Home – Home – Jornals – Russian Geology and Geophysics 2008 number 12

Experimental data on the diffusion coefficients of Fe, Mn, Mg, and Ca in garnets are generalized. Frequency factors (cm²/s), activation energies (cal/mole), and activation volumes (cm³/mole) are optimized. Based on the compensation law, the dependences of diffusion coefficients on pressure (kbar) and temperature (K) have been derived:
D _Fe = 1.0 · 10^-3 exp [ - (61450 + 23.9 · 8 · P ) / (RT) ] ,
D _Mn = 2.3 · 10^-6 exp [ - (44600 + 23.9 · 6 · P) / (RT) ] ,
D _Mg = 4.9 · 10^-3 exp [ - (65900 + 23.9 · 9.2 · P ) / (RT) ] ,
D _Ca = 4.1 · 10^-5 exp [ - (62450 + 23.9 · 11.2 · P) / (RT)] .

Three zones of layered series - lower, middle, and upper - composed of dunites and plagiodunites, troctolites and olivine gabbros, gabbros and gabbronorites, respectively, have been recognized in the Luchina massif. The melt that produced the massif rocks was of picrite-basaltic composition (15-16% MgO), and its crystallization took place at 1300-1000

We discovered unusual very small (2 to 70 cm) mafic bodies intruded into metamorphosed Early Carboniferous sandstone and shale in the Late Paleozoic Tastau volcanoplutonic complex (Char shear zone, eastern Kazakhstan). The small intrusions possibly emplaced during shearing when sediments experienced cataclasis and ensuing viscosity decrease. The shear rate was comparable to that in historic crustal earthquakes. Rapid shear motion concurrent with magmatism caused fragmentation of the injecting low-viscosity melt and its dispersal in globular and other bodies along linear breccia zones. The origin of the intrusions is explained in a tectonic model.

The mechanisms and species of gold incorporation into crystals of simple sulfides are described. The concept of endocrypty in its modern treatment and the corresponding technique of experimental study were used. The technique is based on the principle of phase composition correlation and variation of parameters specifying the concentrations of active crystal defects. Gold species are determined with the method of statistical samples of analytical data for single crystals (SSADSC). The highest gold incorporation limits have been established for PbS and CdS under high sulfur fugacity (2.4 · 10^-2 and 7 · 10^-3 wt.%, respectively) at 500

Comprehensive studies have been applied to a core from well 126 in the Chara basin (eastern Baikal-Stanovoy upland). The 1180 m thick drilled section comprises Upper Pleistocene sediments (0-173.1 m) with two intervals of varved silt coeval with the Wurm Glacial, two Middle Pleistocene glacial intervals at 180-263.5 m and 337-424.7 m, earliest Pleistocene (424.7-550 m), Pliocene (550-1036 m), and Miocene (1036-1180 m) strata. The core records the history of Late Cenozoic climate and vegetation for the past 20 Myr (with two large gaps), which has been reconstructed using the pollen analysis. Interpolation of long- and medium-period climate oscillations tied to the time scale allows predicting a trend of possible climate change for the future 2-2.5 kyr.

We have located earthquake hypocenters in the area of central Lake Baikal using the Hypoellipse inversion of direct P traveltimes collected by a local seismological network of seven stations in 2001 through 2005. The location accuracy depends on the agreement between the reference velocity model and the real subsurface. Traveltime residuals have no bearing on the accuracy of depth estimates due to origin time errors.
Hypocenter location with reference to a DSS-derived layered velocity model predicts that the crust is seismogenic between 10 and 22 km. The hypocenters cluster densely in belts trending in NE and SE directions along and across Lake Baikal. Earthquakes become deeper from 10 to 22 km toward the Selenga basin.

