the terrestrial alteration of saharan shergottites dar al gani 476 and 489 a case study of weathering in a hot desert environment abstract rare earth element ree and other selected trace and minor element concentrations were determined in various phases of dar al gani 476 and 489 two basaltic shergottites recently found in the libyan sahara whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites olivine and pyroxenes commonly show light ree enrichments sometimes accompanied by ce anomalies that are attributed to terrestrial alteration sr and ba enrichments are also observed the calcium carbonate that resides in most cracks is essentially devoid of ree but a fine grained amorphous silicate material that fills some veins and pockets has striking light ree enrichments and elevated p sr and ba it is argued that this material likely to be impact melt as well as the notoriously light ree poor olivine and pyroxenes were preferentially affected by a crustal light ree rich contaminant caution is urged when using whole rock or even mineral separate compositional and isotopic data for hot desert meteorites

geochemical diversity of shergottite basalts mixing and fractionation and their relation to mars surface basalts the chemical compositions of shergottite meteorites basaltic rocks from mars provide a broad view of the origins and differentiation of these martian magmas the shergottite basalts are subdivided based on their al contents high al basalts al 5 wt are distinct from low al basalts and olivine phyric basalts both with al 4 5 wt abundance ratios of highly incompatible elements e g th la are comparable in all the shergottites abundances of less incompatible elements e g ti lu hf in olivine phyric and low al basalts correlate well with each other but the element abundance ratios are not constant this suggests mixing between components both depleted and enriched high al shergottites deviate from these trends consistent with silicate mineral fractionation the depleted component is similar to the yamato 980459 magma approximately 67 crystal fractionation of this magma would yield a melt with trace element abundances like que 94201 the enriched component is like the parent magma for nwa 1068 approximately 30 crystal fractionation from it would yield a melt with trace element abundances like the los angeles shergottite this component mixing is consistent with radiogenic isotope and oxygen fugacity data these mixing relations are consistent with the compositions of many of the gusev crater basalts analyzed on mars by the spirit rover although with only a few elements to compare other mars basalts fall off the mixing relations e g wishstone at gusev gale crater rocks their compositions imply that basalt source areas in mars include significant complexities that are not present in the source areas for the shergottite basalts

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

a new martian meteorite from morocco the nakhlite north west africa 817 north west africa nwa 817 is a single stone of 104 g found in the sahara morocco by meteorite hunters in november 2000 the meteorite is an unbrecciated medium grained olivine bearing clinopyroxenite with a cumulate texture it consists of zoned euhedral subcalcic augite wo 42 en 38 22 f 20 36 olivine spanning a wide range of compositions from fa 56 in the core to fa 86 with rare magmatic inclusions and an intercumulus mesostasis made of fe bearing albitic plagioclase si rich glass ti magnetite with unusual skeletal growth morphologies containing ilmenite exsolutions acicular pyroxene olivine and cristobalite trace minerals are sulfide droplets and cl apatite mineral modes in vol are augite 69 olivine 10 mesostasis 20 and fe ti oxides 1 pervasive alteration produced a reddish clay mineral hydrous ferrous silicate in both olivine crystals and the mesostasis the major element composition of nwa 817 is very similar to that of the other nakhlites high feo mgo and cao concentrations reflect the abundance of cumulus augite and olivine key element ratios such as feo mno 37 na al 0 40 k la 449 ga al 3 9 x 10 4 and oxygen isotopic composition delta 17 o 0 37parts per thousand are clear evidence for a martian origin the incompatible trace element pattern as in nakhla displays a strong light rare earth element enrichment relative to chondrite la n yb n 4 89 however when compared to the other nakhlites nwa 817 has specific features 1 a higher modal proportion of mesostasis 2 quench textures of ti magnetite and fe rich clinopyroxene 3 more mg rich olivine core compositions whereas the augite core composition is identical for all nakhlites 4 a stronger fe enrichment toward crystal rims of these cumulus minerals the intercumulus minerals ti magnetite with skeletal growth morphology acicular chains of clinopyroxene and fe3 rich feldspar indicate rapid crystallization in response to a high degree of undercooling at the end of the sample story c 2002 elsevier science b v all rights reserved

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

sayh al uhaymir 094 a new martian meteorite from the oman desert sayhal uhaymir sau 094 is a 223 3 g partially crusted strongly to very strongly shocked melanocratic olivine porphyric rock of the shergottite group showing a microgabbroic texture the rock consists of pyroxene 52 0 58 2 vol dominantly prismatic pigeonite en60 68fs20 27wo7 9 associated with minor augite en46 49fs15 16wo28 31 brown shock oxidized olivine fo65 69 22 1 31 completely isotropic interstitial plagioclase glass maskelynite an50 64or0 3 0 9 8 6 13 0 chromite and titanian magnesian chromite 0 9 1 0 traces of ilmenite ilm80 86 pyrrhotite fe92 100 0 1 0 2 merrillite 0 1 and pockets 4 8 6 7 consisting of green basaltic to basaltic andesitic shock glass that is partially devitrified into a brown to black product along boundaries with the primary minerals the average maximum dimensions of minerals are olivine 1 5 mm pyroxene 0 3 mm and maskelynite 0 3 mm primary melt inclusions in olivine and chromite are common and account for 0 1 0 6 of the rock x ray tomography revealed that the specimen contains 0 4 vol of shock melt associated vesicles up to 3 mm in size which show a preferred orientation fluidization of the maskelynite melting and recrystallization of pyroxene olivine and pyrrhotite indicate shock stage s6 minor terrestrial weathering resulted in calcite veining and minor oxidation of sulfides the meteorite is interpreted as paired with sau 005 008 051 the modal composition is similar to dar al gani 476 489 670 735 876 with the exception that neither mesostasis nor titanomagnetite nor apatite are present and that all phases show little zonation the restricted mineral composition predominance of chromite among the oxides and abundance of olivine indicate affinities to the lherzolitic shergottites

ejection ages from krypton 81 krypton 83 dating and pre atmospheric sizes of martian meteorites cosmic ray exposure cre ages and mars ejection times were calculated from the radionuclide 81 and stable kr isotopes for seven martian meteorites the following 8lkr kr cre ages were obtained los angeles 3 35 0 70 ma queen alexandra range 94201 2 22 0 35 ma shergotty 3 05 0 50 ma zagami 2 98 0 30 ma nakhla 10 8 4 0 8 ma chassigny 10 6 2 0 ma and allan hills 84001 15 4 5 0 ma comparison of these ages with previously obtained cre ages from the stable noble gas nuclei 3he 21ne and 38ar shows excellent agreement this indicates that the method for the production rate calculation for the stable nuclei is reliable in all martian meteorites we observe effects induced by secondary cosmic ray produced epithennal neutrons epithermal neutron fluxes 30 300 ev are calculated based on the reaction 79br n yp gokr we show that the neutron capture effects were induced in free space during mars earth transfer of the meteoroids and that they are not due to a pre exposure on mars before ejection of the meteoritic material neutron fluxes and slowing down densities experienced by the meteoroids are calculated and pre atmospheric sizes are estimated we obtain minimum radii in the range of 22 25 cm and minimum masses of 150 220 kg these results are in good agreement with the mean sizes reported for model calculations using current semiempirical data

crystallization conditions of los angeles a basaltic martian meteorite the texture of los angeles stone 1 is dominated by relatively large 0 5 2 0 mm anhedral to subhedral grains of pyroxene and generally subhedral to euhedral shocked plagioclase feldspar maskelynite minor phases include subhedral titanomagnetite and ilmenite fe rich olivine olivine augite dominated symplectites some of which include a si rich phase and some which do not pyrrhotite phosphate s and an impact shock related alkali and silica rich glass closely associated with anhedral to euhedral silica grains observations and model calculations indicate that the initial crystallization of mg rich pigeonitic pyroxenes at 1150 c probably concomitantly with plagioclase was followed by pigeonitic and augitic compositions between 1100 and 1050 c whereas between 1050 and 920 to 905 c pyroxene of single composition crystallized below 920 to 905 c single composition fe rich clinopyroxene exsolved to augite and pigeonite initial appearance of titanomagnetite probably occurred near 990 c and fmq 1 5 whereas at and below 990 c and fmq 1 5 titanomagnetite and single composition fe rich clinopyroxene may have started to react producing ilmenite and olivine however judging from the most common titanomagnetite compositions we infer that most of this reaction likely occurred between 950 and 900 c at fmq 1 0 0 2 and nearly simultaneously with pyroxene exsolution thus producing assemblages of pigeonite titanomagnetite olivine ilmenite and augite we deem this reaction as the most plausible explanation for the formation of the olivine augite dominated symplectites in los angeles but we cannot preclude possible contributions to the symplectites from the shock related alkali and silica rich glass or shocked plagioclase and the breakdown of fe rich pigeonite compositions to olivine augite silica below 900 c reactions between fe ti oxides and silicate minerals in los angeles and other similar basaltic martian meteorites can control the t fo2 equilibration path during cooling which may better explain the relative differences in fo2 among the basaltic martian meteorites

