petrogenesis of the elephant moraine a79001 meteorite multiple magma pulses on the shergottite parent body abstract the eeta 79001 achondrite consists of two distinct igneous lithologies joined along a planar non brecciated contact both are basaltic rocks composed primarily of pigeonite augite and maskelynite but one contains zoned megacrysts of olivine orthopyroxene and chromite that represent disaggregated xenoliths of harzburzite both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small shallow chamber many similarities between the two virtually synchronous magmas suggest that they are related possible mechanisms to explain their differences involve varying degrees of assimilation fractionation from similar parental magmas or partial melting of a similar source peridotite of these assimilation of the observed megacryst assemblage seems most plausible however some isotopic contamination may be required in any of these petrogenetic models the meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body both basaltic lithologies and the inferred ultramafic protolith of the megacryst assemblage are petrologically similar to other members of the shergottite group and all may have been derived from a volcanic plutonic complex on a planetary body

outgassed water on mars constraints from melt inclusions in snc meteorites the snc shergottite nakhlite chassignite meteorites thought to be igneous rocks from mars contain melt inclusions trapped at depth in early formed crystals determination of the pre eruptive water contents of snc parental magmas from calculations of the solidification histories of these amphibole bearing inclusions indicates that martian magmas commonly contained 1 4 percent water by weight when combined with an estimate of the volume of igneous materials on mars this information suggests that the total amount of water outgassed since 3 9 billion years ago corresponds to global depths on the order of 200 meters this value is significantly higher than previous geochemical estimates but lower than estimates based on erosion by floods these results imply a wetter mars interior than has been previously thought and support suggestions of significant outgassing before formation of a stable crust or heterogeneous accretion of a veneer of cometary matter

lateral heterogeneity and azimuthal anisotropy in the north atlantic determined from ss s differential travel times to explore upper mantle heterogeneity beneath the north atlantic we have measured 70 ss s differential travel times using the waveform cross correlation method both the two way preliminary reference earth model prem and j b jeffreys bullen residuals exhibit a maximum variation of 17 s ranging from 10 to 7 and 9 to 8 s respectively the lack of correlation between ss s and s residuals along with the strong correlation between ss s and ss residuals suggests that ss s differential travel times eliminate source and receiver effects and sample the upper mantle anomalies near the ss bounce points without being strongly affected by lower mantle heterogeneities we find evidence for a strong local anomaly in the north atlantic residuals for bounce points immediately to the north of the azores gibraltar plate boundary average about 4 s faster than for the bounce points to the south of the boundary we infer that this velocity contrast exists in the lithosphere and continues below a depth of 200 km a series of linear multiple regression experiments demonstrate that variation in velocity with increasing age of the seafloor and azimuthal anisotropy are both significant contributors to the prem and j b residuals assuming that travel time delays are a linear function of the square root of the seafloor age we find the coefficient for age to be about 1 0 s m y this is smaller than but not significantly different from the corresponding slope for the s delays of intraplate earthquakes in the atlantic reported by j d duschenes and s c solomon 1977 and favors the presence of small amounts of water e g 0 1 in the upper mantle in modeling anisotropy we carry out an experiment using synthetic seismograms to examine the shear wave splitting phenomena in the anisotropic medium and investigate three possible forms for sh wave delay as a function of azimuth sinusoidal variations as a function of 2 4 and a combination of 4 predominant and 2 that mimics the delay expected in olivine crystals when the axis is aligned horizontally our regression models strongly prefer the predominance of a 4 to a 2 variation and the last type of anisotropy explains our data best from the preferred anisotropy model the olivine axis or the upper mantle shearing flow is inferred to be oriented n s the magnitude of the azimuthal variation suggests that anisotropy extends over a depth range of several hundred kilometers in the upper mantle

seismic anisotropy of the pacific ocean inferred from long period surface waves dispersion abstract the dispersion of surface rayleigh and love waves in the period range 40 300 s along a large number of paths allows the estimation of both the azimuthal anisotropy and the shear wave polarization anisotropy the regional dispersion is determined taking into account simultaneously its dependence with age and an azimuthal factor the pacific ocean has been divided into 5 regions for rayleigh waves and into 3 regions for love waves this partition discriminates the regions of extreme age which show a fast variation of dispersion with age from the regions of intermediate age where the variation is weak a variation of 2 of rayleigh wave group velocity with the azimuth of the path measured with respect to the direction of spreading is displayed up to very long period on the contrary the azimuthal anisotropy for love waves is difficult to resolve for rayleigh waves the present day direction of plate motion seems to agree best with the direction of maximum velocity on the other hand the isotropic inversion of the regional dispersion curves indicates except for young regions a discrepancy between rayleigh wave and love wave models with this hypothesis sh velocities are higher than sv velocities for the regions older than 23 ma down to a depth of 300 km which is indicative of the presence of polarization anisotropy the latter very weak for the young part of the ocean increases with age and reaches 7 for the oldest region

deep earth structure major developments in earth structure in the last four years have been concentrated in the description of the earth s lateral heterogeneity the regions that are heterogenous and the per cent variation of velocity and density in each region most studies find that lateral variation is concentrated in the upper 400 and lower 200 km of the mantle a radially symmetric earth model has been defined that represents the best average fit to seismic data in a broad frequency band sampling many regions p and s velocity is found to increase in zones of 50 km or less at 400 and 650 to 700 km depth the model is transversely anisotropic in the upper mantle it possesses a vertical axis of symmetry such that the elastic constants are different for vertical propagation than for horizontal and intermediate angles of propagation the real earth generally exhibits azimuthal anisotropy as well but the azimuthal anisotropy cannot be resolved by a global average of data the nature and magnitude of the anisotropy agrees with that found in ultramafic samples of the upper mantle in attenuation models of intrinsic attenuation have included the dispersive properties of intrinsic anelasticity and constructed relaxation models consistent with an observed frequency dependence of q in the body wave band there has been progress in mapping the scattering properties of the lithosphere attenuation due to scattering in the crust and lithosphere has been shown to have strong effects on the amplitudes of seismic waves at local and teleseismic distances

lateral variations in mantle pvelocity from tectonically regionalized tau estimates summary estimates of tau functions for a tectonically regionalized earth are obtained from over 1 25 million seismic ray paths of isc bulletin data to study the correlation of potential lateral variations in mantle p wave velocities with recognized surface heterogeneity the use of regionalized travel time data relies on statistical regularity criteria to check the consistency of the global regionalization estimates of tau perturbations attributed to velocity structure at the seismic source and receiver regions are derived by a simple algebraic formulation contributions from near surface heterogeneity are thereby removed and permit the assessment of lateral velocity variations at depth estimates of single region equivalent tau functions are constructed and inverted to obtain velocity depth functions and extremal bounds at the 99 9 per cent confidence level for seven different tectonic regions deviations from a regionally weighted reference mean velocity function which agrees well with prem dziewonski anderson indicate significant differences particularly between oceanic and continental tectonic regions extending to a depth of 700 km p wave velocity anomalies are typically less than 1 per cent of the reference velocity the age dependence of the shallow oceanic mantle is observed by increased velocities from young 25 myr to old 100 myr regions and similarly from orogenic zones and magmatic belts to stable continental regions unlike for young and old oceanic regions stable continental regions do not show a pronounced gradient in the mean velocity residuals above 250 km continental platforms and particularly shields however show a compensation in the sign of the mean velocity residual at depths between about 350 and 700 km evidence for a velocity anomaly between 700 and 950 km is indicated significant negative residuals are observed centred at a depth of about 780 km below oceanic ridges and about 880 km below active continental regions this anomaly may be related to a boundary layer between the upper and lower mantle the level of velocity variations decreases below 950 km lateral variations are also suggested within 250 km of the core boundary