We apply the spectral Laguerre transform in the time domain to solve 2D Maxwell's equations for propagation of electromagnetic waves in lossy anisotropic media. The new algorithm is simple and efficient as Maxwell's equations are reduced to a harmonic series of linear algebraic equations where the matrix is independent of the harmonic order and is the same for all harmonics.
The efficiency of the algorithm is improved by fitting a specially introduced free parameter of the Laguerre transform. If it is large, the solution spectrum shifts toward higher harmonics which is formally equivalent to the case of ray approximation.
The Laguerre solution is comparable with high-order accurate finite-difference time-domain (FDTD) solutions. The method is stable both in the region of the wavefield, where conductivity approaches zero and the spectral Fourier method is unstable, and in the high-conductivity region, where the explicit FDTD code requires a too small time step.

We discuss a two-loop frequency-domain electromagnetic induction sounding system which allows vertical focussing of the primary magnetic field thus reducing the disturbance from shallow subsurface. The frequency dependence of apparent resistivity estimated from the real part of the measured magnetic field turns out to be more sensitive than that found from the absolute total field. The advantage of the suggested FD EMI system has been validated by experiments.

Sea-level change has been commonly interpreted to be of eustatic origin, and many eustatic events were hypothesized for the Phanerozoic, including several 1-3 Myr long cycles in the Ordovician with magnitudes up to 100 or 200 m. However, sea-level change modeling using stratigraphic data from Northern Estonia, which was an area of slow shallow-marine (≤10 m) deposition through most of the Ordovician, indicates fluctuations of no more than 20 m. In the Late Ordovician the sea level fell only twice for ~100 m within 1 Myr during the Gondwanian glaciation. Although the sea level remained relatively stable, there were frequent 100-200 m changes of sea depths we inferred with reference to the time spans of stratigraphic units and intervals between tectonic events estimated reliably against stable durations of East Siberian chronozones (biochrons) of the Ordovician. In the absence of eustatic events, the sea-depth changes most likely resulted from rapid crustal uplift and subsidence. According to correlated well-documented Ordovician sections from East Siberia, the rate of crustal subsidence changed rapidly in different periods and in different places of the area, thus being of a regional scale. The controversy between the sea-level stability and the regional-scale variations in sea depths controlled by rates of crustal uplift and subsidence can be resolved assuming a model of variable eclogitization rates in the lower crust caused by lithospheric stress change. Our inferences undermine the traditional petroleum prediction approach implying formation of depositional traps due to rapid eustatic sea-level change.

Apatite fission-track (AFT) thermochronological modeling as a diagnostic tool for periods of stability (peneplanation) and tectonic activity (orogeny) has been broadly used in tectonic studies of Central Asia in recent years. We discuss more than 100 AFT ages of samples from the Kyrgyz Tien Shan and Altai and compare them with AFT data from northern Kazakhstan. Geological, geomorphological, and AFT data indicate intense activity in the Late Cenozoic Eurasian continental interior. The impact from the India-Eurasia collision on the northern Tien Shan, Altai, and northern Kazakhstan regions showed up at 11, 5, and 3 Ma, respectively, as a result of stress propagation into the continent, with the ensuing reactivation and mountain growth. We hypothesize that a distant effect of the Late Cenozoic India-Eurasia collision was to rejuvenate Paleozoic fault zones and to deform the Mesozoic sedimentary cover north of the collision front as far as the West Siberian Plate. The reactivation facilitated formation of tectonic oil and gas traps. The activity in northern Central Asia under the effect of the Indian indentation into Eurasia appears to continue and may evolve to include uplift of southern West Siberian plate with uplift.

We present results of study of the specific composition and parageneses of pyrope-almandine garnets from alluvial deposits of the Muna-Markha interfluve drainage in the Yakutian diamondiferous province. The data are correlated with the specific features of garnets (tentatively crustal) from Yakutian and Guinean kimberlites and their crustal xenoliths and from metamorphic rocks of the Anabar Shield. The conclusion is drawn that most of orange pyrope-almandine garnets from the alluvial deposits were generated from kimberlites with varying contents of disintegrated crustal material. This gives grounds to include the studied garnets into a complex of indicator minerals of kimberlites and use them in search for diamonds in the Yakutian diamondiferous province.

