Mineralogical and geochemical evolution of the 1982–1983 Galunggung eruption (Indonesia)     

Marie-Christine Gerbe  Alain Gourgaud  Olgeir Sigmarsson  Russell S Harmon  Jean-Louis Joron  Ariel Provost 《Bulletin of Volcanology》1992,54(4):284-298

Pyroclastic deposits from the 1982–1983 eruption of Galunggung volcano (Java, Indonesia) reflect preeruptive magmatic evolution which is of interest because of: (1) its duration of nine months, compared to a few hours or days for most historical eruptions; (2) the diversity of eruptive styles, from ash and scoria flows to phreatomagmatic explosions, and to the strombolian activity that marked the end of the eruption; and (3) the progressive variation in chemical composition with time, from andesite (58 wt.% SiO₂) to high-Mg basalt (47 wt.% SiO₂). The 1982–1983 Galunggung basalts are rather primitive: 10 to 12 wt% MgO, 180 to 200 ppm Ni and 550 to 700 ppm Cr. Despite the presence of about 40% phenocrysts, they may represent the most primitive basalts recognized in western Java. Basalts contain phenocrysts of olivine (Fo_90-80), diopside-salite, and plagioclase (An_95-75). Andesites contain plagioclase (An_80–60), augite, hypersthene (En_67-64), and titanomagnetite. The distribution of mineral compositions in each petrographic type is nearly unimodal, although scarce plagioclase and olivine xenocrysts have been observed. Abundance of gabbroic cumulates associated with the pyroclastic flows and evolution of mineral compositions from high-Mg basalts to andesites support crystal fractionation as the main differentiation mechanism, although magma mixing of basaltic andesite and andesite cannot be excluded. Major and trace element trends, which display rough decreases of MgO, CaO, Ni, Cr with increasing degree of differentiation and also linear positive correlations of hygromagmaphile elements, are compatible with both processes. However, some discrepancies are observed between major and trace element modelling, which may be explained to some extent by the influence of in situ crystallization and/or magma mixing. The constancy of ¹⁴³Nd/¹⁴⁴Nd (0.51286±3), ²³⁰Th/²³²Th (0.65±0.02), Th/U (4.08±0.07) ratios, and to a lesser extent ¹⁸O values (+5.8 to +6.4 % SMOW) and ⁸⁷Sr/⁸⁶Sr ratios (0.70440 to 0.70468) is compatible with a magmatic evolution through fractional crystallization without significant crustal contamination. Nevertheless low-¹⁸O and high ⁸⁷Sr/⁸⁶Sr values in basaltic andesites may be due to the introduction of meteoric fluids into the Galunggung magma.  相似文献   

Analysis of the experimental compressibility of deep water marine sediments from the Gulf of Guinea     

Mahdia Hattab  Jean-Louis Favre 《Marine and Petroleum Geology》2010

This study strives to analyze the compressibility of deep water marine sediments originating from the Gulf of Guinea. Our approach is multi-scaled and, on the macroscopic level, based on two equations which link the overburden effective stress with the liquidity index, the Biarez & Favre equation on the one hand, and the Burland equation on the other hand (after calculation of the ICL expression as a function of the I_L parameter). On the local level, the evolution of the microstructures is analysed and compared with GoG remoulded clay. Two additional observation techniques have been used, the scanning electron microscope and the mercury intrusion porosimetry.  相似文献   

Circular Polarization Observed in Interplanetary Type III Radio Storms     

M. J. Reiner  J. Fainberg  M. L. Kaiser  J.-L. Bougeret 《Solar physics》2007,241(2):351-370

We report the detection and analysis of circular polarization in solar type III radio storms at hectometric-to-kilometric wavelengths. We find that a small (usually less than 5%), but statistically significant, degree of circular polarization is present in all interplanetary type III radio storms below 1 MHz. The sense of the polarization, which is right-hand circular for some storms and left-hand circular for others, is maintained for the entire duration of the type III storm (usually many days). For a given storm, the degree of circular polarization peaks near central meridian crossing of the associated active region. At a given time, the degree of circular polarization is found to generally vary as the logarithm of the observing frequency. The radiation characteristics, including the polarization, for one interplanetary type III storm exhibits an unusual 1.6 hour oscillation. Based on the standard plasma emission theory of type III radiation, we discuss the implications of these observations for the magnitude and radial dependence of the solar magnetic field above active regions on the Sun.  相似文献   

