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

geochemistry genesis and health implications of fluoriferous groundwaters in the upper regions of ghana the most appropriate and widely used source of drinking water for the populations of the upper regions of ghana is groundwater in general groundwater quality is acceptable except for some parts of the bolgatanga and bongo districts where there are occurrences of elevated levels of natural groundwater fluoride concentrations of groundwater fluoride in excess of the world health organization who maximum guideline value 1 5 mg l in the bongo area have been known since 1978 however the effect of fluoride on people ingesting the water did not receive public and medical attention until october 1993 when health personnel were asked to investigate the cause of stained teeth in school children the investigation established that 62 of the total population of school children in the bongo area had dental fluorosis against this background a study was initiated to understand the geochemistry genesis and distribution of fluoride in relation to the geology of the area groundwater fluoride in the upper regions ranges from 0 11 to 4 60 ppm with the highest concentrations associated with the fluorine enriched bongo coarse grained hornblende granite and syenite suite the source of groundwater fluoride within the bongo granitoids is dissolution of the mineral fluorite and dissolution of and anion exchange with micaceous minerals and their clay products applying the who recommended guideline values for fluoride in drinking water reveals that 49 of wells in the area deliver water below the optimum level of 0 5 mg l f these populations are thus prone to dental caries twenty eight percent of the wells fall within the optimum interval for good dental health 0 5 1 5 mg l f twenty three percent of the wells have concentrations above the recommended maximum guideline limit of 1 5 mg l f this population is susceptible to dental and possibly skeletal fluorosis climatic conditions of the area suggest that the individual water consumption is in the order of 3 to 4 l which is higher than the who estimate of 2 l adult day in addition dietary intake for the upper region population is probably higher than who baseline values 0 2 0 5 mg day this implies that a much higher population is susceptible to developing dental and skeletal fluorosis than originally suspected geochemical symbol plot maps help geochemists understand factors controlling the distribution and uptake of fluoride in the upper regions but they are of minimal value to health officials responsible for planning epidemiological studies and dental health education programs in the region by casting fluoride data into contoured geochemical health risk maps using intake interval guidelines more closely aligned to regional climatic and dietary conditions health officals can better judge the impacts regional and population based of fluoride on segments of the population such as various sex and age groups

zircon lu hf systematics and the evolution of the archean crust in the southern superior province canada a combined lu hf and u th pb isotopic study was made of 25 zircons and 2 whole rocks from the late archean crust 2 888 2 668 ma in the southern superior province canada the relative abundances of u th lu and hf in zircons from the low grade michipicoten and gamitagama greenstone belts show variable patterns which in part reflect the bulk compositional differences of their parent rocks zircons from the high grade lower crustal regions adjacent to these belts kapuskasing structural zone are distinguished from the low grade zircons by their strong depletions of lu and hf the low hf contents imply that the growth of metamorphic zircon involves a significant fractionation of the zr hf ratio

isotopic and ree studies of lunar basalt 12038 implications for petrogenesis of aluminous mare basalts we report sr nd and sm isotopic studies of lunar basalt 12038 one of the so called aluminous mare basalts a precise internal rb sr isochron yields a crystallization age of 3 35 0 09 ae and initial87sr 86sr 0 69922 2 2 error limits 1ae 109 years 87rb 0 0139ae 1 an internal sm nd isochron yields an age of 3 28 0 23ae and initial143nd 144nd 0 50764 28 present day143nd 144nd is less than the chondritic value i e nd 0 2 3 0 4 where nd is the deviation of143nd 144nd from chondritic evolution expressed as parts in 104 at the time of crystallization nd 3 2ae 1 5 0 6 we have successfully modeled the evolution of the sr and nd isotopic compositions and the ree abundances within the framework of our earlier model for apollo 12 olivine pigeonite and ilmenite basalts the isotopic and trace element features of 12038 can be modeled as produced by partial melting of a cumulate mantle source which crystallized from a lunar magma ocean with a chondrite normalized ree pattern of constant negative slope chondrite normalized la yb 2 2 for this hypothetical magma ocean pattern a plot of i sr versus nd for the apollo 12 basalts clearly shows the influence of varying proportions of olivine clinopyroxene orthopyroxene and plagioclase in the basalt source regions a small percentage of plagioclase 5 in the 12038 source apparently is responsible for low i sr and nd in this basalt aluminous mare basalts from mare crisium luna 24 and by inference mare fecunditatis luna 16 occupy locations on the i sr nd plot similar to that of 12038 implying that some basalts from three widely separated lunar regions came from plagioclase bearing source regions a summary of model calculations for mare basalts shows a record of lunar mantle solidification during the period when ree abundances in the lunar magma ocean increased from 20 chondritic to 100 chondritic although there is a general trend from olivine to clinopyroxene dominated source regions with progressive magma ocean evolution significant mineralogical heterogeneities in mantle composition apparently formed at any given stage of evolution as evidenced in particular by the three apollo 12 magma types

