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1.
The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35%. salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months. The apparent solubility constant determined for calcite of 4.39(±0.20) × 10?7 mol2 kg?2 is in good agreement with other recent solubility measurements and is constant after 5 days equilibration. When we measured aragonite solubility we observed that it decreased with increasing time of equilibration. The value of 6.65(±0.12) × 10?7 mol2 kg?2, determined for equilibration times in excess of 2 months, is significantly less than that found in other recent measurements, which employed equilibration times of only a few hours to days. No statistically significant difference was found among the synthetic, natural and biogenic material. Solid to solution ratio, contamination of aragonite with up to 10 wt% calcite and recycling of the aragonite made no statistically significant difference in solubility when long equilibration times were used.Measured apparent solubility constants of aragonite and calcite are respectively 22( ± 3)% and 20( ± 2)% less than apparent solubility constants calculated from thermodynamic equilibrium constants and seawater total activity coefficients. These large differences in measured and calculated apparent solubility constants may be the result of the formation of surface layers of lower solubility than the bulk solid.  相似文献   

2.
The solubilities of SrSO4 in seawater, 0.65 M NaCl and and distilled water were measured as a function of pressure at 2°C. The thermodynamic solubility product was determined from the distilled water measurements and stoichiometric solubility products were determined from the seawater and Nad measurements. The equilibrium quotient for SrSO4 dissolution at ionic strength of 0.65 was calculated from the NaCl measurements, using the known NaSO4? ionpairing association constant. For each of the solubility products values of Θ V were determined. These experimental values were all 11.0 ± 0.3 ml mole? lower than the theoretical values based on anhydrous SrSO4. This difference may be due to the equilibrating solid phase being a hydrated form of SrSO4.  相似文献   

3.
Current deformation in Pribaikalia, Western and Central Mongolia, and Tuva has been studied from measured horizontal GPS velocities and respective computed strain and rotation rates using 1994–2007 data of the Baikal–Mongolian GPS triangulation network.The GPS velocity field shows two main trends: an NE trend within Jonggaria, the Mongolian Altay, and the Great Lakes Valley and an SE trend in the Hangayn and eastern Gobi Altay mountains, and in the Transbaikalian block of the Amur plate. The velocity magnitudes and vectors are consistent with an SE motion of the Amur plate at a rate of ～2 mm/year.The derived strain pattern includes domains of crustal contraction and extension recognized from the magnitudes of relative strains. Shortening predominates in the Gobi and Mongolian Altay and in the Khamar-Daban Range, where it is at ?2 = (19.2 ± 6.0)×10?9 yr?1 being directed northeastward. Extension domains exist in the Baikal rift and in the Busiyngol–West Hangayn area, where the crust is stretching along NW axes at ?1 = (22.2 ± 3.1) × 10–9 yr–1. The eastern Hangayn dome and the Gobi peneplain on its eastern border show low and unstable strain rates. In central and northern Mongolia (Orhon–Selenge basin), shortening and extension are at similar rates: ?2 = (15.4 ± 5.4)×10?9 yr?1 and ?1 = (18.1 ± 3.1)×10?9 yr?1. The strain pattern changes notably in the area of the Mogod earthquake of 1967.Most of rotation throughout Central Asia is clockwise at a low rate of about Ω = 6×10?9 deg·yr?1. High rates of clockwise rotation are observed in the Hangayn domain (18.1 ± 5.2)×10?9 deg·yr?1, in the Gobi Altay (10.4 ± 7.5)×10?9 deg·yr?1, and in the Orhon–Selenge domain (11.9 ± 5.2)×10?9 deg·yr?1. Counterclockwise rotation is restricted to several domains. One is in western Tuva and northwestern Great Lakes Valley of Mongolia (Ω = 3.7×10?9 deg·yr?1). Two more counterclockwise rotation regions occur on both flanks of the Baikal rift: along the craton edge and in basins of Transbaikalia on the rift eastern border, where rotation rates are as high as (13.0 ± 3.9)×10?9 deg·yr?1, while rotation within the Baikal basin does not exceed the measurement error. Another such domain extends from the eastern Hövsgöl area to the Hangayn northern foothills, with the counterclockwise rotation at a highest rate of (16.3 ± 2.8)×10?9 deg·yr?1.  相似文献   

