Ancient Faults Research Articles

Spatial Analysis and Predictive Modeling of Natural Seismic Activity: A Smoothed Seismicity Approach

ABSTRACT The study uncovers significant disparities in seismic activity patterns between Kerala and Pondicherry. Kerala demonstrates a higher incidence of seismic events on land, particularly concentrated in central Kerala, where multiple faults and lineaments are prevalent. The reactivation of ancient faults emerges as a crucial contributor to the escalated seismicity observed in the region. In addition to ancient fault reactivation, Kerala’s seismicity is influenced by hydrological stress, particularly triggered seismicity induced by the filling of the Idukki reservoir. Regarding Pondicherry, the region displays a distinctive seismic profile characterized by both onshore and offshore seismic activity. Various studies document the reactivation of ancient faults in the area, particularly evidenced by the 2001 earthquake near Pondicherry. The NE-SW and NNE-SSW fault-bounded ridges and depressions, extending from land into the offshore sea, have contributed to the seismic activity. The region is under the influence of land-ocean tectonics (LOTs), attributing moderate seismicity to compressional stress acting on the Indian Plate. Smoothed seismicity analysis supports these observations, highlighting higher G-R parameters in Pondicherry indicative of LOTs along the Eastern continental margin of India (ECMI). Additionally, elevated earthquake probability near Mullaperiyar Dam in the Kerala region underscores the significant role of hydrology in seismic events. In short, the distinct seismic patterns observed in Kerala and Pondicherry underscore the complex relationship of geological, hydrological, and tectonic factors shaping seismic activity in these regions. Reactivated ancient faults, hydrological stress, and land-ocean tectonics stand out as primary contributors to seismic activity, underscoring the intricate nature of assessing and addressing seismic hazards in these regions.

Constraining timing of Proterozoic fault movement in the Capricorn Orogen, Western Australia

Ancient faults dissect low-grade Mesoproterozoic sedimentary rocks of the 1673–1455 Ma Edmund Basin and the 1455–1075 Ma Collier Basin in the Capricorn Orogen, Western Australia, and reveal a protracted history of basin formation and subsequent deformation. K–Ar dating of illite from fine-grained fault gouge separates (ideally <0.1 µm) provide robust dates of the most recent fault movement. From the Godfrey–Mount Vernon Fault, a sample of siltstone from the Kiangi Creek Formation (1590–1514 Ma) in the Edmund Basin, which was collected adjacent to faulting, provided a whole-rock date of 1506 ± 30.2 Ma. This is interpreted as a mixed age, encompassing modification of the depositional age by subsequent faulting during the extensional opening of the Edmund Basin. A fault gouge sample dated at 1141.4 ± 58.6 Ma, also from the Godfrey–Mount Vernon Fault, is consistent with the tectono-thermal 1321–1171 Ma Mutherbukin Tectonic Event identified in underlying high-grade Gascoyne Province basement rocks. Fault gouge sample dates of 885.5 ± 45.9 Ma from the Godfrey–Mount Vernon Fault and 782.2 ± 40.1 Ma from the Quartzite Well Fault define the younger newly identified crustal shortening during the Kuparr Tectonic Event. Concomitant tectonic activity in eastern Australia and South China has been considered as a possible precursor of the breakup of Rodina. In southern Africa, the Zambezi Supracrustal Sequence has been dated at 880–820 Ma and the Munali Intrusive Complex at 862–857 Ma also identified as rift-related.

Anisotropic structure at shallow depths across the Japan Trench

Anisotropic structures within the crust are frequently perceived to originate from stress-induced cracks, which have been mainly estimated on land through different wave speeds of orthogonally polarized S waves propagating in the anisotropic media. However, such estimations of crustal anisotropic structures in ocean areas, particularly for subduction zones around trenches, have not been investigated in detail due to the lack of long-term ocean bottom observations. In this study, we used ocean bottom seismometers of a permanent network deployed across the Japan Trench and the southern part of the Kuril Trench and applied the shear-wave splitting analysis to P-to-s converted waves extracted by receiver function analyses using teleseismic events. We estimated the anisotropic structures in marine sediments and oceanic crust for the incoming Pacific Plate and marine sediments for the overriding North American Plate. The obtained fast polarization directions for the incoming plate are mainly oriented to be parallel to the trench axis for the marine sediment and oceanic crust, which are formed by normal faults and cracks due to the upward plate bending in the outer-rise region, whereas results for marine sediments at the northern part of the Japan Trench are obliquely aligned to the trench axis. The oblique direction is consistent with the magnetic lineations of the incoming plate, indicating that ancient faults within the plate, which were formed in the shallow part of the crust during the creation of the oceanic plate at the ridge, are reactivated by the plate flexure. For the overriding plate, the fast polarization directions in the northern and southern parts of the study area are nearly normal to the trench axis. The central part shows two distinct features: the fast polarization directions parallel to the trench axis and small degrees of anisotropy. These patterns may reflect crack alignments associated with the lateral variation in postseismic crustal deformation after the 2011 Tohoku-Oki earthquake. Our results suggest substantial lateral variations in the stress field at the tip of the overriding plate along the strike direction.Graphical

