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1.
A modified commercial (Setaram C80) calorimeter has been used to measure the isobaric volumetric heat capacities of concentrated alkaline sodium aluminate solutions at ionic strengths from 1 to 6 mol kg−1, with up to 40 mol.% substitution of hydroxide by aluminate, at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar heat capacities for the mixtures, Cp?, derived from these data were found to depend linearly on the aluminate substitution level, i.e., they followed Young’s rule. These quantities were used to estimate the apparent molar heat capacities of pure, hypothetical sodium aluminate solutions, Cp? (‘NaAl(OH)4’(aq)). Slopes of the Young’s rule plots were invariant with ionic strength at a given temperature but depended linearly on temperature. The heat capacities of ternary aqueous sodium hydroxide/aluminate mixtures could therefore be modelled using only two parameters in addition to those needed for the correlation of Cp? (NaOH(aq)) reported previously from these laboratories. An assessment of the standard thermodynamic quantities for boehmite, gibbsite and the aluminate ion yielded a set of recommended values that, together with the present heat capacity data, accurately predicts the solubility of gibbsite and boehmite at temperatures up to 300 °C.  相似文献   

2.
We examined the hydroclimatic signal in a record of annual lamina (varve) thickness from High Arctic Lake A, Ellesmere Island (83°00.00′N, 75°30.00′W). In this unglacierized catchment, nival melt is the dominant source for meltwater and transport of sediment to the lake, and autumn snowfall is highly influential on varve thickness through the amount of snow available for melt in the following year. For the period during which climatic data are available, varve thickness in Lake A was significantly correlated (r = 0.50, p < 0.01) with the cumulative snowfall from August to October (ASO) during the previous year and, to a lesser extent, ASO mean daily temperature (r = 0.39, p < 0.01) at Alert, Nunavut (175 km east). The varve thickness record, interpreted as a proxy record of ASO snowfall and, by extension, ASO temperature, indicated above-mean conditions during five periods of the past millennium, including most of the 20th century. These results corresponded well to other available high-resolution proxy climate records from the region, with some discrepancies prior to AD 1500 and during the period AD 1700-1900.  相似文献   

3.
Rb-Sr and U-Pb isotopic data for granulite facies rocks, forming textural relics with respect to eclogite facies metamorphism in the Western Gneiss Region (WGR) of Norway, highlight the importance of textures and mineral reaction kinetics for the interpretation of geochronological data. Studied rocks from Bårdsholmen, southern WGR, were subjected to granulite facies metamorphism at 955 ± 3 Ma (U-Pb, zircon). Later on, they experienced a subduction-related, kinetically stranded eclogitization (T > 650 °C at ∼20 kbar) at 404 ± 2 Ma (Rb-Sr multimineral internal isochron data), followed by exhumation through amphibolite facies conditions. Full conversion of granulite to eclogite was restricted to zones of fluid infiltration and deformation. Despite the fact that metamorphic temperatures vastly exceeded the commonly assumed ‘closure temperature’ for Rb-Sr in submillimeter-sized biotite for several Ma during eclogite facies overprint, Sr-isotopic signatures of relic biotite have not been fully reset. Large biotite crystals nearly record their Sveconorwegian (Grenvillian) crystallization age. Sr signatures of other granulite facies phases (feldspar, pyroxenes, amphibole) remained unchanged, with the exception of apatite. The results imply that isotopic signatures much closer correspond to the P, T conditions of formation recorded by a dated phase and its paragenesis, than to a temperature history. In texturally well-equilibrated high-grade rocks which experienced no mineral reactions and remained devoid of free fluids during exhumation, like granulites or eclogites, isotopic resetting during cooling is either kinetically locked, or restricted to sluggish intermineral diffusion which demonstrably does not lead to full isotopic homogenization. In texturally unequilibrated rocks, textural relics are likely to represent isotopic relics. It is shown that for both high-grade rocks and for rocks with textural disequilibria, geologically meaningful isotopic ages based on isochron methods can only be derived from sub-assemblages in isotopic equilibrium, which have to be defined by analysis of all rock-forming minerals. Conventional two-point ‘mica ages’ for such rocks are a priori geochronologically uninterpretable, and valid multimineral isochron ages a priori do not record cooling but instead date recrystallization-inducing processes like fluid-rock interaction.  相似文献   