The influence of 6.75 m thick dolerite dike on the sheet coal of the Kaierkan deposit (northwestern Siberian Platform) was studied by organogeochemical methods. It is shown that initial bituminous coal was transformed into anthracite in the immediate vicinity of the dike. Chemical kinetic modeling of the dike-induced cracking of coal's organic matter was performed, and the maximum paleotemperatures were estimated.

In situ data on the daily dynamics of pH, [O₂], and Eh values at five water layer depths were obtained. Some regularities have been established: All these parameters are characterized by significant diurnal fluctuations and their daily cyclic recurrence; the diurnal cycles of pH and [O₂] nearly coincide (they show close extreme points on the time scale); the Eh cycles are less distinct and antisymbatic to the pH and [O₂] cycles, but typical Eh extremes sometimes lag by 2-3 h. These data were analyzed using the principle of equilibrium locality and partiality. The main flows of O₂ and CO₂ in the system have been revealed with regard to the water layer-atmosphere gas exchange, absorption of CO₂ by phytoplankton in the photic layer, breathing of phyto- and zooplankton, birth and die-off of biota, settling of mortomass, and redistribution of detailed components within the water layer as well as between it and the bottom sediments. On the basis of the results obtained, the known technique for estimating the content of primary photosynthesis products (Bruevich's method) was corrected. The used generalized algorithm of chemical thermodynamic analysis of the substance state in aqueous systems can be applied to waters of different classes as well as any surficial waters if Eh, pH, and [O₂] are taken into account.

We revised geological data substantiating the unified 1983 Regional Stratigraphic Chart of Gorny Altai Quaternary deposits. Based on our own and literature data, we showed that Lower and Middle Quaternary glacial horizons are erroneously distinguished in the Yaloman-Katun' zone of southeastern Altai. A new correlation is proposed, according to which the glacial complex of the maximum glaciation (MIS-6) corresponds to the Inya catafluvial series and the glacial complex of the first postmaximum glaciation (MIS-4 unit), to the Sal'dzhar catafluvial series. The lectostratotypes of both series are described. The event history of the second half of the Late Neopleistocene in Gorny Altai (MIS-3 and MIS-2) was less catastrophic for ancient biota and Paleolithic man than it was believed earlier.

We suggest a method of multi-element low-frequency acoustic logging data processing which combines advantages of the semblance and phase velocity processing (PVP) techniques, namely, the interference resistance in the former and better accuracy in the latter. The new method is based on point (windowless) semblance by the Hilbert transformation. The introduced concept of phase semblance makes it possible to estimate the signal distribution semblance and the phase. Also suggested are an algorithm for preliminary estimation of formation S-wave slowness from signal group power variations and improved forms of processed data imaging.

We discuss historical evidence for seismicity on the southern margin of the Siberian craton collected from old local newspapers. The reported earthquakes vary in magnitude from M = 2.5 to 4.5, and their macroseismic locations agree well with the regional tectonic framework. The new data prove seismic activity in the area and can be used in seismic risk assessment.

Brownmillerite, Fe-perovskite, and two intermediate phases (Ca₃Ti(Fe,Al)₂ O₈ and Ca₅Ti(Fe,Al)₄ O₁₃) were found in combustion metamorphic high-temperature larnite rocks of the Hatrurim Basin, Israel. This is the first finding evidencing the existence of the pseudobinary perovskite-brownmillerite series in nature. Fe-perovskite contains the Ca₂ (Fe,Al)₂ O₅ end-member (up to 18 mole %), whereas brownmillerite Ca₂ (Fe_1-x Al _x )₂O₅ with x = 0.15-0.55 is enriched in the CaTiO₃ end-member (up to 15 mole %). The intermediate phases are Ca₃Ti(Fe,Al)₂ O₈ (phase X) and Ca₅Ti(Fe,Al)₄ O₁₃ (phase Y), which have synthetic analogs. In some larnite rocks, the phase X is the only member of the perovskite-brownmillerite series. It is clustered into two compositional groups, Ca₃Ti(Fe _1.3Al_0.7)O₈ and Ca₃Ti(Fe _1.6 Al_0.4)O₈. The phase Y is extremely rare and has the composition Ca₅Ti(Fe _0.76 Al_0.24)₄O₁₃. The presence of minor Si, Cr, Sr, Zr, and LREE is common for all minerals of the series. The Fe-perovskite + brownmillerite paragenesis was found in none of the studied rocks, which is consistent with the CaTiO₃-Ca₂Fe₂O₃ phase diagram. The rocks bear either one phase or two or three phases (Fe-perovskite + phase X; brownmillerite + phase X ± phase Y). According to the CaTiO₃-Ca₂Fe₂O₃ diagram, the minimum formation temperature for the Hatrurim larnite rocks estimated from the Fe-perovskite + phase X paragenesis is 1170-1200

