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排序方式: 共有133条查询结果,搜索用时 296 毫秒
81.
Stefano Silvestri Sulyman Mansour Matteo Marra Johann Distl Marco Furinghetti Igor Lanese Enrique Hernndez-Montes Caterina Neri Michele Palermo Alberto Pavese Elisa Rizzo Parisi Adam Jan Sadowski Francesco Selva Tomoyo Taniguchi Laura Vadrucci Felix Weber 《地震工程与结构动力学》2022,51(1):169-190
This paper reports on a series of shaking table tests on a full-scale flat-bottom steel silo filled with soft wheat, characterized by aspect ratio of around 0.9. The specimen was a 3.64-m diameter and 5.50-m high corrugated-wall cylindrical silo. Multiple sensors were used to monitor the static and dynamic response of the filled silo system, including accelerometers and pressure cells. Numerous unidirectional dynamic tests were performed consisting of random signals, sinusoidal inputs, and both artificial and real earthquake records. The objectives of this paper are (i) to provide a general overview of the whole experimental campaign and (ii) to present selected results obtained for the fixed-base configuration. The measured data were processed to assess the static pressures, the dynamic overpressures (related to the effective mass) and the accelerations of monitored points on the silo wall, and to identify the basic dynamic properties (fundamental frequency of vibration, damping ratio, dynamic amplification factors) of the filled silo. The main findings are discussed and compared with the predictions given by available theoretical models and code provisions. It is found that the fundamental frequency slightly decreases with increasing acceleration, while it slightly increases with increasing compaction of the granular material. For close-to-resonance input, the dynamic amplification (in terms of peak values of accelerations) increases along the height of the silo wall up to values of around 1.4 at the top surface of the solid content. The dynamic overpressures appear to increase with depth (differently from the EN1998-4 expectations), and to be proportional to the acceleration. 相似文献
82.
Raith Johann G. Riemer née Schöner Nina Meisel Thomas 《Contributions to Mineralogy and Petrology》2004,147(1):91-109
Tourmaline rocks of previously unclear genesis and spatially associated with W- (Cu)-bearing calc-silicate rocks occur in Palaeoproterozoic supracrustal and felsic intrusive rocks in the Bonya Hills in the eastern Arunta Inlier, central Australia. Tourmalinisation of metapelitic host rocks postdates the peak of regional low-pressure metamorphism (M1/D1, ~500 °C, ~0.2 GPa), and occurred synkinematically between the two main deformation events D1 and D2, coeval with emplacement of Late Strangways (~1.73 Ga) tourmaline-bearing leucogranites and pegmatites. Tourmaline is classified as schorl to dravite in tourmaline–quartz rocks and surrounding tourmaline-rich alteration zones, and as Fe-rich schorl to foitite in the leucogranites. Boron metasomatism resulted in systematic depletion of K, Li, Rb, Cs, Mn and enrichment of B, and in some samples of Na and Ca, in the tourmaline rocks compared to unaltered metasedimentary host rocks. Whole-rock REE concentrations and patterns of unaltered schist, tourmalinised schist and tourmaline–quartz veins—the latter were the zones of influx of the boron-rich hydrothermal fluid—are comparable to those of post-Archaean shales. Thus, the whole-rock REE patterns of these rocks are mostly controlled by the metapelitic precursor. In contrast, REE concentrations of leucogranitic rocks are low (10 times chondritic), and their flat REE patterns with pronounced negative Eu anomalies are typical for fractionated granitic melts coexisting with a fluid phase. REE patterns for tourmalines separated from metapelite-hosted tourmaline–quartz veins and tourmaline-bearing granites are very different from one another but each tourmaline pattern mirrors the REE distribution of its immediate host rock. Tourmalines occurring in tourmaline–quartz veins within tourmalinised metasediments have LREE-enriched (LaN/YbN=6.3–55), shale-like patterns with higher REE (54–108 ppm). In contrast, those formed in evolved leucogranites exhibit flat REE patterns (LaN/YbN=1.0–5.6) with pronounced negative Eu anomalies and are lower in REE (5.6–30 ppm). We therefore conclude that REE concentrations and patterns of tourmaline from the different tourmaline rocks studied are controlled by the host rock and not by the hydrothermal fluid causing boron metasomatism. From the similarity of the REE pattern of separated tourmaline with the host rock, we further conclude that incorporation of REEs in tourmaline is not intrinsically controlled (i.e. by crystal chemical factors). Tourmaline does not preferentially fractionate specific REEs or groups of REEs during crystallisation from evolved boron- and fluid-rich granitic melts or during alteration of clastic metasediments by boron-rich magmatic-hydrothermal fluids.Editorial responsibility: J. Hoefs 相似文献
83.
