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1.
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
2.
Wind erosion causes severe environmental problems, such as aeolian desertification and dust storms, in arid and semiarid regions.
Reliable prediction of the height profile of the wind-eroded sediment flux is crucial for estimation of transport rates, verification
of computer models, understanding of particle-modified wind flows, and control of drifting sand. This study defined the basic
height profile for the flux of wind-eroded sediment and the coefficients that characterize its equation. Nine grain-size populations
of natural sand at different wind velocities were tested in a wind tunnel to measure the flux of sediment at different heights.
The resulting flux profiles resemble a golf club with a small back-turn where the flux increases with increasing height within
20 mm above the surface. If the small back-turns are neglected, the flux profiles can be expressed by an exponential-decay
function
where q
r(z) is the dimensionless relative flux of sediment at height z, which follows the exponential-decay law proposed by previous researchers for aeolian saltation. Three coefficients (a creep
proportion, a relative decay rate, and an average saltation height) are proposed to characterize the height profile. Coefficients
a and b in the above equation represent the creep proportion and relative decay rate as a function of height, respectively. Coefficient
a varies widely, depending on grain size and wind velocity, but averages 0.09. It is suggested that the grain size and wind
velocity must be specified when discussing creep proportion. Coefficients a and b are nearly linearly correlated and decrease as grain size and wind velocity increase. The average saltation height (the average
height sediment particles can reach) was a function of grain size and wind velocity, and was well correlated with coefficients
a and b. 相似文献
3.
Gao Xuzheng 《中国地球化学学报》1986,5(3):215-225
Geochemical potential field is defined as the scope within the earth’s space where a given component in a certain phase of a certain material system is acted upon by a diffusion force, depending on its spatial coordinatesX, Y andZ. The three coordinates follow the relations: $$NF_{ix} = - \frac{{\partial \mu }}{{\partial x}}, NF_{iy} = - \frac{{\partial \mu }}{{\partial y}}, NF_{iz} = - \frac{{\partial \mu }}{{\partial z}}$$ The characteristics of such a field can be summarized as: (1) The summation of geochemical potentials related to the coordinatesX, Y, Z, or pseudo-velocity head, pseudo-pressure head and pseudo-potential head of a certain component in the earth is a constant as given by $$\mu _x + \mu _y + \mu _z = c$$ or $$\mu _{x2} + \mu _{y2} + \mu _{z2} = \mu _{x1} + \mu _{y1} + \mu _{z1} $$ Derived from these relations is the principle of geochemical potential conservation. The following relations have the same physical significance: $$\mu _k + \mu _u + \mu _p = c$$ or $$\mu _{k2} + \mu _{u2} + \mu _{p2} = \mu _{k1} + \mu _{u1} + \mu _{p1} $$ (2) Geochemical potential field is a vector field quantified by geochemical field intensity which is defined as the diffusion force applied to one molecular volume (or one atomic volume) of a certain component moving from its higher concentration phase to lower concentration phase. The geochemical potential field intensity is given by $$\begin{gathered} E = - grad\mu \hfill \\ E = \frac{{RT}}{x}i + \frac{{RT}}{y}j + \frac{{RT}}{z}K \hfill \\ \end{gathered} $$ The present theory has been inferred to interpret the mechanism of formation of some tungsten ore deposits in China. 相似文献
4.
D. J. Barber H.-R. Wenk J. Gomez-Barreiro E. Rybacki G. Dresen 《Physics and Chemistry of Minerals》2007,34(2):73-84
The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation
mechanisms were established such as mechanical twinning on
in the positive sense and slip on
and
both in the negative sense. More recently it was observed that at higher temperatures
slip in both senses becomes active and, based on slip line analysis, it was suggested that
slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new
torsion experiments on calcite single crystals at 900 K and transmission electron microscopy, this study identifies
slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal
plasticity simulations, enigmatic texture patterns observed in compression and torsion of calcite rocks at high temperature
can now be explained, resolving a long-standing puzzle. 相似文献
5.
Kinetic experiments of dolomite dissolution in water over a temperature range from 25 to 250°C were performed using a flow
through packed bed reactor. Authors chose three different size fractions of dolomite samples: 18–35 mesh, 35–60 mesh, and
60–80 mesh. The dissolution rates of the three particle size samples of dolomite were measured. The dissolution rate values
are changed with the variation of grain size of the sample. For the sample through 20–40 mesh, both the release rate of Ca
and the release rate of Mg increase with increasing temperature until 200°C, then decrease with continued increasing temperature.
