Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Alkali feldspar thermochronologic modeling with the 40Ar/39Ar method has generated marked advances in knowledge of the mechanisms for argon diffusion in feldspars. While the goal in many cases has been to extrapolate the observed and modeled argon behavior in feldspars to natural geological settings, scientific debate surrounding the true feasibility of such extrapolations and indeed, the validity of thermochronologic modeling in itself, have provided much impetus to improve laboratory techniques to test, and increase basic understanding of, argon diffusion. Two cornerstones for the debate over the feasibility of alkali feldspar thermochronology for modeling natural, geologic processes have been: 1. is volume diffusion the main mechanism for argon movement in feldspars? and 2. if volume diffusion is a viable mechanism, does argon then reside in discrete ‘domains' within the feldspar lattice? We describe a study of alkali feldspars from a profile through a well-controlled brittle fault zone in western Norway; the feldspars document argon loss during deformation and strongly suggest the existence of argon ‘domains' within the feldspars, at least during laboratory step heating. The progressive change in the character of argon diffusion is recognizable in the logr/ro diffusion data from the feldspars and is mimicked by physical changes observed optically in the feldspars through progressive degrees of brittle deformation. Modeling results indicate a reduction in size of the biggest domains and the appearance of smaller domains during the strongest stages of deformation. Whether or not this reveals the existence and the transformation of the domain structure in naturo is difficult to prove from our data alone, but interestingly, this behaviour corresponds directly to the physical (optical) appearance of more intense crack networks and subgrains in progressively more brecciated feldspars. Because the thermochronologic histories derived from modeling the feldspar data conform very well to the known tectonic history of the area, the feldspars appear to have successfully retained physical (optical and isotopic) records of episodic tectonic processes operating from ductile through lowtemperature brittle regimes in rocks with a Caledonian history overprinted by several later (younger) geologic events. However, because the ‘cold' brecciation is the last tectonothermal event recorded by these rocks, it is impossible to truly test for the existence of diffusion domains in naturo. Argon loss appears to have been effective only in the most highly brecciated (deformed) samples where the combination of the connected crack network, increased fluid flow and higher temperatures enhanced diffusion via fast diffusion pathways and thus, volume diffusion from the lattice. Only minor argon loss occurred in zones of lower brittle strain, although some development of cracks and brittle features is evident. Independent of the existence of diffusion domains, this study highlights the possible pitfalls when cooling histories are deduced from brecciated feldspars in which age and diffusion charateristics have been decoupled: while the geochronological memory has survived and is identical to that of nonbrecciated feldspars (suggesting no loss and minor effects of deformation), the diffusion characteristics have been completely transposed by brecciation and the appearance of new domains. Modeling feldspars with these latter characteristics would effectively utilise a new feldspar diffusion structure with an ‘old' (relict) age memory.
ISSN: 0016-7037

hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283/document
https://hal.archives-ouvertes.fr/hal-00198283/file/KsparBreccia_Arnaud_Eide_GCA_2000.pdf

