Amplitudes of long-period PcP and the core-mantle boundary     

Gerhard Müller  Abdel Hafiz Mula  Søren Gregersen 《Physics of the Earth and Planetary Interiors》1977,14(1):30-40

The amplitudes of the core reflection PcP are sensitive to the wave velocities and densities in the neighborhood of the core-mantle boundary (CMB). We study the amplitude ratio of the long-period phases PcP and P from two South American deep-focus earthquakes with favorable fault-plane solution, depth and magnitude, as recorded by WWNSS and CSN stations in North America.Comparison is made with long-period PcP/P amplitude ratios, derived from theoretical seismograms for a variety of CMB models. Models from previous studies, which were mainly derived from short-period PcP observations and which are characterized by discrete layers above the CMB, are almost all inconsistent with the long-period data. The data also discriminate against low nonzero S velocities below the CMB. Simple first-order-discontinuity models of the CMB, for instance according to the Jeffreys-Bullen earth model or according to recent models based mainly on free oscillations, explain the data reasonably well.Model improvements are attempted by varying the P-velocity gradient above the CMB. The best amplitude fit is obtained for a rather strong decrease in P velocity with depth in this zone which, however, gives no acceptable traveltime fit for PcP. The scatter in body-wave amplitudes is considerable even for long-period waves and may prevent the correct assessment of that part of the amplitude variation of a phase with distance that is due to the variation of velocities and densities with depth alone.  相似文献   

Die alpidischen Stockwerke der südlichen Ägäis     

Dr. Albrecht Baumann  Dr. Gerhard Best  Prof. Dr. Horst Wachendorf 《International Journal of Earth Sciences》1977,66(1):492-522

Zusammenfassung Im Bereich der südlichen Ägäis überlagern vier allochthone Stockwerke den autochthonen Plattenkalk (Perm-Oligozän). Die allochthonen Serien entstammen ursprünglich konzentrisch angeordneten mesozoisch-alttertiären Faziesräumen der zentralen Ägäis. Die tektonische Abfolge aus neritischen Karbonaten, pelagischen Karbonaten und einem vulkano-sedimentären Komplex, die durch inkompetente Zwischenmittel (Mélange) getrennt werden, besteht über den gesamten Bogen. Fazielle und stratigraphische Merkmale sowie die Art der Deformation ermöglichen die Korrelation der Teilprofile des südägäischen Deckenstapels und dessen Anknüpfung an die südwestliche Türkei. Die kinematische Analyse des Deckenbaus führt zu dem Bild eines sich ausbreitenden Mantel-Diapirs, an dessen geneigter Grenzfläche ein gravitativer Transport ausgelöst wurde.

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In the realm of the Southern Aegean Arc four allochthonous units are piled up above the autochthonous Cherty Limestone (Permian-Oligocene). The allochthonous units are derived from different Mesozoic to Paleogene facies zones which originally were arranged in concentric belts in the Central Aegean Sea. The nappe pile consists — from bottom to top — of neritic carbonates, pelagic carbonates and a volcano-sedimentary complex along the entire arc. These competent units are separated by incompetent members of mainly flyschoid sediments, acting as lubricants. The intercalated sediments were deformed to mélanges due to tectonic transport. Facies analysis, stratigraphy and the style of deformation lead to a correlation of type sections of the southern Aegean nappe pile and its relation to the southwestern part of Turkey. The nappe transport is caused by diapiric uplift and lateral shifting of a thermal dome. A radial gravity transport occurred on its inclined boundary plane.

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Résumé Dans la région de l'Egée méridionale le Calcaire en plaquettes, en position autochthone (Permian-Oligocène) repose sous quatre unités allochthones. Les séries allochthones proviennent de différentes zones de faciès mésozoique-paléogène qui à l'origine étaient disposées concentriquement dans l'Égée centrale. Les nappes sont constituées tout le long de l'arc entier pour des carbonates néritiques, des carbonates pélagiques et un complexe volcano-sédimentaire. Ces unités compétentes sont séparées par des formations incompétentes, notamment des sédiments flyschoides qui ont servi de lubrificant. Ces sédiments intercalés ont été déformés en mélanges par le transport tectonique. Des caractéristiques de faciès et d'ordre stratigraphique, et le style de la déformation rendent possible la corrélation entre les fractions des nappes sud-égéennes et leur rattachement au sud-ouest de la Turquie. Le transport des nappes est lié au déploiement latéral de l'enveloppe d'un dôme diapirique, qui a déclanché un transport radial, par gravité, le long de sa base inclinée.