4.
Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing 109Cd as a tracer to distinguish between ‘labile’ and ‘non-labile’ forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric PCO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd2+ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data (R2 = 0.992). It differentiates between two ‘pools’ of sorbed Cd2+ on calcite, ‘labile’ and ‘non-labile’, in which labile sorbed Cd is in immediate equilibrium with the free Cd2+ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model (R2 = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ∼175 d, for release to a ‘zero-sink’ solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption.  相似文献   

5.
Thermochronology has revolutionized our understanding of the establishment and evolution of lithospheric thermal structure. However, many potential benefits provided by the application of diffusion theory to thermochronology have yet to be fully exploited. This study uses apatite (Tc = 450-550 °C) and titanite (Tc = 550-650 °C) U-Pb ID-TIMS thermochronology at the single- to sub-grain scale to separate the variable effects of volume diffusion of Pb from metamorphic (over)growth above and below the Tc of a mineral. Data are presented from two ca. 3227 Ma tonalite samples from north and south of the Barberton Greenstone Belt (BGB), southern Africa. Two distinct populations of apatite from a sample north of the BGB record fast cooling followed by metamorphic growth ∼10 Myr later. Both apatite and titanite dates from south of the BGB show a strong correlation with the grain size and record 100 Myr of post-emplacement cooling. Complex core-rim zoning observed in cathodoluminescence images of apatite is interpreted to reflect metamorphic overgrowth above the Tc. The age and topology of grain size versus date curves from titanite and apatite are used in combination with a finite-difference numerical model to show that slow, non-linear, cooling and not thermal resetting is responsible for the observed distribution. The thermal histories from either side of the BGB are very different and provide unique insight into the BGB’s tectonic evolution: a ∼70 Myr period of apparent stability after ca. 3.2 Ga terrane assembly was followed by fast exhumation south of the BGB that led to lower-crustal melting and intrusion of granitic batholiths ca. 3.14-3.10 Ga.  相似文献   

6.
By using continuous helium flow during the crushing of calcite speleothem samples, we are able to recover liberated inclusion waters without isotopic fractionation. A paleotemperature record for the Jacklah Jill Cave locality, Vancouver Island, BC, was obtained from a 30-cm tall stalagmite that grew 10.3-6.3 Ka ago, using δ18O values of the crushed calcite and of the inclusion water as inferred from its δD. It is found that the locality experienced mean annual temperature variations up to 11 °C over a 4-Ka period in the early Holocene. At the beginning of the period, local temperature quickly increased from a minimum of ∼1 °C to around 10 °C, but this early climate optimum, about 3 °C warmer than today, only lasted for ∼1200 years. About 8.6 Ka ago, temperature had declined to ∼7 °C, approximately the same as the modern cave temperature. Since then, the study area has experienced only minor temperature fluctuations, but there was a brief fall to ∼4 °C at around 7 Ka ago, which might be caused by a short lived expansion of local alpine glaciers. The long-term T-dependence of δD was 1.47‰/°C, identical to the value in modern precipitation.  相似文献   

