scholarly journals Review for "Throw variations and strain partitioning associated with fault-bend folding along normal faults"

2020 ◽  
Author(s):  
Zoe Mildon
Keyword(s):  
Normal Faults ◽  
Strain Partitioning ◽  
Fault Bend

scholarly journals Throw variations and strain partitioning associated with fault-bend folding along normal faults

2019 ◽  
Author(s):  
Efstratios Delogkos ◽  
Muhammad Mudasar Saqab ◽  
John J. Walsh ◽  
Vincent Roche ◽  
Conrad Childs
Keyword(s):  
Large Scale ◽  
Full Range ◽  
Quantitative Model ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Fault Surface ◽  
Irregular Geometries ◽  
Surface Irregularities ◽  
Fault Bend ◽  
Constant Displacement

Abstract. Normal faults have irregular geometries on a range of scales arising from different processes including refraction and segmentation. A fault with an average dip and constant displacement on a large-scale, will have irregular geometries on smaller scales, the presence of which will generate fault-related folds, with major implications for across-fault throw variations. A quantitative model has been presented which illustrates the range of deformation arising from movement on fault surface irregularities, with fault-bend folding generating geometries reminiscent of normal drag and reverse drag. The model highlights how along-fault displacements are partitioned between continuous (i.e. folding) and discontinuous (i.e. discrete displacement) strain along fault bends characterised by the full range of fault dip changes. Strain partitioning has a profound effect on measured throw values across faults, if account is not taken of the continuous strains accommodated by folding and bed rotations. We show that fault throw can be subject to errors of up to ca. 50 % for realistic fault bend geometries (up to ca. 40°), even on otherwise sub-planar faults with constant displacement. This effect will provide apparently more irregular variations in throw and bed geometries that must be accounted for in associated kinematic interpretations.

scholarly journals Throw variations and strain partitioning associated with fault-bend folding along normal faults

Solid Earth ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 935-945
Author(s):  
Efstratios Delogkos ◽  
Muhammad Mudasar Saqab ◽  
John J. Walsh ◽  
Vincent Roche ◽  
Conrad Childs
Keyword(s):  
Large Scale ◽  
Full Range ◽  
Quantitative Model ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Potential Significance ◽  
Irregular Geometries ◽  
Fault Bend ◽  
Ca 50 ◽  
Constant Displacement

Abstract. Normal faults have irregular geometries on a range of scales arising from different processes including refraction and segmentation. A fault with constant dip and displacement on a large-scale will have irregular geometries on smaller scales, the presence of which will generate fault-related folds and down-fault variations in throw. A quantitative model is presented which illustrates the deformation arising from movement on irregular fault surfaces, with fault-bend folding generating geometries reminiscent of normal and reverse drag. Calculations based on the model highlight how fault throws are partitioned between continuous (i.e. folding) and discontinuous (i.e. discrete offset) strain along fault bends for the full range of possible fault dip changes. These calculations illustrate the potential significance of strain partitioning on measured fault throw and the potential errors that will arise if account is not taken of the continuous strains accommodated by folding and bed rotations. We show that fault throw can be subject to errors of up to ca. 50 % for realistic down-dip fault bend geometries (up to ca. 40∘), on otherwise sub-planar faults with constant displacement. This effect will provide irregular variations in throw and bed geometries that must be accounted for in associated kinematic interpretations.

scholarly journals Stress control of frictional hangingwall accommodation above thrust ramps

2001 ◽  
Vol 34 (1) ◽  
pp. 275
Author(s):  
G. MULUGETA ◽  
D. SOKOUTIS ◽  
Μ. BONINI
Keyword(s):  
Shear Stress ◽  
Stress Ratio ◽  
Kink Band ◽  
Experimental Models ◽  
Tensile Failure ◽  
Normal Faults ◽  
Kink Bands ◽  
Stress Control ◽  
Fault Bend ◽  
And Migration

Experimental models are used to study the stress control of frictional hangingwall accomodation above rigid flat-ramp-flat footwalls. Hangingwall accommodation involves shear or kink-band nucleation above the lower fault bend and migration of these as the hangingwalls climb over the underthrusting footwall. The kinkbands change shape and localise to thrusts as they migrate over the flat-ramp-flat footwall. When the shear stress to gravity stress ratio is low the thrusts reactivate to normal faults. With increase in the shear stress to gravity stress ratio reactivation of the kink bands was by tensile failure, at the upper fault bend. The models show that by changing the strength of materials deforming under otherwise similar conditions it is possible to study the geometry of frictional hangingwall accommodation, at different scales. In nature, hangingwall accommodation by thrust nucleation above thrust ramps and their subsequent normal reactivation may be anticipated in frictional sediments at shallow crustal levels, where temperatures and pressures are low.

