TEM investigation of a microcline from a nepheline syenite

Chess-board (“tiled”) microcline crystals from a nepheline-bearing syenite from Ilimaussaq, W. Greenland, were investigated using transmission electron microscopy (TEM) and were found to consist of a mosaic of slightly misoriented domains, which bear no obvious relationship to the optical microstructure. Part of the misorientation of most pairs of neighbouring domains involves a small rotation about c. However, some are related to adjacent domains by the albite twin law, the pericline law, or diagonal association. This microcline could have crystallized with triclinic symmetry which could account for the differences between the microstructure of this microcline and M-twinned microcline. Metasomatism may explain both the optical microscope and TEM scale structures of this microcline. Examination of the electron diffraction patterns of areas of microcline which contain both diagonally associated and twinned domains draw attention to the fact that each of the few orientations in an M-twinned crystal is related to one of the other orientations by diagonal association. The formation of common cross-hatch twinned microstructures are discussed with reference to diagonal association.     

Effects of pH on isotherm modeling and cation competition for Cd(II) and Cu(II) biosorption on Myriophyllum spicatum from aqueous solutions

The biosorption characteristics of Cd(II) and Cu(II) ions from aqueous solutions obtained using submerged aquatic plant (Myriophyllum spicatum) biomass were investigated in terms of equilibrium, kinetics, thermodynamics, and cation competition. Langmuir and Freundlich models were applied to describe the biosorption isotherm of metal ions by M. spicatum biomass and isotherm constants considering the most important parameter, pH. The variation of sorption isotherm constants showed pH dependence. The Langmuir and Freundlich models fitted the equilibrium data well. The maximum biosorption capacity (q _m) of M. spicatum biomass was determined to be 29.07 mg/g for the Cd(II) ion at pH 5.0 and 12.12 mg/g for the Cu(II) ion at pH 6.0. Chi square analysis showed that the Freundlich model fitted the equilibrium data better than the Langmuir isotherm. Competition of Cd(II) and Cu(II) in a binary solution showed that the Langmuir monolayer capacity of Cd(II) decreased from 29.07 mg/g with only Cd(II) in solution to 12.02 mg/g in the presence of Cu(II). Kinetics results showed that the biosorption processes of both metal ions followed the pseudo-second-order kinetics well. The calculated thermodynamic parameters (?G ⁰, ?H ⁰, and ?S ⁰) showed that biosorption of Cd(II) and Cu(II) ions onto M. spicatum biomass was feasible, spontaneous, and endothermic in nature. Fourier transform infrared spectroscopy spectrum analysis revealed that Cd(II) and Cu(II) sorption was mainly ascribed to carboxyl, hydroxyl, amine, and C–N groups in M. spicatum.     

Avian cholera and organochlorine residues in an American oystercatcher

Pasteurella multocida, the causative bacterium of avian cholera, was isolated from cultures of the liver and heart blood of a female, adult American oystercatcher (Haematopus palliatus) found dead on the Cape Romain National Wildlife Refuge, South Carolina, in May 1973. This is apparently the first record of avian cholera in the oystercatcher. Low levels of DDE were identified in tissues of the oystercatcher.     

Manganese deposits in northeastern European Russia and the Urals: Isotope geochemistry,genesis, and evolution of ore formation

Based on new data on the lithology, mineralogy, chemistry, and isotopic composition of manganese carbonate ores and rocks at the deposits and occurrences in the Novaya Zemlya Archipelago, the Pai-Khoi, and the Urals, as well as using data from the literature, the main Phanerozoic basins of manganese deposition have been established in the geological history of Laurasia, Pangea, and Siberian paleocontinents. The formation conditions of manganese ore gradually changed from hydrothermal-sedimentary in the Middle Paleozoic to sedimentary-diagenetic in Mesozoic and Cenozoic. The ore was also formed under catagenetic conditions. Carbon of oxidized organic matter plays a substantial role in the formation of manganese carbonates.     

