| 1. |
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| 2. |
- Oskooi, B., et al.
(författare)
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A Magnetotelluric Survey on Ophiolites in Neyriz area of southwestern Iran
- 2015
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Ingår i: Pure and Applied Geophysics. - : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136. ; 172, s. 491-502
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Tidskriftsartikel (refereegranskat)abstract
- A wide band magnetotelluric study of the ophiolitic zone of the Zagros orogenic belt was conducted in the Neyriz area of southwestern Iran. The purpose of the study was to image subsurface structures electrically and relocate the main Zagros thrust fault in the region. The thrust fault has a complex structure with obscure behavior and is believed to be located within a zone of ongoing continental plate convergence. The fault zone with a NW–SE geological trend is parallel to the Zagros orogenic belt and separates the Neyriz ophiolite assemblage from the adjacent Sanandaj-Sirjan metamorphic zone. Magnetotelluric data were collected along a SW–NE profile across the geologic strike; the study included 18 stations and modeling was performed using a 2-D inversion scheme. Analysis of both modes of magnetotelluric data (TE and TM) clarifies the signatures of large resistivity variation in the study area. Due to the presence of a high contrast in resistivity between the ophiolites and neighboring rocks, we are able to discern two sharp boundaries as faulting planes and borders of the ophiolite–radiolarite zone in the north-eastern and southwestern parts of the 2-D resistivity models, respectively.
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| 3. |
- Liu, Zhina, et al.
(författare)
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Kinematics and 3-D internal deformation of granular slopes : analogue models and natural landslides
- 2013
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Ingår i: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 53, s. 27-42
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Tidskriftsartikel (refereegranskat)abstract
- This study uses results from a series of analogue models, and field observations, scanned data and sections of natural landslides to investigate the kinematics and internal deformation during the failure of an unstable slope. The models simulate collapse of granular slopes and focus on the spatial and temporal distribution of their internal structures. Using a series of systematically designed models, we have studied the effect of friction and deformability of the runout base on internal deformation within a granular slope. The results of these different models show that the collapse of granular slopes resulted in different-generation extensional faults at the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) at the toe of the slope. The failure surfaces and the volume of the failure mass changed both spatially and temporally. Younger failure surfaces formed in the back of the older ones by incorporating additional new material from the head of the slope. Our model results also show that the nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Model results are compared with natural landslides where local profiles were dug in order to decipher the internal structures of the failure mass. The natural cases show similar structural distribution at the head and toe of the failure mass. As in model results, our field observations indicate the presence of at least two generations of failure surfaces where the older ones are steeper.
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| 4. |
- Liu, Zhina, 1982-, et al.
(författare)
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Kinematics and internal deformation of granular slopes : insights from discrete element modeling
- 2013
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Ingår i: Landslides. - : Springer Science and Business Media LLC. - 1612-510X .- 1612-5118. ; 10:2, s. 139-160
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Tidskriftsartikel (refereegranskat)abstract
- The kinematics and internal deformation of a failure mass during the flow-like moving off a slope were monitored and quantified with the particle flow method in this study. Two kinds of cases were investigated, noncohesive and cohesive granular slopes. Three different internal friction angles and cohesive strengths were considered to systematically investigate their effect on the kinematics and internal deformation of the failure mass. We analyzed the movement within the failure mass and concluded that the mass moves downwards in an undulating pattern. The slope surface topography changes from a straight line to curved lines with slope breaks in a convex geometry. In addition, dilatation within the failure mass, which deforms internally and heterogeneously, is strongly dependent on its mechanical properties. A larger mass moves downslope, and the mass moves faster and further in the model with lower internal friction and cohesion. The internal friction and cohesion have a positive impact on porosity and two-dimensional (or volumetric in 3D) strain within the failure mass.
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| 5. |
- Liu, Zhina, et al.
(författare)
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The impact of a weak horizon on kinematics and internal deformation of a failure mass using discrete element method
- 2013
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 586, s. 95-111
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Tidskriftsartikel (refereegranskat)abstract
- Weak horizons within slopes may induce and/or accelerate failure of slopes. In this study, we focus on the effect of orientation, location and dimension of a weak horizon on the mode and kinematics of downslope movement of a failure mass using discrete element method. Two kinds of cases with weak horizons were studied, one unstable homogeneous slope with low shear strength (c = 50 kPa, μ = 0.57) and two stable homogeneous slopes with high shear strength (c = 60 kPa, μ = 0.57 or c = 50 kPa, μ = 0.7). In the three set of slope models, there was a weak horizon with a finite thickness embedded within the slope. In each set of slope models, two different thicknesses and locations for the weak horizons were considered to systematically investigate the effect of these parameters on the mass movement. In addition, the dip of the weak horizon was changed where in some models, it was parallel to the slope and in others it was dipping either steeper or gentler than the slope. We analyzed both kinematics and internal deformation of the failure mass in all models and conclude that the presence and geometry (i.e., thickness, location and dip) of a weak horizon changes the mode and kinematics of mass movement and governs the location of the failure surface.
