Kinematic Indicators Research Articles

Propagation of frontally confined subaqueous landslides: Insights from combining geophysical, sedimentological, and geotechnical analysis

Subaquatic mass movements are common in marine and lacustrine environments, but due to their barely predictable nature, direct observations of these processes are limited so that knowledge is only indirectly obtained by investigating the resulting mass-transport deposits (MTDs). Most research focuses on the most common frontally emergent slides, fast-moving events able to generate turbidity currents and tsunamis. Geohazards of frontally confined slides and mechanisms behind their typical fold-and-thrust deformation structures are however still poorly understood.We investigate frontally confined MTDs in Lake Lucerne (Switzerland) by integrating bathymetric and high-resolution seismic data with geotechnical information derived from in situ Cone Penetrometer Tests and short core analysis. Investigated MTDs consist of three units: i) a mass-slide deposit, located at the base of the slope consisting of a coherent slope sequence, ii) a fold-and-thrust system developed in basin sediments, and iii) an overrunning mass flow deposit, consisting of remolded slope sediments. The deformed and thrusted basin sediments show higher undrained shear strength compared to the undisturbed basin sequence. We propose that this strengthening is caused by lateral compression leading to fluid expulsion in the high-plasticity basin sediments by the bulldozing sliding mass. Relative kinematic indicators document that the fold-and-thrust deformation structures occur rapidly. Thus, they should be considered in tsunami hazard analysis. Furthermore, our data highlight that the slope angle of the gliding surface and basin topography are key controlling factors for slope stability and propagation of basin-plain deformations, respectively. Our integrated study supports and refines propagation models proposed in marine environments, revealing the potential of investigating smaller-scale easier-to-access MTDs in lakes.

Integrated characterization and failure mechanism for a mid-Pleistocene mass transport complex-dominant interval in the Mars Ursa Basin, northern Gulf of Mexico, USA

The economic and operational risks associated with mass transport complexes (MTCs) in deepwater hydrocarbon exploration act as a principal motivation to investigate their depositional elements using industry data. There is a lack of extensive seismic and well data coverage that limits the understanding of the processes associated with the evolution of MTCs within deepwater sedimentary basins. This study leverages a unique integrated data set to evaluate the depositional character and potential failure mechanisms of seven identified MTCs preserved in a synkinematic mid-Pleistocene MTC-dominant interval that spans the hydrocarbon-bearing Mars Ursa Basin in the northern Gulf of Mexico. Through seismic interpretation and attribute extraction methods using a 3D prestack depthmigrated seismic survey, we have determined the kinematic indicators and preserved the morphodomain geometries of the identified MTCs. The MTC-dominant interval covers an area of 631 km2, a volume of 392 km3, and a maximum thickness of 549 m in minibasin centers. The interval is penetrated by 15 boreholes that provide stratigraphic and lithologic calibration of the morphometric analyses. The lithologic composition of the MTC-rich interval is claystone/mudstone-dominant with a few interbedded, thin sandstones. The identified kinematic indicators and geometric extent of the identified MTCs are a function of the local salt tectonics extrabasinal controls. The stratigraphic framework presented in this study constrains the timing of failures to a period of high sediment deposition related to a major increase of glacial input into the Quaternary Mississippi Fan. This study offers borehole-calibrated MTC morphometrics preserved in an MTC-dominant interval whose failure is triggered by local salt inflation, but ultimately it is a consequence of loading following increased sediment supply into the basin. The results from this robust data set build upon past integrated seismic-well studies that strive to improve the understanding of MTC processes and their implications in hydrocarbon exploration across salt sedimentary basins.

Deformation mechanisms and kinematics of a soft sedimentary bed beneath the Scandinavian Ice Sheet, north-central Poland, revealed by magnetic fabrics

