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  • 201.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Lucchesi, Sergio
    Sapienza Università di Roma.
    Structural refinement of Mn-doped spinel: a case for tetrahedrally coordinated Mn3+ in an oxygen-based structure2007In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 92, p. 27-33Article in journal (Refereed)
  • 202.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    D'Ippolito, Veronica
    Sapienza Università di Roma.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma.
    Blue spinel crystals in the MgAl2O4-CoAl2O4 series: II. Cation ordering over short range and long range scales2012In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 97, p. 1834-1840Article in journal (Refereed)
  • 203.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the magnetite-ulvöspinel series2009In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 94, p. 181-189Article in journal (Refereed)
  • 204.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the MgAl2O4-MgMn2O4-MnMn2O4 system: Analysis of structural distortion in spinel and hausmannite-type structures2010In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 95, p. 602-607Article in journal (Refereed)
  • 205.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the ulvöspinel-qandilite series2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 847-851Article in journal (Refereed)
  • 206.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Stoichiometry of synthetic ulvöspinel single crystals2008In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 93, p. 1312-1316Article in journal (Refereed)
  • 207.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Naitza, Stefano
    Università degli Studi di Cagliari, Italy.
    Secchi, Francesco
    Università degli Studi di Sassari, Italy.
    Conte, Aida M.
    CNR, Sede Secondaria di Roma "Sapienza", Roma, Italy.
    Cuccuru, Stefano
    Università degli Studi di Sassari, Italy.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Petrogenic controls on the origin of tourmalinite veins from Mandrolisai igneous massif (central Sardinia, Italy): Insights from tourmaline crystal chemistry2019In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 342-343, p. 333-344Article in journal (Refereed)
  • 208.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Naitza, Stefano
    Università degli Studi di Cagliari, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Secchi, Francesco
    Università degli Studi di Sassari, Italy.
    Conte, Aida M.
    CNR-Istituto di Georiscienze e Georisose, Rome, Italy.
    Cuccuru, Stafano
    Università degli Studi di Sassari.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    De La Rosa, Nathaly
    Division of Nuclear Physics, Lund University.
    Kristiansson, Per
    Division of Nuclear Physics, Lund University.
    Nilsson, E.J. Charlotta
    Division of Nuclear Physics, Lund University.
    Ros, Linus
    Division of Nuclear Physics, Lund University.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma, Italy.
    Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy): Crystal-chemical study and petrological constraints2018In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 308-309, p. 395-411Article in journal (Refereed)
    Abstract [en]

    Tourmalines from the late-Variscan Arbus pluton (SWSardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges fromschorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na+Fe2+↔▢+Al, which relates schorl to foitite. The homovalent substitution (OH)F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2++(OH, F)Al+O relates schorl/fluor-schorl to oxy-schorl. Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite+quartz →schorl+quartz→fluor-schorl+quartz → foitite+quartz. The schorl→foitite evolution represents a distinct trend towards (Al+!) increase and unit-cell volumedecrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other Li-minerals in the Arbus pluton. Tourmaline-bearing rocks reflect the petrogenetic signi!cance of contribution from a metapelitic crustal component during the evolution of magmas in the middle-upper crust.

  • 209.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk, Russia.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of Al-V-Cr oxy-tourmalines from Sludyanka complex, Lake Baikal, Russia2017In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 29, no 3, p. 457-472Article in journal (Refereed)
  • 210.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vanadio-oxy-chromium-dravite, NaV3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup 2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 1155-1162Article in journal (Refereed)
  • 211.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vanadio-oxy-dravite, NaV3(Al4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 218-224Article in journal (Refereed)
  • 212.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Fregola, Rosa Anna
    Università di Bari Aldo Moro, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of spinels in the system MgAl2O4-MgV2O4-Mg2VO42016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, p. 580-586Article in journal (Refereed)
    Abstract [en]

    Eight spinel single-crystal samples belonging to the spinel sensu stricto-magnesiocoulsonite series (MgAl2O4-MgV2O4) were synthesized and crystal-chemically characterized by X‑ray diffraction, electron microprobe and optical absorption spectroscopy. Site populations show that the tetrahedrally coordinated site (T) is populated by Mg and minor Al for the spinel sensu stricto compositions, and only by Mg for the magnesiocoulsonite compositions, while the octahedrally coordinated site (M) is populated by Al, V3+, minor Mg, and very minor amounts of V4+. The latter occurs in appreciable amounts in the Al-free magnesium vanadate spinel, T(Mg)M(Mg0.26V3+1.48V4+0.26)O4, showing the presence of the inverse spinel VMg2O4. The studied samples are characterized by substitution of Al3+ for V3+ and (Mg2++V4+) for 2V3+ described in the system MgAl2O4-MgV2O4-VMg2O4.

    The present data in conjunction with data from the literature provide a basis for quantitative analyses of two solid-solution series MgAl2O4-MgV23+O4 and MgV23+O4-V4+Mg2O4. Unit-cell parameter increases with increasing V3+ along the series MgAl2O4-MgV2O4 (8.085–8.432 Å), but only slightly increases with increasing V3+ along the series VMg2O4-MgV2O4 (8.386–8.432 Å). Although a solid solution could be expected between the MgAl2O4 and VMg2O4 end-members, no evidence was found. Amounts of V4+ are nearly insignificant in all synthetic Al-bearing vanadate spinels, but are appreciable in Al-free vanadate spinel.

    An interesting observation of the present study is that despite the observed complete solid-solution along the MgAl2O4-MgV2O4 and MgV2O4-VMg2O4 series, the spinel structure seems to be unable to stabilize V4+ in any intermediate members on the MgAl2O4-Mg2VO4 join even at high oxygen fugacities. This behavior indicates that the accommodation of specific V-valences can be strongly influenced by crystal-structural constraints, and any evaluation of oxygen fugacities during mineral formation based exclusively on V cation valence distributions in spinel should be treated with caution. The present study underlines that the V valency distribution in spinels is not exclusively reflecting oxygen fugacities, but also depends on activities and solubilities of all chemical components in the crystallization environment.

