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

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

a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism crystallization of the lunar magma ocean creates a chemically stratified moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior within the magma ocean cumulates the last liquids to crystallize form dense ilmenite rich cumulates that contain high concentrations of incompatible radioactive elements the underlying olivine orthopyroxene cumulates are also stratified with later crystallized denser more fe rich compositions at the top this paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy rayleigh taylor instability causes the dense ilmenite rich cumulate layer and underlying fe rich cumulates to sink toward the center of the moon forming a dense lunar core after this overturn radioactive heating within the ilmenite rich cumulate core heats the overlying mantle causing it to melt in this model the source region for high tio2 mare basalts is a convectively mixed layer above the core mantle boundary which would contain small and variable amounts of admixed ilmenite and kreep this deep high pressure melting as required for the generation of mare basalts occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the moon regardless of details implied by particular model parameters gravitational overturn driven by the high density of magma ocean fe rich cumulates should concentrate high tio2 mare basalt sources and probably a significant fraction of radioactive heating toward the center of the moon this will have important implications for both the thermal evolution of the moon and for mare basalt genesis

absence of large shield volcanoes and calderas on the moon consequence of magma transport phenomena large shield volcanoes and calderas are not observed on the moon theoretical assessments show that melt ascending from the mantle will stall at rheological traps or at the shallower density trap at the base of the low density lunar crust magma will then only reach the surface along dikes propagated from these deep reservoirs and such events will be infrequent and characterized by very large volume eruptions these conditions favor the formation of sinuous rules single long flows and widespread flow units rather than abundant small eruptions from a central edifice the absence of large shield volcanoes and calderas on the moon is interpreted to be related to the fact that shallow neutral buoyancy zones and magma reservoirs are not favored on the moon

multispectral studies of western limb and farside maria from galileo earth moon encounter 1 new visible and near infrared multispectral images of the moon obtained by the galileo solid state imaging system along with lunar orbiter images for crater counts and spectral mixing analyses were used to characterize western limb and eastern farside maria and determine compositional and age relationships in selected regions results indicate that 1 western limb mare deposits have less variability in titanium content 6 wt tio2 mare basalts were observed on the western limb and farside which may reflect the inability of such denser magmas to penetrate the thicker farside crust

a mechanism for the generation of the lunar mare basalts summary according to the magma ocean or magmasphere model of lunar formation rapid accretion would result in the formation of a solid primitive core of undifferentiated material surrounded by a spherical shell of molten silicate as the outer layers of the moon cool by radiation of heat to space the deep interior will warm due to the decay of trace radionuclides this will lead to compression of the remnant magmasphere producing excess pressure in the fluid magma it is proposed that relief of this excess pressure through vents opened by the excavation of the mascon basins was sufficient to drive the major episodes of mare volcanism between 3 9 3 2 ga thermal models of the moon are constructed and a range of initial conditions based on the magmasphere model are identified which satisfy known constraints on lunar evolution the rate at which radial thermoelastic stress accumulates within the moon is calculated and from this estimates of the maximum volume of basaltic magma which could be produced by this mechanism are obtained by comparing these calculated magma generation rates with estimates of the volume of mare basalts residing on the lunar surface we are able to identify a set of initial temperature profiles which both satisfy the known constraints on lunar evolution and are able to produce the observed volume of mare basalts these models are characterised by deep magmaspheres and or initially warm central temperatures

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

the evolution of impact basins cooling subsidence and thermal stress potentially important contributors to the topography and tectonics of multi ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly formed basin that the subsequent cooling may have been an important factor in the tectonic evolution of the orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring to test these concepts we develop models for the anomalous temperature distribution immediately following basin formation and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region all models predict subsidence of the basin floor and a near surface stress field consistent with fissuring in addition the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in orientale the sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation in order to be consistent with the observed topography and the distribution of fissures in the orientale basin the buried heat deposited during the basin forming event was between 1032 and 1033 erg it is likely that most of this heat was concentrated within a distance of 100 200 km from the point of impact

lunar composition a geophysical and petrological synthesis lunar compositional constraints are derived on the basis of geophysical data in particular the lunar seismic model as revised by nakamura and petrological arguments only in the case of extreme assumptions can critical aspects of bulk lunar composition be demonstrated to be equivalent to the present day terrestrial mantle specifically the moon has an mg number that is too low and an alumina abundance that is too high over a broad range of crustal densities the presence of a metallic core at least 150 km in radius is necessary to reconcile the upper mantle lunar seismic model with mass and moment of inertia constraints a significant seismic discontinuity at 500 km depth may mark the lowest extent of early lunar differentiation possibly representing a transition between highly fractionated upper mantle and less fractionated perhaps even primordial middle lower mantle

