57Fe Mössbauer study on compositions of the series Fe3+TaO4-Fe2+Ta2O6

Fe⁵⁷ Mössbauer spectra were measured on compositions of the series Fe_1?x/3Ta_1+x/3O₄, 0≤x≤1. The spectra are characterized by mixed valencies of Fe²⁺ and Fe³⁺ ions for 0<x<1. Starting from x=0 with rutile structure, a trirutile structure forms towards x=1. Quadrupole splitting QS of Fe³⁺ is QS(Fe³⁺)≈0.55 mm/s and isomer shift IS is IS(Fe³⁺)≈0.40 mm/s (referred to Fe); both quantities exhibit minor variations along the series. The Fe²⁺ subspectra for x>0.5 were fitted using one symmetrical doublet; however, for x<0.5 two symmetrical doublets were necessary to describe these patterns. QS(Fe²⁺)=2.0–3.2 mm/s and IS(Fe²⁺)=0.90–1.15 mm/s for all compositions. In the case x<0.5, marked temperature dependent QS values appear to exist. This feature may be related to short range order effects and possibly also in part to intervalence electron transfer betwee Fe²⁺ and Fe³⁺ ions.     

Delamination and ultra‐deep subduction of continental crust: constraints from elastic wave velocity and density measurement in ultrahigh‐pressure metamorphic rocks

Thirty‐three samples, including 22 eclogites, collected from the Dabie ultrahigh‐pressure (UHP) metamorphic belt in eastern China, have been studied for seismic properties. Compressional (V_p) and shear wave (V_s) velocities in three mutually perpendicular directions under hydrostatic pressures up to 1.0 GPa were measured for each sample. At 1.0 GPa, V_p (7.5–8.4 km s^?1), V_s (4.2–4.8 km s^?1), and densities (3.2–3.6 g cm^?3) in the UHP eclogites are higher than those of UHP orthopyroxenite (7.3–7.5 km s^?1, 4.1–4.3 km s^?1, 3.2–3.3 g cm^?3, respectively) and HP eclogites (7.1–7.9 km s^?1, 4.0–4.5 km s^?1, 3.1–3.5 g cm^?3, respectively). Kyanitites (with 99.5% kyanite) show extremely high velocities and density (9.37 km s^?1, 5.437 km s^?1, 3.581 g cm^?3, respectively). The eclogites show variation of V_p‐ and V_s‐anisotropy up to 9.70% and 9.17%, respectively. Poisson’s ratio (σ) ranges from 0.218 to 0.278 (with a mean of 0.255) for eclogites, 0.281–0.298 for granulites and 0.248 to 0.255 for amphibolites. The σ values for serpentinite (0.341) and marble (0.321) are higher than for other lithologies. The elastic moduli K, G, E of kyanitite were obtained as 163, 102 and 253 GPa, respectively. The V_p and density of representative UHP metamorphic rocks (eclogite & kyanitite) were extrapolated to mantle depth (15 GPa) following a reasonable geotherm, and compared to the one dimension mantle velocity and density model. The comparison shows that V_p and density in eclogite and kyanitite are greater than those of the ambient mantle, with differences of up to ΔV_p > 0.3 km s^?1 and Δρ > 0.3–0.4 g cm^?3, respectively. This result favours the density‐induced delamination model and also provides evidence in support of distinguishing subducted high velocity materials in the upper mantle by means of seismic tomography. Such ultra‐deep subduction and delamination processes have been recognized by seismic tomography and geochemical tracing in the postcollisional magmatism in the Dabie region.     

