Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The nucleation, propagation, and associated folding of ramp-flat-ramp normal faults were analyzed from field examples developed in a brittle/ductile multilayer sequence of the Huércal-Overa Basin (SE Spain). Gently dipping sandy silt layers, which display a low cohesive strength (C0 = 7 kPa, μ = 34°), favor the development of extensional detachments. A tectonic origin instead of a possible gravitational origin is supported by the perpendicularity between the paleoslope direction of the fluvial-deltaic environment inferred from imbricated pebbles, and the senses of movement deduced from fault slicken-lines. The link between high-angle normal faults (HANFs) --formed at different levels in the layered sequence-- with horizontal fault segments comes to develop ramp-flat-ramp normal faults with associated roll-over in the hanging wall. Observed extensional duplexes are formed by parallel detachments connected through synthetic Riedel faults. These Riedel faults would produce the back-rotation of the individual blocks (horses), i.e., extensional folding of the originally subhorizontal layers. There is no correlation between the analyzed ramp-flat-ramp normal faults, accommodating south-southeastward extension during Serravallian-lower Tortonian, and either the regional Alpujarride/Nevado-Filabride west-directed extensional shear zone or the top-to-the-north detachments within Alpujarride units, which are clearly sealed by Serravallian-lower Tortonian sediments. Therefore, the studied normal faults are restricted to the brittle/ductile multilayer fluvio/deltaic sequence and accommodate moderate late extension instead of belonging to a large crustal extensional system connected with a regional detachment at depth. Therefore, the basin formed in a moderate crustal thickness context where small and medium-scale extensional systems were subordinate structures. These natural examples support the development of low-angle normal faults at very shallow crustal levels in multilayer sequences with suitable rheological conditions.
ISSN: 0278-7407

hal-00750352
https://hal.archives-ouvertes.fr/hal-00750352
DOI : 10.1029/2012TC003130

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : New-Caledonia island consists of an ultramafic nappe thrusted over a continental and arc-derived basement as the result of the closure of a back-arc basin during the upper Eocene. The morphology of New-Caledonia is mostly characterized by its elongated shape and rectilinear coastline. Indeed, the western and eastern edges of the island are delineated by N140 trending normal faults that are well imaged on seismic lines. Major tectonic lineaments onland, including the scarps corresponding to the main boundary of the ultramafic nappe, also trend N140 suggesting a morphotectonic control by faults having similar kinematics (longitudinal flexure-fault of previous authors). We provide detailed observations from some of these scarps demonstrating indeed that these are not erosional features in origin. We explore the possibility that such surfaces do represent major tectonic limits that accommodated extension and significant tectonic thinning of both the peridotite nappe and its basement. Remnants of a complex extensional fault zone, 200 m wide, are still preserved along the western scarp of the Mont Dore mountain, close to Noumea city. The deformed zone is composed of an early shallow dipping detachment fault, some decimeters thick, offset by a group of late high angle normal faults and is bounded by cataclastic breccias that progressively pass into the fractured host peridotite. The late high angle fault zones have been the site of important syn-tectonic fluid circulation and are underlined by cm-thick silica infills bearing vertical striae. Typical morphology of the main scarps with break of slope is related to the combination of high angle normal faults and low angle detachment. Similar shallow dipping detachment surfaces have been observed along the east coast of southern New-Caledonia as well as within the ultramafic nappe itself and its basement. This study confirms that N140 oriented, large fault zones, with pure-normal to transtensional component of displacement, controlled the morphotectonic evolution of New-Caledonia at the regional scale, after the obduction of ophiolite nappe at the end of the Eocene. Such a fact has to be taken into account when attempting to reconstruct the post-obduction evolution of the island and more particularly when considering the development and distribution of the Ni-rich lateritic surfaces.
EISSN: 1777-5817

hal-00411855
https://hal.archives-ouvertes.fr/hal-00411855
DOI : 10.2113/gssgfbull.179.3.315

Éditeur(s) : HAL CCSD Université des Antilles
Résumé : International audience
The development of the small island territories is often approached under the angle of the vulnerability, the limits and other handicaps which penalize inevitably their growth perspectives. However, it is noticed that some islands display nowadays among the most prosperous economies to the world. The object of this reflection is to propose a frame to study the small islands, the evolution of their positioning and trajectories of development. It’s interesting to see how small islands, with their different political statuses and economic dependences, manage their development in the globalized economy by using conveniently their peculiarity.
Le développement des petits territoires insulaires est souvent abordé sous l'angle de la vulnérabilité, des limites et autres handicaps qui pénalisent inéluctablement leurs perspectives de croissance. Or force est de constate que quelques îles s’affichent désormais parmi les économies les plus prospères au monde. L’objet de cette réflexion est de proposer un cadre pour étudier les petites îles, appréhender l’évolution de leurs positionnements et leurs trajectoires de développement. Il s’agit de voir dans quelle mesure ces petites îles, aux statuts juridiques variables et dépendantes sur le plan économique, peuvent opportunément tirer profit de leur situation – parfois en jouant sur leur singularité- pour se positionner avantageusement dans la configuration actuelle de l’économie mondialisée.
ISSN: 1779-0980

hal-01624763
https://hal.archives-ouvertes.fr/hal-01624763
DOI : 10.4000/etudescaribeennes.7250