petrology and chemistry of the new shergottite dar al gani 476 in 1998 dar al gani dag 476 was found in the libyan desert the meteorite is classified as a basaltic shergottite and is only the 13th martian meteorite known to date it has a porphyritic texture consisting of a fine grained groundmass and larger olivines the groundmass consists of pyroxene and feldspathic glass minor phases are oxides and sulfides as well as phosphates the presence of olivine orthopyroxene and chromite is a feature that dag 476 has in common with lithology a of elephant moraine eet a79001 however in dag 476 these phases appear to be early phenocrysts rather than xenocrysts shock features such as twinning mosaicism and impact melt pockets are ubiquitous terrestrial weathering was severe and led to formation of carbonate veins following grain boundaries and cracks with a molar mgo mgo feo of 0 68 dag 476 is the most magnesian member among the basaltic shergottites compositions of augite and pigeonite and some of the bulk element concentrations are intermediate between those of lherzolitic and basaltic shergottites however major elements such as fe and ti as well as lree concentrations are considerably lower than in other shergottites noble gas concentrations are low and dominated by the mantle component previously found in chassigny a component similar to that representing martian atmosphere is virtually absent the ejection age of 1 35 0 10 ma is older than that of eeta79001 and could possibly mark a distinct ejection dar al gani 476 is classified as a basaltic shergottite based on its mineralogy it has a fine grained groundmass consisting of clinopyroxene pigeonite and augite feldspathic glass and chromite ti chromite ilmenite sulfides and whitlockite isolated olivine and single chromite grains occur in the groundmass orthopyroxene forms cores of some pigeonite grains shock features such as shock twinning mosaicism cracks and impact melt pockets are abundant severe weathering in the sahara led to significant formation of carbonate veins crosscutting the entire meteorite dar al gani 476 is distinct from other known shergottites chemically it is the most magnesian member among known basaltic shergottites and intermediate in composition for most trace and major elements between iherzolitic and basaltic shergottites unique are the very low bulk ree element abundances the ci normalized abundances of lrees are even lower than those of iherzolitic shergottites the overall abundance pattern however is similar to that of que 94201 textural evidence indicates that orthopyroxene as well as olivine and chromite crystallized as phenocrysts from a magma similar in composition to that of bulk dag 476 whether such a magma composition can be a shergottite parent melt or was formed by impact melting needs to be explored further at this time it cannot entirely be ruled out that these phases represent relics of disaggregated xenoliths that were incorporated and partially assimilated by a basaltic melt although the texture does not support this possibility trapped noble gas concentrations are low and dominated by a chassigny like mantle component virtually no martian atmosphere was trapped in dag 476 whole rock splits the exposure age of 1 26 0 09 ma is younger than that of most shergottites and closer to that of eeta79001 the ejection age of 1 35 0 1 ma could mark another distinct impact event

petrogenesis of the zagami meteorite inferences from synchrotron x ray sxrf microprobe and electron microprobe analyses of pyroxenes abstract the zagami meteorite is a shergottite a basalt rich in pigeonite augite and maskelynite glass shocked plagioclase it is one of the snc meteorites which are inferred to have formed on mars major and minor element abundances in pyroxene principally pigeonite from newly available unm samples were determined by electron microprobe abundances of trace elements ni cu zn and ga were obtained by synchrotron x ray sxrf microprobe many pigeonite grains have normally zoned rims and reversely zoned cores so that the most magnesian pigeonite forms rings or annuli in thin section view in three dimensions the most magnesian pigeonite may form tubes or hourglass shapes the cores commonly contain magmatic inclusions other pigeonites have irregular or multiple magnesian regions with magmatic inclusions among and between them abundances of ni and cr in the magnesian zones and cores are partially decoupled from abundances of other compatible mg and incompatible fe ti elements the textures chemical zoning and element decouplings in the pigeonites are consistent with igneous crystal growth at moderate cooling rates not isothermally or near equilibrium from element partitioning and mass balance the unm zagami is estimated to contain 20 5 or less cumulus pyroxene half augite and half pigeonite half the proportion suggested by equilibrium distribution of fe mg between pigeonite and melt this inconsistency may be resolved if all pigeonite melt element partitioning was affected by the rapid growth of the pigeonites the composition of the parental magma for the unm zagami calculated by mass balance on bulk and pyroxene compositions is similar to the 1170 c melt of the bmnh zagami not the 1140 c melt inferred as parental by other workers the inference that the pyroxene zoning patterns reflect only magmatic events is consistent with an igneous age of 180 m y for zagami

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

geoelectromagnetism and geodynamics corona discharge from volcanic and geothermal areas abstract it is proposed that volcanic areas geothermal areas and even some other suitable regions are the site of a corona discharge effect reflecting their short circuiting with the electric currents responsible for the earth s magnetic field such areas may have an electromagnetic coupling with the ionosphere that depends on the local amount of the corona effect correlations between geoelectromagnetism and geodynamics are therefore reconsidered and it is proposed that controversial observations of both telluric and ionospheric effects are the result of different local conditions of the various experiments supporting observational evidence exists although it unavoidably still relies on some speculation which could be resolved by considering simultaneous records of geoelectromagnetic phenomena including underground effects and the eventual associated ionospheric coupling within a suitable network of observing sites their long range multiannual variation ought to be correlated with the planetary trend of the secular variation of the geomagnetic field in any case the earth ought to be treated as a unique and complex planetary object geoelectromagnetic phenomena anomalies of spin rate and pole displacements and whenever possible crustal stress appear to be the key points for working out the problem of earthquake precursors and forecasting

39ar 40ar dating of the zagami martian shergottite and implications for magma origin of excess 40ar the zagami shergottite experienced a complex petrogenetic formation history mccoy et al 1992 1999 like several shergottites zagami contains excess 40ar relative to its formation age to understand the origin of this excess 40ar we made 39ar 40ar analyses on plagioclase and pyroxene minerals from two phases representing different stages in the magma evolution surprisingly all these separates show similar concentrations of excess 40ar 1 x 10 6 cm 3 g we present arguments against this excess 40ar having been introduced from the martian atmosphere as impact glass we also present evidence against excess 40ar being a partially degassed residue from a basalt that actually formed 4 gyr ago we utilize our experimental data on ar diffusion in zagami and evidence that it was shock heated to only 70 c and we assume this heating occurred during an ejection from mars 3 myr ago with these constraints thermal considerations necessitates either that its ejected mass was impossibly large or that its shock heating temperature was an order of magnitude higher than that measured we suggest that this excess 40ar was inherited from the zagami magma and that it was introduced into the magma either by degassing of a larger volume of material or by early assimilation of old k rich crustal material similar concentrations of excess 40ar in the analyzed separates imply that this magma maintained a relatively constant 40ar concentration throughout its crystallization this likely occurred through volatile degassing as the magma rose toward the surface and lithostatic pressure was released these concepts have implications for excess 40ar in other shergottites

