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

magmatic effects of the lunar late heavy bombardment abstract large volumes of mare basalts are present on the surface of the moon located preferentially in large impact basins mechanisms relating impact basins and mare basalt eruptions have previously been suggested lunar impacts removed low density material that may have inhibited eruption and created cracks for fluid flow icarus 139 1999 246 and lunar basins have long been described as catchments for magma e g rev geophys space phys 18 1980 107 and references therein we present a new model for melt creation under near side lunar basins that is triggered by the impacts themselves magma can be produced in two stages first crater excavation depressurizes underlying material such that it may melt in situ second the cratered lithosphere rises isostatically warping isotherms at the lithosphere asthenosphere boundary which may initiate convection in which adiabatic melting can occur the first stage produces by far the largest volume of melt but convective melting can continue for up to 350 ma we propose that giant impacts account for a large portion of the volume and longevity of mare basalt volcanism as well as for several compositional groups including high alumina high titanium kreep rich and picritic magmas

the oxygen isotope composition petrology and geochemistry of mare basalts evidence for large scale compositional variation in the lunar mantle to investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition titanium content and modal mineralogy of a suite of lunar basalts our sample set included eight low ti basalts from the apollo 12 and 15 collections and 12 high ti basalts from apollo 11 and 17 collections in addition we have determined the oxygen isotopic composition of an apollo 15 kreep k potassium ree rare earth element and p phosphorus basalt sample 15386 and an apollo 14 feldspathic mare basalt sample 14053 our data display a continuum in bulk rock delta o 18 values from relatively low values in the most ti rich samples to higher values in the ti poor samples with the apollo 11 sample suite partially bridging the gap calculation of bulk rock delta o 18 values using a combination of previously published oxygen isotope data on mineral separates from lunar basalts and modal mineralogy determined in this study match with the measured bulk rock delta o 18 values this demonstrates that differences in mineral modal assemblage produce differences in mare basalt delta o 18 bulk rock values differences between the low and high ti mare basalts appear to be largely a reflection of mantle source heterogeneities and in particular the highly variable distribution of ilmenite within the lunar mantle bulk delta o 18 variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases thus ilmenite fractionation is important in the case of high ti apollo 17 samples whereas olivine plays a more dominant role for the low ti apollo 12 samples consistent with the results of previous studies our data reveal no detectable difference between the delta o 17 of the earth and moon the fact that oxygen three isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated

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

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

the effect of water on the 410 km discontinuity an experimental study 1 in order to evaluate the effect of h on the pressure and transition interval of the olivine wadsleyite transformation synthesis experiments were carried out in hydrous and anhydrous peridotite compositions at 1400 c under hydrous near saturated conditions the pressure of the transition is 1 0 0 5 gpa lower than under anhydrous conditions in addition the two phase interval appears to broaden from about 0 4 gpa 12 km in the anhydrous system to as much as 1 3 gpa 40 km in the hydrous system under hydrous conditions the spatial distribution of olivine and wadsleyite appears to be controlled by h diffusion extrapolating previously measured diffusion coefficients for h in olivine and in liquids it appears that h diffusion driven by gravitational equilibration may serve to narrow the transition interval between olivine and wadsleyite

re examination of the lunar magma ocean cumulate overturn hypothesis melting or mixing is required abstract there is a long standing hypothesis that the last fraction of the lunar magma ocean crystallized into a layer of dense ti rich cumulate minerals at shallow depths 100 km early in the moon s history many questions remain about the stability of these high ti cumulates it has been suggested that the cumulates subsequently sank deep into the moon because of gravitational instability but high ti material is required at shallower depths by 3 5 ga to create the high ti mare basalts and picritic glasses the high ti material may have re erupted from depth or some or all of it may have remained at shallow depths throughout lunar history data on phase stabilities bulk compositions densities and temperatures of melting and crystallizing in addition to results from numerical modeling suggest that the high ti cumulates would sink only under highly specific conditions five scenarios for sinking high ti cumulate materials are examined and only two are found plausible in particular it is found that simple sinking of solidified high ti cumulates is unlikely because the temperature at which the cumulates solidify is low and viscosity under these conditions is very high it is however possible that high ti cumulates mixed with a substantial fraction of olivine would have viscosity low enough to allow them to sink as solids further because clinopyroxene and ilmenite melt in a ratio of 2 1 remelted high ti cumulates would be negatively buoyant and sink as liquids percolating downward through the underlying mantle and beginning to recrystallize ilmenite at 200 km depth making a hybrid heterogeneous mantle

strong tidal heating in an ultralow viscosity zone at the core mantle boundary of the moon tidal dissipation in the moon depends on the lunar tidal period numerical modelling of the moon s response to tidal forces suggests that tidal dissipation is localized in an ultralow viscosity zone at the core mantle boundary

precise determination of phase relations in pyrolite across the 660 km seismic discontinuity by in situ x ray diffraction and quench experiments abstract mineral assemblage changes in a pyrolite composition with increasing pressure were observed by in situ x ray diffraction and quench experiments at pressures near that of the 660 km seismic discontinuity and at a fixed temperature of 1600 c according to results obtained by in situ x ray diffraction experiments ringwoodite rw was observed with majorite garnet and casio 3 rich perovskite at pressures of about 20 22 gpa dissociation of ringwoodite to mgsio 3 rich perovskite and magnesiowustite mw was completed at 22 0 0 2 gpa according to matsui et al s periclase pressure scale and at 21 7 0 1 gpa according to shim et al s gold pressure scale majorite garnet persisted to about 24 gpa where pyrolite transformed to a lower mantle mineral assemblage i e mgsio 3 perovskite casio 3 rich perovskite and magnesiowustite thus majorite garnet coexists with the lower mantle assemblage at pressures of about 22 24 gpa in the quench experiments an assemblage of mgsio 3 perovskite magnesiowustite casio 3 rich perovskite and majorite garnet was synthesized at 22 5 gpa and 1600 c in which mg perovskite contained 2 8 wt al 2 o 3 and was significantly poorer in fe than coexisting magnesiowustite the fe mg partition coefficient between mg perovskite and magnesiowustite including ferric iron k app 0 27 0 06 is very close to that in the al free system which suggests that these p t conditions are in the vicinity of those of ringwoodite decomposition both the results of in situ x ray diffraction and quench experiments in the present study yield a convergent result that ringwoodite decomposes into mg perovskite and magnesiowustite before the garnet to perovskite transition at 1600 c in pyrolite the relation between the al content in mg perovskite and k app in pyrolite is non linear which is consistent with the fe mg partitioning between mg perovskite and magnesiowustite previously reported for a simpler mgo feo al 2 o 3 sio 2 system

on lunar asymmetries 1 tilted convection and crustal asymmetry 1 it is proposed that lunar crustal asymmetries are the result of convective processes acting early in the moon s history during the magma ocean phase and after synchronous rotation was established buoyant anorthositic crystals were transported to the farside by a large scale circulation called tilted convection known to occur spontaneously in chaotic convective systems the circulation was oriented toward the farside of the moon by a small temperature contrast produced by radiative thermal shielding due to the proximity of earth crustal thickening near the equator resulted from the modification of tilted convection by the coriolis force the anorthosite that was transported to the farside and equator may be a major cause of the observed crustal asymmetries and of the associated offset of the center of figure from the center of mass and bimodal hyposgram the selective transport may have resulted in a nearside excess of incompatible elements leading to the formation of the procellarium kreep terrane

an early lunar core dynamo driven by thermochemical mantle convection although the moon currently has no internally generated magnetic field palaeomagnetic data combined with radiometric ages of apollo samples provide evidence for such a magnetic field from 3 9 to 3 6 billion years gyr ago1 possibly owing to an ancient lunar dynamo1 2 but the presence of a lunar dynamo during this time period is difficult to explain1 2 3 4 because thermal evolution models for the moon5 yield insufficient core heat flux to power a dynamo after 4 2 gyr ago here we show that a transient increase in core heat flux after an overturn of an initially stratified lunar mantle might explain the existence and timing of an early lunar dynamo using a three dimensional spherical convection model6 we show that a dense layer enriched in radioactive elements a thermal blanket at the base of the lunar mantle can initially prevent core cooling thereby inhibiting core convection and magnetic field generation subsequent radioactive heating progressively increases the buoyancy of the thermal blanket ultimately causing it to rise back into the mantle the removal of the thermal blanket proposed to explain the eruption of thorium and titanium rich lunar mare basalts7 plausibly results in a core heat flux sufficient to power a short lived lunar dynamo

