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

crustal attributes of lunar basins from terrain correlated free air gravity anomalies 1 for the major lunar basins between 64 latitude uncompensated mass components as well as crustal ring and transient cavity attributes were evaluated from the free air anomaly components of the lunar prospector gravity model lp75g that are spectrally correlated at 100 km altitude with the gravity effects of the clementine terrain model gltm 2 inversion of the terrain correlated anomalies inferred incipient radial adjustments of the moho that equilibrate the basin topography assuming the lunar crust is mainly compensated by thickness variations nearly all nearside multiring basins are marked by mascon gravity anomalies that reflect mass concentrations from superisostatic mantle plugs plus mare fill farside basins by contrast are mostly characterized by maslite gravity anomalies from mass deficiencies due to subisostatic mantle plugs with marginal or no mare fill the preponderance of maslites on the farside is consistent with crust that responded more rigidly to impacts than the nearside crust which had a higher thermal gradient due to enhanced abundances of radioactive elements in the nearside mantle and crust however the extended thermal evolution of the lunar lithosphere also may have promoted the development of interfering mascon and maslite effects for tectonically complicated regions like the farside freundlich sharonov basin the moho adjustments also revealed well defined concentric zones of maxima and minima about the central basins that are strongly correlated with photogeologically inferred basin rings in addition the innermost zero contour of the radial adjustments provides an effective estimate for the diameter of the transient cavity the inferred transient cavity diameters correlated negatively with crustal thickness for basins with superisostatic mantle plugs and positively with the relative ages of the nearside basins on the farside superisostatic mantle plugs apparently developed in thinner crust up to thicknesses of about 30 km whereas in thicker crust mantle plugs developed only to subisostatic levels for the nearside mass balance calculations between the equilibrium mantle plug and excavated basin materials support the proportional scaling relation of roughly 0 1 for the excavation depth to diameter ratio of the transient cavity that photogeologic studies have obtained however for the serenitatis and imbrium basins with possibly atypical nearside crustal properties this proportionality may overestimate excavation depths by 28 and 37 respectively for nearside and farside basins apparently lacking mare flooding shallow excavation depths were also inferred

estimates of primary ejecta and local material for the orientale basin implications for the formation and ballistic sedimentation of multi ring basins abstract a clear understanding of thickness distributions of primary ejecta and local material is critical to interpreting the process of ballistic sedimentation provenances of lunar samples the evolution of the lunar surface and the origin of multi ring basins the youngest lunar multi ring basin orientale provides the best preserved structure for determining the thicknesses of primary ejecta and local material in general the primary ejecta thickness was often estimated using crater morphometry however previous methods ignored either crater erosion the crater interior geometry or both in addition ejecta deposits were taken as mostly primary ejecta and as far as we know the local material thickness had not been determined for the orientale in this work we proposed a model based on matching measurements of partially filled pre orientale craters pfpocs with the simulations of crater erosion to determine their thicknesses we provided estimates of primary ejecta thickness distribution with the thickness of 0 85 km at cordillera ring and a decay power law exponent of b 2 8 the transient crater radius of 200 km excavation volume of 2 3 10 6 km 3 primary ejecta volume of 2 8 10 6 km 3 these results suggest that previous works e g fassett et al 2011 moore et al 1974 might overestimate the primary ejecta thicknesses of orientale and the primary ejecta thickness model of pike 1974a for multi ring basins may give better estimates than the widely cited model of mcgetchin et al 1973 and the scaling law for impacts into ottawa sand housen et al 1983 structural uplift decays slower than previously thought and rim relief is mostly rim uplift for orientale the main reason for rim uplift may be the fracturing and squeezing upward of the surrounding rocks the proportion of local material to ejecta deposits increases with increasing radial distance from basin center and the thickness of local material is larger than that of primary ejecta at distance larger than certain distance 1 5 basin radius for orientale these results suggest ballistic sedimentation is important for multi ring basins and ejecta deposits can t be considered as mostly primary ejecta everywhere

further constraints on the deep lunar interior 1 we have inverted the most recent set of geophysical observations pertinent to lunar interior properties including mass m and moment of inertia i as determined by lunar prospector the two love numbers k2 and h2 as well as monthly tidal dissipation q obtained from more than 35 years of lunar laser ranging data in wanting to assess the ability of these parameters to constrain lunar mantle and core structure we have used a stochastically based sampling algorithm to invert the geophysical data to obtain radial density and shear wave velocity profiles the results indicate a small liquid fe core r 1 thereby favouring the fluid core hypothesis in addition shear wave velocities for the lower mantle region depths 1100 km are generally found to be lower than upper mantle velocities and can be interpreted as implying the presence of partial melt which can explain the unusually low lunar monthly tidal q of 30

