The trace of the Pacific‐Cocos‐Nazca triple junction in the Central Pacific and the formation of an overlapping spreading centre     

Martin Meschede  Udo Barckhausen  Martin Engels  Wilhelm Weinrebe 《地学学报》2008,20(3):246-251

The `plate tectonic mirror image' to the region of the Cocos and Nazca plates, which are currently being subducted beneath Central America, is preserved in the Central Pacific around 120°W just south of the equator. Cruise SO‐180 investigated this remote area during project CENTRAL and acquired new magnetic and bathymetric data. A plate tectonic model for the ‘mirror image’ is presented based on the newly acquired as well as reprocessed existing data. Discordant magnetic anomaly patterns and bathymetric structures indicate at least two major reorganization events (19.5 and 14.7 Myr), which can be detected both in the Cocos‐Nazca spreading system and in the East Pacific Rise. Irregularities in the anomaly pattern and curvilinear structures on the sea floor of the survey area are interpreted in terms of a fossil overlapping spreading centre at the location where the Farallon break‐up originated.  相似文献   

Synthetic near Σ5 (210)/[100] grain boundary in YAG fabricated by direct bonding: structure and stability     

Katharina Hartmann  Richard Wirth  Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(5):291-300

Several macroscopic physical and chemical properties, such as rheology, elasticity, or transport properties are governed by grain boundary processes. An improved understanding of the structure and evolution of grain boundaries has thus become a key challenge in geosciences and material sciences. Here, we report the structure of near Σ5 (210)/[100] grain boundaries in Y₃Al₅O₁₂ (YAG), which were synthesised by the wafer direct bonding method. The produced grain boundaries were annealed at different temperatures, ranging from 673 to 1,873 K. The grain boundaries annealed at different temperatures are not distinguishable based on their flatness and apparent cohesiveness in high resolution TEM (HRTEM) micrographs, but show a considerable step in their mechanical stability at around 1,273 K, a temperature that corresponds to roughly half the melting temperature of YAG. This study further focuses on the effect of a slight misorientation of the two crystals on the grain boundary structure and we discuss if the boundary can reach a state of minimum energy configuration during annealing. Along the grain boundaries, we observed a long-range strain contrast with a periodicity of 40 nm, which has not been reported for high-angle grain boundaries so far. We conclude that this contrast is caused by faceting along the grain boundary plane, which is needed to achieve minimum energy configuration of the grain boundary plane.  相似文献   

Meso- and bathy-pelagic fish parasites at the Mid-Atlantic Ridge (MAR): Low host specificity and restricted parasite diversity     

Sven Klimpel  Markus Wilhelm Busch  Tracey Sutton  Harry Wilhelm Palm 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):596-603

Seven meso- and bathy-pelagic fish species from the Mid-Atlantic Ridge (MAR) were firstly studied for fish parasites and feeding ecology. With a total of seven parasite species, the 247 meso- and bathy-pelagic deep-sea fish specimens belonging to the families Melamphaidae (3 spp.), Myctophidae (3 spp.) and Stomiidae (1 sp.) revealed low parasite diversity. The genetically identified nematodes Anisakis simplex (s.s.) and Anisakis pegreffii from the body cavity, liver and muscles of Myctophum punctatum were the most abundant parasites, reaching a prevalence of 91.4% and mean intensity of 3.1 (1–14). Anisakis sp. (unidentified) infected Chauliodus sloani and Poromitra crassiceps. Bothriocephalidean and tetraphyllidean cestode larvae infected Benthosema glaciale, the latter also occurring in C. sloani and Scopelogadus beanii, at low prevalences. Adult parasites at low infection rates included the digenean Lethadena sp. (2.9%), and the two copepod species Sarcotretes scopeli (5.7%) and Tautochondria dolichoura (5.3–11.4%). The myctophid Lampanyctus macdonaldi and the melamphaid Scopelogadus mizolepis mizolepis were free of parasites. Analyses of the stomach contents revealed crustaceans, especially copepods and euphausiids for the myctophids and also amphipods for the melamphaids as predominant prey items. While all stomachs showing distinct content comprising often unidentified ‘tissue’ (possibly gelatinous zooplankton), only C. sloani preyed upon fish. Though this feeding habit would enable transfer of a variety of crustacean-transmitted parasites into the fish, the parasite fauna in the meso- and bathy-pelagic fish was species poor. All observed parasites showed low host specificity, demonstrating no distinct pattern of host–parasite co-evolution. The MAR is no barrier for the parasite distribution in the North Atlantic meso- and bathy-pelagial.  相似文献   

Preliminary paleolimnological study of rocha lagoon, SE Uruguay     

Felipe García-Rodríguez  Laura Del Puerto  Carola Castieira  Hugo Inda  Roberto Bracco  Peter Spechmann  Burkhard Wilhelm Scharf 《Limnologica》2001,31(3)