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

lunar volcanic glasses and their constraints on mare petrogenesis abstract volcanic glasses from the apollo 11 14 15 and 16 landing sites have been analyzed for major elements and ni by electron microprobe the 19 varieties of volcanic glass define two distinct chemical arrays that provide new insights into a the petrogenesis of mare basalts and b the structure of the deep lunar interior a simple model is proposed whereby mare basaltic liquids may have been derived from two isolated cumulate systems occurring at depths of 300 km and 400 km each system was itself composed of two lithologic components low ti vs high ti that underwent hybridization assimilation or mixing to generate the large compositional range of magmas observed within each array while the distribution of the two components within each system was locally heterogeneous data indicate that the components themselves were chemically uniform on at least a regional scale the surface correlated volatiles associated with the lunar volcanic glasses seem to have come from some other reservoir within the moon the simplicity of the chemical relationships observed among the lunar volcanic glasses allow specific predictions to be made we believe that they should readily reveal any strengths or weaknesses of this new model

lunar ferroan anorthosites and mare basalt sources the mixed connection global overturn of a hot gravitationally unstable lunar mantle immediately following the solidification of a magma ocean and essentially complete by 4 4 ga explains several characteristics of lunar petrology lunar mare basalt sources are inferred to be depleted in europium and alumina these depletions are consensually attributed to complementary plagioclase floating from a magma ocean however the connection cannot be so simple and direct in contrast to the mare basalt source parent magma the ferroan anorthosite parent magma was more evolved by virtue of its lower mg fe ratio and ni abundances although less evolved in its poverty of clinopyroxene constituents flat rare earth pattern and lower incompatible element abundances the europium anomaly in mare sources is inferred to be present at 400 km depth too deep to have been directly influenced by plagioclase crystallization massive overturning of the post magma ocean mantle would have carried down clinopyroxene ilmenite and phases containing fractionated rare earths europium anomalies and some heat producing radionuclides these phases contributed to deep mare basalt sources upward moving phases would have been magnesian mafic minerals their immediate melting on pressure release contributed the magnesian suite of plutonic norites and troctolites that post date the anorthosites in the highlands crust

an energetic view of the relation between the mediterranean storm track and the north atlantic oscillation the time tendency equation of eddy kinetic energy eke includes some important forcing terms such as baroclinic conversion bcc barotropic conversion btc and energy flux this article compares the ensemble mean distribution of these forcing terms as well as the baroclinic generation bcg term in critical positive and critical negative months of the north atlantic oscillation nao focusing on the mediterranean and middle east regions results show that all the computed terms attain larger values and all the extrema are stronger in the positive phase the energy flux vectors point to energy transfer from the west of the atlantic and north of europe to the mediterranean region with the transfer being weaker in the positive phase there is energy flux divergence over the central region of the mediterranean sea which is more extensive in the positive phase relative to the negative phase the energy flux divergence leads to a radiation source in this region the direction of the energy flux vectors then indicates that the energy radiated from the central mediterranean region is transferred southeastward leading to an energy flux convergence over the red sea and the northeast of africa this convergence is stronger and more extensive in the positive phase which may be responsible for the observed larger value of the upper level eddy kinetic energy in the positive phase the patterns of the bcg and bcc together with the energy flux convergence suggest that while the mediterranean storm track is affected by the north atlantic storm track more strongly in the negative phase it acts as an independent centre of action by radiating energy southeastward in the positive phase copyright 2011 royal meteorological society

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

the depths of the mare basalt source region chemical data for the parental magmas of the nine known vlt array i pyroclastic glasses show statistically significant trends due to olivine fo83 control during their formation by partial melting the compositional scatter is largely due to compositional variations in the source regions on the 1 level this compositional scatter is small when one considers that the scale of the source region is up to 1000 km but is sufficient to make positive identification of the residual phase s in the source regions difficult nevertheless when the effects of the scatter are properly modeled it is relatively clear that olivine is the residual phase in the source region hence these data and additional constraints indicate that the source regions are at shallow depths in the moon

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

on the source region of the lunar mare basalt the lack of pervasive flooding of the south pole aitken spa basin raises questions about the mare basalt source region models whether deep or shallow this paper investigates the dichotomy between the nearside imbrium sized flooded basins and the unflooded spa basin by modeling the effects of giant impacts on the dynamics of the lunar mantle we allow an initially spherically symmetric moon model to evolve through mantle convection for a few hundred million years and then let an imbrium or spa sized impact occur the subsequent thermal convection in the lunar mantle resulting from the thermal energy introduced by an impact is determined for the next 100 m y the mantle is assumed to be incompressible with an infinite prandtl number and a temperature dependent viscosity it is shown that the mantle circulation induced by an imbrium sized impact can only slightly push aside the radioactive rich potassium rare earth element and phosphorous kreep layer from beneath the surrounding crust this concentrates the radioactive elements beneath the low thermal conductive ejecta blanket and provides a suitable condition for enhancement of radioactive heating and subsequent partial melting and basaltic flow to the basin on the other hand a spa sized impact is capable of generating mantle circulation vigorous enough to strip away the kreep layer from beneath the surrounding crust within a time period of 40 m y this removal prevents radioactive heating and partial melting beneath the surrounding crust thus explaining the lack of flooding of spa basin these results are insensitive to the time of impacts but are strongly dependent on their sizes

diapirism and the origin of high tio2 mare glasses high tio2 mare picritic glasses are derived from cumulate source regions that are only modestly endowed with ilmenite enriched crystallization products these sources are mobilized by the heat derived from the primitive interior and evolve into diapirs which rise adiabatically from depths in excess of 700 km as these diapirs undergo pressure release melting they also stir in significant portions of the surrounding mantle

