Navegando por Assunto "Granitóides"

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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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Contexto geológico, estudos isotópicos (C, O e Pb) e associação metálica do depósito aurífero Tocantinzinho, domínio Tapajós, Província Tapajós-Parima
(2013-03) VILLAS, Raimundo Netuno Nobre; SANTIAGO, Érika Suellen Barbosa; CASTILHO, Marília Portela
The Tocantinzinho ore deposit is located along a NW–SE-trending lineament, southwestern of Itaituba (Pará, Brazil), and is the largest known gold deposit of the Tapajós Province. The host Tocantinzinho granite is essentially isotropic and dominated by syenogranites and monzogranites that have been weakly to moderately altered by hydrothermal fluids. Microclinization (earliest), chloritization, sericitization, silicification and carbonatization (latest) are the main types of alteration. Most mineralization was contemporaneous with the sericitization/silicification and is represented by sulfide- and gold-bearing veinlets which locally occur as stockwork. Pyrite, chalcopyrite, sphalerite and galena are the most common sulfides. Among the ore metals, Cu, Pb and Zn present the highest contents, but Mo, As and Bi locally show anomalous concentrations. The relationship of Au with Cu, Pb or Zn is at random and the Au/Ag ratios range from 0.05 to 0.5. The higher the sulfide contents, the higher the Au concentrations, though it occurs mainly included in pyrite. Zircon monocrystals from the Tocantinzinho granite yielded an average Pb-Pb age of 1982 ± 8 Ma and may represent an earlier event of the Creporizão magmatic arc. δ13CPDB values for calcite from the carbonatization stage fall dominantly between -3.45 and -2.29‰, being compatible with a deep crustal source that may include carbonatite reservoirs. In turn, δ18OSMOW values vary from +5.97 to +14.10‰, being indicative of magmatic derivation, although the less positive values suggest contribution from surficial waters. Unpublished fluid inclusion study reveals the presence of aquo-carbonic fluids, whose CO2 could have been dissolved in the granitic magma rather than being related to the shear zone. The available data allow the Tocantinzinho deposit to be classified as a granite-hosted, intrusion-related gold deposit.
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Estudo petrológico e das mineralizações de granitoides Santa Luzia na região de Paraíso do Tocantins-TO
(Universidade Federal do Pará, 1996-03-24) LAMARÃO, Cláudio Nery; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
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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 geológica da região nordeste do estado do Pará com base em estudos estruturais e isotópicos de granitóides
(Universidade Federal do Pará, 2001-07-04) PALHETA, Edney Smith de Moraes; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
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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.
Acesso aberto (Open Access)
Geologia e Geoquímica dos Granitoides Mesoarqueanos da Porção Noroeste do Domínio Rio Maria da Província Carajás: individualização e contexto tectônico das rochas da área de Tucumã.
(Universidade Federal do Pará, 2019-09-16) SILVA, Luana Camile Silva; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
The Carajás Province (CP) represents the largest preserved Archaean core of the Amazonian Craton with worldwide correspondents. Thus the Tucumã área, located in the northwest portion of the Rio Maria Domain (RMD) near the tectonic border with the Carajás Domain (CD), is marked by the occurrence of mesoarchean age granitoids. This study deals with the discrimination and characterization of this region granitoids which according to the regional studies is dominated by the Rio Maria suíte, by Xingu Complex rocks and metamafics of the greenstone belts sequences. However since data obtained in this work with geological mapping in detailed scale showed that the geological framework of Tucumã is much more diverse and complex. So that contrary to previous studies the most expressive unit in the region are high-K leucomonzogranites rocks that occur as a large plúton. Associated to this pluton small enclaves of granitoids of various compositions are presente in the form of lenses, controlled by NE-SW and E-W anastomosed shear zones. These bodies distinction led to the recognition of five groups: i) high-K Leucomonzogranite; ii) high-HFSE Granites subdivided into medium- and high-Ba; iii) porphyry médium-K Granodiorite; iv) high-Mg Granodiorite; and v) high-Na Tonalite. The granitoids have affinity with the calc-alkaline series, other than high-Na tonalites which follow the trondhjemitic trend with TTG affinities. The latter refers to magnesian granitoids Na2O rich (low K2O/Na2O ratio) which also differ from the others due to the N-S structural pattern often found in greenstone belt sequence, associated with an older tectonic in the region. The moderately fractionated REE patterns (medium La/Yb and Sr/Y ratios) and absence or small negative Eu anomaly typical of TTGs, are features similar to those of médium La/Yb ratio Mogno trondhjemite. With regard to the calc-alkaline units the porphyry médium-K granodiorites differ from the others by the magnesian feature and higher enrichment in Na2O (médium K2O/Na2O ratio) which set forth a resemblance to the TTG suites. However the médium-K granodiorites have higher levels of Ba, K and Th than TTG composition rocks, indicating strong similarities to the so-called transitional or enriched TTG suites. The small differences in the geochemical pattern of these two units are related to changes in the source, where the TTGs (high-Na tonalites) would be the product of the partial melting of a hydrated mafic source (metabasalts), on the other hand the transitional TTGs (porphyry médium-K granodiorite) would originate from melts of a heterogeneous crust with intercalation of enriched basalts and felsic layers. The high-Mg granodiorites occurs in a restricted way in Tucumã identified only in two outcrops. They are distinctly more enriched in Sr and mantle elements (Mg, Cr and Ni) and impoverished in HREE regarding the other granitoids. These features show strong affinities with the sanukitoides suites (Rio Maria Granodiorite) linked to the partial deep melting of the metassomatized mantle. The high-HFSE Granites (medium- and high-Ba) share geochemical characteristics with both the sanukitoide suite and the high-K leucogranites