multiscale seismic tomography and mantle dynamics abstract in this article we first introduce the methodology of multiscale seismic tomography and the way to interpret the obtained tomographic images and then review the significant recent results of multiscale seismic tomography with emphasis on mantle plumes and subducting slabs global and regional tomography shows that most of the slab materials under western pacific and east asia are stagnant in the mantle transition zone before finally collapsing down to the core mantle boundary as a result of large gravitational instability from phase transitions local and teleseismic tomography studies have imaged clearly the subducting slabs and arc magma chambers in the upper mantle wedge indicating that geodynamic systems associated with arc magmatism and back arc spreading are related to deep processes such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab because most hotspots are located in poorly instrumented continental and oceanic regions 3 d crust and upper mantle structure is determined for only a few hotspots such as iceland yellowstone and eifel which are covered by seismic networks and plume like slow anomalies are revealed under those hotspots global tomography has revealed deep mantle plumes under the major hotspots such as hawaii iceland kerguelen south pacific and africa strong lateral heterogeneities are revealed at the bottom of the mantle which are associated with the deeply subducted slabs and the birth of mantle plumes a thorough understanding of the deep earth structure will only be achieved by a combination of more effective seismic imaging techniques and dense coverage of global seismic networks particularly in the oceans

petrogenesis of a vitrophyre in the martian meteorite breccia nwa 7034 abstract northwest africa nwa 7034 and its paired meteorites nwa 7533 and nwa 7475 are the first recognized martian polymict breccia samples an unusual large subrounded clast in nwa 7034 shows a vitrophyric texture consisting of skeletal pyroxene and olivine with mesostasis this lithology has not been observed in the paired meteorites it crystallized under disequilibrium conditions as indicated by its olivine and pyroxene kdfe mg partitioning values as well as reversed order of crystallization and mineral compositions relative to those predicted by melts we report the highest bulk ni value 1020 ppm measured in any known martian meteorite or martian igneous rock suggesting an impact melt origin for the vitrophyre addition of 5 3 7 7 chondritic material to the target rock would account for the ni enrichment the bulk major and trace element abundances of the vitrophyre indicate that the protolith was not the host breccia nor any other martian meteorites however the clast is compositionally similar to humphrey rock in gusev crater analyzed by the spirit rover and to a texturally distinct group of clasts in the paired meteorite nwa 7533 thus we propose that the target rock was an igneous lithology similar to gusev basalts which was subsequently contaminated by a chondritic impactor

the effect of post pangea subduction on global mantle tomography and convection there is an excellent correlation between tomographic patterns and global tectonics in the upper 200 km of the mantle below this depth there is little relationship with present tectonic provinces most of the power in the tomography is in the longest wavelengths l 1 3 with l 2 generally dominant this is quite different from expectations based on mantle convection models the question then arises what causes the long wavelength variations mapped by seismic techniques we investigate the hypotheses that past locations of supercontinents and subduction may control temperature variations in the mantle we look for correlations between pangea and post pangeatic subduction and seismic velocity variations at various depths the best correlations with time integrated slab locations occur near the base of the uppermantle suggesting that slabs bottom out in the mesosphere the pangea hemisphere has a colder than average uppermantle probably due to circum and intra pangea subduction hotspots and ridges avoid regions cooled by subduction over the past 180 ma the presence of large continents at the surface and large areas of cold slab at depth explain the dominance of long wavelengths in the mantle s thermal structure despite the high rayleigh number

on the scale of mantle heterogeneity abstract a data set comprising 3313 residuals measured from digital records of 429 earthquakes is analyzed for the heterogeneity of the earth s mantle the smoothed ss residuals reveal a large pattern of heterogeneity and agree well with the major tectonic features on the earth s surface and the residual patterns predicted by upper mantle and whole mantle models the spectrum of ss residuals indicates that the heterogeneity in the earth s mantle which probably reflects the patterns of mantle convection is dominated by long wavelength features our analysis of the power of ss residuals as a function of harmonic degree shows a distinct difference in the rate of decrease of the power below and above degree 8 the rate is first slower than l 1 and then it exceeds l 2 this is also true for ss residuals predicted for model sh 425 2 and love wave phase velocities at 100 s measured by other researchers this indicates that there is a preference for features with dimensions larger than 2500 3500 km we find that the power spectrum of the velocity anomalies associated with the subducted slabs is two orders of magnitude lower for 1 l 8 than that of velocity anomalies obtained by inversion of waveform data for the ocean basins correlation of the ss residuals with the square root of age of the oceanic lithosphere is highly significant however the age correlation predicts only 10 of the variance this means that the thermal signature of the spreading center represents only a small fraction of the thermal anomalies introduced into the upper mantle by convection

global p wave tomography of earth s lowermost mantle from partition modeling 1 determining the scale length magnitude and distribution of heterogeneity in the lowermost mantle is crucial to understanding whole mantle dynamics and yet it remains a much debated and ongoing challenge in geophysics common shortcomings of current seismically derived lowermost mantle models are incomplete raypath coverage arbitrary model parameterization inaccurate uncertainty estimates and an ad hoc definition of the misfit function in the optimization framework in response we present a new approach to global tomography apart from improving the existing raypath coverage using only high quality cross correlated waveforms the problem is addressed within a bayesian framework where explicit regularization of model parameters is not required we obtain high resolution images complete with uncertainty estimates of the lowermost mantle p wave velocity structure using a hand picked data set of pkpab df pkpbc df and pcp p differential travel times most importantly our results demonstrate that the root mean square of the p wave velocity variations in the lowermost mantle is approximately 0 87 which is 3 times larger than previous global scale estimates

the geoid small scale convection and differential travel time anomalies of shear waves in the central indian ocean we have measured 37 differential travel times for the phase pairs ss s sss ss scs2 scs scs2 s sscs2 sscs and sscs2 ss each pair included a surface bounce point in the central indian ocean between 4 n and 21 s and 69 and 85 e residuals were calculated relative to both the j b travel time tables and the pem c earth model and were corrected for the elevation of the bounce points the mean j b residual associated with bounce points in the central indian basin is 2 8 0 7 s fast this contrasts with 4 2 s slow reported for the western pacific by sipkin and jordan and is similar to the 4 0 s found for old continental nucleii after correcting for known differences between continental and oceanic crustal structure and for differences in measurement technique we find that travel times in the mantle beneath the central indian basin are midway in character between those beneath pre cambrian shields and those beneath the western pacific ocean basin the fastest differential travel times occur along a line passing close to the center of the large indian ocean geoidal low there is a clear increase in travel time with distance from the center of the geoid low suggesting that the source of the geoid anomaly may also be largely responsible for the difference between the central indian and pacific basins the chagos laccadive ridge seems to coincide with a transition from the fast differential travel times of the central indian basin to slower differential travel times associated with bounce points beneath young seafloor near active spreading centers there are also variations within the central indian basin that are not related to surface geological features or to the age of the seafloor these variations are periodic with a wavelength of about 640 km and with a nne trend which agrees approximately with the trend that would be expected for linear convective rolls in the upper mantle