Reasons for Spatial Microdistributions of Foraminifers in an Intertidal Pool (Northern Adriatic Sea)
Abstract. The spatial microdistribution of foraminifers was tested by the method of quadratic samplings on 2 sample grids in an intertidal pool of the northernmost Adriatic sea. Abundant species of foraminifers exhibit patchy distributions throughout; the distribution-patterns of some species correspond nearly completely. Using statistical methods (regression- and correlation-analyses) correlations to abiotic and biotic factors (water depth, exposure rate, seagrass, benthonic algae) were ascertained. The significant correlations of the foraminiferal frequencies to blue-green algae and/or diatoms enable an interpretation of these connexions as food dependences. Several foraminiferal species seem to have specific diets. 相似文献
84.
Kimberlite-hosted diamond deposits of southern Africa: A review 总被引:4,自引:0,他引:4
Matthew Field Johann Stiefenhofer Jock Robey Stephan Kurszlaukis 《Ore Geology Reviews》2008,34(1-2):33
Following the discovery of diamonds in river deposits in central South Africa in the mid nineteenth century, it was at Kimberley where the volcanic origin of diamonds was first recognized. These volcanic rocks, that were named “kimberlite”, were to become the corner stone of the economic and industrial development of southern Africa. Following the discoveries at Kimberley, even more valuable deposits were discovered in South Africa and Botswana in particular, but also in Lesotho, Swaziland and Zimbabwe.A century of study of kimberlites, and the diamonds and other mantle-derived rocks they contain, has furthered the understanding of the processes that occurred within the sub-continental lithosphere and in particular the formation of diamonds. The formation of kimberlite-hosted diamond deposits is a long-lived and complex series of processes that first involved the growth of diamonds in the mantle, and later their removal and transport to the earth's surface by kimberlite magmas. Dating of inclusions in diamonds showed that diamond growth occurred several times over geological time. Many diamonds are of Archaean age and many of these are peridotitic in character, but suites of younger Proterozoic diamonds have also been recognized in various southern African mines. These younger ages correspond with ages of major tectono-thermal events that are recognized in crustal rocks of the sub-continent. Most of these diamonds had eclogitic, websteritic or lherzolitic protoliths.In southern Africa, kimberlite eruptions occurred as discrete events several times during the geological record, including the Early and Middle Proterozoic, the Cambrian, the Permian, the Jurassic and the Cretaceous. Apart from the Early Proterozoic (Kuruman) kimberlites, all of the other events have produced deposits that have been mined. It should however be noted that only about 1% of the kimberlites that have been discovered have been successfully exploited.In this paper, 34 kimberlite mines are reviewed with regard to their geology, mantle xenolith, xenocryst and diamond characteristics and production statistics. These mines vary greatly in size, grade and diamond-value, as well as in the proportions and types of mantle mineral suites that they contain. They include some of the world's richest mines, such as Jwaneng in Botswana, to mines that are both small and marginal, such as the Frank Smith Mine in South Africa. They include large diatremes such as Orapa and small dykes such as those mined at Bellsbank, Swartruggens and near Theunissen. These mines are all located on the Archaean Kalahari Craton, and it is apparent that the craton and its associated sub-continental lithosphere played an important role in providing the right environment for diamond growth and for the formation of the kimberlite magmas that were to transport them to the surface. 相似文献
85.
