Book review     

John C. Davis  David B. Kitts  Georges Verly 《Mathematical Geosciences》1992,24(5):577-586

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Théorie du pendule de Zöllner et du pendule de Lettau     

Georges Jobert 《Pure and Applied Geophysics》1959,44(1):25-73

Summary The theory of a Zöllner's horizontal pendulum with perfect wires of suspension is made. We use the Euler's angles of the axes of a system fixed in the moving body relatively to fixed axes and a fourth angle caracterising the amplitude of a motion of translation. We give the conditions for the decoupling of the four types of motion (pure rotation, pitching, rolling, translation) and the equations of forced motions.A rigorous theory of Lettau's double pendulum is initiated. We suppose that the primary pendulum has only one degree of freedom. First the case of a secondary pendulum not disturbing the primary one is examined, and then the case of an indifferent primary pendulum, wich enables us to understand what happens in the normal case. The potential energy of the secondary pendulum is not always a minimum in the central position when the plane of symmetry is vertical and it is possible that parasitesolutions appear, stabler than the central one. This study is extended to the case of a non-vertical plane of symmetry and indications are given for the study of the free motions of the system.In conclusion we could say that this system is simple only at first sight. Its use would be necessary in the case of a real great drift of the underground of the station. But in the contrary case ordinary simple pendulums are sufficient and more easy to understand.

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Resumo La movoj de horizontala Zöllnera pendolo estas difinataj pere de la Euleraj anguloj de triaksa sistemo ligita al la pendolo, rilate al fiksa sistemo, kaj de kvara angulo rilata al translacia movado. Ni donas la kondiojn necesajn por la senkuplado de tiuj kvar movoj (pura rotacio, tangado, ruligado, translacio) kaj la ekvaciojn de la devigataj movoj.La teorio de Lettaùa duobla pendolo estas multe pli kompleksa. Supozente ke la primara pendolo havas nur unu gradon de libereco, ni studas unue la movojn de la sistemo kiam la sekundara pendolo ne perturbas la primaran aù kiam tiu-i estas en indiferenta ekvilibro. Tio permesas kompreni tion kio okazas en la normala kazo. ar la potenciala energio de la sekundara pendolo ne estas iam minimuma en la centra pozicio kiam la simetria ebeno estas vertikala, parazitaj pozicioj povas ekzisti kiuj estas pli stabilaj ol la centra. Ni ekzamenas ankaù la kazon de nevertikala ebeno de simetrio kaj indikas kiel studi la liberajn movojn de la sistemo.

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Georges Blaha 《Journal of Geodesy》1979,53(4):296

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From subduction to transform motion: a seabeam survey of the Hellenic trench system     

Xavier Le Pichon  Jacques Angelier  Jean Aubouin  Nicolas Lyberis  Serge Monti  Vincent Renard  Henri Got  Ken Hsu¨  Yossi Mart  Jean Mascle  Drummond Matthews  Dimitri Mitropoulos  Pandelis Tsoflias  Georges Chronis 《Earth and Planetary Science Letters》1979,44(3):441-450

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.  相似文献   

Etude expérimentale du comportement de l'uranium dans les magmas: États d'oxydation et coordinance     

Georges Calas 《Geochimica et cosmochimica acta》1979,43(9):1521-1531

Depending upon oxygen fugacity, uranium exists in three different oxidation states in magmatic silicate liquids. The hexavalent state, present as the uranyl group, UO²⁺₂, is stable under highly oxidizing conditions, but can still be detected in the presence of the NiNiO buffer. Under the same conditions the pentavalent state forms about 30–40% of total uranium and is also characteristic of relatively high oxygen fugacities. Optical absorption spectra obtained on granitic and basaltic glasses synthesized in the presence of the NiNiO buffer are very different: this is interpreted as being due to the presence of UO⁺₂ complexes in the former and 6-coordinated U(V) in the latter. The tetravalent state is the most stable under reducing conditions: at the FeFeO buffer, it is the only one present. An 8-coordinated U(IV) species seems the most probable, by comparison of the spectra with those of crystallized U(IV) compounds. The trivalent state was not detected, even under the most reducing conditions. Interpretation of the spectra obtained in the glasses in terms of coordination and bonding is however difficult, due to the lack of knowledge of 5f-systems in iono-covalent systems such as oxide glasses. The presence of the pentavalent state must be taken into account in discussing partition coefficients of uranium and trans-uranium compounds in natural and synthetic systems (because of the effect of oxygen fugacity and oxide ion activity on the U(IV) U(V) system). During postmagmatic hydrothermal processes U(V) is destroyed, resulting in the early precipitation of U(IV) containing minerals and possible migration of uranyl ions.  相似文献   

