Principal Displacement Zone Research Articles

Evolution of the transtensional Barreirinhas pull-apart system in the Brazilian Equatorial margin and its correlation with the African conjugate counterpart

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

Characteristics and genesis of the Zhongnan Fault Zone in the South China Sea oceanic basin: Insights from an integrated analysis of multibeam bathymetric and 2D multichannel seismic data

The Zhongnan Fault Zone (ZFZ) is a large-scale tectonic belt in the South China Sea (SCS) oceanic basin and plays an important role in the formation and evolution of the basin. Despite numerous studies over the past few decades, debates persist regarding its location, orientation, nature, time of activity, and genesis. In this study, we evaluate our findings on the characteristics and origin of the fault zone through an integrated analysis of multibeam bathymetric and 2D multichannel seismic data. Our results reveal the ZFZ as a fault zone approximately 400 km long and 50–90 km wide, situated between the east subbasin (ESB) and southwest subbasin (SWSB) of the SCS. The fault zone is oriented N8°W, roughly perpendicular to and laterally displacing the relict spreading center and related spreading lineaments. Bounded by discontinuous linear seamounts, the fault zone comprises two V-shaped subparallel pull-apart basins and a separating basement high. Steeply dipping (>60°) normal basement-involved faults bound these pull-apart basins, forming typical negative flower structures. Numerous northeast-oriented en-echelon linear bathymetric highs within the fault zone are identified as secondary antithetic shears (P′ shears). These shears are characterized by their orientation relative to the principal displacement zones defined along the pull-apart basins. The ZFZ exhibits differences from the adjacent subbasins in water depth, basement burial, stratal thickness, and seismic stratigraphic characteristics. Five seismic sequences (S1–S5 upward) in the ZFZ and nearby ESB and SWSB are defined, dating to the Early Miocene synspreading (S1) and the Middle Miocene to Recent postspreading (S2–S5) stages, respectively. The difficulty in correlating seismic facies in sequences S1–S3, compared with the comparable seismic facies in sequences S4–S5 between the ZFZ and adjacent subbasins, suggests a horizontal displacement during the synspreading and early postspreading stages. We propose that the ZFZ functioned as a right-lateral transform fault zone during the synspreading period (the Early Miocene, approximately 24–16 Ma) of the SWSB and transitioned into a left-lateral strike-slip fault zone during the successive early postspreading period (the Middle-Late Miocene, approximately 16–5.3 Ma).

Geometry and formation mechanism of tension gashes and their implication on the hydrocarbon accumulation in the deep-seated strata of sedimentary basin: A case from Shunnan area of Tarim Basin

With the theoretical and technological developments related to cratonic strike-slip faults, the Shuntuoguole Low Uplift in the Tarim Basin has attracted considerable attention recently. Affected by multi-stage tectonic movements, the strike-slip faults have controlled the distribution of hydrocarbon resources owing to the special fault characteristics and fault-related structures. In contrast, the kinematics and formation mechanism of strike-slip faults in buried sedimentary basins are difficult to investigate, limiting the discussion of these faults and hydrocarbon accumulation. In this study, we identified the characteristics of massive sigmoidal tension gashes (STGs) that formed in the Shunnan area of the Tarim Basin. High-resolution three-dimensional seismic data and attribute analyses were used to investigate their geometric and kinematic characteristics. Then, the stress state of each point of the STGs was calculated using seismic curvature attributes. Finally, the formation mechanism of the STGs and their roles in controlling hydrocarbon migration and accumulation were discussed. The results suggest that: (1) the STGs developed in the Shunnan area have a wide distribution, with a tensile fault arranged in an en échelon pattern, showing an S-shaped bending. These STGs formed in multiple stages, and differential rotation occurred along the direction of strike-slip stress during formation. (2) Near the principal displacement zone of the strike-slip faults, the stress value of the STGs was higher, gradually decreasing at both ends. The shallow layer deformation was greater than the deep layer deformation. (3) STGs are critical for connecting source rocks, migrating oil and gas, sealing horizontally, and developing efficient reservoirs. This study not only provides seismic evidence for the formation and evolution of super large STGs, but also provides certain guidance for oil and gas exploration in this area.

