Coeval development of extensional and contractional features along transform margins: insights from the Diaz Marginal Ridge

2021 ◽  
pp. SP524-2021-88
Author(s):  
D. A. Paton ◽  
E. M. Mortimer ◽  
P. Markwick ◽  
J. Khan ◽  
A. Davids ◽  
...  
Keyword(s):  
Structural Model ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Origin And Evolution ◽  
Existing Structures ◽  
Structural Inversion ◽  
Horizontal Strain ◽  
Minimum Stress ◽  
Cape Fold Belt ◽  
Transform Margin

AbstractThe Diaz Marginal Ridge (DMR), on the southern transform margin of South Africa, is a bathymetric feature parallel to the Agulhas Falkland Fracture Zone (AFFZ) that has long been considered an archetype marginal ridge; and yet its origin and evolution remains unconstrained. Using recently acquired seismic data we present a new structural interpretation of the DMR and its association with the evolution of both the AFFZ and the Southern Outeniqua Basin. In contrast to previous scenarios invoking thermo-mechanical explanations for its evolution, we observe a more straightforward structural model in which the genesis of the DMR results from the structural inversion of a Jurassic rift basin. This inversion resulted in the progressive onlap of latest Valanginian-Hauterivian aged stratigraphic units, important for the formation of stratigraphic plays of the recent Brulpadda discovery.Paradoxically, this contraction is contemporaneous with renewed extension observed in the inboard normal faults. The orientation of the DMR and inboard structures have been demonstrated to be controlled by the underlying Cape Fold Belt (CFB) fabric. The onset of motion across the AFFZ shear system led to east-west orientated maximum stress and north-south orientated minimum stress. We propose this stress re-orientation resulted in strain partitioning across existing structures whereby in addition to strike-slip on the AFFZ there was coeval extension and contraction, the nature of which was determined by fault orientation. The fault orientation in turn was controlled by a change in orientation of the underlying CFB. Our model provides new insights into the interplay of changes in regional stress orientation with basement fabric and localised magmatism along an evolving transform. The application of horizontal strain partitioning can provide an explanation of similar features observed on other transform margins.

scholarly journals Structural Inversion Magnitude and its Impacts on the Hydrocarbon Accumulation

2019 ◽  
Vol 3 (2) ◽  
pp. 1-8
Author(s):  
Mohamed G. El-Behiry ◽  
Adly H. D. El-Nikhely ◽  
Bassem M. El Sayed
Keyword(s):  
Source Rock ◽  
Structural Model ◽  
Western Desert ◽  
Normal Faults ◽  
Structural Restoration ◽  
Structural Geometry ◽  
Strong Inversion ◽  
Structural Inversion ◽  
Half Graben ◽  
Structure Geometry

AbstractWest Wadi El-Rayan is located in the Western Desert at about 140 km SE of Cairo. Also, it lies between Gindi basin to the east and Abu Gharadig basin to the west. In order to construct a 3D structural model and to delineate the subsurface structure styles of the area, seismic structural interpretation and structural restoration are used. The structural geometry within the area is inverted half-graben, since the area was controlled by reactivation of older faults. The magnitude of the inversion-related shortening in the study area was estimated and was suggested to be strong. The result of the strong inversion magnitude occurred toward northeast of the study area can be concluded that, the area suffered shortening and part of the Jurassic / Early Cretaceous normal faults are reactivated as reverse faults. Also the cap, the main reservoirs and the source rock sections are brought to the surface and thus breached, as well any previous mature source rock becoming non-generative where the dry wells are located. However, any less severe inversion structure in this case where producing wells are located that remain buried and will have a better chance or preserving the structure geometry and therefore top and lateral seal.

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.

Quantifying fault reactivation risk in the western Gippsland Basin using geomechanical modelling

2013 ◽  
Vol 53 (1) ◽  
pp. 255 ◽  
Author(s):  
Ernest Swierczek ◽  
Cui Zhen-dong ◽  
Simon Holford ◽  
Guillaume Backe ◽  
Rosalind King ◽  
...  
Keyword(s):  
Structural Model ◽  
Strike Slip ◽  
Fault Reactivation ◽  
Fault System ◽  
Co2 Injection ◽  
Normal Faults ◽  
Surface Geometry ◽  
Northern Margin ◽  
Fault Surface ◽  
Gippsland Basin

The Rosedale Fault System (RFS) bounds the northern margin of the Gippsland Basin on the Southern Australian Margin. It comprises an anastomosing system of large, Cretaceous-age normal faults that have been variably reactivated during mid Eocene-Recent inversion. A number of large oil and gas fields are located in anticlinal traps associated with the RFS, and in the future these fields may be considered as potential storage sites for captured CO2. Given the evidence for geologically recent fault reactivation along the RFS, it is thus necessary to evaluate the potential impacts of CO2 injection on fault stability. The analysis and interpretation of 3D seismic data allowed the authors to create a detailed structural model of the western section of the RFS. Petroleum geomechanical data indicates that the in-situ stress in this region is characterised by hybrid strike-slip to reverse faulting conditions where SHmax (40.5 MPa/km) > SV (21 MPa/km) ~ Shmin (20 MPa/km). The authors performed geomechanical modelling to assess the likelihood of fault reactivation assuming that both strike-slip and reverse-stress faulting regimes exist in the study area. The authors’ results indicate that the northwest to southeast and east-northeast to west-southwest trending segments of the RFS are presently at moderate and high risks of reactivation. The authors’ results highlight the importance of fault surface geometry in influencing fault reactivation potential, and show that detailed structural models of potential storage sites must be developed to aid risk assessments before injection of CO2.

