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141.
The solubility of fluorite in NaCl solutions increases with increasing temperature at all ionic strengths up to about 100°C. Above this temperature, the solubility passes through a maximum and possibly a minimum with increasing temperature at NaCl concentrations of 1.0M or less, and increases continuously with increasing temperature at NaCl concentrations above 1.0M. At any given temperature, the solubility of fluorite increases with increasing salt concentration in NaCl, KCl and CaCl2 solutions. The solubility follows Debye-Hückel theory for KCl solutions. In NaCl and CaCl2 solutions, the solubility of fluorite increases more rapidly than predicted by Debye-Hückel theory: the excess solubility is due to the presence of NaFc, CaF+, and possibly of Na2F+. The solubility of fluorite in NaCl-CaCl2 and in NaCl-CaCl2-MgCl2 solutions is controlled by the common ion effect and by the presence of NaFc, CaF+, and MgF+. The solubility of fluorite in NaCl-HCl solutions increases rapidly with increasing initial HCl concentration; the large solubility increase is due to the presence of HFc. It seems likely that complexes other than those identified in this study rarely play a major role in fluoride transport and fluorite deposition at temperatures below 300°C. 相似文献
142.
Fluorite deposition in hydrothermal systems 总被引:1,自引:0,他引:1
During the formation of fluorite deposits fluorite is precipitated either as a consequence of changes in temperature and pressure along the flow path of hydrothermal solutions or due to fluid mixing, or as the result of the interaction of hydrothermal solutions with wall rocks.A decrease in temperature in the flow direction is the most appealing, though still unproven, mechanism of fluorite deposition in Mississippi Valley fluorite deposits.Mixing can produce solutions which are either undersaturated or supersaturated with respect to fluorite. The most important parameters are the temperature, the salinity, and the calcium and fluoride concentration of the fluids prior to mixing.A variety of wall rock reactions can lead to fluorite precipitation. Among these reactions which increase the pH of initially rather acid (pH ≤ 3) hydrothermal solutions are apt to be particularly important. 相似文献
143.
The Baula-Nuasahi Complex, on the southern flank of the Singhbhum Archaean nucleus in north-eastern India, exposes a series of Mesoarchaean igneous suites. These are (1) a gabbro–anorthosite unit, which is petrographically homogeneous, although mineral-chemistry data hint at a subtle eastward differentiation; (2) a peridotite unit (with three chromitite layers) together with (3) a pyroxenite unit which display cumulate textures, modal layering, and (for the peridotite unit) differentiation trends in both mineralogy and mineral chemistry; and (4) the Bangur gabbro (~3.1 Ga), which defines an oblong intrusion, crosscutting the older igneous suites in the southern part of the complex, with a curvilinear NW-trending apophysis, 2 km long and up to 40 m wide. Magmatic breccia comprising ultramafic and chromitite wall-rock clasts in a gabbro matrix is exposed at the contact of the main Bangur gabbro body and also forms the entire Bangur gabbro apophysis. Concentrations of platinum-group minerals (PGMs) are found where the breccia contains abundant chromitite clasts, and two types of platinum-group-element (PGE) mineralisation are recognised. Type 1 (Pt 1.1–14.2, Pd 0.1–2.1 ppm, with an average Pt/Pd=8–9) is a contact-type mineralisation which occurs in the breccia at the contact between the Bangur intrusion and its ultramafic host. The PGMs—Pt alloys (isoferroplatinum) and sulphides (braggite, malanite)—are enclosed by pyroxene and plagioclase, reflecting a magmatic origin. Significant wall-rock assimilation by the magma (giving rise to the Bangur gabbro) is indicated by changes in pyroxene composition and by the presence of relicts of chromite (from the host) now altered to secondary ferritchromite in the contact zone. Type 2 PGE mineralisation (Pt 0.3–1.6, Pd 1.8–6.0 ppm, with Pt/Pd~0.5–3.0) is restricted to the breccia apophysis of the Bangur gabbro where it occurs in the breccia matrix, associated with an intense hydrothermal alteration which does not exist in the contact zone. PGMs (PGE arsenides, tellurides, bismuthides and antimonides) and, where present, base-metal sulphides (BMSs) form intergrowths with hydrous silicates, reflecting a hydrothermal origin. Oxygen isotope geothermometry documents the main stages of hydrothermal alteration within a decreasing temperature range between 700–1,000 and 500–600 °C, and oxygen, hydrogen and sulphur isotopes show that the hydrothermal fluids were derived from the magma rather than an external source. Pervasive hydrothermal alteration in the breccia apophysis likely represents upward channelling of late-magmatic fluids along a narrow, near-vertical, subplanar conduit which led away from the main magma chamber. We suggest that Type 2 mineralisation was produced by late-magmatic hydrothermal remobilisation and reconcentration of Type 1 PGE mineralisation, and that the composition of the hydrothermal fluids controlled whether BMSs were enriched along with the PGMs.Editorial handling: P. Lightfoot 相似文献
144.
