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Neotectonic evolution of the Serrania Del Interior range and Monagas fold and thrust belt, Eastern Venezuela : Morphotectonics, Seismic Profiles Analyses and Paleomagnetism / Evolution Néotectonique de la Serranía Del Interior et de la ceinture plissée de Monagas, Nord-Est du Venezuela : Morphotectonique, Interprétation Sismique et PaléomagnétismeFajardo, Atiria 19 November 2015 (has links)
La convergence oblique entre les plaques Caraïbes et Amérique du Sud à partir de l'Oligocène a conduit à la formation de la cordillère « Serranía del Interior » (SDI) et de son avant pays au sud (bassin de Maturín) et la ceinture plissée de Monagas. D’abord transpressif (direction NW-SE), le déplacement entre les deux plaques devient à compter de ~12 Ma principalement une translation O-E qui s’accommode principalement sur la faille d’El Pilar. Cependant, des indices de compression active ont été identifiés à la terminaison de la faille d'Urica dans la chaine plissée de Monagas. Pour discuter des mécanismes de cette déformation compressive actuelle, nous avons mis en œuvre une interprétation sismique (2D et 3D), une étude géomorphologique et une étude paléomagnétique. Depuis le front sud de la SDI dans la chaîne plissée de Monagas, l'interprétation sismique et l’analyse géomorphologique se sont concentrées sur les chevauchements de San Félix, Tarragona, Punta de Mata, Jusepín et Amarilis. Deux discordances miocènes (Mid-Miocene Unconformity (MMU) de ~10 Ma et Late Miocene Unconformity (LMU) de ~5,3 Ma) ont été cartographiées sur la sismique. En s’appuyant sur la LMU, il a été calculé à l’aplomb de ces accidents un taux de soulèvement plio-pléistocène de ~0,4 mm/a. Invisibles sur la sismique, des déformations ont aussi été observées en surface sur ces accidents (des terrasses fluviatiles basculées, plissées et faillées et des anomalies de drainage). Datées par des méthodes cosmonucléides (10Be et 26Al), l’âge des terrasses alluviales déformées sont compris entre ~90 ka sur le chevauchement de Tarragona et ~15 ka dans la zone de Punta de Mata. Un taux minimal de soulèvement pléistocène terminal à l’aplomb des chevauchements a été calculé entre 0,1 et 0,6 mm/a. Cette gamme de vitesse recouvre celle renvoyée par la LMU et montre que la déformation n'a pas varié significativement pendant les derniers 5,3 Ma. Ces observations montrent que les chevauchements de Tarragona, Pirital El Furrial et d’autres plus jeunes développés dans la formation Carapita restent actifs. Cette déformation superficielle s’estompe rapidement vers l’est près de la ville Maturín. Nous interprétons cette déformation comme liée au jeu récent de la faille d'Urica qui se termine au sud en queue de cheval. La faille d’Urica accommoderait donc une partie du déplacement entre plaques Caraïbe et Amérique du Sud. Une étude paléomagnétique a été réalisée dans les blocs de Caripe et Bergatín au sein de la SDI où 27 localités ont été échantillonnées dans les sédiments du Crétacé au Paléocène. Une observation clé de cette étude a été la mise en évidence d'une composante paléomagnétique stable déviée vers le Nord Est avec des polarités normale et inverse. Les analyses statistiques de ces composantes indiquent une acquisition postérieure au plissement de la SDI (< ~12 Ma). La déclinaison moyenne dans les blocs de Caripe et de Bergatín indique une rotation horaire de R=37º±4 º autour d’un axe vertical. Le taux de rotation post-Miocene moyen avoisine ~3.7º/Ma et reste probablement actif. Nous proposons de rattacher cette rotation horaire à un système de failles type "Riedel" (Urica et San Francisco) en relation avec la faille d’El Pilar. / In Northeastern Venezuela, the tectonic provinces of the Serranía Del Interior thrust belt (high hills), the Monagas Thrust belt (foothills) and the Maturín foreland basin formed as a result of the oblique convergence between the Caribbean and South American plates since the Oligocene. GPS data show that post 12 My wrenching component between the plates is accommodated predominantly by the E-W strike-slip El Pilar Fault. However, evidence of active compression has been identified in the southern limit of the NW-SE dextral Urica Fault, specifically, in the Monagas Fold and Thrust Belt. In order to constrain the neotectonics of this area, this thesis presents a combined approach, which includes geomorphological study, seismic and paleomagnetism. In the Monagas Fold and Thrust Belt, the geomorphological study and the seismic interpretation were focused on five zones. From the foothills to the deformation front, these zones are: San Felix, Tarragona, Punta de Mata, Jusepín and Amarilis. These areas show surface deformations such as topographic uplifts, tilted terraces, folded terraces, faulted terraces, and