distinguishing high alumina mare basalts using clementine uvvis and lunar prospector grs data mare moscoviense and mare nectaris 1 high alumina ha mare basalts are a unique group of the lunar sample collection sample geochemistry indicates that these basalts are derived from sources composed of late stage cumulates from the lunar magma ocean lmo their aluminous nature suggests their sources contained significant plagioclase which has implications regarding the efficiency of plagioclase separation from earlier forming mafic cumulates in the lmo to form the anorthositic lunar crust and hence the heterogeneity of the lunar mantle the apollo and luna missions sampled ha basalts from four different locations that are separated by 80 equatorial degrees 2400 km radiometric age dating of these samples demonstrates aluminous basaltic volcanism spanned over 1 billion years suggesting ha basalts may be more prevalent on the moon than implied by the sample population knowing their global occurrence would ultimately enhance our understanding of lunar evolution aluminous mare basalts occupy a unique location in th feo compositional space that suggests they can be identified using global remote sensing data of the moon we present our approach for distinguishing exposures of ha basalts using clementine ultraviolet visible infrared uvvis and lunar prospector gamma ray spectrometer lp grs data with constraints based on the feo tio2 and th abundances of apollo and luna ha samples we identified 34 regions of interest rois where ha basalts could be a prominent component of the lunar surface by analyzing the rims and proximal ejecta from small impacts 0 4 4 km in diameter into the mare surface we characterized compositionally distinct basaltic units that make up the mare and thus determined which units represent ha basalt lavas the results were used to generate maps that depict discrete mare units and classify their general basalt type here we focus on two rois mare moscoviense and mare nectaris mare moscoviense is composed of four basaltic units two of which are ha candidates clementine uvvis data of mare nectaris show evidence of up to three mare basalt units one is the remnants of a mid ti unit that capped earlier low ti flows the majority of the basin is filled by a compositionally indistinguishable low fe low ti basalt however spectral profiles suggest there are two units regardless the units both fit the criteria for a ha basalt

constraint on subsurface structures beneath reiner gamma on the moon using the kaguya lunar radar sounder abstract reiner gamma is a sinuous feature in oceanus procellarum it has a higher reflectance of the visible wavelength than the surrounding flat mare basalt and displays a high crustal magnetic field previous studies relating to the origin of reiner gamma have provided contradictory depths of magnetic source bodies in the lunar crust as either shallow or deep if a shallow ejecta layer existed beneath the reiner gamma formation a subsurface lithological boundary between the denser mare basalt and the less dense ejecta blanket would be expected this study examines subsurface stratifications using the lunar radar sounder lrs onboard the kaguya spacecraft taking into account the lrs determined dielectric constants the influence of surface clutter and the energy loss of the lrs radar pulses in the high frequency band 5 mhz no evidence was found of subsurface boundaries down to a depth of 1000 m at reiner gamma given the lrs range resolution of 75 m the source of the magnetic anomaly is considered to be either strongly magnetized thin breccia layers at depths shallower than 75 m or less magnetized thick layers at depths deeper than 1000 m

late accretion to the moon recorded in zircon u th he thermochronometry abstract we conducted zircon u th he zhe analysis of lunar impact melt breccia 14311 with the aim of leveraging radiation damage accumulated in zircon over extended intervals to detect low temperature or short lived impact events that have previously eluded traditional isotopic dating techniques our zhe data record a coherent date vs effective uranium concentration eu trend characterized by 3500 ma dates from low 75 ppm eu zircon grains and ca 110 ma dates for high 100 ppm eu grains a progression between these date populations is apparent for intermediate 75 100 ppm eu grains thermal history modeling constrains permissible temperatures and cooling rates during and following impacts modeling shows that the data are most simply explained by impact events at ca 3950 ma and ca 110 ma and limits allowable temperatures of heating events between 3950 110 ma modeling of solar cycling thermal effects at the lunar surface precludes this as the explanation for the ca 110 ma zhe dates we propose a sample history characterized by zircon resetting during the ca 3950 ma imbrium impact event with subsequent heating during an impact at ca 110 ma that ejected the sample to the vicinity of its collection site our data show that zircon has the potential to retain 4he over immense timescales 3950 myrs thus providing a valuable new thermochronometer for probing the impact histories of lunar samples and martian or asteroidal meteorites

the early geological history of the moon inferred from ancient lunar meteorite miller range 13317 abstract miller range mil 13317 is a heterogeneous basalt bearing lunar regolith breccia that provides insights into the early magmatic history of the moon mil 13317 is formed from a mixture of

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

remote sensing and geologic studies of the schiller schickard region of the moon near infrared reflectance spectra multispectral images and photogeologic data for the schiller schickard ss region were obtained and analyzed in order to determine the composition and origin of a variety of geologic units these include light plains deposits orientale related deposits mare units and dark haloed impact craters dhcs spectral data indicate that the pre orientale highland surface was dominated by noritic anorthosite near ir spectra show that dhcs in the region have excavated ancient 3 8 ga mare basalts from beneath highland bearing material emplaced by the orientale impact ancient mare basalts were widespread in the ss region prior to the orientale event and their distribution appears to have been controlled by the presence of several old impact basins including the schiller zucchius basin and a basin previously unrecognized both near ir spectra and multispectral images indicate that light plains and other orientale related units in the ss region contain major amounts of local pre orientale mare basalt the amounts of local material in these deposits approach but seldom exceed the maximum values predicted by the local mixing hypothesis of oberbeck and co workers

global distribution of lunar impact melt flows abstract in this study we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims many of these craters were only recently discovered due to their unusual radar properties in the near global mini rf data set we find that most craters with exterior deposits of impact melt are small 20 km and that the smallest craters have the longest melt flows relative to their size in addition exterior deposits of impact melt are more common in the highlands than the mare this may be the result of differing target properties in the highlands and mare the difference in titanium content or the greater variation of topography in the highlands we find that 80 of complex craters and 60 of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim implying that pre existing topography plays a dominant role in melt emplacement this is likely due to movement during crater modification complex craters or breached crater rims simple craters we also find that impact melt flows have very high circular polarization ratios compared to other features on the moon this suggests that their surfaces are some of the roughest material on the moon at the centimeter to decimeter scale even though they appear smooth at the meter scale

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

the petrology and geochemistry of miller range 05035 a new lunar gabbroic meteorite miller range mil 05035 is a lunar gabbroic meteorite the mineralogy fe mn ratios in olivine and pyroxene bulk rock chemical composition and the bulk oxygen isotope values 17o 2 86 2 97 and 18o 5 47 5 71 are similar to those of other mare basalts and are taken as supporting evidence for a lunar origin for this meteorite the sample is dominated by pyroxene grains 54 61 by area mode of thin section along with large plagioclase feldspar 25 36 by mode and accessory quartz ilmenite spinel apatite and troilite the bulk rock major element composition of mil 05035 indicates that the sample has a very low ti vlt to low ti lunar heritage we measure bulk tio2 to be 0 9 wt and has low bulk incompatible trace element ite concentrations akin to samples from the vlt mare basalt suite to account for these geochemical characteristics we hypothesize that mil 05035 s parental melt was derived from a mantle region dominated by early cumulates of the magma ocean comprised principally of olivine and orthopyroxene mil 05035 is likely launch paired with the asuka 881757 and yamato 793169 basaltic lunar meteorites and the basaltic regolith breccia met 01210 this group of meteorites y a m m therefore may be a part of a stratigraphic column consisting of an upper regolith environment underlain by a coarsening downwards basalt lava flow

the mixing of lunar regolith vital updates to a canonical model abstract in this work we update the regolith mixing model presented by gault et al 1974 including new input values and reworking key parameters much as gault et al did we present a way to calculate the rate at which lunar regolith is overturned at depth the model describes a mixing front that proceeds downward from the surface following a power law function of time our most important update is the inclusion of secondary impacts our calculations show that secondaries are necessary to produce the reworking rate inferred from the depth distribution of surface correlated material in apollo cores fruchter et al 1977 morris 1978 blanford 1980 from the rate at which splotches rework the top 3 cm of regolith speyerer et al 2016 and from the rate at which diviner cold spots bandfield et al 2014 and crater rays pieters et al 1985 hawke et al 2004 werner and medvedev 2010 are reworked into background regolith overturn calculations that only consider the impact of primaries fail to describe observed reworking rates at all depths and timescales we conclude that secondary impacts dominate mixing in the top meter of lunar regolith

petrogenesis and chronology of lunar meteorite northwest africa 4472 a kreepy regolith breccia from the moon northwest africa nwa 4472 is a polymict lunar regolith meteorite the sample is kreep rich high concentrations of potassium rare earth elements and phosphorus and comprises a heterogeneous array of lithic and mineral fragments these clasts and mineral fragments were sourced from a range of lunar rock types including the lunar high magnesian suite the high alkali suite kreep basalts mare basalts and a variety of impact crater environments the kreep rich nature of nwa 4472 indicates that the sample was ejected from regolith on the nearside of the moon in the procellarum kreep terrane and we have used lunar prospector gamma ray remote sensing data to show that the meteorite is most similar to and most likely sourced from regoliths adjacent to the imbrium impact basin u pb and pb pb age dates of nwa 4472 phosphate phases reveal that the breccia has sampled pre nectarian 4 35 ga rocks related to early episodes of kreep driven magmatism some younger phosphate u pb and pb pb age dates are likely indicative of impact resetting events at 3 9 4 ga consistent with the suggested timing of basin formation on the moon our study also shows that nwa 4472 has sampled impact melts and glass with an alkali depleted incompatible trace element rich high sc low rb th ratios low k compositional signature not related to typical apollo high k kreep or that sampled by kreepy lunar meteorite sayh al uhaymir sau 169 this provides evidence that there are numerous sources of kreep rich protoliths on the moon

