metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

velocity crossover between hydrous and anhydrous forsterite at high pressures article i nfo theelasticpropertiesofhydrousforsterite mg2 xsio4h2x arerelevanttointerpretingseismicvelocityanomalies in the earth s mantle in this study we used brillouin scattering to determine the single crystal elasticity of forsterite with 0 9 1 wt h2 o x 0 14 to 14 gpa aggregate bulk and shear moduli of hydrous forsterite increase with pressure at a greater rate than those of the corresponding anhydrous phase compared with anhydrousforsterite weobservea7 increaseinthepressurederivativeofthebulkmodulus ks0 4 50 5 and a 25 increase in the pressure derivative of the shear modulus g0 1 75 5 for forsterite with near maximum possible water content using our results we calculated the compressional vp and shear vs v elocities of forsteriteasafunctionofpressureat300 k whereasvpandvsofhydrousforsteriteare0 6 and0 4 slowerthan those of anhydrous forsterite at ambient pressure velocity crossovers at 3 4 gpa result in higher hydrous forsterite velocities at pressures corresponding to depths below 120 km at the pressure of the 410 km discontinuity vp and vs of hydrous forsterite exceed those of anhydrous forsterite by 1 1 1 and 1 9 1 respectively this implies that incorporation of water could decrease the magnitude of the velocity contrast at

the depth distribution of mantle anisotropy beneath the tonga subduction zone abstract shear wave splitting recorded by a temporary deployment of broadband seismometers located above the tonga subduction zone yields strong constraints on the depth distribution of anisotropy in the mantle beneath the tonga back arc region splitting parameters obtained for local s and teleseismic sks phases were modeled using a ray based method that predicts shear wave splitting on individual phase paths and determines the best fitting values of anisotropic strength orientation and depth extent splitting in teleseismic sks phases is identical to that in s phases from local earthquakes that occur at the base of the transition zone demonstrating that there is no significant splitting due to anisotropy in the lower mantle splitting times for local s phases do not vary significantly with depth and for models in which the strength of anisotropy is laterally uniform they rule out anisotropy in the transition zone finally the observed splitting indicates that anisotropy of more than 0 8 exists in the upper mantle with a fast symmetry axis at 60 w roughly parallel to the absolute plate motion vector of the subducting pacific lithosphere

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

iron partitioning in a pyrolite mantle and the nature of the 410 km seismic discontinuity pyrolite1 is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the earth s mantle the main pressure induced phase transformations of the olivine component of pyrolite occur at about 13 5 gpa to and 24 gpa to mgsio3 rich perovskite magnesiowustite 2 3 which are thought to be responsible for the seismic discontinuities at 410 and 660 km depths in the mantle recent seismological studies however have demonstrated that the 410 km seismic discontinuity is sharper in some areas than that expected from the to transformation in mantle olivine with a fixed composition4 5 6 7 moreover some mineral physics studies suggest that the seismic velocity jump at the 410 km discontinuity is inconsistent with that associated with the to transformation in olivine8 9 here we present a phase equilibria study of a material having pyrolite composition at pressures of 6 16 gpa we found that the iron content in olivine changes significantly with increasing pressure as a result of the formation of a relatively iron rich majorite phase at these pressures this variation in iron content can overcome or at least reduce both of the above difficulties encountered with the pyrolite model of mantle composition by showing that the component mineral systems cannot be treated as separate

single crystal elasticity of majoritic garnets stagnant slabs and thermal anomalies at the base of the transition zone abstract the elastic properties of two single crystals of majoritic garnet mg 3 24 al 1 53 si 3 23 o 12 and mg 3 01 fe 0 17 al 1 68 si 3 15 o 12 have been measured using simultaneously single crystal x ray diffraction and brillouin spectroscopy in an externally heated diamond anvil cell with ne as pressure transmitting medium at conditions up to 30 gpa and 600 k this combination of techniques makes it possible to use the bulk modulus and unit cell volume at each condition to calculate the absolute pressure independently of secondary pressure calibrants substitution of the majorite component into pyrope garnet lowers both the bulk k s and shear modulus g the substitution of fe was found to cause a small but resolvable increase in k s that was accompanied by a decrease in k s p the first pressure derivative of the bulk modulus fe substitution had no influence on either the shear modulus or its pressure derivative the obtained elasticity data were used to derive a thermo elastic model to describe v s and v p of complex garnet solid solutions using further elasticity data from the literature and thermodynamic models for mantle phase relations velocities for mafic harzburgitic and lherzolitic bulk compositions at the base of earth s transition zone were calculated the results show that v s predicted by seismic reference models are faster than those calculated for all three types of lithologies along a typical mantle adiabat within the bottom 150 km of the transition zone the anomalously fast seismic shear velocities might be explained if laterally extensive sections of subducted harzburgite rich slabs pile up at the base of the transition zone and lower average mantle temperatures within this depth range

