Platinum solubility in a haplobasaltic melt at 1250°C and 0.2 GPa: The effect of water content and oxygen fugacity

Haplobasaltic melts with a 101 kPa dry eutectic composition (An₄₂Di₅₈) and varying water contents were equilibrated with their platinum capsule at 1523 K and 200 MPa in an internally heated pressure vessel (IHPV) equipped with a rapid quench device. Experimental products were inclusion-free glasses representative of the Pt-saturated silicate melts at the experimental conditions. Platinum concentrations were determined using an isotope dilution multicollector inductively coupled plasma mass spectrometer and water contents and distribution by Karl Fischer titration and Fourier transform infrared spectroscopy, respectively.The water content of the melt has no intrinsic effect on platinum solubility, for concentrations between 0.9 wt.% and 4.4 wt.% H₂O (saturation). Platinum solubility increases with increasing water content, but this effect is an indirect effect because increasing water content at fixed f_H2 (imposed by the IHPV) increases the oxygen fugacity of the experiment.The positive oxygen fugacity dependence of Pt solubility in a hydrous silicate melt at 200 MPa is identical to that in anhydrous melts of the same composition determined in previous studies at 101 kPa. This study extends the range of platinum solubilities to oxygen fugacities lower than was previously possible. Combining the data of this and previous studies, Pt solubility is related to oxygen fugacity (in bar) at 1523 K by the equation:

[Pt]_total(ppb)=1389×f_O2+7531×(f_O2)^1/2     

Distribution of clay minerals in surface sediments of the Aegean Sea: a compilation

Extensive published data sets and some new data on the clay mineral composition of surface sediments in the Aegean Sea, northeastern Mediterranean Sea, have been compiled in order to map the distribution patterns of clay mineral assemblages and to decipher source areas and transport paths. We distinguished six provinces, a Northwest Aegean Province, a Marmara-Dardanelles Province, a West Turkey Province, a Southeast Aegean Province, a Kithira Province and a Central Aegean Province. The clay mineral assemblages in the coastal and shelf areas carry the signature of the riverine sediment discharge from southeast Europe and Turkey, respectively. The southern Aegean Sea is probably influenced by the River Nile discharge and transport of clay minerals by surface currents. The clay minerals in the central Aegean Sea form a mixed assemblage comprising components of the other assemblages. A dispersion and dilution of clay minerals by surface currents is obvious.     

Quantification of vertical water fluxes in the vadose zone using particle‐size distribution and pedology‐based approaches to model soil heterogeneities

One‐dimensional flow simulations were conducted at four locations of the shallow alluvial aquifer of the upper Rhine River (at the Erstein polder) to quantify the time‐dependent moisture distribution, the water flux and the water volume infiltrated in the unsaturated zone as a function of soil heterogeneities during a five‐day‐long flooding event. Three methods of estimating the hydraulic parameters of soil in the vadose zone were tested. They are based on the following: (1) experimental data, (2) soil particle‐size distribution and (3) pedology information on soils. Water fluxes calculated from modelling approaches 2 and 3 were compared with those of the experiment‐based values and the effect of these differences on the arrival time and velocity of water at the water table were analysed. Major differences in water fluxes were found among the methods of estimating the hydrodynamic parameters. At the Terrace location, the groundwater recharge predicted using soil data from methods 1 and 2 are approximately 4500 and 2400 mm, respectively. Flow simulations using soil data and the experiment‐based method show the highest velocities of infiltrating water at the soil surface and largest volume of groundwater infiltration but result in the lowest centres of the moisture content mass. The results obtained using soil data based on the pedological method are similar to those calculated using soil parameters based on the particle‐size distribution of extracted soil samples. Water pressure profiles calculated on Terrace and Channel location, 3 and 7 days after the inundation event agreed reasonably well with those observed when using hydrodynamic parameters from the experiment‐based method. However, the flow model using the pedology‐based parameters largely underestimates the time needed to achieve hydrostatic conditions of the soil water profile once water flooding at the soil surface stops. This can be mainly attributed to the low values of estimated van Genuchten parameter α. Copyright © 2012 John Wiley & Sons, Ltd.     

Two UBV sequences,north and south of the galactic cluster NGC 5823

Photoelectric UBV observations of 69 stars, distributed in two sequences north and south of the galactic star cluster NGC 5823, are reported.     

The recent capture of the periodic comet P/Scotti (2000 Y3)

Numerical integrations of 99 orbits centered on that of comet P/Scotti (P/2000 Y3), and of the nominal orbit, were made 4000 days backwards in time, and 73000 days into the future. The integrations show that this comet has been transferred into its present orbit as recently as 1998. The future orbital evolution indicates a stable period for almost 150 years, when another close encounter with Jupiter may lead to further drastic changes of the present orbit.