the shape and internal structure of the moon from the clementine mission global topographic and gravitational field models derived from data collected by the clementine spacecraft reveal a new picture of the shape and internal structure of the moon the moon exhibits a 16 kilometer range of elevation with the greatest topographic excursions occurring on the far side lunar highlands are in a state of near isostatic compensation whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age a global crustal thickness map reveals crustal thinning under all resolvable lunar basins the results indicate that the structure and thermal history of the moon are more complex than was previously believed

compositional heterogeneity of central peaks within the south pole aitken basin 1 using high spectral and spatial resolution moon mineralogy mapper data we investigate compositional variations across the central peak structures of four impact craters within the south pole aitken basin spa two distinct causes of spectral diversity are observed spectral variations across the central peaks of bhabha finsen and lyman are dominated by soil development including the effects of space weathering and mixing with local materials for these craters the central peak structure is homogeneous in composition although small compositional differences between the craters are observed this group of craters is located within the estimated transient cavity of spa and their central uplifts exhibit similar mafic abundances therefore it is plausible that they have all uplifted material associated with melts of the lower crust or upper mantle produced during the spa impact compositional differences observed between the peaks of these craters reflect heterogeneities in the spa subsurface although the origin of this heterogeneity is uncertain in contrast to these craters leeuwenhoek exhibits compositional heterogeneity across its central peak structure the peak is areally dominated by feldspathic materials interspersed with several smaller exposures exhibiting a mafic spectral signature leeuwenhoek is the largest crater included in the study and is located in a region of complex stratigraphy involving both crustal feldspathic and spa mafic melt and ejecta materials the compositional diversity observed in leeuwenhoek s central peak indicates that kilometer scale heterogeneities persist to depths of more than 10 km in this region

on the equipotential surface hypothesis of lunar maria floors the equipotential surface hypothesis suggests that lunar maria floors lie on a surface parallel to the selenoid this is examined using the spherical harmonic representations of the clementine topography and lunar prospector gravity data it is demonstrated that the floors of both circular and noncircular maria significantly deviate from an equipotential surface deeper circular maria and the deeper part of the noncircular maxe tranquillitatis have been subsided under larger mass loads in the crust we calculate the mass beneath the maria to be in excess to the mass required for isostatic compensation of the topography at 60 km depth a global map of this excess mass shows that the noncircular maria are isostatically compensated unlike the circular maria the map also reveals seven new sizable mascons the three largest are associated with mendel rydberg mare humboldtianum and mare moscoviense

compositional variations in the vicinity of the lunar crust mantle interface from moon mineralogy mapper data moon mineralogy mapper spectroscopic data were used to investigate the mineralogy of a selection of impact craters central peaks or peak rings in order to characterize the lunar crust mantle interface and assess its lateral and vertical heterogeneity the depth of origin of the craters central peaks or peak rings was calculated using empirical equations and compared to gravity recovery and interior laboratory crustal thickness models to select craters tapping within 10 20 km of the crust mantle interface our results show that plagioclase is widely detected including in craters allegedly sampling lower crustal to mantle material except in central peaks where low calcium pyroxene was detected olivine detections are scarce and identified in material assumed to be derived from both above and below the crust mantle interface mineralogical detections in central peaks show that there is an evolution of the pyroxene composition with depth that may correspond to the transition from the crust to the mantle the correlation between high calcium pyroxene and some pyroxene dominated mixture spectra with the location of maria and cryptomaria hints at the existence of lateral heterogeneities as deep as the crust mantle interface

distribution and modes of occurrence of lunar anorthosite 1 we have utilized telescopic near infrared spectra and multispectral images of the moon provided by the galileo and clementine missions to determine the distribution and modes of occurrence of pure anorthosite anorthosites have now been identified in all portions of the nearside including the site of the putative procellarum basin anorthosite is associated with the rings of orientale grimaldi humorum nectaris nubium mutus vlaq and balmer basins major portions of the inner rings of grimaldi humorum crisium orientale and nectaris are composed of pure anorthosite the large spatial extent of these anorthosites appears to rule out an origin in the upper portions of discrete differentiated mg suite plutons in every instance the anorthosites were exposed from beneath a shallower near surface layer of more pyroxene rich material more mafic material also occurs beneath the pure anorthosite unit large expanses of the northern farside exhibit very low feo values this region contains abundant anorthosite and stands in stark contrast to the mafic composition exhibited by the interior of the south pole aitken basin spa the distribution of compositional units on large portions of the lunar farside as well as the southern portion of the lunar nearside appears to be largely attributable to the spa impact event the distribution and modes of occurrence of anorthosites clearly indicate that a thick global layer of anorthosite is present at various depths beneath most portions of the lunar surface this anorthosite layer dominated the upper portion of the primordial crust and was produced by plagioclase flotation in the global magma ocean

mineralogy of the mafic anomaly in the south pole aitken basin implications for excavation of the lunar mantle the mineralogy of south pole aitken basin spa the largest confirmed impact basin on the moon is evaluated using five color images from clementine although olivine rich material as well as basalts rich in clinopyroxene are readily identified elsewhere on the farside the dominant rock type observed across the interior of spa is of a very noritic composition this mineralogy suggests that lower crust rather than the mantle is the dominant source of the mafic component at spa the lack of variation in observed noritic composition is probably due to basin formation processes during which extensive melting and mixing of target materials are likely to occur

geophysical consequences of planetary scale impacts into a mars like planet all planetary bodies with old surfaces exhibit planetary scale impact craters vast scars caused by the large impacts at the end of solar system accretion or the late heavy bombardment here we investigate the geophysical consequences of planetary scale impacts into a mars like planet by simulating the events using a smoothed particle hydrodynamics sph model our simulations probe impact energies over two orders of magnitude 2 10 27 6 10 29 j impact velocities from the planet s escape velocity to twice mars orbital velocity 6 50 km s and impact angles from head on to highly oblique 0 75 the simulation results confirm that for planetary scale impacts surface curvature radial gravity the large relative size of the impactor to the planet and the greater penetration of the impactor contribute to significant differences in the geophysical expression compared to small craters which can effectively be treated as acting in a half space the results show that the excavated crustal cavity size and the total melt production scale similarly for both small and planetary scale impacts as a function of impact energy however in planetary scale impacts a significant fraction of the melt is sequestered at depth and thus does not contribute to resetting the planetary surface complete surface resetting is likely only in the most energetic 6 10 29 j slow and head on impacts simulated a crater rim is not present for planetary scale impacts with energies 10 29 j and angles 45 but rather the ejecta is more uniformly distributed over the planetary surface antipodal crustal removal and melting is present for energetic 10 29 j fast 6 km s and low angle 45 impacts the most massive impactors with both high impact energy and low velocity contribute sufficient angular momentum to increase the rotation period of the mars sized target to about a day impact velocities of 20 km s result in net mass erosion from the target for all simulated energies and angles the hypothesized impact origin of planetary structures may be tested by the presence and distribution of the geochemically distinct impactor material

