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

systematics of ni and co in olivine from planetary melt systems lunar mare basalts the systematics of co and ni in olivine from six apollo 12 olivine basalts were studied by sims techniques and correlated with major and minor element data obtained with the electron microprobe our results together with previous studies demonstrate that one of these basalts 12009 was extruded as a liquid onto the lunar surface and was parental to five other cumulates 12075 12020 12018 12040 and 12035 the concentrations of ni in zoned olivine phenocrysts behave as expected for a highly compatible element with initial estimated d ni 9 9 on the other hand co concentrations in olivine vary hardly at all and show flat patterns across crystals that retain normal zoning trends for mg fe mn and ni the explanation for this behavior is not that d co nearly equal 1 our estimated d co 4 or that co zoning has been erased by rapid diffusion of co compared to the other elements e g mg and fe that still show normal zoning the explanation for the behavior as originally suggested by kohn et al 1989 is that the increase in d co with crystallization exactly balances the depletion of co in the melt this decoupling of the behavior of ni and co in olivine results in significant increases in co ni with crystallization

the influence of feo on the solubilities of cobalt and nickel in silicate melts abstract the effect of iron on the solubilities of co and ni in silicate melts was determined at a wide range of oxygen fugacities from 10 8 1 to 10 12 6 atm and at temperatures ranging from 1305 1600 c four different systems were studied in system a an feo free silicate of anorthite diopside eutectic composition was equilibrated with pure co or pure ni metal in system b the same silicate starting material was equilibrated with feconi alloys in systems c and d feo containing silicates basaltic komatiite were equilibrated with pure co and pure ni metal system c and with feco and feni alloys system d experiments at temperatures below 1450 c were performed by equilibrating metal loops with silicates at higher temperature well mixed metal powder and silicates were equilibrated in alumina crucibles concentrations of ni and co in the silicate and in some of the alloys were determined by neutron activation analysis most of the alloy compositions were analyzed by electron microprobe at constant temperature 1400 c but variable oxygen fugacities co ni and fe metal silicate partition coefficients calculated from metal solubilities increase with decreasing oxygen fugacities the extent of the increase suggests that all three metals are dissolved as oxides coo nio feo in the silicate melt no evidence for the presence of metallic co ni or fe as major species in silicate melt was found within the oxygen fugacity range covered by the experiments even at oxygen fugacities three log units below the fe feo equilibrium iw 3 a minor fraction of metallic ni below 20 may be present in the most reducing experiments no difference in ni and co solubility was found for feo free and feo containing silicates depending on temperature all metal silicate partition coefficients of co and ni decrease slightly with increasing temperature along the oxygen fugacity appropriate for core formation 2 3 log units below the fe feo equilibrium iw 2 3 the experiments confirm that the relatively high present day upper mantle concentrations of co ni and fe and in particular the chondritic ni co ratio cannot be explained by equilibrium between coreforming metal and silicates of the earth s mantle in a low pressure environment even at temperatures as high as 4000 c thus supporting models of inhomogeneous accretion of the earth accumulation of differentiated planetesimals i e with metal cores as major building blocks of the earth can also be excluded in these bodies metal silicate equilibration would have occurred at low pressures and equilibration of metal cores of accreting planetesimals with the earth s mantle is unlikely homogeneous accretion models may only be possible if equilibration occurred between lower mantle minerals and liquid core forming metal during differentiation of the earth and if the relevant ni and co partition coefficients are sufficiently high the ni and co partition coefficients between liquid metal and mg wustite and mg perovskite are not well known

