The zone-block structure of the lithosphere is represented by a hierarchically organized pattern of stable blocks and mobile zones which border such blocks and contain highly dislocated geological medium (Fig. 1). Today, different specialists adhere to different concepts of blocks and zones, which are two main elements of the lithosphere structure. Differences are most significant in determinations of ‘interblock zones’ that are named as deformation / destructive / contact / mobile / fracture zones etc. due to their diversity in different conditions of deformation. One of the most effective approaches to studying the zone-block structure of the lithosphere is a combination of geological and geophysical studies of interblock zones tectonic features on various scales, which can make it possible to reveal the most common patterns of the interblock zones, general regularities of their development and relationships between the interblock zones.

The main objectives of our study were (1) to identify the zone-block structure of the crust in the southern regions of East Siberia from tectonophysical analysis of geological and geophysical surveys conducted on four different scales along the 500 km long Shertoy-Krasny Chikoy transect crossing the marginal segment of the Siberian block, the Baikal rift and the Transbaikalian block (Fig. 2); (2) to clarify structural features of the central part of the Baikal rift (representing the tectonic type of interblock extension zone) by applying new research methods, such as radon emanation survey, to the Shertoy-Krasny Chikoy transect and using the previously applied methods, such as magnetotelluric sounding, on a smaller scale; and (3) to study manifestation of interblock zones of various ranks in different geological and geophysical fields, to reveal common specific features of their structural patterns for the upper crust, and to establish regularities of hierarchic and spatial relationships between the interblock zones.

On the global scale, the object of our study at the Shertoy-Krasny Chikoy transect was the Baikal interblock zone (Fig. 2, 15, and 16). On the trans-regional scale, large fault zones were studied (Fig. 6, 11, and 14). On the regional and local scales, the objects of our study were systems of faults and fractures of various ranks which were active at the late Cenozoic stage of tectogenesis (Fig. 4, and 5). The set of geological and geophysical surveys included application of methods for identification of faults and fractures using different criteria, with account of the fact that clusters of such structures are indicative of the interblock zones of the crust. We used structural geological methods for studying faults and fractures, morphostructural analysis (including interpretation of satellite images), self-potential (SP) and resistivity profiling, magnetotelluric (MT) sounding, radon emanation survey, and hydrogeological studies of water occurrences. The region of Lake Baikal is one of the most studied geodynamically active regions of Russia; therefore, published data from previous studies of the Baikal region were used to interpret the data obtained by the authors.

By interpreting the obtained data from the unified tectonophysical positions, the three objectives were met, and the following research results were stated:

1. The principal specific features of the geological structure of the crust along the Shertoy-Krasny Chikoy transect are specified. It is established that the divisibility pattern complies with tectonophysical definitions of the hierarchically organized zone-block structure of the lithosphere (Fig. 2, 6, 11, 14, and 16). It is clearly evidenced, within the depth interval from the near-surface to about 30 km, that the crust is split into slightly broken blocks that are in contact with each other via wide zones that are marked by higher fracturing and fluid saturation. To a first approximation, such blocks are shaped as subhorizontal plates in the stable southern regions of East Siberia (e.g., the southern part of the Siberian platform) and subvertical plates in the areas being active in the Cenozoic (e.g., the Baikal rift). Within the framework of the given model of the zone-block structure of the southern regions of East Siberia, strict hierarchical subordination is established that manifests in spatial relationships of interblock zones (the closed network of the zones, imbedded blocks); its quantitative characteristics are stated at the global, trans-regional and three regional levels (Table 1, Fig. 2, Fig. 22). Average sizes of the zones, that were crossed by the transect, are estimated from the depth of their penetration into the crust; it is shown that Scale Invariant 2.2 (previously set for estimates of square areas) is valid also for the analysis of volumes of interblock structures. Detailed observations show that interblock structures are usually wider towards the earth surface; in the 1st order active zones, dimensions of the interblock structures may exceed dimensions of the adjacent, slightly disturbed blocks of the corresponding hierarchic level (Fig. 6, 11, 14, and 16). This pattern is typical of the actively developing Baikal rift and determines specific features of its structure with regards to the zone-block divisibility of the lithosphere.

