quantitative morphologic analysis of boulder shape and surface texture to infer environmental history a case study of rock breakdown at the ephrata fan channeled scabland washington boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion transport and weathering at present morphologic information at the boulder scale is underutilized as a recorder of environmental processes partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets we develop such a parameter set incorporating a range of measures of boulder form and surface texture we use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser scanned molds the parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the channeled scabland washington 1 basalt outcrop talus 2 flood transported boulders recently excavated from a quarry and 3 flood transported boulders extensively weathered in situ on the ephrata fan surface size and shape data were found to distinguish between flood transported and untransported boulders size and edge angles 120 of flood transported boulders suggest removal by preferential fracturing along preexisting columnar joints and curvature data indicate rounding relative to outcrop boulders surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments past signatures diagnostic of flood transport still persist on surface boulders despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes

siderophile trace elements in alh84001 other snc meteorites and eucrites evidence of heterogeneity possibly time linked in the mantle of mars we report neutron activation analyses including radiochemical determination of trace siderophile elements au ge ir ni os and re for three snc martian meteorites and os and re results for numerous eucrites ratios such as ga al in the snc orthopyroxenite alh84001 confirm its martian affinity its many distinctive characteristics most notably its near primordial age notwithstanding to the list of alh84001 s idiosyncrasies can now be added extraordinarily low concentrations of au ni and especially re 17 pg g for a martian meteorite we consider several possible origins for the anomalously low re content in alh84001 including metasomatism or alteration the pyroxene cumulate nature of this rock probably does not account for its low re content other snc meteorites are also cumulates an examination of re nd variations among terrestrial basalts and komatiites suggests that re is compatible with mantle minerals in general and only incompatible with olivine however olivine dominates the mantle residuum especially during komatiite genesis our preferred model is that the alh84001 parent melt formed in a mantle source region that was far more re depleted and or at a substantially lower oxygen fugacity than the sources of the young snc meteorites such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late accreting matter and similarly derive most planetary water which serves as an oxidant very late in accretion according to this model alh84001 formed before the siderophile rich matter and water had been mixed well into the martian interior possibly the martian mantle never became generally as re rich and or oxidized as the source region s of the younger sncs

ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

the limiting pressure on a circular pile loaded laterally in cohesive soil in the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement if the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory in which the load is calculated on a long cylinder which moves laterally through an infinite medium an exact calculation of the load on such a cylinder is presented if this load is non dimensionalized with respect to the soil strength and the diameter of the pile it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile this result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface la resistance laterale limite en profondeur au seul mouvement horizontal represente un parametre im

metal silicate equilibrium in a homogeneously accreting earth new results for re the accretion and early differentiation of the earth is the starting point of earth history the abundances of metal seeking siderophile elements in the mantle are a powerful probe of those events it has long been known that siderophile element abundances in the earth s mantle are too high to have resulted from metal silicate equilibrium at near surface conditions this mismatch provided support for the idea that the earth accreted heterogeneously we report new experimental results for the highly siderophile element re and show that metal silicate partition coefficients decrease with increasing temperature at fixed pressure and relative oxygen fugacity calculations using these and previously published experimental results indicate that the abundances of the moderately siderophile elements fe ni co mo w p and most importantly the highly siderophile element re in earth s upper mantle are consistent with early equilibration between metal and silicate liquid at the base of a deep 800 1000 km magma ocean reconciliation of mantle abundances of moderately and highly siderophile elements with high temperature and pressure metal silicate equilibrium would obviate the need for heterogeneous accretion these new results indicate that the earth accreted homogeneously rather than heterogeneously or that evidence for heterogeneous accretion was erased by early high temperature and pressure melting events

partitioning of molybdenum between magnetite and melt a preliminary experimental study of partitioning of ore metals between silicic magmas and crystalline phases the partitioning of molybdenum between magnetite mt and two rhyolitic melts has been determined at 800 degrees c 1 kb of pressure and at two oxygen fugacities at an oxygen fugacity one half a log unit above nickel nickel oxide d super mt melt mo 0 21 or 0 08 a decrease in the oxygen fugacity to the graphite methane buffer is accompanied by an increase in d super mt melt mo to 0 52 or 0 13 the differences in melt composition have no discernible effect these data are interpreted by writing balanced chemical potential relationships involving independently variable phase components the nernst partition coefficients given above are then formulated as a function of these equilibria given the observed variation in d super mt melt mo with oxygen fugacity and assuming that fe 2 moo 4 is the molybdenum bearing phase component in magnetite our data suggest that mo iii may be present in naturally occurring silicic magmas further we suggest the establishment of critical bulk partition coefficients for ore forming systems defined in terms of critical values of the efficiency of removal function defined by candela and holland 1986 these preliminary results indicate that the crystallization of ferromagnesian or titanium bearing phases may be important in reducing the amount of molybdenum available for orthomagmatic hydrothermal ore formation oxygen fugacity may play a large role in the melt crystal vapor equilibria ofmolybdenum under magmatic conditions

core mantle differentiation in mars 1 the physical and chemical conditions under which martian core formation took place are not well constrained we modeled the pressure temperature and oxygen fugacity conditions under which it would be possible to match the inferred depletions of moderately siderophile elements ni co w mo ga p and ge in the martian mantle using new constraints on their metal silicate partitioning behavior using literature metal silicate partitioning data we characterize the dependence of the metal silicate partition coefficients d on the temperature pressure oxygen fugacity and composition of the silicate melt and the metal using a uniform parameterization approach for each element our results show that it is impossible to simultaneously account for the martian mantle depletions of moderately siderophile elements if the martian core sulfur content exceeds 10 5 wt at reducing conditions 1 log unit below the iron wustite iw buffer at 10 5 wt core s the conditions that best satisfy martian mantle abundances of the seven siderophile elements are a mean pressure of 13 1 gpa at 2330 k corresponding to the presence of a magma ocean at least 1000 km deep during martian core formation more oxidizing conditions than the iron wustite buffer as suggested by iron meteorites are inconsistent with mantle siderophile element abundances extension of our approach to the highly siderophile elements ru pd re ir and pt shows that their martian mantle abundances are orders of magnitude too high to be accounted for by metal silicate equilibration at high pressure and high temperature in a magma ocean requiring a late veneer stage after core formation

