共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
S. V. Kalenskii V. G. Promislov A. V. Alakoz A. Winnberg L. E. B. Johansson 《Astronomy Reports》2000,44(11):725-737
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
4.
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
5.
The results of SEST millimeter observations of the molecular cloud G345.01+1.79 are presented. Spectra of CH3OH, SO2, SiO, HCO+, C18O, C33S, C34S, HCN, and DCN lines have been obtained. Mapping of the cloud in CH3OH, SiO, and C34S lines indicates that the maximum integrated intensity in the SiO and C34S lines and in low-excitation CH3OH transitions coincide with the northern group of methanol masers, while the corresponding maximum for high-excitation CH3OH transitions coincides with the southern methanol-maser group. The physical parameters are estimated from the quasi-thermal CH3OH lines under the large-velocity-gradient approximation, and their distribution on the sky derived. The density and temperature are higher toward the southern group of methanol masers than in the northern group. This may indicate that star formation is in an earlier stage of evolution in the northern than toward the southern group. A maser component can be distinguished in 14 (of 71) CH3OH lines. We have detected for the first time weak, probably maser, emission in the CH3OH lines at 148.11, 231.28, 165.05, 165.06, and 165.07 GHz. A blue wing is clearly visible in the CH3OH, SiO, C18O, and SO2 lines. The emission in this wing is probably associated with a compact source whose velocity is characteristic of the CH3OH maser emission in the southern group of masers. 相似文献
6.
The paper reports the results of a survey of Galactic star-forming regions 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 a series of J 1–J 0 E lines near 165 GHz. In addition to the methanol lines, lines of methyl cyanide (CH3CN), cyanoacetylene (HC3N), methyl formate (HCOOCH3), and sulphur dioxide (SO2) were detected. Analysis of the data indicates that the methanol emission arises in warm (30–50 K) gas. 相似文献
7.
We have mapped three star-forming regions (G265.14+1.45, G269.16?1.14, G291.27?0.71) in the CS(3–2) and C34S(2–1) lines using the 15 m SEST telescope (Chile), and analyzed the relative positions of methanol and H2O masers, IRAS sources, and emission maxima in the CS lines. In most cases, the maser positions are close to those of the IRAS sources. We compared the radial velocities of the maser sources and high-density CS cores, and estimated the CS column densities assuming LTE. The sizes, densities, and masses of the dense core are estimated; the masses obtained in the LTE approximation agree with the virial masses. 相似文献
8.
L. E. Pirogov 《Astronomy Reports》2009,53(12):1127-1135
Radial density profiles for the sample of dense cores associated with high-mass star-forming regions from southern hemisphere
have been derived using the data of observations in continuum at 250 GHz. Radial density profiles for the inner regions of
16 cores (at distances ≲0.2−0.8 pc from the center) are close on average to the ρ ∝ r
−α dependence, where α = 1.6 ± 0.3. In the outer regions density drops steeper. An analysis with various hydrostatic models showed that the modified
Bonnor-Ebertmodel, which describes turbulent sphere confined by external pressure, is preferable compared with the logotrope
and polytrope models practically in all cases. With a help of the Bonnor-Ebert model, estimates of central density in a core,
non-thermal velocity dispersion and core size are obtained. The comparison of central densities with the densities derived
earlier from the CS modeling reveals differences in several cases. The reasons of such differences are probably connected
with the presence of density inhomogenities on the scales smaller than the telescope beam. In most cases non-thermal velocity
dispersions are in agreement with the values obtained from molecular line observations. 相似文献
9.
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
10.