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

an impact melt origin for lithology a of martian meteorite elephant moraine a79001 mixing models using major and trace elements show that the bulk composition of lithology a xenocryst bearing magnesian basalt of elephant moraine a79001 eeta79001 can be reasonably approximated as a simple mixture of 44 eeta79001 lithology b ferroan basalt and 56 of allan hills a77005 alha7705 light lithology incompatible element poor lherzolite micro instrumental neutron activation analysis inaa data on xenocryst free groundmass samples of lithology a show that about 20 25 of the melt phase could be dissolved lherzolite the bulk and groundmass samples of lithology a have excesses in au which indicates either meteoritic contamination or addition by some unknown martian geochemical process previous workers have suggested that lithology a was formed by either assimilation of cumulates like alha77005 by a basalt like lithology b or by mixing of basaltic and lherzolitic magmas the former scenario is energetically improbable and unlikely to explain the normal fe mg zonation in lithology a groundmass pyroxenes whereas the latter scenario is unlikely to satisfy the constraints of the mixing model indicating the ultramafic component is poor in incompatible elements we suggest rather that eeta79001 lithology a is an impact melt composed dominantly of basalt like lithology b and lherzolitic cumulates like the trace element poor fraction of alha77005 or y 793605 this model can satisfy the energetic petrologic and geochemical constraints imposed by the samples if eeta79001 lithology a is an impact melt this would have considerable consequences for current models of martian petrologic evolution it would call into question the generally accepted age of magmatism of martian basalts and preclude the use of lithology a groundmass as a primary martian basalt composition in experimental studies regardless the latter is required because lithology a groundmass is a hybrid composition

labile trace elements in basaltic achondrites can they distinguish between meteorites from the moon mars and v type asteroids we report data for 14 mainly labile trace elements ag au bi cd cs ga in rb sb se te tl u and zn in eight whole rock lunar meteorites asuka a 881757 dar al gani dag 262 elephant moraine eet 87521 queen alexandra range que 93069 que 94269 que 94281 yamato y 793169 and y 981031 and martian meteorite dag 476 and incorporate these into a comparative study of basaltic meteorites from the moon mars and v type asteroids multivariate cluster analysis of data for these elements in 14 lunar 13 martian and 34 howardite eucrite and diogenite hed meteorites demonstrate that materials from these three parents are distinguishable using these markers of late low temperature episodes this distinguishability is essentially as complete as that based on markers of high temperature igneous processes concentrations of these elements in 14 lunar meteorites are essentially lognormally distributed and generally more homogeneous than in martian and hed meteorites mean siderophile and labile element concentrations in the 14 lunar meteorites indicate the presence of a ci equivalent micrometeorite admixture of 2 6 when only feldspathic samples are considered our data show a slightly higher value of 3 4 consistent with an increasing micrometeorite content in regolith samples of higher maturity concentrations of labile elements in the 8 feldspathic samples hint at the presence of a fractionated highly labile element component possibly volcanic in origin at a level comparable to the micrometeorite component apparently the process es that contributed to establishing lunar meteorite siderophile and labile trace element contents occurred in a system open to highly labile element transport

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

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

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

defining the mechanisms that disturb the sm nd isotopic systematics of the martian meteorites examples from dar al gani 476 and allan hills 77005 microbeam studies of martian meteorites dar al gani dag 476 and allan hills alh 77005 have been conducted to identify potential causes of disequilibrium exhibited in their sm nd isotopic systematics olivine and maskelynite mineral fractions on the dag 476 isochron are displaced relative to their positions as dictated by measured mineral compositions the olivine mineral fractions from alh 77005 not only have a relatively low sm nd ratio but appear to contain an unradiogenic component that shifts the olivine mineral fraction off the isochron defined by the pyroxene and maskelynite mineral fractions trace components such as melt inclusions impact melt high si mesostasis and altered olivine were analyzed using scanning electron microscopy quantitative electron microscopy and secondary ion mass spectrometry to determine their potential for disturbing the isotopic systematics of the mineral fractions assuming that the mineral fractions were not completely pure mixing models indicate that the presence of melt inclusions in the dag 476 olivine mineral fraction lowered its sm nd ratio the maskelynite mineral fraction contains a related but more evolved mesostasis component that raised the sm nd ratio of the fraction the position of two olivine mineral fractions below the alh 77005 isochron is interpreted to reflect small additions of impact melt with a light rare earth element enriched pattern and a non indigenous unradiogenic nd component furthermore the presence of rare earth elements in olivine and maskelynite from both igneous and non igneous components such as melt inclusions mesostasis and impact melt is observed on a fine 30 m scale despite the addition of this material the sm nd ages are not affected this study demonstrates that detailed mineral separation procedures as employed by modern geochronology laboratories permit reliable ages to be derived from shocked and altered samples

petrogenesis of the nwa 7320 enriched martian gabbroic shergottite insight into the martian crust northwest africa nwa 7320 is classified as a gabbroic shergottite the second to be recognized in the martian meteorite record this interpretation is based on 1 the calculated bulk rock rare earth element ree concentrations which show the highest eu positive anomaly eu eu 2 2 of all the shergottites reflecting accumulation of plagioclase and 2 the highest modal abundance of maskelynitized plagioclase 50 mod compared to the other shergottites the three phase symplectite fayalite hedenbergite silica is present in nwa 7320 and formed as a result of the breakdown of metastable pyroxene pyroxenoid margins on coarse grained pyroxenes the latter is indicative of metastable overgrowths on pyroxene cores during the final stages of crystallization followed by relatively slow cooling at subsolidus conditions the nwa 7320 parental melt originated from an incompatible trace element enriched and oxidized fmq source as indicated by sm nd lu hf isotope systematics ilmenite titanomagnetite pairs the partition coefficient of cr in pyroxene and merrillite ree compositions the ti al ratio of pyroxene in nwa 7320 indicates an initial crystallization depth of 30 70 km p 4 9 kbar however the largest impact craters on mars are 8 km in depth indicating that nwa 7320 could not have been ejected from this depth and must have had a polybaric formation history we suggest that the pyroxene phenocrysts began to crystallize at depth but were entrained as antecrysts in a basaltic magma ascending to shallower levels in the martian crust in addition plagioclase likely crystallized during magma ascent followed by subsequent accumulation in a shallow magma intrusion or sill resulting in the gabbroic texture furthermore the similarity in the radiogenic isotope composition of nwa 7320 to that of los angeles and nwa 856 suggest that these meteorites were linked to common volcanic system on mars

new findings for the equilibrated enstatite chondrite grein 002 we report new petrographic and chemical data for the equilibrated el chondrite grein 002 including the occurrence of osbornite metallic copper abundant taenite and abundant diopside as inferred from low si concentrations in kamacite the presence of ferroan alabandite textural deformation chemical equilibration of mafic silicates and a subsolar noble gas component we concur with grein 002s previous classification as an el4 5 chondrite furthermore the existence of pockets consisting of relatively coarse euhedral enstatite crystals protruding large patches of fe ni alloys suggests to us that this el4 5 chondrite has been locally melted we suspect impact induced shock to have triggered the formation of the melt pockets mineralogical evidence indicates that the localized melting of metal and adjacent enstatite must have happened relatively late in the meteorites history the deformation of chondrules equilibration of mafic silicates and generation of normal zoning in fe zn sulfides took place during thermal alteration before the melting event following parent body metamorphism daubreelite was exsolved from troilite in response to a period of slow cooling at subsolidus temperatures exsolution of schreibersite from the coarse metal patches probably occurred during a similar period of slow cooling subsequent to the event that induced the formation of the melt pockets overall shock features other than localized melting correspond to stage s2 and were likely established by the final impact that excavated the grein 002 meteoroid

petrology and trace element geochemistry of tissint the newest shergottite fall the fall and recovery of the tissint meteorite in 2011 created a rare opportunity to examine a martian sample with a known short residence time on earth tissint is an olivine phyric shergottite that accumulated olivine antecrysts within a single magmatic system coarse olivine grains with nearly homogeneous cores of mg 80 suggest slow re equilibration many macroscopic features of this sample resemble those of lar 06319 including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions unlike lar 06319 however no magmatic hydrous phases were found in the analyzed samples of tissint minor and trace element compositions indicate that the meteorite is the product of closed system crystallization from a parent melt derived from a depleted source with no obvious addition of a lree rich crustal component prior to or during crystallization the whole rock ree pattern is similar to that of intermediate olivine phyric shergottite eeta 79001 lithology a and could also be approximated by a more olivine rich version of depleted basaltic shergottite que 94201 magmatic oxygen fugacities are at the low end of the shergottite range with log fo2 of qfm 3 5 to 4 0 estimated based on early crystallized minerals and qfm 2 4 estimated based on the eu in pyroxene oxybarometer these values are similarly comparable to other depleted shergottites including sau 005 and que 94201 tissint occupies a previously unsampled niche in shergottite chemistry containing olivines with mg 80 resembling the enriched olivine phyric shergottite lar 06319 in its crystallization path and comparable to intermediate olivine phyric shergottite eeta 79001a depleted olivine phyric shergottite dag 476 and depleted basaltic shergottite que 94201 in its trace element abundances and oxygen fugacity the apparent absence of evidence for terrestrial alteration in tissint particularly in trace element abundances in the whole rock and individual minerals confirms that exposure to the arid desert environment results in only minimal weathering of samples provided the exposure times are brief