signatures of the martian atmosphere in glass of the zagami meteorite isotopic signatures of nitrogen argon and xenon have been determined in separated millimeter sized pockets of shock melted glass in a recently identified lithology of the meteorite zagami a shergottite the ratio of nitrogen 15 to nitrogen 14 which is at least 282 per mil larger than the terrestrial value the ratio of xenon 129 to xenon 132 2 40 and the argon isotopic abundances match the signatures previously observed in the glassy lithology of the antarctic shergottite eeta 79001 these results show that the signatures in eeta 79001 are not unique but characterize the trapped gas component in shock melted glass of shergottites the isotopic and elemental ratios of nitrogen argon and xenon closely resemble the viking spacecraft data for the martian atmosphere and provide compelling evidence for a martian origin of the two shergottites and by extension of the meteorites in the shergottites nakhlites chassignites snc group

petrology and chemistry of the picritic shergottite north west africa 1068 nwa 1068 we report on the petrology and chemistry of north west africa 1068 nwa 1068 a shergottite recently recovered in morocco this meteorite has a total known mass of about 577 g and comprises 23 fragments the largest fragment is a greenish brown rock devoid of fusion crust it displays a porphyritic texture consisting of a fine grained groundmass and olivine grains excluding the impact melt pockets and the minor carbonate veins produced by terrestrial weathering modal analyses indicate the following mineral proportions 52 vol pyroxenes 22 maskelynite 21 olivine 2 phosphates merrillite and chlorapatite 2 opaque oxides mainly ilmenite and chromite and sulfides and 1 k rich mesostasis olivines with various habits occur as clusters often associated with chromite or single crystals ranging in size from 50 mum to 2 millimeters megacrysts these crystals originate probably from disrupted cumulates with strong affinities with peridotitic shergottites

measurement of mantle wave velocities and inversion for lateral heterogeneity and anisotropy 1 analysis of great circle phase velocities long period 100 330 s fundamental mode love and rayleigh waves have been processed to measure the great circle phase velocities for about 200 and 250 paths respectively the observations are inverted for regionalized phase velocities and for an even order harmonic expansion of the lateral velocity heterogeneity the regionalized inversions achieve a maximum variance reduction of about 65 and 85 for the love and the rayleigh wave data respectively the l max 2 inversions give a maximum variance reduction of about 60 and 90 for love and rayleigh waves respectively the l max 8 inversion does not make a large improvement in the fit the love wave phase velocities have more power in l 4 and 6 relative to l 2 than the rayleigh waves for both love and rayleigh wave data the sectoral component dominates the l 2 harmonics and this component is stable if we increase l max from 2 to 6 heat flow also has strong sectoral components lm 22 which are approximately in phase with those of the phase velocities the l 2 harmonics of the nonhydrostatic geoid are dominated by large zonal lm 20 and moderate sectoral components the sectoral components are in phase with those of the phase velocities the sectoral pattern of heat flow and phase velocity is controlled by high heat flow low velocity of the east pacific rise and western north america which is reinforced by low velocities in the antipodal region red sea gulf of aden east african rift by contrast the geoid l 2 pattern is dominated by geoid highs over the western pacific subduction zones a spherical harmonic expansion of regionalized phase velocities shows that they have l 2 variations similar to those of the l max 2 nonregionalized inversions this means that the regionalization approach is appropriate as a first step for studying lateral heterogeneity of the earth however the great circle phase velocities are not sufficient by themselves to uniquely locate the lateral heterogeneity the same is true for free oscillation data regions of convergence have the interesting property of being slow for short period waves and fast faster than shields for long period waves

mapping convection in the mantle long period 100 250 sec love and rayleigh waves are used to map heterogeneity and azimuthal anisotropy in the upper mantle spherical harmonic descriptions of anisotropy up to l m 3 and 2 are derived azimuthal anisotropy obtains values as high as 1 there is good correlation of fast rayleigh wave directions with upper mantle return flow directions derived from kinematic considerations this is consistent with the a axis of olivine being aligned in the flow direction the main differences between the flow models and the rayleigh wave azimuthal variation maps occur in the vicinity of hotspots hawaii for example appears to perturb the return flow there is strong correlation of the geoid and surface wave velocity at l 4 and 5 slow regions at this scale are associated with geoid highs and high heat flow consistent with upwelling convective flow or with isostatically compensated regions of low density the correlation of azimuthal anisotropy with upper mantle return flow directions rather than with plate directions suggests that part of the return flow is in the upper mantle and this in turn implies a low viscosity channel

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

petrogenesis of shergottite meteorites inferred from minor and trace element microdistributions abstract as an extension of our previous work on the lherzolitic shergottites alha77005 and lew88516 ion microprobe measurements of rees and other selected trace and minor elements were made in individual minerals of the basaltic shergottites shergotty zagami and eeta79001 whole rock ree abundances in these achondrites are dominated by whitlockite which is usually present only in trace amounts one of the most significant features is the extensive zoning of trace and minor elements in pyroxenes this zonation which provides information on the crystallization histories of these meteorites is of primary magmatic origin and not the result of secondary processes such as diffusive reequilibration and or metasomatic infiltration coherent trends in element element plots for low ca pyroxenes indicate that each shergottite formed essentially by progressive closed system fractional crystallization the calculated ree patterns of the parent melts of all shergottites are lree depleted and parallel to their whole rock ree patterns also indicative of closed system fractional crystallization on the basis of observations reported in this study as well as previously determined petrologic and geochemical including isotopic characteristics we present a model that suggests possible relationships among all five known shergottites

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

compression characteristics and index properties of tills and intertill clays in southern saskatchewan canada compression characteristics and index properties of unweathered tills and clays from repeated glaciations follow a predictable pattern at 10 sites along a 1300 km transect across southern saskatche

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

assessment of global phase velocity models summary we construct new love and rayleigh wave phase velocity models based on measurements made from an aspherical starting model and strict data quality control derived from cluster analyses these new models are in good agreement with previous ones and the question arises whether the slight changes show an improved capacity to explain the data to this effect we propose an objective method to compare different phase velocity models published in recent literature the method is based on comparing calculated synthetics to raw seismograms we find a reassuring convergence between all the models we tested at the longest periods and more scatter at the shorter periods at 40 s the different models show gains of up to 3 5 cycles over prem generally the higher the gain over prem the smaller the period considered which confirms that the earth s heterogeneity is strongest in the uppermost parts of the earth apart from assessing different models against each other our method gives an estimate comparable to cluster analyses of the underlying data errors that went into the construction of the models themselves moreover ray coverage is still far from perfect for constructing phase velocity models as a result we find that without precaution degree zero is biased through spectral leakage by 0 1 to 0 2 per cent with respect to prem the earliest information concerning the earth s 3 d structure came from surface waves when tams 1921 noticed clear velocity differences for waves propagating along continental versus oceanic paths gutenberg 1924 attempted an explanation of such differences in terms of regional variations in crustal structure when he noticed that short period surface waves are more sensitive to crustal structure than long period ones this led the way to intensive studies both theoretical and observational to link dispersive properties of surface waves to the internal structure of the earth the first regional models of the earth s dispersive properties of crust and upper mantle are summarized in papers by brune 1969 and dorman 1969 respectively with the start of digital recording of seismograms in the late

