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1.
Multiple-expert hazard/risk assessments have considerable precedent, particularly in the Yucca Mountain site characterization
studies. A certain amount of expert knowledge is needed to interpret the geological data used in a probabilistic data analysis.
As may be the situation in science, experts disagree on crucial points. Consequently, lack of consensus in some studies is
a sure outcome. In this paper, we present a Bayesian approach to statistical modeling in volcanic hazard assessment for the
Yucca Mountain site. Specifically, we show that the expert opinion on the site disruption parameterp is incorporated into the prior distribution, π(p), based on geological information that is available. Moreover, π(p) can
combine all available geological information motivated by conflicting but realistic arguments (e.g., simulation, cluster analysis,
structural control, ..., etc.). The incorporated uncertainties about the probability of repository disruptionp
eventually will be averaged out by taking the expectation over π(p). We use the following priors in the analysis: (1) priors
selected for mathematical convenience: Beta (r,s) for (r,s) = (2, 2), (3, 3), (5, 5), (2, 1),(2, 8), (8, 2), and (1, 1);and (2) three priors motivated by expert knowledge. Sensitivity analysis is performed for each prior distribution. Our study
concludes that estimated values of hazard based on the priors selected for mathematical simplicity are uniformly higher than
those obtained based on the priors motivated by expert knowledge. And, the model using the prior, Beta (8, 2), yields the
highest hazard (=2.97 × 10-2
. The minimum hazard is produced by the “three-expert prior” (i.e., values of
p
are equally likely for
p = 10-3, 10-2,and 10-1
. The estimate of the hazard is 1.39 × 10-3, which is only about one order of magnitude smaller than the maximum value. The term, “hazard, ” is defined as the probability
of at least one disruption of a repository at the Yucca Mountain site by basaltic volcanism for the next 10,000 years. 相似文献
2.
David A. Jay Philip M. Orton Thomas Chisholm Douglas J. Wilson Annika M. V. Fain 《Estuaries and Coasts》2007,30(6):1106-1125
Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities
in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly
advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects
of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability
of scaling parameters and the response of ETM phenomena to a range of river flow (U
r
) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current
amplitude (UT), represented by low values of the Supply number Sr.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to
deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly,
scaling variables and data are combined to express ETM properties in terms of the friction velocity (U*),U
r
, andU
T
, allowing a considerable simplification of the parameters used to describe ETM. 相似文献
3.
QITI GUO 《Journal of Metamorphic Geology》1984,2(4):267-295
Multisystems of n+k (k > 3) phases are very complicated and knowledge of them has suffered as a result. The successful solution of the topological relationships in n+ 3 phase multisystems by Zen (1966, 1967) and Zen & Roseboom (1972) has aroused much interest regarding what will happen in a multisystem of more than n+ 3 phases. Since 1979, some important research results on this topic have been published. These results have expounded the substantial rules governing the appearance of phase relations in phase diagrams of n - k (k > 3) phase multisystems. The most significant conclusions include: (1) It is impossible to incorporate all the possible phase relations in an n+k (k > 3) phase multisystem in a single closed net. Therefore, it is no longer enough to use only a single closed net to depict the topological relations involved in these types of multisystems. Instead, one or more groups of closed nets, namely the complete system(s) of closed nets are necessary for this purpose. (2) A principle called the Combination Principle has been proposed and proved. It states: Any closed net of one n+k (k > 3) phase multisystem must be a combination of two or more distinct n+ 3 order submultisystem closed nets belonging to the given n+k phase multisystem, if it is not one of the n+ 3 order submultisystem closed nets itself. The combination principle provides both a theoretical basis and a practical method for the construction of closed nets and, hence, for the derivation of the real phase diagrams for any n+k (k > 3) phase multisystem. (3) A theorem on divariant-assemblage-characteristic-stability-polygons is also important to our understanding of the n+k (k± 3) phase multisystem closed nets. This theorem can be stated as follows: A divariant assemblage of an n+k (k± 3) phase multisystem will be stable in an l-polygon lacking diagonals in an appropriate set of closed-net-diagrams, and this l-polygon may be at least a triangle, and at most a k-polygon. In addition, the closed-net-diagrams of unary and binary n+ 4 phase multisystems derived respectively by Guo (1980b, 1980c, 1981a) and by Roseboom & Zen (1982) have also been summarized. The combination principle is applied to a practical petrological problem in this paper, dealing with 7 phases in the system FeO-Fe2O3-SiO2. 相似文献
4.
