Style Of Deformation Research Articles

Intracontinental convergence accommodated by underthrusting of Tarim Basin beneath central Tian Shan, Central Asia: Insights from Cenozoic upper crust deformation across the western Kepingtage fold-and-thrust belt in the northern Tarim Basin

The way in which intracontinental convergence caused by remote continent-continent collision has been accommodated remains debatable, but it is attributed to either pure shear thickening or continental subduction/underthrusting. Quantification of the deformation architecture of the upper crust and its shortening is vital for testing these competing models. For this purpose, we conducted quantitative analyses of four seismic reflection profiles along the western Kepingtage fold-and-thrust belt of the intracontinental convergence zone between the northern Tarim Basin and the central Tian Shan, a result of the remote India-Eurasia collision, which capture the structures of the upper crust and constrain the amount of shortening in the region. The structural analyses show a thin-skinned style of deformation of the western Kepingtage fold-and-thrust belt, with minimum north−south shortening estimates of ∼71.1 km (∼46.6% strain), ∼76.3 km (∼51.4% strain), ∼67.1 km (∼56.1% strain), and ∼53.0 km (∼49.9% strain), respectively, from east to west. Assuming that coupling shortening occurred across the entire crust and an initial crustal thickness of ∼41−46 km, these shortening ratios would produce a ∼83−95-km-thick crust along the northern Tarim Basin, which is significantly larger than the actual thickness previously reported. This inconsistency leads us to rule out the pure-shear thickening model, which predicts crustal-scale coupling deformation. Alternatively, our results imply that the crust of the northern Tarim Basin was deformed in a decoupling style. These results, combined with those of previous studies, lend support to the intracontinental underthrusting model. We suggest that both the upper crustal fold-and-thrust belts and the lower crustal underthrusting of the northern Tarim Basin accommodated intracontinental convergence.

Tracing the “missing shortening” in fold-and-thrust belts: Insights from structural analyses of the Hotan-Mazatagh transect in the West Kunlun foreland, NW China

Use of balanced cross-section methods, which assume length and area conservation in two dimensions, to quantitatively analyze fold-and-thrust belts is vital in structural analyses. However, layer-parallel shortening is beyond this assumption and thus indescribable by balanced cross-section methods. The contribution of layer-parallel shortening in accommodating shortening has rarely been quantitatively determined, especially in sections hundreds of kilometers in scale. In this study, we conducted structural analyses on the ∼230-km-long Hotan-Mazatagh transect along the West Kunlun foreland of the NW Tibetan Plateau, based on interpretations of seismic reflection profiles. The results reveal that the transect forms a long thrust sheet detaching along the basal Cenozoic detachment, with deformation localized in the Hotan, Manan, and Mazatagh belts. Out of the ∼23.82 km of cutoff displacement translating into the thrust sheet, only ∼1.4 km and ∼4.94 km are absorbed by the Hotan anticline and the Mazatagh detachment thrust, respectively. The remaining ∼17.48 km extent of shortening is absorbed by layer-parallel shortening in the ∼180-km-long section between the Hotan and Mazatagh belts. The layer-parallel shortening produces a strain rate of ∼2.43 × 10−8 yr−1 and absorbs ∼77.97% of the shortening of the segment. Our results argue for caution when using balanced cross-section methods to determine deformation magnitudes. We suggest that localized deformation and layer-parallel shortening function together to shape the ∼230-km-long Hotan-Mazatagh transect into a combined discrete-and-distributed deformation style.

Southern Tibetan rifting since late Miocene enabled by basal shear of the underthrusting Indian lithosphere

Syncontractional extension is prominent in present-day Tibet, but its origin remains vigorously debated. Several deep-seated geodynamic processes (e.g., Indian underthrusting, horizontal flow, and mantle upwelling) have been linked to Tibetan rifting. Indian underthrusting is a good candidate because it can well explain why surface rifts are more prominent south of the Bangong–Nujiang suture; however, how Indian underthrusting causes extension is not well understood and lacks observational constraints. Seismic anisotropy, measured by exploiting the birefringence effect of shear waves, can be indicative of the deformation styles within the crust. Here, we unveil the dominant convergence-parallel alignment of anisotropic fabrics in the deep crust of the southern Tibetan rifts using seismic recordings collected from our recently deployed and existing seismic stations. This finding suggests that the strong north-directed shearing exerted by the underthrusting Indian plate is key to enabling present-day extension in southern Tibet.