phosphate ages in apollo 14 breccias resolving multiple impact events with high precision u pb sims analyses abstract the u pb systems of apatite and merrillite grains within four separate apollo 14 impact melt breccia samples were analysed by secondary ion mass spectrometry no systematic difference was identified between the 207 pb 206 pb ages of the apatites and merrillites a combined 207 pb 206 pb age of 3927 2 ma 95 conf is determined for three of these samples 14305 103 3926 4 ma 14306 150 3926 6 ma 14314 13 3929 4 ma by combining these data with the ages previously obtained for zircons in apollo 12 impact melt breccia fragments and the lunar meteorite sau 169 a weighted average age of 3926 2 ma 95 conf is obtained which is attributed to the formation of the imbrium basin an age of 3943 5 ma is determined for the fourth breccia 14321 134 which is similar to ages of 3946 15 ma and 3958 19 ma obtained from several older phosphates in 14305 103 and 14314 13 the weighted average of these three older ages is 3944 4 ma 95 conf this is indistinguishable to the age 3938 4 ma 2 obtained for a different apollo 14 impact melt breccia in a previous study after investigating likely sources for this older 3940 ma age we conclude that the humorum or serenitatis basin forming events are likely candidates the potential identification of two large impact events within 15 myrs has important implications for the rate of lunar bombardment around 3 95 3 92 ga this study demonstrates the importance of high precision age determinations for interpreting the impact record of the moon as documented in lunar samples

high resolution u pb ages of ca phosphates in apollo 14 breccias implications for the age of the imbrium impact abstract previous age estimates of the imbrium impact range from 3770 to 3920 ma with the latter being the most commonly accepted age of this basin forming event the occurrence of ca phosphates i

northwest africa 482 a crystalline impact melt breccia from the lunar highlands northwest africa 482 nwa 482 is a crystalline impact melt breccia from the moon with highlands affinities the recrystallized matrix and the clast population are both highly anorthositic clasts are all related to the ferroan anorthosite suite and include isolated plagioclase crystals and lithic anorthosites troctolites and spinel troctolites potassium rare earth element and phosphorus bearing kreep and mare lithologies are both absent constraining the source area ofthis meteorite to a highland terrain with little to no kreep component most likely on the far side of the moon glass is present in shock veins cutting through the sample and in several large melt pockets indicating a second impact event there are two separate events recorded in the 40ar 39ar system one at 3750 ma which completely reset the k ar system and one at 2400 ma which caused onlypartial degassing these events could represent respectively crystallization ofthe impact melt breccia and later formation of the glass or the formation of the glass and a later thermal event the terrestrial age of the meteorite is 8 6 1 3 ka this age corresponds well with the modest amount ofweathering in the rock in the form ofsecondaryphyllosilicates and carbonates based on terrestrial age and location lithology and chemistry nwa 482 is unique among known lunar meteorites

the timing of basaltic volcanism at the apollo landing sites precise crystallisation ages have been determined for a range of apollo basalts from pb pb isochrons generated using secondary ion mass spectrometry sims analyses of multiple accessory phases including k feldspar k rich glass and phosphates the samples analysed in this study include five apollo 11 high ti basalts one apollo 14 high al basalt seven apollo 15 low ti basalts and five apollo 17 high ti basalts together with the samples analysed in two previous similar studies pb pb isochron ages have been determined for all of the major basaltic suites sampled during the apollo missions the accuracy of these ages has been assessed as part of a thorough review of existing age determinations for apollo basalts which reveals a good agreement with previous studies of the same samples as well as with average ages that have been calculated for the emplacement of the different basaltic suites at the apollo landing sites furthermore the precision of the new age determinations helps to resolve distinctions between the ages of different basaltic suites in more detail than was previously possible the proposed ages for the basaltic surface flows at the apollo landing sites have been reviewed in light of these new sample ages finally the data presented here have also been used to constrain the initial pb isotopic compositions of the mare basalts which indicate a significant degree of heterogeneity in the lunar mantle source regions even among the basalts collected at individual landing sites

the sculptured hills of the taurus highlands implications for the relative age of serenitatis basin chronologies and the cratering history of the moon 1 new images from the lunar reconnaissance orbiter camera show the distribution and geological relations of the sculptured hills a geological unit widespread in the highlands between the serenitatis and crisium basins the sculptured hills shows knobby undulating radially textured and plains like morphologies and in many places is indistinguishable from the similarly knobby alpes formation a facies of ejecta from the imbrium basin the new lroc image data show that the sculptured hills in the taurus highlands is imbrium ejecta and not directly related to the formation of the serenitatis basin this occurrence and the geological relations of this unit suggests that the apollo 17 impact melts may not be not samples of the serenitatis basin forming impact leaving their provenance undetermined and origin unexplained if the apollo 17 melt rocks are serenitatis impact melt up to half of the basin and large crater population of the moon was created within a 30 ma interval around 3 8 ga in a global impact cataclysm either interpretation significantly changes our view of the impact process and history of the earth moon system

crustal thickness of the moon new constraints from gravity inversions using polyhedral shape models a new method is presented for estimating crustal thickness from gravity and topography data on the moon by calculating analytically the exterior gravitational field for a set of arbitrarily shaped polyhedra relief along the crust mantle interface can be inverted for that satisfies the observational constraints as this method does not rely upon filtering the bouguer anomaly which was required with previous inversions performed in the spherical harmonic domain and as the dramatic variations in spatial quality of the lunar gravity field are taken into account our crustal thickness model more faithfully represents the available data using our model results we investigate various aspects of the prominent nearside impact basins the crustal thickness in the central portion of the orientale and crisium basins is found to be close to zero suggesting that these basins could have conceivably excavated into the lunar mantle furthermore given our uncertain knowledge of the density of the crust and mantle it is possible that the humorum humboldtianum nectaris and smythii basins could have excavated all the way through the crust as well the crustal structure for most of the young impact basins implies a depth diameter ratio of about 0 08 for their excavation cavities as noted in previous studies however the crustal structure of imbrium and serenitatis is anomalous which is conceivably a result of enhanced rates of post impact viscous relaxation caused by the proximity of these basins to the procellarum kreep terrane impact basins older than smythii show little or no evidence for crustal thinning suggesting that these ancient basins were also affected by high rates of viscous relaxation resulting from higher crustal temperatures early in the moon s evolution the lithosphere beneath many young basins is found to be supporting a downward directed force even after the load associated with the mare basalts is removed and this is plausibly attributed to superisostatic uplift of the crust mantle interface those basins that are close to achieving a pre mare isostatic state are generally found to reside within or close to the procellarum kreep terrane

small scale density variations in the lunar crust revealed by grail abstract data from the gravity recovery and interior laboratory grail mission have revealed that 98 of the power of the gravity signal of the moon at high spherical harmonic degrees correlates with the topography the remaining 2 of the signal which cannot be explained by topography contains information about density variations within the crust these high degree bouguer gravity anomalies are likely caused by small scale 10 s of km shallow density variations here we use gravity inversions to model the small scale three dimensional variations in the density of the lunar crust inversion results from three non descript areas yield shallow density variations in the range of 100 200 kg m 3 three end member scenarios of variations in porosity intrusions into the crust and variations in bulk crustal composition were tested as possible sources of the density variations we find that the density anomalies can be caused entirely by changes in porosity characteristics of density anomalies in the south pole aitken basin also support porosity as a primary source of these variations mafic intrusions into the crust could explain many but not all of the anomalies additionally variations in crustal composition revealed by spectral data could only explain a small fraction of the density anomalies nevertheless all three sources of density variations likely contribute collectively results from this study of grail gravity data combined with other studies of remote sensing data and lunar samples show that the lunar crust exhibits variations in density by 10 over scales ranging from centimeters to 100 s of kilometers

south pole aitken basin magnetic anomalies evidence for the true polar wander of moon and a lunar dynamo reversal the analysis of the lunar prospector magnetic data over south pole aitken basin reveals two categories of magnetic anomalies with distinctly different polarities modeling the anomalies in terms of vertical prism source bodies shows two separate true polar wander paths of the moon one is driven by the giant surface mass deficiency resulted from the formation of the south pole aitken basin and the other by the giant surface mass concentrations mascons formed inside the large impact basins such as serenitatis and imbrium and a vast volcanic deposit on procellarum terrane a total of 100o true polar wander path suggests that the source bodies are formed and magnetized during a long period moreover the distinctly different polarities of the two categories of the anomalies supports the idea that the core dynamo underwent a reversal or shutdown and started up with a different polarity caused by the latter impacts the impact induced shock pressures of 10 20 gpa traveling inside the lunar core the appreciable angular momentum transfer to the lunar mantle by the impacting bodies and the impact induced stratification of the core probably reversed the polarity of the core dynamo we also model the north crisium magnetic anomaly extracted from the lunar prospector magnetic data the paleomagnetic pole position obtained for the source body reveals that the north crisium anomaly belongs to the first category of the anomalies

