erratum to three dimensional distribution of gas hydrate beneath southern hydrate ridge constraints from odp leg 204 earth planet sci lett 222 2004 845 862

composition of aqueous fluid coexisting with mantle minerals at high pressure and its bearing on the differentiation of the earth s mantle in order to understand the role of aqueous fluid on the differentiation of the mantle the compositions of aqueous fluids coexisting with mantle minerals were investigated in the system mgo sio2 h2o at pressures of 3 to 10 gpa and temperatures of 1000 to 1500 c with an ma8 type multianvil apparatus phase boundaries between the stability fields of forsterite aqueous fluid forsterite enstatite aqueous fluid and enstatite aqueous fluid were determined by varying the bulk composition at constant temperature and pressure the composition of aqueous fluid coexisting with forsterite and enstatite can be defined by the intersection of these two phase boundaries the solubility of silicate components in aqueous fluid coexisting with forsterite and enstatite increases with increasing pressure up to 8 gpa from about 30 wt at 3 gpa to about 70 wt at 8 gpa it becomes almost constant above 8 gpa the mg si weight ratio of these aqueous fluids is much higher than at low pressure 0 2 at 1 5 gpa and almost constant 1 2 at pressures between 3 and 8 gpa at 10 gpa it becomes about 1 4 aqueous fluid migrating upward through the mantle can therefore dissolve large amounts of silicates leaving modified mg si ratios of residual materials it is suggested that the chemical stratification of mg si in the earth may have been formed as a result of aqueous fluid migration

geochemical evidence for an initially molten earth abstract the lithophile trace and major element characteristics of the upper mantle reflect crystal liquid fractionations at high temperatures in the interior of a global magma ocean in the earth the combined evidence from the lithophile and siderophile elements in the mantle is indicative of a substantially molten earth at the end of accretion thus the geochemical data from the mantle support the modern theories of planetary accretion which require an initially molten earth

silicate perovskite and majorite signature komatiites from the archean abitibi greenstone belt implications for early mantle differentiation and stratification three komatiite tholeiite sequences from the archean abitibi southern volcanic zone svz which are separated by major terrane boundaries show systematic differences in composition rare earth element ree patterns and high field strength element hfse ree fractionation komatiites from tisdale township are al undepleted with mgo 12 24 al2o3 tio2 13 17 cao al2o3 1 1 3 and high ni 722 1275 ppm and cr 1875 2820 ppm contents mg tholeiites and fe tholeiites are spatially associated with komatiites both komatiites and mg tholeiites have flat ree patterns la yb n 0 6 1 2 and nb nb zr zr and hf hf 1 calculated using primitive mantle normalized values and adjacent rees in the incompatibility sequence of elements in mid ocean ridge basalt morb suggesting that they may have formed by high degree partial melting of primitive mantle materials with olivine as the main liquidus phase at shallow depths 1 consistent with having been derived from mg perovskite enriched sources at depths 700 km below the transition zone whereas spatially associated tholeiites have la yb n 1 2 and nb nb zr zr and hf hf 1 suggesting a shallow undepleted mantle source distinct from the komatiites komatiites and tholeiites from boston township are characterized by mgo 11 29 al2o3 tio2 4 5 5 4 cao al2o3 l 4 2 5 high ni 203 3420 ppm and cr 194 1965 ppm contents al sc y and heavy rare earth element hree depletion and pronounced negative normalized zr and hf anomalies zr zr and hf hf 1 in accord with either partial melting of a majorite depleted mantle source or majorite fractionation during magma formation in the depth range of 300 600 km the fractionated hfses and rees of munro and boston area komatiites indicate that these archean komatiites may have preserved some signatures of early mantle differentiation which so far has only been inferred based on high pressure experimental studies and theoretical predictions further geochemical studies of archean komatiites especially precise multiple trace element analysis combined with improved measurements of partition coefficients over a wide pressure range will provide better understanding on early mantle differentiation stratification and the transition zone

