the compositions of coexisting pyroxenes and garnet in the system cao mgo al2o3 sio2 at 900 1 100 c and high pressures the compositions of coexisting orthopyroxene clinopyroxene and garnet in the cao mgo al2o3 sio2 system are fixed at any givenp andt reversed hydrothermal experiments over thep t range 15 40 kb 900 l 100 c indicate that the garnet composition is nearly constant at py86gr14 the alcontent and ca ca mg values of the pyroxenes vary significantly however t p wt al2o3 frac ca ca mg times 100 c kbar in opx in cpx in opx in cpx 900 15 3 55 2 92 0 72 47 05 900 30 1 62 0 92 0 81 47 30 1 100 20 1 11 0 92 1 22 45 20 1 100 40 1 26 0 88 0 81 45 64 the significant variation of a12o3 content with pressure supports its use as a geobarometer the ca ca mg values of coexisting orthoand clino pyroxene have been used as a geothermometer however the present results show that the presence of a12o3 in the pyroxenes decreases significantly the mutual solubility of the pyroxenes which may cause errors of up to 200 c if the a12o3 effect is ignored

a model of late quaternary landscape development in the delaware valley new jersey and pennsylvania abstract in the delaware valley of new jersey and eastern pennsylvania the late quaternary history of colluviation fluvial adjustment and soil formation is based on the ages of pre wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid latitude climate changes indicated by marine oxygen isotope records the area is divided into four terranes characterized by sandstone gneiss slate and carbonate rocks since the last pre wisconsinan glaciation 130 ka inferred to be late illinoian each terrane responded differently to chemical and mechanical weathering during the sangamon interglacial stage 130 75 ka in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep highly weathered soil and saprolite and dissolution of carbonate rocks cold climatic conditions during the wisconsinan on the other hand induced erosion of the landscape at rates faster than soil development upland erosion during the wisconsinan removed pre wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium grezes litees and alluvial fans on footslopes fluvial gravel and overlying colluvium in the delaware valley both buried by late wisconsinan outwash are inferred to represent episodes of early and middle wisconsinan 75 25 ka upland erosion and river aggradiation followed by river degradation and colluvium deposition early middle wisconsinan colluvium is more voluminous than later colluvium despite colder possibly permafrost conditions during the late wisconsinan 25 10 ka extensive colluviation during the early and middle wisconsinan resulted from a longer 50 kyr generally cold interval of erosion with a greater availability of easily eroded pre wisconsinan surficial materials on uplands than during the late wisconsinan after recession of late wisconsinan ice from its terminal position soil formation and landscape stability were delayed until the holocene by a lingering cold climate slope erosion colluvium and alluvial fan deposition and eolian sedimentation late quaternary erosion in the delaware valley was dominated by glacial and periglacial processes during glacial stages during the warm interglacial stages soils developed on a more stable landscape these souls were easily colluviated by periglacial erosion during periods of intermittent cold climate

gas and water flow in an excavation induced fracture network around an underground drift a case study for a radioactive waste repository in clay rock summary the excavation damaged zone edz surrounding a drift and in particular its evolution is being studied for the performance assessment of a radioactive waste underground repository a specific experiment called cdz was designed and implemented in the meuse haute marne underground research laboratory url in france to investigate the edz this experiment is dedicated to study the evolution of the edz hydrogeological properties conductivity and specific storage of the callovo oxfordian claystone under mechanical compression and artificial hydration firstly a loading cycle applied on a drift wall was performed to simulate the compression effect from bentonite swelling in a repository drift bentonite is a clay material to be used to seal drifts and shafts for repository closure purpose gas tests permeability tests with nitrogen and tracer tests with helium were conducted during the first phase of the experiment the results showed that the fracture network within the edz was initially interconnected and opened for gas flow particularly along the drift and then progressively closed with the increasing mechanical stress applied on the drift wall moreover the evolution of the edz after unloading indicated a self sealing process secondly the remaining fracture network was resaturated to demonstrate the ability to self seal of the cox claystone without mechanical loading by conducting from 11 to 15 repetitive hydraulic tests with monitoring of the hydraulic parameters during this hydration process the edz effective transmissivity dropped due to the swelling of the clay materials near the fracture network the hydraulic conductivity evolution was relatively fast during the first few days low conductivities ranging at 10 10 m s were observed after four months conversely the specific storage showed an erratic evolution during the first phase of hydration up to 60 days some uncertainty remains on this parameter due to volumetric strain during the sealing of the fractures the hydration was stopped after one year and cross hole hydraulic tests were performed to determine more accurately the specific storage as well as the hydraulic conductivity at a meter scale all hydraulic conductivity values measured at the injection interval and at the observation intervals were all below 10 10 m s moreover the preferential inter connectivity along the drift disappeared specific storage values at the observation and injection intervals were similar furthermore they were in agreement with the value obtained at the injection interval within the second hydration phase 60 days after starting hydration the graphical abstract synthesizes the evolution of the hydraulic gas conductivity for 8 intervals since the beginning of the cdz experiment the conductivity limit of 10 10 m s corresponds to the lower bound hydraulic definition of the edz and it is demonstrated that edz can be sealed this is a significant result in the demonstration of the long term safety of a repository

evidence for the transition zone origin of some mg fe o inclusions in diamonds abstract inclusions of mg fe o fpc ferropericlase magnesiowustite were found in natural diamonds from several localities worldwide fpc is typically absent from upper mantle assemblages but expected to be common in the lower mantle in assemblages with mg fe sio3 perovskite this led to proposals that the inclusions originated in the earth s lower mantle reported here are the results from new experiments producing fpc bearing assemblages at 20 24 gpa and 1800 2000 c and the observations are explained with an analysis of the relevant phase relations these results suggest that some fpc inclusions could have originated at the base of the transition zone if the mantle temperatures were higher than 1800 c in this case a reaction of garnet with fpc could cause a seismic discontinuity near 660 km

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

determination of fe mg partitioning between perovskite and magnesiowustite the partition coefficient of fe and mg between perovskite and magnesiowostite k mg fe pv mw has been measured by adopting a b 2 o 3 catalyst technique the present experimental results demonstrate that k mg fe pv mw is a factor of two closer to unity than that obtained in previous studies k mg fe pv mw increases from 0 16 to 0 35 with increasing mg of magnesiowustite from 50 to 86 on the basis of these results the compositions of enstatite and magnesiowustite included in diamond imply that the temperature at the top of the lower mantle is 1870 2040 k the mg 100mg mg fe of perovskite and magnesiowustite at the top of the lower mantle are 93 and 82 83 respectively for a pyrolitic mantle model the upper bound of the lower mantle temperature estimated in this study do not allow a larger fraction of perovskite than the pyrolitic mantle

determining the origin of ultrahigh pressure lherzolites the occurrence of coesite and diamond in regional ultrahigh pressure metamorphic rocks requires that rocks formed at pressures of 3 to 4 gpa 100 to 120 km below the earth s surface have been transported back to the surface 1 1 l dobrzhinetskaya et al suggest that garnet lherzolite from

ultrahigh pressure phase relations in the system mg4si4o12mg3al2si3o12 high pressure phase relations in the system mg4si4o12 mg3al2si3o12 were investigated at pressures from 10 to 22 gpa and at a temperature of 1000 c the experimental results indicate that the maximum solubility of enstatite mg4si4o12 in pyrope mg3al2si3o12 is 80 mol enstatite at 15 gpa at pressures between 15 and 19 gpa the solubility is insensitive to pressure at 19 gpa garnet ilmenite transformation first occurs in enstatite composition at pressures above 19 gpa the compositional range of the ilmenite solid solution expands toward pyrope composition with increasing pressure based on the present experiments if pyrolite mantle is assumed the pyroxene garnet transformation appears at 350 400 km depth and garnet modified spinel and garnet spinel phase assemblages become stable successively up to 580 km depth at greater depths garnet decomposes to ilmenite garnet and hence the pyrolite mantle consists of ilmenite garnet spinel assemblage

