chemical and isotopic characteristics of the didwana rajod h5 chondrite the mineralogical and chemical characteristics of the didwana rajod meteorite are described the mean mineral composition is found to be olivines fo83 2 pyroxenes en83 5wo0 7fs15 8 and feldspar is mainly oligoclase oxygen isotopic analysis shows 18o 3 8 deg and 17o 2 59 deg the nitrogen content of didwana rajod is about 2 ppm with 15n 3 4deg based on microscopic chemical isotopic and electron probe microanalysis the meteorite is classified as h5 chondrite cosmogenic tracks radionuclides and the isotopic composition of rare gases were also measured in this meteorite the track density in olivines varies in a narrow range with an average value of 6 5 0 5 x 105 cm2 for four spot samples taken at the four corners of the stone the cosmic ray exposure age based on neon and argon is 9 8 ma 22na 26al 0 94 is lower than the solar cycle average value of about 1 5 and is consistent with irradiation of the meteoroid to lower gcr fluxes as expected at the solar maximum the track density rare gas isotopic ratios 60co activity and other radionuclide data are consistent with a preatmospheric radius of about 15 cm corresponding to a mass of about 50 kg the cosmogenic properties are consistent with a simple exposure history in the interplanetary space

effects of experimental aqueous alteration on the abundances of argon rich noble gases in the ningqiang carbonaceous chondrite ar rich noble gases the so called subsolar noble gases are a major component of heavy primordial noble gases in unequilibrated ordinary chondrites and some classes of anhydrous carbonaceous chondrites whereas they are almost absent in hydrous carbonaceous chondrites that suffered extensive aqueous alteration to understand the effects of aqueous alteration on the abundance of ar rich noble gases we performed an aqueous alteration experiments on the ningqiang type 3 carbonaceous chondrite that consists entirely of anhydrous minerals and contains ar rich noble gases powdered samples and deionized neutral water were kept at 200 c for 10 and 20 days respectively mineralogical analyses show that during the 10 day alteration serpentine and hematite formed at the expense of olivine low ca pyroxene and sulfide noble gas analyses show that the 10 day alteration of natural ningqiang removed 79 of the primordial 36ar 68 of the 84kr and 60 of the 132xe but only 45 of the 4he and 53 of the primordial 20ne calculated elemental ratios of the noble gases removed during the 10 day alteration are in the range of those of ar rich noble gases these results indicate that ar rich noble gases are located in materials that are very susceptible to aqueous alteration in contrast heavy primordial noble gases remaining in the altered samples are close to q gas in elemental and isotope compositions this indicates that phase q is much more resistant to aqueous alteration than the host phases of ar rich noble gases in the 20 day sample the mineralogical and noble gas signatures are basically similar to those of the 10 day sample indicating that the loss of ar rich noble gases was completed within the 10 day alteration our results suggest that almost all of the ar rich noble gases were lost from primitive asteroids during early low temperature aqueous alteration

trapped xenon in ordinary chondrites a trapped component of heavy noble gates representing a distinct solar system presumably asteroid belt reservoir is known to be concentrated in carbonaceous carriers of chondritic meteorites the isotopic signature of trapped xe in separates of the h4 chondrite forest vale fv was determined by combusting its carrier phases at 600 c in oxygen discriminating against in situ produced nucleogenic components which are released above 600 c the isotopic abundances of fv combustion xe fvc xe are compared to signatures of bulk trapped xe in chondritic meteorites we conclude that fvc xe represents the predominant trapped component in ordinary chondrites oc for which we adopt the term oc xe its isotopic signature differs from xe in ureilites in average carbonaceous chondrites in earth s atmosphere and in the solar wind additional minor xe components were identified in type 3 chondrites and in the metal phase of chondrites we discuss relationships among solar system xe reservoirs and show that oc xe signature is consistent with a mixture of hl xe with slightly mass fractionated solar type xe

degassing of meteorite parent bodies gas permeability of three chondrites was measured a typical time for degassing of a 100 km radius parent body was calculated based on these permeability values it was found that an ordinary chondrite parent body would act as an open system during the metamorphic period 100 m y while an enstatite chondrite parent body would act as a closed system the possibility that volatile element concentrations in chondrites are controlled by permeability is discussed

