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  • 51.
    Harris, Lyal
    et al.
    Tectonics Special Research Centre, Department of Geology and Geophysics, The University of Western Australia, Crawley, Australia.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Centrifuge modelling of folding in high grade rocks during rifting2003In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 25, no 2, p. 291-305Article in journal (Refereed)
    Abstract [en]

    Centrifuge modelling is used to simulate the progressive development of structures in a simplified crustal profile during rifting. This paper focuses on folding of ductile layers representing the middle to lower crust. Displacement along a pre-existing cut in the layer representing mantle lithosphere creates a broad shear zone in overlying ductile layers and an asymmetric rift in upper layers. The footwall of the ‘mantle lithosphere’ layer and overlying shear zone are rotated to sub-horizontal during rise of the basal ductile layer (representing asthenosphere) as an isostatic response to thinning in the extended model. Synthetic and antithetic faults develop in models with thicker ductile ‘crustal’ layers. Although upper, semi-brittle layers, representing upper crust constitute a simple fault-bounded or sag ‘basin’, the underlying ductile layers are complexly folded. Open, upright folds developed over the crest of the footwall ‘mantle lithosphere’ layer are tightened and increased in amplitude as they progressively rotate to a recumbent attitude. Refolding occurs during rise of the basal ductile material representing asthenosphere and from boudinage of overlying competent layers. This study suggests that regional-scale folds in some high-grade terrains previously interpreted as evolving in a convergent margin tectonic setting may instead be produced as a result of flow of the ductile crust during rifting.

  • 52. Harris, Lyal
    et al.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Fossen, Håkan
    Mechanisms for foldingof mid- to lower-crustal rocks in extensional tectonic settings2002In: Earth-Science Review, Vol. 59, p. 163-210Article in journal (Other academic)
    Abstract [en]

    This review of structures developed in extensional high-grade terrains, combined with results of centrifuge analogue modelling, illustrates the range of fold styles and mechanisms for folding of amphibolite to granulite facies rocks during rifting or the collapse of a thrust-thickened orogen. Several extensional fold mechanisms (such as folding within detachment shear zones) are similar to those in contractional settings. The metamorphic P–T–t path, and not fold style or mode of formation, is therefore required to determine the tectonic setting in which some folds developed. Other mechanisms such as rollover above and folding between listric normal shear zones, and folding due to isostatic adjustments during crustal thinning, are unique to extensional tectonic settings. Several mechanisms for folding during crustal extension produce structures that could easily be misinterpreted as implying regional contraction and hence lead to errors in their tectonic interpretation. It is shown that isoclinal recumbent folds refolded by open, upright folds may develop during regional extension in the deep crust. Folds with a thrust sense of asymmetry can develop due to high shear strains within an extensional detachment, or from enhanced back-rotation of layers between normal shear zones. During back-rotation folding, layers rotated into the shortening field undergo further buckle folding, and all may rotate towards orthogonality to the maximum shortening direction. This mechanism explains the presence of many transposed folds, folds with axial planar pegmatites and folds with opposite vergence in extensional terrains. Examples of folds in high-grade rocks interpreted as foring during regional extension included in this paper are from the Grenville Province of Canada, Norwegian Caledonides, Albany Mobile Belt and Leeuwin Complex of Western Australia, Ruby Mountains in the Basin and Range Province of Nevada, the Ataˆ Sund area of Greenland, the Napier Complex of Enderby Land in East Antarctica and the Kigluaik Mountains in western Alaska.

  • 53.
    Hessami, Khaled
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Talbot, Christopher J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Tabasi, Hadi
    International Institute of Earthquake Engineering and Seismology, Tehran, Iran .
    Shabanian, Esmael
    International Institute of Earthquake Engineering and Seismology, Tehran, Iran .
    Progressive unconformities within an evolving foreland fold-thrust belt, Zagros Mountains.2001In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 158, no 6, p. 969-981Article in journal (Refereed)
    Abstract [en]

    A major angular unconformity between the Bakhtyari conglomerates and the underlying Agha Jari Formation has long been interpreted as indicating that orogeny in the Zagros Simply Folded Zone took place in Plio-Pleistocene times. This study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the Zagros Simply Folded Zone has propagated in time and space. These unconformities indicate that deformation started as early as end Eocene in the northeast of the Simply Folded Zone and propagated progressively to the southwest, where unconformable contacts are only seen between younger units. As shortening continued, the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the Persian Gulf and Mesopotamia. The climax of orogeny took place at end Pliocene time when the most extensive unconformity in the Zagros Simply Folded Zone developed between the (upper) Bakhtyari Formation and older units. Active seismicity and documented present uplift imply that the Simply Folded Zone is still propagating southwestward.

