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Ambiente geológico e mineralizações associadas ao granito Serra Dourada (extremidade meridional) Goiás
(Universidade Federal do Pará, 1983-08-29) MACAMBIRA, Moacir José Buenano; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Serra Dourada granite belongs to a set of domic structures, generally mineralized in cassiterite, located in the center-east of Goiás, where rocks of the Uruaçu and Brasília folding belts and the Goiás median massif dominate. In order to contribute to the petrological, metallogenetic and stratigraphic knowledge of these granitic rocks, the southern tip of Serra Dourada was selected for this study. The methodology adopted was mapping at a 1:45,000 scale, petrographic, minerographic and geochronological studies, in addition to the determination of the contents of major elements in rocks and some minerals, and of trace elements in rocks. The granitic rocks of Serra Dourada were classified as syenogranites, presenting three varieties: amphibole-biotite granite, muscovite-biotite granite and biotite granite, the latter being dominant. The K-Rb graph indicates an advanced degree of fractionation for these rocks and suggests a trend that starts from granite to amphibole and ends in muscovite. In turn, the systematic variation of the contents and ratios of some trace elements reveals an intimate relationship between these varieties, meaning multiple intrusions that correspond to different degrees of partial fusion of the original material. In attempts at dating by the Rb-SR method, it was observed that the phenomena subsequent to the initial lodging in the crust introduced possible isotopic rejuvenations. However, these granitic rocks provided maximum conventional ages close to 2 b.a. The last magmatic phases of the Serra Dourada granite were the pegmatites which, in the core of the batholith, are zoned and contain aquamarine, while at the edge they bear tantalite-columbite, emerald, muscovite and monazite. Then, large amounts of hydrothermal solutions enriched in Sn and F reached both the granite and its host, changing them to greisens. Upon contacting the enclaves, the solutions precipitated cassiterite, magnetite, fluorite and sulfides. Veins with wolframite and rutile lodged in the nearest enclaves. At lower temperatures, these solutions generated kaolin when reaching the pegmatites of the contact range. Several types of enclaves have been identified in the granite: biotitite, soda-gneiss, xenoliths of schists and quartzites, and amphibolites. The soda-gneiss enclaves are trondhjemitic in nature and also have amphibole and biotite, biotite and biotite and muscovite varieties. The similarity of the assemblage and chemistry of some mineralogical phases suggests a consanguinity between soda-gneiss and granite, with the possibility that they are partially intact fragments of the rocks that gave rise, by anatexia, to the granitic material. On the other hand, the contents and anomalous ratios of some elements of soda-gneiss indicate reaction with magma, which is emphasized by the position of these rocks in the K-Rb graph. This reaction certainly affected the isotopic ratios, allowing only to suggest an Archean age. In turn, the biotites are possibly restricted. The sequence where the Serra Dourada granite was lodged is composed of intercalations of schists and quartzites from the Serra da Mesa Group. The typical mineralizations of acid magmatism, greissens, pegmatites and granitic sills in the metasediments, in addition to xenoliths from the enclosing rocks and pronounced foliation at the edges of the body, testify to the intrusive character of the granite in these metamorphites, whose late-syntectonic event is associated with the formation of the brachyanticlinium, which agrees with the regional structural pattern. Through the mineralogical assemblage of these rocks, conditions of low amphibolite facies were attested for its formation, where pressures above 4.5 Kb and temperatures around 550°C.
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Aspectos lito-estruturais e evolução crustal da região centro-oeste de Goiás
(Universidade Federal do Pará, 1985-11-13) COSTA, João Batista Sena; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
The study area is bounded by the cities Paraíso do Norte, Gurupi, and Dianópolis in north-central Goiás State. The area contains diverse lithostratigraphic units and various generations of structures related to distinct thermo-tectonic events. Based on the distribution and the petrographic and structural characteristics of the ancient rock assemblage, four litho-structural domains were defined and attributed to the Archean. Domain "1" includes the region of Almas-Dianópolis and is interpreted as part of granite-greenstone terrane. It includes a group of tonalitic gneisses with associated supracrustal rocks (Goiano Complex), a sequence of metavolcanic rocks and metasediments (Riachão do Ouro Group), and various tonalite bodies (Serra do Boqueirão Suite) intruded into the earlier units. The evolution of the domain includes three principal deformational events: a) Formation of the amphibolites and/or biotite gneisses and granitoids characterized by sub-vertical banding oriented N10ºE and accompanied by mineralogical changes under conditions of amphibolite facies; b) deposition of the Riachão do Ouro Group, followed by isoclinal folding oriented N10°E and consequent transformation to greenschist facies. The emplacement of the tonalitic