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : El Caribe colombiano ha experimentado un acelerado proceso de urbanización y desarrollo turístico en los últimos 50 años. Solo en una ciudad como Cartagena de Indias (la ciudad turística por excelencia de Colombia), datos referidos al periodo noviembre 2009 – enero 2015, mostraron un incremento en la llegada de turistas cercano al 20%. Después de un gran número de encuestas realizadas alrededor del mundo, se encontró que los parámetros en que se basan los turistas a la hora de preferir una playa son: i) la seguridad, ii) el paisaje, iii) calidad del agua, iv) basuras, v) instalaciones. El paisaje es uno de los recursos costeros y por lo tanto su evaluación es una herramienta importante para los gestores y planificadores del litoral a la hora de la realización de planes de conservación, protección, desarrollo y manejo. Este trabajo se basa en la evaluación del valor paisajístico de las playas que constituyen la base de la economía de muchas ciudades costeras en el mundo y en especial de la zona central de litoral Caribe colombiano. Un problema importante en la evaluación del paisaje es la incapacidad de algunas metodologías de reflejar correctamente las percepciones de la gente, debido al alto peso que tienen algunos aspectos subjetivos (p. ej. altura de una geoforma).En este trabajo se presenta la evaluación del paisaje realizada para la zona central de Caribe colombiano (37 playas de los departamentos de Sucre, Bolívar y Atlántico) utilizando la lógica matemática y matrices ponderadas (fuzzy logic mathematics - parameter weighting matrices) las cuales permiten disminuir la subjetividad y cuantificar con exactitud la incertidumbre. Para la evaluación se utilizó una lista de chequeo que está conformada por 26 parámetros, 18 físicos (acantilados, playas, plataformas rocosas, dunas, características de los valles, forma del relieve, mareas, paisaje costero, color del agua y restos de vegetación), y 8 antropogénicos (ruido, basura, descarga de aguas residuales, grado de modificación y de construcción del medio, tipos de acceso, línea del horizonte y estructuras antrópicas). Los parámetros fueron calificados en una escala de 1 a 5 (presencia/ausencia o poca/alta calidad) y, con el fin de cuantificar la incertidumbre y excesos derivados de la subjetividad que pudo haber tenido la evaluación de los parámetros, se utilizó la lógica difusa (fuzzy logic). A la par, un sistema de matrices, se empleó para asignar valores de peso de acuerdo a las preferencias y prioridades de los usuarios. Como resultado de estos análisis lógico-estadísticos se obtuvo un valor (D) el cual resume la evaluación del paisaje en 5 clases que van desde la CLASE 1 (zona litoral sumamente atractiva) hasta la CLASE 5 (playas urbanas muy poco atractivas). De los 37 sectores estudiados, ninguno puede ser considerado como una zona litoral sumamente atractiva, mientras que 15 corresponden a zonas litorales urbanas poco atractivas, el resto de las playas (22) se ubicó entre las clases 2, 3 y 4. Los resultados obtenidos son útiles para los gestores costeros en la medida que, aunque no es posible mejorar los aspectos naturales de la clasificación, si es posible mejorar muchos de los parámetros antropogenicos y, de esta forma, hacer que una playa mejore su clasificación y sea paisajísticamente más atractiva.
In the past few years, the Colombian Caribbean coast has experienced rapid tourism development which has not been accompanied with a similar increase in urbanization facilities. For example, the city of Cartagena de Indias (the most famous tourist destination of Colombia), data related to November 2009 – January 2015 period, showed an increase of 20% in tourist arrivals. A large number of surveys developed in Europe found that the most critical parameters for tourists, when they choose a beach, are: i) security, ii) scenery, iii) water quality, iv) litter, v) facilities. Scenery is one of the most significant coastal resources. Therefore, its evaluation is a valuable tool for coastal managers when developing conservation and protection plans. This proposal provides coastal scenery assessment of 37 beaches along the North Colombian Caribbean littoral by analysing 26 physical and human factors. Results were weighted (not all parameters have equal weight) and subjected to fuzzy logic mathematics in order to reduce recorder judgment subjectivity. The sites were categorised into five classes; Class 1 locations had top grade scenery; Class 5 poor scenery. Of the 37 sectors studied, currently none can be considered as an extremely attractive coastal area (class1), while 15 were unattractive urban coastal areas (class 5), the rest of the beaches (22) placed in classes 2, 3 and 4. Classification of analysed sites depends on the geological setting and degree of human occupation. The technique opens new perspectives for analysis of the potential for coastal tourism development in natural areas and scenic quality improvement of current tourist developed areas. Concerning coastal management issues, emphasis should be given to the upgrading of human parameters eliminating litter and sewage evidence, vegetation debris and enhancing beach nourishment works. This proposal can help in moving some locations from their present status to a higher one.
Caraïbes
Colombie

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.9326
http://journals.openedition.org/etudescaribeennes/9326

Éditeur(s) : HAL CCSD MDPI
Résumé : International audience
LiDAR (Light Detection And Ranging) remote sensing has been shown to be a good technique for the estimation of forest parameters such as canopy heights and above ground biomass. Whilst airborne LiDAR data are in general very dense but only available over small areas due to the cost of their acquisition, spaceborne LiDAR data acquired from the Geoscience Laser Altimeter System (GLAS) have a coarser acquisition density associated with a global cover. It is therefore valuable to analyze the integration relevance of canopy heights estimated from LiDAR sensors with ancillary data such as geological, meteorological, and phenological variables in order to propose a forest canopy height map with good precision and high spatial resolution.In this study, canopy heights extracted from both airborne and spaceborne LiDAR, were first extrapolated from available environmental data (e.g. geology, slope, vegetation indices, etc.). The estimated canopy height maps using random forest (RF) regression from the airborne or GLAS calibration datasets showed similar precisions (RMSE better than 6.5 m). In order to improve the precision of the canopy height estimates regression-kriging (kriging of random forest regression residuals) was used. Results indicated an improvement in the RMSE (decrease from 6.5 to 4.2 m) for the regression-kriging maps from the GLAS dataset, and from 5.8 to 1.8 m for the regression-kriging map from the airborne LiDAR dataset. Finally, in order to investigate the impact of the spatial sampling of future LiDAR missions on the precision of canopy height estimates, six subsets were derived from the initial airborne LiDAR dataset with flight line spacing of 5, 10, 20, 30, 40 and 50 km (corresponding to 0.29, 0.11, 0.08, 0.05, 0.04, and 0.03 points/km² respectively). Results indicated that using the regression-kriging approach achieved a precision of 1.8 m on the canopy height map with flight line spacing of 5 km and achieved an average RMSE of 4.8m for the configuration for the 50 km flight line spacing.
ISSN: 2072-4292

hal-01361343
https://hal.archives-ouvertes.fr/hal-01361343
https://hal.archives-ouvertes.fr/hal-01361343/document
https://hal.archives-ouvertes.fr/hal-01361343/file/mt2016-pub00048036.pdf
DOI : 10.3390/rs8030240

