Geophysical excitation of the Earth orientation parameters EOP and its contribution to GGOS     

Vronique Dehant  Olivier de Viron  Jean-Pierre Barriot 《Journal of Geodynamics》2005,40(4-5):394

We discuss how the geophysical fluids affect the Earth orientation parameters (EOP) and in particular polar motion and nutation. We show that the Earth orientation modeling is a perfect example of the integrated approach recommended by GGOS. GGOS considers the Earth system as a whole, including the solid Earth as well as the fluid components; geodesy observes and models the dynamics inside this system through the static and time-varying gravity field, the station displacements, and the Earth orientation parameters and the associated length-of-day variation, nutation and polar motion. Global-scale transfer in the Earth system and its geodetic consequences is proposed to be the central theme of GGOS. We show that the Earth orientation parameters perfectly fit this theme.  相似文献   

Morphology and sedimentology of a complex debris flow in a clay‐shale basin     

Alexandre Remaître  Jean-Philippe Malet  Olivier Maquaire 《地球表面变化过程与地形》2005,30(3):339-348

Coupling morphological, sedimentological, and rheological studies to numerical simulations is of primary interest in defining debris‐flow hazard on alluvial fans. In particular, numerical runout models must be carefully calibrated by morphological observations. This is particularly true in clay‐shale basins where hillslopes can provide a large quantity of poorly sorted solid materials to the torrent, and thus change both the mechanics of the debris flow and its runout distance. In this context, a study has been completed on the Faucon stream (southeastern French Alps), with the objectives of (1) defining morphological and sedimentological characteristics of torrential watersheds located in clay‐shales, and (2) evaluating through a case study the scouring potential of debris flows affecting a clay‐shale basin. Morphological surveys, grain‐size distributions and petrographic analyses of the debris‐flow deposits demonstrate the granular character of the flow during the first hectometre, and its muddy character from there to its terminus on the debris fan. These observations and laboratory tests suggest that the contributing areas along the channel have supplied the bulk of the flow material. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Molybdenite Re–Os dating constrains gravitational collapse of the Sveconorwegian orogen, SW Scandinavia     

Bernard Bingen  Holly J. Stein  Michel Bogaerts  Olivier Bolle  Joakim Mansfeld 《Lithos》2006,87(3-4):328-346

Re–Os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the Sveconorwegian orogen in SW Scandinavia. A 1019 ± 3 Ma planar quartz vein defines a minimum age for brittle behaviour in central Telemark. In Rogaland–Vest Agder, molybdenite associated with deformed quartz and pegmatite veins formed between 982 ± 3 and 947 ± 3 Ma in the amphibolite-facies domain (three deposits) and between 953 ± 3 and 931 ± 3 Ma west of the clinopyroxene-in isograd (two deposits) in the vicinity of the 0.93–0.92 Ga Rogaland anorthosite complex. The data constrain the last increment of ductile deformation to be younger than 0.95 and 0.93 Ga in these two metamorphic zones, respectively. Molybdenite is the product of an equilibrium between biotite, oxide and sulfide minerals and a fluid or hydrated melt phase, after the peak of 1.03–0.97 Ga regional metamorphism. Molybdenite precipitation is locally episodic. A model for gravitational collapse of the Sveconorwegian orogen controlled by lithospheric extension after 0.97 Ga is proposed. In the west of the orogen, the Rogaland–Vest Agder sector is interpreted as a large shallow gneiss dome, formed slowly in two stages in a warm and structurally weak crust. The first stage at 0.96–0.93 Ga was associated with intrusion of the post-collisional hornblende–biotite granite suite. The second stage at 0.93–0.92 Ga, restricted to the southwesternmost area, was associated with intrusion of the anorthosite–mangerite–charnockite suite. Most of the central part of the orogen was already situated in the brittle upper crust well before 0.97 Ga, and did not undergo significant exhumation during collapse. In the east of the orogen, situated against the colder cratonic foreland, exhumation of high-grade rocks of the Eastern Segment occurred between 0.97 and 0.95 Ga, and included preservation of high-pressure rocks but no plutonism.  相似文献   

Germanium isotopic variations in igneous rocks and marine sediments   总被引：1，自引：0，他引：1  

Olivier Rouxel  Albert Galy 《Geochimica et cosmochimica acta》2006,70(13):3387-3400

