Sources of the Late Mesozoic magmatic associations in the northeastern part of the Amurian microcontinent

Based on generalization of available geochronological data, Late Mesozoic magmatic associations in the northeastern part of the Amurian microcontinent are divided into three groups: 142–125, 124–115, and <110 Ma. The age of these associations decreases with approaching the Pacific margin of Asia. In the same direction, they show a change in sources of their parental melts: continental crust (142–125 Ma) → continental crust + PREMA (DM) (124–115 Ma) → continental crust + PREMA (DM) + EMII (<110 Ma). Isotope-geochemical (Sr-Nd) study indicates that intrusive and volcanic rocks of the Late Mesozoic magmatic associations in the northeastern part of the Amurian microcontinent were originated in geodynamic settings that provided access of enriched mantle sources to magma formation. The most probable of these settings are as follows: (1) plate sliding accompanying by the formation of slab window beneath continental margin; (2) passage of the Asian margin over the East Asian mantle hot field in the Late Mesozoic; (3) asthenospheric upwelling due to delamination of the lower crust during closure of the Mongolian-Okhotsk ocean caused by collision between the Amurian microcontinent, Dzhugdzhur-Stanovoy, and Selenga-Stanovoy superterranes in the Central Asian fold belt.     

Time-temperature-transformation (TTT) analysis of cation disordering in omphacite

The kinetics of cation disordering in a natural ordered (P2/n) omphacite have been followed at P=18 and 30 kb, T= 750–1,260° C, for times of between 1.5 min and 16 days in a piston-cylinder apparatus. Time-temperature-transformation (TTT) analysis of the experimental data, using the presence or absence of the 11¯1 reflection in single crystal X-ray precession photographs to indicate the extent of reaction, yields an equilibrium order/disorder temperature (T _ord) of 865±10° C, an activation enthalpy (1 bar) of 71±6 kcal mole^–1 and an activation volume of 9±4 cm³ mole^–1 (plus and minus figures represent the precision of a best fit between experimental data and TTT theory rather than absolute errors). The activation volume is consistent with a vacancy mechanism of cation diffusion. H₂O, added in the form of oxalic acid, appears to speed the process up slightly. The overall transformation mechanism is continuous, involving neither the nucleation of a disordered phase nor a change in antiphase-domain distribution. This is consistent with both first- and non-first-order character for the C2/cP2/n transformation, though a range of ordered states below T _ord is indicated by the weakening of h+k=odd reflections. A simple extrapolation of the disordering rates to geological conditions leads to the first estimate of how long disordered omphacites would take to order in nature, ranging from less than one year at T800° C to more than 10⁷ years at T<350° C.     

Anisotropy of small-scale inhomogeneities in the region of solar-wind acceleration

A model is proposed to explain observational data on the scattering of radio signals, which indicate that small-scale plasma-density inhomogeneities in the region of solar-wind acceleration are strongly elongated in the radial direction, with the degree of elongation sharply decreasing at heliocentric distances of about six solar radii. The evolution of the energy spectra of the fluctuations of the magnetic field and plasma density is studied assuming that the plasma-density fluctuations are generated locally by nonlinear interactions of high-frequency Alfven waves, and that the gradients of the mean plasma parameters are smooth. The growth rates of the main nonlinear processes are estimated. The strong elongation of the inhomogeneities first arises when the Alfven waves travel through the chromosphere-corona transition layer, then survives to considerable distances from the Sun because the associated nonlinear relaxation processes are fairly slow. Estimates of the degree of elongation of the inhomogeneities and the characteristic distance for changes in the angular wave spectra are in good agreement with radio propagation data.     

Quasi-stationary striations in basin-scale oceanic circulation: vorticity balance from observations and eddy-resolving model

Recently, prominent jet-like features of the ocean circulation, called striations, with a meridional scale of O(300–500 ;km) and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this paper, we study quasi-stationary striations, which are best seen in the multi-year time-averaged velocity fields. Using 1993–2002 mean dynamic ocean topography, satellite altimeter observations, and output of the Ocean General Circulation Model for the Earth Simulator, the dynamics of the quasi-stationary striations in the eastern parts of the subtropical North and South Pacific are examined by assessing individual terms in the time-averaged equations of relative and potential vorticity. While non-linear effects are found to be essential in the dynamics of the striations, rejecting some linear hypotheses forwarded in the earlier studies, the relevance of the Rhines mechanism is not confirmed. Eddy flux does not act as a relative vorticity source for the striations. Using the potential vorticity (PV) diagnostics, we show that the time-mean PV is not conserved along the time-mean streamlines, and on the scale of the striations these changes in PV are largely induced by the eddy flux of layer thickness. The fact that eddy fluxes contribute to the striations’ time-mean PV budget suggests that the striations are not a kinematical artifact of time-averaging of westward-propagating eddies.     

Regional Problems in Water Use in Siberian Industrial Agglomerations

Water Resources - The basic indicators of regional water use have been identified and assessed as a component of a single social–natural–technogenic system. These indicators have been...     

Multi-decadal synthesis of benthic–pelagic coupling in the western arctic: Role of cross-shelf advective processes

Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m⁻²) and chlorophyll (>150 mg m⁻²) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m⁻² and <50 mg m⁻², respectively). One notable exception is an area of relatively high biomass (50–100 g m⁻²) and chlorophyll (80 mg m⁻²) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves.     

Tidal effects in geomagnetic variations

Doklady Earth Sciences - This paper reports the results of processing and analysis of geomagnetic variations, estimates of their spectra, and the first identified waves of lunar–solar tides...     

Relationship of galaxies from the second Byurakan survey to Zwicky clusters. II. Discussion

We analyze the data presented in a previous paper by Gyulzadyan and Petrosian, and discuss the results of a statistical investigation of the relationship between SBS galaxies and Zwicky clusters. The main results are that SBS galaxies follow the overall galaxy distribution in clusters and they do not avoid any type of Zwicky cluster. There is a significantly higher probability of finding SBS galaxies occurring in medium compact clusters than in open clusters. They also follow the well-established morphology-density relation. Earlier morphological type, higher luminosity, larger linear size, and redder SBS galaxies tend to be found in clusters with higher compactness, or in more compact regions of the clusters. The number distribution of SBS galaxies in Zwicky open clusters probably follows the distribution of normal galaxies. The number distribution of SBS galaxies in medium compact and compact clusters shows two-maxima structure. Published in Astrofizika, Vol. 52, No. 2, pp. 225–236 (May 2009).