crustal heat production and the thermal evolution of mars the chemical composition of soils and rocks from the pathfinder site and phobos 2 orbital gamma ray spectroscopy indicate that the martian crust has a bulk composition equivalent to large ion lithophile lil and heat producing element k th u enriched basalt with a potassium content of about 0 5 a variety of radiogenic isotope data also suggest that separation of lil enriched crust and depleted mantle reservoirs took place very early in martian history 4 0 ga accordingly if the enriched martian crust is 30 km thick it is likely that a large fraction up to at least 50 of the heat producing elements in mars was transferred into the crust very early in the planet s history this would greatly diminish the possibility of early widespread melting of the martian mantle

petrology chemistry and isotopic compositions of the lunar highland regolith breccia dar al gani 262 lunar meteorite dar al gani 262 dg 262 found in the libyan part of the sahara is a mature anorthositic regolith breccia with highland affinities the origin from the moon is undoubtedly indicated by its bulk chemical composition radionuclide concentrations noble gas n and o isotopic compositions and petrographic features dar al gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to queen alexandra range que 93069 about 52 vol of the studied thin sections of dar al gani 262 consist of fine grained 100 m constituents and 48 vol is mineral and lithic clasts and impact melt veins the most abundant clast types are feldspathic fine grained to microporphyritic crystalline melt breccias 50 2 vol includes recrystallized melt breccias whereas mafic crystalline melt breccias are extremely rare 1 4 vol granulitic lithologies are 12 8 vol intragranularly recrystallized anorthosites and cataclastic anorthosites are 8 8 and 8 2 vol respectively and devitrified glasses are 2 7 vol impact melt veins 5 5 vol of the whole thin sections cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 gpa because the bulk rock never experienced a higher peak shock pressure mafic crystalline melt breccias are very rare in dar al gani 262 and are similar in abundance to those in que 93069 the extremely low abundance of mafic components and the bulk composition may constrain possible areas of the moon from which the breccia was derived the source area of dar al gani 262 must be a highland terrain lacking significant mafic impact melts or mare components on the basis of radionuclide activities an irradiation position of dg 262 on the moon at a depth of 55 85 g cm3and a maximum transit time to earth 0 15 ma is suggested dar al gani 262 contains high concentrations of solar wind implanted noble gases the isotopic abundance ratio 40ar 36ar 3 is characteristic of lunar soils the terrestrial weathering of dg 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of ca ba cs br and as there is also a large amount of terrestrial c and some n in the sample which was released at low temperatures during stepped heating high concentrations of ni co and ir indicate a significant meteoritic component in the lunar surface regolith from which dg 262 was derived

surface mineralogy of martian low albedo regions from mgs tes data implications for upper crustal evolution and surface alteration 1 mars global surveyor thermal emission spectrometer mgs tes data are used to derive the modal mineralogy of spectrally distinct martian low albedo regions and to identify spatial trends in mineralogic assemblages results from this work are consistent with the major results of previous spectroscopic studies 1 plagioclase and clinopyroxene are the dominant minerals of most southern highlands regions 2 the northern plains exhibit the lowest pyroxene abundance within martian low albedo regions and 3 the highest concentrations of high silica phase s are found in the northern plains solis planum and a few southern high latitude regions low albedo regions may be classified into four units on the basis of relative abundances of plagioclase pyroxene and high silica phase s unit distributions between 45 latitude exhibit moderate correlation with distinct provinces e g syrtis major aonium sinus defined by large scale morphology elevation and to some extent surface age suggesting that the spectral and compositional differences between these units are more strongly controlled by original bedrock mineralogy than by surface atmosphere interactions and alteration syrtis major exhibits a difference in mineralogy from the surrounding highlands suggesting a differing degree of fractional crystallization assimilation or source region composition areas with thick crust near the tharsis plateau exhibit lower abundances of olivine and greater plagioclase pyroxene ratios than surrounding highland terrains suggesting that magmas in this region may have undergone increased olivine fractionation regions where surface alteration is more likely to be the primary control on observed spectral signatures are the high latitude areas 45 where globally surfaces dominated by high silica phase s are most commonly found

crystallization history of enriched shergottites from fe and mg isotope fractionation in olivine megacrysts abstract martian meteorites are the only samples available from the surface of mars among them olivine phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores fo 70 85 and rims richer in fe fo 45 60 the northwest africa 1068 meteorite is one of the most primitive enriched shergottites high initial 87 sr 86 sr and low initial e 143 nd it contains olivine crystals as magnesian as fo 77 and is a major source of information to constrain the composition of the parental melt the composition and depth of the mantle source and the cooling and crystallization history of one of the younger magmatic events on mars 180 ma in this study fe mg isotope profiles analyzed in situ by femtosecond laser ablation mc icp ms are combined with compositional profiles of major and trace elements in olivine megacrysts the cores of olivine megacrysts are enriched in light fe isotopes 56 fe irmm 14 0 6 to 0 9 and heavy mg isotopes 26 mg dsm 3 0 0 2 relative to megacryst rims and to the bulk martian isotopic composition 56 fe 0 0 05 26 mg 0 27 0 04 the flat forsterite profiles of megacryst cores associated with anti correlated fractionation of fe mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature we present a 1 d model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles the simulation results suggest that the cooling rate during megacryst core crystallization was slow 43 21 c year and consistent with pooling in a deep crustal magma chamber the megacryst rims then crystallized 1 2 orders of magnitude faster during magma transport toward the shallower site of final emplacement megacryst cores had a forsterite content 3 2 1 5 mol higher than their current composition and some were in equilibrium with the whole rock composition of nwa 1068 fo 80 1 5 nwa 1068 composition is thus close to a primary melt i e in equilibrium with the mantle from which other enriched shergottites derived

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

martian meteorite dhofar 019 a new shergottite dhofar 019 is a new martian meteorite found in the desert of oman in texture mineralogy and major and trace element chemistry this meteorite is classified as a basaltic shergottite olivine megacrysts are set within a groundmass composed of finer grained olivine pyroxene pigeonite and augite and maskelynite minor phases are chromite ulvospinel ilmenite silica k rich feldspar merrillite chlorapatite and pyrrhotite secondary phases of terrestrial origin include calcite gypsum celestite fe hydroxides and smectite dhofar 019 is most similar to the elephant moraine eeta 79001 lithology a and dar al gani dag 476 489 shergottites the main features that distinguish dhofar 019 from other shergottites are lack of orthopyroxene lower ni contents of olivine the heaviest oxygen isotopic bulk composition and larger compositional ranges for olivine maskelynite and spinel as well as a wide range for pyroxenes the large compositional ranges of the minerals are indicative of relatively rapid crystallization modeling of olivine chemical zonations yield minimum cooling rates of 0 5 0 8 c h spinel chemistry suggests that crystallization took place under one of the most reduced conditions for martian meteorites at an f o2 3 log units below the quartz fayalite magnetite qfm buffer the olivine megacrysts are heterogeneously distributed in the rock crystal size distribution analysis suggests that they constitute a population formed under steady state conditions of nucleation and growth although a few grains may be cumulates the parent melt is thought to have been derived from partial melting of a light rare earth element and platinum group element depleted mantle source shergottites eeta79001 lithology a dag 476 489 and dhofar 019 although of different ages comprise a particular type of martian rocks such rocks could have formed from chemically similar source s and parent melt s with their bulk compositions affected by olivine accumulation

composition of the first bulk melt sample from a volcanic region of mars queen alexandra range 94201 antarctic meteorite queen alexandra range que 94201 is a 12 g basaltic achondrite dominated by plagioclase now maskelynite and zoned low and high ca pyroxene petrologic geochemical and isotopic analyses indicate that it is related to previously described basaltic and lherzolitic shergottites which are a group of igneous meteorites that are believed to be from mars unlike previous shergottites however que 94201 represents a bulk melt rather than a cumulate fraction meaning it can be used to infer magmatic source regions and the compositions of other melts on mars this melt has much more fe and p than basaltic melts produced on earth and formed at a much lower oxygen fugacity this has altered the crystallization sequence of the melt removing olivine from the liquidus to produce a plagioclase and 2 pyroxene assemblage if the high phosphorus and low oxygen fugacity conditions represented by que 94201 are common in magmatic regions of mars then olivine may be rare in martian basalts no solar cosmic ray effects were seen in the concentrations of 10be 26al and 36cl with depth in the meteorite implying at least 3 cm of ablation during entry to earth significant excesses of neutron capture noble gas isotopes 80 82kr and 128 131xe suggest that the que 94201 sample came from a depth 22 cm in a meteoroid of at least that radius the meteorite also has very low 21ne 22ne which would often be interpreted to mean little ablation contradicting above evidence but in this case appears to reflect a very low abundance of mg the principal target element for ne in the meteorite consistent with our bulk chemical analyses the meteorite has a terrestrial 36cl age of 0 29 0 05 myr and a 10be exposure age of 2 6 0 5 myr in a 4 geometry implying an ejection age of 2 9 0 5 myr

