Crystallisation sequence and magma evolution of the De Beers dyke (Kimberley,South Africa)

We present petrographic and mineral chemical data for a suite of samples derived from the De Beers dyke, a contemporaneous, composite intrusion bordering the De Beers pipe (Kimberley, South Africa). Petrographic features and mineral compositions indicate the following stages in the evolution of this dyke: (1) production of antecrystic material by kimberlite-related metasomatism in the mantle (i.e., high Cr-Ti phlogopite); (2) entrainment of wall-rock material during ascent through the lithospheric mantle, including antecrysts; (3) early magmatic crystallisation of olivine (internal zones and subsequently rims), Cr-rich spinel, rutile, and magnesian ilmenite, probably on ascent to the surface; and (4) crystallisation of groundmass phases (i.e., olivine rinds, Fe-Ti-rich spinels, perovskite, apatite, monticellite, calcite micro-phenocrysts, kinoshitalite-phlogopite, barite, and baddeleyite) and the mesostasis (calcite, dolomite, and serpentine) on emplacement in the upper crust. Groundmass and mesostasis crystallisation likely forms a continuous sequence with deuteric/hydrothermal modification. The petrographic features, mineralogy, and mineral compositions of different units within the De Beers dyke are indistinguishable from one another, indicating a common petrogenesis. The compositions of antecrysts (i.e., high Cr-Ti phlogopite) and magmatic phases (e.g., olivine rims, magnesian ilmenite, and spinel) overlap those from the root zone intrusions of the main Kimberley pipes (i.e., Wesselton, De Beers, Bultfontein). However, the composition of these magmatic phases is distinct from those in ‘evolved’ intrusions of the Kimberley cluster (e.g., Benfontein, Wesselton water tunnel sills). Although the effects of syn-emplacement flow processes are evident (e.g., alignment of phases parallel to contacts), there is no evidence that the De Beers dyke has undergone significant pre-emplacement crystal fractionation (e.g., olivine, spinel, ilmenite). This study demonstrates the requirement for detailed petrographic and mineral chemical studies to assess whether individual intrusions are in fact ‘evolved’; and that dykes are not necessarily produced by differentiated magmas.

     

Aquifer Discharge Drives Microbial Community Change in Karst Estuaries

Karst estuaries are unique systems governed by freshwater inputs that flow directly to the sea through karst conduits and/or matrices. Because they are found at the interface between terrestrial and marine environments, they can act as sentinels to climate change and as indicators of aquifer health. The physical and geochemical gradients formed in karst estuaries are a direct result of the interactions between inland hydrological conditions and sea level. To examine the influence these gradients have on microbial communities in the water column and sediment of a karst estuary, we studied the spring-fed Double Keyhole Karst Estuary in west central Florida for a 2-year period. Four sites were monitored within this system starting at the Double Keyhole Spring Conduit extending 2 km west through the estuary toward the Gulf of Mexico. Water column and sediment samples were collected quarterly at all sites from September 2011 through September 2013. Archaeal, bacterial, and microbial eukaryote communities were analyzed using quantitative PCR and length-heterogeneity PCR. The biological communities were analyzed in the context of hydrological, physical, and geochemical parameters in order to determine which factor(s) governed the observed changes of microbial abundance and richness. The major finding of this study was that microbial community change in this karst estuary was primarily driven by the volume of aquifer discharge and associated physical gradients, and less by the geochemical fluctuations within the system.     

Determination of the atmospheric neutrino flux from experimental data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this work we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates.      

Distribution and diversity of open-ocean,near-bottom macroplankton in the western Mediterranean: Analysis at different spatio-temporal scales