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

petrography and bulk chemistry of martian lherzolite lew88516 the meteorite lewis cliffs 88516 is a gabbroic lherzolite with geochemical and petrologic characteristics typical of the shergottites a distinct subgroup of basaltic achondrites belonging to the snc martian meteorite clan we report new inaa and microprobe data for lew88516 noting small but significant differences between our results and those previously published for this meteorite these discrepancies are mainly attributed to heterogeneities in the bulk rock powder which was distributed to several laboratories for geochemical studies other discrepancies are attributed to interlaboratory bias we emphasize that even minor variations between datasets may have the potential to significantly affect geochemical models for martian basalts small differences in bulk trace element chemistry between lew88516 and martian lherzolite alh77005 may indicate that they crystallized from different magmas copyright 1997 elsevier science ltd

chassigny petrogenesis melt compositions intensive parameters and water contents of martian magmas abstract the snc meteorites are a class of eight basaltic achondrites that have extremely young crystallization ages 1 3 ga chassigny a unique snc meteorite is a dunite containing fo68 olivines and rare poikilitic ca pyroxenes it is one of the most primitive snc meteorites and thus is most likely to reveal information about the snc basalt source region this study presents a detailed examination of partially crystallized melt inclusions in cumulus olivine grains in chassigny these trapped melts are argued to be representative samples of the melt that existed when chassigny crystallized this melt has been modified however by interaction with the host olivine and by closed system crystallization the phases inside the melt inclusions include hydrous ti rich amphibole kaersutite biotite two pyroxenes and rhyolitic and alkali feldspar glasses all phases have been extensively analyzed with an electron microprobe the new mineralogical information is combined with a complementary experimental study of kaersutite melt equilibria this combined data set can be used to formulate a system of linear equations which can then be solved to determine the composition of the originally trapped melt this calculation reveals that the trapped melt was an feo rich and al2o3 poor basalt the melt composition is shown to be consistent with the crystallization sequence both inside the melt inclusions and in the rock matrix the major element chemistry of this liquid closely resembles terrestrial boninite lavas the new data also allow the intensive conditions temperature total pressure and water fugacity of chassigny crystallization to be estimated two pyroxene geothermometry indicates that equilibration temperatures were 1000 50 c although amphibole does not coexist with melt until t 960 c the trapped liquid initially contained 1 5 wt dissolved water crystallization of anhydrous phases caused water to buildup in the trapped melt prior to kaersutite crystallization the melt must have contained at least 4 wt dissolved water suggesting that a minimum of 1 5 kbar total pressure is required a maximum total pressure cannot be inferred but all available data are consistent with low pressure 5 kbar crystallization finally x h2o in the fluid in the melt inclusion is estimated to have been at least 0 8 in order to stabilize amphibole without plagioclase implying that the water fugacity was 1480 bars the existence of hydrous melts and conditions appropriate for amphibole crystallization suggest that evolved sio2 rich lavas exist on the chassigny parent body mars

interpretation of t bar penetrometer tests at shallow embedment and in very soft soils the cylindrical t bar penetrometer was developed for profiling the undrained strength of soft soils in the centrifuge and is now a widely used offshore site investigation tool the conventional interpretation of the t bar test is to convert the measured penetration resistance to soil strength using a single bearing factor associated with steady flow of soil around the bar this paper describes a new analysis for the interpretation of t bar penetrometer tests at shallow embedment and in soft soils which is an increasingly significant consideration in the design of seabed infrastructure including pipelines the analysis captures two mechanisms that are usually neglected i soil buoyancy and ii the reduced bearing factor arising from the shallow failure mechanism mobilized prior to the full flow of soil around the bar the framework derives from theoretical considerations and is calibrated using large deformation finite element analyses the depth at which the steady deep penetration condition is reach

glass bearing inclusions in olivine of the chassigny achondrite heterogeneous trapping at sub igneous temperatures three types of glass bearing inclusions are present in olivine and chromite of the chassigny achondrite pure glass monocrystal glass plus a single mineral grain and multiphase glass plus a variety of minerals inclusions the occurrence texture and mineralogy of these inclusions and the chemical composition of the glass suggest an origin by heterogeneous trapping of these phases the glass is rich in sio2 al2o3 na2o k2o and poor in mgo feo and cao and contains appreciable amounts of cl the compositional variability of the glass is independent of the mineral content of the inclusions heating experiments with final temperatures of 900 1000 and 1200 c were performed with chassigny inclusions for the first time the glass of the heated inclusions has a chemical composition similar to that of unheated inclusions this situation suggests that the glass cannot be a residual melt but rather is an independent component that was trapped with or without mineral phases the extreme heterogeneity in alkali contents and in particular rb and sr contents also suggests precipitation and mixing of solid precursors the most rb rich glasses have near chondritic rb sr ratios possibly indicating a chondritic source for their precursor s none of the inclusions contain bubbles like those of typical melt inclusions in terrestrial igneous minerals furthermore many inclusions are at the center of radial cracks in the host olivine which indicates development of an overpressure within the inclusions at some time a volume increase of the inclusions could have been achieved by differential thermal expansion of the content of the inclusion during a heating event that mechanism requires bubble free and solid preheating inclusion contents these features are incompatible with an origin of the inclusions by trapping of a silicate melt and point toward heterogeneous trapping of solid phases the first n analyses performed in chassigny glass bearing inclusions by nuclear reaction analysis nra revealed high and variable n contents of the glass which suggests trapping of a solid precursor presumably at relatively low temperatures from a fluid rather than a melt in conclusion the glass bearing inclusions in chassigny olivine are not residuals after a closed system evolution of a trapped melt but rather heterogeneously trapped precipitates of a fluid that existed during formation of chassigny constituents consequently it is very unlikely that the host olivine has an igneous origin

