Navegando por Assunto "Neoproterozóico"

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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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Depósitos carbonáticos de Tangará da Serra (MT): uma nova ocorrência de capa carbonática neoproterozóica no sul do Cráton Amazônico
(2008-12) SOARES, Joelson Lima; NOGUEIRA, Afonso César Rodrigues
Cap carbonates are exceptional deposits related to the end of Neoproterozoic low-latitude glaciations. In the Tangará da Serra region, south Amazon craton, was described a Neoproterozoic carbonatic succession with approximately 20 m thick that includes the upper part of the Mirassol d'Oeste Formation and the base of the Guia Formation, respectively the dolomitic and calcareous caps of basal Araras Group. The cap dolomite is composed of pinkish peloidal dolograinstones with planar to low angle truncated laminations interpreted as deposits of a shallow to moderately deep platform. The cap limestone consists in massive to laminated siltstone and megaripple bedded crystalline limestone interpreted as deposits of moderately deep wave dominated mixed platform. Rippled crystalline limestone with crystals fans (pseudomorphosed aragonite) interbedded with shales were interpreted as oversaturated-CaCO3 deep platform deposits. Limestone with slump structures, convolute bedding and sinsedimentary faults characterize deposits of slope and neptunians dykes, filled by calcareous breccias, and isolated deformed limestone beds suggest seismic activity during the sedimentation. The succession of Tangará da Serra extends the occurrence of cap carbonates in the southern Amazon craton and corroborate with the presence of a large carbonate to mixed platform formed during the transgression after the glaciation Puga, correlate to Marinoan event.
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Depósitos sedimentares neoproterozoicos do Grupo Tucuruí - Cinturão Araguaia, Nordeste do Pará
(2014-03) DUTRA, Alessandra de Cássia dos Santos; GORAYEB, Paulo Sérgio de Sousa; NOGUEIRA, Afonso César Rodrigues
The Tucuruí Group of Neoproterozoic age outcrops in Tucuruí region, northeastern of Pará state, along with the transition between the Amazonian Craton and Araguaia Belt. The group is defined by a volcano-sedimentary sequence containing basaltic flows and diabase sill intrusions interbedded with siliciclastics deposits. The Tucuruí thrust fault override these sets rocky westward resulting in shearing, fracturing and fluid percolation in these rocks. The siliciclastic deposits consist of amalgamated subarkoses and siltstones, whose layers are oriented NNE-SSW direction with low dip to SE. In addition presenting coarsening and thickening upward. In this investigation were recognized two sedimentary facies associations: Deposits of Shoreface and Coastal Tempestites Face. This association suggests easy transport processes and sedimentation linked to a shallow marine environment, following the foreshore zone to zone shoreface under influence of wave storm. The petrographic analysis revealed the compositional and textural immaturity of arkosean sandstone and siltstone indicating nearby source area of provenance of mafic to intermediate igneous rocks. The sequence was subject to the mesodiagenetic sedimentary conditions. Thus, the siliciclastic deposits of Tucuruí Group represent the portion of a preserved segment influenced by coastal storm waves in a rift basin or foreland with nearby source area, composed of igneous rocks with strong relief, and marked predominantly by physical weathering. Basaltic volcanic flows occurred during the evolution of this basin.