  • 54.
    Hillerdal, Gunnar
    et al.
    Lung Medicine, Karolonska Hospital, Stockholm, Sweden.
    Lee, J
    Blomkvist, A
    Rask-Andersen, Anna
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Occupational and Environmental Medicine.
    Uddenfeldt, M
    Koyi, Hemin
    Rasmussen, E
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Occupational and Environmental Medicine.
    Pleural disease during treatment with bromocriptine in patients previously exposed to asbestos1997In: European Respiratory Journal, ISSN 0903-1936, E-ISSN 1399-3003, Vol. 10, no 12, p. 2711-2715Article in journal (Refereed)
    Abstract [en]

    Bromocriptine, which is used in the treatment of Parkinson's disease, can cause adverse pleuropulmonary reactions. Exposure to asbestos can result in similar lesions. Fifteen patients with former exposure to asbestos, who developed pleural fibrosis after treatment with bromocriptine, were observed independently in Sweden (11 patients) and Australia (four patients). The patients complained of malaise, often associated with weight loss, dyspnoea, and a disturbing cough. Laboratory values included increased erythrocyte sedimentation rate and a low haemoglobin level. Lung function tests showed a restrictive lung function defect. Chest radiographs showed bilateral pleural fibrosis, with small amounts of fluid in some cases. Soon after bromocriptine was withdrawn, the patients improved clinically, and the laboratory values returned to normal. However, in most cases, pleural fibrosis and a restrictive lung function defect persisted to some extent. In conclusion, in patients who develop pleuropulmonary fibrosis whilst being treated with bromocriptine, former exposure to asbestos should be investigated. Conversely, when pleural changes develop in a patient on bromocriptine and with prior exposure to asbestos, the possible causative role of the drug should be discussed. Special follow-up may be indicated when bromocriptine is planned in a patient with previous asbestos exposure, and if symptoms or signs of pleural fibrosis develop, bromocriptine withdrawal should be considered.

  • 55. Jakobsson, Martin
    et al.
    Björck, Svante
    O'Regan, Matt
    Floden, Tom
    Greenwood, Sarah L.
    Swärd, Henrik
    Lif, Arne
    Ampel, Linda
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Skelton, Alasdair
    Major earthquake at the Pleistocene-Holocene transition in Lake Vattern, southern Sweden2014In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, no 5, p. 379-382Article in journal (Refereed)
    Abstract [en]

    Lake Vattern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vattern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake floor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vattern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infillings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vattern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the significance of glacio-isostatic unloading.

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  • 56. Karim, K.H.
    et al.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Mushir, K
    Hessami, K.
    Significance of angular unconformities between Cretaceous and Tertiary strata in the Northwestern Segment of the Zagros Fold-Thrust Belt, Kurdistan Region, Iraq2011In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 148, no 5-6, p. 925-939Article in journal (Refereed)
    Abstract [en]

    In this study, two angular unconformities are found and analysed for the first time in the Mesozoic–Cenozoic succession in the northwestern segment of the Zagros fold–thrust belt (ZFTB) in the Kurdistan Region. The first unconformity exists between Lower Cretaceous and Paleocene–Eocene rocks and the second between the Campanian Shiranish Formation and the Maastrichtian Tanjero Formation. Each of these unconformities is found in two different localities in the Zagros Imbricate Zone (i.e. the highly deformed zone immediately SW of the Zagros Suture) of the ZFTB of the Kurdistan Region near the border with Iran. The study uses recent geological mapping, structural and stratigraphic analyses in addition to using previous biozonation of the stratigraphic units that bound the two unconformities. The first unconformity was initiated with obduction of the ophiolite and Lower Cretaceous radiolarite onto the passive margin of the Arabian plate. This unconformity formed during an early phase of the Zagros orogeny, which is associated with the developing of a foreland basin, and resulted in the folding of the radiolarites and their uplift to form high-relief land. The erosion of this high-relief land resulted in the formation of the Paleocene–Eocene Red Bed Series and their deposition on the folded radiolarite. The timing of the deformation that caused this unconformity is hard to determine; however, its stratigraphic position may suggest that it possibly is related to post-Cenomanian movements. The second unconformity is between the tilted Campanian Shiranish Formation (hemipelagite) and Tanjero Formation (500 m of conglomerate in the more proximal area). These unconformities indicate that deformation and uplift of the sedimentary units was variable during ophiolite obduction in this part of the ZFTB. We argue that deformation, ophiolite obduction and collision are likely to have varied in space and time along the c. 2000 km long ZFTB.

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  • 57.
    Koyi, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Deformation in fold-thrust belts caused by multiple detachments2010Conference paper (Refereed)
  • 58.
    Koyi, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Tektonik i minatyr2001In: Geologiskt Forum, Vol. 8, no 30, p. 4-9Article in journal (Other academic)
  • 59.
    Koyi, H. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    How complicated is the simplified geometry of salt diapirs?1995In: Salt, Sediments and hydrocarbons, p. 147-151Article in journal (Refereed)
  • 60.
    Koyi, H.A
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Salt Diapirs as Waste Repositories; Predictions from Analogue and Numerical Modelling.2005In: Structure, Tectonics and Ore Mineralisation Processes (TOMP), Economic Geology Research Unit Contribution 64, 2005, p. 71-Conference paper (Other academic)
  • 61.
    Koyi, H.A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Bahroudi, A
    Sans, M
    Lawa, F
    Modelling the role of multiple salt horizons on deformation in fold-thrust belts2005In: American Association of Petroleum Geologists (AAPG) Annaual Meeting, Abstract Volume AAPG 2005, A7., 2005Conference paper (Other (popular science, discussion, etc.))
  • 62.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Analogue modelling: from a qualitative to a quantitative technique - a historical outline1997In: Journal of Petroleum Geology, ISSN 0141-6421, E-ISSN 1747-5457, Vol. 20, no 2, p. 223-238Article in journal (Refereed)
    Abstract [en]