Steady-state kinetics and equilibrium between ground water and granitic rock

A hypothesis is presented that the dissolution of albite includes the exchange of sodium for hydrogen ion in a surface layer of the mineral and the structural collapse of the residual anionic lattice of the layer. The ion exchange is described by the first law of diffusion (D_25°C = 3 × 10^?22 and 1.5 × 10^?20 cm²sec^?1 at P_CO2 = 0 and 26.2 atm, respectively). The surface residual layer reaches a steady-state thickness ranging from n × 10^?8 to n × 10^?5 cm according to the temperature and P_CO2. The increase in aqueous sodium with time in a continuous ground-water system is described by a simple exponential equation. The equation is used to estimate the percolation time of ground water from the data on the chemical composition of a water sample. The probable times range from 14 to 3840 days for various ground-water systems and are compared to the times of percolation calculated from the geothermal and hydraulic data. Both estimates are found to be in general agreement. The concentrations of Al and Si in cold water from granitic rocks are shown to be controlled by the chemical equilibrium with respect to an aged aluminosilicate. The aluminosilicate precipitates from ground water as an amorphous isoelectric solid. Its chemical composition is represented by a simplified stoichiometric formula [Al(OH)₃](_1?x)[SiO₂]_x and varies linearly with pH of the solution. The atoms of Al, O and H tend to occupy a fixed position in the solid given by the gibbsite structure upon aging in the field. The solubility product of the solid is estimated from the published data on experimental and field research into the dissolution of feldspars: logK = (1 ? x) × log [Al³⁺] + xlog [H₄SiO₄] ? (3 ? 3x) log [H⁺] = 8.56 ? 11.26x, where x is the molar fraction of silica in the aluminosilicate.     

Potassium leaching in undisturbed soil cores following surface applications of gypsum

Displacement studies on leaching of potassium (K⁺) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and 25 cm long). Pulses of K⁺ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl₂) at a rate of 18 mm h⁻¹. The movement of K⁺ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM CaCl₂. The Ca²⁺ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K⁺ was displaced with the distilled water, K⁺ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow and lack of K⁺ sorption. The application of gypsum and CaCl₂ in the reclamation of sodic soils would be expected to leach K⁺ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca²⁺ concentration can also lead to leaching of K⁺ from soil. Average effluent concentration of K⁺ during leaching period was 30.2 and 28.6 mg l⁻¹ for the gypsum and CaCl₂ treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation (12 mg K⁺ l⁻¹).     

Effect of a native forest canopy on rainfall chemistry in China’s Qinling Mountains

This study investigated the effect of a pine/oak forest canopy on rainfall chemistry in the Qinling Mountains. The area is an important water source for China’s North-to-South Water Transfer Project. Rainfall and throughfall samples were collected at the Huoditang Natural Forest in 1999, 2004, and 2009. Analyses of the samples indicated that the forest canopy had several important effects on rainfall chemistry. Rainfall pH generally increased as water passed through the canopy. On average, the rainfall pH increased by 0.54 pH units. The canopy’s effect declined after deciduous trees lost their leaves late in the sampling season. Rainfall NO₃ ^? concentrations generally declined as water passed through the forest canopy, but PO₄ ^3? concentrations generally increased. On average, rainfall NO₃ ^? concentration declined by 0.135 mg/L as it passed though the forest canopy and PO₄ ^3? increased by 0.85 mg/L. The forest canopy had a mitigating effect on the base cation content of throughfall. Specifically, K⁺, Na⁺, Ca²⁺ and Mg²⁺ were leached from the canopy when the concentration of these cations in rainfall was low. In contrast, K⁺, Na⁺, Ca²⁺ and Mg²⁺ were absorbed by the canopy when the concentration of these cations in rainfall was high. The pH of rainfall, as well as its K⁺, Ca²⁺ and Mg⁺ concentration, influenced the effect of the forest canopy on the base cation content of throughfall. The concentration of Cd, Pb, and Zn in rainfall generally decreased as water passed through the forest canopy, but the concentration of Fe in rainfall generally increased. The Cd concentration decreased by an average of 3.938 μg/L, the Pb concentration decreased by an average of 8.457 μg/L, and the Zn concentration decreased by an average of 0.986 mg/L. The Fe concentration increased by an average of 0.009 mg/L. The canopy’s ability to absorb Cd declined after several rainfall events in which rainfall Cd concentrations were relatively high.     

