Jerôme Bascou
email: jerome.bascou@univ-st-etienne.fr

G Delpech

A Vauchez

Bertrand N Moine

Jean-Yves Y Cottin

Guilhem Barruol

An integrated study of microstructural, geochemical, and seismic properties of the lithospheric mantle above the Kerguelen plume (Indian Ocean)

Introduction

[2] The Earth's upper mantle is seismically anisotropic. Studies of naturally and experimentally deformed samples [e.g., [START_REF] Nicolas | Formation of anisotropy in upper mantle peridotites -A review[END_REF][START_REF] Mainprice | The seismic anisotropy of the Earth's mantle: From single crystal to polycrystal, in Earth's Deep Interior: Mineral Physics and Tomography From the Atomic to the Global Scale[END_REF] and numerical simulations [START_REF] Tommasi | Upper mantle tectonics: Three-dimensional deformation, olivine crystallographic fabrics and seismic properties[END_REF][START_REF] Kaminski | Interpretation of seismic anisotropy in terms of mantle flow when melt is present[END_REF] demonstrate that the lattice-preferred orientation (LPO or crystallographic fabric) of olivine crystals induced by mantle flow is the main cause of the observed seismic anisotropy. During plastic deformation of peridotites, the [100] and [010] axes of olivine tend to be preferentially aligned parallel to the flow direction and normal to the flow plane, respectively, in accordance with the dominant activation of the (010) [100] slip system [e.g., [START_REF] Nicolas | Crystalline Plasticity and Solid State Flow in Metamorphic Rocks[END_REF]. Development of olivine LPO induces seismic anisotropy in the lithospheric mantle that may be further affected by reheating and melt percolation within the upper mantle. Although several studies have been devoted to examples of lithosphere-asthenosphere interactions [e.g., [START_REF] Vauchez | Seismic properties of an asthenospherized lithospheric mantle: Constraints from lattice preferred orientations in peridotite from the Ronda Massif[END_REF][START_REF] Tommasi | Seismic anisotropy and compositionally induced velocity anomalies in the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia[END_REF][START_REF] Vauchez | Microstructure, texture and seismic anisotropy of the lithospheric mantle above a mantle plume: Insights from the Labait volcano xenoliths (Tanzania)[END_REF][START_REF] Le Roux | The Lherz spinel lherzolite: Refertilized rather than pristine mantle[END_REF], the effects of these processes on the fabric and the seismic properties of mantle rocks are still not fully understood.

[3] Recent petrophysical studies on peridotite samples suggest than the mineral LPO may be affected by heating and partial melting (asthenospherization) of the lithospheric mantle. For example, LPO measured in samples from the ''asthenospherized'' domain of the Ronda massif subcontinental lithospheric mantle show a weakening of the fabric strength [START_REF] Vauchez | Seismic properties of an asthenospherized lithospheric mantle: Constraints from lattice preferred orientations in peridotite from the Ronda Massif[END_REF]. Moreover, variations in LPO symmetry with depth and the development of uncommon LPO patterns in xenoliths from the Labait volcano in the East African Rift suggest an increasing activity of the (010)[001] slip system [START_REF] Vauchez | Microstructure, texture and seismic anisotropy of the lithospheric mantle above a mantle plume: Insights from the Labait volcano xenoliths (Tanzania)[END_REF]. Regarding the oceanic lithospheric mantle, LPO patterns of minerals in peridotite xenoliths from the Southern Pacific [START_REF] Tommasi | Seismic anisotropy and compositionally induced velocity anomalies in the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia[END_REF] appear little affected by melt percolation processes. The main variation of mineral LPO is a progressive weakening of the olivine LPO in dunites and wherlites in which static recrystallization occurred [START_REF] Tommasi | Seismic anisotropy and compositionally induced velocity anomalies in the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia[END_REF]. On the other hand, experimental work on the deformation of partially molten mantle rocks under anhydrous conditions [START_REF] Holtzman | Melt segregation and strain partitioning: Implication for seismic anisotropy and mantle flow[END_REF] indicates that significant changes of olivine LPO may take place due to melt segregation and strain partitioning. However, the impact of this change on a regionalscale anisotropy is still discussed [START_REF] Kaminski | Interpretation of seismic anisotropy in terms of mantle flow when melt is present[END_REF].

[4] In the last two decades, anisotropy, and particularly splitting of teleseismic shear waves such as the SKS waves, has been widely used to measure and constrain the active or frozen mantle flow and tectonic processes at depth [e.g., [START_REF] Silver | Seismic anisotropy beneath the continents: Probing the depths of geology[END_REF]. Indeed, anisotropy may be related to mantle deformation since it results from strain-induced crystal preferred orientations [START_REF] Nicolas | Formation of anisotropy in upper mantle peridotites -A review[END_REF][START_REF] Babuska | Seismic Anisotropy in the Earth[END_REF]. Polarized shear waves (e.g., SKS, PKS. . .) traveling across a deformed mantle split in two orthogonal waves polarized in two orthogonal planes related to the strain fabric. These two split waves propagate through the anisotropic medium at different veloc-ities that depend on the birefringence generated by the crystallographic fabric. This birefringence depends both on the arrangement and degree of the crystallographic axes concentration of the main minerals in the rocks. These two split shear waves are recorded at 3-components seismic stations and are classically characterized by the orientation (f) of the fast S wave polarization plane, and the delay (dt) between the fast and slow split S wave arrivals.

[5] Whereas a large number of shear waves splitting measurements is available for various continental environments, the coverage is still sparse in oceanic environments. In the Indian Ocean, most of the oceanic stations have been described as isotropic [START_REF] Barruol | Upper mantle anisotropy beneath the Geoscope stations[END_REF] except stations in the Seychelles [START_REF] Barruol | Upper mantle anisotropy beneath the African IRIS and Geoscope stations[END_REF][START_REF] Hammond | Upper mantle anisotropy beneath the Seychelles microcontinent[END_REF]. At the difference, shear wave splitting has been detected beneath most stations located in the Pacific Ocean [START_REF] Russo | Shear wave splitting and upper mantle deformation in French Polynesia: Evidence for smallscale heterogeneity related to the Society hot spot[END_REF][START_REF] Wolfe | Seismic anisotropy of oceanic upper mantle: Shear wave splitting methodologies and observations[END_REF][START_REF] Fontaine | Upper mantle flow beneath French Polynesia from shear wave-splitting[END_REF] except beneath Tahiti [START_REF] Fontaine | Upper mantle flow beneath French Polynesia from shear wave-splitting[END_REF] where two broadband and long-period permanent stations providing more than 15 years of data did not provide any evidence of SKS splitting. On the other hand, surface waves tomographies performed in the Indian Ocean [e.g., Le ´ve ˆque et al., 1998;[START_REF] Debayle | Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia[END_REF] or in the Pacific Ocean [START_REF] Montagner | Global upper mantle tomography of seismic velocities and anisotropies[END_REF][START_REF] Maggi | Azimuthal anisotropy of the Pacific region[END_REF] suggest that both oceanic basins are pervasively anisotropic at both lithospheric and asthenospheric depth. To better understand why some oceanic domains are apparently isotropic for SKS waves and anisotropic for horizontally propagating surface waves, we performed a detailed study of the petrography, geochemistry and petrophysical characteristics of upper mantle rocks brought up to the surface by the Kerguelen volcanism. Indeed, more constraints are needed to discuss mantle processes and dynamics from seismic anisotropy observations.

[6] The Kerguelen Islands result from a particular geodynamic history above the long-lived Kerguelen plume. They started to form about 42 Ma ago when the Kerguelen plume was located beneath or near the South East Indian Ridge (SEIR), whereas it is currently in an intraplate position in the Antarctic plate [START_REF] Gautier | Petrology and geochemistry of the Kerguelen Archipelagos basalts (south Indian Ocean): Evolution of the mantle sources from ridge to intraplate position[END_REF][START_REF] Giret | Les e ´tapes magmatiques de l'e ´dification des ı ˆles Kerguelen, oce ´an Indien[END_REF] (Figure 1). Ultramafic xenoliths brought up to the surface by alkaline magmas of the Kerguelen Islands are predominantly spinel harzburgites and dunites. These rocks represent a lithospheric mantle that underwent a significant degree of partial melting followed by the percolation of large volumes of magma above the Kerguelen plume. The effects of mantle-melt interactions on the petrology and geochemistry of these xenoliths have been extensively studied [START_REF] Mattielli | Kerguelen basic and ultrabasic xenoliths: Evidence for long-lived Kerguelen hot spot activity[END_REF][START_REF] Gre ´goire | Xenoliths evidence for a refractory oceanic mantle percolated by basaltic melts beneath the Kerguelen archipelago[END_REF]Gre ´goire et al., , 2000aGre ´goire et al., , 2000b;;[START_REF] Moine | High field strength element fractionation in the upper mantle: Evidence from amphibole-rich composite mantle xenolith from the Kerguelen Islands (Indian Ocean)[END_REF][START_REF] Moine | Carbonatite melt on oceanic upper mantle beneath the Kerguelen Archipelagos[END_REF][START_REF] Delpech | Feldspar from carbonate rich silicate metasomatism in the shallow oceanic mantle under Kerguelen Islands (south Indian Ocean)[END_REF]. In this contribution, we combine microstructural analyses and seismic properties calculations with existing and new geochemical studies to investigate whether and how magma-peridotite interaction modifies seismic properties of the oceanic mantle. Sixteen ultramafic xenoliths having undergone various degrees of partial melting and metasomatism were selected for this study. This enables us to discuss the olivine LPO evolution, the impact on the seismic properties and the consequence on the interpretation of SKS splitting and surface wave anisotropic tomographies.

Sampling and Petrology

[7] Selected peridotite xenoliths come from various localities in the Kerguelen Archipelago (Figure 1) and display differences in structure, chemical and modal compositions (Table 1).

[8] Harzburgites show mainly protogranular and poikilitic structures [START_REF] Mercier | Textures and fabrics of upper mantle peridotites as illustrated by xenoliths from basalts[END_REF][START_REF] Coisy | Structure et ge ´odynamique du manteau supe ´rieur sous le Massif Central (France) d'apre `s l'e ´tude des enclaves des basaltes[END_REF] (Figure 2). However, some samples tend to develop a porphyroclastic structure with large olivine and orthopyroxene crystals (>2 mm) displaying undulose extinctions and subgrain boundaries. These porphyroclasts are surrounded by fine strain-free neoblasts. Protogranular harzburgites display olivine and orthopyroxene grains ranging from 2 to 10 mm in size. The grain boundaries are curvilinear, suggesting grain boundary migration and the largest grains of olivine and orthopyroxene commonly display evidence of plastic strain such as subgrain boundaries (Figures 2a-2c). Olivine grains in poikilitic harzburgites are large (up to 5 cm long) and contain inclusions of orthopyroxene. Clinopyroxene displays inclusions of resorbed orthopyroxene and spinel grains (Figure 2d). Few samples contain secondary minerals such as amphibole and phlogopite (see Table 1). In the various types of harzburgites vermicular grains of spinel occur between olivine and pyroxene grains and commonly form clusters with orthopyroxene and clinopyroxene. Sample JGM92-1c has 7% modal clinopyroxene and is a clinopyroxene-poor lherzolite (Table 1). It has the same microstructural and geochemical characteristics as the poikilitic harzburgites [Gre ´goire et al., 2000b] and will be hereafter included in the poikilitic harzburgite samples.