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The outstanding exposure of deformation bands in a multilayer sequence of the Orange quarry, Provence, France, motivates a study investigating the development and controls of deformation band geometries by field mapping combined with finite element modeling. Field mapping yields new insights into angular relations between, and evolution of, the deformation bands as well as provides input parameters for the setup and boundary conditions of the numerical simulations using ADELI 2D. In particular, reverse-sense deformation bands are found to have developed within three of the four exposed layers of the multilayer stack with similar orientations to bedding, indicating layer-parallel contraction. Numerical simulations, carried out as a parametric study to investigate the influence on deformation band development and geometry, successfully reproduce the sequential development of deformation bands in the three layers as seen in the field as well as recreate the observed angular geometries of similar to 39 degrees to the maximum compression. This angular relationship is put into context with observations from other field studies and theoretical values to explore controls of deformation band orientations. Furthermore, band localization is impeded in the model by increased layer cohesive strength, demonstrating the importance of host-rock property variations on where localization of bands within the multilayer sequence. Results from both field investigation and numerical simulations are consistent with regional tectonics, where the strata underwent gentle folding due to thrust faulting at depth, and bring further insight into the development and geometry of deformation bands in both extensional and contractional tectonic regimes.
ISSN: 0148-0227

hal-00639452
https://hal.archives-ouvertes.fr/hal-00639452
DOI : 10.1029/2011JB008365

Éditeur(s) : CRPLC : Centre de Recherche sur les Pouvoirs Locaux dans la Caraïbe
Extrait de : Les jeudis de l'Université. Université des Antilles et de la Guyane
Description : Blaise Tchikaya reconnaît d'abord le fait que L'union africaine comme angle d'approche limite quelque peu le sujet de sa communication. Il présente rapidement l'Afrique ainsi que ses forces vives économiques, en portant une attention particulière aux conflits et crises qui la traverse. Il sera d'abord question dans son intervention des causes ou raisons d'être des crises en Afrique. Dans un second temps seront abordées les questions relatives à l'apport de L'union africaine.
Siècle(s) traité(s) : 21
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V14053
V14053

Éditeur(s) : HAL CCSD North Carolina State University
Résumé : Few studies have been conducted about relation between cellulose parameters and biomechanical properties of wood in tropical angiosperms species. For this purpose, on 13 trees from 3 species of French Guyana tropical rainforest in a clear active process of restoring verticality, i) growth strains were measured in situ in order to determine the occurrence of tension wood within samples and ii) cellulose structural parameters were estimated on all the samples using X-ray diffraction method. Crystallite size was estimated from the full-width at half-maximum of the Miller index (002) arc diffraction and angle T was measured following Cave's method. Relationships between these parameters and growth stresses were good and the variations between normal and tension wood were significant, i.e. a lower angle T and a larger crystallite size in tension wood. In order to have a good estimation of the microfibril angle in the main layer of the secondary wall for each species, an experimental calibration was done between angle T and microfibril angle observed with scanning electron microscopy.
ISSN: 19302126

hal-01031799
https://hal.archives-ouvertes.fr/hal-01031799
https://hal.archives-ouvertes.fr/hal-01031799/document
https://hal.archives-ouvertes.fr/hal-01031799/file/42-575-1-PB.pdf

Éditeur(s) : Amer Geophysical Union
Résumé : The origin of the Algerian margin remains one of the key questions still discussed in the Western Mediterranean sea, due to the imprecise nature and kinematics of the associated basin during the Neogene. For the first time, the deep structure of the Maghrebian margin was explored during the SPIRAL seismic survey. In this work, we present a N-S transect off Tipaza (west of Algiers), a place where the margin broadens due to a topographic high (Khayr-al-Din Bank). New deep penetration seismic profiles allow us to image the sedimentary sequence in the Algerian basin and the crustal structure at the continent-ocean boundary. Modeling of the wide-angle data shows thinning of the basement, from more than 15km in the continental upper margin to only 5–6km of oceanic-type basement in the Algerian basin, and reveals a very narrow or absent transitional zone. Analysis of the deep structure of the margin indicates features inherited from its complex evolution: (1) an oceanic-type crust in the deep basin, (2) similarities with margins formed in a transform-type setting, (3) a progressive deepening of the whole sedimentary cover, and the thickening of the Plio-Quaternary sediments at the margin foot, coeval with (4) a downward flexure of the basement in the basin. These features argue for a multiphased evolution of the margin, including (1) an early stage of rifting and/or spreading, (2) a late transcurrent episode related to the westward migration of the Alboran domain, and (3) a diffuse Plio-Quaternary compressional reactivation of the margin.
Journal Of Geophysical Research-solid Earth (0148-0027) (Amer Geophysical Union), 2013-08 , Vol. 118 , N. 8 , P. 3899-3916