improved gravity field of the moon from lunar prospector an improved gravity model from doppler tracking of the lunar prospector lp spacecraft reveals three new large mass concentrations mascons on the nearside of the moon beneath the impact basins mare humboltianum mendel ryberg and schiller zucchius where the latter basin has no visible mare fill although there is no direct measurement of the lunar farside gravity lp partially resolves four mascons in the large farside basins of hertzsprung coulomb sarton freundlich sharonov and mare moscoviense the center of each of these basins contains a gravity maximum relative to the surrounding basin the improved normalized polar moment of inertia 0 3932 0 0002 is consistent with an iron core with a radius of 220 to 450 kilometers

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

structure of the lunar crust at highland site apollo station 16 the seismic crustal structure of the moon is known in the region of oceanus procellarum from the analysis of artificial impact data to extend this knowledge we have used data from natural lunar seismic events to search for secondary seismic wave arrivals in the form of peg leg multiples caused by reflections at crustal interfaces and converted arrivals caused by refractions at crustal interfaces a polarization filter has been applied to the data to enhance the rectilinear particle motion expected for the onset of these body wave arrivals in the scattered coda of lunar seismograms the results of this work tentatively indicate that the highland site at station 16 has a 75 km thick crust with an intermediate 20 km interface compared to the 60 km crust and 20 km interface in oceanus procellarum a mare region since the 20 km upper crust appears to exist at both highland and mare sites it probably does not represent a mare basalt layer but rather a more general feature of the crust crustal thickness may partially control elevation by isostasy

thermal evolution of mercury effects of volcanic heat piping 1 a 1d thermal evolution model of mercury is presented it accounts for stagnant lid convection mantle differentiation and inner core growth early messenger results indicate that contrary to prior conclusions drawn from mariner 10 imagery volcanism has indeed played a significant role in mercury s past to study the effects of mantle heat bypassing the stagnant lid by means of volcanic heat piping contrasting end member models are considered results show how break down of mantle convection and onset of inner core growth are influenced by the mode of heat removal structural models of present day mercury are presented their dependence on the core sulphur contents predominates that on the choice of mantle heat removal however the latter clearly controls the timing of thermal history events

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

argon 40 argon 39 age spectra of apollo 17 highlands breccia samples by laser step heating and the age of the serenitatis basin we have obtained high resolution 21 63 steps 40ar 39ar age spectra using a continuous laser system on 19 submilligram samples of melt rocks and clasts from apollo 17 samples collected from the pre imbrian highlands in the easternmost part of the serenitatis basin the samples include poikilitic melt rocks inferred to have been formed in the serenitatis basin forming impact aphanitic melt rock whose compositions vary and whose provenance is uncertain and granulite gabbro and melt clasts three of the poikilitic melts have similar age spectrum plateau ages 72395 96 3893 16 ma 2 72535 7 3887 16 ma 76315 150 3900 16 ma with a weighted mean age of 3893 9 ma which we interpret as the best age for the serenitatis basin forming impact published 40ar 39ar age spectrum ages of apollo 17 poikilitic melts are consistent with our new age but are much less precise two poikilitic melts did not give plateaus and the maxima in their age spectra indicate ages of 3869 ma 72558 7 and 3743 ma 77135 178 plateau ages of two poikilitic melts and two gabbro clasts from 73155 range from 3854 16 ma to 3937 16 ma and have probably been affected by the ubiquitous older clasts and by post formation heating impact events plateau ages from two of the aphanitic melt blobs and two granulites in sample 72255 fall in the narrow range of 3850 16 ma to 3869 16 ma with a weighted mean of 3862 8 ma two of the aphanitic melt blobs from 72255 have ages of 3883 16 ma and 3894 ma whereas a poikilitic melt clast of different composition from the serenitatis melts has an age of 3835 16 ma which is the upper limit for the accretion of 72255 these data suggest that either the aphanitic melts vary in age as is also suggested by their varying chemical compositions or they formed in the 72255 accretionary event about 3 84 3 85 ga and older relict material is responsible for the dispersion of ages in any case the aphanitic melts do not appear to be serenitatis products our age for the serenitatis impact shows on the basis of the isotopic age evidence alone that serenitatis is 20 25 ma and probably 55 60 ma older than imbrium 3870 ma and probably 3836 ma dalrymple and ryder 1993 noritic granulite sample 78527 has a plateau age of 4146 17 ma representing a minimum age for cooling of this sample in the early lunar crust so far there is no convincing evidence in the lunar melt rock record for basin forming impacts significantly older than 3 9 ga

