Éditeur(s) : HAL CCSD Taylor & Francis: STM, Behavioural Science and Public Health Titles
Résumé : International audience
The dislocation microstructures in a single crystal of olivine deformed experimentally in uniaxial compression at 1090 °C and under a confining pressure of 300 MPa, have been investigated by transmission electron tomography in order to better understand deformation mechanisms at the microscale relevant for lithospheric mantle deformations. Investigation by electron tomography reveals microstructures, which are more complex than previously described, composed of and dislocations commonly exhibiting 3D configurations. Numerous mechanisms such as climb, cross-slip, double cross-slip as well as interactions like junction formations and collinear annihilations are the source of this complexity. The diversity observed advocates for microscale deformation of olivine significantly less simple than classic dislocation creep reported in metals or ice close to melting temperature. Deciphering mechanism of hardening in olivine at temperatures where ionic diffusion is slow and is then expected to play very little role is crucial to better understand and thus model deformation at larger scale and at temperatures (900–1100 °C) highly relevant for the lithospheric mantle.
ISSN: 1478-6443

hal-01667146
https://hal.archives-ouvertes.fr/hal-01667146
DOI : 10.1080/14786435.2017.1367858

Éditeur(s) : HAL CCSD
Résumé : International audience
The way faults control upward fluid flow in extensive hydrothermal systems without an abnormal heat source such as volcanic or plutonic activity is still unclear. In the Eastern Pyrénées, an alignment of 29 hot springs (from 29 • C to 73 • C) along the Têt normal Fault offers the opportunity to study this process. Using an integrated multi-scale geological approach including mapping, remote sensing, macro and microscopic analyses of fault zones, we show that hot springs locate close to high topographic reliefs related to fault throw and segmentation. Emergences are always in crystalline rocks at gneiss-metasediments contacts, mostly in the Têt Fault footwall. In more details, they localize either (1) in brittle fault damage zones at the intersection between the Têt Fault and subsidiary faults, and (2) into hercynian ductile faults where dissolution cavities run along shear zones. Using these observations and 2D preliminary numerical simulations, we propose a hydrogeological model of upward hydrothermal flow. Meteoric fluids infiltrate at high altitude in the fault footwall relief where they acquire temperature because of the geothermal gradient. Hydraulic gradient and buoyancy forces allow them to upflow along fault-related permeability anisotropies. The identification and prioritization of the features controlling this kind of system have important implications for geothermal exploration and for the understanding of fluid-flow into the brittle Earth's crust in general.
EGU 2017
Vienne, Austria

hal-01491096
https://hal-brgm.archives-ouvertes.fr/hal-01491096
https://hal-brgm.archives-ouvertes.fr/hal-01491096/document
https://hal-brgm.archives-ouvertes.fr/hal-01491096/file/EGU2017-Taillefer-etal_4996.pdf

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : International audience
High-resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow-slip events, and to estimate slow transients related to earthquake swarms. However, they are also sensitive to other numerous influences, internal or external. Furthermore, the quality of their coupling to the rock through cementation, and the mechanical properties of the rock mass around them, have a critical influence on their records. Many of the existing strainmeters present such problems, and the correction for these effects often remains a challenge. In this paper, we present the analysis of the records of a high-resolution borehole dilatometer (Sacks–Evertson), located in the seismically active rift of Corinth (Greece) (station TRZ in the Trizonia island). We show that the instrument suffers from an only partial-solid coupling, and that the nearby sea tides have a direct (through elastic response) and indirect (through pore-pressure diffusion) effect on the dilatation signal, which adds up to the solid tidal strain source. We propose a methodology that allows, in a first step, to better separate the internal (solid tide) from the external (air pressure, sea level) influences, by calculating a frequency-dependent transfer function outside the range of the tidal periods. We then extrapolate this function, in particular at the tidal periods. In a second step, the resulting variation with frequency of the coupling coefficients with sea level led us to estimate the proportion of instrument not solidly cemented to rock (thus in contact with water pore pressure), which is about 90 % of the total height. Despite the small proportion of solid coupling, the sensor resolution remains very good up to a few tens of hours of a time period, thanks to the confining effects of the rocks on the local pore pressure. These results allow us to correct for the external effects, and reduce the associated variance by 80–90 % (in the period range of minutes to days). The empirical correction of the sea level effect could be explained using a simple Boussinesq’s approximation and 1D pore-pressure diffusion model, which contributed to better constraint of some of the poro-elastic parameters in the vicinity of the instrument. After correction, the solid tidal signal at the 24-h period is almost anti-correlated with those of the theoretical solid tide. This surprising result is consistent with a similar anti-correlation observed for the longest period surface waves (200 s) comparing the TRZ dilatometer signals to the strain measured by a nearby borehole strainmeter (MOK, 15 km). This could be related to the presence of a shallow fault close to the instrument, which would creep in response to seismic wave-related stress.
ISSN: 0033-4533

