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21.
John F. Mchone Ronald Greeley Kevin K. Williams Dan G. Blumberg Ruslan O. Kuzmin 《Meteoritics & planetary science》2002,37(3):407-420
Abstract— Ten terrestrial impact structures were imaged during two flights of the 1994 space radar laboratory (SRL) experiment. These craters include Wolf Creek, Australia; Roter Kamm, Namibia; Zhamanshin, Kazakhstan; BP and Oasis, Libya; Aorounga, Chad; Amguid, Algeria; and Spider, Connolly Basin and Henbury, Australia. SRL contained two co‐registered instruments; the United States shuttle imaging radar‐C (SIR‐C) polarimetric radar system operating in L‐band (λ = 24 cm) and C‐band (λ = 5.6 cm), and the joint German/Italian synthetic aperture radar (X‐SAR) operating in vertically‐polarized X‐band (λ = 3 cm). Comparisons show SRL images to be complementary to, or in some cases superior to, corresponding optical images for evaluating size, location, and relative age of impact features. Regardless of wavelength or polarization, craters with significant relief appear prominently on radar as a result of slope and roughness effects. In desert regions, longer wavelengths penetrate dry sand mantles to reveal hidden crater dimensions or associated buried landforms. Radar polarities and wavelengths are particularly sensitive to vegetation, surface roughness, and soil moisture or electrical properties. In the more temperate environments of Kazakhstan and Australia, SRL images show detailed stream patterns that reveal the location and structure of otherwise obscured impact features. 相似文献
22.
Nikolay G. Granin Natalia A. Radziminovich Liba Z. Granina Vadim V. Blinov Ruslan Y. Gnatovskiy 《Geo-Marine Letters》2012,32(5-6):453-464
In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4–0.7?mg/kg (0.7?%), and average suspended particle concentration increased strongly to 6–9?mg/l, the background value being 0.2?mg/l. The spatial distribution of these waters was virtually identical to the focal area of the Mw6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20?km3) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake. 相似文献
23.
Ruslan Melian Nicolai Myrlian Alexander Gouriev Constantin Moraru Frank Radstake 《Hydrogeology Journal》1999,7(2):188-196
This paper describes the results of a groundwater quality assessment conducted in two pilot areas, Balatina and Carpineni,
in the Republic of Moldova. Shallow groundwater is the main source of drinking water in rural areas, but reliable data on
its quality are currently insufficient for developing rural water-supply systems with standard designs. The main components
of the study included a field sampling program (including pesticides), an evaluation of the reliability of existing drinking-water
data, an analysis of land use and groundwater-pollution risks using GIS, and the formulation of recommendations to reduce
risks for public health.
Microbiological, nitrate, and selenium contamination are most serious in the villages. These contaminants should be given
priority in addressing drinking-water aspects for rural water-supply development in the two pilot areas. Pollution occurs
mainly due to poor sanitary conditions. In a few shallow wells, traces of selected pesticides were observed, but the effect
of these levels of pesticides on public health is still unclear.
Limited resources of shallow groundwater of good quality occur outside the villages. Additional pilot studies should be implemented
to prove the technical and institutional feasibility of developing and protecting these resources.
Received, September 1997 Revised, September 1998 Accepted, March 1999 相似文献
24.
L. P. Plyusnina T. G. Shumilova S. I. Isaenko G. G. Likhoidov A. V. Ruslan 《Russian Journal of Pacific Geology》2013,7(4):288-298
The regional carbonization of the Riphean metamorphic complexes is discussed using as an example the Tamginskoe and Turgenevskoe graphite deposits located in the northern part of the Khanka terrane. It is shown that the noble metal mineralization associates closely with the graphitization. Isotopic, X-ray, and thermal analyses and Raman spectroscopy were first used for investigating the structural state of the graphite with defining its two varieties. The first of them is represented by nanocrystalline fluidogenic graphite that was formed during gas condensate crystallization from deep-seated reduced ore-bearing fluid. The second variety (large-flake graphite) represents a product of metamorphic recrystallization of carbonaceous terrigenous protoliths. The recrystallization was accompanied by the granitization of the sedimentary protolith, mobilization, and the transfer of the carbonaceous and ore matter of the host rocks. It is inferred that the graphitization associated with noble metal mineralization is a polygenic process. The graphite of the first generation associates closely with amorphous diamond-like carbon. This unexpected find may bear genetic information useful for geological and geochemical reconstructions. 相似文献
25.
