Sinistral Strike-slip Faults Research Articles

Satellite land surface temperature for mapping the structurally controlled geothermal anomalies in the Cretaceous rift, South Egypt

ABSTRACT Exploration of new geothermal systems often requires regional-scale investigation. Satellite Land Surface Temperature (LST) products are essential in geothermal anomaly identification and mapping. In this study, seven thermal anomalies covering Egypt were observed using the Sentinel-3 LST images acquired in 2019 and confirmed using the 2020 LST images. In addition, the LST analysis reveals three new anomalies covering the southern part of Egypt (Kalabsha, Natash, and Wadi Allaqi), which are structurally controlled. Nuqra-Kharit-Natash is a good site for geothermal energy owing to the following reasons: 1) the high geothermal gradient beneath the Wadi Natash region (heat flow ~100 mW/m2); 2) the presence of many geothermal anomalies retrieved from the analyses of the Landsat-8 acquired in August 2018; 3) existence of surface geothermal manifestation at the western boundary of the basin includes warm springs and the tufa deposits. Intricate structural patterns, including NW-oriented normal faults, ENE-to-WNW-oriented right-lateral faults, and NNE-oriented sinistral strike-slip faults, characterise Wadi Natash. Wadi Natash LST anomaly shows a solid relation to fault trends. High values of LST are arranged along NW and NNE faults and recorded the peak at the intersection of two fault trends. Recent seismic activity along the NNE fault system enhances the permeability along this trend and its intersection with the NW-oriented fault.

Spatial Variations of Late Quaternary Slip Rates along the Ganzi–Xianshuihe Fault Zone in the Eastern Tibet

The Ganzi–Xianshuihe Fault Zone is a large-scale sinistral strike-slip fault zone on the eastern Tibet. As the boundary fault zone of the Bayankala Block and the Chuandian Block, it controls the clockwise rotation of the southeastern Tibet. However, there is still controversy regarding the activity changes between fault zones. Therefore, accurately determining the slip rates of faults in the area is crucial for characterizing regional plate motions and assessing associated seismic hazards. We focused on studying four fault segments near the Ganzi–Xianshuihe Fault Zone, including the Manigango, Ganzi, Luhuo, and Daofu segments. In each segment, we selected typical sinistral piercing points and carried out Unmanned Aerial Vehicle (UAV) photogrammetry to obtain high-resolution terrain data. We utilized LaDiCaoz_V2.2 and GlobalMapper software (LaDiCaoz_V2.2 and Global Mapper v17.0) to measure the offsets, together with optically stimulated luminescence (OSL) dating, to constrain the timing of fault activity. The estimated slip rates for the Manigango, Ganzi, Luhuo, and Daofu segments are as follows: 9.2 ± 0.75 mm/yr, 9.59 ± 1.7 mm/yr, 4.23 ± 0.66 mm/yr, and 7.69 ± 0.76 mm/yr, respectively. Integrating previous results with slip rates estimated in this study, our analysis suggests the slip rate of the Ganzi–Xianshuihe Fault Zone is around 8–10 mm/year, exhibiting a consistent slip rate from northwest to southeast. This reflects the overall coordination of the movement on the eastern Tibet, with the strike-slip fault zone only controlling the direction of movement.

Imaging the Fault Plane Structure of Palu-Koro Fault from Earthquake Data Using Python

Abstract Palu-Koro Fault is one of the active faults located in Sulawesi and positioned in the middle of the Island, dividing the west and east-southeast arms. Its long history of earthquakes provides sufficient focal mechanisms data to be analyzed. This research used seven focal mechanism data of shallow magnitude earthquakes surrounding the pull-apart basin area of the Palu-Koro Fault. The focal mechanism data used is secondary data obtained containing the information needed. This research aims to create a 3D model of the pull-apart basin displaying the geometries of the fault planes and providing a closer look at the fault system surrounding the bounding fault zones. Python script was made to classify the mechanism of each earthquake based on its correlation to the trend of the Palu-Koro Fault. Nodal planes are categorized as whether it is presumed to be the fault plane or the auxiliary plane of the focal mechanism. The result found that not all earthquake data was classified through the assumed parameter set. Only five of seven earthquake data managed to be classified, while the rest showed a different focal mechanism. It is found from the python script created revealed the presence of three fault types: normal fault, normal left lateral oblique fault, and left lateral strike-slip. The 3D fault plane interpolation showed two distinct dipping directions, suggesting their association with the basin’s bounding fault, either the west or the east side. From the gathered information, previous research, and geological interpretation, the earthquake data can be concluded into three fault associations to the bounding fault: synthetic extension fault, antithetic extension fault, and sinistral strike-slip fault.

