Graben System Research Articles

Hydrogeochemical similarities and differences between high temperature geothermal systems with similar geologic settings in the Büyük Menderes and Gediz Grabens of Turkey

The Büyük Menderes Graben (BMG) and the Gediz Graben (GG) are two major graben systems and they have important medium-high temperature geothermal systems, with suitable reservoir temperatures (e.g. 170–276 °C) for electricity production such as Kızıldere (Denizli city), Germencik, Salavatlı, Pamukören (Aydın city) in the BMG and Alaşehir (Manisa city) in the GG.These high temperature geothermal systems are located in a highly fractured zone because of the Aegean Extensional Zone effect. Although the main reservoir rocks retain similar compositions for each graben system, the geothermal fluids chemistry characterization can vary along the BMG and GG as a result of differing variables such as a paleo sea effect, the concentration of non-condensable gases (NCG), as well as mineral effects. The water chemistry results and δ18O-δD isotope values show remarkable differences within the Germencik and Kızıldere systems along the BMG, while the main reservoir rocks are of a similar composition. Chemical, isotope compositions and pH values of thermal waters in Alaşehir differ from those in the BMG geothermal systems.Results for δ13C isotopes indicate that the origin of the large amounts of CO2 is the marble in metamorphic rocks in the reservoirs in both graben systems. δ34S, δ34S- SO4 and δ18O-SO4 values indicate that the origin of SO4 indicates gypsum and also bacteria effect in the eastern part of the BMG, while different mechanisms such as; oxidation of sulfur, pH, temperature and possible buffer mineral effects on H2S dissolution to the west of the BMG and GG display a greater impact.

The origin and impact of the Shizhuang ground fissure, Yingxian area, Datong Basin, China

The Datong Basin is part of the regionally extensive Fenwei Graben System, a major tectonic zone impacted by active tectonics and the resulting damage to life and infrastructure. The basin also contains the Shizhuang ground fissure system. In this study, the likely origin, surface extent, and fissure subsurface characteristics are explored by traditional methods: surveying, mapping, trenching, drilling, and seismic exploration. The Shizhuang ground fissure is located at the intersection of the Xiaoshikou fault and the southern Liuleng margin fault in Yingxian County. It has a length of 2.1 km, excellent continuity, and semi-elliptical surface morphology. The dislocation of strata induced by the fissure increases significantly as the depth increases. The strata bend downward and form typical traction structures near the fissure plane, indicating that the fissure has prominent synsedimentary fault characteristics. The fissure causes serious damage to houses, farmlands, roads, and public facilities, featuring large tensile cracks and vertical dislocations. The resulting data and interpretations indicate that: (1) the ground fissures connect to two major subsurface active faults, which lay the tectonic foundation for the fissure; (2) accelerated groundwater extraction has reactivated the underlying faults and exacerbated fissure development; and (3) mitigation is best achieved by cessation of excessive groundwater pumping, appropriate engineering design, and local avoidance for placement of critical structures. This paper provides a heretofore generally unknown example, promotes research on the mechanisms of fissures, and has guiding significance for disaster prevention and reduction in this area.

Thermal History of the Northern Taiwanese Slate Belt and Implications for Wedge Growth During the Neogene Arc‐Continent Collision

AbstractA significant issue in the study of orogenic systems concerns the roles played by frontal and basal accretion in the construction of orogenic wedges. These different accretion mechanisms result in different thermal histories, with underplated materials experiencing significant heating and deformation during tectonic burial. This work provides new thermal data from Raman spectroscopy of carbonaceous material in combination with structural and stratigraphic observations of the northern Taiwan slate belt to address these questions of wedge development. Sedimentary rocks of the Northern slate belt were deposited on the Chinese continental margin immediately before the onset of the Neogene Taiwan arc‐continent collision. In the slates of the northern Hsüehshan Range, a large‐scale pop‐up structure on the prowedge of the Taiwan Orogen, synorogenic metamorphism has been investigated through analyses of peak temperatures and metamorphic field gradients. Results indicate underthrusting of the margin sediments to ~8‐km depth with significant folding in two major duplexes occurring before underplating. Such basal accretion is considered responsible for the distinct culmination of the Hsüehshan Range in central Taiwan and its relative uplift with respect to the Backbone Range to the east along the Lishan Fault. A similar underthrusting scenario is also suggested for the Backbone Range Slate Belt. We propose that basal accretion is the predominant mechanism in the growth and evolution of the Taiwan orogenic wedge and may have been achieved through inversion of a graben system on the ancient passive margin during continental subduction.