  • 213.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Oxy-foitite, □(Fe2+Al2)Al6(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup2017In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 29, no 5, p. 889-896Article in journal (Refereed)
    Abstract [en]

    Oxy-foitite, □(Fe2+Al2)Al6(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. It occurs in high-grade migmatitic gneisses of pelitic composition at the Cooma metamorphic Complex (New South Wales, Australia), in association with muscovite, K-feldspar and quartz. Crystals are black with a vitreous luster, sub-conchoidal fracture and gray streak. Oxy-foitite has a Mohs hardness of ∼7, and has a calculated density of 3.143 g/cm3. In plane-polarized light, oxy-foitite is pleochroic (O= dark brown and E = pale brown), uniaxial negative. Oxy-foitite belongs to the trigonal crystal system, space group R3ma = 15.9387(3) Å, c = 7.1507(1)Å and V = 1573.20(6)Å3,Z = 3. The crystal structure of oxy-foitite was refined to R1 = 1.48% using 3247 unique reflections from single-crystal X-ray diffraction using MoKα radiation. Crystal-chemical analysis resulted in the empirical structural formula: X(□0.53Na0.45Ca0.01K0.01)Σ1.00Y(Al1.53Fe2+1.16Mg0.22Mn2+0.05Zn0.01Ti4+0.03)Σ3.00Z(Al5.47Fe3+0.14Mg0.39)Σ6.00[(Si5.89Al0.11)Σ6.00O18](BO3)3V(OH)3W[O0.57F0.04(OH)0.39]Σ1.00. Oxy-foitite belongs to the X-site vacant group of the tourmaline-supergroup minerals, and shows chemical relationships with foitite through the substitution YAl3++WO2-YFe2++W(OH)1–.

  • 214.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Rome, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Thermally induced cation redistribution in Fe‑bearing oxy‑dravite and potential geothermometric implications2016In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 171, no 5, p. 1-14, article id 47Article in journal (Refereed)
    Abstract [en]

    Iron-bearing oxy-dravite was thermally treated in air and hydrogen atmosphere at 800 °C to study potential changes in Fe, Mg and Al ordering over the octahedrally coordinated Y and Z sites and to explore possible applications to intersite geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that heating Fe-bearing tourmalines results in disordering of Fe over Y and Z balanced by ordering of Mg at Y, whereas Al does not change appreciably. The Fe disorder depends on temperature, but less on redox conditions. The degree of Fe3+–Fe2+ reduction is limited despite strongly reducing conditions, indicating that the fO2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. Untreated and treated samples have similar short- and long-range crystal structures, which are explained by stable Al-extended clusters around the O1 and O3 sites. In contrast to the stable Al clusters that preclude any temperature-dependent Mg–Al order– disorder, there occurs Mg diffusion linked to temperaturedependent exchange with Fe. Ferric iron mainly resides around O2− at O1 rather than (OH), but its intersite disorder induced by thermal treatment indicates that Fe redistribution is the driving force for Mg–Fe exchange and that its diffusion rates are significant at these temperatures. With increasing temperature, Fe progressively disorders over Y and Z, whereas Mg orders at Y according to the order–disorder reaction: YFe + ZMg → ZFe + YMg. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks and imply that successful tourmaline geothermometers may be developed by thermal calibration of the Mg– Fe order–disorder reaction, whereas any thermometers based on Mg–Al disorder will be insensitive and involve large uncertainties.

  • 215.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Thermally induced cation redistribution in fluor-elbaite and Fe-bearing tourmalines2019In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 46, no 4, p. 371-383Article in journal (Refereed)
  • 216.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Ciriotti, Marco
    Associazione Micromineralogica Italiana,Torino, Italy.
    Experimental cation redistribution in the tourmaline lucchesiite, CaFe2+3Al6(Si6O18)(BO3)3(OH)3O2018In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 45, no 7, p. 621-632Article in journal (Refereed)
    Abstract [en]

    Natural Mg-rich lucchesiite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe-, Mg- and Al ordering over the octahedrally coordinated Y-  and Z -sites, and to explore possible applications to intracrystalline geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that thermal treatment of lucchesiite results in an increase of Fetot contents at Z balanced by an increase of Mg and Al at Y . This process is accompanied by a significant deprotonation of the O3 anion site. The Fe order–disorder reaction depends more on temperature, than on redox conditions. During heat treatment in H2 ,reduction of Fe3+ to Fe2+ was not observed despite strongly reducing conditions, indicating that the fO2  conditions do not exclusively control the Fe oxidation state at the present experimental conditions. On the basis of this and previous studies, the intersite order–disorder process induced by thermal treatment indicates that Fe redistribution is an important factor for Fe–Mg–Al-exchange and is significant at temperatures around 800 °C. As a result, Fe–Mg–Al intersite order–disorder is sensitive to temperature variations, whereas geothermometers based solely on Mg–Al order–disorder appear insensitive and involve large uncertainties. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks, and indicate that successful tourmaline geothermometers may be developed by thermal calibration of the Fe-Mg–Al order–disorder reaction.

  • 217.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk.
    Crystallographic and spectroscopic characterization of Fe-bearing chromo-alumino-povondraite and its relationships with oxy-chromium-dravite and oxy-dravite2013In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 98, p. 1557-1564Article in journal (Refereed)
  • 218. Boskabadi, Ahmad
    et al.
    Pitcairn, Iain K.
    Stern, Robert J.
    Ayer, Mokhles K.
    Broman, Curt
    Mohamed, Fathz H.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Carbonatite crystallization and alteration in the Tarr carbonatite–albitite complex, Sinai Peninsula, Egypt2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 239, p. 24-41Article in journal (Refereed)
    Abstract [en]

    Carbonate dykes occurring in the Arabian-Nubian Shield (ANS) are clearly intrusive in origin and carbonatites according to the IUGS classification, yet previous investigations refer to them as “intrusive carbonates”, due mainly to their low Sr, Ba, Nb, Y, Th and rare earth element (REE) contents. The Tarr carbonatite albitite complex (TCA) in SE Sinai, Egypt contains a series of small (<1.2 km2) albitite intrusions surrounded by small veins and dykes of carbonatite, which occur predominantly in a narrow zone of brecciation surrounding the intrusions. Fennitic alteration surrounding TCA has been reported but there is little consensus on the extent and origin of this alteration. Fennitic alteration surrounding the TCA carbonatites is not abundant. Alteration is dominated by precipitation of carbonates in the breccia zone surrounding the albitite intrusion with associated actinolite, chlorite, sericite and epidote. Geochemical compositions are consistent with addition of carbonates and associated secondary minerals because the altered rocks contain higher CaO, MgO, Fe2O3 and MnO and lower SiO2, Al2O3, Na2O and K2O compared to their less altered rocks. Fluid inclusion investigations show that the carbonatite magma contained a high-salinity H2O–CO2–NaCl–CaCl2fluid, although the lack of fennitic alteration implies that this fluid was not abundant. The crystallization conditions of the carbonatite dykes and carbonatite matrix in the breccia zones have been constrained using Zr-in-rutile thermometry and fluid inclusion microthermometry. Crystallization of the carbonatite in the dykes and in the breccia zone occurred between 565 ± 38 °C and 420–480 °C, respectively and at 0.75–1.3 kbar, which corresponds to a depth of 2.8–4.9 km. Rutile hosted within the carbonatite crystallized earlier at high temperature and the carbonate matrix crystallized later after cooling. Immiscible fluid from carbonatite magma would have altered the surrounding country rocks at lower temperature (between 400 °C and 150 °C deduced from the fluid inclusion thermometry) after the intrusion of the carbonatite melt.

