re os systematics in chondrites and the fractionation of the platinum group elements in the early solar system we have investigated the re os system for samples of whole rock metal and sulfide from ordinary chondrites using closed system analytical techniques we found complete exchange between sample and tracer isotopes for silicate containing samples and obtained precise and reliable re os concentration measurements results on two group iva iron meteorites and on a silicate rich iron steinbach iva an are consistent with the iva ivb isochron and support the previous observation that iva ivb irons may be slightly older than iiab irons data on whole rock fragments and metal rich separates from the st severin chondrite ll6 show a large range in 1870re 188 os and in 187 os 188 os which makes possible in principle the determination of a re os internal isochron on a chondrite for the first time this re os fractionation may be due to partial melting of fenis and macroscopic redistribution of metal and sulfide the st severin data show a good correlation line on a 187 re 187 os evolution diagram if this is considered to represent an internal isochron it gives an age t 4 68 0 15 ae 187 re 1 64 10 11 a 1 and an initial 187 os 188 os 0 0 0953 0 0013 this age is in agreement with but slightly older than the more precise 187 re 187 os age for the iiab irons as well as for irons from other groups t 4 61 0 01 ae a st severin sulfide nodule has very low re and os concentrations and shows a young re os model age 2 3 ae indicating recent element remobilization whole rock and metal rich separates of h group chondrites h3 to h6 yield restricted ranges in 187 re 188 os 0 42 0 47 and 187 os 188 os 0 128 0 133 there is a systematic difference between re os in the metal extracted from a chondrite and the bulk chondrite this shows that there is a small but significant re os fractionation within subsystems contained in the chondrites from whole rock samples of h group chondrites we calculate a mean 187 re 188 os 0 423 0 007 and 187 os 188 os 0 12863 0 00046 which may characterize the evolution of an average chondritic reservoir for re os the ordinary chondrite data plot close to the iiab isochron although the deviations found are larger than found for the irons the re os chronometer in iron meteorites is apparently controlled by the re os fractionation due to fractional crystallization of liquid metal re os ages of iron meteorites give the time of crystallization of metal segregations and cores of early planetary bodies in contrast the behavior in ordinary chondrites while also dominated by the metal phases must reflect fractionation and transport on a local macroscopic scale within the chondrites between the metal phases after aggregation due to partial melting of fenis or represent variable re os fractionation of the metal phases prior to the accretion of the chondrites however for st severin we attribute the major re os fractionation to early heating of the meteorite above the fe fes eutectic we do not consider that the re os fractionation observed in other chondrites is due to the redistribution of re and os during chondrite metamorphism including shock but it may plausibly represent earlier stages of re os fractionation for the different feni metal constituents prior to accretion

terrestrial mantle siderophiles and the lunar impact record a simple analytical fit to the lunar cratering record scaled from final to transient crater diameters then to impactor masses implies a total mass 1 0 1020kg incident on the moon subsequent to the solidification of the lunar crust 4 4 gyr ago about half this mass would be retained and a comparable lunar mass would be eroded these results are in good agreement with geochemical estimates of the meteoritic component mixed into the lunar crust which give 0 4 1 5 1020 kg gravitationally scaling to earth and taking account of the statistical probability that the largest impactors incident on earth were more massive than the largest incident on the moon gives an estimate of 1 5 1022 kg of material accumulated by earth subsequent to 4 4 gyr ago this result is in excellent accord with geochemical estimates of post core formation meteoritic input these estimates based on abundances of highly siderophile elements in the terrestrial mantle lie in the range 1 4 1022 kg the significant result is the approximate agreement of the lunar cratering record scaling with both lunar and terrestrial geochemical constraints numerous uncertainties render exact comparisons pointless nevertheless the close agreement suggests the model developed here may credibly be used to estimate exogenous volatile and prebiotic organic delivery

ancient impactor components preserved and reworked in martian regolith breccia northwest africa 7034 abstract northwest africa nwa 7034 and paired stones represent unique samples of martian polymict regolith breccia multiple breccia subsamples characterized in this work confirm highly siderophile element hse re os ir ru pt pd contents that are consistently elevated e g os 9 3 18 4 ppb above indigenous martian igneous rocks mostly 187 os 188 os ratios of 0 119 0 136 record a wider variation than observed for all major chondrite types combined with the measured 187 re 188 os ratios of 0 154 0 994 the range in os isotope ratios indicates redistribution of re and os from originally chondritic components early in the history of the regolith commencing at 4 4 ga superimposed recent re mobility reflects exposure and weathering at or near the martian and terrestrial surfaces elevated os concentrations 38 0 and 92 6 ppb os superchondritic os hse ratios and 187 os 188 os of 0 1171 and 0 1197 measured for two subsamples of the breccia suggest the redistribution of impactor material at 1 5 1 9 ga possibly overlapping with a partial resetting event at 1 4 ga recorded by u pb isotope systematics in the breccia martian alteration of the originally chondritic hse host phases to form os ir rich nuggets and ni rich pyrite implies the influence of potentially impact driven hydrothermal systems multiple generations of impactor component admixture redistribution and alteration mark the formation and evolution of the martian regolith clasts and matrix of nwa 7034 and paired meteorites from the pre noachian until impact ejection to earth

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

analysis of lunar samples implications for planet formation and evolution the analysis of lunar samples returned to earth by the apollo and luna missions changed our view of the processes involved in planet formation the data obtained on lunar samples brought to light the importance during planet growth of highly energetic collisions that lead to global scale melting this violent birth determines the initial structure and long term evolution of planets once past its formative era the lunar surface has served as a recorder of more than 4 billion years of interaction with the space environment the chronologic record of lunar cratering determined from the returned samples underpins age estimates for planetary surfaces throughout the inner solar system and provides evidence of the dynamic nature of the solar system during the planet forming era

structure and tectonics of the upper cenozoic puerto rico virgin islands carbonate platform as determined from seismic reflection studies the puerto rico virgin islands carbonate platform was deposited over an area of 18 000 km2 from early oligocene to holocene on top of an inactive and subsiding cretaceous earliest oligocene island arc regional single channel and multichannel seismic reflection lines presented in this study provide the first information on the regional stratigraphy and structure of this platform that has previously been known mainly from onshore stratigraphic sections of a relatively small 2250 km2 portion of the platform exposed by late neogene tectonic uplift along the north coast of puerto rico seismic reflection lines are used to map the thickness of the carbonate platform strata and to correlate this thickness with onshore outcrop and well data from northern and southern puerto rico st croix u s virgin islands and the saba bank limestone thickness variations from a little over 2 km to almost zero are used to subdivide the puerto rico virgin islands platform into five distinct carbonate provinces 1 north puerto rico area including the onshore exposures 2 virgin islands area 3 st croix and saba bank area 4 south puerto rico area and 5 mona passage area carbonate thickness and structural information from each area are used to test five previously proposed models for the deformation and vertical movements of the platform the most prominent feature of the platform in the puerto rico virgin islands area is a large east west trending arch the northern limb of this arch exhibits a smoother more uniform dip than the steeper more abruptly faulted southern limb the core of the arch is responsible for the exposure of arc basement rocks on puerto rico the origin of this arch which occurs over a 300 km wide area is best explained by north south shortening and arching caused by interaction at depth of subducted slabs of the north america and caribbean plates other important evidence for this model can be found in the benioff zones observed in the earthquake profiles loading of the caribbean plate results in downward flexing of the north america plate and causes the 4 km subsidence of the carbonate platform north of puerto rico

an unusual clast in lunar meteorite macalpine hills 88105 a unique lunar sample or projectile debris lunar meteorite macalpine hills mac 88105 is a well studied feldspathic regolith breccia dominated by rock and mineral fragments from the lunar highlands thin section mac 88105 159 contains a small rock fragment 400 350 m in size which is compositionally anomalous compared with other mac 88105 lithic components the clast is composed of olivine and plagioclase with minor pyroxene and interstitial devitrified glass component it is magnesian akin to samples in the lunar high mg suite and also alkali rich akin to samples in the lunar high alkali suite it could represent a small fragment of late stage interstitial melt from an mg suite parent lithology however olivine and pyroxene in the clast have fe mn ratios and minor element concentrations that are different from known types of lunar lithologies as fe mn ratios are notably indicative of planetary origin the clast could either 1 have a unique lunar magmatic source or 2 have a nonlunar origin i e consist of achondritic meteorite debris that survived delivery to the lunar surface both hypotheses are considered and discussed the meteoritical society 2014

