Eo-Alpine Metamorphism in the Uppermost Unit of the Cretan Nappe System — Petrology and Geochronology

The uppermost unit of the Cretan nappe system contains a variegated series of high-grade metamorphic rocks. In the Léndas area, amphibolites are present characterized by the assemblage

$$\text{brown}\;\text{hornblende}\;+\;\text{diopside}\;+\;\text{plagioclase}\;\text{(An 50)}$$

while associated metapelitic gneisses consist of

$$\text{garnet}\;+\;\text{cordierite}\;+\;\text{biotite}\;+\;\text{sillimanite (andalusite)}\;\pm\;\text{K-feldspar}\;+\;\text{plagioclase (An 40-50)}\;+\;\text{quartz}.$$

Judging from relevant experimental data for the gneiss assemblage including the Fe/Mg distribution on coexisting garnet and cordierite, the P-T conditions of metamorphism are estimated at about 700° C and 5 kb water vapour pressure.K/Ar determinations on hornblendes from three amphibolites yielded cooling ages of 71.3, 71.2, and 71.1 (±1.7) m.y. respectively; biotites from three paragneisses gave 70.2 ± 1.4, 69.7 ± 1.2, and 67.9 ± 1.4 m.y. respectively. Assuming a sealing temperature against argon diffusion of 300° C, for biotite, and 500° C, for hornblende, a cooling rate of 100–200° C/m.y. is calculated. Thus a late Cretaceous (eo-Alpine) metamorphic event is established in the post-Cretaceous nappes of Crete.     

Sparse matrix algorithms applied to dem generation

A method for generating a digital elevation model (DEM) was suggested byEbner. The heights of grid points are interpolated from arbitrarily distributed reference points using the finite element method. The requested grid heights of the DEM are defined as unknowns and estimated from the available reference points and a general curvature minimization of the interpolation surface with filtering at the reference points. This problem can be interpreted as an adjustment of indirect observations and can be solved using the least squares method. This leads to a banded structured system of normal equations in case of numbering the unknowns in a row-wise order. This ordering may not be the best strategy for the solution of the normal equations, because the band contains many zero elements. Therefore algorithms which exploit the nonzero/zero structure to better advantage have been applied in combination with the pivot strategies of “Nested Dissection” and “Minimum Degree Ordering” (OPTORD). The operational characteristics of these algorithms are compared with those of the band-algorithm for several DEM problems that vary in size to over 4000 unknowns. The result shows that the number of nonzeros and the number of essential operations can be reduced drastically when using sparse algorithms, but that because of the very high bookkeeping expenses, band algorithms are to be preferred.     

Morphologie und Infraciliatur einiger limnischer Ciliaten (Protozoa: Ciliophora)

The morphology, the infraciliature, and the silverline system of the fresh-water ciliatesUrotricha armata Kahl, 1927,Longifragma obliqua (Kahl, 1926) nov. gen., andTrochilioides fimbriatus nov. spec. are described. The new genusLongifragma is characterized by aProrodon-like “brosse” and an incompleteUrotricha-like somatic infraciliature. A new species,Urotricha dragescoi nov. spec., is suggested for theU. armata Kahl, 1927 of Dragesco et al. (1974).Trochilioides fimbriatus differs by its complex cyrtos from the other members of the genus.      

Seismicity of Bulgaria

Summary Using the concerning data of the Bulgarian earthquakes with magnitude greater 4 the seismicity of the period 1901–1965 was computed after a method byUllmann andMaaz and represented cartographically by isolines. The map lets us interpret the relation of the seismicity to the tectonic situation of Bulgaria. Further, the annual frequency of earthquakes of different magnitude basing on the same data is given.     

Experimentelle Magnesitbildung aus Dolomit+MgCl2

Zusammenfassung Es wurde die Arbeitshypothese entwickelt, daß die Mg-Metasomatose, die zur Bildung von Spatmagnesitlagerstätten führte, in chloridischer Lösung erfolgte. Deshalb wurde die Reaktion CaMg(CO₃)₂ (Dolomit)+MgCl₂ (gelöst) MgCO₃ (Magnesit)+CaCl₂ (gelöst) experimentell untersucht. Dieses Reaktionsgleichgewicht ist trivariant; die Gleichgewichtstemperatur wird bestimmt durch den Druck der fluiden Phase, durch die Gesamtkonzentration an gelöstem Salz und durch das Ca-Mg-Verhältnis der Lösung.Die Versuche haben ergeben, daß (im untersuchten Temperaturbereich von 200–400° C, P _f=2000 Bar) bei einem bestimmten Angebot an MgCl₂ bei höheren Temperaturen mehr Magnesit aus Dolomit gebildet wird als bei niedrigen. Um z.B. bei 200° C aus einer vorgegebenen Dolomitmenge quantitativ Magnesit zu bilden, wird das 2 1/2fache der Menge an MgCl₂ benötigt, die bei 400° C für quantitative Magnesitbildung erforderlich ist. Hohe Temperaturen begünstigen also die Magnesitbildung. — Die durchgeführten Experimente vermögen nicht nur die Magnesitbildung aus Dolomit, sondern auch die Redolomitisierung von Magnesit gut zu erklären.

