Éditeur(s) : HAL CCSD
Résumé : This thesis compiles two distinct studies that both document the control of microstructures on rock seismic properties. The first part deals with the development of crystallographic preferred orientations (CPO) in the uppermost mantle associated with melt/fluid-rock interactions, recorded in peridotites xenoliths from the Japan sea back-arc basin. The microstructural and geochemical characteristics of the studied samples reveal that active spreading is associated to uppermost mantle deformation similar to that observed in the Oman ophiolite. At the onset of back-arc spreading, there are no strong interactions between melt percolation and deformation in comparison to continental rift zones, probably due to the relatively small size and short duration of the spreading event. The second part presents a unique database of plagioclase CPO from variously deformed mafic rocks. CPO are grouped in three main types; their characteristics as a function of deformation regime (magmatic or crystal-plastic) are outlined and discussed. Calculated seismic properties of gabbroic rocks show that anisotropy tends to increase as a function of fabric strength, although it is generally weak, due to the competing effect of olivine/clinopyroxene and plagioclase.
Cette thèse regroupe deux études distinctes, qui documentent le contrôle des microstructures sur les propriétés sismiques des roches. La première partie traite du développement des orientations préférentielles cristallographiques (OPC) dans le manteau supérieur, associé aux interactions liquide/magma-roche, enregistré dans des xénolites de péridotites du bassin d'arrière-arc de la mer du Japon. Les caractéristiques microstucturales et géochimiques des échantillons étudiés montrent que l'ouverture arrière-arc active est associée à une déformation du manteau supérieure similaire à celle observée dans l'ophiolite d'Oman. L'initiation de l'extension d'arrière-arc n'est pas associée à de fortes interactions entre percolation magmatique et déformation, en comparaison avec les zones de rifting continentales, probablement en raison des taille et durée relativement petites de l'épisode d'ouverture. La seconde partie présente une base de données unique d'OPC de plagioclase de roches mafiques plus ou moins déformées. Les OPC sont classées en 3 types principaux; leurs caractéristiques en fonction du régime de déformation (magmatique ou plastique) sont présentées et discutées. Les propriétés sismiques calculées des roches gabbroiques montrent que l'anisotropie tend à croitre avec l'intensité des fabriques, bien qu'elle soit généralement faible, en raison des effets opposés des olivines/clinopyroxènes et du plagioclase.
https://tel.archives-ouvertes.fr/tel-00795505

tel-00795505
https://tel.archives-ouvertes.fr/tel-00795505
https://tel.archives-ouvertes.fr/tel-00795505/document
https://tel.archives-ouvertes.fr/tel-00795505/file/Satsukawa_thesis_UM2.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We performed torsional deformation experiments on pre-hydrated fine-grained olivine aggregates using an innovative experimental assembly to investigate water weakening in mantle rocks at high shear strains. San Carlos olivine powder was cold-pressed and then hot-pressed under hydrous conditions, producing aggregates with average grain sizes of 7 or 15 μm. Deformation experiments were performed in a high-resolution gas-medium apparatus equipped with a torsional actuator, under a confining pressure of 300 MPa, a temperature of 1200 °C, and constant shear strain rates ranging from 8 × 10−5 to 1.4 × 10−4 s−1. Maximum shear stresses range from 150 to 195 MPa. These values are 30% lower relative to those determined in previous torsion experiments on dry, fined-grained dunites under similar conditions. Textures and microstructures of the starting and deformed specimens were characterized by scanning and transmission electron microscopy. All deformed aggregates exhibit a shape-preferred orientation marking a foliation and lineation, as well as a reduction in mean grain size from 15 μm down to 3-4 μm due to dynamic recrystallization. Olivine crystallographic fabrics developed rapidly (γ < 0.1), but their strength, characterized by the J-index, is low compared to naturally deformed peridotites or to polycrystalline olivine deformed at similar finite shear strains under dry conditions. The crystallographic fabrics are consistent with deformation by a dislocation accommodated creep mechanism with activation of multiple {0 k l}[1 0 0] systems, among which the (0 1 0)[1 0 0] slip system is dominant, and minor participation of the (0 1 0)[0 0 1] slip system. Transmission electron microscopy confirmed the occurrence of dislocations with [1 0 0] and [0 0 1] Burgers vectors in most grains. Analysis of unpolarized infrared spectra indicates that hydrogen concentration in the olivine lattice is below the saturation level of 18 ppm wt H2O, which is similar to those typically observed in spinel-bearing peridotite xenoliths, and also provide evidence for water-rich inter-granular material trapped in pores and grain boundaries. Seismic properties computed from the CPO observations correspond to those most commonly observed in naturally deformed mantle peridotites with fast P-wave propagation and S-wave polarization subparallel to the shear direction. These torsion experiments on fine-grained olivine polycrystals under hydrous conditions indicate that water weakening under lithospheric conditions is linked to various defects with hydrogen in the olivine structure, as well as with water-derived species in grain boundaries or pores.
ISSN: 0031-9201

hal-00745170
https://hal.archives-ouvertes.fr/hal-00745170
DOI : 10.1016/j.pepi.2012.05.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Talc is a hydrous magnesium rich layered silicate that is widely disseminated in the Earth from the seafloor to over 100 km depth, in ultra-high pressure metamorphism of oceanic crust. In this paper we determine the single crystal elastic constants at pressures from 0 to 12 GPa of talc triclinic (C 1¯) and monoclinic (C2/c) polytypes using ab initio methods. We find that talc has an extraordinarily high elastic anisotropy at zero pressure that reduces with increasing pressure. The exceptional anisotropy is complemented by a negative Poisson's ratio for many directions in crystal space. Calculations show that talc is not only one of very few common minerals to exhibit auxetic behaviour, but the magnitude of this effect may be the largest reported so far for a mineral. The compression (Vp) and shear (Vs) wave velocity anisotropy is 80% and 85% for the triclinic polytype. At pressures where talc is known be stable in the Earth (up to 5 GPa) the Vp and Vs anisotropy is reduced to about 40% for both velocities, which is still a very high value. Vp is slow parallel to the c-axis and fast perpendicular to it. This remains unchanged with increasing pressure and is observed in both polytypes. The shear wave splitting (difference between fast and slow S-wave velocities) at low pressure has high values in the plane normal to the c-axis, with a maximum near the alow asterisk-axis in the triclinic and the b-axis in the monoclinic polytype. The c-axis is the direction of minimum splitting. The pattern of shear wave splitting does not change significantly with pressure. The volume fraction of talc varies between 11 and 41% for hydrated mantle rocks, but the lack of data on the crystallographic preferred orientation (CPO) precludes a detailed analysis of the impact of talc on seismic anisotropy in subduction zones. However, it is highly likely that CPO can easily develop in zones of deformation due to the platy habit of talc crystals. For random aggregates of talc, the isotropic Vp, Vs and Vp/Vs ratio have significantly lower values than those of antigorite and may explain low-velocity regions in the mantle wedge. Vp/Vs ratios are more complex in anisotropic media because there are fast and slow S-waves, resulting in Vp/Vs1 and Vp/Vs2 ratios for every propagation direction, making interpretation difficult in deformed polycrystalline talc with a CPO. Talc on the subduction plate boundary can strongly influence guided wave velocity as CPO would develop in this region of intense shearing. The very low coefficient of friction (< 0.1) of talc above 100 °C could also explain silent earthquakes at shallow depths (ca 30 km) along the subduction plate boundaries, frequently responsible for tsunami.
ISSN: 0012-821X

