a new martian meteorite from oman mineralogy petrology and shock metamorphism of olivine phyric basaltic shergottite sayh al uhaymir 150 the sayh al uhaymir sau 150 meteorite was found on a gravel plateau 43 3 km south of ghaba oman on october 8 2002 oxygen isotope 17o 2 78 18o 4 74 cre age 1 3 ma and noble gas studies confirm its martian origin sau 150 is classified as an olivine phyric basalt having a porphyritic texture with olivine macrocrysts set in a finer grained matrix of pigeonite and interstitial maskelynite with minor augite spinel ilmenite merrillite pyrrhotite pentlandite and secondary terrestrial calcite and iron oxides the bulk rock composition in particular mg 68 molar mg mg fe 100 fe mn 37 9 and na al 0 22 are characteristic of martian meteorites based on mineral compositions cooling rates determined from crystal morphology and crystal size distribution it is deduced that the parent magma formed in a steady state growth regime magma chamber that cooled at 70 365 c sau 150 is essentially identical to sau 005 094 all representing samples of the same fall that are similar to but distinct from the dag shergottites

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

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

terrestrial alteration mineral assemblages in the nwa 10416 olivine phyric shergottite abstract we report on the alteration history of the olivine phyric highly depleted hd shergottite northwest africa nwa 10416 paying particular attention to the origin of the aqueous alteration seen affecting the meteorite s olivine megacrysts the rock s interior displays 1 mm zoned altered olivine megacrysts set in a groundmass of clinopyroxene unzoned olivine and interstitial plagioclase and maskelynite synchrotron micro x ray diffraction xrd and transmission electron microscopy tem show that plagioclase and maskelynite have been partially replaced by kaolinite the relict olivine megacryst cores display a unique concentric colouration for martian meteorites having central amber coloured zones surrounded by a brown mantle zone with the rims remaining clear and unaltered this colouration is a result of fluid alteration and partial replacement with hydration tem analysis revealed the 200 nm scale banded and largely amorphous nature of the alteration but with some 20 relict crystalline olivine patches although the coloured olivine zones show cation and anion site vacancies compared to stoichiometric olivine a relict igneous compositional trend is preserved in the megacrysts from mg rich altered cores mg 76 to unaltered stoichiometric rims fo53 synchrotron fe k x ray absorption near edge structure xanes analysis revealed that the coloured zones of the megacryst have different fe oxidation values high ferric contents are present in the brown mantle zones fe3 fe 0 92 and the amber zones fe3 fe 0 30 whereas the clear rims are ferrous this suggests alteration occurred in an oxidising environment and that the sharp contrast in colour of the megacryst brown to clear is a record of a relict fluid reaction front in order to test the terrestrial or extraterrestrial origin of the alteration olivine material from a shock melt vein was analysed by tem the analysis revealed 0 952 nm curved d spacing s from clay alteration undisturbed by any shock effects strongly suggesting a terrestrial origin the d spacing values most likely represent a collapsed saponite or vermiculite showing that in some places olivine has been replaced by crystalline clay oxygen isotope analysis of bulk 17o 0 309 0 009 2 and amber coloured megacryst material 0 271 0 002 2 are also consistent with terrestrial alteration we propose a model in which during the meteorite s time in northwest africa low temperature likely acidic groundwater exploited fractures the fluid altered the olivine megacrysts in a way that was controlled by the pre existing igneous compositional zonation with mg rich olivine being more susceptible to alteration in this fluid environment the plagioclase and maskelynite were also altered to a high degree after the alteration event it is likely that nwa 10416 had a significant residence time in northwest africa accounting for terrestrial calcite and the dehydration of some clay phases

