In terms of tectonics, the Deryugin basin (Fig. 1) is a part of the epi-Mesozoic Okhotsk plate comprising the heterogeneous basement that is mainly pre-Cenozoic (the lower structural stage) and the sedimentary cover that is mainly represented by the Paleogenic-Neogenic-Quaternary deposits with the Upper Cretaceous sedimentary rocks observed locally without a visible hiatus (the upper structural stage).

The acoustic basement (AB) is composed of the metamorphosed Upper Cretaceous-Paleogenic silty-clayey-siliceous deposits (the western part of the region), amphibolites, gneisses, crystalline schists, weakly metamorphosed sandstones, siltstones, and mudstones (often siliceous), as well as intrusive and effusive rocks of basic, intermediate, and rarely persilic composition (the eastern part of the region). AB is generally dated as Mesozoic–Paleozoic.

Results of tectonic zoning of the sedimentary cover based on material (lithophysical) indicators (Fig. 2) are represented in the format of maps showing lithophysical complexes (LC) within the limits of four regional seismo-stratigraphic complexes/structural layers (RSSC I-IV) corresponding to the following time intervals: the pre-Oligocene К2–P1-2 (RSSC I), the Oligocene – Lower Miocene P3–N11 (RSSC II), the Lower – Mid Miocene N11–2 (RSSC III), and the Upper Miocene – Pliocene N13–N2 (RSSC IV). Diverse lithological-facies associations composing the RSSCs are grouped into the following lithophysical complexes (LC): 1 - coal-bearing silty-clayey-sandy terrigenous, 2 - sandy-silty-clayey terrigenous, 3 - silty-clayey-siliceous, and 4 - sandy-silty-clayey volcanic [Sergeyev, 2006]. In the studied area (Fig. 2), the deposits of the pre-Oligocene RSSC are identified in limited areas within its northern, northwestern, and southwestern parts; they are represented by coal-bearing silty-clayey-sandy terrigenous and silty-clayey-siliceous LCs. Other RSSCs (II, III, and IV) in this area represented mostly by sandy-silty-clayey terrigenous and silty-clayey-siliceous LCs, and only the extreme southwestern part along the eastern Sakhalin coast contains narrow bands of the coal-bearing silty-clayey-sandy LC. The sandy-silty-clayey volcanic LC is absent in the Deryugin basin.

Tectonic zoning of the sedimentary cover based on structural indicators is carried out with reference to the sediment-thickness map [Sergeyev, 2006] that was significantly revised in its segment showing the area of the Deryugin basin. Results of such zoning are represented in the format of a structural-tectonic map (Fig. 3) showing orientations and morphology of the structural elements of the sedimentary cover, the thickness of the sedimentary cover, and amplitudes of relative uplifts and troughs.

With reference to the structural-tectonic map (see Fig. 3), the structural elements of different orders are grouped by their sizes, spatial positions and orientations and thus comprise structural zones (Fig. 4) that include relative uplifts and troughs that are considered as structural elements of smaller sizes (Fig. 5).

Tectonic zoning of the sedimentary cover based on structural-material (lithophysical) indicators (Fig. 7–10) is carried out with reference to the maps of the lithophysical complexes of the four regional seismo-stratigraphic complexes/structural layers (see Fig. 2) and the map of high-order structural elements in the sedimentary cover (see Fig. 5).

 

 

Based on analysis of modern concepts describing changes in the stress-and-strain state of rocks, it is revealed that the elastic energy is not fully released and residual/own stresses occur in core samples taken out of the rock massif.

The paper describes a model aimed at explanation of causes for residual stresses of the type. The model is composed of two elastic elements that are subject to different states of stresses; it shows major previous stages of formation of the initial state of gravity stresses of the detrital sedimentary rock which were followed by cementation and changes of the state of stresses during unloading. Being an element of the history, the sequence of formation of the rock under the ‘loading – cementing’ pattern leads to formation of two systems of stresses in the rock elements (according to K. Terzaghi), i.e. effective stresses in the rock matrix (or groundmass) that is subject to main loading, and neutral stresses in the connate fluid that is not involved in the process. Upon hardening of the solution, the effective stresses become bound by the cementing material.

