Navegando por Assunto "Geologia regional"

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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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Aspecto tectôno-sedimentares do fanerozóico do nordeste do estado do Pará e noroeste do Maranhão, Brasil
(Universidade Federal do Pará, 1992-09-16) IGREJA, Hailton Luiz Siqueira da; FARIA JUNIOR, Luis Ercílio do Carmo; http://lattes.cnpq.br/2860327600518536
A synthesis of the tectono-sedimentary evolution of the Phanerozoic at Northeastern Pará and Northwestern Maranhão is discussed with enphasis to the Bragança-Viseu and São Luis basins. This research is based on field observations, gravity (Bouguer Anomalies), magnetic, seismic, and borehole data interpretations. Five sedimentary sequences are defined: 1) Piriá-Camiranga (Cambrian-Ordovician to Silurian), 2) Lower Itapecuru (Lower Cretaceous), 3) Upper Itapecuru (Upper Cretaceous), 4) Pirabas-Barreiras (Oligocene-Mioceneto Pliocene) and 5) Pará (Quaternarg). The regional basement is an igneous-metamorphic assemblage which outcrops in two windows. The sedimentary and structural features of the Piriá-Camiranga sequence are consistent with a tectono-sedimentary model of coastal environment with fluvio-glacial influence related to a tilted blocks system induced by strike-slip motion. This sequence represents an evolutive stage coincident to the Eo-Hercynian paroxysm (Paleozoic) which ended with the closure of the Atlantic I (first geotectonic cycle of the Gondwana). The Lower and Upper Itapecuru, as well as the Pirabas-Barreiras and Pará sequences, are related to the Equatorial Atlantic opening during the Mesozoic and Cenozoic times. They are analysed by severa), authors which reached the interpretations refered to as Models of: Fracture Zones; Anti-clockwise rotation of Africa; Intumescence and fracturing; Clockwise rotation of the South America Nate; and Wrench Tectonics. These models were experimented for the studied area. The time and environments of the sedimentary processes are related to the rift and pos-rift phases of the equatorial coastal basins, but these models were not adequate to explain the structural features. A new model is proposed to explain the origin and development of the basins taking into account a regional NE-SW extension axis and formation of the Bragança-Viseu and São Luís basins with similar polarities. The tectono-sedimentary map for the Phanerozoic of the Northeastern Pará / Northwestern Maranhão enhances the compatibility of the depositional and tectonics systems with two periods of oceanic opening of the Northern Gondwana border.
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Evolução geotectônica do pré-cambriano da região meio norte do Brasil e sua correlação com a África Ocidental
(Universidade Federal do Pará, 1990-12-04) ABREU, Francisco de Assis Matos de; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
This study presente a proposal for the geotectonic evolution for the pre-Cambrian portion of mid north region of Brazil and its correlation with western Africa based on the Integration of multldisciplinary geologic Information. Two types of geotectonic units are recognized: estabilized areas at the lower Proterozoic/early mid-Proterozoic (cratonic nuclei) and adjacent areas whose tectonic instability continued until the Phanerozoic (mobile belts). In the first case, one finds the Amazonian craton, not analysed in this work, and the Western African Craton/São Luis. The second case, assesses the vast reglon known In Brazil as Araguaia Belt and northwest of the Borborema Province that along with the southwest portion of the Tentugai Belt provide south continuity to the Parnaíba basin emergence. On the African side, the easternmost part of the West African Craton corresponding to the Pharusian, Daomeinian and to the west side of the Rocklides and Mauritanides belts, this last one with configurated evolution until the Hercynian Orogeny. In the cratonic nuclei one finds preserved geometric