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

geochemistry and geochronology of the blueschist in the heilongjiang complex and its implications in the late paleozoic tectonics of eastern ne china abstract the paleozoic to early mesozoic tectonic framework and evolution of northeast china especially the jiamusi block and its related structural belts are highly debated in this paper geochemical geochronological and isotopic analyses were carried out on the blueschist in the heilongjiang complex to address these issues the heilongjiang complex defines the suture belt between the jiamusi block and the songliao block in ne china and the blueschist is a major composition for this complex coexisting with mafic ultramafic rocks greenschist quartzite and mica schist the blueschist has a mineral association of sodic amphibole epidote chlorite phengite albite and quartz with accessory phases of apatite titanite zircon and ilmenite together with the lithological association the major and trace element compositions present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have oib affinities formed in an ocean island setting indicated by the la yb n values of 3 57 11 54 and the la sm n values of 0 69 3 64 the high and positive e nd t values of 3 7 to 9 0 and relative enrichment in nb vs th and ta vs u show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle with insignificant crustal contamination magmatic zircons from the blueschist in yilan area yield a 206 pb 238 u age of 281 3 ma interpreted as its protolithic age the youngest ages of 200 ma of the detrital zircons in the associated mica schist from mudanjiang area place constraints on the timing of metamorphism for the blueschist these indicate that a big ocean existed between the jiamusi and songliao blocks at least since the early permian and the blueschist formed since the late triassic to late jurassic by the subduction of this ocean such an ocean during the permian jurassic is difficult to be interpreted by the tectonic evolution of the paleo asian ocean

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

apollo 15 yellow brown volcanic glass chemistry and petrogenetic relations to green volcanic glass and olivine normative mare basalts abstract apollo 15 yellow brown glass is one of twenty five high mg primary magmas emplaced on the lunar surface in pyroclastic eruptions forty spherules of this glass were individually analyzed by electron microprobe and inaa for major and trace elements e g sc v cr co la ce nd sm eu ho tm yb lu hf ta and u the abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle models are developed to explain the possible source regions of several apollo 15 and apollo 12 low ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean a early olivine orthopyroxene cumulates b late stage clinopyroxene pigeonite ilmenite plagioclase cumulates and c late stage inter cumulus liquid isotopic constraints on sm nd fractionation and least squares tests of potential mixing models require models of apollo 15 yellow brown glass and apollo 12 and 15 olivine mare basalts involving low f 3 cumulate remelting of sources in which olivine and orthopyroxene are residual phases models of the apollo 15 green glass composition indicate higher 4 7 degrees of melting but with only a slight preference for orthopyroxene rich relative to orthopyroxene free sources the modeled dependence on residual orthopyroxene in mare source regions places source depths at 400 km or greater in order to maintain olivine and orthopyroxene on the liquidus hybridization at such depths would likely result from convective overturn of the primordial magma ocean and suggests that separate fractionating masses were positioned at various depths our models for developing hybridized source regions of primary low ti mare magmas do not require selective contamination of primary liquids the preferred model for apollo 15 yellow brown glass is presented as the commingling of 95 early cumulate olivine orthopyroxene 1 9 clinopyroxene 0 27 pigeonite 1 7 plagioclase 0 02 ilmenite and 0 56 trapped liquid respective proportions for the apollo 15 olivine mare basalt source model are 98 5 0 37 0 0 79 0 16 and 0 13 and the proportions used for the preferred apollo 12 olivine mare basalt model are 97 6 0 73 0 24 0 77 0 42 and 0 21 our preferred model for the green glass source composition f 0 07 requires the commingling of 97 4 early olivine orthopyroxene 0 18 clinopyroxene 1 32 pigeonite 0 85 plagioclase and 0 28 trapped liquid