Characteristics of the gold-bearing and barren quartz veins at the Zaylik-Sarilar epithermal deposit, Ahar-Arasbaran Zone, NW Iran: Evidence from mineralogy, alteration, texture and fluid inclusion

The Zaylik-Sarilar epithermal deposit is located 35 km southeast of Ahar in the Ahar-Arasbaran Zone in the Alborz-Azerbaijan Magmatic Belt, NW Iran. Exposed rocks in the Zaylik-Sarilar deposit are mainly composed of Eocene volcanic rocks and Miocene dacite-rhyodacite that are intruded by younger intrusions. The deposit occurs within a sequence of Eocene porphyritic andesite and andesitic lithic tuff. Mineralization occurs as open space filling, taking place as irregular veins, veinlets, and hydrothermal breccias. The mineralization zones can be categorized into two main groups according to sulfides and sulfosalts mineralogy, alteration assemblages, ore textures, and fluid inclusion data. The first group consists of gold-bearing quartz-sulfide ± breccia veins, silicified-phyllic ± argillic zones, and a few quartz-calcite veins. The second group is composed of barren milky (or white) quartz veins, silicified lithocaps, and argillic-kaolinite ± silicic zones. Pyrite, chalcopyrite, bornite, galena, sphalerite, and Au-Ag sulfosalts were identified in ore paragenesis of the gold-bearing veins. Pyrite is the main sulfide mineral in the barren quartz veins and silicified lithocaps. Gold and silver were enriched during oxidation and supergene alteration of the gold-bearing veins. Textural evidences from the gold-bearing veins, such as mosaic breccia monomicts, floating clast breccias, hydrothermal breccias, colloform-crustiform textures, ginguro bands, dendrite textures, and rarely lattice- and parallel-bladed calcite replacement textures, suggest that boiling occurred in the veins. Comb, cockade, reed molds, zonal, and feathery textures are common in the barren veins and silicified lithocaps. Fluid inclusion data show a decreasing trend in salinity and homogenization temperature (Th) from the gold-bearing quartz veins to the barren ones. The average salinity and homogenization temperature (Th) of fluid inclusions from the gold-bearing veins are 1.05 wt% NaCl equiv. and 297 °C, respectively; higher than the average salinity (0.68 wt% NaCl equiv.) and homogenization temperature (192 °C) of fluid inclusions from the barren quartz veins. Th versus salinity diagram suggests that boiling was the main mechanism of ore deposition in the gold-bearing quartz veins and silicified zones. These data propose that the barren quartz veins and silicified lithocaps were formed by cooling. A combination of the geologic, mineralogic, alteration, and fluid inclusion data from the Zaylik-Sarilar deposit represents an epithermal system of low-sulfidation type. Structurally, mineralization has been controlled through the NW-trending strike-slip principal displacement zone and it’s subsidiary Riedel fractures in response to a N-trending compression in the Arabia-Eurasia collision zone.

The effect of tectonic subsidence on the evolution of depocenters and development of the Mundaú sub-basin, Brazilian Equatorial margin

Located on the Brazilian Equatorial Margin, the Mundaú Sub-Basin is the only offshore hydrocarbon-producing region of the Ceará Basin. The origin and evolution of the Mundaú Sub-basin are a consequence of the rupture of the Pangea supercontinent during the Early Cretaceous, which led to the opening and development of the Equatorial Atlantic Ocean. This area has been considered a new exploration frontier, promoting research to be developed in recent years. However, the interactions between transtensive events and spatial-temporal distributions of tectonic subsidence have been poorly studied. To cover this gap, fifty-seven wells and approximately 5800 km of 2D seismic lines were analyzed to understand these events. From these data, stratigraphic and structural interpretations were performed throughout the sub-basin, enabling the construction of 43 pseudo-wells. Using descompactation of the wells and pseudo-wells using the backstripping method, it was possible to reconstruct seven tectonic phases for the Sub-Basin, which correspond to the rift sequence (RP01, RP02, and RP03), the transition sequence (BP01), and the drift sequence (DP01, DP02, and DP03). Four sets of faults of three zones of the three zones (WZ, CZ and EZ) proposed for the Mundaú Sub-Basin were also analyzed. The faults are distributed in two orthogonal families, formed in two distinct events. Older R and P faults, respectively trending NWW-SEE and NNESSW, formed during RP01 (first event). Younger R and P faults, respectively trending NNW-SSE and NEE-SWW, formed during RP02 (second event). Tectonic reconstruction revealed the diachronic formation of two depocenters, one in the West Zone (WZ) during RP01, and the other in the Central Zone (CZ) during RP02. Despite the intense tectonic activity in WZ and CZ, the East Zone (EZ) showed low subsidence rates and little development during the entire rift phase. In turn, BP01 showed faster subsidence rates when compared to RP03, indicating tectonic influence even during the breakup phase. Finally, the drift phase showed the lowest subsidence rates, spatially distributed in an opposite pattern to the rift phase. From these results, a rotation of the Principal Displacement Zone (PDZ) was identified, with initial parallel motion vectors, forming the WZ depocenter and generating the first fault family during RP01; after RP02, motion vectors were oblique, forming the second depocenter in CZ and generating the second fault family. Significant thermal control associated with magmatic events was identified during the drift phase. This study also describes the main structures formed along with the overlap of parallel and oblique PDZ displacement.