Characterising deformable substrates of modern and past ice sheets is a key factor in understanding ice mass behaviour and dynamics. This is challenging when field-scale signatures of deformation in soft sedimentary beds are weakly developed or absent. To overcome these difficulties, in this study, we combine micro- and macroscale studies and quantitative analyses to decipher the nature of subglacial sediment deformation under a Pleistocene fast-flowing (streaming) ice sheet. We investigated a complex sedimentary succession at Nieszawa in north-central Poland. A multi-proxy approach involving till micromorphology in thin sections, ripple-cross lamination orientation, till fabric, clast microfabric and the anisotropy of magnetic susceptibility (AMS) data in a closely sampled vertical profile throughout the fluvial sand and till was used to reveal subglacial bed deformation mechanisms and kinematics. This records subglacial deformation of the sedimentary succession at Nieszawa under low basal shear stresses, where simple shear was the dominant bed deformation mechanism. Intergranular advection, decoupling at the ice-bed interface related to high subglacial water pressure, clast ploughing, and basal sliding also took place. The main finding of this study is that AMS reveals the shear strain development and ice flow direction in the structurally and texturally complex deposits under weak coupling conditions at the ice-bed interface beneath a fast flowing/streaming ice sheet, where strain and kinematic indicators other than AMS fabrics are vague or absent.

Structural and kinematic evolution of strike-slip shear zones around and in the Central Tianshan: Insights for eastward tectonic wedging in the southwest Central Asian Orogenic Belt

In order to better understand the late Paleozoic tectonic evolution of the southwestern Central Asian Orogenic Belt (CAOB), we carried out structural and geochronological studies on the poorly investigated Xiaergou and Wulasitai shear zones around and in the Chinese Central Tianshan. The Xiaergou shear zone is the connecting segment between the North Tianshan Fault and Main Tianshan Shear Zone along the northern margin of the Yili - Central Tianshan blocks, it strikes NW-SE with a width of ~3–5 km and shows predominant dextral kinematics. Zircon U–Pb ages of pre- and syn-kinematic granitic dykes within the Xiaergou shear zone indicate that the dextral shearing was active at ~312-295 Ma. The Wulasitai shear zone is a high-strain belt occurring in the interior of the Central Tianshan block, it extends NW-SE for more than 40 km with variable widths of ~1–5 km, steep mylonitic foliations and sub-horizontal stretching lineation are well developed and various kinematic indicators suggest prevailing sinistral shearing. New biotite 40Ar/39Ar ages of two meta-sedimentary rocks, together with the published metamorphic zircon ages constrain the timing of the sinistral shearing at ~312-301 Ma. Our new results combined with the previous studies reveal that the dextral strike-slip shear zones framing the Central Tianshan formed almost simultaneously in the latest Carboniferous (~310 Ma) and lasted until the middle to late Permian. They resulted from the eastward tectonic wedging and relative rotations between continental blocks in the SW CAOB. The sinistral shearing of the Wulasitai shear zone within the Central Tianshan was likely generated due to differential eastward motions of the northern and southern parts of the Central Tianshan.

Study on the Technical Characteristics and Basic Training of Junior Sprinters on the Way

Teenagers have a strong ability to imitate, and they are in a period of rapid development of the central economic system. This period is also a sensitive period for the formation of preliminary stereotypes of technical actions. Sprinting is the basic project of all sports, and running on the way is an important part of the development and maintaining the maximum speed of long distances in the sprinting process. Therefore, through the upper limb swing technique, lower limb support technique, the ratio of support time to flight time, step length and center of gravity Analysis of the kinematics indicators of Xi'an, summarized the technical characteristics of young sprint training players in some training institutions in Xi'an, explored the factors that affect the basic training of young sprinters’ skills on the way, and based on the research conclusions, proposed corresponding improvement measures in order to improve their technical movements , Create excellent results to provide theoretical basis.

Deformations in the Episcopal Basilica in Varna: Evidences of Strong Historical Earthquakes in Northwestern Bulgaria

Our archeoseismological investigations in the Episcopal basilica in Varna have revealed signs of seismic deformations in its walls: numerous shifts, tilts, and rotations of the wall parts around the vertical axis, as well as subvertical through-going joints cutting several stone blocks. A cluster of (at least) three seismic events occurred for a hundred years (from the early 5th to the early 6th centuries AD). Judging by kinematic indicators in the basilica structures built of high-quality stone blocks, the source of seismic motions was located north-northeast of the basilica. Strong seismic oscillations propagated apparently from the southwest. The seismic sources were along seismically active faults localized north and south of Varna. The local seismic intensity of seismic oscillations could reach Il ≤ 9 on MSK-64 scale. The intensity of the seismic oscillations increased due to unfavorable ground conditions at the location of the basilica. These data should be taken into account when assessing the seismic hazard assessment of Varna to build a new map of seismic zoning of northeastern Bulgaria.

