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111.
Dr. B. Lehmann 《International Journal of Earth Sciences》1987,76(1):177-185
Metallogenic provinces are not self-evident geochemical provinces. A scheme to quantify the processes of »geochemical heritage« and »magmatic differentiation« in the evolution of tin granites is presented. Geochemical heritage can be limited to a maximum contribution in the 5–10 ppm Sn range. The crucial process in the formation of tin granites is magmatic differentiation. A variable bulk Sn distribution coefficient controls the tin ore potential of granites.
Zusammenfassung Metallogenetische Provinzen stehen nicht zwangsläufig mit einer spekulativen regionalen geochemischen Spezialisierung im Zusammenhang. Am Beispiel der Zinngranite wird ein Schema zur Quantifizierung der beiden Komponenten »geochemische Vererbung« und »magmatische Differentiation« vorgestellt. Geochemische Vererbung kann dabei auf den Bereich von maximal 5–10 ppm Sn eingegrenzt werden. Entscheidender Prozess für die Bildung von Zinngraniten ist die magmatische Differentiation, wobei ein variabler Bulk-Zinn-Verteilungskoeffizient das mögliche Zinn-Potential bestimmt.
Résumé Les provinces métallogéniques ne correspondent pas nécessairement à des domaines à permanence géochimique. Prenant l'exemple des granites à étain, l'auteur présente un schéma qui quantifie les deux composants que sont »l'héritage géochimique« et la »différenciation magmatique«. L'héritage géochimique peut Être limité à une contribution maximale de 5 à 10 ppm Sn. Le processus décisif dans la formation des granites à étain est la différenciation magmatique, au cours de laquelle le coefficient de répartition de Sn est variable et détermine le potentiel-métal du granite.
. , , . 5–10 . .相似文献
112.
A new method for the sampling of sublimates from high-temperature volcanic gases has been used at Merapi volcano, Java, in 1978. The sublimates were collected on the inner walls of silica tubes introduced into fumarolic vents. Volcanic gases were allowed to move freely through the tubes and as they cooled, a fraction of the volatile components condensed on the inner walls of the tubes along the temperature gradient. The sublimates were then analyzed by a combination of light microscopy, scanning electron microscopy, electron microprobe and X-ray diffraction.Six successive zones of different compositions and mineralogical associations have been identified along the covered range of temperatures (900° to around 400°C). From the high to the low temperatures, these zones are composed of: (1) cristobalite, magnetite, hercynite; (2) molybdenite; (3) acmite; (4) halite, sylvite; (5) sphalerite, pyrite; and (6) galena. Equilibrium calculations show that these crystalline phases are stable for pS2, pC1, and pO2, values typical of magma-buffered gases that have not been contaminated by atmospheric oxygen.The deposits observed in the tubes may be useful in aiding the understanding of the mechanisms acting during the cooling of the gaseous phase on its way to the surface and before its emission into the atmosphere. 相似文献
113.
The frequency-independent foundation impedances, commonly used in soil-structure dynamic interaction problems, are developed for a circular footing resting on a homogeneous halfspace. As they ignore the structure attached to the foundation, the error introduced in the structural response may be 50 per cent or more in the neighbourhood of the fundamental frequency of the soil-structure system. The present study proposes a new method developed for most dynamic soil-structure interaction problems. The key idea is to retain for the frequency-independent impedances values computed for the fundamental frequency of the soil-structure system; thus these values include the dynamic characteristics of the whole soil-structure system and lead to a satisfactory approximation of the exact solution over a wide frequency range. The method is developed here for the horizontal and rocking modes of a structure with a circular base resting on a homogeneous halfspace. Numerical applications are given for a simple linear oscillator in order to make possible a thorough parametric study. The response of some idealized building-foundation systems to harmonic excitation or to a seismic input is next examined in order to illustrate the efficiency of the proposed model. 相似文献
114.
In natural citrines five new hole centers were detected and analyzed by electron paramagnetic resonance. An additional one was observed in rose-colored quartz crystals with radiation defects as the cause of coloration. Characteristic hyperfine patterns due to an adjacent aluminum impurity were resolved in the spectra of three of these centers. Their relations to other hole centers of well-known structure in quartz and fused silica are discussed and possible models for their structures are proposed. 相似文献
115.
Observation under the electron microscope of diatom frustules from Bolivian Altiplano saline lakes shows that many of these are coated with particles occurring as tiny sheets. The frustules can be found to be almost completely replaced by these sheets. Isolated sheet aggregates seem to have resulted from completely transformed frustules. Section observations of altered frustules bear out that the sheets have grown from biogenic silica through replacement. Selected area diffraction, dark field observation, microdiffraction, and elemental microanalysis show that the particles on the diatom frustules consist of a poorly crystallized MG-smectite.The unambiguous localisation of this authigenesis allows us to reconstruct its hydrochemical and sedimentological environment. Observation of the most recent lake sediments has pointed out that at least two main conditions are required for this authigenesis at 5°C: saturation with respect to amorphous silica, and a pH above 8.2. Variations in the Mg concentration have no significant effect. 相似文献
116.