a seismic model of the lunar mantle and constraints on temperature and mineralogy abstract we determine seismic profiles of the moon s interior using travel times obtained from a re analysis of the apollo data due to the limited number of quakes and stations travel times errors were determined and used in the inversions our model has a mean crustal thickness of about 30 km in the region of the apollo network with a 10 km zone of brecciation below the crust mean values of seismic velocities in the upper mantle are rather well constrained and are in the range 7 6 7 8 and 4 35 4 45 km s 1 for p and s waves respectively velocity variations in the middle mantle are less well defined in the zone of deep moonquakes below 740 km depth velocities increase slightly to 8 15 0 23 and 4 5 0 10 km s 1 for p and s waves respectively we analyse the seismic profile in term of mineralogy and temperature constraints our preferred models are a pyroxenite model for the upper mantle and a magnesian rich model for the lower mantle with increasing mg with depth we find temperatures of about 1100 k elastic lithosphere limit and 1500 k thermal lithosphere limit for radii of about 1400 and 1000 km respectively and show that the lunar mantle is probably depleted in th and u by at least 70 compared to an earth reference value of 25 7 ppb u for a crustal thickness of 40 km with a mean 1010 ppb th concentration we then find bulk th and u abundances comparable to and possibly lower than currently accepted terrestrial values

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

lunar crustal analysis of mare orientale from topographic and gravity correlations we investigated the use of spectral correlation analysis for modeling the crustal features of mare orientale from lunar 70th degree spherical harmonic topographic and gravity field models derived from clementine satellite and earlier investigations the analysis considered a 64 by 64 region of the moon centered roughly on mare orientale at an altitude of 100 km the topography of the study region which includes over 11 km of relief was modeled for its gravity effects in lunar spherical coordinates by gauss legendre quadrature integration assuming a terrain density of 2 8 g cm3 we observed substantial positive and negative correlations between terrain gravity effects and free air gravity anomalies that seriously limit the utility of simple bouguer gravity anomalies for subsurface studies using the wavenumber correlation spectrum between the two data sets we designed correlation filters to extract the common features possible interpretations for the terrain correlated free air gravity anomalies include isostatic crustal mass imbalances that may be equilibrated by radial adjustments of the moho of up to 44 km assuming airy heiskanen compensation and a mantle density contrast of 0 5 g cm3 with the crust these moho adjustments define mass variations that account for most of the mascon and flanking negative free air gravity anomalies furthermore their remarkable correlation with the topographic rings of mare orientale points to the possible influence of a strong local stress field of the crust in the development of the ring structures subtracting the terrain correlated free air anomalies from the free air gravity anomalies and terrain gravity effects yielded terrain decorrelated free air and isostatically compensated terrain gravity anomalies respectively that show zero correlation this lack of correlation may be interpreted for a moho that involves over 100 km of relief assuming airy heiskanen compensation of the crust beneath mare orientale we observed a minimum crustal thickness of about 17 km corresponding terrain decorrelated free air gravity anomalies of mare orientale may be related to a central cone shaped body of 0 5 g cm3 density contrast with apex extending nearly 5 km below the surface which is surrounded by a ringed shaped body of 0 5 g cm3 density contrast that may extend about 7 km below the surface these bodies resulted possibly from meteorite impact that produced a roughly circular region of breccia and highly fractured crust with a higher density core where some remelting of the rocks about the impact site may have occurred

inversion of combined gravity and bathymetry data for crustal structure a prescription for downward continuation abstract we propose a new and improved recipe for inverting for crustal thickness variations from combined gravity and bathymetry data the new ingredients with respect to previous studies are the posing of this problem as an inverse problem and the use of a downward continuation filter which can be tailored to find the crustal thickness solution which satisfies a minimum slope or maximal smoothness criteria or a weighted combination of these desired solution features we explore several suggestions for determining the optimum smoothing parameters for a given crustal thickness inversion then we compare this new method to that used previously in marine gravity studies we find it to be an improved recipe for dealing with gravity data with observation errors of 3 5 mgal but not by much this recipe will be most useful in extracting more geological information from marine gravity data where apparent observation errors are 1 mgal e g from future global positioning satellite navigated studies