diapirs of the Serra do Boqueirão Suite is related to this event; c) a foliation gently inclined to the SE resulting from a simple low-angle ductile-brittle shearing process which affected the west part of this domain, transforming the rocks of the Goiano Complex into mylonitic gneisses under amphibolite facies conditions. Domain 2 includes the counties of Porto Nacional, Brejinho de Nazaré, and Natividade in the east-central part of the area. It is characterized by granulitic gneisses (Porto Nacional Complex), by tonalitic gneisses with associated supracrustal rocks (Manoel Alves Complex), including metasediments and metavolcanics (Morro do Aquiles Formation), and by pegmatitic granites such as the Xobó Suite. The different lithologic units take the form of lenses or sub-horizontal concordant to sub-concordant bodies with strike N30°E. They show structural features produced by a low-angle ductile-brittle shearing process under amphibolite facies conditions. Superposed on the low-angle features are various zones of high-angle directional shear having different intensities of deformation, but all in greenschist facies conditions. Domain 3 is within the NW part of Paraiso do Norte county and is interpreted as a granite-greenstone terrane similar to that of Domain 1. This Domain includes the Colméia Complex, the Rio do Coco Group, and the alkaline gneisses of Monte Santo. Two principal deformational phases are responsible for the structures in this domain: a) folding (S) of the gneissic granitoids of the Colméia Complex into recumbent folds oriented E-W. The axial plane schistosity (S1) formed in medium to amphibolite facies conditions; b) deposition of the Rio do Coco Group, discordant with the Colméia Complex, followed by sub-vertical folding oriented E-W. The second generation of folds in the Colméia Complex is related to this deformational event. Domain 4, in the west-central part of the area, includes parts of Paraíso do Norte, Fatima, Gurupi, and Porto Nacional counties. This domain is composed of the Rio dos Mangues Complex, the Matança and Serrote Suites, and the alcaline gneisses of the Serra da Estrela, distributed in sub-concordant sheets oriented N30°E. Similarly to that observed in Domain 2, these rock assemblages show structural features related to low-and high-angle shearing events. The transition between Domains 1 and 2 and between Domains 3 and 4 is gradational, such that two ancient blocks of crust are defined (Domains 1+2 and 3+4] separated by a belt of granulitic rocks (Porto Nacional Complex). The zone of juxtaposition corresponda to a belt of low-angle ductile shearing developed by the overthrusting of the Brazilian block, on the east, onto the Araguacema block to the west. Similar geologic conditions have been well characterized in South Africa, in western Greenland, and in NW Scotland and are beginning to be described in various regions in Brazil, constituting a new way to understand the relations between Archean terranes. Granite bodies of the Lajeado Suite at the end of the Lower Proterozoic and ultrabasic bodies in the first half of the Middle Proterozoic were injected into this crustal segment stabilized at the end of the Archean. During this epoch the Transbrazilian Lineament became defined as a brittle shear zone. Basins were developed in the second half of the Middle Proterozoic, with deposition of the Baixo Araguaia Supergroup and the Natividade Group. These two are separated today by a block limited by the cities of Paraíso do Norte, Gurupi, and Porto Nacional. The Transbrazilian Lineament was reactivated in this period.At the end of the Middle Proterozoic an E-W regional compression produced the Araguaia and Uruaçu fold belts. The evolution of the Araguaia fold belt involved four stages of structural deformation. In the first stage, N-S recumbent folds were formed having axial plane schistosity (S1) developed in intermediate amphibolite facies to intermediate greenschist facies conditions. The intermediary stages involved folding and refolding of the S1. The last stage is related to the formation of domai structures resulting from the intrusion of the granite bodies of the Santa Luzia Suite. As a result of this evolution, the Araguaia belt has an importent asymmetry characterized by intensification of deformation and mineralogical transformations from west to east. The Uruaçu fold belt is In general characterized by folds with variably-oriented axial planes and mineralogical changes tipical of greenschist facies. In the studied region, regular variations In deformational intensity and metamorphic degree were not found. The immature sediments of the Monte do Carmo Formation are the products of the last lithogenetic processes of the Middle Proterozoic in the area. During the evolution of the Araguaia and Uruaçu fold belts, the north part of the Goiano massif had a limited participation in such a way that it functioned as a rigid block with respect to the folding on either side. The final products related to the polycyclic evolution of this crustal segment during the Priecambrian are represented by directional fault systems oriented principally N40º -60ºE and N40º -50º W. The NE system of faults reflects a reactivation of the Transbrazilian Lineament in the Upper Proterozoic. Thick sedimentary sequences were deposited in the Phanerozoic and new movements on the Transbrazilian Lineament caused the development of important block faulting which is reflected in part by the present-day geomorphology of the area.