a 4 2 billion year old impact basin on the moon u pb dating of zirconolite and apatite in lunar melt rock 67955 abstract a sharp rise in the flux of asteroid size bodies traversing the inner solar system at 3 9 ga has become a central tenet of recent models describing planetary dynamics and the potential habitability of early terrestrial environments the prevalence of 3 9 ga crystallization ages for lunar impact melt breccias and u pb isotopic compositions of lunar crustal rocks provide the primary evidence for a short lived cataclysmic episode of late heavy bombardment at that time here we report u pb isotopic compositions of zirconolite and apatite in coarse grained lunar melt rock 67955 measured by ion microprobe that date a basin scale impact melting event on the moon at 4 22 0 01 ga followed by entrainment within lower grade ejecta from a younger basin approximately 300 million yr later significant impacts prior to 3 9 ga are also recorded by lunar zircons although the magnitudes of those events are difficult to establish other isotopic evidence such as 40 ar 39 ar ages of granulitic lunar breccias regolith fragments and clasts extracted from fragmental breccias and re os isotopic compositions of lunar metal is also suggestive of impact related thermal events in the lunar crust during the period 4 1 4 3 ga we conclude that numerous large impactors hit the moon prior to the canonical 3 9 ga cataclysm that some of those pre cataclysm impacts were similar in size to the younger lunar basins and that the oldest preserved lunar basins are likely to be significantly older than 3 9 ga this provides sample based support for dynamical models capable of producing older basins on the moon and discrete populations of impactors an extended period of basin formation implies a less intense cataclysm at 3 9 ga and therefore a better opportunity for preservation of early habitable niches and hadean crust on the earth a diminished cataclysm at 3 9 ga suggests that the similarity in the age of the oldest terrestrial continental crust with the canonical lunar cataclysm is likely to be coincidental with no genetic significance

northwest africa 773 lunar mare breccia with a shallow formed olivine cumulate component inferred very low ti vlt heritage and a kreep connection abstract lunar meteorite northwest africa 773 herein referred to as nwa773 is a breccia composed predominantly of mafic volcanic components including a prominent igneous clast lithology the clast lithology is an olivine gabbro cumulate which on the basis of mineral and bulk compositions is a hypabyssal igneous rock related compositionally to volcanic components in the meteorite the olivine gabbro lithology exhibits cumulus textures and in our largest section of it includes some 48 olivine fo 64 to fo 70 average fo 67 27 pigeonite en 60 fs 24 wo 16 to en 67 fs 27 wo 6 11 augite en 50 fs 17 wo 33 to en 47 fs 13 wo 40 2 orthopyroxene en 70 fs 26 wo 4 11 plagioclase an 80 to an 94 and trace barian k feldspar ilmenite cr spinel re merrillite troilite and fe ni metal the mg fe ratios of the mafic silicates indicate equilibration of fe and mg however the silicates retain compositional variations in minor and trace elements that are consistent with intercumulus crystallization accessory mineralogy reflects crystallization of late stage residual melt both lithologies breccia and olivine cumulate of the meteorite have very low ti vlt major element compositions but with an unusual trace element signature compared to most lunar vlt volcanic compositions i e relative enrichment in light ree and large ion lithophile elements and greater depletion in eu than almost all other known lunar volcanic rocks the calculated composition of the melt that was in equilibrium with pyroxene and plagioclase of the cumulate lithology exhibits a kreep like ree pattern but at lower concentrations melt of a composition calculated to have been in equilibrium with the cumulate assemblage plus excess olivine yields a major element composition that is similar to known green volcanic glasses one volcanic glass type from apollo 14 in particular green glass b type 1 has a very low ti concentration and ree characteristics including extremely low eu concentration that make it a candidate parent melt for the olivine gabbro cumulate we infer an origin for the parent melt of nwa773 volcanic components by assimilation of a trace element rich partial or residual melt by a magnesian vlt magma deep in the lunar crust or in the mantle prior to transportation to the near surface accumulation of olivine and pyroxene in a shallow chamber eruption onto a volcanic surface and incorporation of components into local predominantly volcanic regolith prior to impact mixing of the volcanic terrain and related hypabyssal setting and ejection from the surface of the moon volcanic components such as these probably occur in the oceanus procellarum region near the site of origin of the green volcanic glasses found in the apollo 14 regolith

partitioning in ree saturating minerals theory experiment and modelling of whitlockite apatite and evolution of lunar residual magmas we present compositions including rees determined by ion microprobe of apatite and whitlockite in lunar rock assemblages rich in incompatible trace elements total concentrations of ree oxides in whitlockites range from 9 13 wt and those in apatites range from 0 15 to 1 wt ratios of ree concentrations in whitlockite to those in coexisting apatite range from 10 to 60 the distribution of mg and fe between apatite and whitlockite is correlated to that of coexisting mafic silicates magnesium is strongly preferred by whitlockite and fe is preferred by apatite incorporation of rees in whitlockite is dominated by the coupled substitution of 2ree3 in ca b sites vacancy in ca iia for 2ca 2 in ca b sites and ca2 na in ca iia other substitutions account for only a small portion of the rees in whitlockite over the observed concentration range thus ree concentrations become partially saturated as the primary substitution approaches its stoichiometric limit of two rees per fifty six oxygens leading to reduced whitlockite melt distribution coefficients e g decreasing from twenty five to ten for nd the ree concentrations of lunar residual melts are not depleted by whitlockite crystallization in assemblages consisting mainly of other minerals in typical proportions distribution coefficients for the rees in lunar apatite appear to be low and variable e g 0 2 0 8 for nd variations in the modal ratio of whitlockite to apatite specifically the abundance of whitlockite lead to a range of ree concentrations in the phosphates and variations in the magnitude of ree concentration ratios between whitlockite and apatite if apatite crystallizes before whitlockite or in the absence of whitlockite as textures in several samples indicate then apatite zoned in rees and apatite crystals of different ree concentrations may occur in a given sample provided there is some amount of fractional crystallization and apatite does not later equilibrate this may occur because in the absence of whitlockite in the crystallizing assemblage the rees are highly incompatible relative to the crystalline assemblage so ree concentrations in lunar residual melts increase strongly during small increments of late stage crystallization once whitlockite begins to crystallize bulk distribution coefficients for the rees although still 1 are only mildly incompatible so the change in ree concentrations of residual melts with further crystallization is small consistent with the lack of ree zoning in whitlockite the ree concentrations in lunar whitlockites are modelled as resulting mainly from equilibrium crystallization of the assemblages in which they occur metasomatism or other secondary metamorphic processes are not indicated local melt pocket equilibrium at advanced stages of crystallization may lead to variable ree concentrations and variable whitlockite apatite concentration ratios within the same sample parent melts with extremely high ree concentrations are not required in order to crystallize ree rich lunar whitlockite if modal proportions of whitlockite are low

ages of pristine noritic clasts from lunar breccias 15445 and 15455 abstract rb sr and sm nd isotopic studies were undertaken of two apollo 15 breccias 15445 and 15455 collected near spur crater on the apennine front seven pristine lithic clasts including four norites one anorthositic norite one troctolitic anorthosite and one spinel troctolite as well as a matrix sample of 15445 were analysed in addition a k ar age determination was also made for a plagioclase separate from a different anorthositic norite clast sm nd isotopic data of a pristine mg norite sample 15445 17 from the large white clast b of breccia 15445 yielded a precise internal isochron age of 4 46 0 07 ga for 147 sm 0 00654 ga 1 and an initial 143 nd 144 nd of 0 506058 0 000078 normalized to 148 nd 144 nd 0 24308 corresponding to an initial nd of 0 71 however sm nd isotopic results of another mg norite sample 15445 247 chipped from the same clast b about 1 cm away from 15445 17 yielded a significantly younger isochron age of 4 28 0 03 ga and a higher initial 143 nd 144 nd of 0 506246 0 000037 corresponding to an initial nd of 0 35 the sm nd data indicate that clast b is heterogeneous and contains at least two similar lithologies the rb sr isotopic systems were severely disturbed for both norites no useful isochron ages were observed the sm nd age and nd data for a 15 mg norites 15445 17 and 15445 247 a 17 mgnorite 78236 and two mg gabbronorites 73255 27 45 and 67667 are clearly resolved from each other four distinct parental magmas are required for derivation of these two major groups of mg suite noritic rocks the rb sr isotopic system of an anorthositic norite clast 15455 228 was slightly disturbed and isotopic data defined an isochron age of 4 59 0 13 ga for 87 rb 0 0139 ga 1 or 4 55 0 13 ga for 87 rb 0 01402 ga 1 the corresponding initial 87 sr 86 sr for the rock is 0 69899 0 00006 and is in satisfactory agreement with the luni value of nyquist et al 1974 the sm nd system is more disturbed than the rb sr system for this rock a tie line between whole rock samples and a pyroxene separate gives a sm nd age of 4 53 0 29 ga which is in nominal agreement with the rb sr isochron age the 39ar40ar age of a plagioclase separate of the rock has a weighted average value of 3 83 ga suggesting that the age was reset by the imbrium impact event probably the sm nd and rb sr systems of the clast were also partly reset by this event our age results indicate that some mg suite rocks are as old as ferroan anorthosite suite rocks furthermore age data of three major crustal rocks a mg suite a ferroan anorthosite suite and an evolved suite show that they all have variable ages these observations are difficult to explain by the magma ocean hypothesis alone petrogenetic processes such as production of mg suite rocks by serial magmatism walker 1983 of ferroan anorthosite suite rocks by multiple diapiric intrusions longhi and ashwal 1985 and evolved suite rocks by continuous magmatism meyer et al 1988 1989 probably all played a role these processes seem to be able to accommodate the wide ranges of ages and different origins observed for lunar crustal rocks