drainage anomalies. The dating of the river terraces through 10Be and 26Al methods indicates that these terraces formed in the Late Pleistocene. The oldest terrace located in the Tarragona zone has a maximum exposure age of ~90 ky and the youngest located in the Punta de Mata zone of ~15 ky. From this dating, a minimum vertical deformation rate between ~0.6-0.1 mm/y was calculated for this area. Using the seismic interpretation of a 3D block, the surfaces of two unconformities (MMU and LMU) have been mapped. The age obtained for the LMU (~5.3 My), yield a Plio-Pleistocene uplift rate between ~0.3-0.4 mm/y, which is close to the vertical deformation rate calculated from the terraces dated. These similar rates seem to indicate that the deformation rate in the MFTB has not changed significantly for the last 5.3 My. The deformed surfaces observed in the field and in DEM images coincide vertically with the deep structures interpreted in the seismic lines. I propose that the deformation on the surface is linked to the Tarragona, Pirital, Furrial thrusts and the Amarilis Backthrust activity and to the youngest thrusts developed in the Carapita Formation. However, this surface deformation dies out near the city of Maturín, therefore, the neotectonic deformation is inferred to be caused by local tectonics. I propose that this local compressive deformation could have been generated by a horsetail termination in the southern limit of the Urica Fault which reactivated the oldest thrusts (Tarragona and Pirital thrusts) and deformed the post-Middle Miocene units until reaching the surface. In the zones where the El Pilar Fault mainly accommodates the wrenching component, block rotation is likely. For that reason, a paleomagnetic study was conducted in the Caripe and Bergatín blocks of the Serranía Del Interior where 27 sites were sampled in Cretaceous to Paleocene sediments. Statistics analyses of the components yield a negative bedding-tilt test, indicating that this component was acquired post ~12 My after the folding process in the Serranía del interior. The average declination indicates a clockwise block rotation of R = 37º ± 4º and a post-Middle Miocene rotation rate of ~3.7º/My in both the Caripe and Bergatín blocks. This rotation rate is probably still active. I propose to relate the regional clockwise rotation to the development of a synthetic Riedel shear system formed by the El Pilar Fault (master regional fault) and by the Urica and San Francisco synthetic Riedel shears.
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Análise tectono-estratigráfica da Faixa de dobramento Paraguai meridional na Serra da Bodoquena e depressão do Rio Miranda, MS / Tectonostratigraphic analysis of the southern Paraguay fold belt in Serra da Bodoquena and Rio Miranda depression, MSSa, Fernanda Rostirola de 30 October 2009 (has links)
No presente trabalho buscou-se compor um quadro geológico-estrutural da Faixa Paraguai meridional e compreender as relações estratigráficas entre os litotipos da Formação Puga e grupos Cuiabá e Corumbá. Foram realizados trabalhos de reconhecimento geológico e perfis geológico-estruturais de detalhe, com análise estrutural e petrográfica, em conjunto com a integração de dados e mapas existentes, análise de imagens de satélite, fotos aéreas e modelos digitais de terreno. A Faixa Paraguai meridional evoluiu como um típico fold-andthrust belt. A evolução geológica do cinturão principia por processos de rifteamento, provavelmente no final do Criogeniano, evoluindo para mar restrito e margem passiva até o final do Ediacarano. A fase rifte é caracterizada pelas formações Puga e Cerradinho. A fase margem passiva está representada pelas formações Bocaina, Tamengo e Guaicurus. Propõe-se que o Grupo Cuiabá na área estudada seja constituído por depósitos marinhos profundos, turbidíticos distais depositados comitantemente aos sedimentos do Grupo Corumbá. O processo colisional responsável pela inversão da bacia com a deformação e metamorfismo associados ocorreu durante o Cambriano, com magmatismo pós-colisional no Cambriano Superior. O estilo estrutural torna-se progressivamente mais complexo de oeste para leste. São observadas até três fases de dobramento coaxiais sobrepostas com eixos subhorizontais de direção N-S. Associam-se a sistemas de falhas de empurrão com deslocamento da capa para oeste. As lineações de estiramento e indicadores cinemáticos observados sugerem que a convergência colisional em direção ao bloco Rio Apa que deu origem à faixa móvel não foi completamente frontal, existindo algum grau de obliquidade, com vetores de convergência em torno de WNWENE. Os micaxistos do Grupo Cuiabá mostram o estilo estrutural mais complexo, com três fases de dobramentos coaxiais e foliações tectônicas mais intensas. Haveria correlação