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Evolução geológica pré-cambriana e aspectos da metalogênese do ouro do cráton São Luís e do Cinturão Gurupi, NE-Pará/ NW-Maranhão, Brasil
(Universidade Federal do Pará, 2004-07-06) KLEIN, Evandro Luiz; GIRET, André; HARRIS, Christopher; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
In the Gurupi region, located at the border between the Pará and Maranhão states in northern Brazil, igneous and metamorphic rocks crop out as part of the Parnaíba Structural Province. Early geochronological studies, based on the Rb-Sr and K-Ar methods have shown two geochronological domains. The rocks that crop out towards the Atlantic margin showed a Paleoproterozoic signature, around 2000 Ma, whereas the rocks that crop out towards the inner portions of the continent showed a Neoproterozoic signature, especially between 800 and 500 Ma. These domains have been then defined as the São Luís Craton and Gurupi Belt, respectively. Several lithostratigraphic propositions have been developed throughout more than two decades. However, these propositions always lack robust geochronological support. Geotectonic models discussed a one- or two-phase evolution for the Gurupi Belt, also lacking robust geochronological and isotopic data to consubstantiate the interpretations. Furthermore, among the several gold deposits that occur in both the cratonic and belt areas, only a few have geological and genetic information. These subjects are addressed in more or less depth by this thesis. New propositions for the regional lithostratigraphy and geological evolution have been achieved in this work by revaluating the available geological, geochemical, geochronological and isotopic dataset, as well as by adding new geochronological data on zircon (Pb-evaporation, U-Pb ID-TIMS, and LAM-ICP-MS) for most of the igneous and orthometamorphic rocks in the region. Whole rock Nd isotope data have also been obtained, allowing the discussion of crustal accretion and reworking. The results show a rather complex geological evolution with intensive and extensive crustal growth between 2.24-2.15 Ga and crustal reworking, involving melting, migmatization, metamorphism, and deformation around 2.10 Ga. The following results have been obtained for the São Luís Craton: Aurizona Group, metavolcano-sedimentary sequence, maximum age of 2241 Ma (juvenile) that possibly evolved until c.a. 2200 Ma; Tromaí Intrusive Suite, calc-alkaline, metaluminous tonalites of oceanic island arc, 2168 Ma (juvenile); Areal Granite, calc-alkaline, weakly peraluminous, 2150 Ma (mixing of juvenile and arc materials). In the Gurupi Belt, the following results have been obtained: Igarapé Grande Metatonalite, small and localized granoblastic tonalite, 2594 Ma; Itapeva Complex, weakly migmatized tonalitic orthogneiss, 2167 Ma (mostly juvenile); Chega Tudo Formation, metavolcano-sedimentary sequence (back-arc basin?), 2150-2160 Ma; Maria Suprema Granite, syntectonic, peraluminous muscovite-bearing granite, 2100 Ma (similar to other peraluminous granitoids in the Gurupi Belt). The Gurupi Group is tentatively placed in the Paleoproterozoic (>2160 Ma), but this must still be proved. The above data are interpreted on a plate tectonics basis, as follows. An oceanic basin is open at ca. 2260 Ma and is followed by the onset of subduction, formation of island arcs and voluminous calc-alkaline magmatism in oceanic settings, and concomitant reworking of the arcs between 2170-2150 Ma. This set of oceanic terranes has been accreted (soft-collision) onto an Archean continental margin to southwest (Archean part of the Amazonian Craton or a present day concealed cratonic nuclei). The collision provoked the metamorphism, deformation, and partial melting of the newly formed Paleoproterozoic crust and of part of the Archean bloc, or their erosive detritus, migmatization, and emplacement of peraluminous granitoids at 2100-2080 Ma. The region has been the locus of a second event in the Neoproterozoic. A continental rift developed in the bloc that was assembled in the Paleoproterozoic, as attested by the intrusion of a nepheline syenite (Boca Nova) at 732 Ma. Sedimentary rocks that filled this rift (Marajupema Formation) have detrital zircon crystals that show the youngest ages around 1100 Ma. The rift evolved probably to an oceanic basin, as suggested by the widespread occurrence of detrital zircons with ages around 550 Ma in small sedimentary basins that have been filled with immature sediments. The precise time of orogenesis climax that followed basin closure, with mass transport from SSW to NNE and accompanying metamorphism, is not yet constrained. Equivocal geochronological information point to 650-520 Ma (zircon of the nepheline syenite, Rb-Sr and KAr ages in minerals). The metallogeny of selected gold deposits occurring in both the São Luís Craton and the Gurupi Belt is addressed using varied information, such as geology, chlorite chemistry, fluid inclusion geochemistry, and stable (O, H, C, S) and radiogenic (Pb) isotopes. Structural and textural relationships, and Pb isotope data indicate a post metamorphic peak and late- to posttectonic timing for the gold mineralization with respect to the Paleoproterozoic events (post 2080 Ma). At a regional scale, the deposits show a similar signature characterized by formation temperatures between 280° and 380°C; pressures of 2-3 kbars; low-salinity (5 mass % NaCl equiv), reduced and moderately dense aqueous-carbonic (CO2 <20 mol%, traces of CH4 and N2), showing strong evidence for phase separation. Stable isotope studies suggest distinct sources for fluids and solutes. The carbonate, graphite, and fluid inclusion carbon comes from two sources: a depleted organic source, and an unknown source that may be magmatic, metamorphic or mantlederived (or both). Sulfide sulfur derived directly from magmas or from the dissolution of magmatic sulfides. Combined oxygen and hydrogen isotopes attest a metamorphic source for the fluids. Therefore, dehydration and decarbonization reactions during the metamorphism of the Paleoproterozoic metavolcano-sedimentary sequences appear to have produced the mineralizing fluids. Gold was transported as a reduced sulfur complex, such as the Au(HS)2 - and precipitated in response to the breakdown of this complex due to phase separation and fluid-rock interactions. The geological and genetic constraints are consistent with the orogenic gold model, found in metamorphic belts of all ages. As a whole the results of this study have implications for the understanding of the Paleoproterozoic and Neoproterozoic orogenies that built up the South American Platform and for the assembly and break-up of the Atlantica, Rodinia, and West-Gondwana supercontinents. The geological scenario outlined here for the Paleoproterozoic shows good correlations with those found especially in the southeastern Guyana Shield and in the southern portion of the West- African Craton. For the Neoproterozoic, the available information is still insufficient to draw major correlations.