revisiting the field geology of taurus littrow abstract integration of apollo 17 field observations and photographs sample investigations lunar reconnaissance orbiter camera images chandrayaan 1 moon mineralogy mapper m3 spectra and miniature radio frequency mini rf s band radar images provides new insights into the geology of the valley of taurus littrow on the moon connecting the various remote observations to sample data enables a set of new conclusions to be drawn regarding the geological evolution of the valley structural considerations and published and recalculated 40ar 39ar analyses of samples from the north massif and the sculptured hills indicate that the crisium basin formed about 3 93 ga the serenitatis basin about 3 82 ga and the imbrium basin no earlier than 3 82 ga and no later than the average of 3 72 ga for 33 age dates from samples of the valley s mare basalts strong evidence continues to support the conclusion of others lucchitta 1972 spudis et al 2011 fassett et al 2012 that the sculptured hills physiographic unit consists of imbrium ejecta interpretation of m3 spectral data and apollo 17 samples indicate that rock units of the sculptured hills consist of a largely coherent mg suite pluton lroc nac stereo images and mini rf data indicate the presence of several exposed pyroclastic fissures across the sculptured hills rim boulders at camelot crater constitute nearly in situ wall rocks of that crater rather than ejecta and provide an opportunity for investigations of remanent magnetic field orientation at the time of the eruption of late mare basalt lavas in the valley paleomagnetic field orientation information also may be obtained relative to melt breccia contacts in north massif boulders that suggest original horizontal orientations lroc images indicate the existence of two temporally separate light mantle avalanche deposits the origin potential flow mechanisms and geology of the youngest avalanche from the south massif have been clarified the existence of two distinct light mantle avalanches raises doubt about the association of either light mantle avalanche with secondary impacts related to the tycho impact event alternatively the lee lincoln thrust fault appears to have triggered the second light mantle avalanche between 70 and 110 ma a simple structural analysis shows that this thrust fault dips 20 25 to the southwest where it crosses the north massif and to the west where it crosses the valley floor mini rf data reveal a line of reduced reflections roughly perpendicular to contours on the north massif about 3 km to the east of the lee lincoln fault although this line is possibly an older ancillary fault lroc nac stereo images indicate that it may be best explained as a pyroclastic fissure a debris flow of dark apparent pyroclastic ash lies below the southeast end of the potential fissure finally young lunar impact glass sample 70019 has been precisely located within lroc nac images and oriented for the first time using 60 mm f l sample documentation photographs sample 70019 can now be employed in lunar paleomagnetic field orientation studies

thermal history recorded by the apollo 17 impact melt breccia 73217 abstract lunar breccia 73217 is composed of plagioclase and pyroxene clasts originating from a single gabbronorite intrusion mixed with a silica rich glass interpreted to represent an impact melt a study of accessory minerals in a thin section from this breccia 73217 52 identified three different types of zircon and anhedral grains of apatite which represent distinct generations of accessory phases and provide a unique opportunity to investigate the thermal history of the sample equant anhedral zircon grains that probably formed in the gabbronorite referred to as type 1 have consistent u pb ages of 4332 7 ma a similar age of 4335 5 ma was obtained from acicular zircon type 2 grains interpreted to have formed from impact melt a polycrystalline zircon aggregate type 3 occurs as a rim around a baddeleyite grain and has a much younger age of 3929 10 ma similar to the 3936 17 ma age of apatite grains found in the thin section a combined apatite type 3 zircon age of 3934 12 ma is proposed as the age of the serenitatis impact event and associated thermal pulse x ray mapping and electron probe analyses showed that ti is inhomogeneous in the zircon grains on the sub micrometer scale however model temperatures estimated from shrimp analyses of ti concentration in the 10 m diameter spots on the polished surfaces of type 1 and type 2 zircons range between about 1300 and 900 c respectively whereas ti concentrations determined for the type 3 zircon are higher at about 1400 1500 c a combination of u pb ages ti concentration data and detailed imaging and petrographic studies of the zircon grains shows that the gabbronorite parent of the zircon clasts formed shortly before the 4335 5 ma impact which mixed the clasts and the felsic melt and projected the sample closer to the surface where fast cooling resulted in the crystallization of acicular zircon type 2 the 3934 12 ma serenitatis event resulted in partial remelting of the glass and formation of polycrystalline zircon type 3 this event also reset the u pb system of apatite formed merrillite coronas around some apatite grains and probably re equilibrated some pyroxenes in the clasts although there have been arguments for pre 3 9 ga impacts based on other types of samples the age of the acicular zircon at 4335 5 ma provides the first evidence of impact melt significantly predating the lunar cataclysm our data combined with other chronological results demonstrate the occurrence of pre 3 9 ga impacts on the moon and suggest that the lunar impact history consisted of a series of intense bombardment episodes interspersed with relatively calm periods of low impact flux

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

the case for a younger imbrium basin new 40ar 39ar ages of apollo 14 rocks petrographically and chemically well characterized rocks of the apollo 14 landing site 12 impact melt breccias 3 clast free impact melt rocks 2 granulitic rocks 1 cataclastic noritic anorthosite 1 shocked gabbronorite 1 mare basalt and 1 plagioclase single crystal have been dated by the 40ar 39ar technique the samples represent two different formations at the apollo 14 site 1 small lithic clasts 10 specimens from fragmental breccia 14063 ejected from the 26 ma old cone crater and one clast mare basalt from cone crater soil 14140 and 2 large rock samples 10 specimens collected throughout the regolith of the landing site the first group of samples has exposure ages close to 26 ma and 40ar 39ar ages ranging from 3 86 to 4 09 ga which indicates that breccia 14063 was assembled 3 86 ga ago the second group of samples displays lower 40ar 39ar ages ranging from 3 73 to 3 85 ga we interpret breccia 14063 as part of a nectarian megabreccia unit which was incorporated into the fra mauro formation as a megablock by secondary mass wasting of the ejecta blanket of a local pre imbrian crater the remaining samples are thought to represent clasts of the apollo 14 subregolith basement megabreccia defined as the fra mauro formation consequently the reported ages of these clasts confirm previous suggestions that the fra mauro formation and therefore the imbrium basin is only 3 75 ga old and not 3 85 ga as commonly assumed

the effect of 1 9 and 1 4 ga impact events on 4 3 ga zircon and phosphate from an apollo 15 melt breccia 1 zircon and phosphate grains from matrix and quartz monzodiorite qmd clasts in two thin sections of apollo 15 impact melt breccia 15405 were investigated using optical microscopy scanning electron microscopy raman spectroscopy and ion microprobe u pb analyses u pb results for zircon grains with well defined cathodoluminescence zoning define the primary i e magmatic crystallization age as 4330 6 ma 2 one zircon consists of a preserved inner part surrounded by a porous polycrystalline granular mixture of zircon and baddeleyite indicating incomplete reaction of the zircon with melt previous work showed that this microstructure could form at pressures above 60 gpa and a temperature close to 1700 c and is evidence of an impact related melting event the u pb system of this grain indicates a resetting event at 1940 10 ma interpreted as the age of this impact impact 1 other zircon and phosphate grains also have disturbed u pb systems showing an even younger reset event impact 2 at 1407 57 ma evidence of impact is supported by microstructures of zircon and baddeleyite such as secondary rims these impacts are tentatively identified as those having formed autolycus and aristillius craters

annealing of radiation damage in zircons from apollo 14 impact breccia 14311 implications for the thermal history of the breccia impact breccia 14311 was collected from the apollo 14 landing site as a potential sample of the underlying fra mauro formation published zircon u pb ages of 4000 ma date the source material of the breccia and the apatite u pb age of 3940 ma is interpreted as dating thermal resetting of the apatite u pb systems in this contribution we present new age information on the late stage thermal history of the breccia based on the annealing of radiation damage in the zircons from raman spectroscopic determination of the radiation damage within sims analytical spots on the zircons and the u and th concentrations determined on these spots we demonstrate that the radiation damage in the zircons has been annealed and we estimate the age of annealing at 3410 80 ma this age is interpreted as a cooling age following heating of the breccia to above the annealing temperature of 230 c for stage 1 radiation damage in zircon but below the temperature needed to reset the u pb system of apatite 500 c it is proposed that this thermal event was associated with the prolonged period of mare volcanism from 3150 to 3750 ma that generated massive basalt flows in the vicinity of the sample location

annealing history of zircons from apollo 14083 and 14303 impact breccias abstract breccia boulders scattered around the 25 ma cone crater near the apollo 14 landing site provide a potential source of material ejected from the underlying fra mauro formation which is int

density and porosity of the lunar crust from gravity and topography 1 newly obtained gravity and topography data of the moon combined with a lithospheric flexure model that considers both surface and subsurface loading are used to place constraints on the density of the upper crust from a localized spectral admittance analysis subsurface loads are found to be relatively unimportant in the highlands and when subsurface loads are neglected the best fitting bulk densities for a number of highland regions are found to vary from 2590 to 2870 kg m 3 with a mean value of 2691 kg m 3 crustal rock densities estimated from geochemical considerations and global iron and titanium abundances imply somewhat greater densities which we interpret as porosity affecting the gravity derived bulk density estimates the average porosity in the upper few kilometers of crust is calculated to be about 7 7 which is consistent with porosity estimates of impact fractured meteorites and terrestrial impact craters

