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21.
Daniel Paradis Laurie Tremblay René Lefebvre Erwan Gloaguen Alfonso Rivera Michel Parent Jean-Marc Ballard Yves Michaud Patrick Brunet 《Environmental Earth Sciences》2014,72(5):1325-1348
Providing a sound basis for aquifer management or remediation requires that hydrogeological investigations carried out to understand groundwater flow and contaminant transport be based on representative data that capture the heterogeneous spatial distribution of aquifer hydraulic properties. This paper describes a general workflow allowing the characterization of the heterogeneity of the hydraulic properties of granular aquifers at an intermediate scale of a few km2. The workflow involves characterization and data integration steps that were applied on a 12-km2 study area encompassing a decommissioned landfill emitting a leachate plume and its main surface water receptors. The sediments composing the aquifer were deposited in a littoral–sublittoral environment and show evidence of small-scale transitional heterogeneities. Cone penetrometer tests (CPT) combined with soil moisture and electrical resistivity (SMR) measurements were thus used to identify and characterize spatial heterogeneities in hydraulic properties over the study area. Site-specific statistical relationships were needed to infer hydrofacies units and to estimate hydraulic properties from high-resolution CPT/SMR soundings distributed all over the study area. A learning machine approach was used due to the complex statistical relationships between colocated hydraulic and CPT/SMR data covering the full range of aquifer materials. Application of this workflow allowed the identification of hydrofacies units and the estimation of horizontal hydraulic conductivity, vertical hydraulic conductivity and porosity over the study area. The paper describes and discusses data acquisition and integration methodologies that can be adapted to different field situations, while making the aquifer characterization process more time-efficient and less labor-intensive. 相似文献
22.
H. Albert Gilg Yves Krüger Heinrich Taubald Alfons M. van den Kerkhof Martin Frenz Giulio Morteani 《Mineralium Deposita》2014,49(7):861-877
Fluid inclusion studies in combination with hydrogen, oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst-bearing geodes in Early Cretaceous Paraná continental flood basalts at Amestita do Sul, Brazil. Monophase liquid inclusions in colourless quartz, amethyst, calcite, barite and gypsum were analysed by microthermometry after stimulating bubble nucleation using single femtosecond laser pulses. The salinity of the fluid inclusions was determined from ice-melting temperatures and a combination of prograde and retrograde homogenisation temperatures via the density maximum of the aqueous solutions. Four mineralisation stages are distinguished. In stage I, celadonite, chalcedony and pyrite formed under reducing conditions in a thermally stable environment. Low δ34SV-CDT values of pyrite (?25 to ?32?‰) suggest biogenic sulphate reduction by organotrophic bacteria. During the subsequent stages II (amethyst, goethite and anhydrite), III (early subhedral calcite) and IV (barite, late subhedral calcite and gypsum), the oxidation state of the fluid changed towards more oxidising conditions and microbial sulphate reduction ceased. Three distinct modes of fluid salinities around 5.3, 3.4 and 0.3 wt% NaCl-equivalent characterise the mineralisation stages II, III and IV, respectively. The salinity of the stage I fluid is unknown due to lack of fluid inclusions. Variation in homogenisation temperatures and in δ18O values of amethyst show evidence of repeated pulses of ascending hydrothermal fluids of up to 80–90 °C infiltrating a basaltic host rock of less than 45 °C. Colourless quartz and amethyst formed at temperatures between 40 and 80 °C, while the different calcite generations and late gypsum precipitated at temperatures below 45 °C. Calculated oxygen isotope composition of the amethyst-precipitating fluid in combination with δD values of amethyst-hosted fluid inclusions (?59 to ?51?‰) show a significant 18O-shift from the meteoric water line. This 18O-shift, high salinities of the fluid inclusions with chloride-sulphate composition, and high δ34S values of anhydrite and barite (7.5 to 9.9?‰) suggest that sedimentary brines from deeper parts of the Guaraní aquifer system must have been responsible for the amethyst mineralisation. 相似文献
23.
