Trending Faults Research Articles

Electric Machine Bearing Health Monitoring and Ball Fault Detection by Simultaneous Thermo-Mechanical Fibre Optic Sensing

This article reports the use of fiber Bragg grating (FBG) sensors for electric machines' in-service bearing condition monitoring. The proposed method enables simultaneous extraction of thermal and mechanical information on the bearing operational status for health monitoring and fault diagnosis purposes. The work first reports the instrumentation, calibration and the measurements interpretation methods of an FBG array sensor fitted to the drive-end bearing of an operating inverter driven induction motor. Experimental tests are then undertaken on a purpose build test rig to evaluate the proposed in-situ sensing scheme's performance under healthy and faulted bearing conditions. The results demonstrate that the measurements acquired by individual FBG sensors fitted in the bearing architecture contain concurrent thermal and mechanical information, which can be clearly differentiated to enable understanding of the examined motor bearing's thermal only and mechanical only operating conditions. Furthermore the in-situ measurements obtained in fault conditions are shown to contain clearly defined time and frequency domains fault signatures, which can enable unambiguous fault diagnosis and trending.

Spatio-temporal foreshock evolution of the 2019 M 6.4 and M 7.1 Ridgecrest, California earthquakes

The 2019 M 6.4 and M 7.1 Ridgecrest, California earthquake sequence provides an ideal opportunity to study the seismicity evolution and interaction among multiple complex fault structures. Here, we apply the matched-filter detection method to obtain a relatively complete (magnitude of completeness ≈ 0.9) and precisely relocated earthquake catalog. The results show a short-duration (∼ 31 minutes) foreshock sequence with 28 events, before the M 6.4 earthquake. The foreshock sequence started with a M 4.0 event and was aligned along the NW-SE direction. This implies that the M 6.4 rupture initiated on a NW trending fault segment, before rupturing the primary SW trending fault. Repeating earthquakes before and after the M 7.1 event are separated in space and bound the areas of large coseismic slip in the M 6.4 and M 7.1 events. This might reflect local slow slip acceleration near the edges of coseismic rupture asperities. The NW-striking fault zones illuminated by seismicity are separated into several sub-regions with distinct pre-M7.1 seismicity rate evolutions. The M 7.1 event nucleated in a region of local seismicity concentration which intensified ∼ 3 hr before the M 7.1 mainshock. The M 7.1 nucleation zone is characterized by a significantly low b value of events that occurred since the M 6.4 event, which might indicate local failure conditions approaching a critical state.

Machining centre performance monitoring with calibrated artefact probing

Maintaining high levels of geometric accuracy in five-axis machining centres is of critical importance to many industries and applications. Numerous methods for error identification have been developed in both the academic and industrial fields; one commonly-applied technique is artefact probing, which can reveal inherent system errors at minimal cost and does not require high skill levels to perform. The primary focus of popular commercial solutions is on confirming machine capability to produce accurate workpieces, with the potential for short-term trend analysis and fault diagnosis through interpretation of the results by an experienced user. This paper considers expanding the artefact probing method into a performance monitoring system, benefitting both the onsite Maintenance Engineer and visiting specialist Engineer with accessibility of information and more effective means to form insight. A technique for constructing a data-driven tolerance threshold is introduced, describing the normal operating condition and helping protect against unwarranted settings induced by human error. A multifunctional graphical element is developed to present the data trends with tolerance threshold integration to maintain relevant performance context, and an automated event detector to highlight areas of interest or concern. The methods were developed on a simulated, demonstration dataset; then applied without modification to three case studies on data acquired from currently operating industrial machining centres to verify the methods. The data-driven tolerance threshold and event detector methods were shown to be effective at their respective tasks, and the merits of the multifunctional graphical display are presented and discussed.

1D‐CNN based real‐time fault detection system for power asset diagnostics

Electromagnetic interference (EMI) diagnostics aid in identifying insulation and mechanical faults arising in high voltage (HV) electrical power assets. EMI frequency scans are analysed to detect the frequencies associated with these faults. Time-resolved signals at these key frequencies provide important information for fault type identification and trending. An end-to-end fault classification approach based on real-world EMI time-resolved signals was developed which consists of two classification stages each based on 1D-convolutional neural networks (1D-CNNs) trained using transfer learning techniques. The first stage filters the in-distribution signals relevant to faults from out-of-distribution signals that may be collected during the EMI measurement. The fault signals are then passed to the second stage for fault type classification. The proposed analysis exploits the raw measured time-resolved signals directly into the 1D-CNN which eliminates the need for engineered feature extraction and reduces computation time. These results are compared to previously proposed CNN-based classification of EMI data. The results demonstrate high classification performance for a computationally efficient inference model. Furthermore, the inference model is implemented in an industrial instrument for HV condition monitoring and its performance is successfully demonstrated in tested in both a HV laboratory and an operational power generating site.