ultramafic impact melt sheet beneath the south pole aitken basin on the moon 1 the spectral profiler onboard the japanese lunar explorer kaguya conducted the first hyperspectral survey around the south pole aitken basin spa on the moon that is one of the largest impact structures in the solar system the radiative transfer modeling revealed that fresh crater central peaks inside spa are commonly composed of an ultramafic assemblage dominated by magnesium rich orthopyroxene suggesting a homogeneous layer buried under spa the extensive ultramafic layer could be a relic of a gigantic impact melt pool produced by the spa forming impact the preponderance of orthopyroxene could have resulted from significant fractional crystallization of the lunar magma ocean prior to the onset of plagioclase floatation

on the relative and absolute ages of seven lunar front face basins ii from the crater counts abstract from counts of postbasin craters larger than 30 km in diameter lying within or near to seven giant front face lunar basins relative ages for the basins may be obtained these relative ages correlate well with absolute basin ages found from viscosity arguments in r b baldwin 1987 icarus 70 from crater counts the basins are in the following sequence of increasing relative age orientale imbrium crisium serenitatis nectaris humorum and the unnamed basin lying between werner and the altai ring the absolute ages from baldwin 1987 range from 3 80 to 4 30 109 years while a correlation with the relative ages of this paper yields a range of 3 79 to 4 27 109 years the discrepancy is largely due to serenitatis where the debris from imbrium has presumably buried some post serenitatis craters from both sets of data there is no evidence that a terminal lunar cataclysm ever occured

the clementine mission to the moon scientific overview in the course of 71 days in lunar orbit from 19 february to 3 may 1994 the clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths these data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side in addition laser ranging measurements provided the first view of the global topographic figure of the moon the topography of many ancient impact basins has been measured and a global map of the thickness of the lunar crust has been derived from the topography and gravity

recent shallow moonquake and impact triggered boulder falls on the moon new insights from the schrodinger basin shallow moonquakes are thought to be of tectonic origin however the geologic structures responsible for these moonquakes are unknown here we report sites where moonquakes possibly occurred along young lobate scarps in the schrodinger basin our analysis of lunar reconnaissance orbiter and chandrayaan 1 images revealed four lobate scarps in different parts of the schrodinger basin the scarps crosscut small fresh impact craters 1500 boulders associated with trails and bouncing marks their origins are largely controlled by recent impact events ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed schrodinger and triggered significant boulder falls about 17 ma therefore a combination of recent shallow moonquakes and impact events triggered the boulder falls in the schrodinger basin

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

new lunar meteorite northwest africa 2996 a window into farside lithologies and petrogenesis the northwest africa nwa 2996 meteorite is a lunar regolith breccia with a mingled bulk composition and slightly elevated incompatible element content nwa 2996 is dominated by clasts of coarse grained noritic and troctolitic anorthosite containing calcic plagioclase an 98 and magnesian mafic minerals mg 75 distinguishing it from apollo ferroan anorthosites and magnesian suite rocks this meteorite lacks basalt and owes its mingled composition to a significant proportion of coarse grained mafic clasts one group of mafic clasts has pyroxenes similar to anorthosites but contains more sodic plagioclase an 94 distinguishing it as a separate lithology another group contains mg rich very low titanium pyroxenes and could represent an intrusion parental to regional basalts other clasts include granophyric k feldspar disaggregated phosphate bearing quartz monzodiorites and alkali suite fragments an 65 these evolved lithics are a minor component but contain minerals rich in incompatible elements several anorthosite clasts contain clusters of apatite suggesting that the anorthosites either assimilated evolved rocks or were metasomatized by a liquid rich in incompatible elements we used lunar prospector gamma ray spectrometer remote sensing data to show that nwa 2996 is most similar to regoliths in and around the south pole aitken spa basin peripheral regions of eastern mare nectaris crisium and southern areas of mare humorum however the mineralogy of nwa 2996 is distinctive compared with apollo and luna mission samples and is likely consistent with an origin near the spa basin anorthosite clasts could represent local crustal material mafic clasts could represent intrusions beneath basalt flows and apatite bearing rocks could carry the spa kreep signature

lunar polar topography derived from clementine stereoimages clementine stereoimagery has been used to produce digital elevation models of the moon at a scale of 1 km pixel these models cover regions poleward of 60 in both hemispheres and reveal topography beyond that covered by the clementine laser altimeter or earth based radar by combining these polar terrain models with the current clementine laser altimeter data we have produced a global topographic map of the lunar surface several topographic features in the new polar topographic data set are described including three previously unrecognized pre nectarian impact basins several known basins have also been mapped including the southern extent of the south pole aitken basin and other previously suspected basins have been verified

engineering risk mitigation measures for the landslide dams induced by the 2008 wenchuan earthquake abstract more than 257 sizable landslide dams were induced by the 2008 wenchuan earthquake which required timely risk mitigation measures this paper aims to summarize the engineering measures taken to mitigate the landslide dam risks provide a method for optimal design of spillways to minimize the risks and quantitatively evaluate practical options for spillway design with a physically based dam breach model the engineering measures taken to mitigate the risks of 37 highly hazardous landslide dams induced by the wenchuan earthquake are summarized an optimization method is proposed and applied to the spillway design for the tangjiashan landslide dam which is the largest one caused by the wenchuan earthquake it is found that the peak outflow rate could be reduced from the recorded 6500 m3 s to 2900 m3 s using the optimal design a spillway with a shallow and broad cross section is suitable for low erodibility dams while a spillway with a deep and narrow cross section is suitable for high erodibility dams a spillway with a large longitudinal gradient is beneficial for high erodibility dams with large dam widths and gentle downstream dam slopes a spillway close to one bank can reduce the peak outflow rate if the bank is erosion resistant

ancient multiring basins on the moon revealed by clementine laser altimetry analysis of laser altimetry data from clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon these basins were formed during the early bombardment phase of lunar history have been filled to varying degrees by mare lavas and regional ejecta blankets and have been degraded by the superposition of large impact craters the mendel rydberg basin a degraded three ring feature over 600 kilometers in diameter on the lunar western limb is about 6 kilometers deep from rim to floor only slightly less deep than the nearby younger and much better preserved orientale basin 8 kilometers deep the south pole aitken basin the oldest discernible impact feature on the moon is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers rim crest to floor this feature is the largest deepest impact crater yet discovered in the solar system several additional depressions seen in the data may represent previously unmapped ancient impact basins

evidence of impact melt sheet differentiation of the lunar south pole aitken basin the south pole aitken spa basin is the largest basin on the moon the basin forming impact likely melted the upper part of the mantle and formed an impact melt sheet impact melt of large terrestrial craters differentiated following a general magmatic differentiation sequence however it is still debated whether or not the spa melt sheet underwent differentiation to address this we investigated the vertical and lateral variations in mineral composition of the spa impact melt sheet area by analyzing the surface mineralogy including 277 post spa craters using remote sensing reflectance data we identified a 7 km thick high ca pyroxene rich layer and below that a 8 km thick low ca pyroxene rich layer both filled the entire impact melt sheet area 630 km in diameter considering the vast distribution of these two layers their thicknesses their feo abundances around 13 5 wt which are lower than most of the lunar mare basalt but within the estimated range of the differentiated spa impact melt and that the observed lithologies are consistent with a differentiation model we conclude that the spa impact melt was differentiated moreover based on the lunar magma ocean differentiation model al2o3 and cao abundances of the upper part of the mantle would be much lower after the mantle overturn if the spa impact occurred after overturn these elemental abundances of the initial impact melt would be much lower than that of the before overturn impact case and result in different solidified layers our observation matches only the after overturn case which may imply that the spa impact occurred after overturn

