implications of the carbonaceous chondrite mn cr isochron for the formation of early refractory planetesimals and chondrules abstract an excellent 53 mn 53 cr isochron for bulk ci cm co cv cb and ungrouped c3 chondrites seems to suggest that each carbonaceous chondrite group acquired its mn cr ratio 4568 1 myr ago this age is indistinguishable from the age of ca al rich inclusions cais which is considered to be the start of the solar system t 0 however carbonaceous chondrites were not assembled until at least 1 5 5 myr after t 0 to judge by the 207 pb 206 pb and 26 al 26 mg ages of the chondrules within them and by the fact that they were not melted by heat from the decay of 26 al presumably therefore these meteorites inherited their bulk mn cr isochron from precursor materials which experienced mn cr fractionation at t 0 as a possible physical mechanism for how the isochron was established initially and later inherited by the carbonaceous chondrites we propose the rapid formation at t 0 of planetesimals that were variably depleted in moderately volatile elements and hence had variably low mn cr the planetesimals and the undepleted high mn cr primitive dust from which they were made shared the same initial e 53 cr and therefore evolved on an isochron we suggest that later impact disruption of the planetesimals produced dusty debris which became mixed in various proportions with unprocessed high mn cr dust before accreting to the carbonaceous chondrite parent bodies with mixing in a closed system the isochron was unchanged we infer that some debris rich material was converted to chondrules prior to accretion the chondrules could have been formed by flash melting of the mixed dust or could instead have been made directly by the impact splashing of molten planetesimals or by condensation from impact generated vapor plumes

the meteoritical bulletin no 81 1997 jul meteoritical bulletin no 81 lists 181 new meteorites noteworthy among these are a new lunar meteorite dar al gani 262 four observed falls dong ujimqin qi galkiv mount tazerzait and piplia kalan four irons albion great sand sea 003 hot springs and mont dieu two mesosiderites dong ujimqin qi and lamont an acapulcoite fro 95029 a eucrite piplia kalan two probably paired ureilites dar al gani 164 and 165 an r chondrite hammadah al hamra 119 an ungrouped type 3 chondrite hammadah al hamra 180 a highly unequilibrated ordinary chondrite wells ll3 3 and a variety of carbonaceous and unequilibrated ordinary chondrites from libya and antarctica all italicized abbreviations refer to addresses listed in the appendix

oxygen isotope compositions of chondrule phenocrysts and matrix grains in kakangari k grouplet chondrite implication to a chondrule matrix genetic relationship abstract to investigate a possible relationship between chondrules and matrix we studied mineralogy mineral chemistry and in situ o isotope compositions of chondrules clastic matrix grains and amoeboid olivine aggregates aoas in the kakangari k grouplet chondrite most olivines and low ca pyroxenes in the kakangari chondrules matrix and aoas have similar magnesium rich compositions fo 95 97 0 3 0 5 wt mno and en 90 96 respectively these rather uniform chemical compositions of the different chondritic components are likely due to partial fe mg mn equilibration during thermal metamorphism experienced by the host meteorite oxygen isotope compositions of olivine and low ca pyroxene grains in chondrules and matrix plot along a slope 1 line on a three o isotope diagram and show a range from 16 o enriched composition similar to that of the sun to 16 o depleted composition similar to the terrestrial o isotope composition most olivines and low ca pyroxenes in chondrules are 16 o poor and plot on or close to the terrestrial mass fractionation line mean 17 o values 2 standard deviations 0 0 0 8 and 0 2 0 9 for olivine and pyroxene respectively consistent with the previously reported compositions of bulk chondrules 17 o 0 16 0 70 in addition to these 16 o poor grains a coarse grained igneous rim surrounding a porphyritic chondrule contains abundant 16 o rich relict olivines 17 o 24 oxygen isotope compositions of olivines and low ca pyroxenes in matrix show a bimodal distribution 12 out of 13 olivine and 4 out of 17 pyroxene grains measured are similarly 16 o rich 17 o 23 5 2 9 others are similarly 16 o poor 17 o 0 1 1 7 due to slow oxygen self diffusion olivines and low ca pyroxenes largely retained their original oxygen isotope compositions the nearly identical o isotope compositions between the chondrule phenocrysts and the 16 o poor matrix grains suggest both chondrules and matrix of kakangari sampled isotopically the same reservoirs in addition the presence of abundant 16 o rich grains in matrix and the chondrule igneous rim suggests both components acquired similar precursor inventories these observations imply that chondrules and matrix in kakangari are genetically related in the sense that material that formed matrix was one of the precursors of chondrules and chondrules and some fraction of matrix experienced the same thermal processing event the 16 o enriched bulk matrix value compared to the bulk chondrules reported previously is likely due to presence of abundant 16 o rich grains in the kakangari matrix

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

the classification and complex thermal history of the enstatite chondrites we have carried out instrumental neutron activation analyses of 11 enstatite chondrites and electron microprobe analyses of 17 enstatite chondrites most of which were previously little described we report here the third known eh5 chondrite lew 88180 and an unusual el6 chondrite lew 87119 new data on four el3 chondrites alh 85119 eet 90299 pca 91020 and mac 88136 which is paired with mac 88180 and mac 88184 the second el5 chondrite til 91714 and an unusual metal rich and sulfide poor el3 chondrite lew 87223 the often discussed differences in mineral composition displayed by the eh and el chondrites are not as marked after the inclusion of the new samples in the database and the two classes apparently experienced a similar range of equilibration temperatures however texturally the el chondrites appear to have experienced much higher levels of metamorphic alteration than eh chondrites of similar equilibration temperatures most of the petrologic type criteria are not applicable to enstatite chondrites and unlike the ordinary chondrites texture and mineralogy reflect different aspects of the meteorite history we therefore propose that the existing petrologic type scheme not be used for enstatite chondrites we suggest that while textural type reflects peak metamorphic temperatures the mineralogical type reflects equilibration during postmetamorphic probably regolith processes unlike the ordinary chondrites and eh chondrites el chondrites experienced an extensive low temperature metamorphic episode there are now a large number of enstatite meteorite breccias and impact melts and apparently surface processes were important in determining the present nature of the enstatite chondrites

lunar meteorites from oman abstract sixty named lunar meteorite stones representing about 24 falls have been found in oman in an area of 10 7 103 km2 in southern oman lunar meteorite areal densities average 1 g km 2 all lunar meteorites from oman are breccias although two are dominated by large igneous clasts a mare basalt and a crystalline impact melt breccia among the meteorites the range of compositions is large 9 32 al2o3 2 5 21 1 feo 0 3 38 g g 1 sm and 1 to 22 5 ng g 1 ir the proportion of nonmare lunar meteorites is higher among those from oman than those from antarctica or africa omani lunar meteorites extend the compositional range of lunar rocks as known from the apollo collection and from lunar meteorites from other continents some of the feldspathic meteorites are highly magnesian high mgo mgo feo compared with most similarly feldspathic apollo rocks two have greater concentrations of incompatible trace elements than all but a few apollo samples a few have moderately high abundances of siderophile elements from impacts of iron meteorites on the moon all lunar meteorites from oman are contaminated to various degrees with terrestrial na k p zn as se br sr sb ba u carbonates or sulfates the contamination is not so great however that it seriously compromises the scientific usefulness of the meteorites as samples from randomly distributed locations on the moon

inter diffusion coefficients parallel to the c axis in iron rich clinopyroxenes calculated from microstructures subsolidus marginal zoning in calcium poor clinopyroxenes and intermediate zoning in discontinuously zoned subcalcic to calcium rich clinopyroxenes from ironrich igneous rocks is used to calculate the interdiffusion coefficient dca fe mg parallel to the crystallographic caxis wagner s mathematical models describing the displacement of interfaces in solids as the result of isothermal diffusion are adopted the steady state heat flow equation is used to approximate the diffusion times the calculated interdiffusion coefficients are of a reasonable order of magnitude viz 6 0 10 20 2 0 10 17cm2 sec 1 at about 900 c