A Fast Soft Continuum Catheter Robot Manufacturing Strategy Based on Heterogeneous Modular Magnetic Units.

Developing small-scale continuum catheter robots with inherent soft bodies and high adaptability to different environments holds great promise for biomedical engineering applications. However, current reports indicate that these robots meet challenges when it comes to quick and flexible fabrication with simpler processing components. Herein, we report a millimeter-scale magnetic-polymer-based modular continuum catheter robot (MMCCR) that is capable of performing multifarious bending through a fast and general modular fabrication strategy. By preprogramming the magnetization directions of two types of simple magnetic units, the assembled MMCCR with three discrete magnetic sections could be transformed from a single curvature pose with a large tender angle to a multicurvature S shape in the applied magnetic field. Through static and dynamic deformation analyses for MMCCRs, high adaptability to varied confined spaces can be predicted. By employing a bronchial tree phantom, the proposed MMCCRs demonstrated their capability to adaptively access different channels, even those with challenging geometries that require large bending angles and unique S-shaped contours. The proposed MMCCRs and the fabrication strategy shine new light on the design and development of magnetic continuum robots with versatile deformation styles, which would further enrich broad potential applications in biomedical engineering.

Measurements of Rayleigh wave ellipticity anisotropy and implications for distinct crustal deformation styles across the SE Tibet margin

Plateau growth of southeastern Tibet is often understood by applying the end-member conceptual models, such as ductile material flow in the deep crust, and lateral extrusion of coherently deforming or rigid blocks. Though recent studies suggest the local crustal flow and movements of rigid blocks may be compatible in a way, ambiguities still persist in the formation of the gently sloping margin of southeastern Tibet and interactions between the plateau and the outer forelands. Here we present a 3D crustal deformation model in southeastern Tibet and adjacent regions, by summarizing different types of seismic anisotropy measurements including a newly obtained continuous map of uppermost crustal anisotropy, which are derived from observations of the directionally dependent teleseismic Rayleigh wave ellipticity. Layered deformation is observed within the crust beneath the southeastern Tibet Plateau, while the outer foreland shows an overall coherently deforming mode. The conspicuous change of the crustal deformation styles across the southeastern Tibet margin is against the idea that the low topographic gradients of the plateau margin were produced by leakage of ductile deep crust beneath the plateau. We argue that both the crustal flow beneath the plateau interior and lateral extrusion of the outer foreland accommodate the intracontinental convergence at southeastern Tibet.

Pre-Andean deformation and its influence on the shortening of the Southern Precordillera, Mendoza, Argentina

Andean structures preserve evidence of previous periods of deformation along the proto-Pacific margin of Gondwana. Particularly, the Southern Precordillera, in the southern Central Andes, presents a combination of different structural domains and a double vergence related to the reactivation of pre-Andean structures. This combination and the superposition of deformational events make it difficult to understand the stratigraphic systems and the evolution of the region. This contribution presents detailed information about the structures and evolution of the Southern sector of the Precordillera, focusing on the control exerted by Paleozoic structures over the recent Andean deformation, and the deformational styles of this fold-and-thrust belt. Three main structural domains are recognized. The western domain is characterized by high-angle back-thrusts that concentrate the highest amount of uplift. The central domain is composed of reverse double-vergence faults, and high-angle strike-slip faults. The eastern domain is characterized by pure contractional deformation and only east-verging structures. Four deformational events are recorded and analyzed along the Southern Precordillera at 32°30′S: (1) an Early Paleozoic compressional event, (2) a Late Paleozoic compressional event, (3) a Triassic extensional event, and (4) the Cenozoic Andean compressional event. Our model for the Cenozoic deformation of the Southern Precordillera is restricted to three stages of deformation. During the first stage, Paleozoic west-verging faults are reactivated. The second stage implies reactivation of Paleozoic and Permian-Triassic structures and the generation of reverse Andean faults. The final stage consists of the generation of NE-SW Andean thrusts.

