对变质岩区加强岩石学研究的几点看法

文章对1:5万区调工作中变质岩区加强基础岩石学工作的以下3个方面提出了一些看法,1．岩石薄片的研究;2．矿物化学和地质温压计;3．变质岩的岩石组合和构造环境。     

Crystal chemistry of some Mg,Cr, V normal spinels from Sludyanka (Lake Baikal,Russia): the influence of V<Superscript>3+</Superscript> on structural stability

A suite of vanadian magnesiochromites from the Sludyanka metamorphic complex (South Lake Baikal, Russia) were investigated by means of X-ray single-crystal structural refinements and microprobe analyses. Various morphological types of Cr–V-bearing Mg spinels are located in calc–silicate metamorphic rocks, in an assemblage that also contains other Cr–V minerals such as escolaite–karelianite, uvarovite–goldmanite, Cr–V-bearing clinopyroxene, tourmaline, amphibole, mica, etc. Along the suite there is widespread V–Cr substitution (0.14 V³⁺ 0.95 afu, 1.02 Cr³⁺ 1.80 afu), and minor, variable Al contents. The Mg content of slightly lesser than 1 afu, is almost constant. Cell parameters and octahedral bond distances increase with V³⁺. Unexpectedly, the Mg–O tetrahedral bond distance also increases slowly with V³⁺. This weak dragging effect contributes towards maintaining distortion of the oxygen array with respect to the ideal CCP, thus providing a shielding effect, which reduces V³⁺–V³⁺ repulsion. This leads to the energetic stabilization of the structure, in spite of the increase of bond strain with increasing V³⁺ contents.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

The Influence of Oxalate on Fe-Catalyzed S(IV) Oxidation by Oxygen in Aqueous Solution

This study demonstrates that oxalate has a strong inhibiting effect onFe-catalyzed S(IV) oxidation by oxygen in aqueous solution. While thepseudo-first order rate constant of S(IV) oxidation was determined to be1.6 × 10³ M^-1 s^-1 in experimentswithout oxalate, the oxidation of S(IV) was totally inhibited at a molarconcentration ratio of iron:oxalate = 1:5 at an oxalate concentration of 4M. Under these conditions, the Fe(II)/Fe(III) ratio remained nearlyconstant during the observed reaction time. The determined rate constants wereindependent of the initial oxidation state of iron. However, with increasingconcentrations of oxalate, a longer induction period is observed forexperiments with iron initially in the Fe(II) oxidation state.     

Semiannual and annual variations in the height of the ionospheric F2-peak

Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately isobaric, in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not isobaric. The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere.     

The role of sodium bicarbonate in the nucleation of noctilucent clouds

It is proposed that a component of meteoric smoke, sodium bicarbonate (NaHCO₃), provides particularly effective condensation nuclei for noctilucent clouds. This assertion is based on three conditions being met. The first is that NaHCO₃ is present at sufficient concentration (10⁴ cm^–3) in the upper mesosphere between 80 and 90 km. It is demonstrated that there is strong evidence for this based on recent laboratory measurements coupled with atmospheric modelling. The second condition is that the thermodynamics of NaHCO₃(H₂O)_n cluster formation allow spontaneous nucleation to occur under mesospheric conditions at temperatures below 140 K. The Gibbs free energy changes for forming clusters with n = 1 and 2 were computed from quantum calculations using hybrid density functional/Hartree-Fock (B3LYP) theory and a large basis set with added polarization and diffuse functions. The results were then extrapolated to higher n using an established dependence of the free energy on cluster size and the free energy for the sublimation of H₂O to bulk ice. A 1-dimensional model of sodium chemistry was then employed to show that spontaneous nucleation to form ice particles (n > 100) should occur between 84 and 89 km in the high-latitude summer mesosphere. The third condition is that other metallic components of meteoric smoke are less effective condensation nuclei, so that the total number of potential nuclei is small relative to the amount of available H₂O. Quantum calculations indicate that this is probably the case for major constituents such as Fe(OH)₂, FeO₃ and MgCO₃.     

IMPACT: an implicit time integration scheme for chemical species and families

The implicit time integration scheme of Stott and Harwood (1993) was proposed as an efficient scheme for use in three-dimensional chemical models of the atmosphere. The scheme was designed for chemistry schemes using chemical families, in which species with short lifetimes are grouped into longer-lived families. Further study with more complex chemistry, more species and reactions showed the scheme to be non-convergent and unstable under certain conditions; particularly for the perturbed chemical scenarios of polar stratospheric winters. In this work the scheme has been improved by revising the treatment of families and the convergence properties of the scheme. The new scheme has been named IMPACT (IMPlicit Algorithm for Chemical Time-stepping). It remains easy to implement and produces simulations that compare well with integrations using more accurate higher order schemes.     

Fog and rain water chemistry at Mt. Fuji: A case study during the September 2002 campaign

Measurements of fog and rain water chemistry at the summit of Mt. Fuji, the highest peak in Japan, as well as at Tarobo, the ESE slope of Mt. Fuji in September 2002. The pH of fog and rain water sampled at Mt. Fuji varied over a range of 4.0–6.8. Acidic fogs (pH < 5.0) were observed at the summit when the air mass came from the industrial regions on the Asian continent. The ratio of [SO₄²⁻]/[NO₃⁻] in the fog water was lower at Tarobo than at the summit. High concentrations of Na⁺ and Cl⁻ were determined in the rain water sampled at the summit, possibly because of the long-range transport of sea-salt particles raised by a typhoon through the middle troposphere. The vertical transport of sea-salt particles would influence the cloud microphysical properties in the middle troposphere. Significant loss of Mg²⁺ was seen in the rain water at the summit. The concentrations of peroxides in the fog and rain water were relatively large (10–105 μM). The potential capacity for SO₂ oxidation seems to be strong from summer to early autumn at Mt. Fuji. The fog water peroxide concentrations displayed diurnal variability. The peroxide concentrations in the nighttime were significantly higher than those in the daytime.