aspects which are fundamental for the past relationship between the more ancient sialitic crust where one visualizes the presence of globular batholiths, incrusted in high degree gneiss highly deformed and its cover often represented by sequences of the "greenstone belt type". The formation of this continental crust would have ocurred initlally by underplating being increased horizontaliy afterwards by primary cratonic nuclei. In the areas where tectonic Instability continued, continental Ilthosphere was extremely modified providing conditions for the establishment of sedimentary basins by colapse of the superstructure, generating magma simultaneously with plastic deformation that established complex relationships between gneiss and the roots of these basins, generating high degree terrain, low dip follations and migmatization zones. In the studied region, mostly on the Brazilian portion, these areas, where the Instability continued, involves a NE-SW macro shear beit, extending Itself from Africa, crossing the northwest of Ceará and continuing south under the sediment of the Parnaiba basin. These directions modify to E-W as they approach the African border at Sierra Leone and Ivory Coast at the border of the Amazonian. Craton reaching a NW-SE direction In the Guiana Shield. Basically, they encompass the northwest of Ceará In the NE-SW direction and the NE-SW strong gravimetric references. The high and medium degree rocks of this region are replaced in the northwest direction by low to medium degree rocks of the São Luis Craton and by the birrimian complex of volcano-sedimentary basins: the NW-SE Tentugai Belt establishes itself discontinually in relation to the NE-SW structures of the northwest belt of Ceará. Area of less expressive width with these same directions are found west of the Amazonlan Craton. There, it would have occurred a wide range of phenomena In terms of deformation processes that reached an expressive granitogenesis and cratonization with Rb/Sr ages with range of 1900-2000 Ma determining, therefore, the period in which these pheneomena ocurred in the Arquean and eariy Proterozoic. Plane and linear elements define geometrically in the various segments analyzed the special positions of the main axis of the ellipsoid of deformation. The general movement along the NE-SW and E-W segmente was dextral, with NW-SE and ENW-SSE secondary sinistrai directions of shear. The prevalling metamorphlc conditions in this period mark the presence of stabilized groups of minerais with inciplent to medium degree in the cratonic domaln, while at the beit the conditions of high degree and anatexia might have occurred for large areas. Such geotectonic matrix has conditioned geologic phenomena occurred in the region. The tectonic stability occurred was followed by the emergent of conditions for the deposition of important platform sequences with start around 1600-1700 Ma (Tarkwaiano, Gorotire, Guelb at Hadid etc.). The unstable conditions reappearred around 800-1000 Ma on a more restricted fashion in terms of their area of influence, and it resulted In the formation of an extensive crusta) mobility zone contouring stabilized cratonic areas in the early Proterozoic responsible by the development of the Farausian, Daomenian, northwest of Ceará, Tentugal, Rockelian, Mauritian and Araguaia belts. The distention processes were more important In the Faruslan Beit with the formation of an ocean crust (Bou Azzer ofiolites - Marrocos) and a continental crust strongiy percolated at the Araguaia Belt. In other areas the distention processes were lesa important. Large scale crustal reworking with total or partial rehomonization of rocke occurs in this region as well as granitogenesis with age around 500-600 Ma. Tardl-kinematic effects expressed through tectonic movements among the narrow linear zones and restrict molasses may have followed all these processes and are represented by the Jalbaras Group, Piriá Formation, Rio das Barreiras Formation, among others, In the early Eon Phanerozoic.
