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

quantifying noble gas contamination during terrestrial alteration in martian meteorites from antarctica we investigated exterior and interior subsamples from the martian shergottite meteorites allan hills alh a77005 and roberts massif rbt 04261 for secondary minerals oxygen isotopes ar ar and noble gas signatures electron microprobe investigations revealed that rbt 04261 does not contain any visible alteration even in its most exterior fractures whereas fracture fillings in alha77005 penetrate into the meteorite up to 300 m beyond which the fractures are devoid of secondary minerals light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites thus a shock metamorphic overprint of 30 35 gpa can be deduced from the helium measurements in rbt 04261 oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples the measurements on irradiated samples ar ar showed a clear martian atmospheric contribution in alha77005 but this is less apparent in our sample of rbt 04261 exterior and interior subsamples show slight differences in apparent ages but the overall results are very similar between the two in contrast krypton and xenon are severely affected by terrestrial contamination demonstrating the ubiquitous presence of elementally fractionated air in rbt 04261 although seemingly contradictory our results indicate that rbt 04261 was more affected by contamination than alha77005 we conclude that irrespective of on which planet the alteration occurred exposure of martian rocks to atmosphere or brine introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

microanalysis of nitrogen isotope abundances association of nitrogen with noble gas carriers in allende current research efforts to explore and account for the distribution of nitrogen isotope abundances in the ancient and present day solar wind and in meteorites often require measurement of nitrogen abundances and isotopic compositions in very small samples of rare extraterrestrial materials isotopic analysis of 1 g of n2 is possible with modern techniques of dynamic mass spectrometry but even this high sensitivity is a limiting factor for certain critical samples we have utilized a statistically operated mass spectrometer coupled to an ultrahigh vacuum gas extraction and processing system to lower this limit by approximately four orders of magnitude quantities of n2 ranging from 100 ng to 100 pg are measurable with permil to percent precision in isotope ratios nitrogen and all noble gases evolved during stepwise combustion of fine grained matrix material separated from the allende meteorite have been meausred simultaneously in a pilot experiment using this technique isotopically heavy h xe ccf xe and isotopically light n are co sited in a carbonaceous carrier phase supporting a nucleosynthetic origin for15n depleted nitrogen in allende the great isotopic uniformity of trapped ar in all carrier phases indicates that simple physical mass fractionation in gravitational escape of volatiles from the primitive nebula cannot have played a significant role in generating the nitrogen compositions observed in solar system matter

noble gases released by vacuum crushing of eeta 79001 glass abstract gases released by in vacuo crushing of an eeta 79001 glass sample 15 of total gas concentrations were a mixture of a small amount of spb type gas with larger proportions of another more air like component though fractionated air is unlikely crush released 84kr 132xe 31 6 3 1 and36ar 132xe 809 49 higher than spb gas 15ncrush 13 2 1 4 xenon in the second eetv component has 129xe 132xe 1 21 while argon from this component has40ar 36ar 680 and is constrained by ar xe systematics to be 430 the eetv36ar 38ar ratio of 4 9 0 2 is lower than air but not as low as the estimated spb ratio which agrees with earlier measurements of 4 1 less than 5 of the spb gas was released by crushing while 36 40 of the eetv gas was crush released these results are consistent with a siting of the eetv component in 10 100 m vesicles seen in the glass while the spb component must be in vesicles 6 m diameter or more likely is primarily sited elswhere

