Strike-slip Duplex Research Articles

Strain accumulation in the Mentawai Forearc Sliver, Indonesia, inferred from continuous GNSS-derived strain rate

The Mentawai Forearc Sliver (MFS) is characterized by oblique deformation formed as slip partitioned between normal and parallel trench plate convergence. The surge of great earthquakes from 2004 to 2012 along the adjacent Sunda trench left a large unbroken segment known as the Mentawai Seismic Gap. Here, we adopted continuous Global Navigation Satellite System (GNSS) observation data to identify the present regional crustal deformation using geodetic strain rates. The principal strain rate, dilatation rate, and maximum shear strain rate are about 0.13 microstrain/yr, 0.2 microstrain/yr, and 0.1 microstrain/yr, respectively, with the range of its uncertainties between 0.01 and 0.04 microstrain/yr. The dilatation and maximum shear strain rates reveal the spatial coverage of strike-slip duplex and backthrust tectonics along the Mentawai Forearc Sliver.

Segmentation and lateral growth of intracratonic strike-slip faults in the northern Tarim Basin, NW China: influences on Ordovician fault-controlled carbonate reservoirs

Intracratonic strike-slip faults have been recognized as a major factor controlling the formation of fracture-cave carbonate reservoirs in deep buried basins, yet which properties and how the strike-slip faults influence reservoir distribution and their connectivity are still ambiguous. This uncertainty significantly restricts hydrocarbon exploration and development, such as in the Fuman oilfield, northern Tarim Basin, NW China. Using a high-resolution 3D seismic reflection survey and borehole data, we investigated the geometry and kinematic evolution of the FI17 fault zone in the Fuman oilfield. This fault zone is characterized by a single fault zone, pop-up or pull-apart structures, right-stepping en echelon normal faults, and much smaller displacement (<30 m) normal fault arrays from bottom to top. The FI17 fault zone consists of four genetic segments, including the extensional strike-slip duplex, Riedel left-lateral shear, right-stepping horsetail splay, and horizontal slip segments in map view. In particular, the formation of the ∼18 km Riedel shear zone is characterized by the growth and linkage of segmented shear faults (synthetic and secondary synthetic shears). We observed that the large-scale fault-controlled fracture-cave reservoirs are distributed in positions with wider fault zones, which are characterized by overlapping of neighboring secondary shear faults. Furthermore, the reservoir width examined in this study is natural logarithmic correlated (positively) to the fault zone width. The reservoirs linked by the same shear faults show better internal connectivity. The spatial coherence between fault geometry and reservoir features indicates that segmentation and lateral growth of intracratonic strike-slip faults controls the occurrence of fracture-cave reservoirs, which may provide support for reservoir prediction in the Fuman oilfield and other deeply buried fault-controlled carbonate reservoirs in general.

Flexural-slip folding in buckling phases of orogenic belts: Insight into the tectonic evolution of fault splays in the East Iran orogen

Introduction: The East Iran orogen has experienced multiple buckling phases resulting in the formation of strike-slip fault splays. The geometric and kinematic characteristics of these splays are influenced by folding mechanisms. This study focuses on investigating the structural characteristics and tectonic evolution model of the Khousf splay, located in the northern terminus of the Nehbandan right-lateral strike-slip fault system.Methods: Field visits and geometrical properties from map views were used to analyze the structural features of the Khousf splay. The splay was found to consist of a multi-plunging anticline and syncline, referred to as the Khousf anticline and Khousf syncline, respectively. Flexural slip was identified as a significant mechanism for the formation of these structures. Structural evidence, including parasitic folds, active folds, and strike-slip duplexes, suggested that flexural slip occurred on discrete movement horizons among the rock units.Results: Analysis of the parasitic folds in the cores and limbs of the Khousf anticline and syncline revealed M, W, Z, and S shapes, with complex slicken-line patterns observed on faults parallel to the beds at the limbs. The analysis results indicated strain partitioning and inclined left- and right-lateral transpressional zones. Shortening estimates obtained from profiles in the Shekarab inclined transpressional zone were approximately 33%, 65%, and 68% for NE-SW, N-S, and NW-SE profiles, respectively. In the Arc area, which is the core of the anticline, shortening estimates from NE-SW and N-S profiles ranged from 14% to 10%. Structural analysis of the folds in this area revealed broad, close, semi-elliptical, and parabolic shapes, suggesting that secondary folds with NW-SE axis directions have been superimposed on the first-generation folds with E-W axis directions in the Khousf refolded splay.Discussion: The findings of this study highlight the structural characteristics and tectonic evolution model of the Khousf splay in the northern terminus of the Nehbandan right-lateral strike-slip fault system. The results suggest that flexural slip played a crucial role in the formation of the multi-plunging anticline and syncline in the Khousf splay. The presence of parasitic folds and complex slicken-line patterns on faults indicate the complexity of deformation processes. The observed strain partitioning and inclined transpressional zones suggest a complex tectonic history in the study area. The superimposition of secondary folds with different axis directions on first-generation folds adds further complexity to the structural evolution of the Khousf refolded splay. Overall, this study provides new insights into the structural characteristics and tectonic evolution of the Khousf splay in the East Iran orogen.