A new technique for the precise and accurate determination of Ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal. The analyses were performed using a continuous flow hydride generation system coupled to a MC-ICPMS. Samples have been purified through anion- and cation-exchange resins to separate Ge from matrix elements and eliminate potential isobaric interferences. Variations of ⁷⁴Ge/⁷⁰Ge ratios are expressed as δ⁷⁴Ge values relative to our internal standard and the long-term external reproducibility of the data is better than 0.2‰ for sample size as low as 15 ng of Ge. Data are presented for igneous and sedimentary rocks, and the overall variation is 2.4‰ in δ⁷⁴Ge, representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of Ge is not unique. Co-variations of ⁷⁴Ge/⁷⁰Ge, ⁷³Ge/⁷⁰Ge and ⁷²Ge/⁷⁰Ge ratios follow a mass-dependent behaviour and imply natural isotopic fractionation of Ge by physicochemical processes. The range of δ⁷⁴Ge in igneous rocks is only 0.25‰ without systematic differences among continental crust, oceanic crust or mantle material. On this basis, a Bulk Silicate Earth reservoir with a δ⁷⁴Ge of 1.3 ± 0.2‰ can be defined. In contrast, modern biogenic opal such as marine sponges and authigenic glauconite displayed higher δ⁷⁴Ge values between 2.0‰ and 3.0‰. This suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the δ⁷⁴Ge of the seawater to +3.0‰.This suggests that seawater is isotopically heavy relative to Bulk Silicate Earth and that biogenic opal may be significantly fractionated with respect to seawater. Deep-sea sediments are within the range of the Bulk Silicate Earth while Mesozoic deep-sea cherts (opal and quartz) have δ⁷⁴Ge values ranging from 0.7‰ to 2.0‰. The variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz. Further work is now required to determine Ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification.  相似文献   

Unusual variations of dissolved As, Sb and Ni in the Rhône River during flood events     

Patrick Ollivier  Olivier Radakovitch  Bruno Hamelin 《Journal of Geochemical Exploration》2006,88(1-3):394

Dissolved major and trace element concentrations were determined from November 2000 to December 2003 in the lower Rhône River (France). Subsurface water samples were collected about twice a month and more regularly during flood events. An unusual trend was observed for As, Sb, Ni and Ba concentrations which increased with river discharge at the beginning of the floods, in contrast with other elements. Variations of Sb/Na and As/Na molar ratios show that it is related to higher contributions of waters from western tributaries of the Rhône River enriched in As, Sb, Ni and Ba due to ancient mining activities. These unusual variations of dissolved element concentrations are thus interpreted as mark of a water mass origin within the watershed.  相似文献   

Origine des eaux des émergences karstiques chlorurées du Languedoc-Roussillon     

Olivier Hébrard  Séverin Pistre  Nicolas Cheynet  Jean Dazy  Christelle Batiot-Guilhe  Jean-Luc Seidel 《Comptes Rendus Geoscience》2006,338(10):703-710

The origin of chloride-rich karstic spring waters representative of the Languedoc-Roussillon region has been investigated with a hydrochemical approach. To this end, the major and trace elements most often used in the study of saline environments have been considered (Cl, SO₄, Br, B, Li). This study allowed distinguishing the different end-members of the various chloride-rich karstic spring waters (evaporitic, marine, geothermal). Associated with the Cl, Br and B contents, the Li/SO₄ ratio appeared as a relevant tracer for the determination of the origin of lithium and by extension of the considered waters. To cite this article: O. Hébrard et al., C. R. Geoscience 338 (2006).  相似文献   

Is the instrumental drift of superconducting gravimeters a linear or exponential function of time?     

Michel Van Camp  Olivier Francis 《Journal of Geodesy》2007,81(5):337-344

The instrumental drift of the superconducting gravimeter in Membach, Belgium, is estimated using 9 years of co-located and episodic absolute gravity measurements. We show that the best model of the long-term drift of the SG-C021 is an exponential. The thermal levelers used to compensate tilts are unlikely to induce the observed drift. Rather, the capacitance bridge, magnetic variations, gas adsorption on the levitating sphere, or helium gas pressure variations around it are most likely the possible combined causes of the observed instrumental drift. In practice, either linear or exponential drift models are equivalent as long as the record duration does not exceed 10 years. For longer records, this study demonstrates that an exponential models the drift better than a simple linear trend.  相似文献   

Were the 2.1-Gyr fossil colonial organisms discovered in the Francevillian basin (Palaeoproterozoic,Gabon) buried by turbidites?     