numerous unpaired meteorites exposed on a deflating playa lake at lucerne valley california abstract out of 16 well characterized 1 to 37 g meteorite specimens recovered from lucerne dry lake an approximately 3 7 km playa in the southern mojave desert of california there are 9 separate ordinary chondrite finds the ratio of independent meteorites to total number of specimens 0 6 is among the highest in the world this is due to lack of initial deep burial of the small meteorites significant deflation of the lake exposing falls of individual stones or small numbers of paired meteorites and the absence of a large meteorite shower in the region playas appear to be excellent candidates for high yield meteorite collecting areas

feldspathic lunar meteorites pecora escarpment 02007 and dhofar 489 contamination of the surface of the lunar highlands by post basin impacts abstract pca pecora escarpment 02007 and dhofar 489 are both meteorites from the feldspathic highlands of the moon pca 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface it has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites dhofar 489 is a feldspathic breccia composed mainly of impact melted material from an unknown depth beneath the regolith concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites among 19 known feldspathic lunar meteorites all of which presumably originate from random locations in the highlands concentrations of incompatible elements like sm and th tend to increase with those of siderophile elements like ir feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure micrometeorites have low concentrations of incompatible elements however so the correlation must reflect a three component system we postulate that the correlation between sm and ir occurs because the surface of the feldspathic highlands terrane has become increasingly contaminated with time in sm rich material from the procellarum kreep terrane that has been redistributed across the lunar surface by impacts of moderate sized post basin impacts the most sm rich regolith breccias among feldspathic lunar meteorites are about 3 enriched compared to the most sm poor breccias but this level of enrichment requires only a few percent sm rich material typical of the procellarum kreep terrane the meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of k rare earths and th measured by the lunar prospector mission at the surface representative of the underlying bedrock all surfaces covered by old regolith as opposed to fresh ejecta are at least slightly contaminated dhofar 489 is one of 15 paired lunar meteorite stones from oman total mass of meteorite 1037 g on the basis of its unusually high mg fe ratio the meteorite is likely to have originated from northern feldspathic highlands

three dimensional spectral analysis of compositional heterogeneity at arruntia crater on 4 vesta using dawn fc abstract we introduce an innovative three dimensional spectral approach three band parameter space with polyhedrons that can be used for both qualitative and quantitative analyzes improving the characterization of surface compositional heterogeneity of 4 vesta it is an advanced and more robust methodology compared to the standard two dimensional spectral approach two band parameter space the dawn framing camera fc color data obtained during high altitude mapping orbit resolution 60 m pixel is used the main focus is on the howardite eucrite diogenite hed lithologies containing carbonaceous chondritic material olivine and impact melt the archived spectra of heds and their mixtures from relab hoserlab and usgs databases as well as our laboratory measured spectra are used for this study three dimensional convex polyhedrons are defined using computed band parameter values of laboratory spectra polyhedrons based on the parameters of band tilt r0 92 m r0 96 m mid ratio r0 75 m r0 83 m r0 83 m r0 92 m and reflectance at 0 55 m r0 55 m are chosen for the present analysis an algorithm in idl programming language is employed to assign fc data points to the respective polyhedrons the arruntia region in the northern hemisphere of vesta is selected for a case study because of its geological and mineralogical importance we observe that this region is eucrite dominated howarditic in composition the extent of olivine rich exposures within an area of 2 5 crater radii is 12 larger than the previous finding thangjam g et al 2014 meteorit planet sci 49 1831 1850 lithologies of nearly pure cm2 chondrite olivine glass and diogenite are not found in this region although there are no unambiguous spectral features of impact melt the investigation of morphological features using fc clear filter data from low altitude mapping orbit resolution 18 m pixel suggests potential impact melt features inside and outside of the crater our spectral approach can be extended to the entire vestan surface to study the heterogeneous surface composition and its geology

shisr 043 iiiab medium octahedrite the first iron meteorite from the oman desert the iron meteorite shisr 043 is a single mass of 8267 g found in the south oman desert 42 km ne of the shisr village it is the first iron identified among the 1400 individual meteorites reported from oman the meteorite is a slightly elongated mass showing only minor rusting a partially smooth and partially rough surface with octahedral cleavage and a partially preserved metallic fusion crust typically 0 75 mm thick the undeformed widmanstatten pattern with a mean kamacite bandwidth of 1 0 0 1 mm n 97 indicates structural classification as a medium octahedrite from the bulk composition ni 8 06 wt ga 18 8 ppm ge 37 25 ppm and ir 3 92 ppm the meteorite is classified as iiiab the most common group of iron meteorites the cosmic ray exposure cre age based on 3he 21ne 38ar concentrations and 10be 21ne 26al 21ne and 36cl 36ar ratios is 290 20 ma this age falls within the range observed for type iiiab iron meteorites but does not coincide with the main cluster the cosmogenic noble gas and radionuclide data indicate that shisr 043 had a relatively small preatmospheric mass the low degree of weathering is consistent with a young terrestrial age of 10 000 years based on the saturated 41ca concentration shisr 043 is not paired with any of the other eight known iron meteorites from the arabian peninsula

meteorite reconnaissance in saudi arabia meteorite searches in saudi arabia between 2008 and 2014 yielded 46 meteorites from the yabrin area 23 n 49 e 35 meteorites from the rub al khali sand desert 19 20 n 48 51 e and 1 meteorite from al haddar no meteorites were found near hafar al batin 29 n 45 e the 82 new meteorites represent 57 falls comprising 43 ordinary chondrites 4 carbonaceous chondrites 2 enstatite chondrites 3 ureilites 3 eucrites 1 acapulcoite and 1 lunar meteorite the median of 31 14c terrestrial ages is 6 2 ka significantly younger than the oman population 19 5 ka n 128 a further assessment of terrestrial 14c contamination is advised by a 11 15 ka 14c terrestrial age of heavily weathered meteorite khawr al fazra 014 geology indicating a terrestrial age 100 ka find densities of 0 4 2 8 km 2 for yabrin and the western rub al khali are similar to 0 5 km 2 observed in oman higher find densities of 135 km 2 29 km 2 for masses 10 g exist on small pleistocene outcrops in blowouts in the south central rub al khali 21 unpaired meteorites four 10 g were found in 11 blowouts with a combined area of 0 14 km2 the rub al khali meteorites show a relatively high degree of weathering median w 3 6 2 5 for yabrin low median mass 4 3 138 g and a high h l ratio 2 3 1 1 the high density of small meteorites is explained by prolonged sand protection and recent deflation the high meteorite density and relatively high proportion of rare meteorite types render the rub al khali blowouts an interesting target for future exploration

cosmic ray exposure ages of four acapulcoites and two differentiated achondrites and evidence for a two layer structure of the acapulcoite lodranite parent asteroid abstract we determined the he ne and ar isotopic abundances in the four acapulcoites dhofar dho 125 dho 290 dho 312 and graves nunataks 98028 the metal rich diogenite northwest africa nwa 1982 and a unique achondrite nwa 1058 that resembles the acapulcoites in its chemical composition the noble gases in these meteorites consist of three components trapped gases cosmic ray produced nuclides and nuclides produced by k th and u decay the four acapulcoites yield cosmic ray exposure cre ages in the range of 5 0 5 7 ma and confirm earlier conclusions concerning break up of all acapulcoites from a common s type parent asteroid possibly in three events 4 9 5 9 and 14 8 ma ago we also discuss the other characteristics mineralogy chemistry formation ages and oxygen and trapped noble gas isotopes of all other acapulcoites and their relatives the lodranites we propose that the acapulcoite lodranite parent asteroid had a shell structure similar to that of the h chondrites the less metamorphosed acapulcoites correspond to the h3 and h4 chondrites and originate from the exterior layers whereas the more severely metamorphosed lodranites similar to the h5 and h6 chondrites represent the inner regions of their parent body ungrouped achondrite nwa 1982 probably a diogenite shows a cre age of 18 9 2 0 ma that falls on the major exposure age cluster of the diogenites the unique achondrite nwa 1058 differs in cosmic ray exposure age 38 9 4 0 ma and in oxygen isotopic composition from the acapulcoites and lodranites and is probably a winonaite

