Navegando por Assunto "Geocronologia"

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Arcabouço estrutural e geocronologia dos granitóides da região de Várzea Alegre: implicações para a evolução crustal da Província Borborema
(Universidade Federal do Pará, 2024-07-25) SOUSA, Luis Kennedy Andrade de; DOMINGOS, Fabio Henrique Garcia; http://lattes.cnpq.br/3975188208099791; https://orcid.org/0000-0002-2447-3465; GALARZA TORO, Marco Antonio; http://lattes.cnpq.br/8979250766799749; https://orcid.org/0000-0002-7271-4737
In the Borborema Province, in northeastern Brazil, several granitic batholiths and plutons are found, which are records of subduction and collision episodes related to the Brasiliano Orogeny. Within this large orogenic system, the emplacement mechanisms of many granites are closely related to the development of deep-seated shear zones, one of which is the Patos Shear Zone, which in its western segment is composed of slices of rocks such as granites, gneisses, metapelites, quartzites, and amphibolites that form an imbricated system. In this context, the present work was carried out with the aim of bringing new geochronological and microstructural data to add to the understanding of the nature of the processes that formed and modified the undifferentiated granitoids in the Várzea Alegre region (CE). The granites are classified as Biotite Monzogranite and Garnet Monzogranite, they present phaneritic and porphyritic textures, in some places, their mineralogical composition is mainly composed of plagioclase, K-feldspar, and quartz, in addition to biotite, muscovite, and garnet. The granitoids are composed of elongated bodies concordant with the host rocks. The deformation imposed on the granitic bodies developed ductile structures with NE-SW orientation and kinematic criteria indicate that the deformation occurred predominantly dextral. Microstructural features, observed mainly in rocks near the edges of the granitic bodies, show that quartz crystals exhibit microstructures such as sutured to lobate contacts, undulating extinction, ribbons, and the chessboard pattern, indicative of recrystallization by grain boundary migration (GBM), compatible with temperatures of 500ºC. Biotite crystals that define the mylonitic foliation characterize a spaced foliation that separates microlite domains formed by aggregates of quartz and plagioclase, with asymmetric lenticular geometry in the granites, similar to the foliation impressed on the gneisses of the Granjeiro Complex. Based on EBSD data, the granites exhibit a grain size distribution with a concentration of crystals <100 μm. From the pole figures, the quartz OPC shows that the dominant system was rhombohedral to prismatic, indicating a medium to high deformation temperature, in a context of progressive non-coaxial deformation. However, from the interpretation of the misorientation angle, it is shown that during the deformation history of the granites, these bodies underwent lower temperature deformation. U-Pb geochronological data on zircon provided crystallization ages of 573 to 576 Ma for this granitic magmatism. The Hf-TDM C model ages of these granitoids ranged from 2.84 to 3.30 Ga and the ƐHf(t) values from -21.9 to -29.6 suggesting a strong incorporation of mesoarchean crustal source. Similar Sm-Nd data in whole rock show that these granitoids have Nd-TDM model ages between 2.14 and 3.33 Ga and ƐNd(t) values between -20.02 and -31.79, suggesting a strong contribution from meso paleoarchean and paleoproterozoic crust (orosirian to riacian) to the formation of the granitic magma that originated the granites in the Várzea Alegre region (CE). These granitic bodies are classified as Itaporanga type and sin-transcurrent, as they have similar ages and structural features to other sin-transcurrent granitic bodies in the Borborema Province. These granites were generated from magmatism associated with the change in the predominant deformation in the Borborema Province, which was the result of the final stages of the Brasiliano Orogeny within the context of simple deformation, with the development of large shear zones.
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Aspectos texturais do magmatismo e tramas da tectônica impostas ao Granito Chaval na Zona de Cisalhamento Santa Rosa, extremo Noroeste da Província Borborema
(2014-12) GORAYEB, Paulo Sérgio de Sousa; LIMA, Aline Maria Meiguins de
The Northwestern region of Borborema Province features a wide variety of granitic bodies with diverse nature and tectonic evolution, since the Paleoproterozoic to Early Paleozoic, presenting higher incidence related to Neoproterozoic emplaced at different stages of Brasiliano (Panafrican) orogeny. One of these examples is the Chaval Granite representing a batholith body intruded in orthogneisses of Granja Complex and supracrustal rocks of Martinópole Group, outcropped near the Ceará and Piauí Atlantic coasts, Northeastern Brazil. The batholith is partly covered by Cenozoic coastal deposits and sedimentary rocks of the Paleozoic Parnaíba Basin. The Chaval Granite has a striking textural feature, which is represented by porphyritic highlighting microcline megacrysts in syenogranites and monzogranites, and many others textural/structural features of magmatic origin. They allowed interpreting the plutonic evolution at relatively shallow crustal level emplacement acting processes of fractional crystallization, magma mixing with intense magmatic flow, and gravitational force due to density difference of magma that lead to fluctuation of megacrysts of microcline and plagioclase in the residual magma, and accommodation of small bodies of leucogranite and pegmatites in the final stages of plutonic magmatic evolution of such plutonism. On the other hand, across the Eastern half of the pluton, there is a rich collection of shear structures related to the tectonic construction of the Santa Rosa Transcurrent Shear Zone, which led to tectono-metamorphic transformations superimposed on magmatic features that reached peak metamorphic conditions in the low amphibolite facies. Cartographically, three homogeneous structural domains were individualized, and each of them presents a variety of petrographic-structural features of the Chaval of igneous or tectonic nature. The plutonic rocks were deformed and progressively modified Eastward, in which the rocks change to darker gray, and comminution and dynamic recrystallization processes are reduced, as well as the coarse-grained granites are progressively, as well as the size of the phenocrysts to thinner dimensions, keeping their porphyroid characteristics, being accentuated the mylonitic features to achieve the main portion of Santa Rosa Transcurrent Shear Zone. As main structural features, there is the ondulatory extinction, cleavage and twining bending, twinning deformation, anastomosing foliation, badinage, S-C foliation, mineral stretching lineation, rotated and segmented crystals, lenticular, almondy or fish forms of porphyroclasts, pressure shadow, and ribbon quartz. The products of this shear deformation result in the formation of protomylonites, mylonites, and ultramylonites. These mylonite zones represent areas with the highest concentration of deformation that can gradually follow their textural and mineralogical changes, setting up a classic sequence of progressive heterogeneous deformation by simple shear in brittle-ductile and ductile conditions. The emplacement of Chaval Granite happened at the end of the Cryogenian (approximately 630 Ma) and can be interpreted as syn-tardi tectonic magmatism regarding the Brasiliano event. The process that generated the Santa Rosa Shear Zone resulted from lateral extravasation crustal masses in ductile flow took place in the final increments of deformation of a continental collision on an oblique thrust system, which built the Northwest Ceará Shear Belt, and happened at the end of Brasiliano (Panafrican) orogeny in Northwest Borborema Province.
