Axial Trend Research Articles

Consistent decrease in conifer embolism resistance from the stem apex to base resulting from axial trends in tracheid and pit traits.

Drought-induced embolism formation in conifers is associated with several tracheid and pit traits, which vary in parallel from stem apex to base. We tested whether this axial anatomical variability is associated with a progressive variation in embolism vulnerability along the stem from apex to base. We assessed the tracheid hydraulic diameter (Dh), mean pit membrane area (PMA) and the xylem pressure at 50% loss of conductivity (P50) on longitudinal stem segments extracted at different distances from the stem apex (DFA) in a Picea abies and an Abies alba tree. In both trees, Dh and PMA scaled with DFA 0.2. P50 varied for more than 3 MPa from the treetop to the stem base, according to a scaling of -P50 with DFA-0.2 . The largest Dh, PMA and P50 variation occurred for DFA<1.5 m. PMA and Dh scaled more than isometrically (exponent b=1.2). Pit traits vary proportionally with tracheid lumen diameter. Apex-to-base trends in tracheid and pit traits, along with variations in P50, suggest a strong structure-function relationship that is influenced by DFA. Although the effect of DFA on P50 has not been extensively explored previously, we propose that analyzing the relationship between P50 and DFA could be crucial for a comprehensive assessment of embolism vulnerability at the individual level.

Structural Analysis and Petrography of High-Grade Gneisses and Associated Mafic / Ultramafic Dikes Around Salem, Southern India

Southern Granulite Terrane (SGT) of India preserves extensive high-grade granulite facies rocks of Archaean and Proterozoic age. The SGT is divided into number of blocks by several suture/shear zone. Structural investigations on the basement gneisses and younger mafic/ultramafic dikes have been carried out within the Salem block which is part of Northern Granulite Block (NGB), north of the Cauvery Suture Zone (CSZ). The present work emphasizes various scale fold styles and other structural patterns of the area, which includes regionally metamorphosed high-grade rocks as basement for the multiple ultramafic intrusions to the north of Cauvery Suture Zone (CSZ) which highlights the finite strain geometry, complex deformation pattern and high-grade metamorphism. Structural map of the study area is prepared showing two generations of folding, namely F1 whose axial trend is NE-SW, subparallel with general trend of gneissic foliation and are tight isoclinal folds while F2 which are open folds with axial trend NW-SE.E-W structural cross section across the foliation planes, characterizes antiformal and synformal fold patterns of the basement due to varying dip directions which also reflects type-3 interference pattern of folding. Mesoscopic scale shear zones of dextral kinematics in response to E-W collision during Paleo-Meso Archean time, delta type porphyroclasts, S-C fabrics with the dextral movement of CSZ system, Riedel shear, thrust imbricates implying duplex structures, rotation of mafic boudins along shear zones are the most prominent ductile structural features of this area. Brittle structures like different sets of cross cutting joints and faults indicate younger deformation as well. Petrography of major lithologies has classified them into amphibolite gneiss, migmatite gneiss, charnockites, granulites and mylonites as basement rocks to the younger pyroxenite intrusions. Typical textures like, perthite, granulose, reaction rims, sieve textures and microstructures like S-C fabrics, kink bands, rotated porphyroclasts, etc are observed within the basement rocks. Coarse grained textures with fractured porphyroclasts of garnets indicating the water interactions and retrogradations within the granulite facies rocks. Reaction rims observed in charnockites and granulites are indicative of retrogression during shearing. The coarse grained cummulate nature of pyroxenites neither represent deformation nor metamorphism. Keywords: Southern Granulite Terrane, Salem, Structural Analysis, Mafic/Ultramafics, Dikes, Petrography