STRUCTURAL FEATURES OF THE PSHEKHA-ADLER FAULT ZONE OF THE GREATER CAUCASUS ACCORDING TO STRUCTURAL STUDIES

The study of minor faults carried out in the valley of the Belaya River made it possible to establish the tectodynamic conditions for the formation of the Pshekha-Adler fault zone of the Greater Caucasus. In this zone, the presence of strike-slip displacements of different scales and the predominance of the situation of horizontal displacement are shown. Using the method of cataclastic analysis, differences in the parameters of the stress-and-strain state in different tectonic complexes and structures of the region have been established. The revealed structural pattern of meridional and northeastern compression determine the regional dextral strike-slip fault and extensional fault nature of the meridional Pshekha-Adler fault zone with the development of sinistral strike-slip faults and extensional faults of the northeastern strike inside the deformation zone.

Three-dimensional displacement and slip distribution of the 2021 Mw 7.4 Maduo (Tibetan Plateau) earthquake determined by GNSS and InSAR

On May 22, 2021, an Mw 7.4 earthquake occurred on the Maduo-Jiangcuo fault, located in Maduo County, Qinghai Province (China). According to the co-seismic deformation and the three-dimensional displacement reached from the interferometric synthetic aperture radar (InSAR) and the global navigation satellite system (GNSS), the rupture trace in the NWW direction was mapped, spanning a length of approximately 160 km and the earthquake happened on a typical sinistral strike-slip fault. In three-dimensional displacement, the displacement in E-W was bigger than that in N-S and vertical, with the RMSE 3.01 mm, 15.28 mm, and 5.16 mm respectively. Moreover, the slip distribution inverted with the homogeneous half-space model and layered half-space model, indicated that the corresponding magnitude was 7.3 Mw and 7.4 Mw, and the corresponding peak slip was 5.53 m and 5.96 m. The correlation coefficients of observed and predicted both exceeded 0.791, meeting the need for slip inversion. What is more, the peak inversion depth was no more than 15 km with strike angle and dip angle of 269° and 82.9° in the homogeneous half-space model and 265° and 83.7° in the layered half-space model, respectively. In addition, the Coulomb stress changes decreased on the Maduo-Jiangcuo fault and accumulated on the East Kunlun fault, which might cause aftershocks and future earthquakes were still possible. In short, the 2021 Mw7.4 Maduo earthquake made it possible to unravel seismic behavior in the Tibet plateau, which is of great significance for seismic hazard research.

ANALISIS STRUKTUR GEOLOGI BERDASARKAN DATA PERMUKAAN DAERAH BANJARHARJO, KABUPATEN BREBES, PROVINSI JAWA TENGAH

The research area is administratively located in Banjarharjo Village, Banjarharjo District, Brebes Regency, Central Java Province. Geographically, the research area is located at coordinates 108o 49 '15.4 "- 108o 52' 30.8" East Longitude and 06o 59 "21.8" - 07o 02 '04.8 "LS. The research area is included in The North Central Java Basin (The North Serayu Through/Basin) which is a Back Arc Basin. Based on the stratigraphic and sedimentological composition, the research area is classified into five geological units, (old to young), namely: (1) Sandstone and Claystone Interchange Unit, (2) Carbonate Claystone Unit, (3) Sand Limestone Unit, (4) Volcanic Breccia Unit and (5) Andesite Intrusion Unit. According to Pulonggono and Martodjojo (1994) Java Island, there are three straight lines of dominant structure, including: (1) East Laur - Southwest (Meratus Pattern), (2) North - South (Sundanese Pattern) and (3) West - East (Pattern Java). Based on the strike dip and stockiness data at the research location, the results of the force with the direction of the main stress are relatively Northeast-Southwestern, with the combination of Harding modeling, (1977) and Moody and Hill, (1956). The structural arrangements in the research area that are formed are (1) Cibuluh thrust fault, (2) Maibah sinistral strike-slip fault, (3) Cikuya sinistral strike-slip fault, and (4) Cikuya dextral strikeslip fault.