The estimation of snow hazard and load faces the small sample size effect because of the short snow depth record at a station. To reduce such an effect, we propose to estimate the return period value of the annual maximum ground snow depth S, sT, for Canada sites by applying the regional frequency analysis (RFA) and the region of influence approach (ROIA). The use of RFA and ROIA to map Canadian snow hazard is new. The comparison of their performance for snow hazard mapping has not been explored in the literature. We also consider the at-site analysis approach (ASA) for estimating sT by using three often used probability distributions for S. A comparison of the estimated sT by using the three approaches (ASA, RFA, ROIA) indicates that there is considerable scatter between the estimated sT value although the identified overall spatial trends of sT are similar. It is shown that the two-parameter lognormal distribution for S at most Canadian sites, based on the at-site analysis, is preferred; this differs from the Gumbel distribution used to develop the design snow load in Canadian structural design code. The new findings indicate that it is valuable to consider the lognormal distribution for developing design snow load for Canadian sites.
相似文献5.
The heat balance for crystal fractionation and assimilation processes is the enthalpy difference between the initial and final states of a system. To order the calculations, the process is viewed as one of assimilation; the heat change for a crystallization process is obtained by changing the signs of the pertinent heat effects. The initial state is a mineral assemblage at T
s
and P and an initial magma at T
m and P. The final state is a magma at T
m
and P.The net heat change results from: (a) Unmixing of solid solutions, (b) Heating (cooling) each component to its fusion temperature, (c) Fusion of each component, (d) Cooling (heating) of each fused component to the magma temperature, (e) Mixing of each fused component in succession with the melt.The heat required to form a basaltic melt from its equilibrium mineral assemblage is approximately twice that required for a granitic melt. A zero heat balance, with the heat of crystallization from phases with which the magma is saturated supplying the energy for assimilation, necessitates that the mass crystallized be approximately twice that assimilated. The heat effects attendant on release of H2O from silicic melts depends on the state of the H2O in the external environment; a low fugacity could cause the magma to cool.The uncertainties in the calculations are estimated at ±10%. 相似文献
6.
The analysis of the extended energy-loss fine structure (EXELFS) of the Si K-edge for sixfold-coordinated Si in synthetic stishovite and fourfold-coordinated Si in natural α-quartz is reported by using
electron energy-loss spectroscopy (EELS) in combination with transmission electron microscopy (TEM). The stishovite Si K-edge EXELFS spectra were measured as a time-dependent series to document irradiation-induced amorphization. The amorphization
was also investigated through the change in Si K- and O K-edge energy-loss near edge structure (ELNES). For α-quartz, in contrast to stishovite, electron irradiation-induced vitrification, verified by selected area electron diffraction (SAED), produced no detectable changes of the EXELFS. The Si K-edge EXELFS were analysed with the classical extended X-ray absorption fine structure (EXAFS) treatment and compared to ab initio curve-waved multiple-scattering (MS) calculations of EXAFS spectra for stishovite and α-quartz. Highly accurate information
on the local atomic environment of the silicon atoms during the irradiation-induced amorphization of stishovite is obtained
from the EXELFS structure parameters (Si−O bond distances, coordination numbers and Debye-Waller factors). The mean Si−O bond
distance R and mean Si coordination number N changes from R=0.1775 nm and N=6 for stishovite through a disordered intermediate state (R≈0.172 nm and N≈5) to R≈0.167 nm and N≈4.5 for a nearly amorphous state similar to α-quartz (R=0.1609 nm and N=4). During the amorphization process, the Debye-Waller factor (DWF) passes through a maximum value of as it changes from for sixfold to for fourfold coordination of Si. This increase in Debye-Waller factor indicates an increase in mean-square relative displacement
(MSRD) between the central silicon atom and its oxygen neighbours that is consistent with the presence of an intermediate
structural state with fivefold coordination of Si. The distribution of coordination states can be estimated by modelling the
amorphization as a decay process. Using the EXELFS data for amorphization, a new method is developed to derive the relative
amounts of Si coordinations in high-pressure minerals with mixed coordination. For the radiation-induced amorphization process
of stishovite the formation of a transitory structure with Si largely in fivefold coordination is deduced.
Received: 18 December 1996 / Revised, accepted: 20 June 1997 相似文献
7.
