Physical modelling of gelifluction and frost creep: Some results of a large-scale laboratory experiment   总被引：1，自引：0，他引：1  

Charles Harris  Michael Gallop  Jean-Pierre Coutard 《地球表面变化过程与地形》1993,18(5):383-398

An experimental slope was constructed in a 5 m × 5 m square refrigerated tank. The slope was formed of four sections, each consisting of regolith (soil) collected from a distinct bedrock lithology. The four lithologies utilized were granite, limestone, mudstone and slate. The slope was subjected to freezing and thawing from the surface downwards. Water was supplied at the base of the soil during freezing. Frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles, and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle. The experimental soils were non-cohesive; those derived from granite and limestone were respectively sandy and gravelly in texture, while those derived from mudstone and slate were silt-rich. Mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice. In the mudstone and slate soils, gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice. Mean per cycle rates of downslope soil transport for the granite, limestone, mudstone and slate soils were 5·8 cm³ cm^?1, 6·9 cm³ cm^?1, 21·2 cm³ cm^?1 and 31·2 cm³ cm^?1 respectively, units referring to the volume of soil passing a unit width of slope per cycle. Mass movement rates were shown to be strongly related to the silt content of the soils.  相似文献   

Radiation-induced paramagnetic defects in natural kaolinites: Alpha dosimetry with ion beam irradiation     

Thierry Allard  Jean-Pierre Muller  Jean-Claude Dran  Marie-Thérèse Ménager 《Physics and Chemistry of Minerals》1994,21(1-2):85-96

Three types of paramagnetic radiation-induced defects (RID), namely A, A′ (Si-O^?-centers) and B (Al-O^?-Al center), had been identified in natural kaolinites by means of electron paramagnetic resonance spectroscopy. The A-center, stable at the scale of geological periods, was thought to be of particular relevance to quantify past transits of radionuclides in the geosphere. Alpha radiation being likely the main source of RID in kaolinite, the objective of this paper is to define the role of α-particles on the creation of RID and to test the use of A-centers for an α-dosimetry. Three kaolinites with different crystalline order and containing other clays as impurities were irradiated with He⁺ ion beams. The radiation dose range (0–750 MGy) was consistent with natural radioactivity in environments from the Earth's surface. Irradiation drastically enhanced the original signals due to RID. An important increase of concentration of the unstable B-center, partly due to unrealistic dose rate provided by accelerator ion beam, was observed from the lower doses. The most stable defects remained of the Atype all along experimental irradiations. The contribution of ancillary phyllosilicates to EPR spectra was negligible. The concentration of the three types of RID was related to radiation doses up to 30 MGy. Dosimetry growth curves for the A-centers exhibited variable efficiencies and saturation levels that were related to the structural order and the chemical purity of the kaolinites: the more ordered and purer the kaolinite, the higher the efficiency and the lower the saturation plateau. Moreover, these results are of geochemical significance: dosimetry based on A-centers could be directly used to quantify past migrations of radioelements in the geosphere, by determination of the naturally-cumulated doses (paleodose) of kaolinites.  相似文献   

Origine et signification des galets de rhyolites (ignimbrites) dans la partie sud de la plaine orientale corse (région de Saint Antoine à Linguizzetta)     

A. Gauthier  P. Weydert 《Sedimentary Geology》1976,15(2):165-171

The study of the percentages of rhyolitic pebbles in the deposits of the rivers which cross the meridional part of the eastern plain of Corsica permits us to reconstitute the ancient shoreline in Mio-Pliocene times. The Fiumorbo is the only stream at present which removes pebbles of rhyolites (5%) before penetrating on to the plain. This kind of petrographic element comes from a single outcrop over which flows a tributary: “la Finosa”. Along the limit of the metamorphic area of Corsica, the edge of the eastern plain is constituted by a detrital formation consisting of conglomerates in which, near Saint Antoine, one can recognize the ancient delta of the Fiumorbo. Rhyolites represent 50% of all pebbles in it. This percentage regularly decreases with distance to the northeast. All river deposits contain rhyolitic pebbles but only after they have crossed this conglomerate and never before.We consider this formation to be the ancient shoreline of Corsica in the Mio-Pliocene.  相似文献   

Paleomagnetic record of two successive Miocene geomagnetic reversals in western Crete     

Jean-Pierre Valet  Carlo Laj 《Earth and Planetary Science Letters》1981,54(1):53-63

