42 research outputs found
SPECIALIZED MAPPING OF CRUSTAL FAULT ZONES. PART 2: MAIN STAGES AND PROSPECTS
No full textThe article is to complete the description of the special mapping method which theoretical basis and principles were published in [Seminsky, 2014]. With reference to data on the Ulirba site located in Priolkhonie (Western Pribaikalie), the content of special mapping is reviewed in detail. The method is based on paragenetical analysis of abundant jointing which specific feature is the lack of any visible displacement indicators. There are three stages in the special mapping method (Fig. 3) as follows:Stage I: Preparation and analysis of previously published data on the regional fault structure (Fig. 1, А–Г), establishment of a networks of stations to conduct structural geological monitoring and mass measurements of joints, record of rock data (Fig. 2, А), general state of the fault network (Fig. 1, Д–З), fracture density (Fig. 2, Б) and, if any, structures of the above-jointing level (Fig. 1, Е, З; Fig. 2, А).Stage II is aimed at processing of field data and includes activities in four groups (II.1–II.4) as follows: Group II.1: construction of circle diagrams, specification of characteristics of joint systems and their typical scatters (Fig. 4, А), identification of simple (generally tipple) paragenesises, and determination of dynamic settings of their formation (translocal rank) (Table 1), evaluation of densities and complexity of the joint networks, analysis of their spacial patterns within the site under mapping, and identification of the most intensively destructed zones in the rock massif (Fig. 2, Б–В). Group II.2: comparison of jointing diagrams with reference ones showing joint poles (Fig. 4, Б–В; Е–З; Л–Н), and, in case of their satisfactory correlation, making a conclusion of potential formation of a specific joint pattern in the local zone of strike-slip, normal faulting or reverse faulting (Fig. 4, Г–Д, И–К, О–П; Fig. 5; Fig. 7, Б), and determination of relative age relationships between such zones on the basis analysis of the scatter of joint systems, shearing angles and other relevant information. Group II.3: construction of a circle diagram for the specified mapping site with local fault poles (Fig. 8, Б), identification of conjugated systems and dynamic settings of their formation (Fig. 2), plotting the information onto the schematic map of the location under study, and marking the transregional fault zones (Fig. 7, В–К) with observation sites showing similar settings and paragenesises of local faults. Group II.4: comparison between diagrams of fault poles of local ranks with reference patterns selected according to the availability of conjugated pairs of fractures (Fig. 9, Б–Г); based on the above comparison, decision making on potential formation of a paragenesis of local faults in the strike-slip, normal and reserve/thrust fault zones (Fig. 9, Д–Ж), and delineation of boundaries of such zones in the schematic map by connecting the observation sites with similar solutions (Fig. 7, Л–Н).Stage III is aimed at interpreting and includes comprehensive analyses of mapping results and priori information, construction of a final scheme of the fault zones showing their subordination by ranks (Fig. 7, О) and schemes of fault zones for various structure formation stages, showing types of faults and specific features of their internal patterns, i.e. definition of the peripheral sub-zone, sub-zones of fractures of the 2nd order and, if established, the sub-zone of the major fault (Fig. 7, Л–Н).Prospects of the special mapping method can be highlighted upon its comparison with the conventional structural methods applied in studies of faults. On the one side, the method requires time-consuming mass measurements and special processing of 'dumb' joints; on the other side, it provides for analyses of abundant jointing data, ensures a high level of detail in mapping of patterns of fault zones, reveals rank subordination of faults and helps to determine other specific features of fractures and faults. Hence, a conventional study of sites with evident tectonics can be based on traditional structural methods, while the special mapping method is recommendable as an additional means of analyses providing information on specific elements of the fault patterns, including establishment of the internal zoning of faults, hierarchy of dynamic settings of faulting etc. In cases when direct observation of faults is limited as the study area is poorly outcropped, or in case of specialized studies such as drilling of wells, the special mapping method can be most useful when applied in its full scope.With account of its specific features, this method is a promising tool for solution of theoretical problems related to studies of divisibility of the Earth's crust into zones and blocks and researches of regularities in development of fault zones in space and time. It can be useful for application-oriented surveys in geology, ore geology, engineering geology and hydrogeology that require detailed mapping of fault zones controlling many associated processes of key importance
RADON IN GROUNDWATERS IN THE BAIKAL REGION AND TRANSBAIKALIA: VARIATIONS IN SPACE AND TIME