experimental study of incongruent evaporation kinetics of enstatite in vacuum and in hydrogen gas variations in bulk mg si ratios in the various groups of chondritic meteorites indicate that mg si fractionation occurred in the primitive solar nebula enstatite mgsio3 evaporates incongruently forming forsterite mg2sio4 as an evaporation residue therefore evaporation of enstatite produces mg si variations in solid mg rich and gas si rich and must be considered as a probable process responsible for mg si fractionation recorded in chondrites to understand the evaporation kinetics of enstatite incongruent evaporation experiments on enstatite single crystals have been carried out in vacuum and in hydrogen gas at temperatures of 1300 to 1500 c a polycrystalline forsterite layer is formed on the surface of enstatite by preferential evaporation of the sio2 component both in vacuum and in hydrogen gas the thickness of the forsterite layer in vacuum increases with time in the early stage of evaporation and later the thickness of the forsterite layer remains constant several microns this is due to the change in the rate limiting process from surface reaction plus nucleation and growth to diffusion in the surface forsterite layer the activation energy of the diffusion controlled evaporation rate constant of enstatite is 457 58 kj mol a thinner forsterite layer is formed on the surface of enstatite in hydrogen gas than in vacuum evaporation of enstatite in hydrogen gas is also considered to be controlled by diffusion of ions through the forsterite layer the thin forsterite layer formed in hydrogen gas is ascribed to the enhanced evaporation rate of forsterite in the presence of hydrogen gas the results are applied to incongruent evaporation under the solar nebular conditions the steady thickness of the forsterite of nebular pressure temperature conditions is estimated to be submicron because of the enhanced evaporation rate of forsterite under hydrogen rich nebular conditions if evaporated gases are taken away immediately and no back reaction occurs an open system because enstatite grains in the solar nebula would be comparable to the estimated steady thickness of forsterite evaporation of such enstatite grains under kinetic conditions could play an important role in producing variations in mg si ratios between solid and gas in the solar nebula

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

the meteoritical bulletin no 82 1998 july abstract meteoritical bulletin no 82 lists information for 974 new meteorites including 521 finds from antarctica 401 finds from the sahara 21 finds from the nullarbor region of australia and 7 falls ban rong du burnwell fermo jalanash juancheng monahans 1998 and silao many rare types of meteorites are reported counting pairing groups as one these include one cr chondrite two ck chondrites two co chondrites four cv chondrites one ch chondrite or bencubbin like six c2 unclassified chondrites two eh chondrites two el chondrites three r chondrites thirty unequilibrated ordinary chondrites one un grouped chondrite three eucrites six howardites one diogenite eleven ureilites nine iron meteorites one mesosiderite two brachinites one lodranite one winonaite and two lunar meteorites dar al gani 400 and eet 96008 all italicized abbreviations refer to addresses tabulated at the end of this document

the frontier mountain meteorite trap antarctica the frontier mountain blue ice field is an important antarctic meteorite trap which has yielded 472 meteorite specimens since its discovery in 1984 remote sensing analyses and field campaigns from 1993 to 1999 have furnished new glaciological data on ice flow ice thickness bedrock topography ice ablation and surface mass transport by wind along with detailed descriptions of the field situation at the trap this solid set of data combined with an updated meteorite distribution map and terrestrial ages available from literature allows us to better describe the nature of the concentration mechanism in particular we observe that the meteorite trap forms in a blue ice field 1 located upstream of an absolute and a shallow sub ice barriers 2 characterized by compressive ice flow with horizontal velocities decreasing from 100 to 10 cm year on approaching the obstacle 3 undergoing mean ablation rates of 6 5 cm year 4 nourished by a limited snow accumulation zone extending 20 km upstream of the blue ice area we also draw the following conclusions 1 the origin of the meteorite trap can be explained according to the present day glaciological situation 2 the meteorite concentration develops according to the general principles of the ice flow model 3 the accumulation model can be described as stagnant ice or slow moving ice against an absolute and submerged barriers according to the descriptive schemes present in literature 4 the frontier mountain ice field is an effective trap for meteorites weighing more than 200 g for smaller masses the combination of wind and glacial drift may remove meteorites in less than a few tens of thousands of years 5 although the activation age of the frontier mountain trap is not yet constrained we infer that one of the most important findsites may be as old as 50 ka predating the last glacial maximum

beni m hira a new chondritic l6 meteorite fall from tunisia the beni m hira meteorite fell on january 8 2001 in southeastern tunisia this is only the fifth observed fall from tunisia on the basis of mineralogical petrographic and geochemical data the stone can be classified as an l6 chondrite of shock stage s5

the antarctic achondrite grove mountains 021663 an olivine rich winonaite abstract the grove mountains grv 021663 meteorite was collected from the grovemountains region of antarctica the meteorite is composed primarily of olivine fa 5 4 orthopyroxene fs 4 7 wo 3 0 chromian diopside en 53 6 fs 2 4 wo 44 troilite kamacite andplagioclase ab 74 5 or 4 an 21 5 minor phases include schreibersite and k feldspar themeteorite is highly weathered w3 and weakly shocked s2 we determine a whole rockoxygen isotopic composition of d 18 o 7 50 d 17 o 3 52 comparisons of these datawith other primitive achondrites have resulted in the reclassi cation of this meteorite as amember of the winonaite group the occurrences of troilite metal and schreibersite in grv021663 indicate that these minerals were once completely molten euhedral inclusions ofpyroxene within plagioclase further suggest that these may have crystallized from a silicatemelt while the depletion of plagioclase metal and troilite indicates that grv 021663 couldrepresent a residuum following partial melting on its parent asteroid trace elementdistributions in silicate minerals do not however con rm this scenario as with otherwinonaite meteorites the formation of grv 021663 probably relates to brecciation andmixing of heterogeneous lithologies followed by varying degrees of thermal metamorphismon the parent body asteroid peak metamorphic conditions may have resulted in localizedpartial melting of metal and silicate mineralogies but our data are not conclusive introductionthe primitive achondrite meteorites winonaites arecharacterized by having chondritic mineralogies andchemical compositions but achondritic recrystallized textures for the most part they are ne to mediumgrained equigranular rocks some samples however contain what appear to be relic chondrules e g pontlyfni mt morris wisconsin and northwest africa nwa 1463 benedix et al 1998 2003 their oxidationstates are intermediate between those of enstatite and hchondrites and feni fes veins that constitute the rstpartial melts of a chondritic precursor material arecommon see figs 1a and 2a meteorites of this groupare primarily composed of orthopyroxene olivine diopside plagioclase troilite fe ni alloy and minoramounts of chromite and phosphate in addition theymay contain characteristic accessory minerals such asalabandite daubree lite schreibersite benedix et al 1998 amphibole is reported in at least one sample hammadah al hamra hah 193 floss et al 2007 there are several attributes that collectivelydistinguish the winonaites from other achondritemeteorite groups such as 1 highly reduced mineralassemblage s 2 distinct oxygen isotopic compositions 3 the abundance and distribution of metal s andtroilite and 4 characteristic accessory mineralogies benedix et al 1998 winonaites may derive from a1329

