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1.
Observations of 26 regions of low-mass star formation and 17 regions of massive star formation in the 5−1-40 E, 70-61 A +, 80-71 A +, and 2K-1K methanol lines at 44.1, 84.5, 95.2 GHz, and 96.7 GHz yielded detections of methanol emission in 11 low-mass and 12 high-mass regions. The strongest lines in the low-mass regions were found towards bipolar outflows driven by Class 0 protostars with luminosities higher than or of the order of 10 L . These lines usually consist of cores 1–2 km s−1 in width, which are emitted by quiescent gas, and broader wings, emitted by gas accelerated by high-velocity jets. The temperature of the accelerated gas derived from rotational diagrams and statistical equilibrium calculations is roughly 20–50 K. This means that a significant fraction of the accelerated gas cools to such temperatures. The widths of the lines detected in the massive star-forming regions are 2–3 km s−1 or higher. Weak, broad wings were found towards only two sources: L1287 and AFGL5142. For most sources, the statistical-equilibrium calculations yielded gas temperatures of about 20–30 K and densities of about 104–106 cm−3, which are typical for warm clouds. However, different transitions emit in regions with different physical conditions located within the main beam of the telescope. Most of the 96.7 GHz emission arises in warm gas with kinetic temperatures of about 30 K, while most of the 95.2 GHz emission may arise in hot regions around Young Stellar Objects and/or be related to the wings of bipolar outflows. Published in Russian in Astronomicheskiĭ Zhurnal, 2007, Vol. 84, No. 1, pp. 48–59. The article was translated by the author.  相似文献   

2.
We present the results of VLA observations of a maser candidate in the low-mass star formation region L1157 in the 70-61 A + transition at 44 GHz. The line is emitted by a compact, undoubtedly maser source associated with clump B0a, which is seen in maps of L1157 in thermal lines of methanol and other molecules. A much weaker compact source is associated with clump B1a, which is brighter than B0a in thermal methanol lines. The newly detected masers may form in thin layers of turbulent post-shock gas. In this case, the maser emission may be beamed, so that only an observer located in or near the planes of the layers can observe strong masers. On the other hand, the maser lines are double with a “red” asymmetry, indicating that the masers may form in collapsing clumps. A detailed analysis of collapsing-cloud maser models and their applicability to the masers in L1157 will be developed in subsequent papers.  相似文献   

3.
An analysis of the flux densities of the 51-60 A + (6.7 GHz) and 20-3?1 E (12.2 GHz) class II methanol maser lines in a large and homogeneous sample of maser sources has been carried out. For convenience, the maser lines were divided into three groups: group I contains spectral features for the lines most prominent in the 51-60 A + (6.7 GHz) transition, group II contains spectral features for the lines strongest in the 20-3?1 E (12.2 GHz) transition, group III contains spectral features for which the velocities of the emission maxima of the two lines coincide. The same dependence was found for group II and group III: log S 6.7=(0.79±0.05)×log S 12.2+(0.79±0.05). The spectral features in group I do not obey this relation, and deviations from a linear dependence are considerably greater. It is suggested that methanol class II masers be divided into a subclass IIa, which has special conditions favoring 6.7 GHz masers, and a subclass IIb, which is comprised of the 12.2 GHz masers and those 6.7 GHz masers that necessarily accompany them under the same conditions.  相似文献   

4.
A spectral survey of the W51 e1/e2 star-forming region at 84–115 GHz has yielded detections of 105 molecules and their isotopic species, from simple diatomic or triatomic molecules, such as CO, CS, HCN, up to complex organic compounds, such as CH3OCH3, CH3COCH3, and C2H5OOCH. Ninety-three lines that are absent from the Lovas list of molecular lines observed from space were detected, and approximately half of these were identified. A significant number of the detectedmolecules are typical for hot cores. These include the neutral molecules CH3OCHO, C2H5OH, CH3COCH3 etc., which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited SiO, C4H, HCN, l-C3H, HCCCN, CH3CN, CH3OH, H2O, and SO2 lines with upper-level temperatures of several hundred Kelvin were found. Such lines can arise only in hot gas with temperatures of the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (N2H+, HCO+, HCS+) usually exist in molecular clouds with high visual extinctions A V . At the same time, the CF+ ion should be observed in photon-dominated regions with A V values of about unity or lower. An interesting result is the tentative detection of two molecules that have thus far been observed only in the atmospheres of late-type giant stars—MgCN and NaCN. This suggests that the conditions in the hottest W51 regions (probably, in the vicinities of protostars) are close to those in the atmospheres of giant stars. It would be desirable to search for other lines of these molecules to verify these tentative detections. Analysis of the radial velocities of the detected molecules suggests that the contribution from the e2 core dominates the emission of some O-bearing molecules (CH3OCHO, CH3CH2OH), while the contribution of the e1 core dominates the emission of some N-bearing molecules (e.g., CH3CH2CN). Thus, the molecular composition of the e2 core may be closer to the composition of the “Compact Ridge” in OMC-1, while the composition of the e1 core is closer to that for the “Hot Core” in the same cloud.  相似文献   