DEM analysis of passive arching in a shallow trapdoor under eccentric loading

This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models. The numerical models were validated by comparison with laboratory test results. The deformation pattern, soil arching ratio, force chain distribution, and coordination number under various surcharge magnitudes and deviation distances were analyzed. The numerical results showed that the deformation diagram of soil particles can be divided into three zones: principal displacement zone, transition zone, and static zone. With an increase in the surcharge magnitude, the range of the principal displacement zone decreased, but the range of the transition region increased. The curve of the soil arching ratio on the trapdoor can be divided into three phases, which can be well characterized by the tangent modulus. The passive arching effect is degraded by a surcharge. The ultimate soil arching ratio could be approximated as a W-shaped distribution along the +x-direction. With an increase in the trapdoor displacement, the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape. The most powerful force on the trapdoor was mainly distributed on its edge. The average coordination number decreased gradually as the trapdoor moved upward.

Magnetic fabric of deformed Quaternary sediments: contributions to the understanding of the neotectonic activity in the surroundings of the Aburrá Valley, Central Cordillera, Colombia

The origin of the Aburrá Valley (AV) is proposed as a set of coalescent tectonic subbasins located along the northern portion of the Central Cordillera of Colombia, the Northern Andes of Colombia. The Itagüí, Medellín, Bello, and Barbosa subbasins have developed between the Romeral Shear Zone (RSZ) and the Antioqueño Batholith starting in the Late Cenozoic. The aim of this study is to contribute to the understanding of the AV neotectonic framework using the anisotropy of magnetic susceptibility (AMS) and structural analysis. For this, we measure the magnetic fabric ellipsoid shape of faulted sediments and compare them with the geometry and kinematics of fault planes to determine their relationship with the present-day stress field and the regional fault architecture. The principal directions of the elongation axes along the La Brizuela and Yarumalito sites were NE-SW, following the magnetic lineation trend and marking a normal displacement with a dextral component. A marked NW-SE magnetic cleavage was found for the La Caimana site along a strike-slip tectonic setting. Holocene ruptures of the principal displacement zone (i.e., the RSZ) and their surroundings, may indicate normal faulting, with fault bends and steps over basins controlled primarily by R´ and P structures. Moreover, the active faults located to the east of the AV indicate post Plio-Pleistocene deformations with normal faulting through 90/80 to 150/70 antithetic faults. This work identifies the AMS technique as a powerful tool, for understanding the neotectonic framework along urban and surrounding areas.

Further evidence for the East Coast fault system and faults associated with the Summerville restraining bend and their possible relationship to the 1886 Charleston, South Carolina, earthquake, USA