[9] Dunites display both unequigranular and equigranular structures (Figures 2e and2f). Grain size for the unequigranular structure ranges from 1 to 6 mm (samples MG91-114, GM92-468). The largest grains are frequently slightly elongated and display evidence of plastic strain such as widely spaced subgrain boundaries. The smallest grains usually display a polygonal shape, without evidence of plastic deformation. Equigranular dunites (MG94-54, GM92-214, BOB93-640.1, MM94-97) display olivine grains 0.5 to 1 mm in diameter, free of internal strain and polygonal in shape with frequent 120°triple-point boundary. This equilibrated microstructure suggests static recrystallization through grain boundary migration. Isolated globular to anhedral grains of spinel are either interstitial or occur as inclusions in olivine. Secondary minerals such as clinopyroxene and phlogopite are commonly interstitial.

Geochemistry of the Mantle Xenolith Suite

[10] The petrography and geochemistry of eleven samples out of the sixteen used in the present paper have been previously studied by Gre ´goire et al. [2000a, 2000b], who also calculated equilibration temperatures. Data for the five remaining samples and MG91-114 (dunite) have been obtained using similar analytical methods as those described by Gre ´goire et al. [2000a, 2000b]. Average major and trace element data for these samples can be found in auxiliary material Table S1.1 Samples 3f). Compared to minerals in abyssal peridotites [START_REF] Dick | Abyssal peridotites, very slow spreading ridges and ocean ridge magmatism, in Magmatism in the Ocean Basins[END_REF], which represent the composition of a typical oceanic lithosphere (without a plume influence), minerals in protogranular harzburgites have higher [2000a, 2000b] for details). Equilibration temperatures estimated for these samples are higher than in protogranular harzburgites and range between 1015 and 1125°C.

Dunites

[13] Minerals in dunites (olivine, clinopyroxene, spinel) display Mg# that are in the range of those for olivine and clinopyroxene in poikilitic harzburgites (Table 1 andFigure 3). The Mg# in olivine displays a wide range of variation, from 89.8 in GM92-468 to more Fe-rich olivines in sample MM94-54 (Mg# = 86.8). Clinopyroxene is Mg-Al diopside with Mg# varying between 88.1 and 90.2 (Table 1) which has variable major element compositions between those of clinopyroxene in protogranular samples and those of the poikilitic samples (JGM91-1c, GM92-453; Figures 3b-3e).

The decrease in Mg# is accompanied by an increase in basaltic components Al, Na, Ti and a decrease in Ca (Figure 3). Spinel is a magnesian chromite with a wide range of major element compositions in Mg# (49.7 -73.5) and Cr# (25.0-51.3) (Figure 3f). Most dunites have spinels with Mg# lower than for harzburgites except in dunite GM92-214 (73.5, Table 1). However, the Cr# is highly variable and covers the range displayed by spinels in both types of harzburgites (Figure 3f). [La-Nd]) and in the most incompatible elements (Rb, Th, U) but are less enriched in Ba, Nb, Sr, Zr, Ti compared to their neighboring elements.

Poikilitic Harzburgites

[15] Trace element contents of clinopyroxenes in poikilitic harzburgites are much higher and rather uniform compared to clinopyroxenes in protogranular samples (Figure 4), except sample BY96-394.

Clinopyroxenes in poikilitic samples show a smooth enrichment from HREE to LREE with a peak at Nd (Figure 4b) and are enriched in the most incompatible elements (Rb, Ba, Th, U, Nb). They commonly have lower concentration of Pb, Zr, Hf and Ti than neighboring elements. Clinopyroxene in harzburgite BY96-394 has much lower trace element contents, similar to trace element concentrations in protogranular samples.

Dunites

[16] Clinopyroxenes in dunites have very variable trace element contents (Figure 4c). Clinopyroxene in dunite MG91-114 is depleted in LREE compared to MREE and HREE and it has the lowest LREE, MREE and Th, U contents. Clinopyroxene in the phlogopite-bearing dunite GM92-468 has a convex upward trace element pattern with a peak at Hf and has the highest REE contents (La-Lu) of the dunite xenolith suite. Other clinopyroxenes display trace element patterns with smooth enrichments from HREE to LREE (GM92-214, BOB93-640, MM94-54, MM94-97) and all are enriched in the most incompatible elements (Th, U, Ta, Sr ± Zr) but have lower concentrations of Rb, Ba, Nb ± Ta and Ti (Figure 4c). Clinopyroxenes in dunites GM92-468 and MM94-97 have trace element con-centrations that are in the range of those of clinopyroxenes in poikilitic harzburgites.

Melt-Rock Reaction Processes in the

Lithosphere Beneath the Kerguelen Archipelago

[17] In an olivine Mg# versus olivine modal % diagram (Figure 5) some protogranular harzburgites plot near the oceanic trend. This likely indicates that they represent residues of partial melting at relatively shallow depth in the spinel stability field [START_REF] Boyd | Compositional distinction between oceanic and cratonic lithosphere[END_REF]. Some other harzburgites from Kerguelen Islands plot off this trend and show higher Mg# of olivine for low olivine modal abundances. This deviation from the oceanic trend and the enrichment in orthopyroxene of these harzburgites have been explained as a result of partial melting in the stability field of spinel although at a higher pressure under which, orthopyroxene is stable during melting (>1.5 GPa [START_REF] Hassler | Plume-lithosphere interaction: geochemical evidence from upper mantle and lower crustal xenoliths from the Kerguelen Islands[END_REF]). In addition, the high Mg# of mineral phases (and Cr# for spinel, Table 1), the depletion in basaltic components (Al 2 O 3 , Na 2 O, TiO 2 , FeO; Figure 3) and the low HREE contents in clinopyroxenes (Figure 4) are characteristic features of a lithospheric mantle that has undergone extensive partial melting, close to exhaustion of clinopyroxene (>20% [START_REF] Gre ´goire | Xenoliths evidence for a refractory oceanic mantle percolated by basaltic melts beneath the Kerguelen archipelago[END_REF][Gre ´goire et al., , 2000b]]). However, the enrichment in the most incompatible trace elements observed in clinopyroxene (Figure 4) suggests that the protogranular harzburgite suite has later experienced metasomatism by small amount of silicate melts without crystallizing new minerals (''cryptic'' metasomatism).

[18] In contrast, minerals in the poikilitic harzburgites are characterized by Mg# or Cr# similar or lower than in protogranular harzburgites. Clinopyroxene has higher contents of basaltic components (Al 2 O 3 , Na 2 O, TiO 2 ; Figure 3) and it shows a global enrichment in the most incompatible elements. In Figure 5, most poikilitic harzburgites plot below the oceanic trend and display lower Mg# of olivine for higher olivine modal abundances. They also contain more clinopyroxene (2.5 -7 wt%; Table 1) and minerals such as amphibole and more rarely phlogopite also occur in close association with clinopyroxene. This global enrichment in Fe, Al, Na, Ti, Cr (Figure 3) as well as in the most incompatible trace elements in clinopyroxene (Figure 4), and the crystallization of new minerals Clinopyroxenes in protogranular harzburgites (Figure 4a) have low contents of trace elements compared to clinopyroxenes in poikilitic harzburgites (Figure 4b), which are enriched in the most incompatibles elements as a result of metasomatism at high melt/rock ratio. Clinopyroxenes in dunites have variable trace elements contents that attest to equilibration with heterogeneous silicate melts.

(amphibole, phlogopite) are the consequences of modal metasomatism (i.e., metasomatism at high melt/rock ratio) into the depleted (protogranular) harzburgites and mafic alkaline silicate melts from the Kerguelen plume [Gre ´goire et al., 2000b]. This metasomatic event resulted in a global re-enrichment in basaltic components and incompatible elements of the initially depleted lithospheric mantle beneath the Kerguelen Archipelago, at least in the vicinity of major melt pathways to the surface. The reaction between depleted (protogranular) peridotite and mafic alkaline silicate melts essentially led to the dissolution of orthopyroxene in the protogranular samples and crystallization of olivine and clinopyroxene (±volatile-bearing minerals) in poikilitic harzburgites. The ultimate end product of this metasomatic process at high melt/rock ratio is the formation of clinopyroxene-bearing dunite bodies with low Mg# of olivine as shown in Figure 5. These dunites derive from former harzburgites in which all the orthopyroxene was consumed during melt-rock reactions. Dunites sometimes contain volatile-bearing minerals (amphibole, phlogopite, Table 1). These minerals have likely crystallized from volatile and alkali-enriched silicate melt fractions at the end of the melt-rock reaction process.

A secondary mineralogy (carbonate, plagioclase, K-feldspar, apatite) is sometimes observed in harzburgites and dunites as veins crosscutting the primary mineralogy or as reaction zones (Table 1). They correspond to late-stage metasomatic events that occurred shortly before eruption and that are [1989]. Data for Kerguelen [START_REF] Hassler | Plume-lithosphere interaction: geochemical evidence from upper mantle and lower crustal xenoliths from the Kerguelen Islands[END_REF]Gre ´goire et al., 2000aGre ´goire et al., , 2000b;; this study]; Samoan xenoliths from [START_REF] Hauri | Constraints on melt migration from mantle plumes: A trace element study of peridotites xenoliths from Savai'i, Western Samoa[END_REF] and Canary Islands xenoliths from Wulff-Pedersen et al. [1996]. The dashed line represents the evolution of the Mg# of olivine and the olivine modal content of a peridotite undergoing progressive partial melting at relatively shallow depth in the lithosphere (<1.5 GPa [START_REF] Boyd | Compositional distinction between oceanic and cratonic lithosphere[END_REF]).

related to metasomatism by small volumes of evolved melts through repeated reactions with the lithospheric mantle [START_REF] Gre ´goire | Xenoliths evidence for a refractory oceanic mantle percolated by basaltic melts beneath the Kerguelen archipelago[END_REF]Moine et al., 2004;[START_REF] Delpech | Feldspar from carbonate rich silicate metasomatism in the shallow oceanic mantle under Kerguelen Islands (south Indian Ocean)[END_REF].

Lattice-Preferred Orientation

[19] Crystallographic orientation data were obtained by indexation of Electron Backscattered Diffraction patterns (EBSD technique) generated in the JEOL 5600 Scanning Electron Microscope (SEM-EBSD, Geosciences-Montpellier, France). Indexation of the observed patterns of Kikuchi bands was performed through a comparison with diffraction predicted for the analyzed crystal using the HKL CHANNEL 5+ software [START_REF] Schmidt | Computer-aided determination of crystal-lattice orientation from electronchanneling patterns in the SEM[END_REF]]. The relative precision of crystal orientations measured from electron backscattering patterns is better than 1° [START_REF] Krieger Lassen | The relative precision of crystal orientations measured from electron backscattering patterns[END_REF]. For all samples, the whole surface of the thin sections was investigated. The crystallographic orientation of minerals was measured following a grain-by-grain, operator-controlled indexing procedure to avoid possible bias due to oversampling of the largest grains and pseudo symmetry of olivine.