  • 219. Bosshard-Stadlin, Sonja A.
    et al.
    Mattsson, Hannes B.
    Keller, Joerg
    Magma mixing and forced exsolution of CO2 during the explosive 2007-2008 eruption of Oldoinyo Lengai (Tanzania)2014In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 285, p. 229-246Article in journal (Refereed)
    Abstract [en]

    Oldoinyo Lengai is probably most famous for being the only active volcano on Earth which is erupting natrocarbonatitic magma. However, the mildly explosive natrocarbonatitic activity is alternating with highly explosive, nephelinitic eruptions of which the most recent episode occurred in September 2007 (and lasted until April 2008). Here we present petrographic observations, mineral chemistry as well as major- and trace element analyses of samples covering the evolution of the eruption with time. In the early phases of the eruption, the phenocryst assemblages are dominated by the carbonate minerals nyerereite and gregoryite, but as the eruption progresses the mineralogy becomes dominated by silicate minerals like nepheline, pyroxene, garnet, alumoakermanite, combeite and wollastonite. The observed major- and trace element variations during the 2007-2008 eruption indicate mixing between a natrocarbonatitic magma and a combeite-wollastonite-bearing nephelinitic magma (CWN), with higher portions of natrocarbonatite in the early stages of the eruption. Euhedral and uncorroded clinopyroxene crystals are abundant in the late 2007 deposits but quickly start to break-down and corrode as the eruption continues, indicating that the natrocarbonatite and the CWN are not in fact conjugate magmas derived from a single magma reservoir, but must have evolved separately in the crust from the point of immiscibility. When these magmas interact beneath the volcano, a hybrid silicate magma forms (where clinopyroxene is no longer stable) and the composition of this hybrid causes the overall solubility of CO2 in the system to decrease drastically. This results in rapid exsolution of CO2 (g) which is allowed to expand during ascent, and we conclude that this is most likely the reason behind the unexpected vigor in the explosive eruptions of Oldoinyo Lengai. This massive release of CO2 during ascent may also explain the petrographic features of the pyroclasts as these are dominated by near-spherical droplets with moderate vesicularities, indicative of being transported in a hot gas-stream/jet in the upper conduit and forming an aerosol-type spray. (C) 2014 Elsevier B.V. All rights reserved.

  • 220. Bosshard-Stadlin, Sonja A.
    et al.
    Mattsson, Hannes B.
    Stewart, Carol
    Reusser, Eric
    Leaching of lava and tephra from the Oldoinyo Lengai volcano (Tanzania): Remobilization of fluorine and other potentially toxic elements into surface waters of the Gregory Rift2017In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 332, p. 14-25Article in journal (Refereed)
    Abstract [en]

    Volcanic ash leachate studies have been conducted on various volcanoes on Earth, but few have been done on African volcanoes until now. Tephra emissions may affect the environment and the health of people living in this area, and therefore we conducted a first tephra (ash and lapilli sized) leachate study on the Oldoinyo Lengai volcano, situated in northern Tanzania. The recent explosive eruption in 2007-2008 provided us with fresh samples from the first three weeks of the eruption which were used for this study. In addition, we also used a natrocarbonatitic sample from the activity prior to the explosive eruption, as the major activity at Oldoinyo Lengai is natrocarbonatitic. To compare the leaching process affecting the natrocarbonatitic lavas and the tephras from Oldoinyo Lengai, the 2006 natrocarbonatitic lava flow was resampled 5 years after the emplacement and compared to the initial, unaltered composition. Special interest was given to the element fluorine (F), since it is potentially toxic to both humans and animals. A daily intake of fluoride (F-) in drinking water of >1.5 mg/l can lead to dental fluorosis, and higher concentrations lead to skeletal fluorosis. For this reason, a guideline value for fluoride in drinking water was set by the WHO (2011) to 1.5 mg/l. However, surface waters and groundwaters in the Gregory Rift have elevated fluoride levels of up to 9.12 mg/l, and as a consequence, an interim guideline value for Tanzania has been set at 8 mg/l. The total concentration of fluorine in the samples from the natrocarbonatitic lava flow is high (3.2 wt%), whereas we observed a significant decrease of the fluorine concentration (between 1.7 and 0.5 wt%) in the samples collected three days and three weeks after the onset of the explosive 2007-08 eruption. However, the total amount of water-extractable fluoride is lower in the natrocarbonatitic lavas (319 mg/l) than in the nephelinitic tephra (573-895 mg/l). This is due to the solubility of the different F-bearing minerals. In the natrocarbonatites, fluorine exists predominantly in fluorite (CaF2), and in the early tephra as Na-Mg bearing salts such as neighborite (NaMgF3) and sellaite (MgF2). All these three minerals have very low solubility in water (16-130 mg/l). The later nephelinitic tephras contain surface coating of villiaumite (NaF), which is highly soluble (42,200 mg/l) in water and can thus release the fluoride more readily upon contact with water. Although there is still the need for further data and a more precise study on this topic in Tanzania, we can already draw a first conclusion that the intake of water during or directly following the deposition of the tephra is not advisable and should be avoided, whereas the release of fluoride from the lava flow has less influence on the river waters. 2017 Elsevier B.V. All rights reserved.

  • 221.
    Boström, Kurt
    Luleå tekniska universitet.
    Laangban: an exhalative sedimentary island arc deposit?1980In: Vol. 102, no 2, p. 185-186Article in journal (Other academic)
  • 222.
    Boström, Kurt
    Luleå tekniska universitet.
    On the formation of magnetite-hematite-apatite "magmas" from metalliferous sediments at subduction zones1982In: Stockholm Contributions in Geology, ISSN 0585-3532, no 37, p. 21-42Article in journal (Refereed)
    Abstract [en]

    One interpretation of the plate tectonic theory suggests that marine sediments are brought down to large depths in the Earth and become intensely metamorphosed at subduction zones. A considerable fraction of these subducted sediments would consist of Fe, Mn and P rich exhalative-sedimentary deposits that have formed at spreading centers. A thermodynamic model for such alteration processes shows that exhalative sedimentary deposits would serve as source beds for magmatic magnetite-hematite-apatite rich ores whereas Mn would be lost due to reduction by organic matter, and subsequent removal in acid solutions, formed from interactions between clays and NaCl in pore waters. The alteration products show several similarities with the many magnetite-hematite-apatite ores which are located in the circumpacific orogenic belt