Changes of the stress-and-strain state of the model in case of induced or natural unloading are analyzed on the basis of stress–strain curves that are reconstructed for the rock elements prior to unloading and compared in the same systems of coordinates, and the process of unloading is reviewed with account of the condition of their joint deformation. By applying the method of superposition of the two fields of stresses during unloading, it is possible to reveal the cause-and consequence relationship between the initial state of stresses and the occurrence of own stresses and, subsequently, to trace the self-stress state. The proposed definition ensures a ‘transparent’ representation of changes of stresses between the model’s elements during unloading, changes of the potential energy and distribution of its components after unloading, which provides an explanation of the incomplete release of the potential energy.

 

 

 The evolution and specific features of seismogynamics of the Baikal zones are reviewed in the context of interactions between deep deformation waves and the regional structure of the lithospheric mantle. The study is based on a model of the mantle structure with reference to chemical compositions of mantle peridotites from ophiolotic series located in the south-western framing of the Siberian craton (Fig. 1). The chemical zonation of the lithospheric mantle at the regional scale is determined from results of analyses of the heterogeneity of compositions of peridotites (Fig. 2, Table 1) and variations of contents of whole rock major components, such as iron, magnesium and silica (Fig. 3). According to spatial variations of the compositions of peridotites, the mantle has the concentric zonal structure, and the content of SiO2 is regularly decreasing, while concentrations of FeO∑ and MgO are increasing towards the centre of such structure (Fig. 4). This structure belongs to the mantle of the Siberian craton, which deep edge extends beyond the surface contour of the craton and underlies the north-western segment of the Central Asian orogenic belt.

Results of the studies of peridotites of the Baikal region are consistent with modern concepts [Snyder, 2002; O’Reilly, Griffin, 2006; Chen et al., 2009] that suggest that large mantle lenses underlie the Archaean cratons (Fig. 5). The lenses are distinguished by high-density ultrabasic rocks and compose high-velocity roots of cratons which have remained isolated from technic processes. Edges of the mantle lenses may extend a few hundred kilometers beyond the limits of the cratons and underlie orogenic belts that frame the cratons, and this takes place in the south-western segment of the Siberian craton.

The revealed structure of the lithospheric mantle is consistent with independent results of seismic and magmatectonical studies of the region. The Angara geoblock is located above the central part of the mantle lense (Fig 6, A); it is one of four main tectonical units that compose the basement of the Siberian craton [Mironyuk, Zagruzina, 1983]. As evidenced by the zonal composition of the mantle lense, the centre of the lense is highly dense, and this explains the location of a seismic anomaly there (Fig. 6, B) which is determined to a depth of about 50–60 km [Pavlenkova G.A., Pavlenkova N.I., 2006]. The high-velocity root located in this segment of the craton is traced by seismic tomography [Koulakov, Bushenkova, 2010] to a depth of about 600 km (Fig. 7). The southward-stretching edge of the sub-cratonic mantle has played a major role in the evolution of the Central Asian orogenic belt. In the Paleozoic, the position and the configuration of the accretional margin of the Siberian paleocontinent were determined by the hidden boundary of the craton (Fig. 8, A). Along the craton’s boundary, rifting zones of various ages are located, and intrusions are concentrated, which genesis was related to extension settings (Fig. 8, B). The Cenozoic sedimentary basins are located above the hidden edge of the Siberian craton, which gives evidence of involvement of the deep lithospheric structure in the formation of the recent destruction zone. The basin of Lake Baikal is located along the mantle edge of the Siberian craton, and the basin’s crescent shape accentuates the strike of the mantle edge.

In the region under study, the wave nature of seismicity is most evidently manifested by the cyclicity of the strongest earthquakes in the Baikal zone (Table 2). Three seismic cycles are distinguished as follows: (1) at the turn of the 20th century (earthquakes in the period from 1885 to 1931, M=6.6–8.2), (2) the middle of the 20th century (earthquakes from 1950 to 1967, M=6.8–8.1), and (3) at the turn of the 21st century (earthquakes from 1991 to 2012, M=6.3–7.3). While moving in the mantle, the deformation front collapses with the craton’s basement, partially releases its energy to the lithosphere and involves the fragmented edge of the crust overlying the craton’s edge into deformation (Fig. 9, A). This interaction resulted in the formation of the Mongolia-Baikal and the Altai-Baikal seismic sutures whereat all the strong earthquake took place in seismic cycles (1) and (3), respectively (Fig. 9, B). The third, West Amur seismic suture framing the boundary of the Amur plate comprises locations of strong earthquakes that occurred in cycle (2) (Fig. 10). An important specific feature of the Baikal seismic zone is orthogonal migration of earthquakes within seismic sutures. In each of the sutures, epicenters of strong earthquakes (M>6.0) migrated in the transverse direction, which established the orientation of maximum compression during interaction of deformation waves with the mantle structures (Fig. 9, and 10). The less strong seismic events (М<6.0) (Fig. 11) migrated along the seismic sutures. At the western flank of the zone, in the Altai-Baikal and Mongolia-Baikal sutures, latitudinal migration took place in the direction from west to east with account of the trajectory of the deformation wave. In the northern part of the West Amur suture, latitudinal migration was directed from east to west, and its direction was gradually changed to meridional in the southern part, which reflected the anticlockwise rotation of the Amur plate. This conclusion can explain a paradox of counter migration of seismicity in the Baikal zone, which is revealed by S.I. Sherman [Sherman, Zlogodukhova, 2011].