7.
Spontaneous combustion, less than 1 Ma ago, affected a 60-m thick sediment pile of biomicrite at the Khushaym Matruck site (Jordan). The present study shows that three retrograde alteration stages occurred: weathering, thermal stress and oxidative alkaline perturbation. μ-FT-i.r. spectra of isolated kerogens and oxygen index of whole rocks indicate that oxidation of organic matter occurred down to ∼10 m beneath the metamorphosed zone at Khushaym Matruck. The occurrence of the oxidative weathering bacterially mediated, as suggested by the mass chromatograms of saturated hydrocarbons, can explain high Rock-Eval Tmax values and low petroliferous potential measured along the sedimentary pile. On the other hand, the thermal extent of combustion events was limited to the first 2 m from the contact. The mean reflectance of 0.20–0.24% and porosity of ca. 50% of the grey clayey biomicrites indicate that organic matter was very immature and sediments were unconsolidated at the time of the combustion event. Using mineralogy, microscopic analyses of vegetable debris and magnetic susceptibility, a suite of characteristic points corresponding to the thermal imprint can be assessed: (i) x = 0m, T ∼ 1000 °C, (ii) x = 1 m, T ∼ 350 °C, (iii) x = 2 m, T ∼ 150 °C and (iv) x > ∼ 8 m, T ∼ 30 °C. Paleocirculation of meteoric groundwater in the ‘cement-marbles’ generated high-pH fluids that have circulated via fractures and through the matrix porosity of the underlying biomicrites but have also induced alkaline hydrolysis and oxidative attack of the organic matter. The polysaccharide/lignin ratio derived from μ-FT-i.r. analyses shows that the delignification of vegetable debris and degradation of polysaccharides progressively decline in the indurated zone, which indicates a decrease in the pH of migrating solutions. The latter also severely oxidized organic matter at 2.10 and 3.05 m as revealed by the oxygen index and induced the generation of bitumen. The spatial correlation between the oxidation levels of organic matter and the metal contents (Fe, Ti and Cr) suggests that redox reactions were responsible for the immobilization of metals in the indurated biomicrites. The intensity of these reactions is attributed to changes in the fluid flow regime within the sedimentary column.  相似文献   

8.
The Pitzer’s interaction parameters, λN–M, involving the Mth cationic Al species Al3+ or AlOH2+ or AlO+ and the Nth neutral species SiO2(aq) (at temperatures of 25–300 °C) or CO2(aq) (at temperatures of 25–150 °C), have been evaluated through empirical linear relationships between λN–M and the surface electrostatic field of the ionic species of interest. These relationships have been obtained starting from the known λN–M for both SiO2(aq) and CO2(aq) with the main dissolved cations. The Pitzer’s interaction parameter thus estimated for the pair CO2(aq)–Al3+ at 25 °C, 0.327, is 20–40% higher than the corresponding values obtained from CO2 solubilities in concentrated solutions of AlCl3, 0.272 ± 0.010 (2σ), and Al2(SO4)3, 0.232 ± 0.002 (2σ), partly corroborating the empirical approach adopted in this study. To test the Pitzer’s interaction coefficients for cationic Al species with aqueous SiO2, the log K values of the kaolinite dissolution reaction have been computed starting from available experimental data at 23–25 °C and ionic strengths of 0.0001–0.12 mol/kg adopting, alternatively, the Pitzer’s equations and the Debye–Hückel equation. A satisfactory agreement has been found between the log K values obtained through these two approaches, with maximum deviations of 0.11–0.12 log units. This good convergence of results is encouraging as it represents a necessary condition to prove the reliability of the Pitzer’s interaction coefficients estimated in this work. These results are a first step to take into account specific interactions among solutes in concentrated electrolyte solutions, such as those hosted in sedimentary basins or geothermal waters, for instance through the Pitzer’s equations. However, experimental or field data at higher ionic strengths are absolutely necessary to validate the reliability of the Pitzer’s interaction coefficients determined in this study.  相似文献   