[20] Since the studied xenoliths are harzburgites and dunites, the LPO of olivine and orthopyroxene only has been measured (Figures 6789). The fabric strength of olivine was calculated and expressed by the dimensionless texture J index [START_REF] Bunge | Texture Analysis in Materials Sciences[END_REF],

Figure 6. Olivine LPO in harzburgites. Equal area, lower hemisphere projections. Assumed foliation (XY plane) is marked by a black line, and lineation (X) is horizontal in the foliation plane; relationship between structural and crystallographic fabric is detailed in the text. N is the number of measurements. The density contours are in Multiple Uniform Distribution (MUD); M.D. is the maximum of density. The olivine fabric strength is given by the J index number.

which equals unity for a random distribution and tends toward infinity for a single crystal. Ben Ismaı ¨l and [START_REF] Ismaı ¨l | An olivine fabric database: An overview of upper mantle fabrics and seismic anisotropy[END_REF] have shown that the fabric strength of olivine becomes stable from 100 measured grains. In this study, the minimum number of measurements for olivine is N = 106 (GM92-31) due to the large size of crystals (pluri-millimetric). The average number of measurements for olivine is N = 253. a horizontal EW and NS position and these orientations were labeled X and Z (Figures 6 and9). In the dunites, constrains on the crystallographic and structural fabrics relationships provided by the orthopyroxene LPO are missing and we have considered that olivine LPO in dunites resulted from plastic deformation mechanisms and dominant activation of (010)[100] slip system, as in harzburgites. Olivine LPO in dunites as therefore been rotated in the same way as in harzburgites. It is noticeable than in the dunite MG91-114 where the foliation is relatively well marked by the shapepreferred orientation of minerals (olivine and spinel grains) a correlation between the [010] axes of olivine and the apparent pole of the foliation plane (Z) is observed.

Crystallographic and Structural Fabrics

Olivine Crystallographic Fabric

[22] LPO of olivine in harzburgites is characterized by a J index value ranging from 6.31 to 12.07 (Figure 6). Olivine LPO with medium to high J index value (J index > 7) systematically displays a [010]-fiber type pattern, according to the [START_REF] Bunge | Texture Analysis in Materials Sciences[END_REF] [24] Figure 8 shows the P (point), G (girdle), and R (random) fabric components defined from the eigenvalue analysis formulated by [START_REF] Vollmer | Modeling plastic deformation of peridotite with the self-consistent theory[END_REF].

We observe that the olivine [100] and [010] axes of protogranular harzburgites with high J index value (higher than 11) and dunites define two distinct groups. Contrarily, the poikilitic and protogranular harzburgites with lower J index value (<7, samples BY96-397 and GR97-38) are relatively scattered (around the protogranular harzburgite with high J index value and dunite group).

Orthopyroxene Crystallographic Fabric

[25] For orthopyroxene, it was not always possible to measure a large enough number of grains and we have therefore not calculated its J index. However, the orthopyroxene fabric pattern is well defined even if the number of grains is low (for example, sample OB93-3, N = 32; Figure 9). Orthopyroxene LPO is characterized by a strong clustering of [100] and [001] axes. This LPO is accounted by the dominant activation of (100)[001], which is the easiest and the most common slip system observed in naturally and experimentally deformed orthopyroxene [START_REF] Naze | TEM study of lattice defects in naturally and experimentally deformed orthopyroxenes[END_REF]. Interestingly, most samples display a significantly higher concentration of [100] axes than of the other axes and a tendency for the [001] axes to have a girdle distribution. Thus, orthopyroxene and olivine LPO appear symmetrical compared to the structural frame, with the highest concentration of crystallographic axes perpendicular to the foliation.

Seismic Properties

[26] Seismic properties of the studied harzburgites and dunites were computed from single crystal elastic stiffness matrix, crystal orientation and density via the Christoffel equation [START_REF] Crosson | Voigt and Reuss prediction of anisotropic elasticity of dunite[END_REF]] using the [START_REF] Mainprice | A FORTRAN program to calculate seismic anisotropy from the lattice preferred orientation of minerals[END_REF] software. Input parameters are as follows: (1) the readjusted modal compositions of Table 1 ignoring the contribution of phlogopite, amphibole (present as accessory components, < 1%) and alteration minerals (e.g., serpentine), (2) the EBSD-measured LPO of major minerals (olivine and orthopyroxene), and (3) the elastic stiffness matrix of olivine, orthopyroxene, clinopyroxene and spinel using a Voigt-Reuss-Hill average [Mainprice et al., 2000, and references therein]. The single crystal elastic constants and density data are taken from studies on olivine [START_REF] Abramson | The elastic constants of San Carlos olivine up to 17 GPa[END_REF], enstatite [START_REF] Duffy | Elasticity of enstatite and its relationships to crystal structure[END_REF], diopside [START_REF] Collins | Elasticity of an upper mantle clinopyroxene[END_REF]] and spinel [START_REF] Li | Elastic stability of high dose neutron irradiated spinel[END_REF]. Due to the lack of statistically reliable LPO measurements for clinopyroxene and spinel we used the calculated isotropic elastic stiffness matrix of these minerals.

In addition, the elastic stiffness matrix and the density of olivine were recalculated in order to take into account the variation of the forsterite content. 3-D seismic body waves velocity and azimuthal and polarization anisotropy are pre-sented in a lower hemisphere projection and structural reference frame (Figures 10 and11).

[27] Seismic properties of harzburgites displaying olivine [010]-fiber type LPO with medium and high J index value (J index > 7) and well-defined orthopyroxene LPO pattern show rather similar seismic properties (Figure 10a). Vp max ranges from 8.48 to 8.66 km/s and Vp min ranges from 7.90 to 8.06 km/s, resulting in a quite strong azimuthal axis of olivine (pole of the foliation, Z). The fast split shear wave is polarized in a plane defined by the propagation direction and the maximum of olivine [001] (lineation). To better enhance the first-order characteristics of harzburgites from the Kerguelen mantle, we calculated an average harzburgite using samples OB93-426, OB93-58, OB92-31, OB93-3, OB-93-5, GM96-394 (Figure 10b). Averaging the seismic properties by giving the same weight to each sample is an interesting way to integrate the small-scale variations in composition and in microstructures, in a similar way to seismic waves. The average seismic properties are determined from calculation of the mean density and the 6x6 matrix coefficients of the stiffness tensor Cij describing the average elastic properties of the harzburgite samples (Figure 10b). The average harzburgite shows fast P wave parallel to the lineation and high P wave anisotropy (7%). The minimum of S wave polarization anisotropy (AVs) is $0.2% (quasi isotropy) for a direction orthogonal to the foliation and the maximum of S wave anisotropy forms a girdle in the foliation with a maximum close to the Y axis. The maximum of S wave azimuthal anisotropy is higher than 2% (AVs1 = 4.8%, AVs2 = 2.8%).

[28] Most dunite samples are characterized by a stronger clustering of the olivine [100] axes and a distribution of [010] axes in a plane normal to the [100] axes. They display consistent seismic properties for P and S waves that differ from the properties of harzburgites described above particularly for S waves. The fast velocities of P waves are always parallel to the lineation and the slowest velocities form a girdle perpendicular to the [100] maximum of concentration and thus to the assumed foliation (Figure 11a). Figure 9. Orthopyroxene LPO in harzburgites. Projections and symbols for structural and crystallographic fabrics are similar to those in Figure 7.

Figure 10 anisotropy (9%) and by a girdle of high S wave anisotropic directions normal to the lineation with a maximum perpendicular to the foliation and a minimum parallel to the lineation. The maximum of S wave azimuthal anisotropy is higher than 4% (AVs1 = 4.95%, AVs2 = 5.4%).

[29] Seismic properties computed for harzburgites GM97-38 and GM96-397 and dunites BOB93-Figure 10. Calculated seismic properties of Kerguelen harzburgites. Data are presented in an equal area lower hemisphere projection. Reference frame as in Figure 6. Vp (km/s), P wave velocity; AVp (%), anisotropy of P waves defined as 100 Â [(Vp max À Vp min )/((Vp max + Vp min )/2)]; AVs (%), polarization anisotropy of S waves defined for a specific direction as 100 Â [(Vs 1 À Vs 2 )/[((Vs 1 + Vs 2 )/2)], where Vs 1 and Vs 2 are the fast and slow S wave velocities, respectively; S 1 P.P., polarization plane of the fast shear wave (S 1 ) as a function of the orientation of the incoming wave relative to the foliation (XY plane, full line) and lineation (X). Maximum and minimum values are shown on the plots as black squares and white spots, respectively.

Figure 11. Calculated seismic properties of Kerguelen dunites. Data are presented in an equal area lower hemisphere projection; reference frame as in Figure 7. Vp (km/s), P wave velocity; AVp (%), anisotropy of P waves defined as 100 Â [(Vp max ÀVp min )/((Vp max +Vp min )/2)]; AVs (%), polarization anisotropy of S waves defined for a specific direction as 100 Â [(Vs 1 À Vs 2 )/[((Vs 1 + Vs 2 )/2)], where Vs 1 and Vs 2 are the fast and slow S wave velocities, respectively; S 1 P.P., polarization plane of the fast shear wave (S 1 ) as a function of the orientation of the incoming wave relative to the foliation (XY plane, full line) and lineation (X). Maximum and minimum values are shown on the plots as black squares and white spots, respectively.

640.1 and MM94-97 are rather similar and show differences with those of harzburgites and dunites mentioned above. The P wave velocity pattern is orthorhombic with Vp max parallel to the lineation and Vp min perpendicular to the foliation. Vp max ranges from 8.64 to 8.71 km/s and Vp min from 7.96 to 8.00 km/s, resulting in a Vp anisotropy (AVp) of 8.1 to 8.7%. AVs ranges from $5.6 to 6% with the highest anisotropy close to Y (i.e., normal to both [100] and [010] maximum of concentration) and the lowest anisotropies perpendicular to the foliation pole and close to the lineation. As for the dominant harzburgite and dunite types, Vs1 is polarized in a plane that contains the propagation direction and the lineation. These properties are intermediate between those of the samples displaying an olivine [010]-fiber pattern (Figure 10b) and to the samples displaying a stronger clustering of the olivine [100] axes (Figure 11b). For the two dunites BOB93-640.1 and MM94-97, the change in LPO and seismic properties pattern is correlated to the decrease of olivine fabric strength due to static recrystallization.

