Features of seismic activation of the Middle Baikal region, 2008–2011

Scenarios for developing focal zones of strong (M _w = 5.3) earthquakes that occurred in the Middle Baikal region in 2008 and 2011 are considered. The new (submeridional and sublatitudinal) lines of destruction of the Earth’s crust in the water area of the lake are recorded. The facts of seismoactive structures forming in the surrounding mountains (to the southeast) under typical rift conditions of movements are established, which indicates that the basin of Lake Baikal is expanding and growing due to active capturing and processing of its mountain surroundings.     

Sorption of P by ferric hydroxide film, cover particles of sediments of Lake Baikal

We investigated in more detail the adsorption phenomenon which was described earlier. It was clearly established that the hydroxyl apatite was not participated in P adsorption. This phenomenon takes place because of ferric hydroxide film. Modem sediments from the Southem Basin of Lake Baikal were taken and stirred with Baikal water. Carrier-free [^32p]-orthophosphate was added in this system. Similar experiments were made with carrier-free [^35S]-sulphate. Sulphate stayed in supematant completely. The influence of pH on the system with inorganic phosphate was also studied. In low alkali conditions phosphate migrated in supematant, in low acid, in sediments. Baikal sediment was stripped of iron-hydroxous film by treatment with 1% oxalic acid. Investigation of striped sediment shown that phosphate stays in supematant only. Hence, hydroxyl apatite cannot be the phase of the sediments of Lake Baikal which binds phosphate. This all showed by our group before. Now we have found the limit of phosphate sorption in Lake Baikal sediments and the stehiometry of the sorption. The sorption limit of Lake Baikal sediments was studied. An experiment with inorganic ^31P phosphate was made. 0.025% K2HPO4 solution with adding ^32P radioactive mark into it was prepared. 100 μL of mixture of ^31PO4^3- and ^32PO4^3- seven times were added in a ＂Baikal water-Baikal sediment＂ system and blank （100 ml BW only）. Concentrations of inorganic ^31PO4^3- were very low so the bend dot on the diagram was found and sorption limit of sediment was estimated. Baikal sediment stopped assimilating phosphate in the bend dot. The stehiometry of sorption was estimated by supematant-sediment radioactive ratio, which equals 3, that is, three Fe （Ⅲ） atoms associate one PO4^3- anion. The only Fe （Ⅲ） substance which could associate P is -Fe-O-Fe- polymer film. It also dissolves in acid conditions.     

Modeling the Seismicity of the Altai–Sayan–Baikal Region

Doklady Earth Sciences - Numerical modeling of the dynamics of the block structure and the resulting seismicity of the Altai–Sayan–Baikal region has been carried out. The earthquake...     

Metals in coniferous vegetation of PreBaikal National Park （Olkhon District of Lake Baikal）

A comprehensive assessment of man-made impact on the environment is much kept behind because of missing unified systems of environmental monitoring. They represent sources of reliable information on the current status of the environment, as well as the absence of approaches to assess the impact of chemical pollution by different anthropogenic sources. Vegetation, being the component of environmental systems, is very sensitive to atmospheric man-made load. However, permissible concentrations of elements in plants, causing deflection in their development are differently estimated in different regions and vegetation species. As to the Baikal region, it is commonly the sanitary state of woods, that is primarily assessed. Coniferous trees, in particular pine, represent the main tree species in the region. In the Olkhon region we investigated the trace element compositions in pine needles to obtain the background contents of toxic metals. This region of the National park lies 300 km away from the industrial sources of pollutants, beyond the zone of wind effect, and has no industry. The research was made on the healthy （green） and dried up （red） pine needles. The elements like Zn, Al, Mn, Fe, Cr, Cu, Co, Ni, Sr, Cd, Pb, Li, Rb, Sb and As were measured by atomic absorption and flame emission photometry. The samples were decomposed in autoclaves with the mixture of nitric acid and hydrogen peroxide. Distinct differences were found in a series of elements contained in the green and dried needles. The red needles are characterized by higher contents of Zn, Al, Cu and low Mn, Fe, Pb with similar contents of other elements.     