Current active fault distribution and slip rate along the middle section of the Jiali-Chayu fault from Sentinel-1 InSAR observations (2017–2022)

The Jiali-Chayu fault, situated on the eastern side of the eastern Himalayan syntaxis, is the southeastern margin of the large strike-slip fault zone of the Jiali Fault. The study of the distribution and activity within this fault zone is imperative for a comprehensive understanding of the tectonic movement patterns in the southeastern Tibetan Plateau. Previous studies have established that the kinematic characteristic of the Jiali-Chayu fault diverges significantly from that of other segments within the Jiali fault. Nonetheless, the current tectonic characteristics, including the slip sense, slip rate, and geometric deformation of this fault, are still not well resolved, leading to divergent interpretations regarding its contemporary activity intensity. This paper introduced an optimized time-series InSAR method with phase compensation designed for regions characterized by low coherence and exhibiting slow deformation. Using Sentinel-1 SAR data from both ascending and descending orbits spanning the period between 2017 and 2022, we successfully derived deformation rates for the middle part of the Jiali-Chayu fault at a spatial resolution of 150 m. The slip and dip rates of active faults are determined by considering the fault movement rates from two different observation angles, in conjunction with strike angle and the assumed dip angle of the fault. The results show that the deformation rates of the three branches are very different, with F2-1 and F2-2 exhibiting notable activity, while other areas exhibit relatively weaker activity. The strike-slip rates for F2-1 and F2-2 faults range between 3.6 and 5.3 mm/a and 3.05 to 5.13 mm/a, respectively, while their respective dip-slip rates fall within the range of 1.1–2.7 mm/a and 2.99–5.02 mm/a. In accordance with the fault slip directions, we classify the F2-1 fault as a sinistral (left-lateral) strike-slip fault and the F2-2 fault as a dextral (right-lateral) strike-slip fault. This study addresses a gap in remote sensing methods for detecting active fault activity in this region, providing a systematic foundation for identifying weak activity characteristics within the fault zone.Graphical

Tectonic setting of the northwestern andes Constrained by a high-resolution earthquake catalog: Block Kinematics

A high-precision earthquake catalog was generated using source-specific station terms and waveform cross-correlation techniques. This detailed catalog serves to interpret the crustal structure and deformation related to the tectonic setting in Northwestern South America. The Panamá-Chocó Block (PCB) is in contact with the Northwestern Andes causing crustal deformation and hence, fault interaction in the brittle regime leading to a high earthquake production concentrated in the Murindó Seismic Cluster (MSC) which is located in the northeastern corner of the PCB. Slip on the Uramita Fault Zone (UFZ) is a response to the accommodation of the PCB against the North Andean block (NAB), splitting the fault into two segments, marked by an abrupt change in its strike. The north segment of the UFZ, a dextral transform fault (strike = S52°E and near vertical plane), which produced the Mutatá earthquake (2016-09-14, Mw = 6.2). The central segment of the UFZ strikes N12°E and exhibits mainly reverse slip with a subvertical fault plane which produced the 1987-03-19 Mw = 5.4 and 1987-11-11 Mw = 5.3 events. The Murindó sinistral strike-slip fault (strike = N9°W), which produced the great Murindó earthquake (1992-10-18, Mw = 7.1, epicentral intensity XI) is characterized by its wide zone of brittle deformation as a response to internal deformation of the PCB under a compressional NW-SE stress. Intermediate depth earthquakes are widely observed in the area, where we find evidence of the Caribbean slab subducting southwards beneath Panamá. The subduction of the Malpelo microplate to the south, shows high productivity within the Cauca Cluster and the presence of at least three finger-shaped mantle zones of seismicity.