Discussion

[30] The Kerguelen Islands represent the apex of the northern part of the Kerguelen-Heard oceanic plateau, the second largest oceanic plateau in the world [START_REF] Coffin | Large igneous provinces: Crustal structure, dimensions, and external consequences[END_REF]. It results from a geodynamic context that evolved from continental rifting (125-100 Ma ago) to a stage during which an oceanic ridge formed above a mantle plume (around 42 Ma) and finally to an intraplate hot spot-mantle plume location [START_REF] Giret | Les e ´tapes magmatiques de l'e ´dification des ı ˆles Kerguelen, oce ´an Indien[END_REF][START_REF] Duncan | A time for construction of the Kerguelen plateau and Broken ridge[END_REF]. Metasomatism resulting from magma percolation above the Kerguelen plume affects a strongly deformed and structured mantle as supported by microstructural observations, LPO measurements and fabric strength values in protogranular harzburgites. The presence of spinel in the harzburgite xenolith suite together with the thermobarometric estimates [Gre ´goire et al., 2000b] indicate a mantle slice between 30 and 70 km in depth. Protogranular harzburgites represent the part of the mantle the least affected by magma-rock interactions as indicated by geochemical data. These rocks have only experienced incipient metasomatism by small melt volumes, which resulted in enrichment of clinopyroxene in the most incompatible elements. Metasomatism at higher melt/ rock ratio is accompanied by the development of a poikilitic structure in the harzburgites. From a mineralogical point of view, the reaction between harzburgites and silicate melt leads to dissolution of orthopyroxene and crystallization of olivine, and ultimately produces dunites when all the orthopyroxene has reacted out. Dunites represent therefore a former harzburgitic mantle, which reacted with large volumes of silicate melts. Dunite bodies likely represent a limited volume of mantle rocks located along and close to melt pathways or localized near the crust-mantle boundary where melts may segregate and react with the uppermost lithospheric mantle [Gre ´goire et al., 1997].

Significance of LPO Patterns in Harzburgites

[31] Harzburgites display olivine LPO pattern of [010]-fiber type characterized by the dispersion of [100] and [001] within a plane orthogonal to the maximum concentration of [010] (foliation plane). The interpretation of this LPO is still not fully understood. Two main types of causes have been suggested to explain its development: a departure from simple shear and an increasing activity of the (010)[001] slip system during deformation.

[32] From numerical modeling of LPO development due to various strain regimes, Tommasi et al.

[1999] have shown that [010]-fiber LPO pattern may develop under mantle conditions of transpression and axial compression. This LPO pattern in such case, results from the activation of the high temperature (010)[100] slip system and the dispersion of the [100] axes is due to the compressional component.

[33] From experiments, [START_REF] Jung | Water-induced fabric transitions in olivine[END_REF] have suggested that the (010)[001] slip system may become dominant for dislocation creep under high water content and/or high stress (or strain rate) conditions, resulting in a LPO (''B-type'') characterized by a concentration of [001] and [010], respectively, close to the lineation and the pole of the foliation plane. According to [START_REF] Holtzman | Melt segregation and strain partitioning: Implication for seismic anisotropy and mantle flow[END_REF] this LPO may also be a result of strain partitioning associated to melt segregation. Activation of the (010)[001] slip system may also result from a change in dominant slip system due to high pressure [START_REF] Couvy | Shear deformation experiments of forsterite at 11 GPa-1400°C in the multianvil apparatus[END_REF][START_REF] Mainprice | Pressure sensitivity of olivine slip systems and seismic anisotropy of Earth's upper mantle[END_REF].

[34] The dominant activation of the (010)[001] slip system would result in the development of an orthorhombic LPO with [001] close to the lineation and [010] close to the foliation pole rather than a [010]-fiber pattern as observed in the Kerguelen xenoliths. Moreover, in the Kerguelen xenoliths, orthopyroxene LPO show the same tendency as olivine LPO, i.e., a strong concentration of (100), the slip plane and a dispersion of [001], the slip direction; such a correlation is regarded as a strong argument supporting a transpressional strain regime shear [Wenk et al., 1991;[START_REF] Tommasi | Upper mantle tectonics: Three-dimensional deformation, olivine crystallographic fabrics and seismic properties[END_REF]. The role of pressure on the mechanical behavior of olivine is also excluded, the Kerguelen peridotite xenoliths being representative of a relatively shallow mantle (<70 km).

[35] We suggest that olivine LPO in Kerguelen harzburgite xenoliths results from a transpressional deformation of the lithospheric mantle under hightemperature and relative low-stress conditions. The simultaneous action of the asthenospheric upwelling due to the Kerguelen mantle plume and the emplacement of a very large oceanic plateau over a young oceanic lithosphere may induce a strain regime combining vertical flattening and simple shear accommodating the plate motion. Although there is yet no firm evidence of a relationship between the LPO pattern and the geographical location of the samples, harzburgites BY96-397 and GR97-38 that differ of the others ones by their orthorhombic olivine LPO, both come from the northern part of the Kerguelen Islands (Figure 1). The lithosphere under the northern part of Kerguelen Islands displays a specific fabric suggesting simple shear [START_REF] Tommasi | Upper mantle tectonics: Three-dimensional deformation, olivine crystallographic fabrics and seismic properties[END_REF], which may be due to the presence of deep fracture zones between the South East Indian Ridge and the Kerguelen plateau (e.g., transform faults) clearly visible on the satellite gravity maps [START_REF] Rotstein | The Kerguelen Province revisited: Additional constraints on the early development of the southeast Indian Ocean[END_REF].

Melt-Rock Interactions, LPO, and Seismic Properties

[36] Partial melting, percolation and interaction of melts with the host mantle rocks are the processes that affect the lithospheric mantle above a mantle plume. For the Kerguelen lithospheric mantle, Gre ´goire et al.

[1997] estimated a high degree ($15-25 wt%) of partial melting, which created a depleted protogranular harzburgitic mantle. Petrological and geochemical studies support that the evolution from protogranular to poikilitic harzburgites and finally to dunites is the result of increasing metasomatism at higher melt/rock ratio and that this evolution leads to a global Fe-enrichment of minerals (olivine, orthopyroxene, clinopyroxene ± spinel). To better understand the effects of metasomatism on the LPO and therefore on the seismic properties, the relationship between the Mg# of olivine and the fabric strength (J index) as well as the seismic properties parameters (Vp, Vs, AVp and AVs) are investigated in Figure 12. Indeed, high J index values are observed for depleted protogranular harzburgites (J $ 12) characterized by high Mg# of olivine. The fabric strength is very sensitive to the onset of metasomatism at high melt/rock ratio, i.e., when the poikilitic microstructure starts to develop (Figure 12a), while J index decreases in poikilitic harzburgites and stabilizes in dunites. The crystallization of new olivine that is coupled with decreasing olivine Mg# induces a decrease of the fabric strength (Figure 12b).

[37] The relationship between seismic properties and metasomatism for harzburgites is not straightforward due to the variations in modal contents of olivine and orthopyroxene between the different samples. The results obtained for Kerguelen xenoliths are in general agreement with those obtained by [START_REF] Tommasi | Seismic anisotropy and compositionally induced velocity anomalies in the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia[END_REF] for xenoliths from French Polynesia islands. For dunites, the velocity of P waves (Vp) appears to decreases with the Fe enrichment (decreasing Mg#) in olivine (Figure 12c). The velocity of P waves is higher for dunites (mainly > 8.45 km/s) than for harzburgites (<8.35 km/s) whereas the Vs average of dunites and harzburgites are very close, about 4.80 km/s for dunites and slightly higher for harzburgites (Figure 12d). The P wave velocity (Vp) is therefore more sensitive than Vs to Mg# variations. The seismic anisotropy (AVp and AVs) does not depend on Mg# variations but is mainly controlled by the LPO of minerals (Figures 12e and12f). The calculated seismic anisotropies remain large (AVp > 5%) in spite of significant petrological and geochemical modifications of the original lithospheric mantle. A major difference with xenoliths from French Polynesia is that the geochemical and mineralogical changes induced by the harzburgite-silicate melt interactions, in particular the dissolution of orthopyroxene and crystallization of olivine, is coupled with a modification of the LPO pattern which results in contrasted seismic anisotropy distribution pattern (especially AVs) with regard to the crystallographic/ structural referential (see seismic properties of harzburgites and dunites Figures 10b and11b, respectively).

Seismic Anisotropy Beneath the Kerguelen Plateau

[38] Various seismic investigations have been performed on the Kerguelen plateau as follows: P and S waves seismic tomography revealed a wide and deep-rooted (from the core-mantle boundary) neg-ative velocity anomaly related to the Kerguelen (and Crozet) hot spots [START_REF] Montelli | A catalog of deep mantle plumes: New results from finitefrequency tomography[END_REF]. Seismic refraction and reflection profiles [START_REF] Recq | The Kerguelen Isles (southern Indian Ocean): New results on deep structure from refraction profiles[END_REF][START_REF] Rotstein | Structure and tectonic of the southern Kerguelen plateau (Indian Ocean) deduced from reflection data[END_REF][START_REF] Charvis | Deep structure of the northern Kerguelen plateau and hot spotrelated activity[END_REF][START_REF] Operto | Deep structure of the southern Kerguelen Plateau (southern Indian Ocean) from ocean bottom ocean bottom seismometer wide-angle seismic data[END_REF] have evidenced an increase in crustal thickness from $15-20 km beneath the northern Kerguelen Plateau (including the archipelago) to 25 km beneath the southern [2001] provide additional constraints on the seismic refraction profiles, and in particular the lithology of crust-mantle boundary.

[39] To characterize the mantle flow beneath the Kerguelen Islands, [START_REF] Barruol | Upper mantle anisotropy beneath the Geoscope stations[END_REF] studied the seismic anisotropy of the mantle by measuring the splitting of teleseismic shear waves recorded at the Geoscope station PAF (Port aux Franc ¸ais, Figure 1) of Kerguelen. No clear splitting was observed but numerous ''nulls'' (unsplit core shear waves) were found for events from various backazimuths, suggesting apparent isotropy. By contrast, Rayleigh wave azimuthal anisotropy measurements [START_REF] Debayle | Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia[END_REF] evidence a clear anisotropic pattern in the southern Indian Ocean at 100 km depth. Surface wave phase velocity studies of the Indian Ocean [Le ´ve ˆque et al., 1998] and of the Antarctic plate [START_REF] Roult | Antarctica II: Upper-mantle structure from velocities and anisotropy[END_REF] and surface wave polarization anomalies [START_REF] Pettersen | Lithospheric anisotropy on the Kerguelen hot spot track inferred from Rayleigh wave polarization anomalies[END_REF] also argue for a rather strong anisotropy located in the 100 uppermost km beneath and in the vicinity of the Kerguelen Islands. Interestingly, results from surface wave data stand in better agreement with the seismic properties obtained from the Kerguelen xenoliths than S wave splitting measurements. Indeed, our results strongly suggest an anisotropic mantle beneath the Kerguelen Islands.

