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Alik Ismailzadeh - One of the best experts on this subject based on the ideXlab platform.
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three dimensional forward and backward modelling of diapirism numerical approach and its applicability to the evolution of salt structures in the pricaspian basin
Tectonophysics, 2004Co-Authors: Alik Ismailzadeh, Igor Tsepelev, Chistopher Talbot, Alexander KorotkiiAbstract:Abstract Numerical studies of ductile deformations induced by salt movements have, until now, been restricted to two-dimensional (2D) modelling of diapirism. This paper suggests a numerical approach to model the evolution of three-dimensional (3D) salt structures toward increasing maturity. This approach is also used here to restore the evolution of salt structures through successive earlier stages. The numerical methodology is applied to study several model examples. We analyse a model of salt diapirs that develop from an initial random perturbation of the interface between salt and its Overburden and restore the evolved salt diapirs to their initial stages. We show that the average restoration errors are less than 1%. An evolutionary model of a 2D salt wall loaded by a 2D pile of sediments predicts a decomposition of the salt wall into 3D diapiric structures when the Overburden of salt is supplied by 3D synkinematic wedge of sediments. We model salt extrusion feeding a gravity current over the depositional surface and estimate an average rate of extrusion and horizontal velocity of salt spreading. Faulting of the Overburden to salt overhangs initiates new secondary diapirs, and we analyse the growth of these secondary diapirs. We also study how lateral flow effects the evolution of salt diapirs. The shape of a salt diapir can be very different if the rate of horizontal flow is much greater than the initial rate of diapiric growth solely due to gravity. We discuss the applicability of the results of the models to the evolution of Late Permian salt structures in the Pricaspian basin (Russia and Kazakhstan). These structures are distinguishable into a variety of styles representing different stages of growth: salt pillows, diapirs, giant salt massifs, 2D diapiric walls and 3D stocks complicated by large overhangs. The different sizes, shapes and maturities of salt structures in different parts of the Pricaspian basin reflect areal differences in salt thickness and loading history. Our results suggest that the numerical methodology can be employed to analyse the evolution of all salt structures that have upbuilt through younger ductile Overburdens.
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analytical modelling of viscous diapirism through a strongly non newtonian Overburden subject to horizontal forces
Journal of Geodynamics, 2001Co-Authors: Alik Ismailzadeh, Herbert E Huppert, John R ListerAbstract:Abstract We study the early stages of diapirism and analyse the gravitational and buckling instabilities of a buoyant viscous layer overlain by a layer of strongly non-Newtonian power-law rheology (when a power-law exponent tends to infinity). This situation models rocksalt under a layer of a perfectly plastic Overburden. The growth rate of small perturbations on the interface between the two layers and the wavelength of the most unstable perturbations are found and compared with those of structures consisting of two Newtonian or two strongly non-Newtonian viscous layers. Effects due to the effective viscosity and thickness ratios between the two layers are assessed. Considering the effective viscosity of the Overburden to be much greater than the viscosity of the buoyant salt layer, we obtain the following results. In the case of simple gravitational instability and no-slip boundary conditions, the instability pattern is similar to that in a strongly non-Newtonian power-law material. An increase in the thickness of the Overburden decreases the dominant wavelength of the most unstable mode, while the dominant wavelength is lengthened in the case of Newtonian viscous layers. When the system of layers is subjected to either horizontal extension or shortening, and the upper boundary of the system is stress-free, the buckling instability overwhelms the gravitational instability, and the dynamic growth rate of the instability depends linearly on the effective viscosity ratio. We conclude that the introduction of strongly non-Newtonian power-law rheology into diapir Overburdens greatly affects instability parameters such as growth rate and dominant wavelength of perturbations and hence, alters interdiapir spacings.
Rozal, Edilberto Oliveira - One of the best experts on this subject based on the ideXlab platform.