Magmatic Origins of Extensional Structures in Tempe Terra, Mars

AbstractNumerous graben features transect the Tempe Terra plateau in the northeastern Tharsis Rise, Mars, making it one of the most heavily structured regions of Tharsis. The origin of the complex fault geometries, generated over three distinct stages of tectonic activity, is poorly understood. This work distinguishes between Tempe Terra structures of local and regional origin, to isolate regional deformation patterns related to the general development of the Tharsis Rise from the patterns due to effects of local stress mechanisms. Comparison of structural observations to predicted deformation patterns from different drivers of graben formation in the Martian crust demonstrates the important role of magmatic activity at a variety of scales in driving tectonism in Tempe Terra. Noachian (Stage 1) faulting resulted from local magmatic underplating and associated heating and uplift, which formed part of an incipient stage of widespread Tharsis volcanism that predated development of the main Tharsis Rise. Early Hesperian (Stage 2) faults reflect the interaction of regional stresses from growth of Tharsis with magmatic activity highly localized along the Tharsis Montes Axial Trend—a linear volcanotectonic trendline including the alignment of the Tharsis Montes volcanoes. Early–Late Hesperian (Stage 3) faulting resulted from a series of dyke swarms from a Tharsis‐centered plume, which propagated in a regional stress field generated by growth of the Tharsis Rise. As only Stage 2 NNE faults and Stage 3 ENE faults are linked to regional, Tharsis‐related stresses, other observed Tempe Terra fault trends can be excluded when evaluating models of Tharsis's tectonic evolution.

Macroseismic Study of 4th January 2016, Manipur Earthquake, and its Implications

Abstract An earthquake of magnitude 6.7 M (Latitude 24.834N; Longitude 93.656E) on the Richter scale rocked in the Noney area, Tamenglong district, Manipur on 4th January 2016. The shock was strongly felt in most parts of the Northeastern states of India viz. Manipur, Nagaland, Meghalaya, Assam, and its neighboring countries Myanmar and Bangladesh. Macroseismic study was conducted to assess the intensity of ground motion and related damages caused by the earthquake. The damage incidences were mainly reported in structures constructed over the alluvial fill material. Deformations and development of ground fissures were observed in the epicentral tracts of Manipur and liquefaction phenomenon was observed in the Silchar area Assam. The study revealed that higher damage was confined to the area around Noney, Kabuikhullen, Nungba, Leimakhong, and Imphal valley areas in Manipur and Silchar town areas in Assam. Based on field observation, the degree of damage to building structures, and data gathered from the local population using the standard questionnaire, different intensity values were assigned to each locality. Isoseismal map was prepared by drawing the boundaries between different intensity areas at MSK-64 scale. The result indicates that the intensity was within the range of IV to VII. The maximum intensity was found VII in parts of Imphal, Tamenglong, and Silchar and very close to the epicentral tract area of Noney; and lowest intensity IV was observed in other parts of the northeastern states around Dimapur and Kohima in Nagaland state. The location of the epicenter of main shock (M 6.7) was at the intersection of the two major lineaments trending to ENE-WSW and NW-SE. The trend and shape of isoseismals drawn on seismotectonic/geological maps are elliptical along ENE-WSW direction and are found more closely spaced in the north and southern parts of the affected area. The elliptical nature of the isoseismals indicates that this seismic event was caused by movement along a linear surface. Furthermore, the orientation of elliptical isoseismals with a major axis trend in an ENE-WSW direction is almost parallel to the ENE-WSW trend of major lineament/fault in the area. As a result, the ENE-WSW lineament/fault trend appears to be the causative fault for this quake. In addition, one of the nodal plane (NP2) striking 83°, with dip 81° and slip (rake) 38° obtained from fault plane solution USGS shows a similar trend to the direction of generated elliptical isoseismals pattern confirming the event ocurred along a major tectonic lineament in a strike-slip mechanism.

