comment on cosmogenic neon in grains separated from individual chondrules evidence of precompaction exposure in chondrules by j p das j n goswami o v pravdivtseva a p meshik and c m hohenberg das et al 2012 claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule the authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early sun similar to what is observed in x ray emissions of recent naked t tauri stars here we show that the production rates of cosmogenic ne used by das et al 2012 to derive nominal cosmic ray exposure ages of their olivine grains are often much too low as the reported major element concentrations in many cases sum up to considerably less than 100 even if converted to oxides in contrast adopted element concentrations for matrix samples are basically self consistent a precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by das et al 2012 das et al 2012 claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule the authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early sun similar to what is observed in x ray emissions of recent naked t tauri stars here we show that the production rates of cosmogenic ne used by das et al 2012 to derive nominal cosmic ray exposure ages of their olivine grains are often much too low as the reported major element concentrations in many cases sum up to considerably less than 100 even if converted to oxides in contrast adopted element concentrations for matrix samples are basically self consistent a precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by das et al 2012

bombardment history of asteroid 4 vesta recorded by brecciated eucrites large impact event clusters at 4 50 ga and discreet bombardment until 3 47 ga abstract the thermal impact histories of sixteen eucrite meteorites were investigated three monomict eucrites nwa 999 a 87272 87 and stannern five polymict eucrites nwa 1000 nwa 1666 nwa 5601 y 980066 100 and y 980255 100 three quench textured eucrite melt rocks y 981646 21 y 981651 105 and mil 0766214 one eucrite dominantly comprised of quench textured clasts que 99005 11 three unclassified eucrite breccias lap 031316 9 lar 06870 5 que 99799 4 and one unbrecciated eucrite eet 92004 17 included here due to its shock features we have measured fifteen high precision new 40 ar 39 ar plateau ages on plagioclase and matrix for ten of these meteorites with a tight cluster of nine ages obtained from three different polymict breccias these ages range from 4534 56 ma to 4491 16 ma resulting in a concordant age population p 0 16 the fact that such a cluster of ages is recorded in unrelated breccias which are made of a priori unrelated components leads us to propose that those ages recorded a single heating event on a large scale and is interpreted here as a high energy impact event early in the history of vesta at 4500 4 ma we propose that the debris was ejected and isolated from subsequent large impacts in a secondary rubble pile asteroid where the energy of the outgoing shock wave from an impact is significantly reduced as it compacts the target material holsapple et al 2002 and references therein the other analyses define a spread of five plateau ages ranging from 3851 21 ma to 3469 35 ma over 380 ma an additional apparent plateau age of 4288 38 ma but with a diffusion profile of cumulative 39 ar release along with published u pb apatite age of 4 14 ga suggests that the data might either define a true continuum normal background bombardment from 4 5 ga to 3 47 ga or cluster between 3 85 ga and 3 47 ga excavation of a fresh surface at 3 85 ga continuously bombarded until 3 47 ga both scenarios are compatible with a final ejection age of 3 47 ga when a major impact liberates the bulk of the brecciated meteorites into another secondary rubble pile asteroid where the brecciated eucrites stayed relatively well protected from subsequent major impacts based on these results and recent crater counting measurements we propose that the excavation and bulk ejection were caused by the rheasilvia ca 3 47 ga basin forming impact diffusion models on plagioclase crystals with different ar age spectrum signatures from a single breccia nwa1666 4501 7 ma suggest that either 1 the formation of the breccia is very young or 2 different plagioclase crystals have different diffusion characteristics and or 3 the porosity caused heterogeneous temperatures during an impact heating event particularly likely if the 4 5 ga brecciated eucrites were stored in a rubble pile asteroid many or possibly most large asteroids being re accumulated rubble piles with potential large porosity holsapple et al 2002 scenarios 2 and 3 preclude the usage of multi grain aliquots to decipher the time temperature history of most impact breccia using 40 ar 39 ar thermochronology

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

a simple effective medium model for water saturation in porous rocks a general equation for water saturation is derived from effective medium theory a simpler low frequency equation is also derived both equations are directly solvable for water saturation the model should be applicable to any granular water wet formation additional relationships are derived specifically for application to shaly sandstones but the model should be applicable to a wide range of rock types water conductivities and tool frequencies in the derivation hydrocarbons are included in the matrix component of the equation and the combined matrix elements are treated as resistors in parallel the low frequency equation is compared to various approaches to calculation of water saturation such as dual water waxman smits and bussian the general equation is compared to three component effective medium porosity index and complex refractive index models crim the model is proven to work on experimental data under a wide range of frequencies and water conductivities it is recommended that

40ar 39ar dating of microgram feldspar grains from the paired feldspathic achondrites gra 06128 and 06129 abstract 40 ar 39 ar ages of single feldspar grains from the paired meteorites graves nunatak 06128 gra8 8 grains and 06129 gra9 26 grains are presented plateau ages 70 of the 39 ar released ranged from 4000 to 4600 ma with an average 1 uncertainty of 90 ma the most precise ages obtained were 4267 17 ma for a grain from gra8 and 4437 19 ma and 4321 18 ma for two grains from gra9 isotope correlation diagrams yield less precise ages ranging from 3800 to 5200 ma with an average 1 uncertainty of 250 ma they indicate a negligible trapped component plateau ages integrated total fusion ages and isochron ages are internally concordant at the 95 confidence level the distribution of the plateau ages for gra9 is bimodal with peaks at 4400 and 4300 ma in contrast the plateau age distribution for gra8 peaks at about 4260 ma with broad wings extending toward younger and older ages to explain the distributions of grain ages we prefer a scenario that includes a major post formation event about 4400 ma ago and a later melt intrusion event that heated gra8 more than some parts of gra9

cosmic ray exposure age and preatmospheric size of the bunburra rockhole achondrite abstract bunburra rockhole is the first meteorite fall photographed and recovered by the desert fireball network in australia it is classified as an ungrouped achondrite similar in mineralogical and chemical composition to eucrites but it has a distinct oxygen isotope composition the question is if achondrites like bunburra rockhole originate from the same parent body as the howardite eucrite diogenite hed meteorites or from several separate differentiated parent bodies to address this question we measured cosmogenic radionuclides and noble gases in the bunburra rockhole achondrite the short lived radionuclides 22na and 54mn confirm that bunburra rockhole is a recent fall the concentrations of 10be 26al and 36cl as well as the 22ne 21ne ratio indicate that bunburra rockhole was a relatively small object r approximately 15 cm in space consistent with the photographic fireball observations the cosmogenic 38ar concentration yields a cosmic ray exposure cre age of 22 3 myr whereas 21ne and 3he yield approximately 30 and approximately 60 lower ages respectively due to loss of cosmogenic he and ne mainly from plagioclase with a cre age of 22 myr bunburra rockhole is the first anomalous eucrite that overlaps with the main cre peak of the hed meteorites the radiogenic k ar age of 4 1 gyr is consistent with the u pb age while the young u th he age of approximately 1 4 gyr indicates that bunburra rockhole lost radiogenic 4he more recently

the meteoritical bulletin no 85 2001 september meteoritical bulletin no 85 lists information for 1376 newly classified meteorites comprising 658 from antarctica 409 from africa 265 from asia 262 of which are from oman 31 from north america 7 from south america 3 from australia and 3 from europe information is provided for 11 falls dergaon dunbogan gujba independence itqiy moravka oued el hadjar sayama sologne valera and worden noteworthy non antarctic specimens include 5 martian meteorites dar al gani 876 northwest africa 480 and 817 and sayh al uhaymir 051 and 094 6 lunar meteorites dhofar 081 280 and 287 and northwest africa 479 482 and 773 an ungrouped enstatite rich meteorite itqiy a bencubbin like meteorite gujba 9 iron meteorites and a wide variety of other interesting stony meteorites including ch ck cm co cr cv r enstatite and unequilibrated ordinary chondrites primitive achondrites hed achondrites and ureilites

a new solar system basalt meteorites can provide important insights into the early universe and the properties of other planets or asteroids and they continue to be good for surprises in his perspective palme highlights the report by yamaguchi et al who have analyzed a meteorite from northwest africa nwa011 this meteorite clearly originated from a partially molten object but does not match the properties of known basalts from the inner solar system of the inner planets only mercury cannot be ruled out as a possible source of this meteorite