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

a petrologic and trace element study of dar al gani 476 and dar al gani 489 twin meteorites with affinities to basaltic and lherzolitic shergottites we present the results of a combined mineralogic petrologic and ion microprobe study of two martian meteorites recently recovered in the lybian sahara dar al gani 476 dag 476 and dar al gani 489 dag 489 having resided in a hot desert environment for an extended time dag 476 and dag 489 were subjected to terrestrial weathering that significantly altered their chemical composition in particular analyses of some of the silicates show light rare earth element lree enrichment resulting from terrestrial alteration in situ measurement of trace element abundances in minerals allows us to identify areas unaffected by this contamination and thereby to infer the petrogenesis of these meteorites no significant compositional differences between dag 476 and dag 489 were found supporting the hypothesis that they belong to the same fall these meteorites have characteristics in common with both basaltic and lherzolitic shergottites possibly suggesting spatial and petrogenetic associations of these two types of lithologies on mars however the compositions of fe ti oxides and the size of eu anomalies in the earliest formed pyroxenes indicate that the two saharan meteorites probably experienced more reducing crystallization conditions than other shergottites with the exception of queen alexandra range que 94201 as is the case for other shergottites trace element microdistributions in minerals of the dag martian meteorites indicate that closed system crystal fractionation from a lree depleted parent magma dominated their crystallization history furthermore rare earth element abundances in the orthopyroxene megacrysts are consistent with their origin as xenocrysts rather than phenocrysts

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

geochemistry of intermediate olivine phyric shergottite northwest africa 6234 with similarities to basaltic shergottite northwest africa 480 and olivine phyric shergottite northwest africa 2990 the newly found meteorite northwest africa 6234 nwa 6234 is an olivine ol phyric shergottite that is thought based on texture and mineralogy to be paired with martian shergottite meteorites nwa 2990 5960 and 6710 we report bulk rock major and trace element abundances including li abundances of highly siderophile elements re os isotope systematics oxygen isotope ratios and the lithium isotope ratio for nwa 6234 nwa 6234 is classified as a martian shergottite based on its oxygen isotope ratios bulk composition and bulk element abundance ratios fe mn al ti and na al the li concentration and d 7 li value of nwa 6234 are similar to that of basaltic shergottites zagami and shergotty the rare earth element ree pattern for nwa 6234 shows a depletion in the light ree la nd compared with the heavy ree sm lu but not as extreme as the known depleted shergottites thus nwa 6234 is suggested to belong to a new category of shergottite that is geochemically intermediate in incompatible elements the only other basaltic or ol phyric shergottite with a similar intermediate character is the basaltic shergottite nwa 480 rhenium osmium isotope systematics are consistent with this intermediate character assuming a crystallization age of 180 ma we conclude that nwa 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in mars

element zoning trends in olivine phenocrysts from a supposed primary high magnesian andesite an electron and ion microprobe study electron and ion probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high magnesian andesite from shodo shima island southwest japan this rock was previously thought to represent undifferentiated primary magma some crystals have unzoned cores while others show cores which are reversely zoned with respect to mg mg fe ni mn and cr in addition some ni profiles show a normally zoned hump at the most central portions of the reversely zoned crystals all crystals show normally zoned rims the li concentrations are constant throughout the cores of all crystals studied but rise sharply by a factor of up to at least six in the rims the ca and co concentrations are essentially constant throughout all the crystals mechanisms for producing the observed zoning profiles are discussed and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew the reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma or phenocrysts introduced into a more primitive magma by a magma mixing process the ni profiles are used to estimate the residence time of these crystals in the more primitive magma the following trace element partition co efficients have been estimated for the olivine groundmass system in this rock dni 16 dmn 1 1 dco 4 2 dca 0 02 dti 0 005 dv 0 05 dsc 0 2 dna 0 0002 studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas and a better understanding of other disequilibrium processes are required to fully exploit the new data