isotope analysis of crystalline impact melt rocks from apollo 16 stations 11 and 13 north ray crater rubidium strontium and sm nd isotopic data were obtained for lunar impact melt rocks from apollo 16 stations 11 and 13 as part of the north ray crater target rock consortium study rubidium strontium whole rock data define an isochron age t 3 69 0 16 b y 0 0142 b y 1 and initial 87sr 86sr isr 0 69918 5 for feldspathic microporphyritic fm samples internal rb sr isochrons of t 3 86 0 05 b y isr 0 69952 10 and t 3 76 0 04 b y isr 0 69916 4 were determined for very high alumina vha melt rock 67747 and anorthositic noritic melt rock anmr 67559 respectively t isr for these and other lunar melt rocks were examined to infer the nature of the protolith for the rocks isr values for the an mr and fm rocks are consistent with an anorthositic protolith probably a mixture of nonpristine anorthositic gabbros and pristine anorthosites anorthositic norites norites troctolites and possibly dunites the source protolith of the vha rocks apparently had a significant kreep component and the protolith for apollo 16 kreep must have had nearly the same rb sr ratio as that of apollo 14 kreep two stage model calculations using the t isr parameters suggest that some of the melt rocks were open rb sr systems during impact melting rubidium strontium model ages for the fm and vha rocks show a smoothly monotonic decrease with increasing rb content model ages of the anmr are uniformly low relative to 4 56 b y it is suggested that these effects are due to formation of these rocks by impact partial melting rubidium strontium model ages of the kreep rocks do not vary with rb content suggesting that they were closed rb sr systems during impact melting samarium neodymium data for mineral separates of 67747 showed only a small variation in sm nd ratio and yield an imprecisely defined isochron of 3 6 0 4 b y plagioclase separates of 67559 appear not to have reached nd isotopic equilibrium during impact melting consequently the internal isochron age is also imprecisely defined at 4 0 0 4 b y nd values for the melt rocks are about 1 to 2 at their rb sr or 40ar 39ar ages are consistent with the protolith compositions inferred from the rb sr data and show that lunar crustal sm nd evolution departed from chondritic evolution early in lunar history the average chondritic uniform reservoir chur model age of those anmr and fm rocks that apparently remained closed rb sr and sm nd systems during impact melting is 4 37 0 10 b y consistent with earlier suggestions that the lunar crust formed at about that time the average chur model age of two vha rocks is 4 10 0 15 b y suggesting that these rocks were open sm nd systems as well as open rb sr systems during impact partial melting current hypotheses for the site geology stratigraphy and radiometric age data lead us to suggest that the nectaris basin and the descartes formation were formed about 4 1 b y ago and the imbrium basin and the cayley formation were formed about 3 81 3 86 b y ago the ages of some individual melt rocks probably date local cratering events however

highly siderophile element depletion in the moon abstract coupled 187 os 188 os and highly siderophile element hse os ir ru pt pd re abundance data are reported for apollo 12 12005 12009 12019 12022 12038 12039 12040 apollo 15 15555 and apollo 17 70135 mare basalts along with mare basalt meteorites la paz icefield lap 04841 and miller range mil 05035 these mare basalts have consistently low hse abundances at 2 10 5 to 2 10 7 the chondritic abundance the most magnesian samples have broadly chondrite relative hse abundances and chondritic measured and calculated initial 187 os 188 os the lower abundances and fractionated hse compositions of more evolved mare basalts can be reproduced by modeling crystal liquid fractionation using rock melt bulk partition coefficients of 2 for os ir ru pt and pd and 1 5 for re lunar mare basalt bulk partition coefficients are probably higher than for terrestrial melts as a result of more reducing conditions leading to increased hse compatibility the chondritic relative abundances and chondritic 187 os 188 os of the most primitive high mgo mare basalts cannot readily be explained through regolith contamination during emplacement at the lunar surface mare basalt compositions are best modeled as representing 5 11 partial melting of metal free sources with low os ir ru pd 0 1 ng g 1 pt 0 2 ng g 1 re 0 01 ng g 1 and s 75 g g 1 with sulphide melt partitioning between 1000 and 10 000 apollo 12 olivine pigeonite and ilmenite normative mare basalts define an imprecise 187 re 187 os age of 3 0 0 9 ga with an initial 187 os 188 os of 0 107 0 010 this age is within uncertainty of 147 sm 143 nd ages for the samples the initial os isotopic composition of apollo 12 samples indicates that the source of these rocks evolved with re os within 10 of chondrite meteorites from the time that the mantle source became a system closed to siderophile additions to the time that the basalts erupted similarity in absolute hse abundances between mare basalts from the apollo 12 15 and 17 sites and from unknown regions of the moon la paz mare basalts mil 05035 indicates relatively homogeneous and low hse abundances within the lunar interior low absolute hse abundances and chondritic re os of mare basalts are consistent with a late accretion addition of 0 02 wt of the moon s mass to the mantle prior to the formation of the lunar crust late accretion must also have occurred significantly prior to cessation of lunar mantle differentiation 4 4 ga to enable efficient mixing and homogenization within the mantle low lunar hse abundances are consistent with proportionally 40 times more late accretion to earth than the moon disproportional late accretion to the two bodies is consistent with the small 182 w excess 21 28 ppm measured in lunar rocks compared to the silicate earth

mid eocene early oligocene sinistral transcurrent faulting in puerto rico associated with formation of the northern caribbean plate boundary zone left lateral transcurrent wrench faulting through the southern puerto rico fault zone sprfz in central southern puerto rico is indicated by fault orientations and motion direction indicators the sprfz is a west northwest trending 3 8 km wide diffuse system of faults and folds that within the study area bounds paleocene and eocene volcaniclastic rocks the eocene belt and is flanked by cretaceous volcanic and volcaniclastic rocks structural data show that much of central southern puerto rico is cut by strike and oblique slip faults whereas locally in the southeastern part of the eocene belt rocks are pervasively thrust northeastward over cretaceous rocks of central puerto rico structural data and the distribution of fault types support two local evolutionary scenarios 1 different structural horizons of the transpressional sprfz i e upper thrust dominated horizon and lower strike slip dominated horizon were juxtaposed along post transpressional normal faults that border the ponce basi

sims u pb study of zircon from apollo 14 and 17 breccias implications for the evolution of lunar kreep abstract we report the results of a sims u pb study of 112 zircons from breccia samples from the apollo 14 and 17 landing sites zircon occurs in the breccia matrices as rounded irregular shaped broken and rarely euhedral grains and as constituent minerals in a variety of lithic clasts ranging in composition from ultra mafic and mafic rocks to highly evolved granophyres crystallisation of zircon in magmatic rocks is governed by the zirconium saturation in the melt as a consequence the presence of zircon in mafic rocks on the moon implies enrichment of their parent melts in the kreep component our sims results show that the ages of zircons from mafic to ultramafic clasts range from ca 4 35 ga to ca 4 00 ga demonstrating multiple generations of kreepy mafic and ultramafic magmas over this time period individual zircon clasts in breccia matrices have a similar age range to zircons in igneous clasts and all represent zircons that have been incorporated into the breccia from older parents the age distributions of zircons from breccias from both the apollo 14 and apollo 17 landing sites are essentially identical in the range 4 35 4 20 ga however whereas apollo 14 zircons additionally show ages from 4 20 to 3 90 ga no zircons from apollo 17 samples have primary ages less than ca 4 20 ga also in contrast to previous suggestions that the magmatism in the lunar crust is continuous our results show that the zircon age distribution is uneven with distinct peaks of magmatic activity at ca 4 35 ga ca 4 20 ga in apollo 14 and 17 and a possible third peak in zircons from apollo 14 at ca 4 00 ga to explain the differences in the zircon age distributions between the apollo 14 and 17 landing sites we propose that episodes of kreep magmatism were generated from a primary reservoir and that this reservoir contracted over time towards the centre of procellarum kreep terrane we attribute the peaks in kreep magmatism to impact induced emplacement of kreep magma from a primary mantle source or to a progressive thermal build up in the mantle source until the temperature exceeds the threshold for generation of kreep magma which is transported into the crust by an unspecified possibly plume like process

targeting the impactors siderophile element signatures of lunar impact melts from serenitatis abstract highly siderophile element compositions of lunar impact melt breccias provide a unique record of the asteroid population responsible for large cratering events in the inner solar system melt breccias associated with the 3 89 ga serenitatis impact basin resolve at least two separate impact events kreep rich melt breccias representing the apollo 17 poikilitic suite are enriched in highly siderophile elements 3 6 15 8 ppb ir with ci normalized patterns that are elevated in re ru and pd relative to ir and pt the restricted range of lithophile element compositions combined with the coherent siderophile element signatures indicate formation of these breccias in a single impact event involving an eh chondrite asteroid probably as melt sheet deposits from the serenitatis basin one exceptional sample a split from melt breccia 77035 has a distinctive lithophile element composition and a siderophile element signature more like that of ordinary chondrites indicating a discrete impact event the recognition of multiple impact events and the clear signatures of specific types of meteoritic impactors in the apollo 17 melt breccias shows that the lunar crust was not comprehensively reworked by prior impacts from 3 9 to 4 5 ga an observation more consistent with a late cataclysm than a smoothly declining accretionary flux late accretion of enstatite chondrites during a 3 8 4 0 ga cataclysm may have contributed to siderophile element heterogeneity on the earth but would not have made a significant contribution to the volatile budget of the earth or oxidation of the terrestrial mantle siderophile element patterns of apollo 17 poikilitic breccias become more fractionated with decreasing concentrations trending away from known meteorite compositions to higher re ir and pd pt ratios the compositions of these breccias may be explained by a two stage impact melting process involving 1 deep penetration of the serenitatis impactor into meteorite free lower crust followed by 2 incorporation of upper crustal lithologies moderately contaminated by prior meteoritic infall into the melt sheet trends to higher re ir with decreasing siderophile element concentrations may indicate an endogenous lunar crustal component or a non chondritic late accretionary veneer in the pre serenitatis upper crust