Fault kinematic and Plio-Quaternary paleostress evolution of the Bakırçay Basin, Western Turkey

ABSTRACT At the end of the Cenozoic, western Turkey was fragmented by intense intra-continental tectonic deformation resulting in the formation of two extensional areas: a transtensional pull-apart basin systems in the northwest, and graben systems in the central and southwest areas. The question of the connection of this Late Cenozoic extensional tectonics to plate kinematics has long been an issue of discussion. This study presents the results of the fault slip data collected in Bakırçay Basin in the west of Turkey and addresses changes in the direction of extensional stresses over the Plio-Quaternary. Field observations and quantitative analysis show that Bakırçay Basin is not a simple graben basin that has evolved during a single phase. It started as a graben basin with extensional regime in the Pliocene and was transformed into a pull-apart basin under the influence of transtensional forces during the Quaternary. A chronology of two successive extensional episodes has been established and provides reasoning to constrain the timing and location of subduction-related back-arc tectonics along the Aegean region and collision-related extrusion tectonics in Turkey. The first NW–SE trending extension occurred during the Pliocene extensional phase, characterized by slab rollback and progressive steepening of the northward subduction of the African plate under the Anatolian Plate. Western Turkey has been affected, during the Middle Quaternary, by regional subsidence, and the direction of extension changed to N–S, probably in relation with the propagation of the North Anatolian Fault System. Since the Late Quaternary, NE–SW extension dominates northwest Turkey and results in the formation and development of elongated transtensional basin systems. Counterclockwise rotation of Anatolian block which is bounded to the north by the right-lateral strike-slip North Anatolian Fault System, accompanies to this extensional phase.

Crustal density structures and isostasy beneath the Western North China craton, Trans-North China Orogen, and surrounding regions

To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton, the Trans-North China Orogen, and the surrounding regions, the wavelet multi-scale structures, Moho depth, crustal density structures, and isostatic state are modelled using Bouguer gravity anomaly data, topography, and earthquake focal mechanisms. We obtained homogeneous crustal densities and deviations of <1 ​km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block, the Inner Mongolia Suture Zone, the Sichuan Basin, and the Jizhong Depression. These results provide new evidence for relatively simple and stable continental crustal structures, and indicate that these regions will remain stable in both the vertical and lateral directions. The Hetao Graben, Yinchuan Graben, Weihe Basin, and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated. In contrast, the crust beneath the Yinshan Uplift, Lvliang Uplift, and northern and central Taihang Uplift is thin and under-compensated. The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions. Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia, we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces. The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.

Structure of the Büyük Menderes Graben systems from gravity anomalies

The Buyuk Menderes Graben (BMG) of western Turkey is bounded by E-W oriented normal faults and has been a depositional center for thick sedimentary layers since the Miocene. Four Mio-Pliocene depressions (from west to east, the Cine, Bozdogan, Karacasu, and Denizli basins) having overall N-S trends are situated just south of the BMG. In this study, we focused on the structural characteristics of the BMG using Bouguer gravity data covering the area between 37°N and 39°N and 26°30'E and 30°E and gravity data along 4 profiles to estimate the discontinuous basement relief of the BMG. Our main objectives were to investigate the geometry of the faults bounding the BMG and surrounding faults, and to describe the extent of the cross-graben structures. Boundary analysis, analytical signals, and second derivative methods were applied to Bouguer gravity data in order to determine tectonic border lines. The 2D inversion of gravity data together with the analysis of the power spectrum for each profile exposed an image of the subsurface. As a result of both methods, the thickness of the sedimentary cover was determined to be 1.44-2.3 km in the BMG. According to model geometry, the thickness of the sedimentary deposits decreases to the south of the graben.