hal-01122853
https://hal.archives-ouvertes.fr/hal-01122853
DOI : 10.1007/s00024-013-0742-2

Éditeur(s) : HAL CCSD
Résumé : International audience
Seismic anisotropy is a ubiquitous feature of the subcontinental mantle. This can be inferred both from direct seismic observations of shear wave splitting from teleseismic shear waves, as well as the petrofabric analyses of mantle nodules from kimberlite pipes. The anisotropy is principally due to the strain-induced lattice preferred orientation (LPO) of olivine. The combined use of these mantle samples, deformation experiments on olivine, and numerical modeling of LPO, provides a critical framework for making inferences about mantle deformation from observed seismic anisotropy. In most cases there is a close correspondence between mantle deformation derived from seismic observations of anisotropy, and crustal deformation, from the Archean to the present. This implies that the mantle plays a major, if not dominant role in continental deformation. No clear evidence is found for a continental asthenospheric decoupling zone, suggesting that continents are probably coupled to general mantle circulation.
Mantle Petrology: Field Observations and high Pressure experimentations: a Tribute to Francis R. (Joe) Boyd

hal-01391514
http://hal.univ-reunion.fr/hal-01391514
http://hal.univ-reunion.fr/hal-01391514/document
http://hal.univ-reunion.fr/hal-01391514/file/Silver_et_al_BoydVolume 1999_hal.pdf

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Impact of GPS (Global Positioning System) data assimilation is assessed here using a high-resolution numerical weather prediction system at 2.5 km horizontal resolution. The Zenithal Tropospheric Delay (ZTD) GPS data from mesoscale networks are assimilated with the 3DVAR AROME data assimilation scheme. Data from more than 280 stations over the model domain have been assimilated during 15-day long assimilation cycles prior each of the two studied events. The results of these assimilation cycles show that the assimilation of GPS ZTD with the AROME system performs well in producing analyses closer to the ZTD observations in average. Then the impacts of assimilating GPS data on the precipitation forecast have been evaluated. For the first case, only the AROME runs starting a few hours prior the triggering of the convective system are able to simulate the convective precipitation. The assimilation of GPS ZTD observations improves the simulation of the spatial extent of the precipitation, but slightly underestimates the heaviest precipitation in that case compared with the experiment without GPS. The accuracy of the precipitation forecast for the second case is much better. The analyses from the control assimilation cycle provide already a good description of the atmosphere state that cannot be further improved by the assimilation of GPS observations. Only for the latest day (22 November 2007), significant differences have been found between the two parallel cycles. In that case, the assimilation of GPS ZTD allows to improve the first 6 to 12 hours of the precipitation forecast.
ISSN: 0992-7689

hal-00403847
https://hal.archives-ouvertes.fr/hal-00403847
https://hal.archives-ouvertes.fr/hal-00403847/document
https://hal.archives-ouvertes.fr/hal-00403847/file/angeo-27-2739-2009.pdf