the case for an imbrium origin of the apollo thorium rich impact melt breccias abstract mafic th rich impact melt breccias most of which are identified with the composition known as low k fra mauro lkfm are the most common rock type in the nonmare regoliths of the apollo lunar landing sites the origin of mafic impact melt breccias bears on many lunar problems the nature of the late meteoroid bombardment cataclysm the spatial distribution of kreep both near the surface and at depth the ages of the major basins and the composition of the early crust of the nearside lunar highlands thus it is crucial that the origin of mafic impact melt breccias be accurately understood because of both intra and intersite differences in compositions of mafic impact melt breccia samples apparent differences in crystallization age and differences in siderophile element ratios previous studies have argued that either 1 most mafic impact melt breccias are the products of several large craters local to the site at which they were found but that some are of basin origin or that 2 they are all from the imbrium apollos 14 and 15 nectaris apollo 16 and serenitatis apollo 17 basins here we reconsider the hypothesis that virtually all of the th rich mafic impact melt breccias from the apollo missions are products of the imbrium impact ejecta deposit modeling based on modern crater scaling indicates that the imbrium event produced ejecta deposits that average hundreds of meters thick or more at all apollo highland sites which is thicker than some previous estimates substantial amounts of imbrium ejecta should have been sampled at every apollo highland site we suggest that the mafic impact melt breccias may be the principal form of those ejecta the imbrium projectile impacted into th rich material that we regard as part of a unique mafic lunar geochemical province we call the high th oval region based on the surface distribution of th only basins within the high th oval region excavated th rich material the th concentrations of the highlands as observed by the apollo orbiting ray experiments are consistent with the estimates from ejecta modeling of the younger basin forming impacts only imbrium was large enough to produce the copious amount of melt required by the ubiquitous presence of mafic impact melt breccias in the apollo sampled regolith the high th oval region still may have been molten or hot at shallow depths 4 ga ago when the imbrium projectile struck we reason that compositional heterogeneity of ejected melt breccia is to be expected under these circumstances we argue that siderophile element fingerprints of mafic impact melt breccias are not inconsistent with production of all common types by a single projectile we suggest that the narrow range of ages of 3 7 4 0 ga for all successfully dated mafic impact melt breccias may reflect a single event whose age is difficult to measure precisely rather than a number of discrete impact events closely spaced in time such that reported age variations among mafic impact melt breccias reflect the ability to measure 40ar 39ar ages with greater precision than the accuracy with which measured portions of mafic impact melt breccias have recorded the time of their formation

does the moon possess a molten core probing the deep lunar interior using results from llr and lunar prospector 1 it is the main purpose of this study to examine the deeper structure of the moon in the light of four numbers these are lunar mass m mean moment of inertia i second degree tidal love number k2 and the quality factor q accounting for tidal dissipation within the solid body of the moon the former two have been measured by lunar prospector to high precision and more than 30 years of lunar laser ranging llr data have led to an estimate of the second degree tidal love number and quality factor the inverse problem dealt with here of obtaining information on the lunar density and s wave velocity profile from the four numbers follows our earlier investigations by employing an inverse monte carlo sampling method we present a novel way of analyzing the outcome using the bayes factor the advantage lies in the fact that rather than just looking at a subset of sampled models we investigate all the information sampled in different runs i e take into account all samples in order to estimate their relative plausibility the most likely outcome of our study based on the data their uncertainties and prior information is a central core with a most probable s wave velocity close to 0 km s density of 7 2 g cm3 and radius of about 350 km this is interpreted as implying the presence of a molten or partially molten fe core in line with evidence presented earlier using llr regarding the dissipation within the moon