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

ar ar ages and trapped ar components in martian shergottites rbt 04262 and lar 06319 abstract we made 39ar 40ar ar ar analyses of whole rock wr and mineral samples of two martian shergottites rbt 04262 rbt and lar 06319 lar in order to determine their ar ar ages and the 40ar 36ar ratios of the trapped martian ar they contain all samples released trapped excess 40ar and 36ar and suggested ar ar ages older than their formation ages because trapped ar components having different 40ar 36ar were released at different extraction temperatures we utilized only a portion of the data to derive preferred ar ar ages we obtain ar ar ages of 171 8 ma for rbt plagioclase and 163 13 ma for lar whole rock we identify two trapped ar components at low temperatures particularly for plagioclase trapped a with 40ar 36ar 285 3 was released and we believe this is most likely absorbed terrestrial air at high extraction temperatures particularly for pyroxene trapped b with 40ar 36ar 1813 127 was released the poikilitic non poikilitic texture of rbt and the presence of large pyroxene oikocrysts allowed a clear definition of trapped b this ar component is martian and its isotopic similarity to the martian atmospheric composition suggests that it may represent martian atmospheric ar incorporated into the shergottite melt via crustal rocks trapped b partitioned into pyroxene at a constant molar ratio of k 36artr 33 2 9 5 106 for rbt 04262 and 80 21 106 for lar 06319 trapped a mixed in different proportions with trapped b could give apparently intermediate trapped 40ar 36ar compositions commonly observed in shergottites

shergottites dhofar 019 sau 005 shergotty and zagami 40ar 39ar chronology and trapped martian atmospheric and interior argon we report a high resolution 40ar 39ar study of mineral separates and whole rock samples of olivine phyric dhofar 019 sayh al uhaymir sau 005 and basaltic shergotty zagami shergottites excess argon is present in all samples the highest 40ar 36ar trapped ratios are found for argon in pyroxene melt inclusions 1500 maskelynite 1200 impact glass 1800 of shergotty and impact glass of sau 005 1200 a high 40ar 36ar trapped componentusually uniquely ascribed to martian atmosphere can also originate from the martian interior indicating a heterogeneous martian mantle composition as additional explanation of variable high 40ar 36ar trapped ratios in shocked shergottites we suggest argon implantation from a transient atmosphere during impact induced degassing the best 40ar 39ar age estimate for dhofar 019 is 642 72 ma maskelynite sau 005 samples are between 700900 ma old relatively high 40ar 39ar ages of melt inclusions within dhofar 019 1086 252 ma and sau 005 olivine 885 66 ma could date entrapment of a magmatic liquid during early olivine crystallization or reflect unrecognized excess 40ar components the youngest 40ar 39ar age of shergotty separates maskelynite is 370 ma that of zagami is 200 ma the 40ar 39ar chronology of dhofar 019 and sau 005 indicate 1 ga ages apparent ages uncorrected for trapped e g martian atmosphere mantle argon components approach 4 5 ga but are not caused by inherited 40ar because excess 40ar is supported by 36artrapped young ages obtained by 40ar 39ar and other chronometers argue for primary rather than secondary events the cosmic ray exposure ages calculated from cosmogenic argon are 15 7 0 7 ma dhofar 019 1 0 1 6 ma sau 005 2 1 2 5 ma shergotty and 2 2 3 0 ma zagami

a search for nitrates in martian meteorites martian atmospheric nitrogen is highly enriched in n 15 nitrates formed by interaction of the atmosphere with the martian regolith should therefore also be characterized by an elevated delta 15 n value a search has been made for nitrates in two martian meteorites in order to determine the extent of possible regolith atmosphere interaction shock produced glass from the elephant moraine eet a79001 shergottite e1 149 and a water soluble extract from nakhla were analyzed by fourier transform infrared ftir spectroscopy and stepped combustion stable isotope mass spectrometry ftir of both meteorites had features at 1375 cm 1 and 1630 cm 1 consistent with nitrates on account of their low thermal stability nitrates break down at temperatures below 600 degrees c in this temperature range e1 149 yielded similar to 1250 ppb nitrogen with delta 15 n 8 5 parts per thousand if this nitrogen is from a nitrate then it cannot be distinguished from terrestrial salts by its isotopic composition the water soluble extract from nakhla also released nitrogen at low temperatures approximately 17 ppb with delta 15 n approximately 11 4 parts per thousand since nakhla is an observed fall this is unlikely to be a terrestrial weathering product nitrates apparently occur in e1 149 and nakhla but in very low abundance and their origin is unclear the isotopic composition of the salts which is within the range of that proposed for martian magmatic volatiles is far removed from that of nitrogen in the present day martian atmosphere if the nitrates are martian in origin they did not form in recent times from reactions involving atmospheric gases rather the nitrates could be the result of an earlier episode of atmospheric interaction with the regolith or with implantation of magmatic volatiles introduced during degassing