the role of magma buoyancy on the eruption of lunar basalts it has long been recognized that mare basalts on the moon are preferentially located both on the earth facing hemisphere and within large impact basins a popular model that accounts for this observation assumes that these magmas were denser than the lunar crust that they accumulated at the crust mantle interface and that eruptions occurred only when this magma chamber became overpressurized in this paper we re evaluate this model and argue that it is not consistent with the available data nor with models of dike propagation as an alternative hypothesis we propose that magma buoyancy is the predominant factor that determines whether mare basalts erupt at the surface or form crustal intrusions instead we have computed the densities of mare basaltic magmas and find that some are in fact less dense than the moon s upper anorthositic crust based on the widely accepted view that the lunar crust becomes more mafic with depth we also show that all mare basaltic magmas should be less dense than the lower portion of the crust thus if the upper anorthositic crust was regionally removed by an impact event then any mare basaltic magma could have risen to the surface there based on buoyancy considerations alone in support of this model we note that mare basalts are indeed found wherever geophysical crustal thickness models predict the upper crust to be absent furthermore many of the basalts that erupted within the anorthositic highlands are predicted to be less dense than the underlying crust based on remote sensing data the high titanium flows within oceanus procellarum are somewhat problematical to our model in that an anorthositic crust is predicted to be present beneath them using results from recent lunar thermal models we suggest that these magmas may have overcome their negative buoyancy in the crust by possessing superliquidus temperatures if magma buoyancy does indeed control whether or not a basaltic eruption will occur then this implies that the quantity of magma produced beneath the south pole aitken basin was about 10 times less than that of the nearside fl 2001 elsevier science b v all rights reserved

asymmetric thermal evolution of the moon 1 the moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres the most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the procellarum kreep terrane pkt and the mare basaltic lava flows that erupted in or adjacent to this terrane we model the thermochemical evolution of the moon using a 3 d spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the pkt on the moon s global evolution we find that in addition to localizing most of the melt production on the nearside such an enriched concentration of heat sources in the pkt crust has an influence down to the core mantle boundary and leaves a present day temperature anomaly within the nearside mantle moderate gravitational and topographic anomalies that are predicted in the pkt but not observed may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt

thermal core mantle coupling in an early lunar dynamo implications for a global magnetic field and magnetosphere of the early moon 1 a theoretical model suggests a short lived lunar dynamo driven by a mantle overturn forming crustal thickness dichotomy while the lunar paleomagnetic data and crustal magnetic fields suggest both of presence and absence of a global magnetic field of the moon 4 billion years gyr ago here we carry out numerical simulations of a possible lunar dynamo including effects of mantle overturn on heat flux heterogeneity at the core mantle boundary as a result the surface field intensity of the lunar dynamo is about 100 nt in this case a lunar magnetosphere could be present with a sunward size of 1 4 times the moon s radius considering the 4 6 gyr orbit evolution of the moon the magnetic field intensity and the magnetosphere size could be larger suggesting the lunar crustal magnetization acquired in the ancient dynamo field

delineating fracture zones using surface tunnel surface seismic data p s and s p mode conversions a surface tunnel surface seismic experiment was conducted at the aspo hard rock laboratoryto study the seismic response of major fracture systems intersecting the tunnel a newly developedthree com

the effect of ilmenite viscosity on the dynamics and evolution of an overturned lunar cumulate mantle lunar cumulate mantle overturn and the subsequent upwelling of overturned mantle cumulates provides a potential framework for understanding the first order thermochemical evolution of the moon upwelling of ilmenite bearing cumulates ibc after the overturn has a dominant influence on the dynamics and long term thermal evolution of the lunar mantle an important parameter determining the stability and convective behaviour of the ibc is its viscosity which was recently constrained through rock deformation experiments to examine the effect of ibc viscosity on the upwelling of overturned lunar cumulate mantle here we conduct three dimensional mantle convection models with an evolving core superposed by an ibc rich layer which resulted from mantle overturn after magma ocean solidification our modelling shows that a reduction of mantle viscosity by one order of magnitude due to the presence of ilmenite can dramatically change convective planform and long term lunar mantle evolution our model results suggest a relatively stable partially molten ibc layer that has surrounded the lunar core to the present day

magma source transition of lunar mare volcanism at 2 3 ga mare basalts provide insights into the composition and thermal history of the lunar mantle the ages of mare basalts suggest a first peak of magma activity at 3 2 3 8 ga and a second peak at 2 ga in this study we reassess the correlation between the titanium contents and the eruption ages of mare basalt units using the compositional and chronological data updated by selene kaguya using morphological and geological criteria we calculated the titanium content of 261 mare units across a representative area of each mare unit in the procellarum kreep terrane where the latest eruptions are located an increase in the mean titanium content is observed during the eratosthenian period as reported by previous studies we found that the increase in the mean titanium content occurred within a relatively short period near approximately 2 3 ga suggesting that the magma source of the mare basalts changed at this particular age moreover the high titanium basaltic eruptions are correlated with a second peak in volcanic activity near 2 ga the high titanium basaltic eruptions occurring during the last volcanic activity period can be explained by the three possible scenarios 1 the ilmenite bearing cumulate rich layer in the core mantle boundary formed after the mantle overturn 2 the basaltic material layers beneath the lunar crust formed through upwelling magmas and 3 ilmenite bearing cumulate blocks remained in the upper mantle after the mantle overturn

on lunar asymmetries 2 origin and distribution of mare basalts and mascons 1 a novel mechanism is proposed for the emplacement of mare basalts and the formation of mascons that does not involve melting or remelting of the source region the source magmas are the remnants of the primordial lunar magma ocean and are rich in incompatible elements including radioactive isotopes potassium rare earth elements and phosphorus kreep and volatiles exsolution of volatiles as the magmas cooled and crystallized a process called second boiling produced overpressures which drove the dense basalts upward to the surface creating the mascons this process occurred preferentially beneath nearside mare basins where the crust is thinnest and lithostatic pressure is lowest the delay between impact and magmatic extrusion reflects the time needed for the volatile rich magma to cool to its second boiling point radioactive heating buffered the magmas against cooling and solidification allowing for an extended period of magmatism

the tidal rotational shape of the moon and evidence for polar wander analysis of the moon s topography reveals that when its largest basins are removed the lunar shape is consistent with processes controlled by early earth tides and implies a reorientation of the moon s principal shape axes attempts to assess the various theories for the formation of the moon and to determine its true shape are complicated by the presence of several large basins on its surface that formed after the crust solidified here ian garrick bethell et al concentrate on the topography and gravity outside these basins and propose that the long wavelength shape of the moon has evolved through a combination of two early tidal processes first a crust building process controlled by early tidal heating throughout the moon and second the later development of a frozen tidal rotational bulge the authors also infer that an uneven distribution of internal density eventually reoriented the moon s polar axis by about 36 to the configuration that we see today the origin of the moon s large scale topography is important for understanding lunar geology1 lunar orbital evolution2 and the moon s orientation in the sky3 previous hypotheses for its origin have included late accretion events4 large impacts5 tidal effects6 and convection processes7 however testing these hypotheses and quantifying the moon s topography is complicated by the large basins that have formed since the crust crystallized here we estimate the large scale lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the spherical harmonic degree 2 topography is consistent with a crust building process controlled by early tidal heating throughout the moon the remainder of the degree 2 topography is consistent with a frozen tidal rotational bulge that formed later at a semi major axis of about 32 earth radii the probability of the degree 2 shape having both tidal heating and frozen shape characteristics by chance is less than 1 we also infer that internal density contrasts eventually reoriented the moon s polar axis by 36 4 to the configuration we observe today together these results link the geology of the near and far sides and resolve long standing questions about the moon s large scale shape gravity and history of polar wander