hal-00411481
https://hal.archives-ouvertes.fr/hal-00411481
DOI : 10.1016/j.epsl.2008.07.047

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
The variation of elastic- wave velocities as a function of the direction of propagation through the Earth's interior is a widely documented phenomenon called seismic anisotropy. The geometry and amount of seismic anisotropy is generally estimated by measuring shearwave splitting, which consists of determining the polarization direction of the fast shear- wave component and the time delay between the fast and slow, orthogonally polarized, waves. In subduction zones, the teleseismic fast shear- wave component is oriented generally parallel to the strike of the trench(1), although a few exceptions have been reported (Cascadia(2) and restricted areas of South America(3,4)). The interpretation of shear- wave splitting above subduction zones has been controversial and none of the inferred models seems to be sufficiently complete to explain the entire range of anisotropic patterns registered worldwide(1). Here we show that the amount and the geometry of seismic anisotropies measured in the forearc regions of subduction zones strongly depend on the preferred orientation of hydrated faults in the subducting oceanic plate. The anisotropy originates from the crystallographic preferred orientation of highly anisotropic hydrous minerals (serpentine and talc) formed along steeply dipping faults and from the larger- scale vertical layering consisting of dry and hydrated crust - mantle sections whose spacing is several times smaller than teleseismic wavelengths. Fault orientations and estimated delay times are consistent with the observed shear- wave splitting patterns in most subduction zones.
ISSN: 0028-0836

hal-00412016
https://hal.archives-ouvertes.fr/hal-00412016
DOI : 10.1038/nature07376

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Garnet growth in high-pressure, mafic garnet granulites formed by dehydration melting of hornblende-gabbronorite protoliths in the Jijal complex (Kohistan palaeo-island arc complex, north Pakistan) was investigated through a microstructural EBSD-SEM and HRTEM study. Composite samples preserve a sharp transition in which the low-pressure precursor is replaced by garnet through a millimetre-sized reaction front. A magmatic foliation in the gabbronorite is defined by mafic-rich layering, with an associated magmatic lineation defined by the shape-preferred orientation (SPO) of mafic clusters composed of orthopyroxene (Opx), clinopyroxene (Cpx), amphibole (Amp) and oxides. The shape of the reaction front is convoluted and oblique to the magmatic layering. Opx, Amp and, to a lesser extent, Cpx show a strong lattice-preferred orientation (LPO) characterized by an alignment of [001] axes parallel to the magmatic lineation in the precursor hornblende-gabbronorite. Product garnet (Grt) also displays a strong LPO. Two of the four < 111 > axes are within the magmatic foliation plane and the density maximum is subparallel to the precursor magmatic lineation. The crystallographic relationship < 111 >(Grt)//[001](Opx,Cpx,Amp) deduced from the LPO was confirmed by TEM observations. The sharp and discontinuous modal and compositional variations observed at the reaction front attest to the kinetic inhibition of prograde solid-state reactions predicted by equilibrium-phase diagrams. The P-T field for the equilibration of Jijal garnet granulites shows that the reaction affinities are 5-10 kJ mol.(-1) for the Grt-in reaction and 0-5 kJ mol.(-1) for the Opx-out reaction. Petrographic and textural observations indicate that garnet first nucleated on amphibole at the rims of mafic clusters; this topotactic replacement resulted in a strong LPO of garnet. Once the amphibole was consumed in the reaction, the parallelism of [001] axes of the mafic-phase reactants favoured the growth of garnet crystals with similar orientations over a pyroxene substrate. These aggregates eventually sintered into single-crystal garnet. In the absence of deformation, the orientation of mafic precursor phases conditioned the nucleation site and the crystallographic orientation of garnet because of topotaxial transformation reactions and homoepitaxial growth of garnet during the formation of high-pressure, mafic garnet-granulite after low-pressure mafic protoliths.
ISSN: 0263-4929