petrology and geochemistry of olivine phyric shergottites lar 12095 and lar 12240 implications for their petrogenetic history on mars larkman nunatak lar 12095 and lar 12240 are recent olivine phyric shergottite lnds we report the results of petrographic and chemical analyses of these two samples to understand their petrogenesis on mars based on our analyses we suggest that these samples are likely paired and are most similar to other depleted olivine phyric shergottites particularly dar al gani dag 476 and sayh al uhaymir sau 005 and samples paired with those the olivine megacryst cores in lar 12095 and lar 12240 are not in equilibrium with the groundmass olivines we infer that these megacrysts are phenocrysts and their major element compositions have been homogenized by diffusion the cores of the olivine megacrysts have mg 70 whereas megacryst rims and groundmass olivines typically have mg 58 60 the rare earth element ree microdistributions in the various phases olivine low and high ca pyroxene maskelynite and merrillite in both samples are similar and support the likelihood that these two shergottites are indeed paired the calculated parent melt i e in equilibrium with the low ca pyroxene which is one of the earliest formed ree bearing minerals has an ree pattern parallel to that of melt in equilibrium with merrillite i e one of the last formed minerals this suggests that the lar 12095 12240 paired shergottites represent the product of closed system fractional crystallization following magma emplacement and crystal accumulation utilizing the europium oxybarometer we estimate that the magmatic oxygen fugacity early in the crystallization sequence was iw finally petrographic evidence indicates that lar 12095 12240 experienced extensive shock prior to being ejected from mars

the ksar ghilane 002 shergottite the 100th registered martian meteorite fragment we report on the discovery of a new shergottite from tunisia ksar ghilane kg 002 this single stone weighing 538 g is a coarse grained basaltic shergottite mainly composed of maskelynitized plagioclase approximately 52 vol and pyroxene approximately 37 vol it also contains fe rich olivine approximately 4 5 vol large ca phosphates including both merrillites and cl apatites approximately 3 4 vol minor amounts of silica or sio 2 normative k rich glass pyrrhotite ti magnetite ilmenite and accessory baddeleyite the largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm pyroxenes fs 26 96 en 5 50 wo 2 41 they typically range from cores of about fs 29 en 41 wo 30 to rims of about fs 68 en 14 wo 17 maskelynite is ab 41 49 an 39 58 or 1 7 in composition but some can be as anorthitic as an 93 olivine fa 91 96 occurs mainly within symplectitic intergrowths in paragenesis with ilmenite or at neighboring areas of symplectites kg 002 is heavily shocked s5 as indicated by mosaic extinction of pyroxenes maskelynitized plagioclase the occurrence of localized shock melt glass pockets and low radiogenic he concentration oxygen isotopes confirm that it is a normal member of the snc suite kg 002 is slightly depleted in lree and shows a positive eu anomaly providing evidence for complex magma genesis and mantle processes on mars noble gases with a composition thought to be characteristic for martian interior is a dominant component measurements of 10 be 26 al and 53 mn and comparison with monte carlo calculations of production rates indicate that kg 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35 65 cm radius kg 002 strongly resembles los angeles and nwa 2800 basaltic shergottites in element composition petrography and mineral chemistry suggesting a possible launch pairing the similar cre ages of kg 002 and los angeles may suggest an ejection event at approximately 3 0 ma

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

the 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

ancient impact and aqueous processes at endeavour crater mars the rover opportunity has investigated the rim of endeavour crater a large ancient impact crater on mars basaltic breccias produced by the impact form the rim deposits with stratigraphy similar to that observed at similar sized craters on earth highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits gypsum rich veins cut sedimentary rocks adjacent to the crater rim the gypsum was precipitated from low temperature aqueous fluids flowing upward from the ancient materials of the rim leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate rich sandstones of the meridiani region

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

noble gases in mineral separates from three shergottites shergotty zagami and eeta79001 this study provides a complete data set of all five noble gases for bulk samples and mineral separates from three martian shergottites shergotty bulk pyroxene maskelynite zagami bulk pyroxene maskelynite and elephant moraine eet a79001 lithology a bulk pyroxene we also give a compilation of all noble gas and nitrogen studies performed on these meteorites our mean values for cosmic ray exposure ages from 3he 21ne and 38ar are 2 48 myr for shergotty 2 73 myr for zagami and 0 65 myr for eeta79001 lith a serious loss of radiogenic 4he due to shock is observed cosmogenic neon results for bulk samples from 13 martian meteorites new data and literature data are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic ray effects while a contribution of this low energy irradiation is strongly indicated for all of the shergottites spallation ne in chassigny allan hills alh 84001 and the nakhlites is fully explained by galactic cosmic ray spallation implanted martian atmospheric gases are present in all mineral separates and the thermal release indicates a near surface siting we derive an estimate for the 40ar 36ar ratio of the martian interior component by subtracting from measured ar in the k poor pyroxenes the small radiogenic component as well as the implanted atmospheric component as indicated from 129xe excesses unless compromised by the presence of additional components a high ratio of 2000 is indicated for martian interior argon similar to that in the martian atmosphere since much lower ratios have been inferred for chassigny and alh 84001 the result may indicate spatial and or temporal variations of 40ar 36ar in the martian mantle

noble gases and nitrogen in martian meteorites dar al gani 476 sayh al uhaymir 005 and lewis cliff 88516 efa and extra neon meteorite finds from the terrestrial hot deserts have become a major contributor to the inventory of martian meteorites in order to understand their nitrogen and noble gas components we have carried out stepped heating experiments on samples from two martian meteorites collected from hot deserts we measured interior and surface bulk samples glassy and non glassy portions of dar al gani 476 and sayh al uhaymir 005 we have also analyzed noble gases released from the antarctic shergottite lewis cliff 88516 by crushing and stepped heating for the hot desert meteorites significant terrestrial ar kr xe contamination is observed with an elementally fractionated air efa component dominating the low temperature releases the extremely low ar kr xe ratios of efa may be the result of multiple episodes of trapping loss during terrestrial alteration involving aqueous fluids we suggest fractionation processes similar to those in hot deserts to have acted on mars with acidic weathering on the latter possibly even more effective in producing elementally fractionated components addition from fission xenon is apparent in dag 476 and sau 005 the ar kr xe patterns for lew 88516 show trends as typically observed in shergottites including evidence for a crush released component similar to that observed in eeta 79001 a trapped ne component most prominent in the surface sample of dag 476 may represent air contamination it is accompanied by little trapped ar 20ne 36ar 50 and literature data suggest its presence also in some antarctic finds data for lew 88516 and literature data on the other hand suggest the presence of two trapped ne components of martian origin characterized by different 20ne 22ne possibly related to the atmosphere and the interior caution is recommended in interpreting nitrogen and noble gas isotopic signatures of martian meteorites from hot deserts in terms of extraterrestrial sources and processes nevertheless our results provide hope that vice versa via noble gases and nitrogen in meteorites and other relevant samples from terrestrial deserts martian secondary processes can be studied

remote laser induced breakdown spectroscopy analyses of dar al gani 476 and zagami martian meteorites 1 laser induced breakdown spectroscopy libs was recently selected to provide active remote sensing compositional information on the mars science laboratory msl rover the ability of libs to remotely determine differences between basaltic rock types on mars is investigated by analyzing two martian basaltic shergottite meteorites whose compositions differ slightly and which also differ slightly in texture using 14 analysis spots of 400 m diameter on dar al gani dag 476 and 9 analysis spots on zagami the libs technique at a 5 4 m standoff distance clearly distinguished the olivine phyric dag 476 from the basaltic zagami shergottite on the basis of mgo and cao mean elemental abundances agreed with literature values for these meteorites to within 12 for most of the major elements the ability of libs to remotely distinguish between basaltic and andesitic compositions in a martian environment was also investigated by analyzing a known andesite standard and comparing its spectra to the martian basaltic shergottite spectra yielding agreement with the literature andesite composition within 9 the data presented here demonstrate the ability of libs to provide reasonable estimates of whole rock composition as well as determine relatively subtle differences in rock types from a distance

experimental petrology crystallization history and parental magma characteristics of olivine phyric shergottite nwa 1068 implications for the petrogenesis of enriched olivine phyric shergottites abstract northwest africa nwa 1068 is one of the few olivine phyric shergottites e g nwa 1068 larkman nunatak lar 06319 and roberts massif rbt 04262 that is not depleted in light rare earth elements lree its ree pattern is similar to that of the basaltic shergottite shergotty suggesting a possible connection between the olivine phyric and the basaltic shergottites to test this possible link we have investigated the high pressure near liquidus phase equilibria for the nwa 1068 meteorite bulk composition our results show that the nwa 1068 bulk composition does not represent an unmodified mantle derived melt the olivine and pyroxene in our near liquidus experiments are more magnesian than in the rock itself which suggests that nwa 1068 contains cumulate minerals extra olivine we have then used these experimental results combined with the pyroxene compositions in nwa 1068 to constrain the possible high pressure crystallization history of the parental magma these results suggest that nwa 1068 had a complex polybaric history finally we have calculated a model parental magma composition for the nwa 1068 meteorite the calculated parental magma is an evolved basaltic composition which is too ferroan to be a primitive melt directly derived from the mantle we suggest that it ponded and crystallized at approximately the base of the crust this provided an opportunity for the magma to become contaminated by an enriched crustal component prior to crystallization the results and modeling from these experiments are applicable not only to the nwa 1068 meteorite but also to lar 06319 and possibly any other enriched olivine phyric shergottite