incipient metamorphism and deformation in the variscides of sw dyfed wales first steps towards isotopic equilibrium incipient metamorphism accompanying thrusting folding and cleavage development has been investigated in a varied sequence of palaeozoic sediments near the variscan front in sw dyfed wales the aim was to evaluate a critical stage in the progression from heterogeneous sediment whose detrital phases are neither in equilibrium with one another nor with pore fluids through indurated sedimentary rock to metamorphic rock comprising newly formed crystals that equilibrated with one another as they grew quartz veins are widely developed in the area especially in the more psammitic lithologies while finer grained rocks became cleaved during tectonic deformation mineralogical constraints and fluid inclusion measurements suggest maximum temperatures around 200 310d c slightly higher in the marloes musselwick thrust sheet than in other parts of the structural succession at depths of the order of 6 13 km quartz veins yield distinctly heavier oxygen isotopic compositions than detrital quartz grains in the adjacent wall rocks although care must be taken in interpreting the data because slivers of detrital grains may become incorporated into veins while matrix detrital grains may incorporate veinlets or rims of newly formed quartz it is concluded that vein quartz grew in isotopic equilibrium with a fluid phase whose isotopic composition was primarily controlled by exchange with phyllosilicates not detrital quartz grains vein and matrix quartzes from the marloes musselwick thrust sheet are distinctly lighter 18oveins 14 to 18 and 18omatrix 11 to 14 than those from other thrust sheets 18o 17 to 20 and 14 to 17 respectively we conclude that vein quartz and phyllosilicate grains in cleavage domains probably attained equilibrium with a locally buffered pore fluid at the peak of metamorphism but many relict grains of different chemical and isotopic composition remained elsewhere in the rock local fluid migration along veins and through cleavage lamellae facilitated the attainment of equilibrium but there is little evidence for large scale infiltration of externally derived fluids with further metamorphism the quartz in these rocks would attain an isotopic composition intermediate between that of the heavy vein material and light detritus which coexist here

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

argon 39 argon 40 ages and trapped argon in martian shergottites chassigny and allan hills 84001 abstract argon isotopic abundances were measured in neutron irradiated samples of martian meteorites chassigny allan hills alh 84001 alh 77005 elephant moraine eet 79001 yamato y 793605 shergotty zagami and queen alexandra range que 94201 and in unirradiated samples of alh 77005 chassigny gives a 39ar 40ar age of 1 32 0 07 ga which is similar to radiometric ages of the nakhlites argon 39 argon 40 data for alh 84001 indicate ages between 3 9 and 4 3 ga a more precise definition of this age requires detailed characterization of the multiple trapped ar components in alh 84001 and of 39ar recoil distribution all six shergottite samples show apparent 39ar 40ar ages substantially older than the 165 200 ma range in ages given by other isotope dating techniques shergottites appear to contain ubiquitous ar components acquired from the martian atmosphere the martian mantle and commonly terrestrial atmospheric contamination zagami feldspar also suggests inherited radiogenic 40ar these data analyses indicate that the recent martian atmospheric component trapped in shergottites has a 40ar 36ar ratio possibly as low as 1750 and no greater than 1900 these ratios are less than the value of 3000 500 reported by viking the 40ar 36ar ratio for the martian mantle component is probably 500 but is poorly constrained the correlation between trapped 40ar 36ar and 129xe 132xe ratios in shergottite impact glasses and unirradiated samples of alh 77005 shows considerable scatter and suggests that the 36ar 132xe ratio in the martian components may vary resolution of martian atmospheric 40ar 36ar ratio at different time periods i e at 4 0 and 0 2 ga is also difficult without an understanding of the composition of various trapped components