2. The Baikal interblock zone is a global one in the hierarchy of the zone-block structure of Asia. It develops under tension conditions at the contact of the Siberian and Trans-Baikal lithospheric blocks (Fig. 16). Within the transect, the width of the Baikal interblock zone is about 200 km. At the trans-regional level of the hierarchy, the zone is comprised of the Obruchevsky, Chersky-Barguzin and Dzhida-Vitim fault systems (Fig. 6, 11, and 14). The first two of them act as the western and eastern borders of the subsided block of the Baikal basin and thus constitute the major area of the lithospheric extension. The second area is the Dzhida-Vitim fault system separating from the first one by the uplifted Khamar-Daban block; within the transect, it is morphologically manifested by the Ivolgino-Uda basin (Fig. 11, and 16). In this area, due to localization of deformation in the South Baikal basin, the process of fracturing is less pronounced, although indicators of the recent activity, such as seismicity, heat flow, gas emanations etc., are clearly at maximums over the Dzhida-Vitim zone, which makes it evident that this zone is distinguished from the adjacent Transbaikalian block (Fig. 15). Each of the three trans-regional fault systems has a width of about 50 km and consists of regional interblock zones that undergo the intensive development within the Baikal area wherein the crust is subject to extension (Fig. 6, 11, and 14). By their internal patterns, they represent zones of major faults: the Prikhrebtovy, Primorsky, and Morskoy faults constituting the Obruchevsky fault system, as well as the Bortovoy and Deltovy faults from the Chersky-Barguzin system. The Prikhrebtovy and Bortovoy fault zones are located at the periphery of the systems and flatten out in the direction of the rift axis from depths of about 20 km, and, consequently, the area of the most intensive deformations in the Pribaikalie has a ‘bowl-shaped’ profile (Fig. 16). Due to the intensive fracturing occurring in the conditions of the overall stretching of the crust, this area is saturated with meteoric water and deep fluids penetrating into the regional fault zones and partially into the adjacent blocks also belonging to the internal pattern of the Obruchevsky and Chersky-Barguzin fault systems. The block represented by the Baikal basin (located between these two fault systems) is no exception as its central part is disturbed by the regional-scale zone wherein fluidization is most intense due to localization of deformation (Fig. 8, and 16). The zone of the anomalously low resistivity has a width of about 7-10 km and shows no trend to any drastic narrowing in the lower crust, which gives grounds to consider it as the main channel for migration of deep fluids towards the surface.

3. As shown by experiences gained during the research at the Shertoy-Krasny Chikoy transect, in East Siberia the applied methods and techniques are informative for identification and analyses of the internal patterns of the interblock zones of different ranks. The methods and techniques used in studies along the transect complement each other and make it possible to investigate different properties of interblock zones. In general, in comparison with blocks, the zones are distinguished by the relief lowering, anomalous water exchange conditions, gas anomalies that are positive and complex in shape, and low resistivity values both near the surface and at depth (Fig. 3–6, 8, and 11–16). Integrated interpretation of the data is challenging: when applied separately, the methods and techniques reveal various specific features of interblock zone that differ in the degree of heterogeneity of the internal patterns depending on conditions of their formation and development. At the current stage of research, the boundaries of the interblock zones can be determined, to a first approximation, from average positions of anomalies, to determine which the deviations of measured parameters from their mean values are used.

In the future, it is necessary to conduct detailed surveys using the above geological and geophysical methods in order to reveal specific features of manifestation of the interblock zones that differ in (1) kinematic types, ranks and degrees of activity, (2) properties of infill material and the surrounding medium, and (3) impacts of external factors (e.g., those of the planetary level). Upon comparison of results of such studies, it will be possible to update and improve the proposed generalized models accounting for manifestation of the interblock zones in the geological and geophysical fields (Fig. 17, 20, and 21) and to ensure that the methods and techniques used can be applied more effectively for identification of interblock zones in regions where rock outcrops are poor or lacking.

The series of five papers are reports presented at the Third All-Russia Tectonophysical Conference ‘Tectonophysics and Current Issues of the Earth Sciences’ held from 08 to 12 October 2012 in Moscow; it was also attended by foreign researchers. A number of modern research methods applied in tectonophysics, which are described in this issue, deserve a scientific discussion.