[40] To test the [START_REF] Barruol | Upper mantle anisotropy beneath the Geoscope stations[END_REF] conclusions and discuss the causes of the discrepancy between core shear wave and surface wave anisotropies, we have reprocessed the whole data set recorded at PAF during the period 1993-2007 (Figure 13). About 700 events of magnitude (m b ) greater than 6.0 occurring at epicentral distances in the range 85°to 120°have been selected. The measurements were performed using the [START_REF] Silver | Shear wave splitting and subcontinental mantle deformation[END_REF] algorithm and the SplitLab software [START_REF] Wu ¨stefeld | SplitLab: A shear wave splitting environment in Matlab[END_REF]. This new data set provided 26 non-null splitting measurements among which only one has been qualified as ''good'' (event occurring on February 7, 1997, backazimuth of 123°, f = N93°, dt = 1.8 s). The others are close to nulls and are of lower quality. We also measured 90 ''nulls'' (no splitting) among which 66 are qualified as ''good'' and originate from a wide range of backazimuths. We conclude therefore that the updated S wave splitting measurements confirm the apparent isotropy proposed by [START_REF] Barruol | Upper mantle anisotropy beneath the Geoscope stations[END_REF] for the PAF station. There is however a narrow azimuthal window in which the shear waves evidence an unambiguous splitting. This non-null splitting measurement among numerous nulls suggests a complex upper mantle structure beneath Kerguelen either due to multiple anisotropic layers or more likely to heterogeneity of mantle seismic properties. Dunites that show different seismic properties than harzburgites may carry a large part of the seismic heterogeneity above the Kerguelen mantle plume.

[41] The seismic core shear phases (SKS, SKKS. . .) propagate from the core-mantle boundary to the Earth's surface with a near vertical incidence. They therefore sample seismic properties of the anisotropic medium at rather steeply dipping incidence, i.e., within a rather limited cone. The measured delay time (dt) between the two split wave arrivals and, to lesser extent, the orientation of the fast split wave polarization plane (f), besides being proportional to the thickness of the anisotropic medium, are dependent upon the characteristics and the orientation of its elastic tensor. This means that the observed anisotropy depends on the LPO of the rock-forming minerals and on the orientation of the structural reference frame (foliation, lineation), with respect to the vertical direction.

[42] The mantle xenoliths suite shows that the lithospheric mantle beneath Kerguelen Islands is primarily harzburgitic whereas the dunites probably represent restricted volumes of mantle rocks [START_REF] Gre ´goire | Xenoliths evidence for a refractory oceanic mantle percolated by basaltic melts beneath the Kerguelen archipelago[END_REF]. Both protogranular and poikilitic harzburgites display [010]-fiber LPO pattern that induces specific seismic properties characterized by the lowest S wave polarization anisotropy (AVs) close to the pole of the foliation.

Assuming that the lithospheric mantle beneath Kerguelen Archipelago is characterized by a dominant [010]-fiber texture and a penetrative horizontal foliation, the vertically propagating core shear waves arriving beneath the Kerguelen Archipelago would sample mantle in a direction for which it is apparently weakly anisotropic or even isotropic. This may explain the apparent isotropy revealed by the core S waves recorded at PAF. On the other hand, surface waves sample the mantle in a direction close or parallel to the foliation plane. The velocity of the Rayleigh waves would vary according to the propagation direction relative to the mantle fabric and an azimuthal anisotropy would be recorded. This may account for the clear azimuthal anisotropy observed at 100 km depth in Rayleigh wave tomography [e.g., [START_REF] Debayle | Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia[END_REF] in the southern Indian Ocean around Kerguelen. If one considers a lithospheric mantle beneath Kerguelen structured with the foliation to be close to horizontal, what is expected in the lithospheric mantle and uppermost asthenosphere beneath a moving oceanic plate [e.g., [START_REF] Forsyth | The early structural evolution and anisotropy of the oceanic upper mantle[END_REF][START_REF] Nicolas | Formation of anisotropy in upper mantle peridotites -A review[END_REF], the independent isotropic SKS and anisotropic surface wave seismological observations appear therefore fully consistent together with the seismic properties computed for the Kerguelen xenoliths.

Conclusion

[43] Mantle xenoliths from the Kerguelen Islands represent various degrees of rock-melt interaction as supported by petrologic and geochemical studies. In particular, the Mg content in olivine decreases from protogranular to poikilitic harzbur- gite and finally to dunite, which represents the ultimate stage of metasomatism. This process is correlated in harzburgite with a decrease in crystallographic fabric strength (J index is around 12 in most protogranular harzburgites and decreases down to 6.3 in poikilitic harzburgites). Dunites are affected by static recrystallization, which also weakens the fabric strength without however erasing it completely (J index ! 3.8). Lattice preferred orientation of olivine in harzburgites is characterized by a [010]-fiber pattern with strong concentration of [010] perpendicular to the foliation and by [100] distributed in the foliation plane with a maximum concentration close to the lineation. This olivine LPO is interpreted as due to a transpressional deformation regime resulting from a combination of simple shear accommodating the plate motion with vertical forces due to both the buoyancy of the mantle plume and the weight of the oceanic plateau. Olivine LPO in dunites is characterized by orthorhombic symmetry with high concentrations of [100] axes parallel to the lineation and [010] axes perpendicular to the foliation plane.

From a seismic point of view, metasomatic processes at high melt/rock ratios result in a decrease of P wave velocities. The most significant difference between the Kerguelen harzburgites and dunites concerns the distribution of S wave splitting.

Harzburgites display directions of high birefringence within the foliation plane and directions of minimum birefringence normal to the foliation plane, whereas the lowest birefringence is parallel to the lineation for dunites. This may have two consequences:

[44] 1. Assuming that harzburgites are representative of the initial composition of the lithosphere and that the foliation and lineation are subhorizontal, SKS splitting measurements may enhance an apparent isotropy while surface waves may support a significant anisotropy in the upper mantle. This may reconcile the apparent isotropy suggested by SKS wave splitting measurements for stations located on various Indian Ocean Islands, for instance Kerguelen, Crozet or New Amsterdam and the rather high anisotropy evidenced in the southern Indian Ocean using surface waves.

[45] 2. If the consequence of the metasomatism on the seismic properties of the mantle is at a scale significant for seismic waves, then this may result in a modification of the apparent anisotropy deduced from S waves splitting. Heterogeneous results at the regional scale might arise from such an evolution.

[46] Finally, beneath the Kerguelen Islands, lithosphere-plume interaction resulted in significant modifications of the composition, microstructure, texture and seismic properties of the initial mantle. This likely increased the heterogeneity of the mantle. Regarding texture and seismic properties, it is noteworthy that these processes did not erase the initial LPO and seismic anisotropy of the mantle but entailed significant modifications that may represent interesting constraints to refine the interpretation of seismic data.

Figure 1 .

 1 Figure 1. Location of dikes hosting xenoliths, modified after Gre ´goire et al. [1997]: 1, Lac Miche `le (BY96-394, BY96-397); 2, Table de l'Oiseau (GR97-38); 3, Mont du Chateau (OB93-3, OB93-5); 4, Val Studer (OB93-58, JGM92-1c); 5, Trie `dre (GM92-453, GM92-468); 6, Do ˆme Rouge (OB93-426, GM92-31); 7, Plateau Central (BOB93-640.1); 8, Valle ´e Ring (MM94-54, MM94-97); 9, Pointe de l'Espe ´rance (GM92-214); 10, Mont Tizard (MG91-114). Geochronological data of flood basalts after Nicolaysen et al. [2000]. The Geoscope station of Kerguelen (PAF: À49.351°N, 70.213°E) is also plotted on this map.

Figure 2 .

 2 Figure 2. Photomicrographs (crossed polarizers) showing typical microstructures of the Kerguelen peridotite xenoliths. (a) Protogranular harzburgite GM92-31. (b and c) Details of olivine and orthopyroxene grains in protogranular harzburgite GM92-31. The grains display a well-developed substructure, which suggests dislocation-flow. (d) Poikilitic clinopyroxene with spongy rims interpreted as product of interaction between harzburgites and alkaline basaltic melt, courtesy of M. Gre ´goire. (e) Unequigranular dunite MG91-114. (f) Equigranular dunite MM94-97.

Figure

  Figure3. Major element compositions of minerals (olivine, spinel, clinopyroxene) in harzburgites and dunites from Kerguelen Islands. Grey field, abyssal peridotites after[START_REF] Dick | Abyssal peridotites, very slow spreading ridges and ocean ridge magmatism, in Magmatism in the Ocean Basins[END_REF]; dark blue circles, protogranular harzburgites; empty circles, protogranular harzburgite BY96-397; dark blue triangles, poikilitic harzburgites; green squares, dunites. PM indicates the approximate composition of clinopyroxene and spinel of the Primitive Mantle. The arrows indicate the effect on the PM of progressive melt-rock reactions between the depleted protogranular harzburgites and percolating silicate melts (metasomatism) and the effect of partial melting. In Figure3athe bars indicate the 1s deviation for each sample analyzed. Typical %RSD (relative standard deviation) on the analyses of major elements by EMP (electron microprobe) are of the order of 0.3 for TiO 2 , <0.3 for Al 2 O 3 , 0.4 for CaO, <0.9 for Na 2 O, 0.3 for MgO, 0.5 for FeO, and 0.04 for Mg#. Uncertainties are smaller than symbol size.

Figure 4 .

 4 Figure 4. Trace element concentrations in clinopyroxenes from (a and b) harzburgites and (c) dunites from Kerguelen Islands. Normalizing values for primitive mantle estimate after McDonough and Sun [1995].Clinopyroxenes in protogranular harzburgites (Figure4a) have low contents of trace elements compared to clinopyroxenes in poikilitic harzburgites (Figure4b), which are enriched in the most incompatibles elements as a result of metasomatism at high melt/rock ratio. Clinopyroxenes in dunites have variable trace elements contents that attest to equilibration with heterogeneous silicate melts.

Figure 5 .

 5 Figure5. Mg# of olivine versus modal olivine for harzburgites and dunites from Kerguelen Islands after[START_REF] Boyd | Compositional distinction between oceanic and cratonic lithosphere[END_REF]. Data for Kerguelen[START_REF] Hassler | Plume-lithosphere interaction: geochemical evidence from upper mantle and lower crustal xenoliths from the Kerguelen Islands[END_REF] Gre ´goire et al., 2000a Gre ´goire et al., , 2000b;; this study]; Samoan xenoliths from[START_REF] Hauri | Constraints on melt migration from mantle plumes: A trace element study of peridotites xenoliths from Savai'i, Western Samoa[END_REF] and Canary Islands xenoliths from Wulff-Pedersen et al.[1996]. The dashed line represents the evolution of the Mg# of olivine and the olivine modal content of a peridotite undergoing progressive partial melting at relatively shallow depth in the lithosphere (<1.5 GPa[START_REF] Boyd | Compositional distinction between oceanic and cratonic lithosphere[END_REF]).

[ 21 ]

 21 Figure 6. (continued)

Figure 7 .

 7 Figure 7. Olivine LPO in dunites. Equal area, lower hemisphere projections. Assumed foliation (XY plane) is marked by a dotted line and lineation (X) is horizontal in the foliation plane; relationship between structural and crystallographic fabric is detailed in the text. N is the number of measurements. The density contours are in Multiple Uniform Distribution (MUD); M.D. is the maximum of density. The J index number gives the olivine fabric strength.

Figure 8 .

 8 Figure 8. Eigenvalues analysis. Olivine LPO of each sample is plotted in a triangular diagram according to the P (point), G (girdle), and R (random) indexes of the distribution of the [100] and [010] crystallographic axes. Protogranular harzburgites with high J index values (higher than 11) are plotted in the gray zone, and dunites are in the circles.