experimental constraints on melting temperatures in the mgo sio2 system at lower mantle pressures eutectic melting curves in the system mgo sio2 have been experimentally determined at lower mantle pressures using laser heated diamond anvil cell lh dac techniques we investigated eutectic melting of bridgmanite plus periclase in the mgo mgsio3 binary and melting of bridgmanite plus stishovite in the mgsio3 sio2 binary as analogues for natural peridotite and basalt respectively the melting curve of model basalt occurs at lower temperatures has a shallower dt dp slope and slightly less curvature than the model peridotitic melting curve overall melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at 25 gpa liebske and frost 2012 de koker et al 2013 however at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low pressure experimental data and those calculated from atomistic simulations we find that our data are inconsistent with previously computed melting temperatures and melt thermodynamic properties of the sio2 endmember and indicate a maximum in short range ordering in mgo sio2 melts close to mg2sio4 composition the curvature of the model peridotite eutectic relative to an mgsio3 melt adiabat indicates that crystallization in a global magma ocean would begin at 100 gpa rather than at the bottom of the mantle allowing for an early basal melt layer the model peridotite melting curve lies 500 k above the mantle geotherm at the core mantle boundary indicating that it will not be molten unless the addition of other components reduces the solidus sufficiently the model basalt melting curve intersects the geotherm at the base of the mantle and partial melting of subducted oceanic crust is expected

coupled effects of phase transitions and rheology in 2 d dynamical models of subduction author s arredondo km billen mi abstract 2017 american geophysical union all rights reserved observations of seismicity and seismic tomography provide a present day constraint on the geometry of slabs within the mantle however it is challenging to directly relate the observed shape of slabs to their time evolution phase transitions modify the buoyancy forces within slabs affecting how slabs deform as they sink into the lower mantle and how forces are transmitted to the surface plates here we show that if the crustal shear zone is sufficiently weak 1020 pa s then the coupled effects of a compositionally dependent phase transition model and a stress dependent rheology lead to oscillatory plate speeds and trench motion in response to buckling and folding of the slab on average subducting plate velocity is 4 cm yr and trench motion is 0 7 cm yr however during folding subducting plate speed and trench motion increases by a factor of 3 and trench motion switches from advance to retreat in models with a higher viscosity shear zone 1021 pa s average plate speed is lower 2 cm yr and there is only trench advance stress dependent weakening due to increasing driving stresses can also cause unexpected changes in plate velocity i e decrease or no change in addition due to the added negative buoyancy from the phase transitions slab breakoff occurs in models with a yield stress 500 mpa because of the oscillatory motion of the trench long flat slabs do not form in the transition zone this suggests that other factors such as interaction of the slab with deep mantle flow may be required to create long flat slabs

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

melting experiments on the enstatite diopside join at 70 224 kbar including the melting of diopside melting relations on the enstatite diopside en mg2si2o6 di camgsi2o6 join including the compositions of crystalline phases and melts coexisting along the solidi were experimentally determined in the pressure range 70 224 kbar with a split sphere anvil apparatus ussa 2000 melting is peritectic in enstatite rich compositions at 70 124 kbar 1840 2100 c and eutectic at higher pressures while the diopside rich clinopyroxene melts azeotropically at 70 165 kbar and up to 300 c lower temperatures than the eutectic orthopyroxene is replaced with enstatite rich clinopyroxene at 120 kbar and 2090 c first garnet with 17 mol di forms on the solidus at 158 kbar and 2100 c two garnets coexist on the solidus at 165 183 kbar and 2100 c garnet coexists with casio3 perovskite at 183 224 kbar 2100 2230 c and two coexisting perovskites are stable at higher pressures the melting curve of diopside was determined at 80 170 kbar the slope becomes negative at 140 kbar and 2155 c at 170 kbar and 2100 c diopside with 96 di breaks down to garnet with 89 di and casio3 perovskite the new data were used to calculate an improved temperature pressure phase diagram for the cmas system which can be useful for estimating the mineralogy of the earth s upper mantle

peridotitic minerals of the nidar ophiolite in the nw himalaya sourced from the depth of the mantle transition zone and above the nidar ophiolite complex noc consists of a c 10 km thick ophiolite suite in the nw himalaya india the c 7 km thick lower ultramafic part of the ophiolite body terminates against the tso morari crystallines which represent the leading edge of the indian continental margin mineral inclusions from the peridotites in the lower ultramafic part of the noc were studied including c 2 c clinoenstatite disordered coesite and high pressure mg 2 sio 4 probably mg 2 sio 4 these minerals found in two lherzolite bodies from the ophiolite s mantle section were characterized by laser raman spectroscopy and electron micro probe analysis textural evidence supporting decompression from an ultra high pressure condition was also observed such as cr spinel exsolution needles in olivine crystals the systematic mineral phase transitions of coesite quartz high pressure clinoenstatite orthoenstatite and mg 2 sio 4 cr spinel exsolution needles in olivine suggest that the mantle section of the nidar ophiolite evolved from the deep mantle beneath a palaeo spreading centre the phase stabilities of these high pressure minerals require derivation from the depth of the mantle transition zone 410 660 km a transport mechanism for these minerals is suggested via dunite channels along a mantle adiabat in the focused convective flow below the spreading centre this mechanism brought these deep mantle phases into the ultramafic part of the noc these observations suggest that some part of the mantle section of the noc in the nw himalaya originated in a mid ocean ridge setting

high pressure minerals in shocked meteorites heavily shocked meteorites contain various types of high pressure polymorphs of major minerals olivine pyroxene feldspar and quartz and accessory minerals chromite and ca phosphate these high pressure minerals are micron to submicron sized and occur within and in the vicinity of shock induced melt veins and melt pockets in chondrites and lunar howardite eucrite diogenite hed and martian meteorites their occurrence suggests two types of formation mechanisms 1 solid state high pressure transformation of the host rock minerals into monomineralic polycrystalline aggregates and 2 crystallization of chondritic or monomineralic melts under high pressure based on experimentally determined phase relations their formation pressures are limited to the pressure range up to 25 gpa textural crystallographic and chemical characteristics of high pressure minerals provide clues about the impact events of meteorite parent bodies including their size and mutual collision velocities and about the mineralogy of deep planetary interiors the aim of this article is to review and summarize the findings on natural high pressure minerals in shocked meteorites that have been reported over the past 50 years

