velocity density systematics mean atomic weight and the interior of the moon abstract mean atomic weight profiles for the lunar mantle have been calculated from velocity density systematic relations using lunar density and seismic velocity models despite large variability among the models the calculation including poisson s ratio yields a range of mean atomic weight values between 22 and 23 g mol 1 below 150 km a similar calculation for the earth s mantle produces a mean atomic weight of 21 1 0 4 g mol 1 this suggests that the moon cannot be derived directly from the earth s mantle or that it has had a differentiation history different from the earth s the lunar m s require an fe mole fraction between 0 25 and 0 33 for a pure olivine mantle or between 0 33 and 0 45 for pure pyroxene the present profiles are 0 5 3 0 g mol 1 higher than those calculated from lunar compositional models based on lunar rock compositions and petrology and assumed lunar histories indicating inadequacies in either the seismic or compositional models or in both the mean atomic weight approach provides a method of comparing the consistency of seismic and compositional models of planetary interiors

elasticity of mgsio3 in the ilmenite phase abstract the single crystal elastic moduli of the ilmenite phase of mgsio 3 have been determined from brillouin spectroscopy they are c 11 472 c 12 168 c 33 382 c 13 70 c 44 106 c 14 27 c 66 152 and c 25 24 in gpa these elastic properties are consistent with a structural mechanical model where the silicon octahedra are very stiff under compression and shear this latter property yields an unexpectedly high shear modulus for the magnesium silicate ilmenite as compared with analogue compounds the further transformation to perovskite will probably be associated with a significant increase in elastic properties since the strong silicon polyhedra form a structural network in this phase the transformation of spinel and stishovite to ilmenite is associated with a slight density increase and a slight decrease in acoustic velocities this transformation will probably not produce a seismic discontinuity even if it does occur in the earth s mantle

shock temperatures of sio2 and their geophysical implications the temperature of sio 2 in high pressure shock states has been measured for samples of single crystal quartz and fused quartz pressures between 60 and 140 gpa have been studied using projectile impact and optical pyrometry techniques at lawrence livermore national laboratory both data sets indicate the occurrence of a shock induced phase transformation at 70 and 50 gpa along the and fused quartz hugoniots respectively the suggested identification of this transformation is the melting of shock synthesized stishovite with the onset of melting delayed by metastable superheating of the crystalline phase some evidence for this transition in conventional shock wave equation of state data is given and when these data are combined with the shock temperature data it is possible to construct the stishovite liquid phase boundaries the melting temperature of stishovite near 70 gpa pressure is found to be 4500 k and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of 2 7 and 2 4 mj kg respectively the solid stishovite hugoniot centered on quartz is well described by the linear shock velocity particle velocity relation u s 1 822 up 1 370 km s while at pressures above the melting transition the hugoniot centered on quartz has been fit with u s 1 619 u p 2 049 km s up to a pressure of 200 gpa the melting temperature of stishovite near 100 gpa suggests an approximate limit of 3500 k for the melting temperature of sio 2 bearing solid mantle mineral assemblages all of which are believed to contain si 4 in octahedral coordination with o 2 thus 3500 k is proposed as an approximate upper limit to the melting point and the actual temperature in the earth s mantle moreover the increase of the melting point of stishovite with pressure at 70 gpa is inferred to be 11 k gpa using various adiabatic temperature gradients in the earth s mantle and assuming creep is diffusion controlled in the lower mantle the current results could preclude an increase of viscosity by more than a factor of 10 3 with depth across the mantle

olivine spinel transitions experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity the sequence of high pressure phase transitions in olivine is traditionally used as a model for seismic velocity variations in the 200 to 650 km depth interval in a mantle of peridotitic bulk composition it has been proposed that the observed seismic velocity increase at 400 km depth is too sharp and of too small a magnitude to be attributable to the phase change and that the upper mantle must thus be chemically stratified with the 400 km discontinuity being due either to a combination of phase changes in a layer of pyroxene garnet rich piclogite composition or to a chemical boundary between such a piclogite layer and an overlying peridotitic layer using available calorimetric thermoelastic and synthesis data and their associated experimental uncertainties we have derived internally consistent high pressure phase relations for the mg2sio4 fe2sio4 join we find that the divariant transition which is generally regarded as occurring over a broad depth interval for mantle olivine compositions is in fact extremely sharp the seismic discontinuity corresponding to the transition in mg0 9fe0 1 2sio4 should occur over a depth interval isothermal of about 6 km at a depth of approximately 400 km the sharpness of this transition is quite insensitive to uncertainties in the constraining calorimetric thermoelastic and synthesis data in addition we have computed seismic velocity profiles for a model mantle consisting of pure olivine of mg0 9fe0 1 2sio4 composition comparison of these computed profiles to those derived from recent seismic studies indicates that the magnitude of the observed velocity increase at 400 km depth is consistent with a mantle transition zone composed of about 60 70 olivine we conclude that there is no need to infer the existence of pyroxene garnet rich compositions such as eclogite or piclogite in the transition zone since an upper mantle of homogeneous olivine rich peridotitic composition is consistent with the available seismic velocity data