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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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Estudo hidrodinâmico e sedimentológico do Estuário Guajará - Belém (PA)
(Universidade Federal do Pará, 1987-08-22) PINHEIRO, Roberto Vizeu Lima; FARIA JUNIOR, Luis Ercílio do Carmo; http://lattes.cnpq.br/2860327600518536
This work presents the hydrodynamic and sedimentological characteristics of the Guajará Estuary, in the vicinity of the city of Belém. Its approach covers geological and geomorphological aspects, the behavior of waves, winds, tides, tidal currents and the investigation of the physical-chemical parameters of the waters, with the objective of sketching a quantitative model for this environment in addition to presenting a proposal for the evolution region physics. From the oceanographic point of view, the Guajará Estuary is characterized by the absence of marked thermal stratification, being classified as partially mixed, type B in the Pritchard classification (1955), with appreciable lateral variations in salinity. It is subject to a circulation mechanism controlled by strong tidal currents, which define easily individualized flood and ebb channels. Two main wind systems are responsible for the formation of several sets of waves with characteristics that will depend on their speed, intensity, duration time and direction in relation to the geography of the estuary. The tides and tidal currents interfere decisively in the formation of waves. The dynamic tide has an average amplitude in syzygy and quadrature, in the Port of Belém, around 3.0 m and 2.5 m respectively. The tidal currents on the surface, during the moments of change of direction, show a complex mechanism of circulation, always obeying the characteristics of individualization of the flood and ebb channels. The salt tide inflow mechanism also follows this pattern. Conductivity proved to be the most important parameter for defining the salt tide intrusion mechanism. Important variations in the average values of pH, O2 concentration, concentration of suspended material and conductivity in estuarine waters follow, approximately, the seasonal variations during the year marked by very rainy periods followed by the dry season. Hourly variations during tidal cycles, as well as variations arising from the fortnightly movements of the Moon (syzygy and quadrature) are similarly important. The water temperature follows the air temperature variations in the region, with expressive daily amplitudes. The Holocene sediments that fill the estuarine trough are predominantly sandy, ranging from selected to well selected, sometimes silty. The sedimentation is marked by the hydrodynamic conditions of the environment, being recognized two important textural facies: Muddy Facies and Sandy Facies. The distribution of these textural facies apparently oscillates as a function of tidal periodicity. The pelitic fraction of the estuarine sediments is composed of kaolinite, illite, smectite and stratified illite-smectite, with traces of chlorite still occurring. In the sandy fraction, quartz is the main mineral in association with iron oxide grains. Among the transparent heavy minerals, staurolite, tourmaline, kyanite, zircon, epidote and amphiboles predominate, in addition to garnet, rutile and andalusite. As main source areas, the Tocantins and Guamá rivers are pointed out. In addition to these, the Barreiras Group and the Holocene Lands must supply the estuarine bed with sediments. A geological-geomorphological evolutionary model for the Guajará Estuary is proposed, assuming the age of its implantation from the Lower to Middle Holocene, associated with the manifestations of the Flandrian Transgression.
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Evolução geológica da região de Tucuruí - Pará
(Universidade Federal do Pará, 1982-05-27) MATTA, Milton Antonio da Silva; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
The northern part of the Araguaia Belt is exposed in the Tucuruí region and their stratigraphic, structural, metamorphic and magmatic features had been studied aiming at contributing for the understanding of the geological evolution of the area. The oldest stratigraphic unit of the area is represented by the Xingu Complex, composed by gneisses and granitos and subordinated schists and anphibolites. These rocks show evidence of a polycyclic metamorphic and structural history. Over this unit, during the niddle Proterozoic, the Tucuruí Group was developed. The bottom of this unit is composed by a sequence of tholeiitic basal-tic flows which were hera enclosed in the Caripé Formation. The Morrote Formation, is made up of graywackes, and constitutes the upper part of the Tucurui Group. The geossinclinal evolution of the Araguaia Belt took place during the Uruaçuano Cycle. This geotectonic unit is represented in the studied area by the Couto Magalhães Formation (Tocantins Group) which comprises pelitic and psamitic metasediments. These rocks show a greenshist facies metamorphism and structures generated by two phases of deformation in conditions of lower structures level. After the metamorphism of the Araguaia Belt, the Couto Magalhães Formation acted as the place of mafic and ultramafic intrusion and, lately, the Tucuruí Fault thrusted the metamorphic rocks of the Tocantins Group over the Tucuruí Group lithotypes. This faulting, besides generating a. series of structural features in the both groups as well as in the later migmatites, has also induced a dynamic metamorphic event into the rocks under green-schist facies conditions. Through the statistic treatment of structural data from the denso fault population which cuts the area, it was possible to deduce the shertening and the eterlding directiors related to the progressivo deformation induced by the thrust faulting had acted from E to W. Post-faulting mafic dykes represent the last magmatic event related to the Mesozoic Era. During the Cenozoic the area was a place of Tertiary sedimentation (Barreiras Formation), with sand, clays and conglomeratic levels. A final reactivation was responsible for the fracturing and faulting showed by the Barreiras Formation lithotypes Quatérnaty deposits mostly alluvial sediments, are the final units of the area.
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Evolução recente da cobertura de alteração no platô N1-Serra dos Carajás.
(Universidade Federal do Pará, 1995-04-26) MAURITY, Clovis Wagner; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
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Geologia e aspectos metalogenéticos dos elementos do Grupo da Platina no complexo máfico-ultramáfico da Serra da Onça – Sul do Pará
(Universidade Federal do Pará, 1997-08-12) MACAMBIRA, Edesio Maria Buenano; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
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Geologia e gênese do veio de cristal de rocha do Garimpo da Lagoa, Xambioá – TO.