volumes of lunar lava ponds in south pole aitken and orientale basins implications for eruption conditions transport mechanisms and magma source regions in an effort to characterize individual eruptive phases and events 86 isolated mare deposits ponds in the lunar south pole aitken and orientale regions were analyzed to obtain information on areas volumes and other characteristics deposits likely to represent single eruptive episodes have area mean values of 2000 km2 in the south pole aitken basin and 1100 km2 in the orientale basin pond volumes range from 35 to 8745 km3 with a mean value of 860 km3 for south pole aitken and 10 to 1280 km3 with a mean value of 240 km3 for the orientale region no evidence was found for shallow crustal magma reservoirs the relatively common occurrence of sinuous rilles in orientale is consistent with very high effusion rates and the large volumes of individual eruptive episodes tens to many hundreds of km3 are comparable to flood basalt eruption volumes on earth pond morphologies are consistent with extrusion from deep probably subcrustal reservoirs distribution of deposits suggests that many ponds may be derived from single reservoirs comparison of ponds in both basins shows a higher areal density and average volume of lava ponds in the south pole aitken basin relative to the orientale area this is plausibly attributed to the extreme depths of the south pole aitken basin and the correspondingly thinner crust there relative to the orientale region these observations are consistent with magma ascent and eruption mechanisms that are strongly dependent on the overpressurization of deep seated source regions the subsequent propagation of dikes and the thickness of the intervening lunar crust through which these dikes must rise

does crater saturation equilibrium occur in the solar system abstract similarity is found in crater densities on the most heavily cratered surfaces throughout the solar system this is hypothesized to result from a steady state saturation equilibrium being approached or achieved by cratering processes this hypothesis conflicts with some recent interpretations however it accounts for 1 a similarity in maximum relative crater density below certain theoretically predicted values on all heavily cratered surfaces 2 a leveling off at this same relative density among 100 m scale secondary craters in populations on lunar maria and other sparsely cratered lunar surfaces 3 the approximate uniformity of maximum relative densities on saturn satellites in spite of dramatic variations predicted from nonsaturation models assuming heliocentric impactors the lunar frontside upland crater population sometimes described as a well preserved production function useful for interpreting other planetary surfaces is found not to be a production function it was modified by intercrater plains formed at least partly by early upland basaltic lava flooding recently confirmed spectrophotometrically consistent with this counts in pure uplands those lacking intercrater plains match the proposed saturation equilibrium density variations among large d 64 km crater populations are found but these may involve several hypothesized mechanisms that rapidly obliterate large craters especially on icy surfaces recent models in which different populations of interplanetary bodies hit different planets need further appraisal

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

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

compositional studies of mare moscoviense new perspectives from chandrayaan 1 vis nir data abstract moscoviense is one of the prominent mare filled basin on the lunar far side holding key insights about volcanic activity on the far side here we present spectral and elemental maps of mare moscoviense using the moon mineralogy mapper m3 and infrared spectrometer 2 sir 2 data sets the different mare units are mapped based on their spectral properties analyzing both quantitatively band center band depth and qualitatively integrated band depth composite images and also using their elemental compositions we find a total of five distinct spectral units from the basin floor based on the spectral properties our analysis suggests that the northern part which was mapped as iltm unit imbrian low ti low fe by earlier researchers is actually a distinct unit which is different in composition and age named as ivltm unit imbrian very low ti and very low fe we obtain the absolute model age of 3 2 ga with uncertainties of 0 2 0 5 ga for the unit ivltm the newly identified basalt unit ivltm is compositionally intermediate to the units im and iltm in feo and tio2 abundances we find a total of five distinct spectral units from the basin floor based on the spectral properties the units im imbrian very low ti from southern and northern regions of the basin floor are spectrally distinct in terms of band center position and corresponding band depths but considered a single unit based on the elemental abundance analysis the units ivltm and im are consistent with a high al basalt composition our detailed analysis of the entire moscoviense basin indicates that the concentrations of orthopyroxene olivine and mg rich spinel named as oos rock family are widespread and dominant at the western and southern side of the middle ring of the basin with one isolated area found on the northern side of the peak ring

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

compositional diversity and geologic insights of the aristarchus crater from moon mineralogy mapper data 1 the moon mineralogy mapper m3 acquired high spatial and spectral resolution data of the aristarchus plateau with 140 m pixel in 85 spectral bands from 0 43 to 3 0 m the data were collected as radiance and converted to reflectance using the observational constraints and a solar spectrum scaled to the moon sun distance summary spectral parameters for the area of mafic silicate 1 and 2 m bands were calculated from the m3 data and used to map the distribution of key units that were then analyzed in detail with the spectral data this analysis focuses on five key compositional units in the region 1 the central peaks are shown to be strongly enriched in feldspar and are likely from the upper plagioclase rich crust of the moon 2 the impact melt is compositionally diverse with clear signatures of feldspathic crust olivine and glass 3 the crater walls and ejecta show a high degree of spatial heterogeneity and evidence for massive breccia blocks 4 olivine strongly concentrated on the rim wall and exterior of the southeastern quadrant of the crater is commonly associated the impact melt 5 there are at least two types of glass deposits observed pyroclastic glass and impact glass

