BDTD - Biblioteca Digital de Teses e Dissertações

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2289

Biblioteca Digital de Teses e Dissertações da UFPA (BDTD). Sistema Eletrônico de Teses e Dissertações (TEDE). Projeto BDTD/UFPA e Instituto Brasileiro de Informação em Ciência e Tecnologia (IBICT).

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Acesso aberto (Open Access)
Estratigrafia e evolução estrutural do segmento setentrional da faixa de desdobramentos Paraguai - Araguaia
(Universidade Federal do Pará, 1979-06-13) ABREU, Francisco de Assis Matos de; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
The northern part of the Paraguai-Araguaia orogenic belt comprises a significant portion of the South American Platform. Here, the Brazilian geotectonic cycle (550-900 m.y), produced a mountain chain through a complex sequence of sedimentary metamorphic, magmatic, and structural events along the eastern margin of the Amazon craton. The lithologic sequence is designated stratigraphically as the Baixo Araguaia Supergroup which comprises the Estrondo Group and the overlying Tocantins Group. The basal formation in the Estrondo Group is the Morro do Campo Formation which consists of quartzites and subordinate schists and gneisses. The Xambioá overlies the Morro do Campo and includes several kinds of schists. The Tocantins Group is formed by Couto Magalhães Formation, represented by phyllites and intercalated quartzites and the overlying Pequizeiro Formation consiwts of pelitic sediments and Mg-rich igneous derivatives. The Estrondo and the Tocantins groups are intruded by ultramafic, mafic, and granitic rocks that are associated with late and post-tectonic igneous events. The Rio das Barreiras Formation, a sedimentary sequence represented by a polymictic conglomerate with carbonate matrix and sandy and silty interlayers, unconformably overlies the Pequizeiro Formation and may represent erosional remnants of a final phase of the Brazilian cycle. Primary lithologic structures in Baixo Araguaia Su pergroup are preserved as relict compositional stratification, inclined, parallel, and graded bedding in metasediments, and flow structures in the igneous rocks. Superposed penetrative planar and linear deformation structures are present in several generations. The regional N-S striking schistosity is of axial-plane type and is related to the intrafolial folds, with an easterly dip getting vergence to Amazon craton. The regional dip is 309 and decreases to abaut 159 adjacent to the Amazon craton. Gneissic banding parallels schistosity of overlying schists in the larger folds and they share a common mineral lineation. Polyphase deformation is recorded by a fold sequence which varies in scale from 1 cm to 30 km and is related to the differents structural levels within the crust. The lower structural level includes: a) similar-type intrafolial isoclinal folds which are contemporaneous with regional metamorphism; b) similar tight folds which involve the s.chistosity and transposed bedding; c) shear folds of crenulation developed near to the top of the level in the more plastic horizons. The intermediate level comprises; d) isolated regional flexures near the localities of Colméia, Xambioà-, Lontra, Muricizal; e) two generations of open and cross folds associated with the Iriri-Martírios lineament zone. N-S and NW-SE fracture and fault systems cut ali stratigraphi.c units of the Baixo Araguaia Supergroup. The faults consist of: 1) NW treding transcurrent fault with strike iengths of severa]. Kilometers; 2) thrust faults with N-S- strike such as those near Andorinhas and Muricizal mountains; 3) N-S striking normal faults developed at the edge of the Parnaíba basin and elsewhere. The mapped facies sequence ranges from incipient greenschist facies in the west to amphibolite facies in the east implying an Bastward increase in metamorphic grade. Sericite to garnet isograds are discernibles. Three magmatic events are distinguished. They comprises: a) pre-tectonic basic and ultrabasic plutonic-volcanic magmatism; b) late-tectonic granitic intrusion; c) post- tectonic unfoliated granitic intrusions. Eleven K-Ar mica dates from gneisses and schists of the orogenic belt yield values in the range of 516 ± 10 m.y to 358 ± 19 m.y. (Brazilian Cycle). Five Rb/Sr determinations from the gneissic core of the Colméia fold gives values around 2,000 m.y (Amazonic cycle). The geologic evolution of the northern Paraguai-Araguaia orogenic belt consists of three sequential stages: I) deposition of psammitic and pelitic sediments comprising the Estrondo and lower Tocantins Groups. Basic and ultrabasic igneous activity in late Tocantins time result in the deposition of mixture of pelitic sediments and Mg-rich igneous material which comprise the Pequizeiro Formation. II) polyphase deformation, metamorphism, magmatism, and orogenic uplift followed. These events are subdivided as follows: 1) F1 - deformation and regional metamorphism (Ma) in which So (original bedding) was transposed by isoclinal folding to S1 (regional schistosity) and progressive metamorphism produced sericite and garnet map zunes; 2) F2 - deformation produced tight folds in the schistosity (S1) resulting an axial plane surface (S2); well-marked mineral lineation (L2); 3) F3 deformation developed crenulation folds and a second phase of transposition (S3); e) F4 - deformation produced large folds accopanied by migmatization and late-tectonic granitic intrusions; 5) F5 - deformation formed small-scale plastic folds in cataclastic zones along the Iriri-Martírios lineament. III) The post-metamorphic Rio das Barreiras Formation was then deposited unconformably over this structural sequente and the final deformation event produced fault movements (transcurrent, thrust and normal), established joints, and permitted the rise of post-tectonic granitic plutons. This stage marks a transition from an environment of compressional stress to one of tensional stress on the regional scale. Subsequent to stageIII, consolidation of the South American platform occurred. Related erosional, sedimentary, magmatic, and'tectonic processes affedted this ares at numerous times throughout post-Brazilian cycle time.
Acesso aberto (Open Access)
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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