temporal entre S3 gerada nos micaxistos, comumente referidos como Grupo Cuiabá, a leste com a foliação S2 gerada na porção central e a clivagem S1 gerada no limite da área cratônica a oeste, padrão que pode ser explicado pela migração do front deformacional de leste para oeste. É sugestivo que as principais falhas de empurrão coincidam com limites bacinais importantes, onde ocorrem variações de espessura e representatividades das formações basais. No processo de inversão da bacia provavelmente os empurrões reativaram as antigas falhas lístricas principais do estágio rifte. / This work aims to characterize the geological and structural context of the Southern Paraguay Folded Belt, and to understand the stratigraphic relationships between the Puga Formation, Corumbá and Cuiabá groups. Regional geological reconnaissance work and detailed geological-structural field sections were carried out, with petrographic and structural analysis, together with integration of existing data and maps and analysis of satellite images, aerial photos and digital terrain models. The southern Paraguay Belt is a typical fold-andthrust belt. Its geological evolution began with rifting (Puga and Cerradinho formations), probably at the end of Criogenian, and evolved to restricted sea and passive margin (Bocaina, Tamengo and Guaicurus formations) in the late Ediacaran. It is proposed that the Cuiabá Group in the study area consists of distal marine deposits coeval with the Corumbá Group. The collisional process responsible for basin inversion and associated deformation and metamorphism occurred in the Cambrian, with post-collisional magmatism in the Upper Cambrian. The structural style becomes increasingly complex from west to east. Up to three overprinted coaxial folding phases are observed with north / south upright axial planes dipping to east and axes plunging gently to North or South. A system of thrust faults is associated with displacement of the hangwall to the west. Down-dip to oblique and strike-slip stretching lineations are also observed, with kinematic indicators showing movement varying from inverse to sinistral. This suggests that the collisional convergence toward the Rio Apa block which generated the mobile belt was not strictly frontal, but had some degree of obliquity, with convergence vectors around SSW - ENE. The Cuiabá Group mica-schists show the most complex structural style with three superimposed coaxial fold phases and more intense tectonic foliations. It is proposed that there would be time correlation between the S3 foliation in the mica-schists in the easternmost area, with the S2 foliation in the central area and the S1 cleavage at the limit of the cratonic area to the west. This pattern can be explained by the westward migration of the deformational front. It is suggestive that the main thrusts coincide with major basin boundaries, where greater variations in thickness and expression of the basal formations occur. During the basin inversion the thrusts probably reactivated the former main listric faults of the rift stage.
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Ground Movements in the Zagros Fold-Thrust Belt of SW Iran Measured by GPS and InSAR Compared to Physical ModelsNilfouroushan, Faramarz January 2007 (has links)
<p>This thesis uses geodetic satellite data to measure present-day crustal deformation in the Zagros fold-thrust belt (SW Iran). Geodetic-type measurements are also used in down-scaled models that simulate the surface deformations seen in convergent settings like the Zagros fold-thrust belt.</p><p>Global Positioning System (GPS) measurements of three surveys between 1998 and 2001 indicate 9 ± 3 mm/yr and 5 ± 3 mm/yr shortening across the SE and NW Zagros respectively. GPS results show that in addition to the different rates and directions of shortening on either side of the NS trending Kazerun fault, local along-belt extension occurs to the east. </p><p>Differential SAR interferograms of ERS1 & 2 images between 1992 and 1999 detect 8 ± 4 mm/yr uplift rate across a newly recognized fault in SW Qeshm Island. This can be attributed to a steep imbricate thrust that may still represent the local Zagros deformation front.</p><p>The salt diapirs in the Zagros rise from a source layer that acts as a low-frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern Zagros whereas the cover to the west deforms above a high-friction decollement. Physical models were prepared to simulate cover deformation in the Zagros by shortening a sand pack above adjacent high- and low-frictional decollements (represented by a ductile layer). The strain distributions differed above the two types of decollements; it was more heterogeneous above the salt where local extension in the shortening direction was dominant. A separate work also investigated systematically the role of basal friction on cover deformation in convergent settings. Accurate height measurements of the model surface by laser-scanner indicated a deformation front more distal than usual, particularly in the low-basal frictional models. The volume reduction in our shortened sand models correlated directly with their basal friction.</p>
