Propriétés thermodynamiques des solutions (Na,K)ClH2O entre 400 et 800°C, 1–2 Kb: une revue des équilibres d'échange avec les silicates sodipotassiques

Several independant determinations of the difference in Gibbs free energy of formation (from the elements at 25°, 1 bar) between NaCl⁰ and KCl⁰ in aqueous solutions (molality > 0.5) are derived from equilibrium data between alkali feldspars, feldspathoids (nepheline-kalsilite), micas (muscoviteparagonite) and hydrothermal (Na, K)Cl-H₂O solutions. These results along with other data from the literature are discussed. The relation: $\text{Δ}{}^0\text{?,}\text{KCl}{}^0\text{? Δ}{}^0\text{/tf,}\text{NaCl}{}^0\text{(}\text{J}\text{) = ?16500(± 2500) ? 18(± 4) T(}\text{K}\text{)}$. is proposed from 400 to 800°C and 1 to 2 Kbar.     

Seismotectonics of the Papua New Guinea—Solomon Islands region

Earthquakes for the period 1964–1973 are relocated by the method of Joint Hypocenter Determination in order better to resolve the configuration and the structure of the New Guinea—New Britain—Solomon Islands region. Focal mechanism solutions are integrated with the seismicity and interpreted closely with it. A zone of subduction exists beneath New Britain and the Solomon Islands, a zone of left-lateral strike-slip movement extends from New Ireland to New Guinea. The zone of seismicity in northern New Guinea has developed as a result of a continent—island-arc collision in late Oligocene—Miocene times and does not exhibit a well-developed inclined seismic zone. It is proposed that plate tectonics theory does not apply rigorously, but slip-line field theory allows the presentation of a new geodynamic model for this region.     

Acquisition des ions alcalino-terreux par les eaux thermales carbogazeuses

Nous présentons différents arguments tendantàmontrer qu'une proportion importante deséléments alcalinoterreux présents dans les sources thermominérales du Massif Central français est acquise en subsurface lors de la remontée de l'eau. Au cours de ces réactions subsuperficielles, le rapport Na/K est peu modifié. Les hautes teneurs en Ca²⁺ et Mg²⁺ de ces eaux ne constituent pas un argument suffisant pour rejeter l'information fournie par le géothermomètre Na/K.Nous montronségalement que l'utilisation des rapports isotopiques du strontium comme indicateur d'origine doite?tre menée avec précautions.     

The influence of pressure,temperature and bulk composition on the appearance of garnet in orthogneisses — an example from South Harris,Scotland

Granulite facies metamorphism of the igneous complex of South Harris has produced garnet-clinopyroxene-plagioclase assemblages from olivine-normative rocks and 2 pyroxene-plagioclase-quartz assemblages from quartz-normative rocks. The appearance of garnet can be considered in terms of two complex reactions:Olivine + plagioclase₁ → (Ca, Mg, Fe) garnet + plagioclase₂(olivine-normative) (A)Orthopyroxene + plagioclase₁ → (Ca, Mg, Fe) garnet + plagioclase₂ + quartz (quartz-normative) (B)For bulk compositions of the South Harris rocks the equilibrium pressure for reaction (A) has been exceeded whereas that for reaction (B) was not reached. Estimated physical conditions of metamorphism bracketed by these and other reactions are: 800–860°C and 10–13 kbar. These estimates, based on experimental data on simple systems combined with thermodynamic models of the solid solutions involved are in good agreement with extrapolated pressures for the experimentally determined appearance of garnet in basaltic compositions (Green and Ringwood, 1967). The latter give 9–12 kbar in the temperature range of interest. The calculations are also consistent with the occurrence of kyanite in associated metapelites and with the stability of spinel-lherzolite during the granulite metamorphism.     

Sur la Solution du Problème d'Ekman

Sommaire On peut grouper sous le nom de problème d'Ekman les problèmes suivants: Calcul du flux (de quantitÉ de mouvement) induit dans une mer fermÉe par un champ de vent — Calcul du flux induit dans une mer fermÉe par un champ de «sources» et de «puits» existant en surface — Calcul du flux induit dans une mer ouverte par. un flux donnÉ sur son contour.Ces problèmes ont la forme d'un problème de Diriehlet.On peut les rÉsoudre par l'analyse pour des mers limitÉes par des courbes gÉomÉtriques simples et par un calcul analogique (cuve rhÉoÉlectrique de profondeur variable) ou par un calcul aux diffÉrences finies (rÉseaux de rÉsistances ou calculatrice Électronique) pour des mers rÉelles.