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

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

the deep structure of lunar basins implications for basin formation and modification we present models for the structure of the crust and upper mantle beneath lunar impact basins from an inversion of gravity and topographic data from the nearside of the moon all basin models display a thinner crust and an elevated moho beneath the central basin region compared to surrounding areas a signature of the processes of basin excavation and mantle uplift during collapse of the transient cavity there is a general decrease in the magnitude of apparent uplift of mantle material with increasing basin age we attribute this relation primarily to enhanced rates of ductile flow of crustal material early in lunar history when crustal temperatures were relatively high and the effective elastic lithosphere was thin the more relaxed topographic and moho relief associated with older basins on the central nearside may in particular be at least partly a consequence of the extensive subsurface heating associated with the formation of the large procellarum basin the deep structure of the youngest basins constrains the geometry of the cavity of excavation and the amount of crustal material ejected beyond the basin rim from the volumes of the topographic basin of mare basalt fill and of uplifted mantle material the volume of crustal material ejected beyond the basin rim for an orientale sized event was of the order of 107 km 3 a near constant thickness of nonmare crustal material beneath the central regions of young basins of various diameters and preimpact crustal thicknesses suggests that the transient cavity excavated to at least the base of the crust for the largest basins significant excavation into the mantle may have been impeded by an abrupt increase in strength at the lunar moho

magnetic fields of lunar multi ring impact basins we survey the magnetic fields of lunar multi ring impact basins using data from the electron reflectometer instrument on the lunar prospector spacecraft as for smaller lunar craters the primary signature is a magnetic low that extends to 1 5 2 basin radii suggesting shock demagnetization of relatively soft crustal magnetization a secondary signature as for large terrestrial basins is the presence of central magnetic anomalies which may be due to thermal remanence in impact melt rocks and or shock remanence in the central uplift the radial extent of the anomalies may argue for the former possibility but the latter or a combination of the two are also possible central anomaly fields are absent for the oldest pre nectarian basins increase to a peak in early nectarian basins and decrease to a low level for imbrian basins if basin associated anomalies provide a good indication of ambient magnetic fields when the basins formed this suggests the existence of a magnetic era possibly due to a lunar core dynamo similar to that implied by paleointensity results from returned lunar samples however the central basin anomalies suggest that the fields peaked in early nectarian times and were low in imbrian times while samples provide evidence for high fields in nectarian and early imbrian times

geochemical constraints on the seismic properties of the lunar mantle abstract thermodynamic modeling of phase relations and physical properties in the na2o tio2 cao feo mgo al2o3 sio2 fe fes system and a monte carlo inversion procedure have been used to calculate the density and velocity distribution in the mantle and core radii of the moon from the mass and moment of inertia constraints from recent lunar prospector gravity measurements for the computation of the phase diagram for a given chemical composition we have used a method of minimization of the total gibbs free energy and self consistent thermodynamic data for minerals and solid solutions for the crustal thickness and density of 60 km and 3 0 g cm 3 the largest core radii are estimated to be 530 km for an fes troilite core 4 1 of total mass 490 km for a eutectic fe fes core 3 4 445 km for an fe 10 wt s core 2 9 and 350 km for an fe core 2 the existence of an fe fes core of intermediate radius of 250 400 km is compatible with recent lunar core information and lend support to a chemically stratified lunar mantle the sensitivity of density and seismic velocities to temperature pressure and composition variations is examined the modeling results indicate that we can determine the permissible density and velocity ranges in the zoned lunar mantle with confidence the maximum and minimum density changes at depths of the lunar mantle consistent with geochemical constraints and mass and moment of inertia requirements are found to be 3 22 g cm 3 3 44 g cm 3 at depths of 60 500 km and 3 34 g cm 3 3 52 g cm 3 at depths between 500 km and the core mantle boundary core free models of the moon are possible only if the lower mantle densities are between 3 49 and 3 52 g cm 3 20 wt feo wt the calculated field of seismic velocities in the zoned lunar mantle shows that over a broad range of mantle compositions temperatures and densities the maximum variations are as follows 4 23 km s 1 v s 4 69 km s 1 and 7 41 km s 1 v p 8 24 km s 1 at depths of 60 500 km and 4 24 km s 1 v s 4 64 km s 1 and 7 63 km s 1 v p 8 39 km s 1 at depths between 500 km and the core mantle boundary these petrologically and geophysically admissible ranges of velocities and densities may constitute a significant constraint for the analysis of internal structure of the moon using the apollo seismic data

