Fluid geochemistry in the Ivigtut cryolite deposit, South Greenland

The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na₃AlF₆] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO₂, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO₂ and H₂O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ¹³C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ¹⁸O of CO₂ (+ 21 to + 42‰ VSMOW) and δ¹⁸O of H₂O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H₂O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.     

Density and pressure change in an occluding cyclone

Summary On October 20, 1974, an occluding cyclone, which did not intensify any more crossed central Europe. Considerable pressure tendencies reflecting the displacement of the storm were observed during its passage. Although horizontal density advection contributed least to density and thus pressure changes, it was still of decisive importance for both. The other larger contributors, whose net effect was usually opposed to the effect of horizontal advection, nearly cancelled each other. Thus there was a fair correlation between horizontal advection and density tendency, and the actual density and pressure changes frequently turned out smaller than if caused by advection alone.It has been shown that in the lowest 3 km usually. For the mass divergence this inequality was observed in the frontal zones where horizontal advection was considerable. In particular, warm air advection reduced the effect of horizontal velocity convergence near the warm front. Thus, vertical mass divergence became predominant and caused a density decline. Cold air advection accompanying the cold front was responsible for horizontal divergence to be overcompensated by vertical mass convergence which induced rising density.With 11 Figures     

Circuiti equivalenti dell'effetto sismo-elettrico

Riassunto Il modello circuitale di equivalenza approssimata dell'effetto sismoelettrico (Thompson-Slotnick) è stato in questa Nota riesaminato, sia nella forma originaria dei precitati A.A., sia con altre forme più semplici, della resistenza ohmica in serie nel circuito stesso.Quando la resistenza ohmica assume una forma oscillante (equivalenza ipotetica degli impulsi oscillanti elastici), lo stato di regime della corrente elettrica che si determina possiede una componente indipendente del tempo e una dipendente dal tempo, con infinite armoniche.Così si spiega, tra l'altro (almeno parzialmente), uno dei risultati sperimentali caratteristici dell'effetto sismo-elettrico. Esso non riproduce (nella rappresentazione dell'intensità della corrente), le forme dell'oscillazione di carattere meccanico, impressa al suolo, ma la frequenza meccanica, conforme a quanto rilevabile oscillograficamente.

---

Summary In this note is again, examined the circuital model of the approximate equivalence of the seismic-electric effect (Thompson-Slotnick) in the original form given by the mentioned authors as well as in other more simple forms of the ohmic resistance set in the circuit.When the ohmic resistance takes an oscillating form (hypotetical equivalence of oscillating elastic impulses) the steady state of electric current, which on determines, has a time indipendent and a time dipendent component with an infinite number of harmonics.This explains oneself, among others (at least partially), one of the characteristic experimental results of the seismic-electric effect. It does not reproduce (in the magnitude of current reproduction) the oscillation froms of mechanical character impressed to the soil, but reproduces the mechanical frequency conforming with the oscillographic obtainable data.

---

Zusammenfassung In dieser Note wird das Stromkreismodell der angenäherten Äquivalenz des seismisch-elektrischen Effektes (Thompson-Slotnick) erneut geprüft, sowohl in der von den erwähnten Verfassern gegebenen Originalform als auch in anderen einfacheren Formen des im Stromkreis in Reihe geschaltetenOhm'schen Widerstandes.Wenn derOhm'sche Widerstand eine schwingende Form annimmt (hypothetische Äquivalenz de elastischen schwingenden Impulse), so besitzt der Betriebszustand des elektrischen Stromes den man bestimmt, eine zeitlich unabhängige und eine zeitlich abhängige Komponente mit unendlich vielen harmonischen Schwingungen.In dieser Weise erklärt sich u. a.. (wenigstens teilweise) eines der experimentellen charakteristischen Ergebnisse des seismisch-elektrischen Effektes. Derselbe gibt (in der Darstellung der Stromstärke) nicht die Formen der dem Boden aufgeprägten Schwingung mechanischen Charakters wieder, sondern die mechanische Frequenz gemäss den oszillographisch feststellbaren Angaben.

     

Palynology of the circum-mediterranean triassic: Phytogeographical and palaeoclimatological implications

Following a tentative evaluation of palynological information from Ladinian and, more particularly, Karnian successions, there seems to be every indication that qualitative and quantitative compositional differences of palynological assemblages could well be applied in testing concepts of Triassic phytogeography and palaeoclimatology. The following implications are emphasized:

1. There is sufficient palynological evidence that the Mediterranean region includes a domain of mixed northern (Laurasian) and southern (Gondwana) types of floras.
2. The concept of an essentially arid nature of a wide equatorial climatic belt during Triassic times finds palynological support.
3. Palynological evidence does not contradict a concept of pronounced decrease in precipitation towards the western part of the Mediterranean region.
4. In Europe, occurrences of hygrophytic palynofloras and coals within an arid climatic zone can be explained by the water-supply of extensive river-systems.