Structural characteristics of the curved Königsee-Lammertal-Traunsee fault system in Salzkammergut (Northern Calcareous Alps, Austria)

In the Miocene, the Eastern Alps (Austria) experienced strike-slip faulting, due to Eastward extrusion tectonics. Sinistral movement along the Salzach-Ennstal-Mariazell-Puchberg fault, with transpressive and strike-slip tectonics, resulted into N–S and SW-NE compression in the Northern Calcareous Alps (NCA). That led to the development of several faults, including the Königsee-Lammertal-Traunsee (KLT): a sinistral fault cross-cutting the NCA with a curved path. Here, we focus on the eastern termination of the KLT, previously interpreted as two SSW-NNE and SW-NE strike-slip faults, connected by an E-W thrust with top-to-NE motion. Our structural/petrographic data indicate that the two sectors of the KLT are linked also by an E-W strike-slip fault, between Triassic carbonates and Late Cretaceous clastics. The associated damage zone is complex and includes strike-slip duplexes and small-scale thrusts, associated to various fault rocks. Furthermore, our new data indicate that the E-W oriented thrust is confined between two stepping strike-slip fault, suggesting a restraining bend, like other sectors of the KLT.The structure of the KLT, with the strike-slip segments characterized by small-scale duplexes and flowers, but where significant shortening is mainly accommodated within the restraining area closely resembles that of other strike-slip systems, which typically extended over hundreds of km.

Kinematics and Geochronology of Late Paleozoic–Early Mesozoic Ductile Deformation in the Alxa Block, NW China: New Constraints on the Evolution of the Central Asian Orogenic Belt

Abstract Strike-slip faults are widely developed throughout the Central Asian Orogenic Belt (CAOB), one of the largest Phanerozoic accretionary orogenic collages in the world, and may have played a key role in its evolution. Recent studies have shown that a large number of Late Paleozoic–Early Mesozoic ductile shear zones developed along the southern CAOB. This study reports the discovery of a NW–SE striking, approximately 500 km long and up to 2 km wide regional ductile shear zone in the southern Alxa Block, the Southern Alxa Ductile Shear Zone (SADSZ), which is located in the central part of the southern CAOB. The nearly vertical mylonitic foliation and subhorizontal stretching lineation indicate that the SADSZ is a ductile strike-slip shear zone, and various kinematic indicators indicate dextral shearing. The zircon U-Pb ages and the 40Ar/39Ar plateau ages of the muscovite and biotite indicate that the dextral ductile shearing was active during Middle Permian to Middle Triassic (ca. 269–240 Ma). The least horizontal displacement of the SADSZ is constrained between ca. 40 and 50 km. The aeromagnetic data shows that the SADSZ is in structural continuity with the coeval shear zones in the central and northern Alxa Block, and these connected shear zones form a ductile strike-slip duplex in the central part of the southern CAOB. The ductile strike-slip duplex in the Alxa Block, including the SADSZ, connected the dextral ductile shear zones in the western and eastern parts of the southern CAOB to form a 3000 km long E-W trending dextral shear zone, which developed along the southern CAOB during Late Paleozoic to Early Mesozoic. This large-scale dextral shear zone was caused by the eastward migration of the orogenic collages and blocks of the CAOB and indicates a transition from convergence to transcurrent setting of the southern CAOB during Late Paleozoic to Early Mesozoic.