mineralogy and composition of the upper mantle seismic velocities are calculated for two petrological models of the upper mantle an olivine rich assemblage pyrolite and a garnet clinopyroxene rich olivine bearing assemblage piclogite these are compared with recent seismic profiles for various tectonic provinces the shield data is most consistent with a cold olivine and orthopyroxene rich lid the seismic lithosphere extending to 150 km followed by a high temperature gradient and or a change in mineralogy that serves to decrease the velocity from 200 to 400 km the velocities follow a 1400 c adiabat the rise tectonic mantle is much slower presumably hotter and is likely to be above the solidus to depths of at least 300 km the high v p v s ratio of the lower oceanic lithosphere in the western pacific is most consistent with eclogite

elasticity of single crystal orthoferrosilite the elastic moduli of a synthetic single crystal of pure fesio3 orthoferrosilite have been measured at 1 bar and 20 c by brillouin spectroscopy the moduli are in megabars c11 1 98 c22 1 36 c33 1 75 c44 0 59 c55 0 58 c66 0 49 c12 0 84 c13 0 72 c23 0 55 a comparison of the pyroxene crystal structure with elasticity data shows that distortion of the tetrahedral chains parallel to c is related to c33 straight or extended chains increase c33 and highly kinked chains weaken the structure however the ferrosilite data show that beyond a certain degree of distortion the tetrahedral chains are essentially passive previous models of pyroxene elasticity have indicated that c11 should be most sensitive to composition this is supported by the current study and is reflected in the elasticity data via a positive linear correlation of c11 with the size of the m1 octahedron as measured by the average m1 0 distance the average longitudinal modulus c 11 c11 c22 c33 3 varies linearly with composition in the system orthoenstatite orthoferrosilite whereas the average shear moduli c 44 and c 12 are constant for fe contents of at least 20 by comparison data for the solid solution forsterite fayalite are consistent with a linear variation of modulus versus composition between the end members for all three average moduli we suggest that this difference between orthopyroxene and olivine is due to a strong preference of fe2 for the m2 octahedral site in pyroxene the isotropic shear modulus is 30 lower for ferrosilite than enstatite despite a similar contrast in end member values of the olivine data are consistent with a linear variation of between fo100 and fa100 at high temperatures fe and mg in orthopyroxene will be randomly distributed and a linear variation of with molar content of fe is expected a comparison of laboratory elasticity data with observed mantle properties shows that vp vs and of the upper mantle are satisfied by pure olivine however the data strongly suggest that without the coexistence of a garnet phase no more than 10 orthopyroxene may be present in a model mantle assemblage ca clinopyroxene increases the upper limit on mantle garnet content but does not greatly affect constraints on the quantity of orthopyroxene in the upper mantle

ultrasonic measurements of vp and qp relaxation spectrum of complex modulus on basalt melts abstract ultrasonic compressional wave velocity v p and quality factor q p have been measured in alkali basalt olivine basalt and basic andesite melts in the frequency range of 3 4 22 mhz and in the temperature range of 1100 1400 c velocity and attenuation of the melts depend on frequency and temperature showing that there are relaxation mechanisms in the melts complex moduli are calculated from the ultrasonic data the results fit well a complex modulus of arrhenius temperature dependence with log normal gaussian distribution in relaxation times of attenuation the analysis yields average relaxation time its activation energy relaxed modulus unrelaxed modulus and width of gaussian distribution in relaxation times relaxed modulus is smaller 17 5 gpa for basic andesite melt of high silica and high alumina contents than for the other two basalt melts 18 1 18 4 gpa the most probable relaxation times decrease from 3 10 10 s for basic andesite to 10 11 s for alkali basalt at 1400 c activation energies of attenuation ranging from 270 to 340 kj mol 1 in the three melts are highest in basic andesite longitudinal viscosity values and their temperature dependences are also calculated from v p and q p data the volume viscosity values are estimated from the data using the shear viscosity values longitudinal volume and shear viscosities and their activation energies are highest in the basic andesite melt of the most polymerized structure

shock wave properties of anorthosite and gabbro shock wave experiments have been conducted on san gabriel anorthosite and san marcos gabbro to peak stresses between 5 and 11 gpa using a 40 mm bore propellant gun particle velocity wave profiles were measured directly at several points in each target by means of electromagnetic gauges and hugoniot states were calculated by determining shock transit times from the gauge records the particle velocity profiles yielded sound velocities along the release adiabats which indicate a retention of shear strength upon shock compression for anorthosite with a loss of strength upon release to nearly zero stress sound velocities of anorthosite shocked to peak stresses between 6 and 10 gpa were measured to be between 5 1 and 5 3 km s upon release to nearly zero stress as compared to 6 9 and 5 4 km s for the expected longitudinal and bulk wave speeds stress density release paths in the anorthosite indicate possible transformation of albite to jadeite quartz or coesite with the amount of albite transformed ranging from as low as 0 05 to as much as 0 19 mass fraction in the 6 10 gpa shock stress range electrical interference effects precluded the determination of accurate release paths for san marcos gabbro because of the apparent loss of shear strength during unloading from the shocked state the fluidlike rheology of anorthosite which is indicated implies that calculations of energy partitioning due to impact onto planetary surfaces based on elastic plastic models will underestimate the amount of internal energy deposited in the impacted surface material