hal-00411323
https://hal.archives-ouvertes.fr/hal-00411323
DOI : 10.1111/J.1525-1314.2008.00789.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The mantle above a subducting slab is the site of complex interactions between deformation, partial melting, fluid migration and magma transport. To constrain these interactions and their effects on olivine deformation, we analyze microstructures, crystal preferred orientations, and water contents of peridotite xenoliths entrained by andesites of the Avacha volcano, southern Kamchatka arc. These xenoliths are refractory spinel harzburgites that have coarse-grained microstructures with widely spaced subgrain boundaries and sinuous grain boundaries in olivine, consistent with deformation by dislocation creep under low deviatoric stress (< 13 MPa) and with a significant contribution from diffusional processes. Analysis of crystal preferred orientations (CPO) indicates dominant activation of high-temperature, low-stress {0kl}[100] slip systems in olivine and of(100)[001] in orthopyroxene. In most samples, coarse opx crystals, elongated parallel to the lineation, enclose small olivine grains in crystallographic continuity with neighbouring crystals, indicating crystallization of orthopyroxene at the expense of olivine as a result of reactive percolation of Si-rich fluids coeval with the high-temperature deformation. Secondary crystallization of interstitial orthopyroxene led locally to development of opx-rich lenses parallel to the foliation, characterized by a decrease in olivine grain size and dispersion of the olivine CPO without changing the dominant slip systems. Half of the samples also show acicular orthopyroxene aggregates with which is associated a fine-grained matrix composed of rounded strain-free olivine, orthopyroxene, spinel, and rare amphibole crystals. This matrix occurs pervasively along grain boundaries or forms millimeter-scale irregular lenses and anastomosing veinlets that crosscut the coarse crystals and their ductile deformation structures. Both acicular orthopyroxene and the fine-grained matrix are interpreted as resulting from reactive transport of H2O-rich fluids under static conditions, probably in the lithospheric mantle. Infrared analyses show that olivine contains 1-8 center dot 6 ppm by weight of water. These low water contents are similar to those observed in spinel peridotites from other subduction zones and probably record both the low solubility of water in olivine at low pressure and dehydration during exhumation of the xenoliths. Water contents in orthopyroxene are highly variable (25-506 ppm H2O), probably recording spatially heterogeneous interaction with fluids or melts and compositional disequilibrium in the studied samples. Change in the dominant percolation mechanism from porous flow to fracturing suggests cooling, consistent with the low temperatures estimated from pyroxene thermometry (< 800-900 degrees C). The Avacha xenoliths therefore record pervasive deformation of a region of the mantle under asthenospheric conditions, followed by its accretion to the base of the lithosphere, probably as a result of cooling of the mantle wedge. Percolation of Si-rich fluids or hydrous melts is recorded at all stages; this probably enhanced diffusion and lowered deviatoric stresses during ductile deformation, but did not change the dominant slip direction in olivine from [100] to [001].
ISSN: 0022-3530

hal-00456053
https://hal.archives-ouvertes.fr/hal-00456053
DOI : 10.1093/petrology/egp085

Éditeur(s) : HAL CCSD Elsevier
Résumé : Folds with hinge lines subparallel to stretching lineation are common features in shear zones and represent extreme cases of fold modification. However, their microstructures and in particular their kinematic significance remain poorly understood. Here we describe the meso- and micro-scale structures and crystallographic preferred orientation (CPO) of quartz and muscovite from a metric-scale shear-modified fold from Plattjen, Saas Fee, Western Internal Alps. The studied fold is of class-2 and the samples collected around the fold have essentially the same microstructures. Quartz [c]-axes plotted in the tectonic coordinate system exhibit an apparent reverse obliquity on opposing limbs. Muscovite fabrics are controlled essentially by the orientation of {001} planes. If the CPO data are plotted in a common reference frame (e.g. either fold or geographical), all samples exhibit essentially the same patterns for both minerals. In particular, relative to the fold axis and axial surface, the reversal of quartz CPO obliquity on opposing limbs is no longer evident. The small obliquity (~ 15°) between the intersection lineation of the two planes of {001} of muscovite and the fold axis results in the apparent reversal of shear sense on opposite limbs when viewing the CPO related to the macroscopic fabric. The homogeneity of the microstructures and CPOs of quartz and muscovite across the fold support the interpretation that the fold developed during simultaneous activation of heterogeneous and homogeneous simple shear, with the former responsible for fold development and the latter responsible for fold rotation and the overwhelming of the heterogeneous deformation. These processes led to the observed parallelism between fold hinge line and local stretching lineation.
ISSN: 0040-1951

hal-00824537
https://hal.archives-ouvertes.fr/hal-00824537
DOI : 10.1016/j.tecto.2011.03.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Thermal diffusivity of synthetic quartz single-crystals and natural polycrystalline aggregates were measured using a modified Angstrom method at ambient pressure and up to 800 degrees C in order to investigate the effect of crystal preferred orientation on thermal diffusivity of quartz rich rocks. The thermal diffusivity tensor of quartz was determined by measuring the thermal diffusivity of an oriented synthetic quartz single-crystal along the [100] and [001] directions. A naturally deformed, fine-grained quartzite mylonite, was used to compare the single crystal properties with aggregate properties. Using the crystal preferred orientations (CPO) measured by the Electron Back Scattered Diffraction (EBSD) method and the measured thermal diffusivity tensor of quartz, the three-dimensional aggregate thermal diffusivity was modelled using volume averaging models. In order to test the validity of these models that are only based on the properties of the constituent minerals, the thermal diffusivity was then measured on oriented cores as a function of temperature, along three orthogonal directions, parallel to the (X-lineation, Y, Z-pole to foliation) structural frame. Both modelled and direct measurement of thermal diffusivity show an anisotropy of thermal diffusivity, heat transport being more effective parallel to Y-direction and less effective parallel to the lineation X-direction. Thermal diffusivities measured in a given direction on the natural rock are lower by less than 10% than the modelled thermal diffusivity in the same direction, showing that rock imperfections have a weak effect on heat transport. In addition, the modelled thermal diffusivity anisotropy based on the characterization of crystal orientations and thermal diffusivity tensor shows a good agreement with measurements in both alpha and beta stability field. This validation of the petrophysical simulation allows for evaluating the 3D thermal diffusivity of quartz rich rocks in different crustal conditions. The 3D thermal diffusivity of five naturally deformed quartzites displaying quartz fabrics expected in different crustal pressure and temperature ranges were simulated. The resulting thermal diffusivity anisotropies of quartzites range between 40% and 10%, depending on temperature, crystallographic fabric patterns and fabric strength. Under crustal conditions, quartzites deformed in the granulite facies display a high thermal diffusivity in the (XZ) foliation plane, whereas quartzites deformed in greenschist facies have highest thermal diffusivity in the (Z) direction normal to the foliation plane.
ISSN: 0040-1951

