Buchbesprechungen

Ohne Zusammenfassung     

Petrologic constraints on rift-zone processes

The Puu Oo eruption in the middle of Kilauea volcano's east rift zone provides an excellent opportunity to utilize petrologic constraints to interpret rift-zone processes. Emplacement of a dike began 24 hours before the start of the eruption on 3 January 1983. Seismic and geodetic evidence indicates that the dike collided with a magma body in the rift zone. Most of the lava produced during the initial episode of the Puu Oo eruption is of hybrid composition, with petrographic and geochemical evidence of mixing magmas of highly evllved and more mafic compositions. Some olivine and plagioclase grains in the hybrid lavas show reverse zoning. Whole-rock compositional variations are linear even for normally compatible elements like Ni and Cr. Leastsquares mixing calculations yield good residuals for major and trace element analyses for magma mixing. Crystal fractionation calculations yield unsatisfactory residuals. The highly evolved magma is similar in composition to the lava from the 1977 eruption and, at one point, vents for these two eruptions are only 200 m apart. Possibly both the 1977 lava and the highly evolved component of the episode 1 Puu Oo lava were derived from a common body of rift-zone-stored magma. The more mafic mixing component may be represented by the most mafic lava from the January 1983 eruption; it shows no evidence of magma mixing. The dike that was intruded just prior to the start of the Puu Oo eruption may have acted as a hydraulic plunger causing mixing of the two rift-zone-stored magmas.     

Mineralogische Untersuchungen an Lösungsrückständen eines württembergischen Keupergipsvorkommens

Zusammenfassung Die untersuchten Proben stammen aus einem Abbau im unteren Gipskeuper bei Kayh, Kreis Böblingen, Württemberg, Deutschland. Die unlöslichen Rückstände wurden durch Auflösung des Gipses mit NaCl-Lösung gewonnen. Die mineralogische Untersuchung mit dem Mikroskop und mit Hilfe der Röntgenbeugung ergab, daß die Lösungsrückstände überwiegend aus Mineralneubildungen bestehen.In den mikroskopischen Fraktionen herrscht Dolomit vor. Daneben enthalten alle Proben authigene Quarze und Kalifeldspäte. Diese sind im Innern monoklin mit sanidinähnlicher Optik. Auf die (010)-Flächen sind außen trikline Lamellen mit mikroklinartiger Optik aufgewachsen.In allen Tonfraktionen kommt Illit vor, der jedoch in den meisten Proben mengenmäßig von Corrensit übertroffen wird. Aus dem Vorkommen von Pseudomorphosen aus Corrensit nach Glimmer in einer der Proben kann man schließen, daß der Corrensit durch Einwirkung magnesiumreicher Lösungen auf Glimmer entstanden ist. Es ist wahrscheinlich, daß das bei dieser Reaktion freiwerdende Kalium die Neubildung der Kalifeldspäte bewirkt hat. Jedenfalls würde eine solche Reaktion das Fehlen von authigenem Albit erklären.

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Mineralogical study of insoluble residues of gypsum from the Keuper

Summary The samples come from a gypsum quarry situated in the lower part of the gypsum bearing Keuper near Kayh, Württemberg, Germany. The insoluble residues were obtained by dissolving the gypsum in an aqueous solution of NaCl. The mineralogical study with the microscope and with X-ray diffraction has shown that the residues consist almost entirely of authigenic minerals.Dolomite is the prevailing mineral of the microscopic grain size fractions. All samples contain euhedral quartz and potash feldspars which have formed in the sediment after deposition. The latter have optical properties similar to sanidine in the interior of the crystals whereas lamellar overgrowths on the (010) faces exhibit oblique extinction similar to microcline.All of the clay fractions contain illite. In most samples, however, corrensite is the predominant clay mineral. From the occurrence of pseudomorphs of corrensite after a micaceous mineral in one of the samples it may be concluded that corrensite originated by the reaction of mice with solutions rich in magnesium. It is inferred that the potassium liberated by this reaction caused the neoformation of the potash feldspars. This mechanism would explain the total absence of authigenic albite.

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Mit 9 Abbildungen     

Ton,Geoden und Minerale des Barrême von Hoheneggelsen

Zusammenfassung Der Ton wurde röntgenographisch, mikroskopisch und mit der Differentialthermoanalyse untersucht. Aus den Ergebnissen von Beobachtungen in der Natur und petrographischen Untersuchungen an den Geoden können Einzelheiten über ihre Entstehung abgeleitet werden. Insbesondere wird gezeigt, daß aus dem Karbonatgehalt der Geoden der Wassergehalt des Tones zur Zeit der Bildung der Geoden auf einfache Weise berechnet werden kann. Die Minerale in den Geodenspalten, insbesondere der Whewellit, werden beschrieben und in eine Ausscheidungsfolge gegliedert. Die Bildung und Anreicherung der Minerale in den Geodenspalten wird auf Löslichkeitserhöhung durch höheren Druck im Ton im Vergleich zu dem in den Geodenspalten zurückgeführt.     

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.     

Geological structure and kinematics of normal faults in the Otway Basin,Australia, based on quantitative analysis of 3‐D seismic reflection data

The Otway Basin in the south of Victoria, Australia underwent three phases of deformation during breakup of the southern Australian margin. We assess the geometry and kinematics of faulting in the basin by analysing a 3‐D reflection seismic volume. Eight stratigraphic horizons and 24 SW‐dipping normal faults as well as subordinate antithetic faults were interpreted. This resulted in a high‐resolution geological 3‐D model (ca. 8 km × 7 km × 4 km depth) that we present as a supplementary 3‐D PDF (Data S1). We identified hard‐ and soft‐linking fault connections over the entire area, such as antithetic faults and relay ramps, respectively. Most major faults were continuously active from Early to Late Cretaceous, with two faults in the northern part of the study area active until at least the Oligocene. Allan maps of faults show tectonic activity continuously waned over this time period. Isopach maps of stratigraphic volumes quantify the amount of syn‐sedimentary movement that is characteristic of passive margins, such as the Otway Basin. We show that the faults possess strong corrugations (with amplitudes above the seismic resolution), which we illustrated by novel techniques, such as cylindricity and curvature. We argue that the corrugations are produced by sutures between sub‐vertical fault segments and this morphology was maintained during fault growth. Thus, they can be used to indicate the kinematics vector of the fault movement. This evidences, together with left‐stepping relay ramps, that 40% of the faults had a small component (up to 25°) of dextral oblique slip as well as normal (dip‐slip) movement.     

Über einen Keuperton von Zaisersweiher bei Maulbronn

Zusammenfassung Durch röntgenographisehe und differentialthermoanalytische Untersuchungen wurde in einem roten Keuperton (km 3) von Zaisersweiher bei Maulbronn ein quellfähiges chloritisches Mineral (Corrensit) als Hauptbestandteil gefunden, das sick durch doppelten Basisabstand (28 Å) auszeichnet. Daneben treten Illit (Glimmer) und Quarz auf. Nebengemengteile sind Hämatit und Feldspat.Herrn Professor Dr.Carl W. Correns zum 60. Geburtstag gewidmet.