Crustal Imaging across the Princess Elizabeth Land, East Antarctica from 2D Gravity and Magnetic Inversions

The Princess Elizabeth Land landscape in East Antarctica was shaped by a complex process, involving the supercontinent’s breakup and convergence cycle. However, the lack of geological knowledge about the subglacial bedrock has made it challenging to understand this process. Our study aimed to investigate the structural characteristics of the subglacial bedrock in the Mount Brown region, utilizing airborne geophysical data collected from the China Antarctic Scientific Expedition in 2015–2017. We reconstructed bedrock density contrast and magnetic susceptibility models by leveraging Tikhonov regularized gravity and magnetic inversions. The deep bedrock in the inland direction exhibited different physical properties, indicating the presence of distinct basement sources. The east–west discontinuity of bedrock changed in the inland areas, suggesting the possibility of large fault structures or amalgamation belts. We also identified several normal faults in the western sedimentary basin, intersected by the southwest section of these survey lines. Furthermore, lithologic separators and sinistral strike-slip faults may exist in the northeast section, demarcating the boundary between Princess Elizabeth Land and Knox Valley. Our study provides new insights into the subglacial geological structure in this region, highlighting the violent impact of the I-A-A-S (Indo-Australo-Antarctic Suture) on the subglacial basement composition. Additionally, by identifying and describing different bedrock types, our study redefines the potential contribution of this region to the paleocontinent splicing process and East Antarctic basement remodeling.

Tectonic Analysis of the Tall Al Qarn Pressure Ridge, Dead Sea Transform Fault, Jordan

Jordan's Dead Sea Transform is made up of three morphotectonic elements: Wadi Araba, Dead Sea Basin, and Jordan Valley. A few pressure ridges and depressions exist in the Jordan Valley Fault. Among these, the Tall Al Qarn pressure ridge is one of the active Dead Sea Transform's morphotectonic features. Stratigraphically, the Waqqas (Miocene), Ghor Al Katar (Early Pleistocene), and Lisan (Late Pleistocene) Formations constitute the rock outcrops in the study area. The ridge was created when the sinistral strike-slip fault of the Jordan Valley bent rightward. The major structures include the Waqqas and Ghor Al Katar inclined beds, the NW-SE oriented normal and NE-SW reverse faults and the ESE-WNW oriented dextral strike-slip faults. Faults and folds indicate a local NW-SE compressional stress caused by the sinistral Jordan Valley Fault's right bending. The steeply dipping Ghor Al Katar strata, which are overlain by the horizontal Lisan beds, display a prominent angular unconformity. Many horizontal Lisan beds exhibit abundant synsedimentary deformational features, indicating the energetic seismic activity at that time.

WHAT IS THE MAIN FACTOR CONTROLLING THE SUKADANA BASALT IN THE SUMATRA BACK ARC?

The mechanism of the presence of the Sukadana basalt in the back arc of Sumatra is still an enigma, especially since the Sukadana basalt has a wide coverage area in Sumatra Island and even the Sunda Arc. In this study, we used the published research data as the main contributor to an in-depth analysis to determine the mechanism of the presence of Sukadana basalt in the back arc. This study is supported by other studies from different regions around the world. These strengthen our conclusion that the emergence of Sukadana basalt on the surface is controlled by extensional deformations associated with the northwest-southeast-trending normal fault, which are formed by the mechanism of gravitational subsidence due to the movement of the Sumatra fault. In this study we suppose that the Nishimura fracture is a sinistral strike-slip fault as it is consistent with the Riedel shear model.

Fault Delineation and Geological Carbon Storage (GCS) Characterization for the CCS and CCUS Facilities Based On Gravity Dataset. A Case Study in the Northern Part of East Java, Indonesia

