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31.
Zusammenfassung Nach einleitenden Bemerkungen zu früheren Arbeiten über die Calina werden die Voraussetzungen ihres Entstehens besprochen. Eine kritische Auswahl der Calinameldungen aus den Resumenes de los observaciones meteorologicas wird der Ableitung einer räumlichen Verteilung dieses Phänomens zugrunde gelegt. Schließlich wird der Jahresgang der Calinahäufigkeit untersucht.
Summary After introductory remarks about former papers on the calina the conditions for the development are discussed. A critical selection of calina data from the Resumenes de los observaciones meteorologicas is used for the design of the space distribution of this phenomenon. Finally the annual variation of the frequency of calina is studied.

Résumé Après quelques allusions à d'anciennes recherches sur la calina, l'auteur expose les conditions de sa formation et fonde sur un choix critique des messages de los observaciones meteorologicas la répartition géographique de ce phénomène. Enfin, la variation annuelle de la fréquence d'apparition est etudié.


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32.
High-TiO2, quartz-normative (HTQ) tholeiite sheets of Early Jurassic age have intruded mainly Late Triassic sedimentary rocks in several early Mesozoic basins in the eastern United States. Field observations, petrographic study, geochemical analyses and stable isotope data from three HTQ sheet systems in the Culpeper basin of Virginia and Maryland and the Gettysburg basin of Pennsylvania were used to develop a general model of magmatic differentiation and magmatic-hydrothermal interaction for HTQ sheets. The three sheet systems have remarkably similar major-oxide and trace-element compositions. Cumulus and evolved diabase in comagmatic sheets separated by tens of kilometers are related by igneous differentiation. Differentiated diabase in all three sheets have petrographic and geochemical signatures and fluid inclusions indicating hydrothermal alteration beginning near magmatic temperatures and continuing to relatively low temperatures. Sulfur and oxygen isotope data are consistent with a magmatic origin for the hydrothermal fluid.The three sheet systems examined apparently all had a similar style of crystal-liquid fractionation that requires significant lateral migration of residual magmatic liquid. The proposed magmatic model for HTQ sheets suggests that bronzite-laden magma was intruded in an upper crustal magma chamber, with bronzite phenocrysts collecting in the lower part of the magma chamber near the feeder dike. Early crystallization of augite and Ca-poor pyroxene before significant plagioclase crystallization resulted in density-driven migration of lighter residual magmatic liquids along lateral and vertical pressure gradients towards the upper part of the sheet. The influence of water on the physical properties of the residual liquid, including density, viscosity and liquidus temperature, may have facilitated the lateral movement more than 15 km up dip in the sheets. Exsolution of a Cl- and S-rich metal-bearing aqueous fluid from residual magma resulted in concentration and redistribution of incompatible and aqueoussoluble elements in late-stage differentiated rocks. This proposed hydrothermal mechanism has important economic implications as it exerts a strong control on the final distribution of noble metals in these types of diabase sheets.  相似文献   
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Late Precambrian crustal evolution in the North Eastern Desert of Egypt occurred in a strongly extensional tectonic environment and was accompanied by abundant bimodal igneous activity. The extrusive and intrusive expressions of this magmatism, known as the Dokhan Volcanics and Pink Granites, respectively, were studied in detail from two areas. The Dokhan Volcanics and associated feeder dikes consist of a mafic suite dominated by andesites (60% SiO2) and smaller volumes of basalt and a felsic suite composed of rhyolite tuffs, ignimbrites and hypabyssal intrusions (72–78% SiO2). The rocks of the mafic suite display calc-alkaline trends on an AFM diagram but are enriched in incompatibles such as TiO2, P2O5, K2O, Rb, Sr, Ba, Zr, Y, Nb, and LREE. Rare earth element patterns are steep, with (Ce/Yb)n = 7.7 to 16.8. They contain moderate Ni (60 ppm) and Cr (95 ppm), indicating limited low-P fractionation. The melts of the mafic suite are interpreted to have formed either by 25% batch melting of eclogite or by 10% batch melting of LREE-enriched garnet lherzolite. The rocks of the felsic suite include Dokhan rhyolites and the epizonal Pink Granites. These contain 72–78% SiO2, are metaluminous and peraluminous, and have the high K2O/Na2O and FeO*/(FeO*+MgO) characteristic of post-tectonic, A-type granites. They are moderately enriched in incompatible elements, but their REE patterns overlap with those of the mafic suite, from which they can be distinguished by deep europium anomalies (Eu/Eu*=0.08–0.64) and flat HREE patterns=((Yb/Er)n=0.90–1.16). They share with the rocks of the mafic suite isotopic characteristics of depleted mantle, precluding anatexis of much older continental crust. The europium anomalies covary with Sr contents and indicate that plagioclase control was important, while the flat HREE patterns preclude residual garnet in the source. Hence the felsic melts could not have formed by anatexis of garnet-bearing mafic lower crust. Such melts could have formed by anatexis of amphibolite-facies crust, an interpretation which is not favored because the melts are not saturated with P2O5. Alternatively, the felsic melts may have formed via low-P fractional crystallization of the mafic melts, with about 2/3 removal of mostly plagioclase and amphibole along with minor apatite and zircon. This may have been accompanied in the latest stages of magmatic evolution by liquid-state fractionation such as thermo-gravitational diffusion or halide complexing.  相似文献   
34.