uplift driven expansion delayed by middle holocene desiccation in lake winnipeg manitoba canada new findings of paleoenvironmental change in lake winnipeg southern manitoba reveal evidence of unexpectedly dry conditions from 7 5 to 4 ka 7500 to 4000 radiocarbon years before present with reduced lake area in the north and a desiccated lake basin in the south changes in extent of this large lake now 400 km long can be explained by a combination of 1 expansion due to postglacial differential uplift tilting and 2 lake area reduction due to drier climates associated with the former presence of dry grassland vegetation comparing lake areas sustainable by grassland climate with computed potential lake areas based on the assumption of open overflowing conditions we quantify the atmospheric moisture reduction represented by the middle holocene dry conditions this approach holds promise for calibrating regional models of climate change and exploring the effects of dry paleoclimates in other large lake basins such as the laurentian great lakes the ongoing postglacial tilting is of societal concern because it contributes to long term lakeshore erosion and to the decrease in discharge capacity of the inflowing flood prone red river in a populated region

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

hf nd isotope evidence for a transient dynamic regime in the early terrestrial mantle modern basalts have seemingly lost all memory of the primitive earth s mantle except for an ambiguous isotopic signal observed in some rare gases1 2 although the earth is expected to have reached a thermal steady state within several hundred million years refs 3 4 of accretion it is not known how and when the initial chemical fractionations left over from planetary accretion and perhaps a stage involving a magma ocean were overshadowed by fractionations imposed by modern style geodynamics because of the lack of samples older than 4 gyr this early dynamic regime of the earth is poorly understood here we compare published hf nd isotope data on supracrustals from isua greenland with similar data on lunar rocks and the snc martian meteorites and show that about 3 8 gyr ago the geochemical signature of the archaean mantle was partly inherited from the initial differentiation of the earth the observed features seem to indicate that the planet at that time was still losing a substantial amount of primordial heat the survival of remnants from an early layering in the modern deep mantle may account for some unexplained seismological thermal and geochemical characteristics of the earth as observed today

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

high precision lu and hf isotope analyses of both spiked and unspiked samples a new approach 1 the functional form of instrumentally produced mass fractionation associated with mc icp ms analysis is not accurately known and therefore cannot be fully corrected by traditional approaches of internal normalization using power linear or exponential mass bias laws we present a method for robust correction of instrumentally produced mass fractionation of both spiked and unspiked samples that can be applied to mass analysis of hf as well as nd sr os etc correction of 176hf 177hf for unspiked samples follows a traditional approach of internal normalization using an exponential law followed by normalization to a standard of known composition such as jmc 475 for spiked samples standards are used to characterize a linear instrumental mass bias coefficient the mass bias coefficient is defined by the slope of a tie line between measured and true values of a standard this approximation results in identical precision and accuracy of measurements for spiked and unspiked samples 0 005 2 external reproducibility the effects of the spike on the 176hf 177hf ratio and calculation of the molar spike sample ratio is determined by a closed form solution modified from the double spike approach used for fe isotope analysis by tims johnson and beard 1999 the measured 176lu 175lu ratios are corrected by doping the sample with er and using the 167er 166er ratio to externally normalize the 176lu 175lu ratio using an exponential law finally spike sample equilibration is confirmed for our sample dissolution protocol through analysis of varying physical mixtures of 1 ga garnet and hornblende where all the data lie on a mixing line within error on a 176lu 177hf 176hf 177hf diagram precision of 176lu 177hf ratios is determined to be 0 2 2 for standards and for physical mixtures of garnet and hornblende

