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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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   

Sediment accretion against a buttress beneath the Peruvian continental margin at 12° S as simulated with sandbox modeling     

N. Kukowski  R. von Huene  J. Malavieille  S. E. Lallemand 《International Journal of Earth Sciences》1994,83(4):822-831

Reflection seismic data from the Peruvian continental margin at 12° S clearly reveal an accretionary wedge and buttress. Sandbox experiments applying the physical concept of the Coulomb theory allow the systematic investigation of the growth and deformation of such an accretionary structure. The style of deformation of the buttress and the internal structure of the wedge is observed in the sandbox models. The possibility of underplating material beneath the buttress and the amount of tectonic erosion depend on the physical properties of the materials, mainly internal friction, cohesion and basal friction. Boundary conditions such as the height of the subduction gate and the thickness of incoming sand also constrain the style of growth of the model accretionary structure.The configurations of two experiments were closely scaled to reflection seismic depth sections across the Peruvian margin. A deformable buttress constructed of compacted rock powder is introduced to replicate the basement rock which allows deformation similar to that in the seismic data. With the sandbox models it is possible to verify a proposed accretionary history derived from seismic and borehole data. The models also help in understanding the mechanisms which control the amount of accretion, subduction and underplating as a function of physical properties, boundary conditions and the duration of convergence.  相似文献   

Loch Macumber (early Carboniferous) of Atlantic Canada     

Paul E. Schenk  Ryo Matsumoto  Peter H. von Bitter 《Journal of Paleolimnology》1994,11(2):151-172

Following the Acadian Orogeny, Atlantic Canada accommodated several, large, relatively deep lakes within a wrench-fault basin complex called the Maritime Basin. Late Devonian and Tournaisian lakes were hydrologically open, shallow to deep, mainly fresh water bodies. Middle Visean lakes, here collectively called Loch Macumber, were closed, deep, and meromictic. Their deposits comprise the first and thickest of five sequences in the Maritime Basin. Salinity in the loch increased with time from restricted marine or penesaline, to saline. Basin-centre facies consist of a thin, but extensive, sheet of black, peloidal laminated lime mudstones and an overlying thick evaporite complex. The carbonate sheet grades laterally into both laminated to thinly bedded marlstones, siliciclastic sandstones, and microbial, biocementstone mounds. Laminae consist of alternating carbonate and either silty carbonaceous shale or siliciclastic clay and silt. The mudstone and marlstone are locally interbedded with siliciclastic and carbonate turbidites, resedimented (?deep water) breccias, and olistostromes. Seasonal changes in anoxia and/or carbonate production produced rhythmic laminae of carbonate and carbonaceous shale. Carbonate grains consist of silt-sized microbial clots and rare arthropod carapaces and brachiopod shells. The mounds originated as tufa precipitated around subaqueous hydrothermal springs that supported chemosynthetic communities. Resedimentation processes including incipient brecciation, sliding, slumping, debris flows, and turbidity currents were common. The mounds trapped hydrocarbons from the surrounding laminite and sulphides from underlying hydrothermal vents. Increasing salinity with time resulted in sulphate and chloride precipitation that filled the basins and ended the life of Loch Macumber. After the deposition of thick evaporites the topography became less accentuated, the seas less saline, and the faunas more normal marine.  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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