the shallowater aubrite evidence for origin by planetesimal impacts shallowater is the only known unbrecciated igneous aubrite enstatite achondrite it is a coarse grained orthopyroxenite consisting of in vol poikilitic orthoenstatite crystals 80 up to 4 5 cm in size which contain as inclusions and in the interstices xenoliths of an assemblage of twinned low ca clinoenstatite 1 forsterite 2 9 plagioclase 2 5 metallic fe ni 3 3 troilite 2 9 schreibersite 0 4 weathered opaques 8 and traces of niningerite and oldhamite conclusions 1 shallowater is of igneous origin 2 shallowater could not have formed by internal igneous nor by impact melting processes either on the h or l enstatite chondrite or aubrite parent bodies instead shallowater appears to be a sample of yet a fourth enstatite type asteroid 3 shallowater experienced an extraordinarily complex and unusual three stage cooling history as determined by mineral stability considerations and modelling of micro structural evolution as a function of cooling rate stage 1 very fast cooling from 1 580 c to somewhere above 712 c at a rate of 100 c hour through 1000 c above 1000 c the rate was probably much faster stage 2 very slow cooling annealing from 712 to 680 c at a rate of 7 5 c 106 y stage 3 fast cooling from 680 to 600 c at a rate of 0 5 c day and from 600 to 300 c at a rate of 0 4 c day 4 this complex cooling history suggests an equally unusual origin for shallowater as follows a completely or partly molten asteroid of nearly pure enstatite composition was broken up by low velocity impact with a solid e like object the melt cooled very fast stage 1 due to incorporation of cold 20 projectile debris the xenoliths fragments reassembled into a rubble pile body while t was 712 c and deeply buried materials like the object that is now shallowater cooled very slowly from 712 to 680 c stage 2 the anneal of stage 2 requires burial at a depth of 40 km on a 100 km diameter asteroid excavation from this depth by impact to account for the fast cooling of stage 3 can be accounted for in two scenarios scenario 1 during catastrophic impact the shallowater object could have been by chance near the surface within 10 m of a very large fragment thus accounting for the fast cooling and for surviving for 4 5 109 y scenario 2 the shallowater object may have been excavated by break up and subsequently buried near the surface of a gravitationally reassembled body this would require yet a second break up and reassembly episode 5 the xenoliths represent an enstatite like meteorite type unknown as an individual fall not unexpected for a rock type from an asteroid that appears to have been largely destroyed early in the history of the solar system

compositional differences in enstatite chondrites based on carbon and nitrogen stable isotope measurements carbon and nitrogen abundance and isotopic compositions from four eh4 one eh5 five el6 chondrites and one aubrite were determined by using stepped pyrolysis n only and combustion n and c extractions in attempts to distinguish the components present carbon contents range from 0 15 to 0 70 wt with no systematic relationship between carbon content and meteorite group or petrologic type whole rock 13c values range from 28 5 to 4 1 most c occurs as graphite and when temperature steps above 700 c are considered there is a difference between eh4 5 13c 9 1 to 5 8 and el6 chondrites 13c 6 7 to 4 2 carbon in bustee aubrite is isotopically lighter 13c 24 than in any enstatite chondrite nitrogen occurs as osbornite sinoite and in isostructural substitution for oxygen in silicate lattice sites nitrogen abundances and isotopic compositions are more variable than c due to the heterogenous distribution of n bearing minerals three el6 s containing osbornite have higher n concentrations than other type 6 enstatite chondrites sinoite where present is depleted in 15n relative to osbornite nitrogen in the bustee aubrite has a similar abundance and 15n value to those of el6 s again dominated by the presence of osbornite in addition to the refractory c and n bearing minerals there is also organic material largely terrestrial contamination and evidence for at least two exotic components the first is a host for xe hl and is characterized by 13c 47 and 15n 73 whereas the second is less well defined but is marked by 15n 269

acfer 182 and paired samples an iron rich carbonaceous chondrite similarities with alh85085 and relationship to cr chondrites three samples of a new fe rich chondrite were found in the sahara in 1990 and 1991 acfer 182 acfer 207 acfer 214 the samples are paired and the meteorite will be designated as acfer 182 the chondrite is chemically texturally and mineralogically similar to the allan hills meteorite alh85085 one important difference between the two meteorites is the smaller average chondrule size in alh85085 the major components of acfer 182 in decreasing abundance are 1 1 highly altered by terrestrial weathering matrix 2 2 mineral and polymineralic silicate fragments and aggregates 3 3 chondrule fragments 4 4 chondrules 5 5 metal 6 6 fine grained dark inclusions the abundance of chondrules is lower and the average chondrule size 90 m smaller than in most other chondrites chondrule fragments are often so large that they cannot be derived from the present chondrule population apparently size sorting has prevented accumulation of the larger parent chondrules several spectacular ca al rich inclusions were found rich in ca dialuminate hibonite or zr y sc bearing phases the chemical composition of acfer 182 and of alh85085 are almost indistinguishable major chemical signatures are 1 1 uniform enrichment of fe and other nonvolatile metals relative to ci chondrites by about 70 2 2 absence of enrichment in refractory lithophiles characteristic of most type 2 and 3 carbonaceous chondrites 3 3 strong depletion of volatile and moderately volatile elements based on the oxygen isotopic composition the chemical composition and the abundances of chondrules and matrix acfer 182 should be classified as a carbonaceous chondrite considering their affinity to carbonaceous chondrites and their high bulk iron content the two meteorites acfer 182 and alh85085 are designated as ch chondrites there are mineralogical and chemical similarities among acfer 182 alh85085 and cr chondrites which distinguish these meteorites from other types of carbonaceous chondrites 1 1 low feo contents of olivine and pyroxene and correspondingly high metal contents 2 2 high cr content in olivine 3 3 abundant fine grained dark inclusions 4 4 abundant ca dialuminate caal4o7 in cais 5 5 similarities in oxygen isotopic composition 6 6 low contents of moderately volatile elements 7 7 low refractory element contents 8 8 presence of a unique component of subsolar rare gases these observations suggest similar conditions of formation for the components of these meteorites a single common parent body is unlikely in view of the differences in chemical composition and in the size distribution of individual components