5.
We present images of the star-forming regionG23.01–0.41 at 6.7GHz in the Class II methanol maser transition 51–60 A +, produced from archival observations on the European VLBI Network. Our map of the source and its maser spots contains 24 maser components. The data for each spot—absolute coordinates, coordinates relative to the calibration feature, peak flux and flux integrated over the spot, size, position angle, velocity along the line of sight, and line full width at half-maximum—are collected in tabular form. The spatial region occupied by the maser spots is approximated by a 200×130 milliarcsec ellipse in position angle PA = −0.40°, centered on the absolute coordinates α 0 = 18h34m40.282s, δ 0 = −09°00′38.27″ (J2000). If the source is a protoplanetary disk, then, for the distance estimate derived from trigonometric parallax, its diameter is 1800 AU, and the mass of the central protostar is 23.5M .  相似文献   

6.
The results of spectral observations of the region of massive star formation L379IRS1 (IRAS18265–1517) are presented. The observations were carried out with the 30-m Pico Veleta radio telescope (Spain) at seven frequencies in the 1-mm, 2-mm, and 3-mm wavelength bands. Lines of 24 molecules were detected, from simple diatomic or triatomic species to complex eight- or nine-atom compounds such as CH3OCHO or CH3OCH3. Rotation diagrams constructed from methanol andmethyl cyanide lines were used to determine the temperature of the quiescent gas in this region, which is about 40–50 K. In addition to this warm gas, there is a hot component that is revealed through high-energy lines of methanol and methyl cyanide, molecular lines arising in hot regions, and the presence of H2O masers and Class II methanol masers at 6.7 GHz, which are also related to hot gas. One of the hot regions is probably a compact hot core, which is located near the southern submillimeter peak and is related to a group of methanol masers at 6.7 GHz. High-excitation lines at other positions may be associated with other hot cores or hot post-shock gas in the lobes of bipolar outflows. The rotation diagrams can be use to determine the column densities and abundances of methanol (10?9) and methyl cyanide (about 10?11) in the quiescent gas. The column densities of A- and E-methanol in L379IRS1 are essentually the same. The column densities of other observedmolecules were calculated assuming that the ratios of the molecular level abundances correspond to a temperature of 40 K. The molecular composition of the quiescent gas is close to that in another region of massive star formation, DR21(OH). The only appreciable difference is that the column density of SO2 in L379IRS1 is at least a factor of 20 lower than the value in DR21(OH). The SO2/CS and SO2/OCS abundance ratios, which can be used as chemical clocks, are lower in L379IRS1 than in DR21(OH), suggesting that L379IRS1 is probably younger than DR21(OH).  相似文献   

7.
Forty-eight objects were detected in the 5?1–40 E methanol line at 84.5 GHz during a survey of Class I maser sources. Narrow maser features were found in 14 of these. Broad quasi-thermal lines were detected toward other sources. One of the objects with narrow features at 84.5 GHz, the young bipolar outflow L1157, was also observed in the 80–71 A + line at 95.2 GHz; a narrow line was detected at this frequency. Analysis showed that the broad lines are usually inverted. The quasi-thermal profiles imply that there are no more than a few line opacities. These results confirm the plausibility of models in which compact Class I masers appear in extended sources as a result of a preferential velocity field.  相似文献   

