Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Progress in seismic methodology and ambitious large-scale seismic projects are enabling high-resolution imaging of the continental crust. The ability to constrain interpretations of crustal seismic data is based on laboratory measurements on rock samples and calculations of seismic properties. Seismic velocity calculations and their directional dependence are based on the rock microfabric, which consists of mineral aggregate properties including crystallographic preferred orientation (CPO), grain shape and distribution, grain boundary distribution, and misorientation within grains. Single-mineral elastic constants and density are crucial for predicting seismic velocities, preferably at conditions that span the crust. However, high-temperature and high-pressure elastic constant data are not as common as those determined at standard temperature and pressure (STP; atmospheric conditions). Continental crust has a very diverse mineral composition; however, a select number of minerals appear to dominate seismic properties because of their high-volume fraction contribution. Calculations of microfabric-based seismic properties and anisotropy are performed with averaging methods that in their simplest form takes into account the CPO and modal mineral composition, and corresponding single crystal elastic constants. More complex methods can take into account other microstructural characteristics, including the grain shape and distribution of mineral grains and cracks and pores. Dynamic or active wave propagation schemes have recently been developed, which offer a complementary method to existing static averaging methods generally based on the use of the Christoffel equation. A challenge for the geophysics and rock physics communities is the separation of intrinsic factors affecting seismic anisotropy, due to properties of crystals within a rock and apparent sources due to extrinsic factors like cracks, fractures, and alteration. This is of particular importance when trying to deduce crustal composition and the state of deformation from seismic parameters.
ISSN: 8755-1209

Droits : info:eu-repo/semantics/OpenAccess
hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568/document
https://hal.archives-ouvertes.fr/hal-01685568/file/Almqvist_et_al-2017-Reviewssur Geophysics.pdf
DOI : 10.1002/2016RG000552

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gulf of Cadiz lies astride the complex plate boundary between Africa and Eurasia west of the Betic-Rif mountain belt. We report on the results of recent bathymetric swathmapping and multi-channel seismic surveys carried out here. The seafloor is marked by contrasting morphological provinces, spanning the SW Iberian and NW Moroccan continental margins, abyssal plains and an elongate, arcuate, accretionary wedge. A wide variety of tectonic and gravitational processes appear to have shaped these structures. Active compressional deformation of the wedge is suggested by folding and thrusting of the frontal sedimentary layers as well as basal duplexing in deeper internal units. There is evidence for simultaneous gravitational spreading occurring upslope. The very shallow mean surface and basal slopes of the accretionary wedge (1° each) indicate a very weak decollement layer, geometrically similar to the Mediterranean Ridge accretionary complex. Locally steep slopes (up to 10°) indicate strongly focused, active deformation and potential gravitational instabilities. The unusual surface morphology of the upper accretionary wedge includes “raft-tectonics” type fissures and abundant sub-circular depressions. Dissolution and/or diapiric processes are proposed to be involved in the formation of these depressions.
ISSN: 0264-8172

insu-00401683
https://hal-insu.archives-ouvertes.fr/insu-00401683
DOI : 10.1016/j.marpetgeo.2007.11.008

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata.
ISSN: 2169-9313

hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061/document
https://hal.archives-ouvertes.fr/hal-00138061/file/Bernard_et_al-2007-Journalsur Geophysical_Research__Solid_Earth_%281978-2012%29.pdf
DOI : 10.1029/2005JB004149

