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  • 1
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Chemical data for 139 natural paragonite-muscovite (Pg-Ms) pairs illustrate the effects of ferromagnesian components on the P-T-X topology of the Pg-Ms solvus. The pairs were selected on the basis of: reasonably accurate knowledge of the P-T conditions of formation; evidence for close approach to equilibrium at peak metamorphic conditions; exclusion of pairs in which paragonite contains more than 5 mol% margarite; and exclusion of pairs from polymetamorphic rocks that contain more than one set of cogenetic Pg-Ms pairs. Graphical analysis reveals considerable scatter in the data; nevertheless, it is evident that the muscovite limb of the solvus shifts markedly toward end-member muscovite with increasing pressure from approximately 7 kbar to 21 kbar. This shift is attributed to a pressure-induced increase of the ferromagnesian content of muscovite, which increases the size of the XII alkali site - to the effect that K is more readily accommodated than Na. The data also suggest that the paragonite limb of the solvus migrates slightly toward end-member paragonite with increasing pressure. Broadening of the Pg-Ms solvus with increasing pressure reflects increasingly nonideal Na-K mixing as the phengite content of muscovite increases. Due to the wide scatter of data for Pg-phengitic-Ms pairs, it is concluded that, at the present time, Pg-Ms solvus thermometry is only viable for quasibinary Pg-Ms pairs.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 89 (1988), S. 299-315 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 139 (2000), S. 298-315 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Coesite-bearing eclogites from Dabieshan (central China) have been studied by ion microprobe to provide information on trace element distributions in meta-basaltic mineral assemblages during high-pressure metamorphism. The primary mineralogy (eclogite facies) appears to have been garnet and omphacite, usually with coesite, phengite and dolomite, together with high-alumina titanite or rutile, or both titanite and rutile; kyanite also occurs occasionally as an apparently primary phase. It is probable that there was some development of quartz, epidote and apatite whilst the rock remained in the eclogite facies. A later amphibolite facies overprint led to partial replacement of some minerals and particularly symplectitic development after omphacite. They vary from very fine-grained dusty-looking to coarser grained Am + Di + Pl symplectites. The eclogite facies minerals show consistent trace element compositions and partition coefficients indicative of mutual equilibrium. Titanite, epidote and apatite all show high concentrations of REE relative to clinopyroxene. The compositions of secondary (amphibolite facies) minerals are clearly controlled by local rather than whole-rock equilibrium, with the composition of amphibole in particular depending on whether it is replacing clinopyroxene or garnet. REE partition coefficients for Cpx/Grt show a dependence on the Ca content of the host phases, with D REE Cpx/Grt decreasing with decreasing D Ca . This behaviour is very similar to that seen in mantle eclogites, despite differences in estimated temperatures of formation of 650–850 °C (Dabieshan) and 1000–1200 °C (mantle eclogites). With the exception of HREE in garnet, trace elements in the eclogites are strongly distributed in favour of minor or accessory phases. In particular, titanite and rutile strongly concentrate Nb and Zr, whilst LREE–MREE go largely into epidote, titanite and apatite. If these minor/accessory minerals behave in a refractory manner during melting or fluid mobilisation events and do not contribute to the melt/fluid, then the resultant melts and fluids will be strongly depleted in LREE–MREE.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 157 (1988), S. 187-192 
    ISSN: 1573-5117