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Efeitos do manto de intemperismo sobre anomalias “VLF” dos corpos tabulares inclinados
1997Co-Authors: Rozal, Edilberto OliveiraAbstract:A utilização dos métodos indutivos de propagação E.M. na exploração mineral em regiões tropicais, apresenta grandes dificuldades devido a presença de uma camada superficial condutiva (manto de intemperismo) comumente encontrada nestas regiões. Na região Amazônica, o manto apresenta-se bastante desenvolvido e condutivo, e em regiões semi-áridas, pode-se formar uma fina crosta superficial de sal. Em conseqüência disto, a interpretação dos dados E.M. obtidos para modelos que não consideram uma cobertura condutiva levam a erros consideráveis. Objetivando-se estudar os efeitos do manto sobre anomalias VLF devidas a corpos tabulares inclinados em contato com o manto (manto ohmico), foi realizada uma série de experimentos através do modelamento analógico, considerando-se diferentes parâmetros de resposta para o manto e o corpo. O manto de intemperismo foi simulado por soluções de cloreto de amônia (NH4Cl) dispostas horizontalmente e o corpo condutor por chapas de grafite colocadas em posições inclinadas verticalmente. Utilizou-se quatro corpos condutores e três mantos com diferentes espessuras e condutividades, simulando, desta forma, diversas situações geológicas. Os resultados são dados por simples situações dos corpos localizados em um meio não condutor (ar), onde os parâmetros variados são: profundidade do topo, condutividade e mergulho do corpo. Os efeitos da condutividade da cobertura são amplamente ilustrados e avaliados. Para a análise dos resultados, foi plotado um conjunto de curvas considerando-se os valores pico-a-pico das anomalias de "tilt angle" e de elipsidade. Os resultados foram sintetizados em um outro conjunto de curvas reunidas em diagramas de Argand. Estando ou não o manto presente, observou-se, tanto para o tilt angle quanto para a elipsidade, o efeito do aumento da profundidade é o de reduzir a magnitude pico-a-pico e a forma do pico da anomalia, fazendo com que este afaste-se do ponto de "cross-over". Para um condutor de mesma espessura, o aumento da condutividade causa um ligeiro aumento nas anomalias de tilt angle, e uma atenuação nas anomalias de elipsidade. O efeito geral na variação do mergulho do condutor é o de causar uma assimetria nos perfis de tilt angle e de elipsidade. O aumento da condutância do manto de intemperismo causa um acréscimo nas anomalias de elipsidade e uma ligeira diminuição nas anomalias de tilt angle; porém, a partir de um certo valor de condutância do manto (mantos mais condutivos) tanto as anomalias de tilt angle quanto as anomalias de elipsidade começam a atenuar. Há rotação de fase no sentido anti-horário, sendo mais intensa para grandes valores de número de indução do corpo. Na presença do manto, o corpo parece estar a uma profundidade inferior à verdadeira e a ser menos condutivo.ABSTRACT: Application of eletromagnetic methods for mineral exploration in tropical regions is complicated due to a presence of a conducting Overburden encountered in these regions. In the Amazon region, Overburden is well developed and conductive; while in semi-arid regions there may be a fine layer containing salts. Consequently, considerable error is introduced in the interpretation of EM data if the presence of the conducting Overburden is ignored. In order to study the Overburden effects, on VLF anomalies due inclined tabular bodies in contact with the former (Ohmic - Overburden), a number of analog model experiments were conducted for varying response parameters of the Overburden and the ore body. Overburden is simulated by an amonium chloride solution (NH4Cl) and the ore body by inclined grafite sheets of different thicknesses. Three Overburdens of varying conductance were used to simulate diverse geological situations. Both, tilt-angle and elipsity anomalies decrease in amplitude with the increase in depth of the ore body and the position of the peak in the profile is removed further away from the crossover irrespective of the presence of the Overburden or not. There is some increase and tilt-angle anomaly profiles. Eliptisity anomaly increases with the increase in the condutance of the Overburden while tilt-angle anomaly decreases a little bit. However, at higher Overburden condutances both of then are attenuated. Phase angle are rotated anti-clockwise with the Overburden. This rotation is more intense at higher induction number of the conductor. In the presence of the ohmic-Overburden and at moderate values of their condutance, the conductor appears (i) at lower depth than the real, due to the increase in the anomaly amplitude, and ii) less conducting due to the anti-clockwise rotation of the Argand diagram
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Efeitos do manto de intemperismo sobre anomalias “VLF” dos corpos tabulares inclinados
