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41.
Bastian Joachim Emmanuel Gardés Rainer Abart Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2011,161(3):389-399
Growth rates of monomineralic, polycrystalline åkermanite (Ca2MgSi2O7) rims produced by solid-state reactions between monticellite (CaMgSiO4) and wollastonite (CaSiO3) single crystals were determined at 0.5 GPa dry argon pressure, 1,000–1,200°C and 5 min to 60 h, using an internally heated pressure vessel. Inert Pt-markers, initially placed at the monticellite–wollastonite interface, indicate symmetrical growth into both directions. This and mass balance considerations demonstrate that rim growth is controlled by transport of MgO. At 1,200°C and run durations between 5 min and 60 h, rim growth follows a parabolic rate law with rim widths ranging from 0.4 to 16.3 μm indicating diffusion-controlled rim growth. The effective bulk diffusion coefficient \( D_{\text{eff,MgO}}^{\text{Ak}} \) is calculated to 10?15.8±0.1 m2 s?1. Between 1,000°C and 1,200°C, the effective bulk diffusion coefficient follows an Arrhenius law with E a = 204 ± 18 kJ/mol and D 0 = 10?8.6±1.6 m2 s?1. Åkermanite grains display a palisade texture with elongation perpendicular to the reaction interface. At 1,200°C, average grain widths measured normal to elongation, increase with the square root of time and range from 0.4 to 5.4 μm leading to a successive decrease in the grain boundary area fraction, which, however, does not affect \( D_{\text{eff,MgO}}^{\text{Ak}} \) to a detectible extent. This implies that grain boundary diffusion only accounts for a minor fraction of the overall chemical mass transfer, and rim growth is essentially controlled by volume diffusion. This is corroborated by the agreement between our estimates of the effective MgO bulk diffusion coefficient and experimentally determined volume diffusion data for Mg and O in åkermanite from the literature. There is sharp contrast to the MgO–SiO2 binary system, where grain boundary diffusion controls rim growth. 相似文献
42.
Bernhard Krautzer Wilhelm Graiss Giovanni Peratoner Christian Partl Sonia Venerus Brigitte Klug 《Natural Hazards》2011,56(2):547-557
Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is
one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine
vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of
natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success.
Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces
soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups
and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education
Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The
aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones,
especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a
statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation
cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first
two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss
be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of
the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the
following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five
experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses
and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period.
In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically
adapted species. 相似文献
43.
In the night from 8/9 April 2009, shortly after midnight on Maundy Thursday before Easter, several people in Gross Flottbek,
Hamburg, felt unusual strong ground shocks so that some of them left their houses in fear of earthquake shaking. Police and
fire brigade received phone calls of worried residents. A few days later, Internet pages were published where people reported
their observations. On 21 April 2009 at about 8 p.m. local time, a second ground-shaking event was felt. Damage to buildings
or infrastructure did not occur to our knowledge. The Institute of Geophysics, University of Hamburg, installed from 22 April
to 17 May 2009 three temporal seismic stations in the epicentral area. Seismological data from two nearby stations at the
Deutsches Elektronen-Synchrotron at 1 km and the Geophysical Institute at 7 km distance were collected and integrated to the
temporal network. The events occurred above the roof of the shallow Othmarschen Langenfelde salt diapir, in an area known
for active sinkhole formation and previous historic ground-shaking events. The analysis of the seismological data shows that
three shallow micro-earthquakes occurred from 8 to 21 April at a depth of about 100 m, the largest one with a moment magnitude
of about M
W 0.6. Depth location of such shallow events is difficult with standard methods and is here constrained by waveform modeling
of surface waves. Earthquakes occurring in soft sediments within the uppermost 100 m are a rare phenomena and cannot be explained
by standard models. Rupture process in soft sediments differs from those on faults in more competent rock. We discuss the
rupture and source mechanism of the events in the context of previous historic shocks and existing sinkhole and deformation
data. Although the event was weak, the rupture duration of 0.3 s was unusual long. Three possible models for the generation
of repeated ground-shaking events in Gross Flottbek are developed and discussed, implying quit different hazards for subsidence,
ground motion, and sinkhole formation. Our favored model postulates that roof failure occurs in an existing soil cavity beneath
the epicenter at a depth of about 100 m. Other models bearing a smaller geo-hazard cannot be disproved with the data available,
but future geophysical experiments may be planned to resolve this question. 相似文献
44.
Four small freshwater river systems in Hessen, Germany, have been investigated with respect to seasonal and spatial concentration variations and transported load of the organophosphates tri‐n‐butyl phosphate (TBP), tris(2‐butoxyethyl)phosphate (TBEP), tris(2‐chloroethyl)phosphate (TCEP), tris(1‐chloro‐2‐propyl)phosphate (TCPP), and tris(1,3‐dichloro‐2‐propyl)phosphate (TDCPP) and the synthetic musk fragrances 1,3,4,6,7,8‐hexahydro‐4,6,6,7,8,8‐hexa‐methylcyclopenta‐[γ]‐2‐benzopyran (HHCB) and 7‐acetyl‐1,1,3,4,4,6‐hexamethyl‐1,2,3,4‐tetrahydronaphthalene (AHTN). Data originate from water samples collected in the time span from September 2003 to April 2005 at 25 sampling locations. The detection frequency for all compounds was about 90%. Mean concentration levels of organophosphates were 502 ng/L (TCPP), 276 ng/L (TBP), 183 ng/L (TBEP), 118 ng/L (TCEP), and 117 ng/L (TDCPP). The synthetic musk fragrances HHCB and ATHN were detected with mean concentrations of 141 and 46 ng/L, respectively. The variability of the concentration of all compounds was high with respect to space and time. The highest concentrations were observed in the Schwarzbach system characterized by the highest proportion of wastewater compared to the other river systems. Concentration levels of synthetic musk fragrances were significantly lower in summer times compared to winter times. 相似文献
45.