cosmic ray exposure histories of apollo 14 apollo 15 and apollo 16 rocks we investigate the exposure history of six lunar rocks using the abundances of cosmic ray produced noble gas isotopes and the 81kr kr ages single stage exposure histories are inferred for basalt 14053 breccia 14305 and anorthosite 65315 we propose that basalt 14053 with a 81kr kr age of 21 2 5 0 m y is a cone crater ejecta and that anorthosite 65315 1 3 0 7 m y originates from south ray crater we present a comprehensive comparison of all cosmogenic noble gas ratios and abundances for rocks with single stage exposure and show that the agreement with values predicted by nuclear systematics and target element chemistry is good in particular for isotope ratios basalt 14310 experienced a multistage exposure the apparent 81kr kr age the depth sensitive isotopic ratios and fission 136xe mainly from 235u induced by secondary cosmic ray neutrons lead to the conclusion that this sample was preexposed 1 75 ae ago to cosmic rays for a duration of 350 m y basalt 15058 and anorthosite 15415 also reveal multistage exposures the abundance of the radionuclide 81kr in 15058 increases toward the surface of the rock reflecting an enhanced production rate due to solar flare particles whereas stable 83kr concentrations are constant with increasing depth within the rock this indicates that basalt 15058 received most of its irradiation in a more shielded location than that effective during the last million years

an unusual hadrosaurid braincase from the dinosaur park formation and the biostratigraphy of parasaurolophus ornithischia lambeosaurinae from southern alberta the lambeosaurine hadrosaurid parasaurolophus is known from rare occurrences in campanian deposits of western north america a previously undescribed large hadrosaurid braincase from the dinosaur p

new eucrite dar al gani 872 petrography chemical composition and evolution dar al gani 872 dag 872 is a new meteorite from libya that we classified by means of instrumental neutron activation analysis inaa electron microprobe and optical microscopy according to our results dag 872 is a mg rich main group eucrite i e a monomict noncumulate basaltic eucrite displaying a predominant coarse grained relict subophitic and a fine grained granulitic texture the meteorite also shows pockets of late stage mesostasis and is penetrated by several calcite veins due to terrestrial weathering finally it exhibits shock phenomena of stage 12 including heavily fractured mineral components undulose extinction of plagioclase kinked lamellae and mosaicism in pyroxenes corresponding to peak pressures of 20 gpa in view of petrographic criteria as well as compositional and exsolution characteristics of its pyroxenes the sample represents a metamorphic type 5 eucrite assuming the metamorphic type to be a function of burial depth on the parent body and taking into account the relatively high shock stage the excavation of dag 872 was likely induced by a major impact event prior to this point dag 872 apparently underwent a 4 stage geological evolution that is reflected by intricate textural and mineralogical features

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

complexities on the acapulcoite lodranite parent body evidence from trace element distributions in silicate minerals the trace element distributions of individual minerals from seven acapulcoites and lodranites have been studied systematic differences are evident between some members of the two groups specifically pyroxenes from the lodranites macalpine hills mac 88177 and lewis cliff lew 88280 exhibit depletions of the rare earth elements ree and other incompatible trace elements ti zr y relative to acapulcoite acapulco allan hills alh a81261 pyroxenes that are consistent with the formation and removal of 15 or more silicate partial melts from these meteorites phosphate ree patterns in these lodranites also support this scenario however other members of the acapulcoite lodranite clan exhibit more complex trace element variations elephant moraine eet 84302 which has been classified as transitional between the acapulcoites and lodranites generally has trace element characteristics similar to the acapulcoites however its plagioclase ree compositions suggest a somewhat greater degree of metamorphism than that experienced by acapulcoites such as acapulco and alha81261 similar and elevated ree abundances in the silicate phases from acapulcoite alha81187 and lodranite graves nunataks gra 95209 suggest that these two meteorites in fact experienced similar thermal histories this probably included some silicate partial melting although little melt appears to have been lost from the samples the observed variations in the trace element abundances of these samples from the acapulcoite lodranite clan emphasize the complex and varied processes that have acted on their parent body the simple bimodal classification of these meteorites based primarily on petrographic criteria which has been used to date appears to be inadequate to describe this diverse group of samples as they represent a range of degrees of partial melting both with and without accompanying melt migration in some instances secondary processes on the parent body such as cryptic metasomatism have further modified sample compositions

81kr terrestrial ages and grouping of yamato eucrites based on noble gas and chemical compositions the ages and the groupings of yamato eucrites recovered in antarctica as well as terrestrial ages of nine yamato eucrites were determined based on cosmic ray produced noble gases including the radionuclide 81kr the terrestrial ages of y 792511 y 793164 and y 794043 are 0 14 0 11 and 0 28 ma respectively due to the relatively long storage time in ice the ce anomaly caused by the terrestrial alteration was significant in these three eucrites short terrestrial ages of 0 08 ma and long cosmic ray exposure ages of about 65 ma as well as similar noble gas and ree compositions for six eucrites y 75011 791826 793547 793548 793570 and 794002 strongly suggest that they belong to a single fall for these eucrites negative eu anomalies were found considering the data of yamato eucrites previously reported 1 fall s are required for monomict and 5 falls for polymict eucrites during the past 0 3 ma fissiogenic xe from 244pu was observed in nine eucrites in which the concentration of 244pu at the beginning of xe retention was calculated to be 0 5 2 2 ppb the 244pu nd weight ratio of 1 1 2 1 10 4 agrees with that reported for angra dos reis 244pu nd 1 5 10 4 within 40 244pu u ratios of y 793164 and y 793548 are 0 0027 0 0004 and 0 0045 0 0011 respectively assuming the u abundances occurred at 4 5 ga ago these ratios are somewhat lower than the ratio of 0 004 0 007 for the solar system

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

volatile mobile trace elements in bholghati howardite abstract we determined ag au bi cd co cs ga in rb sb se te tl u and zn by rnaa in two kinds of material from the bholghati howardite a carbonaceous chondrite clast bh 4 that originated by primary nebular condensation accretion processes whole rock samples and clasts resulting from parent body processes especially igneous differentiation the trace element pattern for clast bh 4 is inconsistent with its petrologic characteristics that suggest a cm classification trace elements are at chondritic levels in bh 4 some exceed c1 zci levels others are in the c2 zcm range while still others are at c3 zco cv levels the pattern observed will not conform to a c2 one even if thermal devolatilization or enrichment is invoked either cm chondrites are chemically heterogeneous at the 3 mg size level or bh 4 is carbonaceous chondrite material different from those of discrete meteorites how many other cm clasts classified petrologically in 40 meteorites would be corroborated as cm by trace element or oxygen isotopic study trace element contents in bholghati whole rock matrix samples and or white eucritic clasts in it are high for an achondrite and variable these characteristics are indicative of random condensation of volcanic emanations admixed with pre existing eucrite diogenite and howardite layers in the hed parent body other hed samples show similar patterns and the conclusion that these reflect extensive volcanism in an asteroidal sized object is supported by other consortium noble gas and cosmochronologic measurements

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

seismic and electrical properties of sandstones at low saturations laboratory measurements of elastic wave velocities attenuation and electrical resistivity of sandstones all show distinct changes in the measured properties at very low levels of water saturation velocity decreases attenuation reaches a maximum and electrical resistivity decreases over a limited range in saturation we assume that all the water at low saturations is present in the rock as a layer of uniform thickness covering the entire internal surface area of the sample with this model we calculate the thickness of surface water that corresponds to the distinct low saturation region in all cases for both the seismic and the electrical data the thickness is equal to one to four monolayers of water this is interpreted as marking the transition in the behavior of water in a sandstone from that of a surface adsorbed phase to a bulk water phase the changes in seismic properties can be modeled by considering the effect of adding surface and bulk water to grain contacts in a similar treatment the role of contacts is shown to be a dominant factor in the electrical resistivity of sandstones at low saturations such that the addition of water to the contact area causes a dramatic decrease in the electrical resistivity

evidence for common breakup events of the acapulcoites lodranites and chondrites acapulcoites and lodranites are believed to originate on a common parent body and to represent some of the earliest events in the differentiation of the chondritic asteroids we have conducted isotopic studies of the noble gases he ne ar kr and xe and determinations of the concentrations of the major elements and of the radionuclides 10be 26al and 36cl in an attempt to constrain the cosmic ray exposure history of two members of the acapulcoite lodranite clan recovered in antarctica frontier mountain fro 95029 and graves nunataks gra 95209 from cosmic ray produced 3he 21ne and 38ar and appropriate production rates we derive parent body breakup times of 4 59 0 60 and 6 82 0 60 ma for for 95029 and gra 95209 respectively these times are consistent with those obtained from the pairs 10be 21ne and 26al 21ne whereas the times inferred from the pair 36cl 36ar are slightly longer perhaps because the 36cl activities decreased as a result of decay on earth terrestrial ages up to 50 ka for the two meteorites are consistent with the measured 36cl activities of the metal phases all acapulcoites and lodranites dated until now show cosmic ray exposure ages in the range of 4 10 ma this is the same range as that found for the major exposure age cluster of the h chondrites as a common parent body is improbable on the basis of the o isotopic systematics a common set of impactors might have affected the asteroid belt 4 10 ma ago

