Chlorit-Hornblende-Felse des Bergsträßer Odenwaldes und ihre Phasenpetrologie     

Wolfgang Schubert 《Contributions to Mineralogy and Petrology》1969,21(4):295-310

Ultrabasic metamorphic rocks with typical mineral assemblage of cummingtonitic hornblende+Mg-chlorite+talc (described byMatthes u.Okrusch, 1965, and called “hösbachit”) were found for the first time in Odenwald/Germany. Three steps of metamorphic development can be described: the primary magmatic ultrabasic rock consisted of (1) orthopyroxene (bronzite), clinopyroxene (diallage), poikilitic olivine, and some hornblende. This is indicated by textural relicts, structural and geochemical investigations. A regional metamorphic process under conditions of the staurolite-almandine-subfacies ofWinkler’s andTurner andVerhoogen’s almandine-amphibolite facies transformed this assemblage to (2): cummingtonitic hornblende I+Mg-chlorite I (clinochlore)+talc. The third step followed under more diaphthoritic conditions and brought mineral assemblage (3): tremolitic hornblende II+Mg-chlorite II (pennine)+talc.  相似文献   

Compressional angles of isallo stress theory for a circular-cylindrical,spherical and elliptic-cylindrical elastic inhomogeneity in an elastic medium     

Hans Pulpan  Adrian E. Scheidegger 《Pure and Applied Geophysics》1969,76(1):147-152

Summary The compressional angle of isallo stress theory for the case of a cylindrical (circular and elliptic) and spherical subsurface inhomogeneity, assuming that the conjugate fracture surfaces are inclined at a Mohr angle of 30° toward the largest compression, has been calculated. The solution for a spherical and cylindrical inclusion in an infinite medium subject to a uniform stress field (at infinity) were taken as the basis for the stress analysis. The stress angle was then calculated for the mentioned types of inclusions.  相似文献   

Directional permeability of porous media to homogeneous fluids     

Dr. Adrian E. Scheidegger 《Pure and Applied Geophysics》1954,28(1):75-90

Summary Investigations have shown that in groundwater- and oil-bearing strata there are preferential directions of flow that are often maintained over wide areas.Johnson & Hughes (1948, see Ref.) analysed a series of oil well cores by cutting them into small horizontal plugs and they obtained directional permeabilities which they plotted in the form of polar graphs. They were not able to give a physical explanation of this phenomenon. On the other hand, there exists a theory of permeability in which the latter is represented as a symmetric tensor. This theory has been developed byFerrandon (1948, see Ref.), but no experimental substantiation of it seems ever to have been attempted.In the present paper, the author undertakes to compare the two sets of findings. FromFerrandon's theory, the directional permeabilities (denoted byk) corresponding to the experiments ofJohnson & Hughes are calculated and it is shown thatk ^–1/2 if plotted as polar graph, should form an ellipse. The data ofJohnson & Hughes are then are drawn. In this manner, a substantiation of the tensor theory ofFerrandon is obtained.

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Zusammenfassung Untersuchungen der Permeabilität von Grundwasser und Erdöl führenden Gesteinsschichten haben gezeigt, dass dieselbe in vielen Fällen richtungsabhängig ist. Hierbei bleibt die Richtung extremaler Permeabilität oft über weite Gebiete konstant.Johnson & Hughes untersuchten eine Reihe von Bohrkernen von Oelquellen auf Richtungsabhängigkeit der Permeabilität. Hierzu schnitten sie aus denselben kleine, waagrechte Stücke, bestimmten deren Permeabilität und stellten das Ergebnis ihrer Messungen in der Form von Permeabilitätspolardiagrammen dar. Sie waren nicht im Stande, eine theoretische Erklärung der erhaltenen Kurven zu geben. Auf der anderen Seite existiert eine Theorie der Permeabilität, wobei die letztere als symmetrischer Tensor behandelt wird. Diese Theorie wurde vonFerrandon vorgeschlagen; es scheint aber, dass keine experimentelle Bestätigung davon je versucht worden ist.In der vorliegenden Arbeit vergleicht der Verfasser die zwei Typen von Untersuchungen. Nach derFerrandon'schen Theorie wird die «gerichtete» Permeabilität (mitk bezeichnet), die den Experimenten vonJohnson & Hughes entspricht, berechnet. Es wird gezeigt, dassk ^–1/2, als Polardiagramm dargestellt, die Gestalt einer Ellipse haben sollte. Die Resultate vonJohnson & Hughes werden dann in die Form vonk ^–1/2 umgerechnet und als entsprechende Polardiagramme dargestellt. In dieser Weise wird eine experimentelle Bestätigung der Tensortheorie vonFerrandon erhalten.

