anisotropy of vp and vs in an amphibolite of the deeper crust and its relationship to the mineralogical microstructural and textural characteristics of the rock abstract laboratory seismic measurements of compressional v p and shear wave v s velocities have been carried out on a deformed amphibolite from the ivrea zone at pressures and temperatures up to 600 mpa and 600 c respectively amphibolite is considered to be an important rock of the deeper crust from crystallographic orientations of the component minerals hornblende plagioclase and diopside and the respective elastic constants we calculated the average elastic constants voigt average for the rock specimen compressional and shear wave velocities in three orthogonal directions normal and parallel to foliation measured at high confining pressure 600 mpa are in good agreement with the calculated velocity surface this suggests that seismic wave velocity anisotropy is controlled by preferred orientations of minerals in rocks texture at high confining pressure where the effect of microcracks on seismic wave velocities is eliminated in the amphibolite sample the velocity anisotropy is dominated by the texture of hornblende because of the strong preferred orientation and large volume fraction of this mineral species a large s wave splitting is documented in the directions parallel to the foliation particularly in the lineation which strongly argues against the microcrack origin of s wave splitting at least at conditions of high effective pressure

alpe arami a peridotite massif from depths of more than 300 kilometers the abundance of fetio 3 and chromite precipitates in olivine of the alpe arami peridotite massif switzerland requires a much higher solubility for highly charged cations than is found in mantle xenoliths from depths of 250 kilometers three previously unknown crystal structures of fetio 3 were identified that indicate that the originally exsolved phase was the high pressure perovskite polymorph of ilmenite implying a minimum depth of origin of 300 kilometers these observations coupled with the unique lattice preferred orientation of olivine further suggest that the original composition of olivine may reflect that of a precursor phase perhaps wadsleyite that is stable only at depths greater than 400 kilometers

b type olivine fabric in the mantle wedge insights from high resolution non newtonian subduction zone models several hypotheses have been proposed to explain trench parallel shear wave splitting in the mantle wedge of subduction zones these include 3 d flow effects parallel melt filled cracks and b type olivine fabric we predict the distribution of btype and other fabrics with high resolution thermal and stress models of subduction zones a composite viscous rheology is used that incorporates wet diffusion creep wet dislocation creep and a stress limiting approximated peierls creep law rheological parameters for dislocation and diffusion creep are based on deformation experiments the effects of variable viscous coupling between the slab and mantle are explored using kinematic boundary conditions that change along the top of the slab two end member models are observed which depend on the depth of partial viscous coupling between the slab and mantle 1 deep partial coupling which gives rise to cold high stress conditions in the forearc mantle and high temperature low stress conditions in the arc and back arc mantle 2 full viscous coupling at the base of a 40 km conducting lid which is characterized by high temperature and low stress the case with deep partial coupling which produces a better match with attenuation tomography and heat flow shows a large region with suitable conditions for b type fabric in the forearc mantle and a rapid transition toward the back arc to conditions that are more suitable for a c or e type fabrics full viscous coupling gives rise to high temperature low stress conditions unsuitable for b type fabric our modeling predicts that the best candidates for regions with b type fabric are the forearc mantle and a cold 10 15 km layer above the slab d 2005 elsevier b v all rights reserved

deformation fabrics of the cima di gagnone peridotite massif central alps switzerland evidence of deformation at low temperatures in the presence of water we report a new observation of the olivine b type lattice preferred orientation lpo from the garnet peridotite at cima di gagnone switzerland the olivine b type fabric forms at low temperatures and or high stress in the presence of water and is of particular interest because it may be used to explain the trench parallel shear wave splitting that is often observed at subduction zones in conjunction with the olivine b type fabric we have found strong orthopyroxene lpo that is identical to those formed under water free conditions this suggests that water may not have a significant effect on orthopyroxene fabric from the olivine microstruc ture we determine that a stress of 22 8 mpa was applied during the deformation event that formed the olivine lpo using an olivine flow law and assuming geological strain rates we determine the temperature of deformation to be 800 175c this does not preclude an ultra deep origin for the ultramafic rocks at cima di gagnone but indicates that much of the deformation recorded in the microstructure occurred at modest temperatures