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

compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration we present new compositional data for 30 lunar stones representing about 19 meteorites most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites 3 7 feo and the basaltic lunar meteorites 17 23 feo all but one are polymict breccias some as implied by their intermediate composition are mainly mixtures of brecciated anorthosite and mare basalt with low concentrations of incompatible elements such as sm 1 3 g g these breccias likely originate from points on the moon where mare basalt has mixed with material of the fht feldspathic highlands terrane others however are not anorthosite basalt mixtures three 17 75 g g sm consist mainly of nonmare mafic material from the nearside pkt procellarum kreep terrane and a few are ternary mixtures of material from the fht pkt and maria some contain mafic nonmare lithologies like anorthositic norites norites gabbronorites and troctolite these breccias are largely unlike breccias of the apollo collection in that they are poor in sm as well as highly feldspathic anorthosite such as that common at the apollo 16 site several have high th sm compared to apollo breccias dhofar 961 which is olivine gabbronoritic and moderately rich in sm has lower eu sm than apollo samples of similar sm concentration this difference indicates that the carrier of rare earth elements is not kreep as known from the apollo missions on the basis of our present knowledge from remote sensing among lunar meteorites dhofar 961 is the one most likely to have originated from south pole aitken basin on the lunar far side

lunar floor fractured craters modes of dike and sill emplacement and implications of gas production and intrusion cooling on surface morphology and structure abstract lunar floor fractured craters ffcs represent the surface manifestation of a class of shallow crustal intrusions in which magma filled cracks dikes rising to the surface from great depth encounter contrasts in host rock lithology breccia lens rigid solidified melt sheet and intrude laterally to form a sill laccolith or bysmalith thereby uplifting and deforming the crater floor recent developments in the knowledge of lunar crustal thickness and density structure have enabled important revisions to models of the generation ascent and eruption of magma and new knowledge about the presence and behavior of magmatic volatiles has provided additional perspectives on shallow intrusion processes in ffcs we use these new data to assess the processes that occur during dike and sill emplacement with particular emphasis on tracking the fate and migration of volatiles and their relation to candidate venting processes ffcs result when dikes are capable of intruding close to the surface but fail to erupt because of the substructure of their host impact craters and instead intrude laterally after encountering a boundary where an increase in ductility base of breccia lens or rigidity base of solidified melt sheet occurs magma in dikes approaching the lunar surface experiences increasingly lower overburden pressures this enhances co gas formation and brings the magma into the realm of the low pressure release of h2o and sulfur compounds both factors adding volatiles to those already collected in the rising low pressure part of the dike tip high magma rise velocity is driven by the positive buoyancy of the magma in the part of the dike remaining in the mantle the dike tip overshoots the interface and the consequent excess pressure at the interface drives the horizontal flow of magma to form the intrusion and raise the crater floor if sill intrusion were controlled by the physical properties at the base of the melt sheet dikes would be required to approach to within 300 m of the surface and thus eruptions rather than intrusions would be very likely to occur instead dynamical considerations strongly favor the sub crustal breccia lens as the location of the physical property contrast localizing lateral intrusion at a depth of several kilometers the end of lateral and vertical sill growth occurs when the internal magma pressure equals the external pressure the intrusion just supports the weight of the overlying crust dynamical considerations lead to the conclusion that dike magma volumes are up to 1100 km3 and are generally insufficient to form ffcs on the lunar farside the estimated magma volumes available for injection into sills on the lunar nearside up to 800 km3 are comparable to the observed floor uplift in many smaller ffcs and thus consistent with these ffcs forming from a single dike emplacement event in contrast the thickest intrusions in the largest craters imply volumes requiring multiple dike contributions these are likely to be events well separated in time rather than injection of new magma into a recently formed and still cooling intrusion we present a temporal sequence of 1 dike emplacement 2 sill formation and surface deformation 3 bubble rise foam layer formation and collapse 4 intrusion cooling and a synthesis of predicted deformation sequence and eruption styles initial lateral injection of the sill at a depth well below the upper dike tip initiates upbowing of the overburden leveraging deformation of the crater floor melt sheet above this is followed by lateral spreading of the sill toward the edges of the crater floor where crater wall and rim deposit overburden inhibit further lateral growth and the sill grows vertically into a laccolith or bysmalith uplifting the entire floor above the intrusion subsidiary dikes can be emplaced in the fractures at the uplift margins and will rise to the isostatic level of the initial dike tip if these contain sufficient volatiles to decrease magma density eruptions can also occur this initial phase of intrusion sill lateral spreading and floor uplift occurs within a few hours after initial dike emplacement during the subsequent cooling of the sill bubbles can rise hundreds of meters to the top of the intrusion to create a foam layer when drainage of gas bubble wall magma occurs in the foam layer a continuous gas layer forms above the foam gas formation and upward migration produces an increase in sill thickness while subsequent cooling and solidification cause a thickness decreases and subsidence the total topographic evolution history following an initial 2 km thick sill intrusion and floor uplift hours includes further floor uplift by gas formation and migration decades 30 m followed by cooling solidification and subsidence a century 350 m an initial 2 km thick sill is predicted to have a final thickness of 1 7 km this predicted sequence of events can be compared with the sequence of floor deformation and volcanism in ffcs in order to test and refine this model

the density and porosity of lunar rocks 1 accurate lunar rock densities are necessary for constructing gravity models of the moon s crust and lithosphere most apollo era density measurements have errors of 2 5 or more and few include porosity measurements we report new density and porosity measurements using the bead method and helium pycnometry for 6 apollo samples and 7 lunar meteorites with typical grain density uncertainties of 10 30 kg m 3 0 3 0 9 and porosity uncertainties of 1 3 comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space basalt grain densities are a strong function of composition varying over at least 3270 kg m 3 high aluminum basalt to 3460 kg m 3 high titanium basalt feldspathic highland crust has a bulk density of 2200 2600 kg m 3 and porosity of 10 20 impact basin ejecta has a bulk density of 2350 2600 kg m 3 and porosity of 20

position of the disastrous 1999 puebla earthquake in the seismotectonic pattern of mexico the location of the 1999 puebla earthquake shows that this earthquake belongs to the class of disastrous intraplate earthquakes generated by fracturing of the continental lithosphere caused by the process of subduction this is obvious from the vertical section across the middle american wadati benioff zone and from its position in the revised seismically active los azufres rio salado fracture zone delineated in the continental lithosphere of the north american plate

re examination of the formation ages of the apollo 16 regolith breccias abstract the lunar regolith is exposed to irradiation from the solar wind and to bombardment by asteroids comets and inter planetary dust fragments of projectiles in the lunar regolith can potentially provide a direct measure of the sources of exogenous material being delivered to the moon constraining the temporal flux of their delivery helps to address key questions about the bombardment history of the inner solar system here we use a revised antiquity calibration after eugster et al 2001 that utilises the ratio of trapped 40 ar 36 ar parentless 40 ar derived from radioactive decay of 40 k against solar wind derived 36 ar to semi quantitatively calculate the timing of the assembly of the apollo 16 regolith breccias we use the trapped 40 ar 36 ar ratios reported by mckay et al 1986 our model indicates that the apollo 16 ancient regolith breccia population was formed between 3 8 and 3 4 ga consistent with regoliths developed and assembled after the imbrium basin forming event at 3 85 ga and during a time of declining basin forming impacts the material contained within the ancient samples potentially provides evidence of impactors delivered to the moon in the late imbrian epoch we also find that a young regolith population was assembled probably by local impacts in the apollo 16 area in the eratosthenian period between 2 5 and 2 2 ga providing insights to the sources of post basin bombardment the soil like regolith breccia population and the majority of local apollo 16 soils were likely closed in the last 2 ga and therefore potentially provide an archive of projectile types in the eratosthenian and copernican periods

comparative zircon u pb geochronology of impact melt breccias from apollo 12 and lunar meteorite sau 169 and implications for the age of the imbrium impact abstract the ages of zircons from high th impact melt breccias imbs from meteorite sayh al uhaymir sau 169 and from rock fragments in soil samples from apollo 12 have been determined using the shrimp ii ion microprobe the imbs are very similar to each other in chemistry mineralogy and texture and the zircons from the kreep rich high th crystalline impact melt have similar u and th contents and identical ages within uncertainties of 3920 13 2 ma sau 169 and 3914 7 2 ma apollo 12 the age results support the idea that the high th imbs apollo 12 and sau 169 formed in the same impact event the similarity of composition and age suggest that sau 169 and the high th imb fragments of apollo 12 originated from the same area of the procellarum kreep terrane we interpret the age of zircon grains in the apollo 12 high th imb as a precise and direct determination of the age of the imbrium impact this age is significantly older than the commonly cited age of 3 85 ga but is similar to recent determinations from sims u pb dating of apollo 14 apatite grains and with anticipated revision of ages by 40 ar 39 ar and 87 rb 86 sr the present zircon 207 pb 206 pb age is the first direct zircon age determination of the imbrium impact event from an apollo sample previous measurements of zircon ages of apollo imbs have recorded events pre dating the imbrium basin forming event