Olivier Parize  Jean-Louis Feybesse  François Guillocheau  Thierry Mulder 《Comptes Rendus Geoscience》2013,345(2):101-110

The Francevillian series (Gabon) in which the Earth's oldest large colonial organisms were recently discovered (El Albani et al., 2010) were deposited 2 Gyr ago. These series are usually interpreted as a fining-upward basin-fill sequence composed by five superimposed lithological terms noted FA to FE. New studies initiated by AREVA, allowed new data to be collected on the southwestern edge of the Francevillian basin, particularly on newly excavated outcrops. Facies interpretations show that the Poubara sandstones and associated shales and black shales (upper part of FB,FB2a), correspond to turbidites deposited on an upper slope rather than one a shelf, submitted to tidal currents or storm wave action. These new interpretations based on facies association, sedimentary geometries, and basin evolution show that the depositional environment could be a turbidite lobe set at a palaeobathymetry deeper than 200 m.  相似文献   

Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images     

Brett W. Denevi  Steven D. Koeber  Mark S. Robinson  W. Brent Garry  B. Ray Hawke  Thanh N. Tran  Samuel J. Lawrence  Laszlo P. Keszthelyi  Olivier S. Barnouin  Carolyn M. Ernst  Livio L. Tornabene 《Icarus》2012,219(2):665-675

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.  相似文献   

Trojans’ Odyssey: Unveiling the early history of the Solar System     

Philippe Lamy  Pierre Vernazza  Joel Poncy  Vincent Martinot  Emmanuel Hinglais  Elisabet Canalias  Jim Bell  Dale Cruikshank  Olivier Groussin  Joern Helbert  Francesco Marzari  Alessandro Morbidelli  Pascal Rosenblatt  Holger Sierks 《Experimental Astronomy》2012,33(2-3):685-721

In our present understanding of the Solar System, small bodies (asteroids, Jupiter Trojans, comets and TNOs) are the most direct remnants of the original building blocks that formed the planets. Jupiter Trojan and Hilda asteroids are small primitive bodies located beyond the ‘snow line’, around respectively the L₄ and L₅ Lagrange points of Jupiter at ～5.2?AU (Trojans) and in the 2:3 mean-motion resonance with Jupiter near 3.9?AU (Hildas). They are at the crux of several outstanding and still conflicting issues regarding the formation and evolution of the Solar System. They hold the potential to unlock the answers to fundamental questions about planetary migration, the late heavy bombardment, the formation of the Jovian system, the origin and evolution of trans-neptunian objects, and the delivery of water and organics to the inner planets. The proposed Trojans’ Odyssey mission is envisioned as a reconnaissance, multiple flyby mission aimed at visiting several objects, typically five Trojans and one Hilda. It will attempt exploring both large and small objects and sampling those with any known differences in photometric properties. The orbital strategy consists in a direct trajectory to one of the Trojan swarms. By carefully choosing the aphelion of the orbit (typically 5.3?AU), the trajectory will offer a long arc in the swarm thus maximizing the number of flybys. Initial gravity assists from Venus and Earth will help reducing the cruise time as well as the ΔV needed for injection thus offering enough capacity to navigate among Trojans. This solution further opens the unique possibility to flyby a Hilda asteroid when leaving the Trojan swarm. During the cruise phase, a Main Belt Asteroid could be targeted if requiring a modest ΔV. The specific science objectives of the mission will be best achieved with a payload that will perform high-resolution panchromatic and multispectral imaging, thermal-infrared imaging/ radiometry, near- and mid-infrared spectroscopy, and radio science/mass determination. The total mass of the payload amounts to 50?kg (including margins). The spacecraft is in the class of Mars-Express or a down-scaled version of Jupiter Ganymede Orbiter. It will have a dry mass of 1200?kg, a total mass at launch of 3070?kg and a ΔV capability of 700?m/s (after having reached the first Trojan) and can be launched by a Soyuz rocket. The mission operations concept (ground segment) and science operations are typical of a planetary mission as successfully implemented by ESA during, for instance, the recent flybys of Main Belt asteroids Steins and Lutetia.  相似文献