Programa de Pós-Graduação em Geofísica, 1997Co-Authors: Rozal, Edilberto OliveiraAbstract:Application of eletromagnetic methods for mineral exploration in tropical regions is complicated due to a presence of a conducting Overburden encountered in these regions. In the Amazon region, Overburden is well developed and conductive; while in semi-arid regions there may be a fine layer containing salts. Consequently, considerable error is introduced in the interpretation of EM data if the presence of the conducting Overburden is ignored. In order to study the Overburden effects, on VLF anomalies due inclined tabular bodies in contact with the former (Ohmic - Overburden), a number of analog model experiments were conducted for varying response parameters of the Overburden and the ore body. Overburden is simulated by an amonium chloride solution (NH4Cl) and the ore body by inclined grafite sheets of different thicknesses. Three Overburdens of varying conductance were used to simulate diverse geological situations. Both, tilt-angle and elipsity anomalies decrease in amplitude with the increase in depth of the ore body and the position of the peak in the profile is removed further away from the crossover irrespective of the presence of the Overburden or not. There is some increase and tilt-angle anomaly profiles. Eliptisity anomaly increases with the increase in the condutance of the Overburden while tilt-angle anomaly decreases a little bit. However, at higher Overburden condutances both of then are attenuated. Phase angle are rotated anti-clockwise with the Overburden. This rotation is more intense at higher induction number of the conductor. In the presence of the ohmic-Overburden and at moderate values of their condutance, the conductor appears (i) at lower depth than the real, due to the increase in the anomaly amplitude, and ii) less conducting due to the anti-clockwise rotation of the Argand diagram.UFPA - Universidade Federal do ParáPETROBRAS - Petróleo Brasileiro S.A.FADESP - Fundação de Amparo e Desenvolvimento da PesquisaA utilização dos métodos indutivos de propagação E.M. na exploração mineral em regiões tropicais, apresenta grandes dificuldades devido a presença de uma camada superficial condutiva (manto de intemperismo) comumente encontrada nestas regiões. Na região Amazônica, o manto apresenta-se bastante desenvolvido e condutivo, e em regiões semi-áridas, pode-se formar uma fina crosta superficial de sal. Em conseqüência disto, a interpretação dos dados E.M. obtidos para modelos que não consideram uma cobertura condutiva levam a erros consideráveis. Objetivando-se estudar os efeitos do manto sobre anomalias VLF devidas a corpos tabulares inclinados em contato com o manto (manto ohmico), foi realizada uma série de experimentos através do modelamento analógico, considerando-se diferentes parâmetros de resposta para o manto e o corpo. O manto de intemperismo foi simulado por soluções de cloreto de amônia (NH4Cl) dispostas horizontalmente e o corpo condutor por chapas de grafite colocadas em posições inclinadas verticalmente. Utilizou-se quatro corpos condutores e três mantos com diferentes espessuras e condutividades, simulando, desta forma, diversas situações geológicas. Os resultados são dados por simples situações dos corpos localizados em um meio não condutor (ar), onde os parâmetros variados são: profundidade do topo, condutividade e mergulho do corpo. Os efeitos da condutividade da cobertura são amplamente ilustrados e avaliados. Para a análise dos resultados, foi plotado um conjunto de curvas considerando-se os valores pico-a-pico das anomalias de "tilt angle" e de elipsidade. Os resultados foram sintetizados em um outro conjunto de curvas reunidas em diagramas de Argand. Estando ou não o manto presente, observou-se, tanto para o tilt angle quanto para a elipsidade, o efeito do aumento da profundidade é o de reduzir a magnitude pico-a-pico e a forma do pico da anomalia, fazendo com que este afaste-se do ponto de "cross-over". Para um condutor de mesma espessura, o aumento da condutividade causa um ligeiro aumento nas anomalias de tilt angle, e uma atenuação nas anomalias de elipsidade. O efeito geral na variação do mergulho do condutor é o de causar uma assimetria nos perfis de tilt angle e de elipsidade. O aumento da condutância do manto de intemperismo causa um acréscimo nas anomalias de elipsidade e uma ligeira diminuição nas anomalias de tilt angle; porém, a partir de um certo valor de condutância do manto (mantos mais condutivos) tanto as anomalias de tilt angle quanto as anomalias de elipsidade começam a atenuar. Há rotação de fase no sentido anti-horário, sendo mais intensa para grandes valores de número de indução do corpo. Na presença do manto, o corpo parece estar a uma profundidade inferior à verdadeira e a ser menos condutivo
Sierd Cloetingh - One of the best experts on this subject based on the ideXlab platform.