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

controls on basalt terrace formation in the eastern lesotho highlands abstract the objective of this study is to ascertain the relative importance of lithological controls and geomorphological processes in the development of drakensberg basalt terraces various hypotheses for terrace formation are considered including geological controls macroscale geomorphology and climatic geomorphological controls the variations in strength and relative age differences for scarp surface exposures on two slopes of varying aspect are determined so that a comparison can be made between various scarp outcrops and relative rates of weathering scarp outcrops were measured for their rock mass strength rock surface roughness and percentage lichen cover the ethylene glycol test was performed on prepared rock samples to determine susceptibility to tensional breakup a satellite image depicting the distribution of late lying contemporary snow was used to assist in the construction of topo climatic linkages with scarp terrace localities findings show that terraces are most common on southeast facing aspects and coincide with the major joint strike direction lithological factors are thus considered the primary control to such terrace development it is suggested that a different set of geomorphological processes operates on various slope altitudinal and slope orientational positions at any given time

predicting the resistance profile of a spudcan penetrating sand overlying clay assessment of the risk of punch through failure of spudcan foundations on sand overlying clay requires prediction of the full penetration resistance profile from touchdown and through punch through to equilibrium of the vertical resistance at depth in the underlying clay layer this study uses the coupled eulerian lagrangian approach a large deformation finite element analysis method to model the complete penetration resistance profile of a spudcan on sand overlying clay the sand is modeled using the mohr coulomb model while the clay is modeled using a modified tresca model to account for strain softening the numerical method is then used to simulate a series of spudcan penetration tests performed in a geotechnical centrifuge on medium dense sand overlying clay the punch through behavior observed in the experiments is replicated and the penetration resistance profiles from numerical analyses are generally a reasonable match to the experimental measure ments the influences of the sand layer height to foundation diameter ratio sand clay interface shear strength and strength gradient in clay on the penetration resistance profiles are explored in a complementary parametric study the penetration resistance in the underlying clay layer is well predicted using a simple linear expression for the bearing capacity factor for the spudcan and underlying sand plug this expression is combined with an existing failure stress dependent model for predicting peak resistance to form a simplified method for prediction of the full penetration resistance profile this new method provides estimates of the vertical penetration that the spudcan will run during the punch through event it is validated against both medium dense and dense sand centrifuge tests

molybdenum in eucrites evidence for a metal core in the eucrite parent body molybdenum concentrations from 15 to 70 ppb in eucrites have been determined with a new method of neutron activation these values are very low compared to chondrites and are in agreement with the large depletions of other siderophile elements in eucrites the eucrites have a mean mo la ratio of 0 0066 which is a factor of 570 lower than the ci chondritic ratio 3 75 the depletions of siderophiles in eucrites were presumably caused by segregation of metal molybdenum however is fractionated as an incompatible element similar to la among the individual eucrites the variable concentrations but roughly constant ratio of mo to la indicate that metal was absent during the fractionation that produced the eucrites and imply that core formation occurred before the fractionation the need for a relatively large degree of partial melting to completely segregate metal argues for a fractional crystallization model for the production of the eucrite magmas the amount of metal in the eucrite parent body epb required to obtain the observed depletion of the mo la ratio depends on the degree of partial melting during metal silicate equilibrium the depletion of co has a dependence on the degree of partial melting different from mo and w and using co together with mo and w the metal content and degree of partial melting can be estimated a metal content of 30 to 50 and metal segregation at approximately 50 partial melting of the silicates is consistent with the data if the epb had a ratio of co to refractory lithophile elements less than ci chondrites a metal content as low as 20 with metal segregation at 20 partial melting is possible a large metal core in the epb vesta may therefore be detectable from a spacecraft

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

evidence for mo isotope fractionation in the solar nebula and during planetary differentiation abstract mass dependent mo isotope fractionation has been investigated for a wide range of meteorites including chondrites enstatite ordinary and carbonaceous chondrites iron meteorites and achondrites eucrites angrites and martian meteorites as well as for lunar and terrestrial samples magmatic iron meteorites together with enstatite ordinary and most carbonaceous chondrites define a common 98 95 mo value of 0 16 0 02 relative to the nist srm 3134 mo standard which is interpreted to reflect the mo isotope composition of bulk planetary bodies in the inner solar system heavy mo isotope compositions for iab iron meteorites most likely reflect impact induced evaporative losses of mo from these meteorites carbonaceous chondrites define an inverse correlation between 98 95 mo and metal content and a positive correlation between 98 95 mo and matrix abundance these correlations are mainly defined by cm and ck chondrites and may reflect the heterogeneous distribution of an isotopically light metal and or an isotopically heavy matrix component in the formation region of carbonaceous chondrites alternatively the elevated 98 95 mo of the cm and ck chondrites could result from the loss of volatile isotopically light mo oxides that formed under oxidized conditions typical for the formation of these chondrites the mo isotope compositions of samples derived from the silicate portion of differentiated planetary bodies are heavy compared to the mean composition of chondrites and iron meteorites this difference is qualitatively consistent with experimental evidence for mo isotope fractionation between metal and silicate the common 98 95 mo values of 0 05 0 03 of lunar samples derived from different geochemical reservoirs indicate the absence of significant mo isotope fractionation by silicate differentiation or impact metamorphism volatilization on the moon the most straightforward interpretation of the mo isotope composition of the lunar mantle corresponds to the formation of a lunar core at a metal silicate equilibration temperature of 1800 200 c the investigated martian meteorites angrites and eucrites exhibit more variable mo isotope compositions which for several samples extend to values above the maximum 98 95 mo 0 14 that can be associated with core formation for these samples post core formation processes such as partial melting metamorphism and in the case of meteorite finds terrestrial weathering must have resulted in mo isotope fractionation estimates of the metal silicate equilibration temperatures for mars 2490 770 c and the angrite parent body 1790 230 c are thus more uncertain than that derived for the moon although the mo isotope composition of the bulk silicate earth has not been determined as part of this study a value of 0 16 98 95 mo 0 can be predicted based on the chondrite and iron meteorite data and by assuming a reasonable temperature range for core formation in the earth this estimate is in agreement with four analyzed basalt standards 0 10 0 10 improved application of mass dependent mo isotope fractionation to investigate core formation most of all requires an improved understanding of potential mo isotope fractionation during processes not related to metal silicate differentiation

petrography mineral chemistry and petrogenesis of antarctic shergottite lew88516 abstract lew88516 lew like its near twin alh77005 alh is a maskelynite bearing harzburgite and a member of the snc family of achondrites lew is texturally heterogenous exhibiting both poikilitic pyroxene oikocrysts enclosing subhedral olivine and euhedral chromite and non poikilitic cumulus framework of olivine and minor pyroxene with interstitial maskelynite and secondary minerals textures pyroxenes in lew appear to be slightly more iron rich and more varied in composition than those in alh lew olivines have distinctly higher fe contents most of the olivine grains in lew have compositions more iron rich than any alh olivine observed lew olivine in non poikilitic areas is substantially more iron rich than olivine armored by pyroxene trace element and minor element patterns of lew and alh minerals are essentially identical and are consistent with closed system large volume crystallization of the major phases followed by development of later phases after assembly of the crystal pile major element compositions show the effects of moderate near solidus re equilibration in both meteorites the compositions of possible lew parent magmas calculated from mass balance methods using the components of magmatic inclusions in large olivine grains are very similar to those proposed earlier for alh and the eeta79001 shergottite while the subtle differences between lew and alh suggest they are not part of the same fall it is likely that they are derived from the same igneous processes