Gas seeps in Lake Baikal—detection, distribution, and implications for water column mixing 总被引：4，自引：4，他引：0
Nikolay Grigorievich Granin Mikhail M. Makarov Konstantin M. Kucher Ruslan Y. Gnatovsky 《Geo-Marine Letters》2010,30(3-4):399-409
Echo sounders served to locate a large number of shallow- and deepwater gas seeps at the bottom of all three basins of Lake Baikal during the years 2005 to 2008. A substantial proportion of the shallow gas seeps was located near the delta of the Selenga River, and at the Posolskii uplift. Deepwater gas seeps were recorded at the lake bed both inside and outside of areas where a bottom-simulating reflector was identified in seismic profiles. By monitoring the activity of gas emissions at the gas seeps, times of episodic gas ebullition could be distinguished from times of persistent gas bubble streams. A maximum gas flare height of more than 950 m above the bottom was recorded at the St. Petersburg mud volcano located in the central basin of Lake Baikal. Based on calculations from echo sounder data, the ascent velocity of gas bubbles reached 40 cm/s. In the area of gas seepage, there was a thick near-bottom layer, in which the gradient of water temperature was equal to the adiabatic gradient. This implies complete mixing of the water close to the lake bed, resulting from ascending gas bubbles released at seep sites. Analyses of vertical temperature profiles indicate possibly localized upwelling up to the lake surface when gas emissions are intensive. 相似文献
26.
Late Cretaceous palaeomagnetic results from Sikhote Alin, far eastern Russia: tectonic implications for the eastern margin of the Mongolia Block 总被引：3，自引：0，他引：3
27.
28.
Summary Titanite varieties doped with rare earth elements (REE) have been prepared by ceramic synthesis and quenching in air. Their crystal structure was determined by Rietveld analysis of the powder X-ray diffraction patterns. Two different substitution schemes, Ca1–xNax/2Smx/2TiSiO5 and Ca1–xDyxTi1–x
SiO5, are studied at x=0.2. Both synthetic varieties of titanite adopt space group A2/a. This implies that both single-site and complex multivalent substitutional schemes destroy the coherence of the off-centering of octahedral chains in the titanite structure resulting in a P21/aA2/a phase transition. Unit cell dimensions obtained for the REE-bearing titanite varieties are as follows: a=7.0541(1)Å; b=8.7247(1)Å; c=6.5664(1)Å; =113.732(1)° for Ca0.8Na0.1Sm0.1TiSiO5; and a=7.0021(1)Å; b=8.7256(1)Å; c=6.5427(1)Å; =113.294(1)° for
. Both REE-doped titanite samples and a control sample of the pure titanite end member have similar unit cell parameters and consist of polyhedra distorted to a similar extent with the exception of more-distorted SiO4 tetrahedron in CaSiTiO5. The structural data suggest that the Ca1–xNax/2Smx/2TiSiO5 and Ca1–xDyxTi1–xFexSiO5 solid solutions adopting the titanite structure might extend to x sufficiently greater than 0.2 and involve both heavier and lighter trivalent rare earth elements.Permanent address: Geological Institute KSC RAS, 14 Fersmana St., Apatity, 184200 Russia 相似文献
29.