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A associação anortosito-mangerito-granito rapakivi (AMG) do Cinturão Guiana Central, Roraima, e suas encaixantes paleoproterozóicas: evolução estrutural, geocronologia e petrologia
(Universidade Federal do Pará, 2002-12-19) FRAGA, Lêda Maria; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286
The geological mapping on a scale of 1:250,000, of an area of approximately 22,500 km2 in the central region of the state of Roraima, combined with the petrographic and microtectonic study and new geochronological, lithochemical and isotopic data, allowed the characterization of an anorthosite-mangerite association -rapakivi granite (AMG), Mesoproterozoic and its Paleoproterozoic host. Orthogneisses, foliated granitoids and charnockite rock bodies from the Serra da Prata Intrusive Suite show Pb-Pb (zircon evaporation) ages around 1.94 Ga, also inferred for the associated norites and gabbronorites. The Paleoproterozoic igneous suites were placed syn-kinematically, during Deformational Event D1, with the evolution of petroweaves indicative of high temperatures, from 600º-650ºC. These features include recrystallized feldspars by subgrain rotation, recrystallized perthitic alkali feldspars and quartz with checkerboard subgrains and have been observed in syn-plutonic dykes that cut the early-kinematic D1 fabric in the host country. The NE-NW arrangement of the Paleoproterozoic bodies was controlled by the previous structure of this sector of the Central Guiana Belt (CGC). The orthogneisses and foliated granitoids comprise two distinct suites, with lithochemical characteristics of type A granitoids, probably related to different oxidation conditions at the source. The charnockite rocks show chemical characteristics approaching those described for C-type magmatism. Sm-Nd TDM model ages between 2.19 Ga and 2.05 Ga, with ƐNd(T) values ranging from +0.68 to +2 ,47 suggested sources of limited crustal residence. The age of the orogenic events in Roraima has not yet been properly clarified, however, despite the limited data, a post-collisional positioning is proposed for the Paleoproterozoic suites studied after the accretion of transamazonian magmatic arcs. The Paleoproterozoic units constitute the basement of the Mesoproterozoic igneous suites, which comprise the anorthosites of the Repartimento unit and associated gabbronorites, the rapakivi granitoids of the Mucajaí Intrusive Suite (SIM), and the fine, porphyritic charnockites, of punctual occurrence and uncertain geochronological positioning. In SIM, three granite facies were identified (fayalite-pyroxene-quartz-mangerites to syenites; hornblende-biotite-granites; and biotite-porphyritic granites) geochemically and petrographically very similar to rapakivi granites from classical areas of Finland. The presence of fayalite in the most primitive rocks of the SIM indicates conditions of low oxygen fugacity, observed in several rapakivi granite complexes. Fine charnockites show no cpm to SIM chemical correlation. The Mesoproterozoic suites are part of an AMG (Anortosito-Mangerito-Granito rapakivi) association placed in an anorogenic environment between 1.54 and 1.53Ga. Model ages Sm-Nd, from 2.07 Ga to 2.01 Ga with ƐNd(T) values ranging from -2.37 to -1.27 suggest, for the granitoids in the association, crustal sources separate from the mantle in the Paleoproterozoic , probably during the Transamazônico. Mylonitic features related to the D2 Deformational Event, registering conditions of moderate to low temperatures (400º-450ºC), in a brittle-ductile environment, locally obliterate the igneous textures of the Mesoproterozoic units, as well as the high temperature D1 petrowebs in the Paleoproterozoic basement. These features are especially well developed in some shear zones that show dextral transpressive kinematics. The D2 event aged around 1.26 Ga relates to the K'Mudku Deformational Episode. The main D2 mylonitic zones were reactivated in the Mesozoic at shallow crustal levels and brittle conditions, during the evolution of Graben Tacutu.
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Caracterização geológica, petrográfica, geoquímica e geocronológica do magmatismo granítico da região de Porto Nacional-TO
(Universidade Federal do Pará, 2003-02-28) CHAVES, César Lisboa; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
In the Palmas-Porto Nacional region, Tocantins state, a series of granitic bodies has been assigned to two distinct magmatics events: a) Paleoproterozoic Granites (Areias, Carmo, Itália and Ipueiras plutons); b) Neoproterozoic Granites (Lajeado, Aroeira, Matança and Palmas plutons). Cartographic, petrographic, lithochemical and geochronological studies revealed the main characteristic of these granitic bodies and allowed to improve the knowledge of the granitic magmatism of this region. The Paleoproterozoic granites constitute large bodies affected by small strike-slip zones. Petrographically they are represented by sienogranite, monzogranite and quartz syenite, with different amounts of amphibole and biotite. The geochemical signature of the Paleoproterozoic granites are similar. The show a subalcaline character, and are peraluminous to metaluminous. They are rich in REE and, generally, more fractioned in LREE, with negative Eu anomaly and may be classified as A-type granites. Single zircon Pb-evaporation dating of Areias, Ipueiras and Itália granites gave ages of 2086  5 Ma, 2073  2 Ma and 2078  4 Ma, respectively, interpreted as age of emplacement of these plutons. Sm-Nd TDM model ages between 2.19 Ga and 2.15 Ga suggest that these granites were formed by partial melting of Paleoproterozoic juvenile crust. The Nd(2,08Ga) values between +2.26 and +2.89 indicate the mantelic contribution for the formation of these plutons. The Neoproterozoic granites are petrographically classified as sienogranite, monzogranite and quartz sienite with different amounts of ortopyroxene, amphibole and biotite, In general, they may be called charnockites. The geochemical date revealed similarities among the Neoproterozoic granites. They show subalkaline nature and have metaluminous to peraluminous character. These granites are rich in REE and are more fractioned in HREE than LREE. In the geochemical diagrams they plot in the field of the A-type granites. The Sm-Nd isotopics studies for Neoproterozoic granites revealed TDM ages between 2.1 Ga and 1.71 Ga and the Nd(0,55Ga) values between –13.34 and –9.77 that are interpreted as evidence of strong crustal contribution, but probably with some mixtures of younger of sources. This study corroborated the presence of two main events of granite geration in the Porto National-Palmas region. The older is represented by the Paleoproterozoic Carmo, Areias, Ipueiras and Italia granites, with age around 2.08 Ga. The younger granitogenesis is represented by Lajeado, Palmas, Matança and Aroeira bodies emplaced in the Neoproterozoic at 0.55 Ga.