  • 223.
    Boström, Kurt
    Luleå tekniska universitet.
    Particulate and dissolved matter as sources for pelagic sediments1976In: Stockholm Contributions in Geology, ISSN 0585-3532, Vol. 30, p. 15-79Article in journal (Refereed)
    Abstract [en]

    Compositional data for pelagic sediments, for denudation products from the continents and for marine biological matter can explain how much material is deposited on the ocean floor in dissolved and particulate form. Geochemical mixing models demonstrate that only 2 particulate phases, namely average biological matter and average continental matter, have to be mixed in various proportions to reproduce most pelagic sediments in regard to the elements Si, Al, Ti, Zr, V, Cu, Ni, Zn, Fe, and Cr. CaCO SUB-3 , B, Mn and to some extent Ba usually do not fit the models, since these elements partake in redissolution and migration processes. These latter processes to a large extent occur in hemipelagic and shelf areas. It is probable that such 'hemipelagic pumping' of elements over to the pelagic domain also affects constituents like Cu, P SUB-2 0 SUB-5 , and probably also Ni, Y, La and Co, but the effects are too small to show up in the mixing models. Improved mixing models are produced if a volcanic phase also is involved; the volcanic phase containing Fe, Mn, V and Ba, and possibly additional trace elements in proportions similar to those found in the East Pacific Rise deposits. The models suggest that continental detritus delivers most of the Al, Ti, Zr, Fe, Mn and V, and that biological detritus delivers the main fraction of the Ca, Sr, Cu, Pb, B, Ba, Ni, and Zn to the sediments. In most areas the main fraction of the SiO SUB-2 is terrigenous

  • 224.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Burman, Jan-Ola
    Boström, B.
    Ponter, Christer
    Brandlöf, S.
    Alm, B.
    Geochemistry, mineralogy and origin of the sediments in the Gulf of Bothnia1978In: Proceedings of the Finnish-Swedish seminar on the Gulf of Bothnia: Vaasa, Finland, March 8th-9th, 1978 / [ed] D. Ross, Merentutkimuslaito , 1978, p. 8-35Conference paper (Refereed)
    Abstract [en]

    and DWD at larger depths, but DWD does also occur in some protected depressions where bottom depths may be 20-30 meters or less. DWD represents Postglacial deposits, whereas SWD represents more or less reworked tills. SWD largely consist of little altered rock detritus and are rich in silty, sandy or coarser fractions. DWD contains much clay sized material, but silts and sand may occur occasionally. In general SWD are rich in quartz and feldspars, whereas the DWD are poor in these minerals, but instead show higher contents of X-ray amorphus (background producing) matter, and clay-minerals. The relation Quartz-Feldspar also varies latitudinally, the feldspar-richest sediments occurring towards the North. DWD are enriched in Ti, Fe, Mn, Ba and probably some trace elements (e.g. Cu, Cr) whereas SWD are relatively rich in Si. Al, Ca, Na, and some traces occur in the same concentrations in both sediment types. DWD are identical to average shale in composition and SWD to average granite. This is probably due to a mechanical action, the panning of sediments by waves, bottom currents etc. preferentially moving clay and mica minerals into the deep basins, whereas coarse weathering residues, rich in quartz and feldspar, remain in shallow waters. Iron-manganese concretions occur extensively on the bottom areas that are protected from excessive abrasion and rapid accumulation. The nodules in the Bothnian Bay, are richer in Mn, Cu, Ni and Co than in other parts of Gulf of Bothnia. It is concluded that, in addition to organic matter, hydroxides and other fines may be important adsorbers of pollutants in sediments

  • 225. Boström, Kurt
    et al.
    Burman, J-O
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pontér, Christer
    Accumulation and selective loss patterns for Mn, Ba and other trace metals in the Baltic Sea1983In: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 64, no 18, p. 243-Article in journal (Other academic)
  • 226. Boström, Kurt
    et al.
    Burman, J-O
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pontér, Christer
    Accumulation and selective loss patterns for Mn, Ba and other trace metals in the Baltic Sea1984In: Abstracts: 16e Nordiska geologiska vintermötet, Stockholm 9-13 januari 1984 / [ed] G. Armands; S. Schager, Stockholm: Stockholm: Institutionen för musik- och teatervetenskap, Stockholms universitet, 1984, p. 33-Conference paper (Other academic)
  • 227.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Burman, J-O
    Luleå tekniska universitet.
    Pontér, Christer
    Luleå tekniska universitet.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Selective removal of trace elements from the Baltic by suspended matter1981In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 10, no 4, p. 335-354Article in journal (Refereed)
    Abstract [en]

    Suspended matter was collected at 30 stations in the Baltic and Kattegatt, at the thermocline and at the bottom, and analysed for Na, Ca, Mg, Si, Ti, Al, Fe, Mn, Ba, Sr, Ni and V. The composition of the suspended matter varies considerably, but can be described as a mixture of: (1) 12-25% terrigenous detritus with much Si, Al, Ti and Fe; (2) 75-88% biological matter with much Ni, V and Ba; and (3) some Mn-oxyhydroxide.The annual efflux of water from the Baltic is about 460 km3, with a suspended load in the Baltic straits of 1.2-3.6 mg ash material l-1 These values imply that much Si, Ti, Al, Fe, Sr, Ni and V and particularly much Ba and Mn are lost from the Baltic in the suspended load.The average suspended matter is richer in Mn(5×), Ba(2.5×), Sr(4×) and V(1.8×) than permanently depositing Baltic sediments. These constituents are relatively enriched in pelagic deposits, i.e. it is likely that much Mn, Ba and V in deep-sea sediments derive from the continents via suspended transport. This conclusion is supported by the similarity between suspended matter and average Atlantic pelagic sediment.

  • 228.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Glaccum, R.
    University of Miami.
    (Na, K)-phillipsite: its stability conditions and geochemical role in the deep sea1976In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 21, no 1, p. 47-58Article in journal (Refereed)
    Abstract [en]

    Phillipsite occurs in the deep sea in areas of very slow sedimentation and as the final alteration product of basalt, suggesting that it is thermodynamically stable. The thermodynamic data for gibbsite, kaolinite, K-feldspar, Na-feldspar, analcime and H4 SiO4 (aq), as well as the activities of seawater constituents are reasonably well known. These values and estimated entropies for Na- and K-phillipsites permit an estimate of the free energy of formation (at 25°C) for Na-phillipsite (5337.6 ± 6.7 kcal/mole) and for K-phillipsite (5382.4 ± 1.9 kcal/mole). The decomposition of phillipsite to analcime at 250°C yields the same result, suggesting that phillipsite is indeed a stable mineral. Phillipsite does not regulate the concentration of Na+ and K+ in seawater, but probably affects the pH of bottom waters and the composition of interstitial waters. No indications exist of "frozen in" equilibria from hydrothermal reactions at 100-200°C as could be expected by submarine volcanism.

