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1.
定量度量动力变质作用下组成糜棱岩矿物颗粒的不规则变化是一项挑战性的研究.以基于GIS的PA(周长-面积)模型定量地描述糜棱岩中具自相似性石英形态的不规则变化.研究实例是苏格兰西北地区Moine逆冲断裂带前缘变质程度不同的5种类型的糜棱岩.石英是糜棱岩的主要矿物成分,其镜下的显微图片经扫描转换成数字图像,再通过GIS技术转换成矢量图,并计算出每颗石英的周长和面积.研究结果表明,随变质程度的增加,其PA分形维数分别从1.20、1.28、1.38、1.46,逐步增加到1.60.这表明,随变质程度的增加,变形程度与动态重结晶作用加强,石英颗粒从规则到不规则. 相似文献
2.
Schists from two mylonitic localities in the footwall of a low-angle normal fault in the eastern Alps record different degrees
of embrittlement during exhumation, depending on the extent to which fluid–rock reactions proceeded. At one site, graphitic
schists preserve textural evidence for two metamorphic reactions that modified
and/or fluid volume: (1) reaction between graphite and aqueous fluid that increased without changing the molar amount of fluid, and (2) replacement of titanite by rutile, calcite, and quartz. The latter reaction
involved net consumption of increasingly CO2-rich fluid. Areas where the first reaction proceeded are associated with abundant Mode I microcracks. Fluid inclusion arrays
within the microcracks show that increased from ∼0.1 to 0.6 during decompression from 4.75 to 2 kbar at a reference temperature of 500°C. Titanite consumption
is most pronounced within transgranular Mode I microcracks, but microcracks do not crosscut products of this reaction; fluid
consumption during reaction was coeval with the end of microcracking, at least on a local scale. At the other site, graphitic
schists lack small-scale Mode I cracks as well as evidence for graphite consumption during decompression. SEM imaging shows
that graphite is anhedral and pitted at the first site, but occurs in clusters of euhedral grains at the second site. Mass
balance calculations demonstrate that rocks with partially consumed graphite were infiltrated by an externally derived, H2O-rich fluid that drove subsequent graphite-fluid reaction. Evidence for similar fluid infiltration is absent at the second
site. Variations in the degree of reaction progress indicate that fluid pathways and deformation style were heterogeneous
on the scale of millimeters to kilometers during exhumation from mid-crustal depths. 相似文献
3.
The carbon and hydrogen isotopic composition of biogenic gas is of great importance for the study of its generation pathway
and reservoiring characteristics. In this paper, the formation pathways and reservoiring characteristics of biogenic gas reservoirs
in China are described in terms of the carbon and hydrogen isotopic compositions of 31 gas samples from 10 biogenic gas reservoirs.
The study shows that the hydrogen isotopic compositions of these biogenic gas reservoirs can be divided into three intervals:
δ>−200‰, −250‰<δ<-−200‰ and δ<−250‰. The forerunners believed that the main generation pathway of biogenic gas under the condition of continental fresh
water is acetic fermentation. Our research results showed that the generation pathway of biogenic gas under the condition
of marine facies is typical CO2- reduction, the biogenic gas has heavy hydrogen isotopic composition: its δ values are higher than −200‰; that the biogenic gas under the condition of continental facies also was generated by the same
way, but its hydrogen isotopic composition is lighter than that of biogenetic gas generated under typical marine facies condition:
−250‰<δ<−200‰, the δ values may be related to the salinity of the water medium in ancient lakes. From the relevant data of the Qaidam Basin, it
can be seen that the hydrogen isotopic composition of biogenic methane has the same variation trend with increasing salinity
of water medium. There are biogenic gas reservoirs formed in transitional regions under the condition of continental facies.