isotopic composition of xenon and krypton in silicate graphite inclusions of the el taco campo del cielo iab iron meteorite noble gases extracted by temperature stepped pyrolysis from acid resistant silicate schreibersite and graphite residues of inclusions from the iab iron meteorite el taco campo del cielo have been analyzed for their isotopic composition the concentrations of spallogenic light gases agree with previous data on adjacent specimens nominal feldspar and pyroxene fractions have lost up to 80 of their 3he during or towards the end of the exposure of el taco to the cosmic radiation in olivine the 3ne21ne and nepne ratios are as low as 2 18 0 01 and 1 09 0 03 respectively presumably because the silicates were irradiated within a feni matrix under extremely heavy shielding argon kr and xe in the silicates are dominated by a trapped planetary component with 100 36ar132xe 700 and 1 7 84kr132xe 2 2 xenon released from the silicates at extraction temperatures 1000 c is isotopically close to ureilite xe while the high t xe from graphite and schreibersite is unlike any of the presently well established types of xe the isotopic composition of this xe can be generated as a mixture of mass fractionated u xe with light isotopes depleted by 2 2 0 1 per atomic mass unit and 244pu xe the fission component 10 in the case of 136xe is not due to in situ production it must have been added prior to incorporation of the xe into the el taco parent body and presumably underwent the mass fractionation process together with u xe from the silicates 127i n produced 128xe and radiogenic 129xe are released together with the same 128xe 129xe ratio in nominal olivine pyroxene and feldspar although the maximum release from pyroxene occurs about 300 c higher than from feldspar from this the cooling rate of silicates for the temperature range 1500 1200 c is deduced to be 100 c per million years the 80kr82kr ratio of 79 81br n produced 80 82kr is 2 86 0 04 in agreement with the value found in inclusions of the iab linwood but higher than observed in almost all stone meteorites

itqiy a study of noble gases and oxygen isotopes including its terrestrial age and a comparison with zaklodzie we report noble gas oxygen isotope 14c and 10be data of itqiy as well as noble gas 14c and 10be results for zaklodzie both samples have been recently classified as anomalous enstatite meteorites and have been compared in terms of their mineralogy and chemical composition the composition of enstatite and kamacite and the occurrence of specific sulfide phases in itqiy indicate it formed under similar reducing conditions to those postulated for enstatite chondrites the new results now seem to point at a direct spatial link the noble gas record of itqiy exhibits the presence of a trapped subsolar component which is diagnostic for petrologic types 4 6 among enstatite chondrites the concentration of radiogenic 4he is very low in itqiy and indicates a recent thermal event its 21ne cosmic ray exposure age is 30 1 3 0 ma and matches the most common age range of enstatite chondrites mostly el6 chondrites but not that of zaklodzie itqiy s isotopic composition of oxygen is in good agreement with that observed in zaklodzie as well as those found in enstatite meteorites suggesting an origin from a common oxygen pool the noble gas results on the other hand give reason to believe that the origin and evolution of itqiy and zaklodzie are not directly connected itqiy s terrestrial age of 5800 500 years sheds crucial light on the uncertain circumstances of its recovery and proves that itqiy is not a modern fall whereas the 14c results from zaklodzie suggest it hit earth only recently