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We decipher late-orogenic crustal flow characterized by feedback relations between partialmelting and deformation in the Variscan Montagne Noire gneiss dome. The dome shape and finite strainpattern of the Montagne Noire Axial Zone (MNAZ) result from the superimposition of three deformations(D1, D2 and D3). The early flat-lying S1 foliation is folded by D2 upright ENE-WSW folds and transposed in thecentral and southern part of the MNAZ into steep D2 high-strain zones consistent with D2 NW-SE horizontalshortening, in bulk contractional coaxial deformation regime that progressively evolved to noncoaxial dextraltranspression. The D2 event occurred under metamorphic conditions that culminated at 0.65 ± 0.05 GPa and 720± 20°C. Along the anatectic front S1 and S2 foliations are transposed into a flat-lying S3 foliation with top-to-NEand top-to-SW shearing in the NE and SW dome terminations, respectively. These structures define a D3 transitionzone related to vertical shortening during coaxial thinning with a preferential NE-SW to E-W directedstretching. Depending on structural level, the metamorphic conditions associated with D3 deformation rangefrom partial melting conditions in the dome core to subsolidus conditions above the D3 transition zone. Wesuggest that D2 and D3 deformation events were active at the same time and resulted from strain partitioningon both sides of the anatectic front that may correspond to a major rheological boundary within the crust.
ISSN: 0278-7407

hal-01208098
https://hal.archives-ouvertes.fr/hal-01208098

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure (lambda(fract)) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of lambda(fract), are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetiy) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks. (C) 2011 Elsevier B.V. All rights reserved.
ISSN: 0012-821X

hal-00745640
https://hal.archives-ouvertes.fr/hal-00745640
DOI : 10.1016/j.epsl.2011.10.029

Éditeur(s) : HAL CCSD
Résumé : This study is designed to improve the understanding of structural, mechanical and petrophysical characteristics of deformation bands in porous sandstone such as their potential influence on fluid storage or migration in reservoir setting. Structural and petrophysical analysis of band networks from Provence show that permeability of band is mainly controlled by the degree of cataclasis and diagenetic processes at depth. Map-scale analysis of band networks underlines the major influence of tectonic regime on band distribution, organization and permeability. Band associated to normal-fault regime (cataclasis and low-permeability) are located around map-sclae-fault whereas band associated to thurst-fault regime (moderate cataclasis and permeability) are pervasively distributed in all the area. Reverse-sense band are cataclastic and low-permeabiilty around the Roquemaure thrust, which show the potential role of large-scale fault on structural and petrophysical characteristics of bands. This analysis also shows the influence of fault propagation on formation of low permeability catacastic bands. This analysis suggests also granulometry as factor controlling organization of band networks.A mechanical analysis of deformation bands is realized based on results from Provence. Yield envelopes of these materials are calculated from analytical solution. Triaxial tests done on sandstone (L'Etang quarry, Orange) confirm the shape of yield envelope theoretically calculated. Triaxial tests done on the poorly-lithified sands (Boncavaï quarry, Uchaux) show grain size, sorting and packing influencing yield envelope and cataclastic band localization at shallow burial depth. Stress paths are calculated for burial and tectonic event (extension and contraction) using the relationship between main stress and secondary stresses (K0) calibrated from well data. These different results are integrated into a model which allows to estimate type and structural characteristics of bands susceptible to form for a known geological setting.A structural, mechanical and petrophysical model is established form these results. This model is calibrated by permeability data from deformation bands of Provence and results from the mechanical model of strain localization. This model is also confronted to a synthesis of permeability data from literature, which confirms the influence of the different controlling parameters integrated to the model. This model is applied for two sites of uranium exploration/exploitation in porous sandstone reservoirs and validated by field observations.
Cette étude est destinée à améliorer la compréhension des caractéristiques structurales, pétrophysiques et mécaniques des bandes de déformation dans les grès poreux ainsi que de leur rôle potentiel sur la migration ou le piégeage des fluides en milieu réservoir. L'analyse structurale et pétrophysique des réseaux de bandes de Provence montre que leur perméabilité découle principalement de l'intensité de la cataclase dans leur microstructure et des processus diagénétiques qui peuvent s'y localiser avec la profondeur. L'analyse régionale de ces réseaux de bandes souligne l'influence majeure du régime tectonique sur leur distribution, leur organisation et leur perméabilité. Les bandes associées au régime normal (cataclactiques et peu perméables) sont localisées autour des failles cartographiques, tandis que les bandes associées au régime inverse (modérement cataclastiques et perméables) sont distribuées dans toute la région. Les bandes inverses sont fortement cataclastiques et imperméables uniquement autour du chevauchement de Roquemaure ce qui montre le rôle potentiel de la présence de grande faille sur les caractéristiques structurales et pétrophysiques de ces bandes. D'autre part, cette analyse suggère que la granulométrie de l'encaissant peut influencer l'initiation et l'organisation des réseaux. L'analyse mécanique des bandes de déformation a ensuite été réalisée à partir des résultats obtenus en Provence. L'enveloppe de plasticité de ces matériaux est calculée à l'aide d'une solution analytique. Les essais triaxiaux menés sur le grès de la carrière de l'Etang (orange) confirment la forme de ces enveloppes estimées théoriquement. Les essais réalisés sur les sables de Boncavaï (Uchaux) montrent que la taille des grains, le tri et de la compaction dans ces matériaux peu lithifiés influent sur leurs enveloppes de plasticité et la localisation des bandes cataclastiques à faibles profondeurs. Les trajets de contraintes sont estimés pour les phases d'enfouissement et de chargement tectonique (extension et compression) à partir de la relation entre contrainte principale et contraintes secondaires (K0), calibrée à partir de données de forage. Ces résultats sont intégrés à un modèle permettant d'estimer la nature et les caractéristiques structurales des bandes susceptibles de se former dans un contexte géologique donné. Un modèle structural, mécanique et pétrophysique a été établir à partir de ces différents résultats. Ce modèle est calibré à partir des données de perméabilité mesurées sur les bandes de Provence et des résultats du modèle mécanique de localisation cité précédemment. Ce modèle a ensuite été confronté à une synthèse des données de perméabilité disponibles dans la littérature et confirme l'influence des différents paramètres de contrôle pris en compte dans le modèle. Ce modèle a enfin pu être appliqué sur deux sites d'explorations/exploitations d'uranium en réservoir gréseux poreux et validé par les résultats obtenus, en concordance avec les observations de terrain.
https://tel.archives-ouvertes.fr/tel-01001389