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

centrifuge modeling of the cyclic lateral response of a rigid pile in soft clay a series of centrifuge model tests of the lateral response of a fixed head single pile in soft clay is reported both monotonic and cyclic episodes of loading are described with varying amplitude and with intervening periods of reconsolidation the soil conditions are characterized by cyclic t bar penetrometer tests the ultimate capacity under monotonic load for virgin and for postcyclic conditions was found to be comparable with calculations based on existing design methods including theoretical plasticity solutions and empirical methods the lateral stiffness was observed to degrade with cycles with the rate of degradation being greater for larger cycles the degradation pattern has been tentatively linked to the cyclic t bar response by considering the damage associated with the cumulative displacement and remolding in each case this approach provides a consistent interpretation of the tests although episodes of pile movement and soil remolding led to a reduction in lateral resistance interv

timescale and morphology of martian mantle overturn immediately following magma ocean solidification energy of accretion in terrestrial planets is expected to create liquid silicate magma oceans their solidification processes create silicate differentiation and set the initial mantle structure for the planet solidification may result in a compositionally unstable density profile leading to cumulate rayleigh taylor overturn if a sluggish rather than stagnant lithosphere existed in the early stages of planetary history the pattern and timescale of overturn in which cold dense surface material sinks to the core mantle boundary have implications for core dynamo production volatile escape and fundamental differences between differently sized bodies our fully spherical mantle models reaffirm previous work suggesting that harmonic degree of overturn is dependent on viscosity contrast and layer thickness we find that cumulate overturn would likely have occurred with short wavelengths in an isoviscous model thermal convection ensues rapidly after overturn however when viscosity is temperature dependent compositional stability in the mantle suppresses the onset of whole mantle thermal convection for a viscosity of 1018 pa s the mantle could fully overturn in as little as 3 ma

the possible role of clay minerals in salt weathering abstract results of a salt weathering experiment on a laminated sandstone are reported it is observed that laminae which contain smectite clays break down more readily than those with little clay this preferential breakdown may be related to the swelling of the clays which assists salt weathering processes per se and or secondary microporosity created by the clays which could enhance salt weathering effects it is not possible at this point in time to state definitively the effects that the presence of clay has upon salt weathering but suggestions for future research are made

core formation in earth s moon mars and vesta stimulated by new experimental results on metal silicate partitioning of elements at elevated temperatures and pressures we have revisited the question of core formation in earth s moon mars and vesta the probable source of the eucritic meteorites earlier studies suggested metal silicate equilibrium in mars but led to the paradox that mars accreted homogeneously while the earth accreted heterogeneously using new elevated pressure and temperature metal silicate partition coefficients we show that abundances of the moderately siderophile elements in the mantles of the moon mars and vesta are consistent with early magma oceans on these bodies the most successful model for explaining the lunar mantle siderophile element abundances requires a core of 5 of the mass of the moon 500 km radius siderophile element abundances in mars are consistent with intermediate pressure metal silicate equilibrium as has also been recently suggested for the earth the most successful model for explaining the martian siderophile element abundances requires a bulk planetary composition that has greater than ci chondritic abundances of the moderately siderophile elements and a core of 30 of the mass of mars siderophile element abundances in the mantle of vesta are consistent with low pressure liquid metal liquid silicate equilibrium as expected for an asteroid sized body and a core of 10 of the mass of vesta comparison of our best fit oxygen fugacities for vesta with thermodynamic calculations of oxygen fugacity for silicate bearing iron meteorites indicates that parts of the inner solar system were homogeneous with respect to redox state at 4 5 ga approximately 2 log fo2units below the fe feo buffer much higher than estimates for the solar nebula similar comparisons for mars and the earth indicate that these bodies have undergone oxidation since 4 5 ga because the oxygen fugacities associated with metal silicate equilibrium in both mars and the earth moon system are much lower than those recorded in martian and terrestrial basaltic and periodotitic samples the oxidation on mars is most likely due to atmospheric effects whereas earth s much wider range of oxygen fugacities must be due to both atmospheric and plate tectonic effects

the parent magma of the nakhla snc meteorite inferred from magmatic inclusions abstract the nakhla meteorite one of the snc group of putative martian origin is an igneous rock a cumulate of augite and olivine that does not represent a magma composition samples of its parent magma were trapped as magmatic inclusions in its cumulus olivine crystals the inclusions range from 10 350 m in diameter and consist of augite rich in ti and al silica rich glass iron oxides ilmenite apatite and rare amphibole each inclusion has a rind of augite and chromite against its host olivine and a core of radiating sprays of augite set in glass and feldspar these textures are consistent with an origin as trapped silicate liquid twenty four inclusions were analyzed by electron microprobe by averaging series of rastered beam analyses on average the analyses are independent of the size of the inclusion most clearly for inclusions larger than 70 m diameter and variations among analyses are consistent with small differences in the proportions of augite glass and iron oxides exposed on thin section surfaces the average inclusion analysis is calculated to represent 28 host olivine and 72 inclusion composition the inclusion rinds are calculated to be 13 of the inclusion composition for which a small correction is made the inclusion composition is then corrected for mg fe exchange with the host olivine to chemical equilibrium with the cumulus augite cores and crystallization of 13 olivine onto the host crystal to yield a magma composition with the proper mgo feo ratio and with olivine and augite on its liquidus this composition nk93 is an estimate of nakhla s parent magma originally trapped in the inclusions nk93 is basaltic rich in iron and poor in aluminum compared to terrestrial basalts its abundances of al ti and na are consistent with the geochemistry of the snc meteorites as a whole nk93 is similar to the parent magmas proposed in an independent study of magmatic inclusions in nakhla but unlike other proposed compositions one proposed parent magma based on mass balance and the assumption that nakhla was a closed system after crystal accumulation is inconsistent with the magmatic inclusion studies and nakhla s petrography this suggests that nakhla was not a closed system but was infiltrated by post cumulus basaltic magmas another suggested parent magma was derived from element distribution between augite and basaltic magma but that calculation relied on an incorrect augite composition using a correct augite composition in that calculation yields a parent magma much closer in composition to nk93 thus three independent approaches converge in requiring that nakhla originally formed from a low al low mgo feo basalt like nk93

