Experimental study of aluminum speciation in fluoride-rich supercritical fluids   总被引：2，自引：0，他引：2  

Boris TagirovJacques Schott  Jean-Claude HarrichourryStefano Salvi 《Geochimica et cosmochimica acta》2002,66(11):2013-2024

The solubility of the albite-paragonite-quartz mineral assemblage was measured as a function of NaCl and fluorine concentration at 400°C, 500 bars and at 450°C, 500 and 1000 bars. Decreasing Al concentrations with increasing NaCl molality in F-free fluids of low salinity (mNaCl < 0.01) demonstrates that Al(OH)₄⁻ dominates Al speciation and is formed according to the reaction 0.5 NaAl₃Si₃O₁₂H_2(cr)+2 H₂O = 0.5 NaAlSi₃O_8(cr)+Al(OH)₄⁻+H⁺. Log K results for this reaction are −11.28 ± 0.10 and −10.59 ± 0.10 at 400°C, 500 bars and 450°C, 1000 bars, respectively. Upon further salinity increase, Al concentration becomes constant (at 400°C, 500 bars) or even rises (at 450°C, 1000 bars). The observed Al behavior can be explained by the formation of NaAl(OH)₄⁰_(aq) or NaAl(OH)₃Cl_(aq)⁰. The calculated constant for the reaction Al(OH)₄⁻+Na⁺=NaAl(OH)₄⁰_(aq) expressed in log units is equal to 2.46 and 2.04 at 400°C, 500 bars and 450°C, 1000 bars, respectively. These values are in good agreement with the predictions given in Diakonov et al. (1996). Addition of fluoride at m(NaCl) = const = 0.5 caused a sharp increase in Al concentration in equilibrium with the albite-paragonite-quartz mineral assemblage. As fluid pH was also constant, this solubility increase indicates strong aluminum-fluoride complexation with the formation of NaAl(OH)₃F_(aq)⁰ and NaAl(OH)₂F₂⁰_(aq), according to 0.5 NaAl₃Si₃O₁₂H_2(cr)+Na⁺+HF_(aq)⁰+H₂O = 0.5 NaAlSi₃O_8(cr)+ NaAl(OH)₃F_(aq)⁰+H⁺, log K = −5.17 and −5.23 at 400°C and 450°C, 500 bars, respectively, and 0.5 NaAl₃Si₃O₁₂H_2(cr)+Na⁺+2 HF_(aq)⁰ = 0.5 NaAlSi₃O_8(cr)+NaAl(OH)₂F₂⁰_(aq)+H⁺, log K = −2.19 and −1.64 at the same P-T conditions. It was found that temperature increase and pressure decrease promote the formation of Na-Al-OH-F species. Stability of NaAl(OH)₂F₂⁰_(aq) in low-density fluids also increases relative to NaAl(OH)₃F_(aq)⁰. These complexes, together with Al(OH)₂F_(aq)⁰ and AlOHF₂⁰_(aq), whose stability constants were calculated from the corundum solubility measured by Soboleva and Zaraisky (1990) and Zaraisky (1994), are likely to dominate Al speciation in metamorphic fluids containing several ppm of fluorine.  相似文献   

Une méthode de quantification de la dégradation d'un escarpement de faille au cours des cycles climatiques du Quaternaire : la faille de Jobourg (Nord Cotentin,France)Quantification of a fault-scarp degradation through Quaternary: the Jobourg fault (North Cotentin,France)     

Marianne Font  Jean-Louis Lagarde  Daniel Amorese  Jean-Pierre Coutard  Jean-Claude Ozouf 《Comptes Rendus Geoscience》2002,334(3):171-178

The degradation of the Jobourg fault-scarp occurred by cryoclastic processes in a periglacial environment during a part of Quaternary time. An attempt of quantification indicates a bulk scarp erosion of about 39 m³ m^?2, while the head accumulated at the bottom of the fault scarp only represents 4.6 m³ m^?2. To cite this article: M. Font et al., C. R. Geoscience 334 (2002) 171–178.  相似文献   

Effect of the environment on the hydrochemical characteristics of an alluvial aquifer following an exceptional multiyear drought (Mediterranean Seashore,Hérault,France): Part II—Climatology and agronomy     

Jean-Claude Grillot  Isabelle Chaffaut  Moumtaz Razack 《Environmental Geology》1988,11(2):163-173

The hydrochemical evolution of an alluvial groundwater located along the Mediterranean seashore is analyzed with respect to its agricultural and climatic environment, including degree of saturation of the soil; types of cultures, chemical fertilizers and phytosanitary treatments; selective irrigations of the cultivated areas; precipitations. It is shown that the environmental effect on the groundwater's vulnerability depends on two groups of factors:

1. Transfers from surface to groundwater of nitrates, chlorides, sulfates, and potassium, which are governed by: (a) the climatic conditions before the agricultural activities begin, (b) the kinds of agricultural activities and their distribution in time with respect to a given climatic context. Phenomena of retention of and/or rapid diffusion are related to the sedimentary heterogeneities of the reservoir and to the differences of temperatures between irrigation waters and precipitations.
2. Cationic exchanges related to the presence of clays of Montmorillonite-Kaolinite type.