9.
Goethite (Ax-2) from Axel Heiberg Island (∼80°N) on the margin of the Arctic Ocean is the dominant mineral in a sample of “petrified” Eocene wood, but U, Th, and He measurements suggest that the goethite (α-FeOOH) crystallized in the latest Miocene/Pliocene (ca. 5.5 to 2.8 Ma). Measured δD and δ18O values of Ax-2 are −221 (±6)‰ and −9.6 (±0.5)‰, respectively. The inferred δD and δ18O values of the ancient water were about −139‰ and −18.6‰, respectively, with a calculated temperature of crystallization of 3 (±5)°C, which compares with the modern summer (J-J-A) temperature of 3 °C and contrasts with a modern MAT of −19 °C. Published results from various biological proxies on nearby Ellesmere Island indicate a Pliocene (∼4 Ma) MAT of either −6 or −0.4 °C and corresponding seasonal amplitudes of about 18 or 13 °C. A conductive heat flow model suggests that a temperature of 3 °C could represent goethite crystallization at depths of ∼100-200 cm (for MAT = −6 °C) or ∼250-450 cm (for MAT = −0.4 °C) over seasonally restricted intervals of time.The δ18O value of the Ax-2 water (−18.6‰) is more positive than the modern J-J-A precipitation (−22‰). In combination, the paleotemperatures and δ18O values of ancient waters (from Ax-2 and published results from three Eocene or Pliocene proxy sites on Axel Heiberg and Ellesmere Islands) are consistent with a warm season bias in those isotopic proxies. The results are also consistent with higher proportions of J-J-A precipitation in the annual total. If so, this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates, and suggests that the Arctic hydrologic cycle, as expressed in the seasonal distribution and isotopic composition of precipitation (perhaps modified by a warmer Arctic Ocean), differed from modern.The δ13C value of the Fe(CO3)OH component in the Ax-2 goethite is +6.6‰, which is much more positive than expected if crystallizing goethite incorporated CO2 derived primarily from oxidation of relict Eocene wood with δ13C values of about −24‰. This apparent paradox may be resolved if the goethite is a product of oxidation of 13C-rich siderite, which had previously replaced wood in an Eocene methanogenic burial environment. Thus, the goethite retains a carbon isotope “memory” of a diagenetic Eocene event, but a δD and δ18O record of the latest Miocene/Pliocene Arctic climate.  相似文献   

10.
An empirical calibration for the oxygen isotope fractionation between biogenic silica and water was determined for diatom frustules sampled from living diatom communities in the Jemez Mountains of northern New Mexico, USA. Over a temperature range from 5.1 to 37.8 °C, the silica-water fractionation is defined by the equation 1000 ln α(silica-water) = 2.39(±0.13) × 106T−2 + 4.23(±1.49). This relationship is in close agreement with other published silica-water fractionation factors for laboratory cultured diatom samples; however, it is as much as 8‰ lower than equilibrium quartz-water fractionations and 3-4‰ lower than observed silica-water fractionations in diatomaceous silica collected from sediment traps and sediment cores. There are three possible explanations for the disparate silica-water fractionation factors observed in diatom silica: (1) silica does not precipitate in equilibrium with ambient water, (2) silica does precipitate in equilibrium with ambient water, but the silica-water fractionation factor for diatom silica is considerably less than the equilibrium fractionation factor for quartz-water, or (3) silica precipitation is influenced by a ‘vital’ effect, where the δ18O value of the water inside the diatom cell walls is lower than the δ18O values of ambient water.Post-mortem loss of organic material results in an alteration or ‘maturation’ of diatom silica in which silica reequilibrates with a silica-water fractionation closer to the equilibrium quartz-water fractionation. Alteration is likely to occur rapidly after the diatom frustule loses its organic coating, either as it settles through the water column or at the sediment-water interface; δ18O values recorded by paleo-diatom silica therefore do not record growing conditions but more likely record conditions at the sediment-water interface. In the case of lacustrine environments, where the bottom water remains at a nearly constant 4 °C, the reequilibration of diatom silica with bottom conditions could reduce or remove the conflating effects of temperature on δ18O values recorded by paleo-diatom silica and provide direct information on the δ18O value of the lake water.  相似文献   