Strain partitioning around an indenter during oroclinal bending: kinematics of the Circum-Moesian fault system of the Carpatho-Balkanides

2021 ◽  
Author(s):  
Nemanja Krstekanic ◽  
Liviu Matenco ◽  
Uros Stojadinovic ◽  
Ernst Willingshofer ◽  
Marinko Toljić ◽  
...  
Keyword(s):  
Large Scale ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Strain Partitioning ◽  
The South ◽  
The Carpathians ◽  
The North ◽  
Moesian Platform ◽  
Parallel Extension

<p>The Carpatho-Balkanides of south-eastern Europe is a double 180° curved orogenic system. It is comprised of a foreland-convex orocline, situated in the north and east and a backarc-convex orocline situated in the south and west. The southern orocline of the Carpatho-Balkanides orogen formed during the Cretaceous closure of the Alpine Tethys Ocean and collision of the Dacia mega-unit with the Moesian Platform. Following the main orogen-building processes, the Carpathians subduction and Miocene slab retreat in the West and East Carpathians have driven the formation of the backarc-convex oroclinal bending in the south and west. The orocline formed during clockwise rotation of the Dacia mega-unit and coeval docking against the Moesian indenter. This oroclinal bending was associated with a Paleocene-Eocene orogen-parallel extension that exhumed the Danubian nappes of the South Carpathians and with a large late Oligocene – middle Miocene Circum-Moesian fault system that affected the orogenic system surrounding the Moesian Platform along its southern, western and northern margins. This fault system is composed of various segments that have different and contrasting types of kinematics, which often formed coevally, indicating a large degree of strain partitioning during oroclinal bending. It includes the curved Cerna and Timok faults that cumulate up to 100 km of dextral offset, the lower offset Sokobanja-Zvonce and Rtanj-Pirot dextral strike-slip faults, associated with orogen parallel extension that controls numerous intra-montane basins and thrusting of the western Balkans units over the Moesian Platform. We have performed a field structural study in order to understand the mechanisms of deformation transfer and strain partitioning around the Moesian indenter during oroclinal bending by focusing on kinematics and geometry of large-scale faults within the Circum-Moesian fault system.</p><p>Our structural analysis shows that the major strike-slip faults are composed of multi-strand geometries associated with significant strain partitioning within tens to hundreds of metres wide deformation zones. Kinematics of the Circum-Moesian fault system changes from transtensional in the north, where the formation of numerous basins is controlled by the Cerna or Timok faults, to strike-slip and transpression in the south, where transcurrent offsets are gradually transferred to thrusting in the Balkanides. The characteristic feature of the whole system is splaying of major faults to facilitate movements around the Moesian indenter. Splaying towards the east connects the Circum-Moesian fault system with deformation observed in the Getic Depression in front of the South Carpathians, while in the south-west the Sokobanja-Zvonce and Rtanj-Pirot faults splay off the Timok Fault. These two faults are connected by coeval E-W oriented normal faults that control several intra-montane basins and accommodate orogen-parallel extension. We infer that all these deformations are driven by the roll-back of the Carpathians slab that exerts a northward pull on the upper Dacia plate in the Serbian Carpathians. However, the variability in deformation styles is controlled by geometry of the Moesian indenter and the distance to Moesia, as the rotation and northward displacements increase gradually to the north and west.</p>

scholarly journals Linked thick- to thin-skinned inversion in the central Kirthar Fold Belt of Pakistan

Solid Earth ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 425-446 ◽  
Author(s):  
Ralph Hinsch ◽  
Chloé Asmar ◽  
Muhammad Nasim ◽  
Muhammad Asif Abbas ◽  
Shaista Sultan
Keyword(s):  
Structural Control ◽  
Large Scale ◽  
Sedimentary Cover ◽  
Motion Vector ◽  
Focal Mechanisms ◽  
Plate Motion ◽  
Normal Faults ◽  
Accretionary Wedge ◽  
Strain Partitioning ◽  
Fold Belt