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Fractal reconstruction of sea-floor topography     

Jean-Claude Mareschal 《Pure and Applied Geophysics》1989,131(1-2):197-210

Sea-floor bathymetric profiles exhibit features at many different scales of length; this suggests that they could be described as fractals. An algorithm interpolating a fractal line between points has been used to reconstruct bathymetric profiles from a few data points. In general, this fractal line has the same Fourier amplitude spectrum as real bathymetry, and, if the parameters of the interpolation are suitably chosen, it has a very similar appearance. The success of this fractal reconstruction algorithm for the sea-floor raises the possibility that it could be used to extrapolate, from data collected at one scale, the properties of the sea-floor at finer scales, and that similar techniques could be used to interpolate a surface between bathymetric profiles. The fractal character is a sign that the processes that shape the sea-floor are scale invariant and suggests that the renormalization group technique could be used to model these processes.  相似文献   

Penetration of bomb radiocarbon in the tropical Indian Ocean measured by means of accelerator mass spectrometry     

Edouard Bard  Maurice Arnold  H. Gte stlund  Pierre Maurice  Patrick Monfray  Jean-Claude Duplessy 《Earth and Planetary Science Letters》1988,87(4)

Radiocarbon measurements performed on seawater samples by means of accelerator mass spectrometry (AMS) enable to reduce by a factor of 2000 the water sample size needed for the¹⁴C measurements. Therefore no chemical treatment on board the oceanographic vessel is required. Seventy-four AMS¹⁴C determinations on samples collected in the tropical-equatorial Indian Ocean during the second leg of the INDIGO program (1986) are presented and compared with the β-counting results obtained during the same campaign and the GEOSECS program (1978). A pronounced reduction of the equatorial¹⁴C deficit suggests that substantial amounts of bomb-¹⁴C are associated with the westward flowing Pacific water which enters the Indian Ocean via passages through the Indonesia archipelago and/or to meridional mixing with¹⁴C-rich water of the southern subtropical gyre.  相似文献   

The 1902–1905 eruptions of Montagne Pelée, Martinique: anatomy and retrospection     

Jean-Claude Tanguy 《Journal of Volcanology and Geothermal Research》1994,60(2)

The 1902–1905 activity of Montagne Pelée represents a moderately large eruptive cycle typical of a subduction zone volcano. It followed a three-centuries-long repose interrupted only in 1792 by two small phreatic explosions and minor (phreatomagmatic?) eruptions in 1851–1852. The volcano decidedly awakened in early 1902 with increasing fumaroles at l'Etang Sec summit crater, light earthquakes and phreatic activity from 23 April onwards. On 2–3 May the eruption became phreatomagmatic and much more active. Destructive lahars culminated on 5 May and during the night of 7–8 May, causing 23 casualties at the Guérin factory and about 400 others at Le Prêcheur. On 8 May at 08:02 local time a climactic ‘nuée ardente’ destroyed the city of Saint-Pierre, 8 km south of the crater, and killed all its 27–28,000 inhabitants but one, or possibly two. Testimonies from eyewitnesses of this event, calculations made on its effects, and careful studies of its deposits support the interpretation of a powerful lateral blast (175−140 m/s) accompanied by a fast-moving pyroclastic flow which was directed N-S, i.e. toward the town itself. The temperature of the flow decreased from that of the acid andesite magma (about 900°C) at the crater to 400–200°C as it reached Saint-Pierre. Climactic ‘pelean’ eruptions, initiated by strong explosions, were renewed on 20 May and 30 August. This latter produced 1,000 additional victims at Morne Rouge, making a total of about 29,000 victims for the entire eruptive period. Less violent eruptions, without major explosions, took place on 26 May, 6 June, 9 July and from late 1902 to July 1905, generating slow-moving pyroclastic flows (50 m/s or less), linked to relatively quiet dome growth.The catastrophe of Saint-Pierre resulted from an insufficient knowledge of volcanic hazards at the time and particularly from the total ignorance of pyroclastic flow (nuée ardente) phenomena. Future hazards in Martinique include the renewal of pelean eruptions and widespread plinian activity, such as has occurred in the past 5,000 years, together with a less probable sector collapse triggering tsunami. As major magmatic eruptions of Montagne Pelée may be separated by repose periods of more than 500 years, a long-term instrumental surveillance of the volcano is needed, and adequate concepts in urban planning should be developed and sustained in the next centuries.  相似文献   

Comparison between natural and artificial maturation series of humic coals from the Mahakam delta,Indonesia     

Marc Monthioux  Patrick Landais  Jean-Claude Monin 《Organic Geochemistry》1985,8(4):275-292