extinct i129 in c3 chondrites abstract eight c3 chondrites were examined by the i129 xe129 dating method to see whether their i xe ages better initial i 129 i 127 ratios r0 correlate with any other properties the r0 s range from 1 60 10 4 to 1 09 10 4 corresponding to i xe ages from 2 0 myr before to 6 7 myr after murchison magnetite three c3o s lance felix ornans have essentially indistinguishable r0 s of 1 41 0 13 to 1 17 0 10 10 4 the fourth c3o warrenton is undatable owing to homogenization of radiogenic and trapped xe four c3v s show a distinct spread vigarano and grosnaja are highest r0 1 60 0 07 and 1 57 0 14 10 4 mokoia is intermediate and kaba is lowest r0 1 38 0 06 and 1 09 0 10 10 4 literature values for allende place it near kaba these r0 s correlate inversely with 4 other properties i br and cd content and olivine composition both percent mean deviation pmd and proportion of iron poor olivine grains 2 fayalite it is difficult to accept the 9 myr spread in r0 as a true age reflecting either nebular or parent body processes this time span is more than an order of magnitude longer than the lifetime of the solar nebula inferred from astronomical evidence nor does the degree of thermal metamorphism which is slight for c3 s anyway correlate with r0 a more plausible interpretation is that the variations in r0 reflect mainly isotopic heterogeneity of iodine the simplest model that accounts for the correlations with r0 involves mixing of two iodine components in the solar nebula associated with gas and grains respectively the second of lower i 129 i 127 ratio predominated at later times and thus became enriched in late formed meteorites along with other volatiles such as cd and br the low fe content and large pmd of olivine may reflect either less metamorphism owing to shallow location in the parent body or greater reduction of fe2 during chondrule formation

actinide microdistributions in the enstatite meteorites oldhamite is a major th and u bearing phase in the enstatite meteorites oldhamite from e 6 chondrites has mean th and u abundances of 1550 80 ppb th and 410 20 ppb u with th u 3 8 2 with the exception of ferroan alabandite which contains 25 1 ppb u no other th or u enriched phases were located in the e 6 chondrites and nearly all of the total rock th and u can be accounted for by oldhamite in khairpur e6 excess fossil fission tracks were observed in enstatite grains in contact with oldhamite which indicates the presence of 244 pu in oldhamite oldhamite from st mark s e5 and abee e4 also shows actinide enrichments but at levels about half the e 6 results niningerite in abee contains 45 5 ppb u and due to its high reported modal abundance is an important u reservoir in abee the u content of oldhamite from the aubrite pena blanca spring is 1920 100 ppb all th u values measured in this study cluster tightly around a value of 4 which indicates a lack of th u fractionation in both oldhamite and in the enstatite meteorites themselves this lack of fractionation along with the presence of 244 pu in oldhamite and reported rare earth enrichments also in oldhamite suggests that the enstatite chondrites may be well suited for pu u chronology and for providing the initial pu u value in the early solar system

paired renazzo type cr carbonaceous chondrites from the sahara ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite renazzo were recovered at two locations of the sahara acfer 059 087 097 114 139 186 187 209 270 and el djouf 001 although the el djouf location is more than 500 km away from the acfer location all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry noble gas record and similar 26al contents the acfer el djouf meteorite is classified as a cr renazzo type carbonaceous chondrite this group presently comprises three non antarctic members al rais renazzo acfer el djouf and five antarctic meteorites the major lithological components of the acfer el djouf meteorite are large chondrules up to 1 cm in size mean diameter 1 0 0 6 mm chondrule and mineral fragments ca al rich inclusions feni metal about 8 10 vol and dark inclusions embedded in a fine grained fragment bearing groundmass mineral compositions of the ten acfer el djouf samples are similar to those of other cr chondrites most of the ca al rich inclusions are below 300 m in size and rich in melilite and spinel in some cais the rare phase caal4o7 is dominant fo rich cr bearing olivine fa0 4 and enstatite fs0 4 are the major phases of the chondrite the meteorite is mildly shocked with a shock stage of s2 indicating a peak shock pressure of 5 10 gpa for the bulk meteorite the oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the acfer el djouf samples are very similar to those of the other cr type chondrites the major element composition of the acfer el djouf meteorite is indistinguishable from cr chondrites when compared to renazzo the acfer el djouf samples however have systematically lower contents of the moderately volatile elements zn ga as au sb and se and the highly volatile elements br c and n this is thought to reflect primary differences between renazzo and the acfer el djouf meteorite

shock effects in eh6 enstatite chondrites and implications for collisional heating of the eh and el parent asteroids abstract of the six chondrites that were listed as eh6 or eh6 an during the course of this study we confirm the eh classification of y 8404 y 980211 and y 980223 and the eh an classification of y 793225 two chondrites a 882039 and y 980524 are reclassified as el the former contains ferroan alabandite and both contain kamacite with 1 wt si all of the meteorites contain euhedral enstatite grains surrounded by metal sulfide although this texture is rare in y 793225 consistent with enstatite crystallizing from a mixed melt all contain enstatite with 0 5 mg