shock induced p t conditions and formation mechanism of akimotoite pyroxene glass assemblages in the grove mountains grv 052082 l6 meteorite akimotoite mg fe sio 3 ilmenite was encountered in shock induced melt veins of grove mountains grv 052082 a highly equilibrated low iron ordinary chondritic meteorite l6 coexistence of ringwoodite majorite and majorite pyrope solid solution indicates the shock pressure at 18 23 gpa and temperature of 2000 2300 c during the natural dynamic event most low ca pyroxene clasts entrained in the melt veins have been partially or entirely transformed into akimotoite pyroxene glass assemblages which contain micrometer sized areas with various brightness in the backscattered electron images different from the chemically homogeneous grains in the host rock fs 20 5 21 3 the transmission electron microscopy study of a focused ion beam fib slice from the heterogeneous areas shows that the assemblages are composed of feo depleted and heterogeneous akimotoite fs 6 19 crystals 100 nm up to 400 nm in size scattered in feo enriched and relatively homogeneous pyroxene glass fs 31 39 all analyses of the akimotoite pyroxene glass assemblages plot on a fractionation line in feo mgo diagram with the host rock pyroxene at the middle between the compositions of feo depleted akimotoite and the feo enriched pyroxene glass these observations are different from previous reports of almost identical compositions of akimotoite bridgmanite mg fe sio 3 perovskite or pyroxene glass to the host rock pyroxene chen et al 2004 ferroir et al 2008 ohtani et al 2004 tomioka and fujino 1997 which is consistent with solid state transformation from pyroxene to akimotoite and preexisting bridgmanite that could be vitrified the observed fractionation trend and the granular shapes of akimotoite suggest crystallization from liquid produced by shock melting of the host rock pyroxene and the pyroxene glass matrix was probably quenched from the residual melt however this interpretation is inconsistent with the static experiments that expect crystallization of majorite mg fe sio 3 garnet instead of akimotoite from pyroxene liquid sawamoto 1987 our discovery raises the issue on formation mechanisms of the high pressure polymorphs of pyroxene and places additional constraints on the post shock high pressure and high temperature conditions of asteroids

garnet and pyroxenes in the mantle a test of the majorite fractionation hypothesis experimental data are reported for the compositions of garnets and pyroxenes that coexist with liquid in the system cao mgo al2o3 sio2 cmas at 80 160 kbar all experiments were run using the uniaxial split sphere apparatus at stony brook our data have permitted a refinement of gasparik s 1990a thermodynamic analysis of garnets and pyroxenes that occur at arid below the solidus our results should provide precise estimates of the temperature pressure conditions at which peridotite and garnet xenoliths equilibrated in the mantle an examination is also made of the composition of garnet that crystallizes as a liquidus phase it is demonstrated to be a function of both composition and pressure pressure has the effect of changing the composition of garnet from pyropic at around 80 kilobars to pyroxene like majorite at pressures in excess of 140 kbar changes that mirror those seen for garnets in the subsolidus failure to consider the effects of pressure on the composition of liquidus garnet can result in an erroneous test of the hypothesis that garnet fractionation occurred in early earth history it is shown that primitive mantle peridotite could have formed as a liquid by 35 majorite garnet fractionation from a cv chondrite like allende at 200 260 kbar these results support the hypothesis that extensive or possibly total melting occurred during the growth of the earth by accretion of planetesimals e g davies 1985 abe and matsui 1985 stevenson 1987 wetherill 1990 and that majorite fractionation could have occurred during this time ohtani and sawamoto 1987 removal of majorite to the lower mantle during the crystallization of a magma ocean is a successful way of explaining differences in mgo sio2 and cao al2o3 between mantle peridotite and chondrite

melting and subsolidus relations of sio2 at 9 14 gpa experiments were performed on amorphous silica at temperatures of 1000 2850 c and pressures of 9 14 gpa using a 2000 t uniaxial split sphere multianvil apparatus ussa 2000 the melting curve of coesite was extended from 8 to 13 7 gpa and the melting temperatures indicate a slope that is almost independent of pressure melting of stishovite was observed at 2850 c and 14 gpa the triple point for coexisting coesite stishovite and melt was located at 2800 c and 13 7 gpa the coesite stishovite phase transition was determined between 2000 and 2800 c and is described by the equation p gpa 5 8 4 0 0028 2 t c the resulting dp dt slope is more than twice that determined in the in situ x ray study of yagi and akimoto 1976 the present coesite stishovite boundary cannot be predicted by existing thermodynamic data e g fei et al 1990 which suggests some uncertainties in the extrapolation of heat capacities of coesite and stishovite at high temperatures thermodynamic extrapolations of the metastable melting curves of quartz and coesite show a strongly negative slope and thus are consistent with the proposal that the room temperature amorphization of quartz and coesite results from crossing of the metastable extension of their melting curves

structure and sharpness of phase transitions and mantle discontinuities the structure of phase transitions expected from equilibrium thermodynamics is examined we show that in binary systems the shape of the coexistence region phase loop is controlled primarily by the partition coefficient k we derive a general and simple one parameter expression for the pressure dependence of the yield of the high pressure phase and show that this function can be highly nonlinear most of the transition occurs in a narrow interval near the boundary of the phase loop estimates of the effective width of binary phase transitions are less than half the total width of the coexistence region even for relatively mild partitioning k 1 4 we generalize these results to multiphase and multicomponent transitions we show that the presence of nontransforming phases can affect the width of the transition substantially we predict that the width of the olivine to wadsleyite transition in the presence of pyroxene and garnet is approximately half that of the binary phase loop at typical transition zone temperatures the estimated effective width of this transition in the mantle 4 8 km is marginally consistent with observations of high frequency 0 5 1 0 hz p wave reflections from the 410 km discontinuity we show that the effective width of the garnet to perovskite transition is sufficiently narrow to reflect s wave energy in the frequency range of scs reverberations 10 40 mhz and that this transition can account for the observed properties of the 710 km discontinuity

thermal and petrological consequences of melt migration within mantle plumes the high temperatures and high degrees of melting expected in the core of mantle plumes have virtually no expression in the eruption temperatures of hotspot lavas nor in the composition of their glasses which is restricted in the basaltic field a solution to this paradox is looked for in the melt migration processes within the melting region of mantle plumes three dimensional convective calculations at rayleigh number of 10 6 allow estimates of the possible temperature melt fraction and stress fields within a plume two regions with different melt migration patterns can be distinguished a lower zone ranging in depth from the base of the melting region 150 km to around 80 100 km where the first melt fraction is redistributed in a sub horizontal vein network and convects in response to the steep horizontal temperature gradient this process is able to homogenize the temperature within the melting region very efficiently the high 300 c temperature contrast between the centre of the plume and the surrounding mantle can be reduced to a few tens of degrees at the top of this zone fractional crystallization of high pressure phases will strongly modify the composition of the melt as it circulates toward the periphery of the melting region a second upper zone where the sub vertical vein orientation will make possible rapid melt migration toward the surface extends to the base of the lithosphere due to the buffering of the plume temperature around a value close to the mean upper mantle temperature the degree of adiabatic melting within this upper zone will not greatly exceed that beneath normal spreading centres even in the case of on ridge hotspots the lavas erupted at hotspots are likely to result from the mixing in various proportions of these low pressure melts basalts with the highly evolved liquids possibly with kimberlitic to alkalic affinities resulting from fractional crystallization of the high pressure melt fractions produced at the base of the melting region this scenario could account for the low eruption temperatures and mg contents of hotspot lavas in spite of a complex high pressure and thus high temperature history evidenced by some geochemical trends

melting of enstatite mgsio3 from 10 to 16 5 gpa and the forsterite mg2sio4 majorite mgsio3 eutectic at 16 5 gpa implications for the origin of the mantle a split sphere multianvil apparatus clissa 2000 has been used to determine the melting curve of enstatite mgsio3 from 10 to 16 5 gpa and the forsterile mgio majoritc mgsio3 euteetic at 16 5 gpa use of a new capsule material rhenium allowed long runs of up to 2 hours at temperatures up to 2380oc with no observed contamination of the sample and with stable temperature control melting temperatures of enstatite are up to 160oc higher than those of kato and kumazawa 1986a two invariant points have been located one for orthoenstatite linoenstatite liquid at 2230oc 11 9 gpa and one for clinoenstatite majoritc liquid at 2370oc 16 4 gpa forsteritc melts incongruently at 2350oc 16 5 gpa to liquid and anhb 0vlglnsiso24 in the system mg2sio4 mgsio3 at 16 5 gpa the forsterite majorite eutectic has been located at 34 wt mg2sio4 a composition similar to that determined by karo and kumazawa 1986a at 20 gpa but much lower in mg2sio4 than several previous estimates based on melting experiments on mantle peridotitc compositions this forstefite poor location for the cuteerie is in apparent conflict with the suggestion that the peridotitic upper mantle is a crystallized cuteeric like liquid formed at about 16 gpa