application of seismic velocity tomography in investigation of karst collapse hazards guangzhou china this paper describes seismic velocity tomography applied to the investigation and assessment of karst collapse hazards to facilitate accurate characterization of geological conditions of karst sinkhole formation in the survey areas of xiamao guangzhou china and huangchi foshan china seismic velocity tomography was used to explore the structures of rock and soil associated with karst collapse the results show that sand intercalated with clay or clay intercalated with soft soil dominates the cover of these two areas the overburden is 20 33 m thick and underlain by carboniferous limestone in the limestone there are well developed karst caves and cracks as well as highly fluctuating bedrock surfaces the seismic velocities are less than 2500 m s in the cover 2500 4500 m s in the karst fracture zones and caves of xiamao and 1500 2000 m s in the huangchi collapse area the karst fracture zones relief of bedrock surfaces and variations of soil thicknesses revealed by seismic velocity tomography are well constrained and in agreement with those in the drilling borehole profiles this paper demonstrates that seismic velocity tomography can delineate anomalies of rock and soil with the advantages of speed intuitive images and high resolution

evidence of chemical heterogeneity within lunar anorthosite parental magmas abstract lunar anorthosites are known for displaying a limited range of plagioclase an content an 94 to 98 here we demonstrate that plagioclase trace element variations from apollo ferroan anorthosites fan samples collected by the apollo 15 and 16 missions display more significant chemical heterogeneity e g chondrite normalized la sm 0 33 5 42 than previously reported we report mineral plagioclase pyroxene and olivine major and trace element abundances for a suite of apollo fan samples in addition to anorthositic clasts within apollo 16 regolith breccias this suite of data extends the compositional range currently reported for apollo anorthosites and for anorthositic clasts previously found within lunar meteorites petrological classifications of the regolith breccia clasts e g anorthosite versus noritic anorthosites cannot always be accurately assessed due to the limited size

origin of the lunar highlands mg suite an integrated petrology geochemistry chronology and remote sensing perspective the mg suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation this review examines the mineralogy geochemistry petrology chronology and the planetary scale distribution of this suite of highlands plutonic rocks presents models for their origin examines petrogenetic relationships to other highlands rocks and explores the link between this style of magmatism and early stages of lunar differentiation of the models considered for the origin of the parent magmas for the mg suite the data best fit a process in which hot solidus temperature at 2 gpa 1600 to 1800 c and less dense 3100 kg m3 early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn some decompressional melting would occur but placing a hot cumulate horizon adjacent to the plagioclase rich primordial crust and kreep rich lithologies at temperatures of 1300 c would result in the hybridization of these divergent primordial lithologies producing mg suite parent magmas as urkreep primeval kreep is not the petrologic driver of this style of magmatism outside of the procellarum kreep terrane pkt mg suite magmas are not required to have a kreep signature evaluation of the chronology of this episode of highlands evolution indicates that mg suite magmatism was initiated soon after primordial differentiation 10 m y alternatively the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust petrogenetic relationships between the mg suite and other highlands suites e g alkali suite and magnesian anorthositic granulites are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources

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

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

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

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

geologic evolution of the martian dichotomy in the ismenius area of mars and implications for plains magnetization 1 the origin of the martian dichotomy which divides highlands from lowlands is unknown we examine a section of the dichotomy 50 90e defined by steep scarps and normal faults stratigraphy and age relationships preclude the formation of the 2 5 km high boundary via erosion the abrupt disappearance of topographic knobs 300 500 km to the northeast is interpreted as a buried fault alignment of the buried fault with grabens stratigraphy and age determinations using crater counts indicate that the lowland bench is down faulted highlands crust the estimated local strain 3 5 and fault pattern are broadly consistent with gravitational relaxation of a plateau boundary magnetic and gravity anomalies occur on either side of the buried fault admittance analysis indicates isostatic compensation although nonunique a model with a 10 km thick intracrustal block under the lowland bench a 20 km thick block under the plains and an excess density of 200 kg m3 provides a good fit to the isostatic anomaly a good fit to a profile of the magnetic field perpendicular to the dichotomy is produced using uniformly polarized intracrustal blocks 10 20 km thick an intensity of 6 am m a field inclination of 30 and gaps aligned with the isostatic anomalies one interpretation is that high density intrusions demagnetized the crust after dynamo cessation and that low lying magnetized areas could be down faulted highlands crust another model inclination of 30 has magnetized crust beneath the isostatic anomalies separated by gaps the gaps could result from hydrothermal alteration of the crust along fault zones

localized pluton deformation and linked focused flow of low volume fraction residual melt in deforming plagioclase cumulates shear hosted sub cm to 50 m wide fe ti zr ree ftzr rich melt bands occur exclusively at folded margins of the bolangir anorthosite pluton eastern india transverse to margin parallel foliation in anorthosite the n to nnw trending ftzr melt bands are oriented at a low angle 90 fractionation of anorthosites from crustally contaminated high al gabbro hag parent melt at the high degree of crystal fractionation crystal content higher than the particle locking threshold the ftzr melts during last stages of crystallization were locked within the plagioclase dominated cumulus pile the occurrence of ftzr melt bands exclusively at folded as opposed to straight segments of pluton margin is attributed to melt enhanced strain localization in the pluton induced by the ftzr melts locked within anorthosite further melt induced straining led to focusing of the ftzr melts along dilatant shear zones formed synchronously with the east west shortening deformation the variable widths of the melt bands correspond to the varying sizes of actively deforming magmatic plagioclase in anorthosite the extraction and transport of locked in low volume fraction melt documented here suggest long duration far field stresses may segregate and transport large volumes of low volume fraction melts in planetary interior over considerable distance

wet subduction versus cold subduction 1 in situ x ray diffraction study of post spinel transformation in hydrous peridotite 2 wt h2o indicates that the phase boundary is shifted to higher pressures by 0 6 gpa relative to anhydrous peridotite at 1473 k whereas it shows no obvious shift at high temperature around 1873 k a linear equation for the boundary is p gpa 0 002 t k 26 3 which is applicable for temperatures below 1800 k the present data shows that a significant part of the depressions seen in the 660 km seismic discontinuity may be affected by existence of water it is also well resolved that the olivine wadsleyite phase transformation corresponding to the 410 km seismic discontinuity is shifted to lower pressures by 1 2 gpa by the addition of water thus the topography of seismic discontinuities in the transition zone associated with slabs can be attributed not only to cold subduction but also wet subduction

onset of solid state mantle convection and mixing during magma ocean solidification energy sources involved in the early stages of planetary formation can cause partial or even complete melting of the mantle of terrestrial bodies leading to the formation of magma oceans upon planetary cooling solidification is expected to take place from the bottom upwards because of the steeper slope of the liquid adiabat with respect to the liquidus elkins tanton 2012 solomatov 2015 fractional solidification in particular can lead to the formation of a compositional layering that can play a fundamental role for the subsequent long term dynamics and evolution of the interior tosi et al 2013 plesa et al 2014 in order to assess to what extent primordial compositional heterogeneities generated upon magma ocean solidification can be preserved we investigate the cooling and solidification of a whole mantle magma ocean along with the conditions that allow solid state convection to start mixing the mantle before solidification has completed to this end we run 2 d numerical simulations in cylindrical geometry using the finite volume code gaia huttig et al 2013 we treat the liquid magma ocean in a parametrized fashion while we self consistently solve the conservation equations of thermochemical convection in the growing solid mantle accounting for pressure temperature and melt dependent rheology we consider two end member cases fractional crystallization where melt is instantaneously extracted into the overlying liquid leaving beneath a differentiated mantle and batch crystallization where melt remains in contact with the silicate matrix throughout solidification causing no differentiation by testing the effects of different cooling rates and rayleigh numbers we show that for a lifetime of the liquid magma ocean between 1 and 10 myr lebrun et al 2013 the onset of solid state convection prior to complete mantle crystallization is possible and that part or even all of the compositional heterogeneities generated upon fractionation can be erased by efficient mantle stirring figure 1 we discuss the consequences of our findings in relation to the early and long term evolution of compositional heterogeneities generated via fractional crystallization of magma oceans in terrestrial bodies with emphasis on mars thermochemical history

