Shaw A.M.,Lorax Environmental Services Ltd.Vancouver |
Escartin J.,French National Center for Scientific Research |
Hamelin C.,Center for Geobiology
Geochemistry, Geophysics, Geosystems | Year: 2015
Here we present volatile, major, and trace element concentrations of 64 olivine-hosted melt inclusions from the Lucky Strike segment on the mid-Atlantic ridge. Lucky Strike is one of two locations where a crustal melt lens has been seismically imaged on a slow-spreading ridge. Vapor-saturation pressures, calculated from CO2 and H2O contents of Lucky Strike melt inclusions, range from approximately 300-3000 bars, corresponding to depths of 0.5-9.9 km below the seafloor. Approximately 50% of the melt inclusions record crystallization depths of 3-4 km, corresponding to the seismically imaged melt lens depth, while an additional ∼35% crystallize at depths>4 km. This indicates that while crystallization is focused within the melt lens, significant crystallization also occurs in the lower crust and/or upper mantle. The melt inclusions span a range of major and trace element concentrations from normal to enriched basalts. Trace element ratios at all depths are heterogeneous, suggesting that melts are not efficiently homogenized in the mantle or crust, despite the presence of a melt lens. This is consistent with the transient nature of magma chambers proposed for slower-spreading ridges. To investigate the petrogenesis of the melt inclusion compositions, we compare the measured trace element compositions to theoretical melting calculations that consider variations in the melting geometry and heterogeneities in the mantle source. The full range of compositions can be produced by slight variations in the proportion of an Azores plume and depleted upper mantle components and changes in the total extent of melting. © 2014. American Geophysical Union. All Rights Reserved.
Luttinen A.V.,University of Helsinki |
Leat P.T.,British Antarctic Survey |
Furnes H.,Center for Geobiology
Journal of Volcanology and Geothermal Research | Year: 2010
Geochemical provinciality of the Karoo continental flood basalt (CFB) province is complicated by the great diversity of magma types. Our geochemical and Nd and Sr isotopic data indicate derivation of Karoo-related low-Ti CFBs of Björnnutane and Sembberget, Dronning Maud Land, Antarctica, from different magma plumbing systems that were typified by generation of magma subtypes largely by variable degrees of fractional crystallization and crustal contamination. We associate these plumbing systems with different mantle sources and propose that the Karoo CFBs of Dronning Maud Land can be grouped into two provinces derived from these sources. The Grunehogna province magmas include high-Ti and some low-Ti magma types, have high (Sm/Yb)N (>2), are enriched in Sr and Eu, and show wide range of initial εNd (+9 to -16). Grunehogna province magmas dominate at Björnnutane, Vestfjella, and Ahlmannryggen. The Maud province magmas show low-Ti affinity, have low (Sm/Yb)N (<2), lack Sr and Eu enrichment, and have relatively narrow range of initial εNd (+3 to -4). Maud province magmas are restricted to Sembberget, Kirwanveggen and the Utpostane gabbros in Vestfjella. The enrichment of Sr and Eu and the depletion of heavy rare earth elements in Grunehogna province magmas, and, specifically, geochemical indications of recycled oceanic crust in the least-contaminated high-Ti and low-Ti basalts and picrites lend support to a recycled source component. Grunehogna magmas are ascribed to partial melting of eclogite-bearing asthenospheric mantle source at depth below the Grunehogna craton and contamination of the magmas with lithospheric mantle (high-Ti types) and crust (low-Ti types). The Maud province magmas can be ascribed to relatively low-pressure partial melting probably of a lithospheric mantle source within the zone of rifted lithosphere associated with the Weddell triple junction and lateral flow of magmas to present outcrops overlying thick Maud Belt lithosphere. Geochemical comparison with Karoo CFBs in southern Africa implies a broadly similar division between the high-Ti and low-Ti magma types associated with the Limpopo structure and the low-Ti magma types of the Central Area and Botswana. © 2010 Elsevier B.V.
Holovachov O.,University of California at Riverside |
Bostrom S.,Swedish Museum of Natural History |
Reid N.,University of California at Riverside |
Waren A.,Swedish Museum of Natural History |
And 2 more authors.