Éditeur(s) : HAL CCSD
Résumé : 38 pages
Rapport
The Chicxulub impact crater, México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.During International Ocean Discovery Program (IODP) Expedition 364, Paleogene sediments and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude section that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of the impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the chronology of the peak-ring rocks; and any observations from the core that may help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate impact crater models for crater formation and environmental effects. The proposed drilling directly contributes to IODP Science Plan goals:Climate and Ocean Change: How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% level mass extinction. The impact basin may also record key hyperthermals within the Paleogene.Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and effects on biodiversity.Earth Connections/Earth in Motion: What are the composition, structure and dynamics of Earth’s upper mantle? What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Mantle uplift in response to impacts provides insight into dynamics that differ between Earth and other rocky planets. Impacts generate earthquakes, landslides, and tsunami, and scales that generally exceed plate tectonic processes yield insight into effects, the geologic record, and potential hazards.IODP Expedition 364 was a Mission Specific Platform expedition to obtain subseabed samples and downhole logging measurements from the sedimentary cover sequence and peak ring of the Chicxulub impact crater. A single borehole was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.7 to 1334.73 m below seafloor with ~99% core recovery and acquiring downhole logs for the entire depth.
International Ocean Discovery Program

hal-01639520
https://hal.archives-ouvertes.fr/hal-01639520
DOI : 10.14379/iodp.pr.364.2017

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Forty years after the image of the Mediterranean transformed into a giant salty lake was first conceived, the fascinating history of the Messinian Salinity Crisis (MSC) still arouses great interest across a large and diverse scientific community. Early outcrop studies which identified severe palaeoenvironmental changes affecting the circum-Mediterranean at the end of the Miocene, were followed by investigations of the marine geology during the 1950s to 1970s. These were fundamental to understanding the true scale and importance of the Messinian event. Now, after a long period of debate over several entrenched but largely untested hypotheses, a unifying stratigraphic framework of MSC events has been constructed. This scenario is derived mainly from onshore data and observations, but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep Mediterranean basins.The MSC was an ecological crisis, induced by a powerful combination of geodynamic and climatic drivers, which had a great impact on the subsequent geological history of the Mediterranean area, and on the salinity of the global oceans. These changed the Mediterranean's connections with both the Atlantic Ocean and the freshwater Paratethyan basins, causing high-amplitude fluctuations in the hydrology of the Mediterranean. The MSC developed in three main stages, each of them characterized by different palaeoenvironmental conditions. During the first stage, evaporites precipitated in shallow sub-basins; the MSC peaked in the second stage, when evaporite precipitation shifted to the deepest depocentres; and the third stage was characterized by large-scale environmental fluctuations in a Mediterranean transformed into a brackish water lake.The very high-resolution timescale available for some Late Miocene intervals in the Mediterranean makes it possible to consider environmental variability on extremely short time scales including, in some places, annual changes. Despite this, fundamental questions remain, some of which could be answered through new cores from the deepest Mediterranean basins. Improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal Messinian succession for the first time. The resulting data would allow us to decipher the causes of this extreme environmental change and its global-scale consequences.
ISSN: 0025-3227

hal-01115664
https://hal.archives-ouvertes.fr/hal-01115664
DOI : 10.1016/j.margeo.2014.02.002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We review the geodynamic evolution of the Aegea-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (1) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the Late Miocene have isolated a narrow stripe of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust).
ISSN: 0040-1951

insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950/document
https://hal-insu.archives-ouvertes.fr/insu-00715950/file/Jolivet-Aegean_Tectonophysics-2012.pdf
DOI : 10.1016/j.tecto.2012.06.011

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Strain and strain rate partitioning in partially molten rocks are two of the important mechanisms that govern the process of coupling and/or decoupling of the partially molten lithosphere. Consequently, the proportion of partial melt and crystals and their network in partially molten rocks influence the degree of the partitioning along with the bulk rheology of the system. This study explores the possible role of finite strain and strain rate on the rate and volume of partial melting and crystallization in a metapelitic system undergoing deformation. Cylinders of synthetic quartz-muscovite aggregate (7: 3 volume ratio) were deformed in torsion at 750 C, 300 MPa and constant shear strain rate ((gamma) over dot = 3 x 10(-4) s(-1)) for finite shear strains (gamma) 1-15. The deformed samples were studied along the longitudinal tangential ( LT) and axial ( LA) sections to obtain the data along a range of strain rates for a given finite strain and vice versa. The results showed that deformation plays an important role on the kinetics of partial melting and crystallization. With increasing strain rate, amount and rate of crystallization comprise the volumetrically dominant process compared to partial melting at a given finite strain. In contrast, when the strain rate is constant, partial melting is the dominant process over crystallization up to moderate strain (gamma < 5). The dominant process reverses at higher strain, and the system shows more crystallization than partial melting. Application of the experimental data to geological systems implies that for metapelites a significant amount (similar to 20%) of partial melt can generate at high strain rate and moderate strain (gamma similar to 7), but at high strain (gamma = 15) the system is melt depleted. Under such conditions, decoupling should take place in brittle-ductile mode. On the other hand, rocks undergoing deformation with low strain rates and strain (gamma < 3) contain more than 25% partial melt, which can act as a major decoupling agent by localizing ductile shear zones.
ISSN: 0148-0227

hal-00617714
https://hal.archives-ouvertes.fr/hal-00617714
DOI : 10.1029/2010JB007865