The integrated approach combining kinematic and structural-paragenetic field tectonophysics techniques allows us to construct a continuous time scan of the stress-strain state (SSS) and deformation modes (DM) from sediment lithification to the final orogenic process for the studied areas. Definitions of the continuous sequence of SSS and DM provide for control of the known geodynamic reconstructions and adjustment of geodynamic models. An example is the tectonophysical study of the Alpine structural stage of the Western Mountainous Crimea (WMC) and the Pre-Cambrian complexes of the Ukrainian Shield (USh).

Data from WMC allow us to make adjustments to the geodynamic model of the Mountainous Crimea. In particular, trajectories of the principal normal stresses (Fig. 4 and 5), both for shifts and shear faults with reverse components/ normal faults, suggest the reverse nature of movements of the Eastern and Western Black Sea microplates with their overall pushing onto the Crimean peninsula in the south-east, south and south-west (Fig. 7). In the Precambrian USh complexes (Fig. 8), 13 stages of regional deformation are revealed between ≥2.7 and 1.6 billion years ago. Until the turn of 2.05–2.10 billion years, the region was subject to transtension and transpression, as the Western (gneiss-granulite) and Eastern (granite-greenstone) Archean microplates of USh moved to separate from each other in the Neo-Archean and then diverged and converged in the Paleoproterozoic (movements at a sharp angle). It is assumed that in the Archean the Western and Eastern microplates were separated by the oceanic or sub-oceanic lithosphere (Fig. 12, 13). During the period of 2.3–2.4 billion years, the plates fully converged creating a zone of collision. It may be suggested that a possible mechanism for the oceanic window close-up was underthrusting of the upper suboceanic lithosphere layers beneath the crust-mantle plates on gently sloping break-up surfaces (non-subduction option), and one of them is Moho.

Spreading of the Western and Eastern microplates of USh began at the turn of 2.05–2.10 billion years, as evidenced by the available tectonophysical data on fields of latitudinal extension of the crust. During spreading 2.1–2.05 billion years ago, emanations and solutions were able to ascend into the upper crust and thus stimulate palingenesis (Novoukrainsky and Kirovogradsky granites), and during repeated spreading 1.75 billion years ago, magma of the basic and acid composition (Pluto gabbro-anorthosite and rapakivi) intruded into the upper crust. The spreading zone coincided with the former collisional suture and became the site wherein the inter-regional Kherson-Smolensk suture was formed; it stretches submeridionally across the East European platform.

 

The article presents new data on the geoelectrical structure of Chuya, Kuray and Uymon intermountain basins, which are the three largest ones in Mountainous Altai, Russia. Geoelectrical models of the basins were constructed using the data obtained from field studies with application of a complex of electromagnetic methods, including transient electromagnetic, vertical electric soundings and electric tomography. Different amounts of field geoelectric data were collected for each basin. Chuya and Kuray basins are studied better, and their basic geoelectrical models were constructed; however, the structure of their marginal parts is still unclear, and additional measurements are underway there. The structure of Uymon basin has not been properly studied by geophysical methods yet; therefore during 2011–2012 field seasons, it was subject to comprehensive electromagnetic (direct- and alternating-current) surveys carried out with the use of modern equipment sets. Measuring equipment ensured high accuracy and efficiency of field measurements. Software systems for modeling and inversion were applied for quantitative electromagnetic data interpretation based on geological data and parametrical measurements in known profiles. The conclusions are supported by results of joint analysis of the available electromagnetic and geological data and confirmed by multidimensional modeling.

The article presents results of field studies and interpretation of tectonophysical data from profiles in the valleys of Bystritsa Nadvornyanskaya, Prut, Pistynka (the right-side tributary of the Prut river), Belyi and Chernyi Cheremosh, and Seret rivers. The stress fields reconstructed from different groups of joints and slickensides in flysch and molasse sediments of the Skyba and Boryslav-Pokuttya nappes are analyzed.

