Hydrogeochemical peculiarities of the composition of nitric thermal waters in the Baikal Rift Zone

The chemical, gas, and isotopic compositions of nitric thermal waters in the Baikal Rift Zone are considered. It is shown that the behavior of sulfate and carbonate ions in hydrothermal systems is different, which indicates that they are of two different origins. The studied thermal waters are of five chemical types formed in different geologic conditions. Special attention is given to the genesis of hydrotherms, the geologic and geomorphologic conditions of their recharge, and their equilibrium with rocks. It has been established that most of chemical elements of the waters migrated from rocks, but a significant portion of them is bound by secondary minerals, which results in their deep differentiation, accumulation, or precipitation. Thus, the so-called redundant elements appear, which were earlier considered to be of mantle origin.     

Major factors of the evolution of basins and faults in the Baikal Rift Zone: Tectonophysical analysis

In order to identify the major factors of the formation of the Baikal Rift Zone, tectonophysical analysis is carried out based on physical modeling with the application of similarity criteria. A single-layer model of elastoplastic clayey paste is superposed on two metal plates. One of the metal plates is displaced leftward according to the simple shear mechanism and its contact with the second metal plate has a bend morphologically similar to the Baikal segment of a marginal suture of the Siberian Craton. This scheme of loading corresponds, to a great extent, to the passive mechanism of rifting; i.e., the deformed layer is destructed due to strikeslip displacement of blocks and development of pull-apart structure in the model without any uplift and thermal impact related to the influence of mantle asthenolith in nature. The series of runs reproduces the major spatiotemporal trends in the evolution of the Baikal Rift Zone. Some experiments achieve for the first time a high degree of similarity in the morphology and mutual alignment of its main basins. This makes it possible to conclude that the evolution of basins and faults in the Baikal Rift Zone was governed by the following factors: (1) elastoplastic response of the substrate with a regular localization of strain; (2) left-lateral displacement of blocks; and (3) the presence of curved (in plan view) initiating structural heterogeneity.     

Geothermal field and distribution for earthquake source depths in the Baikal Rift Zone

A comparison between values of thermal flux and the deep temperatures calculated by them and the depths of earthquake sources in three areas of the Baikal Rift Zone is made. It has been shown that during transit from the Baikal depression to the adjacent mountain massif, the thermal flux decreases almost 2–3 times. The corresponding deep temperatures decrease to a similar degree. The available data for these areas on earthquake depths show that their lower boundary both beneath the depression and the massif is located at almost the same depth, which is about 20 km. In this paper, the conclusion is made that the cause of the absence of an interrelation between thermal and seismic fields lies in the discrepancy between the measured values of thermal flux and its deep values. This discrepancy arises because conductive heat transfer in the upper part of the Earth’s crust, up to 5–10 km depth, is highly distorted by heat-and-mass transfer of ground waters. In the middle part of the crust, the difference in temperatures beneath depressions and ridges is leveled horizontally, which is reflected in almost the same depth for the basement of the seismogenerating layer beneath these main rift structures.     

Contribution of biogenic and volcanogenic factors to formation of ferromanganese nodules of Olkhon Island (Lake Baikal)

The first data on the structure, textural features, and geochemical and mineral composition of Fe–Mn nodules of the Sasin Formation, Olkhon Island (Baikal), have been determined. A significant role in the formation of the nodules was played by hydrothermal processes with varying contributions of hydrogenic factors. The presence of reduced inclusions in the nodules and their textural features indicate the presence of various components of organic matter in the nodules, creating the conditions for local concentration of ore components. Activation of hydrothermal processes is typical for the Baikal Rift Zone in the Late Miocene–Early Pliocene, which is reflected in the composition of Fe–Mn nodules from the Sasin Formation.

     

Mineralogical and geochemical features of bacterial mats and travertines of the Khoito-Gol thermal spring (East Sayan)

The mineralogical and geochemical features of the Khoito-Gol ecosystem (fresh thermal waters-microorganisms-travertines) of the Baikal Rift Zone and the aspects of the interaction among its components were studied. The research has shown that the behavior, distribution, and accumulation of trace elements are determined mostly by the geochemical barriers of geologic and biologic genesis in the flowing-water habitat of bacteria of the Khoito-Gol spring. Formation of biominerals by different functional groups of its bacterial community is considered.     