4.
Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (FDIC?+?TOC) to the ocean during outgoing tides ranged from ??1.8±0.5?×?103 to 9.5±0.7?×?103?mol C h?1 during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10±4?×?106?mol C year?1. Following a major rain event (36 mm rain in 3 days), FDIC?+?TOC increased and reached values as high as 29.0 ±?0.7?×?103?mol C h?1. Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 ±?4?×?106?mol C year?1. These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small.  相似文献   

5.
4He accumulated in fluids is a well established geochemical tracer used to study crustal fluid dynamics. Direct fluid samples are not always collectable; therefore, a method to extract rare gases from matrix fluids of whole rocks by diffusion has been adapted. Helium was measured on matrix fluids extracted from sandstones and mudstones recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling in California, USA. Samples were typically collected as subcores or from drillcore fragments. Helium concentration and isotope ratios were measured 4?C6 times on each sample, and indicate a bulk 4He diffusion coefficient of 3.5?±?1.3?×?10?C8 cm2?s?C1 at 21°C, compared to previously published diffusion coefficients of 1.2?×?10?C18 cm2?s?C1 (21°C) to 3.0?×?10?C15 cm2?s?C1 (150°C) in the sands and clays. Correcting the diffusion coefficient of 4Hewater for matrix porosity (??3%) and tortuosity (??6?C13) produces effective diffusion coefficients of 1?×?10?C8 cm2?s?C1 (21°C) and 1?×?10?C7 (120°C), effectively isolating pore fluid 4He from the 4He contained in the rock matrix. Model calculations indicate that <6% of helium initially dissolved in pore fluids was lost during the sampling process. Complete and quantitative extraction of the pore fluids provide minimum in situ porosity values for sandstones 2.8?±?0.4% (SD, n?=?4) and mudstones 3.1?±?0.8% (SD, n?=?4).  相似文献   

6.
The infinite dilution diffusion coefficient for Al(OH)4? necessary to calculate fluxes of dissolved Al between sediments and overlying waters, was determined at 25°C. Measurements were made using the diaphragm-cell method by diffusing Al(OH)4? spiked KBr solutions against KCL over a range of ionic strengths. The mean of 9 separate measurements gives 1.04 ± .02 × 10?5cm2/s as the infinite dilution diffusion coefficient for Al(OH)4? at 25°C.  相似文献   

7.
Total trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn), Al, and pyrite- and reactive-associated metals were measured for the first time in a microbial mat and its underlying anoxic-sulfidic sediment collected in the saltern of Guerrero Negro (GN), Baja California Sur, Mexico. It is postulated that the formation of acid volatile sulfide (AVS) and pyrite in the area of GN could be limited by the availability of reactive Fe, as suggested by its limited abundance (mat and sediment combined average value of only 19 ± 10 ??mol g?1; n = 22) as well as the low pyrite (0.89?C7.9 ??mol g?1) and AVS (0.19?C21 ??mol g?1) concentrations (for anoxic-sulfidic sediments), intermediate degrees of pyritization (12?C50%), high degrees of sulfidization (14?C100%), generally low degrees of trace metal pyritization, and slight impoverishment in total Fe. This is a surprising result considering the large potential reservoir of available Fe in the surrounding desert. Our findings suggest that pyrite formation in the cycling of trace metals in the saltern of GN is not very important and that other sedimentary phases (e.g., organic matter, carbonates) may be more important reservoirs of trace elements. Enrichment factors [EFMe = (Me/Al)sample/(Me/Al)background] of Co, Pb, and Cd were high in the mat (EFMe = 2.2 ± 0.4, 2.8 ± 1.6 and 34.5 ± 9.8, respectively) and even higher in the underlying sediment (EFMe = 4.7 ± 1.5, 14.5 ± 6.2 and 89 ± 27, respectively), but Fe was slightly impoverished (average EFFe of 0.49 ± 0.13 and 0.50 ± 0.27 in both mat and sediment). Organic carbon to pyrite-sulfur (C/S) molar ratios measured in the mat (2.9 × 102?C27 × 102) and sediment (0.81 × 102?C6.6 × 102) were, on average, approximately 77 times higher than those typically found in marine sediments (7.5 ± 2.1). These results may indicate that ancient evaporation basins or hypersaline sedimentary environments could be identified on the basis of extremely high C/S ratios (e.g., >100) and low reactive Fe.  相似文献   