We analyzed the distribution, diversity, and composition of western Mediterranean macroplankton (excluding gelatinous taxa) in the water column over depths of ca. 550–850 m, with special attention to near-bottom (0–1.5 and ca. 5–77 m above the bottom, mab) levels, and including data from three areas (off the coasts of Catalonia, and to the NW, and SE of Mallorca, Balearic Islands) in the period 1991–2008. Spatio-temporal changes in macroplankton abundance were evaluated as follows: (i) by seasonal sampling in 2007 off the Catalonian coast, (ii) by comparing Catalonian and Balearic Island slopes, and (iii) by comparing a fixed station on the Catalonian slope (at 550–800 m depth) at decadal (1991/1992–2007/2008) time scales. Diversity (in terms of species richness, S) was greater (i) at ca. 5–77 mab than at 0–1.5 mab, (ii) over the insular slopes of the Balearic Island (around Mallorca) than over the mainland Catalonian slopes, and (iii) in the period 1991/1992 than in 2007, likely related to higher values of the North Atlantic Oscillation (NAO) index in 1991/1992. In most analyses species composition was strongly influenced by the degree of stratification and homogenization of the water column in summer–autumn and winter–spring respectively and by location (longitude). Changes consisted mainly of higher density of macroplankton (e.g. abundance of the dominant euphausiids Nematoscelis megalops, Meganyctiphanes norvegica and Euphausia krohni and of the fish Cyclothone braueri) between June and October, parallel to an increase in the T and S close to the bottom. This coincided with changes in the flow of Levantine intermediate water (LIW) in the area. Aggregation of adult forms of the dominant species close to the bottom in summer–autumn could be favored because summer is the period of highest density of food – copepods, mainly Calanus helgolandicus – near the bottom off the Catalan slope. The formation of a thermocline in the water column and the reinforcement of the permanent thermohaline front at the shelf-slope break during summer at ca. 400 m in the Balearic Basin may also enhance this tendency toward greater aggregation of deep macroplankton under stratified water column conditions.     

Compressional reworking of the East African Orogen in the Uluguru Mountains of eastern Tanzania at c. 550 Ma: implications for the final assembly of Gondwana

The Uluguru Mountains of eastern Tanzania represent a key area to unravel the tectonic history of Gondwana assembly along the Neoproterozoic East African Orogen. On the basis of combined structural and ⁴⁰Ar/³⁹Ar geochronological investigations, we have re‐interpreted the structural architecture of the region. Texturally‐late, ductile to cataclastic low‐angle tectonic contacts are recognized, which delimit the contacts between the main lithological units that form a post‐metamorphic, NW‐verging nappe stack. ⁴⁰Ar/³⁹Ar geochronology places this nappe‐forming event at c. 550 Ma, post‐dating tonalitic dyke emplacement at c. 580 Ma. Results from this study (i) demonstrate that a distinct and later episode of convergence occurred in the region at c. 550 Ma, when previous structural elements of the East African Orogen were finally juxtaposed; and (ii) extends models involving the polyphase assembly of Gondwana to East Africa.     

Very long baseline interferometry detection of an Infrared-Faint Radio Source

Infrared-Faint Radio Sources represent a new and unexpected class of object which is bright at radio wavelengths but unusually faint at infrared wavelengths. If, like most mJy radio sources, they were either conventional active or star-forming galaxies in the local Universe, we would expect them to be detectable at infrared wavelengths, and so their non-detection by the Spitzer Space Telescope is surprising. Here, we report the detection of one of these sources using very long baseline interferometry, from which we conclude that the sources are driven by active galactic nuclei. We suggest that these sources are either normal radio-loud quasars at high redshift or abnormally obscured radio galaxies.     

Dechlorinating and Iron Reducing Bacteria Distribution in a TCE-Contaminated Aquifer

Dehalorespiration bioremediation has been considered for chlorinated compound removal from two trichloroethene contaminated groundwater plumes in the OU 5 area of Hill Air Force Base, Utah. The distributions and population densities of the 16S rRNA genes of Bacteria, Dehalococcoides ethenogenes, Desulfuromonas michiganensis, Geobacter spp. and Rhodoferax ferrireducens -like bacteria, as well as the functional genes trichloroethene reductive dehalogenase ( tce A) and vinyl chloride reductase ( vcr A) were determined in contaminated aquifer material samples. The influence of aquifer physical and chemical properties, including iron availability, on these distributions was evaluated. Twenty aquifer cores were collected. DNA was extracted and analyzed using real-time quantitative polymerase chain reaction (RT-qPCR) to quantify the gene densities. Dehalococcoides population densities were low and unevenly distributed. D. michiganensis was found in 12 cores while Geobacter spp. were found in 8 cores. Rhodoferax ferrireducens -like bacteria were widely distributed. The vcr A gene distribution was relatively uniform and broad but the tce A gene was detectable in only 2 cores. Gene distribution was not related to core clusters derived from physical/chemical characteristics.     