Ring-shape and linear gold mining districts of zimbabwe: estimation of residual gold resources

Background. Despite the long history of exploitation and study of Zimbabwe’s geological potential, the ranks of gold ore formations at the level of regions and fields remain unclear. Assessment of the residual primary gold deposits in Zimbabwe appears an important research direction.Aim. Identification of ring-shaped and linear ore districts confined to greenstone belts corresponding in configuration within the gold province of the Zimbabwe craton.Materials and methods. The main method for analyzing gold ore deposits was ore formation analysis. To analyze the residual gold resources in the regions of Zimbabwe, the Zipf-Lotke-Bradford rule was applied according to the ratio of an outstanding rare event in the form of a large deposit, rather rare events in the form of medium-sized deposits, and fairly rare events in the form of small ore objects in a certain ore region.Results. A hypothesis is proposed for the formation of ring-shaped belts as ore-bearing volcano-tectonic structures of the central type. Within the gold province of the Zimbabwe craton, ore districts of ring-shaped and linear shape, confined to greenstone belts corresponding in configuration, are identified for the first time. It is shown that the localization of deposits in ore regions is due to a combination of the following criteria: ancient faults, arc fragments of greenstone belts, and the development of post-tectonic multiphase granitoid magmatism. A ranking of deposits was carried out in the ore districts of Darwin, Shamva, Midlands, Bulawayo, Gwanda, Busha Mwezi - Fort Victoria, Shashe - Ozi-Umatli, and Sinoia. Five gold mining areas corresponding to volcano-plutonic ring-shape structures and three linear areas were identified. Productivity is predicted to be highest in the Midlands, Bulawayo, and Shamva ring-shape regions. An assessment of the residual gold resources of each of the selected areas is given. The feasibility of detailing important forecast criteria — Late Archean linear and arc faults and post-tectonic granitoids — with the development of additional criteria for further metallogenic zoning and localization of promising areas is established.Conclusions. The presented data serve as the basis for assessing the prospects of industrially important primary gold deposits in Zimbabwe and carrying out their forecast in the identified gold mining areas.

Sequence stratigraphic analysis of Devonian organic-rich shales in northern Guangxi

Deep-water sediments are widely developed in Devonian sedimentary strata around the world. The Devonian's unique climate change, relative sea-level fluctuations, biological evolutionary stages and tectonic activities resulted in the widespread deposition of organic-rich shales across the globe in this era. The Devonian deep-water facies shales in northern Guangxi are widely distributed along the syn-sedimentary faults, such as the Ziyun–Luodian–Nandan–Du'an ancient fault zone and the Yishan fault, forming a series of special depositional successions under the deep-water system. Based on the stratigraphic cyclicity and spatial distribution of the Devonian strata, in conjunction with the total organic carbon content (TOC) of the dark shales at the Tonggong, Luzhai, Dongxing and Shuiyuan sections, it is determined that the Devonian system in northern Guangxi can be divided into 13 third-order sequences. Additional, the organic-rich shales, which are mainly composed of carbonaceous Tentaculitic shales in SQ5–SQ11 (1) developed in the TSTs of SQ5–SQ9 and mainly distributed in the Nandan–Hechi region in the west of the study area, and (2) developed in the HSTs of SQ10–SQ11 and extended along the fault zone from Nandan to the Luzhai region in the east of the study area. The spatial and temporal distribution of these Devonian organic-rich shales indicate that their formation is controlled by a relative sea-level change. The current study provides important clues for future unconventional oil and gas exploration and development in northern Guangxi.