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O cenozoico superior do centro-oeste da Bacia do Amazonas: paleobotânica do embasamento cretáceo e evolução do Rio Amazonas
(Universidade Federal do Pará, 2018-11-08) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
At the end of the Neogene and during the Quaternary, the development of the Amazon River caused significant paleoenvironmental and geomorphological changes that generated current ladscape at Amazonia. Previous models elaborated on a continental scale were based on data obtained from a drill core carried out on the Atlantic continental shelf, distant 200 km of the Amazon River mouth, suggesting the establishment of this drainage with Andean provenance from the Middle to Upper Miocene. In contrast, studies based on outcrops in the western and central portions of the Amazon have indicated younger ages for this ecosystem, from Pliocene to Quaternary. The sedimentological-stratigraphic study of the fluvial terraces of the Amazon River, exposed in the center-west portion of the Amazon Basin, assisted by luminescence geochronology, allowed to sequence the sedimentation events and discuss the paleoenvironmental and paleogeographic since Late Neogene. The studied Neogene- Quaternary deposits overlies Cretaceous rocks whose sedimentological and paleobotanical study revealed the preservation of impressions and counter-impressions of leaves and other macro-plant remains in pelites interpreted as flood plain and abandoned channel deposits of meandering rivers. The first record of angiosperms in this unit with possible affinities to the families Moraceae, Fagaceae, Malvaceae, Sapindaceae and Anarcadiaceae with appearance from Late Cretaceous, and the family Euphorbiaceae with record starting in the Mid- Cretaceous confirm the Cretaceous age for these rocks. The terraces of the Amazon River informally subdivided into lower and upper units are composed of sand, gravel and clay, organized in finning upward cycles representative of channel filling and overbank deposits. The lower unit was interpreted as a record of the proto-Amazonas, with migration to the east and deposition around 2 Ma. During this stage, the alluvial plain was restricted, preferentially following weakness zones coincident with fractures in the Paleozoic and Cretaceous basement. The climatic oscillations during the Quaternary and the increase of the volume of orographic rains in the headwaters region of the fluvial systems, in the eastern flank of the Andean ridge modified the hydrological regime, amplifying the escarpment erosion. The gradual expansion of the alluvial plain formed a large area of 120 km around 1 Ma to 140 ka, recorded by the upper unit deposits. At this stage, the eastern portion of the Amazon Basin topographically higher restricted the Pleistocene sedimentation in minimum accommodation space. The lower unit deposits are correlate in part to the Miocene-Pliocene deposits of the Amazon Basin, while the upper units are correlate with the Pleistocene deposits of the Solimões and Amazon basins. The dynamics of the construction of the Amazon River valley during the end of the Neogene and Quaternary was influenced by neotectonics (106 yr) and climatic oscillations (104-105 yr). The landscape of the central-eastern portion of the Amazon dominated no Pleistoceno by terra firme in elevated areas was governed by the dynamics of expansion and contraction of the alluvial plain. At the end of the Quaternary, the várzea formed by floodplains within the alluvial plain, which used to occupy a wide area, became increasingly restricted by the continuous processes of fluvial incision during the glacial maximum (18 to 22 ka). The continuous lateral migration of the meandering channel to the north led to the confinement of the channel by the fluvial scarps developed in the Cretaceous basement, which culminated in the current landscape in the Center-East of the Amazon. Testing the reliability and accuracy of some Pleistocene and older OSL ages for Amazon River deposits revealed that are much more minimum ages than buried ages for pre- Quaternary deposits.
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Cerro Porã Batholith: post-orogenic A-type granite from the Amoguijá Magmatic Arc - Rio ApaTerrane - South of the Amazonian Craton
(2013-09) PLENS, Dalila Pexe; RUIZ, Amarildo Salina; SOUSA, Maria Zélia Aguiar de; BATATA, Maria Elisa Fróes; LAFON, Jean Michel; BRITTES, Ana Flávia Nunes
The Cerro Porã Batholith has an approximately area of 30 km by 4 km, situated at the region of Porto Murtinho, Mato Grosso do Sul. It is located in Rio Apa Terrane, at the southern portion of the Amazonian Craton. It consists of Pink Syenogranitic Facies and Gray Monzogranitic Facies. The first facies is characterized by xenomorphic equigranular texture to essentially inequigranular texture with graphic and granophiric intergrowths. Both facies are composed of alkali feldspar, quartz, and plagioclase with biotite as the only primary mafic mineral. The Gray Monzogranitic Facies has porphyritic texture with graphic to granophiric fine-grained groundmass. It consists of quartz, plagioclase, alkali feldspar, and mafic aggregates (biotite and amphibole). Both facies were metamorphosed at greenschist facies and the Pink Syenogranitic Facies, which is milonytic in nature when it is in shear zones. One event of ductile–brittle deformation was identified, originated in a compressive system. It was responsible for the schistosity and mineral-stretching lineation. The development of the Esperança shear zone is related to this deformational phase and reflects the cinematic history of the reverse convergent system with top transport to NWW. Chemically, these rock types are classified as A2-type granitoids of range alkaline potassium saturated on silica. Geochronological data obtained by U-Pb (Sensitive High Resolution Ion Microprobe) method in zircon resulted in an age of 1749 ± 45 Ma, interpreted as crystallization age of the batholith. From the geotectonic point, the Cerro Porã Granite is considered to be the product of a magmatism associated with a magmatic arc developed in Statherian and emplaced in late-orogenic to post-orogenic stage.
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Datação Sm-Nd em rocha total e granada do metamorfismo granulítico da região de Tartarugal Grande, Amapá Central
(2008-03) OLIVEIRA, Elma Costa; LAFON, Jean Michel; GIOIA, Simone Maria Costa Lima; PIMENTEL, Márcio Martins
The experimental procedure for Sm-Nd method performed at the Pará-Iso Isotope Geology laboratory, (Federal University of Pará) is described in details as a reference for the customers of the Pará-Iso. Sm-Nd dating of felsic granulites from the Tartarugal Grande area, northeastern of the Archean Amapá Block, (Southeastern Guyana Shield) furnished whole rock - garnet isochron ages of 2017 ± 12 Ma, 1981.6 ± 2.8 Ma e 2018 ± 2.3 Ma. Dating of the same samples at the UnB geochronological laboratory yielded ages of 2037 ± 8.4 Ma, 1988 ± 11 Ma e 2013 ± 15 Ma, respectively. Such results indicate that temperature of at least 700°C was reached by the Tartarugal Grande granulites between 2.04 - 1.98 Ga, as a proxy of a late Transamazonian high grade metamorphic event in the northeastern sector of the Archean Amapá Block. TDM(Nd) model ages between 3.15 Ga and 2.79 Ga are a further evidence of a major Mesoarchean crustal growth episode in the southeastern Guyana Shield.
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Depósitos flúvio-costeiros da Formação Raizama, Ediacarano-Cambriano da faixa Paraguai Norte, região de Nobres, Mato Grosso, Brasil
(2014-12) SANTOS, Hudson Pereira; SILVA JÚNIOR, José Bandeira Cavalcante da; NOGUEIRA, Afonso César Rodrigues; ABRANTES JÚNIOR, Francisco Romério
The Ediacaran-Cambrian Raizama Formation presents siliciclastic deposits exposed discontinuously along of the southern margin of the Amazon Craton and the Northern Paraguay Belt, Central-Western Brazil. These deposits are interpreted as progradational coastal succession conformably overling the carbonate platform succession of the Upper Araras Group. The facies and stratigraphic analysis of outcrop section were carried out in the Nobres region, State of Mato Grosso, allowed the individualization of seventeen facies, grouped into five facies associations (FA): FA1) lower shoreface, consisting of sandstone with parallel and wave-truncated lamination (microhummocky) parted by laminated mudstones, locally bioturbed by Skolithos; FA2) upper shoreface, composed by parallel and swaley cross bedded sandstone; FA3) subtidal, represented by sandstones with tangential and through cross stratifications drapped by siltstone/very fine sandstone laminae interpreted as channel and bar deposits; FA4) tidal flat is characterized by sandstones with tangential and sigmoidal cross bedding, even parallel stratification, low-angle cross bedding, mud cracks, siltstone/very fine sandstone rhythmites with flaser bedding, organized in shallowing-meter scale cycles; and FA5) distal braid plain consisting of sandstones with through cross-bedding and laterally discontinuous lags, parallel stratification and low-angle cross stratification partially reworked by wave. The sedimentation of the Raizama Formation suggests an increase in the siliciclastic supply linked to uplift regions of the Craton in the northwest of the studied area, succeeding the Araras carbonate platform deposits. Tubular trace fossils in the FA1 indicate, by the first time, the presence of burrowed organisms, what strongly points to an age near of the Ediacaran-Cambrian boundary.
