Northwest Africa 1500: Plagioclase‐bearing monomict ureilite or ungrouped achondrite?     

Cyrena Anne Goodrich  Frank Wlotzka  D. Kent Ross  Rainer Bartoschewitz 《Meteoritics & planetary science》2006,41(6):925-952

Abstract— Northwest Africa (NWA) 1500 is an ultramafic meteorite dominated by coarse (?100–500 μm) olivine (95–96%), augite (2–3%), and chromite (0.6–1.6%) in an equilibrated texture. Plagioclase (0.7–1.8%) occurs as poikilitic grains (up to ?3 mm) in vein‐like areas that have concentrations of augite and minor orthopyroxene. Other phases are Cl‐apatite, metal, sulfide, and graphite. Olivine ranges from Fo 65–73, with a strong peak at Fo 68–69. Most grains are reversezoned, and also have ?10–30 μm reduction rims. In terms of its dominant mineralogy and texture, NWA 1500 resembles the majority of monomict ureilites. However, it is more ferroan than known ureilites (Fo ≥75) and other mineral compositional parameters are out of the ureilite range as well. Furthermore, neither apatite nor plagioclase have ever been observed, and chromite is rare in monomict ureilites. Nevertheless, this meteorite may be petrologically related to the rare augite‐bearing ureilites and represent a previously unsampled part of the ureilite parent body (UPB). The Mn/Mg ratio of its olivine and textural features of its pyroxenes are consistent with this interpretation. However, its petrogenesis differs from that of known augite‐bearing ureilites in that: 1) it formed under more oxidized conditions; 2) plagioclase appeared before orthopyroxene in its crystallization sequence; and 3) it equilibrated to significantly lower temperatures (800–1000 °C, from two‐pyroxene and olivine‐chromite thermometry). Formation under more oxidized conditions and the appearance of plagioclase before orthopyroxene could be explained if it formed at a greater depth on the UPB than previously sampled. However, its significantly different thermal history (compared to ureilites) may more plausibly be explained if it formed on a different parent body. This conclusion is consistent with its oxygen isotopic composition, which suggests that it is an ungrouped achondrite. Nevertheless, the parent body of NWA 1500 may have been compositionally and petrologically similar to the UPB, and may have had a similar differentiation history.  相似文献   

The influence of Hall drift on the magnetic fields of neutron stars     

Rainer Hollerbach †  Günther Rüdiger 《Monthly notices of the Royal Astronomical Society》2002,337(1):216-224

We consider the evolution of magnetic fields under the influence of Hall drift and Ohmic decay. The governing equation is solved numerically, in a spherical shell with   r _i / r _o = 0.75  . Starting with simple free-decay modes as initial conditions, we then consider the subsequent evolution. The Hall effect induces so-called helicoidal oscillations, in which energy is redistributed among the different modes. We find that the amplitude of these oscillations can be quite substantial, with some of the higher harmonics becoming comparable with the original field. Nevertheless, this transfer of energy to the higher harmonics is not sufficient to accelerate significantly the decay of the original field, at least not at the   R _B = O (100)  parameter values accessible to us, where this Hall parameter   R _B   measures the ratio of the Ohmic time-scale to the Hall time-scale. We do find clear evidence though of increasingly fine structures developing for increasingly large   R _B   , suggesting that perhaps this Hall-induced cascade to ever-shorter length-scales is eventually sufficiently vigorous to enhance the decay of the original field. Finally, the implications for the evolution of neutron star magnetic fields are discussed.  相似文献   

The effect of long-term low-temperature exposure on apatite fission track stability: A natural annealing experiment in the deep ocean   总被引：2，自引：0，他引：2  

Cornelia Spiegel  Barry Kohn  Thomas Rainer 《Geochimica et cosmochimica acta》2007,71(18):4512-4537