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Evolução tectono-estrutural da região de Dianópolis-Almas, SE do estado de Tocantins
(Universidade Federal do Pará, 1993-12-17) BORGES, Maurício da Silva; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286
Several geological sequences of rocks with distinct ages of evolution were mapped in the Dianopólis-Almas region (southwestern part of the State of Tocantins) in the Brasília block: an extensive segment of an Archean-Lower Proterozoic granite-greenstone terrain, Proterozoic metasediments of the Bambuí Group, Cretaceous continental deposits of the Urucuia Formation, colluvial and alluvial (partially lateritized) and Holocenic fluvial-lacustrine deposits. The granite-greenstone terrains include several strands of supracrustal rocks (Riachão do Ouro Group) and granitoid bodies (Serra do Boqueirão Suite), both developed over migmatized tonalitic gneisses, granulites and amphibolites of the Alto Paranã Complex. The Riachão do Ouro Group is composed of phyllite, schist, meta-rhyolite, meta-dacite, iron formation, quartzite, metaconglomerate and breccia; phyllite, schist and metavolcanic rocks are the dominant lithologies. The Serra do Boqueirão Suite includes granitoids of tonalitic, trondhjemitic, granodioritic and granitic compositions, which were strongly deformed in the border zones and cut by pegmatite and aplite veins. All there lithological units underwent ductile deformation which formed an anastomosed pattern of N10-20E, N45E, and N55W transcurrent shear zones. Along the shear zones there are asymmetric or symmetric transpressive duplexes alternating with straigth segments. These structures can be seen extensively developed at supracrustal rock-granitoid boundaries and are characterized by mylonitic foliation parallel to the tectonic layering; other structures are represented by internal duplexes, shear bands, pods of less deformed rocks, extensional cleavage of C' type (crenulation cleavage) and brittle-ductile shear zones expressed by dilatation structures (tension gashes). The stretching lineation is defined by rods of quartz, axes of agregates of elliptical minerais and elongated micas. Dextral sense of shearing is determined from kinematic criteria. Microfabric investigation suggest that the deformation was accommodated mainly by crystal plasticity and the crystallographic shape fabrics confirm the dextral sense of shearing. Only the N55W shear zones underwent sinistral movement. The observed sets of structures is interpreted as linked to a N20E dextral strike-slip system and, in this case, the N10-20E, N45E, N25W and N55W zones correspond respectively to Y, R, P and R' zones. The Archean-Lower Proterozoic evolution is understood in terms of an oblique collision of continental segments which uplifted the granulitic rocks and was followed by transtension regime which originated several basins in where the supracrustal rocks of the Riachão do Ouro Group were deposited, and the granitoids of the Serra do Boqueirão Suite were emplaced. The progressive deformation involved transpression characterized by ductile shear zones. The Middle to Upper Proterozoic is represented by the Bambuí Group which includes slates, metasiltites, phyllites and carbonate rocks. The tectonic structures linked to the São Francisco Basin inversion in the Upper Proterozoic, are represented by N-S oblique thrusts and NE-SW lateral ramps. During the Mesozoic (Upper Cretaceous) the Alto Sanfranciscana Basin was filled by continental sediments of the Urucuia Formation. The lithostratigraphic sequence is composed of the following lithofacies: 1) conglomeratic facies which represents residual paviments of.deflation and in part interdune deposits and wadifans related to an intermittent drainage system; 2) sandstone facies formed by ortoquartzite, arkose and subarkose which constitute wind deposits; 3) and stratified chert facies which represent chemical lacustrine deposits. The basin architecture includes also NNW-SSE listric normal faults and NE-SW transfer faults related to a N5OE extensional axis. During the Tertiary coluvial and aluvial deposits, which underwent lateritization as an immature profile, were formed. The Quaternary is represented by a lacustrine-fluvial sedimentary system. The drainage system is related to the basin of the Manoel Alves and Araguaia rivers, strongly controlled by NE-SW lineaments and associated to pull-apart structures linked to a dextral system.
