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161.
Rainer Altherr Friedhelm Henjes-Kunst Alan Matthews Hans Friedrichsen Bent Tauber Hansen 《Contributions to Mineralogy and Petrology》1988,100(4):528-541
Sr, O, and D/H isotopic compositions have been analyzed in Miocene metaluminous to slightly peraluminous (I-type) granitoids of the central Aegean. Individual plutonic complexes display significant variations in their
18O and initial87Sr/86Sr compositions.D and
18O compositions of minerals and whole-rocks are mostly in the magmatic range. Some samples from Naxos and Mykonos/Delos show low D and
18O values characteristic of meteoric-water-hydrothermal interaction, but as a whole the changes in
18O and Sr isotopic compositions as a result of hydrothermal alteration were slight, even in instances where marked alteration is petrographically observable. Consequently, the bulk-rock variations of
18O from 8.1 to 12.0 and of87Sr/86Sr from 0.70438 to 0.71450 may be regarded as primary and indicative of the conditions of their evolution. Heterogeneous isotopic compositions observed in the individual plutons of Serifos, Ikaria, Samos and Kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses, with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization. The granitoids of Serifos, Ikaria and Kos display weak correlations between the initial87Sr/86Sr and
18O and 1/Sr. The granitoid province shows a positive correlation between87Sr/86Sr and
18O and a non-linear relationship between87Sr/86Sr and 1/Sr, whereby 1/Sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases. It is argued that assimilation of older continental material by mantle-derived arc magmas with combined fractionation (AFC) is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock-types trend from granodiorites in the (south)west, near the inferred Oligocene-Miocene suture, to granites in the center and monzonites in the (north)east of the province. 相似文献
162.
The paper presents numerical simulations of water infiltration in unsaturated porous media containing coarse-textured inclusions embedded in fine-textured background material. The calculations are performed using the two-phase model for water and air flow and a simplified model known as the Richards equation. It is shown that the Richards equation cannot correctly describe flow in the presence of heterogeneities. However, its performance can be improved by introducing appropriately defined effective capillary and permeability functions, representing largescale behaviour of the heterogeneous medium. 相似文献
163.
Rainer Putz 《Aquatic Sciences - Research Across Boundaries》1997,59(1):74-93
Chlorophyll a-concentrations, AFWD (ash-free-dry-weight) and photosynthesis rates were estimated for periphyton assemblages in Amazonian black-and white-water habitats over 14 months. Cellulose-acetate strips were incubated in situ and showed few major differences in periphyton quality as compared to natural substrata. The only exceptions were submersed Igapó forest leaves, which exhibited higher proportions of green algae and cyanobacteria though not producing differences in total periphyton biomass. Enclosure experiments showed a considerable nutrient release by inundated non-senescent Igapó forest leaves. Periphyton biomass and productivity were found to be highest in black-and white water mixing zones, where biomass peaked at 41.6 mg Chla/m2 and 19.8 g/m2 AFDW. Production was estimated to be 380 gC/m2·a. Maximum biomass of periphyton in floating meadows was 46 mg Chla/m2 and 10.6 g/m2 AFDW, with an annual production of 170 gC/m2·a. Solimões main channel periphyton values were low: maximum Chla was 7.1 mg/m2, AFDW 0.8 g/m2 and annual production was estimated to be 30 gC/m2. Blackwater periphyton values were lower compared to whitewater and mixed water values but an enlarged trophogenic zone has to be taken into account. Highest Chla content reached 30.9 mg/m2, AFDW 1.43 g/m2. Estimated annual production was 110 gC/m2. Observed mean periphyton productivity of Amazonian blackwater habitats approximately corresponded to mesotrophic attached algae productivity in temperate zones, whereas productivity of whitewater periphyton approached those of temperate eutrophic lakes. The role of periphyton in the Amazon food web is discussed. 相似文献
164.
Dislocation structure of the crust-mantle boundary and low-velocity body within the crust beneath the Dabie Shan collision orogen 总被引:6,自引:2,他引:6
LIU Qiyuan Rainer Kind CHEN Jiuhui YUAN Xiaohui LI Shuncheng GUO Biao Kurt Wylegalla & LAI Yuangen . State Key Laboratory of Earthquake Dynamics Institute of Geology China Earthquake Administration Beijing China . GeoForschungZentrum Potsdam Telegrafenburg A Potsdam D- Germany 《中国科学D辑(英文版)》2005,48(7)
The Dabie Shan is located on the eastern side of the Qinling-Dabie orogenic belt, which marks a geological boundary between the Sino-Korean and Yangtze cra- ton. Since the 1980s, the discovery of coesite and mi- crodiamond in the Dabie Shan orogen motivates an extensive interest to the ultra-high pressure (UHP)metamorphism and its exhumation[1,2]. Many results about them were published, which deal with different disciplines, including tectonics, petrology and chro- nology[3?8]. Up to now,… 相似文献
165.