rhodium gold and other highly siderophile element abundances in chondritic meteorites abstract the abundances of the highly siderophile elements hse re os ir ru pt rh pd and au and 187os 188os isotope ratios have been determined for a set of carbonaceous ordinary enstatite and rumuruti chondrites using an analytical technique that permits the precise and accurate measurement of all hse from the same digestion aliquot concentrations of re os ir ru pt and pd were determined by isotope dilution icp ms and n tims analysis the monoisotopic elements rh and au were quantified relative to the abundance of ir differences in hse abundances and ratios such as re os 187os 188os pd ir and au ir between different chondrite classes are further substantiated with new data and additional rh and au data including new data for ci chondrites systematically different relative abundances of rh between different chondrite classes are reminiscent of the behaviour of re carbonaceous chondrites are characterized by low average rh ir of 0 27 0 03 1s which is about 20 lower than the ratio for ordinary 0 34 0 02 and enstatite chondrites eh 0 33 0 01 el 0 32 0 01 r chondrites show higher and somewhat variable rh ir of 0 37 0 07 well defined linear correlations of hse in particular for bulk samples of ordinary and el chondrites are explained by binary mixing and or dilution by silicates the hse carriers responsible for these correlations have a uniform chemical composition indicating efficient homogenization of local nebular heterogeneities during or prior to the formation of the host minerals in chondrite components excepting rumuruti chondrites and au in carbonaceous chondrites these correlations also suggest that metamorphism alteration and igneous processes had negligible influence on the hse distribution on the bulk sample scale depletion patterns for rh pd and au in carbonaceous chondrites other than ci are smoothly related to condensation temperatures and therefore consistent with the general depletion of moderately volatile elements in carbonaceous chondrites fractionated hse abundance patterns of ordinary enstatite and rumuruti chondrites however are more difficult to explain fractional condensation combined with the removal of metal phases at various times and later mixing of early and late formed metal phases may provide a viable explanation planetary fractionation processes that may have affected precursor material of chondrite components cannot explain the hse abundance patterns of chondrite groups hse abundances of some but not all rumuruti chondrites may be consistent with solid sulphide liquid sulphide fractionation processes during impact induced melting

phosphate halogen metasomatism of lunar granulite 79215 impact induced fractionation of volatiles and incompatible elements in the last decade it has been recognized that the moon contains significant proportions of volatile elements h f cl and that they are transported through the lunar crust and across its surface here we document a significant segment of that volatile cycle in lunar granulite breccia 79215 impact induced remobilization of volatiles and vapor phase transport with extreme elemental fractionation 79215 contains 1 volume of fluorapatite ca 5 po 4 3 f cl oh in crystals to 1 mm long which is reflected in its analyzed abundances of f cl and p the apatite has a molar f cl ratio of 10 and contains only 25 ppm oh and low abundances of the rare earth elements ree the chlorine in the apatite is isotopically heavy at 37 cl 32 7 1 6 hydrogen in the apatite is heavy at d 1060 180 much of that d came from spallogenic nuclear reactions and the original d was lower between 350 and 700 unlike other p rich lunar rocks e g 65015 79215 lacks abundant k and ree and other igneous incompatible elements characteristic of the lunar kreep component here we show that the p and halogens in 79215 were added to an otherwise normal granulite by vapor phase metasomatism similar to rock alteration by fumarolic exhalations as observed on earth the ultimate source of the p and halogens was most likely kreep it being the richest reservoir of p on the moon and 79215 having h and cl isotopic compositions consistent with kreep a kreep rich rock was heated and devolatilized by an impact event this vapor was fractionated by interaction with solid phases including merrillite a volatile free phosphate mineral a fe ti oxide and a zr bearing phase these solids removed ree th zr hf etc from the vapor and allowed the vapor to transport primarily p f and cl with lesser proportions of ba and u into 79215 vapor deposited crystals of apatite to 30 m are known in some lunar regolith samples but lunar vapor has not before this been implicated in significant mass transfer it seems unlikely however that phosphate halogen metasomatism is related to the high th sm abundance ratios of this and other lunar magnesian granulites the metasomatism of 79215 emphasizes the importance of impact heating in the lunar volatile cycle both in mobilizing volatile components into vapor and in generating strong elemental fractionations

fault zone deformational constraints on paleogene tectonic evolution in southern puerto rico paleogene deformation in south central puerto rico of cretaceous eocene volcaniclastic sediments and volcanic rocks is characterized by west northwest trending sinistral strike slip faults northeast directed thrusts and fault related mesoscopic folds a west northwest trending belt of predominantly eocene age sediments is flanked by upper cretaceous rocks a 8 15 km wide fault zone is spatially coincident with this lithologic belt structural data and deformational style indicate that the area is a sinistrally transpressive slightly north vergent asymmetric flower structure of which the upper portion is presently exposed in the belt of predominantly eocene sediments deformational characteristics in combination with sedimentary and tectonic evidence constrain evolutionary scenarios of the fault zone specifically age and amount of displacement and the northeastern caribbean as discussed herein

osmium isotope and highly siderophile element constraints on ages and nature of meteoritic components in ancient lunar impact rocks abstract the concentrations of highly siderophile elements hse re os ir ru pt rh pd au and 187os 188os isotope compositions have been determined for 67 subsamples of six lunar impact rocks from the apollo 14 16 and 17 landing sites and the lunar meteorite dar al gani dag 400 using inductively coupled plasma mass spectrometry icp ms and negative thermal ionization mass spectrometry n tims we report the first re os isochron age on a lunar impact melt rock 187re 187os isotope systematics for apollo 16 sample 67935 define an isochron age of 4 21 0 13 ga mswd 1 5 which is interpreted to reflect localized partitioning processes between solid metal liquid metal as this rock melted the new age adds further constraints on the significance of pre 4 0 ga basin forming impacts on the moon and possible mixing of ancient impactor compositions in lunar impact rocks linear correlations displayed by subsamples of a given impact rock in plots of hse versus ir concentrations are explained by dilution processes through essentially hse free anorthositic lunar crustal target rocks or binary mixing between a high hse meteoritic end member and a low hse end member composition slope derived hse ratios and 187os 188os of the meteoritic component in granulitic impactites 67915 67955 and 79215 are similar to slightly volatile element depleted carbonaceous chondrites suprachondritic ratios of ru ir pt ir rh ir and pd ir for apollo 14 impact melt rock 14310 are similar to ratios observed for other apollo 14 samples and apollo 17 poikilitic impact melt rocks apollo 16 poikilitic and subophitic impact melt rocks 60315 and 67935 show slightly subchondritic os ir and suprachondritic ratios of 187os 188os ru ir pt ir rh ir pd ir and au ir their strongly fractionated hse compositions are similar to some members of the iva iron meteorite group and provide further evidence for an iron meteorite impactor component in apollo 16 impact melt rocks the range of chondritic to suprachondritic ratios of 187os 188os ru ir pt ir pd ir and chondritic to slightly subchondritic os ir of apollo 17 and 14 impact melt rocks may be explained by variable mixing of a carbonaceous chondrite like hse composition as in granulitic impactites with a suprachondritic iron meteorite like impactor composition as inferred from 67935 and 60315 and subsequent homogenization by younger impact events the inferred dispersal of these two components across the lunar nearside and their antiquity 4 2 ga suggest at least two basin forming impacts that predate the 3 9 3 8 ga basin forming era the hse composition of the silicate earth can be matched by a late veneer comprised of 80 volatile depleted carbonaceous chondrite like material and 20 differentiated meteoritic metal similar to what has been identified in ancient lunar impact rocks

chromium isotopic homogeneity between the moon the earth and enstatite chondrites abstract among the elements exhibiting non mass dependent isotopic variations in meteorites chromium cr has been central in arguing for an isotopic homogeneity between the earth and the moon thus questioning physical models of moon formation however the cr isotopic composition of the moon relies on two samples only which define an average value that is slightly different from the terrestrial standard here by determining the cr isotopic composition of 17 lunar 9 terrestrial and 5 enstatite chondrite samples we re assess the isotopic similarity between these different planetary bodies and provide the first robust estimate for the moon in average terrestrial and enstatite samples show similar e 54 cr on the other hand lunar samples show variables excesses of 53cr and 54cr compared to terrestrial and enstatite chondrites samples with correlated e 53 cr and e 54 cr per 10 000 deviation of the 53cr 52cr and 54cr 52cr ratios normalized to the 50cr 52cr ratio from the nist srm 3112a cr standard unlike previous suggestions we show for the first time that cosmic irradiation can affect significantly the cr isotopic composition of lunar materials moreover we also suggest that rather than spallation reactions neutron capture effects are the dominant process controlling the cr isotope composition of lunar igneous rocks this is supported by the correlation between e 53 cr and e 54 cr and 150sm 152sm ratios after correction of these effects the average e 54 cr of the moon is indistinguishable from the terrestrial and enstatite chondrite materials reinforcing the idea of an earth moon enstatite chondrite system homogeneity this is compatible with the most recent scenarios of moon formation suggesting an efficient physical homogenization after a high energy impact on a fast spinning earth and or with an impactor originating from the same reservoir in the inner proto planetary disk as the earth and enstatite chondrites and having similar composition