mantle flow entrained by the hindu kush continental subduction inferred from source side seismic anisotropy abstract the intermediate depth seismicity below the hindu kush orogen is thought to mark the indian plate subduction with the bottom half of the slab currently breaking off unique features of this continental subduction are the near vertical slab and the roughly stationary convergence boundary how this subduction affects the mantle flow patterns remains to be understood in this study we measured source side shear wave splitting on the s waves from hindu kush intraslab events to sample the surrounding mantle the observed fast polarization directions exhibit a circular pattern around the slab resembling that predicted for the toroidal flow driven by slab rollback however the rollback scenario is not favored because it hardly sustains in dynamic models without a considerable retreat of convergence boundary we propose that the observed pattern is produced by the sub vertical shear flow entrained by the steep descent of the slab and the ongoing breakoff this scenario requires the existence of a type or ag type olivine fabrics with strong orthorhombic anisotropy in mid to lower upper mantle which is consistent with the global models of azimuthal and radial anisotropy this interpretation circumvents the debate on the cause of trench parallel anisotropy in some oceanic subduction zones where slab entrainment and rollback may coexist and supports the notion that orthorhombic anisotropy of olivine may play an important role in shaping mantle anisotropy

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

elasticity of single crystal olivine at high pressures and temperatures abstract elasticity of single crystal san carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure temperature conditions up to 20 gpa and 900 k using in situ brillouin spectroscopy and single crystal x ray diffraction in externally heated diamond anvil cells these experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature while the longitudinal modulus c 11 and the off diagonal moduli c 12 and c 13 exhibit greater temperature dependence at higher pressures than at relatively lower pressures using a finite strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm our results show that the magnitude of the v p and v s jumps at the 410 km depth are 6 and 6 4 respectively which are greater than that found in seismic observations suggesting a mantle olivine content of 40 50 vol which is less than what is expected for the pyrolite model our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6 and 10 lower than those of wadsleyite and ringwoodite respectively at corresponding depths of the normal mantle our modeled results also show that metastable olivine in the cold slabs could have strong v p and v s anisotropies the maximum v p anisotropy is estimated to be 19 22 at transition zone depth whereas the maximum v s splitting is 13 23 and increases with depth as a result the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle

elasticity of mg0 87fe0 13 2sio4 wadsleyite to 12 gpa and 1073 k abstract elasticity of mg0 87fe0 13 2sio4 wadsleyite has been measured at simultaneous high pressure and high temperature to 12 gpa and 1073 k using ultrasonic interferometry in conjunction with synchrotron x radiation the elastic moduli and their pressure and temperature derivatives are precisely determined using pressure standard free third order and fourth order finite strain equations combined with previous thermoelastic data on olivine the density velocity and acoustic impedance contrasts between and mg0 9fe0 1 2sio4 at 410 km depth are calculated along a 1673 k adiabatic geotherm both the third and fourth order finite strain equation fitting results give estimation of 33 58 olivine content in the upper mantle to account for a seismic discontinuity of 5 velocity jumps and 8 5 p wave and 11 1 s wave impedance jumps at 410 km depth

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

melrose green rhyolite its geologic setting and petrographic and geochemical characteristics abstract fine grained lithic material called melrose green is common in middle archaic to late woodland period archaeological sites in southeastern new england a quarried source of this material crops out on a hillside in melrose massachusetts at this site a crystal rich volcanic tuff is intruded by three fine grained felsic dikes composed of rock similar to archaeological materials identified as melrose green locally parts of the dikes are pockmarked and saddle shaped in cross section due to removal of quarried material the aphanitic dike rock is characterized by sparse feldspar microphenocrysts in a matrix of granular quartz and feldspar epidote titanite opaque minerals and calcite are accessory minerals flow bands and relict shard texture are also present the rock is of rhyolitic dacitic composition some previous workers interpreted melrose green artifacts as chert or argillite field relationships petrography and geochemistry demonstrate that melrose green is of igneous parentage while geochemistry shows that melrose green is similar to felsic volcanic rocks of the nearby lynn mattapan volcanics the trace element composition of the dikes distinguish them from most other known prehistoric quarry sites within the lynn mattapan complex chipping debris from the dikes is widespread at the melrose quarry site demonstrating that the dikes were extensively worked for sources of raw material three artifacts macroscopically similar to melrose green rhyolite were collected from three coastal sites within boston harbor analyses showed that two of these are of igneous origin and generally similar to rocks of the lynn mattapan complex only one of these yielded data consistent with a source from the dike outcrops in melrose the third artifact is most likely a non igneous argillite these examples show the importance of using petrographic and geochemical analysis to correctly characterize macroscopically similar lithic material

