New paleomagnetic results from the Aegean extensional province

Various Oligocene formations from NE Greece (ignimbrites from the Medousa area, rhyolites from Zagradenia, granodiorites from Elatia) show discordant paleomagnetic signatures, in each case indicating small cw (clockwise) rotation and also inclination flattening. Marls from Pithion were partly remagnetized in a present-day field. Samples that contain ancient magnetization components also indicate small cw rotation and inclination flattening. However, the magnetization of andesites from Peplos reflects a considerably larger rotation, likely owing to local tectonics. In the context of previous work in the area, these results are used to propose a subdivision of NE Greece into four structural zones of distinctive rotational behaviour (from east to west): sites in zone 1, east of the Kavala-Xanthi-Komotini fault (KXK), show various cw and ccw (counterclockwise) rotation angles owing to complex kinematics resulting from the interaction of the KXK and the north-Anatolian fault zone. However, zone 2, between the KXK and the Strymon valley, is structurally homogeneous ( 10° cw rotation). The paleomagnetic signature of the Vertiskos massif (zone 3) implies a larger (> 30°) cw rotation, whereas sites in the Vardar basin (zone 4) contain a paleomagnetic signature similar to that of zone 2. This suggests a motion of the Vertiscos massif, a meta-ophiolitic nappe, relative to underlying strata. Indeed, zones 2 and 4 may be parts of the same structural unit which underlies this nappe.     

Escape models of the Alpine-Carpathian-Pannonian region in the light of palaeomagnetic observations

Recent tectonic models of the Alpine-Carpatho-Pannonian region (ALCAPA) assume a large eastward shift of the Transdanubian Range domain, in the Cenozoic. Since palaeomagnetism is one of the most powerful tools in solving geodynamic processes, the authors present an approach to the escape problem by using all available and relevant palaeomagnetic data. This data set demonstrates consistency with models put forward by geologists for Jurassic and older ages. From the mid-Jurassic on the Northern Calcareous Alps (NCA) did not share the rotations of the Transdanubian Range domain and of the Southern Alps. After individual movements from Neocomian to Miocene, the Transdanubian Range domain must have drifted northward in the mid-Miocene up to the Southern margin of the Northern Calcareous Alps, before starting the escape in the geologists' definition.     

The identification of magnetite in limestones using the low-temperature transition

The low-temperature (K₁) transition has been measured in prepared samples with a low concentration of magnetite to test the validity of the technique for identifying magnetite in weakly magnetized rocks. Using an astatic magnetometer, magnetite concentrations as low as 1 part in 100,000 can be satisfactorily detected.Measurements on natural samples show the presence of magnetite in a variety of limestones which are known to have a stable natural remanent magnetization.     

Paleomagnetic investigations in the Thüringer Forest (G.D.R.)

In the Thüringer Forest, the whole “Rotliegende” is well exposed, and was chosen as beginning of a Permian traverse via Czechoslovakia, Austria into Italy. Rockmagnetic experiments established haematite as main carrier of the NRM, except a few localities, where magnetite was found to be present. Sediments and volcanites show consistent ChRM directions. The comparison with KrŠ's (1978) compilation proves a good Permian pole position.     

Palaeomagnetic investigations on the East African rift in Northern Tanzania

Near Lake Manyara and north of Monduli, Northern Tanzania, Precambrian gneisses and Neogene basalts on the East African rift were sampled. Rock magnetic and microscope investigations established coarse and fine grained magnetite as carrier of the NRM in the basalts, and hematite in the gneisses. In all three sections only reversed magnetization directions were found. The Precambrian gneisses show very hard magnetizations which is known to be prefolding and possibly of Proterozoic age.     

Geophysical investigations of large landslides in the Carnic Region of southern Austria

The area under investigation for the past two decades is in the vicinity of the Gailtal lineament, which is the most dominant tectonic feature of the eastern Alps of southern Austria. An area of about 8 km² is in a state of constant instability, as documented by movement of road tracks of several centimetres per year. Geotechnical and surveying techniques have been used to measure these movements in the past but without solving the problem of the mechanism of these failure processes. Geophysical methods (seismic refraction, geoelectrics, and electromagnetics) were applied in order to determine the validity of one of the discussed movement models. In-situ velocity measurements were used to identify different lithologies beneath surficial talus deposits. The thickness of these talus deposits, of about 4–30 m, found by seismic refraction clearly demonstrates that huge ‘blocks’ (i.e. more or less undisturbed lithologic units) within the talus/debris are in close contact with the basement. This basement, which shows lower seismic velocities in different parts combined with low electric resistivities, is obviously strongly disturbed by different failure surfaces. The different gliding velocity of the blocks and the talus/debris deposits leads to a geological model in which huge rock blocks move slowly in relation to the disintegrating basement, whereas the talus/debris deposits move over the surface of these blocks at a higher velocity. The interpretation of these landslide studies is not a straightforward analysis. It is a complex problem with a complex solution, including all information from geotechnical, geophysical, and surveying investigations.     

