trace element geochemistry of martian iddingsite in the lafayette meteorite the lafayette meteorite contains abundant iddingsite a fine grained intergrowth of smectite clay ferrihydrite and ionic salt minerals both the meteorite and iddingsite formed on mars samples of iddingsite olivine and augite pyroxene were extracted from lafayette and analyzed for trace elements by instrumental neutron activation our results are comparable to independent analyses by electron and ion microbeam methods abundances of most elements in the iddingsite do not covary significantly the iddingsite is extremely rich in hg which is probably terrestrial contamination for the elements si ai fe mn ni co and zn the composition of the iddingsite is close to a mixture of 50 lafayette olivine 40 lafayette siliceous glass 10 water concordant behavior among these elements is not compatible with element fractionations between smectite and water but the hydrous nature and petrographic setting of the iddingsite clearly suggest an aqueous origin these inferences are both consistent however with deposition of the iddingsite originally as a silicate gel which then crystallized neoformed nearly isochemically the iddingsite contains significantly more magnesium than implied by the model which may suggest that the altering solutions were rich in mg 2

transmission electron microscope analyses of alteration phases in martian meteorite mil 090032 abstract the nakhlite group of martian meteorites found in the antarctic contain varying abundances of both martian and terrestrial secondary alteration phases the aim of this study was to use transmission electron microscopy tem to compare martian and terrestrial alteration embodied within a single nakhlite martian meteorite find mil 090032 martian alteration veins in mil 090032 are composed of poorly ordered fe smectite phyllosilicate this poorly ordered smectite appears to be equivalent to the nanocrystalline phyllosilicate hydrated amorphous gel phase previously described in the martian alteration veins of other nakhlites chemical differences in this nanocrystalline phyllosilicate between different nakhlites imply localised alteration which occurred close to the martian surface in mil 090032 both structurally and compositionally the nakhlite nanocrystalline phyllosilicate shows similarities to the amorphous poorly ordered phase recently discovered in martian soil by the mars curiosity rover at rocknest gale crater terrestrially derived alteration phases in mil 090032 include jarosite and gypsum amorphous silicates and fe oxides and hydroxides similarities between the mineralogy and chemistry of the mil 090032 terrestrial and martian alteration phases suggest the alteration conditions on mars were similar to those in the antarctic at both sites a small amount of fluid at low temperatures infiltrated the rock and became acidic as a result of the conversion of fe2 to fe3 under oxidising conditions

tides and tidal energetics of the strait of gibraltar a modelling approach abstract the main semidiurnal m2 and s2 and diurnal o1 and k1 tidal waves in the strait of gibraltar are simulated by employing a 2d high resolution non linear boundary fitted coordinate model agreement between observational evidence and model results is good for the m2 and s2 tidal waves and satisfactory for the o1 and k1 tidal waves the model reproduces all the known features of the spatial structure of these waves and predicts some new ones namely the general direction of the m2 and s2 mean tidal energy fluxes to the west with a clear increase at the camarinal sill the o1 amphidrome with anticlockwise rotation of cotidal lines in the tarifa narrows and small scale eddies in the m2 s2 and o1 mean tidal energy flux fields in the vicinity of the western and eastern boundaries of the strait