Georg?M.?PartzschEmail author Dominique?Lattard Catherine?McCammon 《Contributions to Mineralogy and Petrology》2004,147(5):565-580
One of the most widely used methods to estimate magmatic oxygen fugacity involves the use of empirical equations relating fO2 to the iron redox state in quenched silicate liquids; however none of the equations have been calibrated experimentally under subliquidus conditions at temperatures and oxygen fugacities that are relevant to natural magmas. To address this problem, we tested two empirical relationships [Eq. (1) in Kress and Carmichael 1991; Eq. (6) in Nikolaev et al. 1996] on synthetic glasses synthesized from a ferrobasaltic and a transitional alkali-basaltic composition at sub- to superliquidus temperatures (1,132–1,222°C) and controlled oxygen fugacities (FMQ=–2 to +1.4). Fe3+/Fe was determined using conventional and milliprobe Mössbauer spectroscopy, and verified using wet chemical analysis on selected samples. For the ferrobasaltic bulk composition SC1-P, both empirical models reproduce the Fe3+/Fe ratio of the quenched liquids generally within 0.03 for sub- as well as superliquidus temperatures, although agreement is worse at higher oxygen fugacities (FMQ>+1) at subliquidus temperatures. For the transitional alkali-basaltic composition 7159V-P, both models reproduce the Fe3+/Fe ratio of the quenched liquids generally within 0.04, although agreement is worse for both models at high oxygen fugacities (FMQ>+1). Such behaviour may be related to a change in melt structure, where a progressive change in Fe3+ coordination is inferred to occur as a function of Fe3+/Fe based on Mössbauer center shifts. Recasting the data in terms of oxygen fugacity shows that calculated oxygen fugacities deviate from those actually maintained during the equilibration of the sample material by generally no more than 0.5 log-bar unit, with maximum deviations that only rarely exceed one log-bar unit.Editorial responsibility: J. Hoefs 相似文献
145.
Time series of velocity profiles at two Chesapeake Bay entrance sites were used to characterize the subtidal variability of transverse flows off a cape. A shallow sampling site was located near Cape Henry over 6 m of water and separated from a deep site, 20 m deep, by a distance of 4 km. The velocity profiles showed that wind-induced subtidal variations in general masked curvature effects (centrifugal accelerations) that may produce secondary circulation associated with tidal flow around a cape. Such secondary circulation, consisting of flow away from the cape at surface and toward the cape at depth, was observed only during periods of weak winds. Most of the time, transverse flows were unidirectional throughout the water column and moved in opposite directions at the two sites examined. This caused convergence of transverse flow between the two sites under the influence of northerly winds and divergence of transverse flow with southwesterly winds. In addition to unidirectional and curvature-induced secondary flows, other modes of subtidal variability consisted of (1) two-layered responses with surface flow toward the cape, and (2) three-layered responses. These two- and three-layered structures were observed more frequently at the deep site, where greater stratification is expected, than at the shallow site.Responsible Editor: Iris Grabemann 相似文献
146.
Undressing the researcher: feminism, embodiment and sexuality at a queer bathhouse event 总被引:2,自引:0,他引:2
In this paper we examine how the researcher's body can be used as a tool for data collection in the process of ethnographic fieldwork. We focus in particular on the tensions inherent in undertaking embodied ethnographic research in the sexualized setting of a queer women's bathhouse event in Toronto, Canada. Our discussion addresses three moments within the research process: preparing our bodies to attend the bathhouse; positioning our bodies within the spaces of the bathhouse; and interacting with our bodies during the event. Through this discussion we argue that the body of the researcher is a contested site of knowledge production. 相似文献
147.