The Dudica Epithermal Cu–Au Deposit (Republic of North Macedonia)

The Dudica deposit is located in the southern part of the Republic of North Macedonia (RNM), not far from the border with Greece in the Kozuf–Aridean volcanic region. The deposit is genetically associated with the Neogene igneous event (≥6 Ma, K/Ar), which is manifested at the intersection of northeast trending faults with the northwest trending Vardar fault zone. The REE spectrum of volcanic rocks here is characterized by a weak negative Eu anomaly and enrichment in light REE (LREE) relative to heavy REE (HREE). Mineralization is found in veins, veinlets, and dissemination; Cu concentration is around 0.5%; Au, up to 1 g/t. The principal ore minerals are chalcopyrite, bornite, enargite, covellite, chalcocite, and digenite; pyrite, galena, sphalerite, marcasite, and native gold are less frequent. The δ34S isotope composition falls within a narrow interval of +1.00 to +2.50‰, indicative of the igneous origin. The data obtained suggest that the Dudica deposit belongs to the class of the high-sulfidation epithermal deposits.

Zircon U–Pb dating, geochemical, and Sr–Nd–Pb–Hf isotopic constraints on the age and origin of intermediate to felsic igneous rocks at South Altyn, Xinjiang, China

As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strike-slip fault is present, the Altyn Orogenic belt (AOB) has become an important focus for research. Magmatic rocks are widely distributed across the AOB. However, many investigations have focused primarily on Paleozoic igneous rocks; discussion of Mesozoic related igneous activity is often ignored. Here we present the result of studies of representative diorite and granite rocks outcropping in the AOB, within the Xinjiang Uygur Autonomous Region, South Altyn, China. We present new zircon LA-ICP-MS U–Pb age, geochemical, and Sr–Nd–Pb–Hf isotopic data for these sample suites, identifying them as typical igneous rocks formed between 238 ± 1.5 and 238.8 ± 1.1 Ma. The rocks that we studied fall into the alkaline series, also enriched in light rare earth elements (LREE), some large ion lithophile elements (LILE; e.g., Rb, Ba, Sr, and K), Pb, Th and U, and depleted in heavy rare earth elements (HREE), Nb, Ta, Hf, and Ti. The granite and diorite have high initial 87Sr/86Sr ratios (0.7062–0.7114), negative eNd (t) values (− 8.8 to − 11.3), eHf (t) values (− 8.7 to − 18.7), and relatively constant Pb isotopic ratios ((206Pb/204Pb)i = 6.74–17.884, (207Pb/204Pb)i = 15.51–15.58, and (208Pb/204Pb)i = 35.36–38.04), respectively. This suggests that the magmas parental to these rocks were generated from the partial melting of the ancient crust. The parental magmas to these rocks experienced a degree of fractionation of plagioclase, K-feldspar, and hornblende, possibly during rapid magma ascent. Based on these studies, we propose a reasonable model for the origin of the investigated rocks from the Xinjiang Uygur Autonomous Region of South Altyn, which involves crustal thickening, lithospheric extension, and asthenosphere upwelling, that induced crustal melting.

STUDY ON THE APPLICATION OF AIRBORNE LIDAR IN SEISMIC ACTIVE FAULTS IN THE NORTHERN RIM OF QINLING MOUNTAIN AND THE PIEDMONT OF HUASHAN IN CHINA

Abstract. Seismic active faults are closely related to earthquake disasters. Active faults determine the location and magnitude of destructive earthquakes. Therefore, strengthening active fault investigation and research is one of the main ways to reduce earthquake disasters. Airborne LiDAR, as a measurement method that can quickly obtain large-area and high-precision DEM results, can not only obtain structural distribution features of large-scale study areas on a macro scale, and determine the location and trend of active faults, but also be used to identify microstructural landforms and take researches on fine geomorphic structural features. In this paper, based on the detailed introduction, analysis and summary of the technical schemes, data processing and application of the airborne LiDAR technique in the northern margin of the Qinling Mountains and the Huashan Piedmont Fault Zone, it was demonstrated on the basic methods and technical advantages in seismic active faults and geomorphological research work of the airborne LiDAR technology, and a new and efficient method for seismic fault study was provided.

