Sapphirine I

Microprobe analyses of 26 natural sapphirines from 17 localities indicate that the predominant chemical substitutions in this mineral occur along the solid solution join^VI(Mg,Fe)²⁺+^IVSi⁴⁺=^VI(Al, Fe)³⁺+^IVAl³⁺. Chromium and manganese are minor substituents. Evidence for the substitution SiAl+1/2Mg+1/2 vacancy is absent within the limits of analytical error.A partitioning scheme based on electrostatic charge balance considerations has been devised permitting calculation of Fe²⁺ and Fe³⁺ from total iron content. Results are in good agreement with previous Mössbauer studies which indicate Fe³⁺ is sometimes in octahedral and/or tetrahedral coordination.Distribution coefficients for Fe²⁺-Mg exchange equilibria between sapphirine-spinel and sapphirine-orthopyroxene are similar for most mineral pairs and suggest that most of the assemblages equilibrated at about the same temperature or that the exchange reactions are insensitive to temperature.Compositions of synthetic sapphirines as a function of temperature and pressure are qualitatively predictable from crystal chemical considerations. Changes in sapphirine composition along the MgSi= AlAl solid solution join toward more aluminous compositions stabilize the sapphirine structure at high temperatures and low pressures. The limited extent of MgSi=AlAl solid solution observed in natural sapphirines appears to be related to the requirements of geometrical fit among octahedra and tetrahedra in the almost idealized cubic closest-packed anion framework.     

I/I ratios in surface waters of the English Lake District

Accelerator Mass Spectrometry (AMS) was used to measure ¹²⁹I/¹²⁷I ratios in surface sea, lake, and river water samples collected in 2004 and 2005 from the English Lake District and from SW Scotland, areas which are in relatively close proximity to the Sellafield nuclear fuel reprocessing plant in NW England. The ¹²⁹I/¹²⁷I ratios in surface water collected from the shore of the Irish Sea were in the range 2.8 × 10⁻⁶ to 8.2 × 10⁻⁶. These ratios are one order of magnitude higher than that of seawater collected from the Irish Sea in 1992, correlating with the increase in ¹²⁹I content of the Sellafield liquid effluent discharge over the last decade. The ¹²⁹I/¹²⁷I ratios in lakes in the Lake District were in the range 0.7 × 10⁻⁶ to 6.4 × 10⁻⁶ and decreased exponentially as a function of distance from Sellafield. Consideration of the relative variation of stable I concentrations and ¹²⁹I/¹²⁷I ratios suggests that Sellafield gaseous discharges may be the dominant source of ¹²⁹I to the lakes.     

Robust estimation of the variogram: I

It is a matter of common experience that ore values often do not follow the normal (or lognormal) distributions assumed for them, but, instead, follow some other heavier-tailed distribution. In this paper we discuss the robust estimation of the variogram when the distribution is normal-like in the central region but heavier than normal in the tails. It is shown that the use of a fourth-root transformation with or without the use of M-estimation yields stable robust estimates of the variogram.Visiting Scientist, NRIMS, during the period in which this work was carried out.     

Finite layer analysis of consolidation. I

A method for the analysis of the consolidation of a horizontally layered soil under plane conditions is developed. The method depends upon the transformation of the governing equations by a Fourier trasform. This transformation has the effect of reducing the partial differential equations of consolidation to ordinary differential equations. The ordinary differential equations are then solved using a finite layer or finite difference approach. Once the solution in the transformed plane has been found, the actual solution is synthesized by Fourier inversion. The method leads to a considerable reduction in the amount of core storage necessary for solution and enables the solution of quite significant problems to be obtained on a mini-computer.     

Zur Baugeschichte der Ardennen I

Zusammenfassung Die bereits kaledonisch gefalteten Massive in den Ardennen wurden von der variscisdien Tektogenese (asturische Phase) mehr oder weniger überprägt. Vorstellungen über diese Überprägung älterer Strukturen und deren Vergitterung mit jüngeren Verformungsrichtungen sowie über den Einfluß der kaledonischen Kerne (Unterstockwerk) auf das Faltenstreichen der devonischen Mantel-Schichten (Oberstockwerk) lassen sich vor allem in der Antiklinalzone der Hochardennen im Massiv von Rocroi, im Massiv von Serpont und im Massiv von Stavelot gewinnen.

