共查询到20条相似文献，搜索用时 156 毫秒
1.
The temperature-sensitive Fe,Mg exchange equilibrium, |
相似文献
2.
The equilibrium partitioning of Fe 2+ and Mg between olivine and liquid along a liquid line of descent has been determined for a calc-alkaline system, ranging in composition from picritic to andesitic. Experiments were conducted between 1000–1450° C and 1 bar to 30 kbar. Within the compositional range investigated
and
, the compositional dependence of the Fe 2+ and Mg partitioning is a function of the Mg-content of the liquid. The Mg-content of the liquid correlates strongly with temperature. The variation of the Fe 2+ and Mg partitioning were therefore evaluated individualy as functions of composition and temperature alone. The composition dependence of the cation-partitioning coefficients (Kd) is given by the following two equations: |
相似文献
3.
Earthquake recurrence intervals for large and great shallow mainshocks in 12 seismogenic sources along the North Pacific seismic zone (Alaska-Aleutians-Kamchatka-Kuril Islands) have been estimated and used for the determination of the following relations: |
相似文献
4.
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
5.
Dislocations in intermediate plagioclase feldspars, which were deformed under granulite facies conditions, have been analysed. The study reveals extensive ductile deformation by intracrystalline slip and by twinning. Six out of the seven possible Burgers vectors were identified: \(b = \left[ {001} \right],\tfrac{1}{2}\left[ {110} \right],\tfrac{1}{2}\left[ {1\bar 10} \right],\left[ {101} \right],\tfrac{1}{2}\left[ {112} \right]and\tfrac{1}{2}\left[ {1\bar 12} \right]\) . Most, perhaps all, dislocations are dissociated by up to 200 Å. The microstructure is dominated by [001] screw dislocations, most of which appear to be dissociated in (010). The dominant slip system appears to be (010) [001]. Large grain-to-grain variations in the density of free dislocations indicate that the plastic strain in individual grains depended upon the Schmid factor for (010) [001]. The microstructure suggests that the rate-controlling step for high-temperature creep of plagioclase is cross-slip of extended [001] screw dislocations. The rheological contrast between feldspar and quartz is partly due to a difference in stacking fault energy. 相似文献
6.
Macroseismic data of earthquakes felt in Israel and also recorded instrumentally are analyzed. The analysis yields the following empirical relations: |
相似文献
7.
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, say Y and Z 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
for Y and Z: (ii) defining new variables by
and
and letting A= C+ D and B= C– D, and obtaining MLE for variances,
and
for A and B; (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
8.
Observations in the North Sea Basin max indicate significant overpressure in sediments over horst blocks but not over grabens at the same submudline depth. The purpose is to show that over a horst, of top width W, with grabens on either side of top widths G 1 and G 2, respectively, the equivalent mud density. r can be estimated approximately from the simple equation. |
相似文献
9.
Three independent Pb isotope homogenizing processes operating on large volumes of rock material during limited intervals in the Phanerozoic have been used to define a unique evolutionary curve for rock and ore lead isotopic compositions of the southern Massif Central, France. The model is |
相似文献
10.
The chemical potential of oxygen defined by the equilibrium: |
相似文献
11.
Thorium(IV) sorption onto hematite (-Fe 2O 3) was examined as a function of pH and ionic strength. Sorption behaved Langmuirian over an eleven order of magnitude range in adsorption densities, : 10 –12 to 10 –1 moles Th sorbed per mole hematite sites, indicating that the overall free energy of Th adsorption is independent of adsorption density. Modeling of Th sorption was conducted with the Triple Layer Model of Davis and Leckie; reactions considered included solution-phase hydroxy and carbonato complexes of thorium, and carbonate/hematite surface complexes. The entire Th sorption isotherm can be modeled with a single surface complex formation reaction |
相似文献
12.