suíte similar to Hybrid granites like the Closepet-type. These suites represent different degrees of interaction processes (mingling or mixing), in the middle crust between crustal melts (tonalites/metassediments) and enriched mantle differentiated melts. Whilst the high-K leucomonzogranites represent the most evolved rocks in the region, where its enrichment in LILEs (Ba, K and Rb) and presence of the negative Eu anomaly indicates crustal reworking processes of an ancient felsic (tonalitic) crust at intermediate crustal levels. This unit has affinities with tha Xinguara and Mata Surrão granites. Regarding the deformation pattern, the rocks with the highest degree of deformation are the high-Na tonalities, in the other units this pattern is only identified in the portions where the shear zones are located. The observed textures (mantle-core and microcracks textures) suggest the operation of deformation processes during the magma crystallization typical of sintectonic granitoids under high temperature conditions (>500ºC). Less deformed granitoids present evidence of dynamic recrystallization at temperatures below 400°C. Thus, in RMD two phases of magmatism are identified, being the first one (2,98-2,92 Ga) related to a subduction setting under an oceanic plateau or a thickened mafic crust with melting at different crustal levels (crust root and slab), and mantle metassomatization by TTG melts and fluids. The second phase (~2.87 Ga) starts from thermal events (slab breakoff, delamination or mantle plumes) that results in partial meltilng of the metassomatized mantle with production of sanukitoide magmas and hybrid granites. This results in changes of the crustal root thickness that lead to substancial temperature variations sufficient to generate partial melting in and beneath the crust associated to generation of high-K granites.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero do Palito, Província Tapajós, Itaituba - Pa
(Universidade Federal do Pará, 2008-07-17) COSTA, Rodrigo de Melo; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The Palito Gold Deposit lies in the Jamanxim river region, easternmost part of the Tapajós Gold Province, sonthern Pará State. The Palito deposit comprises a mineralized quartz vein system hosted by Palito and Rio Novo Paleoproterozoic granites and is controlled by a NW-SE brittleductile stike-slip shear zone which belongs to a regional structure so called Tocantinzinho Lineament. The Palito Granite crosscuts the Rio Novo Granite and is the main host rock for the gold mineralization. The Rio Novo and Palito granites are two oxidized calc-alkaline monzogranitic stocks correlated respectively to Creporizão and Tropas Suites, characterized as magmatic arc granites. The thicker lodes, of metric width, are hosted by the NW-SE main fractures, whereas thinner veins, of centimetric width, associated with the thicker lodes, make both low angle (around E-W direction) and middle to high angle (NE-SW direction) in relation to the main shear direction. Such a structural situation is compatible to the Riedel system, with parallel lodes (D), low-angle veins (R and P), middle-angle veins (gash) and high-angle veins (R’ and X). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration ( quartz + phengite + pyrite) and chloritization (chamosite) are the two main hydrothermal alteration types which are followed by potassic alteration (K- feldspar + biotite), carbonatization (calcite + siderite + sericite) and subordinated sufidation (pyrite + chalcopyrite + sphalerite). The gold ore, hosted by quartz veins, is always associated to iron and copper sulfides (chiefly pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, native bismuth and gold are minor metallic phases. Three generations of pyrite, two generation of chalcopyrite and one generation of sphalerite were recognized. Substitution of chalcopirite1 for pyrite1 and pyrite2 for chalcopirite1 are widespread, whereas sphalerite crystallization is controlled by temperature and Cu/Zn ratio of the system, that is, substitution of sphalerite for chalcopirite1 ocurrs when temperature and Cu/Zn ratio are low and, vice versa, substitution of chalcopirite1 for sphalerite occurs in higher temperature and Cu/Zn ratio conditions. The gold is always associated or included in chalcopyrite, bismuthinite and native bismuth. Late sulfide generations are represented by veinlets of pyrite3 and chalcopirite2. The main gangue minerals associated to gold ore are quartz, phengite and chlorite, besides minor carbonate, fluorite, rutile, zircon and ilmenite Three kinds of fluids were recognized in the fluid inclusion study: 1) low salinity H2O-NaCl (up to 2,0 wt.% NaCl equiv.), interpreted as meteoric water; 2) high salinity H2O-NaCl-FeCl2-MgCl2 (45-50 wt.% NaCl equiv.) interpreted as magmatic brines, 3) low salinity H2O-CO2-NaCl (1,0-1,7 wt.% NaCl equiv.), probably of magmatic origin. The temperature and pressure conditions for the Palito gold deposit formation were estimated by combination of hydrothermal chlorite geothermometry and isochores calculated from the fluid inclusion microthermometric data. P-T values for trapping of the brines range from 340 to 405oC and 2 to 4,7 kb. The magmatic brines were interpreted as the main mineralized fluid, that is, sulphur, chlorine and metals (chiefly Au and Cu) were originated and concentrated from the residual phase of the granitic magma which gave rise the Palito Granite. The brines transported the metals as chloride complexes at high temperature (over 400oC). Fluid-rock interaction and mixing between mineralized fluid and low-T and low salinity fluids (probably meteoric water) promote a raising of pH and lowering of fS2 through hydrolysis and sulfidation reactions which have triggered ore deposition at lower temperature conditions (below 400oC) in transtension sites of the shear zone. The geological and hydrothermal alteration features and the mineralizing fluid characteristics are consistent to a structurally controlled intrusion related gold deposit model for the genesis of the Palito deposit. The host granitic rocks of the gold deposit, the vein style, the hydrothermal alteration (seritization and chloritization with minor potassic alteration), the Au-Cu-Zn (Pb-Bi) metallic association and the mineralizing fluid (H2O-NaCl-FaCl2-MgCl2) are consistent to a genetic relationship between the Palito Granite and the gold deposit. The granite supplied fluids, metals and heat to move the hydrothermal system, whereas the shear zone provided the structural traps for the ore deposition.