11.
The analysis of gaseous compositions from Solfatara (Campi Flegrei, South Italy) fumaroles since the early 1980s, clearly reveals a double thermobarometric signature. A first signature at temperatures of about 360 °C was inferred by methane-based chemical-isotopic geoindicators and by the H2/Ar geothermometer. These high temperatures, close to the critical point of water, are representative of a deep zone where magmatic gases flash the hydrothermal liquid, forming a gas plume. A second signature was found to be at around 200-240 °C. At these temperatures, the kinetically fast reactive species (H2 and CO) re-equilibrate in a pure vapor phase during the rise of the plume. A combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species, i.e. H2O and CO2, shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 °C by the vaporization of hydrothermal liquids. A typical ‘andesitic’ water type (δD ∼ −20‰, δ18O ∼10‰) and a CO2-rich composition (XCO2∼0.4) has been inferred for the magmatic fluids, while for the hydrothermal component a meteoric origin and a CO2 fugacity fixed by fluid-rock reaction at high temperatures have been estimated. In the time the fraction of magmatic fluids in the fumaroles increased (up to ∼0.5) at each seismic and ground uplift crisis (bradyseism) which occurred at Campi Flegrei, suggesting that bradyseismic crises are triggered by periodic injections of CO2-rich magmatic fluids at the bottom of the hydrothermal system.  相似文献   

12.
431 oriented samples were collected from 27 dolerite dykes at 17 sites, belonging to 2.95, 2.65, and 1.90 Ga swarms, that trend SE, E and NE, respectively from the Bushveld Igneous Complex into the eastern Kaapvaal Craton (ages determined by Olsson et al., 2010; Olsson in Söderlund et al., 2010). Samples were analyzed for paleomagnetism and also anisotropy of magnetic susceptibility (AMS). For the 2.95 Ga SE-trending dykes high temperature/coercivity ‘P’ component has unblocking temperatures up to 590 °C and coercivity 40–90 mT and demonstrate SSW declination and intermediate positive inclination. Based on positive contact and conglomerate tests we argue for a primary origin of this component. The paleopole (BAD), calculated from ‘P’ component, does not correspond to any of the previously obtained Archean–Paleoproterozoic paleopoles for the Kaapvaal Craton, and represents a new key pole for 2.95 Ga. The high-coercivity ‘H’ component for the 2.65 Ga-old E-trending dykes has a SSW declination and steep positive inclination. Paleomagnetic pole (RYK), recalculated from this component, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78 Ga Ventersdorp volcanics. The third group, NE-trending dykes of the 1.90 Ga Black Hill swarm demonstrate an ‘M’ component with dual polarity high-coercivity component with SSE-declination and negative intermediate inclination. The paleopole (BHD), calculated from this component is close to the 1.87 Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Overprint directions include a very well developed thermo-chemical overprint (Dec = 329° Inc = −36°), which is believed to be associated with a ∼0.18 Ga regional ‘Karoo’ thermal event.  相似文献   

13.
In order to investigate the incorporation of Sr, Mg, and U into coral skeletons and its temperature dependency, we performed a culture experiment in which specimens of the branching coral (Porites cylindrica) were grown for 1 month at three seawater temperatures (22, 26, and 30 °C). The results of this study showed that the linear extension rate of P. cylindrica has little effect on the skeletal Sr/Ca, Mg/Ca, and U/Ca ratios. The following temperature equations were derived: Sr/Ca (mmol/mol) = 10.214(±0.229) − 0.0642(±0.00897) × T (°C) (r2 = 0.59, p < 0.05); Mg/Ca (mmol/mol) = 1.973(±0.302) + 0.1002(±0.0118) × T (°C) (r2 = 0.67, p < 0.05); and U/Ca (μmol/mol) = 1.488(±0.0484) − 0.0212(±0.00189) × T (°C) (r2 = 0.78, p < 0.05). We calculated the distribution coefficient (D) of Sr, Mg, and U relative to seawater temperature and compared the results with previous data from massive Porites corals. The seawater temperature proxies based on D calibrations of P. cylindrica established in this study are generally similar to those for massive Porites corals, despite a difference in the slope of DU calibration. The calibration sensitivity of DSr, DMg, and DU to seawater temperature change during the experiment was 0.64%/°C, 1.93%/°C, and 1.97%/°C, respectively. These results suggest that the skeletal Sr/Ca ratio (and possibly the Mg/Ca and/or U/Ca ratio) of the branching coral P. cylindrica can be used as a potential paleothermometer.  相似文献   

