Constraints on reflective bodies below the 8° discontinuity from reflectivity modelling     

Lars Nielsen  Hans Thybo  Anatoly V. Egorkin 《Geophysical Journal International》2001,145(3):759-770

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加拿大阿尔伯达省西部上泥盆统凯恩组白云岩的成因   总被引：1，自引：0，他引：1  

金振奎 Spen.  RJ 《地质论评》1993,39(6):529-534

加拿大阿尔伯达省西部上泥盆统凯恩组主要由粉晶白云岩和细晶白云岩组成，另外还常见一种充填溶蚀孔洞的亮晶白云石。粉晶白云岩纹理、泥裂和鸟眼等构造发育，其δ＾１３Ｃ为＋１．０‰－＋３．０‰，δ＾１８Ｏ为－６．０‰－－４．３‰，为潮坪上混合水白云化形成。细晶白云岩分布于假整合面之下，其δ＾１３Ｃ为＋０．２‰－＋２．９‰，δ＾１８Ｏ为－６．９‰－－４．６‰，也是混合水白云化的产物。亮晶白云石洁净明亮、晶粒粗  相似文献   

The effect of a regional increase in ocean surface roughness on the tropospheric circulation: a GCM experiment     

Uwe Ulbrich  Gerd Bürger  Dierk Schriever  Hans von Storch  Susanne L Weber  Gerhard Schmitz 《Climate Dynamics》1993,8(6):277-285

The sensitivity of the atmospheric circulation to an increase in ocean surface roughness in the Southern Hemisphere storm track is investigated in a paired general circulation model experiment. Such a change in sea roughness could be induced by ocean waves generated by storms. Two extended permanent-July runs are made. One with standard sea surface roughness, the other with ten times as a large surface roughness over open sea poleward of 40° S. The regional increase in ocean surface roughness significantly modifies the tropospheric circulation in the Southern Hemisphere. The strongest effect is the reduction of tropospheric winds (by 2 m/s or 10%) above the area with increased roughness. The poleward eddy momentum flux is reduced in the upper troposphere and the meridional eddy sensible heat flux is reduced in the lower troposphere. Zonal mean and eddy kinetic energy are consistently reduced.  相似文献   

Influence of fluorine on the enrichment of high field strength trace elements in granitic rocks   总被引：26，自引：2，他引：26  

Hans Keppler 《Contributions to Mineralogy and Petrology》1993,114(4):479-488

The solubilities of zircon, rutile, manganocolumbite (MnNb₂O₆), manganotantalite (MnTa₂O₆), and the rare earth phosphates LaPO₄, GdPO₄, and YbPO₄ in water-saturated haplogranitic melts containing 0–6 wt.% F were measured at 800° C and 2 kbar. The melt compositions investigated differ only in their F content, the proportions of Na, K, Al, and Si are identical in all experiments. While the solubilities of the rare earth phosphates are independent of F, the solubilities of all other minerals studied strongly increase with F. The TiO₂ content of haplogranitic melt in equilibrium with rutile increases linearly from 0.26 wt.% without F to 0.47 wt.% for melts containing 6 wt.% F. Over the same range of F concentrations, the ZrO₂ content of the melt in equilibrium with zircon increases with the square of the F content from less than 0.01 wt.% to 0.25 wt.%. The linear increase for rutile and the quadratic relationship for zircon suggest a complexing mechanism. Probably nonbridging oxygen atoms (NBO) expelled from coordination with Al by reaction with F form complexes with Ti and Zr, the ratio of NBO: metal cation being 1:1 for Ti, and 2:1 for Zr. Direct complexing by F is also a possibility. As titanium oxide phases and zircon are major sinks for HFS elements such as Ti, Nb, Ta, Zr, Hf, Th and REE in granites, their increased solubility in the presence of F favors the enrichment of these elements in residual mels. The Nb and Ta content of rutile in granitic pegmatites is due to extended solid solution of rutile with columbite group minerals, such as manganocolumbite and manganotantalite. The solubility of these components also increases with F, MnTa₂O₆ being more soluble than MnNb₂O₆. Rutile fractionation could therefore account for the increase in Ta/Nb frequently observed in highly differentiated granites. The solubility of the rare earth phosphates increases strongly from LaPO₄ to GdPO₄ to YbPO₄, which explains the enrichment of heavy rare earth elements in highly evolved granites. In the presence of F, many HFS elements will be highly incompatible in granitic systems. Therefore, in a suite of granitic rocks generated by differentiation from the same source magma, a strong correlation should exist between HFS elements and F. However, because of the influence of F on the solubility of refractory phases such as zircon, a similar correlation could also result from different batches of magma containing different amounts of F equilibrating with the same refractory phase.  相似文献   

