Polarized electronic absorption spectra of 3d3-configurated tetravalent manganese in octahedral fields of Mn(SeO3)2

Polarized optical absorption spectra of Mn(IV) in octahedral crystal fields of Mn(SeO₃)₂ have been studied by means of microscope-spectrometry in the range 40000-4000 cm^?1 and at temperatures between 113 K and 293 K. Intense charge-transfer absorptions (linear absorption coefficient α ? 30000 cm^?1) completely mask the d-d transitions in the UV and VIS region above ≈23000 cm^?1. The optical electronegativity χ _opt of Mn(IV) in Mn(SeO₃)₂ is estimated to be 2.7. In accordance with the d ₃ configuration of tetravalent manganese three d-d bands observed at ambient temperatures at 13250, 14137 (α≈50 cm^?1) and ≈18500 cm^?1 (α≈500–800 cm^?1) are assigned to the spin forbidden ⁴ A _2g →² E _g and ⁴ A _2g →² T _1g transitions as well as to the first spin allowed ⁴ A _2g →⁴ T ^2g transition, respectively. These assignments allow the calculation of the following ligand field parameters: Dq ≈ 1850 cm^?1, B ₅₅ = 869 cm^?1 (β ₅₅ = 0.82), and C = 2346 cm^?1 (293 K).     

Matrix corrections in trace-element analysis by X-ray fluorescence: An extension of the Compton scattering technique to long wavelengths

Mass absorption coefficients (A₂) for a series of standard rocks, have been calculated in the wavelength region 0.492–3.03 $\text{a}\text{?}$. Plots of these data against the intensity of the Compton scattered peak [(I) Compton] give an excellent correlation for the wavelengths 0.429 $\text{a}\text{?}$ to the Fe-absorption edge (1.74 $\text{a}\text{?}$); the data confirm the observations of Reynolds. Hence, routine measurement of one peak will give the mass absorption coefficient of a sample in an analytically important region (Sn/1bK_α to Ni/1bK_α). A₂ has also been directly measured on three of the samples and systematic differences between calculated and measured are attributed to the measuring technique. At wavelengths longer than the Fe-absorption edge, (up to 3.03 $\text{a}\text{?}$) A₂ can be estimated using a combination of (I) Compton and Fe/1bK_α c.p.s. This technique enables meaningful matrix corrections to be carried out on the elements Co, Mn, Cr, V, Ti, Sc (K spectra) and Ba (L spectra). Cr and Ba results are presented for some standard rocks.     

Diversity of Mn oxides produced by Mn(II)-oxidizing fungi

Manganese (Mn) oxides are environmentally abundant, highly reactive mineral phases that mediate the biogeochemical cycling of nutrients, contaminants, carbon, and numerous other elements. Despite the belief that microorganisms (specifically bacteria and fungi) are responsible for the majority of Mn oxide formation in the environment, the impact of microbial species, physiology, and growth stage on Mn oxide formation is largely unresolved. Here, we couple microscopic and spectroscopic techniques to characterize the Mn oxides produced by four different species of Mn(II)-oxidizing Ascomycete fungi (Plectosphaerella cucumerina strain DS2psM2a2, Pyrenochaeta sp. DS3sAY3a, Stagonospora sp. SRC1lsM3a, and Acremonium strictum strain DS1bioAY4a) isolated from acid mine drainage treatment systems in central Pennsylvania. The site of Mn oxide formation varies greatly among the fungi, including deposition on hyphal surfaces, at the base of reproductive structures (e.g., fruiting bodies), and on envisaged extracellular polymers adjacent to the cell. The primary product of Mn(II) oxidation for all species growing under the same chemical and physical conditions is a nanoparticulate, poorly-crystalline hexagonal birnessite-like phase resembling synthetic δ-MnO₂. The phylogeny and growth conditions (planktonic versus surface-attached) of the fungi, however, impact the conversion of the initial phyllomanganate to more ordered phases, such as todorokite (A. strictum strain DS1bioAY4a) and triclinic birnessite (Stagonospora sp. SRC1lsM3a). Our findings reveal that the species of Mn(II)-oxidizing fungi impacts the size, morphology, and structure of Mn biooxides, which will likely translate to large differences in the reactivity of the Mn oxide phases.     