These gas reservoirs resulted from both CO2-reduction and acetic fermentation, the formation of which may be related to the non-variant salinity of ancient water medium
and the relatively high geothermal gradient, as is the case encountered in the Baoshan Basin. The biogenic gas generating
in these regions has light hydrogen isotopic composition: δ<−250‰, and relatively heavy carbon isotopic composition. There is a fairly strong negative correlation between the carbon
isotopic composition and the hydrogen isotopic composition. The generation mechanism and pathway of carbon, and the hydrogen
isotopic composition of biogenic gas may be used to ascertain whether biogenic gas samples from the natural world are of industrial
utilization value. In general, the biogenic gas formed by way of acetic fermentation is not propitious to the formation of
gas reservoirs. 相似文献
4.
The incorporation and diffusion of hydrogen in San Carlos olivine (Fo90) single crystals were studied by performing experiments under hydrothermal conditions. The experiments were carried out either at 1.5 GPa, 1,000°C for 1.5 h in a piston cylinder apparatus or at 0.2 GPa, 900°C for 1 or 20 h in a cold-seal vessel. The oxygen fugacity was buffered using Ni–NiO, and the silica activity was buffered by adding San Carlos orthopyroxene powders. Polarized Fourier transform infrared (FTIR) spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. The resulting infrared spectra reproduce the features of FTIR spectra that are observed in olivine from common mantle peridotite xenoliths. The hydrogen concentration at the edges of the hydrogenated olivine crystals corresponds to concentration levels calculated from published water solubility laws. Hydrogen diffusivities were determined for the three crystallographic axes from profiles of water content as a function of position. The chemical diffusion coefficients are comparable to those previously reported for natural iron-bearing olivine. At high temperature, hydrogenation is dominated by coupled diffusion of protons and octahedrally coordinated metal vacancies
where the vacancy diffusion rate limits the process. From the experimental data, we determined the following diffusion laws (diffusivity in m2 s−1, activation energies in kJ mol−1):
for diffusion along [100] and [010];
for diffusion along [001]. These diffusion rates are fast enough to modify significantly water contents within olivine grains in xenoliths ascending from the mantle. 相似文献
5.
New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers 总被引：75，自引：22，他引：53
The models recognize that ZrSiO4, ZrTiO4, and TiSiO4, but not ZrO2 or TiO2, are independently variable phase components in zircon. Accordingly, the equilibrium controlling the Zr content of rutile
coexisting with zircon is ZrSiO4 = ZrO2 (in rutile) + SiO2. The equilibrium controlling the Ti content of zircon is either ZrSiO4 + TiO2 = ZrTiO4 + SiO2 or TiO2 + SiO2 = TiSiO4, depending whether Ti substitutes for Si or Zr. The Zr content of rutile thus depends on the activity of SiO2
as well as T, and the Ti content of zircon depends on and as well as T. New and published experimental data confirm the predicted increase in the Zr content of rutile with decreasing and unequivocally demonstrate that the Ti content of zircon increases with decreasing . The substitution of Ti in zircon therefore is primarily for Si. Assuming a constant effect of P, unit and that and are proportional to ppm Zr in rutile and ppm Ti in zircon, [log(ppm Zr-in-rutile) + log] = A1 + B1/T(K) and [log(ppm Ti-in-zircon) + log − log] = A2 + B2/T, where the A and B are constants. The constants were derived from published and new data from experiments with buffered by either quartz or zircon + zirconia, from experiments with defined by the Zr content of rutile, and from well-characterized natural samples. Results are A1 = 7.420 ± 0.105; B1 = −4,530 ± 111; A2 = 5.711 ± 0.072; B2 = −4,800 ± 86 with activity referenced to α-quartz and rutile at P and T of interest. The zircon thermometer may now be applied to rocks without quartz and/or rutile, and the rutile thermometer
applied to rocks without quartz, provided that and are estimated. Maximum uncertainties introduced to zircon and rutile thermometry by unconstrained and can be quantitatively assessed and are ≈60 to 70°C at 750°C. A preliminary assessment of the dependence of the two thermometers
on P predicts that an uncertainty of ±1 GPa introduces an additional uncertainty at 750°C of ≈50°C for the Ti-in-zircon thermometer
and of ≈70 to 80°C for the Zr-in-rutile thermometer. 相似文献
6.