Tectonics,stress state,and geodynamics of the Mesozoic and Cenozoic Rift basins in the Baikal region

The results of geological, structural, tectonic, and geoelectric studies of the dry basins in the Baikal Rift Zone and western Transbaikalia, combined under the term Baikal region, are integrated. Deformations of the Cenozoic sediments related to pulsing and creeping tectonic processes are classified. The efficiency of mapping of the fault-block structure of the territories overlapped by loose and poorly cemented sediments is shown. The faults mapped at the ground surface within the basins are correlated with the deep structure of the sedimentary fill and the surface of the crystalline basement, where they are expressed in warping and zones of low electric resistance. It is established that the kinematics of the faults actively developing in the Late Cenozoic testifies to the relatively stable regional stress field during the Late Pliocene and Quaternary over the entire Baikal region, where the NW-SE-trending extension was predominant. At the local level, the stress field of the uppermost Earth’s crust is mosaic and controlled by variable orientation of the principal stress axes with the prevalence of extension. The integrated tectonophysical model of the Mesozoic and Cenozoic rift basin is primarily characterized by the occurrence of mountain thresholds, asymmetric morphostructure, and block-fault structure of the sedimentary beds and upper part of the crystalline basement. The geological evolution of the Baikal region from the Jurassic to Recent is determined by alternation of long (20–115 Ma) epochs of extension and relatively short (5.3–3.0 Ma) stages of compression. The basins of the Baikal Rift System and western Transbaikalia are derivatives of the same geodynamic processes.     

Variations of stress fields in the Tunka Rift of the southwestern Baikal region

The stress fields in the Tunka Rift at the southwestern flank of the Baikal Rift Zone are reconstructed and analyzed on the basis of a detailed study of fracturing. The variation of these fields is of a systematic character and is caused by a complex morphological and fault-block structure of the studied territory. The rift was formed under conditions of oblique (relative to its axis) regional NW-SE extension against the background of three ancient tectonic boundaries (Sayan, Baikal, and Tuva-Mongolian) oriented in different directions. Such a geological history resulted in the development of several en echelon arranged local basins and interbasinal uplifted blocks, the strike-slip component of faulting, and the mosaic distribution of various stress fields with variable orientation of their principal vectors. The opening of basins was promoted by stress fields of a lower hierarchical rank with a near-meridional tension axis. The stress field in the western Tunka Rift near the Mondy and Turan basins is substantially complicated because the transform movements, which are responsible for the opening of the N-S-trending rift basins in Mongolia, become important as Lake Hövsgöl is approached. It is concluded that, for the most part, the Tunka Rift has not undergone multistage variation of its stress state since the Oligocene, the exception being a compression phase in the late Miocene and early Pliocene, which could be related to continental collision of the Eurasian and Indian plates. Later on, the Tunka Rift continued its tectonic evolution in the transtensional regime.     

Bottom sediments and pore waters near a hydrothermal vent in Lake Baikal (Frolikha Bay)

We discuss the redox environments and the compositions of bottom sediments and sedimentary pore waters in the region of a hydrothermal vent in Frolikha Bay, Lake Baikal. According to our results, the submarine vent and its companion nearby spring on land originate from a common source. The most convincing evidence for their relation comes from the proximity of stable oxygen and hydrogen isotope compositions in pore waters and in the spring water. The isotope composition indicates a meteoric origin of pore waters, but their major- and minor-element chemistry bears imprint of deep water which may seep through permeable faulted crust. Although pore waters near the submarine vent have a specific enrichment in major and minor constituents, hydrothermal discharge at the Baikal bottom causes a minor impact on the lake water chemistry, unlike the case of freshwater geothermal lakes in the East-African Rift and North America.     

Mercury Emanations from the Baikal Rift: Evidence from the Study of Annual Tree Rings (an Example of the Tunka Depression)

Doklady Earth Sciences - The phenomenon of natural degassing of mercury in the Baikal Rift Zone is considered on the basis of study of the annual rings of poplar (Populus suaveolens Fisch.) and...     

On generation conditions of strong earthquakes in southern Baikal

In this paper the features of seismic process in the southern depression of Lake Baikal are considered. By the data on focal mechanisms of the earthquakes of February 25, 1999 (M _w = 6.0), and August 27, 2008 (M _w = 6.3), as well as based on configuration of their aftershock fields, it is determined that foci of strong seismic events in southern Baikal are controlled by the greatest structural elements of sublatitudinal and submeridional strikes. It has been shown that a substantial role in the formation of focal zones is played by low-scale destruction of the Earth’s crust, revealed by geological-geophysical data and proved by clustering of seismic shocks. New data on the August 27, 2008, earthquake have proved the high level of seismic danger of this part of the Baikal Rift Zone and allowed us to determine generation conditions of strong earthquakes more precisely.