Geological Structures Controlling Au/Ba Mineralization from Aeromagnetic Data: Harrat ad Danun Area, Saudi Arabia

Positive and negative magnetic anomalies occupied the total aeromagnetic (TM) map of the Harrat ad Danun area, Saudi Arabia. Reduction to the pole (RTP) maps display the range of magnetic values (−312.4 to 209.4 nT) that vary in shape, size, and magnitude. These anomalies generally follow the NNW–SSE (Red Sea axis trend), NE–SW, and NNE–SSW trends. The NNW-SSE linear negative and positive magnetic anomalies could be brought on by buried faults, shear zones, or subsurface dikes. In the central part, the position of Au and Ba mineralization was connected to this trend. It is concluded that the principal structures are represented by the NNW–SSE, NE–SW, and NNE–SSW tendencies. Based on gridded RTP magnetic data, the 2-D power spectrum was computed and revealed the frequency of the near-surface and deep magnetic components. It is believed that the depths of the shallow and deep magnetic sources are typically 80 m and 570 m, respectively. Additional negative and positive magnetic anomalies with varied amplitudes and frequencies, trending in the NNW–SSE, ENE–WSW, and NE–SW directions, are seen when the high-pass and low-pass maps are closely examined. Many faults in various directions cut into these anomalies. The occurrence of negative linear magnetic anomalies (−36.6 nT to −137.3 nT) at this depth (80 m) is also confirmed by this map. The TDR filter and the Euler deconvolution method were used to identify the horizontal variations in magnetic susceptibility as well as the source position and depth of magnetic sources. The linear clustering rings are thought to be caused by contacts or faults with depths between 1 m to 474 m that are oriented WNW–ESE, NNE–SSW, and NNW–SSE. These faults or contacts are thought to be particularly prominent in the western, eastern, southern, northern, and central zones. The majority of felsic and mafic dikes are found to be connected to subsurface structures, showing that three structural trends—WNW–ESE, NNE–SSW, and NNW–SSE—affect the studied area. This demonstrates that important features and shear zones control the majority of Saudi Arabia’s gold deposits. A negative magnetic anomaly that is centered in the area, trending NNW–SSE and crossing the NNE–SSW fault, is connected to the plotted gold and barite mineralization in the study area. This may imply that these two tendencies are responsible for mineralization. This result raises the possibility of mineralization in the NNW negative magnetic feature located in the western part of the area. The occurrence of gold and barite was significantly impacted by the NNW–SSE and NNE–SSW structural lineaments.

High-resolution three-dimensional azimuthal velocity anisotropy of S-waves in southern-central Japan, based on ambient noise tomography

To investigate the dominant deformational patterns and stress conditions in the upper crustal structure of the Kinki region, southern-central Japan, we constructed a high-resolution 3D azimuthal anisotropy model to a depth of ~ 11 km. We used 6-month-long ambient noise data recorded by the densely distributed permanent and temporary stations. From this dataset, cross-correlations were retrieved. We then obtained a 3D isotropic velocity model by inverting Rayleigh wave dispersion data, followed by a direct joint inversion for both 3D azimuthal anisotropy and additional isotropic velocity perturbation. The resolved 3D azimuthal anisotropy reveals significant contrasts of anisotropy across the Kinki region. The predominant fast axes observed in the northwestern Kinki region align with the direction of the maximum horizontal compressional stress and the principal strain rate axes, suggesting that the observed anisotropy is mainly stress-induced. In the southern part of the study area, furthermore, the predominant fast axes trend NE–SW and near E–W, also indicating the presence of stress-induced anisotropy. On the depth profile of the anisotropy, we found depth-dependent variation of azimuthal anisotropy. There exists a significant consistency between the anisotropy observed beneath 3 km depth and the dense distribution of earthquake hypocenters. This interrelationship between anisotropy and seismicity demonstrates that the observed anisotropy could be linked to local crustal stress or fractures relevant to earthquake ruptures. Our 3D anisotropy model therefore contributes towards understanding the locations and features of the seismicity region.Graphical

Interphase and Intergroup Mass Transfer in the Two-Group Two-Fluid Model in Flows with Phase Change

The Two-Fluid Model (TFM) has long been the backbone of engineering-scale two-phase flow simulation in system-analysis codes and computational fluid dynamics codes. The classical TFM is limited in how it can capture the differences in the transport of small and large bubbles. The two-group TFM provides the ability to specify the unique transport characteristics of small and large bubbles separately. Expanding to two sets of conservation equations for the two bubble groups presents the additional challenge of bubble group accounting as bubbles can cross the group boundary. The three mass transfer terms in the two-group TFM are evaluated for flashing, condensing, and boiling flows using a partitioning method. The axial trends in the source terms are examined for these flow conditions with the available intergroup models. Two-group interphase models are implemented and evaluated against experimental data for flashing, condensing, and boiling flows with accurate two-group results. The capabilities of the two-group TFM are evaluated for these flow types, demonstrating the ability to predict two-group vapor properties without the need for flow regime transitions.