(Universidade Federal do Pará, 2000-08-31) FERREIRA, Iêda de Oliveira; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The crystal rock occurrences from Xambioá region, situated in the northem part of the Araguaia Belt, are associated with quartzites of the base of the Morro do Campo Formation and schists of the Xambioá Formation, both of the Upper Proterozoic Estrondo Group. The crystal rock occurs mainly as irregular pockets within milky to grayish translucent quartz veins. The “Garimpo da Lagoa” crystal rock vein is hosted by biotite - schists of the Xambioá Formation, displays a general sub-meridian direction and is up to 5 m thick. Petrography and microthermometry of vein samples revealed the presence of two distinct fluids types: 1) oversaturated aqua - carbonic fluids in pseudo - secondary inclusions, containing up to 4 solid phases and 2) aqueous fluids of low to high salinity in secondary inclusions. The aqua — carbonic fluid inclusions contain almost pure CO», with traces of N; due probably due to the presence of carbonatic rocks and graphite in the area. Most fluid inclusions underwent crepitation before they reached Th. Even so, the minimum trapping temperature for these fluids was estimated in 550 to 600º C. It is believed that fluids are basically of deep metamorphic origin, though they also show significant contribution of magma derived solutions. The aqueous fluids were found in three-phase oversaturated, two-phase and monophase inclusions. The solutions contained in the three-phase inclusions revealed a salinity from 30 to 40% in weight of NaCl and a minimum trapping temperature between + 182 and + 321ºC. K is believed that these fluids were injected after the aqua — carbonic ones and were essentially of magmatic origin. Concemning the fluids contained in the two-phase inclusions, were distinguished solutions of low salinity (1,23 to 11,81% in weight of NaCl) and a minimum trapping temperature from + 123,8 to + 150,9ºC, and solutions of high salinity, sub-divided in two categories (a) and (b), mainly based on their morphology. The (a) type revealed a salinity of about 23% in weight of NaCl and a minimum trapping temperature between +130 and 210%, more frequently at + 160ºC, while the (b) type indicated a salinity ffom 20 to 25% in weight of NaCl and a minimum trapping temperature from + 65 to + 114,Sth C, more frequently at + 70ºC. The fluids contained in the monophase inclusions displayed a salinity of 1.91% to 18.22% in weight of NaCl. The solutions trapped in two-phase and monophase inclusions would represent late injections of hydrothermal fluids of magmatic origin, which underwent progressive cooling and composition modifications in agreement with the importance of the contribution of more superficial (meteoric, conate, etc.) waters. During the final phase of the Araguaia Belt evolution, in predominantly distensive conditions, at first aqua — carbonic fluids were injected, that resulted, in formation of a hyaline quartz vein, poor in fluid inclusions. Later on, the vein suffered multiple fracturing phases and aqueous solutions were injected showing a progressive lowering of the temperature and, in a less systematic and less regular way, of the salinity. These late injections were responsible in variable degree for the transformation of the original hyaline quartz into translucent or milky quartz. Pockets which were not affected by these late hydrothermal displays remained as crystal rock. Crystal rock, mainly as third quality chips is used as raw material for production of synthetic crystal. Prismatic, well developped quartz crystals and first quality chips are used in mineral craft for production of adornment pieces, balls, key rings and cut stones. Crystal rock is mainly exported to Belo Horizonte, Sete Lagoas, Governador Valadares, where already cut stones are commercialized , and to São Paulo and Rio de Janeiro, where raw crystals are mainly appreciated.
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Geologia e geocronologia da região a sul de Paraíso do Tocantins-TO
(Universidade Federal do Pará, 1996-04-22) SOUZA, Silvia Helena Pereira de; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
The most recent geochronological studies carried out in the basement of the northern segment of the Araguaia Belt indicated the occurrence of rocks from both the Archean and the Lower Proterozoic. The oldest rocks, predominantly represented by trondhjemitic orthogneisses, with ages around 2.85 Ga, were grouped in the Colméia Complex. On the other hand, granitic orthogneisses, with a minimum age of 1.85 Ga, called Cantão Gneisse, constitute the youngest rocks, hitherto known, from the basement of the Araguaia Belt. In its southern segment, the basement of the Araguaia Belt is represented by tonalitic gneisses, associated with calciosilicate gneisses, which were correlated to the Colméia Complex, and which serve as host for the Serrote Granite, located south of the city of Paraíso do Tocantins. Calciosilicate gneisses, quartzites and tonalitic gneisses were also described, gathered in a distinct unit called Complexo Rio dos Mangues. Although the units mentioned above were considered Archean in age, there is practically no geochronological information about them. This work, therefore, aims to determine the ages of the basement rocks in the southern portion of the Araguaia Belt, and to investigate the correlation or not of these rocks with those outcroppings within the dome structures of the northern portion of this belt. This information is important for the organization of the lithostratigraphic framework of the basement of the southern portion of the Araguaia Belt, which in turn is fundamental for understanding the geological evolution of this belt. In the geochronological investigation, the method of evaporation of Pb in zircon single crystals (Pb-Pb in zircon) was used, which provides the crystallization age of zircon obtained from its gradual heating, in a thermal ionization mass spectrometer. A plateau age of the zircon grain is then calculated, on a 207Pb/206Pb versus temperature plot. Granodiorite gneisses with associated leucosomes and calciosilicate gneisses originally correlated to the Colméia Complex (samples SH12, SH15 and SH40), tonalytic gneisses and syenitic gneisses included in the Rio dos Mangues Complex (samples SH36 and SH33) and a sample of Serrote Granite. In the set of rocks that had been correlated to the Colméia Complex, the ages obtained were concentrated around 2.0 Ga, and the zircons of the leucosomes of the calcosilicate gneisses provided a relatively younger age of 1.8 Ga. In the group of rocks mapped as Complexo Rio dos Mangues, the age obtained for the zircons of the syenitic gneisses was relatively younger (1.0 Ga). These gneisses, due to their proximity to the alkaline gneisses of Serra da Estrela and because they are compositionally similar to them, should be part of the Monte Santo Suite. In the analysis of the zircons of the tonalytic gneisses, a plateau age was not defined and, on the contrary, it showed a pattern of continuous growth of the ratio , 207Pb/206Pb, and at higher temperatures, the ages systematically presented values slightly higher than 2.0 