frontier mountain meteorite specimens of the acapulcoite lodranite clan petrography pairing and parent rock lithology of an unusual intrusive rock in this paper we reconstruct the heterogeneous lithology of an unusual intrusive rock from the acapulcoite lodranite al parent asteroid on the basis of the petrographic analysis of 5 small 8 3 g meteorite specimens from the frontier mountain ice field antarctica although these individual specimens may not be representative of the parent rock lithology due to their relatively large grain size by putting together evidence from various thin sections and literature data we conclude that frontier mountain fro 90011 fro 93001 fro 99030 and fro 03001 are paired fragments of a medium to coarse grained igneous rock which intrudes a lodranite and entrains xenoliths the igneous matrix is composed of enstatite fs13 3 0 4 wo3 1 0 2 cr rich augite fs6 1 0 7 wo42 3 0 9 and oligoclase ab80 5 3 3 or3 2 0 6 the lodranitic xenoliths show a fine grained average grain size 488 201 m granoblastic texture and consist of olivine fa9 5 0 4 and fe ni metal and minor amounts of enstatite fs12 7 0 4 wo1 8 0 1 troilite chromite schreibersite and ca phosphates crystals of the igneous matrix and lodranitic xenoliths are devoid of shock features down to the scanning electron microscope scale from a petrogenetic point of view the lack of shock evidence in the lodranitic xenoliths of all the studied samples favors the magmatic rather than the impact melting origin of this rock fro 95029 is an acapulcoite and represents a separate fall from the al parent asteroid i e it is not a different clast entrained by the fro 90011 fro 93001 fro 99030 and fro 03001 melt as in genomict breccias common in the meteoritic record the specimen to meteorite ratio for the al meteorites so far found at frontier mountain is thus 2 5

thermal history of the enstatite chondrites from silica polymorphs here we report the results of our petrologic and mineralogical study of enstatite e chondrites in order to explore their thermal histories we studied silica phases in 20 e chondrites by laser micro raman spectroscopy to determine the silica polymorphs they contain silica phases are commonly present in e chondrites and their polymorphs reflect the physical conditions of formation the samples studied here include eh3 5 el3 6 e chondrite melt rocks and an anomalous e chondrite we identified quartz tridymite cristobalite and silica glass in the samples studied eh4 5 and eh melt rocks are divided into high and low temperature classes based on niningeritealabandite solid solutions eh3 el3 and some eh melt rocks of the high temperature class contain tridymite and cristobalite we suggest that tridymite and cristobalite crystallized in chondrules and e chondrite melts followed by rapid cooling leading to the survival of these silica polymorphs eh4 and el4 chondrites also contain tridymite and cristobalite in their chondrules indicating that these silica polymorphs survived low temperature metamorphism as estimated from opaque mineral geothermometers because of the sluggishness of the transition to a more stable polymorph tridymite and cristobalite in el6 chondrites reflect the high temperature processes experienced by these meteorites on the other hand some eh5 chondrites and eh melt rocks of the low temperature class contain quartz which may be a product of the transition from tridymite or cristobalite during a long period of low temperature metamorphism although the thermal history of e chondrites have been previously estimated from opaque minerals such compositions mainly reflect low temperature processes however we can reconstruct the primordial thermal processes and subsequent cooling histories of e chondrites from their silica polymorphs the e chondrites have complicated thermal histories which produced the observed variations among them

history of the paired lunar meteorites mac88104 and mac88105 derived from noble gas isotopes radionuclides and some chemical abundances abstract noble gas isotopes radionuclides and chemical abundances were studied in the lunar meteorites mac88104 and mac88105 collected in the macalpine hills area of antarctica the concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical proving that the two meteorites are paired from 40k 40ar dating we obtain a gas retention age of 3550 400 ma typical for lunar surface material probably before breccia compaction the mac88104 5 material resided for 630 200 ma at an average shielding depth of 85 g cm 2 that is about 50 cm below the lunar surface in the lunar regolith as judged from the concentration of cosmic ray produced kr and xe isotopes although this duration of lunar regolith residence is relatively long mac88104 5 represent immature regolith material the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil the reason for that might be the relatively high average shielding the 40 ar 36ar ratio of the trapped component is 5 7 1 0 indicating an intermediate antiquity of the material we estimate that the solar wind and lunar atmospheric particles were implanted about 2000 ma ago the radionuclide activities allow us to derive the exposure history of the mac88104 5 material the duration of the moon earth transfer was 0 24 ma production of the radionuclides on the lunar surface immediately before ejection is possible but duration and shielding depth for such an exposure cannot be determined from our data we obtain a terrestrial age of 0 1 tterr 0 6 ma and an ejection time of mac88104 5 from the moon of 0 1 tejection 0 8 ma the exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the moon our first noble gas results for lunar meteorite yamato 793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gases and a duration of several hundred million years of exposure to cosmic rays

an experimental study of enstatite formation reaction between forsterite and si rich gas experiments on the reaction between forsterite and si rich gas were carried out in a vacuum furnace using a newly designed double capsule technique a thin layer of enstatite was formed on the surface of the forsterite by the reaction the thickness of the enstatite layer changes in proportion to the square root of time parabolic rate law indicating that the rate is controlled by diffusion in the enstatite layer the activation energy and the logarithm of the pre exponential term of the parabolic rate constant were obtained at505 188 kj mol and3 6 5 6 cm2 s respectively it is difficult to definitely determine the mechanism of the reaction from these values but consideration of strain generation due to volume change during the reaction may suggest that the counter diffusion of silicon and magnesium takes place along the grain boundary in the enstatite layer the degree of the reaction of forsterite with si rich residual gas in the primordial solar nebula is discussed based upon the measured reaction rate and it is suggested that very little enstatite was formed by this reaction in the cooling nebula if the grain size of the forsterite crystals was controlled by homogeneous nucleation theory

new lunar meteorites impact melt and regolith breccias and large scale heterogeneities of the upper lunar crust we have analyzed nine highland lunar meteorites lunaites using mainly inaa several of these rocks are difficult to classify dhofar 081 is basically a fragmental breccia but much of its groundmass features a glassy fluidized texture that is indicative of localized shock melting also much of the matrix glass is swirly brown suggesting a possible regolith derivation we interpret dar al gani dag 400 as an extremely immature regolith breccia consisting mainly of impact melt breccia clasts we interpret dhofar 026 as an unusually complex anorthositic impact melt breccia with scattered ovoid globules that formed as clasts of mafic subophitic impact melt the presence of mafic crystalline globules in a lunar material even one so clearly impact heated suggests that it may have originated as a regolith our new data and a synthesis of literature data suggest a contrast in al2o3 incompatible element systematics between impact melts from the central nearside highlands where apollo sampling occurred and those from the general highland surface of the moon impact melts from the general highland surface tend to have systematically lower incompatible element concentration at any given al2o3 concentration than those from apollo 16 in the case of dhofar 026 both the bulk rock and a comparatively al poor composition 14 wt al2o3 7 g g sm extrapolated for the globules manifest incompatible element contents well below the apollo 16 trend impact melts from luna 20 57e distribute more along the general highland trend than along the apollo 16 trend siderophile elements also show a distinctive composition for apollo 16 impact melts ni ir averaging 1 8x chondritic in contrast lunaite impact melt breccias have consistently chondritic ni ir impact melts from luna 20 and other apollo sites show average ni ir almost as high as those from apollo 16 the prevalence of this distinctive ni ir ratio at such widely separated nearside sites suggests that debris from one extraordinarily large impact may dominate the megaregolith siderophile component of a nearside region 2300 km or more across highland polymict breccia lunaites and other kreep poor highland regolith samples manifest a strong anticorrelation between al2o3 and mg the magnesian component probably represents the chemical signature of the mg suite of pristine nonmare rocks in its most pure form unaltered by the major kreep assimilation that is so common among apollo mg suite samples the average composition of the ferroan anorthositic component is now well constrained at al2o3 29 30 wt implying about 17 19 wt modal mafic silicates in good agreement with the composition predicted for flotation crust over a ferroan magma ocean warren 1990

trapped noble gases indicate lunar origin for antarctic meteorite the isotopic abundances of the noble gases he ne ar kr xe are reported for antarctic meteorite alha81005 it contains solar wind implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites alha81005 also contains a large excess 40ar component which is identical to the component in lunar fines implanted from the lunar atmosphere large concentrations of cosmogenic 21ne 82kr and 126xe in alha81005 indicate a total cosmic ray exposure age of 2 108 years the noble gas data alone are strong evidence for a lunar origin of this meteorite