Biogenic Microstructures in Stromatolites of the Baikal–Patom Highland: Results of Complex Study

Precambrian stromatolites were studied with a complex approach including two complementary methods. The biogenic origin of ultramicrostructures examined with SEM was supported by the traditional optical microscopy. The paper addresses columnar-stratiform stromatolites of the Vendian Chencha Formation in the Ura Uplift (Baikal–Patom Highland, Central Siberia) and fossilized remains of coccoidal and filamentous microorganisms therein: cyanobacteria Eoentophysalis, hormogonian cyanobacteria Siphonophycus and, probably, Eomicrocoleus. The unraveled community of stromatolite builders includes the major organisms commonly observed in the Precambrian microbiota. Stromatolites of the Chencha Formation contained not only cyanobacteria, but also remains of eukaryotic microorganisms, including likely testate amoebae and acanthomorphic acritarchs. It is shown that the complex approach rules out incorrect determination of biota and significantly enhances concepts of the origin and formation of stromatolites, as well as the participation of microorganisms in their formation.     

Biogenic sedimentation factors of mineralization in the Neoproterozoic strata of the Baikal–Patom region

The formation environments of stratiform ore deposits in the Neoproterozoic Baikal–Patom region (BPR) have been considered. A model for the formation of the Sukhoi Log gold ore deposit in the Bodaibo zone has been put forward. The first stage is gold concentration by a chemolithotrophic bacterial community. Independently established facts suggest that bacterial communities may also have contributed to initial metal accumulation in the sediments of the Kholodnaya Pb–Zn deposit. The ore beds occur in the high-carbon sediments of the side and trough of a back-arc basin. Sedimentation (Dal’nyaya Taiga and Zhuya regional horizons) took place during the “back-arc basin–foreland basin” transition. This transition is characterized by increased sediment bioproductivity, which is clearly evidenced from the increased biophile-element content and taxonomic diversity of organic remains. Hundreds of microfossil sites in the Neoproterozoic BPR host littoral benthos (cyanobacteria and brown algae) and plankton (green algae). Most microfossils in the outer shelf, on the basin side, and in its trough belong to chemolithotrophic bacteria. These bacteria are assumed to have accumulated metals in the vent field of the back-arc basin. Studies showed the ability of microorganisms (bacteria, algae, fungi, etc.) to accumulate Fe, Mn, Au, Pb, Zn, and other metals. Bacterial communities are particularly important for metal accumulation in the vent fields of rift zones and areas of arc volcanism. All these conditions were observed in the Neoproterozoic BPR.     

Early Hercynides of the Baikal–Vitim Fold System,western Transbaikal region

New data on the composition, age, structure, and geodynamic settings of the Upper Silurian–lower Middle Carboniferous rocks in the Baikal–Vitim Fold System (BVFS) are reported. These rocks make up the Early Hercynian structural stage of the BVFS, within which the Uda–Vitim, Vitimkan–Tsipa, and Turka–Kurba lithotectonic zones are recognized. The Early Hercynian stage combines rocks of two stratigraphic levels: Upper Silurian–Upper Devonian (S₂–D₃) and Upper–Devonian–Middle Carboniferous (D₃–C₂¹). On the basis of lithostratigraphic and spatiotemporal relationships between sedimentary and volcanic–sedimentary complexes of the Early Hercynian stage three formations are identified, which characterize the main tectonic regimes of the early half of the Late Paleozoic. It has been established that a common paleobasin that evolved through consecutively changing geodynamic settings at the passive and active continental margins existed in the Silurian (?)–early Middle Carboniferous in the northeastern part (in present-day coordinates) of the western Transbaikal region.     

Study of the elemental composition of suspended particles in large northern-Asian lakes （Baikal and Khubsugul）

Lakes Baikal （Russia） and Khubsugul （Mongolia） are rift freshwater water bodies. The maximal depth of Baikal is 1642 m, that of Khubsugul -238 m. One of the important aspects in the study of suspended matter is its geochemical composition which depends on mineralogy and granulometry of the suspended matter. As the concentration of suspended matter in the sites of deep lakes is not high - about 1 mg/L, to determine the elements in the suspended matter the monochromatized synchrotron radiation method （SRXFA, Novosibirsk, Russia） was used. Water sampling was conducted in three basins of Lake Baikal and in Lake Khubsugul on central vertical cross-sections and in near-coastal sites. The water samples were collected with 10-liter batometers. The suspension was extracted from the water by filtration under vacuum through ＂Nuclepore＂ filters of 47 mm in diameter with pore size of 0.4 mkm. The mean weight of dry suspension on the filters was about 1 rag. The results of study of lacustrine suspended matter show that such elements as Fe, Ca, Mn, Ti, V, Cr, Cu, Zn, Pb dominate in lakes Baikal and Khubsugul. The concentration of other elements is low. On the whole, the vertical distribution of total amount of suspended matter in open Baikal decreases from the surface to the bottom. As for Lake Khubsugul, it increases.     