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : TECTO LITHO
On the basis of a section across the northwestern Alpine wedge and foreland basin, analogue modeling is used to investigate the impact of surface processes on the orogenic evolution. The basis model takes into account both structural and lithological heritages of the wedge. During shortening, erosion and sedimentation are performed to maintain a critical wedge. Frontal accretion leads to the development of a foreland thrust belt; underplating leads to the formation of an antiformal nappe stack in the internal zones. Important volumes of analogue materials are eroded out of the geological record, which in the case of the Alps suggests that the original lengths and volumes may be underestimated. The foreland basin evolves differently depending on the amounts of erosion/sedimentation. Its evolution and internal structuring is governed by the wedge mechanics, thought to be the main controlling mechanism in the development of the Molasse basin in a feedback interaction with surface processes.
ISSN: 0278-7407

hal-00404424
https://hal.archives-ouvertes.fr/hal-00404424
DOI : 10.1029/2006TC002048

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The Iberian Massif is the best exposed segment of the European Variscan Belt. It includes relatively well preserved terranes that were accreted by transpression along time and resulted in a number of geotectonic units that formed part of the Late Paleozoic assembly of the Pangaea Supercontinent. In SW Iberia, these units are the Central Iberian Zone (CIZ), Ossa Morena Zone (OMZ), and the South Portuguese Zone (SPZ). A 210 km long NE-SW magnetotelluric profile was carried out through the CIZ, from the OMZ-CIZ boundary toward the north, reaching the Tagus (Cenozoic) basin. Data dimensionality analysis resulted in a suitable 2-D electrical resistivity structure, allowing a 2-D inversion of the data set. Complementary available geophysical data (deep seismic, gravity and aeromagnetic) and a comparison with a detailed geological cross section led us to constrain the interpretation of the 2-D electrical resistivity structure of the CIZ crust. The results show, for the upper crust, the existence of diverse conductive/resistive bodies that correlate well with known geological features (sedimentary basins, faults, granitic plutons, mineralized systems). A mild but steady conductive band is located along the middle and lower crust that is interpreted as a mafic granulite basement. The upper section of this band connects with several elongated shallow conductors, providing further evidence for the existence, in the Central Iberian Zone, of a complex decollement system where the major faults are rooted. Such a crustal architecture is viewed as the northward continuation of the Variscan large-scale structures previously recognized in the southern sectors (OMZ and SPZ).
ISSN: 0148-0227

hal-00671036
https://hal.archives-ouvertes.fr/hal-00671036
DOI : 10.1029/2010JB007538

Éditeur(s) : HAL CCSD
Résumé : The presence of biological matter (biofilms) in deep geological sites for storage of, for instance, toxic elements or groundwater in aquifers was clearly proved. That biomass triggers physical and chemical processes which greatly modify the durability and the sustainability of the sites. These processes, mainly from oxidative/reductive reactions, are poorly understood. This is mainly due to the fact that former studies were done at the macroscopic level far away from the micrometric scale where relevant processes induced by bacteria take place. Investigations at microscopic level are needed. Thus, we developed an experimental set-up based on the combined use of optical microscopy (transmission), atomic force microscopy (AFM) and electrical and electro-chemical AFM microscopy (EC_AFM) in order to get simultaneous information on topographic and electro-chemical processes. The first highly sensitive step was to use AFM with biological samples in liquid environment: wepresent here a study about AFM imaging of living, moving or self-immobilized bacteria, in their genuine physiological liquid medium and in true in vivo conditions. No external immobilization protocol, neither chemical nor mechanical was needed. For the first time, the native gliding movements of Gram negative Nostoc cyanobacteria upon the surface were studied by AFM. AFM height and mechanical stiffness data were simultaneously acquired. From these, mechanical parameters, inner turgor pressure and Young modulus, were derived for different bacterial species (Anabaenopsis circularis, Rhodococcus wratislaviensis). Our study revealed that AFM imaging is thus possible on moving living species. These results open a large window on new studies of both dynamical phenomena of practical and fundamental interests such as the formation of biofilms and dynamic properties of bacteria in real physiological conditions. The second delicate step was to combine AFM and optical measurements with electrical ones. We mounted a new experimental set-up coupling real-time (i) monitoring of optical properties as the optical density (OD) evolution related to bulk bacterial growth in liquid or as the counting of number of bacteria adhering on the surface of the sample as well and (ii) electrical and electrochemical measurements. Furthermore, these results will shortly be applied to the optimized monitoring of the in-situ activity of bacteria consuming oil pollutants, following this way, in real-time, the bioremediation of an oilcontaminated soil (ANR ECOTECH_BIOPHY program).
La présence de matière biologique (biofilms) dans les sites de stockage géologique profond, d'éléments toxiques ou encore de l'eau potable des aquifères est maintenant clairement démontrée. Cette biomasse est à l'origine de processus physiques et chimiques qui modifient considérablement la durabilité et la pérennité des sites concernés. Ces processus, principalement de type oxydo-réductif, sont encore mal compris. Ceci est principalement dû aux méthodes d'investigation, principalement macroscopiques, loin de l'échelle micrométrique caractéristique des bactéries. Seules des études, basées sur des méthodes d'investigation locale, peuvent apporter les informations requises. Ainsi, nous avons développé un dispositif expérimental basé sur l'utilisation combinée de la microscopie optique (en transmission), la microscopie à force atomique (AFM) et la microscopie AFM en mode électrique et électrochimique (EC_AFM) afin d'obtenir des informations simultanées sur la topographie de l'échantillon et sur les processus électrochimiques à l'échelle des bactéries. La première étape sensible consistait à utiliser l'AFM sur des échantillons biologiques en milieu liquide: nous présentons ici les résultats de l'imagerie AFM en milieu liquide de plusieurs types de bactéries dans leurs conditions physiologiques naturelles (conditions in vivo). Aucun protocole d'immobilisation, ni chimique ni mécanique, n'a été nécessaire; et pour la première fois, les mouvements de reptation de cyanobactéries Nostoc ont été étudiés par l'AFM. Les études AFM ont permis d'acquérir des données topographiques mais aussi mécaniques : nous avons pu ainsi mesurer le module d'Young, la pression de turgescence de différentes souches bactériennes (Anabaenopsis circularis, Rhodococcus wratislaviensis). Cette étude complète, a révélé que l'imagerie AFM est donc possible sur des espèces vivantes en mouvement. Ces résultats ouvrent une grande fenêtre sur de nouvelles études d'intérêts tels que la formation de biofilms et les propriétés dynamiques de bactéries dans des conditions physiologiques réelles. La deuxième étape délicate était de combiner l'AFM aux mesures optiques et électriques. Nous avons développé un nouveau dispositif expérimental permettant (i) le suivi de l'évolution de la croissance bactérienne par la mesure des propriétés optiques comme la densité optique DO (pour le développement bactérien en volume - milieu planctonique) , ou l'analyse de l'image du substrat par comptage du nombre de bactéries sur la surface de l'échantillon (biofilm), et (ii) les mesures électriques et électrochimiques. L'ensemble de ces résultats sera prochainement appliqué au développement de nouveaux outils de surveillance d'une biodépollution de terrain contaminé par les hydrocarbures, par le suivi in situ et en temps réel de l'activité de bactéries dépolluantes (ECOTECH_BIOPHY ANR).
https://tel.archives-ouvertes.fr/tel-01044714

