The age of the Saltpan impact crater,South Africa     

Christian Koeberl  Dieter Storzer  Wolf Uwe Reimold 《Meteoritics & planetary science》1994,29(3):374-379

Abstract— The 1.13-km-diameter Pretoria Saltpan impact crater is located about 40 km NNW of Pretoria, South Africa. The crater is situated in 2.05 Ga old Nebo granite of the Bushveld Complex that is locally intruded by about 1.3 Ga old volcanic rocks. In 1988, a borehole was drilled in the center of the crater. At depths >90 m, breccias were found that contained minerals with characteristic shock-metamorphic features, thus confirming the impact origin of the crater. Fragments of impact glass were recovered from the melt breccias and several hundred sub-millimeter-sized glass fragments were subjected to fission track analysis. The measurements were complicated by the inhomogeneous composition of the impact glasses, but analysis of a large number of tracks yielded an age of 220 ± 52 ka for the Saltpan crater.  相似文献   

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*     

Richard A. F. Grieve  Falko Langenhorst  Dieter Stffler 《Meteoritics & planetary science》1996,31(1):6-35

Abstract— The occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies. Its utility is due to its almost ubiquitous occurrence in terrestrial rocks, its overall stability and the fact that a variety of shock metamorphic effects, occurring over a range of shock pressures, have been well documented. These shock effects have been generally duplicated in shock recovery experiments and, thus, serve as shock pressure barometers. After reviewing the general character of shock effects in quartz, the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored. The short pulse lengths in experiments may account for the difficulty in synthesizing the high-pressure polymorphs, coesite and stishovite, compared to natural occurrences. In addition, post-shock thermal effects are possible in natural events, which can affect shock altered physical properties, such as refractive index, and cause annealing of shock damage and recrystallization. The orientations of planar microstructures, however, are unaffected by post-impact thermal events, except if quartz is recrystallized, and provide the best natural shock barometer in terms of utility and occurrence. The nature of planar microstructures, particularly planar deformation features (PDFs), is discussed in some detail and a scheme of variations in orientations with shock pressure is provided. The effect of post-impact events on PDFs is generally limited to annealing of the original glass lamellae to produce decorated PDFs, resulting from the exsolution of dissolved water during recrystallization. Basal (0001) PDFs differ from other PDF orientations in that they are multiple, mechanical Brazil twins, which are difficult to detect if not partially annealed and decorated. The occurrence and significance of shock metamorphosed quartz and its other phases (namely, coesite, stishovite, diaplectic glass and lechatelierite) are discussed for terrestrial impact structures in both crystalline (non-porous) and sedimentary (porous) targets. The bulk of past studies have dealt with crystalline targets, where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures. In sedimentary targets, the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature, which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets. This is discussed, along with examples of variations in the relative abundances of planar microstructures and their orientations, which are attributed to textural variations in sedimentary target rocks. Examples of the shock metamorphism of quartz in distal ejecta, such as at the K/T boundary, and from nuclear explosions are illustrated and are equivalent to that of known impact structures, except with respect to characteristics that are due to long-term, post-shock thermal effects. Finally, the differences between the deformation and phase transformation of quartz by shock and by endogenic, tectonic and volcanic processes are discussed. We confirm previous conclusions that they are completely dissimilar in character, due to the vastly different physical conditions and time scales typical for shock events, compared to tectonic and volcanic events. Well-characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment.  相似文献   

The Chicxulub Scientific Drilling Project (CSDP)     

Jaime Urrutia‐Fucugauchi  Joanna Morgan  Dieter Stffler  Philippe Claeys 《Meteoritics & planetary science》2004,39(6):787-790

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Microscopic search for the carrier phase Q of the trapped planetary noble gases in Allende,Leoville and Vigarano     

R. D. Vis  A. Mrowiec  P. J. Kooyman  K. Matsubara  D. Heymann 《Meteoritics & planetary science》2002,37(10):1391-1399

Abstract— High‐resolution transmission electron microscopy micrographs of acid‐resistant residues of the Allende, Leoville, and Vigarano meteorites show a great variety of carbon structures: curved and frequently twisted and intertwined graphene sheets, abundant carbon black‐like particles, and hollow “sacs”. It is suggested that perhaps all of these are carriers for the planetary Q‐noble gases in these meteorites. Most of these materials are pyrocarbons that probably formed by the pyrolysis of hydrocarbons either in a gas phase, or on hot surfaces of minerals. An attempt was made to analyze for argon with particle‐induced x‐ray emission in 143 spots of grains of floating and suspended matter from freeze‐dry cycles of an Allende bulk sample in water, and floating “black balls” from sonication in water of samples from the Allende meteorite. The chemical compositions of these particles were obtained, but x‐ray signals at the wavelength of argon were obtained on only a few spots.  相似文献   