Active ages of metallogenic structures in the Liangyan lead–zinc deposit, northwestern Guizhou: Constraints from geometric, kinematic, and sphalerite Rb-Sr dating analyses

More than ten lead–zinc deposits formed under the control of the Yadu-Mangdong fault (YMF) are known to have undergone multi-stage activity. However, ore control processes in such fault zones are poorly understood, such as in the Liangyan deposit in northwestern Guizhou. The internal geometrical structure, mineralization, alteration, tectonic stress, and kinematics of the YMF were investigated in three sections (1605, 1655, and 1720) of the Liangyan deposit. The ore-forming age (214.8 ± 4.3 Ma) was obtained by rubidium-strontium dating of sphalerite. The YMF is defined by double-fault cores and superimposed faults that indicate at least three stages of deformation since the mineralization period. The first stage is characterized by the ore-bearing dolomitization ancient fault core formed in the Indosinian period. The principal compressive stress direction was northwest to southeast (NW-SE). The second stage of Yanshanian was the tectonic breccia fault stage (new fault core). The principal compressive stress was northeast to southwest (NE-SW). The third stage was dominated by superposed faults that destroyed the new fault core in the Himalayan period. The principal compressive stress direction was east to west (E-W). In summary, we established a model of evolution for the YMF since the metallogenic period. In conclusion, based on the above research, we consider that the YMF turning point of the Liangyan deposit is prone to orebodies. Additionally, the prospecting target should be concentrated in the footwall (NW-trending) and hanging wall (NE-trending) of the Liangyan deposit YMF model.

Frictional power dissipation in a seismic ancient fault

The frictional power per unit area Q˙ (product of frictional traction τ and slip rate u˙ in MW m−2) dissipated during earthquakes triggers fault dynamic weakening mechanisms that control rupture nucleation, propagation and arrest. Although of great relevance in earthquake mechanics, Q˙ cannot, with rare exceptions, be determined by geophysical methods. Here we exploit theoretical, experimental and geological constraints to estimate Q˙ dissipated on a fault patch exhumed from 7-9 km depth. According to theoretical models, in polymineralic, silicate rocks the amplitude (< 1 mm) of the grain-scale roughness of the boundary between frictional melt (pseudotachylyte) and host rock decreases with increasing Q˙. The dependence of grain-scale roughness with Q˙ is due to differential melt front migration in the host rock minerals. This dependence is confirmed by friction experiments reproducing seismic slip where pseudotachylytes were produced by shearing tonalite at Q˙ ranging from 5 to 25 MW m−2. In natural pseudotachylytes across tonalites, the grain-scale roughness broadly decreases from extensional to compressional fault domains where lower and higher Q˙ are expected, respectively. Analysis of the natural dataset calibrated by experiments yields Q˙ values in the range of 4-60 MW m−2 (16 MW m−2 average value). These values, estimated in small fault patches, are at the lower end of broad estimates of Q˙ (3-300 MW m−2) obtained from frictional tractions (30-300 MPa) and fault slip rates (0.1-1 m/s) assumed as typical of upper crustal earthquakes.

Mid-crustal reactivation processes linked to frictional melting and deep void development during seismogenic slip: examples from the Lewisian Complex, NW Scotland

Exhumed examples of ancient fault voids formed during seismic slip at depths &gt;10 km are well preserved in the Assynt Terrane of the Lewisian Complex, NW Scotland. They are interpreted to have formed during regional Mesoproterozoic ( c. 1.55 Ga; ‘Assyntian’) strike-slip faulting. Deformation is characterized by sinistral reactivation of pre-existing NW–SE-trending features including intrusive contacts of ( c. 2.4 Ga) mafic dykes and Paleoproterozoic ductile shear zone fabrics ( c. 1.75 Ga). Reactivation occurred at palaeodepths of 10–15 km, where frictional–viscous deformation synchronous with co-seismic frictional melting led to cycles of millimetre- to decimetre-scale cavity dilation and collapse. Although individual melt-generating slip surfaces may have become rapidly welded, faulting was able to repeatedly localize along adjacent pre-existing planar anisotropies favourably oriented for slip, leading to the creation of a mesh of foliation-parallel melt generation surfaces linked by foliation-perpendicular dilational voids. The latter features are filled by chaotic clast-supported wall rock collapse breccias, localized injected frictional melts and hydrothermal mineralization. The fills act as natural props, holding cavities open and preserving them as long-term, pipe-like fluid flow conduits. These exhumed features are likely to be typical of multi-rupture seismogenic fault systems formed by direct reactivation of pre-existing basement structures.