lunar granulites and their precursor anorthositic norites of the early lunar crust lunar granulites are breccias with metamorphic textures they are not pristine having been contaminated with meteoritic siderophiles nonetheless they constitute an abundant class of highlands rocks that are important because they are ancient and kreep free they may represent our best samples of the early lunar crust the granulites can be divided into ferroan and magnesian groups and each group can be subdivided on the basis of mineral composition and ree concentrations textural and compositional data show that some of the granulites especially 67215 and 67415 may be derived from distinct anorthositic norite precursors while some other granulites 79215 78155 are clearly polymict even the polymict granulites probably had anorthositic norites as their dominant precursors and not anorthosites norites or troctolites the granulites have compositions similar to those of the two lunar meteorites one of which yamato 791197 is ferroan the other alha81005 magnesian these meteorites are soil breccias from an unknown location distant from the apollo landing sites and contain anorthositic norites as abundant clasts compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands as determined by remote sensing than do those of any other returned lunar samples the predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from apollo missions

examining the compositions of impactors striking the moon using apollo impact melt coats and anorthositic regolith breccia meteorites abstract impactors striking the moon since the formation of its crust have left an indelible imprint on the lunar surface in the guise of craters and associated impact rocks the lunar crust has low intrinsic abundances of the highly siderophile elements hse re os ir ru pt rh pd au at greater than 3000 times lower than in chondrite meteorites consequently during impact bolides with chondritic or differentiated iron rich compositions should impart elevated hse signatures to the lunar crust here we examine glassy lunar impact melt coats imc from the outside rims of apollo 16 cataclastic anorthosites 60015 65325 and breccias 65035 as well as both fragments and powders of antarctic anorthositic regolith breccia arb meteorites miller range 090034 36 70 75 and macalpine hills 88105 for their petrography mineral chemistry and bulk rock compositions the hse concentrations for imc range from 0 001 to 0 1 ci chondrite with measured 187os 188os between 0 1189 and 0 1366 anorthositic regolith breccia meteorites which have components with 2 6 4 1 ga ages have similar hse concentrations to imc but typically have lower 187os 188os 0 1164 0 1284 these latter os ratios are generally less radiogenic than those measured in 3 8 3 9 ga apollo impact melt breccias the apollo 16 imc are not well dated but their kreepy trace element signatures and associated ages of 3 7 to 3 8 ga for apollo 16 glasses might imply at least in part an origin from the imbrium or serenitatis basin forming impacts within the imc metal schreibersite troilite assemblages record significant inter element hse fractionation which is also reflected in bulk hse patterns for both imc and arb meteorites variations in relative and absolute hse compositions directly reflect the control of metal and sulfide segregation within and between impact melt and breccia lithologies collectively imc and arb meteorites exhibit approximately 50 of the variation in ru ir and 187os 188os observed in lunar impact melt breccias these results imply that significant variations in inter element compositions can occur during impact brecciation and melting and so some impact melt rock hse compositions may not record the compositions of impactors that struck the moon with fidelity nonetheless the generally low 187re 188os of lunar impact melt rocks means that osmium isotope ratios provide evidence for impact composition and a change from ordinary to carbonaceous like impactors either with time or location striking the moon

cretaceous paleogene thrust emplacement of serpentinite in southwestern puerto rico serpentinite emplacement mechanisms along convergent plate boundaries are complex and not well understood this investigation combined structural and stratigraphic data from serpentinite in puerto rico to suggest an emplacement mechanism along the north american caribbean plate boundary northward dipping thrust faults and foliations along the southern margins of the monte del estado and rio guanajibo serpentinite bodies in southwestern puerto rico indicate southwestward thrust movement of serpentinite structural analysis of faults folds and foliation recorded within the serpentinite bodies and analysis of contact relationships with volcano sedimentary rocks lead to the interpretation that thrust movements record contractional deformations occurring during the maastrichtian paleocene and late eocene early oligocene intervals the conclusion that serpentinite has been most recently emplaced above thrust faults during transpression between the caribbean north america plates is in contrast to the earlier hypothesis that serpentinite was emplaced in response to diapirism late eocene transpression reactivated older faults and also displaced the serpentinite although the timing of the serpentinite emplacement in southwestern puerto rico is similar to emplacement events in cuba and hispaniola there are differences in the origin mechanism and direction of emplacement of the serpentinite masses the heterogeneity in the serpentinite emplacement mechanism and transport direction evokes reconsideration of the deformation history along the caribbean north american plate boundary

the significance of stylolitization and intergranular pressure solution in the formation of pressure compartment seals in the st peter sandstone ordovician michigan basin the middle to late ordovician st peter sandstone of the michigan basin is a fine to medium grained quartz sandstone extensive stylolitization and intergranular pressure solution have been major factors in reducing the porosity of certain horizons within the st peter resulting in pressure compartmentation of the reservoir pressure versus depth data for various michigan basin wells indicate that the basin contains compartments that are overpressured by as much as 500 psi horizons bounding these compartments are often affected by intense stylolitization or intergranular pressure solution and quartz cementation and have been correlated with zones of low porosity and permeability phi 0 3 k 50 mu d these tight zones can be correlated within single gas fields and some may extend across the michigan basin the st peter sandstone has been buried to depths of about 3 500 m in the central part of the basin and 1 500 m at the margins intensely stylolitized zones are found at all depths throughout the basin and do not appear to change in abundance or style with depths factors that influence the formation morphology and abundance of stylolites in the st peter include 1 clay intraclasts 2 intergranular clay and 3 fine grained feldspar rich sand stylolitesmore also occur at contacts between quartz cemented and carbonate cemented zones and within well cemented sands intergranular pressure solution and stylolites may be responsible for the formation of a compartment seal understanding their genesis can allow prediction of variations in porosity in michigan basin well cores less

182w and hse constraints from 2 7 ga komatiites on the heterogeneous nature of the archean mantle abstract while the isotopically heterogeneous nature of the terrestrial mantle has long been established the origin scale and longevity of the heterogeneities for different elements and isotopic systems are still debated here we report nd hf w and os isotopic and highly siderophile element hse abundance data for the boston creek komatiitic basalt lava flow bcf in the 2 7 ga abitibi greenstone belt canada this lava flow is characterized by strong depletions in al and heavy rare earth elements ree enrichments in light ree and initial e143nd 2 5 0 2 and intial e176hf 4 2 0 9 indicative of derivation from a deep mantle source with time integrated suprachondritic sm nd and lu hf ratios the data plot on the terrestrial nd hf array suggesting minimal involvement of early magma ocean processes in the fractionation of lithophile trace elements in the mantle source this conclusion is supported by a mean 142nd 3 8 2 8 that is unresolvable from terrestrial standards by contrast the bcf exhibits a positive 182w anomaly 182w 11 7 4 5 yet is characterized by chondritic initial 187os 0 1 0 3 and low inferred source hse abundances 35 5 of those estimated for the present day bulk silicate earth bse collectively these characteristics are unique among archean komatiite systems studied so far the deficit in the hse coupled with the chondritic os isotopic composition but a positive 182w anomaly are best explained by derivation of the parental bcf magma from a mantle domain characterized by a predominance of hse deficient differentiated late accreted material according to the model presented here the mantle domain that gave rise to the bcf received only 35 of the present day hse complement in the bse before becoming isolated from the rest of the convecting mantle until the time of komatiite emplacement at 2 72 ga these new data provide strong evidence for a highly heterogeneous archean mantle in terms of absolute hse abundances and w isotopic composition and also indicate slow mixing on a timescale of at least 1 8 billion years additionally the data are consistent with a stagnant lid plate tectonic regime in the hadean and archean prior to the onset of modern style plate tectonics