Modified passive capillary samplers for collecting samples of snowmelt infiltration for stable isotope analysis in remote,seasonally inaccessible watersheds 2: field evaluation

Twelve modified passive capillary samplers (M‐PCAPS) were installed in remote locations within a large, alpine watershed located in the southern Rocky Mountains of Colorado to collect samples of infiltration during the snowmelt and summer rainfall seasons. These samples were collected in order to provide better constraints on the isotopic composition of soil‐water endmembers in the watershed. The seasonally integrated stable isotope composition (δ¹⁸O and δ²H) of soil‐meltwater collected with M‐PCAPS installed at shallow soil depths < 10 cm was similar to the seasonally integrated isotopic composition of bulk snow taken at the soil surface. However, meltwater which infiltrated to depths > 20 cm evolved along an isotopic enrichment line similar to the trendline described by the evolution of fresh snow to surface runoff from snowmelt in the watershed. Coincident changes in geochemistry were also observed at depth suggesting that the isotopic and geochemical composition of deep infiltration may be very different from that obtained by surface and/or shallow‐subsurface measurements. The M‐PCAPS design was also used to estimate downward fluxes of meltwater during the snowmelt season. Shallow and deep infiltration averaged 8·4 and 4·7 cm of event water or 54 and 33% of the measured snow water equivalent (SWE), respectively. Finally, dominant shallow‐subsurface runoff processes occurring during snowmelt could be identified using geochemical data obtained with the M‐PCAPS design. One soil regime was dominated by a combination of slow matrix flow in the shallow soil profile and fast preferential flow at depth through a layer of platy, volcanic rocks. The other soil regime lacked the rock layer and was dominated by slow matrix flow. Based on these results, the M‐PCAPS design appears to be a useful, robust methodology to quantify soil‐water fluxes during the snowmelt season and to sample the stable isotopic and geochemical composition of soil‐meltwater endmembers in remote watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

40Ar/39Ar and K–Ar age constraints on the timing of regional deformation,south coast of New South Wales,Lachlan Fold Belt: Problems and implications

Four slate samples from subduction complex rocks exposed on the south coast of New South Wales, south of Batemans Bay, were analysed by K–Ar and ⁴⁰Ar/³⁹Ar step‐heating methods. One sample contains relatively abundant detrital muscovite flakes that are locally oblique to the regional cleavage in the rock, whereas the remaining samples appear to contain sparse detrital muscovite. Separates of detrital muscovite yielded plateau ages of 505 ± 3 Ma and 513 ± 3 Ma indicating that inheritance has not been eliminated by metamorphism and recrystallisation. Step‐heating analyses of whole‐rock chips from all four slate samples produced discordant apparent age spectra with ‘saddle shapes’ following young apparent ages at the lowest temperature increments. Elevated apparent ages associated with the highest temperature steps are attributed to the presence of variable quantities of detrital muscovite (<1–5%). Two whole‐rock slate samples yielded similar ⁴⁰Ar/³⁹Ar integrated ages of ca 455 Ma, which are some 15–30 million years older than K–Ar ages for the same samples. These discrepancies suggest that the slates have also been affected by recoil loss/redistribution of ³⁹Ar, leading to anomalously old ⁴⁰Ar/³⁹Ar ages. Two other samples, from slaty tectonic mélange and intensely cleaved slate, yielded average ⁴⁰Ar/³⁹Ar integrated ages of ca 424 Ma, which are closer to associated mean K–Ar ages of 423 ± 4 Ma and 409 ± 16 Ma, respectively. Taking into account the potential influences of recoil loss/redistribution of ³⁹Ar and inheritance, the results from the latter samples suggest a maximum age of ca 440 Ma for deformation/metamorphism. The current results indicate that recoil and inheritance problems may also have affected whole‐rock ⁴⁰Ar/³⁹Ar data reported from other regions of the Lachlan Fold Belt. Therefore, until these effects are adequately quantified, models for the evolution of the Lachlan Fold Belt, that are based on such whole‐rock ⁴⁰Ar/³⁹Ar data, should be treated with caution.