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The values δ¹⁸O obtained from belemnite rostra of Subpolar Urals show extremely high paleotemperatures (20

The paper presents results of complex studies of lacustrine and palustrine deposits from three boreholes drilled on the eastern and southern shores of Lake Baikal: data of palynological study and seeds and fruits analyses, botanic composition of peat, and AMS ¹⁴C age. The radiocarbon age is brought to conformity with the actual age by a calibration scale. The general features as well as the specifics of the vegetative-cover structure and climate at separate localities of the lake shore are considered for a period of >13 kyr, with a minuteness of 50-250 years. It is shown that from 13 to 9.3(8.5) kyr ago, the climate and vegetation underwent a series of short-term (200-1000 years) changes. In the first three periods of changes (13-10.3(9.5) kyr ago), the climate remained continental cold-temperature and insufficiently humid, and the vegetation was dominated by forest-tundra and tundra landscapes (mainly spruce, larch, and birch insular forests). In the next three periods (10.3-9.3(8.5) kyr ago), the continental climate became milder, and cedar pine and fir forests appeared. Later on, from 9.3(8.5) to ~6.9(5.5) kyr ago, the climate was continental humid-temperate, and the vegetation was dominated by dark-coniferous cedar pine and fir forests. The decrease in cyclone activity ~5.5 kyr ago might have been responsible for the reduction in the natural geographical range of dark-coniferous fir taiga. At the last stage of the vegetation evolution ~6.9(5.5)-0 kyr ago), the forests were dominated by cedar pine, larch, and pine. Analysis of the climatic and ecologo-edaphic factors determining forest plant spreading on different Baikal shores suggests the existence of two long-term optimal periods in the Holocene: humid (9.3(8.9)-6.9(5.5) kyr ago) and thermal (recent 5.5 kyr).

Contributions of various diatom species to deposition were investigated in surface sediments (0-1 cm) sampled at eighty two geographically dispersed stations in the three subbasins of Lake Baikal. The species composition shows the highest contribution of planktonic diatoms, especially the endemic species of Aulacoseira baicalensis , Cyclotella minuta and Cyclotella baicalensis , in pelagic regions. The contribution of pennate benthic algae that are delivered by the Selenga and live near the delta is restricted to shallow waters along the shore. Aulacoseira baicalensis amount to 87% of the diatom and cyst total in northern North Baikal and to 60% in Central Baikal. Spores of Aulacoseira skvortzowii have rather high percentages in the Selenga delta region (about 30%) and in South Baikal (up to 20%) but are within 5% in the Northern and Central subbasins. Thick-wall frustules of Aulacoseira baicalensis reach the highest weight percent, up to 0.4 g per 1 g of dry sediment. The density of diatoms simulated in a 3D model on the basis of mean sedimentation rates and mean cell sizes correlates with mean annual particle fluxes to the three Baikal subbasins and the Selenga delta region.

The thermal conditions under which thermochemical plumes formed and ascended were analyzed. A thermochemical plume forms at the boundary of two layers, with heat flow coming from the lower layer. Locally, a chemical dope is supplied, which lowers the melting point near the base of the upper layer. As soon as the melting point becomes lower than the temperature at the boundary, the upper layer begins to melt and the plume ascends.
The physicochemical conditions at the core-mantle boundary at which a thermochemical plume forms were explored. Plausible reactions at core-mantle boundary involving H₂ and CH₄ are presented, which produce compounds reducing the melting point of the lower mantle. Probable composition and eutectic temperatures resulting from the reactions at the core-mantle boundary have been assessed.
General criteria and related equations have been deduced for heat and mass transfer of a thermochemical plume. Heat and mass transfer was analyzed near the base and roof of the plume. Formulas have been derived for the plume source heating power, source diameter, and mass flux of a chemical dope. The velocity and time of plume ascent as well as ultimate height of the plume have been determined. Basic equations have been derived to calculate the main plume parameters. Using these equations, we have determined patterns of temperature distribution and dope concentrations in the plume channel. We have also estimated plausible concentrations of a chemical dope at the base of the plume and a decrease in melting point owing to the dope. The minimum diameter, mean velocity and time of the plume ascent have been calculated, with physical properties of the lower mantle taken into account.

We performed Rb-Sr isotope dating of dikes of granite pegmatites breaking through the alkali gabbroids and syenites of the Oshurkovsky Massif. The refined age of the massif is 125 Ma. Pegmatites form a field including several tens of bodies. We have established that the pegmatites formed in two stages: 1132 Ma and 1202.4 Ma ago. Pegmatites of these intrusion stages differ in geochemical features. The close ratios of Sr isotopes in the pegmatites of the first stage and in the massif gabbroids suggest participation of alkaline-basaltic magmas in granitoid pegmatite formation.

This paper considers the composition, structure, spatial location, and paleotectonic formation conditions of Precambrian rocks of the Tien Shan and adjacent regions analogous to the Sinian series in China and the Tamian-Vendian strata of the cover of the Russian Platform. A model is proposed for the Precambrian evolution of the Central Asian ocean basin with pre-Sinian accretion and Vendian orogeny. The major events are dated: subduction and continent-marginal volcanism – 830 20 Ma BP, pre-Sinian accretion

On the basis of harmonic analysis of the data for 125 thousand earthquakes from the catalog of the National Earthquake Information Center of the U.S. Geological Survey for the period 1964-90 and of a series of time-dependent changes of the Earth's angular velocity (t) during the same period, significant positive correlation has been established between graphs of |d/dt| and (t), an annual number N(t) of earthquakes for different regions of the Earth averaged over several years depending on their hypocenter depths (so-called T-component of seismic activity). Besides, special attention was paid to studies of spreading and subduction zones. At the same time, in any two adjacent areas along the both sides of the tectonic plate (in subduction zones and in the system of mid-ocean ridges and continental mountain ranges) the correlation coefficient between the functions [N₁(t)

The paper contains a summary of heat flow studies in the Tien Shan since the early 1960s and the "Catalog of heat flow determinations in the Tien Shan and adjacent territories" published for the first time. Heat flow in the region varies in a broad range from 16 to 134 mW/m²) with the average of 50

This paper presents the characteristics of the first 3D velocity model of the Tien Shan crust, inferred from the traveltimes of P- and S-waves from local and regional earthquakes, recorded by seismic stations in Kyrgyzstan and adjacent regions. Seismic tomography imaging provided new data on the deep structure of the Tien Shan orogen.
Velocity section along the profile crossing source zones of five strong earthquakes (M 6) shows different structural types of the crust. We describe the peculiarities of the velocity structure of strong-earthquake zones and criteria for their distinguishing: waveguides, subvertical weakened channels, and high-velocity bodies to which the foci of strong events are confined.
We also give examples of geological and geophysical interpretation of the first velocity model and show its weakness. The necessity of new imaging is shown. For this purpose a data set was enlarged and described in detail. The principles of collection of data and calculation of a new model are also considered. Much attention was paid to calculation of a 1D model which is the basis for further computation of the new 3D model. Some preliminary results of 3D inversion for P-wave velocities are presented. We believe that the new model, describing the velocity structure of the Tien Shan in regional scale, will provide a more argued judgment about the geodynamic processes there.

Measurements performed by means of tiltmeters and expansometers in special-purpose underground observatories are important part of the research of the crustal kinematic parameters in the northern Tien Shan. Long runs of tilts and deformations observed at the Ala-Archa underground station (42.63 ^o N, 74.50 ^o E) have been analyzed. Results of tidal analysis are reported. Slow variations in tilts and deformations reveal seasonal changes and slope effects caused by seismic activity of the region. The annual average rate of meridional compression was 3 10