osmium isotope and highly siderophile element systematics of the lunar crust abstract coupled 187os 188os and highly siderophile element hse os ir ru pt pd and re abundance data are reported for pristine lunar crustal rocks 60025 62255 65315 ferroan anorthosites fan and 76535 78235 77215 and a norite clast in 15455 magnesian suite rocks mgs osmium isotopes permit more refined discrimination than previously possible of samples that have been contaminated by meteoritic additions and the new results show that some rocks previously identified as pristine contain meteorite derived hse low hse abundances in fan and mgs rocks are consistent with derivation from a strongly hse depleted lunar mantle at the time of formation the lunar floatation crust represented by fan had 1 4 0 3 pg g 1 os 1 5 0 6 pg g 1 ir 6 8 2 7 pg g 1 ru 16 15 pg g 1 pt 33 30 pg g 1 pd and 0 29 0 10 pg g 1 re 0 00002 ci and re os ratios that were modestly elevated 187re 188os 0 6 to 1 7 relative to ci chondrites mgs samples are on average characterised by more elevated hse abundances 0 00007 ci compared with fan this either reflects contrasting mantle source hse characteristics of fan and mgs rocks or different mantle crust hse fractionation behaviour during production of these lithologies previous studies of lunar impact melt rocks have identified possible elevated ru and pd in lunar crustal target rocks the new results provide no supporting evidence for such enrichments if maximum estimates for hse in the lunar mantle are compared with fan and mgs averages crust mantle concentration ratios d values must be 0 3 such d values are broadly similar to those estimated for partitioning between the terrestrial crust and upper mantle with the notable exception of re given the presumably completely different mode of origin for the primary lunar floatation crust and tertiary terrestrial continental crust the potential similarities in crust mantle hse partitioning for the earth and moon are somewhat surprising low hse abundances in the lunar crust coupled with estimates of hse concentrations in the lunar mantle implies there may be a missing component of late accreted materials as much as 95 to the moon if the earth moon mass flux estimates are correct and terrestrial mantle hse abundances were established by late accretion

identifying impact events within the lunar cataclysm from 40ar 39ar ages and compositions of apollo 16 impact melt rocks abstract lunar impact melt breccias provide a unique record of the timing and frequency of collisional events during the early history of the inner solar system prior to the development of a significant rock record on earth the predominance of ages clustering between 3 8 and 4 0 ga was a major unexpected discovery obtained from geochronological studies of lunar impact melts and is the basis of the concept that a cataclysmic bombardment of large planetesimals struck the earth and moon and possibly the entire inner solar system about 3 85 0 10 billion years ago as a test of the cataclysm hypothesis we measured high resolution 20 50 steps 40 ar 39 ar age spectra on 25 samples of apollo 16 impact melt breccias using a continuous laser heating system on sub milligram fragments twenty one of these 25 breccias produced multi step plateaus that we interpret as crystallization ages with 20 of these ages falling in the range 3 75 3 96 ga we propose that at least four different melt producing impact events can be distinguished based on the ages bulk compositions and petrographic characteristics of apollo 16 melt breccias the recognition of multiple impact events within the apollo 16 melt breccia suite shows that numerous impact events occurred on the lunar surface within a relatively narrow time interval providing additional evidence of a heavy bombardment of the moon during the early archean

feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust we present new compositional data for six feldspathic lunar meteorites two from cold deserts yamato 791197 and 82192 and four from hot deserts dhofar 025 northwest africa 482 and dar al gani 262 and 400 the concentrations of feo or al2o3 and th or any other incompatible element together provide first order compositional information about lunar polymict samples breccias and regoliths and regions of the lunar surface observed from orbit concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft although the derived concentrations have large uncertainties and some systematic errors compared to sample data within the uncertainties and errors in the concentrations derived from orbital data the distribution of feo and th concentrations among lunar meteorites which represent 18 source regions on the lunar surface is consistent with that of 18 random samples from the surface approximately 11 of the lunar meteorites are low feo and low th breccias consistent with large regions of the lunar surface particularly the northern farside highlands almost all regoliths from apollo sites on the other hand have larger concentrations of both elements because they contain fe rich volcanic lithologies from the nearside maria and th rich lithologies from the high th anomaly in the northwestern nearside the feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands and we provide such an estimate based on the eight most well characterized feldspathic lunar meteorites the variable but high on average mg fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high mg fe feldspathic rocks such as magnesian granulitic breccia not ferroan anorthosite geochemically the high mg fe breccias appear to be unrelated to the mafic magnesian suite rocks of the apollo collection models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites

antarctic meteorite alha81005 not just another lunar anorthositic norite seven subsamples of meteorite alha81005 a regolith breccia from the lunar highlands were analyzed by inaa for 32 elements four of them were also studied petrographically in bulk composition the rock corresponds to anorthositic norite with a very small component of kreep and is very similar to estimates of average lunar highlands surface compositions of the white clasts and the dark matrix are similar but the clasts are more magnesian and 30 50 as rich in kreep related elements the white clasts have fine grained granulitic textures and are generally similar to apollo 16 and 17 granulitic anorthositic norites but are more magnesian and only 20 as rich in kreep related elements some granulitic clasts are dominated by a magnesian anorthositic norite component not represented among the pristine apollo samples

osmium isotope and highly siderophile element systematics of lunar impact melt breccias implications for the late accretion history of the moon and earth abstract to characterize the compositions of materials accreted to the earth moon system between about 4 5 and 3 8 ga we have determined os isotopic compositions and some highly siderophile element hse re os ir ru pt and pd abundances in 48 subsamples of six lunar breccias these are apollo 17 poikilitic melt breccias 72395 and 76215 apollo 17 aphanitic melt breccias 73215 and 73255 apollo 14 polymict breccia 14321 and lunar meteorite nwa482 a crystallized impact melt plots of ir versus other hse define excellent linear correlations indicating that all data sets likely represent dominantly two component mixtures of a low hse target presumably endogenous component and a high hse presumably exogenous component linear regressions of these trends yield intercepts that are statistically indistinguishable from zero for all hse except for ru and pd in two samples the slopes of the linear regressions are insensitive to target rock contributions of ru and pd of the magnitude observed thus the trendline slopes approximate the elemental ratios present in the impactor components contributed to these rocks the 187 os 188 os and regression derived elemental ratios for the apollo 17 aphanitic melt breccias and the lunar meteorite indicate that the impactor components in these samples have close affinities to chondritic meteorites the hse in the apollo 17 aphanitic melt breccias however might partially or entirely reflect the hse characteristics of hse rich granulitic breccia clasts that were incorporated in the impact melt at the time of its creation in this case the hse characteristics of these rocks may reflect those of an impactor that predated the impact event that led to the creation of the melt breccias the impactor components in the apollo 17 poikilitic melt breccias and in the apollo 14 breccia have higher 187 os 188 os pt ir and ru ir and lower os ir than most chondrites these compositions suggest that the impactors they represent were chemically distinct from known chondrite types and possibly represent a type of primitive material not currently delivered to earth as meteorites

the meteorite component of apollo 16 noritic impact melt breccias noritic melt rocks alias lkfm and vha from apollo 16 have concentrations of ni approximately three to five times those of impact melt rocks of similar composition from other lunar landing sites the melt rock associated with apollo 16 dimict breccias has the highest mean concentration of ni of any lunar rock type 1150 g g in 11 samples the ni is contained in fe ni metal that is dissimilar in composition to metal from ordinary chondrites in having a lower ni concentration 6 and lower ni co ratio 17 it also has ir ni and ir au ratios of about one half and one third those of chondrites the metal in the noritic impact melts is the carrier of the siderophile element signature of ancient meteorite group 1h the composition of the fe ni metal is dissimilar to that of chondrites because it derives from metal rich meteorites probably irons that created the impact melts 3 9 ga ago the metal from these iron meteorites dominates the siderophile element concentrations of polymict samples at apollo 16 models that attempt to estimate indigenous concentrations of ni and co in apollo 16 materials overestimate their abundance by assuming that the meteoritic component has chondritic ratios of ir to ni and co the type 2 melt vha associated with the dimict breccias and the type 1 melt apollo 16 lkfm were most likely produced by impact of two related iron meteoroids that impacted near the apollo 16 site the type 2 melt found in samples from station 7 is probably from the same impact as that producing the dimict breccias although it could represent the impact of a third related iron

rapid effects of terrestrial alteration on highly siderophile elements in the sutter s mill meteorite the 187re 187os isotopic systematics of many bulk chondrites plot well beyond analytical uncertainties of a primordial isochron limited variations in 187os 188os coupled with large variations in re os ratios among chondrites suggest that this apparently open system behavior is a result of the comparatively recent gain or loss of re and or os in order to assess whether or not rapid alteration in the terrestrial environment could be responsible for open system behavior in chondrites four pieces of the sutter s mill meteorite were examined for os isotopic systematics and abundances of highly siderophile elements pieces sm1 and sm2 were collected prior to a rain event within 2 days of the fall pieces sm51 and sm53 were collected after a rain event there are significant but minor relative and absolute variations in the abundances of the highly siderophile elements as well as 187os 188os among the four pieces rhenium os isotopic data for sm1 and sm2 plot within analytical uncertainties of a primordial isochron while powders made from sm51 and sm53 do not these results suggest that interactions with rain caused some redistribution of re and to a lesser extent os within small pieces of the meteorite thus re os isotopic systematics of dm size pieces of chondrites must be considered susceptible to modification after only a short time on the surface where exposed to rain