South and East African fracture zones: a long lifespan since the breakup of Gondwana

Abstract Gondwana started to split up during the Early Jurassic ( c. 180 Ma) with the separation of Antarctica and Madagascar from Africa, followed by the separation of South America and Africa during the Early Cretaceous. Thanks to recent seismic profiles, the architecture of rifted margins and the transform fault zones, which developed as a result of the relative motion between tectonic plates, have been recently evidenced and studied along the whole eastern and southeastern Africa margins (i.e. in the Western Somali Basin, the Mozambique Basin, the Natal Basin and the Outeniqua Basin). But, the structure and overall kinematic evolution of the three major transform fault zones – such as the Agulhas, the Davie and the Limpopo fracture zones (FZ) – that together control the opening of major oceanic basins (Antarctic Ocean, Weddell Sea and Austral South Atlantic) remain poorly studied. The interpretation of an extensive regional multi-channel seismic dataset coupled with recent studies allows us to propose a detailed regional synthesis of the crustal domains and major structural elements of the rifted margins along the whole eastern and southeastern Africa. We provide new constraints on the structure and evolution of these three transform systems. Although our findings indicate common features in transform style (e.g. a right-lateral transform system, a wide sheared corridor), the deformation and magmatism along these systems appear quite different. In particular, our results show that the Davie and Agulhas transform faults postdate the development of the rift zone-controlling faults, whereas the Limpopo margin seems to be a simple intra-continental transform. Moreover, the Davie and Agulhas FZ recorded spectacular inversions during the transform stage, whereas transtensional deformation is developed along the Limpopo FZ. This different style of deformation may be explained by two main forcing parameters: (i) the far-field forces that may induce a rapid change of regional tectonic stress and (ii) the magmatic additions that modify mainly the crustal rheology. In the post-drift history, several reactivations of transform fault zones are recorded, implying that some transform margins are excellent recorders of large plate kinematic changes. Such reactivations can serve also as drains for magmatic fluids in the vicinity of hotspots emplacement.

Middle–Late Cenozoic Stepwise Deformation Propagation in Eastern Tibet

AbstractThe uplift and deformation styles of the Tibetan Plateau have been long debated on stepwise growth and crustal channel flow. Here, we offer new insight into this issue by constraining the pulsed exhumation history of the Yalong thrust belt in eastern Tibet, using apatite and zircon (U–Th)/He data from three ∼1 km vertical transects. The results revealed two rapid cooling pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35 °C/m.y.), respectively, which we ascribe to the staged‐thrusting faulting of this belt. These thrust faulting events indicated upward and eastward growth of the Tibetan Plateau, further suggested that the high topographic relief across the Yalong thrust belt mainly formed (at least) since the Late Oligocene. The available documents from paleoaltimetry, basin sediment accumulation, and thermochronometers and our new results reveal a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet.

Compositional variation of the Zechstein Group in the Norwegian North sea: Implications for underground storage in salt caverns

