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1.
Thibault Damour 《Astrophysics and Space Science》2003,283(4):445-456
In string theory the coupling `constants' appearing in the low-energy effective Lagrangian are determined by the vacuum expectation
values of some (a priori) mass less scalar fields (dilaton, moduli). This naturally leads one to expect a correlated variation
of all the coupling constants, and an associated violation of the equivalence principle. We review some string-inspired theoretical
models which incorporate such a space time variation of coupling constants while remaining naturally compatible both with
phenomenological constraints coming from geochemical data (Oklo; Rhenium decay) and with present equivalence principle tests.
Barring a very unnatural fine-tuning of parameters, a variation of the fine-structure constant as large as that recently `observed'
by Webb et al. in quasar absorption spectra appears to be incompatible with these phenomenological constraints. Independently
of any model, it is emphasized that the best experimental probe of varying constants are high-precision tests of the universality
of free fall, such as MICROSCOPE and STEP.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Origin of spongy textures in clinopyroxene and spinel from mantle xenoliths, Hessian Depression, Germany 总被引:1,自引:0,他引:1
Summary Spongy textures are observed in anhydrous Group 1 mantle xenoliths (harzburgite, lherzolite and wehrlite) hosted in Tertiary
alkali basaltic lavas from the Hessian Depression, Germany. These textures are developed only on clinopyroxene and spinel,
and occur as rims or cross-cutting veinlets and patches showing optical continuity with the host grain. They are often associated
with pools of amorphous glassy material. There is no preferential development of spongy domains against the xenolith-lava
contact suggesting that the host magma did not play any significant role in their formation. Spongy clinopyroxene and spinel
occur in all rock types, but, are more pervasive in wehrlite.
Chemically, spongy domains of clinopyroxene and spinel are more refractory than unaffected areas, which is consistent with
their formation through a partial melting event. The associated glassy material shows chemical characteristics which suggest
that the melt pools are genetically related to the development of the spongy textures. The partial melting event was probably
triggered by the infiltration of a low-density fluid. The fluid may have evolved from a silicate melt responsible for the
metasomatic Fe-enrichment recorded in wehrlite. In this context, the more pervasive development of spongy clinopyroxene in
wehrlite may be explained by a higher concentration of the evolved fluid phase at proximity to its silicate melt source.
Received March 15, 2000; revised version accepted September 6, 2001 相似文献
3.
Stephen J. Lynton Richard J. Walker Philip A. Candela 《Geochimica et cosmochimica acta》2005,69(13):3337-3347
The fractionation of lithium isotopes among quartz, muscovite, and a chloride-bearing aqueous fluid has been investigated experimentally at 400°-500°C and 50-100 MPa. Experiments were performed for 15-60 days in cold seal vessels with natural mineral specimens. Lithium was introduced primarily through the fluid, which also contained KCl and HCl. In most runs, the fluid was prepared with the L-SVEC standard (δ7Li = 0) and was 1 M in total chloride with K/Li/H = 100/10/1. In two experiments, a 6Li spike was employed. The experiments demonstrate that quartz and muscovite are susceptible to pronounced, rapid shifts in Li isotopic composition by diffusion through interaction with a Li-bearing fluid, particularly at 500°C. At 500°C, fractionation factors were determined to be Δquartz-aqueous ≅ +8 to + 12‰ and Δmuscovite-aqueous ≅ +18 to + 20‰. An intermineral fractionation factor is given by Δmuscovite-quartz ≈ +9‰. At 400°C, the results suggest Δquartz-aqueous ≈ +4 to + 6‰. The study provides evidence of systematic fractionation in lithium isotopes at the temperatures of some magmatic processes, such as those associated with porphyry-type ore systems and pegmatites. 相似文献
4.