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

pt re os systematics of group iiab and iiiab iron meteorites the pt re os isotopic and elemental systematics of 13 group iiab and 23 group iiiab iron meteorites are examined as has been noted previously for iron meteorite groups and experimental systems solid metal liquid metal bulk distribution coefficients d values for both iiab and iiiab systems show dos dre dpt 1 during the initial stages of core crystallization assuming closed system crystallization the latter stages of crystallization for each core are generally characterized by dpt dre dos the processes governing the concentrations of these elements are much more complex in the iiiab core relative to the iiab core several crystallization models utilizing different starting parameters and bulk distribution coefficients are considered for the re os pair each model has flaws but in general the results suggest that the concentrations of these elements were dominated by equilibrium crystallization and subsequent interactions between solid metal and both equilibrium and evolved melts late additions of primitive metal to either core were likely minor or nonexistent the 187re 187os systematics of the iiab and iiiab groups are consistent with generally closed system behavior for both elements since the first several tens of ma of the formation of the solar system consistent with short lived chronometers the re os isochron ages for the complete suites of iiab and iiiab irons are 4530 50 ma and 4517 32 ma respectively and are similar to previously reported re os ages for the lower ni endmembers of these two groups both isochrons are consistent with but do not require crystallization of the entire groups within 10 30 ma of the initiation of crystallization the first high precision 190pt 186os isochrons for iiab and iiiab irons are presented the pt os isochron ages for the iiab and iiiab irons calculated using the current best estimate of the for 190pt are 4323 80 ma and 4325 26 ma respectively the re os and pt os ages do not overlap within the uncertainties the younger apparent ages recorded by the pt os system likely reflect error in the 190pt decay constant the slope from the pt os isochron is combined with the age from the re os isochron for the iiiab irons to calculate a revised of 1 415 10 12 a 1 for 190pt although additional study of this decay constant is still needed

pieces of the ancient lunar crust ages and composition of clasts in consortium breccia 67915 we discuss the composition and chronology of clasts representing three minor lithologies in consortium breccia 67915 the lithologies studied are sodic ferrogabbro pristine troctolitic anorthosite 67915 26 and granulitic troctolitic anorthosite 67915 67 these lithologies were presumed to represent samples of the ancient lunar crust the pristine troctolitic anorthosite a typical member of the pristine anorthosite suite contains little or no trapped liquid consistent with its two phase mineralogy the plagioclase separates have 39ar 40ar plateau ages of 4 10 0 06 b y and a final rise in the age pattern may represent a memory of the earlier evolution the granulitic troctolitic anorthosite which has 13 times larger ree abundances displays a continuous rise of the 40ar 39ar ratio the last 25 of the 39ar release data establish a minimum age of 3 5 b y but the 244pu nd chronology suggests an age of 4 3 b y the sodic ferrogabbro samples which appear to be members of the mg gabbronorite group of pristine rocks show large ar losses but indicate plateaus in the low temperature data suggesting a metamorphic event more recently than 260 m y ago a time that is consistent with the north ray impact event 50 m y ago

are high temperature fractionations in the solar nebula preserved in highly siderophile element systematics of the earth s mantle the relative abundances of the highly siderophile elements hse os ir ru pt rh and pd in relatively pristine lherzolites differ from solar abundance ratios and are several orders of magnitude higher than predicted for equilibrium distribution between metal silicate core mantle the samples are characterized by a mean ca al ratio of 1 18 0 09 m and a mean ca si ratio of 0 10 0 01 m overlapping with a mean ca al of 1 069 0 044 m and a mean ca si of 0 081 0 023 m found in chondrites wasson and kallemeyn 1988 interestingly the ci normalized abundance pattern shows decreasing solar system normalized abundances with increasing condensation temperatures the abundance of the moderately volatile element pd is about 2x higher than those in the most refractory siderophiles ir and os thus the hse systematics of upper mantle samples suggest that the late bombardment which added these elements to the accreting earth more closely resembles materials of highly reduced eh or el chondrites than carbonaceous chondrites in fact the hse in the earth mantle are even more fractionated than the enstatite chondritesan indication that some inner solar system materials were more highly fractionated than the latter

petrography geochronology and source terrain characteristics of lunar meteorites dhofar 925 961 and sayh al uhaymir 449 abstract dhofar dho 925 961 and sayh al uhaymir sau 449 are brecciated lunar meteorites consisting of mineral fragments and clasts from a range of precursor lithologies including magnesian anorthositic gabbronorite granulites crystalline impact melt breccias clast bearing glassy impact melt breccias lithic fragmental breccias mare basalts and evolved silica rich rocks on the similarity of clast type and mineral chemistry the samples are likely grouped and were part of the same parent meteorite phosphate pb pb ages in impact melt breccias and matrix grains demonstrate that dho 961 records geological events spanning 500 ma between 4 35 and 3 89 ga these pb pb ages are similar to the ages of ancient intrusive magmatic samples and impact basin melt products collected on the lunar nearside by the apollo missions however the samples bulk rock composition is chemically distinct from these types of samples and it has been suggested that they may have originated from the farside south pole aitken impact basin i e jolliff et al 2008 we test this hypothesis and conclude that although it is possible that the samples may be from the south pole aitken basin there are other regions on the moon that may have also sourced these complex breccias

geochemical studies of feldspathic fragmental breccias and the nature of north ray crater ejecta major and trace element analyses of clasts and matrix from feldspathic fragmental breccias show that these breccias are not all alike but vary widely in their bulk compositions and clast assemblages these studies together with analyses of other north ray crater large rocks reveal the major components to be anorthosites ferroan anorthositic norites magnesian granulites feldspathic melt rocks and vha impact melts the ferroan anorthositic norites are important lunar crustal rocks identified here for the first time the kreepy vha melts are found to be much more important in north ray crater ejecta than was previously assumed sodic ferrogabbro is an important minor component the compositional characteristics of bulk breccias and feldspathic melt rocks are modeled quantitatively as mixtures of two to five components anorthosites ferroan anorthositic norites magnesian granulites sodic ferrogabbros and vha melt rocks breccia 67455 is unique in consisting wholly of ferroan kreep free components

the granulitic impactite suite impact melts and metamorphic breccias of the early lunar crust abstract an important and poorly understood group of rocks found in the ancient lunar highlands is called feldspathic granulitic impactites rocks of the granulite suite occur at most of the apollo highlands sites as hand samples rake samples clasts in breccias and soil fragments most lunar granulites contain 70 80 modal plagioclase but they can range from anorthosite to troctolite and norite previous studies have led to different interpretations for the thermal history of these rocks including formation as igneous plutons long duration metamorphism at high temperatures and short duration metamorphism at low temperatures this paper reports on a study of 24 polished thin sections of lunar granulites from the apollo 15 16 and 17 missions we identify three different textural types of granulitic breccias poikilitic granoblastic and poikilitic granoblastic breccias these breccias have similar equilibration temperatures 1100 50 c as well as common compositions crystal size distributions in two granoblastic breccias reveal that ostwald ripening took place during metamorphism solid state grain growth and diffusion calculations indicate relatively rapid cooling during metamorphism 0 5 to 50 c year and thermal modeling shows that they cooled at relatively shallow depths 200 m in contrast we conclude that the poikilitic rocks formed by impact melting whereas the poikilitic granoblastic rocks were metamorphosed and may have partially melted these results indicate formation of lunar granulites in relatively small craters 30 90 km in diameter physically associated with the impact melt breccia pile and possibly from fine grained fragmental precursor lithologies

tungsten isotopic evidence for disproportional late accretion to the earth and moon examination of three lunar samples reveals that the moon s mantle has an excess of the tungsten isotope 182w of about 20 parts per million relative to the present day earth s mantle this suggests that the two bodies had identical compositions immediately following the formation of the moon and that the compositions then diverged as a result of disproportional late accretion of chondritic material to the earth and moon two papers published in this issue of nature present precise measurements of tungsten isotope composition in lunar rocks that are best explained by the earth and moon having had similar composition immediately following formation of the moon and then having diverged as a result of disproportional late accretion of material to the two bodies mathieu touboul et al found small 182w excess of about 21 parts per million relative to the present day earth s mantle in metals extracted from two kreep rich apollo 16 impact melt rocks while thomas kruijer et al measured tungsten isotopes in seven kreep rich whole rock samples that span a wide range of cosmic ray exposure ages and found a 182w excess of about 27 parts per million over the present day earth s mantle characterization of the hafnium tungsten systematics 182hf decaying to 182w and emitting two electrons with a half life of 8 9 million years of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant impact theory for the formation and evolution of the moon and for testing the late accretion hypothesis uniform terrestrial mantle like w isotopic compositions have been reported1 2 among crystallization products of the lunar magma ocean these observations were interpreted to reflect formation of the moon and crystallization of the lunar magma ocean after 182hf was no longer extant that is more than about 60 million years after the solar system formed here we present w isotope data for three lunar samples that are more precise by a factor of 4 than those previously reported1 2 the new data reveal that the lunar mantle has a well resolved 182w excess of 20 6 5 1 parts per million 2 standard deviations relative to the modern terrestrial mantle the offset between the mantles of the moon and the modern earth is best explained by assuming that the w isotopic compositions of the two bodies were identical immediately following formation of the moon and that they then diverged as a result of disproportional late accretion to the earth and moon3 4 one implication of this model is that metal from the core of the moon forming impactor must have efficiently stripped the earth s mantle of highly siderophile elements on its way to merge with the terrestrial core requiring a substantial but still poorly defined level of metal silicate equilibration