Petrogenetic processes in the ultramafic, alkaline and carbonatitic magmatism in the Kola Alkaline Province: A review 总被引：1，自引：0，他引：1
Hilary Downes Elena Balaganskaya Andrew Beard Ruslan Liferovich Daniel Demaiffe 《Lithos》2005,85(1-4):48-75
Igneous rocks of the Devonian Kola Alkaline Carbonatite Province (KACP) in NW Russia and eastern Finland can be classified into four groups: (a) primitive mantle-derived silica-undersaturated silicate magmas; (b) evolved alkaline and nepheline syenites; (c) cumulate rocks; (d) carbonatites and phoscorites, some of which may also be cumulates. There is no obvious age difference between these various groups, so all of the magma-types were formed at the same time in a relatively restricted area and must therefore be petrogenetically related. Both sodic and potassic varieties of primitive silicate magmas are present. On major element variation diagrams, the cumulate rocks plot as simple mixtures of their constituent minerals (olivine, clinopyroxene, calcite, etc). There are complete compositional trends between carbonatites, phoscorites and silicate cumulates, which suggests that many carbonatites and phoscorites are also cumulates. CaO / Al2O3 ratios for ultramafic and mafic silicate rocks in dykes and pipes range up to 5, indicating a very small degree of melting of a carbonated mantle at depth. Damkjernites appear to be transitional to carbonatites. Trace element modelling indicates that all the mafic silicate magmas are related to small degrees of melting of a metasomatised garnet peridotite source. Similarities of the REE patterns and initial Sr and Nd isotope compositions for ultramafic alkaline silicate rocks and carbonatites indicate that there is a strong relationship between the two magma-types. There is also a strong petrogenetic link between carbonatites, kimberlites and alkaline ultramafic lamprophyres. Fractional crystallisation of olivine, diopside, melilite and nepheline gave rise to the evolved nepheline syenites, and formed the ultramafic cumulates. All magmas in the KACP appear to have originated in a single event, possibly triggered by the arrival of hot material (mantle plume?) beneath the Archaean/Proterozoic lithosphere of the northern Baltic Shield that had been recently metasomatised. Melting of the carbonated garnet peridotite mantle formed a spectrum of magmas including carbonatite, damkjernite, melilitite, melanephelinite and ultramafic lamprophyre. Pockets of phlogopite metasomatised lithospheric mantle also melted to form potassic magmas including kimberlite. Depth of melting, degree of melting and presence of metasomatic phases are probably the major factors controlling the precise composition of the primary melts formed. 相似文献
30.
Synthetic titanite, CaTiOSiO4, and the series of (Ca1−x
Na
x
)(Ti1−x
Ta
x
)OSiO4 and Ca(Ti1−2x
Ta
x
Al
x
)OSiO4 solid solutions have been prepared by ceramic methods, and their crystal structure determined by the Rietveld analysis. At ambient conditions, titanite can contain up to 20 mol% NaTaOSiO4 or 60 mol% Ca(Al0.5Ta0.5)OSiO4. These limits might differ in natural samples due to combination with substitutions involving fluorine and/or hydroxyl replacing oxygen together with vacancies at cationic sites. All cations located at the vii
X- and vi
Y-sites in the structures of tantalian titanite are disordered. Expansion of the <Si–O> bond from 1.618 to 1.621 Å in CaTi0.8Ta0.1Al0.1OSiO4 and CaTi0.6Ta0.2Al0.2OSiO4 to 1.644 Å in the CaTi0.4Ta0.3Al0.3OSiO4 titanite suggests the possible presence of some Al3+ in the tetrahedral site replacing Si4+ in the latter. All tantalian titanites crystallize in the space group A2/a. This implies that both single-site and complex double-site substitutional schemes induce P21/a → A2/a phase transition(s). The (Ca1−x
Na
x
)(Ti1−x
Ta
x
)OSiO4 substitution scheme incorporates larger cations at both the vii
X and vi
Y sites, whereas the Ca(Ti1−2x
Ta
x
Al
x
)OSiO4 scheme involves only vi
Y-site (Al3+,Ta5+) cations with a slightly smaller “average” radius. Unit cell dimensions change insignificantly or increase incrementally with increase of average cationic radii in the (Ca1−x
Na
x
)(Ti1−x
Ta
x
)OSiO4 series, and with an insignificant decrease in the viR
Y
average cationic radii in the Ca(Ti1−2x
Ta
x
Al
x
)OSiO4 series. Both Ta-doped titanite and CaTiOSiO4 consist of distorted polyhedra with the XO7, YO6 coordination polyhedra and the SiO4 tetrahedron in tantalian titanite being less distorted compared to those of the pure CaTiOSiO4. 相似文献