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1.
Observations of the molecular cloud G1.6-0.025 in the 2K-1K and J0-J?1E series and 5?1-40E line of CH3OH, the (2-1) and (3-2) lines of SiO, and the 7?7-6?6 line of HNCO are described. Maps of the previously observed extended cloud with Vlsr～50 km/s and high-velocity clump with Vlsr～160 km/s, as well as a newly detected clump with Vlsr～0 km/s, have been obtained. The extended cloud and high-velocity clump have a nonuniform structure. The linewidths associated with all the objects are between 20 and 35 km/s, as is typical of clouds of the Galactic center. In some directions, emission at velocities from 40 to 160 km/s and from ?10 to +75 km/s is observed at the clump boundaries, testifying to a connection between the extended cloud and the high-velocity clump and clump at Vlsr～0 km/s. Compact maser sources are probaby contributing appreciably to the emission of the extended cloud in the 5?1-40E CH3OH line. Non-LTE modeling of the methanol emission shows that the extended cloud and high-velocity clump have a relatively low hydrogen density (<104 cm?3). The specific column density of methanol in the extended cloud exceeds 6×108 cm?3s, and is 4×108?6×109 cm?3s in the high-velocity clump. The kinetic temperatures of the extended cloud and high-velocity clump are estimated to be <80 K and 150–200 K, respectively. Possible mechanisms that can explain the link between the extended cloud with Vlsr～50 km/s and the clumps with Vlsr～0 km/s and ～160 km/s are briefly discussed.  相似文献   

2.
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ～0.2–0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ～2 × 104–3 × 105, depending on the source. The clump densities range from ～3 × 105–106 cm?3, and the sizes and volume filling factors of the clumps are ～(1–3) × 10?3 pc and ～0.03–0.12. The clumps are surrounded by inter-clump gas with densities not lower than ～(2–7) × 104 cm?3. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ～104–105 yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.  相似文献   

3.
Twenty-eight CS molecular clouds toward HII regions with Galactocentric distances from ～ 4 to 20 kpc have been studied based on observations obtained in the J=2→1 lines of CS and C34S on the 20-meter radio telescope of the Onsala Space Observatory (Sweden) in March 2001. All 28 clouds have been mapped with an angular resolution of ～40″. The peak intensity in the C34S line has been measured for 20 objects. An LTE analysis has been performed and the parameters of the molecular cloud cores derived. The core sizes are dA=0.3–4.8 pc, with a median value of ～1.6 pc. The mean hydrogen densities in the cloud cores are nH2=3.5×102–3.7 × 104 cm?3, with a median value of ～7.2×103 cm?3. The value of nH2 ends to decrease with increasing Galactocentric distance of the cloud. The masses of most clouds are 102?6×103M⊙, with the most probable value being MCS～103M⊙. The data follow the dependence MCS ∝d A (2.4–3.2) . As a rule, the cloud masses are lower than the virial masses for MCS<103M⊙.  相似文献   

4.
The results of a survey of 63 Galactic star-forming regions in the 6K–5K and 5 K –4K methyl acetylene lines at 102.5 and 85.5 GHz are presented. Fourty-three sources were detected at 102.5 GHz, and twenty-five at 85.5 GHz. Emission was detected toward molecular clouds with kinetic temperatures of 20–60 K (so-called “warm clouds”). The CH3CCH abundances in these clouds are about several ×10?9. Five sources (NGC 2264, G30.8-0.1, G34.26+0.15, DR 21(OH), S140) were mapped using the maximum-entropy method. The sizes of the mapped clouds fall in the range 0.1–1.7 pc, and the clouds have virial masses of 90–6200 M⊙ and densities between 6×104 and 6×105 cm?3. The CH3CCH sources coincide spatially with the CO and CS sources. Chemical-evolution simulations show that the typical methyl acetylene abundances in the observed clouds correspond to ages of ≈6×104 years.  相似文献   

5.
The present analysis adjusts previous estimates of global ocean CaCO3 production rates substantially upward, to 133 × 1012 mol yr?1 plankton production and 42 × 1012 mol yr?1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO3 production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO3 mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO3 sediment accumulation rates remain about the same as they have been for some years: ~20 × 1012 mol yr?1 on shelves and 11 × 1012 mol yr?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 1012 mol yr?1 (~50 %) of shelf benthonic carbonate production and 122 × 1012 mol yr?1 (>90 %) of planktonic production. Most CaCO3 production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO2 release to CaCO3 precipitation (CO2↑/CaCO3↓) is <1.0 and varies with depth. This ratio, Ψ, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO2 associated with CaCO3 reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 1012 mol C yr?1, at a time scale of 102–103 years. The CaCO3-mediated influx of CO2 is approximately offset by CO2 release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO3 and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.  相似文献   