Defining manganese(II) removal processes in passive coal mine drainage treatment systems through laboratory incubation experiments

Oxic limestone beds are commonly used for the passive removal of Mn(II) from coal mine drainage (CMD). Aqueous Mn(II) is removed via oxidative precipitation of Mn(III/IV) oxides catalyzed by Mn(II)-oxidizing microbes and Mn oxide (MnO_x) surfaces. The relative importance of these two processes for Mn removal was examined in laboratory experiments conducted with sediments and CMD collected from eight Mn(II)-removal beds in Pennsylvania and Tennessee, USA. Sterile and non-sterile sediments were incubated in the presence/absence of air and presence/absence of fungicides to operationally define the relative contributions of Mn removal processes. Relatively fast rates of Mn removal were measured in four of the eight sediments where 63–99% of Mn removal was due to biological oxidation. In contrast, in the four sediments with slow rates of Mn(II) removal, 25–63% was due to biological oxidation. Laboratory rates of Mn(II) removal were correlated (R² = 0.62) to bacterial biomass concentration (measured by phospholipid fatty acids (PLFA)). Furthermore, laboratory rates of Mn(II) removal were correlated (R² = 0.87) to field-scale performance of the Mn(II)-removal beds. A practical recommendation from this study is to include MnO_x-coated limestone (and associated biomass) from an operating bed as “seed” material when constructing new Mn(II)-removal beds.     

The surface chemistry of sediments from the Panama Basin: The influence of Mn oxides on metal adsorption

The solid Mn content of sediments at a site in the Panama Basin (5°21′N 81°56′W) decreases from 3.9% in the interfacial sediment to 1% at 1.5 cm and <0.2% below 5 cm. These conditions provide an opportunity to examine the influence of Mn oxides on the metal adsorption characteristics of natural marine sediments.The adsorption of 14 metals on interfacial sediment and sediment from depths of 0.5 to 3 cm and 15 to 19 cm from the Panama Basin site was studied, and distribution coefficients (K_D) were determined. A comparison of the K_D values for a variety of samples containing different Mn contents (i.e., Panama Basin sediments, MANOP site H interfacial sediment, red clay, and buserite) indicates that an increase in the solid Mn content enhances the ability of the particles to bind certain metals (e.g., Zn, Pb, Co, Cd, and Ba) while the binding ability for other metals (e.g., Cs, Be, Sc, Pu, Sn, and Fe) is not significantly affected. For the Panama Basin sediment, the K_D values for Ni, Co, Cd, Ba, and Mn for the Mn enriched interfacial sediment are 5 to 23 times greater than the K_D values for the Mn depleted deep sediment. The K_D values for Cs, Be, Sc, Pu, and Fe for the two types of sediment are essentially the same. The correlation between the Mn content and the binding ability of the sediment for particular metals coincides with the Mn-metal correlations observed in bulk compositional data for ferromanganese nodules and sediments. This implies that the observed metal enrichments in nodules or hemipelagic sediments are most likely caused by preferential adsorption of the metals by Mn enriched phases.     

Rapid, oxygen-dependent microbial Mn(II) oxidation kinetics at sub-micromolar oxygen concentrations in the Black Sea suboxic zone

Microbial Mn(II) oxidation kinetics in response to oxygen concentration were assessed in suboxic zone water at six sites throughout the Black Sea. Mn(II) oxidation rates increased asymptotically with increasing oxygen concentration, consistent with Michaelis-Menten enzyme kinetics. The environmental half-saturation constant, K_E, of Mn(II) removal (oxidation) varied from 0.30 to 10.5 μM dissolved oxygen while the maximal environmental rate, V_E−max, ranged from 4 to 50 nM h⁻¹. These parameters varied spatially and temporally, consistent with a diverse population of enzymes catalyzing Mn oxide production in the Black Sea. Coastally-influenced sites produced lower K_E and higher V_E−max constants relative to the Western and Eastern Gyre sites. In the Bosporus Region, the Mn(II) residence time calculated using our K_E and V_E−max values with 0.1 μM oxygen was 4 days, 25-fold less than previous estimates. Our results (i) indicate that rapid Mn(II) oxidation to solid phase Mn oxides in the Black Sea’s suboxic zone is stimulated by oxygen concentrations well below the 3-5 μM concentration reliably detected by current oceanographic methods, (ii) suggest the existence of multiple, diverse Mn(II)-oxidizing enzymes, (iii) are consistent with shorter residence times than previously calculated for Mn(II) in the suboxic zone and (iv) cast further doubt on the existence of proposed reactions coupling solid phase Mn oxide production to electron acceptors other than oxygen.     