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

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

noble gas retention chronologies for the st severin meteorite abstract 40 ar 39 ar and 129 xe 128 xe analyses were performed on two lithologies light and dark of the st severin ll6 chondrite for the light and dark fractions respectively we obtained 40 ar retention ages of 4 38 and 4 42 ae and 129 xe retention ages of 8 4 and 15 2 myr after bjurbole the two methods give age differences of opposite sense and by both methods the differences are significant both the 40 ar and the 129 xe ages are interpreted as dating relaxation of metamorphic conditions these two chronometers are decoupled however and do not date the same events 40 ar 39 ar reflect chondritic metamorphisrn on a 10 8 yr time scale the 129 xe 128 xe ages reflect isotopic closure at higher temperatures and earlier times

the record of cosmogenic radiogenic fissiogenic and trapped noble gases in recently recovered chinese and other chondrites abstract we performed a comprehensive study of the noble gas isotopic abundances in thirty six chondrites including twenty seven chondrites recovered in china the large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter the comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200 c whereas 85 of these gases in carbonaceous chondrites are degassed at 200 c there exists a clear correlation of the fraction of trapped xe released at 1200 c and petrologic type of chondrites it thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same the ngawi ll3 chondrite is solar gas rich the solar gases in meteorites and lunar surface material are mixtures of solar wind sw and solar energetic particles sep we show that the variations of the 3 he 4 he and 20 ne 22 ne ratios for solar gas rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of he and ne or due to a change of the sw sep flux ratio with time furthermore we demonstrate that the 81kr concentration is a function of the shielding depth of a sample within the meteoroid deviations from this depth dependency curve are observed for jilin h5 lishui l5 suizhou l6 and dongtai ll6 a complex exposure history for jilin is thus confirmed and is possible for the other three chondrites cosmic ray exposure ages are calculated based on six different nuclides 3he 21ne 38ar 83kr 126xe and 81kr kr in most cases good agreement is observed for the ages derived from the different methods quality classes are assigned to the exposure ages and the age distributions are discussed in some meteorites we observe effects induced by secondary cosmicray produced neutrons epithermal neutron fluxes jn 30 300 ev and fast neutron fluxes jn 5 mev are derived based on the reactions 79br n 80kr and 24mg n 21ne respectively and preatmospheric masses of the meteoroids are estimated we show that the ratio j n 30 300 ev j n 5 mev increases with increasing preatmospheric mass we introduce a 3he exposure age 21ne exposure age vs 4he gas retention age 40ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids finally in some chondrites we observe xe produced by 244pu fission and calculate the time span between fission xe retention in these chondrites and that of the angra dos reis achondrite we find that the ordinary chondrites started to retain fission xe 48 30 ma earlier than angra dos reis we do not observe systematic differences between h l and ll or type 5 and 6 chondrites with respect to the time of fission xe retention

mn cr systematics in primitive meteorites insights from mineral separation and partial dissolution abstract cr isotopic compositions have been measured on carbonaceous chondrites cc tafassasset paris niger i nwa 5958 nwa 8157 and jbilet winselwan in bulk samples the 54 cr 52 cr ratios expressed as e 54 cr range from 0 93 to 1 58 e units these values are in agreement with values characteristic for distinct petrologic types despite this 54 cr heterogeneity the variability in the 53 cr 52 cr ratios expressed as e 53 cr of 0 2 e units and the mn cr ratios is consistent with the previous finding of an isochron in the mn cr evolution diagram the mn cr ratio in cc corresponds to variable abundances of high t condensate formed and separated at the beginning of the solar system thus the canonical 53 mn 55 mn ratio can be defined based on a consistent chronology for u pb and mn cr between the earliest objects formed in the solar nebula and the d orbigny angrite we define a canonical 53 mn 55 mn ratio and e 53 cr i of 6 8 10 6 and 0 177 respectively the internal mn cr systematics in tafassasset and paris were studied by two approaches leaching technique and mineral separation despite variable e 54 cr values up to 30 e linear co variations were found between e 53 cr and mn cr ratio the mineral separates as well as the leachates of tafassasset fall on a common isochron indicating that 1 cooling of the tafassasset s parent body occurred at 4563 5 0 25 ma and that 2 54 cr is decoupled from the other isotopes even though temperatures 900 c have been reached during metamorphism in the case of paris the leachates form an alignment with a 53 mn 55 mn ratio higher than the canonical value this alignment is not an isochron but rather a mixing line based on leachates from various cm and ci we propose the occurrence of three distinct cr reservoirs in meteoritic material pure54 high53 and low53 characterized by a e 53 cr and e 54 cr of 0 and 25 000 2 17 and 8 and 0 5 and 151 respectively pure54 has already been described and is carried by highly refractory nano spinel high53 is mn rich and most probably carried by sulfides in the matrix whereas low53 is characterized by low mn cr ratios and it is sensitive to metamorphism this component could correspond to mineral phases such as refractory oxides and carbide variable mixing proportions of high53 and low53 would explain the larger than expected uncertainty mswd of 5 5 on the cc bulk regression line a monte carlo simulation allows us to evaluate the impact of the dispersion of the initial cr isotopic ratios as a function of variable high53 the co variation of the mn cr ratio and the e 53 cr defined by the mineral separates from paris corresponds to an age of 4566 44 0 66 0 75 ma while their e 54 cr still differ by at least 0 42 e this age is likely to date the segregation of forsteritic olivines most probably from type i chondrules from fayalitic olivines from type ii chondrules and given the sampling procedure by handpicking of hundreds of grains corresponds to the average age of chondrule formation

terrestrial 81kr kr ages of antarctic meteorites the production rate of 38ar in meteorites p 38 has been determined as a function of the sample s chemical composition from 81kr kr exposure ages of four eucrite falls the cosmogenic 78kr 83kr ratio is used to estimate the shielding dependence of p 38 from the true 38ar exposure ages and the apparent 81kr kr exposure ages of nine antarctic eucrite finds terrestrial ages are calculated they range from about 3 105a pecora escarpment 82502 to very recent falls thiel mountains 82502 polymict eucrites from the allan hills a78132 a79017 and a81009 have within the limits of error the same exposure age 15 2 106a and the same terrestrial age 1 1 105a this is taken as strong evidence that these meteorites are fragments of the same fall a similar case are the elephant moraine polymict eucrites a79005 a79006 and 82600 with an exposure age of 26 106a and a terrestrial age of 1 8 105a eeta79004 may be different from this group because its exposure age and terrestrial age are 21 106a and 2 5 105a respectively the distribution of terrestrial ages of allan hills meteorites is discussed meteorites from this blue ice field have two sources directly deposited falls and meteorites transported to the allan hills inside the moving antarctic ice sheet during the surface residence time meteorites decompose due to weathering processes the weathering half life is about 1 6 105a from the different age distributions of allan hills and yamato meteorites it is concluded that meteorite concentrations of different antarctic ice fields need different explanations

a petrologic and isotopic study of lodranites evidence for early formation as partial melt residues from heterogeneous precursors abstract we have conducted petrologic chemical and isotopic studies of lodranites in an attempt to constrain their genesis lodran gibson y 791491 y 791493 y 74357 y 8002 y 75274 mac 88177 lew 88280 eet 84302 fro 90011 and que 93148 are classified as lodranites lodranites and acapulcoites are indistinguishable on the basis of oxygen isotopic compositions but are distinct in average grain sizes of their mafic silicates with lodranites being significantly coarser grained lodranites exhibit a diverse range of petrologic and mineralogic features they range widely in mafic silicate compositions fa3 13 plagioclase 0 11 4 vol fe ni metal 0 5 20 vol and troilite 0 2 5 3 vol contents and shock levels s1 s4 they appear to have experienced high peak temperatures and rapid cooling in the temperature range recorded by metallographic cooling rates i e 700 350 c the only dated lodranite gibson cooled to ar closure temperatures at 4 49 0 01 ga lodranites formed from chemically and isotopically heterogeneous precursors in which the mineral and oxygen isotopic compositions were correlated heating of their parent body to temperatures between 1050 1200 c resulted in formation of fe ni fes and basaltic partial melts depletions of troilite and or plagioclase in most lodranites testify to the removal of some of these partial melts although melt migration was complex lodranites appear to have experienced a complex cooling history of slow cooling at high temperatures followed by rapid cooling at intermediate temperatures possibly related to breakup of the parent body lodranites were liberated from their parent body during 1 3 impact events with most having cosmic ray exposure ages of 5 5 7 ma the acapulcoites are samples from the same parent body but were heated to lower temperatures and thus experienced lower degrees of partial melting

