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991.
I. Yu. Melekestseva V. A. Kotlyarov P. V. Khvorov V. N. Ivanov V. E. Beltenev I. G. Dobretsova 《Geology of Ore Deposits》2010,52(8):800-810
The porous fine-grained to microcrystalline copper-zinc ore of the Semenov-2 hydrothermal field, a site in the Semenov hydrothermal
cluster discovered in 2007 (13°31′N, MAR), is anomalously enriched in Au (22–188 ppm) and Ag (127–1787 ppm). Chalcopyrite,
isocubanite, würtzite, and opal are major minerals; sphalerite, marcasite, pyrite, and covellite are auxiliary; and galena,
pyrrhotite, native gold, silver telluride, barite, and aragonite are sporadic. Gold containing 0.31 to 23.07 wt % Ag occurs
as up to 9-μm-sized subhedral, dendritelike, and elongated grains mostly hosted in opal and less frequently in sphalerite
and in pores within isocubanite-chalcopyrite aggregate. An elongated grain (2 × 4 μm in size) of the Ag-Te phase was found
in a pore. So far only basalts have been dredged from the Semenov-2 field, but anomalous gold and silver concentrations suggest
the influence of ultramafic rocks; the latter were found 1.5 km westward, in the Semenov-1 hydrothermal field. Mineral assemblage
and morphology of gold particles indicate its primary origin in contrast to the hydrothermal fields hosted in basalts, where
gold is a product of remobilization. Zonal gold grains, found on oceanic floor for the first time, are characterized by low
Ag content in the cores and high Ag content in the outer rims, reflecting variation in formation conditions. 相似文献
992.
993.
M. A. Akhmet’ev N. I. Zaporozhets A. I. Iakovleva G. N. Aleksandrova V. N. Beniamovsky T. V. Oreshkina Z. N. Gnibidenko Zh. A. Dolya 《Stratigraphy and Geological Correlation》2010,18(6):635-659
The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene
revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations
between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West
Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages
characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the
Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related
to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean. 相似文献
994.
In recent years, spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis. In the present study, commercially available finite difference numerical code FLAC 5.0 is used for modeling the permeability parameter as spatially correlated log-normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied. Considering the case of a 5.0 m high cohesive–frictional soil slope of 30°, a range of coefficients of variation (CoV%) from 60 to 90% in the permeability values, and taking different values of correlation distance in the range of 0.5–15 m, parametric studies, using Monte Carlo simulations, are performed to study the following three aspects, i.e., (i) effect of stochastic soil permeability on the statistics of seepage flow in comparison to the analytic (Dupuit′s) solution available for the uniformly constant permeability property; (ii) strain and deformation pattern, and (iii) stability of the given slope assessed in terms of factor of safety (FS). The results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties. 相似文献
995.
A.E. Kontorovich A.N. Fomin V.O. Krasavchikov A.V. Istomin 《Russian Geology and Geophysics》2009,50(11):917-929
Thermal maturation for the top and base of the Jurassic in the West Siberian megabasin was modeled on the basis of the vitrinite reflectance (Rvt0) data using mathematical modeling and computer simulations. The values of thermal maturation are found to vary within substages PC3-MC32 for the top (or being equivalent to PC3-MC12 on the periphery and southern part of the basin, or to MC2-MC32 in the north) and PC3-AC3 for the base of the Jurassic (or being equivalent to PC3-MC2 on the periphery and southern part of the basin or MC31-AC3 in the north). Thermal maturity levels of the Jurassic in West Siberia are controlled by depths of burial and peak temperatures which the source rocks were subjected to during this period. The situation is further complicated by high heat flows superimposed on the regional background, which are observed in deep fault zones and in the proximity of numerous igneous bodies. 相似文献
996.
Ajith G. Nair D.S. Suresh Babu K.T. Damodaran R. Shankar C.N. Prabhu 《Journal of Asian Earth Sciences》2009,34(2):115-122
The magnetic fractions of ilmenite from the beach placer deposit of Chavara, southwest India have been studied for mineralogical and chemical composition to assess the range of their physical and chemical variations with weathering. Chavara deposit represents a highly weathered and relatively homogenous concentration. Significant variation in composition has been documented with alteration. The most magnetic of the fractions of ilmenite, separated at 0.15 Å, and with a susceptibility of 3.2 × 10?6 m3 kg?1, indicates the presence of haematite–ilmenite intergrowth. An iron-poor, titanium-rich component of the ilmenite ore has been identified from among the magnetic fractions of the Chavara ilmenite albeit with an undesirably high Nb2O5 (0.28%), Cr2O3 (0.23%) and Th (149 ppm) contents. The ilmenite from Chavara is compared with that from the nearby Manavalakurichi deposit of similar geological setting and provenance. The lower ferrous iron oxide (2.32–14.22%) and higher TiO2 (56.31–66.45%) contents highlight the advanced state of alteration of Chavara. This is also evidenced by the relatively higher Fe3+/Fe2+ ratio compared to Manavalakurichi ilmenite. In fact, the ilmenite has significantly been converted to pseudorutile/leucoxene. 相似文献
997.
N. Brice Orange Hakeem M. Oluseyi David L. Chesny Maulik Patel Katie Hesterly Lauren Preuss Chantale Neira Niescja E. Turner 《Solar physics》2014,289(5):1557-1584
Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets. 相似文献
998.
The field equations of the New General Relativity NGR, constructed by Hayashi and Shirafuji (1979), have been applied to two geometric structures, given by Robertson (1932), in the domain of cosmology. In the first application a family of models, involving two of the parameters characterizing the field equations of the NGR, is obtained. In the second application the models obtained are found to involve one parameter only. The cosmological parameters in both applications are calculated and some cosmological problems are discussed in comparison with the corresponding results of other field theories . 相似文献
999.
E. V. Ruban G. A. Alekseeva A. A. Arkharov E. I. Hagen-Thorn V. D. Galkin I. N. Nikanorova V. V. Novikov V. P. Pakhomov T. Yu. Puzakova 《Astronomy Letters》2006,32(9):604-607
We present the results of our visual and near-infrared spectrophotometric observations for 77 variable stars obtained during 1971–1991 in Chile, Armenia, and Bolivia. The quasi-monochromatic, extraatmospheric fluxes from the stars are given in absolute energy units (W m?2 m?1) at all wavelengths of the spectral range at 2.5-nm intervals. 相似文献
1000.
We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic
changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations
(few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much
less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification
in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that
weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears
and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread
away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests
that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament
channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally
explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric
flux concentrations evolve. 相似文献