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71.
Guido Schreurs Jörg Giese Alfons Berger Edwin Gnos 《International Journal of Earth Sciences》2010,99(8):1827-1847
The Ranotsara shear zone in Madagascar has been considered in previous studies to be a >350-km-long, intracrustal strike-slip
shear zone of Precambrian/Cambrian age. Because of its oblique strike to the east and west coast of Madagascar, the Ranotsara
shear zone has been correlated with shear zones in southern India and eastern Africa in Gondwana reconstructions. Our assessment
using remote sensing data and field-based investigations, however, reveals that what previously has been interpreted as the
Ranotsara shear zone is in fact a composite structure with a ductile deflection zone confined to its central segment and prominent
NW–SE trending brittle faulting along most of its length. We therefore prefer the more neutral term “Ranotsara Zone”. Lithologies,
tectonic foliations, and axial trace trajectories of major folds can be followed from south to north across most of the Ranotsara
Zone and show only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of
E–W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar
Block during a late phase of the Neoproterozoic/Cambrian East African Orogeny (c. 550–520 Ma). The Ranotsara Zone shows significant
NW–SE striking brittle faulting that reactivates part of the NW–SE striking ductile structures in the flexure zone, but also
extends along strike toward the NW and toward the SE. Brittle reactivation of ductile structures along the central segment
of the Ranotsara Zone, confirmed by apatite-fission track results, may have led to the formation of a shallow Neogene basin
underlying the Ranotsara plain. The present-day drainage pattern suggests on-going normal fault activity along the central
segment. The Ranotsara Zone is not a megascale intracrustal strike-slip shear zone that crosscuts the entire basement of southern
Madagascar. It can therefore not be used as a piercing point in Gondwana reconstructions. 相似文献
72.
Adnand Bitri Jean-Pierre Brun Denis Gapais Florence Cagnard Charles Gumiaux Jean Chantraine Guillaume Martelet Catherine Truffert 《Comptes Rendus Geoscience》2010,342(6):448-452
We present results and interpretation of a 72 km long deep seismic reflection profile acquired across the internal zone of the Hercynian belt of South Brittany. The profile is of excellent quality, most of the crust being highly reflective. The “ARMOR 2 South” profile, is correlated with the “ARMOR 2 North” profile that was published in 2003. Correlation of the main subsurface reflections with surface geological and structural data provides important information about the crustal structure that resulted from thickening during Late Devonian and regional-scale extension during Late Carboniferous. In particular, seismics image shows a very high reflectivity zone, lying flat over more than 40 km at about 10–12 km depth. This zone is interpreted as a major zone of ductile crustal thinning. 相似文献
73.
74.
Philippe Besson Jefferson Degboe Benjamin Berge Valérie Chavagnac Sébastien Fabre Gilles Berger 《Geostandards and Geoanalytical Research》2014,38(3):355-362
We report a measurement procedure to determine simultaneously the major cation concentrations (Na, Ca, K and Mg) of seawater‐derived solutions by inductively coupled plasma‐atomic emission spectrometry. The best results were obtained when the IAPSO (‘standard’) seawater reference material was diluted by thirty times with Milli‐Q® water. We obtained an average reference value rK (the ratio of the mass fraction of potassium to that of chlorine, i.e., (g kg?1)/(g kg?1)) for IAPSO seawater of 0.0205 ± 0.0006 (2.9% RSD), not significantly different from 0.0206 ± 0.0005 (2.4% RSD) for seawater composition reported in the literature. The measured Na, Ca and Mg concentrations correspond to rNa, rCa and rMg values of 0.5406 ± 0.0026 (0.5% RSD), 0.02192 ± 0.00048 (2.2% RSD) and 0.06830 ± 0.00047 (0.7% RSD), respectively, in line with previous values measured by wet‐chemistry and atomic absorption spectrophotometry or wet‐chemical titration. Our measurement procedure was used successfully on synthetic seawater solutions and high‐temperature hydrothermal fluids. 相似文献
75.
We derive the magnetic helicity for configurations formed by flux tubes contained fully or only partially in the spatial domain
considered (called closed and open configurations, respectively). In both cases, magnetic helicity is computed as the sum
of mutual helicity over all possible pairs of magnetic flux tubes weighted by their magnetic fluxes. We emphasize that these
mutual helicities have properties which are not those of mutual inductances in classical circuit theory. For closed configurations, the mutual helicity of two closed flux
tubes is their relative winding around each other (known as the Gauss linkage number). For open configurations, the magnetic
helicity is derived directly from the geometry of the interlaced flux tubes so it can be computed without reference to a ground
state (such as a potential field). We derive the explicit expression in the case of a planar and spherical boundary. The magnetic
helicity has two parts. The first one is given only by the relative positions of the flux tubes on the boundary. It is the
only part if all flux tubes are arch-shaped. The second part counts the integer number of turns each pair of flux tubes wind
about each other. This provides a general method to compute the magnetic helicity with discrete or continuous distributions
of magnetic field. The method sets closed and open configurations on an equal level within the same theoretical framework. 相似文献
76.
Jean-Pierre Macquart Lucyna Kedziora-Chudczer David Jauncey David Rayner 《Astrophysics and Space Science》2001,277(1-2):135-138
It is found that velocity shear enables the extraction of kinetic energy from the background flow by Dust-Acoustic waves.
It is also shown that the velocity shear leads to the appearance of a new mode of the dust particles collective behaviour, called shear dust vortices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):279-296
Conclusion To summarize, the readout and the control system of the CCD mosaic camera are running since December 1991 at the La Silla Observatory (ESO). The overall performance of the camera has been good. About 12000 pictures (data and flat-fields) have been successfully registered up to now. We will report in the near future preliminary scientific results of the EROS experiment. 相似文献
78.
ABSTRACT This paper presents high-precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB-type isotopic characteristics generated 99–92-Ma-old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a >600-Ma-old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82-Ma-old felsic peraluminous dykes have MORB-type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex. 相似文献
79.
80.
Michael De Becker Gregor Rauw Jean-Pierre Swings 《Astrophysics and Space Science》2005,297(1-4):291-298
We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6+O5.5
binary system with a period of about 21.9 days. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter.
We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the
radio waveband to γ-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic
electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for
a putative γ-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified
EGRET source 3EG J2033+4118.
Based partly on data Obtained at the Observatoire de Haute-Provence, France. 相似文献