AbstractHalite beds in the upper Permian Zechstein Group represent an opportunity for the future development of underground storage caverns. However, geological factors such as lithological heterogeneities, cap rock characteristics and depth can affect the sealing capacity and the integrity of the cavern or contaminate the stored fluid. The main objective of this paper is to evaluate these factors focusing on the compositional variation of the Zechstein Group in different salt structures in the Norwegian North Sea, and related opportunities and challenges for salt cavern storage. Based on deformation style, geometry, height and thickness of the salt structures, we have divided the Zechstein Group into four main categories: (1) thin beds, which can be either carbonate‐anhydrite or clastic dominated. Halite is absent and therefore there is no potential for the development of salt caverns. (2 and 3) bedded to weakly deformed evaporites and intermediate size salt structures, where thick halite beds of more than 300 m are present, but they are usually deeper than 2000 m. Lithological heterogeneities in the halite consist of a mix of competent and incompetent (K‐Mg salts) lithologies. (4) Tall diapirs, characterized by shallower structures (<2000 m), with large deformation and poor seismic image. Thin layers of incompetent K‐Mg salts are observed in these diapirs. The composition, thickness and deformation of the cap rock vary greatly in the area. Thick halite beds are recognized in most salt structures, suggesting an opportunity for underground storage. The challenges are related to the depth of the halite, amount and type of heterogeneities, characteristics of the cap rock and deformation in the different salt structures. These results also have implications for the distribution of reservoir and source rocks, and the evolution of the Northern Permian Basin.

Formation of multi-stage and clustered fractures at 3.6–4.9 km in the Shizigou structure, SW Qaidam basin

In the Eocene Upper Xiaganchaigou Formation from depths of about 3.6–4.9 km in the Shizigou (SZG) Structure in the SW Qaidam basin, core and image logs reveal three fracture assemblages (A-C) comprising opening-mode fractures and faults. Assemblages are defined by structural style (groups of fracture types), and orientation patterns and thus kinematics and separated by relative timing by the unlithified rock style of deformation of assemblage A and fracture crosscutting relations between assemblages B and C. Correlation of fracture kinematics with the structural history of the basin suggests a multi-stage fracture population in the Shizigou Structure arising as a response to Eocene transtension, Miocene transpression, and Quaternary shortening under the influence of the Cenozoic evolution of two boundary faults, the Altyn Tagh Fault (ATF) and the Qimen Tagh-Eastern Kunlun Fault (QTEKF). To clarify the relation, we document formation process of multi-stage fractures in cores and their preferred orientations in log images in five wells. Using image logs from horizontal wells (Shi A and B) at ca. 3.7–3.9 km depth and statistical methods for quantifying spatial arrangement patterns, we identified statistically significant conductive fracture clusters; opening-mode fractures of the assemblage B are significantly hierarchically clustered. Combining fracture mode and their preferred orientations with reconstructed stress history, we propose that the deformation history of the fracture population is kinematically related to the Cenozoic activity of the ATF and the QTEKF. The initial stage of fracture formation is associated with Eocene strike-slip faulting along the ATF, followed by the Early Miocene initial transpressional faulting along the QTEKF and finally intensified shortening since the Quaternary, respectively.

Coseismic and Postseismic Imaging of a Composite Fault System: The Samos 2020 Mw 7.0 Sequence

ABSTRACT The 2020 Mw 7.0 Samos earthquake (eastern Aegean Sea) provides a rare chance to study the ongoing interaction of normal and strike-slip faulting during an aftershock sequence in a suspected transfer zone with differential deformation style. After assessing them for possible site-effect influence, we first backproject local strong-motion data to elicit the high-frequency (HF) radiation for the main seismic event using the Source Scanning Algorithm. Our results indicate the existence of multiple HF radiators during the main rupture. Second, we construct a new, high-precision catalog for the aftershock sequence utilizing a deep-learning-based detector and picker. This new catalog contains thousands of additional seismic events compared with the routine catalogs built by local agencies and is accompanied by an enhanced dataset of fault-plane solutions determined with automated techniques. Complex fault networks activated during the aftershock period are mapped in detail, indicating the existence of an active transtensional, possibly asymmetric, basin offshore Samos Island. This detailed seismological characterization of Samos sequence leads to an improved understanding of the controlling mechanisms that operate concurrently during a sequence in a transtensional type of system.