thermal elasticity of fex mg1 x 2sio4 olivine and wadsleyite 1 we present first principles results for elastic moduli bulk k and shear g and acoustic velocities compressional vp shear vs and bulk v of olivine and wadsleyite fex mg1 x 2sio4 at high pressure p and temperature t with varying iron content 0 x 0 125 pressure and temperature derivatives of these properties are analyzed we show that adding 12 5 of fe in forsterite softens vp and vs by 3 6 the same effect as raising temperature by 1000 k in dry olivine at 13 5 gpa the same is true in wadsleyite this study suggests that fe is effective in producing seismic velocity heterogeneity at upper mantle and transition zone conditions and should be another key ingredient in addition to temperature and water content variations in interpreting seismic heterogeneities in the transition zone the effect of fe on density elastic and velocity contrasts across the transition is also addressed at relevant conditions we show that simultaneous changes of composition temperature and pressure do not affect significantly the relative density contrasts we also find that compressional and shear impedance contrasts result primarily from velocity discontinuities rather than density discontinuity

elasticity of hydrous wadsleyite to 12 gpa implications for earth s transition zone knowledge of the pressure effect on elasticity of hydrous olivine polymorphs is necessary to model seismic wave speeds for potential hydrous regions of the mantle here we report single crystal elastic properties of wadsleyite beta mg2sio4 with 0 84 wt h2o measured to 12 gpa by brillouin scattering pressure derivatives of the aggregate bulk modulus k prime s0 and shear modulus g prime 0 of hydrous wadsleyite are 4 1 1 and 1 4 1 respectively these values are indistinguishable within uncertainty from those of anhydrous wadsleyite we estimate that approx 1 wt h2o in wadsleyite at 410 km depth can reconcile seismic bulk sound velocities with a pyrolite composition mantle by using our measured high pressure elastic constants if the h2o content of the mantle is much less than 1 wt then other factors need to be considered to explain the velocity contrast of the 410 km discontinuity variations in water content with depth may also contribute to the anomalously steep seismic velocity gradient in the mantle transition zone

3 d shear wave radially and azimuthally anisotropic velocity model of the north american upper mantle summary using a combination of long period seismic waveforms and sks splitting measurements we have developed a 3 d upper mantle model sawum na2 of north america that includes isotropic shear velocity with a lateral resolution of 250 km as well as radial and azimuthal anisotropy with a lateral resolution of 500 km combining these results we infer several key features of lithosphere and asthenosphere structure a rapid change from thin 70 80 km lithosphere in the western united states wus to thick lithosphere 200 km in the central cratonic part of the continent closely follows the rocky mountain front rmf changes with depth of the fast axis direction of azimuthal anisotropy reveal the presence of two layers in the cratonic lithosphere corresponding to the fast to slow discontinuity found in receiver functions below the lithosphere azimuthal anisotropy manifests a maximum stronger in the wus than under the craton and the fast axis of anisotropy aligns with the absolute plate motion as described in the hotspot reference frame hs3 nuvel 1a in the wus this zone is confined between 70 and 150 km decreasing in strengthwithdepthfromthetop fromthermftothesanandreasfaultsystemandthejuande fuca gorda ridges this result suggests that shear associated with lithosphere asthenosphere couplingdominatesmantledeformationdowntothisdepthinthewesternpartofthecontinent the depth extent of the zone of increased azimuthal anisotropy below the cratonic lithosphere is not well resolved in our study although it is peaked around 270 km a robust result radial anisotropy is such that predominantly 1 where vsh vsv 2 under the continent and its borders down to 200 km with stronger in the bordering oceanic regions across the continent and below 200 km alternating zones of weaker and stronger radial anisotropy with predominantly 1 correlate with zones of small lateral changes in the fast axis direction of anisotropy and faster than average vs below the lab suggesting the presence of small scale convection with a wavelength of 2000 km finally in the western united states complex 3 d patterns of isotropic velocity and anisotropy reflect mantle dynamics associated with the rich tectonic history of the region

