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Ulf Strohmayer 《GeoJournal》1993,30(4):463-472
Current developments within the human sciences in general and social geography in particular have challenged the paradigm of representation that has prevailed here as elsewhere for the longest time since the Enlightenment. The paper at hand seeks to explore some of the wider ramifications of this so-called postmodern challenge for those forms of expression that geographers have become accustomed to. Primarily the map, unique in its importance for the pursuit of geographical knowledge, will be analyzed from a decidedly abstract point of view. 相似文献
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Chemical and Sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the Gardar Province can be used to elucidate magma-chamber and emplacement processes. The megacrysts occur either as single crystals or assembled as anorthosite xenoliths. The size of the megacrysts varies from <1 cm to 1 m. They consist of a large core with variable zonation (An58-39) and a relatively small (<600 µm), normally zoned rim (An62-27). The contact between core and rim is sharp and marked by a sharp increase in anorthite content which can reach 11 mol% An. This gap is interpreted as having formed during dyke emplacement due to a sudden pressure release. Some of the megacryst cores show a fairly constant composition whereas others exhibit an unusual wavy-oscillatory zoning which has not been reported elsewhere to our knowledge. The oscillatory zoning has wavelengths of up to 2,500 µm and a maximum amplitude of 7 mol% An. It is interpreted as reflecting movements of the crystals in the magma reservoir. The Sr isotopic composition of one crystal shows a radiogenic inner core ((87Sr/86Sr)i=0.7044) and a less radiogenic outer core ((87Sr/86Sr)i=0.7039-0.7036). The lack of a significant change between outer core and rim ((87Sr/86Sr)i=0.7037) is consistent with formation of the more An-rich rim due to pressure release. Variations in the core may be related to movements of the crystal and/or magma mixing. A trace-element profile across a megacryst shows a small increase in Sr and small decreases in Ba and La contents of the recalculated melt composition across the core-rim boundary, whereas P, Ce, Nd and Eu remain constant. Melt compositional changes upon emplacement are therefore considered to be of minor importance. Constant ratios of incompatible trace elements in the megacryst cores indicate a dominant influence of a lower crustal source on trace-element budgets. 相似文献
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An anisotropic fractured poroelastic effective medium theory 总被引：1，自引：0，他引：1
S. R. Tod 《Geophysical Journal International》2003,155(3):1006-1020
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S. R. Tod 《Geophysical Journal International》2001,146(1):249-263
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Hurley K Strohmayer T Li P Kouveliotou C Woods P van Paradijs J Murakami T Hartmann D Smith I Ando M Yoshida A Sugizaki M 《The Astrophysical journal》2000,528(1):L21-L23
We present a 2-10 keV ASCA observation of the field around the soft gamma repeater SGR 1627-41. A quiescent X-ray source, whose position is consistent both with that of a recently discovered BeppoSAX X-ray source and with the Interplanetary Network localization for this soft gamma repeater, was detected in this observation. In 2-10 keV X-rays, the spectrum of the X-ray source may be fit equally well by a power-law, blackbody, or bremsstrahlung function, with unabsorbed flux approximately 5x10-12 ergs cm-2 s-1. We do not confirm a continuation of a fading trend in the flux, and we find no evidence for periodicity, both of which were noted in the earlier BeppoSAX observations. 相似文献
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The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR
1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers
a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. We
review the observational data on the magnetar oscillations, including new timing analysis of the SGR 1806-20 giant flare using
data from the Ramaty High Energy Solar Spectroscopic Imager and the Rossi X-ray Timing Explorer. We discuss the implications for the study of neutron star structure and crust thickness, and outline areas for future investigation.
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Alessandro Sandrin sa Edfelt Tod E. Waight Robert Berggren Sten-ke Elming 《Journal of Geochemical Exploration》2009,103(2-3):80-96
The Tjårrojåkka Fe–Cu-prospect in northern Sweden is considered an example of a Fe-oxide Cu–Au (IOCG) deposit and is hosted in metamorphosed Paleoproterozoic volcanic and intrusive rocks. Rock samples from 24 outcrops were collected for petrophysical analysis (magnetic susceptibility, remanent magnetization, variation of magnetic susceptibility with temperature, Curie temperature and density). The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that intersects the main Cu-mineralized body.The magnetic analyses show that magnetite is the dominant magnetic mineral, while hematite and other Fe-minerals are present in minor amounts. The electron microprobe observations confirm the presence of magnetite and further indicate that hematite is an alteration product of magnetite. Moreover, microprobe observations indicate that Fe-sulfides are present in negligible amounts in the samples from the Tjårrojåkka area. The strong spatial relationship of Cu-minerals (e.g., chalcopyrite) and the oxidation of magnetite to hematite suggest that the presence of rocks with low magnetic susceptibility in areas dominated by high susceptibility rocks may be a signal of related Cu-prospects. 相似文献