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51.
52.
Ismaïla Ngounouno Bernard Déruelle Raymond Montigny Daniel Demaiffe 《Comptes Rendus Geoscience》2006,338(8):537-544
Camptonites have been discovered at Mount Cameroon. They contain phenocrysts of olivine + clinopyroxene + plagioclase ± kaersutite ± bi and ocelli of nepheline or analcite and carbonates. 87Sr/86Sri values are similar to those of the basalts of Mount Cameroon . The camptonites are interpreted as resulting from fractional crystallization of a basaltic magma generated by a low degree of melting of an infra-lithospheric metasomatized mantle tapped by huge lithospheric cracks. To cite this article: I. Ngounouno et al., C. R. Geoscience 338 (2006). 相似文献
53.
The significance of variations in the sediment flux from western Scandinavia during the Cenozoic has been a matter of debate for decades. Here we compile the sediment flux using seismic data, boreholes and results from other publications and discuss the relative importance of causal agents such as tectonism, climate and climate change. Western Scandinavia, the northern British Isles and the Faeroe‐Shetland Platform were significant sediment sources during the Paleocene, which is well founded in tectonic causes related to the opening of the North Atlantic. From the Eocene and onward, variations in the sediment flux from western Scandinavia correlate better with climate and climate change. During the Eocene, sediment production was low. From the late Eocene onward, increased seasonality may have contributed to stimulating the sediment flux. Significant climatic cooling episodes correlate with Oligocene deposits in the North Sea, the post‐mid‐Miocene Molo and Kai Formations of the Norwegian Shelf, the southern North Sea delta system and large volumes of the Late Pliocene‐Holocene Naust Formation. The sediment flux from Scandinavia during the Cenozoic is in general agreement with the detrital flux to the world's oceans. Furthermore, the large variations in the size of sediment catchment areas as well as the possibility of submarine and glacial erosion must be incorporated to understand regional variations in climate driven sediment flux. 相似文献
54.
Laurent Jolivet Fabien Trotet Patrick Monié Olivier Vidal Bruno Goffé Loïc Labrousse Philippe Agard Bad'r Ghorbal 《Tectonophysics》2010,480(1-4):133-148
Syn-orogenic detachments in accretionary wedges make the exhumation of high-pressure and low-temperature metamorphic rocks possible with little erosion. The velocity of exhumation within the subduction channel or the accretionary complex, and thus the shape of P–T paths, depend upon the kinematic boundary conditions. A component of slab retreat tends to open the channel and facilitates the exhumation. We document the effect of slab retreat on the shape of P–T paths using the example of the Phyllite–Quartzite Nappe that has been exhumed below the Cretan syn-orogenic detachment during the Miocene in Crete and the Peloponnese. Data show a clear tendency toward colder conditions at peak pressure and during exhumation where the intensity of slab retreat is larger. This spatial evolution of P–T gradient is accompanied with an evolution from a partly coaxial regime below the Peloponnese section of the detachment toward a clearly non-coaxial regime in Crete. 相似文献
55.
Efraïm Mendelovici Rafael Villalba Amaya Sagarzazu 《International Journal of Mineral Processing》1983,11(2):131-138
A dry grinding process at several periods has been used successfully in order to differentiate among the different minerals forming a natural diaspore clay. This is achieved by selective and incongruent destruction of the clay minerals of this admixture, on the basis of their disparate structural stability, hardness and relative amount present. Kaolin clays (represented mainly by kaolinite + halloysite) are destroyed after >3 hr grinding, anatase after ~40 hr, whereas the structure of α-AlOOH is still preserved after >250 hr, as ascertained from XRD. From IR spectroscopy analysis it is inferred that as a consequence of grinding prototropy takes place in some of the clay hydroxyls. This is supported by water losses results at 600°C. 相似文献
56.