Microfracturing of rock is a complicated damage evolution process. Inaccurate prediction of micro-fracturing behaviours suggests a need for the development of a better modelling method. Analysis of acoustic emission (AE) measurements in double-torsion tests indicates that micro-fracturing behaviours during the loading stage have fractal time structures. This fractal behaviour can be described by C(t) ∝ tD, where D is the correlation exponent, t is the time and C(t) is the correlation integral. Furthermore, by utilizing measured AE data, a new method has been developed to model the AE behaviours of micro-fracturing in rock, in air, and following soaking in water and in a chemical solution of DTAB. The neutral models NN (10,21,2) and NN (10,20,2) were found to describe reasonably well the AE behaviours of micro-fracturing in rock under air and DTAB conditions, and water conditions, respectively. The cumulative AE events and the cumulative AE counts predicted by the neural models agreed well with those measured in experiments. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
8.
The mechanisms that govern porphyroblast crystallization are investigated by comparing quantitative textural data with predictions from different crystallization models. Such numerical models use kinetic formulations of the main crystallization mechanism to predict textural characteristics, such as grain size distributions. In turn, data on porphyroblast textures for natural samples are used to infer which mechanism dominated during their formation. Whereas previous models assume that the rate‐limiting step for a porphyroblast producing reaction is either transport or growth, the model advanced in this study considers the production of nutrients for porphyroblasts as a potentially rate‐limiting factor. This production reflects the breakdown of (metastable) reactants, which at a specific pressure (P) and temperature (T) depends on the bulk composition of the sample. The production of nutrients that potentially contribute to the formation of porphyroblasts is computed based on thermodynamic models. The conceptual model assumes that these nutrients feed into some intergranular medium, and products form by nutrient consumption from that medium, with rates depending on reaction affinity. For any sequence of P–T conditions along a P–T–t path, the numerical model first computes an effective supersaturation (σeff) of the product phase(s), then an effective nucleation rate (J), and finally the amount of (porphyroblast) growth. As a result, the model is useful in investigating how the textural characteristics of a sample (of given bulk composition) depend on the P–T–t path followed during porphyroblast crystallization. The numerical model is tested and validated by comparing simulation results with quantitative textural data for garnet porphyroblasts measured in samples from the Swiss Central Alps. 相似文献
9.
Chen-Chang Lee Cheng-Haw Lee Hsin-Fu Yeh Hung-I Lin 《Environmental Earth Sciences》2011,63(6):1199-1211
Spatial fracture intensity (P
32, fracture area by volume) is an important characteristic of a jointed rock mass. Although it can hardly ever be measured,
P
32 can be modeled based on available geological information such as spatial data of the fracture network. Flow in a mass composed
of low-permeability hard rock is controlled by joints and fractures. In this article, models were developed from a geological
data set of fractured andesite in LanYu Island (Taiwan) where a site is investigated for possible disposal of low-level and
intermediate-level radionuclide waste. Three different types of conceptual models of spatial fracture intensity distribution
were generated, an Enhanced Baecher’s model (EBM), a Levy–Lee Fractal model (LLFM) and a Nearest Neighborhood model (NNM).
Modeling was conducted on a 10 × 10 × 10 m synthetic fractured block. Simulated flow was forced by a 1% hydraulic gradient
between two vertical x–z faces of the cube (from North to South) with other boundaries set to no-flow conditions. Resulting flow vectors are very
sensitive to spatial fracture intensity (P
32). Flow velocity increases with higher fracture intensity (P
32). R-squared values of regression analysis for the variables velocity (V/V
max) and fracture intensity (P
32) are 0.293, 0.353, and 0.408 in linear fit and 0.028, 0.08, and 0.084 in power fit. Higher R
2 values are positively linked with structural features but the relation between velocity and fracture intensity is non-linear.
Possible flow channels are identified by stream-traces in the Levy–LeeFractal model. 相似文献
10.
During experiments with digital stations in the period 1985–1987, twenty five earthquakes with magnitudes m
b
in the range 2.9 to 4.8 and epicentres located within the area 36°–42.3° (N) and 4.5°–13.6° (W) were recorded at Montemor (MOE) and Montachique (MTH). The three-component recordings were obtained by Geotech S13 instruments with 1 second period. A preliminary analysis of the recordings consisted in the determination of amplitudes and spectral contents of P and S waves, and led to the following observations: (1) The attenuation of waves is expressed by the equation V = exp(C
2).R
C
1. exp(C
3.M), where V stands for acceleration, velocity or displacement; M-magnitude; R-focal distance; C
1, C
2 and C
3 are constants to be obtained by least square fitting. The application of this equation led to C
1 of the order 1.7 for displacement, 1.8 for velocity and 2.0 for acceleration, with an average mean square error 0.8. (2) The ratios L/T (longitudinal/transversal amplitudes), for velocity and displacement, showed a tendency to reduce with increasing focal distance, being 2 for short distances (<50 km) and 1 for long distances (400 km). (3) The ratios S/P (S-wave/P-wave amplitudes), although with a large dispersion, showed a slight tendency for increasing with focal distance. (4) The predominant frequencies also showed a slight tendency to decrease with increasing focal distance and with magnitude. (5) The dependence of C
1 with frequency (3 to 12 Hz) is well behaved from 0.95 to 1.75 (for the velocity trace). 相似文献
11.