Responses of a multifrequency, multicoil airborne electromagnetic (AEM) system were modelled numerically for 3D electrical conductors embedded in a resistive bedrock and overlain by an overburden of low to moderate conductivity. The results cover a horizontal coplanar coil configuration and two frequencies, 7837 Hz and 51 250 Hz. The models studied are single or multiple, poor conductors (conductance lower than 0.1 S) embedded in a host rock of high but finite resistivity (5000 Ωm) and overlain by a layer of overburden with finite thickness and low to moderate conductivity (conductance up to 2 S). On the basis of the modelling results, limits of detectability for poor conductors have been studied for the various model structures. The results indicate that the anomaly from a steeply dipping, plate-like conductor will decrease significantly when the conductor is embedded in a weakly conductive host rock and is overlain by a conductive overburden. However, an anomaly is obtained, and its magnitude can even increase with increasing overburden conductivity or frequency. The plate anomaly remains practically constant when only the overburden thickness is varied. Changes in overburden conductivity will cause the plate-anomaly values to change markedly. If the plate conductance is less than that of the overburden, a local anomaly opposite in sign to the normal type of anomaly will be recorded. Another major consequence is that conductors interpreted with free-space models will be heavily overestimated in depth or underestimated in conductance, if in reality induction and current channelling in the host rock and overburden make even a slight contribution to the anomalous EM field. The lateral resolution for the horizontal coplanar coil system was found to be about 1.7 times the sensor altitude. Similarly, the lateral extension of a horizontal conductive ribbon, required to reach the semi-infinite (half-space) behaviour, is more than three times the sensor altitude. Finally, screening of a steeply dipping plate, caused by a small, conductive horizontal ribbon, is much more severe than screening of the same plate by an extensive horizontal layer. 相似文献
166.
Cr(III) sorbed at the solid/water interface of latex and hectorite was studied by ESR spectroscopy in the presence of different inorganic ligands. The ESR spectra of the surface obtained in the presence of selenite, phosphate and fluoride can be explained in terms of ternary surface complex formation. This is contrasted by the behaviour of sulfate and selenate ions which were found to have no effect on the ligand field of Cr(III), either in the adsorbed state or in solution. 相似文献
167.
168.
George Delisle Ian Franchi Antonio Rossi Rainer Wieler 《Meteoritics & planetary science》1993,28(1):126-129
Abstract— A team from EUROMET (a joint initiative of scientific institutions in Europe interested in meteorites) was sent for the first time to Antarctica in the 1990/91 season to undertake a systematic search for meteorites. The project was organised within the framework of the Italian Antarctic Program (Programma Nationale di Richerche in Antartide, PNRA). The search was carried out in the vicinity of Frontier Mountain (North Victoria Land) and 256 meteorite fragments were discovered, most of which were wind-blown across the blue-ice field to the NE of Frontier Mountain and finally caught in an ice depression about 5 km to the N. The larger meteorites which remained on the ice surface from which they were uncovered may have been transported down to the mountain edge where they have subsequently been destroyed or covered in debris. A search for meteorites at neighbouring Sequence Hills, where similar glaciological conditions as at Frontier Mountain exist, proved unsuccessful. At this location the surface of the blue ice in the valleys with suspected meteorite concentrations was covered by meltwater lakes. 相似文献
169.
170.
Volker?St?hleEmail author Rainer?Altherr Mario?Koch Lutz?Nasdala 《Contributions to Mineralogy and Petrology》2004,148(2):150-159
A dense (~3.34 g cm–3) garnet–sillimanite-rich metamorphic rock from the suevite breccia of the Ries impact crater was studied by scanning-electron microscopy and Raman microprobe spectroscopy. In the strongly shocked rock clast kyanite was formed from sillimanite under momentary high pressures of natural shock waves. Kyanite aggregates were found as thin (~0.3–2.0 m) seams along grain boundaries between, and fractures within, sillimanite grains. Within these seams kyanite c-axes are oriented perpendicular to original grain boundaries and fractures. In addition, larger (up to 10 m) isolated kyanite grains were rarely found within host sillimanite. Filamentary kyanite aggregates and isolated crystals typically show shrinkage cracks due to volume decrease (~10%). Locally, broad interstices between sillimanite crystals are filled with aluminosilicate glass containing a high volume fraction of sub-micrometer-sized euhedral crystals. The silica-rich glass suggests incongruent melting of sillimanite at local post-shock temperatures significantly higher than 1,300°C. The edges of adjacent sillimanite grains are thermally and chemically altered. The local generation of temperature spikes is attributed to strong shock wave interactions due to very high shock impedance contrasts. 相似文献