lu hf constraints on the evolution of lunar basalts very low ti basalts and green glass samples from the moon show high lu hf ratios and low hf concentrations low ti lunar basalts show high and variable lu hf ratios and higher hf concentrations whereas high ti lunar basalts show low lu hf ratios and high hf concentrations kreep basalts have constant lu hf ratios and high but variable hf concentrations using the lu hf behavior as a constraint we propose a model for the mare basalts evolution this constraint requires extensive crystallization of the primary lunar magma ocean prior to formation of the lunar mare basalt sources and the kreep basalts mare basalts are produced by the melting of the cumulate rocks and kreep basalts represent the residual liquid of the magma ocean lu and hf concentrations and the hf isotopic data of lunar rocks suggest that assimilation cannot be accepted as a major process to explain the diversity of the lunar mare basalts the urkreep hypothesis is also unnecessary both high and low ti basalts show enough iron enrichment to be regarded as melting products of the last stage cumulate rocks from the lunar magma ocean the kreep basalts are also rich in iron and may be regarded as the final residual liquid left after the crystallization of the major portion of the primary lunar magma ocean

high temperature silicon isotope geochemistry abstract silicon si is the defining element of silicate reservoirs yet despite its dominance in major earth processes there is still no clear understanding of how much is hosted in earth s core how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering erosion and subduction with the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small 100 ppm level mass dependent variations in si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions this paper reviews the technique developments the new data and the veracity of current interpretations only a small si isotopic effect is associated with basalt formation via mantle melting however there now is compelling evidence based on a considerable number of samples 100 that the silicate earth is isotopically fractionated by 100 200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites this could reflect variability in the circumstellar disc but this is not well supported by data for enstatite chondrites which are isotopically light the most plausible current explanation is that si is a light element in earth s core and that differences in the bond stiffness between silicate and metal hosted si resulted in substantial fractionation interestingly the moon has the same si isotope composition as earth s mantle which is hard to explain unless the moon s atoms were mainly derived from earth differentiated magmatic sequences such as those of hekla iceland display a systematic relationship between isotopic composition and si content more complex magmatic suites such as i and s type granites reveal a range of isotopic compositions not well correlated with chemical composition similar effects are found in lower crustal granulite facies xenoliths nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle in fact the effect is barely resolvable therefore the amounts of surface dissolved heavy si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay

the estherville mesosiderite upb rbsr and smnd isotopic study of a polymict breccia abstract a systematic u pb sm nd and rb sr isotopic study shows that the estherville mesosiderite was formed between 4 56 and 4 43 ga observed isotopic heterogeneity is in agreement with multiple generations of meteoritic impacts described in other mesosiderites at least part of the estherville silicate fraction was formed early in solar system history as indicated by the pb pb 4555 35 ma u pb 4560 31 ma rb sr 4542 203 ma and sm nd 4533 94 ma ages mesosiderites therefore present not only petrological but also geochronological similarities with eucrites the pb isotopic composition of the metal phase plots on the same isochron as the silicates indicating formation and subsequent mixing with silicates early in the history of the solar system this is consistent with previous observations indicating that iron was reduced during the silicate magmatic stage most likely a consequence of mixing with metal in addition to these more ancient portions of the estherville breccia other parts were formed later as suggested by the pb pb 4422 50 ma and u pb 4437 11 ma ages observed in a second group of leaches and residues this age is similar to some cumulate eucrite ages and may represent the formation of a second mesosiderite component the sm nd and the rb sr ages obtained on estherville show large errors that may be a consequence of the mixing between the 4 56 and 4 43 ga endmembers estherville like most mesosiderites was affected by a major heating event around 3 5 3 7 ga as shown by the ar ar ages bogard et al 1990 this heating event partially disturbed the rb sr isotopic system rb sr metamorphic ages range between 3 81 and 4 08 ga

the origin of geochemical diversity of lunar mantle sources inferred from the combined u pb rb sr and sm nd isotope systematics of mare basalt 10017 the results of our combined u pb rb sr and sm nd isotope study of mare basalt 10017 contribute to the understanding of the petrogenetic processes involved in the origin of geochemical diversity in lunar mare basalt sources as well as the u pb isotope systematics of the moon the rb sr sm nd and 238 u 206 pb isotope systems yield concordant crystallization ages of 3 633 0 057 ga 3 678 0 069 ga and 3 616 0 098 ga respectively the 235 u 207 pb isochron yields an older though still concordant age of 3 80 0 12 ga neither the 206 pb 207 pb system nor u pb concordia system yields an age for 10017 that is concordant with the age determined from the sm nd rb sr and 238 u 206 pb systems the initial 87 sr 86 sr of 10017 is 0 69941 7 and the initial end is 3 2 0 4 initial pb isotopic compositions determined from the u pb isochrons are 206 pb 204 pbi 31 11 and 207 pb 204 pbi 34 15 together these initial pb compositions constrain the l value of the 10017 source to be 70 30 assuming a single stage pb growth model this is considerably lower than l values typically estimated for mare basalt sources 100 600 regardless the l values calculated for the sources of mare basalts as well as other lunar samples show a range that is larger than can be explained by fractionation of u from pb solely by crystallization of silicate phases and ilmenite during magma ocean solidification and formation of lunar mantle sources the u pb isotope systematics may reflect late stage formation of a sulfide phase which strongly fractionates pb from u but has minimal effect on rb sr or sm nd compositions during crystallization of the lunar magma ocean 2007 elsevier ltd all rights reserved