paleointensity of the earth s magnetic field recorded by two late quaternary volcanic sequences at the island of la reunion indian ocean a paleomagnetic study has been undertaken on two late quaternary volcanic sequences from the piton de la fournaise volcano island of la reunion in order to provide absolute paleointensities of the earth s magnetic field from a site in the southern hemisphere the pattern of secular variation recorded by both sequences clearly indicates that the extrusion rate of the lava flows was not constant with time a detailed investigation of the magnetic properties of the samples was carried out in parallel with paleointensity experiments which were performed with the thellier method samples with minimum overprint composed by single domain or pseudo single domain magnetite showing good thermal stability and a narrow blocking temperature spectrum were the most successful during thellier s experiments values of the paleofield strength from 19 to 55 mt have been obtained on 23 flows among the 30 which were sampled few variations 7 5 9 9 1022 a m2 are observed in the virtual dipole moments vdms determined on the youngest sequence 5 12 ka those values are within the range of fluctuations of the worldwide variations of vdms for this period on the other hand data from the oldest sequence 82 98 ka are the first paleointensity values obtained in that time period and the observed vdms extend from 4 1 to 8 8 1022 a m2 these results suggest that for this time interval the field did not depart from its average behavior

petrogenetic linkages among martian basalts implications based on trace element chemistry of olivine the shergottites exhibit a range of major and trace element compositions crystallization ages and initial sr nd hf and pb isotopic compositions to constrain the physical mechanisms by which shergottites obtain their compositional characteristics we examined the major and trace element record preserved in olivine in the more primitive shergottites based on such characteristics as the mg v zoning calculated dni co the olivine in y 980459 are most likely phenocrysts many of these same characteristics indicate that the olivines in other shergottites are not in equilibrium with the adjacent melt however in most cases they are not xenocrystic but additions of olivine from the same basaltic system elephant moraine eet a79001 may be an exception with the olivine data suggesting that it is xenocrystic in this case the olivine crystallized from a reduced and lreedepleted melt and was incorporated into an oxidized and enriched basalt vanadium and cao in olivine appear to record the appearance of spinel and pyroxene on the liquidus of most of the shergottites most of the olivine shergottites represent basalts produced by melting of reduced iw to iw 1 depleted mantle sources olivine data indicate that many of the primary melts derived from this source had similar ni co and mn shergottites such as northwest africa nwa 1110 1068 and perhaps roberts massif rbt 04261 that appear to be derived from more enriched sources have distinctly different olivine in the case of nwa 1110 1068 the olivine data suggests that the enriched component was added to system prior to olivine crystallization

the behavior of co and ni in olivine in planetary basalts an experimental investigation cobalt and nickel in olivine from lunar martian and terrestrial basalts show systematic differences that appear to be related to planetary parentage we present results from a series of 1 atm experiments designed to examine the partitioning of co and ni in olivine over a range of conditions relevant to planetary basalts our results confirm the suggestions of previous workers that the partitioning of co is such that an increase in d cool with crystallization is balanced by a decrease in co concentration in the melt resulting in constant co in olivine either within olivine showing otherwise normal igneous zoning or within a suite of basalts related by fractionation it is evident that the partitioning of co and ni into planetary olivine is influenced by such intensive variables as temperature oxygen fugacity and composition although separating these effects is not possible our data demonstrate that over the range of oxygen fugacity of lunar martian and terrestrial basalts oxygen fugacity has no significant effect on co and ni partitioning into olivine we propose that an increase in melt polymerization with decreasing temperature coupled with the preference of co and ni for the octahedral sites in olivine is the mechanism by which d cool and d niol increase with crystallization with our experimental results as a baseline we interpret data from co and ni in olivine from lunar martian and terrestrial basalts and conclude that the cause of increases in co concentrations in olivine either core to rim or within a co genetic suite and observed primarily in martian and terrestrial basalts is enrichment of the melt as crystallization progresses we hypothesize that this enrichment is attributable either to crystallization of a phase in which co is incompatible such as plagioclase or replenishment of the igneous system with co enriched melt