Humid lithogenesis is characterized by the accumulation and postsedimentary transformation of eluvial products within terrigenous and terrigenous-carbonate (with calcite) formations containing mainly dioctahedral clay minerals. Platform fresh-water sediments of early-catagenesis zone accumulate 1 : 1 and 2 : 1 varieties, with a predominance of expanding layers in the latter. In sand-silty rocks authigenic kaolinite also appears. Trioctahedral chlorite of generation I is developed from the top of this zone in both clayey and sand-silty marine deposits. Also, mixed-layer minerals are synthesized: montmorillonite-glauconite at the top of the zone and montmorillonite-hydromica at the bottom.
Arid lithogenesis is controlled by the accumulation of sediments of terrigenous-carbonate (with dolomite), carbonate, and halogen formations. In contrast to the terrigenous and aclimatic volcanogenic formations, these ones are dominated by trioctahedral clay minerals: chlorite, sepiolite, and mixed-layer chlorite-based minerals. In early-catagenesis zone, sepiolite, palygorskite (di-analog of sepiolite), and halloysite quickly transform into talc- and chlorite-saponite and kaolinite, respectively. In hypergenesis zone climate is the main factor, whereas in early-catagenesis zone, especially in arid environments, the chemical composition of the medium plays a significant role. In late-catagenesis zone, degradation products of mica and montmorillonite transform first into varieties with less than 40% and somewhat more than 40% expanding layers, respectively, whereas trioctahedral minerals preserve up to 50% such layers. This process is accompanied by the recrystallization of both allothigenic and authigenic minerals with the transition of scaly montmorillonite into bladed hydromica, with the authigenic minerals of halogen-formation sediments characterized by the most perfect crystal habits and regular structures. In metagenesis zone, di-minerals of orogenic-area sediments transform into sericite, and trioctahedral minerals, into more magnesian chlorite of generation II. This indicates that in late-catagenesis and metagenesis zones, the PT-conditions of the environment are of crucial importance.

The effect of high temperature on sulfide inclusions in diamonds was studied. The object of study was sulfide-bearing diamond crystals from Yakutian kimberlite pipes. The experiments were carried out on a multiple anvil apparatus BARS with a solid-phase refractory oxide cell at 5.0 GPa and 1000-1600

Large gold-brannerite aggregates (nuggets up to 50 g in weight) were found in placers of the Ozernoe ore cluster, western Transbaikalia. Brannerite occurs as large crystals and crystal aggregates and has the near-stoichiometric composition UTi₂O₆. It lacks REE, contains little, if any, Th, and has admixtures of FeO (2.0-3.7 wt.%), CaO (up to 2.7 wt.%), and SiO₂ (up to 2.14 wt.%). It also bears fine (<1 μm) inclusions of Au-Ag- and Bi-containing tellurium minerals and bismuth minerals. Gold occurs in cracks of brannerite or aggregates with it on coprecipitation from solutions. Gold was also found as fine (1-3 μm) segregations in muscovite. Accessory minerals are hematite, barite, rutile (containing 0.36-3.61 wt.% FeO and up to 7.5 wt.% WO₃), dolomite, siderite, and muscovite. High contents of Te and Bi were detected in Fe, Ti, and U hydroxides. A specific relationship between gold and rutile has been revealed both in large aggregates and in gold microinclusions (<1 μm) in rutile grains. In composition and paragenesis the studied gold-brannerite association is similar to ores of the El'kon type (Central Aldan) related to the Mesozoic magmatism.