Structural Analysis of Ranikot Anticline, Southern Kirthar Fold Belt, Pakistan

In this paper, different applications of stereographic projections are utilized for the structural analysis of Ranikot anticline. Structural data of Ranikot anticline from Southern Kirthar Fold Belt of Pakistan is used to construct different diagrams such as beta-diagrams, pi-diagrams and contour diagrams. These diagrams are used to visualize the inter-limb angle, plunge and trend of fold axis, dip and strike of axial surface, fold symmetry, vergence and principle stress axes. This study shows that studied anticline is nearly N-S trending, open, shallow to horizontal, asymmetrical, and east-vergent anticline. Principle stress axis σ1 and σ2 lie in profile plane while σ1 and σ3 lie in axial surface.

Structural Architecture and Deformation History of Tempe Terra, Mars

AbstractThe structurally complex region of Tempe Terra, located in the northeast of the Tharsis Rise on Mars, preserves deformation related to the growth of Tharsis and lies along the trendline formed by the Tharsis Montes volcanoes. We characterize the spatiotemporal tectonic evolution of Tempe Terra based on comprehensive structural mapping. From this mapping, we identified 16 cross‐cutting fault sets and placed these in relative time order, based on a hybrid approach using cross‐cutting relationships and buffered crater counting. We are thus able to provide a broad framework for understanding the timing of development for the Tharsis Rise and Tharsis Montes axial trend (TMAT). Our work shows that Tempe Terra has experienced three distinct stages of tectonic activity from the Middle Noachian to the Late Hesperian. Stage 1 involved E–W extension followed by localized NE–SW extension, which produced local zones of N and NW faulting through the center and west of Tempe Terra in the Noachian. Stage 2 produced intense NE‐oriented faulting concentrated along the TMAT in the Early Hesperian as a result of a discrete period of NW–SE extension and local volcanism. Stage 3 involved NW–SE extension coinciding with Tharsis volcanic activity, which generated a regional fabric of ENE‐trending graben distributed across Tempe Terra from the Early to Late Hesperian. We observe an overall peak in tectonic activity in the Early Hesperian and find that Tharsis‐related extensional deformation in the form of NE‐oriented radial faulting did not start in Tempe Terra until this time.

Pliocene Drainage in Manitoba and Northwestern Ontario, Canada

This study presents the restored Pliocene topography along northerly trending profiles in Manitoba, northwestern Ontario, eastern North Dakota, Minnesota, and western Wisconsin. A top-of-bedrock slope profile of the Red River/Lake Winnipeg/Nelson River and 19 south-trending landscape topographic and top-of-bedrock slope profiles of the region were made from published elevation data. These profiles reveal a clear change in slope and slope direction (flexure) in the top-of-bedrock elevation. The flexure axis trends southeasterly across Manitoba into northwestern Ontario. The profiles were then tilted southerly by lifting the profiles along the southern margin of Hudson Bay to restore remaining glacial isostatic rebound. When imposing a minimum 80 m of isostatic rebound to the Nelson River/Lake Winnipeg/Red River profile, the northern portion of the profile slopes north but the southern portion of the profile slopes south at 0.01%. When imposing a minimum 60 m of isostatic rebound to all 19 top-of-bedrock profiles, the bedrock slopes north to Hudson Bay northeast of the flexure; however, southwest of the flexure, the southern portions of the 19 top-of-bedrock profiles slope south. We interpret the flexure axis to have been the northern divide of the Pliocene Mississippi River basin in Manitoba and northwestern Ontario and the divide that will lie between the north-flowing Nelson River and south-flowing Red River with future glacial isostatic adjustment.

