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Gwénaël Jouet Claude Augris Bernard Hallegouët Pascal Le Roy Joël Rolet 《Comptes Rendus Geoscience》2003,335(5):487-494
Interpretation of the recent high-resolution survey, CANADOU 2000, in the Bay of Douarnenez (Finistère, France) allowed us to restore the morphology of the substratum and the sedimentary filling of the bay. The Brioverian and Palaeozoic substratum reveals a well-defined network of incised valleys as results of successive emergence stages of the Bay during the Quaternary. Valleys join in a westward-widened mean valley, called Ys Valley. The present-day sedimentary fill of the bay of Douarnenez appears mainly controlled by the Holocene rise and the consecutive highstand. It comprises fluvial and estuarine deposits filling up incised valleys and marine sedimentation extending out of the incised valleys. To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003). 相似文献
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The South Armorican shear zone is one of the major occurrences of Variscan basement in Europe. The objectives of the study were to compile a lineament and a structural map from remotely sensed SPOT imagery. Transparent color films, enhanced by high-pass filtering and by stretching color composites, and spatial filtered images were analysed. The major structure mapped corresponds to a dextral transcurrent shear belt in which C and S axes have been described. Late Paleozoic and Tertiary fracturations truncate these structures. The localisation, extension and geometry of granite domes were also precised. Lastly, this study provides a good example of structural interpretation of a moderate-relief terrain using high-resolution SPOT imagery. 相似文献
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Rift propagation at craton margin.: Distribution of faulting and volcanism in the North Tanzanian Divergence (East Africa) during Neogene times 总被引：1，自引：0，他引：1
B. Le Gall P. Nonnotte J. Rolet M. Benoit H. Guillou M. Mousseau-Nonnotte J. Albaric J. Deverchre 《Tectonophysics》2008,448(1-4):1-19
A revised kinematic model is proposed for the Neogene tectono-magmatic development of the North Tanzanian Divergence where the axial valley in S Kenya splits southwards into a wide diverging pattern of block faulting in association with the disappearance of volcanism. Propagation of rifting along the S Kenya proto-rift during the last 8 Ma is first assumed to have operated by linkage of discrete magmatic cells as far S as the Ngorongoro–Kilimanjaro transverse volcanic belt that follows the margin of cratonic blocks in N Tanzania. Strain is believed to have nucleated throughout the thermally-weakened lithosphere in the transverse volcanic belt that might have later linked the S Kenya and N Tanzania rift segments with marked structural changes along-strike. The North Tanzanian Divergence is now regarded as a two-armed rift pattern involving: (1) a wide domain of tilted fault blocks to the W (Mbulu) that encompasses the Eyasi and Manyara fault systems, in direct continuation with the Natron northern trough. The reactivation of basement fabrics in the cold and intact Precambrian lithosphere in the Mbulu domain resulted in an oblique rift pattern that contrasts with the orthogonal extension that prevailed in the Magadi–Natron trough above a more attenuated lithosphere. (2) To the E, the Pangani horst-like range is thought to be a younger (< 1 Ma) structure that formed in response to the relocation of extension S of the Kilimanjaro magmatic center. A significant contrast in the mechanical behaviour of the stretched lithosphere in the North Tanzanian diverging rift is assumed to have occurred on both sides of the Masai cratonic block with a mid-crustal decoupling level to the W where asymmetrical fault-basin patterns are dominant (Magadi–Natron and Mbulu), whereas a component of dynamical uplift is suspected to have caused the topographic elevation of the Pangani range in relation with possible far-travelled mantle melts produced at depth further N. 相似文献
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This paper describes results from a detailed study of circular anomalies—related to outcrops of granitic domes over the western part of the Armorican Massif—using SPOT, Landsat TM, Seasat, and composite imagery in conjunction with aerial photographs. Two types of features have been distinguished: (1) simple and circular, related to small granitic bodies or to hidden domes, which correspond with concentric networks of fractures formed during the cooling of the granite, and (2) complex and composite of the onion skin type, related to the larger plutonic domes. This type of feature could also be related to the concentric cooling networks but would more probably correspond to the magmatic foliation planes. Semi-circular features of the “half-moon” type, derived from these described structures, are located on the periphery of plutonic domes. These could correspond to preliminary intrusions cross cut by the major structures. From the lineament maps and based on the relationship between regional foliation fracturing networks and circular features, the