Percolation flux and transport velocity in the unsaturated zone,Yucca Mountain,Nevada

The percolation flux for borehole USW UZ-14 was calculated from ¹⁴C residence times of pore water and water content of cores measured in the laboratory. Transport velocity is calculated from the depth interval between two points divided by the difference in ¹⁴C residence times. Two methods were used to calculate the flux and velocity. The first method uses the ¹⁴C data and cumulative water content data directly in the incremental intervals in the Paintbrush nonwelded unit and the Topopah Spring welded unit. The second method uses the regression relation for ¹⁴C data and cumulative water content data for the entire Paintbrush nonwelded unit and the Topopah Spring Tuff/Topopah Spring welded unit. Using the first method, for the Paintbrush nonwelded unit in borehole USW UZ-14 percolation flux ranges from 2.3 to 41.0 mm/a. Transport velocity ranges from 1.2 to 40.6 cm/a. For the Topopah Spring welded unit percolation flux ranges from 0.9 to 5.8 mm/a in the 8 incremental intervals calculated. Transport velocity ranges from 1.4 to 7.3 cm/a in the 8 incremental intervals. Using the second method, average percolation flux in the Paintbrush nonwelded unit for 6 boreholes ranges from 0.9 to 4.0 mm/a at the 95% confidence level. Average transport velocity ranges from 0.6 to 2.6 cm/a. For the Topopah Spring welded unit and Topopah Spring Tuff, average percolation flux in 5 boreholes ranges from 1.3 to 3.2 mm/a. Average transport velocity ranges from 1.6 to 4.0 cm/a. Both the average percolation flux and average transport velocity in the PTn are smaller than in the TS/TSw. However, the average minimum and average maximum values for the percolation flux in the TS/TSw are within the PTn average range. Therefore, differences in the percolation flux in the two units are not significant. On the other hand, average, average minimum, and average maximum transport velocities in the TS/TSw unit are all larger than the PTn values, implying a larger transport velocity for the TS/TSw although there is a small overlap.     

An SF<Subscript>6</Subscript> Tracer Study of the Flow Dynamics in the Stockton Deep Water Ship Channel: Implications for Dissolved Oxygen Dynamics

A sulfur hexafluoride (SF₆) tracer release experiment was conducted in the Stockton Deep Water Ship Channel (DWSC) to quantify mixing and transport rates. SF₆ was injected in the San Joaquin River upstream of the DWSC and mapped for 8 days. From the temporal change in SF₆ distributions, the longitudinal dispersion coefficient (K _x ) was determined to be 32.7 ± 3.6 m² s⁻¹ and the net velocity was 1.75 ± 0.03 km day⁻¹. Based on the decrease in SF₆ inventory during the experiment, the pulsed residence time for waters in the DWSC was estimated at ∼17 days. Within the DWSC from Stockton downstream to Turner Cut, dissolved oxygen concentrations maintained a steady state value of 4 mg l⁻¹. These values are below water quality objectives for the time of year. The low flow rates observed in the DWSC and the inability of oxygen-rich waters from downstream to mix into the DWSC upstream of Turner Cut contribute to the low dissolved oxygen concentration.     

A two-phase model for the description of the influence of cracks on the P- and S-wave velocities in dry and saturated rock samples

The premonitory variations of seismic-wave velocities before earthquakes originate from various cracking processes before the fracture. It can be shown that these variations are comparable with wave-velocity variations in porous model samples with defined pore sizes. Furthermore, it is possible to describe analytically the variation of wave velocities as a function of the parameter K₀, which describes the fracturing process, and a material/depth parameter AP. On the basis of the wave velocity vs. pressure curves of rocks, it is possible to determine K₀ and A. Using the material/depth parameter AP sediments in covering strata and eruptive rocks in regions of earthquakes of shallow to medium depth can be descirbed. A relationship between Δυ_D and ΔK₀ can be established. For acid to ultrabasic rocks, a variation of up to 2 km/s indicates a variation of K₀ of 0.1–1.0.Moreover, it is possible to establish a relationship between K₀ and the number as well as the mean length of cracks in the rock. The solutions differ depending on the cracks being closed or open. For closed cracks a wave-velocity minimum of 6% results. For oper cracks the variations of the number and mean length of cracks are taken into account by means of a stochastic process; the resulting variations of K₀ and the wave velocity car adequately explain the variations in seismic-wave velocity. Variations of the pore pressure have an influence on K₀and the wave velocity only under most favourable geologica conditions; generally they are insignificant. Also for S-wavc velocities and for the ratio υ_p/υ_s the wave velocity vs. pressure equations are valid; it is possible to state K₀ and A-values.     