the role of iron partitioning in mantle composition evolution and scale of convection the effect on composition and evolution of the mantle of the recently observed strong concentration of iron in mg fe o magnesiowustite mw at the expense of mg fe sio 3 perovskite pv structure is studied by calculating a temperature and pressure dependent iron partitioning coefficient for the lower mantle the value of the standard entropy for mgsio 3 perovskite is found to be 69 4 10 3 j mole deg from the recently determined phase diagram of forsterite iron remains concentrated in mg fe o throughout the entire lower mantle if account is taken of an feo phase change with the partitioning coefficient x pv fe x pv mg x mw fe x mw mg increasing from 0 04 to 0 8 between 670 km a the core mantle boundary partitioning has negligible effect on gross density and elastic properties of the lower mantle by using recent shock wave and static compression results for feo and mgsio 3 perovskite we find that the lower mantle is more pyroxene rich than the upper mantle and as iron rich or somewhat less so than the upper mantle mg mg fe 0 93 0 95 for the lower mantle compared with 0 85 0 90 for the uppermost mantle the lower mantle mg si ratio is closer to chondritic values 0 99 0 03 1 5 for a peridotite with px ol 0 4 molar thus supporting the idea of a chemically layered mantle with implications for the style of mantle convection while partitioning of iron has no significant effect on gross lower mantle density we find that the mg fe o and perovskite components of the lower mantle have essentially the same densities mantles with higher bulk iron contents have mg fe o denser than the perovskite component for a bulk magnesium mole fraction of 0 80 the density difference is 0 7 0 8 g cm 3 we investigate the feasibility of the mao bell and yagi gravitational separation hypothesis of mantle evolution in which a mantle more iron rich than present loses iron through gravitational sinking of the denser mg fe o and we conclude that the process cannot successfully compete with solid state convection unless implausibly large grain sizes or unacceptably low viscosities are invoked a likely explanation for removal of iron from an initially iron rich lower mantle is upward extraction of feo enriched basalts or picrites and concentration of iron in upper mantle garnets during accretion of the earth or subsequent convection with the entire mantle passing through the partial melt zone thus the lower mantle was depleted of iron relative to both the upper mantle and the mantles of the small terrestrial planets and satellites which do not have mantle pressures sufficient to form perovskite structure silicates or which had lower accretional temperatures and less extensive melting on this basis venus would be expected to have a mantle similarly depleted in iron

the eclogite to garnetite transition experimental and thermodynamic constraints we have found that the forms of the experimentally determined phase diagrams for pyroxene garnet transformations require the volume changes for these reactions to be much smaller at 130 kbar 400 km than at 1 atm using these volume data we calculated the width of the eclogite garnetite transition in natural quartz tholeiite and alkali olivine basalt compo sitions taking account of mixing in multicom ponent pyroxene and garnet phases we find that the eclogite garnetite transition does not exhi bit any discontinuity in bulk sound velocity in the pressure range 110 to 230 kbar in addition this velocity when plotted as a function of pressure possesses a curvature which is in the opposite sense to that given by the preliminary reference earth model prem this phase transi tion therefore does not appear to be a satis factory model for the 400 km seismic discon tinuity

thermal equation of state of mg0 91fe0 09 2sio4 ringwoodite abstract in situ synchrotron x ray diffraction xrd experiments were conducted using the speed 1500 multi anvil press of spring 8 on mg0 91fe0 09 2sio4 ringwoodite rw whose composition is similar to that expected in the earth s mantle transition zone pressure volume temperature data were collected using a nacl or mgo capsule up to 21 gpa and 1273 k a fit to high temperature birch murnaghan htbm equation of state eos with fixed values of ambient cell volume v0 527 83 7 a3 and isothermal bulk modulus kt0 187 gpa yielded a pressure derivative of isothermal bulk modulus kt 4 41 1 a temperature derivative of bulk modulus kt t p 0 028 5 gpa k 1 and a volumetric thermal expansivity a bt with values of a 1 9 2 10 5 k 1 and b 1 2 4 10 8 k 2 these properties are consistent with the analysis using the thermal pressure th p eos the derived kt and kt t p are consistent with previous studies on mg2sio4 ringwoodite however consistent with measurements at 0 gpa the present equation of state yields significantly higher thermal expansivity than derived by diamond anvil experiments on mg2sio4 ringwoodite to 30 gpa and 700 k on the basis of the equation of state the density jump around 660 km depth expected for pyrolitic homogeneous mantle caused by ringwoodite mg perovskite mgpv magnesiowustite mw and garnet grt mgpv transitions was estimated the density jump calculated for pyrolite 9 2 is significantly larger than that across the 660 km discontinuity derived by recent seismological studies 4 6 one possible explanation for this is that the recent seismic data reflect only the sharp transition concerned with the rw mgpv mw transition

