Die autometamorphe retrograde Umwandlung von Biotiten in Chlorite und Muskowite in sauren Tiefengesteinen

The autometamorphic transformation of iron-rich biotite to chlorite and muscovite with the by-products hematite, ilmenite, sphene, and rutile has been studied in thin-sections of about 50 granitic rocks of Austria and Bavaria.From 19 granitic rock samples the magmatic biotites, their secondary chlorites, and muscovites were separated, purified by hand-picking, and investigated by optical, x-ray, and chemical methods. The silicatic products of biotite transformation were found to be iron-rich chlorites and iron-poor muscovites.The essentiall process of biotite alteration to chlorite is based in the emigration of 9,5–12, 2 Eq.wt.% Si and nearly the complete alcali. This leak is only compensated by the importation of 23,3–27,6 Eq.wt.% H₂O⁺.The chemical changes of biotite alteration to muscovite are characterized by the emigration of 15–20 Eq.wt.% Fe, Mg, Ti and the importation of 9,3–14,2 Al, 4,6–7,1 Si, and 1,3–4,3 Eq.wt% H₂O⁺.Owing to the transformation of biotite unit cell dimensions considerable changes. As a result of biotite replacement by chlorite c ₀·sin increases about 40%. a ₀ and b ₀ only extends for 0,8%.In comparison with these facts of chloritisation biotite transformation to muscovite was found to reduce a ₀ and b ₀ (–2,6%) much stronger than c ₀·sin (–0,7%).Modal analysis data of retrograde alterations of biotite and feldspar in the granites were connected with the observed and calculated values of main element changing. In the granitic samples about 50% of iron and titanium have been converted from silicatic into oxidic minerals like hematite, ilmenite, sphene, and rutile during the biotite transformation.59–92% of H₂O⁺ in these rocks fall to the share of secondary sheet silicate forming during the latest phases of granite crystallisation.The balance account of the various chemical reactions shows for the closed system a deficit of H₂O and Al, and a surplus of Fe, Ti, and F. The deficit or surplus of Si, Mg, Mn, Ca, Na, K, and Li in the samples is very different and dependent on the values of biotite chloritisation, feldspar sericitisation, and so forth.At the present time quantitative control of the complete chemical exchanges during the automorphism of these granites is not possible, because the quartz-feldspar-reactions have not yet been investigated.

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Für Anregungen, Diskussionen, sachliche Hilfen und förderndes Interesse bin ich den Herren Prof. Dr. C. W. Correns, Göttingen; Dr. H. Fesser, Hannover; Prof. Dr. H. R. v. Gaertner, Hannover; Dr. H. Gundlach, Hannover; Dipl.-Min. U. Haack, Göttingen; Dr. W. Harre, Hannover; Prof. Dr. F. Karl, Kiel; Prof. Dr. R. Mannkopff, Göttingen; Dr. C. Savelli, Göttingen; Prof. Dr. W. Schreyer, Kiel; Dr. F. Seifert; Kiel; Dipl.-Phys. W. Stahl, Hannover; Prof. Dr. K. H. Wedepohl, Göttingen, und Prof. Dr. H. G. F. Winkler, Göttingen, zu großem Dank verpflichtet.

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Folgende Institutionen haben meine Arbeit durch die Erlaubnis der Benutzung von wissenschaftlichen Geräten und durch sachliche und finanzielle Mittel in dankenswerter Weise unterstützt: Bundesanstalt für Bodenforschung, Hannover, Deutsehe Forschungsgemeinschaft, Bad Godesberg, Geochemisches Institut der Universität, Göttingen, und das Mineralogisch-Petrographische Institut der Universität, Kiel.

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Meinen Assistentinnen Frl. G. Klaetsch, Frl. B. Köhler und Frau H. Grapp bin ich für ihre große Geduld und ihren ausdauernden Fleiß bei der jahrelangen mühsamen Trennung und Reinigung der Mineralphasen von Herzen dankbar.     

Ein Vergleich des Tektonischen Musters im Sahara-Feld mit dem deutschen Saxonikum