8.
Celestite solubility measurements have been conducted in pure water at temperatures from 10 to 90°C. Equilibrium was achieved with respect to a crystalline solid phase from both undersaturated and supersaturated solutions. The measurements show that the solubility undergoes a maximum near 20°C. LogK values for the solubility reaction are adequately described by the following expression over the temperature range 283.15 to 363.15 K: −logK= −35.3106+0.00422837T+318312/T2+14.99586 logT.The following thennodynamic values for the dissolution reaction of SrSO4(s), at 25°C have been derived: ΔGR0 = 37852 ± 30 Jmol−1ΔHR0 = −1668±920Jmol−1ΔSR0= −132.6±3.2JK−1mol−1Celestite solubility measurements were also determined in NaCl solutions up to 5 m concentration and from 10 to 40°C. These data are in good agreement with the work of StrÜbel (1966), who reports solubility measurements to temperatures of 100°C.The application of the Pitzer relations and the solubility constants determined in this study to calculate celestite solubility in NaCl solutions yields excellent agreement between predicted values and experimental measurements over the entire range of temperature and NaCl concentration conditions. For the limited number of solubility measurements in seawater-type solutions and mixed-salt brines, the agreement using the Pitzer relations is within three percent of the measured solubility.  相似文献   

9.
The experimental dissolution of zircon into a zircon-undersaturated felsic melt of variable water content at high pressure in the temperature range 1,020° to 1,500° C provides information related to 1) the solubility of zircon, 2) the diffusion kinetics of Zr in an obsidian melt, and 3) the rate of zircon dissolution. Zirconium concentration profiles observed by electron microprobe in the obsidian glass adjacent to a large, polished zircon face provide sufficient information to calculate model diffusion coefficients. Results of dissolution experiments conducted in the virtual absence of water (<0.2% H2O) yield an activation energy (E) for Zr transport in a melt ofM=1.3 [whereM is the cation ratio (Na+K+2Ca)/(Al·Si)] of 97.7±2.8 kcal-mol?1, and a frequency factor (D 0) of 980 ?580 +1,390 cm2-sec?1. Hydrothermal experiments provide an E=47.3±1.9 kcal-mol?1 andD 0=0.030 ?0.015 +0.030 cm2-sec?1. Both of these results plot close to a previously defined diffusion compensation line for cations in obsidian. The diffusivity of Zr at 1,200° C increases by a factor of 100 over the first 2% of water introduced into the melt, but subsequently rises by only a factor of five to an apparent plateau value of ～2×10?9 cm2-sec?1 by ～6% total water content. The remarkable contrast between the wet and dry diffusivities, which limits the rate of zircon dissolution into granitic melt, indicates that a 50 μm diameter zircon crystal would dissolve in a 3 to 6% water-bearing melt at 750° C in about 100 years, but would require in excess of 200 Ma to dissolve in an equivalent dry system. From this calculation we conclude that zircon dissolution proceeds geologically instantaneously in an undersaturated, water-bearing granite. Estimates of zircon solubility in the obsidian melt in the temperature range of 1,020° C to 1,500° C confirm and extend an existing model of zircon solubility to these higher temperatures in hydrous melts. However, this model does not well describe zircon saturation behavior in systems with less than about 2% water.  相似文献   

10.
We report a measurement procedure to determine simultaneously the major cation concentrations (Na, Ca, K and Mg) of seawater‐derived solutions by inductively coupled plasma‐atomic emission spectrometry. The best results were obtained when the IAPSO (‘standard’) seawater reference material was diluted by thirty times with Milli‐Q® water. We obtained an average reference value rK (the ratio of the mass fraction of potassium to that of chlorine, i.e., (g kg?1)/(g kg?1)) for IAPSO seawater of 0.0205 ± 0.0006 (2.9% RSD), not significantly different from 0.0206 ± 0.0005 (2.4% RSD) for seawater composition reported in the literature. The measured Na, Ca and Mg concentrations correspond to rNa, rCa and rMg values of 0.5406 ± 0.0026 (0.5% RSD), 0.02192 ± 0.00048 (2.2% RSD) and 0.06830 ± 0.00047 (0.7% RSD), respectively, in line with previous values measured by wet‐chemistry and atomic absorption spectrophotometry or wet‐chemical titration. Our measurement procedure was used successfully on synthetic seawater solutions and high‐temperature hydrothermal fluids.  相似文献   