geochronology and petrogenesis of apollo 14 very high potassium mare basalts rb sr k ar and sm nd isotopic studies were undertaken for two apollo 14 very high potassium vhk mare basaltic clasts from breccias 14305 and 14168 the samples are distinctly more radiogenic than other lunar mare basalts rb sr data for the whole rock and mineral separates determine internal isochrons corresponding to essentially identical ages of 3 83 0 08 b y and 3 82 0 12 b y for samples 14305 and 14168 respectively for 87rb 0 0139 b y 1 their corresponding initial 87sr 86sr ratios are indistinguishable and are 0 6995 0 0005 and 0 6997 0 0004 respectively the 39ar 40ar age spectra for the two samples are very similar and give identical plateau ages of 3 85 0 02 b y for 14305 and 3 85 0 05 b y for 14168 the identical rb sr and k ar isotopic results for the two rocks indicate that they could be derived from the same flow the sm nd isotopic data of whole rock and mineral separates for the two vhk basalts define an internal isochron age of 3 94 0 16 b y for 147sm 0 00654 b y 1 and an initial 143nd 144nd of 0 50673 21 the averaged model age relative to the chondritic initial 143nd 144nd of 0 505893 for the basalts is 4 56 0 04 b y the concordance of rb sr k ar and sm nd ages strongly suggests that vhk basalts crystallized from a melt 3 85 b y ago the rb sr and sm nd isotopic data indicate that vhk basalts show very large rb sr fractionation but no significant sm nd fractionation at the time of crystallization the source material for these basalts had a rb sr ratio similar to those of apollo 14 high a1 mare basalts and a nearly chondritic sm nd ratio extreme enrichments of rb sr and k la during the formation of vhk basalts can be adequately explained by an assimilation model that involves basalt granite interaction k rb rich components of granitic wall rocks in highland crust were selectively introduced into ascending hot high a1 mare basaltic magma upon contact a similar crustal assimilation process has been frequently observed in terrestrial mantle derived magma that ascended through the continental crust

lu hf and sm nd evolution in lunar mare basalts lu hf and sm nd data for mare basalts combined with rb sr and total ree data taken from the literature suggest that the mare basalts were derived by small or 10 degrees of partial melting of cumulate sources but that the magma ocean from which these sources formed was light ree and hf enriched calculated source compositions range fromm lherzolite to olivine websterite nonmodal melting of small amounts of ilmenite or 3 in the sources seems to be required by the lu hf data a comparison of the hf and nd isotopic characteristics between the mare basalts and terrestrial oceanic basalts reveals that the epsilonhf epsilonnd ratios of low ti mare basalts are much higher than in terrestrial oceanic basalts the results are qualitatively consistent with the hypothesis that terrestrial basalt sources are partial melt residues whereas mare basalt sources are cumulates alternatively the results may imply that the terrestrial mantle has evolved in two or more stages of evolution and that the net effect was depletion of the mantle during the first approx 1 3 b y followed by enrichment during the last 1 2 b y or simply that there is a difference in lu hf crystal liquid partitioning relative to sm nd between the lunar and terrestrial mantles