Surface and Crustal Response to Deep Subduction Dynamics: Insights From the Apennines, Italy

AbstractThe topography of orogenic belts responds to several contributions operating at short and long temporal and spatial (i.e., wavelengths) scales, from the surface to the deep mantle. Here, we aim to investigate the connection between morphometric characteristics, exhumation, and crustal deformation along and across the Italian Apennines, by comparing superficial with deeper data. Specifically, we present four sets of observations that are constructed by gathering previous data and adding new analyses and inferences, that include: (a) a new geomorphological set of analyses; (b) a database of available low temperature thermochronological cooling ages; (c) a reconstruction of drainage divide evolution in time and space based on the age of the youngest lacustrine deposits within each extensional basin; (d) Moho depth from receiver functions, gathering previous estimates and 13 new ones. From these sets of data, it emerges that across the main drainage divide of the Apennines, the morphological characteristics, the style of deformation and the spatial distribution of exhumation correlate with the geometries of the Moho and are associated with a strong asymmetry in the Northern‐Apennines and a clear symmetry in the Central‐Apennines. We interpret these results as evidence of a strong coupling between shallower and deeper geometries, that are most likely related to complex along‐strike variations in the Apennines geodynamic setting.

Pre‐Subduction Architecture Controls Coherent Underplating During Subduction and Exhumation (Nevado‐Filábride Complex, Southern Spain)

AbstractThe interplay between structural and metamorphic processes operating along the deep plate interface in subduction zones remains elusive as much of the geologic record is recycled into the mantle. In some cases, metamorphosed subducted rocks are underplated and exhumed to the surface, providing critical constraints on structural processes and the rheological evolution of subduction interfaces at convergent margins. One such exhumed high‐pressure/low‐temperature subduction complex is the Cenozoic Nevado‐Filábride Complex (NFC) in Southern Spain. This study presents new data from the NFC that elucidate the syn‐metamorphic deformation, stacking, and underplating of continental slivers along the subduction interface. The structurally lowest NFC dominantly comprises lithologically monotonous Paleozoic metamorphic basement rocks recorded by apatite U‐Pb ages and shows no evidence for large‐scale internal duplications suggesting it behaved as a coherent basement succession during subduction. In contrast, structurally higher levels of the NFC are characterized by the stacking of older‐on younger coherent slices and distinctly different metamorphic ages. These relationships document syn‐subduction structural repetitions and tectonic stacking of imbricate thin slivers (∼100s m) during subduction underplating. Structurally higher levels of the NFC exhibit both Eocene and Miocene metamorphic zircon rims and apatite ages, along with microstructures indicative of relatively higher temperature metamorphism. Large‐scale underplating and antiformal stacking of slivers in the subduction channel can provide buoyancy forces to underplate and assist exhumation. We demonstrate that the presubduction stratigraphic architecture is a key control on the style and timing of deformation and metamorphism, facilitating coherent subduction underplating.

Review of the deformation styles during the Cretaceous Tethyan period: inferred from slumps and fault Kinematics analysis along Northern Tunisia

Review of the deformation styles during the Cretaceous Tethyan period: inferred from slumps and fault Kinematics analysis along Northern Tunisia

Tectonic geomorphology of the Ottawa-Bonnechere Graben, Eastern Canada: implications for regional uplift and intraplate seismicity