low s velocities under the tornquist teisseyre zone evidence for water injection into the transition zone by subduction a strong low s velocity anomaly at 300 500 km depth coincides with the western boundary of the russian platform the anomaly is too large to be explained by a simple temperature anomaly or by compositional variations nor is it an artifact induced by seismic anisotropy we present a model that explains the anomaly through the injection of water at the time of closure of the tomquist ocean that separated the continents of avalonia and baltica in the early paleozoic dense hydrous magnesium phases are the most likely agents for transporting water to the transition zone but an important role may also be played by nominally anhydrous clinopyroxene when these minerals are brought out of their stability field water is released it may accumulate in spinel or k amphibole and may be released when the mantle warms up after subduction halts the effect of this water is to induce weakening of the shear modulus or even creation of a heavy melt by a conservative estimate a subduction episode lasting 85 m y would inject enough water to saturate a large volume of mantle rock with 0 3 h2o low velocities or low q anomalies have also been observed in the transition zones near currently active slabs

the breakdown of diopside to ca rich majorite and glass in a shocked h chondrite fine grained assemblages of majorite and glassy grains are for the first time identified in a shock induced melt vein in an h chondritic meteorite the bulk chemical composition of these aggregates is similar to that of diopside camgsi2o6 in the host rock both majorite and glassy grains are ca rich and their formulae can be approximated as mg0 65fe0 09ca0 26 sio3 and mg0 23fe0 05ca0 72 sio3 respectively these ca rich assemblages are dissociation products of the host diopside and were produced at 18 24 gpa by a shock event the casio3 rich glass is inferred to have crystallized in a perovskite structure but was vitrified during the pressure release

sh velocity and compositional models near the 660 km discontinuity beneath south america and northeast asia 1 we constrain sh wave velocity structures near the 660 km discontinuity beneath south america and northeast asia using triplicated phases near the discontinuity recorded in the epicentral distance range of 10 35 for three deep events we then explore mineralogical and compositional models appropriate for explaining the inferred seismic structures between the two regions sh velocity structures near the 660 km discontinuity are found to be different in the two regions beneath south america the velocity gradient above the 660 km discontinuity is larger than that of preliminary earth reference model prem while the velocity jump across the discontinuity is the same as prem beneath northeast asia the velocity gradient above the 660 km discontinuity is the same as that of prem while the velocity jump across the discontinuity is larger than prem both regions are characterized by a large velocity gradient extending about 80 km deep below the 660 km discontinuity the different velocity structures require different mineralogical models in the transition zone in the two regions the larger velocity gradient above the 660 km discontinuity beneath south america requires existence of the ilmenite phase in the bottom of transition zone while that beneath northeast asia can be explained by the temperature and pressure dependence of elastic properties of the major mantle mineral assemblages the observed large velocity gradients in the top of the lower mantle can be explained by gradual transformation of garnet to perovskite persisting to greater depths the velocity jump across the 660 km discontinuity beneath south america in the presence of the ilmenite phase in the bottom of the transition zone requires a bulk composition of more garnet than the pyrolite model while a larger velocity jump across the discontinuity beneath northeast asia requires a larger fraction of garnet transforming to perovskite across the discontinuity than what is required for explaining prem these different mineralogical models can be caused by different mantle temperature or composition especially the aluminum content in mantle composition the presence of garnet 80 km below the 660 km discontinuity in the two regions may be explained by a uniform composition in the lower mantle with an aluminum content of 3 4 the existence of ilmenite in the bottom of the transition zone beneath south america and the absence of ilmenite beneath northeast asia can be explained by either a difference in mantle temperature of about 100 c with that beneath south america being lower between the two regions assuming a uniform mantle composition or alternatively a difference in aluminum content of about 1 with that beneath south america being lower between the two regions without invoking a temperature difference between the two regions we also discuss conditions of mantle composition and temperature that double discontinuities may occur near the 660 km depth as well as the depth separation and velocity jumps of the double discontinuities for the inferred mantle temperature and composition beneath south america and northeast asia the maximum separation of the double discontinuities is 20 km and cannot be resolved by the sh wave data

stability of dense hydrous magnesium silicate phases and water storage capacity in the transition zone and lower mantle abstract we evaluated the water storage capacity in the mantle based on the phase relations of silicate systems containing water we conducted high pressure and temperature synthesis experiments on some silicate systems such as the superhydrous phase b phase c and phase g phase d and f compositions in the mgo sio2 h2o system and the cmas pyrolite 2 wt h2o system up to the uppermost part of the lower mantle superhydrous phase b is stable at temperatures below 1200 c at 18 gpa and below 1300 c at 20 gpa the following reaction sequences were observed with increasing temperature from 1200 to 1600 c in the pressure range from 18 to 20 gpa superhydrous phase b phase b liquid wadsleyite periclase liquid anhydrous phase b periclase liquid phase g is stable at temperatures below 1000 c at 18 gpa below 1100 c at 20 22 gpa and below 1200 c at 25 gpa wadsleyite stishovite liquid are stable above 1000 c at 18 gpa ringwoodite or phase e stishovite liquid above 1100 c at 22 gpa ilmenite stishovite liquid above 1100 c at 23 5 gpa and perovskite stishovite liquid above 1200 c at 25 gpa superhydrous phase b is stable at 1200 c at 18 5 and 25 gpa in cmas pyrolite 2 wt h2o composition whereas it decomposes at around 1400 c at 25 gpa in the composition there may be a layered structure in the mantle in its water storage potential solubility of water per unit mass i e the upper and lower mantles have relatively small water storage potentials whereas the transition zone has a larger potential the water content in the transition zone might be large because the primordial water trapped in the lower mantle and the recycled water transported by the slab subduction might have been released upwards and stored in the transition zone during geological time

metastability of enstatite in deep subducting lithosphere olivine and mg fe sio3 pyroxene the most abundant minerals in the earth s upper mantle are believed to transform to high pressure phases at 400 km depth1 5 the possible metastable persistence of olivine to greater depths in some subduction zones with consequences for the origin of deep focus earthquakes and the dynamics of subduction has been discussed extensively6 14 but the role of other mantle minerals has not been considered we report here an experimental study of the kinetic behaviour of the magnesian pyroxene enstatite mgsio3 at upper mantle conditions we find that whereas forsterite mg olivine mg2sio4 transforms rapidly to phase at 1 200 c and 16 gpa the transformation of enstatite to phase plus stishovite on the same timescale requires much higher temperatures at lower temperatures enstatite transforms directly to the ilmenite structure but only at pressures greater than 20 gpa enstatite should therefore persist metastably to greater depths than olivine in subduction zones transforming directly to the ilmenite structure the enstatite ilmenite transformation is accompanied by a large decrease in volume which should increase the stresses in subducting slabs change the buoyancy forces that drive subduction and might also contribute to the origin of deep focus earthquakes