lobal warming, the impact of greenhouse-gases emission has triggered climate change and caused various geological and hydro-meteorological disasters in the world. Most countries have carried out decarbonization efforts following the Paris Agreement, which aims to reduce carbon emissions from 29% of domestic effort up to 41% with international support by 2030. Sustainable Development Goal number 13 states combating climate change is a globally accepted framework adopted by the Indonesian Ministry of Development Planning. One aspect of decarbonization efforts involves establishing successful CCS/CCUS facilities, which requires readiness of geological carbon storage (GCS). The GCS has limited capacity, locate specifically underneath, and must consider nearby faulting system to avoid leakage and uncontrollable behavior after the injection phase of the liquefied (high-pressure) carbon. This study optimizes gravity dataset analysis to identify the existing faults and characterize the initial stage of proposed GCS in the northern part of East Java, Indonesia. Synthetic modeling of a strike slip fault was conducted to support data interpretation. The GCS characterizations, which include shape, depth, and storage capacity estimations, are inferred through 3D gravity inverse modeling. This study deduced the presence of a large-scale anticline closure without any intersecting of strike-slip fault in the area. The existing fault system is identified as the Baribis-Kendeng Reverse Fault Zone, trending west-east, and intersected by a sinistral strike-slip fault in the northeast-southwest direction. The study area is suggested as a potential GCS location with low-risk of leakage, located adjacent to the Central Processing Plant Gundih and Sukowati in East Java, Indonesia

Crustal structure and the seismogenic environment in Yunnan imaged by double-difference tomography

The large-scale faulting and earthquake activities that developed extensively in the Yunnan area are associated with the collision of India and Eurasia. The fine crustal structure can provide a better understanding of the crustal deformation, seismogenic environment, and rupture processes. We performed a new 3-dimensional (3D) P wave velocity structure and seismic relocation using double-difference tomography based on seismic observations. The tomography images show that large-scale low-velocity anomalies spread around the margin of the south Chuan–Dian Block, Xiaojiang fault (XJF), and the Lijiang–Xiaojinhe fault (LJ-XJHF) in the middle and lower crust. There is an obvious high-speed anomaly in the Emeishan large igneous province (ELIP). We infer that the low-velocity anomaly under the LJ-XJHF zone may be derived from the lower crustal flow extruded from the central Tibetan plateau and obstructed by the ELIP, while the velocity anomalies around the XJF might be caused by shear heating, which is associated with the large-deep strike–slip fault and the transmission of stress in the southeast direction. The inversion results also show that the Yangbi earthquake occurred at the NW–SE boundary of high and low velocity from the upper crust to the lower crust, which coincides well with the location of the Yangbi earthquake sequence and the Weixi–Qiaohou fault. Meanwhile, the earthquake relocations show that the aftershocks are mainly distributed at low velocities. All the aforementioned research results indicate that the Yangbi earthquake might be attributed to the intrusion of the soft material flow along the Weixi–Qiaohou fault in the NW–SE direction. These low-viscosity crustal materials would cause brittle fractures and result in NW–SE sinistral strike–slip faults.

Formation of the Permo-Triassic Ondor Sum thrust system and its constraint on Solonker Ocean closure

ABSTRACT A previously unidentified overthrust system has recently been discovered in the Ondor Sum area at the boundary between the Solonker – Xar Moron Suture Zone (SXSZ) and the Early to Mid – Paleozoic Subduction – accretion Belt to the south. The overthrusting occurred during the middle Permian and was overprinted by late Permian to Middle Triassic dextral shearing. The overthrusting (D1) was characterized by the development of WSW – ENE-trending folds and reverse faults, implying NNW – SSE shortening. The later deformation (D2) involved WSW – ENE dextral strike-slip shearing with a minor reverse component, as indicated by slightly plunging striae on slickensides. A comparison of geochronological and structural data for ophiolites in the SXSZ suggests that the overthrust system formed in response to the closure of the Solonker Ocean and the collision along the SXSZ. The earlier NNW – SSE shortening and later WSW – ENE dextral shearing indicate that a tectonic transformation took place along the SXSZ from the middle Permian to the Late Triassic. Dextral and sinistral strike-slip faults are, respectively, distributed to the south and northwest of the Songliao – Xilinhot Block to the north of the SXSZ, implying eastward extrusion of the Songliao – Xilinhot Block after the closure of Solonker Ocean. The tectonic transformation and extrusion might have been a part of the intracontinental tectonic transformation of the eastern segment of the southern Central Asian Orogenic Belt.