Figure 12 .

 12 Figure12. J index and seismic parameters (Vp (average), Vs (average), AVp and AVs) as a function of the mean forsterite content of olivine or modal olivine content in each sample.

Figure 13 .

 13 Figure13. ''Null'' backazimuths observed at the Geoscope station PAF. Analysis of SKS data from 1993 to 2007 provided about 100 unsplit SKS phases arriving from a large range of backazimuths, suggesting that the upper mantle beneath the station is isotropic to the vertically propagating shear waves. This diagram displays the backazimuths of the events showing unsplit phases (black indicate good quality nulls, and dashed gray lines represent the fair quality nulls). Surrounding are a few examples of unsplit SKS phases. The radial (dashed line) and transverse (black line) components of the SKS phases are shown. For each event the magnitude (Mw), backazimuth (Baz, in degrees from north), epicentral distance (Dist., in degrees), and signal-to-noise ratio of the radial SKS phase are indicated.

Table 1 .

 1 Petrography, Calculated Modal Composition, and Mg# and Cr# Numbers of Minerals for Mantle Xenoliths from the Kerguelen Islands a

  Mg#, clinopyroxenes have lower contents of basaltic components and spinels higher Cr# for a given Mg#. Equilibration temperatures estimated from these samples range between 910 and 1000°C (seeGre ´goire et al. [2000aGre ´goire et al. [ , 2000b] ] for details).

	3. Major element compositions of minerals (olivine, spinel, clinopyroxene) in harzburgites and dunites from Kerguelen Islands. Grey field, abyssal peridotites after Dick [1989]; dark blue circles, protogranular harzburgites; empty circles, protogranular harzburgite BY96-397; dark blue triangles, poikilitic harzburgites; green squares, dunites. PM indicates the approximate composition of clinopyroxene and spinel of the Primitive Mantle. The arrows indicate the effect on the PM of progressive melt-rock reactions between the depleted protogranular harzburgites and percolating silicate melts (metasomatism) and the effect of partial melting. In Figure 3a the bars indicate the 1s deviation for each sample analyzed. Typical %RSD (relative standard deviation) on the analyses of major elements by EMP (electron microprobe) are of the order of 0.3 for TiO 2 , <0.3 for Al 2 O 3 , 0.4 for CaO, <0.9 for Na 2 O, 0.3 for [12] Samples OB93-3, OB93-5, JGM92-1c, GM92-453 and BY96-394 have minerals with lower Mg# than in protogranular harzburgites, except in sample BY96-394. They display very variable Mg# (and Cr# for spinels) compared to protogranular samples (Mg#(Ol) = 86.6 -91.3; MgO, 0.3.1.1.2. Poikilitic Harzburgites Mg#(Cpx) = 86.6-93.7; Cr#(Sp) = 27.8-44.1;

5 for FeO, and 0.04 for Mg#. Uncertainties are smaller than symbol size. Table

1 and Figure

3

). Clinopyroxene is a magnesian augite that has higher contents of basaltic components (i.e., higher Al 2 O 3 , TiO 2 , Cr 2 O 3 and Na 2 O contents and lower CaO contents) than the clinopyroxene in protogranular harzburgites (Figures

3b-3e

). Although the sample BY96-394 displays microstructural characteristics of poikilitic harzburgites, the major element compositions are similar to those in protogranular harzburgites (Figure

3

). Most spinels are also enriched in TiO 2 compared to protogranular samples (0.26 -1.67 wt%; see Gre ´goire et al.

  Equilibration temperatures estimated for dunites range between 940 and 1090°C (see Gre ´goire et al. [2000b] for details).

	3.1.2. Trace Elements
	3.1.2.1. Protogranular Harzburgites
	[14] Trace element contents of clinopyroxenes in
	protogranular harzburgites are very low (Figure 4)
	compared to the primitive mantle estimate of
	McDonough and Sun [1995] and are highly vari-
	able between samples. Clinopyroxene in protogra-
	nular harzburgites displays a U-shaped pattern from
	Lu to La (Figure 4a). Clinopyroxenes in samples
	BY96-397 and GR97-38 have the lowest heavy rare

earth element contents (HREE [Dy-Lu]; <1 Â CI-Chondrite) and medium rare earth element contents (MREE [Sm-Gd]). These clinopyroxenes exhibit enrichments in the light rare earth elements (LREE

Auxiliary materials are available at ftp://ftp.agu.org/apend/gc/

2007gc001879.

Acknowledgments

[47] We thank C. Perrache and C. Nevado for the thin sections and A. Tommasi for constructive discussion and support through a DyETI project of INSU-CNRS, M. Gre ´goire, G. Michon, and the other members of Geology Department of St-Etienne University for lecture on the manuscript and scientific dialog. This work benefited greatly from software developed by D. Mainprice to generate pole figures and calculate rock seismic properties. We thank for their support the French Polar Institute (IPEV). We thank also the GEO-SCOPE network for the accessibility and the quality of their data. For the geochemical work at GEMOC, Macquarie University, we would like to thank T. Bradley for the polished thin sections, A. Sharma, S. Elhlou, and C. Lawson for assistance with the analytical work, and S. O'Reilly, W. Griffin, and N. Pearson for ever-ready advice, assistance, and discussion. Analytical work at GEMOC was carried out using instrumentation funded by ARC LIEF and DEST Systemic Infrastructure Grants and Macquarie University. Support for geochemical analyses was provided from an ARC Discovery Grant (S.Y.O'R and others), the GEMOC ARC National Key Centre, an ARC IREX Grant (S.Y.O'R and W. L. Griffin), a Macquarie University Postgraduate Research Grant (G.D.) and a Macquarie University International Postgraduate Scholarship (G.D.). This is publication 509 in the GEMOC ARC National Key Centre. The manuscript has benefited from constructive reviews by M. Savage and G. Lloyd and comments by the editor, P. Van Keken.


Temperature dependent extension of a hysteresis model

Fabien Sixdenier 1 , Oualid Messal 2 , Alaa Hilal 1 , Christian Martin 1 , Marie-Ange Raulet 1 1 Université de Lyon, Université Lyon 1, CNRS UMR5005 AMPERE, 41, Blvd Latarjet, Villeurbanne, F69622, France 2 Grenoble INP -UJF Grenoble 1 -CNRS UMR 5269 (G2Elab), Saint Martin d'Hères Cedex, 38402, France Some soft magnetic materials (like ferrites but not only) are strongly dependent of the temperature. In order to predict their behaviour in electrical devices, engineers need hysteresis models able to take into account the temperature. This paper is an attempt to take into account the temperature in an existing model of hysteresis through its parameters. Variations of some parameters are issued from Weiss's works and others have to be fitted numerically. Simulation results are compared to measurements and discussed.

Index Terms-Temperature dependance, magnetic losses, thermal stresses,. . .

I. INTRODUCTION

I N order to reduce the volume/mass of soft magnetic ma- terials in electrical devices, there are two main solutions: increase the "working" induction level B or increase the frequency f . The both solutions lead to increase the magnetic losses p f e of the device and consequently increase the temperature due to self heating. Moreover, soft magnetic materials are strongly dependent on the temperature and this behaviour is highly non-linear. Thus, designers need models able to predict the magnetic behaviour in a "large" temperature range, from 25 • C to the Curie temperature T c . In [START_REF] Raghunathan | Modeling the temperature dependance of hysteresis based on jiles-atherton theory[END_REF], the authors used the Jiles-Atherthon (JA) model and analytical equations for each parameter. They retrieved qualitatively the measured behaviour with monotonic evolution of each parameter but the errors were quite high. In [START_REF] Messal | Temperature dependent extension of the jiles-atherton model: Study of the variation of microstructural hysteresis parameters[END_REF], the authors used an optimization method to identify the parameters. The results were very good regarding the accuracy, but the evolution of some parameters with temperature was erratic. By using both analytical laws [START_REF] Weiss | La constante du champ moléculaire. equation d'état et calorimétrie[END_REF] and optimization methods in [START_REF] Messal | Thermal behavior of iron-nickel-chromium alloys and correlation with magnetic and physical properties -part a: Static effects modeling[END_REF], a good compromise between the error levels and the monotony of the parameters has been achieved. Nevertheless, for complex induction b(t) waveforms, JA model fails to predict excitation field h(t) with accuracy due to several intrinsic drawbacks of the models well detailed in [START_REF] Zirka | On physical aspects of the jiles-atherton hysteresis models[END_REF]. Engineers need, then, a reliable model of hysteresis able to take into account both complex inductions waveforms and the temperature. We propose here to adapt an existing model of hysteresis [START_REF] Franc ¸ois-Lavet | Vectorial incremental nonconservative consistent hysteresis model[END_REF] recently improved in [START_REF] Bergqvist | Temperature-dependent vector hysteresis model for permanent magnets[END_REF], in order to take into account the temperature, through its parameters especially the magnetic polarization. It differs from [START_REF] Lin | Improved vector play model and parameter identification for magnetic hysteresis materials[END_REF] where the authors consider, in other things, the evolution of the coercive field instead.

II. MODELLING APPROACH

A. Vectorial Incremental Nonconservative Consistent Hysteresis model

The Vectorial Incremental Nonconservative Consistent Hysteresis (VINCH) model [START_REF] Franc ¸ois-Lavet | Vectorial incremental nonconservative consistent hysteresis model[END_REF], is used to model the hysteresis phenomenon. Its advantages are: it is a readily vectorial model and it relies on a consistent thermodynamic formulation. Unlike the JA model, its number of parameters is not limited. We will here present just a reminder of the principle, the equations and the parameters of the model. The model consists on minimizing, at each time step (one value of h), the functional Ω (1).

Ω = N k=1 Ω k = N k=1 u(J k ) -h • J k + χ k |J k -J k p | (1)
In [START_REF] Raghunathan | Modeling the temperature dependance of hysteresis based on jiles-atherton theory[END_REF], N is the number of functional equations to minimize, h is the applied field, J k p is the magnetic polarization of the functional Ω k at the the previous step, χ k is a model parameter and J k is the value of J that minimizes the functional Ω k . Finally u(k) is defined by (2)

u J k = J k o h k r (x)dx (2)
h k r (J) = α • tanh -1 (J k /J k s ) (3)
In (3), J k s is the saturation polarisation of the k functional. For N functionals, one has to identify 2N + 1 parameters (J k s , χ k , α). The initial saturation slope α is supposed identical for all functionals. The pairs (J k s , χ k ) can be identified for increasing values of χ k thanks to the first magnetization curve [START_REF] Franc ¸ois-Lavet | Vectorial incremental nonconservative consistent hysteresis model[END_REF] or thanks to the curve of the coercive field h c (h peak ) [START_REF] Henrotte | An energy-based vector hysteresis model for ferromagnetic materials[END_REF]. For a given time step, one has to find all values of J k that minimize Ω. b can be retrieved by [START_REF] Messal | Thermal behavior of iron-nickel-chromium alloys and correlation with magnetic and physical properties -part a: Static effects modeling[END_REF].

b = µ 0 h + N k=1 J k (4)

B. Temperature extension

As the saturation polarization J s of a ferromagnetic material can be assumed to be function of the temperature T following the law (5) [START_REF] Weiss | La constante du champ moléculaire. equation d'état et calorimétrie[END_REF], with J s0 the polarization at T = 0 K and T c the Curie temperature. It is assumed in this approach that each J k s will follow the same law.

