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431.
A possible mechanism of the ascent of material within the Earth’s crust and mantle is the mechanism of hydroextrusion, i.e.,
the effect of squeezing of material under excess pressure. The major factors that predetermine the high plasticity of the
material and its ability to produce hydroextrusions are high lithostatic pressures and temperatures. The phenomenon of hydroextrusion
can be most clearly illustrated by the example of the origin of salt diapirs. The driving force of hydroextrusions of material
in the crust and mantle is excess pressure, which can result from lateral differences between the densities of rocks (as is
the case during the development of salt diapirs) and phase transitions associated with a volume increase. When the material
of the upper mantle undergoes partial melting with the derivation of basaltic melts at depths of 60–100 km, excess pressures
reach 80 MPa, whereas the plasticity limit of 20% melted rocks is no higher than 5 MPa. As a result, the partially molten
material is forced from the melting region toward zones with lower lithostatic pressures. A local temperature increase in
the transitional zones in the Earth’s mantle at positive dP/dT values of the phase transitions also gives rise to excess pressures, whose values can range from 100 to 800 MPa at a 0.5–3.0%
volume change and which can be the driving force during the origin of mantle plumes.
Original Russian Text ? V.N. Anfilogov, Yu.V. Khachai, 2006, published in Geokhimiya, 2006, No. 8, pp. 873–878. 相似文献
432.
433.
434.
A. V. Maslov M. V. Isherskaya Yu. L. Ronkin M. T. Krupenin N. P. Gorbunova T. Ya. Gulyaeva O. P. Lepikhina O. Yu. Popova G. M. Yatluk 《Lithology and Mineral Resources》2006,41(3):250-270
Variation of geochemical modules and indices in mudstones from the Upper Vendian Kairovo and Shkapovo groups of the Shkapovo-Shikhan Basin provides the comprehensive information on changes in maturity of the fine aluminosiliciclastic material delivered in the basin, characterizes the redox environment in bottom water, and makes it possible to reconstruct the rock composition in provenance and its evolution through time. The generally moderate maturity of the fine terrigenous clastic material suggests that a nearly semiarid-semihumid climate dominated in paleodrainage area throughout the Late Vendian. It has been established that reducing environment did not exist in bottom water of the central Shkapovo-Shikhan Basin throughout the Late Vendian. Intermediate rocks prevailed in the paleodrainage area. More silicic rocks could occur only in the early Staropetrovo and late Salikhovo times. Data points of mudstones from the Kairovo and Shkapovo Groups plotted on the Cr-Ni, Co-V, Co/Hf-Ce/Cr, La-Th, and La/Sm-Sc/Th diagrams indicate that both Archean and more mature Paleoproterozoic crustal blocks existed in different proportions in the Late Vendian within source areas. 相似文献
435.
436.
437.
438.
V. A. Marinov S. V. Meledina O. S. Dzyuba O. S. Urman O. V. Yazikova V. A. Luchinina A. G. Zamirailova A. N. Fomin 《Stratigraphy and Geological Correlation》2006,14(4):418-432
Paleontological study of Upper Jurassic and Lower Cretaceous sediments recovered by boreholes in the Agan-Vakh and Nadym-Vengapur interfluves clarified environments of their deposition. As is shown, influx of siliciclastic material to central areas of the West Siberian sea basin varied through time. Taxonomic composition and ecological structure of nektonic and benthic fossil assemblages are analyzed and considered in terms of environmental factors such as hydrodynamics, aeration, temperature, and salinity of seawater. 相似文献
439.
Much of southern and eastern Africa is semi-arid and heavily groundwater dependent. Borehole drilling commenced over a hundred years ago with magnetic and electrical resistivity surveys for borehole siting being introduced from 1936. Formalised training of hydrogeologists led in the 1970s to an almost standard approach to hydrogeological investigation and a period of stability followed, during which some major investigations were carried out. A period of decentralisation and fragmentation has since taken place in many parts of southern and eastern Africa, and groundwater monitoring and management are inadequate in many countries. All but six of the 14 SADC (Southern African Development Community) member states reportedly have an adequate monitoring network in place. However, groundwater demand is increasing and hydrogeologists need to promote the use of appropriate methodologies as an essential part of tackling the severe issues now facing the water sector in the region. 相似文献
440.
N. S. Bortnikov 《Geology of Ore Deposits》2006,48(1):1-22
Data on fluid inclusions and stable isotope compositions (O, H, C, and S) in minerals have been summarized for large-and middle-scale mesothermal gold deposits (Nezhdaninsk, Berezovsk, Kochkar’, Svetlinsk, Darasun, and Maisk), cassiterite-silicate-sulfide deposits of Sikhote Alin (Solnechnoe, Arsen’evsk, and Vysokogorsk), vein silver-base metal deposits in the Southern Verkhoyansk region (Prognoz and Kupol’noe), and epithermal copper-bismuth-silver-base metal deposits of the Karamazar district in Tajikistan (Kanimansur, Tary Ekan, and Zambarak). It is shown that ores precipitated from fluids with salinity varying from brines (up to 60 wt % NaCl equiv) to dilute fluids (1–3 wt % NaCl equiv). As a rule, fluids of different compositions entered the hydrothermal-magmatic system. A fluid mixture of H2O-CO2-NaCl±CH4±N2 predominated in the orogenic (mesothermal) gold-bearing hydrothermal systems, with deposition of the final-stage gold-bearing sulfosalts from aqueous-salt fluid. Brines played a significant role in the formation of cassiterite-silicate-sulfide and vein silver-base metal deposits. The brines often coexisted with a low-density vapor-rich fluid at the ore deposition site. The obtained data suggest a predominant magmatic component in the hydrothermal-magmatic systems, with a significant contribution of meteoric waters. 相似文献