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

lunar magma ocean crystallization revisited bulk composition early cumulate mineralogy and the source regions of the highlands mg suite abstract crystallization of the lunar magma ocean lmo has been numerically modeled and its products inferred from sample observations but it has never been fully tested experimentally this study is a reexamination of the lmo hypothesis by means of the first experimental simulation of lunar differentiation two end member bulk moon compositions are considered one enriched in refractory lithophile elements relative to earth and one with no such enrichment a two stage model of magma ocean crystallization based on geophysical constraints is simulated and features early crystal suspension and equilibrium crystallization followed by fractional crystallization of the residual magma ocean an initially entirely molten moon is assumed part 1 of this study presented here focuses on stage 1 of this model and considers the early cumulates formed by equilibrium crystallization differences in mantle mineralogy resulting from different bulk moon compositions and implications for the source regions of the highlands mg suite refractory element enriched bulk moon compositions produce a deep mantle that contains garnet and trace cr spinel in addition to low ca pyroxene and olivine in contrast compositions without refractory element enrichment produce a deep dunitic mantle with low ca pyroxene but without an aluminous phase the differences in bulk composition are magnified in the residual melt the residual lmo from the refractory element enriched composition will likely produce plagioclase and ilmenite earlier and in greater quantities both compositions produce mg rich early cumulate piles that extend from the core mantle boundary to 355 km depth if 50 equilibrium crystallization and whole moon melting are assumed these early lmo cumulates provide good fits for the source regions for a component of the high mg ni and co poor parental magmas of the mg suite cumulates if certain conditions are called upon the olivine in early lmo cumulates produced by either bulk moon composition is far too rich in cr to be reasonable for the source regions of the mg suite meaning either core formation in the presence of s and or c must be invoked to deplete the lmo and the crystallizing olivine in cr or that current estimates of the bulk lunar cr content are too high we infer that melts meeting the criteria of the mg suite parents could be produced from early lmo cumulates by solid state kreep and plagioclase hybridization near the base of the crust and subsequent partial melting additionally we propose a revised model for mg suite petrogenesis

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

melting equilibria in multicomponent systems and liquidus solidus convergence in mantle peridotite the melting of undepleted mantle peridotite proceeds through a temperature interval which decreases with increasing pressure if liquidus and solidus actually meet in the range 100 150 kb as suggested by herzberg 1983 peridotite must transform there directly to a melt of its own composition thermodynamic analysis shows that such a liquidus solidus meeting would be very unlikely in a system as chemically complex as mantle peridotite and would require that unanticipated phase equilibrium relations suppress all incongruent melting behavior but takahashi and scarfe s 1985 preliminary experiments suggest that the upper mantle itself may indeed have a special composition with respect to phase equilibrium relations between liquids and solids at very high pressure if so mantle peridotite composition cannot be generated as a crystal accumulate or melting residue because these two popular theories of origin are difficult to reconcile with a supposed eutecticlike composition if upper mantle peridotite were itself a solidified liquid composition produced either as a partial melt or more likely as a crystallization residue of some more primitive melt composition representative of the whole mantle an approach of liquidus to solidus might be expected at high pressure although the phase relations of herzberg 1983 and herzberg and o hara 1985 remain implausible

melting of forsterite mg2sio4 up to 15 gpa the melting curve of forsterite has been studied by static experiment up to a pressure of 15 gpa forsterite melts congruently at least up to 12 7 gpa the congruent melting temperature is expressed by the kraut kennedy equation in the following form tm k 2163 1 3 0 v0 v v0 where the volume change with pressure was calculated by the birch managhan equation of state with the isothermal bulk modulus k0 125 4 gpa and its pressure derivative k 5 33 the triple point of forsterite mg2sio4 liquid will be located at about 2600 c and 20 gpa assuming that congruent melting persists up to the limit of the stability field of forsterite the extrapolation of the previous melting data on enstatite and periclase indicates that the eutectic composition of the forsterite enstatite system should shift toward the forsterite component with increasing pressure and there is a possibility of incongruent melting of forsterite into periclase and liquid at higher pressure although no evidence on incongruent melting has been obtained in the present experiment