In intraplate areas where regional tectonic strain is accommodated by the reactivation of pre-existing structures, the level of seismic hazard associated with faults may be underestimated due to the poor surface expression of faults, scattered earthquake distribution, and long earthquake recurrence intervals. The cause(s) of seismicity in eastern Canada remains unresolved. This is partially because surface expressions of faults have been eroded during glacial and deglacial periods and in the Ottawa-Bonnechere Graben (OBG) are undetectable until a seismic event. Morphotectonic analysis has been widely applied to assess relative tectonic activity in various geological settings. To establish whether active uplift is occurring and to investigate the spatial distribution of relative uplift rates, 131 bedrock drainage basins in OBG were analysed. The aim of this was to (1) test the applicability of geomorphic indices for quantifying active deformation, (2) quantify the spatiotemporal distribution of relative uplift rates, and (3) explore the implications for faulting mechanisms, deformation styles, and ultimately regional seismic hazard. We measured valley floor width-to-height ratio ( Vf), basin elongation ratio ( Re), basin hypsometric integral, and normalized channel steepness index ( ksn). The results show that high relative uplift rates exist in all the six bedrock escarpment sections investigated, suggesting that they are presumably related with regional broad wavelength uplift (epeirogeny) caused by a complex interaction between far-field tectonic stress and glacial isostatic adjustment (GIA). Our analysis showed that Vf, Re, and ksn reveals no considerable spatial differences in high relative uplift rates, consistent with the Canadian Base Network GPS uplift rates. Highlights Geomorphic indices are applied in a low relief and low-medium seismicity area. Geomorphic indices reveal a broad wavelength regional uplift and show relative tectonic activity in the OBG. Relatively high geomorphic indices values provide longer term deformation history compared to global positioning system (GPS) records. Landscape formation and river incision is driven by a complex interaction between GIA and far-field tectonic stresses. Relative uplift rate results show similar patterns to published GPS uplift rates. Possible link between relative tectonic activity and current seismicity.

Paleozoic Gondwanan structure along the Maule river valley between Toconey and Constitución (35.4°S, Chilean Pacific Coast)

During the late Carboniferous–middle Permian, the basement of the Chilean Coastal Cordillera was deformed by the Gondwanan Orogeny, developed by the subduction of the Paleo-Pacific plate under Gondwana from the early Carboniferous. In the Maule sector (35.4°S), the following metamorphic rock units are distinguished: (i) Western Series, formed by metapelites, metabasites, metacherts, metaconglomerates, and marbles, mixed in a subduction channel, with probably ages between the Cambrian and the Carboniferous; (ii) Eastern Series, consisting of metasediments of a fore-arc basin, Carboniferous in age. In the Eastern Series two units are recognized in terms of lithology and deformation style: the Eastern Pelitic Series and the Eastern Sandy Series. Three Gondwanan deformation episodes have been distinguished, affecting both series unequaly. In the Western Series, D1 structures consist of a foliation (S1) developed under high-pressure and low-temperature conditions, while in the Eastern Series it comprise tight east-verging folds, with the associated S1 developed under low PT metamorphic conditions (greenschist facies). D2 structures are only present in the Western Series and Eastern Pelitic Series and represent the exhumation of the accretionary prism and its emplacement to the east over the fore-arc basin, with the development of east-verging recumbent folds and a thick shear-zone. Difficulties in the propagation of the deformation by the presence of the Coastal Batholith to the east led to the development of the D3 deformation event, only well developed in the Eastern Sandy Series, and represented by the Los Tablones Back-thrust and associated folds, as well as N–S open right folds formed under low PT metamorphic conditions.

Dynamic strain localization into a compaction band via a phase-field approach

We present a new phase-field formulation for the formation and propagation of a compaction band in high-porosity rocks. Novel features of the proposed formulation include (a) the effects of inertia on the rate of development of compaction bands, and (b) degradation mechanisms in tension, compression, and shear appropriate for dynamic strain localization problems where disturbances propagate in time in a wave-like fashion to induce micro-cracking, grain crushing, and frictional grain rearrangement in the rock. We also present a robust numerical technique to handle the spatiotemporal formation and evolution of the compaction band. We validate the model by simulating a benchmark problem involving a V-shape notched cylindrical specimen of Bentheim sandstone tested in conventional triaxial compression. The model is shown to reproduce different geometric styles of deformation that include pure compaction, shear-enhanced compaction, and a combination of pure and shear-enhanced compaction, where the combination mechanism consists of a straight primary compaction band surrounded by secondary chevron bands.

