Mechanism and kinetics of the reaction: 1 dolomite + 2 quartz = 1 diopside + 2 CO2: a comparison of rock-sample and of powder experiments     

Andreas Lüttge  Paul Metz 《Contributions to Mineralogy and Petrology》1993,115(2):155-164

Two experiments using cylindrical samples of a dolomite-quartz rock were carried out in a conventional hydrothermal apparatus for the forward reaction: 1 dolomite + 2 quartz = 1 diopside + 2 CO₂, in order to compare the mechanism and the kinetics with results from experiments using mineral powders of dolomite and quartz at the same P-T-X conditions. Experimental conditions were as follows: total pressure 500 MPa; temperature 680° C (overstepping 65° C); CO₂ content of the fluid phase, consisting of carbon dioxide and water, was nearly 90 mol%; the fluid/rock ratio was 1:37, and the H₂O/rock ratio was about 1:740; run duration was 92 days. Scanning electron microscope (SEM) examination of a polished axial section of the rock cylinders after the run, using back-scattered electrons (BSE), shows that the reaction produced corona textures. The diopside crystals nucleate and grow exclusively on dolomite surfaces adjacent to quartz grains, i.e. in regions where there is intimate contact between the reactants. The dolomite matrix, in contrast, is diopside free. A concept of microsystems is used to compare directly the rock cylinder results with those from runs done with mineral powders. The microsystems, which consist of quartz, dolomite and diopside, are connected by the intergranular space which is filled by the fluid phase. The SEM analysis of the rock cylinders indicates a dissolution-crystallization mechanism operating in the microsystems; this is consistent with the results of experiments using dolomite quartz powders (Lüttge et al. 1989). It can be demonstrated that reaction kinetics in mineral powder runs are interface controlled as long as the newly formed diopside crystals do not cover the dolomite surfaces completely (Lüttge and Metz 1991 c). This result is applicable to each microsystem of the rock cylinder, since the reaction mechanism and the resulting textures are the same in both kinds of experiments. The reaction is much slower outside the microsystems, i.e. in the dolomite matrix but in the close vicinity of the quartz grains. At these places, the reaction is controlled by the transport of Si-species in the CO₂-rich fluid phase filling the intergranular space. The reaction is absent in quartz-free regions of the dolomite matrix. Calculations and measurements of the extent of reaction progress in both kinds of experiments give results of the same order of magnitude: the conversion, and therefore the reaction rate, differs by less than a factor of two. The conclusion is that there are no differences, in principle, concerning mechanisms, rate controls, rates, and resulting textures between rock cylinder experiments, and mineral powder experiments.  相似文献   

Vulnerability of a public supply well in a karstic aquifer to contamination     

Katz BG  McBride WS  Hunt AG  Crandall CA  Metz PA  Eberts SM  Berndt MP 《Ground water》2009,47(3):438-452

To assess the vulnerability of ground water to contamination in the karstic Upper Floridan aquifer (UFA), age-dating tracers and selected anthropogenic and naturally occurring compounds were analyzed in multiple water samples from a public supply well (PSW) near Tampa, Florida. Samples also were collected from 28 monitoring wells in the UFA and the overlying surficial aquifer system (SAS) and intermediate confining unit located within the contributing recharge area to the PSW. Age tracer and geochemical data from the earlier stage of the study (2003 through 2005) were combined with new data (2006) on concentrations of sulfur hexafluoride (SF₆), tritium (³H), and helium-3, which were consistent with binary mixtures of water for the PSW dominated by young water (less than 7 years). Water samples from the SAS also indicated mostly young water (less than 7 years); however, most water samples from monitoring wells in the UFA had lower SF₆ and ³H concentrations than the PSW and SAS, indicating mixtures containing high proportions of older water (more than 60 years). Vulnerability of the PSW to contamination was indicated by predominantly young water and elevated nitrate-N and volatile organic compound concentrations that were similar to those in the SAS. Elevated arsenic (As) concentrations (3 to 19 μg/L) and higher As(V)/As(III) ratios in the PSW than in water from UFA monitoring wells indicate that oxic water from the SAS likely mobilizes As from pyrite in the UFA matrix. Young water found in the PSW also was present in UFA monitoring wells that tap a highly transmissive zone (43- to 53-m depth) in the UFA.  相似文献   

Dwarf spheroidal satellites: are they of tidal origin?     

Manuel Metz  Pavel Kroupa 《Monthly notices of the Royal Astronomical Society》2007,376(1):387-392

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Development in Nepal: Investment in the status quo     

John J. Metz 《GeoJournal》1995,35(2):175-184

Despite billions of dollars provided by donors, Nepal's quest for development remains unfulfilled. Nepal's rugged topography is a serious obstacle, but this development failure has social roots. The first root is Nepal's power structure. A feudal elite, supported by British India, controlled Nepal until 1951, extracted and wasted the agricultural surplus, and excluded all modern influences. The post-1951 government adopted development as its goal and justification, but was still controlled by the same elite. Rivalries between the superpowers and between India and China produced a flow of foreign aid which has tripled each decade. Through its control of the state, Nepal's elite has directed and diverted foreign aid into channels which consolidate its power. This is manifested in the pervasive corruption, which is essential, not accidental, to the system. The second root of Nepal's development failure is inappropriate development theories, which have emphasized investment in infrastructure, but have ignored most of the 90% of the population who are subsistence farmers. The third root is the consistently dismal implementation of development projects by indigenous and expatriate development workers. The institutional ignoring of corruption amounts to collusion between foreign aid donors and indigenous elite.  相似文献   

Geologie von österreich. Band 1. Die zentralalpen: A. Tollmann. Fr. Deuticke, Vienna, 1977., 766 pp., 200 figs., 25 tables     