core formation in the earth and shergottite parent body spb chemical evidence from basalts constraints on processes of core formation in terrestrial planets may be inferred from the abundances of siderophile and chalcophile elements in their mantles of particular interest is a comparison of processes of core formation in the earth and in the shergottite parent body spb a terrestrial planet tentatively inferred to be mars to this end we i present new inaa and rnaa analyses of the non antarctic snc meteorites ii infer the composition of the spb mantle from the compositions of the snc meteorites iii infer the composition of the earth s mantle from the compositions of terrestrial basalts and iv deconvolve the effects of volatile depletion core formation and mineral melt fractionation on the abundances of siderophile and chalcophile elements in the spb and the earth element abundances in the mantles of the spb and the earth are estimated from element element correlations observed among basalt samples in basalts from the spb the snc meteorites four groups of covariant elements are observed highly incompatible moderately incompatible indifferent and compatible from correlations within these groups the spb mantle is found to be depleted in volatile elements and strongly depleted in siderophile and chalcophile elements for the earth the element element correlation method gives a mantle composition similar to previous estimates compared to the earth the spb mantle is richer in moderately siderophile elements e g w p consistent with its inferred higher oxidation state chalcophile elements in the spb mantle are more depleted than in the earth s mantle particularly when compared to estimates of the original abundances of volatile chalcophile elements in the two planets in the spb mantle the nico ratio is nonchondritic in contrast to the chondritic ratio in the earth s mantle abundances of siderophile and chalcophile elements in the spb mantle may be modelled by equilibrium with solid metal and metallic sulfide liquid with some metal and sulfide trapped in the mantle i e homogeneous accretion and inefficient core formation neither this model nor a heterogeneous accretion model is satisfactory in explaining element abundances in the earth s mantle particularly the abundances of ni co mo and w nevertheless it appears that core formation in the spb and the earth left quite different chemical signatures in their planetary mantles

development of cyclic p y curves for laterally loaded pile based on t bar penetration tests in clay offshore pile foundations are always subjected to cyclic lateral loads which can result in the remolding and softening of the surrounding seabed soil cyclic t bar penetrometer testing provides a rapid and effective method for assessing the remolded shear strength it is widely believed that the soil strength degrades with the accumulation of plastic strain but the strain cannot be measured numerical analysis described in this paper shows that the accumulated plastic displacement of the t bar in a cyclic range of two diameters is approximately equal to its accumulated displacement by using t bar test data a cyclic degradation model based on the accumulated plastic displacement is developed to describe the soil strength degradation at a given depth furthermore an improved p y curve model based on the cyclic degradation model is proposed to estimate the lateral response of pile under cyclic loads the improved p y curve model was embedded into the opensees program to investigate the cyclic lateral

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

chemical systematics of the shergotty meteorite and the composition of its parent body mars abstract we report chemical data for 60 elements by inaa and rnaa in two bulk samples for 30 elements in various mineral separates of shergotty and results of leaching experiments with 1m hcl on powdered aliquots of shergotty and beta 79001 lithologies a and b shergotty is homogeneous in major element composition but heterogeneous with respect to lil trace elements 20 the heterogeneity is even greater for volatile and siderophile trace elements the mineral data including three clinopyroxene fractions with variable feo contents maskelynite and minor phases ti magnetite ilmenite quartz k rich phase show that major minerals do not account for the rare earth elements ree in the bulk meteorite instead the ree are to a large extent concentrated in accessory whitlockite and apatite shown by leaching with 1m hcl together with the majority of ree la 96 yb 70 cl and br are quantitatively dissolved by leaching the ree patterns of the leachate of shergotty and eeta 79001 are different the shergotty leachate may consist of two components component l is similar to that of eeta 79001 leachate whitlockite component 2 is enriched in light ree and may be responsible for the higher lree contents of shergotty in comparison to the other shergottites there is some evidence that shergotty was an open system and component 2 was introduced after crystallization the ree patterns of the residues of shergotty and eeta 79001 are identical indicating that the parent magmas of both meteorites are compositionally similar based on cpx separates with the lowest ree content the ree pattern in the shergotty parent magma was calculated it is enriched in lree and has a subchondritic nd sm ratio the negative eu anomaly in the phosphates indicates that at least some plagioclase crystallized before phosphate based on several element correlations in snc meteorites it was suggested dreibus and wanke 1984 that both the shergotty parent body spb very probably mars and the earth accreted from the same two chemically different components component a highly reduced and devoid of volatile elements and an oxidized component b containing also volatile elements the spb mars mantle is 2 4 times richer in volatile and moderately siderophile elements than the earth indicating a higher portion of component b in the spb the concentrations of chalcophile elements in the spb mantle are low reflecting equilibration with a sulfide phase and subsequent segregation of sulfide into the core unlike the earth wanke 1981 the spb mars may therefore have accreted almost homogeneously

in situ exhumation from bedrock of large rounded boulders at the giant s causeway northern ireland an alternative genesis for large shore boulders mega clasts abstract very large boulders mega clasts are found on some coasts the size and position of the boulders has been used to suggest that contemporary marine processes acting within their normal spatial and energy range are unlikely to have moved them explanations for the presence of such boulders include transport by infrequent very high energy marine processes storms or tsunamis mass movement from backing cliffs transport by ice or exhumation from glacial deposits this paper advances an alternative explanation which does not involve transport by any of the marine or glacial processes or gravity it is proposed that in a very specific geological and topographic setting large boulders are exhumed in situ by storm waves acting on heavily weathered jointed basalts eventually wave action liberates residual blocks from the deeply weathered matrix these liberated boulders will be mobile only if they lie within wave competence and the larger ones will remain as stationary residuals the same in situ weathering processes followed by removal of the friable matrix material debris by wave action also progressively round the boulders consequently despite their appearance of being transport rounded the larger boulders have not transported at all in specific locations the assumption that the presence and rounding of such large clasts in the shore zone can be attributed to marine transport can lead to erroneous interpretations of very high energy storm wave or tsunami activity