Ga . In this case, the oldest ages were assumed as minimum crystallization ages for these zircons. For the Serrote Granite, the age obtained through this method was 1851 ± 41 Ma (2σ). The ages of the gneissic rocks in the basement of the southern segment of the Araguaia Belt, located between 1.8 and 2.1 Ga, indicate the absence of gneisses of Archean ages in this portion of the belt. Consequently, it is advised against correlating them with those of the Colméia Complex. It is additionally suggested to abandon the aforementioned term and extend the name of Complexo Rio dos Mangues to the calciosilicate and orthogneisses that have expression in the vicinity of Paraíso de Tocantins. The crystallization ages of Serrote Granite (1851 ± 41 Ma, 2σ) and Cantão Gneiss (1846 ± 64 Ma) are very similar. Due to this similarity, an additional geochronological study was carried out using the Pb-Pb method in whole rock and feldspars, aiming to investigate the correlation between these granitic rocks. For the Serrote Granite, an age of 1872 ± 140 Ma (1σ) was obtained and for the Cantão Gneiss, an age of 1744 ± 27 Ma (1σ). These ages, when compared with those obtained by the Pb-Pb method in zircon, show that the Pb-Pb system in whole rock was partially opened, during a thermo-tectonic event subsequent to the crystallization of these rocks, rejuvenating their ages. A comparative study was also carried out between these units and some anorogenic granites of Proterozoic age from the Amazon region and the Median Massif of Goiás, where it was verified that the Serrote Granite is very similar to the same ones, also adjusting to the curves of evolution of Pb, proposed in the plumbotectonics model. The Cantão Gneiss does not fit the plumbotectonic model, due to the high 206Pb/204Pb ratios found in the feldspars of the samples from this unit. These high Pb ratios in these rocks reveal that they are enriched in U, and this enrichment may have come from the magma that generated them or have been acquired in a metamorphic event subsequent to its crystallization.
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Geologia e geoquímica do maciço granítico arqueano Xinguara e de sua encaixantes, sudeste do estado do Pará
(Universidade Federal do Pará, 1995-12-12) LEITE, Albano Antônio da Silva; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
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Geologia, geoquímica e geocronologia do granito Serra do Rabo, província mineral de Carajás
(Universidade Federal do Pará, 2002-03-25) SARDINHA, Alex Souza; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
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Geologia, geoquímica e geocronologia do magmatismo paleoproterozóico da região de Vila Riozinho, Província Aurífera do Tapajós, Cráton Amazônico
(Universidade Federal do Pará, 2001-09-27) LAMARÃO, Cláudio Nery; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Several Paleoproteroic granitoids and two volcanic sequences were studied in the Vila Riozinho region. This region is located in the eastern area of the Tapajós Gold Province, near the border between the Tapajós and Central Amazonian tectonic provinces in the south-central part of the Amazonian craton. In the southern part of the region, it was identified the Vila Riozinho volcanic sequence composed of basaltic andesite, basaltic trachyandesite, trachyte and rhyolite, with a high-K calc-alkaline to shoshonitic geochemical signature. Pb-Pb zircon dating indicate ages of 2000 + 4 Ma and 1998 + 3 Ma for this sequence. The São Jorge granite pluton is spatially associated with this volcanic sequence. Two granitoids were distinguished in the pluton, the Old São Jorge granite, with Pb-Pb zircon ages of 1981 + 2 Ma and 1983 + 8 Ma, and the Younger São Jorge granite with an age of 1891 + 3 Ma. The Older São Jorge granite, largely dominant in the pluton, is composed of an expanded magmatic series including biotite-amphibole monzodiorite/quartz monzodiorite, amphibole-biotite monzogranite/quartz monzonite, biotite leucomonzogranite/syenogranite and granite porphyry. It has a metaluminous to mildly peraluminous character, and high-K cale-alkaline signature, similar to that of volcanic arc granitoids. The Younger São Jorge granite was initially identified in drill cores obtained in the gold mineralized area of the pluton. In that area, it corresponds to a hornblende-biotite monzogranite, but biotite leucogranites occur in the southern part of the pluton. This granite also has a high-K calc-alkaline signature, but it differs from the Older São Jorge granite in some geochemical and mineralogical aspects and it is comparatively younger. In the northern part of the Vila Riozinho region, it was identified the Moraes Almeida volcanic sequence, the Maloquinha and Jardim do Ouro granites and a granite porphyry distinct from that associated with the Older São Jorge granite. The Moraes Almeida Formation is composed of ignimbrite and rhyolite with subordinate trachyte, with Pb-Pb zircon ages of 1875 + 4 Ma, 1890 + 6 Ma and 1881 + 4 Ma, respectively. The 1880 + 9 Ma old Maloquinha granite is composed of leucosyenogranite and subordinate leucomonzogranite. This granite and the rhyolite and ignimbrite of the Moraes Almeida Formation show affinities with aluminous, A-type series. The strong petrographic and geochemical similarities between these rocks suggest that they are cogenetic. An age of 1880 + 3 Ma, similar to that of the Maloquinha grafite, was obtained for the Jardim do Ouro hornblende-biotite monzogranite. However, preliminary data indicate that it differs from the former, as well as from the Older São Jorge and Younger São Jorge granites, in petrographic and geochemical aspects. Geochemical and mineralogical data allow the distinction of two different types of grafite porphyries. The first one is spatially associated and similar to the Older São Jorge granite. The second occurs along the contact between the Maloquinha granite and the ignimbrite of the Moraes Almeida Formation and is geochemically similar to the Jardim do Ouro granite and trachyte of the Moraes Almeida Formation. The magmatic activity in the Vila Riozinho region is concentrated into two distinct periods, near the end of the Paleoproterozoic. The Vila Riozinho Formation and the Older São Jorge granite formed during the first period between 2010 and 1970 Ma. At the second period, between 1900 and 1870 Ma, the Moraes Almeida Formation, Maloquinha, Younger São Jorge and Jardim do Ouro granites were formed. The high-K calc-alkaline magmatism that was formed during the first period is probably related to subduction processes. Two hypotheses are considered to explain the diversified magmatic activity registered during the second period: (1) the different magmas could result from late tectonic activity related to the subduction processes; (2) these magmas are related to taphrogenetic processes that affected the Amazonian craton at 1.88 Ga and lasted the entire Mesoproterozoic. It implies to admit a crustal source for the magmas originated during the second period. The second hypothesis is assumed as the more plausible at this stage, but the need for additional isotopic information is emphasized.