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Fácies e isótopos de carbono e oxigênio da Formação Nobres, Neoproterozóico da Faixa Paraguai Norte, Mato Grosso.
(Universidade Federal do Pará, 2011-06-16) RUDNITZKI, Isaac Daniel; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The lastest stages of orogenic evolution of the Northern Paraguay Belt, south of the Amazon Craton, are related to a closure of a passive margin in the Neoproterozoic-Cambrian transition. In this basin, the predominant carbonate sedimentation of the Araras Group was succeeded by siliciclastic deposits of the Alto Paraguay Group. Events that led to the inhibition of carbonate sedimentation were partially recorded in the Nobres Formation, uppermost unit of the Araras Group. In the southern part of the Northern Paraguay Belt, in the Cáceres region, state of Mato Grosso, Central Brazil, the Nobres Formation overlies in unconformity the dolostones of the Serra do Quilombo Formation, and is overlain unconformably by coastal siliciclastic deposits of the Raizama Formation of the Alto Paraguai Group. The Nobres Formation consists of shallowing / brining upward small-scale arid peritidal cycles subdivided into two members: (i) lower member, composed of massive dolostone, intraclastic dolopackstones with enterolithic and megaripple bedding, wavy lamination with mud drapes, dolostone with silicified evaporite molds and domic to stratiform stromatolites, interpreted as tidal flat/sabkha deposits; and (ii) upper member, consisting of massive dolostone, dolomitic sandstone with megaripple bedding, wavy lamination with mud drapes, domic to stratiform and wrinkled stromatolites, dolostones with silicified evaporates molds, sandstones with low angle and climbing ripple cross lamination and mudstones with even parallel and wavy lamination, interpreted as mixed tidal flat deposits. The chemostratigraphic framework of Nobre Formation includes values of 13C and 18O between -2.19 and 0, 27‰VPDB and -7.42 and -4.25‰VPDB, respectively. The δ13C values are primary and representative of the original composition of Neoproterozoic seawater. The analysis of the δ13C stratigraphic curve in combination with the facies interpretation and following the Ediacaran stratified ocean model, allowed the identification of four isotopic patterns of the studied succession: type I, related to the storm wave to storm influenced shallow platform of Serra do Quilombo, with δ13C values near zero ranging from -0.27 to 0.4 ‰VPDB interpreted as a mixing of stratified waters of the ocean; type II, which refers to the transition between Serra do Quilombo and Nobres formations, with δ13C values ranging from -0.12 to 0.41 ‰VPDB, whose positive trend is interpreted as the fixation of 12C by biological activity; type III, defined as the typical isotopic signal of the Nobres Formation, trending and ranging from uniform values δ13C from -1.80 to -0.13‰VPDB related to changes in sea level; and type IV, that consist of crinkled pattern with δ13C values from -2.19 to -0.73‰VPDB indicative of isotopic reequilibrium of peritidal waters. The stacking of peritidal cycles, up to 200 m thick, suggests continuous and recurrent generation of accommodation with probably linked to tectonic subsidence. The siliciclastic inflow in the end of the deposition of the Nobres Formation, hindered the carbonate sedimentation, and it is attributed to uplift of source areas linked to the initial phase of the closure of Clymente Ocean, during the Pampean-Araguaia orogeny at the Neoproterozoic-Cambrian limit.