Two geomagnetic reversals(R→N followed by N→R) have been recorded in a sequence of Miocene marine clays of Tortonian-Messinian age in western Crete (Greece). The time span of each transition is found to be of the order of 5000–10,000 years. The transitional VGP paths are largely constrained in longitude either near the site longitude(R→N) or opposite to it(N→R). A normalized magnetization intensity record has also been obtained and its variations during reversals are found to be in excellent agreement with the predictions of Hoffman's phenomenological model.  相似文献   

La sismicité en corse: Revue historique et etude macrosismique de quelques evénéments récents     

F. Marillier  A. Gauthier  J. Vogt 《Pure and Applied Geophysics》1982,120(1):167-185

Résumé L'étude des documents (archives, presse et catalogues sismiques) que nous avons consultés, nous a permis de remonter jusqu'à la fin du XVIIIe siècle dans l'histoire sismologique corse. Le nombre des séismes ressentis (épicentres en mer ou sur l'île) recensés pendant ces deux siècles et demi est relativement faible. Les intensités maximales ont parfois atteint le degré VI, plus rarement VII. L'activité sismique touche principalement une région située au Nord-Est de la Corse, au voisinage de failles au rejeu récènt et séparent le domaine de la Corse schisteuse (alpin) du domaine de la Plaine Orientale (Quaternaire, Néogène). Une crise sismique récente (1978–1979) a de nouveau secoué cette même région où on a suggéré l'activité actuelle de certaines de ces failles. Les plus importants de ces séismes (I _max=VI et V) ontifait l'objet d'enquêtes macrosismiques qui permettent d'en préciser les épicentres. Deux d'entre-eux ont été étudiés en détail (3 avril 1978 et 27 mars 1979); en utilisant la relation de Kövesligethy, les hypocentres se situent respectivement à 4,5±0.5 km et vers 5 km, pour des coefficients d'absorption de 0,020 et 0,031. Ces profondeurs indiquent que ces deux séismes ont mis en jeu des éléments superficiels de la croûte corse (30 km).

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The documents that we have compiled (archives, newspaper reports and seismic catalogues) enabled us to go back to the end of the 18th century in the seismic history of Corsica. The number of felt earthquakes (epicentres off shore or on the island) which were documented during the two and a half centuries is relatively low. Maximum intensities have reached VI or rarely VII. The seismic activity is mainly located in the North-East of Corsica, near faults which have recently been active between the Corse schisteuse (Alpine domain) and the Plaine Orientale (Quaternary, Neogene). A seismic crisis happened recently (1978–1979) in this area where present activity of some of these faults has been suggested. Macroseismic studies have been conducted for the main shocks (I _max=VI and V) in order to locate them accurately. Two among them (April 3, 1978 and March 27, 1979) are studied here in detail. Using the Kövesligethy formula hypocenters are respectively found at 4.5±0.5 km and around 5 km, whereas the corresponding absorption factors are 0.020 and 0.031. Such depths show that the two events affected the upper crust of Corsica (30 km).

Contribution n^o 321 de l'Institut de Géophysique, Ecole Polytechnique Fédérale de Zürich.  相似文献   

Telemediators in the marine environment     

M Aubert  J Aubert  M Gauthier 《Marine pollution bulletin》1978,9(4):93-95

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Rosia Poieni copper deposit,Apuseni Mountains,Romania: advanced argillic overprint of a porphyry system   总被引：2，自引：0，他引：2  

Viorica?Milu  Jean-Pierre?Milesi  Jacques?Léon?LeroyEmail author 《Mineralium Deposita》2004,39(2):173-188