Structure, Rheology, Petrology, and Geodynamics of the Tectonosphere of the Sea of Japan

The geological-structural, magmatic, seismic, and thermometric models of the Earth’s crust and upper mantle of the Sea of Japan region are considered in relation to three-dimensional rheological gravity models reflected in horizontal and vertical sections of density contrast of the tectonosphere. In the crust and the upper mantle, formal manifestations of a right-lateral strike-slip duplex were found, in association with rift-related extension zones and central vortex structures. In the central regions of the Sea of Japan, a mushroomlike low-viscosity zone of typical of plumes is mapped in the depth interval of 60–200 km. The gravity models show signs of Late Cretaceous subduction of the Pacific Plate under the continental margin and Eocene–Oligocene subduction of this plate under the Japanese island arc. The Pacific lithosphere is split into crustal and lower lithospheric plates. The depth and thickness of rigid crustal and lithospheric plates have been estimated, faults of which are observed in rift-related extension zones. Petrochemical analysis of volcanic rocks dredged from the floor of the Sea of Japan confirms the existence of two extension stages, accompanied by volcanism of an initially postsubduction (ACMB), then spreading (N-MORB) and postspreading plume (OIB) nature.

Growth and linkage of the Xiakou fault in the Linnan Sag, Jiyang Depression, Eastern China: Formation mechanism and sedimentation response

Abstract Detailed geometric and kinematic analyses of a large multi-stage normal fault in the Jiyang Depression, eastern China, have been conducted using high-quality 3D seismic data. The Xiakou fault is a serrated fault zone consisting of four connected segments that alternately appear NE trending and EW trending. There are two tension stages, namely, the Ek stage (65 Ma) and Es4-Ed stage (50–23.5 Ma). The evolution process can be divided into four stages under the control of the regional geological background. In the Ek stage (65 Ma), only the NE-trending segments are active. The whole Xiakou fault zone is in the isolated fault growth stage. As the regional stress transformed from NW-SE to nearly S–N, the NE-trending segments in the Es4 stage (50 Ma) continued their activities and EW-trending faults started to develop. Soft connections were formed between the NE-trending segments. The Es3 stage (42 Ma) experienced intense SN-trending extension, and hard connections were formed in the Xiakou fault zone. The segmented faults in different directions became connected, forming a serrated fault zone that alternately appears NE-trending and EW-trending. Es2-Ed (38–23.5 Ma) is the stage of strike-slip transformation. Horsetail and strike-slip duplex structures developed in different positions. Local tension or extrusion of different fold segments occurred, which reflects the superposition effect of strike slip against an extension background. Hence, the spatial and temporal differences in the development and evolution of the Xiakou fault zone have important controlling effects on the distribution of the settlement depocentres and the source channels in this area.

Uchaminsky Be–W–Au Ore Cluster in the Regional and Local Structures of the Lower Amur Region

The Uchaminsky ore cluster is located on the Pilda–Limuri watershed in the long-known gold-mining area of the Lower Amur region. It is shown that the distribution of polygenetic and polychronous Be–W–Au mineralization is associated with the northeastern left-lateral strike-slip ore-magmatic tension duplex that was developed in a transtensional regime under general submeridional compression (transpression). The structural, lithological, and magmatic features of the strike-slip duplex are favorable for searching for new large-volume stockwork gold deposits and ore bodies.