a discussion of isotopic systematics and mineral zoning in the shergottites evidence for a 180 m y igneous crystallization age abstract proposed igneous and metamorphic ages of the shergottites a suite of achondritic basaltic meteorites are examined in terms of the shergottites petrography and mineral chemistry no metamorphic or hydrothermal event appears capable of resetting the refractory sr and nd isotopic systems of the shergottites since the time of their igneous crystallization the approximately concordant rb sr 180 20 m y and u th pb 190 30 m y internal isochrons are thus interpreted as representing the time of igneous crystallization the sm nd internal isochrons which yield older apparent ages also show large scatter and are regarded as artifacts of the shergottites complex igneous history rubidium sr sm nd and pb pb wholerock isochrons are interpreted as mixing lines and are reasonably attributed to igneous processes such as wall rock assimilation and magma mixing if the shergottites are indeed less than 200 m y old they represent the youngest known extraterrestrial basalts this conclusion is supportive of the hypothesis that the snc meteorites are samples of the planet mars

silicate mineralogy of martian meteorites abstract basalts and basaltic cumulates from mars delivered to earth as meteorites carry a record of the history of that planet from accretion to initial differentiation and subsequent volcanism up to recent times we provide new microprobe data for plagioclase olivine and pyroxene from 19 of the martian meteorites that are representative of the six types of martian rocks we also provide a comprehensive wds map dataset for each sample studied collected at a common magnification for easy comparison of composition and texture the silicate data shows that plagioclase from each of the rock types shares similar trends in ca na k and that k2o na2o wt of plagioclase multiplied by the al content of the bulk rock can be used to determine whether a rock is enriched or depleted in nature olivine data show that meteorite y 980459 is a primitive melt from the martian mantle as its olivine crystals are in equilibrium with its bulk rock composition all other olivine bearing shergottites have been affected by fractional crystallization pyroxene quadrilateral compositions can be used to isolate the type of melt from which the grains crystallized and minor element concentrations in pyroxene can lend insight into parent melt compositions in a comparative planetary mineralogy context plagioclase from mars is richer in na than terrestrial and lunar plagioclase the two most important factors contributing to this are the low activity of al in martian melts and the resulting delayed nucleation of plagioclase in the crystallizing rock olivine from martian rocks shows distinct trends in ni co and cr systematics compared with olivine from earth and moon the trends are due to several factors including oxygen fugacity melt compositions and melt structures properties which show variability among the planets finally fe mn ratios in both olivine and pyroxene can be used as a fingerprint of planetary parentage where minerals show distinct planetary trends that may have been set at the time of planetary accretion although the silicate mineralogical data alone cannot support one specific model of martian magmatism over another the data does support the basic igneous reservoirs proposed for mars and may also be used to constrain some aspects of specific petrogenetic models examples include enriched and depleted reservoirs that can be identified by plagioclase k na and al composition multivalent element partitioning in olivine and pyroxene v cr elucidates oxygen fugacity conditions of the reservoirs and minor element concentrations i e cr in pyx show that proposed fractional crystallization models linking y 980459 to que 94201 will not work

petrography and mineralogy of two basalts and olivine pyroxene spinel fragments in achondrite eeta79001 three lithologies occur in shocked achondrite eeta79001 a1 exotic irregular crystals and clusters of coarse grained olivine fo81 55 cao 0 2 cr2o3 0 06 nio 0 5 wt low ca pyroxene en82wo2 en58wo12 and low ti chromite cr2o3 59 feo 27 tio2 0 7 wt a2 basaltic host to a1 containing pyroxene mainly pigeonite en67wo12 en52wo13 maskelynite an61 55or0 7 high ti chromite some rimming low ti chromite whitlockite minor cl apatite ilmenite pyrrhotite and mesostasis and b a homogeneous basalt containing augite laths en40 50wo25 35 in a matrix of pigeohite augite maskelynite an62 56 or1 2 ulvospinelilmenite intergrowth whitlockite cl apatite and mesostasis mineral compositions indicate an oxidation state similar to that of shergottites lithology a1 represents an unmetamorphosed cumulate that was disrupted and partly resorbed by a basaltic magma incorporation of low ca magnesian pyroxenes and olivine increased the mg fe ratio of the basaltic magma responsible for a2 and resulted in abundant crystallization of pigeonite lithology b was generated from a distinct magma lacking fragments of a1 the parental spinel harzburgite of a1 was not annealed and is probably a near surface igneous cumulate from a shergottite type basalt ringwood and majorite were found in shock veins