u pb dating of granodiorite and granite units of the los pedroches batholith implications for geodynamic models of the southern central iberian zone iberian massif the first u pb geochronological results on the magmatic alignment of the los pedroches batholith are presented the batholith is composed of a main granodioritic unit several granite plutons and an important acid to basic dyke complex all of them intrusive after the main variscan regional deformation phase d1 along the boundary between the ossa morena and central iberian zones sw iberian massif zircons from samples on both extremes of the granodiorite massif record nearly simultaneous magmatic crystallization at ca 308 ma while the emplacement of granite plutons was diachronic between 314 and 304 ma the u pb results combined with new field and textural observations allow to better constrain the age of variscan deformations d2 and d3 across the region while the age of d1 remains imprecise transcurrent d2 shearing tightening of d1 folds occurred around 314 ma lower westphalian in relation to the emplacement of the first granitic magmas d3 faults and shear bands bearing a strong extensional component developed at ca 308 ma upper westphalian associated to the intrusion of the main granodiorite pluton granodiorite of the batholith together with available geochemical and geophysical information these results point to the variscan reactivation of lithospheric fractures at the origin and subsequent emplacement of hybrid magmas within this sector of the massif

seismic anisotropy in the mantle transition zone induced by shear deformation of wadsleyite abstract mantle flow in the earth s mantle transition zone between 410 and 660 km depth plays a key role to understand the nature of mantle convection which can be mapped by observed seismic anisotropy combined with crystallographic preferred orientations of mantle minerals although wadsleyite is the most important mineral to cause seismic anisotropy observed in the mantle transition zone there have been limited experimental data on its crystallographic preferred orientation because of experimental limitations we experimentally evaluated the preferred orientation of wadsleyite developed by shear deformation at pressure temperature conditions of the mantle transition zone 17 6 gpa and 1800 1900 k using a deformation dia apparatus the deformation experiments reveal that the 0 0 1 axis and the 0 1 0 plane of wadsleyite tend to be subparallel to the shear direction and the shear plane during deformation respectively these results demonstrate that polarization seismic anisotropy velocity contrast between horizontally polarized and vertically polarized s waves vsh vsv observed in the mantle transition zone might be attributed to the preferred orientation of wadsleyite caused by horizontal mantle flow

seismic anisotropy changes across upper mantle phase transitions the mantle transition zone is believed to play an important role in the thermochemical evolution of our planet and in its deep water cycle constraining mantle flow at these depths can help elucidate its nature and better understand mantle dynamics and the history of plate tectonics seismic anisotropy i e the directional dependence of seismic wave velocity provides us with the most direct constraints on mantle deformation its detection below 250 km depth is challenging and it is often assumed that the deep upper mantle is seismically isotropic due to a change in mantle deformation mechanism here we present a global model of azimuthal anisotropy for the top 1000 km of the mantle we used a dataset composed of fundamental and higher mode rayleigh wave phase velocity maps which provides resolution of azimuthal anisotropy to much greater depths than in previous studies our model unravels the presence of significant anisotropy in the transition zone challenging common views of mantle deformation mechanisms and reveals a striking correlation between changes in anisotropy amplitudes and in the fast direction of wave propagation where upper mantle phase transitions occur the newly found relation between anisotropy changes and phase transformations gives new insight on the nature of the mtz and suggests that the anisotropy originates from the lattice preferred orientation of anisotropic material while the interpretation of our results in terms of mantle deformation is not straightforward due to many possible scenarios possible explanations for our findings include recrystallization during phase transformations or changes in the slip system across the mtz boundaries which in turn could be explained by changes in the water content of mantle material consistent with the idea that the transition zone acts as a water filter 2013

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

brillouin scattering and x ray diffraction of san carlos olivine direct pressure determination to 32 gpa the single crystal elastic moduli of san carlos olivine mg 0 9fe0 1 2sio4 were determined at seven pressures between 2 5 and 32 5 gpa by brillouin spectroscopy in a diamond anvil cell the unit cell volume was also determined at each pressure and ambient pressure by single crystal x ray diffraction the shear elastic moduli exhibit non linear pressure dependencies in particular a non linear dependence is required for the elastic modulus c55 above 10 gpa aggregate bulk and shear moduli were determined from hashin shtrikman averages of the individual constants pressures were determined by fitting the bulk modulus reuss bound and volume data to a third order eulerian finite strain equation and integrating the results are compared to independent pressure measurements made using the ruby fluorescence scale the ruby measurements yield pressures that are in good agreement with the brillouin results on average the ruby fluorescence measurements produce pressures that are larger than the brillouin determinations by 1 6 1998 elsevier science b v all rights reserved