A combination of the structural-paragenesis and kinematic analysis methods provided for determination of deformation modes, their sequences, and  average azimuth values of orientations of the principal axes of regional paleostress fields (σ1, σ2, σ3) which were manifested through the Alpine stage of the Ukrainian Carpathians development.

The paleostress fields were reconstructed for the south-eastern part of the Skyba nappe of the Ukrainian Carpathians and the Boryslav-Pokuttya nappe of the Carpathian foretrough. The article describes similarities and differences in the stress-and-strain states, specific features of the paleostress fields, and the ratio of joints in different groups (oblique and perpendicular to the rock layers) and slickensides in the area under study.

The available data on well-studied areas of the Turan platform (as an example) are reviewed and analyzed to reveal the role of con-sedimentation and post-sedimentation tectonic movements in formation of dislocations of the sedimentary cover. At the background of the long-term (tens and hundreds of million years) quiet evolution of the territory under study, short-term intervals are distinguished, which duration amounts to the first millions of years (typically manifested in one or two stratigraphic layers); in such time intervals, tectonic movements were dramatically boosted and accompanied by land uplifting, sea regression, erosion of sediments accumulated earlier and manifestation of deformation processes.

The paleotectonic reconstructions show that during such ‘revolutionary’ stages, large tectonic elements occurred along with local uplifts that added to their complexity. In the region under study, the Pre-Jurassic, Pre-Cretaceous (Late Okoma), Pre-Danish and the Pre-Middle Miocene gaps in sedimentation are studied in detail. It is shown that only during the above four periods of sedimentation gaps and accompanying erosion-denudation processes, the regional structures gained from 50 to 80% of their current amplitudes at the bottom of the cover, and the Pre-Danish and Pre-Middle Miocene washout periods were most important.

Local uplift also developed impulsively and primarily due to the post-sedimentation movements. Cross-sections of anticlines studied in detail (Figures 1 to 3) are discussed as examples that clearly show the increase of erosional shearing of the sediments accumulated earlier towards domes of uplifts without any con-sedimentation decrease of their thicknesses. During these periods of the geologic history, regardless of their short duration, folded dislocation gained up to 65–90% of their current amplitudes. The periods of activation were separated by long relatively quiescent tectonic periods with the gradually slowing down growth of anticlines to complete cessation.

Dislocations in other regions, such as the Azov Sea (Fig. 4), the Dnieper-Donets basin, Donbas, etc. were formed under a similar scenario.

Impulsiveness of tectonic processes is well illustrated by events that recently took place at the Taman peninsula. In 2011, the sea bottom uplifted dramatically along the coastal line of the Azov Sea and formed a new land segment (Figures 5 to 8). The vertical movement amplitude amounted to minimum 5 metres. This new structure formation was due to a short-term renewal of growth of the Kamenny Cape. After the short-term activation of tectonic movements, the period of tectonic quiescence is in place, and the majority of the uplift has been destroyed by marine erosion.

Impulsiveness of tectonic movements may be caused by the tangential stress that periodically puts an impact on the lithospheric plates. Horizontal tectonic movement and associated stresses can lead to both interplate and intraplate deformations.

The most informative geological indicators of tectonic stress are faults on all scales and minor structural forms, such as dikes, mineralized veins, shear fractures, cleavage, slikenlines on slip planes of any genesis, foliation, cleavage, stilo­lite joints, hinges and axial planes of folds and flexures, etc. These indicators are analysed by various field tectonophysical methods developed in different countries. The article gives an overview of the history of the most widely used methods of tectonophysical paleotectonic stress reconstructions for geological structures of various scales. Reviewed are results of re­gional tectonophysical studies aimed at mapping paleotectonic stress and solution of possible mechanisms of formation of the structures located mainly in the territory of Russia and CIS countries. Special attention is given to application of results of the tectonic stress studies for solution of practical problems.

 The article provides information about “Continental rifting, accompanying processes” Symposium dedicated to the memory of N.A. Logachev and E.E. Milanovsky, ‘Academicians of Rifting’. The symposium took place on 20–23 August 2013. It was initiated and arranged by the Institute of the Earth's Crust SB RAS and the Geological Faculty of the Irkutsk State University (Irkutsk) with participation of the Geological Faculty of Moscow State University. Topics of the symposium are reviewed.