samarium neodymium and rubidium strontium systematics of nakhlite governador valadares abstract the sm nd systematics of whole rock and mineral separate samples from nakhlite governador valadares define a good 147sm 143nd mineral isochron age of 1 37 0 02 ga this age is in excellent agreement with the 39ar 40ar and rb sr ages obtained previously for this meteorite however the rb sr isotopic data for our sample show that the isotopic system is disturbed the lack of isotopic equilibrium is probably caused by the weathering of the sample as indicated by the presence of secondary alteration phases the whole rock and acid washed mineral data yield a rb sr age of 1 20 0 05 ga which probably represents a lower limit to the crystallization age of the rock the petrographic evidence indicates that this meteorite is a clinopyroxene cumulate that probably crystallized in a subsurface sill mcsween 1994 thus the sm nd isotopic age probably represents the age of such a magmatic event the initial e143nd value determined for the rock at 1 37 ga is 17 1 indicating that the parent magma of the rock came from a light rare earth element depleted source of 147sm 144nd 0 237 based on a simple two stage evolution model results of the same model calculation for the initial 87sr 86sr ratio of the rock suggest that its source material was depleted in 87rb 86sr by 50 relative to the estimated martian value at 1 37 ga both the high sm nd and low rb sr values support a clinopyroxene rich cumulate source for the genesis of the nakhlite governador valadares furthermore our sm nd age and e143nd data and the previously published e142nd datum for the rock harper et al 1995 are consistent with early differentiation of the parent planet formation of cumulate sources 4 56 ga ago and late melting of the sources and formation of the rock 1 37 ga ago the good agreement of isotopic ages and petrographic features among governador valadares nakhla and lafayette strongly suggests that all three nakhlites have undergone similar evolutionary histories the nakhlite age data suggest that isotopic heterogeneity in the martian mantle sources existed up to 1 37 ga ago and early mantle structures probably have not been disturbed for a significant portion of martian history

accretion of southern alaska abstract paleomagnetic data from southern alaska indicate that the wrangellia and peninsular terranes collided with central alaska probably by 65 ma ago and certainly no later than 55 ma ago the accretion of these terranes to the mainland was followed by the arrival of the ghost rocks volcanic assemblage at the southern margin of kodiak island poleward movement of these terranes can be explained by rapid motion of the kula oceanic plate mainly from 85 to 43 ma ago according to recent reconstructions derived from the hot spot reference frame after accretion much of southwestern alaska underwent a counterclockwise rotation of about 50 as indicated by paleomagnetic poles from volcanic rocks of late cretaceous and early tertiary age compression between north america and asia during opening of the north atlantic 68 44 ma ago may account for the rotation

experimental meteoric water basalt interactions characterization and interpretation of alteration products abstract the products from experimental alteration of crystalline and glassy basalt by meteoric water at 45 and 70 c have been analyzed with transmission electron microscopy tem selected area electron diffraction saed and x ray analytical electron microscopy aem the principal solid alteration products include quartz chrysotile talc kerolite calcite kaolinite smectite and amorphous silicate material with spongy smectite like morphology these solids act as sinks for elements that are released during the basalt alteration and they are important for controlling the chemistry of the altering fluid comparison of the reaction quotients for the various solid phases and the fluid composition shows that the approach to equilibrium between altering fluid and basalt depends on both temperature and the ratio of fluid to basalt surface area the degree of supersaturation with respect to equilibrium values for the precipitated phases can be explained by the enhanced solubility resulting from small crystal size of the alteration products the results of this study underscore the importance of metastabile phenomena in the low temperature alteration or weathering of both crystalline and glassy basalt

alteration assemblages in the nakhlites variation with depth on mars secondary mineral assemblages in the nakhlite meteorites lafayette governador valadares gv nakhla yamato y 000593 y 000749 have been studied using scanning electron microscopy transmission electron microscopy and electron probe micro analysis the different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases showing compositional fractionation correlated with their relative depths below the martian surface fracture filled veins in lafayette at the bottom of the pile consist of a siderite phyllosilicate fe oxide hydrated silicate gel assemblage corresponding veins in nakhla and gv further up the pile are predominantly a siderite gel assemblage with additional evaporites including gypsum y 000593 y 000749 veins are dominated by gel the gel s mg mg fe ratio decreases from lafayette 0 37 to gv 0 32 nakhla 0 24 and y 000593 0 15 we suggest that hydrothermal fluid flowed up this depth profile initiated by melting of buried h2o co2 ice our results show a complex mix of fe rich phyllosilicate within the veins and mesostasis of lafayette with d spacings of 0 7 1 1 nm suggesting a mixture of smectite and serpentine the phyllosilicate formed at close to neutral ph 150 c we also suggest that water rock ratios w r of 1 10 occurred in lafayette with smaller values for the other nakhlites this is reflected in the volume of alteration minerals 10 of olivine in lafayette to 3 in nakhla textural evidence of rapid cooling together with the w r and likely fluid velocities suggest that the secondary assemblages formed quickly e g within months a model is proposed in which the secondary assemblages formed in an impact induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