an experimental and petrographic investigation of elephant moraine 79001 lithology a implications for its petrogenesis and the partitioning of chromium and vanadium in a martian basalt a composition approximating the lithology a groundmass ofthe elephant moraine eet 79001 martian basalt eg mcsween and jarosewich 1983 has been used to investigate the petrogenesis ofthe meteorite and the behavior ofcr and v at different oxygen fugacities crystallization experiments were carried out over a range of temperatures and oxygen fugacities of either iron wustite iw or iw 2 i e 1 5 log units below the quartz fayalite magnetite qfm buffer comparison oftrace element concentrations obtained by secondary ion mass spectrometry sims analysis in experimental silicates with those of natural silicates supports the fe ti oxide derived oxygen fugacity of qfm 1 8 0 3 for this basalt herd et al 2001 experimental distribution coefficients in conjunction with sims analyses of rims from the olivine and pyroxene xenocrysts in lithology a as well as analyses of lithology a groundmass pigeonite cores are used to calculate coexisting liquid concentrations of v and cr liquid compositions derived from pigeonite xenocryst rims and groundmass pigeonite cores are similar suggesting that the rims of orthopyroxene xenocrysts are overgrowths which have not previously been accounted for when reconstructing the groundmass composition this implies that the eg composition requires modification a similar exercise for the ferroan rims on olivine xenocrysts yields very different liquid compositions indicating that these rims are not overgrowths but are part of the xenocryst assemblage these results are shown to be consistent with the petrography of lithology a xenocrysts

rare earth elements in minerals of the alha77005 shergottite and implications for its parent magma and crystallization history abstract rare earth element ree and selected trace element abundances were measured in individual grains of pyroxenes whitlockite maskelynite and olivine of the alha77005 shergottite minor 1 whitlockite which displays a negative eu anomaly indicative of co crystallization with plagioclase dominates the bulk rock ree pattern detectable ce anomalies in 20 of the pyroxene grains analyzed appear to be the result of weathering in the antarctic environment and indicate that pyroxene is particularly susceptible to element remobilization mineral compositions and textural observations suggest that alha77005 is a cumulate with 50 cumulus material olivine chromite olivine re equilibrated with intercumulus liquid on cooling the intercumulus liquid then crystallized as a closed system to form successively poikilitic low ca and high ca pyroxene followed by interstitial pyroxenes plagioclase whitlockite and other minor phases and reacted with cumulus crystals to form rims of different composition this crystallization sequence provides a constraint on the shergottite source region composition the alha77005 and shergotty intercumulus liquids had similar ree compositions however as opposed to shergotty if alha77005 was formed during the last 0 72 ga its parent melt was not contaminated by lree enriched material

mineralogy and petrology of the dar al gani 476 martian meteorite implications for its cooling history and relationship to other shergottites dar al gani 476 the 13th martian meteorite was recovered from the sahara in 1998 it is a basaltic shergottitic rock composed of olivine megacrysts reaching 5 mm 24 vol set in a finegrained groundmass of pyroxene 59 vol and maskelynitized plagioclase 12 vol with minor amounts of accessory phases spinel merrillite ilmenite dar al gani 476 is similar to lithology a of elephant moraine a79001 eeta79001 in petrography and mineralogy but is distinct in several aspects low ca pyroxenes in the dar al gani 476 groundmass are more magnesian en76fs21 wo3 en58fs30wo12 than those in lithology a of eeta79001 en73fs22wo5 en45fs43wo12 rather similar to pyroxenes in lherzolitic martian meteorites en76fs21 wo3 en63fs22wo15 dar al gani 476 olivine is less magnesian and shows a narrower compositional range fo76 58 than eeta79001 olivine fo81 53 and is also similar to olivines in lherzolitic martian meteorites fo74 65 the orthopyroxene olivine chromite xenolith typical in the lithology a of eeta79001 is absent in dar al gani 476 it seems that dar al gani 476 crystallized from a slightly more primitive mafic magma than lithology a of eeta79001 and several phases olivine pyroxene chromite and ilmenite in dar al gani 476 may have petrogenetic similarities to those of lherzolitic martian meteorites olivine megacrysts in dar al gani 476 are in disequilibrium with the bulk composition the presence of fractured olivine grains in which the most mg rich parts are in contact with the groundmass suggests that little diffusive modification of original olivine compositions occurred during cooling this observation enabled us to estimate the cooling rates of dar al gani 476 and eeta79001 olivines giving similar cooling rates of 0 03 3 c h for dar al gani 476 and 0 05 5 c h for eeta79001 this suggests that they were cooled near the surface burial depth shallower than about 3 m at most probably in lava flows during crystallization of groundmass as is proposed for lithology a of eeta79001 it may be possible to consider that dar al gani 476 has an impact melt origin a mixture of martian lherzolite and other martian rock queen alexandra range 94201 nakhlites