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Estudo da razão isotópica 87 Sr /86 em macrofosséis da Formação Pirabas, nordeste do estado do Pará
(Universidade Federal do Pará, 2001-10-10) BELÚCIO, Elcinice Ferreira; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
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Estudo de Proveniência das rochas metassedimentares do Complexo Ceará, na região de Sobral e adjacências, com base em datação U-Pb de zircão e idades-modelo Sm-Nd
(Universidade Federal do Pará, 2015-06-05) FEITOSA, Jeremias Vitório Pinto; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
The Borborema Province is an important tectonic province, with approximately 450,000 square kilometers in the northeastern Brazil, which registered numerous and remarkable geological processes that occurred on Earth over time. This province has great similarities with existing provinces in Africa, as the Benin/Nigeria. Successive geological cycles are recorded in rock types of the Borborema Province, dating back to a very complex geologic evolution started in the Archean, culminating at the end of the Neoproterozoic, with the occurrence of tectonic-thermal events and magmatism called the Brazilian Cycle, which resulted in the closure of an oceanic domain in this region. The Tamboril-Santa Quitéria Complex (TSQC) is the most significant unit of this final process of continental collision observed in Ceará Central Domain of the Borborema Province. The existent geochronological and isotopic data allow to understand the context and the geological evolution of the unit. However, for the metasedimentary rocks that flank the TSQC, assembled in the Ceará Complex, are lacking studies and information that permits to propose more refined geological models to better understand the evolutionary framework of this region. The suggested Paleoproterozoic age initially suggested for the metasedimentary rocks of Ceará Complex can questioned due to the presently known geological context. Thus, the sedimentary provenance study proposed here using U-Pb detrital zircon dating and Sm-Nd model-age (TDM), aims to investigate the maximum age of deposition of this metasedimentary unit, and the probable the crustal source of these rocks, to contribute to the understanding of the evolution and stratigraphic framework of Ceará Central Domain. This work included the sampling of 20 outcrops of these metasedimentary rocks that occur in the western and in the eastern flanks of the TSQC. Six samples of quartzite were collected for U-Pb zircon analysis using a laser ablation system attached to a multicollector mass spectrometer with inductively coupled plasma (LA-MC-ICPMS). Sm-Nd model-age determination was carried out in 14 samples. Petrographic study of the non-friable samples preceded the isotope analyses. The rocks of the western flanks of the TSQC were garnet gneiss and kyanite gneiss, with dominantly lepidoblastic and even granoblastic textures. Besides, sillimanite quartzite and muscovite quartzite occurs presenting polygonal granoblastic textures. In the eastern portion, the rocks were observed garnet gneiss with lepidoblastic and granoblastics textures in addition to garnet amphibolite with mainly nematoblastic and minor porphyroblastic textures. The Sm-Nd model-ages between 2.12 and 2.7 Ga., and positive values of Nd (2,1Ga) (+3.30 to + 2.60 ) suggests a strong contribution to Paleoproterozoic crust for the sediments located east of TSQC. This contribution is also recorded in the rocks sampled in the west of TSQC. However, TDM model-age of 1.66 Ga found in a rock also suggests contribution of younger crustal source for these metasedimentary rocks. The U-Pb data for quartzites of the Ceará Complex, in general, have prevalence of detrital zircons of Paleoproterozoic ages, more frequently of the Orosirian (1800-2050) and Rhyacian (2050-2300 Ma) periods, suggesting that the main source area of the sediments are Paleoproterozoic age. However the presence of detrital zircon grains of Statherian (1750± 50 , 1777± 58, 1628± 53 Ma) and Stenian age (1154 ± 29 Ma) found in rocks located east of TSQC indicates the input of younger rocks, corroborating the contribution of younger crustal source for the sedimentary succession of Ceará Complex. The age of 1154 Ma, indicates the maximum age of deposition of these sediments suggesting that this depositional event may even have occurred in the Neoproterozoic, as it is suggested by geological and geochronological evidences pointed out by some authors who studied this succession in other regions of Ceará Central Domain.
Acesso aberto (Open Access)
Estudo geocronológico e de geoquímica isotópica da área Pojuca (Província Mineral de Carajás - PA)
(Universidade Federal do Pará, 1996-03-15) SOUZA, Sandro Rogério Balieiro de; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Pojuca area, located in the northern portion of the Mineral Province of Carajás (southeast of the State of Pará – Brazil), presents Archean units such as: metavolcano-sedimentary sequences of the Igarapé Pojuca Group, with important deposits of Cu (Au, Ag, Mo); deformed granites (Itacaiúnas Deformed Granite); sedimentary rocks of the Águas Claras Formation; and metagabbroic dykes. The Pojuca Granite is an intrusive Proterozoic body in Archean rocks. Geochronological and isotopic geochemical studies were carried out on these lithologies using the methods Pb-Pb by evaporation in zircon, Pb-Pb in whole rock and phosdspar and Rb-Sr in whole rock and minerals (all results calculated with deviations of 2σ) . In the metavolcanic rocks of the Igarapé Pojuca Group two distinct types of zircon (metamictic and non-metamictic) were observed. Metamitic zircons show high contamination of foreign Pb, possibly caused by the action of hydrothermal fluids during thermal events (Archaean regional metamorphism, intrusions of the Itacaiúnas Deformed Granite and the Pojuca Granite). The non-metamictic zircons did not show Pb amounts detectable by the mass spectrometer. The analyzes carried out by the Pb-Pb method in whole rock and feldspars did not provide good results due to the dispersion of the analytical points in the graph 206Pb/204Pb vs. 207Pb/204Pb. However, the values of the Th/U ratios (2.5) indicated a mantle source for the metavolcanic rocks. The Pb-Pb method by zircon evaporation was successfully applied to the Itacaiúnas Deformed Granite, obtaining an age of 2560 ± 37 Ma, interpreted as the minimum crystallization age of these rocks. Confirming for this body an Archean age close to that previously obtained by the Rb-Sr method in whole rock (2480 ± 40 Ma), being the same correlated to the age of the Ancient Salobo Granite (2573 ± 2 Ma, U-Pb in zircon). Analyzes by the Pb-Pb method on whole rock and feldspars did not provide good results on the Itacaiúnas Deformed Granite. The ages obtained (1597 ± 13 Ma and 2215 ± 86 Ma) indicate a disturbance of the Pb isotopic system, possibly caused by the intrusion of the Pojuca Granite. This same event affected and rehomogenized, on a mineral scale, the Rb-Sr system of this body, as indicated by the Rb-Sr age in whole rock and minerals (1810 ± 57 Ma). In the Pojuca Granite, only one zircon made it possible to obtain an age of 1873 ± 59 Ma, similar to the previously obtained U-Pb age in zircon (1874 ± 2 Ma). Using the Pb-Pb method in whole rock and minerals, the age of 1856 ± 23 Ma was obtained for the Pojuca Granite, also interpreted as the crystallization age of the body. The value of µ = 10.5 ± 0.32, as well as the high ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, indicate a crustal source for the granitic magma. The zircons of metagabbroic rocks (dikes) are petrographically similar to the metamict zircons of volcanic rocks. It is not possible to obtain satisfactory geochronological results. In the rocks analyzed by the Pb-Pb method in whole rock and feldspars from the Pojuca area, very high 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios were found. In the Itacaiúnas Deformed Granite and in the Pojuca Granite these ratios are interpreted as a product of the enrichment of the source magmas of these granites in the U and Th elements. In metavolcanic rocks it is believed that the high ratios reflect an isotopic contamination due to hydrothermal fluids associated with the intrusions of the Itacaiúnas Deformed Granite and the Pojuca Granite. Plotting the Pb isotopic ratios on the 206Pb/204Pb vs. 208Pb/204Pb, 204Pb/206Pb vs. 207Pb/206Pb and 204Pb/206Pb vs. 208Pb/206Pb, it is noted that each studied unit occupies a different domain. However, there is a slight overlap between the fields defined by the isotopic ratios of the metavolcanic rocks and the Pojuca Granite, which may indicate contamination of the metavolcanic rocks by granite.
