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

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

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

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

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

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

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

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

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

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

localized shock melting in lherzolitic shergottite northwest africa 1950 comparison with allan hills 77005 the lherzolitic martian meteorite northwest africa nwa 1950 consists of two distinct zones 1 low ca pyroxene poikilically enclosing cumulate olivine fo70 75 and chromite and 2 areas interstitial to the oikocrysts comprised of maskelynite low and high ca pyroxene cumulate olivine fo68 71 and chromite shock metamorphic effects most likely associated with ejection from the martian subsurface by large scale impact include mechanical deformation of host rock olivine and pyroxene transformation of plagioclase to maskelynite and localized melting pockets and veins these shock effects indicate that nwa 1950 experienced an equilibration shock pressure of 35 45 gpa large millimeter size melt pockets have crystallized magnesian olivine fo78 87 and chromite embedded in an fe rich al poor basaltic to picro basaltic glass within the melt pockets strong thermal gradients minimum 1 c m existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite dendritic and skeletal olivine crystallized in the melt pocket center has a nucleation density 1 0 x 10 3 crystals mm 2 that is two orders of magnitude lower than olivine euhedra near the melt margin 1 6 x 10 5 crystals mm 2 based on petrography and minor element abundances melt pocket formation occurred by in situ melting of host rock constituents by shock as opposed to melt injected into the lherzolitic target despite a common origin nwa 1950 is shocked to a lesser extent compared to allan hills alh 77005 45 55 gpa assuming ejection in a single shock event by spallation this places nwa 1950 near to alh 77005 but at a shallower depth within the martian subsurface extensive shock melt networks the interconnectivity between melt pockets and the ubiquitous presence of highly vesiculated plagioclase glass in alh 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting

martian regolith in elephant moraine 79001 shock melts evidence from major element composition and sulfur speciation abstract shock veins and melt pockets in lithology a of martian meteorite elephant moraine eeta 79001 have been investigated using electron microprobe em analysis petrography and x ray absorption near edge structure xanes spectroscopy to determine elemental abundances and sulfur speciation s 2 versus s 6 the results constrain the materials that melted to form the shock glasses and identify the source of their high sulfur abundances the xanes spectra for eeta79001 glasses show a sharp peak at 2 471 kev characteristic of crystalline sulfides and a broad peak centered at 2 477 kev similar to that obtained for sulfide saturated glass standards analyzed in this study sulfate peaks at 2 482 kev were not observed bulk compositions of eeta79001 shock melts were estimated by averaging defocused em analyses vein and melt pocket glasses are enriched in al ca na and s and depleted in fe mg and cr compared to the whole rock petrographic observations show preferential melting and mobilization of plagioclase and pyrrhotite associated with melt pocket and vein margins contributing to the enrichments estimates of shock melt bulk compositions obtained from glass analyses are biased towards fe and mg depletions because in general basaltic melts produced from groundmass minerals plagioclase and clinopyroxene will quench to a glass whereas ultramafic melts produced from olivine and low ca pyroxene megacrysts crystallize during the quench we also note that the bulk composition of the shock melt pocket cannot be determined from the average composition of the glass but must also include the crystals that grew from the melt pyroxene en 72 75 fs 20 21 wo 5 7 and olivine fo 75 80 reconstruction of glass crystal analyses gives a bulk composition for the melt pocket that approaches that of lithology a of the meteorite reflecting bulk melting of everything except xenolith chromite our results show that eeta79001 shock veins and melt pockets represent local mineral melts formed by shock impedance contrasts which can account for the observed compositional anomalies compared to the whole rock sample the observation that melts produced during shock commonly deviate from the bulk composition of the host rock has been well documented from chondrites rocks from terrestrial impact structures and other martian meteorites the bulk composition of shock melts reflects the proportions of minerals melted large melt pockets encompass more minerals and approach the whole rock whereas small melt pockets and thin veins reflect local mineralogy in the latter the modal abundance of sulfide globules may reach up to 15 vol we conclude the shock melt pockets in eeta79001 lithology a contain no significant proportion of martian regolith