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Geologia do setor nordeste da zona de cisalhamento de Granja - noroeste do Ceará
(Universidade Federal do Pará, 1992-03-20) GAMA JÚNIOR, Theodomiro; OLIVEIRA, Marcos Aurélio Farias de; http://lattes.cnpq.br/6704755061378988
This work is about the geology of the northeast part of the Granja Shear Zone, in the northwest portion of State of Ceará, Brazil. This part of shear zone consist of rocks from Gameleira and Granja complexes, and Martinópole Group. These units were individualized from geologic mapping, petrography, lithochemistry, tectonic regime and geocronology. The Gameleira Complex is present in the northern part of area, and in conventional air photos and image of radar shows a peneplanized relief Pattern. The lithological types are represented by kizingitic gneisses and ultramaficy mafic and enderbitic granulites. From lithochemistry study these rocks can be interpreted from and orthoderived origin. The milonitic foliation shows anastomosed pattern with trend NE - SW, with strong dips to SE, and the stretching lineations concentrated in poles around N 75 E, dipping not over than 25'. Radiometric ages obtained from Rb/Sr methods, Total Rock, were 1.915±19 Ma and 1.929+60 Ma. The Granja Complex is located in the center part of the area and shows either a peneplanized relief. The main lithological type is the tonalitic-granodioritic gneisses with trondhjemitic and monzo-granitic gneisses, and amphibolite lenses with subordinated ocurrence. Probably these rocks are derived from igneous rocks with calc-alkaline trend. The geometric pattern of milonitic foliation presents the same regional trend NE - SW, dipping to SE, with stretching lineations poles concentrated near those observed in Gameleira Complex. Radiometric ages obtained from Rb/Sr methods, Total Rock, were 2.40282 Ma, i.796±105 Ma, 1.791±141 Ma, 1.581±43 Ma and 498±31 Ma. The Martinópole Group occurs in southern part of the area, as elongated hills with trend NE - SW. The lithological type are represented by quartzites and calc-silicate gneisses, of paraderivated origin. The S milonitic foliation has NE SW trend, with strong to moderate dips to SE. The isotopic age of 2.4 Ga obtained from gneisses of Granja Complex, suggest that the Granja Shear Zone formation is related to a tectonic event of the end of Archaean, when rocks from lower crust upflit to higher level through an oblique sistem during the movement of Ceará Block to WSW overridding the São Luis Block. The goungest ages from rocks of Granja Complex are interpretated as due importants isotopft resetting related to sheary metamorphism and partial melting during the Lower Proterozoic and Upper Proterozoic thermal effects.
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Geologia e petrogênese do “Greenstone Belt” identidade: implicações sobre a evolução geodinâmica do terreno granito - “Greenstone” de Rio Maria, SE do Pará
(Universidade Federal do Pará, 1994-10-07) SOUZA, Zorano Sérgio de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
This thesis deals to the geology and petrogenesis of the Identidade greenstone belt, located between Xinguara and Rio Maria towns, SE of Pará state. The data of this area permitted the discussion of the tectonic evolution of the gravite greenstone terrain of the Rio Maria region in the context of the Província Mineral de Carajás, SE of the Amazonian craton. The greenstone studied compose a synformal belt in the WNW-ESE direction, corresponding to one metavolcanic pile, formed predominantly by ultramafic schists (UM), basalts (BAS) and gabbros (GB) at the base, and hypabyssal dacitic rocks (DAC - ca. 2.94 Ga, Pb/Pb) at the top. The whole was intruded by metaplutonic rocks of Mesoarchean ages, the older one being quartz diorites, followed successively by granodiorites, trondhjemites / tonalites and leucogranites. The gneissic basement (GN - outcroping toward north and recognized for having an older fabric Sn-1/D1), the greenstone and the metagranitoids were intruded by hypabyssal rhyolitic (ca. 1.60 Ga, Rb/Sr) and basic dykes at the end of the