The 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.
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Jan 1, 2020
Ellen Rieloff + 1
Open Access