6.
Eighteen regions (bipolar outflows and methanol masers) are mapped in the CS(2-1) line using the 20-m Onsala radio telescope. The coordinates of the CS emission peaks are refined. The sizes and masses of dense regions are estimated for 13 maps. Measurement of the angular sizes of regions of emission indicates that all the sources were resolved by the Onsala radio telescope. The lower limit for the linear dimensions of the CS condensations studied is 0.2–2.1 pc. The hydrogen densities and masses of the CS condensations are estimated to be n(H2)=(0.3–13.1)×104 cm?3 and (M ≈ 7–2800M ⊙). Methanol masers are associated with denser and more massive regions, whether or not the maser condensation is connected with a bipolar outflow.  相似文献   

7.
A new synchrotron X-ray diffraction study of chromium oxide Cr2O3 (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K 0,T0), 206 ± 4 GPa; its pressure derivative K′0,T , 4.4 ± 0.8; (?K 0,T /?T) = ?0.037 ± 0.006 GPa K?1; a = 2.98 ± 0.14 × 10?5 K?1 and b = 0.47 ± 0.28 × 10?8 K?2, where α 0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr2O3 was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α 0,T0 was determined to be 2.95 × 10?5 K?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α 0 value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K 0,T0 = 205 ± 3 GPa, K′0,T  = 4.0, Grüneisen parameter (γ 0) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr2O3 undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr2O3 is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.  相似文献   

8.
A novel ionic liquid carbon paste electrode has been developed using sol–gel/Au nanoparticle (SGAN) involving (NS)2 compound of N,N′-di-(cyclopentadienecarbaldehyde)-1, 2-di (o-aminophenylthio) ethane (CCAE) as an appropriate neutral ion-carrier for ultrahigh-sensitive potentiometric determination of Ag(I). Colloidal gold nanoparticles (AuNPs) also well dispersed self-assembly into the 3-(mercaptopropyl)-trimethoxysilane (MPTS)-derived sol–gel network through Au–S covalent bond engendering continuous and super-conductive nanoporous three-dimensional array. The room-temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIM.PF6), was applied as a super-conductive pasting agent (binder). The SGAN/CCAE/IL-CPE exhibited a significantly enhanced sensitivity and preferential selectivity toward Ag(I) over a wide concentration range of 2.4 × 10?9 to 2.2 × 10?2 mol L?1 (R 2 = 0.9996) with a lower limit of detection of 7.9 × 10?10 M and a Nernstian slope of 58.5 (±0.3) mV decade?1. The electrode has a short response time of ～5 s and long-time durability of about 2 months without any considerable divergence in potentials. Moreover, the potentiometric examinations could be carried out within the wide pH range of 3.5–9.5. Eventually, the practical utility of the proposed Ag(I)-sensor was evaluated by volumetric titration of AgNO3 solution by sodium chloride and recovery of silver content in some real samples using flame atomic absorption spectroscopy as a confident reference.  相似文献   

9.
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   

10.
Hydroxylborite, a new mineral species, an analogue of fluoborite with OH > F, has been found at the Titovsky deposit (57°41′N, 125°22′E), the Chersky Range, Dogdo Basin, Sakha-Yakutia Republic, Russia. Prismatic crystals of the new mineral are dominated by the {10\(\overline 1 \)0} faces without distinct end forms and reach (1?1.5) × (0.1?0.2) mm in size. Radial aggregates of such crystals occur in the mineralized marble adjacent to the boron ore (suanite-kotoite-ludwigite). Calcite, dolomite, Mg-rich ludwigite, kotoite, szaibelyite, clinohumite, magnetite, serpentine, and chlorite are associated minerals. Hydroxylborite is transparent colorless, with a white streak and vitreous luster. The new mineral is brittle. The Mohs’ hardness is 3.5. The cleavage is imperfect on {0001}. The density measured with equilibration in heavy liquids is 2.89(1) g/cm3; the calculated density is 2.872 g/cm3. The wave numbers of the absorption bands in the IR spectrum of hydroxylborite are (cm?1; sh is shoulder): 3668, 1233, 824, 742, 630sh, 555sh, 450sh, and 407. The new mineral is optically uniaxial, negative, ω = 1.566(1), and ε = 1.531(1). The chemical composition (electron microprobe, H2O measured with the Penfield method, wt %) is 18.43 B2O3, 65.71 MgO, 10.23 F, 9.73 H2O, 4.31-O = F2, where the total is 99.79. The empirical formula calculated on the basis of 6 anions pfu is as follows: Mg3.03B0.98[(OH)2.00F1.00]O3.00. Hydroxylborite is hexagonal, and the space group is P63/m. The unit-cell dimensions are: a = 8.912(8) Å, c = 3.112(4) Å, V = 214.05(26) Å3, and Z = 2. The strongest reflections in the X-ray powder pattern [d, Å (I, %)(hkil)] are: 7.69(52)(01\(\overline 1 \)0), 4.45(82)(11\(\overline 2 \)0), 2.573(65)(03\(\overline 3 \)0), 2.422(100)(02\(\overline 2 \)1), and 2.128(60)(12\(\overline 3 \)1). The compatibility index 1 ? (K p/K c) is 0.038 (excellent) for the calculated density and 0.044 (good) for the measured density. The type material of hydroxylborite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow (inventory number 91968) and the Geological Museum of the All-Russia Institute of Mineral Resources, Moscow (inventory number M-1663).  相似文献   