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

shear wave anisotropy beneath the volcanic front in south kyushu area japan development of c type olivine cpo under h2o rich conditions 1 shear wave splitting from local intermediate depth earthquakes is investigated to detect the anisotropic structure in the mantle wedge beneath the south kyushu area japan we observed shear wave splitting with nee sww to nww see polarization directions and delay times of 0 04 0 63 s trench normal shear wave polarization anisotropy with a delay time greater than 0 3 s probably overlaps in the high vp vs region at a depth of 100 150 km beneath the volcanic front model calculations for the cause of the anisotropy suggest that the development of c type olivine crystallographic preferred orientation cpo with a trench parallel b axis concentration and a trench normal a axis concentration best reproduces observations compared to a b or e type olivine cpos and antigorite cpo we conclude that a thick anisotropic layer approximately 50 km is formed by concentration of interstitial fluid in peridotite we briefly discuss the mechanism carrying water to the deep mantle wedge a possible explanation is that interstitial fluids in the mantle wedge are effectively released because of a decrease in dihedral angles of olivine fluid interfaces at 150 km depth our results imply a close relation between the high density of explosive volcanoes in the south kyushu area and the underlying water rich mantle

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

effect of temperature on the b to c type olivine fabric transition and implication for flow pattern in subduction zones abstract the effect of temperature on the b to c type fabric transition in olivine was investigated by large strain shear deformation experiments a new series of deformation experiments was conducted at 1273 1373 k 2 0 gpa and strain rates ranging from 3 8 10 4 to 3 2 10 5 s 1 under water saturated conditions and combined with previous results at 1473 k the influence of temperature on deformation fabrics was investigated two types of olivine fabrics were identified one in which the olivine 0 0 1 axis is subparallel to the shear direction and the 0 1 0 plane is parallel to the shear plane b type and another one in which the 0 0 1 axis is parallel to the shear direction and the 1 0 0 plane is parallel to the shear plane c type the b type olivine fabric occurs at higher stress than the c type but the stress magnitude at which the b to c type fabric transition occurs decreases significantly with decreasing temperature the temperature dependence of the transition stress is parameterized using a range of exponential flow law that is constrained by the experimental study when the experimental results are extrapolated to lower temperatures the fabric transition between b and c type is predicted to occur at 1 mpa and 1000 k this prediction is consistent with the olivine fabrics in naturally deformed peridotites found in plate convergent regions the present study indicates that when some amounts of water 200 ppm h si are present the b type fabric will dominate in low temperature regions of the upper mantle whereas the c type or e type fabric will dominate at high temperatures the complex seismic anisotropy in subduction zones can be explained by changes in the dominant type of olivine fabrics caused by spatial variations in physical and chemical variables such as temperature and water content rather than by complexities in mantle wedge flow pattern

olivine 100 normal to foliation lattice preferred orientation in prograde garnet peridotite formed at high h2o activity cima di gagnone central alps automated electron backscattered diffraction ebsd was applied using a scanning electron microscope to obtain lattice preferred orientation lpo data for olivine in garnet peridotites of the central alps as a reference frame the lpos of enstatite were also investigated in the garnet peridotite at cima di gagnone cdg a weak foliation carrying a distinct lineation is present the lineation is characterized by elongated enstatite olivine and poikiloblastic garnet olivine shows a very unusual lpo with 100 normal to foliation and 001 parallel to lineation achsenverteilungsanalyse ava maps demonstrate that 001 of olivine grains corresponds quite well to their maximum length axes which are preferentially parallel to the lineation numerous planar hydrous defects within 001 planes of olivine are marked by palisades of ilmenite rods and show a preferred orientation normal to lineation calculated p wave velocities for cdg are fastest 8 32 km s 1 normal to foliation with a relatively low anisotropy 2 9 compared to mantle peridotites with the usual 010 100 lpo where the fastest vp direction is towards the lineation the relationship between flow geometry and seismic anisotropy is significantly different at cdg several mechanisms for the formation of the lpo type at cdg are considered with glide possible on 100 001 of olivine on the basis of field data as well as petrographic and petrologic evidence it has been demonstrated that the cdg garnet peridotite formed by prograde metamorphism from a hydrous protolith at pressures and temperatures of about 3 0 gpa and 750 c respectively the cdg lpo is interpreted to have formed during hydrous subduction zone metamorphism the same interpretation may hold for the previously investigated olivine lpo at alpe arami which is similar to that at the nearby cdg the observed anomalous lpo is no proof for ultradeep 3 0 gpa conditions

