Magnetotelluric sounding of Kamchatka

The MTS data acquired in Kamchatka during the last 30 years have been analyzed and summarized. Our interpretation is based on curves oriented along and across Kamchatka. Longitudinal and transverse curves can be affected by local geoelectric inhomogeneities. These were suppressed by conformal averaging. A bimodal interpretation of average longitudinal and transverse curves yielded a deep geoelectric model, which can be adopted as a starting point to be subsequently refined by 3D numerical modeling. The model involves a crustal conductive layer extending along central Kamchatka. In the east of the peninsula this layer is connected with crustal transverse conductive zones as wide as 50 km. Those zones have extensions toward the Pacific Ocean. Major centers of present-day volcanism occur in the transverse zones. The upper mantle contains an asthenospheric conductive layer forming an uplift beneath the present-day volcanic belt of Kamchatka.     

Comparative analysis of biotic indices in the monitoring system of running water in a biospheric reserve

Comparative analysis of six indices (TBI, FBI, BMWP, ASPPT, BBI, and EPT) was performed at nine sites in the Berezina River basin in the area of the Berezina Biospheric Reserve. The criterion for comparison was the coefficient of variations of an index for different sites in the same time moment and for the same site in different periods. The indices TBI, BMWP, and EPT were found to demonstrate the highest sensitivity and most adequate response to variations in water quality, which allows them to be recommended to be taken as standard.Translated from Vodnye Resursy, Vol. 32, No. 2, 2005, pp. 223–226.Original Russian Text Copyright © 2005 by Semenchenko, Moroz.     

A geoelectric model for the Uzon caldera,Kamchatka

The results of magnetotelluric and magnetovariational studies in the Uzon caldera are considered. An analysis of magnetotelluric parameters yielded the required method of interpretation. The MTS curves were interpreted in the framework of a 2D model using the REBOCC program. Geoelectric cross sections of the caldera were constructed along two orthogonal lines. Anomalies of high electrical conductivity were identified in the sediments and in the basement and were found to be confined to the locations of geothermal springs. The higher conductivity of these anomalies is here related to the presence of highly mineralized hydrothermal solutions. Electrical conductivity was used for an approximate estimation of porosity in the sediments and basement. A subvertical zone of higher porosity was identified at depths of 1.5–3.5 km in the caldera with a connection to the channelways of fluids rising into the sediments. It is hypothesized that highly mineralized solutions are diluted with vadose water in that zone and come through fissures onto the ground surface in the form of hot springs. The totality of these data suggested a conceptual model to characterize the main features in the generation of hydrothermal springs in the Uzon caldera.     

Uranium in saline lakes of Northwestern Mongolia

Analysis of major- and trace-element compositions of water in hypersaline soda closed basin lakes of Northwestern Mongolia and Chuya basin (Gorny Altai) shows high enrichment in ²³⁸U (up to 1 mg/l). Proceeding from new data, uranium accumulation in water has been attributed to (i) location of the lakes and their watersheds in potential provinces of U-bearing rocks and (ii) uranium complexing with carbonate in presence of carbonate (bicarbonate) anions. Among the explored hypersaline soda lakes of the area, the greatest uranium resources are stored in Lake Hyargas Nuur (about 6000 ton).     

Geodynamics of the Russian Arctic Shelf and Relief-Forming Processes in the Central Kara Basin

Oceanology - The article deals with the issues of the geodynamic evolution of the Kara–Barents Sea shelf and influence of structure-forming processes on the nature of relief formation. The...     