Zusammenfassung Die europäischen und nordafrikanischen Lineamentnetze zeigen große Ähnlichkeit miteinander. Beide sind ungefähr gleichorientiert, obwohl das nordafrikanische Muster vielfach näher an den Meridianen liegt, als das europäische. Beide passen aber in das gleiche Streßfeld. In beiden Regionen, d.h. in Nordafrika wie in Europa, setzt die gemusterte Zerbrechung mit von Zeit zu Zeit wechselnden Vorzeichen (Dehnung/Pressung, NW/NE-Prävalenz) ungefähr zur gleichen Zeit ein.Der mechanische Plan, dem die offenbar korrelaten Schwächeflächennetze untergeordnet scheinen, stimmt etwa mit dem Streßplan des späteren alpidischen Orogens überein, dessen frühesten geosynklinalen Vorspielen sie vorauslaufen, bzw. z. T. synchron sind.Hier scheint ein großräumiger Motor wirksam gewesen zu sein, dessen Effekt sich regional, breit und durch ganz verschieden-struierte Stockwerke bemerkbar macht.Die Lineamentmuster sind in beiden Testregionen nahezu gleichmäßig zu den heutigen Meridianen angeordnet (obwohl, wie bemerkt, das afrikanische Netz etwas steiler zu sein scheint). So darf vermutet werden, daß seit dem Beginn ihres Erscheinens (oder ihrer Aktivierung) im Spätkarbon bis heute keine merkliche, relative Schollenrotation Afrikas gegen Europa stattgefunden hat.Wie die Rotationsachse der Erde zur Aktivierungszeit dieser Fugensysteme gelegen hat, läßt sich noch nicht ganz eindeutig sagen, wenn auch auf Grund paläoklimatologischer und paläomagnetischer Beobachtungen Vermutungen erlaubt sind. Auch die — anders gestellte — Frage, ob es sich bei solcher Fugenaktivierung um Auswirkungen eines neu-einsetzenden oder eines in seiner Stärke veränderten Stresses handelt, oder aber um eine Positionsänderung der beanspruchten Felder gegenüber einer gleichbleibenden Beanspruchungsursache, kann noch nicht beantwortet werden. Im Hinblick auf Fragen der Epeirophorese bzw. von Polverschiebungen relativ zur Erdkruste wäre es wichtig, solche Antworten zu finden.

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European and North-African fracture patterns (lineament-systems) are similar to each other.Both show fairly equal orientations within the Meridian-grid of the globe. The North-African system appears nearer or steeper to the Meridians than the European patterns, both however seem to belong to the same, global mechanical plan; besides, the systems display about the same activation-age.Both schemes fit into the (mechanically or originally different) stressplan of the Alpine events beginning with geosynclinal preparations.Judging by the present mutual relation of both fracture patterns in NorthAfrica and Europe no serious lateral or rotational displacement or shifting of Europe relative to North-Africa seems to have taken place since the first time of appearance of the patterns. No conclusions are drawn concerning the original situation of the Earth's rotation axis in relation to activation-time and orientation of the patterns in question.

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Résumé Les réseaux de linéaments européens et nord-africains montrent une grande ressemblance. Tous les deux ont à peu près la même orientation, bien que le motif nord-africain se trouve souvent beaucoup plus rapproché des méridiens que le motif européen. Tous les deux cependant montrent le même champ de tensions. Dans les deux régions, en Afrique du Nord et en Europe, la dislocation produisant le motif a débuté à peu près au même moment avec, de temps à autre, un changement des signes: extension-compression, prévalence nordouest ou nord-est.Le plan mécanique suivant lequel les réseaux conjugués des plans de faible résistance semblent subordonnés, coïncide plus ou moins avec le plan des tensions lié à l'orogenèse alpine ultérieure, soit qu'ils soient postérieurs ou synchrones aux premiers évènements géosynclinaux relatifs à cette dernière. Il semble qu'ici un moteur de grande dimension ait été en action, dont l'effet s'est fait sentir régionalement avec ampleur et à travers des étages très différemment structurés.Les motifs linéamentaires dans les deux régions comparés sont presque semblablement ordonnés par rapport aux méridiens actuels (bien que, comme on l'a déjà mentionné, le réseau africain semble être davantage redressé). Aussi peut-on supposer que, depuis le commencement de son apparition (ou de son activation) au Carbonifère supérieur jusqu'à l'heure actuelle, il n'y a pas eu de rotation bien sensible de l'Afrique par rapport à l'Europe.On ne peut pas encore dire avec exactitude quelle était la position de l'axe terrestre à l'époque où ont joué ces systèmes de joints, bien que des observations paléoclimatologiques et paléomagnétiques permettent certaines suppositions. De même, on ne peut dire si une telle activation des joints est due à une nouvelle tension ou à une tension modifiée dans son intensité, ou bien s'il s'agit d'une changement dans la position des champs relativement à une sollicitation des forces restée constante.En ce qui regarde la question de l'épeirophorèse, c'est-à-dire du déplacement des pôles relatif à l'écorce terrestre, il serait important de trouver une réponse à cette question.