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

a model for the layered upper mantle abstract numerical modeling of mantle convection by liu 1994 science 264 1904 1907 favors a two layer convection if the results are reinterpreted for the correct phase relations in mg fe 2sio4 the resulting chemical isolation of the upper and lower mantle suggests a highly differentiated and layered upper mantle to account for the discrepancy between the observed compositions of mantle xenoliths and the cosmic abundances of elements it is shown that a layered upper mantle with a hidden reservoir can have a structure consistent with the observed seismic velocity profiles and an average bulk composition corresponding to the cosmic abundances the evolution of the upper mantle and the origin of komatiites are discussed in the context of the proposed model

partitioning of rare earth elements between casio3 perovskite and coexisting phases constraints on the formation of casio3 inclusions in diamonds minerals with casio3 composition were found as inclusions in diamonds and are considered to be originally of perovskite structure to constrain their genesis and consequently the extent of circulation of mantle material rare earth element ree partitioning between casio3 perovskite and coexisting majoritic garnet 20 gpa 1520 c or mgsio3 perovskite 25 gpa 1600 c was determined by combining the technologies of high pressure synthesis and trace element analysis using ion probe it is consistent with previous experiments and confirms that casio3 perovskite is the main ree depository especially of the light ree kce capv gt is 1900 and decreases gradually to 18 5 of kyb capv gt for capv mgpv it decreases gradually from 57 7 of kce to about 10 of kyb estimated ree concentrations in the source lithology of the casio3 inclusions according to these partitioning coefficients either peridotitic or eclogitic paragenesis show strong enrichment in light ree e g cen 18 163 very different from normal mantle peridotite and subducted oceanic crust it is proposed that interaction with carbonatic melt in the deep mantle may have played an important role in the formation of these casio3 inclusions in diamonds as well as in their ascending transportation

phase relations and formation of sodium rich majoritic garnet in the system mg 3 al 2 si 3 o 12 na 2 mgsi 5 o 12 at 7 0 and 8 5 gpa the pseudo binary system mg3al2si3o12 na2mgsi5o12 modelling the sodium bearing garnet solid solutions has been studied at 7 and 8 5 gpa and 1 500 1 950 c the na bearing garnet is a liquidus phase of the system up to 60 mol na2mgsi5o12 nagrt at higher content of nagrt in the system enstatite up to 80 mol and then coesite are observed as liquidus phases our experiments provided evidence for a stable sodium incorporation in garnet 0 3 0 6 wt na2o and its control by temperature and pressure the highest sodium contents were obtained in experiments at p 8 5 gpa near the liquidus t 1 840 c the equilibrium concentration of na2o in garnet is 0 7 0 8 wt 6 mol na2mgsi5o12 with the temperature decrease na concentration in grt increases and the maximal na2mgsi5o12 content of 12 mol 1 52 wt na2o is gained at the solidus of the system t 1 760 the data obtained show that most of natural diamonds with inclusions of na bearing garnets usually containing 1 wt na2o may crystallize at a pressure range of 7 0 8 5 gpa however the upper pressure limit for the formation of naturally occurring na bearing garnets is restricted by the eclogite garnetite bulk composition

phase relations on the diopside jadeite hedenbergite join up to 24 gpa and stability of na bearing majoritic garnet abstract phase relations on the diopside di hedenbergite hd jadeite jd system modeling mineral associations of natural eclogites were studied for the compositions mol di70jd30 di50jd50 di30jd70 di20hd80 and di40hd10jd50 using a toroidal anvil with hole 7 gpa and a kawai type 6 8 multianvil apparatus 12 24 gpa we established that di hd and jd form complete series of solid solutions at 7 gpa and melting temperatures of pure di 1980 c and jd 1870 c for that pressure were estimated experimentally the melting temperature for the di50jd50 composition at 15 5 gpa is 2270 c the appearance of garnet is clearly dependent on initial clinopyroxene composition at 1600 c the first garnet crystals are observed at 13 5 gpa in the jadeite rich part of the system di30jd70 whereas diopside rich starting material di70jd30 produces garnet only above 17 gpa the proportion of garnet increases rapidly above 18 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites are produced from diopside rich starting materials in all experiments garnet coexists with stishovite st at a pressure above 18 gpa pyroxene is completely replaced by an assemblage of majorite maj st casio3 perovskite ca pv in ca rich systems whereas maj is associated with almost pure jd up to a pressure of 21 5 gpa above 22 gpa maj and st are associated with naalsio4 with calcium ferrite structure cf we established that an hd component also spreads the range of pyroxene stability up to 20 gpa in the di70jd30 system at 24 gpa an assemblage of maj ca pv mgsio3 with ilmenite structure mg il was obtained the experimentally established correlation between na si and al contents in maj and pressure in grt maj pyroxene assemblages may be the basis for a majorite geobarometer the results of our experiments are applicable to the upper mantle and the transition zone of the earth 400 670 km and demonstrate a wide range of transformations from eclogite to perovskite bearing garnetite in addition the mineral associations obtained from the experiments allowed us to simulate parageneses of inclusions in diamonds formed under the conditions of the transition zone and the lower mantle

tem observations of several spinel garnet assemblies toward the rheology of the transition zone in order to better identify the mineral phase which controls the rheology of the transition zone between 410 and 660 km depth transmission electron microscopy observations were made on several coexisting spinel garnet assemblies alkremite xenolith pyrope rich mgo 1 1al2o3 spinel assembly deformed at 1173k 800 mpa in a griggs apparatus mg fe 3 al mg si 2si3o12 majorite mg fe 2sio4 spinel assembly synthesized in a laser heated diamond anvil cell it was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed these results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel in the conditions of the transition zone

upper mantle sh and p velocity structures and compositional models beneath southern africa abstract we constrain sh and p wave velocity structures in the upper mantle beneath southern africa using triplicated phases recorded in the epicentral distance range of 11 28 for one shallow event we then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region both sh and p wave data suggest presence of a low velocity zone with velocity reductions of at least 5 for s waves and 2 for p waves beneath a 150 km thick high velocity lithospheric lid seismic observations also suggest that the p s ratio is larger 1 88 in the transition zone than in the lithospheric lid 1 70 the inferred p wave velocity jump across the 660 km discontinuity is small

the al 2 o 3 contents of enstatite in equilibrium with garnet in the system mgo al 2 o 3 sio 2 at 15 40 kbar and 900 1 600 c forty six reversed determinations of the al2o3content of enstatite in equilibrium with garnet were made in the p t range 15 40 kbar 900 1 600 c in the mgo al2o3 sio2 system starting materials were mixtures of synthetic pyrope al free enstatite and pyrope enstatite 5 12 al2o3 al2o3 contents in reversal run pairs closely approached common values from both the high and low al sides most experiments were done in a piston cylinder device using a nacl medium some runs at very high temperatures were made in pyrex nacl or pyrex talc assemblies the measured enstatite compositions expressed as mole fractions of mg2 mgal alsi3 o12 x opy en were fitted by a monte carlo method to the equilibrium condition begin gathered delta h 970 0 970 delta s 970 0 hfill mathop smallint limits 1 p delta v 970 0 dp mathop smallint limits 970 t delta s t 0 dt rt ln x opy en 0 hfill end gathered where the best fit parameters of h s and v 1 bar 970 k for the reaction pyrope opy are 2 040 cal mol 2 12 eu and 9 55 cc mol in addition to the determination of al2o3 contents of enstatite the univariant reaction pyrope forsterite enstatite spinel was reversibly located in the range 1 100 1 400 c a best fit line passes through 22 22 5 and 25 kbar at 1 040 1 255 and 1 415 c respectively our results for the univariant reaction are in agreement with previous studies of macgregor 1974 and haselton 1979 however comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated h f 970 1 0 value for enstatite a value of 8 32 rather than 8 81 kcal mole charlu et al 1975 is consistent with the present data application of garnet enstatite spinel forsterite equilibria to natural materials is fraught with difficulties the effects of nonternary components are poorly understood and the low solubilities of al2o3 in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive more detailed studies including reversed determinations in low friction assemblies are sorely needed before the effects of important diluents such as fe ca and cr can be fully understood