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

terrestrial and martian weathering signatures of xenon components in shergottite mineral separates abstract xenon isotopic ratios step heating release patterns and gas concentrations of mineral separates from martian shergottites roberts massif rbt 04262 dar al gani dag 489 shergotty and elephant moraine eet 79001 lithology b are reported concentrations of martian atmospheric xenon are similar in mineral separates from all meteorites but more weathered samples contain more terrestrial atmospheric xenon the distributions of xenon from the martian and terrestrial atmospheres among minerals in any one sample are similar suggesting similarities in the processes by which they were acquired however in opaque and maskelynite fractions martian atmospheric xenon is released at higher temperatures than terrestrial atmospheric xenon it is suggested that both martian and terrestrial atmospheric xenon were initially introduced by weathering low temperature alteration processes however the martian component was redistributed by shock accounting for its current residence in more retentive sites the presence or absence of detectable 129xe from the martian atmosphere in mafic minerals may correspond to the extent of crustal contamination of the rock s parent melt variable contents of excess 129xe contrast with previously reported consistent concentrations of excess 40ar suggesting distinct sources contributed these gases to the parent magma

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 chemical composition of shergotty mineral fractions chassigny and yamato 793605 the trapped argon 40 argon 36 ratio and ejection times of martian meteorites we report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene maskelynite mesostasis glass and bulk material of shergotty and of bulk samples from chassigny and yamato 793605 the 40k 40ar isochron for the shergotty minerals yields a gas retention age of 196 ma which is within errors in agreement with previously determined rb sr internal isochron ages argon that was trapped at this time has a 40ar 36ar ratio of 1100 for chassigny and y 793605 we obtain trapped 40ar 36ar ratios of 1380 and 950 respectively using these results and literature data we show that the three shergottites shergotty zagami and que 94001 the lherzolites alh 77005 lew 88516 and y 793605 as well as chassigny and alh 84001 contain a mixture of martian mantle and atmospheric ar whereas the trapped 40ar 36ar ratio of the nakhlites nakhla lafayette and governador valadares cannot be determined with the present data we show that martian atmospheric trapped ar in martian meteorites is correlated with the shock pressure that they experienced hence we conclude that the martian atmospheric gases were introduced by shock into the meteoritic material for the shergotty minerals we obtain 3he 21ne and 38ar based cosmic ray exposure ages of 3 0 ma and for the lherzolite y 793605 4 0 ma which confirms our earlier conclusion that the lherzolites were ejected from mars 1 ma before the shergottites chassigny yields the previously known ejection age of 11 6 ma

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

helium and argon from an atlantic morb glass concentration distribution and isotopic composition data are reported for detailed he and ar measurements on a single morb glass from the atlantic ch 98 dr 11 30 41 n 41 49 w depth 3500 m grain size fractions prepared under ambient conditions are strongly affected by diffusive loss of he from grains and by adsorption of atmospheric argon on grain surfaces both effects could be controlled by crushing gram sized chunks of glass under vacuum and analyzing the powder without any further handling in particular without its exposure to the atmosphere gases from vesicles released upon crushing are characterized by a4he 40ar ratio of6 1 and a40ar 36ar ratio of up to 22 600 in dissolved gases the4he 40ar ratio was found to be 7 2 1 6 times higher and the40ar 36ar ratio to be about ten times lower than in vesicles the difference of theelemental ratio he ar is as anticipated from the ratio of the solubilities ca nine in the investigated basalt of he and ar thus whileelemental abundance ratios are compatible with equilibrium between vesicles and basalt the grossly different argonisotopic ratios are not it is proposed that two basalts chemically very similar but with different40ar 36ar ratios were mixed shortly before eruption the overall4he 40ar ratio in the vesiculated basalt is12 2 so that for the ratio in the primary magma we find6 4he 40ar 12 which is considerably higher than the radiogenic production ratio in all conceivable sources of morb preferential removal from a melt of argon via vesicles is suggested to be the most likely explanation whereas any metasomatic transfer seems unrealistic