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Herrn Prof. Dr. Dr. h. c.Erich Bederke zum 70. Geburtstag gewidmet     

Momentum Transfer By A Mountain Meadow Canopy: A Simulation Analysis Based On Massman's (1997) Model

Using a mountain meadow as a case study it is the objective of the present paper todevelop a simple parameterisation for the within-canopy variation of the phytoelementdrag (C_d) and sheltering (P_m) coefficients required for Massman's model of momentum transfer by vegetation. A constant ratio between C_d and P_m is found to overestimate wind speed in the upper canopy and underestimate it in the lower canopy.Two simple parameterisations of C_d/P_m as a function of the plant area density and the cumulative plant area index are developed, using values optimised by least-squares regression between measured and predicted within-canopy wind speeds. A validation with independently measured data indicates that both parameterisations work reliably for simulating wind speed in the investigated meadow. Model predictions of the normalised zero-plane displacement height and the momentum roughness length fall only partly within the range of values given in literature, which may be explained by the accumulation of plantmatter close to the soil surface specific for the investigated canopies. The seasonal course of the normalised zero-plane displacement height and the momentum roughness length are discussed in terms of the seasonal variation of the amount and density of plant matter.     

Dislocation microstructure and phase distribution in a lower crustal shear zone – an example from the Ivrea-Zone, Italy

The analysis of fabric and microstructure across an amphibolite facies shear zone of mafic composition reveals that the strain-dependent change from grain size insensitive to grain size sensitive creep is associated with a fundamental reorganization of the mylonitic fabric. At moderate strain a banded mylonite evolves from a metagabbro, which displays a mechanically-induced compositional layering. Strain is concentrated in monomineralic layers of dynamically recrystallized plagioclase. At higher strain and decreasing grain size (10-30 µm) the phase segregation is progressively destroyed and replaced by a phase mixture of amphibole and plagioclase. Phase mixing in these ultramylonites is developed and stabilized by heterogeneous nucleation processes of amphibole and plagioclase within unlike phases and at dilatant sites. Nucleation appears to be controlled by grain-scale gradients in stress. A dispersed phase distribution in fine-grained ultramylonites indicates (water-assisted) diffusion processes that accommodate grain boundary sliding. Although diffusion-controlled creep plays a dominant role in these ultramylonites, the dislocation densities remain high (2.0-4.0᎒⁹ cm^-2) and indicate that two competing mechanisms (dislocation and diffusion creep) accommodate grain boundary sliding. Commonly accepted criteria for superplastic or granular flow derived from monomineralic aggregates must be applied with caution to polymineralic rocks of mafic composition.     

Influence of a Xenobiotic Mixture (PCB and TBT) Compared to Single Substances on Swimming Behavior or Reproduction of Daphnia magna

Aroclor 1254, a technical PCB mixture (polychlorinated biphenyls) and TBT (tributyltinchloride) are environmental pollutants that cause a broad spectrum of acute toxic and chronic effects in aquatic animals. In this paper, the sensitivity of Daphnia magna to chronic exposure to mixed xenobiotics was evaluated under laboratory conditions. The results show that xenobiotic mixtures (50 % each of the single compounds) were more toxic than individual xenobiotics alone. By measuring behavioral parameters of animals, it becomes evident that exposure to single xenobiotics significantly affects daphnids: exposure led finally to a rapid decrease in mean swimming activity and also caused changes in preferred swimming depth, with daphnids preferring the upper layers of aquaria. The mixture altered the swimming behavior even more strongly compared to the group stressed by single chemicals. Finally, all daphnids sank to the bottom of the aquaria, still alive, but inactive at the end of the exposure period. In addition, we investigated the reproductive capacity (number of newborn per female and day). PCB did not affect the number of newborn significantly, TBT‐stress led to an evidently decreased number of young daphnids and the xenobiotic mixture decreased reproduction even more. In conclusion, we found significant effects of the single compounds as well as approximately additive (swimming behavior) and synergistic (reproduction) effects of the chemical mixture on daphnids indicating the possibility of dramatic ecological consequences of the occurrence of mixed xenobiotic substances in the aquatic environment.     

Spawning and egg development ofPerca fluviatilis in Lake Zürich

Egg survival and development rate of perch eggs were investigated in Lake Zürich, Switzerland. A transplant experiment was carried out to examine whether individual females choose different depths for spawning because of an expected advantage for the development of their eggs. Egg masses which had been deposited on fir branches stuck into the ground of the lake were either left untouched or transplanted horizontally or vertically at depths of 3 and 6 m. Spawning occurred between 28 April and 9 June 1987. Egg survival to the eye pigment stage (EPS) was high in all treatments ( , minimum 92%). There was no significant difference in egg survival between treatments, suggesting that females do not choose the spawning site because of individual fitness differences related to the depth of spawning. Early egg masses which were exposed to lower temperatures developed more slowly (120–140 day degrees to the EPS) than late egg masses which were exposed to higher temperatures (80–100 day degrees). The observed differences are in agreement with the hypothesis of a constant sum of day degrees necessary for egg development using the corrected formula derived by Guma'a (1978) which deducts an estimated threshold temperature of 5°C below which development of perch eggs effectively stops, from the actual temperature.