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Geologia, mineralogia, geoquímica e gênese dos fosfatos de Jandiá, Cansa Perna, Itacupim no Pará e Pirocaua e Trauira no Maranhão
(Universidade Federal do Pará, 1980-05-13) COSTA, Marcondes Lima da; SÁ, José Haroldo da Silva; http://lattes.cnpq.br/9442263243312377
The phosphate occurrences of Northeastern Pará and Northwestern Maranhão were formed by strong lateritic weathering of phosphorus-rich Precambrian rocks. The rock formation affected by those processes were phyllites and schists of the Gurupi Group in Cansa Perna and Pirocaua, a complex of felsic to mafic and ultramafic rocks metamorphosed in the greenschist facies in Itacupim and Trauira and probably phosphoritic "sandstone" in Jandiá. The lithologic sequente observed (A=horizon: ferric oxide-hydroxide and ferric and aluminium phosphate; B=horizon: aluminium phosphate; C=horizon: kaolinite) is generally comparable with that of bauxite deposits, especial.ly those of the Amazon region which were also developed, like the phosphate deposits, during the Tertiary. The mineralogy of the phosphates consists of crandalite-goyazite, wavellite, augelite, mineral-A and wardite-millisite (these are particularly abundant in the "B" horizon); dufrenite, mitridatite, beraunite, mineral-B, lazulite and ferric oxide-hidroxide (in the "A" horizon), apatite (in the bedrock of Itacupim). Dravite, gibbsite and other oxides were also found. These secondary mineral associations are common to all deposits and show only slight variations related to the bedrock. The geochemistry of these deposits is unusual and differs from that of normal bauxites. In particular high concentrations of. Sr, Rb, Ba, Ce, La, Nd, Zr and Nb are observed in the "B" horizon, some of these elements are found in the crandalite goyazite series in which the Sr0-content can be as high as 7%. The geological, mineralogical and geochemical characteristics of these deposits are similar to the secondary phosphate occurrences of Florida, Utah, and Tennessee CUSPA and also to these of Senegal.
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Geologia, petrografia e geoquímica das associações leucograníticas e TTG arqueanos da área de Nova Canadá (PA) Domínio Carajás
(Universidade Federal do Pará, 2014-02-25) SANTOS, Pablo José Leite dos; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
The geological mapping carried out in the Nova Canada and Velha Canada villages, south portion of the Carajas Domain, ally to the petrographic and geochemical data allowed to the characterization of new geological units before inserted in the Xingu Complex geological context. In abundance order they are: (i) Nova Canada Leucogranodiorite composed predominantly by leucogranodiorite rocks that are more enriched in Al2O3, CaO, Na2O, Ba, Sr and in the Sr/Y ratio. They show strong geochemical affinities with Guarantã Suites from the Rio Maria Domain, which are also correlated to Transitional TTGs from Yilgarn Craton. Their REE pattern is slightly fractionated with low (La/Yb)N ratios with Eu negative anomalies absent or discrete; (ii) Velha Canadá Leucogranite comprised essentially by leucogranitic rocks that show higher contents of SiO2, Fe2O3, TiO2, K2O, Rb, HFSE (Zr, Y e Nb), and K2O/Na2O, FeOt/(FeOt+MgO), Ba/Sr e Rb/Sr ratios. The Velha Canada area rocks are characterized by two distinct patterns REE of: (a) moderate to low (La/Yb)N ratios with accentuated Eu negative anomalies, and (b) high to moderate (La/Yb)N ratios with discrete Eu negative anomalies. A concave HREE pattern is observed. In several aspects, the Velha Canada granite show similarities with K-Leucogranites like Xinguara and Mata Surrão granites from Rio Maria Domain, and more discretely with low-Ca granites from Yilgarn Craton. To origin of Nova Canadá Leucogranodiorite rocks is admitted fractional crystallization by sanukitoid liquids, following by mixing with trondhjemitic magmas, while for those high-K rocks is assumed partial melting of metatonalites rocks related to TTG Suites on different crustal levels, for give rise to these liquids; and (iii) Trondhjemitic associations with high-Al and low-K calc-alkaline TTG series affinities. Two varieties were distinguished: (a) biotite-trondhjemite with deformational features like compositional banding, folds and evidence of migmatization, suggesting the presence at least two compressional events during the sin- and post magmamtic stages; and (b) (muscovite) biotite-trondhjemite that differs from the previous one by the presence of muscovite, plagioclase saussuritization, medium evengrained texture and discrete deformation features with development of a low-angle foliation with E-W direction. The restrict occurrence of the first one, ally with intense deformation and eventual anatexie processes that affected these rocks, can indicate a crustal rework linked to generation of the leucogranites described in the Nova Canadá area. The trondhjemites of the southern part of area are more enriched in Fe2O3, MgO, TiO2, CaO, Zr, Rb, an in the Rb/Sr ratio in relation to those of the northern part. The arrangement of trends defined by the set of analyzed samples, suggests that theses varieties are not cogenitc or comagmatic. These rocks also show fractionated REE patterns, with variations in contents of the heavy REE and Strong light REE enrichment, besides the absence of the Eu and Sr anomalies, and low contents of Yb and Y. Such aspects are tipically attributed to magmas generated from partial melting of a mafic source at different depths, with increasing of the garnet influence in the residue, as well as the lack of plagioclase in both residual and fractionating phases. Geochemical affinities between the rocks studied with those of the mesoarchean Rio Maria domain, suggest the extension of Rio Maria Domain to north until the Nova Canadá area, while that the leuocogranodiorites of the Velha Canadá area, that are younger and generated in the neoarchean, discard the hypothesis to associate the generation of these rocks to the same tectonic-magmatic events that acted in Rio Maria.
