L'intertextualité vernienne dans "W ou Le souvenir d'enfance"

(Cet article est un extrait du mémoire de DEA de l'auteur.) Perec offre diverses clefs pour une lecture intertextuelle : allusions à des situations connues, phrases, bribes de phrases, mots étrangers ou étranges, noms et prénoms, lettres, fautes d'orthographe. Une poignée de signes tracés dans W ou le souvenir d'enfance nous mènera vers l'Épave du Cynthia , les Cinq Cents Millions de la Bégum , les Enfants du Capitaine Grant eux-mêmes à la recherche de leur père, etc. Nous parviendrons ainsi via Verne à Edmond About, à la Frankfurter Zeitung ou à Tintin, à toute une horde de globe-trotters, à toute une famille culturelle dont les liens de parenté sont aussi insoupçonnables que terrifiants.(This article is part of the author's DEA dissertation.) An intertextual reading of Perec may use many keys: references to a number of circumstances, sentences and fragments, foreign (or unusual) words, names, letters and misspellings. Thus, a handful of printed characters in W ou le souvenir d'enfance set the reader on the trail of l'Épave du Cynthia, les Cinq Cents Millions de la Bégum, les Enfants du Capitaine Grant, themselves in search of their father, and so on. Thence the reader pursues his journey, via Verne, to Edmond About, the Frankfurter Zeitung, Tintin, hordes of globetrotters, to an entire cultural family whose relationships are as inconceivable as they are terrifying

Mode of formation of gold-bearing mineralization on top of the boboras (Galicia, Spain) - The combined role of mechanical instabilities, strain localization and vein formation.

International audienceThe Galician Hercynian segment constitutes the core of the Ibero-Armorican orogenic arc, characterized by few tectonic units that record three main phases of deformation (D1 to D3). Four generations of granite, syn- to post-D3 intruded the major tectonic units. From older to younger, we find: i) syn-kinematic biotite-rich granodiorite (G1); ii) syn-kinematic two micas granites (G2) ; iii) biotite-dominant granites (G3) and iii) late-kinematic biotite-rich granodiorite (G4). Numerous sills, dykes and vein systems are widespread within the metasediments of the para-autochton unit. Gold-bearing quartz veins were spatially associated with G3 granites likely the Boborás intrusion, concerned by this work. The Boborás granite (G3) outcrops as a small NS-elongated elliptical intrusion. Granite is homogeneous and exhibits an equigranular texture composed of quartz, oligoclase, microcline, biotite dominant and muscovite

Combination of Numerical Tools to Link Deep Temperatures, Geological Structures and Fluid Flow in Sedimentary Basins: Application to the Thermal Anomalies of the Provence Basin (South-East France)

International audienceIn the Provence basin, south-eastern France, more than 230 Bottom Hole Temperature (BHT) data have been compiled and corrected for transient disturbances to provide a thermal model of this Mesozoic to Cenozoic sedimentary basin. The thermal gradient of the area averages 29.9°C/km (32.5°C/km in all France), but some places show gradients reaching 36°C/km or 22°C/km. To characterize thermal anomalies, a three-dimensional model of the temperatures was built between the surface and 5km depth, allowing us to elaborate sets of thermal maps and cross-sections. The newly identified temperature anomalies may reach temperature difference up to 40°C at 3km depth through the basin. After attempting to find correlations between thermal anomalies and large scale features (Moho depths, sediment cover thickness), it appears that fluid circulation may better explain locations, amplitudes and wavelengths of thermal anomalies along faulted zones. In fact, spatial evolution of anomalous cold/warm zones follow directions of main faulted zones. In addition, it is shown that the account of a depth-dependent permeability allows the superimposition of positive and negative thermal anomalies. Away from permeable zones, thermal anomalies should be explained by conductive processes, among which heat refraction due to thermal conductivity contrasts may be significant. In particular, anisotropy of thermal conductivity of clayey formation is shown to enable the development of thermal anomalies similar to those observed between permeable zones. Evolution of fluid circulation in faulted zones (involving enhanced vertical heat transfer) combined with thick anisotropic sediments (involving enhanced horizontal heat transfer) may explain complex thermal patterns deduced from present-day temperature measurements

Geological and thermal conditions before the major Palaeoproterozoic gold-mineralization event at Ashanti, Ghana, as inferred from improved thermal modelling