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Diese Untersuchungen wurden im Rahmen des Schwerpunktprogrammes Geodynamik des mediterranen Raumes der Deutschen Forschungsgemeinschaft durchgeführt und gefördert. Ausgehend von einer Geländetätigkeit auf Kreta in den Jahren 1973–1975 erfolgten im Herbst 1975 Vergleichsbegehungen auf dem Peloponnes, auf Rhodos und den Kykladen. Von den Mitarbeitern des Institutes für Geologie und Paläontologie der TU Braunschweig übernahmen dankenswerterweise FrauBeddies und FrauBusch die Niederschrift des Manuskriptes sowie Übersetzungsarbeiten. HerrStosnach führte freundlicherweise die Reinzeichnung der Abbildungen und Fotoarbeiten aus.  相似文献   

Creep response of the lunar crust in mare regions from an analysis of crater deformation     

A.W. Gerhard Kunze 《Physics of the Earth and Planetary Interiors》1974,8(4):375-387

The settling trends of 318 lunar mare craters are compared with predictions of numerical finite-element models in order to determine the creep response of the upper lunar mare crust. No settling is evident in craters smaller than 5 km in diameter. Settling rates of larger craters increase as function of crater size in a manner suggesting a non-linear lunar creep response corresponding to the power law $\text{ε}\text{?}\text{= 8.3 · 10}{}^{\mathrm{?34}}\text{σ}{}^2$ where έ is the strain rate and σ is the differential stress. However, the observed nonlinearity is probably an apparent nonlinearity resulting from the temperature induced viscosity decrease with depth due to a lunar crustal temperature gradient of 3° C/km and a creep activation energy of 20 kcal/mole. It is concluded that creep in the lunar medium is essentially Newtonian, and that the effective viscosity of the upper lunar mare crust is (1.6 ± 0.3) · 10²⁵ poise.  相似文献   

Synthesis and thermal stability of 2 \frac{1}{2}-octahedral sodium mica,NaMg2.5 (OH)2∫i4O10]     

Gerhard Franz  Prof. Dr. Egon Althaus 《Contributions to Mineralogy and Petrology》1974,46(3):227-247

A new 2 \(\frac{1}{2}\) -octahedral sheet silicate, NaMg_2.5 Si₄O₁₀ (OH)₂, has been synthesized from oxide mixtures in the temperature range 500–600°C at pressures between 1 and 5 kb. The lattice parameters are a ₀ = 5.298 Å, b ₀ = 9.047 Å, c ₀ = 9.479 Å and ß=99.55°. X-ray data are given in the text. At temperatures above 605° C/1 kb and 630° C/5 kb, it decomposes to magnesiorichterite plus quartz.  相似文献   

Evidence for enhanced hydration on the northern flank of Olympus Mons, Mars     

Giancarlo Bellucci  Joern Helbert  Francesca Altieri  Dennis Reiss  Jean-Pierre Bibring  Stephan van Gasselt  Harald Hoffmann  Yves Langevin  Gerhard Neukum  Franois Poulet 《Icarus》2007,192(2):361-377

In this paper we report about a small region on the northern scarp of Olympus Mons showing an increase of the 3 μm hydration band in the OMEGA spectra, together with low superficial temperatures. Although water ice clouds can occurs on the flank of big martian volcanoes, radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band. A fit of the 1.9–3 μm absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin (τ=0.08 at 3 μm) layer of dust. Thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere. If water ice is responsible for the observed spectral behavior, it might consist of a number of ice or snow patches possibly deposited in small depressions.  相似文献   

Light-induced disassembly of dusty bodies in inner protoplanetary discs: implications for the formation of planets     

Gerhard Wurm 《Monthly notices of the Royal Astronomical Society》2007,380(2):683-690

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Mineralization of vestimentiferan tubes at methane seeps on the Congo deep-sea fan     

Antonie Haas  Crispin T.S. Little  Heiko Sahling  Gerhard Bohrmann  Tobias Himmler  Jörn Peckmann 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(2):283-293