diverse impactors in apollo 15 and 16 impact melt rocks evidence from osmium isotopes and highly siderophile elements abstract concentrations of highly siderophile elements hse and 187 os 188 os isotopic compositions for eleven impact related rocks from the apollo 15 and 16 landing sites are reported and combined with existing geochronological data to investigate the chemical nature and temporal changes in the large impactors implicated in the formation of the lunar basins data for the samples all define linear trends on plots of hse versus ir concentrations whose slopes likely reflect the relative hse compositions of the dominant impactors that formed the rocks the inferred imbrium basin impactor that generated apollo 15 impact melt rocks 15445 and 15455 was characterized by modestly suprachondritic 187 os 188 os ru ir pt ir and pd ir ratios diverse impactor components are revealed in the apollo 16 impact melt rocks the 187 os 188 os and hse ir ratios of the impactor components in melt rocks 60635 63595 and 68416 with reported ages 4 0 ga by contrast the impactor components in melt rocks 60235 62295 and 67095 with reported ages of 3 9 ga are characterized by suprachondritic 187 os 188 os and hse ir ratios similar to the apollo 15 impact melt rocks and may also sample the imbrium impactor three lithic clasts from regolith breccias 60016 and 65095 also with 3 9 ga ages contain multiple impactor components of which the dominant composition is considerably more suprachondritic than those implicated for imbrium and serenitatis apollo 17 impactors the dominant composition recorded in these rocks was most likely inherited from a pre imbrium impactor consideration of composition versus age relations among lunar impact melt rocks reveals no discernable trend virtually all lunar impact melt rocks sampled by the apollo missions as well as meteorites are characterized by 187 os 188 os and hse ir ratios that when collectively plotted define linear trends ranging from chondritic to fractionated compositions the impact melt rocks with hse signatures within the range of chondritic meteorites are interpreted to have been derived from impactors that had hse compositions similar to known chondrite groups by contrast the impact melt rocks with non chondritic relative hse concentrations could not have been made by mixing of known chondritic impactors these signatures may instead reflect contributions from early solar system bodies with bulk chemical compositions that have not yet been sampled by primitive meteorites present in our collections alternately they may reflect the preferential incorporation of evolved metal separated from a fractionated planetesimal core pre 4 0 ga ages for at least some impactor components with both chondritic and fractionated hse raise the possibility that the bulk of the hse were added to the lunar crust prior to the later stage basin forming impacts such as imbrium and serenitatis as proposed by fischer godde and becker 2012 for this scenario the later stage basin forming impacts were more important with respect to mixing prior impactor components into melt rocks rather than contributing much to the hse budgets of the rocks themselves

siderophile elements in brecciated hed meteorites and the nature of projectile materials in hed meteorites abstract petrological mineralogical and geochemical studies were performed on five brecciated hed meteorites alh 76005 eet 92003 lew 85300 lew 87026 and gro 95633 in order to elucidate the nature of impactors on the hed parent body some brecciated hed meteorites contain exotic materials such as feni metal grains with low co ni ratios alh 76005 eet 92003 and gro 95633 and carbonaceous chondrite clasts lew 85300 in a clastic and or impact melt matrix such exotic materials were incorporated during brecciation platinum group element pge abundances vary significantly ci 0 002 0 05 but are higher than those of pristine rocks from the hed parent body the pge ratios for the five hed meteorites are inconsistent with each other implying that the impactor components of each hed meteorites are different from each other the various pge ratios are consistent with those for metals from chondrites and iron meteorites and carbonaceous chondrites this study provides the evidence that iab and iva iron meteorites and carbonaceous chondrites cm co cv ck cb and cr ordinary chondrites l and h and enstatite chondrite el are candidates of the impactor materials on the hed parent body it is highly probable that significant amounts of siderophile elements were incorporated into the inner solar system objects like the hed parent body from both chondritic materials and differentiated materials like iron meteorites during heavy bombardment the hed meteorites in this study and metals from mesosiderite have different pd ir ratios probably implying that hed meteorites and mesosiderites formed either at distinct settings on one common parent body or on similar parent bodies

complex magmatic and impact history prior to 4 1 ga recorded in zircon from apollo 17 south massif aphanitic breccia 73235 abstract sample 73235 is one of several aphanitic impact melt breccias collected by the apollo 17 mission at stations 2 and 3 on the slopes of the south massif this study presents a detailed investigation of internal structures and u pb ages of large zircon grains from this breccia sample new data combined with the results of previous studies of zircon grains from the same location indicate that most zircon clasts in breccias from stations 2 and 3 formed during multiple magmatic events between 4 37 and 4 31 ga although the oldest zircon crystallized at about 4 42 ga and the youngest at 4 21 ga in addition zircons from the aphanitic breccias record several impact events prior to the 3 9 ga late heavy bombardment the results indicate that the zircons probably crystallized at different locations within the procellarum kreeep terrane and were later excavated and modified by several impacts and delivered to the same locality within separate ejecta blankets this locality became a source of material that formed the aphanitic impact melt breccias of the south massif during a 3 9 ga impact however the zircons showing old impact features are not modified by this 3 9 ga impact event suggesting that i this common source area was located at the periphery of excavation cavity and ii the 3 9 ga ages recorded by the zircon grains could date large basin forming events as significant as major later 3 9 ga collisions such as imbrium and serenitatis

a protracted timeline for lunar bombardment from mineral chemistry ti thermometry and u pb geochronology of apollo 14 melt breccia zircons new zircon u pb and trace element investigations from apollo 14 lunar impact breccia sample 14311 reveal at least three distinct concordia 2 age populations at 4334 10 4245 10 and 3953 10 ma titanium in zircon thermometry tixln results correlated with u pb ages range from 800 1200 oc lattice strain models used to infer zircon versus whole rock rare earth element contents and partitioning calculations against lunar impact breccia component compositions quantitatively constrain formation conditions for the different age populations a compilation of new data with published work shows that apollo 14 zircons older than ca 4300 ma formed by igneous processes associated with lunar crust formation compositional variability in the ca 4240 ma zircon age population is interpretable however via a mixture of inherited and melt generated components from one or more large impacts perhaps related to a marked increase in bombardment flux ages from the youngest zircon group at ca 3950 ma coincide with the classical late heavy bombardment lhb as documented from previous lunar geochronologies these results lend support to the idea that instead of a simple unimodal lhb scenario or a monotonic decline in impacts the moon was battered by multiple cataclysms since ca 4240 ma such a picket fence like bombardment to the moon best describes the mode and tempo of impacts that accompanied the late stages of solar system formation and giant planet migration

cratering history and lunar chronology the moon is exceptional and important because it is the only planetary body besides the earth for which we have both a detailed stratigraphic history and datable rock samples that can be related to specific geomorphologic units fig 5 1 the moon has preserved much of its magmatic and impact record of at least the last 4 billion years while its endogenic history is of great interest for the fundamentals of planetary interiors and surfaces the moon has become a calibration plate for the cratering record of the earth moon system and by extrapolation of the entire inner solar system if one assumes a heliocentric origin for impactor populations these populations range from asteroids through long and short period comets to interplanetary dust and cover a size range from hundreds of kilometers to micrometers figure 5 1 telescopic view of the nearside of the earth s moon with landing sites of the apollo and luna missions this chapter reviews the presently available data sets in support of this paradigmatic assumption as follows 1 the phenomenology of lunar impact craters 2 the terrestrial record of the impact cratering process and the interpretation of terrestrial impactites as far as this ground truth is relevant for the interpretation of lunar impact craters and datable lunar impact breccias and melt rocks 3 the theory and numerical simulation of the cratering process and the characteristics of the earth moon crossing population of impactors asteroids and comets 4 the principles of relative age dating of lunar surface units and the general lunar stratigraphy 5 the stratigraphic significance and ages of lunar samples impactites and basalts and based on this data set the absolute ages of lunar surface units 6 the cratering rate of the moon as a function of time and 7 the time calibration of this cratering rate based on the