Gold partitioning in melt-vapor-brine systems 总被引:5,自引:0,他引:5
Adam C. Simon Mark R. Frank Philip A. Candela Christoph A. Heinrich 《Geochimica et cosmochimica acta》2005,69(13):3321-3335
We used laser-ablation inductively coupled plasma mass spectrometry to measure the solubility of gold in synthetic sulfur-free vapor and brine fluid inclusions in a vapor + brine + haplogranite + magnetite + gold metal assemblage. Experiments were conducted at 800°C, oxygen fugacity buffered at Ni-NiO (NNO), and pressures ranging from 110 to 145 MPa. The wt% NaCl eq. of vapor increases from 2.3 to 19 and that of brine decreases from 57 to 35 with increasing pressure. The composition of the vapors and brines are dominated by NaCl + KCl + FeCl2 + H2O. Gold concentrations in vapor and brine decrease from 36 to 5 and 50 to 28 μg/g, respectively, and the calculated vapor:brine partition coefficients for gold decrease from 0.72 to 0.17 as pressure decreases from 145 to 110 MPa. These data are consistent with the thermodynamic boundary condition that the concentration of gold in the vapor and brine must approach a common value as the critical pressure is approached along the 800°C isotherm in the NaCl-KCl-FeCl2-HCl-H2O system.We use the equilibrium constant for gold dissolution as AuOH0, extrapolated from lower temperature and overlapping pressure range, to calculate expected concentrations of AuOH0 in our experimental vapors. These calculations suggest that a significant quantity of gold in our experimental vapors is present as a non-hydroxide species. Possible chloridogold(I) species are hypothesized based on the positively correlated gold and chloride concentrations in our experimental vapors. The absolute concentration of gold in our synthetic vapor, brine, and melt and calculated mass partition coefficients for gold between these physicochemically distinct magmatic phases suggests that gold solubility in aqueous fluids is a function of aqueous phase salinity, specifically total chloride concentration, at magmatic conditions. However, though we highlight here the effect of salinity, the combination of our data with data sets from lower temperatures evinces a significant decrease in gold solubility as temperature drops from 800°C to 600°C. This decrease in solubility has implications for gold deposition from ascending magmatic fluids. 相似文献
5.
Recent perspectives on temporary river ecology 总被引:1,自引:0,他引:1
6.
Morten Bjerager Finn Surlyk Holger Lykke-Andersen Nicolas Thibault Lars Stemmerik 《Marine and Petroleum Geology》2010
Danian (Paleocene) reefs formed by ahermatypic scleractinian corals in relatively deep water are known in a few localities in southern Scandinavia. Reflection and shallow seismic profiles, and samples from drilling and scuba diving in bridge pier excavations in Øresund, the strait between Denmark and Sweden, for the first time allow interpretation of the factors that controlled the localisation of the reefs. 相似文献
7.
Two Approaches to Design of Monitoring Networks 总被引:5,自引:0,他引:5
8.
M. Boucarut M. Clin P. Pouchan Cl. Thibault 《International Journal of Earth Sciences》1985,74(1):123-137
The volcanic and sedimentary successive paleogeographic reconstructions, as well the volcanic emissions as the fluvial, lacustrine and marine deposits, are compared to the tectonic mechanisms, and show that the geologic history is controlled:
- During Pliocene and lower Pleistocene times, by a collapse tectonics in the Red Sea - Aden Gulf area with a correlative uplift of the Tadjoura - Ali Sabîh hörst (a southern prolongation of the Danakil horst), and by a tectonic shear according to a NE-SW trend, which gives rise to NW-SE trending uplifts and basins (Nazaret phase of the Ethiopian rift).
- From the middle Pleistocene time, by the progressive opening, according to an EW direction, of the Gulf of Tadjoura, as a western prolongation of the Aden rift. A correlative epiglyptic arching, according to an EW direction, is located westwards. It appears as a superimposed structure with respect to the previous building.
9.
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
10.
Sophie Raous Thierry Becquer Jérémie Garnier Éder de Souza Martins Guillaume Echevarria Thibault Sterckeman 《Applied Geochemistry》2010
An understanding of the biogeochemical behaviour of metals in mine spoil materials is a prerequisite to rehabilitate Ni mining sites. The objective of this study was to characterize the fate of metals in different Ni ore spoil materials as influenced by hydrological conditions and fertilisation practices. In tropical ultramafic complexes, the different stages of lateritic weathering lead to two types of ores, and therefore, to two spoil types. They are mainly either a clay-rich saprolite, so-called “garnierite”, enriched in phyllosilicates, or a limonitic material, enriched in Fe oxides. Lysimeter columns were designed to monitor leaching waters through both spoil materials. The garnieritic spoil released higher concentrations of Mg (mean = 2.25 mg L−1), Ni (0.39 mg L−1) and Cr (1.19 mg L−1) than the limonitic spoil (Mg = 0.5 mg L−1; Ni = 0.03 mg L−1 and Cr = 0.25 mg L−1). Chromium was mainly in an anionic form in leaching solutions. As exchangeable pools of Cr(VI) in limonite (980 mg kg−1 of KH2PO4-extractable Cr) are considerable its release in water may still occur in the case of a pH increase. In mixed spoil, metal concentrations were almost as low as in the limonitic one. The effect of mineral-N fertilisation was a strong release of cations (Ni, Mg) into the leachate. Phosphate amendment did not affect the soil solution composition under experimental conditions. 相似文献