scholarly journals Impact of basement thrust faults on low-angle normal faults and rift basin evolution: a case study in the Enping sag, Pearl River Basin

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2327-2350
Author(s):  
Chao Deng ◽  
Rixiang Zhu ◽  
Jianhui Han ◽  
Yu Shu ◽  
Yuxiang Wu ◽  
...  
Keyword(s):  
Growth Pattern ◽  
Northern South China Sea ◽  
Spatial Relationship ◽  
Normal Faults ◽  
Rift System ◽  
Nucleation Density ◽  
Thrust Faults ◽  
Pearl River Basin ◽  
Existing Structures ◽  
The Impact

Abstract. Reactivation of pre-existing structures and their influence on subsequent rift evolution have been extensively analysed in previous research on rifts that experienced multiple phases of rifting, where pre-existing structures were deemed to affect nucleation, density, strike orientation, and displacement of newly formed normal faults during later rifting stages. However, previous studies paid less attention to the extensional structures superimposing onto an earlier compressional background, leading to a lack of understanding of, e.g. the reactivation and growth pattern of pre-existing thrust faults as low-angle normal faults and the impact of pre-existing thrust faults on newly formed high-angle faults and subsequent rift structures. This study investigating the spatial relationship between intra-basement thrust and rift-related faults in the Enping sag, in the northern South China Sea, indicates that the rift system is built on the previously deformed basement with pervasive thrusting structures and that the low-angle major fault of the study area results from reactivation of intra-basement thrust faults. It also implies that the reactivation mode of basement thrust faults is dependent on the overall strain distribution across rifts, the scale of basement thrust faults, and the strain shadow zone. In addition, reactivated basement thrust faults influence the nucleation, dip, and displacement of nearby new faults, causing them to nucleate at or merge into downwards it, which is representative of the coupled and decoupled growth models of reactivated thrust faults and nearby new faults. This work not only provides insights into the growth pattern of rift-related faults interacting with reactivated low-angle faults but also has broader implications for how basement thrust faults influence rift structures, normal fault evolution, and syn-rift stratigraphy.

scholarly journals Late Carboniferous dextral transpressional reactivation of the crustal-scale Walls Boundary Fault, Shetland: the role of pre-existing structures and lithological heterogeneities

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-078
Author(s):  
Timothy B. Armitage ◽  
Lee M. Watts ◽  
Robert E. Holdsworth ◽  
Robin A. Strachan
Keyword(s):  
Late Carboniferous ◽  
Strain Partitioning ◽  
Boundary Fault ◽  
Existing Structures ◽  
Tectonic Events ◽  
Tectonic Environment ◽  
Western Side ◽  
East West ◽  
Lithological Heterogeneity

The Walls Boundary Fault in Shetland, Scotland, formed during the Ordovician–Devonian Caledonian orogeny and underwent dextral reactivation in the Late Carboniferous. In a well-exposed section at Ollaberry, westerly verging, gently plunging regional folds in the Neoproterozoic Queyfirth Group on the western side of the Walls Boundary Fault are overprinted by faults and steeply plunging Z-shaped brittle–ductile folds that indicate contemporaneous right-lateral and top-to-the-west reverse displacement. East of the Walls Boundary Fault, the Early Silurian Graven granodiorite complex exhibits fault-parallel fractures with Riedel, P and conjugate shears indicating north–south-striking dextral deformation and an additional contemporaneous component of east–west shortening. In the Queyfirth Group, the structures are arranged in geometrically and kinematically distinct fault-bounded domains that are interpreted to result from two superimposed tectonic events, the youngest of which displays evidence for bulk dextral transpressional strain partitioning into end-member wrench and contractional strain domains. During dextral transpressional deformation, strain was focused into pelite horizons and favourably aligned pre-existing structures, leaving relicts of older deformation in more competent lithologies. This study highlights the importance of pre-existing structures and lithological heterogeneity during reactivation and suggests the development of a regional transpressional tectonic environment during the Late Carboniferous on the Shetland Platform.