Continental Reworking in the Eastern South China Block and Its Adjacent Areas Revealed by F‐J Multimodal Ambient Noise Tomography

AbstractThe eastern South China Block (SCB) has experienced complex and drastic reworking processes since the early Neoproterozoic, the mechanisms of which remain unclear. To better understand the continental reworking mechanisms in the eastern SCB, we imaged the shear‐wave velocity structure of the crust and upper mantle in the eastern SCB and its adjacent areas with the F‐J multimodal ambient noise tomography method. The seismic ambient noise data were acquired by 652 seismic stations in this area. The shear‐wave velocity model presents widespread mid‐crustal low‐velocity zones (MCLVZs) and upper mantle low‐velocity zones (UMLVZs), the distribution of which shows a good correlation with regional tectonics. The MCLVZs formed due to compositional and structural layering during the late Neoproterozoic to the early Phanerozoic. The disrupted MCLVZs near the Qinling‐Dabie orogen can be linked to metamorphism caused by a continental collision between the SCB and the North China Craton during the Triassic Indosinian event. The thin crustal and lithospheric thicknesses east of the North‐South Gravity Lineament may be the result of asthenospheric upwelling due to the subduction of the Pacific plate since the late Mesozoic. In the areas near the Shaoxing‐Jiangshan‐Pingxiang fault zone and the Tanlu fault zone, upheaval UMLVZs indicate that these ancient fault zones were reactivated by the subduction of the Pacific plate, providing channels for asthenospheric upwelling. Well‐preserved MCLVZs north of the Qinling‐Dabie orogen can be used to assess compressions and extensions induced by the subduction of the Pacific plate.

A morphotectonic approach to the study of earthquakes in Rome

Abstract. Rome has the world's longest historical record of felt earthquakes, with more than 100 events during the last 2600 years. However, no destructive earthquake has been reported in the sources, and all of the greatest damage suffered in the past has been attributed to far-field events. While this fact suggests that a moderate seismotectonic regime characterizes the Roman area, no study has provided a comprehensive explanation for the lack of strong earthquakes in the region. Through the analysis of the focal mechanism and the morphostructural setting of the epicentral area of a “typical” moderate earthquake (Ml= 3.3) that recently occurred in the northern urban area of Rome, we demonstrate that this event reactivated a buried segment of an ancient fault generated under both a different and a stronger tectonic regime than that which is presently active. We also show that the evident structural control over the drainage network in this area reflects an extreme degree of fragmentation of a set of buried faults generated under two competing stress fields throughout the Pleistocene. Small faults and a present-day weaker tectonic regime with respect to that acting during the Pleistocene might explain the lack of strong seismicity in the long historical record, suggesting that a large earthquake is not likely to occur.

Mineralogical Criteria for the Prediction of Gold Mineralization in the Structures of the Siberian Craton

Generalization of the results of the study of placer gold and the mechanisms of its distribution in the east of the Siberian Platform made it possible for the first time to reveal that the ore sources of gold-bearing placers were mainly mineralization of the gold-sulfide formation formed under the influence of hydrothermal metasomatic processes occurred in deep fault zones. It is determined that the gold-bearing hydrothermal-metasomatic formations of the gold-sulfide rock formation are amagmatic, near-surface, low-temperature and spatially confined to deep faults. These formations are widespread in terrigenous-carbonate strata and sand deposits of PZ-MZ age and are observed in the zones of brecciation, silicification, and ferruginization. The analysis of the mechanisms of distribution of hydrothermal-metasomatic gold-bearing formations in the east of the Siberian Platform, based on previously conducted research of predecessors and our field observations, allowed us to establish the following. In the northeast, hydrothermal-metasomatic formations occur in the field of development of the Zhigansky fault, the Molodo-Popigai and Anabar-Eekite fault system, in the central part of the east of the Siberian Platform, the Vilyui paleorift (Kempendyai dislocations), and in the southeast in the Baikal-Patom thrust belt in ancient faults (Bappagai, Khorinsky, etc.). Metasomatites of hydrothermal origin form extended narrow formations along ancient faults activated in the Mesozoic, as well as conformable deposits in the Vendian, Cambrian carbonate strata, Jurassic and Cretaceous sandstones. It is proved that these formations are amagmatic and are not related to the widespread magmatism of the basic composition, which is confirmed by the homogenous mineral composition of metasomatites, independent of the composition of magmatic bodies spatially located with them. Zones of metasomatites with gold mineralization contain Au from 0.5 to 3.0 g/t, and in isolated cases up to 24–32 g/t. Gold is represented from finely-dispersed to visible fine, with a size from 0.01 to 0.5 mm or more. It is known that hydrothermal-metasomatic processes on the territory of Central Aldan contributed to the formation of large deposits such as Kuranakh, Tabornoye and others. It is possible that the identified gold-ore metasomatites, developed along the zones of regional faults and not confined to magmatic formations, widely occurred both in the northeast and in the southeast of the Siberian Platform, represent a huge metallogenic potential.