14.
Mineral-associated organic matter (OM) represents a large reservoir of organic carbon (OC) in natural environments. The factors controlling the extent of the mineral-mediated OC stabilization, however, are poorly understood. The protection of OM against biodegradation upon sorption to mineral phases is assumed to result from the formation of strong bonds that limit desorption. To test this, we studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as ‘ligand exchange’, ‘Ca2+ bridging’, and ‘van der Waals forces’. Organic matter extracted from an Oa forest floor horizon under Norway spruce (Picea abies (L.) Karst) was reacted with minerals at dissolved OC concentrations of ∼5-130 mg/L at pH 4. Goethite retained up to 30.1 mg OC/g predominantly by ‘ligand exchange’; pyrophyllite sorbed maximally 12.5 mg OC/g, largely via ‘van der Waals forces’ and ‘Ca2+ bridging’, while sorption of OM to vermiculite was 7.3 mg OC/g, mainly due to the formation of ‘Ca2+ bridges’. Aromatic OM components were selectively sorbed by all minerals (goethite ? phyllosilicates). The sorption of OM was strongly hysteretic with the desorption into 0.01 M NaCl being larger for OM held by ‘Ca2+ bridges’ and ‘van der Waals forces’ than by ‘ligand exchange’. Incubation experiments under aerobic conditions (initial pH 4; 90 days) revealed that OM mainly bound to minerals by ‘ligand exchange’ was more resistant against mineralization than OM held by non-columbic interactions (‘van der Waals forces’). Calcium bridges enhanced the stability of sorbed OM, especially for vermiculite, but less than the binding via ‘ligand exchange’. Combined evidence suggests that the extent and rate of mineralization of mineral-associated OM are governed by desorption. The intrinsic stability of sorbed OM as related to the presence of resistant, lignin-derived aromatic components appears less decisive for the sorptive stabilization of OM than the involved binding mechanisms. In a given environment, the type of minerals present and the solution chemistry determine the operating binding mechanisms, thereby the extent of OM sorption and desorption, and thus ultimately the bioavailability of mineral-associated OM.  相似文献   

15.
Aqueous alteration of primitive meteorites was among the earliest geological processes during the evolution of our solar system. ‘Clumped-isotope’ thermometry of carbonates in the CM chondrites, Cold Bokkeveld, Murray, and Murchison, demonstrates that they underwent aqueous alteration at 20-71 °C from a fluid with δ18OVSMOW of 2.0‰ to 8.1‰ and δ17OVSMOW of −0.1‰ to 3.0‰. The δ13CVPDB values of these carbonates exhibit a negative correlation with the δ18OVSMOW of their formation waters, consistent with formation and escape of 13C-depleted CH4 during aqueous alteration. Methane generation under these conditions implies that the alteration fluid was characterized by an Eh ? −0.67 and pH ? 12.5 (or lower at the highest alteration temperatures). Our findings suggest that methane generation may have been a widespread consequence of planetesimal and planetary aqueous alteration, perhaps explaining the occurrence of methane on Titan, Triton, Pluto, and other Kuiper-belt objects.  相似文献   