on the occurrence of mg fe sio3 in the lower mantle summary the purpose of this investigation involves the estimation of compression of the solid solution series mg fe sio within a shock wave induced high pressure phase and the application of the results to an assessment of the gross chemical composition ofthe lower mantle raw data were provided in the form of hugoniot measurements on several rocks of general abo bulk chemistry which were available in the literature corrections were applied according to anderson s additivity of 0 rule to compensate for the deviation in chemistry of each individual rock from that of an idealized mg fe sio composition the results are critically dependent upon the interpretation that the structural form of mg fe si03 in the high pressure modification appropriate for the lower mantle is most likely related closely to corundum or ilmenite reduction and analysis of the pertinent shock wave data yield the following results for the isentropic bulk moduli of the end member compositions ks mgsio 2 55 mb and ks fesio 3 28 mb the estimated uncertainty in these values is 10 per cent the results of the study were used to determine the composition of the lower mantle in terms of the relative proportions of pyroxene mg fe sio and olivine mg fe 2si04 comparison of the seismic parameter and density for the high pressure phase of pyroxene considered in this investigation with the elastic requirements of the lower mantle indicate that the pyroxene component of the lower mantle relative to olivine must be minor therefore in terms of this simple two component model a fundamental olivine mg fe si04 chemistry remains the most likely possibility for the bulk composition of the lower mantle

shock temperatures in anorthite glass temperatures of caal 2si 2o 8 anorthite glass shocked to pressures between 48 and 117 gpa have been measured in the range from 2500 to 5600 k using optical pyrometry techniques the pressure dependence of the shock temperatures deviates significantly from predictions based on a single high pressure phase either a variable specific heat or the existence of three phase transitions at pressures of about 55 85 and 100 gpa and with transition energies of about 0 5 mj kg 1 each 1 5 mj kg 1 total can explain the shock temperature data the proposed phase transition at 100 gpa can possibly be identified with the stishovite melting transition theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm 1 to greater than 24 mm 1 an increasing function of shock pressure the assumption that the shocked material radiates as a black body is supported by the theoretical model and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength

a decade of progress in earth s internal properties and processes a major component of the inter union commission on geodynamics project labeled internal properties and processes included certain experimental and theoretical research in tectonophysics seismology geochemistry petrology volcanology and planetology this review focuses on a few research areas in which there have been surprises and reversals in particular attention is given to the attempts to quantify the thermal profile in the earth s interior and the material properties of the earth s interior

elasticity of olivine α beta β and spinel γ polymorphs of germanates and silicates summary ultrasonic data for the velocities of germanate and silicate compounds in the olivine a beta 8 and spinel y crystal structures have been determined as a function of pressure to 7 5 kbar at room temperature for polycrystalline specimens hot pressed at pressures up to 65 kbar the a y phase transformations are characterized by the following velocity u density p relationships a the velocity jumps are twice the percentage magnitude of the density jumps b the ratio vp v of the compressional to shear velocity is either approximately constant or increases slightly across the transitions and c the slopes linear or logarithmic on v p diagrams for the a y transition are comparable to those produced by isothermal compression or isobaric expansion of the low pressure olivine phase the behaviour of up u is a feature common to many phase transformations however the observed relationships a and c while similar to those for the quartz coesite transition in si02 are in marked contrast with those for the coesite rutile pyroxene garnet and pyroxeneilmenite transformations these latter transitions involve increases in cation anion co ordination and nearest neighbour distances whereas the olivine spinel and olivine beta phase transformations do not such crystallographic details may be diagnostic for interpretations of the composition and mineralogy of the earth s transition zone systematic trends in the elastic properties for isostructural sequences support the concept of germanates as models for the elasticity of their silicate analogues this scheme is applied to estimate the bulk modulus of the spinel polymorph of mg si04 k 2 06 0 05 mbar comparison of the new elasticity data with recent earth models in the vicinity of the 400 km discontinuity reveals that only model 1066b of gilbert dziewonski is compatible with the experimental data for the u y and a 8 transformations

the earth as a planet paradigms and paradoxes the independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical geochemical geological and planetological models for the composition and evolution of a terrestrial planet evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive still undifferentiated and homogeneous terrestrial mantle in comparison with the moon the earth has an extraordinarily thin crust the geoid which should reflect convection in the mantle is apparently unrelated to the current distribution of continents and oceanic ridges if the earth is deformable the whole mantle should wander relative to the axis of rotation but the implications of this are seldom discussed the proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources these and other paradoxes force a reexamination of some long held assumptions

