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Pyroxenite xenoliths in Miocene Vitim picrite basalts were produced by polybaric fractional crystallization of melts in the mantle, as determined from their morphology and major- and trace-element chemistry. Black coarse-grained pyroxenites and megacrysts make a long trend (F# = 0.12-0.23) as a result of polybaric cotectic Gar-Cpx fractionation, possibly, during initiation of the feeding system for the basaltic eruption. Low-temperature black pyroxenites are products of interaction of residual melts with the lower crust into which they intruded. The highest-temperature hybrid websterites may result from mixing of basaltic melts with 5-10% partial melts from metasomatic mantle lherzolites. Anatectic Cr-pyroxenites were formed mostly by segregation of partial melts from lherzolite material and remelting of former veins. Low-temperature hybrid garnet pyroxenites were produced by interaction of metasomatic lherzolites (or earlier Cr-diopside veins) and differentiated basaltic melt enriched with volatiles. Remelting of earlier mineral generations, which occurs in all rising melt systems, is reflected by mirror peaks on spidergrams, and LREE and HFSE (and ore element) enrichment.

Black shale formations in Sayan-Baikal mountainous province (Kotera depression in Northern Baikal and Ilchir and Oka depressions in southeastern East Sayan) are considered in terms of their geochemistry and metallogeny. The rocks formed in the Late Riphean-Early Paleozoic in different geodynamic environments of active continental margin (turbidite terrane), back-arc spreading zone (oceanic terrane), or shelf (carbonate deposition). Several intervals of the section show noble-metal mineralization. The black shales associated with ophiolites typically demonstrate a high auriferous potential of sulphides, which are equivalents of sulphides from back-arc spreading zones. The carbonaceous shales of continental margins show platinum and palladium enrichment, their elevated concentrations being attributed to zones of high Ba, Mo, and U abundances. The isotope composition of sulphide sulphur varies from -10÷17 – outside these zones to +3-+6.8 within them.

It is suggested to determine three independent elastic parameters of the medium (VP, VS, and ) by combined inversion of AVO data on compressional, converted, and shear waves recorded by three-component land seismic profiling. A linear solution to the problem is considered on the assumption of nearly constant elastic properties on a rigid plane boundary between two isotropic elastic half-spaces. The solution is obtained through an iterative algorithm that yields stable estimates of the model parameters. The stability and exactness of the solution has been tested by fitting and comparison of various wave combinations: (PP + PS), (PP + SH), and (PP + SV). The combination of (PP + SV) waves provides the optimum inversion on P (and S) waves, in the presence of up to 50% (100%) noise. The parameters determined from (PP + PS) and (PP + SH) waves are less accurate, as stable estimates can be obtained at lower noise (25 or 40% of the signal) on P, S, and converted waves.

The paper presents preliminary data of Sm-Nd systematics in granitoids from the central Dzhugdzhur-Stanovoy folded area. The Nd ages range from 3.1 to 1.0 Ga, _Nd( T ) =

Organic matter of the fossilized excrement is subject to biological decomposition and transformation. But the nature of the organisms engaged in this process in the past is usually unknown and can be established only by examination of microfossils in ancient coprolites. The data obtained during the study of Paleogene phosphate coprolites from the Zaisan Depression, Kazakhstan, suggest that fungi were involved in these processes.

Inclusions in minerals were studied from the point of view of thermobarogeochemistry. On the basis of the Peng-Robinson two-parameter equation of state and conditions of diffusion and mechanical stability of fluid mixtures, programs were developed to calculate isochors of entrapping of gas-liquid inclusions and to estimate critical parameters of gas-liquid transition in the quaternary mixture H₂O-CO₂-CH₄-N₂. The difficulties related to the sensitivity to selection of initial conditions in Newton's method on solving systems of nonlinear equations have been overcome by using experimental and calculated data for ternary mixtures. The obtained P-T characteristics of critical mixtures are given in the form of sections of a multidimensional domain at a constant content of nitrogen and are in agreement with the known characteristics for triple mixtures H₂O-CO₂-CH₄. The critical data for quaternary mixtures were used as initial values for finding parameters of homogenization, from which isochors of entrapping of gas-liquid inclusions in minerals have been calculated. The calculations show that ignoring even a small portion (relative to CO₂) of water in highly carbon dioxide inclusions can lead to a serious error in estimation of P and T of mineral formation.

Within the Late Precambrian crystalline complexes of the Arzybei and Shumikha blocks two contrasting geochemical types of tonalite-trondhjemite granitoids have been distinguished - high- and low-alumina, similar in petrogeochemistry to continental and oceanic plagiogranitoids (according to classification by J.Art). The geologic position, composition, and petrogenesis of the granitoids evidence their formation under strongly different PT-conditions related to the development of island-arc systems. The available data show that such associations of tonalites and trondhjemites of two types are also present in other Precambrian subductional complexes. The coexistence of high- and low-alumina tonalities and trondhjemites testifies to contrasting PT -conditions of formation of their parental melts in subductional settings. The high-alumina varieties resulted from high-pressure melting of metabasic rocks of the subducting oceanic plate, whereas the low-alumina ones are the products of fractional crystallization of basaltic melt or low-pressure melting of metabasic rocks at the initial stage of development of island arc or during the back-arc spreading. The above association can be considered typical of Precambrian oceanic suprasubductional settings.

Altai in the Cenozoic structural framework of Central Asia is a zone of crystal breccia surrounded by more stable large blocks. The mobile zone is expressed in the surface topography as mountains and the stable blocks as plains. The sedimentary section of the latter includes Permian, Jurassic, and Quaternary molasse, which attests to structural inheritance from the older framework. The Late Paleozoic and Middle Mesozoic activity stages were associated with strike-slip faulting and granitoid magmatism, there is no evidence for granite intrusion in the Cenozoic yet.
Altai is bounded by reactivated Paleozoic master faults, but the neotectonics within the province does not show such an obvious relation to Paleozoic structures. Spatial correlation of large Cenozoic faults in southeastern Russian Altai with Paleozoic faults of the same scale shows that the recent faults result from reactivation of older fractures over less than a half of their total length. The reactivation involved WE trending segments of most of major faults, and many blocks of metamorphic rocks underwent uplifting.

Fracturing in the Primorsky fault, a master fault in the Baikal rift system, is investigated using high-resolution structural data. The fault zone consists of several roughly parallel fault segments and elongate wedge-shaped blocks cut by large transversal faults that belong to a fault running along the Sarma valley. Fracturing parameters were used to distinguish the influence areas of separate fault planes having a regularly zoned structure. The Cenozoic activity of the Primorsky fault has been selective and is restricted to the influence areas of individual fault planes. Right-lateral oblique-slip and normal faulting occurs in NNW and NE extension stress fields along fractures parallel to the Primorsky and Sarma faults. The breadth of the Primorsky fault zone involved in the Cenozoic activity exceeds 3 km.

The paper presents the outlines of a new approach and the respective computing techniques for regional structural mapping of the sedimentary cover of the West Siberian Plate on the basis of synthetic interpretation of poorly correlated geological and geophysical data. Processing involves log data, absolute altitudes on seismic exploration profiles and digitized elevation contour lines of the model surface (or surfaces correlated to the model surface), vector images of geological discontinuities and faults, etc. The new approach makes it possible to reveal and, under certain conditions, to eliminate most obvious inconsistency in raw data and to process any number of irregularly positioned paper or electronic maps of different scales by various techniques, including smooth conjugation along curvilinear boundaries. The new method has been tested in application to Jurassic hydrocarbon reservoirs in West Siberia.