analysis of the cooling of a variable viscosity fluid with applications to the earth summary analysis shows that the convective cooling of a fluid with a temperature dependent viscosity should exhibit simple behaviour which is consistent with geophysical data on the cooling of the oceanic lithosphere and asthenosphere the cooling rate of convecting fluid is predicted to vary approximately linearly with time 12 this relationship has also been demonstrated for numerical solutions of the full governing equations of convection it is found that a similarity solution can describe the evolution of temperature within the stagnant high viscosity lid which forms over an actively convecting region the rate of thickening of the lid or lithosphere is directly proportional to a single parameter a and the overall cooling rate is also a function of a expressions are derived which relate changes in the parameter a to the initial average viscosity or temperature of the fluid and to the temperature and pressure dependence of viscosity with assumptions about how the cooling of variable viscosity fluids can be used to describe the cooling of the oceanic lithosphere and asthenosphere values of sea floor depth and the isostatic geoid height can be predicted as a function of time sea floor depth is predicted to increase linearly with and geoid height to vary nearly linearly with time in agreement with observations the rate of change of the depth or geoid height is a strong function of the initial temperature of the convecting region the mantle is taken to have physical properties appropriate for olivine a change in the mantle temperature under the ridge of 150k causes only about a 20 per cent change in the rate of subsidence but causes nearly a 100 per cent change in the rate of change of the geoid height with time the observed variations in these rates over different sections of oceanic ridges are of about this magnitude simple conductive cooling would require more than l000k variation in mantle temperature to account for the geoid height observations this analysis can also be used to estimate the cooling rate of magma sills

que94201 shergottite crystallization of a martian basaltic magma abstract basaltic shergottites are commonly described as having crystallized from magmas that contained entrained or cumulus pyroxenes complexly zoned clinopyroxenes in que94201 a newly recovered antarctic shergottite are similar to those formed during continuous growth in some lunar basaltic melts pyroxene cores have nuclei of magnesian pigeonite mantled by augite in turn rimmed by strongly zoned ferroan pigeonite with outer rims of pyroxferroite fe ti oxide compositions indicate that this meteorite crystallized under relatively reducing conditions more like lunar basalts than other shergottites ree and other trace element abundances in zoned pyroxenes maskelynite and phosphates are consistent with continuous pyroxene crystallization from an evolving magma punctuated by the appearance of new phases on the liquidus the higher proportion of maskelynite in que94201 suggests that its composition may be closer to multiple saturation with pyroxenes plagioclase than other shergottites and all pyroxene zones show negative eu anomalies thus this meteorite may represent the first example of a martian magma unaffected by crystal accumulation the fe fe mg ratio and proportions of incompatible elements reflected in 4 modal whitlockite are high implying that this is a fractionated melt the calculated bulk ree pattern shows extreme lree depletion suggesting either less contamination with enriched crustal materials or a more lree depleted source than other basaltic shergottites

rayleigh wave phase velocities in the pacific with implications for azimuthal anisotropy and lateral heterogeneities summary the lateral distribution of fundamental mode rayleigh wave phase velocities in the pacific has been calculated in order to determine the variation in velocity as a function of the age of the oceanic plate the importance of azimuthal anisotropy and the presence of secondary lateral heterogeneities the data set used in this study consists of phase velocity measurements in the period range 20 125 s for 178 paths traversing the pacific both the pure path and spherical harmonic inversion techniques are used in this investigation with an emphasis placed on determining the effectiveness and resolving power of these methods in calculating the velocity distribution in an oceanic regime the first order velocity age relation which dominantly characterizes surface wave dispersion in an oceanic environment can be adequately modelled by either the pure path or spherical harmonic techniques azimuthal anisotropy is the dominant second order effect and is best developed in regions less than 80 myr in age in this age zone the faster direction of wave propagation is either in the direction of fossil seafloor spreading or in the direction of present day absolute plate motion in the western pacific there is a correlation with paleo relative motion fossil seafloor spreading for periods less than 50 s lateral velocity heterogeneities which are not related to the age of the oceanic plate are found by pure path inversions and are correlated with regions associated with shallow residual depth anomalies this effect slow velocities with respect to the velocity age model monotonically decreases as a function of period and is indicative of a shallow origin age independent anomalies were also modelled by the application of the pure path and spherical harmonic methods in a sequential inversion

scholte wave tomography for shallow water marine sediments summary we determine the 3 d in situ shear wave velocities of shallow water marine sediments by extending the method of surface wave tomography to scholte wave records acquired in shallow waters scholte waves are excited by air gun shots in the water column and recorded at the seafloor by ocean bottom seismometers as well as buried geophones our new method comprises three steps 1 we determine local phase slowness values from slowness frequency spectra calculated by a local wavefield transformation of common receiver gathers areal phase slowness maps for each frequency used as reference in the following step are obtained by interpolating the values derived from the local spectra 2 we infer slowness residuals to those reference slowness maps by a tomographic inversion of the phase traveltimes of fundamental scholte wave mode 3 the phase slowness maps together with the residuals at different frequencies define a local dispersion curve at every location of the investigation area from those dispersion curves we determine a model of the depth dependency of shear wave velocities for every location we apply this method to a 1 km2 investigation area in the baltic sea northern germany the phase slowness maps obtained in step 2 show lateral variation of up to 150 per cent the shear wave velocity models derived in the third step typically have very low values 60 80 m s 1 in the top four meters where fine muddy sands can be observed and values exceeding 170 m s 1 for the silts and sands below that level the upper edge of glacial till with shear wave velocities of 300 400 m s 1 is situated approximately 20 m below sea bottom a sensitivity analysis reveals a maximum penetration depth of about 40 m below sea bottom and that density may be an important parameter best resolvable with multimode inversion

magmatic cristobalite and quartz in the nwa 856 martian meteorite silica rich late stage crystallization pockets in the martian meteorite northwest africa nwa 856 were investigated by transmission electron microscopy tem the pockets occur as wedges between maskelynite laths or between maskelynite and pyroxene they consist of elongated grains of cristobalite and quartz embedded in a silica rich glass interstitial to the amorphous phase and silica minerals a number of small accessory minerals have been identified typical for late stage crystallization products they are ilmenite tranquillityite fayalite troilite baddeleyite apatite and chloroapatite cristobalite and quartz are shocked as revealed by the occurrence of numerous amorphous lamellae this assemblage suggests metastable dendritic crystallization under hydrous conditions cristobalite crystallization was probably facilitated by the presence of impurities such as na or h2o our observations show that silica minerals can be formed under magmatic conditions on mars

in situ compositions of martian volcanics implications for the mantle the primary objective of this analysis is to determine the mineralogic composition of relatively pristine terrains exposed on the surface of mars this analysis is conducted using imaging spectrometer data acquired in 1989 by the imaging spectrometer for mars ism instrument that was onboard the phobos ii spacecraft the ism instrument acquired some of the highest spectral 64 channels between 0 77 and 3 14 m and spatial resolution 22 km pixel observations to date of mars focused on the equatorial region relatively unaltered surfaces were identified in these data on the basis of their spectral properties low albedo weak spectral slope absence of ferric absorptions and were found in volcanic terrains of syrtis major valles marineris ophir planum and sinus meridiani oxia palus spectra representative of the diversity among terrains were extracted for detailed analysis using the modified gaussian model to determine the primary mafic mineralogy it was determined that the mafic mineralogy of the regions investigated is dominated by low calcium and high calcium pyroxene lcp hcp and that there was homogeneity within a given region but some heterogeneity between regions in the relative abundance of lcp to hcp the two pyroxene mineralogy is consistent with the mineralogies of the basaltic snc meteorites believed to have originated on mars two pyroxene volcanic mineralogies are indicative of large degrees of partial melting e g komatiites or a mantle source depleted in aluminum integration of these findings with previous studies of mars and the snc meteorites indicates that 1 the snc mineralogies are representative of large volcanic regions of mars with surface ages as old as 2 3 ga 2 the martian mantle was depleted in aluminum at least as long ago as the oldest terrain analyzed ophir planum and 3 there has been little evolution in the composition of mantle source regions as the 180 ma snc mineralogies are comparable to those of the oldest terrains analyzed

