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71.
Romano Rinaldi G. D. Gatta G. Artioli K. S. Knight C. A. Geiger 《Physics and Chemistry of Minerals》2005,32(8-9):655-664
The thermal expansion, structural changes and the site partitioning of Co and Mg in synthetic CoMgSiO4 olivine have been studied by in situ time-of-flight neutron powder diffraction as a function of temperature, between 25 and
1,000°C. Thermal expansion of the unit cell dimensions and volume are linear within this temperature range and give no indications
of a phase transition, although the thermoelastic behaviour indicates a slight strain minimum around 700°C. Co2+ shows a strong preference for the M1 site throughout this temperature range with an oscillatory behaviour; it decreases slightly
at about 300°C, climbing up to nearly its original value at around 800°C and then decreasing by about 30% at 1,000°C. This
behaviour is in contrast with that of (Fe, Mg)2SiO4 olivine, in which the initial Fe2+ site preference for the M1 site switches to the M2 site beyond a cross-over temperature. The oscillatory site preference
in (CoMg)-olivine as a function of temperature is reflected in the M–O polyhedral volume changes and M–O bond lengths, as
well as, thermoelastic strain and atomic thermal displacement parameters. The imbalance between the increasing vibrational
and decreasing configurational entropy contributions, together with covalent bonding effects rather than crystal field contributions,
seem to drive the cation partitioning in (CoMg)-olivine. 相似文献
72.
Andreas Schlatter Dieter Schneider Alain Geiger Hans-Gert Kahle 《International Journal of Earth Sciences》2005,94(4):507-514
The southern end of the Upper Rhine Graben is one of the zones in Switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region. Therefore, in 1973 a control network with levelling profiles across the eastern Rhine Graben fault was installed and measured in the vicinity of the city of Basel in order to measure relative vertical movements and investigate their relationship with seismic events. As a contribution to EUCOR-URGENT, the profiles were observed a third time in the years 2002 and 2003 and connected to the Swiss national levelling network. The results of these local measurements are discussed in terms of accuracy and significance. Furthermore, they are combined and interpreted together with the extensive data set of recent vertical movements in Switzerland (Jura Mountains, Central Plateau and the Alps). In order to be able to prove height changes with precise levelling, their values should amount to at least 3–4 mm (1). The present investigations, however, have not shown any significant vertical movements over the past 30 years. 相似文献
73.
Pumpellyite of the general formula W8X4Y8-Z12O56-n(OH)n contains Fe, Al and Mg in two crystallographically different octahedral sites. Three different pumpellyite samples covering the known compositional field from Al- to Fe-rich have been studied to determine the valence state and intracrystalline partitioning of the Fe cations between the two independent octahedral sites. Fe+2 and Fe+3 cation partitioning is interpreted on the basis of results obtained by 57Fe Mössbauer spectroscopy at 293 and 77 K and from Rietveld structure analysis performed on powder X-ray diffraction data. Pumpellyite from low-grade metamorphic rocks typically contains a majority of iron in the Fe+3 oxidation state, which is found in the smaller and less symmetrical octahedral Y-site. Fe+2 was also present in all pumpellyite samples studied and it is located in the larger and more symmetrical octahedral X-site. 相似文献
74.
Dr. René Gächter Dr. Wolfgang Geiger 《Aquatic Sciences - Research Across Boundaries》1979,41(2):277-290
Phytoplankton, periphyton and zooplankton samples, chironomid andSialis sp. larvae, and fry of trout and bream collected from unpolluted and artificially metal-polluted limno-corrals were analyzed
for mercury, copper, cadmium, zinc and lead. The results indicate that these metals are not accumulated through the food chain
and suggest that increased metal concentrations in the environment favor the growth of phytoplankton organisms with a low
metal sorption capacity. 相似文献
75.
The most recent results of uplift rates determined by repeated precise levelling, are analyzed in terms of geodynamic processes still going on in the region of the Alpine-Mediterranean plate boundary. Special emphasis is focused on levelling nets in the Swiss Alps which have been remeasured for the second time. A comparison of these geodetic results with geophysical information, such as gravity anomalies and explosion seismic results, as well as seismicity, provides further evidence that these sets of data are interrelated with each other. An attempt is made to estimate the strain energy associated with the crustal deformation by introducing first-order stress-strain relationships. 相似文献
76.
Raman spectra of silicate garnets 总被引:2,自引:1,他引:1
The single-crystal polarized Raman spectra of four natural silicate garnets with compositions close to end-members almandine,
grossular, andradite, and uvarovite, and two synthetic end-members spessartine and pyrope, were measured, along with the powder
spectra of synthetic pyrope-grossular and almandine-spessartine solid solutions. Mode assignments were made based on a comparison
of the different end-member garnet spectra and, in the case of pyrope, based on measurements made on additional crystals synthesized
with 26Mg. A general order of mode frequencies, i.e. R(SiO4)>T(metal cation)>T(SiO4), is observed, which should also hold for most orthosilicates. The main factors controlling the changes in mode frequencies
as a function of composition are intracrystalline pressure (i.e. oxygen-oxygen repulsion) for the internal SiO4-vibrational modes and kinematic coupling of vibrations for the external modes. Low frequency vibrations of the X-site cations
reflect their weak bonding and dynamic disorder in the large dodecahedral site, especially in the case of pyrope. Two mode
behavior is observed for X-site cation vibrations along the pyrope-grossular binary, but not along the almandine-spessartine
join.