International audienceHeat transfer processes before a major mineralizing event in the Paleoproterozoic continental crust of southern Ghana are the subject of a detailed regional thermal modelling study. The area of the Ashanti belt is the most mineralized for gold in West Africa, and it is believed that prior to the main gold mineralization event, crustal-scale thermal processes may have played a critical role in ore deposit formation. The thermal regime before and after the crustal shortening events that affected the region during the Eburnean orogeny (2130–1980 Ma) is calculated just before the main mineralization event which corresponds to late orogenic hydrothermal gold deposit formation. Measured thermal properties of lithological units are incorporated into the model, which is geometrically constrained by field studies. Computed pressure–temperature paths, compared to thermobarometric data, allow calibration of the model parameters. The temperature-dependence of thermal properties and the influence of compaction on vertically varying conductivities have been considered in the crustal-scale thermal modelling. The predictions from this model indicate that the most probable mantle heat flow value at this time in the region of the Ashanti belt is not, vert, similar30 mW m−2. Such a value is two to three times higher than present-day values below stable cratonic areas and could be considered as an upper limit in geodynamic models of the Paleoproterozoic mantle. This relatively high value might be related to the thermal input from a Paleoproterozoic mantle event such as a mantle plume, as previously suggested by several authors to explain metallogenic crises in West Africa. The P–T paths inferred from numerical modelling also allow discrimination between extreme geological scenarios. Indeed, the results of the modelling suggest that the basement is likely to be of continental rather than of oceanic type in the Ashanti area

Geochronological constraints on the magmatic and hydrothermal evolution of the tras-os-montes hercynian domain (Galica, Spain) : position of the AU, SN-W mineralizing events.

International audienceThe study area is located in the Galicia-Trás-os-Montes Zone (GTMZ zone, Arenas et al. 1986, Fig. 1), that belongs to the internal zone of the Hercynian belt and is composed of a relative autochthonous and parautochthonous units overthrusted by allochthonous complexes (Ribeiro et al. 1990). This domain of Palaeozoic schists is affected by a low to high temperature – medium pressure metamorphism. These rocks exhibit a well-developed regional schistosity related to nappes emplacement (D1 and D2 events) and are affected by NS-trending crenulation lineation and folds (D3 event) The late D3 event is characterized by a high-temperature metamorphism leading to development of local migmatite. Both parautochthonous and allochthonous units are intruded by syn- and post-kinematic plutons. Four generations of granites (G1 to G4) are identified by their textural and geochemical characteristics and by crosscutting relationships. Gold deposits are spatially associated with the G3 granites whereas Sn-W deposits are represented, in the study area, by disseminated and vein-type mineralization spatially close to the G2 granites (fig. 1)

Deep temperatures in the Paris Basin using tectonic-heat flow modelling

International audienceThe determination of deep temperatures in a basin is one of the key parameters in the exploration of geothermal energy. This study, carried out as part of the CLASTIQ-2 project, presents a 3 temperatures in the Paris Basin derived through a thermal-tectonic forward modelling method, calibrated using subsurface temperature values. The temperature dataset required for the calibration was compiled in 2007 as part of the CLASTIQ-1 project. The temperature measurement dataset is largely composed of BHT (some 2443 values). These BHT measurements required correction due to the thermal disturbance created during drilling. After correction, which was carried out using the Instantaneous Cylinder Source (ICS) method, 494 corrected BHT (BHTx) values were available for the modelling of the Paris Basin. In addition to these BHTx, some 15 DST measurements that are considered as close to the thermal equilibrium (i.e., ±5°C) were added to the temperature calibration values. According to this dataset of BHTx and DST, the average gradient in the Paris Basin was calculated as 34.9°C/km when the surface temperature is fixed at 10°C. The temperature values collected were then used to calibrate the tectonic-heat flow modelling. The model was computed at the lithospheric scale but focused on the temperature field in the sedimentary basin fill. The model takes into account the geodynamic evolution of the last 20 My, the heat production, and the specific heat conduction of each defined sedimentary layer. The result is a 3D thermal block that is presented in the form of isodepth maps. The results are strongly influenced by thermal conductivity variations such as those due to differences in sediment composition while faults create some more localised influences. The presence of anomalously radiogenic bodies beneath the basin, and/or by variations in lithosphere thickness resulting in possible heat production anomalies strongly influence the thermal variations the Paris Basin. The Alpine Orogeny created a slight temperature increase in the south-eastern part of the basin and inhomogeneities in the lithology of the basement generating additional sources of variation in the sedimentary pil

Crustal structure of Guadeloupe Islands and the Lesser Antilles Arc from a new gravity and magnetic synthesis