    Analogue modelling is a simplification of Nature; using this method, structures formed due to the deformation of rocks, whose in situ properties may be poorly known, can be modelled and investigated. Our lack of knowledge about “real” rocks is one of the major limitations to any kind of modelling of deformation. However, unlike their counterparts in Nature, the initial (undeformed) stages of analogue models can be documented, and can easily be compared with their later, deformed stages. This comparison is essential to gain an understanding of the evolution of the resulting structures. Analogue modelling is a relatively simple and inexpensive technique which can be very valuable as long as its limitations are well understood.

    In rock mechanics, real rocks are strained over human time scales. As many of the properties of rocks are time-dependent, the results of this type of experiment cannot directly be extrapolated to geologic time scales. Instead, modellers diminish the temporal and spatial dimensions by substituting carefully-chosen analogue materials for real rocks. Unlike field geologists, analogue modellers are able to follow the development of their models in a fixed reference frame.

    Cloos (1955) noted that: “Many interpretations would never have been published if the author had only once tried his suggested mechanism of folding or faulting in an experiment….”; he also concluded that “[analogue] experimenting is a good deal of fun”!

  • 63.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Compressional Salt‐Related Structures in the Western Quele Area, Kuqa Depression, Tarim Basin, China: Wu, Zh., Yin, H., and Koyi, H.A.2018In: Atlas of Structural Geological Interpretation from Seismic Images / [ed] Achyuta Ayan Misra; Soumyajit Mukherjee, Wiley-Blackwell Publishing Inc., 2018, p. 163-166Chapter in book (Refereed)
  • 64.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    De-risking plays in the highly folded zone foreland basin of the Zagros fold-thrust belt, Kurdistan Region, Iraq.: Mansurbeg, H., Koyi, H.A., Othman, R., Kolo, K., Harchegani, F.2018In: Tectonic and Structural Framework of the Zagros Fold-and-Thrust Belt / [ed] Farzipour-Saein; Mukherjee, Elsevier, 2018Chapter in book (Refereed)
  • 65.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Experimental modeling of the role of gravity and lateral shortening in the Zagros mountain belt1988In: AAPG Bulletin, Vol. 72, p. 1381-1394Article in journal (Refereed)
    Abstract [en]

    Dynamically scaled analogs of the geologic structures of the Zagros mountain belt are used to argue that different parts of the Zagros Mountains of Iran record different combinations of the effects of a gravity-driven overturn and a southwest-northeast lateral shortening superimposed on the Zagros overturn.

    Partially scaled material models have been used to simulate the Zagros geodynamics, which involve layer-parallel compression of a 6 to 7 km-thick Phanerozoic carbonate cover containing a pattern of preshortening diapirs. The folds in the Zagros form rapidly (1.5 mm/yr in a 20 to 30 km-wide zone), reactive some of the preshortening diapirs, and generate new synshortening listric diapirs. A third set of postshortening diapirs rises from the Hormuz decollement behind the fold-thrust front.

    Model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs, which flatten in the synclines. Model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs. I suggest that any salt pillows in currently diapir-free zones of the Zagros fold-thrust belt may surface as diapirs through the anticlines in the future.  In the absence of well data, seismic, and field observations, I have used only three map pattern criteria to recognize the timing of diapirs; these are locally obscured by extrusive salt sheets. Preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines. Synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines. Postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular; they are more common in the anticlines.

  • 66.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Gravity overturn, extension and basement fault activation1991In: Journal of Petroleum Geology, Vol. 14, no S1, p. 117-142Article in journal (Refereed)
    Abstract [en]

    Rayleigh-Taylor instabilities occur when low-density layers of viscous fluids are overlain by denser layers. Gravity overturn of such instabilities leads to the rise of the unstable light (source) fluid as diapirs (e.g. of salt) through the denser (overburden) layers (e.g. of clastic sediments). Lnteral extension or movements of faults in the bottom boundary at any stage during such gravity overturns are expected to have a great effect on the geometry, growth rate and location of onv salt structures.

    Two groups of material models, each consisting of three series, were used to study the effect of uniform extension. and the non-uniform extension due to reactivation of pre-existing basement faults. on gravity-driven overturns at different stages. The overburden in a third group model consisted of a stiffer non-Newtonian fluid. All the models were loose& scaled to an early stage of the North Sea. All the diapirs were upbuilt, because all the overburden was in place from the start.