learning of dynamic soil behavior from downhole arrays an increasing number of downhole arrays are deployed to measure motions at the ground surface and within the soil profile measurements from these arrays provide an opportunity to improve site response models and to better understand underlying dynamic soil behavior parametric inverse analysis approaches have been used to identify constitutive model parameters to achieve a better match with field observations however they are limited by the selected material model nonparametric inverse analysis approaches identify averaged soil behavior between measurement locations a novel inverse analysis framework self learning simulations selfsim is employed to reproduce the measured downhole array response while extracting the underlying soil behavior of individual soil layers unconstrained by prior assumptions of soil behavior selfsim is successfully applied to recordings from lotung and la cienega the extracted soil behavior from few events can be used to reliably predict the measured response for other events the field extracted soil behavior shows dependencies of shear modulus and damping on cyclic shear strain level number of loading cycles and strain rate that are similar qualitatively to those reported from laboratory studies but differ quantitatively

scenario liquefaction hazard maps of santa clara valley northern california maps showing the probability of surface manifestations of liquefaction in the northern santa clara valley were prepared with liquefaction probability curves these curves were based on complementary cumulative frequency distributions of the liquefaction potential index lpi for surficial geologic units in the study area lpi values were computed with extensive cone penetration test soundings maps were developed for three earthquake scenarios an m 7 8 event on the san andreas fault comparable to the 1906 event an m 6 7 event on the hayward fault comparable to the 1868 event and an m 6 9 event on the calaveras fault ground motions were esti mated with the boore and atkinson 2008 attenuation relation liquefaction is pre dicted for all three events in young holocene levee deposits along the major creeks liquefaction probabilities are highest for the m 7 8 earthquake ranging from 0 33 to 0 37 if a 1 5 m deep water table is assumed and from 0 10 to 0 14 if a 5 m deep water table is assumed liquefaction probabilities of the other surficial geologic units are less than 0 05 probabilities for the scenario earthquakes are generally consistent with observations during historical earthquakes

evidence of high water content in the deep upper mantle inferred from deformation microstructures deep upper mantle rocks from the norwegian caledonides show evidence for large strain deformation in both olivine and garnet under varying water contents using microstructural observations including lattice preferred orientation of olivine and subgrain boundaries of majoritic garnet we infer the following deformation history at depths exceeding 150 km large strain deformation occurred at low stress 10 mpa and modest temperature 1300 k involving high water content 1000 h 10 6 si in olivine this was followed by low strain deformation at lower water content 200 1000 h 10 6 si and modest stress 40 mpa in the shallower parts these observations show that the deep upper mantle in this region had a considerably higher water content than the upper mantle near mid ocean ridges

olivine fabric transitions and shear wave anisotropy in the ryukyu subduction system recent shear wave splitting measurements from the fore arc region of the ryukyu subduction system show large magnitude 0 3 1 6 s trenchparallel splitting in both local and teleseismic phases the similarity of splitting parameters associated with shallow local s and teleseismic phases suggests that the source of anisotropy is located in the fore arc mantle one explanation for this pattern of shear wave splitting involves a transition from commonly observed high temperature olivine fabrics with flow parallel seismically fast directions to a flow normal b type olivine fabric in the cold fore arc mantle of the ryukyu wedge we test the b type fabric hypothesis by comparing observed splitting parameters to those predicted from geodynamic models that incorporate olivine fabric development the distribution of olivine fabric is calculated with high resolution thermomechanical models of the ryukyu subduction zone that include realistic slab geometry and an experimentally based wet olivine rheology we conclude that b type fabric can explain the magnitude and trench parallel orientation of deep local s phases that sample the core of the forearc mantle however our calculations show that b type fabric alone cannot account for large magnitude trench parallel splitting associated with teleseismic phases that sample the shallow tip of the fore arc mantle alternative models for trench parallel teleseismic splitting in the shallow tip of the fore arc mantle involve the addition of crustal or slab anisotropy and highly anisotropic foliated antigorite serpentinite 2008 elsevier b v all rights reserved