marine geotechnical engineering in canada marine geotechnical engineering in canada is over one hundred years old having started with overwater drilling and testing for bridges and nearshore structures its growth has been sporadic with not much attention being directed to the geotechnical properties of marine soils until the late 1970 s when design of artificial islands made up of large caissons started to develop for about the last 15 years marine geotechnical engineering has been driven by the oil and gas industry most of the action has been in the beaufort sea where complex site conditions have necessitated detailed geotechnical field drilling sampling programs and in situ testing very little geotechnical engineering research work or site invesigation has been carried out off the east coast except for the hibernia site on the grand banks in the coming years we can expect to see dramatic changes in site investigation methods the use of robotics and expert systems coupled with innovative geophysical techniques could dramatically change our methods of site charcterization and measurement of geotechnical properties

thermal modeling of shock melts in martian meteorites implications for preserving martian atmospheric signatures and crystallization of high pressure minerals from shock melts the distribution of shock melts in four shergottites having both vein and pocket geometry has been defined and the conductive cooling time over the range 2500 c to 900 c calculated isolated 1 mm2 pockets cool in 1 17 s and cooling times increase with pocket area an isolated vein 1 7 mm in northwest africa nwa 4797 cools to 900 c in 4 5 s interference between thermal haloes of closely spaced shock melts decreases the thermal gradient extending cooling times by a factor of 1 4 to 100 this is long enough to allow differential diffusion of ar and xe from the melt small pockets 1 mm2 lose 2 2 ar and 5 2 xe during cooling resulting in a small change in the ar xe ratio of the dissolved gas over that originally trapped with longer cooling times there is significant fractionation of xe from ar and the ar xe ratio increases rapidly the largest pockets show less variation of ar xe and likely preserve the original trapped gas composition considering all of the model calculations even the smallest isolated pockets have cooling times greater than the duration of the pressure pulse i e 0 01 s the crystallization products of these shock melts will be unrelated to the peak shock pressure experienced by the meteorite

exposure history of shergottites abstract the cosmogenic nuclides 36 cl t 1 2 3 0 10 5 years 26 al 7 05 10 5 years 10 be 1 6 10 6 years and 53 mn 3 7 10 6 years were measured in three shergottites alha 77005 eeta 79001 and shergotty by accelerator mass spectrometry and neutron activation the cosmogenic nuclide data constrain the history and origin of shergottites alha 77005 was ejected from its parent body about 2 7 my ago and was exposed to cosmic rays as a body of 5 6 cm radius solar cosmic ray produced 26 a1 and 53 mn were first clearly observed in this meteorite the exposure age of eeta 79001 was 0 6 my and the preatmospheric radius was about 15 cm the exposure age of shergotty was calculated to be 2 2 my and the preatmospheric size was about 10 15 cm in radius the terrestrial age of alha 77005 was 0 2 my and that of eeta 79001 was less than 0 06 my all cosmogenic nuclide data indicate that the three shergottites were never exposed to cosmic rays in their parent bodies whether that parent body was mars or an asteroid all shergottites were ejected from greater than a 3 m depth in their parent bodies the ejection of eeta 79001 was a different event from that of the other shergottites

martian meteorite tissint records unique petrogenesis among the depleted shergottites tissint a new unaltered piece of martian volcanic materials is the most silica poor and mg fe rich igneous rock among the depleted olivine phyric shergottites fe mg zoning of olivine suggests equilibrium growth 0 1 c h 1 in the range of fo80 56 and olivine overgrowth fo55 18 through a process of rapid disequilibrium 1 0 5 0 c h 1 the spatially extended up to 600 m flat top fe mg profiles of olivine indicates that the early stage cooling rate of tissint was slower than the other shergottites the chemically metastable outer rim of olivine fo55 consists of oscillatory phosphorus zoning at the impact induced melt domains and grew rapidly compared to the early to intermediate stage crystallization of the tissint bulk high ca pyroxene to low ca pyroxene and high ca pyroxene to plagioclase ratios of tissint are more comparable to the enriched basaltic and enriched olivine phyric shergottites dominance of augite over plagioclase induced augite to control the ca buffer in the residual melt suppressing the plagioclase crystallization which also caused a profound effect on the al content in the late crystallized pyroxenes mineral chemical stability phase assemblage saturation and pressure temperature path of evolution indicates that the parent magma entered the solidus and left the liquidus field at a depth of 40 80 km in the upper mantle petrogenesis of tissint appears to be similar to lar 06319 an enriched olivine phyric shergottite during the early to intermediate stage of crystallization a severe shock induced deformation resulted in remelting 10 15 vol recrystallization most fe rich phases and exhumation of tissint in a time scale of 1 8 yr tissint possesses some distinct characteristics e g impact induced melting and deformation forming phosphorus rich recrystallization rims of olivine and shock induced melt domains without relative enrichment of lrees compared to the bulk and shared characteristics e g modal composition and magmatic evolution with the enriched basaltic shergottites evidently reflecting unique mantle source in comparison to the clan of the depleted members

a reappraisal of the martian 36ar 38ar ratio the currently used value of 4 1 0 2 for the 36 ar 38 ar isotopic ratio in the martian atmosphere is reappraised and a significantly lower ratio is suggested previous analyses of noble gases in impact glass from some martian meteorites demonstrate that large quantities of martian atmospheric gases were shock emplaced into these samples however several observations indicate that this trapped martian gas is composed of two components one atmospheric and one probably from the martian mantle these observations include large variations in 36 ar 38 ar during stepwise gas release variations in the ar kr xe elemental ratios among martian meteorites and variations in the cosmogenic corrected trapped 36 ar 38 ar ratios over 3 5 4 3 among shock glass samples uncertainties in applied corrections for cosmogenic ar cannot explain these variations by assuming a range of reasonable values for martian atmospheric and mantle 40 ar 36 ar the observed 40 ar 36 ar ratios in shock glass are used to correct for the mantle component and to derive a more precise ratio for the atmospheric component using this procedure one obtains an upper limit for martian atmospheric 36 ar 38 ar of 3 9 and a probable but poorly defined range for martian atmospheric 36 ar 38 ar of 3 0 3 6 these lower ratios imply that the degree of mass fractionation during ar loss from mars upper atmosphere is considerably larger than that previously calculated

10be 26al 53mn and light noble gases in the antarctic shergottite eeta 79001 a abstract the radionuclides 10 be 26 al and 53 mn as well as the noble gases he ne and ar were measured on aliquots of a sample of lithology a from the shergottite eeta 79001 the radionuclide data yield and exposure age of 0 78 0 14 ma and a terrestrial residence time of 0 32 0 17 ma the exposure ages derived from 3 he 21 ne and 38 ar all range between 0 4 and 0 6 ma these data rule out a common ejection of all known shergottites from their parent body as small objects in a single event about 2 5 ma ago

the basaltic shergottite northwest africa 856 petrology and chemistry we report on the discovery of a new shergottite from south morocco this single stone weighing 320 g is referenced as northwest africa nwa 856 with djel ibone as a synonymous name it is a fresh fine grained basaltic rock consisting mainly of two pyroxenes total similar to68 vol 45 pigeonite en 61 16 wo 9 22 fs 26 68 23 augite en 46 26 wo 34 29 fs 21 43 and plagioclase converted to maskelynite similar to23 vol ab 43 57 or 1 5 an 54 36 accessory minerals include merrillite cl apatite pyrrhotite ilmenite ulvospinel silica stishovite and glass amorphous k feldspar and baddeleyite amorphous mixtures of maskelynite and silica occur most commonly as median layers inside maskelynite laths in addition melt pockets similar to2 vol were recognized with relics of maskelynite pyroxene and both dense silica glass and stishovite occurring as both grains and submicrometer needles the compositions of the melt pockets are consistent with mixtures of maskelynite and pyroxenes with an average of similar to50 vol maskelynite the meteorite is highly fractured at all scales

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

no martian soil component in shergottite meteorites we report on the major and trace element geochemistry of the impact melts contained in some shergottite meteorites it has been previously proposed that some of these impact melts formed from a mixture of the host rock and a martian soil component e g rao et al 1999 or from partially weathered portions of the host rock chennaoui aoudjehane et al 2012 our results contradict both of these theories trace element abundances of a glass pod from the eeta 79001a meteorite are identical to those of the host lithology and indicate that no additional component is required in this case the impact melts in tissint share the same trace element features as the host rock and no secondary phases produced by martian secondary processes are involved the light rare earth enrichments displayed by two small samples of tissint chennaoui aoudjehane et al 2012 are possibly the result of some contamination of small stones on desert soil before the recovery of the meteorites

glaciomarine model for upper precambrian diamictites of the port askaig formation scotland descriptive techniques lithofacies codes and vertical profile analysis emphasizing lithofacies contacts and geometry allow objective characterization and comparison of diamict ite sequences irrespective of geologic age upper precambrian diamictites 650 600 m y of the middle dalradian port askaig formation in scotland are traditionally interpreted as products of repeated ice sheet advances over an emergent shallow marine shelf and deposition by in situ basal melt out the dalradian sequences are however fundamentally different from modern and pleistocene diamicts deposited by either lodgment or basal melt out and fail to show evidence of tractional processes associated with basal ice movement scottish diamictite sequences are similar to assemblages of massive and stratified diamict lithofacies of late pleistocene age deposited subaqueously below floating ice and recently described from the lake ontario basin of north america a glaciomarine depositional model may have implications for the origin and paleogeographical setting of other upper precambrian diamictites of similar age and stratigraphic context in east greenland spitsbergen and scandinavia