Its maximum dissolution rate occurs at 200°C. The maximum dissolution rates for the sample through 40–60 mesh and 60–80 mesh
happen at 100°C. Experimental results indicate that the dissolution of dolomite is incongruent in most cases. Dissolution
of fresh dolomite was non-stoichiometric, the Ca/Mg ratio released to solution was greater than in the bulk solid, and the
ratio increases with rising temperatures from 25 to 250°C. Observations on dolomite dissolution in water are presented as
three parallel reactions, and each reaction occurs in consecutive steps as
where the second part is a slow reaction, and also the reaction could occur as follows:
The following rate equation was used to describe dolomite dissolution kinetics
where refers to one of each reaction among the above reactions; k
ij
is the rate constant for ith species in the jth reaction, a
i
stands for activity of ith aqueous species, n is the stoichimetric coefficience of ith species in the jth reaction, and define . The experiments prove that dissolved Ca is a strong inhibitor for dolomite dissolution (release of Ca) in most cases. Dissolved
Mg was found to be an inhibitor for dolomite dissolution at low temperatures. But dissolution rates of dolomite increase with
increasing the concentration of dissolved Mg in the temperature range of 200–250°C for 20–40 mesh sample, and in the temperature
range of 100–250°C for 40–80 mesh sample, whereas the Mg2+ ion adsorption on dolomite surface becomes progressively the step controlling reaction. The following rate equation is suitable
to dolomite dissolutions at high temperatures from 200 to 250°C.
where refers to dissolution rate (release of Ca), and are molar concentrations of dissolved Ca and Mg, k
ad stands for adsorption reaction rate constant, K
Mg refers to adsorption equilibrium constant.
At 200°C for 40–60 mesh sample, the release rate of Ca can be described as:
相似文献
6.
Fractionation of yttrium (Y) and the rare earth elements (REEs) begins in riverine systems and continues in estuaries and the ocean. Models of yttrium and rare earth (YREE) distributions in seawater must therefore consider the fractionation of these elements in both marine and riverine systems. In this work we develop a coupled riverine/marine fractionation model for dissolved rare earths and yttrium, and apply this model to calculations of marine YREE fractionation for a simple two-box (riverine/marine) geochemical system. Shale-normalized YREE concentrations in seawater can be expressed in terms of fractionation factors (
ij
) appropriate to riverine environments (
) and seawater (
):
where
and
are input-normalized total metal concentrations in seawater and
is the ratio of total dissolved Y in riverwater before
and after
commencement of riverine metal scavenging processes. The fractionation factors (
ij
) are calculated relative to the reference element, yttrium, and reflect a balance between solution and surface complexation of the rare earths and yttrium. 相似文献
7.
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
8.
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
9.
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
10.
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
11.
The standard enthalpies of formation of FeS (troilite), FeS2 (pyrite), Co0.9342S, Co3S4 (linnaeite), Co9S8 (cobalt pentlandite), CoS2 (cattierite), CuS (covellite), and Cu2S (chalcocite) have been determined by high temperature direct reaction calorimetry at temperatures between 700 K and 1021 K. The following results are reported: $$\Delta {\rm H}_{f,FeS}^{tr} = - 102.59 \pm 0.20kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,FeS}^{py} = - 171.64 \pm 0.93kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_{0.934} S} = - 99.42 \pm 1.52kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_9 S_8 }^{ptl} = - 885.66 \pm 16.83kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_3 S_4 }^{In} = - 347.47 \pm 7.27kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,CoS_2 }^{ct} = - 150.94 \pm 4.85kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Cu_2 S}^{cc} = - 80.21 \pm 1.51kJ mol^{ - 1} ,$$ and $$\Delta {\rm H}_{f,CuS}^{cv} = - 53.14 \pm 2.28kJ mol^{ - 1} ,$$ The enthalpy of formation of CuFeS2 (chalcopyrite) from (CuS+FeS) and from (Cu+FeS2) was determined by solution calorimetry in a liquid Ni0.60S0.40 melt at 1100 K. The results of these measurements were combined with the standard enthalpies of formation of CuS, FeS, and FeS2, to calculate the standard enthalpy of formation of CuFeS2. We found \(\Delta {\rm H}_{f,CuFeS_2 }^{ccp} = - 194.93 \pm 4.84kJ mol^{ - 1}\) . Our results are compared with earlier data given in the literature; generally the agreement is good and our values agree with previous estimates within the uncertainties present in both. 相似文献
12.