Hydrogeochemical investigation and qualitative assessment of surface water resources in West Bokaro coalfield,India

A hydrogeochemical study of surface water of the West Bokaro coalfield has been undertaken to assess its quality and suitability for drinking, domestic and irrigation purposes. For this purpose, fourteen samples collected from rivers and ponds of the coalfield were analysed for pH, conductivity, total dissolved solids (TDS), major cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺), major anions (HCO₃^-, F^-, Cl^-, SO₄^2- and NO₃^-) and trace metals. The pH of the analysed water samples varied from 7.3 to 8.2, indicating slightly alkaline in nature. The electrical conductivity (EC) value varied from 93 μs cm^-1 to 906 μs cm^-1 while the TDS varied from 76 mg L^-1 to 658 mg L^-1. HCO₃^- and SO₄^2- are the dominant anion and Ca²⁺ and Na⁺ the cation in the surface water. The concentration of alkaline earth metals (Ca²⁺ + Mg²⁺) exceed the alkali metals (Na⁺ + K⁺) and HCO₃^- dominates over SO₄^2- + Cl^- concentrations in the majority of the surface water samples. Ca²⁺ -Mg²⁺ -HCO₃^- and Ca²⁺ -Mg²⁺ -Cl^- are the dominant hydrogeochemical facies in the surface water of the area. The water chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. For quality assessment, analyzed water parameter values compared with Indian and WHO water quality standard. In majority of the samples, the analyzed parameters are well within the desirable limits and water is potable for drinking purposes. However, concentrations of TDS, TH, Ca²⁺, Mg²⁺ and Fe are exceeding the desirable limits in some water samples and needs treatment before its utilization. The calculated parameters such as sodium absorption ration, percent sodium, residual sodium carbonate, permeability index and magnesium hazard revealed good to permissible quality and suitable for irrigation purposes, however, higher salinity, permeability index and Mg-ratio restrict its suitability for irrigation at few sites.     

Estimation of shearwave velocity in drifts using multichannel analysis of surface wave (MASW) technique — A case study from Jammu & Kashmir,India

Multichannel analysis of surface waves (MASW) is a non-destructive seismic prospecting method utilizing Rayleigh waves for imaging and characterizing shallow sub-surface structure. Multichannel analysis of surface waves (MASW) studies were conducted in drift areas of two bridge sites in the hilly terrain of J&K for imaging and characterizing shallow sub-surface structure. The purpose of the present study is to estimate the shear wave velocity (V_S) and subsurface structure in four drifts made in a hilly terrain for construction of two bridges. Rayleigh waves are having dispersive properties, travelling along or near the ground surface and are usually characterized by relatively low velocity, low frequency, and high amplitude. The study area comprises of Tertiary group of rocks which are underlain by Siwalik group. The main rock type in the study area is dolomite which has undergone various geological processes like weathering, jointing, fracturing and shearing. MASW data was collected inside four drifts in the mountainous terrain of J&K state which are located on either sides of Chenab river. The data was analyzed by relevant processing software using dispersion and inversion technique. Shear wave velocities were estimated up to 30 m depth. Average shear wave velocity (V_S ³⁰) up to top 30m was also computed. It is observed that, V_S in the range 400–800 m/s upto 10–15 m corresponding to weathered rock, followed by compact dolomite rock up to the depth of about 30 m with V_S in the range 1200–1600 m/s. Some low velocity zones are also identified from these sections which represent shear zones.     

Detection of radio emission from the AXP 4U 0142+61

The detection of pulsed radio emission from the X-ray pulsar AXP 4U 0142+61 with a period of P = 8.68832935(6) s and a period derivative of $ \dot P $ \dot P = 18.713(4) × 10⁻¹³ s/s is reported. The observations were carried out on two high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory: the Large Phased Array at 111MHz and the DKR-1000 at 40MHz.Mean pulse profiles are presented; the measured flux density is S ₁₁₁ = 30 ± 20 mJy. The estimated distance derived from the dispersion measure, 27 pc/cm³, is 1.4 kpc, and the integrated radio luminosity is L _R = 1.5 × 10²⁷ erg/cm. Comparison with X-ray data shows an appreciable difference in the pulse duration (the radio pulse is about a factor of 20 more narrow) and strong variations in the flux density.     