on the relative and absolute ages of seven lunar front face basins i from viscosity arguments the seven basins orientale imbrium crisium nectaris humorum and an unnamed basin between werner and the altai ring show rims whose absolute and relative heights are correlated with the sharpness and crispness of the features on the assumption that the decline in average outer rim height not scarp height measures the age of the basin and also that the decline represents a hot creep of rocks of very high viscosity absolute ages were derived basins were found to increase in age in the sequence listed above with a range from about 3 82 to 4 30 109 years the average or effective viscosity of the surface layers down to whatever level was involved in the creep was calculated as increasing from 9 46 1024 poises at about 4 30 109 years to 1 86 1030 poises at present it should be clear at the outset what the assumptions and associated observations are and why they are necessary to a solution they will be listed in this abstract and expanded upon in the text 1 1 the original rim height of each basin was a function only of basin diameter 2 2 the original rim height was given by pike s 1983 relation for fresh craters extrapolated to basin diameters 3 3 the present rim height is that of the most prominent ring structure 4 4 the smaller rim height of all seven basins relative to the height predicted by 2 is due largely to creep in the lunar rocks down to some undetermined level other forces may contribute to the sinking of the rims but these are considered to be of lesser importance and are discussed in the text 5 5 the relative ages of the seven basins are as given in table i this sequence differs slightly from that of wilhelms 1984 for example but it is that found in baldwin 1974 1987 and is consistent with the results of this paper 6 6 the age of formation of the imbrium basin 3 85 109 years inferred from lunar sample studies particularly apollo 15 is correct 7 7 the age of formation of the serenitatis basin 3 87 04 109 years inferred from petrologic and geochemical studies of apollo 17 boulders is incorrect this is not an assumption but is a result of the analysis of this paper 8 8 the rheology of the moon may be described for the purposes of this paper by an effective viscosity valid throughout the layers involved in the creep 9 9 this effective viscosity is used as a tool to determine basin ages and is not important in itself it does appear to vary in the same range as terrestrial rocks but not the lithosphere 10 10 other factors such as isostasy shaking due to jar from later impacts modification due to rim relief by ejecta and erosion from small impacts are all close to exponential in nature declining toward the present and hence may be included in the determination of the effective viscosity 11 11 the rim height of the imbrium basin subsided by 25 m in the last 2 5 109 years this value was chosen arbitrarily it could have been 250 300 m and the basin ages would not have been affected except for orientale and that only minutely 12 12 the effective viscosity of the moon was observed to change continuously and monotonically with time 13 13 judging by table iii the probable error of an absolute age is in the range of 10 to 50 106 years it is difficult to determine exactly what this means it will be constrained by points 14 15 and 16 14 14 an error in the age determination should not be large enough to alter the relative ages of the basins judging by crater counts baldwin 1974 1987 15 15 if the viscosity of the moon declined in the post imbrium period of mare formation the only basin to be affected would be orientale and this by no great amount inasmuch as the basin is older than nearby maria 16 16 if the effective viscosity were less than about 1022 poises at the time of the oldest basin then presaturation surfaces would not show the numerous craters and portions of craters that are obvious in this time span 17 17 considerably prior to the time of saturation the outer layers of the moon had a low enough viscosity so that they could not retain the record of the then occuring cratering 18 18 the approximations of this paper were adopted because it does not appear possible to make an unambiguous selection from the more elegant mathematical treatments of creep and isostasy that would lead toward reasonable ages for the giant basins

lunar impact basins stratigraphy sequence and ages from superposed impact crater populations measured from lunar orbiter laser altimeter lola data 1 impact basin formation is a fundamental process in the evolution of the moon and records the history of impactors in the early solar system in order to assess the stratigraphy sequence and ages of impact basins and the impactor population as a function of time we have used topography from the lunar orbiter laser altimeter lola on the lunar reconnaissance orbiter lro to measure the superposed impact crater size frequency distributions for 30 lunar basins d 300 km these data generally support the widely used wilhelms sequence of lunar basins although we find significantly higher densities of superposed craters on many lunar basins than derived by wilhelms 50 higher densities our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains the transition from a lunar impact flux dominated by population 1 to population 2 occurred before the mid nectarian this is before the end of the period of rapid cratering and potentially before the end of the hypothesized late heavy bombardment lola derived crater densities also suggest that many pre nectarian basins such as south pole aitken have been cratered to saturation equilibrium finally both crater counts and stratigraphic observations based on lola data are applicable to specific basin stratigraphic problems of interest for example using these data we suggest that serenitatis is older than nectaris and humboldtianum is younger than crisium sample return missions to specific basins can anchor these measurements to a pre imbrian absolute chronology

archean magmatism and deformation were not products of plate tectonics abstract the granite and greenstone terrains that dominate upper crust formed from about 3 6 to about 2 6 ga and record magmatic and tectonic processes very different from those of a younger time they indicate heat loss by the archean earth primarily by voluminous magmatism from a mantle much hotter than that of the present plate tectonic processes were not then operating the distinctive array of petrologic structural and stratigraphic features that characterize phanerozoic convergent plate systems ophiolites magmatic arcs accretionary wedges fore arc basins etc have no viable analogues in archean terrains purported archean plate tectonic indicators consist merely of rock types that even superficially resemble actual phanerozoic indicators only when considered in isolation from their association and structure archean ultramafic and mafic volcanic rocks neither resemble ophiolitic rocks in petrology nor occur in ophiolite type successions they often depositionally overlie felsic basement rocks and often overlie and are intercalated with sedimentary and felsic volcanic rocks and they require a mantle about 200 c hotter than now archean graywackes are coherent strata derived from nearby volcanic rocks late in the histories of their regions and they lack the setting and disruption that characterize modern accretionary wedges the lithologic structural and stratigraphic assemblages that typify proterozoic and phanerozoic rifted and reassembled margins also lack archean analogues and no evidence has been found for archean rifting rotation and reassembly of continental plates conversely characteristic archean assemblages lack modern equivalents in any tectonic setting ultramafic lavas erupted at liquidus temperatures are voluminous granite and greenstone terrains have no modern analogues greenstone belts are typically anastomosing networks of upright synforms formed by crowding aside by and sinking between large rising diapiric elliptical composite batholiths the batholiths include both the products of new crustal melts and variably remobilized mid crustal gneisses the greenstone belts are defined by late deformation of regionally semiconcordant volcanic and sedimentary successions and are not relics of successively formed volcanic chains little deformation generally preceded the diapirism and metamorphism was primarily of contact type the regionally uniform areal density and accordant crustal level of the diapiric batholiths their contacts primarily against the oldest strata of the synforms their general age 10 20 million years younger than most of the flanking stratiform rocks and considerations of high archean radiogenic heat productivity all fit the explanation that the batholiths were mobilized by partial melting of hydrous lower crust by radiogenic heating diapirism was accompanied by modest regional orthogonal shortening and extension of the hot upper crust producing the orientations of the batholiths rise of the batholiths greatly increased the petrologic fractionation of the crust and the concentration of radionuclides high in it resulting in cooling of the deeper crust and subjacent mantle and thus cratonization the upper crust containing the granite and greenstone aggregates was decoupled from the gneissic middle crust which underwent flattening and extension subparallel to the elongation of the shallow batholiths this deep deformation may have been driven by flow of dense restites toward delamination loci from which they sank into the mantle the early earth was probably wholly molten the surface of the earth like that of the moon must have been wholly recycled by impacts before 3 9 ga and heavily modified by them until 3 8 ga zircons as old as 4 2 ga have been found as clastic grains in much younger archean quartzites and polycyclic migmatites last partly melted and reconstituted under hydrous conditions only after 3 6 ga contain relict zircons as old as 4 0 ga the lithologies of the early earth protoliths in which these zircons formed have not been established but impact melts and breccias must be represented and magma ocean fractionates may be the nature of the transition in tectonic style into the granite and greenstone mode is unknown plate tectonic rifting and convergence were operating by about 2 0 ga and were in an essentially modern mode by about 0 8 ga the nature of the transition from the granite and greenstone mode at about 2 6 ga to plate mode by about 2 0 ga has yet to be defined the change may have been facilitated by the increasing content of water and carbon dioxide in the mantle as dense but hydrated delaminated archean crust sank into it

