Navegando por Assunto "Paleoproterozoico"

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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.
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Estudo geoquímico e isotópico (U-Pb/Lu-Hf) de novas ocorrências de granitos tipo-A no Domínio Carajás.
(Universidade Federal do Pará, 2023-04-18) AFONSO, Jully Mylli Lopes; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Carajás Mineral Province was the setting of an extensive magmatic event, marked by anorogenic granitic intrusions and associated dykes. Geological mapping methods carried out in the central portion of the Canaã dos Carajás Domain allowed the individualization of two new anorogenic granitic stocks. These granites occur as isotropic, semicircular shaped stocks, which occur as intrusions in Archean granitic rocks of the Vila União and Cruzadão granite suites. And are classified as monzogranites and divided into biotite-monzogranite equigranular facies (BMzE) and biotite monzogranite porphyritic (BMzP) facies, where biotite is the main ferromagnesian mineral and are often associated with fluorite, in addition to allanite, zircon, apatite and epidote. They are meta- to peraluminous, with a high content of HSFE iron-related with a reduced to moderately oxidized character. When compared to others type-A granites of the Carajás Mineral Province, these granites display significant contrasts with the Jamon and Velho Guilherme suites and are similar to those observed in the Serra dos Carajás suite and, consequently, the Gogó da Onça Granite. Geochronological data of U-Pb in zircon revealed that crystallization age of these granites is ~1893 ± 13 Ma, and associated with isotopic data of Lu-Hf indicate crustal sources for these rocks, with strongly negative ƐHf values ranging from -14 at -17°C and TDM between 3.38 Ga to 3.57 Ga. Based on this informations, the geochemical modeling imply that these granites were generated from partial melting of tonalitic granites of similar composition to the Arco Verde Tonalite or Caracol Tonalite from the Rio Maria Domain. Such results are suitablewith the hypothesis that these granites were generated from a fusion of Archean granitoids and placed in a shallow crust between 1.88 and 1.86 Ga.
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Fácies deposicionais, estratigrafia e aspectos estruturais da cobertura sedimentar paleoproterozoica na serra do Tepequém, Escudo das Guianas, Estado de Roraima
(Universidade Federal do Pará, 2010-12-09) FERNANDES FILHO, Lucindo Antunes; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553; 5463384509941553
In the northern South America, occurs the largest continuous exposure of Paleoproterozoic sedimentary deposits related to the Roraima Supergroup, forming the Pacaraima Block with 73,000 km2. This siliciclastic succession of more than 2 km thick is inserted in the Guyana Shield, northern Amazon Craton, extending from in the border of Brazil, Venezuela, Guyana and Suriname. Near of the Pacaraima Block occur isolated mountains with little-known siliciclastic successions of the faciologic and stratigraphic point view, which does not allow a better correlation with the Roraima Supergroup and, consequently, hinders the paleogeographic and paleoenvironmental reconstitution of the Paleoproterozoic in this part of Amazonia. Outcrop-based stratigraphic and facies studies in the Serra do Tepequém and Uiramutã region, State of Roraima, northern Brazil, allowed redefined and redescribed the lower unit of Roraima Supergroup as Arai Group. The Arai Group of approximately 400 m thick overlies acid volcanic rocks of the Surumu Group, is covered by siliciclastic deposits of the Suapi Group and has been subdivided into two formations. The lower one, similar in both areas, generally consists of polymictic conglomerates, cross-bedded sandstones with microplacers of hematite, and subordinate mudstones interpreted as braided stream deposits. In contrast, the upper formation, in the Uiramutã region, is composed of silty fine-grained sandstones with medium-scale trough cross bedding and convolute lamination deposited in a more distal braided stream environment. This unit, in the Serra do Tepequém region, consists of fine to medium-grained cross-bedded sandstones with mudstones, sandstone/mudstone rhythmites and subordinate conglomerates and breccias interpreted as coastal, tide-influenced deposits. The top of the Arai Group is marked by an expressive unconformity covered with diamond-bearing conglomerates and pebbly sandstones of the basal Suapi Group, interpreted as braided stream deposits. This study confirms the previous interpretation of a big braided stream system migrating to southwest in the central part of the Guyana Shield. In addition it could be shown that the fluvial system in its distal part (Serra do Tepequém) was influenced by tidal processes. The stratigraphy of the Arai Group has established the basis for a regional correlation included deposits of isolated occurrences in the Guyana Shield and points to the presence of a large intracratonic Paleoproterozoic basin connected to the open sea. The structural framework of Serra do Tepequém indicates that major sinistral oblique, normal and reverse NE-SW fault zones bound domains whose bedding dips mainly towards SE and NW. Regional scale forced folds are represented by kilometer scale kink bands and chevron folds compatible with upper-to-middle crustal level. These findings differ from previous regional models based on folding under ductile conditions related to collisional tectonics and evidence the importance of Guiana Shield early basement structures, reactivated probably during the K'Mudku event (~ 1.2 Ga).
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Petrografia e geoquímica do Granito Manda Saia, Província Carajás.
(Universidade Federal do Pará, 2020-09-09) SANTOS, Marcelo Reis; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; 0294264745783506
The Manda Saia granite is located to southeast of the of Xinguara town and it is represented by two semicircular plutons separated by the Mesoarquean basement of the Rio Maria Domain. The bodies crosscut in the northern portion the Mesoarquean TTG granitoids and the Rio Maria Granodiorite, and in the south, eastern and western portions they are intrusive in the metabasalts of the sequence greenstone belt of the Babaçu Group. The Manda Saia pluton is formed by rocks of isotropic aspect, grayish pink in color and monotonous textural variation. They are hololeucocratic rocks of medium-to-coarse heterogranular texture, occasionally porphyritic, which are classified as monzo- and syenogranites. Biotite is the main ferromagnesian mineral and amphibole is rare and interstitial. Secondary minerals are clay minerals, sericite, muscovite, fluorite and chlorite. Manda Saia pluton is formed by peraluminous rocks that present a restricted and high SiO2 contents (74.80 and 77.70wt.%), and high Fe/(Fe+Mg) ratios. Their REE pattern is marked by enrichment in light and heavy REE and moderate negative Eu anomaly. The pluton can be classified as ferrous type-A granite and akin to the reduced types and those most evolved from the oxidized granites of the Carajás Province. The occurrence of interstitial amphibole identified in the Manda Saia granite also is observed in the plutons of the Velho Guilherme Suite. On the other hand, the frequent occurrence of magnetite combined with the compositional aspects of its rocks, also shows that the Manda Saia granite is akin to the leucogranitic facies of the oxidized granites from Jamon Suite. The emplacement of the Granite Manda Saia is linked to extensional tectonics and the transport of magma that resulted in the emplacement of the plutons in shallow crustal levels (~ 1.0 ± 0.5 kbar) through a dyke feeding system.