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

ca al rich inclusions amoeboid olivine aggregates and al rich chondrules from the unique carbonaceous chondrite acfer 094 i mineralogy and petrology based on their mineralogy and petrography 200 refractory inclusions studied in the unique carbonaceous chondrite acfer 094 can be divided into corundum rich 0 5 hibonite rich 1 1 grossite rich 8 5 compact and fluffy type a spinel melilite rich 50 3 pyroxene anorthite rich 7 4 and type c pyroxene anorthite rich with igneous textures 1 6 ca al rich inclusions cais pyroxene hibonite spherules 0 5 and amoeboid olivine aggregates aoas 30 2 melilite in some cais is replaced by spinel and al diopside and or by anorthite whereas spinel pyroxene assemblages in cais and aoas appear to be replaced by anorthite forsterite grains in several aoas are replaced by low ca pyroxene none of the cais or aoas show evidence for fe alkali metasomatic or aqueous alteration the mineralogy textures and bulk chemistry of most acfer 094 refractory inclusions are consistent with their origin by gas solid condensation and may reflect continuous interaction with sio and mg of the cooling nebula gas it appears that only a few cais experienced subsequent melting the al rich chondrules arcs 10 wt bulk al2o3 consist of forsteritic olivine and low ca pyroxene phenocrysts pigeonite augite anorthitic plagioclase spinel feni metal and crystalline mesostasis composed of plagioclase augite and a silica phase most arcs are spherical and mineralogically uniform but some are irregular in shape and heterogeneous in mineralogy with distinct ferromagnesian and aluminous domains the ferromagnesian domains tend to form chondrule mantles and are dominated by low ca pyroxene and forsteritic olivine anorthitic mesostasis and fe ni metal nodules the aluminous domains are dominated by anorthite high ca pyroxene and spinel occasionally with inclusions of perovskite have no or little feni metal and tend to form cores of the heterogeneous chondrules the cores are enriched in bulk ca and al and apparently formed from melting of cai like precursor material that did not mix completely with adjacent ferromagnesian melt the inferred presence of cai like material among precursors for al rich chondrules is in apparent conflict with lack of evidence for melting of cais that occur outside chondrules suggesting that these cais were largely absent from chondrule forming region s at the time of chondrule formation this may imply that there are several populations of cais in acfer 094 and that mixing of normal cais that occur outside chondrules and chondrules that accreted into the acfer 094 parent asteroid took place after chondrule formation alternatively there may have been an overlap in the cai and chondrule forming regions where the least refractory cais were mixed with fe mg chondrule precursors this hypothesis is difficult to reconcile with the lack of evidence of melting of aoas which represent aggregates of the least refractory cais and forsterite grains

petrology and origin of amoeboid olivine aggregates in cr chondrites amoeboid olivine aggregates aoas are irregularly shaped fine grained aggregates of olivine and ca al rich minerals and are important primitive components of cr chondrites the aoas in cr chondrites contain feni metal and some aoas contain mn rich forsterite with up to 0 7 mno and mn fe ratios greater than one additionally aoas in the cr chondrites do not contain secondary phases nepheline and fayalitic olivine that are found in aoas in some cv chondrites the aoas in cr chondrites record a complex petrogenetic history that included nebular gas solid condensation reaction of minerals with the nebular gas small degrees of melting and sintering of the assemblage a condensation origin for the mn rich forsterite is proposed the mn rich forsterite found in idps unequilibrated ordinary chondrite matrix and aoas in cr chondrites may have had a similar origin a type a calcium aluminum rich inclusion cai with an aoa attached to its wark lovering rim is also described this discovery reveals a temporal relationship between aoas and type a inclusions additionally a thin layer of forsterite is present as part of the wark lovering rim revealing the crystallization of olivine at the end stages of the wark lovering rim formation the ca al rich nodules in the aoas may be petrogenetically related to the ca al rich minerals in wark lovering rims on type a cais aoas are chondrite components that condensed during the final stage of wark lovering rim formation but in general were temporally spatially or kinetically isolated from reacting with the nebula vapor during condensation of the lower temperature minerals that were commonly present as chondrule precursors

accessory silicate mineral assemblages in the bilanga diogenite a petrographic study the petrographic relationships in diogenites between orthopyroxene and minor phases such as chromite troilite diopside plagioclase and silica are often obscured by the intense brecciation that characterizes these meteorites although brecciated bilanga preserves numerous clasts displaying primary textural relations between orthopyroxene and these minor phases that are large enough to analyze by electron microprobe in this study we focus on the distribution composition and origin of the minor phases in bilanga to provide new insights into the crystallization and metamorphic history of these rocks the samples examined consist mainly of orthopyroxene grains plus five types of assemblages containing diopside a fe rich phase chromite troilite and or fe ni metal plagioclase silica we interpret type 1 assemblages as being remnants of intercumulus melt trapped in the interstices between orthopyroxene grains after crystal settling in a magma chamber type 2 assemblages appear to have formed by heterogeneous exsolution during thermal metamorphism type 3 assemblages are believed to be remnants of other assemblages that have been shocked melted and rapidly recrystallized by impact events type 4 assemblages consist of veins that also appear to have formed from trapped intercumulus melt regions of silica rich mesostasis type 5 appear to be larger patches of more evolved intercumulus melt that have been significantly affected by late stage impact melting finally large clasts containing plagioclase diopside are interpreted to be exotic fragments of a different but possibly related rock type incorporated in the bilanga breccia

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

discussion of placed rock as protection against erosion by flow down steep slopes by w l peirson j figlus s e pells and r j cox

composition and evolution of the lunar crust in the descartes highlands apollo 16 samples from the north ray crater ejecta blanket apollo 16 were investigated by petrographic microscope electron microprobe instrumental neutron activation and xray fluorescence analyses and 40ar 39ar and rb sr dating techniques nine major groups of monomict and polymict breccias were defined on the basis of microscopic texture and these were further subdivided into chemical subgroups on the basis of characteristic elements such as al mg fe cr ree ni and co the polymict breccias fragmental breccias granulitic breccias and impact melt breccias are the result of multiple impact induced mechanical mixing and melting and of thermal and impact metamorphism of rock and mineral clasts derived from primordial igneous crustal rocks for calculations of mixing models it was found that end members consisting of the pristine igneous rock components present as discrete samples at the apollo 16 site and supplemented by kreep dunite and a meteoritic component yield the best fits for the composition of polymict breccias the end member rocks a re ferroan anorthosite various magnesian gabbronorites including sodic ferrogabbro and feldspathic lherzolite and spinei troctolite the following model is proposed for the composition and stratigraphy of the target for north ray crater the lower section of the stratigraphy is composed of a megabreccia with clasts of highly feldspathic polymict breccias kreep free old eastern highland rock suite interpreted as nectaris ejecta descartes formation the top section contains kreep bearing polymict breccias kreep bearing young western highland rock suite and appears to be similar to the lithologies found in the cayley plains this material interpreted as cayley formation may be a distant facies of imbrium basin ejecta deposits of the imbrium basin the petrographic differences between these two major selenographic units the descartes and the cayley formations in the apollo 16 area are more distinct than the chemical differences the petrographic and chemical composition of the primordial igneous upper crust in the regions of the nectaris and imbrium basins has been calculated by subtraction of the kreep and meteoritic components from the bulk composition of the descartes and cayley materials the nectaris crust which is better constrained consists of 86 87 a northosite 4 sodic ferrogabbro 0 5 1 3 feldspathic lherzolite 6 8 regular magnesian gabbronorite 1 8 2 8 dunite and 0 1 spinel troctolite a model for the evolution of the upper lunar crust in the descartes highlands is proposed on the basis of isotope ages and clast matrix relationships of polymict breccias essential features of this model in sequenial order are 1 development of multiple layers of kreep free early feldspathic fragmental megabreccias and impact melt sheets on the primordial crust in the time period from 4 4 aeons to the time of the nectaris impact which could have occurred as late as 3 85 aeons ago 2 excavation of these megabreccias by the nectaris event and deposition of a nectarian feldspathic fragmental megabreccia in the descartes area 3 introduction of kreep basaltic material into the upper crust mainly west and northwest of the descartes site and formation of kreepy impact melt sheets most probably from 4 05 to 3 80 aeons ago 4 imbrium impact at 3 8 aeons ago and deposition of kreep bearing imbrian feldspathic fragmental breccias at the descartes site which form the cayley formation and 5 redeposition mixing and melting of all preexisting breccias yielding kreep bearing and kreep poor post cayley fragmental breccias and melt ejecta glass bombs as the result of small impacts craters 1 5 km in diameter in the cayley plains and the descartes mountains respectively