high temperature rheology of enstatite implications for creep in the mantle high temperature deformation experiments have been performed on oriented single crystals of enstatite at 1 atm under controlled conditions of oxygen fugacity and silica activity the results indicate that creep on the weakest high temperature slip system in enstatite within the protoenstatite stability field is independent of oxygen fugacity and obeys a power law relation with a stress exponent of n 3 8 0 5 and activation energy of q 820 80 kj mol a decrease in creep rate with increasing aluminum and iron content suggests that aluminum or iron ions play an active role in maintaining charge neutrality within the crystals the single crystal strengths are greater than those reported for polycrystalline enstatite deforming predominantly on the same slip system suggesting that the polycrystalline samples may have been water weakened a comparison of the single crystal results with those for olivine deformed at 1 atm indicates that enstatite is probably stronger than olivine under upper mantle conditions unless the presence of water results in a greater weakening of enstatite than olivine

deformation of olivine spinel aggregates in the system mg ni 2geo4 deformed to high strain in torsion implications for upper mantle anisotropy 1 deformation of mantle phases to high strain is fundamental for understanding mantle dynamics however it is technically challenging to perform deformation experiments yielding accurate mechanical results at the high pressures required for certain mantle phases such as wadsleyite and ringwoodite deformation experiments on analog materials of such high pressure phases can provide insight into the deformation properties of the mantle the mg ni 2geo4 system undergoes the olivine spinel transformation at much lower pressures than the silicate counterpart hence the high strain deformation properties of an olivine spinel rock can be studied at experimentally tractable pressures and temperatures experiments were conducted in a gas medium deformation apparatus at constant angular velocity a temperature of 1473 k and 300 mpa confining pressure at these conditions with a mg mg ni ratio of 0 9 the resulting aggregate comprised 70 olivine 30 spinel and 1 orthopyroxene the applied strain rate ranged from 10 4 to 10 5 s 1 yielding shear stresses supported by the samples of between 100 and 250 mpa samples were deformed to a range of shear strains between 1 and 7 in order to study the microstructural development during high strain deformation in these experiments the spinel phase did not deform to produce a crystallographic preferred orientation cpo the olivine phase produced a cpo which is consistent with slip on the 001 hk0 slip system if this slip system is dominant in olivine below 250 300 km in the upper mantle the observed seismic anisotropy can be explained without resorting to changes in flow regime or deformation mechanism at this depth

crystallographic preferred orientation development by dissolution precipitation creep abstract crystallographic preferred orientations cpos in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms where deformation is achieved by the movement of dislocations in this paper we investigate the possibility of cpo development by dissolution precipitation creep or pressure solution a numerical model is presented which simulates the development of a grain aggregate that deforms by reaction controlled dissolution precipitation creep grains are simulated as rectangular boxes that change their shape by growth or dissolution of their surfaces depending on the normal stresses acting on the individual surfaces grains can also rotate due to an applied vorticity for non coaxial deformation and if they have a non equidimensional shape for each strain increment stress that is applied to the grains is the same for all grains while individual grains deform and rotate by different amounts a variety of cpos develop at moderate strains depending on the reaction rates of the different crystal surfaces and type of deformation uni axial shortening plane strain pure shear and simple shear the modelling results confirm that dissolution precipitation creep may play a role in cpo development in rocks

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

from geometry to dynamics of microstructure using boundary lengths to quantify boundary misorientations and anisotropy the microstructure of a quartzite experimentally deformed and partially recrystallised at 900 jc 1 2 gpa confining pressure and strain rate 10 6 s was investigated using orientation contrast and electron backscatter diffraction ebsd boundaries between misoriented domains grains or subgrains were determined by image analysis of orientation contrast images in each domain ebsd measurements gave the complete quartz lattice orientation and enabled calculation of misorientation angles across every domain boundary results are analysed in terms of the boundary density which for any range of misorientations is the boundary length for that range divided by image area this allows a more direct comparison of misorientation statistics between different parts of a sample than does a treatment in terms of boundary number the strain in the quartzite sample is heterogeneous a 100 150 am low strain partially recrystallised subarea c was compared with a high strain completely recrystallised subarea e the density of high angle 10j boundaries in e is roughly double that in c reflecting the greater degree of recrystallisation low angle boundaries in c and e are produced by subgrain rotation in the low angle range 0 10j boundary densities in both c and e show an exponential decrease with increasing misorientation the densities scale with exp h k where k is approximately 2j in c and 1j in e in other words e has a comparative dearth of boundaries in the 8 10j range we explain this dearth in terms of mobile high angle boundaries sweeping through and consuming low angle boundaries as the latter increase misorientation through time in e the density of high angle boundaries is larger than in c so this sweeping would have been more efficient and could explain the relative paucity of 8 10j boundaries the boundary density can be generalised to a directional property that gives the degree of anisotropy of the boundary network and its preferred orientation despite the imposed strain the analysed samples show that boundaries are not on average strongly aligned this is a function of the strong sinuosity of high angle boundaries caused by grain boundary migration low angle boundaries might be expected on average to be aligned in relation to imposed strain but this is not found