pyroxene structures cathodoluminescence and the thermal history of the enstatite chondrites in order to explore the thermal history of enstatite chondrites we examined the cathodoluminescence cl and thermoluminescence tl properties of 15 eh chondrites and 21 el chondrites including all available petrographic types both textural types 3 6 and mineralogical types alpha delta the cl properties of el3 alpha and eh3 alpha chondrites are similar enstatite grains high in mn and other transition metals display red cl while enstatite with low concentrations of these elements show blue cl a few enstatite grains with greater than 5 wt feo display no cl in contrast the luminescent properties of the metamorphosed eh chondrites are very different from those of metamorphosed el chondrites while the enstatites in metamorphosed eh chondrites display predominantly blue cl the enstatites in metamorphosed el chondrites display a distinctive magenta cl with blue and red peaks of approximately equal intensity in their spectra the tl sensitivities of the enstatite chondrites correlate with the intensity of the blue cl and unlike other meteorite classes are not simply related to metamorphism the different luminescent properties of metamorphosed eh and el chondrites cannot readily be attributed to compositional differences but x ray diffraction data suggests that the enstatite in eh5 gamma delta chondrites is predominantly disordered orthopyroxene while enstatite in el6 beta chondrites is predominantly ordered orthopyroxene the difference in thermal history of metamorphosed el and eh chondrites is so marked that the use of single petrographic types is misleading and separate textural and mineralogical types are preferable our data confirm earlier suggestions that metamorphosed eh chondrites underwent relatively rapid cooling and the metamorphosed el chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field

holocene coastal dune development and environmental changes in apulia southern italy abstract the coastal area of southern apulia is characterised by marine deposits of pleistocene and holocene ages it shows the effects of different phases of coastal morphology evolution during the middle and upper pleistocene a number of marine terraces were shaped in some places they are characterised by thin beach deposits along with a dune belt and relative back dune deposits two important morphogenetic phases occurred during the holocene the former was characterised by deposition of beach deposits placed slightly above present mean sea level and by formation of dune belts which were radiometrically aged about 6000 years bp this event marks the end of the rapid postglacial transgression that occurred during the holocene climatic optimum during the younger phase dated at about 2500 years bp deposition of aeolian sands occurred archaeological and morphological evidences suggest that this phase should be related to a low sea level stand followed by a slow sea level rise up to the present position and by humid temperate climatic conditions the collected data about the holocene dune belts occurring along the apulian coastline suggest that main phases of dune development could be related to the effects of sea level changes climatic conditions and in a subordinate way to human activity

prediction of sediment thickness in the norwegian greenland sea from gravity inversion 1 we explore the feasibility of inverting freely available altimetry derived gravity grids for sediment thickness on oceanic crust a four layer earth model is adopted assuming that the gravity signal from the base of the sedimentary layer can be fully isolated from the observed free air gravity the following additional data are required 1 shipboard bathymetry for reliable bouguer correction 2 oceanic crustal ages to correct for gravity anomalies related to the thermal history of lithospheric breakup and seafloor spreading and 3 some wide angle seismic observations of sediment thickness a fixed relationship between the base of the sedimentary layer and the moho is also required because of limited gravity resolution at large depths the final inversion setup searches for three control parameter values density of uppermost sediments density of oceanic crystalline crust and thermal diffusivity of mantle rock that minimize misfit between the earth model and observations applied to the norwegian greenland sea the inversion successfully predicts locations of 20 25 km wide depocenters and crystalline crustal highs yet 1 km thickness errors are common even in well constrained areas the largest errors are associated with underplated crust active mid ocean ridges and the continent ocean boundary indicating locally incorrect assumptions of mantle thermal structure and crystalline crustal thickness the thicknesses of 4 km thick submarine fans are underpredicted probably because of too low sedimentary densities in the earth model if these limitations are acceptable or do not apply because of simple crustal structure gravity inversion may be used for mapping regional sedimentary patterns e g in the arctic ocean

differences in isotopic composition of carbonaceous components in enstatite chondrites abstract carbon stable isotopic composition of the major carbonaceous component in enstatite chondrites varies with petrologic type investigation of a suite of hf hcl resistant residues has shown that this variation is due to an inherent difference in 13 c of the carbon and is not a result of the presence of small amounts of isotopically anomalous carbon bearing components these latter do occur in type eh3 and eh4 chondrites in concentrations similar to those found in c1 and c2 carbonaceous chondrites combustion of the major carbon component apparently elemental carbon not necessarily graphite occurs at relatively higher temperatures in enstatite chondrites of increasing petrologic type this is considered to reflect an increase in crystallinity or ordering of the carbonaceous component and is a measure of the degree of thermal processing to which the meteorites have been subjected during accretion and or metamorphism

