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1.
Si K- and L-edge ELNES spectroscopy and multiple-scattering (MS) calculations are used to examine mixed Si coordination compounds
varying in SiVI:SiIV ratio. As in previous studies, the edges are influenced mainly by silicon coordination (tetrahedral vs. octahedral), as supported
by the MS calculations. We demonstrate two methods semi-quantitatively to extract the value of SiVI/(SiVI+SiIV): (1) A linear relationship between the L2,3-L1 splitting and SiVI/(SiVI+SiIV) is observed, (2) a fitting method based on the coaddition of reference tetrahedral and octahedral Si spectra is applied
to both Si K- and L-edge ELNES spectra.
Received: February 10, 1997 / Revised, accepted: May 23, 1997 相似文献
2.
3.
To assess differences between object and pixel-based reservoir modeling techniques, ten realizations of a UK Continental Shelf braided fluvial reservoir were produced using Boolean Simulation (BS) and Sequential Indicator Simulation (SIS). Various sensitivities associated with geological input data as well as with technique-specific modeling parameters were analyzed for both techniques. The resulting realizations from the object-based and pixel-based modeling efforts were assessed by visual inspection and by evaluation of the values and ranges of the single-phase effective permeability tensors, obtained through upscaling. The BS method performed well for the modeling of two types of fluvial channels, yielding well-confined channels, but failed to represent the complex interaction of these with sheetflood and other deposits present in the reservoir. SIS gave less confined channels and had great difficulty in representing the large-scale geometries of one type of channel while maintaining its appropriate proportions. Adding an SIS background to the Boolean channels, as opposed to a Boolean background, resulted in an improved distribution of sheetflood bodies. The permeability results indicated that the SIS method yielded models with much higher horizontal permeability values (20–100%) and lower horizontal anisotropy than the BS versions. By widening the channel distribution and increasing the range of azimuths, however, the BS-produced models gave results approaching the SIS behavior. For this reservoir, we chose to combine the two methods by using object-based channels and a pixel-based heterogeneous background, resulting in moderate permeability and anisotropy levels. 相似文献
4.
Britta Bielefeld 《GeoJournal》1997,42(2-3):329-336
In recent years, attention has increasingly been paid to the question of the stability of the earth's climate. It has been observed that changes in climate are usually related to changes in the earth's surface. On this question, Liedtke writes ‘A change in climate can lead to considerable landscape changes’ (Liedtke 1990, p. 38). There seems to be some form of interaction between climate and the condition of the earth's surface. If solar radiation is taken to be the primary energy source for the earth's climate, the question arises as to how insolation affects the character of the earth's surface, and vice versa, how does the character of the earth's surface affect the insolation which occurs? Reconstructions of the last great Pleistocene glaciation 18,000 years ago show that the form of the earth's surface at that time was considerably different to its present form. In view of the interaction mentioned above between climate and earth surface, does this suggest a difference between the earth's radiation budget 18,000 years ago and that of today? If, as is widely believed, the area of the earth's surface covered by ice 18,000 years ago was approximately three times the current area (Liedtke 1990, p. 42), this presumably would have had at least some influence on the earth's radiation budget. The ice-covered areas may have modified the radiation budget by means of their high reflexivity. In other words, an albedo-related loss of radiation may have occurred. The results of this investigations show, that the global radiation budget at 18,000 B.P was about 7- -10% less than that of today. 相似文献
5.
Britta Planer-Friedrich Corinne Lehr Jörg Matschullat Darrell Kirk Nordstrom 《Geochimica et cosmochimica acta》2006,70(10):2480-2491
Geothermal features in the Yellowstone National Park contain up to several milligram per liter of aqueous arsenic. Part of this arsenic is volatilized and released into the atmosphere. Total volatile arsenic concentrations of 0.5-200 mg/m3 at the surface of the hot springs were found to exceed the previously assumed nanogram per cubic meter range of background concentrations by orders of magnitude. Speciation of the volatile arsenic was performed using solid-phase micro-extraction fibers with analysis by GC-MS. The arsenic species most frequently identified in the samples is (CH3)2AsCl, followed by (CH3)3As, (CH3)2AsSCH3, and CH3AsCl2 in decreasing order of frequency. This report contains the first documented occurrence of chloro- and thioarsines in a natural environment. Toxicity, mobility, and degradation products are unknown. 相似文献
6.
R. Thomas J.D. Webster D. Rhede W. Seifert K. Rickers H.-J. Frster W. Heinrich P. Davidson 《Lithos》2006,91(1-4):137-149
Fractional crystallization of peraluminous F- and H2O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions.
We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters. 相似文献
7.