group iva irons new constraints on the crystallization and cooling history of an asteroidal core with a complex history we report analyses of 14 group iva iron meteorites and the ungrouped but possibly related elephant moraine eet 83230 for siderophile elements by laser ablation icp ms and isotope dilution eet was also analyzed for oxygen isotopic composition and metallographic structure and fuzzy creek currently the iva with the highest ni concentration was analyzed for metallographic structure highly siderophile elements hse re os and ir concentrations vary by nearly three orders of magnitude over the entire range of iva irons while ru pt and pd vary by less than factors of five chondrite normalized abundances of hse form nested patterns consistent with progressive crystal liquid fractionation attempts to collectively model the hse abundances resulting from fractional crystallization achieved best results for 3 wt s compared to 0 5 or 9 wt s consistent with prior studies concentrations of hse and other refractory siderophile elements estimated for the bulk iva core and its parent body are in generally chondritic proportions projected abundances of pd and au relative to more refractory hse are slightly elevated and modestly differ from l ll chondrites which some have linked with group iva based on oxygen isotope similarities abundance trends for the moderately volatile and siderophile element ga cannot be adequately modeled for any s concentration the cause of which remains enigmatic further concentrations of some moderately volatile and siderophile elements indicate marked progressive depletions in the iva system however if the iva core began crystallization with 3 wt s depletions of more volatile elements cannot be explained as a result of prior volatilization condensation processes the initial iva core had an approximately chondritic ni co ratio but a fractionated fe ni ratio of 10 indicates an fedepleted core this composition is most easily accounted for by assuming that the surrounding silicate shell was enriched in iron consistent with an oxidized parent body the depletions in ga may reflect decreased siderophilic behavior in a relatively oxidized body and more favorable partitioning into the silicate portion of the parent body phosphate inclusions in eet show d 17 o values within the range measured for silicates in iva iron meteorites eet has a typical ataxitic microstructure with precipitates of kamacite within a matrix of plessite chemical and isotopic evidence for a genetic relation between eet and group iva is strong but the high ni content and the newly determined rapid cooling rate of this meteorite show that it should continue to be classified as ungrouped previously reported metallographic cooling rates for iva iron meteorites have been interpreted to indicate an inwardly crystallizing 150 km radius metallic body with little

magnetic anomalies in the imbrium and schrodinger impact basins orbital evidence for persistence of the lunar core dynamo into the imbrian epoch approximate maps of the lunar crustal magnetic field at low altitudes in the vicinities of the three imbrian aged impact basins orientale schrodinger and imbrium have been constructed using lunar prospector and kaguya orbital magnetometer data detectable anomalies are confirmed to be present well within the rims of imbrium and schrodinger anomalies in schrodinger are asymmetrically distributed about the basin center while a single isolated anomaly is most clearly detected within imbrium northwest of timocharis crater the subsurface within these basins was heated to high temperatures at the time of impact and required long time periods up to 1 myr to cool below the curie temperature for metallic iron remanence carriers 1043 k therefore consistent with laboratory analyses of returned samples a steady long lived magnetizing field i e a former core dynamo is inferred to have existed when these basins formed the asymmetrical distribution within schrodinger suggests partial demagnetization by later volcanic activity when the dynamo field was much weaker or nonexistent however it remains true that anomalies within imbrian aged basins are much weaker than those within most nectarian aged basins the virtual absence of anomalies within orientale where impact melt rocks the maunder formation are exposed at the surface is difficult to explain unless the dynamo field was much weaker during the imbrian period

crystal accumulation in a 4 2 ga lunar impact melt abstract the ages of lunar impact basins and the role of fractional crystallization in producing compositional heterogeneity of lunar melt sheets are long standing problems with significant implications for solar system dynamics and the petrologic evolution of the lunar crust here we document the formation of a basin scale impact on the moon at 4 20 0 07 ga based on the 147 sm 143 nd isochron age of a magnesian noritic anorthosite melt rock from lunar breccia 67955 major element compositions of plagioclase and mafic silicates in the melt rock imply a substantial component of primary mg suite cumulates or related lithologies in the pre impact crustal stratigraphy trace element compositions of the plagioclase including diagnostic ratios such as sr ba are also mostly similar to those in plagioclase from mg suite cumulates with a small number of grains trending toward compositions observed in ferroan anorthosites mineral melt distribution coefficients applied to trace element compositions of the 67955 plagioclase and pyroxene predict parental melt compositions that contrast strongly with the bulk rock compared to the whole rock parental melts calculated from the plagioclase are enriched in ree ree la yb 131 885 average 619 ppm vs 39 8 ppm and they have more fractionated ree patterns la yb n 1 2 9 8 average 4 9 vs 1 5 with deep negative eu anomalies eu eu 0 09 0 40 vs 1 36 trace element data for the pyroxenes also imply incompatible element enriched parental melts subsolidus equilibration between the plagioclase and the pyroxene apparently rotated the ree patterns but the conclusion that the parental melt was highly enriched in ree relative to the whole rock appears robust quantitative modeling shows that fractional crystallization of the 67955 whole rock composition cannot reproduce the range of ba sr ti and la concentrations measured in the 67955 plagioclase rather the models require an initial melt composition that was strongly enriched in these elements and they suggest that fractional crystallization became less efficient as crystallization proceeded the contrast between the inferred parental melt composition and the bulk rock implies formation of the 67955 noritic anorthosite as a crystal cumulate and that the cogenetic residual melt was strongly enriched in incompatible elements if so this would be the first documented example of fractional crystallization in a lunar impact melt sheet the petrological and geochemical characteristics of the 67955 noritic anorthosite suggest that it formed by an impact in the procellarum kreep terrane and was transported to the apollo 16 site as imbrium ejecta inheritance of ejecta related to this pre imbrium basin may contribute to the common occurrence of 4 2 ga 40 ar 39 ar plateau ages in breccia clasts and regolith fragments from the rim of north ray crater in that case those data may provide no constraints on the age of the nectaris basin despite its proximity to the apollo 16 site

new constraints on the paleoarchean meteorite bombardment of the earth geochemistry and re os isotope signatures of spherule layers in the barb5 icdp drill core from the barberton greenstone belt south africa abstract archean spherule layers resulting from impacts by large extraterrestrial objects to date represent the only remnants of the early meteorite asteroid and comet bombardment of the earth only few archean impact debris layers have been documented all of them embedded in the 3 23 3 47 billion year old successions of the barberton greenstone belt bgb in south africa and the pilbara craton in western australia some of them might be correlated with each other given the scarcity of archean spherule deposits four spherule layer intersections from the recently recovered barb5 drill core from the central barberton greenstone belt analyzed in this study provide an opportunity to gain new insight into the early terrestrial impact bombardment despite being hydrothermally overprinted siderophile element abundance signatures of spherule rich samples from the barb5 drill core at least in part retained a meteoritic fingerprint the impact hypothesis for the generation of the barb5 spherule layers is supported by correlations between the abundances of moderately cr co ni and highly siderophile re os ir pt ru and pd elements whose peak concentrations and interelement ratios are within the range of those for chondrites rhenium osmium isotope evidence further support the impact hypothesis collectively this study provides evidence for extraterrestrial admixtures ranging between 40 and up to 100 to three of the four analyzed barb5 spherule layers and a scenario for their genesis involving i impact of a chondritic bolide into a sedimentary target ii varying admixtures of meteoritic components to target materials iii spherule formation via condensation in an impact vapor plume iv transportation of the spherules and sedimentation under submarine conditions followed by v moderate post impact remobilization of transition metals and highly siderophile elements

thermal history recorded by the apollo 17 impact melt breccia 73217 abstract lunar breccia 73217 is composed of plagioclase and pyroxene clasts originating from a single gabbronorite intrusion mixed with a silica rich glass interpreted to represent an impact melt a study of accessory minerals in a thin section from this breccia 73217 52 identified three different types of zircon and anhedral grains of apatite which represent distinct generations of accessory phases and provide a unique opportunity to investigate the thermal history of the sample equant anhedral zircon grains that probably formed in the gabbronorite referred to as type 1 have consistent u pb ages of 4332 7 ma a similar age of 4335 5 ma was obtained from acicular zircon type 2 grains interpreted to have formed from impact melt a polycrystalline zircon aggregate type 3 occurs as a rim around a baddeleyite grain and has a much younger age of 3929 10 ma similar to the 3936 17 ma age of apatite grains found in the thin section a combined apatite type 3 zircon age of 3934 12 ma is proposed as the age of the serenitatis impact event and associated thermal pulse x ray mapping and electron probe analyses showed that ti is inhomogeneous in the zircon grains on the sub micrometer scale however model temperatures estimated from shrimp analyses of ti concentration in the 10 m diameter spots on the polished surfaces of type 1 and type 2 zircons range between about 1300 and 900 c respectively whereas ti concentrations determined for the type 3 zircon are higher at about 1400 1500 c a combination of u pb ages ti concentration data and detailed imaging and petrographic studies of the zircon grains shows that the gabbronorite parent of the zircon clasts formed shortly before the 4335 5 ma impact which mixed the clasts and the felsic melt and projected the sample closer to the surface where fast cooling resulted in the crystallization of acicular zircon type 2 the 3934 12 ma serenitatis event resulted in partial remelting of the glass and formation of polycrystalline zircon type 3 this event also reset the u pb system of apatite formed merrillite coronas around some apatite grains and probably re equilibrated some pyroxenes in the clasts although there have been arguments for pre 3 9 ga impacts based on other types of samples the age of the acicular zircon at 4335 5 ma provides the first evidence of impact melt significantly predating the lunar cataclysm our data combined with other chronological results demonstrate the occurrence of pre 3 9 ga impacts on the moon and suggest that the lunar impact history consisted of a series of intense bombardment episodes interspersed with relatively calm periods of low impact flux