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

water solubility in mg perovskites and water storage capacity in the lower mantle the water storage capacity of the major constituent of the lower mantle mg perovskite is a matter of debate here we report water solubility of mg perovskites with different compositions observed in peridotite and morb systems ir spectra of pure mgsio3 perovskite show bands at 3397 3423 3448 and 3482 cm 1 and suggest about 100 ppm h2o the h2o content in al mg perovskite 4 7 wt al2o3 mg 100 is 1000 1500 ppm major band at 3448 cm 1 whereas al fe mg perovskite in morb al2o3 13 17 wt mg 58 61 contains 40 110 ppm h2o major band at 3397 cm 1 the h2o content in al fe mg perovskite observed in peridotite al2o3 5 6 wt mg 88 90 is 1400 1800 ppm major band at 3397 cm 1 al fe mg perovskite from the morb system has a high fe3 content fe3 fe 0 6 determined by electron energy loss spectroscopy measurements water can enter into the perovskite structure with oxygen vacancies originating from the substitution of si by al and fe3 oxygen vacancy incorporation is favored for aluminous perovskite synthesized from the mgo rich peridotite system the substitution of si4 mg2 2 al fe 3 prevails however in the al fe mg perovskite from the morb system mgo poor al and fe rich explaining its restricted water solubility the maximum amount of water stored in the lower mantle is estimated to be 3 42 1021 kg which is 2 5 times the present ocean mass comparison of the phase relations in hydrous pyrolite and hydrous morb indicates that pyrolite is more important as water container and water carrier in the mantle pyrolite contains 1 dense hydrous magnesium silicates existing under conditions of subducting slabs and 2 hydrous wadsleyite hydrous ringwoodite and water bearing perovskite under the normal mantle and hotter conditions distribution of water to the morb is restricted at the conditions of the transition zone and lower mantle

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

degree 1 mantle convection and the crustal dichotomy on mars the surface of mars consists of an old heavily cratered and elevated southern hemisphere and younger resurfaced and depressed northern hemisphere a feature often termed the crustal dichotomy the global crustal structure zuber et al 2000 revealed by topography and gravity data from the mars global surveyor spacecraft and the possible late formation of the boundary zone between the hemispheres mcgill and dimitriou 1990 have been proposed to indicate an endogenic origin for the dichotomy however degree 1 mantle convection that is required for any endogenic process to be viable cannot be produced with conventional mantle convection models schubert et al 1990 we have studied the role of radially stratified viscosity on mantle deformation by using rayleigh taylor instability analyses in a spherical shell geometry our analyses reveal that when mantle viscosity is stratified with a weak asthenosphere deformation at long wavelengths is more efficient than that at short wavelengths the weaker the asthenosphere the longer the wavelength at which the deformation is the most efficient a thicker asthenosphere also favors the deformation at long wavelengths both the rayleigh taylor instability analyses and numerical modeling of mantle convection show that degree 1 convection can be produced within the martian mantle provided that the mantle had a weak asthenosphere v500 km thick and v10 2 times weaker than the underlying mantle early in planetary history the degree 1 convection causes preferential heating of one hemisphere that may explain the primary features associated with the dichotomy in crustal structure fl 2001 elsevier science b v all rights reserved

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

constraints on volatile concentrations of pre eruptive lunar magma abstract until recently the moon had long been thought to be depleted of volatiles such as h 2 o s co x and cl 2 researchers have recently measured volatile concentrations in the minerals glasses and inclusions of lunar samples and the results show that lunar rocks contain volatiles that are more similar to terrestrial materials than was previously thought mare basalts are located on the earth facing hemisphere in large impact basins and they are not representative of the feldspathic highlands thus it is likely that the density of lunar mafic magma exceeds that of the highland rocks based on buoyancy alone according to this observational fact we calculate the density of mare basalt to give a constraint for the maximum amount of water mare basalt can contain because water can effectively decrease the density of mare magma our result shows that water contained in the pre eruptive magma could not have been more than 1000 ppm otherwise the density of very low ti basaltic magma would be less than that of the highland rocks additionally if magma contains other species of volatiles such as c o s f or cl 2 the water in the pre eruptive magma would have to be much less than 1000 ppm because volatiles such as co 2 can effectively decrease the solubility of water in silicate melts based on these calculations on densities and a comparison with water in morb we conclude that the moon s water is not as great as has been recently suggested

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

correlation of deep moonquakes and mare basalts implications for lunar mantle structure and evolution abstract the genesis of mare basalts and deep moonquakes are important events that have major implications for understanding the thermal evolution and interior dynamics of the moon the eruption of mare basalts predominantly from 3 9 ga to 3 ga ago represents one of the most important events in lunar geological history deep moonquakes recorded by the apollo seismic network show the dynamic nature of the present day lunar mantle in this study we have correlated the presence of the mare basalts using feo concentration as a proxy with the epicenters of 52 well located deep moonquake dmq clusters we determine feo concentrations of 13 wt or higher to be representative of the mare basalt deposits our analysis shows that over 63 of the dmqs occur within 1 from the mare basalt deposits while over 80 of the dmqs are within 5 from the mare basalt deposits our analysis also shows that for the same amount of randomly distributed dmqs within a spherical cap on the nearside that encompasses all the nearside dmqs the probability of over 80 of the dmqs occurring within 5 from the mare basalt deposits is about 0 01 thus rejecting a random distribution of the dmqs with respect to the mare basalts the correlation between mare basalts and the dmqs from our analysis suggests that the mare basalts may be derived from melting processes at relatively large depths consistent with previous petrology and geodynamic studies we propose that the water and volatiles in the mare basalt source material i e a mixture of ilmenite cumulates and olivine orthopyroxene together called mic play an important role in causing the dmqs and that the dmqs delineate the present day locations of mic in the deep mantle since the mare basalts are predominately distributed on the nearside our results further suggest that the dmqs may indeed be largely nearside features which is a prediction that can be tested in future lunar seismic exploration

effect of mantle plumes on the growth of d by reaction between the core and mantle the core mantle boundary is a fundamental compositional discontinuity in the earth where molten iron alloy from the core meets solid silicate minerals from the mantle heat flow from the core to the mantle creates a thermal boundary layer at the base of the mantle at the same time chemical reactions may create a layer of different composition and density than the overlying mantle using a finite element model of convection in a spherical shell that includes formation of dense material at the base of the shell we investigate how a layer forms at the base of the mantle development of a layer at the base of the mantle by this method depends both on the composition of the material forming at the core mantle boundary and on the rate at which the material diffuses into the mantle if the material is less than 3 6 denser than the overlying mantle assuming reasonable choices of lower mantle thermodynamic parameters the reactant material will be swept away by upwelling plumes more dense material on the other hand forms an internally convecting layer that entrains material from above the varying thickness and composition of the layer is consistent with geophysical observations of the characteristics of the deep mantle

can tidal tomography be used to unravel the long wavelength structure of the lunar interior 1 the moon displays a number of hemispherically asymmetric features that may be related to long wavelength structure and dynamics in the lunar mantle here we propose to use observations of the non degree 2 gravitational response of the moon to degree 2 tidal forcing to constrain the long wavelength lunar mantle structure for a planetary body with laterally varying structure degree 2 tidal forces excite gravitational response at non degree 2 harmonics due to mode coupling effects using a new numerical model we determine that for a lunar mantle with 5 hemispherical variations in seismic shear wave velocityvs the degree 3 response could reach 2 of the degree 2 response the larger the hemispherical variations invs the larger the degree 3 response we suggest that if observations from recent lunar missions such as selena and grail could be used to determine the non degree 2 tidal response it might be possible to place constraints on the lunar mantle structure

a wet heterogeneous lunar interior lower mantle and core dynamo evolution while recent analyses of lunar samples indicate the moon had a core dynamo from at least 4 2 3 56 ga mantle convection models of the moon yield inadequate heat flux at the core mantle boundary to sustain thermal core convection for such a long time past investigations of lunar dynamos have focused on a generally homogeneous relatively dry moon while an initial compositionally stratified mantle is the expected consequence of a postaccretionary lunar magma ocean furthermore recent re examination of apollo samples and geophysical data suggests that the moon contains at least some regions with high water content using a finite element model we investigate the possible consequences of a heterogeneously wet compositionally stratified interior for the evolution of the moon we find that a postoverturn model of mantle cumulates could result in a core heat flux sufficiently high to sustain a dynamo through 2 5 ga and a maximum surface dipolar magnetic field strength of less than 1 t for a 350 km core and near 2 t for a 450 km core we find that if water was transported or retained preferentially in the deep interior it would have played a significant role in transporting heat out of the deep interior and reducing the lower mantle temperature thus water if enriched in the lower mantle could have influenced core dynamo timing by over 1 0 gyr and enhanced the vigor of a lunar core dynamo our results demonstrate the plausibility of a convective lunar core dynamo even beyond the period currently indicated by the apollo samples