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

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

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

the age of the martian meteorite northwest africa 1195 and the differentiation history of the shergottites samarium neodymium isotopic analyses of unleached and acid leached mineral fractions from the recently identified olivine bearing shergottite northwest africa 1195 yield a crystallization age of 347 13 ma and an end143 value of 40 1 0 9 maskelynite fractions do not lie on the sm nd isochron and appear to contain a martian surface component with low 147sm 144nd and 143nd 144nd ratios that was added during shock the rb sr system is disturbed and does not yield an isochron terrestrial sr appears to have affected all of the mineral fractions although a maximum initial 87sr 86sr ratio of 0 7016 is estimated by passing a 347 ma reference line through the maskelynite fraction that is least affected by contamination the high initial end143 value and the low initial 87sr 86sr ratio combined with the geologically young crystallization age indicate that northwest africa 1195 is derived from a source region characterized by a long term incompatible element depletion the age and initial sr and nd isotopic compositions of northwest africa 1195 are very similar to those of queen alexandra range 94201 indicating these samples were derived from source regions with similar sr nd isotopic systematics these similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano the meteorites yamato 980459 dar al gani 476 sayh al uhaymir 005 008 and dhofar 019 also have relatively old ages between 474 and 575 ma and trace element and or isotopic systematics that are indicative of derivation from incompatible element depleted sources this suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible element depleted sources closed system fractional crystallization of this suite of meteorites is modeled with the melts algorithm using the bulk composition of yamato 980459 as a parent these models reproduce many of the major element and mineralogical variations observed in the suite in addition the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by melts other shergottites that demonstrate enrichments in incompatible elements and have evolved sr and nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group most notably although they exhibit a very limited range of incompatible trace element and isotopic compositions they have highly variable major element compositions this is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization if this scenario is correct it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element trace element and isotopic diversity of all shergottites

two stage polybaric formation of the new enriched pyroxene oikocrystic lherzolitic shergottite nwa 7397 northwest africa nwa 7397 is a newly discovered enriched lherzolitic shergottite the third described example of this group this meteorite consists of two distinct textural lithologies 1 poikilitic comprised of zoned pyroxene oikocrysts with chadacrysts of chromite and olivine and 2 nonpoikilitic comprised of olivine low ca and high ca pyroxene maskelynite and minor abundances of merrillite spinel ilmenite and pyrrhotite the constant ti al ratios of pyroxene oikocrysts suggests initial crystallization of the poikilitic lithology at depth equivalent to pressures of approximately 10 kbar followed by crystallization of the nonpoikilitic lithology at shallower levels oxygen fugacity conditions become more oxidizing during crystallization ranging from fo2 conditions of approximately qfm 2 to qfm 0 7 magma calculated to be in equilibrium with the major rock forming minerals is lree enriched relative to depleted or intermediate shergottites and has flat overall profiles therefore we suggest that the parental magma for nwa 7397 had sampled an enriched oxidized martian geochemical source similar to that of other enriched basaltic and olivine phyric shergottites we present a polybaric formation model for the lherzolitic shergottite nwa 7397 to account for the petrologic constraints three successive stages in the development of nwa 7397 are discussed 1 formation of a ree enriched parental magma from a distinct martian mantle reservoir 2 magma ponding and development of a staging chamber concomitant with initial crystallization of the poikilitic lithology and 3 magma ascent to the near surface with entrainment of cumulates from the staging chamber and subsequent crystallization of the nonpoikilitic lithology en route to the surface

accretion timescale and impact history of mars deduced from the isotopic systematics of martian meteorites abstract high precision sm nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on mars associated with the formation of their mantle sources these data are used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic ages determined from the sm nd isotopic systematics of individual samples are strongly dependent on the assumed nd isotopic composition of the bulk planet this assumption is problematic given differences observed between the nd isotopic composition of earth and chondritic meteorites and the fact that these materials are both commonly used to represent bulk planetary nd isotopic compositions ages determined from the slope of 146sm 142nd whole rock isochrons are not dependent on the assumed 142nd 144nd ratio of the planet but require the sample suite to be derived from complementary contemporaneously formed reservoirs in this work we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a 143nd 142nd whole rock isochron and is also independent of any a priori assumptions regarding the bulk isotopic composition of the planet this expression is also applicable to mineral isochrons and has been used to successfully calculate 143nd 142nd model crystallization ages of early refractory solids as well as lunar samples this permits ages to be obtained using only nd isotopic measurements without the need for 147sm 144nd isotope dilution determinations when used in conjunction with high precision nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504 6 ma because the sm nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the solar system recent thermal models however suggest that mars sized bodies cool rapidly in less than 5 ma after accretion ceases even in the presence of a thick atmosphere assuming these models are correct an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504 ma late accretional heating of mars could either be associated with protracted accretion occurring at a quasi steady state or alternatively be associated with a late giant impact if this scenario is correct then accretion of mars sized bodies takes up to 60 ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation this further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed

helium loss from martian meteorites mainly induced by shock metamorphism evidence from new data and a literature compilation noble gas data from martian meteorites have provided key constraints about their origin and evolution and their parent body these meteorites have witnessed varying shock metamorphic overprinting at least 5 to 14 gpa for the nakhlites and up to 45 55 gpa e g the lherzolitic shergottite allan hills alh a77005 solar heating cosmic ray exposure and weathering both on mars and earth influences on the helium budgets of martian meteorites were evaluated by using a new data set and literature data concentrations of 3he 4he u and th are measured and shock pressures for same sample aliquots of 13 martian meteorites were determined to asses a possible relationship between shock pressure and helium concentration partitioning of 4he into cosmogenic and radiogenic components was performed using the lowest 4he 3he ratio we measured on mineral separates 4he 3he 4 1 pyroxene of alha77005 our study revealed significant losses of radiogenic 4he systematics of cosmogenic 3he and neon led to the conclusion that solar radiation heating during transfer from mars to earth and terrestrial weathering can be ruled out as major causes of the observed losses of radiogenic helium in bulk meteorites for bulk rock we observed a correlation of shock pressure and radiogenic 4he loss ranging between 20 for chassigny and other moderately shocked martian meteorites up to total loss for meteorites shocked above 40 gpa a steep increase of loss occurs around 30 gpa the pressure at which plagioclase transforms to maskelynite this correlation suggests significant 4he loss induced by shock metamorphism noble gas loss in rocks is seen as diffusion due to 1 the temperature increase during shock loading shock temperature and 2 the remaining waste heat after adiabatic unloading post shock temperature modeling of 4he diffusion in the main u th carrier phase apatite showed that post shock temperatures of 300 c are necessary to explain observed losses this temperature corresponds to the post shock temperature calculated for bulk rocks shocked at about 40 gpa from our investigation data survey and modeling we conclude that the shock event during launch of the meteorites is the principal cause for 4he loss

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

ejection times of martian meteorites noble gas isotopic analyses were made for four meteorites whose origin is mars basaltic shergottites queen alexandra range 94201 zagami the iherzolite lew88516 and orthopyroxenite allan hills 84001 the latter one was separated into orthopyroxene chromite and maskelynite fractions ejection times were calculated for all martian meteorites using cosmic ray exposure ages based on 3he 21ne and 38ar concentrations and literature data on the terrestrial ages we discuss the arguments for a scenario in which they were ejected from mars by asteroidal or cometary impact as small meteoroids and were delivered to earth within and up to 15 million years the basaltic shergottites que94201 shergotty and zagami show an ejection age cluster at 2 76 ma the fourth basaltic shergottite eet79001 being younger 0 82 ma lherzolites lew88516 and alh77005 were ejected by a later event 3 84 ma ago all nakhlites nakhla governador valadares and lafayette originate from an event 11 0 ma ago although chassigny is chemically distinct from the nakhlites its ejection age is 11 6 ma whether this is a separate event cannot be decided from the available data finally orthopyroxenite alh84001 was launched from mars 14 4 ma ago the distribution of the delivery times for martian meteorites to earth reflect individual impact events onto five or six different source terrains this result is significant in the context of a comprehensive knowledge of the martian crust composition finally we derived the k 40ar gas retention age of alh84001 mineral fractions adopting two different models assuming a component of martian atmospheric ar with 40ar36ar 1790 trapped by this meteorite we obtained an age of 3390 ma on the other hand assuming no contribution of martian atmospheric ar the resulting k 40ar age is about 4100 ma that is roughly 500 ma younger than the reported sm nd crystallization age