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| 6. |
- Koyi, Hemin, et al.
(författare)
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Shear zones between rock units with no relative movement
- 2013
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Ingår i: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 50:SI, s. 82-90
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Tidskriftsartikel (refereegranskat)abstract
- Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two “blocks” that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other. Such deformation zones, which we call wakes, form due to the movement of exotic blocks within a viscous medium (denser blocks sinking within a salt structure, (the paths) between separated boudins), melt in partially molten surroundings (melt movement during migmatisation), or solid blocks sinking through a partially molten magma body (stoping). From the fluid dynamics perspective these shear zones can be regarded as low Reynolds number deformation zones within the wake of a body moving through a viscous medium. While compact moving bodies (aspect ratio 1:1:1) generate axial symmetric (cone like) shear zones or wakes, elongated bodies (vertical plates or horizontal rod-like bodies) produce tabular shear zones or wakes. Unlike conventional shear zones across which shear indicators usually display consistent symmetries, shear indicators on either side of the shear zone or wake reported here show reverse kinematics. Thus profiles exhibit shear zones with opposed senses of movement across their center-lines or -planes.We have used field observations and results from analytical and numerical models to suggest that examples of wakes are the transit paths that develop where denser blocks sink within salt structures, bodies of melt rise through migmatites, between boudins separated by progressive extension and (perhaps) where slabs of subducted oceanic lithosphere delaminate from the continental crust and sink into the asthenosphere. We also argue that such shear zones may be more common than they have been given credit for and may be responsible for some reverse kinematics reported in shear zones.
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| 7. |
- Lawa, F., et al.
(författare)
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Tectono-stratigraphic evolution of the NW segment of the Zagros fold-thrust belt, Kurdistan, NE Iraq
- 2013
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Ingår i: Journal of Petroleum Geology. - : Wiley. - 0141-6421 .- 1747-5457. ; 36:1, s. 75-96
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Tidskriftsartikel (refereegranskat)abstract
- The Kurdistan (NW) segment of the Zagros fold-thrust belt, located in the Kurdistan Region of NE Iraq, forms the external part of the Zagros orogen and is bounded by the Zagros suture to the NE. To the SW is the Arabian Plate into which the deformation front has migrated progressively, beginning in the Late Cretaceous and culminating in the Tertiary. Regional compression resulted in obduction of the Mawat ophiolites and emplacement of the Avroman and Qulqula nappes onto the continental margin, and the formation of the Kurdistan foreland basin. In this paper, structural, stratigraphic and palaeontological data together with new field observations are used to investigate the tectono-stratigraphic evolution of this basin, and to study the propagation of the deformation front from the Zagros Imbricate Zone in the NE towards the Mesopotamian foredeep in the SW. Six unconformities within the Kurdistan foreland basin succession are recognized: Turonian (base-AP9; 92 Ma); Danian (base-AP10; 65 Ma); Paleocene–Eocene (intra-AP10; 55 Ma); late Eocene (top-AP10; 34 Ma); middle-upper Miocene (a local unconformity; intra-AP11; 12 Ma); and Pleistocene. These unconformities can be divided into two groups; obduction-related (Turonian, Danian, and Paleocene-Eocene); and collision-related (late Eocene, middle-upper Miocene, and Pleistocene).The geographical position of the unconformities is used to determine the rate of propagation of the deformation front, which is estimated at ca. 3 mm/yr. This is in agreement with previous studies which suggested a NW-ward decrease in the propagation rate. The rate was most rapid (2.95 mm/yr) in the Low Zagros Fold-Thrust Zone and slower (2.06 mm/yr) in the High Zagros Fold-Thrust Zone. The more rapid propagation rate in the former area may be attributed to the presence there of the Miocene Lower Fars Formation which acted as a shallow décollement surface.Within the Zagros fold-thrust belt, the intensity of deformation decreases towards the foreland (SW). Deformation in the High Zagros Fold-Thrust Zone is characterized by thrust imbricates and high amplitude fault-propagation folds at the surface separated by narrow synclines. However, the Low Zagros Fold-Thrust Zone (Simply Folded Belt) is characterised by detachments and low amplitude fault propagation folds separated by broad synclines. In the foredeep area, folds are confined to the subsurface. Deeply buried Jurassic units, together with Upper Cretaceous – Paleocene siliciclastics, and the evaporite-dominated Lower Fars Formation may have acted as décollement surfaces in the NW segment of the Zagros fold-thrust belt, and controlled the structural geometry and evolution of the area.
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| 8. |
- Fuchs, Lukas, 1984-, et al.