Paleogene geological framework and tectonic evolution of the central anticlinal zone in Lufeng 13 sag, Pearl River Mouth Basin

The Paleogene geological framework and evolution process in the central anticline zone in the Lufeng 13 sag in Pearl River Mouth Basin is well analyzed through seismic data and drilling data, and control of tectonic evolution on hydrocarbon accumulation is also discussed. The results show that the central anticline zone in the Lufeng 13 sag develops the upper deformation layer and lower deformation layer. The “arched graben system” is developed in the upper deformation layer, and the magmatic diapir structure and flowing deformation of plastic strata is developed in the lower deformation layer. The evolution process of the central anticline zone can be divided into four stages, i.e. fault block uplifting stage, prototype stage, strengthening stage and finalization stage. The geological framework and tectonic evolution of the central anticline zone control Paleogene hydrocarbon accumulation. The Paleogene two-layer geological framework is favorable for development of structural traps and composite traps; the paleostructure highs are the direction of hydrocarbon migration, and the gravitational gliding faults are the main carrier bed for vertical hydrocarbon migration; the tectonic uplift is a key factor for reservoir diagenesis improvement and preservation of primary pores, and also controls distribution of high-quality reservoirs.

Mechanism of Fuping ground fissure in the Weihe Basin of northwest China: fault and rainfall

The special geological conditions of the Weihe Basin, located in the southern Fenwei Graben System, are the cause of many of the ground fissures developing in this area. The Tingzi ground fissure in Fuping County is one of the typical and particular ground fissures found in the Weihe Basin. The ground fissure is famous for its sudden appearance after heavy rainfall. To explore the characteristics and mechanism of the fissure, some geological methods were carried out in the study area for this study, such as surveying, mapping, trenching, drilling, and seismic exploration. The main conclusions are as follows: (1) the fissure is located on the hanging side of the secondary fault of the Liquan–Pucheng–Heyang fault, with a NE40°–NE75° strike and a length of 2.7 km. (2) The fissure is steeply inclined and presents a “funnel” shape in the shallow strata. There are many secondary cracks near the main fissure. (3) The fissure is connected with underlying fault and possesses the characteristics of synsedimentary faults reflecting the historical stages of fissure activities. (4) The fissure destroys farmlands and houses along the fissure, and mainly causes tensile damage. (5) The fissure was controlled by regional extension and fault, and it was promoted and enlarged by rainfall and other influential factors.

Morphotectonic and paleoseismological studies of Late Holocene deformation along the Primorsky Fault, Baikal Rift

The Baikal Rift is the largest Cenozoic continental rift in Asia and has developed at the boundary between the Siberian craton and a collage of microplates composing the Amurian lithospheric plate. GPS data show that the Amurian plate moves southeastward at a rate of 3–4 mm/yr with respect to stable Eurasia but the slip rates along the main faults that control the opening of basins within the Baikal Rift System, are still poorly quantified. The recent graben system of the Olkhon region of the central Baikal Rift is a key example for studying of synrift faulting. We discovered a previously unknown paleoseismic structure in the course of our morphometric study of the Primorsky fault scarp, one of the youngest grabens within the Baikal Rift. Detailed topographic mapping of the deformation area and trenching across the fault scarp revealed two paleoseismic events responsible for scarp formation. Dating of organic remnants found in the trench walls allowed us to estimate a late Holocene age for the paleoearthquakes and bracket the vertical slip rates along the Primorsky Fault to between 0.5 ± 0.1 mm/yr (min) and 0.9 ± 0.2 mm/yr (max) over the last ~2.5 kyr. The geomorphological and paleoseismological data, in combination with the analysis of recent seismicity and horizontal geodetic rates, suggest that the Primorsky Fault has accumulated elastic stress with the potential for a ~M 6.6 earthquake. Large earthquakes of this magnitude have occurred at least twice on the investigated fault segment during the last ~1.4 kyr.

