma) and recycled components (felsic end-member – leucogranitic magma).
Acesso aberto (Open Access)
Petrologia e evolução crustal das rochas de alto grau de Porto Nacional - TO
(Universidade Federal do Pará, 1996-03-03) GORAYEB, Paulo Sérgio de Sousa; OLIVEIRA, Marcos Aurélio Farias de; http://lattes.cnpq.br/6704755061378988
The Porto Nacional region, located at central-southern portion of the Tocantins State, is part of Structural Tocantins Province. That region forms a crustal segment mainly composed by granulitic and gneissic terraines, with a wide variety of lithotypes due to the effects of successive magmatic, sedimentary, tectonic and metamorphic processes during the Precambrian Eon. In the oldest units, from the Lower Proterozoic, have been recognized orthoderived rocks, as tholeiitic basalts type TH-1, calc-alkaline basalts and tonalites as well as paraderived rocks as graywackes, pelites, graphitic and silicic-iron-manganesiferous, submited to high grade metamorphism (Porto Nacional Complex, Morro do Aquiles Formation). Another set of rocks includes tonalites associated with minor granodiorites and granites, occurring along with a supracrustal sequence made up of calc-silicate gnaisses, pelites, psamites and gondites, metamorphosed in the amphibolite facies (Rio dos Mangues Complex). Meta-igneous bodies of anorthositic (Carreira Comprida Anorthosite), nepheline-sienitic (Estrela Suite) and K-rich granitic rock compositions (Matança and Serrote Suite), metamorphosed in the amphibolite facies, constitutes batholites and stocks enclosed by the former units. They represent magmatic events of different origins and ages. Other units from the end of Lower Proterozoic are represented by the Monte do Carmo Formation, composed by conglomerates, arkoses, graywackes and acid to intermediary volcanic rocks, and the Lajeado Suite, which encloses a set of granites. These unites represent intra-continental volcanic and plutonic magmatic processes related to extensional tectonic environment. The Upper Proterozoic and the Phanerozoic are represented, respectivelly, by psamo-pelites low grade metassediments (Natividade Group) and by sedimentary rocks of the Parnaiba Basin (Serra Grande and Pimenteiras Formations). The tectono-structural framework is here designed by the Tocantins Shear Belt, which trends NE-SW between the Amazônico and Paramiririm Archean cratons. This belt defines a regional imbricated system wide about 300 km, where mixed segments of different crustal level. The evolution of the belt is related to the oblique colision of Porangatu and Araguacema crustal blocks during the Lower Proterozoic, and to late transcurrent shears. The metamorphic studies developed in the Tocantins Shear Belt allowed characterize rocks of high grade metamorphism (Domine 1), with maximum temperature of 850°C and pressure of 8 kbar, which indicate that the rocks reached the granulite facies in a depth of about 30-35 km. The second terrain (Domine 2) includes rocks of high amphibolite facies with temperatures of 680°C and pressures of 6-5 kbar, indicating depths of about 20 km. The Domine 3 includes a migmatized gnaissic terrain, that underwent a middle to high amphibolite facies metamorphism, above the hornblende isograde and the curve of granite melt in high H2O activity. The petrogenetic records suggest a anticlockwise P-T-t path for the high grade metamorphism. This path is initially progressive with an increase of temperature, and crosses muscovite, biotite, andaluzite, garnet and sillimanite isogrades in the aluminous sequences, and hornblende, clivo and orthopyroxene in mafic compositions. The metamorphic path cross cuts the curve of granite melt in low H2O activity and generates S-type granites, and charnockites. The thermal peak is reached near 880°C and is followed by a significative increasing in pressure, with the stabilization of kyanite and garnet. Later, there was stablished retrograde pattern whose records suggest an overprinting in amphibolite and greenschist facies conditions at temperatures lower than 600°C and pressures about 5 kbar. The geochronologic data obtained by whole-rock Rb-Sr and single zircon Pb evaporation analysis suggests a minimum ages 2,1 - 2,2 Ga for the high grade metamorphism, indicating effects of the Transamazonian thermo-tectonic event. The petrogenetic interpretations based on lithochemical and tectonic data, suggest that the evolution of the high grade rocks may be related to the rupture of the pre-existent Archean crust. In this crust affected by extensional tectonism, and strongly controled by magmatic underplating, restricted oceans were installed. The crustal evolution was followed by A subduction, delamination and crustal-stacking wedge, which end up with the transportation of infracrustal segments to upper leveis of the crust.