Geochemistry of stream sediments along the western coast of the Gulf of Elat (Aqaba)

One hundred twenty-eight samples of heavy-mineral fractions from sand-size sediments whose mineralogy was previously studied by A. Ayalon, were chosen for this geochemical study. The samples represent the stream sediments along the coastal belt from Elat to Sherm el-Sheikh. This study supplements the geochemical study of A. Zilberfarb and R. Bogoch on the Precambrian terrain of Sinai.The mineral composition of the samples was determined by X-ray diffraction and optical microscopy. In all samples, 14 elements were analyzed: B, Co, Cr, Cu, Ga, Mn, Mo, Nb, Ni, Pb, Sn, Ti, V and Zr. Seven magnetic fractions were separated from twenty of these samples and in these fractions 14 to 20 elements were analyzed, according to the sample. The chemical determinations were mainly by DC emission spectrography.The results were submitted to factor analysis and to association analysis (D. Gill and co-workers). Since the environment is typically arid, there is relatively little chemical weathering. The combined results of both statistical analyses show clearly that three types of source areas can be differentiated: sandstone, metamorphic and granitic terrain. Furthermore, a distinct Mn anomaly was found in the Sherm el-Sheikh area.     

Co-existing calcic amphiboles in calc-alkaline andesites: Possible evidence of a zoned magma chamber

Hornblende-biotite andesites erupted from Mount Price and Clinker Peak volcanoes, southwestern British Columbia, contain two texturally and compositionally distinct calcic amphiboles: pargasitic hornblende xenocrysts and magnesio-hornblende microphenocrysts. Disequilibrium relationships exhibited by these amphiboles and associated minerals suggest that the magnesio-hornblendes precipitated under chemical and thermal conditions that were intermediate between those under which pargasitic hornblende and biotite, respectively, crystallized. Experimental studies of crystallization in double-diffusive systems (Chen and Turner, 1980; Turner, 1980; McBirney, 1980) suggest that these varied magmatic environments can be explained as a consequence of progressive crystallization within a zoned magma chamber. Although gravitational settling may have played a role, the observed mineral assemblages probably developed by convective mixing of crystals precipitated at the cooling margins with those crystallized in the interior of the compositionally stratified magma column.     

DETERMINATION OF WATER IN NINETEEN USGS GEOCHEMICAL REFERENCE STANDARDS USING COULOMETRY AND NEUTRON-CAPTURE PROMPT GAMMA-RAY SPECTROSCOPY

Nineteen USGS GRSs were analyzed with a Dupont 903-H Moisture Analyzer at 110°C and 1000°C to obtain H₂O-and H₂O⁺, and by thermal neutron induced gamma-ray spectrometry to obtain total H₂O. The values are compared with the current literature and the two techniques evaluated. Except for QLO-1 by coulometry, no significant differences were obtained when the results were compared to the the literature.     

Differential effects of salinity and soil saturation on native and exotic plants of a coastal salt marsh

In many southern California salt marshes, increased freshwater inflows have promoted the establishment of exotic plant species. A comparative study showed that a native, perennial, high marsh dominant,Salicornia subterminalis, and an invasive, exotic annual grass,Polypogon monspeliensis, responded differently to soil salinity and saturation.Salicornia subterminalis seeds and young plants were more salt tolerant, and the native grew best at high salinities (23 g 1^?1 and 34 g 1^?1) in greenhouse experiments. In contrast, the exotic had reduced growth at high salinities relative to nonsaline controls. The native,S. subterminalis, grew poorly as the duration of soil saturation increased from 2 wk to 32 wk, butP. monspeliensis grew equally well for all durations tested. The response ofS. subterminalis andP. monspeliensis to increased salinity indicated that salt applications might be used to protect native vegetation in salt marshes where salt-sensitive exotics are a problem. A field experiment verified that a salt application of 850 g m^?2 mo^?1 for 3 mo was sufficient to control the exotic, while not noticeably affecting the native. Thus, salt applications may be a practical method for controllingP. monspeliensis invasions in areas receiving urban runoff or other unwanted freshwater inflows.     