Fluid and gas migration in the North German Basin: fluid inclusion and stable isotope constraints 总被引:1,自引:0,他引:1
Volker Lüders Christian Reutel Peer Hoth David A. Banks Birgit Mingram Thomas Pettke 《International Journal of Earth Sciences》2005,94(5-6):990-1009
Fluid inclusions have been studied in minerals infilling fissures (quartz, calcite, fluorite, anhydrite) hosted by Carboniferous
and Permian strata from wells in the central and eastern part of the North German Basin in order to decipher the fluid and
gas migration related to basin tectonics. The microthermometric data and the results of laser Raman spectroscopy reveal compelling
evidence for multiple events of fluid migration. The fluid systems evolved from a H2O–NaCl±KCl type during early stage of basin subsidence to a H2O–NaCl–CaCl2 type during further burial. Locally, fluid inclusions are enriched in K, Cs, Li, B, Rb and other cations indicating intensive
fluid–rock interaction of the saline brines with Lower Permian volcanic rocks or sediments. Fluid migration through Carboniferous
sediments was often accompanied by the migration of gases. Aqueous fluid inclusions in quartz from fissures in Carboniferous
sedimentary rocks are commonly associated with co-genetically trapped CH4–CO2 inclusions. P–T conditions estimated, via isochore construction, yield pressure conditions between 620 and 1,650 bar and temperatures between
170 and 300°C during fluid entrapment. The migration of CH4-rich gases within the Carboniferous rocks can be related to the main stage of basin subsidence and stages of basin uplift.
A different situation is recorded in fluid inclusions in fissure minerals hosted by Permian sandstones and carbonates: aqueous
fluid inclusions in calcite, quartz, fluorite and anhydrite are always H2O–NaCl–CaCl2-rich and show homogenization temperatures between 120 and 180°C. Co-genetically trapped gas inclusions are generally less
frequent. When present, they show variable N2–CH4 compositions but contain no CO2. P–T reconstructions indicate low-pressure conditions during fluid entrapment, always below 500 bar. The entrapment of N2–CH4 inclusions seems to be related to phases of tectonic uplift during the Upper Cretaceous. A potential source for nitrogen
in the inclusions and reservoirs is Corg-rich Carboniferous shales with high nitrogen content. Intensive interaction of brines with Carboniferous or even older shales
is proposed from fluid inclusion data (enrichment in Li, Ba, Pb, Zn, Mg) and sulfur isotopic compositions of abundant anhydrite
from fissures. The mainly light δ34S values of the fissure anhydrites suggest that sulfate is either derived through oxidation and re-deposition of biogenic
sulfur or through mixing of SO42−-rich formation waters with variable amounts of dissolved biogenic sulfide. An igneous source for nitrogen seems to be unlikely
since these rocks have low total nitrogen content and, furthermore, even extremely altered volcanic rocks from the study area
do not show a decrease in total nitrogen content. 相似文献
11.
G. V. Gibbs A. F. Wallace R. T. Downs N. L. Ross D. F. Cox K. M. Rosso 《Physics and Chemistry of Minerals》2011,38(4):267-291
Electron density distributions, bond paths, Laplacian and local-energy density properties have been calculated for a number
of As4S
n
(n = 3, 4 and 5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As–S and As–As interactions
classify as shared bonded interactions, and the intermolecular As–S, As–As and S–S interactions classify as closed-shell van
der Waals (vdW) bonded interactions. The bulk of the intermolecular As–S bond paths link regions of locally concentrated electron
density (Lewis-base regions) with aligned regions of locally depleted electron density (Lewis-acid regions) on adjacent molecules.
The paths are comparable with intermolecular paths reported for several other molecular crystals that link aligned Lewis base
and acid regions in a key–lock fashion, interactions that classified as long-range Lewis acid–base-directed vdW interactions.
As the bulk of the intermolecular As–S bond paths (~70%) link Lewis acid–base regions on adjacent molecules, it appears that
molecules adopt an arrangement that maximizes the number of As–S Lewis acid–base intermolecular bonded interactions. The maximization
of the number of Lewis acid–base interactions appears to be connected with the close-packed array adopted by molecules: distorted
cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal
close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from
aqueous species that maximizes the number of long-range Lewis acid–base vdW As–S bonded interactions with the resulting directed
bond paths structuralizing the molecules as a molecular crystal. 相似文献
12.