U-Pb and 39Ar/40Ar dating and Sm-Nd and Pb-Pb isotopic study of the Kalguty molybdenum-tungsten ore-magmatic system, Southern Altai

The Kalguty ore-magmatic system comprises two intrusive complexes: the Kalguty granite-leucogranite complex and Eastern Kalguty complex of dikes and small intrusions. U-Pb dating of individual zircon grains from granites of the main intrusive phase demonstrated that the crystallization age of small grains of magmatic habits and outer rims of large grains is almost concordant and is 216 ± 3 Ma. Ar-Ar isotope study shows that the K-Ar system of biotites from granites of the main phase within the Kalguty ore field was disturbed (radiogenic Ar was partially lost) and gave an age of 202 ± 1 Ma. The Ar-Ar dating of muscovites from intraore and postore dikes of the Eastern Kalguty complex devoid of signatures of postmagmatic recrystallization and superimposed greisenization gave similar ages of 205–201 Ma. This date is considered as the emplacement age of the Eastern Kalguty dikes and associated complex W-Mo-Bi-Be ore mineralization. Sm-Nd and Pb-Pb isotopic study of granites, ongonites, and elvans of the Kalguty ore-magmatic system and host rocks shows that these systems were closed. For example, recalculation of Nd isotopic ratios for corresponding ages of crystallization of magmatic systems (216 and 205 Ma) shows that ?_Nd(T) values decrease from ?1.9 to ?3.5 ... ?5.08 with transition from granite-leucogranite to subvolcanic granite porphyry, ongonite, and elvan dikes with corresponding increase of model ages of protoliths from 1.0 to 1.25 Ga. Lead isotopic ratios for leaching residues of whole-rock samples of all rock varieties (²⁰⁶Pb/²⁰⁴Pb = 18.305–18.831; ²⁰⁷Pb/²⁰⁴Pb = 15.527–15.571) are plotted well below the line of average crustal lead evolution according to the Stacey-Kramers model.     

Emissivity measurements of analogue materials for the interpretation of data from PFS on Mars Express and MERTIS on Bepi-Colombo

The Planetary Fourier Spectrometer (PFS) onboard the Mars Express Mission provides thermal infrared, hyperspectral images of Mars and in the future the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS), part of the selected payload for the Bepi-Colombo Mission, will collect analogous data for Mercury. To interpret these remote sensing data it is essential to understand the spectral emittance of planetary analogue materials and a spectral library of emissivity measurements is needed. Here we introduce the emissivity device built at DLR (Berlin). The device is coupled to a Fourier transform infrared spectrometer (Bruker IFS 88), purged with dry air and equipped with a cooled MCT-detector. We discuss theoretical background of our thermal emission measurements and describe our standard experimental procedures, which are being used to create the Berlin emissivity database (BED). This study presents and discuss the 6.3-22 μm thermal emission spectra of fine-grained feldspar separates ranging from <25 to 90-125 μm. We discuss diagnostic potential of the features present in the emission spectra of plagioclase and alkali feldspars and the particle size effects.     

Search for anomalous effects in geophysical fields in relation to earthquakes in the Baikal rift zone

The paper presents data of electrical conductivity monitoring for the upper crust obtained with the use of a controllable electromagnetic source by the dipole, vertical electromagnetic, and transient electromagnetic sounding methods, as well as variations in the geomagnetic field and the Lake Baikal water level. With the help of spectral, spectral time, and multivariate analyses, main spatial and temporal patterns of variations in geophysical parameters are determined. The present study revealed anomalous effects in the behavior of the canonical coherence (parameter K) and aggregated signal (parameter A) and other anomalous variations in geophysical parameters related to earthquakes in the Baikal rift zone.     

Comparative analysis of two approaches to the assessment of water quality by biological indices: Case Study Of Dnieper tributaries

Water quality in several tributaries of the Dnepr in the southeastern part of its basin in the territory of the Republic of Belarus was estimated by six biotic indices and by the comparison with reference sites as accepted in the European Water Framework Directive. Water quality estimates obtained by different indices for the same sites are significantly different. The most adequate estimates were obtained from the British and Belgian indices for the assessment of the state of flowing waters. The comparative analysis of the two approaches showed that the method based on reference sites yields a more stringent estimate of river water quality than biotic indices.