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Résumé Les massifs des Ardennes, déjà plissés à l'ère caledonienne furent plus ou moins remaniés par la tectogénèse hercynienne (phase asturienne). C'est surtout dans la zone anticlinale des hautes Ardennes, dans le massif de Rocroi, dans le massif de Serpont et dans le massif de Stavelot qu'on peut se faire une idée en bons affleurements de ce remaniement de structures plus anciennes et de leurs interférences avec des directions de déformation plus jeunes ainsi que de l'influence des anciens massifs calédoniens (étage inférieur) sur la direction du plissement des couches de revêtement dévoniennes (étage supérieur).Dans ces massifs, les couches du dévonien sont plus ou moins fortement plissés ou disposés par écailles avec le socle calédonien. Dans le massif de Rocroi, dans le massif de Serpont et dans la partie ouest du massif des Stavelot les couches du socle présentent des structures qui sont totalement différentes des couches de revêtement dévoniennes et coupé de façon discordante des couches gedinniennes inférieures.Dans le massif de Rocroi et surtout dans le massif de Serpont, la tectogénèse hercynienne a exercé le même effet que l'orogénèse calédonienne plus ancienne sous l'influence d'un plan d'efforts semblable orienté Nord-Sud. L'auteur, à l'aide d'un exemple, celui du massif de Serpont, essaye d'analyser la structure du plissement calédonien originel déroulement des plis des couches gedinniennes et reformation constructive de la déformation conditionnée par le clivage hercynien.A la différence des deux massifs occidentaux, dans le massif de Stavelot, les structures de plissement calédoniens orientées d'est en ouest furent remaniées sous angle oblique par la tectogénèse hercynienne. Ce mouvement a entraîné, à différents endroits, le déplacement des axes calédoniens en direction hercynienne. C'est ce qui a produit un style de mouvement et de structure étranger aux autres massifs. Le fort rétrécissement hercynien eut pour conséquence des charriages à différents endroits.

     

In memory of I. K. Korolyuk

Chronicle

In memory of I. K. Korolyuk     

A general catalog of class I methanol masers

A catalog of class I methanol masers discovered so far in the Southern and Northern hemispheres is presented. The catalog contains 160 sources. A statistical analysis shows that, within 2’ of the telescope pointing (which corresponds approximately to the field of view of single antennas used in search surveys), 50% of class I methanol masers are associated with objects characteristic of active starforming regions: IRAS sources, ultracompact HII regions, and dense gas—dust clouds, as well as OH and H₂O interstellar masers. At the same time, bipolar outflows (which could play an active part in pumping the methanol masers) are associated with fewer than 25% of class I methanol masers. In 72% of cases, class I methanol masers are associated with class II methanol maser sources. These results suggest that methanol maser condensations are more appropriately classified by the transition type (that is, the pumping mechanism) than their association with other astronomical objects.     

Manganese olivine I: Electrical conductivity

To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn₂SiO₄, electrical conductivity () of single crystals was measured along either the [100] or the [010] direction. The experiments were carried out at temperatures T=850–1200 °C and oxygen fugacities atm under both Mn oxide (MO) buffered and MnSiO₃ (MS) buffered conditions. Under the same thermodynamic conditions, charge transport along [100] is 2.5–3.0 times faster than along [010]. At high oxygen fugacities, the electrical conductivity of samples buffered against MS is 1.6 times larger than that of samples buffered against MO; while at low oxygen fugacities, the electrical conductivity is nearly identical for the two buffer cases. The dependencies of electrical conductivity on oxygen fugacity and temperature are essentially the same for conduction along the [100] and [010] directions, as well as for samples coexisting with a solid-state buffer of either MO or MS. Hence, it is proposed that the same conduction mechanisms operate for samples of either orientation in contact with either solid-state buffer.The electrical conductivity data lie on concave upward curves on a log-log plot of vs , giving rise to two regimes with different oxygen fugacity exponents. In the low- regime , the exponent, m, is 0, the MnSiO₃-activity exponent, q, is 0, and the activation energy, Q, is 45 kJ/mol. In the high regime 10^{ - 7} {\text{atm}}} \right)$$ " align="middle" border="0"> , m=1/6, q=1/4–1/3, and Q=45 and 200 kJ/mol for T<1100 °c=" and=">T>1100 °C, respectively.     

Disjunctive kriging revisited: Part I

Difficulties in applying disjunctive kriging (D.K.) with an anamorphosis to a normal distribution have led to an interest in D.K. based on other distributions. After reviewing Gaussian D.K., this paper reviews other types of D.K. based on other infinitely divisible distributions (gamma, Poisson, and negative binomial).     

