Noble gases in the St. Mesmin chondrite: Implications to the irradiation history of a brecciated meteorite

Helium, neon and argon were analysed in matrix samples and in different clasts of the polymict-brecciated LL-chondrite St. Mesmin. All clasts have high K-Ar ages with a mean value of4.40 ± 0.26Ga. One exotic H-group xenolith, however, has a K-Ar age of only1.36 ± 0.05Ga. The low age indicates that the St. Mesmin breccia was compacted to its present structure relatively late in its history and that the St. Mesmin meteorite developed from regolith material on the meteorite's parent body. This is further demonstrated by the high concentrations of solar noble gases in the matrix and the cosmic ray pre-exposure of one individual clast.     

Mineralogische Untersuchungen an fünf Bodenprofilen über Basalt,Muschelkalk und Buntsandstein

Zusammenfassung Drei Bodenprofile caber Basalt, eins über Trochitenkalk und eins über Buntsandstein wurden mineralogisch untersucht. Die Schlämmanalyse brachte sehr ähnliche Ergebnisse in der Korngrößenverteilung der über Basalt liegenden Böden, während die beiden anderen Profile ihnen erst an der Erdoberfläche ähnlich wurden. Die mikroskopische Untersuchung zeigt, wie sich die Minerale im Boden verhalten und welche nicht aus dem anstehenden Gestein stammen. Die Tonfraktionen wurden mit Debye-Scherrer- und Texturaufnahmen röntgenograpbisch untersucht. Dabei wurde Halloysit als einziges Tonmineral in den Basaltprofilen und in mürbem Gestein festgestellt. Im Trochitenkalk wurden Illit und Montmorillonit, im Boden darüber gleichfalls Illit gefunden. Im Boden über Buntsandstein ist neben Kaolinit etwas Illit an Tonmineralen nachgewiesen wurden.Herrn Professor Dr.Carl W. Correns zum 60. Geburtstag gewidmet.     

Zur Charakterisierung suspendierter Wasserinhaltsstoffe. Teil 2: Erste Ergebnisse der praktischen Anwendung der Analysenmethoden

Nachdem in Teil 1 (Schultz ) die Bedeutung der Feststoffe für den Betrieb von Wasseraufbereitungsanlagen und Analysenmethoden zur Charakterisierung der Feststoffe diskutiert wurden, enthält Teil 2 die Ergebnisse von Untersuchungen an einem ausgewählten Vorfluter. Verschiedene Analysenmethoden werden getestet, miteinander verglichen und ihre Eignung zur Einschätzung des Leistungsverhaltens der Aufbereitungsanlagen überprüft.     

Allan Hills 77081—an unusual stony meteorite

Allan Hills (ALHA) 77081 is achondritic in texture while the mineral composition and the chemistry are chondritic with the exception of a few elements. An assignment to one specific group of ordinary chondrites is therefore difficult. In many respects this meteorite is similar to the unusual stone meteorite Acapulco. The REE pattern of ALHA 77081 is essentially flat and the distribution ratios of siderophile elements between metal and silicates are high compared to ordinary chondrites.Gas retention ages are 3.5±0.5 AE for U, Th-He and 4.50±0.15 AE for K-Ar. In spite of the high degree of recrystallisation the meteorite contains trapped noble gases in amounts comparable to type 4 chondrites.Cosmic ray tracks and spallogenic noble gases indicate a small preatmospheric radius of about 2–3 cm. Spallogenic nuclides produced by solar cosmic rays or stopped solar flare ions may be present.     

Scaling the Microphysics Equations and Analyzing the Variability of Hydrometeor Production Rates in a Controlled Parameter Space

A set of microphysics equations is scaled based on the convective length and velocity scales.Comparisons are made among the dynamical transport and various microphysical processes.From the scaling analysis,it becomes apparent which parameterized microphysical processes present off-scaled influences in the integration of the set of microphysics equations. The variabilities of the parameterized microphysical processes are also studied using the approach of a controlled parameter space.Given macroscopic dynamic and thermodynamic conditions in different regions of convective storms,it is possible to analyze and compare vertical profiles of these processes.Bulk diabatic heating profiles for a cumulus convective updraft and downdraft are also derived from this analysis. From the two different angles,the scale analysis and the controlled-parameter space approach can both provide an insight into and an understanding of microphysics parameterizations.     