Ignimbrites from the central North Island consist mainly of glass or its devitrified product (70–95%); their phenocryst mineralogy is varied and includes plag., hyp., ti-mag., ilm., aug., hblende, biot., san., qtz, ol., with accessory apatite, zircon and pyrrhotite. The Fe-Mg minerals can be used to divide the ignimbrites into four groups with hyp.+aug. reflecting high quench temperatures and biot.+hblende +hyp.+aug., low quench temperatures. Oxygen fugacities lie above the QMF buffer curve and even in ignimbrites with low crystal contents the solid phases apparently buffered fO 2. Some ignimbrites contain the assemblage actinolite, gedrite, magnetite and hematite, reflecting post-eruption oxidation. The mineralogy also allows estimation of
using pyrrhotite and thence
,
. The assemblage biotite-sanidine can be used to estimate
and thence
. Water fugacity is calculated in a variety of ways using both biotite and hornblende as well as the combining reaction
. It is high and approaches P
total in most ignimbrites (~4kb) but is lower in unwelded pumice breccias. Comparison of temperature estimates using mineral geothermometers for the various phenocryst phases suggests that the ignimbrite magmas showed temperature differences of 60–100 °C and pressure differences of several kilobars. Individual magma chambers therefore, would have extended over several kilometres vertically. The chemical potential of water may have been constant through the magma. 相似文献
13.
Summary The crystallography of roscherite is more complicated than previously thought. Single crystal X-ray work on material from Foote Mine (California) gave triclinic symmetry. The unit cell corresponding to the one adopted for monoclinic roscherite has a=15.921, b=11.965, c=6.741 Å, =91°04, =94°21, =89°59 1/2, space group
. The least-squares refinement of the structure using 2380 non zero reflections with anisotropic temperature factors resulted in a conventional reliability factor R=0.060.The X-ray study indicates the formula
while that proposed for monoclinic roscherite is
The atomic arrangements of both varieties of roscherite are very similar. The lowering of symmetry is caused by the segregation of the trivalent cations into only half of the sites of a monoclinic point position. Crystallochemical considerations suggest that the symmetry of roscherite does not depend on the kind of trivalent cations occupying the 6-coordinated position, but rather by the ratio between trivalent and divalent metal ions.
Die Kristallstruktur eines triklinen Roscherites Zusammenfassung Die Kristallographie des Roscherites ist komplizierter als man bisher annahm. Einkristall-Röntgenuntersuchungen an Material von Foote Mine (Kalifornien) ergaben trikline Symmetrie. Die Elementarzelle, welche der für monoklinen Roscherit angenommenen entspricht, hata=15,921,b=11,965,c=6,741 Å, =91°04, =94°21, =89°59 1/2, Raumgruppe
. Die Verfeinerung der Struktur mit der Methode der kleinsten Quadrate ergab unter Verwendung anisotroper Temperaturfaktoren für 2380 beobachtete Reflexe einen konventionellen ZuverlässigkeitsindexR=0,060.Die Röntgenuntersuchung weist auf die Formel
, während für monoklinen Roscherit
vorgeschlagen wurde. Die Atomanordnungen beider Abarten des Roscherites sind sehr ähnlich. die Symmetrieerniedrigung wird dadurch hervorgerufen, daß die dreiwertigen Kationen nur die Hälfte der Positionen einer monoklinen Punktlage besetzen. Kristallchemische Überlegungen weisen darauf hin, daß die Symmetrie nicht von der Art der dreiwertigen Kationen, welche eine 6-koordinierte Punktlage besetzen, abhängt, sondern vielmehr von dem Mengenverhältnis zwischen 3-wertigen und 2-wertigen Metallionen.
With 1 Figure 相似文献
14.
Diffusion rates of 18O tracer in quartz ( c, 1 Kb H 2O) and Amelia albite ( 001, 2 Kb H 2O) have been measured, using Secondary Ion Mass Spectrometry (SIMS). A new technique involving hydrothermal deposition of labelled materials has removed the possibility of pressure solution-reprecipitation processes adversely affecting the experiments. Reported diffusion constants are: -quartz ( c),
, Q=98±7 KJ mol –1 (600–825° C, 1 Kb); Amelia albite ( 001),
, Q=85±7 KJ mol –1, (400–600° C, 2 Kb). Measured quartz 18O diffusivities decrease discontinuously at the - transition, reflecting strong structural influences. The reported albite data agree with previously recorded studies, but -quartz data indicate significantly lower activation energies. Possible causes of this discrepancy, and some geological consequences, are noted. 相似文献
15.