new noble gas data of primitive and differentiated achondrites including northwest africa 011 and tafassasset this work reports on the noble gas inventory of 3 new acapulcoites 3 brachinites 2 new eucrites from the dar al gani region in libya the unique achondrite dar al gani dag 896 from the same locality the new eucrite like achondrite northwest africa nwa 011 and the controversial sample tafassasset we determined cosmic ray exposure and gas retention ages evaluated shielding conditions and discuss the trapped noble gas component of the specimens all exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters shielding conditions vary suggesting substantial shielding for all 3 brachinites and tafassasset we cannot exclude however that the mg rich composition of brachinites simply simulates heavy shielding regarding the trapped component we found q like compositions only for the acapulcoite thiel mountains til 99002 the brachinite elephant moraine eet 99402 yields a high subsolar 36ar 132xe ratio of 400 along with a slightly elevated 84kr 132xe ratio indicating minor atmospheric contamination all the other samples particularly the eucrite dag 983 are characterized by clearly elevated ar kr xe ratios due to significant terrestrial alteration tafassasset exhibits noble gas parameters that are different from those of cr chondrites including a relatively high cosmic ray exposure age the absence of a solar component low 132xe concentrations a low trapped 36ar 132xe ratio of 30 and a noticeable amount of radiogenic 129xe similar attributes have been observed for some primitive achondrites these attributes are also consistent with the metamorphic character of the sample we therefore consider tafassassets noble gas record to be inconclusive as to its classification primitive achondrite versus metamorphosed cr chondrite

cosmic ray exposure ages of the ordinary chondrites and their significance for parent body stratigraphy 21ne cosmic ray exposure ages have been calculated from literature data for 201 h 203 l and 38 ll chondrites corrected for shielding differences when possible the distributions of exposure ages again show the familiar peaks at 4 5 and 20 myr for the h s but no outstanding events for the l s and ll s if the l chondrite distribution is interpreted as a series of discrete events then at least 6 peaks between 1 and 35 myr are needed to model it the observations that every petrologic type occurs in every large peak and that even the higher petrologic types contain solar wind gases suggest that the parent bodies have been fragmented and reassembled into a megabreccia for the h chondrites both large and small peaks contain about 15 solar gas bearing meteorites which could mean that surface material has been mixed to depths represented by the largest event on the order of a kilometer in contrast only 3 of the l s contain solar wind which may be related to breakup of their parent planet those l s with especially low radiogenic he u th he ages 1 ae tend to have low exposure ages their distribution may be biased by a subgroup that had orbits coupling short capture lifetimes with significant solar heating

fractionation of highly siderophile and chalcogen elements in components of eh3 chondrites abstract abundances of highly siderophile elements hse re platinum group elements and au chalcogens te se and s 187os 188os and the major and minor elements mg ca mn fe ni and co were determined in the components of sahara 97072 eh3 find and kota kota eh3 find in order to understand the element fractionation processes in a 187re 187os isochron diagram most magnetic components lie close to the 4 56 ga iiia iron meteorite isochron whereas most other components show deviations from the isochron caused by late redistribution of re presumably during terrestrial weathering metal and sulfide rich magnetic fractions and metal sulfide nodules are responsible for the higher 187os 188os in bulk rocks of eh chondrites compared to ci chondrites the hse and chalcogens are enriched in magnetic fractions relative to slightly magnetic and nonmagnetic fractions and bulk compositions indicating that fe ni metal is the main host phase of the hse in enstatite chondrites hse abundance patterns indicate mixing of two components a ci chondrite like end member and an au enriched end member because of the decoupled variations of au from those of pd or the chalcogens the enrichment of au in eh metal cannot be due to metal sulfide silicate partitioning processes metal and sulfide rich nodules may have formed by melting and reaction of pre existing refractory element rich material with volatile rich gas a complex condensation and evaporation history is required to account for the depletion of elements having very different volatility than au in eh chondrites the depletions of te relative to hse se and s in bulk eh chondrites are mainly caused by the depletion of te in metal s se and s mn are lower than in ci chondrites in almost all components and predominantly reflect volatility controlled loss of sulfur the latter most likely occurred during thermal processing of dust in the solar nebula e g during chondrule formation followed by the non systematic loss of s during terrestrial weathering

noble gases in individual chondrules of the allende cv3 chondrite we analyzed noble gases in nine individual chondrules an assemblage of small chondrules and four whole rock samples of the allende cv3 chondrite major elements were also determined for five chondrules the cosmic ray exposure ages are calculated from cosmogenic 3he to be 5 17 0 38 and 5 15 0 25 myr for the averages of the chondrules and whole rocks respectively showing no significant pre exposure evidence for the studied chondrules large amounts of 36ar 80 82kr and 128xe produced by neutron capture are observed in most samples the abundances of these nuclides are correlated among the samples the epithermal neutron flux and neutron slowing down density are calculated based on 80kr n from which a sample depth of about 30 cm can be calculated the measured chondrules contain variable amounts of radiogenic 129xe the abundance ratios of radiogenic 129xe to neutron capture produced 128xe are rather constant among the studied chondrules four chondrules give more precise ratios at the high temperature fractions ranging from 1920 80 to 2280 140 which corresponds to a time difference of 3 9 2 4 myr it is noticeable that most chondrules also contain 244pu derived fission xe the average 244pu 238u ratio for nine chondrules is 0 0069 0 0018 which agrees well with the preferred ratio reported for chondrites