NNT : 2013MON20067
tel-01001389
https://tel.archives-ouvertes.fr/tel-01001389
https://tel.archives-ouvertes.fr/tel-01001389/document
https://tel.archives-ouvertes.fr/tel-01001389/file/36072_BALLAS_2013_archivage-1_cor.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Deep-seated gravitational spreading (DSGS) affects the slopes of formerly glaciated mountain ridges. On Mars, DSGS has played a key role in shaping the landforms of the giant Valles Marineris troughs. Though less spectacular, DSGS is common in terrestrial orogens, where understanding its mechanics is critical in the light of the ongoing climate change because it is a potential source of catastrophic landslides in deglaciated valleys. We conducted parametric numerical studies in order to identify important factors responsible for DSGS initiation. DSGS models are computed using an elastoviscoplastic finite element code. Using ADELI's software, we reproduce topographic ridge spreading under the effect of valley unloading. Two types of spreading topographic ridges are investigated, homogeneous or with horizontal rheological layering. We find that gravitational instabilities are enhanced by high slopes, which increase gravitational stress, and low friction and cohesion, which decrease yield stress. In the unlayered ridge, instability is triggered by glacial unloading with plastic strain concentration inside the ridge and at the base of the high slopes. Vertical fractures develop in the upper part of the slope, potentially leading to fault scarps. Ridge homogeneity promotes a deformation mode controlled by uphill-facing normal faulting and basal bulging. In the second case, the ridge encompasses horizontal geological discontinuities that induce rock mass anisotropy. Discontinuity located at the base of the slope accumulates plastic strain, leading to the formation of a sliding plane evolving into a landslide. The presence of a weak layer at ridge base therefore promotes another slope deformation mode ending up with catastrophic failure. Mechanical conditions and slope height being equal, these conclusions can probably be extrapolated to Earth. Compared with Mars, DSGS on Earth is inhibited because terrestrial topographic gradients are lower than in Valles Marineris, an effect counterbalanced by increased gravitational stress, where the intensity of deformation is enhanced because of the Earth gravity potential.
ISSN: 0169-555X