plastic deformation of olivine rich diogenites and implications for mantle processes on the diogenite parent body numerous petrologic and geochemical studies so far on the howardite eucrite and diogenite hed meteorites have produced various crystallization scenarios for their parent body believed to be the differentiated asteroid 4 vesta structural analyses of diogenites can reveal important insights into postcrystallization deformation on the parent body recently published results tkalcec et al 2013 of structural analysis on the olivine rich diogenite nwa 5480 reveal that it underwent solid state plastic deformation although not at the base of a magma chamber dynamic mantle downwelling has been proposed as a plausible deformation mechanism tkalcec et al 2013 the purpose of this study is to investigate whether the plastic deformation found in nwa 5480 is an isolated case we expand the structural analysis on nwa 5480 and extend it to nwa 5784 and mil 07001 6 two other samples of rare olivine rich diogenites using electron backscattered diffraction ebsd techniques our ebsd results show that the diogenites analyzed in this study underwent solid state plastic deformation confirming that the observed deformation of nwa 5480 was not an isolated case on the diogenite parent body the lattice preferred orientations lpos of olivine in nwa 5784 and nwa 5480 are clearly distinct from that typical for cumulate rocks at the base of magma chambers indicating a different stress environment and a different deformation mechanism the lpo of olivine in mil 07001 is less conclusive the structural results of this study suggest that plastic deformation occurred on the diogenite parent body at high temperatures 1273 t 1573 k in the solid state i e after crystallization of the diogenites themselves in a dynamic environment with active stress fields

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

genesis of ilmenite rods and palisades along humite type defects in olivine from alpe arami rod shaped ilmenite inclusions in olivine have been observed in numerous peridotite lenses of the adula cima lunga unit central alps the rods are elongated parallel to 010 ol and identical in size shape and concentration to those reported from garnet peridotite at alpe arami aa tem investigation of the rods at aa cima di gagnone cdg and monte duria md demonstrates that the titanate inclusions correspond to a mg bearing ilmenite with exclusively a trigonal crystal structure no other fetio3 polymorphs have been identified the shape of the ilmenite inclusions concurs with minimum topotactic misfits between the lattices of olivine and mg bearing ilmenite optical microscopy reveals that the ilmenite rods are not randomly distributed within olivine but have at all localities a preferred alignment parallel to 001 ol forming palisades tem images of the ilmenite palisades at aa and cdg show that they are controlled by the presence of 001 planar defects in olivine along which the rods nucleated the defects have been characterised by high resolution tem and identified as 4 4 a wide humite type layers i e mg2sio4 mg oh f 2 intergrown within olivine in such layers substitution of up to 50 mol mgh2 by ti4 is possible assuming ti saturated humite slabs the maximum density of 001 faults observed at aa approximately 1900 mm 1 can accommodate about 170 ppm tio2 in olivine this represents about half the values obtained by uv laser ablation icp ms and empa analysis evidence for annealing of the defects however suggests that only parts of the defects are still preserved the formation of ilmenite rods is considered to be a consequence of the breakdown of isolated humite layers in olivine the apparent tio2 content in olivine at aa cdg and md is regarded as a function of the ti humite defect density