In the western Baikal area, the structural position, composition, and age of volcanic rocks in the section of the Riphean margin of the Siberian craton were studied. The age of these rocks, earlier assigned to the Khotskaya Formation, is estimated at 274±3 Ma (concordia constructed over 11 zircon grains, SHRIMP-II). The geochemical and isotope compositions of volcanics evidence that they resulted from the melting of mantle source of EM-I type contaminated by crustal material. The intrusion of volcanics into the upper crustal horizons might have been caused by the evolution of the Permian active margin of the Siberian continent, which took place on the background of the closure of the Mongolo-Okhotsk ocean. Based on the results of studies, a new subvolcanic complex of Early Permian age has been recognized in the region, which includes the above-mentioned volcanics and earlier described porphyrite dikes of close age in the Sharyzhalgai uplift. The data obtained disprove the concept that the studied volcanics are of Riphean age; therefore, the available stratigraphic charts of the Siberian Precambrian must be revised.

A Jurassic accretionary prism in the Sikhote-Alin-Amur area is an assembly of terranes, which are tectonic-sedimentary complexes consisting of multiple strongly deformed fragments of an oceanic plate. The stack of tectonic-stratigraphic units (complexes) in the prism section records its geodynamic history, each unit being signature of a geologic event on the Paleoasian eastern margin. The succession of accretion events brought together fragments of a Paleozoic oceanic plateau in the Early Jurassic and abyssal plain fragments of different ages in Middle and Late Jurassic time.

The lithospheric structure in Asia has been analyzed in terms of sizes of blocks and mobile zones between them on local (northeastern Olkhon area in western Baikal region), regional (Baikal region), and global (Central and Eastern Asia) scales. A single approach to reference mapping was used to update Sadovskii's hierarchy of blocks and to rank the mobile zones. According to the updated model, the 1ithospheric structure of Central and Eastern Asia includes eleven hierarchic levels.

We suggest a new technique for processing head-wave data with a multistage Wiener filter, which provides conversion and stacking of head waves from a receiver array into a user-specified point. Different conversion algorithms are compared and shown to be a combination of parallel and serial Wiener filters.
The Wiener filter accuracy for a conversion iteration depends on the in-line fold and on the coherence spectrum. The latter describes the signal/noise ratio dependence where head waves are the signal and the noise includes all other components and microseisms. Equations for the accuracy of head-wave traces have been derived from a corresponding equation for a single conversion iteration using the multistage Wiener filter schemes and proceeding from the theory of coupling stochastic systems. The obtained equations are applicable to different field data processing algorithms.
The discussed conversion algorithms differ in noise regularization and are fit for data of any quality.

We suggest new inversion techniques for IP-affected TDEM data. The method implies joint inversion of inductive and galvanic measurements, the galvanic array being configured in a way to separate the polarization and induction components of transient responses from a layered polarizable earth. The IP effects turned out to be reducible at a certain receiver configuration, which was predicted theoretically and proved valid in field tests.

New data on the conditions and time of formation of eclogites in the Atbashi Ridge (South Tien Shan) were obtained. The PT -conditions of crystallization of high-pressure minerals from eclogites have been established: 23-25 kbar, 510-570

With geological, mineralogical, and petrographic methods, thermometry, and microprobe analysis of fluid inclusions, the structure and formation conditions of a specific orebody (zone 12) of the Ermakovskoe F-Be deposit have been established. This orebody is similar in fluorite content to other orebodies of the deposit (28.7 and 24.6%, respectively) but has the lowest average content of Be (~0.1% BeO against 1.19%). It is shown that in contrast to high-grade apocarbonate ores, the Ermakovskoe deposit formed mainly through the filling of the cavities of host rocks (syenites and schists) rather than the rock replacement. Calcium necessary for the formation of fluorite was supplied, most likely, as complexes Na₂CaF₄ and Ca₂Cl₃F by moderately saline (11.5-12.5 wt.% NaCl equiv.) F-rich (=0.3 mole/kg) solutions. The fluorite was deposited as a result of the solution cooling from ≥430 to 250