induced polarization of shaly sands equations have been developed that relate induced polarization ip in shaly sands to measurable petrophysical parameters the induced polarization process has been modeled in terms of two mechanisms clay counterion displacement and membrane blockage the resulting equations can be used to determine shaliness brine conductivity and oil saturation from in phase and out of phase conductivities laboratory measurements have confirmed the ip dependence on these variables as well as on temperature

glass veins in the unequilibrated eucrite yamato 82202 the unequilibrated eucrite yamato 82202 y82202 contains a network of relatively thick up to 1 mm in width glass veins the host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized 4 3 ga ago as a lava flow on the surface of 4 vesta the veins formed 3 90 0 04 ga ago probably as a result of frictional melting associated with impact under conditions of low effective oxygen fugacity and higher sulfur fugacity the glass contains disordered structural elements characteristic of pyroxene and feldspar reminiscent of the eucritic target lithology the unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava hence it was not affected by regional metamorphism caused by burial to a significant depth or by long term contact metamorphism associated with a thick lava flow large intrusion or hot layer of impact ejecta the meteorite resided at a shallow depth though not at the surface on 4 vesta or on one of the vestoids until it was ejected and traveled to earth probably with other hed materials that have 36ar exposure ages of 13 ma these data suggest that the surface of the asteroid 4 vesta has significant though probably small proportions of glass as well as unequilibrated volcanic rock

a petrologic chemical and isotopic study of monument draw and comparison with other acapulcoites evidence for formation by incipient partial melting abstract we have conducted petrologic chemical and isotopic studies of acapulcoites acapulco monument draw yamato 74063 alh a77081 alh a81261 alh a81315 alh 78230 alh a81187 and alh 84190 in an attempt to constrain their genesis acapulcoites have distinctly different oxygen isotopic compositions than silicate inclusions in iab and iiicd irons winonaites and ureilites and thus formed on a different parent body oxygen isotopic compositions which are slightly heterogeneous within the group overlap with lodranites indicating a likely origin on a common parent body these groups can be distinguished on the basis of mafic silicate grain size all acapulcoites have mafic silicate compositions intermediate between e and h chondrites roughly chondritic mineralogies achondritic equigranular textures micrometer to centimeter sized veins of fe ni fes which cross cut silicate phases rapid metallographic cooling rates at 600 400 c 103 105 c myr and trapped noble gas abundances comparable to type 3 4 ordinary chondrites they exhibit variable mafic silicate zoning abundance of fe ni fes veins ree abundances and patterns and possibly cosmic ray exposure ages 5 7 ma momument draw and yamato 74063 retain rare relict chondrules phosphates are associated with fe ni fes veins or form separate veins in monument draw and acapulco heating and cooling of acapulcoites occurred very early in the history of the solar system as evidenced by the 39ar 40ar ages of 4 51 ga these ages appear distinctly younger than the likely formation time for acapulco of 4 557 ga but are older than analogous 39ar 40ar ages for most chondrites acapulcoites formed from a precursor chondrite which differs from known chondrites in mineral and oxygen isotopic compositions heating to 950 1000 c resulted in melting at the fe ni fes cotectic but silicates did not melt silicate textures resulted from extensive solid state recrystallization heating was by noncollisional sources e g 26al electromagnetic induction despite uncertainties owing to a lack of data acapulcoites may have experienced a three stage thermal history of slow cooling at high temperature rapid cooling at intermediate temperatures and slow cooling at low temperatures possibly resulting from breakup and gravitational reassembly of the parent body the complex thermal history is also reflected in disequilibrium ree abundances one or at most two impact events 7 ma and possibly 5 ma ago are consistent with the cosmic ray exposure ages of all four acapulcoites for which cosmogenic noble gas data exist

the cooling history of the acapulco meteorite as recorded by the 244pu and 40ar 39ar chronometers 244pu fission track densities recorded in phosphates merrillite and apatite and in orthopyroxenes adjacent to phosphates along with 40ar 39ar dating were used to retrace the cooling evolution in the low temperature regime of the acapulco meteorite over a time interval of 110 ma high resolution 40ar 39ar dating yielded a plateau age of 4514 16 ma and a precise 40ar closure temperature of 560 20 k in plagioclase this ar closure temperature is essentially indistinguishable from the 50 retention temperature of fission tracks registered in orthopyroxene 550 25 k this allows us to anchor the floating relative 244pu timescale to the absolute timescale defined by the 40ar 39ar chronometer plutonium contents of bulk phosphates inferred from fission xenon are 2x higher than those inferred from tracks in the same phosphates reflecting the low track retention temperatures of phosphates however the pu contents from tracks in orthopyroxenes adjacent to phosphates agree with those from fission xenon suggesting similar retention temperatures and times our results together with an estimated peak metamorphic temperature 1300 k and the u pbpb datum of acapulco phosphates gopel et al 1992 outline an early thermochronological history of acapulco that is more detailed than obtained by earlier attempts and spans a time of 160 ma fast cooling in the high temperature regime 1300 720 k of 100 40 k ma was followed by a drastic change of the cooling rate between 720 and 560 k 3 7 k ma down to a very slow cooling 1 7 0 5 k ma from 550 to 360 k the fast cooling at high temperatures shared also by other acapulcoite lodranites a l suggests that the parent body of acapulco was distinctly smaller than the h chondrite asteroid in contrast the very slow cooling in the low temperature regime should imply that acapulco like material became effectively insulated during a later stage of its history 6 ma after the asteroid formation if a formation time of 4565 ma is assumed for the a l body extrapolations back in time of the pu contents of phosphates give initial 244pu 238u ratios of 0 4 10 2 and 11 10 2 for apatite and merrillite respectively for the bulk phosphates an initial pu u value of 0 8 0 16 10 2 is obtained for acapulco which is in full agreement with the preferred chondritic ratio of 0 7 10 2 proposed by hagee et al 1990 trapped ar contents are surprisingly high both primordial 36ar at levels of type 4 ordinary chondrites and excess radiogenic 40ar were detected in our sample as in some acapulcoites by other authors this partial closed system behaviour could be the result of the partial melt and sintering effects that the high peak metamorphic temperatures have induced in a l meteorites in addition the spread in the early peak temperatures 1300 1450 k as reflected by the diverse degrees of partial melting observed in a l meteorites suggests heterogeneously distributed short lived heating sources 26al60fe and disfavours the homogeneous heating expected from an electromagnetic induction arising from an active pre main sequence sun the possibility that some specific collisional event s with or without disruption of the a l planetesimal could satisfactorily explain the thermal histories and diverse characteristics of these meteorites appears difficult to envision in the absence of evident shock effects in most if not all a l meteorites

tectonic stratigraphic and sedimentologic significance of a regional discontinuity in the upper judith river group belly river wedge of southern alberta saskatchewan and northern montana the lithostratigraphic interval between the taber and lethbridge coal zones in the upper portion of the nonmarine judith river group of southeastern alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity the lower unit referred to here as the oldman formation is characterized by very fine grained to fine grained sandstones that contain fewer than 2 volcanic rock fragments sandstone bodies with numerous sets of horizontally stratified sandstone showing little or no evidence of lateral accretion siliceous paleosols ganisters and a relatively high gamma ray signal in the upper half of the formation the oldman formation comprises deposits of a low sinuosity perhaps ephemeral fluvial system that originated in the southern cordillera of canada and northern montana and flowed northeastward perpendicular to the axis of the alberta basin the upper unit is assigned to a new formation the dinosaur park formation and is characterized by