Juan L. Fernández Martínez José P. Fernández Alvarez Luis M. Pedruelo González 《Mathematical Geology》2006,38(3):343-374
Transmission tomography methods show a great sensibility to data variability, which eventually includes data errors, often present in field experiments. Local optimization methods, traditionally used to solve this inverse problem, are very sensitive to these difficulties, failing to converge properly in the presence of spurious data. Regularization methods partially cope with these weaknesses, damping the instabilities.A complementary approach, adopted here, is to perform a structured analysis of data variability before the inversion, oriented to discriminate the contribution of errors from that of true geological heterogeneities. The key concept of mean traveltime curves ( and ) is introduced and described. Their analytical equations are deduced for isotropic homogeneous media and any recording geometry. Empirical mean traveltime curves can be inferred based solely on traveltime data, using the corresponding discrete estimators. The methodology proposed here proceeds through a user-defined subdivision of the domain of interest into isotropic homogeneous areas. Least squares velocity estimations and associated data misfits are used to scrutinize the behaviour of the implied source-receiver sets and of the ray-swept part of the geologic medium. Data are considered suspicious if zonal estimated velocities are non-consistent with a priori information. Also, independent fitting of both empirical curves helps to classify the genesis of the residuals: some situations are illustrated.Finally, we show the application of this technique to a data set from the Grimsel test site in Switzerland. Using this methodology, we detect some anomalous gathers, which may be responsible for the large range of velocities found in the initial imaging with this data set. Also, we give some indications of the possible sources of these anomalies. This approach offers a quick data variability analysis in the pre-processing stage, which, even if no data editing algorithms are finally used, always improves the understanding of the data structure. 相似文献
7.
Yongjun Jiang Cheng Zhang Daoxian Yuan Gui Zhang Raosheng He 《Hydrogeology Journal》2008,16(4):727-735
The impact of land-use change on the quality of groundwater in the Xiaotjiang watershed, China was assessed for the period
1982–2004. Groundwater samples were collected from 30 monitoring points across the watershed, and were representative of the
various changes, determined by remote sensing and geographical information systems. The results indicate that 610 km2 (60% of the total watershed area) were subject to land-use change during the period. The most important changes were the
conversion of 135 km2 of forested land to cultivated land, and 211 km2 of unused land to cultivated land. The main impact was ascribed to diffuse pollution from fertilizers applied to newly cultivated
land, and from building development. Overall the groundwater pH value was significantly increased, as were the concentrations
of ions , , , , and Cl− in groundwater whilst the concentrations of Ca2+ and declined. More precisely, in the regions where forested land and unused land were converted into cultivated land, the pH
value and the concentrations of Mg2+, , , , , Cl− increased whilst the concentrations of Ca2+ and declined. However in the region where cultivated land was converted into construction land, the pH value and the concentrations
of Ca2+, Mg2+, , , , , , Cl− increased.
Résumé L’impact des changements de l’utilisation du territoire sur la qualité de l’eau souterraine dans le bassin versant de Xiaojiang, en Chine, a été évalué de 1982 à 2004. Des échantillons d’eau souterraine ont été récoltés à partir de 30 points d’observation éparpillés sur le bassin, représentant les divers changements déterminés par télédétection et système d’information géographique. Les résultats indiquent que 610 km2 (soit 60% de la surface du bassin) ont été sujets à des modifications de l’utilisation du territoire sur cette période. Les changements les plus importants furent la conversion de 135 km2 de forêt et 211 km2 de terres inutilisées en terres cultivées. Le principal impact est attribué à la pollution diffuse des engrais utilisés en agriculture et pour les batiments. De manière générale le pH de l’eau souterraine a augmenté significativement, ainsi que les concentrations des ions , , , , et Cl−, tandis que les concentration en Ca2+ et ont diminué. Plus précisément dans les régions transformées en terres cultivées, la valeur du pH et les concentrations en Mg2+, , , , , Cl− ont augmenté tandis que les concentrations en Ca2+ et ont diminué. Toutefois dans les régions cultivées converties en zones de construction, le pH et les concentrations en Ca2+, Mg2+, , , , , , Cl− ont augmenté.