    Keywords: Reefs ; Seaweeds ; degradation ; nutrients ; bioassay ; Phaeodactylum tricornutum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extensive beds of benthic, non-calcareous macroalgae are associated with reef formations in oligotrophic coastal waters of Northeastern Brazil. Large amounts of these algae constantly and naturally detach and decay. Part of them is deposited on the beach, remains exposed during low tides, and decomposes. Field experiments on decomposition were carried out in a tidal pool (temperatures fluctuating from 29 to 43°C salinity from 6 to 35 at Ponta do Seixas (Paraiba, Brazil), and laboratory studies were made in aerobic and anaerobic conditions. High values of NO 3 − (up to 148.92 μg at 1−1), NO 2 − (up to 3.14 μg at 1−1) and PO 3 4− (up to 22.95 μg at 1−1) were released during algal degradation. Nitrogen values were higher in the tidal pool than in aerobic and anaerobic experiments, as opposed to phosphorus where the opposite phenomenon occurred. The diatom Phaeodactylum tricornutum inoculated in seawater enriched with decomposition products of algae showed intense growth, sometimes similar to that in complete algal culture medium. Inhibition and death of this diatom was observed in some other experiments. The importance of drift seaweed as a source of nutrients for the local ecosystem is stressed.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1435-1463
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Autoren haben die Wichtigkeit der Schätzung der effektiven Halbzeit — d. h., daß die Radioaktivität der Schilddrüse nach Darreichung einer Spurendosis radioaktiven Jods um die Hälfte abnehme — als Maß der Schilddrüsenfunktion aufgezeigt. Sie haben daher die durch Verabreichung des TSH hervorgerufene Variation bei Personen, die klinisch offenkundig keine Kropfträger waren, aber hohe Werte abgelagerten J131 und verlängerte Halbzeit aufwiesen, studiert. Nachdem konstatiert wurde, daß bei einigen Personen nach Einverleibung des TSH sich die Halbzeit verkürzte, bei anderen diese aber gleich blieb oder sich sogar verlängerte, haben die Autoren die Ursachen dieses verschiedenen Verhaltens zu analysieren versucht. Demzufolge haben sie die Hypothese aufgestellt, daß bei den Personen der ersten Gruppe — mit Halbzeiten-Reduktion nach Einverleibung von TSH — die Sekretion des TSH normal oder auch vermindert in Abhängigkeit von nicht pituitären Reizen wäre, bei jenen der zweiten Gruppe die Sekretion des TSH hingegen erhöht wäre, welcher Reiz auf eine Aktivität der Schilddrüse hinwiese, die als preoder substrumigen anzusehen sein dürfte.
    Abstract: Résumé Les auteurs ont démontré l'importance de la valeur du demi-temps effectif de l'iode radioactif fixé par la glande thyroïde, après l'administration d'une dose-trace, comme mesure de la fonction thyroïdienne. Ensuite ils ont étudié les variations provoquées par l'administration de la TSH chez des sujets sans constatation évidente d'un goitre, mais qui pourtant montrèrent des valeurs considérables de la fixation de l'I131 et une prolongation du demitemps. Comme on a trouvé chez quelques sujets, après l'administration de la TSH, une diminution du demi-temps, qui, au contraire, ne changeait pas en d'autres cas, les auteurs ont essayé d'analyser les causes de ces différentes observations. Pour cela ils ont évalué l'hypothèse que, chez les malades du premier groupe, la sécrétion de la TSH pourrait être normale ou même diminuée, l'augmentation de l'iode radioactif fixé par la glande thyroïde ayant dépendu de stimulations non pituitaires, tandis que, chez les malades du deuxième groupe, la sécrétion de la TSH pourrait être augmentée avec une fonction thyroïdienne orientée vers la goitregenèse.
    Notes: Summary The Authors emphasize the value of the effective half-time of radioiodine uptaken by the thyroid as a measure of intrathyroidal iodine turnover and then of thyroid function. Studying the variations induced on this parameter by TSH in patients without goiter and with high per cent uptake and short effective half-time, the Authors have selected two groups of patients. In the first are classified the patients with a significant shortening of T 1/2 after TSH; in the second group are classified the patients without any change of T 1/2 after stimulation test. The Authors, trying to elucidate the different behaviour of the patients of two groups, suggest the hypothesis that in the first group the secretion of TSH may be normal or decreased and the high thyroid uptake may be due to non-pituitaric stimulation, whereas in patients of second group the secretion of TSH may be increased with thyroid function modified toward goiter.
    Type of Medium: Electronic Resource
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