Application of a new approach to the calculation of electrostatic energies of expanded Di- and trioctahedral micas

The electrostatic lattice energies of expanded and unexpanded micas are calculated starting from a “generic” structure the ionic charges of which are varied. The mode of expansion is to move the layers apart perpendicular to (001), the K⁺ ions remaining midway between the layers. The energy required for expansion is a quadratic function of the layer charge. It is larger when the layer charge is in the octahedral sites (K _x Al_2?x Mg _x Si₄O₁₀(OH)₂) than when it is in the tetrahedral sites (K _x Mg₃Si_4?x Al _x O₁₀(OH)₂). Fluormicas have a slightly larger expansion energy than OH-micas. With the tetrahedral layer charge, dioctahedral micas have a slightly larger expansion energy than trioctahedral micas. This mode of expansion is less favourable than the mode usually adopted, viz. an expansion whereby the K ions divide themselves between the layers. The energy difference increases with the separation distance and is about 60 kJ mol^?1 at 2.5 Å expansion. An intercalated water layer would be necessary to stabilize the K ions in positions midway between the layers.     

Characterization of hydrogeochemical process and evaluation of water quality of seven geothermal springs,Bakreswar, India

A study was conducted in seven geothermal springs located in Bakreswar, District Birbhum, West Bengal, India, in order to assess numerous geochemical processes which were responsible for chemical composition of thermal and mineralized water. The study area lies over the Sone, Narmada, and Tapti lineament of Precambrian Chotanagpur Gneissic Complex. Water chemistry has been carried out based on reaction stoichiometry and geo-statistical tools to identify geochemical process. Piper and Gibbs diagram suggest that the spring water belongs to Ca²⁺-Mg²⁺-HCO₃^??+?CO₃^2? water type and are controlled by rock dominance. Dissolution and precipitation of calcite, dolomite, gypsum, and fluorite minerals were identified as principle source of major ions in seven geothermal spring water. Principle component analyses revealed that major ions of spring water are derived from geogenic processes such as weathering, dissolution, and precipitation of various minerals. Overall results suggest that major ions of the spring’s water are derived from natural origin because no evidence of anthropogenic sources was observed during the study period. This study has also revealed that water quality of spring’s water is not suitable for drinking purposes and quite suitable for irrigation because of high abundance of Na⁺, K⁺, Cl^?, and HCO₃^? ions.     

In situ Mössbauer spectroscopy: Evidence for green rust (fougerite) in a gleysol and its mineralogical transformations with time and depth

A miniaturized Mössbauer spectrometer, adapted to the Earth’s conditions from the instrument developed for Mars space missions, has been used for the first time to study in situ variations with depth and transformations with time of iron minerals in a gleysol. The instrument is set into a PVC tube and can be moved up and down precisely (±1 mm) at the desired depth. Mössbauer spectra were obtained from 15 to 106 cm depth and repeated exactly at the same point at different times to follow mineralogical transformations with time. X-ray diffraction (XRD) and selective extraction techniques were performed on soil samples. The piezometric level of the water table was measured and the composition of the soil solution was monitored in situ and continuously, with a multiparametric and automatic probe. All the Mössbauer spectra obtained are characteristic of Fe(II)-Fe(III) green rust-fougerite, a natural mineral of the meixnerite group, that is, whose structural formula is: [Fe_{1 − x}^II Mg_y Fe_x^III (OH)_2+2y]^x+[xA, mH₂O]^x−, where x is the ratio Fe³⁺/Fe_tot. and A the intercalated anion. The name of fougerite has been formally approved by the Commission on New Minerals and Mineral Names of IMA (number 2003-057), on January 29, 2004. No other iron phases have been found by this way or by XRD. About 90% of total iron is extractible by dithionite-citrate-bicarbonate, and 60% by citratebicarbonate. In the horizons showing oximorphic properties that are in the upper part of the studied soil profile, x ratio in fougerite, deduced from Mössbauer spectra, is approximately 2/3. In the deepest horizons that show reductomorphic properties, x ratio is only 1/3. Fast mineralogical transformations were observed at well-defined points in soil, as evidenced by x ratio variations observed when Mössbauer spectra were acquired at different times at the same depth. Variations of the level of the water table and of pe and pH of the soil solution were simultaneously observed and could explain these mineralogical transformations. A ternary solid solution model previously proposed for OH-fougerite has been extended to chloride, sulphate, and carbonate green rusts to estimate the Gibbs free energies of formation of fougerite, providing for possible anions other than OH⁻ in the interlayer and for Mg substitution. Soil solutions appear as largely oversaturated with respect to OH-fougerite, either oversaturated or undersaturated to “carbonate-fougerite” and “sulphate-fougerite”, and largely undersaturated with respect to “chloro-fougerite”. Fougerite forms most likely from oversaturated solutions by coprecipitation of Fe³⁺ with Fe²⁺ and Mg²⁺. Oxidation and reduction are driven by pH and pe variations, with both long timescale variations and short duration events. Exactly as synthetic green rusts are very reactive compounds in the laboratory, fougerite is thus a very reactive mineral and readily forms, dissolves, or evolves in soils.     