Resumen El impacto del cambio en uso de la tierra en la calidad del agua en la cuenca Xiaojiang, China fue evaluado para el periodo 1982–2004. Muestras de agua subterránea fueron tomadas de 30 puntos de monitoreo a través de la cuenca, y fueron representativas de los múltiples cambios, determinados por sensores remotos y sistemas de información geográfica. Los resultados indican que 610 km2 (60% del área total de la cuenca) estaban sujetos a cambios de uso de la tierra durante el periodo estudiado. Los cambios más importantes fueron la conversión de 135 km2 de bosques a tierra cultivada, y 211 km2 de tierra sin uso (ociosa) a tierra cultivada. El impacto principal fue causado por contaminación difusa de fertilizantes aplicados a la tierra recientemente cultivada, y a desarrollo de construcciones. En general el pH en agua subterránea creció significantemente, al igual que las concentraciones de los iones , , , , y Cl− en agua subterránea mientras que las concentraciones de Ca2+ y decrecieron. Mas precisamente, en las regiones donde bosque y tierra ociosa fueron convertidas en tierra cultivada, el valor de pH y las concentraciones de Mg2+, , , , , Cl− crecieron mientras las concentraciones de Ca2+ y decrecieron. Sin embargo en la región donde tierra cultivada fue convertida en construcciones, el valor de pH y las concentraciones de Ca2+, Mg2+, , , , , , Cl− crecieron.相似文献
8.
Chang-Jo F. Chung 《Mathematical Geology》1993,25(7):851-865
Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances,
,
,
, and
forY andZ: (ii) defining new variables by
and
and lettingA=C+D andB=C–D, and obtaining MLE for variances,
and
forA andB; (iii) estimating the correlation coefficient YZ by
and the covariance
YZ
by
. The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada. 相似文献
9.
The diffusion of water in a peralkaline and a peraluminous rhyolitic melt was investigated at temperatures of 714–1,493 K
and pressures of 100 and 500 MPa. At temperatures below 923 K dehydration experiments were performed on glasses containing
about 2 wt% H2O
t
in cold seal pressure vessels. At high temperatures diffusion couples of water-poor (<0.5 wt% H2O
t
) and water-rich (~2 wt% H2O
t
) melts were run in an internally heated gas pressure vessel. Argon was the pressure medium in both cases. Concentration profiles
of hydrous species (OH groups and H2O molecules) were measured along the diffusion direction using near-infrared (NIR) microspectroscopy. The bulk water diffusivity
() was derived from profiles of total water () using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between and Both methods consistently indicate that is proportional to in this range of water contents for both bulk compositions, in agreement with previous work on metaluminous rhyolite. The
water diffusivity in the peraluminous melts agrees very well with data for metaluminous rhyolites implying that an excess
of Al2O3 with respect to alkalis does not affect water diffusion. On the other hand, water diffusion is faster by roughly a factor
of two in the peralkaline melt compared to the metaluminous melt. The following expression for the water diffusivity in the
peralkaline rhyolite as a function of temperature and pressure was obtained by least-squares fitting:
where is the water diffusivity at 1 wt% H2O
t
in m2/s, T is the temperature in K and P is the pressure in MPa. The above equation reproduces the experimental data (14 runs in total) with a standard fit error
of 0.15 log units. It can be employed to model degassing of peralkaline melts at water contents up to 2 wt%. 相似文献
10.