hal-01420007
https://hal.archives-ouvertes.fr/hal-01420007
DOI : 10.1016/j.geomorph.2016.06.011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We developed a new granular material (MatIV) to study experimentally landscape evolution in active mountain belt piedmonts. Its composition and related physical properties have been determined using empirical criteria derived from the scaling of deformation, erosion-transport and sedimentation natural processes. MatIV is a water-saturated composite material made up with 4 granular components (silica powder, glass microbeads, plastic powder and graphite) whose physical, mechanical and erosion-related properties were measured with different laboratory tests. Mechanical measurements were made on a modified Hubbert-type direct shear apparatus. Erosion-related properties were determined using an experimental set-up that allows quantifying the erosion/sedimentation budget from tilted relaxation topographies. For MatIV, we also investigated the evolution of mean erosion rates and stream power erosion law exponents in 1D as a function of slope.;Our results indicate that MatIV satisfies most of the defined criteria. It deforms brittlely according to the linear Mohr-Coulomb failure criterion and localizes deformation along discrete faults. Its erosion pattern is characterized by realistic hillslope and channelized processes (slope diffusion, mass wasting, channel incision). During transport, eroded particles are sorted depending on their density and shape, which results in stratified alluvial deposits displaying lateral fades variations. To evaluate the degree of similitude between model and nature, we used a new experimental device that combines accretionary wedge deformation mechanisms and surface runoff erosion processes. Results indicate that MatIV succeeded in producing detailed morphological and sedi-mentological features (drainage basin, channel network, terrace, syntectonic alluvial fan). Geometric, kinematic and dynamic similarity criteria have been investigated to compare precisely model to nature. Although scaling is incomplete, it yields particularly informative orders of magnitude. With all these characteristics, MatIV appears as a very promising material to investigate experimentally a wide range of scientific questions dealing with relief dynamics and interactions between tectonics, erosion and sedimentation processes.
ISSN: 0040-1951

hal-00669904
https://hal.archives-ouvertes.fr/hal-00669904
DOI : 10.1016/j.tecto.2011.09.029

Éditeur(s) : HAL CCSD The Geochemical Society of Japan
Résumé : International audience
The Western Cordillera of Ecuador consists of Cretaceous crustal fragments of oceanic plateaux and superimposed insular arcs, which were accreted to the northwestern South American margin during the Late Cretaceous and Paleocene. Slices of high-grade metabasites, ultramafic rocks, gabbros and basalts, unmetamorphosed radiolarian cherts and scarce garnet-bearing metasediments were randomly exhumed along Miocene to Recent transcurrent faults crosscutting the Western Cordillera. The basalts show geochemical characteristics of oceanic plateau basalts (flat REE patterns, La/Nb = 0.85). The gabbros differ from the basalts in having lower REE levels, positive Eu anomalies, and negative Nb and Ta anomalies; they are interpreted as resulting from arc magmatism. The amphibolites and banded amphibolites have major and trace element chemistry similar to that of oceanic plateau basalts (flat REE patterns, La/Nb = 0.86) or to cumulate gabbros. The granulite shares with oceanic plateaus similar trace element chemistry (flat REE patterns, La/Nb < 1) and εNdi values (+7.6). Continent-derived metasediments are depleted in heavy REE (La/Y = 4.8) and have a negative Eu anomaly. Foliated lherzolites, melagabbronorites and pyroxenites consist of serpentinized olivine + cpx + opx ± Ca-plagioclase. Lherzolites, melagabbronorites and pyroxenites are LREE depleted with positive Eu anomalies, while the harzburgite displays a U-shaped REE pattern. The trace element abundances of the ultramafic rocks are very low (0.1 to 1 times the chondritic and primitive mantle values). The ultramafic rocks represent fragments of depleted mantle, deformed cpx-rich cumulate, and continental lithospheric mantle or mantle contaminated by subduction-fluid. Except the scarce quartz-rich metasediments, all these rocks likely represent remnants of accreted oceanic crustal fragments and associated depleted mantle. Since these samples were randomly sampled at depth by the fault, we propose that the Western Cordillera and its crustal root are mainly of oceanic nature.
ISSN: 0016-7002

