Equilibria in a sulfide rich water from Enghien-les-Bains,France

A complete analysis of a sulfide rich water from a sedimentary area has been achieved. The formation of metastable sulfur species (polysulfide ions, colloidal sulfur and thiosulfate) is very important. The relative concentrations of the sulfur species is controlled by bacterial processes (Desulfovibrio and Thiobacteriaceae). Electrochemical measurements and results of the analyses are in agreement. A possible repartition of polysulfide ions is S^2?₆ ≈- S^2?₅ >S^2?₄. This repartition, although out of equilibrium, is characteristic of the processes leading to the formation of the metastable sulfur species.The water is in equilibrium with amorphous FeS formation. When sulfide, polysulfide and thiosulfate complexing of trace metals Cu, Cd and Pb is taken into account, an agreement is reached between their concentrations in water and their concentrations in the FeS precipitate.     

Experiments on phase transformations and chemical reactions of mechanically activated minerals by grinding: Petrogenetic implications

Prolonged grinding increases the energy of solids by the production of stored energy in the form of new surfaces and internal defects. Moreover, grinding also generates quasi-hydrostatic pressures which can result in polymorphic transformations and mineral decomposition. Here we demonstrate the solid-state transformation of metastable to stable polymorphs (aragonite → calcite, anatase → rutile); the transformation of low-pressure to high-pressure phases (calcite → aragonite); and the lowering of the dehydration and decarbonation temperatures of minerals (siderite → magnetite or hematite, diaspore → corundum).In the presence of a fluid phase, stored energy from grinding can be released, resulting in accelerated reaction rates and, more importantly, phase transformations. In this paper we demonstrate the following transformations: ground calcite → magnesian calcite (at low Mg²⁺ concentration in solution), ground calcite → aragonite (at high Mg²⁺ concentration), ground magnesite → hydromagnesite, and ground dolomite → aragonite + Mg²⁺.Assuming an analogy between laboratory and natural grinding, tectonic activity may have important consequences on the release of hydrothermal fluids, the solubilization of minerals and on solid-state transformations. As examples the possible role of deformation on the formation of metamorphic aragonite and diaspore-bauxites is discussed.     

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.     

The composition of the precambrian ocean waters

The composition of the Precambrian oceans was different from the present composition; this is a direct consequence of a CO₂-atmosphere depleted in oxygen. At the beginning the mineralization was lower. The oceans waters were chloro-dicarbonated with a lower tenor of chlorine, richer in phosphates and they were depleted in sulphates; sulphur was in the reduced state of sulphides. The abundance of phosphates supported the expansion of life. The cations Na⁺ and Mg²⁺ coexisted with Ca²⁺, Fe²⁺ and Ba²⁺ whose levels were higher than they are today. The main trends of the evolution are schematized in the figure.     

Spectral analysis of earthquake migration in South America

Earthquake migration along linear seismic belts is investigated by analyzing spacetime diagrams using spectral analysis. In order to sample the earthquakes in the space-time domain, they must first be convolved with a (sinx sint)/xt surface to obtain an unbiased and alias free twodimensional Fourier spectrum. Further enhancements are provided by selectively stacking patterns (a pattern is defined as the distribution of earthquakes in space and time before a particular earthquake), thereby reinforcing the similarities within the various patterns. With these techniques, it is possible to quantitatively estimate the migration rates (from theirspatial frequencies) and recurrence intervals (from theirtemporal frequencies) of large earthquakes in South America.Preliminary examination of the spectra for South America indicates that a low frequency peak occurs at approximately 2500 km and 27 years for earthquakes with magnitudes greater than 7.7. The results suggest a migration rate of approximately 95 km/yr from south to north and a recurrence interval of 27 years.     