(författare)
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Numerical models of salt diapir formation by down-building : the role of sedimentation rate, viscosity contrast, initial amplitude and wavelength
- 2011
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 186:2, s. 390-400
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Tidskriftsartikel (refereegranskat)abstract
- Formation of salt diapirs has been described to be due to upbuilding (i. e. Rayleigh-Taylor like instability of salt diapirs piercing through a denser sedimentary overburden) or syndepositional down-building process (i. e. the top of the salt diapir remains at the surface all the time). Here we systematically analyse this second end-member mechanism by numerical modelling. Four parameters are varied: sedimentation rate nu(sed), salt viscosity eta(salt), amplitude delta of the initial perturbation of the sedimentation layer and thewavenumber k of this perturbation. The shape of the resulting salt diapirs strongly depends on these parameters. Small diapirs with subvertical side walls are found for small values of nu(sed) and eta(salt) or large values of delta, whereas taller diapirs with pronounced narrow stems build for larges values of nu(sed) and eta(salt) or small values of delta. Two domains are identified in the four-parameter space, which separates successful down-building models from non-successful models. By applying a simple channel flow law, the domain boundary can be described by the non-dimensional law nu(sedcrit)' = C(1)1/2 delta(0)'rho(sed)'k'(2/)k'(2) + C2, where rho(sed)' is the sediment density scaled by the density contrast Delta rho between sediment and salt, the wavelength is scaled by the salt layer thickness h(salt), and velocity is scaled by eta(salt)/(h(salt)(2)Delta rho g), where eta(salt) is the salt viscosity and g is the gravitational acceleration. From the numerical models, the constants C(1) and C(2) are determined as 0.0283 and 0.1171, respectively.
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| 9. |
- Abdelmaksoud, Ahmed, et al.
(författare)
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Petroleum system of the fold-and-thrust belt of the United Arab Emirates : New insights based on 1D and 2D basin modeling
- 2023
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- The hydrocarbon potential of the fold-and-thrust belt (FTB) in the United Arab Emirates (UAE)-Oman mountains has received limited attention to date, leading to a poor understanding of the petroleum systems in this region. Despite the existence of hydrocarbon fields within the FTB, the source rock potential has not been adequately studied. This study aims to address this knowledge gap using 1D and 2D basin modeling approaches to evaluate the petroleum system of the FTB. In addition, gas chromatographs are also used to correlate hydrocarbon occurrences with their source rock. This study's findings identify the Silurian, Upper Cretaceous, Paleocene-Eocene, and Oligocene formations as the primary source rocks in the study area. Silurian shales, encountered in a well in the northern UAE, are currently considered overmature. The Cenozoic source rocks exhibit a spectrum of Total Organic Carbon (TOC) content, ranging from less than 1 to as high as 2 wt%, leading to variable degrees of expulsion efficiency. The maturity of these rocks varies based on their position in relation to the FTB and foredeep, with increasing maturity towards the north. The Upper Cretaceous sequences display low TOC and Hydrogen Index, indicating very low expulsion efficiency. The present-day distribution of maturity is largely influenced by Late Cretaceous and Oligocene-Miocene compressional events that affected the northern and northeastern Arabian Plate. This analysis shows that hydrocarbon expulsion from the Silurian source rocks was initiated during the Middle-Late Jurassic. These hydrocarbons are presumed to have migrated through Upper Permian, Jurassic, and Lower and middle Cretaceous reservoirs. Westward hydrocarbon migration, towards a regional bulge, may have also occurred following compressional events that resulted in lithospheric flexure and formation of the foreland basin. Notably, certain exceptions to migration towards the bulge include structural entrapment of hydrocarbons beneath the main frontal thrust zone of FTB and some structural traps beneath the Lower Fiqa Formation.
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| 10. |
- Koyi, Hemin, et al.
(författare)
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Modelling role of basement block rotation and strike-slip faulting on structural pattern in cover units of fold-and-thrust belts
- 2016
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Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 153:5-6, s. 827-844
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Tidskriftsartikel (refereegranskat)abstract
- A series of scaled analogue models are used to study (de)coupling between basement and cover deformation. Rigid basal blocks were rotated about a vertical axis in a 'bookshelf'€™ fashion, which caused strike-slip faulting along the blocks and in the overlying cover units of loose sand. Three different combinations of cover–basement deformations are modelled: (i) cover shortening before basement fault movement; (ii) basement fault movement before cover shortening; and (iii) simultaneous cover shortening with basement fault movement. Results show that the effect of the basement faults depends on the timing of their reactivation. Pre- and syn-orogenic basement fault movements have a significant impact on the structural pattern of the cover units, whereas post-orogenic basement fault movement has less influence on the thickened hinterland of the overlying belt. The interaction of basement faulting and cover shortening results in the formation of rhombic structures. In models with pre- and syn-orogenic basement strike-slip faults, rhombic blocks develop as a result of shortening of the overlying cover during basement faulting. These rhombic blocks are similar in appearance to flower structures, but are different in kinematics, genesis and structural extent. We compare these model results to both the Zagros fold-and-thrust belt in southwestern Iran and the Alborz Mountains in northern Iran. Based on the model results, we conclude that the traces of basement faults in cover units rotate and migrate towards the foreland during regional shortening. As such, these traces do not necessarily indicate the actual location or orientation of the basement faults which created them.
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