In each of the three seismic/deformation sutures, stresses are released via orthogonal multi-directional migration of earthquakes (Fig. 12), and the sutures are regularly combined to compose a complex structure of the stress field in the Baikal seismic zone. Their positions predetermine locations of the major riftogenic structures, primarily sedimentary basins from Tunka to Ubsunur (Fig. 9, B). The three seismic sutures join and overlap each other in the area of Lake Baikal and thus set up the maximum intensity of deformation in this area. Apparently, each of the deformation sutures corresponds to one of the three basins of Lake Baikal (Fig. 13, A). Their depths are correlated with widths of the sutures, which is explained by ‘weakening’ of the deformation wave in the successive cycles of its interaction with the deep structure of the lithosphere. Seismicity of the Baikal zone and its Cenozoic rifting reflect the character of the stress field generated by interaction between the deep deformation wave and the organization of the lithospheric mantle.

 

 

This issue of Geodynamics & Tectonophysics contains five articles based on materials presented at the All-Russia Conference on Tectonics and Current Issues of the Earth Sciences held on 8–12 October 2012 in Moscow and recommended for publication by its Organizing Committee. The articles presenting modern research method that are currently applied in tectonophysics can trigger useful scientific discussions.

The article describes a tectonophysical model showing evolution of structures in the Sailag granodiorite massif in relation to its gold-bearing capacity. The model takes into account the load patterns according to geological data, accumulated deformation, and gravity stresses. This model provides for updating the structural-geological model showing development of the intrusion body and the ore field. Forecasted are destruction patterns in the apical and above-dome parts of the massif  in the intrusion and contraction phase, formation of the long-term shear zone at the steeply dipping slope of the intrusion body, and subvertical fractures associated with the long-term shear zone and vertical mechanical ‘layering’ of the intrusive body.

 

 

Structural paragenetic and cataclastic analysis methods were applied to study tectonic fracturing within one of the folds of the southern wing of the North-Western Caucasus fold-and-thrust belt. The object of the study was the Semisamskaya anticline (Fig. 1 and 2) comprising the Upper Cretaceous and Paleogenic layered terrigenic-carbonate sediments that contain various well-developed geological indicators of palaeostresses (Fig. 3, 5, 7, and 9).

In the folded structure under study, a paragenesis is revealed which is associated with the effect of sub-horizontal minimum compression (deviator extension) stresses of the north-western orientation (NW 320°) and traced by detached normal fault systems striking in the north-eastern direction (Fig. 6, 8, 10, 11, and 17). Upthrust-overthrust systems of the north-western strike (NW–SE), which are of importance for the whole folded structure of the North-Western Caucasus, are mainly manifested in the wings of the Semisamskaya anticline (Fig. 6, 12, and 13).

The overall field of stresses related to formation of the folded structure is significantly variable as evidenced by the pattern of local parameters of the paleostress field, which are calculated by the cataclastic analysis method (Figure 15, 16, and 17).

It is established that the geodynamic regime within the anticline is considerably variable by types (Fig. 18). Areas with horizontal extension in the axial part of the fold are replaced by areas of horizontal compression at its wings (Fig. 19).

 

 

The goal of the research is to develop components of the method aimed at output of information on relief-forming processes from archival and current remote sensing (RS) data with the use of the latest data-processing technologies, including photogrammetry and geoinformation systems (GIS). The proposed components of the methods are highly informative and economically effective. The object under study is located at the border of two active tectonic structures, the South Tatar arch and Melekesskian depression in the south-eastern part of the East European platform (Fig. 1). Based on the study results, it is confirmed that neotectonic movements in the area under study and its recent geodynamical setting are directly related (Fig. 5). It is demonstrated that the morphometric method can be efficiently applied to predict zones of high geodynamic activity and to determine locations of such zones.