Rift–Related Sediments of the Passive Continental Margin of the Paleo-Asian Ocean (Baikal Segment)

The geological position, composition, and age of detrital zircons of sedimentary deposits of the Nugan Formation of the Western Baikal region underlying the Golousta Formation of the Baikal series of Ediacaran age have been studied. The formation of both stratigraphic units due to the same sources of detrital material, located within the southern flank of the Siberian Craton, has been proved. The deposits of the Nugan Formation have been demonstrated to mark the rifting stage of the formation of the passive margin of the Paleo-Asiatic Ocean: their accumulation occurred in the Late Cryogenian during the interval 720–640 Ma.     

Paleoproterozoic Age of Gneiss-Granites of the Mamskaya Zone (Baikal–Patom Belt): Geological Implications

Doklady Earth Sciences - This article presents the results of U–Pb geochronological study of gneiss-granites of the Mamskaya zone. The age estimate of 1874 ± 9 Ma (SIMS method) obtained...     

Successive recognition of significant and strong earthquake-prone areas: The Baikal–Transbaikal region

Doklady Earth Sciences - This report continues a series of works by the authors on earthquake-prone areas recognition by the algorithmic system FCAZ. For the first time, successive earthquake-prone...     

U-Pb isotopic dating of zircons (SHRIMP-II) from granulites of the Ol’khon region of Western Baikal area

Doklady Earth Sciences -     

Gas–oil fluids in the formation of travertines in the Baikal rift zone

Active participation of gas–oil fluids in the processes of mineral formation and petrogenesis in travertines of the Arshan and Garga hot springs is substantiated. The parageneses of the products of pyrolytic decomposition and oxidation of the gas–oil components of hydrothermal fluids (amorphous bitumen, graphite-like CM, and graphite) with different genetic groups of minerals crystallized in a wide range of P–T conditions were established. Travertines of the Baikal rift zone were formed from multicomponent hydrous–gas–oil fluids by the following basic mechanisms of mineral formation: chemogenic, biogenic, cavitation, fluid pyrometamorphism, and pyrolysis.     

Recognition of Strong Earthquake Prone Areas in the Altai–Sayan–Baikal Region

The locations of areas prone to strong earthquakes (M ≥ 6.0) in the Altai–Sayan–Baikal region are determined. Based on a scheme of morphostructural zoning of the region and by using the CORA-3 pattern recognition algorithm, all intersections of morphostructural lineaments are separated into two classes: the highly seismic intersections in the vicinities of which strong earthquakes can occur and low seismic in the vicinities of which only earthquakes with M < 6.0 are possible. Recognition was performed for the vectors the components of which were measured values of the geological–geophysical characteristics describing the respective intersection. The result obtained allows the zones of high seismic hazard to be identified more reliably in the region.

     

Typomorphism of Pyrite from the Ugakhan Gold Deposit (Baikal–Patom Highlands)

Doklady Earth Sciences - The results of studying the isotopic, geochemical, and TEDS properties of various generations of pyrite and pyrrhotite from the Ugakhan deposit, Bodaibo district of Irkutsk...     