insu-00679228
https://hal-insu.archives-ouvertes.fr/insu-00679228

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : The Zagros Simply Folded Belt (ZSFB) is an active fold-and-thrust belt resulting from the still continuing continental collision between the Arabian plate and the Iranian plate, which probably started in the Oligocene. The present-day shortening (N25°) is well documented by focal mechanisms of earthquakes and global positioning system (GPS) surveys. We propose in this study a comparison of published palaeostress markers, including magnetic fabric, brittle deformation and calcite twinning data. In addition, we describe the magnetic fabric from Palaeocene carbonates (10 sites) and Mio-Pliocene clastic deposits (15 sites). The magnetic fabrics are intermediate, with magnetic foliation parallel to the bedding, and a magnetic lineation mostly at right angles to the shortening direction. This suggests that the magnetic fabric retains the record of an early layer-parallel shortening (LPS) that occurred prior to folding. The record of LPS allows the identification of originally oblique folds such as the Mand Fold, which have developed in front of the Kazerun Fault. The shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the ZSFB. The palaeostress datasets, covering the Palaeocene to Pleistocene time interval, support several folding episodes accompanied by a counter-clockwise rotation of the stress field direction. The Palaeocene carbonates in the ZSFB record a N47 LPS during early to middle Miocene detachment folding in the High Zagros Belt (HZB). The Mio-Pliocene clastic deposits recorded a N38 LPS prior to and during detachment folding within the ZSFB at the end of the Miocene-Pliocene. Similarly, fault slip and calcite twin data from the ZSFB also support a counter-clockwise rotation from NE to N20 between the pre-folding stage and the late rejuvenation of folds. This counter-clockwise trend of palaeostress data agrees with fault slip data from the HZB. During the late stage of folding in the ZSFB, the Plio-Quaternary palaeostress trends are consistently parallel to the present-day shortening direction.
Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic-Cenozoic

hal-00545036
https://hal.archives-ouvertes.fr/hal-00545036
DOI : 10.1144/SP330.6

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Search String Advanced > Saved Searches >ARTICLE TOOLS Get PDF (3653K) Save to My Profile E-mail Link to this Article Export Citation for this Article Get Citation Alerts Request PermissionsMore Sharing ServicesShare|Share on citeulikeShare on facebookShare on deliciousShare on www.mendeley.comShare on twitter Abstract Article References Cited ByView Full Article (HTML) Enhanced Article (HTML) Get PDF (3653K)AbstractFor the first time, the crystallized remnant of an oceanic ridge magma chamber is documented in the Oman ophiolite. It exists in the centre of a 40 km long monoclinal ridge (Jebel Dihm, Wadi Tayin massif), exposing a full crustal section perpendicular to the spreading direction. New detailed mapping supported by U-Pb zircon geochronology suggests that the active, fast-spreading ridge that died just prior to detachment of the ophiolite is preserved and largely intact. Our observations provide insights into the crystallizing mush zone of a magma chamber, before it crosses the external walls and solidifies as deformed gabbros. Our data provide new constraints on the shape and internal dynamics of a magma chamber, including gabbro subsidence from the floor of a perched melt lens and the limited contribution of sills to crustal accretion. By locating precisely the palaeo-ridge axis, prior full spreading rate estimates can be increased to ~140 km Ma−1.
ISSN: 0954-4879

hal-01121586
https://hal.archives-ouvertes.fr/hal-01121586
DOI : 10.1111/ter.12130