Hideo Aochi Marc Cushing Oona Scotti Catherine Berge-Thierry 《Geophysical Journal International》2006,165(2):436-446
The Middle Durance fault system, southeastern France, is a slow active fault that produced moderate-size historical seismic events and shows evidence of at least one M w ≳ 6.5 event in the last 29 000 yr. Based on dynamic rupture simulation, we propose earthquake scenarios that are constrained by knowledge of both the tectonic stress field and of the 3-D geometry of the Durance fault system. We simulate dynamic rupture interaction among several fault segmentations of different strikes, dips and rakes, using a 3-D boundary integral equation method. 50 combinations of reasonable stress field orientations, stress field amplitudes and hypocentre locations are tested. The probability of different rupture evolutions is then computed. Each segment ruptures mainly as a single event (44 per cent of the 50 simulations test in this paper). However, the probability that an event triggers simultaneously along three segments is high (26 per cent), leading to a potential rupture length of 45 km. Finally, 2 per cent of the simulations occur along four adjacent segments, producing the greatest total rupture length of 55 km. The simulation results show that the southernmost segment is most easily ruptured (40 per cent), because of its favourable orientation with respect to the tectonic stress and of its favourable location for interaction with the other segments. South-bound unilateral propagation is slightly preferable (41 per cent), compared to north-bound unilateral and bilateral propagation modes. Although, these rupture scenarios cannot be directly translated into probabilities of occurrence, they do provide a better insight as to which rupture scenarios are more likely, an important element to better estimate near-field strong ground motion and seismic hazard. 相似文献
148.
Innokenty Kantor Leonid Dubrovinsky Catherine McCammon Anastasia Kantor Sakura Pascarelli Giuliana Aquilanti Wilson Crichton Maurizio Mattesini Rajeev Ahuja Jailton Almeida Vadim Urusov 《Physics and Chemistry of Minerals》2006,33(1):35-44
Combined X-ray powder diffraction, Mössbauer, and XANES spectroscopy in situ experiments revealed the transformation of cubic (Mg0.8Fe0.2)O ferropericlase to a rhombohedrally distorted phase at 35(1) GPa and room temperature. The Mössbauer spectroscopy results show that the rhombohedral distortion does not involve magnetic ordering. Combined with data from the literature, our results imply that the cubic to rhombodedral transition occurs in (Mg,Fe)O under conditions of non-hydrostatic stress over a wide range of composition (0.2≤x Fe≤1). 相似文献
149.
Marc Kamionkowski Arif Babul Catherine M. Cress & Alexandre Refregier 《Monthly notices of the Royal Astronomical Society》1998,301(4):1064-1072
Weak lensing by large-scale mass inhomogeneities in the Universe induces correlations in the observed ellipticities of distant sources. We first review the harmonic analysis and statistics required of these correlations and discuss calculations for the predicted signal. We consider the ellipticity correlation function, the mean-square ellipticity, the ellipticity power spectrum and a global maximum-likelihood analysis to isolate a weak-lensing signal from the data. Estimates for the sensitivity of a survey of a given area, surface density, and mean intrinsic source ellipticity are presented. We then apply our results to the FIRST radio-source survey. We predict an rms ellipticity of roughly 0.011 in 1 × 1 deg2 pixels and 0.018 in 20 × 20 arcmin2 pixels if the power spectrum is normalized to σ8 Ω0.53 = 0.6, as indicated by the cluster abundance. The signal is significantly larger in some models if the power spectrum is normalized instead to the COBE anisotropy. The uncertainty in the predictions from imprecise knowledge of the FIRST redshift distribution is about 25 per cent in the rms ellipticity. We show that FIRST should be able to make a statistically significant detection of a weak-lensing signal for cluster-abundance-normalized power spectra. 相似文献
150.
Majorite of bulk composition Mg0.86Fe0.15SiO3 was synthesized at 19 GPa and 1900 °C at an oxygen fugacity close to the Re/ReO2 buffer. Optical absorption spectra of polycrystalline samples were measured from 4000 to 25000cm?1. The following features were observed: (1) Three bands at 4554, 6005 and 8093 cm?1 due to the 5Eg → 5T2g transition of Fe2+ in a distorted dodecahedral site. (2) A band at 9340 cm?1 due to the transition 5T2g → 5Eg of octahedral Fe2+. (3) A band at 22784 cm?1 resulting from Fe3+, probably in an octahedral site (6A1g → 4A1g, 4Eg). (4) A very intense system of Fe2+ → Fe3+ intervalence charge transfer bands which can be modelled by two Gaussian components centered at 16542 and 20128 cm?1. The existence of two components in the charge transfer spectrum could be related to the fact that the tetragonal majorite structure may contain Fe3+ in two different octahedral sites. The crystal field splitting Δ of Fe2+ in dodecahedral coordination is 5717 cm?1. If a splitting of the ground state in the order of 1000 cm?1 is assumed, this yields a crystal field stabilization energy (CFSE) of 3930 cm?1, comparable to the CFSE of Fe2+ in pyrope-rich garnet. However, the splitting of 5T2g is significantly higher than in pyrope. This would be consistent with Fe2+ preferentially occupying the more distorted one of the two dodecahedral sites in the majorite structure. For octahedral Fe2+, Δ= 9340 cm?1 and CFSE=3736 cm?1, assuming negligible splitting of the ground state. 相似文献