A general account of Karoo vulcanicity in southern Africa

Volcanic rocks of late Triassic to early Cretaceous age which today cover more than 140 000 km² of the southern African sub-continent are discussed. The rocks occur as scattered outliers and represent small eroded remnants of an originally more extensive volcanic province. The rocks are best preserved in three main areas of southern Africa, in Namibia, in central South Africa, Transkei and Lesotho and in the southeastern areas of the sub-continent including South Africa, Swaziland, Mozambique and Zimbabwe. A history of previous work done on Karoo volcanism is presented and accounts of the geological relationships of the main, and some subsidiary, areas as well as events preceding the major phase of extrusive vulcanism are discussed. Relationships between dolerite dykes and basaltic lavas are noted. Volcano-stratigraphic and geochemical mapping have been used to subdivide the volcanic successions found in the different areas, and recently adopted nomenclature is presented. Considerable more variability has been recognised in the volcanic succession than was previously recognised, the flood basalt pile being more complex than was originally thought. Rocks from the central Karoo areas are primarily of basaltic composition whereas those from the western and eastern marginal areas include basic, and felsic types. Age relationships of the volcanics based on recent studies are outlined and geochemical variations within the entire province discussed. The classification system adopted for the Karoo volcanics is described briefly and chemical relationships of extrusive and intrusive rocks are included. In concluding some new ideas concerning the overall development of the Karoo volcanic province and related fragmentation of Gondwanaland are presented.     

Intrinsic oxygen Fugacity measurements on chromites from the Bushveld Complex and their petrogenetic significance

Oxygen Fugacity measurements were carried out on chromites from the Eastern Bushveld Complex (Maandagshoek) and are compared with former measurements on chromites from the western Bushveld Complex (Zwartkop Chrome Mine). These results together with those of Hill and Roeder (1974) yield the following conditions of formation for the massive chromitite layers: Western Bushveld Complex (Zwartkop Chrome Mine) $$\begin{gathered} Layer{\text{ }}T(^\circ C) p_{O_2 } (atm) \hfill \\ LG3{\text{ 1160}} - {\text{1234 10}}^{ - {\text{5}}} - 10^{ - 7.6} \hfill \\ LG4{\text{ 1175}} - {\text{1200 10}}^{ - 6.35} - 10^{ - 7.20} \hfill \\ LG6{\text{ 1162}} - {\text{1207 10}}^{ - 6.20} - 10^{ - 7.50} \hfill \\ \hfill \\ \end{gathered} $$ Eastern Bushveld Complex (Farm Maandagshoek) $$\begin{gathered} {\text{LXI 1115}} - {\text{1150 10}}^{ - 7.80} - 10^{ - 8.80} \hfill \\ ( = {\text{Steelpoort Seam)}} \hfill \\ {\text{LX 1125 10}}^{ - 8.25} \hfill \\ {\text{V 1120 10}}^{ - 8.55} \hfill \\ {\text{LII 1120 10}}^{ - 8.0} - 10^{ - 8.60} \hfill \\ \end{gathered} $$ The comparison of the data shows, that the chronitite layers within each particular sequence were formed under approximately identicalp _{o 2}- andT-conditions. The chromites from the western Bushveld Complex, however, were formed at higher temperatures and higher oxygen fugacities than the chromites from the eastern Bushveld Complex. Fromp _{o 2}-T-curves of disseminated chromites and the temperatures derived above, the following conditions of formation for the host rocks were obtained: Western Bushveld Complex $$T = 1200^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 7.25} - 10^{ - 7.50} $$ Eastern Bushveld Complex $$T = 1125^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 8.50} - 10^{ - 9.25} $$ Consequently, the host rocks in the Zwartkop-Chrome-Mine, were formed under higher temperatures and higher oxygen fugacities than the host rocks at Maandagshoek. The rock sequence in the Zwartkop-Chrome-Mine therefore originated in an earlier stage of the differentiation of the Bushveld magma. Comparison of the chromites from the host rocks with the chromites from massive layers supports Ulmer's (1969) thesis that an increase of the oxygen fugacity is responsible for the formation of massive chromitite layers. The values in this investigation show that increases of only about 0.5–1.0 log units are necessary to enhance chromitite layer formation.     

Moho structure of Central America based on three-dimensional lithospheric density modelling of satellite-derived gravity data

The Central American isthmus hosts a highly variable Moho structure due to the diverse origin and composition of the crustal basement and the influence of large-scale neotectonic processes. Gravity data from the combined geopotential model EGM2008 were interpreted via forward modelling to outline the three-dimensional lithospheric density structure along the Middle American Trench, as well as the segmentation of the oceanic Cocos and Nazca plates and the overriding Caribbean plate. In this work, results for the depth of the Moho obtained from the density model are presented. The Quaternary volcanic arc correlates with a maximum Moho depth of 44 km in western Guatemala. To the south-east of the continental shelf, the Caribbean plate shows Moho depths between 20 and 12 km whereas to the north, values as shallow as 8 km are observed at the Cayman trough. For the oceanic Cocos plate, depths between 16 and 21 km are obtained for the Moho along the Cocos ridge, contrasting with values between 15 and 12 km for the seamount segment and 8 and 11 km for the segments of the crust that are not affected by the Galapagos hot-spot track.     