oxygen and iron isotope constraints on near surface fractionation effects and the composition of lunar mare basalt source regions oxygen and iron isotope analyses of low ti and high ti mare basalts are presented to constrain their petrogenesis and to assess stable isotope variations within lunar mantle sources an internally consistent dataset of oxygen isotope compositions of mare basalts encompasses five types of low ti basalts from the apollo 12 and 15 missions and eight types of high ti basalts from the apollo 11 and 17 missions high precision whole rock d 18 o values referenced to vsmow of low ti and high ti basalts correlate with major element compositions mg tio2 a l 2o3 the observed oxygen isotope variations within low ti and high ti basalts are consistent with crystal fractionation and match the results of mass balance models assuming equilibrium crystallization whole rock d 56 fe values referenced to irmm 014 of high ti and low ti basalts range from 0 134 to 0 217 and 0 038 to 0 104 respectively iron isotope compositions of both low ti and high ti basalts do not correlate with indices of crystal fractionation possibly owing to small mineral melt iron fractionation factors anticipated under lunar reducing conditions the d 18 o and d 56 fe values of low ti and the least differentiated high ti mare basalts are negatively correlated which reflects their different mantle source characteristics e g the presence or absence of ilmenite the average d 56 fe values of low ti basalts 0 073 0 018 n 8 and high ti basalts 0 191 0 020 n 7 may directly record that of their parent mantle sources oxygen isotope compositions of mantle sources of low ti and high ti basalts are calculated using existing models of lunar magma ocean crystallization and mixing the estimated equilibrium mantle olivine d 18 o value and equilibrium oxygen fractionation between olivine and other mineral phases the differences between the calculated whole rock d 18 o values for source regions 5 57 for low ti and 5 30 for high ti mare basalt mantle source regions are solely a function of the assumed source mineralogy the oxygen and iron isotope compositions of lunar upper mantle can be approximated using these mantle source values the d 18 o and d 56 fe values of the lunar upper mantle are estimated to be 5 5 0 2 2r and 0 085 0 040 2r respectively the oxygen isotope composition of lunar upper mantle is identical to the current estimate of earth s upper mantle 5 5 0 2 and the iron isotope composition of the lunar upper mantle overlaps within uncertainty of estimates for the terrestrial upper mantle 0 044 0 030

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

origin and evolution of the nakhla meteorite inferred from the sm nd and u pb systematics and ree ba sr rb and k abundances analyses of sm nd and u th pb systematics ree ba sr rb and k concentrations were carried out for whole rock and mineral separates from the nakhla meteorite the 1 26 07 b y sm nd age obtained in this work is in good agreement with those previously obtained by the rb sr and ar ar methods the high initial nd value of 16 suggests that nakhla was derived from a light ree depleted old planetary mantle source u th pb data after correction for pre analytical terrestrial pb contamination assuming an age of 1 26 b y suggest that the age of the nakhla source is 4 33 b y the agreement in the age determined by three independent radiometric methods and the high initial nd value strongly suggest that the 1 3 b y age dates one thorough igneous event in the parent body which not only reset these isotopic systems but also established the chemical and petrologic characteristics observed for the nakhla meteorite using a three stage sm nd evolution model in combination with lil element data and estimated partition coefficients we have tested partial melting and fractional crystallization models to estimate lil element abundances in a possible nakhla source our model calculations suggest that partial melting of the light ree depleted source followed by extensive fractional crystallization 50 of the partial melt could account for the ree abundances in the nakhla constituent minerals the estimated source is depleted in the light ree ba rb and k and therefore may resemble the morb source in the earth s upper mantle or the upper 60 300 km of the moon the significantly younger age of nakhla than the youngest lunar rock the young differentiation age inferred from the u th pb data and the estimated lil element abundances including those of k u and th in the source suggest that the nakhla meteorite may have been derived from a relatively large well differentiated planetary body such as mars

earliest high ti volcanism on the moon 40ar 39ar sm nd and rb sr isotopic studies of group d basalts from the apollo 11 landing site high ti basalts from the apollo collections span a range in age from 3 87 ga to 3 55 ga the oldest of these are the common apollo 11 group b2 basalts which yield evidence of some of the earliest melting of the lunar mantle beneath mare tranquillitatis rare group d high ti basalts from mare tranquillitatis have been studied in an attempt to confirm a postulated link with group b2 basalts jerde et al 1994 the initial sr isotopic ratio of a known group d basalt 0 69916 3 at 3 85 ga lies at the lower end of the tight range for group b2 basalts 87sr 86sr 0 69920 to 0 69921 one known group d basalt and a second postulated group d basalt yield indistinguishable initial nd 1 2 0 6 and 1 2 0 3 and again lie at the lower end of the range for the group b2 basalts from apollo 11 2 0 0 4 to 3 9 0 6 at 3 85 ga a third sample has isotopic 87sr 86sr 0 69932 2 nd 2 5 0 4 at 3 59 ga as per snyder et al 1994b and elemental characteristics similar to the group a high ti basalts returned from the apollo 11 landing site ages of 40ar 39ar have been determined for one known group d basalt and a second postulated group d basalt using step heating with a continuous wave laser suspected group d basalt 10002 1006 yielded disturbed age spectra on two separate runs which was probably due to 39ar recoil effects using the reduced plateau age method of turner et al 1978 the ages derived from this sample were 3898 19 and 3894 19 ma three separate runs of known group d basalt 10002 116 yielded 40ar 39ar plateau ages of 3798 9 ma 3781 8 ma and 3805 7 ma all errors 2 furthermore this sample has apparently suffered significant 40ar loss either due to solar heating or due to meteorite impact the loss of a significant proportion of 40ar at such a time means that the plateau ages underestimate the true crystallization age of the sample modelling of this ar loss yields older true ages of 3837 18 3826 16 and 3836 14 ma these ages overlap the ages of group b2 high ti basalts weighted average age 3850 20 ma range in ages 3 80 to 3 90 ga the combined evidence indicates that the group d and b2 high ti basalts could be coeval and may be genetically related possibly through increasing degrees of melting of a similar source region in the upper mantle of the moon that formed 4 2 ga ago the group d basalts were melted from the source first and contained 3 5 more trapped kreep like liquid than the later by possibly only a few million years group b2 basalts furthermore the relatively lree and rb enriched nature of these early magmas may lend credence to the idea that the decay of heat producing elements enriched in the kreep like trapped liquid of upper mantle cumulates such as k u and th could have initiated widespread lunar volcanism