Droits : 2013. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00152/26333/24412.pdf
DOI:10.1002/jgrb.50318
http://archimer.ifremer.fr/doc/00152/26333/

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The reactivation of faults with near-optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip-slip and strike-slip mechanisms are dominant, and oblique slips are relatively rare for well-constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike- slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40-60 degrees and 0-20 degrees friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
ISSN: 8755-1209

hal-00412159
https://hal.archives-ouvertes.fr/hal-00412159
DOI : 10.1029/2007RG000240

Éditeur(s) : Université des Antilles AIHP-GEODE : Archéologie Industrielle, Histoire, Patrimoine/Géographie- Développement Environnement de la Caraïbe HARCMAR : Histoire et Archéologie Maritimes des Petites Antilles
Extrait de : "Entre exclusif et contrebande, le commerce colonial aux Antilles XVIIe-début XIXe siècle" : journées d'étude, du 24 au 26 octobre 2019. Université des Antilles
Description : « Tempora mutantur et Nos mutamur in illis », (Les temps changent et nous changeons avec eux). Cette citation tirée d'une lettre écrite en 1664 par Adam Erckelens, chirurgien du Sieur Nicolaas Claesz, planteur à Capesterre de Guadeloupe, résume bien l'attitude et la force des Hollandais de cette époque. Elle illustre également la situation incertaine dans laquelle ils se trouvaient à la fin de l'année 1664. En effet, 1664 - 1665, fut une période délicate pour le commerce néerlandais dans les Antilles. A partir de lettres de marchands, planteurs et commissionnaires hollandais saisies par les navires anglais, se dessinent les relations commerciales exclusives légales ou illégales des différents ports de Pays-Bas avec la zone caraïbe et notamment les Antilles françaises ; type de marchandises échangées, traite des Noirs, méthodes commerciales. Ces lettres mettent en lumière les protagonistes aussi bien en Europe que sur place. Tout ceci dans une situation politique en évolution par la volonté des autorités françaises et notamment de Colbert désireux d'éliminer les Hollandais du commerce antillais par le biais de la création de la Compagnie des Indes Occidentales. L'incertitude sur l'avenir est également due à la tension entre Pays-Bas et l'Angleterre qui aboutira à la Seconde guerre anglo-hollandaise (1665 - 1667).
Siècle(s) traité(s) : 17
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V19115
V19115

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : We have applied transmission electron microscopy (TEM) analyses coupled with viscoplastic self-consistent (VPSC) numerical modelling to identify the active slip systems and to better understand the crystal preferred orientation (CPO) development of the Torridon quartz mylonite (NW Scotland). TEM analyses showed evidence of activation of 1/3〈a〉{π′}, 1/3〈a〉{z} and possible 〈a〉(c) slip systems, as well as dislocation climb and dynamic recrystallization. All the CPOs generated by VPSC models share common characteristics with the Torridon quartz mylonite, but only Models 2 and 3 reproduce the [c]-axes maxima at low angle (<20°) to the foliation pole along the YZ plane, as observed in the mylonite. In Model 2, this concentration only occurs at γ≥2.6, whereas in Model 3 this maxima occurs at lower shear strains. The models that start with a previous preferred orientation acquire very strong CPOs after small-imposed strains, followed by the rapid rotation of the fabric in relation to the new imposed finite strain axes. The combined activation of 〈a〉{π′}, 〈a〉{z} and possibly 〈a〉(c) slip systems, as demonstrated by TEM analyses, suggests that the VPSC model that best predicts CPO development in the Torridon quartz mylonite is Model 2, where the critical resolved shear stress (CRSS) of 〈a〉{π/π′} is assumed to be slightly stronger than 〈a〉(c).
Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

