Age, geodynamic setting, and mantle enrichment processes of a K-rich intrusion from the Meissen massif (northern Bohemian massif) and implications for related occurrences from the mid-European Hercynian

The plutonic complex of the Meissen massif (northern margin of the Bohemian massif) comprises dioritic to mainly monzonitic and granitic rocks. The diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series. The chemical signatures of less crustally contaminated diorites are similar to arc-related shoshonitic rocks derived from continental lithospheric mantle (CLM) sources previously enriched by subduction of altered oceanic crust. Laser step heating ⁴⁰Ar/³⁹Ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329.1±1.4 to 330.4±1.4?Ma and from 330.4±2.1 to 330.6±1.8?Ma, respectively. These cooling ages are indistinguishable from sensitive highresolution ion microprobe (SHRIMP) ²³⁸U/²⁰⁶Pb intrusion ages measured on magmatic zircon rims from the monzonite (Nasdala et al., submitted). This shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent Saxonian Erzgebirge by approximately 20?Ma. The shoshonitic magmas intruded during strike-slip tectonism along the Elbe valley zone. The enrichment of their mantle sources may be of Upper Devonian/Lower Carboniferous age or older. Intrusions of shoshonitic to ultra-potassic (K-rich) rocks during the Upper Visean/Namurian are widespread in the Moldanubian zone. Based on similar ages and structural relationships a similar post-collisional setting to the Meissen shoshonitic rocks can be demonstrated. Most of these occurrences cut high-grade nappe units which were subducted during the Upper Devonian/Lower Carboniferous. In contrast to the Meissen massif, at least the ultra-potassic members of the Central and the South Bohemian batholiths were derived from CLM sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material. Despite the similar post-collisional geodynamic setting of the K-rich intrusions, different enrichment processes generated mid-European Hercynian CLM sources with heterogeneous major and trace element and isotopic signatures.     

Frontal substructures within the planetary boundary layer

A two-dimensional mesoscale model, extended by a TKE closure for the subgrid-scale terms and coupled with a soil model, is used to investigate the role of the Planetary Boundary Layer (PBL) for the development and the substructures of two different types of cold fronts. The effects of turbulent friction, large-scale (geostrophic) forcing and the diurnal variation of the terms of the surface energy balance (SEB) equation on the frontal development are studied by 10 different model runs. The ageostrophic cross-frontal circulation in the lowest two kilometres of a cold front results from friction as well as from large-scale forcing. The first one dominates the PBL processes and causes a special boundary-layer structure, which becomes apparent through the existence of seven characteristic zones defined for the x-z cross sections of potential temperature. The arrangement of these characteristic zones depends on the sense of rotation of the frictionally induced part of the ageostrophic circulation and hence on the direction of the along-front jet within the boundary layer. The daytime increase of the terms of the SEB equation for a midlatitude midsummer case leads to a strong enhancement of the frictionally induced cross-frontal circulation. The arrangement of the seven characteristic zones, however, is approximately conserved.     

The case for a martian origin of the shergottites: nitrogen and noble gases in EETA 79001

Nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite EETA 79001. A nitrogen component trapped in the glass, but not present in the matrix, has a δ¹⁵N value at least as high as +190‰. Ratios of⁴⁰Ar/¹⁴N and¹⁵N/¹⁴N in the glass are consistent with dilution of a martian atmospheric component (δ¹⁵N = 620 ± 160‰,⁴⁰Ar/¹⁴N= 0.33 ± 0.03) by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock. Trapped noble gases in the glass reproduce, within error, the elemental and isotopic compositions measured in Mars' atmosphere by Viking, and are in general agreement with previous measurements except for much lower abundances of neutron-generated krypton and xenon isotopes. The most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the EETA 79001 glass, and that this meteorite, and thus the shergottites and probably the nakhlites and chassignites as well, originated on Mars.Nitrogen in the non-glassy matrix of EETA 79001 amounts to less than 0.5 ppm and has a spallation-corrected δ¹⁵N value in the range 0 to ?20‰; it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen. Spallogenic noble gases yield single-stage exposure ages between 400,000 and 900,000 years, depending on irradiation geometry. Trapped argon may have an unusually low³⁶Ar/³⁸Ar ratio. Trapped krypton, except for a small excess at⁸⁰Kr, is smoothly mass-fractionated with respect to either terrestrial or chondritic Kr. The trapped xenon composition is consistent with addition of neutron-capture, radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric Xe. The elemental⁸⁴Kr/¹³²Xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio.     

