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  • 1
    Electronic Resource
    Electronic Resource
    Peroxidative membrane damage in human erythrocytes induced by a concerted action of iodoacetate, vanadate and ferricyanide
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 901 (1987), S. 67-77 
    Details
    ISSN: 0005-2736
    Keywords: (Human erythrocyte) ; Erythrocyte membrane ; Ferricyanide ; Lipid peroxidation ; Membrane permeability ; Vanadate
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2736(87)90257-4
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  • 2
    Electronic Resource
    Electronic Resource
    Nd and Sr isotopic compositions and REE abundances of cretaceous MORB (Holes 417D and 418A, Legs 51, 52 and 53)
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 48 (1980), S. 171-184 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(80)90180-6
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  • 3
    Electronic Resource
    Electronic Resource
    Anomalous Sm−Nd ages for the early Archean Onverwacht Group Volcanics (1990)
    Springer
    Contributions to mineralogy and petrology 104 (1990), S. 27-34 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract New Sm−Nd isotopic data for eight samples of basalt and komatiite from the Tjakastad Subgroup (lower Onverwacht Group) of the Barberton Greenstone Belt (BGB) of the Kaapvaal craton in southern Africa are reported. They give new constraints on the interpretation of Sm−Nd ages for the Subgroup and highlight the petrogenesis of Tjakastad volcanics. Although Sm−Nd isotopic data earlier reported for volcanic rocks from the Tjakastad Subgroup yielded an “isochron” age of 3526±48 Ma, the new results give a much younger “isochron” date of 3269±84 Ma. The 3526±48 Ma “isochron” age has been obtained in combining samples ranging in composition from felsic volcanics to ultrabasic komatiites and is thus considered suspect with regard to the pre-requisite of geochronology that all the studied rocks must have had identical initial isotopic compositions. The new “isochron” date of 3269±84 Ma has been obtained in combining samples solely of basic/ultrabasic composition. It might thus represent a more correct age for the eruption of the Tjakastad Subgroup volcanism. In fact, owing to the potential problem of source heterogeneity and also in the light of geochronological and geochemical arguments we show that this date also has little chance to have any strict chronological meaning. Most likely, the Tjakastad volcanics were formed 3450 Ma ago. Also most likely, their source rocks were isotopically heterogeneous and the 3530 Ma and 3270 Ma linear arrays are not true but apparent “isochrons”. Based on the calculated ɛNd (3450) values and other geochemical arguments, we show that three possible sources might have been involved: depleted mantle, primitive mantle and older continental crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310643
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  • 4
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    Biosynthesis of fungal melanins and their importance for human pathogenic fungi (2003)
    In:  EPIC3Fungal genetics and biology, 38(2), pp. 143-158
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Response of tropical African and East Atlantic climates to orbital forcing over the last 1.7 Ma (2007)
    In:  Geological Society Special Publication 247: 65-84.
    Details
    Publication Date: 2007-10-08
    Description: Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.
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    Enhancement of human immunodeficiency virus 1 replication in monocytes by 1,25-dihydroxycholecalciferol. (1991)
    National Academy of Sciences
    Details
    Publication Date: 1991-08-01
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Discovery of in situ super-reducing, ultrahigh-pressure phases in the Luobusa ophiolitic chromitites, Tibet: New insights into the deep upper mantle and mantle transition zone (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-06-03
    Description: Previous research on super-reducing ultrahigh-pressure (SuR UHP) phases from the Tibetan ophiolitic chromitites were mainly conducted on isolated grains extracted from extremely large samples. This approach has been questioned because of possible contamination. To elucidate the occurrence and origin of these SuR UHP minerals, we studied 33 thin sections and rock chips of three ophiolitic chromitites from the Yarlung Zangbo suture zone. Here we report and analyze unambiguously in situ SuR UHP assemblages from the ophiolitic chromitites by electron probe micro-analyzer, scanning microscope and Laser Raman spectroscope. The SuR UHP and associated phases include: (1) blue moissanite as inclusions in olivine (Fo 96–98 ), and in olivine domains between disseminated chromite grains; (2) multiple inclusions of moissanite + wüstite + native Fe in olivine; (3) FeNi and FeCr alloys in olivine and chromite; and (4) native Fe and Si in chromite. Crustal asphaltum and h-BN also occur as inclusions in chromite. Our documented in situ SuR UHP phases, combined with the previously inferred existence of ringwoodite + stishovite, all indicate that these assemblages formed under a highly reducing environment (oxygen fugacities several orders of magnitude lower than that of the iron-wüstite buffer) in the mantle transition zone (MTZ) and in the deep upper mantle. Diamond + moissanite with distinct 13 C-depleted compositions from chromitites have a metasedimentary carbon source. Associations with existing crustal minerals in chromitites demonstrate that carbon-bearing metasedimentary rocks were recycled into the mantle through subduction, and locally modified its composition. Finally we propose a three-stage model to explain the formation of SuR UHP phase-bearing chromitite. Discoveries of SuR UHP phases in Luobusa and other ophiolitic podiform chromitites from the polar Ural Mountains and from Myanmar imply existence of a new type of ophiolitic chromitite. Such occurrences provide an additional window to explore the physical-chemical conditions of the MTZ, mantle dynamics, and the profound recycling of crustal materials.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 8