11.
The pressure–volume–temperature (P–V–T) relation of CaIrO3 post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus \( K_{T0} \) at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative \( K_{T0}^{\prime } \) = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO3 ppv are: temperature derivative of bulk modulus \( (\partial K_{T} /\partial T)_{P} \) = ?0.038 ± 0.011 GPa K?1, \( \alpha K_{T} \) = 0.0039 ± 0.0001 GPa K?1, \( \left( {\partial K_{T} /\partial T} \right)_{V} \) = ?0.012 ± 0.002 GPa K?1, and \( \left( {\partial^{2} P/\partial T^{2} } \right)_{V} \) = 1.9 ± 0.3 × 10?6 GPa2 K?2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter \( \gamma_{0} \) = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K T0  = 5406.0/V(molar) + 5.9 GPa.  相似文献   

12.
Interdiffusion coefficients of Al + Al vs. Mg + Si in the gehlenite–åkermanite system of melilite were determined by coupled annealing of synthesized end-member single crystals. The observed diffusion coefficients for a couple-annealed sample vary for about 2 orders of magnitude, showing strong dependence on the gehlenite–åkermanite composition: diffusion coefficient observed at 1350 °C, for example, is 3 × 10?13 cm2 s?1 at 5 mol% åkermanite composition (Ak5), increases to 2 × 10?11 cm2 s?1 at Ak80, and then decreases to 1 × 10?12 cm2 s?1 at Ak95. The diffusion coefficient–temperature relation indicates high activation energy of diffusion of about 420 kJ mol?1 for gehlenite-rich melilite. The observed diffusion coefficient–composition relation may be explained by a combination of (1) the diffusion coefficient–melting temperature relation (Flynn's rule) and (2) the feasibility of local charge compensation, which can possibly be maintained more easily in the intermediate chemical composition. The high activation energy value for gehlenitic melilite appears to correspond to the complex diffusion mechanism. The observed highly variable diffusion coefficients suggest that gehlenite–åkermanite zoning in the melilite crystals in Ca, Al-rich inclusions in the carbonaceous meteorites may provide a sensitive indicator for the thermal history of the inclusions.  相似文献   

13.
Our analysis of many years of infrared photometry of the unique object FG Sge indicates that the dust envelope formed around the supergiant in August 1992 is spherically symmetrical and contains compact, dense dust clouds. The emission from the spherically symmetrical dust envelope is consistent with the observed radiation from the star at 3.5–5 µm, and the presence of the dust clouds can explain the radiation observed at 1.25–2.2 µm. The mean integrated flux from the dust envelope in 1992–2001 was ～(1.0±0.2)×10?8 erg s?1cm?2. The variations of its optical depth in 1992–2001 were within 0.5–1.0. The maximum density of the dust envelope was recorded in the second half of 1993 and corresponded to mean optical depths as high as unity. Several times in the interval from 1992 to 2001, the dusty material of the envelope partially dissipated and was then replenished. For example, the optical depth of the dust cloud at λ=1.25 µm during the last brigthness minimum in the J band was τ1.25≈4.3, which is much higher than the optical depth of the dust envelope of FG Sge. During maxima of the J brightness, the mean spectral energy distribution at 0.36–5 µm can be represented as a combination of radiation from a G0 supergiant that is attenuated by a dust envelope with a mean optical depth of 0.65±0.15 and emission from the spherically symmetrical dust envelope itself, with the temperature of the graphite grains being 750±150 K. At minima of the J brightness, only radiation from the dust envelope is observed at 1.65–5 µm, with the radiation from the supergiant barely detectable at 1.25 µm. As a result, the integrated flux during J minima is almost half that during J maxima. The mean mass of the spherically symmetrical dust envelope of FG Sge in 1992–2001 was (3 ± 1) × 10?7M⊙. This envelope’s mass varied by nearly a factor of two during 1992–2001, in the range (2 – 4) × 10?7M⊙. In Autumn 1992, the mass-loss rate from the supergiant exceeded 2 × 10?7M⊙/yr. The average rate at which matter was injected into the envelope during 1993–2001 was 10?8M⊙/yr. The mean rate of dissipation of the dust envelope was about 1 × 10?8M⊙/yr. During 1992–2001, the supergiant lost about 8.7 × 10?7M⊙. The parameters of the dust envelope were relatively constant from 1999 until the middle of 2001.  相似文献   