J.Michael Moldowan Wolfgang K. Seifert Edward Arnold Jon Clardy 《Geochimica et cosmochimica acta》1984,48(8):1651-1661
Two C28H48-pentacyclic triterpanes were isolated from Monterey shale. X-ray crystallography of a crystal containing both compounds proved their structures as 17β,18α,21α(H)-28,30-bisnorhopane and 17β,18α,21β(H)-28,30-bisnorhopane. Several differences are found between 28,30-bisnorhopanes and the regular hopanes. Unlike the regular hopane epimers, for practical purposes the three epimeric 28,30-bisnorhopanes [17α,21β(H)-, 17β,21α(H)-, and 17β,21β(H)-]cannot be distinguished by their mass spectra. Special conditions are needed to separate them by gas chromatography. The diagenetically first-formed epimer is thought to be 17α,21β(H)- because it predominates in immature shales. The order of thermodynamic stability is 17β,2lα(H) < > 17α,21β(H) > 17β,21β(H), and all three epimers are present in petroleum. 25,28,30-Trisnorhopanes can be analyzed in similar fashion and are found to have similar thermodynamic characteristics. The percent of the ring D/E cis epimer of 28,30-bisnorhopane and/or 25,28,30-trisnorhopane is a useful maturation parameter similar to the 20S/20R sterane ratio. Evidence indicates 25-demethylation of 28,30-bisnorhopane to 25,28,30-trisnorhopane during advanced stages of biodegradation. Hence, percent ring cis 25,28,30-trisnorhopane has an application to maturation assessment in heavily biodegraded oils. 相似文献
8.
Oxygen deficient perovskites in the system CaSiO3–CaAlO2.5 and implications for the Earth’s interior
U. W. Bläß F. Langenhorst D. J. Frost F. Seifert 《Physics and Chemistry of Minerals》2007,34(6):363-376
Oxygen deficient perovskites of the system CaSiO3–CaAlO2.5 have been synthesised at high-pressure and -temperature conditions relevant to the Earth’s transition zone in order to investigate
their stabilities in the Earth’s mantle and determine structural properties associated with vacancy incorporation. Two polysomes
of thermodynamically stable defect perovskites with Ca(Al0.4Si0.6)O2.8 and Ca(Al0.5Si0.5)O2.75 stoichiometry have been identified. The ordering of oxygen defects into pseudo-cubic (111) layers results in well-ordered
ten- or eightfold superstructures, respectively. At all other compositions examined, a metastable formation of perovskites
has been observed instead, which are assumed to grow initially disordered. These are now characterised by tiny domains, formed
due to subsequent ordering of vacancies along various pseudo-cubic {111} layers. Both ordered defect perovskites show a large
P–T stability field ranging from about 9–18 GPa and 4–12 GPa, respectively. Microstructural TEM analyses revealed the presence
of growth and ferroelastic twins, which indicate a phase transition from rhombohedral to monoclinic symmetry during quenching.
Electron energy loss spectroscopy of Si and Al K edges point at the presence of tetrahedral, octahedral and maybe some pentacoordinated silicon, whereas aluminium is predominantly
octahedrally coordinated with minor fractions in lower coordination. Observed properties are interpreted in terms of a new
structural model, explaining the observed phase transition and formation of different twin laws as well as giving reasons
for the development of such large superstructures. With respect to phase relations of the transition zone, the potential occurrence
of such defect perovskites in the Earth’s interior is discussed. 相似文献
9.
10.
Nikolay V. Tsukanov Wolfgang Kramer Sergey G. Skolotnev Marina V. Luchitskaya Wolfgang Seifert 《Island Arc》2007,16(3):431-456
Abstract The geological, geochemical and mineralogical data of dismembered ophiolites of various ages and genesis occurring in accretionary piles of the Eastern Peninsulas of Kamchatka enables us to discriminate three ophiolite complexes: (i) Aptian–Cenomanian complex: a fragment of ancient oceanic crust, composed of tholeiite basalts, pelagic sediments, and gabbroic rocks, presently occurring in a single tectonic slices (Afrika complex) and in olistoplaques in Pikezh complex of the Kamchatsky Mys Peninsula and probably in the mélange of the Kronotsky Peninsula; (ii) Upper Cretaceous complex, composed of highly depleted peridotite, gabbro and plagiogranite, associated with island arc tholeiite, boninite, and high-alumina tholeiitic basalt of supra-subduction origin; and (iii) Paleocene–Early Eocene complex of intra-island arc or back-arc origin, composed of gabbros, dolerites (sheeted dykes) and basalts produced from oceanic tholeiite melts, and back-arc basin-like dolerites. Formation of the various ophiolite complexes is related to the Kronotskaya intra-oceanic volcanic arc evolution. The first ophiolite complex is a fragment of ancient Aptian–Cenomanian oceanic crust on which the Kronotskaya arc originated. Ophiolites of the supra-subduction zone affinity were formed as a result of repeated partial melting of peridotites in the mantle wedge up to the subduction zone. This is accompanied by production of tholeiite basalts and boninites in the Kamchatsky Mys segment and plagioclase-bearing tholeiites in the Kronotsky segment of the Kronotskaya paleoarc. The ophiolite complex with intra-arc and mid-oceanic ridge basalt geochemical characteristics was formed in an extension regime during the last stage of Kronotskaya volcanic arc evolution. 相似文献