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81.
B. Bühn 《Mineralogy and Petrology》2008,92(3-4):453-470
Summary Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting
carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone
or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in the bulk rocks from s?vites
to beforsites is due to crystallization of calcite and fluorapatite. All carbonatites show a negative Y anomaly in normalised
REE plots. Fractionation is accompanied by successively lower HREE contents between Tb and Yb, expressed by the ratios Nd/Ho
and Ho/Lu. The evolution of this downward-facing hump goes along with decreasing Y contents in bulk rocks and minerals. All
this requires an additional phase coexisting with the carbonate liquid during fractionation. Comparison between the bulk rocks
and the expelled fluid shows that the latter had preferentially accumulated the HREE and Y. Further evidence for this process
are hydrothermal, HREE, Y-rich fluorites in other carbonatite complexes which reflect the composition of the expelled fluid.
The high strength of fluoride complexes suggests that fluoride complexing in the carbonatitic fluid is the process responsible
for extracting HREE and Y from the carbonatite magma, leaving fractionated carbonatite rocks depleted in these elements. The
geochemical evolution of carbonatite magmas along fractionation has therefore to be considered in a melt-mineral-fluid system.
Correspondence: B. Bühn, Instituto de Geociências, Universidade de Brasilia, Campus Universitário Darcy Ribeiro, Brasilia
70910-900, Brazil 相似文献
82.
83.
Abstract The Taiwan orogen has been the focus of a number of models of mountain building processes, but little attention has been paid to high‐pressure (HP) metamorphic rocks that are found as exotic blocks intermingled within the deepest units of the mountain belt. In this study, we re‐appraise from updated petrological and thermodynamic databases the physical conditions of HP metamorphism in Taiwan, and we combine our findings with available geochronological data to estimate the thermal history of these rocks. Our results indicate that peak metamorphic conditions of ~550 °C and 10–12 kbar have been followed by a rapid isothermal decompression, with exhumation possibly as rapid as burial. These units have subsequently been stored at a pressure of ~3 kbar for ~4–5 Myr, before their final exhumation, probably facilitated by the accretion of passive margin sequences during the Late Cenozoic collision. Therefore, HP units in Taiwan maintain a record of processes at depth from the early stages of oceanic subduction to the present arc‐continent collision. 相似文献
84.
A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σs = 10−4, σi = 10−2 and (b) σs = 10−1, σi = 10−2 are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σs and σi are the ratios of the beam density Ns and the helium ion (H6+) density Ni to the total positive ions in the plasma-beam system. 相似文献
85.
Zusammenfassung Die Davoser Windverh?ltnisse werden in ihrem tages- und jahreszeitlichen Ablauf sowie in ihrer Abh?ngigkeit von verschiedenen
typischen Wetterlagen untersucht. Neben den ungest?rten Sch?nwetterlagen mit ihrem ausgepr?gten Talwind, der wie der Malojawind
talabw?rts weht, werden die F?hnstr?mung aus Südwest und die Nordoststr?mung bei Staulagen und Bise kurz besprochen. Gegenüber
dem benachbarten Dischmatal zeigt sich ein sp?terer Beginn des Talwindes bei Sch?nwetterlagen, w?hrend im Vergleich zu anderen
T?lern, z. B. zum Wallis, ein früheres und schw?cheres nachmitt?gliches Windmaximum auftritt.
Mit 6 Textabbildungen
Herrn Dr.W. M?rikofer zu seinem 70. Geburtstag gewidmet. 相似文献
Summary The wind at Davos is analysed in his diurnal and annual variation and in the depence on the different weather types. The fair and undisturbed weather shows a typical valley breeze during the day, but not in the normal direction towards the higher part of the valley, but downstream, similar to the Malojawind in the Engadine. The opposite wind direction, from southwest, characterises the foehn-situation. Northeasterly winds develop in the case of higher pressure north of the Alps (e. g. in situations of barrage). The valley-breeze begins later than in the adjacent Dischma Valley, but it is weaker and reaches the highest intensity earlier than in other valleys, as e. g. in the Valais.