    Pre-extension/prefaulting model diapirs are essentially vertical, symmetrical and finger-like with circular planforms and with isotropic lateral spacings predictable by Ramberg theory. When reactivated and deformed by Inter extension. these diapirs become inclined in profile, and develop elliptical planforms elongate in the direction of extension. Diapirs which rise in an tnstable sequence already thinned uniformly are only smaller, closer and slower.

    Post faulting model diapirs (in group 2 models) rise as asymmetric walls or rows of fingers, some above the, fault-scarps in the basement. others above the fault blocks.

    Synextension model diapirs rise from a thinning source layer; some are inclined and osymmetric in profile; some hove circular planforms, while others are elliptical and elongate in the extension direction. Synfaulting diapirs which form during reactivation of extensional basement, faults. develop as inclined and asymmetric walls overhanging the fault scarps. Finger-like diapirs separated from synfaulting walls occur in rows parallel to the faults, and have elliptical planforms elongate in the extension direction or. if located in local regimes of shallow compression, perpendicular to it,

    When the overburden was non-Newtonian with a power law component n=8.1. diapirs of the source surfaced only along extensional faults in the overburden.

    The model results are used to comment on recent interpretations of how halokinesis and extension interacted in the North Sea.

  • 67.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Gravity overturn, extension and basement fault activation1992In: Journal of Petroleum Geology, Vol. 15, no 3, p. 362-366Article in journal (Refereed)
  • 68.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Local thrust formed within a decollement zone during extension, Upper Rhine Graben, France.: Place J., Diraison M., Géraud Y. and Koyi H.A.2018In: Atlas of Structural Geological Interpretation from Seismic Images / [ed] Achyuta Ayan Misra, Wiley-Blackwell Publishing Inc., 2018, p. 47-49Chapter in book (Refereed)
  • 69.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Mode of internal deformation in sand wedges1995In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 17, no 2, p. 293-300Article in journal (Other academic)
    Abstract [en]

    Sequential sections of a sand box model are used to quantify displacement along imbricate surfaces and their rotation and volume loss history within an accreting sand wedge. Model results show that both displacement along the imbricate surfaces and compac

  • 70.
    Koyi, Hemin
    Bureau of Economic Geology, The University of Texas at Austin, Texas .
    Modeling of segmentation and emplacement of salt sheets in anisotropic overburden1992In: Mesozoic and Early Cenozoic Development of the Gulf of Mexico and Caribbean Region: A Context for Hydrocarbon / [ed] John M. Armentrout, Roger Bioch, Hilary C. Olson, and Bob F. Perkins., GCSSEPM Foundation , 1992, 13, p. 135-142Chapter in book (Refereed)
    Abstract [en]

    Two centrifuged models are used to study the segmentation and emplacement of allochthonous salt sheets. In the first model, a uniformly thick buoyant silicone layer simulating salt with a horizontal lower boundary, was overlain by a uniformly thick layer of anisotropically layered overburden (brittle-ductile microlaminates). During centrifuging, the model was allowed to extend at one end, termed the basin. As a result, the buoyant layer flowed basinward, resulting in extension at the toe and faulting of the overburden units as individual blocks. The buoyant material was then segmented by the sinking overburden blocks and penetrated the overburden through the faulted zones.

    The second model consisted of a buoyant wedge of silicone, with a dipping lower boundary simulating an asymmetrically spreading salt sheet. This sheet was overlain by several wedges of anisotropic microlaminate overburden at different times. Simulating a progradational wedge in nature, the overburden produced a pressure difference ranging from 144 Pa at the rear to 80 Pa at the toe. The buoyant layer flowed basinward due to higher loading at the rear relative to the toe area. Sequential addition of overburden wedges resulted in flow of the buoyant layer up through the stratigraphic section and formation of secondary sheets basinward. During further addition of overburden wedges, these secondary sheets were progressively segmented by deforming overburden which display extensional structures at the rear and contractional structures (folding and thrusting) at the toe. A similar deformation pattern is reported from the Gulf of Mexico.

    Comparison of model results suggests that differential loading and presence of a slope at the lower contact of the buoyant layer (or abrupt lateral margin) are two essential factors in the flow of the buoyant material up through the stratigraphic section, its segmentation, and formation of secondary buoyant sheets.

  • 71.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Modeling the influence of sinking anhydrite blocks on salt diapirs targeted for hazardous waste disposal2001In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 29, no 5, p. 387-390Article in journal (Refereed)
    Abstract [en]

    Due to the low permeability and high ductility of rock salt, many salt diapirs, such as those in Germany and the Netherlands, are targeted as long-term repositories for disposal of high-level radioactive and chemical wastes. Geophysical and subsurface dat