Éditeur(s) : HAL CCSD
Résumé : International audience
In many geological reservoirs, open fractures or fault zones generally induce high spatial variability of hydrodynamical properties and shape the main deep-seated flow paths. It is of crucial interest to determine their structure and properties in order to achieve a sound and sustained exploitation of resources or to estimate the risk of failure of any underground storage. Tiltmeters have emerged as new tools to observe deformation generated by groundwater flow. As such instruments are highly sensitive to pressure gradients, they are perfectly suited for monitoring channelized flow in connected fractures and fault zones. Hence, they provide a unique insight of these reservoirs' geometry and dynamics over broad time scales. Here we demonstrate that continuous tilt data from surface long baseline tiltmeters (LBT) can be used alone to evaluate the general functioning of a fractured hardrock system and estimate the hydraulic properties of its main conductive features. The study is applied to the pumping site of Ploemeur observatory (Brittany, France) which is well documented and instrumented, and therefore forms a convenient setting for introducing LBT as tools for fractured media hydrology. On the short term, tilt signals are strongly correlated with pumping cycles and associated head level changes in well-connected boreholes. Besides, when pumps are stopped the maximal tilt direction is systematically perpendicular to a subvertical fault zone whose azimuth of strike has thereby been refined down to degree precision. By using a semi-analytical model of deformation, we establish the link between tilt and pressure change during pumping interruptions which then allows for hydraulic properties estimation from tilt measurements only. Finally, we validate our results with previous estimates obtained from other studies and discuss the orientation of future work that could enhance these estimates.
AGU Fall Meeting 2014
San Francisco, United States

insu-01093437
https://hal-insu.archives-ouvertes.fr/insu-01093437

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Before attaining the mantle wedge, where they trigger partial melting, volatiles released from dehydration reactions in the slab have to migrate across a relatively cold (<750 degrees C), peridotite-layer above the incoming slab. In order to unravel the mechanisms allowing for this initial stage of fluid transport, we performed a detailed field and microstructural study of metamorphic prograde peridotites in the Cerro del Almirez ultramafic massif (Betic Cordillera, Spain), where evidences of one of the most important dehydration reactions in subduction zones, the high-pressure antigorite breakdown (P = 1.6-1.9 GPa and T approximate to 680 degrees C), can be mapped in the field. This reaction led to arborescent growth of centimeter-size olivine and orthopyroxene, producing a chlorite-harzburgite with a spinifex-like texture. Microstructural observations and crystal preferred (CPO) mapping show no evidences of solid-state deformation during the prograde growth of olivine and orthopyroxene at the expenses of antigorite. However, a few tens to a hundred meters away from the reaction front, the metamorphic texture is partially obliterated by grain-size reduction in roughly planar conjugate zones, a few mm to meters wide. Grain size reduction zones (GSRZ) are characterized by (1) sharp contacts with undeformed spinifex-like texture domains, (2) important reduction of the olivine grain size (60-250 mu m), (3) olivine color change from brownish to colorless, (4) decrease in the modal amount of orthopyroxene, and (5) at the mm- to cm-scale, irregular shapes and abrupt terminations. Field and microstructural observations exclude that relative displacement took place across these GSRZ. Changes in modal composition imply reactions with fluids undersaturated in silica. Analysis of olivine crystal-preferred orientations (CPO) in GSRZ shows patterns similar, but more dispersed, than those in neighboring spinifex-like domains. It also reveals mm- to cm-scale discrete domains with rather homogeneous crystallographic orientations suggesting inheritance from the preexisting spinifex-like olivines in the host peridotite. Misorientation angles between neighboring grains in the GSRZ show peaks at similar to 5-10 degrees and similar to 20 degrees, but rotations are not crystallographically controlled. Based on these observations, we rule out the formation of the GSRZ by dynamic recrystallization during dislocation creep and propose that they record brittle deformation (microcraking) of the spinifex-like chlorite-harzburgite, probably induced by hydrofracturing at high pressure and relative low temperature conditions (680-710 degrees C). High-pressure hydrofracturing can, thus, be invoked as an efficient mechanism for fluid flow across the cold top-slab mantle layer, hence allowing the slab-derived fluids to ingress in the wedge.
ISSN: 0012-821X

hal-00534035
https://hal.archives-ouvertes.fr/hal-00534035
DOI : 10.1016/j.epsl.2010.06.029