effect of hydration on the single crystal elasticity of fe bearing wadsleyite to 12 gpa the single crystal elastic properties of fe bearing wadsleyite with 1 93 wt h2o mg1 634fe0 202h0 305sio4 have been determined by brillouin scattering at ambient conditions the aggregate bulk and shear moduli ks0 g0 of this wadsleyite are 156 2 5 and 98 0 3 gpa respectively compared to the corresponding anhydrous wadsleyite 1 93 wt h2o lowers ks0 and g0 by 8 1 and 9 3 respectively high pressure measurements up to 12 gpa show that the pressure derivative of

heterogeneous seismic anisotropy in the transition zone and uppermost lower mantle evidence from south america izu bonin and japan summary measurements of seismic anisotropy are commonly used to constrain deformation in the upper mantle observations of anisotropy at mid mantle depths are however relatively sparse in this study we probe the anisotropic structure of the mid mantle transition zone and uppermost lower mantle beneath the japan izu bonin and south america subduction systems we present source side shear wave splitting measurements for direct teleseismic s phases from earthquakes deeper than 300km that have been corrected for the effects of upper mantle anisotropy beneath the receiver in each region we observe consistent splitting with delay times as large as 1 s indicating the presence of anisotropy at mid mantle depths clear splitting of phases originating from depths as great as 600km argues for a contribution from anisotropy in the uppermost lower mantle as well as the transition zone beneath japan fast splitting directions are perpendicular or oblique to the slab strike and do not appear to depend on the propagation direction of the waves beneath south america and izu bonin splitting directions vary from trench parallel to trench perpendicular and have an azimuthal dependence indicating lateral heterogeneity our results provide evidence for the presence of laterally variable anisotropy and are indicative of variable deformation and dynamics at mid mantle depths in the vicinity of subducting slabs

elasticity and strength of hydrous ringwoodite at high pressure oh bearing hydrous ringwoodite compressed non hydrostatically in a diamond anvil cell supports a differential stress that increases from 2 9 to 4 5 gpa over the pressure range of 6 7 13 2 gpa at room temperature this result suggests a significant water weakening effect when compared with results from similar experiments on the anhydrous counterpart kaver and duffy geophys res lett 28 2001 2691 2694 the elastic anisotropy 2c44 c11 c12 of hydrous ringwoodite is measured to be 0 87 7 throughout this pressure range similar to measured values for anhydrous ringwoodite kaver and duffy geophys res lett 28 2001 2691 2694 this lattice anisotropy cannot be explained by anelastic effects such as faulting and twinning within the structure these results suggest that hydrous minerals in the upper mantle and transition zone may have higher ductile strain rates for a fixed shear stress at high temperature resulting in stronger preferred lattice orientation this in turn may be seismically detectable which opens the possibility of using seismic anisotropy as a marker for local volatile containing areas within the upper mantle and transition zone

single crystal elasticity of β mg2sio4 to the pressure of the 410 km seismic discontinuity in the earth s mantle the complete set of elastic stiffness coefficients of a single crystal of mg2sio4 in the modified spinel wadsleyite structure are reported at eight pressures from ambient to 14 gigapascals gpa all moduli vary linearly with pressure within the resolution of the data third order birch murnaghan equation fits to aggregate elastic moduli yield values of 170 2 gpa and 4 3 0 2 for the adiabatic bulk modulus and its first pressure derivative and 115 2 gpa and 1 4 0 2 for the shear modulus and its pressure derivative these data together with previous results for mg2sio4 enable us to make the first in situ determination of the velocity increase due to the transition at the pressure 13 8 gpa of the 410 km discontinuity the room temperature velocity increase at the transition pressure is 9 8 for compressional waves and 12 4 for shear waves

elastic properties of iron bearing wadsleyite to 17 7 gpa implications for mantle mineral models abstract the sound velocities and single crystal elastic moduli of iron bearing wadsleyite with fe fe mg molar ratio of 0 075 have been measured by brillouin scattering experiments at high pressures up to 17 7 gpa pressure derivatives for the adiabatic bulk modulus k s0 and shear modulus 0 are 4 1 1 and 1 45 4 respectively a comparison of our results with previous brillouin scattering results on the mg end member wadsleyite shows that incorporating 7 5 mol iron in wadsleyite at high pressure conditions decreases the shear moduli by 4 5 but does not have a discernable effect on the bulk modulus the effects of iron on the elastic moduli of wadsleyite at ambient pressure persist to high pressure conditions at a relatively constant level using our results on iron bearing wadsleyite at high pressure we conclude that less olivine than in the pyrolite model of mantle composition provides a satisfactory explanation for 410 km seismic discontinuity at the top of the transition zone

sound velocities in olivine at earth mantle pressures the independent elastic constants of an upper mantle mineral san carlos olivine mg1 8fe0 2 sio4 were measured from 0 to 12 5 gigapascals evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400 kilometer discontinuity and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers in the absence of high temperature data at high pressures estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers in contrast with low pressure laboratory data the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle

correction to effects of hydration on the elastic properties of olivine 1 in the paper effects of hydration on the elastic properties of olivine by s d jacobsen et al geophysical research letters 35 l14303 doi 10 1029 2008gl034398 2008 the sample of hydrous olivine labeled hy fo97 with 001 orientation in the bottom plot of original figure 1b has been subsequently identified by raman spectroscopy as oh chondrodite mg fe 5si2o8 oh 2 e g lin et al 1999 the oh chondrodite co existed with hydrous forsterite in the synthesis run and all other samples in the study have been confirmed to be hydrous forsterite upon removing the oh chondrodite platelet from the fit we obtain a corrected set of elastic constants cij and crystallographic orientations for hy fo97 using a two plane fit displayed in corrected figure 1 and presented in corrected table 1 the original table 2 of anisotropy factors has been updated and presented here in corrected table 2 brillouin spectra from the two remaining orientations of hy fo97 determine eight of the nine cij leaving c12 unconstrained as a result c12 was fixed to the value obtained for hy fo100 and a large uncertainty of 5 gpa in this parameter was assumed in calculating the aggregate bulk ks0 and shear g moduli 2 in addition a minor correction to the elastic constants of hydrous forsterite hy fo100 is presented in revised table 1 because the original calculation used an earlier estimated density of 3 19 g cm instead of the actual measured x ray density of 3 180 3 g cm the measured x ray density of 3 180 3 g cm was correctly reported in the original text but not used in the calculation of cij the revised cij of hydrous forsterite are affected by only 0 2 0 3 from the original calculation as a result of the error 3 the revised values of elastic properties for hy fo100 and hy fo97 presented in the corrected table 1 apply to the following statements in the text 4 the last four sentences of paragraph 1 should read the adiabatic bulk ks0 and shear g0 moduli of hy fo100 are 125 4 0 2 gpa and 79 6 0 1 gpa respectively for hy fo97 we obtain ks0 125 2 0 8 gpa and g0 77 7 0 3 gpa compared with anhydrous forsterite the combined effects of 3 mol fe and 0 8 wt h2o reduce bulk and shear moduli by 2 9 0 6 and 4 5 0 4 respectively with greater reductions expected for more iron rich fo90 mantle compositions although lattice preferred orientation lpo studies have not been carried out under relevant conditions of water or pressure analysis of idealized single crystal anisotropy for various known lpo types predicts no more than 2 effect of hydration on swave splitting anisotropy in olivine 5 the last sentence of paragraph 9 should read we measured two platelets of hy fo97 with fitted orientations of 100 and 010 shown in the corrected figure 1b 6 the last two sentences of paragraph 10 should read the addition of 0 89 wt h2o to forsterite in our hy fo100 samples shows a reduction of all cij by 1 8 4 3 except c33 which is reduced by only 0 8 for hy fo100 we obtain ks0 125 4 0 2 gpa and g0 79 6 0 1 gpa which are about 2 7 and 2 2 lower than anhydrous forsterite respectively 7 the first two sentences of paragraph 11 should read comparing the cij of hy fo97 with anhydrous fo100 to ascertain the net effect of iron and hydration shows that there is a large reduction in cij by 2 4 6 4 except for c23 which increased by 2 1 for hy fo97 we obtain ks0 125 2 0 8 gpa and g0 77 7 0 3 gpa which are 2 9 and 4 5 lower than anhydrous forsterite 8 the last sentence of paragraph 11 should read the aggregate hy fo97 velocities vp and vs with only 3 mol fe are 2 1 and 2 4 lower respectively than anhydrous forsterite suggesting that hydrous fo90 olivine closer to mantle composition would exhibit even further reduced velocities