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

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

noble gases in 21 saharan ll chondrites exposure ages and possible pairings nineteen ll chondrites and two l ll chondrites adrar 003 and tanezrouft 010 from the saharan desert of algeria and libya have been analysed for their he ne and ar composition as well as for their abundance of 84kr and 132xe calculated 21ne cosmic ray exposure ages vary between 2 and 35 ma the age distribution is consistent with that of modern ll chondrite falls except that no dominant peaks can be observed especially not the one related to a 15 ma collisional event however the lack of young exposure ages of 8 ma is obvious this is a characteristic feature of ll chondrites only one of the 21 ll chondrites namely acfer 066 contains solar gases and is thus considered a regolith breccia three specimens reveal considerable loss of 3he probably due to periods of elevated temperatures in orbits with small perihelion distances furthermore severe loss of 4he and 40ar is found in two samples considering possible pairings we suggest 14 individual falls basically on the basis of the noble gas data the petrographic sub classification and by taking the find location into consideration however there are constraints on confirming pairings solely on the basis of our studies thus we can only exclude individual samples with a unique noble gas fingerprint from paired specimens

the bholghati howardite chemical study bholghati is homogeneous on a cm scale in major element composition but heterogeneous in trace elements such as the rare earth elements rees the rees are concentrated in accessory phosphates and their sampling can influence the ree patterns of eucritic clasts which in turn can govern the bulk ree patterns bholghati can be reasonably modeled with 56 eucritic 45 diogenitic and 3 dark clast components however an additional component feldspathic is required to match the bulk composition dark clasts represent carbonaceous cm type material that was admixed with other components during regolith formation on the eucrite parent body epb one eucritic clast fine grained is light ree lree depleted relative to heavy ree hree which is unusual in normal eucrites the lree depletion pattern cannot be modeled from one stage partial melting of a chondritic source however it can be modeled from a non chondritic source depleted in lrees or multi stage melting of a chondritic source provided that the lree depletion is not from undersampling of phosphates bholghati has a complex history that involved early multiple magmatic events later annealing and fragmentation and low temperature mixing of eucritic diogenitic and carbonaceous components on the howardite parent body

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

partial melting and melt migration in the acapulcoite lodranite parent body we review petrologic evidence that the acapulcoites and lodranites formed by 1 vol to probably 20 vol whole rock partial melting of a chondritic precursor material at low degrees of partial melting only fe ni fes cotectic melting occurred migration distances for partial melts were short resulting in the formation of acapulcoites with essentially chondritic troilite and plagioclase contents but achondritic textures at high degrees of partial melting both fe ni fes and basaltic plagioclase pyroxene partial melts formed and the melts may have migrated out of the source rock the partial melt residues which are more or less depleted in fe ni fes and plagioclase are the lodranites melt migration was complex most acapulcoites which experienced relatively low degrees of partial melting lost little if any of the partial melt one acapulcoite lew 86220 represents a unique case in which fe ni fes and basaltic partial melts appear to have migrated from a lodranite source region into a cooler acapulcoite region where they were trapped in cases of the relatively high degrees of partial melting experienced by lodranites melts may have been partly selectively or totally removed from the rocks and fe ni fes and or basaltic partial melts may have been removed to different degrees and may in fact have been trapped on occasion in greater than chondritic proportions we model vein and dike formation and melt migration by calculating the excess pressures and vein and dike sizes for varying degrees of partial melting our calculations are broadly consistent with observations indicating that melt migration is inefficient at low degrees of partial melting and extremely efficient at high degrees of partial melting although the size of the acapulcoite lodranite parent body and the volatile contents of the chondritic precursor rocks are poorly constrained the lack of basaltic rocks in the world s meteorite collections complementary to the lodranites suggests that basaltic partial melts may have been accelerated off the body by explosive volcanism of the type envisioned by wilson and keil 1991 and ejected into space the diversity of rocks from the acapulcoite lodranite parent body may provide a basis for better understanding the diverse range of spectral subtypes recognized among the s type asteroids

40ar 39ar chronology of lunar meteorites northwest africa 032 and 773 the 40ar 39ar dating technique has been applied to the lunar meteorites northwest africa 032 nwa 032 an unbrecciated mare basalt and northwest africa 773 nwa 773 composed of cumulate and breccia lithologies to determine the crystallization age and timing of shock events these meteorites may have experienced stepped heating analyses of several different samples of nwa 032 gave complex age spectra but indistinguishable total ages with a mean of 2 779 0 014 gyr possible causes of the complex age spectra obtained from nwa 032 include recoil of 39ar or the presence of pre shock 40ar incorporated into shock melt veins the effects of shock veins were investigated by laser fusion of 20 small samples expected to contain varying proportions of the shock veins the laser ages show a narrow age distribution between 2 61 2 86 gyr and a mean of 2 73 0 03 gyr identical to the total age of 2 80 gyr obtained for the bulk sample diffusion calculations based on the stepped heating data indicate that ar release can be reconciled by release from feldspar and possibly shock veins at low temperatures followed by pyroxene at higher temperatures the exposure age of nwa 032 is 212 11 myr and it contains low trapped solar ar stepped heating of cumulate and breccia portions of nwa 773 also give a relatively young age of 2 91 gyr the presence of trapped ar in the breccia makes the age determination of this component less precise but release of ar appears to be from the same mineral phase assumed to be plagioclase in both lithologies a marked difference in exposure age between the 2 lithologies also exists with the breccia having spent 81 myr longer at the lunar surface this finding is consistent with the higher trapped ar content of this lithology assuming that 2 80 gyr and 2 91 gyr are the crystallization ages of nwa 032 and nwa 773 respectively these two meteorites are the youngest lunar mare basalts available for study

resistivity of partially saturated triassic sandstone the variation in resistivity with saturation of poorly cemented triassic sandstone samples from a site in the english midlands has been measured the measurements were obtained using an adapted four electrode technique which utilizes conductive gelling agents between electrodes avoiding the need to sputter electrodes directly on to samples a difficult process with such friable samples the measurements provide important information regarding the way in which resistivity varies with saturation in the triassic sandstone the resulting variation in the observed resistivity versus saturation curves indicates the presence of significant pore scale variation between samples measurements have also been conducted on fully saturated samples these indicate significant variation in the matrix conductivity between samples the results have important implications for field scale monitoring of the unsaturated zone

pinpointing the source of a lunar meteorite implications for the evolution of the moon the lunar meteorite sayh al uhaymir 169 consists of an impact melt breccia extremely enriched with potassium rare earth elements and phosphorus thorium 32 7 parts per million ppm uranium 8 6 ppm potassium oxide 0 54 weight percent and adherent regolith the isotope systematics of the meteorite record four lunar impact events at 3909 13 million years ago ma 2800 ma 200 ma and 0 34 ma and collision with earth sometime after 9 7 1 3 thousand years ago with these data we can link the impact melt breccia to imbrium and pinpoint the source region of the meteorite to the lalande impact crater

a new source of basaltic meteorites inferred from northwest africa 011 eucrites are a class of basaltic meteorites that share common mineralogical isotopic and chemical properties and are thought to have been derived from the same parent body possibly asteroid 4 vesta the texture mineralogy and noble gas data of the recently recovered meteorite northwest africa nwa 011 are similar to those of basaltic eucrites however the oxygen isotopic composition of nwa011 is different from that of other eucrites indicating that nwa011 may be derived from a different parent body the presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies perhaps similar to 4 vesta in the early solar system

a new centrosaurine ceratopsid from the oldman formation of alberta and its implications for centrosaurine taxonomy and systematics centrosaurus brinkmani sp nov is distinguished from centrosaurus apertus by key features of its cranial ornamentation including the shape and orientation of the postorbital horn and parietal ornamentation at parietal locus 3 the shape of the parietal ornamentation at locus 2 and the possession of accessory parietal ossifications developed as short spines on the caudal parietal ramus this species is restricted to the oldman formation of southern alberta and is the oldest ceratopsid represented by diagnostic material in canada phylogenetic analysis of the centrosaurinae suggests that the development of spike like ornamentation at the parietal locus 3 parietal locus is inversely related to the development of the p1 parietal ornamentation