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Geocronologia U-Pb e geologia isotópica Sm-Nd do Granito Rio Verde, Neoproterozoico no Terreno Granjeiro -Várzea Alegre (CE)
(Universidade Federal do Pará, 2019-12-20) COELHO, Dayane do Nascimento; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
Several magmatic events, from the late Archean to the beginning of the Phanerozoic, are recognized in Borborema Province. The plutonic Ediacaran-Cambrian activity (Brasiliano cycle) is one of the most important geological features of this Province since it generated a large number of granitic bodies of different ages and nature. In this context, there are several granitoids emplaced in the Neoarchean rocks of the Granjeiro Terrain, of the Rio Grande do Norte Domain. Undergraduate geology students of the UFPA mapped some granitic bodies hitherto not described in this terrain yet. Among the new occurrences, a small granitic pluton located southwest of the city of Várzea Alegre-CE is the object of geochronological investigation of this dissertation. It is being referred here as Rio Verde Granite. The pluton presents porphyritic texture with feldspar phenocrysts (1,0 to 5,0 cm in size) immersed in a medium-grained matrix. The Rio Verde Granite has three lithofacies. Titanite-biotite-hornblende granodiorite (TnBtHbGdr), biotite monzogranite (BtMzg), and enclaves of quartz diorite composition. It also shows evidence of magmas mingling. The rocks are deformed; however, magmatic structures are also observed. The U-Pb zircon dating of the BtMzg and associated intermediate enclaves by LA-MC-ICP-MS was carried out to correlate this magmatism with one of the magmatic events recognized in the Borborema Province. In parallel, the Sm-Nd isotopic systematics was performed to characterize the source of the granitic magma (crustal rework or juvenile crust). U-Pb zircon dating provided a concordant age of 592 ± 3.2 Ma (2σ, n = 5) for the BtMzg. In turn, zircon dating in two samples of the quartz diorite enclave was not good enough due to the degree of metamictization of zircon crystals, which resulted in poor preservation of primary igneous features. Nevertheless, it was possible to define, in one of the samples, the concordant age of 607 ± 4.8 Ma (2σ, n = 3), which is indicative of the timing of the intermediate rocks. Thus, the contemporaneity between the granitic and the more mafic magmatism is suggested. However, additional geochronological studies are needed to define the age of the mafic magmatism accurately. The use of the Sm-Nd isotopic system in whole-rock revealed negative εNd (590Ma) values of -18.26 and -19.42, indicating the reworking old crust as source of the granitic magma. The Nd-TDM ages, calculated in two-stage, of 2.48 and 2.56 Ga, show the contribution of the Archean crust, probably of the Granjeiro Complex, to the formation of the magma that originated the Rio Verde Granite. However, the mixing of Archean crust with younger crustal material cannot be discarded as the Nd-TDM ages are in the Archean-Paleoproterozoic boundary. Considering the petrographic and geochronological features the Rio Verde Granite, it may be associated with the 570-590Ma syn-transcurrent granitic magmatism that occurred in the Borborema Province. This magmatic event has the granitoids of the Itaporanga Intrusive Suit as one of its representatives.