No full textThis study aimed to provide a systematic overview of water sources in the Baikal region and Transbaikalia by the content of radon (Q) and establish regularities in variations of Q values in space and time.We collected and analyzed our evaluations of Q and the available published Q values for many dozens of water sources in the study area (Fig. 1), and reviewed the monitoring data of eight water sources that belong to the Angarsky fault impact zone in Southern Priangarie (Fig. 5). Radon content in water samples was measured in accordance with the standard procedure using a RRA-01M-03 radiometer (sensitivity of at least 1.4∙10–4 s–1∙Bq–1∙m3; maximum allowable relative error of 30 %).Based on the frequency patterns of Q values measured in the Baikal region and Transbaikalia (Fig. 2) and the analysis of the known classifications of the water sources by radioactivity, we propose a uniform regional classification of groundwaters with respect to 222Rn content (Table 1). In seismically active Baikal region, wherein water sources with Q>185 Bq/l are practically lacking, we distinguish the first three groups with the following Q ranges: Group I – Q≤15 Bq/l, Group II – 16≤Q≤99 Bq/l, and Group III – 100≤Q≤184 Bq/l. Most of the water sources sampled in the Baikal region and Transbaikalia belong to Groups I and II, which allows us to recommend an objectively existing value of 100 Bq/l as the level of intervention in the preparation of drinking water in this region, instead of the limit of 60 Bq/l that is now approved in Russia.In order to identify the special patterns of groundwater sources in the Baikal region and Transbaikalia, which belong to different radioactivity groups, we sampled these sources along the transect from Bayanday to Muhorshibir, across the Baikal rift and other large regional tectonic structures (Fig. 4). On a larger scale, we analysed the radon content variability in the groundwater sources within the zones influenced by the Tunka normal fault (Fig. 3), Primorsky normal fault, Angarsky strike-slip fault with a normal component, and other active faults located in the study region. Within the framework of the spatial aspect, the material and structural factors determining the radioactivity of groundwaters in the study region are identified. Our data support the results of the previous studies showing a generally lower radon content in groundwaters in the Baikal region in comparison with those in Transbaikalia that is characterized by a higher radioactivity due to the abundant granitoids of different types. The background concentrations of the radioactive gas in the Baikal region correspond to Group I, and in those in Transbaikalia to Group II. The boundary between the regions with different levels of radioactivity of groundwaters is shifted southeastward from the central structures of the Baikal rift. Within the Bayanday–Muhorshibir transect, it coincides with the known boundary between the Transbaikalia province of cold carbonic acid waters and the Baikal province of nitrogen and methan terms (see Fig. 4). The structural factor of formation of the emanation field refers to an increase in radioactivity of water associated with the faults, whereat an increased permeability and higher geodynamic activity cause a more intensive radon emanation and/or the occurrence of emanating reservoirs (see Fig. 3, and 4). In the Baikal region, water sources of Group II are generally associated with faults, while in Transbaikalia, groundwater sources belonging to groups III and VI are typically related to faults.To clarify the pattern of temporal variations in groundwater radioactivity, we analysed long rows of the monitored Q values (9 to 30 months) in eight water sources in the Angarsky fault zone in Southern Priangarie (see Fig. 5, and 6).According to the adopted classification (see Table 1), three water sources belong to the near-surface sources (Group I), and there are five deeper near-fault water sources (Group II). Despite the distinct variations in radioactivity, the Q values recorded through most of the monitoring time do not exceed the threshold Q values for the respective groups. It appears that the observed periodic anomalously high and low contents of radon are due to seasonally variable meteorological parameters (see Fig. 6).The correlation analysis of Q values and atmospheric pressure (P), air humidity (U) and temperature (T) shows a clear dependence of the content of radon in groundwater on T and P values (Table 3). Following the major seasonal trend of air temperature, the level of radioactivity is increased in the water samples taken in winter and decreased in summer (see Fig. 6). Q values are indirectly influenced by parameter T via changes of water temperature, variations in flow rates of water sources, freezing of the top layer of soil and other processes, which parameters require further research.According to the monitoring data (see Table 3, and Fig. 6, A), the content of radon in near-surface water sources (Group I) can vary by a few and the first dozens of units, while changes by tens of becquerel per liter are recorded in the deeper near-fault water sources (Group II). As a consequence, in short periods of extreme Q values, the content of radon in a water source may increase or decrease to a value corresponding to a neighbouring radon-radioactivity group.This paper provides an overview of the radon activity of groundwater in the Baikal region and Transbaikalia with a focus on regularities in the spatial and temporal patterns of 222Rn in the water sources with Q<185 Bq/l. The nonradon waters are more abundant in the Baikal region, including areas of active use of natural resources. Although the content of 222Rn in low, such waters should be a target of further research aimed to explore medicinal water sources, assess drinking water quality, and discover the emanation precursors of strong earthquakes in the study region
SPECIALIZED MAPPING OF CRUSTAL FAULT ZONES. PART 1: BASIC THEORETICAL CONCEPTS AND PRINCIPLES