a dynamic origin for the global asymmetry of lunar mare basalts we propose that the hemispheric asymmetry fig 1 of mare basalts may be explained as a result of hydrodynamic instabilities associated with a layer of mixed ilmenite rich cumulates ic and olivine orthopyroxene opx overlying a metallic core this mixed layer mic should form shortly after the solidification of the magma ocean p c hess and e m parmentier earth planet sci lett 134 1995 501 514 because of gravitational differentiation of chemically dense ic material that is expected to form below the anorthositic crust in the final stages of magma ocean crystallization a e ringwood and s e kesson proc lunar planet sci conf 7 1976 1697 1722 ic material is rich in heat producing elements and thermal expansion due to radiogenic heating causes the mic layer to become less dense than overlying mantle the time required for the mic layer to become thermally buoyant may explain a delay of mare volcanism until about 500 ma after solidification of the magma ocean our analyses of the resulting rayleigh taylor instability and numerical modeling of thermo chemical convection show that the instabilities produce spherical harmonic degree 1 thermal and compositional structure if a lunar metallic core is sufficiently small less than 250 km in radius fl 2000 elsevier science b v all rights reserved

formation and evolution of a lunar core from ilmenite rich magma ocean cumulates abstract in the absence of comprehensive seismic data coverage the size composition and physical state of the lunar core are still debated it has been suggested that a dense ilmenite rich layer which originally crystallised near the top of the lunar magma ocean may have sunk to the centre of the moon to form either an outer core surrounding a small metallic inner core or a complete core if the lunar metallic iron content is insignificant here we study the formation gravitational stability and thermal evolution of both an ilmenite rich outer core and a full ilmenite rich core using a two dimensional cylindrical thermo chemical convection model gravity acceleration in the lunar mantle decreases quickly with depth since the gravity acceleration directly influences the buoyancy of materials the low gravity acceleration near the centre was explicitly taken into account core formation and evolution were investigated by assessing the effects of varying two parameters the mg density and the internal heat production of the ilmenite rich layer varying these parameters changes the compositional and thermal buoyancy of the dense layer models show that a stable ilmenite rich outer core may indeed have formed in the lunar interior and that its density depends on the internal heating in and the mg of the ilmenite rich layer furthermore the sharpness of the core mantle boundary is shown to depend on the internal heat production in the ilmenite rich material surprisingly a higher internal heat production results in a sharper core mantle boundary and a higher ilmenite content in the core this is caused by lower viscosities as a result of higher temperatures although maximum core temperatures vary between different models by 700 1000 k around 2 gyr after the start of the models present day estimates vary by only about 350 500 k further narrowing of the range of internal heating values is essential for a better determination of both the present day lunar core temperature and its physical state

geophysical constraints on the lunar procellarum kreep terrane 1 the moon s procellarum kreep terrane pkt is distinguished by unique geochemistry and extended volcanic history previous thermal conduction models using enhanced radionuclide abundances in subcrustal potassium rare earth elements and phosphorus kreep predicted the existence of a contemporary upper mantle melt zone as well as heat flow consistent with apollo measurements here i show that such models also predict large gravity or topography anomalies that are not observed if the topography is suppressed by a rigid lithosphere it is possible to eliminate the gravity anomaly and still match heat flow by completely fractionating the excess radionuclides into a thin crust this implies that upper mantle heat sources for mare volcanism were spatially discontinuous or transient and that radionuclides defining the pkt are not necessarily directly related to mare volcanic sources however the mantle temperature of a crustally fractionated pkt is insufficient to match the observed electrical conductivity globally enhanced mantle heating or a thick megaregolith may be required alternatively upper mantle enrichment in iron hydrogen or aluminum can provide the requisite conductivity iron is the most plausible the derived lower limit to the upper mantle magnesium number 75 80 is consistent with seismic modeling regardless of the specific mechanism for electrical conductivity enhancement the overall excellent match to simple thermal conduction models indicates that the lunar upper mantle is not convecting at present

lateral heterogeneity of lunar volcanic activity according to volumes of mare basalts in the farside basins estimates for volumes of mare basalts are essential to understand the thermal conditions of the lunar mantle and its lateral heterogeneity in this study we estimated the thicknesses and volumes of mare basalts within five farside basins apollo ingenii poincare freundlich sharonov and mendel rydberg using pre mare craters buried by mare basalts and post mare craters that penetrated non penetrated mare basalts employing topographic and multiband image data obtained by selene kaguya furthermore using the grail crustal thickness model and the mare volumes estimated by this and previous studies we investigated the relationship between the volumes of the mare basalts and the crustal thicknesses the results suggest that the minimum crustal thicknesses within the basins were a dominant factor determining whether magma erupted at the surface and that the critical crustal thicknesses for magma eruption were 10 km on the farside and 20 km on the nearside the total areas of the regions in which magmas could erupt at the surface are 10 times larger on the nearside than on the farside a comparison between the mare volumes within the mare basins on the nearside and the farside shows that magma production in the farside mantle might have been 20 times smaller than that in the nearside mantle implying a stronger dichotomy than previously estimated these results suggest that the mare hemispherical asymmetry should be attributed to both the difference in the crustal thickness distribution and the difference in the quantity of magma production between the nearside and farside mantles

distinct oxygen isotope compositions of the earth and moon the virtually identical oxygen isotope compositions of the earth and moon revealed by apollo return samples have been a challenging constraint for lunar formation models for a giant impact scenario to explain this observation either the precursors to the earth and moon had identical oxygen isotope values or extensive homogenization of the two bodies occurred following the impact event here we present high precision oxygen isotope analyses of a range of lunar lithologies and show that the earth and moon in fact have distinctly different oxygen isotope compositions oxygen isotope values of lunar samples correlate with lithology and we propose that the differences can be explained by mixing between isotopically light vapour generated by the impact and the outermost portion of the early lunar magma ocean our data suggest that samples derived from the deep lunar mantle which are isotopically heavy compared to earth have isotopic compositions that are most representative of the proto lunar impactor theia our findings imply that the distinct oxygen isotope compositions of theia and earth were not completely homogenized by the moon forming impact thus providing quantitative evidence that theia could have formed farther from the sun than did earth high precision measurements suggest that the earth and moon have distinct oxygen isotope compositions this implies distinct oxygen isotopic compositions of the proto earth and its impactor that were not fully homogenized by the moon forming impact

the effect of water on mantle phase transitions water has played an important role in the earth s evolution the incorporation of water as hydroxyl into solid mineral phases or as coexisting hydrous fluids and melts affects the chemical and physical properties of crust and mantle constituents i e it weakens rocks and minerals reduces viscosity and strength of the materials and depresses dramatically the melting temperature of silicate minerals e g karato 1990 inoue 1994 hirth and kohlstedt 1996 chen et al 1998 kubo et al 1998 mei and kohlstedt 2000 many recent studies have suggested the possible existence of water in the earth s mantle especially in the transition zone e g smyth and frost 2002 ohtani et al 2004 litasov et al 2005a hae et al 2006 where wadsleyite and ringwoodite can accommodate up to 3 wt of h2o in their structures e g kohlstedt et al 1996 low velocity zones observed seismologically at the top of the 410 km discontinuity may indicate the existence of trapped high density melt e g revenaugh and sipkin 1994 song et al 2004 matsukage et al 2005 sakamaki et al 2006 which is likely to be hydrous as it is not possible to melt the base of the upper mantle without water at these conditions electrical conductivity anomalies in the upper mantle and transition zone that are related to subduction zones have also been interpreted as an effect of water in the mantle e g fukao et al 2004 tarits at el 2004 hae et al 2006 koyama et al 2006 studies of the kinetics of the hydrous olivine wadsleyite transformation ohtani et al 2004 hosoya et al 2005 seem to be consistent with seismological observations e g koper et al 1998 that indicate the absence of a metastable olivine wedge in subducting