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
13.
通过砾质戈壁风沙流野外实测数据的分析以及风洞模拟实验研究发现：戈壁风沙流结构具有与沙漠风沙流完全不同的风沙流特征,戈壁风沙地表的粗糙度随风速的增大而增加,其表面风沙流输沙量高度分布表现出独特的"象鼻"效应,在一定高度处呈现最大值,并随风速的增加而增高。该"象鼻"效应导致戈壁风沙流结构特征值λ远大于 1,不论风速多大,风沙流都处于未饱和状态的非堆积搬运状态。这种特殊性质比较清楚地解释了敦煌莫高窟千年来不被沙山埋没的谜底。并且在风沙防治工程实践中,采用砾石压沙措施,构造类似与砾质戈壁的下垫面,人工促使风沙流结构呈现"象鼻"形状,可使防沙工程达到理想的输导作用。 相似文献
14.
Near-liquidus phase relationships of a spinel lherzolite-bearing olivine melilitite from Tasmania were investigated over a P, T range with varying
,
, and
. At 30 kb under MH-buffered conditions, systematic changes of liquidus phases occur with increasing
(
= CO2/CO2 +H2O+olivine melilitite). Olivine is the liquidus phase in the presence of H2O alone and is joined by clinopyroxene at low
. Increasing
eliminates olivine and clinopyroxene becomes the only liquidus phase. Further addition of CO2 brings garnet+orthopyroxene onto the liquidus together with clinopyroxene, which disappears with even higher CO2. The same systematic changes appear to hold at higher and lower pressures also, only that the phase boundaries are shifted to different
. The field with olivine- +clinopyroxene becomes stable to higher
with lower pressure and approaches most closely the field with garnet+orthopyroxene+clinopyroxene at about 27 kb, 1160 °C,
0.08 and
0.2 (i.e., 6–7% CO2+ 7–8% H2O). Olivine does not coexist with garnet+orthopyroxene+clinopyroxene under these MH-buffered conditions. Lower oxygen fugacities do not increase the stability of olivine to higher
and do not change the phase relationships and liquidus temperatures drastically. Thus, it is inferred that olivine melilitite 2927 originates as a 5% melt (inferred from K2
O and P2O5 content) from a pyrolite source at about 27kb, 1160 dg with about 6–7% CO2 and 7–8% H2O dissolved in the melt. The highly undersaturated character of the melt and the inability to find olivine together with garnet and orthopyroxene on the liquidus (in spite of the close approach of the respective liquidus fields) can be explained by reaction relationships of olivine and clinopyroxene with orthopyroxene, garnet and melt in the presence of CO2. 相似文献
15.
16.
Interaction of freshly precipitated silica gel with aqueous solutions was studied at laboratory batch experiments under ambient
and near neutral pH-conditions. The overall process showed excellent reversibility: gel growth could be considered as an opposite
process to dissolution and a linear rate law could be applied to experimental data. Depending on the used rate law form, the
resulting rate constants were sensitive to errors in parameters/variables such as gel surface area, equilibrium constants,
Si-fluxes, and reaction quotients. The application of an Integrated Exponential Model appeared to be the best approach for
dissolution data evaluation. It yielded the rate constants k
dissol ∼ (4.50 ± 0.68) × 10−12 and k
growth ∼ (2.58 ± 0.39) × 10−9 mol m−2 s−1 for zero ionic strength. In contrast, a Differential Model gave best results for growth data modeling. It yielded the rate
constants k
dissol ∼ (1.14 ± 0.44) × 10−11 and k
growth ∼ (6.08 ± 2.37) × 10−9 mol m−2 s−1 for higher ionic strength (I ∼ 0.04 to 0.11 mol L−1). The found silica gel solubility at zero ionic strength was somewhat lower than the generally accepted value. Based on the
and standard Gibbs free energy of silica gel formation was calculated as and −850,318 ± 20 J mol−1, respectively. Activation energies for silica gel dissolution and growth were determined as and respectively. An universal value for growth of any silica polymorph, is not consistent with the value for silica gel growth, which questions the hypothesis about one unique activated complex
controlling the silica polymorph growth. 相似文献
17.