The Red Basin is a tectonic structure. Master stream is the Jialing Jiang, the most important tributary of the Chang Jiang in this area. The landforms are a cuesta landscape, climate is subtropic. Under irrigation 3 harvests of grain are possible. Small farms dominate. The region is overpopulated. Industrialization is in its infancy. Intense deforestation, extension of arable land and increasing grazing of animals on slopes and scarps of field-terraces have caused a change in precipitation, water regime and discharge of stream-borne material in the catchment area of the Rating Jiang. This differs distinctly from the neighbouring rivers and can be compared with the rivers of the loess areas of N China. Severe soil erosion destroys arable land at a growing rate. Unlike the loess area in the Red Basin, there is only a thin layer of soil which can be regenerated only over a long period of time. Afforestation and hydraulic engineering are intended to retard soil erosion. More effective would be diminished intensity of land use and the supply of organic material from plant decay — hitherto used as fuel - for soil. formation. But lack of employment outside agriculture prevents more extensive land use. So the destructive intervention into the ecosystem reflects the strain of increasing population in the stage of beginning industrialization. *** DIRECT SUPPORT *** ABI02050 00004 相似文献
46.
Experimental study of a biotite-bearing granitic system under water-saturated and water-undersaturated conditions 总被引:6,自引:0,他引:6
Phase relationships in haplogranitic melts containing ferromagnesian minerals were investigated in the temperature range 760–850°C, atP
total=2 kbar,
=0.25 1.00, and at NNO buffer conditions. The compositions of coexisting biotite, orthopyroxene, magnetite and granitic melt were determined by electron microprobe. Biotite was the only Fe–Mg mineral in the starting material. It disappeared in water-undersaturated melts at temperatures above 830°C and in melts saturated with water above 810°C. Magnetite was present in all runs. Orthopyroxene became stable between 780 and 800°C. The Mg/(Mg+Fe) ratios of biotite (0,63–0,72) and orthopyroxene (0,63–0,71) are similar in water-saturated and undersaturated melts at comparable temperatures and increase slightly with increasing temperature. The solubility of Mg in haplogranitic melts is very low (0,07–0,24 wt% MgO). It increases slightly with temperature and is independent of the prevailing water activity. The solubility of Fe is low (0,91–1,37 wt% FeO); it also increases with increasing temperature, and it is higher in water-saturated than in water-undersaturated melts. 相似文献
47.
Rolf Zimmermann M. Gottschalk Wilhelm Heinrich Gerhard Franz 《Contributions to Mineralogy and Petrology》1997,126(3):252-264
The cation exchange equilibrium has been investigated by hydrothermal experiments at 700 and 800°C at 200 MPa. To avoid equilibration problems of conventional exchange experiments, we synthesized amphiboles with an excess fluid allowing exchange between solid and fluid during the experiment. The exchangeable cations Na and K were provided as excess 1 to 2n chloridic solution. These exchange syntheses can be described by the reaction equation with (aq) for hydroxides and chlorides in aqueous solutions and ( s ) and ( p )?=?start and product fluid. The amphiboles grew in presence of the exchange fluid and adjusted their stoichiometry in equilibrium with the fluid phase. The solid products consist of more than 99% amphibole (Na,K-richteritess) with traces of diopside and quartz. The amphiboles are up to 1?mm long and often ≈ 40 μm thick. Detailed EMP- and HRTEM-observations show that they are chemically homogeneous and structurally wellordered. The experimental results give consistent phase relations in the reciprocal ternary system Na-richterite–K-richterite–NaCl–KCl. We analysed the product fluid with AAS- and ICP-methods. The Na-K distribution coefficients between fluid and amphiboles of the richterite–K-richterite join are close to unity at 700°C and 800°C at 200 MPa. Small systematic deviations are explained by a symmetric solution model for the A-position of the amphiboles. Using ideal mixing for H2O-NaCl-KCl fluids, a mixing model for the system richterite–K-richterite is presented. We suggest that the composition of richterite solid solutions can be used as a sensor for NaCl/KCl-ratios in metamorphic fluids. 相似文献
48.
49.
Wilhelm F. Schmidt 《International Journal of Earth Sciences》1951,39(1):143-147
Ohne Zusammenfassung 相似文献
50.
Wilhelm Delhaes 《International Journal of Earth Sciences》1915,6(4-6):202-206
Ohne ZusammenfassungDer Verfasser ist in der Nacht vom 25./26. September 1915 in der Champagne gefallen. 相似文献