evidence for geochemical terranes on mercury global mapping of major elements with messenger s x ray spectrometer abstract we have mapped the major element composition of mercury s surface from orbital messenger x ray spectrometer measurements these maps constitute the first global scale survey of the surface composition of a solar system body conducted with the technique of planetary x ray fluorescence full maps of mg and al together with partial maps of s ca and fe each relative to si reveal highly variable compositions e g mg si and al si range over 0 1 0 8 and 0 1 0 4 respectively the geochemical variations that we observe are consistent with those inferred from other messenger geochemical remote sensing datasets but they do not correlate well with units mapped previously from spectral reflectance or morphology location dependent rather than temporally evolving partial melt sources were likely the major influence on the compositions of the magmas that produced different geochemical terranes a large 5 10 6 km 2 region with the highest mg si ca si and s si ratios as well as relatively thin crust may be the site of an ancient and heavily degraded impact basin the distinctive geochemical signature of this region could be the consequence of high degree partial melting of a reservoir in a vertically heterogeneous mantle that was sampled primarily as a result of the impact event

elliptical structure of the lunar south pole aitken basin abstract the south pole aitken basin sp a is the largest and oldest basin on the moon the basin has usually been interpreted to exhibit a degraded circular structure but here we demonstrate that the topography iron and thorium signatures of the basin are well described by ellipses with axes measuring 2400 by 2050 km and centered at 53 191 e topography abundances of iron thorium and the distribution of mare basalts are all elevated in the northern halves of the ellipses we also identify an outer topographic ellipse whose semiminor axis scales with the main topographic ellipse by approximately 2 taken together these data imply that the basin was created by an oblique impact along an azimuth of approximately 19 measured counterclockwise from longitude 191 e the geometry of the elevated central farside topography surrounding sp a suggests that it predates the impact the elliptical ring structures of sp a and their scaling relationships will help to understand the formation of large and elliptical basins elsewhere in the solar system this refined basin shape will also inform local geology geochemistry and geophysics of the region

on estimating contributions of basin ejecta to regolith deposits at lunar sites we have developed a quantitative model for predicting characteristics of ejecta deposits that result from basin sized cratering events this model is based on impact crater scaling equations housen schmitt and holsapple 1983 holsapple 1993 and the concept of ballistic sedimentation oberbeck 1975 and takes into account the size distribution of the individual fragments ejected from the primary crater using the model we can estimate for an area centered at the chosen location of interest the average distribution of thicknesses of basin ejecta deposits within the area and the fraction of primary ejecta contained within the deposits model estimates of ejecta deposit thicknesses are calibrated using those of the orientale basin moore hodges and scott 1974 and of the ries basin horz ostertag and rainey 1983 observed densities of secondary craters surrounding the imbrium and orientale basins are much lower than the modeled densities similarly crater counts for part of the northern half of the copernicus secondary cratering field are much lower than the model predicts and variation in crater densities with distance from copernicus is less than expected these results suggest that mutual obliteration erases essentially all secondary craters associated with the debris surge that arises from the impacting primary fragments during ballistic sedimentation if so a process other than ballistic sedimentation is needed to produce observable secondary craters regardless our ejecta deposit model can be useful for suggesting provenances of sampled lunar materials providing information complementary to photogeological and remote sensing interpretations and as a tool for planning rover traverses e g haskin et al 1995 2002

measurements of the elastic thickness under ancient lunar terrain abstract the part of a planet s gravity that is coherent with its topography provides information about the deflection of its crust after loading and hence the resistance of its lithosphere to bending at the time the load was emplaced we used observed line of sight accelerations from lunar prospector together with the accelerations we would have expected if anomalies in the gravity field were only caused by topography to estimate the admittance and coherence between topography and gravity over several regions of the lunar nearside we then compared our estimates to what we would expect if the lithosphere behaved as a floating elastic plate or shell assuming a linear relationship between topography and gravity we found in the region surrounding the southern highland crater clavius that the data can be modeled using a thin plate with t e 12 5 km and uncorrelated loads at the surface and base of the upper crust a spherical shell model with surface loading is less satisfactory to fit the admittance adequately requires topography with wavelengths over 400 km to be formed when t e 1 km and the remainder when t e 7 5 km by contrast the apparent lack of compensation around the youngest giant impact basins requires a plate with t e 80 km or a shell with t e 25 km our results indicate the thickness of the lunar lithosphere increased from 12 km in the pre nectarian to 25 km in the nectarian

modal mineralogic distribution in the regolith at apollo landing sites we have reduced published petrographic data on 90 surface soils from apollo sample return sites in terms of olivine pyroxene plagioclase and opaques mostly ilmenite for a best estimate to do so we have recast the best estimates of modal mineralogy of mare and highland lithic fragments to add to the monomineralic population of soils we have assumed that agglutinates and regolith breccias mimic those of local soils we have thus arrived at a working summary of mineral distribution in areas traversed by apollo astronauts in addition we have proportioned these averages to geologic units in the premission maps to estimate the average mineral composition of areas up to 30 km 30 km around the landing sites the calibration and testing of remote sensing signals for planetary exploration depend largely on the ground truth provided by lunar samples chemical compositions and the modal distribution of petrologic constituents of most lunar soils are known these can be grouped spatially to represent areas that coincide with pixels of remote sensing observations and measurements signals from certain petrographic constituents such as lithic fragments breccias and agglutinates however are understandably ambiguous petrologic inference from remote sensing signals would be facilitated if petrographic data from actual samples were to be reduced and expressed as sums of single phases occurring in each pixel of observation

mineralogy of the lunar crust results from clementine received 1997 december 5 accepted in revised form 1998 september 15 abstract the central peaks of 109 impact craters across the moon are examined with clementine ultraviolet visible uvvis camera multispectral data the craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5 30 km beneath the surface to form the peaks including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins representative five color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters including key ratio which is related to mafic mineral abundance and spectral curvature linked to absorption band shape which distinguishes between low and high ca pyroxene and olivine the spectral parameters are correlated to mineralogical abundances related in turn to highland plutonic rock compositions the derived rock compositions for the various central peaks are presented in a global map from these results it is evident that the lunar crust is compositionally diverse both globally and at local 100 m scales found within individual sets of central peaks although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure they also indicate a more anorthositic crust than generally assumed with a bulk plagioclase content of 8 1 evolving from pure anorthosite near the surface towards more mafic low ca pyroxene rich compositions with depth comparable to anorthositic norite evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types however the lower crust is more compositionally diverse than the highlands with both a greater range of rock types and more diversity within individual sets of central peaks