The integration of aeromagnetic, LiDAR, and previously acquired seismic-reflection data and surficial geologic maps supports the existence of the East Coast fault system ( and faults associated with its 12⁰ Summerville restraining bend beneath the South Carolina Coastal Plain. Aeromagnetic data revealed a 10- to 15-km-wide zone of subtle, 22- to 35-km-long linear magnetic anomalies trending ~N10°E across the southern meizoseismal area of the 1886 Charleston earthquake that we postulate are associated with Cenozoic low-displacement brittle faults in the crystalline basement west of Charleston. We hypothesize that lineaments ML4 and ML5 represent the principal displacement zone along the southern end of the ECFS because they coincide with steeply dipping, west-side-up buried faults interpreted from previously acquired seismic-reflection profiles and a ~320-m dextral offset in the Brownsville Pleistocene beach ridge deposit. The alignment of the NNE-SSW-oriented Edisto dome, uplift along releveling line 9, gently upwarped longitudinal profiles along the Caw Caw and Horse Savanna swamps, local incision along the Ashley River, and exposures of the early Oligocene Ashley Formation near the incised part of the Ashley River support Quaternary uplift along the southern ECFS. The 12⁰ change in trend formed by lineaments ML4 and ML5 supports the existence of the Summerville restraining bend in the ECFS, east of which are numerous ENE-WSW- to NW-SE-oriented LiDAR lineaments that we postulate are surface expressions of faults that formed to compensate for the increased compression produced by dextral motion along the bend. Sinistral displacement along one of these proposed faults associated with the ~40-km-long, east-west-oriented Deer Park lineament may have produced the main shock of the 1886 Charleston earthquake.
 

Architecture and tectonostratigraphic evolution of the Pescadero Basin Complex, southern Gulf of California: Analysis of high-resolution bathymetry data and seismic reflection profiles

The Pescadero Basin Complex (PBC) comprises three distinctive rhomb-shaped pull-apart basins separated by short and highly overlapped transform faults. Multibeam bathymetric data collected from ship at 40-m resolution, combined with the interpretation of three 2D high-resolution multichannel seismic reflection profiles, were used to establish the architecture of the PBC. Detailed mapping and cross-sectional kinematic modeling based on the seismic images of the North Pescadero Basin reveal a highly evolved pull-part geometry, characterized by a well defined ∼1.8 km-wide axial graben extending ∼32 km in a NNE-SSW direction. Among the fundamental elements controlling basin architecture and evolution of the PBC are the geometry of the initial configuration of the master strike-slip fault step-over and fault dynamics, which may cause transients in fault system activity and basin reconfigurations. Structural analyses carried out in this study point out the PBC pull-apart basins developed under sustained transtensional deformation, where the relative motion of the crustal blocks is oblique and divergent to the transforms or principal displacement zones. Cross-cutting relationships between the main fault systems controlling basin's subsidence and evolution, indicate that underdeveloped basin-crossing faults terminate against basin bounding normal faults, suggesting that ongoing pull-apart rifting continues to dominate basin evolution of the PBC. Furthermore, we propose that the undeveloped cross-basin faults of the PBC initiated as synthetic Riedel faults that, with progressive deformation along the divergent-wrench fault zone, rotated clockwise around a vertical axis to acquire their present orientation oblique to the master bounding transforms. Basin-crossing faults with lesser obliquities control the subsidence along the basin-side faulted segments of the narrow graben systems that characterize the plate boundary at the corners of the PBC pull-apart basins. These narrow transtensional synforms may have served as connections facilitating marine waters to flood the PBC during the early stages of formation of the Gulf of California.

Rus detachment in Dammam Dome, Eastern Saudi Arabia: a new soft-sediment structure as a ‘sensitive stress sensor’ for the Zagros collision

AbstractThis paper describes in detail hydroplastic structures, which are ‘odd’ kinematic indicators in the basal part of the Eocene Middle Rus Formation. Such structures were previously ignored or falsely interpreted. These hydroplastic structures are found in the massive limestone exposures on the King Fahd University of Petroleum and Minerals (KFUPM) campus. They occur in relation to a principal displacement zone along the boundary/interface between the Lower/Middle Rus, which is referred to as the Rus soft-sediment detachment. The structures are fist-sized vugs associated with carrot- or comet-trail imprints (VCT structures) which were previously translated calcite geodes that have been weathered out. VCT structures show transport/slip towards the NNW (345°) and are found on flat to low-dipping surfaces classified as Y, R and P shears with respect to the orientation of the Rus detachment. Palaeostress analysis indicates an Andersonian transtension stress regime, though it does not facilitate the activation of the Rus soft-sediment detachment. Detachment activity occurred due to the negative effective principal stress σ3′ and the abnormally low frictional coefficient caused by fluid pressure. The soft-sediment Rus detachment can be considered a ‘sensitive stress sensor’ for the Zagros collision since it indicates the Arabian platform’s instability in the wider area of the Dammam Dome during the Late Eocene. This instability is attributed to the inception of the Zagros collision, which was previously considered to occur during the Oligocene based on the well-established pre-Neogene unconformity.