Tidal stress modeling of Ganymede: Strike-slip tectonism and Coulomb failure

High-resolution Galileo data of Ganymede's complex surface provide strong and ubiquitous evidence of strike-slip motion: en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and strained craters. In a previous study, we performed a detailed mapping of these strike-slip morphologies within nine regions of Ganymede: Dardanus Sulcus, Tiamat Sulcus, Nun Sulci, Byblus Sulcus, Nippur and Philus Sulci, the Transitional Terrain of Northern Marius Regio, Anshar Sulcus, Arbela Sulcus, and Uruk Sulcus. Strike-slip indicators were inferred in various combinations at each site, in addition to extensional processes. However, the prominence of strike-slip indicators suggests shearing has been an important process to the structural development of Ganymede's surface. Moreover, tidal stresses on Ganymede, under particular circumstances, may have been sufficient to induce Coulomb failure and generate strike-slip faulting. Here we investigate the role of both diurnal and non-synchronous rotation (NSR) tidal stresses on Ganymede using the numerical code SatStress. We resolve normal and shear tractions onto discrete fault segments of specified orientation and assess Coulomb failure potential for the nine inferred fault zones. Testing a range of subsurface fault depths (z = 0–5 km) and ice friction (μf = 0.2–0.6), we find that tidal stress models of combined diurnal and NSR stress readily promote Coulomb failure within each studied fault zone. High friction (μf = 0.6) limits failure depths to ∼1 km, while low friction (μf = 0.2) extends failure depths to ∼2 km, consistent with elastic thickness estimates. We also compare each fault zone's predicted shear sense to the inferred shear sense from our structural mapping efforts and find compatible senses of shear among six of the nine regions that exhibit notable fault offset and/or prevalent inferences of en echelon, duplexes, and strained craters. In addition, principal stress orientations and failure feasibility computed on a global scale suggest that combined diurnal and NSR tidal stresses promote Coulomb failure within the shallow (< 2 km) icy lithosphere across much of Ganymede. Coulomb failure is limited near the equator by large compressive NSR stresses, but stresses at mid- to high-latitudes readily promote Coulomb failure along a wide range of fault orientations. Based on these results, we infer that nonsynchronous rotation may have assisted the formation and evolution of strike-slip structures on Ganymede.

Morphological mapping of Ganymede: Investigating the role of strike-slip tectonics in the evolution of terrain types

The heavily fractured surface of Ganymede displays many morphologically distinctive regions of inferred distributed shear and strike-slip faulting that may be important to the structural development of its surface. To better understand the role of strike-slip tectonism in shaping this complex icy surface, we perform detailed mapping at nine sites using Galileo and Voyager imagery, noting key examples of strike-slip morphologies where present. These four morphological indicators are: en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and possible strained craters. We map sites of both light, grooved terrain (Nun Sulci, Dardanus Sulcus, Tiamat Sulcus, Uruk Sulcus, and Arbela Sulcus), and terrains that are transitional from dark to light terrains (Nippur and Philus Sulci, Byblus Sulcus, Anshar Sulcus, and the Transitional Terrain of Northern Marius Regio). At least one, if not more, of the four strike-slip morphological indicators are observed at every site, suggesting strike-slip tectonism is indeed important to Ganymede's evolutionary history. Byblus Sulcus is the only mapped site where the presence of strike-slip indicators is limited to only a few en echelon structures; every other mapped site displays examples of at least two types, with Arbela Sulcus containing candidate examples of all four. In addition, quantification of morphological characteristics suggests related rotation between sites, as evidenced by the predominant NW/SE trend of mapped features within the light terrain present in five different sites (Nun, Tiamat, Uruk, Nippur/Philus, Byblus, and Anshar Sulcus). Moreover, incorporation of strike-slip tectonism with pre-existing observations of extensional behavior provides an improved, synoptic representation of Ganymede's tectonic history.

Stress heterogeneity and its impact on seismicity pattern along the equatorial bifurcation zone of the Great Sumatran Fault, Indonesia

A stress transfer modeling revealed the stress heterogeneity and its correlation with the seismicity pattern in the bifurcation zone of the Great Sumatran Fault (GSF), where the GSF is divided into two separate sub-parallel segments up to 35 km apart, i.e. Angkola and Barumun, forming a strike-slip duplex at around equator. The analysis was conducted using a seismic catalog compiled from five institutions, i.e. the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG), United States Geological Survey USGS), Harvard and Global Centroid Moment Tensor (GCMT), International Seismological Center (ISC), and Geoforschungzentrum (GFZ) Germany, in the period of 1970–2017. Our frequency-magnitude distribution analysis indicates that this zone has a high stress regime. Especially at the tip of the bifurcation zone, in which 20° clockwise rotation of principal stress and 20% increase in stress ratio are observed from the stress inversion. Consequently, events with magnitude larger than 6.0 are concentrated in this area. In addition, our stress transfer modeling reveals the mechanism of the stress heterogeneity at the bifurcation zone and a possible interaction between segment ruptures. Two main internal structures perpendicular to the strike-slip duplex are also observed from the displacement vector. Due to its high stress concentration and its close distance to populous cities of Padang Sidempuan, Bukittinggi, Solok and Padang Panjang in western Sumatra, the tip of GSF bifurcation poses a big potential of seismic hazard. The information of the principal stress rotation and stress ratio obtained in this study can be used further to assess the potential of great ruptures and estimate the possible damage in the study area.