Manganese chemistry in rivers and streams

The speciation of Mn has been determined in 15 rivers and streams representing a wide variety of physico-chemical conditions. Using the technique of anodic stripping voltammetry (asv), specific for reduced Mn(II) species, it is found that a major part of the <0.015 μm Mn size fraction is present in a reduced Mn(II), asv-labile, form. In some waters there is also a significant asv inactive Mn fraction considered to be present as a ‘small colloidal’ species. The soluble (<0.015 μm) Mn fraction represents 15–95% of total Mn and does not appear to be dependent upon pH, alkalinity, specific conductance or humic substance concentration in the water. It is argued that under the dynamic, short residence time, conditions that apply in most rivers the paniculate and soluble Mn fractions are decoupled, their respective presence being dependent principally upon the catchment hydrogeological conditions. This contrasts with a previously held view that the paniculate phase is coupled to the dissolved phase by the pH dependent oxidation of dissolved Mn(II) to highly insoluble Mn(IV) species (Graham et al., 1976). Consideration of manganese speciation in waters which were incubated for five months showed that pH becomes the controlling factor when equilibrium is approached.     

Simultaneous incorporation of Mn and Al in the goethite structure

Two series of (Al,Mn)-substituted goethites were synthesized from ferrihydrite made in alkaline media, with different Al/Mn mole ratios ([Al + Mn]/Fe molar ratio up to 0.12). Powder X-ray diffraction and extended X-ray absorption fine structure (EXAFS) techniques were used to assess the structural characteristics of the simultaneous substitution in goethite. XRD patterns revealed that all the obtained solids remain in a goethite-like structure. Rietveld refinement of X-ray diffraction data indicates that the increasing Mn substitution and consequent decrease of Al substitution causes an increase in the unit cell volume. This change is accompanied by the increment of the various Me-Me distances. XANES spectra at the Al and Mn K-edge confirm the octahedral coordination of Al and the trivalent oxidation state of the Mn ion in all the synthesized samples. EXAFS spectra at the Fe K-edge indicate that the local order around the Fe atom remains practically constant upon (Mn,Al) substitution. Measurements in the Mn K-edge show that distances Mn-Me suffer different changes with the increase in Mn substitution: a marked decrease in E and a slight decrease in E′, while DC remains constant. E and E′ values correspond to the distance between one Mn and one neighboring Me (Fe, Mn, Al) atom, both situated in two polyhedra linked by an edge. These polyhedra belong to the same double row of the goethite structure. DC value corresponds to the distance between one Mn and one Me (Fe, Mn, Al) atom, situated in two octahedral linked by one corner and belonging to two adjacent double chains. All the intermetallic distances are minor than the corresponding singly substituted goethites, this fact is attributed to the structure contraction due to the presence of Al(III) which restrains the axial distortion of Mn. Dissolution-time curves, resulting from exposure to 6 M HCl at 318 K, show that the dissolution rate slows with increasing Al substitution and consequent decrease of Mn substitution, and the shape of the curve becomes increasingly sigmoidal for mixed goethite with large Al content and Al-goethite. Dissolution kinetics of most samples are well described by the Kabai equation. Al dissolves almost congruently with respect to Fe, implying that it is homogeneously distributed in the structure. However, the convex χ_Mn:χ_Fe curve indicates that Mn tends to be concentrated in the outer layers of the goethite particles.     