Journal of the Marine Biological Association of the United Kingdom | Year: 2011
A new species, Endeolophus skeneae sp. nov., epibiotically associated with the gastropod Skenea profunda, is described from light microscope and scanning electron microscope observations. The new species is characterized by homogeneous ornamentation of the cuticle with annules with very fine and numerous longitudinal ridges, equally distributed around the body, subcuticular discontinuity in cuticle pattern along the lateral sectors of the body, relatively long body (1.1-1.6 mm) and relatively long tail (141-188 μm, c'=7.5 - 11.4), short (19-22 μm) L-shaped spicules with ventrally bent blade and simple plate-like gubernaculum without apophysis. Symbiotic associations between aquatic nematodes and molluscs are discussed, with special emphasis on Dreissena polymorpha, zebra mussels. It is suggested that nematodes find food and shelter in the mantle cavity of the bivalve molluscs, and in the umbilicus and aperture of the gastropods, but to reveal the exact mechanisms of symbiotic associations of nematodes with aquatic molluscs requires further research. © Marine Biological Association of the United Kingdom 2010.
Dronen K.,University of Bergen |
Roalkvam I.,Center for Geobiology |
Beeder J.,Statoil |
Torsvik T.,University of Bergen |
And 3 more authors.
Environmental Science and Technology | Year: 2014
Heavy carbon steel corrosion developed during nitrate mitigation of a flow rig connected to a water injection pipeline flowing anaerobe saline aquifer water. Genera-specific QPCR primers quantified 74% of the microbial biofilm community, and further 87% of the community of the nonamended parallel rig. The nonamended biofilm hosted 6.3 × 106 SRB cells/cm2 and the S35-sulfate-reduction rate was 1.1 μmol SO 4 2-/cm2/day, being congruent with the estimated SRB biomass formation and the sulfate areal flux. Nitrate amendment caused an 18-fold smaller SRB population, but up to 44 times higher sulfate reduction rates. This H2S formation was insufficient to form the observed Fe3S4 layer. Additional H2S was provided by microbial disproportionation of sulfur, also explaining the increased accessibility of sulfate. The reduced nitrate specie nitrite inhibited the dominating H2-scavenging Desulfovibrio population, and sustained the formation of polysulfide and Fe3S4, herby also dissolved sulfur. This terminated the availability of acetate in the inner biofilm and caused cell starvation that initiated growth upon metallic electrons, probably by the sulfur-reducing Desulfuromonas population. On the basis of these observations we propose a model of heavy nitrate corrosion where three microbiological processes of nitrate reduction, disproportionation of sulfur, and metallic electron growth are nicely woven into each other. © 2014 American Chemical Society.
Daae F.L.,Center for Geobiology |
Okland I.,Center for Geobiology |
Dahle H.,Center for Geobiology |
Jorgensen S.L.,Center for Geobiology |
And 2 more authors.
Geobiology | Year: 2013
Water-rock interactions in ultramafic lithosphere generate reduced chemical species such as hydrogen that can fuel subsurface microbial communities. Sampling of this environment is expensive and technically demanding. However, highly accessible, uplifted oceanic lithospheres emplaced onto continental margins (ophiolites) are potential model systems for studies of the subsurface biosphere in ultramafic rocks. Here, we describe a microbiological investigation of partially serpentinized dunite from the Leka ophiolite (Norway). We analysed samples of mineral coatings on subsurface fracture surfaces from different depths (10-160 cm) and groundwater from a 50-m-deep borehole that penetrates several major fracture zones in the rock. The samples are suggested to represent subsurface habitats ranging from highly anaerobic to aerobic conditions. Water from a surface pond was analysed for comparison. To explore the microbial diversity and to make assessments about potential metabolisms, the samples were analysed by microscopy, construction of small subunit ribosomal RNA gene clone libraries, culturing and quantitative-PCR. Different microbial communities were observed in the groundwater, the fracture-coating material and the surface water, indicating that distinct microbial ecosystems exist in the rock. Close relatives of hydrogen-oxidizing Hydrogenophaga dominated (30% of the bacterial clones) in the oxic groundwater, indicating that microbial communities in ultramafic rocks at Leka could partially be driven by H2 produced by low-temperature water-rock reactions. Heterotrophic organisms, including close relatives of hydrocarbon degraders possibly feeding on products from Fischer-Tropsch-type reactions, dominated in the fracture-coating material. Putative hydrogen-, ammonia-, manganese- and iron-oxidizers were also detected in fracture coatings and the groundwater. The microbial communities reflect the existence of different subsurface redox conditions generated by differences in fracture size and distribution, and mixing of fluids. The particularly dense microbial communities in the shallow fracture coatings seem to be fuelled by both photosynthesis and oxidation of reduced chemical species produced by water-rock reactions. © 2013 John Wiley & Sons Ltd.