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Numerical modelling of salt diapirism: influence of the tectonic regime
Tectonophysics, 1994Co-Authors: Betrand Daudre, Sierd CloetinghAbstract:Abstract In the context of sedimentary basin mechanics, salt diapirism has usually been described as a phenomenon initiated and driven by gravity instabilities associated with buoyant forces or differential loading. This result holds essentially for an approximation of linear rheologies of both salt and Overburden. This has been contested by recent analog models and analytical studies: buoyancy alone cannot drive salt diapirism through a brittle Overburden. Regional extension or compression could be a necessary mechanism likely to promote salt diapirism. Numerical models are presented here to describe the relative effects of gravity and lateral forces on the dynamics of salt diapirism. The numerical scheme is based on a viscoplastic approximation of deformations and an updated Lagrangian description of kinematics, which allows a study of large non linear deformations of salt bodies and the evolution of material interfaces. This scheme takes into account brittle and ductile deformations of sediments. Moreover, it describes the initiation and evolution of shear bands which play a crucial role in basin mechanics and. especially in the dynamics of salt diapirism We show why extension is the most propitious driving mechanism of diapirism: necking and faulting induced by extension promote and drive salt diapirism. In the case of a brittle Overburden, this result holds with or without buoyancy forces. This demonstrates that buoyancy, which alone is not sufficient to break a brittle Overburden, is not a necessary mechanism either. Buoyancy, however, enhances diapirism induced by lateral forces. In contrast with extension, salt diapirism during compression is strongly constrained by the rheology of the Overburden: a brittle mode of deformation favours faulting rather than buckling. Induced thrusting and thickening of the Overburden inhibit massive diapirism and favour the confinement of small salt plugs. Finally, the post-extension stability of a mature diapir produced by extension is presented.
Torsten Dahm - One of the best experts on this subject based on the ideXlab platform.
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geomechanical modelling of sinkhole development using distinct elements model verification for a single void space and application to the dead sea area
Solid Earth, 2018Co-Authors: Djamil Alhalbouni, Eoghan P Holohan, Abbas Taheri, Martin P J Schopfer, Sacha Emam, Torsten DahmAbstract:Abstract. Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and Overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the Overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the Overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth ∕ diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth ∕ diameter values in each material type may partly reflect sinkhole growth trends.
Luis F O Silva - One of the best experts on this subject based on the ideXlab platform.
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geochemistry and nano mineralogy of feed coals mine Overburden and coal derived fly ashes from assam north east india a multi faceted analytical approach
International Journal of Coal Geology, 2015Co-Authors: Binoy K Saikia, Colin R Ward, Marcos L S Oliveira, James C Hower, Felipe B De Leao, Michelle N Johnston, Alice Obryan, Arpita Sharma, Bimala P Baruah, Luis F O SilvaAbstract:Abstract In order to address the scarcity of information on the nature and mode of occurrence of minerals and elements in coal, coal mine Overburden and coal ashes from North-east India, and also the relations between coal mineralogy and ash chemistry, the petrology, mineralogy and nano-mineralogy, and ash chemistry of some industrially important high-sulfur coals, mine Overburden materials and fly ash samples from Assam (India) have been evaluated. A combined approach, using petrography, low-temperature ashing plus X-ray diffraction (LTA-XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscope (HR-TEM), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS), has provided new information on the mineralogy and nano-mineralogy of these sub bituminous coals and associated mine Overburden. The presence of rare earth elements and yttrium (REY) in Northeast Indian coal, mine Overburden and fly ash samples is also reported for the first time. The identification of these components may be significant from an economic point of view. Some Northeast Indian fly ashes, with REE oxides up to 1580 ppm on an ash basis, might possibly represent sources for recovery of rare earth elements.