beginning and end of lunar mare volcanism mare volcanism on the moon is commonly attributed to an important but relatively short lived epoch of internal heating after 3 900 myr bp but before about 2 500 myr bp refs 1 2 although some studies suggested that mare volcanism had started earlier3 5 than times indicated by dated lunar samples only recently have photogeological spectral and geochemical data6 8 documented the importance of a pre 4 000 myr bp epoch similarly early earth based geological mapping revealed a bright rayed crater lichtenberg superposed by mare units9 thereby indicating that mare volcanism must have extended to times significantly more recent than 3 100 myr bp lunar orbital photography confirmed this inferred strati graphical relationship10 but crater statistics indicated that the youngest units were at least twice the age of copernicus or between 1 700 and 2 000 myr bp refs 11 13 we present here the inferred distribution and style of the early phases of mare volcanism based on current evidence and conclude that certain regions of the moon underwent two distinct pulses of igneous activity we then examine crater statistics for the post lichtenberg mare unit and other selected units and conclude that mare volcanism extended to a time comparable with that of the copernicus impact or 1 myr bp these reassessments of the oldest and youngest maria provide new constraints on geophysical models of the internal thermal history of the moon

viscoelastic evolution of lunar multiring basins 1 we investigate the evolution of multiring basins on the moon the orbital geophysical and geochemical data collected by lunar prospector allow three distinct groups of basins to be identified group 1 basins show well preserved topography a bull s eye gravity signature and little mare basalt fill group 2 basins contain large amounts of mare basalt and show mare dominated gravity and topography signatures group 3 basins are characterized by low amplitude topographic relief and weak gravity anomalies while the crustal structures of group 1 and 2 basins appear to date from the collapse of the transient cavity group 3 basins are highly degraded and show very little crustal thinning using a viscoelastic model we explore the evolution of the lunar multiring basins with the goal of explaining the degraded condition of group 3 basins our results show that while viscous relaxation is a plausible explanation for the state of group 3 farside basins requiring heat flux 25 40 mw m 2 the thin nearside crust renders subsolidus ductile flow in the crust unlikely the existence of many degraded basins on the nearside points to a weakened and possibly partially molten lower crust that south pole aitken appears not to have relaxed suggests that similar conditions did not exist there and that the nearside was hotter than the farside early on this is likely a consequence of the nearside farside crustal thickness dichotomy which would have caused the farside to reach full crystallization first leaving the nearside with the remaining liquid and an excess of heat producing elements

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

comment concerning the review by w mckinnon and r korotev of p d spudis book the geology of multi ring basins

geology of the moscoviense basin 1 the moscoviense basin on the northern portion of the lunar farside displays topography with a partial peak ring in addition to rings that are offset to the southeast these rings do not follow the typical concentric ring spacing that is recognized with other basins suggesting that they may have formed as a result of an oblique impact or perhaps multiple impacts in addition to the unusual ring spacing present the moscoviense basin contains diverse mare basalt units covering the basin floor and a few highland mafic exposures within its rings new analysis of previously mapped mare units suggests that the oldest mare unit is the remnant of the impact melt sheet the moscoviense basin provides a glimpse into the lunar highlands terrain and an opportunity to explore the geologic context of initial lunar crustal development and modification

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

galileo imaging observations of lunar maria and related deposits the galileo spacecraft imaged parts of the western limb and far side of the moon in december 1990 ratios of 0 41 0 56 gin filter images from the solid state hnaging ssi experiment provided information on the titanium content of mare deposits ratios of the 0 76 0 99 gm images indicated 1 gin absorptions associated with fe 2 in mafic minerals mare ages were derived froin crater statistics obtained from lunar orbiter images results on mare coinpositions in western oceanus procellarum and the humorurn basin are consistent with previous earth based observations thus providing confidence in the use of galileo data to extract compositional information mare units in the grimaldi and riccioli basins range in age froin 3 25 to 3 48 ga and consist of medium to medium high titanium 4 to 7 tio2 content lavas the schiller zucchius basin shows a higher 0 76 0 99 gm ratio than the surrounding highlands indicating a potentially higher mafic mineral content consistent with previous interpretations that the area includes mare deposits blanketed by highland ejecta and light plains materials the oldest mare materials in the orientale basin occur in south central mare orientale and are 3 7 ga old youngest mare materials are in lacus autumni and are 2 85 ga old these units are medium to medium high titanium 4 to 7 tio2 basalts thus volcanism was active in orientale for 0 85 ca but lavas were relatively constant in composition galileo data suggest that mendel rydberg mare is similar to mare orientale cryptomare are present as well thus the mare lavas on the western limb and far side to 178oe are remarkably uniform in coinposition being generally of medium to medium high titanium content and having relatively low 0 76 0 99 gin ratios this region of the moon is between two postulated large impact structures the procellarum and the south pole aitken basins and may have a relatively thick crust in areas underlain by an inferred thinner crust i e zones within large basins as at apollo titanium content is often higher however no mare deposits with titanium abundances approaching those of the high titanium 9 to 14 tio2 apollo 11 and 17 basalts nor of the high titanium regions of central oceanus procellarum are seen on the western limb or eastern far side light plains deposits are generally indistinct froin the surrounding highlands in the ssi data and are inferred to be derived primarily from the same material that forins the highlands some of the light plains are too young to be related to basin forming impacts suggesting possible volcanic origin dark mantle deposit compositions derived from ssi data are consistent with earth based observations of similar near side deposits and are interpreted to be pyroclastic materials however the modernitc albedo and 1 gin absorption of the dark mantle deposit on the southwest margin of the orientale basin suggest it is a local pyroclastic deposit contaminated with underlying highland materials from the orientale impact

rock types of south pole aitken basin and extent of basaltic volcanism the enormous pre nectarian south pole aitken spa basin represents a geophysically and compositionally unique region on the moon we present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution rock types are derived from clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials individual areas are characterized as noritic dominated by low ca pyroxene gabbroic basaltic dominated by high ca pyroxene feldspathic 3 6 feo and olivine gabbro dominated by high ca pyroxene and olivine the anorthositic crust has effectively been removed from the interior of the basin the style of volcanism within the basin extends over several 100 myr and includes mare basalt and pyroclastic deposits several areas of ancient pre orientale volcanism or cryptomaria have also been identified the nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically we interpret this to represent impact melt breccia deposits derived from the lower crust a few localized areas are identified within the basin that contain more diverse lithologies gabbro olivine gabbro some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the spa event

lunar impact basins and crustal heterogeneity new western limb and far side data from galileo multispectral images of the lunar western limb and far side obtained from galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution the data reveal that the ejecta from the orientale impact basin 900 kilometers in diameter lying outside the cordillera mountains was excavated from the crust not the mantle and covers pre orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts the inside of the far side south pole aitken basin 2000 kilometers in diameter has low albedo red color and a relatively high abundance of iron and magnesium rich materials these features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta

a 20 km diameter multi ringed impact structure in the north sea most craters found on earth are highly eroded poorly preserved and only exposed on land here we describe a multi ringed impact structure discovered in the north sea from the analysis of three dimensional seismic reflection data the structure is 20 km in diameter and has at least ten distinctive concentric rings located between 2 and 10 km from the crater centre the structure affects cretaceous chalk and jurassic shales and is well preserved below several hundred metres of post impact tertiary strata which constrains its age to be 60 65 myr old the formation of concentric ringed impact structures at this relatively small scale had not previously been thought possible especially on the terrestrial planets we have mapped the ring structures at a resolution of tens of metres both laterally and in depth and show that the rings are fault bounded graben structures similar to fault arrays formed in low strain rate detachment tectonic settings strata deeper than 500 m palaeodepth appear unfaulted and we infer that the concentric ring structures may have accommodated post impact extension towards the excavated crater through detachment on weak layers within the chalk