40ar 39ar studies of whole rock nakhlites evidence for the timing of formation and aqueous alteration on mars 20 25 mg whole rock samples of the nakhlites lafayette and nakhla have been analyzed via the 40ar 39ar technique in part to verify their formation ages but primarily in an attempt to determine the timing of aqueous alteration in these martian meteorites as in previous studies plateaus in apparent age are observed at about 1300 ma 1322 10 for lafayette 1332 10 and 1323 11 for nakhla presumably corresponding to crystallization ages the plateaus are not entirely flat perhaps reflecting the effects of recoil during creation of 39ar in the nuclear irradiation the first 5 20 of the k derived ar released from all three samples give apparent ages 1300 ma coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance we believe the low temperature pattern represents more recent than 1300 ma formation of martian aqueous alteration products such as iddingsite no low temperature plateaus are observed this is consistent with petrographic evidence for multiple formation events although the lack of low temperature plateaus is far from conclusive on the other hand if there was a single time of alteration we believe that it will be difficult if not impossible to determine it using the k ar system

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

clues to martian brines based on halogens in salts from nakhlites and mer samples 1 chlorine and br abundances in fracture filling secondary salts in nakhla veins determined in this study by synchrotron x ray microprobe br and electron microprobe cl techniques compare well to the halogens determined recently by apxs instruments in soils and rock rinds at the gusev and meridiani sites the salts in these mars rocks arise from martian brines that have undergone evaporative or freezing concentration the halogen abundances in these salts are corrected for dilution effect because of mixing with halogen poor phases to obtain their true abundances which seem to be close to the halogen abundances in terrestrial sea brines consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate sulfate halite in nakhlite meteorites nakhla veins yield high br 250 ppm and low cl br ratios 10 50 suggesting possible salt deposition from concentrated brines whereas lafayette iddingsite with low br 11 ppm and high cl br ratios 250 300 indicates salt deposition from dilute brines on mars the low cl br ratios 20 to 80 in salts from gusev and meridiani rock rinds indicate that they presumably originate from concentrated subsurface martian brines the high cl br ratio 270 in salts deposited by dilute solutions in lafayette and adirondack is similar to the chondritic cl br ratio which seems to characterize the dilute brines on mars prior to halite precipitation including early mars waters noachian or earlier our results seem to be consistent with the burt knauth model involving density stratification during evaporation freezing of brine solutions in martian regolith

opal a in the nakhla meteorite a tracer of ephemeral liquid water in the amazonian crust of mars the nakhlite meteorites are clinopyroxenites that are derived from a 1300 million year old sill or lava flow on mars most members of the group contain veins of iddingsite whose main component is a fine grained and hydrous fe and mg rich silicate siderite is present in the majority of veins where it straddles or cross cuts the fe mg silicate this carbonate also contains patches of ferric oxy hydroxide despite 40 years of investigation the mineralogy and origins of the fe mg silicate is poorly understood as is the paragenesis of the iddingsite veins nanometer scale analysis of fe mg silicate in the nakhla meteorite by electron and x ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal a this hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine each opal a nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine siderite crystallized subsequently and from solutions that were alkaline and reducing and replaced both the nanoparticles and olivine the fluids that formed both the opal a ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the martian atmosphere the last event recorded by the veins was alteration of the carbonate to a ferric oxy hydroxide that probably took place on mars although a terrestrial origin remains possible these results support findings from orbiter and rover based spectroscopy that opaline silica was a common product of aqueous alteration of the martian crust