8.
The results of a search for maser emission in the methanol lines 8?1-70 E at 229.8 GHz, 3?2-4?1 E at 230.0 GHz, 00-1?1 E at 108.9 GHz, and in the J 1-J 0 E series near 165 GHz in star-forming regions are reported. At least two masers and two candidates have been detected at 229.8 GHz. Thus, methanol masers have been detected in the 1-mm band for the first time. At 108.9 GHz, masers have been detected toward G345.01+1.79 and possibly toward M8E as well. Thermal emission was found toward 28 objects. The 229.8-GHz sources are class I masers, whereas the 108.9-GHz sources are class II masers. An analysis using a large velocity-gradient method shows that the 229.8-GHz masers can appear at densities of about 3×104 cm?3. The ratios of the flux densities in different class I lines toward DR 21(OH) and DR 21 West can be approximated in models with gas kinetic temperatures of about 50 K. Detection of the 108.9 GHz masers toward G345.01+1.79 and M8E may provide information about the geometry of these objects.  相似文献   

9.
 The IR spectrum of ammonium-exchanged natural analcime (basalt, Nidym River, Siberian platform) exhibits several features that suggest a lowered symmetry for the NH4 + ion and that this is influenced by hydrogen bonding within the framework. These features are: the pronounced splitting into three components and high-frequency shift of the ν4-bending mode; appearance of the ν1-stretching mode which is predicted to become IR-active when the ideal T d symmetry of NH4 + ion is violated, and the low-frequency shift of the ν1- and ν3-stretching modes. The absence of absorption lines in the 1800–2400-cm−1 region indicates that hydrogen bonding between the framework and the NH+ 4 ion is very weak. The three-component splitting of the ν4-bending mode indicates that the symmetry of NH+ 4 ion is lower than C3v. This implies that at least two N–H bonds of the NH+ 4 ion are disturbed by hydrogen bonding. Computer analysis of the normal vibrations of the NH+ 4 molecule for different symmetry types (using harmonic approximation) indicates that the best fit to the observed ν4 triplet frequencies for C1 symmetry implies a deviation of the valent angle ∠H–N–H from ideal T d symmetry of around ±2.5°. The factors governing the behaviour of the NH+ 4 ion in the analcime structure are discussed. The geometry of the nearest environment of the NH+ 4 ion in the analcime structure is analyzed with respect to the present IR data. Received: 2 January 2002 / Accepted: 26 June 2002 Acknowledgements We thank Dr. D. Harlov and an anonymous reviewer for their helpful comments, as well as Dr. I.A. Belitsky and Dr. S.V. Goryainov for discussion of the material. This work is supported by RFBR grants 01-05-65414, 00-05-65305 and 02-05-65313.  相似文献   

10.
Observations of various types of objects in the northern sky were obtained at 44 GHz in the 70-61 A + methanol line on the 20-m Onsala radio telescope (Sweden), in order to search for Class I methanol maser emission in the interstellar medium: regions of formation of high-mass stars, dust rings around HII regions, and protostellar candidates associated with powerful molecular outflows and Galactic HII regions. Seven new Class Imethanolmasers have been discovered toward regions of formation of highmass stars, and the existence of two previously observed masers confirmed. The following conclusions are drawn: (1) neither the association of a bipolar outflow manifest in the wings of CO lines with a highmass protostellar object (HMPO) nor the presence of thermal emission in lines of complex molecules are sufficient conditions for the detection of Class I methanol emission; no association with HMPOs radiating at 44 GHz was found for EGOs (a new class of object tracing bipolar outflows); (2) the existence of H2O masers and Class II methanol masers in the region of aHMPOenhances the probability of detecting Class I methanol emission toward the HMPO; Class II methanol masers with stronger line fluxes are associated with Class I methanol masers.  相似文献   