Christine Destrigneville Jacques Schott Yves Caristan Pierre Agrinier 《Earth and Planetary Science Letters》1991,104(2-4)
Evidence for a deuteric alteration process induced by a magmatic fluid has been found in the feeder zone of the Mururoa volcano (French Polynesia). Within the dikes, where basaltic glass does not show any evidence of pervasive alteration, vesicles are filled with dioctahedral smectites and calcite, while olivine phenocrysts are replaced by dioctahedral smectites, ankerite and calcite.The 13C signature of carbonates, the carbon and H2O content of the whole rocks and their impoverishment in deuterium are compatible with the presence of magmatic CO2 during the crystallization of intruding lavas and exclude contamination by seawater. Mass balance calculations on selected thin sections photographs of partly filled up vesicles and replaced olivine crystals, constrain, assuming a closed system interaction, the chemical composition of the initial fluid and the respective amounts of the initial solid phases involved in the alteration process. Thermodynamic modelings using the EQ3/6 software package correctly predict the mineralogic, chemical and isotopic exchanges accompanying alteration, thus validating the closed system assumption. The model which allows prediction of the influence of CO2 on the alteration products, shows that, above a 0.25 CO2 mole fraction in the initial fluid, the alteration is entirely controlled by the chemical composition of the initial solid phases. The presence of CO2 implies the precipitation of dioctahedral smectites and carbonates instead of the magnesian smectites commonly observed in CO2-free systems.The Mururoa feeder zone shows alteration features typical of a closed system interaction between the basaltic rock and a magmatic fluid in which seawater did not take part. 相似文献
24.
Frédéric Gueydan Yves M. Leroy Laurent Jolivet 《International Journal of Earth Sciences》2001,90(1):181-196
Localized shear zones along low-angle normal faults have been identified in regions of extension at the brittle-ductile transition of the continental crust. The possibility of the strain localizing at a depth of 10 km is interpreted here as a consequence of an increase in the equivalent shear stress applied to the flow of the lower crust. This enhancement of the flow stress is seen as a prerequisite for the triggering of brittle deformation mechanisms leading to strain localization. The lower crust rheology used to examine this stress increase is strain-rate, temperature and grain-size dependent, due to the coupling of dislocation and diffusion creep. The model structure proposed consists of a top layer, the upper crust, gliding rigidly above a bottom layer, the lower crust, which deforms in simple shear. During a short time interval (1400 years), the equivalent shear stress is found to increase by a factor of up to 3 (67 MPa for anorthite and 17 MPa for quartz). For anorthite, this stress could explain the activation of a Mohr-Coulomb failure with a friction coefficient of 0.2, which is reasonable at the depth of 10 km. Dislocation creep is activated during a rapid change in the prescribed velocity, whereas diffusion creep dominates if the velocity is held constant, highlighting the importance of grain-size sensitivity for lower crustal rheology. 相似文献
25.
A large number of studies have documented the structural and sedimentary architecture of the Corinth Gulf, especially the major E–W trending normal faults important in accommodating the main extensional strain and associated growth of the Gilbert fan deltas. However, the role of several N–S oriented structures that crop out at the surface and are detectable at depth by seismic reflection and gravity surveys are not clearly understood. Based on new geological data, collected near Xylokastro, we describe the N–S oriented tectonic activity of this area. The mapped inland faults correspond to off-shore structures identified in re-interpreted seismic lines and appear to have acted as a major transfer zone during the opening of the Corinth Gulf. Reconstruction of the paleo-topography based on sedimentary facies and the environment of clay mineral formation suggest these transfer zones played an important role in controlling both local structural relief and depositional conditions of the Gilbert fan deltas. 相似文献
26.
A Discussion of IGS Solutions and Their Impact on Geodetic and Geophysical Applications 总被引:1,自引:0,他引:1
The International Association of Geodesy officially established the International GPS Service (IGS) on Janaury 1, 1994. Its
prime objective is to provide support and a rerefence system for a wide variety of scientific and practical applications involving
GPS. To fulfill its role the IGS also generates, in addition to its fundamental products (orbital/staion positions and consistent
Earth orientation parameters), additional reference-system products providing the necessary infrastructure, standards, and
means of calibrations for timing and various atmospheric applications of GPS. The generation and efficient application of
IGS products and their impact on a number of positioning and atmospheric applications, including low earth orbit satellites,
is reviewed and discussed. @ 1998 John Wiley & Sons, Inc. 相似文献
27.
Shaw Cliff S. J. Thibault Yves Edgar Alan D. Lloyd Felicity E. 《Contributions to Mineralogy and Petrology》1998,132(4):354-370
Experiments dissolving orthopyroxene (En93) in a variety of Si-undersaturated alkaline melts at 1 atmosphere and variable f
O2 demonstrate that orthopyroxene dissolves to form olivine, Si-rich melt and clinopyroxene. These phases form a texturally
and chemically distinct boundary layer around the partly dissolved orthopyroxene crystals. The occurrence of clinopyroxene
in the boundary layer is due to inward diffusion of Ca from the solvent melt to the boundary layer causing clinopyroxene saturation.