Physical, chemical and biological data from a sedimentary profile of Rocha lagoon (Uruguay) are presented. Analyses of silica remains showed that opal phytoliths, diatoms, sponge spicules and chrysophyte cysts were the most important contributors to biogenic silica. Organic matter, total nitrogen and total phosphorus were used to infer past trophic development. Physical analysis of sediments allowed us to identify five lithological units related to sea level variation and climatic events.  相似文献   

Analytical solution of a basic geothermal equation     

H. Wilhelm 《Geophysical Journal International》1994,119(2):684-685

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Die geodynamische Entwicklung der Thiersee- und der Karwendelmulde (Nördliche Kalkalpen)     

Nagel  Karl -Heinz  Schütz  Karsten -Ingo  Schütz  Sylvia  Wilmers  Wilhelm  Zeil  Werner 《International Journal of Earth Sciences》1976,65(1):536-557

Zusammenfassung Die Thiersee- und die Karwendelmulde in den Nördlichen Kalkalpen sind als zwei getrennte, E-W-verlaufende Synklinen entwickelt. Ihre Länge zwischen Kufstein und Mittenwald beträgt über 70 km.Systematische geologische Aufnahmen — Kartierung, Stratigraphie, Sedimentologie und Gefügekunde — ergaben, daß die Thierseemuide im Raum von Achenkirch nicht — wie früher vermutet wurde — in die Karwendelmulde umbiegt. Die Auswertung von mehr als 45 000 Gefügemessungen mit Hilfe eines EDV-Programms bewies vielmehr, daß Thierseemuide und Karwendelmulde zwei parallele, unabhängige Strukturen sind, die durch die komplizierte tektonische Zone von Achenkirch getrennt werden.Die paläogeographische Entwicklung und der Ablauf der Bewegungen werden im Überblick skizziert.

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Systematic geological survey showed that the Thiersee and Karwendel synclines in the Northern Calcareous Alps are two parallel structures, separated by a slightly folded intersection. The synclines do not turn into each other, as was presumed by earlier workers.The tectonic situation in the area of Achenkirch was cleared by evaluation of more than 45,000 field texture data by a computer program. Mapping as well as stratigraphical and sedimentological analysis supports the tectonic model. The paleogeographic development and tectonic history are briefly described.

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Résumé Les dépressions du «Thiersee» et du «Karwendel», dans les Alpes calcaires du Nord, sont deux synclinaux indépendants de direction Est-Ouest. Elles font 70 km de long entre Kufstein et Mittenwald.Des relevés géologiques systématiques — levés géologiques, stratigraphie, sédimentologie et structurologie — démontrèrent que, dans la région d'Achenkirch, la dépression du «Thiersee» ne contourne pas la dépression du «Karwendel» (comme on l'a longtemps supposé!). L'exploitation par ordinateur de plus de 45.000 mesures structurales révéla au contraire, que ces dépressions sont deux structures parallèles et indépendantes, séparées par la zone tectonique complexe d'Achenkirch.Le développement paléogéographique et le déroulement des mouvements font l'objet d'une vue d'ensemble.

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U-Pb investigations on zircons from pre-Variscan gneisses—I. A study from the Schwarzwald,West Germany     

Wolfgang A. Todt  Wilhelm Büsch 《Geochimica et cosmochimica acta》1981,45(10):1789-1801

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Zur Bildung von Gangspalten eine Einführung in die Untersuchungen der Siegerländer Eisenerzgänge     

Wilhelm Bierther 《International Journal of Earth Sciences》1955,44(1):306-325

Ohne Zusammenfassung  相似文献   

Über pleistozäne Gebirgsbildung und rezente Krustenbewegungen in der Niederrheinischen Bucht     

Hans Wilhelm Quitzow  Otto Vahlensieck 《International Journal of Earth Sciences》1955,43(1):56-67

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The geochemical cycle of boron: Constraints from boron isotope partitioning experiments between mica and fluid   总被引：8，自引：0，他引：8  

Bernd Wunder  Anette Meixner  Rolf L. Romer  Richard Wirth  Wilhelm Heinrich 《Lithos》2005,84(3-4):206-216

The fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3.0 GPa/500 °C and 3.0 GPa/700 °C. For near-neutral fluids Δ¹¹B_(mica-fluid) = δ¹¹B_(mica) − δ¹¹B_(fluid) is − 10.9 ± 1.3‰ at 500 °C, and − 6.5 ± 0.4‰ at 700 °C. This supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas, clays and melts. The T-dependence of this effect is approximated by the equation Δ¹¹B_{(mica,clay,melt–neutral fluid)} = − 10.69 · (1000/T [K]) + 3.88; R² = 0.992, valid from 25 °C for fluid–clay up to about 1000 °C for fluid–silicate melt. Experiments at 0.4 GPa that used strongly basic fluids produced significantly lower fractionations with Δ¹¹B_{(mica–fluid)} of − 7.4 ± 1.0‰ at 400 °C, and − 4.8 ± 1.0‰ at 500 °C, showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated. Field studies have shown that boron concentrations and ¹¹B/¹⁰B-ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench, thus reflecting the thermal structure of the subducting slab. Our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct P–T range. Continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs.  相似文献