Neue Vorstellungen über den Tiefbau von Vorsenken

Zusammenfassung Der geologische Tiefenbau und die Entwicklungsgeschichte der Kopetdag-, Terek-Kaspi-, Indol-Kuban- und Karpaten-Vorsenke sind ähnlich. Es zeigt sich, daß die genannten Vorsenken keine Zonen kurzzeitiger Durchbiegungen sind, die sich in der orogenen Schlußentwicklungsetappe des alpidischen Faltengebietes gebildet haben, sondern daß sie langlebige negative Strukturen darstellen. Die Intensität ihrer Durchbiegung zu Beginn des alpidischen geotektonischen Zyklus (in der Jura und Kreidezeit) ist mit der Größe der Absenkung im Neogen-Quartär vergleichbar. Im Verlaufe des gesamten alpidischen Zyklus entwickelten sich die Senken posthum.Überall dort, wo notwendige geophysikalische Untersuchungen durchgeführt wurden, wurde unter diesen Senken unterhalb eines mächtigen alpidischen Gesteinskomplexes ein genauso mächtiger Sedimentkomplex variszischen Alters festgestellt. Territorial fallen die Zonen der maximalen Mächtigkeiten des variszischen und alpidischen Gesteinskomplexes zusammen.

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Structure and development of the Pre-Copetdag, Terek-Caspian, Indol-Kuban, and Pre-Carpathian fore deeps are similar. The fore deeps were not zones of short term subsidence during the final stage of orogenic development of the Alpine folded belt, but they were long term subsidence zones. The rates of subsidence at the beginning of the Alpine geotectonic cycle (during Jurassic and Cretaceous) and at the end of the cycle (during Neogene and Quaternary) are comparable.Wherever geophysical investigations were carried out in this zone, beneath the Alpine sediments a Hercynian sediment complex of equal thickness was found. The areas of maximum thickness in both complexes coincide.

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Résumé La structure géologique et le développement historique des avant-fosses de Copetdag, Terek-Caspienne, Indol-Kouban et des Carpates sont semblables. Il appert que ces dépressions ne sont pas des zones d'inflexion de courte durée qui se sont formées pendant l'étape finale du plissement alpin, mais qu'ils présentent des structures négatives de longue durée. L'intensité de leur affaissement au commencement du cycle géotectonique alpin (au Jurassique et au Crétacé) est comparable, en grandeur, avec celui de la période néogène-quaternaire. Au cours de l'ensemble du cycle alpin, les dépressions se sont développées de façon posthume.Partout où ont eu lieu des explorations géophysiques, nous avons découvert sous ces avant-fosses, un épais complexe de roches alpines, et sous elles un complexe aussi puissant de sédiments varisques. Spatialement les zones des puissances maximum des complexes alpins et varisques coïncident.

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Cytochrome P4501A expression,chemical contaminants and histopathology in roach,goby and sturgeon and chemical contaminants in sediments from the Caspian Sea,Lake Balkhash and the Ily River Delta,Kazakhstan

Roach, goby and sturgeon were examined for cytochrome P4501A (CYP1A) expression and histopathology, in relation to contaminant burdens in fish and sediment. Gradients of induction of CYP1A were observed. Roach from the Ural and Ily River Deltas and roach and goby from the two stations nearest the Caspian Sea oil fields displayed higher levels of CYP1A expression in several organs than was observed in fish from further offshore. Great sturgeon and Russian sturgeon showed higher levels of CYP1A expression than was seen in starred sturgeon and gobies in the Ural delta. No fish showed evidence of contaminant-related histopathologies in the organs examined, despite the elevated CYP1A levels. Low levels of polychlorinated biphenyls and elevated levels of inshore and riverine petroleum hydrocarbons from these habitats suggest that this ongoing hydrocarbon exposure, and that from natural sources and long-term oil exploration on the Northeastern Caspian shore, contributed to the CYP1A induction observed.     

Time constraints for Mesoproterozoic upper amphibolite facies metamorphism in NW Namibia: a multi-isotopic approach