Paleoproterozoic. The greenstone presents igneous structures and textures still recognized, although obliterated near the contacts with the metagranitoids and shear zones. The ultramafics occur as tremolitites, tremolite - talc schists and talc schists; the amphibole is very elongated and thin, commonly in parallel arrays, interpreted as ghosts of spinifex textures. The basalts are massive or pillowed and frequently variolitic. They show different degrees of recrystallization, with some relicts of hyalophitic, pilotaxitic and traquitoid textures. Clinoamphibole (actinolitic hornblende), epidotes and plagioclase (albite - andesine) are the most abundant minerais. The gabbros may be massives to porphyritics (plagioclase phenocrysts), still with some relicts of subophitic and granophyric textures. The dacites are porphyritic, with phenocrysts of quartz and plagioclase (oligoclase), besides hornblende and mafic clots (biotite, chlorite, opaque minerais, epidotes, sphene, apatite) in the less evolved samples. Concerning the metagranitoids, the leucogranites and trondhjemites have chloritized biotite, whereas the granodiorites and some tonalites comprise biotite or biotite + hornblende (also in quartz diorites). The greenstone and the metagranitoids were affected by one event of heterogeneous, ductile deformation, that evolved to mylonitic zones. The structural framework of the area is marked by a planar fabric (Sn//Sm/D2) in the WNW-ESE to E-W direction, with moderate to strong dips in a divergent fan. E-W, WNW-ESE or NW-SE stretching lineations, meso and asymmetric S-C microstructures, mica and clinoamphibole fishes, and rotation of o and i porphyroclasts indicated one megastructure resulting from a binary system with NW-SE shortening direction. The actual geometry of the greenstone would be derived from a dextral transpression, with the greenstone forming a positive flower structure. The transpressional regime favored the grow of transtensional cites and subsequent emplacement of granitic plutons on the NW contact, and extensional crenulation cleavage (Sn+1/D2) on the SW of the greenstone. Strain measurements displayed a ca. 60% shortening, subhorizontal extension of ca. 60 to 500% parallel to the greenstone trend, and vertical extension of ca. 101 to 280%. The strain ellipsoid may be oblate to prolate, with changes in density and rotation of the axis of maximum stretching (X) toward the mylonitic zones. The inversion of the deformation permitted the reconstruction of the original shape of the greenstone, that would be also elongated WNW-ESE, but with lesser eccentricity than today. These data, together with the quartz petrofabric, suggested that the deformation has been accommodated by pure and simple shear mechanisms, the final framework resulting essentially from the later. The last event (D3) are represented by faults and fractures which also affected the felsic and basic dykes. The paragenesis of the main metamorphic event (Mn/M2) is represented by static recrystallization, which modified some textures and almost ali minerais within the greenstone. The minerais formed phases were bluish green amphibole (actinolitic hornblende), epidotes, sphene and quartz in BAS and GB; tremolite, talc and chlorite in UM. The metagranitoids show transformations of plagioclase (saussurite, fine white mica), amphibole (to biotite and/or sphene) and biotite (to chlorite). The coexistence of hornblende + plagioclase (An>17) and/or actinolitic hornblende + chlorite in metabasic rocks shows that this event was of low pressures and temperatures in the transitional field of the greenschist and amphibolite facies. This episode should reflect a regional crustal heating produced by the plutonism at the end of the Mesoarchean, that obliterated the previous associations of ocean floor metamorphism. Slightly coeval to subsequently, it occurred one event of extensive dynamic recrystallization (Mm/M2) in the greenschist facies, specially within shear zones and lithological contacts. In these places, there are evidences of fluid incoming (schistose blastomylonites and abundant quartz