Éditeur(s) : HAL CCSD
Résumé : International audience
In this paper we present a microfluidic architecture dedicated to the study of Red Blood Cells (RBCs) deformability in microchannel smaller than the cell shape (biconcave disc of 7-8 μm in diameter) and cell capability to pass through slits separated by a gap value down to 2 μm, acting as a filter. This device is use in the context of RBCs disorders affecting their deformability, which is analysed versus number of cells trapped in the filter. This device can be seen as mimicking the human spleen. Microfabrication of the chip is based on polydimethylsiloxane (PDMS) associated to a two level thick photoresist mould (SU8). One level is used for microfluidic access with a 25 μm thickness towards the studied zone. The second level concerns the mimicking zones where RBCs flow through 5 μm down to 2 μm-wide slits acting like a mechanical filter. This level has a thickness of 5 μm. Devices have been tested on RBCs having specific disorder on their mechanical elasticity in order to validate the design principle. Two cases are presented in this paper: a.) Sickle RBCs inducing cell rigidity at two levels b.) Parasitized RBCs by Plasmodium falciparum. On both cases, we clearly show that deformability of RBCs influences the capability to pass through small slits (down to 2um) and thus is in relation with the pathology stage. This spleen-like microfluidic chip mimicking the RBCs filtering function is a promising tool for the exploration of RBC disorders combined with mechanical alterations.
4th European Conference on Microfluidics
Limerick, Ireland

hal-01113061
https://hal.archives-ouvertes.fr/hal-01113061

Éditeur(s) : HAL CCSD
Résumé : The Tyrrhenian Sea is usually interpreted to be a Neogene back-arc basin that opened by continental rifting and oceanic spreading caused by the eastward migration of the Apennine subduction system from Tortonian to Pliocene times. Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times. The " METYSS " project aims at better constraining the relations between crustal tectonics, salt tectonics and sedimentation from Messinian times to present-day. The " METYSS 1 " cruise (2009, R/V "Téthys II"-INSU) allowed us to obtain about 1200 km of high-resolution seismic reflection profiles along the SE Corsican margin, and along the upper and middle parts of the Eastern Sardinian margin, Western Tyrrhenian. This new dataset clearly illustrates that this area has been highly dissected during the rifting stage by N-S trending normal faults delineating ridges and basins, as previously described. The Messinian seismic markers (UU and MU) locally display fan-shaped stratal geometries, but the mechanism responsible for such geometries, i.e., salt tectonics or rifting, has yet to be carefully deciphered. We also mapped the spatial distribution of the mobile salt (MU). The highly variable thickness of the confined salt basins may be related to the initial pre-Messinian basin geometry or to the fact that sediment deposition was syn-rift. Southeastward, salt tectonics appears highly vigorous. More surprisingly, our data demonstrate that some of the major faults have been significantly reactivated during the post-rift period, up to late Quaternary time. Such recent fault activity has been recorded by bathymetric scarps and associated footwall debris flows. Moreover, some of this post-rift deformation can be evidenced within the Plio-Quaternary sequence by a regional unconformity. The post-Miocene deformation style varies greatly between different areas of the margin, and can also be strongly influenced by the presence or absence of mobile Messinian evaporites (MU).
13ème Congrès Français de Sédimentologie
Dijon, France