The major stochastic elements in the fission track dating method are (i) the number of spontaneous fission tracks (N
s
) in a sample, and (ii) the number of induced tracks (N
i
) observed when the sample is irradiated with neutrons. The foundations for the statistical uncertainty in these measures are of two kinds: (i) there exists a definite probability of uranium fission by means of natural decay and by neutron activation, and (ii) within a crystal the distribution of uranium is not uniform and perhaps follows something like a Poisson law. In any event, the natural logarithm of the ratio (N
s
/N
i
) is proportional to age. A plausible statistical fission track dating model should, therefore, start by considering the joint distribution of N
s
and N
i
. In this paper a joint bivariate normal model is described which allows the rigorous definition of the probability distributions of Ns, N
i
, the ratio N
s
/N
i
, and age itself. A general computer program (FISSION) has been developed to perform all the necessary computations. By accounting for the correlation between N
s
and N
i
, the statistical model here ascribes smaller standard errors to N
s
/N
i
(and therefore age) than do previous methods. In addition, the error associated with neutron flux is a significant factor in the age relationships and has been incorporated into the model. 相似文献
12.
13.
A three-dimensional kinematic limit analysis approach based on the radial point interpolation method (RPIM) has been used to compute collapse loads for rectangular foundations. The analysis is based on the Mohr-Coulomb yield criterion and the associated flow rule. It is understood that the internal plastic power dissipation function and flow rule constraints can be expressed entirely in terms of plastic strain rates without involving stresses. The optimization problem has been solved on basis of the semidefinite programming (SDP) by using highly efficient primal-dual interior point solver MOSEK in MATLAB. The results have been presented in terms of the variation of the shape factors with changes in the aspect ratio (L/B) of the footing for different values of soil internal friction angle (ϕ). Computations have revealed that the shape factors, sc and sq, due to effects of cohesion and surcharge increase continuously with (1) decrease in L/B and (2) increase in ϕ. On the other hand, the shape factor sγ, due to the effect of soil unit weight, increases very marginally with an increase in L/B up to (1) ϕ = 25° for a rough footing and (2) ϕ = 35° for a smooth footing. Thereafter, for greater values of ϕ, the variation of sγ with L/B has been found to be quite similar to that of the factors sc and sq. The variations of (1) nodal velocity patterns, (2) plastic power dissipation, and (3) maximum plastic shear strain rates have also been examined to interpret the associated failure mechanism. 相似文献
14.
The Shear Behavior of Bedding Planes of Weakness Between Two Different Rock Types with High Strength Difference 总被引：4，自引：2，他引：2
A. H. Ghazvinian A. Taghichian Mahmoud Hashemi S. A. Mar’ashi 《Rock Mechanics and Rock Engineering》2010,43(1):69-87
In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types
with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities
are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster
mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities
with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths
by showing that Barton’s empirical criterion is not appropriate for the former discontinuities. After that, some correlation
equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters,
and the normal stress range of Barton’s strength criterion is also modified to be used for such discontinuities. Then, a new
empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log10(JCS/σ
n) as i
0(σ
c/σ
n)a/[b + (σ
c/σ
n)
a
] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal
stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i
0, a, and b. The reason for separation of i
0 from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients
(a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c
a
. Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation
angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data. 相似文献
15.