veins) and remobilization of chemical elements (Al, Fe, Ca, K, Na, Rb, Sr, Zr). Finally, under lower PT conditions, it occurred a less expressive event related to crenulation cleavages and forming chlorite, epidotes and quartz (Mn+1/M2). The M2 event, as well as the one detected only in GN (M1 under amphibolite facies), was of ductile nature and cleary distinguished from the last one (D3/M3). The later was placed at the end of the Paleoproterozoic, being of hydrothermal character and associated to high crustal structures. The progressive evolution of the M2 metamorphism with its thermal peak predating the deformation suggested a counterclockwise P-T-t path, corresponding to the metamorphic evolution of Phanerozoic marginal basins. Some chemical analysis of the metavolcanic rocks permitted the definition of magmatic series and a discussion of petrogenetical modeling. It was possible to recognize three geochemical series, that is, from the older to the younger, komatiitic (UM), tholeiitic (BAS and GB) and calc-alkaline (DAC). The first one corresponds to peridotitic komatiites with MgO>18 weight % (volatile-free basis), with an enrichment trend in Al, such as in Geluk and Munro, and less calcic than the Barberton one. The light rare earth element patterns are irregular with (La/Sm)N ratios between 0.42 and 4.2 and negative Eu anomalies. The heavy rare earth elements seem less affected by post-eruptive processes, being plate or slightly fractionated (1.0<(Gd/Yb)N<2.3). The quantitative models were of hard execution due to the remobilization of several elements. It was possible estimate cumulates rich in olivine and orthopyroxene. With regarding to tholeiites, the BAS and GB showed very similar geochemical signatures, both being low potassium tholeiites comparable to depleted Archean tholeiites. The rare earth elements are almost plate, with values 10X the chondrite, and slight or no Eu anomaly. Preliminary modeling suggested similar cumulates for BAS and GB, composed essentially by clinopyroxene and plagioclase. The magma sources that originated the komatiites and tholeiites would be a garnet lherzolite. The DAC presented geochemical characteristics of modern and Archean metavolcanics and metaplutonics of trondhjemitic nature. The magmatic differentiation would be achieved by fractionation of plagioclase>quartz>hornblende>K-feldspar, with subordinated amount of biotite, magnetite, sphene, allanite and zircon. The source of the dacitic magma would be a tholeiite metamorphosed to the garnet amphibolite facies and somewhat enriched in light rare earth elements. The geodynamical model proposed admit the existence of a gneissic basement prior to 2.96 Ga. Between 2.96 and 2.90 Ga, the interplay of high geothermal gradients and lithospheric extension was responsible for extensive rifting, forming marginal basin systems, where extruded the komatiitic and tholeiitic rocks. At 2.94(?)-2.90 Ga, the DAC were generated from partia' melting of oceanic crust in subduction zone settings, and evolved by low pressure fractional crystallization. The same mechanisms that generated the DAC are extended also to the calc-alkaline plutonism, this one being responsible for the structural inversion of the greenstone, crustal thickening and final shape of the granite - greenstone terrain (dextral transpression ca. 2.88-2.86 Ga). The region still suffered a late episode (end of Eoarchean, 2.69-2.50 Ga) of (re)heating, registered only in sorne mineral, without any evidente of deformation and/or metamorphism. Finally, it occurred the intrusion of felsic (1.60 Ga, Rb/r) and basic dykes at the end of the Paleoproterozoic. The correlation with the actual understanding of the Província Mineral de Carajás permitted envisage that the Rio Maria granite - greenstone terrain was then configured at the moment of implantation of the Itacaiúnas Supergroup (ca. 2.76 Ga) and alkaline granitic plutonism at the Serra dos Carajás. So the sinistrai transpression that inverted that supergroup would correspond to a newer event, very distinct as regards as the dextral transpression of the Rio Maria region.