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

oxygen isotope thermometry based on a refined increment method and its application to granulite grade rocks from sri lanka abstract in this paper we first present a revision of the increment method a semi empirical technique which allows the calculation of o isotope fractionation factors between all silicates provided their structure and chemical composition is known for the temperature dependency the experimentally calibrated high pressure mineral calcite fractionation factors of chiba et al 1989 are taken as a basis then this method is applied to granulite facies parageneses from sri lanka including quartz k feldspar sillimanite garnet pyroxenes amphiboles cordierite magnetite and ilmenite it can be shown that o isotope equilibration occurred at granulite facies conditions at about 830 c due to static recrystallization locally retrograde re equilibration occurred also at much lower temperatures due to late d4 in most cases however o isotope disequilibria resulted from retrograde oxygen intracrystalline diffusion it can be proved by model calculations that the o diffusion data for water saturated systems reported in the literature are too high by two orders of magnitude to explain the measured isotopic compositions the fractionation patterns allow the discrimination between open and closed system behaviour the regional distribution of open and closed system patterns corresponds to the frequency of occurrence of late stage migmatization western part and to differences in amount and composition of fluid inclusions

the matuyama brunhes and upper jaramillo transitions recorded in a loess section at weinan north central china abstract the paleomagnetic records of the matuyama brunhes mb and upper jaramillo uj polarity reversals have been obtained from a loess section at weinan shaanxi province in china an investigation of the rock magnetic properties using stepwise irm acquisition hysteresis loops thermomagnetic analysis and x ray diffraction on magnetic extracts identifies pseudo single domain magnetite as the carrier of the main fraction of the remanence associated with maghemite and hematite the total duration of the directional change based upon independent loess accumulation rates is about 5000 yr for the mb reversal and about 3200 yr for the uj reversal these values are consistent with previous estimates obtained from marine or lacustrine sediments apart from a few intermediate points observed on north america mb and in the pacific uj the transitional virtual geomagnetic pole vgp paths are situated in two longitudinal bands over eastern asia and australia mb and the americas uj the bulk of the uj record and the part of the mb record over the americas are not consistent with the hypothesis of a record arising from smoothing of pre and post transitional directions 1 a reappraisal of the statistical approach of mcfadden et al 2 shows that the longitudinal distribution of the records of reversals is consistent with the hypothesis of genuine geographically preferred sectors for the paths independent of site longitude with a probability higher than 0 45 when the two weinan records are considered thus these results obtained from wind blown loess sustain the hypothesis of two preferential longitudinal bands for reversing transitional vgps suggested from the study of marine and lacustrine sediments

martian volatiles in shergottite eeta 79001 new evidence from oxidized sulfur and sulfur rich aluminosilicates abstract high vacuum pyrolysis of individual petrologically documented chips of lithology a pyroxenemaskelynite host rock and lithology c glass inclusion from the same interior portion of eeta 79001 produced sulfur in substantially different proportions of oxidized so2 and reduced h2s s2 species sulfur pyrolyzed from lith a possessed a bulk atomic ratio of s ox s red 0 21 whereas sulfur from lith c displayed a bulk ratio of 0 54 and included a component with a ratio of 1 83 that was released at 950 c most of the oxidized sulfur in lith c was probably dissolved or occluded in glass although some of the sulfate probably existed in sulfur and chlorine rich aluminosilicate mineraloids that occurred as trace quantities of 10 m sized grains parallel sem eds and pyrolysis analyses of control samples including weathered exterior chips of eeta 79001 and of eucrite eeta 79004 produced evidence against antarctic weathering as the source of oxidized sulfur and sulfur rich aluminosilicates in lith c oxidized sulfur evolved from control samples including lith a was accompanied by substantial amounts of h2o and co2 although virtually none of the latter species were found in lith c gypsum was abundant in the weathered eucrite and in weathered lith a but was not found in lith c because lith c contains trapped noble gases and nitrogen of martian atmospheric affinity a logical explanation for its oxidized sulfur would be rock atmosphere reactions that occurred on mars prior to or during the melting event that produced lith c bulk elemental compositions of two varieties of sulfur rich aluminosilicates in lith c can be arithmetically mixed to produce a composition that agrees remarkably well with that of surface fines at the viking landing sites suggesting that lith c might actually contain relict grains of martian weathering or alteration products