element abundances patterns and mobility in nakhlite miller range 03346 and implications for aqueous alteration abstract nakhlite miller range mil 03346 contains many secondary phases resulting from aqueous processes including formation of poorly crystalline iddingsite like veins in olivine the precipitation of ca sulfates and fe k sulfates from evaporating fluids alteration of titanomagnetite to secondary fe oxides and the dissolution of magmatic ca phosphates and residual glass in the mesostasis a surprising variety of alteration products occur in association with olivine in mil 03346 including patches of incipiently altered olivine large si enriched olivine hosted veins up to 10 m across some of which are complex in morphology and are composed of several phases small fe s k rich veinlets that crosscut the si enriched veins ca sulfates filling cracks in olivine and secondary ca phosphates elemental abundances and distributions in these alteration products are consistent with the mobilization of elements from readily dissolved phases in the mesostasis such as phosphates and residual glass under favorable weathering conditions these phases dissolve more readily than pyroxenes plagioclase and even olivine at low ph the occurrence crosscut and devolatilized by the fusion crust and composition of si enriched alteration veins in olivine are consistent with their formation on mars si enriched poorly crystalline alteration products and secondary ca sulfates commonly occur in nakhlites but the habit and composition of these alteration products differ between meteorites elemental distributions in these secondary phases suggest at least two episodes of alteration have affected mil 03346 and subtle differences in secondary minerals and chemistry indicate that each nakhlite experienced its own unique alteration history either on mars earth or both the variable al content and range of morphologies of the olivine hosted si enriched veins suggest variable alteration conditions consistent with a water limited regime if the secondary phases in mil 03346 can be shown to have formed on mars their chemistry will provide important clues to the aqueous environments and processes at the time of their formation however elevated s and rees ce anomalies and association of secondary minerals with post impact cracks and voids indicate that terrestrial weathering has significantly affected mil 03346 this work highlights the difficulty in distinguishing pre terrestrial aqueous alteration from later chemical weathering of susceptible mineral phases even in meteorites with limited terrestrial modification

clay mineraloid weathering products in antarctic meteorites abstract clay mineraloids are associated with gypsum k fe sulfates possibly jarosite cryptocrystalline rust and possibly with zeolites and or secondary alkali feldspars as terrestrial weathering products in stony meteorites from the allan hills alh and elephant moraine eet collection areas in victoria land antarctica weathering formed fracture fillings in fusion crusts of eucrites eeta79004 and eeta79005 diogenites alha77256 and eeta79002 shergottite eeta79001 and h5 chondrite alh82102 and decomposition products of glass and plagioclase in interior samples of achondrites clay mineraloids displayed massive to incipient vermicular forms with elemental compositions that suggest smectite and mica like phases deposits were too small to yield pure material for phase identification although x ray diffractometry and differential scanning calorimetry of bulk samples suggested that the clay mineraloids were not well crystallized a typical structural formula calculated on a smectite basis follows k 0 26 ca 0 04 al 0 97 ti 0 02 fe 3 0 77 mg 0 03 si 4 00 o 10 oh 2 n 2 o net charge 0 28 excessions 0 58 si 0 02 cl 0 09 so 4 0 02 po 4 hydrocryogenic diagenesis can initiate clay mineral formation on timescales of 10 4 10 6 y even with only limited supplies of liquid water cosmochemists must take care not to confuse possible weathering induced elemental and isotopic fractionations in antarctic meteorite samples with signatures of pre terrestrial cosmic processes given proper sample selection and testing though occurrence of clay mineraloid and other weathering products should probably not impede progress in studies of antarctic meteorites

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

aqueous corrosion of olivine in the mars meteorite miller range mil 03346 during antarctic weathering implications for water on mars abstract several nakhlites clinopyroxenite meteorites from mars contain olivine phenocrysts with corrosion features identical in size shape and distribution to the smaller etch pits of well characterized weathered terrestrial olivine miller range mil 03346 is an antarctic nakhlite find recovered after long exposure to antarctic conditions the distribution of discrete olivine etch pits almost exclusively within a few hundred microns of allocation mil 03346 171 s documentably exposed surface suggests that they formed by terrestrial weathering in antarctica the small size of olivine etch pits in mil 03346 171 relative to commonly much larger etch pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short or the weathering conditions to which it was exposed did not favor olivine corrosion in the form of etch pit formation or both time scales for the formation of etch pits estimated from experimentally determined dissolution rates of olivine over a range of phs are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on mars etch pits of the observed size on mil 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic antarctic conditions but the terrestrial age of mil 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline antarctic water the paucity of similar etch pits in olivine from the interior of mil 03346 suggests that olivine in this mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1 3 billion years on mars than its exterior was subjected to during its pleistocene holocene exposure to antarctic weathering conditions