14.
Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1–0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064–1266 kg/mm2 (load 30 g), and the mean value is 1180 kg/mm2. The Mohs hardness is about 7.0–7.5. The calculated density is 4.66(2) g/cm3. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm-R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)Å3, Z = 4. The strongest reflections in the X-ray powder pattern [d, Å, (I in 5-number scale)(hkl)] are 3.28 (5) (20\(\bar 2\)); 2.88 (5) (11\(\bar 2\)); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42\(\bar 2\)); 1.633 (5) (31\(\bar 4\)); 1.446 (4) (33\(\bar 2\)); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO2, 73.13 V2O3 (53.97 V2O3calc, 21.25 VO2calc), 10.76 Cr2O3, 0.04 Fe2O3, 0.01 Al2O3, 0.02 MgO, total is 100.03. The empirical formula is (V 1.70 3+ Cr0.30)2.0(V 0.59 4+ Ti0.41)1.0O5. Oxyvanite is the end member of the oxyvanite-berdesinskiite series with homovalent isomorphic substitution of V4+ for Ti. The type material has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.  相似文献   

15.
A new mineral barioferrite—a natural analogue of synthetic barium ferrite Ba Fe 12 3+ O19—has been identified in the central part of a metamorphosed barite nodule in the rock of the Haturim Formation (Mottled Zone) on the southern slope of Mount Ye’elim in Israel. The mineral is associated with barite, calcite, magnetite, and maghemite and occurs as tiny platy crystals up to 3 × 15 × 15 μm and their irregular aggregates. Barioferrite is black with streaks of brown, and its luster is submetallic. Its Calculated density is 5.31 g/cm3. The mineral is brittle; cleavage is absent. IR absorption bands (cm?1) are observed at 635 (shoulder), 582, 544, 433, and 405 (shoulder). Barioferrite is characterized by ferrimagnetic behavior. Under a microscope in reflected light, barioferrite is grayish white with brownish red internal reflections, the pleochroism is weak (from gray-white on R o to gray-white with a brown tint on R e), and the bireflectance is weak with distinct anisotropy. The reflectance values of R o/R e, % (λ, nm) are 24.51/22.80 (470), 24.17/22.25 (546), 23.65/21.68 (589), and 22.67/20.85 (650). The chemical composition (electron microprobe, wt %; the ranges are given in parentheses) is BaO 13.13 (12.5–13.8), Fe2O3 86.47 (85.5–87.5), and 99.60 in total. The empirical formula is Ba0.95Fe 12.03 3+ O19. Barioferrite is hexagonal with space group P63/mmc, a = 5.875 (3) Å, c = 23.137 (19) Å, V = 691.6 (5) Å3, and Z = 2. The strongest lines of the X-ray powder diffraction pattern [d, Å, (I, 5) (hkl)] are 2.938(46) (110), 2.770(100) (107), 2.624 (84) (114, 200), 2.420(44) (203), 2.225(40) (205), and 1.627(56) (304, 2.0.11). The holotype specimen of barioferrite is deposited at the Mineralogical Museum of St. Petersburg State University; its catalogue number is 1/19436.  相似文献   

