Programa de Pós-Graduação em Geologia e Geoquímica - PPGG/IG

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2603

O Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA) surgiu em 1976 como uma necessidade de desmembramento do então já em pleno desenvolvimento Curso de Pós-Graduação em Ciências Geofísicas e Geológicas (CPGG), instalado ainda em 1973 nesta mesma Universidade. Foi o primeiro programa stricto sensu de Pós-Graduação (mestrado e doutorado) em Geociências em toda Amazônia Legal. Ao longo de sua existência, o PPGG tem pautado sua atuação na formação na qualificação de profissionais nos níveis de Mestrado e Doutorado, a base para formação de pesquisadores e profissionais de alto nível. Neste seu curto período de existência promoveu a formação de 499 mestres e 124 doutores, no total de 623 dissertações e teses.

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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.
Acesso aberto (Open Access)
A capa carbonática do sudoeste do cráton amazônico, estado de Rondônia: nova ocorrência e extensão dos eventos pós-glaciação marinoana (635 Ma)
(Universidade Federal do Pará, 2014-11-27) GAIA, Valber do Carmo de Souza; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
In the Western Amazon Craton, specifically in Western Parecis Basin, Rondônia State, carbonate rocks exposed on border of Pimenta Bueno and Colorado Grábens are considered to be part of the eopaleozoic basin fill. The facies and microfacies analysis together with chemostratigraphy of theses rocks in Chupinguaia and Pimenta Bueno Region, confirmed the occurrence of pinkish dolostone that overlie glaciogenic diamictite, previously interpreted as alluvial fan. Previous works reported δ13C negative excursions, confirmed in this work as well, ranging from -4.6 e -3,8‰VPDB in Chupinguaia, and average of -3,15‰VPDB in Pimenta Bueno. This sedimentation and chemostratigraphic pattern, uncommon in paleozoic rocks, is widely found in the anomalous neoproterozoic carbonates. In the Southern Amazon Craton, Mato Grosso State, rocks with the same features were described as cap carbonates related to the Marinoan Glaciation (635 Ma). Therefore this work considers this dolostones at the same context of the cap carbonate in Mato Grosso. Additionally we stand out the sharp and loaded contact between dolostone and diamictite, which happens in both occurrences, and is seemingly a typical feature of cap carbonates in the Amazon Craton. This paradoxal relationship has been interpreted as rapid change from icehouse to greenhouse conditions, and the loaded contact is attributed to isostatic rebound. The Rondônia cap carbonate presents two facies associations (FA2 and FA3) that overlie glaciomarine deposits (FA1) subdivided in two facies: Polymitic paraconglomerates (Pp) and laminated pebbly sandstone (Asl). The FA2 consists into: peloidal dolomudstone/dolopackstone with planar to quasi-planar laminations and low-angle truncations (Dp), megarriple bedding (Dm) and wave truncated laminations. This association is interpreted as shallow platform deposits wave influenced. This coastal succession is overlaid by FA3, which comprises the facies: dolomudstone/dolopackstone and dolomudstone/ dolograinstone with shale partition (Df) and laminated shaly siltstone (Sl). Df comprises 6m-thick of dolomite with parting shale, showing laterally continuous laminations of fibrous calcite (pseudomorph of gypsum) and dolomite with current wavy lamination. The Sl comprises 5m-thick of planar-laminated shaly siltstone. This association is interpreted as shallow platform deposits tide influenced. Finally, this inner platform succession is overlaid unconformably, in angular contact, by eopaleozoic glaciogenic diamictite. The isotopic values of C and O are negative and reflect the primary signal of C, however it can be considered a slight influence of meteoric diagenesis in the signal. The main shifts in negative signals are associated with meteoric influences, expressed by replacement and pores filling by calcite, and also by its proximity of stratigraphic surfaces, which reflect some patterns of diagenetic alteration, represented by the most negative signals. Differently from Mato Grosso cap carbonate, the Rondônia occurrence presents levels of pseudomorph of evaporites and dolomite with parting shale (rhythmites), order in succession of shallow marine facies, where the dolomites of wavy influenced shallow platform pass up-section to rhythmites and shaly siltstone of tide influenced shallow platform, setting up a retrogradational succession. This new occurrence of cap carbonate has strong implications to the stratigraphy of the base of Parecis Basin, since it excludes these carbonate rocks from the eopaleozoic sequence. Moreover, it provides information that allows reconstruct the coastal paleogeography of neoproterozoic basin that accumulated deposits of Araras Platform, as well extends the postmarinoan events of the Snowball/Slushball Earth hypothesis to the southwesternmost Amazon Craton, exposed in the Rondônia State.