the mare basalt magma source region and mare basalt magma genesis given the available data we find that the wide range of mare basaltic material characteristics can be explained by a model in which 1 the mare basalt magma source region lies between the crustmantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73 80 olivine 11 14 pyroxene 4 8 plagioclase 0 2 9 ilmenite and 1 1 5 chromite 2 the source region consists of two or more density graded rhythmic bands whose compositions grade from that of the very low tio2 magma source regions 0 2 ilmenite to that of the very high tio2 magma source regions 9 ilmenite these density graded bands are proposed to have formed as co crystallizing olivine pyroxene plagioclase ilmenite and chromite settled out of a convecting magma which was also parental to the crust in which these crystals were suspended since the settling rates of the different minerals were governed by stoke s law the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase the reverse being the case for those units deposited near the ascending sides of the convection cells simultaneously with this density controlled settling of the crystals the heating of the magma at the bottom of the convection cells resulted in the partial remelting of significant amounts of suspended but settling plagioclase ilmenite and pyroxene this partial remelting process was also partially responsible for the decrease in the ilmenite content from 9 to 0 2 between the very high tio2 and the very low tio2 source regions and caused the plagioclases and pyroxenes in the former source regions to be more sodic and clinopyroxene richer respectively than in the latter 3 during the mare basalt epoch radiogenic induced remelting of various parts of the density graded bands led to the formation of the initial mare basalt magmas the viscosity of melting systems which decreases rapidly at about 30 5 partial melting appears to have limited the degree of partial melting of the source region to about 30 2 4 these 30 partial melts rose to the crust mantle boundary where they pooled in magma storage chambers the magmas remained in these chambers for different lengths of time cooled to different degrees and lost 0 to 30 olivine or 30 olivine plus 0 to 20 pyroxene by fractional crystallization those magmas which remained in the chambers for very short times and lost no or essentially no olivine before eruption were the parental magmas of the pyroclastic glass units those magmas which lost increasing amounts of olivine pyroxene were the parental magmas of the apollo 12 and 15 magmas the apollo 11 and 17 magmas and the luna 16 and 24 magmas respectively this fractional crystallization phase in the genesis of the magmas explains both the pattern of the mare basalt magmas in the pseudo quaternary phase diagrams and the decrease in the siderophile contents of the magmas as a function of their degree of fractionation 5 the magma storage chambers being located at the crust mantle boundary were located in the zone where urkreep formed during the initial differentiation of the moon due to the low melting point of kreep compared with the initially high temperatures of the magmas residuals of the urkreep layer were assimilated by the cooling magmas since the urkreep materials underwent varying degrees of fractional melting early in lunar history these urkreep residuals had varying degrees of light ree depletion thus the assimilation of up to a few percent of these residuals caused the magmas to have differing eu and light ree depletion patterns as well as a wide range in their ree abundances 6 the fractional crystallization and urkreep residual assimilation phase of mare basalt magma genesis ended with the eruption of the magmas onto the lunar surface

lunar fe and ti abundances comparison of lunar prospector and clementine data the lunar prospector neutron spectrometer data correlate well with iron and titanium abundances obtained through analysis of clementine spectral reflectance data with the iron and titanium dependence removed the neutron spectrometer data also reveal regions with enhanced amounts of gadolinium and samarium incompatible rare earth elements that are enriched in the final phases of magma crystallization these regions are found mainly around the ramparts of the imbrium impact basin but not around the other basins including the much larger and deeper south pole aitken basin this result confirms the compositional uniqueness of the surface and interior of the imbrium region

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

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

compressibility of molten high ti mare glass evidence for crystal liquid density inversions in the lunar mantle static compression density measurements of molten apollo 14 black glass have been performed at liquidus conditions in the pressure range 1 0 11 5 gpa a range of values for the birch murnaghan isothermal bulk modulus k2173 k 13 23 gpa and the pressure derivative dkdp 7 3 respectively fit the data within the uncertainties k2173 k 15 5 gpa and dkdp 5 2 provides the best fit to the four measured pressure density pairs corrected to isothermal conditions the ultramafic high ti mare glass is significantly more compressible than other ultrabasic and basic silicate liquids previously studied the compressibility appears to be related to tio2 content the apollo 14 black glass sample has the highest tio2 content of the pristine mare glasses which are thought to be primary melts from a differentiated and strongly heterogeneous lunar mantle our density measurements confirm the prediction that molten black glass will be denser than equilibrium olivine and orthopyroxene at pressures greater than 2 0 and 0 5 gpa respectively these density inversions correspond to depths greater than approximately 410 and 100 km in the lunar mantle since orthopyroxene replaces olivine at 1 5 gpa 300 km on the liquidus our results constrain the maximum depth of buoyancy for high ti magmas at 400 km in the lunar mantle

the role of impact bombardment history in lunar evolution abstract the lunar surface features diverse impact structures originating from its early bombardment the largest among them are the lunar basins basin forming impacts delivered large amounts of energy to the target and expelled lots of material that deposited as an insulating blanket in the vicinity of the impact here we investigate how such processes may have altered the lunar evolution we combine lunar basin chronologies with numerical models of basin formation and 3d thermochemical mantle convection and analyse the role of single generic impacts resulting in basins with varying diameter formation time location and ejecta properties the direct effects of a single impact are enhanced melt generation as well as thermal and heat flux anomalies but these are limited to 100 myr following the impact we use these insights in multi impact scenarios more relevant for the moon which lead to a widespread ejecta blanket and make impact induced effects more substantial lunar contraction history may be altered by the impact bombardment in favour of an early expansion phase as suggested by recent observations moreover imprints of the early bombardment may be kept in the thermal and compositional state of the moon s interior until modern times these can be as large as those induced by uncertainties in bulk lunar heat content if surface insulation due to ejecta is efficient in this case model predicted present day thermal profiles match independent constraints better if the bulk moon is not significantly enriched in refractory elements compared to earth