Using cocrystallization coefficients of isomorphous admixtures for determination of element concentrations in ore-forming solutions (by the example of Mn/Fe ratio in magnetite)

The cocrystallization coefficient of Mn and Fe (D_Mn/Fe) in magnetite crystals is determined in hydrothermal-growth experiments with internal sampling at 450 and 500 °C and 100 MPa (1 kbar). It is weakly dependent on temperature in the studied PT-region and is constant over a wide range of Mn/Fe values. This permits using the magnetite composition as an indicator of Mn/Fe in the fluid under equilibrium: (Mn/Fe)_aq ≈ 100 (Mn/Fe)_mt. Since Mn is often a macrocomponent of the fluid and a microcomponent of magnetite, local analysis of fluid inclusions for Mn might help to determine Fe even in iron minerals. This will permit evaluation of the contents of other ore metals if the D_Me/Fe values are known. For fine crystals (< 0.1–0.2 mm) with low contents of Mn (< 0.01–0.02%), it is necessary to take into account the fractionation of Mn into the surficial nonautonomous phase, in which its content can reach several percent. Comparison of these data with earlier data on the distribution of Mn in the system magnetite–pyrite–pyrrhotite–greenockite–hydrothermal solution shows that D_Mn/Fe remains constant in the presence of sulfur and sulfides. Precipitation of magnetite, in which Mn is a compatible admixture, cannot affect radically Mn/Fe in the solution because of the low D_Mn/Fe value. This effect is still more unlikely for pyrrhotite and pyrite, in which Mn is an incompatible admixture. The most probable mechanism of Mn fractionation into the solid phase is crystallization of FeOOH at lower temperatures. This is indirectly supported by the strong fractionation of Mn into the nonautonomous oxyhydroxide phase on the surface of magnetite crystals. The necessity of a more rigorous validation of “the new Fe/Mn geothermometer for hydrothermal systems” is substantiated.     

The search for giant radio galaxies in the PS 102 survey

The possibility of selecting extended radio sources that are potential candidates for giant radio galaxies among objects in the Pushchino catalog at 102 MHz is considered. The method used is based on the analysis of objects in a α ₁–α ₂ diagram, where α ₁ and α ₂ are two-frequency spectral indices (S _ν ～ ν ^?α ), formally calculated using 102–365 and 365–1400 MHz data, based on the identifications of Pushchino radio sources with objects of the Texas (365 MHz) and Green Bank (1400 MHz) catalogs. The calculated spectra are abnormally steep at 102–365 MHz and flat or even inverted at 365–1400 MHz, due to the fact that the 365-MHz flux densities of extended radio sources measured with the Texas radio interferometer are appreciably underestimated. Ten objects among the fifteen Pushchino radio sources selected using this criterion proved to be already known large radio galaxies. The possibility of improving the efficiency of the method by using larger samples and applying some additional criteria selecting candidate giant radio galaxies is considered.     

Pathways of manganese in an open estuarine system

The distribution of Mn was examined in the bottom sediments and water column (suspended paniculate matter) of the Laurentian Trough. Gulf of St. Lawrence. A characteristic profile of Mn with depth in the sediment consisted of a Mn-enriched surface oxidized zone, less than 20 mm thick, and a Mn-depleted subsurface reducing zone. A subsurface Mn maximum occurred within the oxidized zone. Below this maximum the concentration dropped sharply to nearly constant residual levels in the reducing zone. The accumulating estuarine sediments are deficient in Mn compared to the river input of suspended matter and are definitely not the ultimate sink for manganese. Manganese escapes from the sediment by diffusion and resuspension, forming Mn-enriched, fine-grained particles which are flushed out in the estuarine circulation. 5.0 × 10⁹gyr^?1 of Mn, or 50% more than the river input of dissolved Mn. are exported to the open ocean. In spite of the efficient mobilization and export of Mn, the quantity exported is a small fraction (0.2%) of the total flux to the deep-sea sediments. This is related to the low levels of paniculate matter transported by the St. Lawrence River. The export phénomenon, however, is probably true of many coastal regions of muddy sediments and thus has interesting implications for the oceanic budget of Mn.     