A New Discovery of Ag-Pb-Zn Mineralization via Modern Portable Analytical Technology and Stream Sediment Data Processing Methods in Dajiacuo Area, Western Tibet (China)

Tibet, which is rich in mineral resources, is a treasure trove for geological explorers. However, prospecting work has been slow, especially in the western part, due to the precipitous terrain, changeable climate and low access. Hence, modern advanced field analytical technology and effective data processing methods play significant roles in rapid and efficient exploration in Tibet. In this paper, spectrum-area fractal modeling and portable X-ray fluorescence analysis (pXRFA) were used to identify and verify geochemical anomalies associated with Ag-Pb-Zn mineralization based on a stream-sediment dataset of 39 elements in the Dajiacuo-Xurucuo region of western Tibet. First, staged factor analysis (SFA) was used to obtain the Ag-Pb-Zn-Cd geochemical assemblage. Second, the first-factor pattern obtained using SFA was dissociated by a spectrum-area (S-A) fractal model and a digital elevation model (DEM)-based geochemical model (DGM) was constructed. Finally, the sections of Ag, Cd, Pb, and Zn were obtained using pXRFA. The results show that Ag-Pb-Zn-Cd enrichment zones were mostly located around the contact belt of volcanic rocks and intrusions, or along SE-NW trending faults. Considering the variable terrain and catchment basin, the extension of long axes of Ag-Pb-Zn-Cd anomalies into higher elevation areas that are favorable for Ag-Pb-Zn mineralization should be investigated. Anomaly maps created with the aid of a DGM show promising potential for mineralization in the Dajiacuo-Xurucuo region, and abundant Ag-Pb-Zn mineralization was identified with the assistance of pXRFA in the source areas for the geochemical anomalies in the Dajiacuo. We conclude that SFA and the S-A fractal model constitute a valid tool to identify or verify geochemical anomalies in areas of low-density stream-sediment sampling. The pXRFA can accurately determine the source of geochemical anomalies and improve anomaly verification efficiency.

Seismotectonics and Seismic Source Parameters of the Mid-Eastern Iraq - Western Iran Using Moment Tensor Inversion Technique

The study area is encompassed by the 33.59-34.93°N latitudes and 45.44-46.39°E longitudes and divided into four groups with respect to earthquake event locations. We determined fault plane solutions, moment magnitudes, focal depths, and trend of slip with the direction of the moment stress axes (P, N, and T) for 102 earthquakes. These earthquakes had a local magnitude in the range between 4.0 and 6.4 for the time period from January 2018 to the end of August 2019, with focal depths ranged between 6 and 17 km. Waveform moment tensor inversion technique was used to analyze the database constructed from seismic stations on local and neighboring country networks (Iraq, Iran, and Turkey). We separated the studied events into four regional subsets (circles). The types of the obtained fault plane solutions are predominantly thrust fault and strike-slip, with the focal depths ranging from 8 to 21 km.
 A new scaling relation between local magnitude (Ml) and the estimated moment magnitude (Mw) has been developed utilizing a linear regression. Good match results obtained in the present research good match with both seismic trends concluded from earthquake locations and mapped faults. Generally, direction shows NW–SE striking focal planes corresponding with the tectonic framework of the Arabian–Eurasian continental collision zone. The anticlockwise rotation of the Arabian plate that appears accountable for strike-slip displacements on fault surfaces.

Structural analysis of the Smeaheia fault block, a potential CO2 storage site, northern Horda Platform, North Sea