  • 72.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Modelling oblique inversion of pre-existing grabens. In: ‘Folding and Fracturing of Rocks: 50 Years of Research since the Seminal Text Book of J. G. Ramsay’.: Deng,D., Koyi, H.A., Zhang, J.In: Journal of the Geological Society of LondonArticle in journal (Refereed)
  • 73.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Modelling of role of gravity and lateral shortening in Zagros mountain belt1990In: Proceeding of Symposium on Diapirism with special reference to Iran, 1990, p. 483-486Conference paper (Refereed)
  • 74.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. berggrundsgeologi.
    Multiphase halokinesis in Nordkapp Basin1993In: Arctic Geology and Petroleum potential, 1993, p. 665-668Conference paper (Other academic)
  • 75.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Mushroom diapirs penetrating overburdens with high effective viscosities1991In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 19, no 12, p. 1229-1232Article in journal (Refereed)
  • 76.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Salt flow by aggrading and prograding overburdens1996In: Geological Society Special Publication, ISSN 0305-8719, E-ISSN 2041-4927, Vol. 100, p. 243-258Article in journal (Refereed)
    Abstract [en]

    The mechanisms responsible for segmentation of salt sheets and their emplacement into higher stratigraphic levels are not separable and act simultaneously. Three sets of centrifuge models with strongly planar anisotropic (anisotropy, δ, the ratio between the effective viscosities in pure and simple shear, ranging between 4.8 and 16.4) microlaminate overburdens are used to study the effect of aggradation and progradation on segmentation and emplacement of allochthonous salt sheets.

    In the first set of models, a tabular buoyant source layer was overlain by tabular anisotropic overburden simulating aggradation. During centrifuging, the underlying ductile source layer was segmented into individual wall-like diapirs by the subsiding blocks formed due to extension and faulting of the overburden. The extensional zone in these models started at the spreading edge (free face) of the model and migrated backwards.

    In the second set of models, a tabular buoyant source layer was overlain successively by wedges of anisotropic overburdens simulating progradation. During centrifuging, the buoyant layer was displaced from the back of the model, where loading was higher, towards the free face in the front of the model, where overburden units were thinner. Overburden units extended at the back and the middle of the model while contractional structures dominated at the front, where asymmetric diapirs formed overhangs that spread ‘basinward’ to form ‘salt’ sheets.

    In the third set of models, a wedge-shaped buoyant source layer was overlain successively by wedges of anisotropic overburden simulating progradation. The overburden wedge created a lateral pressure gradient ranging from 144 Pa at the back of the model to 80 Pa at the front when deformed in the centrifuge. In these models, as in the second set of models, the underlying buoyant mass was displaced ‘basinward’ by the subsiding thicker overburden units at the back of the model. Contractional structures dominated the deformation at the leading edge of the wedge.

    Comparison of model results suggests that progradation (as in the second and third sets of models) loads underlying ‘salt’ differentially, displaces it downdip and segments it. As it segments at the back, the ‘salt’ flows laterally to areas of lower loading by intruding through the thinner overburden units and forming secondary ‘salt’ sheets at the front. On the other hand, aggradation of uniform overburden segments a buoyant sheet into two-dimensional salt walls or stocks, as in the first set of models.

  • 77.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Secondary compaction through area loss during accretion: a sand model approach1997In: Orogenic Belts, Geological Mapping: Proceedings of the 30th International Geological Congress / [ed] Xu Zhiqin, Ren Yufeng, Qiu Xiaping, VSP International Science Publishers, 1997, 7, , p. 168p. 1-6Chapter in book (Refereed)
  • 78.
    Koyi, Hemin A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Estimation of salt thickness and restoration of cross-sections with diapiric structures: a few critical comments on two powerful methods1994In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 16, no 8, p. 1121-1128Article in journal (Refereed)
    Abstract [en]

    Estimation of the initial thickness of a salt layer that has produced diapirs in a sedimentary basin provides information about basin history and evolution of the resulting salt structures. In many cases quantifying sedimentation and deformation history assists the understanding of hydrocarbon entrapment by salt structures. Limitations of the methods that are used to estimate salt thickness and restoration of profiles with salt structures may cause great error in thickness calculation or interpretation of deformation history. These limitations also cause confusion if they are not explained clearly during presentation of results.

    Restoration of profiles of extension areas where salt structures are present could give erroneous results when the regional extension and the flow of salt in and out of the profile along strike and within the profile are not incorporated in the restoration. Scaled analogues demonstrate that restored profiles of diapiric structures may show incorrect evolution history of salt structure and initial salt thickness.

  • 79.
    Koyi, Hemin A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Berggrundsgeologi.
    Femtio år sedan Mt Everest bestegs för första gången2002Other (Other (popular science, discussion, etc.))
  • 80.
    Koyi, Hemin A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Maillot, Bertrand
    Tectonic thickening of hanging-wall units over a ramp2007In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 29, no 6, p. 924-932Article in journal (Refereed)
    Abstract [en]

    In this article, we use results of analogue models and published numerical models to study the elements that influence the amount of thickening of hanging-wall units during their transport over a ramp. The models, consisting of granular layers, were shortened over a single-pass, rigid ramp dipping at 15, 30 or 45° and friction coefficient (μ) that was large (0.67), intermediate (0.42) or null. Model results show that the amount of thickening depends on the ramp angle and its friction. Thickening increases dramatically with increasing ramp friction and dip. The maximum amount of thickening (80%) is observed over steepest ramps (45°) with largest ramp friction (μ = 0.67), whereas the minimum amount of thickening (2.5%) occurs over frictionless ramps dipping 15°. For the same friction coefficient along the ramp, steeper ramps cause larger amounts of thickening. The tectonic thickening demonstrated by our models was compared with thickening of hanging-wall units of natural examples, and other experimental and model studies. This comparison shows that thickening occurs whether the material considered is brittle, viscous, or plastic. It also confirms the importance to thickening of ramp angle and fault friction. Finally, it reveals also that ramp shape (round or sharp bend), its changes due to footwall deformations, and the topographic relief, are additional boundary conditions for thickening. More generally, our model results and other published model results demonstrate that retardation during the transport of hanging-wall units over a ramp results in hanging-wall thickening.