Tectono-stratigraphic evolution, regional structure and fracture patterns of the Zagros fold-thrust belt in the Duhok region, Kurdistan, northern Iraq

This study is the first detailed investigation of the tectono-stratigraphy, regional structure and mesoscopic fractures of the Zagros fold-thrust belt in the Duhok region, Kurdistan, Northern Iraq, and is based on field studies, remote sensing-GIS analyses, cross-section restorations, and tectonic analysis of key structures. The Duhok fold belt is a frontal zone of the north-western part of the Zagros fold and thrust belt in the Kurdistan region near the north-eastern margin of the Arabian Plate. It is characterized by WNW-ESE striking, doubly-plunging, upright symmetric to asymmetric detachment folds that involve ~8.2–10.9 km of Paleozoic to Quaternary strata. These folds vary from 5 to 75 km long, 4–20 km wide and have a surface relief (caused by basement uplift) up to 3.2 km. Five regional and twelve local structural cross-sections were constructed parallel to the regional SSW tectonic transport and perpendicular to the fold axial trends. Section lengths vary between 4.94 km and 101.55 km. Two main detachment levels have been inferred for the Duhok fold belt. A deep basal detachment was placed at the base of the Paleozoic successions within the Ordovician shales of the Khabour Formation at depths from 8 km to 10 km. Shallower, intermediate detachment levels occur within the shales and evaporites of the Mid-Upper Permian and Upper Jurassic strata at depths 1.7 km in the frontal sectors to around 5.5 km in the hinterland. The thickness of the Paleozoic succession in the Duhok fold belt is ~2 km. Deformation by thin-skinned detachment folding together with thick-skinned thrusting is inferred to have occurred in the Duhok region from the Mid Miocene through to the Present-Day. The maximum NNE-SSW-directed shortening produced by detachment folding was about 18.62 km (19.71%) over a section length of 94.45 km. The maximum shortening along thrust faults was around 1.98 km (1.95%) over a section length of 101.55 km. The mesoscopic fracture patterns in the study area were grouped into two major extension sets, four major shear-hybrid sets and eight minor shear-hybrid sets. Field characteristics and relative chronology indicate that most of the fractures are tectonic in origin, and they developed before (i.e., pre-folding fractures) and during (i.e., early- and late-folding fractures) the Mid Miocene folding in the Duhok fold belt.

Evolution of the Western Ghats: Constraints from receiver function imaging and harmonic decomposition

The Western Ghats (WG), with an average elevation of ~1.2 km, is one of the greatest escarpments that spans ~1500 km parallel to the west coast of India. It is a mosaic of disparate geological formations having distinct structural and physical characteristics. In this study, the lithospheric structure in terms of crustal thickness, sub-Moho layer and deformation along and across the WG are investigated using receiver functions (RFs) at 30 broadband seismological stations. Techniques like slant stacking, common conversion point imaging and harmonic decomposition are applied to the RFs. Results reveal a large crustal thickness of ~45 km in the central part of the WG, which decreases to ~39 km in the southern and ~ 37 km in the northern parts, in conformity with the geology. The variation in crustal thickness beneath the WG could be due to the effect of hotspot impingement and subsequent rifting mechanism. Further, the RFs reveal a strong sub-Moho low velocity layer (LVL) along the WG. This observation gains support from a previous inference of a low-density zone in the uppermost mantle beneath the west coast of India. Harmonic decomposition of the RFs reveals that this LVL is anisotropic, while the Moho is dipping/ anisotropic in nature. The trend of the symmetry axis of anisotropy (of the LVL) varies from 58.2∘ to 134.4∘, almost perpendicular to the west coast of India. We postulate that the origin of this LVL can be linked to different rifting episodes along the west coast of India, since LVLs are manifestations of thermal/chemical anomalies. These results support the rifting model proposed for the evolution of WG.