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Estudo geoquímico e isotópico dos processos metalogenéticos associados ao depósito de Pb-Zn (Cu-Ag) Santa Maria, região de Caçapava do Sul, Rio Grande do Sul
(Universidade Federal do Pará, 2018-05-11) PEREIRA, David Ramos; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
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Estudo isotópico do depósito aurífero Volta Grande, domínio Bacajá, sudeste do cráton amazônico
(Universidade Federal do Pará, 2024-03-22) PIMENTEL, Helmut Sousa; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The area of the Volta Grande of the Xingu River is crucial for the geological understanding of the Siderian and Riacian periods in the Bacajá Domain, Maroni-Itacaiúnas Province, Amazonian Craton, which hosts significant gold mineralizations. The Bacajá Domain is composed of tectonic associations with NW-SE orientation that contain reworked Archean and Siderian fragments, mainly during the Riacian, with significant crustal growth during the Transamazonian Cycle (2.26 to 2.06 Ga). The objective of this thesis is to investigate the tectonic environment and discuss the crustal evolution in accretionary and continental collision settings. The study relied on field surveys, geological-geophysical mapping, petrography, geochemistry, geochronology, and isotopic geochemistry, employing U-Pb and Lu-Hf methods in zircon via SHRIMP and LA-ICP-MS, U-Pb in titanite via LA-ICP-MS and Sm-Nd on whole rock via TIMS. The geological-geophysical integration reveals the NW-SE trending Bacajá Shear Zone with well-defined edges and foliated terrains of high magnetic susceptibilities, plastically deforming the lithotypes within. Petrographic analyses identified metavolcanosedimentary rocks of the Três Palmeiras sequence, the Intrusive Oca Suite (composed of granodiorite, quartz monzodiorite, quartz monzonite, monzodiorite, and diorite), as well as granodiorite, monzogranite, and sienogranite of the Bacajaí Complex and the Arapari Intrusive Suite. The zoned hydrothermal orogenic gold mineralization occurs at the contact between the Três Palmeiras Group and the Intrusive Oca Suite. The geochemistry of mafic volcanic rocks from the lower Itatá Formation of the Três Palmeiras Group indicates evolved tholeiitic character in a mid-oceanic ridge and juvenile island arc setting, while the volcanic rocks of the upper Bacajá Formation are related to calc-alkaline volcanic arcs in active compressional continental margins. Three groups of granitoids representing different phases of magmatic and tectonic evolution in the Bacajá Domain during the Riacian were distinguished, with ages spanning around 110 M.y.: granitoids from the Intrusive Oca Suite at 2.20-2.17 Ga, syenogranite with biotite from the Bacajaí Complex at 2.17 Ga, and biotite-bearing monzogranite from the Arapari Intrusive Suite at 2.09 Ga. The Intrusive Oca Suite comprises intermediate to acid, calcic to alkali-calcic, ultramafic to medium-mafic, metaluminous to peraluminous rocks formed in a cordilleran granitic setting related to volcanic arcs. The REE of Intrusive Oca Suite granitoids exhibit strong magmatic fractionation, reflected in high (La/Lu)N ratios, enrichment in Rb, Th, and K, and depletion in Ba, Nb, P, and Ti, sourced from mafic rocks with varying K contents. The Bacajaí Complex consists of calcic to alkali-calcic, medium-mafic, and peraluminous quartz monzonite, granite, and granodiorite, sourced from x mafic rocks with low-K and high-K components and some input from metasediments. The rocks of the Arapari Intrusive Suite are medium-mafic, calcium-alkali to alkali-calcic, and metaluminous, sourced from mafic rocks with high-K content. The syn- to late-collisional granitoids (Bacajaí Complex and Arapari Intrusive Suite) are enriched in LILE and LREE, exhibiting negative anomalies in Ni, P, and Ti, and depletion in HFSE, typical of orogenic granites in volcanic arcs. In terms of isotopes, the Três Palmeiras sequence has Nd-TDM values ranging from 2.35 to 2.58 Ga, with εNd(t) varying from -0.41 to +3.20. The Intrusive Oca Suite includes rocks with Nd-TDM between 2.24 and 3.06 Ga and εNd(t) ranging from -5.99 to +2.44. U-Pb zircon crystallization ages for this suite are 2203 ± 23 Ma, with Hf-TDM C values between 2.4 and 2.8 Ga and εHf(2.20Ga) ranging from -0.45 to +5.24 for the Ouro Verde body; 2173 ± 7 Ma with Hf-TDM C ranging between 2.3 and 2.6 Ga, and ɛHf(2.17Ga) between +2.04 and +7.65, added to a U-Pb age of 2171 ± 17 Ma in titanite, for the Central body, and 2171 ± 13 Ma, with Hf-TDM C values between 2.4 and 3.4 Ga and εHf(2.17Ga) ranging from -10.32 to +4.34 for the Buma body, indicating distinct crustal generations between the Mesoarchean and Siderian/Riacian. The Bacajaí Complex has a crystallization age of 2165 ± 10 Ma, Hf-TDM C values between 2.5 and 2.8 Ga, and εHf(2.16Ga) ranging from -0.35 to +3.04, with mantelic sources from the Neoarchean. The Arapari Intrusive Suite has a crystallization age of 2094 ± 13 Ma, Nd-TDM at 2.38 Ga, εNd(2.09Ga) at -1.15, Hf-TDM C values between 2.6 and 2.8 Ga, and εHf(2.09Ga) varying from -2.77 to +1.59, indicating a mixture of mantle and crustal sources generated from the Neoarchean to the Siderian. The geological evolution of the study region is marked by various events. In the Siderian, volcanic-sedimentary sequences with tholeiitic basalts and island arc andesites were followed by the emplacement of diorites to granites around 2.20 to 2.09 Ga and collision, originating continental arcs. The most advanced and late stage of the Transamazonian orogeny in the Volta Grande region is represented by the emplacement of peraluminous granitoids from the Arapari Intrusive Suite, closing the complex geological bevolution of the region. The analyses in this study highlight the proposed similarity based on petrographic, geochronological, and isotopic similarities between the Volta Grande region and the Lourenço and Carecuru domains, located in the state of Amapá, in the northeastern portion of the Maroni-Itacaiúnas Province.