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
13.
We have investigated melting relations in the Fe–O–S ternary system in the pressure range of 15–27 GPa and 1873 K. Subsolidus
phase relations are Fe, Fe3S2, and FeO up to 17 GPa and Fe, Fe3S, and FeO above this pressure. The eutectic temperature slightly decreases from ambient pressure to 17 GPa, whereas increases
above this pressure. The eutectic temperature in this study is 100 K lower than that in the Fe–S binary system. The oxygen
content in the Fe–O–S eutectic liquid drops when the coexisting solid phases changes from FeS to Fe3S2. The cotectic lines in the ternary phase diagram lie close to the Fe–FeS binary axis. The isothermal sections indicate that
oxygen solubility in the Fe–O–S liquid increases with increasing temperature, and with increasing sulfur content. The solubility
of sulfur in the solid Fe has a maximum value at the eutectic temperature, and decreases with increasing temperature. Our
results could have important implications for formation and composition of the Martian core. 相似文献
14.
A. V. Alakoz S. V. Kalenskii V. G. Promislov L. E. B. Johansson A. Winnberg 《Astronomy Reports》2002,46(7):551-566
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
15.
Diffusion of water was experimentally investigated for melts of albitic (Ab) and quartz-orthoclasic (Qz29Or71, in wt %) compositions with water contents in the range of 0 to 8.5 wt % at temperatures of 1100 to 1200 °C and at pressures
of 1.0 and 5.0 kbar. Apparent chemical diffusion coefficients of water (D
water) were determined from concentration-distance profiles measured by FTIR microspectroscopy. Under the same P-T condition and water content the diffusivity of water in albitic, quartz-orthoclasic and haplogranitic (Qz28Ab38 Or34, Nowak and Behrens, this issue) melts is identical within experimental error. Comparison to data published in literature
indicates that anhydrous composition only has little influence on the mobility of water in polymerized melts but that the
degree of polymerization has a large effect. For instance, Dwater is almost identical for haplogranitic and rhyolitic melts with 0.5–3.5 wt % water at 850 °C but it is two orders of magnitude
higher in basaltic than in haplogranitic melts with 0.2–0.5 wt % water at 1300 °C. Based on the new water diffusivity data,
recently published in situ near-infrared spectroscopic data (Nowak 1995; Nowak and Behrens 1995), and viscosity data (Schulze et al. 1996) for hydrous
haplogranitic melts current models for water diffusion in silicate melts are critically reviewed. The NIR spectroscopy has
indicated isolated OH groups, pairs of OH groups and H2O molecules as hydrous species in polymerized silicate melts. A significant contribution of isolated OH groups to the transport
of water is excluded for water contents above 10 ppm by comparison of viscosity and water diffusion data and by inspection
of concentration profiles from trace water diffusion. Spectroscopic measurements have indicated that the interconversion of
H2O molecules and OH pairs is relatively fast in silicate glasses and melts even at low temperature and it is inferred that
this reaction is an active step for migration of water. However, direct jumps of H2O molecules from one cavity within the silicate network to another one can not be excluded. Thus, we favour a model in which
water migrates by the interconversion reaction and, possibly, small sequences of direct jumps of H2O molecules. In this model, immobilization of water results from dissociation of the OH pairs. Assuming that the frequency
of the interconversion reaction is faster than that of diffusive jumps, OH pairs and water molecules can be treated as a single
diffusing species having an effective diffusion coefficient . The shape of curves of Dwater versus water content implies that increases with water content. The change from linear to exponential dependence of Dwater between 2 and 3 wt % water is attributed to the influence of the dissociation reaction at low water content and to the modification
of the melt structure by incorporation of OH groups.
Received: 26 March 1996 / Accepted: 23 August 1996 相似文献
16.