Johann Waringer Wolfram Graf Steffen U. Pauls Heinrich Vicentini Verena Lubini 《Limnologica》2008,38(1):34-42
At three alpine locations in Switzerland adults of Drusus melanchaetes and unknown Drusinae larvae which could not be identified with existing keys were sampled. Based on DNA association with adults, we identified the unknown larvae as D. melanchaetes. To further support the association of specimens a phylogeny was estimated with the putative closest relatives of D. melanchaetes – D. monticola and D. nigrescens – and five other species of Drusus (D. chrysotus, destitutus, discolor, muelleri and romanicus). A highly supported monophyletic clade groups unknown larvae and D. melanchaetes specimens from the central Alps and Austria (Vorarlberg), confirming the association.Based on morphology, larvae of D. melanchaetes key out together with D. destitutus in existing keys. D. melanchaetes is separated from the latter species by the shape of the lateral head profile which is almost straight and shows a small step at the height of the antenna, whereas in D. destitutus the lateral head profile is evenly rounded. In addition, in frontal view, the shape of the lateral head outline is straight in D. melanchaetes and rounded in D. destititus. There are also differences in the shape of the pronotum and in the number of the posterodorsal setae at the eighth abdominal dorsum. 相似文献
86.
The recent development of activity–composition relations for mineral and melt phases in high‐grade metamafic rocks allows mineral equilibria tools to be used to further aid our understanding of partial melting and the mineralogical consequences of melt segregation in these rocks. We show that bulk compositional data from natural amphibolites cover a wide compositional range, with particular variability in the content and ratios of Ca, Na and K indicating that low‐grade metasomatic alteration can substantially alter the igneous protolith chemistry and potentially affect the volume and composition of melt generated. Mineral equilibria calculations for five samples that span the compositional variability in our data set indicate that melting occurs primarily via the fluid‐absent breakdown of amphibole+quartz to produce a pressure‐sensitive peritectic assemblage of augite, orthopyroxene and/or garnet. The introduction of orthopyroxene at the onset of the amphibolite‐to‐granulite‐facies transition at lower pressure results in an increased rate of melt production until quartz is typically exhausted, and this is similarly seen for the introduction of garnet at higher pressure. Calculated melt compositions are dependent on the protolith composition, but initial solidus melting and biotite breakdown produce 1–3 mol.% of K‐rich granitic melts. As hornblende melting proceeds, 15–20 vol.% of either more granodioritic‐to‐tonalitic or granodioritic‐to‐trondhjemitic melt is produced. Once quartz is exhausted, intermediate to mafic melt compositions are produced at ultrahigh‐temperature conditions. Quartz‐rich lithologies with high Ca coupled to low Na and K are the most fertile under orogenic conditions, yielding up to 25 mol.% of sub‐alkalic granitic melt by 850°C. Such rocks did not experience significant subsolidus alteration. Altered compositions with low Ca and elevated Na and K are not as fertile, yielding less than 15 mol.% of alkalic granitic melt by 850°C. These melt volumes are enough to be segregated, and can make a contribution to granite magmatism and intracrustal differentiation that should not be overlooked. 相似文献
87.
Alain?ChauvetEmail author Laurent?Bailly Anne-Sylvie?André Patrick?Monié Daniel?Cassard Fernando?Llosa?Tajada Juan?Rosas?Vargas Johann?Tuduri 《Mineralium Deposita》2006,41(4):387-410
The epithermal Shila-Paula Au–Ag district is characterized by numerous veins hosted in Tertiary volcanic rocks of the Western Cordillera (southern Peru). Field studies of the ore bodies reveal a systematic association of a main E–W vein with secondary N55–60°W veins—two directions that are also reflected by the orientation of fluid-inclusion planes in quartz crystals of the host rock. In areas where this pattern is not recognized, such as the Apacheta sector, vein emplacement seems to have been guided by regional N40°E and N40°W fractures. Two main vein-filling stages are identified. stage 1 is a quartz–adularia–pyrite–galena–sphalerite–chalcopyrite–electrum–Mn silicate–carbonate assemblage that fills the main E–W veins. stage 2, which contains most of the precious-metal mineralization, is divided into pre-bonanza and bonanza substages. The pre-bonanza substage consists of a quartz–adularia–carbonate assemblage that is observed within the secondary N45–60°W veins, in veinlets that cut the stage 1 assemblage, and in final open-space fillings. The two latter structures are finally filled by the bonanza substage characterized by a Fe-poor sphalerite–chalcopyrite–pyrite–galena–tennantite–tetrahedrite–polybasite–pearceite–electrum assemblage. The ore in the main veins is systematically brecciated, whereas the ore in the secondary veins and geodes is characteristic of open-space crystallization. Microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15.5 wt% NaCl equivalent and homogenization temperatures bracketed between 200 and 330°C. Secondary CO2-, N2- and H2S-bearing fluid inclusions are also identified. The age of vein emplacement, based on 40Ar/39Ar ages obtained on adularia of different veins, is estimated at around 11 Ma, with some overlap between adularia of stage 1 (11.4±0.4 Ma) and of stage 2 (10.8±0.3 Ma). A three-phase tectonic model has been constructed to explain the vein formation. Phase 1 corresponds to the assumed development of E–W sinistral shear zones and associated N60°W cleavages under the effects of a NE–SW shortening direction that is recognized at Andean scale. These structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation. Phase 2 is a reactivation of earlier structures under a NW–SE shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce N50°E-striking S2-cleavage planes filled by the stage 2 pre-bonanza minerals. Phase 3 coincides with the bonanza ore emplacement in the secondary N45–60°W veins and also in open-space in the core of the main E–W veins. Our combined tectonic, textural, mineralogical, fluid-inclusion, and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation. 相似文献
88.