Study on Segmental Growth Characteristics of Main Faults in Southern Aer Sag

The segmental growth of faults plays an important role in controlling oil and gas. This time, the southern part of the Aer sag is taken as the main research object to analyze the growth process of the faults. This paper uses the fault distance-distance curve, the fault distance-buried depth curve and the growth index to study the active stage of the segmental growth of the fault. The maximum fault distance subtraction method is used to strip back the faults, restore the ancient faults, and clarify the development characteristics of the main faults in each period. It is concluded that the Altala fault is a three-segment growth fault, and the fault continued to act during the depositional period of the A3 to Teng2 members, and the activity of the A4 was the most intense. The Hanwula fault is a two-segment growth fault. The faults continued to move during the depositional period of the A4 to Teng2 members, and the fault activity was most intense in the upper Teng1 sub-member. Hanwu Ladong belongs to a two-stage segmental growth fault, and the faults continued to be active during the strata depositional period from the first sub-member of Teng 1 to the second member of Teng 2, and the fault activity was most intense in the first sub-member of Teng. This study enriches the theory of the structure of the Erlian Basin's Aer sag and supports further breakthroughs in oil and gas exploration.

THE MECHANISMS OF THE DISTRIBUTION OF HYDROTHERMAL-METASOMATIC GOLD- BEARING FORMATIONS (EAST OF THE SIBERIAN PLATFORM)

Hydrothermal-metasomatic formations with Au content from 0.5 to 3.0 g/t, sometimes up to 24-32 g/t, were found in the east of the Siberian platform in the brecciated zones. They form, along ancient faults activated in the Mesozoic, extended narrow formations in terrigenous-carbonate and sandy layers of PZ-MZ age. The comparison of metasomatites with gold-ore metasomatites of the Kuranakh and Tabornoye deposits makes it possible for the first time to predict ore sources formed as a result of hydrothermal-metasomatic processes. Perhaps these sources represent a huge metallogenic potential.

Signs of Seismicity and Neotectonic Activity of Ancient Faults in the Area of the Sloboda Geodynamic Intersection in the West of the East European Platform

Signs of Seismicity and Neotectonic Activity of Ancient Faults in the Area of the Sloboda Geodynamic Intersection in the West of the East European Platform

Using morphometric and geomorphic indices to assess Western São Francisco Craton neotectonic traces

Recently, geomorphometric properties of river networks and catchments have been described and applied as an efficient tool in the investigation of the landforms' response to neotectonics. Geometric parameters of the Cotovelo River catchment extracted from an Alos-Palsar digital elevation model were used to compute morphometric and geomorphic indices to investigate whether the bedrock structure and recent active tectonics influence the local drainage network. The Cotovelo catchment is situated in the Middle to Upper Proterozoic western foreland basin of the São Francisco craton, in northwestern Minas Gerais, Southeastern Brazil; it is presumed to be a stable piece of earth’s crust. The automatically generated streams were processed at the sub-catchment scale to calculate the hypsometric integral, relief ratio, stream frequency, and drainage density morphometric indices as well as supported a geomorphic study based on the basin shape, asymmetry factor, valley floor width-to-height ratio, mountain front sinuosity, transverse topographic symmetry factor, and stream-length gradient index. Achieved results revealed recent and low-rate tectonic activity and structural control on the fluvial morphology. Prominent knickpoints, aligned with mapped fault scarps, disclose straight erosive fronts away from stratigraphic borders, indicating these features are unrelated to lithological changes. Despite the catchment location, the area exhibits impressive fluvial anomalies, and dissection occurs preferentially along ancient faults and fractures densely occurring in the rocky strata. Channel parallelism in context of medium to high relief and steep slopes, remarkably structurally drive fluvial dissection, asymmetric and elongated drainage catchments, and aligned landforms suggest neotectonic influence on the drainage network.