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

solid state plastic deformation in the dynamic interior of a differentiated asteroid diogenite meteorites are thought to represent mantle rocks that formed as cumulates in magma chambers on 4 vesta or a similar differentiated asteroid microstructural analysis of olivine grains from a diogenite meteorite show that the preferred orientation of their crystal lattice was formed through plastic deformation indicating dynamic planet like processes in its parent body

seismic properties of the upper mantle beneath lanzarote canary islands model predictions based on texture measurements by ebsd abstract we present a petrophysical analysis of upper mantle xenoliths collected in the quaternary alkali basalt fields series iii and iv from the island of lanzarote the samples consist of eight harzburgite and four dunite nodules 5 to 15 cm in size and exhibit a typical protogranular to porphyroclastic texture an anomalous foliation resulting from strong recovery processes is observed in half of the specimens the lattice preferred orientations lpo of olivine orthopyroxene and clinopyroxene were measured using electron backscatter diffraction ebsd in most samples olivine exhibits lpos intermediate between the typical single crystal texture and the 100 fiber texture occasionally the 010 fiber texture was also observed simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime probably dominated by a simple shear component under low strain rate and moderate to high temperature orthopyroxene and clinopyroxene display a weaker but significant texture the lpo data were used to calculate the seismic properties of the xenoliths at pt conditions obtained from geothermobarometry and were compared to field geophysical data reported from the literature the velocity of p waves 7 9 km s obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation our results are consistent with a roughly w e oriented fastest p wave propagation direction in the uppermost mantle beneath the canary islands and with the lithosphere structure proposed by previous authors involving a crust mantle boundary at around 18 km in depth overlaid by intermediate material between 11 and 18 km

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

petrofabrics and seismic properties of garnet peridotite from the uhp sulu terrane china implications for olivine deformation mechanism in a cold and dry subducting continental slab abstract lattice preferred orientations lpo of olivine diopside enstatite and garnet from the zhimafang garnet peridotite body in the sulu ultrahigh pressure uhp metamorphic terrane china were measured using the electron backscatter diffraction ebsd technique the peridotite was captured from a mantle wedge immediately adjacent the subducted yangtze slab and then experienced the uhp metamorphism at 750 950 c and 4 7 gpa the olivine lpo is characterized by the 001 axis close to the stretching lineation and the 100 plane subparallel to the foliation indicating the prevailing of 100 001 slip enstatite lpo displays the dominance of 100 001 slip diopside developed complex lpo patterns that are difficult to explain using a single slip system of 100 001 garnet is almost randomly oriented due to its low volume fractions cubic symmetry and the presence of numerous slip systems calculated seismic properties of the peridotite yield a maximum p wave velocity normal to the foliation and a minimum along the foliation with anisotropy up to 8 in strongly sheared samples the s wave velocity pattern is complex but the fast polarization plane generally normal to the foliation the inferred shear sense from the olivine lpo is top to se in contrary to exhumation induced top to nw thrusting recorded in the quartz lpo implying that the olivine lpo formed at early uhp metamorphic conditions the olivine crystals have relatively low water contents 141 475 h 106 si indicating a fluid deficient environment for the lpo formation the present study suggests that a combination of low temperature and uhp plays a much more important role than the water content to promote the activation of 100 001 slip in olivine

deformation of olivine at subduction zone conditions determined from in situ measurements with synchrotron radiation abstract we report measurements of the deformation stress for san carlos olivine at pressures of 3 5 gpa temperatures of 25 1150 c and strain rates of 10 7 10 5 s 1 we determine a deformation stress of approximately 2 5 gpa that is relatively temperature and strain rate independent in the temperature range of 400 900 c the deformation experiments have been carried out on a deformation dia d dia apparatus sam85 at x17b2 nsls powder samples are used in these experiments enstatite mgsio 3 3 5 total quality of sample is used as the buffer to control the activity of silica ni foil is used in some experiments to buffer the oxygen fugacity water content is confirmed by ir spectra of the recovered samples samples are compressed at room temperature and are then annealed at 1200 c for at least 2 h before deformation the total plastic and elastic strains macroscopic are derived from the direct measurements of the images taken by x ray radiograph technique the differential stresses are derived from the diffraction determined elastic strains in the regime of 25 400 c there is a small decrease of stress at steady state as temperature increases in the regime of 400 c to the transition temperature the differential stress at steady state 2 5 gpa is relatively insensitive to the changes of temperature and strain rate however it drastically decreases to about 1 gpa and becomes temperature dependent above the transition temperature and thereafter the transition temperature is near 900 c above the transition temperature the flow agrees with power law creep measurements of previous investigations the anisotropy of differential stress in individual planes indicates that the deformation of olivine at low temperature is dominated by 0 0 1 1 0 0 accounting to a slower strain rate in the natural system the transition temperature for the olivine in the slab is most likely in the range of 570 660 c