Exoelectron spectroscopy of traps in surface layers of phenakite and quartz

The possibilities of exoelectron spectroscopy to investigate defects in dielectrics are demonstrated for phenakite Be₂SiO₄, its structural analogs Zn₂ SiO₄, Be₂GeO₄, solid solutions Be₂Si_1?x Ge _x O₄ (x=0÷1) and α-quartz. Emission maxima at 330 and 670 K in phenakite have been found to be due to [GeO₄]^5? andE' centers, respectively. Structural disturbances in the silicon and oxygen positions have been shown to control the exoemission activity of the crystals. Radiation induced decrease of exoemission activity connected with generation ofE' centers by neutron irradiation has been discovered. The energy level scheme of active centers in the subsurface region of Be₂SiO₄ has been established.     

Magnetic structure and cation distribution in (Fe,Mn)2SiO4 (olivine) by neutron diffraction

The cation distribution in the synthetic samples of olivine-type structure with composition (Fe _x Mn_1?x )₂SiO₄ was determined at room temperature and confirms previous Mössbauer results. At low temperature an antiferromagnetic ordering is observed. The magnetic structures can be described in the crystallographic cell (i.e. k=0). They are interpreted on the basis of the irreducible representations (modes) of the symmetry groups which are compatible with Pnma. The dominant modes observed for all compounds, including Fe₂SiO₄ and Mn₂SiO₄, only differ in their direction. The main direction of magnetization is dominated by the Fe²⁺ single-ion anisotropy. At 4.2K, for x=0.29, it is parallel to the c-axis, whereas for x=0.76 the direction is parallel to the b-axis. The anisotropy of the M1-sites dominates in the first case, whereas M2-anisotropy dominates in the second case. The influence of temperature is demonstrated for x=0.50 where c is the main direction at 4.2K, when it is b at 38K.     

The structural role of Al2O3 and TiO2 in immiscible silicate liquids in the system SiO2-MgO-CaO-FeO-TiO2-Al2O3

The effects of the addition of Al₂O₃ on the large stable two liquid field in the SiO₂-TiO₂-CaO-MgO-FeO system were experimentally determined. The increase of Al₂O₃ content in the starting composition results in the decrease of critical temperature, phase separation and liquidus temperature of the two liquid field until it is rendered completely metastable. The shrinkage of the two liquid field indicates that Al₂O₃ is acting in the role of a network former and homogenizes the structure of the two melts. In this alkali-free system Al⁺³ utilizes the divalent cations, Ca⁺² and Mg⁺², for local charge balance with a preference for Ca⁺² over Mg⁺². Thus, AlO₄ tetrahedra combine with SiO₄ tetrahedra to form an aluminosilicate framework which polymerizes the SiO₂-poor melt and makes it structurally more similar to the SiO₂-rich melt. However, Ca⁺² and Mg⁺² are not as efficient in a charge balancing capacity as the monovalent K⁺ and Na⁺ cations. The lack of alkalis in this system limits the stability of AlO₄ tetrahedra in the highly polymerized SiO₂-rich melt and results in the preference of Al₂O₃ for the SiO₂-poor melt. The partitioning systematics of Ti are virtually identical to those of Al. It is concluded that Ti occurs in tetrahedral coordination as a network forming species in both the high — and low — SiO immiscible melts.     

The tetrahedral framework in glasses and melts — inferences from molecular orbital calculations and implications for structure,thermodynamics, and physical properties

Results of ab initio molecular orbital (MO) calculations provide a basis for the interpretation of structural and thermodynamic properties of crystals, glasses, and melts containing tetrahedrally coordinated Si, Al, and B. Calculated and experimental tetrahedral atom-oxygen (TO) bond lengths are in good agreement and the observed average SiO and AlO bond lengths remain relatively constant in crystalline, glassy, and molten materials. The TOT framework geometry, which determines the major structural features, is governed largely by the local constraints of the strong TO bonds and its major features are modeled well by ab initio calculations on small clusters. Observed bond lengths for non-framework cations are not always in agreement with calculated values, and reasons for this are discussed in the text. The flexibility of SiOSi, SiOAl, and AlOAl angles is in accord with easy glass formation in silicates and aluminosilicates. The stronger constraints on tetrahedral BOB and BOSi angles, as evidenced by much deeper and steeper calculated potential energy versus angle curves, suggest much greater difficulty in substituting tetrahedral B than Al for Si. This is supported by the pattern of immiscibility in borosilicate glasses, although the occurrence of boron in trigonal coordination is an added complication. The limitations on glass formation in oxysulfide and oxynitride systems may be related to the angular requirements of SiSSi and Si(NH)Si groups. Although the SiO and AlO bonds are the strongest ones in silicates and aluminosilicates, they are perturbed by other cations. Increasing perturbation and weakening of the framework occurs with increasing ability of the other atom to compete with Si or Al for bonding to oxygen, that is, with increasing cation field strength. The perturbation of TOT groups, as evidenced by TO bond lengthening predicted by MO calculations and observed in ordered crystalline aluminosilicates, increases in the series Ca, Mg and K, Na, Li. This perturbation correlates strongly with thermochemical mixing properties of glasses in the systems SiO₂-M ₁ ^n/n+ AlO₂ and SiO₂-M ⁿ⁺O _n/2 (M=Li, Na, K, Rb, Cs, and Mg, Ca, Sr, Ba, Pb), with tendencies toward immiscibility in these systems, and with systematics in vibrational spectra. Trends in physical properties, including viscosity at atmospheric and high pressure, can also be correlated.     