The Caroline Ridge fault system and implications for the bending-related faulting of incoming oceanic plateaus

The latest multichannel seismic data from the Yap subduction zone is presented to investigate the Caroline Ridge fault system, developed by faulting and bending processes within the incoming oceanic plateau. We reveal that horst and graben structures exist along the entire incoming Caroline Ridge adjacent to the trench and that pervasive bending-related faults trending ~N30°E have developed subparallel to the trench. However, the widths of the horst and graben structures decrease gradually from north to south. The two-stage ancient abyssal hill fabrics overlap the incoming Caroline Ridge. Abyssal hill faults trending ~N65°W present large trench-ridge angles (85–90°); in the southern segment, abyssal hill faults trending ~N70°E have relatively low trench-ridge angles (~35–40°). From the Caroline Ridge to the horst and graben structures, the topography decreases, and slump bodies with deformed internal reflections have developed above an irregular reflector. Little stable pelagic sediment with horizontal reflectors accumulates on the horst and graben structures, suggesting that the faulting and bending processes involve long and intense tectonic processes that affect the sedimentary environment. The sedimentary strata and fault distributions differ between the North and South Caroline Ridge, which is primarily attributable to the different rifting processes. Furthermore, we propose that N65°W-trending ancient faults sufficiently decrease the yield strength of the incoming Caroline Ridge to facilitate the bending-related faulting. During subduction, the incoming North Caroline Ridge that has a large degree of rifting and the Sorol Trough, which has a thin crust, may resist less flexural bending and generate the wide horst and graben structures. The ancient faults and rifting model of incoming oceanic plateaus play a significant role in bending-related faulting

Map of fossil resins of Ukraine

Finding out the conditions of the geological past under which tar secretions were fossilised and primary bio-sedimentary deposits of protoamber were accumulated and amber-succinite placers formed in the marine environment is an important link in scientific research. Insufficient study of amber-succinite as an organic formation, which has gone through a difficult path of transition from wildlife to minerals, leads to irrational use and search for such valuable raw materials and its extraction is much less beneficial than planned.&#x0D; The authors have carried out a comprehensive systematization of accumulated knowledge on amber-succinite and other mineral types of mineral resins in Ukraine and the entire Baltic-Dnipro amber province.&#x0D; The article discusses the creation of a new map of mineral fossil resins in Ukraine. In addition to the known amber-bearing zones, deposits and occurrences of amber, the map carriespaleogeological and predicted loads, is closely related to the formation of both secondary placers of amber-succinite and primary biogenic-sedimentary deposits – resin bodies, transitional composition in the first half of the Middle Eocene (Buchakian time).&#x0D; In order to develop a reasonable forecast of the deposits, the authors identified the root source of amber-succinite placers, which is represented by biogenic-sedimentary deposits of resin bodies. These deposits were formed in the Lower Middle Eocene during the Buchakian time on land of the Ukrainian Shield, most often within swampy accumulative depressions associated with ancient faults and structural tectonic traps. The conditions of the geological past, under which tar secretions were fossilized and primary biogenic-sedimentary deposits of the protoamber were accumulated, as well as the formation of amber-succinite placers, the first intermediate collectors in the coastal-marine, liman delta and deep-water parts of the paleoshelf, have been clarified.&#x0D; The work carried out by the authors resulted in predicted conclusions about the possibility of finding new areas promising for the discovery of industrial deposits of the most valuable type of fossil resins – amber succinite.

Quantifying and modelling the effects of pre-existing basement faults on folding of overlying strata in the Surat Basin, Australia: Implications for fault seal potential

Ancient basement fault geometry has a systematic effect on the folding of overlying sedimentary successions. Using aeromagnetic, Bouguer gravity, as well as 2D and 3D seismic datasets, the characteristics of the basement structure underlying the Jurassic-Cretaceous Surat Basin were examined and used to contextualise the nature of its folded strata. Using Fault-Forward modelling software, the deformation of the basement structural layers was modelled and analysed for its influence on the reactivation of faulting. The results show that the major fault trends in the eastern Surat and Bowen basins consist of five key features with N- and NE-trending orientations: the Goondiwindi, Moonie, Undulla Transition Zone, Burunga-Leichhardt, and Cockatoo fault systems. Most of the major fault deformation ceased in the Late Triassic. However, some faults (i.e., the Moonie and Goondiwindi fault systems) were variably reactivated along their lengths during the Jurassic. Three models of pre-existing basement reactivation are proposed to explain the observed variability in folding style with application to different parts of the basin. Ancient fault systems with dip angles greater than 45° were readily reactivated and produced tight monocline structures with high strain (ε > 0.35) and fault throw (>60 m) (e.g. Moonie Fault System), while faults with small dip (<30°) or large apical angles generated folds with low strain and uplift of the hanging wall. This variability in fault reactivation according to differences in fault throw potentially influences across-fault juxtaposition of strata and sealing potential for CO2 storage. Modelling such as this should be undertaken elsewhere in situations where trishear structural domains are expected, to better understand and predict the deformation of overlying stratal successions.