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Maciço granítico Musa: mapeamento, petrologia e petroquímica, Rio Maria, SE do Pará
(Universidade Federal do Pará, 1987-07-01) GASTAL, Maria do Carmo Pinto; DALL'AGNOL, Roberto
The Musa granitic massif, located in the extreme-southeast of the state of Pará (southern portion of the Mineral'de Carajás Province), is a permissive intrusion, placed in shallow crustal levels. It cuts rocks from the regional basement, formerly included in the Xingú Complex, including the Rio Maria granodiorite, the Pedra Preta greenstone belt type sequence and the Archean gneisses. Pre-existing faults and fractures played an important role in placing the massif. There are important wolframite mineralizations in quartz veins, adjacent to the granite, where it cuts the greenstone-like sequence, in the Pedra Preta area (to the west). Its origin is due to the thermometamorphic reworking of the W contained in the rocks of the greenstone sequence, at the time of the intrusion of the Musa massif. The contact relationships with the host regions reveal a high viscosity contrast between the granitic magma and the same, and that conditions of medium degree metamorphism and pressures below 4 kbar were reached. The faciology of the massif includes leucocratic to hololeucocratic biotite granites, containing amphibole and titanite, which were divided into monzogranites and syenogranites, and intermediate and acidic hypoabyssal rocks (microdiorites, porphyry dacites and porphyry granites). The relationships between the different facies indicate that the monzogranites are the most precociously placed, being cut by the dykes and both, in turn, truncated by the syenogranites. In monzogranites, the existence of enclaves of monzo to granodiorite composition is common, interpreted as crystalline residues carried in equilibrium by the magma. Texture and mineralogical variations observed in the two groups of granitic facies allowed us to subdivide them into seven distinct petrographic facies: Biotite-amphibole monzogranite, amphibole-biotite monzogranite, biotite-monzogranite, leucomonzogranite, amphibole-biotite syenogranite, leucosyene-granite and microsyenogranite. Some granitic rocks that occur associated with the mineralized veins of Pedra Preta resemble heterogranular leucosyenogranitic facies, laughing because they are more intensely transformed by late-magmatic events. The different granitic facies exhibit sub-alkaline composition, are calc-alkaline, metaluminous to slightly peraluminous and are relatively enriched in Si02, K20, FeO(t), Ti02, P205, Ba and Y and depleted in MgO. Together, they show greater analogies with the Cordilleran granites (type I - Chappell and White, 1974) or the Magnetite series (Ishihara, 1981), although the terms of hololeucocratic syenogranites differ a little from the others. According to the classification by Pearce et alii (1984) , they are classified as intraplate granites, developed in attenuated continental crust. The behavior of the trace elements does not characterize the different facies as metallogenetically specialized granites, however some samples of microsyenogranites can be seen as such. Geochronological data, Rb/Sr in T.R., obtained for the different facies present in the Musa massif, although not entirely conclusive, seem consistent with the observed order of placement. On the other hand, the given age, taking the set of samples from the various facies, is 1692 ± 11 Ma and R.I. 0.78777 : 0.00023. This age shows that this massif is not related to the Uatumã event, bringing it closer to the Jamon massif intrusion (1601 ± 21 Ma). The chemistry of the hypoabyssal rocks does not confirm their relationship with the volcanic ones of the Uatumã group. The "trend of tholeiitic affinities" in the AFM diagram, presented by the set of samples from the massif differs from that of the "calci-alkaline" of the Uatumã volcanoes. The spatial and temporal proximity between the Musa and Jamon massifs and the presence in them of very similar monzogranitic facies leads to the interpretation that they originated and evolved through analogous processes. This allows the definition of Acidic and Intermediate Magmatism of Rio Maria from the Middle Proterozoic (1700-1600 Ma), including the two massifs, intermediate and acidic hypoabyssal rocks and Marajoara granite. The dataset confirms the cogeniticity of the various facies occurring in the massif, but reveals possible variations in the source rocks. , which would be mixed. The expansion of partial melting processes led to the inclusion of more superficial rocks, related to volcanic sedimentary sequences. This model, coherent with the ideas of Hildreth (1981), reveals the existence of, at least, two slightly different magmatic liquids (monzogranitic and syenogranitic), formed at different depths of the crust and which would have evolved independently, but through of prolonged fractional crystallization processes. Regarding the tectonic environment at the time of generation of the Musa massif, the data leave doubts as to whether it is an intraplate, anorogenic granite or whether it is related to a Proterozoic continental margin.
Acesso aberto (Open Access)
Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS
(Universidade Federal do Pará, 2015-09) REDES, Letícia Alexandre; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; LAFON, Jean Michel
The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS), near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1) and the other brittle (F2). Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga) values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.