An FTIR product study of the photooxidation of dimethyl disulfide

The products of the 254 nm photolysis of ppm levels of DMDS have been studied as a function of the O₂ partial pressure at 760 Torr (N₂ + O₂) and 298±2 K. The major sulfur containing compounds detected were SO₂ and CH₃SO₃H (methane sulfonic acid, MSA) and the major carbon containing compounds were CO, HCHO, CH₃OH and CH₃OOH (methyl hydroperoxide). Within the experimental error limits the observed sulfur and carbon balances were approximately 100%. CH₃OOH has been observed for the first time in such a photooxidation system. Its observation provides evidence for the formation of CH₃ radicals by the further oxidation of the CH₃S radicals formed in the primary photolysis step.From the behavior of the DMDS photolysis products as a function of the O₂ partial pressure, O₃ concentration and added OH radical source it is postulated that the further reactions of CH₃SOH (methyl sulfenic acid), formed in the reaction OH + CH₃SCCH₃ CH₃SOH + CH₃S, are the main source of MSA in the 254 nm photolysis of DMDS.Some of the possible implications of the results of this study for the degradation mechanisms of other atmospherically important organic sulfur compounds, in particular DMS, are briefly considered.     

Near UV absorption spectra and photolysis products of difunctional organic nitrates: Possible importance as NO x reservoirs

Difunctional organic nitrates are important products of the atmospheric reaction of NO₃ radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH₃CH(ONO₂)CH₂(ONO₂); 1,2-butandiol dinitrate, CH₃CH₂CH(ONO₂)CH₂(ONO₂); 2,3-butandiol dinitrate, CH₃CH(ONO₂)CH(ONO₂)CH₃;cis 1,4-dinitrooxy-2-butene, CH₂(ONO₂)CH=CHCH₂(ONO₂); 3,4-dinitrooxy-1-butene, CH₂(ONO₂CH(ONO₂)CH=CH₂; -nitrooxy acetone, CH₃COCH₂(ONO₂); 1-nitrooxy-2-butanone, CH₃CH₂COCH₂(ONO₂); 3-nitrooxy-2-butanone, CH₃CH(ONO₂)COCH₃.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO₂ is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO _y in the atmosphere, especially during the night, is briefly discussed.     

Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO3 Chemistry in the City Air

In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C₂–C₁₀ aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO₂ converter were used for measuring NO and NO₂. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5ppbv para-cresol and 4.4 ppbv benzaldehyde, in comparison with themeasured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first timeselectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO_x ratios from 0.6 up to 3.0ppbC/ppb in the traffic tunnel air and 3.4± 0.5 in the city air of Wuppertal were obtained. From the observed para-cresol/toluene and ortho-cresol/toluene ratios in the city air, evidence was found thatalso during daytime NO₃ radical reactions play an important role in urban air.     

Origin of lunar fragmental matrix breccias—Highly siderophile element constraints

Ejecta at North Ray crater (Apollo 16) sampled a unique section of the lunar highlands not accessible at most other landing sites and provide important constraints on the composition of late accreted materials. New data on multiple aliquots of four fragmental matrix breccias and a fragment‐laden melt breccia from this site display a variety of highly siderophile element patterns which may represent the signatures of volatile element‐depleted carbonaceous chondrite‐like material, primitive achondrite, differentiated metal, and an impactor component that cannot be related to known meteoritic material. The latter component is prevalent in these rocks besides characterized by depletions in Re and Os compared to Ir, Ru and Pt, chondritic Re/Os, and a gradual depletion of Pd and Au. The observed characteristics are more consistent with fractionations by nebular processes, like incomplete condensation or evaporation, than with lunar crustal processes, like partial melting or volatilization. The impactor signature preserved in these breccias may stem from primitive meteorites with a refractory element composition moderately different from known chondrites. The presence of distinct impactor components within the North Ray crater breccias together with observed correlations of characteristic element ratios (e.g., Re/Os, Ru/Pt, Pd/Ir) in different impact lithologies of four Apollo landing sites constrains physical mixing processes ranging from the scale of gram‐sized samples to the area covered by the Apollo missions.