Periclinal fold systems in thick-bedded mudstones: A case study of the Early Cretaceous Hekou Group, Lanzhou Basin, NW China

A new type of structural association comprising periclinal folds is present in thick-bedded calcareous mudstones and siltstones of the Early Cretaceous Hekou Group in the Lanzhou Basin, NW China. The periclinal fold system consists of meso-scale, open anticlines and synclines with fold axial trends in two perpendicular orientations (NE-SW and NW-SE) and two sets of conjugate thrust faults that form intersections in the same two orientations. Folded and faulted layers of the periclinal fold system are not sedimentary bedding surfaces but sub-parallel curviplanar foliations formed by compaction of the original strata soon after deposition. Many folded curviplanar foliations connect with the unfolded, conjugate thrust faults, indicating that faulting was active during and/or soon after folding. The NE-SW and NW-SE-trending fold axes and fault planes indicate bilateral, subhorizontal contraction acting simultaneously during the formation of the periclinal fold system. In some cases, converging slickenlines on curviplanar foliation planes within anticline cores point to localized isotropic contraction probably caused by scaping fluids and increased hydrostatic pressure. Similarities with the better-known polygonal fault system include development in fine-grained sediments and layer boundness, whereas main differences are a dominance of contractional faults in the periclinal fold system versus extensional faults in the polygonal fault system and a higher consolidation of sediments needed for the development of the periclinal fold system. This study suggests that collision between the Lhasa and Qiangtang Blocks combined with oblique convergence and subsequent collision along the southeastern margin of the Eurasian plate following compaction-related volume loss of fine-grained sediments led to the formation of the periclinal fold system in the Hekou Group in the Late Cretaceous.

Seismotectonic analysis of the 2021 Damasi-Tyrnavos (Thessaly, Central Greece) earthquake sequence and implications on the stress field rotations

In early March 2021, three shallow earthquakes, two mainshocks with M6.3 and M6.0 and one major aftershock with M5.6 impacted both the mountainous Damasi-Tyrnavos region (northern Thessaly, Greece) and the adjacent Plio-Quaternary basin. Each major event was followed by rich aftershock activity recorded by local and regional seismographs and accelerographs. Herein, we present a comprehensive analysis of the seismic sequence, from its foreshock activity starting on 28 February, 2021 and for a period of two months using new high-resolution catalogues of relocated earthquakes and hundreds of focal mechanisms. The results indicate that the aftershocks form a zone that spans ~50 km NW-SE, while focal depths range between 5 and 15 km. More than 400 focal mechanisms, computed for events with M≥ 2.5, mainly exhibit normal faulting in a NW-SE direction, while WNW-ESE to E-W normal faulting is also evidenced, in particular after the occurrence of the last major event on 12 March. The stress-field was reconstructed on a local and broader scale by inverting focal mechanism data, revealing a rotation of the σ3 axis trend from NNE-SSW, in the Damasi-broader region, to NW-SE northwards, to the region of Kozani-Grevena that hosted an Mw = 6.6 shallow mainshock in 1995. Subcrustal seismicity, present beneath those areas, implies that large-scale tectonics and plate dynamics are likely involved in the deformation of the upper crust. Coulomb stress transfer after the 3 major events of the 2021 Damasi-Tyrnavos sequence reveals that stress-loaded areas include those where most aftershocks were triggered. The analysis provides implications to the seismic hazard of the activated area, as a major NW-SE active normal fault close to Larissa city became stress-loaded, constituting a possible candidate source for significant future earthquakes.