Structural architecture and tectonic evolution of Haimour block, Gulf of Aqaba, Egypt: An example of multiphase deformed stepover

A unique outcrop of a dilational NNE-oriented stepover takes place between two left-stepping NE sinistral faults at the Haimour block along the western margin of the Gulf of Aqaba basin. Detailed surface geological mapping was achieved in order to unravel structural architecture and deformation style of the Haimour stepover (HSO). The HSO comprises N- to NNE- oriented transtensional and normal faults that affect all the sedimentary succession including the syn-kinematic sediments. Contrarily, the southern part includes a remarkable push-up structure that comprises NNE-to NE-oriented compressional structures affecting the Upper Cretaceous rock units. The southern end of the HSO is marked by a NNE-oriented Principal Displacement Zone (PDZ), which encloses NNE- and NE-oriented sinistral faults. Structural analysis of field data considering the previous analogue and numerical models indicates a well-developed basin side-walls and basin cross-fault zone of the HSO. Additionally, divergent-oblique slip model (30° transtension) is suggested for the HSO. The proposed tectonic model of the HSO revealed that the initiation of the pull-apart basin took place during the Oligocene times concurrently with the opening of the Red Sea rift and continued to the Post-Miocene times. The outcomes of this study provide a model for architecture and evolution of similar structural style along Gulf of Aqaba and Dead Sea Transform. Moreover, the proposed architecture of the HSO should provide an analogue for subsurface mapping and exploration at strike-slip zones.

Deformation styles related to intraplate strike-slip fault systems of the Saharan-Tunisian Southern Atlas (North Africa): New kinematic models

The complex geometry and tectonic evolution of the Saharan-Tunisian Southern Atlas strike-slip fault systems, North Africa, have not been investigated comprehensively to date. This paper proposes new conceptual models to better understand the structural styles along these intraplate fault zones. We use a multidisciplinary approach including field observations, geological mapping, stress analysis and seismic data to investigate the development and interaction of major strike-slip fault segments. The regional fault system is dominated by the E-W trending Biskra, Alima, Orbata, Bouhedma and Chotts basement faults that constitute the Principal Displacement Zones (PDZs).Our analyses and interpretations reveal that each PDZ has a typical dextral strike-slip architecture comprising multi-scale fault segments that are linked through dilational and contractional stepovers/bends. During Mesozoic times, under NE-SW Shmin, the transtensional fault segments of Biskra and Alima formed the boundaries of the Khanguet Sidi Neji-Gafsa (KSG) Basin, which developed as a Z-shaped dextral releasing stepover. During the Cenozoic, the KSG Basin was inverted, under NW-SE SHmax, in response to the Africa-Eurasia convergence. This inversion occurred mainly along basin sidewalls by reactivation of the pre-existing normal-oblique faults as right-lateral transpressional shears. Further east, the E-W dextral strike-slip faults of Orbata and Bouhedma connected via a NE-SW restraining stepover.Finally, all E-W dextral strike-slip fault segments are associated with ENE right-stepping en echelon folds and Riedel shear patterns of different scales, in response to basement wrenching. Currently, most fault zones are still active with deep strike-slip earthquakes.

Geological model and development of the Cenozoic Wiang Pa Pao Basin, Chiang Rai Province, Northern Thailand, based on gravity data modelling and surface structural interpretation

