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981.
Véronique Lavastre Nathalie Jendrzejewski Marc Javoy 《Geochimica et cosmochimica acta》2005,69(21):4949-4961
The marine Callovo-Oxfordian clay formation is found at a depth around 410m in the eastern part of the Paris Basin (France). It is a very low permeability formation investigated by the French agency for nuclear waste management (ANDRA) to study the feasibility of a radioactive waste disposal. Examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation. This study uses chlorine isotopes to investigate long-term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks. Detailed chlorine concentration and δ37Cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers (the Dogger at the bottom and the Oxfordian/Kimmeridgian/Tithonian unit at the top). They are discussed in terms of chlorine budget and hydrogeological processes.Clay pore waters and aquifer waters show strong chlorine concentration depletion (<3000 mg/L) relative to the original marine interstitial water (∼19000 mg/L). This probably results from an early dilution by meteoric water in limestones (as also indicated by oxygen and hydrogen isotopes).A steep Cl-concentration gradient from the Dogger at ∼500m in depth (∼2500 mg/L) to the Oxfordian/Kimmeridgian/Tithonian aquifer near the surface (≈ 10 mg/L) is associated to a ‘v-shaped’ profile of the δ37Cl values. Modelling Cl transport shows that a hydrodynamic dispersion process explains Cl concentration and δ37Cl profiles in Oxfordian Limestone. This process implies a mean upward flux of chloride in the 2.6 10−8-8.2 10−8 mole/m2/yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride. The modelling and knowledge of underground water transfer suggest a maximum effective Cl-hydrodynamic vertical dispersion coefficient (= vertical Cl-transport coefficient) of ∼7.6 10−10 m2/s.Chlorine transfer through the Callovo-Oxfordian clay, since deposition 160My ago, can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events (such as early diffusion, ion filtration etc.). 相似文献
982.
Estimate of recharge of a rising water table in semiarid Niger from 3H and 14C modeling 总被引:1,自引:0,他引:1
Favreau G Leduc C Marlin C Dray M Taupin JD Massault M Le G Babic M 《Ground water》2002,40(2):144-151
A hydrodynamic survey carried out in semiarid southwest Niger revealed an increase in the unconfined ground water reserves of approximately 10% over the last 50 years due to the clearing of native vegetation. Isotopic samplings (3H, 18O, 2H for water and 14C, 13C for the dissolved inorganic carbon) were performed on about 3500 km2 of this silty aquifer to characterize recharge. Stable isotope analyses confirmed the indirect recharge process that had already been shown by hydrodynamic surveys and suggested the tracers are exclusively of atmospheric origin. An analytical model that takes into account the long-term rise in the water table was used to interpret 3H and 14C contents in ground water. The natural, preclearing median annual renewal rate (i.e., recharge as a fraction of the saturated aquifer volume) lies between 0.04% and 0.06%. For representative characteristics of the aquifer (30 m of saturated thickness, porosity between 10% and 25%), this implies a recharge of between 1 and 5 mm/year, which is much lower than the estimates of 20 to 50 mm/year for recent years, obtained using hydrological and hydrodynamic methods and the same aquifer parameters. Our study, therefore, reveals that land clearing in semiarid Niger increased ground water recharge by about one order of magnitude. 相似文献
983.
Frédéric Masson Mohammad Anvari Yahya Djamour rea Walpersdorf Farokh Tavakoli Marc Daignières Hamid Nankali Sébastien Van Gorp 《Geophysical Journal International》2007,170(1):436-440
A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr−1 at about N11°, 2 ± 1 mm yr−1 of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr−1 of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation. 相似文献
984.
Heavy off-season rains in the tropics pose significant natural hazards largely because they are unexpected and the popular
infrastructure is ill-prepared. One such event was observed from January 9 to 11, 2002 in Senegal (14.00° N, 14.00°␣W), West
Africa. This tropical country is characterized by a long dry season from November to April or May. During this period, although
the rain-bearing monsoonal flow does not reach Senegal, the region can occasionally experience off-season rains. We conducted
a numerical simulation of the January 9–11, 2002 heavy off-season rain using the Fifth-Generation NCAR/Pennsylvania State
University Mesoscale Model (MM5) and the Weather Research and Forecasting (WRF) model. The objective was to delineate the
meteorological set-up that led to the heavy rains and flooding. A secondary objective was to test the model’s performance
in Senegal using relatively simpler (default) model configurations and local/regional observations. The model simulations
for both MM5 and WRF agree satisfactorily with the observations, particularly as regards the wind patterns, the intensification
of the rainfall, and the associated drop in temperatures. This situation provided the environment for heavy rainfall accompanied
by a cold wave. The results suggest that off-the-shelf weather forecast models can be applied with relatively simple physical
options and modest computational resources to simulate local impacts of severe weather episodes. In addition, these models
could become part of regional hazard mitigation planning and infrastructure. 相似文献
985.