tel-01044714
https://tel.archives-ouvertes.fr/tel-01044714
https://tel.archives-ouvertes.fr/tel-01044714/document
https://tel.archives-ouvertes.fr/tel-01044714/file/theseDhahri2013.pdf

Résumé : Les forêts tropicales contiennent dans leur biomasse aérienne un stock de carbone important à l’échelle de la planète. Mesurer ce stock et comprendre son fonctionnement permet de mieux saisir les enjeux liés à sa protection, sa destruction ou sa modification, ainsi que son rôle dans le cycle du carbone et les mécanismes climatiques globaux. Dans le cadre des problématiques économiques et écologiques liés au climat, les forêts sont progressivement prises en compte dans les programmes internationaux de mesures visant à réduire l’impact anthropique sur le climat (Protocole de Kyoto, 1998 ; Accord de Copenhague, 2009). L’intégration des forêts dans les mécanismes financiers liés au marché du carbone est clairement envisagée dans les années à venir (marché de carbone « d’origine forestière »).L’estimation de la biomasse aérienne d’une parcelle de forêt inventoriée nécessite l’utilisation successive de plusieurs modèles. Dans ces parcelles, le diamètre et l’espèce de chaque arbre sont renseignés. Ensuite, ces parcelles sont utilisées comme références pour l’extrapolation spatiale des valeurs de biomasse. Cette extrapolation repose souvent sur le traitement de signaux aériens (avions, satellites). Il est aussi possible d’utiliser covariables environnementales (climat, géologie, …).L’incertitude associée à l’estimation de la biomasse d’une région est le résultat de toutes les incertitudes associées à ces différents processus. Les connaissances actuelles ne nous permettent pas de quantifier cette incertitude. L’objectif de la thèse est de développer une méthodologie d’estimation de la biomasse qui permette la propagation des incertitudes ainsi que l’identification des sources de cette incertitude.Modèle de hauteur : Nous proposons un nouveau modèle de hauteur pour les forêts tropicales. Les paramètres de ce modèle ont un sens écologique et peuvent être prédits par des variables décrivant le peuplement sur lequel il est appliqué. Nous avons utilisé les données des projets Amalin et Bridge et sélectionné 42 parcelles réparties en Guyane dans lesquelles le diamètre et la hauteur de chaque arbre ont été mesurés.Modèle de densité de bois : Un modèle à été conçu pour associer à chaque espèce une distribution de densité de bois et non une valeur fixe. Nous avons utilisé les données du projet Bridge dans lequel la densité de bois a été mesurée sur 2504 arbres représentant 466 espèces.Modèle de biomasse: Nous avons montré par une analyse de sensibilité que les incertitudes des prédictions de hauteur et de densité de bois n’avaient qu’une part négligeable dans l’incertitude des prédictions de biomasse. L’amélioration de la précision de ces modèles n’est donc pas une priorité. En revanche, le modèle de hauteur peut être une source de biais.Modélisation spatiale : Les modèles développés ont été appliqués à différents réseaux de parcelles couvrant bien la zone littorale guyanaise : inventaires papetiers de l’ONF, réseau Guyafor, projet Amalin… Les prédictions de biomasse de ces parcelles sont utilisées dans un modèle spatiale. Nous produisons ainsi une carte de biomasse guyanaise associée à une carte de l’incertitude de cette estimation.
Tropical forest yield and important part of the aerial vegetation carbon stock on earth. Measuring and understanding this stock distribution is crucial for the management of the tropical forests facing the actual environmental challenges (REDD+, carbon market).Aerial Biomass estimation of forest census plots requires few models depending on the precision of the inventory: diameter models, height models, wood density models. Spatial extrapolation between census plots relies on aerial data (satellite measurements, images) or ground-based data (geology, altitude).The uncertainty of the estimation of a region’s biomass is the result of the uncertainty brought by all these models. The aim of the thesis is to develop models and methods to estimate the biomass of a region while propagating the uncertainties. This is applied to the neo-tropical forest of French Guiana (South America, Guianas Plateau).