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

isotopic evolution of the mantle a model we investigate a model of mantle evolution which acknowledges the importances in early earth history of large degrees of partial melting and crystal fractionation rather than as in recent models small degrees of partial melting operating on primary mantle the major source regions are in the upper mantle and evolve from a primitive mantle melt by crystal fractionation and the formation of chemically distinct cumulate layers the rb sr and sm nd ratios in melts are relatively unfractionated in processes involving large 15 degrees of partial melting the ratios are even less fractionated in orthocumulates forming from these melts small degrees of partial melting or removal of residual fluids after nearly complete crystalization of cumulate layers are the processes that lead to significant fractionation the importance of these processes increases as the upper mantle cools the observation of nearly primitive isotopic ratios does not necessarily imply the presence of ancient primitive undifferential reservoirs the transfer of intercumulus fluids from a crystalizing cumulate layer gives time dependent rb sr and sm nd ratios in both the donor and receiving reservoirs since the late stage fluids become more enriched as crystalization proceeds enrichment in such a system is progressive with time time integrated nd sm and rb sr ratios therefore need not depart much from primitive ratios even though current values for lile concentration rb sr nd sm etc may be large the time constant for lile enrichment appears to be 2 gyr about the same as required for the u pb system and the same as the characteristics time associated with mantle cooling the mantle reservoirs may be much more ancient than generally assumed

re evaluating 142nd 144nd in lunar mare basalts with implications for the early evolution and bulk sm nd of the moon abstract the moon likely accreted from melt and vapor ejected during a cataclysmic collision between proto earth and a mars sized impactor very early in solar system history the identical w o k and cr isotope compositions between materials from the earth and moon require that the material from the two bodies were well homogenized during the collision process as such the ancient isotopic signatures preserved in lunar samples provide constraints on the bulk composition of the earth two recent studies to obtain high precision 142nd 144nd ratios of lunar mare basalts yielded contrasting results in one study after correction of neutron fluence effects imparted to the nd isotope compositions of the samples the coupled 142nd 143nd systematics were interpreted to be consistent with a bulk moon having a chondritic sm nd ratio rankenburg k brandon a d and neal c r 2006 neodymium isotope evidence for a chondritic composition of the moon science 312 1369 1372 the other study found that their data on the same and similar lunar mare basalts were consistent with a bulk moon having a superchondritic sm nd ratio boyet m and carlson r w 2007 a highly depleted moon or a non magma origin for the lunar crust earth planet sci lett 262 505 516 delineating between these two potential scenarios has key ramifications for a comprehensive understanding of the formation and early evolution of the moon and for constraining the types of materials available for accretion into large terrestrial planets such as earth to further examine this issue the same six lunar mare basalt samples measured in rankenburg et al rankenburg k brandon a d and neal c r 2006 neodymium isotope evidence for a chondritic composition of the moon science 312 1369 1372 were re measured for high precision nd isotopes using a multidynamic routine with reproducible internal and external precisions to better than 3 ppm 2 for 142nd 144nd ratios the measurements were repeated in a distinct second analytical campaign to further test their reproducibility evaluation of accuracy and neutron fluence corrections indicates that the multidynamic nd isotope measurements in this study and the 3 in boyet and carlson boyet m and carlson r w 2007 a highly depleted moon or a non magma origin for the lunar crust earth planet sci lett 262 505 516 are reproducible while static measurements in the previous two studies show analytical artifacts and cannot be used at the resolution of 10 ppm to determine a bulk moon with either chondritic or superchondritic sm nd ratios the multidynamic data are best explained by a bulk moon with a superchondritic sm nd ratio that is similar to the present day average for depleted morb hafnium isotope data were collected on the same aliquots measured for their 142nd 144nd isotope ratios in order to assess if the correlation line for 142nd 143nd systematics reflect mixing processes or times at which lunar mantle sources formed based on the combined 142nd 143nd 176hf obtained we conclude that the 142nd 143nd correlation line measured in this study is best interpreted as an isochron with an age of 229 24 20ma after the onset of nebular condensation the uncertainties in the data permit the sources of these samples to have formed over a 44 ma time interval these new results for lunar mare basalts are thus consistent with a later sm nd isotope closure time of their source regions than some recent studies have postulated and a superchondritic bulk sm nd ratio of the moon and earth the superchondritic sm nd signature was inherited from the materials that accreted to make up the earth moon system although collisional erosion of crust from planetesimals is favored here to remove subchondritic sm nd portions and drive the bulk of these bodies to superchondritic in composition removal of explosive basalt material via gravitational escape from such bodies or chondrule sorting in the inner solar system may also explain the compositional features that deviate from average chondrites that make up the earth moon system this inferred superchondritic nature for the earth similar to the modern convecting mantle means that there is no reason to invoke a missing subchondritic reservoir to mass balance the earth back to chondritic for sm nd ratios however to account for the subchondritic sm nd ratios of continental crust a second superchondritic sm nd mantle reservoir is required