Solid–water partitioning of elements in Czech freshwaters

Partitioning of 41 elements between solids and water was studied by filtration and dialysis in situ in Czech freshwaters. Field-based distribution (partition) coefficients, K_D, between suspended particulate matter (SPM) and filtrate (‘dissolved’ fraction) differed by 4 orders of magnitude. The highest K_D values (log K_D>2.0 l/g) were exhibited by Zr, Al, Ce, Pb, La, Ti, Fe, Sm, Th and Cr which are extremely insoluble in near-neutral water or generally poorly soluble (Zr,Ti). The K_Ds decrease with element and DOC loading due to the relative increase of the element in the low molecular fraction. Log K_D mostly increased linearly with pH within a range from 3.5 to 9. K_D^U decreased at pH >6 due to carbonate complexation. The colloidal fraction (>1 kDa <0.4 μm) in a reservoir with a pH of 6.8 was mainly preferred by Fe, Pb, Be, Nb, Y, Al, Ni, U and Zr. When the colloidal fraction is not differentiated from true solution, then incorrect information about partitioning may be obtained and the highest K_D may decrease.     

Numerical modeling of the June 24, 2015, Hongyanzi landslide generated impulse waves in Three Gorges Reservoir,China

Subaerial landslides falling into confined water bodies often generate impulsive waves. Damaging landslide tsunamis in Three Gorges Reservoir, China, have struck several times in the last 15 years. On June 24, 2015, a 23?×?10⁴ m³ slope failure occurred on the east bank of the Daning River opposite Wushan Town. The sliding mass intruded into the Three Gorges Reservoir and initiated a reservoir tsunami that resulted in two deaths and significant damage to shipping facilities. A post-event survey revealed the landslide geometry and wave run-up distribution, while an eyewitness video captured most of the landslide motion. Employing these firm constraints, we applied the Tsunami Squares method to simulate the 2015 Hongyanzi landslide and tsunami. The simulation revealed that the landslide experienced a progressive failure in the first few seconds and impacted the water with a maximum velocity of ~?16 m/s. The initial wave propagated to the opposite shore in an arch shape, and the water surface reached a maximum amplitude of ~?11 m near the landslide. Wave amplitude-time curves at four points on the river cross section show that the initial wave reached Wushan town in about 50 s with an average wave velocity of ~?30 m/s. The maximum wave run-ups on the shoreline opposite the landslide are around 6 m and attenuate to less than 1 m beyond 2-km distance. The landslide simulation matches the observed geological profile and the eyewitness video, and the numerical results coincide with the observed wave run-up heights. Nearly 80% of landslide energy is lost due to frictional resistances, but the remaining fraction imparted to the tsunami carried catastrophic consequences to a large region. The numerical results emphasize the efficiency and accuracy of Tsunami Squares method for a “Quick Look” simulation of a potential landslide.     