topography of the moon from the clementine lidar range measurements from the lidar instrument carried aboard the clementine spacecraft have been used to produce an accurate global topographic model of the moon this paper discusses the function of the lidar the acquisition processing and filtering of observations to produce a global topographic model and the determination of parameters that define the fundamental shape of the moon our topographic model a 72nd degree and order spherical harmonic expansion of lunar radii is designated goddard lunar topography model 2 gltm 2 this topographic field has an absolute vertical accuracy of approximately 100 m and a spatial resolution of 2 5 the field shows that the moon can be described as a sphere with maximum positive and negative deviations of 8 km both occurring on the farside in the areas of the korolev and south pole aitken s p aitken basins the amplitude spectrum of the topography shows more power at longer wavelengths as compared to previous models owing to more complete sampling of the surface particularly the farside a comparison of elevations derived from the clementine lidar to control point elevations from the apollo laser altimeters indicates that measured relative topographic heights generally agree to within 200 m over the maria while the major axis of the lunar gravity field is aligned in the earth moon direction the major axis of topography is displaced from this line by approximately 10 to the east and intersects the farside 24 north of the equator the magnitude of impact basin topography is greater than the lunar flattening 2 km and equatorial ellipticity 800 m which imposes a significant challenge to interpreting the lunar figure the floors of mare basins are shown to lie close to an equipotential surface while the floors of unflooded large basins except for s p aitken lie above this equipotential the radii of basin floors are thus consistent with a hydrostatic mechanism for the absence of significant farside maria except for s p aitken whose depth and lack of mare require significant internal compositional and or thermal heterogeneity a macroscale surface roughness map shows that roughness at length scales of 10 1 10 2 km correlates with elevation and surface age

lateral variations of lunar crustal thickness from the apollo seismic data set seismic waves generated by meteoroid impacts have been detected by the apollo lunar seismic network these waves are sensitive to the crustal structure beneath both the seismic stations and the impact sites we use a markov chain monte carlo algorithm in order to invert for lateral variations of crustal thickness on the moon the inversion uses travel times of seismic waves originating from multiple meteoroid impact locations previous seismic investigations constrained the crustal thickness solely for apollo stations 12 14 and 16 whereas our approach enables to estimate the crustal thickness at locations far from the apollo network and to build a first crustal thickness map based on seismic data here we compare our crustal thickness estimates based on seismic travel times to those based on inversions of the topography and gravity field both methods turn out to be coherent in the sense that highland sites possess a thicker crust than mare sites

a stress interpretation scheme applied to lunar gravity and topography data 1 we present an approach of the inverse gravimetric problem that allows the gravity to be directly related to the deviatoric stresses without any rheological assumptions in this approach a new set of parameters is considered 1 the density variations over equipotential surfaces and the height of interfaces above the corresponding equipotential surfaces and 2 the stress difference the method is applied to lunar topographic and gravimetric data that are interpreted in term of transversally isotropic deviatoric stress within the moon it also provides inference on density and crustal thickness variations the estimated lateral variation in deviatoric stress is about 500 bars within the crust and upper mantle in the crust because of topography the strongest stress differences take place on the far side with large lateral compressions beneath the south pole aitken basin vertical compression under the mascons of the nearside is the main feature within the upper mantle

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

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

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

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

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

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

comprehensive mass modeling of the moon from spectrally correlated free air and terrain gravity data 1 a lunar crust to core mass model for the region 64 latitude was developed using gravity components evaluated from available spherical harmonic gravity and topographic field models that include lunar prospector clementine and earlier satellite observations terrain gravity effects were computed at 100 km altitude in spherical coordinates from 1 topography gltm 2 by gauss legendre quadrature integration corresponding free air gravity anomalies lp75g were spectrally correlated with the terrain effects to differentiate the terrain correlated and terrain decorrelated free air components the absence of correlation between these free air components was interpreted for a moho that may involve over 120 km of relief assuming the lunar crust was mainly compensated by its thickness variations lacking the strong regional gravity effects of the terrain the terrain decorrelated anomalies may be interpreted for their subcrustal components on the basis of their correlation spectrum with the free air anomalies inversions of the subcrustal anomalies inferred boundary undulations for the core mantle asthenosphere lithosphere and middle upper mantle that are remarkably correlated with surface impacts the elevated core topography revealed beneath the procellarum basin is consistent with the uplifting effects of the imbrium impact and the development of the great lunar hotspot topographic undulations inferred for the lower and middle mantle reflect the dichotomized thermal evolution of the lunar near and far sides during bombardment time on the nearside the results support the development of relatively thinner and hotter lithosphere by mantle convection that facilitated the diapiric rise of magma and mare flooding of the basins for the farside the results favor the development of thicker and cooler lithosphere by viscous entrainment of lower density material into the lower mantle that limited basin flooding