  • 229.
    Boström, Kurt
    et al.
    Stockholms Universitet.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Boström, B.
    Andersson, Per
    Arvantides, N.
    Galanopoulos, V.P.
    Kalogeropoulos, S.
    Papavassiliou, C.
    Paritsis, S.
    Chemistry of hydrothermal solutions in drill hole GPK-1, Palaea Kameni, Santorini, Greece1990In: Thera and the Aegean world, III: proceedings of the third international congress, Santorini, Greece, 3-9 September 1989. Vol. 2, Earth sciences / [ed] David A. Hardy; Kurt Boström, The Thera Foundation , 1990, Vol. 3, p. 257-260Conference paper (Refereed)
  • 230.
    Boström, Kurt
    et al.
    Stockholms Universitet.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Boström, B.
    Andersson, Per
    Löfvendahl, R.
    Metallogenesis at Santorini: a subduction-zone related process; II, Geochemistry and origin of hydrothermal solutions on Nea Kameni, Santorini, Greece1990In: Thera and the Aegean world, III: proceedings of the third international congress, Santorini, Greece, 3-9 September 1989. Vol. 2, Earth sciences / [ed] David A. Hardy; Kurt Boström, The Thera Foundation , 1990, Vol. 3, p. 291-299Conference paper (Refereed)
  • 231.
    Boström, Kurt
    et al.
    Stockholms Universitet.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pontér, Christer
    Luleå tekniska universitet.
    Origin of iron-manganese-rich suspended matter in the Landsort Deep, NW Baltic Sea1988In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 24, no 1, p. 93-98Article in journal (Refereed)
    Abstract [en]

    Water sampling was undertaken in 1982 in the Landsort Deep, NW Baltic Sea, at eight depth levels. In the 0-150 m interval oxidizing conditions prevailed, with suspended phases being particularly rich in Fe (with a maximum at 150 m), Mn and Ba (with maxima at 100 m). The anoxic zone below 150 m showed high concentrations of dissolved Fe and particularly dissolved Mn which were much higher than in the Black Sea, for instance. This is probably due to the migratory behavior of the redoxcline in the Landsort Deep. The metal-rich suspended matter probably arises when dissolved Fe and Mn from the anoxic zone precipitate as hydroxyoxides at the redoxcline; lateral transport of such suspended matter may explain the large-scale selective loss of Mn and Ba from the Baltic basin.

  • 232.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Joensuu, Olivia
    Rosenstiel School of Marine and Atmospheric Science, University of Miami.
    Plankton: its chemical composition and its significance as a source of pelagic sediments1974In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 14, no 4, p. 255-271Article in journal (Refereed)
    Abstract [en]

    The absolute concentrations of minor and trace elements vary considerably in plankton. However, normalization of elemental abundances versus the minor elements Fe, Al and Zn (instead of the commonly used normalization versus seawater concentrations) demonstrates that these elements show remarkably constant proportions vis à vis each other. Thus, Ti, Fe, Al, Mn, V, and Zr occur in marine lower organisms in the same proportions as in the average shale, whereas Ba, Cr, Cu, Ni, Cd, Pb, Zn and B are enriched relative to the shale abundances, as are also Ca, Mg, Na, K, and Sr. These patterns appear to suggest that marine plankton are rich in lithogenic matter, but this is probably not the normal case.Contrary to the uniformity of plankton, sediments from the Pacific vary considerably in composition. Under the Equatorial high-productivity region the sediments show striking similarities with a mixture of average shale and average plankton mass, as could be expected, whereas sediments from the East Pacific Rise differ considerably from such mixtures. An iron-manganese phase (of deep-seated origin?), mixed with biological matter, on the other hand, yields model sediments with remarkable similarities to the East Pacific Rise deposits. It is therefore likely that biological processes account for a considerable fraction of some elements such as Cu, Ni, Zn and Ba also in the East Pacific Rise metalliferous sediments

  • 233.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Lysén, Lars
    Luleå tekniska universitet.
    Moore, Cynthia
    Marine Geology and Geophysics, Rosenstiel School of Marine Sciences, Miami.
    Biological matter as a source of authigenic matter in pelagic sediments1978In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 23, no 1-4, p. 11-20Article in journal (Refereed)
    Abstract [en]

    Pelagic sediments are rich in components that appear to have formed from seawater, so-called authigenic deposits. Such authigenic components are commonly well oxidized and are rich in many metals such as Cu, Co and Ni. On the other hand, most of these metals have restricted solubilities and very short residence times in seawater. True authigenesis can therefore only account for little of the "authigenic"-looking matter in the deep sea.Conservative mixing models, using average terrigenous matter, average marine biological matter, average volcanic matter (East Pacific Rise-emanation) and average basaltic matter, produce model sediments that are strikingly similar to real sediments.In the model sediments several of the trace-element abundances for instance those for Cu, Ni and Ba can only be explained by a large admixture of biological matter. Several of these elements are enriched in the authigenic phases in deep-sea sediments. This implies that most components that generally have been considered as authigenic are rearranged decay products of biological material.

  • 234.
    Boström, Kurt
    et al.
    Stockholms Universitet.
    Perissoratis, C.
    Galanopoulos, V.
    Papavassiliou, C.
    Boström, B.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kalogeropoulos, S.
    Geochemistry and structural control of hydrothermal sediments and new hot springs in the caldera of Santorini, Greece1990In: Thera and the Aegean world, III: proceedings of the third international congress, Santorini, Greece, 3-9 September 1989. Vol. 2, Earth sciences / [ed] David A. Hardy; Kurt Boström, The Thera Foundation , 1990, Vol. 3, p. 325-336Conference paper (Refereed)
  • 235.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Rydell, H.
    Geochemical behavior of U and Th during exhalative sedimentary processes1978In: Genesis of the manganese nodules: symposia of the Centre National de la Recherche Scientifique. Gif-sur-Yvette. 25-30 September 1978 / [ed] B.M. Sorensen, Centre National de la Recherche Scientifique, CNRS , 1978, p. 151-166Conference paper (Refereed)
    Abstract [en]