Five specimens deformed at differential stresses between 220 and 980 bar were selected for a transmission electron microscopy study from the suite of Yule Marble specimens of Heard and Raleigh (1972). The electron micrographs show twinning, curved free dislocations, sessile dislocation loops, and small angle boundaries. Both free dislocations and dislocation boundaries contain dislocation reactions which most likely involve the Burgers vectors 1/61¯102 and 1/121¯210 reacting to form 1/1210¯14. The dislocation densities of specimens deformed at the higher stresses were greater than the starting density and fit the relation
. However, the dislocation densities of specimens deformed at the lower stresses decreased only partially with respect to the starting density during the deformation experiments and thus are larger than predicted by this relation. 相似文献
16.
Zusammenfassung Durch Gangunterschiedsbestimmungen in der auf dem Drehtisch eingemessenen Kreisschnittebene optisch einachsiger Kristalle läßt rich eine mittlere Lichtbrechung
theoretisch ableiten and experimentell direkt bestimmen. Ein graphisches and ein rechnerisches Verfahren zur Gewinnung der
aus den Ganguntersehieden wird entwickelt and an Quarz, Korund, Zirkon, Turmalin und Eisenorthoklas ausprobiert. Man erhält für die mittlere Lichtbrechung Werte, die günstigenfalls mit der Immersionsmethode an Genauigkeit vergleichbar sind. 相似文献
17.
The principle of maximum entropy can be used to determine the shear strain in natural shear zones. When the margin of a shear zone is assumed, the principle leads to the truncated exponential distribution of the shear strain. If x is the distance remote from the shear zone center, which possesses the maximum shear strain, the shear strain ( x) is given by |
相似文献
18.
Titanite and rutile are a common mineral pair in eclogites, and many equilibria involving these phases are potentially useful in estimating pressures of metamorphism. We have reversed one such reaction, |
相似文献
19.
A nonuniform glacio-isostatic uplift results in differential uplift for different parts of a lake. If the lake outlet is situated in the area with the greatest rate of uplift, then the lake will be continuously transgressed. Ancient lake levels can be estimated by dating transgressed peat at different depths in such a lake. Two lakes in southwestern Sweden have been investigated by this method and the course of glacio-isostatic uplift has been determined empirically. The uplift can be expressed by an exponential function through the following formula |
相似文献
20.
The partitioning of Mg and Fe 2+ between coexisting olivines and orthopyroxenes in the system MgO-FeO-SiO 2 has been investigated experimentally at 1173, 1273, 1423 K and 1.6 GPa over the whole range of Mg/Fe ratios. The use of barium borosilicate as a flux to promote grain growth, and the identification by back-scattered electron imaging of resulting growth rims suitable for analysis by electron microprobe, results in coexisting olivine and orthopyroxenene compositions determined to a precision of±0.003 to 0.004 in molar Fe/(Mg+Fe). Quasi-reversal experiments were performed starting with Mg-rich olivine and Fe-rich orthopyroxene (low K D) and vice versa (high K D), which produced indistinguishable results. The distribution coefficient, K D, depends on composition and on temperature, but near Fe/(Mg+Fe)=0.1 (i.e. mantle compositions) these effects cancel out, and K D is insensitive to temperature. The results agree well with previous experimental investigations, and constrain the thermodynamic mixing properties of Mg-Fe olivine solid solutions to show small near-symmetric deviations from ideality, with
between 2000 and 8000 J/mol. Multiple non-linear least squares regression of all data gave a best fit with
(implying 5450 J/mol at 1 bar) and
, but the two W
G
parameters are so highly correlated with each other that our data are almost equally well fit with
, as obtained by Wiser and Wood. This value implies
, apparently independent of temperature. Our experimental results are not compatible with the assessment of olivine-orthopyroxene equilibria of Sack and Ghiorso. 相似文献
|
|
|
|
|
|
|
|
|
|
|
|