Literal solution for Hill's lunar problem     

Dieter S. Schmidt 《Celestial Mechanics and Dynamical Astronomy》1979,19(3):279-289

A computer program for the manipulation of power series in several variables is used to find the first order solution to Hill's lunar problem. The ratiom of the mean motion of the Sun to that of the Moon is kept as a formal parameter. The series inm are known to converge very poorly. It is shown how efficient algorithms among them the Lie transformation allow us to compute the series inm as far as they are needed. When the series are evaluated at Brown's numerical value form the results achieve or exceed his accuracy.  相似文献   

Preface     

Jean Chapront  Jacques Henrard  Dieter Schmidt 《Celestial Mechanics and Dynamical Astronomy》1982,26(1):2-3

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Site Correction for Long Period Seismometers, Tiltmeters and Strainmeters     

Geoffrey King  Walter Zurn  Russ Evans  Dieter Emter 《Geophysical Journal International》1976,44(2):405-411

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Exact Brans-Dicke-Bianchi types-II,VIII, and IX stiff matter solutions     

Dieter Lorenz-Petzold 《Astrophysics and Space Science》1984,98(2):281-286

Exact solutions of the Brans-Dicke field equations of Bianchi types-II, VIII, and IX are derived. The solutions represent locally rotationally symmetric universes with stiff matter content.  相似文献   

Provenance of Palaeozoic sandstones from the Carnic Alps (Austria): petrographic and geochemical indicators   总被引：1，自引：0，他引：1  

Dieter?MaderEmail author  Franz?Neubauer 《International Journal of Earth Sciences》2004,93(2):262-281

An integrated approach of petrographic analysis, whole rock geochemistry and microprobe analysis has been applied to obtain information on the geodynamic development and the provenance for Ordovician to Permian siliciclastic successions exposed within the Carnic Alps (Austria). Sandstone detrital mode and geochemical results refine previous geodynamic interpretations. Late Ordovician samples indicate a stable craton and recycled orogenic and, possible, extensional setting. The Early Carboniferous is interpreted to represent a compressional environment, followed by a Late Carboniferous molasse-type foreland basin, and a Permian extensional geodynamic setting. Contrasting geochemical patterns of post-Variscan and Permian sequences suggest a rift setting. Electron microprobe data of detrital white mica also indicate changes in the provenance. Compositional data reflect a shift from low- to medium-grade metamorphic (Ordovician) to high-grade metamorphic (Carboniferous) to low- to medium-grade metamorphic and plutonic source rocks (Permian). Additionally, our data show that various chemical discrimination diagrams do not include all possible ranges of sandstones, and that high contents of detrital mica and ultra-stable heavy minerals may cause misclassification. Consequently, we propose the use of multi-method approach for provenance studies, including the control of geochemical data by modal analysis and heavy mineral investigations.  相似文献   

SNR Surface Density Distribution in Nearby Galaxies     

Manami Sasaki  Dieter Breitschwerdt  Rodrigo Supper 《Astrophysics and Space Science》2004,289(3-4):283-286

Since supernova remnants (SNRs) are believed to be the primary sources of Galactic cosmic rays (CRs), their distribution in galaxies is an important basis for modelling and understanding the distribution of the CRs and their γ-ray spectrum. We analysed the radial surface density of X-ray and radio selected SNRs in the Large Magellanic Cloud (LMC) and M 33. Both in X-rays and in radio, the surface densities of the SNRs are in excellent agreement in both galaxies, showing an exponential decay in radius. The results were compared to the SNR distribution in the spiral galaxies M 31 and NGC 6946 as well. The radial scale length of the distribution is $\frac{1} {4} $ ? $\frac{1} {3} $ of the radius of the galaxies, fully consistent with values derived for the Milky Way, the LMC, and M 33. Therefore, not only the radio SNRs, but also the X-ray detected SNR sample can be interpreted to be representative for the CR sources within a galaxy.  相似文献