Structural and hydrothermal evolution of a strike-slip shear zone during a ductile-brittle transition, Sierra Nevada, CA

The incursion of meteoric-hydrothermal fluids into the ductile crust can be evaluated with the stable isotope ratios of minerals in exhumed ductile shear zones, but the incursion mechanisms are yet to be well-demonstrated. Field structural and microstructural relations and regional oxygen isotope patterns from an exhumed, Late Cretaceous shear zone-fault system in the central Sierra Nevada, CA, are used to reconstruct the deformation history and develop insights into fluid incursion mechanisms. A ductile-to-brittle transition was partially accommodated by a strike-slip duplex involving flexural slip-accommodated folding along faults. Two main NNW-striking brittle fault strands overlap, the northern fault curves into the southern fault, which is sealed by a >4 m wide composite quartz vein. Based on structural relationships, we interpret the transition from ductile to brittle deformation to have occurred during cooling of the adjacent Late Cretaceous Tuolumne Intrusive Complex. Quartz-sealed fault veins in the pendant have δ18O values ranging from −3.2 to 14.5‰, and are interpreted to have precipitated partially or fully from meteoric-hydrothermal fluids, including quartz veins that have been recrystallized. The lowest values are only found within the region of the jog. The δ18O values for pseudotachylyte matrix in one sample from this fault system are δ18O = 3.3‰, δ2H = −137‰. Together, these data indicate meteoric-hydrothermal incursion into a deforming, seismogenic brittle-ductile transition.

Deep Fault Plane Revealed by High‐Precision Locations of Early Aftershocks Following the 12 September 2016 ML 5.8 Gyeongju, Korea, Earthquake

An M-L 5.8 earthquake, which is large for a stable continental region, occurred in southeastern Korea on 12 September 2016. Ten days of data from a temporary seismic network deployed immediately after the mainshock are combined with data from permanent seismic stations to determine high-precision locations of early aftershocks to reveal the geometry of the causative structure at depth. Well-constrained relative earthquake hypocenters and focal mechanisms are used to define the subsurface fault plane with a strike of similar to N28 degrees E and dip of similar to 78 degrees to the east-southeast. This fault plane extends from 12 to 15 km depth and may have been responsible for most of the early earthquakes in the Gyeongju earthquake sequence. A pre-existing weak zone in a strike-slip duplex that formed from subsidiary Riedel shears beneath the Yangsan fault system may have been reactivated to nucleate the mainshock and aftershocks.

States of stress and slip partitioning in a continental scale strike-slip duplex: Tectonic and magmatic implications by means of finite element modeling

Orogenic belts at oblique convergent subduction margins accommodate deformation in several trench-parallel domains, one of which is the magmatic arc, commonly regarded as taking up the margin-parallel, strike-slip component. However, the stress state and kinematics of volcanic arcs is more complex than usually recognized, involving first- and second-order faults with distinctive slip senses and mutual interaction. These are usually organized into regional scale strike-slip duplexes, associated with both long-term and short-term heterogeneous deformation and magmatic activity. This is the case of the 1100 km-long Liquiñe–Ofqui Fault System in the Southern Andes, made up of two overlapping margin-parallel master faults joined by several NE-striking second-order faults. We present a finite element model addressing the nature and spatial distribution of stress across and along the volcanic arc in the Southern Andes to understand slip partitioning and the connection between tectonics and magmatism, particularly during the interseismic phase of the subduction earthquake cycle. We correlate the dynamics of the strike-slip duplex with geological, seismic and magma transport evidence documented by previous work, showing consistency between the model and the inferred fault system behavior. Our results show that maximum principal stress orientations are heterogeneously distributed within the continental margin, ranging from 15° to 25° counter-clockwise (with respect to the convergence vector) in the master faults and 10–19° clockwise in the forearc and backarc domains. We calculate the stress tensor ellipticity, indicating simple shearing in the eastern master fault and transpressional stress in the western master fault. Subsidiary faults undergo transtensional-to-extensional stress states. The eastern master fault displays slip rates of 5 to 10 mm/yr, whereas the western and subsidiary faults show slips rates of 1 to 5 mm/yr. Our results endorse that favorably oriented subsidiary faults serve as magma pathways, particularly where they are close to the intersection with a master fault. Also, the slip of a fault segment is enhanced when an adjacent fault kinematics is superimposed on the regional tectonic loading. Hence, finite element models help to understand coupled tectonics and volcanic processes, demonstrating that geological and geophysical observations can be accounted for by a small number of key first order boundary conditions.