The influence of hydrous Mn–Zn oxides on diel cycling of Zn in an alkaline stream draining abandoned mine lands

Many mining-impacted streams in western Montana with pH near or above neutrality display large (up to 500%) diel cycles in dissolved Zn concentrations. The streams in question typically contain boulders coated with a thin biofilm, as well as black mineral crusts composed of hydrous Mn–Zn oxides. Laboratory mesocosm experiments simulating diel behavior in High Ore Creek (one of the Montana streams with particularly high Zn concentrations) show that the Zn cycles are not caused by 24-h changes in streamflow or hyporheic exchange, but rather to reversible in-stream processes that are driven by the solar cycle and its attendant influence on pH and water temperature (T). Laboratory experiments using natural Mn–Zn precipitates from the creek show that the mobilities of Zn and Mn increase nearly an order of magnitude for each unit decrease in pH, and decrease 2.4-fold for an increase in T from 5 to 20 °C. The response of dissolved metal concentration to small changes in either pH or T was rapid and reversible, and dissolved Zn concentrations were roughly an order of magnitude higher than Mn. These observations are best explained by sorption of Zn²⁺ and Mn²⁺ onto the secondary Mn–Zn oxide surfaces. From the T-dependence of residual metal concentrations in solution, approximate adsorption enthalpies of +50 kJ/mol (Zn) and +46 kJ/mol (Mn) were obtained, which are within the range of enthalpy values reported in the literature for sorption of divalent metal cations onto hydrous metal oxides. Using the derived pH- and T-dependencies from the experiments, good agreement is shown between predicted and observed diel Zn cycles for several historical data sets collected from High Ore Creek.     

Environmental contamination of trace elements in the vicinity of Okpara coal mine, Enugu, Southeastern Nigeria

Water, sediment, and mine spoil samples were collected within the vicinity of the Okpara coal mine in Enugu, Southeastern Nigeria, and analyzed for trace elements using ICP-MS to assess the level of environmental contamination by these elements. The results obtained show that the mine spoils and sediments are relatively enriched in Fe, with mean values of 1,307.8(mg/kg) for mine spoils and 94.15% for sediments. As, Cd, Cr, Mn,Ni, Pb, and Zn in the sediments were found to be enriched relative to the mean values obtained from the study area, showing contamination by these elements. The mean values of Fe, Mn, Cu, and Cr in the mine spoils and mean values of Fe, Cu, Pb, Zn, Ni, Cr, and Mn in sediments, respectively, are above the background values obtained from coal and shale in the study area, indicating enrichment with these elements. The water and sediments are moderately acidic, with mean pH values of 4.22?±?1.06 and 4.66?±?1.35, respectively. With the exception of Fe, Mn, and Ni, all other elements are within the Nigerian water quality standard and WHO limits for drinking water and other domestic purposes. The strong to moderate positive correlation between Fe and Cu (r?=?0.72), Fe and Zn (r?=?0.88), and Fe and As (r?=?0.60) at p?<?0.05 as obtained for the sediments depict the scavenging effect of Fe on these mobile elements. As also shows a strong positive correlation with Mn (r?=?≥ 0.70, p?<?0.05), indicating that Mn plays a major role in scavenging elements that are not co-precipitated with Fe. In water, the strong positive correlation observed between Cr and Cd (r?=?1.00), Cu and Ni (r?=?0.94), Pb and Cu (r?=?0.87) and Zn and Cu (r?=?0.99); Ni and Pb (r?=?0.83) and Zn and Ni (r?=?0.97); and between Pb and Zn (0.84) at p?<?0.05 may indicate similar element–water reaction control on the system due to similarities in chemical properties as well as a common source. Elevated levels of heavy metals in sediments relative to surface water probably imply that sorption and co-precipitation on Al and Fe oxides are more effective in the mobilization and attenuation of heavy metals in the mine area than acid-induced dissolution. The level of concentration of trace elements for the mine spoils will serve as baseline data for future reference in the study area.     

Characterization of manganese oxide precipitates from Appalachian coal mine drainage treatment systems

The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnO_x). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20–150 mg/L), system construction (±inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 °C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnO_x precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnO_x precipitates from all sites was coarse and “sponge-like” composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnO_x precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnO_x mineral assemblages in CMD treatment systems.     