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Geologia, petrografia e geoquímica dos diques da região de Rio Maria, SE-PA
(Universidade Federal do Pará, 1996-09-09) SILVA JÚNIOR, RENATO OLIVEIRA DA; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In the region of Rio Maria, SE of Pará, several dykes were mapped, mainly intrusive in the Granodiorite Rio Maria (GdRM) and, subordinately, in the anorogenic granite Musa (GM). Forming small elongated ridges that stand out in the morphology with a positive relief, arranged mainly according to NW-SE and E-W trends and, subordinately, N-NE. The maximum width of these bodies is 30 m, and they have an outcropping length of 1,500 to 2,000 m, reaching 3,000 m. Five groups of dykes were identified petrographically: diabases, diorites, quartz-diorites, dacites and rhyolites. The transverse and longitudinal profiles in the direction of these bodies show a decrease in rock granulation, in the center-edge direction of the body, usually culminating in aphanitic rocks, which represent, as a rule, the cooling edge of the dyke. Close to these edges, enclaves and tonsils filled with quartz-feldspathic material are frequently observed. The contacts with its host country are abrupt, sometimes marked by the presence of cooling edges, whose thickness varies from a few centimeters to, exceptionally, 2 m. The K-Ar ages of these dykes are: (1) 700 ± 8 Ma in qz-diorite (whole rock); (2) 883 ± 10 Ma in diorite (plagioclase); (3) 1,099 ± 39 Ma in diabase (plagioclase); (4) 1,802 ± 22 Ma in diabase with olivine (mafic concentrate). The first three ages are interpreted as minimum ages for these bodies. The age of 1,802 ± 22 Ma is compatible with the age of 1,707 ± 17 Ma (Rb-Sr in RT) obtained for dacites and porphyry granites. The geochronological data available for the dikes in the Rio Maria region allow placing them in the Proterozoic, and the most reliable ages suggest that at least part of these dikes is contemporary with the anorogenic granitic magmatism. Diabases have been divided into four subtypes: (1) diabase with olivine - exhibits subophytic texture. It consists of labradorite (An55-65), augite + pigeonite, olivine, opaques and hornblende; (2) porphyritic microdiabase - cuts diabase with olivine, formed by plagioclase phenocrysts immersed in a pilotaxitic matrix formed by plagioclase, augite, opaque and amphibole slats; (3)) amphibole-diabase- exhibits a granular texture with a subphytic tendency, is made up of labradorite (An54-64), opaque minerals augite, late amphibole (tremolite-actinolite) and, rarely, hypersthene; (4) auginite-diabase (RJ-18B) with ophitic texture, it is formed by labradorite (An56), augite, opaques and, secondary amphibole. Diorites and quartz-diorites show, in general, a granular texture tending to subphytic or porphyritic with a matrix rich in granophyric intergrowths. Diorites are formed by very saussuritized plagioclase, augite, quartz, hornblende and opaques. Quartz-diorites have similar mineralogy to diorites, differing only in the modal content of quartz and granophyric intergrowths. Some diorites and diabases present plagioclase phenocrysts with sieve texture, suggesting the action of mixing and/or mingling processes. The dacites are formed by porphyry dacites and porphyry dacites rich in mafics. Both have a porphyritic texture, locally glomeroporphyritic, formed by aggregates of plagioclase phenocrysts, quite saussuritized, hornblende locally involving augite, in addition to isolated quartz phenocrysts. The two subtypes have a predominantly granophyritic matrix, sometimes spherulitic. The presence of microcrystalline quartz was noted forming almond-shaped aggregates (spots), attributed to mixing processes. The rhyolites exhibit a porphyritic texture, locally glomeroporphyritic, formed by plagioclase and quartz phenocrysts, immersed in a microcrystalline matrix with a micrographic tendency. Microcrystalline aggregates consisting of chlorite, biotite and opaques also occur. The TAS diagram shows good correlation between the modal classification and the geochemical data. In this diagram the diabases and diorites plot within the field of their volcanic counterparts. Quartz-diorites generally fall into the field of low-silica dacites. The dacites themselves are a little richer in silica than the preceding group, although both focus on the same field. In the AFM diagram the samples are located in the tholeitic subalkaline field. The presence of compositional gaps between groups, mainly between diabases and diorites, and from these to quartz-diorites, reinforces the hypothesis that these rock groups studied do not present a continuous magmatic evolution. The RJ-18B sample, although presenting characteristics of diabase, shows geochemically greater affinities with the diorites. The geochemical data also reinforce the hypothesis that the dikes of Rio Maria, although showing a tholeitic affiliation, were probably generated from different liquids, since the compositional gaps between the various groups are very accentuated. The dacites, although they present, in some diagrams, an overlap with the quartz-diorites, they differ from them petrographically and geochemically, too, and, in terms of occurrence in the field. There is petrographic evidence that the crystallization of diabases was driven mainly by the fractionation of olivine, while in diorites, augite and plagioclase played a dominant role. The petrographic and geochemical data show that the diabases, with the exception of sample RJ-18B, are entirely different from the other groups in terms of magmatic evolution. Diorites and quartz-diorites, in turn, although petrographically similar, present a compositional gap that weakens and immediate hypothesis since the latter represents a more evolved term, derived from the former. Sample RJ-18B is interpreted as a mafic concentrate of these diorites. This hypothesis can be justified by the modal and chemical composition of this sample. Dacites and rhyolites are probably genetically linked to anorogenic granitic magmatism, with probable associated mixing processes, mainly in the case of dacites.