Structure and tectonic significance of high- and low-temperature deformation along the lateral escape-related Guaçuí and Batatal shear zones, southern Araçuaí Orogen (southeastern Brazil)

The Guacuí and Batatal lineaments in the southern region of the state of Espírito Santo (southeastern Brazil) can be traced from satellite images for tens of kilometers. They are considered shear zones associated to the final tectonic stages of the Araçuaí-West Congo (A-WC) Orogen during the Ediacaran-Cambrian period. In order to understand their nature and tectonic implications for the development of the orogeny, we integrated geological and structural data based on fieldwork and detailed microstructural analysis. Data was collected along two profiles located at the central segments of both structures. The results demonstrated that the Guaçuí shear zone (GSZ) is a typical ductile transpressive shear zone with approximately 9 km width that shows numerous dextral kinematic indicators and records metamorphism of upper amphibolite facies. The GSZ shows different levels of intensity of dynamic deformation. The Batatal shear zone (BSZ) is a narrow brittle shear zone that shows essentially brittle microstructures (intercrystalline microfractures) revealing deformation at low-grade conditions (frictional regime). Based on their characteristics and the level of erosion of the rocks exposed in the region, we interpret that GSZ developed prior to BSZ.

Seismic characterization of a blocky mass-transport deposit in the Trealla Limestone Formation, North Carnarvon Basin, Australia

The deepwater Cenozoic strata in the North Carnarvon Basin, Australia, represent an interval of interest for stratigraphic studies in passive margins settings of mixed siliciclastic-carbonate environments. We have explored the geomorphological characteristics of a mass-transport deposit (MTD) within the Trealla Limestone Formation to describe in detail the differences among the blocks. To characterize the individual geometry and structural configuration of the blocks within the MTD, we used geometric seismic attributes such as coherence, curvature, dip azimuth, and dip magnitude using horizon slices and vertical profiles. The evaluation finds two types of blocks: remnant and glide (or rafted) blocks. Remnant blocks are in situ and stratigraphically continuous fragments with the underlying strata. This type of block is frequently fault-bounded and displays low deformation evidence. Glide blocks are part of the transported material detached from a paleoslope. These blocks are deformed and occasionally appear as “floating” fragments embedded within a chaotic matrix in the MTD. Glide blocks are used as kinematic indicators of the direction of deposition of MTDs. We evaluate these elements in a modern continental analog that resembles a similar setting for a better understanding of the slide occurrence. Geological feature: Glide blocks, North Carnarvon Basin, Australia Seismic appearance: Discrete angular blocks with internal reflectors Alternative interpretations: Differential dissolution in a mixed siliciclastic-carbonate environment Features with a similar appearance: Carbonate buildups, differential dissolution blocks Formation: Trealla Limestone Formation, North Carnarvon Basin Age: Early-Middle Miocene Location: Offshore Northwest Australia, North Carnarvon Basin Seismic data: Obtained from Western Australian Petroleum and Geothermal Information Management System, Draeck 3D seismic data set Analysis tools: Visualization software (Petrel 2019) and attribute performance software (AASPI 6.0)

Macro- and microstructural analysis of the Zhujiafang ductile shear zone, Hengshan Complex: Tectonic nature and geodynamic implications of the evolution of Trans–North China orogen

AbstractIn worldwide orogenic belts, crustal-scale ductile shear zones are important tectonic channels along which the orogenic root (i.e., high-grade metamorphic lower-crustal rocks) commonly experienced a relatively quick exhumation or uplift process. However, their tectonic nature and geodynamic processes are poorly constrained. In the Trans–North China orogen, the crustal-scale Zhujiafang ductile shear zone represents a major tectonic boundary separating the upper and lower crusts of the orogen. Its tectonic nature, structural features, and timing provide vital information into understanding this issue. Detailed field observations showed that the Zhujiafang ductile shear zone experienced polyphase deformation. Variable macro- and microscopic kinematic indicators are extensively preserved in the highly sheared tonalite-trondhjemite-granodiorite (TTG) and supracrustal rock assemblages and indicate an obvious dextral strike-slip and dip-slip sense of shear. Electron backscattered diffraction (EBSD) was utilized to further determine the crystallographic preferred orientation (CPO) of typical rock-forming minerals, including hornblende, quartz, and feldspar. EBSD results indicate that the hornblendes are characterized by (100) <001> and (110) <001> slip systems, whereas quartz grains are dominated by prism <a> and prism <c> slip systems, suggesting an approximate shear condition of 650–700 °C. This result is consistent with traditional thermobarometry pressure-temperature calculations implemented on the same mineral assemblages. Combined with previously reported metamorphic data in the Trans–North China orogen, we suggest that the Zhujiafang supracrustal rocks were initially buried down to ∼30 km depth, where high differential stress triggered the large-scale ductile shear between the upper and lower crusts. The high-grade lower-crustal rocks were consequently exhumed upwards along the shear zone, synchronous with extensive isothermal decompression metamorphism. The timing of peak collision-related crustal thickening was further constrained by the ca. 1930 Ma metamorphic zircon ages, whereas a subsequent exhumation event was manifested by ca. 1860 Ma syntectonic granitic veins and the available Ar-Ar ages of the region. The Zhujiafang ductile shear zone thus essentially record an integrated geodynamic process of initial collision, crustal thickening, and exhumation involved in formation of the Trans–North China orogen at 1.9–1.8 Ga.