pliocene quaternary volcanism and faulting at the intersection of the gulf of california and the mexican volcanic belt the junction of the western mexican volcanic belt and the gulf of california represents a superposition of subduction and continental rifting tectonic regimes in the late cenozoic subduction of the oceanic rivera plate has caused late cenozoic uplift of western mexico forming the jalisco block this paper addresses three questions where is the northern boundary of the jalisco block how is the continental fracture system related to that offshore and what is the spatial distribution and composition of subduction related lavas 40 ar 39 ar dates on cretaceous to paleogene silicic ash flows show that the northern boundary of the jalisco block may be defined by the abrupt change in basement age from cretaceous to miocene 40 ar 39 ar and k ar dates on faulted lavas from the nayarit region indicate that extension at the edge of the jalisco block has occurred since ca 4 2 ma the least principal stress 3 direction associated with these faults has had two different orientations from 4 2 ma to the present several pliocene to holocene 4 20 1 05 and 0 65 ma lava flows and aligned cinder cones have a n45 w associated least principal stress direction whereas three pliocene 3 36 3 38 and 3 11 ma lava flows are cut by faults indicating a north to north northeast least principal stress direction the two different stress directions may arise either from structural features in the basement of the arc or from changes in offshore plate boundaries e g 2 5 ma when the rivera and mathematicians plates were locked together whole rock major and trace element analyses of lavas from the coastal nayarit region reveal three different lava types an alkali basalt series basaltic andesite and andesite the alkali basalts show feo and tio 2 enrichment and have low ba zr and ba la ratios consistent with derivation from an oceanic island type mantle the basaltic andesites and andesites are both alkaline and calc alkaline contain hydrous phenocrysts and have high sr zr and la nb ratios consistent with a subduction related source among these lavas there is a correlation between sr zr oxygen fugacity and h 2 o contents suggesting that an oxidized hydrous fluid is involved in the genesis of the subduction related lavas the distribution of subduction related volcanic centers in the coastal nayarit region and areas southeast within the jalisco block defines front that parallels the middle america trench and is consistent with a 45 dip on the subducted rivera plate

core formation in the shergottite parent body and comparison with the earth the mantle of the shergottite parent body spb is depleted relative to the bulk spb in siderophile and chalcophile elements these elements are inferred to reside in the spb s core our chemical model of these depletions rests on a physically plausible process of segregation of partially molten metal from partially molten silicates as the spb grows and is heated above silicate and metallic solidi during accretion metallic and silicate phases equilibrate at low pressures as new material is accreted to the spb surface later movement of the metallic phases to the planet s center is so rapid that high pressure equilibration is insignificant partitioning of siderophile and chalcophile elements among solid and liquid metal and silicate determines their abundances in the spb mantle using partition coefficients and the spb mantle composition determined in earlier studies we model the abundances of ag au co ga mo ni p re s and w with free parameters being oxygen fugacity proportion of solid metal formed proportion of metallic liquid formed and proportion of silicate that is molten abundances of all elements except au mo and re may be reproduced adequately with oxygen fugacity near one log unit below the iron wustite buffer proportion of molten silicate near 0 3 and a core composed of subequal parts of solid and liquid metal constituting approximately 30 of the mass of the spb the abundances of au and re may be reproduced using different but still permissible partition coefficients by invoking a small chondritic veneer mixed into the mantle after core formation or by assuming that small fractions of solid and liquid metal are trapped in the mantle during core formation molybdenum cannot be modeled adequately problems may include inaccurate partition coefficients inaccurate estimation of the abundance of mo in the spb mantle and the possibility that the mantle source of the snc meteorites is not representative of the whole spb mantle in contrast to the spb there is at present no hypothesis capable of quantitatively reproducing elemental abundances in the earth s mantle the contrast suggests that these two terrestrial planets may have accreted or differentiated differently but the cause of such differences is unclear

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

silver contents and cu ag ratios in martian meteorites and the implications for planetary differentiation abstract silver and cu show very similar partitioning behavior in sulfide melt silicate melt and metal silicate systems at low and high pressure temperature p t experimental conditions implying that mantle melting fractional crystallization and core mantle differentiation have at most modest within a factor of 3 effects on cu ag ratios for this reason it is likely that cu ag ratios in mantle derived magmatic products of planetary bodies reflect that of the mantle and in some circumstances also the bulk planet composition to test this hypothesis new ag mass fractions and cu ag ratios in different groups of martian meteorites are presented and compared with data from chondrites and samples from the earth s mantle silver contents in lherzolitic olivine phyric and basaltic shergottites and nakhlites range between 1 9 and 12 3 ng g the data display a negative trend with mgo content and correlate positively with cu contents in spite of displaying variable initial 143 nd values and representing a diverse spectrum of magmatic evolution and physiochemical conditions shergottites and nakhlites display limited variations of cu ag ratios 1080 320 1 s n 14 the relatively constant cu ag suggests limited fractionation of ag from cu during the formation and evolution of the parent magmas irrespectively of whether sulfide saturation was attained or not the mean cu ag ratio of martian meteorites thus reflects that of the martian mantle and constrains its ag content to 1 9 0 7 ng g 1 s carbonaceous and enstatite chondrites display a limited range of cu ag ratios of mostly 500 2400 ordinary chondrites show a larger scatter of cu ag up to 4500 which may have been caused by ag redistribution during parent body metamorphism the majority of chondrites have cu ag ratios indistinguishable from the martian mantle value indicating that martian core formation strongly depleted cu and ag contents but probably did not significantly change the cu ag ratio of the mantle compared to bulk mars bulk mars is richer in moderately volatile elements than earth however the martian mantle displays a much stronger depletion of the moderately volatile elements cu and ag e g by a factor of 15 for cu this observation is consistent with experimental studies suggesting that core formation at low p t conditions on mars led to more siderophile behavior of cu and ag than at high p t conditions as proposed for earth in contrast cu ag ratios of the mantles of mars and earth cu ag earth 3500 1000 display only a difference by a factor of 3 which implies restricted fractionation of cu and ag even at high p t conditions the concentration data support the notion that siderophile element partitioning during planetary core formation scales with the size of the planetary body which is particularly important for the differentiation of large terrestrial planets such as earth collectively the ag and cu data on magmatic products from the mantles of mars and earth and the data on chondrites confirm experimental predictions and support the limited fractionation of cu and ag during planetary core formation and high temperature magmatic evolution and probably also in early solar nebular processes