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

the origins of yakutian eclogite xenoliths owing to the association with diamonds eclogite xenoliths have samples were derived from typical depleted mantle however two groups of three samples each indicate both enriched mantle and received disproportionate attention given their low abundance in kimberlites several hypotheses have been advanced for the origin of possible ultra depleted mantle present beneath yakutia during the late archean and early proterozoic the vast majority of eclogites eclogite xenoliths from the subduction and high pressure melting of oceanic crust to cumulates and liquids derived from the upper studied from the obnazhennaya pipe also exhibit characteristics of mantle we have amassed a comprehensive data set including group a eclogites and are probably derived directly from the mantle majorand trace element mineral chemistry carbon isotopes in however the eclogites from the mir kimberlite are more typical of diamonds and rb sr sm nd re os and oxygen isotopes in other eclogites world wide and show convincing evidence of a recycled ultrapure mineral and whole rock splits from eclogites of the udoceanic crustal affinity we concur with the late ted ringwood achnaya kimberlite pipe yakutia russia furthermore eclogites that eclogites can be formed in a variety of ways both within the from two other yakutian kimberlite pipes mir and obnazhennaya mantle and from oceanic crustal residues have been studied in detail and offer contrasting images of eclogite protoliths relative to eclogites from southern africa and other yakutian localities udachnaya eclogites are notable in the absence of chemical zoning in mineral grains as well as the degree of light

generation of komatiite magma and gravitational differentiation in the deep upper mantle abstract the densities of silicate liquids with basic picritic and ultrabasic compositions have been estimated from the melting curves of minerals at high pressures silicate liquids generated by partial melting of the upper mantle are denser than olivine and pyroxenes at pressures higher than 70 kbar and garnet is the only phase which is denser than the liquid at pressures from 70 kbar to at least 170 kbar in this pressure range garnet and some fraction of liquid separate from ascending partially molten diapirs it is therefore suggested that aluminium depleted komatiite with a high ca oal2o3 ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar 200 400 km in depth where selective separation of pyropic garnet occurs effectively on the other hand aluminium undepleted komatiite is probably derived from diapirs originating at shallower depths

the primodial terrestrial magma ocean and its implication for stratification of the mantle fractional crystallization behaviour of a magma ocean extending to lower mantle depths was deduced from estimations of melting relations for the deep mantle and the density relationships between ultrabasic liquid and mantle minerals the accretional growth of the earth necessarily involves a molten zone magma ocean in the outer layer of the growing earth the fractionation by melting during accretion results in primary stratification composed of a molten ultrabasic upper mantle magma ocean a perovskite rich lower mantle and an iron core a certain amount of al2o3 and cao was removed from the magma ocean and retained in the lower mantle due to eclogite fractionation in the early stage of accretion and the perovskite fractionation in the later stage of accretion models of the stratification of the upper mantle arising from fractional crystallization of the magma ocean and subsequent convective disturbance were deduced on the basis of estimations of melting relations for the deep mantle and the density relationships between the ultrabasic liquid and mantle minerals the stratification of the mantle which is consistent with geophysical constraints is as follows the upper mantle is composed of two layers the upper olivine rich layer and the lower garnet rich layer with a thickness around 200 km and the lower mantle with a perovskite rich composition in this model both the 400 and 650 km discontinuities are the chemical boundaries

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

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

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

solidus and liquidus temperatures and mineralogies for anhydrous garnet lherzolite to 15 gpa abstract a review of experimental data for systems pertaining to anhydrous fertile garnet lherzolite shows strong convergence in the liquidus and solidus temperatures for the range 6 5 15 gpa these can converge either to a common temperature or to temperatures which differ by only 100 c the major element composition of magmas generated by even minor degrees of partial melting may be similar to the primordial bulk silicate earth composition in an upper mantle stratigraphic column extending over 160 km in depth the convergence of the solidus and liquidus temperatures is a consequence of the highly variable d t d p of the fusion curves for minerals which crystallize in peridotite systems in particular d t d p for the forsterite fusion curve is much less than that for diopside and garnet whether or not the solidus and liquidus intersect the liquidus mineralogy for undepleted garnet lherzolite compositions changes from olivine at low pressures to pyroxene garnet or a complex pyroxene garnet solid solution at pressures in excess of 10 15 gpa geochemical data for the earliest archean komatiites are consistent with an upper mantle phase diagram having garnet as a liquidus phase for garnet lherzolite compositions at high pressures all estimates of the anhydrous solidus and liquidus for the range 10 15 gpa are consistent with silicate liquid compressibility data which indicate that olivine may be neutrally buoyant in ultramafic magmas at these pressures