Role of N-S strike-slip faulting in structuring of north-eastern Tunisia; geodynamic implications

Three major compressional events characterized by folding, thrusting and strike-slip faulting occurred in the Eocene, Late Miocene and Quaternary along the NE Tunisian domain between Bou Kornine-Ressas-Msella and Cap Bon Peninsula. During the Plio-Quaternary, the Grombalia and Mornag grabens show a maximum of collapse in parallelism with the NNW-SSE SHmax direction and developed as 3rd order distensives zones within a global compressional regime. Using existing tectonic and geophysical data supplemented by new fault-kinematic observations, we show that Cenozoic deformation of the Mesozoic sedimentary sequences is dominated by first order N-S faults reactivation, this sinistral wrench system is responsible for the formation of strike-slip duplexes, thrusts, folds and grabens. Following our new structural interpretation, the major faults of N-S Axis, Bou Kornine-Ressas-Messella (MRB) and Hammamet-Korbous (HK) form an N-S first order compressive relay within a left lateral strike-slip duplex. The N-S master MRB fault is dominated by contractional imbricate fans, while the parallel HK fault is characterized by a trailing of extensional imbricate fans. The Eocene and Miocene compression phases in the study area caused sinistral strike-slip reactivation of pre-existing N-S faults, reverse reactivation of NE-SW trending faults and normal-oblique reactivation of NW-SE faults, creating a NE-SW to N-S trending system of east-verging folds and overlaps. Existing seismic tomography images suggest a key role for the lithospheric subvertical tear or STEP fault (Slab Transfer Edge Propagator) evidenced below this region on the development of the MRB and the HK relay zone. The presence of extensive syntectonic Pliocene on top of this crustal scale fault may be the result of a recent lithospheric vertical kinematic of this STEP fault, due to the rollback and lateral migration of the Calabrian slab eastward.

The kyanite quartzite of Bosland (Suriname): evidence for a Precambrian metamorphosed alteration system

AbstractThis article investigates the origin of a rare occurrence of kyanite quartzites in the Palaeoproterozoic greenstone belt of Suriname. The rocks form elongated hills in the Bosland area, Brokopondo district, where they are associated with meta-sedimentary, meta-volcanic and granitic lithologies. Their mineral content and unusual Si- and Al-rich chemical composition are inferred to be the result of advanced argillic alteration of felsic volcanic tuffs and a later overprint by regional metamorphism up to lower amphibolite facies during the Trans-Amazonian orogeny. Structurally, the Bosland area seems centred within a contractional strike-slip duplex of a major dextral fault system. The alteration was probably associated with a high-sulphidation environment and involved significant to almost complete removal of alkali and alkaline earth elements. Pseudosection modelling and textures suggest that the precipitation–temperature (P–T) history of the kyanite quartzites started with shallow (&lt;2kbar) hydrothermal alteration of the acidic tuffaceous volcanics, possibly in the andalusite stability field (T&gt;350°C), and ended in peak metamorphic conditions in the kyanite–staurolite stability field (P&gt;4kbar andT=500–650°C). Alteration events that preceded the peak of Trans-Amazonian metamorphism may be more common in the rock record of Suriname's greenstone belt, which lends support to the hypothesis that gold mineralisations in the region can be pre-orogenic.

The Mentawai forearc sliver off Sumatra: A model for a strike-slip duplex at a regional scale

At the Sumatran oblique convergent margin the Mentawai Fault and Sumatran Fault zones accommodate most of the trench parallel component of strain. These faults bound the Mentawai forearc sliver that extends from the Sunda Strait to the Nicobar Islands. Based on multi-channel reflection seismic data, swath bathymetry and high resolution sub-bottom profiling we identified a set of wrench faults obliquely connecting the two major fault zones. These wrench faults separate at least four horses of a regional strike-slip duplex forming the forearc sliver. Each horse comprises an individual basin of the forearc with differing subsidence and sedimentary history. Duplex formation started in Mid/Late Miocene southwest of the Sunda Strait. Initiation of new horses propagated northwards along the Sumatran margin over 2000km until Early Pliocene. These results directly link strike-slip tectonics to forearc evolution and may serve as a model for basin evolution in other oblique subduction settings.