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Geoquímica isotópica Sr e geocronologia Pb-Pb da capa carbonática neoproterozoica do Grupo Araras, Tangará da Serra, MT
(Universidade Federal do Pará, 2012-04-24) ROMERO, John Alexander Sandoval; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The Neoproterozoic cap carbonates have been the subject of countless paleoenvironmental and chemicalstratigraphy studies in almost all Cratons around the world. Those were deposited after global glacial events deposits, are composed of dolostones and limestones, overlying glacial diamictites with specific features as stromatolits, tubes like structures, megaripples and crystal fans of calcite. In Brazil this ocucurrence, principal objetive of this work is exposed in Mirassol d ́Oeste and Tangará da Serra towns at Southeast of Mato Grosso State, Southeastern of Amazon Craton, recovering glacial diamictites with age of ≈ 630 Ma, The cap carbonate is part of base of Araras Group compoused by dolostone of Mirassol d ́Oeste and limestones of base of the Guia Formation. The main goal of this work is consolidate an Early Ediacaran age for the cap carbonate of the Tangará da Serra area by Pb-Pb geochronology and bring new Sr isotopic data to understand the paleoemviromental conditions as well as the increasing Sr marine evolution curve of during Neoproterozoic. Were collected 36 samples from top of Mirassol d ́Oeste (13 samples) and base of Guia Formation (23 samples), for petrography, X-ray difractometry, X- fluorescence as well as Sr isotopic analyses and Pb-Pb dating, using mass spectrometer TIMS and ICP-MS. The petrography allow recognize diagenetic features as stylolits, dolomite grains recristalized, spatic dolomite, iron oxides and autigenic quartz in dolostones of Mirassol d ́Oeste Formation. In Guia Formation, were observed partial substitution from crystal fans of calcite to spatic dolomite, stilolits as well as microfractures filled by calcite and secondary dolomite. The X-difractometry complemented the determination of mineralogical assemblage about carbonates, identificating the presence of secondary dolomite as well as quartz and feldspar in limestones of Guia Formation. The X-ray fluorescence allows determinate the teors of Fe, Mn, Ca and Sr, which were used to help the interpretation of Sr isotopic signatures. The Sr isotopic signature in 5 samples in dolostones of Mirassol d ́Oeste Formation and 6 limestones samples of base of Guia Formation, were determinated by sequential leaching with acetic acid. For dolostones the 87 Sr/ 86 Sr ratios ranging 0.708 to 0.709. For limestones the 87 Sr/ 86 Sr ratios ranging 0.707093 to 0.707289, after eliminate the leaching by probably terrigenous contribution for 87 Sr/ 86 Sr ratios until 0.7114. The lowest 87 Sr/ 86 Sr ratios were found in samples with lowest Mn/Sr ratios (0.31-0.45) and Fe/Sr (6.03-9.8). The differences in analytical procedure used to obtain the 87 Sr/ 86 Sr ratios, allow to explain the differences a out the isotopic Sr signatures in limestones from Tangará da Serra área (sequential leaching) with which, more radiogenic from limestones from Mirassol d ́Oeste área (total dissolution), previously published. The 87 Sr/ 86 Sr ratios ranging 0,70709 – 0,70729 in limestones from Tangará da Serra area, are positioned above from Sr marine curve in late Neoproterozoic, in transition from Cryogenian to Ediacaran, before the abrupt rise in early Ediacaran. Six dolostones samples and 17 limestones samples were analyzed, for determination of isotopic Pb composition, the samples were leached with HCl. The isotopic Pb signatures are homogeneous in dolostones (19.05< 206 Pb/ 204 Pb < 19.50; 15.69 < 207 Pb/ 204 Pb < 16.89) and were not used for elaborate the Pb-Pb isochron. From 17 limestones samples just 15 provided and age of 622 ± 33 Ma (2σ), despite de limited isotopic variations of the isotopic composition (18.77 < 206 Pb/ 204 Pb < 31.18; 15.71 < 207 Pb/ 204 Pb < 16.46). This result reinforces the Ediacaran early age to cap carbonate of Araras Group and check their association with the events after the last Criogenian glaciation at South of Amazon Craton.
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Reavaliação paleoambiental e estratigráfica da Formação Nobres do Grupo Araras, Neoproterozóico da Faixa Paraguai, região de Cáceres (MT)
(2012-12) RUDNITZKI, Isaac Daniel; NOGUEIRA, Afonso César Rodrigues
Outcrop-based facies and stratigraphic studies in the region of Cáceres, State of Mato Grosso, Brazil, subdivided the Nobres Formation into: lower member, composed of dolostone, intraclastic dolopackstones, sandy dolostones, stratiform stromatolites and evaporitic molds, interpreted as tidal flat/sabkha deposits; and upper member, constituted of dolostone, dolomitic sandstone, stratiform to domal and wrinkled stromatolites, evaporite molds, sandstones and mudstones, interpreted as mixed tidal flat deposits. The stacking of these deposits up to 200 m thick is composed by meter-thick shallowing/brining upward cycles related to a hot arid climate. The peritidal cycles also suggest continuous and recurrent generation of accommodation linked to tectonic subsidence. The siliciclastic inflow at the end of the deposition of the Nobres Formation that hindered the carbonate sedimentation and is attributed to the uplift of source areas linked to the initial phase of closure of the Clymene Ocean, during the Pampean-Araguaia Orogeny, at the limit Neoproterozoic-Cambrian.