Prognosis of the state （eutrophication and pollution） of freshwater ecosystems on the example of long-term research into Lake Baikal

Systematic （monthly） observations of changes in the components of trophic status in the pelagic zone of Baikal were carried out during years of spring blooms of almost pure cultures： Gymnodinium （1965）, Aulocoseira bai-calensis （1968）, Synedra acus （1969）, Nitzschia acicularis （1984 and 1987）, picocyanobacteria （2004-2005）. The research period coincided with various anthropogenic impacts on Baikal ecosystem： （1） the period of the natural state of the lake （until 1969）; （2） the period of weak anthropogenic impact （until 1985）; and （3） the period of acute anthropogenic impact. In the third period the following was found in the deep-water part of the lake： the episodic appearance of ammonium and nitrite nitrogen; change in the components of suspended matter （SM）; disturbed patterns of seasonal changes in SM content, chlorophyll-a, organic forms of carbon, nitrogen and phosphorus; the average annual concentrations of suspended organic carbon, nitrogen and phosphorus have increased considerably; the vertical distribution pattern of minerals and organic forms of nitrogen and phosphorus have been disturbed; finally, an observed inverse correlation between winter nitrogen content and the spring concentration of chlorophyll-a （1986-1989） would indicate the presence of toxins in the lake. This led to the study of POPs in Baikal and the Baikal region. Investigations undertaken during 2004-2005 in the pelagic coastal zones of the lake indicated the presence of toxic pollutants in southern Baikal （the correlation between winter nitrogen content and spring concentration of chlorophyll-a is inverse and equals 0.99 and 1.00 respectively）. Toxicants that enter the lake during the iced-over period mainly enter the trophogenic layer, as wastewaters are warmer than the lake waters, depress the development of endemic spring diatomic algae and lead to a rise in the trophic status.     

Study of the elemental composition of suspended particles in large northern- Asian lakes (Baikal and Khubsugul)

Lakes Baikal (Russia) and Khubsugul (Mongolia) are rift freshwater water bodies. The maximal depth of Baikal is 1642 m, that of Khubsugul -238 m. One of the important aspects in the study of suspended matter is its geochemical composition which depends on…     

Thermochronology of the Chernorud granulite zone,Ol’khon Region,Western Baikal area

Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to upper crustal levels. The process is subdivided into four discrete stages, which corresponded to metamorphism to the granulite facies (500–490 Ma), metamorphism to the amphibolite facies (470–460 Ma), metamorphism to at least the epidote-amphibolite facies (440–430 Ma), and postmetamorphic events (410–400 Ma). The earliest two stages likely corresponded to the tectonic stacking of the backarc basin in response to the collision of the Siberian continent with the Eravninskaya island arc or the Barguzin microcontinent, a process that ended with the extensive generation of synmetamorphic granites. During the third and fourth stages, the granulites of the Chernorud nappe were successively exposed during intense tectonic motions along large deformation zones (Primorskii fault, collision lineament, and Orso Complex). The comparison of the histories of active thermal events for Early Caledonian folded structures in the Central Asian Foldbelt indicates that active thermal events of equal duration are reconstructed for the following five widely spiced accretion-collision structures: the Chernorud granulite zone in the Ol’khon territory, the Slyudyanka crystalline complex in the southwestern Baikal area, the western Sangilen territory in southeastern Tuva, Derbinskii terrane in the Eastern Sayan, and the Bayankhongor ophiolite zone in central Mongolia. The dates obtained by various isotopic techniques are generally consistent with the four discrete stages identified in the Chernorud nappe, whereas the dates corresponding to the island-arc evolutionary stage were obtained only for the western Sangilen and Bayankhongor ophiolite zone.     

Activity rating of Pliocene–Quaternary faults: a formalized approach (example of the Baikal rift system)

It is suggested to estimate the Pliocene–Quaternary fault activity in a formalized way from synthesis of different data. The respective database consists of two main sections: (i) general information and basic fault parameters and (ii) geomorphic, structural, paleoseismic, seismological, geophysical, geodetic, engineering-geological, hydrological, and meteorological data. The fault characteristics are scored according to their significance, and the cumulative score measures the fault activity. With this approach, the faults in the Barguzin and Tunka rift basins and in the northeastern flank of the Baikal rift system have been divided into five activity classes (low, medium, relatively high, high, and very high activity) and mapped correspondingly. It has been recommended that the concept of an hazardous fault, as updated with regard to the activity rating, refers to faults of relatively high, high, and very high activity. Thus identified hazardous faults within the study area are quite few (4–8%), though this percent may increase slightly as more input data become available. The underestimation cannot be dramatic because all known seismological and structural characteristics of faults essential for the activity rating have been already taken into account. The new approach may be useful in seismic risk assessment and in choice of sites for instrumental monitoring of seismicity.