low degree mantle convection with strongly temperature and depth dependent viscosity in a three dimensional spherical shell 1 a series of numerical simulations of thermal convection of boussinesq fluid with infinite prandtl number with rayleigh number 10 7 and with the strongly temperature and depth dependent viscosity in a three dimensional spherical shell is carried out to study the mantle convection of single plate terrestrial planets like venus or mars without an earth like plate tectonics the strongly temperature dependent viscosity the viscosity contrast across the shell is 10 5 makes the convection under stagnant lid short wavelength structures numerous cylindrical upwelling plumes are developed because of the secondary downwelling plumes arising from the bottom of lid this convection pattern is inconsistent with that inferred from the geodesic observation of the venus or mars additional effect of the stratified viscosity at the upper lower mantle the viscosity contrast is varied from 30 to 300 are investigated it is found that the combination of the strongly temperature and depth dependent viscosity causes long wavelength structures of convection in which the spherical harmonic degree l is dominant at 1 4 the geoid anomaly calculated by the simulated convections shows a long wavelength structure which is compared with observations the degree one l 1 convection like the martian mantle is realized in the wide range of viscosity contrast from 30 to 100 when the viscosity is continuously increased with depth at the lower mantle

thermal evolution of a thicker kreep liquid layer we consider the thermal evolution of the thickened potassium rare earth element and phosphorous kreep liquid layer that extends over a significant fraction of the lunar nearside with a prescribed thickness and heat production and beneath an insulating anorthosite crust this layer represents a subcrustal heat source beneath the procellarum imbrium terrane and may be responsible for the localized and anomalous enrichments of highly incompatible elements in this terrane in some models this thickened liquid layer is the thermal source for the remelting of mare basalts and also produces the parent magmas of the magnesian suite indeed a kreep liquid layer thickened from 5 to 10 km with more than 200 times chondritic heat producing elements does not continue to cool but undergoes a reheating and grows in thickness by dissolving several times its mass of anorthosite and ultramafic cumulates however such a liquid layer cannot give rise to the parent magmas to the magnesian suite because it cannot account for the extraordinarily high incompatible element content the primitive major element content or the positive end of the magnesian suite this growing layer will also form an impenetrable barrier to the eruption of mare basalts and is generally inconsistent with a number of geophysical constraints of the moon specifically the existence of mascons subsequent to the basin filling by mare basalts a thickened kreep liquid layer can however explain the asymmetry in the distribution of kreep rich rock on the lunar crust such a kreep layer must be efficiently cooled and be quickly solidified to avoid some of the difficulties described above a thinned anorthosite crust would allow efficient heat loss and induce crystallization of such a layer early in lunar history

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

a flow law for ilmenite in dislocation creep implications for lunar cumulate mantle overturn we present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite the flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures using the flow law we predict that lunar ilmenite bearing cumulates ibc will be weakened by the presence of low viscosity ilmenite dense low viscosity ibc are expected to flow into the lunar interior by a process known as cumulate mantle overturn low viscosity ibc that sink to the core mantle boundary may be dynamically stable with respect to upwelling a hot stable layer of ibc surrounding the lunar core would suppress the development of a core dynamo a layer of partially molten ibc can also explain the inferred zone of seismic attenuation around the lunar core as well as a low viscosity layer suggested by tidal dissipation

wet and gassy zones in a municipal landfill from p and s wave velocity fields abstract the knowledge of the distribution of leachate and gas in a municipal landfill is of vital importance to the landfill operators performing improved landfill treatments and for environmental protection and efficient biogas extraction we have explored the potential of using the velocity fields of seismic s and p waves to delineate the wet and gassy relatively dry gas air filled zones inside a landfill we have analyzed shallow s and p wave reflection data and seismic surface wave data acquired at a very heterogeneous landfill site where biogas was extracted a joint interpretation of the independently estimated velocity fields from these various approaches has allowed us to localize anomalously low and high velocity zones in the landfill from the complementary information provided by p and s wave velocity fields we have inferred the leachate bearing wet zones and the gassy zones inside the landfill independent measurements of gas flow and mechanical tip resistance to waste deformation va

os pb and nd isotope geochemistry of the permian emeishan continental flood basalts insights into the source of a large igneous province abstract the nature of the source of continental flood basalts cfb is a highly debated topic proposed mantle sources for cfbs including both high and low ti basalts include subcontinental lithospheric mantle sclm asthenospheric mantle and deep plume related mantle re os isotope systematics can offer important constraints on the sources of both ocean island basalts oib and cfb and may be applied to distinguish different possible melt sources this paper reports the first re os isotope data for the late permian emeishan large igneous province lip in southwest china twenty one cfb samples including both low and high ti basalts from five representative sites within the emeishan lip have been analyzed for os nd and pb isotopic compositions the obtained os data demonstrate that crustal assimilation affected os isotopic compositions of some emeishan basalt samples with low os concentrations but not all of the samples and the emeishan basalts with high os contents likely experienced the least crustal contamination the low and high ti basalts yield distinct os signatures in terms of 187os 188os and os content the low ti basalt with the highest os concentration 400 ppt has a radiogenic os isotopic composition os t 6 5 similar to that of plume derived oib because the os isotopic composition of basalts with relatively high os concentrations typically 50 ppt likely represents that of their mantle source this result implies a plume derived origin for the low ti basalts on the other hand the high ti basalts with high os concentration over 50 ppt have unradiogenic os isotopic signatures os t values range from 0 8 to 1 4 suggesting that a subcontinental lithosphere mantle sclm component most likely contributed to the generation of these magmas combining pb and nd isotopic tracers with the os data we demonstrate that the low ti basaltic magmas in the emeishan cfb were mainly sourced from a mantle plume reservoir whereas the high ti basaltic magmas were most likely derived from a sclm reservoir or were contaminated by a significant amount of lithospheric mantle material during plume related magma ascent through the sclm

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

isostasy of the moon from high resolution gravity and topography data implication for its thermal history 1 the lunar prospector line of sight acceleration data after terrain correction have been inverted to the high resolution bouguer gravity anomalies of the lunar nearside lithospheric thicknesses of the early moon were investigated by comparing the gravity anomalies of craters and impact basins of various dimensions the lithosphere was already thick enough to support craters with diameters up to 300 km in the pre nectarian and nectarian periods degree of isostatic compensation of larger impact basins suggested lithospheric thickness of 20 60 km at that time which depended more on localities rather than age differences

timing of mantle overturn during magma ocean solidification abstract solidification of magma oceans mos formed early in the evolution of planetary bodies sets the initial condition for their evolution on much longer time scales ideal fractional crystallization would generate an unstable chemical stratification that subsequently overturns to form a stably stratified mantle the simplest model of overturn assumes that cumulates remain immobile until the end of mo solidification however overturning of cumulates and thermal convection during solidification may act to reduce this stratification and introduce chemical heterogeneity on scales smaller than the mo thickness we explore overturning of cumulates before the end of mo crystallization and the possible consequences for mantle structure and composition in this model increasingly dense iron rich layers crystallized from the overlying residual liquid mo are deposited on a thickening cumulate layer overturn during solidification occurs if the dimensionless parameter r c measuring the ratio of the mo time of crystallization m o to the timescale associated with compositional overturn o v g h exceeds a threshold value if overturn did not occur until after solidification this implies that the viscosity of the solidified mantle must have been sufficiently high possibly requiring efficient melt extraction from the cumulate for a given rate of solidification for the lunar mo possible implications for the generation of the mg suites and mare basalt are suggested

degree one mantle convection dependence on internal heating and temperature dependent rheology 1 geophysical and geological observations suggest that a degree one mantle flow pattern consisting of one upwelling and one downwelling may have existed at some time in the mantles of mars the moon and perhaps even for the earth during times of supercontinent formation simple fluid experiments utilizing isoviscous rheologies predict shorter wavelength flow patterns and it is therefore important to determine fluid dynamical parameter sets which lead to larger wavelength flow patterns consistent with observations we perform a series of numerical fluid dynamics calculations in a spherical 3 d geometry in which we vary rayleigh number rheological activation parameter and the degree of internal heating in order to define which parameter choices can lead to degree one mantle convection we find that increasing the degree of internal heating increases the interior temperature of the mantle which leads to a larger viscosity contrast across the top thermal boundary layer and that degree one mantle flow occurs only in cases which exhibit internal heating utilize activation coefficients which lead to 103 or higher viscosity contrasts across the mantle and have viscosity contrasts across the top thermal boundary layer within the range of 200 3000