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A working hypothesis, that MgCl₂ solution brings about the magnesium metasomatism giving rise to the coarse grained magnesite deposits (Spatmagnesitlagerstätten), was set up. The reaction CaMg(CO₃)₂ (Dolomite)+MgCl₂ (dissolved) MgCO₃ (Magnesite)+CaCl₂ (dissolved), bearing on this process, was experimentally investigated. This reaction represents a case of trivariant equilibrium; the equilibrium temperature being determined by the following parameters: the fluid pressure, the total concentration of the dissolved salts and the Ca Mg ratio in the solution.It was found that within the limits of the experimental conditions (P _f=2000 bars, Temp.: 200–400° C), more magnesite is formed out of dolomite at higher temperature if the amount of MgCl₂ is kept constant. For instance, for a total transformation of dolomite to magnesite at 200° C 2 1/2 times the amount of MgC1₂ is required as compared to the amount needed for the same reaction at 400° C. In other words, higher temperatures favour the formation of magnesite. The investigations carried out do not only explain the origin of magnesite from dolomite but also the reversed process of redolomitisation of magnesite.

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Herrn Prof. Dr. H. G. F. Winkler danke ich herzlich für sein Interesse an dieser Arbeit und für wertvolle Kritik. Die benutzten Apparaturen wurden Herrn Prof. Winkler von der Deutsehen Forschungsgemeinschaft zur Verfügung gestellt. Für die Arbeitsmöglichkeit an diesen Apparaturen sei ebenfalls gedankt.     

Boron-isotope fractionation between tourmaline and fluid: an experimental re-investigation

The fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700°C at 200 MPa and at 500°C, 500 MPa. Tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess. In one series of experiments, [B]_fluid/[B]_tour was 9 after the run; in another series it was 0.1. All experiments produced tourmaline as the sole boron-bearing solid, along with traces of quartz and talc. Powder XRD and Rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline. ¹¹B always preferentially fractionated into the fluid. For experiments where [B]_fluid/[B]_tour was 9, a consistent temperature-dependent boron isotope fractionation curve resulted, approximated by Δ¹¹B_{(tour–fluid)} = −4.20 · [1,000/T (K)] + 3.52; R ² = 0.77, and valid from 400 to 700°C. No pressure dependence was observed. The fractionation (−2.7 ± 0.5‰ at 400°C; and −0.8 ± 0.5‰ at 700°C) is much lower than that previously presented by Palmer et al. (1992). Experiments where [B]_fluid/[B]_tour was 0.1 showed a significant larger apparent fractionation of up to −4.7‰. In one of these runs, the isotopic composition of handpicked tourmaline crystals of different size varied by 1.3‰. This is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline, thus indicating larger fractionation than observed at equilibrium. The effect is eliminated or minimized in experiments with very high boron excess in the fluid. We therefore suggest that values given by the above relation represent the true equilibrium fractionations.     

Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – I. Line Emission and Time Dependence

EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981, were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral lines formed in the transition region and corona show considerable structure and large deviations from a uniform spatial distribution over the active region. Enhanced EUV emissions in transition region lines are concentrated in small regions outside the umbra of the sunspot throughout most of the observing sequence. Only during a short, active period do we find an enhanced line emission that reaches into the umbra. Preliminary values for the umbral intensity are given.Marked changes are detected between the spatial distribution of line emission in the transition region and the low corona. The difference is not limited to cool and hot non-flaring loops not being cospatial, but includes differences both regarding the time variability and the orientation and size of the emission features. Whereas both rapid ( 4 and 2 min) and slow ( 10 and 12 h) temporal variations are found in the chromosphere (Hei 584 Ú) and transition region (Ov 629 Ú), the response in the low corona (Mgix 368 Ú) is slow ( 5 h). Furthermore, marked differences between the spatial distributions in the Mgviii 315 Ú, Mgix 368 Ú lines formed in the low corona and the coronal Fexiv 334 Ú, Fexvi 360 Ú lines are detected.     