hal-00688840
https://hal.archives-ouvertes.fr/hal-00688840

Éditeur(s) : HAL CCSD
Résumé : Different applications of linear elasticity in structural geology are presented in this thesis through the development of three types of numerical computer codes. The first one uses forward modeling to study displacement and perturbed stress fields around complexly faulted regions. We show that incorporating inequality constraints, such as static Coulomb friction, enables one to explain the angle of initiation of jogs in extensional relays. Adding heterogeneous material properties and optimizations, such as parallelization on multicore architectures and complexity reduction, admits more complex models. The second type deals with inverse modeling, also called parameter estimation. Linear slip inversion on faults with complex geometry, as well as paleo-stress inversion using a geomechanical approach, are developed. The last type of numerical computer code is dedicated to restoration of complexly folded and faulted structures. It is shown that this technique enables one to check balanced cross-sections, and also to retrieve fault chronology. Finally, we show that this code allows one to smooth noisy 3D interpreted faulted and folded horizons using geomechanics.
Différentes applications de l'élasticité linéaire en géologie structurale sont présentées dans cette thèse à travers le développement de trois types de codes numériques. Le premier utilise la modélisation directe pour étudier les déplacements et champs de contraintes autour de zones faillées complexes. On montre que l'ajout de contraintes inégalitaires, telles que la friction de Coulomb, permet d'expliquer l'angle d'initiation des dominos dans les relais extensifs. L'ajout de matériaux hétérogènes et d'optimisations, telles la parallélisation sur processeurs multi-coeurs ainsi que la réduction de complexité des modèles, permettent l'étude de modèles beaucoup plus complexes. Le second type de code numérique utilise la modélisation inverse, aussi appelée estimation de paramètres. L'inversion linéaire de déplacements sur les failles ainsi que la détermination de paléo-contraintes utilisant une approche géomécanique sont développées. Le dernier type de code numérique concerne la restauration de structures complexes plissées et faillées. Il est notamment montré qu'une telle méthode permet de vérifier l'équilibre de coupes géologiques, ainsi que de retrouver la chronologie des failles. Finalement, nous montrons que ce même code permet de lisser des horizons 3D faillés, plissés et bruités en utilisant la géomécanique.
https://tel.archives-ouvertes.fr/tel-00537899

tel-00537899
https://tel.archives-ouvertes.fr/tel-00537899
https://tel.archives-ouvertes.fr/tel-00537899/document
https://tel.archives-ouvertes.fr/tel-00537899/file/thesemaerten.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We use first first-principle methods and the Peierls-Nabarro model to evaluate the resistance to glide, characterized by the Peierls stress, of glide systems for end-member MgSiO3 Perovskite at mantle pressures. [010](100) is the easiest glide system in Mg-Perovskite at all pressures. Peierls stresses increase systematically with pressure for all systems except [001](010), indicating the importance of lattice friction at lower mantle pressures. The ratio of the maximum Peierls stress for each system relative to the [010](100) value defines their critical resolved shear stress (CRSS). These CRSS are used in a visco-plastic self-consistent homogenization model to predict the evolution of crystal preferred orientations (CPO) during deformation of polycrystalline Mg-Perovskite. In axial compression, [100] tends to align with the compression direction, in agreement with in situ observations in axial compression experiments. In simple shear, [010] concentrates near the shear direction and (100), although more dispersed, tends to align near the shear plane, consistent with the dominant activity of the easier [010](100) system. The calculated seismic anisotropy for a 100% Mg-Perovskite aggregate using the CPO in simple shear and the elastic constants Of MgSiO3 perovskite at lower mantle pressures and temperatures is weak (>3% for P-waves with and >2% for S-waves) and decreases with increasing temperature and pressure. P-waves show the fastest propagation parallel to the lineation and S-waves fast polarization is in the foliation at 38 GPa and normal to the lineation at 88 GPa. This weak anisotropy is consistent with global seismological observations of a nearly isotropic lower mantle. There are however two regions where strain-induced Mg-Perovskite CPO could contribute to anisotropy; a) low temperature regions in the uppermost lower mantle, where the predicted S-wave polarization anisotropy may attain 1.6% with a fast polarization parallel to the foliation, b) in high high-temperature domains in the D '' layer, where Mg-Perovskite may be the major stable phase, leading to polarization of fast S-waves normal to the lineation for propagation directions at high angle to the lineation and an apparent isotropy for all other propagation directions.
ISSN: 0012-821X

hal-00411460
https://hal.archives-ouvertes.fr/hal-00411460
DOI : 10.1016/j.epsl.2008.03.058