Résumé Les vents de Davos sont analysés selon leurs variations diurnes et annuelles et selon des types de temps caractéristiques. La situation de beau temps montre un vent de vallée assez accentué, soufflant du haut en bas, donc dans une direction anormale, mais analogue au vent de la Maloja en Engadine. En cas de ?foehn? le vent souffle du sud-ouest tandis qu'un vent du nord-est se manifeste par situations de surpression au nord des Alpes. Le vent de vallée se met à souffler plus tard à Davos que dans la vallée de Dischma toute proche. Il y atteint par contre sa vitesse maximale plus t?t que les vents correspondants d'autres vallées p. ex. du Valais. Le maximum y est cependant moins élevé.
Mit 6 Textabbildungen
Herrn Dr.W. M?rikofer zu seinem 70. Geburtstag gewidmet. 相似文献
86.
Dozent Dr. Siegfried Haussühl Dozent Dr. German Müller 《Contributions to Mineralogy and Petrology》1963,9(1):28-39
Summary Argillaceous sediments of jurassic and lower cretaceous age in NW-Germany contain in several localities authigenous ZnS-polytypes. The crystals with a maximum height of 2 mm exhibit hexagonal-pyramidal and trigonal-pyramidal habit.With X-ray rotation and precession technique the following polytypes could be identified: Sphalerite (3 R = 3 C) 211, 411, 6H 9R, 12R, 15R and 21R.The 9 R-, 12 R- and 21 R-polytypes have not until now been described elsewhere.The structures of the new polytypes were determined as 9R=(21), 12R=(13) and 21R=(3112).Oriented intergrowths of R- and H-polytypes were frequently observed. From the intergrowth-phenomena arguments for the environmental conditions of formation can be deducted.[/p] 相似文献
87.
Dr. Necip Güven 《Contributions to Mineralogy and Petrology》1963,9(1):40-64
Zusammenfassung Nach der Profilaufnahme sind die Sedimente der Tongrube der Ziegelei von Willershausen in zwei Gruppen einzuteilen : A. Die unteren hellen Schichten, B. die oberen dunklen Schichten.Die unteren hellen Schichten bestehen aus Sandsteinen, Sanden, tonigen Sanden und Grobtonen, welche Quarz, Feldspäte und Glimmer als Hauptminerale und in geringeren Mengen Illit, Chlorit und manchmal Montmorillonit füren. Als Schwerminerale dieser Sande und Sandsteine treten der Häufigkeit nach Apatit, Zirkon, Granat, Anatas, Rutil, Turmalin und Opakminerale auf.Die oberen dunklen Schichten bestehen hauptsächlich aus mm-rhythmisch geschichteten Tonen mit Einschaltung einzelner Mergelbänke und toniger Sandschichten. Dioktaedrischer Illit ist das häufigste Tonmineral, dann folgen Chlorit und in geringeren Mengen in feinen Fraktionen Montmorillonit. Die Chlorit-Reflexe verschwinden bereits bei Erhitzung auf 450° C. Chemisch handelt es sich um die dem Pennin naheliegenden Diabantite.Die Unterschiede in Beschaffenheit und Menge der Quarze, Feldspäte und Glimmer, die unterschiedliche Verteilung der Schwerminerale sprechen dafür, daß die hellen Schichten wahrscheinlich zum Mesozoikum, vielleicht zum Buntsandstein gehören.Von der Mathematisch-Naturwissenschaftlichen Fakultät der Georg-August-Universität zu Göttingen genehmigte Dissertation. 相似文献
88.
F. Steinhauser W. Mörikofer K. Cehak W. Müller 《Theoretical and Applied Climatology》1965,13(4):558-568
Ohne Zusammenfassung 相似文献
89.
The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater. 相似文献
90.
The motion and the drift force of a floating OWC (oscillating water column) wave energy device in regular waves are studied taking account of the oscillating surface-pressure due to the pressure drop across the duct of the air chamber. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine-type Green function while the outer problem with the Kelvin-type Green function. The added mass, wave damping and excitation coefficients as well as the motion and drift force of the OWC device are calculated for various values of parameter related to the pressure drop. 相似文献