147sm 143nd and 176lu 176hf in eucrites and the differentiation of the hed parent body the 147sm 143nd and 176lu 176hf systematics of 21 whole rock eucrites including five cumulates have been investigated by mc icp ms a statistically significant sm nd isochron was obtained on 18 samples with an age of 4464 75 ma mswd 1 26 and an intercept of 0 50680 0 00010 this age clearly is controlled by the cumulate eucrites the 21 basaltic and cumulate eucrites together do not form a statistically significant lu hf isochron basaltic eucrites however form an errorchron with an age of 4604 39 ma mswd 4 52 which becomes an acceptable isochron if the error on the lu hf ratio is doubled with respect to the laboratory estimate the initial 176hf 177hf is 0 27966 0 00002 three of the cumulate eucrites regressed together further yield a statistically significant age of 4470 22 ma indistinguishable from their sm nd age we therefore conclude that cumulate eucrites are 100 myr younger than basaltic eucrites and basaltic eucrites are close in age to the solar system there is no evidence in the present data to support a decay constant of 176lu significantly different from 1 93 10 11 yr 1 sguigna can j phys 60 1982 361 364 the broad range of variation and strong correlation of lu hf and sm nd ratios require that eucrites are partial melts and not residual magmas the relative lu hf and sm nd fractionation is controlled by the plagioclase to mafic mineral ratio in the residue the steep correlation between these two ratios is explained by the enhancement of plagioclase saturation in the low gravity field of the eucrite parent body basaltic eucrites probably formed as large degree melts of a chondritic source the strong lu hf and sm hf fractionation observed in cumulates clearly reflects the presence of residual ilmenite during melting our preferred interpretation is that cumulates were impregnated by small degree melts of ilmenite bearing gabbros since pressure on the eucrite parent body never reaches the garnet stability field this observation questions the ubiquitous presence of residual garnet in the mantle sources of magmas formed on larger planets such as the moon mars and possibly earth

hafnium isotope results from mid ocean ridges and kerguelen abstract 176hf 177hf ratios are presented for oceanic volcanics representing both extremes of the range of mantle hf nd sr isotopic variation hf from critical mid ocean ridgebasalts shows that 176hf 177hf does indeed have a greater variability than 143nd 144nd and 87sr 86sr in the depleted mantle this extra variation is essentially of a random nature and can perhaps be understood in terms of known rb sr sm nd lu hf fractionation relationships at the other extreme of mantle isotopic composition 176hf 177hf ratios for igneous rocks from the indian ocean island of kerguelen show a closely similar variation to published 143nd 144nd ratios for the same samples comparison of hf nd sr c relationships for tristan da cunha kerguelen and samoa reveals divergences in the mantle array for ocean island magma sources and perhaps suggests that these irregularities are largely the result of an extra component of 87sr 86sr variation