Transition from volcano-sagging to volcano-spreading

Many volcanoes exhibit evidence of long-term deformation driven by gravity. This deformation influences the development of magmatic plumbing systems and volcanic vent locations, and it manifests as earthquakes and ground surface motions. Two end-member deformation styles are volcano sagging (flexure) and volcano spreading. Previous modeling studies indicated that the mechanical and geometric properties of basement rocks below the volcano can control whether a volcano spreads or sags, but these works differed on exactly how. Furthermore, evidence in nature that a volcano may progress from sagging to spreading as it grows has not been tested experimentally. Using Digital Image Correlation (DIC) and a revised scaling approach, we here revisit the classic experiments in which a sand–plaster cone is emplaced upon a basement comprising an upper brittle layer and a lower ductile layer. In a first experiment series, we emplaced the cone instantaneously. By normalizing both brittle and ductile layer thicknesses to cone height, we provide new insight into the dimensionless geometric controls on spreading and sagging. In a novel second experiment series, we emplaced the cone incrementally. We show that as a growing cone migrates through the dimensionless geometric parameter space, its deformation style changes successively in time from sagging to spreading. DIC shows that the horizontal velocity of the cone flank increases linearly or non-linearly during cone construction, but it decreases exponentially after construction ceases. Despite their geometric simplification and the omission of several sedimentological, magmatic, and regional-tectonic processes, our models' results are compatible with a range of observations of volcanoes on Earth and Mars. In particular, they help to explain: (i) why lithosphere-scale loading results in sagging rather than spreading, and (ii) why ocean island volcanoes of >2-3 km in height develop stellate forms and rift zones.

Editorial: Style of deformation, sedimentation, kinematic and thermal evolution of thrust-top basins: From natural examples to models

Thrust-top basins (or "piggyback", "wedge-top", or "structural" basins) are a fairly common feature in the accretionary and orogenic wedges worldwide. The formation of thrust-top basins provides information on compressional deformation history in various subductioncollisional settings, and was mainly controlled by the kinematics of competing growth faultrelated fold and thrust sequences. The aim of this research topic was to assemble geoscientists interested in thrust-top basins, spanning a broad array of different tectonic settings, geographical locations, and geological times. This research topic presents a collection of some of the diverse research that is being carried out on this topic. We believe that these studies contribute to a better understanding of orogenic processes in foreland basin systems.

Crustal study based on integrated geophysical techniques in the Northwestern Himalayas, Pakistan

The present research aims to explicate the tectonics of the northwest Himalayas, Pakistan, based on integrated gravity, magnetic and earthquake data. The raw gravity and magnetic data were processed, and seven isoanomaly maps were prepared for qualitative interpretation, whereas a gravity model was prepared along the selected profile for quantitative interpretation. The local earthquake data have also been used to identify the various seismogenic layers in the subsurface and to understand how seismicity relates to regional structural features. Three northwest‐trending thick‐skinned blind basement faults are identified from the present study, namely the Indus Kohistan Seismic Zone (IKSZ), Bagh Basement Fault and Hazara Lower Seismic Zone. The IKSZ is the tectonically most active among them and responsible for the 2005 Kashmir earthquake (Mw = 7.6) and 1974 Pattan earthquake (Mw = 6.2) in the region. The present study also delineated the prominent location of the Main Central Thrust in which the high‐grade metamorphic rocks of Higher Himalayan Crystalline thrust over low‐grade metamorphic rocks of Lesser Himalayas along this thick‐skinned fault. The field evidence such as ductile deformation, zone of inverted metamorphism, and brittle deformation also confirm this location. The sharp bending of the crystalline crust, as well as deep basement just south of Kohistan Island Arc (KIA), indicate that the high density and susceptibility rocks of this arc thrust on the leading margin of the Indian Plate along the Main Mantle Thrust. This thrust fault is a major suture zone separating the KIA in the north from the Indian Plate in the south. The other faults in the region exist in the sedimentary/meta‐sedimentary wedge and are thin‐skinned. It is inferred from the current investigation that the study area exhibits a composite style of deformation. Moreover, the gravity model combined with earthquake data suggested the existence of multiple décollement zones below the Hazara‐Kashmir Syntaxis. The model envisaged an increase in the thickness of the Indian Plate continental crust in the northeast direction.