11.
 The cation distribution of Co, Ni, and Zn between the M1 and M2 sites of a synthetic olivine was determined with a single-crystal diffraction method. The crystal data are (Co0.377Ni0.396Zn0.227)2SiO4, M r  = 212.692, orthorhombic, Pbnm, a = 475.64(3), b = 1022.83(8), and c = 596.96(6) pm, V = 0.2904(1) nm3, Z = 4, D x  = 4.864 g cm−3, and F(0 0 0) = 408.62. Lattice, positional, and thermal parameters were determined with MoKα radiation; R = 0.025 for 1487 symmetry-independent reflections with F > 4σ(F). The site occupancies of Co, Ni, and Zn were determined with synchrotron radiation employing the anomalous dispersion effect of Co and Ni. The synchrotron radiation data include two sets of intensity data collected at 161.57 and 149.81 pm, which are about 1 pm longer than Co and Ni absorption edges, respectively. The R value was 0.022 for Co K edge data with 174 independent reflections, and 0.034 for Ni K edge data with 169 reflections. The occupancies are 0.334Co + 0.539Ni + 0.127Zn in the M1 sites, and 0.420Co + 0.253Ni + 0.327Zn in the M2 sites. The compilation of the cation distributions in olivines shows that the distributions depend on ionic radii and electronegativities of constituent cations, and that the partition coefficient can be estimated from the equation: ln [(A/B)M1/(A/B)M2] = −0.272 (IR A -IR B ) + 3.65 (EN A EN B ), where IR (pm) and EN are ionic radius and electronegativity, respectively. Received: 8 April 1999 / Revised, accepted: 7 September 1999  相似文献   

12.
A natural datolite CaBSiO4(OH) (Bergen Hill, NJ, USA), before and after gamma-ray irradiation (up to ~70 kGy), has been investigated by single-crystal and powder electron paramagnetic resonance (EPR) spectroscopy from 10 to 295 K. EPR spectra of gamma-ray-irradiated datolite show the presence of a boron-associated oxygen hole center (BOHC) and an atomic hydrogen center (H0), both of which grow with increasing radiation dose. The principal g and A(11B) values of the BOHC at 10 K are: g 1 = 2.04817(3), g 2 = 2.01179(2), g 3 = 2.00310(2), A 1 = −0.401(7) mT, A 2 = −0.906(2) mT, A 3 = −0.985(2) mT, with the orientations of the g 1 and A 1 axes approximately along the B–OH bond direction. These experimental results suggest that the BOHC represents hole trapping on the hydroxyl oxygen atom after the removal of the proton (i.e. a [BO4]0 center): via a reaction O3BOH → O3BO· + H0, where · denotes the unpaired electron. Density functional theory (DFT) calculations (CRYSTAL06, B3PW, all-electron basis sets, and 1 × 2 × 2 supercell) support the proposed structural model and yield the following 11B hyperfine coupling constants: A 1 = −0.429 mT, A 2 = −0.901 mT, A 3 = −0.954 mT, in excellent agreement with the experimental results. The [BO4]0 center undergoes the onset of thermal decay at ~200°C and is completely annealed out at 375°C but can be restored readily by gamma-ray irradiation. Isothermal annealing experiments show that the [BO4]0 center exhibits a second-order thermal decay with an activation energy of 0.96 eV. The confirmation of the [BO4]0 center (and its formation from the O3BOH precursor) in datolite has implications for not only understanding of BOHCs in alkali borosilicate glasses but also their applications to nuclear waste disposal.  相似文献   

13.
A survey has been made of 27 Galactic star-forming regions in the (CH3CN) 6K–5K, 5K–4K, and 8K–7K lines of methyl cyanide (CH3CN) at 110, 92, and 147 GHz. Twenty-five sources were detected at 110 GHz, nineteen at 92 GHz, and three at 147 GHz. The strongest CH3CN emission arises in hot cores in regions of massive star formation. The abundance of CH3CN in these objects exceeds 10?9 as a consequence of grain mantle evaporation. Weaker CH3CN lines were found in a number of sources. These can arise in either warm (30–50 K), dense (>104 cm?3) clouds or in hot regions with cooler gas.  相似文献   