hal-00413568
https://hal.archives-ouvertes.fr/hal-00413568
DOI : 10.1016/j.tecto.2008.11.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We combined microstructural observations and high-resolution crystallographic preferred orientation (CPO) mapping to unravel the active deformation mechanisms in garnet clinopyroxenites, garnet-spinel websterites, and spinel websterites from the Beni Bousera peridotite massif. All pyroxenites display microstructures recording plastic deformation by dislocation creep. Pyroxene CPOs are consistent with dominant slip on [001]{110} in clinopyroxene and on [001](100) or [001](010) in orthopyroxene. Garnet clinopyroxenites have however high recrystallized fractions and finer grain sizes than spinel websterites. Recrystallization mechanisms also differ: subgrain rotation dominates in garnet clinopyroxenites, whereas in spinel websterites nucleation and growth also contribute. Elongated shapes and strong intracrystalline misorientations suggest plastic deformation of garnet, but CPOs are weak. Clinopyroxene porphyroclasts in spinel websterites show deformation twins underlined by orthopyroxene exsolutions. Thermodynamic calculations indicate that garnet clinopyroxenites deformed at 2.0 GPa and 950-1000 °C and spinel pyroxenites at 1.8 GPa and 1100-1150 °C. The lower temperatures may explain the faster work rates implied by the finer grained microstructures in garnet clinopyroxenites. Greater stresses may have also reduced the competence contrast between garnet and pyroxene in the garnet pyroxenites and, at the outcrop scale, lowered the competence contrast between pyroxenites and peridotites, favoring mechanical dispersion of pyroxenites in the cooler lithospheric mantle.
ISSN: 0191-8141

hal-00750322
https://hal.archives-ouvertes.fr/hal-00750322
DOI : 10.1016/j.jsg.2012.02.019

Éditeur(s) : HAL CCSD
Résumé : A section of ancient fast-spreading ocean crust was sampled at Wadi Gideah, located in the Wadi Tayin Massif of the Oman ophiolite. This sample suite was used for generating a coherent data set combining various petro-geochemical and structural investigations, with the aim of building a reference section for advancing our understanding of crustal accretion processes at fast-spreading mid-ocean ridges. Additionally, this study focuses on one outcrop that represents part of the fossil axial melt lens (AML).Major and trace element analyses reveal a trend of chemical evolution up section in the lower crust, with a marked difference between the layered gabbros and the foliated gabbros above. Petrological modeling shows that the chemical evolution up section can be produced by hydrous fractionation crystallization, with melt H2O contents of ~0.8 wt% and 0.8 to 1.2 wt% for the lower and upper crust, respectively. Together with the observed very steep bulk Zr/Hf vs. Zr gradient, high F and Cl content of magmatic amphibole, general Nb-Ta depletion of melts compared with NMORB, and high Sr87/Sr86 ratio compared with modern fast-spread crust, this suggests that Wadi Gideah layered gabbros were accreted by crystallization of ascending melts in sills, in a context of subduction initiation. The distinct changes in chemical trends and average grain size at the layered to foliated gabbro transition are tentatively explained by enhanced hydrothermal cooling deeper than the AML. The gabbro/dike transition displays complex structural and lithological relationships that, together with fractional crystallization modeling, point to episodic vertical movements of the AML. Plagioclase crystallographic preferred orientations (CPO) measured over the whole gabbro section are always consistent with magmatic flow. The CPO strength generally increases downward, with more scattering in the layered gabbro section. From the top to the bottom of the layered gabbros, CPO become progressively more prolate, possibly reflecting increasing shear induced by active mantle flow underneath.Wadi Gideah lower crust recorded a formation history consistent with a hybrid accretion model, combing several processes such as downward magmatic flow and/or upward melt migration in the upper foliated gabbros, sill intrusions in the layered gabbros, and deep hydrothermal circulation. The latter was presumably focused in channels, preserved today as several, up to 100 m wide zones of extensively altered former layered gabbro, cross-cutting the magmatic layering. These metagabbros display significantly higher Sr87/Sr86 ratio, late stage magmatic phases, and evidence for high temperature partial melting.
Une coupe d'ancienne croute océanique rapide a été échantillonnée dans le Wadi Gideah, situé dans le Massif de Wadi Tayin de l'Ophiolite d'Oman. Cette série d'échantillons a permis de générer un jeu de données cohérent, combinant des études pétro-géochimiques et structurales, dans le but de construire une coupe de référence pour mieux contraindre notre compréhension des processus d'accrétion crustale aux dorsales océaniques rapides. Ce travail intègre aussi l'étude détaillée d'un affleurement représentant en partie la lentille magmatique axiale (LMA) fossile.Les analyses d'éléments majeurs et traces révèlent une évolution chimique dans la croûte inférieure, avec une nette différence entre les gabbros lités et les gabbros foliés sus-jacents. La modélisation pétrologique montre que l'évolution chimique vers le haut peut être produite par cristallisation fractionnée hydratée, avec des teneurs en H2O des magmas de ~0.8 wt% dans la croute inférieure et 0.8 to 1.2 wt% dans la croute supérieure. Combiné aux forts gradients de Zr/Hf vs. Zr, aux teneurs élevées de F et Cl dans les amphiboles magmatiques, à l'appauvrissement général en Nb-Ta des magmas comparé aux NMORB, et aux rapports Sr87/Sr86 élevés comparés à la croûte rapide moderne, ceci suggère que les gabbros lités du Wadi Gideah ont été formés par la cristallisation des magmas ascendants dans des sills, dans un contexte d'initiation de subduction. Les changements de signature géochimique et de taille de grain à la transition entre gabbros lités et gabbros foliés témoignent possiblement d'un fort refroidissement hydrothermal plus profond que la LMA. La transition complexe filonien/gabbro montre des relations structurale et lithologiques complexes, qui, combinées o la modélisation de la cristallisation fractionnée, traduisent les mouvements verticaux épisodiques de la LMA. Les orientations préférentielles cristallographiques (OPC) des plagioclases mesurées sur l'ensemble de la coupe dans les gabbros témoignent toujours d'une déformation magmatique. L'intensité des OPC a tendance à augmenter vers le bas, avec une plus forte variabilité dans les gabbros lités. Dans les gabbros lités, les OPC sont de plus en plus linéaires vers le bas, résultant possiblement d'un cisaillement plus fort induit par l'écoulement actif du manteau sous-jacent.La croûte inférieure dans le Wadi Gideah a enregistré une histoire compatible avec un modèle d'accrétion hydride, combinant plusieurs processus tels que l'écoulement magmatique vers le bas et/ou la migration de liquides magmatiques vers le haut dans les gabbros foliés supérieurs, l'intrusion de sills dans les gabbros lités, et une circulation hydrothermale profonde. Cette dernière était probablement concentrée dans des chenaux, préservés aujourd'hui sous la forme de plusieurs zones, dont l'épaisseur atteint 100 m, de gabbros lités fortement altérés, recoupant le litage magmatique. Ces métagabbros ont des rapports Sr87/Sr86 élevés, comportent des phases magmatiques tardives et montrent des évidences de fusion partielle.
https://hal.archives-ouvertes.fr/tel-01302675

tel-01302675
https://hal.archives-ouvertes.fr/tel-01302675
https://hal.archives-ouvertes.fr/tel-01302675/document
https://hal.archives-ouvertes.fr/tel-01302675/file/Th%C3%A8se_Tim-Mueller_2015.pdf