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

the compensation state of intermediate size lunar craters abstract the compensation state of 49 intermediate size 120 to 600 km diameter lunar craters are investigated using the most recent spherical harmonic models of the lunar topography and gravity truncated at degree n 110 the total mass anomalies per unit area i e the lateral variations of the vertically integrated density perturbations per unit area within an otherwise uniform crust of 60 km thickness are determined such that together with the surface topography give rise to the model gravity anomalies crustal thicknesses of 40 and 80 km are also considered but the general results of this study are not significantly affected excess mass anomalies are obtained by subtracting from the total mass anomalies the mass anomalies that are required for the isostatic compensation of the surface topography the excess mass anomaly of a crater denotes its particular state of compensation dependencies of the excess mass anomalies on crater location size and age are investigated but in general few discernable trends are evident although the vast majority of craters indicate some compensation no correlation exists between age or size and the state of compensation roughly 16 of the craters show no compensation and in some cases have mass deficiencies most likely due to the shock fractured bedrock the breccia lens of lower density the crust in these regions was likely cold and rigid enough at the time of impact to rigidly support the stress caused by crater excavation these features are seen throughout different geological periods demonstrating that the lunar crust cooled quickly and strengthened soon after formation a comparison of the compensation state of craters apollo korolev and hertzsprung suggests that the thermal and mechanical properties of the crust prior to impact had an appreciable effect on the compensation and that crustal thickness may be the single most important factor controlling the compensation of intermediate size craters the characteristics of the excess mass a nomaly profiles of the eight well known near side mascon basins are used to identify new mascon like craters ten newly found mascons are confirmed humboldtianum moscoviense mendel rydberg lorentz hertzsprung korolev schrodinger freundlich sharonov coulomb sarton and schiller zucchius while two more deslandres and dirichlet jackson are very plausible these results show that mare flow is not necessarily required to produce mascon like characteristics

lunar magma transport phenomena abstract an understanding of the most significant events during the first ga or so of lunar history global differentiation associated with a lunar magma ocean lmo and the later generation of about 107 km3 of mare basalts depends profoundly on magma transport dynamics lmo evolution is dominated by the characteristics of hard turbulent convection of a fluid undergoing phase change quench protocrust formed at the ocean surface in early times is repeatedly disrupted by bolide impact ocean body tides and associated crustal foundering during this epoch the ocean temperature is set by the balance between convective heat brought to the surface and brown body radiation from the surface at later times the convective flow is organized into a number of regimes from top to bottom these include conductive crustal lid a viscous sublayer an inertial core a lower viscous sublayer and a mushy cumulate region crystal settling and flotation is restricted to the viscous sublayer regions dilatancy pumping may prevent the efficient expulsion of intercumulus melt during cumulate formation typical velocities within the inertial region are of order 10 m s because late stage ti rich cumulates are dense relative to the earlier mg rich cumulates hyper to sub solidus convection tends to mix lmo crystallization products numerical simulations that account simultaneously for compositional and thermal buoyancy effects indicate a characteristic mixing time 200 ma statistical measures of mixing variance and spatial correlation length quantify the details of mixing the darcy percolative and vein drain models of melt extraction are briefly discussed because compaction lengths are small 102 m the rate of melt extraction is governed by the balance between melt buoyancy and darcy friction differential melt matrix velocities are of order 10 km ma for nominal values appropriate for mare basalt melt extraction from a heterogeneous mixed lmo source transport of magma through the lunar lithosphere via a connected crack network seems highly probable for the range of inferred discharge rates applicable for lunar mare volcanism lmv 103 to 107 m3 s typical fracture widths and ascent speeds are 10 1 to 50 m and 10 1 to 10 m s respectively a simple model is proposed to evaluate the extent of fractionation as magma traverses cold lunar lithosphere if apollo green glasses are primitive and have not undergone significant fractionation en route to the surface then mean ascent rates of 10 m s and cracks of widths 40 m are indicated lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics the predominant vapor species appear to be co co2 and cos near the lunar surface the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high speed ejection of vapor and pyroclasts to form lunar fire fountain deposits such as the apollo 17 orange and black glasses and apollo 15 green glass