E -an Zen 《Contributions to Mineralogy and Petrology》1973,39(1):65-80
Reversed univariant hydrothermal phase-equilibrium reactions, in which a redox reaction occurs and is controlled by oxygen buffers, can be used to extract thermochemical data on minerals. The dominant gaseous species present, even for relatively oxidizing buffers such as the QFM buffer, are H2O and H2; the main problem is to calculate the chemical potentials of these components in a binary mixture. The mixing of these two species in the gas phase was assumed by Eugster and Wones (1962) to be ideal; this assumption allows calculation of the chemical potentials of the two components in a binary gas mixture, using data in the literature. A simple-mixture model of nonideal mixing, such as that proposed by Shaw (1967), can also be combined with the equations of state for oxygen buffers to permit derivation of the chemical potentials of the two components. The two mixing models yield closely comparable results for the more oxidizing buffers such as the QFM buffer. For reducing buffers such as IQF, the nonideal-mixing correction can be significant and the Shaw model is better.The procedure of calculation of mineralogical thermochemical data, in reactions where hydrogen and H2O simultaneously appear, is applied to the experimental data on annite, given by Wones et al. (1971), and on almandine, given by Hsu (1968). For annite the results are: Standard entropy of formation from the elements, S
f
0
(298, 1)=–283.35±2.2 gb/gf, S
0 (298, 1) =+92.5 gb/gf. G
f
0
(298, 1)=–1148.2±6 kcal, and H
f
0
(298, 1)=–1232.7±7 kcal. For almandine, the calculation takes into account the mutual solution of FeAl2O4 (Hc) in magnetite and of Fe3O4 (Mt) in hercynite and the temperature dependence of this solid solution, as given by Turnock and Eugster (1962); the calculations assume a regular-solution model for this binary spinel system. The standard entropy of formation of almandine, S
f,A
0
(298, 1) is –272.33±3 gb/gf. The third law entropy, S
0 (298, 1) is +68.3±3 gb/gf, a value much less than the oxide-sum estimate but the deviation is nearly the same as that of grossularite, referring to a comparable set of oxide standard states. The Gibbs free energy G
f,A
0
(298, 1) is –1192.36±4 kcal, and the enthalpy H
f,A
0
(298, 1) is –1273.56±5 kcal.Publication authorized by the Director, U. S. Geological Survey. 相似文献
16.
C. M. Holl J. R. Smyth M. H. Manghnani G. M. Amulele M. Sekar D. J. Frost V. B. Prakapenka G. Shen 《Physics and Chemistry of Minerals》2006,33(3):192-199
Fe-bearing dense hydrous magnesium silicate Phase A, Mg6.85Fe0.14Si2.00O8(OH)6 has been studied by single-crystal X-ray diffraction at ambient conditions and by high-pressure powder diffraction using synchrotron radiation to 33 GPa. Unit cell parameters at room temperature and pressure from single crystal diffraction are a=7.8678 (4) Å, c=9.5771 (5) Å, and V=513.43 (4) Å3. Fitting of the P–V data to a third-order Birch-Murnaghan isothermal equation of state yields V
0=512.3 (3) Å3, K
T,0=102.9 (28) GPa and K′=6.4 (3). Compression is strongly anisotropic with the a-axes, which lie in the plane of the distorted close-packed layers, approximately 26% more compressible than the c-axis, which is normal to the plane. Structure refinement from single-crystal X-ray intensity data reveals expansion of the structure with Fe substitution, mainly by expansion of M-site octahedra. The short Si2–O6 distance becomes nearly 1% shorter with ~2% Fe substitution for Mg, possibly providing additional rigidity in the c-direction over the Mg end member. K
T obtained for the Fe-bearing sample is ~5.5% greater than reported previously for Fe-free Phase A, despite the larger unit cell volume. This study represents a direct comparison of structure and K
T–ρ relations between two compositions of a F-free dense hydrous magnesium silicate (DHMS) phase, and may help to characterize the effect of Fe substitution on the properties of other DHMS phases from studies of the Fe-free end-members. 相似文献
17.
György Less Gianluca Frijia Ercan Özcan Pratul K. Saraswati Mariano Parente Pramod Kumar 《Geodinamica Acta》2018,30(1):183-211
Due to its intermediate geographical position between the Mediterranean and W Pacific, the Oligocene shallow-marine sequence of Kutch (India) is of key importance in paleobiogeographical interpretations. Larger benthic foraminifera (LBF) are a fundamental link for the correlation between the Mediterranean shallow benthic zones (SBZ) and the W Pacific ‘letter stages’. LBF were re-evaluated by morphometric studies of the internal test from five stratigraphic sections of the Maniyara Fort Formation. Based on their significant affinity to coeval fauna in the Mediterranean, they were assigned to W Tethyan SBZ zones, supported by Sr-isotope stratigraphy. In the Basal Member, traditionally considered as early Rupelian, we identified Nummulites bormidiensis, N. kecskemetii and Heterostegina assilinoides assigning it to the early Chattian SBZ 22B Zone. The Coral Limestone Member, previously considered as late Rupelian, is also assigned to this zone, for the presence of N. bormidiensis, Eulepidina formosoides-dilatata and Nephrolepidina morgani-praemarginata. Its early Chattian age (26.5–29 Ma) is further supported by Sr-isotope data. Miogypsinoides complanatus and Spiroclypeus margaritatus in the Bermoti Member (the top of the formation) document the late Chattian SBZ 23 Zone and the Sr-isotope data (22.5–24 Ma) place it close to the Oligocene–Miocene boundary. 相似文献
18.
