The solubility mechanisms of volatiles in silicate melts and their relations to crystal-andesite liquid equilibria

The anionic structure of magmatic liquids has been estimated at 1 atm and at pressures corresponding to those of the upper mantle. These estimates are based predominantly on spectroscopic data on binary metal oxide-silica and ternary metal oxide-silica-alumina melts. Structural information on melt compositions in aluminate-silica joins has been used to provide detailed information on the role of Al³⁺ in natural magma at atmospheric and high pressure.Regardless of pressure, andesitic melts may be described as combinations of chain, sheet, and three-dimensional network units. Nearly all Al³⁺ in the magmatic liquid resides in the three-dimensional network units. This Al³⁺ is locally charge-balanced with Na⁺, K⁺, Ca²⁺, and Mg²⁺. In the latter two cases, Al³⁺ and Si⁴⁺ are ordered, whereas for Na⁺ and K⁺, Si⁴⁺ and Al³⁺ are randomly mixed. Solution of water in natural magma results in the formation of new nonbridging oxygens in addition to OH groups attached to Si⁴⁺ and metal cations.On the basis of determined solution mechanisms of CO₂ and H₂O in silicate melts, thermodynamic properties of HO+CO₂, fluids and hydrous silicate melts and melting phase relations in peridotite-H₂O-CO₂, systems, it is found that natural andesitic magma in equilibrium with spinel Iherzolite in the upper mantle (10–20 kbar) must contain at least 5–7 wt.% H₂O. Andesitic magma with 5–7 wt.% H₂O in solution may be described as a mixture of Al-free three-dimensional units, sheets, and chains with a small proportion (less than 10%) of monomers.     

Solar almucantar radiance and aerosol scattering: Comparative data from one tropical station and one mid-latitude station

Solar, sky, and aureole radiance data from Kensington, Australia, and Lagos, Nigeria, are analysed. The values of the aerosol optical thickness at Lagos are comparable to measured values elsewhere in the subregion (Abidjan) under light haze. The values at Kensington are close to those of the “background aerosol.” Identical and anomalous values of aerosol optical thickness occurred at 1.67 μm at both stations as less than 15% of the values can be accounted for by aerosols. The high optical depths are therefore explained in terms of absorption, possibly mainly by CO₂ (59–65%) and, to a lesser extent, by H₂O (20–26%). Following correction for molecular multiple scattering, the aerosol scattering phase function increases substantially at 0.5 μm in Kensington and decreases considerably at 0.76 μm in Lagos when compared to the uncorrected function, confirming the relative fineness of the Kensington aerosol. The Lagos aerosol size distribution for moderately dusty air is reasonably bimodally log-normal with modal radiusr _m=0.49 μm (1.36 μm) for the moder≤1 μm (r>1 μm). The Kensington aerosol resembles one withr _m=0.05 μm forr<1 μm. There the Born approximation appears appropriate, and the weighted mean square radiusp ²=0.13 μm². In the near forward direction the aerosol scattering phase funciton for Lagos resembles Deirmendjian’s simulations for a silicate-L haze and, for Kensington, a silicate-H haze.     

A world model of soil carbon dioxide

Mean growing season soil PCO₂ data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO₂) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO₂. An improved soil PCO₂-AET model was developed by assuming (1) that as AET approaches zero, soil PCO₂ approaches the atmospheric value and (2) that there is an upper limit to soil PCO₂ at very high AET. This model has the form log(PCO₂) = ?3·47 + 2·09 (1 ?e^{?0·0172 AET}) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO₂ data, predicts a soil log(PCO₂) of ? 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO₂) = ? 1·45) for mean growing season soil PCO₂ at AET values of 2000 mm and above. The results of this study suggest that soil PCO₂ levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.     