Acesso aberto (Open Access)
Evolução geológica das seqüências do embasamento na porção sul do Cinturão Araguaia - Região de Paraíso do Tocantins
(Universidade Federal do Pará, 2002-09-12) ARCANJO, Silvia Helena de Souza; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
The basement rocks in the south segment of the Araguaia Belt, due to the scarcity of geochronological information, were firstly considered as of Archean age. This interpretation began to be reviewed after the geochronological investigations were carried out during the last decade, which showed an important contribution of geological processes of the Paleoproterozoic in the formation of those basement rocks. In this work an isotopic study was carried out on the basement sequences of the southern segments of the Araguaia Belt and its results were based on the single zircon Pb-evaporation technique (Pb-Pb in zircon) and the Sm-Nd (whole rock) systematic. These techniques were used in order to improve and reconstruct the geological evolution of this crustal segment where Rio do Coco Group, Rio dos Mangues Complex, and Serrote Granite occur, as well as Monte Santo Suite that also appear in this context. The geological processes identified for the region took place from the Archean through the Neoproterozoic Era. The first evidences from the archean source were obtained in some restricted orthoderivated bodies in the east sector of the mapped area in which the TDM ages varied between 3.25 and 2.78 Ga. In a clear way, the Archean occurs in the northwest portion of the studied area being represented by a metabasic rock belonged to the Rio do Coco Group (greenstone belt sequence), with 2.618 ± 14 Ma. This age is interpreted as the age of the extrusion of the volcanic protolith. They would represent the two crustal preterit segments found in the region. During the Paleoproterozoic the Rio dos Mangues Complex was constituted, representing the most expressive unit of the basement. Ortogneisses of the Rio dos Mangues Complex were dated and their Pb-Pb in zircon ages varied between 2.054 ± 4 Ma and 2.086 ± 16 Ma. They were formed from a mantelic and juvenile source, with a small crustal contribution and their TDM ages are between 2.35 e 2.21 Ga. The geological processes that marked this period, involved crustal shortening with the participation of collision and thrusting that induced partial fusion of some parts of the thickened crust. The results were the generation of some igneous bodies (1.85 and 1.82 Ga) and of the Serrote Granite (1.86 Ga). Although the emplacement of the Serrote Granite took place at the end of the Paleoproterozoic, it was developed from older sources (2.50 e 2.43 Ga) than those of the Rio dos Mangues Complex. So, The continental crust established, with rocks from different ages and sources may be projected to the east, far from the studied area, inside the context of the architecture from the Atlantic Super Continent, formed definitively at the end of the Paleoproterozoic. At the end of a period without tectonic registers (end of Mesoproterozoic) a new phase took place in the region marked by tafrogenetic processes as the appearing of alkaline and basic magmatism as well as depositional basins that show an extensive context along the whole area. One of these basins received the sediments that originated the Araguaia Belt Supracrustals, which, during its evaluative process, reach the proto-rifte stage. Far from here, at the north portion of Goiás Massif, this rifting process seemed to permit the constitution of an oceanic domain, that, by evolution and recycling, may have be formed the rocks of the Magmatic Arc of Goiás. At the worked area, this arc terrain could be only be predicted by the appearing of one tonalitic gneiss with the age of 840 Ma and TDM model ages of 1.83 Ga. The effects of this tafrogenetic processes, from which the most important evidences are sienitic gneisses, found at Monte Santo Suit, with 1.051 ± 17 Ma, are related to the fission processes in the whole world which made the break up of the Rodinia Super Continent possible. The protolith of this suit were also been formed during the Mesoproterozoic as they can be seen in the TDM model age between 1.49 e 1.70 Ga. Finally, passing to the Neoproterozoic, through the inversion in the geodinamic conditions, processes of horizontal shortening again took place in the region, with the participation of crustal thickening as well as distinct volumetric and spatial fusions that may have generated the Matança and Santa Luzia Granites. The last one found inside the domain of Araguaia Belt. The Araguaia Belt was built from this tectonic motion, and has registers of past structural formations, also present in the older litostructural groups. The mass tectonic transport in the Amazonian Craton way might have occurred, resulting in the actual architecture found nowadays in the form of imbricated slices.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
O mar epicontinental Itaituba na região central da Bacia do Amazonas: paleoambiente e correlação com os eventos paleoclimáticos e paleoceanográficos do carbonífero