the quest for regolithic howardites part 2 surface origins highlighted by noble gases we report noble gas data of helium he neon ne argon ar krypton kr and xenon xe cosmic ray exposure cre ages and nominal gas retention k ar u th he ages for seven howardites cre 01400 eet 87513 eet 87518 eet 99400 gro 95535 gro 95602 san 03472 in continuing research to identify regolithic samples and better understand the vestan regolith in our previous work we found little correlation between suggested regolith parameters of ni 300 g g al 2o 3 8 9 wt and eucrite diogenite e d ratio of 2 1 warren et al 2009 and trapped solar wind sw fractionated solar wind fsw or planetary noble gas components from impacted material noble gas indicators of a regolithic origin here we have expanded our data set to include samples outside of these parameters to further explore composition and the differences in ni content as indicators for the presence of non vesta material in addition our sample set includes two potentially paired meteorites from the gro suite finally in our petrographic studies the samples selected showed no evidence for carbonaceous chondrite fragments which should reduce the effect of contamination by planetary noble gas components and will allow us to better identify sw fsw components where present of the samples studied here three howardites gro 95535 gro 95602 and eet 87513 show evidence for a regolithic origin with both isotopic and element noble gas ratios clearly pointing to the presence of trapped components similar to sw fsw or planetary the two gro howardites gro 95535 and gro 95602 show similar noble gas ratios to our previously defined sw fsw dominated regolithic group lew 85313 and met 00423 suggesting a surface origin for these samples however interestingly the gro samples show vastly different cosmogenic noble gas abundances and thus different cre ages which suggests that they are not paired for howardite eet 87513 the data hint to the presence of cm material with a neon release pattern similar to our defined planetary fsw dominated regolithic group cm rich samples pra 04401 sco 06040 our petrological investigations found no evidence for cm fragments within eet 87513 though a single clast was reported previously buchanan et al 1993 aside from the ne release pattern the remaining noble gas data show more similarity with sw fsw components the remaining four howardites cre 01400 eet 87518 eet 99400 and san 03472 and are dominated by cosmogenic noble gases and show no evidence for a regolithic origin our data suggest that a cm composition is likely present in all samples to some degree but that this can be overprinted by sw components or cosmogenic components obtained in situ on the vestan surface or during transit to earth respectively the presence of cm material is an important parameter for understanding the evolution of vesta s surface while we have uncovered three further regolithic howardites 13 regolithic total of 41 analysed further noble gas analysis of hed meteorites is needed to not only determine regolithic origins but to better characterise the abundance of carbonaceous chondrite material and its effect on the noble gas signatures of such samples

differentiated achondrites asuka 881371 an angrite and divnoe noble gases ages chemical composition and relation to other meteorites abstract we present a study of the noble gas isotopic abundances in two achondrites divnoe and the asuka 881371 angrite for divnoe we also performed chemical analyses of the major elements and of some minor and trace elements that are relevant for the comparison with other meteorite types and for the interpretation of the noble gas data based on the cosmic ray produced noble gases an exposure age of 5 4 0 7 ma for asuka 881371 was obtained this ejection time from the parent asteroid differs from those of the other three angrites angra dos reis 55 5 ma lew 86010 17 6 ma and lew 87051 0 2 ma whereas the u th 4 he and k 40 ar gas retention ages of asuka 881371 are 3750 1000 ma and 3910 500 ma respectively we derive for the 244 pu 136 xe system a formation age of 4533 40 ma which is contemporaneous with that of the other angrites angra dos reis and lew 86010 for divnoe the abundance patterns of the major lithophile siderophile refractory and volatile elements the isotopic abundance pattern for primordial trapped xe and the oxygen isotopes indicate that this unique meteorite is related to the brachinite achondrites assuming no pre exposure to cosmic rays on the parent body divnoe s asteroid ejection event occurred 17 2 2 3 ma ago

anatomy of a partially differentiated asteroid a near sighted view of acapulcoites and lodranites with the insertion of the near spacecraft into orbit around the asteroid 433 eros a new stage of asteroid exploration has begun with the return of spatially resolved mineralogical geological and chemical information from specific asteroids in this paper we outline the features of a partially differentiated asteroid using the acapulcoite and lodranite meteorites as a guide such a body would likely contain a variety of lithologies including chondritic rocks largely unaltered by melting residues of partial melts and basaltic and fe ni fes rocks crystallized from the partial melts the presence or nature of the regolith remains largely unconstrained mineralogical and isotopic heterogeneities preserved in these rocks suggest spatial separation of these rock types by distances in excess of 200 m spacecraft based remote sensing instrumentation should detect substantial spectral heterogeneity most prominently manifested in the band area ratio and chemical heterogeneity observation of these various lithologies in situ would provide important new constraints on the processes involved during the earliest differentiation of asteroids

the tafassasset primitive achondrite insights into initial stages of planetary differentiation abstract tafassasset is an exceptional meteorite that has been linked to both the cr chondrites and the primitive achondrites because previous evidence suggests it might be a primitive achondrite from a known chondrite type we have undertaken a study of the petrology geochemistry and formation history of the meteorite tafassasset is predominantly feo rich olivine 58 yet contains abundant fe ni metal 10 vol and sulfide 3 vol other phases include high and low ca pyroxene plagioclase chromite and phosphate it has a recrystallized texture containing equigranular grains that often meet at 120 triple junctions there are no relict chondrules in the thin sections examined although they have been reported previously electron microprobe analyses reveal homogeneous olivine fa 28 6 both low and high ca pyroxene fs 23 6 wo 3 7 and fs 12 2 wo 39 3 1 a range of plagioclase composition an 23 47 fe ni metal with 5 3 36 6 wt ni and 0 1 0 8 wt co troilite chromite and ca phosphate bulk composition analyses reveal two chips depleted in refractory lithophile and some siderophile elements compared to ci chondrites exceptions are enrichments in fe ni and co a third chip is essentially chondritic in bulk composition different stones of the meteorite have slightly different oxygen isotope composition yet all lie in the cr chondrite trend with one in the acapulcoite lodranite field thermodynamic calculations show that tafassasset equilibrated at a temperature above the fe ni fes eutectic and at an oxygen fugacity of iw 1 the texture heterogeneous distribution of mineral phases plagioclase composition two mineral closure temperatures and bulk composition all provide evidence that tafassasset partially melted on its parent body a comparison with the cr chondrites the brachinites and two anomalous achondrites indicates that tafassasset is most similar to ungrouped primitive achondrites lewis cliff lew 88763 and divnoe and to the brachinites in overall petrography modal mineralogy mineral compositions oxidation state and bulk composition the comparison also excludes the possibility that tafassasset formed by partial melting of a cr chondrite tafassasset is a primitive achondrite and likely evolved on a parent body that experienced incomplete melting never reached isotopic homogeneity and was from the same oxygen isotopic reservoir as the cr chondrite parent body

aubrites and diogenites trace element clues to their origin we have analyzed by rnaa 25 aubrite and 9 diogenite samples for 13 to 29 siderophile volatile and lithophile trace elements both meteorite classes show a typically igneous siderophile element pattern with ir os re ge more depleted than au ni pd sb but aubrites tend to have about 10 higher abundances 10 3 10 4 cl for the first 4 and 10 2 10 3 cl for the last 4 siderophiles apparently reflecting smaller metal silicate distribution coefficients at lowerf o2 or less complete segregation of metal se is surprisingly abundant in aubrites up to 0 4 cl but te is less so sete 5 cl apparently due to its stronger siderophile character other volatiles ag zn in cd bi t1 show depletions intermediate between lunar dunite and the earth s mantle of 7 aubrites analyzed for ree ce nd eu tb yb lu 6 are depleted in ree 0 08 0 5 cl and 5 show negative eu anomalies the exceptions are bishopville and mt egerton silicate this supports an igneous origin as already noted by boynton and schmitt 1972 no samples of the complementary basaltic and feldspathic rocks have been found thus far but one of our samples of khor temiki dark is a candidate for the basalt it is 5 7 enriched in ree and only slightly less so in rb cs and u though shocked and enriched in siderophiles to 0 05 cl it apparently represents a new meteorite class three diogenites analyzed for ree show very diverse patterns from strongly depleted in light ree for tatahouine ce 0 01 cl to flat for garland 2 5 cl the data confirm the trends found by fukuokaet al 1977 as well as their interpretations factor analysis shows several parallel groupings for aubrites and diogenites siderophiles re ir os pd ge chalcophiles se te volatiles ag in tl and incompatibles u ree and cs or rb but there are some differences for elements such as ni sb cd bi au and zn most of which behave more sensibly in aubrites than in diogenites several element pairs that differ greatly in volatility cs u ge ir correlate closely in aubrites in approximately cl chondrite proportions these correlations and other lines of evidence suggest strongly that aubrites originated by igneous processes in their parent body not by direct nebular condensation the source material may have resembled el chondrites in oxidation state and depletion of refractories metal and volatiles