Liquidus temperatures and phase compositions in the system Qz-Ab-Or at 5 kbar and very low water activities

Liquidus phase relations have been experimentally determined in the systems Qz-Ab-Or-(H₂O), Qz-Ab-(H₂O) and Qz-Or-(H₂O) at H₂O-undersaturated conditions (a _H2O = 0.07) and P = 5 kbar. Starting materials were homogeneous synthetic glasses containing 1 wt% H₂O. The liquidus temperatures were bracketed by crystallization and dissolution experiments. The results of kinetic studies showed that crushed glasses are the best starting materials to overcome undercooling and to minimize the temperature difference between the lowest temperature of complete dissolution (melting) and the highest temperature at which crystallization can be observed. At P = 5 kbar and a _H2O = 0.07, the Qz-Ab eutectic composition is Qz₃₂Ab₆₈ at 1095 °C (±10 °C) and the Qz-Or eutectic is Qz₃₈Or₆₂ at 1030 °C (±10 °C). The minimum temperature of the ternary system Qz-Ab-Or is 990 °C (±10 °C) and the minimum composition is Qz₃₂Ab₃₅‐ Or₃₃. The Qz content of the minimum composition in the system Qz-Ab-Or-H₂O remains constant with changing a _H2O. The normative Or content, however, increases by approximately 10 wt% with decreasing a _H2O from 1 to 0.07. Such an increase has already been observed in the system Qz-Ab-Or-H₂O-CO₂ at high a _H2O and it is concluded that the use of CO₂ to reduce water activities does not influence the composition of the minima in quartz-feldspar systems. The determined liquidus temperature in melts with 1 wt% H₂O is very similar to that obtained in previous nominally “dry” experiments. This discrepancy is interpreted to be due to problems in obtaining absolutely dry conditions. Thus, the hitherto published solidus and liquidus temperatures for “dry” conditions are probably underestimated. Received: 27 March 1997 / Accepted: 1 October 1997     

Formation and ascent of granitic magmas

New results obtained by the investigation of liquidus and solidus phase relationships in the haplogranite system Qz-Ab-Or are used to discuss the evolution of magmas during their ascent in the crust. It is assumed that the magmas are formed at 720°C, 820°C, 920°C and at a depth corresponding to a pressure of 8 kbar. The starting composition of the magma is taken as 50% melt plus 50% quartz and feldspars. In case of a closed system (no heat exchange and no transfer of elements) the melt fraction of magmas, the water activity and the viscosity increase with decreasing pressure. The temperature slightly decreases. At 700°C the viscosity is approximatively 2 orders of magnitude lower than at 900°C. This is related to the higher amount of water in the (H₂O-undersaturated) melt at low T. It is also shown that dehydration melting is only realistic at high T (900°C). At lower temperatures water has to be added from outside to obtain an intrusive magma with approximatively 50% melt.

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Zusammenfassung Neue Ergebnisse, erzielt durch Untersuchungen von Liquidus und Solidus Phasenbeziehungen des Granitsystems Qz-Ab-Or, werden benutzt, um die Entwicklung eines granitoiden Magmas während seines Aufstiegs zu diskutieren. Es wird vorausgesetzt, daß die Magmen bei Temperaturen von 720°C, 820°C und 920°C gebildet werden, sowie in einer Tiefe die einem Druck von 8 kbar entspricht. Die anfängliche Zusammensetzung des Magmas wird mit einem Verhältnis von 50% Schmelze sowie 50% Quarz und Feldspäten angenommen. Im Falle eines geschlossenen Systems (kein Austausch von Wärme und Elementen) steigt die Teilschmelzbildung von Magmen, die Aktivität des Wassers und die Viskosität bei abnehmenden Druck; hierbei sinkt die Temperatur leicht. Bei 700°C ist die Viskosität um ca. 2 Größenordnungen geringer als bei 900°C. Dies wird bedingt durch den höheren Gehalt an Wasser in der (H₂O-untersättigten) Schmelze bei tieferen Temperaturen. Es wird außerdem gezeigt, daß Magmenbildung durch Dehydratation nur bei hohen Temperaturen realistisch ist (900°C). Bei tieferen Temperaturen muß Wasser von außen zugeführt werden um ein intrusives Magma zu erhalten, das ungefähr 50% Schmelze besitzt.

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Résumé L'évolution des magmas granitiques au cours de leur ascension dans la croûte est discutée à la lumière de données nouvelles relatives aux relations entre phases liquides et solides dans le système Q-Ab-Or. On suppose que les magmas se forment à des températures de 720°C, 820°C, 920°C et à une profondeur correspondant à une pression de 8 Kb. On admet pour leur composition initiale un mélange de 50% de liquide et 50% de quartz + feldspaths. Dans le cas d'un système fermé (pas d'échange de chaleur ni de matière), la fraction liquide du magma, l'activité de l'eau et la viscosité augmentent quand la pression diminue; en même temps, la température décroît légèrement. A 700°C, la viscosité est d'environ 2 ordres de grandeur plus basse qu'à 900°C. Cette propriété est en relation avec la teneur en eau plus élevée dans le liquide (sous-saturé en eau) à basse température. On peut également montrer qu'une fusion déshydratante n'est vraisemblable qu'à haute température (900°C). Aux températures plus basses, de l'eau doit être apportée de l'extérieur pour l'obtention d'un magma à 50% de liquide.

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Verbreitung und Ausbildung der Siegener Schichten in der Osteifel

Ohne ZusammenfassungVortrag, gehalten auf der Hauptversammlung der Geologischen Vereinigung zu Frankfurt a. M., Januar 1933.