A mathematical model is proposed to describe the dynamics of phase fronts in volcanogenic orthomagmatic fluid systems (VOFS). It has been shown that these systems require rather short geologic times to reach a quasi-stationary state. This process is accompanied by slow cooling and pressure decrease as the bubbling front within the intrusive body submerges and magmatic fluid discharge decreases. Decompression boiling zone seems to develop in near-surface VOFS part for a certain combination of such parameters as porosity, permeability, and upper boundary condition. In evolving VOFS the existence of this zone is ephemeral. However in areas of seismic tremor and in mixed hydrothermal systems this zone can be stable and can produce brines below the level of hydrotherm discharge.

The recognition of pre-Riphean metamorphosed residual crust of deep chemical weathering on the Chuya-Nechera (Chuya-Kodar) granites on the basis of found gravel-like quartz-sericite rocks (apparently, residual products of feldspar hydrolysis) is still debatable. Study of this crust in relation with deep-level hypergenesis shows that it consists of not only quartz pseudogravelstones of dispersed paleozone but also pseudoquartzite schists, pseudoquartzites of lithomarge paleozone, and physically weathered granites of clastic and fissure zones in its bottom. Inequigranular (pisolitic, fine- and thin-grained) fissured quartz differentiated with depth is the main indicator of this crust. This quartz and associated sericite are the lithified and metamorphosed direct (hydrolysate alumina), side (hydrolysate silica), and residual (large-ingrowth quartz) products of the chemical decomposition of feldspar. Some of them accumulated in situ - in lateritic crust, and others were redeposited - first, in the lower layers of the weathering profile and then, in the residual crust. The early quartz and sericite accumulations in the weathering profile date the formation of peneplain, and the late ones, marking the residual crust, date the beginning of the marginal-sea transgression onto the passive continental margin, the peneplain erosion, and the origin of the Bodaibo inner trough.

A new type of Cambrian section penetrated by the Vostok-1 stratigraphic test well in the east of the West Siberian Plate, Tomsk Region, is described in terms of paleontology. It can be considered a key section for this region. According to a complex of geological and geophysical characteristics, the section in the depth range of 2766-5010 m was divided into the Churbiga, Paidugina, Pudzhelga, Podelga, Kondes, Shedelga, and Pyzhina Formations, and their first description was made. The Cambrian section in Vostok-1 well is most similar to those of the Kotui-Igarka area of the northwestern Siberian Platform, where Cambrian deposits formed in the pre-reef zone of an open sea basin. In the lower section of the borehole the highly carbonaceous siliceous-argillaceous-carbonate Paidugina Formation was stripped, which is an analog of the Lower-Middle Cambrian Shumnaya and Kuonamka Formations of the Siberian Platform. The Paidugina Formation, which accumulated on the shelf and slope of the open sea facing the Paleo-Asian ocean, is considered oil-producing and suggests the high petroleum potential of the cis-Yenisei basin. Also, a highly promising generation-accumulation petroleum system has been revealed.

The theory of orbital climate forcing implies an approximate Earth rotation model which has never been checked against other methods. We simulate the rotating Earth in compound models as a system of equal peripheral parts that orbit a central body and investigate the orbital evolution as affected by the gravity pull from the Sun, the Moon, and the planets. The predicted nutation cycles agree well with estimates by other methods. The model of periodic convergence and divergence of peripheral bodies may be useful to explain interaction of continents.