http://www.theses.fr/2012AGUY0567/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In southeastern Taiwan a slice of forearc basement belonging to the Philippine Sea Plate upper-plate is suspected to subduct under the Luzon arc as a consequence of the transition from oceanic to incipient continental subduction. Effects on the morphology, deformation, geometry of structures and tectonic evolution of the orogenic wedge in the collision area are numerous. This study examines the impact of foreare lithosphere subduction on forearc basin and accretionary wedge deformation. A morpho-structural analysis of the geological features observed onland and offshore allows describing in detail the complex deformation suffered by the area. A combined approach by analogue modeling is applied to better understand the phenomenon. Comparison between nature and experimental results shows that subduction of a forearc basement slice induces intense shortening and concomitant deformation in the foreare domain. Such process involves deformation of the foreare basin previously developed in a setting of oceanic subduction. Sediments of the forearc basin are involved in the growth of a new thrust ridge backthrusted against the basement slope of the volcanic arc edifice. Sediments coming from the growing orogenic wedge are trapped in the trough developed between its backpart and the topographic high of the new rising ridge. A syn-collisional orogenic basin develops which structural evolution characterizes the progressive shortening of the forearc domain. Most of the deformation and tectonic events recorded offshore or onland in the complex area south of Taiwan can be explained using results of our specific modeling which well describe the tectonic processes associated with continental subduction under a volcanic are.
ISSN: 0040-1951

hal-00420080
https://hal.archives-ouvertes.fr/hal-00420080
DOI : 10.1016/j.tecto.2007.11.016

Éditeur(s) : HAL CCSD
Résumé : This historical perspective provides an overall view of the main steps that led to the acceptance of the concept of mantle exhumation accompanying lithosphere stretching and extreme crustal thinning. We first remember that the presence of exposures of mantle rocks along oceanic spreading ridges was early reported in the 60's due to the results of sediment cores and dredge hauls collected along the Mid-Atlantic Ridge. In the meantime, detailed analysis of the relationships between oceanic sediments of Late Jurassic age and their primary basement in the Apennine ophiolites led many authors to point to the importance of exhumation of mantle rocks on ancient seafloors. By contrast to the thick sections of classical ophiolites (e.g. Oman), the Alpine-Corsican-Appennine ophiolites are characterized by a relatively small amount of mafic rocks (gabbros and basalts), by the absence of any sheeted dyke complex and by the frequent occurrence of oceanic sediments stratigraphically overlying mantle-derived peridotites and associated gabbroic intrusions. They display some of the characteristics of slow-spreading ridge systems, but, due to their highly tectonized character, they have been interpreted successively either as remnants of oceanic fracture zones of normal ocean or as remnants of very-poorly organized, abnormal oceanic basement. This review shows how the concept of mantle exhumation has been elaborated more or less in the same period both by marine geoscientists and by geologists conducting investigations in ophiolitic units of the Alps-Apennines mountain belt. Dredging and diving results from the Gorringe Bank, the Iberia margin, the Thyrrenian Sea and the Central Atlantic in the 1980's and 1990's provided additional proofs that the mantle is currently exhumed in various oceanic environments, including distal continental margins, back-arc basins and slow-spreading ridges of wide oceans. It is shown finally how renewed cross-information from mountain belts and the oceans, multiplying the examples of sedimentary reworking of mantle material, help better constrain the mechanisms of mantle exhumation. This mechanism progressively appeared as a fundamental step during the processes of extension of both continental and oceanic lithospheres in numerous geological situations worldwide.
Bollettino della Società Geologica Italiana

hal-00475653
https://hal.archives-ouvertes.fr/hal-00475653
DOI : 10.3301/IJG.2009.128.2.279

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
This special issue includes papers covering various topics of importance in the Caribbean such as geodynamics, environmental evolutions and natural hazards (fig. 1). This collection of articles focuses in particular on geodynamic processes occurring along the Caribbean plate boundaries, on volcanic hazards and on flooding. Given the recently increased societal importance of these subjects, we hope that the regional geological community and the local policy makers and government officials of the Caribbean countries will find this a timely and valuable update regarding research advances on these topics. We decided to publish this issue following the Caribbean Geological Conference, which has been held every 3 years since 1955 and took place in Guadeloupe for its 19th meeting from the 21st to the 24th of March 2011.
EISSN: 1777-5817

hal-00830337
https://hal.archives-ouvertes.fr/hal-00830337
DOI : 10.2113/gssgfbull.184.1-2.3