following networks can be distinguished: (1) radial networks centered on plutonic diapirs, which seem to be contemporary with the granitic intrusions; (2) transverse networks that pass around or across circular features, creating fan-shaped forms and which are late with respect to the granitic intrusions; (3) post-tectonic fracturing networks that cross all previously described structures; and (4) a network, parallel to the regional foliation N070, which crosses or twists the circular features. This system documents the syntectonic pattern of the granites. Translated by Judit Ozoray, Chicoutimi, Quebec from: “Structures circulaires et réseaux de fractures en pays granitique. Analyse de données SPOT, Landsat TM et Seasat sur le Massif armoricain,” Bull. Soc. géol. France, 1993, Vol. 164, No. 2, pp. 199-214, with permission of the Société Gèologique de France (please cite original paper). 相似文献
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Mohamed A. Daoud René C. Maury Jean-Alix Barrat Rex N. Taylor Bernard Le Gall Hervé Guillou Joseph Cotten Joël Rolet 《Lithos》2010,114(3-4):327-336
Major, trace element and isotopic (Sr, Nd, Pb) data and unspiked K–Ar ages are presented for Quaternary (0.90–0.95 Ma old) basalts from the Hayyabley volcano, Djibouti. These basalts are LREE-depleted (Lan/Smn = 0.76–0.83), with 87Sr/86Sr ratios ranging from 0.70369 to 0.70376, and rather homogeneous 143Nd/144Nd (εNd = + 5.9–+ 7.3) and Pb isotopic compositions (206Pb/204Pb = 18.47–18.55, 207Pb/204Pb = 15.52–15.57, 208Pb/204Pb = 38.62–38.77). They are very different from the underlying enriched Tadjoura Gulf basalts, and from the N-MORB erupted from the nascent oceanic ridges of the Red Sea and Gulf of Aden. Their compositions closely resemble those of (1) depleted Quaternary Manda Hararo basalts from the Afar depression in Ethiopia and (2) one Oligocene basalt from the Ethiopian Plateau trap series. Their trace element and Sr, Nd, Pb isotope systematics suggest the involvement of a discrete but minor LREE-depleted component, which is probably an intrinsic part of the Afar plume. 相似文献
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Jean-Claude Dauvin Céline Rolet Sandrine Alizier Thierry Ruellet 《Journal of Sea Research》2011,65(1):182-185
The purpose of this paper was to establish the main characteristics of the suprabenthic communities of the English Channel including those found in a potential aggregate extraction zone located in the central part. Sampling was carried out with a Macer-GIROQ sledge during four periods in 2007. In this offshore site, the suprabenthic faunal composition and abundance were close to those observed in other similar sites in coarse sand to pebbles in the western and eastern parts of the English Channel. But, the species richness was low (65 species). Amphipods were the dominant group in terms of diversity and abundance. Only a few species, mostly amphipods and decapods, showed significant daily migration. Seasonal variations were moderate. Due to the similar suprabenthic fauna having good swimming ability, the aggregate extraction zone in the central part of the Channel could be rapidly colonized after exploitation and thus could rapidly insure a feeding resource for fish, which are attracted by abundant prey. 相似文献
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N.?MoussaEmail author Y.?Fouquet B.?Le?Gall A.?M.?Caminiti J.?Rolet M.?Bohn J.?Etoubleau C.?Delacourt M.?Jalludin 《Mineralium Deposita》2012,47(5):563-576
The geology of the Republic of Djibouti, in the SE Afar Triangle, is characterized by intense tectonic and bimodal volcanic activity that began as early as 25–30 Ma. Each magmatic event was accompanied by hydrothermal activity. Mineralization generally occurs as gold–silver bearing chalcedony veins and is associated with felsic volcanism. Eighty samples from mineralized hydrothermal chalcedony, quartz ± carbonate veins and breccias were studied from ten sites representing four major volcanic events that range in age from early Miocene to the present. The most recent veins are controlled by fractures at the edges of grabens established during the last 4 Myr. Gold in excess of 200 ppb is present in 30% of the samples, with values up to 16 ppm. Mineralogical compositions allowed us to identify different types of mineralization corresponding to different depths in the hydrothermal system: (1) surface and subsurface mineralization characterized by carbonate chimneys, gypsum, silica cap and quartz ± carbonate veins that are depleted in metals and Au; (2) shallow banded chalcedony ± adularia veins related to boiling that contain up to 16 ppm Au, occurring as native gold and electrum with pyrite, and tetradymite; (3) quartz veins with sulfides, and (4) epidote alteration in the deepest hydrothermal zones. Samples in which pyrite is enriched in As tend to have a high Au content. The association with bimodal volcanism, the occurrence of adularia and the native Au and electrum in banded chalcedony veins are typical of epithermal systems and confirm that this type of mineralization can occur in a young intracontinental rift system. 相似文献
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