Practical versus absolute salinity measurements: New advances in high performance seawater salinity sensors     

Philippe Grosso  Marc Le Menn  Jean-Louis De Bougrenet De La Tocnaye  Zong Yan Wu  Damien Malardé 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):151-156

Optical salinity sensors described here measure directly the seawater refractive index and thus enable a measurement of the seawater density and composition variation. We detail the measurement dependence to environmental parameters (in particular temperature and pressure) compared to conductivity sensors, and demonstrate that it may be advantageous to directly measure refractive index rather than electrical conductivity and so obtain a more direct route to density and absolute salinity.  相似文献   

Fine Structure of Solar Radio Bursts Observed at Decametric and Hectometric Waves     

G. P. Chernov  M. L. Kaiser  J.-L. Bougeret  V. V. Fomichev  R. V. Gorgutsa 《Solar physics》2007,241(1):145-169

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997?–?2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200?–?300 kHz for slow-drifting fibers in type II bursts, and 700?–?1000 kHz for fast-drifting fibers in type II?+?IV (continuum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable frequency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejections (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actually observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14?–?8 MHz were seen as the direct expansion of similar fine structure (as fibers or “herringbone” structure) in the decametric range observed with the Nançay and IZMIRAN spectrographs.  相似文献   

Antimony speciation in saline hydrothermal fluids: A combined X-ray absorption fine structure spectroscopy and solubility study   总被引：2，自引：0，他引：2  

Gleb S. Pokrovski  Anastassia Yu. Borisova  Jean-Louis Hazemann  Marie Tella 《Geochimica et cosmochimica acta》2006,70(16):4196-4214

Solubility of senarmontite (Sb₂O₃, cubic) in pure water and NaCl-HCl aqueous solutions, and local atomic structure around antimony in these fluids were characterized using in situ X-ray absorption fine structure (XAFS) spectroscopy at temperatures to 450 °C and pressures to 600 bars. These experiments were performed using a new X-ray cell which allows simultaneous measurement of the absolute concentration of the absorbing element in the fluid, and atomic environment around the absorber. Results show that aqueous Sb(III) speciation is dominated by the complex in pure water, mixed Sb-hydroxide-chloride complexes in acidic NaCl-HCl solutions (2 m NaCl-0.1 m HCl), and by Sb-chloride species in concentrated HCl solutions (3.5 m HCl). Interatomic Sb-O and Sb-Cl distances in these complexes range from 1.96 to 1.97 Å and from 2.37 to 2.47 Å, respectively. These structural data, together with senarmontite solubility determined from XAFS spectra, were complemented by batch-reactor measurements of senarmontite and stibnite (Sb₂S₃, rhombic) solubilities over a wide range of HCl and NaCl concentrations from 300 to 400 °C. Analysis of the whole dataset shows that Sb(III) speciation in high-temperature moderately acid (pH > 2-3) Cl-rich fluids is dominated by mixed hydroxy-chloride species like Sb(OH)₂Cl° and Sb(OH)₃Cl⁻, but other species containing two or three Cl atoms appear at higher acidities and moderate temperatures (?300 °C). Calculations using stability constants retrieved in this study indicate that mixed hydroxy-chloride complexes control antimony transport in saline high-temperature ore fluids at acidic conditions. Such species allow for a more effective Sb partitioning into the vapor phase during boiling and vapor-brine separation processes occurring in magmatic-hydrothermal systems. Antimony hydroxy-chloride complexes are however minor in the neutral low- to moderate-temperature solutions (?250-300 °C) typical of Sb deposits formation; the antimony speciation in these systems is dominated by Sb(OH)₃ and potentially Sb-sulfide species.  相似文献   

Bioaccumulation of heavy metals and radionuclides from seawater by encased embryos of the spotted dogfish Scyliorhinus canicula     

Jeffree RA  Warnau M  Oberhansli F  Teyssie JL 《Marine pollution bulletin》2006,52(10):1278-1286