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

on the siting of gases shock emplaced from internal cavities in basalt abstract noble gases were extracted by stepped combustion and crushing from basalts which contained gas filled cavities of controlled sizes prior to shock at 40 gpa analysis of fractions enriched and depleted in shock glass from a single sample gave a factor of 2 higher gas abundances in the glass rich separate release patterns were nearly identical suggesting similar siting in glass in both fractions crushing of a sample released 45 of implanted noble gases but only 17 of n 2 indicating that most or all of the noble gas was trapped in vesicles analysis by sem eds confirmed the presence of vesicles in glassy areas with an average diameter of 10 m samples with relatively large pre shock cavities were found to consist of up to 70 80 glass locally and generally exhibit greater local shock effects than solid and densely packed paniculate targets at the same shock pressure though the latter give higher gas emplacement efficiencies the petrographic results indicate that in situ production of glassy pockets grossly similar to those in the shergottite eeta 79001 is possible from shock reverberations in the vicinity of a vug however the siting of the gases points to a more complex scenario in which spb gas and melt material were probably injected into eeta 79001

the oxygen isotope fractionation behaviour of kyanite in experiment and nature the oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures in the range between 625 and 775 c at 13 kbar because of low exchange rates the isotopic reaction was enhanced by polymorphic transformation of andalusite to kyanite with this experimental modification a close approach to equilibrium was reached in all runs the temperature dependence of the equilibrium fractionation is described by the equation 1000 ln ky cc 2 62 106 t 2 application of the experimental results to natural quartz kyanite garnet assemblages indicates the preservation of the oxygen isotope composition of kyanite acquired during its formation reflecting its extremely low oxygen diffusivity this refractory behaviour restricts the use of kyanite for thermometry but opens the possibility to use its o isotope composition as an indicator for recognition of polymetamorphic rock histories and reconstruction of the prograde evolution of a metamorphic sequence

a nitrogen and argon stable isotope study of allan hills 84001 implications for the evolution of the martian atmosphere the abundances and isotopic compositions of n and ar have been measured by stepped combustion of the allan hills 84001 alh 84001 martian orthopyroxenite material described as shocked is n poor n approximately 0 34 ppm delta 15n approximately 23 although during stepped combustion 15n enriched n delta 15n approximately 143 is released in a narrow temperature interval between 700 degrees c and 800 degrees c along with 13c enriched c delta 13c approximately 19 and 40ar cosmogenic species are found to be negligible at this temperature thus the isotopically heavy component is identified in part as martian atmospheric gas trapped relatively recently in the history of alh84001 the n and ar data show that alh84001 contains species from the martian lithosphere a component interpreted as ancient trapped atmosphere in addition to the modern atmospheric species and excess 40ar from k decay deconvolution of radiogenic 40ar from other ar components on the basis of end member 36ar 14n and 40ar 36ar ratios has enabled calculation of a k ar age for alh 84001 as 3 5 4 6 ga depending on assumed k abundance if the component believed to be martian palaeoatmosphere was introduced to alh 84001 at the time the k ar age was set then the composition of the atmosphere at this time is constrained to delta 15n or 200 40ar 36ar or 17 x 10 5 in terms of the petrogenetic history of the meteorite alh 84001 crystallised soon after differentiation of the planet may have been shocked and thermally metamorphosed in an early period of bombardment and then subjected to a second event this later process did not reset the k ar system but perhaps was responsible for introducing recent atmospheric gases into alh 84001 and it might mark the time at which alh 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages

martian xenon components in shergotty mineral separates locations sources and trapping mechanisms isotopic signatures and concentrations of xenon have been measured in shergotty mineral separates by laser step heating martian atmosphere and martian interior xenon are present as is a spallation component martian atmospheric xenon is 510 times more concentrated in opaque minerals magnetite ilmenite and pyrrhotite and maskelynite than in pyroxenes perhaps reflecting grain size variation this is shown to be consistent with shock incorporation a component consisting of solar xenon with a fission contribution similar to components previously identified in martian meteorites and associated with the martian interior is best defined in the pyroxene dominated separates this component exhibits a consistent 129xe 129xe 132xe 1 2 excess over solar planetary 129xe 132xe 1 04 we suggest that gas present in the melt perhaps a mixture of interior xenon and martian atmosphere was incorporated into the pyroxenes in shergotty as the minerals crystallized

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