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Estudo petrográfico, geocronológico e tipológico de zircão de rochas associadas às do grupo Grão Pará, Serra dos Carajás, Pará
(Universidade Federal do Pará, 2018-10-24) RODRIGUES, Anderson Sérgio Batista; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
In the Carajás basin, northern Mineral Province of Carajás, sequences of volcanosedimentary rocks with ages between 2.76 and 2.73 Ga make up the Itacaiúnas Supergroup. This supergroup encompasses the Igarapé Salobo (2.76 Ga), Grão Pará (2.76 Ga), Igarapé Bahia (2.74 Ga) and Igarapé Pojuca (2.73 Ga) groups. The proximity of ages and the lithological affinity of these units indicate that possibly these rocks have been formed under the same geological context, being different expressions of the same event. The Grão Pará Group consists of two formations: a thick sequence of volcanic rocks (Parauapebas Formation; 2758 ± 2 Ma, U-Pb in zircon), and jaspilites with iron ore (Carajás Formation). In view of the great difficulty of understanding the geographic and geochronological limits of the Grão Pará Group, it was carried on petrographic, geochronological (Pb-evaporation in zircon) and typological study of zircon crystals from of samples associated with the Carajás and Parauapebas formations. Rocks from the Grão Pará Group, as well as the majority of the archaean rocks of the Carajás basin, are hydrothermally altered in different degrees of intensity, irrespective of their lithological type. However, a great number of primary textural features were preserved and petrographic studies allowed the classification of the igneous rocks into two distinct groups: the basalt of dark gray to greenish coloration, fine granulation, mainly intergranular texture, from the Parauapebas Formation; and gabbro with intergranular texture, subofitic to micrographic intensively hydrothermalized (mainly serecitization) from dikes which cut the whole sequence. For the Serra Sul of the Carajás basin, two samples of saprolite of volcanic rocks interbeded with the iron formation and collected in cores from drill holes, were analyzed in this work. Due to the advanced weathering that affected these samples, a typological study of zircon was used in an attempt to identify the previous rocks, which allowed to classify the lithotypes as monzogranitealkaline granite affinity. Pb-evaporation method on zircon crystals, in two samples of volcanic rock saprolite interspersed with the iron formations belonging to the Carajás Formation indicated, indicated ages of 2745 ± 2 Ma for sample FS11D-161 and 2746 ± 2 Ma for sample FS11D-122, understood as time of crystallization of the analyzed crystals and the formation of volcanic rock which contains them. In addition to the high accuracy of these data, they are in perfect agreement with each other and within the gap established for the Itacaiúnas Supergroup. Moreover, because the dated samples come from rocks interbeded with the iron formation, they can be coeval (lava flow) or xi younger (intrusive), and establish a minimum limit for the deposition age of this formation. On the other hand, the age of the Parauapebas Formation, button of the Grão Pará Group, establishes the maximum age for Carajás Formation as 2759 ± 2 Ma. Therefore, the Carajás Formation was deposited in about 15 million of years, which is coherent for the estimated thickness of 400 m. In addition, the Grão Pará Group is covered by the Igarapé Bahia Group, whose volcanic rocks from the button are 2745 ± 1 million years old, which perfectly coincides with the ages obtained in this work. This age corroborates the the gap proposed for the deposition of the Carajás Formation, that is, a maximum of 15 million years. Additionally, the insignificant age difference proposed here for the Carajás Formation and for the volcanic from the Igarapé Bahia Group suggests that all these rocks are part of a same sequence.
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Estudos isotópicos de U-Pb, Lu–Hf e δ18o em zircão: implicações para a petrogênese dos granitos tipo-A paleoproterozóicos da província Carajás – Cráton Amazônico
(Universidade Federal do Pará, 2018-04-05) TEIXEIRA, Mayara Fraeda Barbosa; SANTOS, João Orestes Schneider; http://lattes.cnpq.br/5516771589110657; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In ca. 1880 Ma an extensive magmatic event generated A-type granites with rapakivi affinity in the Amazonian Craton, especially in the Carajás Province. In this Province these granites are grouped into three main suites according to mineralogy, geochemistry, and state of oxidation of their magmas – Jamon, Velho Guilherme, and Serra dos Carajás – and include also the Gogó da Onça, Seringa, São João, Gradaús, and Rio Branco plutons. The Gogó da Onça Granite (GOG) comprise a stock composed by biotite-amphibole granodiorite, biotiteamphibole monzogranite and amphibole-biotite syenogranite. The GGO crosscut discordantly the Archean country rocks and are not foliated. All Gogó da Onça Granite varieties are metaluminous, ferroan A2-subtype granites with reduced character. The major and trace element behavior suggests that its different facies are related by fractional crystallization. Zircon and titanite U–Pb SHRIMP ages show that the pluton crystallized at ~1880-1870 Ma. This is more akin to the Serra dos Carajás Suite and to the Seringa and São João granites of Carajás and to the Mesoproterozoic Sherman granite of USA and the Paleoproterozoic Suomenniemi Batholith of Finland. New U-Pb SHRIMP data for the Serra dos Carajás, Velho Guilherme and Jamon Suite and for Seringa and São João Granite show that these plutons crystallized between 1880 Ma to 1857 Ma. Some granites of the Velho Guilherme and Jamon suites and of the Seringa Granite presented 1920 to 1900 m. y. old zircon and titanite crystals interpreted here as antecrysts from an earlier pulse of magma that were incorporated in the main later pulse of 1880 Ma. We also obtained ages of 1865 Ma to 1857 Ma in the leucogranite facies of the Redenção and Bannach plutons, which indicate that the leucogranites of these plutons are younger than their ~1880 Ma old granites and were generated by independent magma pulses that are not cogenetic with the less evolved facies of the respective plutons. Besides it, an age of 1732 ± 6 Ma obtained in the leucogranite facies of the Antônio Vicente pluton of the Velho Guilherme Suite that could represent a magmatic event in the Xingu Region not yet reported or, eventually, could correspond to an isolate hydrothermal event that allowed the growth of zircons. This ranites have been also analysed by Lu–Hf and Oxygen isotopes and few granites also by Nd isotopes. Zircons from all the granites have remarkably restricted initial 176Hf/177Hf (0.281156 and 0.281384) and strongly negative εHf(t) values ranging from –9 to -18, and δ18O fairly homogeneous varying from 5.50‰ to 7.00‰. Small differences were observed internally in the plutons or between them. The ƐHf(t) values of the analysed plutons are strongly negative and similar to Nd isotopic data. The Serra dos Carajás Suite has ƐHf(t) values of -14 to -15.5, the Jamon Suite of -9.5 to -15 and values of -12 to -15 for the Velho Guilherme Suite, while São João, Seringa and Gogó da Onça granites have stronger negative values (ƐHf(t)= -12 to -18). Crustal model ages indicate a Paleoarchean source (3.3 Ga to 3.6 Ga) with a minor contribution from Mesoarchean (3.0 Ga to 3.2 Ga) melts for these granites. This model ages are older than the exposed Archean country rocks of the Orosirian granites of the Carajás Province and more investigation is needed to verify the real existence of that older Archean crust. The studied samples have Hf– O isotopic compositions that overlap within error, and evidence of contamination (crustal assimilation or mixing) of a mantle-derived magma cannot be seen. These plutons crystallized from magmas generated by melting of pre-existing igneous rocks with possibly in the Velho Guilherme Suite a minor contribution from a supracrustal (metasedimentary) component. The Nd, Hf, and O isotope compositions of the Paleoproterozoic granites of Carajás Province clearly attest to an igneous ancient crustal source in the origin of their magmas. The differences observed can result for contrasts in the crustal domains of the Carajás Province that were the source of the granites or of local contamination processes.