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Geologia, petrografia e geoquímica dos granitóides de Canaã dos Carajás, SE do estado do Pará
(Universidade Federal do Pará, 2003-10-11) GOMES, Alan Cardek Brunelli; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
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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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Geology, petrology, U-Pb (shrimp) geochronology of the Morrinhos granite -Paraguá terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignácio orogeny
(2014-09) FRANÇA, Ohana; RUIZ, Amarildo Salina; SOUSA, Maria Zélia Aguiar de; BATATA, Maria Elisa Fróes; LAFON, Jean Michel
Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km2 long; it is located in the municipality of Vila Bela da Santíssima Trindade of the state of Mato Grosso, Brazil, in the Paraguá Terrane, Rondonian-San Ignácio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the greenschist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S1) and open folds (D2), and both phases were most likely related to the San Ignácio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350 ± 12 Ma, TDM of approximately 1.77 Ga and εNd(1.35) with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignácio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite.
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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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Metodologia de interpretação radargeológica: exemplo da sinéclise do Parnaíba e de seu embasamento
(Universidade Federal do Pará, 1995-09-29) LIMA, Mário Ivan Cardoso de; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286
This thesis develops the Radargraphic Elements Sistematic method, unknown throughout the world, in the geologic interpretation with Side-Looking Radar (Radargeology), a technique of major relevante in the field of natural resources, considering that the 1990s are the Radar's decade. The Radargraphic Elements Sistematic (SER) method reveals in a sistematic form the methodological route adopted , be it trough the text, trough schematic figures, or in Side-Looking Radar (SLR), with the radargraphic elements (features), ordered in five different stages: Reading, Recognizing, Identifying, Analisys and Interpretation (stricto senso). The stage Reading seeks to understand the meaning of the image elements in the terrain, with the goal of understand their meaning ; the Recognizing stages seek to group them according to the texture and tone radargraphic, so as to obtain homogeneous radargraphic zones; Identification seeks to study the relief forms in such zones, with regard to top and pending, as well as the studying of the drainage patterns, dissection degree and erosion resistance ;and the Analysis establishes the spacial and temporal relation of the relief forms researched through linear, planar and tabular features. With such information in hand , the Interpretation stage itself is reach, in which is possible to define lithologies, rounded structures, unconformities, discontinuities, folds and their interrelations,with a view to executing the Radargeological Map.In effect, a model area was selected to serve a paradigm for the the different methodological stages. To apply the Radargraphic Elements Sistematic method, the region encompassed by Parnaíba Sineclyse and its embasement was selected, with an area of around 925 000 km2, involving mostly Maranhão e Piauí states, located in northeastern region of Brazil. Such an example seeks to emphasys the applicability of the remote sensing in sedimentar terrains and their metamorphic embasement, due to academic and economic importance involved.. To carry out this stage, 52 SLR images mosaics were utilized, scale, I: 250 000, GEMS, X band, resulting in the definition of 39 basic radargeologicals unities, with a temporal stratigraphy, and 19 regional strucutures and 30 local ones, of which more than half were unpublished. These results are expressed in an explanatory text with ilustrations, including a Radargological Map on the milionth scale , and a structural sketch on the scale of 1:2 000 000. The study reaches a favorable conclusion regarding the potentialities of SLR images in geological whose difficulties in defining the radargraphic elements (features) due mainly to extensive shadows, foreshortening , layover and paralaxe effects, will be overcome with the use of more sophisticated Radar Systems (digital mode, stereoscopy, multifrequency, differents angles of incidence,etc) , as is the case with SIR-C and RADARSAT. Finally, the study attests of the excelence of Radargraphic Elements Sistematic method considering the results achieve with the study of the Parnaíba Sineclyse and its embasement, such as : definition of radargeological units, which mantain a strict relation with the lithostratigraphic units already described in the literature; structural setting with the identification of almost 50 morphostructures of regional and local character , and a perfect correlation with aeromagnetic maps.