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51.
A local density approximation (LDA) method is developed for reconstructing the trajectories of type III radio bursts through the interplanetary medium. The method uses the measured source directions and the measured frequency drift rates of the type III burst to determine the locations of the radio source in the interplanetary medium at consecutive frequency levels. The technique is used to reconstruct the trajectory of an actual type III burst and the results are compared to the trajectory obtained from the global density law method. The LDA method represents an improvement in that it utilizes more observed data on the type III burst and that it takes full account of the local density variations at the source locations.  相似文献   
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俯冲洋壳的脱水作用对于岛弧火山岩的成因具有重要意义。西天山高压低温变质带中切割主岩蓝片岩/榴辉岩的榴辉岩相脉体记录了古生代俯冲带中的脱水过程。脉体具有典型高压矿物组合:石榴石(>8%)+绿辉石(15%)+石英(>55%)+蓝闪石(5%)+冻蓝闪石(10%)±黝帘石±方解石。高压脉及其主岩的岩相学与矿物化学研究表明流体是在俯冲过程中蓝片岩向榴辉岩进变质条件下释放。脉的主量元素成分显示流体富Si。主岩的稀土元素和微量元素表明其原岩为洋岛玄武岩(OIB)。脉和主岩具有相似的微量元素配分模式,并且相对N-MORB都显示富Li、Be、Cs、Rb、Ba、Pb、La的特点。通过模拟计算,在高压脉、与脉平衡的流体以及模拟的原生流体中都富集流体活动性元素(Li、Be、Pb)和LILE(Cs、Rb、Ba),贫HFSE(Nb)和REE(Nd、Sm)。证实了在古生代南天山洋俯冲时洋岛玄武岩脱水释放出富Li、Be、LILE、La和Pb,贫HFSE和HREE的流体。  相似文献   
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Zircon populations of Neoproterozoic and early Paleozoic age occur in metabasites of a high-pressure amphibolite-facies unit of the Austroalpine basement south of the Tauern Window. The host rocks for these zircons are eclogitic amphibolites of N-MORB-type character, hornblende gneisses with volcanic-arc basalt signature, and alkaline within-plate-basalt amphibolites. Bulk rock magmatic trace element patterns were preserved during amphibolite-facies high-pressure and subsequent high-temperature events, as well as a greenschist-facies overprint. Positive Ce and negative Eu anomalies and enrichment of HREE in normalized zircon REE patterns, as analysed by LA-ICP-MS, are typical for an igneous origin of these zircon suites. Zircon Y is well correlated to HREE, Ce, Th, U, Nb, and Ta and allows discrimination of compositional fields for each host rock type. Low Th/U ratios are correlated to low Y and HREE abundances in zircon from low bulk Th/U host rocks. This is likely a primary igneous characteristic that cannot be attributed to metamorphic recrystallization. Variations of zircon/host rock element ratios confirm that ionic radii and charges control abundances of many trace elements in zircon. The trace element ratios—presented as mineral/melt distribution coefficients—indicate a selectively inhibited substitution of Zr and Si by HREE and Y in zircon which crystallized from a N-MORB melt. Correlated host rock and zircon trace element concentrations indicate that the metabasite zircons are not xenocrysts but crystallized from mafic melts, represented by the actual host rocks.  相似文献   
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Orthopyroxene and olivine exposed along the rim of a harzburgite xenolith from La Palma (Canary Islands) show polycrystalline selvages and diffusion zones that result from contact with mafic, alkaline, silica-undersaturated melts during at least 10-100 years before eruption. The zoned selvages consist of a fine-grained reaction rim towards the xenolith and a coarser grained, cumulate-like layer towards the melt contact. The diffusion zones are characterized by decreasing magnesium number from about 89-91 in the xenolith interior to 79-85 at the rims, and clearly result from Fe-Mg exchange with surrounding mafic melt. The width of the diffusion zones is 80-200 µm in orthopyroxene and 1,020-1,730 µm in olivine. Orthopyroxene also shows decreasing Al2O3 and Cr2O3 and increasing MnO and TiO2 towards the reaction rims. Textural relations and comparisons with dissolution experiments suggest that orthopyroxene dissolution by silica-undersaturated melt essentially ceased after days to weeks of melt contact, possibly because of decreasing temperature and formation of the reaction rims. The short dissolution phase was followed by prolonged growth of diffusion zones through cation exchange between xenolith minerals and melt across the reaction rims, and by the growth