Geomorphic and stratigraphic evidence of Quaternary diapiric activity enhanced by fluvial incision. Navarrés salt wall and graben system, SE Spain

The structural and stratigraphic geological features associated with salt structures have received extensive attention from geologists. However, there is limited work on the geomorphic and Quaternary record of diapiric activity despite its practical implications (e.g., salt and hydrocarbon extraction, geostorage activities). This work analyses the Quaternary geomorphic and stratigraphic evidence of diapiric activity in the Navarrés salt wall (SE Spain), developed along the axis of a Neogene graben. This salt system is located in a region characterized by a peculiar network of orthogonal grabens that control the configuration and evolution of the drainage network. The protruding salt walls are spatially associated with the erosionally unloaded and deeply entrenched graben sections situated close to the regional base level. Evidence of recent/current activity in the Navarrés salt wall include: (1) internally drained areas in a marginal withdrawal basin with long-sustained aggradation; (2) distorted drainage network (defeated and deflected streams, wind gaps, knickpoints, changes in fluvial style), which changed from an initial axial longitudinal pattern to a longitudinal marginal distribution at the flanks of the salt wall; (3) development of diapiric fault scarps at the edge of the salt wall; (4) tilted fluvial terraces dipping away from the salt wall and with localized sediment thickening. The available data indicate along-strike variability in deformation style and long-term vertical deformation rates. These range from ≤0.09 mm/yr, to significantly higher values (>0.2–0.4 mm/yr) in the section where the salt wall displays a more prominent relief and is affected by deep fluvial entrenchment. The regional analysis and the characterization of the Navarrés salt wall suggest that Quaternary diapirism in the region is enhanced by erosional unloading related to fluvial entrenchment, which expands from the regional base level through the upstream propagation of an incision wave.

Early Jurassic magmatism of the Kobyuminsky system of grabens (Verkhoyansk frame of the Siberian platform) and its geodynamic nature

The Kobyuminsky system of grabens was formed in the Early Jurassic within the Verkhoyansk passive margin of the Siberian platform. The volcanic complex of grabens is represented by basalts with elevated TiO2 contents (&gt; 1.8 wt%). According to geochemical characteristics, the rocks of the volcanic series occupy an intermediate position between the basalts of the oceanic islands (OIB) and the basalt-rich mid-oceanic ridges (E-MORB). The data obtained led to the conclusion that the Kobuminsky system of grabens within the passive margin of the Siberian continent arose in connection with the activity of a small mantle plume.

Linking regional unconformities in the Barents Sea to compression-induced forebulge uplift at the Triassic-Jurassic transition

The Triassic-Jurassic transition marks an important change in the basin configuration of the Greater Barents Sea. A contiguous basin with km-thick sedimentary successions changed into a partitioned basin with uplift in the west and foreland basins in the east with significant implication for the basin infill history. Our study employs a range of different high-resolution datasets from a distal part of the basin which unravels the complex pattern of differential uplift and erosion in the basin during this period.We record for the first time distinct angular unconformities between Upper Triassic strata and overlying Lower Jurassic strata within the basin, showing that large parts of it formed topographic highs. Our study links these angular unconformities to compression induced by the Novaya Zemlya Fold and Thrust Belt. A heterolithic basement below a thick sedimentary succession where the fold belt developed created a complex uplift pattern in the basin, at the same time similar to but different from typical forebulge areas. Compression caused inversion of older basement rooted faults defining platforms and graben systems throughout western parts of the Barents Sea basin, in addition to salt remobilization that resulted in differential uplift and erosion. These local zones of uplift controlled the sediment distribution pattern to the basin at a time when the most important reservoir units in the basin were deposited. This new understanding of the basin development explains hitherto enigmatic sequence boundaries that has inspired complex paleogeographic models in the past.