No full textLong-term studies of shear zones have included collection of data on fractures showing no indication of displacement which are termed as 'blank' fractures. A method aimed at mapping fault structures and stress fields has been developed on the basis of results of paragenetic analysis of measurements of abundant fractures. The method is termed as 'specialized mapping', firstly, due to its specific structural goal so that to distinguish it from the conventional geological mapping of regions in nature, and, secondly, because of the specific procedure applied to refer to fractures as references to decipher fault-block patterns of natural regions. In Part 1, basic theoretical concepts and principles of specialized mapping are described. Part 2 is being prepared for publication in one of the next issues of the journal; it will cover stages of the proposed method and describe some of the cases of its application.In terms of general organizational principles, specialized mapping is similar to other methods based on structural paragenetic analysis and differs from such methods in types of paragenesises viewed as references to reveal crustal fault zones. Such paragenesises result from stage-by-stage faulting (Fig 2 and Fig. 7) during which stress fields of the 2nd order are regularly changeable within the shear zone. According to combined experimental and natural data, a complete paragenesis of fractures in the shear zone includes a major (1st order) fault plane and fractures of other seven types, R, R’, n, n’, t, t’ and T (2nd order) (Fig. 4 and Fig 8). At the fracture level, each of them corresponds to a paragenesis including three nearly perpendicular systems of early ruptures (Fig. 1), which are based on two classical patterns of conjugated fractures, one of which is consistent with the position of the fault plane (Fig. 3). Taking into account that strike-slip, reverse and normal faults are similar in terms of mechanics (i.e. they are formed due to shearing), standard patterns of fractures systems for their impact zones are members of the above described paragenesis of faults and fractures, which is spatially oriented in such a way that its position and displacements along Y-shears are correspondent to the right- or left-lateral strike-slip faults and also to normal and reverse faults with different dip angles. Under this approach, it has become possible to construct standard circle diagrams / patterns, each containing a complete set of fracture systems of one of the main types of fault zones (Fig. 6). In the process of specialized mapping, the patterns are compared with diagrams based on mass crustal fracture measurements taken on sites in the regions of studies. This procedure yields local solutions showing a presence of fault zones of specific types and spatial orientations; such solutions are shown as points at the corresponding sites on the schematic map of the territory under study, and points with similar paragenesises are then connected by lines so that to outline the boundaries of the revealed fault zones.Besides construction of a schematic map of a fault structures, specialized mapping provides for identification of stress fields wherein elements of such a fault structure has formed or activated at some stages. With this goal, the identified fault zones are classified by ranks. At the first phase of such analysis, types and orientations of all the initial local solutions are compared with types and orientation of the members of the ‘ideal’ paragenesis of the 2nd order, which corresponds to a strike-slip, reverse (thrust) or normal fault (Fig. 8). This procedure reveals solutions showing the presence of fault zones varying in types and classified in the higher rank, which correspond to the regional stress field known form the history of the region under study. Such regional solutions are used as a basis for further iterations with reference to ‘ideal’ fault paragenesises, until possibilities to classify the fault zones into the fault networks of some specific types are exhausted. A few (typically, three to four) remaining solutions, showing orientations of the fault zone and the dynamic setting of its formation, are indicative of the lowest (regional or geostructural) level of the process of destruction in the region under study. Their simultaneous development is impossible, and therefore they correspond to different stages of faulting in the territory under study. Indirect (statistical) indicators of frequencies and angle ratios of fault systems and direct (apriory) information are used to determine ages and to reveal evolutional stages in time. At a final stage of specialized mapping, a reversed procedure provides for construction of schematic maps of fault zones for every main stage of formation of the structure under study. With this goal, faults that occurred or activated in a specified stress field are distinguished from the fault network.In addition to the paragenesis principle applied to reveal fault zones and the evolution-in-time principle used to reveal stages of structure formation, the method of specialized mapping employs statistical methods of data collection and processing, and its application is consistent and computerized through all the work stages. It provides for solution of problems dealing with ‘blank’ fracturing with account of seemingly chaotic fracture patterns, local initial observations, uncertainties of age relations, impacts of structural and material inhomogeneities, and long timelines of statistical data collection and processing. In view of the above, specialized mapping can be proposed as one of the most efficient methods of studying the fault structure of the Earth’s crust.Part 2 will describe cases of application of the proposed method to map fault zones and to identify fault types and stress fields varying in ages in the regions of faulting, including areas wherein rocks are poorly outcropped. The main results of application of the proposed method of specialized mapping is schematic maps of fault zones, showing the fault zones that were active at various stages of formation of the structure under study. Such maps can be used as a basis for finding solutions to the main problems of endo- and exogeodynamics as well as for assurance of structural control over mineral deposits associated with faulting