舒兰北东向韧性剪切带位于佳木斯-伊通断裂带(佳-伊断裂带)中南段, 剪切带内糜棱岩具有明显左行走滑特征, 片麻理产状近NNE向.糜棱岩中长石有限应变Flinn图解判别岩石类型为L-S型构造岩, 属拉长型应变.石英C轴EBSD组构分析表明, 石英组构以中低温菱面为主, 滑移系为{0001} < 110>.剪切带内糜棱岩的剪应变为0.44, 不同方法计算所得运动学涡度值均大于0.95, 指示剪切变形以简单剪切为主.综合矿物变形温度计、石英C轴EBSD组构、石英的粒度-频数图及Kruhl温度计综合估计该韧性剪切带变形机制以位错蠕变机制为主, 变质相为低绿片岩相, 发生韧性变形和糜棱岩化温度范围在400~500 ℃之间.糜棱岩内石英动态重结晶新晶粒边界普遍具有锯齿状或港湾状结构, 利用分形方法对其重结晶新晶边界研究表明, 这些晶粒边界具有自相似性, 表现出分形特征, 分形维数值为1.195~1.220.根据石英重结晶粒径估算差应力值为24.35~27.59 MPa, 代表了舒兰韧性剪切带糜棱岩化作用过程的差异应力下限.使用不同实验方法估算、比较和分析了该剪切带古应变速率, 认为该速率应为10-12.00~10-13.18 s-1, 与区域性应变速率10-13.00~10-15.00 s-1对比, 说明舒兰韧性剪切带的应变速率与世界上大多数韧性剪切带中的糜棱岩应变速率一致, 是缓慢变形的结果, 其形成可能与早白垩世伊泽纳崎板块向欧亚大陆俯冲发生转向有关. 相似文献
11.
We present here a numerical modelling study of dislocations in perovskite CaTiO3. The dislocation core structures and properties are calculated through the Peierls–Nabarro model using the generalized stacking
fault (GSF) results as a starting model. The GSF are determined from first-principles calculations using the VASP code. The
dislocation properties such as collinear, planar core spreading and Peierls stresses are determined for the following slip
systems: [100](010), [100](001), [010](100), [010](001), [001](100), [001](010),
and All dislocations exhibit lattice friction, but glide appears to be easier for [100](010) and [010](100).
[001](010) and [001](100) exhibit collinear dissociation. Comparing Peierls stresses among tausonite (SrTiO3), perovskite (CaTiO3) and MgSiO3 perovskite demonstrates the strong influence of orthorhombic distortions on lattice friction. However, and despite some quantitative
differences, CaTiO3 appears to be a satisfactory analogue material for MgSiO3 perovskite as far as dislocation glide is concerned. 相似文献
12.
ABSTRACT In the Woodroffe Thrust mylonite zone, central Australia, recrystallization in plagioclase and K-feldspar involved subgrain rotation, assisted by grain-boundary or kink band boundary bulging, without contribution from a change in the chemical composition from host grains to new grains. The size of subgrains and new grains changes across the mylonite zone, apparently as a function of the strain rate and the H2O content of the rock. The partitioning of deformation into zones of progressive shearing and progressive shortening controls the sites of recovery and recrystallization in feldspar during mylonitization. The size of feldspar porphyroclasts in well developed mylonites is governed by the scale of deformation partitioning reached in the earlier stages of mylonitization, before the formation of a large proportion of fine-grained matrix that can accommodate the progressive shearing component of the deformation. Recrystallization occurs in microcline, apparently without involving a translation to a monoclinic structure, as microcline-twinned new grains are common adjacent to microcline-twinned host grains. K-feldspar triclinicity values calculated from XRD traces increase from the margins to the interior of the mylonite zone, in conjunction with deformation intensity. K-feldspar host grains locally have cores of orthoclase or untwinned microcline, surrounded by mantles of twinned microcline, suggesting a relationship between the presence of microcline twinning and the degree of K-feldspar triclinicity. 相似文献
13.