Issam Mouayn Ben Aissa Tadili Lahsen Aït Brahim Mohamed Ramdani Mohamed Limouri Nacer Jabour 《Pure and Applied Geophysics》2004,161(5-6):1061-1080
— The first empirical duration magnitude (MD) formula is developed and tested for the Northern Morocco Seismic Network (NMSNET). This relationship is obtained by relating the IGN (Instituto Geografico National, Madrid) body-waves mbLgIGN to the duration (), and the epicentral distance (), at 25 analogue stations of the NMSNET for 479 earthquakes with 2.5 mb 5.4, from March 1992 to February 2001. MD estimates are significantly more precise while introducing a correction term for each of these stations, cStaj. The magnitude for the ith event (MD)i is the mean value of individual MDij=–0.14+1.63log10(ij)+0.031(ij)+cStaj. The cStaj corrections reduce considerably the local site effects which influence the recorded durations and cause stations to either overestimate, or underestimate MD up to 0.5 magnitude units. Average station MD residuals (–cStaj) are found to be independent of the distance from the epicenter to at least 10 degrees. It seems evident that regional geological features in the immediate behavior of stations have a systematic effect on the corresponding obtained residuals: older well-consolidated Precambrian crystalline rocks produce high negative residuals (shorter durations), younger unconsolidated sediments produce high positive residuals (longer durations), whereas, intermediate MD site residuals appear to be the result of the effect of various factors, principally age and state of consolidation of the bedrock, combined with the local tectonic. 相似文献
57.
Our study presents preliminary biostratigraphic results from the Jurassic siliceous series of northwestern Tunisia. For the first time, radiolarians are extracted from the Jédidi formation and provide a direct age determination. They are the first radiolarian fauna documented from Tunisia. Two age assignments are comprised within the following intervals: (1) Late Bathonian–Early Callovian, (2) Late Bathonian–Early Oxfordian. These ages are compatible with recent stratigraphic synthesis proposed for the Jurassic series of Tunisia. The data suggest the correlation of the Jédidi formation with siliceous series of Middle–Late Jurassic age from the external zone of the Maghrebides belt rather than with true oceanic units from the Maghrebian flyschs or the internal zones of western Tethys. To cite this article: F. Cordey et al., C. R. Geoscience 337 (2005). 相似文献
58.
The survey of sedimentological and lithostratigraphic Liassic facies of the Todrha–Dades area (southwestern part of the central High Atlas) permits to establish new data on the Tagoudite formation. Its environment deposit and its micropalaeontological content are evidenced in relation with the geodynamic evolution of the High Atlas Basin during the Early Toarcian. To cite this article: M. Ettaki, E.H. Chellaï, C. R. Geoscience 337 (2005). 相似文献
59.
Krzysztof Goździewski 《Celestial Mechanics and Dynamical Astronomy》1998,70(1):41-58
In this paper we consider the problem of motion of an infinitesimal point mass in the gravity field of an uniformly rotating
dumb-bell. The aim of our study is to investigate Liapunov stability of Lagrangian libration points of this problem. We analyze
the stability of libration points in the whole range of parameters ω, μ of the problem. In particular, we consider all resonance
cases when the order of resonance is not greater than five.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
L. Aït Brahim B. Tadili C. Nakhcha I. Mouayn M. Ramdani M. Limouri A. El Qadi F. Sossey Alaoui M. Benhalima 《Pure and Applied Geophysics》2004,161(5-6):1081-1091
— The aim of this study is to conduct a probabilistic seismic hazard analysis for the eastern Rif area in northern Morocco. The source zones were established on the basis of the seismicity database, the fracturing analysis deduced from Landsat7 ETM digital enhancement and marine seismic reflection profiles. By the use of this information together with the selected attenuation relationship, the peak ground acceleration contour maps are produced for specific return periods. The map has been divided into intervals of 0.1 degrees in both latitude and longitude to calculate the values at each grid point and draw the seismic hazard curves. The results of seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures. 相似文献