A transferable interatomic potential for crystalline phases in the system MgO—SiO2

A central interatomic potential model is presented for compounds in the binary system MgO-SiO₂. The potential, of a simple form which consists of a Coulombic term, a Born repulsive term, and a Van der Walls term for oxygen-oxygen interactions, is designed to predict the properties of magnesium silicates containing Si in octahedral and tetrahedral coordination. This is achieved by fitting simultaneously to forsterite and MgSiO₃ ilmenite crystal structure data, and fixing the partial ionic charges using elastic data for forsterite. The potential is found to transfer successfully to γ-Mg₂SiO₄ and MgSiO₃ perovskite. The potential results in local structural errors around the bridging oxygen ions in clinoenstatite and β-Mg₂SiO₄. The predicted structure for MgSiO₃ garnet is similar to the experimentally measured structure of the MnSiO₃ analogue. Calculated elastic constants average to K=2.41 Mbar and μ=1.44 Mbar for the bulk and shear moduli of MgSiO₃ perovskite, and K=1.87 Mbar and μ=1.10 Mbar for the bulk and shear moduli of MgSiO₃ garnet.     

The Albert Formation of New Brunswick: a paleozoic lacustrine model

Recent work on the Lower Carboniferous Albert Formation of New Brunswick, Canada, has confirmed it to be mainly limnitic (lacustrine) in origin. Within its smallsized basin (ca. 4,000 sq. km.) over 1,300 m of sediment were deposited. These greyish beds are stratigraphically bounded below, above, and toward the south by terrestrial, mainly redbed, formations. Abundant organic varves in a dolomitic marlstone are present, and in places contain articulated fish skeletons. Elsewhere, symmetrical ripple-marks predominate, testifying to gentle water-current movements. The crossopterygianLatvius sp. dates basal beds, in part at least, as Upper Devonian. Ostracodes from an upper member —Euestheria sp., cf.E. lirella; Hilboldtina sp.,Carbonita sp., cf.C. subula — are from the Carboniferous. It is concluded that the Albert Formation was deposited in a tropical or sub-tropical environment, probably in an east-trending rift valley or fault-block basin, over a period of several hundred thousand years, and terminating with evaporitic deposits, at least a part of which were non-marine in origin.     

Cattail invasion and persistence in a coastal salt marsh: The role of salinity reduction

The hypothesis thatTypha domingensis (cattail) can invade tidal marshes only after soil salinities are substantially reduced was tested experimentally by comparing the salt tolerance of seeds, seedlings, and plants reared from rhizomes. Germination rates for four southern California populations reached 100% in fresh water, decreasing to 2% at 20‰. The salt tolerance of seeds from three coastal populations was lower than that of the Salton Sea population. Salt tolerance of plants grown in the lab did not increase with age for seedlings up to 8 weeks old. Rhizome-bearing plants had greatly decreased growth at 10‰ and no growth at 25‰ However, rhizomes of about 5% of the plants survived 9 months at 45‰. The seeds and seedlings are salt sensitive, which explains why invasion into tidal marshes is restricted to prolonged periods of low soil salinity. The older, rhizome-bearing plants are salt tolerant, which explains how invading plants persist persist under hypersaline conditions.     