inhomogeneity parameter of a homogeneous earth adiabatic and chemically homogeneous solid regions of the earth are expected to appear otherwise because of the bulk attenuation to seismic waves that occurs in polyphase aggregates such as the earth s mantle because the seismologically measured bulk modulus is only partially relaxed compared with the hydrostatic pressure density relation or relaxed modulus of the earth s mantle an apparently nonadiabatic contribution1 to the geotherm is expected to be inferred from seismological observations on regions of the mantle that are well mixed by vigorous convection using a recent analysis of bulk attenuation in polyphase assemblages2 we estimate the total nonadiabatic contribution to the geotherm through the lower mantle to be approximately 300 to 800 k the magnitude of this effect is significant in that it is of the same order as the temperature change within a thermal boundary layer which represents the largest perturbation of the geotherm resulting from convection within the earth moreover if the lower mantle is truly homogeneous and adiabatic it should appear to be subadiabatic according to the seismological data

shock temperatures in cao blackbody temperatures of cao shocked to pressures from 140 to 182 gpa have been measured in the 3750 to 6000 k range using the lawrence livermore national laboratory light gas gun these shock temperatures along with hugoniot data for single crystal and porous cao and isothermal data are used to construct equations of state for the high pressure b2 phase of cao the zero pressure density of the b2 phase is between 3 8 and 4 0 mg m 3 and the b1 b2 transition energy is 2 1 to 2 3 mj kg the density and bulk modulus at pressures from 70 to 135 gpa are similar to seismically determined values for the lower mantle of the earth thus the lower mantle could have a substantial inventory of ca bearing minerals and mixed oxide models for the composition of the lower mantle will be insensitive to the quantity of cao assumed

elasticity of majorite and a majorite pyrope solid solution to high pressure implications for the transition zone 1 high seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals such as majorite garnet here we present brillouin scattering measurements of the elasticity of polycrystalline mg majorite mj100 mg4si4o12 and a mj50py50 majorite pyrope solid solution to pressures similar to those at the top of the transition zone 15 1 1 gpa and 12 8 1 gpa respectively the pressure derivatives of the adiabatic bulk ks and shear moduli of both mj50py50 and mj100 are 4 2 3 and 1 4 2 respectively and are equal to those of pyrope within the experimental uncertainties we conclude that neither the adiabatic compression of majorite garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically high velocity gradients are consistent with gradual transformations between minerals with very different elastic properties the transformation of 25 or more of clinopyroxene into majorite above 520 km and the formation of ca silicate perovskite below 520 km could produce the observed seismic gradients

high pressure elasticity of sodium majorite garnet na2mgsi5o12 garnet is the second most abundant mineral phase in the upper mantle and transition zone settings the crystal structure of garnet is quite flexible and hence it is able to accommodate various cations including large incompatible cation such as sodium we used first principles simulation based on density functional theory and two widely used approximations local density approximation lda and generalized gradient approximation gga to explore the crystal structure equation of state and elasticity of sodium bearing majorite garnet with na 2 mgsi 5 o 12 stoichiometry at pressures relevant to the upper mantle and transition zone we find that the pressure volume results based on lda can be explained by a birch murnaghan finite strain equation of state with v 0 1447 6 0 1 a 3 k 0 177 4 0 4 gpa and k 0 3 93 0 02 the results based on gga can be explained by a birch murnaghan finite strain equation of state with v 0 1525 8 0 2 a 3 k 0 160 2 0 4 gpa and k 0 3 96 0 02 the full elastic moduli tensor for na majorite with tetragonal symmetry exhibits slight deviation from the cubic symmetry with c 11 c 33 c 12 c 13 and c 44 c 66 the magnitude of the tetragonal strain also captures the slight deviation from the cubic symmetry at pressures corresponding to the upper mantle and mantle transition zone the compressional wave velocity v p and shear wave velocity v s for the na majorite garnet are fast compared to a wide variety of garnets such as pyrope grossular almandine and majorite garnet although single crystal anisotropy of na majorite is greater than pyrope it is still low compared to the major mantle phases