Abstract. The Kirthar Fold Belt is part of the transpressive transfer zone in Pakistan linking the Makran accretionary wedge with the Himalaya orogeny. The region is deforming very obliquely, nearly parallel to the regional S–N plate motion vector, indicating strong strain partitioning. In the central Kirthar Fold Belt, folds trend roughly N–S and their structural control is poorly understood. In this study, we use newly acquired 2-D seismic data with pre-stack depth migration, published focal mechanisms, surface and subsurface geological data, and structural modelling with restoration and balancing to constrain the structural architecture and kinematics of the Kirthar Fold Belt. The central Kirthar Fold Belt is controlled by Pliocene to recent linked thick-skinned to thin-skinned deformation. The thick-skinned faults are most likely partially inverting rift-related normal faults. Focal mechanisms indicate dip-slip faulting on roughly N–S-trending faults with some dip angles exceeding 40∘, which are considered too steep for newly initiated thrust faults. The hinterland of the study area is primarily dominated by strike-slip faulting. The inverting faults do not break straight through the thick sedimentary column of the post-rift and flexural foreland; rather, the inversion movements link with a series of detachment horizons in the sedimentary cover. Large-scale folding and layer-parallel shortening has been observed in the northern study area. In the southern study area progressive imbrication of the former footwall of the normal fault is inferred. Due to the presence of a thick incompetent upper unit (Eocene Ghazij shales) these imbricates develop as passive roof duplexes. In both sectors the youngest footwall shortcut links with a major detachment and the deformation propagates to the deformation front, forming a large fault-propagation fold. Shortening within the studied sections is calculated to be 18 %–20 %. The central Kirthar Fold Belt is a genuine example of a hybrid thick- and thin-skinned system in which the paleogeography controls the deformation. The locations and sizes of the former rift faults control the location and orientation of the major folds. The complex tectonostratigraphy (rift, post-rift, flexural foreland) and strong E–W gradients define the mechanical stratigraphy, which in turn controls the complex thin-skinned deformation.

scholarly journals Structural Features of the Central Labrador Trough: A Model for Strain Partitioning, Differential Exhumation and Late Normal Faulting in a Thrust Wedge under Oblique Shortening

2019 ◽  
pp. 5-30 ◽  
Author(s):  
Elena Konstantinovskaya ◽  
Gennady Ivanov ◽  
Jean-Louis Feybesse ◽  
Jean-Luc Lescuyer
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Structural Features ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Oblique Collision ◽  
Fold And Thrust Belt ◽  
Thrust Tectonics ◽  
Oblique Convergence ◽  
Longitudinal Variations

The west-verging fold and thrust belt of the Central Labrador Trough originated as a part of the New Quebec Orogen from rift inversion as a result of oblique collision and dextral transpression between the Archean Superior craton and the Archean block of the Core Zone during the Trans-Hudson orogeny (1.82−1.77 Ga). The structures associated with dextral transpression are well established in the northern segment of the orogen but not in the central part. We present new field structural observations along the ca. 70 km long W−E Minowean-Romanet transect that include not only elements of thrust tectonics but also previously undocumented examples of strike-slip shear zones and late brittle, semi-brittle and ductile extensional structures which occurred both in the frontal and rear parts of the thrust wedge. The newly described low-angle mineral lineation, axes of cylindrical folds and dextral mylonitic shear zones in the footwall of the Romanet Fault are oriented subparallel to the orogen and reflect the early phase of oblique convergence. Mineral lineations and striations on planes of normal faults in the hanging wall of the Romanet Fault are oriented orthogonal to the orogen and correspond to a later phase of exhumation driven by the combined effects of erosion and underplating. To explain the increase in the degree of exhumation along the orogen in the study area from NW to SE, we propose a model of strain partitioning and differential exhumation that resulted from longitudinal variations of shortening and erosion under an oblique convergence setting.RÉSUMÉLa partie centrale de la ceinture de plissement et de chevauchement de la Fosse du Labrador de vergence vers l’ouest fait partie intégrante de l’Orogène du Nouveau-Québec, et résulte de la collision oblique avec transpression dextre entre le craton Supérieur archéen et le bloc archéen de la Zone noyau pendant l’Orogenèse trans-hudsonienne (1.82−1.77 Ga). Les structures associées à la transpression dextre sont bien établies dans la partie nord de l’orogène mais pas dans la partie centrale. Nous présentons de nouvelles observations structurales de terrain le long de la traverse ouest−est Minowean-Romanet d’environ 70 km de long, qui comprennent non seulement des évidences de tectonique de chevauchement, mais également des exemples encore non documentés de zones de cisaillement ductile et de structures d’extension fragiles, demi-fragiles et ductiles à la fois dans les parties frontales et arrière du prisme d’accrétion tectonique. La linéation minérale à faible plongement récemment décrite, les axes de plis cylindriques et les zones de cisaillement mylonitique dextre dans le compartiment inférieur de la faille de Romanet sont subparallèles à l’orogène et reflètent une phase précoce de la convergence oblique. La linéation et les stries minérales sur les plans des failles normales dans le compartiment supérieur de la faille de Romanet sont orientées orthogonalement à l’orogène et correspondent à la phase ultérieure d’exhumation induite par les effets combinés de l’érosion et de l’accrétion basale. Pour expliquer l’augmentation du degré d’exhumation le long de l’orogène du nord-ouest au sud-est dans la zone d’étude, nous proposons un modèle de partitionnement de la déformation et de l’exhumation différentielle résultant des variations longitudinales du raccourcissement et de l’érosion dans un contexte de convergence oblique.

