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461.
462.
463.
详细研究了燕山东段地区花岗岩类的侵入时代、产出形式和成因类型 ,指出该区与花岗岩有关的三个金属成矿系列。 相似文献
464.
Data are presented on phosphorus mobility during the weathering of rhyolite–dacite tephra of the modern and ancient eruptions. Distal tephra cannot be considered a phosphorus source, since phosphorous has low mobility during weathering both in subaerial and subaqueous sedimentation conditions. However, volcanic ashes exert a fertilization effect, providing the supply of nutrient elements into the ecosystem of internal basins and coastal zones. 相似文献
465.
Origin of a large breccia-vein system in the Sanerlin uranium deposit, southern China: a reinterpretation 总被引:1,自引:0,他引:1
The early Tertiary Sanerlin uranium deposit is located near the southwestern margin of the Chaling-Yongxing pull-apart basin defined by the Chaling-Yongxing and Chenxian-Linwu sinistral strike-slip faults in southern China. The uranium ores are hosted in 15 breccia-vein bodies, which are separately located in the cores of three secondary anticlines of the Upper Permian Dangchong Formation. Individual breccia-vein bodies are composed of fragments of silicified shale and sandstone from the Dangchong Formation, and quartz veinlets as cements. These fragments, together with quartz veins, form a mosaic texture. Hydrothermal pitchblende is the only commercial uranium mineral, mainly occurring as disseminated grains within quartz veins or coating fragments. Other metallic minerals include molybdenite, pyrite, chalcopyrite, galena, sphalerite, and red microcrystalline hematite. Fluid inclusions in quartz veins have homogenization temperatures ranging from 150 to 280 °C, and calculated salinity values between 5.6 and 13.4 wt% NaCl equivalent. Stable isotope analyses show that the mineralizing fluid was characterized by '18O values of -2.2 to +2.6 and 'DH2O values of -134 to -110. These analytical data demonstrate that hydrothermal fluids were mainly derived from formation waters (brines) of the Chaling-Yongxing basin. Fluid overpressuring was caused by an abnormal geothermal gradient and impermeable shales in the deposit area. The geometry, texture, and structure of the breccia-vein system, along with the fluid pressure estimates, suggest that hydraulic fracturing generated the mineralized breccia-vein system. Pitchblende and associated minerals were deposited when gaseous phases were released abruptly from the ore fluids due to the hydraulic fracturing. 相似文献
466.
Yu. N. Efremov 《Astronomy Reports》2002,46(10):791-804
The nature of stellar complexes with peculiar populations and morphologies is investigated. The existence in the LMC of complexes made up of isolated stars, on the one hand, and consisting exclusively of clusters, on the other hand, could be due to different turbulence patterns in the initial gaseous medium. Arc-shaped stellar complexes are unlikely to be the result of star formation in a gaseous shell swept up by a central source of pressure, and instead probably reflect the shape of a bow shock that develops when a sufficiently dense cloud is subject to dynamical pressure. A peculiar arc-shaped complex in NGC 6946, which contains a young, massive cluster, may be the result of an oblique infall of a high-velocity cloud onto a region of the gaseous disk of the Galaxy with a strong, regular magnetic field; the properties of this complex can be explained as the result of a collision of the resulting shocks. The arc-shaped complexes in the LMC were also probably produced by high-velocity clouds moving obliquely through the more tenuous gas of the LMC disk. A similar complex in NGC 300 may owe its origin to the effect produced on a dense cloud by the shock from an extremely powerful external explosion, whose stellar remnant may have survived as an X-ray source now located along the line of symmetry of the arc of the complex. The rareness of such structures can be explained by the narrow range of conditions under which they can develop. 相似文献
467.
D. V. Bisikalo A. A. Boyarchuk E. Yu. Kilpio O. A. Kuznetsov 《Astronomy Reports》2002,46(12):1022-1029
A new mechanism is proposed to account for transitions between the quiescent and active states of symbiotic stars. A numerical study of the gas dynamics of the flows in the symbiotic star Z And shows that even small variations in the velocity of the wind from the cool giant can abruptly change the flow structure near the hot component. Such changes alter the accretion regime as the wind velocity increases: disk accretion makes a transition to accretion from the flow. Our calculations indicate that the accretion rate increases by a factor of several tens over a short time interval (~0.1 of the orbital period) during the rearrangement of the flow, when the accretion disk is destroyed. 相似文献
468.
O. V. Verkhodanov A. I. Kopylov Yu. N. Pariiskii N. S. Soboleva A. V. Temirova O. P. Zhelenkova 《Astronomy Reports》2002,46(7):531-542
BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m R <23.5m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (~20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8. 相似文献
469.
I. E. Paukov N. K. Moroz Yu. A. Kovalevskaya I. A. Belitsky 《Physics and Chemistry of Minerals》2002,29(4):300-306
The heat capacity of paranatrolite and tetranatrolite with a disordered distribution of Al and Si atoms has been measured
in the temperature range of 6–309 K using the adiabatic calorimetry technique. The composition of the samples is represented
with the formula (Na1.90K0.22Ca0.06)[Al2.24Si2.76O10]·nH2O, where n=3.10 for paranatrolite and n=2.31 for tetranatrolite. For both zeolites, thermodynamic functions (vibrational entropy, enthalpy, and free energy function)
have been calculated. At T=298.15 K, the values of the heat capacity and entropy are 425.1 ± 0.8 and 419.1 ±0.8 J K−1 mol−1 for paranatrolite and 381.0 ± 0.7 and 383.2 ± 0.7 J K−1 mol−1 for tetranatrolite.
Thermodynamic functions for tetranatrolite and paranatrolite with compositions corrected for the amount of extraframework
cations and water molecules have also been calculated. The calculation for tetranatrolite with two water molecules and two
extraframework cations per formula yields: C
p
(298.15)=359.1 J K−1 mol−1, S(298.15) −S(0)=362.8 J K−1 mol−1. Comparing these values with the literature data for the (Al,Si)-ordered natrolite, we can conclude that the order in tetrahedral
atoms does not affect the heat capacity. The analysis of derivatives dC/dT for natrolite, paranatrolite, and tetranatrolite has indicated that the water- cations subsystem within the highly hydrated
zeolite may become unstable at temperatures above 200 K.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
470.
Refined analytical expressions for the frequencies corresponding to the Chandler motion of the pole and the diurnal rotation of the deformable Earth are derived. Numerical estimates of the period and amplitude of the polar oscillations are presented. The trajectory of the Chandler polar motion derived via numerical modeling is in qualitative and quantitative agreement with experimental data from the International Earth Rotation Service (IERS). An evolutionary model describing slow variations in the Earth’s rotation parameters under the action of the dissipative moments of the tidal gravitational forces on time scales considerably longer than the precession period of the Earth’s axis is constructed. The axis of the Earth’s figure tends to approach the angular momentum vector of the proper rotation. 相似文献