evidence for metasomatism of the lunar highlands and the origin of whitlockite abstract the presence of rare earth element rich ree rich whitlockite in the relatively primitive ree poor lunar highlands presents a paragenetic problem to the petrologist comparison with occurrences in mare basalt mesostasis assemblages demonstrates that whitlockite in the lunar highlands has not resulted from the crystallization of the residual interstitial melt furthermore by the nature of ree partition coefficients for whitlockite it is demonstrated that they cannot have crystallized from kreepy melts rather we suggest that the only lunar melt which contains high enough ree abundances is the basic immiscible melt derived from a kreepy liquid we envisage that whitlockite found in the lunar highlands is a post cumulus metasomatic phase precipitated from a melt formed when urkreep underwent silicate liquid immiscibility the basic immiscible melt thus produced was able to percolate through the lunar highlands due to its low viscosity and act as a metasomatizing agent apatite is occasionally found as either epitactic overgrowths on the whitlockites mantled by whitlockite or in composite grains with whitlockite in all cases these apatites contain much lower ree contents than the corresponding whitlockite experimental results suggest either 1 1 apatite and whitlockite have essentially the same ree kd s 2 2 apatite has lower ree kd s than whitlockite both scenarios can be used to explain certain apatite whitlockite associations for example apatite and whitlockite having the same ree kd s can explain the situation where apatite appears to have crystallized after whitlockite this is because apatite crystallization requires a certain level of halogens in the melt these levels are only realized after whitlockite crystallization which enriches the residual melt in f and cl but depletes it in the rees therefore when apatite crystallizes it will contain lower ree abundances than whitlockite however relationships where apatite and whitlockite appear to have co crystallized or apatite crystallized before whitlockite require apatite to have lower ree kd s even if both experimental results are correct the whitlockite parental melt still requires ree abundances greater than in kreep urkreep the parental melt has similar ree abundances to a calculated reepy immiscible melt from kreep urkreep

a concise compilation of petrologic information on possibly pristine nonmare moon rocks ansrn q cr to facilitate systematic study of the surviving compositionally pristine endogenously igneous rocks of the ancient lunar crust a compilation has been generated of all likely samples along with key information on the petrologic characteristics and chemistry of each sample the compilation includes 260 samples besides information related to the likelihood of each sample being truly pristine i e mainly its texture and siderophile element abundances information is compiled on mineral content listing major phases present as well as basic information on mineral compositions on size expressed as mass and on whether a reasonably comprehensive chemical analysis has been published the compilation also classifies the samples into seven categories of confidence in the pristine composition of the samples reflecting an estimation of the relative likelihood that each arguably pristine sample is in fact pristine for many purposes it is crucial to avoid inclusion of polymict rocks in a data base on petrologic diagrams such as a plot of average mg mg 100 x molar mg mg fe in a low ca mafic silicate vs average an content in plagioclase rocks in the top three categories of the confidence in pristine character appear distinctly bimodal in composition with roughly half belonging to a ferroan suite characterized by high an despite relatively low mg when samples of low to moderate pristine character are included the bimodality appears less distinct sample mass can also be important with a data base restricted to samples more massive than i g there is a clear distinction in feldspar content and bulk density between ferroan and nonferroan mgsuite rocks such that only the ferroan suite rocks are likely to have formed as flotation cumulates with a data base including smaller samples the same basic pattern is seen but only in a blurred form as the two rock types show considerable overlap in their modal feldspar contents

petrogenesis of mare basalts a record of lunar volcanism returned rock and soil samples from our nearest planetary neighbor have provided the basis for much of our understanding of the origin and evolution of the moon of particular importance are the mare basalts which have revealed considerable information about lunar volcanism and the nature of the mantle as well as post magma generation processes this paper is a critical review of the petrogenetic models for the generation of mare basalts formulated over the last twenty years we have used all available mare basalt analyses to define a six fold classification scheme using tio2 contents as the primary division i e 1 wt very low ti or vlt 1 6 wt low ti 6 wt high ti a secondary division is made using al2o3 contents i e 11 wt low al 11 wt high al and a tertiary division is defined using k contents i e 2000 ppm low k 2000 ppm high k such divisions and subdivisions yield a classification containing twelve categories of which six are accounted for by the existing apollo and luna collections therefore we present our discussions in the form of six mare basalt rock types 1 1 high ti low al low k referred to as high ti low k 2 2 high ti low al high k referred to as high ti high k 3 3 low ti low al low k referred to as low ti 4 4 low ti high al low k referred to as high alumina 5 5 low ti high al high k referred to as vhk 6 6 vlt low al low k basalts referred to as vlt a variety of post magma generation processes have been invoked such as fractional crystallization either alone or combined with wallrock assimilation to explain the compositional ranges of the various mare basalt suites in order to evaluate these proposed petrogenetic processes this review is by rock type and is non site specific but for each rock type reference to particular lunar sample return missions is brought forth this permits a comparison of similarities and differences of broadly similar rock types correlated with geography on the moon which in turn allows a more thorough petrogenetic evaluation high ti mare basalts i e high ti low al low k are found at apollo 11 and apollo 17 sites however the a 11 basalts contain lower tio2 abundances a considerably larger range in trace element contents and the only occurrence of high ti high k mare basalts fractional crystallization and source heterogeneity within each site are the keys to understanding the petrogenesis of the high ti basalts low ti basalts including both low al k and high al k varieties are found at apollo 12 14 and 15 and luna 16 sites the low ti basalts exhibit a wide range of major and trace element compositions and require source heterogeneity fractional crystallization and some assimilation the high alumina mare basalts i e low ti high al low k are found at apollo 14 and luna 16 sites and exhibit a wide range of major and trace element compositions however in these examples source heterogeneity is not a major factor indeed fractional crystallization coupled with kreep assimilation particularly for the apollo 14 variants can explain the compositional ranges of these high alumina basalts the vhk mare basalts i e low ti high al high k have been sampled only at the apollo 14 locale and are products of a parental highalumina magma assimilating lunar granite very low ti vlt mare basalts i e vlt low al low k are found at apollo 17 and luna 24 sites fractional crystallization has had a major influence upon the range in vlt compositions but luna 24 vlt basalts have been derived from a source slightly different in composition from that for apollo 17 vlt varieties for example the luna 24 vlt basalts generally exhibit positive eu anomalies a unique property for mare basalts which almost always have negative eu anomalies the concept of a lunar magma ocean lmo is generally accepted and source modelling of all basalts invokes a mafic lmo cumulate source this is the only unifying model for mare basalt petrogenesis but the semantics and logistics of it are and will be debated for many years for example major convective overturn of the lmo appears plausible but whether this occurred on a local or planet wide scale to produce source heterogeneity remains to be determined

the late heavy bombardment heavily cratered surfaces on the moon mars and mercury show that the terrestrial planets were battered by an intense bombardment during their first billion years or more but the timing sources and dynamical implications of these impacts are controversial the late heavy bombardment refers to impact events that occurred after stabilization of the planetary lithospheres such that they could be preserved as craters and basins lunar melt rocks and meteorite shock ages point toward a discrete episode of elevated impact flux between 3 5 and 4 0 4 2 ga and a relative quiescence between 4 0 4 2 and 4 4 ga evidence from precambrian impact spherule layers suggests that a long lived tail of terrestrial impactors lasted to 2 0 2 5 ga dynamical models that include populations residual from primary accretion and destabilized by giant planet migration can potentially account for the available observations although all have pros and cons the most parsimonious solution to match constraints is a hybrid mode

3 1 ga crystallization age for magnesian and ferroan gabbro lithologies in the northwest africa 773 clan of lunar meteorites abstract the northwest africa nwa 773 clan of meteorites is a group of paired and or petrogenetically related stones that contain at least six different lithologies magnesian gabbro ferroan gabbro anorthositic gabbro olivine phyric basalt regolith breccia and polymict breccia uranium lead dates of baddeleyite in the magnesian gabbro ferroan gabbro and components within breccia lithologies of paired lunar meteorites nwa 773 nwa 3170 nwa 6950 and nwa 7007 indicate a chronologic link among the meteorites and their components a total of 50 baddeleyite grains were analyzed and yielded weighted average 207pb 206pb dates of 3119 4 9 4 n 27 3108 20 n 13 and 3113 15 n 10 ma for the magnesian gabbro ferroan gabbro and polymict breccia lithologies respectively a weighted average date of 3115 6 6 8 ma n 47 50 was calculated from the baddeleyite dates for all lithologies a single large zircon grain found in a lithic clast in the polymict breccia of nwa 773 yielded a u pb concordia date of 3953 18 ma indicating a much more ancient source for some of the components within the breccia a u pb concordia date of apatite and merrillite grains from the magnesian gabbro and polymict breccia lithologies in nwa 773 is 3112 33 ma identical to the baddeleyite dates magnesian and ferroan gabbros as well as the dated baddeleyite and ca phosphate bearing detritus in the breccia lithologies formed during the same igneous event at about 3115 ma these data also strengthen proposed petrogenetic connections between magnesian and ferroan gabbro lithologies which represent some of the youngest igneous rocks known from the moon

bistatic radar observations of the moon using mini rf on lro and the arecibo observatory the miniature radio frequency mini rf instrument aboard nasa s lunar reconnaissance orbiter lro is a hybrid dual polarized synthetic aperture radar sar that operated in concert with the arecibo observatory to collect bistatic radar data of the lunar nearside from 2012 to 2015 the purpose of this bistatic campaign was to characterize the radar scattering properties of the surface and near surface as a function of bistatic angle for a variety of lunar terrains and search for a coherent backscatter opposition effect indicative of the presence of water ice a variety of lunar terrain types were sampled over a range of incidence and bistatic angles including mare highland pyroclastic crater ejecta and crater floor materials responses consistent with an opposition effect were observed for the ejecta of several copernican aged craters and the floor of the south polar crater cabeus the responses of ejecta material varied by crater in a manner that suggests a relationship with crater age the response for cabeus was observed within the portion of its floor that is not in permanent shadow the character of the response differs from that of crater ejecta and appears unique with respect to all other lunar terrains observed analysis of data for this region suggests that the unique nature of the response may indicate the presence of near surface deposits of water ice