water extractable and exchangeable phosphate in martian and carbonaceous chondrite meteorites and in planetary soil analogs abstract aqueous extraction contributes to the formation and weathering of planetary materials and renders electrolytes such as phosphate available for biology in this context the solubility of phosphate is measured in planetary materials represented by the mars meteorites nakhla dar al gani 476 dag 476 elephant morraine 79001 eeta 79001 and terrestrial analogs and in the murchison cm2 and allende cv3 carbonaceous chondrites the mars meteorites contain high levels of phosphate that is readily extracted by water up to 15 mg kg 1 in nakhla and dag 476 and 38 mg kg 1 in eeta 79001 while the terrestrial analogs and the carbonaceous chondrites contain 0 5 to 6 mg kg 1 correspondingly high phosphate concentrations of 4 to 28 mg l 1 are obtained in extracts of the mars meteorites at high solid solution ratios exceeding the concentrations of 0 4 to 2 0 mg l 1 in the extracts of the terrestrial analogs a wide range of planetary conditions including n 2 and co 2 atmospheres solid solution ratios of 0 01 to 1 0 kg l 1 extraction times of 1 to 21 d and temperatures of 20 to 121 c affect the amounts of extractable phosphate by factors of only 2 to 5 in most materials phosphate fixing capacity and exchangeable phosphate are assessed by the isotopic exchange kinetics iek method which quantifies the amount of p isotopically exchangeable within 1 min e 1min and between 1 min and 3 months e 1min 3m and the amount of p that cannot be exchanged within 3 months e 3m the iek results show that the dag 476 mars meteorite and terrestrial analogs have low p fixing capacities while the carbonaceous chondrites have high p fixing capacities aqueous processing under early planetary co 2 atmospheres has large effects on the available phosphate for example the fraction of total p that is exchangeable in 3 months increases from 1 6 to 11 13 to 51 6 and 43 9 to 90 4 in the dag 476 mars meteorite allende and murchison respectively the results show that solutions with high phosphate concentrations can form in the pores of planetary lava ash and basalts and in carbonaceous asteroids and meteorites these solutions can help prebiotic synthesis and early microbial nutrition the martian and carbonaceous chondrite materials contain sufficient phosphate for space based agriculture

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

crystallization kinetics of olivine phyric shergottites crystal size distribution csd and spatial distribution pattern sdp analyses are applied to the early crystallizing phases olivine and pyroxene in olivine phyric shergottites elephant moraine eet 79001a dar al gani dag 476 and dhofar dho 019 from each sampling locality inferred from mars ejection ages trace element zonation patterns p and cr in olivine are also used to characterize the crystallization history of these martian basalts previously reported 2 d csds for these meteorites are re evaluated using a newer stereographically corrected methodology kinks in the olivine csd plots suggest several populations that crystallized under different conditions csds for pyroxene in dag 476 and eet 79001a reveal single populations that grew under steady state conditions pyroxenes in dho 019 were too intergrown for csd analysis magma chamber residence times of several days for small grains to several months for olivine megacrysts are calculated using the csd slopes and growth rates inferred from previous experimental data phosphorus imaging in olivines in dag 476 and dho 019 indicate rapid growth of skeletal sector zoned or patchy cores probably in response to delayed nucleation followed by slow growth and finally rapid dendritic growth with back filling to form oscillatory zoning in rims spd analyses indicate that olivine and pyroxene crystals grew or accumulated in clusters rather than as randomly distributed grains these data reveal complex solidification histories for martian basalts and are generally consistent with the formation at depth of olivine megacryst cores which were entrained in ascending magmas that crystallized pyroxenes small olivines and oscillatory rims on megacrysts

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

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

terrestrial 14c age of the antarctic shergottite eeta 79001 abstract the terrestrial age of the elephant moraine shergottite eeta 79001 lithology a has been determined from measurement of its cosmogenic 14 c content as 12 2 kyr the results on saturated and blank samples of l g or less are also discussed the age calculated for eeta 79001 is compared to exposure and terrestrial ages of other shergottites in the light of possible origins of these meteorites on mars

petrology and geochemistry of the unbrecciated achondrite northwest africa 1240 nwa 1240 an hed parent body impact melt nwa 1240 is an unusual eucrite recently recovered in morocco as a single stone of 98 g it is an unbrecciated greenish brown rock nearly devoid of fusion crust it displays porphyritic texture consisting of skeletal hollow low ca pyroxene phenocrysts set in a variolitic fan spherulitic mesostasis of fine elongate pyroxene and plagioclase crystals minor phases are skeletal chromite iron silica troilite ilmenite and minute amounts of phosphate and fayalite pyroxenes are unequilibrated and show one of the widest ranges of composition so far described for a eucrite from en 76 0 wo 1 9 fs 22 1 to compositions nearly devoid of mg unusual ferrosilite and fe augite symplectites and possibly pyroxferroite plagioclase crystals contain significant amounts of fe and mg which are possibly controlled by the ca mg fe2 si3o8 plagioclase component

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

geochemistry and petrology of witwatersrand and dwyka diamictites from south africa search for an extraterrestrial component abstract diamictites are poorly sorted sediments characteristically carrying coarse grained clasts in a fine grained matrix they have generally been considered of glaciogenic or glaciomarine origin recently however it has been suggested that some massive tillite diamictite layers could represent impact breccias an earlier petrographic study of rock and mineral clasts from dwyka group diamictites revealed no evidence for shock metamorphism such as planar deformation features detailed geochemical studies of diamictite samples from the archean witwatersrand supergroup and the dwyka group of the mesozoic karoo supergroup from south africa are reported we studied the contents of the siderophile elements in these breccias as elevated abundances of such elements especially iridium could be indicative for an impact origin by use of coincidence spectrometry and other trace element analysis geochemical tracers of extraterrestrial components were sought however no enrichments of indicator elements for extraterrestrial components compared with ordinary continental crust were found thus neither geochemical nor petrographic evidence supports an impact origin of the diamictites from the dwyka group and the witwatersrand supergroup in south africa

shock implantation of martian atmospheric argon in four basaltic shergottites a laser probe 40ar 39ar investigation spatially resolved argon isotope measurements have been performed on neutron irradiated samples of two martian basalts los angeles and zagami and two martian olivine phyric basalts dar al gani dag 476 and north west africa nwa 1068 with a similar to 50 mu m diameter focused infrared laser beam it has been possible to distinguish between argon isotopic signatures from host rock matrix minerals and localized shock melt products pockets and veins the concentrations of argon in analyzed phases from all four meteorites have been quantified using the measured j values ar 40 ar 39 ratios and k2o wt in each phase melt pockets contain on average 10 times more gas 7 24 ppb ar 40 than shock veins and matrix minerals 0 3 3 ppb ar 40 the ar 40 ar 36 ratio of the martian atmosphere estimated from melt pocket argon extractions corrected for cosmogenie ar 36 is los angeles similar to 1852 zagami similar to 1744 and nwa 1068 similar to 1403 in addition los angeles shows evidence for variable mixing of two distinct trapped noble gas reservoirs 1 martian atmosphere in melt pockets and 2 a trapped component possibly martian interior ar 40 ar 16 480 490 in matrix minerals average apparent ar 40 ar 39 ages determined for matrix minerals in the four analyzed meteorites are 1290 ma los angeles 692 ma zagami 515 ma nwa 1068 and 1427 ma dag 476 these ar 40 ar 39 apparent ages are substantially older than the similar to 170 0474 ma radiometric ages given by other isotope dating techniques and reveal the presence of trapped 40ar cosmic ray exposure cre ages were measured using spallogenic ar 16 and ar 38 production los angeles 3 1 0 2 ma zagami 2 9 0 4 ma and nwa 1068 2 0 0 5 ma yielded ages within the range of previous determinations dag 476 however yielded a young cre age 0 7 0 25 ma attributed to terrestrial alteration the high spatial variation of argon indicates that the incorporation of martian atmospheric argon into near surface rocks is controlled by localized glass bearing melts produced by shock processes in particular the larger mm size melt pockets contain near end member martian atmospheric argon based on petrography composition and argon isotopic data we conclude that the investigated melt pockets formed by localized in situ shock melting associated with ejection three processes may have led to atmosphere incorporation 1 argon implantation due to atmospheric shock front collision with the martian surface 2 transformation of an atmosphere filled cavity into a localized melt zone and 3 shock implantation of atmosphere trapped in cracks pores and fissures

39ar 40ar ages and origin of excess 40ar in martian shergottites we report new 39ar 40ar measurements on 15 plagioclase pyroxene and or whole rock samples of 8 martian shergottites all age spectra suggest ages older than the meteorite formation ages as defined by sm nd and rb sr isochrons employing isochron plots only los angeles plagioclase and possibly northwest africa nwa 3171 plagioclase give ages in agreement with their formation ages isochrons for all shergottite samples reveal the presence of trapped martian 40ar 40arxs which exists in variable amounts in different lattice locations some 40arxs is uniformly distributed throughout the lattice resulting in a positive isochron intercept and other 40arxs occurs in association with k bearing minerals and increases the isochron slope these samples demonstrate situations where linear ar isochrons give false ages that are too old after subtracting 40ar that would accumulate by 40k decay since meteorite formation and small amounts of terrestrial 40ar all young age samples give similar 40arxs concentrations of 1 2 x 10 6 cm 3 g but a variation in k content by a factor of 80 previously reported nasa johnson space center data for zagami shergotty yamato y 000097 y 793605 and queen alexandra range que 94201 shergottites show similar concentrations of 40arxs to the new meteorite data reported here similar 40arxs in different minerals and meteorites cannot be explained as arising from martian atmosphere carried in strongly shocked phases such as melt veins we invoke the explanation given by bogard and park 2008 for zagami that this 40arxs in shergottites was acquired from the magma similarity in 40arxs among shergottites may reveal common magma sources and or similar magma generation and emplacement processes