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

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

anisotropy of akimotoite a molecular dynamics study elastic constants of akimotoite at high temperatures and pressures are calculated by using molecular dynamics simulations to study the anisotropic properties of akimotoite we find that akimotoite becomes more anisotropic with increasing temperature but less with increasing pressure on the 0 0 1 face s wave splitting and azimuthal anisotropy will occur simultaneously while the p wave velocity remains almost constant polarization directions of the two s waves are neither strictly perpendicular nor parallel to the crystallographic face the polarization direction of the fast s wave is more parallel with the plane than that of the slow s wave for all wave propagation directions on the 1 0 0 face no s wave splitting will occur for waves passing along the crystallographic c axis and the p wave velocity along the axis is smaller than that in other directions polarization anisotropy changes its sign with the variation of wave propagation directions giving rise to the dependence of the relative magnitude of vsh and vsv on the seismic wave propagation directions we further calculate the anisotropic properties of a mineral assemblage containing ringwoodite akimotoite and ca perovskite to infer the effect that akimotoite may have on the anisotropy of the lower portion of the mantle transition zone we find that the mineral assemblage is much less anisotropic than akimotoite but possesses many anisotropy features of akimotoite comparison of the anisotropy features with seismological observations indicates that a vertical flow direction is required in areas close to the subduction zones which may be caused by the downward penetration of slabs to the lower mantle as well as upwelling of fluids and light materials in the mantle wedge associated with deep dehydration reactions of the slabs 2005 elsevier b v all rights reserved

study of the mggeo 3 polymorphs orthopyroxene clinopyroxene and ilmenite structures by calorimetry spectroscopy and phase equilibria

high temperature deformation of diopside single crystal 1 mechanical data laboratory deformation experiments were carried out on diopside single crystals creep tests were made in a dead load apparatus at temperatures t 1020 to 1320 c axial compressive stresses 50 to 170 mpa with strain rates e ranging from 2 10 9 s 1 to 4 10 7 s 1 the specimens were oriented such that mechanical twinning was not possible the experiments were designed to activate 110 1 2 a b slip systems our results demonstrate that they are the major operative systems for t 1000 c and appear to be predominant over the 100 c slip system the mechanical data are fitted to a power law e a n exp e rt an inversion method was used to determine the parameter in a the activation energy e and the stress exponent n below a critical temperature tc 1130 1140 c e is found to be 440 30 kj mol associated with the 110 1 2 a b slip systems activated symmetrically without any contribution from the 100 c system orientation 2 e is found equal to 740 30 kj mol if all three systems have the same resolved shear stresses orientation 1 for t tc values of e drop to 50 15 and 85 30 kj mol for orientations 2 and 1 respectively so that the creep law of diopside becomes nearly temperature independent the law derived from the orientation 2 crystals could be consistent with natural deformations for this orientation and within the range of temperatures covered n is 6 5 0 4 the strong decrease in the activation energy at tc may be ascribed unambiguously to the occurrence of partial melting leading to microdroplets which pin the mobile dislocations ingrin et al this issue the high value found for the stress exponent n in the creep law suggests that clinopyroxene is softer than olivine at high stresses at t 900 c stress 20 mpa and e 10 15 s 1 while olivine is softer at lower stresses this competence inversion is predicted to occur within the ranges of stresses and strain rates expected in the lower crust and upper mantle

dislocation microstructures in majorite garnet experimentally deformed in the multi anvil apparatus majorite garnets with the composition mj70py30 have been deformed in the multi anvil apparatus at 17 gpa and 2000 c the microstructure has been characterized by transmission electron microscopy it is shown that under these conditions majorite garnet is ductile dislocations with and burgers vectors are observed with a density 1 5 1012 m 2 the absence of clear glide planes and the occurrence of subgrain boundaries suggest the importance of diffusion and climb in the plasticity of majorite garnets in mantle transition zone conditions

stability of clinopyroxene at pressure temperature conditions of the transition region abstract the stability of diopside at conditions of 16 19 gpa and 1250 1900 c was determined using a 6 8 type multi anvil apparatus at pressures of 17 18 gpa diopside undergoes a decomposition reaction to an assemblage of casio3 perovskite ca mg sio3 garnet or ilmenite depending on temperature the clapeyron slope for the breakdown reaction download download full size image is 2 mpa k 1 when coupled with a re examination of clinopyroxene stability in other more complex peridotite systems the experimental data are consistent with a recent proposal that the 520 km discontinuity in the transition region is caused by the exsolution of casio3 rich perovskite from garnet rich in majorite component

effects of phase transions and possible compositional changes on the seismological structure near 650 km depth if the lower mantle is enriched in fe si relative to the upper mantle the compositional boundary is expected to be an interface with a density jump of 5 2 and with depth varying laterally by 100 300 km but with changes in seismic velocities that are nearly unobservable 0 to 1 0 2 5 discontinuities in compressional vp and shear vs wave velocities in contrast the polymorphic transformation of transition zone minerals to the perovskite bearing assemblage of the lower mantle is estimated to produce a jump of 5 10 percent in density vp and vs near 650 km depth and the depth of the seismological discontinuity due to the phase transition is relatively independent 50 150 km variation of temperature or horizontal position if present a compositional boundary is not in general expected to occur at the identical depth 650 km as the phase transition to the perovskitebearing assemblage although the depths of the two may be linked

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

elastic wave velocities of pyrope majorite garnets py62mj38 and py50mj50 to 9 gpa abstract polycrystalline specimens of two pyrope majorite garnets 2 py 62 mj 38 and py 62 mj 38 were synthesized in a 2000 ton uniaxial split sphere apparatus ussa 2000 at pressures of 16 gpa and temperatures of 1670 k for run durations of about 2 h using homogeneous glasses as starting materials ultrasonic interferometric measurements on these specimens were conducted at pressures up to 9 gpa at room temperature using a 1000 ton uniaxial split cylinder apparatus usca 1000 with bi as an internal pressure marker from the measurements of the travel times for compressional p and shear s waves the velocities and elastic moduli are calculated using length density changes determined from the travel time data third order eulerian finite strain analysis of these data yield the longitudinal l and shear g moduli and their pressure derivatives m 0 m p t for py 62 mj 38 l 0 291 6 gpa and l 0 9 1 0 6 g 0 90 1 gpa and g 0 1 9 0 2 from which we calculate the values for the adiabatic bulk modulus k l 4 3 g to be k 0 171 5 gpa and k 0 6 2 0 5 these new data for the shear modulus and its pressure derivative are in agreement with the previous values for the same composition rigden s m gwanmesia g d liebermann r c 1994 elastic wave velocities of a pyrope majorite garnet to 3 gpa phys earth planet inter 86 35 44 but the p wave velocity the bulk modulus and its pressure derivative are somewhat higher for the py 50 mj 50 composition these values are l 0 289 6 gpa l 0 9 2 0 7 g 0 89 1 gpa g 0 2 1 0 2 k 0 170 5 gpa and k 0 6 4 0 5 the high pressure derivatives of k and g for these py mj garnets may be important in explaining the high velocity gradients observed in seismic models of the transition zone of the earth s mantle

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

modeling lower mantle anisotropy development in a subducting slab a model is presented that simulates anisotropy development in a subducting slab from the upper lower mantle boundary 661 km to the core mantle boundary 2891 km two phases are considered orthorhombic mgsio3 perovskite and cubic magnesiowuestite mg fe o single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmonic approximation it is assumed that deformation is accommodated by slip a polycrystal plasticity model predicts strong texture development for perovskite and weaker texture for magnesiowuestite when averaging single crystal elastic properties with the orientation distribution this results for both phases in weak p wave anisotropy and shear wave splitting in the upper part of the lower mantle but pronounced anisotropy near the core mantle boundary up to 4 for vp and 7 for vs the anisotropy pattern is complex and asymmetric and local heterogeneity is expected these predictions are consistent with seismic observations