    Exhalative sediments are formed on a large scale on spreading (or active) ridges. Such sediments on the crest of the East Pacific Rise (EPR) are on the average rich in U (38 ppm) and poor in Th (2.4 ppm), contrary to other pelagic sediments that contan 3-6 ppm U and 3-11 ppm Th in the non-biogenic fraction. Most U in active ridge deposits is absorbed from sea water but some derives from different volcanic sources: (a) Shallow hydrothermal leaching of basalts form solutions with high SUP-234 U/SUP-238 U values; (b) Deep seated sources deliver solutions which are very rich in U but with radiochemical equilibrium between SUP-234 U and SUP-238 U; (c) Hydrothermal leaching of sediments is possibly an additional process. Bottom waters over the EPR show normal sea-water values for SUP-234 U/SUP-238 U, suggesting that volcanic U is delivered intemittently. Terrigenous matter delivers most of the Th, whereas biological matter probably is of negligible importance on active ridges as a source for Th. Volcanic processes are negligible sources of U in deposits formed far from spreading centers, such as the bauer Deep sediments and manganese nodules, since any adsorbed U is redissolved during diagenesis. Metamorphic alterations of U rich exhalative deposits could give them the reappearance of vein deposits; a detailed study of such deposits will probably reveal that many of them originally were sedimentary deposits.

  • 236.
    Boström, Kurt
    et al.
    Luleå tekniska universitet.
    Wiborg, Lars
    Luleå tekniska universitet.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geochemistry and origin of ferromanganese concretions in the Gulf of Bothnia1982In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 50, no 1-2, p. 1-24Article in journal (Refereed)
    Abstract [en]

    Ferromanganese concretions cover large areas of the Gulf of Bothnia. They are flat to well-rounded, the rounded ones being richer in oxyhydroxides of iron and manganese. Rounded and ellipsoidal nodules, particularly those in the northern Gulf of Bothnia, are richest in Mn, Ni, Ba and Cu, which probably coexist in a Mn oxyhydroxide phase. Flat nodules are enriched in Fe, P, rare earths and As, probably associated with an Fe oxy-hydroxide component. Aluminum, V, Cr and Ti occur in still another phase. The sediments of the gulf generally consist of a 10-50 mm-thick layer of oxidized surface sediment, enriched in Mn, Ba, P and Ni lying on top of reduced sediments which are diagenetically depleted in these elements. The remobilized elements have redeposited in the nodules, but this process cannot explain the origin of all the nodular material. Some released Mn, Ba and Ni furthermore enter into suspended phases, which eventually leave the Baltic Sea. The economic value of the nodules in the Gulf of Bothnia is probably limited at present.

  • 237. Bouvier, Laura
    et al.
    Costa, Maria
    Connelly, James
    Jensen, Ninna
    Wielandt, Daniel
    Storey, Michael
    Nemchin, Alexander
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Bellucci, Jeremy
    Swedish Museum of Natural History, Department of Geology.
    Moynier, Frederic
    Agranier, Arnaud
    Gueguen, Bleuenn
    Schonbachler, Maria
    Bizzarro, Martin
    Evidence for extremely rapid magma ocean crystallization and crust formation on Mars2018In: Nature, ISSN 1476-4687, Vol. 558, p. 586-589Article in journal (Refereed)
    Abstract [en]

    The formation of a primordial crust is a critical step in the evolution of terrestrial planets but the timing of this process is poorly understood. The mineral zircon is a powerful tool for constraining crust formation because it can be accurately dated with the uranium-to-lead (U–Pb) isotopic decay system and is resistant to subsequent alteration. Moreover, given the high concentration of hafnium in zircon, the lutetium-to-hafnium (176Lu–176Hf) isotopic decay system can be used to determine the nature and formation timescale of its source reservoir (1,2,3) Ancient igneous zircons with crystallization ages of around 4,430 million years (Myr) have been reported in Martian meteorites that are believed to represent regolith breccias from the southern highlands of Mars (4,5) These zircons are present in evolved lithologies interpreted to reflect re-melted primary Martian crust4, thereby potentially providing insight into early crustal evolution on Mars. Here, we report concomitant high-precision U–Pb ages and Hf-isotope compositions of ancient zircons from the NWA 7034 Martian regolith breccia. Seven zircons with mostly concordant U–Pb ages define 207Pb/206Pb dates ranging from 4,476.3 ± 0.9 Myr ago to 4,429.7 ± 1.0 Myr ago, including the oldest directly dated material from Mars. All zircons record unradiogenic initial Hf-isotope compositions inherited from an enriched, andesitic-like crust extracted from a primitive mantle no later than 4,547 Myr ago. Thus, a primordial crust existed on Mars by this time and survived for around 100 Myr before it was reworked, possibly by impacts (4,5) to produce magmas from which the zircons crystallized. Given that formation of a stable primordial crust is the end product of planetary differentiation, our data require that the accretion, core formation and magma ocean crystallization on Mars were completed less than 20 Myr after the formation of the Solar System. These timescales support models that suggest extremely rapid magma ocean crystallization leading to a gravitationally unstable stratified mantle, which subsequently overturns, resulting in decompression melting of rising cumulates and production of a primordial basaltic to andesitic crust (6,7).

  • 238.
    Bowles, John F. W.
    et al.
    Univ Manchester, Sch Earth & Environm Sci, Manchester, Lancs, England.
    Cook, Nigel J.
    Univ Adelaide, Sch Chem Engn, Adelaide, Australia.
    Sundblad, Krister
    Univ Turku, Dept Geog & Geol, Turku, Finland; St Petersburg State Univ, Inst Earth Sci, St Petersburg, Russia.
    Jonsson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Geol Survey Sweden, Dept Mineral Resources, Uppsala, Sweden.
    Deady, Eimear
    Lyell Ctr, British Geol Survey, Res Ave South, Edinburgh, Midlothian, Scotland; Univ Exeter, Camborne Sch Mines, Penryn Campus, Penryn, England.
    Hughes, Hannah S. R.
    Univ Exeter, Camborne Sch Mines, Penryn Campus, Penryn, England.
    Critical-metal mineralogy and ore genesis: contributions from the European Mineralogical Conference held in Rimini, September 20162018In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 82, p. S1-S4Article in journal (Other academic)
  • 239.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Raedler, K-H
    Yoshizawa's cross-helicity effect and its quenching2013In: Geophysical and Astrophysical Fluid Dynamics, ISSN 0309-1929, E-ISSN 1029-0419, Vol. 107, no 1-2, p. 207-217Article in journal (Refereed)
    Abstract [en]

    A central quantity in mean-field magnetohydrodynamics is the mean electromotive force , which in general depends on the mean magnetic field. It may however also have a part independent of the mean magnetic field. Here we study an example of a rotating conducting body of turbulent fluid with non-zero cross-helicity, in which a contribution to proportional to the angular velocity occurs (Yoshizawa, A., Self-consistent turbulent dynamo modeling of reversed field pinches and planetary magnetic fields. Phys. Fluids B 1990, 2, 15891600). If the forcing is helical, it also leads to an effect, and large-scale magnetic fields can be generated. For not too rapid rotation, the field configuration is such that Yoshizawa's contribution to is considerably reduced compared to the case without effect. In that case, large-scale flows are also found to be generated.