Acesso aberto (Open Access)
Petrogenesis, U-Pb and Sm-Nd geochronology of the Furna Azul Migmatite: partial melting evidence during the San Ignácio Orogeny, Paraguá Terrane, SW Amazon Craton
(Universidade Federal do Pará, 2016-06) NASCIMENTO, Newton Diego Couto do; RUIZ, Amarildo Salina; PIEROSAN, Ronaldo; LIMA, Gabrielle Aparecida de; MATOS, João Batista; LAFON, Jean Michel; MOURA, Candido Augusto Veloso
The Furna Azul Migmatite is a ~10 km2 complex located in Pontes e Lacerda city, Mato Grosso, Brazil. It belongs to Paraguá Terrane, limit with Rio Alegre Terrane, southeast of San Ignacio Province, in Amazon Craton. It consists of transitional metatexites with amphibolite enclaves and dioritic injections. The rocks were divided in residuum rich and leucosome rich; both have three deformation phases marked by folded stromatic layers affected by spaced foliation and metamorphosed in amphibolite facies, represented by garnet, biotite, sillimanite, and by the clinopyroxene in the enclaves. The metamorphic retrograde to greenschist is marked by formation of chlorite, muscovite and prehnite. Residuum-rich metatexites show higher CaO and Na2O contents, separating them from K2O, Ba and Rb enriched transitional metatexites. U-Pb on zircon and Sm-Nd whole-rocks dating indicates that the residuum-rich metatexite crystallized at 1436 ± 11 Ma, with a TDM age of 1.90 Ga and εNd(1.43) of -0.54, whereas the dioritic injection crystallized at 1341,7 ± 17 Ma with a TDM age of 1.47 Ga and εNd(1.34) of 3.39. These results indicate that the Furna Azul Migmatite protolith was formed during the San Ignácio Orogeny and was reworked during the same orogeny, as basement for collisional to post-magmatic granites from Pensamiento Intrusive Suite.
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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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Quartzo magmático e hidrotermal do depósito de ouro São Jorge, Província Aurífera do Tapajós, Pará: petrografia, microscopia eletrônica de varredura-catodoluminescência e implicações metalogenéticas
(Universidade Federal do Pará, 2015-12) SOTERO, Aldemir de Melo; LAMARÃO, Cláudio Nery; MARQUES, Gisele Tavares; RODRIGUES, Paulo Roberto Soares
Studies in crystals of quartz present in the mineral associations to the area of the São Jorge gold deposit, Tapajós Gold Province, southwest of the Pará state, identified four morphological and textural types (Qz1, Qz2, Qz3 and Qz4) by scanning electron microscopy-cathodoluminescence images. In the more preserved rocks of the Younger São Jorge Jovem granite, rich in amphibole and biotite (associations 1 and 2), anhedral crystals of magmatic quartz with high to moderate luminescence (Qz1) dominate. In the partly altered rocks (associations 2 and 3), post-magmatic to hydrothermal fluids affected the granite, and filled fractures in Qz1 and crystallized not luminescent (dark) Qz2. In the most intensely altered rocks (association 4), successive alteration, dissolution and recrystallization processes gave rise to typically hydrothermal zoned, subhedral (Qz3) and euhedral (Qz4) quartz crystals. Images by backscattered electrons and semiquantitative analysis by energy dispersive spectroscopy identified two generations of gold: Au1, enriched in Ag (4.3 to 23.7%) and associated to pyrite crystals; Au2, enriched in Te (1.1 to 17.2%) and included or associated to Qz4. The scanning electron microscopy-cathodoluminescence study provided important information that was preserved in the quartz structure. The morphological and textural evolution of this mineral in different stages shows the gradual action of the hydrothermalism in the rocks and minerals associations of São Jorge deposit. Gold mineralization of the deposit was chemically (energy dispersive spectroscopy) and paragenetically (pyrite, sphalerite and Qz4) characterized, and it can be divided into different generations or mineralizing events. The effectiveness of the methodology used in this study was established, allowing its application in studies of other hydrothermal deposits.