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The eclogite contains relicts of a high pressure stage (ca. 700 °C and > 17.5 kbar) characterised by matrix omphacite with Jd40–35. This assemblage was overprinted by a lower pressure, higher temperature metamorphic event (ca. 820 °C and 15.5–17.5 kbar), as indicated by the presence of clinopyroxene (Jd35–20) and plagioclase. Biotite and pargasitic amphibole represent a later stage, probably related to an influx of fluids. Zircons separated from the eclogite contain magmatic relicts indicating Permian crystallization of a quartz-bearing gabbroic protolith. Inclusions diagnostic of the high temperature, post-eclogitic overprint are found in metamorphic zircon domain Z2 which ages spread over a long period (160 – 95 Ma). Based on zircon textures, zoning and chemistry, we suggest that the high-temperature peak occurred at or before ca. 160 Ma and the zircons were disturbed by a later event possibly at around 115 Ma. Small metamorphic zircon overgrowths with a different composition yield an age of 79 ± 3 Ma, which is related to a distinct amphibolite-facies metamorphic event.
The metapelitic host rock consists of a mesosome with garnet, mica and kyanite, and a quartz- and plagioclase-bearing leucosome, which formed at granulite-facies conditions. Based on previously reported micro-diamond inclusions in garnet, the mesosome is assumed to have experienced UHP conditions. Nevertheless, (U)HP mineral inclusions were not found in the zircons separated from the diamond-bearing metapelite. Inclusions of melt, kyanite and high-Ti biotite in a first metamorphic zircon domain suggest that zircon formation occurred during pervasive granulite-facies metamorphism. An age of 171 ± 1 Ma measured on this zircon domain constrains the high-temperature metamorphic event. A second, inclusion-free metamorphic domain yielded an age of 160 ± 1 Ma that is related to decompression and melt crystallization.
The similar age data obtained from the samples indicate that both rock types recorded a high-T metamorphic overprint at granulite-facies conditions at ca. 170 – 160 Ma. This age implies that any high pressure or even ultra-high pressure metamorphism in the Kimi Complex occurred before that time. Our findings define new constraints for the geodynamic evolution for the Alpine orogenic cycle within the northernmost Greek part of the Rhodope Metamorphic Complex. It is proposed that the rocks of the Kimi Complex belong to a suture zone squeezed between two continental blocks and result from a Paleo-ocean basin, which should be located further north of the Jurassic Vardar Ocean. 相似文献
Summary From an extensive material of records and observations within the air layer near the ice surface of Alpine glaciers the days with glacier wind were extracted. New results concerning daily variation, velocity distribution, and thermal structure of this gravity-wind are communicated. Thedaily variation shows two maxima of equal significance (before sunrise and before sunset) and two minima (before noon and before midnight). The same double variation becomes also manifest in the vertical temperature gradient as a consequence of the different daily variation of air and ice temperature. The verticalvelocity distribution shows a maximum approaching 3 m/sec below 2.5 m height. The relation between level and velocity of the maximum can be described by a simple exponential law. Using the formula ofA. Defant for the velocity of a stationary gravity-wind, it can be shown that, most likely, the height of the layer of cold air moving downward on Alpine glaciers as glacier wind hardly exceeds the order of magnitude of decameters. Thethermal structure of the air layer near the ice surface reveals its origin: air of glacial origin flowing down as glacier wind is characterized, in case of a stable stratification, by a great vertical temperature gradient after intensive emission of heat; non-glacial air arriving by advection from parts clear of ice has a considerably smaller temperature gradient. There is a linear relation between temperature gradient and irregular variations of temperature the amplitudes of which reach a maximum in glacier wind. They are principally an effect of the turbulent mixing process of the air near the ice surface and make possible estimating a mixing length for the heat transfer. As the quantum of heat being transferred by turbulent mixing from air to ice is directly proportional to the vertical temperature gradient, the relatively highest amount of heat passes from air to ice with glacier wind, independently of the absolute height of temperature. Therefore, there are no objective arguments for attributing to the glacier wind a conserving effect which protects the ice from rapid melting.
Résumé A partir d'un vaste matériel d'observations de la couche d'air voisine de la glace, l'auteur établit une liste des jours avec brise de glacier. Il communique de nouveaux résultats concernant la variation diurne, la répartition des vitesses et les conditions thermiques de ce vent. Lavariation diurne présente deux maxima (avant le lever et avant le coucher du soleil) et deux minima (avant midi et avant minuit). Le gradient vertical de température accuse la même périodicité par suite des variations diurnes différentes des températures de l'air et de la glace. Ladistribution de la vitesse selon la verticale fait ressortir le maximum atteignant 3 m/s au-dessous de 2,5 m de hauteur; l'altitude et la vitesse du maximum sont liées par une loi exponentielle simple. Grâce à la formule deA. Defant concernant la vitesse d'un courant de gravitation stationnaire, on peut montrer que l'épaisseur des brises des glaciers alpins ne dépasse probablement pas une dizaine de mètres. Lastructure thermique de la couche d'air proche de la glace trahit son passé immédiat: cette couche est en effet caractérisée par un fort gradient vertical de température par suite de la perte de chaleur intense, tandis que l'air provenant par advection des parties avoisinantes, libres de glace, possède un gradient notablement plus faible. Il y a en outre des variations de température irrégulières, linéairement liées au gradient de température et dont l'amplitude est maximum par la brise de glacier; elles résultent essentiellement du mélange turbulent de la couche voisine de la glace et permettent d'estimer un parcours de mélange du transfert de chaleur. Comme la quantité de chaleur transmise à la glace par le mélange turbulent de l'air sus-jacent est directement proportionnelle au gradient vertical de température, relativement la plus grande quantité de chaleur passe, par brise de glacier, de l'air à la glace, et cela indépendamment de la valeur absolue de la température. Il n'est donc pas justifié d'attribuer à la brise de glacier la propriété de protéger la glace d'une fusion rapide.
Mit 7 Textabbildungen. 相似文献
Summary An observation of an unusually luminous inferior parhelion is communicated. From the appearance of weak colours it may be surmised that refraction takes part in the phenomenon which was found to originate in falling stellate snowflakes.
Résumé Il s'agit de l'observation d'un parhélie inférieur particulièrement lumineux. La présence d'une faible coloration laissait supposer un phénomène de réfraction se produisant dans des cristaux étoilés de neige.
Mit 1 Textabbildung. 相似文献
Summary Development of a characteristic distribution of snow density in the snow cover during winter is the consequence of the temperature stratification. Snow density increases with depth reaching a maximum at a medium level of the layer, while a minimum is found at the bottom of the snow cover. It is shown that, in the firn regions of the glaciers in the East Alps, this density distribution lasts for several years and down to considerable depths. For this reason it can be used as a means for determining the limits of the annual economy of snow.
Résumé Par suite de la stratification de température, la densité dans la couche de neige gisante augmente à partir de la surface et atteint vers le milieu de la couche son maximum, puis diminue jusqu'au minimum qui se trouve an fond de celle-ci. Cette répartition verticale de la densité persiste pendant plusieurs années et jusqu'à de grandes profondeurs dans les névés des glaciers des Alpes orientales; elle peut de ce fait servir de base pour la recherche des limites des couches annuelles.
Mit 2 Textabbildungen
Herrn Prof. Dr.H. Ficker zum 75. Geburtstag gewidmet. 相似文献