shock metamorphism of enstatite chondrites abstract we have extended the shock metamorphism classification scheme of stoffler et al 1991 to account for shock effects in orthopyroxene and applied it to sixty enstatite chondrites orthopyroxene exhibits the following sequence of progressive shock effects shock stage s1 unshocked sharp optical extinction s2 very weakly shocked undulose extinction s3 weakly shocked development of clinoenstatite lamellae parallel to 100 s4 moderately shocked weak mosaicism s5 strongly shocked strong mosaicism as in the stoffler et al 1991 scheme stage s5 is characterized principally by the solid state transformation of crystalline plagioclase into maskelynite most el3 chondrites exhibit foliations caused by impact deformation of chondrules and metal particles el5 and el6 chondrites are all shock stage s2 because opaque veins are rare in s2 ordinary chondrites it is plausible that the centimeter size kamacite veins in atlanta and blithfield and the 1 6 cm long oldhamite rich vein in jajh deh kot lalu all el6 formed when their hosts were shocked to s3 s5 levels because removal of shock stage s3 s5 features including repair of shock damaged orthopyroxene requires levels of metamorphism comparable to those experienced by petrologic type 5 to 6 chondrites we infer that proto el6 material was shocked to s3 s5 levels prior to peak metamorphism and shocked again to stage s2 after metamorphism overall enstatite chondrites appear to have suffered greater shock damage than ordinary and carbonaceous chondrites

itqiy a metal rich enstatite meteorite with achondritic texture itqiy is a unique coarse grained metal rich enstatite meteorite that was found in the western sahara and consists of two rocks together weighing 4 72 kg which are both completely coated with fusion crust we report results from our electron microprobe and instrumental neutron activation analysis techniques itqiy consists of subhedral equigranular millimeter sized enstatite 25 vol of millimeter sized kamacite and a few tiny intergrowths of sulfides and kamacite relic chondrules are absent pyroxene fs0 2 is chemically similar to enstatite in el chondrites but the metal is closer in composition to that in eh chondrites sulfides resemble those in e chondrites but their compositions are distinct from those in both el and eh chondrites itqiy clearly formed under very reducing conditions but it does not appear to have formed from eh or el chondrites two thermal events can be distinguished silicate compositions including rare earth element abundances indicate loss of partial melt and slow cooling heterogeneous sulfides indicate a subsequent reheating and quenching event which may have been due to shock as many enstatite grains show shock stage s3 features

geochemistry petrology and ages of the lunar meteorites kalahari 008 and 009 new constraints on early lunar evolution abstract kalahari 008 and 009 are two lunar meteorites that were found close to each other in botswana kalahari 008 is a typical lunar anorthositic breccia kalahari 009 a monomict breccia with basaltic composition and mineralogy based on minor and trace elements kalahari 009 is classified as vlt very low ti mare basalt with extremely low contents of incompatible elements including the ree the lu hf data define an age of 4286 95 ma indicating that kalahari 009 is one of the oldest known basalt samples from the moon it provides evidence for lunar basalt volcanism prior to 4 1 ga pre nectarian and may represent the first sample from a cryptomare the very radiogenic initial 176hf 177hf ehf 12 9 4 6 the low ree th and ti concentrations indicate that kalahari 009 formed from re melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history this unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low ti mare basalt volcanism apparently the moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types evidence that kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine the identical initial hf isotope composition the exceptionally low exposure ages of both rocks and the fact that they were found close to each other since cryptomaria are covered by highland ejecta it is possible that these rocks are from the boundary area where basalt deposits are covered by highland ejecta the concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks although kalahari 008 contains slightly higher concentrations a likely reason for this difference is that kalahari 008 is a polymict breccia containing a briefly exposed regolith while kalahari 009 is a monomict brecciated rock that may never have been at the surface of the moon altogether the compositions of kalahari 008 and 009 permit new insight into early lunar evolution as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions the very low th and ree content of kalahari 009 as well as the depletion in sm and the lack of a kreep like signature in kalahari 008 point to a possible source far from the influence of the procellarum kreep terrane possibly the lunar farside

round shaped riprap stabilization in overtopping flow a series of 26 tests was performed on a riprap layer in which median round shaped stones ranging from 32 3 to 99 1 mm from 1 27 to 3 90 in were subjected to overtopping flow conditions embankment slopes range from 10 to 45 with median stone sizes ranging from 23 9 to 104 2 mm from 0 94 to 4 1 in the database was analyzed yielding a unique expression in which the median size of a round shaped stone can be predicted as a function of the unit discharge embankment slope and coefficient of uniformity it was determined that the requisite round shaped stones range from 5 to 42 larger than angular stones to stabilize the riprap layer for similar flow conditions with unit flows of 0 2 cm s and slopes of 40 the maximum deviation between rounded and angular shaped stone may approach 70 as flow and bed conditions are extrapolated

the zaklodzie enstatite meteorite mineralogy petrology origin and classification the zaklodzie meteorite was found in september 1998 about 40 km west of zamo c in southeast poland macroscopic and microscopic observations in transmitted and reflected light microprobe analyses cathodoluminescence images and x ray diffraction data show that the meteorite is composed of clino and orthoenstatite two generations of feldspars relict olivine forsterite a polymorph of sio2 apparently cristobalite and opaque minerals fe ni alloy kamacite and taenite troilite schreibersite graphite and sulfide mg mn fe s which is probably keilite the texture is fine to inequigranular of cumulate type locally intergranular the mgs fes thermometer indicates that the sulfides crystallized at 580 600 oc thus the zaklodzie meteorite formed by the nearly complete melting of an enstatite chondrite protolith probably at 4 4 ga the process was likely caused by the decay of the 26al nuclide in the planetesimal interior the second stage of its evolution which could have happened at 2 1 ga involved partial re melting of most fusible components probably due to collision with another body the structure composition and origin of the meteorite and its relation to the parent rock indicate that zaklodzie may represent a primitive enstatite achondrite

the origin of alteration orangettes in dhofar 019 implications for the age and aqueous history of the shergottites the shergottites are the largest group of martian meteorites and the only group that has not been found to contain definitive evidence of martian aqueous alteration given recent reports of current liquid water at the surface of mars this study aimed to investigate in detail the possibility of martian phyllosilicate within shergottite dhofar 019 optical and scanning electron microscopy followed by transmission electron microscopy confirmed the presence of alteration orangettes with a layered structure consisting of poorly ordered mg phyllosilicate and calcite these investigations identified maskelynite dissolution followed by mg phyllosilicate and calcite deposition within the dissolution pits as the method of orangette production the presence of celestine within the orangette layers the absence of shock dislocation features within calcite and the mg rich nature of the phyllosilicate all indicate a terrestrial origin for these features on dhofar 019