Since studies on deep-sea cores were carried out in the early 1990s it has been known that ambient temperature may have a marked affect on apatite fission track annealing. Due to sluggish annealing kinetics, this effect cannot be quantified by laboratory annealing experiments. The unknown amount of low-temperature annealing remains one of the main uncertainties for extracting thermal histories from fission track data, particularly for samples which experienced slow cooling in shallow crustal levels. To further elucidate these uncertainties, we studied volcanogenic sediments from five deep-sea drill cores, that were exposed to maximum temperatures between ∼10° and 70 °C over geological time scales of ∼15-120 Ma. Mean track lengths (MTL) and etch pit diameters (Dpar) of all samples were measured, and the chemical composition of each grain analysed for age and track length measurements was determined by electron microprobe analysis. Thermal histories of the sampled sites were independently reconstructed, based on vitrinite reflectance measurements and/or 1D numerical modelling. These reconstructions were used to test the most widely used annealing models for their ability to predict low-temperature annealing. Our results show that long-term exposure to temperatures below the temperature range of the nominal apatite fission track partial annealing zone results in track shortening ranging between 4 and 11%. Both chlorine content and Dpar values explain the downhole annealing patterns equally well. Low chlorine apatite from one drill core revealed a systematic relation between Si-content and Dpar value. The question whether Si-substitution in apatite has direct and systematic effects on annealing properties however, cannot be addressed by our data. For samples, which remained at temperatures <30 °C, and which are low in chlorine, the Laslett et al. [Laslett G., Green P., Duddy I. and Gleadow A. (1987) Thermal annealing of fission tracks in apatite. Chem. Geol. 65, 1-13] annealing model predicts MTL up to 0.6 μm longer than those actually measured, whereas for apatites with intermediate to high chlorine content, which experienced temperatures >30 °C, the predictions of the Laslett et al. (1987) model agree with the measured MTL data within error levels. With few exceptions, predictions by the Ketcham et al. [Ketcham R., Donelick R. and Carlson W. (1999) Variability of apatite fission-track annealing kinetics. III: Extrapolation to geological time scales. Am. Mineral. 84/9, 1235-1255] annealing model are consistent with the measured data for samples which remained at temperatures below ∼30 °C. For samples which experienced maximum temperatures between ∼30 and 70 °C, and which are rich in chlorine, the Ketcham et al. (1999) model overestimates track annealing.  相似文献   

Multiple advances of Alpine glaciers into the Jura Mountains in the Northwestern Switzerland     

Angela Graf  Naki Akçar  Susan Ivy-Ochs  Stefan Strasky  Peter W. Kubik  Marcus Christl  Martin Burkhard  Rainer Wieler  Christian Schlüchter 《Swiss Journal of Geoscience》2015,108(2-3):225-238

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Dynamical evolution of rotating stellar systems – III. The effect of the mass spectrum     

Eunhyeuk Kim  Hyung Mok Lee  Rainer Spurzem 《Monthly notices of the Royal Astronomical Society》2004,351(1):220-236

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Advances in radiative transfer     

Rainer Wehrse  Wolfgang Kalkofen 《Astronomy and Astrophysics Review》2006,13(1-2):3-29

This review describes advances in radiative transfer theory since about 1985. We stress fundamental aspects and emphasize modern methods for the numerical solution of the transfer equation for spatially multidimensional problems, for both unpolarized and polarized radiation. We restrict the discussion to two-level atoms with noninverted populations for given temperature, density and velocity fields. Unfortunately this article was originally published with typesetter's errors: The correct publication date was 25 February 2006, not 3 January 2006. The content was not in the final form. The publishers wish to apologize for this mistake. The online version of the original version can be found at /10.1007/s00159-005-0025-8.  相似文献   

Morphology of interacting elliptical galaxy pairs     

Rainer Madejsky 《Astrophysics and Space Science》1989,156(1-2):223-228

CCD-photometry of 20 elliptical galaxy pairs was obtained in order to study the effects of galaxy interactions. Deviations from undisturbed brightness profiles are interpreted in terms of ongoing tidal interaction. The deviations include asymmetrical isophotes, distortions of the outer isophotes, twisting of the major axes of the outer isophotes with respect to the line connecting both galaxy centers, nonconcentric isophotes and extended or truncated brightness profiles.In particular, nonconcentric isophotes represent strong evidence in favour of ongoing interaction since they are generally not detected in undisturbed elliptical galaxies. The displacement of the nuclei with respect to the underlying galaxy is most probably explained as the consequence of a velocity impulse due to the perturbing galaxy. Brightness profiles of the brighter components in galaxy pairs are generally extended in comparison with brightness profiles of isolated elliptical galaxies. Truncated brightness profiles prevalent in most of the smaller components of galaxy pairs are interpreted as consequence of a tidally limited galaxy radius imposed by the more massive component.  相似文献   

Azimuthal anisotropy in the lithosphere from observations of long-period S-waves   总被引：5，自引：0，他引：5  

L. P. Vinnik  R. Kind  L. I. Makeyeva  G. L. Kosarev 《Geophysical Journal International》1989,99(3):549-559

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Neuere Veröffentlichungen     

Joachim W. Dippner  Detlev Machoczek  Rainer Rudloff 《Ocean Dynamics》1995,47(3):247-252

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Synthesis of complete SH seismograms     

S. F. Ingate  G. Bock  R. Kind 《Geophysical Journal International》1983,75(1):261-274

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