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

worldwide distribution of group velocity of mantle rayleigh waves as determined by spherical harmonic inversion we have determined the worldwide distribution of group velocity of mantle rayleigh waves for periods between 100 and 300 sec without assuming any regionalization group slowness 1 u is expressed by spherical harmonics and the coefficients up to angular order 7 have been determined from travel times of rayleigh waves by a least squares method from these u has been synthesized since we cannot obtain information about the odd terms of the expansion from one circuit measurements around the world we have used group velocities of mainly r 2 and r 3 the overall pattern of u for periods between 100 and 200 sec is consistent with results of previous pure path and regional studies group velocities for tectonically active regions are low and those of the shields and the northwestern pacific are high

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

three dimensional seismic models of the earth s mantle accurate models of the distribution of elastic heterogeneity in the earth s mantle are important in many areas of geophysics the purpose of this paper is to characterize and compare quantitatively a set of recent three dimensional models of the elastic structure of the earth to assess their similarities and differences and to analyze their fit to one class of data in order to highlight fruitful directions for future research the aspherical models considered are the following m84c woodhouse and dziewonski 1984 lo2 56 dziewonski 1984 mdlsh tanimoto 1990a sh 10c 17 masters et al 1992 and s12 wm13 su et al 1994 through much of the discussion m84c and lo2 56 are combined into a single whole mantle model m84c lo2 56 the fit of each model to previously tabulated even degree normal mode structure coefficients taken from smith and masters 1989a and ritzwoller et al 1988 for multiplets along the normal mode fundamental and first second and fifth overtone branches is also presented rather than concentrating on detailed comparisons of specific features of the models analyses of these models are general and statistical in nature in particular we focus on a comparison of the amplitude and the radial and geographical distribution of heterogeneity in each model and how variations in each affect the fit to the normal mode observations in general the results of the comparisons between the models are encouraging especially with respect to the geographical distribution of heterogeneity and in the fit to the normal mode data sensitive to the upper mantle and lowermost lower mantle there remain however significant discrepancies in amplitude and in the radial distribution of heterogeneity especially near the top of the upper mantle and near the top of the lower mantle the confident use of these models to constrain compositional and dynamical information about the mantle will await the resolution of these discrepancies the factors that may be responsible for the differences in the models and or for the misfit between the observed and predicted normal mode data are divided into two types intrinsic or procedural and extrinsic or structural we discuss only three extrinsic factors at length here including errors in the reference crustal models unmodeled topography on discontinuities in the interior of the mantle and errors in the assumed relationships between shear s and compressional p heterogeneity

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

new bulk sulfur measurements of martian meteorites and modeling the fate of sulfur during melting and crystallization implications for sulfur transfer from martian mantle to crust atmosphere system abstract sulfur storage and transport between different reservoirs such as core mantle crust and atmosphere of mars are tied to igneous processes martian meteorites carry a record of mantle melting and subsequent differentiation history of martian magmas investigation of s geochemistry of martian meteorites can thus provide an understanding of how s is transferred from the martian interior to the exosphere in this study we measured bulk s concentration of 7 martian meteorites and modeled the behavior of s during both isobaric crystallization of primary martian magmas and isentropic partial melting of martian mantle comparisons between measured data and modeled results suggest that 1 sulfides may become exhausted at the source during decompression melting of the mantle and mantle derived basalts may only become sulfide saturated after cooling and crystallization at shallow depths and 2 in addition to degassing induced s loss mixing between these differentiated sulfide saturated basaltic melts and cumulus minerals with without cumulate sulfides could also be responsible for the bulk sulfur contents in some martian meteorites in this case a significant quantity of s could remain in martian crust as cumulate sulfides or in trapped interstitial liquid varying from 2 to 95 percent by weight our modeling also suggests that generation of sulfide undersaturated parental magmas requires that the mantle source of martian meteorites contain

los angeles a tale of two stones we compare and contrast the mineralogy and petrology of the 2 stones of the extremely ferroan and cr poor martian meteorite los angeles the 2 stones are similar in many characteristics strongly suggesting that they originated from a single flow or shallow intrusion however stone 2 is more ferroan and enriched in late stage materials than its larger and more widely studied sibling stone 2 has a far higher abundance 25 vol than stone 1 10 vol of combined opaques meaning not only conventional opaque minerals but also and more abundantly fine grained symplectitic intergrowths of fayalite ferroan augite silica interpreted as pyroxferroite breakdown material pbm the bulk composition of the pbm is close to that of stoichiometric pyroxferroite with roughly 45 wt feo extensive zonation within the pyroxenes of both stones is consistent with origin by closed system fractional crystallization of the parent basaltic melt s however the compositional and modal disparity between the two stones suggests that they formed in an environment where at least mild multi cm scale differentiation occurred probably in both stones crystallization began from similar melts with mg 27 28 mol but during crystallization significant migration of the melt component occurred perhaps by crystal settling and or filter pressing stone 2 acquired an enhanced proportion of residual melt and thus higher proportions of late stage materials such as pbm oxides and phosphates within the pbm clinopyroxene poikiloblastically encloses fayalite and silica at least some of the pbm had already formed by decomposition of pyroxferroite before the major shock that caused the very scarce brecciation within los angeles however the low abundance of fractures within pbm in comparison to pyroxene and some other minerals may be an indication that the textures of pbm regions typically did not assume their final detailed configuration until after the last major shock the steep slope of a pyroxene mg cr correlation suggests that igneous crystallization occurred at higher fo2 in los angeles than in otherwise similar shergottites such as que 94201 shergotty and zagami

seismic heterogeneities in the indian lithosphere abstract rayleigh wave group velocity distributions over the indian region were obtained by the backus gilbert method for time periods 15 25 40 50 and 60 s the observed velocity variations reveal sharp lithospheric heterogeneities in this region southern peninsular india is marked by high velocities in contrast to the northern indo gangetic plain and the himalaya highest surface wave velocities are observed over the southern part of the deccan traps and the dharwar craton whereas the metamorphic terrains and rift zones exhibit anomalous low velocities the nepal himalaya and indo burmese collision zones are characterised by contrasting velocities which reflect their diverse orogenesis the bay of bengal is marked by an anomalous 6 12 higher velocity as compared with the indian continental region for the periods 25 50 s