CH4 and CO2 fluxes from a high-cold swamp meadow and an alpine meadow on the Qinghai-Tibetan Plateau, subject to different degrees of
degradation, were measured over a 12-month period. Air temperature, soil temperature and moisture, and the depths of the water
table and thawing-freezing layer were determined. For swamp meadows, the greater the degradation, the lesser the carbon efflux.
CH4 emissions at the nondegraded swamp meadow site were 1.09–3.5 and 2.5–11.27 times greater, and CO2 emissions 1.08–1.69 and 1.41–4.43 times greater, respectively, than those from moderately and severely degraded sites. For
alpine meadows, the greater the degradation, the greater the CH4 consumption and CO2 emissions. CH4 consumption at the severely degraded alpine meadow site was 6.6–21 and 1.1–5.25 times greater, and CO2 emissions 1.05–78.5 and 1.04–6.28 times greater, respectively, than those from the nondegraded and moderately degraded sites.
The CH4 and CO2 fluxes at both sites were significantly correlated (R
2 > 0.59, P < 0.05) with air temperature, soil temperature, and topsoil (0–5 cm depth) moisture, indicating these to be the main environmental
factors affecting such fluxes. 相似文献
17.
I. V. Pekov N. V. Zubkova Ya. E. Filinchuk N. V. Chukanov A. E. Zadov D. Yu. Pushcharovsky E. R. Gobechiya 《Geology of Ore Deposits》2010,52(8):767-777
New minerals, shlykovite and cryptophyllite, hydrous Ca and K phyllosilicates, have been identified in hyperalkaline pegmatite
at Mount Rasvumchorr, Khibiny alkaline pluton, Kola Peninsula, Russia. They are the products of low-temperature hydrothermal
activity and are associated with aegirine, potassium feldspar, nepheline, lamprophyllite, eudialyte, lomonosovite, lovozerite,
tisinalite, shcherbakovite, shafranovskite, ershovite, and megacyclite. Shlykovite occurs as lamellae up to 0.02 × 0.02 ×
0.5 mm in size or fibers up to 0.5 mm in length usually combined in aggregates up to 3 mm in size, crusts, and parallel-columnar
veinlets. Cryptophyllite occurs as lamellae up to 0.02 × 0.1 × 0.2 mm in size intergrown with shlykovite being oriented parallel
to {001} or chaotically arranged. Separate crystals of the new minerals are transparent and colorless; the aggregates are
beige, brownish, light cream, and pale yellowish-grayish. The cleavage is parallel to (001) perfect. The Mohs hardness of
shlykovite is 2.5–3. The calculated densities of shlykovite and cryptophyllite are 2.444 and 2.185 g/cm3, respectively. Both minerals are biaxial; shlykovite: 2V
meas = −60(20)°; cryptophyllite: 2V
meas > 70°. The refractive indices are: shlykovite: α = 1.500(3), β = 1.509(2), γ = 1.515(2); cryptophyllite: α = 1.520(2), β
= 1.523(2), γ = 1.527(2). The chemical composition of shlykovite determined by an electron microprobe (H2O determined from total deficiency) is as follows, wt %: 0.68 Na2O, 11.03 K2O, 13.70 CaO, 59.86 SiO2, 14.73 H2O; the total is 100.00. The empirical formula calculated on the basis of 13 O atoms (OH/H2O calculated from the charge balance) is (K0.96Na0.09)Σ1.05Ca1.00Si4.07O9.32(OH)0.68 · 3H2O. The idealized formula is KCa[Si4O9(OH)] · 3H2O. The chemical composition of cryptophyllite determined by an electron microprobe (H2O determined from the total deficiency) is as follows, wt %: 1.12 Na2O, 17.73 K2O, 11.59 CaO, 0.08 Al2O3, 50.24 SiO2, 19.24 H2O, the total is 100.00. The empirical formula calculated on the basis of (Si,Al)4(O,OH)10 (OH/H2O calculated from the charge balance) is (K1.80Na0.17)Σ1.97Ca0.99Al0.01Si3.99O9.94(OH)0.06 · 5.07H2O. The idealized formula is K2Ca[Si4O10] · 5H2O. The crystal structures of both minerals were solved on single crystals using synchrotron radiation. Shlykovite is monoclinic;
the space group is P21/n; a = 6.4897(4), b = 6.9969(5), c = 26.714(2)?, β = 94.597(8)°, V = 1209.12(15)?3, Z = 4. Cryptophyllite is monoclinic; the space group is P21/n; a = 6.4934(14), b = 6.9919(5), c = 32.087(3)?, β = 94.680(12)°, V= 1451.9(4)?, Z = 4. The strongest lines of the X-ray powder patterns (d, ?-I, [hkl] are: shlykovite 13.33–100[002], 6.67–76[004], 6.47–55[100], 3.469–45[021], 3.068–57[$
\bar 1
$
\bar 1
21], 3.042–45[121], 2.945–62[ 23], 2.912–90[025, 12, 211]; cryptophyllite 16.01–100[002], 7.98–24[004], 6.24–48[101], 3.228–22[$
\bar 1
$
\bar 1
09], 3.197–27[0.0.10], 2.995–47[122], 2.903–84[123, 204, $
\bar 1
$
\bar 1
24, 211], 2.623–20[028, 08, 126]. Shlykovite and cryptophyllite are members of new related structural types. Their structures
are based on a two-layer packet consisting of tetrahedral Si layers linked with octahedral Ca chains. Mountainite, shlykovite
and cryptophyllite could be combined into the mountainite structural family. Shlykovite is named in memory of Russian geologist
V. G. Shlykov (1941–2007); the name cryptophyllite is from the Greek words meaning concealed and leaf that allude to its layered structure (phyllosilicate) in combination with a lamellar habit and intimate intergrowths with
visually indistinguishable shlykovite. Type specimens of the minerals are deposited at the Fersman Mineralogical Museum of
the Russian Academy of Sciences, Moscow. 相似文献
18.
Quartz–carbonate–chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks
in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate
subsolvus unmixing of a homogenous H2O–CO2–CH4–(N2)–Na–(K)–Cl fluid into a H2O–Na–(K)–Cl solution and a vapour-rich CO2–(H2O, CH4, N2) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities
ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a
burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic
conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid
system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between
200 and 250°C and salinities of <5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite,
and dolomite by decrepitation yielded δDH2O values from −89 to −113 ‰, δ13CCH4 from −26.9 to −28.9‰ (VPDB) and δ13CCO2 from −12.8 to −23.3‰ (VPDB). The low δD and δ13C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial
isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from
the epizonal metamorphic domains of the Stavelot–Venn massif. The metamorphic fluid was focused along major thrust faults
of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall
of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water
with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion
characteristics. 相似文献
19.