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    Geochemistry and geochronology of the Troodos ophiolite: An SSZ ophiolite generated by subduction initiation and an extended episode of ridge subduction? (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-12-11
    Description: New trace-element, radiogenic isotopic, and geochronologic data from the Troodos ophiolite, considered in concert with the large body of previously published data, give new insight into the tectonic history of this storied ophiolite, as well as demonstrating the variability of suprasubduction-zone ophiolites, and differences between them and commonly used modern analogs. Similar to earlier studies, we find that island-arc tholeiite of the lower pillow lava sequence erupted first, followed by boninite. We further divide boninitic rocks into boninite making up the upper pillow lava sequence, and depleted boninites that we consider late infill lavas. We obtained an Ar-Ar age from arc tholeiite of 90.6 ± 1.2 Ma, comparable to U-Pb ages from ophiolite plagiogranites. New biostratigraphic data indicate that most of the basal pelagic sedimentary rocks that conformably overlie the boninitic rocks are ca. 75 Ma. This suggests that voluminous eruption of boninitic rocks persisted until ca. 75 Ma. Limited eruption of boninitic lavas may have continued until 55.5 ± 0.9 Ma, based on the Ar-Ar age we obtained. The duration of arc magmatism at Troodos (at least 16 m.y., with some activity perhaps extending 35 m.y.) without the development of a mature arc edifice greatly exceeds that of other well-studied suprasubduction-zone ophiolites. We propose that Troodos was formed over a newly formed subduction zone, similar to many proposed models, but that the extended period of magmatism (boninitic) resulted from a prolonged period of ridge subduction.
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Oldest Paleo-Tethyan ophiolitic melange in the Tibetan Plateau (2016)
    Geological Society of America (GSA)
    Details
    Publication Date: 2016-03-01
    Description: An early Paleozoic ophiolitic mélange has recently been documented in the west Gangma Co area, north-central Tibetan Plateau. It is composed of serpentinite, isotropic and cumulate gabbros, basalt, and plagiogranite. Whole-rock geochemical data suggest that these rocks were formed in an oceanic-ridge setting, and the depletion in Nb and Ti indicates their suprasubduction zone nature. Furthermore, whole-rock Nd ( t ) (+3.5 to +10.6) and zircon Hf ( t ) values (+11.4 to +14.5) suggest that these rocks were derived from a long-term depleted mantle source. These geochemical features, combined with the rock types and their field relationships, suggest the rocks represent an ophiolite suite. Zircon U-Pb dating of isotropic gabbros and plagiogranites yielded weighted mean ages ranging from 437 to 501 Ma, which makes the west Gangma Co ophiolitic mélange the oldest Paleo-Tethys ophiolitic mélange in the Tibetan Plateau. The main Paleo–Tethys Ocean basin probably opened in the Middle Cambrian; it continued to grow throughout the Paleozoic and closed in the later Triassic. The Paleo–Tethys Ocean was formed by the breakup of the northern margin of Gondwana, with southward subduction of the proto-Tethys oceanic lithosphere along the northern margin of the supercontinent.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    U-Pb geochronology of zircon and rutile from the Kokchetav metamorphic belt, northern Kazakhstan, and its tectonic implications (2017)
    Schweizerbart
    Details
    Publication Date: 2017-03-03
    Description: The Kokchetav ultrahigh-pressure ( UHP ) metamorphic belt, located in the western part of the Central Asia Orogenic Belt (CAOB), consists of a well-studied diamond-bearing western domain and a less well-known coesite-bearing domain. To better understand the time of subduction and exhumation of the eastern domain and the tectonic evolution of the entire Kokchetav microcontinent, we conducted SIMS U-Pb dating of zircon from eclogite and rutile from whiteschist of the eastern domain. We identified two types of zircon from the Kulet eclogite: type-I zircon grains possess a large, low-cathodoluminescence (CL) magmatic core with high Th/U ratios of 1.0–1.5, yielding a Proterozoic protolith age (1437±29 Ma), and a thin rim of intermediate or high-CL. Type-II zircon crystals are rounded to ovoid, and have very low Th/U ratios (〈0.1–0.2), yielding two population ages (532±58 and 497±5 Ma), which we interpret as the ages of peak metamorphism and decompression metamorphism, respectively. Rutile separates from three samples of whiteschist have low Th/U ratios (〈〈0.1). U-Pb isotopic analyses yielded two ages (526±9 and 498±11 Ma), interpreted to represent two stages of retrograde metamorphism. Combined with geochronological data from the literature and our results indicate that UHP rocks from both the eastern and western domains represent Proterozoic protoliths, and that they were subjected to nearly coeval UHP metamorphism at 527–537 Ma, even though the two domains formed at different peak P-T conditions. Exhumation took place during 526–498 Ma for the eastern domain, comparable to the western domain (526–507 Ma). The UHP slabs were exhumed from depths of 100–200 km to a mid-crustal level over 20–25 My. The final suturing of the uplifted Kokchetav microcontinent against the Stepnyak paleo-island arc occurred at ≤500 Ma. Our new SIMS U-Pb age data and previous petrological and structural analyses provide new constraints on the metamorphism and tectonic evolution of the Kokchetav microcontinent, and on the continental history in the western part of the CAOB.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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