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

magnetic fabrics in the bjerkreim sokndal layered intrusion rogaland southern norway mineral sources and geological significance abstract magnetic anisotropy can provide important information about mineral fabrics and thus magmatic processes particularly when it is known how multiple mineral species contribute to the anisotropy it may also affect the direction of induced or remanent magnetization with important consequences for paleomagnetic studies or the interpretation of magnetic anomalies here we aim at describing the magnetic fabrics in the bjerkreim sokndal layered intrusion and identifying their carriers anisotropies of magnetic susceptibility and remanence were measured on samples covering different geographic locations and stratigraphic units within the bjerkreim sokndal layered intrusion the intrusion is characterized by magmatic layering and has a synform structure with strong foliation on the limbs detailed comparison between magnetic and mineral fabric shows that they are not necessarily coaxial but the minimum susceptibility and minimum anhysteretic remanence are generally normal to the foliation or the magmatic layering the minimum susceptibility and anhysteretic remanence are associated with pyroxene 100 axes and the maximum susceptibility and anhysteretic remanence are sub parallel to the pyroxene 001 axes in layers mcu ivc and mcu ive for which electron backscatter data are available however the paramagnetic anisotropy of pyroxene is too weak to explain the observed anisotropy we propose that the magnetic anisotropy of magnetite free specimens is carried by hemo ilmenite exsolutions within pyroxene in addition to pyroxene itself when present multi domain magnetite dominates both the anisotropy of magnetic susceptibility and anhysteretic remanence due to shape preferred orientation and distribution anisotropy the orientation of the magnetic fabric appears independent of carrier due to their common deformation history but the degree of anisotropy is stronger for magnetite bearing specimens the results of this study will facilitate future structural interpretations and may be used to correct for magnetization deflection

experimental study of the elasticity of single crystalline calcite under high pressure the calcite i calcite ii transition at 14 6 kbar abstract the length variations and the ultrasonic wave velocities were measured along principal single crystal calcite axes under high pressure we have observed that six independent elastic constants undergo drastic changes at the calcite i calcite ii transition point at 14 6 kbar furthermore we have determinated the length and volumetric variations in the phases i and ii and during the i ii transition these results allow us to deduce the following important points influence of the planar co3 groups on the strong linear compressibility anisotropy in phase i reciprocal relation between the decrease of elastic constants at the transition point and the anomaly of compressibility of the calcite ii compatibility of our data with the monoclinic structure of calcite ii

adiabats of quartz coesite olivine and magnesium oxide to 50 kbar and 1000 k and the adiabatic gradient in the earth s mantle the adiabats of olivine magnesium oxide and quartz were measured up to 50kbar and 1000 k an end loaded piston cylinder apparatus with an in situ pressure gauge and a very fine thermocouple was used to measure t p s during adiabatic compression a power law between t p s and compression yields values of the power n ln t p s ln that agree with previous results from salts metals and fluids assuming constant values for n the adiabtic gradient for an olivine upper mantle and a magnesium oxide lower mantle was calculated the results agree well with some previous theoretical estimates the volume dependence of the gruneisen parameter was calculated from the thermodynamic equation ln ln b p n where b is the isothermal bulk modulus is found to a good approximation to be proportional to volume table 6 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 002 1 00 payment must accompany order

a simple model of the 1982 83 californian el nino steric height steric height anomaly sea level and sea level anomaly show that the 1940 41 and the 1982 83 californian el nino events were resonant responses of the california current to the expansion and intensification of the aleutian low and decrease in strength of the north pacific high in both cases the subsurface anomalies were dynamically produced by onshore transport of subarctic water and a downward tilt of the inshore thermocline sea surface temperature anomalies however resulted from thermodynamic as well as dynamic processes most previous californian el nino or anti el nino events probably were resonant or anti resonant responses of the seasonal cycle of the california current to anomalous large scale atmospheric forcing

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

are anharmonicity corrections needed for temperature profile calculations of interiors of terrestrial planets abstract it is shown that there is linearity between the thermal pressure p th and t between the debye temperature and some high temperature t t has been measured at 1 atm and is reported for several minerals including for example mgo 1300 k and forsterite 1200 k the change in thermal pressure from room temperature for five solids so far measured indicate striking linearity with t at high temperatures it is further shown that the value of t increases greatly as the pressure increases it is therefore concluded that p th is probably linear with t for mantle minerals under mantle conditions the proportionality constant is derived from the measurements of thermal expansivity and bulk modulus at high temperature and zero pressure the argument is then reversed assuming that the thermal pressure is in fact linear with t for the various shells in a planet the resulting density and temperature profile of the planet is derived the resulting density profile of the earth compares favorably with corresponding values of recent seismic profiles

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

thermodynamics of the system fe feo mgo at high pressure and temperature and a model for formation of the earth s core summary recent shock wave data of jeanloz ahrens have established the presence of a phase transformation in fe0 94 o occurring at approximately 70 gpa which has profound implications for the phase behaviour of the geophysically important system feo mgo at high pressure we calculate the phase diagram based on the available shock wave data for feo and mgo and suggest that an increase of pressure in the system feo mgo will result in a gradual exsolution of an almost pure feo high pressure phase hpp leaving an iron depleted fe mg o rocksalt bl phase using current geophysical data exsolution of feo hpp from the rocksalt phase in the present day lower mantle is calculated to occur only in the region immediately overlying the core before core segregation took place however the increased iron content of the rocksalt phase could place the exsolution region at lesser depths perhaps 2000 km extrapolation of the solubility data of oxygen in liquid iron indicates that the liquid miscibility gap in the system fe feo at atmospheric pressure should close at approximately 4250k we construct schematic phase diagrams for the system fe feo at high pressure by considering the effect of pressure upon end member melting points upon the extent of liquid immiscibility and upon eutectic temperatures and compositions we suggest that at high pressure p 90 gpa the phase diagram of fe feo becomes qualitatively similar to the system fe fes displaying complete liquid miscibility and a eutectic temperature well below the melting point of pure iron on the basis of our inferences regarding behaviour in the system fe feo mgo at high pressure we have constructed a model for core segregation assuming the earth to have accreted from the primordial solar nebula as a relatively homogeneous mixture of metallic iron and silicate phases core segregation involving oxygen as the principal light alloying element in the core would commence at a depth where pressure is sufficiently high to cause exsolution of feo hpp from the rocksalt phase and temperature is sufficiently high to allow formation of an fe feo hpp melt without extensively melting the silicate phases a gravitational instability arises leading to vertical differentiation of the earth as molten blobs of the metal phase sink downwards to form the core and the residual depleted silicate material coalesces to form large bodies which rise diapirically upwards to form the mantle