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Geologia, petrologia e geoquímica dos granitóides cálcico-alcalinos da região de Portovelo-Zaruma, El Oro-Equador
(Universidade Federal do Pará, 1996-07-30) LOYOLA PAZ, Jorge Eduardo; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In the Portovelo-Zaruma region, southwest Equator, occidental side of Cordillera Occidental of the Equatorian Andes, were mapped, at 1: 60.000 scale, five granite bodies: El Prado, Guayabo-Porotillo, Ambocas, Rios Luis-Ambocas anda Amarillo-Pindo. The other geological units are the Paleozoic Tahuim Group, composed by the San Roque Formation (quartzites, schists, gneisses, migmatites and amphibolites) and the Capiro Formation (quartzites, schists and phyllites); the Cretaceous Celica Formation (basalts and andesites), folded and discordantly overlay by Tertiary pyroclastics and andesitic flows. The granite bodies outcrop in very close areas, and probably are part of a unique batholith, only discontinuously exposed by the erosive processes. The granites are not dated, and are supposed to be of Triassic to Cretaceous age. The El Prado Granite intrude the Capiro Formation. It shows a elongated shape in the NW-SE trend (10 x 3 km). The Guayabo-Potillo Granite cuts the Tahuim Group, also showing an elongated shape in the NW-SE trend (7 x 3 km). The Ambocas Granite shows a near circular shape small bodies, and intrude the San Roque and Capiro formations, respectively. The relationships between all these granites and the Celica Formation are not conclusive due to the inaccessibility of the contact zones or by the fact that they are covered by colluvial deposits. The modal compositions of the granites shows span a expanded range, including gabbros, quartz gabbros, quartz diorites, tonalites, granodiorites and monzogranites. In the QAP diagram the rock follow preferentially the calc-alkaline tonalitic trend, but some granodiorites and monzogranites display a calc-alkaline granodioritic trend. Two rock groups were distinguished: (a) mafic to intermediate mafic-rich rocks - gabbros, quartz gabbros and quartz diorites; (b) felsic granitoids rocks - tonalites, granodiorites, and monzogranites. The dominant mafic minerals of the (a) group are pyroxenes, amphiboles and biotite, and biotite in the (b) group. The felsic rocks of the Guayabo-Porotillo body commonly show primary muscovite, are quartz-rich, and were affected by a strong hydrothermal alteration. Muscovite is also relatively abundant in the granitoids of the Ambocas, Luis-Ambocas rivers and Pindo-Amarillo rivers bodies. Amphibole is an important phase only in some granitoids of the El Prado body. The textures of the mafic and intermdiate rocks are porphyritic, pilotaxitic or seriated. Locally the plagioclase shows sieve texture. The felsic rocks are not deformed, and display a medium grained hypidiomorphic texture. According to the geochemical data about these granites there is a compositional gap between the mafic/intermediate and felsic rocks. Nevertheless, the studied rocks, fit the calc-alkaline trend displayed by the continental arc plutonic magmatism of the Andean chain. The mafic rocks are metaluminous and the amphibole-bearing felsic rocks are weakly metaluminous. The muscovite-bearing rocks are strongly peraluminous. A deep compositional gap between the two sets is clearly seen. In the diagram Ca+alkalis vs. SiO2 the rocks plot in the normal arc-related calc-alkaline granites field. However, some samples do not follow the general trend, probably due to crustal contamination or hydrothermal alteration. The El Prado rocks are less disturbed, following a trend very similar to that dis played by New Guinea Series or by the late granodiorites of Panama. The trace elements contents are similar to that of the volcanic arc granites (VAG). The metaluminous granites are petrographic and geochemically very similar to the I-type granites, but their tectonic enviroment is close to that of the Cordilleran I-type granites. The peraluminous granites, at a first sight, are similar to the S-type granites Australian granites, but are not cordierite-bearing, an index mineral of the Australian S-type granites. To explain the constrasting aspects between the metaluminous and the strongly peraluminous granitoids, it is proposed the hypothesis that the latter are derived from an I-type magma, contaminated by metasedimentary crustal rocks, by an assimilation process, similar to that described in the SW of USA. Other hyphotesis, considered more specifically for the extremely peraluminous granitoids, are: (a) their derivation from sedimentary sources; (b) a leaching of alkalis related to strong subsolidus hydrothermal processes, modifying the primary igneous compositions.
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Geoquímica e geocronologia U-Pb shrimp dos granitóides TTG da área de Ourilândia-Tucumã, Província Carajás-SE do cráton amazônico.