  • 81.
    Koyi, Hemin A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Mancktelow, Neil
    Tectonic Modeling: A Volume in Honor of Hans Ramberg2001Collection (editor) (Other academic)
  • 82.
    Koyi, Hemin A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Berggrunds geologi.
    Sans, Maura
    University of Barcelona, Barcelona, Spain.
    Modelling the deformation front of fold-thrust belts containing multiple weak horizons.2004Conference paper (Other academic)
  • 83.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Aasen, J.O.
    Nybakken, S.
    Hogstad, K.
    Tørudbakken, K.
    Determining geometry of salt diapirs by depth modelling of seismic velocity pull-up1992In: Oil and Gas Journal, Vol. 90, p. 97-100Article in journal (Refereed)
  • 84.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Chemia, Z.
    Schmeling, H.
    Modelling some of the parameters that govern the geometry and evolution history of a salt diapir2010Conference paper (Refereed)
  • 85.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Harris, Lyal
    Formation of multiple basins above low-angle detachments; a centrifuge-model approach.2001In: Energy exploration & exploitation, ISSN 0144-5987, E-ISSN 2048-4054, Vol. 19, no 4, p. 365-374Article in journal (Refereed)
    Abstract [en]

    Extended scaled centrifuge models, simulating lithospheric deformation, show that depocenters of sedimentary basins, formed above lithospheric detachment zones, migrate both in space and time. If associated with a low-angle mantle detachment, this migration results in formation of multiple basins from a single phase of model extension. Unlike the multiple detachment model proposed for formation of multiple basins or models invoking transtensional deformation, the current analogue models suggest that multiple basins may form due to continuous displacement along one single low-angle detachment during orthogonal rifting. Model results suggest that the geometry and location of sedimentary basins are strongly dependent on the coupling between the upper crust and mantle lithosphere by the ductile lower crust, and the dip of the prescribed "fault/shear zone" in the mantle lithosphere. Steeply dipping lithospheric detachment enhances coupling and hence formation of a single basin in the upper crust above the maximum asthenospheric upwelling in the centre of the rift. In contrast, low-angle detachment in the lithosphere promotes decoupling of the upper crust and any resulting basins from the underlying mantle lithosphere. The dip angle of the mantle detachment affects both location and geometry of the basin. A low-angle shear zone in the mantle lithosphere decouples the broad sag in the upper crust, whereas a steep shear zone promotes coupling and initiates narrow, but deep basins.

  • 86.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Hessami, K
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Teixell, A
    Departament de Geologia, Universitat Autonoma de Barcelona, Bellaterra, Spain..
    Epicenter distribution and magnitude of earthquakes in fold-thrust belts: insights from sandbox models2000In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, ISSN 0094-8276, Vol. 27, no 2, p. 273-276Article in journal (Refereed)
    Abstract [en]

    Scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth-quakes in the sedimentary cover of active fold-thrust belts.Model results suggest that in fold-thrust belts shortenedabove low-friction ductile decollements (rock salt or over-pressured mudstone), low- to moderate-magnitude earth-quakes (Mw=5:3−5:6), distributed over a wide area, occuralong several long-lived thrust faults. Conversely, in areasshortened above high-friction decollements large-magnitudeearthquakes (Mw=6:6−6:8), distributed over a narrowzone are likely to occur along few short- lived thrust ramps.Calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat-tern from the Zagros mountain belt, which is partially short-ened above a ductile decollement of Hormuz salt formation.Model results also showed that erosion reactivates older in-active thrusts and promotes formation of out-of-sequencethrusts.

  • 87.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Jenyon, M.
    Petersen, K.
    The effect of basement faulting on diapirism1993In: Journal of Petroleum Geology, ISSN 0141-6421, E-ISSN 1747-5457, Vol. 16, no 3, p. 285-312Article in journal (Refereed)
    Abstract [en]

    Experimental and natural examples illustrate the influence of sub-salt horizon basement faults on diapirism. In a series of experimental models, viscous diapirs were observed to form above or close to basement faults. In all the models, basement faults initiated a half-graben, where thicker overburden units enhanced differential loading on an underlying buoyant layer. The buoyant material flowed updip to the low-pressure zones in the uplifted block, and updip along the tilted upper boundary of the hanging-wall. Basement faulting extended the overburden, and provided the space through which the buoyant layer could rise. Subsidence and faulting of overburden layers allowed diapirism along the faulted zones. In all cases, the deformation in the overburden was accommodated within a wider zone of faulting than the discrete basement fault which initiated the deformation. Differential compaction enhances differential loading and accumulation of thicker overburden on the downthrown sides of basement faults.