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Tension wood of Laetia procera (Poepp.) Eichl. (Flacourtiaceae), a neo-tropical forest species, shows a peculiar secondary wall structure, with an alternance of thick and thin layers, while opposite wood of this species has a typical secondary wall structure (S1 + S2 + S3). Samples for the study of microstructural properties were collected upon the estimation of growth stresses in the living tree, in order to analyze the correlation of the former with the latter. Investigation using optical microscopy, scanning electron microscopy and UV microspectrophotometry allowed the description of the anatomy, ultra-structure and chemistry of this peculiar polylaminate secondary wall. In the thick layers, cellulose microfibril angle is very low (i.e., microfibril orientation is close to fibre axis) and cellulose microfibrils are well organized and parallel to each other. In the thin layers, microfibrils (only observable in the inner layer) are less organized and are oriented with a large angle relative to the axis of the cell. Thick layers are lightly lignified although thin layers show a higher content of lignin, close to that of opposite wood secondary wall. The more the wood was under tensile stress, the less the secondary wall was lignified, and lower the syringyl on guaiacyl lignin units' ratio was. The innermost layer of the secondary wall looks like a typical S3 layer with large microfibril angle and lignin occurrence. The interest of this kind of structure for the understanding of stress generation is discussed.
ISSN: 0931-1890

hal-00194923
https://hal.archives-ouvertes.fr/hal-00194923
https://hal.archives-ouvertes.fr/hal-00194923/document
https://hal.archives-ouvertes.fr/hal-00194923/file/Trees_RuelleYoshidaClairThibaut_submitted2006.pdf
DOI : 10.1007/s00468-007-0128-0

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Grain deviations and high extractives content are common features of many tropical woods. We aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content, and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young's modulus (E'L/ρ, where r stands for specific gravity) and damping coefficient (tanδL), were measured. GA dependence was analyzed by a mechanical model which allowed to identify the specific Young's modulus (E'3/ρ) and shear modulus (G'/ρ) along the grain (3), as well as their corresponding damping coefficients (tanδ3, tanδG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0-25° GA and in variations of a factor 2 in E'L/ρ and tanδL. Along the grain, Padauk wood was characterized, as compared to typical hardwoods, by a somewhat lower E'3/ρ and elastic anisotropy (E'/G'), due to a wide microfibril angle plus a small weight effect of extracts; and a very low tanδ3 and moderate damping anisotropy (tanδG/tanδ3). Extraction affected mechanical parameters in the order: tanδ3 ≈ tanδG > G'/ρ >> E'3/ρ. That is, extractives' effects were nearly isotropic on damping but clearly anisotropic on storage moduli.
ISSN: 0043-7719

hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382/document
https://hal.archives-ouvertes.fr/hal-00544382/file/Identification_anisotropic_vibrational_properties_Bremaud_al.pdf
DOI : 10.1007/s00226-010-0348-0