(Universidade Federal do Pará, 2023-11-17) REIS, Yury Haresson da Costa; OLIVEIRA, Davis Carvalho de
The rocks that make up the TTG crust in the northern area of Ourilândia do Norte - Tucumã are predominantly tonalitic and show strong petrographic and geochemical affinities with other TTG occurrences in the Carajás Province, which occur in the Rio Maria Domain and Carajás Domain. The granitoids were differentiated based on the occurrence domains of rocks from the Xingu Complex. They exhibit a varied structural pattern, with a tendency towards N-S and concentric patterns. These granitoids are predominantly composed of tonalites with subordinate trondhjemites and granodiorites. The U-Pb zircon crystallization age obtained from the tonalitic variety was 3.00 Ga. The trondhjemites are characterized by higher sodium concentration (Na2O/K2O ratio between 4.24-7.89) and low content of ferromagnesian elements (6 < FeO* + Mg + TiO2 + MnO < 8), while tonalites show sodium depletion (Na2O/K2O ratio between 1.79-3.20) and tend to be enriched in ferromagnesian elements (8 < FeO* + Mg + TiO2 + MnO < 13), with some samples falling within the field of hybrid granitoids, and they are also metaperaluminous (A/NK 1.5-2.0; A/CNK ~1). The Archean is characterized by developing thick sequences of greenstone and TTG plutons, forming dome-like structures and ridges in some cratons, such as those reported in the eastern Pilbara (Australia) and Dharwar (India) cratons. In the model adopted for the Ourilândia-Tucumã area, the generation of the initial stages of TTG magma in the Carajás Province sourced from metabasalts of the Tucumã-Gradaús Group's greenstone belt sequence. This occurred in a scenario involving the partial melting of the base of a thickened mafic oceanic protocrust due to interactions between the lithosphere and convective currents in the asthenospheric mantle, resulting in high-ETRP TTG melt. Dispersed crustal drips formed under increasing pressure and temperature conditions in this context. The partial melting of metabasalt within these drips produced felsic melts that intruded the overlying crust, forming low-ETRP TTG.
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Geoquímica, petrogênese e evolução estrutural dos granitóides arqueanos da região de Xinguara, SE do Cráton amazônico
(Universidade Federal do Pará, 2001-05-25) LEITE, Albano Antônio da Silva; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Xinguara region is situated in the northern sector of the Rio Maria Granite-Greenstone Terrain (RMGGT), southeastern Amazonian craton. The RMGGT is composed by greenstone belts and diversified granitoid plutons. Granitoids and gneisses, formeriy included indistinctly in the Xingu Complex, have been individualized in two new stratigraphic units: The Caracol tonalitic complex (CTc), which shows enclaves of the greenstone belts and the Água Fria trondhjemite (THaf). The Iatter is intrusive in the Sapucaia greenstone belt and in the CTc, and coeval with the Xinguara granite (Gxg). Some granodioritic bodies exposed in the Xinguara region are correlated with the Rio Maria granodiorite (GDrm). They are younger than the CTc and older than the THaf and Gxg. The dominant regional structures follow a WNW-ESE trend, observed in the south portion of the CTc and also in the comparatively younger granitoid plutons. The CTc preserves a N-S banding in its NW sector, but this structure is transposed to the WNW-ESE regional trend. The GDrm shows strongly flattened mafic enclaves, which defines a foliation; The THaf displays a magmatic banding; The Gxg pluton has an elongated shape; ali these structures follow the regional trend. The Gxg displays a weak foliation, subhorizontal at the center and dipping at high angles along the borders of the intrusion. The G1 axis of the regional stress during the intrusion of the granitoids was horizontal and trending N40E. The regional stress remained active during the submagmatic stage of the CTc evolution, as indicated by the presence of folds or boudins affecting its banding. It was responsible by the transposition to WNW-ESE of N-S structures. The stress field orientation was similar during the two phases of the Archean evolution of the region. This is suggested by the main submagmatic to subsolidus deformation structures in the GDrm, THaf, and Gxg. The changing trends of the CTc foliation suggest that the CTc was formed by domic plutons, intruded and sectionated by the younger granitic intrusions. Al-in amphibole geobarometer data suggest that the GDrm crystallized under a lithostatic pressure of —3 kbar, equivalent to a —10 km depth. The contact metamorphic effects of the Rio Maria granodiorite in the metabasaltic rocks of the Identidade greenstone belt are coherent with this data and suggest also that its emplacement was not diapiric-controlled. The variation in the intensity and orientation of the foliation in the Xinguara pluton and the deformation imprinted on its country rocks suggest its emplacement by bailooning. The emplacement of the THaf was probably controlled by diapiric processes. The CTc is a typical TTG, similar to those of the Archean trondhjemite series. Two different geochemical signatures have been identified in this granitoid on the basis of accentuated contrasts in LaN/YbN ratios. The GDrm is different of the TTG series. It follows the calc-alkaline trend and is similar to the Mg-rich granodiorites of the Sanukite Series. The THaf is geochemically similar to the CTc and by extension to the Archean TTG, but it is comparatively enriched in K2O. The Gxg is a high-K2O, strongly fractionated, calc-alkaline Archean leucogranite. Its REE pattern is indicative of a crustal origin. The dominant, high LaN/YbN ratio CTc group crystallized from a liquid probably originated from the partial melting of garnet amphibolites derived from 'normal' tholeiites. The latter should be similar in composition to the Archean metabasalts or to the metabasalts from the Identidade greenstone belt and the degree of partial fusion required would be, respectively, 25-30% and 10-15. On the other hand, the tonalites with Iow LaN/YbN ratios crystallized from a liquid derived from a garnet-free similar source. Nd isotopic data indicate a mantle source and a juvenile character for the tonalites of the first group. A tonalite sample of the second group and an enclave in the Gxg yielded negative ONd values and >3.2 Ga TDM ages. These data suggest that the tonalites of this group could derive from an older source with a longer crustal residence time. The THaf may have been generated by 5-10% partial melting of garnet amphibolites derived from metabasalts, chemically similar to the metabasalts from Identidade. The liquids of the Gxg were originated by variable degrees of partial melting of a source similar to the oldest TTG granitoids. The Archean geologic evolution of the Xinguara region occurs in two stages. The first starts in the interval of <2.95 to 2.91 Ga and is apparently similar to those of the Pilbara and Darwhar cratons. The second stage starts at 2.88 Ga and it is coincident with a sharp change in crustal behavior. At this time, the increasing thickening and stabilization of this Archean crustal segment, turned more effective the processes of plate subduction and convergence. In this tectonic context, the partial melting of an enriched mantie wedge would generate the parental magma of the GDrm and the partial fusion of garnet amphibolites derived from the subducted ocean crust would generate the THaf magma. Finally, the upward movement of the THaf and GDrm magmas would induce the melting of the TTGs in the lower crust, thus generating the granitic magmas of the Xinguara pluton.
