Contrasted melting relations in a pyrolite upper mantle under mid-oceanic ridge,stable crust and island arc environments

The pyrolite model composition provides a satisfactory source composition for mantle-derived magmas insofar as major elements and “compatible” trace elements are concerned but there is evidence for mantle inhomogeneity in the abundances of “incompatible” minor and trace elements (e.g., K, Ti, P, Rb, Sr, light rare earth elements etc.). The composition of a magma, assuming a constant source composition, varies according to the pressure, temperature and water pressure or water content of the source region. The latter two variables essentially determine the degree of partial melting of the source region and in considering the chemical composition of the melt and nature of the residual phases, this parameter is of prime importance.For high degrees (> 20% approx.) of partial melting of a pyrolite source region, magmas are of tholeiitic character but are of increasingly undersaturated and alkaline type for lower degrees of partial melting and high pressures. For any chosen degree of melting and fixed water content of the source region, magmas are more olivine-rich at higher pressures. For any chosen pressure and chosen degree of partial melting, magmas are less olivine-rich at high water contents (and thus lower temperatures). Quartz tholeiite magmas may be derived by ~ 30% melting of pyrolite under water-saturated conditions at pressures up to between 17 kbar and 20 kbar. These generalizations may be applied to understand the characteristic magmatism of mid-oceanic ridges, island chains, oceanic islands and orogenic regions.     

Particle size distribution and dissolution properties of metals in cyclone fly ash

The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution.     

Reservoir sediments – a witness of mining and industrial development (Malter Reservoir, eastern Erzgebirge, Germany)

The Malter Reservoir is situated about 30 km south of Dresden (eastern Germany) in a historical mining area of the eastern Erzgebirge. It was built in 1913 for the protection from floodwaters, droughts and for generating electricity. The river Rote Wei?eritz is the main source of clastic input into the lake. Geochemical and sedimentological data of gravity-and piston-cores, recovered from the deepest point of the lake, document the environmental history of the drainage area since 1963. ¹³⁷Cs dating gives an average sedimentation rate of ∼2.9 cm/year. Within the whole core, heavy metals are strongly enriched (parentheses refer to enrichment factors as compared with average shale): cadmium (290), silver (140), bismuth (90), antimony (25), lead (21), zinc (14), tin (13), uranium (9), tungsten (9), molybdenum (5), copper (4), thallium (3) and chromium (2). Enrichments are detectable for the whole registered time-period of 81 years. Peaks of up to 27 mg/kg silver, 37 mg/kg bismuth, 91 mg/kg cadmium, 410 mg/kg chromium, 240 mg/kg copper, 20 mg/kg molybdenum, 14000 mg/kg phosphorus, 740 mg/kg lead, 6,5 mg/kg antimony, 74 mg/kg tin, 52 mg/kg tungsten and 1900 mg/kg zinc reflect local events caused by human impact. Inputs from different pollution sources at different times are represented by highly variable elemental concentrations and ratios within the core. High pH values within the water and the sediment column, the large adsorption capacity of the fine-grained C_org.-rich sediment, and the presence of low Eh-values and sulphide ions in the sediment prevent the remobilisation of the toxic elements. Erosion of these contaminated sediments during floods, channel flows or resuspension during removal of the sediments may lead to a downstream transfer of pollutants. Contents of P and C_org., as well as diatom abundance, indicate a change from oligotrophic to eutrophic conditions in the lake during ∼1940–1950. This was mainly caused by high agricultural activity in the drainage area. Reduced contents of Cu, Zn, Cd and Cr since the reunification of East and West Germany are obviously caused by increasing environmental protection measures, such as wastewater purification and especially the closing of contaminating industries. Revision received: 23 September 1999 · Accepted: 17 December 1999     

Quaternary Antarctic Bottom-Water history: Deep-sea benthonic foraminiferal evidence from the southeast Indian Ocean