Structural evolution of the Cruzeiro do Nordeste shear zone (NE Brazil): Brasiliano-Pan-African- ductile-to-brittle transition and Cretaceous brittle reactivation

The Borborema Province (NE Brazil) is characterized by the development of continental-scale transcurrent shear zones related to the Neoproterozoic Brasiliano-Pan-African Orogeny. These shear zones commonly border Cretaceous intraplate sedimentary basins. This work presents a structural and microstructural study of the Cruzeiro do Nordeste shear zone (CNSZ), which limits the northern border of the Jatobá Basin. The ductile deformation of the CNSZ is marked by high-angle, ENE-trending foliation bearing subhorizontal stretching lineation, with numerous kinematic indicators showing dextral shearing. We documented a continuous transition from high-temperature (high-T) to low-temperature (low-T) (c. 650 °C to c. 300 °C) ductile fabrics characterized, at the high-T end, by quartz recrystallization by grain boundary migration and feldspar recrystallization by subgrain rotation, and, at the low-T end, by bulging recrystallization of quartz and extensive fracturing of feldspars. The cooler semi-brittle to brittle deformation superimposed on the mylonites is characterized by conjugate pairs of strike-slip mesoscopic faults. The orientation of these faults (WNW-ESE, dextral, and N–S, sinistral) suggests they were formed under the same stress field than the ductile fabrics and thus evidence a continuum deformational from the ductile to the brittle field associated with exhumation during transcurrent tectonics. Brittle reactivation of the CNSZ is characterized by normal faults overprinting the mylonitic foliation. We report a U–Pb age from fault-hosted calcite slickenfibres of 135 ± 4.7 Ma, which provides constraints on the timing of brittle reactivation that can be associated with opening of the South Atlantic Ocean.

Fault inversion in central Iran: Evidence of post Pliocene intracontinental left lateral kinematics at the northern Iranian Plateau margin

Structural inversion of strike–slip faults in response to plate kinematic changes and interactions of large–scale basement blocks is a significant phenomenon in continental collision zones. In the Alborz Mountains, at the northern margin of the Iranian Plateau, Late Cenozoic kinematic of major fault systems changed in the late Pliocene from dextral to sinistral strike–slip. This kinematic change has been attributed to the clockwise rotation of the rigid South Caspian Block. However, the spatial extent and distribution of this kinematic change toward the south and into the Iranian Plateau is controversial. Here we present a detailed structural analysis of the West Saveh fault system located at the northwestern margin of the Iranian Plateau to unravel the regional distribution of this kinematic change. The West Saveh fault system is composed of the WNW–ESE trending Kushk–e Nosrat, Khalkhab, Saveh, and Nashveh faults. We identified several different sets of strike–slip related structures, which are classified into three categories based on their cross–cutting relationship and superimposition of kinematic indicators. We document dextral, dextral transpression and sinistral kinematics and their relative timing since Miocene time in the West Saveh fault system. Our structural analysis indicates recent slip sense inversion from dextral transpression to sinistral strike–slip, which possibly occurred in post Pliocene time. This kinematic change is regional and can be explained by the clockwise rotation of the South Caspian Block similarly to the kinematic change documented in the Alborz Mountains. We propose that the kinematic change due to South Caspian Block rotation is not restricted to the Alborz Mountains, but also affected the Iranian Plateau during post Pliocene time.