Éditeur(s) : Université Nice Sophia Antipolis
Résumé : The Lesser Antilles is a case study of a very slow subduction (~2 cm/yr) of an old oceanic lithosphere (~84-100 Ma). The region presents a relatively low seismic activity, especially along the interplate contact, and the seismic hazard associated with a possible mega-thrust earthquake is still poorly known. This PhD thesis is a first step toward assessing the ability of the Lesser Antilles subduction zone to produce such a large subduction event. To do so, it aims at constraining the downdip width of the interplate's seismogenic zone. The lack of coverage of permanent seismological stations is a major limitation in the exploration of the Lesser Antilles subduction zone. It is due to the presence of only small aligned islands at far distances from the potentially seismogenic interplate area. Several oceanographic cruises were therefore planned that notably allowed the repeated deployment of ocean bottom seismometers; some of them being left for a few months of background seismicity recording. This thesis specifically focuses on two sets of wide-angle seismic data acquired offshore the Dominica and Martinique islands. From their analysis 3D and 2D tomographic models were produced respectively over the forearc region and across the whole subduction complex. These models constrain the plates' seismic structure as well as their geometry. They allow the discussion of how the imaged structures affect the subduction processes and give a first estimation of the downdip width of the seimogenic zone, defined as the segment of the interplate between the backstop and the upper plate's Moho. The joint interpretation of seismic models and earthquake localizations then refine this first assessment. Epicenter distribution from height months of seismic recording shows indeed that seismicity concentrates within the inner forearc region. The strong velocity gradient that characterize its basement suggests it is denser and more rigid than the more deformable outer forearc basement. The updip limit of the seismogenic zone could then lie arcward of the backstop at the contact of the interplate and the seaward end of the inner forearc crust. At depth, interplate earthquake mechanisms are observed between 35 and 45 km depth and interpreted to have occurred at the downdip limit of the seismogenic zone. The latter could reach a depth over 10,km deeper than the contact of the upper plate's Moho with the interplate, and therefore lie within the mantle wedge. All together, these results imply a large downdip width of the seismogenic zone (~70 km) offshore the Dominica and Martinique islands. Further work is, however, needed in order to fully comprehend the ability of the Lesser Antilles subduction zone to produce a possible mega-thrust earthquake. This would necessitate the evaluation of seismic coupling at the interplate contact and the possible segmentation of the seismogenic zone, for instance, due to the subduction of oceanic ridges.
Les Petites Antilles présentent un contexte géodynamique caractérisé par la subduction à très faible vitesse (~2 cm/an) d'une lithosphère océanique âgée (~84-100 Ma). L'activité sismique y est relativement faible, notamment à l'interplaque, où l'aléa sismique lié à un éventuel séisme de méga-chevauchement reste encore mal contraint. Cette thèse se veut être une première étape dans l'évaluation de la capacité de la zone de subduction des Petites Antilles à générer un tel évènement. Dans ce but, ces travaux tentent d'appréhender l'extension en profondeur du domaine sismogène de l'interplaque. Le manque de couverture des stations sismologiques permanentes est un inconvénient majeur dans l'exploration des Petites Antilles. Il s'explique en raison du peu de terres émergées et de leur éloignement de la zone potentiellement sismogène de l’interplaque. La région a donc fait l'objet de plusieurs campagnes océanographiques qui ont permis, notamment, le déploiement de sismomètres fond de mer (OBS); certains instruments étant restés immergés plusieurs mois afin de procéder à une écoute de la sismicité. Les travaux réalisés au cours de cette thèse se sont focalisés sur deux jeux de données de sismique grand-angle acquis au large des îles de la Dominique et de la Martinique. Leur analyse a permis la construction de modèles tomographiques 3D et 2D respectivement à l'échelle de l'avant-arc et de l'ensemble de la subduction. Ces modèles renseignent sur la structure sismique des plaques en convergence ainsi que sur leur géométrie. Ils permettent de discuter le rôle de la structure dans le fonctionnement de la subduction et d’obtenir une première estimation de l'extension en profondeur de la zone sismogène en considérant la portion de l'interplaque comprise entre le butoir et le Moho de la plaque supérieure. Dans un second temps, l'interprétation conjointe des modèles tomographiques et des localisations des séismes locaux a permis d'affiner cette estimation. Huit mois d'enregistrement de la sismicité montrent en effet une concentration des épicentres dans la région interne de l’avant-arc. Celle-ci présente un socle épais, à fort gradient de vitesse interprété comme plus dense et rigide que le socle de la région externe de l'avant-arc, plus déformable. La limite amont de la zone sismogène pourrait donc se situer en retrait de la position du butoir au contact de l'interplaque et de la limite entre ces deux zones de l'avant-arc. En profondeur, des mécanismes interplaques sont observés entre 35 et 45 km et interprétés comme des marqueurs de la limite aval de la zone sismogène. Cette dernière pourrait donc atteindre une profondeur jusqu'à 10 km supérieure à la limite précédemment évoquée et se trouver, par conséquent, au contact du manteau lithosphérique. L'ensemble de ces résultats suggèrent une extension en profondeur de la zone sismogène (i.e une largeur) de près de 70 km face aux îles de la Dominique et de la Martinique. Ces travaux doivent cependant être poursuivis afin d’évaluer pleinement la capacité de la zone de subduction des Petites Antilles à générer un éventuel séisme de méga-chevauchement. Le taux de couplage à l'interplaque doit être précisé ainsi que sa possible segmentation en lien, par exemple, avec à l'entrée en subduction des rides océaniques.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00172/28335/26628.pdf
http://archimer.ifremer.fr/doc/00172/28335/

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high-angle fault, scarps show extensive mass wasting that reduces their slope. Flexural rotation further lowers scarp slope, hinders mass wasting, resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface. Extension and drag along the fault plane uplifts a wedge of hangingwall material (apron). The detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble, while local slumping emplaces rubble ridges overlying corrugations. The detachment fault zone is a set of anostomosed slip planes, elongated in the along-extension direction. Slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar. Fault planes with extension-parallel stria are exposed along corrugation flanks, where the rubble cover is shed. Detachment fault rocks are primarily basalt fault breccia at 13°20′N OCC, and gabbro and peridotite at 13°30′N, demonstrating that brittle strain localization in shallow lithosphere form corrugations, regardless of lithologies in the detachment zone. Finally, faulting and volcanism dismember the 13°30′N OCC, with widespread present and past hydrothermal activity (Semenov fields), while the Irinovskoe hydrothermal field at the 13°20′N core complex suggests a magmatic source within the footwall. These results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution.
ISSN: 1525-2027

hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973v2/document
https://hal.archives-ouvertes.fr/hal-01571973/file/Escart-n_et_al-2017-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2016GC006775