Type III (humic) organic matter from the Mahakam delta (Indonesia) was chosen to compare artificial and natural coal series. Powdered and concentrated immature organic matter was heated in sealed gold tubes for 24 hr at temperatures ranging from 250 to 550°C and under pressures ranging from 0.5 to 4 kb, with and without water. Both elemental and Rock-Eval analyses were used to characterize the products. A comparison between our results, published data and the natural model shows that, quantitatively, natural maturation is simulated better when pyrolysis is performed under confined conditions (no free volume, no diluting inert gas). Thus, pyrolysis in a medium swept by an inert gas, vacuum pyrolysis and some pyrolysis in sealed glass tubes must be considered to be poor simulation tools. The presence of water does not seem to have an essential effect. Allowing the hydrocarbons formed to reach a certain value of partial pressure seems to be important. Results are unchanged when external pressure varies from 0.5 to 4 kb.  相似文献   

Reply to ‘comments and further analysis on effective roughness lengths for use in numerical three-dimensional models’, by P. Taylor     

Jean-Claude André  Christian Blondin 《Boundary-Layer Meteorology》1987,39(4):419-419

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Cumulating processes at the crust-mantle transition zone inferred from Permian mafic-ultramafic xenoliths (Puy Beaunit,France)     

Julien Berger  Olivier Féménias  Nicolas Coussaert  Jean-Claude C. Mercier  Daniel Demaiffe 《Contributions to Mineralogy and Petrology》2007,153(5):557-575

Ultramafic and mafic xenoliths of magmatic origin, sampled in the Beaunit vent (northern French Massif Central), derive from the Permian (257 Ma) Beaunit layered complex (BLC) that was emplaced at the crust-mantle transition zone (∼1 GPa). These plutonic xenoliths are linked to a single fractional crystallisation process in four steps: peridotitic cumulates; websteritic cumulates; Al-rich mafic cumulates (plagioclase, pyroxenes, garnet, amphibole and spinel) and finally low-Al mafic cumulates. This sequence of cumulates can be related to the compositional evolution of hydrous Mg basaltic magma that evolved to high-Al basalt and finally to andesitic basalt. Sr and Nd isotopic compositions confirm the co-genetic character of the various magmatic xenoliths and argue for an enriched upper mantle source comparable to present mantle wedges above subduction zones. LILE, LREE and Pb enrichment are a common feature of all xenoliths and argue for an enriched sub-alkaline transitional parental magma. The existence of a Permian magma chamber at 30 km depth suggests that the low-velocity zone observed locally beneath the Moho probably does not represent an anomalous mantle but rather a sequence of mafic/ultramafic cumulates with densities close to those of mantle rocks.  相似文献   

Volcanic edifice stability during cryptodome intrusion     

Franck Donnadieu  Olivier Merle  Jean-Claude Besson 《Bulletin of Volcanology》2001,63(1):61-72

Limit equilibrium analyses were applied to the 1980 Mount St. Helens and 1956 Bezymianny failures in order to examine the influence on stability of structural deformation produced by cryptodome emplacement. Weakening structures associated with the cryptodome include outward-dipping normal faults bounding a summit graben and a flat shear zone at the base of the bulged flank generated by lateral push of the magma. Together with the head of the magmatic body itself, these structures serve directly to localize failure along a critical surface with low stability deep within the interior of the edifice. This critical surface, with the safety coefficient reduced by 25-30%, is then very sensitive to stability condition variation, in particular to the pore-pressure ratio (r_u) and seismicity coefficient (n). For r_u=0.3, or n=0.2, the deep surface suffers catastrophic failure, removing a large volume of the edifice flank. In the case of Mount St. Helens, failure occurred within a material with angle of friction ~40°, cohesion in the range 10⁵-10⁶ Pa, and probably significant water pore pressure. On 18 May 1980, detachment of slide block I occurred along a newly formed rupture surface passing through the crest of the bulge. Although sliding of block I may have been helped by the basal shear zone, significant pore pressure and a triggering earthquake were required (r_u=0.3 and n=0.2). Detachment of the second block was guided by the summit normal fault, the front of the cryptodome, and the basal shear zone. This occurred along a deep critical surface, which was on the verge of failure even before the 18 May 1980 earthquake. The stability of equivalent surfaces at Bezymianny Volcano appears significantly higher. Thus, although magma had already reached the surface, weaker materials, or higher pore pressure and/or seismic conditions were probably required to reach the rupture threshold. From our analysis, we find that deep-seated sector collapses formed by removing the edifice summit cannot generally result from a single slide. Cryptodome-induced deformation does, however, provide a deep potential slip surface. As previously thought, it may assist deep-seated sector collapse because it favors multiple retrogressive slides. This leads to explosive depressurization of the magmatic and hydrothermal systems, which undermines the edifice summit and produces secondary collapses and explosive blasts.  相似文献