Structural analysis of the Planchón-Peteroa Volcanic Complex: Insights for the geothermal system

The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Transitional Southern Volcanic Zone of the Andean Ridge. Structural control of the main NNE-striking El Fierro fault system (EFFS) over the volcanic activity has been commonly assumed, although a paucity of evidence remains. The aim of this paper is to explore the relationship between the local stress field, the superficial structural setting and the geothermal fluid flow paths related to the volcanic complex. To conduct the structural analysis, this work combines remote sensing determination of lineaments, recognition of fracture patterns, with the inversion of kinematic indicators on outcrop scale faults, to finally evaluate the role of the local stress field over the 2D slip and dilation tendencies of the recognized structures. Mesoscale morphostructural lineaments present three main directions: ~E-W, ~NE-SW, and ~NW-SE. Major lineaments develop inflections, giving rise to left bends between the NW-SE to E-W along the strike, compartmentalized by ~ NNE trending lineaments. Strike-slip fault solutions with an ENE-WSW to NE-SW oriented shortening axis were obtained from fault-slip data analysis. The inversion of fault kinematic indicators constrains a Quaternary to recent strike-slip regime, with a ~ENE-WSW trending σ1, and a subvertical σ2. Under the defined local stress field, ~NE-SW and ~WNW-ESE oriented structures have high slip tendency, while those spanning from NE-SW to E-W are prone to dilate. Our analysis suggests that these transverse structures exert first-order controls on the location of Vergara Pass Hill, and Peñón River and Azufre River Valleys hydrothermal manifestations. It seems that intersection zones with submeridian structures, as EFFS, increase structural damage and facilitate hot fluid migration. Circulation would profit the most from ~ENE-WSW and ~NW-SE striking outcrop-scale faults and fractures associated with the damage zones.

Клинико-биомеханические результаты многоуровневых ортопедических вмешательств при crouch gait

The aim of this study was to evaluate the results of multilevel interventions in patients with spastic diplegia and crouch gait. Materials and methods The study cohort consisted of 39 patients (10 females, 29 males). The average age of the patients was 16.3 ± 4.29 years (range, 7 to 26 years). In 19 cases, the GMFCS level was III, in 16 cases it corresponded to level II and in 4 cases to level I. The gait study data were analyzed in two groups of patients. In group 1, patients did not have any previous orthopedic interventions, and the crouch gait pattern was considered to have developed naturally (15 patients). In group 2, patients underwent previous operations on the tendon-muscular apparatus (in other medical institutions) such as fibromyotomy (16 patients) or open lengthening of the Achilles tendon (8 patients). The crouch gait pattern in group 2 was considered iatrogenic. Gait analysis using the Edinburgh Scale and 3D analysis was performed before surgery, and at one to 2 years after the interventions. Results Upon comparing the pre- and postoperative indicators of the Edinburgh scale, there was an improvement in the indicators of movements in the ankle joint both in the supporting and in the non-supporting phases of the stride cycle for both groups: a decrease in the maximum dorsal flexion of the foot under load, an improvement in the maximum extension in the knee joint during the support phase, practically complete elimination of the pathological orientation of the foot relative to the motion vector, as well as improvement of the position in the knee joint immediately before the initial contact with the supporting surface. Computer gait analysis showed that multilevel surgical interventions improved the parameters of the knee flexion angle at the time of initial contact, increased the amplitude of knee joint extension in the support phase of the stride, normalized the orientation of the foot relative to the motion vector, reduced or completely corrected the pathological values of the dorsal flexion of the foot in the support phase of the stride and reduced the energetic intensity of movements. There was no significant increase in the indicators reflecting the strength characteristics of the plantar flexors, which reflects a pronounced suppression of the function of these muscles in the development of crouch gait. GPS changed from 17.1 ± 3.01 to 13.4 ± 3.19 for natural crouch gait and from 15.9 ± 6.16 to 14.8 ± 4.6 for iatrogenic one. Conclusion The crouch gait pattern is not homogeneous, both in terms of natural and iatrogenic development, and in terms of orthopedic disorders. The iatrogenic pattern develops with excessive surgical weakening of the plantar flexors of the foot, even if there is no pathological rotation of the lower limb segments in younger patients and with lower GMFCS levels. The planning of multilevel surgical treatment is based on 3D gait analysis and should be aimed at eliminating orthopedic components of the pathology that determine the crouch gait pattern. Surgical treatment enables to improve the kinetics and kinematics in the knee joint and the kinematic indicators of the ankle joint and, in general, increase the gait profile indicator.