Incorporating critical fault properties controlling hydrocarbon accumulation in 3D basin and petroleum system modelling: a case study in the northern North Sea

Fault properties are very important parameters in migration and accumulation of hydrocarbons in sedimentary basins. However, there are still several different schools of thought on how to incorporate such prospect-bounding fault properties into petroleum system migration and modelling studies. This paper investigates how shale gouge ratio (SGR), which defines the sealing/non-sealing capacity of faults, can be incorporated in basin modelling using the Gullfaks, Visund, Kvitebjorn and Huldra fields in the northern North Sea as a case study. The paper also presents the results from the most likely model representing the present day reality in the basin by varying the faults properties defined by SGR until the reserves-in-place in the four fields are obtained. Our results show that gas accumulations are more sensitive to SGR than the oil accumulations. The oil accumulation in the Gullfaks field is controlled by three main faults. The first fault bounding the field is a non-sealing fault with SGR = 10%. The second fault located further south in the field is a sealing fault, and the third fault located in the north is a non-sealing fault. A NE–SW non-sealing trending fault controls the hydrocarbon accumulation in the Visund field. In the Kvitebjørn field, another NE–SW trending fault surrounding the field with an SGR of 30% controls the hydrocarbon accumulation. The gas-in-place in the Huldra field is controlled by two N–S trending faults. The first fault is located in the west of the field and is defined by SGR of 40%, while the second fault is defined as open. Analysis of the burial history curves of the most likely petroleum system model obtained after the fault properties modelling shows that the Late Jurassic to Early Cretaceous uplift in the basin is more pronounced in the footwall of the triple rift graben system in the basin. In the same period, the axis of the graben system is characterized by non-deposition of sediments.

Structure and evolution of Belomorian-Severodvinsk shear zone in the Late Proterozoic and Phanerozoic, East-European Platform

Tectonics, morphological features and development stages of Belomorian-Severodvinsk shear zone (north-western part) found in the East European platform are considered. We traced the shear zone (length ≈1000 km) from NW to SE from the Baltic shield to the Russian plate sedimentary cover. It inherited Paleoproterozoic structures of Belomorian-Lapland mobile belt and Riphean grabens of the White Sea rift system. Belomorian-Severodvinsk zone was represented in the modern structure by a system of neotectonic grabens limited by normal and normal–strike sleep faults and segmented by the transform fault zones. We came to conclusion that the shear zone experienced multiple repeated activation in different dynamic conditions in the Riphean–Phanerozoic. Cyclic alternation of riftogenic trans-tension and compression or transpression conditions in the sequence stages of its development was noted. We defined three cycles of transtensive-transpressive transformations of Belomorian-Severodvinsk shear zone in the Riphean and the Early Vendian. At least four times shear zone suffered changes of deformation mode and directions of shear displacement in the Phanerozoic. The postglacial neotectonic deformations in the Belomorian-Severodvinsk shear zone revealed under the Kola block horizontal movement to the S–E and subsequent counterclockwise rotation.

Early Jurassic Magmatism of the Kobyumé Graben System (Verkhoyansk Framing of the Siberian Craton) and Its Geodynamic Nature

Data on the Early Jurassic volcanic rocks of the Kobyume graben system, which formed at the Verkhoyansk passive margin of the Siberian Craton, are presented. The volcanic complex contains products of basaltic eruptions that occurred under conditions of a shallow sea. The basalts have elevated TiO2 contents (>1.8 wt%), and variations of their composition were controlled by fractionation processes. By their geochemical characteristics, the volcanic rocks are transitional between ocean island basalts and enriched basalts of mid-oceanic ridges. Taking into account the remote location of the Kobyume graben region from the convergent boundaries of lithospheric plates and from the nearest areas of contemporaneous magmatism, the data obtained support the conclusion that the Kobyume tectono-magmatic areal is a result of a small mantle plume effect onto the passive margin of the Siberian continent.