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Granitóides proterozóicos como marcadores da evolução geotectônica da região nordeste do Pará, Brasil
(2009-12) PALHETA, Edney Smith de Moraes; ABREU, Francisco de Assis Matos de; MOURA, Candido Augusto Veloso
Granitoids cropping out inside Phanerozoic sedimentary cover in northeast Pará, Brazil (Gurupi region), records the geotectonic evolution of this region. 207Pb/206Pb single zircon evaporation ages were obtained for different granitoid bodies of the region, besides Sm-Nd isotopic studies. Almost all the plutons are genetically related with regional geological processes operative during this crustal segment formation, which includes the São Luís Craton. Such processes are associated with amalgamation of island arcs and Archean nuclei during the Palaeoproterozoic (2.15 to 2,07 Ga). The reworking of the southwestern margin of the São Luís Craton at the end of the Neoproterozoic formed the Gurupi Belt and is recorded by the occurrence of a granitic pluton of 549 ± 4 Ma.
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Petrogênese e história tectônica dos granitóides mesoarqueanos de Ourilândia (PA) – Província Carajás
(Universidade Federal do Pará, 2022-09-16) SILVA, Luciano Ribeiro da; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
Zircon U-Pb-Hf isotopic data from the main Mesoarchean units in the Ourilândia do Norte area (Carajás Province, Amazon Craton) were combined with a review of the main geological-structural, petrographic and geochemical aspects of these rocks, which allowed a redefinition of local stratigraphy, as well as a better understanding of the nature of the sources, based on geochemical modeling. In addition, a modern framework of the tectonostratigraphic correlations and the main events that led to the stabilization of the province was presented, as well as their implications for the origin of the plate tectonics. The Ourilândia granitoids are composed of interdigitated batholiths of sanukitoids and potassic granites, with subordinate TTG. (1) The TTG represent the oldest event in the area (2.92 Ga) and they are composed of tonalitic xenoliths (Mogno suite) and a porphyritic trondhjemite stock (Rio Verde suite), in which biotite is the main mafic mineral. The xenoliths are intensely deformed and the trondhjemite presents small mafic enclaves. The xenolith provided chondritic values of εHf(2.92 Ga) = +2.0 to –0.2 and was formed by partial melting of hydrated metabasalts, while the trondhjemite presented εHf(2.92 Ga) = +2.3 to –3.5 suggesting a more complex origin involving mixing between TTG-type melt and a subchondritic component, reflecting its longer crustal residence time (Hf-TDMC = 3.2–3.5 Ga) in relation to the xenolith (Hf- TDMC = 3.2–3.3 Ga). (2) The sanukitoids were grouped in the Ourilândia sanukitoid suite, which integrates the Arraias granodiorite (2.92 Ga) and the Ourilândia tonalite-granodiorite complex (2.88 Ga), which is composed of tonalites and granodiorites with subordinate quartz monzodiorite, quartz diorite and mafic enclaves. In general, these rocks show hornblende, biotite and epidote as the main mafic phases. The Arraias granodiorite is the oldest sanukitoid unit in the province and one of the oldest in the world. It provided εHf(2.92 Ga) values ranging from chondritic to subchondritic (+1.9 to –4.4) and can be generated by 29% melting of the mantle metasomatized by 40% TTG- type melt, under oxidizing conditions, leaving a residue composed of orthopyroxene, garnet, clinopyroxene and magnetite. Meanwhile, the Ourilândia complex provided values of εHf(2.88 Ga) = +3.4 to –2.0 and its different varieties of granitoids (including quartz monzodiorite) were formed from 18–33% melting of the mantle enriched by 20–40% TTG-type melt, under oxidizing conditions, leaving a residue composed of orthopyroxene, clinopyroxene, garnet, magnetite ±olivine. The mafic enclaves and the quartz diorite show distinct petrogenetic histories and were assumed to be a product of partial melting from the mantle metassomatized by fluids at lower pressures, outside the garnet stability zone. (3) The equigranularmonzogranite represents the largest unit in the area and was correlated with the Boa Sorte batholith (Canaã dos Carajás granitic suite). Its parental magma can be formed by 18% melting from a TTG-type trondhjemite (analogous to those of Água Azul do Norte) under relatively oxidizing conditions, leaving a residue composed of plagioclase, quartz, biotite, magnetite and ilmenite. The U-Pb data allowed to distinguish four zircon populations (3.04 Ga, 2.97 Ga, 2.93 Ga and 2.88 Ga). The youngest population was interpreted as the magmatic crystallization age (coeval to the Ourilândia complex) and provided subchondritic values of εHf(2.88 Ga) = –0.8 to – 4.1, which confirms its crustal origin. The 2.93 Ga population was interpreted as crystals C inherited from the TTG-type source and provided chondritic εHf(2.93 Ga) = +2.8 to –0.7 (Hf-TDMC = 3.1–3.4 Ga), indicating a shorter crustal residence time than the 2.88 Ga population (Hf-TDMC = 3.3–3.5 Ga). The populations dated at 3.04 Ga and 2.97 Ga were interpreted as xenocrystals with εHf(3.04 Ga) = –1.7 to –2.2 (Hf-TDMC = 3.5 Ga) and εHf(2.97 Ga) = +1.4 to –5.7 (Hf-TDMC = 3.3–3.7 Ga), respectively. (4) The high-Ti porphyritic granodiorite and the associated heterogranular monzogranite are closely related to the Boa Sorte granite and were grouped in the Tucumã granodiorite-granite suite, which has affinity with the Closepet (Dharwar craton, India) and the Matok (Pietersburg block, South Africa) granites. The high-Ti granodiorite can be formed by 30% melting from the mantle enriched with 40% of TTG-type melt under oxidizing conditions, leaving a residue composed of