olivine flotation in mantle melt abstract molten komatiite and peridotite have been compressed in an octahedral multi anvil device up to 10 gpa densities of the melts were measured at pressure intervals in the range 7 to 10 gpa by observing sinking and floating san carlos olivines and synthetic forsterite marker spheres the multi anvil results for komatiite when combined with piston cylinder measurements done at 4 to 6 gpa and a calculated reference density at 105 pa yield a birch murnaghan isothermal bulk modulus of k1900c 26 gpa and pressure derivativek 4 25 the pressure of neutral buoyancy for olivine in komatiite is confirmed to be near 8 gpa as predicted in earlier work olivine flotation in the experimental komatiite commences at a pressure close to where the liquidus phase changes from olivine to denser garnet leading to the possibility of density driven crystal sorting during fractionation molten peridotite klb 1 shows an isothermal compression 2000 c of 0 065 g cm 3 gpa 1 in the interval 105 pa to 8 2 gpa the olivine liquid peridotite density crossover is predicted to lie between 9 and 11 gpa indicating that olivine flotation can operate at depths of 300 500 km in a molten peridotitic mantle

density and thermal expansion of a peridotite melt at high pressure abstract density of a feo rich peridotite ma a model composition of martian mantle melt was investigated by high pressure experiments conducted at 6 3 18 0 gpa and 1800 2570 c we adopted the sink float method i e the sinking and flotation of a certain crystal density marker in the silicate melt is judged from its position in the run product recovered from high pressure and high temperature conditions the density marker moves in a vertical direction driven by the density difference between the melt and the marker we used olivine and diamond for the density marker the third order birch murnaghan equation of state was applied for a feo rich peridotite melt and its thermal expansion coefficients at 1980 c and bulk moduli at 1980 c and 2330 c were determined from the constraints obtained by sinking and flotation of olivine and diamond assuming that the pressure derivative of bulk modulus k equals 10 1 as the same value as that of fayalite melt agee 1992a the thermal expansion coefficients at 1980 c are 6 2 2 0 10 5 k 1 at 8 1 gpa and 5 9 1 8 10 5 k 1 at 15 1 gpa and the isothermal bulk moduli are 17 9 3 3 gpa at 1980 c and 17 7 4 5 gpa at 2330 c the density relations between the martian mantle melt and the liquidus crystals obtained in the present study suggest the enrichment of olivine at 600 km depth and of majorite at the bottom of the mantle in the crystallizing martian magma ocean

effect of a hadean terrestrial magma ocean on crust and mantle evolution this paper presents a model for the thermal and chemical evolution of a global magma ocean created by impact heating during the earth s accretion detailed calculations are given for a melt depth of 120 km for end member picritic and peridotitic compositions application of fluid mechanics and heat transfer principles shows as a first approximation that the chemical evolution can be portrayed by idealized fractional crystallization occurring only on the the bottom of the magma ocean the fractional crystallization sequence for the picritic model is 90 km of mafics overlain by 15 km of ol sp gabbronorite and topped by 15 km of iron rich leucodiorite whereas the peridotite sequence consists of 99 km of dunite harzburgite and websterite overlain by 5 km of ol sp gabbronorite and capped by 16 km of ferroleucogabbronorite although subsolidus convection would rehomoginize all but the felsic layers of the picritic model the layers of the peridotite would remain intact owing to their stable density profile the mineralogy of the felsic layers is largly independent of the basic model assumptions however the composition of the mafic layers is model dependent the most likely results for the mafic mafic layers lherzolite or primitive mantle peridotite are similar to mantle xenoliths suggesting that a terrestrial magma ocean may have existed however comparison of the chemistry of the calculated upper felsic layer with that of the canadian shield shows that crystallization of a global magma ocean would not directly produce the archean continental crust multiple melting and differentiation of the fe leucodiorite to fe leucogabbronorite layer and of the underlying primitive mantle would be required to form an archean granitoid crust