porosities of lunar meteorites strength porosity and petrologic screening during the meteorite delivery process porosity has been directly measured for eight lunar meteorite breccias and calculated for two more on the basis of literature density measurements lunar meteorite regolith breccias display systematically low porosity in comparison to otherwise analogous apollo regolith breccias among seven meteoritic regolith breccias porosity ranges from 1 to 11 and averages 7 5 1 3 2 whereas for 44 analogous apollo samples porosities mostly calculated from literature density data the average is 25 1 7 the origin of this disparity is enigmatic but the trend probably reflects mainly a bias in favor of strong compact breccias among fragments that manage to survive the violent process of launch to lunar escape velocity 2 38 km s in addition compaction during launch may play an important role the population of lunar meteorites is clearly not a random unmodified sample of lithic materials near the surface of the parent body

rumuruti chondrites noble gases exposure ages pairing and parent body history in this paper we present concentration and isotopic composition of the light noble gases he ne and ar as well as of 84kr 132xe and 129xe in bulk samples of 33 rumuruti r chondrites together with previously published data of six r chondrites exposure ages are calculated and compared with those of ordinary chondrites a number of pairings especially between those from northwest africa nwa are suggested so that only 23 individual falls are represented by the 39 r chondrites discussed here eleven of these meteorites or almost 50 contain solar gases and are thus regolithic breccias this percentage is higher than that of ordinary chondrites howardites or aubrites this may imply that the parent body of r chondrites has a relatively thick regolith concentrations of heavy noble gases especially of kr are affected by the terrestrial atmospheric component which resides in weathering products compared to ordinary chondrites 129xe 132xe ratios of r chondrites are high

petrogenesis of acapulcoites and lodranites a shock melting model abstract acapulcoites are modeled as having formed by shock melting cr like carbonaceous chondrite precursors the degree of melting of some acapulcoites was low enough to allow the preservation of 3 6 vol relict chondrules shock effects in acapulcoites include veins of metallic fe ni and troilite polycrystalline kamacite fine grained metal troilite assemblages metallic cu and irregularly shaped troilite grains within metallic fe ni while at elevated temperatures acapulcoites experienced appreciable reduction because graphite is present in some acapulcoites and lodranites it seems likely that carbon was the principal reducing agent reduction is responsible for the low contents of olivine fa 4 14 mol and low ca pyroxene fs 3 13 mol in the acapulcoites the observation that in more than two thirds of the acapulcoites the fa value is lower than the fs value in contrast to the case for equilibrated ordinary chondrites the low feo mno ratios in acapulcoite olivine 16 18 compared to 32 38 in equilibrated h chondrites the relatively high modal orthopyroxene olivine ratios e g 1 7 in monument draw compared to 0 74 in h chondrites and reverse zoning in some mafic silicate grains lodranites formed in a similar manner to acapulcoites but suffered more extensive heating loss of plagioclase and loss of an fe ni s melt acapulcoites and lodranites experienced moderate post shock annealing presumably resulting from burial beneath material of low thermal diffusivity the annealing process repaired damaged olivine crystal lattices lending acapulcoites and lodranites the appearance of unshocked i e shock stage s1 rocks any high pressure phases that may have formed during initial shock reverted to their low pressure polymorphs during annealing some samples were subsequently shocked again several acapulcoites reached shock stage s2 levels alh 84190 reached s3 and the lodranite mac 88177 reached s5

the meteoritical bulletin no 84 2000 august meteoritical bulletin no 84 lists information for 1341 newly classified meteorites comprising 842 from antarctica 341 from africa 66 from australia 48 from asia including 42 from the arabian peninsula 38 from north america 4 from europe and 2 from south america information is provided for 11 recent falls bilanga devri khera djoumine guangmingshan kitchener kobe leighlinbridge sabrum songyuan tagish lake and vissannapeta 4 martian meteorites dar al gani 670 735 dhofar 019 los angeles and sayh al uhaymir 005 008 3 lunar meteorites northwest africa 032 dhofar 025 and 026 an ungrouped enstatite rich meteorite zaklodzie 11 iron meteorites and a wide variety of other interesting stony meteorites including ck cm co cr cv r enstatite and unequilibrated ordinary chondrites primitive achondrites hed achondrites ureilites and aubrites

evolution and classification of acapulcoites and lodranites from a chemical point of view we examined 15 bulk samples of the acapulcoite lodranite clan for their major minor and trace element concentrations using inaa techniques among the analyzed meteorites are 2 new acapulcoites dhofar dho 290 thiel mountains til 99002 as well as an additional acapulcoite that has been described previously only in very brief form graves nunataks gra 98028 the petrographic attributes of these 3 samples are addressed thoroughly we also include petrographic information on 2 acapulcoites from africa northwest africa nwa 725 and nwa 1058 in general our study strongly supports the widely accepted idea that acapulcoites and lodranites evolved through partial melting and melt migration of metal sulfide phases and plagioclase furthermore we concur with previous researchers that the original bimodal classification scheme for acapulcoites and lodranites proves to be too simple based on our data set we introduce an alternative extended scheme with respect to their elemental distribution patterns we distinguish 5 subtypes comprising primitive typical transitional and enriched acapulcoites on one hand and lodranites on the other the chemical distinction between the primitive typical and transitional acapulcoites is rather subtle and gradual it stands in contrast to the clear modifications observed for the signatures of the enriched acapulcoites and the lodranites the definition of subcategories basically reflects the concentrations of 2 key elements k and se we note however that the assignment of subgroups may not be exclusively inferred from elemental abundances but should also consider additional petrographic information

nebular history of amoeboid olivine aggregates minor element ca cr and mn concentrations in amoeboid olivine aggregates aoas from primitive chondrites were measured and compared with those predicted by equilibrium condensation in the solar nebula cao concentrations in forsterite are low particularly in porous aggregates a plausible explanation appears that an equilibrium ca activity was not maintained during the olivine condensation cao and mno in forsterite are negatively correlated with cao being higher in compact aggregates this suggests that the compact aggregates formed either by a prolonged reheating of the porous aggregates or by condensation and aggregation of forsterite during a very slow cooling in the nebula

amoeboid olivine aggregates with low ca pyroxenes a genetic link between refractory inclusions and chondrules amoeboid olivine aggregates aoas in primitive unmetamorphosed and unaltered carbona ceous chondrites are uniformly 16 o enriched 17 o 20 and consist of forsterite fa2 feni metal and a refractory component individual cais and fine grained minerals interspersed with forsterite grains composed of al diopside anorthite spinel and exceptionally rare melilite a u k15 some cais in aoas have compact igneous textures melilite in aoas is replaced by a fine grained mixture of spinel al diopside and anorthite spinel is corroded by anorthite or by al diopside in 10 of 500 aoas studied in the cr cv cm co ch cb and ungrouped carbonaceous chondrites acfer 094 adelaide and lew85332 forsterite is replaced to a various degree by low ca pyroxene there are three major textural occurrences of low ca pyroxene in aoas i thin 10 m discontinuous layers around forsterite grains or along forsterite grain boundaries in aoa peripheries ii haloes and subhedral grains around feni metal nodules in aoa peripheries and iii thick up to 70 m continuous layers with abundant tiny inclusions of feni metal grains around aoas aoas with low ca pyroxene appear to have experienced melting of various degrees in the most extensively melted aoa in the cv chondrite leoville only spinel grains are relict forsterite anorthite and al diopside were melted this aoa has an igneous rim of low ca pyroxene with abundant feni metal nodules and is texturally similar to type i chondrules based on these observations and thermodynamic analysis we conclude that aoas are aggregates of relatively low temperature solar nebular condensates originated in 16 o rich gaseous reservoir s probably cai forming region s some of the cais were melted before aggregation into aoas many aoas must have also experienced melting but of a much smaller degree than chondrules before and possibly after aggregation melilite and spinel reacted with the gaseous sio and mg to form ca tschermakite caal2sio6 diopside camgsi2o6 solid solution and anorthite solid or incipiently melted olivine in some aoas reacted with gaseous sio in the cai or chondrule forming regions to form low ca pyroxene mg2sio4 sio g h2o g mg2si2o6 h2 g some low ca pyroxenes in aoas may have formed by oxidation of si bearing feni metal mg2sio4 si in feni 2h2o g mg2si2o6 2h2 g and by direct gas solid condensation mg g sio g h2o g mg2si2o6 s h2 g from fractionated mg si ratio solar nebular gas although bulk compositions of aoas are rather similar to those of type i chondrules on the projection from spinel onto the plane ca2sio4 mg2sio4 al2o3 these objects plot on different sides of the anorthite forsterite thermal divide suggesting that type i chondrules cannot be produced from aoas by an igneous fractionation formation of low ca pyroxene by reaction of aoas with gaseous sio and by melting of silica rich dust accreted around aoas moves bulk compositions of the aoas towards chondrules and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors the rare occurrences of low ca pyroxene in aoas may indicate that either aoas were isolated from the hot nebular gas before condensation of low ca pyroxene or that condensation of low ca pyroxene by reaction between forsterite and gaseous sio was kinetically inhibited if the latter is correct then the common occurrences of pyroxene rich type i chondrules may require either direct condensation of low ca pyroxenes or sio2 from fractionated nebular gas or condensation of gaseous sio into chondrule melts copyright 2004 elsevier ltd