Patterns of crystallographic preferred orientation are referred to as texture. The specific subject of texture analysis is
the experimental determination and interpretation of the statistical distribution of orientations of crystals within a specimen
of polycrystalline material, which could be metals or rocks. The objective is to relate an observed pattern of preferred orientation
to its generating processes and vice versa. In geosciences, texture of minerals in rocks is used to infer constraints on their
tectono-metamorphic history. Since most physical properties of crystals, such as elastic moduli, the coefficients of thermal
expansion, or chemical resistance to etching depends on crystal symmetry and orientation, the presence of texture imparts
directional properties to the polycrystalline material.
A major issue of mathematical texture analysis is the resolution of the inverse problem to determine a reasonable orientation
density function on SO(3) from measured pole intensities on
, which relates to the inverse of the totally geodesic Radon transform. This communication introduces a wavelet approach into
mathematical texture analysis. Wavelets on the two-dimensional sphere
and on the rotational group SO(3) are discussed, and an algorithms for a wavelet decomposition on both domains following the
ideas of Ta-Hsin Li is given. The relationship of these wavelets on both domains with respect to the totally geodesic Radon
transform is investigated. In particular, it is shown that the Radon transform of these wavelets on SO(3) are again wavelets
on
. A novel algorithm for the inversion of experimental pole intensities to an orientation density function based on this relationship
is developed. 相似文献
14.
《International Geology Review》2012,54(3):348-367
The Diancang Shan metamorphic massif, the northwestern extension of the Ailao Shan Massif, is a typical metamorphic complex situated along the NW–SE-trending Ailao Shan–Red River shear zone. Diancang Shan granitic and amphibolitic mylonites collected from sheared high-grade metamorphic rocks were studied using petrographic and electron-backscatter diffraction techniques. Sensitive high-resolution ion microprobe U–Pb dating of zircon grains from the granitic mylonites constrains the timing of shearing. Macro- and microstructural and textural analysis reveals intense plastic deformation of feldspar, quartz, and amphibole under amphibolite-facies conditions, all consistently document left-lateral shearing. Porphyritic monzogranitic mylonite within the shear zone possesses evidence supporting a sequential, progressive process from crystallization during magma emplacement, through submagmatic flow to solid-state plastic deformation. We suggest that the early-kinematic pluton subsequently underwent strong left-lateral strike–slip shearing. The development of complex textures of quartz, feldspar, and amphibole from the granitic and amphibolitic mylonites apparently records successive variation of conditions attending coherent, solid-state high-temperature ductile deformation during regional left-lateral shearing. All magmatic zircons from the mylonitized porphyritic monzogranite give U–Pb ages of 30.95 ± 0.61 million years for the crystallization of the granite. This age provides the timing of onset of left-lateral shearing along the Ailao Shan–Red River shear zone in the Diancang Shan high-grade metamorphic massif. 相似文献
15.
Kyuichi Kanagawa Hirobumi Shimano Yoshikuni Hiroi 《Journal of Structural Geology》2008,30(9):1150-1166
The mylonitization of the Pankenushi gabbro in the Hidaka metamorphic belt of central Hokkaido, Japan, occurred along its western margin at ≈600 MPa and 660–700 °C through dynamic recrystallization of plagioclase and a retrograde reaction from granulite facies to amphibolite facies (orthopyroxene + clinopyroxene + plagioclase + H2O = hornblende + quartz). The reaction produced a fine-grained (≤100 μm) polymineralic aggregate composed of orthopyroxene, clinopyroxene, quartz, hornblende, biotite and ilmenite, into which strain is localized. The dynamic recrystallization of plagioclase occurred by grain boundary migration, and produced a monomineralic aggregate of grains whose crystallographic orientations are mostly unrelated to those of porphyroclasts. The monomineralic plagioclase aggregates and the fine-grained polymineralic aggregates are interlayered and define the mylonitic foliation, while the latter is also mixed into the former by grain boundary sliding to form a rather homogeneous polymineralic matrix in ultramylonites. However in both mylonite and ultramylonite, plagioclase aggregates form a stress-supporting framework, and therefore controlled the rock rheology. Crystal plastic deformation of pyroxenes and plagioclase with dominant (100)[001] and (001)1/2 slip systems, respectively, produced distinct shape- and crystallographic-preferred orientations of pyroxene porphyroclasts and dynamically recrystallized plagioclase grains in both mylonite and ultramylonite. Euhedral to subhedral growth of hornblende in pyroxene porphyroclast tails during the reaction and its subsequent rigid rotation in the fine-grained polymineralic aggregate or matrix produced clear shape- and crystallographic-preferred orientations of hornblende grains in both mylonite and ultramylonite. In contrast, the dominant grain boundary sliding of pyroxene and quartz grains in the fine-grained polymineralic aggregate of the mylonite resulted in their very weak shape- and crystallographic-preferred orientations. In the fine-grained polymineralic matrix of the ultramylonite, however, pyroxene and quartz grains became scattered and isolated in the plagioclase aggregate so that they were crystal-plastically deformed leading to stronger shape- and crystallographic-preferred orientations than those seen in the mylonite. 相似文献
16.