J s J s0 = tanh J s /J s0 T /T c ( 5
)
The χ k are keeped constant, it lets only α to identify numerically (fitting). α is normally inversely proportional to the slope of the B(H) loop.

III. RESULTS

We chose to test this approach on an alloy, named Phyterm260 commercialized by the APERAM company [10]. This alloy is normally dedicated to induction cookwares. It is a N i 50 F e bal Cr 9 alloy with a Curie temperature around 260 • C. The table I shows the values of the parameters χ k and J k s for the temperature of 19 • C. For other temperatures, χ k are kept constant and J k s follow the law given by ( 5), with J s0 = 0.83 T and T c = 260 • C. The table II shows the values of the α parameter after fitting. Finally, Fig. 1 and Fig. 2 show the measured and simulated hysteresis loops at different temperatures respectively . The evolution of the simulated hysteresis loops with the increasing temperature is globally respected. Some problems still remain, such as α is overestimated (it flattens the loops too much) and the saturation is quite an horizontal line (this is not the case for the measured loops). These both problems are mainly due to (3) where the tanh -1 function is not the best one for the case of this material. Some more realistic functions (like Langevin function) but less convenient (not explicit) functions can be chosen [START_REF] Henrotte | An energy-based vector hysteresis model for ferromagnetic materials[END_REF]. In this paper, a first attempt to take into account the temperature in an existing hysteresis model has been made. The concept is to adapt some of the parameters values with the temperature (J k s and α). The J k s values follow the same variations of the macroscopic saturation polarization J s defined by Weiss (5) and α is fitted numerically. First results are promising but some efforts have to be made in order to increase the accuracy. In the extended paper, more realistic functions for (3) will be tested in this last aim. Some other materials (like ferrites) will also be tested with the same approach to test the robustness of the approach.

Fig. 1 .

 1 Fig. 1. Measured hysteresis loops at different temperatures

Fig. 2 .

 2 Fig. 2. Simulated hysteresis loops at different temperatures

TABLE II α

 II VALUES


Pascale Krejbich-Trotot

Essia Belarbi

Miora Ralambondrainy

El Chaker

Wildriss Kalamouni

Pierre Viranaicken

Philippe Roques

Gilles Desprès

Gadea

Chaker El Kalamouni

Wildriss Viranaicken

Pierre Roques

Philippe Desprès
email: philippe.despres@univ-reunion.fr

Gilles Gadea
email: gilles.gadea@inserm.fr

The growth of arthralgic Ross River virus

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

SUMMARY

Alphaviruses such as Chikungunya and Ross River (RRV) viruses are associated with persistent arthritis and arthralgia in humans. Monocytes and macrophages are believed to play an important role in alphaviral arthritides. In this study, we evaluated RRV permissiveness of the human acute leukemia MM6 cell line. Viral growth analysis showed that RRV infection of MM6 cells resulted in a very low virus progeny production with daily output. Using recombinant RRV expressing the reporter gene Renilla luciferase, a weak viral replication level was detected in infected cells at the early stages of infection. The infection restriction was not associated with type-I interferon and pro-inflammatory cytokines release. Apoptosis hallmarks (i.e. mitochondrial BAX localisation and PARP cleavage) were observed in infected MM6 cells indicating that RRV can trigger apoptosis at late infection times. The long-term persistence of RRV genomic RNA in surviving MM6 cells identifies human monocytic cells as potential cellular reservoirs of viral material within the infected host.

KEY WORDS

Ross River Virus; alphavirus; persistent infection; arthritis; apoptosis; human monocytic cells.

MAIN TEXT

Ross River virus (RRV) is a mosquito-borne alphavirus of medical concern in the South Pacific with thousands of human cases of RRV infection [START_REF] Aaskov | An epidemic of Ross River virus infection in Fiji, 1979[END_REF]. Myalgia and headache are common symptoms in patients suffering from RRV-related disease.

Most patients recovered within 6 months after the disease onset without symptoms after 2 years but symptoms can persist for up to 3 years [START_REF] Fraser | Epidemic polyarthritis and Ross River virus disease[END_REF]. RRV-related disease can be severe at onset with level of disability that is comparable to patients with osteoarthritis, Lyme disease, or chronic rheumatoid arthritis. Inflammatory cell infiltration in joints, muscles, and associated tissues during alphavirus infection has been reported in mouse models of RRV infection, suggesting that muscular and articular damages are part of an immunopathological inflammatory disorder [START_REF] Heise | Sindbis-group alphavirus replication in periosteum and endosteum of long bones in adult mice[END_REF][START_REF] Lidbury | Specific ablation of antiviral gene expression in macrophages by antibody-dependent enhancement of Ross River virus infection[END_REF][START_REF] Morrison | Characterization of Ross River virus tropism and virus-induced inflammation in a mouse model of viral arthritis and myositis[END_REF]. In RRV infections, the cellular infiltrate reaches synovial tissue, evidencing a strong hyperplasia [START_REF] Gardner | Chikungunya virus arthritis in adult wild-type mice[END_REF][START_REF] Morrison | Characterization of Ross River virus tropism and virus-induced inflammation in a mouse model of viral arthritis and myositis[END_REF][START_REF] Morrison | A mouse model of chikungunya virus-induced musculoskeletal inflammatory disease: evidence of arthritis, tenosynovitis, myositis, and persistence[END_REF]. Monocytes, macrophages, NK cells, and CD4+ and CD8+ T lymphocytes are the main cellular components of the inflammatory infiltrate in animal models, suggesting their possible involvement in the pathogenesis of the RRV-mediated arthritis [START_REF] Gardner | Chikungunya virus arthritis in adult wild-type mice[END_REF][START_REF] Labadie | Chikungunya disease in nonhuman primates involves long-term viral persistence in macrophages[END_REF], Lidbury et al 2000[START_REF] Morrison | Characterization of Ross River virus tropism and virus-induced inflammation in a mouse model of viral arthritis and myositis[END_REF][START_REF] Morrison | A mouse model of chikungunya virus-induced musculoskeletal inflammatory disease: evidence of arthritis, tenosynovitis, myositis, and persistence[END_REF]. It is also interesting to mention that murine macrophage-like cell cultures continued to harbor RRV infection for more than 1.5 month without obvious cytopathic effects [START_REF] Linn | Antibody-dependent enhancement and persistence in macrophages of an arbovirus associated with arthritis[END_REF][START_REF] Way | Persistent Ross River virus infection of murine macrophages: an in vitro model for the study of viral relapse and immune modulation during long-term infection[END_REF]. In agreement with the data obtained in animal models, macrophages and NK cells have been detected in synovial exudates from patients that have experienced arthralgic alphavirus infection [START_REF] Fraser | Cytology of synovial effusions in epidemic polyarthritis[END_REF][START_REF] Hazelton | The inflammatory response in the synovium of a patient with Ross River arbovirus infection[END_REF][START_REF] Hoarau | Persistent chronic inflammation and infection by Chikungunya arthritogenic alphavirus in spite of a robust host immune response[END_REF][START_REF] Soden | Detection of viral ribonucleic acid and histologic analysis of inflamed synovium in Ross River virus infection[END_REF]. Little is yet known on the susceptibility of human monocytes to arthralgic alphaviruses. The purpose of the present study is to investigate again the RRV permissiveness of human monocytic Mono Mac 6 (MM6) cells, which have been initially claimed as refractory cells to RRV infection [START_REF] Linn | Antibody-dependent enhancement and persistence in macrophages of an arbovirus associated with arthritis[END_REF].

To evaluate the susceptibility of MM6 cells to laboratory-adapted RRV strain T48 (RRV-T48) and Australian (RRV-AUS) clinical isolate (Welcome Trust, National Collection of Pathogenic Viruses, No:0005281v), MM6 cells were infected with a multiplicity of infection (MOI) of 1 PFU/cell. RT-PCR analysis of total RNA extracted from RRV-infected MM6 cells detected the presence of genomic RNA of both RRV strains as late as 7 days post-infection (p.i) (Fig. 1A). The kinetic of RRV-T48 growth in MM6 cells showed that virus titers slightly increased between 1 day and 3 days p.i.

to reach at maximum almost 3.2 log PFU.mL -1 at 3 days p.i. compared to a progeny production upper than 8 log PFU.mL -1 in HEK-293 and VERO cells [START_REF] Lidbury | Identification and characterization of a ross river virus variant that grows persistently in macrophages, shows altered disease kinetics in a mouse model, and exhibits resistance to type I interferon[END_REF] (Fig. 1B). After 3 days of infection, the virus progeny production daily declined to a basal virus titer of 100 PFU.mL -1 at day 7 p.i. Taken together, these results show that a low level of RRV growth can occur in MM6 cells giving a new highlight on RRV permissiveness of human monocytic cells.

Figure 1: RRV can infect MM6 monocytes. In (A), MM6 cells were infected with RRV Australian strain or T48 molecular clone at MOI of 1. Total RNAs were extracted from MM6 cells each day from day 1 to day 7 p.i. and from VERO cells at 24 hours p.i.. Total RNAs were analyzed for the expression of viral E1 mRNA by RT-PCR. GAPDH mRNA was used as loading control. In (B), MM6 cells were infected with RRV T48 molecular clone at MOI of 1. Culture supernatants were collected each day from day 1 to day 7 post-infection. Viral progeny was determined by plaque assay on VERO cells. Virus titers are presented for one representative experiment. In (C), HEK293T cells were infected with RRV-renLuc or RRV-GFP at MOI of 1 or mock-infected. A time course of luciferase activity and fluorescence signal was realized. Results are expressed as the mean (± SEM) of three independent experiments (six replicates per experiment). In (D), MM6 cells were infected with RRV-renLuc at MOI

of 1 or mock-infected. Cells were collected at each time points and analyzed for luciferase activity. Shown is the mean (± SEM) from six replicates in one representative of four independent experiments. In (E), MM6 cells were infected with RRV-renLuc at MOI of 1 or mock-infected. 100 µM Ribavirin was added to culture medium 2 h p.i.. Cells were collected 6 h or 24 h p.i. and analyzed for luciferase activity. Shown is the mean (± SEM) from three replicates in one representative experiment. Dotted line shows the threshold.

Recombinant viruses encoding reporter genes represent useful tools to follow up viral replication and spread in cell culture, but also in animals or mosquitoes (Kummerer et al 2012[START_REF] Pohjala | A luciferase-based screening method for inhibitors of alphavirus replication applied to nucleoside analogues[END_REF]. To better understand the mechanisms of MM6 cells infection by RRV, we decided to generate molecular clones of RRV-T48 containing either the reporter gene Renilla luciferase (RRV-renLuc) integrated into the nonstructural protein region of the genomic RNA or the reporter gene VisGreen GFP (RRV-GFP) into the subgenomic RNA. The renLuc gene was inserted in frame between nsP3 and nsP4, using a strategy similar to that previously described with Chikungunya virus [START_REF] Gad | The E2-E166K substitution restores Chikungunya virus growth in OAS3 expressing cells by acting on viral entry[END_REF]. The codon-optimized VisGreen GFP sequence followed by the Thosea asigna virus 2A protease was inserted into the structural protein region in frame with the first amino acids of RRV E2 protein.