The activity of silica in kimberlites,revisited 总被引：1，自引：1，他引：0
Robert W. Luth 《Contributions to Mineralogy and Petrology》2009,158(2):283-294
The activity of silica in a silicate liquid in equilibrium with olivine and orthopyroxene decreases with increasing pressure. In contrast, the activity of silica in
an unbuffered silicate liquid changes little with pressure. Although the implications of these pressure dependencies have
been considered by previous authors in terms of inferring pressures of origin of magmas, less consideration has been given
to the implications of these dependencies on the evolution of the magma en route to the surface, or to the mantle through
which the magma passes. In this paper, a combination of Schreinemakers’ analysis in isothermal section and calculated reactions in space is used to (a) rationalize the absence of orthopyroxene xenocrysts in kimberlites and the relative abundance of olivine
“megacrysts” therein, (b) propose another reason for the paucity of xenocrystic mantle-derived carbonates in kimberlites,
(c) explain why clinopyroxene is much less reactive in the kimberlite melt than is orthopyroxene, and (d) explore the implications
of the relative stabilities of olivine, orthopyroxene, and clinopyroxene in kimberlitic magma for the mantle through which
the magma transits.
相似文献
| Robert W. LuthEmail: |
18.
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
19.
This paper presents a design approach for strip footings upon glacier ice. Safety against ultimate limit state is proved by
the geotechnical slip-line field solution by Prandtl. Glacier ice at 0°C can be modelled as purely cohesive material. Statistical
evaluation of uniaxial compression tests with high strain rate revealed a mean value of the cohesion of 600 kPa and a characteristic
value c
k
= 355 kPa (5% fractile). With a coefficient of variation V
c
= 0.3, the partial safety factor turns out to be γ
c
= 1.9. An approximate solution for estimating the creep settlement rate is presented to check the serviceability limit state: with the width b of the strip foundation, p the foundation pressure and for ice at 0°C. Experiences on Stubai glacier with grate shaped footings showed that creep settlements occurring per year
due to maximum foundation pressures 250 kPa did not influence the operation and the maintenance of the cable cars. 相似文献
20.
The Skaergaard liquid line of descent revisited 总被引：1，自引：0，他引：1
Peter Thy Charles E. Lesher Christian Tegner 《Contributions to Mineralogy and Petrology》2009,157(6):735-747
There is a fundamental conflict between the suggestion that the iron content of Skaergaard liquids increases during Fe–Ti
oxide fractionation and the observation that at the same time oxygen fugacity () drops by two log-units below the fayalite-magnetite-quartz oxygen buffer (FMQ). A new petrographic study of average Skaergaard
gabbros shows that the total modal content of Fe–Ti oxides is about 22% in the early LZc and markedly decreases to below 5%
in the UZc. Forward modeling based on these modal constraints, as well as experimental results on Skaergaard-related dikes,
predicts that fractionation of troctolitic LZa gabbros drives the derivative liquid towards a high-iron content. Strong iron
enrichment continues, together with a small decline in silica, during LZb crystallization due to the appearance of augite
as a fractionating phase. The fractionation of Fe–Ti oxides in the LZc initially suppresses iron enrichment and reverses the
silica trend to one of slight enrichment. However, continued evolution into the UZ produces liquids with maximum UZc FeO*
content of 23–25 wt.% and SiO2 content of 53 wt.% (FeO* is total iron as FeO). The maximum in FeO* is dependent on several factors of which the Fe–Ti oxide
mode has the strongest effect. The during crystallization of the LZc is widely thought to have been at, or slightly below, the fayalite-magnetite-quartz oxygen
buffer (FMQ). Under closed system evolution, incorporation of ferric iron into augite during formation of the LZb restricts
the increase in to about 0.1 log-units above FMQ (=0.1 ΔFMQ). Likewise, crystallization of the LZc through the UZa, involving Fe–Ti oxide
minerals, leads to a decline in of less than 0.1 ΔFMQ. Crystallization of the UZb-c gabbros results in oxidation to a maximum of 0.5 ΔFMQ. This behavior
can account for the iron-rich character of the UZ gabbros, as well as, the low modal content of Fe–Ti oxides. Thus, evolved
Skaergaard liquids are high in iron and contain a modest amount of SiO2. Our modeling result do not account for a strong drop in through the layered series. Such a drop would require an unacceptably high proportion of Fe–Ti oxides and high-magnetite
content in the fractionating assemblage.
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