Petrophysical investigations in the Southern Bohemian Massif (Austria): Data-acquisition, -organisation and-interpretation

Summary The petrophysical parameters Density (p), Susceptibility (SUS), as well as Natural Remanent Magnetisation (NRM) and Koenigsberger ratio (Q_n) were measured on approx. 2600 core samples (magmatic and a few metamorphic rocks) from the Southern Bohemian Massif. These and associated data have been organized into primary and subsidiary dBASE IV databases. The quantity and kind of information now available through the databases are described.40 sampled types of rocks have been statistically analysed and a detailed delimitation of different rocks as well as their varieties is attempted with the aid of various graphic software.The lowest susceptibility values (SUS < 0.1 × 10^–3 SI) were measured for the leucocratic Altenberg and Haibach granites, above it for the acid Eisgarn granite and for aplites. The only fine grained granite with a higher average (M = l.32 × 10^–3 SI) than the other granites is the Schlägl granite.Average values of NRM vary over a range of 10⁴ mA/m. The Altenberg and Haibach granites (fine-to medium-grained, two-mica leucogranites) are again (see SUS) in the group with the lowest values (< 1 mA/m). The average values of coarse-grained, older synorogenic granites (Finger andHöck, 1986), Weinsberg and Engerwitzdorf (medium-to coarse grained) granites, Schlieren granite and Rastenberg granodiorite are generally uniform (< 5 mA/m), with the exception of the stronger remanent magnetism of the Schlieren granite (25 mA/m).The Q_n, values of all investigated coarse grained granites are less than 0.25 (exception: Schlieren granite) whereas the fine-middle grained granites Peuerbach, Schaerding, Schrems and the fine grained granites in general all have Q_n > 1.The densities of all studied granite types vary only from 2600 kg/m³ to the upper limit of 2710 kg/m³ (average of rock types). Therefore consideration of only one petrophysical parameter does frequently not suffise for characterisation of a rock type. However, a combined study of NRM-SUS or p-SUS proved to be useful in many cases e.g. petrophysical distinction between Schrems granite and Mauthausen granite.

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Petrophysikalische Untersuchungen in der südlichen Böhmischen Masse (Österreich): Daten-Akquisition, -Organisation und -Interpretation

Zusammenfassung Die petrophysikalischen Parameter Dichte (p), Suszeptibilität (SUS), sowie Natürliche Remanente Magnetisierung (NRM) und Königsberger Faktor (Q_n) wurden an rund 2600 Bohrkernen (Magmatite und einige Metamorphite) aus der Böhmischen Masse ermittelt. Diese und damit im Zusammenhang stehende Daten wurden in einer dBASE IV Hauptdatenbank und gekoppelten Nebendatenbestanden organisiert. Es wird die Art von Information, die über die Datenbank nun zugänglich ist näher erläutert. 40 beprobte Gesteinstypen werden einer statistischen Analyse unterzogen und unter zu Hilfenahme diverser Graphiksoftware wird eine detailliertere Abgrenzung der einzelnen Gesteine und ihrer Varietaten versucht.Die geringsten Suszeptibilitätswerte (SUS < 0.1 × 10^–3 SI) wurden an Proben der leukokraten Altenberger und Haibacher Granite, darüber hinaus auch an Kernen des sauren Eisgarner Granits und der Aplite gemessen. Der einzige feinkörnige Granit mit einem überdurchschnittlichen Mittelwert (M = 1.32 × 10^–3 SI) im Vergleich zu anderen Graniten ist der Schlägl Granit.Die errechneten Mittelwerte der NRM streuen über einen Bereich von 10⁴ mA/m. Der Altenberger und der Haibacher Granit (fein- bis mittelkörnige Zweiglimmergranite) weisen auch hier wieder die geringsten Werte (< 1 mA/m) auf. Die Gruppe der grobkörnigen, älteren synorogenen Granite (Finger undHöck, 1986), nämlich Weinsberger und Engerwitzdorfer (mittel- bis grobkörnig), Schlierengranit und Rastenberger Granodiorit bleiben mit ihren NRM Werten unter 5 mA/m mit Ausnahme des offensichtlich stärker remanent magnetisierten Schlierengranits (25 mA/m).Alle untersuchten grobkörnigen Granite weisen Q_n Werte < 0.25 (Ausnahme: Schlierengranit) auf, während hingegen die fein- bis mittelkörnigen Peuerbacher, Schärdinger und Schremser Granit, sowie die Feinkorngranite im allgemeinen, alle Q_n > 1 erreichen.Die Dichten der verschiedenen Granite variieren nur von 2600 kg/m³ bis 2710 kg/m³ (Gesteinsmittelwerte). Dies zeigt, daß die Betrachtung nur eines einzigen petrophysikalischen Parameters in vielen Fällen nicht alleine ausreicht um ein Gestein petrophysikalisch eindeutig zu bestimmen. Vielmehr stellte sich für eine Charakterisierung der Gesteine eine kombinierte Untersuchung von NRM-SUS oder p-SUS oft als zielführend heraus, wie z.B. im Falle des Schremser Granits und des Mauthausener Granits.

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With 15 Figures