impact induced convection as the main mechanism for formation of lunar mare basalts 1 using a suite of numerical models we show that impact induced convection in the moon can explain the formation of lunar mare basalts the depth range of their source region the observed delay between impact basin formation and starting time of mare flows and the long duration of the basaltic flows the effects of an impact on the thermal evolution of the moon and melt production in the mantle are investigated using convection calculations in an axisymmetric cylindrical coordinate system an ascending mantle plume is allowed to melt as it crosses the depth of the solidus temperature we consider two different models permeable and impermeable five different viscosity models and three different impact basin sizes are examined the total amount of melt produced by the permeable model with 1000 times viscosity contrast across the computation domain is comparable to the observed mare flows in imbrium and orientale basins moreover the starting time of major melting in the mantle and its duration are also compatible with the observations the model also allows a rigid lithosphere to develop beneath the basins that is capable of supporting the mascons largely created during the peak mare flow period the model for south pole aitken basin results in a substantial amount of melting in the mantle which does not seem to be compatible with the observations a potassium rare earth elements and phosphorus kreep layer with high concentration of radioactive elements incorporated directly beneath the crust has minor effects on the melt production in the mantle

lunar cryptomaria physical characteristics distribution and implications for ancient volcanism cryptomaria lunar volcanic deposits obscured by crater and basin impact ejecta can provide important information about the thermal and volcanic history of the moon the timing of cryptomare deposition has implications for the duration and flux of mare basalt volcanism in addition knowing the distribution of cryptomaria can provide information about mantle convection and lunar magma ocean solidification here we use multiple datasets e g m3 lola lroc diviner to undertake a global analysis to identify the general characteristics e g topography surface roughness rock abundance albedo etc of lunar light plains in order to better distinguish between ancient volcanic deposits cryptomaria and impact basin and crater ejecta deposits we find 20 discrete regions of cryptomaria covering approximately 2 of the moon which increase the total area covered by mare volcanism to 18 of the lunar surface comparisons of light plains deposits indicate that the two deposit types volcanic and impact produced are best distinguished by mineralogic data on the basis of cryptomaria locations the distribution of mare volcanism does not appear to have changed in the time prior to its exposed mare basalt distribution there are several hypotheses explaining the distribution of mare basalts which include the influence of crustal thickness mantle convection patterns asymmetric distribution of source regions kreep distribution and the influence of a proposed procellarum impact basin the paucity of farside mare basalts means that multiple factors such as crustal thickness variations and mantle convection are likely to play a role in mare basalt emplacement

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

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

remelting mechanisms for shallow source regions of mare basalts abstract two mechanisms are studied which could induce remelting at shallow depths within the moon a radioactive heating model in which remelting is the result of lateral variations of the heat source concentration emplaced by the end of the initial differentiation event and a thermal insulation model in which remelting is induced by lateral variations of near surface conductivity as a result of a high porosity ejecta blanket created by basin forming impacts the effects of these perturbations are studied by evaluating the thermal evolution of an otherwise radially symmetric lunar model the radioactive heating models predict extensive pre basin volcanism which would probably remove from the source region many of the heat producing elements potentially responsible for melting therefore localized high concentrations of heat producing elements emplaced early would most probably not be heat sources for the basin filling mare basalts however they are plausible heat sources for pre basin mare basalts the thermal insulation model predicts a delay of about 200 m y between impact and volcanism thermal insulation may also allow for the persistence of source regions for young basalts at shallow depths if greater basin ages are correct from 4 2 to 3 9 ga and most volcanism occurred between 3 8 and 3 6 ga then the thermal insulation model may explain the delay between impact and basin filling if the basins formed during a terminal cataclysmic event at about 3 9 ga then the earliest stages of basin filling at about 3 8 ga may have been a result of melting beneath the basin as a result of mantle uplift basin filling may have been characterized by a migration of the source region from beneath the basin to beneath the adjacent highlands cooling of the top 200 km beneath the basin after 200 m y because of its high surface conductivity is consistent with the mascon support requirement

a 70th degree lunar gravity model glgm 2 from clementine and other tracking data a spherical harmonic model of the lunar gravity field complete to degree and order 70 has been developed from s band doppler tracking data from the clementine mission as well as historical tracking data from lunar orbiters 1 5 and the apollo 15 and 16 subsatellites the model combines 361 000 doppler observations from clementine with 347 000 historical observations the historical data consist of mostly 60 s doppler with a noise of 0 25 to several mm s the clementine data consist of mostly 10 s doppler data with a data noise of 0 25 mm s for the observations from the deep space network and 2 5 mm s for the data from a naval tracking station at pomonkey maryland observations provided clementine provide the strongest satellite constraint on the moon s low degree field in contrast the historical data collected by spacecraft that had lower periapsis altitudes provide distributed regions of high resolution coverage within 29 of the nearside lunar equator to obtain the solution for a high degree field in the absence of a uniform distribution of observations we applied an a priori power law constraint of the form 15 10 5 l2 which had the effect of limiting the gravitational power and noise at short wavelengths coefficients through degree and order 18 are not significantly affected by the constraint and so the model permits geophysical analysis of effects of the major basins at degrees 10 12 the glgm 2 model confirms major features of the lunar gravity field shown in previous gravitational field models but also reveals significantly more detail particularly at intermediate wavelengths 103 km free air gravity anomaly maps derived from the new model show the nearside and farside highlands to be gravitationally smooth reflecting a state of isostatic compensation mascon basins including imbrium serenitatis crisium smythii and humorum are denoted by gravity highs first recognized from lunar orbiter tracking all of the major mascons are bounded by annuli of negative anomalies representing significant subsurface mass deficiencies mare orientale appears as a minor mascon surrounded by a horseshoe shaped gravity low centered on the inner and outer rook rings that is evidence of significant subsurface structural heterogeneity although direct tracking is not available over a significant part of the lunar farside glgm 2 resolves negative anomalies that correlate with many farside basins including south pole aitken hertzsprung korolev moscoviense tsiolkovsky and freundlich sharonov