16.
Preliminary measurements were carried out of the solubility of the O2-buffering assemblage bismuth + bismite (Bi2O3) in aqueous liquid–vapor and vapor-only systems at temperatures of 220, 250 and 300 °C. All experiments were carried out in Ti reaction vessels and were designed such that the Bi solids were contained in a silica tube that prevented contact with liquid water at any time during the experiment. Two blank (no Bi solids present) liquid–vapor experiments at 220 °C yielded Bi concentrations (±1σ) in the condensed liquid of 0.22 ± 0.02 mg/L, whereas the solubility measurements at this temperature yielded an average value of approximately 6 ± 9 mg/L, with replicate experiments ranging from 0.3 to 26 mg/L. Although the 6 mg/L value is associated with a considerable degree of uncertainty, the experiments do indicate transport of Bi through the vapor phase. Measured Bi concentrations in the condensed liquid at 250 °C were in the same range as those at 220 °C, whereas those at 300 °C were significantly lower (i.e., all below the blank value). Vapor-only experiments necessarily contained much smaller initial volumes of water, thereby making the results more susceptible to contamination. Single blank runs at 220 and 300 °C yielded Bi concentrations of 82 and 16 mg/L, respectively. Measured concentrations (±1σ) of Bi in the vapor-only solubility experiments at 220 °C were 235 ± 78 mg/L for an initial water volume of 0.5 mL, and at 300 °C were 56 ± 30 mg/L and 33 ± 21 for initial water volumes of 1 and 2 mL, respectively, suggesting strong preferential partitioning of Bi into the vapor. The results indicate a negative dependence of Bi solubility on temperature, but are inconclusive with respect to the dependence of Bi solubility on water density or fugacity.  相似文献   

17.
The isopiestic method has been used to determine the osmotic coefficients of the binary solutions NaBr-H2O (from 0.745 to 5.953 mol kg−1) and KBr-H2O (from 0.741 to 5.683 mol kg−1) at the temperature t = 50 °C. Sodium chloride solutions have been used as isopiestic reference standards. The isopiestic results obtained have been combined with all other experimental thermodynamic quantities available in literature (osmotic coefficients, water activities, bromide mineral’s solubilities) to construct a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the NaBr-H2O, KBr-H2O and Na-K-Br-H2O systems from dilute to high solution concentration within the 0-300 °C temperature range. The Harvie and Weare [Harvie C., and Weare J. (1980) The prediction of mineral solubilities in naturalwaters: the Na-K-Mg-Ca-Cl-SO4-H2O system from zero to high concentration at 25 °C. Geochim. Cosmochim. Acta44, 981-997] solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer [Pitzer K. (1973) Thermodynamics of electrolytes. I. Theoretical basis and general equations. J. Phys. Chem.77, 268-277] is employed. The model for binary systems is validated by comparing activity coefficient predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solutions model due to data insufficiencies are discussed. This model expands the variable temperature sodium-potassium model of Greenberg and Moller [Greenberg J., and Moller N. (1989) The prediction of mineral solubilities in natural waters: a chemical equilibrium model for the Na-K-Ca-Cl-SO4-H2O system to high concentration from 0 to 250 °C. Geochim. Cosmochim. Acta53, 2503-2518] by evaluating Br− pure electrolyte and mixing solution parameters and the chemical potentials of three bromide solid phases: NaBr-2H2O (cr), NaBr (cr) and KBr (cr).  相似文献   

18.
We have determined Cr diffusion coefficients (D) in orthopyroxene parallel to the a-, b-, and c-axial directions as a function temperature at f(O2) corresponding to those of the wüstite-iron (WI) buffer. Diffusion is found to be significantly anisotropic with D(//c) > D(//b) > D(//a), conforming to an earlier theoretical prediction. Increase of f(O2) from WI buffer conditions to 4.5 log unit above the buffer at 950 and 1050 °C leads to decrease of D(Cr) by a factor of two to three, possibly suggesting significant contribution from an interstitial diffusion mechanism. We have used the diffusion data to calculate the closure temperatures (Tc) of the Mn-Cr decay system in orthopyroxene as a function of initial temperature (T0), grain size (a) and cooling rate for spherical and plane sheet geometries. We also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of Mn-Cr ages in orthopyroxene during cooling, T0 and a. Application of these relations to the Mn-Cr age data of the cumulate eucrite Serra de Magé yields a Tc of 830-980 °C, and cooling rates of 2-27 °C/Myr at Tc and ∼1-13 °C/Myr at 500 °C. It is shown that the cooling of Serra de Magé to the closure temperature of the Mn-Cr system took place at its original site in the parent body, and thus implies a thickness for the eucrite crust in the commonly accepted HED parent body, Vesta, of greater than 30 km. This thickness of the eucrite crust is compatible only with a model of relatively olivine-poor bulk mineralogy in which olivine constitutes 19.7% of the total asteroidal mass.  相似文献   