The effects of low-temperature on the crystal structure of a natural epidote [Ca1.925Fe0.745Al2.265Ti0.004Si3.037O12(OH), a = 8.8924(7), b = 5.6214(3), c = 10.1547(6)? and β = 115.396(8)° at room conditions, Sp. Gr. P21
/m] have been investigated with a series of structure refinements down to 100 K on the basis of X-ray single-crystal diffraction
data. The reflection conditions confirm that the space group is maintained within the T-range investigated. Structural refinements at all temperatures show the presence of Fe3+ at the octahedral M(3) site only [%Fe(M3) = 70.6(4)% at 295 K]. Only one independent proton site was located and two possible
H-bonds occur, with O(10) as donor and O(4) and O(2) as acceptors. The H-bonding scheme is maintained down to 100 K and is
supported by single crystal room-T polarised FTIR data. FTIR Spectra over the region 4,000–2,500 cm−1 are dominated by the presence of a strongly pleochroic absorption feature which can be assigned to protonation of O(10)–O(4).
Previously unobserved splitting of this absorption features is consistent with a NNN influence due to the presence of Al and
Fe3+ on the nearby M(3) site. An additional relatively minor absorption feature in FTIR spectra can be tentatively assigned to
protonation of O(10)–O(2). Low-T does not affect significantly the tetrahedral and octahedral bond distances and angles, even when distances are corrected
for “rigid body motions”. A more significant effect is observed for the bond distances of the distorted Ca(1)- and Ca(2)-polyhedra,
especially when corrected for “non-correlated motion”. The main low-T effect is observed on the vibrational regime of the atomic sites, and in particular for the two Ca-sites. A significant reduction
of the magnitude of the thermal displacement ellipsoids, with a variation of U
eq
(defined as one-third of the trace of the orthogonalised U
ij
tensor) by ~40% is observed for the Ca-sites between 295 and 100 K. Within the same T-range, the U
eq
of the octahedral and oxygen sites decrease similarly by ~35%, whereas those of the tetrahedral cations by ~22%. 相似文献
19.
Giulio Bigazzi Aldo Del Moro Patrizia Macera 《Contributions to Mineralogy and Petrology》1986,94(1):46-53
A development of De Paolo's mathematical procedure (1981) for magmatic AFC (Assimilation-Fractional Crystallization) processes is discussed with respect to both trace element and Sr isotopic ratio behaviours during the genesis and evolution of Adamello batholith (northern Italy). Resolution of a two equation-system (one relative to 87Sr/86Sr ratio variation in a magma generated by an AFC process, the other to its trace element content variations) gives the F (mass of magma at time t/mass of initial magma) and D (bulk partition coefficient) values, by which one can deduce the r (rate of assimilation/rate of crystallization) value during each step of magmatic evolution. This quantitative approach suggests that: 1) there was a common precursor magma for all the Adamello granitoids, with a Mg-rich tholeiitic composition; 2) each intrusive unit appears to have been generated by different extents of AFC; 3) the trace element distribution in the magma seems essentially influenced by mineral fractionation, rather than by the composition of the assimilated crustal material. 相似文献
20.
The recently published Iraqi earthquake data file over the period 1905–1984 is used to derive a local I
o
-M
s
formula. This is then combined with a local intensity attenuation relationship to compile the observed I
o
(MM) zoning map for Iraq. Earthquake risk is calculated using the log N (M
s
)relation for selected design magnitudes and periods and is mapped as the (%) probability of occurrence using a 0.5 deg latitude/longitude grid system. It is observed that the intensity zones and contour distributions are highly influenced by the presence of large magnitude shocks while risk maps reveal the Tauros seismogenic zone as having a greater risk of occurrence than the Zagros zone. The compiled zoning maps are intended for the use of local practising engineers for earthquake-resistant design procedures that are currently being adopted in the country. 相似文献