Inheritance and style of rifting: incremental structural restoration of the Laptev Sea Rift System, north-eastern Russian Arctic

The Laptev Sea Rift System, on the north-eastern continental margin of the Russian Arctic, is a key area to understand the opening of the Eurasia Basin. The rifts developed since Cretaceous/Early Cenozoic times and consists of five, roughly north–south trending depocentres, controlled by major listric normal faults. Three cross-sections from the rift system were incrementally restored to quantify the amount of extension over time and to reconstruct the geological evolution. We show that since the beginning of rifting, fault activity in the Anisin Basin was unevenly distributed between two symmetrical graben systems. The central Ust’ Lena Rift has a completely different structure: regularly spaced west-dipping faults are interrupted by minor east-dipping faults in only three places. Fault dip decreases from west to east, from 60° to 30°, respectively.

High-Angle Normal Faulting at the Tangra Yumco Graben (Southern Tibet) since ∼15 Ma

Several active graben systems in Tibet and the Himalaya are the expression of ongoing east-west extension, but the significance and history of normal faulting in this large region are still debated. Here, we present geo- and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fault at the Tangra Yumco graben to constrain the onset and history of normal faulting. Crystallization of the granitic rocks occurred at 87±1 Ma, as revealed by U/Pb zircon dating. After an initial phase of rapid cooling from magmatic temperatures, a later phase of slow cooling is recorded by Rb/Sr biotite ages between ∼72 and ∼60 Ma. The elevation dependence of the Rb/Sr ages suggests that cooling was controlled by erosion, which proceeded at a rate of ∼0.05 km/My during the latest Cretaceous and early Paleocene. The subsequent history of normal faulting is recorded by zircon (U-Th)/He ages of 12.5±1.1 and 9.7±0.7 Ma, apatite fission-track ages between 10.8±1.7 and 7.8±1.2 Ma, and apatite (U-Th)/He ages from 4.9±0.4 to 3.0±0.2 Ma. Thermokinematic modeling of these age data indicates that normal faulting started at 14.5±1.8 Ma at a rate of ∼0.3 km/My and accelerated to ∼0.7 km/My in the Pliocene. Our age constraint for the initiation of faulting supports a widespread onset of rifting in Tibet at ∼15–10 Ma, as reported for other graben systems. Finally, we suggest that the distribution of high-angle and low-angle normal faults is controlled by their position relative to the India-Asia convergence vector and by lateral variations in the thermal state of the lithosphere.

Geophysical Contribution to the Determination of the Limit between Laayoune and Foum El Oued Aquifers, Origin of Supply Sources of Oued Sakia El Hamra, Laayoune Province, Morocco

Laayoune and the Foum El Oued aquifers are in hydraulic communication only at the level of Oued Saguia El Hamra. The present study has accordingly made use of all the hydrogeological, hydrological, geological and geophysical data that preceded the watershed of Oued Saguia El Hamra in its downstream part. These data are by no means omplementary with the objective of having a better understanding of the boundary line between Laayoune and Foum El Oued aquifers and the origin of feeding the sources of Oued Saguia El Hamra. This study will focus only on the previous geophysical studies where a reinterpretation of electrical soundings has proved useful as a result of the recent well-logging results. It makes it possible to highlight the presence of a significant rise in the truncated marly substratum of Oued Saguia El Hamra and depressions (left and right banks) which could correspond to stream channels or depressed areas. At the level of the Wadi bed, there has been a regular immersion of the conductive level roofs from east to west towards Foum El Oued favoring the flow of wastewater from the zone and spraying the brackish water sources towards the groundwater of Foum El Oued. In the light of the reinterpretation of electric polls, plus as well as the geophysical surveys by electrical tomography and high definition made at the right and left banks of the Oueed Saguia El-Hamra, it was possible to verify the existence of dry ridge separating the two webs of Laayoune and Foum El Oued and stream channels or depressed areas of the left bank for drainage of brackish water to sources located along Oued Saguia El Hamra. The true resistivity models tomography profiles confirm the presence of the backbone at the left and right banks and the graben of the left bank for underground water drainage of the web Laayoune to sources welling the river Saguia El Hamra. They reveal the presence of a quaternary plio-cover (coastal platform Moghrebian) as being heterogeneous and affected by many electrical discontinuities, particularly in the level resistant R2 (coquina sandstone). These discontinuities could correspond to lateral changes in facies and/or synsedimental faults compartmentalizing the plio-quaternary formations into a system of Horsts and Grabens that relies on the whole (D1, Cs) attributed to formations from the Miocene to the Upper Cretaceous. The contours of the map show the distribution of the three families of electrical soundings A, B and C limited by two main electrical discontinuities D and M. East of discontinuity million, this map reflects the look of the wall of the Pliocene-Quaternary resting on the impermeable upper Cretaceous floor. To the west of this electrical discontinuity M, the map reflects the behavior of the roof of marl deposits of Miocene age.