Vestimentiferan tube worms are prominent members of modern methane seep communities and are totally reliant as adults on symbiotic sulphide-oxidizing bacteria for their nutrition. The sulphide is produced in the sediment by a biochemical reaction called the anaerobic oxidation of methane (AOM). A well-studied species from the Gulf of Mexico shows that seep vestimentiferans ‘mine’ sulphide from the sediment using root-like, thin walled, permeable posterior tube extensions, which can also be used to pump sulphate and possibly hydrogen ions from the soft tissue back into the sediment to increase the local rate of AOM. The ‘root-balls’ of exhumed seep vestimentiferans are intimately associated with carbonate nodules, which are a result of AOM. We have studied vestimentiferan specimens and associated carbonates from seeps at the Kouilou pockmark field on the Congo deep-sea fan and find that some of the posterior ‘root’ tubes of living specimens are enclosed with carbonate indurated sediment and other, empty examples are partially or completely replaced by the carbonate mineral aragonite. This replacement occurs from the outside of the tube wall inwards and leaves fine-scale relict textures of the original organic tube wall. The process of mineralization is unknown, but is likely a result of post-mortem microbial decay of the tube wall proteins by microorganisms or the precipitation from locally high flux of AOM derived carbonate ions. The aragonite-replaced tubes from the Kouilou pockmarks show similar features to carbonate tubes in ancient seep deposits and make it more likely that many of these fossil tubes are those of vestimentiferans. These observations have implications for the supposed origination of this group, based on molecular divergence estimates.  相似文献   

The dependence of clustering on galaxy properties     

Cheng Li  Guinevere Kauffmann  Y. P. Jing  Simon D. M. White  Gerhard Börner  F. Z. Cheng 《Monthly notices of the Royal Astronomical Society》2006,368(1):21-36

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Experimental evidence for an effect of early-diagenetic interaction between labile and refractory marine sedimentary organic matter on nitrogen dynamics     

Robert Turnewitsch  Bettina Domeyer  Gerhard Graf 《Journal of Sea Research》2007,57(4):270-280

In most natural sedimentary systems labile and refractory organic material (OM) occur concomitantly. Little, however, is known on how different kinds of OM interact and how such interactions affect early diagenesis in sediments. In a simple sediment experiment, we investigated how interactions of OM substrates of different degradability affect benthic nitrogen (N) dynamics. Temporal evolution of a set of selected biogeochemical parameters was monitored in sandy sediment over 116 days in three experimental set-ups spiked with labile OM (tissue of Mytilus edulis), refractory OM (mostly aged Zostera marina and macroalgae), and a 1:1 mixture of labile and refractory OM. The initial amounts of particulate organic carbon (POC) were identical in the three set-ups. To check for non-linear interactions between labile and refractory OM, the evolution of the mixture system was compared with the evolution of the simple sum of the labile and refractory systems, divided by two. The sum system is the experimental control where labile and refractory OM are virtually combined but not allowed to interact. During the first 30 days there was evidence for net dissolved-inorganic-nitrogen (DIN) production followed by net DIN consumption. (Here ‘DIN’ is the sum of ammonium, nitrite and nitrate.) After  30 days a quasi steady state was reached. Non-linear interactions between the two types of OM were reflected by three main differences between the early-diagenetic evolutions of nitrogen dynamics of the mixture and sum (control) systems: (1) In the mixture system the phases of net DIN production and consumption commenced more rapidly and were more intense. (2) The mixture system was shifted towards a more oxidised state of DIN products [as indicated by increased (nitrite + nitrate)/(ammonium) ratios]. (3) There was some evidence that more OM, POC and particulate nitrogen were preserved in the mixture system. That is, in the mixture system more particulate OM was preserved while a higher proportion of the decomposed particulate N was converted into inorganic N. It can be concluded that during the first days and weeks of early diagenesis the magnitude and composition of the flux of decompositional dissolved N-compounds from sediments into the overlying water was influenced by non-linear interactions of OM substrates of different degradability. Given these experimental results it is likely that the relative spatial distributions of OM of differing degradability in sediments control the magnitude and composition of the return flux of dissolved N-bearing compounds from sediments into the overlying water column.  相似文献   

Molecular and isotopic partitioning of low-molecular-weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high-flux seepage site     

Thomas Pape  André Bahr  Janet Rethemeyer  John D. Kessler  Heiko Sahling  Kai-Uwe Hinrichs  Stephan A. Klapp  William S. Reeburgh  Gerhard Bohrmann 《Chemical Geology》2010,269(3-4):350-363

Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone.Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (> 99.85 mol.% of ∑[C₁–C₄, CO₂]). Molecular ratios of LMWHC (C₁/[C₂ + C₃] > 1000) and stable isotopic compositions of methane (δ¹³C = ? 53.5‰ V-PDB; D/H around ? 175‰ SMOW) indicated predominant microbial methane formation. C₁/C₂₊ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by > 0.03 mol.% (∑[C₁–C₄, CO₂]) relative to the other gas types and the virtual lack of ¹⁴C–CH₄ indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely.As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% ∑(C₁–C₄, CO₂)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of ¹⁴C–CH₄ (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.  相似文献