Zonas de cisalhamento normais no SW do Cráton Amazônico: análise microestrutural das rochas miloníticas do Granito Indiavaí

Zonas de cisalhamento dúcteis de cinemática normal em orógenos continentais previamente espessados por eventos orogênicos compressivos têm suscitado grande interesse na comunidade científica. Na porção sudoeste do Cráton Amazônico, na região de Indiavaí, porção centro-oeste do Brasil, ocorrem as zonas de cisalhamento Água Rica e Cristo Rei, que afetam as rochas do Granito Indiavaí. Análise das estruturas em escala mesoscópica revela progressiva transformação de um protólito granítico com foliação fraca, passando a rochas com textura protomilonítica, milonítica até ultramilonítica. Análise microestrutural demonstra gradual diminuição do tamanho dos grãos ocasionando o aumento da matriz. As rochas com foliação incipiente não apresentam matriz. Observam-se quartzo recristalizado, extinção ondulante nos feldspatos, intensos processos de sericitização no plagioclásio e ortoclásio com pertitas em chamas. Nos protomilonitos, a matriz perfaz de 20 a 30% da rocha e é composta de quartzo e biotita. São observados porfiroclastos de feldspato potássico, com fraturas, falhas e extinção ondulante. Nos milonitos, a matriz perfaz de 60 a 75% da rocha e é composta de quartzo, biotita e muscovita. Ocorrem porfiroclastos de quartzo comumente na forma de fitas, que apresentam recristalização por migração de limite de grão. Feldspato potássico e plagioclásio exibem extinção ondulante e recristalização por protuberância. Nos ultramilonitos predomina a matriz, que é basicamente composta de quartzo, muscovita e biotita de granulação média. Estima-se que os processos que atuaram no desenvolvimento da foliação milonítica ocorreram em temperaturas entre 400 e 600°C. Análise dos indicadores cinemáticos revela que o movimento tectônico foi normal. Interpreta-se que as zonas de cisalhamento Cristo Rei e Água Limpa são parte de um sistema de cisalhamento extensional desenvolvido em crosta intermediária durante período Toniano.

Quartz textural analysis from an anastomosing shear zone system: Implications for the tectonic evolution of the Ribeira belt, Brazil

Strain localization and influence of grain-size reduction processes were investigated from field and microstructural observations, and from quartz textural analysis using EBSD, in rocks deformed along an anastomosing network of shear zones in the Ribeira belt in Brazil. Rocks deformed along the Lancinha shear zone (LSZ) display high percentage of recrystallized grains, in which quartz recrystallized grain size from rocks in the southern LSZ reaches a maximum of 50 μm, and in the northern LSZ a maximum of 200 μm. The dominant serrated grain boundaries and the widespread (50–85%) presence of very small (>10–50 μm) recrystallized quartz grains, suggest that BLG was the dominant recrystallization mechanism responsible for grain-size reduction in the south portion of the LSZ. In the northern LSZ the presence of large recrystallized grains with sizes close to subgrains, suggests that grain-size reduction occurred by SGR, and the presence of lobate grain boundaries point to GBM recrystallization, which led to an increase in recrystallized grain size. This suggests grain-size reduction by dynamic recrystallization as a major factor leading to weakening and strain localization. Evidence of intracrystalline deformation and the well-developed quartz crystallographic fabrics suggest that strain localization in the LSZ occurred by dislocation creep deformation mechanisms. Dislocation creep is recorded by dominant activation of basal <a> slip and secondary contribution of rhomb <a> slip, in the southeast of the LSZ, and by activation of rhomb <a> + basal <a> and prism <a> in the northeast. These slip systems together with microstructural observations suggest that plastic deformation occurred at around 400 °C in the southern region, and at around at >400–500 °C in the northern region. S–C foliation, quartz <c> axis distribution and several kinematic indicators suggest sinistral sense of shear along the LSZ, and strain partitioning during progressive deformation. The dominance of sinistral indicators observed in the LSZ are also found in parallel shear zones to the east, such as the Putunã and Serra do Azeite. The sinistral kinematics in this overall dextral transpressional orogenic system may be explained by dual sense of shear on shear zones bounding extruding blocks, likely formed during progressive orogenic evolution instead of the polyphase evolution previously suggested for this southern part of the Ribeira belt.