numerical experiments on thermal convection in a chemically stratified viscous fluid heated from below implications for a model of lunar evolution abstract compositional density differences resulting from the initial differentiation or secular evolution of planetary mantles can create buoyancy forces comparable to or even larger than those caused by thermal expansion this study examines two and three dimensional numerical experiments on thermal convection in a stably stratified infinite prandtl number fluid heated from below at a prescribed rate a thermally and chemically well mixed convecting layer forms and thickens with time the layer thickness and temperature as functions of time are determined for a range of thermal and compositional rayleigh numbers in some cases a second layer forms above the first and we examine a criterion for its formation based on the critical rayleigh number of the conductive thermal boundary layer above the first convecting layer when a second layer is not present the thickness of the convecting well mixed layer increases approximately as the square root of time at a rate that depends on the ratio of compositional and thermal buoyancy but which is independent of the thermal rayleigh number we show that this thickening rate and the temperature in the mixed layer are well described by a simple physical parameterization that assumes a thermally and compositionally uniform mixed layer and a density at the top of the mixed layer that is the same as that in the immediately overlying still stably stratified fluid these results may have a variety of implications for planetary evolution here we focus on a model for the evolution of the moon in which gravitational differentiation of the unstable stratification resulting from solidification of a magma ocean creates a stably stratified mantle with dense late stage ilmenite cumulates forming a u and th rich core which heats the overlying mantle compositional stratification in the mantle traps heat in the interior and prevents the rapid formation of plumes capable of generating surface volcanism melting at the top of a gradually thickening heated mixed layer in the mantle can explain the age of onset and the depth of origin of the high and low ti mare basalts this may also explain the thick elastic lithosphere and mascon gravity anomalies that developed at the time of mare volcanism the results of our numerical experiments allow a more rigorous examination of this model of lunar evolution

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

a chemical model for generating the sources of mare basalts combined equilibrium and fractional crystallization of the lunar magmasphere abstract it is generally considered that mare basalts were generated by the melting of a cumulate mantle formed in an early moon wide magma ocean or magmasphere however the nature and chemistry of this cumulate mantle and the logistics of its origin have remained elusive extensive studies of terrestrial layered mafic intrusions over the past sixty years have emphasized the imperfection of fractional crystallization and attendant crystal crystal and crystal liquid separation in a convecting magma chamber crystal liquid and crystal crystal separations were similarly inefficient during evolution of the lunar magma ocean lmo allowing for the trapping of interstitial liquid and entrainment of a small proportion of less dense plagioclase into the denser mafic cumulate mush indeed petrography of lunar highlands samples demonstrates this for anorthosites with 1 10 olivine the residual liquid after 80 90 crystallization was very evolved in fact kreepy and even in small proportions 1 5 would have a noticeable effect on the trace element chemistry of melts generated from these cumulates this trapped residual liquid would elevate total ree abundances in the cumulate pile while synchronously deepening the already negative eu anomaly essentially this trapped liquid will make the cumulate more fertile for melting to generate both kreep basalt and mare basalt magmas plagioclase entrained in the mafic cumulate pile adds an essential al component to the high ti basalt source and will moderate the requisite negative eu anomaly in the cumulate early in the evolution of the lunar mantle when the lmo still was largely liquid it is likely that vigorous convection was an important factor in crystallization such convection would allow crystals to remain suspended and in equilibrium with the lmo liquid for relatively long periods of time this extended period of equilibrium crystallization would then have been followed by fractional crystallization once plagioclase became a liquidus phase and began to float to form the lunar highlands crust previous authors have proposed a three component model for the evolution of high ti mare basalt source regions this model includes kreep early olivine rich high mg cumulates and late ilmeniterich low mg cumulates in various proportions however we propose a model for high ti basalt parent magmas which is in accord with studies of terrestrial layered intrusions this model for the high ti source includes trapped instantaneous residual liquid tirl 1 3 and entrainment of a small 2 5 proportion of plagioclase into the late stage cumulate pile in order to account for both the observed al compositions and trace element characteristics of high ti mare basalts melting of this relatively shallow ilmenite and clinopyroxene bearing late stage cumulate can generate high ti mare basalt magmas furthermore we are in agreement with other workers that only through a process of nonmodal melting will the high ti values for the parent magmas be realized large scale convective overturn of the cumulate pile and mixing of kreep with early and late stage cumulates is not required however localized overturn of the upper tenth of the cumulate pile is likely and in fact required to achieve an appropriate major element balance for the high ti mare basalt source region