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Ground Movements in the Zagros Fold-Thrust Belt of SW Iran Measured by GPS and InSAR Compared to Physical ModelsNilfouroushan, Faramarz January 2007 (has links)
This thesis uses geodetic satellite data to measure present-day crustal deformation in the Zagros fold-thrust belt (SW Iran). Geodetic-type measurements are also used in down-scaled models that simulate the surface deformations seen in convergent settings like the Zagros fold-thrust belt. Global Positioning System (GPS) measurements of three surveys between 1998 and 2001 indicate 9 ± 3 mm/yr and 5 ± 3 mm/yr shortening across the SE and NW Zagros respectively. GPS results show that in addition to the different rates and directions of shortening on either side of the NS trending Kazerun fault, local along-belt extension occurs to the east. Differential SAR interferograms of ERS1 & 2 images between 1992 and 1999 detect 8 ± 4 mm/yr uplift rate across a newly recognized fault in SW Qeshm Island. This can be attributed to a steep imbricate thrust that may still represent the local Zagros deformation front. The salt diapirs in the Zagros rise from a source layer that acts as a low-frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern Zagros whereas the cover to the west deforms above a high-friction decollement. Physical models were prepared to simulate cover deformation in the Zagros by shortening a sand pack above adjacent high- and low-frictional decollements (represented by a ductile layer). The strain distributions differed above the two types of decollements; it was more heterogeneous above the salt where local extension in the shortening direction was dominant. A separate work also investigated systematically the role of basal friction on cover deformation in convergent settings. Accurate height measurements of the model surface by laser-scanner indicated a deformation front more distal than usual, particularly in the low-basal frictional models. The volume reduction in our shortened sand models correlated directly with their basal friction.
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Cenozoic structural evolution of the eastern margin of the Middle Magdalena Valley basin, Colombia : integration of structural restorations, low-temperature thermochronology, and sandstone petrographySánchez, Carlos Javier, M.S. in geological Sciences 10 November 2011 (has links)
Structural analysis of surface and subsurface data from the Middle Magdalena Valley basin and Eastern Cordillera fold-thrust belt to construct a kinematic model for its Cenozoic structural and stratigraphic evolution. The La Salina west-vergent thrust system marks the boundary between the Paleogene foreland basin of the Middle Magdalena basin and the Eastern Cordillera fold-thrust belt. New low-temperature thermochonological and sandstone petrographic analyses provide constraints on ages of thrust deformation and sediment dispersal. Apatite fission track (AFT) and U-Th/He thermochronological results show the timing of three structural events along the La Salina fault system: (1) late Eocene-early Oligocene (~43–35 Ma) initial hanging wall exhumation; (2) continued middle Miocene (~15 Ma) exhumation; and (3) continued but more rapid late Miocene (~12–3 Ma) hanging wall exhumation. Vitrinite reflectance results provide estimates of maximum burial depths for the hanging wall of the La Salina fault ranging from 4 to 6 km., this depth of burial estimates constrain the basin geometry during its late Eocene to late Miocene evolution.
The eastern hanging wall of the La Salina fault displays a broad anticline-syncline pair affecting Cretaceous to Eocene strata with no significant faulting, whereas the western footwall contains a complex series of tight, thrust-related folds in Eocene-Quaternary strata. For foreland basin province, a proposed triangle zone accommodates a small amount of east-west shortening (< 1000 m) along the frontal thrust system by east-vergent backthrusting within a broader passive-roof duplex. East-west shortening in the Cenozoic stratigraphic section was also accommodated by detachment folding, which produced localized areas of steep dips. In the proposed kinematic restoration, the most recent phase of deformation represents out-of-sequence reactivation of the La Salina fault that is consistent with irregular crosscutting relationships of some footwall structures.