Role of Basement Structural Inheritance and Strike-Slip Fault Dynamics in the Formation of the Pataz Gold Vein System, Eastern Andean Cordillera, Northern Peru

2021 ◽  
Author(s):  
Daniel Wiemer ◽  
Steffen G. Hagemann ◽  
Nicolas Thébaud ◽  
Carlos Villanes
Keyword(s):  
Structural Control ◽  
Structural Model ◽  
Gold Mineralization ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Vein System ◽  
Structural Inheritance ◽  
Andean Cordillera ◽  
Northern Peru

Abstract New regional- to vein-scale geologic mapping and structural analysis of the Carboniferous Pataz gold vein system (~10 Moz Au) reveal critical insights into the structural control on gold mineralization along the Eastern Andean Cordillera of northern Peru. The Pataz basement comprises continental volcanic arc and marginal to marine sedimentary rocks, which experienced intensive D2 deformation associated with Late Famatinian northeast to southwest compressive fold-and-thrust belt development. The D2 event produced an E-NE–dipping structural grain, including (1) tilted and F2 folded S1 foliations, (2) local F2 axial planar S2 foliations, and (3) subparallel D2 thrust faults. Intrusions, constituting the ca. 342 to 332 Ma (Mississippian) Pataz batholith, were emplaced along strike of the prominent Río Marañón fault and inherited the D2 basement structures, as evident in the orientation of suprasolidus magmatic flow zones and intrusive contacts within the batholith. Progressive horst-and-graben development affecting the volcanic carapace of the Pataz batholith records late syn- to postmagmatic uplift and transition into a NW-SE–extensional regime. We show that the E-NE–dipping, batholith-hosted gold vein system formed through synchronous activation of two geometric fault-fill vein types, following (1) the moderately E-NE–dipping D2 basement-inherited competency contrasts within the batholith and (2) shallow NE-dipping Andersonian footwall thrusts, during NE-directed shortening (D3a). Both geometric vein types display an early paragenetic stage (I) of quartz-pyrite, progressing texturally from hydraulic breccia into crack-seal laminated shear veins. A second (II), undeformed quartz-pyrite-sphalerite-galena paragenetic stage is observed to fill previously established dilational sites adjacent to newly formed D3b normal faults, which likely formed during regional NW-SE–extensional horst-graben development. Kinematics and relative timing indicate that, upon batholith solidification, D3a transpressional dextral strike-slip ruptures along the Río Marañón fault superimposed a lower-order Riedel-type fault system. Fluid-assisted fault activation preferentially impinged on the D2 basement-inherited competency contrasts within the batholith. Subsequent transition into a transtensional regime led to the D3b normal faulting, providing a feeder system for stage II fluid influx. The tectonic switch may be explained either by increasing tensile strain accommodation upon progressive strike-slip movement within a regional dilational jog or by larger-scale crustal relaxation of the late Gondwana margin upon final Pangea assembly. Our new structural model for the Pataz vein system evolution highlights the importance of basement structural inheritance in controlling the localization of gold mineralization along polycyclic supercontinent margins. We provide valuable insights for exploration targeting of complex vein arrays within rheologically heterogeneous host rocks.

Miocene structural inversion of the Adjara-Trialeti back-arc basin as a far-field effect of the Arabia-Eurasia collision

2021 ◽  
Author(s):  
Thomas Gusmeo ◽  
William Cavazza ◽  
Victor Alania ◽  
Onise Enukidze ◽  
Massimiliano Zattin ◽  
...  
Keyword(s):  
Late Miocene ◽  
Field Effect ◽  
Stress Transfer ◽  
Normal Faults ◽  
Far Field ◽  
Magmatic Arc ◽  
Late Middle Miocene ◽  
Structural Inversion ◽  
Lesser Caucasus ◽  
Back Arc

<p>Young back-arc rift basins, because of the not yet dissipated extensional thermal signature, can be easily inverted following changes in the geodynamic regime and/or far-field stress transmission. Structural inversion of such basins mainly develops through reactivation of normal faults, particularly if the latter are favourably oriented with respect to the direction of stress transfer. The Adjara-Trialeti fold-and-thrust belt of SW Georgia is an example of this mechanism, resulting from the structural inversion of a continental back-arc rift basin developed on the upper plate of the northern Neotethys slab in Paleogene times, behind the Pontides-Lesser Caucasus magmatic arc. New low-temperature thermochronological data [apatite fission-track (AFT) and (U-Th)/He (AHe) analyses] were obtained from a number of samples, collected across the Adjara-Trialeti belt from the former sedimentary fill of the basin and from syn-rift plutons. AFT central ages range between 46 and 15 Ma, while AHe ages cluster mainly between 10 and 3 Ma. Thermal modelling, integrating AFT and AHe data with independent geological constraints (e.g. depositional/intrusion age, other geochronological data, thermal maturity indicators and stratigraphic relationships), clearly indicates that the Adjara-Trialeti back-arc basin was inverted starting from the late Middle Miocene, at 14-10 Ma. This result is corroborated by many independent geological evidences, found for example in the adjacent Rioni, Kartli and Kura foreland basins and in the eastern Black Sea offshore, which all suggest a Middle-Late Miocene phase of deformation linked with the Adjara-Trialeti FTB building. Adjara-Trialeti structural inversion can be associated with the widespread Middle-to-Late Miocene phase of shortening and exhumation that is recognised from the eastern Pontides to the Lesser Caucasus, the Talysh and the Alborz ranges. This tectonic phase can in turn be interpreted as a far-field effect of the Arabia-Eurasia collision, developed along the Bitlis suture hundreds of kilometres to the south.</p>

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>

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