Komatiites I: Eruption and Flow

Because of their high eruption temperatures and ultrabasic composition,komatiite lavas had low viscosities, which typically rangedfrom 0-1 to 10 Pa s. A major consequence of this low viscosityis that most lavas erupted as turbulent flows. An analysis oftheir ascent through the lithosphere suggests ascent velocitiesin the range of 1 to over 10ms^–1 and Reynolds numbersmuch greater than the critical value of 2000. The lavas wouldhave remained turbulent for most or all of their subsequentflow and emplacement. Typical horizontal flow rates are estimatedto range from 0?5 to 100 m² s^–1 per unit width of flow.Such turbulent lava flows would have lost their heat by convectionto the surroundings, at rates which are orders of magnitudegreater than the rates for laminar flows, which cool by conduction.A quantitative analysis of the cooling of komatiites indicatescooling rates from over 1000 ?C hr^–1 to a few ?C hr^–1,while the flows remained turbulent. These rates are in an appropriaterange to cause phenomena such as high nucleation rates, strongsupersaturation of the lava, delayed nucleation of olivine,and skeletal or dendritic crystal morphologies. Komatiites often flowed over ground composed of rocks with lowermelting temperatures. It is proposed that the turbulent lavasmelted the ground to form deep thermal erosion channels. Meltingrates at the lava source are calculated at several metres perday, and deep troughs with depths of several metres to hundredsof metres and lengths of several kilometres probably formed.Laboratory experiments performed to simulate thermal erosionshow qualitative agreement with the theory with channel depthdecreasing downstream. The experiments also revealed that thechannel margins become undercut during thermal erosion to formoverhanging sides of the channel. Some sinuous rilles observedin the mare regions of the Moon are thought to have formed bythermal erosion (Hulme, 1973). They provide analogues of thechannels postulated to form in komatiite eruptions, where conditionswere in fact more favourable for thermal erosion. An assessmentof the role of olivine crystals, precipitated in the cooling,turbulent flows, indicates that they will remain in suspensionuntil the lava has come to rest. Contamination of komatiite lava by underlying rock can be asmuch as 10 per cent. Some illustrative calculations show howthe major element and trace element compositions of residualmelts can be significantly modified by combined assimilationand fractional crystallization in a moving flow. Assimilationof tholeiitic basalt into a komatiite can cause incompatibletrace element ratios, such as Ti/Zr and Y/Zr, and the rare earthpatterns of derivative lavas, to vary substantially. Some ofthe variations in such geochemical parameters, which are oftenascribed to mantle heterogeneity, also could have resulted fromassimilation of the ground. Assimilation could have modifiedthe isotope geochemistry of lava suites and led to apparentages which differ from the true eruption age. The thermal erosionmodel also provides an explanation of the formation of somenickel sulphide ores found at the bottom of thick komatiiteflows. It is proposed that ores can form by assimilation ofsulphur-rich sediment, which combines with Ni from the komatiiteto form an immiscible liquid.     

V.I. Vernadskiy,founder of radiogeology

The life of V. I. Vernadskiy is reviewed at the time of his 100th anniversary. He is considered a father of radiogeology, having devoted most of his adult life to the study of radioactive materials. — J.J. Finney     

Mechanism of feldspar weathering—I. Experimental studies

It has been widely accepted that a chemically altered, protective surface layer regulates the dissolution, and hence the weathering, of plagioclase feldspars under Earth's surface conditions. In this study, we examine this hypothesis in detail with the aid of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Using these techniques, we have been unable to find any direct evidence suggesting the presence of a chemically altered coating on feldspar surfaces which have been weathered in the lab. Instead, our results suggest that the mechanism controlling feldspar weathering is a surface controlled reaction.Based on SEM observations and measurements of rate of release of silica, we postulate that the process of feldspar dissolution proceeds in two stages in the lab. Initially, one observes the dissolution of ultrafine (? 1 μm diameter) particles which are produced during grinding of the sample, and which adhere tenaciously to the surfaces of larger grains. This is the stage which results in the non-linear rates of dissolution which are commonly observed in the lab (parabolic kinetics). Secondly, the dissolution occurs at sites of excess surface energy such as at dislocations or similar crystal defects. This process yields linear rates of dissolution, and it dominates the weathering of feldspars in the field.