(Universidade Federal do Pará, 2019-03-14) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous paleogeography of the West Gondwana was dominated by epicontinental seas connected with the Panthalassa Ocean to the west. 50m-thick Pennsylvanian mixed siliciclastic-carbonate transgressive succession of the Amazonas Basin, Northern Brazil, were studied in outcrops and cores using facies and stratigraphic analysis in combination with O- and C-isotopic stratigraphy. Thirty-four facies, representative of coastal to shelf depositional systems grouped in three facies associations (FA): FA1) coastal desertic deposits, consisting of fine to medium-grained sandstone, mudstone and fine-grained dolostone that corresponds to a complex association of aeolian dunes, sand sheets, interdunes, fluvial channels and lagoon deposits bioturbated by Palaeophycus, Lockeia, Thalassinoides and Rosselia trace fossils; FA2) mixed tidal flat setting, constituted by fine to medium-grained sandstone, mudstone, shale, siltstone, lime mudstone and fine dolostone interpreted as supratidal, tidal channel, tidal delta and lagoon deposits with some brachiopod and echinoderm body fossils; and FA3) carbonate shelf deposits, consisting of lime mudstone, wackestone, packstone and grainstone with allochems (ooids and peloids), terrigenous grains and abundant and diversified open shallow marine benthic organisms, including, fish remains, foraminifers, brachiopods, echinoderms, gastropods, bryozoans, trilobites, corals, ostracodes, and conodonts, interpreted as bioclastic bars and carbonate shelf deposits. The conodonts species Neognathodus symmetricus, Streptognathodus sp. and Ellisonia sp. in the FA3 indicate the Baskirian-Moscovian age. The dolomitization affected the limestone and sandstone of AF1 and AF2 replacing the micritic matrix and occur as saddle dolomite indicating mixed of meteoric and marine waters and late burial. The neomorphism of opaque micritic matrix and bivalve shells are indicated by the growing of xenotopic mosaic of calcite crystals. In contrast, the secondary calcite cement is equant, fiber, bladed and espatic. Micritization is found in the bioclast shells exhibiting micritic coatings. The autigenesis of quartz and biogenic pyrite is commonly found in FA2 and FA3. The mechanic and chemical compaction in limestone caused the porosity reduction, cementation, fractures and development of dissolution seams and stylolite. The sandstones were cemented by quartz, calcite and iron hydroxides/oxides and show concave-convex and sutured contacts between quartz grains. The predominance of eodiagenetic and subordinate mesodiagenetic features in the Monte Alegre-Itaituba succession indicated less modified framework by the diagenesis corroborating the pristine signature of δ13C values ranging from ~ -2 to ~+5.28‰. This enriched trend upsection coadunate with high organic productivity triggered by massive flourishment of euphotic-controlled benthic organisms mainly in the FA3. Five types of shallowing upward asymmetric cycles characterize the Monte Alegre-Itaituba succession. Peritidal cycles in coastal desertic (Cycle I) were formed by alternance of dolostone and sandstone with δ13C values ranging from -1.5 to +0.3‰. Cycles II consist in interbedded of sandstone-mudstone and sandstone-mudstone-floatstone rhythmites and the Cycle III constitute dolostone interbedded with sandstone. These cycles II and III were interpreted as tidal flat and lagoon deposits with δ13C values ranging from +3,98%₀ to +4, 62%₀. The Cycle IV is a rhythmite formed by wackestones/mudstones couplets while the Cycle V consists of alternance of grainstones, wackestones and lime mudstone (ABC cyclicity) passing upsection for cycles composed by wackestones and lime mudstone (AB cyclicity). The cycles IV and V are shelf deposits with δ13C values ranging from +3,65%₀ a +5,28%₀. The stacking of 53 cycles with average thickness of 1,1 m, combined with Fisher plot diagram, indicated an aggradational to retrogradational stacking pattern inserted in the lowstand to early transgressive system tract (Cycles I-III) and late transgressive system tract (Cycles IV and V). The succession was deposited in ~13 Ma and individual cycles accumulated in an approximately 0.25 my typical of fourth order cycles related to high-frequency fluctuations of relative sea level. These data were correlated to the global δ13C and sea-level curves that positioned the Monte Alegre-Itaituba succession in the Late Serpukhovian to Early Moscovian age. The influence of Late Misssipian glaciation was negligible in these deposits but the post-glacial transgression combined with slow subsidence of the Amazonas basin caused the generation of allogenic cycles I, IV and V. The cycles II and III were formed by autochthonous processes during a period of equilibrium between supply and glacioeustasy. The Monte Alegre-Itaituba succession is the record of a large Amazonia epicontinental sea that was directly connected with the Panthalassa Ocean during Pennsylvanian.