basalt and olivine dissolution under cold salty and acidic conditions what can we learn about recent aqueous weathering on mars 1 to test which variables may be important for weathering on mars the effects of temperature 22 c 6 c and 19 c high ionic strength and oxygen concentrations were investigated in batch dissolution experiments containing forsterite fayalite and basalt glass cacl2 nacl h2o brine can remain liquid to temperatures of 55 c and thus may be liquid in the cold dry climate that currently characterizes mars to understand weathering under such conditions dissolution rates were measured in experiments in distilled water with and without cacl2 and nacl as observed by others dissolution rates increased with temperature and only fayalite dissolution was significantly affected by the presence or absence of oxygen enhanced fayalite dissolution under anoxic conditions suggests that fe rich olivine would dissolve more rapidly than mg rich olivine on mars dissolution in the two most dilute experimental solutions deionized water and cacl2 nacl h2o solution of ionic strength 0 7 m were the same within uncertainty but apparent dissolution rate constants in cacl2 nacl h2o brines were significantly slower steady silica concentrations are decreased in the brines consistent with other work and precipitation rates of silica decrease with decreasing temperatures these results suggest that enhanced silica precipitation could be an indicator of high ionic strength solutions on mars consistent with these observations weathering of basalt has been observed to sometimes be accompanied by precipitated layers of silica in cold dry environments on earth if dissolution on mars occurs or occurred under conditions similar to our experiments cation leaching would be expected to be accompanied by silica precipitates on weathering surfaces

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

the nakhlite hydrothermal brine on mars abstract water is the basis of habitability and formation conditions of hydrous alteration minerals are key to temperature and chemical conditions of that water using new detailed observations on nakhlite martian meteorite alteration composition temperature and redox conditions of the water that formed the observed hydrous alteration can be determined through thermochemical modelling we show that the nakhlite parent rocks on mars encountered a co2 rich hydrothermal fluid at 150 t 200 c ph 6 8 with a water rock ratio w r 300 under these conditions fe rich carbonate was precipitated within brittle fractures as the fluid cooled to 50 c at ph 9 and w r of 6 fe rich phyllosilicate precipitated followed in turn by rapid precipitation of an amorphous gel it was enriched in the most soluble species e g k na of alkaline ph and similar to terrestrial i e not seawater influenced dilute brines in basaltic terrains on earth our results show that environments associated with this type of fluid were habitable unlike those associated with acid sulphate fluids considering the timing of the nakhlite alteration the most likely cause is impact generated hydrothermal alteration of the nakhlite pile at the margins of an impact crater the martian subsurface fluid forming phyllosilicates provided habitable temperatures and many of the nutrients required for life

evidence in tissint for recent subsurface water on mars we report unambiguous chemical evidence for subsurface water activity in the martian crust at 600 ma based on the data from tissint a fresh martian meteorite fall with minimal terrestrial weathering the impact melt pockets in tissint contain abundant volatiles h 2o co 2 f and cl and their concentrations are positively correlated with each other higher h 2o concentrations also accompany higher deuterium contents these correlations suggest mixing between two volatile sources the first source is h 2o in the precursor basalt inherited from martian magma magmatic h 2o in the basalt had low deuterium concentration and was likely stored in the nominally anhydrous minerals this source contributed little co 2 or halogens to the impact melts the second source is inferred to be aqueous alteration products introduced to the basalt by water activity after the basalt erupted these alteration materials contributed more volatiles to the impact melts than the magmatic source and had high deuterium abundance reflecting isotope equilibrium with recent martian atmosphere the water activities occurred beneath the martian surface after 600 ma crystallization age but before 1 ma ejection age the chemical and isotopic signatures of the alteration products in tissint resemble previously known martian samples associated with old water activities on mars which can be traced back to 4 2 billion years ago e g the mudstone at gale crater this similarity in chemistry and the wide age span indicate that such water activities were common on mars throughout its history which had the potential to form habitable environment however the rarity of the volatile rich zone in tissint suggests that martian crustal aqueous processes where they have occurred are generally limited in their extent of water rock reaction