Sinistral strike-slip shearing along the Jiali shear zone around the Eastern Himalaya syntaxis region: Evidences for oligocene eastward limited translation of Tibet

In and around the Eastern Himalaya Syntaxis (EHS), the metamorphic complex and its structural boundaries are key tectonics to investigate the kinematics and thermal evolution of the continental collision. We provide new structural, kinematic and geochronological data along the northeastern boundary of the EHS, namely the Jiali strike-slip shear zone. Structures and various kinematic indicators record sinistral strike-slip shearing in the zone. Based on the microstructural features, crystallographic preferred orientation patterns of quartz and their slip systems, coupled with Raman Spectroscopy of Carbonaceous Materials (RSCM) geothermometry, the ductile sinistral shearing fabrics formed at upper greenschist and amphibolite facies (>500 °C). Two hornblende, one muscovite and five biotite separates from the mylonites in the shear zone were dated by the 40Ar/39Ar method. A hornblende plateau age of 23.7 Ma is interpreted as representing or being close to the time of sinistral movement. Muscovite and biotite 40Ar/39Ar ages from 22.9 to 16.9 Ma represent cooling ages following sinistral shearing. It is concluded on the basis of these data that the Jiali sinistral strike-slip shear zone was active in latest Oligocene. This sinistral movement on the Jiali shear zone is considered to link with the Ailao Shan-Red River shear zone, and form a unique, continuous structural boundary around the EHS. The Jiali-Ailao Shan-Red River sinistral shear zone and Gaoligong dextral shear zone formed a huge conjugate strike-slip shear pair around the EHS to accommodate the N–S shortening corresponding to northward indentation of the folded Indian continent. The conjugate strike-slip shear systems also contribute to transporting Tibet southeastward in a limited scale.

Tectonic evolution of the intra-uplift Vigodi-Gugriana-Khirasra-Netra Fault System in the seismically active Kachchh rift basin, India: Implications for the western continental margin of the Indian plate

The E-W striking Kachchh Rift Basin (KRB) at the western continental margin of Indian plate is located in the northern part of Gujarat state, India. KRB has undergone polyphase deformation owing to changing stress-field since Late Triassic. We establish the kinematic framework along the NW striking intra-uplift Vigodi-Gugriana-Khirasra-Netra Fault System (VGKNFS) located at the western part of the KRB. The VGKNFS consists of 0.25–50 km long, sub-parallel, striated, reactivated dip-slip faults. A total of 1150 fault-slip data consisting of fault planes and striations attitude were recorded from 66 sites (including a single site with systematic joints). Slip-sense of faults was determined by documenting kinematic indicators. Paleostress analysis was carried out using Win-Tensor, T-Tecto, FaultKin and SG2PS to compare and validate the results. The chi-square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present-day compressional stress field. Geophysical investigations were conducted at selected sites using Ground Penetrating Radar (GPR) to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover. 15–17 m long, 2D GPR cross-sections were recorded across faults using monostatic antenna of 200 MHz frequency.Two major deformation events – D1 and D2 are determined in the present study. The extension event D1 shows W and NW–NNW extension during Late Triassic to Late Cretaceous. It occurred during the rift phase of KRB in response of the break-up of Gondwanaland. The latest event D2 shows NNE–NE compression from Late Cretaceous up to the present. It is interpreted to have developed during post-rift inversion phase, induced by collision of the Indian plate with the Eurasian plate at ~55 Ma.

Anticline growth by shortening during crustal exhumation of the Moroccan Atlantic margin

It is unclear how the crustal-scale erosional exhumation of continental domains of the Moroccan Atlantic margin and the excessive subsidence of its rifted domains affected the Late Jurassic-Early Cretaceous post-rift evolution of the margin. To constrain the km-scale exhumation, we study the structural evolution of the Jbel Amsittene. This anticline is located on the coastal plain of the Moroccan Atlantic margin, and is classically considered to have been developed initially in the Late Cretaceous by halokinesis, and by contraction during the Neogene. Contrarily, our structural analysis indicates that the anticline is a fault-propagation fold verging north with Triassic salts at its core and that it formed by shortening shortly after continental breakup of the Central Atlantic. The anticline grew by NNW-SSE to NNE-SSW contraction, as shown by syn-tectonic wedges, regional kinematic indicators and synsedimentary structures in Upper Jurassic to Lower Cretaceous rocks. It grew further and tightened during the Cenozoic, presumably in relation to the Atlas/Alpine contraction. Thus, our data and interpretation suggest that “tectonic-drives-salt” in the anticline early growth, which is coeval with the growth of other anticlines along the Moroccan Atlantic margin and widespread km-scale exhumation farther onshore. Anticline growth due to shortening argues for intraplate far-field stresses potentially linked to the geodynamic evolution of the African, American and European plates.