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

time evolving seismic tomography the method and its application to the 1989 loma prieta and 2014 south napa earthquake area california we propose a time evolving approach to conduct traveltime seismic tomography in the 1989 mw 6 9 loma prieta earthquake and 2014 mw 6 0 south napa earthquake area california the recording period of the chosen seismic data between january 1 1967 and the day before the 2014 south napa earthquake is divided into two time windows separated by the 1989 loma prieta earthquake in each time window the subsurface velocity structure is iteratively updated starting from the final model of the first time window the velocity model has been successively improved throughout iterations in the second time window indicating that the traveltime data of later time windows have provided extra information to refine the subsurface images strong heterogeneities are observed in the final p wave velocity model both of the two large earthquakes occurred at transition zones in between high vp and low vp anomalies in all this study shows the effectiveness of the time evolving seismic tomography method

anelastic structure of the iberian peninsula obtained from an automated regionalization algorithm and stochastic inversion abstract an automated regionalization of a reduced domain of the earth s surface without a priori seismotectonic information and the corresponding anelastic structures are achieved by means of a sequential application of a principal component analysis a clustering procedure and the stochastic inversion algorithm to anelastic attenuation coefficients of rayleigh waves our database is formed by path averaged attenuation coefficients derived from fundamental mode rayleigh waves crossing the iberian peninsula the wavetrains were recorded at the broad band stations installed some years ago in the iberian peninsula for the iliha project before the sequential application of the algorithms the area covered by the seismic paths was characterized by 22 maps of local attenuation coefficients corresponding to the 10 120 s period range all these maps were obtained by applying yanovskaya s formulation for laterally heterogeneous media to the set of path averaged attenuation coefficients mentioned above after that we divided the iberian peninsula into six homogeneous regions in terms of the local attenuation coefficients for 22 different periods and by means of the principal component analysis and the clustering algorithm we then obtained by stochastic inversion the respective anelastic structure down to a depth of 225 km for the six homogeneous regions the coefficients vary from 1 0 to 2 0 10 3 km 1 and the q 1 structures ranging from 110 10 3 to 40 10 3 suggest for five of the regions an asthenosphere with its upper and lower boundaries close to 80 and 180 km depth respectively a shallow beginning of the asthenosphere is detected for the sixth homogeneous region this range is very similar to the depths deduced from previous tomographic studies of the iberian peninsula based on rayleigh wave phase and group velocities finally correlations obtained between the regions and some seismotectonic characteristics of the peninsula are discussed it is noteworthy that we cannot associate each of the six homogeneous regions with a single hercynian alpine or neogene domain

petrology and chemistry of the basaltic shergottite north west africa 480 north west africa nwa 480 is a new martian meteorite of 28 g found in the moroccan sahara in november 2000 it consists mainly of large gray pyroxene crystals the largest grains are up to 5 mm in length and plagioclase converted to maskelynite excluding the melt pocket areas modal analyses indicate the following mineral proportions 72 vol pyroxenes extensively zoned 25 maskelynite 1 phosphates merrillite and chlorapatite 1 opaque oxides ilmenite ulvospinel and chromite and sulfides and 1 others such as silica and fayalite the compositional trend of nwa 480 pyroxenes is similar to that of queen alexandra range que 94201 but in nwa 480 the pyroxene cores are more mg rich en 77 en 65 maskelynites display a limited zoning an 42 50 ab 54 48 or 2 4 our observations suggest that nwa 480 formed from a melt with a low nuclei density at a slow cooling rate the texture was achieved via a single stage cooling where pyroxenes grew continuously a similar model was previously proposed for que 94201 by mcsween et al 1996 nwa 480 is an al poor ferroan basaltic rock and resembles zagami or shergotty for major elements and compatible trace element abundances the bulk rock analysis for oxygen isotopes yields delta 17 o 0 42parts per thousand a value in agreement at the high margin with those measured on other shergottites clayton and mayeda 1996 romanek et al 1998 franchi et al 1999 its ci normalized rare earth element pattern is similar to those of peridotitic shergottites such as allan hills alh a77005 suggesting that these shergottites shared a similar parent liquid or at least the same mantle source

fire lake depression a glacially eroded feature in southwestern saskatchewan canada fire lake depression which is 9 km long 5 km wide and about 100 m deep was formed by surface removal of about 40 m of drift mainly till and 60 m of cretaceous sands silts and clays the depression which was formed during the last glaciation was partly filled with hummocky glaciolacustrine sands and silts the bedrock beneath the depression is slickensided folded brecciated softened and gouged typical of structures formed by shear the physical dimensions stratigraphy structure and age last glaciation indicate that the fire lake depression was formed by glacial erosion the folding faulting brecciation gouge and softening of the bedrock beneath the depression are indicative of shear and suggest glacial thrusting the process of glacial thrusting was not verified however because the sediments excavated from the depression were not found the fact that the base of the depression corresponds to the uppermost most clayey bed least shear resistance suggests that the depression was fo

effects of lateral heterogeneity and source process time on the linear moment tensor inversion of long period rayleigh waves spectra of mantle rayleigh waves recorded on the ida network are inverted to determine the seismic moment tensor of the 9 june 1980 california mexico border earthquake the 29 july 1980 vanuatu islands earthquake and the 9 july 1980 santa cruz islands earthquake examinations are made to correct for phase velocity lateral heterogeneity and source process time a simple regionalization stable continent tectonic region young ocean and old ocean improves results of the linear inversion but the phase correction is not large enough and the discontinuous change of phase velocity across the boundary between regions causes an artificial rapid change in apparent phase velocity as a function of azimuth therefore a more detailed but gradual representation of the lateral heterogeneity is desirable to correct for the propagation effect in the linear inversion a source process time which consists of the nondirectional part of the apparent duration of main faulting and the delay time of the faulting from initial break is estimated by a phase analysis of rayleigh waves the source process time is generally proportional to the seismic moment on the log log scale but some earthquakes deviate considerably from the general relation therefore the measurement of the source process time should be made before the moment tensor inversion the phase errors introduced by the lateral heterogeneity and source process time may cause a bias to low scalar moment

the dirt hills structure an ice thrust feature in southern saskatchewan canada the dirt hills structure is expressed at the surface as a broad arcuate moraine 7 5 km wide 120 m high and 40 km long the structure is composed mainly of bedrock and drift consisting of three slabs stacked to form a single block 215 m thick the shear zones that bound the slabs are mainly in clays of the bearpaw formation the dirt hills structure originated during the last deglaciation when the glacier under compressive flow readvanced up the missouri coteau escarpment and stacked the subglacial slabs of bedrock and drift the subparallel arcuate ice thrust ridges are formed presumably by imbricate thrust faults originating from the uppermost shear zone

objective regionalization of rayleigh wave dispersion data by clustering algorithms summary an objective regionalization of a restricted domain of the earth s surface in terms of phase and group velocity data without previous tectonic information is presented we apply our working scheme to local rayleigh wave velocities which were determined from the study of teleseismic events recorded at the broad band stations of the network of autonomously recording seismographs nars installed in the iberian peninsula during the iliha project according to the phase and group velocity maps computed at different wave periods each point of the domain studied is characterized by two dispersion curves corresponding respectively to phase and group velocities the procedure that we propose consists of the application of principal component analysis pca to those velocities defining the local dispersion characteristics of the medium and then an average linkage al algorithm it is worthy of mention that the pca procedure enhances the relationship between local phase and group velocities in this way we obtain a classification of the domain into 10 homogeneous regions each homogeneous area is almost coincident from a seismotectonic point of view with either neogene alpine or hercynian domains after the classification we are able to deduce by stochastic inversion eight different shear velocity structures for eight of the 10 homogeneous regions all the structures deduced suggest a well developed lowvelocity channel from 80 to 180 km in depth for the whole iberian peninsula but with a clearly distinct evolution of their shear velocities with depth some of the models reach shear velocities close to 4 75 km s at depths beneath this channel the highest shear velocities close to 5 0 km s l are obtained at a depth of 50 km and down to 200 km for region 3 neogene and two possible low velocity channels down to a depth of 225 km appear for models 7 and 8 hercynian domains the existence of low velocity channels in some models at depths of less than 30 km is discussed in terms of the resolving kernels and the generation of compatible models in short the main realistic differences between the models come from the shear velocities modelling each low velocity channel as an example the shear velocities for depths ranging from 80 to 180 km vary according to the region from 3 82 km s l to 4 42 km s