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

modification of caloris ejecta blocks by long lived mass wasting a volatile driven process abstract the caloris basin is the largest well preserved impact basin on mercury as such caloris ejecta afford us an opportunity to study material from mercury s deep interior with remote sensing we have made observations of the geomorphology colour distribution and flank slopes of the circum caloris knobs our observations suggest that these circum caloris knobs are modified ejecta blocks from the caloris impact high resolution messenger images show that knobs are conical and relatively uncratered compared with the surrounding plains which implies the knobs have undergone resurfacing we have observed material that has sloughed off knobs superposing impact craters that demonstrably postdate the caloris impact which requires some knob modification to have been more recent we have observed hollows depressions in mercury s surface generally believed to have been caused by volatile loss on and closely associated with several knobs which indicates that many knobs contain volatile material and that knob modification could extend into mercury s recent past our measurements show that knob flanks typically have slopes of 21 which is steep for a mound of unconsolidated material that was originally emplaced 3 8 ga the conical shape of knobs their steep slopes the dearth of superposed craters on knobs and knob superposition relationships with other landforms suggest that caloris ejecta blocks of arbitrary original shape were modified into their present shapes by long lived mass wasting mass wasting must have dominated over impact gardening which would have produced domal morphologies only we suggest that mass wasting was probably driven by volatile loss in a manner analogous to terrestrial landforms called molards if the circum caloris knobs are analogous to molards then they represent a landform and a process hitherto undocumented on mercury with implications for the volatile content of the planet s interior these knobs therefore are prime targets for bepicolombo which could search for fresh failures and volatile exposures in the knobs

chemical variation of the large apollo 15 olivine normative mare basalt rock samples most chemical analyses of apollo 15 olivine normative mare basalts have been conducted on subsamples of 4 g to obtain greater whole rock representivity these subsamples were individually ground and homogenized and splits were taken for analysis furthermore we used both x ray fluorescence and neutron activation techniques to analyze for a comprehensive set of elements suitable for petrogenetic interpretation the analyses show that the samples form a single coherent suite with almost all of the variation corresponding with olivine control 15 range a few of the coarser rocks are not quite represented even at this sampling size the analyses show that the rocks are individually distinct and that analyses are not merely of unrepresentative pieces of a single rock undifferentiated rock unit or rocks differing only by short range unmixing of residual fluids the petrographic features including the low abundance of olivine and its small size and the vesicularity of even some of the coarser samples show that the olivine that controlled the chemical variation is not accumulated in any of the rocks the apollo 15 olivine normative mare basalts were extruded as a series of magmas from a shallow but not locally surficial olivine accumulating magma system and formed a sequence of thin flows a greater understanding of the relationships within and among other mare basalt sequences would be obtained by obtaining comprehensive chemical analyses on splits taken from subsamples of 5 g of all rocks large enough to obtain such subsamples

diverse impactors in apollo 15 and 16 impact melt rocks evidence from osmium isotopes and highly siderophile elements abstract concentrations of highly siderophile elements hse and 187 os 188 os isotopic compositions for eleven impact related rocks from the apollo 15 and 16 landing sites are reported and combined with existing geochronological data to investigate the chemical nature and temporal changes in the large impactors implicated in the formation of the lunar basins data for the samples all define linear trends on plots of hse versus ir concentrations whose slopes likely reflect the relative hse compositions of the dominant impactors that formed the rocks the inferred imbrium basin impactor that generated apollo 15 impact melt rocks 15445 and 15455 was characterized by modestly suprachondritic 187 os 188 os ru ir pt ir and pd ir ratios diverse impactor components are revealed in the apollo 16 impact melt rocks the 187 os 188 os and hse ir ratios of the impactor components in melt rocks 60635 63595 and 68416 with reported ages 4 0 ga by contrast the impactor components in melt rocks 60235 62295 and 67095 with reported ages of 3 9 ga are characterized by suprachondritic 187 os 188 os and hse ir ratios similar to the apollo 15 impact melt rocks and may also sample the imbrium impactor three lithic clasts from regolith breccias 60016 and 65095 also with 3 9 ga ages contain multiple impactor components of which the dominant composition is considerably more suprachondritic than those implicated for imbrium and serenitatis apollo 17 impactors the dominant composition recorded in these rocks was most likely inherited from a pre imbrium impactor consideration of composition versus age relations among lunar impact melt rocks reveals no discernable trend virtually all lunar impact melt rocks sampled by the apollo missions as well as meteorites are characterized by 187 os 188 os and hse ir ratios that when collectively plotted define linear trends ranging from chondritic to fractionated compositions the impact melt rocks with hse signatures within the range of chondritic meteorites are interpreted to have been derived from impactors that had hse compositions similar to known chondrite groups by contrast the impact melt rocks with non chondritic relative hse concentrations could not have been made by mixing of known chondritic impactors these signatures may instead reflect contributions from early solar system bodies with bulk chemical compositions that have not yet been sampled by primitive meteorites present in our collections alternately they may reflect the preferential incorporation of evolved metal separated from a fractionated planetesimal core pre 4 0 ga ages for at least some impactor components with both chondritic and fractionated hse raise the possibility that the bulk of the hse were added to the lunar crust prior to the later stage basin forming impacts such as imbrium and serenitatis as proposed by fischer godde and becker 2012 for this scenario the later stage basin forming impacts were more important with respect to mixing prior impactor components into melt rocks rather than contributing much to the hse budgets of the rocks themselves

lunar anorthosite 60025 the petrogenesis of lunar anorthosites and the composition of the moon systematic variations of the mineral chemistry of ferroan anorthosite 60025 which is probably a mixture of closely related materials suggest that lunar anorthosites formed by strong fractional crystallization and near perfect adcumulate growth without trapping liquid the parent liquid for the most primitive samples was saturated with olivine plagioclase pigeonite and chromite and evolved to one saturated with plagioclase pigeonite high ca pyroxene and ilmenite the parent liquid also had a very low na2o content and combined with strong fractional crystallization this explains the steep trend of anorthosites on an mg atomic 100 mg mg fe v an diagram the mineral and chemical data for other anorthosites are consistent with such a model near perfect adcumulation can occur if growth takes place at the crystal liquid interface without the physical accumulation of crystals grown elsewhere and is encouraged by the shifts in phase boundaries with pressure anorthosites are probably the remnants of a crust floating on and crystallizing at the surface of a magma ocean originally of bulk moon composition mineralogical and trace element data suggest that the parental liquid for the most primitive anorthosites had previously crystallized no plagioclase and some but perhaps very little pyroxene hence the bulk moon appears to be similar to that proposed by ringwood 1976 but to have even lower alkalis a subchondritic caal ratio and ree abundances and patterns close to chondritic the mare basalt sources are not directly complementary to the feldspathic crust because experimental and trace element data indicate that they are too magnesian and contain too much high ca pyroxene other crustal rocks such as the mg suite samples are not closely related to anorthosites in addition to their chemical differences they have a different crystallization sequence ol plag px in contrast with the ol px plag inferred for anorthosite parental liquid evolution

the comparative behavior of apatite zircon u pb systems in apollo 14 breccias implications for the thermal history of the fra mauro formation we report secondary ion mass spectrometry sims u pb analyses of zircon and apatite from four breccia samples from the apollo 14 landing site the zircon and apatite grains occur as cogenetic minerals in lithic clasts in two of the breccias and as unrelated mineral clasts in the matrices of the other two sims u pb analyses show that the ages of zircon grains range from 4023 24 ma to 4342 5 ma whereas all apatite grains define an isochron corresponding to an age of 3926 3 ma the disparity in the ages of cogenetic apatite and zircon demonstrates that the apatite u pb systems have been completely reset at 3926 3 ma whereas the u pb system of zircon has not been noticeably disturbed at this time the apatite u pb age is slightly older than the ages determined by other methods on apollo 14 materials highlighting need to reconcile decay constants used for the u pb ar ar and rb sr systems we interpret the apatite age as a time of formation of the fra mauro formation if the interpretation of this formation as an imbrium ejecta is correct apatite also determines the timing of imbrium impact the contrast in the pb loss behavior of apatite and zircon places constraints on the temperature history of the apollo 14 breccias and we estimate from the experimentally determined pb diffusion constants and an approximation of the original depth of the excavated samples in the fra mauro formation that the breccias experienced an initial temperature of about 1300 1100 c but cooled within the first five to ten years

dating phosphates of the strongly shocked suizhou chondrite impacts on undifferentiated asteroidal bodies provide invaluable information for understanding the solar system evolution nevertheless dating early and small scale impact events is technically challenging uranium lead u pb systematics of u bearing phases within shock induced melt veins smvs of chondrites may be significantly disturbed by localized heating thus providing opportunities to date these impact events as one of the major u hosts in chondrites apatite in the suizhou l6 chondrite has been compositionally and structurally modified to varying degrees by shock metamorphism apatite grains in the host remained largely intact during the impact and have recorded the initial thermal cooling time similar to 4550 ma on their parent body apatite grains in regions less than 100 mu m bordering the smvs or in relatively cold regions within the smvs were partly decomposed to tuite driven by the localized transient heating within the smvs their u pb systematics were disrupted to varying extents apatite in regions close to the center of the smvs has been completely transformed to tuite which yields an age of 4481 30 ma 2 sigma providing an upper limit to the impact event this study clearly demonstrates that by integrating in situ u pb isotope analysis with detailed microstructural and compositional analysis of phosphates it is possible to deduce the timing of early and small scale celestial impact events and hence create a more comprehensive understanding of the impact history of the solar system