of cumulus crystals. The observations indicate that orthopyroxene xenocrysts and harzburgite xenoliths can survive in mafic, silica-undersaturated, subliquidus magmas at 1,050-1,200 °C and 200-800 MPa for tens of years. Modeling and comparison of the diffusion zones indicate that the average Fe-Mg interdiffusion coefficient DFeMg in orthopyroxene is 2 log units lower than that in olivine; at 1,130 °C and QFM-buffered oxygen fugacity, DFeMgopx = 3 ×10 - 19  m2  s- 1D_{FeMg}^{opx} = 3 \times 10^{ - 19} \,{\rm m}^2 \,{\rm s}^{{\rm - 1}} . The new data overlap well with recently published data for DFeMg in diopside, and indicate that DFeMg opxD_{FeMg\,}^{opx} (as predicted by previous authors) may be extrapolated to higher temperatures and oxygen fugacities. It is suggested that DFeMg opx D_{FeMg\,}^{opx} and DFeMg in Mn-poor ferromagnesian garnet are similar within 0.5 log units at temperatures between 1,050 and 1,200 °C.  相似文献   
57.
The mineral assemblages in the eclogites and meta-sediments of the Münchberg gneiss complex suggest minimum pressures of about 15 kbar, and temperatures of 600±30° C for the eclogite-facies metamorphism. Both rock types underwent a subsequent amphibolite-facies metamorphism at almost the same temperature range. In the Weissenstein borehole the eclogites and meta-sediments show an intimate interlayering on a centimetre scale. Contacts between the two rock types are often sharp and untectonized suggesting in-situ metamorphism of the eclogites. The following features indicate that the gneisses were subjected to eclogite-facies metamorphism:
  1. Phengite relics and phengite inclusions in garnet contain up to 3.45 Si per formula unit while amphibolite facies phengites have considerably lower Si-contents (3.0–3.25 p.f.u.).
  2. Omphacite relics occur in the form of Na-augite (6–9 mol% jadeite)-oligoclase symplectites.
  3. Garnets with up to 40 mol% of the pyrope component occur.
The geological and mineral-chemical data indicate that large volumes of crustal material have been buried to depths possibly exceeding 70 km. The preservation of primary eclogitic textures as well as symplectitic textures in the presence of a fluid phase, are indicative of a rapid decompression. This would suggest a tectonic uplift (e.g. underthrusting) as is also indicated by the virtually constant temperature range during the uplift.  相似文献   
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Summary A time-dependent study of the formation, distribution and destruction of atmospheric ozone is made for a meridional plane between 15 km and 45 km under the assumption of zonal symmetry. Included are time-effects of photochemistry, advection and turbulence, using presently available information on theoretical and observational data. The attempt is made to investigate the important part played by pure photochemistry, by the various transport processes and by the combination of both.In the photochemical calculations the equations of a pure oxygen photochemistry and solar ultraviolet energy data obtained from recent rocket observations are used.Murgatroyd andSingleton's results of a possible meridional circulation andPrabhakara's pattern of large-scale eddy diffusion, derived from the spread of radioactive tungsten in the stratosphere, are assumed to be the basic transport meachanisms.Several combinations of these non-photochemical processes are tested in the model and compared with recent observations.The relatively largest seasonal variations of the O3-concentration take place in the upper stratosphere with a maximum concentration in the high-latitude winter-hemisphere. In the midstratosphere the maximum concentration appears over the equatorial latitudes following the sun's position. In the lower stratosphere the highest O3-concentrations are over the polar latitudes throughout the year.The seasonal variation of the total ozone at middle and high latitudes can be explained by photochemical effects, the increase of total ozone with increasing latitude by the combined effects of photochemistry and transport processes only. With an advective transport of 70% ofMurgatroyd andSingleton's circulation we have reasonably well reproduced an observed spring distribution of O3 in the northern hemisphere.