Oxidation of manganese by spores of a marine bacillus: Kinetic and thermodynamic considerations

The catalytic properties of spores of a marine Bacillus known to oxidize divalent manganese were used to perform laboratory Mn(II) oxidation experiments at environmental conditions of pH and Mn(II) concentration. We found that at pH 7.8 the initial kinetics of Mn(II) oxidation facilitated by the spores was four orders of magnitude greater than that which would be expected for abiotic autocatalysis on a colloidal MnO₂ surface. The rate progressively decreased as the spores became coated with manganese oxide, eventually becoming very near that predicted for abiotic surface catalysis. Transmission electron microscopic observations and oxidation state measurements of solids precipitated at pH 7.5 and [Mn(II)] < 50 nM indicated that the initial oxidation product was hausmannite (Mn₃O₄ or MnO_x where x = 1.33) which aged to more highly oxidized MnO₂ (x = 1.9) in the time scale of weeks. By utilizing spores to catalyze the oxidation rate, we were able to maintain our experimental system within the seawater range of pH and Mn(II) where highly oxidized manganese oxide precipitates are thermodynamically stable. In doing so we obtained, for the first time, laboratory precipitates with oxidation states similar to that found in marine particulate material. These results suggest that the concentration of manganese in seawater and the oxidation state of marine manganese oxides are controlled by the rapid precipitation of Mn₃O₄, which can be microbially mediated, followed by the disproportionation to MnO₂.     

Kinetics of Mn(II) oxidation by Leptothrix discophora SS1

The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O₂, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 μM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O₂ and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 μM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 μM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈μg/L) concentrations of Mn oxidizing bacteria.     

Oxygen isotopes in synthetic goethite and a model for the apparent pH dependence of goethite-water O/O fractionation

Goethite synthesis experiments indicate that, in addition to temperature, pH can affect the measured value of the ¹⁸O/¹⁶O fractionation factor between goethite and water (α_G-W). A simple model was developed which expresses α_G-W in terms of kinetic parameters associated with the growth of goethite from aqueous solution. The model predicts that, at a particular temperature, the range of pH over which α_G-W changes as pH changes is expected to be comparatively small (∼3 pH “units”) relative to the range of pH values over which goethite can crystallize (pH from ∼1 to 14). Outside the range of sensitivity to pH, α_G-W is predicted to be effectively constant (for constant temperature) at either a low-pH α_G-W value or a high-pH α_G-W value. It also indicates that the values of α_G-W at high pH will be disequilibrium values. Values of α_G-W for goethite crystallized at low pH may approach, but probably do not attain, equilibrium values. For goethite synthesized at values of pH from ∼1 to 2, data from two different laboratories define the following equation for the temperature dependence of 1000 ln α_G-W (T in degrees Kelvin)

(IV)     

Geometrical classification of multilayered folds

A new classification scheme based on the degree of fluctuation in the geometry of different layers of a multilayered fold is suggested. The classification scheme uses the degree of fluctuation in geometry in terms of the standard deviation (σ_n) of the thickness parameters t_α′ (orthogonal thickness parameter) and T_α′ (axial plane parallel thickness parameter) for n number of layers, and dip angle α. The degree of fluctuation in the geometry of a multilayered fold can be represented by σ_n(t_α′) or σ_n(T_α′) versus α plots on a Cartesian plane. In the proposed classification scheme, multilayered folds have been divided into two broad categories, namely `isodeviatoric' and `anisodeviatoric'. Isodeviatoric folds have a constant fluctuation in the geometry of different layers recorded in terms of σ_n(t_α′) or σ_n(T_α′) for α>10°. A special type of isodeviatoric fold is recognised as `analogous fold' in which each layer exhibits identical geometry [σ<sub>n</sub>(t<sub>α</sub>′) or σ<sub>n</sub>(T<sub>α</sub>′)=0]. Plots of isodeviatoric folds lie parallel to the abscissa (α) and those of analogous folds lie along the abscissa in the σ<sub>n</sub>(t<sub>α</sub>′) or σ<sub>n</sub>(T<sub>α</sub>′) (ordinate) versus α (abscissa) diagram. Analogous folds have been divided into ten varieties (1A1, 1A2, 1A3, 1B, 1C, 2, 3A, 3B, 3C and composite-analogous types). The anisodeviatoric folds do not exhibit constant fluctuation (deviation) in the geometry of different constitutive layers. Such folds have been subdivided into `peri-analogous', `sub-analogous', `sub-non-analogous', `non-analogous' and `strongly non-analogous' types. This classification scheme is applied to folds developed in low-grade metasedimentary rocks of the Mahakoshal Group and low- to medium-grade rocks of the Chhotanagpur Granite Gneiss Complex in central India.     

