Provenance and depositional environment of Rhenohercynian synorogenic greywackes from the Giessen Nappe,Germany     

P. A. Floyd  B. E. Leveridge  W. Franke  R. Shail  W. Dörr 《International Journal of Earth Sciences》1990,79(3):611-626

The Giessen Nappe of the south-eastern Rhenish Massif can be subdivided into a northern group and southern group of Frasnian-?Lower Carboniferous greywackes that differ slightly in their sedimentology, clast petrography, heavy mineral assemblages and bulk geochemistry. Petrographic and geochemical tectonic setting discrimination diagrams indicate that both the northern and the southern Giessen Greywacke groups were derived from a predominantly acidic continental arc source. However, due to the nature of basin development, generation of significant volumes of acidic arc material as a result of southwards directed subduction of Rhenohercynian oceanic crust is considered unlikely. A large part of the arc source may have been contributed by earlier, predominantly acidic, Precambrian terranes together with minor basic igneous and sedimentary components.  相似文献   

Structural evolution and strike-slip tectonics off north-western Sumatra     

Kai Berglar  Christoph Gaedicke  Dieter Franke  Stefan Ladage  Frauke Klingelhoefer  Yusuf S. Djajadihardja 《Tectonophysics》2010,480(1-4):119-132

Based on new multi-channel seismic data, swath bathymetry, and sediment echosounder data we present a model for the interaction between strike-slip faulting and forearc basin evolution off north-western Sumatra between 2°N and 7°N. We examined seismic sequences and sea floor morphology of the Simeulue- and Aceh forearc basins and the adjacent outer arc high. We found that strike-slip faulting has controlled the forearc basin evolution since the Late Miocene. The Mentawai Fault Zone extends up to the north of Simeulue Island and was most probably connected farther northwards to the Sumatran Fault Zone until the end of the Miocene. Since then, this northern branch jumped westwards, initiating the West Andaman Fault in the Aceh area. The connection to the Mentawai Fault Zone is a left-hand step-over. In this transpressional setting the Tuba Ridge developed. We found a right-lateral strike-slip fault running from the conjunction of the West Andaman Fault and the Tuba Ridge in SSW-direction crossing the outer arc high. As a result, extrusion formed a marginal basin north of Simeulue Island which is tilted eastwards by uplift along a thrust fault in the west. The shift of strike-slip movement in the Aceh segment is accompanied by a relocation of the depocenter of the Aceh Basin to the northwest, forming one major Neogene unconformity. The Simeulue Basin bears two major Neogene unconformities, documenting that differences in subsidence evolution along the northern Sumatran margin are linked to both forearc-evolution related to subduction processes and to deformation along major strike-slip faults.  相似文献   

Distribution of radioactive elements in three progressively metamorphosed pelite series of the Bohemian Massif     

Jiří Fiala  Věra Vaňková  Milan Krešl  Werner Franke  Reviewer M. Chlupáčová  J. Losert 《Studia Geophysica et Geodaetica》1980,24(1):65-87

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Geodynamic evolution of the European Variscan fold belt: palaeomagnetic and geological constraints     

J. A. Tait  V. Bachtadse  W. Franke  H. C. Soffel 《International Journal of Earth Sciences》1997,86(3):585-598

The Variscan fold belt of Europe resulted from the collision of Africa, Baltica, Laurentia and the intervening microplates in early Paleozoic times. Over the past few years, many geological, palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt. Whereas it is now fairly well established that Avalonia drifted from the northern margin of Gondwana in Early Ordovician times and collided with Baltica in the late Ordovician/early Silurian, the nature of the Gondwana derived Armorican microplate is more enigmatic. Geological and new palaeomagnetic data suggest Armorica comprises an assemblage of terranes or microblocks. Palaeobiogeographic data indicate that these terranes had similar drift histories, and the Rheic Ocean separating Avalonia from the Armorican Terrane Assemblage closed in late Silurian/early Devonian times. An early to mid Devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow Rhenohercynian basin which closed progressively between the late Devonian and early Carboniferous. In this contribution, we review the constraints provided by palaeomagnetic data, compare these with geological and palaeobiogeographic evidence, and present a sequence of palaeogeographic reconstructions for these circum-Atlantic plates and microplates from Ordovician through to Devonian times.  相似文献   

Adaptive unstructured grid finite element simulation of two-dimensional magnetotelluric fields for arbitrary surface and seafloor topography   总被引：7，自引：0，他引：7  

Antje Franke  Ralph-Uwe Börner  Klaus Spitzer 《Geophysical Journal International》2007,171(1):71-86

We present an adaptive unstructured triangular grid finite element approach for effectively simulating plane-wave diffusive electromagnetic fields in 2-D conductivity structures.
The most striking advantage of irregular grids is their potential to incorporate arbitrary geometries including surface and seafloor topography. Adaptive mesh refinement strategies using an a posteriori error estimator yield most efficient numerical solutions since meshes are only refined where required.
We demonstrate the robustness of this approach by comparison with analytical solutions and previously published numerical simulations. Maximum errors may systematically be reduced to, for example, 0.8 per cent for the apparent resistivity and 0.2° in the phase.
An additional accuracy study of the thickness of the air layer in E-polarization suggests to keep a minimum thickness depending on lateral conductivity contrasts within the earth.
Furthermore, we point out the new quality and flexibility of our simulation technique by addressing two marine magnetotelluric applications. In the first case, we discuss topographic effects associated with a synthetic sinusoidal sea bottom model and in the second case, we show a close-to-reality scenario using real bathymetry data from the East Pacific Rise at 17°S.  相似文献   

<Emphasis Type="Italic">In memoriam</Emphasis> Wolfgang Engel     

Wolfgang Franke 《International Journal of Earth Sciences》2007,96(4):793-793

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Corrosion enhancement of an undersea repeater due to the hall effect     

Franke  E. 《Oceanic Engineering, IEEE Journal of》1979,4(3):89-93

The analysis of the failure mechanism of an undersea telecommunication repeater has pointed to the corrosion-accelerating electric current generated by the Hall effect. The interaction between the earth's magnetic field and the moving ionic sea water of the Gulf Stream produced an electric potential on the outer conductor of the coaxial cable. With an outer-conductor fracture there was a net unbalance of induced circulating electrical current in each repeater section. This paper considers the velocity profile of the Gulf Stream across the cable route, measured Hall potentials on other cable systems, the interfacial resistance of a repeater housing in sea water, and the continuity of the cable outer conductor to show that the necessary conditions for corrosion acceleration were indeed satisfied.  相似文献   

Variations in bottom water activity at the southern Argentine margin: indications from a seismic analysis of a continental slope terrace     

Jens Gruetzner  Gabriele Uenzelmann-Neben  Dieter Franke 《Geo-Marine Letters》2011,31(5-6):405-417

Continental slope terraces at the southern Argentine margin are part of a significant contourite depositional system composed of a variety of drifts, channels, and sediment waves. Here, a refined seismostratigraphic model for the sedimentary development of the Valentin Feilberg Terrace located in ~4.1?km water depth is presented. Analyzing multichannel seismic profiles across and along this terrace, significant changes in terrace morphology and seismic reflection character are identified and interpreted to reflect variations in deep water hydrography from Late Miocene to recent times, involving variable flow of Antarctic Bottom Water and Circumpolar Deep Water. A prominent basin-wide aggradational seismic unit is interpreted to represent the Mid-Miocene climatic optimum (~17?C14?Ma). A major current reorganization can be inferred for the time ~14?C12?Ma when the Valentin Feilberg Terrace started growing due to the deposition of sheeted and mounded drifts. After ~12?Ma, bottom water flow remained vigorous at both margins of the terrace. Another intensification of bottom flow occurred at ~5?C6?Ma when a mounded drift, moats, and sediment waves developed on the terrace. This may have been caused by a general change in deep water mass organization following the closure of the Panamanian gateway, and a subsequent stronger southward flow of North Atlantic Deep Water.  相似文献   

A combined study of radar facies,lithofacies and three‐dimensional architecture of an alpine alluvial fan (Illgraben fan,Switzerland)          下载免费PDF全文

Daniel Franke  Jens Hornung  Matthias Hinderer 《Sedimentology》2015,62(1):57-86

Alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development. Economically, they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems. The interpretation of these archives and the evaluation of their reservoir architecture, however, are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult. This problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high‐resolution subsurface analytical techniques. To overcome this limitation of standard outcrop–analogue studies, a geophysical survey of an alpine alluvial fan was performed using ground‐penetrating radar to devise a scaled three‐dimensional subsurface model. Radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three‐dimensional model of the sedimentary architecture and identify evolutionary fan stages. The Illgraben fan in the Swiss Alps was selected as a case study and a network of ca 60 km sections of ground‐penetrating radar was surveyed. Seven radar facies types could be distinguished, which were grouped into debris‐flow deposits and stream‐flow deposits. Assemblages of these radar facies types show three depositional units, which are separated by continuous, fan‐wide reflectors; they were interpreted as palaeo‐surfaces corresponding to episodes of sediment starvation that affected the entire fan. An overall upward decline in the proportion of debris‐flow deposits from ca 50% to 15% and a corresponding increase in stream‐flow deposits were identified. The uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide, which was subsequently filled up mostly by stream‐flow deposits. The pronounced palaeo‐surfaces and depositional trends suggest that allocyclic controls governed the evolution of the Illgraben fan, making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the Alps. The results of the integrated outcrop–geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties.  相似文献   

Very low-grade metamorphism of Rheno-Hercynian allochthons (Variscides, Germany): facts and tectonic consequences     

Michael Patrick Doublier  Sébastien Potel  Wolfgang Franke  Tony Roache 《International Journal of Earth Sciences》2012,101(5):1229-1252

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