On the impact of alternative seismic time imaging methods on subsurface fault mapping in the northernmost Molasse Basin, Switzerland

The identification and characterization of tectonic faults in the subsurface represent key aspects of geologic exploration activities across the world. We have evaluated the impact of alternative seismic time imaging methods on initial subsurface fault mapping in three dimensions in the form of a case study situated in the most external foreland of the European Central Alps (the northernmost Molasse Basin). Four different seismic amplitude volumes of one and the same 3D seismic data set, differing in imaging technologies and parameterizations applied, were considered for the interpretation of a fault zone dissecting a Mesozoic sedimentary sequence that is characterized by a pronounced mechanical stratigraphy and has witnessed a multiphase tectonic evolution. For this purpose, we interpreted each seismic amplitude volume separately. In addition, we computed a series of seismic attributes individually for each volume. Comparison of the different data interpretations revealed consistent results concerning the mapping of the seismic marker horizons and main fault segments. Deviations concern the apparent degree of vertical and lateral fault zone segmentation and the occurrence of small-scale fault strands that may be regarded as important fault kinematic indicators. The compilation of all fault interpretations in map form allows the critical assessment of the robustness of the initial seismic fault mapping, highlighting well-constrained from poorly defined fault zone elements. We conclude that the consideration of multiple seismic processing products for subsurface fault mapping is advisable to evaluate general imaging uncertainties and potentially guide the development of fault zone model variants to tackle previously discussed aspects of conceptual interpretation uncertainties.

Magnetic properties of pseudotachylytes from western Jämtland, central Swedish Caledonides

Abstract. Fault kinematics can provide information on the relationship and assembly of tectonic units in an orogen. Magnetic fabric studies of faults where pseudotachylytes form have recently been used to determine direction and sense of seismic slip in prehistoric earthquakes. Here we apply this methodology to study magnetic fabrics of pseudotachylytes in field structures of the Köli Nappe Complex (central Swedish Caledonides), with the aim to determine fault kinematics and decipher the role of seismic faulting in the assembly of the Caledonian nappe pile. Because the pseudotachylyte veins are thin, we focused on small (ca. 0.2 to 0.03 cm3) samples for measuring the anisotropy of magnetic susceptibility. The small sample size challenges conventional use of magnetic anisotropy and results acquired from such small specimens demand cautious interpretation. Importantly, we find that magnetic fabric results show inverse proportionality among specimen size, degree of magnetic anisotropy and mean magnetic susceptibility, which is most likely an analytical artifact related to instrument sensitivity and small sample dimensions. In general, however, it is shown that the principal axes of magnetic susceptibility correspond to the orientation of foliation and lineation, where the maximum susceptibility (k1) is parallel to the mineral lineation, and the minimum susceptibility (k3) is dominantly oriented normal to schistosity. Furthermore, the studied pseudotachylytes develop distinct magnetic properties. Pristine pseudotachylytes preserve a signal of ferrimagnetic magnetite that likely formed during faulting. In contrast, portions of the pseudotachylytes have altered, with a tendency of magnetite to break down to form chlorite. Despite magnetite breakdown, the altered pseudotachylyte mean magnetic susceptibility is nearly twice that of altered pseudotachylyte, likely originating from the Fe-rich chlorite, as implied by temperature-dependent susceptibility measurements and thin-section observations. Analysis of structural and magnetic fabric data indicates that seismic faulting occurred during exhumation into the upper crust, but these data yield no kinematic information on the direction and sense of seismic slip. Additionally, the combined structural field and magnetic fabric data suggest that seismic faulting was postdated by brittle E–W extensional deformation along steep normal faults. Although the objective of finding kinematic indicators for the faulting was not fully achieved, we believe that the results from this study may help guide future studies of magnetic anisotropy with small specimens (&lt;1 cm3), as well as in the interpretation of magnetic properties of pseudotachylytes.