thermally induced phase changes lateral heterogeneity of the mantle continental roots and deep slab anomalies pressure induced solid solid phase changes are responsible for most of the increase of density and seismic velocity with depth in the upper mantle lateral variations in temperature cause a similar effect abrupt changes of density and seismic velocity due to phase changes are superposed on smaller changes associated with thermal expansion temperature induced isobaric phase changes are as important in explaining various recent geophysical data as are the more familar pressure induced phase changes in cold slabs the equilibrium mineral assemblage contains high density high velocity phases which are not stable in hotter mantle in particular the ilmenite form of mgsio 3 and the spinel form of mg 2sio 4 have broad stability fields in cold mantle which increase the density and velocity of deep slabs to values in excess of those which have been used in geoid and seismic travel time modeling recent arguments for slab penetration into the lower mantle and whole mantle convection are based on thermal models of the slab which ignore the large density and seismic velocity anomalies associated with temperature induced phase changes when these effects are taken into account the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and layered models of mantle convection the seismicity cutoff and evidence for slab thickening at 670 km also favor this style of convection mantle seismic velocities between 200 and 400 km depth in tectonic and young oceanic regions are lower than in shield regions and this is due to the presence of a melt phase and lower velocity high temperature phase assemblages deep 200 km long lived continental roots differing in chemistry from normal mantle are not required when isobaric phase changes are taken into account high velocity subshield mantle is closer to normal subsolidus mantle than is suboceanic mantle which is affected by the presence of high temperature phase assemblages the whole mantle convection thick continental root and deep slab penetration hypotheses are not supported by seismic and geoid data when isobaric phase changes are included in the analysis phase changes are more effective in changing density and seismic velocity than are lateral variations in temperature and composition the lack of correlation of the geoid with ridges shields heat flow and upper mantle velocity variations suggests a low geoid sensitivity to the upper mantle consistent with layered convection

chemical stratification in the silicate earth abstract the largest density contrast between magmas and common ferromagnesian minerals in the mantle occurs at two locations these are nearest the earth s surface and at about 650 700 km depth where the lower mantle mineral assemblage becomes stable at solidus temperatures the large density contrast between magmas and olivine nearest the surface diminishes to zero somewhere between the middle and lower stratigraphic sections of the upper mantle it is also here where the composition of all anhydrous magmas is most similar to that of an undepleted garnet iherzolite composition for an earth that has differentiated by fractional crystallization and melting processes which depend on the separation of crystalline phases from silicate liquids having different densities the 650 km discontinuity could represent a chemical boundary layer the chemical change in the early archean could have been from primordial upper mantle compositions above the boundary layer to differentiated lower mantle compositions below a primary stratigraphic model is offered for the distribution of depleted enriched and primordial isotopic mantle components formed by the transport fate of magmas in the beginning of earth history depleted morb source regions were established in the uppermost part of the upper mantle primordial mantle was located at the middle to the deepest regions of an upper mantle which was processed by anhydrous melting and crystallization enriched and depleted components could have been formed at these levels also by igneous processing in the presence of h 2 o or co 2 and involving highly compressible magmas the lower mantle became heterogeneous with enrichments at the top and depletions elsewhere it is suggested that the present day isotopic structure of the mantle has inherited elements of this primary stratification primordial 143 nd 144 nd and 87 sr 86 sr observed in oceanic islands basalts are located in the middle of upper mantle convection cells enriched ratios found in both oceanic islands basalt and kimberlite could have originated near and on either side of the 650 km chemical boundary layer