FAULTING OF THE LITHOSPHERE IN THE CENTRAL ASIA AND ACCOMPANYING PROCESSES: TECTONOPHYSICAL APPROACH
No full textThe article describes the history, the staff, researches and scientific activities of the Laboratory of Tectonophysics of the Institute of the Earth’s Crust, which are focused on problems of faulting in the lithosphere. The Laboratory was established 35 years ago. The article reviews the major results of scientific research projects implemented from 2009 to 2013. The main objects of the complete cycle of tectonophysical studies were the zone-block structure of the lithosphere in the Central Asia, fault tectonics, stress fields, mechanisms of formation and seismicity of the Baikal rift zone, emanation activity of crustal faults, regimes of displacements at fault segments etc. It is shown that the team of the Laboratory views its scientific prospects in development of comprehensive models of inter-block zone of destruction, taking into account regular fault patterns and regularities of accompanying processes (such as seismic, emanation and other types of activity) which are predetermined by such fault patterns
BASIC PRINCIPLES OF STRUCTURAL AND HYDROGEOLOGICAL MAPPING OF THE BAIKAL REGION
No full textStructural and hydrogeological zonation of the Baikal region is based on allocation of hydrogeological structures within the large tectonic complexes differing in development history. It is a southeast part of the Siberian platform, the Sayan-Baikalian folded belt and the western part of the Transbaikal folded region. The Cenozoic activation of the region which has led to emergence of the Baikal rift and movements on a series of large fault zones in Transbaikalia has substantially influenced on formation of collecting properties of rocks.Structural and hydrogeological zonation of the Baikal region is based on allocation of hydrogeological structures within the large tectonic complexes differing in development history. It is a southeast part of the Siberian platform, the Sayan-Baikalian folded belt and the western part of the Transbaikal folded region. The Cenozoic activation of the region which has led to emergence of the Baikal rift and movements on a series of large fault zones in Transbaikalia has substantially influenced on formation of collecting properties of rocks
BASIC PRINCIPLES OF STRUCTURAL AND HYDROGEOLOGICAL MAPPING OF THE BAIKAL REGION
No full textStructural and hydrogeological zonation of the Baikal region is based on allocation of hydrogeological structures within the large tectonic complexes differing in development history. It is a southeast part of the Siberian platform, the Sayan-Baikalian folded belt and the western part of the Transbaikal folded region. The Cenozoic activation of the region which has led to emergence of the Baikal rift and movements on a series of large fault zones in Transbaikalia has substantially influenced on formation of collecting properties of rocks
РАЗЛОМООБРАЗОВАНИЕ В ЛИТОСФЕРЕ ЦЕНТРАЛЬНОЙ АЗИИ И СОПУТСТВУЮЩИЕ ПРОЦЕССЫ: ТЕКТОНОФИЗИЧЕСКИЙ ПОДХОД
No full text The article describes the history, the staff, researches and scientific activities of the Laboratory of Tectonophysics of the Institute of the Earth’s Crust, which are focused on problems of faulting in the lithosphere. The Laboratory was established 35 years ago. The article reviews the major results of scientific research projects implemented from 2009 to 2013. The main objects of the complete cycle of tectonophysical studies were the zone-block structure of the lithosphere in the Central Asia, fault tectonics, stress fields, mechanisms of formation and seismicity of the Baikal rift zone, emanation activity of crustal faults, regimes of displacements at fault segments etc. It is shown that the team of the Laboratory views its scientific prospects in development of comprehensive models of inter-block zone of destruction, taking into account regular fault patterns and regularities of accompanying processes (such as seismic, emanation and other types of activity) which are predetermined by such fault patterns. В статье представлены сведения об истории, кадровом составе, научной и научно-организационной деятельности лаборатории тектонофизики Института земной коры СО РАН, проводящей в течение 35 лет исследования разломообразования в литосфере. Основная часть статьи посвящена результатам научных работ 2009–2013 гг., в процессе которых сотрудники лаборатории провели полный цикл тектонофизических исследований. Их главными объектами были зонно-блоковая структура литосферы Центральной Азии, разломная тектоника, поля напряжений, механизм формирования и сейсмичность Байкальской рифтовой зоны, эманационная активность разломов земной коры, режим смещений на их фрагментах и другие. Показано, что научные перспективы лаборатории тектонофизики связаны с разработкой комплексных моделей межблоковых деструктивных зон, в основе которых лежат особенности разломного строения, а содержательную часть составляют обусловленные ими закономерности проявления сопутствующих процессов (сейсмическая, эманационная и другие виды активности).