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Terrane accretion and intraplate deformation are both common processes occurring during the assembly of large continental masses. The relative roles of these mechanisms are at the heart of a debate concerning the tectonic evolution of the Borborema Province, northeastern Brazil. In the Central subprovince, four terranes or domains have been proposed. In the Alto Moxotó domain, paragneiss of the Sertânia Complex were considered to record a distinct structural and geochronological evolution compared to those in the adjacent Rio Capibaribe domain, in the East. Here, we report the results of a geological study conducted in the type area of the Sertânia Complex. Kinematic criteria and metamorphic mineral assemblages indicate that the main foliation record top-to-the-W tectonic transport under upper amphibolite facies conditions (650–700 °C). The main foliation was affected by overturned folds and upright to inclined folds; the latter two formed coevally with the development of transcurrent shear zones. Samples of mafic orthogneiss and paragneiss tectonically intercalated in the same outcrop were dated by LA-ICP-MS. The orthogneiss sample yields a crystallization age of 1978 ± 8 Ma. Detrital zircons in the paragneiss sample show a multimodal pattern with a well-defined age peak at c. 700 Ma, showing that the paragneiss is younger than 700 Ma and so the main foliation is also younger than this age. In turn, these findings suggest that the occurrence of exclusively Paleoproterozoic zircons in three other dated samples of paragneiss cannot be used to accurately define the deposition age of the detritus. The structural and geochronological characteristics of the Sertânia Complex are similar to those of the Surubim Complex in the Rio Capibaribe domain. Together with previous results showing that the basement of the Alto Moxotó and Rio Capibaribe domains is also similar, we interpret these sequences as having been deposited on a once contiguous tract of continental crust. An accretionary terrane model is thus not required to account for the tectonic evolution of this portion of the Borborema Province. Instead, a model of intracontinental deformation of a preexistent continent is fully supported by the data and also by the lack of evidence for oceanic subduction.
ISSN: 0301-9268

hal-01622825
https://hal.archives-ouvertes.fr/hal-01622825
DOI : 10.1016/j.precamres.2017.07.006

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Mélange rocks outcrop widely in the central and western frontal sectors of the Betic Cordillera, as in many other collisional orogens where they form part of the accretionary wedges. Extrusion of Triassic plastic clays and evaporites was favored by the progressive accretion of the Betic External Zones, mixing rocks of different provenance and forming a synorogenic frontal mélange unit. MT data coupled with gravity data are a valid combined methodology to characterize the geometry of these mélange units, since the characterization of plastic rocks geometry is usually uncertain using seismic techniques. The results correlate well with known geological features (sedimentary basins, calcareous ranges, evaporitic rocks) and reveal the deep geometry. A resistive body, slightly dipping toward the SE, points to the continuity of the Iberian Massif below the Guadalquivir basin (2°) and the External Zones (6-8°). To the south, gravity models show the Iberian continental crust subducting below the Internal Zones with a roughly 20-35° slope. The main conductive bodies are related to the location of evaporitic rocks involved in the frontal mélange. They overlie the Iberian Massif and, southwards, the frontal Jurassic and Cretaceous limestone sequences of the External and Median Subbetics. In this setting, thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction, and being progressively accreted toward a frontal mélange.
ISSN: 1525-2027

hal-00750364
https://hal.archives-ouvertes.fr/hal-00750364
DOI : 10.1029/2012GC004153

Éditeur(s) : HAL CCSD Society of Economic Geologists
Résumé : International audience
The ~8-Moz Sadiola Hill gold deposit is located in the Kédougou-Kénieba inlier, a window of deformed ca. 2200 to 2050 Ma rocks that crop out in eastern Senegal and western Mali. The geology of the inlier differs from other Paleoproterozoic granite-greenstone belts and sedimentary basins by the abundance of carbonate rocks. The Sadiola Hill gold deposit occurs within 3 km of the Senegal-Mali shear zone, and country rocks in the region have undergone polycyclic deformation. The lithostratigraphy of the open pit consists of impure limestones overlain by younger sequences of detrital sedimentary rocks, which include arenite, wacke, and siltstone. The sedimentary rocks have been subjected to regional greenschist-facies metamorphism and have been intruded by multiple generations of synkinematic, calc-alkaline stocks and dikes. The bulk of the ore is hosted within a N-S- to NNW-trending, 10- to 50-m-wide, brittle-ductile dilational shear zone defined as the Sadiola shear zone. Gold lodes also occur along an array of steep NNE-trending shear zones. Geometric and kinematic analyses indicate that the ore-hosting structures were undergoing sinistral displacement at the time of mineralization, locally defined as the D3s NNW-SSE-shortening event. Hydrothermal alteration is polyphase and includes an early high-temperature calc-silicate phase (i.e., porphyroblastic growth of actinolite-tremolite) followed by a potassic phase (i.e., biotite-calcite-quartz ± K-feldspar-tourmaline-actinolite) that was synchronous with ore mineral deposition. Paragenetic studies reveal a multistage ore development that includes an As-rich sulfide stage, followed by an Au-Sb stage. The ore is associated with a metal enrichment suite of Au-As-Sb ± Cu-Fe-W-Mo-Ag-Bi-Zn-Pb-Te. The Sadiola Hill deposit shares a similar relative timing and structural setting to that of other world-class orogenic gold systems in the West African craton (e.g., Ashanti, Loulo), with gold deposition occurring during a period of transcurrent tectonics, after the cessation of region-wide compressional deformation. The high-temperature paragenesis at Sadiola Hill is atypical of gold mineralization in the craton and indicates that the late Eburnean tectono-magmatic activity between ca. 2080 and 2060 Ma played an important role in the dynamics of hydrothermal fluid circulation along the Senegal-Mali shear zone.
ISSN: 0361-0128

hal-01583358
https://hal.archives-ouvertes.fr/hal-01583358
DOI : 10.2113/econgeo.112.1.23