Éditeur(s) : American Geophysical Union
Résumé : [1] Extreme weather events such as tropical cyclones are difficult to observe with conventional means. Satellite-based observations provide essential measurements of key parameters governing tropical cyclones. They are critical for short-term forecasting. Radiometers onboard the Defense Meteorological Satellite Program satellite series, WindSat and Tropical Rainfall Measuring Mission satellites, scatterometers onboard the ERS, ADEOS, and QuikScat satellites offer unprecedented synoptic observations of surface wind and atmospheric liquid water content, revealing the storm structures with good accuracy. However, satellite estimates do not provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors characteristics, such as the signal wavelength and polarization or the measurement incidence angle. For example, measurements at Ku band are strongly affected by rain. Still, each observing system can offer specific information that can be combined with the others. In particular, we highlight the capabilities of dual-frequency altimeter to provide very high resolution measurements of rain rate, surface wind speed, and wave characteristics. A method is proposed to obtain continuous along-track 5 km resolution measurements of these parameters in the tropical cyclone Isabel. The results shows that dual-frequency altimeters can provide useful information to complement and validate the operational fields provided by the atmospheric numerical models and by NOAA observing systems.
Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2006 , Vol. 111 , N. C1 , P. NIL_38-NIL_50

Droits : 2006 American Geophysical Union
http://archimer.ifremer.fr/doc/2006/publication-1033.pdf
DOI:10.1029/2005JC003068
http://archimer.ifremer.fr/doc/00000/1033/

Éditeur(s) : HAL CCSD De Gruyter
Résumé : International audience
This study aims at better understanding the respective influences of specific gravity (γ), microfibril angle (MFA), and cell-wall matrix polymers on viscoelastic vibrational properties of wood in axial direction. The wide variations of properties between normal wood (NW) and compression wood (CW) are in focus. Three young bent trees (Picea abies, Pinus sylvestris and Pinus pinaster) that recovered verticality were sampled. Several observed differences between NW and CW were highly significant in terms of anatomical, physical (γ, shrinkage, CIELab colorimetry), mechanical (compressive strength), and vibrational properties. Specific dynamic modulus of elasticity (E'/γ) decreases with increasing MFA, and Young's modulus (E') can be satisfactorily explained by γ and MFA. Apparently, the type of the cell wall polymer matrix is not influential in this regard. The damping coefficient (tanδ) does not depend solely on MFA of NW and CW. The tanδ - E'/γ relationship evidences that, at equivalent E'/γ, the tanδ of CW is approx. 34% lower than that of NW. This observation is ascribed to the more condensed nature of CW lignins, and this is discussed in the context of previous findings in other hygrothermal and time/frequency domains. It is proposed that the lignin structure and the amount and type of extractives, which are both different in various species, are partly responsible for taxonomy-related damping characteristics.
ISSN: 0018-3830

hal-00808062
https://hal.archives-ouvertes.fr/hal-00808062
https://hal.archives-ouvertes.fr/hal-00808062/document
https://hal.archives-ouvertes.fr/hal-00808062/file/Changes_viscoelastic_vibrational_Bremaud_al.pdf
DOI : 10.1515/hf-2011-0186