lunar deep materials observed by chang e 4 rover abstract china s chang e 4 spacecraft achieved the first ever soft landing within the south pole aitken spa basin on the farside of the moon the chang e 4 rover named yutu 2 made in situ spectral observations on lunar regolith and a rock fragment at 11 locations during a nominal three month mission period the lunar regolith has a relative high olivine pyroxene ratio with the pyroxene being chiefly mg rich low ca pyroxene lcp the rock fragment has a similar mg rich composition to that of the regolith according to the surrounding topographic and geologic context though originating from the lower base of a differentiated melt pool cannot be excluded here the rover observed regolith and rock fragment are very likely to be lunar mantle materials excavated from nearby finsen crater

long wavelength topographic relaxation for self gravitating planets and implications for the time dependent compensation of surface topography the support of planetary surface topography is controlled by the thickness of the elastic lithosphere and thus has implications for the thermomechanical structure of shallow planetary interiors previous analyses of the support of long wavelength topography have generally utilized elastic formulations which preclude consideration of the time evolution of lithospheric stresses and thermal state here we formulate a viscoelastic model for the support of topography on a spherical planet our stress relaxation model employs a multilayer linear viscoelastic rheology and includes the effect of self gravitation in these models we approximate internal rheology with an olivine flow law and we estimate the internal thermal structure assuming simple conductive cooling we analyze how relief at the surface and internal density interfaces evolves with time in response to a surface or internal load our analysis demonstrates that crustal compensation is strongly dependent on planetary radius with a tendency for a large terrestrial planet like earth to reach complete airy isostasy at long wavelengths within a time scale controlled by the mantle viscosity the correlation of degree of compensation with planetary radius is consistent with previous work turcotte et al 1981 which showed that membrane stress can support significant long wavelength gravity anomalies applied to the moon the degree of compensation associated with loading of 100 ma lithosphere is less than 0 3 and the load love numbers are greater than 0 6 for all harmonics including degree 2 even after 109 years of relaxation this conclusion does not change significantly even with a moderately low viscosity for the crust the tendency for a small body like the moon to support long wavelength stresses may be relevant in understanding the anomalously large degree 2 terms in the lunar shape the results also suggest that major impact basins would not be compensated throughout lunar geological history 4 b y even if the surfaces on which the basins were initially formed were relatively young i e 100 300 ma the fact that the south pole aitken basin is largely compensated suggests that the lateral variations in thermal and or mechanical structure induced by impact processes play significant roles in the compensation of this structure

global petrologic variations on the moon a ternary diagram approach ltrbil kreep rich rocks 5j portions of the east limb and 4 highlands have considerable amounts of a mafic chondritic th ti component like mare basalt whose occurrences coincide with mapped concentrations of light plains that display dark halo craters the presence of this component supports the hypothesis that mare volcanism had occurred within this highland region before the end of final heavy bombardment

lunar impact basins new data for the western limb and far side orientale and south pole aitken basins from the first galileo flyby compositional aspects of impact basin materials can be analyzed using multispectral image data acquired by the galileo solid state imaging ssi experiment during the december 1990 lunar encounter these data provide important information on the spectral properties of the western lunar limb and parts of the far side the ssi images cover the wavelength range 0 4 1 0 m allowing measurement of spectral slope and estimation of the strength of the 1 m absorption due to iron in the mafic minerals olivine and pyroxene among deposits of the 930 km diameter orientale basin exterior ejecta comprising the hevelius formation is relatively homogeneous and spectrally similar to mature apollo 16 soils suggesting an upper crustal source the centrally located maunder formation is distinct from the younger mare basalts but comparable to the hevelius formation in its spectral reflectance properties supporting an interpretation as basin impact melt the montes rook formation located in an annulus between the maunder and the hevelius shows a slightly stronger mafic absorption and may be the deepest crustal material excavated the distal orientale deposits show local mafic enhancements in the schiller schickard and mendel rydberg regions interpreted to represent pre orientale mare deposits or cryptomaria intermixed with overlying basin ejecta in this case maria of sizes comparable to those presently observed were widespread in this region before the orientale impact mixing model analyses are consistent with the ballistic erosion and sedimentation model for ejecta emplacement in the distal regions beyond the continuous ejecta deposit on the southern lunar farside a huge area with an enhanced mafic absorption corresponds to the interior and rim of the pre nectarian south pole aitken impact basin 2000 2500 km in diameter the anomaly is interpreted to be due to several factors including excavation into the more mafic lower crust and the presence of extensive early volcanic fill cryptomare similar to that seen in ancient basins such as smythii and australe these results show that although basin forming events are an important factor in producing lateral heterogeneities in crustal composition and in modifying preexisting deposits such as cryptomaria the majority of material in even the largest basins was excavated from crustal levels our results suggest a gradational vertical crustal stratigraphy consisting of an uppermost mixed crustal layer of anorthosite basin ejecta and cryptomaria deposits generally corresponding to the megaregolith an upper crustal layer of anorthosite and a lower more noritic layer many of the basic questions remaining from this study could be addressed by global high resolution geochemical and mineralogical data obtained by polar orbiting spacecraft

surviving the heavy bombardment ancient material at the surface of south pole aitken basin 1 the oldest deepest and largest basin recognized on the lunar surface is the south pole aitken spa basin in the time since its formation several processes have modified the original interior of the basin including the introduction of foreign material by impact basins during the period of heavy bombardment these later basins redistributed material ballistically across the lunar surface forming a mixed and crushed zone on the scale of about one kilometer deep models of crater excavation ejected material transport and mixing during emplacement are used to estimate the amount of foreign material from each basin event introduced into spa and the degree to which that material mixes with the surface of the interior of spa we varied the size of the transient craters for all basins the degree of mixing between foreign and local material and the number of basins considered in our evaluation our modeling results indicate that materials derived from the original spa melt breccia comprise at least 15 of the present regolith the most realistic combinations of model parameters predict a spa melt breccia component that ranges from 50 80 of the current surface regolith the compositional character of the spa interior has apparently not been obliterated by aeons of subsequent basin forming events

lunar farside volcanism in and around the south pole aitken basin abstract we identified and mapped 129 mare basalt deposits in and around the south pole aitken spa basin and determined absolute model ages amas for 101 of these units by performing crater size frequency distribution csfd measurements the derived amas range from 2 2 ga to 3 7 ga with the youngest deposits within antoniadi crater and the oldest deposits at jules verne crater our investigations indicate a major peak in volcanic activity between 3 6 ga and 3 2 ga which is a similar time range as the major volcanic activity on the nearside and the rest of the farside however a second peak in volcanic activity 2 2 2 5 ga as observed for the nearside and parts of the farside is not observed for the mare deposits within the spa basin combining all amas derived for farside mare basalts reveals that volcanic activity was more abundant and lasted longer on the nearside than on the farside we propose that the stripping of insulating crust by the large spa forming impact event in combination with lower amounts of heat producing elements like th might be responsible for the reduced volcanic activity in the spa basin in addition we estimated the thicknesses and volumes of the investigated mare deposits with thicknesses between 31 m and 273 m and volumes of 1 km to 2630 km the mare basalt deposits in and around the spa basin show a wide range of dimensions similar to other mare basalts of the near and farsides a trend between the amas and the estimated volumes was not observed but the mare deposits within the large northern craters e g apollo ingenii or leibnitz seem to be generally larger and more voluminous than the mare basalt deposits at the center of the spa basin