the great lunar hot spot and the composition and origin of the apollo mafic lkfm impact melt breccias thorium rich mafic impact melt breccias from the apollo 14 17 missions that is those breccias identified with the composition known as lkfm are regarded largely as products of basin forming impacts that penetrated the feldspathic crust and sampled underlying mafic material and magma ocean residuum carrying the compositional signature of kreep potassium rare earth elements phosphorous despite considerable compositional variation among such breccias compositions of all of them correspond to mixtures of only four components 1 a norite with composition generally similar to that of apollo 15 basalt mean abundance 58 range 30 95 2 fo 90 dunite mean 13 range 1 27 3 feldspathic upper crust mean 29 range 4 50 and feni metal 0 1 1 7 petrographic evidence has shown that much of the feldspathic component but none of the kreep component is clastic this observation and the high proportion of kreep norite component in the breccias suggest that the melt zone of the impact or impacts forming the breccias contained little feldspathic material but consisted predominantly of material with the average composition of kreep norite the dunite component probably derives ultimately from the upper mantle these conclusions support the hypothesis that the breccias were not formed in typical feldspathic crust but instead by one or more impacts into what is designated here the great lunar hot spot that is the anomalous th rich terrane in the imbrium procellarum area identified by the apollo and lunar prospector gamma ray spectrometers the lkfm composition is a special product of the great lunar hot spot and is not the average composition of the lower crust in typical feldspathic highlands similarly mg suite and alkali suite plutonic rocks of the apollo collection are likely all differentiation products of the hot spot not of plutons that might occur in typical feldspathic crust

radar mapping of lunar cryptomaria east of orientale basin 1 lunar cryptomare deposits represent early basaltic volcanic material that has been mantled by or incorporated into highland rich ejecta from basin or crater forming impacts mapping these buried basalts is important for understanding regional stratigraphy and the history and extent of lunar volcanism we use new 70 cm wavelength radar images collected using arecibo observatory and the green bank telescope and clementine data to study cryptomaria east of orientale basin earlier multispectral analyses showed that mare material is mixed with the highland terrain along the western margin of oceanus procellarum leading to a detectable increase in the feo and tio2 abundance of the regolith surface the highland margin of western procellarum is also characterized by low 70 cm radar returns consistent with an increased regolith loss tangent due to ilmenite in the mare derived material the low 70 cm radar echo however persists well to the west of the mixed zone evident in multispectral data and includes the region surrounding cruger crater it is likely that mare basalt or a mixed zone of mare and highland material exists at depth across the region and only reaches the visible surface near the western procellarum margin the plausible depth to this mixed zone is dependent upon the loss tangent of the overlying pure highland ejecta if orientale ejecta is primarily low loss anorthosite then the mixed zone could lie at depths of up to several tens of meters we propose that pre orientale mare deposits flooded the region between cruger grimaldi and oceanus procellarum and also patches west and northwest of humorum basin the total area of these deposits represents 178 103 km2 or an additional 0 5 of the lunar surface covered by mare basalts

practical considerations in the use of edge detectors for geologic mapping using magnetic data abstractlocating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data much recent effort has been expended on developing improvements to existing edge detection methods resulting in purported increases in accuracy and continuity along edges reduction of noise effects and limiting the influences of variable depth to source magnetization direction and source dip these endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data nevertheless survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved using model studies we quantify the effects that source size depth and interference between sources have on calculated edge locations based on the known behavior of established edge detectors we found that many of the newer approaches offer limited advantages over older methods consequently we studi

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

the composition and origin of the lunar crust constraints from central peaks and crustal thickness modeling spectral reflectance data of lunar central peaks haverevealedthatthemoon scrustvariesbothlaterallyand vertically in composition we correlate the depths of origin of materials that make up central peaks with a geophysi cally derived dual layered crustal thickness model and nd that the peak compositions are consistent with this strati edmodel specically peakscomposedexclusivelyofrocks containing more than 85 plagioclase by volume come from this model s upper crust whereas peaks that contain some norite or gabbro norite come from the model s lower crust extrapolating these data we nd that the moon s upper crust is composed of 884 plagioclase correspond ingto29to32wt al 2o3 t hemost maclowerportion of the crust is composed of 658 plagioclase having an al2o3 content that lies between 18 and 25 wt we show that the lower portion of the crust is consistent with having formed by cumulateflotation in a lunar magma ocean