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On the solution of the Ekman problem

Summary The following points may be comprised under the term Ekman problem: Mass transport caused by a wind field in a closed ocean — mass transport caused in a closed ocean by a field consisting of sources and sinks at the sea surface — mass transport caused in an open ocean by some transport on its boundary.These problems have the form of a Dirichlet problem.They can be solved by an analysis for oceans that are limited by a simple geometric curve and by analoguous computation (rheoelectric basin of variable depth) or by finite differential calculus (resistance grid or electronic computer) for real oceans.

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Zusammenfassung Man kann unter dem Begriff Ekmansches Problem die folgenden Punkte zusammenfassen: Massentransport, verursacht in einem geschlossenen Meer durch ein Windfeld. — Massentransport, verursacht in einem geschlossenen Meer durch ein Feld, bestehend aus Quellen und Senken an der Oberfläche — Massentransport, verursacht in einem offenen Meer durch einen Transport, der auf seinen Rand einwirkt.Diese Probleme besitzen die Form eines Dirichlet-Problems.Man kann sie lösen durch die Analyse fÜr Meere, die durch eine einfache geometrische Kurve begrenzt sind, und durch die Analogie-Rechnung (rheoelektrisches Becken von variabler Tiefe) oder durch ein endliches Differenzverfahren (Widerstandsnetz oder elektronische Rechenmaschine) fÜr wirkliche Meere.

     

Tidal observations near an amphidrome

The signal to noise ratio in tidal data in the diurnal and semidiurnal frequency bands is ordinarily so large that the noise contribution to the tidal harmonic constants is unimportant. However, as the observational locations are selected progressively closer to an amphidrome (point of no tide), the signal to noise ratio decreases, making the tidal harmonic constants less dependable. Standard deviations in amplitude of M₂ and S₂ obtained from 12 29-day analyses of a year of tide data obtained at a standard tide station, estimated to be 280 and 550 km away from the amphidromes for these constituents in the eastern Caribbean, are roughly one-third of the mean amplitudes for these constituents; the standard deviations in epoch are 38° and 30° respectively. Therefore, a program to locate an amphidrome precisely is self-defeating and the location can only be approximated by a grid of tide observations spanning the geographic position and/or by longer series of observations, using higher resolution to increase the signal to noise ratio. Amplitudes of 0.64 cm and 1.24 cm were calculated for M₂ and S₂ from a one-month series of pelagic observations obtained very close to an inferred position of the M₂ amphidrome in the northeast Caribbean Sea.Abbreviations C&GS Coast and Geodetic Survey - CICAR Cooperative Investigation of the Caribbean and Adjacent Regions - IAPSO International Association for the Physical Sciences of the Ocean - ICOT Institute of Coastal Oceanography and Tides - IDOE International Decade of Ocean Exploration - NOAA National Oceanic and Atmospheric Administration - NOS National Ocean Survey - NSF National Science Foundation - SCOR Scientific Committee of Oceanic Research - UNESCO United Nations Educational, Scientific, and Cultural Organization     

The crystal chemistry of a naturally occurring magnesium hydroxide sulfate hydrate,a precipitate of heated seawater

The crystal chemistry of a naturally occurring magnesium hydroxide sulfate hydrate, $\text{MgSO}{}_4\text{·}\text{1}\text{3}\text{Mg(OH}{}_2\text{) ·}\text{1}\text{3}\text{H}{}_2\text{O}$ (designated MHSH($\text{2}\text{3}$)), and a number of existing and predicted compounds which are structurally related to MHSH($\text{2}\text{3}$) are discussed. An x-ray diffraction powder pattern for MHSH($\text{2}\text{3}$) is calculated from single crystal data to aid in the identification of this phase, recently found associated with active hydrothermal vents along the East Pacific Rise. It is suggested that this MHSH-type crystal structure can have a variable composition due to a novel chemical substitution, Mg²⁺ → 2 H⁺, which this particular structure may be able to accommodate. In relation to this, a method for determining the stoichiometry of MHSH crystals via density measurements is also proposed. Finally, the leaching properties of heated seawater, instrumental in the genesis of metalliferous deposits on the sea-floor, may be due in part to the growth of MHSH-type phases in certain seawater-rock systems.