estimating compositions of natural ringwoodite in the heavily shocked grove mountains 052049 meteorite from raman spectra a combined raman spectroscopy and electron probe microanalysis study of the heavily shocked grove mountains grv 052049 meteorite revealed the largest chemical fractionation of natural ringwoodite and composition dependent variation of the intensities and or wavenumbers of raman bands with fa content atomic ratio of fe fe mg of ringwoodite varying from 27 8 to 81 6 mol the peak position of the single band around 290 cm 1 sb1 which relates to the sio4 translation mode shifts from 296 0 to 284 6 cm 1 and one of the doublets around 790 cm 1 db1 which relates to the symmetric stretching of sio4 shifts from 796 3 to 782 7 cm 1 in addition the relative intensities of sb1 and the other band of the doublet around 840 cm 1 db2 which relates to asymmetric stretching of sio4 increases with fa content based on the paired raman epma data single peak and two peak calibrations were established which can be used to derive fa contents of ringwoodite from the raman spectra the accuracy of raman derived fa content of ringwoodite is better than 5 mol the correlation of sb1 intensity with the fa content of ringwoodite suggests that the vibration of sb1 is enhanced with the substitution of mg2 by fe2 the correlation between raman spectra and the chemical composition of ringwoodite have potential applications in on line measurement of high pressure experiments and in situ mineralogical determination in future planetary explorations

topographic compositional units on the moon and the early evolution of the lunar crust the distribution of elevations on the moon determined by clementine deviates strongly from a normal distribution suggesting that several geologic processes have influenced the topography the hypsograms for the near side and far side of the moon are distinctly different and these differences correlate with differences in composition as determined by apollo orbital geochemistry clementine global multispectral imaging and ground based spectroscopy the hypsograms and compositional data indicate the presence of at least five compositional altimetric units the lack of fill of the south pole aitken basin by mare basalts suggests poor production efficiency of mare basalt in the mantle of this area of the moon

outcrops on lunar crater rims implications for rim construction mechanisms ejecta volumes and excavation depths the raised rims of impact craters consist of ejecta deposited onto structurally uplifted target rocks although it is commonly accepted that ejecta makes up 50 75 of the total rim height no previous measurements on well preserved naturally occurring impact craters exist relying on data from the lunar reconnaissance orbiter i report the first direct measurements of the rim forming constituents from 21 lunar craters ranging in diameter from 2 2 km to 45 km results show that the ejecta deposit accounts for no more than 20 of rim relief and structural uplift is the primary mechanism of rim development in both simple and complex craters thick quasi horizontal outcrops of coherent bedrock indicate that this uplift is the result of subsurface injection of debris or melt into the surrounding target rocks crater growth at least during the latest portion of the excavation stage therefore proceeds mainly through injection rather than ejection of material these results suggest that ejecta volumes and excavation depths may be factors of 3 to 4 less than previously considered

olivine rich exposures in the south pole aitken basin abstract the distribution and the geological context of the olivine rich exposures in the south pole aitken spa basin on the moon were investigated based on the spectral data obtained from the spectral profiler sp and multiband imager mi onboard the japanese lunar explorer kaguya selene the olivine rich exposures are found only in the peak rings or central peaks of the schrodinger basin and zeeman crater which are located in the outer region of the spa basin and not in the center region on a localized scale the olivine rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings another observational finding is the co existence of olivine rich and plagioclase rich materials on a kilometer scale spanning most of the olivine rich sites in the schrodinger basin pyroxene rich materials are found in fresh craters outside the peak rings or the central peaks with olivine rich materials based on these results the following scenario are proposed 1 the impact to form the spa basin melted a large amount of the lunar upper mantle and crust and distributed the melted materials to the outer region 2 local differentiation of melted materials hid the olivine rich materials in the center region of the spa basin 3 later impacts that formed the schrodinger and zeeman craters excavated and exposed the olivine rich materials to the surface again and 4 space weathering and regolith gardening obscured the olivine rich spectra at the exposure sites but recent small scale impacts or landslides on the sloped wall exposed fresh olivine rich materials allowing the identification of the olivine rich exposures by spectral remote sensing this suggests that several different scale events play an important role in forming the surface distributions of originally deep seated materials on the moon as well as on other planetary bodies

evidence for water ice on the moon results for anomalous polar craters from the lro mini rf imaging radar 1 the mini rf radar instrument on the lunar reconnaissance orbiter spacecraft mapped both lunar poles in two different rf wavelengths complete mapping at 12 6 cm s band and partial mapping at 4 2 cm x band in two look directions removing much of the ambiguity of previous earth and spacecraft based radar mapping of the moon s polar regions the poles are typical highland terrain showing expected values of radar cross section albedo and circular polarization ratio cpr most fresh craters display high values of cpr in and outside the crater rim the pattern of these cpr distributions is consistent with high levels of wavelength scale surface roughness associated with the presence of block fields impact melt flows and fallback breccia a different class of polar crater exhibits high cpr only in their interiors interiors that are both permanently dark and very cold less than 100 k application of scattering models developed previously suggests that these anomalously high cpr deposits exhibit behavior consistent with the presence of water ice if this interpretation is correct then both poles may contain several hundred million tons of water in the form of relatively clean ice all within the upper couple of meters of the lunar surface the existence of significant water ice deposits enables both long term human habitation of the moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant

iron distribution of the moon observed by the kaguya gamma ray spectrometer geological implications for the south pole aitken basin the orientale basin and the tycho crater abstract in this study we describe the distribution of iron on the moon as obtained by the kaguya high energy resolution gamma ray spectrometer kgrs we achieved for the first time the identification of iron based on the fast neutron flux obtained by the kgrs the iron distribution obtained by kgrs is compared to that of the lunar prospector gamma ray spectrometer lp grs showing that the feo distributions observed by kgrs and lp grs in general are in good agreement furthermore we compare the iron content data obtained by kgrs and lp grs to spectral reflectance measurements of the clementine kaguya and chandrayaan 1 spacecraft as well as those inferred from returned samples we found differences in feo concentration and distribution in areas of moderate abundance 6 15 wt of the south pole aitken basin mare orientale and around the crater tycho crater it implies that high concentrations of feo at mare ingenii in the south pole aitken basin and mare orientale are due to the presence of mare basalts whereas the enriched feo content in the central depression of the south pole aitken basin and the tycho crater indicates the presence of mafic materials such as impact melt breccia

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