Éditeur(s) : HAL CCSD
Résumé : International audience
Spermatogenesis is a highly sophisticated process involved in the transmission of genetic heritage. It includes halving ploidy, repackaging of the chromatin for transport, and the equipment of developing spermatids and eventually spermatozoa with the advanced apparatus (e.g., tightly packed mitochondrial sheat in the mid piece, elongating of the tail, reduction of cytoplasmic volume) to elicit motility once they reach the epididymis. Mammalian spermatogenesis is divided into three phases. In the first the primitive germ cells or spermatogonia undergo a series of mitotic divisions. In the second the spermatocytes undergo two consecutive divisions in meiosis to produce haploid spermatids. In the third the spermatids differentiate into spermatozoa in a process called spermiogenesis. Paracrine, autocrine, juxtacrine, and endocrine pathways all contribute to the regulation of the process. The array of structural elements and chemical factors modulating somatic and germ cell activity is such that the network linking the various cellular activities during spermatogenesis is unimaginably complex. Over the past two decades, advances in genomics have greatly improved our knowledge of spermatogenesis, by identifying numerous genes essential for the development of functional male gametes. Large-scale analyses of testicular function have deepened our insight into normal and pathological spermatogenesis. Progress in genome sequencing and microarray technology have been exploited for genome-wide expression studies, leading to the identification of hundreds of genes differentially expressed within the testis. However, although proteomics has now come of age, the proteomics-based investigation of spermatogenesis remains in its infancy. Here, we review the state-of-the-art of large-scale proteomic analyses of spermatogenesis, from germ cell development during sex determination to spermatogenesis in the adult. Indeed, a few laboratories have undertaken differential protein profiling expression studies and/or systematic analyses of testicular proteomes in entire organs or isolated cells from various species. We consider the pros and cons of proteomics for studying the testicular germ cell gene expression program. Finally, we address the use of protein datasets, through integrative genomics (i.e., combining genomics, transcriptomics, and proteomics), bioinformatics, and modelling.
Systems Biology in Reproductive Medicine

hal-00877749
https://hal.archives-ouvertes.fr/hal-00877749
DOI : 10.3109/19396368.2012.691943
PUBMED : 22788530

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Estimations of zenith total delays (ZTD) were obtained during postprocessing of a high-resolution (2.4 km) nonhydrostatic atmospheric model (Méso-NH). These estimations were used to determine their sensitivity with respect to formulations of atmospheric refractivity, the approximation of zenith hydrostatic delays (ZHD) deduced from ground pressure, and the contributions of hydrometeors. The factor k for the conversion of zenith wet delay (ZWD) to integrated water vapor (IWV) was examined. Méso-NH is applied here to the extreme flash flood event of 8–9 September 2002 in southeastern France. The use of the hydrostatic formulation (to infer ZHD) leads to an overestimation of up to 18 mm with respect to the vertical integration of refractivity. Delay contributions of hydrometeors simulated by the high-resolution model reached more than 70 mm (%11 kg/m 2 IWV) in the heart of the convective cells in the case of the extreme flood event. The mean variations of IWV due to the use of different conversion factors (k used to transform ZWD to IWV) are evaluated to be less than 0.3 kg/m 2. This is less than the mean underestimation of IWV by 0.6 kg/m 2 relative to the GPS-like evaluation of IWV using the hydrostatic formulation and the ground temperature. In this study we also use GPS ZTD observations to validate three different numerical simulations of this extreme flood event. The simulation with the best fit to the GPS observations is also in best agreement with the surface rainfall measurements.
ISSN: 2169-897X

hal-01417608
https://hal.archives-ouvertes.fr/hal-01417608
https://hal.archives-ouvertes.fr/hal-01417608/document
https://hal.archives-ouvertes.fr/hal-01417608/file/Brenot_JGR_2006.pdf
DOI : 10.1029/2004JD005726

Éditeur(s) : HAL CCSD Institute for Scientific Computing and Information
Résumé : International audience
The production of oil in soft highly compacted reservoirs produces a significant reduction in the pore space which in turn causes the surface to subside. The authors couple two simulators to model the mechanical deformations in the presence of a Darcy flow, both one- and two-phase. The simulators solve for flow in a porous medium using a finite volume method, and solve for the mechanical deformation of the porous media using a finite element method. The flow equations and the deformation equations are coupled using Biot's law. The authors use two different methods for the coupling: the first uses a staggered algorithm; the second is based on a preconditioned conjugate method. The authors use a multiscale method in both approaches. The authors show that the inf-sup condition is not satisfied, because of the mixed discretization which is done by using two separate simulators. The authors give convergence comparisons for the two methods for several examples. Two of the examples are for the linear problem (one-phase) where they know the exact solution and one is for the nonlinear problem (two-phase). In all cases, the preconditioned conjugate algorithm is faster and more robust, in particular when the inf-sup condition is not satisfied. In the nonlinear problem the authors state that the results agree with physical predictions but do not give actual empirical data. Finally, they show the effects of grid orientation on the nonlinear problem.
ISSN: 1705-5105