3-D Inverse gravity modelling, constrained by surface geological data across the Neogene Wiang Pa Pao Basin (WPB), Northern Thailand, provides new subsurface models of the basin geometry and its structural development. The intermontaine WPB is seismically active and exhibits many geothermal sites; both are indicative of active fault zones. Six hundred thirty-six terrestrial gravity stations with ~500 m spacing were acquired. The residual Complete Bouguer Anomaly map (CBA) reveals an N–S elongate basin characterized by gravity lows bounded by gravity highs on the eastern margin of the basin (metasedimentary basement), and moderate gravity anomalies on the western margin (granitic basement). Structural edge detection revealed N–S trending faults along the eastern and western margins linked by NE–SW and NW–SE trending lineaments. The 3-D gravity model indicates an asymmetric graben; with a maximum depocenter depth of ~1300 m. Surface structure and seismicity confirm the gravity interpretation that the WPB is a dextral transtensional basin characterized by WSW–ENE trending R'-shears and NNE–SSW R-shears distributed in duplex-like geometries along the N–S trending principal displacement zone. The WPB displays unusually well-developed R’-shears, where Palaeozoic metasedimentary rocks in the basement and Cenozoic basin sediments are present, these faults disappear to the south, where the main N–S fault resides entirely within the granite. The WPB is associated with Cenozoic multi-phase rifting: in the Late Oligocene–Miocene, major rift basins formed under W–E extension, strongly influenced by WSW–ENE to NE–SW and NW–SE pre-existing trends. In the Latest Miocene–Recent, the younger basins, including the WPB, underwent dextral strike-slip along new and existing N–S dextral fault trends.

Spatial Characteristics and Controlling Factors of the Strike‐slip Fault Zones in the Northern Slope of Tazhong Uplift, Tarim Basin: Insight from 3D Seismic Data

AbstractThe detailed characteristics of the Paleozoic strike‐slip fault zones developed in the northern slope of Tazhong uplift are closely related to hydrocarbon explorations. In this study, five major strike‐slip fault zones that cut through the Cambrian‐Middle Devonian units are identified, by using 3D seismic data. Each of the strike‐slip fault zones is characterized by two styles of deformation, namely deeper strike‐slip faults and shallower en‐echelon faults. By counting the reverse separation of the horizon along the deeper faults, activity intensity on the deeper strike‐slip faults in the south is stronger than that on the northern ones. The angle between the strike of the shallower en‐echelon normal faults and the principal displacement zone (PDZ) below them is likely to have a tendency to decrease slightly from the south to the north, which may indicate that activity intensity on the shallower southern en‐echelon faults is stronger than that on the northern ones. Comparing the reverse separation along the deeper faults and the fault throw of the shallower faults, activity intensity of the Fault zone S1 is similar across different layers, while the activity intensity of the southern faults is larger than that of the northern ones. It is obvious that both the activity intensity of the same layer in different fault zones and different layers in the same fault zone have a macro characteristic in that the southern faults show stronger activity intensity than the northern ones. The Late Ordovician décollement layer developed in the Tazhong area and the peripheral tectonic events of the Tarim Basin have been considered two main factors in the differential deformation characteristics of the strike‐slip fault zones in the northern slope of Tazhong uplift. They controlled the differences in the multi‐level and multi‐stage deformations of the strike‐slip faults, respectively. In particular, peripheral tectonic events of the Tarim Basin were the dynamic source of the formatting and evolution of the strike‐slip fault zones, and good candidates to accommodate the differential activity intensity of these faults.

The Jal Az-Zor escarpment as a product of complex duplex folding and strike-slip tectonics; A new study in Kuwait, northeastern Arabian Peninsula

The origin of Jal Az-Zor escarpment has been equivocal due to limited exposure and subsurface data. The escarpment was assumed to be a result of differential weathering and erosion. Most recently mapping of basement lineaments suggested a deep fault system as a most likely cause. The aim of this article is to use shallow seismic data acquired across various locations along the escarpment to investigate the underlying geology, structural elements and link these features to surface observations.To understand the near subsurface geology, post-stack time processing was applied to 2D seismic data acquired recently in the area. The objective was to focus on the shallow intervals, represented by the Rus, Dammam and Kuwait Formations. The analyses revealed a train of tight concentric folds that increase in stage development towards the escarpment in the Dammam Formation. The shallower Kuwait Formation shows early stages of fault propagation folding as a result of the Kuwait Arch uplift towards the south of the escarpment. We suggest that friction along the Dammam Formation upper contact detachment planes increased towards the south, thus promoting the propagation of the fold reaching the surface, resulting in the Jal Az-Zor escarpment that we see today. Structural kinematic analysis suggests that the Jal Az-Zor escarpment is also a principal displacement zone (PDZ) that is dominated by dextral strike-slip motion and exhibits a series of restraining bends, positive-flower structures, and a horsetail splay. 2D structural restoration and balancing suggest a total shortening magnitude of approximately 6.25 km. Considering the Arabian and Eurasian plates velocity vectors, along with the relatively large amount of shortening, this deformation initiated during the early Pleistocene (Calabrian). The presence of tight concentric and fault propagation folds combined with dextral strike kinematics introduce new complexities into the structural styles and assemblages of the area otherwise thought to follow the overall northern Arabian Peninsula tectonics.