Evidence for transpression during formation of the Candelaria Punta del Cobre IOCG -district and regional implications

The youngest and best exposed Iron Oxide Cu–Au (IOCG) deposits currently recognized are found in the coastal belt of the Andes. Their formation has been attributed to back-arc extension or transtension associated with the convergent Andean margin. Here we document transpressional deformation synchronous with Cu mineralization in the Candelaria-Punta del Cobre district, the largest IOCG district of the Andean belt. A northwest-southeast shortening direction is recorded by north-northwest sinistral strike-slip faults that host mineralization, northwest dikes, and north-northeast compressive structures. Batholith emplacement synchronous with mineralization formed a north-northeast oriented foliation zone parallel to the intrusive contact and associated folds in the host rock sequences that face inwards towards the intrusive contact. Age constraints indicate that transpressional deformation in the Cretaceous arc, at least locally, begun earlier than previously documented, and IOCG mineralization may have spanned the transition from extension to the initial phase of compression.

Subduction transition and relation to upper plate faults revealed by the 2019 Mw 6.0 and 6.2 Costa Rica-Panama border earthquakes

We study the May 12, 2019, Mw 6.0 (hereafter Laurel earthquake) and a June 26, 2019, Mw 6.2 (hereafter Manaca earthquake) earthquakes located in a complex strike-slip to subduction transition zone in the Costa Rica-Panama border using a dense local network of broadband and strong-motion instruments, concluding that the Laurel mainshock data (hypocenter, centroid, and focal mechanism), concurrently with its aftershock distribution, indicate an almost vertical north-south oriented, dextral strike-slip fault. This fault ruptured at depths between 10 and 30 km in the lower crust of Panama Microplate and the geometry implies a shallow influence of the Panama fracture zone. Meanwhile, for the Manaca earthquake, the aftershocks are concentrated on a 25 km long NW-SE trend, with a depth between 20 and 45 km. One of the nodal planes of the focal mechanism of the Manaca earthquake, as well as the centroid location coincides with the aftershock locations trend, supporting the hypothesis that a nearby steeply dipping sinistral strike-slip fault originated this event. Earthquake locations and focal mechanism analyses of collected data from global and local earthquake catalogs suggest that the strong coupling caused by the subduction of the Cocos Ridge and Nazca plate is largely accommodated by outer arc crustal block migration with a combination of NW-SE sinistral and N-S dextral strike-slip faults deforming the overriding Panama Microplate. Sinistral motion of crustal blocks, on the Costa Rica side, are consistent with observed motions along with the Azuero-Sona fault system and Coiba Faults on the Panamanian side.

Study on the Applicability of Various In-situ Stress Inversion Methods and Their Application on Sinistral Strike-Slip Faults

Study on the Applicability of Various In-situ Stress Inversion Methods and Their Application on Sinistral Strike-Slip Faults

A new model for the segmentation, propagation and linkage of the Tan-Lu fault zone, East Asia

• The Tan-Lu Fault formed by coalescence of two kinematically independent segments. • The northern and southern Tan-Lu faults exhibit contrasting displacement profiles. • The northern and southern Tan-Lu faults propagated in opposite directions. • Southward indentation of the Siberian craton initiated the northern Tan-Lu Fault. • The northern and southern Tan-Lu faults linked in the early Late Jurassic. The Tan-Lu fault zone (TLF) is a major strike-slip fault with a long and complex history in East Asia, whose evolution provides a new perspective on the formation of large-scale faults (>1000 km long). Fault displacement analysis, geological mapping and U-Pb LA-ICP-MS dating have been performed to understand the evolution of the TLF. Along-strike displacement variation reveals that the TLF consists of two kinematically independent segments, the northern and southern TLF, with opposite long-term propagation directions. Structural and geochronological studies in the eastern Yanshan belt, located around the linkage area of the southern and northern TLF, indicates that NNE-trending sinistral strike-slip faults initiated at 167-164 Ma and were reactivated at 124-121 Ma. Structural analysis suggests that these early NNE-trending strike-slip faults transferred sinistral motion along the northern TLF into southward thrusting along the Yanshan belt, representing the Middle Jurassic southern termination of the northern TLF. Our studies suggest that the through-going TLF formed when the younger southward-propagating northern TLF merged with the older northward-propagating southern TLF in the Late Jurassic. A new model is thus proposed for the Mesozoic evolution of the TLF. The initiation and southward propagation of the northern TLF is interpreted to have resulted from the southward indentation of the Siberian craton into the amalgamated Central Asian Orogenic Belt and North China block. The divergent mega-splays of the northern TLF likely resulted from westward-younging formation during the clockwise rotation of northeast Asia. Coalescence of two genetically unrelated faults could be an alternative mode for large-scale fault formation.