19.
The solubilities of the assemblages albite + paragonite + quartz and jadeite + paragonite + quartz in H2O were determined at 500 and 600 °C, 1.0-2.25 GPa, using hydrothermal piston-cylinder methods. The three minerals are isobarically and isothermally invariant in the presence of H2O, so fluid composition is uniquely determined at each pressure and temperature. A phase-bracketing approach was used to achieve accurate solubility determinations. Albite + quartz and jadeite + quartz dissolve incongruently in H2O, yielding residual paragonite which could not be retrieved and weighed. Solution composition fixed by the three-mineral assemblage at a given pressure and temperature was therefore bracketed by adding NaSi3O6.5 glass in successive experiments, until no paragonite was observed in run products. Solubilities derived from experiments bounding the appearance of paragonite thus constrain the equilibrium fluid composition. Results indicate that, at a given pressure, Na, Al, and Si concentrations are higher at 600 °C than at 500 °C. At both 500 and 600 °C, solubilities of all three elements increase with pressure in the albite stability field, to a maximum at the jadeite-albite-quartz equilibrium. In the jadeite stability field, element concentrations decline with continued pressure increase. At the solubility maximum, Na, Al, and Si concentrations are, respectively, 0.16, 0.05, and 0.48 molal at 500 °C, and 0.45, 0.27, and 1.56 molal at 600 °C. Bulk solubilities are 3.3 and 10.3 wt% oxides, respectively. Observed element concentrations are everywhere greater than those predicted from extrapolated thermodynamic data for simple ions, monomers, ion pairs, and the silica dimer. The measurements therefore require the presence of additional, polymerized Na-Al-Si-bearing species in the solutions. The excess solubility is >50% at all conditions, indicating that polymeric structures are the predominant solutes in the P-T region studied. The solubility patterns likely arise from combination of the large solid volume change associated with the albite-jadeite-quartz equilibrium and the rise in Na-Al-Si polymerization with approach to the hydrothermal melting curves of albite + quartz and jadeite + quartz. Our results indicate that polymerization of Na-Al-Si solutes is a fundamental aspect of fluid-rock interaction at high pressure. In addition, the data suggest that high-pressure metamorphic isograds can impose unexpected controls on metasomatic mass transfer, that significant metasomatic mass transfer prior to melting should be considered in migmatitic terranes, and that polymeric complexes may be an important transport agent in subduction zones.  相似文献   

20.
Marcus Power 《Geoforum》2009,40(1):14-24
One important (though often neglected) part of the ‘development business’ committed to principles of partnership is the Commonwealth, a voluntary association of 54 independent countries, almost all of which were formerly under British rule. This paper focuses on the Commonwealth’s contemporary sense of ‘responsibility’ for shaping African development through ‘partnership’ and by promoting ‘good governance’ and examines the particular example of Mozambique, which joined the Commonwealth in 1995. In exploring exactly what membership of this post-colonial ‘family’ has meant for Mozambique the paper explores the neocolonial paternalism and sense of trusteeship that the Commonwealth has articulated in its often very apolitical vision of African development which seems to lock the continent into a permanent stage of tutelage and to repetitively reduce Africa to a set of core deficiencies for which externally generated ‘solutions’ must be devised. More generally, the paper also examines the wider context of the Commonwealth’s involvement in Africa by looking at the connections it has made to British industry, British charities and the British Department for International Development (DFID). The paper concludes with an assessment of the ‘showcase’ potential of Mozambique and its importance to Commonwealth and DFID narrations of an African ‘success’ story of peace, stability and growth since the end of the country’s devastating civil war in 1992.  相似文献   

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