For equally spaced observations from a one-dimensional, stationary, Gaussian random function, the characteristic function of the usual variogram estimator
for a fixed lag k is derived. Because the characteristic function and the probability density function form a Fourier integral pair, it is possible to tabulate the sampling distribution of a function of a
using either analytic or numerical methods. An example of one such tabulation is given for an underlying model that is simple transitive. 相似文献
17.
Melchor González-Dávila J. Magdalena Santana-Casiano Frank J. Millero 《Aquatic Geochemistry》2007,13(4):339-355
The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes
have been used to calculate the activity coefficients for Hg(OH)
n
(2–n)+ and HgCl
n
(2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for
the hydroxide and chloro complexes and C
ML). The values of and have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log to ±0.01 from I = 0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants
for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl− in natural waters over a wide range of conditions. 相似文献
18.
Sytle M. Antao Ishmael Hassan Willem H. Mulder Peter L. Lee Brian H. Toby 《Physics and Chemistry of Minerals》2009,36(3):159-169
The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO3, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite transforms
from to at about T
c = 1,240 K. A CO3 group occupies, statistically, two positions with equal frequency in the disordered phase, but with unequal frequency in the partially ordered phase. One position for the CO3 group is rotated by 180° with respect to the other. The unequal occupancy of the two orientations in the partially ordered
phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x − 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T
c, where the CO3 groups disorder in a rapid process. Using a modified Bragg–Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
In gravel-bedded streams where bed material of a tributary differs distinctly in lithology from that of the main stream, rock-type percentages can be used to estimate bed-load contributions of the two streams. The rock type that shows the greatest difference in abundance between the two streams is selected as the indicator lithology. Percentages of this lithology are estimated in both the main stream and tributary stream above their junction, and also in the main stream at a distance sufficiently downstream from the junction to allow complete mixing. The fraction of bed load contributed by the main stream, p,is estimated by
,where
is an estimate of the proportion of indicator rock fragments in the bed of the main stream above the junction,
is an estimate of the proportion in the bed of the tributary above the junction, and
is an estimate of the proportion in the bed of the main stream below the junction. The variance of
is obtained as var (
)= [p1q1(pr – p2)2/n(p1 – p2)4] + [p2q2(pr – p1)2/n(p1 – p2)4] + [prqr/n(p1 – p2)2].Although no estimate of actual quantity of bed load is provided, the indicator rock technique supplies data that can serve as a check on data obtained by means of empirical formulas or actual transport measurements. 相似文献
20.
The characteristics of wind-blown sand on Gobi/mobile sand surface have been investigated through field observation and wind
tunnel experiments. On moving sand surface, the pattern of wind speed profile in sand flow follows the power function
and its power exponent is about 0.20. While on Gobi surface, due to collision of sand grains with gravels, the structure
of sand flow differs from that on moving sand surface, which decreases exponentially with height. The height of blown sand
activities on Gobi surface is mainly concentrated below 20 cm. In addition, the structure of sand flow can reach a peak at
a certain height and increases with inlet wind velocity. 相似文献