Smeaheia, a prominent fault block located on the Horda Platform, northern North Sea is identified as a potential subsurface CO2 storage site. We utilise the GN1101 3D seismic survey to generate a high-resolution subsurface geomodel to inform the structural style and evolution of the fault block, to investigate geological controls on proposed CO2 storage and provide a geometric framework as a basis for future analyses. Two basement-involved (first-order) north-south trending fault systems, the Vette Fault Zone (VFZ) and the Øygarden Fault Complex (ØFC), bound the 15 km-wide fault block. The VFZ bifurcates down-section where it is hard-linked with two separate basement structures, a phenomenon we term as “dual rooted”. Apart from activity during the Permo-Triassic (Rift Phase 1) and the Late Jurassic–Early Cretaceous (Rift Phase 2), we present evidence that rifting in this part of the North Sea continued into the Late Cretaceous with minor reactivation in the Palaeocene–Eocene. Two segments of the VFZ interacted and linked at a relay ramp during Rift Phase 2. Second-order (thin-skinned) faults show basement affinity and developed during Rift Phase 2 in two distinct pulses. A population of polygonal faults intersects the overburden and developed during the Eocene to middle Miocene. We have revised the areal extent of two structural closures that define the Smeaheia fault block, Alpha (VFZ footwall) and Beta (ØFC hanging wall) which consist of Upper Jurassic Viking Group target formations. Simplified cross-fault juxtaposition analysis of the VFZ and second-order intra-block faults are presented and inform pressure communication pathways between the Smeaheia and Tusse fault block, as well as reservoir integrity and compartmentalisation. The geomodel further identifies important geological controls on CO2 storage in the fault block including a thinning caprock above the Alpha structure, and identification of hard-linkage between deep tectonic faults and shallow polygonal faults.

ASTER and WorldView-3 satellite data for mapping lithology and alteration minerals associated with Pb-Zn mineralization

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and WorldView-3 (WV-3) satellite remote sensing data were used for mapping lithological units and hydrothermal alteration zones associated with Pb-Zn mineralization in the Kerman–Kashmar Tectonic Zone (KKTZ), Iran. The visible near infrared (VNIR), shortwave infrared (SWIR) and thermal infrared (TIR) bands of ASTER were used to map iron oxide/hydroxides, Al-OH minerals, Fe,Mg-OH minerals, quartz and carbonate minerals. The VNIR bands of WV-3 were used to discriminate Fe3+ and Fe2+ absorption intensities. Selective Principal Component analysis (SPCA), Spectral Angle Mapper (SAM), Linear Spectral Unmixing (LSU) and Automatic Lineament Extraction techniques were implemented. Lithological units were discriminated based on Al/Fe-OH, Fe2+/Fe3+ and Mg-Fe-OH/CO3 absorption properties. The spatial distribution of hematite, goethite, jarosite, gypsum, calcite, dolomite, kaolinite and muscovite were comprehensively detected. Some prospective zones were identified in the intersection of N-S, NW-SE and NE-SW trending fault systems, gossan, argillic/phyllic and dolomitic units.

Morphology of the basement and Hormuz salt distribution in offshore Abu Dhabi from constrained 3-D inversion of gravity and magnetic data

Many seismic surveys and exploration wells have been conducted in offshore Abu Dhabi, United Arab Emirates. However, the Neoproterozoic basement and the Infracambrian Hormuz salts were not imaged or penetrated by seismic and well data. To delineate the morphology of the basement and distribution of salt bodies, we applied a 3-D constrained inversion method to aerogravity and aeromagnetic data covering offshore Abu Dhabi. Well and seismic data were used to constrain and validate the inversion results. The magnetic inversion model resulted in a robust basement model that varies in depth from 8 to 10 km with two highs at 8 and 8.5 km highlighting possibly magmatic bodies. In contrast, the gravity inversion model does not delineate very well the basement morphology, possibly due to the lower density salt bodies masking the gravity response of the higher density basement. By calculating and removing the gravity response of the magnetic basement model from the observed gravity data, we recovered the residual gravity response of the Hormuz salts. The 3-D gravity inversion of the residual shows that the Hormuz salts are more wide-spread and thicker than previously thought with a depth to top of salt varying from 5.5 to 8.5 km. This salt model suggests that the giant oilfields in offshore Abu Dhabi, such as Umm Shaif, Nasr, Abu Al-Bukhoosh, Zakum, Sarb and Hail, occur exactly above crests of salt pillows. In addition, a series of smaller oilfields are found located at the margin of the northern basement high, and three structural lineament trends (NE-SW, NW-SE, and N-S) were identified from the inverted basement and salt models. Reactivation of these fault trends and associated diapiric salt uplifts, as observed in the seismic sections and curvature map, played a major role in shaping the basement morphology and mobilization of the Hormuz salts.