Éditeur(s) : HAL CCSD
Résumé : IODP Hole U1309D (IODP Exp. 304-305, 30°N) and ODP Site 1275 (ODP Lag 209, 15°45?N) sampled two oceanic core complexes, at the Mid-Atlantic Ridge. The recovered rocks are mostly gabbroic with some very primitive and olivine rich (Ol>70%). In Hole U1309D, trace element compositions of clinopyroxene and plagioclase poikiloblasts from olivine-rich rocks ndicate that they crystallized from the same melt in all lithologies. Olivine trace element compositions are in disequilibrium with the two other minerals. Olivine crystallographic preferred orientations are weak, with a relatively strong uncommon [001] concentration but consistent with deformation by dislocation creep with activation of the high temperature (010) [100] slip system, commonly described in asthenospheric mantle. The joint study of geochemical processes and microstructures in these rocks suggest a complex crystallization history in an open system with percolation of large volume of MORBtype melt and interaction with the depleted shallow mantle. Olivine-rich rocks are interpreted as the ultimate residue of these melt-mantle reaction processes. At Site 1275, the formation of the more evolved rocks of the gabbroic series is not related to the impregnation event creating olivine-rich rocks.
These rocks represent late magmatic injections, which are completely crystallized at depth as intrusivegabbroic bodies. The results presented in this thesis are consistent with the formation of oceanic core complexes associated with relatively strong magmatic activity, and with the crystallization of most of melt in the lithosphere without basaltic counterpart erupted on the seafloor.
Le puits IODP U1309D (Exp. IODP 304-305, 30°N) et le Site ODP 1275 (Leg ODP 209, 15°45'N) ont permis d'échantillonner deux core complexes océaniques de la dorsale Médio-Atlantique. Les roches récupérées sont principalement gabbroïques dont certaines très primitives et riches en olivine (ol >70%). Dans le puits U1309D, les compositions en éléments en trace des poeciloblastes de clinopyroxène et de plagioclase des roches riches en olivine indiquent qu'ils précipitent depuis le même magma dans toutes les lithologies. La composition en éléments en trace des olivines est en déséquilibre avec ces deux minéraux. Les fabriques cristallographiques de l'olivine sont faibles avec une concentration sur [001] inhabituelle, néanmoins compatibles avec une déformation plastique de haute température, avec l'activation du système de glissement (010) [100] communément décrit dans le manteau asthénosphérique. L'étude conjointe des caractéristiques géochimiques et microstructurales de ces roches met en lumière une histoire complexe de cristallisation dans un système ouvert où de larges volumes de magma de type MORB ont percolé et interagi avec le manteau appauvri superficiel. Ces roches riches en olivine représenteraient le résidu ultime de ces réactions liquide-manteau. Au site 1275, la formation des roches les plus évoluées de la série n'apparaît pas liée à l'événement d'imprégnation formant les roches riches en olivine. Ces roches correspondent à des injections tardives de magma qui ont entièrement cristallisé en profondeur sous forme de plutons intrusifs. Les résultats présentés dans ce mémoire sont compatibles avec une formation des core complexes océaniques associée à une activité magmatique relativement importante, et à une cristallisation complète de tout ou partie de ces magmas dans la lithosphère sans contre-partie volcanique en surface.
https://tel.archives-ouvertes.fr/tel-00354807

tel-00354807
https://tel.archives-ouvertes.fr/tel-00354807
https://tel.archives-ouvertes.fr/tel-00354807/document
https://tel.archives-ouvertes.fr/tel-00354807/file/these_MD.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
To better understand the microstructural evolution of a "serpentinized" mantle rock and the influence of various hydrous phases on the seismic properties of the mantle wedge, we have conducted the detailed microstructural analyses of a sample of tremolite-chlorite-antigorite schist collected from the Moses Rock dike (central part of the Colorado Plateau). We performed differential effective media (DEM) modelling to study the effect of three hydrous phases forming two-phase aggregates with olivine, considering the crystallographic preferred orientation (CPO) of each phase and the shape ratio of the hydrous phases. We have demonstrated that in a partially serpentinized peridotite, the olivine CPO characteristic of [100](010) dislocation glide is still preserved, and the high-temperature asthenospheric flow is preserved with a foliation normal to that of antigorite schist. The transformation of olivine into antigorite occurs predominantly (~ 75%) by the relationship (100)ol || (001)atg with [001]ol || [010]atg, with the (010)ol || (001)atg and [001]ol || [010]atg relationship observed in areas of weak antigorite CPO. Chlorite results from the phase transformation of olivine in a relatively static environment, as shown by the correlation between the olivine-chlorite CPOs with (100)ol || (100)ch, (010)ol || (001)ch and (001)ol || (010)ch. The fluid percolation that caused the localized metasomatism and partial hydration of the mantle occurred possibly along trans-lithospheric shear zones. The presence of chlorite induces the most important drop on the P-wave velocities and may help to explain some local low velocities in the fore-arc mantle wedges, but is unlikely to be of global importance due to its very high Vp/Vs ratio ~ 1.9. On the other hand, antigorite is the only phase that causes important modification on the propagation directions of P and S-waves, and the only phase to explain the polarization of the fastest shear waves parallel to the subduction trench.
ISSN: 0040-1951