Earliest exhumation by ~45–30 Ma in the Eastern Cordillera fold-thrust belt province matches (1) an increased proportion of sedimentary lithic fragments; and (2) a high degree of compositional maturity (Q88F4Lf8). Exhumation since ~15 Ma in the foreland province coincides with (1) the highest accumulation rates observed for the upper Miocene Real Group; and (2) a decrease in compositional maturity (Q55F8Lf36). / text
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Architecture of the Silurian sedimentary cover sequence in the Cadia porphyry Au-Cu district, NSW, Australia : implications for post-mineral deformationWashburn, Malissa 11 1900 (has links)
Alkalic porphyry style Au-Cu deposits of the Cadia district are associated with
Late-Ordovician monzonite intrusions, which were emplaced during the final phase of
Macquarie Arc magmatism at the end of the Benambran Orogeny. N-striking faults,
including the curviplanar, northerly striking, moderately west-dipping basement thrust faults of the Cadiangullong system, developed early in the district history. NE-striking faults formed during rifting in the late Silurian. Subsequent E-W directed Siluro- Devonian extension followed by regional E-W shortening during the Devonian
Tabberabberan Orogeny dismembered these intrusions, thereby superposing different
levels porphyry Au-Cu systems as well as the host stratigraphy.
During the late Silurian, the partially exhumed porphyry systems were buried
beneath the Waugoola Group sedimentary cover sequence, which is generally preserved
in the footwall of the Cadiangullong thrust fault system. The Waugoola Group is a
typical rift-sag sequence, deposited initially in local fault-bounded basins which then transitioned to a gradually shallowing marine environment as local topography was
overwhelmed. Basin geometry was controlled by pre-existing basement structures, which
were subsequently inverted during the Devonian Tabberabberan Orogeny, offsetting the unconformity by up to 300m vertically. In the Waugoola Group cover, this shortening
was accommodated via a complex network of minor detachments that strike parallel to
major underlying basement faults. For this reason, faults and folds measured at the
surface in the sedimentary cover can be used as a predictive tool to infer basement
structures at depth.
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Thermal and Structural Constraints on the Tectonic Evolution of the Idaho-Wyoming-Utah Thrust BeltChapman, Shay Michael 16 December 2013 (has links)
The timing of motion on thrust faults in the Idaho-Wyoming-Utah (IWU) thrust belt comes from synorogenic sediments, apatite thermochronology and direct dating of fault rocks coupled with good geometrical constraints of the subsurface structure. The thermal history comes from the analyses of apatite thermochronology, thermal maturation of hydrocarbon source rocks and isotope analysis of fluid inclusions from syntectonic veins. New information from zircon fission track and zircon (U-Th)/He analysis provide constraints on the thermal evolution of the IWU thrust belt over geological time. These analyses demonstrate that the time-temperature pathway of the rocks sampled never reached the required conditions to reset the thermochronometers necessary to provide new timing constraints. Previous thermal constraints for maximum temperatures of IWU thrust belt rocks, place the lower limit at ~110°C and the upper limit at ~328°C. New zircon fission track results suggest an upper limit at ~180°C for million year time scales. ID-TIMS and LA-ICPMS of syntectonic calcite veins suggest that new techniques for dating times of active deformation are viable given that radiogenic isotope concentrations occur at sufficient levels within the vein material.
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Architecture of the Silurian sedimentary cover sequence in the Cadia porphyry Au-Cu district, NSW, Australia : implications for post-mineral deformationWashburn, Malissa 11 1900 (has links)
Alkalic porphyry style Au-Cu deposits of the Cadia district are associated with
Late-Ordovician monzonite intrusions, which were emplaced during the final phase of
Macquarie Arc magmatism at the end of the Benambran Orogeny. N-striking faults,
including the curviplanar, northerly striking, moderately west-dipping basement thrust faults of the Cadiangullong system, developed early in the district history. NE-striking faults formed during rifting in the late Silurian. Subsequent E-W directed Siluro- Devonian extension followed by regional E-W shortening during the Devonian
Tabberabberan Orogeny dismembered these intrusions, thereby superposing different
levels porphyry Au-Cu systems as well as the host stratigraphy.
During the late Silurian, the partially exhumed porphyry systems were buried
beneath the Waugoola Group sedimentary cover sequence, which is generally preserved
in the footwall of the Cadiangullong thrust fault system. The Waugoola Group is a
typical rift-sag sequence, deposited initially in local fault-bounded basins which then transitioned to a gradually shallowing marine environment as local topography was
overwhelmed. Basin geometry was controlled by pre-existing basement structures, which
were subsequently inverted during the Devonian Tabberabberan Orogeny, offsetting the unconformity by up to 300m vertically. In the Waugoola Group cover, this shortening
was accommodated via a complex network of minor detachments that strike parallel to
major underlying basement faults. For this reason, faults and folds measured at the
surface in the sedimentary cover can be used as a predictive tool to infer basement
structures at depth.