Résumé L'analyse géométrique et cinématique de la fracturation dans le Jura franconien et la bordure occidentale du Massif bohémien met en évidence les mécanismes de la tectonique cassante d'âge teriaire, essentiellement ceux des grands accidents SE-NW (lignes de Pfahl et de Franconie) qui ont présenté successivement des jeux en coulissement dextre, en faille normale et en faille inverse. Cinq états de contrainte ont été caractérisés et comparés à ceux définis antérieurement dans le Jura souabe, en liaison avec la cinématique des plaques Europe et Afrique: compression N-S, distension E-W, compression NE-SW puis E-W, distension N-S.
The analysis of both the geometric and the kinematic cenozoic faulting in the Franconian Jura and in western Bohemia enables to characterize the mechanisms of cenozoic tectonics. More especially dextral strike-slip, normal fault and reverse fault have successively occurred along large SE-NW fault line, as the Pfahl and the Franconian fault systems. Five main stress patterns have thus been identified and then compared with those previously described in Swabian Jura. They are related to the kinematic of Europe and Africa plates, i. e.: (1) N-S compression, (2) E-W distension, (3) SW-NE compression, (4) E-W compression, (5) N-S distension.
Zusammenfassung Durch die geometrische und kinematische Analyse der Brüche wird die tertiäre Bruchtektonik (tectonique cassante) im Fränkischen Jura und am westlichen Rand des Böhmischen Massifs belegt. Es handelt sich im wesentlichen um die großen SE-NW orientierten Störungen der Linie von Pfahl und der Fränkischen Linie, die nacheinander als dextrale Blattverschiebungen, als Normalverwerfungen und als inverse Verwerfungen wirkten. Fünf Spannungszustände können charakterisiert und mit jenen, die bereits im Schwäbischen Jura definiert wurden, verglichen werden. Sie spiegeln die verschiedenen Stadien der kinematischen Entwicklung der europäischen und afrikanischen Platte wider: Kompression N-S, Zerrung E-W, Kompression NE-SW, sodann E-W, Zerrung N-S.
(tectonique cassante) . , , SE-NW , , , . 5 . : - , - , - , - - .相似文献
117.
A climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric
General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity
waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved
waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects
of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model’s
ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the
stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation
(AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the
parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents
much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the
downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the
surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal
from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used
tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic
AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this
result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment
of the model parameters that affect the tropospheric variability. 相似文献
118.
A large ensemble modeling experiment with the Melbourne University General Circulation Model is presented. Thirty 17-year-long independent simulations were performed. All integrations were forced by the same observed sea surface temperatures, obtained from the Atmospheric Model Intercomparison Project II. The simulations were analyzed to assess the sensitivity of the North Atlantic Oscillation (NAO) to the El Niño/Southern Oscillation (ENSO) polarity. The results show signals of the ENSO phases both in the mean strength of the NAO as well as in its internal variability. During the cold ENSO phase, the probability density function of the NAO index presents a small but positive mean value, whereas it is negative during the warm ENSO phase. Also, the NAO variability associated with each ENSO phase shows a different behavior: during the warm phase the probability density function of the NAO index presents a larger variance and suggests a bimodality, whereas no bimodality is suggested in the cold phase. 相似文献
119.
Within the frame of the ESCOMPTE program, a spatial emission inventory and an emission database aimed at tropospheric photochemistry intercomparison modeling has been developed under the scientific supervision of the LPCA with the help of the regional coordination of Air Quality network AIRMARAIX. This inventory has been established for all categories of sources (stationary, mobile and biogenic sources) over a domain of 19,600 km2 centered on the cities of Marseilles–Aix-en-Provence in the southeastern part of France with a spatial resolution of 1 km2. A yearly inventory for 1999 has been established, and hourly emission inventories for 23 days of June and July 2000 and 2001, corresponding to the intensive measurement periods, have been produced. The 104 chemical species in the inventory have been selected to be relevant with respect to photochemistry modeling according to available data. The entire list of species in the inventory numbers 216 which will allow other future applications of this database. This database is presently the most detailed and complete regional emission database in France. In addition, the database structure and the emission calculation modules have been designed to ensure a better sustainability and upgradeability, being provided with appropriate maintenance software. The general organization and method is summarized and the results obtained for both yearly and hourly emissions are detailed and discussed. Some comparisons have been performed with the existing results in this region to ensure the congruency of the results. This leads to confirm the relevance and the consistency of the ESCOMPTE emission inventory. 相似文献
120.
Summary We document a rare case of micron-sized gold inclusions in Ir–Os alloy and overgrowth rims on Pt–Fe alloy from an alluvial
Au-PGE placer derived from an Uralian/Alaskan type intrusion in Primorye, Russia. The gold inclusions occasionally form complex
aggregates with cooperite [PtS] or tolovkite [IrSbS], and replace magmatic inclusions of Ir-rich Pt–Fe alloy which exsolved
from the Ir–Os–Pt matrix. Gold has a relatively constant composition (>90 wt.% Au, a few wt.% Ag, and up to 8 wt.% Pt).
The gold rims form superfine (3–5 μm) discontinuous films on the Pt–Fe alloy crystals often followed by cooperite overgrowth.
Both gold textures suggest an electrochemical control of gold precipitation via selective Pt–Fe leaching during low-temperature
overprint and/or weathering of PGE alloy. 相似文献