hal-00858061
https://hal.archives-ouvertes.fr/hal-00858061
DOI : 10.1016/j.tecto.2013.03.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Peridotite xenoliths with a broad range of textures provides evidence for consistent microstructural evolution in a vertical transect of the shallow lithospheric mantle (35?55 km depth) beneath the Persani Mountains, SE Carpathians, Romania, due to ongoing plate convergence in the Carpathian Arc nearby. The recrystallized grain size, crystal preferred orientations strength, and resulting seismic anisotropy vary continuously and display a strong correlation to equilibrium temperatures, suggesting a continuous change in deformation conditions with depth. The shallowmost xenoliths have microstructures typical of high stress deformation, marked by strong recrystallization to fine grain sizes, which results in weak crystal preferred orientations and anisotropy. The deepest xenoliths have coarse-grained porphyroclastic microstructures and strong crystal preferred orientations. Replacive orthopyroxene structures, consuming olivine, and high H2O concentrations in the pyroxenes are observed in some xenoliths indicating limited percolation of fluids or volatile-rich melts. Despite the high stress deformation and high H2O contents in some of the studied xenoliths, analysis of olivine crystallographic orientations indicates that [100] slip systems, rather than ?wet? [001] accommodate most of the deformation in all samples. Seismic anisotropy estimated from the measured olivine and pyroxene crystal preferred orientations suggests that the strike-parallel fast SKS polarization directions and ~ 1 s delay times measured in the SE Carpathians are likely the consequence of convergence-driven belt-parallel flow in the lithospheric mantle.
ISSN: 0012-821X

hal-00317303
https://hal.archives-ouvertes.fr/hal-00317303
DOI : 10.1016/J.EPSL.2008.04.035

Éditeur(s) : HAL CCSD
Résumé : This work provides new constraints on the interactions between deformation and percolation of melt or fluids, as well as on the implications of these processes for the seismic properties of the mantle wedge. It is based on the analysis of spinel peridotites from the massif of Ronda (Spain) and two xenolith suites from active subduction zones (Kamchatka, Papua New Guinea). A coupled structural, petrological and geochemical study of these samples shows that they underwent a reactive percolation of melts or Si-rich fluids, which was synchronous to a deformation event occurring under high temperature and low stress conditions, consistent with the PT conditions at the base of the lithosphere or in the asthenosphere. This reactive percolation is responsible for enrichment in pyroxenes, mainly orthopyroxene, which is often localized in bands parallel to the high-temperature foliation. This enrichment is associated with grain size reduction and dispersion of the crystallographic orientation of olivine. The dominant slip system in olivine is {0kl}[100], which results in fast S-wave polarization parallel to the flow direction in the mantle. The decrease in the intensity of the olivine crystal preferred orientations associated with the enrichment in pyroxene results in significant decrease of the anisotropy that may induce an underestimation of the thickness of the anisotropic layer by up to 33%. The observed orthopyroxene enrichment also lowers the Vp/Vs ratio, but cannot explain Vp/Vs < 1.7 mapped locally in the fore-arc mantle in Japan and the Andes. Such low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites, which is generally ignored in large-scale Vp/Vs ratio mapping of the mantle wedge. Infrared analyses show that olivine from the both xenolith collections contains less water than the theoretical saturation calculated for their estimated equilibrium temperature in the spinel stability field. These low water content are similar to those observed in spinel peridotites from other subduction zones and probably record both the low solubility of water in olivine at relatively low pressure and dehydration during exhumation of the xenoliths. These measured water contents as well as theoretical saturation estimations are not sufficient to change the dominant slip direction of in olivine from [100] to [001].
Ce travail apporte de nouvelles contraintes sur les interactions entre déformation et processus d'hydratation et de percolation de magma ou de fluides dans le manteau à l'aplomb d'une zone de subduction et leurs implications sur les propriétés sismiques dans le coin mantellique. Il se base sur l'analyse de péridotites à spinelle provenant du massif de Ronda (Espagne) et deux séries de xénolites issues de zones de subduction actives (Kamchatka, Papouasie-Nouvelle-Guinée). L'étude structurale, pétrologique et géochimique de ces échantillons montrent qu'ils ont subit une percolation réactive de magma ou de fluide synchrone d'une déformation de haute température basse contrainte cohérente avec les condition PT de la base de la lithosphère ou de l'asthénosphère. Cette percolation réactive est responsable d'un enrichissement en pyroxènes, qui est souvent localisé dans des bandes parallèles à la foliation. Cet enrichissement est associé à une dispersion de l'orientation cristallographique de l'olivine. Les systèmes de glissement dominant dans l'olivine sont dans tous les cas {0kl}[100], ce qui implique que la direction de polarisation rapide des ondes S dans la partie supérieure du coin mantellique est parallèle à la direction d'écoulement dans le manteau. La décroissance de l'intensité des OPR de l'olivine associée à l'enrichissement en pyroxènes a pour conséquence une réduction non négligeable de l'anisotropie sismique qui peut induire jusqu'à 33% d'erreur sur l'interprétation de l'épaisseur de la couche anisotrope. Un enrichissement en orthopyroxène peut aussi entraîner une baisse du rapport Vp/Vs, mais ne peut expliquer les rapports Vp/Vs <1,7 cartés dans certains avant-arcs. Cependant de telles valeurs peuvent être expliquées si l'anisotropie des péridotites du coin mantellique est prise en compte. Les analyses par spectroscopie infra-rouge montrent que les olivines des deux séries de xénolites étudiées contiennent moins d'eau que la saturation théorique calculée pour leurs températures d'équilibre dans le domaine du spinelle. Ces faibles concentrations en eau sont similaires à celles observées dans les olivines des péridotites à spinelle des autres zones de subduction. Elles enregistrent probablement la faible solubilité de l'eau dans l'olivine à des pressions relativement basses et la déshydratation au cours de l'exhumation des xénolites. Ces teneurs en eau mesurées ainsi que les estimations de la saturation théorique ne sont pas suffisantes pour changer la direction de glissement dominante dans l'olivine de [100] à [001].
https://tel.archives-ouvertes.fr/tel-00689832

tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832/document
https://tel.archives-ouvertes.fr/tel-00689832/file/These-Soustelle2010.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A series of two-stage torsion experiments on Carrara marble were conducted to constrain the influence of known prior deformation on rheological response and microstructural evolution. Comparison with previous experimental data on Carrara marble flow and fabric evolution during single-stage torsion deformation experiments provided direct insights into the significance of initial deformation at various conditions. Our experiments were conducted at 727 degrees C temperature and 300 MPa confining pressure, while maintaining a constant strain rate of 3 x 10(-4) s(-1) on the periphery of the cylindrical samples. Under these conditions, the marble is known to deform in power-law (n = 6-10) ductile flow. All torsion experiments were performed with a Paterson type gas-medium testing machine equipped with a torsion actuator module.;Prior (D1) and subsequent (D2) deformation are accomplished by two torsion experiments in sequence on same sample segments. The effect of D1 strain history is investigated during D2 by applying counter-clockwise torsion to a sandwich sample consisting of three segments with different D1 rotation sense. D2 samples experienced continued, first and reversed shearing deformation in top, centre and bottom segments, respectively. D2 bulk strain was chosen equal to D1 strain in top and bottom segments.;D1 experiments followed the typical single-stage deformation behaviour of Carrara marble under the applied experimental conditions. Yielding was followed by strain hardening until a peak stress was reached at a shear strain around 1, after which work softening occurred. Weakening gradually evolved into a constant stress regime. During hardening, a shear microstructure and crystallographic preferred orientation (CPO) developed. Afterwards the volume fraction of smaller dynamic recrystallised grains increased continuously, resulting in a recrystallisation microstructure and CPO at shear strains of 5 and higher. The new D2 experiments displayed a strain variation between homogeneously deformed sample segments that increased with increasing D1 strain. The stress-strain behaviour of the D2 bulk sandwich samples showed less pronounced work-hardening and -softening when compared with single-stage deformation experiments. Furthermore, constant flow stress was attained at increasingly lower strain with increasing D1 strain. In most D2 segments, fabric development is equivalent to single-stage experiments at corresponding absolute strain. The fabrics differed markedly from those in single-stage experiments in the case of reversed two-stage deformation at moderate strain (D1 shear strain 1 and 2.6). Experiments show that grain shape by shearing of relict grains is defined by finite strain and thus affected by strain reversal. Recrystallisation is controlled by absolute strain and not influenced by strain reversal.
ISSN: 0040-1951

hal-00617686
https://hal.archives-ouvertes.fr/hal-00617686
DOI : 10.1016/j.tecto.2010.09.029

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Tahalgha district (southwestern Hoggar, Algeria), the Cenozoic volcanism has sampled subcontinental mantle beneath two crustal terranes that collided during the Pan-African orogeny: the “Polycyclic Central Hoggar” to the east and the “Western Hoggar” to the west. Two major lithospheric shear zones separate these terranes: the “4°35” and the “4°50” faults. Mantle xenoliths were collected between the two faults and across the 4°35 fault. In addition to a range in equilibrium temperatures and chemical compositions reported elsewhere, the samples show variations in their microstructures and crystallographic preferred orientations. Equilibrium temperatures and geochemical characteristics allow dividing them into low — (LT; 700–900 °C), intermediate — (IT; 900–1000 °C), and high-temperature (HT; 1000–1100 °C) xenoliths. The LT and IT peridotites occur on both sides of the 4°35 fault; they are usually coarse-grained. HT xenoliths are present only east of the 4°35 fault, in the narrow domain stuck between the two faults; they are fine-grained and extensively affected by annealing and melt–rock reactions. Microstructures and crystallographic textures indicate that deformation in the LT- and IT-xenoliths occurred through dislocation creep under relatively high-temperature, low-pressure conditions, followed by post-kinematic cooling. The fine-grained HT-xenoliths were deformed under relatively high-stress conditions before being annealed.Combining microstructural and CPO data with petrological and geochemical informations suggests that: (1) the LT xenoliths are remnants of the Neoproterozoic lithospheric mantle that preserved microstructural and chemical characteristics inherited from the Pan-African orogeny, and (2) the HT xenoliths record localized Cenozoic deformation associated with melt channeling through feed-back processes that culminated in the formation of high-permeability porous-flow conduits. Limited grain-growth in HT xenoliths suggests that advective heating of melt conduits was transient and rapidly followed by thermal relaxation due to conductive heat loss into wall-rock peridotites represented by the IT xenoliths, then by exhumation due to volcanic activity.
ISSN: 0040-1951

hal-01171761
https://hal.archives-ouvertes.fr/hal-01171761
DOI : 10.1016/j.tecto.2014.11.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Middle Atlas is a region where xenolith-bearing volcanism roughly coincides with the maximum of lithospheric thinning beneath continental Morocco. It is therefore a key area to study the mechanisms of lithospheric thinning and constrain the component of mantle buoyancy that is required to explain the Moroccan topography. Samples from the two main xenolith localities, the Bou Ibalghatene and Tafraoute maars, have been investigated for their mineralogy, microstructures, crystallographic preferred orientation, and whole-rock and mineral compositions. While Bou Ibalghatene belongs to the main Middle Atlas volcanic field, in the ‘tabular’ Middle Atlas, Tafraoute is situated about 45 km away, on the North Middle Atlas Fault that separates the ‘folded’ Middle Atlas, to the South-East, from the ‘tabular’ Middle Atlas, to the North-West. Both xenolith suites record infiltration of sub-lithospheric melts that are akin to the Middle Atlas volcanism but were differentiated to variable degrees as a result of interactions with lithospheric mantle. However, while the Bou Ibalghatene mantle was densely traversed by high melt fractions, mostly focused in melt conduits, the Tafraoute suite records heterogeneous infiltration of smaller melt fractions that migrated diffusively, by intergranular porous flow. As a consequence the lithospheric mantle beneath Bou Ibalghaten was strongly modified by melt–rock interactions in the Cenozoic whereas the Tafraoute mantle preserves the record of extensional lithospheric thinning, most likely related to Mesozoic rifting. The two xenolith suites illustrate distinct mechanisms of lithospheric thinning: extensional thinning in Tafraoute, where hydrous incongruent melting triggered by decompression probably played a key role in favouring strain localisation, vs. thermal erosion in Bou Ibalghatene, favoured and guided by a dense network of melt conduits. Our results lend support to the suggestion that lithospheric thinning beneath the Atlas mountains results from the combination of different mechanisms and occurred in a piecewise fashion at a short wavelength scale.
ISSN: 0040-1951

hal-01171756
https://hal.archives-ouvertes.fr/hal-01171756
DOI : 10.1016/j.tecto.2014.11.020