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

dhofar 081 a new lunar highland meteorite the lunar meteorite dhofar 081 found as a single fragment of 174 g in the dhofar region of oman is a shocked feldspathic fragmental highland breccia dominated by anorthosite rich lithic and mineral clasts embedded into a fine grained mostly shock melted clastic matrix major mineral phases in the bulk rock are ca rich plagioclase an96 5 99 5 pyroxene fs21 9 46 2wo3 0 41 4 and olivine fa29 3 47 8 accessory phases include fe ni metal ilmenite and ti cr rich spinel dhofar 081 contains subordinate crystalline fragments of large anorthosites intersertal impact melt rocks microporphyritic impact melt breccias dark fine grained impact melt breccias large cataclastic feldspars and irregularly shaped brown glass clasts mafic components are rare and no genuine regolith components were found in the sections studied minerals in dhofar 081 show homogeneously distributed shock features intergranular recrystallization strong fracturing and mosaicism in feldspar as well as a high density of mostly irregular fractures in pyroxene and olivine localized impact melting caused by one or several impacts led to a strong lithification based on these effects an equilibration shock pressure of about 15 20 gpa is estimated for the strongest shock event in dhofar 081 devitrification of the glassy material in the rock indicates thermal annealing after shock melting suggesting that the 15 20 gpa shock event predated the ejection event according to the concentrations of implanted solar noble gases dhofar 081 represents a polymict clastic breccia deposit with possibly a minor regolith component a similar noble gas record of dhofar 081 and macalpine hills 88104 05 suggests the possibility of a source crater pairing of both meteorites as indicated by noble gas measurements pairing of dhofar 081 with the other lunar meteorites found in oman dhofar 025 and dhofar 026 is unlikely

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

a noble gas data collection of lunar meteorites we collected the published noble gas data of altogether 35 lunar meteorites this compilation includes the stable isotopes of he ne ar kr and xe we also give a summary of cosmogenic trapped and radiogenic noble gas components of lunar meteorites for which data are available in the literature

design of rock protection to prevent erosion by water flows down steep slopes conventional stability analysis methods for determining rock armor size to protect steep tan 0 1 embankments from erosion due to downslope flow do not predict the correct dependency of armor size on the slope consequently such methods become very conservative discharge factor of safety 8 at high slopes we review published large scale measurements recorded in the literature and show that adequate representation of flow aeration is important as proposed by hartung and scheuerlein in 1970 however the assembled measurements show that the hartung and scheuerlein design method is not conservative the aerated flow equations of hartung and scheuerlein when combined with a correctly formulated stability equation yield good collapse of the available large scale data and a conservative design method

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

ca al rich inclusions in rumuruti r chondrites rumuruti chondrites r chondrites constitute a well characterized chondrite group different from carbonaceous ordinary and enstatite chondrites many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type ca al rich inclusions cais occur within all lithologies here we present the results of our search for and analysis of al rich objects in rumuruti chondrites we studied 20 r chondrites and found 126 ca al rich objects 101 cais 19 al rich chondrules and 6 spinel rich fragments based on mineralogical characterization and analysis by sem and electron microprobe the inclusions can be grouped into six different types 1 simple concentric spinel rich inclusions 42 2 fassaite rich spherules 3 complex spinel rich cais 53 4 complex diopside rich inclusions 5 al rich chondrules and 6 al rich spinel rich fragments the simple concentric and complex spinel rich cais have abundant spinel and based on the presence or absence of different major phases fassaite hibonite na al cl rich alteration products can be subdivided into several subgroups although there are some similarities between cais from r chondrites and inclusions from other chondrite groups with respect to their mineral assemblages abundance and size the overall assemblage of cais is distinct to the r chondrite group some ca al rich inclusions appear to be primitive e g low feo contents in spinel low abundances of na al cl rich alteration products abundant perovskite whereas others were highly altered by nebular and or parent body processes e g high concentrations of feo and zno in spinel ilmenite instead of perovskite abundant na al cl rich alteration products there is complete absence of grossite and melilite which are common in cais from most other groups cais from equilibrated r chondrite lithologies have abundant secondary ab rich plagioclase oligoclase and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead

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

feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust we present new compositional data for six feldspathic lunar meteorites two from cold deserts yamato 791197 and 82192 and four from hot deserts dhofar 025 northwest africa 482 and dar al gani 262 and 400 the concentrations of feo or al2o3 and th or any other incompatible element together provide first order compositional information about lunar polymict samples breccias and regoliths and regions of the lunar surface observed from orbit concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft although the derived concentrations have large uncertainties and some systematic errors compared to sample data within the uncertainties and errors in the concentrations derived from orbital data the distribution of feo and th concentrations among lunar meteorites which represent 18 source regions on the lunar surface is consistent with that of 18 random samples from the surface approximately 11 of the lunar meteorites are low feo and low th breccias consistent with large regions of the lunar surface particularly the northern farside highlands almost all regoliths from apollo sites on the other hand have larger concentrations of both elements because they contain fe rich volcanic lithologies from the nearside maria and th rich lithologies from the high th anomaly in the northwestern nearside the feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands and we provide such an estimate based on the eight most well characterized feldspathic lunar meteorites the variable but high on average mg fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high mg fe feldspathic rocks such as magnesian granulitic breccia not ferroan anorthosite geochemically the high mg fe breccias appear to be unrelated to the mafic magnesian suite rocks of the apollo collection models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites

northwest africa 011 a eucritic basalt from a non eucrite parent body we have carried out a detailed petrographic mineralogical and trace element study of northwest africa nwa 011 this meteorite bears many similarities to the eucrites it was initially identified with although oxygen isotopic compositions rule out a genetic relationship like many eucrites nwa 011 crystallized from a source with approximately chondritic proportions of ree although a slightly lree enriched bulk composition with a small positive eu anomaly as well as highly fractionated fe mg ratios and depleted sc abundances korotchantseva et al 2003 suggest that the nwa 011 source experienced some pyroxene and or olivine fractionation thermal metamorphism resulted in homogenization of ree abundances within grains but nwa 011 did not experience the intergrain ree redistribution seen in some highly metamorphosed eucrites despite a similarity in oxygen isotopic compositions nwa 011 does not represent a basaltic partial melt from the acapulcoite lodranite parent body the material from which nwa 011 originated may have been like some ch or cb chondrites members of the cr chondrite clan which are all related through oxygen isotopic compositions the nwa 011 parent body is probably of asteroidal origin possibly the basaltic asteroid 1459 magnya