Tectonic evolution of the La González pull-apart basin in the Mérida Andes: combination of geological data and satellite radar interferometry (InSAR)

The 500-km-long Bocono strike-slip fault runs as a major active fault along the backbone of the Merida Andes fold-and-thrust belt. The recent right-lateral motion on the fault led to formation of numerous structures such as pull-apart basins which have formed in releasing bends and/or right-step offsets along the fault strands. The La Gonzalez pull-apart is the biggest basin generated as an extensional strike-slip duplex in the central part of the fault. This duplex is made up of two strands of the Bocono fault as master/first-order faults, while normal right-lateral faults which formed during evolution of the basin are second-order faults. The extension of the basin is associated with seismic activities and surface offsets along the Bocono fault. InSAR investigations over a 31-month period also support active deformation within the basin. These data indicate that the La Gonzalez basin is continuously being extended as a result of motion along the Bocono fault and formation of subsequent normal faults. In addition, the basin is being transversely shortened in NW–SE direction due to regional shortening across the Merida Andes range followed by convergence between the Maracaibo microplate and the Guyana shield.

Stress fields recorded on large-scale strike-slip fault systems: Effects on the tectonic evolution of crustal slivers during oblique subduction

In continental margins, large-scale, strike-slip fault-systems resulted from oblique subduction commonly exhibit a complex pattern of faulting where major faults define the inland boundary of tectonic slivers that can be detached from the margin. In turn, subsidiary faults bound and define internal tectonic blocks within the sliver which are expected to rotate, translate and/or internally disrupt in order to accommodate the internal deformation. The geometrical and spatial arrangement of faults and tectonic blocks thus determines the evolution of the sliver given a particular stress field regime. The Paposo segment of the Atacama Fault System in northern Chile displays a series of brittle faults whose orientations are hierarchically arranged: low-order faults splay off higher-order faults forming Riedel-type and strike-slip duplexes geometries at several scales. The master (1st- and highest-order) Paposo Fault defines the inland boundary of a tectonic sliver whereas subsidiary faults bound and disrupt internal tectonic blocks. By using newly collected brittle fault-slip data we estimated the orientations and regimes of the stress fields that acted upon the entire sliver, the different fault-orders and the tectonic blocks. Results indicate that an overall transtensional – with NW-compressional and NE-tensional principal axes – strike-slip regime affected the sliver and triggered the development of left-lateral strike-slip structures. An incomplete split of the stress field imposed by the subduction process resulted in the generation of a nested pattern of R-type faults as well as in a combined strike-slip/normal faulting disruption of the tectonic blocks within the sliver.

Structure and evolution of the Sura-Kama strike-slip zone in the Cenozoic (the Volga-Ural anteclise of the East European Platform)

The Sura-Kama zone (SKZ) complicates the central area of the Volga-Ural anteclise and extends sublaterally from the Sura River basin towards the Kama River at a distance of 700–750 km. Based on the analysis of geological-geophysical data and structural studies, a model for the tectonic structure and the evolution of the SKZ is developed. This is a deep tectonic fault that shows the features of long-term polystage development. During the latest Cimmerian-Alpine period of tectonic reactivation, the SKZ represented a zone of strike-slip and consecutive manifestation of early transpressional right-lateral strike-slip dislocations that changed to left-lateral strike-slip displacements under transtension settings as a result of kinematic inversion. Features of the heterogeneous structure of the SKZ are revealed. The segments formed by the system of strike-slip duplexes are alternated along the strike by the principle of rotation-fold and “domino” structures. The particular models of evolution of these segments are proposed by the examples of the widely known Karlin, Tetyushin, and Lower Kama dislocations. It is assumed that kinematic inversion and compression-decompression phenomena on the flanks of the SKZ, as well as the tectonic environments in the area of its dynamic influence were highly important for the development of the processes of migration and redistribution of hydrocarbon components.