11.
The kinetics of oxygen isotope self-diffusion in natural samples of hornblende, tremolite, and richterite have been measured. Samples were run under hydrothermal conditions using 18O enriched water. Profiles of 18O(16O + 18O)vs depth into the crystal were obtained using an ion microprobe; the depths of sputtered holes were measured using an optical interferometer. At 1000 bars (100 MPa) water pressure, the activation energies (Q) and pre-exponential factors (D0) for diffusion parallel to c are: D0(cm2/sec) Q (kcal/gm-atom) T (°C) Hornblende 1+20?1 × 10?741 ± 6 650–800 Tremolite 2+30?2× 10?8 39 ± 5 650–800 Richterite 3+5?2 × 10?4 57 ± 2 650–800The diffusion coefficient (D) for hornblende at 800°C and 1000 bars water pressure measured parallel to the c crystallographic direction is at least ten times greater than that parallel to the a or b directions. An increase in water pressure from 200 to 2000 bars increases D by a factor of 2.7 for diffusion parallel to c at 800°C. The D value for hornblende at 800°C is about 0.01 that for quartz and 0.001 that for anorthite. As a result, closure temperatures for oxygen exchange in natural primary amphiboles are significantly higher than for quartz or feldspars. It is unlikely that amphiboles will exchange oxygen isotopes by diffusion under most crustal conditions.  相似文献   

12.
Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (Kv) and oedometer (Kid, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B10CS20T70 mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: kv20° = 1.97 × 10?9 and kid from 7 × 10?9 to 1.83 × 10?10 < 10?9m/s; leachate permeated: kv20° = 2.91 × 10?9 and kid from 7 × 10?9 at 1.44 × 10?10 < 10?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (Kd) test and oedometer test (Kid) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B10CS20T70 perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.  相似文献   

13.
Surface seawater samples from Kamaran Strait of Yemen were collected for physical and chemical parameter determinations. This work reports the results of air and surface seawater temperature, salinity, pH, and total alkalinity measurements. The air temperature ranged from 29.9°C to 36.5°C with an average value of 31.5?±?1.5°C, whereas the seawater surface temperature ranged from 34.0°C to 36.0°C with a mean value of 34.5?±?0.5°C. The salinity was observed to be high, ranging from 38.03 to 38.81 with an average value of 38.45?±?0.22. The pH ranged from 7.74 to 8.27 with a mean value of 8.11?±?0.10. The total alkalinity was found to range from 2.3860 to 2.5000 meq L?1 with an average value of 2.4288?±?0.0351 meq L?1. The result of the study showed that there was a negative correlation between the pH and surface seawater temperature and salinity. The surface seawater of the Kamaran Strait was found to be several fold supersaturated with respect to calcium carbonate. The measured percent degree of saturation ranged from 454% to 668% with respect to calcite and from 246% to 361% with respect to aragonite. The lowest value of supersaturation with respect to both calcite and aragonite were found in front of as-Salif port, where human and developmental activities are intensively increased. The visual inspection of coral reefs distribution and their intensity were obviously observed in areas of high value of supersaturation with respect to both minerals, high transparency of seawater column, and low human activities. Further studies are needed to investigate the occurrence, distribution, and mineralogy of corals and the effects of physical and chemical parameters upon their growth in the region.  相似文献   

14.
Solubility curves were determined for a synthetic gibbsite and a natural gibbsite (Minas Gerais, Brazil) from pH 4 to 9, in 0.2% gibbsite suspensions in 0.01 M NaNO3 that were buffered by low concentrations of non-complexing buffer agents. Equilibrium solubility was approached from oversaturation (in suspensions spiked with Al(NO3)3 solution), and also from undersaturation in some synthetic gibbsite suspensions. Mononuclear Al ion concentrations and pH values were periodically determined. Within 1 month or less, data from over-and undersaturated suspensions of synthetic gibbsite converged to describe an equilibrium solubility curve. A downward shift of the solubility curve, beginning at pH 6.7, indicates that a phase more stable than gibbsite controls Al solubility in alkaline systems. Extrapolation of the initial portion of the high-pH side of the synthetic gibbsite solubility curve provides the first unified equilibrium experimental model of Al ion speciation in waters from pH 4 to 9.The significant mononuclear ion species at equilibrium with gibbsite are Al3+, AlOH2+, Al(OH)+2 and Al(OH)?4, and their ion activity products are 1K50 = 1.29 × 108, 1Ks1 = 1.33 × 103, 1Ks2 = 9.49 × 10?3 and 1Ks4 = 8.94 × 10?15. The calculated standard Gibbs free energies of formation (ΔG°f) for the synthetic gibbsite and the A1OH2+, Al(OH)+2 and Al(OH)?4 ions are ?276.0, ?166.9, ?216.5 and ?313.5 kcal mol?1, respectively. These ΔG°f values are based on the recently revised ΔG°f value for Al3+ (?117.0 ± 0.3 kcal mol?1) and carry the same uncertainty. The ΔG°f of the natural gibbsite is ?275.1 ± 0.4 kcal mol?, which suggests that a range of ΔG°f values can exist even for relatively simple natural minerals.  相似文献   