TECTONIC DEFORMATIONS AND PALEOSTRESS FIELDS IN THE ROCK COMPLEXES OF THE PIENINY KLIPPEN BELT IN THE CITY OF SZAWNYCTA (POLAND)

Purpose of the paper is study of faults and folds and reconstruction of paleostress fields in rock complexes of the Pieniny Klippen Belt in Pieniny Mts. area (Southern Poland). Methods of field geological and structural research were involved, including the kinematic method with subsequent reconstruction of paleostress fields using the program Win-Tensor. The results. On the right bank of the Danube River in the south-western outskirts of the city of Szczawnytsia (Southern Poland), numerous fold and fault deformations, their kinematic types and structural patterns were studied in the large rootless block of the PKB. Paleostress fields of the thrust, normal and strike-slip kinematic types have been restored. In the inverse stress field, thrusts were formed on the border of competent and incompetent rocks. Drug-folds, mélange and broken formations zones were formed in the more ductile rocks of the lower block. In the normal-type stress field, the former thrusts were activated as normal faults and cuted by the ortogonal and oblique sinistral strike-slip faults. The kinematic sence of the thrusts changed to an oblique normal faults with a component of the sinistral strike-slip, in the bodering zones of the activated faults, drag folds ans s-type folds were formed. In the youngest stress field, the former thrust surfaces were activated as strike-slip ones. Shear deformations were also recorded along thrust-limiting orthogonal and oblique surfaces. Kinematic types of tectonic deformation and folded structures in the different parts of the studed rootless block vitnesses the rotation of the fault wings in the horizontal and vertical planes. The wavy shape of the surface of the movement of the rootless block may be the reason for the simultaneous existence of a field of compression and tension in its various segments. Scientific novelty. As a result of the research, the kinematic types of fault, their relationships and features of development in various paleostress fields were determined. The features of the structure of the thrust and the faults that cut them, the relationships of folded and faulted deformation are established. Changes of the kinematic types of faults in time from the inverse to the strike-slip type have been established. Practical impact. The obtained results complement the history of the formation of the Pieniny Klippen Belt and can be used to refine tectonic maps and select a geodynamic model of the region. Key words: Pieniny Klippen Belt, paleostress, thrust, strike-slip, mélange.

Petrogenesis of the Wadi El-Faliq Gabbroic Intrusion in the Central Eastern Desert of Egypt: Implications for Neoproterozoic Post-Collisional Magmatism Associated with the Najd Fault System

The late Neoproterozoic gabbroic intrusion of the Wadi El-Faliq area in the central Eastern Desert of Egypt (north Arabian–Nubian Shield; henceforth, ANS) is a fresh, undeformed elliptical body elongated in a NW–SE trend following the main sinistral strike-slip faults of the Najd fault system. Mineralogical and geochemical evidence suggest that they were derived from hydrous tholeiitic mafic magmas with arc-like geochemical fingerprints resembling the post-collisional gabbroic intrusions in Saudi Arabia. Despite the arc-like signatures, their fresh and undeformed nature, together with the field relationships, indicates that the studied gabbroic intrusion post-dates the main collisional phase, supporting its emplacement after subduction ceased and during the post-collisional stage. As a result, the arc-like signatures were possibly transmitted from the earlier ANS subduction episode. Indeed, the high (La/Sm)N, and negative-Nb and positive-Pb anomalies suggest contributions from subduction components. Lithospheric delamination was possibly facilitated by the Najd faults and shear zones formed during the post-orogenic crustal extension associated with the Pan-African orogenic collapse. The delamination process could have generated a rapid upwelling and melting of the asthenosphere mantle. The melt-rock reaction process likely played an important role in the genesis of the studied rocks through the interaction of the asthenosphere melts with lithosphere mantle rocks during ascent. The HREE fractionation suggests a probable mixing between melts from both spinel- and garnet-bearing peridotites. We suggest that the Wadi El-Faliq gabbroic intrusion was likely emplaced due to the stretching and thinning of the lithosphere during the extensional tectonism following the Pan-African orogeny.