development of a type olivine fabric in water rich deep upper mantle abstract water controls the activity of slip systems in olivine resulting in various types of olivine crystallographic preferred orientation i e fabric in mantle rocks the a type olivine fabric is the most commonly observed olivine fabric in natural peridotites development of a type olivine fabric developed by the 010 100 slip system is known to be limited to the water poor conditions of the shallow upper mantle 2130 ppm h si in olivine while b type fabric by the 010 001 slip system was observed under moderately wet conditions 750 2130 ppm h si developments of c type by the 100 001 slip system fabric was limited to water poor conditions v sh v sv the ratio of horizontally and vertically polarized shear waves with depth in the global one dimensional models is well explained by the olivine fabrics developed in the horizontal flow of a water poor mantle only a type olivine fabric can explain the vertical mantle flow which associates the seismic anisotropy of v sh v sv 200 km depth a strong anomaly of v sh v sv

a review of water contents and ductile deformation mechanisms of olivine implications for the lithosphere asthenosphere boundary of continents abstract water plays an important role in the ductile deformation and evolution of the upper mantle water contents of natural olivine from 240 samples reveal a wide variation of 0 170 ppm h2o suggesting heterogeneous water distribution in the continental upper mantle the average water contents 17 13 ppm h2o in kimberlite nodules provide the best estimation of water concentrations in olivine in the lithosphere beneath cratons the very low water contents 7 9 ppm h2o of olivine from basalt xenoliths are caused by significant hydrogen loss during transport while the high values 44 34 ppm h2o in olivine megacrysts from kimberlites reflect restricted fluid rich conditions in the upper mantle to compare deformation in different tectonic environments the western superior province canada the dabie mountains and the north jiangsu basin china are selected to represent an archean craton an orogenic belt and a rift basin respectively using recent flow laws of olivine deformation maps of dry and wet olivine are constructed under p t conditions of the three tectonic units and in a continental subduction zone characterized by p 6 28 gpa and t 900 c for dry olivine diffusion creep is the dominant mechanism in all the cases which is contrary to the widely observed crystal preferred orientation of olivine in peridotites and seismic anisotropy observations for wet olivine only a small amount of water 50 h 106 si can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine the strain rate profiles of olivine indicate a transition from dislocation creep to diffusion creep at a depth of 220 km which can be related with the lehmann discontinuity characterized by a rapid decrease in seismic anisotropy however the pressure induced fabric transition from 100 slip to 001 slip may be responsible for the lehmann discontinuity in subduction zones therefore rheology of the continental upper mantle is controlled by power law creep of wet olivine and diffusion creep is the dominant deformation mechanism in the deep upper mantle especially for fine grained peridotites the mechanical lithosphere asthenosphere boundary lab can be defined by the characteristic pressure derivative of effective viscosity the sharp lab beneath the dabie mountains and the sulu terrane favors the lithosphere asthenosphere decoupling while the diffuse lab beneath the western superior province will protect the continental root from convective erosion and mantle metasomatism the long term preservation of the continental roots can be attributed to a large viscosity contrast temperature contrast at a depth of 150 km

geochemistry of high grade eclogites and metarodingites from the central alps analyses for major minor and trace element contents of metamorphosed variably rodingitized mafic rocks demonstrate substantial removal of na and as much as three fold gains in ca as a consequence of rodingitization modest declines in si and fe can be explained in terms of dilution effects losses in k and ba do not correlate with ca and may have been caused by an alteration process not related to the rodingitization the ca metasomatism was not accompanied by a gain in sr the relative contents of ti zr hf y co sc and heavy ree show no readily detectable changes despite the rodingitization other alteration and subsequent metamorphisms namely eclogite facies t 800 c p 20kbar followed by amphibolite facies sillimanite zone protoliths were tholeiitic basalt or diabase and gabbro with trace element contents indicative of a spreading center origin trace element and ree patterns indicate low pressure fractionation of this magma with plagioclase stable this petrogenesis is consistent with prior conclusions on the shallow crustal origin of the protolith of the eclogite metarodingite garnet lherzolite suite in the cima lunga adula nappe central alps based on their bulk chemical composition the mafic rocks in this suite could be the equivalent of mesozoic ophiolitic rocks in the more external parts of the alps