geological constraints on the thermodynamic properties of the stilbite stellerite solid solution in low grade metabasalts abstract standard state thermodynamic data for stilbite ca2naal5si13o36 16h2o and stellerite ca2al4si14o36 14h2o together with mixing properties of the stilbite stellerite solid solution stilbite ss are derived through assessment of geological observations of stilbite ss compositions in metabasalts experimental phase equilibria and calorimetric observations measured compositions of stilbite ss in tertiary metabasalts in iceland and icelandic geothermal systems change systematically towards the stellerite endmember with increasing stratigraphic depth and temperature standard molal volumes heat capacities and entropies for the endmembers of the solid solution are derived through critical review of published crystallographic and calorimetric data for natural stilbite ss standard molal gibbs energies of formation at 298 15 k and 1 bar for stilbite 4 946 475cal mol 1 and stellerite 4 762 036 cal mol 1 and the mixing properties of the solid solution are retrieved from observed phase and compositional relations in metabasalts at berufjordur iceland measured temperatures of zeolite mineral distribution in active geothermal systems and published observations of reversed phase equilibria mixing in stilbite ss can be described with an athermal solid solution model thermodynamic data resulting from our analysis provide close correlation between compositions of stilbite ss in icelandic geothermal systems predicted from compositions of geothermal solutions and observed compositions of these minerals in low grade metabasalts of iceland as well as the observed temperature of the stilbite ss to laumontite leonhardite transition in icelandic geothermal systems stilbite ss composition in metabasalts is a sensitive function of temperature fluid composition coexisting minerals especially silica polymorphs and geothermal gradient

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

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

magmatic water in the martian meteorite nakhla abstract mars does not recycle crustal materials via plate tectonics for this reason the magmatic water reservoir of the martian mantle has not been affected by surface processes and the deuterium hydrogen d h ratio of this water should represent the original primordial martian value following this logic hydrous primary igneous minerals on the martian surface should also carry this primordial d h ratio assuming no assimilation of martian atmospheric water during crystallization and no major hydrogen fractionation during melt degassing hydrous primary igneous minerals such as apatite and amphibole are present in martian meteorites here on earth providing these minerals have not been affected by terrestrial weathering martian atmospheric water or shock processes after crystallization they should contain a good approximation of the primordial martian d h ratio as nakhla was seen to fall in the egyptian desert in 1911 terrestrial contamination is minimized in this meteorite the nakhlites are also among the least shocked of the martian meteorites therefore apatite within nakhla could contain primordial martian hydrogen isotope ratios we produced in situ measurements of the d h ratios in nakhla apatite grains using a cameca ims 1280 ion microprobe our measurements produced d h values in nakhla apatite similar to terrestrial values despite strong evidence that our samples were not significantly contaminated by terrestrial hydrogen these results suggest that water trapped in the martian mantle has a similar d h to that of the earth therefore the water of these two planets may have originated from the same source material the d h ratios of the carbonaceous chondrite meteorites and the jupiter family comet 103p hartley 2 are similar to the d h of the two planets making both these primitive inner solar system materials strong candidates for the source of the terrestrial planets water these results support recent dynamical models of the formation of the solar system which suggest material in the inner solar system was homogenized by the migration of jupiter

experimental determination of plagioclase dissolution rates as a function of its composition and ph at 22 c abstract the steady state far from equilibrium dissolution rates of nine distinct plagioclases ranging in composition from an2 to an89 were measured in mixed flow reactors at 22 2 c and ph from 2 to 11 the dissolution rates of all plagioclases based on silica release show a common u shaped behaviour as a function of ph where rates decrease with increasing ph at acid condition but rise with increasing ph at alkaline conditions consistent with literature findings constant ph plagioclase dissolution rates increase with increasing anorthite content at acidic conditions measured anorthite dissolution rates are 2 5 orders of magnitude faster than those of albite at ph 2 perhaps more significantly rates are independent of plagioclase composition at alkaline conditions interpretation and data fitting suggests that plagioclase dissolution rates are consistent with their control by the detachment of si rich activated complexes formed by the removal of al from the mineral framework taking account of this mechanism and transition state theory yields equations describing plagioclase dissolution rates r as a function of both the mineral and aqueous fluid compositions found in natural earth surface systems for ph 6 rates are consistent with log r mol cm 2 s 0 35 log a h 3 a al 3 11 53 and for ph log r mol cm 2 s n acid log a h 3 a al 3 0 033 an 14 77 where an represents the percent anorthite in the plagioclase solid solution ai corresponds to the activity of the ith aqueous species and nacid is given by n acid 0 004 an 0 05