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

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

petrology of the miller range 03346 nakhlite in comparison with the yamato 000593 nakhlite we petrologically examined the miller range mil 03346 nakhlite the main phase modal abundances are 67 7 vol augite 0 8 vol olivine and 31 5 vol mesostasis among all known nakhlites mil 03346 s modal abundance of olivine is the smallest and of mesostasis is the largest augite occurs as cumulus phenocrysts having a homogeneous core composition en36 38fs24 22wo40 which is identical with other nakhlites they accompany thin ferroan rims divided into inner and outer rims with a compositional gap at the boundary between the two rims olivine grains have magnesian cores fa 55 and show normal zoning toward ferroan rims fa 84 mesostasis consists mostly of glass 26 0 vol with minor skeletal fayalites skeletal titanomagnetites acicular phosphate massive cristobalite and sulfides we conclude that mil 03346 is the most rapidly cooled nakhlite among all known nakhlites based on the petrography we obtain the intercumulus melt composition for mil 03346 from the mass balance calculation using the modal abundances and discuss the crystallization sequence of mil 03346 in comparison with that of yamato y 000593 although magnesian olivines of y 000593 are phenocrystic magnesian olivine grains of mil 03346 seem to have texturally crystallized from the intercumulus melt after the mil 03346 magma intruded upward to the martian surficial zone the magnesian olivine crystallized and then the ferroan inner rim formed on phenocrystic core augite the outer rim of phenocrystic augites formed after the crystallization of skeletal fayalites and skeletal titanomagnetites resulting in a compositional gap between the inner and outer rims finally glassy mesostasis formed from the residual melt this crystallization sequence of mil 03346 is different from those of other nakhlites including y 000593

a review of meteorite evidence for the timing of magmatism and of surface or near surface liquid water on mars 1 there is widespread photogeological evidence for ubiquitous water flowing on the surface of mars however the age of surface and near surface water cannot be deduced with high precision from photogeology while there is clear evidence for old and young fluvial features in the photogeologic record the uncertainty in the absolute calibration of the martian crater flux results in uncertainties of 1 5 gyr in the middle period of martian geologic history aqueous alteration of primary igneous minerals produces secondary minerals in martian meteorites here we use the ages of secondary alteration minerals in martian meteorites to obtain absolute ages when liquid water was at or near the surface of mars aqueous alteration events in martian meteorites occurred at 3929 37 ma carbonates in alh84001 633 23 ma iddingsite in nakhlites and 0 170 ma salts in shergottites furthermore these events appear to be of short duration suggesting episodic rather than continuous aqueous alteration of the meteorites the martian meteorites appear to be contaminated by martian surface pb characterized by a 207pb 206pb ratio near 1 lead of this composition could be produced by water based alteration on the martian surface the high 129xe 132xe ratio in the martian atmosphere compared to martian meteorites indicates fractionation of i from xe within 100 myr after nucleosynthesis of 129i such fractionation is difficult to achieve through magmatic processes however water very efficiently fractionates i from xe raising the intriguing possibility that mars had a liquid water ocean within its first 100 myr 1

mineral chemistry of the shergottites nakhlites chassigny brachina pallasites and urelites the mineral chemistry is compared for selected achondrites olivine in the alha 77005 and eeta79001 shergottites olivine rich chassigny and brachina and the nakhlites contains ni indicative of oxidizing conditions whereas pallasitic and ureilitic olivines contain much lower ni due to reducing conditions the brachina olivine and pyroxene have distinctively higher fe mn than the shergottites and chassigny further indicating that brachina is unique the chassigny and 77005 olivines contain lower cr2o3 0 03 wt than the brachina and 79001 olivines values of fe mn for cumulus augites in nakhlites are higher than for the shergottites whereas those for ferropigeonites are not the 77005 shergottite contains troilite fes in contrast to 79001 shergotty zagami and chassigny which contain pyrrhotite further analyses are needed but the present survey indicates that at least brachina is not chemically cogenetic with the other oxidized achondrites and that the fe mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites shergottites and chassigny to a single genetic group