Modelling observed and future runoff from a glacierized tropical catchment (Cordillera Blanca, Perú)   总被引：1，自引：1，他引：0  

Irmgard Juen  Georg Kaser  Christian Georges 《Global and Planetary Change》2007,59(1-4):37

Monthly runoff from the 34.3% glacierized tropical catchment of Llanganuco in the tropical Cordillera Blanca, Perú, is successfully simulated and compared with a measured 44 year time series. In the investigation area, the climate is characterized by all-year round homogenous temperature conditions and a strong variability in air humidity and moisture content of the atmosphere. Thus, contrary to the mid latitudes, the seasonal variation in glacier melt strongly depends on moisture-related variables, rather than on air temperature. The here presented ITGG-2.0-R model aims for these requirements. The lack of moisture-related input data other than precipitation demands for an intermediate calibration step. Net shortwave radiation, the emissivity of the atmosphere and a sublimation/melt ratio are related to precipitation amounts. Runoff is well simulated and correlates with the measured record with r² = 0.76. Seasonally obtained r² are only slightly smaller. On a long-term, the cumulative deviation is minor, and the mean annual cycle of runoff is reproduced rather well (r² = 0.99). Based on four different IPCC climate change scenarios, future runoff is simulated. All runoff scenarios are modelled for the respective steady-state glacier extent. This leads to a reduction in the glacier size and a decreased amount of glacier melt. On the other hand, direct runoff increases due to larger glacier free areas. Consequently, mean annual runoff remains almost unchanged, but the seasonality intensifies considerably with more runoff during the wet and less runoff during the dry season.  相似文献   

Multi-scale slope instabilities along the Nile deep-sea fan,Egyptian margin: A general overview     

Lies Loncke  Virginie Gaullier  Laurence Droz  Emmanuelle Ducassou  Sébastien Migeon  Jean Mascle 《Marine and Petroleum Geology》2009,26(5):633-646

The Nile deep-sea fan (NDSF), turbiditic system reaching a size of about 90,000 km², has been investigated since 1998 by several geophysical methods (multibeam bathymetry, backscatter imagery, seismic data, 3–5 kHz echo-sounding). The analysis of this important data set evidenced that the NDSF is the locus of numerous multi-scale slope instabilities. Three main types of instabilities have been defined, mainly on the basis of their size or origin. (1) First type of instabilities related to the generalized gravity spreading of the Plio-Quaternary deep-sea fan on Messinian salt layers. This global spreading is accommodated by numerous localized slides. (2) Second type of instabilities correspond to giant mass movements probably triggered either by earthquakes, fluids, or climate and eustatic oscillations. Finally, (3) third type of instabilities correspond either to localized levee liquefactions or to thin-skinned slides on the steep slopes of the Eratosthenes seamount. The deposits generated by these slope movements greatly participate in the building of the NDSF. The characterization of these different instabilities, in a petroleum province as the NDSF, has important implications in terms of risk assessments when considering drilling operations.  相似文献   

Alteration geochemistry of the Nopal I uranium deposit (Sierra Peña Blanca,Mexico), a natural analogue for a radioactive waste repository in volcanic tuffs     

Georges Calas  Pierre Agrinier  Thierry Allard  Philippe Ildefonse 《地学学报》2008,20(3):206-212

Natural analogues provide an approach to characterize and test the long‐term modelling of a repository performance. This article presents geochemical information about the alteration conditions of the Nopal I uranium deposit, Mexico, an analogue for the proposed Yucca Mountain radioactive waste repository. Mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous, according to petrographic observations. Trace element geochemistry (U, Th, REE) provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions. O‐ and H‐isotope geochemistry of kaolinite, smectite, opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25–75 °C, a low‐temperature context, unusual for volcanic‐hosted uranium deposits. This temperature range is compatible with some post‐closure evolution models of the proposed Yucca Mountain repository.  相似文献   

Thick sections of layered ultramafic cumulates in the Oman ophiolite revealed by an airborne hyperspectral survey: Petrogenesis and relationship to mantle diapirism     

Harold Clénet  Georges Ceuleneer  Patrick Pinet  Bénédicte Abily  Yves Daydou  Esther Harris  Isma Amri  Céline Dantas 《Lithos》2010,114(3-4):265-281