  • 240.
    Breitbarth, E.
    et al.
    Department of Chemistry, University of Otago, Dunedin.
    Achterberg, E.P.
    National Oceanography Center Southampton, University of Southampton.
    Ardelan, M.V.
    Norwegian University of Science and Technology, Department of Chemistry, Trondheim.
    Baker, A.R.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Buccarelli, E.
    Université Européenne de Bretagne.
    Chever, F.
    Université Européenne de Bretagne.
    Croot, P.L.
    IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Marine Biogeochemistry, Kiel.
    Duggen, S.
    IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Dynamics of the Ocean Floor, Kiel.
    Gledhill, M.
    National Oceanography Center Southampton, University of Southampton.
    Hassellöv, Martin
    University of Gothenburg.
    Hassler, C.
    Centre for Australian Weather and Climate Research (CAWCR), Hobart.
    Hoffmann, L.J.
    Department of Chemistry, University of Otago, Dunedin.
    Hunter, K.A.
    Department of Chemistry, University of Otago, Dunedin.
    Hutchins, D.A.
    Department of Biological Sciences, University of Southern California, Los Angeles.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jickells, T.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Lohan, M.C.
    Marine Institute, University of Plymouth.
    Nielsdóttir, M.C.
    National Oceanography Center Southampton, University of Southampton.
    Sarthou, G.
    Université Européenne de Bretagne.
    Schoemann, V.
    Ecologie des Systémes Aquatiques, Université Libre de Bruxelles.
    Trapp, J.M.
    University of Miami, Rosenstiel School of Marine and Atmospheric Science, Department of Marine and Atmospheric Chemistry, Miami.
    Turner, D.R.
    Department of Chemistry, University of Gothenburg.
    Ye, Y.
    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven.
    Iron biogeochemistry across marine systems: progress from the past decade2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 3, p. 1075-1097Article in journal (Refereed)
    Abstract [en]

    Based on an international workshop (Gothenburg, 14-16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas

  • 241.
    Breitbarth, Eike
    et al.
    Department of Chemistry, University of Otago, Dunedin.
    Gelting, Johan
    Walve, Jakob
    Department of Systems Ecology, Stockholm University.
    Hoffmann, Linn
    Department of Chemistry, University of Otago, Dunedin.
    Turner, David
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Hassellöv, Martin
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no Special issue, p. 2397-2420Article in journal (Refereed)
    Abstract [en]

    Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA). Up to 0.9 nmol Fe(II) L−1 were detected in light penetrated surface waters, which constitutes up to 20% to the dissolved Fe pool. This bioavailable iron source is a major contributor to the Fe requirements of Baltic Sea phytoplankton and apparently plays a major role for cyanobacterial bloom development during our study. Measured Fe(II) half life times in oxygenated water exceed predicted values and indicate organic Fe(II) complexation. Potential sources for Fe(II) ligands, including rainwater, are discussed. Fe(II) concentrations of up to 1.44 nmol L−1 were detected at water depths below the euphotic zone, but above the oxic anoxic interface. Mixed layer depths after strong wind events are not deep enough in summer time to penetrate the oxic-anoxic boundary layer. However, Fe(II) from anoxic bottom water may enter the sub-oxic zone via diapycnal mixing and diffusion.

  • 242. Breitbarth, Eike
    et al.
    Oschlies, A.
    National Oceanography Centre, Southampton, European Way, Southampton.
    LaRoche, J.
    Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Dusternbrooker Weg 20, 24105 Kiel.
    Physiological constraints on the global distribution of Trichodesmium: effect of temperature on diazotrophy2007In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 4, no 1, p. 53-61Article in journal (Refereed)
    Abstract [en]

    The cyanobacterium Trichodesmium is an important link in the global nitrogen cycle due to its significant input of atmospheric nitrogen to the ocean. Attempts to incorporate Trichodesmium in ocean biogeochemical circulation models have, so far, relied on the observed correlation between temperature and Trichodesmium abundance. This correlation may result in part from a direct effect of temperature on Trichodesmium growth rates through the control of cellular biochemical processes, or indirectly through temperature influence on mixed layer depth, light and nutrient regimes. Here we present results indicating that the observed correlation of Trichodesmium with temperature in the field reflects primarily the direct physiological effects of temperature on diazotrophic growth of Trichodesmium. Trichodesmium IMS-101 (an isolate of T. erythraeum) could acclimate and grow at temperatures ranging from 20 to 34C.Maximum growth rates (μmax=0.25 day-1) and maximum nitrogen fixation rates (0.13 mmol N mol POC-1 h-1) were measured within 24 to 30C. Combining this empirical relationship with global warming scenarios derived from state-of-the-art climate models sets a physiological constraint on the future distribution of Trichodesmium that could significantly affect the future nitrogen input into oligotrophic waters by this diazotroph.

  • 243.
    Brown, James R.
    Luleå tekniska universitet.
    Microearthquakes and seismic risk1978In: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 100, no 3, p. 307-13Article in journal (Refereed)
    Abstract [en]

    This paper is presented in the nature of a review of the potential of microearthquake surveys in seismotectonic studies, particularly seismic-risk analyses. Microearthquakes are generally considered as shocks with magnitude less than 3. They radiate, in general, higher frequencies than larger earthquakes and therefore microearthquake seismographs must be sensitive to frequencies typically up to 30 or 40 Hz. Mircroearthquakes are useful in seismotectonic studies because: (1) a greater number of small than large shocks occur in the same time, (2) extension to lower magnitudes of frequency-of-occurrence curves can yield more reliable seismic-risk statistics, (3) due to the reduced scale, both in space and time, very precise focal location is possible, often enabling mapping of fracture surfaces, (4) focal-mechanism solutions can further determine the fault surface and, in addition, the direction of slip, and (S) continuous monitoring of seismic activity is possible through the means of a permanent network of microearthquake systems.