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

phase transformations in diopside camgsi2o6 at pressures up to 25 gpa phase transformations in diopside have been studied at pressures up to 25 gpa and at temperatures of 1100 and 1500 c by a multiple anvil apparatus the following phase assemblages are found to be stable at given pressures diopside 15 and 18 gpa mg2sio4 spinel stishovite casio3 perovskite 19 and 20 gpa mgsio3 ilmenite casio3 perovskite 22 gpa and mgsio3 perovskite casio3 perovskite 24 5 gpa electron microprobe analysis reveals that the solubility of the mgsio3 molecule in casio3 cubic perovskite is limited to between 2 5 the solubility of the casio3 molecule in mgsio3 orthorhombic perovskite is more restricted being of the order of 2 or less these results are contradictory to earlier work in which diopside is reported to transform into a cubic perovskite structure of the same composition above 22 23 gpa

transformation induced faulting requires an exothermic reaction and explains the cessation of earthquakes at the base of the mantle transition zone abstract in many subduction zones earthquakes occur continuously to the bottom of the mantle transition zone and stop abruptly at the endothermic phase change marking the top of the lower mantle suggesting cause and effect new experiments on polycrystals undergoing the ilmenite perovskite transformation show that transformation induced faulting occurs only in the exothermic direction of the reaction the close structural and thermodynamic analogies between the transformation studied here in cdtio 3 and those expected in the silicates of the earth s mantle argue strongly that these results are relevant to transformations occurring in subducting lithosphere moreover consideration of the thermodynamics of this asymmetry show that this result should be a general phenomenon if so it follows that faulting by this mechanism cannot occur in the lower mantle providing a natural explanation for the termination of earthquakes just before 700 km depth if a wedge containing metastable olivine exists at depth in subduction zones and is necessary for deep earthquakes our results remove the constraint that this wedge must taper to zero where the deepest earthquakes occur the characteristics of the large deep earthquakes of 1994 and their aftershocks show that deep earthquakes can propagate beyond the zone of previous hypocenters and trigger aftershocks there providing important new information about the mechanism of deep earthquakes and pointing to the need for additional experiments

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

shock induced transition of naalsi3o8 feldspar into a hollandite structure in a l6 chondrite natural naalsi3o8 hollandite was found in the tenham chondrite it occurs as aggregates of extremely fine grains of several tens of nanometers the hollandite phase seems to have formed from host feldspar in a solid state reaction during the shock event it is very sensitive to electron beam irradiation and easily becomes amorphous similar to mgsio3 perovskite contained in the same chondrite the existence of crystalline silicate perovskite and hollandite in tenham indicates that the peak pressure and the post shock temperature were much lower than previously believed

microstructure and composition of brittle faults in claystones of the mont terri rock laboratory switzerland new data from petrographic studies geophysical borehole logging and permeability tests abstract claystones are considered as a geological barrier however the properties of claystone may be modified if these are cut by brittle faults and fractures investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations the present study is dealing with the characterization of naturally and artificially deformed opalinus clay of the mont terri rock laboratory in nw switzerland complete core sections covering the artificially excavation damaged zone edz and several tectonic fault zones have been studied using a multidisciplinary approach consisting of geophysical geotechnical mineralogical geochemical and lithological structural data the fault zones encountered are characterized by a high density of planar discontinuities which often show slickenside striations under the microscope the fault zones turned out to be pervasively deformed resulting in open veins and pore space now filled with calcite and celestine fault zone reactivation led to very fine grained cohesionless fault gouge and fragmentation of the previously formed calcite veins packer tests in boreholes reveal excavation induced enhanced permeabilities up to 3 m borehole depth 1 9 m to gallery floor seismic borehole measurements indicate that seismic attributes which are typical for undisturbed opalinus clay are not reached until 7 5 m borehole depth 4 8 m to gallery floor which is larger than in the usual gallery configuration we interpret the anomalies in geophysical measurements as well as the elevated permeabilities measured in the main fault 3 6 m to 4 2 m to gallery floor to result from an enlarged edz influenced by the presence of the brittle fault structures the up to two orders of magnitude higher permeability compared to the intact claystone most probably results from excavation induced stress and a local reactivation of fault planes the results suggest that the presence of a fault zone can alter the extent of the edz significantly and thereby affect the rock integrity at least in the near field of a repository tunnel

melting experiments on the enstatite pyrope join at 80 152 kbar melting temperatures of the assemblage pyroxene garnet on the enstatite pyrope join were experimentally determined at 11 different pressures between 80 and 152 kbar with a split sphere anvil apparatus ussa 2000 the compositions of pyroxene garnet and melt coexisting along the solidus were also determined comparison with previous data at lower temperatures revealed a large temperature dependence of the compositions of garnet coexisting with pyroxene it is proposed that the observed variation in the garnet composition is caused by disorder in garnet the obtained alumina contents of orthopyroxene coexisting with garnet on the solidus at 80 110 kbar contributed to an improvement of the garnet peridotite thermobarometry an internally consistent set of thermodynamic parameters was derived which allows calculation of the temperature pressure phase diagram for the enstatite pyrope join at 20 260 kbar

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

variations in p wave speeds and outboard earthquakes evidence for a petrologic anomaly in the mantle transition zone we investigate the nature of laterally varying p wave speeds vp and their relationship to a group of unusual deep earthquakes beneath the backarc of tonga this subhorizontal swath of outboard earthquakes occurs within the transition zone of the mantle but is several hundred kilometers away from the inclined wadati benioff zone surprisingly the seismogenic region is not associated with fast vp it follows that the effect of cold temperature as implied by the presence of large earthquakes must have been counteracted by other factors such as compositional or mineralogical effects our results are based on a sequence of seismic profiles in a fan shot geometry for a given azimuthal sector we seek the simplest model of radially varying vp that explains observed broadband waveforms and travel times the lateral extent of anomalous vp is then constrained by comparing the results from a wide range of azimuths this approach fully utilizes information from triplicate p arrivals that are sensitive to seismic wave speeds at the depths of interest our results identify prominent anomalies of fast vp 3 over average earth models both in the transition zone and in the lower mantle beneath the tonga backarc however the region of fast vp in the transition zone is offset by 300 km to the south of that in the lower mantle and the region of offset coincides with the outboard earthquakes a straightforward interpretation is that a large flux of subducted pacific lithosphere lingers in the transition zone before descending into the lower mantle within this broad remnant of subducted lithosphere the outboard earthquakes occur in a region where impounding of subducted material is most significant a condition favorable for the accumulation of met astable olivine or volatiles such materials reduce vp and are candidates for triggering earthquakes thus accounting for the absence of fast vp in the source zone of deep earthquakes

slabs and shear wave reflectors in the midmantle 1 an extensive analysis of multiple scs reverberation data sets sampling regions of active or recent subduction reveals evidence of midmantle reflections apparently stemming from fragments of subducted slabs or from the interaction between subducted slabs and the surrounding mantle transition zone reflectors are detected beneath the southwest pacific ocean and melanesia with mean depths of 850 and 1100 km in the majority of source receiver corridors crossing the study area the observations are most spatially coherent beneath the coral and tasman seas coincident observations of the two reflectors along most seismic corridors suggests but does not mandate the existence of two distinct reflectors rather than bimodal depth distribution of a single reflector or distributed scatterers beneath north america reflectors at depths of 1380 and 1530 km are seen in the midcontinent region further east the reflections are shallower with depths near 940 and 1130 km unlike the southwest pacific the reflectors are not paired in any of the individual source receiver corridors this and the depth variability of the observations indicate that the reflector or reflectors in the americas is are fragmented from west to east transecting source receiver corridors the impedance contrasts of these features rival that of the 660 km discontinuity suggesting that individual fragments of the reflecting surfaces must be relatively continuous and flat from north to south along individual corridors to maintain a strong apparent impedance contrast the reflections in both study areas are unlikely to be the result of slabs interacting with a chemical boundary layer or small scale scatterers within the midmantle more likely these reflectors result from a pressure temperature dependent phase transition within or around subducting slabs