Local accuracy measures for digital terrain models   总被引:1,自引:0,他引:1  
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A comprehensive global navigation satellite system (GNSS) based radio occultation (RO) data set is available for meteorology and climate applications since the start of GNSS RO measurements aboard the CHAllenging Mini-satellite Payload (CHAMP) satellite in February 2001. Global coverage, all-weather capability, long-term stability and accuracy not only makes this innovative use of GNSS signals a valuable supplement to the data set assimilated into numerical weather prediction (NWP) systems but also an excellent candidate for global climate monitoring. We present a 3D variational data assimilation (3D-Var) scheme developed to derive consistent global analysis fields of temperature, specific humidity, and surface pressure from GNSS RO data. The system is based on the assimilation of RO data within 6 h time windows into European Centre for Medium-Range Weather Forecasts (ECMWF) short-term (24 h, 30 h) forecasts, to derive climatologic monthly mean fields. July 2003 was used as a test-bed for assessing the system’s performance. The results show good agreement with climatologies derived from RO data only and recent NWP impact studies. These findings are encouraging for future developments to apply the approach for longer term climatologic analyses, validation of other data sets, and atmospheric variability studies.  相似文献   
38.
New databases motivate improvements and extensions of the catalogue by Grünthal and Wahlström (J Seismol 7:507–531, 2003a) – G&;W03 – of earthquakes in central, northern, and northwestern Europe with M w?≥?3.50. Data from over 30 regional catalogues, the International Seismological Centre and U.S. National Earthquake Information Center bulletins for the NE Atlantic Ocean, and many special studies were analysed, largely along the lines of the previous study. Non-tectonic, non-seismic, and non-existing as well as duplicate events were identified and removed according to our current stage of knowledge. If not given by the original source, the moment magnitude, M w, was calculated for each event with a specified epicentral location and a given strength measure (i.e., an original magnitude of any type or, for onshore events only, an intensity). The calculations follow transformation relations derived in the present or in our previous study. The investigated area is subdivided into 22 polygons, in each of which one or more local catalogues, supplemented by data from special studies, are used. If more than one catalogue lists an event, one entry was selected according to a priority algorithm specific for each polygon. If the selected catalogue entry contains more than one strength type, one was selected for the M w calculation according to another priority scheme. The final catalogue, CENEC, is confined to the time period 1000–2004 and magnitudes M w?≥?3.50. This is an extension of the time period covered by G&;W03 (1300–1993). The number of events has increased from about 5,000 to about 8,000. For each entry, available information on the date, time, location (including focal depth), intensity I 0, magnitude M w, and source (i.e., the local catalogue or special study) are given. The strength type and value from which M w was calculated are also indicated. The catalogue is available on the website of the GFZ German Research Centre of Geosciences.  相似文献   
39.
The area south and east of the Baltic Sea has very minor seismic activity. However, occasional events occur as illustrated by four events in recent years, which are analysed in this study: near Wittenburg, Germany, on May 19, 2000, M w = 3.1, near Rostock, Germany, on July 21, 2001, M w = 3.4 and in the Kaliningrad area, Russia, two events on September 21, 2004 with M w = 4.6 and 4.7. Locations, magnitudes (M L and M w) and focal mechanisms were determined for the two events in Germany. Synthetic modeling resulted in a well-confined focal depth for the Kaliningrad events. The inversion of macroseismic observations provided simultaneous solutions of the location, focal depth and epicentral intensity. The maximum horizontal compressive stress orientations obtained from focal mechanism solutions, approximately N–S for the two German events and NNW–SSE for the Kaliningrad events, show a good agreement with the regionally oriented crustal stress field.  相似文献   
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