Vol 56, No 12 (2018)

All major, rock-forming lower-mantle minerals (bridgmanite, CaSi-perovskite, ferropericlase and stishovite) are “nominally anhydrous minerals” (NAMs), in which hydrogen comprises less than 1 wt % and whose chemical formula would be normally written without hydrogen. In NAMs, hydrogen occupies various defects of the crystal lattice and is bonded to structural oxygen, forming hydroxyl groups. Currently, two main techniques can be used for water determination in the mantle minerals: Fourier transform infrared spectrometry (FTIR) and secondary ion mass spectrometry (SIMS). They produce different results: determinations by SIMS are usually higher than quantifications of FTIR. As a result, the estimates of water concentrations in lower-mantle minerals vary widely. Most reliable concentrations of water are 1400–1800 ppm in bridgmanite, 10–80 ppm in ferropericlase, and 20–150 ppm in stishovite. The average concentration of water in the lower mantle is ~1500 ppm. Despite such minor concentrations in lower-mantle minerals, water forms a great reservoir within the lower mantle, probably amounting ~45.45 × 10²³ grams H₂O, i.e., ~3.3 times the mass of the Earth’s oceans. Some amount of water is transported into the lower mantle by subducting lithospheric slabs; this amount is balanced by the water flux from the lower mantle to the transition zone. Within areas of partial melting in the lower and upper parts of the lower mantle, as well as in some local areas, stress and thermal increase initiate release of water from lower-mantle minerals into melt. The enrichment of partial melts with H₂O depends on the P–T conditions, oxygen fugacity values, and percentage of melting. It causes major geodynamic processes that are initiated within the deep Earth. The major source of the water reservoir in the lower mantle is primordial water stored early in the Earth’s evolution.

Some properties of depolymerized ultramafic (pyroxenite, peridotite, kimberlite, and dunite) melts under P–T parameters of the upper mantle and crust are still known inadequately poorly. These properties are, first of all, the concentration, temperature, and pressure functions of the viscosity of these melts. This publication reports the first experimental–theoretical data on the temperature and pressure dependences of the viscosity of model dunite melts (degree of depolymerization 100NBO/T = 340) within broad ranges of temperature (1300–1950°C) and pressure 100 MPa to 7.5 GPa in comparison with such dependences for more strongly polymerized basalt melts (100NBO/T = 58). Our experimental data (accurate to ±30 relative %) on the viscosity of model dunite melts are compared with analogous calculated dependences of the viscosity of dunite melts obtained with a practically experimental error using a modified physicochemical model for predicting the viscosity of magmatic melts. The experimentally determined viscosity of extremely depolymerized dunite melts is very low at both medium and high pressures: 0.09–0.63 Pa s. The viscosity of model dunite melts is demonstrated to exponentially decrease with increasing temperature under medium (100 MPa) and high (up to 7.5 GPa) pressures and, conversely, exponentially increase with increasing pressure by approximately one order of magnitude as the pressure increases from 100 MPa to 7.5 GPa at a constant temperature. The pressure function of the viscosity of basalt melts has an minimum at ~5.5 GPa. Our first experimental data prove that the viscous flow activation energy of dunite melts linearly increases with increasing pressure. Based on analysis of newly obtained and preexisting literature data, we developed a generalized concentration dependence of the viscous flow activation energy of depolymerized ultramafic melts over the whole compositional range of melts from pyroxenite to dunite.

In this paper, isothermal solubility equilibrium method was used to study the mineral solubilities of two ternary systems sodium chloride-lead chloride-water and magnesium chloride-lead chloride-water at 373 K. The solubilities of the salt minerals and the densities of saturated solution in these systems were measured at 373 K. Based on the determined equilibrium solubility data and the corresponding equilibrium solid phase, the isothermal solubility diagrams of the ternary systems were shown, respectively. The results show that both the two ternary systems are simple total saturated at 373 K that neither double salt nor solid solution produced under the condition. Besides, the isothermal solubility diagrams of the two ternary systems at 373 K are both constituted of a eutectic point, two isothermal solubility curves and two solid crystalline phase regions. The two equilibrium solid phases corresponding to the eutectic point of the sodium chloride-lead chloride-water ternary system are NaCl and PbCl₂. The two equilibrium solid phases corresponding to the eutectic point of the magnesium chloride-lead chloride−water ternary system are MgCl₂ · 6H₂O and PbCl₂. The experimental result of density was simply discussed.

In this paper, we report new data on the lithological and chemical compositions of the surface layer (0–2 cm) of bottom sediments from various zone of the Kara Sea: the estuaries of the Ob and Yenisei rivers, open part of the shelf, Eastern Novaya Zemlya Trough, Voronin Trough, and Novaya Zemlya bays. The sediments were collected during five cruises of the R/V Akademik Boris Petrov (2000, 2001, and 2003) and the R/V Akademik Mstislav Keldysh (2015 and 2016). Based on the statistical analysis of the obtained data array, all the bottom sediments were divided into cluster groups comprising their lithological and geochemical types. The obtained clusters and REE + Y systematics were used to distinguish facies genetic types of the bottom sediments and determine the accumulation zones of Holocene sequences. They are bounded by river estuaries, a shallow marine zone adjoining the southeastern coast of the sea, and deep troughs. The main sources of Holocene sediments in the Kara Sea are the suspended particulate materials of the Ob and Yenisei and materials transported by glacial meltwater from the Novaya Zemlya and Severnaya Zemlya archipelagoes. The dispersion of fine suspensions is controlled by the circulation of surface sea currents. The accumulation of suspended materials on the bottom is complicated by wave effects and circulation of bottom sea currents, which remove fine sediment fractions from the shallow regions of the sea and transport them into the deepest hydrodynamically calm parts of troughs.