melting temperature distribution and fractionation in the lower mantle abstract the melting curve of perovskite mgsio3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates the initial slope of the melting curve of perovskite mgsio3 was obtained as d t m d p 77 k gpa 1 at 23 gpa the melting curve of perovskite was expressed by the kraut kennedy equation as t m k 917 1 29 6 v v 0 where tm 2900 k and p 23 gpa and by the simon equation p gpa 23 21 2 t m k 2900 1 75 1 the liquidus curve of the lower mantle was estimated as t liq 0 9 t m perovskite and this gives the liquidus temperature tliq 7000 500 k at the mantle core boundary the solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowustite at high pressures the solidus temperature is 5000 k at the base of the lower mantle if the temperature distribution of the mantle was 1 5 times higher than that given by the present geotherm in the early stage of the earth s history partial melting would have proceeded into the deep interior of the lower mantle estimation of the density of melts in the mgo feo sio2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt thus the melt generated in the lower mantle would tend to move downward toward the mantle core boundary this downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle such as in the d layer and the distribution of the radioactive elements between mantle and core

formation of olivine textures in pallasites and thermal history of pallasites in their parent body an analysis of the textures of pallasites has been made using data concerning the kinetic and rheological properties of silicates and metals pallasites containing rounded olivines e g the springwater and brehnam pallasites have been heated to above the solidus temperature of the metallic iron phases 1270 k the rounded olivines of grain size 0 5 1 0 cm observed in the springwater pallasites were formed between 1270 and 1370 k on the other hand those of grain size 0 5 1 0 mm as found in the brehnam pallasites may have been heated to above 1370 k however the duration of heating at such high temperatures must have been less than 5 103 y pallasites containing angular olivines with microscopically rounded corners e g the eagle station dora pallasites have suffered shock events fracturing the olivine grains which may correspond to collisions during the accretional stage of the parent body and experienced successive annealing during cooling from a temperature between 1150 and 1270 k

high temperature compression of ferropericlase and the effect of temperature on iron spin transition abstract high temperature compression experiments with in situ x ray diffraction of ferropericlase fp with a composition of mg 0 81 fe 0 19 o were made in a laser heated diamond anvil cell to pressures p of 116 gpa at a constant temperature t of 1600 1900 k room temperature experiments with a laser annealing technique were also carried out on the same material anomalous unit cell volume reductions that can be explained by the spin transition of ferrous iron were observed at p 63 96 gpa and 45 63 gpa at t 1600 1900 k and 300 k respectively indicating that the spin transition pressure interval expands with increasing temperature the observed density changes across this spin transition at t 1600 1900 k and 300 k are about 1 6 and 1 0 respectively indicating that the spin transition pressure interval expands with increasing temperature the thermal expansivity of fp is large in the mid lower mantle due to the effect of the spin transition in a peridotitic composition the spin transition in fp increases the rock density by 0 35 at the lowermost mantle conditions calculated densities show that both perovskitic and peridotitic mantle models may explain the prem lower mantle density however the peridotitic lower mantle model requires less assumption to satisfy the prem density and is more self consistent

melting relations of peridotite and the density crossover in planetary mantles melting relations of primitive peridotite were studied up to 25 gpa the change of the liquidus phase from olivine to majorite occurs at 16 gpa we confirmed the density crossover of the feo rich peridotite melt and the equilibrium olivine fo90 at 7 gpa sinking of equilibrium olivine fo95 in the primitive peridotite melt was observed up to 10 gpa the compression curves of feo rich peridotitic and komatiite melts reported in this and earlier work suggest that the density crossover in the earth s mantle will be located at 11 12 gpa at 2000 c consistent with an previous estimation by c b agee and d walker the density crossover can play a key role in the moon and the terrestrial planets such as the earth venus and mars majorite and some fraction of melt could have separated from the ascending diapir and sunk downwards at the depths below the density crossover this process could have produced a garnet rich transition zone in the earth s mantle the density crossover may exist in the feo rich lunar mantle at around the center of the moon the density crossover which exists at the depth of 600 km in the martian mantle plays a key role in producing a fractionated mantle which is the source the parent magmas of the snc meteorites

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date