petrology of unique achondrite queen alexandra range 93148 a piece of the pallasite howardite eucrite diogenite parent body abstract queen alexandra range que 93148 is a small 1 1 g olivine rich achondrite mg 86 that contains variable amounts of orthopyroxene mg 87 and kamacite 6 7 wt ni with minor augite olivine in que 93148 contains an unusual suite of inclusions 1 5 100 m sized lamellae with a cao and cr2o3 rich 10 and 22 wt respectively composition that may represent a submicrometer scale intergrowth of chromite and pyroxene s 2 75 500 m sized lamellar symplectites composed of chromite and two pyroxenes with minor metal 3 15 20 m sized irregularly shaped symplectites composed of chromite and pyroxene s 4 100 150 m sized elliptical inclusions composed of chromite two pyroxenes metal troilite and rare whitlockite type 1 2 and 3 inclusions probably formed by exsolution from the host olivine during slow cooling whereas type 4 more likely resulted from early entrapment of silicate and metallic melts followed by closed system oxidation queen alexandra range 93148 can be distinguished from most other olivine rich achondrites ureilites winonaites lodranites acapulcoites brachinites eagle station type pallasites and pyroxene pallasites as well as from mesosiderites by some or all of the following properties o isotopic composition fe mn mg relations of olivine cao and cr2o3 contents of olivine orthopyroxene compositions molar cr cr al ratios of chromite metal composition texture and the presence of the inclusions in terms of many of these properties it shows an affinity to main group pallasites nevertheless it cannot be identified as belonging to this group meteorite que 93148 appears to be a unique achondrite possibly it should be considered to be a pyroxene pallasite that is genetically related to main group pallasites alternatively it may be derived from the mantle of the pallasite howardite eucrite diogenite parent body

the formation and evolution of the moon s crust inferred from the sm nd isotopic systematics of highlands rocks abstract ages determined for magnesian and ferroan anorthosite crustal rock suites overlap suggesting they formed contemporaneously about 4 3 4 5 ga a notable exception is the sm nd age previously determined on mg suite gabbronorite 67667 which is at least 100 ma younger than the youngest ferroan anorthosite new chronologic measurements of 67667 presented here yield concordant sm nd and rb sr mineral isochron ages of 4349 31 ma and 4368 67 ma suggesting the sample is older than previous estimates furthermore a whole rock sm nd isochron of mg suite rocks from the apollo 14 15 16 and 17 landing sites yields an age of 4348 25 ma indicating that mg suite magmatism was widespread and roughly contemporaneous on the lunar nearside analysis of sm nd internal isochron ages confirms that mg suite magmatism was restricted to a period between about 4 33 and 4 35 ga at the apollo 14 15 16 and 17 landing sites and was synchronous with magmatism at the apollo 16 site associated with the ferroan anorthosite suite between 4 35 and 4 37 ga magnesian and ferroan anorthosite suite rocks with ages younger than 4 33 ga appear to have experienced slow cooling in the deep lunar interior so that the ages record when the samples cooled below the closure temperature of the sm nd isotopic system and not the time they crystallized the ages determined for mg suite and ferroan anorthosite suite rocks are concordant with the age determined for the formation of urkreep of 4350 34 ma using the sm nd isotopic systematics of 67667 and measurements completed on norite 78238 troctolite 76535 kreep basalt 15386 and gabbronorite nwa 773 crystallization ages of mg suite and fas are also concordant with the average of 146sm 142nd ages previously determined for the formation of the mare basalt source region of 4333 30 ma the similarity of ages for mg suite magmatism ferroan anorthosite suite magmatism urkreep formation and formation of the mare basalt source regions implies the processes that produced these rocks were petrogenetically linked it also implies that both early stage and late stage lunar magma ocean cumulates formed over a relatively short duration of

age of a eucrite clast from the bholghati howardite 39ar 40ar rb sr and sm nd investigations of the large eucrite clast 1 studied by the bholghati consortium show that it crystallized from a melt 4 51 ga ago the crystallization age is given most precisely by a sm nd internal isochron of 4 510 0 034 ga 2 error limits for 147sm 0 00654 ga 1 142nd144nd measurements show that the clast contained live 146sm at the time of crystallization a solar system initial 146sm144sm0 0 00431 0 0039 0 0026 at 4 555 ga ago can be calculated from a 146sm 142nd isochron and the age of the clast alternatively using 146sm144sm 0 0 0045 as previously reported in the literature a 146sm142nd formation interval of 0 05 0 12 0 08 ga can be calculated which is concordant with the 147sm 143nd isochron age and in agreement with pu u xe and pu nd xe formation intervals reported in a companion consortium paper the initial 143nd144nd ind of the clast was ind 0 505958 50 2 error limits normalized to 146nd 144nd 0 724140 and is consistent with the chur reference value for evolution in a source having chondritic relative ree abundances prior to magma generation however when interlaboratory bias is considered the data are also permissive of a lree depleted source as suggested in a companion consortium paper a primary rb sr isochron yields an age of 4 54 0 06 ga 2 error limits for 87rb 0 01402 ga 1 in agreement with the more precise sm nd age the initial 87sr86sr isr of the clast was isr 0 699006 21 and was the same within error limits as isr previously determined for a pristine eucrite clast from polymict eucrite y75011 compatible with a common parent body the 39ar 40ar data and some of the rb sr data show that bholghati was affected by a major thermal event 2 3 ga ago and also provide weak evidence for a minor thermal event 1 ga ago the age and isotopic systematics of the clast are consistent with those of other eucrites and support the widely held assumption of a common parent body for howardites and eucrites the isotopic investigations of polymict eucrites and howardites point to a prolonged cratering record on the howardite eucrite diogenite hed parent body and suggest that it survived the cataclysm affecting the moon 3 8 4 0 ga ago

a new concept in modeling the dielectric response of sandstones defining a wetted rock and bulk water system experimental data for the real part of the dielectric constant k of three sandstone samples are considered as a function of the level of water saturation sw in the frequency range 60 khz to 4 mhz existing theoretical models have previously shown poor agreement with k versus sw data for rock samples undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects in analyzing the data presented here we find a pronounced increase in k in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock water interface when this increase in k is accounted for by defining wetted matrix parameters the data show excellent agreement with existing theoretical models

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

the new polymict eucrite dar al gani 983 petrography chemical composition noble gas record and evolution mineralogical and chemical studies of dar al gani 983 show that this meteorite is a eucrite its texture is that of an impact breccia it contains cumulate pyroxene and feldspar megacrysts a variety of recrystallized melt clasts clasts of subophitic basalt and mesostasis these components are embedded in a matrix of fragmental pyroxene and plagioclase in addition the entire rock is penetrated by glassy melt veins and patches and displays features of strong shock the mineralogical and chemical evidence obtained for dag 983 indicates that this meteorite experienced a complex evolutionary history the presence of cumulate silicate crystals implies substantial large scale cratering events on the hed asteroid as a result of these impacts rocks from different intrusive bodies to extrusive surface layers were laterally and vertically transported to form a thoroughly mixed megaregolith dag 983 represents a sample of this megabreccia

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

noble gases bulk chemistry and petrography of olivine rich achondrites eagles nest and lewis cliff 88763 comparison to brachinites eagles nest and lewis cliff lew 88763 are olivine rich achondrites that have been suggested to be related to brachina and alh 84025 both are ultramafic although lew 88763 has 10 plagioclase which eagles nest lacks olivine in eagles nest fo68 is virtually identical in composition to that in brachina fo68 70 and that in lew 88763 is only slightly different fo63 64 the meteorites cosmic ray exposure ages differ from each other and from brachina and alh 84025 like brachina eagles nest has a substantial amount of radiogenic 129xe and an apparent k ar age of 4 5 ga lewis cliff 88763 on the other hand has no detectable radiogenic 129xe an apparent k ar age of 4 5 ga and a substantial amount of trapped xe the chemical composition of lew 88763 is within a factor of two of chondritic for virtually every element analyzed including siderophiles which suggests that it was melted or at least heated and recrystallized in a closed system analyses of the chemical composition of eagles nest are hampered by extensive terrestrial weathering but it appears to be broadly chondritic also although it like brachina is depleted in siderophiles our data suggest that eagles nest is genetically related to brachina but that lew 88763 is not which is a conclusion that is consistent with the o isotopic data of clayton and mayeda 1996

the meteoritical bulletin no 86 2002 july abstract meteoritical bulletin no 86 lists information for 1154 newly classified meteorites comprising 661 from antarctica 218 from africa 207 from asia 203 of which are from oman 62 from north america 3 from south america and 3 from europe information is provided for 5 falls el idrissia undulung dashoguz el tigre and yafa noteworthy specimens include 7 martian meteorites dhofar 378 grove mountains 99027 northwest africa 856 1068 and 1110 and sayh al uhaymir 060 and 090 4 lunar meteorites dhofar 301 302 303 and 489 9 new iron meteorites a mesosiderite northwest africa 1242 an ungrouped stony iron meteorite dar al gani 962 and a wide variety of other interesting stony meteorites including ch ck cm cr cv r enstatite unequilibrated ordinary and ungrouped chondrites primitive achondrites howardite eucrite diogenite hed achondrites and ureilites