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Published by Permission of Imperial Oil Limited, Calgary, Alberta (Canada).  相似文献   

Magnetism and thermal evolution of the terrestrial planets     

David J. Stevenson  Tilman Spohn  Gerald Schubert 《Icarus》1983,54(3):466-489

Of the terrestrial planets, Earth and probably Mercury possess substantial intrinsic magnetic fields generated by core dynamos, while Venus and Mars apparently lack such fields. Thermal histories are calculated for these planets and are found to admit several possible present states, including those which suggest simple explanations for the observations; whule the cores of Earth and Mercury are continuing to freeze, the cores of Venus and Mars may still be completely liquid. The models assume whole mantle convection, which is parameterized by a simple Nusselt-Rayleigh number relation and dictates the rate at which heat escapes from the core. It is found that completely fluid cores, devoid of intrinsic heat sources, are not likely to sustain thermal convection for the age of the solar system but cool to a subadiabatic, conductive state that can not maintain a dynamo. Planets which nucleate an inner core continue to sustain a dynamo because of the gravitational energy release and chemically driven convection that accompany inner core growth. The absence of a significant inner core can arise in Venus because of its slightly higher temperature and lower central pressure relative to Earth, while a Martian core avoids the onset of freezing if the abundance of sulfur in the core is ?15% by mass. All of the models presented assume that (I) core dynamos are driven by thermal and/or chemical convection; (ii) radiogenic heat production is confined to the mantle; (iii) mantle and core cool from initially hot states which are at the solidus and superliquidus, respectively; and (iv) any inner core excludes the light alloying material (sulfur or oxygen) which then mixes uniformly upward through the outer core. The models include realistic pressure and composition-dependent freezing curves for the core, and material parameters are chosen so that the correct present-day values of heat outflow, upper mantle temperature and viscosity, and inner core radius are obtained for the earth. It is found that Venus and Mars may have once had dynamos maintained by thermal convection alone. Earth may have had a completely fluid core and a dynamo maintained by thermal convection for the first 2 to 3 by, but an inner core nucleates and the dynamo energetics are subsequently dominated by gravitational energy release. Complete freezing of the Mercurian core is prohibited if it contains even a small amount of sulfur, and a dynamo can be maintained by chemical convection in a thin, fluid shell.  相似文献   

A theory for the interpretation of lunar surface magnetometer data     

Gerald Schubert  Kenneth Schwartz 《Earth, Moon, and Planets》1969,1(1):106-117

The solution to the problem of the motion of the Moon relative to spatial irregularities in the interplanetary magnetic field is found. The lunar electrical conductivity is modeled by a two-layer conductivity profile. For the interaction of the Moon with the corotating sector structure of the interplanetary magnetic field it is found that the magnetic field in the lunar shell is the superposition of an oscillatory uniform field, an oscillatory dipole field and anoscillatory field that is toroidal about the axis of the motional electric field. With various lunar conductivity models and the theory of this paper, lunar surface magnetometer data can be quantitatively interpreted to yield information on the conductivity and consequently the temperature of the lunar core.Presently visiting the Max-Planck-Institut für Physik und Astrophysik, München, Germany.  相似文献   

Shear deformation zones along major transform faults and subducting slabs   总被引：1，自引：0，他引：1  

D. A. Yuen  L. Fleitout  G. Schubert  C. Froidevaux 《Geophysical Journal International》1978,54(1):93-119

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Meteorological monitoring of an active volcano: Implications for eruption prediction     