We performed modified iterative sandwich experiments (MISE) to determine the composition of carbonatitic melt generated near
the solidus of natural, fertile peridotite + CO2 at 1,200–1,245°C and 6.6 GPa. Six iterations were performed with natural peridotite (MixKLB-1: Mg# = 89.7) and ∼10 wt% added
carbonate to achieve the equilibrium carbonatite composition. Compositions of melts and coexisting minerals converged to a
constant composition after the fourth iteration, with the silicate mineral compositions matching those expected at the solidus
of carbonated peridotite at 6.6 GPa and 1,230°C, as determined from a sub-solidus experiment with MixKLB-1 peridotite. Partial
melts expected from a carbonated lherzolite at a melt fraction of 0.01–0.05% at 6.6 GPa have the composition of sodic iron-bearing
dolomitic carbonatite, with molar Ca/(Ca + Mg) of 0.413 ± 0.001, Ca# [100 × molar Ca/(Ca + Mg + Fe*)] of 37.1 ± 0.1, and Mg#
of 83.7 ± 0.6. SiO2, TiO2 and Al2O3 concentrations are 4.1 ± 0.1, 1.0 ± 0.1, and 0.30 ± 0.02 wt%, whereas the Na2O concentration is 4.0 ± 0.2 wt%. Comparison of our results with other iterative sandwich experiments at lower pressures indicate
that near-solidus carbonatite derived from mantle lherzolite become less calcic with increasing pressure. Thus carbonatitic
melt percolating through the deep mantle must dissolve cpx from surrounding peridotite and precipitate opx. Significant FeO*
and Na2O concentrations in near solidus carbonatitic partial melt likely account for the ∼150°C lower solidus temperature of natural
carbonated peridotite compared to the solidus of synthetic peridotite in the system CMAS + CO2. The experiments demonstrate that the MISE method can determine the composition of partial melts at very low melt fraction
after a small number of iterations. 相似文献
986.
Anil K. Chopra 《地震工程与结构动力学》2007,36(1):3-12
This is the first contribution in a new series of Historical Notes on seminal concepts in earthquake engineering and structural dynamics. It records the origins and early developments (up to the late 1960's) of the elastic response spectrum. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
987.
Udumbanchola Taluk, located in the fragile zone of Western Ghats in the Idukki District of Kerala has undergone severe land
use changes in the past century. The changing land use scenario of Udumbanchola Taluk was assessed using remote sensing technique.
The historic land use map was derived from topographic maps of Survey of India, surveyed in 1910 and published during 1912–14.
The land use map of 1997 was generated through the visual interpretation of IRS—1 C LISSIII images supported by ground truths and was observed that the original land use system was highly modified.
The comparative study shows that the settlement areas that occupied hardly 0.73 % in 1910 were increased to 30.57 % in 1997
by transferring forest lands, grassland and cardamom plantations. Due to the depletion of natural vegetation and grassland
system by the establishment of houses, cash crops and infrastructure facilities, combined with the absence of sufficient land
management measures in the side slopes resulted severe land degradation and the present status of degraded lands is about
14.12 % of the total geographical area. It is also observed that the prevailing agro-climatic conditions favorable for the
sustenance of sensitive crops like cardamom has undergone changes mainly due to the impact of large-scale land use modifications. 相似文献
988.
Quenching of fluorescence emission by the Cu2+ ion is measured in five samples from the Gironde Estuary (France). Non-linear regression analysis allows us to calculate from experimental data the values of CL (complexing capacities or total ligand concentrations), K (conditional stability constants) and IML (residual fluorescence at the end of the titration). The results obtained on the Gironde estuarine samples indicate that CL values are very low (<0.1 micromolar) and K values decrease from upstream to downstream. The relatively high values of IML are an indication that much of the organic fluorescing matter does not bind to Cu2+. 相似文献
989.
The effect of bulk composition on the solidus of carbonated eclogite from partial melting experiments at 3 GPa 总被引:1,自引:0,他引:1
Rajdeep?DasguptaEmail author Marc?M.?Hirschmann Nikki?Dellas 《Contributions to Mineralogy and Petrology》2005,149(3):288-305
To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe–Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + FeT)=32, 1.63 wt% Na2O, and 5 wt% CO2) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73–85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na2O, and 4.4 wt% CO2) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na2O, and 15 wt% CO2) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na2O, and 2.2 wt% CO2) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite–magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO3-MgCO3 join have lower solidus temperatures. Variations in total CO2 have significant effect on the solidus if CO2 is added as CaCO3, but not if CO2 is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO2 than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO2 do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca–Mg exchange equilibrium between carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO2 concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO2 may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO2 enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite. 相似文献
990.
Ruitton S Javel F Culioli JM Meinesz A Pergent G Verlaque M 《Marine pollution bulletin》2005,50(10):1061-1068
The introduced green alga Caulerpa racemosa var. cylindracea has been rapidly spreading in the Mediterranean Sea since 1990. It was first observed in France in 1997 (Marseilles). In early 2004, the stretch of the French Mediterranean coastline and the surface area affected by the invasion were estimated at about 83 km and 4014 ha, respectively. The depth range of colonized areas was usually 10-35 m depth. Shallow (0-10 m) and deep (down to 40 m) dense meadows were rarely observed. In contrast to the dead matte of Posidonia oceanica, which constituted the most widely colonized substratum, dense P. oceanica meadows and fine sand with large ripple-marks were not invaded. Few rocky areas were colonized and coarse sand bottoms were usually colonized below 20 m depth. All the colonized areas were exposed to human activities and more than 40% were fishing areas. Mild climate, suitable substrata, presence of vectors of dispersal and absence of efficient biological control make the French Mediterranean coast particularly vulnerable to the further spread of the alga. 相似文献