Compositional profiles through the solvent and the boundary layer for a number of experiments demonstrate rapid diffusion
of cations across the boundary layer – solvent interface. SiO2 diffuses outward from the boundary layer whereas CaO and Al2O3 diffuse toward the Si-enriched boundary layer melt. The rate of Al diffusion is slower under reducing conditions compared
to the rates in experiments performed in air. Concentrations of FeO and MgO in the boundary layer and solvent are approximately
equal indicating rapid diffusion and attainment of equilibrium despite ongoing crystallisation of clinopyroxene within the
boundary layer. The behaviour of Na2O and K2O is strongly affected by f
O2. Under reducing conditions Na2O and K2O concentrations are approximately equal in the boundary layer and solvent indicating normal diffusion down the concentration
gradient and attainment of equilibrium. Under oxidising conditions, K2O and to a lesser extent Na2O, have compositional profiles indicative of uphill diffusion likely due to their preference for more polymerised Si- and
Al-rich melts. Under reduced conditions Al-enrichment in the boundary layer melt is not as extreme and uphill diffusion did
not occur. The composition of the solvent melt after the experiments indicates that it was contaminated by the boundary layer
by convective mixing due to the onset of hydrodynamic instabilities brought on by density and viscosity contrasts between
the two melts. Despite using a wide variety of solvent melt compositions we find that the boundary layer melts converge toward
a common composition at high SiO2 contents. The composition of glass generated by orthopyroxene dissolution at 1 atmosphere is similar in many respects to
Si-rich glass found in many orthopyroxene-rich mantle xenoliths that have been attributed to high pressure in situ processes
including mantle metasomatism. The results of this study suggest that at least some Si-rich melts are likely to have formed
by dissolution of xenolith orthopyroxene at low pressure possibly by their Si-undersaturated host magmas.
Received: 30 August 1996 / Accepted: 15 April 1998 相似文献
28.
Yves Grosdidier Anthony F.J. Moffat Agnès Acker 《Astrophysics and Space Science》1998,260(1-2):181-184
We present HST-WFPC2/Hα deep images of the ejected nebula M1-67. Our data suggest that M1-67 is the imprint of a previous,
slow LBV wind ejected from the central star WR124, now a WN8 star. We find evidence that the LBV wind is highly variableand anisotropic. Some dense, persisting clumps have possibly been ejected directly from the stellar surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
29.
30.
Alix Lombard Anny Cazenave Pierre Yves Le Traon Stephanie Guinehut Cécile Cabanes 《Ocean Dynamics》2006,56(5-6):445-451
In this paper, we first discuss the controversial result of the work by Cabanes et al. (Science 294:840–842, 2001), who suggested that the rate of past century sea level rise may have been overestimated, considering the limited and heterogeneous
location of historical tide gauges and the high regional variability of thermal expansion which was supposed to dominate the
observed sea level. If correct, this conclusion would have solved the problem raised by the IPCC third assessment report [Church
et al, Cambridge University Press, Cambridge, pp 881, 2001], namely, the factor two difference between the 20th century observed sea level rise and the computed climatic contributions.
However, recent investigations based on new ocean temperature data sets indicate that thermal expansion only explains part
(about 0.4 mm/year) of the 1.8 mm/year observed sea level rise of the past few decades. In fact, the Cabanes et al.’s conclusion
was incorrect due to a contamination of abnormally high ocean temperature data in the Gulf Stream area that led to an overestimate
of thermal expansion in this region. In this paper, we also estimate thermal expansion over the last decade (1993–2003), using
a new ocean temperature and salinity database. We compare our result with three other estimates, two being based on global
gridded data sets, and one based on an approach similar to that developed here. It is found that the mean rate of thermosteric
sea level rise over the past decade is 1.5±0.3 mm/year, i.e. 50% of the observed 3 mm/year by satellite altimetry. For both
time spans, past few decades and last decade, a contribution of 1.4 mm/year is not explained by thermal expansion, thus needs
to be of water mass origin. Direct estimates of land ice melt for the recent years account for about 1 mm/year sea level rise.
Thus, at least for the last decade, we have moved closer to explaining the observed rate of sea level rise than the IPCC third
assessment report. 相似文献