K. Metz 《Tectonophysics》1979,54(3-4)

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Die obere Stabilitätsgrenze von Tremolit bei der Metamorphose von kieseligen Karbonaten     

Paul Metz 《Contributions to Mineralogy and Petrology》1967,15(3):272-280

During the metamorphism of siliceous carbonates, decomposition of tremolite yields diopside, enstatite, quartz and H₂O according to the following reaction: 1 tremolite 2 diopside + 3 enstatite + 1 quartz + 1 H₂O.For the application to natural processes, it is of special interest to evaluate the equilibrium temperature of this reaction, as a function of the CO₂-content of the H₂O-CO₂ fluid phase for several total pressures. These values were calculated for the total pressures of 1000 and 2000 bars, usingBoyd's experimentally determined univariant equilibrium data [Fig. 1 (Boyd, 1954 and 1959)]. Curves (a) and (b) of Fig. 3 give the results in a temperature-X _{CO 2}-diagram.The decomposition curves of tremolite intersect the equilibrium curves of other reactions which also take place during metamorphism of siliceous carbonates. If the total pressure can be estimated, these points of intersection together with the appropriate field observations will give information on the temperature and composition of the fluid phase during metamorphism.  相似文献   

Records of nutrient-enhanced coastal ocean productivity in sediments from the Louisiana continental shelf   总被引：1，自引：0，他引：1  

Brian J. Eadie  Brent A. McKee  Margaret B. Lansing  John A. Robbins  Simonne Metz  John H. Trefry 《Estuaries and Coasts》1994,17(4):754-765

Shelf sediments from near the mouth of the Mississippi River were collected and analyzed to examine whether records of the consequences of anthropogenic nutrient loading are preserved. Cores representing approximately 100 yr of accumulation have increasing concentrations of organic matter over this period, indicating increased accumulation of organic carbon, rapid early diagenesis, or a combination of these processes. Stable carbon isotopes and organic tracers show that virtually all of this increase is of marine origin. Evidence from two cores near the river mouth, one within the region of chronic seasonal hypoxia and one nearby but outside the hypoxic region, indicate that changes consistent with increased productivity began by approximately the mid-1950s when the inorganic carbon in benthic forams rapidly became isotopically lighter at both stations. Beginning in the mid-1960s, the accumulation of organic matter, organic δ¹³C, and δ¹⁵N all show large changes in a direction consistent with increased productivity. This last period coincides with a doubling of the load of nutrients from the Mississippi River, which levelled off in the mid-1980s. These data support the hypothesis that anthropogenic nutrient loading has had a significant impact on the Louisiana shelf.  相似文献   

Transport of particulate organic carbon by the Mississippi River and its fate in the Gulf of Mexico     

John H. Trefry  Simone Metz  Terry A. Nelsen  Robert P. Trocine  Brian J. Eadie 《Estuaries and Coasts》1994,17(4):839-849

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l^?1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×10¹² moles y^?1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l^?1 in the river to <0.8 μmol l^?1 in offshore waters. In contrast, the organic carbon fraction of the suspended matter increased from <2% of the total mass in the river to >35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ～60 μmol l^?1 to >200 μmol l^?1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ¹³C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.  相似文献   

Identifying key environmental variables shaping within-river fish distribution patterns     

Caroline Senay  Camille Jacqueline Macnaughton  Gabriel Lanthier  Simonne Harvey-Lavoie  Michel Lapointe  Daniel Boisclair 《Aquatic Sciences - Research Across Boundaries》2015,77(4):709-721

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Oxygen isotope exchange and disequilibrium between calcite and tremolite in the absence and presence of an experimental C–O–H fluid     

Y.-F.?ZhengEmail author  M.?Satir  P.?Metz 《Contributions to Mineralogy and Petrology》2004,146(6):683-695

Oxygen isotope exchange between minerals during metamorphism can occur in either the presence or the absence of aqueous fluids. Oxygen isotope partitioning among minerals and fluid is governed by both chemical and isotopic equilibria during these processes, which progress by intragranular and intergranular diffusion as well as by surface reactions. We have carried out isotope exchange experiments in two- and three-phase systems, respectively, between calcite and tremolite at high temperatures and pressures. The two-phase system experiments were conducted without fluid either at 1 GPa and 680 °C for 7 days or at 500 MPa and 560 °C for 20 days. Extrapolated equilibrium fractionations between calcite and tremolite are significantly lower than existing empirical estimates and experimental determinations in the presence of small amounts of fluid, but closely match calculated fractionations by means of the increment method for framework oxygen in tremolite. The small fractionations measured in the direct calcite–tremolite exchange experiments are interpreted by different rates of oxygen isotope exchange between hydroxyl oxygen, framework oxygen and calcite during the solid–solid reactions where significant recrystallization occurs. The three-phase system experiments were accomplished in the presence of a large amount of fluid (CO₂+H₂O) at 500 MPa and 560 °C under conditions of phase equilibrium for 5, 10, 20, 40, 80, 120, 160, and 200 days. The results show that oxygen isotope exchange between minerals and fluid proceeds in two stages: first, through a mechanism of dissolution-recrystallization and very rapidly; second, through a mechanism of diffusion and very slowly. Synthetic calcite shows a greater rate of isotopic exchange with fluid than natural calcite in the first stage. The rate of oxygen diffusion in calcite is approximately equal to or slightly greater than that in tremolite in the second stage. A calculation using available diffusion coefficients for calcite suggests that grain boundary diffusion, rather than volume diffusion, has been the dominant mechanism of oxygen transport between the fluid and the mineral grains in the later stage.Editorial responsibility: T.L. Grove  相似文献