Ries impact crater,southern Germany: search for meteoritic material

Twenty-three samples from the Ries crater, representing a wide range of shock metamorphism, were analyzed for seven siderophile elements (Au, Ge, Ir, Ni, Os, Pd, Re) and five volatile elements (Ag, Cd, Sb, Se, Zn). Taking Ir as an example, we found siderophile enrichments over the indigenous level of 0.015 ppb Ir occur in only eight samples. The excess is very modest; even the most enriched samples (a weakly shocked biotite gneiss and a metal-impregnated amphibolite) have Ir, Os corresponding to ~4 × 10^?4 C1 chondrite abundances. Of five flädle glasses analyzed only one shows excess Ir. Suevite matrix and vesicular glass have slight enrichment, but homogenous glass from the same rock does not. In flädle glasses, Ni and Se are strongly correlated and apparently reside in Ir, Os-poor Sulfides [pyrrhotite, chalcopyrite, pentlandite(?)]of terrestrial, probably sedimentary, origin. The Ir, Os and Ni enrichments of the metal-bearing amphibolite are compatible with chondritic ratios, but these are ill-defined because of uncertainty in Ni. In the other samples enriched in siderophiles Ir(Os), Ni and Se are mutually correlated; $\text{Ni}\text{Ir}$ and $\text{Ni}\text{Os}$ ~ 11 × C1 and are much higher than any chondritic ratios; $\text{Se}\text{Ni}\text{~ 2 × C1}$ and suggests a sulfide phase, rather than metal may be the host of the correlated elements. Lacking a plausible local source, this material is apparently meteoritic in origin. The unusual elemental ratios, coupled with the very low enrichments, tend to exclude chondrites and most irons as likely projectile material. Of the achondrites, aubrites seem slightly preferable. Ratios of excess siderophiles in Ries materiel match tolerably those of an aubrite (possibly atypical) occurring as an inclusion in the Bencubbin meteorite, Australia. The Hungaria group of Mars-crossing asteroids may be a source of aubritic projectiles.     

Alkali feldspar liquid equilibrium relationships in peralkaline oversaturated systems and volcanic rocks

A critical review of both experimental data and natural rock sequences allows a comparison of liquid lines of descent in peralkaline oversaturated systems. Available experimental data have been used to draw the liquidus surfaces and the fractionation curves in various planes including the alkali feldspar join. The thermal valley becomes steeper, the fractionation curves being channeled faster towards the thermal valley with increasing alkali-silica ratio. The slope of the thermal valley varies so that the higher the peralkalinity, the more sodic the most fractionated liquids. Rock series from Easter Island, Gran Canaria, Pantellaria Island, Boina (Afar), Fantale (Ethiopia) and Menengai (Kenya) in which there is good evidence for alkali feldspar fractionation, show that such variations do occur in nature. Factors other than the peralkalinity of the series, such as additional components and changes in the confining pressure are shown to affect the orientation and location of the thermal valley.     

Utilisation du radon comme indicateur de l'intensite des echanges pres du sol (0–100 M)

Resumé Les donées moyennes relatives à deux années de mesures continues du radon à 1.5–30 et 100 m au-dessus du sol sont présentées sous forme de variations diurnes standard; ces dernières sont étudiées par une analyse de Fourier (amplitude et phase). On précise l'évolution des variations au cours du cycle annuel.Le but de l'étude des donées moyennes étant d'accéder aux informations relatives à la variation diurne des échanges, on a recherché des relations entre la variation diurne standard des concentrations et celles des échanges; d'autre part on a défini des critères, déduits des paramètres météorologiques, classiques susceptibles de caracteriser l'intensité de la variation diurne des échanges.

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Continuous measurement of radon concentrations at, 1.5, 30 and 100 m has been carried out for 2 years, from October 1966 to October 1968. The mean diurnal variations of the concentrations are characterized in a simple manner using a Fourier analysis, revealing the diurnal and annual waves, and showing the variations with altitude of the radon concentrations. The amplitude of this diurnal wave can be considered as representative of the mean diurnal variation of the intensity of the vertical exchange processes.This method of analysis is applied to the study of influence of standard meteorological elements measured at the site on the diurnal variation of the exchanges. Additional indicators are derived from temperature, humidity and wind (speed and direction) measurements, and their daily cycles (mean winds, mean direction, temperature diurnal variation amplitude...) are shown to be related to the cycles of radon concentrations.The mean diurnal variations of the radon concentrations classified according to several meteorological parameters are used to characterize the intensity of mixing, in terms of a mixing coefficient.This characterization is achieved both from the average gradients (local value) and from the diurnal wave at the soil.

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Equipe de Recherche Associée au CNRS, No. 378.     

L'évolution magmatique du Complexe de Morin et son apport au problème des anorthosites

The Morin Plutonic Complex, in the southern part of the Grenville tectonic province (Canadian Shield) consists of a rock suite ranging from troctolite to farsundite. The centre of the complex is a large domical anorthosite body. Twenty-six chemical analyses have been carried out in order to compare the Morin Complex with similar complexes in the Grenville and Nain provinces. Variation diagrams constructed by plotting the major oxides vs. the differentiation index Al₂O₃+CaO+MgO show a gap between troctolite and anorthosite in the Morin Complex whereas this gap is absent in the anorogenic complexes of Labrador (Nain province). It is inferred that this gap is the result of intrusion, from the same magma chamber, of two distinct pulses separated by an intervening period of crustal uplift.A second gap occurs between anorthosites and farsundites in all complexes as yet investigated. This gap is an argument for an independent, possibly anatectic, origin of the farsundites.Mineral assemblages in the Morin Complex are compatible with cooling in the lower crust, at a depth of approximately 30 km.