Petrology, Structural and Geochemistry of the Copper-Nickle-Iron Bearing Rocks in Korr-Marsabit Area, Northern Kenya

The main objective of this study was to investigate copper-Nickle-Iron bearing rocks of the northern Kenya, and understand their mode of formation. The area of study is bounded by latitudes 2º52'00"N and 1º52'00"N and longitudes 37º19'00"E and 37º36'00"E, South West of Marsabit town. The methods involved geological field mapping between September, 2020 and December 2020. Elemental analyses of the samples were done using an XRF. Pearsonian correlation on the analyzed elements was done using Oasis Montaj 8.4. Fabric8 software was used to analyze structural data. The area comprises metamorphic, igneous and sedimentary rocks. Metamorphic rocks include biotite hornblende gneisses, biotite gneisses, biotite muscovite gneisses and marbles. Basalts of different mineralogy were also found in the area. Colluvium and alluvium sediments were found covering some of the metamorphic rocks in some areas. Malachite occurs in gneisses in the central part of the area. The area has undergone deformation, which includes jointing and folding. The fold axis trend in the North-South direction and plunges to the southern part of the area. Correlation of the elements shows that there is a positive correlation of Copper-Nickel-Iron. This indicates similar mode of delivery within the host rocks. Kriging indicates spatial distribution of these elements within the study area. The average size of distribution can easily be computed from the maps produced by kriging.

Structural Evolution of the Parmelan Anticline (Bornes Massif, France): Recording the Role of Structural Inheritance and Stress Field Changes on the Finite Deformation Pattern

AbstractIn many orogenic wedges, foreland basin systems are preferential sites for economical resource accumulation, typically hydrocarbons. Understanding how structural inheritance perturbs the evolution of folding‐related deformation and impacts on subsurface fracture patterns bears first order economic and environmental implications, when also CO2 storage is considered. Studying properly selected field analogs of buried anticlines provides fundamental information on fracture patterns at the subseismic scale. The Parmelan anticline is a flat‐topped box‐fold located in the Bornes Massif (France) involving Lower Cretaceous platform carbonates (Urgonian Limestones). We studied this field analogue by combining structural analysis with syntectonic calcite vein petrography and geochemistry to unravel the progression of deformation and to obtain constraints on the regional stress field evolution. We documented (a) a network of pre‐folding hinge‐parallel and hinge‐perpendicular extensional fault zones, (b) two deformation assemblages developed during pre‐folding layer‐parallel‐shortening under different stress configurations including veins, bed‐perpendicular stylolites and subsidiary reverse faults, (c) a limited occurrence of localized syn‐folding deformation structures (i.e., hinge‐parallel veins), and (d) an association of veins and stylolites oblique to the fold axial trend, formed in a post‐folding stage. We propose that pre‐ and syn‐orogenic inherited structures controlled first‐order fold geometry and partial development of classical syn‐folding deformation features. Moreover, our data reveal a complex stress history marked by permutations of the vertical principal stress axis from strike‐slip to purely compressional stress regimes and vice versa, accompanied by a progressive counterclockwise rotation of the horizontal maximum stress axis.

Paleostress reconstruction of the southeast Ukrainian Outer Carpathians

ABSTRACT The paleostress analysis of the southeast part of the Ukrainian Outer Carpathians (UOC) was carried out with the separation and stress inversion TR method (TRM). The analysis includes site and bulk stress tensors through which the late-orogenic processes of the frontal part of UOC can be better described. In particular, three bulk compressive stress regimes dated to Miocene describe a compressional deformation that changes progressively from real to hybrid. The first stress regime is a pure compression and changes progressively to transpression, while the trend of the greatest principal stress axis ( constantly remains ENE-WSW (065°), perpendicular to the main trend of the UOC. This progressive deformation spans the Late Burdigalian to Sarmatian period and reflects the driving stresses during the Alcapa and Tisza-Dacia mega-units drifting and docking with the Eastern European Platform. During the transpressional stress regime, the thrust displacements waned, and transfer (strike-slip) faults accommodated the deformation. The third stress regime is also a hybrid compression, i.e. transpression, but the greatest principal stress axis () trends NNE-SSW (029°). It reflects the post-docking deformation giving rise to mesoscale NW-WNW thrusts and transfer (strike-slip) faults. However, these thrusts and strike-slip faults have not modified the NNW-SSE rectilinear trend of the UOC. This hybrid compression outlasted the Late Miocene (Latest Sarmatian–Early Maeotian), and it is related to the separation and left-lateral movement of the Tisza-Dacia plate from the Alcapa plate. In addition, two extensional stress regimes with the least principal stresses () trending NE-SW and NW-SE have been defined. We interpret them to represent subsidiary stresses in the Carpathians’ uppermost part due to orogen collapse both normal and parallel to the orogen after the Late Miocene.