hal-00657310
https://hal-brgm.archives-ouvertes.fr/hal-00657310

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation
ISSN: 0191-8141

hal-01172423
https://hal.archives-ouvertes.fr/hal-01172423
DOI : 10.1016/j.jsg.2015.03.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Imaging deep active volcanic areas remains a challenge in our understanding of their activity and evolution, especially in subduction zones. Study of magnetic anomalies is appropriate to access such dynamics in depth. The magnetic anomaly pattern of the Lesser Antilles Arc (LAA) subduction is studied through Curie Point Depth (CPD), interpreted as the depth of the 580 °C isotherm, and developed to better assess the deep thermal structure of the arc. The depth of the estimated CPD exhibits a complex topography. Keeping in mind the overall uncertainty associated with this method, a main doming is evidenced below the Guadeloupe archipelago. Its apex is shifted towards the ancient arc, suggesting a very hot state of the fore-arc/arc domain. To better understand the LAA thermal state, we perform 2D thermo-mechanical simulations of the subduction zone. Recalling that magnetite is a serpentinization by-product, we simulate water transfer triggered by slab dehydration to test the assumption of fore-arc serpentinization suggested by the positive magnetic anomaly in the vicinity of the Guadeloupe archipelago. In this area, the subduction-induced arc lithosphere hydration and related weakening trigger a fast heating of the upper plate by basal convective removal. This process of fast arc lithosphere thinning may apply where simultaneously the volcanic arc is split in two and normal convergence is high enough. As serpentinization strongly decreases P-wave velocity, we propose a new interpretation of a published seismic profile below Guadeloupe. The seismic layer previously interpreted as the arc lower crust may rather be a layer of serpentinized mantle, as supported by spatial correlations between gravimetric and magnetic anomalies. Consequently, at the scale of Guadeloupe Island, the fore-arc Moho would be shallower than initially assumed, with a dome shape more consistent with both the extensive deformation active since the Oligocene in the inner fore-arc and the CPD doming.
ISSN: 0040-1951

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300/document
https://hal-insu.archives-ouvertes.fr/insu-01505300/file/Gailler-2017.pdf
DOI : 10.1016/j.tecto.2017.03.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Field study, thermochronology and geochemistry of the east Lungmu Co (LMC) range highlight some of the geological events that shaped western Tibet. The LMC fault zone has long been interpreted as the boundary between the Tianshuihai terrane of Laurasian affinity and the Qiangtang block of Gondwanian affinity. In the LMC range, the Paleozoic series is intruded by the Mangtsa leucogranite whose zircon have a U/Pb age of 116.9 ± 1 Ma and by mafic rocks with U/Pb zircon ages ranging from 116.9 ± 1 to 95.1 ± 1.7 Ma. Geochemistry of the mafic rocks indicates that they have been emplaced in a supra-subduction zone setting, probably the north dipping Nujiang suture zone. 40Ar/39Ar micas ages of the granite indicate that cooling below ~ 350 °C occurred between 105 and 85 Ma. 40Ar/39Ar K-feldspar data suggest a fast cooling event at 60-55 Ma, which we relate to the reactivation of the LMC suture zone as a thrust at the onset of the India-Eurasia collision. The last, and still active, deformation event corresponds to left-lateral strike-slip faulting along the ENE-WSW LMC fault.
ISSN: 1342-937X

hal-00660491
https://hal.archives-ouvertes.fr/hal-00660491
DOI : 10.1016/j.gr.2011.07.026

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Crystal growth driven by a flowing solution is modeled for a flow with low Reynolds number using a computational dynamic software. Considering equivalent crystallographic faces, the chemical flux is calculated along upstream and downstream faces. Upstream flux is higher compared to downstream and leads to a symmetry breakdown of the crystal shape and develops mirror symmetry parallel to the flow velocity. Moreover the ratio of these two fluxes (upstream / downstream) gives a quantitative relation between the relative crystal growth rate and the flow velocity. Thus, using an inverse method, the flow direction and velocity can be deduced by the study of the variation of the growth band thicknesses of equivalent crystallographic faces. This new method was applied to the formation of metasomatic tourmalinite associated with a leucogranite sill. The approach is complemented by a study of the chemistry of the tourmaline. In the studied case, the application of the new method gives the high fluid velocities in pores (10-3 - 10-4 m/s) during metasomatism. Equivalent Darcy velocities are estimated and discussed accounting for the major role played by the regional deformation. Finally, a two-stage tectono-hydrodynamic model is proposed for the metsomatism. The first stage is genetically linked to the sill injection, and the second is characterized by a wider event with hydrothermal flow passing along the leucogranite sills.
ISSN: 0012-821X

Droits : info:eu-repo/semantics/OpenAccess
insu-00352307
https://hal-insu.archives-ouvertes.fr/insu-00352307
https://hal-insu.archives-ouvertes.fr/insu-00352307/document
https://hal-insu.archives-ouvertes.fr/insu-00352307/file/Sizaret_et_al_final.pdf
DOI : 10.1016/j.epsl.2009.01.013

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