In this paper, we introduce a novel stochastic model for the permeability tensor associated with stationary random porous media. In the light of recent works on mesoscale modeling of permeability, we first discuss the physical interpretation of the permeability tensor randomness. Subsequently, we propose a nonparametric prior probabilistic model for non‐Gaussian permeability tensor random fields, making use of the information theory and a maximum entropy procedure, and provide a physical interpretation of the model parameters. Finally, we demonstrate the capability of the considered class of random fields to generate higher levels of statistical fluctuations for selected stochastic principal permeabilities. This unique flexibility offered by the parameterization of the model opens up many new possibilities for both forward simulations (e.g. for uncertainty propagation in predictive simulations) and stochastic inverse problem solving. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
89.
Progressive formation of modern drumlins at Múlajökull,Iceland: stratigraphical and morphological evidence 下载免费PDF全文
Ívar Örn Benediktsson Sverrir A. Jónsson Anders Schomacker Mark D. Johnson Ólafur Ingólfsson Lucas Zoet Neal R. Iverson Johann Stötter 《Boreas: An International Journal of Quaternary Research》2016,45(4):567-583
The drumlin field at Múlajökull, Iceland, is considered to be an active field in that partly and fully ice‐covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto‐drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto‐drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat. 相似文献
90.
Walter Kurz Andreas Wölfler Robert Rabitsch Johann Genser 《Swiss Journal of Geoscience》2011,104(2):323-343
The Lavanttal Fault Zone (LFZ) is generally considered to be related to Miocene orogen-parallel escape tectonics in the Eastern
Alps. By applying thermochronological methods with retention temperatures ranging from ~450 to ~40°C we have investigated
the thermochronological evolution of the LFZ and the adjacent Koralm Complex (Eastern Alps). 40Ar/39Ar dating on white mica and zircon fission track (ZFT) thermochronology were carried out on host rocks (HRs) and fault-related
rocks (cataclasites and fault gouges) directly adjacent to the unfaulted protolith. These data are interpreted together with
recently published apatite fission track (AFT) and apatite (U-Th)/He ages. Sample material was taken from three drill cores
transecting the LFZ. Ar release spectra in cataclastic shear zones partly show strongly rejuvenated incremental ages, indicating
lattice distortion during cataclastic shearing or hydrothermal alteration. Integrated plateau ages from fault rocks (~76 Ma)
are in parts slightly younger than plateau ages from HRs (>80 Ma). Incremental ages from fault rock samples are in part highly
reduced (~43 Ma). ZFT ages within fault gouges (~65 Ma) are slightly reduced compared to the ages from HRs, and fission tracks
show reduced lengths. Combining these results with AFT and apatite (U-Th)/He ages from fault rocks of the same fault zone
allows the recognition of distinct faulting events along the LFZ from Miocene to Pliocene times. Contemporaneous with this
faulting, the Koralm Complex experienced accelerated cooling in Late Miocene times. Late-Cretaceous to Palaeogene movement
on the LFZ cannot be clearly proven. 40Ar/39Ar muscovite and ZFT ages were probably partly thermally affected along the LFZ during Miocene times. 相似文献