Using the HyMap instrument, we have acquired visible and near infrared hyperspectral data over the Maqsad area of the Oman ophiolite (~ 15 × 60 km). This survey allowed us to identify and map the distribution of clinopyroxene-rich cumulates (inter-layered clinopyroxenites and wehrlites) whose occurrence was previously undocumented in this area. The cumulates reach several hundred meters in thickness and crop out at distances exceeding 15 km on both sides of the Maqsad former spreading centre. They occur either in mantle harzburgites, as km-sized layered intrusions surrounded by fields of pegmatitic dykes consisting of orthopyroxene-rich pyroxenite and gabbronorites, or at the base of the crustal section where they are conformably overlain by cumulate gabbros. These ultramafic cumulates crystallized from silica- and Mg-rich melts derived from a refractory mantle source (e.g. high Cr#, low [Al₂O₃], low [TiO₂]). These melts are close to high-Ca boninites, although, strictly speaking, not perfect equivalents of present-day, supra-subduction zone, boninites. Chemical stratigraphy reveals cycles of replenishment, mixing and fractional crystallization from primitive (high Mg#) melts, typical of open magma chambers and migration of inter-cumulus melts. The TiO₂ content of clinopyroxene is always low (≤ 0.2 wt.%) but quite variable compared to the associated pegmatites that are all derived from a source ultra-depleted in high field strength elements (HFSE). This variability is not caused by fractional crystallization alone, and is best explained by hybridization between the ultra-depleted melts (parent melts of the pegmatites) and the less depleted mid-ocean ridge basalts (MORB) parent of the dunitic–troctolitic–gabbroic cumulates making up the crustal section above the Maqsad diapir.We propose that, following a period of magma-starved spreading, the Maqsad mantle diapir, impregnated with tholeiitic melts of MORB affinity, reached shallow depths beneath the ocean ridge. This diapir induced melting of the formerly accreted and hydrothermally altered lithosphere. At this stage, these boninitic-like lithospheric melts crystallized as pegmatitic dykes. As the diapir continued to rise, the amount of MORB reaching shallow depths increased, together with the surrounding temperature, leading to the formation of magma chambers where the crystallization of layered cumulates became possible. These cumulates remained rich in pyroxene and devoid of plagioclase as long as the contribution of MORB-derived melts was moderate relative to the lithospheric-derived melts. As the contribution of MORB to the refilling of the magma chamber increased, gabbroic cumulates started to crystallize.  相似文献   

Authigenic carbonates related to active seepage of methane-rich hot brines at the Cheops mud volcano,Menes caldera (Nile deep-sea fan,eastern Mediterranean Sea)   总被引：1，自引：0，他引：1  

Catherine Pierre  Germain Bayon  Marie-Madeleine Blanc-Valleron  Jean Mascle  Stéphanie Dupré 《Geo-Marine Letters》2014,34(2-3):253-267

On the passive margin of the Nile deep-sea fan, the active Cheops mud volcano (MV; ca. 1,500 m diameter, ~20–30 m above seafloor, 3,010–3,020 m water depth) comprises a crater lake with hot (up to ca. 42 °C) methane-rich muddy brines in places overflowing down the MV flanks. During the Medeco2 cruise in fall 2007, ROV dives enabled detailed sampling of the brine fluid, bottom lake sediments at ca. 450 m lake depth, sub-surface sediments from the MV flanks, and carbonate crusts at the MV foot. Based on mineralogical, elemental and stable isotope analyses, this study aims at exploring the origin of the brine fluid and the key biogeochemical processes controlling the formation of these deep-sea authigenic carbonates. In addition to their patchy occurrence in crusts outcropping at the seafloor, authigenic carbonates occur as small concretions disseminated within sub-seafloor sediments, as well as in the bottom sediments and muddy brine of the crater lake. Aragonite and Mg-calcite dominate in the carbonate crusts and in sub-seafloor concretions at the MV foot, whereas Mg-calcite, dolomite and ankerite dominate in the muddy brine lake and in sub-seafloor concretions near the crater rim. The carbonate crusts and sub-seafloor concretions at the MV foot precipitated in isotopic equilibrium with bottom seawater temperature; their low δ¹³C values (–42.6 to –24.5‰) indicate that anaerobic oxidation of methane was the main driver of carbonate precipitation. By contrast, carbonates from the muddy lake brine, bottom lake concretions and crater rim concretions display much higher δ¹³C (up to –5.2‰) and low δ¹⁸O values (down to –2.8‰); this is consistent with their formation in warm fluids of deep origin characterized by ¹³C-rich CO₂ and, as confirmed by independent evidence, slightly higher heavy rare earth element signatures, the main driver of carbonate precipitation being methanogenesis. Moreover, the benthic activity within the seafloor sediment enhances aerobic oxidation of methane and of sulphide that promotes carbonate dissolution and gypsum precipitation. These findings imply that the coupling of carbon and sulphur microbial reactions represents the major link for the transfer of elements and for carbon isotope fractionation between fluids and authigenic minerals. A new challenge awaiting future studies in cold seep environments is to expand this work to oxidized and reduced sulphur authigenic minerals.  相似文献