    Seismic profiles from the Danish Basin, Dutch Central Graben, Gulf of Mexico and North Sea show that diapirs are spatially associated with basement faults. However, model results show that diapirs triggered by basement faults are not necessarily located directly above the faults.

    Basement faults extend the cover sequences. If detached from the cover by a ductile layer, thick-skinned extension is accompanied by thin-skinned extension and decoupling of the cover. The influence of basement faults on diapirs depends on: the thickness and effective viscosity of the ductile layer (e.g. rock salt); the thickness ratio between the buoyant layer and the overburden; the mechanical properties of the brittle cover in the case of clastic sediments; the rate of sedimentation; the displacement rate throw and the dip of the basement faults.

  • 88.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Berggrundsgeologi. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Maillot, Bertrand
    Quantifying thickening of hanging wall units.2006In: Tectonic Studies Group: Tectonic Studies Group, 2006Conference paper (Refereed)
  • 89.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Milnes, AG
    Schmeling, H
    Talbot, Christopher J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Zeyen, H
    Numerical models of ductile rebound of crustal roots beneath mountain belts1999In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 139, no 2, p. 556-562Article in journal (Other academic)
    Abstract [en]

    Crustal roots formed beneath mountain belts are gravitationally unstable structures, which rebound when the lateral forces that created them cease or decrease significantly relative to gravity. Crustal roots do not rebound as a rigid body, but undergo intensive internal deformation during their rebound and cause intensive deformation within the ductile lower crust. 2-D numerical models are used to investigate the style and intensity of this deformation and the role that the viscosities of the upper crust and mantle lithosphere play in the process of root rebound. Numerical models of root rebound show three main features which may be of general application: first, with a low-viscosity lower crust, the rheology of the mantle lithosphere governs the rate of root rebound; second, the amount of dynamic uplift caused by root rebound depends strongly on the rheologies of both the upper crust and mantle lithosphere; and third, redistribution of the rebounding root mass causes pure and simple shear within the lower crust and produces subhorizontal planar fabrics which may give the lower crust its reflective character on many seismic images.

  • 90.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Nilfouroushan, Faramarz
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Univ Gavle, Dept Ind Dev IT & Land Management, Gavle, Sweden.
    Hessami, Khaled
    IIEES, Tehran, Iran.
    Modelling role of basement block rotation and strike-slip faulting on structural pattern in cover units of fold-and-thrust belts2016In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 153, no 5-6, p. 827-844Article in journal (Refereed)
    Abstract [en]

    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.

  • 91.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Petersen, K.
    Geologisk Institut, Aarhus University, Århus, Denmark.
    The influence of basement fault on the development of salt structures in the Danish Basin.1993In: Marine and Petroleum Geology, ISSN 0264-8172, E-ISSN 1873-4073, Vol. 10, no 2, p. 82-94Article in journal (Refereed)
    Abstract [en]

    Scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the Danish Basin. The models consisted of a viscous layer simulating rock salt, overlain by layers of cohesive sand that mimic brittle failure in natural overburdens. Model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the Danish Basin. In plan view, model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement. With further burial, single diapirs rose from these buoyant walls. Some of the diapirs surfaced through the faulted overburden, a few were trapped beneath the competent ‘Cretaceous’ units and others were starved due to lack of supply from below. In section, model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks. Model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation. Models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south, where they rise diapirically. In the model, the pressure due to loading by overburden layers changed from 1.3 × 102 Pa in the south to 2.3 × 102 Pa in the northern part of the basin. In general, the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half-grabens and introducing a slope and steps at the base of the buoyant layer, weakening its overburden and causing differential loading and compaction. The spreading overhangs of salt diapirs beneath the Cretaceous chalk in the Danish Basin would seal any potential pre-Cretaceous reservoir rocks.