topography of the transition zone seismic discontinuities phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities nominally at 410 520 and 660 km depth thermodynamic principles govern phase transformations making them sensitive to changes in the mantle s ambient conditions through the thermodynamic response changes in temperature or composition shift the transformation to a different pressure creating topography on a level discontinuity with this use as an exploratory tool for the mantle in mind we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities reviewing the evidence for and against the phase transition model we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone

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

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

signature of magmatic processes in strainmeter records at campi flegrei italy volcanic unrest at campi flegrei caldera southern italy is characterized by episodes of ground deformation seismicity and enhanced fumarolic activity whether its origin is purely hydrothermal or magmatic is highly debated we have identified ground deformation patterns in strainmeter records from a heightened unrest period in late 2006 closely resembling synthetic signals from numerical simulations of shallow magma chamber replenishment and mixing together with other recent findings our results depict a situation whereby periodic arrivals of deep magma feed a shallow intrusion at 3 4 km depth these results suggest that the analysis of strainmeter records coupled with advanced numerical simulations of magma dynamics could lead to new approaches in imaging subsurface dynamic processes in volcanic areas

ultrasonic studies on a basalt melt compressional wave attenuation qp 1 and velocity vp for an alkalic olivine basalt have been measured from 1250 to 1450 c and from 5 to 10 mhz by an ultrasonic interferometric technique vp shows no significant frequency or temperature dependence and qp 1 increases with increasing frequency and decreasing temperature for the conditions of this study the melt can be modeled as a viscoelastic material with a single thermally activated structural relaxation mechanism having an activation energy of 2 2 ev and a relaxation time on the order of 1 ns the data presented here fall in the region of the relaxation spectrum where the frequency f is much smaller than the relaxation frequency and the absorption coefficient is proportional to f analysis of the data suggests that 1 compressional wave losses will be negligible in a basalt melt at seismic frequencies and 2 the volume viscosity of basalt melt is comparable in magnitude to shear viscosity

thermodynamically consistent decompression implications for lower mantle composition estimates of the composition of the lower mantle are commonly obtained by a process of adiabatic decompression in which zero pressure mantle parameters are determined with a least squares fit of an equation of state to mantle densities we show that this procedure may lead to biased estimates of the zero pressure density and compressibility of the mantle the bias can be eliminated or minimized by subjecting the equation of state fit to a thermodynamic constraint at zero pressure such inversions provide equations of state that are compatible with the lower mantle as well as the thermal properties of selected mineral models we used this method to evaluate assemblages containing mg fe sio3 perovskite and mg fe o with fe fe mg ratios as high as 0 2 thermodynamic systematics were used to place bounds on the anderson gruneisen parameter s for perovskite we find a fairly large range of acceptable models for the composition of the lower mantle they range from uppermantle like compositions to assemblages that are enriched in both si and fe relative to the upper mantle however a pure perovskite lower mantle whether enriched in fe or not seems improbable small fe enrichments of the order of 1 given density contrasts across the 670 km discontinuity that are probably insufficient to prevent convective mixing of the upper and lower mantles we therefore suggest that unless the mantle is homogeneous in its major oxide components the lower mantle is likely to be enriched in fe by at least several percent

compression of ice vii to 500 kbar the isothermal compression of ice vii up to 500 kbar has been measured at 23 2 c by high pressure x ray diffraction technique using a diamond anvil cell water transforms to ice vi at 9 3 0 3 kbar ice vi transforms to ice vii at 20 8 0 5 kbar and no other phase has been observed up to 500 kbar the compression data fitted to the birch equation of state yield k 0 240 9 kbar and k 0 4 5 and the volume for ice vii extrapolated to zero pressure is 0 704 0 003 cm 3 g no theoretical equations of state for h 2 o which satisfy the data are available at present the index of refraction for ice vii is observed to be the same as ruby at the pressure interval 350 400 kbar and it becomes greater than ruby above these pressures