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"Deformação polifásica e metamorfismo do Grupo Cuiabá na região de Poconé (MT), cinturão de dobras e cavalgamentos Paraguai" / Deformação polifásica e metamorfismo do Grupo Cuiabá na região de Poconé (MT), cinturão de dobras e cavalgamentos ParaguaiVasconcelos, Bruno Rodrigo 28 October 2014 (has links)
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Previous issue date: 2014-10-28 / Vários modelos deformacionais foram propostos para o Cinturão Paraguai diferindo principalmente quanto ao número de fases de deformação, sentido da vergência e estilo tectônico. Feições estruturais apresentadas neste trabalho indicam tectônica dominada por escamas de baixo ângulo de mergulho na fase inicial, seguida por duas fases deformacionais progressivas. A primeira fase de deformação (F1) é caracterizada por clivagem ardosiana (S1), com recristalização de minerais da fácies xisto verde, plano axial de dobras isoclinais recumbentes (D1) de direção NE associadas a zonas de falhamento reverso subhorizontais com movimentação de topo para SE. A segunda fase deformacional (F2) mostra vergência para NW, caracterizada por clivagem de crenulação (S2) plano axial de dobras abertas (D2) do acamamento e foliação S1, localmente associada a falhas reversas. A terceira fase de deformação é caracterizada por falhas e fraturas sub-verticais com direção NW mostrando movimentação sinistral, comumente preenchidas por veios de quartzo. O acervo de estruturas tectônicas e paragênese metamórfica descrita indicam que a deformação mais intensa, em nível crustal mais profundo, alcançou a fácies xisto verde durante F1. Acomodando expressivo encurtamento crustal por meio de dobras recumbente e zonas de cisalhamento de baixo ângulo com movimentação de topo para SE, em regime tectônico do tipo pelicular delgado. A fase F2 teve deformação menos intensa e se comportou de maneira rúptil-dúctil, acomodando discreto encurtamento por meio de dobras normais abertas e falhas inversas subverticais desenvolvidas em nível crustal mais raso, com vergência em direção ao Cráton Amazônico. A terceira fase deformacional (F3) foi menos intensa e acomodou encurtamento na forma de fraturas e falhas sinistrais subverticais, comumente preenchidas por veios de quartzo. / Several deformation models have been proposed for the Paraguay Belt, differing mainly in the number of deformation phases, sense of vergence and tectonic style. Structural features presented in this work indicate tectonic dominated by an initial phase of low dipping thrust sheets, followed by two progressive deformation phases. The first deformation phase (F1) is characterized by a slaty cleavage (S1), axial plane of isoclinal recumbent folds (D1) in the NE direction, with recrystallization of minerals from the greenschist facies, related to horizontal shear zones with top-to-the-SE sense of movement. The second stage shows a NW-vergence, characterized by crenulation cleavage, S0 and S1 axial planes of open folds, locally associated with reverse faults. The third deformation phase is characterized by subvertical faults and fractures in the NW direction showing sinistral movement, commonly filled by quartz veins. The collection of tectonic structures and metamorphic paragenesis described indicate that the most intense deformation, at deeper crustal level, reached the greenschist facies during F1. Accommodating significant crustal shortening through isoclinal recumbent folds and low-angle shear zones showing top-to-the SE sense of movement during a thin-skinned tectonic regime. The phase F2 showed more subtle deformation, with more competent rock types developing brittle behavior and less competent rock types developing ductile behavior, by accommodating slight shortening through normal open folds and subvertical reverse faults nucleated in shallower crustal level with vergence towards the Amazonian Craton. The third phase was less intense and shortening is accommodated in the form of fractures and subvertical sinistral faults, commonly filled by quartz veins.