scholarly journals Impact of Timanian thrusts on the Phanerozoic tectonic history of Svalbard

2020 ◽  
Author(s):  
Jean-Baptiste Koehl
Keyword(s):  
Fault Zone ◽  
Barents Sea ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Tectonic Event ◽  
Svalbard Archipelago ◽  
Basement Rocks ◽  
Caledonian Orogeny ◽  
Early Cenozoic ◽  
Northwestern Russia

<p>Despite more than a century of investigation, the relationship between basement rocks throughout the Svalbard Archipelago is still a mystery. Though these rocks display similar geochronological ages, they show significantly different metamorphic grades and structures. Thus far, Svalbard was believed to be composed of three terranes of rocks formed hundreds–thousands of kilometers apart and accreted in the mid-Paleozoic during the Caledonian and Ellesmerian orogenies.</p><p>New evidence from seismic, gravimetric, aeromagnetic, seismological, bathymetric, and field data show that these terranes might have already been juxtaposed in the late Neoproterozoic. Notably, the data show that at least three–four, crustal-scale, WNW–ESE-striking fault systems segment Spitsbergen and merge with Timanian thrusts in the northern Barents Sea and northwestern Russia. These thrusts were reactivated as and/or overprinted by sinistral-reverse oblique-slip faults and partly folded during the Caledonian Orogeny and Eurekan tectonic event, and reactivated as and/or overprinted by sinistral-normal faults during Devonian–Mississippian extensional collapse of the Caledonides, thus offsetting N–S-trending Caledonian grain and post-Caledonian basins, and explaining the juxtaposition of basement rocks with seemingly different origin.</p><p>The presence of Timanian faults explains basement heterogeneities throughout the Svalbard Archipelago, strain partitioning during the Caledonian Orogeny and Eurekan tectonic event and, thus, the western vergence of early Cenozoic folds in Devonian rocks in central–northern Spitsbergen (previously ascribed to the Late Devonian Ellesmerian Orogeny) and the arch shape of the early Cenozoic West Spitsbergen Fold-and-Thrust Belt in Brøggerhalvøya, the distribution of Mississippian rocks and Early Cretaceous intrusions along a WNW–ESE-trending axis in central Spitsbergen, the transport of Svalbard in the Cenozoic from next to Greenland to its present position (c. 400 km southwards), the strike and location of transform faults and oceanic core complexes and gas leakage along the Vestnesa Ridge west of Spitsbergen, the continental nature and NW–SE strike of basement fabrics in the Hovgård Ridge between Greenland and Svalbard, and the occurrence of recent (< 100 years old) earthquakes in Storfjorden and Heer Land in eastern Svalbard.</p><p>Further implications of this work are that the tectonic plates constituting present-day Arctic regions (Laurentia and Baltica) have retained their current geometry for the past 600 Ma, that the Timanian Orogeny extended from northwestern Russia to Svalbard, Greenland and, potentially, Arctic Canada, that the De Geer Zone does not exist, that the Billefjorden Fault Zone (Svalbard) and the Great Glen Fault (Scotland) were not part of the same fault complex, and that the Harder Fjord Fault Zone (northern Greenland) possibly initiated (or was reactivated) as a Timanian thrust.</p>

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