16.
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17.
About possibility of isotope dating of native gold by the (U-Th)/He method   总被引：2，自引：0，他引：2  
For investigation of helium in native gold, a new measuring complex was created and used: the high sensitivity mass spectrometer MSU-G (ZAO SKB “SPECTRON”). The sensitivity of measuring 4He was 5.3 × 10?13 cm3/g per impulse. Experiments in stepwise heating of samples have been carried out, and the kinetics of radiogenic 4He emanation from native gold was investigated. Migration parameters (activation energy and frequency factor) were determined. Model calculations of stability (closure temperature) of radiogenic 4He in the native gold structure with a given time and temperature of thermal influences were made using the data received. The concentration of 4He in native gold from the original deposit Nesterovskoe is (4.7 ± 0.1) × 10?5 cm3/g in the sample from the placer; from Chudnoe deposit, it is (3.8 ± 0.1) × 10?5 cm3/g; from sulfide deposits of Kitoiskii knot of Eastern Sayani, it is (1.9 ± 0.1) × 10?5 cm3/g; and from the South Muiskii ore region it is (8.7 ± 0.5) × 10?7 cm3/g. The received curve lines of kinetics of 4He emanation from native gold show that radiogenic helium is well bonded in the native gold structure: in all the examined samples, most 4He emanates only by reaching the temperature of 950–1000°C. A specific feature of the kinetics of radiogenic 4He emanation in all examined samples is an outburstlike emanation in the form of a peak of large amplitude in the area of temperatures near the melting temperature point of gold. This is stipulated by the existence of helium bubbles released by metals only while they melt. The spectrum of helium thermal desorption from native gold has a complicated form and is a result of superposition of several peaks. This proves the migration of groups of atoms located in the gold structure in different energy states. Very large values of the activation energy of helium migration from native gold were received: up to 161–176 kcal/mol. Extremely large values of the frequency factor, from 2 × 1018 to 3 × 1032, correspond to such values of activation energies. This is caused probably by helium migration in the form of gas bubbles. The received data indicate the very high stability of the (U-Th)/He isotope system in native gold. Using the (U-Th)/He method of isotope geochronology seems to be very promising for isotope dating of these strategic raw materials.  相似文献   

18.
The kinetics of zoned garnet porphyroblast growth is exemplified in a sample of garnet-staurolite-biotite schist from the northern Ladoga region. The diffusion-controlled porphyroblast growth was accompanied by a decrease in the kinetic coefficient during phase reactions. Even at insignificant (1–2°C) thermal overstepping, the leading role of diffusion as a factor that controls kinetics of porphyroblast growth in medium-grade metapelites is consistent with the parameters of metamorphic crystallization: T = 500–650°C, t = 1 Ma; D A1 app = 10?14 cm2/s, L = 0.2–0.6 cm, r = 1–3 mm, ΔC Al = 1.5 × 10?4–1.5 × 10?3 mol/cm3.  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.
Abstract In the Twin Lakes area, central Sierra Nevada, California, most contact metamorphosed marbles contain calcite + dolomite + forsterite ± diopside ± phlogopite ± tremolite, and most calc-silicate hornfelses contain calcite + diopside + wollastonite + quartz ± anorthite ± K-feldspar ± grossular ± titanite. Mineral-fluid equilibria involving calcite + dolomite + tremolite + diopside + forsterite in two marble samples and wollastonite + anorthite + quartz + grossular in three hornfels samples record P± 3 kbar and T± 630° C. Various isobaric univariant assemblages record CO2-H2O fluid compositions of χCO2= 0.61–0.74 in the marbles and χCO2= 0.11 in the hornfelses. Assuming a siliceous dolomitic limestone protolith consisting of dolomite + quartz ° Calcite ± K-feldspar ± muscovite ± rutile, all plausible prograde reaction pathways were deduced for marble and hornfels on isobaric T-XCO2 diagrams in the model system K2O-CaO-MgO-Al2O3-SiO2-H2O-CO2. Progress of the prograde reactions was estimated from measured modes and mass-balance calculations. Time-integrated fluxes of reactive fluid which infiltrated samples were computed for a temperature gradient of 150 °C/km along the fluid flow path, calculated fluid compositions, and estimated reaction progress using the mass-continuity equation. Marbles and hornfelses record values in the range 0.1–3.6 × 104 cm3/cm2 and 4.8–12.9 × 104 cm3/cm2, respectively. For an estimated duration of metamorphism of 105 years, average in situ metamorphic rock permeabilities, calculated from Darcy's Law, are 0.1–8 × 10?6 D in the marbles and 10–27 × 10?6 D in the hornfelses. Reactive metamorphic fluids flowed up-temperature, and were preferentially channellized in hornfelses relative to the marbles. These results appear to give a general characterization of hydrothermal activity during contact metamorphism of small pendants and screens (dimensions ± 1 km or less) associated with emplacement of the Sierra Nevada batholith.  相似文献   

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