self consistent generation of single plume state for enceladus using non newtonian rheology the thermal dichotomy of enceladus suggests an asymmetrical structure in its global heat transfer so far most of the models proposed that obtained such a distribution have prescribed an a priori asymmetry i e some anomaly in or below the south polar ice shell we present here the first set of numerical models of convection that yield a stable single plume state for enceladus without prescribed mechanical asymmetry using the convection code stagyy in a 2 d spherical annulus geometry we show that a non newtonian ice rheology is sufficient to create a localized single hot plume surrounded by a conductive ice mantle we obtain a self sustained state in which a region of small angular extent has a sufficiently low viscosity to allow subcritical to weak convection to occur due to the stress dependent part of the rheological law we find that the single plume state is very unlikely to remain stable if the rheology is newtonian confirming what has been found by previous studies in a second set of numerical simulations we also investigate the first order effect of tidal heating on the stability of the single plume state tidal heating reinforces the stability of the single plume state if it is generated in the plume itself lastly we show that the likelihood of a stable single plume state does not depend on the thickness of the ice shell

thermal and magmatic evolution of the moon as with all science our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data this process invigorates the intellectual foundation on which old models are tested and new concepts are built just as the application of new observational tools to lunar science in 1610 galileo s telescope and 1840 photography yielded breakthroughs concerning the true nature of the lunar surface the computational and technological advances highlighted by the apollo and post apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the moon 1 1 pre apollo view of the thermal and magmatic evolution of the moon many of the early views of the moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the sun and the moon prophetically myths involving the lunar deities mwuetsi from zimbabwe and coyolxauhqui from mexico told of rather violent or catastrophic events in which the moon was expunged from the earth numerous ancient scientific observations were made about the nature of the moon ranging from those uncovered in early neolithic sites that correctly identified mare crisium and mare humorum to the insights made by greek philosophers such as anaxagoras ca 500 428 b c and democritus ca 460 370 b c who attached terrestrial analogues to its character stone mountains with the advent of the telescope 1610 and photography 1840 as scientific tools for lunar exploration semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation initially modern terrestrial geological analogs were extended to the moon lunar highlands volcanic craters seas combined with the rigors of computational modeling these observational data were extended to predict the original thermal state of the moon and its thermal and magmatic history its proximity to the earth

subsurface morphology and scaling of lunar impact basins impact bombardment during the first billion years after the formation of the moon produced at least several tens of basins the gravity recovery and interior laboratory grail mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions allowing for detailed subsurface and morphological analyses to be made across the entire globe grail derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins which represents a less unambiguous measure of a basin size than those based on topographic features the formation of lunar impact basins was modeled numerically by using the isale 2d hydrocode with a large range of impact and target conditions typical for the first billion years of lunar evolution in the investigated range of impactor and target conditions the target temperature had the dominant effect on the basin subsurface morphology model results were also used to update current impact scaling relationships applicable to the lunar setting based on assumed target temperature our new temperature dependent impact scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by grail as the formation of lunar impact basins is associated with the first approximately 700 myr of the solar system evolution when the impact flux was considerably larger than the present day our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the moon and terrestrial planets in the early solar system

the timeline of the lunar bombardment revisited abstract the timeline of the lunar bombardment in the first gy of solar system history remains unclear basin forming impacts e g imbrium orientale occurred 3 9 3 7 gy ago i e 600 800 my after the formation of the moon itself many other basins formed before imbrium but their exact ages are not precisely known there is an intense debate between two possible interpretations of the data in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail end here we revisit the work of morbidelli et al 2012 that examined which scenario could be compatible with both the lunar crater record in the 3 4 gy period and the abundance of highly siderophile elements hse in the lunar mantle we use updated numerical simulations of the fluxes of asteroids comets and planetesimals leftover from the planet formation process under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation we conclude that only the cataclysm scenario can explain the data the cataclysm should have started 3 95 gy ago however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization due to iron sulfide exsolution o neil 1991 rubie et al 2016 we show that this is likely true also for the moon if mantle overturn is taken into account based on the hypothesis that the lunar magma ocean crystallized about 100 150 my after moon formation elkins tanton et al 2011 and therefore that hses accumulated in the lunar mantle only after this timespan we show that the bombardment in the 3 4 gy period can be explained in the accretion tail scenario this hypothesis would also explain why the moon appears so depleted in hses relative to the earth we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars the accretion tail scenario requires a global resurfacing event on mars 4 4 gy ago possibly associated with the formation of the borealis basin and it is consistent with the hse budget of the planet moreover it implies that the noachian and pre noachian terrains are 200 my older than usually considered

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

excavation of the lunar mantle by basin forming impact events on the moon abstract global maps of crustal thickness on the moon derived from gravity measurements obtained by nasa s gravity recovery and interior laboratory grail mission have shown that the lunar crust is thinner than previously thought hyperspectral data obtained by the kaguya mission have also documented areas rich in olivine that have been interpreted as material excavated from the mantle by some of the largest lunar impact events numerical simulations were performed with the isale 2d hydrocode to investigate the conditions under which mantle material may have been excavated during large impact events and where such material should be found the results show that excavation of the mantle could have occurred during formation of the several largest impact basins on the nearside hemisphere as well as the moscoviense basin on the farside hemisphere even though large areas in the central portions of these basins were later covered by mare basaltic lava flows surficial lunar mantle deposits are predicted in areas external to these maria our results support the interpretation that the high olivine abundances detected by the kaguya spacecraft could indeed be derived from the lunar mantle

a 3 d numerical study of the thermal evolution of the moon after cumulate mantle overturn the importance of rheology and core solidification 1 models in which the mantle of the moon evolves from an initially stratified state following magma ocean solidification and overturn have been applied to address important features of long term thermal evolution of the moon including convective instability of overturned ilmenite bearing cumulates ibc at the lunar core mantle boundary generation of mare basalts core sulfur content and inner core radius paleomagnetism and the present day mantle structure whether a dense overturned ibc rich layer at the bottom of the mantle can become thermally unstable to generate a single upwelling is controlled largely by the temperature dependence of viscosity the activation energy convective instability of the ibc rich layer controls the heat flux out the core and the presence of an internally generated magnetic field a long period of 700 ma high positive core mantle boundary cmb heat flux after the instability of the ibc rich layer is expected from our models present day deep mantle temperatures inferred from seismic and gravitational inversion constrain the magnitude of mantle viscosity from 5 1019 to 1 1021 pa s the cmb temperature and solidified inner core radius inferred from seismic reflection constrain the core sulfur content our evolution models with 5 10 wt sulfur content can produce the observed 240 km radius inner core at the present day the asymmetrical distribution of the deep moonquakes only in the nearside mantle could be explained as the remnant structure of the single chemical upwelling generated from ibc rich layer our evolution model after the overturn results in an early 0 55 km expansion in radius for 1000 ma due to the radiogenic heating associated with ibc in the deep mantle and may provide a simple explanation for the early expansion inferred from the gravity recovery and interior laboratory mission

modeling the tonga slab can travel time data resolve a metastable olivine wedge we present the results of detailed modeling of the tonga slab with the goals of determining whether high resolution travel time data 1 can be fit by simple thermal and petrological slab models and 2 can resolve a metastable olivine wedge at depths greater than the equilibrium olivine spinel phase boundary we model arrival times recorded by a 1000 km line of 23 ocean bottom seismometers obs and island broadband seismic stations extending from the lau backarc basin across the tonga trench and onto the pacific plate the data consist of 388 local p wave travel times from 17 deep and 3 intermediate earthquakes recorded during the 3 month obs deployment in late 1994 we locate the events using both local and teleseismic arrival times and apply a relocation operator to the theoretical travel times to simulate the biases introduced in the data by locating the events with a reference earth model the modeling consists of grid searches using a three dimensional finite difference algorithm to compute local first arriving travel times for equilibrium and metastable p wave velocity models constructed from thermal mineralogical and morphological constraints the travel time anomalies are well fit by standard slab thermal models and p velocity temperature derivatives of 0 4 to 0 3 ms 1 c 1 forward calculations indicate that the presence of a metastable olivine wedge has a subtle effect on the travel times due to the tendency of first arriving waves to avoid the low velocity region wedge velocity models provide a slightly better fit to the data than equilibrium models but f tests indicate the improvement is not significant at the 95 level our results suggest that providing direct seismological evidence of a wedge of metastable olivine in subduction zones will require either waveform modeling or the observation of later arriving phases created by the depressed phase boundary

