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

constitution of the moon 2 composition and seismic properties of the lower mantle abstract to constrain the composition of the moon we have calculated the stable phase assemblages and their seismic properties by the method of minimization of gibbs free energy to determine whether various compositional models are consistent with the seismic observations for the lunar lower mantle at depths between 500 and 1000 km p wave and s wave velocities have been calculated for a series of proposed bulk composition models compositional models for the moon impactor composition orgueil composition etc and earth like compositions lherzolite and pyrolite have been considered it is found that impactor and orgueil models are unlikely for the lower mantle within reasonable temperature adjustment in the temperature profile all of the terrestrial compositional models come close to the seismic data below the 500 km discontinuity it is found that a composition enriched in al 2 o 3 up to about 6 wt and having pyrolite content of the other major oxides lunar pyrolite is adequate to describe the seismic properties of the lunar lower mantle within the uncertainty of calculations and resolution of seismic data an al rich model with a terrestrial ol px ratio and unusually enriched in garnet gives the best fit to the lunar lower mantle seismic properties despite the uncertainty of the seismic data it is shown that none of the analysed compositional models satisfies the seismic constraints simultaneously in the middle and lower mantle phase changes in any model considered are not able to explain the nature of the 500 km discontinuity it is concluded that the lunar mantle is chemically stratified

the source region and melting mineralogy of high titanium and low titanium lunar basalts deduced from lu hf isotope data five high ti basalts from the apollo 11 and 17 landing sites have been analyzed for their hafnium isotope composition these data serve to better constrain the hafnium isotope variation of the moon s mantle variations in initial hf and nd values of low and high ti basalts imply that the source region mineral assemblages of these lunar magma types are distinct low ti basalts have higher initial hf values at a given nd value than high ti basalts the differences in the hafnium and neodymium isotopic composition of low and high ti basalts reflect the fact that the source of low ti basalts had a lu hf n ratio approximately four times greater than its sm nd n ratio in contrast the high ti source region had subequal lu hf n and sm nd n ratios if it is assumed that mare basalts are partial melts of the moon s cumulate mantle the differences between low and high ti basalts can only be explained by these mare magma types being generated from melting sources with distinctly different mineral assemblages the large lu hf fractionations relative to sm nd fractionations of low ti basalts can best be produced by an assemblage of olivine and orthopyroxene with trace amount of clinopyroxene that crystallized early in the history of the lunar magma ocean lmo the subequal lu hf n and sm nd n fractionations of high ti basalts can be produced from a variety of ilmenite bearing mineral assemblages low and high ti basalts have similar lu hf ratios approximately 0 6 times chondrite the low lu hf ratios measured for these mare magmas contrast sharply with the high lu hf ratios greater than chondritic calculated for their sources from initial hf values and an assumed chondritic bulk moon initial hf value the difference between the measured lu hf of a lava vs the calculated lu hf of its source implies that during partial melting lu was preferentially retained in the residual source relative to hf in order to explain the extreme fractionation of measured lu hf ratios we suggest mare basalts can best be explained using a polybaric melting model initial melting of a garnet bearing source followed by continued melting in the spinel stability field can produce the required lu hf fractionations and produce a liquid that last equilibrated with a residuum of olivine and orthopyroxene

inter and intra group compositional variations in apollo 15 pyroclastic green glass an electron and ion microprobe study abstract representative samples of the five compositionally distinct groups a e of apollo 15 pyroclastic green glass were systematically analyzed for major and trace element abundances by electron and ion microprobe techniques these primary magma compositions define a high co trend groups a and d and a low co trend groups b and c on sr zr ba and nd versus co variation diagrams group e glasses are significantly enriched in sr relative to the glass groups of the two trends pearce element ratio analyses and sr ca ba ca systematics indicate that olivine orthopyroxene and clinopyroxene controlled green glass compositions simple crystal liquid igneous fractionation processes involving such an assemblage however cannot explain the observed inter and intra group trace element variation trends the magmas represented by the high and low co trends are interpreted to have been erupted from two distinct but compositionally variable source regions a source mixing model involving differentiated cumulate trapped residual liquid and extremely fe rich components can successfully account for the compositional ranges of the two sources required to produce the observed chemical variations upon partial melting group e glasses appear to represent a magma erupted from a source with a more limited chemical variability the apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions assuming that this mixing model is correct

constitution of the moon 3 composition of middle mantle from seismic data abstract the constitution of the lunar middle mantle which is located between two prominent discontinuities at depths of 270 and 500 km has been investigated by a method of thermodynamic modeling on the basis of the thermoseism data base self consistent phase equilibrium assemblages and synthetic seismic profiles have been calculated for various geochemical models with different contents of the major petrogenic oxides it is shown that none of the analyzed compositional models satisfies the seismic velocity profiles simulataneously in the middle and lower mantle phase changes in any petrological model considered do not explain the nature of the 500 km discontinuity pyroxenite models having 50 52 sio2 and 15 16 feo mg number 74 76 have the best fit to the middle mantle mean velocities of nakamura j geophys res 88 677 686 1983 and satisfy the mean density and lower mantle density constraints these results and the calculations of kuskov and fabrichnaya phys earth planet inter 83 197 216 1994 strongly reinforce the case for a chemically stratified moon interior