Guadeloupe Island (West French Indies) is one of the twenty islands that compose the Lesser Antilles Arc, which results from the subduction of the Atlantic Ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents the compilation and processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe Islands and at the scale of the Lesser Antilles Arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer Arc, the long wavelength positive anomaly is interpreted, at least along the Karukera Spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer Arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism. At the scale of Guadeloupe Island, joined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre Island ; ii) the ancient volcanic complexes of Basse-Terre Island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The EW models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre Island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles Arc and Guadeloupe volcanic system

Geochronological and geochemical characterization of magmatic-hydrothermal events within the Southern Variscan external domain (Ce'vennes area, France)

International audienceGeochronological, mineralogical, and geochemical analyses have been focussed on the Mont-Loze're- Borne plutonic complex and surrounding rocks (Ce'vennes, French Massif Central) in which B-W-Sn and As-Au-Sb mineralization is encountered. Two main results are highlighted: (1) the existence of a 301-306 Ma magmatohydrothermal event unrelated to the emplacement of the Pont-de-Montvert-Borne plutonic body at 316 Ma; (2) the magmatic and hydrothermal features are strongly associated, both in time and in space, thus demonstrating an intimate connection between mineralizing processes and magmatism in this part of the French Massif Central. We also show that mineralization and associated hydrothermal occurrences do not correspond to a simple and single geochemical signature and that a contamination model must be invoked in order to account for the complexity of isotopic results. This study demonstrates that the application of the O and H isotopic signatures as tracers of the source and nature of fluids in an orogenic context requires some specific care. Finally, a model of the tectonic-magmatic- hydrothermal evolution of the study area is suggested in which we discuss two alternative scenarios. The first one implies the existence of two different hydrothermal/ mineralizing events (Bo-W-Sn and As-Au-Sb ones). The second one suggests the same source for all hydrothermal and mineralized structures

3-D Magnetotelluric Investigations for geothermal exploration in Martinique (Lesser Antilles). Characteristic Deep Resistivity Structures, and Shallow Resistivity Distribution Matching Heliborne TEM Results

Within the framework of a global French program oriented towards the development of renewable energies, Martinique Island (Lesser Antilles, France) has been extensively investigated (from 2012 to 2013) through an integrated multi-methods approach, with the aim to define precisely the potential geothermal ressources, previously highlighted (Sanjuan et al., 2003). Amongst the common investigation methods deployed, we carried out three magnetotelluric (MT) surveys located above three of the most promising geothermal fields of Martinique, namely the Anses d'Arlet, the Montagne Pel{\'e}e and the Pitons du Carbet prospects. A total of about 100 MT stations were acquired showing single or multi-dimensional behaviors and static shift effects. After processing data with remote reference, 3-D MT inversions of the four complex elements of MT impedance tensor without pre-static-shift correction, have been performed for each sector, providing three 3-D resistivity models down to about 12 to 30 km depth. The sea coast effect has been taken into account in the 3-D inversion through generation of a 3-D resistivity model including the bathymetry around Martinique from the coast up to a distance of 200 km. The forward response of the model is used to calculate coast effect coefficients that are applied to the calculated MT response during the 3-D inversion process for comparison with the observed data. 3-D resistivity models of each sector, which are inherited from different geological history, show 3-D resistivity distribution and specificities related to its volcanological history. In particular, the geothermal field related to the Montagne Pel{\'e}e strato-volcano, is characterized by a quasi ubiquitous conductive layer and quite monotonic typical resistivity distribution making interpretation difficult in terms of geothermal targets. At the opposite, the resistivity distribution of Anse d'Arlet area is radically different and geothermal target is thought to be connected to a not so deep resistive intrusion elongated along a main structural axis. Beside these interesting deep structures, we demonstrate, after analyzing the results of the recent heliborne TEM survey covering the whole Martinique, that surface resistivity distribution obtained from 3-D inversion reproduce faithfully the resistivity distribution observed by TEM. In spite of a very different sampling scale, this comparison illustrates the ability of 3-D MT inversion to take into account and reproduce static shift effects in the sub-surface resistivity distribution.Comment: Wordl Geothermal Congress 2015, Apr 2015, Melbourne, Australi

Relations between Au / Sn-W mineralizations and late hercynian granite: Preliminary results from the Schistose Domain of Galicia-Trás-os-Montes Zone, Spain

International audienceAu and W-Sn mineralization of the Schistose Domain of Galicia-Trás-os-Montes are spatially related to late hercynian granites. The Bruès (Au) and the Mina Soriana W-(Sn) deposits are studied. Both show some similarities and are assumed to form in the same tectonic and metamorphic context, on top of the granites. The role of the granite as a source for mineralizing fluids and rheological control for vein emplacement is re-adressed and discussed