comparative reos smnd and rbsr isotope and trace element systematics for archean komatiite flows from munro township abitibi belt ontario abstract a series of komatiite flows from munro township ontario have re and os concentrations that range from 0 545 to 1 27 ppb and 1 00 to 2 20 ppb respectively the187re 186os in the suite range from 14 05 to 52 37 and the187os 186os range from 1 49 to 3 22 giving a crystallization age of2726 93ma and an of initial187os 186os of0 873 0 035 this age is in good agreement with the crystallization ages that have been reported for these rocks using other isotopic systems the re os isochron indicates that the system was resistant to the low grade metamorphism that altered the rocks the initial os isotopic composition is consistent with the derivation of the melts from a mantle source s that originated with a chrondritic 187os 186os i and evolved with an approximately chondriticre os sm nd data for the same suite cluster about anend value at 2 72 ga of 2 to 3 rb sr isotope data indicate significant mobilization of these elements by the greenschist grade metamorphism that has altered the rocks comparisons of re and os concentrations with those of mgo feo ni cr and s suggests that re was incompatible d 1 os concentrations were likely controlled by the presence or precipitation of trace metallic or sulfide phases both during melting and crystallization and not by the modally predominant silicate minerals

pipe soil interaction on free span shoulder subject to vortex induced vibration free span refers to a subsea pipeline section that is suspended over the seabed such a pipe section is vulnerable to vortex induced vibration leading to possible fatigue pipe damage existing stud

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

a simple model for the effect on soil strength of episodes of remoulding and reconsolidation many geotechnical processes related to offshore foundations and pipelines on clay soils involve intermittent episodes of remoulding and reconsolidation to assess the resulting response it is necessary to predict the operative soil strength which decreases due to remoulding but can increase due to reconsolidation a simple framework that allows these processes to be linked via concepts from critical state soil mechanics is described the framework is illustrated by back analysing a t bar penetrometer test that involved episodes of both remoulding and reconsolidation which was conducted in a geotechnical centrifuge it is shown that the model can capture the surprising increases in both the intact and the remoulded strength that are observed between episodes of remoulding

mineralogy of the martian interior up to core mantle boundary pressures in order to determine the mineralogy of the martian interior along a high temperature areotherm multianvil experiments have been performed with a model martian mantle composition up to 23 5 gpa the dreibus and wanke 19851 martian mantle composition yields an upper mantle that consists of olivine clinopyroxene orthopyroxene garnet at pressures up to 9 gpa above 9 gpa orthopyroxene is no longer present the transition zone is marked by the appearance of spinel at 13 5 gpa up to 15 gpa clinopyroxene and majorite coexists with phase and or spinel by 17 gpa clinopyroxene is entirely replaced by majorite and the modal abundance of spinel increases at the expense of phase the dominant assemblage throughout most of the transition zone is spinel majorite two experiments completed in the perovskite stability field indicate that the lower mantle consists of mg fe silicate perovskite magnesiowustite and majorite casio 3 perovskite is not present in these experiments both the presence of a martian lower mantle i e an mg fe silicate perovskite bearing zone and the phase assemblage stable in the martian lower mantle are very sensitive to the temperature profile of the interior a low temperature profile may stabilize stishovite in the lower mantle or it may lead to the absence of the lower mantle because of the higher transition pressure required for forming perovskite at lower temperatures regardless of the temperature profile assumed the martian upper mantle and transition zone will account for a larger proportion of the planet s interior than is the case for the earth s interior because of the smaller size of mars

centrifuge modelling of a tetrapod jacket foundation under lateral cyclic and monotonic loading in soft soil the tetrapod jacket foundation is one of the most common types of foundations used for offshore structures although the static bearing capacity of the jacket foundation is important a safe design

contrasting re os magmatic fractionation in planetary basalts abstract this work reports the first re os isotopic results for lunar basalts and eucrites both re and os concentrations are found to be very low and re os ratios are close to chondritic this contrasts with the much higher than chondritic re os ratio of terrestrial basalts osmium displays a rather uniform solid liquid fractionation in different planetary bodies moon earth eucrite parent body mars whereas rhenium is about three orders of magnitude more incompatible in terrestrial basalt genesis we argue that this is a function of oxygen fugacity in the source regions of basalts

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

accretion and core formation on mars molybdenum contents of melt inclusion glasses in three snc meteorites abstract molybdenum cerium barium yttrium and rubidium contents of glasses in melt inclusions in three snc meteorites lew 88516 governador valadares and chassigny have been measured by ion microprobe ratios of mo ba and mo ce have been used to estimate the mo content of the primitive martian mantle 120 60 ppb abundances of five moderately siderophile elements ni co mo w and p and re in the martian mantle are consistent with metal silicate equilibrium between s bearing metallic liquid in a core 22 wt of the planet and peridotite melt at 75 kb 1620 c and oxygen fugacity 1 4 logfo2 units below the iw buffer this homogeneous accretion scenario is different than many heterogeneous accretion models for the earth but similar to recent studies suggesting homogeneous accretion in the presence of a deep terrestrial magma ocean

assessing the punch through hazard of a spudcan on sand overlying clay a complete analytical method to describe the full load penetration resistance profile of a mobile jack up spudcan footing penetrating a sand over clay stratigraphy is described it is based on both large deformation finite element analyses and geotechnical centrifuge experiments the coupled eulerian lagrangian cel approach is used to accommodate the large deformations of a spudcan footing penetrating sand overlying clay modified mohr coulomb and tresca models describe the sand and clay behaviour with modifications accounting for the effects of strain softening on the response of the soil the cel results are shown to match centrifuge tests well allowing the numerical study to be extended parametrically and with confidence to cover the range of layer geometries sand relative densities and footing shapes that are of practical interest to offshore jack ups the results are used to a assess the performance of an existing model to predict the peak resistance in the sand layer extending its range of