Michael A. Henderson 《Geochimica et cosmochimica acta》2003,67(5):1055-1063
Insight into the complexation of organic molecules on hematite surfaces was obtained from molecular-level studies of a simple probe molecule (methanol) with the R-cut surface of hematite. The R-cut crystal orientation of hematite, designated in this paper as α-Fe2O3(012), has two stable surface structures under ultrahigh vacuum (UHV) conditions based on low-energy electron diffraction (LEED) measurements. These are a (1×1) structure consisting of a bulk terminated arrangement of undercoordinated Fe3+ and O2− surface sites and a (2×1) reconstructed structure with unknown atomic structure. Whereas the (1×1) surface is essentially free of Fe2+, the (2×1) surface possesses a high surface concentration of Fe2+ sites based on electronic structure measurements using electron energy loss spectroscopy (EELS). Methanol adsorbs dissociatively on the (1×1) surface by coordination of the molecule’s oxygen atom at a Fe3+ site followed by transfer of the alcohol proton to a bridging O2− surface site, resulting in terminal OCH3 and bridging OH groups. Most of the dissociated methanol molecules recombine during heating and desorb in vacuum as methanol at 365 and 415 K for the (1×1) and (2×1) surfaces, respectively. However, a significant amount of the terminal OCH3 and bridging OH groups interchange as the surface is heated above room temperature (RT), resulting in bridging OCH3 and terminal OH groups. The bridging OCH3 groups are retained on the surface to higher temperature than the terminal OCH3 groups, but eventually decompose at about 550 K via a disproportionation reaction that forms gaseous CH3OH and H2CO. As a result of the disproportionation reaction, some surface Fe3+ sites are reduced to Fe2+ sites. The exchange process competes more successfully with recombinative desorption of methanol (from reaction of terminal OCH3 and bridging OH groups) on the (2×1) surface, despite the fact that this surface is already partially reduced, because terminal OCH3 groups are more stable on this surface than on the (1×1) surface. Based on these molecular-level findings, extensive exchange terminal organic ligands and bridging OH groups may play a significant role in stabilizing organics on hematite mineral surfaces. Such exchange processes may also play a role in destabilizing hematite surfaces toward reductive dissolution. 相似文献
20.
Wen Su Ming Zhang Simon A. T. Redfern Jun Gao Reiner Klemd 《International Journal of Earth Sciences》2009,98(6):1299-1309
Chemically-zoned amphibole porphyroblast grains in an eclogite (sample ws24-7) from the western Tianshan (NW-China) have been
analyzed by electron microprobe (EMP), micro Fourier-transform infrared (micro-FTIR) and micro-Raman spectroscopy in the OH-stretching
region. The EMP data reveal zoned amphibole compositions clustering around two predominant compositions: a glaucophane end-member
(
B
Na2
C
M2+
3 M3+
2
T
Si8(OH)2) in the cores, whereas the mantle to rim of the samples has an intermediate amphibole composition (
A
0.5
B
Ca1.5Na0.5
C
M
2+
4.5 M
0.53+
T
Si7.5Al0.5(OH)2) (A = Na and/or K; M
2+ = Mg and Fe2+; M
3+ = Fe3+ and/or Al) between winchite (and ferro-winchite) and katophorite (and Mg-katophorite). Furthermore, we observed complicated
FTIR and Raman spectra with OH-stretching absorption bands varying systematically from core to rim. The FTIR/Raman spectra
of the core amphibole show three lower-frequency components (at 3,633, 3,649–3,651 and 3,660–3,663 cm−1) which can be attributed to a local O(3)-H dipole surrounded by
M(1) M(3)Mg3,
M(1) M(3)Mg2Fe2+ and
M(1) M(3) Fe2+
3, respectively, an empty A site and
T
Si8 environments. On the other hand, bands at higher frequencies (3,672–3,673, 3,691–3,697 and 3,708 cm−1) are observable in the rims of the amphiboles, and they indicate the presence of an occupied A site. The FTIR and Raman data from the OH-stretching region allow us to calculate the site occupancy of the A, M(1)–M(3), T sites with confidence when combined with EPM data. By contrast M(2)- and M(4) site occupancies are more difficult to evaluate. We use these samples to highlight on the opportunities and limitations
of FTIR OH-stretching spectroscopy applied to natural high pressure amphibole phases. The much more detailed cation site occupancy
of the zoned amphibole from the western Tianshan have been obtained by comparing data from micro-chemical and FTIR and/or
Raman in the OH-stretching data. We find the following characteristic substitutions Si(T-site) (Mg, Fe)[M(1)–M(3)-site] → Al(T-site) Al[M(1)–M(3)-site] (tschermakite), Ca(M4-site)□ (A-site) → Na(M4-site) Na + K(A-site) (richterite), and Ca(M4-site) (Mg, Fe) [M(1)–M(3)-site] → Na(M4-site) Al[M(1)–M(3)-site] (glaucophane) from the configurations observed during metamorphism. 相似文献