The Lithium, Boron and Beryllium content of serpentinized peridotites from ODP Leg 209 (Sites 1272A and 1274A): Implications for lithium and boron budgets of oceanic lithosphere

Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 μg g⁻¹) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 μg g⁻¹), depleted in Li (most values below 1 μg g⁻¹) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 μg g⁻¹), H₂O and Cl contents and to lower Li contents (0.07-3.37 μg g⁻¹) of peridotites, implying that—contrary to alteration of oceanic crust—B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at 1 and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of 1 m × 1 m × thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li.     

The residential segregation of San Antonio,Texas in 1910: an analysis of ethno-racial and occupational spatial patterns with the colocation quotient

The segregation of cities can be traced to a time when the compartmentalization of space and people was based on factors other than race. In segregation research, one of the limiting factors has always been the geographic scale of the data, and the limited knowledge that exists of segregation patterns when the household is the unit of analysis. Historical census data provides the opportunity to analyze the disaggregated information, and this paper does so with San Antonio during 1910. A spatial analysis of residential segregation based on race, ethnicity, and occupations is carried out with the colocation quotient to map and measure the attraction of residents. Results reveal the presence of residential segregation patterns on different sectors of the city based on households’ ethno-racial and occupational attributes; therefore, providing evidence of the existence of residential segregation prior to the commonly cited determinants of segregation of the 20th century.     

Iron distribution in the octahedral sheet of dioctahedral smectites. An Fe K-edge X-ray absorption spectroscopy study

The distribution of iron atoms in the octahedral sheet of a series of dioctahedral smectites with varying unit-cell composition and iron content was investigated by Fe K-edge XAS spectroscopy. First-step analysis reveals that the patterns corresponding to backscattering by atoms located between 3 and 4 Å from the absorbing atom are very sensitive to the relative amount of light (Si, Al, Mg) and heavy (Fe) atoms. Detailed modelling of this domain then provides valuable information on the number of iron atoms surrounding octahedral iron. By comparing the number of iron neighbours deduced from EXAFS with that determined from unit-cell composition assuming a statistical distribution, three groups of montmorillonites can be distinguished: (1) clay samples from Wyoming display an ordered distribution of iron atoms; (2) clay samples from Georgia, Milos, China and Washington exhibit a close to random distribution of iron atoms; (3) clay samples from North Africa, Germany, Texas and Arizona display extensive iron clustering. These results complement previously obtained IR results and show that the combination of these two spectroscopic techniques could provide an additional crystal-chemistry-based framework for typological analysis of montmorillonite deposits.     

Sea-to-air flux of contaminants via bubbles bursting. An experimental approach for tributyltin

Although seawater concentration of tributyltin (TBT) should decrease when the direct inputs from ship hulls will cease after the incoming world ban of organotin-based antifouling paints in 2003 or later, the TBT environmental issue will still be present for decades as contaminated sediments in shallow waters will be acting as a long-lasting reservoir for TBT and its degradation products. The lost of TBT to the atmosphere by volatilization has already been proposed as a part of its molecular motion through the aquatic environment but most recent calculated values of water-to-air rate of exchange of TBT (from 20 to 510 nmol m⁻² year⁻¹) do not take into account the potential contribution of aerosols ejection to the atmosphere upon bubbles bursting, an important process for pollutants transport in the marine environment. In this work, an experimental approach to measure the seawater-to-air flux of TBT mediated by bubbles bursting is described, and the influence of phytoplankton cells and dissolved organic matter from exudates and culture weathering on flux rates was assessed. The results demonstrate that TBT can be transferred from water to air via the ejection of droplets from bubbles bursting and that cell density strongly affected the transfer. Under a bubbling regime, the water-to-air flux (pmol TBT cm⁻² min⁻¹ level) is estimated up to 1000-fold the flux measured for the molecular diffusion and volatilization under static quiescent conditions. The surface microlayer acted as a transient boundary between the water column and the atmosphere where the dynamic of TBT accumulation has the same trend as the dynamic of TBT ejection. This physical transfer mechanism might be of high significance in nearshore environments, harbors, and shallow channels where clouds of bubbles generated in the wake of large ships play an important role for the atmosphere/seawater chemical exchanges.