orthopyroxene, olivine, plagioclase, clinopyroxene and magnetite, with the participation of a component enriched in HFSEs, such as sediments, fluids and/or asthenosphere materials. The petrogenesis of the monzogranite of this suite involved mixing between 40% crust-derived magmas (Boa Sorte granite) and 60% enriched mantle-derived magmas (high-Ti granodiorite). A three-stage tectonic model is assumed to explain the C origin and isotopic signature of the studied granitoids. In general, the Hf-TDMC ranging from 3.7 to 3.1 Ga, indicating the existence of a Paleoarchean crustal component, which was generated in long-lived dome-and-keel tectonics (~600 Ma) and later recycled in the mantle allowing its enrichment from low-angle subduction in Mesoarchean (2nd setting), where the TTG-type granitoids and the first sanukitoid generation were formed at 2.92 Ga. Then, a short-lived collision (3rd setting) defined by the peak regional metamorphism (2.89–2.84 Ga) and associated with crustal thickening and slab breakoff allowed the origin of large volumes of mantle- and crust-derived magmas at ~2.88 Ga, where the ascent and emplacement were conditioned by shear zones.
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Petrologia dos granitóides brasilianos da região de Caraúbas-Umarizal, oeste do Rio Grande do Norte
(Universidade Federal do Pará, 1993-05-07) GALINDO, Antonio Carlos; MCREATH, Ian; http://lattes.cnpq.br/5299851252167587; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Six major granitoid plutons were mapped in the Caraúbas-Umarizal area, in the West of Rio Grande do Norte State, Northeast Brazil. These are the Umarizal, Tourão, Caraúbas, Prado , Complexo Serra do Lima e Quixaba plutons. Excepting the Umarizal granitoid, all plutons were deformed during the Brasiliano Cycle, displaying a NE-trending foliation dipping mostly to SE. This fabric is related to the main Brasiliano tectonic episode. Brittle-ductile deformation is represented by fractures, faults and shear zones, which are common features of the area. The Portalegre shear zone (ZCP) is an prominent structure with more than 200 km long and up to 2 km wide. The emplacement of most of these granitoids was largely controlled by shear zones. The common occurrence of magmatic breccia structures in the Umarizal granitoid suggest its intrusion into relatively cool crust. Regarding the Tourão granitoid and similar plutons, it is envisaged an emplacement by diapirism followed by ballooning. The Umarizal granitoid is dominated by rocks with quartz monzonite and quartz syenite composition and coarse-grained textures, with biotite, amphibole, and clinopyroxene ± fayalite in variable proportions, and rare orthopyroxene. The Quixaba granitoid has a coarse to very coarse texture and quartz monzodiorite to quartz monzonite compositions. The Tourão, Caraúbas and Prado granitoids and the Serra do Lima complex closely resemble each other. They are dominantly represented by porphyritic monzogranites with subordinate occurrences of leuco-microgranites. The Prado granitoid has an associated diorite facies, which occurs mainly as enclaves in the granites. From the geochemical point of view these granites fali into four families: the Quixaba granitoid, the Prado diorite association, the Umarizal granitoid and the whole group of the Tourão, Caraúbas, Prado (grafite facies) and Serra do Lima complex granitoids. The first two present low silica and a geochemical signature of shoshonitic plutonic rocks, though they are more alkaline than is usual in this kind of association. The latter (Umarizal, Tourão, Caraúbas, Prado e Complexo Serra do Lima) display intermediate to high silica. The Umarizal granitoid has alkaline affnnities and several characteristics of A-type gravites. The remaining type display geochemical signature of subalkaline acid associations. Rb-Sr whole-rock dating show that the Caraúbas and Prado granitoid (630 23 Ma) are the oldest in the area, being followed by the Tourão granitoid and Serra do Lima complex (600 + 7 - 575 ± 15 Ma), and finally by the Umarizal granitoid (the youngest at 545 ± 7 Ma). Initial 87Sr/86Sr rations above 0,708 point to a dominantly crustal source for these magmas. The Quixaba granitoid and the Prado diorite association display geochemical features of a mantle source. Considering the presence of pyroxene and fayalite in the Umarizal granitoid and of clino-and orthopyroxene in the Quixaba granitoid, it is estimated that crystallization of these granitoids began at temperatures around 900 °C and pressures between 8 to 9 kbars. During crystallization, conditions of low oxygen fugacities prevailed in the near FMQ buffer. In the case of Umarizal granitoid the oxygen fugacites was controlled by the FMQ buffer and possibly also for the Quixaba one. Concerning the Umarizal granitoid, melting of rocks with mangeritic composition is assumed to generate its parent magma, while the magmas which formed the Tourão, Caraúbas, Prado (gravite facies) and Serra do Lima complex granitoids probably originated by melting of a monzonitic source. Fractional crystallization was the dominant process in the evolution of the magmas of these granitoids. The Meruoca gravite in Ceará State also displays a fayalite-bearing facies and is the only granitoid described up to now in the Borborema Province that lias analogies wíth the Umarizal grafite. Nevertheless they differ in some petrographical and geochemical aspects. Plutonic shoshonitic associations have been frequently described in this province, but they are compositionally distinct from the Quixaba granitoid. The Tourão, Caraúbas, Prado (gravite facies) and Serra do Lima complex granitoids are similar to a large number of plutons throughout the Borborema Province, representing the most common types of Brasiliano-age granitoids.