The modes of occurrence of trace elements in coal reveal essential information about environmental impact during coal exploitation and utilization. Utilizing improvements on a recently published sequential leaching protocol, this study investigated the modes of occurrence of Cr, Co, Ni, Cu, Cd, and Pb (water-soluble, ion-exchangeable, carbonate-bound, sulfide-bound, organic-bound, and silicate-bound) in coal samples collected from the Nantong coalfield in southwestern China. Results suggest the improved method favorably affected the sequential leaching experiment. The ashing temperature did not exceed 390°C and did not damage the structure of the silicate minerals, facilitating the effective extraction of trace elements within the organic matter. The case study in the Nantong coalfield demonstrated that the water-soluble and ion-exchangeable fractions account for only a small portion of the six elements. Specifically, chromium exhibited affinities with carbonates and silicates. The percentages of different target fractions for cobalt varied significantly in different samples. Nickel was almost evenly distributed in the fractions of carbonates, sulfides, organic matter, and silicates. For cadmium, silicate was the main fraction, followed by sulfides. Lead predominantly appeared in carbonates and sulfides. The correlativity of different elements in the corresponding fractions revealed carbonates and sulfides as the primary carriers for all six elements, followed by silicates and organic matter. Overall, Cr, Co, Ni, and Cu exhibited very close relationships and similar distribution patterns in different coal samples. Organic-bound Cr, Co, and Ni were noticeable in the No. 4 and 6 coal seams, though they were not the dominant fractions. The affinity between Pb and Cd indicated they have similar modes of occurrence.

Small rivers commonly drain in a few lithologies making their sediments as a good candidate for investigating provenance and weathering environments. We investigated spatial variation in compositional changes in the sediments of a modern river (Khurar River) from its source to sink for 35 km in Khajuraho area, Madhya Pradesh, India. The Khurar River in its entire course is surrounded by the Bundelkhand granitic complex that provides uniform source to the sediments. The possible physical and chemical controls on the bed-load sediments i.e. grain-size, mineralogy, geochemistry and their climatic control are investigated in detail here. Bed- load sediments of the Khurar River are very coarse to coarse sand-size ranging from –0.63 to 0.80 phi and they are devoid of fine sediments such as clay. The mineralogy of the sediments suggests that they are arkosic in composition. The spatial variation in the chemical composition of the sediments is negligible in the river basin from source to sink in the very coarse to coarse sand size range. The sediments are rich in SiO₂ (≤82.93) and Al₂O₃ (≤11.03 wt %) and they have lower values of TiO₂ (≤0.27), Fe₂O₃ (≤1.49), CaO (≤1.12), MgO (≤0.77), K₂O (≤5.25) and Na₂O (≤3.48 wt %). The trace elements such as Cr (≤66), Co (≤8), Cu (≤19) and Ni (≤12 ppm) have lower values than UCC; but the Pb (≤21) and Rb (≤142 ppm) have higher values than UCC. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these sediments, a feature also confirmed by the mineralogical study. The high Zn content at some stations suggests anthropogenic contamination in the sediments. A-CN-K ternary plot suggests total alteration of plagioclase resulting in more removal of CaO and Na₂O due to continuous weathering in the catchment area. Also, in this plot, sediments lie near to the albite concentration above the anorthite-albite line with gradual depletion in anorthite indicating that they are the weathering products of albite-enriched parent material. The A-CNK-FM ternary plot shows that all the samples plot close to the feldspar apex indicating higher abundance of feldspars. Further, the CIA (54 to 57), PIA (58 to 64) and CIW (70 to 78) values of the sediment samples suggest low to intermediate weathering environment. Chondrite-normalized pattern of REE (Rare earth elements) exhibits depletion of HREE with weak positive Eu anomaly suggesting low fractionation of the plagioclase feldspar. Thus, the major, trace and rare earth elements geochemistry of the bed-load sediments from the Khurar River suggest that they are derived from the weathering of felsic rocks and the original signatures of the granitic provenance remain there even after weathering under sub-humid climatic conditions in the river basin.

The major and trace element compositions of stratified frozen peatlands in the forest–tundra of Northeastern European Russia were determined for the first time. The upper level of trace element accumulation was confined to the active (seasonally thawed) layer owing to airborne contamination over a long time span and related to the bioaccumulation of Hg, Cd, Pb, Cu, and other heavy metals (HMs) by plants and humus materials. The character of element accumulation and migration in the active layer is controlled by the stability of HM humates. Under high-acidity conditions, HMs are highly mobile and migrate to the lower boundary of the active layer, which is indicated by an increase in the fraction of water-soluble forms of a number of elements. Analysis with a scanning electron microscope revealed the presence of spherical and semispherical particles up to 1 μm in size containing Pb, Zn, Cr, and Ni in the upper peat levels, which indicates an anthropogenic source of their input owing to long-distance and local transport of air masses. The central level of element accumulation was confined to peat layers in the permafrost zone (60–120 cm), where enrichment in As and Cd relative to the mean contents in the Earth’s crust (and approximate permissible concentrations, APC, for soils) and accumulation of Fe, Al, S, and siderophile elements were observed. The source rocks of the peatlands are loams enriched in Cd, Zn, and As. The statistical analysis of relations of the contents of major and trace elements in the stratified peat horizons with the composition of peat-forming materials showed a significant contribution of the biogenic accumulation of elements.