geochemical components in martian soil abstract trends in element compositional variation among samples at the viking lander sites on mars provide evidence for multiple geochemical components in the soils a simple two component model can explain all pair wise trends of eight elements analyzed component a contains si and most or all the al ca ti and fe component b which is 16 3 by weight of the total contains s and most or all the cl and mg these results constrain several models of martian soil mineralogy but are consistent with a mixture of silicates and salts

kinetic effects on trace element partitioning kinetic effects on trace element partitioning have been measured for anorthite forsterite and diopside grown from synthetic compositions doped with ree a seeding technique allowed determination of crystal growth rates and partitioning information was obtained from electron microprobe analyses compositional deviations from equilibrium values were sought in the crystals and as gradients in the quenched liquids adjacent to the crystals the principal result is that large deviations in trace element distribution coefficients from equilibrium values do not occur because of a compensating effect rapid growth depletes the melt adjacent to the crystal in the elements of which the crystal is composed leading to different values for apparent distribution coefficients however as the boundary layer melt becomes depleted in the components of the crystal growth slows and the size of the compositional perturbations decreases crystals grown at very high rates e g 0 2 m sec for diopside tended to be too small for accurate microprobe analyses but are probably not compositionally extreme since the melts adjacent to the crystals did not acquire sizable compositional gradients at moderately high growth rates e g 0 02 m sec crystals form in the presence of boundary layer compositions perturbed by as much as 10 from bulk melt values and in diopside attain concentrations for excluded trace elements about 70 higher than equilibrium values for crystals plus bulk melt at the slower growth rates typical of igneous systems kinetic effects on trace element partitioning are probably negligible

trace element identification of three chemically distinct very low titanium vlt basalt glasses from apollo 17 abstract lunar basaltic samples of vlt very low titanium composition occur primarily as small glass fragments in the regolith at the apollo 17 landing site electron microprobe analyses of glasses from the double drive tube 79001 2 90 150 m size fraction of soils from mean depths of 0 8 16 8 cm indicate that 34 of 90 38 are of vlt composition a subset of twenty glasses was removed from the thin sections using a micro coring device and analyzed using special micro inaa techniques to obtain major and trace element abundances on the basis of the results we delineate three distinct groups which have been named for their relative amounts of co hico meco and loco apollo 17 vlts the most magnesian hico basalt glasses 4 of 34 or about 12 of the vlt glasses are probably pristine pyroclastics soil breccias 79135 and 70295 apparently contain only this type of vlt glass the medium co meco glasses 6 of 34 18 strongly resemble the largest sample of vlt composition the olivine vitrophyre 78526 as well as all three of the apollo 17 vlt lithic fragments that have been analyzed for trace elements the loco vlt glasses 23 of 34 68 are more enigmatic trace element concentrations require that these three vlt compositions cannot be related by simple igneous processes the distribution of the three types provides important information on the sequence of events that produced the regolith at the apollo 17 site

comparisons of the four miller range nakhlites mil 03346 090030 090032 and 090136 textural and compositional observations of primary and secondary mineral assemblages abstract petrological and geochemical analyses of miller range mil 03346 indicate that this meteorite originated from the same augitic cumulate layer s as the nakhlite martian meteorites but underwent rapid cooling prior to complete crystallization as with the other nakhlites mil 03346 contains a secondary alteration assemblage in this case consisting of iddingsite like alteration veins in olivine phenocrysts fe oxide alteration veins associated with the mesostasis and ca and k fe sulfate veins we compared the textural and mineralogical compositions of mil 090030 090032 and 090136 with mil 03346 focusing on the composition and raman spectra of the alteration assemblages these observations indicate that the meteorites are paired and that the preterrestrial olivine bound alteration assemblages were produced by weakly acidic brine although these alteration assemblages resemble similar assemblages in nakhla the absence of siderite and halite in the miller range nakhlites indicates that the parental alteration brine was comparatively hco3 depleted and less concentrated than that which altered nakhla this indicates that the miller range nakhlite alteration brine experienced a separate evolutionary pathway to that which altered nakhla and therefore represents a separate branch of the lafayette nakhla evaporation sequence thin sections cut from the internal portions of these meteorites away from any fusion crust or terrestrially exposed edge contain little ca sulfate identified as gypsum and no jarosite whereas thin sections with terrestrially exposed edges have much higher sulfate abundances these observations suggest that at least the majority of sulfate within the miller range nakhlites is terrestrially derived