14.
Binary, ternary, and quaternary rhombohedral ordered titanates, Ni1/2Mn1/2TiO3, Ni1/2Mg1/2TiO3, Ni1/3Zn1/3Mg1/3TiO3, and Ni1/4Zn1/4Mg1/4Mn1/4TiO3, were obtained by solid-state synthesis at 1095°C at ambient pressure in a nitrogen atmosphere. All of the compounds adopt ATiO3 (A = Ni, Mn, Zn, and Mg) stoichiometry. Crystal structures were refined by the Rietveld method from powder X-ray diffraction data. Unit cell parameters and unit cell volumes decrease with decreasing average radius of the vi A 2+ cation. All the synthetic titanates adopt the space group and the ilmenite structure consisting of distorted AO6 and TiO6 octahedra. The divalent cations and Ti4+ are distributed in layers of octahedra alternating along c with no evidence for disorder. In common with pyrophanite, NiTiO3, and ilmenite sensu stricto, the distortion of the AO6 octahedra is less than that of the TiO6 octahedra. The Ti4+ and A-site cations in the titanates are off-centred within the coordination polyhedra. Deviation of the z positional parameters from their theoretical values for the A and Ti atoms indicate that in the titanates with the larger A 2+ cations and Goldschmidt tolerance factors, t ≥ 0.745, the AO6 octahedral layer is more “puckered” above and below planes parallel to (001) than that of the TiO6 octahedra, and vice versa in the titanates with smaller R A 2+ for which t≤0.745. Data are given for the volumes and distortion indices of all the coordination polyhedra. This study confirms the existence and stability of complex solid solutions between ordered rhombohedral titanates of Ni and first-row transition metals at ambient conditions over a range of t from 0.786 to 0.737. These experimental data suggest that the formation of ilmenite-type titanates enriched in Ni is possible in exotic mineral-forming systems at low pressure and/or in extraterrestrial rocks.  相似文献   

15.
Summary Phosphates of compositions (Na1–xLix)1.5Mn1.5Fe1.5(PO4)3 were synthesized by solid state reactions in air, and pure alluaudite-type compounds were obtained for x=0.00, 0.25, and 0.50. Rietveld refinements of X-ray powder diffraction data indicate the occurrence of Mn2+ in the M(1) site, and of Fe3+ and Mn2+ in the M(2) site. For x=0.25 and 0.50, A(1) is occupied by Li+ and Na+, whereas A(2) is occupied by Na+ and vacancies. A careful examination of the number of electrons occurring in the A sites of the alluaudite-type compounds (Na1–xLix)MnFe2(PO4)3 and (Na1–xLix) CdIn2(PO4)3 confirms that lithium occupies only the A(1) crystallographic site of the alluaudite structure.  相似文献   

16.
Observations at 44 GHz in the 70−61 A + methanol line have been carried out on the 20-m telescope of the Onsala Space Observatory (Sweden) in the directions of the poorly studied region G27.4–0.2 and of several supernova remnants, at the coordinates of the OH(1720) maser satellite emission, with the aim of searching for Class I methanol maser emission in these sources. The region G27.4–0.2 has beenmapped, and contains maser sources and two supernova remnants with similar coordinates and radial velocities, which may accelerate condensation of the ambient gas-dust medium. This may play a role in enhancing the probability of methanol formation and maser emission. This is the first detection of 44 GHz maser emission in this source, and this maser is among the 10% of the strongest Class I methanol masers, within the uncertainties in the integrated flux (of a total of 198 currently knownmasers). A 27′ × 27′ region around the maser has been mapped at 44 GHz in steps of 1′. The 44-GHz emission forms only within the previously known maser region. Further studies in water lines are needed to estimate the influence of shocks from supernovae. No 44-GHz Class I methanol maser emission was detected at the 3σ level at the coordinates of the OH(1720) satellite emission in six supernova remnants; i.e., the presence of OH(1720) emission is not a sufficient condition for the detection of Class I methanol masers.  相似文献   

17.
 Enthalpies of drop solution (ΔH drop-sol) of CaGeO3, Ca(Si0.1Ge0.9)O3, Ca(Si0.2Ge0.8)O3, Ca(Si0.3Ge0.7)O3 perovskite solid solutions and CaSiO3 wollastonite were measured by high-temperature calorimetry using molten 2PbO · B2O3 solvent at 974 K. The obtained values were extrapolated linearly to the CaSiO3 end member to give ΔH drop-sol of CaSiO3 perovskite of 0.2 ± 4.4 kJ mol−1. The difference in ΔH drop-sol between CaSiO3, wollastonite, and perovskite gives a transformation enthalpy (wo → pv) of 104.4 ± 4.4 kJ mol−1. The formation enthalpy of CaSiO3 perovskite was determined as 14.8 ± 4.4 kJ mol−1 from lime + quartz or −22.2 ± 4.5 kJ mol−1 from lime + stishovite. A comparison of lattice energies among A2+B4+O3 perovskites suggests that amorphization during decompression may be due to the destabilizing effect on CaSiO3 perovskite from a large nonelectrostatic energy (repulsion energy) at atmospheric pressure. By using the formation enthalpy for CaSiO3 perovskite, phase boundaries between β-Ca2SiO4 + CaSi2O5 and CaSiO3 perovskite were calculated thermodynamically utilizing two different reference points [where ΔG(P,T )=0] as the measured phase boundary. The calculations suggest that the phase equilibrium boundary occurs between 11.5 and 12.5 GPa around 1500 K. Its slope is still not well constrained. Received: 20 September 2000 / Accepted: 17 January 2001  相似文献   

18.
Phase transitions in MgGeO3 and ZnGeO3 were examined up to 26 GPa and 2,073 K to determine ilmenite–perovskite transition boundaries. In both systems, the perovskite phases were converted to lithium niobate structure on release of pressure. The ilmenite–perovskite boundaries have negative slopes and are expressed as P(GPa)=38.4–0.0082T(K) and P(GPa)=27.4−0.0032T(K), respectively, for MgGeO3 and ZnGeO3. Enthalpies of SrGeO3 polymorphs were measured by high-temperature calorimetry. The enthalpies of SrGeO3 pseudowollasonite–walstromite and walstromite–perovskite transitions at 298 K were determined to be 6.0±8.6 and 48.9±5.8 kJ/mol, respectively. The calculated transition boundaries of SrGeO3, using the measured enthalpy data, were consistent with the boundaries determined by previous high-pressure experiments. Enthalpy of formation (ΔH f°) of SrGeO3 perovskite from the constituent oxides at 298 K was determined to be −73.6±5.6 kJ/mol by calorimetric measurements. Thermodynamic analysis of the ilmenite–perovskite transition boundaries in MgGeO3 and ZnGeO3 and the boundary of formation of SrSiO3 perovskite provided transition enthalpies that were used to estimate enthalpies of formation of the perovskites. The ΔH f° of MgGeO3, ZnGeO3 and SrSiO3 perovskites from constituent oxides were 10.2±4.5, 33.8±7.2 and −3.0±2.2 kJ/mol, respectively. The present data on enthalpies of formation of the above high-pressure perovskites were combined with published data for A2+B4+O3 perovskites stable at both atmospheric and high pressures to explore the relationship between ΔH f° and ionic radii of eightfold coordinated A2+ (R A) and sixfold coordinated B4+ (R B) cations. The results show that enthalpy of formation of A2+B4+O3 perovskite increases with decreasing R A and R B. The relationship between the enthalpy of formation and tolerance factor ( R o: O2− radius) is not straightforward; however, a linear relationship was found between the enthalpy of formation and the sum of squares of deviations of A2+ and B4+ radii from ideal sizes in the perovskite structure. A diagram showing enthalpy of formation of perovskite as a function of A2+ and B4+ radii indicates a systematic change with equienthalpy curves. These relationships of ΔH f° with R A and R B can be used to estimate enthalpies of formation of perovskites, which have not yet been synthesized.  相似文献   

19.
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   

20.
 The stability of pargasite in the presence of excess quartz has been determined in the range of 0.5–6.0 kbar and 500–950 °C in the system Na2O– CaO–MgO–Al2O3–SiO2–H2O, using synthetic minerals. The experimental results from this study indicate the presence of two distinct mineral assemblage regions: (1) a high temperature supersolidus region containing tremolitic amphibole+melt+quartz; (b) a low temperature subsolidus region consisting of Al-rich amphibole+plagioclase+enstatite+quartz. Compositional reversals have been determined for the following three equilibria: (a) 2 pargasite+9 quartz=tremolite+4 plagioclase (An50)+1.5 enstatite+H2O, (b) 2 pargasite+10 quartz=tremolite+4 plagioclase (An50)+talc, and (c) pargasite+diopside+5 quartz=tremolite+2 plagioclase (An50). These experiments indicate a continuous change of amphibole composition from pargasite to tremolite with increasing temperature, and an opposite effect with increasing pressure. The third equilibria is used to constrain a site-mixing model for the pargasitic amphiboles, which favor a single-coupled NaA-AlT1 site mixing. The thermochemical data for pargasite estimated from the reversal data of the three equilibrium reactions is estimated as for ΔG 0 f ,Pg=−12022.11±5.2 kJ mole-1, and S 0 Pg=591.7 ±7.9 JK-1 mole-1. Received: 31 July 1995/Accepted: 3 June 1996  相似文献   

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