Xanes analysis on pyroxenes with different ca concentration in M2 site

X-ray Absorption Near-Edge Structure (XANES) analysis of the calcium K-edge of a series of natural pyroxenes is reported. The samples belong to the solid solution series diopside (CaMgSi₂O₆) — jadeite (NaAlSi₂O₆). In diopside, the M2 site is occupied by Ca only, but along the join Na substitutes Ca in this position. From XANES analysis of different samples we found a distortion of the polyhedron around the M2 site varying as a function of Ca content. This is probably due to compression of the site in a selected direction with an unchanged average distance, so that the coordination around the Ca atom changes from the 4-2-2 configuration typical of the diopside structure to the 6-2 configuration typical of Na in the jadeite structure. Intermediate pyroxenes exhibit both configurations, and acquire therefrom the structural order as already detected by X-ray diffraction techniques.     

Types of copper deposits related to volcanic environment in the Bor district,Yugoslavia

The principal copper deposits associated with Upper Creataceous — Laramian calc-alkaline volcano-plutonic complexes in the Bor district are classified as follows: Volcanogenic massive sulphide deposits are situated in andesitic volcanics, and are composed of pyrite and copper sulphides. Multistage deposition of mineral associations in this area was controlled mainly by secondary boiling of hydrothermal fluids rich in sulphur. Apart from cupriferous pyrite deposits, volcanogenic massive polymetallic deposits, containing a pyritic ZnCu+Pb association, have been found recently in hydrothermally altered dacite- and esite pyroclastics. Porphyry copper deposits are mainly situated in volcanic piles related to subvolcanic intrusions and/or hypabyssal plutons. Some porphyry copper deposits occur in the same structures with massive sulphide orebodies, lying above the porphyry copper system. Conglomerate-type ores consisting of clasts of massive sulphide in an andesitic pile have been discovered recently.     

Temporal and spatial patterns in abundance and diversity of fish assemblages in Elkhorn Slough,California

Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.     

Quantitative analysis of morphometric parameters of Kali River basin,southern India,using bearing azimuth and drainage (bAd) calculator and GIS

This study deals with the application of visual basic program ‘bearing, azimuth and drainage (bAd) calculator’ which employs a new and easy methodology for extraction of watershed morphometric parameters. Using bAd calculator, morphometric analysis was carried out for the Kali River basin of southwest coast of India. The basin forms a part of the Western Ghats, which is an important mountain range of the Indian sub-continent and runs nearly parallel to the coast. Spatial maps of six morphometric parameters have been prepared from the results obtained. Various linear, areal, shape and relief morphometric parameters of fifth and sixth order basins have been calculated and interpreted. Majority of the sub-basins show less uniform values (~3 to 4) of R _bm which indicate the uniform and systematic branching pattern of streams. High D _d zones are found in the Western Ghats region, whereas low D _d zones are observed in the eastern part of the basin and near the estuary. The eastern part of the basin shows low F _s values, whereas NW and SW parts of the basin show high F _s values. Compared to manual measurement, bAd calculator requires minimal time to quantify the morphometric parameters. Experimental results show that the software is effective in calculating drainage parameters such as drainage density, frequency, bifurcation ratio, etc., using the text file of ESRI shapefile.     

Phonon spectra and rigid-ion model calculations on andalusite

Polarised Raman and infrared spectra of (ir) andalusite (Al₂SiO₅) single crystals have been measured and interpreted on the basis of a rigid-ion model calculation. The Al-O bond strength is found to be about 70% ionic in character whereas the mainly covalently bound SiO₄ tetrahedra show ca. 40% ionicity. The interatomic short range forces are strongest between silicon and oxygen and rather weak around the fivefold coordinated aluminium. Thermal soft modes appear above 200°C and are correlated with a weakening of the Al-O bonds.     

Characteristics of the changes in tropical cyclones influencing the South Korean region over the recent 10 years (2001–2010)

Through the investigation of tropical cyclone (TC) characteristics related to climate change, this study found that the frequency of TCs occurring over the Western North Pacific has recently decreased slightly, while their average intensity has increased. The number of overall TCs that passed within the vicinity of South Korea has also been reduced, but the number of strong typhoons in the area, those with maximum wind speeds of more than 44 m/s, has significantly increased. These changes are closely related to the following phenomena. (1) The average genesis region of TCs that influence South Korea has moved eastward. Accordingly, the TCs tend to strengthen as they move westward for long distances along the Intertropical Convergence Zone (ITCZ) trade easterlies and the southern boundary of the North Pacific Subtropical High (NPSH). (2) The NPSH and Asia Monsoon trough, which are known to affect TC tracks, have extended to the northwest and southeast. This has caused TCs that travel to higher latitudes and curve back toward the Korean Peninsula to become more frequent. (3) TCs have approached the Korean Peninsula without hitting land. In addition, the sea surface temperature became higher than it was before. These factors have caused TCs to maintain their strength or become stronger than before.