Encased embryos of spotted dogfish Scyliorhinus canicula absorbed six radio-isotopes (241Am, 109Cd, 57Co, 134Cs, 54Mn and 65Zn) directly from seawater during short-term experimental exposure, demonstrating the permeability of the egg-case to these contaminants. Embryo to water concentration factors (CFs) ranged from 0.14 for 134Cs to 7.4 for 65Zn. The 65Zn and 57Co CFs increased exponentially with embryo length, whereas the CF for 109Cd declined with length. Among different components of the encased embryo the egg case was the major repository (69-99%) of all six radio-isotopes that were distributed throughout its wall. Egg-case CFs were as high as 10(3) for 57Co and 65Zn, making it the major source of gamma radiation exposure to the embryo and potentially of radio-isotopes for continued absorption by the embryo, following the uptake phase of the experiment. The patterns of uptake by the egg-case approximated linearity for most isotopes and loss rates were isotope-specific; egg-case biokinetics were not greatly affected by the viability of the contained embryo. Within the embryo initial data on radio isotopic distribution show that the skin is their major site of uptake, as previously demonstrated for juveniles.  相似文献   

Structural control of the distribution of trace elements between silicates and hydrothermal solutions     

Marcel Volfinger  Jean-Louis Robert 《Geochimica et cosmochimica acta》1980,44(10):1455-1461

Over several years many partition coefficients have been measured between framework silicates, sheet silicates and hydrothermal solutions. Only trace alkaline cations are considered in the present work. It is well known that the difference between ionic radii of the trace cation and the major cation is replaces is not satisfactory for a good correlation with the partition coefficients P_X. A structural parameter δ_c is therefore defined, taking into consideration the adaptation of the trace cation to the cavity in which it occurs. This cavity may be the entire site of the major element, or a part of this site in the case of small cations, or a structural cavity located out of the alkali-ion site. The adaptation parameter δ_c is the difference between the ionic radius of the trace cation and the radius of that cavity. This paper shows that the partition coefficient P_X of the trace alkali-ion from the hydrothermal solution is an exponential function of the adaptation parameter δ_c, whatever the silicate may be.  相似文献   

The worldwide character of the 1969–1970 impulse of the secular acceleration rate     

Jean-Louis Le Mouël  Joël Ducruix  Chau Ha Duyen 《Physics of the Earth and Planetary Interiors》1982,28(4):337-350

This paper continues earlier studies to ascertain whether the distribution of the 1969–1970 jump of the secular variation rate has a worldwide character. The geometry of the jump presents some similarities with the geometry of the secular variation itself. We give a new estimation of the westward drift rate and information about spatial and temporal variations of the secular variation field.  相似文献   

Experiments on phase transformations and chemical reactions of mechanically activated minerals by grinding: Petrogenetic implications     

Jean-Louis Dandurand  Robert Gout  Jacques Schott 《Tectonophysics》1982,83(3-4)

Prolonged grinding increases the energy of solids by the production of stored energy in the form of new surfaces and internal defects. Moreover, grinding also generates quasi-hydrostatic pressures which can result in polymorphic transformations and mineral decomposition. Here we demonstrate the solid-state transformation of metastable to stable polymorphs (aragonite → calcite, anatase → rutile); the transformation of low-pressure to high-pressure phases (calcite → aragonite); and the lowering of the dehydration and decarbonation temperatures of minerals (siderite → magnetite or hematite, diaspore → corundum).In the presence of a fluid phase, stored energy from grinding can be released, resulting in accelerated reaction rates and, more importantly, phase transformations. In this paper we demonstrate the following transformations: ground calcite → magnesian calcite (at low Mg²⁺ concentration in solution), ground calcite → aragonite (at high Mg²⁺ concentration), ground magnesite → hydromagnesite, and ground dolomite → aragonite + Mg²⁺.Assuming an analogy between laboratory and natural grinding, tectonic activity may have important consequences on the release of hydrothermal fluids, the solubilization of minerals and on solid-state transformations. As examples the possible role of deformation on the formation of metamorphic aragonite and diaspore-bauxites is discussed.  相似文献