an extremely low source in the moon uthpb smnd rbsr and isotopic systematics and age of lunar meteorite asuka 881757 abstract we have undertaken u th pb sm nd rb sr and 40 ar 39 ar isotopic studies on asuka 881757 a coarse grained basaltic lunar meteorite whose chemical composition is close to low ti and very low ti vlt mare basalts the pb pb internal isochron obtained for acid leached residues of separated mineral fractions yields an age of 3940 28 ma which is similar to the u pb 3850 150 ma and th pb 3820 290 ma internal isochron ages the sm nd data for the mineral separates yield an internal isochron age of 3871 57 ma and an initial 143 nd 144 nd value of 0 50797 10 the rb sr data yield an internal isochron age of 3840 32 ma 87 rb 1 42 10 11 yr 1 and a low initial 87 sr 86 sr ratio of 0 69910 2 the 40 ar 39 ar age spectra for a glass fragment and a maskelynitized plagioclase are relatively flat and give a weighted mean plateau age of 3798 12 ma we interpret these ages to indicate that the basalt crystallized from a melt 3 87 ga ago the sm nd age and an impact event disturbed the rb sr system and completely reset the k ar system at 3 80 ga the slightly higher pb pb age compared to the sm nd age could be due to the secondary pb from terrestrial and or lunar surface pb contamination that remained in the residues after acid leaching alternatively the following interpretation is also possible the meteorite crystallized at 3 94 ga the pb pb age and the sm nd rb sr and k ar systems were disturbed by an impact event at 3 80 ga the crystallization age obtained here is older than those reported for low ti basalts 3 2 3 5 ga and for vlt basalts 3 4 ga but similar to ages of some mare basalts indicating that the basalt may have formed from a magma related to a basin forming event imbrium the age span for vlt basalts from different sampling sites suggest that they were erupted over a wide area during an interval of at least 500 million years the impact event that thermally reset the k ar system of asuka 881757 must have been post imbrium perhaps orientale in age the lead isotopic composition of asuka 881757 is nonradiogenic compared with typical apollo mare basalts and the estimated 238 u 204 pb value for the basalt source is 10 3 this source value is the lowest so far measured for lunar rocks a large positive nd value 7 4 0 5 and the time averaged 147 sm 144 nd ratio for the basalt source are similar to those for some apollo 12 15 and 17 basalts suggesting a lree depleted mantle which is consistent with the global magma ocean hypothesis the u th pb sm nd and rb sr data on asuka 881757 suggest that the basalt was derived from a low u pb low rb sr and high sm nd source region mainly composed of olivine and orthopyroxene with minor amounts of plagioclase or clinopyroxene and with sulfides enriched in volatile chalcophile elements the basalt source may be deep in origin and different in chemistry from those previously estimated from studies of apollo and luna mare basalts indicating heterogeneous sources for mare basalts

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

constraining the timing and sources of volcanism at the apollo 12 landing site using new pb isotopic compositions and crystallisation ages abstract the basaltic suites collected at the apollo 12 landing site have been interpreted as representing a stratigraphic sequence of volcanic flows emplaced in the oceanus procellarum region between approximately 3100 3300 ma this study presents secondary ion mass spectrometry sims pb isotopic analyses of samples from each of the basaltic suites which have been used to constrain precise crystallisation ages and initial pb isotopic compositions the new crystallisation ages are consistent with the three main basaltic suites olivine pigeonite and ilmenite being emplaced over a period of approximately 60 million years and the improved precision of these ages has made it possible to reinterpret the stratigraphic sequence of basalt flows underlying the apollo 12 landing site contrary to previous studies the three ilmenite basalts are determined as having the oldest ages with a weighted average of 3187 6 ma 2 and are therefore interpreted as representing the lowest unit in the sequence underlying the olivine and pigeonite basalts with an age range constrained by the oldest and youngest pigeonite basalts 3176 6 ma and 3129 10 ma 2 the initial pb isotopic compositions have been compared with recalculated initial sr and nd isotopic compositions and are consistent with the three main basaltic suites originating from magmatic sources that incorporated different proportions of a common primitive mafic cumulate and the residual trapped liquid fraction remaining after a majority of the lunar magma ocean had crystallised our data also demonstrate that the feldspathic basalt 12038 is unique both in terms of its crystallisation age 3242 13 ma and its derivation from a distinct mantle reservoir