origin of planetary cores evidence from highly siderophile elements in martian meteorites we present new bulk compositional data for 6 martian meteorites including highly siderophile elements ni re os ir and au these and literature data are utilized for comparison versus the siderophile systematics of igneous rocks from earth the moon and the hed asteroid the siderophile composition of alh84001 is clearly anomalous whether this reflects a more reducing environment on primordial mars when this ancient rock first crystallized or secondary alteration is unclear que94201 shows remarkable similarity with eet79001 b for siderophile as well as lithophile elements both are extraordinarily depleted in the noblest siderophiles os and ir to roughly 0 00001 ci chondrites as in terrestrial igneous rocks among martian rocks ni os and ir show strong correlations vs mgo in the case of mgo vs ni the martian trend is displaced toward lower ni by a large factor 5 but the os and ir trends are not significantly displaced from their terrestrial counterparts for mars re shows a rough correlation with mgo indicating compatible behavior in contrast to its mildly incompatible behavior on earth among martian mgo rich rocks au shows a weak anticorrelation vs mgo resembling the terrestrial distribution except for a displacement toward 2 3 times lower au the same elements ni re os ir and au show similar correlations with cr substituted for mgo data for lunar and hed rocks generally show less clear cut trends relatively few mgo rich samples are available these trends are exploited to infer the compositions of the primitive earth mars moon and hed mantles by assuming that the trend intercepts the bulk mgo or cr content of the primitive mantle at the approximate primitive mantle concentration of the siderophile element results for earth show good agreement with earlier estimates for mars the implied primitive mantle composition is remarkably similar to the earth s except for 5 times lower ni the best constrained of the extremely siderophile elements os and ir are present in the martian mantle at 0 005 times ci in comparison to 0 007 times ci in earth s mantle this similarity constitutes a key constraint on the style of core mantle differentiation in both mars and earth successful models should predict similarly high concentrations of noble siderophile elements in both the martian and terrestrial mantles high compared to the lunar and hed mantles and to models of simple partitioning at typical low pressure magmatic temperatures but only predict high ni for the earth s mantle models that engender the noble siderophile excess in earth s mantle through a uniquely terrestrial process such as a moon forming giant impact have difficulty explaining the similarity of outcome except for ni on mars the high ni content of the terrestrial mantle is probably an effect traceable to earth s size for the more highly siderophile elements like os and ir the simplest model consistent with available constraints is the veneer hypothesis core mantle differentiation was notably inefficient on the largest terrestrial planets because during the final 1 of accretion these bodies acquired sufficient h2o to oxidize most of the later accreting fe metal thus eliminating the carrier phase for segregation of siderophile elements into the core

centrifuge modeling of laterally loaded pile groups in improved soft clay abstracta series of centrifuge tests were performed to investigate the behavior of laterally loaded pile groups in improved and unimproved soft clay the soil profile consisted of four lightly overconsolidated clay layers overlying a dense layer of sand the pile groups had a symmetrical layout consisting of 2 2 piles spaced at 3 0 and 7 0 pile diameters d after improving the soft clay in situ using simulated cement deep soil mixing cdsm pile foundations were driven into the improved ground centrifuge tests revealed that cdsm is an effective method to increase the lateral resistance of pile foundations the lateral resistance of the improved pile group at 7d spacing increased by 157 due to pile soil pile interactions the lateral resistance in the 3d pile group increased by only 112 in both improved and unimproved pile groups with 3d spacing the leading row of piles carried larger loads and bending moments than the trailing row of piles no group interaction effects were observed in all pile g

the mean life of continents estimates of continent recycling rates from nd and hf isotopic data and implications for mantle structure an analysis of the initial neodymium and hafnium isotopic compositions of modern and ancient mantle derived rocks shows that the divergence of the mantle 143nd 144nd and 176hf 177hf ratios from the chondritic ratios over the past 2 billion years has been much less than would be expected based on the sm nd and lu hf ratios of the mantle source of mid ocean ridge basalt the most likely explanation is that rock material from the continents has been recycled semi continuously back into the mantle over this time period the required rate of return of continents to the mantle calculated from a simple transport model is about 0 35 0 15 of the continental mass per billion years 2 5 km year this result is consistent with the hypothesis that the mass of the continents has been approximately constant since the late archean and implies that recycled continental material must be an important component of the upper mantle

the role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment findings of a laboratory simulation long term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate cubic rock samples 15 mm 15 mm 15 mm were cut from larger rocks and subjected to time compressed climatic conditions simulating the tropical wet season climate at the ranger uranium mine in the northern territory australia fragmentation moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying to determine the impact of climatic variables five climatic regimes were simulated varying water application temperature and drying one of the climatic regimes reproduced observed temperature and moisture variability at the ranger uranium mine but over a compressed time scale it is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades while wetting and drying alone does produce changes to rock morphology the incorporation of temperature variation further enhances weathering rates although little fragmentation occurred in experiments significant changes to internal pore structure were observed which could potentially enhance other weathering mechanisms moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching finally experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy the samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates copyright 2005 john wiley sons ltd

hydrothermal alteration and earth surface rock weathering a basalt example geomorphologists have not devoted sufficient attention to the formation of clay minerals by hydrothermal activity this paper describes the breakdown of freshly quarried basalt by cyclic wetting and drying breakdown is attributed to the swelling of hydrothermally derived smectite and it is argued that the effects of endogenic processes can exert a significant control upon weathering behaviour under earth surface conditions

is the primordial crust of mars magnetized abstract a meteorite impact capable of creating a 200 km diameter crater can demagnetize the entire crust beneath and produce an appreciable magnetic anomaly at satellite altitudes of 400 km in case the pre existing crust is magnetized in this study we examine the magnetic field over all of the craters and impact related quasi circular depressions qcds with diameters larger than 200 km that are located on the highlands of mars excluding the tharsis bulge in order to estimate the mean magnetization of the highland crust using the surface topography and the gravity of mars we first identify those qcds that are likely produced by impacts the magnetic map of a given crater or impact related qcd is derived using the mars global surveyor high altitude nighttime radial magnetic data two extended ancient areas are identified on the highlands the south province and the tempe terra which have large number of craters and impact related qcds but none of them has an appreciable magnetic signature the primordial crust of these areas is not magnetized or is very weakly magnetized at most we examine some plausible scenarios to explain the weak magnetization of these areas and conclude that no strong dynamo existed in the first 100 myr of mars history when the newly formed primordial crust was cooling below the magnetic blocking temperatures of its minerals

similarities between the shergottites and terrestrial ferropicrites abstract element abundance ratios have been used to both distinguish terrestrial and martian basalts and make estimates on the bulk planetary chemistry however these estimates are based upon ratios that are assumed to have been unaffected by igneous processes since the extent to which this is valid is unknown comparisons of terrestrial and martian rocks are best conducted on rocks with similar mineralogy and petrology and therefore a good likelihood of similar crystallization histories when the geochemistry of terrestrial ferropicrites is compared with the olivine phyric and basaltic shergottites previously observed differences in chemistry are no longer definitive i e mg si al si ca si fe si feo mno al ti na ti na al k la k rb k th k u th u ratios since ferropicrites are geochemical terrestrial analogs for the shergottites their formation history can provide useful information about the formation of the shergottites this suggests that both ferropicrites and shergottites formed from a heavily processed mantle source region

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