Jenni Barclay  Jade E. Johnstone  Adrian J. Matthews   《Journal of Volcanology and Geothermal Research》2006,150(4):241-358

Rainfall data collected on and around the Soufriere Hills Volcano, Montserrat between 1998 and 2003 were analysed to assess the impact on primary volcanic activity, defined here as pyroclastic flows, dome collapses, and explosions. Fifteen such rainfall-triggered events were identified. If greater than 20 mm of rain fell on a particular day, the probability of a dome collapse occurring on that day increased by a factor of 6.3% to 9.2%, compared to a randomly chosen day. Similarly, the probability of observing pyroclastic flows and explosions on a day with > 20 mm of rainfall increased by factors of 2.6 and 5.4, respectively. These statistically significant links increased as the rainfall threshold was increased. Seventy percent of these rainfall-induced dome collapse episodes occurred on the same calendar day (most within a few hours) as the onset of intense rainfall, but an extra 3 occurred one or two calendar days later. The state of the volcano was important, with the rainfall–volcanic activity link being strongest during periods of unstable dome growth and weakest during periods of no dome growth or after a recent major collapse.Over 50% of the heavy rain days were associated with large-scale weather systems that can potentially be forecast up to a few days ahead. However, the remaining heavy rain days were associated with small-scale, essentially unpredictable weather systems. There was significant variability in the amount of rainfall recorded by different rain gauges, reflecting topographic variations around the volcano but also the inherent small-scale variability within an individual weather system. Hence, any monitoring/warning program is recommended to use a network, rather than just a single gauge. The seasonal cycle in rainfall was pronounced, with nearly all the heavy rain days occurring in the May–December wet season. Hence, the dome was at its most vulnerable at the beginning of the wet season after a period of uninterrupted growth. Interannual variability in rainfall was related to tropical Pacific and Atlantic sea surface temperature anomalies, and holds out the prospect of some limited skill in volcanic hazard forecasts at even longer lead times.  相似文献   

Modeling long-period noise in kinematic GPS applications     

Adrian A. Borsa  Jean-Bernard Minster  Bruce G. Bills  Helen A. Fricker 《Journal of Geodesy》2007,81(2):157-170

We develop and test an algorithm for modeling and removing elevation error in kinematic GPS trajectories in the context of a kinematic GPS survey of the salar de Uyuni, Bolivia. Noise in the kinematic trajectory ranges over 15 cm and is highly autocorrelated, resulting in significant contamination of the topographic signal. We solve for a noise model using crossover differences at trajectory intersections as constraints in a least-squares inversion. Validation of the model using multiple realizations of synthetic/simulated noise shows an average decrease in root-mean-square-error (RMSE) by a factor of four. Applying the model to data from the salar de Uyuni survey, we find that crossover differences drop by a factor of eight (from an RMSE of 5.6 to 0.7 cm), and previously obscured topographic features are revealed in a plan view of the corrected trajectory. We believe that this algorithm can be successfully adapted to other survey methods that employ kinematic GPS for positioning.  相似文献   

Maquiladora Myths: Locational and Structural Change in Mexico's Export Manufacturing Industry     

Ian MacLachlan  Adrian Guillermo Aguilar 《The Professional geographer》1998,50(3):315-331

Trends in location, labor force, and procurement practices in maquiladoras are examined using recent data sources. A growing proportion of maquiladoras are selecting interior locations, south of the borderlands. Once dominated by young women, the labor force is rapidly approaching gender parity. While far below prevailing rates in the United States, maquiladora wages are comparable with equivalent manufacturing sectors in Mexico. Majority ownership of maquiladoras is split almost evenly between Mexico and the U.S., however, maquiladoras have failed to develop domestic sources of materials and parts and remain dependent on imported material inputs. As the North American Free Trade Agreement is phased in, the regulatory environment of maquiladoras will change but their role as low cost assembly specialists will persist.  相似文献   

Influence of catchment quality and altitude on the water and sediment composition of 68 small lakes in Central Europe     

Beat Müller  André F. Lotter  Michael Sturm  Adrian Ammann 《Aquatic Sciences - Research Across Boundaries》1998,60(4):316-337

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