Single crystal absorption spectra of synthetic Ti,Fe-substituted pyropes

Synthetic pyrope crystals up to 0.5 mm in diameter, substituted by titanium or by titanium plus iron, were grown under defined conditions of P, T, $f_{O_2 }$ in the presence of water using a piston-cylinder device. The crystals were characterized by X-ray and microprobe techniques. Their single-crystal optical absorption spectra were measured by means of a microscope-spectrometer. Two absorption bands at 16100 and 22300 cm{cm-1} in the spectra of pale-blue Fe-free Ti-bearing pyropes, grown under reduced conditions, were identified as originating from spin-allowed transitions, derived from ² T _2g → ² E _g of octahedral Ti³⁺ ions. The splitting value of the excited ²E _g state, 6200 cm^-1, and the crystal field parameter of Ti³⁺ in pyrope Δ ₀ = 19 200 cm^-1 are both in agreement with literature data. In spectra of brown Fe, Ti-bearing garnets, a broad band at 23000 cm^-1 was interpreted as a Fe^2+[8] → Ti^4+[6] charge-transfer band. The spectral position and width of this band agree with those observed for a FeTi charge transfer band in natural garnets. Fe, Ti-containing garnets synthesized at relatively high oxygen fugacity (10^-11,0 atm), which permits a fraction of Fe³⁺ to enter the garnet, show an additional Fe^2+[8] → Fe^3+[6] charge transfer band at 19800 cm^-1.     

Contrasting the sorption of Zn by oxyhydroxides of Mn and Fe,and organic matter along a mineral-poor to mineral-rich fen gradient

The geochemistry of Mn and Fe in surface pools, pore-waters and surface peats and the sorption of Zn by the surface peats was contrasted among 15 peatlands sampled along a mineral-poor to mineral-rich fen gradient. Sorption of Zn by surficial peats was compared via distribution coefficients, both total (K_DT) and partial (K_DERMn, K_DRFe and K_DORG), where ER Mn, R Fe and ORG are amounts of Zn recovered from the easily reducible Mn oxides, reducible Fe oxides, and organic components of peat, respectively. Apparent stability constants (K_As) for Zn sorption onto oxides of Fe recovered from the surface peats were also calculated and compared along the same gradient. Peat geochemistry was peatland dependent; mineral-poor fens had less easily reducible Mn and greater amounts of organic matter (%Loss on Ignition; LOI) versus mineral-rich fens (range of 0.66–8.6 mm kg⁻¹ for ER Mn and 20–88% LOI for organic matter). Reducible Fe also varied among peatlands (range 51–315 mm kg⁻¹) but was independent of the mineral-poor to mineral-rich fen gradient. Comparison of partial K_Ds for amounts of Zn sorped onto the ER Mn, R Fe and ORG components of peat indicated that sorption was dominated by R Fe in all peatlands. K_DTs ranged from 0.54–2.00. In contrast to other aquatic systems, however, the range in K_DTs was not related to either surface or pore-water pH. K_As ranged from 0.36 to 3.06 and were also independent of surface or pore-water pH. However, average K_As (but not K_DTs), were greater for mineral-poor fens (P<0.02), suggesting greater Zn binding by surface peats of mineral-poor fens versus either the moderately poor or mineral-rich peatlands. Other water chemistry variables, such as pore-water base cation concentrations, weakly correlated to Zn partitioning onto R Fe (r=−0.35, P=0.05), but did not fully explain differences in Zn partitioning among peatlands. Greater average K_As for the mineral-poor peatlands may in part be due to the presence of strong metal-organic matter-Fe oxide complexes in the Sphagnum dominated peatlands as well as lower pore-water base cation concentrations that occur in the mineral-poor peatland as compared to the more mineral-rich fens.     

Influence of magnetic fabric anisotropy on seismic wave velocity in paramagnetic granites from NW Himalaya: Results from preliminary investigations

Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO₂ content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (K_m) having ‘r’ value of 0.86. The correlation between Vs-K_m, V_p-P′, V_p-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, V_p is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone.     

Entrainment of planktonic foraminifera: effect of bulk density

Depositional hydrodynamics have been studied using settling rate distributions of Norwegian deep sea sediments (between Jan Mayen Island and the Vøring Plateau), together with Shields’ critical shear stress velocities. Planktonic foraminifera are the dominant sand sized component of these sediments. The bulk density of the foraminifera was calculated from their settling velocity, sieve size and shape. Density decreases from 2·39 g cm^?3 at 0·05 mm diameter to 1·37 g cm^?3 at 0·35 mm diameter. These density and size data were used to construct a threshold sediment movement curve. From the similarity in their Shield's critical shear-stress velocities and the observed correlation of foraminifera size with decreasing percentage of fine fraction, it is concluded that the two components, the sand size foraminifera and the quartz and carbonate silt, are transport-equivalent.