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Analogue and numerical models have shown that the strength of the lithospheric mantle controls the mode of lithosphere deformation. In extension, the presence or absence of a high strength brittle mantle respectively leads to localized or distributed rifting. However, first order geophysical data question the existence of such a brittle mantle. Here we use 2-D finite-element large strain modelling to quantify the impact of a ductile localizing mantle - instead of brittle - in triggering continental rifting. As a novelty, the mantle rheology considers the effect of grain boundary sliding during strain-induced grain size reduction, which may promote a significant strength drop and subsequent strain localization at low mantle temperature (< 700-800 °C). Our results reveal that such ductile localizing mantle implies varying modes of continental rifting that mainly depend on both the amount of weakening in the ductile mantle and the strength of the lower ductile crust. A medium to strong lower crust implies coupling between the upper crust and ductile localizing mantle, yielding to narrow continental rifting. In contrast, a weak lower crust implies decoupling between the upper crust and ductile localizing mantle, giving rise to a switch from distributed faulting at incipient strain to localized faulting at large strain. Ductile strain localization in the lithospheric mantle is therefore sufficient to trigger continental rifting, although a critical amount of weakening is required. Such ductile localizing mantle provides a relevant geological and mechanical alternative to the brittle mantle. It moreover provides a wider variety of modes of upper crustal faulting that are commonly observed in nature.
ISSN: 0040-1951

Droits : info:eu-repo/semantics/OpenAccess
insu-00924254
https://hal-insu.archives-ouvertes.fr/insu-00924254
https://hal-insu.archives-ouvertes.fr/insu-00924254/document
https://hal-insu.archives-ouvertes.fr/insu-00924254/file/Gueydan_precigout_2014_Tectonophysics.pdf
DOI : 10.1016/j.tecto.2013.11.029

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The Pyrenean peridotites (lherzolites) form numerous small bodies of subcontinental mantle, a few meters to 3 km across, exposed within the narrow north Pyrenean zone (NPZ) of Mesozoic sediments paralleling the north Pyrenean Fault. Recent studies have shown that mantle exhumation occurred along the future NPZ during the formation of the Albian-Cenomanian Pyrenean basins in relation with detachment tectonics. This paper reviews the geological setting of the Pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the Bearn region. Only two types of geological settings have to be distinguished among the Pyrenean ultramafic bodies. In the first type (sedimented type or S type), the lherzolites occur as clasts of various sizes, ranging from millimetric grains to hectometric olistoliths, within monogenic or polymictic debris flow deposits of Cretaceous age, reworking Mesozoic sediments in dominant proportions as observed around the Lherz body. In the second type (tectonic type or T type), the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses. Both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed Triassic rocks and have fault contacts with units of deformed Jurassic and Lower Cretaceous sediments belonging to the cover of the NPZ. These deformed Mesozoic formations are not older that the Aptian-early Albian. They are unconformably overlain by the Albian-Cenomanian flysch formations and have experienced high temperature-low pressure mid-Cretaceous metamorphism at variable grades. Such a tectonic setting characterizes most of the lherzolite bodies exposed in the western Pyrenees. These geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the Mesozoic cover in the preorogenic evolution of the Pyrenean realm. In the light of such evidence, a simple model of basin development can be inferred, involving extreme thinning of the crust, and mantle uprising along a major detachment fault. We demonstrate coeval development of a crust-mantle detachment fault and generalized gravitational sliding of the Mesozoic cover along low-angle faults involving Triassic salt deposits as a tectonic sole. This model accounts for the basic characteristics of the precollisional rift evolution in the Pyrenean realm.
ISSN: 0278-7407

hal-00512818
https://hal.archives-ouvertes.fr/hal-00512818
DOI : 10.1029/2009TC002588

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : International audience
Carbonation of ultramafic rocks in geological reservoirs is, in theory, the most efficient way to trap CO2 irreversibly; however, possible feedback effects between carbonation reactions and changes in the reservoir permeability must be considered to realistically assess the efficiency and sustainability of this process. We investigated changes in the hydrodynamic properties of sintered dunite samples by means of percolation experiments, under conditions analogous to that of in situ carbonation. Our results show that carbonation efficiency is controlled by the local renewal of the reactants and the heterogeneity of the pore structure. Preferential flow zones are characterized by the formation of magnetite and of a silica-rich layer at the olivine surfaces, which eventually inhibits olivine dissolution. Conversely, sustainable olivine dissolution together with coprecipitation of magnesite, siderite, and minor Mg-TOT-phyllosilicates, occur in reduced-flow zones. Thus carbonate precipitation only decreases porosity in zones where diffusion-controlled transport is dominant. Consequently, while high flow rates will decrease the carbonation efficiency of the reservoir and low flow rates may reduce the permeability irreversibly close to the injection point, moderate injection rates will ensure a partial carbonation of the rock and maintain the reservoir permeability.
ISSN: 0013-936X

hal-00424540
https://hal.archives-ouvertes.fr/hal-00424540
DOI : 10.1021/es8018429