This study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb–Pb stepwise leaching technique on garnet and rutile, U–Pb multi-grain analysis on rutile, Sm–Nd–Lu–Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar–Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak. Our age data can be integrated with petrological constraints to provide a more complete understanding of the metamorphic cycle. Our pre-peak metamorphic zircon ages, peak metamorphic garnet ages and peak to late peak metamorphic amphibole ³⁹Ar–⁴⁰Ar ages bracket the upper amphibolite facies metamorphic event including hydration or dehydration processes into a time span of only ca. 20 Ma. The age data obtained by peak metamorphic mineral analyses cluster around 1340–1320 Ma. Based on age data and field observation, we interpret the upper amphibolite facies metamorphism as a large-scale regional mid-crustal event. Spot analyses of inherited zircon cores obtained by SHRIMP reflect the sedimentary origin of the respective rocks of the Orue Unit and derivation from Palaeoproterozoic protoliths. The metamorphic rocks south of the anorthositic Kunene Intrusive Complex (KIC) have previously been ascribed to the Palaeoproterozoic Epupa Complex at the SW margin of the Congo craton and were thus thought to be older than the Mesoproterozoic KIC. Our data show that the high-grade metamorphic overprint took place 30–50 Ma after emplacement of the KIC. Rutile growth ages of 1248 Ma in one sample reflect fluid activity which seems to be a local phenomenon since there is no other evidence of geological activity throughout the Orue Unit at that time. The rutile ages predate the emplacement of satellite intrusions in that area by 30 Ma and there is no causal relation between these two events.     

Effects of trench-zone scattering on receiver functions over a subduction zone: A 3-D finite-difference modelling study

As Morozov [Morozov, I. B. (2004). Crustal scattering and some artefacts in receiver function images. Bull. Seismol. Soc. Am., 94 (4), 1492–1499.] suggested, for a teleseismic array targeting subducting crust in a zone of active subduction, scattering from the strong horizontal velocity heterogeneity beneath the trench zone itself produces subhorizontally-propagating waves that should be observed as coherent dipping events in receiver functions (RF). Due to similar RF delay times and moveouts, these events could be difficult to distinguish from backscattered P- and S-wave modes. To further verify this suggestion, we performed a full-waveform, 3-D visco-elastic finite-difference modelling of teleseismic wave propagation within a simplified model of a subduction zone. The synthetics show strong scattering from the area beneath the trench, dominated by the mantle and crustal P-waves propagating at 6.2–8.1 km/s and slower. These scattered waves occupy the same time and moveout intervals as the backscattered converted modes, and also have similar amplitudes. Although their amplitude decay characters are different, the uncertainty in the knowledge of the velocity and density structure of the subduction zone could make distinguishing between these modes difficult. However, under minimal assumptions, recent observations of receiver function amplitudes decreasing away from the trench support the interpretation of (sub-) trench-zone scattering.Although still limited in its representation of crustal heterogeneity, 3-D modelling suggests that scattering from near-Moho crustal structures plays a key role in the formation of teleseismic wavefields. Recognition of scattered noise in teleseismic records could help to constrain major crustal structures, particularly those with strong horizontal velocity contrasts at near-Moho depths, such as crustal sutures, subduction fault zones, and mountain roots. Matching of the observed arrivals with wavefield synthetics could help constrain the locations and parameters of such structures and also help substantiate the interpretations.     

Thorite versus huttonite: stability, electronic properties and X-ray emission spectra from first-principle calculations

The structural, electronic properties and stability of thorium orthosilicate ThSiO₄ polymorphs: thorite and huttonite are investigated by means of the full-potential linearized augmented-plane-wave method with the generalized gradient approximation for the exchange-correlation potential (FLAPW-GGA). The forbidden gaps of thorite and huttonite are estimated at about 7.8 and 7.6 eV, respectively. It is found that Th5f states in ThSiO₄ partially overlap with occupied O2p bands. The data obtained showed that thorite is more stable than huttonite; in turn both ThSiO₄ polymorphs are unstable with respect to their constituent binary oxides (thorianite ThO₂ and α-quartz SiO₂) in agreement with the experiments. The theoretical shapes of X-ray emission (XES) (Si,O)Kα,β spectra for thorite, huttonite as well as for SiO₂ and ThO₂ are calculated and discussed. We show that the XES spectroscopy near the (Si,O)K edge may be very useful technique not only for detailed investigation of the bulk-electronic structure of Th silicates but also for the phase analysis of complex mineral samples containing these species.     

Raman spectroscopy of water tracer diffusion in zeolite single crystals

The water tracer diffusion in single crystals of natrolite, scolecite, mesolite, heulandite, and chabazite has been studied by Raman micro-spectroscopy. A model of water tracer diffusion is proposed. The H₂O, HDO, and D₂O molecule concentrations are calculated for a crystal of orthorhombic symmetry on deuteration of the initial H₂O-sample. A way is shown to find the diffusion coefficients, the constant of equilibrium, and the deuteron-proton exchange rate from experimental data. The water diffusion coefficients for natrolite placed in liquid D₂O appeared to be 1.5–2 times higher than those for a sample in vaporous D₂O. For natrolite at room temperature, 1.5–1.6 times higher water diffusion occurs along [001] than along [110].