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Petrografia, química mineral e parâmetros de cristalização da suíte Planalto, Província Carajás
(Universidade Federal do Pará, 2015-07-28) CUNHA, Ingrid Roberta Viana da; FEIO, Gilmara Regina Lima; http://lattes.cnpq.br/9344671380219647; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Planalto Suite is located in the Canaã dos Carajás Domain of the Carajás Province in the southeastern part of the Amazonian Craton. The suite has Neoarchean age (~2.73 Ga), ferroan character and affinity with A-type granites. Magnetic petrology studies allowed the distinction of two groups: (1) Ilmenite granites devoid of magnetite and showing low magnetic susceptibility (MS) values (MS between 0.6247x10-3 and 0.0102x10-3 SI; average of 0.1522x10-3); (2) Magnetite-ilmenite-bearing granites which display comparatively higher but still moderate MS values (between 15.700x10-3 and 0.8036x10-3 SI; average of 5.1717x10-3). Textural evidence indicates that amphibole, ilmenite, titanite, and, in the rocks of Group 2, also magnetite formed during magmatic crystallization. However, titanite chemical composition suggests that it was re-equilibrated by subsolidus processes. The amphibole varies from potassian-hastingsite to chloro-potassian-hastingsite and shows Fe/(Fe+Mg) >0.8. Biotite also shows high Fe/(Fe+Mg) ratios and is classified as annite although relatively enriched in Al compared to the annite end member. Plagioclase porphyroclasts are oligoclase (An25-10) and the grains of the recrystallized matrix display oligoclasic or albitic composition (An9-2). Mineral chemistry, magnetic petrology and whole rock geochemistry indicate that the dominant group 1 granites of the Planalto Suite were formed under reduced conditions below the FMQ buffer. The group 2 granites crystallized under more oxidizing conditions on or slightly above the FMQ buffer. Pressures of 900-700 MPa for the origin and of 500-300 MPa for the emplacement were estimated for the Planalto magmas. Geothermometers suggest initial crystallization temperatures between 900 °C and 830 °C and water content in the magma higher than 4 wt %. The mineralogical comparison between the Planalto Suite and the Archean subalkaline Estrela Granitic Complex of the Carajás Province reveals strong compositional analogies indicating that they were probably formed under similar conditions. The amphibole and biotite compositions of Planalto and Estrela granites are relatively enriched in Al being comparable with those of the Neoarchean Matok Pluton of the Limpopo Belt. They differ using the same criteria of the Proterozoic rapakivi A-type granites. On the other hand, in terms of Fe/(Fe+Mg) ratio, the Planalto and Estrela granites approach the reduced Mesoproterozoic rapakivi granites and the reduced to moderately oxidized Paleoproterozoic granites of, respectively, the Velho Guilherme and Serra dos Carajás suites and differ from the oxidized granites (Jamon Suite) of the Carajás province and also of Matok pluton. It is concluded that the Planalto Suite and similar Neoarchean granites of the Carajás Province differ in mineralogical characteristics and crystallization parameters of some classic examples of A-type granites and, except for its reduced character, they are akin to the Neoarchean Fe-K and Mg-K granitoids of the Limpopo Belt, as exemplified by the Matok granitoids. This indicates that the collisional setting of Carajás and Limpopo exerted strong influence in the nature of the Neoarchean granitoid magmas.

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