noble gases in enstatite chondrites ii the trapped component the trapped noble gas record of 57 enstatite chondrites e chondrites has been investigated basically two different gas patterns have been identified dependent on the petrologic type all e chondrites of type 4 to 6 show a mixture of trapped common chondritic rare gases q and a subsolar component range of elemental ratios for e4 6 chondrites 36ar 132xe 582 270 and 36ar 84kr 242 88 e3 chondrites usually contain q gases but also a composition with lower 36ar 132xe and 36ar 84kr ratios which we call sub q 36ar 132xe 37 0 18 0 and 36ar 84kr 41 7 18 1 the presence of either the subsolar or the sub q signature in particular petrologic types cannot be readily explained by parent body metamorphism as postulated for ordinary chondrites we therefore present a different model that can explain the bimodal distribution and composition of trapped heavy noble gases in e chondrites trapped solar noble gases have been observed only in some e3 chondrites about 30 of each group eh3 and el3 chondrites amounting to 9 of all analyzed e chondrites show the solar signature notably only one of those meteorites has been explicitly described as a regolith breccia

noble gases in enstatite chondrites i exposure ages pairing and weathering effects cosmic ray exposure ages calculated from cosmogenic noble gas nuclides are reported for 57 enstatite e chondrites 43 of them were measured for the first time with a total of 62 individual e chondrites literature and this data corrected for pairing the observed spectrum of ages ranges between 0 07 and 66 ma three clusters seem to develop at about 3 5 8 and 25 ma respectively since the uncertainty of ages is estimated to be 20 in contrast to 10 to 15 for ordinary chondrites and the number of examined samples is still comparatively small these peaks have to be confirmed by more measurements regarding the two subgroups eh and el chondrites no systematic trend is apparent in the distribution of cosmic ray exposure ages several e chondrites yield significantly lower 38ar ages compared to those calculated from cosmogenic 3he and 21ne for these e chondrites we suggest a reduction of cosmogenic 38ar as a result of weathering in order to prove the possible influence of terrestrial alteration on the cosmogenic noble gas record of e chondritic material we simulated terrestrial weathering in an experiment of 12 weeks duration the treatment showed that a significant amount of cosmogenic 38ar is lost on earth by the influence of water

noble gas record and cosmic ray exposure history of the new co3 chondrite moss comparison with lance and other co chondrite falls abstract the moss meteorite is the first co chondrite fall after a time period of 70 yr and the least terrestrially contaminated member of its group its cosmic ray exposure cre age t3 13 5 ma t21 14 6 ma is distinct among co chondrites and within witnessed falls is the shortest after lance which we have reanalyzed gas retention ages are approximately 3 95 109 yr u th he and approximately 4 43 109 yr k ar respectively trapped ar kr and xe are present in moss in abundances typical for co chondrites with planetary elemental and isotopic compositions presence of hl xenon from presolar diamonds is observed in the stepwise release analysis of lance it may also be present in moss but it is difficult to ascertain in single step bulk analyses it follows from our new data combined with a survey of the literature that the abundance of trapped gases in co chondrites is not a good indicator of their petrological subtype

a primitive dark inclusion with radiation damaged silicates in the ningqiang carbonaceous chondrite a petrologic and tem study of a remarkable dark inclusion di in the ningqiang cv3 chondrite reveals that it is a mixture of highly primitive solar nebula materials the di contains two lithologies the first lithology a contains micron sized olivine and pyroxene grains rimmed by amorphous materials with compositions similar to the underlying crystalline grains the second lithology b appears to preserve the mineralogy of lithology a before formation of the amorphous rims overall the ningqiang di appears to record the following processes 1 formation condensation and fe enrichment of olivine crystals in the nebula with compositions of fo42 62 2 irradiation resulting in amorphitization of the olivine and pyroxene to varying degrees 3 partial annealing resulting in formation of fairly large euhedral olivine and pyroxene grains with remnant amorphous sharply bounded rims 4 in some cases prolonged annealing resulting in the formation of microcrystalline olivine or pyroxene rims the latter annealing would have been a natural consequence of irradiation near the critical temperature for olivine and 5 mixture of the above materials lithology a with nebular condensate high ca pyroxene and olivine which escaped nebular processing to become lithology b we suggest that the amorphous rims in lithology a formed in an energetic solar event such as a bi polar outflow or fu orionis flare

cosmic ray constancy and cosmogenic production rates in short lived chondrites abstract five chondrites with short cosmic ray exposure ages 26al and 53mn saturation values deduced from short lived chondrites alone agree within 20 with those deduced from all chondrites values of 21p based on 53mn and 26al are 0 30 0 03 and 0 46 0 05 respectively in h chondrites possible causes for the difference include half life errors data selection and a recent 2 5myr increase in the cosmic ray intensity