hal-00730673
https://hal.archives-ouvertes.fr/hal-00730673

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Mantle-derived xenoliths hosted by melilitite lavas from In Teria (Ahaggar, SE Algeria) include garnet and spinel peridotites, pyroxenite and phlogopite megacrysts. The spinel and garnet peridotites record an early deformation event, which formed porphyroclastic microstructures and olivine crystal preferred orientations, followed by static infiltration of hydrous alkaline melts. This metasomatic stage (stage 1) is characterized by the crystallization of phlogopite in the garnet and spinel peridotites, amphibole in the spinel peridotites and clinopyroxene in the garnet peridotite, which record chemical equilibration with an alkaline silicate melt. These early events were largely overprinted by carbonatitic metasomatism (stage 2), which is observed only in the spinel peridotites. Spinel peridotite major and trace element compositions, as well as the compositions of newly formed minerals, are characteristic of interaction with carbonate melt, associated with strong enrichment in incompatible trace elements in clinopyroxene. This second stage was followed by crystallization of pyroxenites (stage 3) in vein conduits, probably segregated from alkaline melts. We propose a scenario in which the different metasomatic imprints record successive stages of interaction between lithospheric mantle and sublithospheric melts throughout the Cenozoic. In Sr–Nd isotope space, the host melilitites and several xenoliths are clustered and plot close to the HIMU mantle end-member. However, some peridotite xenoliths are shifted towards more radiogenic 87Sr/86Sr values. In 207Pb/204Pb–206Pb/204Pb and 208Pb/204Pb–06Pb/204Pb space the In Teria samples define a relatively large domain characterized by high 206Pb/204Pb and 208Pb/204Pb, consistent with a contribution of an HIMU component, considered to represent a sublithospheric signature. The highest 87Sr/86Sr values are comparable with those ascribed to the EM1 mantle end-member, representing the signature of the lower continental lithosphere, and are probably inherited from the pre-metasomatic lithospheric mantle beneath In Teria. Numerical modelling of porous percolation of melt of sublithospheric origin through an EM1-like lithospheric mantle protolith reproduces the In Teria peridotite compositions, using moderately sub-chondritic Sr/Nd values for the peridotite (e.g. In Teria garnet peridotite) and moderately super-chondritic Sr/Nd values in the melt (approximately ocean island basalt values). A few spinel peridotites require a component characterized by a 143Nd/144Nd signature higher than both the EM1 end-member and the local Ahaggar basalts; the 208Pb/204Pb compositions of several samples point to a component with a depleted mid-ocean ridge basalt (MORB) mantle (DMM) signature. Thus the lithospheric mantle beneath In Teria probably did not have a uniform EM1 signature before the onset of metasomatism; it included a DMM peridotite component as well as some peridotites with elevated 143Nd/144Nd values recording long-term LREE depletion.
ISSN: 0022-3530

hal-01356781
https://hal.archives-ouvertes.fr/hal-01356781
DOI : 10.1093/petrology/egw009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Synkinematic phyllosilicates in fault zones can be used to deduce the deformation mechanisms and the conditions of fault activity, as their chemical composition, crystal structure and texture can record the different stages of deformation and fluid-rock interactions. The Pic de Port Vieux, a second-order thrust related to the major Gavarnie thrust in the southern central part of the Pyrenees Axial Zone, juxtaposes Triassic pelites of the hanging wall and Cretaceous limestones of the footwall. In order to investigate the mineralogical and geochemical changes and constrain the deformation conditions of thrusting, characterization of phyllosilicates was performed along a transect in the fault hanging wall pelites. The Triassic pelites are mainly composed of quartz, calcite, phyllosilicates (chlorite and K-white mica) and ± hematite. The core fault zone thickness is estimated to be about one meter of intensively foliated green pelites, whereas the damage zone is composed of several meters of red pelites. XRD data demonstrated that the difference in color is related to hematite which is only present in the damage zone. Phyllosilicates of the damage zone are mainly inherited/diagenetic K-white mica and chlorite. In the core zone, newly formed chlorite is abundant and preferentially located in veins. It is enriched in Fe compared to the chlorite of the red pelites. The well-defined foliation in the core zone is overlaid by preferentially oriented muscovite grains which have homogeneous compositions, with less Na and relatively more Fe than mica from the red pelites. Newly formed chlorite and muscovite in the core zone are synkinematic to the fault activity. They are both related to deformation processes and fluid rock interactions. Kübler index measurements and chlorite thermometry show that synkinematic phyllosilicates have registered a temperature of 270°C ± 23°C for the damage zone and 285°C ± 28°C for the core zone which are corresponding to lower-anchizone/epizone grade conditions. Numerical modelling with the geochemical modelling program PhreeqC was performed to determine the favorable conditions for the mineralogical change between red and green pelites. It suggests that the main critical parameter favoring hematite dissolution and chlorite precipitation in the core zone, is the redox conditions. According to the model, the chemical changes in the core zone occurred due to interactions with highly reductive fluids. In addition, the hematite dissolution maybe the source of iron for newly formed phyllosilicates in the core zone that are more iron rich compared to those from the red pelites.
ISSN: 0169-1317

hal-01536006
https://hal.archives-ouvertes.fr/hal-01536006
DOI : 10.1016/j.clay.2017.05.008

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We present new results on the long-term throw rates of active normal faults in the North Baikal Rift (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Fault-bounded ridges in the NBR display typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from similar to 200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth. Using facet height as an input, model results provide estimates of the long-term fault throw rate. NBR throw rates vary between 0.2 and 1.2 mm yr(-1). The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin (similar to 8Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage.
ISSN: 0278-7407

hal-00455985
https://hal.archives-ouvertes.fr/hal-00455985
DOI : 10.1029/2009TC002555

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Chaperone synthesis in response to proteotoxic stress is dependent on a family of transcription factors named heat shock factors (HSFs). The two main factors in this family, HSF1 and HSF2, are co-expressed in numerous tissues where they can interact and form heterotrimers in response to proteasome inhibition. HSF1 and HSF2 exhibit two alternative splicing isoforms, called α and β, which contribute to additional complexity in HSF transcriptional regulation, but remain poorly examined in the literature. In this work, we studied the transcriptional activity of HSF1 and HSF2 splicing isoforms transfected into immortalized Mouse Embryonic Fibroblasts (iMEFs) deleted for both Hsf1 and Hsf2, under normal conditions and after proteasome inhibition. We found that HSF1α is significantly more active than the β isoform after exposure to the proteasome inhibitor MG132. Furthermore, we clearly established that, while HSF2 had no transcriptional activity by itself, short β isoform of HSF2 exerts a negative role on HSF1β-dependent transactivation. To further assess the impact of HSF2β inhibition on HSF1 activity, we developed a mathematical modelling approach which revealed that the balance between each HSF isoform in the cell regulated the strength of the transcriptional response. Moreover, we found that cellular stress such as proteasome inhibition could regulate the splicing of Hsf2 mRNA. All together, our results suggest that relative amounts of each HSF1 and HSF2 isoforms quantitatively determine the cellular level of the proteotoxic stress response.
ISSN: 1932-6203

inserm-00814784
http://www.hal.inserm.fr/inserm-00814784
http://www.hal.inserm.fr/inserm-00814784/document
http://www.hal.inserm.fr/inserm-00814784/file/journal.pone.0056085.pdf
DOI : 10.1371/journal.pone.0056085