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Evolução da região de Santana do Araguaia (PA) com base na geologia e geocronologia Pb-Pb em zircão de granitoides
(2014-06) CÔRREA, Lívio Wagner Chaves; MACAMBIRA, Moacir José Buenano
The region of Santana do Araguaia, focus of this study, is located in the southeast of Pará State, which, in its turn, lies in the southeastern Amazonian Craton. From the tectonic point of view, it is positioned in the Domain Santana do Araguaia, interpreted as an Archean terrain affected by the Transamazonic Cycle. A petrographic and geochronological study, supported by field data, was undertaken in granitoids of the region in order to unravel the evolution of this field. In modal terms, the studied rocks consist of biotite monzogranite, biotite metagranodiorite, hornblende-biotite granodiorite, hornblende-biotite metatonalite and enderbite. These rocks present themselves undeformed to moderately deformed, with some particularities: the biotite metagranodiorite presents foliation following an E-W trend; the hornblende-biotite metatonalite has a foliation following the NW-SE direction, usually with high to subvertical dives, the biotite monzogranite is isotropic, and lithologies hornblende-biotite granodiorite and enderbite show only a slight orientation of their crystals, mainly noticeable in thin section. These rock types were analyzed by evaporating Pb zircon method and the following ages were obtained: biotite metagranodiorite, 3066 ± 3 Ma and 2829 ± 13 Ma, hornblende-biotite metatonalite, 2852 ± 2 Ma, biotite monzogranite, 2678 to 2342 Ma, hornblende-biotite granodiorite, 1990 ± 7 Ma, and enderbite, 1988 ± 4 Ma. The geochronological data indicate that the rocks crystallized both in the Archean and in the Paleoproterozoic; however, no evidence to prove the action of the Transamazonic Cycle was detected in the region.
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Evolução de um sistema lacustre árido Permiano, parte superior da Formação Pedra de Fogo, borda oeste da Bacia do Parnaíba
(2014-12) ANDRADE, Luiz Saturnino de; NOGUEIRA, Afonso César Rodrigues; SILVA JÚNIOR, José Bandeira Cavalcante da
Stratigraphic and facies analysis in the Filadélfia region, TO, BR, at the western of the Parnaíba Basin, allowed redefine the paleoenvironment of the upper portion of the Pedra de Fogo Formation of Permian age. The studied deposits are a series of approximately 100 m thick, predominantly siliciclastic, with subordinate carbonates and evaporites, where were defined 21 sedimentary facies that could be grouped into six facies associations (AF): AF1) Lacustrine with ephemeral river deposits; AF2) Storm wave-influenced lake deposits; AF3) Continental sabkha deposits; AF4) Central lake deposits; AF5) Eolian dunes field deposits; and AF6) Lake/oasis deposits with inunditos. These associations indicate that during Permian, an extensive lacustrine arid system developed adjacent to eolian dunes fields and continental sabkha, as well as with contributions from ephemeral rivers. Fluvial incursions into lakes propitiated the formation of suspension lobes and sheet flows (AF1). Sabkha plains (AF3) were formed in the marginal portions of the lake that eventually were influenced by storms waves (AF2), while central zone were site of intense pelitic deposition (AF4). The low supply of eolian sand in this system resulted in the formation of restricted dune fields (AF5), with development of interdune lakes (oasis), where proliferating giant ferns, sporadically flooded by ephemeral rivers (AF6). The facies associations data, corroborated by the paleogeography of the region during the Late Permian, indicate that settling of the top part of the Pedra de Fogo Formation was laid during a hot and arid climate.
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Evolução geológica da porção centro-sul do Escudo Guianas com base no estudo geoquímico, geocronológico (evaporação de Pb e U-Pb ID-TIMS em zircão) e isótopo (Nd-Pb) dos granitóides paleoproterozóicos do sudeste de Roraima, Brasil
(Universidade Federal do Pará, 2006-11-17) ALMEIDA, Marcelo Esteves; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
This study focuses the granitoids of center-southern portion of Guyana Shield, southeastern Roraima, Brazil. The region is characterized by two tectono-stratigraphic domains, named as Central Guyana (GCD) and Uatumã-Anauá (UAD) and located probably in the limits of geochronological provinces (e.g. Ventuari-Tapajós or Tapajós-Parima, Central Amazonian and Maroni-Itacaiúnas or Transamazon). The aim this doctoral thesis is to provide new petrological and lithostratigraphical constraints on the granitoids and contribute to a better understanding of the origin and geodynamic evolution of Guyana Shield. The GCD is only locally studied near to the UAD boundary, and new geological data and two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the lithostratigraphic picture in the other areas of CGD (1.96-1.93 Ga). Regional mapping, petrography, geochemistry and zircon geochronology carried out in the UAD have showed widespread paleoproterozoic calc-alkaline granitic magmatism. These granitoids are distributed into several magmatic associations with different paleoproterozoic (1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and geochronological studies have distinguished two main subdomains in UAD. In the northern UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites (1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement (2.03 Ga) crop out to northeastern part of this area, and are formed by metavolcano-sedimentary sequence (Cauarane Group) and TTG-like calc-alkaline association (Anauá Complex). Xenoliths of meta-diorites (Anauá Complex) and paragneisses (Cauarane Group) reinforce the intrusive character of Martins Pereira Granite. On the other hand, xenoliths of Martins Pereira and biotitebearing enclaves are founded in the younger, undeformed, and SiO2-rich Igarapé Azul Granite (1.89 Ga). This last and the high-K calc-alkaline Caroebe Granite (1.90-1.89 Ga, Água Branca Suite), including coeval volcanic rocks (1.89 Ga, Jatapu volcanics) and charnockitoids (1.89 Ga, e.g. Santa Maria Enderbite), crop out in the southern UAD. This subdomain is characterized only by local and slight NE-SW ductile-brittle dextral shear zones. A-type granites such as Moderna (ca. 1.81 Ga) and Mapuera (ca. 1.87 Ga) granites, cross cut both areas of UAD. Furthermore, the geological mapping also identified three main types of metalotects in this region. Gold mineralization is observed in Martins Pereira-Serra Dourada granitoids (northern UAD), alluvial columbite-tantalite is related to Igarapé Azul granitoids (southern UAD), and amethyst is associated to pegmatites from Moderna A-type granites. The Nd-Pb isotope data suggest that all granitoids of UAD are generated by reworking of older and pre-existence crustal sources (sialic Rhyacian-Archean and/or juvenile Transamazonian origin) and mantle input is not problably a viable model. Although the dominant process may be one subduction in the early stage of NUAD evolution, post-colisional magmatism may be a significant process in the production of new continental crust in the southern UAD. It is possible that, following oceanic closure in the Anauá arc system (2.03 Ga) and subsequent collisional orogeny (1.97-1.94 Ga?), underplated mantle melts (basalt liquids) were trapped below preexisting lower crustal rocks of various compositions (e.g. granulites, metatonalites, amphibolites). The basalt liquids and subsequently melted lower crust could produced the immense volumes of granite (and volcanics) observed at 1.90-1.87 Ga. This geological picture is similar to the Tapajós Domain (TD) in the southern Amazonian Craton and suggest that both belongs to the same province (Ventuari-Tapajós or Tapajós-Parima). Nevertheless, the scarcity of S-type granites and high-grade metamorphic rocks show that the collisional stage is not so evident in TD.