Recycled crust controls contrasting source compositions of Mesozoic and Cenozoic basalts in the North China Craton

We explore Fe/Mn and Nb/Ta ratios of basalts as potential tracers for differentiating melts of recycled mafic crustal lithologies from peridotitic melts. Trace elements and Fe/Mn ratios of the Mesozoic and Cenozoic basalts from East China were analyzed by ICP-MS. Low Nb/Ta ratios (15.4 ± 0.3 (2σ, n = 45)), high Nb and Ta contents (60.1 and 4.01 ppm) and high Fe/Mn ratios (64.7 ± 1.5 (2σ, n = 45)) characterize the <110 Ma basalts. Mesozoic basalts with ages >110 Ma are characterized by superchondritic Nb/Ta ratios (20.1 ± 0.3 (2σ, n = 25)), low Nb and Ta contents (10.8 and 0.54 ppm) and slightly lower Fe/Mn ratios (60.0 ± 1.1 (2σ, n = 25)). Both the Mesozoic and Cenozoic basalts have Fe/Mn ratios higher than basaltic melt formed by partial melting of peridotite at the same MgO and CaO levels. Although both the Mesozoic and Cenozoic basalts are characterized by highly fractionated REE patterns, the >110 Ma basalts have island arc-type trace element patterns (i.e., depletion in Nb and Ta), whereas OIB-type trace element patterns (e.g., no depletion in Nb and Ta) are characteristic of the <110 Ma basalts. Based on D_Fe/Mn values for olivine, clinopyroxene, orthopyroxene and garnet, high Fe/Mn ratios and negative correlations of Fe/Mn with Yb (Y) of the <110 Ma basalts suggest clinopyroxene/garnet-rich mantle sources. The lower Fe/Mn ratios and positive correlations of Fe/Mn with Y and Yb in the >110 Ma basalts suggest orthopyroxene/garnet-rich mantle sources. Combining these data with Sr-Nd isotopes, we present a conceptual model to explain the Nb/Ta ratios and PM-normalized trace element patterns of the >110 and <110 Ma basalts. Preferential melting of recycled ancient lower continental crust during Mesozoic lithospheric thinning resulted in (1) peridotite-melt/fluid reaction that formed the orthopyroxene/garnet-rich mantle sources for the >110 Ma basalts, and (2) peridotite + rutile-bearing eclogite mixing that formed the clinopyroxene/garnet-rich mantle sources for the <110 Ma basalts. The choice of models may indeed be arbitrary and non-unique, but the goal is to seek relatively simple forward models that explain the characteristics of the lavas, and the differences between the >110 and <110 Ma basalts, in a relatively consistent geodynamic framework.     

Estimation of maximum temperature of mudstone by two kinetic parameters; epimerization of sterane and hopane

A geochemical method for estimation of the maximum temperature of mudstones is proposed. The extents of epimerization of the sterane and the hopane are used. The temperature function is:

$\text{T}{}_{\mathrm{max.}}\text{(°C) =}\text{6060}\text{15.0?In(dU}\text{dU}\text{dV)}\text{?273}$

where U = ln (1 ? α/0.54), V = ln(1 ? β/0.61), α = 20S-/20S- + 20R-24-ethyl-5α(H), 14α(H), 17α(H)-cholestane(C₂₉-sterane) and β = 22S-/22S- + 22R-17α(H), 21β(H)-bishomohopane(C₃₂-hopane). The value of dU/dV can be obtained from the tangent to the evolution curve in the UversusV. This temperature function is applicable to the temperature analysis in the range of 50°C–150°C.