Tectonic evolution of the Cretaceous Gyeongsang Back-arc Basin, SE Korea: Transition from sinistral transtension to strike-slip kinematics

The Gyeongsang Basin, the largest Cretaceous nonmarine sedimentary basin in Korea, formed as a continental back-arc basin related to NNW-directed subduction of the (proto-) Pacific Plate underneath the Eurasia Plate. The basin can be divided into an earlier-formed western back-arc depression and a later-formed eastern volcanic arc platform. We investigated the basin evolution and the associated tectonic settings, largely based on an analysis of structures individuated in the field in the back-arc region. From 127 Ma, the basin initiated as a NNE-trending narrow depression bordered by NNE-striking sinistral faults, and then progressively expanded under a transtensional kinematics induced by progressive trench roll-back. Sinistral shearing of inherited NNE-striking structures played an important role in basin subsidence, and secondary WNW- to NW-striking transverse faults acted as normal faults. The NNE-striking principal displacement zone in the west of the basin runs along the western marginal area of the Jinju and Daegu domains and passes through the Uiseong domain from south to north, but most of this zone is now preserved as deep structures. Volcanic activity starting at ca. 115 Ma was characterized mainly by episodic basaltic eruptions occurring contemporaneously with back-arc deposition of a sedimentary sequence. After ca. 90 Ma, a transtensional kinematics changed to a strike-slip one, and the basin expansion and sedimentation in the back-arc region terminated. During the strike-slip event, rhyolitic-dacitic volcanism increased in intensity as a large NE-trending volcanic arc developed close to subduction zone and its loading caused the stratal flexure in the back-arc region, and the orientations of the shortening and stretching axes remained NW–SE and NE–SW, respectively. Additionally, continuing sinistral shear generated local depressions along the faults located in the west of the back-arc region and within the volcanic arc.

Analogue Modeling of Plate Rotation Effects in Transform Margins and Rift‐Transform Intersections

AbstractTransform margins are first‐order tectonic features that accommodate oceanic spreading. Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structural complexity is added. This work investigates the evolution of transform margins and associated rift‐transform intersections, using an analogue modeling approach that simulates changing plate motions. We investigate the effects of different crustal rheologies by using either (a) a two‐layer brittle‐ductile configuration to simulate upper and lower continental crust, or (b) a single layer brittle configuration to simulate oceanic crust. The modeled rifting is initially orthogonal, followed by an imposed plate vector change of 7° that results in oblique rifting and plate overlap (transpression) or underlap (transtension) along each transform margin. This oblique deformation reactivates and overprints earlier orthogonal structures and is representative of natural examples. We find that (a) a transtensional shift in the plate direction produces a large strike‐slip principal displacement zone, accompanied by en‐echelon oblique‐normal faults that accommodate the horizontal displacement until the new plate motion vector is stabilized, while (b) a transpressional shift produces compressional structures such as thrust fronts in a triangular zone in the area of overlap. These observations are in good agreement with natural examples from the Gulf of California (transtensional) and Tanzania Coastal Basin (transpressional) shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins.