seismic constraints on mechanisms of deep earthquake rupture 1 observations of the depth distribution of seismicity suggest that several mechanisms cause deep earthquakes cold subducting slabs exhibit a broad peak in seismicity between 300 and 530 km depth that is best explained by transformational faulting of metastable olivine cumulative seismic moment release increases sharply at 530 km depth in both cold and warm slabs implying that events deeper than this are controlled by an equilibrium rather than a metastable phase change which would be temperature dependent this together with the observation that deep seismicity predominates near the garnet rich upper boundary of the subducting plate former oceanic crust suggests that the transformation of garnet to perovskite which may release considerable water is integral in the cause of earthquakes deeper than 530 km where most deep earthquakes occur

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

origin of mantle peridotite and komatiite by partial melting theoretical calculations and some preliminary experimental observations show that the liquidus and solidus temperatures for each of a wide range of upper mantle peridotite and komatiite compositions become coherent at high pressures this suggests that these materials may have been liquids in eutectic like equilibrium rather than peritectic like with mantle assemblages it is shown that the major element geochemistry of 83 mantle peridotites and 61 komatiites define a trend which is not primarily due to an olivine control process rather it is interpreted to represent the pressure induced compositional trace of eutectic liquids in equilibrium with mantle assemblages from 4 to 15 gpa if the bulk earth is chondritic in composition these phase equilibrium constraints would imply that the upper mantle had formed from the whole mantle as an ultrabasic partial melt the transition zone and lower mantle being the complementary eclogite and pyroxenite residua this is consistent with mineralogical interpretations of seismic data for the present day earth which call for a peridotite upper mantle and pyroxene like transition zone and lower mantle

melting of forsterite mg2sio4 from 9 7 to 16 5 gpa a multianvil apparatus has been used to determine the pressure temperature melting curve of forsterite from 9 7 to 16 5 gpa at 10 1 gpa a singular point occurs that marks the change from congruent melting at lower pressures to incongruent melting forsterite periclase liquid at higher pressures the melting curve also passes through two invariant points at one 15 6 gpa 2310 c the phases forsterite periclase anhydrous b and liquid coexist and the melting reaction changes from forsterite periclase liquid at lower pressures to forsterite anhydrous b liquid at higher pressures at the other 16 7 gpa 2315 c the phases forsterite modified spinel anhydrous b and liquid coexist and the melting reaction changes from forsterite anhydrous b liquid at lower pressures to modified spinel anhydrous b liquid at higher pressures the simon equation p gpa 2 44 t k 2171 11 4 1 fits both our melting curve data and the lower pressure data of davis and england 1964 at low pressures the melting curve of forsterite lies at higher temperatures than that of enstatite but the two curves cross at 13 3 gpa because of the lower dt dp slope of the forsterite melting curve this causes the forsterite enstatite eutectic to shift toward forsterite as pressure increases but our data are consistent with earlier findings that the shift is not sufficient to support an origin for the mantle by eutectic like melting at high pressures

elastic wave velocities of a pyrope majorite garnet to 3 gpa abstract the pressure dependence of the elastic wave velocities for a polycrystalline specimen 100 theoretical density of majorite pyrope garnet py 62 mj 38 has been determined at room temperature to 3 gpa by ultrasonic phase comparison interferometry pressure derivatives of the adiabatic bulk modulus dk s dp 5 3 and shear modulus dgdp 2 0 are derived from the travel times of the compressional p and shear s waves these derivatives clearly demonstrate that pressure has a more pronounced effect on the elasticity of the majorite rich garnet than on the pure pyrope end member presumably in response to the coupled substitution of si and mg for al on the octahedral site in the garnet structure when combined with plausible values for the as yet unmeasured temperature derivatives these new data can be used to calculate velocity depth profiles along a 1400 c adiabat for the range of depths in which majorite is expected to be stable in the transition zone of the earth s mantle 450 600 km for shear waves these majorite gradients match those from regional seismic models much better than those for a pure olivine mantle more reliable calculations of elastic wave velocities at mantle temperatures and pressures await measurement of the temperature derivatives of elastic modulus

high pressure polymorphs of magnesian orthopyroxene from a shock vein in the yamato 000047 lherzolitic shergottite abstract we found a simple thin shock vein less than or equal to about 60 m in width and 1 8 mm in length in the poikilitic area in the yamato y 000047 lherzolitic shergottite the shock vein occurs only in magnesian ca poor clinopyroxene which may have transformed from orthopyroxene during the pressure increase at the shock event the shock vein consists of mg0 8 fe0 2 sio3 pyroxene polymorphs such as columnar akimotoite two kinds of pyroxene glasses dendritic akimotoite and framboidal pyroxene glass in the order from the periphery to the center the compositions and textures suggest that columnar akimotoite in the periphery of the shock vein crystallized from solid state phase transition of clinopyoroxene during the cooling of the vein and the remains in the shock vein solidified from shock produced melt the glass includes two kinds of massive glass in the vein and framboidal glass in the vein center the framboidal glass is the most magnesian and may have been vitrified from perovskite crystallized from high pressure melt produced at high temperature 3000 c and high pressure 23 40 gpa dendritic akimotoites in the vein center metastably crystallized from residual shock melt the formation sequences of the constituent phases in the shock vein happen in the following order columnar akimotoites rim glass center glass framboidal glass and dendritic akimotoites the increase of the raman intensity of 660 670 cm 1 in the order of rim glass center glass and framboidal glass suggests that the formation of the pyroxene chain proceeds faster in the vein center than in the vein rim due to its slower cooling the finding of the shock vein consisting merely of high pressure polymorphs of pyroxene akimotoite and framboidal glass vitrified perovskite is the first reported among all martian meteorites

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe

quantitative characterization of the excavation damaged zone fracture network in the meuse haute marne underground research laboratory in situ experiment and numerical interpretation of helium injection test

experimental evidence for the origin of two kinds of inclusions in diamonds from the deep mantle abstract the conditions of origin for the type iii inclusions in diamonds from brazil hutchison thesis 1997 and the napx en inclusion from china wang and sueno miner j 18 1996 9 16 were experimentally determined using a split sphere anvil apparatus ussa 2000 the type iii inclusions formed at a minimum pressure and temperature of 25 gpa and 2000 c while the origin of the napx en inclusion was close to 23 gpa and 1900 c both determinations suggest that the temperature at the corresponding depths is about 300 c higher than predicted by most geotherms for a convecting mantle without a thermal boundary layer at 660 km both kinds of inclusions required rapid single stage transport by carbonate melt to the earth s surface which is consistent with the depths of origin for this melt greater than 660 km the unusual composition of the napx en inclusion is the result of metasomatism by carbonate melt enriched in na k and mg and depleted in si and al since this melt is not kimberlitic in composition exchange of material between the melt and the mantle was necessary for the melt to become kimberlitic by the time it reached the surface the resulting metasomatism taking place over a long period of time could cause major changes in the mineral and chemical composition and the structure of the earth s mantle and thus play an important role in its evolution