Éditeur(s) : HAL CCSD
Résumé : International audience
Extreme rainfall events can trigger numerous landslides in mountainous areas and a prolonged increase of river sediment load. The resulting mass transfer at the Earth surface in turn induces stress changes at depth, which could be sufficient to trigger shallow earthquakes. The 2009 Morakot typhoon represents a good case study as it delivered 3 m of precipitation in 3 days and caused some of the most intense erosion ever recorded. Analysis of seismicity time-series before and after the Morakot typhoon reveals a systematic increase of shallow (i.e. 0-15 km of depth) earthquake frequency in the vicinity of the areas displaying a high spatial density of landslides. This step-like increase in frequency lasts for at least 2-3 years and does not follow an Omori-type aftershock sequence. Rather, it is associated to a step change of the Gutenberg-Richter b-value of the earthquake catalog. Both changes occurred in mountainous areas of southwest Taiwan, where typhoon Morakot caused extensive landsliding. These spatial and temporal correlations strongly suggest a causal relationship between the Morakot-triggered landslides and the increase of earthquake frequency and their associated b-value. We propose that the progressive removal of landslide materials from the steep mountain landscape by river sediment transport acts as an approximately constant increase of the stress rate with respect to pre-typhoon conditions, and that this in turn causes a step-wise increase in earthquake frequency. To test this hypothesis, we investigate the response of a rate-and-state fault to stress changes using a 2-D continuum elasto-dynamic model. Consistent with the results of Ader et al. (2013), our preliminary results show a step-like increase of earthquake frequency in response to a step-like decrease of the fault normal stress. We also investigate the sensitivity of the amplitude and time-scale of the earthquake frequency increase to the amplitude of the normal stress change and to rheological parameters. Our study offers new insights on the potential influence of extreme erosional events on the short-time scale dynamics of faults and earthquakes.
American Geophysical Union Fall Meeting 2016
San Francisco, United States

insu-01416987
https://hal-insu.archives-ouvertes.fr/insu-01416987

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Some major challenges for geophysicists and structural geologists using three-dimensional boundary element method codes (3D-BEM) are: (1) reducing the amount of memory required to solve large and dense systems and (2) incorporation of inequality constraints such as traction inequality constraints (TIC) and displacement inequality constraints (DIC). The latter serves two purposes. First, for example, inequality constraints can be used to simulate frictional slip (using TIC). Second, these constraints can prevent element interpenetration while allowing opening mode (using DIC). We have developed a method that simultaneously incorporates both types of functionality of the inequality constraints. We show that the use of an appropriate iterative solver not only avoids the allocation of significant memory for solving the system (allowing very large model computation and simplifying parallelization on multi-core processors), but also admits interesting features such as natural incorporation of TICs and DICs. Compared to other techniques of contact management (e.g., Lagrange multipliers, penalty method, or complementarity problem), this new simple methodology, which does not use any incremental trial-and-error procedures, brings more flexibility, while making the system more stable and less subject to round-off errors without any computational overhead. We provide validations and comparisons of the inequality constraints implementation using 2D analytical and numerical solutions.
ISSN: 1420-0597

hal-00561035
https://hal.archives-ouvertes.fr/hal-00561035
DOI : 10.1007/s10596-009-9170-x

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
In the Pyrenees, the lherzolites nowhere occur as continuous units. Rather, they always outcrop as restricted bodies, never more than 3 km wide, scattered across Mesozoic sedimentary units along the North Pyrenean Fault. We report the results of a detailed analysis of the geological setting of the Lherz massif (central Pyrenees), the type-locality of lherzolites and one of the most studied occurrences of mantle rocks worldwide. The Lherz body is only 1.5 km long and belongs to a series of ultramafic bodies of restricted size (a few metres to some hundreds of metres), occurring within sedimentary formations composed mostly of carbonate breccias originating from the reworking of Mesozoic platform limestones and dolomites. The clastic formations also include numerous layers of polymictic breccias reworking lherzolitic clasts. These layers are found far from any lherzolitic body, implying that lherzolitic clasts cannot derive from the in situ fragmentation of an ultramafic body alone, but might also have been transported far away from their sources by sedimentary processes. A detailed analysis of the contacts between the Lherz ultramafic body and the surrounding limestones confirms that there is no fault contact and that sediments composed of ultramafic material have been emplaced into fissures within the brecciated carapace of the peridotites. These observations bear important constraints for the mode of emplacement of the lherzolite bodies. We infer that mantle exhumation may have occurred during Albian strike-slip deformation linked to the rotation of Iberia along the proto-North Pyrenean Fault.
ISSN: 0954-4879