rb sr analyses of apollo 16 melt rocks and a new age estimate for the imbrium basin lunar basin chronology and the early heavy bombardment of the moon rb sr model ages on 7 impact glass bombs and internal rb sr isochrons for two crystalline impact melt rocks from the apollo 16 collection have been determined the post cayley glass bombs with model ages between 4 75 0 45 ae and 3 97 0 08 ae can be classified according to their calculated single stage 87rb86sr i ratios 67728 67946 and 67627 8 point to a kreep free precursor terrain the descartes highlands whereas 63566 67567 67627 10 and 67629 are derived from the more heterogeneous cayley plains the very feldspar rich impact melt rock 65795 which is compositionally similar to the group of feldspathic microporphyritic melt breccias fm suite yields a crystallization age of 3 81 0 04 ae 2 87rb 1 42 11yr and isr of 69929 3 in the subophitic impact melt rock 60635 5 two ages were recorded one isochron with 3 87 0 02ae and isr of 0 69920 3 gives the crystallization age of a fine grained internal clast at 3 75 0 03 ae this fragment was incorporated into the host lithology of 60635 which is a member of the anorthositic noritic melt rock anmr group this group has a crystallization age of about 3 75 ae the anmr rocks and several samples of apollo 14 crystalline impact melt rocks belong to a suite of young crystalline impact melt rocks ranging in age from 3 71 to 3 81 ae these ages are in conflict with the canonical age of the imbrium event 3 85 ae it is argued that the young apollo 14 and 16 melt rocks cannot represent solid exotic fragments or melt splashes ejected from post imbrium local or distant craters instead these rocks are derived from coherent impact melt sheets of pre imbrian craters with diameters larger than 5 7 km they are interpreted as clasts of the fra mauro and cayley formation breccia deposits and therefore their ages are used as an upper limit for the age of the imbrium event we suggest that the imbrium basin and the related fra mauro and cayley formations were formed 3 77 0 02 ae ago and could be even as young as 3 75 ae as a consequence we adopt 3 92 0 03 ae 3 87 0 03 ae and 3 84 0 04 ae as ages for the nectaris serenitatis and crisium basins respectively in agreement with the relative crater densities measured on the ejecta blankets of these basins wilhelms 1984 the proposed age sequence leads to an average formation interval for the observed 12 13 nectarian basins of 7 to 14 m y leaving 30 pre nectarian basins of unknown age these facts suggest that there is no late terminal lunar cataclysm in the sense of a culmination of the lunar impact rate at 3 8 ae ago rather the observations are compatible with a steeply and steadily decreasing flux of impactors hartmann 1980 in the sense of an early heavy bombardment which started at the time of the moon s accretion and terminated around 3 75 ae ago

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

40ar 39ar age spectra of apollo 15 impact melt rocks by laser step heating and their bearing on the history of lunar basin formation we have obtained 26 high resolution 16 51 steps 40ar 39ar age spectra using a continuous laser system on submilligram fragments of recrystallized melt and single crystal plagioclase clasts from 12 apollo 15 impact melt rocks collected at the apennine front where the imbrium and serenitatis basins intersect these melt rocks represent a wide range of compositions and at least half a dozen different impacts six of the melt rocks have reproducible intermediate temperature plateaus over 40 or more of the 39ar released the plateaus are interpreted as crystallization impact ages and much of the non plateau behavior is attributable to recoil samples 15294 6 21 15304 7 69 15314 26 156 15357 15 and 15359 12 have mean 40ar 39ar plateau ages that are statistically indistinguishable and fall within the narrow range 3852 14 2 ma to 3870 12 ma with a weighted mean of 3865 5 ma sample 15356 9 has a mean plateau age of 3836 11 ma and may represent a distinctly younger impact a seventh sample 15314 30 158 has a peculiar but reproducible double plateau a low t one at 3873 9 ma which we think records the crystallization age and a high t one of 3831 10 ma which we interpret as an experimental 39ar recoil artifact four of the remaining melt rocks 15308 9 15414 2 37 15436 2 15445 253 have complex 40ar 39ar age spectra that indicate that they either formed in or were disturbed by impacts that occurred 3850 ma but did not completely reset the k ar isotopic system sample 15414 3 36 is different its spectrum may represent release mainly from clasts that were not well degassed in a melt event at 3870 ma the melt phase contains little potassium because most of the apennine front material must be coeval with or predate formation of the imbrium basin it seems likely that the imbrium impact is no older than 3870 ma and probably no older than 3836 ma so far there is no convincing evidence in the lunar record for melt producing impacts such as basin formation older than about 3 9 ga

identifying the geologic context of apollo 17 impact melt breccias abstract the origin of the boulders sampled during the apollo 17 mission to the taurus littrow valley has been debated since the completion of the mission four decades ago no consensus has yet been reached whether the sampled boulders originated in material emplaced as a result of the serenitatis impact i e massifs the imbrium impact i e sculptured hills a combination of both impact events or as a result of another pre or post serenitatis impact event i e massifs or superposed deposits on valley floor these on going debates demonstrate the importance of identifying the geologic context of samples collected during the apollo missions using high resolution imagery and topography data we identify boulder tracks that connect sampled boulders with source outcrops these observations verify astronauts impressions that boulders originated in outcrops within massif walls and that they remain uncontaminated by nearby sculptured hills materials this finding can be used with updated ar ar and u pb ages of analyzed samples to constrain the timing and intensity of the lunar cataclysm epoch

magnetic anomalies in the imbrium and schrodinger impact basins orbital evidence for persistence of the lunar core dynamo into the imbrian epoch approximate maps of the lunar crustal magnetic field at low altitudes in the vicinities of the three imbrian aged impact basins orientale schrodinger and imbrium have been constructed using lunar prospector and kaguya orbital magnetometer data detectable anomalies are confirmed to be present well within the rims of imbrium and schrodinger anomalies in schrodinger are asymmetrically distributed about the basin center while a single isolated anomaly is most clearly detected within imbrium northwest of timocharis crater the subsurface within these basins was heated to high temperatures at the time of impact and required long time periods up to 1 myr to cool below the curie temperature for metallic iron remanence carriers 1043 k therefore consistent with laboratory analyses of returned samples a steady long lived magnetizing field i e a former core dynamo is inferred to have existed when these basins formed the asymmetrical distribution within schrodinger suggests partial demagnetization by later volcanic activity when the dynamo field was much weaker or nonexistent however it remains true that anomalies within imbrian aged basins are much weaker than those within most nectarian aged basins the virtual absence of anomalies within orientale where impact melt rocks the maunder formation are exposed at the surface is difficult to explain unless the dynamo field was much weaker during the imbrian period

the mineralogy of late stage lunar volcanism as observed by the moon mineralogy mapper on chandrayaan 1 1 the last major phases of lunar volcanism produced spectrally unique high titanium basalts on the western nearside of the moon the moon mineralogy mapper m3 on chandrayaan 1 has provided detailed measurements of these basalts at spatial and spectral resolutions necessary for mineralogical interpretation and mapping of distinct compositional units the m3 imaging spectrometer acquired data in 85 spectral bands from 430 to 3000 nm at 140 to 280 m pixel in its global mapping mode during the first half of 2009 reflectance data of several key sites in the western maria were also acquired at higher spatial and spectral resolutions using m3 s target mode prior to the end of the chandrayaan 1 mission these new observations confirm that both fresh craters and mare soils within the western high ti basalts display strong 1 m and weak 2 m absorptions consistent with olivine rich basaltic compositions the inferred abundance of olivine is observed to correlate with stratigraphic sequence across different mare regions and absolute ages the apparent stratigraphic evolution and fe rich compositions of these basalts as a whole suggest an origin from evolved residual melts rather than through the assimilation of more primitive olivine rich sources mare deposits with spectral properties similar to these late stage high ti basalts appear to be very limited outside the procellarum imbrium region of the moon and where present appear to occur as small areas of late stage regional volcanism detailed analyses of these new data and supporting measurements are in progress to provide further constraints on the mineralogy olivine abundance and compositions of these final products of lunar volcanism and the nature and evolution of their source regions

density porosity and magnetic susceptibility of achondritic meteorites as part of a large scale survey of meteorite bulk and grain densities porosities and magnetic susceptibilities we measured these properties for 174 stones from 106 achondritic meteorites these include four lunar meteorites 15 stones from 10 shergottites nakhlites and chassignites sncs 96 stones from 56 howardites eucrites and diogenites heds 17 stones from nine aubrites two angrites and 16 stones from 10 ureilites four stones of three acapulcoites as well as four stones of three lodranites and 15 stones from eight primitive achondrites those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities on an average than the more primitive achondrites which have a higher percentage metal a notable exception is the one chassignite in the study chassigny which has a high grain density of 3 73 0 04 g cm 3 ureilites have magnetic susceptibilities consistent with primitive achondrites but lower grain densities porosities do not vary considerably between most of the groups with most stones 5 14 porous although on an average ureilites and brachinites have lower porosities with most stones less than 7 porous for primitive achondrites the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites with a reduction in grain density magnetic susceptibility and porosity as compared with unweathered falls for lunites sncs and heds no such effect is observed we also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites nakhlites and chassignites from each other shergottites and nakhlites have low grain densities averaging 3 31 and 3 41 g cm 3 respectively whereas chassigny is 3 7 g cm 3 in magnetic susceptibility shergottities and chassignites are similar averaging 2 85 and 2 98 in log units of 10 9 m3 kg 1 respectively with nakhlites averaging higher at 3 42

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