Received: 3 December 1996 / Revised, accepted: 13 April 1997 相似文献
77.
Sedimentologists often find such depositional sequences, which visually, but even for microscopic examinations look homogeneous, and their fossil-content is very low. These sequences can be subdivided into genetic units only with great difficulties or not at all, and their correlation may be problematical.An experiment is presented here, aiming at a subdivision of loess profiles by a combined use of sedimentological, palaeontological and mathematical methods. The loess samples selected for this examination were characterised by their grain size parameters as suggested by Folk and Ward (1957) and by their carbonate content. Using a Q-type cluster analysis these samples were classified into different groups by their similarity. After arranging the samples with their cluster symbols into their real stratigraphic position, the genetic units of the depositional sequence were delimited by an analysis of the vertical series of the previously established cluster-groups. Finally, a method of discriminant analysis was applied to establish the stability, ie the probability, of the existence of the vertical genetic units obtained by this zonation method.Parallel to it the sequence was subdivided from a faunistic point of view, too. These units correlate well with the results of the numeric approach. 相似文献
78.
Bridget O'Neill Jay D. Bass George R. Rossman Charles A. Geiger Klaus Langer 《Physics and Chemistry of Minerals》1991,17(7):617-621
Brillouin spectroscopy was used to measure the single crystal elastic properties of a pure synthetic pyrope and a natural garnet containing 89.9 mol% of the pyrope end member (Mg3Al2Si3O12). The elastic moduli, c
ij
, of the two samples are entirely consistent and agree with previous estimates of the elastic properties of pyrope based upon the moduli of solid solutions. Our results indicate that the elastic moduli of pyrope end-member are c
11=296.2±0.5, c
12=111.1±0.6, c
44=91.6±0.3, Ks=172.8±0.3, =92.0±0.2, all in units of GPa. These results differ by several percent from those reported previously for synthetic pyrope, but are based upon a much larger data set. Although the hydrous components of the two samples from the present study are substantially different, representing both dry and saturated samples, we find no discernable effect of structurally bound water on the elastic properties. This is due to the small absolute solubility of water in pyrope, as compared with other garnets such as grossular. 相似文献
79.
S. Quartieri J. Chaboy G. Antonioli C. A. Geiger 《Physics and Chemistry of Minerals》1999,27(2):88-94
We present an X-ray absorption near-edge structure study performed at the Yb LI- and LIII-edges on synthetic pyrope (Mg3Al2Si3O12) and grossular (Ca3Al2Si3O12) garnets containing about 1% wt of Yb. For the first time Yb L-edge XANES spectra are analyzed by full multiple scattering
theory using clusters of different sizes and different final-state potentials. A comparison between experimental spectra and
model calculations indicates that Yb3+ enters the dodecahedral X-site in both pyrope and grossular, in agreement with the results of an EXAFS study. Based on the
present results, the charge balancing substitution mechanism required by the replacement of divalent Mg and Ca cations with
trivalent Yb3+ is discussed in terms of vacancies in dodecahedral sites surrounding the central Yb3+ absorber.
Received: 7 December 1998 / Revised, accepted: 7 May 1999 相似文献
80.
Zhen-Ming Ge Seppo Kellomäki Heli Peltola Xiao Zhou Hannu Väisänen Harri Strandman 《Climatic change》2013,118(2):259-273
The aim of this study was to estimate the potential impacts of climate change on the spatial patterns of primary production and net carbon sequestration in relation to water availability in Norway spruce (Picea abies) dominated forests throughout Finland (N 60°–N 70°). The Finnish climatic scenarios (FINADAPT) based on the A2 emission scenario were used. According to the results, the changing climate increases the ratio of evapotranspiration to precipitation in southern Finland, while it slightly decreases the ratio in northern Finland, with regionally lower and higher soil water content in the south and north respectively. During the early simulation period of 2000–2030, the primary production and net carbon sequestration are higher under the changing climate in southern Finland, due to a moderate increase in temperature and atmospheric CO2. However, further elevated temperature and soil water stress reduces the primary production and net carbon sequestration from the middle period of 2030–2060 to the final period of 2060–2099, especially in the southernmost region. The opposite occurs in northern Finland, where the changing climate increases the primary production and net carbon sequestration over the 100-year simulation period due to higher water availability. The net carbon sequestration is probably further reduced by the stimulated ecosystem respiration (under climate warming) in southern Finland. The higher carbon loss of the ecosystem respiration probably also offset the increased primary production, resulting in the net carbon sequestration being less sensitive to the changing climate in northern Finland. Our findings suggest that future forest management should carefully consider the region-specific conditions of sites and adaptive practices to climate change for maintained or enhanced forest production and carbon sequestration. 相似文献