     

Colonisation of the Krakatau islands by invertebrates

Arrival of invertebrates on the Krakatau islands, and the development of invertebrate assemblages there since 1883, are reviewed. Many data are imprecise, and difficulties of interpretation are outlined. A few well-known groups, such as butterflies, are used to suggest that much colonisation so far has been by relatively generalist species,and that the rate of addition of new species may become slower as the less vagile specialists characteristic of later successional vegetation may find natural colonisation harder. Studies of the assemblages developing in association with particular plant species are likely to be helpful in assessing future trends of invertebrate colonisation.     

Flood frequencies reveal Holocene rapid climate changes (Lower Moulouya River,northeastern Morocco)

Current high‐resolution palaeoenvironmental records reveal short‐term Holocene coolings. One of these major Holocene rapid climate changes occurred between 3.2 and 2.7 cal. ka BP. The sensitivity of river systems vis‐à‐vis slight and short‐term Holocene climatic variations is a subject of controversy in the scientific community. In this paper, we present a 4.0 to 1.4 cal ka BP palaeoflood record from the Lower Moulouya River (northeastern Morocco) to demonstrate the high sensitivity of semiarid rivers in the southwestern Mediterranean towards Holocene environmental changes. The Lower Moulouya flood deposits are characterised by thick, well‐stratified, predominantly clayey to silty overbank fine sediments. These cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late Holocene flood sequences. The Moulouya palaeoflood record can be interpreted in the context of regional and global high‐resolution proxy data, revealing a strong coupling with Holocene rapid climate changes. The centennial‐scale Moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record (palaeomagnetics, sedimentary charcoal record, anthracological analyses, snail analyses) to generate new ideas about the mid to late Holocene hydrological cycle in the southwestern Mediterranean. The deduced features of pronounced Lower Moulouya flooding and the decreased fire recurrence during Holocene cooling remain somewhat inconsistent with the interpretation of other palaeohydrological and paleaoecological records from the southwestern Mediterranean. However, enhanced Lower Moulouya flood frequencies between 3.2 and 2.7 cal. ka BP agree with increased floodplain aggradation in other major river systems of Mediterranean North Africa. Copyright © 2009 John Wiley & Sons, Ltd.     

Mineral zones and isograds in “impure” calcareous rocks,an alternative means of evaluating metamorphic grade

Although regional mineral zoning in pelitic rocks has been described in numerous metamorphic terrains, relatively little is known about zoning in carbonate-bearing rocks. Regional metamorphism has resulted in a distinctive sequence of mineral zones in calcareous rocks (containing Fe, K and Al) of the Lessard Formation in the Bishop Corners-Madoc area, Grenville Province, Canada. The variation in metamorphic grade represented by the mineral zoning is attributed to a gradient in physical conditions (mainly temperature) at the time of metamorphism.In areas where pelitic schist and siliceous dolomite marble are rare or restricted in distribution, the mineral zones and isograds in impure calcareous rocks provide an alternative to conventional isograds for evaluating variations in metamorphic grade. In a metamorphic terrain where all three rock types occur, comparison of these isograds to those in pelitic and siliceous dolomite rocks results in a more accurate assessment of the distribution of isotherms and may provide some insight into the properties of the metamorphic fluid phase.     

IV. Bücher- und Zeitschriftenschau

Ohne Zusammenfassung     

Rain rate estimation from a synergetic use of SSM/I, AVHRR and meso-scale numerical model data

Summary In this paper a retrieval technique for estimating rainfall rates is introduced. The novel feature of this technique is the combination of two satellite radiometers — the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High-Resolution Radiometer (AVHRR) — with mesoscale weather prediction model data. This offers an adjustment of the model atmospheres to reality which is necessary for calculating brightness temperatures that can be compared with microwave satellite measurements.In sensitivity studies it was found that the estimation of precipitation is determined to a high degree by the particle size distribution of rain and snow, especially by the size distribution of solid hydrometeors. These studies also reveal the influence of the knowledge of the correct cloud coverage inside a SSM/I pixel and the importance of using a realistic temperature profile instead of using standard atmospheres.The retrieval technique is based on radiative transfer calculations using the model of Kummerow et al. (1989). The algorithm consists of two parts: First Guess (FG) brightness temperatures for the SSM/I frequencies are generated as a function of the cloud top height and the cloud coverage, derived from AVHRR data and predictions from a meso-scale model. The rainfall rate of different types of clouds containing raindrops, ice particles and coexisting ice and water hydrometeors is then calculated as a function of the cloud top height. As an example, a strong convective rain event over the western part of Europe and over the Alps is taken to evaluate the performance of this technique. Good agreement with radar data from the German Weather Service was achieved. Compared to statistical rainfall algorithms, the current algorithm shows a better performance of detecting rainfall areas.With 12 Figures