Geoelectrical images of normal fault zones: tectonophysical interpretation of the shallow-depth electrical resistivity tomography data on the Buguldeika-Chernorud graben in the Western Baikal region

In the study of normal fault zones located in the central Baikal rift, a new approach was applied to process and interpret the shallow-depth electrical resistivity tomography data. This approach is based on the concepts of tectonophysics and considers three-stage formation of a fault and the corresponding three degrees of rock material disturbance, which are regularly detected in the rock mass. The degrees are established by statistical analysis of specific electrical resistance (SER) measured from the electrical resistivity tomography profile across the faults under study. Based on a geoelectrical profile, it is possible to identify the sites wherein the disturbed rocks show the indicators of the early, late and final stages of faulting. The profile provides the basis for specifying the boundaries of the fault zone and the main features of its internal structure. The tectonophysical approach was applied to study a series of normal fault zones varying in ranks. The zones are located on the sides of the Buguldeika-Chernorud graben located near the Olkhon Island in the Western Baikal region. By comparing the geoelectrical profiles constructed under the same methodology, it was established that the near-fault anomalies of electrical resistance are qualitatively similar. Their structure is defined by the general mechanism of normal faulting in the upper crust during sliding along a curved (listric) fault plane. The research results are consolidated in an idealized geoelectrical model: a 2D profile showing a low-resistance anomaly that corresponds to a normal fault zone. This anomaly is asymmetrical and mushroom-shaped, and its internal structure is heterogeneous. In the lying wing of the fault, the anomaly reflects the fan-shaped set of secondary faults caused by the subvertical movements in the normal fault zone, which surface is steeply inclined to the horizon. In the hanging wing, the structure of the anomaly reflects a system of lens-like grabens that form above the surface of the main fault plane that becomes less inclined with depth. The structure of the geoelectrical model proposed for the Olkhon region follows the general regularities controlling formation of listric-shaped normal fault zones. This model can be widely used for diagnostics of tectonic settings and crustal extension structures in other regions.

Evidence of transpressional tectonics on the Uruk Sulcus region, Ganymede

The surface of Ganymede is characterized by intense tectonic deformation. The two terrains, light and dark, show morphotectonic features, namely, grooves and furrows. These represent kilometric systems at the regional scale, interpreted as extensional structures (e.g., horst and graben systems). Currently, evidence of significant compression has not yet been recognized, leaving open the opportunity to clarify the tectonic balance of Ganymede's surface. Debate still exists on the geodynamics responsible for surface deformation, and the investigation of these features contributes to understanding the internal processes. To understand the deformation that shapes the surface of the satellite, we explore the tectonic setting of the light terrain region of Uruk Sulcus. Using structural geology methodologies by remote sensing and systematic analysis of grooves, we recognize three groove systems within the sulcus and one furrow system in the neighboring dark terrain. Uruk Sulcus is also characterized by the presence of two domains of lineaments, subtle linear texture anisotropies related to the influence of tectonic processes on morphology. Comparison of the combined results from the analyses of the recognized groove systems with the lineament domains allowed us to infer the stress field responsible for their development in the studied area. According to these results, an evolutionary tectonic scenario for Uruk Sulcus is proposed: a tectonic corridor characterized by dextral transpression, with 58% of the internal compressional component approximately N-S oriented and responsible for localized, E-W extensional features among crustal blocks of the shear zone.