The implications of recent seismological and resistivity data for the geometry and orientations of neotectonic faults are generally consistent with the morphotectonic model of Gorny Altai as an area of crustal failure at the junction of two relatively stable blocks. The model predicts motions under general NW compression mainly on right-lateral strike-slip faults accompanied by systems of pinnate reverse and extensional faults.
The locations and mechanisms of aftershocks that followed the 2003 Chuya earthquake (Gorny Altai) indicate long seismic activity generated by a neotectonic NW right-lateral strike-slip fault which separates the North Chuya and South Chuya ranges from the Kurai-Chuya system of intermontane basins. The plane of the northwestern termination of the active fault zone dips in the SE direction, beneath the ranges, at about 70

Magnetotelluric responses of a 3D inhomogeneous earth excited by an arbitrary EM field are nonlocal, which is essential in processing regional MTS data. Due regard for this effect requires data acquisition by a dense synchronous 2D array. We suggest to invert the nonlocal MT responses applying correlation of the surface telluric and magnetic components recorded simultaneously at all stations. The new inversion algorithm has been tested using synthetic data that reproduce the conditions of the BEAR experiment.

We report forward modeling results for transient magnetic fields excited by horizontal electric or vertical magnetic dipoles. Modeling was performed with reference to resistivity patterns typical of platform areas in East Siberia. We investigate the possibilities to resolve deep reservoirs by measuring the horizontal and vertical components of the transient magnetic field and compare the depth resolution of magnetic and inductive methods.

The Borisikha ophiolite, composed of serpentinites and amphibolites, is an extension of the Isakovka ophiolite belt in the near-Yenisei part of the Yenisei Ridge. It is a slightly disturbed ~3.5 km thick fragment of the ophiolite association; its crustal part is composed of metamorphosed wehrlite, troctolite, and gabbro cumulates. The cumulate composition and the geochemical features, which do not show any suprasubductional overprinting, indicate that the ophiolite is a normal oceanic lithosphere. Zircons extracted from pegmatoid amphibolite show sectorial magmatic zoning, low U contents, and magmatic Th/U values. The zircon age determined on a SHRIMP-II mass spectrometer is 682±13 Ma, which corresponds to the time of formation of oceanic crust. In the second half of the Late Riphean, the oceanic lithosphere that included the Borisikha ophiolite was subducted beneath the margin of the Siberian continent. At the same time, rifting, formation of half-grabens, and alkaline magmatism took place at the rear of the Yenisei Ridge. Similar events took place in southeastern East Sayan. Correlation between the coeval Late Baikalian structures along the southern and western margins of the Siberian Platform calls for special study.

The intensity of postmagmatic processes in the Botuobinskaya pipe kimberlites was estimated from the calculated content of normative secondary quartz (Q). Several simple algorithms are proposed to calculate the Q content from chemical analyses of kimberlites. Ten groups of altered kimberlites have been recognized from the Q contents. The contents of MgO, some trace elements, and LREE in the groups, the contents of Cr and Ca of crimson garnets, the diamond contents of kimberlites, and the average weight of diamonds decrease as the Q content increases. It is shown that the negative SiO₂-MgO correlation is the most effective indicator of the postmagmatic alteration of kimberlites. As the degree of their secondary alteration increases, the kimberlites transform into an assemblage of quartz and clay minerals enriched in some trace elements and almost completely lacking REE and diamonds.

The features of the accumulation of reduced products in the soil of the initial, organics-accumulating, sod and humus-accumulating soil-formation stages are investigated in the industry-affected landscapes of the Kuznetsky Basin. The importance of secondary pedogenic reduced products in the transformation of the initial (primary) lithogenic oxidation-reduction systems is considered.

Multi-annual (1992

The structure of the isolated population of hybrid peony Paeonia hybrida Pall. (Paeoniaceae), the species recorded in the Red Book of Russian Federation (1988) and a number of Russian regions, located at a distance of about 1.5 thousand kilometers from the main natural habitat of this species, is investigated at the territory of the Bashkir trans-Ural region using the isoenzyme markers of 11 loci. Relatively high levels of the genetic diversity were revealed in two detected ecotopes (the average number of alleles A = 1.9

The quantitative determination of Pb, V, As, Se, Cd, Sn, Hg in the plants growing on oil-polluted territories of the Western Surgut deposit in the Khanty