the lodran primitive achondrite petrogenetic insights from electron and ion microprobe analysis of olivine and orthopyroxene the lodran primitive achondrite is thought to represent some of the earliest events in the differentiation of chondritic asteroids most researchers who studied lodran believe that it is a restite from which a melt enriched in the incompatible trace and minor elements was extracted this process is reflected by a lack of feldspar in the lodran mineral assemblage presumably after or during melting a reduction event took place resulting in an increase in mg fe near the rims of both olivine and orthopyroxene the reduction process is far more advanced in olivine than in pyroxene because of the more rapid fe mg diffusion rates in olivine narrow reaction rims 10 m around orthopyroxene grains show a depletion in ca al cr ti rees and y and an increase in mg reverse zoning these systematics are largely the result of melting and to a lesser extent of reduction significant reaction of olivine has taken place by reduction and or sulfidatuon and to a lesser extent by melting this is reflected by a decrease in fe co and ni and an increase in mg towards the rims of olivine the reactions by which reduction and or sulfidation of olivine took place are not confirmed however the following represent two possible reactions

the pattern of ni and co abundances in lunar olivines abstract near liquidus experiments on peridotite and other olivine normative compositions from 1 7 to 6 gpa confirm the applicability of exchange based empirical models of ni and co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite given that most estimates of lunar bulk composition are peridotitic the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean initially 700 km deep reveals a prominent maximum in ni concentration versus fraction crystallized or mg molar mgo mgo feo but a pattern of monotonically increasing co concentration these patterns qualitatively match the puzzling patterns of ni and co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower ni and co abundances than do less magnesian olivines from low ti mare basalts and olivines from the ferroan anorthosite suite fas have lower ni but similar co to mare basalt olivines the ni and co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine orthopyroxene harzburgite layer that is in turn overlain by an upper zone of plagioclase bearing cumulates the ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer which later becomes a portion of the green glass source region to the bottom of the cumulate pile with ni and co rich olivine meanwhile the less dense but hottest most magnesian olivines with much lower ni and co abundances are transported upward to the base of the plagioclase bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite norite and gabbronorite with kreep a k ree p enriched component widely believed to be derived from the very latest stage magma ocean liquid these hybrid melts have al 2 o 3 ni and co abundances and mg appropriate for parent magmas of the magnesian suite ni and co abundances in the fas are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite norite mixtures without kreep