Distinct assemblages of Recent deep-sea benthonic foraminifera from the southeast Indian Ocean have been shown to be associated with Antarctic Bottom Water (AABW) and Indian Bottom Water (IBW). The AABW assemblage is divided into two groups. One is dominated by Epistominella umbonifera and is associated with AABW having temperatures between ?0.2° and 0.4°C. The second group is dominated by Globocassidulina subglobosa and is associated with AABW having temperatures between 0.6° and 0.8°C. The IBW assemblage is marked by the strong dominance of Uvigerina spp. and Epistominella exigua. The faunal-water-mass relationships have been used to infer the history of bottom-water circulation over the last 500,000 yr in this region using faunal data from four Eltanin cores. One core was taken from the Southeast Indian Ridge in association with IBW, and three were taken from the flank of the ridge associated with AABW flowing within a western boundary contour current in the South Australian Basin. Little faunal variation exists in the core beneath IBW (E48-22), indicating that IBW was present on the Southeast Indian Ridge during the last 300,000 yr. A record of the intensity of AABW circulation during the last 500,000 yr is inferred from the benthonic foraminiferal data in the three cores located within the western boundary contour current. Marked oscillations in the relative proportions of AABW and IBW faunal assemblages are found in one core, E48-03. The faunal variations are inferred to have resulted from variation in intensity of AABW circulation between 500,000 and 195,000 yr B.P. In E48-03, the AABW assemblage was present most of the time between 500,000 and 195,000 yr B.P., with low intensity of AABW circulation occurring primarily during the equivalent of stages 8 and 7 (t = 305,000 to 195,000 yr B.P.). The intensity of AABW circulation varied, with a maximum occurring during the equivalent of stage 11 (t = 420,000 yr B.P.). Two additional cores, E45-27 and E45–74, show relatively constant intensity of AABW circulation from 195,000 yr B.P. to the present. The intensity of AABW circulation at the present appears to be intermediate between a maximum during the equivalent of stage 11 (t = 420,000 yr B.P.) and the minimum during the equivalent of stage 8 (t = 275,000 yr B.P.). AABW production has occurred during both glacial and interglacial episodes. Bottom-water productivity has been suggested to play an important role in glacial/interglacial oscillations during the late Quaternary (Weyl, 1968; Newell, 1974). In this study, the relationship between bottom-water circulation and climatic fluctuations appears to be more complex than had been previously suggested, since a simple relationship between Quaternary bottom-water circulation and paleoclimatic fluctuations is not shown.     

Green synthesis of magnetic mesoporous silica nanocomposite and its adsorptive performance against organochlorine pesticides

Green synthesis of nanomaterials has received increasing attention as an eco-friendly technology in materials science. Here, we have used two types of extractions from green tea leaf (i.e., total extraction and tannin extraction) as reducing agents for a rapid, simple and one-step synthesis method of mesoporous silica nanoparticles/iron oxide nanocomposite based on deposition of iron oxide onto mesoporous silica nanoparticles. Mesoporous silica nanoparticles/iron oxide nanocomposite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray, vibrating sample magnetometer, N₂ adsorption and high-resolution transmission electron microscopy. Mesoporous silica nanoparticles/iron oxide nanocomposite was used as a solid adsorbent for removal of lindane pesticide from aqueous solutions. The developed system possesses the advantages of silica as core that include large surface area and advantages of iron oxide (shell) that include the capability to interact with chlorinated compounds and ability to release by using external magnetic field. UV-Vis technique was used as a simple and easy method for monitoring the removal of lindane. Effects of pH and temperature on the removal efficiency of the developed mesoporous silica nanoparticles/iron oxide nanocomposite toward lindane pesticide were also investigated. Fourier transform infrared spectroscopy, high-performance liquid chromatography and gas chromatography techniques were used to confirm the high ability of mesoporous silica nanoparticles/iron oxide nanocomposite for sensing and the capture of lindane molecules with high sorption capacity (about 99%) that could develop a new eco-friendly strategy for detection and removal of pesticide and as a promising material for water treatment.     

Natrolite,part I: Refinement of high-order data,separation of internal and external vibrational amplitudes from displacement parameters

A single crystal of natrolite, Na₂Al₂Si₃O₁₀·2H₂O, was studied by X-ray diffraction methods at room temperature. The intensities were measured with MoKα radiation (λ = 0.7107 Å) in a complete sphere of reflection up to sin θ/λ = 0.903 Å^?1. The structure was refined in the orthorhombic space group Fdd2 with a = 18.2929 (7) Å, b = 18.6407(9) Å, c = 6.5871(6) Å, V = 2246 ų, Z = 8. A refinement of high-order diffraction data yielded reliability factors of R(F) = 0.9%, R _w(F) = 0.8%, GoF = 1.40 for 1856 high-angle reflections (0.7 ?in θ/λ <0.903 Å^?1) and R(F) = 1.0%, R _W(F) = 1.2%, GoF = 3.07 for all 3471 independent reflections in the complete sphere of reflection. The T-O distances as well as the T-O-T angles were found to be strongly influenced by the different bond strengths received by the individual oxygen atoms. The T O distances calculated using Baur's extended valence rule agree on average within 0.003 Å with the observed values. An analysis of the mean square displacement amplitudes allowed a separation of the external and internal vibrational amplitudes along the T-O bonds as well as along the Na O and H₂O-O bond directions and the calculation of force constants. The internal vibrational amplitudes (ΔU) of the T-O vibrations are in the range of 5 to 11 × 10^-4 Ų, that is about one order of magnitude smaller than the mean square displacement amplitudes of the external vibrations. The corresponding force constants are F = 354 to 824 Nm^?1. The values of the force constants of the motion of the Na-ion and the water molecule against the framework oxygen atoms lie in the range between F = 57 and 293 Nm^?1. This is the first instance where displacement amplitudes from a zeolite structure refinement could be apportioned between contributions from internal and external vibrations for individual bonds.     