Éditeur(s) : HAL CCSD
Résumé : International audience
We present a chronological (K-Ar), petrologic and geochemical study (major and trace elements, Sr-Nd isotopes) of Middle Miocene (ca. 16-14 Ma) calc-alkaline rocks (basalts to andesites) extruded in the present-day back-arc region of Central Patagonia (Zeballos Volcanic Sequence (ZVS), 47 S). This magmatism started shortly after mafic plutonism ceased in the arc region (ca. 16 Ma, 200 km west), and ended ca. 2 My before the onset of voluminous slab tear-related back-arc alkaline basaltic magmatism (ca. 12 to Pliocene). The studied calc-alkaline rocks have a typical subduction-related signature (high LILE/HFSE ratios, depletion in Nb, Ta and Ti; Ba/La >20; Ta/Hf <1.5; (Sr-87/Sr-86)(o)=0.70366-0.70402, epsilon(Nd)=+0.1-+3.8). Major and trace elements contents are consistent with their evolution by closed system fractional crystallization of a presumed parental liquid similar in composition to the most basic rock of the suite. Moreover, a strong subducted sediment imprint is recognized (increasing Th/HFSE and decreasing Ce/Pb during differentiation). However, these rocks show striking similarities with volcanic complexes emplaced above areas where a gently dipping slab occurs (high K contents; similar LREE/HREE, Nb/Zr, Ba/Nb; Th/Hf; Th/Ta, Ta/Hf<0.3), particularly the present-day Andean flat-slab region and the Neuquen Basin during the Late Miocene. A comprehensive tectono-magmatic model is here presented to explain the generation and extrusion of these calc-alkaline magmas during the Middle Miocene. The development of a transient low-angle subduction and the resulting eastward migration of the volcanic front are then proposed. Mixing between stored remnants of calc-alkaline magmatism and later primitive alkaline melts is envisioned as the most likely process accounting for the transitional signature (i.e., intermediate between calc-alkaline and alkaline, La/Nb >I; TiO2 <2 wt%) of some basalts extruded synchronously with genuine alkaline lavas in the Neogene Patagonian Plateau Lavas province.
Volcanismo calcoalcalino durante el Mioceno Medio en Patogonia Central (47°S): petrogenesis e implicaciones en la dinamica de placas. En este trabajo se presenta un estudio cronologico (K-Ar), petrologico y geoquimico (elementos mayores y trazas, isotopos de Sr-Nd) de rocas calcoalcalinas (basaltos a andesitas) del Mioceno Medio (16-14 Ma) que ocurren en una posicion de trasarco en Patagonia Central (47°S; Secuencia Volcanica Zeballos, SVZ). Este magmatismo comenzo poco despees de que el plutonismo mafico cesara en la region bajo el arco (ca. 16 Ma, 200 km al oeste), y termino ca. 2 My antes del comienzo de un voluminoso evento magmatico basaltico alcalino desarrollado en el trasarco, relacionado con ventanas astenosfericas, que continuo hasta el Pleistoceno. Las rocas calcoalcalinas estudiadas tienen una quimica tipicamente relacionada con procesos de subduccion (altas razones LILE/HFSE, empobrecimientos en Nb, Ta y Ti; Ba/La>20; Ta/Hf l,5; (87Sr/86Sr)0=0,70366-0,70402, End~O,1±3,8); y sus contenidos de elementos mayores y trazas son consistentes con una evolucion por cristalizacion fraccionada, en un sistema cerrado, desde un liquido parental de composicion similar a la de la roca mas basica del conjunto analizado. Se reconoce, ademas, la influencia de sedimentos subductados en la composicion de estos magmas (aumento de la razon Tb/HFSE y disminucion de la razon Ce/Pb durante la diferenciacion). Sin embargo, estas rocas muestran importantes similitudes composicionales con las de complejos volcanicos emplazados sobre areas donde ocurre subduccion de bajo angulo (altos contenidos de K, similares razones LREF/HREE, Nb/Zr, Ba/Nb; TblHf; TblTa, Ta/Hf O,3), particularmente rocas de la actual region de subduccion plana en Chile central-Argentina y de la cuenca de Neuquen durante el Mioceno Superior. Se propone aqui un modelo tectono-magmatico que explica la generacion y extension de magmas calcoalcalinos en una posicion de trasarco durante el Mioceno Medio en Patagonia mediante el desarrollo de un fenomeno transiente de subduccion de bajo angulo y el consiguiente desplazamiento hacia el este del frente volcanico. Ademas, la mezcla entre remanentes de este magmatismo calcoalcalino almacenados en la corteza y fundidos alcalinos posteriores, provenientes de la astenosfera, se presenta como el proceso responsable de la generacion de la signatura transicional (i.e., intermedia entre calcoalcalina y alcalina, La/Nb>1; TiO2 2 wt%) reconocida en algunos basaltos que ocurren contemporaneamente con otros puramente alcalinos en la provincia de las Lavas Neogenas de Plateau de la Patagonia.
ANDEAN GEOLOGY

insu-00561888
https://hal-insu.archives-ouvertes.fr/insu-00561888
DOI : 10.5027/andgeo2010-678

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New outcrops in the Sinis peninsula (Sardinia, Italy) allow a detailed description of the Messinian erosion surface. The correlation between outcrops, industrial seismic data and data collected offshore Oristano from a recent cruise permits reconstruction of the geometry of this surface from presently emerged interfluves to the deep canyons offshore, with: - onshore: an eroded karstic plateau presently cropping out over a 20 km × 5 km area. Well-preserved karst structures occur locally and can form several metres high reliefs. The southernmost edge of the plateau is limited by a cliff. The karstic plateau and the cliff are sealed by transgressive deposits of Pliocene age; - offshore, an interfluve zone with a mostly flat and low-angle dipping plateau, westward dissected by paleovalleys which were identified down to a depth of 2000 m. In the Oristano Gulf, Messinian paleovalleys were also identified. The Capo San Marco paleocliff was probably located on the edge of a canyon. Onshore, only one major erosion surface was identified, located at the top the Messinian sequence. Offshore, this surface extends down to the abyssal plain. The surface was emplaced above deposits related to the Terminal Carbonate Complex. This indicates that the marginal evaporites are older than the major drawdown of the Mediterranean sea-level. The major drawdown is related to the deposition of the deep evaporites.
ISSN: 0037-0738

hal-00407864
https://hal.archives-ouvertes.fr/hal-00407864
DOI : 10.1016/j.sedgeo.2008.06.005