Recombinant RRV-renLuc and RRV-GFP grown on permissive HEK293T cells allow the monitoring of the early or the late stage of virus replication in RRV infected hostcells, respectively (Fig. 1C). The renLuc activity was significantly detected within the 8-12 hours p.i. and increased linearly during the time course of infection to reach a plateau at 36 h p.i. The autofluorescence of GFP was clearly observed within the 24 h p.i and the intensity of signal progressively increased during the course of infection.

MM6 cells were infected with each recombinant RRV at the MOI of 1. In MM6 cells infected 24 h with RRV-renLuc, we detected a low level of renLuc activity that declined daily to reach a threshold at day 5 of infection (Fig. 1D). To distinguish between the level of renLuc activity derived for the initial translation of the input ZIKV RNA and one related to viral replication, we evaluated the effect of antiviral inhibitor Ribavirin on RRV-renLuc. (Fig. 1E). Addition of 100 µM Ribavirin 2 h after RRV-renLuc exposure reduced by 65% the level of renLuc signal in infected MM6 cells at 24 h p.i. As a control, 100 µM Ribavirin reduced by at least 50% the renLuc activity in VERO cells infected 24 h with RRV-renLuc (data not shown). This is consistent with the assumption that the low level renLuc Luc activity is attributable to a modest production of intracellular viral RNA in infected MM6 cells. Furthermore, no significant GFP signal was observed in MM6 cells infected with RRV-GFP whatever the time-points of infection examined (data not shown). The absence of GFP expression suggests that no synthesis of subgenomic viral RNA nor translation of structural protein region occurred in the late stages of RRV growth in MM6 cells. We can conclude that RRV replication was severely restricted in MM6 cells leading to a very low virus progeny production.

Therefore, we ask if the inability of RRV to establish a highly productive infection in MM6 cells was associated to marked production of Type-I interferons (IFNs). To determine whether RRV infection results in release of soluble IFN-, the supernatants of infected MM6 cells were collected at different time-points of infection, UV-inactivated and then analyzed on HEK-Blue IFN- cells containing the SEAP reporter gene under the control of IFN- inducible ISG54 promoter (Frumence et al., 2016) (Fig. 2A). No SEAP reporter activity was detected in supernatants of MM6 cells during the time course of infection. The addition of exogenous IFN-in the supernatants of RRV-infected cells showed that the absence of SEAP reporter activity was not due to the inhibition of the SEAP or a block in the IFN signaling pathway.

These results suggest that IFN-dependent antiviral pathway does not play a role in the restriction of RRV replication in MM6 cells. We investigated whether RRV infection of MM6 cells leads to increase of major cytokines by RT-qPCR (Fig. 2B to C). No significant difference was observed for IL-1, IL-6 or IL-8 mRNA. By using a quantitative ELISA assay (Ready-SET-Go!®, e-Bioscience), we failed to detect proinflammatory IL-1, IL-6, IL-8, TNF- and chemokine MCP-1 in the supernatants of MM6 cells infected with RRV-T48 (only IL-1 data shown in Fig. 2D). Altogether, these results show an unresponsiveness of MM6 cells to RRV infection with the absence of pro-inflammatory cytokine and IFN- production.

Figure 2 : RRV-infected MM6 monocytes immune response. MM6 cells were infected with RRV-GFP at MOI of 1 or mock infected. Cells or culture supernatants were collected every day from day 1 to day 7 post-infection. In (A), time course of Type 1 IFN release in response to RRV. HEK-Blue™ IFN-α/β cells were incubated 24h with UVinactivated supernatants of RRV-infected cells and the extracellular activity of released IFN/SEAP was measured using

Quanti-blue reagent. Exogenous IFN-was added to the supernatants to confirm that the absence of SEAP reporter activity was not due to the inhibition of the SEAP or to a block in the IFN signaling pathway. One representative experiment is shown. In (B) to (C), cellular mRNA encoding IL-1 beta, IL6 and IL8 were analyzed by qRT-PCR at different times post-infection. Results are the mean (± SEM) from two independent experiments performed in triplicates. In (D), ELISA assays for the measure of IL-1 beta production were performed on the supernatants of infected cells at different times post-infection. Results are the mean (± SEM) from at least three independent experiments performed in triplicates.

At day 5 post-infection, we observed a loss of viability of MM6 cells infected by RRV compared to control. Given that cells were displaying features of apoptotic death, the relocalization of the pro-apoptotic mitochondrial factor Bax, a hallmark of apoptosis, was examined by indirect IF using a specific antibody. As shown in Fig. 3A, mitochondrial Bax was positively stained in MM6 cells infected one week by RRV.

Immunoblot assays with a specific antibody directed against the 85 kDa-cleaved form of PARP, a hallmark of the executive phase of apoptosis, were performed on lysates of RRV-infected MM6 cells (Fig. 3B). The cleaved form of PARP was detected at 5 days post-infection and then accumulated at the later infection times. The progressive disappearance of the 115 kDa-full length form of PARP coincided with the accumulation of its cleaved form within the 5-7 days of infection. Altogether, these results showed that RRV infection results in a late apoptosis in MM6 cells although viral growth was severely restricted. Despite a very low percentage of RRV-infected cells survived to apoptosis, these cells were cultured with fresh growth medium supply every week for up to 45 days. RT-PCR analysis detected the presence of viral genome up to 45 days post-infection suggesting that RRV could potentially persist in MM6 cells on a long-time period (Fig. 3C). To date, the mechanisms by which RRV can trigger very late apoptosis in human monocytic cells remain to be investigated. In alphavirus-infected cells, apoptosis could be initiated at the level of RNA replication or thereafter by the pro-apoptotic factor Bak, which leads to cytochrome c release from mitochondria [START_REF] Urban | Apoptosis induced by Semliki Forest virus is RNA replication dependent and mediated via Bak[END_REF]. The production of alphaviral dsRNA molecules that are potent sensing factors for dsRNA signalling pathways, the retinoic acid inducible gene-I and the melanoma differentiation-associated gene-5 systems, could play an important role in this respect [START_REF] David | Comparative analysis of viral RNA signatures on different RIG-I-like receptors[END_REF].

CHIKV was shown to infect monocytic cells in patients with a poor virus production [START_REF] Her | Active infection of human blood monocytes by Chikungunya virus triggers an innate immune response[END_REF]. Macrophages were also highlighted as a possible cellular reservoir in CHIKV infected patients [START_REF] Hoarau | Persistent chronic inflammation and infection by Chikungunya arthritogenic alphavirus in spite of a robust host immune response[END_REF] and in experimentally infected macaques [START_REF] Labadie | Chikungunya disease in nonhuman primates involves long-term viral persistence in macrophages[END_REF]. Moreover, numerous studies have pointed out the role of macrophages in the RRV pathogeny in either mice or humans (Lidbury andMahalingam 2000, Linn et al 1996). An unexpected observation was that human monocytic cells that survived to apoptosis triggered by RRV still contained viral genetic material suggesting that such cells could be persistently infected. It is therefore urgent to determine whether the human monocytes can act as potential reservoir seed of arthralgic alphaviruses and thereby contribute to the pathogenesis of the chronic forms of RRV and CHIKV-related arthralgies.

Figure 3 :

 3 Figure 3 : RRV-infected MM6 monocytes undergo apoptosis but surviving cells carry viral genome. MM6 cells were infected for seven days with RRV-GFP at MOI of 1 or mock infected. In (A), BAX signal in RRV-infected cells wasanalyzed by immunofluorescence assay using specific antibody. Nuclei were stained with DAPI. Results are presented individually or as merged images. In (B), cells were collected every day from day 1 to day 7 post-infection. The cleavage of PARP in infected cells was analyzed by immunoblot assay using specific antibody against the 85 kDa-cleaved form of PARP. We also visualized total PARP and beta-tubulin as loading control. In (C), Cells were collected at days 40 and 45 post-infection. Total RNAs were extracted and analyzed for the expression of viral E1 mRNA by RT-PCR.

ACKNOWLEDGEMENTS

We thank Patrick Mavingui, Etienne Frumence and Claude Giry for helpful discussions.

We would like to thank R. Kuhn for providing the molecular clone T48 of RRV. This work was supported by Dim Malinf (Région Ile de France #13-521, 13.07.11), INSERM and CNRS, France. EB is a fellow of Dim Malinf (Région Ile de France #130056, 13.07.12).


J Jacques
email: julien.jacques@univ-lyon2.fr

C Ruckebusch

COCLUSTERING FOR HYPERSPECTRAL IMAGES

Keywords: (3-5) : Co-clustering, Guassian models, Spatial-spectral, Hyperspectral imaging

Clustering is often used for hyperspectral images in order to assign sets of pixels into a number of different homogeneous groups called clusters. As a result, pixels in the same cluster have similar spectra, i.e. are close to each other in a certain sense. Clustering is a core technique of the chemometrics toolbox but some limitations can be pointed for hyperspectral imaging. A first limitation of clustering is that it only considers information in the spectral dimension. Another is that it groups whole vectors. This means that if one or a few elements of the vectors differ significantly, the vectors cannot be clustered together. These limitations may result in suboptimal grouping.

Co-clustering [START_REF] Govaert | Co-Clustering[END_REF] is a generalization of unsupervised clustering. Co-clustering approaches allow finding blocks of similar data in a matrix by considering simultaneously information along the rows and columns. It has drawn attention in chemometrics [START_REF] Bro | [END_REF] and, more recently, in hyperspectral imaging [START_REF] Izquierdo-Verdiguier | IEEE International Geoscience and Remote Sensing Symposium[END_REF]. Applied in hyperspectral image analysis, co-clustering is able to simultaneously group the pixels and the spectral features, building co-cluster (blocks) incorporating both spatial and spectral information and revealing patterns/relationships between them.

In this work, we propose using a co-clustering technique based on Gaussian mixture models for high-dimensional data [START_REF] Jacques | Gaussian mixture models for the classification of high-dimensional vibrational spectroscopy data[END_REF]. This appraoch for co-clustering consists in assuming that the distribution of the observations into a block (combination of pixels and wavelengths) have a common univariate distribution, that we can for instance be assumed to be Gaussian for hyperspectral images. Model parameter estimation in the co-clustering context is not as straightforward as in clustering. Indeed, the traditional EM algorithm is not computationally tractable since all the possible blocks cannot be enumerate in the traditional E step. To overcome this problem, we consider a Stochastic EM algorithm incorporating a Gibbs sampler into the SE step in order to simulate the row and column partitions. A further step would be to incorporate information of spatial proximity of pixels and of spectra proximity of wavelength within the Gaussian latent block model. The main challenge is to define a co-clustering model which could be able to take into account these proximities, in order to exhibit compact clusters. In this talk we will show the results obtained on hyperspectral Raman imaging data and remote sensing data.