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
[1] The Pyrenees, north of the North Pyrenean fault, display a complex structure involving a succession of peridotite massifs, basement massifs, and mid-Cretaceous to Late Cretaceous basins located in a narrow domain, which was affected by a mid-Cretaceous, preorogenic, high-temperature, low-pressure metamorphism. The Late Cretaceous basins were interpreted either as pull-apart basins formed during transcurrent motion of Iberia relative to Eurasia or as remnants of a larger extensional basin. Recent models support that peridotite massifs result from the exhumation of the mantle during this preorogenic event. The northern boundary of the Agly basement massif shows evidence of ductile deformation of the basal formations of the Agly sedimentary cover. Macroscopic and microscopic kinematics indicators consistent with asymmetry of crystallographic fabrics suggest normal sense of shear and thus suggest detachment, at least partial, of the Mesozoic cover from its basement. Triassic to Early Cretaceous limestones are mylonitic and consistently shows a foliation, a NS- to NE-trending lineation, shear criteria suggesting top-to-the-north shearing and locally boudinage. At the microscopic scale, mylonites are characterized by a very fine grain size, frequently <10 µm. They contain larger, partially recrystallized calcite parent grains and undeformed quartz grains with calcite fringes crystallized in pressure shadows. In these mylonites, calcite systematically shows a weak but well-defined crystallographic-preferred orientations, suggesting HT dislocation creep combined to diffusion creep and possibly grain boundary sliding in the finest fraction of the mylonites. Paleotemperatures determined using Raman spectrometry suggest synkinematic temperature conditions in the range 340-390°C, in good agreement with observed microstructures and calcite CPO. The mylonitic fabric in Mesozoic limestones is folded by EW-trending Pyrenean folds north of the Agly basement massif, attesting that this fabric formed before the Pyrenean orogeny. These data consistently support preorogenic extension under medium-temperature conditions of the northern Agly massif and likely of the massif itself. Since simultaneously (~100 Ma) a mid-Cretaceous basin opened south of the basement massif, we suggest a model of preorogenic exhumation of the Agly massif in response to the regional extension associated to the rotation of Iberia. This model may explain the exhumation of the North Pyrenean massifs during a single preorogenic event that allowed the opening of extensional basins and the exhumation of the lithospheric mantle. All these structures being subsequently reworked during the Pyrenean orogeny.
ISSN: 0278-7407

hal-00852833
https://hal.archives-ouvertes.fr/hal-00852833
DOI : 10.1002/tect.20015

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Seismic anisotropy originating within the continental crust is used to determine kinematic flow lines within active mountain belts and is widely attributed to regionally aligned mica. However, naturally deformed micaceous rocks commonly show composite (e.g. S-C) fabrics. It is necessary therefore to understand how both varying mica content and differing intensities of multiple foliations impact on seismic interpretations in terms of deformation fields. An outcrop analogue for granitic mid-crustal deformed zones is used here to calibrate the seismic response against both parameters. Seismic responses are modelled using crystallographic preferred orientations for polymineralic, micaceous granitic gneisses, measured using Electron Back-Scatter Diffraction. The sample results are generalised by modelling the effects of variations in modal composition and the relative importance of deformation fabrics of variable orientation, so-called rock and fabric recipes. The maximum P- and S-anisotropy are calculated at 16.6% and 23.9% for single-foliation gneisses but for mixed (i.e. S-C) foliation gneisses these values reduce to 5.8% and 7.5% respectively. Furthermore, mixtures of multiple foliations generate significant variations in the geometry of the seismic anisotropy. This effect, coupled with the geographical orientation of fabrics in nature. can generate substantial variations in the orientation and magnitude of seismic anisotropy (especially for shear waves) as measured for the continental crust using existing receiver function and teleseismic near-vertical incidence methods. Thus, maps of seismic anisotropy varying with depth in deforming continents need not imply necessarily depth-varying deformation kinematics and tectonic decoupling.
ISSN: 0012-821X

hal-00445247
https://hal.archives-ouvertes.fr/hal-00445247
DOI : 10.1016/j.epsl.2009.09.035

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Peridotite xenoliths brought up to the surface by the volcanism of the Kerguelen Islands represent a mantle that has been affected by a high degree of partial melting followed by intense melt percolation above the Kerguelen plume. These xenoliths are therefore particularly suitable to investigate effects of melt-rock interaction on crystallographic fabrics (lattice-preferred orientation (LPO)) of peridotite minerals and on the LPO-induced seismic properties of peridotites above a mantle plume. We have studied a suite of 16 ultramafic samples representative of different degrees of partial melting and magma-rock interaction among which the protogranular harzburgites are the least metasomatised xenoliths and dunites are the ultimate stage of metasomatism. Olivine LPO is characterized by high concentration of [010] axes perpendicular to the foliation and [100] axes close to the lineation or distributed in the foliation plane in harzburgites, whereas the high concentration of [100] axes is parallel to the lineation and [010] axes is perpendicular to the assumed foliation in dunites. Olivine LPO in harzburgites is interpreted as being due to a deformation regime in axial compression or transpression. The fabric strength of olivine decreases progressively from protogranular to poikilitic harzburgites and finally to dunites, for which it remains nevertheless significant (J index 3.8). Seismic properties calculated from LPO of minerals indicate that metasomatism at higher melt/rock ratio lowers the P wave velocities. The most significant difference between harzburgites and dunites corresponds to the distribution of S wave anisotropy. Harzburgites display the maximum of anisotropy within the foliation plane and the minimum of anisotropy perpendicular to the foliation plane, whereas the lowest anisotropy is parallel to the lineation for dunites. These modifications of seismic properties as a result of metasomatic processes may induce seismic heterogeneities in the mantle above the Kerguelen plume. In addition, assuming a lithospheric mantle primarily harzburgitic and structured with a horizontal foliation, the seismic properties calculated for the Kerguelen xenoliths reconcile the rather high anisotropy evidenced by the horizontally propagating surface waves with the apparent isotropy revealed by the absence of splitting of vertically propagating teleseismic SKS waves recorded by the GEOSCOPE Kerguelen station.
ISSN: 1525-2027

hal-00366222
https://hal.archives-ouvertes.fr/hal-00366222
https://hal.archives-ouvertes.fr/hal-00366222/document
https://hal.archives-ouvertes.fr/hal-00366222/file/bascou_Kerguelen_2007GC001879_hal.pdf
DOI : 10.1029/2007GC001879