hal-00412602
https://hal.archives-ouvertes.fr/hal-00412602

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerical programs for simulating flow and reactive transport in porous media are essential tools for predicting reservoir properties changes triggered by CO2 underground injection. At reservoir scale, meshed models in which equations are solved assuming that constant macroscopic properties can be defined in each cells, are widely used. However, the parameterization of the dissolution-precipitation problem and of the feedback effects of these processes on the flow field is still challenging. The problem arises from the mismatch between the scales at which averaged parameters are defined in the meshed model and the scale at which chemical reactions occur and modify the pore network geometry. In this paper we investigate the links between the dissolution mechanisms that control the porosity changes and the related changes of the reactive surface area and of the permeability. First, the reactive surface area is computed from X-ray microtomography data obtained before and after a set of dissolution experiments of pure calcite rock samples using distinctly different brine-CO2 mixtures characterizing homogeneous to heterogeneous dissolution regimes. The results are used to validate the power law empirical model relating the reactive surface area to porosity proposed by Luquot and Gauze (2009). Second, we investigate the spatial distribution of the effective hydraulic radius and of the tortuosity, two structural parameters that control permeability, in order to explain the different porosity-permeability relationships observed for heterogeneous and homogeneous dissolution regimes. It is shown that the increase of permeability is due to the decrease of the tortuosity for homogeneous dissolution, whereas it is due to the combination of tortuosity decrease and hydraulic radius increase for heterogeneous dissolution. For the intermediate dissolution regime, identified to be the optimal regime for increasing permeability with small changes in porosity, the increase of permeability results from a large increase in the mean effective hydraulic radius of the sample.
ISSN: 0169-7722

hal-00617671
https://hal.archives-ouvertes.fr/hal-00617671
DOI : 10.1016/j.jconhyd.2010.07.004

Éditeur(s) : HAL CCSD Oceanography Society
Résumé : In April 1961, 13.5 m of basalts were drilled off Guadalupe Island about 240 km west of Mexico's Baja California, together with a few hundred meters of Miocene sediments, in about 3500 m of water. This fi rst-time exploit, reported by John Steinbeck for Life magazine, aimed to be the test phase for the considerably more ambitious Mohole project, whose objective was to drill through the oceanic crust down to Earth's mantle (Lill and Bascom, 1959; Bascom, 1961). Born in the late 1950s, the Mohole project unfortunately ended in muddy waters and was terminated by the United States Congress in 1965 (Shor, 1985; Greenberg, 1971). Undeterred, the scientifi c community rallied again to launch the Deep Sea Drilling Project (DSDP) in 1968, followed by the Ocean Drilling Program (ODP) in 1985, and the Integrated Ocean Drilling Program (IODP) in 2003. These programs have provided solutions to some of the most pressing and interesting problems in ocean and earth science (see, for example, Oceanography 19-4, December 2006).the early 1970s, almost 15 years after the fi rst Mohole attempt, attendees of a Penrose fi eld conference (Conference Participants, 1972) formulated the concept of a layered oceanic crust composed of lavas, underlain by sheeted dikes, then gabbros (corresponding to the seismic layers 2A, 2B, and 3, respectively), which themselves overlay mantle peridotites. Deep drilling into the oceanic crust would provide the ground truth for the Penrose model; the fl ame of the Mohole project still burned. This article draws from results of more than 30 years of ocean drilling at mid-ocean ridges or in older igneous oceanic crust and briefl y reviews some important milestones that improved understanding of crustalaccretion processes at mid-ocean ridges. Figure 1 shows the locations of the numerous DSDP, ODP, and IODP expeditions to which we refer; Table 1 lists site locations.
ISSN: 1042-8275

hal-00407192
https://hal.archives-ouvertes.fr/hal-00407192