15.
The solubility of silver chloride has been measured in sodium chloride solutions of 5×10?5 ? 3.0 m over the temperature range from 100 to 353°C at the saturated vapour pressure of the system. The solubility product and the cumulative and stepwise formation constants have been calculated from the solubility data. With increasing temperature, there is a trend towards chlorosilver (I) complexes of low coordination number and charge. At T > 270°C, the species of maximum ligand number in concentrated solutions up to 3.0m sodium chloride, is the dichlorosilver (I) complex, AgCl2. In addition, large endothermic enthalpies and large positive entropies, similar to those found for hardhard interactions at low temperature, accompany complex formation at elevated temperatures. It is concluded that chlorosilver (I) complexes play an important role in the transport and deposition of silver from hydrothermal ore solutions.  相似文献   

16.
The dissolution behavior of natural, ordered kutnahorite (Mn1.14Ca0.82Mg0.04Fe0.012(CO3)2) and a disordered, calcian rhodochrosite (Mn1.16Ca0.78Mg0.06(CO3)2) precipitated in the laboratory was investigated in deionized distilled water and artificial seawater in both open and closed systems at 25 °C, one atmosphere total pressure, and various pCO2s. Both solids dissolved congruently in distilled water in an open system and yielded identical long-term equilibration or extrapolated ion activity products, IAPpkt = aCa 2+aMn 2+(aCO 3 2?)2 = 1.7 (±0.12)× 10?21 or pIAPpkt = 20.77 (±0.03). This value is believed to be the thermodynamic solubility product of pseudokutnahorite. In contrast, the steady state ion concentration products, ICPpkt = [Ca2+][Mn2+][CO3 2?]2, measured following the dissolution of both minerals in artificial seawater increase as the CO2 partial pressure decreases and the [Mn2+]:[Ca2+] ratio increases. These observations are interpreted as resulting from the formation of phases of different stoichiometry in response to large variations of the [Mn2+]:[Ca2+] ratio in solution. These data and results of calcite-seawater equilibration experiments in the presence of various dissolved Mn(II) concentrations define the fields of stability of manganoan calcites and calcian rhodochrosites in seawater within Lippmann phase diagrams for the CaCO3–MnCO3–H2O system. Results of this study reveal that the nature (i.e., mineralogy) and composition of manganese-rich carbonate phases that may form under suboxic/anoxic conditions in marine sediments are dictated by the porewater [Mn2+]:[Ca2+] ratio, the abundance of calcite surfaces and reaction kinetics.  相似文献   

17.
The Cadmium‐Lined Outer‐Core Irradiation Tube (CLOCIT) is a new irradiation facility for 40Ar/39Ar geochronology at the Oregon State University TRIGA® reactor. We report fluence (i.e., time‐integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium‐Lined Inner‐Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10?4 J h?1; about 55% of CLICIT. Radial fluence gradients were on the order of 0.2–4.2% cm?1. A planar fit of J‐values results in residuals in the range of uncertainty in the J‐value, but systematic deviations resolve a non‐planar component of the neutron flux field, which has also been observed in CLICIT. Axial neutron fluence gradients were 0.6–1% cm?1, compared with 0.7–1.6% cm?1 for the CLICIT. Production rate ratios of interfering reactions were (40Ar/39Ar)K = (4 ± 6) × 10?4 and (38Ar/39Ar)K = (1.208 ± 0.002) × 10?2, (36Ar/37Ar)Ca =  (2.649 ± 0.014) × 10?4, (38Ar/37Ar)Ca =  (3.33 ± 0.12) × 10?5 and (39Ar/37Ar)Ca =  (9.1 ± 0.28) × 10?4, similar to the CLICIT values.  相似文献   