  • 244.
    Brown, R.J.
    et al.
    Luleå tekniska universitet.
    Friesen, G.H.
    Gulf Oil, Canada.
    Hall, D.H.
    Department of Earth Sciences, University of Manitoba.
    Stephenson, O.G.
    Department of Earth Sciences, University of Manitoba.
    Weighted vertical stacking in crustal seismic reflection studies on the Canadian shield1977In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 25, no 2, p. 251-268Article in journal (Refereed)
    Abstract [en]

    Seismic reflection methods are being developed at the University of Manitoba to aid in determining fine crustal structures in the Precambrian of Manitoba and northwestern Ontario. Present-day environmental concern as well as mineshaft conditions necessitate the detonation of several smaller charges repeated, say, I times and followed by ''vertical'' stacking. To obtain the familiar ..sqrt..I improvement in signal-to-noise (S : N) amplitude ratio applying the straight-sum (SS) method, one assumes, among other things, that both S : N ratio and signal variance are the same on all traces. Dropping these assumptions, as we must for our data, it becomes necessary to apply weighting coefficients to optimize the S : N ratio of the stacked trace. We still assume the signal shapes to be the same for repeated shots, so for the jth trace on the record of the ith shot we model the time series as: t/sub ij/ = a/sub i/(s/sub j/ + n/sub ij/); where a/sub i/ is a scaling factor. The proper weights w/sub i/ are then shown to be proportional to sigma/sub si//sigma/sup 2//sub ni/ where sigma/sup 2/ is variance, or to ..gamma../sub i//a/sub i/ where ..gamma../sub i/ is S : N power ratio. Applying the weighted-stack (WS) method gives S : N amplitude ratios which are, on average, 55% of the optimal ratios expected from WS theory compared with only 24% for the SS method. The 45% shortfall in WS performance is ascribed mainly to trace-alignment (or time-delay) errors. Varying noise levels on individual traces, slight dissimilarity of signal shape, and correlated noise may also contribute to a lesser extent (in decreasing order of significance). This WS method appears to strike a good practical balance between S : N improvement and processing efficiency.

  • 245.
    Bruckman, Viktor
    et al.
    Austrian Academy of Sciences, Section for Mathematics and Natural Sciences.
    Hangx, SuzanneDepartment of Earth Sciences, Utrecht University.Ask, MariaLuleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    European Geosciences Union General Assembly 2014, EGU Division Energy, Resources & the Environment (ERE)2014Collection (editor) (Refereed)
  • 246. Bruggeman, C.
    et al.
    Maes, N.
    Christiansen, B. C.
    Stipp, S. L. S.
    Breynaert, E.
    Maes, A.
    Regenspurg, Simona
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology (moved 20130630).
    Malmström, Maria E.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Liu, X.
    Grambow, B.
    Schaefer, Th
    Redox-active phases and radionuclide equilibrium valence state in subsurface environments - New insights from 6th EC FP IP FUNMIG2012In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 27, no 2, p. 404-413Article in journal (Refereed)
    Abstract [en]

    Within the 6th EC FP Integrated Project "Fundamental Processes of Radionuclide Migration'' (FUNMIG), progress has been made to improve knowledge about the phases and reaction mechanisms involved in complex reduction processes of radionuclide contaminants in natural subsurface environments. This review paper gives an overview of the achievements made by the research groups involved in this project, and puts the scope and results of the studies in a more global context. Firstly, both thermodynamic and experimental evidence show that green rust is present and reactive in subsurface groundwater with a composition that spans the Fe(II)/Fe(III) redox boundary. Green rust has been shown to reduce Np(V), Se(VI) and Se(IV), but the pathways for the redox processes and the reaction products that result are complicated, and change as a function of the reaction parameters. Secondly, considerable evidence has emerged that Se(IV) is reduced on Fe(II)-bearing minerals which are ubiquitous in subsurface environments. The stable Se valence state in the presence of FeS(2) has been shown to be Se(0). Also, natural dissolved humic substances that contain sufficient electron donating capacity are capable of interacting with, and possibly reducing, Se(IV) to lower valence states. Thirdly, the influence of HCO(3)(-) and organic ligands on the uptake and reduction of U(VI) on Fe(II)-bearing minerals was investigated. While it appeared that HCO(3)(-) decreased the extent of U(VI) uptake by the reducing surface, the fraction of reduced U(IV) in the solid phase increased with increasing HCO(3)(-) concentration. In contrast with the observations for HCO(3)(-), organic ligands decreased both the extent of U uptake, as well as the fraction of U(IV) found in the solid phase. The studies performed within FUNMIG show that investigating reduction-oxidation mechanisms require (1) a detailed control over reaction conditions (anoxic atmosphere, purification of solid phases, initial radionuclide speciation), (2) a rigorous follow-up of reaction products (both solution chemistry and spectroscopic methods), and (3) the consideration of slow kinetics in the setting up of an experiment. These requirements make the study and assessment of redox processes one of the most demanding scientific challenges for geochemists who are asked to make predictions for radionuclide transport behaviour in the environment.

  • 247.
    Bruschini, Enrico
    et al.
    Sapienza Università di Roma.
    Speziale, Sergio
    Geoforschungszentrum, Potsdam.
    Andreozzi, Giovanni
    Sapienza Università di Roma.
    Bosi, Ferdinando
    Sapienza Università di Roma.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    The elasticity of MgAl2O4-MnAl2O4 spinels by Brillouin scattering and an empirical approach for bulk modulus prediction2015In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 100, p. 644-651Article in journal (Refereed)
  • 248.
    Brüchert, Volker
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raymond, Caroline
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sediment med nyckelroll i näringsväven2014In: HavsUtsikt, ISSN 1104-0513, Vol. 1, p. 20-21Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    I sedimenten sker processer som kan vara helt avgörande för näringsbalansen i havsvattnet. Omvandlingen av fosfor till olika former är relativt väl känd, medan detaljerna i kvävets kretslopp är betydligt mindre kända. Mer än hälften av den årliga tillförseln av kväve till Östersjön beräknas omsättas till kvävgas i sedimentet, vilket sedan går förlorat för de flesta marina organismer.

  • 249.
    Buckland, Philip I.
    et al.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Eriksson, Erik J.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Palm, Fredrik
    Umeå University, Faculty of Arts, Humlab.
    SEAD - The Strategic Environmental Archaeology Database: Progress Report Spring 20142014Report (Other academic)
    Abstract [en]

    This report provides an overview of the progress and results of the VR:KFI infrastructure projects 2007-7494 and (825-)2010-5976. It should be considered as a status report in an on-going long-term research infrastructure development project.

  • 250. Budd, D.A.
    et al.
    Troll, V.R.
    Deegan, F.M.
    Jolis, E.M.
    Smith, V.C.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Harris, C.
    Freda, C.
    Hilton, D.R.
    Halldorsson, S.A.
    Bindemann, I.N.
    Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 40624Article in journal (Refereed)
    Abstract [sv]

    Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ18O values. Overall, Toba quartz crystals exhibit comparatively high δ18O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ18O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum ∆core−rim = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ18O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ18O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.

2345678 201 - 250 of 1671
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