The Rosia Poieni deposit is the largest porphyry copper deposit in the Apuseni Mountains, Romania. Hydrothermal alteration and mineralization are related to the Middle Miocene emplacement of a subvolcanic body, the Fundoaia microdiorite. Zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions. Four alteration types have been distinguished: potassic, phyllic, advanced argillic, and propylitic. Potassic alteration affects mainly the Fundoaia subvolcanic body. The andesitic host rocks are altered only in the immediate contact zone with the Fundoaia intrusion. Mg-biotite and K-feldspar are the main alteration minerals of the potassic assemblage, accompanied by ubiquitous quartz; chlorite, and anhydrite are also present. Magnetite, pyrite, chalcopyrite and minor bornite, are associated with this alteration. Phyllic alteration has overprinted the margin of the potassic zone, and formed peripheral to it. It is characterized by the replacement of almost all early minerals by abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite, and kaolinite. Pyrite is abundant and represents the main sulfide in this alteration zone. Advanced argillic alteration affects the upper part of the volcanic structure. The mineral assemblage comprises alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite, and enargite (luzonite). Alunite forms well-developed crystals. Veins with enargite (luzonite) and pyrite in a gangue of quartz, pyrophyllite and diaspore, are present within and around the subvolcanic intrusion. This alteration type is partially controlled by fractures. A zonal distribution of alteration minerals is observed from the centre of fractures outwards with: (1) vuggy quartz; (2) quartz + alunite; (3) quartz + kaolinite ± alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; (4) illite + illite-smectite mixed-layer minerals ± kaolinite ± alunite, and e) chlorite + albite + epidote. Propylitic alteration is present distal to all other alteration types and consists of chlorite, epidote, albite, and carbonates. Mineral parageneses, mineral stability fields, and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system. The alteration minerals reflect cooling of the hydrothermal system from >400 °C (biotite), to 300–200 °C (chlorite and illite in veinlets) and to lower temperatures of kaolinite, illite-smectite mixed layers, and smectite crystallization. Hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone. It was followed by phyllic overprint of the early-altered rocks. Nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones. The close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic-hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface.Editorial handling: B. Lehmann  相似文献   

Correlations and sequence stratigraphic model for Messinian carbonate platforms of the western and central Mediterranean   总被引：1，自引：0，他引：1  

Jean-Jacques?CornéeEmail author  Jean-Paul?Saint Martin  Gilles?Conesa  Philippe?Münch  Jean-Pierre?André  Simona?Saint Martin  Stefan?Roger 《International Journal of Earth Sciences》2004,93(4):621-633

Distance correlations of Late Tortonian–Messinian littoral carbonate complexes are proposed from the study of eight platforms in the western and central Mediterranean. Correlations are based on the identification of two major biological sedimentary cycles and of two index surfaces. Surface A is a maximum flooding surface during cycle 1 at around 6.7 Ma. Surface B is a regional marine planation surface at around 5.95 Ma, at the base of cycle 2 (Terminal Carbonate Complex). A general sedimentary model is proposed for the 7–5.6-Ma time-span. The boundary between cycles 1 and 2 is coincident with the onset of the Messinian Salinity Crisis, and appears to be related to major environmental–paleo-oceanographic changes in the Mediterranean, rather than to a major sea-level drop or to climatic change.  相似文献   

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications     

David Besson  Olivier Parize  Jean-Loup Rubino  Jean-Pierre Aguilar  Marie-Pierre Aubry  Bernard Beaudoin  William A. Berggren  Georges Clauzon  Philippe Crumeyrolle  Yann Dexcoté  Nicolas Fiet  Silvia Iaccarino  Gonzalo Jiménez-Moreno  Cécile Laporte-Galaa  Jacques Michaux  Katharina von Salis  Jean-Pierre Suc  Jean-Yves Reynaud  Roland Wernli 《Comptes Rendus Geoscience》2005,337(12):1045-1054

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).  相似文献   

Modes of thickening of analogue weak lithospheres   总被引：4，自引：2，他引：4  

Florence Cagnard  Jean-Pierre Brun  Denis Gapais 《Tectonophysics》2006,421(1-2):145-160

Several compressional contexts, such as those involving juvenile or thickened crust, are expected to be associated with rather hot lithospheres whose mechanical behaviour remains poorly documented. In this paper, we present a series of analogue models dedicated to compression of lithospheres characterized by a thin upper brittle crust overlying a weak ductile crust and a ductile sub-Moho mantle. The models show that (1) deformation is controlled by the ductile layers that undergo distributed thickening, (2) thrust systems are limited to the upper brittle crust, (3) thrusting induces burial and stacking of upper crust pop-downs. The overall deformation patterns can be basically interpreted in terms of pop-down thrusting of the brittle crust and pure-shear type ductile flow of crust and mantle. Moreover, the models show that the sinking of supracrustal units does not require inverse density profiles but can be simply driven by compression. Model deformation patterns are consistent with those shared by many ancient belts, including not only Archaean granite–greenstone belts, but also more generally Paleoproterozoic ones. They provide also insights on deformation modes that may characterize modern thickened and abnormally hot domains like High Plateaus.  相似文献