129i 127i variations among enstatite chondrites abstract this paper presents the 129i 127i composition for 11 different enstatite chondrites there is a well defined hiatus in iodine isotopic compositions separating the enstatite chondrites the hiatus correlates with a similar hiatus defined by variations in chemical composition both major and minor elements eh 4 5 chondrites have 129i 127i ratios 20 higher 4 m y older than el 6 chondrites the enstatite chondrites are the third meteorite group joining silicates in iab irons and c3v carbonaceous chondrites in which 129i 127i correlates with chemical composition within each enstatite chondrite group the variations in initial iodine isotopic composition is less than 4 comparable to the experimental resolution the 20 difference between eh and el may indicate a maximum iodine isotopic heterogeneity between the eh and el nebular reservoirs alternatively if eh and el chondrites evolved from a homogeneous iodine isotopic reservoir then the el group must have evolved 4 0 m y longer than the eh group and either in an environment with a much lower i xe ratio than presently observed or one which was open to the loss of radiogenic 129xe the latter case may imply a nebular environment and would therefore be consistent with the open system evolution required to produce the chemical hiatus the duration of subsequent evolution in the high i xe environment must have been 1 m y and probably represents thermal metamorphism in two different parent bodies

alh 85085 nitrogen isotope analysis of a highly unusual primitive chondrite alh 85085 is an unusual fine grained primitive chondrite which does not fit into any of the known meteorite classes it shows many chemical similarities to the equally unusual meteorites bencubbin weatherford and renazzo nitrogen isotope analysis shows that alh 85085 like bencubbin weatherford and renazzo contains highly 15 n enriched nitrogen indeed alh 85085 has the highest 15 n measured in any whole rock meteorite totalling to 858 but reaching 1497 in the 850 875 c temperature increment however the distribution of isotopically heavy nitrogen in alh 85085 is different from that observed for bencubbin thus precluding a direct relationship between these meteorites isotopically heavy nitrogen occurs in alh 85085 in two sites carbonaceous material 15 n ca 860 13 c ca 1 c n ca 65 75 and in fine grained fe ni metal or opaque chondritic matrix clasts 15 n ca 990 a third very 15 n enriched nitrogen carrier with 15 n 1500 might also be located in the matrix it is probable that there is only a single component with elevated 15 n 1500 and that it occurs in at least three discrete sites mixed with varying amounts of nitrogen having more isotopically normal 15 n 0 50 the identity of the hosts of the isotopically heavy nitrogen have not been fully determined but it is becoming clear that an increasing number of brecciated meteorites some of which do not seem to be related in other ways show evidence of having sampled a reservoir rich in 15 n this may be a result of the introduction of heavy nitrogen during brecciation its 15 n values and distribution throughout the meteorites brought about by mixing with variable amounts of more isotopically normal nitrogen and subsequent vaporization and re condensation processes

noble gases in e chondrites noble gas data are reported for 12 e chondrites combined with literature data they show that k ar ages are 4 ae for 14 out of 18 meteorites yet u th he ages are often shorter perhaps due to late mild reheating cosmic ray exposure ages differ systematically between types 4 and 6 with e4 s mostly below 16 myr and e6 s above 30 myr this may mean that the e chondrite parent body contains predominantly a single petrologic type on the 1 km scale of individual impacts in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites the heavy noble gases consist of at least two primordial components the usual planetary component 36ar132xe 80 and a less fractionated subsolar component 2700 36ar132xe 3800 the latter is found in highest concentration in the e4 chondrite south oman 36ar 760 10 8cc g 36ar132xe 2700 the isotopic compositions of both components are similar to typical planetary values indicating that some factor other than mass controlled the noble gas elemental ratios the heavy xe isotopes occasionally show some of the lowest 134xe132xe and 136xe132xe ratios measured in bulk chondrites suggestive of nearly fission free xe e g 136xe132xe 0 3095 0 0020 amounts of planetary gas in e4 e6 chondrites fall in the range for ordinary chondrites of types 4 6 but in contrast to the ordinary chondrites fail to correlate with petrologic type or volatile trace element contents another unusual feature of e chondrites is that primordial ne is present even in most 4 s and 5 s 20nep 1 to 7 10 8cc g with an isotopic composition consistent with planetary ne analyses of mineral separates show that the planetary gases are concentrated in an hf and hcl insoluble mineral similar to phase q the poorly characterized hno3 soluble carrier of primordial gases in carbonaceous and ordinary chondrites the subsolar gases on the other hand are located in an hcl and hno3 resistant phase possibly enstatite or a minor phase included in enstatite much of the 129xer 50 for e4 s 70 for e6 s is in hcl resistant but hf soluble sites suggestive of a silicate a similar subsolar component may be responsible for the high 36ar132xe ratios of some c3 s unequilibrated ordinary chondrites and the unique aubrite shallowater the planet venus also has a high arkr ratio well above the planetary range and hence may have acquired its noble gases from an e chondrite like material similar to south oman

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar