40ar 39ar ages of lunar impact glasses relationships among ar diffusivity chemical composition shape and size abstract lunar impact glasses which are quenched melts produced during cratering events on the moon have the potential to provide not only compositional information about both the local and regional geology of the moon but also information about the impact flux over time we present in this paper the results of 73 new 40ar 39ar analyses of well characterized inclusion free lunar impact glasses and demonstrate that size shape chemical composition fraction of radiogenic 40ar retained and cosmic ray exposure cre ages are important for 40ar 39ar investigations of these samples specifically analyses of lunar impact glasses from the apollo 14 16 and 17 landing sites indicate that retention of radiogenic 40ar is a strong function of post formation thermal history in the lunar regolith size and chemical composition this is because the ar diffusion coefficient at a constant temperature is estimated to decrease by 3 4 orders of magnitude with an increasing fraction of non bridging oxygens x nbo over the compositional range of most lunar impact glasses with compositions from feldspathic to basaltic based on these relationships lunar impact glasses with compositions and sizes sufficient to have retained 90 of their radiogenic ar during 750 ma of cosmic ray exposure at time integrated temperatures of up to 290 k have been identified and are likely to have yielded reliable 40ar 39ar ages of formation additionally 50 of the identified impact glass spheres have formation ages of 500 ma while 75 of the identified lunar impact glass shards and spheres have ages of formation 2000 ma higher thermal stresses in lunar impact glasses quenched from hyperliquidus temperatures are considered the likely cause of poor survival of impact glass spheres as well as the decreasing frequency of lunar impact glasses in general with increasing age the observed age frequency distribution of lunar impact glasses may reflect two processes i diminished preservation due to spontaneous shattering with age and ii preservation of a remnant population of impact glasses from the tail end of the terminal lunar bombardment having 40ar 39ar ages up to 3800 ma a protocol is described for selecting and analyzing lunar impact glasses

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

major lunar crustal terranes surface expressions and crust mantle origins in light of global remotely sensed data the igneous crust of the moon can no longer be viewed as a simple globally stratified cumulus structure composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual melt kreep sandwich horizon near the base of the lower crust instead global geochemical information derived from clementine multispectral data and lunar prospector gamma ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique 1 the procellarum kreep terrane pkt 2 the feldspathic high lands terrane fht and 3 the south pole aitken terrane spat the pkt is a mafic province coincident with the largely resurfaced area in the procellarum imbrium region whose petrogenesis relates to the early differentiation of the moon here some 40 of the th in the moon s crust is concentrated into a region that constitutes only about 10 of the crustal volume this concentration of th average 5 ppm and by implication the other heat producing elements u and k led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust lower crustal materials within the pkt likely interacted with underlying mantle materials to produce hybrid magmatism leading to the magnesian suite of lunar rocks and possibly kreep basalt although rare in the apollo sample collection widespread mare volcanic rocks having substantial th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources the fht is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation basin impacts into this region do not excavate significantly more mafic material suggesting a thickness of tens of kilometers of anorthositic crust the feldspathic lunar meteorites may represent samples from the anorthositic central region of the fht ejecta from deep penetrating basin impacts outside of the central anorthositic region however indicate an increasingly mafic composition with depth the spat a mafic anomaly of great magnitude may include material of the upper mantle as well as lower crust thus it is designated a separate terrane whether the spa basin impact simply uncovered lower crust such as we infer for the fht remains to be determined

chicxulub multiring impact basin size and other characteristics derived from gravity analysis the buried chicxulub impact structure in mexico which is linked to the cretaceous tertiary k t boundary layer may be significantly larger than previously suspected reprocessed gravity data over northern yucatan reveal three major rings and parts of a fourth ring spaced similarly to those observed at multiring impact basins on other planets the outer ring probably corresponding to the basin s topographic rim is almost 300 kilometers in diameter indicating that chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago

the significance of fractional crystallization in the petrogenesis of apollo 17 type a and b high ti basalts abstract whole rock and mineral analyses of 26 new type a and b apollo 17 basalts are reported the petrography and mineral chemistry of these basalts are similar to previously reported apollo 17 basalts however these new whole rock data extend the compositional ranges of previously reported type a and b basalts and require the division of the type b basalts into type b1 and b2 varieties these three types display similar trends when both major and trace elements are plotted against a fractionation index of cr la ratio major element compositions of basalts from all three types fall on olivine ti oxide control lines the compositional ranges of all three groups can be effectively generated by 40 50 fractional crystallization of observed phenocryst phases the compositions of three type a basalts are only generated after 80 fractional crystallization previous models of different degrees of partial melting and kreep assimilation were developed in order to explain the range in la sm ratio of the type b basalts with the recognition of two types of b basalts these models are no longer valid this study demonstrates that apollo 17 type a b1 and b2 basalts have a relatively simple petrogenesis with the only post magma generation process being fractional crystallization

thorium abundances on the aristarchus plateau insights into the composition of the aristarchus pyroclastic glass deposits 1 thorium th data from the lunar prospector gamma ray spectrometer lp grs are used to constrain the composition of lunar pyroclastic glass deposits on top of the aristarchus plateau our goal is to use forward modeling of lp grs th data to measure the th abundances on the plateau and then to determine if the elevated th abundances on the plateau are associated with the pyroclastic deposits or with thorium rich ejecta from aristarchus crater we use a variety of remote sensing data to show that there is a large homogenous portion of the pyroclastics on the plateau that has seen little or no contamination from the th rich ejecta of aristarchus crater our results show that the uncontaminated pyroclastic glasses on aristarchus plateau have an average th content of 6 7 ppm and 7 wt tio2 these th and ti values are consistent with th rich intermediate ti yellow glasses from the lunar sample suite on the basis of this information we use petrologic equations and interelement correlations for the moon to estimate the composition of the source region from which the aristarchus glasses were derived we find that the source region for the aristarchus glasses contained high abundances of heat producing elements which most likely served as a thermal driver for the prolonged volcanic activity in this region of the moon

sixth foray for pristine nonmare rocks and an assessment of the diversity of lunar anorthosites eleven nonmare samples are characterized generally both compositionally and petrographically five are almost certainly pristine ferroan anorthosite 10056c alkali anorthosite 14047c ferroan anorthosite 14312c anorthositic troctolite 14321c3 and granite 14321c4 and four are probably pristine norite 14318c noritic anorthosite 67215 quasi pristine ferroan anorthosite 73217c and norite 78527 five are unique anorthosites extending the diversity of lunar anorthosites considerably alkali anorthosites particularly 14047c are extremely rich in incompatible elements the first anorthosite from apollo 11 with manifestations of pristinity 10056c appears to be a normal member of the ferroan group however the first pristine ferroan anorthosites from apollo 14 and 17 to be studied in detail 14312c and 73217c both have unusually sodic plagioclase by ferroan standards with only 75 plagioclase 67215 is the first large 273 g probably pristine ferroan sample with less than 83 plagioclase the nature of the correlations between longitude and such parameters as eu and sm concentrations and sc sm ti sm and ca na ratios among pristine ant samples has been elucidated because five of the new pristine samples are from a western site apollo 14 interestingly ferroan anorthosite 14312c has ca na sc sm and ti sm ratios close to the normal ferroan values but significantly displaced in the direction of the nonferroan western pristine rocks this suggests that the composition longitude relationships are as old as the late stages of the crystallization of the putative magma ocean

high resolution measurements of absolute thorium abundances on the lunar surface the lunar prospector lp gamma ray spectrometer grs has been used to map the global abundance of thorium on the lunar surface a global map of absolute thorium abundances on a 2 by 2 equal area pixel scale is presented using new detector modeling results and low altitude lp data because thorium is relatively abundant in kreep rich material these data provide fundamental information regarding the locations and importance of terranes that are rich in kreep bearing materials

concentrations of radioactive elements in lunar materials as an aid to interpreting data obtained remotely on the distribution of radioactive elements on the lunar surface average concentrations of k u and th as well as al fe and ti in different types of lunar rocks and soils are tabulated the u th ratio in representative samples of lunar rocks and regolith is constant at 0 27 k th ratios are more variable because k and th are carried by different mineral phases in nonmare regoliths at the apollo sites the main carriers of radioactive elements are mafic i e 6 8 fe impact melt breccias created at the time of basin formation and products derived therefrom

apollo 17 landing site topography photometric corrections and heterogeneity of the surrounding highland massifs 1 a high resolution digital elevation model for the apollo 17 landing site 20 n 31 e and surrounding region is used to correct the photometry of clementine ultraviolet visible multispectral data to standard viewing and illumination geometry on a pixel by pixel basis feo and tio2 concentrations were derived from these topographic photometrically corrected data and steep sloped highland massifs are used to assess the magnitude of the effects of the correction the effects are significant yielding errors as high as 5 wt feo and 4 wt tio2 absolute on 30 slopes the magnitude of the correction varies for sun facing versus anti sun slopes with greater changes on anti sun slopes because most of the apollo 17 sample stations were on surfaces with low slope values 5 the topography has only a small effect on the use of the apollo 17 site for calibration of feo and tio2 parameters topographically corrected data and derived compositional information are used to show accurately the variation in composition of the highland units such as the massifs and the sculptured hills on a fine scale massif compositions are consistent with mixtures of noritic impact melt and feldspathic granulitic material plus variable amounts of high ti basalt on flanks at low elevations and pyroclastic deposits at high elevations as surmised from previous studies an unexpected enrichment in feo at intermediate elevations in some places where massif surfaces have not been covered by mass wasting of impact melt rich material signals an older volcanic component not previously recognized this component may be correlative with an old high plains volcanic unit exposed northeast of the landing site and north of the sculptured hills downslope movement of regolith on steep slopes appears to have resulted in compositional or grain size sorting leading to an apparent enrichment in feo and tio2 from volcanic glass in valleys and draws the sculptured hills have highly variable compositions ranging from feldspathic patches to exposures of mafic rocks a strong but localized mafic anomaly within the sculptured hills may be a small postbasin volcanic feature consisting of very low ti basalt

a revised algorithm for calculating tio2 from clementine uvvis data a synthesis of rock soil and remotely sensed tio2 concentrations 1 investigating mare basalt compositions at both the sample and remote sensing level for the apollo and luna mare sites reveals the need for a more complex regression procedure than previously proposed in order to extract accurate tio2 concentrations from clementine spectral reflectance csr data the tio2 algorithm of lucey and coworkers is modified by using two different sets of regression parameters to relate measured regolith compositions from sampling locations to the csr properties of these sites one regression trend fits the majority of apollo data and the second regression is a fit to the apollo 11 luna 16 and luna 24 data which were considered to be anomalous in previous tio2 calibrations these three sites have unusually low albedo compared to other mare landing sites and some 32 of nearside mare regions appear to share this characteristic possible reasons for these differences related to proximity of the other sites to mare highland boundaries are discussed using the dual regression method we find 1 that tio2 concentrations calculated for the basaltic landing sites faithfully reproduce a bimodal distribution as seen in the sample data 2 that when coupled with the effects of other thermal neutron absorbers ti concentrations are more consistent with observed epithermal to thermal neutron flux ratios than are previous clementine based derivations of tio2 for basaltic regions and 3 that basalts of intermediate tio2 concentrations occur most frequently in the oceanus procellarum region and that these intermediate concentrations appear to be inherent to the flows underlying the regolith and presumably to the basalt source regions

remote sensing studies of the lomonosov fleming region of the moon 1 lomonosov fleming is a 620 km pre nectarian impact basin centered at 19 n 105 e clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region mare basalt deposits in the lomonosov fleming region are small and exhibit varying degrees of highlands contamination four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped a major expanse of cryptomare was mapped in and around the lomonosov fleming basin spectral and chemical data obtained for dark haloed craters dhc established that these impact craters excavated mare basalt from beneath higher albedo highlands rich surface units the buried basalts exposed by dhcs in the region exhibit a variety of compositions which range from very low titanium basalt to intermediate tio2 mare basalt nectarian aged units with subjacent cryptomare are much more extensive than imbrian aged deposits with underlying basalt at least some of the buried mare basalts in the region may have been emplaced during pre nectarian time while both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type the enhanced feo and tio2 abundances exhibited by these cryptomare surfaces usually light plains units demonstrate that ballistic erosion and sedimentation played an important role in their formation

lunar surface geochemistry global concentrations of th k and feo as derived from lunar prospector and clementine data abstract accurate estimates of global concentrations of th k and feo have an important bearing on understanding the bulk chemistry and geologic evolution of the moon we present empirical ground truth calibrations transformations for lunar prospector gamma ray spectrometer data k and th and a modified algorithm for deriving feo concentrations from clementine spectral reflectance data that incorporates an adjustment for tio 2 content the average composition of soil samples for individual landing sites is used as ground truth for remotely sensed data among the apollo and luna sites apollo 12 and 14 provide controls for the incompatible element rich compositions apollo 16 and luna 20 provide controls for the feldspathic and incompatible element poor compositions and apollo 11 15 and 17 and luna 16 and 24 provide controls for fe rich compositions in addition to these apollo and luna sample data we include the composition of the feldspathic lunar meteorites as a proxy for the northern farside highlands to extend the range of the calibration points thus providing an additional anorthositic end member composition these empirical ground truth calibrations for lunar prospector th and k provide self consistency between the existing derived data and lunar sample data clementine spectral reflectance data are used to construct a tio 2 sensitive feo calibration that yields higher feo concentrations in areas of high fe low ti mare basalt rich surfaces than previous feo algorithms the data set so derived is consistent with known sample compositions and regolith mixing relationships

global distribution of lunar composition new results from lunar prospector 1 maps of thorium th feo the ratio of epithermal to thermal neutrons e t and fast neutrons fn from lunar prospector were studied to determine their global distribution on the moon these distributions are compared to that of the 750 nm lunar albedo from clementine to aid in their interpretation all distributions were parameterized using a spherical harmonic expansion out to order l 30 resultant harmonic coefficients generally decrease with increasing l value as a power law in l for all five variables the axes of all dipole components l 1 cluster closely about a centroid given by 14 1 latitude and 16 4 west longitude this location is very close to the symmetry axes of their quadrupole components l 2 which cluster about a centroid given by 24 6 latitude and 25 1 west longitude both centroids are near the center of a suggested procellarum basin given by whitaker 1981 at 23 latitude and 15 west longitude this suggestion is strengthened by a sharp decrease of the intensities of all three variables at 50 from the centroids which is close to the boundary of the putative procellarum basin the coincidence of the global concentration of heat producing elements through th and mare deposits on the lunar surface through feo t e and fn with the circular outline of a putative procellarum basin suggests that the events that were responsible for producing oceanus procellarum perhaps a single giant impact must figure importantly in shaping the global distribution of surface composition a second apparently older circular structure having its center near 5 latitude and 65 east longitude and a radius of 50 is also hinted at in the data

new links between the chicxulub impact structure and the cretaceous tertiary boundary the 200 km diameter chicxulub structure1 3 in northern yucatan mexico has emerged as the prime candidate for the cretaceous tertiary k t boundary impact crater3 6 concentric geophysical anomalies associated with enigmatic occurrences of upper cretaceous breccias and andesitic rocks led penfield and camargo1 to suspect that this structure was a buried impact basin more recently the discovery of shocked quartz grains in a chicxulub breccia3 and chemical similarities between chicxulub rocks and k t tektite like glasses3 6 have been advanced as evidence that the chicxulub structure is a k t impact site here we present evidence from core samples that chicxulub is indeed a k t source crater and can apparently account for all the evidence of impact distributed globally at the k t boundary without the need for simultaneous multiple impacts or comet showers shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the k t boundary ejecta layer7 8 the chicxulub melt rocks that we studied contain anomalously high levels of iridium up to 13 5 parts per 109 also consistent with the iridium enriched k t boundary layer9 our best estimate of the crystallization age of these melt rocks as determined by 40ar 39ar analyses is 65 2 0 4 1 myr in good agreement with the mean plateau age of 64 98 0 05 myr recently reported10 furthermore these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity the only such episode consistent with40ar 39ar constraints is chron 29r which includes the k t boundary

lunar and martian meteorite delivery services launch mechanisms for lunar and martian meteorites have been investigated by integrating physical modeling constraints geochemical cosmic ray exposure cre constraints and petrologic constraints the potential source region for lunar meteorites is remarkably small compared to the final crater volume cre constraints indicate that most launches start at depths of 3 2 m and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0 3 the final crater diameter the shallow depth provenance is probably related to shock wave interference enhanced by the lunar regolith s extremely low compressional wave velocity cre constraints alone imply that four to five separate launch events are represented among the eight well studied lunar meteorites most of the lunar meteorites are regolith breccias which tend to show only limited compositional diversity within any kilometer scale region of the moon several others are polymict breccias which also show relatively subdued compositional diversity compared to igneous rocks the observed diversity among these samples in terms of abundances of mare basalt and kreep and in mg mg fe ratio implies that among eight well studied lunar meteorites only two potential source crater pairings are plausible between asuka 881757 y 793169 most probable and between y 793274 eet875721 altogether these eight lunar meteorites apparently represent at least six separate source craters including three in the past 105 years and five in the past 106 years cre constraints imply that snc meteorites are launched from systematically greater depths than lunar meteorites sncs are also systematically bigger and all nine well studied sncs are uncommonly young by martian standards mafic igneous rocks comparison between viking and apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith probably due to pervasive weathering a plausible explanation for these trends is that most old small and shallow rocks on mars have been weakened by a two stage process of brecciation followed by pervasive weathering to the point where they seldom survive the stresses of spallation off the planet the scarcity of source crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of rabinowitz 1993 astrophys j 407 412 427 that present day cratering rates for the earth moon region may be higher than previously estimated

rodingite from the beila ophiolite in the bangong nujiang suture zone northern tibet new insights into the formation ofophiolite related rodingite abstract the beila ophiolite is located in the middle part of the bangong nujiang suture zone on the northern tibetan plateau and rodingites are widespread within serpentinized peridotites in the ophiolite according to the mineral assemblages the beila rodingite can be divided into three types type i rodingites have a mineral assemblage of prehnite chlorite and minor diaspore type ii rodingites comprise diopside prehnite chlorite epidote and minor hydrogrossular and type iii rodingites underwent further rodingitization and contain more hydrogrossular and vesuvianite than the type ii rodingites zircon grains from two rodingite samples yielded shrimpu pb ages of 172 164 ma with positive values of hf t 9 0 to 16 3 and mantle like 18o values 4 31 to 6 82 indicating the beila ophiolite formed during the middle jurassic the rodingitization of the beila ophiolite took place in two stages the early stage involved the production of the type i and ii rodingites during metasomatism by ca rich fluids with high co2 h2o ratios and this stage is characterized by the formation of ca silicates diopside prehnite and hydrogrossular the second stage involved the production of type iii rodingites at the shallower depths in exhumed mantle under the influence of fluids with lower co2 h2o ratios estimates of the migration of elements during rodingitization e g ca alkalis fe cr ni nb ti rare earth elements and large ion lithophile elements combined with sr nd isotopic compositions indicate that the formation of the beila rodingite involved an extensive exchange of materials among the protoliths serpentinized peridotite and subduction related materials the results indicate that analyses of rodingites in ophiolites can contribute to our understanding of material exchange during oceanic plate subduction

some things we can infer about the moon from the composition of the apollo 16 regolith randy l korotev department of earth and planetary sciences and mcdonnell center for the space sciences washington university st louis missouri 63130 usa author s e mail address rlk levee wustl edu received 1996 september 16 accepted in revised form 1997 may 12 abstract characteristics of the regolith of cayley plains as sampled at the apollo 16 lunar landing site arereviewed and new compositional data are presented for samples of 1 mm fines soils and 1 2 mm rego lith particles as a means of determining which of the many primary igneous and secondary crystalline brec cias lithoiogic components that have been identified in the soil are volumetrically important and providing anestimate of their relative abundances more than 3 x 106 combinations of components representing nearly everylithology that has been observed in the apollo 16 regolith were systematically tested to determine which com binations best account for the composition of the soils conclusions drawn from the modeling include the fol lowing at the site mature soil from the cayley plains consists of 64 5 2 7 components representing prebasin materials anorthosites feldspathic breccias and a small amount 2 6 1 5 of total soil ofnonmare mafic plutonic rocks mostly gabbronorites on average these components are highly feldspathic with average concentrations of 31 32 a1203 and 2 3 feo and a molar mg mg fe ratio of 0 68 theremaining 36 of the regolith is syn and postbasin material 28 8 2 4 mafic impact melt breccias mimbs i e lkfm and vha basalts created at the time of basin formation 6 0 1 4 mare derived material impact and volcanic glass crystalline basalt with an average tio2 concentration of 2 4 and 1 postbasin meteoritic material the mimbs are the principal 80 90 carrier of incompatible traceelements rare earths th etc and the carrier of about one half of the siderophile elements and elementsassociated with mafic mineral phases fe mg mn cr sc most 71 of the fe in the present regolithderives from syn and postbasin sources mimbs mare derived material and meteorites thus althoughthe bulk composition of the apollo 16 regolith is nominally that of noritic anorthosite the noritic part themimbs and the anorthositic part the prebasin components are largely unrelated there is compositionalevidence that 3 4 of the soil is th rich material such as that occurring at the apollo 14 site and one frag ment of this type was found among the small regolith particles studied here if regolith such as that repre sented by the apollo 16 ancient regolith breccias was a protolith of the present regolith such regolith cannotexceed 71 of the present regolith the rest must be material added or redistributed since closure of theancient regolith breccias the postclosure material includes the mare derived material and the apollo 14 like component compositions of all mature surface soils from apollo 16 even those collected 4 km apart on the cayleyplains are very similar which is in stark contrast to the wide compositional range of the lithologies of whichthe soil is composed this uniformity indicates that the ratio of mimbs to feldspathic prebasin componentsis not highly variable in the megaregolith over distances of a few kilometers that there are no large sub surface concentrations of pure mafic impact melt breccia and that the intimate mixing is inherent to thecayley plains at a gross scale thus the mixing ofmafic impact melt breccias and feldspathic prebasin com ponents must have occurred during formation and deposition of the cayley plains such uniformity could nothave been achieved by small postdeposition impacts into a stratified megaregolith using this conclusion asone constraint and the known distribution of th on the lunar surface as another and the assumption that the im brium impact is primarily responsible for formation of the cayley plains arguments are presented that theapollo 16 mimbs derive from the imbrium region and consequently that one fourth of the apollo 16 regolithis primary imbrium ejecta in the form of mafic impact melt breccias

thorium concentrations in the lunar surface iv deconvolution of the mare imbrium aristarchus and adjacent regions the distribution of th over the mare imbrium and northern oceanus procellarum portions of the apollo 15 lunar ground track has been modeled by deconvolving several fields of orbital gamma ray spectroscopy data including a prior study of the apenninus region a continuous swath from 10 e to 60 w in the northwest quadrant has now been analyzed in the aristarchus region the crater dominates the th distribution with a concentration of 20 ppm other enhancements are seen on the aristarchus plateau and south of the plateau the concentration across the aristarchus plateau is not uniform the average th concentration in oceanus procellarum is less to the west than to the east of the aristarchus plateau substantial enhancements are found in mare regions around brayley and at the ejecta blankets of timocharis and lambert th in the eratosthenian mare regions is generally low with one notable exception lying roughly between the craters euler and carlini the existence of enhanced th concentrations in mare basalt regions suggests that reservoirs of some late stage mare basalts incorporated kreep rich material during formation or transit

lunar farside th distribution measured by kaguya gamma ray spectrometer abstract kaguya gamma ray spectrometer measured thorium th distribution on the lunar farside with the highest sensitivity among past gamma ray remote sensing missions the newly obtained th map has revealed that two regions near the equator on the farside have the lowest th abundances we found that the variation of the th abundance perfectly correlates with the crustal thickness in the farside and the southern nearside and it could be a result of the crystallization of the lunar magma ocean

integration of the clementine uv vis spectral reflectance data and the lunar prospector gamma ray spectrometer data a global scale multielement analysis of the lunar surface using iron titanium and thorium abundances 1 we present a statistical analysis based on a systematic clustering method of a data set integrating the global abundances maps of iron titanium and thorium derived from clementine and lunar prospector homogeneous geological units are compositionally characterized and spatially defined in relation to the major rock types sampled on the moon with the lowest abundances in fe ti and th found on the moon the lunar highlands terrains are quite homogeneous with two major large feldspathic units one being slightly more mafic than the other two distinct regions with unique compositions are unambiguously identified the procellarum kreep terrane pkt and the south pole aitken spa the pkt which includes all the units with th abundances higher than 3 5 ppm kreep rich materials is delimited by an almost continuous ring like unit in particular it includes the western nearside maria except for mare humorum within the pkt a th rich unit corresponding to the highest th concentrations found on the moon may represent kreep volcanic deposits excavated from relatively shallow depth with concentrations in fe ti and th enhanced relative to the surrounding highlands the south pole aitken basin floor represents a large mafic anomaly on the farside suggesting wide deposits of lower crust and possible mantle materials however due to indirect residual latitude effects in the clementine spectral reflectance measurements iron abundances might have been overestimated in spa thus implying that crustal materials rather than mantle materials might represent the dominant contributor to the mafic component exposed on the basin floor

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

isotopic composition of osmium in terrestrial samples determined by accelerator mass spectrometry interest has revived in the rhenium osmium system due to significant advances in detection methods1 4 and because of its use for the identification of extraterrestrial material at the cretaceous tertiary boundary5 another perhaps more important application is its use as a tracer for the origin of crustal material this application is however severely restricted by the very low concentrations typical of crustal rocks we present here the first results for the isotopes 187os 188os and 189os measured in sub p p b parts per 109 level samples by accelerator mass spectrometry ams our first exploratory measurements on extraterrestrial and crustal material with os concentrations between 2 p p m parts per 106 and 0 006 p p b show a detection limit of 0 01 p p b and a precision of better than 10 the 187os 186os ratios measured for samples for the canyon diablo meteorite and from the east clearwater crater in quebec canada were close to 1 typical of extraterrestrial material in contrast ratios in samples from the ries crater in germany were around 10 which is evidence of predominantly crustal osmium in these rocks

rhenium osmium isotope systematics in meteorites i magmatic iron meteorite groups iiab and iiiab abstract using resonance ionization mass spectrometry rims re and os abundances were determined by isotope dilution id and 187 os 186 os ratios measured in nineteen iron meteorites eight from group iiab ten from group iiiab and treysa iiib anomalous abundances range from 1 4 to 4800 ppb re and from 13 to 65000 ppb os and generally agree well with previous id and neutron activation naa results the re and os data suggest that abundance trends in these iron groups may be entirely explained by fractional crystallization addition of late formed metal to produce re os variation in the b subgroups is not essential but cannot be excluded whole rock isochrons for the iiab and iiiab groups are statistically indistinguishable pooled data yield an initial 187 os 186 os of 0 794 0 010 with a slope of 7 92 0 20 10 2 corresponding to a magmatic iron meteorite age of 4 65 0 11 ga using a decay constant of 1 64 10 11 a 1 given the errors in the slope and half life this age does not differ significantly from the canonical chondrite age of 4 56 ga but could be as young as 4 46 ga

the magma ocean concept and lunar evolution the model of lunar evolution in which the anorthositic plagioclase rich oldest crust of the moon is formed over a period of 300 myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies consideration is given to the classification of lunar rocks the evidence for primordial deep global differentiation constraints on the depth of the molten zone the effects of pressure on mineral stability relationships mainly liquid vs mainly magmifer ocean models and the evidence for multiple ancient differentiation episodes a synthesis of the model of primordial differentiation and its aftereffects is presented and the generalization of the model to the earth and to mars mercury venus and the asteroids is discussed

apollo 17 kreepy basalts evidence for nonuniformity of kreep breccia 72275 contains pristine kreepy basalt clasts that are not found among other samples collected at apollo 17 these basalts occur as discrete clasts and as clasts enclosed within basaltic microbreccias mineral and whole rock chemical analyses reveal that the microbreccias are compositionally indistinguishable from the basalt clasts samples of the 72275 matrix also have the same compositions as the basalts and the basaltic microbreccias 72275 was assembled in situ from a single flow or series of closely related flows of apollo 17 kreepy basalt before it was transported to the apollo 17 site as a rock type apollo 17 kreepy basalts are distinct from apollo 15 kreep basalts the apollo 17 samples have lower ree concentrations steeper negative slopes of the hree and are less magnesian than the apollo 15 samples the two basalt types cannot be related by fractional crystallization partial melting or assimilation this is evidence for the compositional nonuniformity of kreep as a function of geography

remote sensing and geologic studies of the balmer kapteyn region of the moon 1 the balmer kapteyn b k region is located just east of mare fecunditatis on the east limb of the moon it is centered on the balmer kapteyn basin a pre nectarian impact structure that exhibits two rings approximately 225 km and 450 km in diameter clementine multispectral images and lunar prospector lp gamma ray spectrometer grs data were used to investigate the composition age and origin of geologic units in the region a major expanse of cryptomare was mapped within the b k basin spectral and chemical data obtained for dark haloed craters dhcs established that these impact craters excavated mare basalt from beneath higher albedo highland rich surface units the buried basalts exposed by dhcs in the region are dominated by low titanium mare basalts the fresh dhc feo values 15 0 15 7 wt that best represent those of buried mare basalts are well within the range of values exhibited by high alumina mare basalts while most cryptomare deposits occur beneath surfaces that range in age from imbrian to nectarian it is possible that some mare flows were emplaced during pre nectarian time most cryptomare deposits in the b k region were formed by the contamination of mare surfaces by highland rich distal ejecta from surrounding impact craters these balmer type cryptomare deposits are usually associated with light plains units major lp grs feo enhancements are associated with cryptomaria in the balmer kapteyn lomonosov fleming schiller schickard and mendel rydberg regions

chemical composition and origin of apollo 15 impact melts to better understand the apennine front we have analyzed 14 apollo 15 impact melt rocks including hand samples rake samples and coarse fines for major fused bead microprobe and trace element inaa abundances the melt rocks show a remarkable diversity of chemical composition although all but one have typical kreep incompatible element patterns they appear to form five chemical groups all but the most kreep rich of which may represent single impacts three groups are of low k fra mauro composition none correspond to very high alumina vha compositions the compositions are unlike nearly all other impact melts and regoliths from highland sites indicating a distinct provenance for the apollo 15 samples serenitatis basin impact melt compositions apollo 17 poikilitic boulders are not duplicated although one apollo 17 aphanitic melt sample 73215 is similar to one of the apollo 15 groups the apollo 15 group consisting only of 15445 and 15455 remains the best candidate for imbrium basin impact melt while the most kreep rich group probably consists of melts produced in varied post imbrium impacts into the apennine bench formation apollo 15 kreep basalt flows the most populated group was previously unrecognized and could be either pre or post imbrium basin it is possible that it not 15445 15455 represents imbrium melt one unique sample has a non kreep incompatible element pattern with low abundances and a positive eu anomaly its target was rather primitive and would not appear to be of regional extent or present in the area in post imbrium times it is either a pre imbrian melt or exotic the apennine front does not consist of a monolithic lkfm composition but shows a much wider diversity of compositions than was previously recognized

viscoelastic deformation of lunar impact basins implications for heterogeneity in the deep crustal paleo thermal state and radioactive element concentration 1 diverse geological characteristics found for the three major lunar provinces i e the feldspathic highlands terrane fht the south pole aitken terrane spat and the procerallum kreep terrane pkt strongly suggest their distinctly different thermal histories quantitative differences among these provinces in their early thermal histories and crustal radioactive element concentrations however are highly unknown one of the few observables that retain a record of the ancient lunar thermal structure is the viscoelastic state of impact basins this study investigates the long term evolution of basin structures using global lunar gravity field data obtained by kaguya tracking and derives constraints for 1 the paleo thermal state of impact basins and for 2 crustal column averaged radioactive element concentrations for each province our calculation results indicate that impact basins in the central anorthositic region of the fht i e the fht an require a very cold interior dt dr 20 k km 1 on the surface this result strongly suggests that the deep portion of the thick farside highlands crust is highly depleted in radioactive elements th 0 5 ppm indicating that the th rich spa basin floor crust is clearly different from the lower crust underneath the fht an and cannot be accounted for by simple exposure of the lower crust our analysis also indicates that the observed basin structure allows as high as 6 ppm of column averaged th concentration in the crust inside the pkt these results indicate that radioactive element concentrations deep in the crust probably vary greatly region by region similarly to those observed on the surface

lunar granulites and their precursor anorthositic norites of the early lunar crust lunar granulites are breccias with metamorphic textures they are not pristine having been contaminated with meteoritic siderophiles nonetheless they constitute an abundant class of highlands rocks that are important because they are ancient and kreep free they may represent our best samples of the early lunar crust the granulites can be divided into ferroan and magnesian groups and each group can be subdivided on the basis of mineral composition and ree concentrations textural and compositional data show that some of the granulites especially 67215 and 67415 may be derived from distinct anorthositic norite precursors while some other granulites 79215 78155 are clearly polymict even the polymict granulites probably had anorthositic norites as their dominant precursors and not anorthosites norites or troctolites the granulites have compositions similar to those of the two lunar meteorites one of which yamato 791197 is ferroan the other alha81005 magnesian these meteorites are soil breccias from an unknown location distant from the apollo landing sites and contain anorthositic norites as abundant clasts compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands as determined by remote sensing than do those of any other returned lunar samples the predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from apollo missions

the basalts of mare frigoris this paper discusses the methodology and results of a detailed investigation of mare frigoris using remote sensing data from clementine lunar prospector and lunar reconnaissance orbiter with the objective of mapping and characterizing the compositions and eruptive history of its volcanic units with the exception of two units in the west mare frigoris and lacus mortis are filled with basalts having low tio2 to very low tio2 low feo and high al2o3 abundances these compositions indicate that most of the basalts in frigoris are high al basalts a potentially undersampled yet important group in the lunar sample collection for its clues about the heterogeneity of the lunar mantle thorium abundances of most of the mare basalts in frigoris are also low although much of the mare surface appears elevated due to contamination from impact gardening with the surrounding high th imbrium ejecta there are however a few regional thorium anomalies that are coincident with cryptomare units in the east the two youngest mare basalt units and some of the scattered pyroclastic deposits and volcanic constructs in addition mare frigoris lies directly over the northern extent of the major conduit for a magma plumbing system that fed many of the basalts that filled oceanus procellarum as interpreted by andrews hanna et al 2014 using data from the gravity recovery and interior laboratory mission the relationship between this deep reaching magma conduit and the largest extent of high al basalts on the moon makes mare frigoris an intriguing location for further investigation of the lunar mantle

evidence for a meteoritic component in impact melt rock from the chicxulub structure abstract the chicxulub structure in yucatan mexico has recently been recognized as a 200 km diameter multi ring impact crater of k t boundary age crystalline impact melt rocks and breccias from within the crater which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects have been studied for trace element and re os isotope compositions re os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact derived rocks a melt rock sample shows elevated indium concentrations an osmium concentration of 25 ppb and a low 187 os 188 os ratio of 0 113 which are incompatible with derivation from the continental crust even though the 187 os 188 os ratio is slightly lower than the range so far measured in meteorites a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material the data support the hypothesis of a heterogeneously distributed meteoritic component in the chicxulub melt rock a sample of impact glass from the haitian k t boundary at beloc yielded about 0 1 ppb osmium and an 187 os 188 os ratio of 0 251 indicating the presence of a small meteoritic component in the impact ejecta as well

thorium abundances of basalt ponds in south pole aitken basin insights into the composition and evolution of the far side lunar mantle 1 imbrian aged basalt ponds located on the floor of south pole aitken spa basin are used to provide constraints on the composition and evolution of the far side lunar mantle we use forward modeling of the lunar prospector gamma ray spectrometer thorium data to suggest that at least five different and distinct portions of the far side lunar mantle contain little or no thorium as of the imbrian period we also use spatial correlations between local thorium enhancements and nonmare material on top of the basalt ponds to support previous assertions that lower crustal materials exposed in spa basin have elevated thorium abundances consistent with noritic to gabbronoritic lithologies we suggest that the lower crust on the far side of the moon experienced multiple intrusions of thorium rich basaltic magmas prior to the formation of spa basin the fact that many of the ponds on the lunar far side have elevated titanium abundances indicates that the far side of the moon experienced extensive fractional crystallization that likely led to the formation of a kreep like component however because the imbrian aged basalts contain no signs of elevated thorium we propose that the spa impact event triggered the transport of a kreep like component from the lunar far side and concentrated it on the nearside of the moon because of the correlation between basaltic ponds and basins within spa we suggest that imbrian aged basaltic volcanism on the far side of the moon was driven by basin induced decompressional melting

hansteen alpha a volcanic construct in the lunar highlands 1 we have used data from the clementine and lunar prospector spacecraft in conjunction with near ir reflectance spectra collected with earth based telescopes to study the composition and origin of hansteen alpha an arrowhead shaped highlands feature located on the southern margin of oceanus procellarum hansteen alpha is a member of a class of lunar spectral anomalies red spots that are characterized by a relatively high albedo and a strong absorption in the uv it has been suggested that at least some of these spectral anomalies were produced by nonmare volcanism the stratigraphic relationships among the geologic and compositional units in the region show that hansteen alpha was emplaced by extrusive igneous processes the imbrian aged craters hansteen and billy emplaced relatively feo and tio2 rich ejecta hansteen alpha exhibits much lower feo and tio2 values if hansteen alpha was present prior to the billy and hansteen impact events it should have been covered with feo and tio2 rich ejecta because it is located within one crater diameter of the rim crest of each crater since it is not hansteen alpha was superposed on these ejecta units nonmare volcanism is the only viable process for the formation of hansteen alpha the morphology and surface texture of hansteen alpha is similar to many terrestrial features of dacitic and rhyolitic composition formed by extrusions of relatively viscous lavas such highly evolved compositions should be very enriched in th but hansteen alpha exhibits th abundances of 6 ppm hence hansteen alpha is not composed of a highly evolved highlands lithology

global elemental maps of the moon the lunar prospector gamma ray spectrometer lunar prospector gamma ray spectrometer spectra along with counting rate maps of thorium potassium and iron delineate large compositional variations over the lunar surface thorium and potassium are highly concentrated in and around the nearside western maria and less so in the south pole aitken basin counting rate maps of iron gamma rays show a surface iron distribution that is in general agreement with other measurements from clementine and the lunar prospector neutron detectors

pristine moon rocks a large felsite and a metal rich ferroan anorthosite we report new chemical analyses and in most cases descriptions for 19 lunar rock samples including 5 mare basalts from apollo 15 and 5 uncommonly feldspathic rocklets from apollo 17 two of the samples studied are most extraordinary a large 1 g felsite from apollo 12 and a pristine ferroan anorthosite from apollo 15 that is unusually rich in fe metal and trace siderophile elements the felsite 12033 507 is mainly a graphic intergrowth of k feldspar and a silica phase with about 6 plagioclase and 1 each of ferroaugite ilmenite and fayalitic olivine this crystalline assemblage is crisscrossed and apparently intruded by thin veins of brownish felsic average sio2 57 wt glass the glass veins are far from uniform in composition evidently after the glass was intruded it reacted to varying extents with the crystalline felsite dark globules scattered at apparent nodes in the network of glass veins are interpreted as the least altered of the intruded glasses these globule glasses are relatively sio2 poor average 48 wt but extremely feo rich average 36 wt they may have formed as liquid immiscibility caused the same melt that produced the crystalline felsite to split into fe rich melt the globule glasses plus fe poor si rich melt according to this model deformation most likely caused by an impact then squeezed the fe rich melt into the still nearby and still hot crystalline felsite the fe metal content of ferroan anorthosite 15363 is 1 2 wt in the thin section we studied but must have been based on mass balance for co and ni considerably lower in the chip we used for bulk rock analysis even so the measured bulk rock concentrations for several siderophile elements re os and ir are far higher than previously observed among pristine lunar anorthosites these results underscore the huge uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon s crust among pristine rocks from the apollo 17 site located on the rim of the serenitatis basin ferroan anorthosites continue to be far outnumbered by mg rich rocks

alkali gabbronorite ultra kreepy melt rock and the diverse suite of clasts in north ray crater feldspathic fragmental breccia 67975 lunar breccia 67975 is a feldspathic fragmental breccia from north ray crater apollo 16 it contains clasts of alkali gabbronorite and ultra kreepy mafic fragment laden melt breccias which are unique among apollo 16 samples both are alkali and iron rich rocks with moderate to high ree concentrations they more strongly resemble apollo 14 gabbronorites and alkali anorthosites and kreep rich rocks than they do other apollo 16 samples the other clasts in 67975 are the ferroan anorthosites feldspathic melt rocks and magnesian granulites which are typical of other feldspathic fragmental breccias examination of bulk and mineral compositions of other breccias and melt rocks suggests that alkali gabbronorite may be a minor component in other north ray crater breccias and feldspathic melt rocks this implies that alkali gabbronorite was a fairly early 4 0 b y crustal component in the north ray crater region

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

kca chronology of lunar granites abstract k ca age determinations were undertaken for three lunar granitic samples 14321 1062 14303 206 and 12013 141 k ca isotopic analyses of bulk samples of seven pristine lunar igneous rocks including four mare basalts 10017 15555 14321 1394 and 14305 304 371 one norite 15445 17 one anorthosite 60025 one kreep basalt 72275 543 and seven meteorites juvinas pasamonte moore county stannern y75011 84b zagami and shergotty were also performed the k ca mineral isochron for lunar granitic clast 14321 1062 yields an age of 4 06 0 07 ga for 40k 0 5543 ga 1 and an initial 40 ca 44 ca of 47 141 0 010 normalized to 42 ca 44 ca 0 31221 the k ca age is in excellent agreement with the rb sr and sm nd ages and is slightly older than the average 39ar 40ar and u pb zircon ages low precision k ca ages of 4 04 0 64 ga and 3 76 0 72 ga were obtained for lunar granites 14303 206 and 12013 141 respectively due to their lower k ca ratios initial 40 ca 44 ca values for seven lunar and seven meteoritic bulk samples are similar and yield an average initial 40 ca 44 ca of 47 136 0 002 2 m and 0 006 2 p assuming this value as the lunar initial 40 ca 44 ca a ten to twenty fold fractionation for k ca during the formation of granite 14321 is calculated for a two stage model the large k ca enrichment is consistent with a granite genesis model involving a silicate liquid immiscibility process literature data for lunar granites studied so far exhibit a wide range of ages from 3 9 to 4 4 ga thus lunar granites probably represent samples from about eight different intrusive bodies the positive k and k ca correlations of lunar rocks strongly supports an early global lunar differentiation however most granites were probably not directly produced from this early differentiation event

antarctic meteorite alha81005 not just another lunar anorthositic norite seven subsamples of meteorite alha81005 a regolith breccia from the lunar highlands were analyzed by inaa for 32 elements four of them were also studied petrographically in bulk composition the rock corresponds to anorthositic norite with a very small component of kreep and is very similar to estimates of average lunar highlands surface compositions of the white clasts and the dark matrix are similar but the clasts are more magnesian and 30 50 as rich in kreep related elements the white clasts have fine grained granulitic textures and are generally similar to apollo 16 and 17 granulitic anorthositic norites but are more magnesian and only 20 as rich in kreep related elements some granulitic clasts are dominated by a magnesian anorthositic norite component not represented among the pristine apollo samples

mixing levels the apennine front soil component and compositional trends in the apollo 15 soils variations in concentrations of lithophile elements in samples of apollo 15 soil can be explained in terms of only four chemical components three components are represented by extrusive rock types found at the apollo 15 site mare basalt kreep basalt and the pyroclastic green glass associated with breccia 15426 the fourth component the highlands component can be represented by soil from the apennine front particularly the soil obtained from the 55 57 cm depth interval of station 2 core 15007 8 among samples of apennine front soil this one appears to be the least contaminated by mare materials and may be our most typical sample of the apennine front highlands although soil fron the apennine front is itself a complex mixture of many types of highlands rocks it behaves as a single component with respect to mixing with the other three rock type components the various subcomponents of the apennine front soil e g melt rock and anorthositic norite that have been used in some mixing models are not required as discrete components in order to explain the compositional variation among samples of apollo 15 soil most of this compositional variation results from mare highlands mixing i e apennine front soil with mare basalt kreep basalt which probably derives from local possibly unexposed sources is also a variable component of the soil and is most prevalent in the soil from stations lm 6 and 9

petrography and geochemistry of the lapaz icefield basaltic lunar meteorite and source crater pairing with northwest africa 032 we report on the bulk composition and petrography of four new basaltic meteorites found in antarcticalap lapaz icefield 02205 lap 02224 lap 02226 and lap 02436 and compare the lap meteorites to other lunar mare basalts the lap meteorites are coarse grained up to 1 5 mm subophitic low ti basalts composed predominantly of pyroxene and plagioclase with minor amounts of olivine ilmenite and a groundmass dominated by fayalite and cristobalite all of our observations and results support the hypothesis that the lap stones are mutually paired with each other in detail the geochemistry of lap is unlike those of any previously studied lunar basalt except lunar meteorite nwa northwest africa 032 the similarities between lap and nwa 032 are so strong that the two meteorites are almost certainly source crater paired and could be two different samples of a single basalt flow petrogenetic modeling suggests that the parent melt of lap and nwa 032 is generally similar to apollo 15 low ti yellow picritic glass beads and that the source region for lap comes from a similar region of the lunar mantle as previously analyzed lunar basalts

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

formation and evolution of a lunar core from ilmenite rich magma ocean cumulates abstract in the absence of comprehensive seismic data coverage the size composition and physical state of the lunar core are still debated it has been suggested that a dense ilmenite rich layer which originally crystallised near the top of the lunar magma ocean may have sunk to the centre of the moon to form either an outer core surrounding a small metallic inner core or a complete core if the lunar metallic iron content is insignificant here we study the formation gravitational stability and thermal evolution of both an ilmenite rich outer core and a full ilmenite rich core using a two dimensional cylindrical thermo chemical convection model gravity acceleration in the lunar mantle decreases quickly with depth since the gravity acceleration directly influences the buoyancy of materials the low gravity acceleration near the centre was explicitly taken into account core formation and evolution were investigated by assessing the effects of varying two parameters the mg density and the internal heat production of the ilmenite rich layer varying these parameters changes the compositional and thermal buoyancy of the dense layer models show that a stable ilmenite rich outer core may indeed have formed in the lunar interior and that its density depends on the internal heating in and the mg of the ilmenite rich layer furthermore the sharpness of the core mantle boundary is shown to depend on the internal heat production in the ilmenite rich material surprisingly a higher internal heat production results in a sharper core mantle boundary and a higher ilmenite content in the core this is caused by lower viscosities as a result of higher temperatures although maximum core temperatures vary between different models by 700 1000 k around 2 gyr after the start of the models present day estimates vary by only about 350 500 k further narrowing of the range of internal heating values is essential for a better determination of both the present day lunar core temperature and its physical state

40ar 39ar age determinations of lunar basalt meteorites asuka 881757 yamato 793169 miller range 05035 la paz icefield 02205 northwest africa 479 and basaltic breccia elephant moraine 96008 40ar 39ar data are presented for the unbrecciated lunar basaltic meteorites asuka a 881757 yamato y 793169 miller range mil 05035 lapaz icefield lap 02205 northwest africa nwa 479 paired with nwa 032 and basaltic fragmental breccia elephant moraine eet 96008 stepped heating 40ar 39ar analyses of several bulk fragments of related meteorites a 881757 y 793169 and mil 05035 give crystallization ages of 3 763 0 046 ga 3 811 0 098 ga and 3 845 0 014 ga which are comparable with previous age determinations by sm nd u pb th pb pb pb and rb sr methods these three meteorites differ in the degree of secondary 40ar loss with y 793169 showing relatively high ar loss probably during an impact event 200 ma ago lower ar loss in mil 05035 and no loss in a 881757 bulk and impact melt glass bearing samples of lap 02205 gave similar ages 2 985 0 016 ga and 2 874 0 056 ga and are consistent with ages previously determined using other isotope pairs the basaltic portion of eet 96008 gives an age of 2 650 0 086 ga which is considered to be the crystallization age of the basalt in this meteorite the ar release for fragmental basaltic breccia eet 96008 shows evidence of an impact event at 631 20 ma the crystallization age of 2 721 0 040 ga determined for nwa 479 is indistinguishable from the weighted mean age obtained from three samples of nwa 032 supporting the proposal that these meteorites are paired the similarity of 40ar 39ar ages with ages determined by other isotopic systems for multiple meteorites suggests that the k ar isotopic system is robust for meteorites that have experienced a significant shock event and not a prolonged heating regime

the procellarum kreep terrane implications for mare volcanism and lunar evolution geophysical remote sensing and sample data demonstrate that the procellarum and imbrium regions of the moon make up a unique geochemical crustal province here dubbed the procellarum kreep terrane geochemical studies of imbrium s ejecta and the crustal structure of the imbrium and serenitatis basins both suggest that a large portion of the lunar crust in this locale is composed of a material similar in composition to apollo 15 kreep basalt kreep basalt has about 300 times more uranium and thorium than chondrites so this implies that a large portion of moon s heat producing elements is located within this single crustal province the spatial distribution of mare volcanism closely parallels the confines of the procellarum kreep terrane and this suggests a causal relationship between the two phenomena we have modeled the moon s thermal evolution using a simple thermal conduction model and show that as a result of the high abundance of heat producing elements that are found in the procellarum kreep terrane partial melting of the underlying mantle is an inevitable outcome specifically by placing a 10 km kreep basalt layer at the base of the crust there our model predicts that mare volcanism should span most of the moon s history and that the depth of melting should increase with time to a maximum depth of about 600 km we suggest that the 500 km seismic discontinuity that is observed in the apollo seismic data may represent this maximum depth of melting our model also predicts that the kreep basalt layer should remain partially molten for a few billion years thus the imbrium impact event most likely excavated into a partially molten kreep basalt magma chamber we postulate that the kreep basalt composition is a by product of mixing urkreep with shallow partial melts of the underlying mantle since mg suite rocks are likely derived from crystallizing kreep basalt the provenance of these plutonic rocks is likely to be unique to this region of the moon

the cretaceous tertiary boundary at beloc haiti no evidence for an impact in the caribbean area abstract the k t boundary at beloc in haiti is characterized by a bed containing more or less spheroidal globules composed of either smectite or calcite a small fraction of these objects still contains well preserved glass particles which have been interpreted as the remains of tektites resulting from a bolide impact in the caribbean area however beloc glasses are markedly different from tektites and microtektites their structure and composition suggest that they are not impact generated products but are likely of volcanic origin on the other hand in sections which have probably preserved their original stratigraphy the globule bed showing well developed grading appears first in the sedimentary column followed by the ubiquitous cretaceous tertiary boundary ktb clay layer containing ir and ni rich spinels granulometric considerations indicate that the globule bed and the ir and spinel rich clay layer correspond to two distinct events we conclude that the globules at the ktb depositional sequence of beloc represent a local volcanic event slightly preceding the great ktb cosmic catastrophe our observations do not provide any unequivocal evidence that a cratering event occurred nearby

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

the mairan domes silicic volcanic constructs on the moon 1 the mairan domes are four features located in northern oceanus procellarum at 312 3e 41 4n on the moon high resolution visible imagery visible to mid ir spectra and lunar prospector th abundance data all indicate that these four domes have a composition that is consistent with derivation from a si rich highly evolved magma

composition of bulk samples and a possible pristine clast from allan hills a81005 abundances of thirty five elements were determined in two bulk samples and a white clast in the allan hills a81005 meteorite high siderophile element content indicates that the sample is a regolith breccia an fe mn ratio of 77 in this meteorite eliminates parent bodies of known differentiated meteorites as the source of alha 81005 the incompatible elements are very similar to those found in most lunar highlands rocks and provide very strong evidence that the sample is lunar in origin the clast sample has the trace element pattern of a lunar anorthosite and is very low in kreep and siderophile elements it may be a fragment of a pristine lunar rock

trace element zoning and incipient metamictization in a lunar zircon application of three microprobe techniques we have determined major si zr hf minor al y fe p and trace element ca sc ti ba ree th u concentrations and raman spectra of a zoned 200 microns zircon grain in lunar sample 14161 7069 a quartz monzodiorite breccia collected at the apollo 14 site analyses were obtained on a thin section in situ with an ion microprobe an electron microprobe and a laser raman microprobe the zircon grain is optically zoned in birefringence a reflection of variable incomplete metamictization resulting from zo nation in u and th concentrations variations in the concentrations of u and th correlate strongly with those of other high field strength trace elements and with changes in raman spectral parameters concentrations of u and th range from 21 to 55 ppm and 6 to 31 ppm respectively and correlate with lower raman peak intensities wider raman peaks and shifted si o peak positions concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt approx 4 b y ago degradation of the zircon structure as reflected by the observed raman spectral parameters has occurred in this sample over a range of alpha decay event dose from approx 5 2 x 10 exp 14 to 1 4 x 10 exp 15 decay events per milligram of zircon as calculated from the u and th concentrations this dose is well below the approx 10 exp 16 events per milligram cumulative dose that causes complete metamictization and indicates that laser raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation induced damage in zircon

petrology and geochemistry of alkali gabbronorites from lunar breccia 67975 clasts of an unusual type of lunar highlands igneous rock alkali gabbronorite have been found in apollo 16 breccia 67975 the alkali gabbronorites form two distinct subgroups magnesian and ferroan modes and bulk compositions are highly varied the magnesian alkali gabbronorites are composed of bytownitic plagioclase or2 5an82 89 hypersthene wo3 5en49 62 augite wo39 42en36 44 a silica mineral and trace ba rich k feldspar the ferroan alkali gabbronorites are composed of ternary plagioclase or11 22an65 74 pigeonite wo6 9en35 47 augite wo38 40en29 35 ba rich k feldspar and a silica mineral trace minerals in both subgroups are apatite ree rich whitlockite and zircon the magnesian and ferroan alkali gabbronorites appear to have formed by progressive differentiation of the same or closely related parent magmas the compositional data indicate that these magmas were ree rich the ternary plagioclase is probably a high temperature metastable phase formed during crystallization in composition and mineralogy the 67975 alkali gabbronorites show many similarities to apollo 12 and 14 alkali norites alkali gabbronorites and alkali anorthosites and all these rocks together constitute a distinctive alkali suite in addition the alkali gabbronorites show some similarities to kreep basalts mg norites and some felsites these data suggest genetic links between some or all of these types of pristine rocks two types of relationships are possible the first is that alkali suite rocks crystallized in plutons of kreep basalt magma and kreep basalts are their extrusive equivalents the second is that the alkali suite rocks and some felsites all crystallized in plutons of mg norite parent magmas and kreep basalt magmas formed by remelting of these plutons additional studies are needed to resolve which of these hypotheses is correct

small area thorium features on the lunar surface 1 using an improved understanding of the lunar prospector gamma ray spectrometer lp grs spatial footprint we have derived a new map of global thorium abundances on the lunar surface this map has a full width half maximum spatial resolution of 80 km 2 and is mapped on the lunar surface using 0 5 0 5 pixels this map has allowed the identification and classification of 42 small area 3 g g in southwestern mare tranquillitatis near the apollo 11 landing site with our better understanding of the lp grs spatial footprint we have been able to constrain the surface thorium abundance at the compton belkovich thorium anomaly to 40 55 g g which is higher than any other measured location on the lunar surface and higher than most samples finally using 1 km pixel feo abundances from clementine and lp grs spatial footprint information we have been able to obtain plausible thorium distributions around kepler crater at a resolution of 1 km pixel the materials around kepler crater appear to be a relatively simple mixing of thorium rich mib compositions and high thorium mare basalts

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

thorium abundances on the lunar surface measurements of absolute thorium abundances on the lunar surface are presented using both the high and low altitude data taken with the lunar prospector gamma ray spectrometer an analysis of the uncertainties shows that the measured uncertainties are 7 g g are likely small area regions 150 km 2 using lunar topographic data we have shown that the thorium abundances in the lunar high lands and portions of south pole aitken spa basin are larger for lower elevations we have also studied a number of regions with anomalously high thorium abundances such as the northwestern region of spa basin the crater arago in western tranquillitatis and the compton belkovich region in the northeastern highlands the compton belkovich region appears to be enriched with evolved rocks such as alkali anorthosite and currently represents the only such extended region on the moon that has been identified in contrast tycho crater has very low thorium abundances which suggests that kreep was not assimilated at depth in this portion of the moon

geochemical studies of feldspathic fragmental breccias and the nature of north ray crater ejecta major and trace element analyses of clasts and matrix from feldspathic fragmental breccias show that these breccias are not all alike but vary widely in their bulk compositions and clast assemblages these studies together with analyses of other north ray crater large rocks reveal the major components to be anorthosites ferroan anorthositic norites magnesian granulites feldspathic melt rocks and vha impact melts the ferroan anorthositic norites are important lunar crustal rocks identified here for the first time the kreepy vha melts are found to be much more important in north ray crater ejecta than was previously assumed sodic ferrogabbro is an important minor component the compositional characteristics of bulk breccias and feldspathic melt rocks are modeled quantitatively as mixtures of two to five components anorthosites ferroan anorthositic norites magnesian granulites sodic ferrogabbros and vha melt rocks breccia 67455 is unique in consisting wholly of ferroan kreep free components

apollo 14 aluminous mare basalts and their possible relationship to kreep thirty six aluminous mare basalt fragments from breccia 14321 and other apollo 14 basalts are statistically divided into two broad groups comprising five subgroups using la sm and yb data major element compositions petrographic characteristics and mineral compositions are similar for the five groups however there is an eight fold increase in ree abundances from group 5 to group 1 with group 1 having a ree pattern similar to kreep groups 1 to 3 may be related by partial melting of a source similar to that proposed by unruh et al 1984 for feldspathic basalt 12038 however groups 4 and 5 cannot be as closely matched by larger degrees of partial melting of this source groups 1 to 4 could also be produced by assimilation of a kreep component by a magma similar in composition to group 5 such a magma can be produced by partial melting of an olivine orthopyroxene source that crystallized from a magma with chondritic relative ree abundances

the imbrium impact event and the thorium distribution at the lunar highlands surface late in the moon s heavy bombardment period the impact that formed the imbrium basin excavated and melted a tremendous volume of material that was subsequently distributed over most of the moon s surface the apollo orbiting ray experiments metzger et al 1977 show that the imbrium projectile struck in a th rich area called the high th oval region here and regarded as a unique lunar geochemical province imbrium primary ejecta were thus probably rich in th it is shown here using ejecta deposit modeling that the distribution of th in the highlands surface along the ground tracks of the ray spectrometers is consistent with the distribution expected for imbrium ejecta deposits deep basins other than imbrium appear to have excavated regions of lower crust that were mafic and fe bearing but not th rich the possibility that the surface th distribution arises mainly from imbrium ejecta has implications for the nature of the moon s igneous differentiation and the nature of the proposed cataclysm or late bombardment with large meteoroids

uranium lead ages for lunar zircons evidence for a prolonged period of granophyre formation from 4 32 to 3 88 ga the ages of a number of small fragments of lunar granophyre have been determined by the in situ u th pb isotopic analysis of zircon using a sensitive high mass resolution ion microprobe shrimp i the zircon from lunar granophyre is characterized by consistently high u and th contents most 200 500 ppm and 100 300 ppm respectively compared to zircon from mafic lunar rocks some fragments of lunar granophyre are found to be as old as 4 32 ga supporting other evidence that the original lunar magma ocean crystallized completely within 200 ma of the formation of the moon itself other fragments are as young as 3 88 ga which is much later than the time of formation of most of the lunar crust the older lunar granophyres have rare earth element ree patterns that are similar to lunar kreep whilst the younger granophyres have bow shaped ree patterns that feature a greater relative enrichment in the heavy ree the wide range of ages of numerous lunar zircons lunar granophyres and other rocks indicates that zircon forming magmatism in the lunar highlands was most active prior to 4 3 ga but continuous until at least 3 88 ga the u pb isotopic composition of much lunar zircon is near concordant but the effects of isotopic disturbance as late as 1 0 ga are observed in some zircon both within granophyre fragments recrystallized by reheating and within fragments in which the original delicate silica k feldspar granophyric intergrowth is well preserved it is therefore essential to make multiple analyses of individual zircon grains and preferably analyses of suites of zircons from lunar igneous rocks if they are to be dated reliably by the u pb method it is possible that some of the younger lunar granophyres are the product of large scale silicate liquid immiscibility within late stage differentiates but this remains unproven until remnants of demonstrably cogenetic fe rich immiscible liquid are positively identified

alha 81005 meteorite chemical evidence for lunar highland origin based on the well established characteristic lunar and meteoritic ratios of feo mno cr2o3 v and k la and ree patterns alha 81005 meteorite is undoubtedly of lunar highland origin the alha 81005 meteorite is an anorthositic gabbro 72 pl and matches closely in chemical composition to apollo 15 15418 and luna 16 21013 highland rocks the rock is a non kreepy and vlt type the siderophiles au ni and ir content is high 1 5 cl equivalent and similar to other lunar highland breccias the clast has a different ancient meteorite component than the bulk and matrix the meteorite has a young terrestrial age implying a recent lunar cratering event therefore during major lunar basins formation in early eons the earth must have received a significant amount of lunar material which is now mixed in the crust the finding of a lunar meteorite lends credibility to the suggestion that snc achondrites may come from mars

geochemistry of impact glasses from the k t boundary in haiti relation to smectites and a new type of glass we have individually analyzed twelve black and seven yellow glasses from the k t boundary section at beloc haiti plus three smectite mantles around black glasses the main chemical differences between black and yellow glasses are higher s ca mg zn as br sb and au but lower k na and si abundances in the yellow glasses we have found high cao yellow glasses with low s contents 0 08 0 17 wt which may be explained by fusion of carbonate rich sediments microprobe studies of individual glasses show that the black glasses are very homogeneous in their composition at the 10 100 m level while yellow glasses show much more variability and different intra sample elemental correlations one of the black glasses has higher sio2 and k2o abundances but lower concentrations of all other major elements this suggests the existence of a third glass type which we have named the high si k variety hsi k glass the glass shows areas consisting of pure sio2 maybe lechatelierite and some schlieren with lower sio2 content the chemical composition indicates that the hsi k glass may have originated from melting of a sedimentary source rock such as shale or argillite severe changes in major and trace element composition occur during alteration of the glass as documented by analyses of adhering smectites the ree patterns in the glass are similar to average upper crust but the smectites exhibit much lower abundances and flat patterns not unlike the patterns observed in claystones at numerous k t boundary sites the suggestion that the chicxulub structure in yucatan may be the source crater for the k t impact glasses is not fully supported by the currently available data impact glasses and tektites are produced from the surface layers of their targets at chicxulub the target stratigraphy comprised mainly carbonates and evaporites although we cannot exclude chicxulub as a source the present data do not provide any firm chemical evidence for a connection we conclude however that the haiti glasses have formed by impact and have later undergone alteration by low temperature hydrothermal processes to produce clays the boundary claystones at k t boundary sites may very well be alteration products of these impact glasses

the uniform k distribution of the mare deposits in the orientale basin insights from chang e 2 gamma ray spectrometer the composition of mare basalt units in the orientale basin are investigated by using the potassium k map derived from chang e 2 gamma ray spectrometer ce 2 grs and feo map derived from clementine uv vis data set together with crater retention ages of the mare basalts from literature data we aim to investigate possible magma sources underneath the orientale basin and their chemical evolution over time analyses of the chemical composition of the resurfaced mare basalts together with the reported eruption ages suggest a unique magma generating process for the resurfaced mare deposits the early mare basalts in the central mare orientale and the later resurfaced mare deposits probably derived from magma generated by heat release due to high radioactive element concentrations based on forward modeling the similar k abundances observed in the small mare deposits of the sw polygon area lacus veris and lacus autumni and those in the central mare orientale imply the same heat source for these lava eruptions the chemical similarities e g k feo and tio2 of these regions suggest that mare basalts within the orientate basin are a result of multiple eruptions from a relatively homogeneous source underneath the basin c 2014 elsevier b v all rights reserved

the relative timing of lunar magma ocean solidification and the late heavy bombardment inferred from highly degraded impact basin structures the solidification of the lunar magma ocean lmo and formation of impact basins are important events that took place on the early moon the relative timing of these events however is poorly constrained the aim of this study is to constrain the formation ages of old impact basins based on inferences of their thermal state most proposed basins formed before pre nectarian pn 5 stage do not exhibit clear concentric features in either topography or gravity suggesting substantial viscous lateral flow in the crust recent geodetic measurements reveal that the lunar crust is thinner than previously estimated indicating that an extremely high crustal temperature is required for lateral flow to occur in this study we calculate lunar thermal evolution and viscoelastic deformation of basins and investigate the thermal state at the

pristine highland clasts in consortium breccia 14305 petrology and geochemistry the apollo 14 site continues to provide pristine non mare rocks that contrast sharply with those from apollo 16 the archetypical highland site we characterize six small 1 cm samples of pristine highland crust that occur as clasts in polymict lunar breccia 14305 one is an alkali anorthosite the others include troctolite norite and anorthosite of the mg suite the alkali anorthosite 400 is a plagioclase adcumulate with minor intercumulus augite cerian fluorapatite with lree contents 30 000 x chondrite occurs as an inclusion in plagioclase enstatite troctolite 358 and magnesian anorthosite 361 have trace element characteristics similar to eastern mg suite rocks highlighting the importance of local variations in geochemical systematics that are superimposed on moon wide longitudinal variations the highly fractionated trace element abundances and highly magnesian mineral compositions of olivine orthopyroxenite 389 suggest a new previously unknown magma type related to the mg suite this magma may have formed in equilibrium with garnet alkali anorthosites and magnesian anorthosites troctolites cannot be related to a single parent magma by fractional crystallization or by variable kreep assimilation these suites represent separate parent magmas each of which may have been modified by mixing with kreep

compositional implications regarding the lunar origin of the alha81005 meteorite geochemically alha81005 has all the attributes expected of a regolith sample from the lunar highlands most important is its fe mn ratio 77 within uncertainty the same as the mean lunar ratio there are significant differences however in comparison to previously sampled lunar regoliths the closest precedents are the apollo 16 and luna 20 regoliths particularly the latter but alha81005 has lower contents of na ti and incompatible elements feldspathic granulitic breccias such as 72559 which texturally resemble the most abundant type of clast in alha81005 are also similar compositionally from its low kreep and na contents we infer alha81005 originated well away from the k th and u rich region near the center of the nearside at least as far away as the eastern limb

statistical analysis of thorium and fast neutron data at the lunar surface 1 a comparison is conducted between the remotely sensed abundances of thorium through gamma ray spectroscopy and major chemical elements through fast neutron spectroscopy on the lunar surface these are key elements in the investigation of lunar evolution correlations of variations of thorium abundance and fast neutron flux are analyzed on a spatial scale of 180 km through the construction of a covariance map this technique is an unbiased mathematical method for developing the borders of major formations such as the procellarum kreep terrane although thorium variations are positively correlated with those of the fast neutron flux over most of the lunar nearside several locations within the procellarum kreep terrane have negative correlations this anticorrelation may denote an emplacement for these materials by transport of impact ejecta furthermore analysis of these data reveals the presence of a distinctive structure in the northwest corner of oceanus procellarum marked by a ring of enhanced thorium this structure may be related to an ancient impact basin the confirmation of such a ring of thorium around the major basins inside procellarum kreep terrane would reinforce the hypothesis of the redistribution of thorium during impact from shallow depth

the materials of the lunar procellarum kreep terrane a synthesis of data from geomorphological mapping remote sensing and sample analyses major features of the moon s procellarum kreep terrane include subdued relief and extensive resurfacing with mare basalt consistent with high concentrations of th and other heat producing elements at depth we relate the chemistry of sampled materials to the geomorphology th surface concentrations determined by the lunar prospector 2 pixels and feo and tio2 concentrations derived from clementine ultraviolet visible spectral data on the basis of geologic maps each pixel was classified as mare terra or mixed near the periphery of the terrane terra pixel compositions are relatively feldspathic in the interior they mainly represent imbrium basin rim or ejecta deposits and are mainly incompatible trace element rich norites and presumably represent materials from a thick section tens of kilometers of the pre imbrium crust of the terrane excavated by the imbrium event although imbrium ejecta are the principal source of surface terra materials the imbrium event did not create the th rich procellarum kreep terrane broad continuous expanses of mare pixels are observed with little interruption from protruding terra or terra penetrating craters the mare basalt dominated regoliths of these areas have a wide range of tio2 concentrations 18 leading to the conclusion that the high th concentrations are in the mare basalts and are not present in the regoliths as terra derived materials volcanic glasses and impact glasses of mare basalt composition collected from the procellarum kreep terrane support this conclusion

antarctic meteorite alha 81005 a piece from the ancient lunar crust a 128 mg sample of the antarctic meteorite alha 81005 was analysed for major and trace elements by instrumental neutron activation techniques the meteorite or at least its major components may be older than 4 billion years and represent a piece of the ancient lunar crust before the formation of the large basins on the front side of the moon the evidence is derived from the low absolute content of incompatible elements and their slightly different fractionation pattern from kreep the dominant source for these elements on the front side the basically chondritic pattern of siderophile elements ni co ir au is clearly distinguished from younger basin related meteoritic components

isotopic comparison of k t boundary impact glass with melt rock from the chicxulub and manson impact structures the discussion of candidate source craters for the catastrophic impact that occurred at the boundary between the cretaceous and tertiary periods k t boundary has recently centred on two buried craters the chicxulub in mexico 200 km diameter and the manson in iowa 35 km diameter both of which have 40ar 39ar ages of 65 myr indistinguishable from that of impact glass spherules found in k t boundary sediments1 4 here we report the strontium neodymium and oxygen isotopic compositions of core samples of impact melt rock recovered from drill holes into both the chicxulub and manson craters and compare these with previously published isotopic data for impact glasses from the k t boundary of the beloc formation in haiti5 7 the chicxulub melt rocks are isotopically indistinguishable from the k t impact glass strongly supporting the proposition that chicxulub is a source crater for the k t catastrophe the manson melt rocks by contrast have a clearly different isotopic composition strongly suggesting that they are unrelated to the k t impact spherules

iron abundances on the lunar surface as measured by the lunar prospector gamma ray and neutron spectrometers i global measurements of iron abundances on the lunar surface are presented using data from the lunar prospector lp gamma ray spectrometer grs and neutron spectrometer ns in this study we derive relative iron abundances from the low altitude high spatial resolution 45 km 2 lp data using the 7 6 mev neutron capture gamma ray doublet as part of the lp grs analysis we demonstrate the importance of accounting for variations in neutron number density across the lunar surface by measuring neutron fluxes using lp ns data in a first step of comparing the lp grs data with previously published iron abundances inferred from clementine spectral reflectance csr data we show that the existing csr feo data are nonlinear with respect to the lp relative iron abundances we use the lp data to linearize the relationship between the csr and the relative iron values then recalibrate the csr data to iron abundance using returned soil abundances we then correlate the csr data except for major anomalies with the lp relative iron measurements to convert the lp data to absolute iron abundances when we compare the lp grs and revised csr data sets we find a very good correspondence there are two locations mare tranquillitatis and south pole aitken spa basin that show major discrepancies suggesting that the csr data are locally overestimating iron abundances in both these regions the discrepancies identified by the lp grs csr comparison are possibly explained by mineralogical differences that are not accounted for in the csr to feo calibration in regards to our understanding of the moon the lp data have found the following i there exist large expanses of mare basalt in the western mare regions that have very high iron abundances 22 23 wt feo that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils which typically contain a significant amount of highlands contamination 2 the low iron abundances in the lunar highlands 5 feo wt are consistent with a previous analysis using thermal and epithermal neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process 3 the comparison of lp and csr derived iron abundances suggests that the material within spa basin is similar to a norite type rock without an enriched mantle feo signature 4 a comparison of lp and csr data at tycho crater shows a large discrepancy such that the csr data show moderate iron abundances of 8 9 wt feo while the lp data show very low iron abundances of 3 4 wt feo this discrepancy cannot yet be easily explained by any known process

a chemical and petrological model of the lunar crust and implications for lunar crustal origin we utilize a variety of lunar sample and orbital geochemical data in conjunction with current knowledge of impact cratering processes to develop a chemical and petrological model of the lunar crust orbital chemical data indicate that the upper highlands surface on the moon has the bulk composition of anorthositic gabbro al2o3 26 28 wt greater than 90 of the area covered is dominated by material having compositional affinities with the ferroan anorthosites rather than with apollo type mg suite rocks considerations of the cumulative bombardment history of the moon indicate that the outer zone of impact brecciation extends tens of kilometers into the crust given the resolution of the orbital gamma ray data the ferroan anorthositic composition derived for the highlands surface may represent the bulk composition of the upper half of the lunar crust the observed enrichment in noritic components in basin ejecta with increasing basin size together with considerations of impact melt petrogenesis in lunar basins suggest that the bulk composition of the lower lunar crust is noritic al2o3 20 wt samples of lower crustal material are probably present in the apollo collections in the form of low k fra mauro lkfm and very high alumina vha basaltic impact melts our estimated value of total crustal al2o3 content 24 25 wt suggests that the lunar crust contains too much aluminum to have originated by a purely serial magmatism mechanism the large abundance of plagioclase within the lunar crust is probably a result of global scale fractionation of plagioclase in early lunar history the magma ocean hypothesis of crustal origin more readily explains the bulk composition of the lunar crust