18.
The heat capacity of natural chamosite (XFe=0.889) and clinochlore (XFe=0.116) were measured by differential scanning calorimetry (DSC). The samples were characterised by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy. DSC measurements between 143 and 623?K were made following the procedure of Bosenick et?al. (1996). The fitted data for natural chamosite (CA) in J?mol?1?K?1 give: C p,CA = 1224.3–10.685?×?103?×?T ??0.5???6.4389?× 106?×T ??2?+?8.0279?×?108?×?T ??3 and for the natural clinochlore (CE): C p,CE = 1200.5–10.908?×?103?×T ??0.5?? 5.6941?×?106?×?T ??2?+?7.1166?×?108?×?T ??3. The corrected C p-polynomial for pure end-member chamosite (Fe5Al)[Si3AlO10](OH)8 is C p,CAcor = 1248.3–11.116?× 103?×?T ??0.5???5.1623?×?106?×?T ??2?+?7.1867?×?108×T ??3 and the corrected C p-polynomial for pure end-member clinochlore (Mg5Al)[Si3AlO10](OH)8 is C p,CEcor = 1191.3–10.665?×?103?×?T ??0.5???6.5136?×?106?×?T ??2?+ 7.7206?×?108?×?T ??3. The corrected C p-polynomial for clinochlore is in excellent agreement with that in the internally consistent data sets of Berman (1988) and Holland and Powell (1998). The derived C p-polynomial for chamosite (C p,CAcor) leads to a 4.4% higher heat capacity, at 300?K, compared to that estimated by Holland and Powell (1998) based on a summation method. The corrected C p-polynomial (C p,CAcor) is, however, in excellent agreement with the computed C p-polynomial given by Saccocia and Seyfried (1993), thus supporting the reliability of Berman and Brown's (1985) estimation method of heat capacities.  相似文献   

19.
The diffusivities of network-forming cations (Si4+, Al3+, Ge4+ and Ga3+) in melts of the jadeitic composition NaAl(Si, Ge)2O6 and Na(Al, Ga)Si2O6 have been measured at pressures between 6 and 20 kbar at 1400°C. The rates of interdiffusion of Si4+-Ge4+ and Al3+-Ge3+ increase with increasing pressure at constant temperature. The results are consistent with the ion-dynamics computer simulations of Jadeite melt by Angellet al. (1982, 1983). The coefficient measured for the Si4+-Ge4+ interdiffusion is between 8 × 10?10 and 2.5 × 10?8cm2sec at 6 kbar, depending on the composition of the melt, whereas at 20 kbar it is between 7 × 10?9 and 2 × 10?7cm2sec. The effect of pressure is greater for more Si-rich compositions (i.e., closer to NaAlSi2O6 composition). The coefficient measured for the Al3+-Ga3+ inter- diffusion is between 9 × 10?10 and 3 × 10?9 cm2/sec at 6 kbar and between 3 × 10?9 and 1 × 10?8cm2sec at 20 kbar. The rate of increase in diffusivity with pressure of Al3+-Ga3+ (a factor of 3–4) is smaller than that of Si4+-Ge4+ (a factor of 7–17).The Si4+-Ge4+ interdiffusion in melts of Na2O · 4(Si, Ge)O2 composition has also been measured at 8 and 15 kbar for comparison. The effect of pressure on the diffusivity in this melt is significantly smaller than that for the jadeitic melts. The increase in diffusivity of the network-forming cations in jadeitic melts with increasing pressure may be related to the decrease in viscosity of the same melt. The present results, as well as the ion-dynamics simulations, suggest that the homogenization of partial melts and mixing of magmas would be more efficient at greater depths.  相似文献   

20.
A capacitance micrometer has been developed for the measurement of thermal expansions of small crystals over moderate temperature ranges (approximately 100 K above laboratory temperature). Linear coefficients are obtained to ±0.5×10?6 K?1 and volume coefficients to ±1.5×10?6 K?1. New values are reported for 13 materials, obtained as crystals down to 1 mm in size. For many of these we obtained satisfactory agreement with earlier data, but exceptions are zircon (volume coefficient 6.6±1.6×10?6 K?1, compared with earlier values up to 21×10?6 K?1) and strontium fluoride (volume coefficient 57.9±2.2×10?6 K?1, compared with 42 to 49×10?6 K?1). The new data are combined with values of incompressibility, density and specific heat to obtain new values of Grüneisen's ratio.  相似文献   

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