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

iron and lree enriched mantle source for early proterozoic intraplate magmatism as exemplified by the pechenga ferropicrites kola peninsula russia ferropicritic magmatism has produced a variety of volcanic and subvolcanic formations in the upper part of the early proterozoic pechenga group including sills tuffs pillowed and massive lavas and thick differentiated lava flows that possess spinifex textured upper parts and lower cumulate parts enriched in olivine various olivine and pyroxene spinifex types can be distinguished the occurrence of the spinifex texture in the pechenga ferropicrites demonstrates that this texture is not restricted to rocks of komatiitic affinity the existence of kaersutitic amphibole in spinifex textured ferropicrites is discussed as a paleodepth indicator of the volcanism the parental ferropicritic magma contained about 15 wt mgo other geochemical characteristics include high feotot and tio2 and low al2o3 contents and high abundances of lree and hfse many incompatible element ratios correspond to those found in modern ocean island basalts a notable exception are ratios involving phssphorous due to the relatively low p2o5 content of ferropicrites the al2o3 vs mgo kd feo diagram is used to show that ferropicritic magma is not simultaneously saturated in olivine and garnet at high pressures and hence it was segregated from a garnet free mantle residue this implies that the lree enriched nature of the magma was inherited from the mantle source region the positive initial nd value 1 4 0 4 suggests a long time integrated depletion and therefore the inferred enrichment event in the mantle source must have taken place relatively shortly prior to melt segregation geochemical and isotopic data are compatible with a mantle plume related origin of the pechenga ferropicrites but the application of this model is limited by the present uncertainty on the duration of the volcanism

volatiles nitrogen noble gases in recently discovered snc meteorites extinct radioactivities and evolution abstract we report noble gas and nitrogen analyses of newly discovered snc meteorites one nakhlite nwa817 and four shergottites nwa480 nwa856 nwa1068 and sau 005 the k ar age 1 3 ga as well as the cosmic ray exposure cre age 10 0 1 3 ma of nakhlite nwa817 agree with data of nakhla the cre ages of nwa480 nwa856 and nwa1068 2 35 0 20 2 60 0 21 and 2 01 0 65 ma respectively are consistent within uncertainties with other basaltic shergottites but the cre age of sau 005 1 25 0 07 ma is distinct and indicates a different ejection event bulk k ar ages of all shergottites exceed the reported radiometric ages and reveal the presence of inherited radiogenic 40 ar in basaltic lavas the isotopic composition of nitrogen trapped in these snc meteorites is not homogeneous since 15 n values of either 15 to 20 or 45 indicate different nitrogen reservoirs all shergottites contain fission xenon from 238 u and fission xe of extinct t 1 2 82 ma 244 pu previously identified in alh84001 in chassigny and in nakhla is also present in at least one shergottite nwa856 the shergottites contain less fissiogenic xe than other snc suggesting that either their source was more degassed or that the magma source region closed at a later time in nakhlites fission xenon from 244 pu correlates with uranium a geochemical proxy of plutonium thus it is possible that fissiogenic xe was not inherited during magma differentiation but rather was produced in situ and retained in refractory mineral assemblages in this interpretation the magma evolution that settled the mineralogy and geochemistry of nakhlites took place at a time when 244 pu was alive and pre dated the late events recorded in their radiometric ages alternatively fissiogenic xenon was trapped from a mantle source during closed system evolution of the parent magmas in which case such evolution might have taken place at considerable depth pressure in order to inhibit magma degassing during the course of differentiation

high density co2 n2 inclusions in eclogite facies metasediments of the munchberg gneiss complex se germany the eclogite facies metasedimentary rocks in the munchberg gneiss complex t 630 30 c p 17 24 kbar locally contain co2 n2 rich fluid inclusions of extremely low molar volumes 32 cm3 mol in quartz these fluid compositions are mainly found in rocks intercalated with calcsilicate bands densities were determined from low temperature phase transitions like stable or metastable homogenization l v l partial homogenization s l v s l and the transition s l l l liquid v vapour s solid the high fluid densities are in agreement with eclogite facies pressure and temperature and subsequent amphibolite facies co2 n2 inclusions were not observed in adjacent eclogites nor in non calcareous metasediments these rock types contain predominantly h2o rich inclusions correlating with amphibolite facies conditions the variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite facies metamorphism