mineral chemistry of the tissint meteorite indications of two stage crystallization in a closed system the tissint meteorite is a geochemically depleted olivine phyric shergottite olivine megacrysts contain 300 600 m cores with uniform mg 80 1 followed by concentric zones of fe enrichment toward the rims we applied a number of tests to distinguish the relationship of these megacrysts to the host rock major and trace element compositions of the mg rich core in olivine are in equilibrium with the bulk rock within uncertainty and rare earth element abundances of melt inclusions in mg rich olivines reported in the literature are similar to those of the bulk rock moreover the p k intensity maps of two large olivine grains show no resorption between the uniform core and the rim taken together these lines of evidence suggest the olivine megacrysts are phenocrysts among depleted olivine phyric shergottites tissint is the first one that acts mostly as a closed system with olivine megacrysts being the phenocrysts the texture and mineral chemistry of tissint indicate a crystallization sequence of olivine mg 80 1 olivine mg 76 chromite olivine mg 74 ti chromite olivine mg 74 63 pyroxene mg 76 65 cr ulvospinel olivine mg 63 35 pyroxene mg 65 60 plagioclase followed by late stage ilmenite and phosphate the crystallization of the tissint meteorite likely occurred in two stages uniform olivine cores likely crystallized under equilibrium conditions and a fractional crystallization sequence that formed the rest of the rock the two stage crystallization without crystal settling is simulated using melts and the tissint bulk composition and can broadly reproduce the crystallization sequence and mineral chemistry measured in the tissint samples the transition between equilibrium and fractional crystallization is associated with a dramatic increase in cooling rate and might have been driven by an acceleration in the ascent rate or by encounter with a steep thermal gradient in the martian crust

petrology and shock metamorphism of the olivine phyric shergottite yamato 980459 evidence for a two stage cooling and a single stage ejection history abstract the basaltic martian meteorite yamato 980459 consists of large olivine phenocrysts and often prismatic pyroxenes set into a fine grained groundmass of smaller more fe rich olivine chromite and an interstitial residual material displaying quenching textures of dendritic olivine chain like augite and sulfide droplets in a glassy matrix yamato 980459 is thus the only martian meteorite without plagioclase maskelynite olivine is compositionally zoned from a mg rich core to a fe rich rim with the outer few micrometers being especially rich in iron with fo84 the cores are the most magnesian olivines found in martian meteorites so far pyroxenes are also mostly composite crystals of large orthopyroxene cores and thin ca rich overgrowths separate pigeonite and augites are rare on basis of the mineral compositions the cooling rates determined from crystal morphologies and crystal grain size distributions it is deduced that the parent magma of yamato 980459 initially cooled under near equilibrium conditions e g in a magma chamber allowing chromite and the mg rich silicates to form as cumulus phases fractional crystallization at higher cooling rates and a low degree of undercooling let to the formation of the ca al and fe rich overgrowths on olivine and orthopyroxene while the magma was ascending towards the martian surface finally and before plagioclase and also phosphates could precipitate the magma was very quickly erupted quenching the remaining melt to glass dendritic silicates and sulfide droplets the shape preferred orientation of olivine and pyroxene suggests a quick thin outflow of lava according to the shock effects found in the minerals of yamato 980459 the meteorite experienced an equilibration shock pressure of about 20 25 gpa its near surface position allowed the ejection from the planet s surface already by a single impact event and at relatively low shock pressures

fish otolith assemblages from recent ne atlantic sea bottoms a comparative study of palaeoecology abstract reconstruction of the paleoenvironment using fish otolith assemblages and depending on the modern analogue to provide precise reference information has been applied on many marine cenozoic sediments although the composition of such assemblages on recent sea bottoms in various environmental settings is still poorly known this study aims at better understanding the characteristics of otolith thanatocoenoses from recent sea bottoms otolith assemblages taken by box corers or van veen grabs on recent sea bottoms of the northeastern atlantic and the north sea at various depths and at various latitudes were analysed the results reveal that the pelagic and benthic benthopelagic taxa in the sea bottoms differ markedly in quantity and diversity the composition of an otolith assemblage differs from location to location reflecting its biogeographic characteristic which is mainly determined by pelagic taxa in the oceanic assemblages the bathymetry on the contrary can be better explained from the benthic benthopelagic taxa especially in the shallow water assemblages in addition otolith size related distribution along the isobaths is discovered in lampanyctus crocodilus in which the proportion of larger specimens in deeper waters increases markedly confirming the observations of its population stratification in the actual assemblages the biogeography and bathymetry obtained from the otolith assemblages could therefore in some cases be used as an indicator of the present ecology