Vulnerability,hunger and famine — interdisciplinary perspectives     

Hans G. Bohle 《GeoJournal》1993,30(2):115-115

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Magnetic measurements on the Norwegian continental margin between 68° and 70° N     

Gholam Ali Dehghani  Hans Bodo Hirschleber  Thomas Liebe  Arne Gidskehaug  Markvard A. Sellevoll 《Ocean Dynamics》1988,41(3-6):257-264

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Radiodensitometric-dendroclimatological conifer chronologies from Lapland (Scandinavia) and the Alps (Switzerland)   总被引：7，自引：0，他引：7  

Fritz Hans  Schweingruber  Thomas  Bartholin  Ernst  Schaur Keith R.  Briffa 《Boreas: An International Journal of Quaternary Research》1988,17(4):559-566

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Mass transfer during sub-seafloor alteration of the upper Troodos crust (Cyprus)     

Ulrich Bednarz  Hans -Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1989,102(1):93-101

Five major alteration zones in the Extrusive Series and the Sheeted Dike Complex of the Troodos Ophiolite are each characterized by (a) distinct elemental changes compared to the original composition and (b) secondary mineralogy. The upper ca. 300 m of the extrusive crust, the highly oxidatedcold seawater alteration zone (CSA), is strongly enriched in K₂O and depleted in Na₂O. It is followed downwards by alow temperature alteration zone (<170° C) which is most widespread in the Troodos extrusives and where Na₂O and K₂O are enriched, the latter less strongly than in the CSA zone. Three types ofhigh temperature alteration zones (<440° C; HTA I–III) are found in the Sheeted Dike Complex. All are marked by thorough leaching of K₂O, while the behavior of Na₂O (e.g. unchanged in type III) and CaO (depleted in type I, enriched in types II, III) is variable. Mass budgets of elemental changes are quantified by calibration of whole rock analyses via systematic stable element variations of fresh glasses found throughout the extrusive section. The Troodos extrusive crust and upper Sheeted Dike Complex are a major sink for MgO, K₂O, and Na₂O, and a source for CaO; the overall scale of fluxes drastically exceeds estimates based on fresh basalt compositions from present ocean crust.  相似文献   

Prediction of the spatial distribution of the modified mercalli intensity using neural networks     

Albert T. Y. Tung  Felix S. Wong  Weimin Dong 《地震工程与结构动力学》1994,23(1):49-62

This paper presents the development of an adaptive, non-parametric forecast model for the direct prediction of the spatial distribution of the Modified Mercalli Intensity (MMI) corresponding to an earthquake scenario. The model is based on recent advances in neural networks computation, and is constructed through supervised learning using historical earthquake and regional geological data as training sets. A MMI forecast model for moderate earthquakes with magnitudes between 6 and 7 was developed based on data from the Loma Prieta, Coalinga and Morgan Hill earthquakes. For these data sets, the neural networks forecast model is shown to have excellent data synthesis capability; multiple sets of data can be encapsulated by a relatively simple network architecture. Limited comparison of forecasts made by the neural networks model and conventional models demonstrates that improved accuracy can be achieved. Implementation and operational advantages of the neural networks approach such as general input features, minimum preconceived knowledge of the data sets, the ability to learn and to adapt incrementally and the autonomous and automatic synthesis of the structure underlying the data sets, have been illustrated.  相似文献   

Analysis of historical seismograms—root mean square Lg magnitudes, yields and depths of explosions at the Semipalatinsk Test Range     

Hans Israelsson 《Geophysical Journal International》1994,117(3):591-609

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