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Petrologia magnética dos Granitoides Neoarqueanos da Suíte Vila Jussara - Província Carajás, Cráton Amazônico.
(Universidade Federal do Pará, 2019-07-30) SOUSA, Luan Alexandre Martins de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Vila Jussara suite (VJs) comprises several granitic stocks of Neoarchean age (~ 2.75-2.73Ga), intrusive in Mesoarchean units and distributed in the central and northern portions of the Sapucaia Domain in Carajás Province. The VJs granitoids consist of reduced and oxidized ferrous granites as well as magnesian granites. Petrographically, four types of rocks were distinguished in the VJs: (1) Biotite-hornblende monzogranite (BHMzG); (2) Biotitehornblende tonalite (BHTnl); (3) biotite monzogranite (BMzG); (4) Hornblende-biotite granodiorite (HBGd). The study of magnetic susceptibility (MS) in VJs rocks showed very variable values (MS, 0.14 x 10-3 to 30.13 x10-3), distributed in three populations (A, B and C). Based on the magnetic behavior and the Fe and Ti oxides, BHMzG was divided into two subgroups: the first with very low to low MS (MS 0.14 x 10-3 and 0.81 x 10-3; populations A and B1 ) marked by the dominance of ilmenite with titanite crowns, as well as the subordinate presence of magnetite and pyrite crystals, the latter evidenced only in subpopulation B1; the second shows moderate to high values of MS (1.91 x10-3 to 6.02 x10-3, subpopulations B3 and C1), being characterized by the dominance of magnetite over ilmenite. The BHTnl presented moderate values of MS (0.85 x10-3 to 1.36 x10-3, subpopulation B2, with the exception of a single sample with high value of MS belonging to subpopulation C2) and present dominance of pyrite, seconded by magnetite which is more abundant than ilmenite. BMzG and HBGd are characterized by relatively higher MS values (MS, respectively, 2.14 x10-3 to 6.01 x10-3 and MS 6.02 x10-3 to 25.0 x10 -3, subpopulations B3, C1 and C2) and both are characterized by the dominance of magnetite over pyrite, with rare occurrences of ilmenite. In geochemical terms, the first subgroup of BHMzG exhibits silica >70% and affinity with the reduced ferrous granites; the second presents silica varying between 63 and 70% and is similar to oxidized ferrous granites. All other groups show magnesium granite characteristics with increasing BHTnl silica for HBGd and BMzG. The biotite compositions vary in the passage of BHMzG from subgroup 1 to subgroup 2 and from these to magnesian granites and are compatible with those from the Ilmenite series for transitional between Ilmenite and Magnetite series and, finally, Magnetite series. In this same sense, amphibole compositions indicate low, moderate and transition between moderate and high oxygen fugacity. The four VJs strains formed in different degrees of oxidation, the first subgroup of BHMzG formed under reduced (
Desconhecido
Petrologia magnética dos granodioritos Água Azul e Água Limpa, porção sul do Domínio Carajás - Pará
(2013-12) GABRIEL, Eleilson Oliveira; OLIVEIRA, Davis Carvalho de
The Água Azul and Água Limpa granodiorites (AAGrd and ALGrd, respectively) outcrop in the extreme southern of the Carajás Domain as two elongated bodies following the EW regional trend and were previously included in the Xingu Complex. The ALGrd consists mainly of biotite-amphibole granodiorites and muscovite-biotite granodiorites, with subordinate amphibole-biotite tonalites; the AAGrd contains dominant epidote-amphibole-biotite granodiorites, epidote-amphibole-biotite tonalite and restricted (amphibole)-epidote-biotite monzogranites. These rocks show geochemical signatures like of archaean sanukitoids. The magnetic susceptibility (MS) values obtained in the ALGrd (average 17.54 × 10-4 SIv) and AAGrd (average 4.19 × 10-4 SIv) are relatively low. The main opaque minerals are magnetite and hematite, and ilmenite is lacking in these rocks. The ALGrd contains titanite associated with magnetite, while the AAGrd contains pyrite, chalcopyrite, and goethite. In the ALGrd, magnetite is more developed and large than in the AAGrd, justifying its highest values of MS. The oxidation of magnetite (martitization) and the alteration of sulfides to goethite, occurred at low temperatures. The positive correlation between MS values and the modal content of opaque, amphibole, epidote + allanite and quartz + K-feldspar, as well as the negative correlation of MS with biotite and mafic observed in these units, reveal a trend of MS increasing in the direction: amphibole tonalites/amphibole granodiorites à biotite granodiorites/biotite monzogranites. The geochemical data confirm this fact, with a negative correlation between the MS values and Fe2O3T, FeO, and MgO, reflecting, for the two units, an upward trend in MS values parallel to magmatic differentiation. The geochemical and mineralogical affinities between these rocks and sanukitoids of the Rio Maria Domain suggest conditions of the oxygen fugacity between HM and FMQ buffers for the studied granitoids.