Evolution of E-W strike-slip fault network, the northwestern foreland of Tunisia

The northwestern foreland of Tunisia (El Kef region and its surroundings) is a key area to study the tectonics of main E-W basement strike-slip faults and related structures. To achieve this goal, we used multidisciplinary approaches including field work, paleo-stress analyses and geophysical data. These approaches allowed us to propose a new structural model based on the evolution in space and time of Riedel shear type faults and to highlight their role in the structuring of the study region. During the Mesozoic, E-W normal oblique-slip basement faults (D1: Ghardimaou fault, D2: El Kef-Ouergha fault, D3: Jebel Harraba-Guern Halfaya fault and D4: Tajerouine fault) controlled the architecture and the subsidence of the El Kef Basin within a transtensive setting by block tilting, NE-SW negative flower structures, Triassic salt ascent and deposits thicknesses and facies variations. During the Eocene and Late Miocene, the NW-SE shortening (tectonic inversion) is expressed by the oblique reactivation of the pre-existing E-W faults as dextral strike-slip faults. This reactivation is accompanied by map-scale Riedel shear type faults, where D1, D2, D3 and D4 formed the principal displacement zones (PDZs). The successive movements of these faults cut the study area in several right-lateral shear bands in which subsidiary Riedel fractures (R, R', X, P, T and Y) and NE-SW folds are developed. Fault slip data and fractures analyses, across the study area, show several fracture systems which interact under a NW-SE SHmax. During Quaternary, the NNW-SSE shortening reactivated the preexisting E-W fault networks (PDZs). It also, formed NS left-lateral strike-slip faults, NW-SE grabens, NE-SW reverse faults, and ENE en echelon folds arranged within Riedel shear bands.

Structural expression of a fading rift front: a case study from the Oligo-Miocene Irbid rift of northwest Arabia

Abstract. Not all continental rifts mature to form a young ocean. The mechanism and duration of their cessation depend on the crustal structure, modifications in plate kinematics, lithospheric thermal response, or the intensity of subcrustal flow (e.g., plume activity). The cessation is recorded in the structure and stratigraphy of the basins that develop during the rifting process. This architecture is lost due to younger tectonic inversion, severe erosion, or even burial into greater depths that forces their detection by low-resolution geophysical imaging. The current study focuses on a uniquely preserved Oligo-Miocene rift that was subsequently taken over by a crossing transform fault system and, mostly due to that, died out. We integrate all geological, geophysical, and previous study results from across the southern Galilee to unravel the structural development of the Irbid failing rift in northwest Arabia. Despite tectonic, magmatic, and geomorphologic activity postdating the rifting, its subsurface structure northwest of the Dead Sea fault is preserved at depths of up to 1 km. Our results show that a series of basins subsided at the rift front, i.e., rift termination, across the southern Galilee. We constrain the timing and extent of their subsidence into two main stages based on facies analysis and chronology of magmatism. Between 20 and 9 Ma grabens and half-grabens subsided within a larger releasing jog, following a NW direction of a deeper presumed principal displacement zone. The basins continued to subside until a transition from the transtensional Red Sea to the transpressional Dead Sea stress regime occurred. With the transition, the basins ceased to subside as a rift, while the Dead Sea fault split the jog structure. Between 9 and 5 Ma basin subsidence accentuated and an uplift of their margins accompanied their overall elongation to the NNE. Our study provides for the first time a structural as well as tectonic context for the southern Galilee basins. Based on this case study we suggest that the rift did not fail but rather faded and was taken over by a more dominant stress regime. Otherwise, these basins of a failing rift could have simply died out peacefully.

Geometry and structure of the pull-apart basins developed along the western South American-Scotia plate boundary (SW Atlantic Ocean)

The South American-Scotia plate boundary is a left-lateral fault system which runs roughly E-W for more than 3000 km across the SW Atlantic Ocean and the Tierra del Fuego Island, reaching to the west the southern Chile Trench. Analyses of a large dataset of single- and multi-channel seismic reflection profiles acquired offshore has allowed to map the trace of the plate boundary from Tierra del Fuego to the Malvinas Trough, a tectonic depression located in the eastern part of the fault system, and to reconstruct the shape and geometry of the basins formed along the principal displacement zone of the fault system. Three main Neogene pull-apart basins that range from 70 to 100 km in length, and from 12 to 22 km in width, have been identified along this segment of the plate boundary. These basins have elongated shapes with their major axes parallel to the ENE-WSW direction of the fault zone. The sedimentary architecture and the infill geometry of the basins suggest that they represent mostly strike-slip dominated transtension basins which propagated from E to W. The basins imaged by seismic data show in some cases geometrical and structural features linked to the possible reactivation of previous wedge-top basins and inherited structures pertaining to the external front of the Magallanes fold-and-thrust compression belt, along which the South American-Scotia fault system has been superimposed. It is suggested that the sequence of the elongated basins occur symmetrically to a thorough going strike-slip fault, in a left-stepping geometrical arrangement, in a manner similar to those basins seen in other transcurrent environments.