lunar mare deposits associated with the orientale impact basin new insights into mineralogy history mode of emplacement and relation to orientale basin evolution from moon mineralogy mapper m3 data from chandrayaan 1 1 moon mineralogy mapper m3 image and spectral reflectance data are combined to analyze mare basalt units in and adjacent to the orientale multiring impact basin models are assessed for the relationships between basin formation and mare basalt emplacement mare basalt emplacement on the western nearside limb began prior to the orientale event as evidenced by the presence of cryptomaria the earliest post orientale event mare basalt emplacement occurred in the center of the basin mare orientale and postdated the formation of the orientale basin by about 60 100 ma over the next several hundred million years basalt patches were emplaced first along the base of the outer rook ring lacus veris and then along the base of the cordillera ring lacus autumni with some overlap in ages the latest basalt patches are as young as some of the youngest basalt deposits on the lunar nearside m3 data show several previously undetected mare patches on the southwestern margins of the basin interior regardless the previously documented increase in mare abundance from the southwest toward the northeast is still prominent we attribute this to crustal and lithospheric trends moving from the farside to the nearside with correspondingly shallower density and thermal barriers to basaltic magma ascent and eruption toward the nearside the wide range of model ages for orientale mare deposits 3 70 1 66 ga mirrors the range of nearside mare ages indicating that the small amount of mare fill in orientale is not due to early cessation of mare emplacement but rather to limited volumes of extrusion for each phase during the entire period of nearside mare basalt volcanism this suggests that nearside and farside source regions may be similar but that other factors such as thermal and crustal thickness barriers to magma ascent and eruption may be determining the abundance of surface deposits on the limbs and farside the sequence timing and elevation of mare basalt deposits suggest that regional basin related stresses exerted control on their distribution our analysis clearly shows that orientale serves as an excellent example of the early stages of the filling of impact basins with mare basalt

geophysical constraints on lunar bulk composition and structure a reassessment theoretical lunar mantle seismic velocity and density profiles are calculated for a series of proposed bulk compositions present day selenotherms and models for early differentiation and evolution the seismic velocity profiles are compared to the most recent observational model derived from the complete apollo data set to evaluate compositional implications the mantle density profiles are compared to mean density moment of inertia and crustal density thickness constraints to evaluate the need for a metallic core the calculated seismic velocity profiles are in qualitative agreement with the observational model in two general respects 1 a quasicontinuous velocity decrease occurs in the upper mantle due to the large thermal gradients that characterize all three of the considered thermal models 2 a discontinuous velocity increase occurs at the spinel to garnet transition approximately 500 km depth due mainly to the higher garnet velocities as compared to olivine and orthopyroxene in the upper mantle all four of the considered bulk compositions spanning a range of plausible feo and al2o3 contents are allowed when uncertainties in the temperature profile and depth of differentiation are taken into account however in the middle mantle depths 500 km the most aluminous models those with larger garnet abundances consistently produce larger velocity increases that are most nearly in accord with the observational model in general models that assume differentiation of the upper mantle only that are more aluminous in bulk composition and that have strong thermal gradients in the upper mantle but smaller gradients in the middle mantle result in calculated velocity profiles that most nearly agree with the observational velocity model an alternate differentiation model in which the middle mantle is dominated by mgo rich mafic silicates is also in accord with the observational seismic velocity model but results in density decreases that appear to violate stability arguments in every case calculated mantle density increases are insufficient to match the one standard deviation upper limit on the moment of inertia even when the most favorable combinations of allowed crustal thickness and density are assumed agreement with the moment of inertia upper limit is obtained if metallic cores representing 1 4 of the lunar mass are added to the bulk composition such cores are larger than needed to explain the observed depletions of lunar siderophile elements if the moon formed entirely from terrestrial mantle material

thermal perturbations caused by large impacts and consequences for mantle convection united states national aeronautics and space administration planetary geology and geophysics program

seismic velocity structure of the lunar mantle i have inverted the recently completed set of seismic arrival times from the apollo lunar seismic network to estimate the average seismic velocities in three sections of the lunar mantle two for the upper mantle and one for the middle mantle the method used is a variation of the linearized least squares inversion where the inversion is accomplished in steps the estimated average velocities in the upper mantle decrease from vp 7 74 km s and vs 4 49 km s in the section above 270 km depth to vp 7 46 km s and vs 4 25 km s in the section between 270 and 500 km depth confirming the earlier finding of negative gradients based on seismic amplitude variations the average velocities in the middle mantle between the depths of 500 km and 1000 km of vp 8 26 km s and vs 4 65 km s are significantly higher than those in the upper mantle contradicting earlier estimates based on more limited data the higher velocities may suggest initial melting of the moon down to at least 1000 km depth