petrology geochemistry and cosmic ray exposure age of lherzolitic shergottite northwest africa 1950 northwest africa nwa 1950 is a new member of the lherzolitic shergottite clan of the martian meteorites recently found in the atlas mountains the petrological mineralogical and geochemical data are very close to those of the other known lherzolitic shergottites the meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine fo66 to fo75 low and high ca pyroxenes en 78 fs 19 wo 2 en 60 fs 26 w 14 en 53 fs 16 wo 31 en 45 fs 14 wo 41 and plagioclase an 57 ab 41 or 1 to an 40 ab 57 or 3 entirely converted into maskelynite during intense shock metamorphism accessory minerals include phosphates merrillite chromite and spinels sulfides and a glass rich in potassium the oxygen isotopic values lie on the fractional line defined by the other snc meteorites delta 17 o 0 312 parts per thousand the composition of nwa 1950 is very similar to the other lherzolitic shergottites and suggests an origin from the same magmatic system or at least crystallization from a close parental melt cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites the intensity of the shock is similar to that observed in other shergottites as shown by the occurrence of small melt pockets containing glass interwoven with stishovite

acapulco and lodran like achondrites petrology geochemistry chronology and origin we have performed petrologic and geochemical studies of five primitive achondrites alha81187 and alha81261 acapulco like eet 84302 transitional but acapulco like and lew 88280 and mac 88177 lodran like we have also performed 39ar 40ar chronology on alha81187 alha81261 and eet 84302 lew 88280 and mac 88177 contain more ferroan olivines orthopyroxenes clinopyroxenes and chromites than do the acapulco like achondrites plagioclase is present in only alha81187 alha81261 and eet 84302 its composition does not track that of the mafic silicates eet 84302 with the most calcic plagioclase contains olivine and pyroxene with an mg intermediate between alha81187 and alha81261 similarly spinels in eet 84302 have the same mg as those in alha81187 while pyroxenes in the former are more ferroan than in the latter acapulco like achondrites have sm sc ratios between 0 8 1 5 times h chondrites and na sc ratios are between 0 81 0 times h chondrites indicating that silicate partial melts have not been lost from these rocks siderophile and chalcophile elements are fractionated and show a trend of increasing ir ni ratios with decreasing se co ratios this variation is consistent with fractionation by partial melting in the fe ni s system eet 84302 is very depleted in se and troilite is a accessory phase indicating essentially total loss of the low temperature fe ni s melt in contrast the lodran like achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements sm sc ratios are 0 2 0 7 times and na sc ratios are 0 04 0 18 times h chondrites these data are consistent with a model for formation of the lodran like achondrites as partial melting residues however the low ir ni and high se co ratios in two lodran like achondrites suggest the metal troilite in these rocks is dominated by the low melting fraction in the fe ni s system this metal troilite was added to the silicates after partial melting depleted them in a basaltic fraction the ar ar release spectra yield good plateau ages of 4 507 0 024 ga alha81187 4 511 0 007 ga alha81261 and 4 519 0 017 ga eet 84302 in good agreement with previously determined ar ar ages for other acapulco like achondrites together the ar ar ages demonstrate that metamorphism on the acapulco lodran parent body occurred 4 51 0 02 ga ago roughly 50 ma after its formation the geochemical and petrologic evidence on the acapulco and lodran like achondrites suggest that heating on the parent body was localized and heterogeneous in space and time the parent body was probably not subjected to parent body wide magmatism in contrast to the case for 4 vesta and the hed meteorites

tafassasset evidence of early incipient differentiation on a metal rich chondritic parent body abstract tafassasset is a primitive meteorite the origin of which is still debated its possible relationship to either the cr chondrites considered among the most primitive meteorites or the brachinites complex primitive achondrites makes it an interesting sample for studying the initial stages of planetary accretion and differentiation in the early solar system here we report tungsten w isotope data for bulk rock samples as well as for mineral fractions from tafassasset along with micro computed tomography of a piece of the meteorite silicates show mass independent w isotope anomalies while the metal phase does not these nucleosynthetic anomalies are interpreted as reflecting the presence of sic presolar grains in the matrix of the meteorite carrying s process 184w after correction of the nucleosynthetic anomalies a correlation is observed between the 182w 184w isotope compositions and the hf w ratios of the different fractions a 182hf 182w age of ca 2 9 ma after cais is inferred from the 182hf 182w chronometer slightly older than other estimates based on the 53mn 53cr 26al 26mg and pb pb chronometers but consistent with the difference in closure temperatures of the different isotopic systems numerical modeling of the thermal evolution of tafassasset indicates accretion of a parent body less than 50 km in diameter 1 ma after the formation of cais at a time when short lived radio nuclides induced metal silicate separation and partial melting of the silicates with extraction of a basaltic component according to our new data tafassasset may represent an inner part of a cr like parent body with a differentiation history similar to but less severe than that of brachinites

cosmic ray exposure histories and 235u 136xe dating of apollo 11 apollo 12 and apollo 17 mare basalts the history of exposure to cosmic rays was studied for nine basaltic rocks based on the cosmic ray produced noble gas isotopes the results for the five basalts 10003 10047 12004 12051 and 77135 are consistent with a single stage exposure four basalts 10057 10069 12040 and 12053 experienced a multistage exposure using the 235u 136xe dating method the time of their early exposure to cosmic rays on the lunar surface was dated to have begun 3 4 aeons ago immediately after rock formation as defined by their crystallization ages the durations and shielding depths for the proposed two stage exposure models of the four basalts were calculated from the shielding at the early stage we estimate a lower limit of 50 cm for the thickness of the lava flows from which the investigated basalts originate

the influence of shale effects upon the electrical resistivity of reservoir rocks the roots of the so called shaly sand problem in hydrocarbon evaluation lie in the effect of relatively fine grained minerals upon measured electrical parameters of granular reservoirs this influence manifests itself as an excess conductivity over and above that due to the purely geometric effects of electrolyte distribution within the pore space for formations with low shaliness this excess conductivity is usually insignificant in typical oilfield situations the influence of shaliness upon observed values of formation resistivity has been appraised by collating core sample data from four different reservoirs it has been demonstrated that during the course of electrical measurement under conditions of full electrolyte saturation any given lithology can exhibit both negligible and highly significant shale effects depending upon the resistivity of the interstitial aqueous electrolyte the effects of shaliness are also governed by the degree of water saturation because the manifestation of shaliness in electrical data is not a function of lithology alone recourse is made to a more realistic concept of shale effects whereby a formation or section of a formation is classified as effectively clean or effectively shaly according to whether it obeys or defies respectively the fundamental empirical laws of archie 1942 in particular since an intrinsic formation factor can be obtained directly in fully saturated effectively clean reservoirs whereas only an apparent quantity may be recorded directly in fully saturated effectively shaly reservoirs the ratio of apparent to intrinsic formation factor serves as a useful conceptual indicator of shale effects attaining the limiting value of unity only under effectively clean conditions in the context of electrical measurement the terms shaliness and shale effects are evidently not synonymous and it is the latter which should be considered when selecting equations for the computation of water saturation the implications for well log analysis follow through formulated guidelines that describe the relative levels of shale effects in different zones of lithologically uniform reservoirs

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

the puerto lapice eucrite puerto lapice is a new eucrite fall castilla la mancha spain 10 may 2007 in this paper we report its detailed petrography magnetic characterization mineral and bulk chemistry oxygen and noble gas isotope systematics and radionuclide data study of four thin sections from two different specimens reveal that the meteorite is brecciated in nature and it contains basaltic and granulitic clasts as well as recrystallized impact melt and breccia fragments shock veins are ubiquitous and show evidence of at least three different shock events bulk chemical analyses suggest that puerto lapice belongs to the main group of basaltic eucrites although it has a significantly higher cr content oxygen isotopes also confirm that the meteorite is a normal member of the hed suite noble gas abundances show typical patterns with dominant cosmogenic and radiogenic contributions and indicate an average exposure age of 19 2 ma and a pu fission xe age well within typical eucrite values cosmogenic radionuclides suggest a preatmospheric size of about 20 30 cm in diameter