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

interior of the moon the presence of garnet in the primitive deep lunar mantle new trace element data have been generated by inductively coupled plasma mass spectrometry icp ms for 65 high and low ti mare basalts from the apollo 11 12 14 15 and 17 landing sites these data demonstrate that ratios of the high field strength elements and yttrium are generally chondritic in the mare source regions for the low ti basalts but nonchondritic in the high ti basalts and potassium rare earth elements and phosphorus kreep such differences can be explained by addition and subtraction respectively of ilmenite this interpretation is consistent with derivation of the basalts from lunar magma ocean lmo cumulates through which late stage ilmenite has sunk and mixed with earlier magma ocean products compositional differences between the mare basalts and volcanic glass beads suggest that at least some of the latter were derived from a garnet bearing source region siderophile and chalcophile element data suggest that the garnet bearing source escaped the lmo melting event and thus represents primitive moon material the remaining glasses are generally very low ti vlt and appear to have been derived from early lmo cumulates i e olivine and orthopyroxene similar to the vlt basalts the remaining glasses were derived from below the lmo cumulates and as the magmas rose they underwent sequential assimilation to varying degrees initially of an ilmenite rich cumulate followed by a kreep component this study presents geochemical evidence for the existence of garnet in a mare source and demonstrates the likelihood that the lmo was not whole moon thus preserving primitive lunar material which has acted as the source region for at least some of the volcanic glasses

origin of lead from green glass of apollo 15426 a search for primitive lunar lead a major obstacle in lunar u pb chronology is the elusiveness of the primary pb isotopic composition and u pb ratio and therefore the pb evolution for the early history of the moon in an attempt to seek the primitive lunar pb isotopic composition green glass from lunar clod 15426 49 was studied for u th pb systematics because it is extremely mg rich and known to be the most primitive among sampled lunar volcanic rocks green glass and yellow impact glass were handpicked washed with water then washed in an acid mixture 0 3 n hbr 0 2 n hf and the washes and residues were analyzed in contrast to the pb from apollo 17 orange glass pb from the surface of the green glass spherules is totally different from that of the spherule interior but is similar to lunar surface lead data for the interior pb yield a 207pb 206pb age of 3 41 ga because of the low pb concentration and high u pb ratio observed for the interior the initial pb was poorly defined nevertheless the data indicate that lunar pb evolved in an environment with 238u 204pb 19 55 which is considerably lower than those for mare basalts around 300 but higher than values for the earth 6 8

distinguishing between basalts produced by endogenic volcanism and impact processes a non destructive method using quantitative petrography of lunar basaltic samples abstract impact processes play an important role in shaping and reshaping the surfaces of airless planetary bodies such processes produce regoliths and generate melts that crystallize and record the homogenization of the geology at the impact site if the volume of melt is substantial the resultant crystallized product has an igneous texture and may be free of xenolithic clasts making it difficult to distinguish from melts produced by endogenic magmatic processes this has been clearly demonstrated during the return of the apollo samples from the moon where apollo 14 basalt 14310 was initially described as a mare basalt and was only subsequently reclassified as an impact melt following detailed and time consuming crystallization experiments another way of distinguishing lunar impact melts from endogenically derived mare basalts is through the quantification of the highly siderophile elements hse pd rh ru ir pt os which have relatively low abundances in pristine lunar samples but are high in meteorites and therefore may be enriched in impact melts however these analyses consume relatively large quantities of valuable sample and because of mass constraints cannot be performed on many lunar samples in this paper we present a quantitative petrographic method that has the potential to distinguish lunar impact melts from endogenically derived mare basalts using plagioclase and olivine crystal size distributions csds the slopes and intercepts of these csds are used to show that olivine from impact melts displays a steeper csd relative to olivine from mare basalts for plagioclase generally impacts melts display csds with shallower gradients than those from endogenous mare basalts and as for olivines plot in a distinct field on a csd slope vs csd intercept plot using just a thin section to distinguish impact melts from mare basalts enables the goals of future robotic sample return missions to determine the age of the south pole aitken basin in the moon because such missions will potentially only return small 2 4 mm rocklets for analysis obviating hse analyses for impact melt identification