Seismic conceptual design and analysis method of Bridges crossing active fault

For bridges crossing active fault, combined with relevant standards and recent research results, the seismic conceptual design such as bridge axis trend planning, bridge type selection, fault trace avoidance distance of substructure, fault span and lap length are systematically summarized; some suggestions on seismic analysis methods such as the value of horizontal and vertical acceleration response spectrum, the generation of ground motion acceleration and displacement time history, and the input mode of time history are put forward.

Integration of satellite data processing with seismic sections for tectonic interpretation and modeling for the breaks and omissions of continuous stratigraphic units

AbstractSatellite thematic maps in geological field studies are an important tool for the delineation, interpretation, representation, and visualization of geological processes, while the development of seismic sections offers an increasingly detailed analysis of subsurface geology and inferring and understanding the subsurface structure of the earth. This combination promoted a fast-growing research in the fields of morphotectonics and neotectonics. The area under investigation is one of the most significant Iraqi places which includes several oil fields. The study area is located in northern Iraq and administratively follows Kirkuk governorate. Landscapes in this area are characterized by asymmetrical, cylindrical and extended folds. Kirkuk, Bai-Hasan and Qarachuq Anticlines reflect these structural elements and their fold axis trends towards northwest-southeast within the Zagros folded zone. The main objective of this study is to use the visual and digital interpretation of Landsat image to discriminate the sudden breaks and omissions of rock beds in the study area. Therefore, a morphotectonic map was created, the accurate location of the sudden breaks was provided and the zones affected by tectonic deformation, which left its imprint on the successive lithological units were detected. Seismic data were used to assess the tectonic impact on subsurface formations and their reflections on exposure rocks. The seismic lines were selected based on the locations of the identified sudden breaks as interpreted from satellite images. The hypothesis derived from this study is that the sudden breaks in the study area were triggered by a series of faults. In addition, the region was affected by the vertical stresses resulting from these faults and morphological aspects of the region were determined by the temporal variations of the above stresses.

Origin of the Caldas Novas dome (Brazil) and its thermal water circulation

The Caldas Novas dome, a 20 × 12 km elliptical structure, with its longer axis trending NNW-SSE, was previously described as a structural window into the south-central part of the Neoproterozoic Brasília belt. The Brasília belt is the central part of the Tocantins Province, a former orogen. Hot springs, broad gravimetric and magnetic features, and a radiometric anomaly over the dome are observed. The dome aligns with the well-known Alto Paranaíba Cretaceous Igneous Province. All these observations have raised questions in the past about a possible magmatic origin of the dome. In this work, existing regional gravimetric, seismologic, magnetic, radiometric, hydro-geochemical data, as well as new isotopic data, were integrated. From the magnetic data, it is clear that a NW-SE trending linear structure is the most significant geophysical feature of the analyzed dataset. We interpret that the NW-SE trending aeromagnetic lineaments may host basaltic dikes. The interpretation is based on the occurrence of basaltic rocks in the eastern portion of the Paraná basin overlying the Brasília belt, observed outcrops of basalt in the Iporá area, and the linear features identified here. Most characteristics identified in the magnetic data are also evident in the radiometrics, and a sharp anomaly in the eTh/K and eU/K ratio map is centered on the Caldas Novas dome. Weathering related depletion of potassium over the dome is the most probable explanation for the observed radiometric anomaly. From chemical and geological evidence, the groundwater in the area likely originates from meteoric processes. The thermal spring water near the dome is associated with deep circulation in fracture systems probably related to a broad shear/fault zone. This is supported by the Cretaceous dike swarm postulated in the region, possibly emplaced into an existing fracture system. We infer that a fracture system, which would continue beyond the limits of the aero-geophysical survey, most likely accounts for the groundwater circulation and heating.