Detailed investigation of preserved maar structures by combined geophysical surveys

The detection of completely preserved maar structures is important not only for underground mapping but also for paleoclimate research because laminated maar lake sediments may contain a very detailed archive of climate history. Objective evidence for the existence of such structures can only be provided by geophysics and boreholes. The combination of gravity and magnetic ground surveys appears to be an excellent tool to detect and identify buried maar structures. Their prominent properties are an almost circular gravity minimum corresponding to a crater filled with limnic sediments of low density, and a magnetic anomaly caused by a pyroclastic or basaltic body in the diatreme which indicates the volcanic character. Seismic measurements provide the most detailed information about the internal structure of the maar sediments. Zones of low seismic reflectivity and very low density represent sediments of the late maar-lake period. The early lake period is indicated by debris flow deposits and turbidites represented by seismic reflectors. The seismic sections clearly reveal the bowl-like structure of the maar. Outside this bowl-like structure, there are only a few reflections, which represent the basement. Taking into account the shape of the gravity anomaly, seismic information allows geometrical modelling of the maar structure. Optimal drilling sites can be selected based on the results of geophysical surveying. Comparing the results of combined geophysical surveys above two maar structures of different ages yields a marked similarity in their geophysical pattern.Editorial responsibility: J McPhie     

Reflections from a randomly grooved interface: ultrasonic modelling and finite-diff erence calculation1

This study utilizes ultrasonic water tank modelling to examine the complexities which can result when seismic energy is diffracted by even a simple 3D interface structure. Ultrasonic laboratory modelling is carried out in our in-house water tank, using an aluminum block to simulate very simple ocean-bottom topography. The topography consists of parallel depressions which simulate valleys running parallel to a mid-ocean spreading ridge. This study shows that the phase and amplitude of primary ocean-bottom reflections can vary strongly with the azimuth of propagation. The trailing energy coda also varies dramatically as a function of propagation direction, showing the importance of developing a seismic model which includes the full 3D azimuthal distribution of interface structure.     

Radiogenic, fissiogenic and nucleogenic noble gases in zircons

The concentrations and isotopic compositions of argon, krypton and xenon have been determined in a grain size suite of zircons separated from pyroxene syenite of the Botnavatn Igneous Complex, southwestern Norway. The UPb systematics of these zircons has been studied previously.Kr and Xe are mixtures of fissiogenic gas from the spontaneous fission of²³⁸U and a component with atmospheric isotopic composition. From correlation diagrams the fissiogenic component is determined to be:⁸³Kr :⁸⁴Kr :⁸⁶Kr = (4.6 ± 1.3) : (11.0 ± 2.0) : 100 and¹²⁹Xe :¹³¹Xe :¹³²Xe :¹³⁴Xe :¹³⁶Xe = (0.6 ± 0.3) : (8.8 ± 0.2) : (56.8 ± 0.3) : (82.8 ± 0.4) : 100. The fissiogenic¹³⁶Xe/⁸⁶Kr is 6.0 ± 0.4.The Ar isotopic composition shows radiogenic⁴⁰Ar and a small excess of³⁸Ar. The excess³⁸Ar of about 1 × 10⁻¹¹ cm³ STP/g can be explained by reactions of α-particles with chlorine. Asymmetric fission of²³⁸U which has been postulated to cause argon isotope anomalies in U-rich minerals is unnecessary to explain the observed³⁸Ar concentrations.UXe ages are (1.19 ± 0.07) Ga, in agreement with UPb ages. However, if the recoil loss of fissiogenic Xe is considered the UXe ages of these zircons are about 1.53 Ga, which is comparable with the KAr ages and some RbSr ages observed in basement rocks in this region. The uncertainty of the product of fission yield times spontaneous fission decay constant of²³⁸U prevents to decide which age is the true crystallization age.