emplacement mechanism of the great whin and midland valley dolerite sills the great whin and midland valley dolerite sill complexes appear to have been emplaced laterally from the walls of feeder dykes the overall thickness of each sill increases with depth as would be expected if the magma finally reached a state of hydrostatic equilibrium variations in the thickness of the sills with estimated intrusion depth imply that the head of magma was about 100 m below the contemporary ground surface in the areas of the present day outcrops at the end of the intrusive episodes before hydrostatic equilibrium was established the magma pressure would probably have been somewhat greater so it is likely that intrusion of the sills was accompanied by the extrusion of flood basalts step and stair transgressions of the bedding are commonly found within the sills mostly stepping downwards in the direction of bedding dip the reason for this directionality is that the weight of sediments floating on an intruding sill has a downdip component that applies a tensile stress to intersecting fractures below the sill when magma is moving downdip and to intersecting fractures above the sill when magma is moving updip

reflection properties of phase transition and compositional change models of the 670 km discontinuity seismic observations of the amplitude ratio amplitude p 670p amplitude p p suggest a reflection coefficient r 7 13 for reflections from the underside of the 670 km discontinuity this can be compared with calculated reflection coefficients to constrain the nature of the mantle transition region velocity and density profiles through the transition region were calculated for olivine pyroxene garnet and olivine garnet model mineral assemblages for models with identical upper and lower mantle compositions the computed reflection coefficients from the phase transitions pertinent to the 670 km discontinuity are less than 0 5 these phase transitions produce their maximum r if they are effectively discontinuous which gives r 2 3 except for the garnet to perovskite transformation which gives r 8 in general given realistic impedance contrasts across a phase transition the change in material properties must occur over a region less than 3 km thick for r to be of the order of 5 a discontinuous change in chemical composition at 670 km depth coupled with a change in phase can also produce a reflection coefficient of the observed magnitude r 2 3 for a first order change in phase at 670 km with different iron concentrations on each side of the discontinuity and r 4 6 for cases with a discontinuous increase in silica content based on our analysis the thermal and chemical boundary layers which would occur across such a chemical discontinuity would probably have negligible effects on the reflection coefficient thus although limited by considerable uncertainties the mineralogical and seismic data suggest a two layered model of the mantle with a discontinuous change in both phase and composition at 670 km

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

a mineral physics test of a pyrolite mantle an homogeneous upper mantle chemical composition defined by the pyrolite model is compatible with the observed seismic velocities such a test is now possible for depths to 670 km as a result of new mineral elasticity and phase equilibria data three specific criteria for comparing the mineralogical velocity model with that of the mantle include i the velocity jump at the 400 km discontinuity ii the velocity increase between 400 and 670 km and iii the absolute value of velocity in the 300 to 400 km region shallower than the discontinuity the first criterion is sensitive to the olivine content of the mantle and the pressure derivatives of the elastic properties of the high pressure phase the application of this criterion suggests a mantle with 40 65 olivine by volume the second criterion is sensitive to the details of the pyroxene to garnet transformation and the relative abundances of the pyroxenes and garnet the third criterion depends on details of this transformation as well as iron content and the temperature of the mantle

the relationship between the physical properties of the assumed pyrolite composition and depth distributions of seismic velocities in the upper mantle abstract assuming that the upper mantle consists of pyrolite composition we determined values of derivatives of bulk modului and shear modului with respect to pressure and temperature and values of the gruneisen anderson parameter for composite minerals of pyrolite composition by comparing depth distributions of p and s wave velocities calculated from the values of physical properties obtained from high pressure and high temperature experiments with those of iasp91 for this purpose we determined the above described values which have not been determined well in high pressure and high temperature experiments within a certain range for each parameter using genetic algorithm ga as a result the values of physical properties for wadsleyite were determined so that seismic velocities can decrease the values of derivative of bulk modulus for perovskite and magnesiowustite were determined so that seismic velocities can increase on the other hand the values of derivative of shear modulus for perovskite and magnesiowustite were determined to be the same values as standard values or the values were determined so that seismic velocities can decrease the values of physical properties for pyroxene garnet and majorite except the values of derivative of bulk modulus with respect to pressure for orthopyroxene and garnet were determined so that seismic velocities can increase depth distributions of seismic velocities calculated from the determined values of physical properties indicate that the velocity jump corresponding to the 410 km seismic discontinuity occurs at a depth shallower than that for iasp91 the amount of velocity jump at the 660 km seismic discontinuity obtained in this study reaches 3 5 for p wave which is smaller than that 5 8 for iasp91 we also investigated the effect of mantle geotherm on depth distributions of seismic velocities the results show that the seismic velocities increase 0 5 when the mantle geotherm becomes low by 100 k for all the depths concerned however the amount of p wave velocity jump at the 660 km seismic discontinuity obtained in this study is too small to explain that for iasp91 for any mantle geotherms if we assume that the upper mantle consists of pyrolite composition these suggest that the amount of p wave velocity jump at the 660 km seismic discontinuity for iasp91 is overestimated