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Análise tectono-estratigráfica da Faixa de dobramento Paraguai meridional na Serra da Bodoquena e depressão do Rio Miranda, MS / Tectonostratigraphic analysis of the southern Paraguay fold belt in Serra da Bodoquena and Rio Miranda depression, MSFernanda Rostirola de Sa 30 October 2009 (has links)
No presente trabalho buscou-se compor um quadro geológico-estrutural da Faixa Paraguai meridional e compreender as relações estratigráficas entre os litotipos da Formação Puga e grupos Cuiabá e Corumbá. Foram realizados trabalhos de reconhecimento geológico e perfis geológico-estruturais de detalhe, com análise estrutural e petrográfica, em conjunto com a integração de dados e mapas existentes, análise de imagens de satélite, fotos aéreas e modelos digitais de terreno. A Faixa Paraguai meridional evoluiu como um típico fold-andthrust belt. A evolução geológica do cinturão principia por processos de rifteamento, provavelmente no final do Criogeniano, evoluindo para mar restrito e margem passiva até o final do Ediacarano. A fase rifte é caracterizada pelas formações Puga e Cerradinho. A fase margem passiva está representada pelas formações Bocaina, Tamengo e Guaicurus. Propõe-se que o Grupo Cuiabá na área estudada seja constituído por depósitos marinhos profundos, turbidíticos distais depositados comitantemente aos sedimentos do Grupo Corumbá. O processo colisional responsável pela inversão da bacia com a deformação e metamorfismo associados ocorreu durante o Cambriano, com magmatismo pós-colisional no Cambriano Superior. O estilo estrutural torna-se progressivamente mais complexo de oeste para leste. São observadas até três fases de dobramento coaxiais sobrepostas com eixos subhorizontais de direção N-S. Associam-se a sistemas de falhas de empurrão com deslocamento da capa para oeste. As lineações de estiramento e indicadores cinemáticos observados sugerem que a convergência colisional em direção ao bloco Rio Apa que deu origem à faixa móvel não foi completamente frontal, existindo algum grau de obliquidade, com vetores de convergência em torno de WNWENE. Os micaxistos do Grupo Cuiabá mostram o estilo estrutural mais complexo, com três fases de dobramentos coaxiais e foliações tectônicas mais intensas. Haveria correlação temporal entre S3 gerada nos micaxistos, comumente referidos como Grupo Cuiabá, a leste com a foliação S2 gerada na porção central e a clivagem S1 gerada no limite da área cratônica a oeste, padrão que pode ser explicado pela migração do front deformacional de leste para oeste. É sugestivo que as principais falhas de empurrão coincidam com limites bacinais importantes, onde ocorrem variações de espessura e representatividades das formações basais. No processo de inversão da bacia provavelmente os empurrões reativaram as antigas falhas lístricas principais do estágio rifte. / This work aims to characterize the geological and structural context of the Southern Paraguay Folded Belt, and to understand the stratigraphic relationships between the Puga Formation, Corumbá and Cuiabá groups. Regional geological reconnaissance work and detailed geological-structural field sections were carried out, with petrographic and structural analysis, together with integration of existing data and maps and analysis of satellite images, aerial photos and digital terrain models. The southern Paraguay Belt is a typical fold-andthrust belt. Its geological evolution began with rifting (Puga and Cerradinho formations), probably at the end of Criogenian, and evolved to restricted sea and passive margin (Bocaina, Tamengo and Guaicurus formations) in the late Ediacaran. It is proposed that the Cuiabá Group in the study area consists of distal marine deposits coeval with the Corumbá Group. The collisional process responsible for basin inversion and associated deformation and metamorphism occurred in the Cambrian, with post-collisional magmatism in the Upper Cambrian. The structural style becomes increasingly complex from west to east. Up to three overprinted coaxial folding phases are observed with north / south upright axial planes dipping to east and axes plunging gently to North or South. A system of thrust faults is associated with displacement of the hangwall to the west. Down-dip to oblique and strike-slip stretching lineations are also observed, with kinematic indicators showing movement varying from inverse to sinistral. This suggests that the collisional convergence toward the Rio Apa block which generated the mobile belt was not strictly frontal, but had some degree of obliquity, with convergence vectors around SSW - ENE. The Cuiabá Group mica-schists show the most complex structural style with three superimposed coaxial fold phases and more intense tectonic foliations. It is proposed that there would be time correlation between the S3 foliation in the mica-schists in the easternmost area, with the S2 foliation in the central area and the S1 cleavage at the limit of the cratonic area to the west. This pattern can be explained by the westward migration of the deformational front. It is suggestive that the main thrusts coincide with major basin boundaries, where greater variations in thickness and expression of the basal formations occur. During the basin inversion the thrusts probably reactivated the former main listric faults of the rift stage.
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