On the deep seated faults in the Northern Caucasus

Research subject . The paper describes large tectonic zones in the North Caucasus, which can be classified as deep faults according to a number of features. Among these formations are the Ancient axial fault zone earlier described by G.D. Azh-girei, which we attributed to Hercynian structures (with the presence of pre-Paleozoic); the Indosinian axial fault zone and the Main Caucasian fault (overthrust). Materials and methods . The Ancient axial fault zone is considered as a suture zone, which arose as a result of Varis с an (Hercynian) folding during the interaction of the Transcaucasian and East European tectonic plates (EETP). The Indosinian axial fault zone contains fragments of Variscan nappes and neoautochthonous deposits of the same age. Results. The surface manifestation of the Indosinian axial fault zone was a tectonic-formational zone of the Front Range, which is located at the junction, on one side, with the newly formed hard crystalline massif crust at the site of the Ancient zone (Main Range), and, on the other side, with EETP. This zone continued to be active later, during the Cimmerian and Alpine tectonic events. At the same time, the formation of new granite magmatic melts could occur. The driving mechanism is assumed to have been opposite undercrust convection flows. Although there are conflicting views on the Main Caucasian fault, it seems clear that this was a deep-seated and magma-producing zone at the pre-Callovian time. This fault is likely to have been formed as a consequence of the intraplate subduction, which is continuing at present. Conclusions. The presence of hyperbasite bodies in the fault zones under consideration is not a sign of their depth in the Caucasus. In the present structure, the mixtite zone lying under the flysch of the southern slope of the Greater Caucasus and overlapping the Transcaucasian massif can be considered as a large collision line currently under development. Some other faults present in the region, which are supposed to be deep, have also been considered.

Tectonic Features and Stages of Evolution of the Baltic–Mezen Shear Zone in the Phanerozoic, Northwestern Russia

The general tectonic features of the Baltic-Mezen zone developed along the border of the Fennoscandian shield and the Russian Plate in the north of the East European platform, are considered. The geophysical remote methods and structural analysis were used. It has been established that the zone has a length of more than 1000 km with a width of 10–40 km and can be traced from the Gulf of Finland in the sub-latitudinal direction along the southern shores of the Lake Ladoga and the Lake Onega in the valley of the River Onega.The Baltic-Mezen zone is represented by a system of folds and faults, fracture zones and brecciation, complicating the complexes of the Archean–Paleoproterozoic basement and the Vendian–Phanerozoic cover. Throughout the zone, changes in the configuration and displacement of the axes of the magnetic anomalies are noted; on seismic sections, the systems of discontinuities penetrating the basement and cover complexes are decrypted. On the surface, the discontinuous structures of the zone are expressed in the various forms of relief, often violate and displace glacial morphostructures. Based on the analysis of materials on the nature of the paleoseismites distribution and surfaces of unconformity in the sediments of the cover, as well as the structural features of various rock complexes, a long period of development of the Baltic-Mezen zone was established during the Caledonian, Hercynian and the latest stages of deformation. The Caledonian stage was associated with the formation of paleoseismites horizons of Kukruz phase (~ 460 Ma), as well as the folded-fault structures formed in the Late Silurian–Early Devonian. The Hercynian stage was manifested by several seismic and tectonic events in the Late Devonian (Frasnian age), in the Early (Visean age) and Late (Kasimovian century) Carboniferous. The newest stage was associated with Neopleistocene glaciodynamic processes and two stages of seismic events in the late and post-glacial period, which were accompanied by activation of ancient faults and local development of folded structures. The developed scale of paleoseismic and deformation events of the Baltic-Mezen zone can be used for tectono-dynamic reconstructions based on additional analysis of materials of structural-kinematic research.