isotopic composition of trapped and cosmogenic noble gases in several martian meteorites isotopic abundances of the noble gases were measured in the following martian meteorites two shock glass inclusions from elephant moraine eet 79001 shock vein glass from shergotty and yamato y 793605 and whole rock samples of allan hills alh 84001 and queen alexandra range que 94201 these glass samples when combined with literature data on a separate single glass inclusion from eet 79001 and a glass vein from zagami permit examination in greater detail of the isotopic composition of ne ar kr and xe trapped from the martian atmosphere the isotopic composition of martian ne if actually present in these glasses remains poorly defined the 40ar 36ar ratio of trapped martian atmospheric ar is probably considerably lower than the nominal ratio of 3000 measured by viking and data on impact glasses suggest a value of 1900 the atmospheric 36ar 38ar ratio is 4 0 martian atmospheric kr may be enriched in lighter isotopes by 0 5 amu compared to both solar wind kr and to the martian composition previously reported the isotopic composition of xe in these glasses agrees with that previously reported in the literature the martian atmospheric 36ar 132xe and 84kr 132xe elemental ratios are higher than those reported by viking by factors of 2 5 1 6 depending on the 40ar 36ar ratio adopted and 1 8 respectively and are discussed in a separate paper cosmogenic gases indicate space exposure ages of 2 7 0 6 ma for que 94201 and shergotty and 14 1 ma for alh 84001 small amounts of 21ne produced by energetic solar protons may be present in que 94201 but are not present in alh 84001 or y 793605 the space exposure age for y 793605 is 4 9 0 6 ma and appears to be distinctly older than the ages for basaltic shergottites however uncertainties in cosmogenic production rates still makes somewhat uncertain the number of martian impact events required to produce the exposure ages of martian meteorites

los angeles the most differentiated basaltic martian meteorite los angeles is a new martian meteorite that expands the compositional range of basaltic shergottites compared to shergotty zagami que94201 and eet79001 b los angeles is more differentiated with higher concentrations of incompatible elements e g la and a higher abundance of late stage phases such as phosphates and k rich feldspathic glass the pyroxene crystallization trend starts at compositions more ferroan than in other martian basalts trace elements indicate a greater similarity to shergotty and zagami than to que94201 or eet79001 b but the mg fe ratio is low even compared to postulated parent melts of shergotty and zagami pyroxene in los angeles has 0 7 4 m thick exsolution lamellae 10 times thicker than those in shergotty and zagami opaque oxide compositions suggest a low equilibration temperature at an oxygen fugacity near the fayalite magnetite quartz buffer los angeles cooled more slowly than shergotty and zagami slow cooling coupled with the ferroan bulk composition produced abundant fine grained intergrowths of fayalite hedenbergite and silica by the breakdown of pyroxferroite shock effects in los angeles include maskelynitized plagioclase pyroxene with mosaic extinction and rare fault zones one such fault ruptured a previously decomposed zone of pyroxferroite although highly differentiated the bulk composition of los angeles is not close to the low ca si composition of the globally wind stirred soil of mars

shear induced ringwoodite formation in the martian shergottite dar al gani 670 abstract shock produced melt veins in the martian shergottite dar al gani 670 crosscut large olivine crystals the upper part of one of these crystals appears to be sheared off and displaced along the shock vein from the olivine vein interface small lamellae of ringwoodite grow into the host crystal the 1 3 m wide and up to 20 m long lamellae consist of small bands and blocks and are orientated along specific crystallographic orientations texture and composition i e more fe rich than the host olivine indicate that lamellae formed via incoherent diffusion controlled growth it is suggested that a combination of high particle velocities and shock induced defects lead to enhanced diffusion rates in addition shearing caused grain size reduction allowing rapid fe mg interchange and induced lattice defects serving as nucleation sites for ringwoodite crystallographic orientation of ringwoodite lamellae indicates that during shock deformation the 001 hk 0 slip system was activated in olivine natural high pressure phases in martian meteorite allow to constrain phase transitions taking place in the inaccessible earth s mantle high pressure shear instabilities of olivine at subduction zones in 400 700 km depth are considered being responsible for deep earthquakes at such p t conditions breakdown of olivine results in formation of ringwoodite filled micro anticracks which interact with each other finally leading to catastrophic shear failure our results strongly suggest that shearing itself contributes to a runaway process of enhanced ringwoodite formation and thus reinforces catastrophic material failure that may result in deep earthquakes

gain and loss of uranium by meteorites and rocks and implications for the redistribution of uranium on mars terrestrial alteration of meteorites results in the redistribution gain or loss of uranium and other elements we have measured the maximum u adsorption capacity of a meteorite and two geochemical reference materials under conditions resembling terrestrial ones ph 5 8 the basaltic eucrite sioux county adsorbs 7 ppm of u the result for the terrestrial granite ac e is similar 5 ppm while the basalt be n adsorbs 34 ppm of u we have also investigated u adsorption in the presence of phosphate 0 01 m or less in imitation of conditions that probably occurred in the earlier history of mars such a process would have alterated martian surface material and would be noticeable in martian meteorites from the affected surface the experiments demonstrated the counteracting effects of phosphate which increases u adsorption but decreases the quantity of dissolved u that is available for adsorption u adsorption by ac e increases to 7 ppm the lowered value for be n of 8 ppm results from the low quantity of dissolved u in the volume of solution used the results from the adsorption experiments and from leaching the martian meteorite zagami and a terrestrial basalt imply that the aqueous redistribution of u on mars was moderate acidic liquids mobilized uranium and other metals but present phosphate impeded the dissolution of u compounds some mobilized u may have reached the global sinks while most of it probably was transported in the form of suspended particles over a limited distance and then settled

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

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

large ion lithophile element fractionation during the early differentiation of mars and the composition of the martian primitive mantle basaltic shergottites display a systematic decrease in k th k u and k la ratios with increasing k content these trends are interpreted as mixing lines between relatively young martian magmas derived from highly depleted mantle sources and an ancient large ion lithophile lil element enriched crustal component one implication of this is that a substantial fractionation of these ratios occurs during the early crustal differentiation on mars isotopic evidence from snc meteorites and compositional data from pathfinder and orbital gamma ray spectroscopy suggest that in excess of 50 of the lil element complement of mars resides in the crustal reservoir if so the primitive mantle of mars is significantly more volatile depleted i e lower k th k u k la than previously thought but probably though not necessarily still less volatile depleted than the primitive mantle of the earth the la th ratios of virtually all snc meteorites are subchondritic including those with the most severe lree depletion extrapolation of the basaltic shergottite trend suggests that both the depleted mantle end member and the enriched crustal end member have subchondritic la th ratios this is in contrast with the earth where basalts from lil element depleted sources such as morb have superchondritic la th ratios complementary to the subchondritic ratios of the continental crust accordingly assuming that the refractory elements are in chondritic proportions for the mars primitive mantle an additional major geochemical reservoir must exist on mars that may not yet have been sampled

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

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

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

trace element inventory of meteoritic ca phosphates most extraterrestrial samples feature the two accessory ca phosphates apatite group minerals and merrillite which are important carrier phases of the rare earth elements ree the trace element concentrations ree sc ti v cr mn co as rb sr y zr nb ba hf ta pb th and u of selected grains were analyzed by la icp ms and or sims ree only this systematic investigation includes 99 apatite and 149 merrillite analyses from meteorites deriving from various asteroidal bodies including 1 carbonaceous chondrite 8 ordinary chondrites 3 acapulcoites 1 winonaite 2 eucrites 5 shergottites 1 ureilitic trachyandesite 2 mesosiderites and 1 silicate bearing iab iron meteorite although ca phosphates predominantly form in metamorphic and or metasomatic reactions some are of igneous origin as late stage phases that often incorporate the vast majority of their host s bulk ree budget the investigated ca phosphates have ree enrichments of up to two orders of magnitude compared to the host rock s bulk concentrations within a single sample each phosphate species displays a uniform ree pattern and variations are mainly restricted to their enrichment therefore indicating similar formation conditions exceptions are brecciated samples i e the adzhi bogdo ll3 6 ordinary chondrite despite this uniformity within single samples distinct meteorite groups do not necessarily have unique ree patterns four basic shapes dominate the ree patterns of meteoritic ca phosphates 1 flat patterns smoothly decreasing from la lu with prominent negative eu anomalies acapulcoites eucrites apatite from the winonaite and the ureilitic trachyandesite merrillite from ordinary chondrites 2 unfractionated patterns with only minor or no anomalies mesosiderites enriched shergottites iab iron meteorite 3 lree enriched patterns with either positive or slightly negative eu anomalies chondritic apatite and 4 strongly lree depleted patterns with negative eu anomalies depleted shergottites the patterns do not correlate with the grade of metamorphism petrologic type specific adjacent mineral assemblages or with ca phosphate grain size neither the proportions of different ree nor particular ree patterns themselves are universally correlated to a specific formation mechanism yet eu i e magnitude of the eu anomaly is a sensitive indicator to evaluate the timing of plagioclase and phosphate crystallization based on our data u and th abundances in apatite increase almost linearly with the grade of metamorphism as well as with the differentiation of their host rock