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991.
Whole-rock and sulfide lead-isotope data from the hydrothermal JADE field in the Okinawa back-arc trough 总被引:7,自引:0,他引:7
The mineralization of the active hydrothermal JADE field resembles in many aspects the Kuroko-type mineralization. The JADE
field is located in a back-arc graben and is associated with a bimodal volcanism. Lead isotope data from igneous rocks, sediments,
and ores further emphasize the similarities with the Kuroko ores and suggest that both sediments and volcanic rocks contributed
comparable amounts of lead to the deposit. When compared to the sediments, a much larger volume of volcanic rocks must have
contributed lead to the deposit, because of the considerably lower lead concentration of volcanic rocks. In contrast to the
crustal type lead of the JADE field and the Kuroko-type sulfide deposits the lead isotope signatures of VMS-type deposits
at mid-ocean ridges is distinctly different. In the absence of a sedimentary cover it reflects the composition of the mantle
source, whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even
be completely dominated by the latter.
Received: 5 October 1995 / Accepted: 10 May 1996 相似文献
992.
Summary A system of 8 seismically active fracture zones was delineated on the basis of the distribution of earthquake foci in the continental lithosphere of Ecuador. The position and width of the outcrop, thickness, dip and maximum depth of the individual fracture zones were estimated and correlated with surface geological and tectonic phenomena, volcanism and hydrothermal manifestations. The existence and strike of the fracture zones was independently confirmed by the occurrence of historical disastrous earthquakes.
Visiting professors at Instituto Geofísico and Facultad de Geología, Minas y Petróleos, Escuela Politécnica Nacional, Quito (Ecuador). 相似文献
uma 8 uu amu a a aa a auu an¶rt;u a mu muma um a¶rt;a. u n¶rt; nu u uua a nmu, mua, u auaaua m¶rt; a . mau mu auu n¶rt;m¶rt;am a¶rt;u umuu aum mu u nmau nmu, mmu, au uu¶rt;mau nuu.
Visiting professors at Instituto Geofísico and Facultad de Geología, Minas y Petróleos, Escuela Politécnica Nacional, Quito (Ecuador). 相似文献
993.
Morphological studies of the females of Calanus finmarchicus, C. glacialis, and C. hyperboreus were performed for specimens sampled in different areas of the Greenland, Barents, Kara, and Laptev seas. Intraspecific variability was found for the ratio of the specimens characterized by different types of setae patterns on the endopodites of C. glacialis and C. finmarchicus. The variability of this parameter did not relate to the environmental peculiarities of the sampling sites and did not depend on the temperature regime. We assume that such differences may be the result of the hybridization of C. glacialis and C. finmarchicus due to the similarity of their reproduction systems and the overlapping of the body size ranges. 相似文献
994.
995.
— Seismic responses of weathered and non-weathered ridge models were simulated to study the ridge effects on the ground motion characteristics. The range of ridge slope from 19.98° to 45° was considered to produce a possible set of generalized results. 2.5-D modeling based on parsimonious staggered grid approximation of elastodynamic wave equations was adopted in simulations. Computed results reveal an increase of amplitude of incoming waves with both elevation and the slope of the ridge. Further, the characteristics of surface waves are highly ridge slope dependent. The analysis of responses of weathered and non-weathered ridge models reveals that ridge has caused a strong generation of surface waves near its top. The surface waves are not dominating on the top of the ridge but at some lower elevation. The increase of weathering of ridge further intensified the ridge effect. Analysis in frequency domain, based on spectral ratio method, does not indicate any pattern in the spectral amplification factor and is very much sensitive to slope, source focal mechanism and location. However, on an average there is a continuous decrease of amplification with slope in the vertical component and increase in the transverse component, and it is increasing in the radial component up to slope =38.0° and thereafter decreasing. 相似文献
996.
997.
The results of studying the forms of aluminum occurrence in water bodies of Ukraine with different water regime and physical and chemical characteristics are discussed. The quantitative relationships between suspended and dissolved forms of aluminum, the relationship between suspended aluminum and the mass of suspended matter, and the role of complexation in Al(III) migration are considered. The distribution of Al(III) among complex compounds with dissolved organic substances with different chemical nature and molecular mass (anionic fraction) is analyzed. Humic substances are shown to play the major role in Al(III) binding. 相似文献
998.
Problematic arumberia-type structures are widespread in Upper Proterozoic sedimentary rocks deposited in depositional environments subject to periodic desiccation and fluctuating salinity. Here we report two new occurrences of arumberia-type structures in the Krutikha Member of the Upper Vendian Chernyi Kamen Formation on the western slope of the Central Urals (Us??va River) and the Zigan Formation of the Asha Group in the South Urals (new road Sterlitamak-Beloretsk). The results of the study of these structures significantly expand paleontological characteristics of the Upper Vendian non-marine rocks and allow us to re-examine the paleontological importance of the hastily forgotten group of arumberia-type organisms. We distinguished six varieties of arumberia-type structures that for the sake of convenience were given formal Latin names in binominal nomenclature although they are not biological species. Two species??Arumberia banski and A. vindhyanensis??were erected by previous researchers, whereas the A. beckeri, A. ollii, A. usvaensis, and A. multykensis varieties are recognized for the first time. Despite similarity to erosional structures on the bottom of turbidite beds, erosion does not explain the genesis of the entire spectrum of arumberia-type structures including those preserved on ripple marks, with evidence of soft-body deformation, or with ribbon and filamentous fabric replaced by clay minerals. The diversity of arumberia could be only a manifestation of living systems. The species of Arumberia are distinguished by their different biostratinomy, the distance between the main structural units, the preservation of the main structural units, and the presence of additional structures between the main structural units. Most likely, the diversity of arumberia reflects not only taphonomic, but also ontogenetic and phenotypic variation. The level of morphological complexity and biostratinomic features of arumberia apparently exceed the organization of microbial mats and represent a non-actualistic type of microbial communities. The occurrence in extremely shallow-water depositional setting suggests that arumberia had evolved an adaption to periodic desiccation and that arumberia-type organisms, along with microbial mats, had been an important factor of sediment biostabilization in the Late Vendian non-marine environments. 相似文献
999.
E. A. Shmonova Al. V. Tevelev Ark. V. Tevelev 《Moscow University Geology Bulletin》2013,68(6):345-355
The Kugarchi folded complex is located on the western slope of the Southern Urals; it is a region of complex disharmonic folding in the Lower Carboniferous limestones. We revealed and studied two systems of mineral veins and accompanying veinlets in limestones. The microstructural analysis was used to recognize several deformation stages and orientations of the principal strain directions. This folded complex is interpreted to have formed under conditions close to uniaxial compression accompanied by a progressive change in the extensional strain direction from vertical to horizontal. 相似文献
1000.
Acceleration of iron ions by a spherical shock wave moving through non-homogeneous solar corona is considered. The energy dependence of the mean charge of iron,
Fe(E), is determined by the characteristic acceleration time, T
a, trapping time, T
tr, and time for charge changes, T
q. The latter varies along with plasma number density during the propagation of the shock wave in the corona. Our calculations have demonstrated that adiabatic energy changes, Coulomb losses and shock broadening do not sufficiently influence the dependence
Fe(E). According to our estimations, the photoionizing processes can scarcely affect the ionic states of accelerated iron, except probably for the most powerful X10 class events. 相似文献