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

global love wave phase velocity variation and its significance to plate tectonics abstract global love wave phase velocity variation was constructed for periods between 80 and 200 s by using approximately 9000 paths from 971 earthquakes with m 5 5 the data set was from gdsn and geoscope networks between 1980 and 1987 we examined both the spherical harmonic expansion method and the block parameterization method with a simple constant damping parameter approach synthetic tests showed that more accurate results were obtained by the block parameterization method than by the spherical harmonic expansion method we adopted the block inversion method with a nearly equal area block 5 5 near the equator discretization the general pattern of the resulting maps were consistent with previous global and local studies with a discretization of 5 by 5 the maps were detailed enough to test some plate tectonic models for the pacific atlantic and indian oceans surface wave velocities increased smoothly to plate ages older than 100 ma simple forward modeling showed that seismic phase velocity variation with a continuous thickening of lithosphere up to about 150 ma fits the present observation disagreeing with the model deduced from the heat flow and ocean depth data which change variations at about 60 80 ma the seismic phase velocity variations in different oceans showed systematic differences at younger ages and convergence beyond 100 ma the difference at younger ages implies a failure of scaling derived from a simple thermal boundary layer model for oceanic plates age seismic phase velocity relationships on each side of ridges were also examined and asymmetric velocity variations were found which suggests differences in thermal states from one side of the ridge to the other in order to further examine the thermal state of the lithosphere average age phase velocity relations were established for each ocean and subtracted from phase velocity variation maps the results indicated broad low velocity regions in the south pacific super swell region the south and west indian ocean and high velocity regions east of the east pacific rise and in the north to northeast indian ocean the results reflect the asymmetry of phase velocity variation about ridges there is some correlation between hot spot locations and low velocity anomalies but additional large scale thermal anomalies exist under old oceanic plate

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

rare earth element carriers in the shergotty meteorite and implications for its chronology ion probe measurements of the rare earth element ree concentrations of individual grains of the shergotty meteorite are reported phases analyzed include whitlockite apatite baddeleyite augite pigeonite maskelynite and k rich glass u concentrations of whitlockite and apatite crystals were also obtained the whole rock ree pattern is dominated by whitlockite which contains over 95 of the light rare earth elements lree ree concentrations in apatite are much lower than estimated by laulet al 1986 all the whitlockites whether intergrown with pyroxene equant or interstitial have the same relative abundances of lree i e patterns are almost flat from la to sm the observation by joneset al 1985 of a skeletal whitlockite with lree enrichment is not confirmed by analyses of the same grain pyroxene rims are not enriched in lree no leachable carrier enriched in lree and associated with pyroxene laulet al 1986 jagoutz and wanke 1986 has been found instead either a laboratory contamination or a petrographically cryptic phase such as a film on grain boundaries is suspected as the carrier of lree enrichments if a grain boundary film carries the enrichments it would not be resistant to the metamorphic resetting which has affected other isotopic reservoirs in this sample thus there is no compelling reason to consider the sm nd pyroxene leachates line jagoutz and wanke 1986 as a 360 m y isochron estimates of ree abundances in the shergotty intercumulus melt indicate that a complex petrogenesis is required in agreement with the conclusions of mckayet al 1986a pyroxene distribution coefficients measured experimentally mckayet al 1986a are compared with estimates from measured ree abundances in augite and pigeonite evolution of ree abundances in the shergotty late stage interstitial melt as inferred from analyses of whitlockite conforms with trends predicted from partitioning considerations and requires no special processes such as metasomatism the average u concentrations of whitlockite and apatite are respectively 540 and 1 550 ppb although the calcium phosphates are enriched in u they contain less than 20 of the u in shergotty

aspherical heterogeneity of the mantle from phase velocities of mantle waves long period surface waves are used to map the lateral heterogeneity of the upper 100 600 km of the mantle there is good correlation of velocity with surface tectonics and heat flow convergence regions are generally slow for love waves and fast for rayleigh waves back arc basins have slower than average shallow mantle some island arcs show evidence of fast material at greater depth deep seated slow anomalies underlie the red sea afar region of north east africa western north american northern east pacific rise indian ocean triple junction and the tasman sea campbell plateau regions the fastest regions are in the north central australia new guinea and the south atlantic

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

new lithologies in the zagami meteorite evidence for fractional crystallization of a single magma unit on mars abstract zagami consists of a series of increasingly evolved magmatic lithologies the bulk of the rock is a basaltic lithology dominated by pigeonite fs 28 7 54 3 augite fs 19 5 35 0 and maskelynite ab 42 53 approximately 20 vol of zagami is a basaltic lithology containing feo enriched pyroxene pigeonite fs 27 0 80 8 and mm to cm sized late stage melt pockets the melt pockets are highly enriched in olivine bearing intergrowths mesostases phosphates both whitlockite and water bearing apatite fe ti oxides and sulfides the systematic increases in abundances of late stage phases fs and incompatible element e g y and the rees contents of pigeonite ab contents of maskelynite and feo concentrations of whitlockite all point to a fractional crystallization sequence the crystallization order in zagami and the formation of these various lithologies was controlled by the abundances of iron phosphorus and calcium during fractional crystallization iron and phosphorus enrichment occurred ultimately forcing the crystallization of calcium phosphates and olivine bearing intergrowths the limited amount of calcium in the melt and its partitioning between phosphates and silicates controlled the crystallization of phosphates plagioclase pigeonite and augite the presence of these feo enriched water poor late stage lithologies has important implications discrepancies between experimental and petrologic studies to infer the history of basaltic shergottites may be partially explained by the use of starting compositions which are too feo poor in the experimental studies the water poor nature of the late stage melt pockets suggests crystallization from a very dry magma although whether this magma was always dry or experienced significant near surface degassing remains an open question finally the presence of fractional crystallization products within zagami suggests that this may be a relatively common process on mars

red deer hill a drumlinized glaciotectonic feature near prince albert saskatchewan canada red deer hill is 5 km long 3 km wide and 70 m high the hill is a glaciotectonic structure formed by a single 106 m thick thrust block presumably derived from the 80 m deep upglacier holmes depression the thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first mennon glaciation the hill depression structure was formed by the battleford glacier which drumlinized red deer hill before depositing a veneer of till over the structure the holmes depression was filled with glacial lake saskatchewan lacustrine and deltaic sediments horizontal displacement along a decollement in the direction of the activating force resulted in a stress environment changing from extension to compression in the zone of extension holmes depression an active rankine state developed and beds stretched and thinned in the zone of compression red deer hill conversely a passive rankine state developed an