on the connection between mare basalts and picritic volcanic glasses the evolution of the major element compositions of mare basaltic liquids and coexisting crystals in low pressure fractionation processes has been modeled in order to examine the postulated link between picritic volcanic glasses and mare basalts existing models of equilibrium and fractional crystallization longhi 1977 1982 have been modified to include expressions for the cr spinel liquidus surface and the boundary between the armalcolite and ilmenite surfaces average molar partition coefficients for armalcolite liquid pairs are also included in the modifications results of the calculations show that most mare basalts are not derived by simple low pressure fractionation from parents with the compositions of picritic glasses as tabulated by delano 1986a also there is no indirect evidence as yet for posteruption fractionation of picritic magmas in the form of sufficiently magnesian mare type olivines at the apollo 12 and 15 landing sites however the calculations do suggest that luna 24 ferrobasalt and apollo 11 high k basalts could have been derived by simple near surface fractionation of known picritic compositions also xenocrystic olivines with mare like concentrations of tio2 and cao in high ti basalt 74275 provide evidence for the existence of a picritic magma at the apollo 17 site more importantly the calculations indicate that the picritic magmas would have fractionated to produce basalts with bulk and mineral compositions generally similar to those of mare basalts these latter results favor the hypothesis that mare basalts have fractionated nonprimary compositions and that the small number of observed linkages between basalts and picritic parents is a consequence of limited sampling

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

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

apollo 15 green glass compositional distribution and petrogenesis abstract we have characterized a comprehensive suite of individual green glass beads from apollo 15 soil to determine interelement behavior and to constrain petrogenetic relationships we analyzed 365 particles for trace elements by instrumental neutron activation analysis and analyzed 52 of them selected to cover the compositional ranges observed for trace elements for major elements by electron microprobe analysis we confirm the observation of delano 1979 that the beads comprise discrete compositional groups although two of the groups he denned are further split on the basis of trace element compositions each of the resulting seven groups has distinct average rare earth abundances the coherence between major and trace element data was masked in previous studies by imprecision correlated error and nonrepresentative sampling of the different groups most of the compositional characteristics of the green glasses can be explained by a model for batch equilibrium melting of a nearly homogeneous ultramafic source region when the complicating effects of high pressure and low oxygen fugacity are taken into account the previously puzzling behavior of ni and co as apparently incompatible elements may arise from partial reduction of those elements to the zero oxidation state resulting in low mineral melt partition coefficients the model also offers explanations for why the green glasses form boomerang shaped trends on many two element variation diagrams and why certain compositions groups a and d are more abundant than glasses with other compositions

apollo 14 mare basalts petrology and geochemistry of clasts from consortium breccia 14321 eleven mare basalt clasts have been extracted from polymict lunar breccia 14321 for a combined petrologic and geochemical study by our consortium ten of these clasts are high al low ti mare basalts similar to those discovered previously at apollo 14 the other is a highly evolved tridymite ferrobasalt with low al and intermediate ti contents a high al ilmenite ferrobasalt from lunar breccia 14305 is the most evolved high al basalt described from the apollo 14 site the major and trace element characteristics of the basalts studied here allow them to be grouped into five compositional types that range from lree depleted to lree enriched some of these types may be related by varying percents of partial melting of the same source but at least two separate sources that differ by a factor of two in incompatible trace element concentrations are required the 14321 type basalts and vitrophyres have steep chondritenormalized hree slopes and may have formed by assimilation of intermediate k fra mauro kreep which is presumed to represent a partial melt of the lower crust the age of these basalts 3 9 aeons suggests that mare volcanism played an important role in the evolution of the early lunar crust

magmatic evolution of the moon although incomplete because of the imperfect and somewhat random sampling of rock types by the apollo and luna missions 1969 1976 the history of lunar magmatism has been reconstructed by numerous researchers over the past three decades these reconstructions have illustrated the continuous nature of lunar magmatism from 4 6 to approximately 2 0 ga and the large influence of early differentiation and catastrophic bombardment on lunar mantle dynamics magmatism and eruptive style in this review we group magmatism into multiple stages of activity based on sampled rock types and evaluate the models for each stage stage 1 is early lunar differentiation and associated magmatism partial melting of the moon soon after accretion was responsible for producing an anorthositic crust and a differentiated lunar interior the extent of lunar melting and mantle processing depends strongly on the mechanisms that induced melting estimates for the time over which melting and crystallization occurred range from tens to hundreds of millions of years stage 2 is the disruption of lunar magma ocean cumulates soon after the crystallization of most of the lunar magma ocean the cumulate pile experienced gravitational overturn this resulted in transport of late forming cumulates into the deep lunar mantle and mixing of magma ocean cumulates on a variety of scales stage 3 is the post magma ocean highland magmatism whereas the ferroan anorthositic crust was probably produced during the crystallization of a magma ocean the slightly younger mg suite and alkali suite plutonic rocks may have been generated by decompressional melting of early magma ocean cumulates during cumulate pile overturn a kreep and crustal signature was incorporated into these primitive basaltic magmas through assimilation near the base of the lunar crust or through melting of a hybridized mantle the alkali suite could represent either the differentiation products of mg suite parental magmas or a separate but contemporaneous episode of basaltic magmatism stage 4 is pre basin volcanism sample analysis and remote sensing data indicate that early lunar volcanism kreep basalts and high alumina basalts was contemporaneous with periods of highlands plutonism and catastrophic bombardment of the lunar surface the relationship between early stages of lunar volcanism and the contemporaneous plutonism is not clear the kreep basalts may be volcanic equivalents to both the mg suite and alkali suite stage 5 is the late remelting of magma ocean cumulates and eruption of mare basalts basin associated eruption of mare basalts occurred during and following the late stages of catastrophic bombardment this volcanic activity was possibly an extension of the thermal event that initiated pre basin volcanism mare basalts exhibit a wide range of composition resulting from near surface fractionation of chemically distinct primary basaltic magmas most likely mare basalts were produced by small to moderate degrees of partial melting of hybrid cumulate sources in the deep lunar mantle alternatively the mixed chemical signatures observed in many mare basalts may be interpreted as indicating assimilation of late stage evolved cumulates by melts produced deep in the cumulate pile the wide range of compositions exhibited by the mare basalts compared with earlier episodes of basaltic magmatism may reflect the thermal regime in the lunar mantle that limited the extent of partial melting and melt source homogenization

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

the role of ilmenite in the source region for mare basalts evidence from niobium zirconium and cerium in picritic glasses abstract to investigate models for the generation of lunar high ti basalts we have analyzed lunar picritic glasses for zr nb ce and ti at high precision using ion microprobe techniques the picritic magmas represented by these glasses have experienced minor crystallization which has allowed us to partially eliminate the effects of post melting processes commonly experienced by crystalline high ti mare basalts the nb zr for these glasses ranges from 05 11 the high ti glasses generally tend to have higher values of nb zr 072 109 than the very low ti glasses 048 085 the crystalline mare basalts tend to have slightly higher nb zr than glasses with similar ti from the same site for example the apollo 17 a17 high ti basalts have nb zr of approximately 09 whereas the a17 high ti glasses have nb zr of 07 kreep has nb zr of approximately 06 thus zr is fractionated from nb to different degrees in the various picritic magmas the concentrations of zr nb and ce increase from the very low ti glasses to the high ti glasses and along the trajectory the nb ce and zr ce increase nb ce 25 1 6 and zr ce 4 15 for the picritic glasses overlap with kreep nb ce 36 and zr ce 5 zr ti and nb ti show a wide range of variation in these glasses both zr ti and nb ti in the glasses range from approximately 0014 to slightly less than 0003 the zr ti and nb ti for these glasses overlap with that of the crystalline mare basalts generally with increasing ti nb and zr zr ti and nb ti decrease the exceptions to this are the apollo 14 a14 glasses that exhibit an increase in nb ti and zr ti based on these data for the picritic glasses and experimentally determined partition coefficients for nb zr and ce the mantle sources for these picritic magmas are slightly to moderately fractionated from c1 chondrite and previous estimates of the bulk silicate moon our best fit model for our data and this observation is that both the very low ti and high ti picritic magmas were derived through small to moderate degrees of nonmodal melting of lunar mantle sources consisting of a mixture of late stage lmo cumulates derived after 95 crystallization of the lmo and early to intermediate lmo cumulates derived prior to 80 crystallization of the lmo the early lmo cumulates had nb zr zr ce and nb ce ratios near c1 chondrite whereas these ratios were fractionated in the late stage lmo cumulates this hybridization of mantle sources occurred during large scale overturning of the lmo cumulate pile the source for the low ti picritic magmas had very minor amounts of ilmenite whereas the source for the high ti picritic magmas probably contained less than 6 ilmenite for all the picritic magmas ilmenite was exhausted from the residua during melting models suggesting that the high ti magmas are derived through the assimilation of an ilmenite bearing cumulate layer or preferential assimilation of ilmenite by low ti primary magmas are not consistent with the nb zr ce and ti data magmas hubbard and minear 1975 wagner and grove 1993 1995 in particular the preferential assimilation by very low ti picritic magmas of ilmenite with expected nb ce 20 000 22 000 and nb zr 55 signatures would displace the resulting high ti magma too far from our observed data large scale overturning of the lmo cumulate pile also accounts for the trace element signatures found in the a14 picritic glasses the evolved signature found in these primitive very low ti picritic glasses is most likely a product of kreep incorporation into the lmo cumulate source rather than either contamination by evolved ilmenite bearing cumulates or incorporation of higher proportions of locally derived intercumulus melt

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 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

the systematics of light lithophile elements li be and b in lunar picritic glasses implications for basaltic magmatism on the moon and the origin of the moon lunar picrites represented by high mg volcanic glasses are thought to be products of either partial melting of the deep lunar mantle followed by rapid ascent or polybaric partial melting initiated in the deep lunar mantle the near primary compositions of these volcanic glasses provide us with a unique perspective for evaluating basaltic magmatism the characteristics and evolution of the lunar mantle and the origin of the moon the light lithophile elements lle li be b in planetary materials have been used to estimate planetary compositions and evaluate magmatic processes ion microprobe analyses of these glasses for lles were conducted using a cameca 4f ion microprobe this suite of glass beads ranged in tio2 from 0 3 to 17 wt seventy one individual glass beads were analyzed for the lles in addition core rim analyses of individual glass beads were made the lles show a wide range of variability with li ranging from 1 2 to 23 8 ppm be ranging from 0 06 to 3 09 ppm and b ranging from 0 11 to 3 87 ppm b be ranges from 0 40 to 4 6 li be ranges from 2 7 to 41 7 although 90 of the li be values range from 14 to 30 both b be and li be values for the picritic glasses are less than chondrite be nd for the glasses ranges from 04 to 06 and are similar to chondrite 058 traverses across individual beads indicate that they are generally homogeneous with regards to lles regardless of tio2 content the individual glass groups show limited variations in lle characteristics the exceptions to this observation are the a17 vlt and the a15 yellow glasses at individual apollo sampling sites the lle content is generally correlated to tio2 the high ti glasses are displaced toward higher li at similar b and be relative to the very low ti glasses lle concentrations also parallel the enrichments of other lithophile elements such as ba zr sr and rees as noted for other trace element characteristics glasses from each sampling site have similar lle signatures for example the apollo 14 glasses generally have higher lle concentrations relative to glasses of similar tio2 content from other sites the lle data support mantle inhomogeneity and lunar magma ocean lmo cumulate overturn models suggested by previous studies a kreep component had been incorporated into some of these picritic glasses this is consistent with other trace elements and probably reflects the recycling of kreep and or other late stage lmo cumulates into the deep lunar mantle the picritic glasses are compositionally distinct from the crystalline mare basalts in lles they are not related by either fractional crystallization or partial melting processes this suggests that they were derived from distinctively different mantle sources estimates of the bulk compositions of the earth and the moon have previously been made based on the assumption that the ratio of li to be is a direct measure of the ratio of the high temperature condensates htc refractory components to the mg silicates less refractory components in a planet we assert that if li be is to be used to estimate bulk moon composition the picritic glasses provide fewer pitfalls and a better estimate than the crystalline mare basalts differences in partition coefficients d for li and be indicate that fractional crystallization and partial melting will modify the libe ratio estimates based on the picritic glasses infer a higher li be for the bulk moon than estimated from the mare basalts this would indicate that the bulk moon is less refractory than previously calculated by li be and approaches the bulk composition of the earth

geochemical applications of noble gases abstract noble gases are unique tracers due to their rarity on earth and their inertness several of their isotopes are produced by nuclear reactions whereas others were trapped when the earth formed they have been widely used for understanding the evolution and structure of the earth dating geological events processes characterizing magma genesis and volcanism in different tectonic environments tracing mantle crust interaction even in non volcanic areas and for monitoring earthquake and volcanic activities some of these topics were presented at the 9th international conferences on gas geochemistry that was held in 2007 in taipei taiwan this special volume includes twelve papers which cover a wide range of applications of noble gases geochemistry such as tracing the thermal evolution of the early earth understanding the mantle source of continental basalts establishing the spatial variations of gas compositions in hot springs and fumaroles from volcanic and forearc areas as well as in key non volcanic areas such as faults and seismic zones and tracing the origin and evolution of ore forming fluids of uranium deposits reproducing the noble gas behavior during faulting and finally using argon as a tracer of large scale geologic processes

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

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

exploring the lunar mantle with secondary ion mass spectrometry a comparison of lunar picritic glass beads from the apollo 14 and apollo 17 sites abstract the major element characteristics of lunar picritic beads indicate that their composition approaches that of primary basaltic liquids and therefore may be our best geochemical mineralogical probes of the lunar interior the picritic magmas appear to represent partial melting of a variety of mantle mineral assemblages secondary ion mass spectrometry sims analysis of individual glass beads collected from the apollo 14 a 14 and apollo 17 a 17 landing sites shows that although there is substantial major minor tio 2 al 2 o 3 and trace element variation at each site the glasses from each site have distinguishable trace element signatures ba sr lree hree the incompatible element characteristics of glasses of nearly identical major element chemistry are strikingly different between sites the contrast between the a 14 and a 17 glasses appears to be the result of a higher kreep component in all the a 14 glasses the incorporation of evolved kreep component into high mg magmas is not a result of either assimilation or magma mixing but incorporation during the partial melting episode that produced the picritic magmas this is a more thermally efficient mechanism for incorporation of the kreep component into a picritic magma calculated mantle chemistries based upon glass compositions low degrees of partial melting and mineralogical components used in previous models suggest that the difference between a 14 and a 17 mantle sources is a 0 1 1 4 kreep intercumulate melt this difference will increase with an increase in the degree of partial melting in the model calculations this intercumulate melt may interstitially reside in an evolved high ti cumulate component the juxtaposition of evolved high ti cumulates kreep and primitive low ti cumulates mantle components has been attributed to original mantle inhomogeneities density contrasts during magma ocean crystallization and sinking of high density evolved cumulates into less dense primitive cumulates within the context of either magma ocean or serial magmatism type models regardless of the model the trace element signatures of glasses and the basalts indicate that the character of the a 14 mantle source is intrinsically different from that of the a 17 mantle source this indicates large scale lateral and vertical inhomogeneities in the lunar mantle

very high potassium vhk basalt complications in mare basalt petrogenesis apollo 14 vhk very high potassium basalt is a newly discovered variety of low ti high al mare basalt characterized by unusually high concentrations of k rb and ba and high ratios of these elements to other incompatible elements that exceed normal lunar values potassium feldspar and k si rich glass are ubiquitous and widespread components of these basalts other phases include magnesian olivine fo 60 73 fe rich olivine fo 31 50 pigeonite plagioclase an 79 95 ilmenite cr ulv spinel fe metal and troilite vhk basalts have low initial 87sr 86sr ratios with rb sr ratios estimated to be 15 higher than their source this rb sr fractionation occurred at their time of formation 3 75 aeons hypotheses involving volatile nonvolatile fractionations or long term enrichment of the source regions in k are inconsistent with the high ba la ratios and low initial 87sr 86sr ratios of vhk basalt the most plausible origin for these rocks is partial assimilation of lunar granite by a normal low ti high al mare basalt assimilation occurs by diffusion controlled exchange of alkalis and ba between two melts trace element compositions of the granitic melt are controlled in part by refractory accessory phases in the granite significant geochemical interaction between the lunar crust and mare basalts is implied

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

distinguishing between apollo 14 impact melt and pristine mare basalt samples by geochemical and textural analyses of olivine abstract apollo 14 a 14 impact melt olivine vitrophyres ovs composed of olivine phenocrysts in an opaque glass matrix with minor amounts of pyroxene and plagioclase are petrographically similar to pristine quenched a 14 high alumina high al and apollo 12 a 12 basalts textural and chemical analyses have been conducted on olivines within impact melt and pristine mare basalt clasts from a 14 breccia 14321 as well as various olivine phyric apollo 12 and 17 basalts to be able to distinguish between the petrographically similar samples the a 14 high al basalts examined here represent samples from each of the three chemical groups a b c examples from the three a 12 basalt suites ilmenite olivine pigeonite and olivine rich apollo 17 a 17 type c basalt 74275 have also been analyzed as a complement to the chemical analyses crystal size distributions csds were determined for approximately half of the samples investigated here due to a small number of olivine crystals that did not produce statistically meaningful csds on half of the samples and confirm that although similar the basalts and impact melts are texturally distinct olivines from a 14 impact melts have the highest average forsterite contents average fo 0 82 and generally the lowest average co 37 ppm and mn 1544 ppm abundances thus chemically distinguishing them from the pristine basalts in addition chemical compositions obtained for olivine from 14321 1486 are most likely representative of an impact melt and thus contradict its previous classification as a high al basalt neal et al 1988 olivine from 1486 have similar average forsterite average fo 0 82 and ti v ratio to the ovs furthermore on the basis of their chemical compositions olivines have been identified within the impact melts that are likely inherited from basalts these olivines are chemically distinct from the rest of the impact melt olivine population with lower forsterite 0 67 0 80 and low ti v 10 which are similar to olivine compositions from the a 14 high al basalts in addition to distinguishing between sample types from a 14 olivine compositions can also be used to distinguish between pristine mare basalts from various missions olivine within the selected samples from the individual a 12 basalt suites can also be distinguished chemically from one another using the ti v ratio where olivine suite basalts have ti v 3 5 the results indicate that combined use of csds and chemical analyses of olivine can be used to reliably distinguish between 1 impact melts and pristine apollo 14 basalts 2 basalts from different landing sites and 3 individual basalt suites from a single site

ion microprobe studies of trace elements in apollo 14 volcanic glass beads comparisons to apollo 14 mare basalts and petrogenesis of picritic magmas abstract the major element geochemistry of picritic lunar glass beads indicates that they represent primary basaltic liquid compositions and as such provide unique information concerning the origin of mare basalts and characteristics of the lunar interior this study used ion microprobe techniques for trace element analysis of individual glass beads representing seven compositionally distinct types of picritic glass beads from the apollo 14 site high ti glasses 17 11 tio2 red black orange intermediate ti glasses 5 4 tio2 yellow low ti glasses 2 8 tio2 lap low alkali picritic papike et al 1989 very low ti glasses ba sr 1 of these glasses are different from low ti mare basalts at other sites but are similar to crystalline basalts at the apollo 14 site the intermediate to high ti picritic glasses exhibit a flat to slightly positive lree slope and a negative hree slope the orange glass has a higher total ree abundance and a slightly larger negative eu anomaly than the red black and yellow glasses relative to the apollo 17 high ti glasses apollo 14 high ti glasses are enriched in ree lree hree y v zr sr ba and ba sr and are similar in alkali elements li rb co and sc trace element modeling within the context of liquid lines of descent and major element characteristics indicates that the picritic glass beads at the a 14 site are not related by low pressure fractional crystallization to each other or to crystalline basalts at the apollo 14 or other landing sites a possible exception is the relationship between lap and basalts of the high al basalt suite the wide range of primary magma compositions and the lack of petrogenetic linkage via crystal fractionation to crystalline basalts indicates that either a wide compositional range of evolved mare basalts has not yet been sampled or a unique mechanism is selectively tapping these picritic magmas directly from their mantle source region the wide range of major and trace element characteristics of the volcanic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine orthopyroxene clinopyroxene ilmenite plagioclase kreep component the evolved kreep component may have been incorporated into these primary picritic magmas by either assimilation fractional crystallization type processes afc or by hybridization of the mantle source the former appears less likely due to the general systematic increase in incompatible elements relative to ti concentration and the apparent lack of crystallization that is required in afc type models the hybridization processes may be the result of sinker mechanisms as proposed by ringwood and kesson 1976 a manifestation of original mantle inhomogeneities or a magma ocean stirred by large impacts

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

basaltic magmatism on the moon a perspective from volcanic picritic glass beads abstract it is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles as such they provide valuable insights into the composition structure and processes of planetary interiors those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution within the collection of lunar samples returned by the apollo and luna missions are homogeneous picritic glass beads of volcanic origin these picritic glasses are our closest approximations to primary magmas as such these glass beads provide a unique perspective concerning the origin of mare basalts the characteristics of the lunar interior and processes in the early differentiation of the moon we have obtained trace element data for these picritic glasses using sims techniques these data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism the volcanic glasses are very diverse in their trace element characteristics for example they have a wide range of ree pattern shapes and concentrations like the crystalline mare basalts all picritic glasses have a negative eu anomaly unlike the crystalline mare basalts there is little correlation between the size of the eu anomaly and overall ree concentrations trace element differences among the various glasses suggests that a kreep component was incorporated into their mantle source this implies large scale mixing of the lunar magma ocean derived cumulate pile subtle differences among glasses suggest that local mixing of sources may also have been an important process preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts these are parallel but no common liquid lines of descent chemical differences between picritic glasses and the more primitive crystalline mare basalts experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts differences in lead isotopic data and the mode of eruption i e fire fountaining for glass beads these data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile rich than that of the mare basalts several petrogenetic models are suggested by the trace element characteristics of the picritic glasses 1 1 partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas picritic for both the mare basalts and picritic glasses picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization 15 30 of similar but not identical picritic magmas 2 2 picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile enriched relative to the mare basalt source heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km 3 3 the picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km a primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models

zr hf ta fractionation during lunar evolution zr hf ratios and other elemental data for 68 lunar basalt kreep and glass samples were obtained by coincidence anticoincidence counting and normal counting techniques during instrumental neutron activation analyses zr hf ratios indicate a complementary relation between a mean zr hf ratio of 41 0 0 4 for kreep and the mean ratios of 30 32 in apollo 11 12 and 17 mare basalts the uniformity of zr hf in 20 apollo 14 16 and 17 kreep samples is consistent with petrogenesis of kreep compositions from a single major source the observed complementary ratios require greater zr hf fractionation than what is predicted by lunar evolutionary models and presently known distribution coefficients the difference requires that either 1 ilmenite and armalcolite the most predominant phases conducive to zr hf fractionation begin to crystallize earlier and in greater amounts than is presently assumed or 2 the relative partitioning of hf over zr in ti oxides and or major minerals and or spinels is greater than what is observed in natural or synthetic systems complementary ratios also support a primordial zr hf ratio of 35 represented by the e c o enstatite c2 and c3 carbonaceous and ordinary chondrites compiled ta and hf data from this laboratory indicate a well defined ta hf trend for most apollo mare basalts and apollo 14 kreep apollo 11 b3 and apollo 17 basalts define an alternate trend of higher ta hf that we attribute to relatively higher ta in assimilated ti bearing urkreep residual phases due to the oxidation of ta 4 to ta 5 under elevated f02 apollo 15 16 and 17 kreep samples exhibit lower ta hf ratios relative to the main trend and have a complementary relation to late stage ti bearing cumulates with enhanced ta hf

petrogenesis of lunar troctolites models of petrogenesis for lunar troctolites are severely constrained by the high mg 88 values of the most primitive members of the mg rich suite melts derived by partial melting of olivine cumulates to the lunar magma ocean have high mg but are strongly undersaturated with respect to plagioclase assimilation of lunar crust cannot bring these melts to the plagioclase liquidus without unduly reducing the mg values of olivine partial melts derived by melting a iherzolite primitive interior have higher normative plagioclase contents but require sources with mg 90 more terrestrial like mg 88 values are permitted if rising thermal plumes are capable of entraining the most mg rich cumulates of the magma ocean the mg values of lunar troctolites may therefore reflect a hybrid source composed of primitive mantle and mg rich cumulates of the magma ocean higher mg values may also arise from the reduction of small amounts of feo to fe alternatively the parent magmas to lunar troctolites may be impact melts of the anorthositic crust and the mg rich dunite cumulates of the magma ocean the latter were brought to the upper mantle during the overturn of the unstable cumulate pile of the magma ocean

deciphering basaltic magmatism on the moon from the compositional variations in the apollo 15 very low ti picritic magmas picritic glass beads of volcanic origin have been interpreted as representing extremely primitive lunar magmas that approach primary magma compositions based on this they have been used for developing models for lunar magmatism estimating the mineralogical and chemical characteristics of their mantle sources constraining the dynamics and structure of the lunar mantle developing models for lunar core formation reconstructing the bulk composition of the moon and evaluating the genetic relationships between the earth and the moon yet we still do not truly understand many aspects of the compositional diversity among individual glass types or even within a single glass type using high precision ion microprobe techniques we have analyzed a total of forty very low ti glass beads from the apollo 15 a15 site and twenty additional picritic glass beads from other sampling sites for a suite of highly compatible ni co weakly compatible to weakly incompatible mn cr v and highly incompatible ce ti zr nb elements within the a15 very low ti glass population ni and co concentrations are positively correlated exhibit limited fractionation of ni co and are distinctive for individual glass groups as defined by major elements manganese is also colinear with both ni and co the highly incompatible elements also appear to be generally colinear with ni co and mn although there are distinguishable compositional offsets in the glass populations the ni co ratio does not differ dramatically among the very low ti glasses from other sampling sites although incompatible element concentrations may differ significantly these trace element data eliminate fractional crystallization and partial melting of a homogeneous source under extremely low fostaggered2 conditions as possible models for the origin of the compositional variations observed in the a15 very low ti glass population these data are consistent with the generation of these magmas through partial melting of a spatially restricted heterogeneous lunar magma ocean lmo cumulate sequence the compositional variation in these magmas can be produced by at least two different melting processes 1 partial melting of a cumulate sequence consisting of relatively early cumulates with a higher proportion of an intercumulus melt component green glass a d e and later cumulates with lower proportions of an intercumulus melt component green glass c 2 different degrees of partial melting of a cumulate sequence small degrees of partial melting less than 5 of a more primitive cumulate mantle source will generate one group of magmas green a d e whereas a group of other picritic magmas green c were produced by larger degrees of partial melting 10 to 20 of a mineralogically similar but a more evolved cumulate mantle source in both models the green b glass group is formed by either cumulate commingling or magma mixing processes these magmas cannot be rapidly transported from the source region to the lunar surface in a single eruptive event without extensive fractional crystallization yet the colinear relationship among ni co and mn is not compatible with extensive and variable fractional crystallization therefore a polybaric melting model as suggested by longhi 1992b appears to be the only alternative to producing relatively unfractionated apollo 15 very low ti picritic magmas with high pressure signatures the trace element data provides additional constrains for this type of model

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

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

origin of lunar very high potassium vhk basalts a combination of endogenous and exogenous processes abstract very high potassium or vhk basalts have been described from the apollo 14 landing site at fra mauro on the lunar near side many of the known samples are clasts in polymict breccias with a few as new work completed on fourteen vhk basalts include crystal size distributions csds and in situ chemical analyses and element maps collected by electron probe microanalysis epma csds completed on three vhk basalt samples indicate that these basalts are not impact melts and represent endogenous melts of the lunar interior potassium k element maps reveal the spatial relationship between the k rich material and the basalt clasts with attached breccia matrix if present in situ epma analyses have identified two distinct types of k rich material k feldspar and k rich glass with these new data an additional mechanism for an exogenic petrogenesis of vhk basalts is proposed that involves the impact process vhk basalts can be divided into two groups based on density and viscosity vhk 1 basalts formed when a hot impact ejecta covered the granite felsite rich matrix material containing high al basalt clasts heat from the impact ejecta partially melted and possibly evaporated nearby k bearing materials which then infiltrated and contaminated the high al clasts vhk 2 basalts are consistent with the hypothesis of granite assimilation by a high al magma as seen in the higher abundances of network forming elements