  • 92.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Petersen, Kenneth
    Basement faulting: a complementary triggering mechanism for diapirism1993In: Mesozoic and early cenozoic development of the Gulf of Mexico and Caribbean region: a context for hydrocarbon exploration / [ed] Lindell, James L & Perkins, Bob F., GCSSEPM Foundation , 1993, 13, p. 103-114Chapter in book (Refereed)
  • 93.
    Koyi, Hemin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Solid Earth Geology. Berggrundsgeologi.
    Sans, Maura
    Deformation transfer in viscous detachments; comparison of sandbox models to the South Pyrenean Triangle Zone2006In: Geological Society London, Special Publication, Vol. 253, p. .117-134Article in journal (Refereed)
  • 94.
    Koyi, Hemin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Berggrundsgeologi.
    Sans, Maura
    Teixell, Antonio
    Cottom, James
    Zeyen, Hermann
    The significance of penetrative strain in the restoration of shortened layers — Insights from sand models and the Spanish Pyrenees.2004In: American Association of Petroleum Geologists Memoir: THRUST TECTONICS AND PETROLEUM SYSTEMS, Vol. 82, p. 207-222Article in journal (Refereed)
  • 95.
    Koyi, Hemin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Sans, Maura
    Teixell, Antonio
    Cotton, James
    Zeyen, Hermann
    The significance of penetrative strain in contractional areas2004In: THRUST TECTONICS AND PETROLEUM SYSTEMS, American Association of Petroluem Geologists , 2004Chapter in book (Refereed)
  • 96.
    Koyi, Hemin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Solid Earth Geology. Berggrundsgeologi.
    Saura, E.
    Teixell, A.
    Maillot, B.
    Ramping a flat; emphasizing some basic thrust teriminologies2007In: Tectonic Studies Group, Glascow, UK, 2007Conference paper (Other scientific)
  • 97.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Schmeling, Harro
    Goethe-University, Institute of Geoscience, Frankfurt am Main, Germany.
    Burchardt, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Talbot, Christopher J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Mukherjee, Soumyajit
    Department of Earth Sciences, Indian Institute of Technology, Bombay, India.
    Sjöström, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Chemia, Zurab
    Department of Geography and Geology, University of Copenhagen, Denmark.
    Shear zones between rock units with no relative movement2013In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 50, no SI, p. 82-90Article in journal (Refereed)
    Abstract [en]

    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.

  • 98.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Schott, B.
    Rise and fall of denser blocks within saltdiapirs2000In: Bollettino di Geofisica Teorica ed Applicata, ISSN 0006-6729, Vol. 42, no 1-2, p. 64-66Article in journal (Refereed)
  • 99.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Sirat, Manhal
    ADCO.
    Morad, Daniel
    Analogue Modeling of Shah Structure in Abu Dhabi; Mode and Structural Evolution2015In: Society of Petroleum EngineersArticle in journal (Refereed)
    Abstract [en]

    Three-dimensional seismic data have been used to construct a series of scaled analogue models simulating the structural evolution of the Shah hydrocarbon Field. Models consisted of a set of layers of loose sand on two basal plates whose contact simulated a basement fault. Depositional history of the Shah structure was simulated in the model by producing syn-kinematic deposition and erosion. Deformation of the model was achieved by moving one of the basement plates in a way that it initiated an oblique slip along the basement fault. This oblique movement induced both a strike slip movement in and shortening of the cover sand layers, which resulted in formation of an open anticline (box fold) along the strike of the fault similar to the Shah structure.

    The 3D seismic mapping of the Shah hydrocarbon Field reveals carbonates dominating lithological units from the Pre Khuff Fm (Permian) to the Dammam Fm (Eocene). A major unconformity in the stratigraphy indicates uplift, exhumation and erosion at Simsima level (U. Cretaceous) with onlapping of the younger units (Eocene-Miocene Formations). The Shah structure is an open SW-NE striking anticline, which changes symmetry along strike; asymmetric in the SW, more symmetric in the middle, and asymmetric open anticline in the NE. Model results indicate that the structure is a basement related cover anticline formed due to the oblique movement along a basement fault, which was reactivated during the obduction of Semail Ophiolite and later collision of Arabia with Iranian plate. These results show that this anticline formed without the need for a shortening component perpendicular to the strike of the structure. An oblique slip along a basement fault, with a relatively small degree of shortening could equally well result in the formation of such open and low-amplitude anticline.

    The modelling results presented here provides an alternative scenario for the formation of Shah structure (low-amplitude, and open) and addresses some of the key questions about its structural constraints (e.g. geometry, timing and evolution history) by linking it with basement structures. Our modelling results are of high significance for understanding entrapment mechanism, migration pathways, and fracture development. This newly proposed mechanism impacts the exploration and development of the Onshore Fields in Abu Dhabi, at the vicinity of Shah Structure.

  • 100.
    Koyi, Hemin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Talbot, Christopher J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Toruddbakken, Björn
    Analogue models of salt diapirs and seismic interpretation in the Nordkapp Basin, Norway1995In: Petroleum Geoscience, ISSN 1354-0793, E-ISSN 2041-496X, Vol. 1, no 2, p. 185-192Article in journal (Refereed)
    Abstract [en]

    Dynamically scaled analogue models with an overburden of cohesive sand and a viscous "salt" layer were deformed in a centrifuge to mimic real salt structures in the Nordkapp Basin. Like their natural prototypes, model diapirs were aligned in rows parallel to the basin margins. In profile, model diapirs were asymmetric, suggesting that the real diapirs will possess asymmetric geometries. Like many of the real salt structures, model diapirs pierced without developing a pillow stage because they rose along basin margin faults which propagated up through the overburden from the basement during thick-skinned extension. Once their overburden was weakened by faulting, differential loading forced model diapirs to rise as long as buoyant material was supplied. Some real salt diapirs initially rose as conformable pillows during the early Triassic, became diapiric during middle Triassic and spread broad overhangs during slow sedimentation in late Triassic and Jurassic times. Later, the overhangs reactivated asymmetrically when buried by Cretaceous and Tertiary sediments.

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