Lithological subdivision and petrology of the Great Himalayan Vaikrita Group in Kumaun,India

The Vaikrita Group made up of coarse mica-garnet-kyanite and sillimanite-bearing psammitic metamorphics constituting the bulk of the Great Himalaya in Kumaun is divisible into four formations, namely theJoshimath comprising streaky, banded psammitic gneisses and schists, the Pandukeshwar consisting predominantly of quartzite with intercalations of schists, thePindari made up of gneisses and schists with lenses of calc-silicate rocks and overwhelmingly injected by Tertiary pegmatites and granites (Badrinath Granite) leading to development of migmatites, and theBudhi Schist comprising biotite-rich calc-schists. The Vaikrita has been thrust along the Main Central Thrust over the Lesser Himalayan Munsiari Formation made up of highly mylonitized low-to meso-grade metamorphics, augen gneisses and phyllonites. Petrological studies demonstrate contrasting nature of metamorphism experienced by the Vaikrita and the Munsiari rocks. Sillimanite-kyanite-garnet-biotite-muscovite (±K-feldspar and ± plagioclase).—quartz metapelites and interbanded calc-schists and calc-gneisses with mineral assemblages of calcite-hornblende-grossular garnet, labradorite (An₅₀?An₆₅), (± K-feldspar)-quartz (± biotite), and hornblende-diopside ± labradorite ± quartz, suggest medium to high grade of metamorphism or indicate upper amphibolite facies experienced by the rocks of the Vaikrita Group. The associated migmatites, granite-gneisses and granites of the Pindari Formation were formed largely as a result of anatexis of metapelites and metapsammites. While, the sericite-chlorite-quartz and muscovite-chlorite-chloritoid-garnet-quartz, assemblages in metapelites and epidote-actinolite-oligoclase (An₂₀)-quartz and epidote-hornblende-andesine (An₂₉) ± quartz in the metabasites suggest a low-grade metamorphism (greenschist facies) for the Munsiari Formation, locally attaining the lower limit of medium-grade (epidote-amphibolite) facies. The inferred P-T conditions obtained from textural relations of various mineral phases and the stability relationship of different coexisting phases in equilibrium, suggest that the temperature ranged between 600° and 650° C and pressure was over 5 kb for the Vaikrita rocks. The mineral assemblages of the Munsiari Formation indicate comparatively lower P-T conditions, where the temperature reached approximately 450° C and pressure was near 4 kb. The rocks of the two groups were later subjected to intense shearing, cataclasis and attendant retrograde metamorphism within the zone of the Main Central (=Vaikrita) Thrust.     

3He4He ratio,noble gas abundance and K-Ar dating of diamonds—An attempt to search for the records of early terrestrial history

The ${}^3\text{He}{}^4\text{He}$ ratios measured in 27 Southern Africa diamond stones, four from Premier Mine and the rest of unidentified origin, range from 4.2 × 10^?8 to 3.2 × 10^?4, with three stones above 1 × 10^?4. We conclude that the initial helium isotopic ratio (${}^3\text{He}{}^4\text{He)}{}_0$ in the earth was significantly higher than that of the planetary helium-A (${}^3\text{He}{}^4\text{He = 1.42 × 10}{}^{\mathrm{?4}}$), but close to the solar helium (${}^3\text{He}{}^4\text{He ? 4 × 10}{}^{\mathrm{?4}}$).The apparent K-Ar ages for the twelve diamonds of unidentified origin show enormously old age, indicating excess argon-40. ${}^3\text{He}{}^4\text{He}$ evolution in diamonds suggests that the diamonds with the high ${}^3\text{He}{}^4\text{He}$ ratio (>2 × 10^?4) may be as old as the earth.Noble gas elemental abundance in the diamonds relative to the air noble gas abundance shows monotonie decrease with a decreasing mass number.This paper discusses the implications of these observations on the early solar system and the origin of diamonds.     

Analysis of Multicolor Observations of 3C 66A in 1993-1998

The results of multicolor observations of the blazar 3C 66A, obtained in the course of the project OJ-94, are analyzed. It is established that the energy distribution of the variable source in the optical and IR ranges can be represented, on the average, by a power law: F ^-0.92. Since the blazar's emission is strongly polarized, there is no doubt of the synchrotron nature of the variable source responsible for the blazar's activity.