http://www.sciencedirect.com/science/article/pii/S167498711100079X

Lower Paleozoic rocks exposed in various regions of Egypt (south central Sinai, north Eastern Desert and southwest Western Desert), in addition to occurring in the subsurface such as north Western Desert and the Gulf of Suez. The Lower Paleozoic rocks in Egypt include surface and subsurface rock units of formational status. The surface rock units are the Taba, Araba and Naqus formations. The subsurface rock units include the Shifa, Kohla and Basur formations. The Infracambrian Taba Formation has been discovered recently in the outcrops of the south eastern Sinai in the Taba-Ras El-Naqab area. It is missing and/or not recognized in the subsurface. The Taba Formation consists mainly of reddish brown, unfossiliferous gravelly fine-to medium-grained sandstones cemented by kaolinite and have subordinate beds of paleosols. The Cambrian Araba Formation and its subsurface equivalent (the Shifa Formation) are essentially composed of reddish brown, fine-grained laminated sandstone and siltstone with abundant Skolithos and Cruziana sp. In contrast, the Ordovician-Silurian Naqus Formation and its subsurface equivalents (Kohla Formation and Basur Formation) are mainly composed of white, unfossiliferous, cross-bedded, medium- to coarse-grained sandstones with haphazardly distributed pebbles and cobbles. Sedimentological analysis indicates that the Araba Formation and its equivalents were deposited in a marginal-marine environment, whereas the Naqus Formation and its equivalents were laid down in a fluvio-glacial environment. Integrated stratigraphic and sedimentological studies of the Lower Paleozoic rocks permit reconstruction of the paleogeography of Egypt at that time. Egypt has been largely controlled since the Cambrian by the pre-existing structural framework of the pre-Phanerozoic basement rocks inherited from the Late Proterozoic Pan-African event. Additionally, sedimentation processes were controlled during Cambro-Ordovician times by tectonic movements, whereas glacio-eustatic control predominated during the Late Ordovician-Silurian Period. These studies suggest that most areas of Egypt were exposed lands with episodically transgression by epicontinental seas related to the paleo-Tethys. These lands formed a part of a stable subsiding shelf at the northern Gondwana margin.     

A subsidiary fast-diffusing substitution mechanism of Al in forsterite investigated using diffusion experiments under controlled thermodynamic conditions

Diffusion of Al in synthetic forsterite was studied at atmospheric pressure from 1100 to 1500 °C in air along [100] with activities of SiO₂, MgO and Al₂O₃ (a_SiO2, a_MgO and a_Al2O3) buffered. At low a_SiO2, the buffer was forsterite + spinel + periclase (fo + sp + per) at all temperatures, while at high a_SiO2 and subsolidus conditions a variety of three-phase assemblages containing forsterite and two other phases from spinel, cordierite, protoenstatite or sapphirine were used at 1100–1350 °C. Experiments at high a_SiO2 and 1400 °C used forsterite + protoenstatite + melt (fo + en + melt), and at 1500 °C, fo + melt. The resulting diffusion profiles were analysed by LA–ICP–MS in scanning mode. Diffusion profiles in the high a_SiO2 experiments were generally several hundred microns in length, but diffusion at low a_SiO2 was three orders of magnitude slower than in high a_SiO2 experiments carried out at the same temperature, producing short profiles only a few microns in length and close to the spatial resolution of the analytical method. Interface concentrations of Al in the forsterite, obtained by extrapolating the diffusion profiles to the crystal/buffer interface, were only a fraction of those expected at equilibrium, and varied among the differing buffer assemblages according to (a_Al2O3)^1/2 and (a_SiO2)^3/4, pointing to the substitution of Al in forsterite by an octahedral-site, vacancy-coupled (OSVC) component with the stoichiometry Al _4/3 ³⁺ vac_2/3SiO₄, whereas the main substitution expected from previous equilibrium studies would be the coupled substitution of 2 Al for Mg + Si, giving the stoichiometry MgAl₂O₄. It is proposed that this latter substitution is not seen on the length scales of the present experiments because it requires replacement of Si by Al on tetrahedral sites, and is accordingly rate-limited by the slow diffusivity of Si. Instead, diffusion of Al by the OSVC mechanism is relatively fast, and at high a_SiO2, even faster than Fe–Mg interdiffusion.