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Evolução geológica das sequências do embasamento do Cinturão Araguaia na região de Paraíso do Tocantins (TO), Brasil
(2013-09) ARCANJO, Silvia Helena de Souza; ABREU, Francisco de Assis Matos de; MOURA, Candido Augusto Veloso
Isotopic studies based on single zircon Pb-evaporation and Sm/Nd (whole rock) methodologies, allowed advances at the lithostratigraphic scene and geologic evolution of basement, in the south segment of Araguaia Belt. The identified geological processes took place from the Achaean (2.6 Ga and TDM ages varying between 2.78 and 3.25 Ga) through Neoproterozoic Era. The Paleoproterozoic ortognaisses, represented by Rio dos Mangues Complex, are placed between 2.05 and 2.08 Ga, and they were formed from a mantellic and youthful source, with a small crustal contribution where TDM ages are 2.35 e 2.21 Ga. At the end of the Paleoproterozoic, a strong crustal shortening happened, and a partial melting of isolated and thickening compartments were facilitated, generating some igneous bodies (1.85 and 1.82 Ga) and Serrote Granite (1.86 Ga), that comes from sources situated between 2.50 and 2.43 Ga. At the end of the Mesoproterozoic, the region was marked by taphrogenetic processes, evidenced by the appearance of alkaline magmatism (1.05 Ga), beyond depositional basins, amongst which the one that received the sediments that had originated the supracrustals of Araguaia Belt. Through the inversion in the geodynamic conditions, in the Neoproterozoic, a process of horizontal shortening with crustal thickening and distinct volumetric and spatial melting occurred, which may have generated Matança and Santa Luzia Granites. The Araguaia Belt was built from this tectonic motion. The tectonic mass transport in the Amazonian Craton might have occurred, resulting in the current architecture in the form of imbricate fans.
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Evolução geológica das seqüências do embasamento na porção sul do Cinturão Araguaia - Região de Paraíso do Tocantins
(Universidade Federal do Pará, 2002-09-12) ARCANJO, Silvia Helena de Souza; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
The basement rocks in the south segment of the Araguaia Belt, due to the scarcity of geochronological information, were firstly considered as of Archean age. This interpretation began to be reviewed after the geochronological investigations were carried out during the last decade, which showed an important contribution of geological processes of the Paleoproterozoic in the formation of those basement rocks. In this work an isotopic study was carried out on the basement sequences of the southern segments of the Araguaia Belt and its results were based on the single zircon Pb-evaporation technique (Pb-Pb in zircon) and the Sm-Nd (whole rock) systematic. These techniques were used in order to improve and reconstruct the geological evolution of this crustal segment where Rio do Coco Group, Rio dos Mangues Complex, and Serrote Granite occur, as well as Monte Santo Suite that also appear in this context. The geological processes identified for the region took place from the Archean through the Neoproterozoic Era. The first evidences from the archean source were obtained in some restricted orthoderivated bodies in the east sector of the mapped area in which the TDM ages varied between 3.25 and 2.78 Ga. In a clear way, the Archean occurs in the northwest portion of the studied area being represented by a metabasic rock belonged to the Rio do Coco Group (greenstone belt sequence), with 2.618 ± 14 Ma. This age is interpreted as the age of the extrusion of the volcanic protolith. They would represent the two crustal preterit segments found in the region. During the Paleoproterozoic the Rio dos Mangues Complex was constituted, representing the most expressive unit of the basement. Ortogneisses of the Rio dos Mangues Complex were dated and their Pb-Pb in zircon ages varied between 2.054 ± 4 Ma and 2.086 ± 16 Ma. They were formed from a mantelic and juvenile source, with a small crustal contribution and their TDM ages are between 2.35 e 2.21 Ga. The geological processes that marked this period, involved crustal shortening with the participation of collision and thrusting that induced partial fusion of some parts of the thickened crust. The results were the generation of some igneous bodies (1.85 and 1.82 Ga) and of the Serrote Granite (1.86 Ga). Although the emplacement of the Serrote Granite took place at the end of the Paleoproterozoic, it was developed from older sources (2.50 e 2.43 Ga) than those of the Rio dos Mangues Complex. So, The continental crust established, with rocks from different ages and sources may be projected to the east, far from the studied area, inside the context of the architecture from the Atlantic Super Continent, formed definitively at the end of the Paleoproterozoic. At the end of a period without tectonic registers (end of Mesoproterozoic) a new phase took place in the region marked by tafrogenetic processes as the appearing of alkaline and basic magmatism as well as depositional basins that show an extensive context along the whole area. One of these basins received the sediments that originated the Araguaia Belt Supracrustals, which, during its evaluative process, reach the proto-rifte stage. Far from here, at the north portion of Goiás Massif, this rifting process seemed to permit the constitution of an oceanic domain, that, by evolution and recycling, may have be formed the rocks of the Magmatic Arc of Goiás. At the worked area, this arc terrain could be only be predicted by the appearing of one tonalitic gneiss with the age of 840 Ma and TDM model ages of 1.83 Ga. The effects of this tafrogenetic processes, from which the most important evidences are sienitic gneisses, found at Monte Santo Suit, with 1.051 ± 17 Ma, are related to the fission processes in the whole world which made the break up of the Rodinia Super Continent possible. The protolith of this suit were also been formed during the Mesoproterozoic as they can be seen in the TDM model age between 1.49 e 1.70 Ga. Finally, passing to the Neoproterozoic, through the inversion in the geodinamic conditions, processes of horizontal shortening again took place in the region, with the participation of crustal thickening as well as distinct volumetric and spatial fusions that may have generated the Matança and Santa Luzia Granites. The last one found inside the domain of Araguaia Belt. The Araguaia Belt was built from this tectonic motion, and has registers of past structural formations, also present in the older litostructural groups. The mass tectonic transport in the Amazonian Craton way might have occurred, resulting in the actual architecture found nowadays in the form of imbricated slices.