Zusammenfassung Die Bildung, Ausbreitung und Zerstörung des atmosphärischen Ozons wird in einem meridionalen Profil zwischen 15 km und 45 km unter der Annahme zonaler Symmetrie als nichtstationäres Problem untersucht. Die Einflüsse der Photochemie, der Advektion und der Turbulenz werden als Funktionen der Zeit behandelt. Es wird versucht, die Bedeutung der photochemischen Einflüsse, der verschiedenen Transportprozesse sowie der Kombination beider in einem numerischen Modell zu studieren; gegenwärtig verfügbare theoretische und experimentelle Daten finden Verwendung.In den photochemischen Berechnungen werden die Gleichungen der reinen Sauerstoff-Photochemie und mit Raketen ermittelte Daten der verfügbaren Sonnenenergie verwendet.Murgatroyds undSinlgetons Ergebnisse einer möglichen meridionalen Zirkulation und die vonPrabhakara benützten Werte der großräumigen Turbulenz, die aus der Verbreitung des radioaktiven Wolframs abgeleitet worden sind, werden als Transportmechanismen betrachtet. Verschiedene Kombinationen dieser Transportgrößen werden im Modell getestet und mit neueren Beobachtungen verglichen.Die relativ größten jahreszeitlichen Schwankungen der Ozonkonzentration treten in der oberen Stratosphäre auf mit einer maximalen Konzentration in der Winterhemisphäre hoher Breiten. In der mittleren Stratosphäre befindet sich das Maximum über den äquatorialen Breiten. In der unteren Stratosphäre findet man die höchsten Ozonkonzentrationen während des ganzen Jahres über den polaren Breiten.Der Jahresgang des Gesamtgehaltes an Ozon über mittleren und hohen Breiten kann durch photochemische Einflüsse erklärt werden, die Zunahme des Gesamtozons mit zunehmender Breite nur durch ein Zusammenwirken von photochemischen und Transport-Prozessen. Mit 70% der Advektion vonMurgatroyd undSingleton haben wir eine beobachtete Frühjahrsverteilung des Ozons in der nördlichen Hemisphäre mit guter Annäherung reproduziert.

Résumé On examine ici la formation, la propagation et la destruction de l'ozone atmosphérique dans un profil méridien entre 15 et 45 km d'altitude. Pour cela, on admet une symétrie zonale et qui'il s'agit d'un problème non stationnaire. On considére les influences de la photochimie, de l'advection et de la turbulence en fonction du temps. On essaie d'étudier au moyen d'un modèle numérique l'importance des influences de la seule photochimie, des différents processus de transport ainsi que la combinaison des deux phénomènes. Dans ce but, on utilise les valeurs théoriques et expérimentales disponibles actuellement.Dans le calcul photochimique, on utilise aussi bien les équations de la photochimie pure de l'oxygène que des valeurs de l'énergie solaire disponible, obtenues au moyen de mesures effectuées avec des fusées. Comme mécanismes de transport, on prend en considération les résultats des études deMurgatroyd etSingleton sur une circulation méridionale possible ainsi que les valeurs de la turbulence des grands espaces utilisées parPrabhakara. Ces dernières découlent de la dissémination du wolfram radioactif. On fait figurer dans le modèle diverses combinaisons de ces grandeurs de transport et on compare les résultats ainsi obtenus aux observations les plus récentes.Les variations saisonnières relativement les plus importantes de la concentration d'ozone se rencontrent dans la stratosphère supérieure. La concentration maximale se situe dans les hautes latitudes de l'hémisphère hivernal. Dans la stratosphère moyenne, le maximum se rencontre au voisinage de l'équateur. Dans la basse stratosphère, on note les plus fortes concentrations d'ozone au voisinage des pôles et cela durant toute l'année.On peut expliquer par des influences photochimiques les fluctuations annuelles de la teneur globale en ozone dans les latitudes moyennes et élevées. L'augmentation de la teneur totale de l'ozone avec la latitude ne s'explique que par les effets conjugués des processus photochimiques et de transport. On a assez bien pu reproduire une répartition de l'ozone observée au printemps sur l'hémisphère nord en utilisant le 70% de l'advection calculée selonMurgatroyd etSingleton.


With 18 Figures

This investigation was begun while the author was on leave at the National Center for Atmospheric Research in Boulder, Colorado, USA.  相似文献   
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