lunar heat flow regional prospective of the apollo landing sites 1 we reexamine the apollo heat flow experiment in light of new orbital data using three dimensional thermal conduction models we examine effects of crustal thickness density and radiogenic abundance on measured heat flow values at the apollo 15 and 17 sites these models show the importance of regional context on heat flux measurements we find that measured heat flux can be greatly altered by deep subsurface radiogenic content and crustal density however total crustal thickness and the presence of a near surface radiogenic rich ejecta provide less leverage representing only minor 1 5 mw m 2 perturbations on surface heat flux using models of the crust implied by gravity recovery and interior laboratory results we found that a roughly 9 13 mw m 2 mantle heat flux best approximate the observed heat flux this equates to a total mantle heat production of 2 8 4 1 1011 w these heat flow values could imply that the lunar interior is slightly less radiogenic than the earth s mantle perhaps implying that a considerable fraction of terrestrial mantle material was incorporated at the time of formation these results may also imply that heat flux at the crust mantle boundary beneath the procellarum potassium rare earth element and phosphorus kreep terrane pkt is anomalously elevated compared to the rest of the moon these results also suggest that a limited kreep rich layer exists beneath the pkt crust if a subcrustal kreep rich layer extends below the apollo 17 landing site required mantle heat flux can drop to roughly 7 mw m 2 underlining the need for future heat flux measurements outside of the radiogenic rich pkt 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

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

gravitational differentiation due to initial chemical stratification origin of lunar asymmetry by the creep of dense kreep abstract models for the evolution of the moon must explain a number of important characteristics of its magmatic history primary among them is the emplacement of mare basalts primarily on one side of the moon and in a region of the surface roughly correlating with that containing high subsurface concentrations of kreep it is thus important to explore mechanisms which will regionally concentrate a kreep layer early in lunar evolution and which 400 500 myr later give rise to mare basalt generation beneath the same region gravitational instability of a chemically dense ilmenite rich cumulate created during the fractionation of an anorthositic crust is one candidate model if so gravitational instability must occur at long wavelength to explain the hemispheric asymmetry we examine the rayleigh taylor instability of a dense layer near the surface of a sphere representing the lunar mantle in which the viscosity varies with depth our results show that spherical harmonic degree 1 is the fastest growing wavelength of instability if the viscosity of the dense layer is sufficiently low relative to that of the deeper mantle or if the viscosity of the mantle increases with depth however the viscosity increase cannot be distributed over a depth that is too large we explore whether a residual kreep like layer near the base of anorthositic crust might give rise to these needed conditions

crosshole seismic tomography and borehole logging for engineering site characterization in sikeston mo usa abstract this paper presents a geophysical investigation performed in the median separating the east and west bound lanes of u s highway 60 approximately 15 km west from the town of sikeston mo usa two boreholes drilled at depth of 45 m approximately located 6 m from the wahite ditch bridge in u s highway 60 were used to carry out the geophysical tests the objective of the survey was to obtain the density distribution of soil materials and high resolution compressional and shear wave velocities of the shallow subsurface for computation of elastic engineering properties of the unconsolidated material interposed between the two investigated boreholes the studied site is located in the new madrid seismic zone nmsz one of the major seismic source zones in the eastern united states although no major seismic events have occurred in the new madrid area since the catastrophic earthquakes of 1811 1812 more intensive studies in this area are required to better understand the local soil effects and the liquefaction potential of unconsolidated earth materials on strong ground motion joint interpretation of borehole logs and velocity images obtained by p and s wave traveltime inversions outlined shallow anomalies which were interpreted as caused by variation in relative porosity and compactness of saturated unconsolidated soil materials in the interval between 17 and 19 m of depth a velocity anomaly with distinct characteristics is recognized analysis of traveltimes of p wave energy propagated from common source receiver depth positions at that depth interval delineated a low velocity zone lower than estimated p wave velocity in water in which propagated s wave energy was negligible analysis of porosity logs did not outline any porosity anomaly for that region the anomaly is interpreted as caused by the presence of a gas bearing zone extending for 1 5 m 0 76 m from the top and the bottom of the depth interval through which propagation of shear energy was almost prevented and compressional energy traveled a very low speed relative lower values of shear modulus were computed for the gas bearing zone the same depth interval also exhibited relative lower values of bulk modulus relative higher values of compressibility and relative high porosity however the low velocity anomaly is not caused by relative increased porosity but rather to replacement of water by gas in the pore volumes of this zone the presence of a shallow thin gas bearing zone is interpreted as hazardous in the occurrence of strong motion in the new madrid seismic zone shallow water table as detected by seismic and log measurements in the area increases the risk of liquefaction of the sampled soil under strong ground motions

inferring earth structure from combined measurements of rotational and translational ground motions we introduce a novel variant of seismic tomography that is based on colocated measurements of rotational and translational ground motions our aim is to assess whether rotations may be incorporated successfully into seismic inverse problems to produce better resolved and more realistic tomographic images our methodology is based on the definition of apparent s wave speed as the ratio of rms velocity and rotation amplitudes the principal advantages of this definition are that 1 no traveltimes measurements are needed and 2 the apparent s wave speed is independent of source magnitude and source timing we derive finite frequency kernels for apparent s wave speed by using a combination of the adjoint method and ray approximation the properties of these kernels as a function of frequency bandwidth can be illustrated along with their usefulness for seismic tomography in multifrequency synthetic inversions we consider local crosshole tomography and regional scale earthquake tomography our results indicate that s wave speed variations can be retrieved accurately from colocated rotation and translation measurements suggesting that our methodology is a promising extension of conventional seismic tomography further apparent s wave speed can be used to increase vertical resolution in teleseismic tomography for local structures

testing the axial dipole hypothesis for the moon by modeling the direction of crustal magnetization orbital magnetic field data show that portions of the moon s crust are strongly magnetized and paleomagnetic data of lunar samples suggest that earth strength magnetic fields could have existed during the first several hundred million years of lunar history the origin of the fields that magnetized the crust are not understood and could be the result of either a long lived core generated dynamo or transient fields associated with large impact events core dynamo models usually predict that the field would be predominantly dipolar with the dipole axis aligned with the rotation axis we test this hypothesis by modeling the direction of crustal magnetization using a global magnetic field model of the moon derived from lunar prospector and kaguya magnetometer data we make use of a model that assumes that the crust is unidirectionally magnetized the intensity of magnetization can vary with the crust and the best fitting direction of magnetization is obtained from a nonnegative least squares inversion from the best fitting magnetization direction we obtain the corresponding north magnetic pole predicted by an internal dipolar field some of the obtained paleopoles are associated with the current geographic poles while other well constrained anomalies have paleopoles at equatorial latitudes preferentially at 90 east and west longitudes one plausible hypothesis for this distribution of paleopoles is that the moon possessed a long lived dipolar field but that the dipole was not aligned with the rotation axis as a result of large scale heat flow heterogeneities at the core mantle boundary

timescale of overturn in a magma ocean cumulate abstract the formation and differentiation of planetary bodies are thought to involve magma oceans stages we study the case of a planetary mantle crystallizing upwards from a global magma ocean in this scenario it is often considered that the magma ocean crystallizes more rapidly than the time required for convection to develop in the solid cumulate this assumption is appealing since the temperature and composition profiles resulting from the crystallization of the magma ocean can be used as an initial condition for convection in the solid part we test here this assumption with a linear stability analysis of the density profile in the solid cumulate as crystallization proceeds the interface between the magma ocean and the solid is a phase change interface convecting matter arriving near the interface can therefore cross this boundary via melting or freezing we use a semi permeable condition at the boundary between the magma ocean and the solid to account for that phenomenon the timescale with which convection develops in the solid is found to be several orders of magnitude smaller than the time needed to crystallize the magma ocean as soon as a few hundreds kilometers of cumulate are formed on a mars to earth size planet the phase change boundary condition is found to decrease this timescale by several orders of magnitude for a moon size object the possibility of melting and freezing at the top of the cumulate allows the overturn to happen before complete crystallization the convective patterns are also affected by melting and freezing at the boundary the linearly most unstable mode is a degree 1 translation mode instead of the approximately aspect ratio one convection rolls found with classical non penetrative boundary conditions the first overturn of the crystallizing cumulate on mars and the moon could therefore be at the origin of their observed degree 1 features