Desconhecido
Petrologia, geologia estrutural e aerogeofísica da porção Leste do Domínio Bacajá, Província Maroni-Itacaiúnas
(Universidade Federal do Pará, 2008-09-30) SOUSA, Cristiane Silva de; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
The Bacajá Domain is located in the centrar-eastern part of the Pará State, in the southern part of the Maroni-Itacaiúnas Province, which is characterized by a large exposure of Paleoproterozoic and Archean rocks reworked during the Transamazonian Cicle Orogeny. The study area is situated in the Novo Repartimento town, to the south of the Maracajá village, where monzogranites, granodiorites and tonalites, as well as quartzites, granulites and gneisses are exposed. Amphibolites occur as xenoliths in the granitoids. Diabasie dikes are found locally. Aerogeophysical data obtained has improved the cartography of the mapped area. The magnetic structures, mainly determined from the horizontal (x, y) and vertical derivatives (z), evidence a major set of lineaments trending WNW-ENE, consistent with the regional structures. NE-SW lineaments comprise mafic dikes. Maps of potassium, uranium and thorium channels, total count and ternary (RGB, CMY) has allowed the individualization of ten gamma-spectrometric domains. High radiometric values correspond to biotite-granites and gneisses. Leucomonzogranites, hornblenda granites and quartzites show moderate to low radiometric values. A penetrative foliation is recognized at regional scale in the granitoids and displays NW-SE and WNW-ESE strikes, generally with subvertical dips. Primary layering showing gentle to steep dip evolves to a secondary foliation and to mylonitic zones, both concordant. The mineral lineation is weak and have gentle plunges. Microstructural features indicate a transition from magmatic flow to solid-state deformation during the development of foliations in granitoids. Structural analysis of the granitoids suggests that the regional deformation and the emplacement of great volume of intermediate to felsic magma were contemporaneous. Pervasive foliation at the regional scale and homogeneous foliation at the outcrop scale are very common features in syntectonic plutonic belts, and generally generated in a magmatic arc setting. Fourteen petrolographic facies are recognized in the granitoids, so they can represent several plutons. These rocks are metaluminous, medium-to high K calcalkaline and distinguished by high light REE and low heavy REE contents. Eu negative anomalies are very weak or absent. Petrological, geochemical and structural features of the granitoids suggest a magmatic arc environment for the studied region, and that granitoid emplacement is contemporaneous with a compressive tectonic event.
Desconhecido
The Tocantinzinho gold deposit, Tapajós province, state of Pará: host granite, hydrothermal alteration and mineral chemistry
(2013-03) SANTIAGO, Érika Suellen Barbosa; VILLAS, Raimundo Netuno Nobre; OCAMPO, Ruperto Castro
This paper presents geological, petrographic and mineralogical data about the granite that hosts the Tocantinzinho gold deposit and aimed at contributing to the understanding of the hydrothermal processes related to the ore genesis. The host granite is a late to post-tectonic biotite monzogranite that fits in the oxidized sub-type of the ilmenite series. It was emplaced at depths of 6 - 9 km and reveals no deformation other than fracturing and brecciation. This intrusion has undergone mild to moderate hydrothermal alteration that generated two main rock varieties (salami and smoky), with no significant mineralogical or chemical differences, though quite distinct macroscopically. Several types of hydrothermal alteration have been recognized in the granitic rocks, greatly represented by filling veins and/or replacement of primary minerals. The hydrothermal history started with microclinization, during which the granitic protolith was in part transformed into the salami variety. This process was followed by chloritization when the temperature dropped to ~330 ºC producing chamosite with XFe in the 0.55 - 0.70 range. Then it evolved to sericitization, at the same time that ore-bearing fluids precipitated pyrite, chalcopyrite, sphalerite, galena and gold. As alteration advanced, solutions saturated in silica and formed quartz veinlets. At the latest stage (carbonatization), aqueous and aqueous-carbonic fluids might have mixed, allowing Ca2+ e CO2 to react to form calcite. Most sulfides are present in veinlets that crosscut the granite, some arranged as stockwork. Gold is normally very fine-grained and occurs mainly as submicroscopic inclusions or along microfractures in pyrite and quartz. The Tocantinzinho deposit is very similar to the Batalha, Palito and São Jorge deposits, and to those of the Cuiú-Cuiú goldfield. Topologically, it has been classed as an intrusion-related gold deposit.