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

ferric saponite and serpentine in the nakhlite martian meteorites abstract transmission electron microscopy and fe k x ray absorption spectroscopy have been used to determine structure and ferric content of the secondary phase mineral assemblages in the nakhlite martian meteorites nwa 998 lafayette nakhla gv y 000593 y 000749 mil 03346 nwa 817 and nwa 5790 the secondary phases are a rapidly cooled metastable assemblage that has preserved mg and ca fractionation related to distance from the fluid source for most of the nakhlites though one nwa 5790 appears not to have experienced a fluid pathway all nine nakhlite samples have also been analysed with scanning electron microscopy electron probe micro analysis bright field high resolution transmission electron microscopy hrtem and selected area electron diffraction by measuring the energy position of the fe k xanes 1 s 3 d pre edge transition centroid we calculate the ferric content of the minerals within the nakhlite meteorites the crystalline phyllosilicates and amorphous silicate of the hydrothermal deposits filling the olivine fractures are found to have variable fe 3 fe values ranging from 0 4 to 0 9 in lafayette the central silicate gel parts of the veins are more ferric than the phyllosilicates around it showing that the fluid became increasingly oxidised the mesostasis of lafayette and nwa 817 also have phyllosilicate which have a higher ferric content than the olivine fracture deposits with fe 3 fe values of up to 1 0 further study via tem analyses reveal the lafayette and nwa 817 olivine phyllosilicates to have 2 1 t o t lattice structure with a the d 001 spacing of 0 96 nm whereas the lafayette mesostasis phyllosilicates have 1 1 t o structure with d 001 spacings of 0 7 nm based on our analyses the phyllosilicate found within the lafayette olivine fractures is trioctahedral ferric saponite ca 0 2 k 0 1 0 3 mg 2 6 fe 2 1 3 fe 3 1 7 mn 0 1 5 7 si 6 7 al iv 0 9 fe 3 0 4 8 0 o 20 oh 4 n h 2 o and that found in the mesostasis fractures is an fe serpentine ca 0 1 mg 0 7 fe 3 1 0 al vi 0 4 2 2 si 2 o 5 oh 4 with a ferric gel of similar composition in lafayette and found as fracture fills throughout the other nakhlites

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

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

the geology of 433 eros the global high resolution imaging of asteroid 433 eros by the near earth asteroid rendezvous near shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small s type asteroid eros displays a variety of surface features and evidence of a substantial regolith large scale facets grooves and ridges indicate the presence of at least one global planar structure directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object as with other small objects impact craters dominate the overall shape as well as the small scale topography of eros depth diameter ratios of craters on eros average 0 13 but the freshest craters approach lunar values of 0 2 ejecta block production from craters is highly variable the majority of large blocks appear to have originated from one 7 6 km crater shoemaker the interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of phobos this lack of mechanical boundaries and the abundant evidence of regolith in nearly every high resolution image suggests a gradation in the porosity and fracturing with depth the density of small craters is deficient at sizes below 200 m relative to predicted slopes of empirical saturation this characteristic which is also found on parts of phobos and lunar highland areas probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith eros displays a variety of regolith features such as debris aprons fine grained ponded deposits talus cones and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith these processes serve to mix materials in the upper loose fragmental portion of the asteroid regolith in the instance of ponded materials and crater wall deposits there is evidence of processes that segregate finer materials into discrete deposits the near observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the near shoemaker spacecraft

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

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