Investigation of groundwater potential using magnetic and satellite image data at Wadi El Amal, Aswan, Egypt

In this study Aeromagnetic, ground-based magnetic and satellite imagery data have been processed and analyzed to delineate surface and subsurface structures to clarify its impacts on groundwater flow direction, and to detect the thickness of groundwater aquifer’s (accumulation) in the study area. To achieve this target, an interpretation of satellite digital elevation data is processed to generate the main drainage pattern in the area to delineate the Watersheds basins and where the surface water can be accumulated. Moreover, Aeromagnetic data have been used to detect the sedimentary cover in the area, and to assess the thickness distribution of the Nubian aquifer to detect the most eligible aquifer with the largest thickness, consequently the largest amount of groundwater reserve. Also, the ground magnetic survey was conducted in Wadi El Amal to reassure the results obtained from the airborne data. Two main approach techniques were applied to the data. Firstly, the trend analysis applied to the first vertical derivative map to detect main trend analysis and faults. The second approach is to calculate the depth to the basement, which represents the base of the Nubian aquifer in the area under consideration. The final results of the main trend found as follow, the ENE-WSW, NW-SE, and NE-SW trend which found to be is the main trend. The water table in this area is about 100 m, the calculated depth to the basement in the deepest parts study area is ranging between −300 and −700 below ground surface. The integration between satellite techniques and geophysical tools can give us the whole picture of groundwater distribution and its recharge sources.

Spatial Analysis on Gold Mineralization in Southwest Saqqez Using Point Pattern, Fry and Fractal Analyses

The Baneh- Saqqez zone is part of the Sanandaj‒Sirjan Zone, northwest of Iran. Generally, this zone is recognized as a gold bearing zone, and the mineralization in it is controlled by faults. In this research, structural lineaments were extracted using Landsat 8 (OLI) image, in which the main lineaments trend NE‒SW, EW and NW‒SE. Spatial distributions of the mineralization are examined by using the point pattern, Fry and fractal analyses. The pattern of structural controls on the gold mineralization in southwest Saqqez, is almost regular, and the trend of gold mineralization and Fry points show NE‒SW and EW trends. Comparison of rose diagrams for the Fry analysis final translation points and faults in southwest Saqqez show that the orientations of mineralization are similar to NE‒SW and EW trending faults and that the mineralization intersects the NW‒SW trending faults. The results of fractal analysis suggest that gold occurrences in the area have higher fractal dimension. The deep regional faults cause a way for ore-bearing fluids to migrate and control the emplacement of the intrusive bodies and the position of ore mineralization in the Saqqez‒Baneh sub-zone. On that basis, a survey of spatial data and its relationship to structural features can be useful for future exploration and discovery of new occurrences of gold mineralization.

A Multiswitch Open-Circuit Fault Diagnosis of Microgrid Inverter Based on Slidable Triangularization Processing

In this article, a robust inverter fault diagnosis algorithm is proposed under microgrid environment considering unbalanced state and overcurrent component interference. First, the detected signals are transformed into different data triangles by the proposed slidable triangularization processing which can conveniently and effectively extract the multiscale trend features and data jitter components. Further, the signed features are obtained by the proposed jitter signing processing method, which can reduce the influence of amplitude, and facilitate the logical operation and mixed operation. Then, a quantitative trend fault degree is calculated by the signed information to reflect the fault degree and location information, which has the characteristics of quantitative change. It can reduce the fluctuation and quantity of fault data features. Finally, echo state network is used to implement the intelligent classification. Because the design of hidden layer and the network training speed is simple and fast, which makes the design, implementation, and debugging of fault diagnosis more convenient. Compared with the existing fault diagnosis algorithms, it is robust to unbalanced state and overcurrent component interference of microgrid. These features make it more suitable for inverter fault diagnosis of microgrid environment. The effectiveness of fault diagnosis algorithm is verified by the experiments and comparisons.

Stratigraphic and structural trapping frameworks in the central Ceduna Sub-basin

Despite a recent renewal in exploration, the Ceduna Sub-basin is underexplored and, as is typical with frontier basins, there is considerable uncertainty regarding lithofacies distribution. As such, there is limited understanding of reservoir and seal coupling as well as structural trapping and thus fluid migration pathways within the prospective Late Cretaceous marine and deltaic intervals from the Tiger and Hammerhead supersequences.To address these uncertainties, a stratigraphic forward model using multiple sediment source points and constrained by recent marine survey data was developed to simulate the deposition and preservation of potential stratigraphic successions across the sub-basin. Pseudo-wells have been extracted from the stratigraphic forward modelling output to forecast vertical and lateral stratigraphic trends. These trends were analysed to predict fault seal and structural trapping likelihood using the Shale Gouge Ratio methodology and triangle juxtaposition diagrams.Over the study area, the modelled facies distributions and geometries are consistent with sequence stratigraphy, seismic stratigraphy and well data. The stratigraphic model shows an overall NW to SE trend of decreasing sand volume and sand interval thickness for the Tiger and Hammerhead supersequences. Although this highlights the general trend of a higher likelihood of reservoir presence to the NW of the study area, and more seal presence to the SE, the model predicts enough vertical variability within the supersequences to create ranges of stacked reservoir-seal couplets.The stratigraphic model and fault seal assessment suggest that, in the marine-influenced Tiger and lower Hammerhead supersequences, the best reservoir and top/fault seal couplets are located along a WSW-NE trend to the NW of the study area where faults with throw≥150 m are expected to yield membrane fault seal. The NW corner of the study area is predicted to have high net-to-gross ratio for the upper Tiger, too high to yield any efficient membrane fault seal. In the deltaic upper Hammerhead supersequence, the best reservoir and top/fault seal couplets are expected along an E-W trend in the central part of the study area. Along this trend faults with throw≥100 m are expected to yield membrane fault seal able to impede lateral hydrocarbon flow in modelled mid Campanian reservoirs and a nearshore interval.These inferred Late Cretaceous structural traps could have been charged by hydrocarbons expelled from local Late Cretaceous source rocks between the Cenomanian to the present-day.

A case study of 3D geomodelling of Frontier Formation Second Wall Creek Sand, Teapot Dome, Wyoming, USA

The research focuses on 3D seismic geomodelling of Cretaceous shoreface reservoir sands of the Frontier formation, Teapot Dome, Wyoming, USA. 3D geomodelling helps in understanding the facies distribution (lateral and vertical) of Frontier Formation Second Wall Creek (F2WC). We have adopted an integration of petrophysical analysis, seismic interpretation and geostatistical evaluations to map the facies. In geostatistical modelling the data distribution of the discrete reservoir properties has been performed using the sequential indicator simulation (SIS) while the continuous data modeled with the help of Sequential Gaussian Simulation (SGS). Total 32 wells have been used in this study along with a synthetic seismogram generation for the time-domain correlation of well-tops with the seismic reflections using wells (67–1-TpX-10 and 25–1-X-14). The study area is a structurally deformed asymmetrical doubly plunging dome of the lower Cretaceous to Eocene, Laramide deformation with EW trending faults that can be easily identified by modelling techniques mentioned. In this study, two blind wells are also used to verify the model, the horizons are also verified using the TDR relation provided for 67–1-TpX-10. Velocity modelling also helped in the verification of correct depth of each formation with the well tops. F2WC is attributed with average permeability ranging between 0 and 100 mD, average porosity is 18%, the average water saturation is 30%. The results suggest that the southern part of Teapot Dome is more prolific due to better spatial distribution of porosity, permeability and less water saturation within the reservoir model.

Geochronology of calcite‐filled joints, southeast Canada: Insight into Late Cretaceous deformation of eastern North America

AbstractResolving the timing of brittle tectonism is a challenge. We examined intra‐cratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are both cut by ENE‐WSW trending fault zones that have historic M4‐5 earthquakes along their trace. Calcite‐filled mode I joints are ubiquitous within the strata, and are parallel to the modern stress field. Calcite δ18O and δ13C values are analogous to the bulk composition of Middle Ordovician limestones, and suggest vein formation from a source dominated by connate fluids of the host rock. U‐Pb geochronology of six calcite veins sealing ENE‐WSW oriented joints produced similar Cretaceous dates and were regressed together yielding a date of 96.8 ± 1.1 Ma (MSWD: 2.9). A Cenomanian age is consistent with the most recent reorientation of North America's compressive stress field, which is attributed to a change in spreading direction along the northern Mid‐Atlantic Ridge and is linked to a global plate reorganization event at ca. 105–100 Ma. These results suggest that the most recent redistribution of lateral stress was not a passive event, and generated brittle deformation and fluid flow at least 500 km inland of North America's Atlantic passive margin.

Unfolding impacts of freaky tectonics on sedimentary sequences along passive margins: Pioneer findings from western Indian continental margin (Offshore Indus Basin)

The Western Passive Continental Margin of the Indian Plate (WCMI) serves as an elegant laboratory for understanding the syn-sedimentary rift-drift tectonics preserving a variety of episodic structural deformations and complex sedimentary infill. Here we present a multidisciplinary study on Offshore Indus Basin (OIB) that is less investigated compared to adjacent marginal basins along WCMI. Reflection seismic, gravity, borehole, and biostratigraphic data have been used to reconstruct the tectono-sedimentary history of the Meso-Cenozoic succession in OIB. Seismic based dynamic stratigraphy helped in mapping seven different depositional sequences grounded on morpho-tectonic considerations. The seismic expression of these sequences provided an idea of the depositional styles with different tectonic episodes since rifting in Jurassic to basin inversion in Miocene continued to present time. The OIB initially filled from the north with the sediments rapidly prograding southwards. In general, the basin deepens in the central and northwestern part where the formations achieve maximum depths. The analysis of 3D structural models revealed that the region experienced poly-phase deformation from the Late Cretaceous to recent times that include steeply dipping normal faults, horst, and graben, half-graben, half-graben with growth faulting, flower structures, anticline, syncline, and uplift with an angular unconformity. The most remarkable tectonic activity happened at the Early Miocene and resulted in the reactivation of extensional faults into strike-slip faults giving rise to a spectacular structural inversion due to transform movement between Indian and Arabian Plates that continues to present day. The most predominant faults are oriented in S20°-50°E with azimuth as 120°–160° and the maximum dip angles are >80° in the southwest flank of the basin. The main fault trend is S20°E-N20°W and dip angles ranging between 40° and 80° and above. A thick crust and the Ocean-Continent Transition (OCT) is imaged with massive felsic, mafic, and ultramafic intrusions by the help of forward gravity modeling. An initial onset of syn-rift tectonic subsidence between 90 and 68 Ma with a post-rift general increase between 68 and 54 Ma is comprehended while two uplift events at ~40 Ma and ~18 Ma are documented through backstripping analysis. It is inferred that the region is rapidly under complex structural inversion with growing folding, faulting, and flowering structures. This study could help in explaining the unanswered reasons of structural complexities, depositional styles, and basin inversion along worldwide passive margins.

Polyphase deformation along the South Bohemian Batholith-Moldanubian nappes boundary – The Freyenstein Fault System (Bohemian Massif/Austria)

Abstract This work describes the Freyenstein Fault System, which extends over 45 km in the southeastern part of the Bohemian Massif (Lower Austria). It represents a ductile shear zone overprinted by a brittle fault located at the eastern edge of the South Bohemian Batholith towards the Moldanubian nappes. It affects Weinsberg- and a more “fine-grained” granite, interlayered aplitic granite and pegmatite dikes as well as paragneiss of the Ostrong Nappe System. The ductile shear zone is represented by approximately 500 m thick greenschist-facies mylonite dipping about 60° to the southeast. Shear-sense criteria like clast geometries, SCC`-type shear band fabrics as well as abundant microstructures show top to the south/ southsouthwest normal shearing with a dextral strike-slip component. Mineral assemblages in mylonitized granitoid consist of pre- to syntectonic muscovite- and biotite-porphyroclasts as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. Dynamic recrystallization of potassium feldspar and the stability of biotite indicate upper green-schist-facies metamorphic conditions during the early phase of deformation. Fluid infiltration at lower greenschist-facies conditions led to local sericitization of feldspar and synmylonitic chloritisation of biotite during a later stage of ductile deformation. Finally, a brittle overprint by a north-south trending, subvertical, sinistral strike-slip fault that shows a normal component is observed. Ductile normal shearing along the Freyenstein Shear Zone is interpreted to have occurred between 320 Ma and c. 300 Ma. This time interval is indicated by literature data on the emplacement of the hostrock and cooling below c. 300°C inferred from two Rb-Sr biotite ages measured on undeformed granites close to the shear zone yielding 309.6 ± 3 Ma and 290.9 ± 2.9 Ma, respectively. Brittle sinistral strike-slip faulting at less than 300°C presumably took place not earlier than 300 Ma. Early ductile shearing along the Freyenstein Fault System may be genetically, but not kinematically linked to the Strudengau Shear Zone, as both acted in an extensional regime during late Variscan orogenic collapse. A relation to other major northeast-southwest trending faults of this part of the Bohemian Massif (e.g. the Vitis-Pribyslav Fault System) is indicated for the phase of brittle sinistral movement.