the northwest africa nwa 5790 meteorite a mesostasis rich nakhlite with little or no martian aqueous alteration northwest africa nwa 5790 is the most recently discovered member of the nakhlite group its mineralogy differs from the other nakhlites with a high abundance mesostasis 38 1 3 6 vol and scarcity of olivine 4 0 2 2 vol furthermore zoning of augite phenocrysts and other petrographic and chemical characteristics suggest that nwa 5790 samples the chilled margin of its parent lava flow sill nwa 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water the calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins the presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin consistent with the carbon and oxygen isotope composition of the calcite the clay minerals are finely crystalline and comprise 0 003 vol of the meteorite d values of the clay minerals range from 212 109 to 96 132 and cannot be used to distinguish between a terrestrial or martian origin as petrographic results are also not definitive we conclude that secondary minerals produced by martian groundwaters are at best very rare within nwa 5790 the meteorite has therefore sampled a region of the lava flow sill with little or no exposure to the aqueous solutions that altered other nakhlites this isolation could relate to the scarcity of olivine in nwa 5790 because dissolution of olivine in other nakhlites by martian groundwaters enhanced their porosity and permeability and provided solutes for secondary minerals

cl amphibole in the nakhlite mil 03346 evidence for sediment contamination in a martian meteorite abstract the pathfinder spirit and opportunity missions revealed that martian soils and rocks are enriched in chlorine up to 0 6 wt cl significant piles of evaporitic sedimentary rocks have also been observed at meridiani planum the snc meteorites inferred to come from mars hardly ever contain cl rich minerals except in secondary alteration products such as clay rich veinlets and massive halite trapped within olivine from nakhla here we describe the first extra terrestrial cl rich amphibole in the newly found nakhlite mil 03346 it is a chloro potassichastingsite up to 8 cl wt that crystallized exclusively as a daughter mineral in some of the melt patches sequestered inside augite phenocryst clusters it is never found as fracture filling material nor as discrete grains in the mesostasis this cl rich amphibole crystallized from the evolved residual liquid at some intermediate magmatic stage this heterogeneous contamination at a magmatic stage provides the first evidence for contamination of a nakhlite parent magma by cl rich particles of evaporitic sediments such a contamination appears to be very limited to melt patches present in a small number of augite crystals because of dilution and devolatilization effects this contamination remains cryptic in the mesostasis

aqueous alteration of the martian meteorite northwest africa 817 probing fluid rock interaction at the nakhlite launch site the nakhlite meteorites characteristically contain iddingsite a hydrous iron magnesium silicate that formed by aqueous alteration on mars iddingsite is most abundant in northwest africa nwa 817 and alteration products in this meteorite also have the lowest deuterium hydrogen ratio of any nakhlite taken together these distinctive properties could be interpreted to show that nwa 817 was altered under different physico chemical conditions than the other nakhlites and by liquid water from a separate reservoir here this interpretation is tested through a petrographic mineralogical chemical and isotopic study of nwa 817 we find that its iddingsite occurs as olivine hosted veins of nanocrystalline smectite and fe oxyhydroxide strong similarities in the mineralogy of iddingsite between nwa 817 and other nakhlites suggest that these meteorites were altered under comparable physico chemical conditions with the fe rich composition of nwa 817 olivine grains rendering them especially susceptible to aqueous alteration analyses of nwa 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium hydrogen ratios but owing to terrestrial weathering of this meteorite the hydrogen isotopic data cannot be used with confidence to infer the origin of martian aqueous solutions nwa 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system one interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of mars and flowed through the nakhlite lava pile under the influence of gravity

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites