magnetism on the angrite parent body and the early differentiation of planetesimals angrites are among the oldest known pristine basaltic meteorites and record the earliest stages of planet formation and differentiation our paleomagnetic analysis of three angrites found that they record a past magnetic field of 10 microteslas on the angrite parent body extending from 4564 to at least 4558 million years ago because the angrite paleomagnetic record extends beyond the expected lifetime of the early circumstellar disk these paleofields were probably generated internally on the angrite parent body possibly by an early dynamo in a rapidly formed metallic core

pb evolution in the martian mantle abstract the initial pb compositions of one enriched shergottite one intermediate shergottite two depleted shergottites and nakhla have been measured by secondary ion mass spectrometry sims these values in addition to data from previous studies using an identical analytical method performed on three enriched shergottites alh 84001 and chassigny are used to construct a unified and internally consistent model for the differentiation history of the martian mantle and crystallization ages for martian meteorites the differentiation history of the shergottites and nakhla chassigny are fundamentally different which is in agreement with short lived radiogenic isotope systematics the initial pb compositions of nakhla chassigny are best explained by the late addition of a pb enriched component with a primitive non radiogenic composition in contrast the pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the martian mantle that can be modeled based on recent results from the sm nd system the shergottites have been linked to a single mantle differentiation event at 4504 ma thus the shergottite pb isotopic model here reflects a two stage history 1 pre silicate differentiation 4504 ma and 2 post silicate differentiation to the age of eruption as determined by concordant radiogenic isochron ages the values 238u 204pb obtained for these two different stages of pb growth are 1 of 1 8 and a range of 2 from 1 4 4 7 respectively the 1 value of 1 8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto earth suggesting this is the initial value for inner solar system bodies when plotted against other source radiogenic isotopic variables sri 187 os e 143 nd and e 176 hf the second stage mantle evolution range in observed mantle values display excellent linear correlations r 2 0 85 and represent a spectrum of martian mantle mixing end members depleted intermediate enriched

timing of crystallization of the lunar magma ocean constrained by the oldest zircon the primitive moon was covered with a thick layer of melt known as the lunar magma ocean whose crystallization resulted in the moon s surface as it is observed today dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the moon s formation

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

lunar volatile depletion due to incomplete accretion within an impact generated disk the moon may have accreted from a disk of debris after a giant impact simulations suggest that part of the moon derives from volatile poor melt in the hot inner disk with most of the volatile elements condensing later and accreting to earth

aerobic microbial oxidation of hydrocarbon gases implications for oil and gas exploration abstract the molecular and carbon and hydrogen isotope compositions associated with the aerobic consumption of methane cl ethane c2 and propane c3 were determined from incubations of marine sediments collected from the seafloor surface of the gas and oil bearing bohai bay in eastern china the fresh sediment samples were incubated aerobically at 28 c and treated with three types of hydrocarbon gas mixtures as follows mixture i c1 c2 c3 100 0 0 ii c1 c2 c3 99 00 0 70 0 30 and iii c1 c2 c3 79 96 10 04 10 00 corresponding to incubations i ii and iii respectively all the hydrocarbons are of thermogenic origin except c1 microbial in incubation ii the oxidation of c1 c3 was observed in all three treatments with variations in carbon isotope fractionation factors ec of c1 and average values of 10 5 0 1 5 7 1 6 and 10 9 2 9 respectively the hydrogen isotope fractionation factors eh of c1 in the three incubations also display variation with average values of 118 4 3 0 68 3 15 0 and 56 3 8 4 respectively experiments with thermogenic c1 display greater carbon fractionation than those with microbial c1 the ec and eh values for c2 and c3 were obtained only in incubation iii compared to c1 c2 and c3 exhibit weaker carbon isotope fractionation but stronger hydrogen isotope fractionation the fractionation factors presented in this study can be applied to estimate the extent of c1 c3 oxidation in natural environments especially at seafloor and terrestrial seeps where aerobic microbes are commonly present our study has important implications in oil and gas exploration with an alert for exercising caution when using the molecular and isotopic characteristics of hydrocarbon gases to evaluate the gas sources because these are susceptible to aerobic microbial oxidation

a young solidification age for the lunar magma ocean abstract the time at which the lunar magma ocean solidified can be determined from the lu hf isotope systematics of lunar rocks derived from magma sources that formed during crystallization of the lunar magma ocean the final magma ocean crystallization product termed urkreep is enriched in incompatible elements including k ree and p we have determined the initial hf isotopic compositions of four samples two kreep basalts and two mg suite norites the incompatible trace element compositions of these samples are controlled by an urkreep component and therefore the initial hf isotopic compositions of these samples represent the hf isotopic evolution of urkreep in order to correct the effects of neutron irradiation on the hf isotopic compositions of these samples we have developed a model that uses the stable hf and sm isotopic compositions measured on an irradiated sample to determine and correct for the thermal and epithermal neutron fluence that has modified the hf isotopic composition of the sample we use our corrected results to calculate a 176 lu 176 hf urkreep model age of 4353 37 ma and the 176 lu 177 hf of urkreep to be 0 0153 0 0033 the lu hf model age is concordant with the re calculated sm nd urkreep model age of 4389 45 ma and we take the average of these ages 4368 29 ma to represent the time at which urkreep formed this age is concordant with the age of the most reliably dated ferroan noritic anorthosite as well as 142 nd model ages for the formation or re equilibration of mare basalt sources taken together these ages indicate that the moon experienced a widespread large scale magmatic event around 4370 ma most plausibly attributed to solidification of the lunar magma ocean

accretion timescales and style of asteroidal differentiation in an 26al poor protoplanetary disk the decay of radioactive 26al to 26mg half life of 730 000 years is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system high resolution chronological information provided by the 26al 26mg decay system is therefore intrinsically linked to the thermal evolution of early formed planetesimals in this paper we explore the timing and style of asteroidal differentiation by combining high precision mg isotope measurements of meteorites with thermal evolution models for planetesimals in detail we report mg isotope data for a suite of olivine rich al mg 0 achondritic meteorites as well as a few chondrites main group pyroxene and the zinder pallasites as well as the lodranite all record deficits in the mass independent component of 26mg 26mg relative to chondrites and earth this isotope signal is expected for the retarded ingrowth of radiogenic 26mg in olivine rich residues produced through partial silicate melting during 26al decay and consistent with their marginally heavy mg isotope composition relative to ordinary chondrites which may reflect the early extraction of isotopically light partial melts from the source rock we propose that their parent planetesimals started forming within 250 000 years of solar system formation from a hot 500 k inner protoplanetary disk region characterized by a reduced initial 26al 27al 0 abundance 1 2 10 5 relative to the 26al 27al 0 value in cais of 5 25 10 5 this effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals these non carbonaceous planetesimals acquired their mass throughout an extended period 3 myr of continuous accretion thereby generating onion shell structures of incompletely differentiated zones consisting of olivine rich residues overlaid by metachondrites and undifferentiated chondritic crusts in contrast individual olivine crystals from eagle station pallasites record variable 26mg excesses suggesting that these crystals captured the 26mg evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26al similar to previous suggestions based on isotopic evidence we suggest that eagle station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by 26al 27al 0 2 7 10 5 protracted planetesimal accretion timescales at large orbital distances with onset of accretion 0 3 1 myr post cais may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting carbonaceous planetesimals

early crust building enhanced on the moon s nearside by mantle melting point depression the moon s earth facing hemisphere hosts a geochemically anomalous region the procellarum kreep terrane which is widely thought to have provided radiogenic heat for mantle melting from 3 9 to 1 billion years ago however there is no agreement on such a link between this region and the earliest pulse of post differentiation crust building magmatism on the moon at 4 37 billion years ago whether this early magmatism was global or regional has been debated here we present results of high temperature experiments that show the nearside geochemical anomaly may have caused asymmetric early crust building via mantle melting point depression our results demonstrate that the anomalous enrichment in incompatible elements of this nearside reservoir dramatically lowers the melting temperature of the source rock for these magmas and may have resulted in 4 to 13 times more magma production under the nearside crust even without any contribution from radioactivity from thermal numerical modelling we show that radiogenic heating compounds this effect and may have resulted in an asymmetric concentration of post magma ocean crust building on the lunar nearside our findings suggest that the nearside geochemical anomaly has influenced the thermal and magmatic evolution of the moon over its entire post differentiation history early magmatism on the moon s nearside may have been enhanced by a geochemical anomaly lowering the melting point of the mantle source region according to high temperature experiments and thermal numerical modelling

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

chemical aspects of the formation of the core the interpretation of data on lead isotopes in mantle material indicates that some of the lead has been pumped into the core during geological time such a continuous lead loss yields an increase of the u pb ratio in the mantle quantitative modelling of this effect permits an evaluation of the core s growth curve in the preferred model 85 of the core would have been formed in the early period of the earth s history 50 200 ma after 4 55 ga ago and 15 later on and its accretion continues some of the consequences of such a process are reviewed

chronological evidence that the moon is either young or did not have a global magma ocean a new age determination for a moon rock collected close to the site of the apollo 16 lander has yielded a surprisingly young age of around 4 360 million years this age would require either that the moon solidified some 200 million years after the formation of the solar system significantly later than is assumed by most lunar formation models or that the long held theory that the moon once had a primordial global magma ocean is flawed in the latter case much of the lunar crust could have been produced by non magma ocean processes such as serial magmatism chemical evolution of planetary bodies ranging from asteroids to the large rocky planets is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth1 2 3 the earth s moon is the archetypical example of this type of differentiation evidence for a lunar magma ocean is derived largely from the widespread distribution compositional and mineralogical characteristics and ancient ages inferred for the ferroan anorthosite fan suite of lunar crustal rocks the fans are considered to be primary lunar flotation cumulate crust that crystallized in the latter stages of magma ocean solidification according to this theory fans represent the oldest lunar crustal rock type2 3 4 attempts to date this rock suite have yielded ambiguous results however because individual isochron measurements are typically incompatible with the geochemical make up of the samples and have not been confirmed by additional isotopic systems5 6 7 8 9 by making improvements to the standard isotopic techniques we report here the age of crystallization of fan 60025 using the 207pb 206pb 147sm 143nd and 146sm 142nd isotopic systems to be 4 360 3 million years this extraordinarily young age requires that either the moon solidified significantly later than most previous estimates or the long held assumption that fans are flotation cumulates of a primordial magma ocean is incorrect if the latter is correct then much of the lunar crust may have been produced by non magma ocean processes such as serial magmatism10

chronology of the angrite parent body and implications for core formation in protoplanets abstract angrites formed by some of the earliest igneous activity in the solar system and provide insights into the early stages of planetary melting and differentiation moreover they are pivotal reference points for early solar system chronology in order to study the processes and timescales of metal segregation in early protoplanets and to assess the distribution of short lived radionuclides in the early solar system the 182 hf 182 w system was applied to a comprehensive suite of angrites 182 hf 182 w isochron ages for angrites are in excellent agreement with previously reported 207 pb 206 pb and 53 mn 53 cr results but are 1 myr older than ages obtained from 26 al 26 mg chronometry these inconsistencies probably reflect a disturbance of the al mg system in the angrite feldspars but could alternatively be explained by a heterogeneous distribution of 26 al in the early solar system based on the hf w results four texturally and temporally resolved groups of angrites can be identified that were derived from at least two distinct mantle sources these mantle sources are the result of separate events of core formation both of which took place within 2 myr of cai formation thus core formation in the angrite parent body did not occur as a single event of metal segregation from a global magma ocean but rather took place under varying conditions by several more local events the disparate hf w systematics of the two distinct angrite source regions indicate that convection in the magma ocean was inefficient in homogenizing the composition of the mantle possibly as a result of a continuous bombardment with small planetesimals during ongoing core formation such impacts could have constantly removed primordial and earlier formed crust facilitating rapid cooling of the magma ocean which solidified as early as 3 6 0 7 myr after cai formation

zinc isotopic evidence for the origin of the moon lunar magmatic rocks are shown to be enriched in the heavy isotopes of zinc and to have lower zinc concentrations than terrestrial or martian igneous rocks these variations represent the large scale evaporation of zinc most probably in the aftermath of the moon forming giant impact event the heavily favoured theory for the origin of the earth moon system is a giant impact between the proto earth and a mars sized body such a cataclysmic event would have left its mark on the isotopic composition of the moon because light isotopes evaporate more readily than heavier ones zinc in particular is a powerful indicator of the volatile histories of planets it undergoes strong isotopic fractionation in planetary rocks but is hardly fractionated following volcanic activity on earth this study compares high precision zinc isotopic data for lunar basalts martian meteorites and terrestrial igneous rocks and finds that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or martian samples the authors conclude that these variations are the result of large scale evaporation of zinc in the aftermath of the moon forming giant impact event volatile elements have a fundamental role in the evolution of planets but how budgets of volatiles were set in planets and the nature and extent of volatile depletion of planetary bodies during the earliest stages of solar system formation remain poorly understood1 2 the moon is considered to be volatile depleted and so it has been predicted that volatile loss should have fractionated stable isotopes of moderately volatile elements3 one such element zinc exhibits strong isotopic fractionation during volatilization in planetary rocks4 5 but is hardly fractionated during terrestrial igneous processes6 making it a powerful tracer of the volatile histories of planets here we present high precision zinc isotopic and abundance data which show that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or martian igneous rocks conversely earth and mars have broadly chondritic zinc isotopic compositions we show that these variations represent large scale evaporation of zinc most probably in the aftermath of the moon forming event rather than small scale evaporation processes during volcanism our results therefore represent evidence for volatile depletion of the moon through evaporation and are consistent with a giant impact origin for the earth and moon

forming a moon with an earth like composition via a giant impact in the giant impact theory the moon formed from debris ejected into an earth orbiting disk by the collision of a large planet with the early earth prior impact simulations predict that much of the disk material originates from the colliding planet however earth and the moon have essentially identical oxygen isotope compositions this has been a challenge for the impact theory because the impactor s composition would have likely differed from that of earth we simulated impacts involving larger impactors than previously considered we show that these can produce a disk with the same composition as the planet s mantle consistent with earth moon compositional similarities such impacts require subsequent removal of angular momentum from the earth moon system through a resonance with the sun as recently proposed

pb pb chronometry and the early solar system abstract of the long lived chronometric systems only the dual decay of 238 u and 235 u to 206 pb and 207 pb respectively have appropriate half lives to resolve the ages of meteorites and their components formed in the first 5 myr of the solar system this paper reviews the theory and methods behind this chronometer offers criteria to critically evaluate pb pb ages and presents a summary of the current state and immediate future of the chronometry of the early solar system we recognize that there is some debate over the age of the solar system but conclude that an age of 4567 30 0 16 ma based on four cais dated individually by the same method in two different laboratories is presently the best constrained published value we further conclude that nebular chondrules dated by the pb pb method require that they formed contemporaneously with cais and continued to form for at least 4 myr a conclusion that implies heterogeneous distribution of the short lived 26 al nuclide in the protoplanetary disk planetesimals were already forming by 1 myr after cai formation consistent with their growth predominantly through the accretion of chondrules nebular chondrule formation was completed by 5 myr after cai formation when the impact generated cba chondrules formed after the disk was cleared of gas and dust we note that the absolute age of the solar system or any single early solar system object is not fundamental to any significant scientific question and that it is important only to know the correct relative ages of objects being used to piece together the formation history of the solar system as such we point out the risks inherent in comparing pb pb ages produced by different approaches in different laboratories at the level of the internal errors of individual ages until a cross calibration exercise using synthetic and natural standards establishes the reproducibility between laboratories only ages from a single laboratory or between laboratories having demonstrated concordance can provide a reliable relative chronometric framework for the formation and evolution of the early solar system

testing the chondrule rich accretion model for planetary embryos using calcium isotopes abstract understanding the composition of raw materials that formed the earth is a crucial step towards understanding the formation of terrestrial planets and their bulk composition calcium is the fifth most abundant element in terrestrial planets and therefore is a key element with which to trace planetary composition however in order to use ca isotopes as a tracer of earth s accretion history it is first necessary to understand the isotopic behavior of ca during the earliest stages of planetary formation chondrites are some of the oldest materials of the solar system and the study of their isotopic composition enables understanding of how and in what conditions the solar system formed here we present ca isotope data for a suite of bulk chondrites as well as allende cv chondrules we show that most groups of carbonaceous chondrites cv ci cr and cm are significantly enriched in the lighter ca isotopes 44 40 ca 0 1 to 0 93 compared with bulk silicate earth 44 40 ca 1 05 0 04 huang et al 2010 or mars while enstatite chondrites are indistinguishable from earth in ca isotope composition 44 40 ca 0 91 to 1 06 chondrules from allende are enriched in the heavier isotopes of ca compared to the bulk and the matrix of the meteorite 44 40 ca 1 00 to 1 21 this implies that earth and mars have ca isotope compositions that are distinct from most carbonaceous chondrites but that may be like chondrules this ca isotopic similarity between earth mars and chondrules is permissive of recent dynamical models of planetary formation that propose a chondrule rich accretion model for planetary embryos

pb isotopes in the impact melt breccia 66095 association with the imbrium basin and the isotopic composition of lithologies at the apollo 16 landing site recent in situ secondary ion mass spectrometry sims pb isotope analyses of lunar basalts have provided precise crystallisation ages and initial pb isotopic compositions for these samples in this

pb pb dating of individual chondrules from the cb a chondrite gujba assessment of the impact plume formation model the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the cba chondrite gujba are interpreted to reflect a single stage impact origin here we report high precision internal isochrons for four individual chondrules of the gujba chondrite to probe the formation history of cb chondrites and evaluate the concordancy of relevant short lived radionuclide chronometers all four chondrules define a brief formation interval with a weighted mean age of 4562 49 0 21 myr consistent with its origin from the vapor melt impact plume generated by colliding planetesimals formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4 8 0 3 myr finally given the well behaved pb pb systematics of all four chondrules a precise formation age and the concordancy of the mn cr hf w and i xe short lived radionuclide relative chronometers we propose that gujba may serve as a suitable time anchor for these systems

isotope geochemistry of quaternary deposits from the arid lands in northern china abstract quaternary deposits of various types lacustrine desert sand river loess and loess like deposits from the southwestern tarim basin north tianshan northeast china and the central loess plateau exhibit an nd 0 range from 5 to 12 8 and a 147 sm 144 nd range from 0 110 to 0 140 their nd depleted mantle model ages are between 1 50 and 1 92 ga with a mean value of 1 7 ga th sc ratios vary over a wide range from 0 1 to 2 comparison of these geochemical signatures with those of the old australian shales and modern pacific ocean dust suggests a continuous input of mantle derived material into the crust over geological time the deposits from the north tianshan show clearly different chemical and isotopic features with significantly higher sm nd high 143 nd 144 nd low 87 sr 86 sr and low la lu and th sc ratios relative to those in the deposits from the other areas this indicates a geological control on the local source which has an overall young age and an enrichment of basic components the ce 0 values of two loess samples from the central loess plateau are 1 8 and 3 9 corresponding to depleted mantle model ages of 2 2 and 3 4 ga like the rb sr system the evolution of the la ce isotopic system in the crust may be to some extent decoupled from the sm nd system due to la ce fractionation by sedimentary processes the loess deposits and the desert sand are not distinguishable in isotopic composition but show somewhat different chemical compositions we conclude that the loess can have originated from desert processes since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation the loess deposits on the central loess plateau chemically and isotopically resemble the desert loess deposits in the southwestern tarim basin but do not resemble those of the north tianshan accordingly the loess on the plateau may have a source region in the tarim basin but clearly not in the north tianshan

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

late stage magmatic outgassing from a volatile depleted moon abstract the abundance of volatile elements and compounds such as zinc potassium chlorine and water provide key evidence for how earth and the moon formed and evolved currently evidence exists for a moon depleted in volatile elements as well as reservoirs within the moon with volatile abundances like earth s depleted upper mantle volatile depletion is consistent with catastrophic formation such as a giant impact whereas a moon with earth like volatile abundances suggests preservation of these volatiles or addition through late accretion we show using the rusty rock impact melt breccia 66095 that volatile enrichment on the lunar surface occurred through vapor condensation isotopically light zn 66zn 13 7 heavy cl 37cl 15 and high u pb supports the origin of condensates from a volatile poor internal source formed during thermomagmatic evolution of the moon with long term depletion in incompatible cl and pb and lesser depletion of more compatible zn leaching experiments on mare basalt 14053 demonstrate that isotopically light zn condensates also occur on some mare basalts after their crystallization confirming a volatile depleted lunar interior source with homogeneous 66zn 1 4 our results show that much of the lunar interior must be significantly depleted in volatile elements and compounds and that volatile rich rocks on the lunar surface formed through vapor condensation volatiles detected by remote sensing on the surface of the moon likely have a partially condensate origin from its interior

the formation and evolution of the moon s crust inferred from the sm nd isotopic systematics of highlands rocks abstract ages determined for magnesian and ferroan anorthosite crustal rock suites overlap suggesting they formed contemporaneously about 4 3 4 5 ga a notable exception is the sm nd age previously determined on mg suite gabbronorite 67667 which is at least 100 ma younger than the youngest ferroan anorthosite new chronologic measurements of 67667 presented here yield concordant sm nd and rb sr mineral isochron ages of 4349 31 ma and 4368 67 ma suggesting the sample is older than previous estimates furthermore a whole rock sm nd isochron of mg suite rocks from the apollo 14 15 16 and 17 landing sites yields an age of 4348 25 ma indicating that mg suite magmatism was widespread and roughly contemporaneous on the lunar nearside analysis of sm nd internal isochron ages confirms that mg suite magmatism was restricted to a period between about 4 33 and 4 35 ga at the apollo 14 15 16 and 17 landing sites and was synchronous with magmatism at the apollo 16 site associated with the ferroan anorthosite suite between 4 35 and 4 37 ga magnesian and ferroan anorthosite suite rocks with ages younger than 4 33 ga appear to have experienced slow cooling in the deep lunar interior so that the ages record when the samples cooled below the closure temperature of the sm nd isotopic system and not the time they crystallized the ages determined for mg suite and ferroan anorthosite suite rocks are concordant with the age determined for the formation of urkreep of 4350 34 ma using the sm nd isotopic systematics of 67667 and measurements completed on norite 78238 troctolite 76535 kreep basalt 15386 and gabbronorite nwa 773 crystallization ages of mg suite and fas are also concordant with the average of 146sm 142nd ages previously determined for the formation of the mare basalt source region of 4333 30 ma the similarity of ages for mg suite magmatism ferroan anorthosite suite magmatism urkreep formation and formation of the mare basalt source regions implies the processes that produced these rocks were petrogenetically linked it also implies that both early stage and late stage lunar magma ocean cumulates formed over a relatively short duration of

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

the u pb systematics of angrite sahara 99555 abstract angrite sahara 99555 hereafter sah precisely dated by baker et al baker j bizzarro m wittig n connelly j and haack h 2005 early planetesimal melting from an age of 4 5662 gyr for differentiated meteorites nature 436 1127 1131 has been proposed as a new reference point for the early solar system timescale and for calculation of the revised minimum age of our solar system the pb pb age of sah of 4566 18 0 14 ma reported by baker et al differs from the pb pb age of d orbigny another basaltic angrite of 4564 42 0 12 ma amelin y 2008 u pb ages of angrites geochim cosmochim acta 72 221 232 despite the fact that the relative 53mn 53cr and 182hf 182w ages of these meteorites are identical here i report u pb data for 21 whole rock and pyroxene fractions from sah analyzed using the same approach as d orbigny amelin 2008 these fractions contain between 1 3 and 8 9 pg of total common pb slightly more than analytical blank measured 206pb 204pb ratios are between 625 and 2817 for d orbigny blank corrected 206pb 204pb ratios are between 1173 and 6675 eight acid washed whole rock fractions yielded an isochron age of 4564 86 0 38 ma mswd 1 5 data for pyroxene fractions plot mostly above the whole rock isochron and do not form a linear array in 207pb 206pb vs 204pb 206pb isochron coordinates the 207pb 206pb model dates of the pyroxene fractions vary from 4563 8 0 3 to 4567 1 0 5 ma the difference between whole rock and pyroxene u pb systematics may be a result of re distribution of radiogenic pb at a mineral grain scale several million years after crystallization complexities of sm nd lu hf and possibly 26al 26mg mineral systematics of sah described previously may be related to the same process that caused the re distribution of radiogenic pb disturbance of isotopic chronometers renders sah an imperfect anchor for the early solar system timescale the problems with age determination revealed by the studies of sah call for greater attention in pb isotopic dating of angrites and other achondrites

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

lead isotope evidence for a young formation age of the earth moon system abstract a model of a giant impact between two planetary bodies is widely accepted to account for the earth moon system despite the importance of this event for understanding early earth evolution and the inventory of earth s volatiles critical to life the timing of the impact is poorly constrained we explore a data based two stage pb isotope evolution model in which the timing of the loss of volatile pb relative to refractory u in the aftermath of the giant impact is faithfully recorded in the pb isotopes of bulk silicate earth constraining the first stage pb isotopic evolution permits calculating an age range of 4 426 4 417 ga for the inflection in the u pb ratio related to the giant impact this model is supported by pb isotope data for angrite meteorites that we use to demonstrate volatility driven planetary scale pb loss was an efficient process during the early solar system the revised age is 100 myr younger than most current estimates for the age of the moon but fully consistent with recent ages for lunar ferroan anorthosite and the timing of earth s first crust inferred from the terrestrial zircon record the estimated loss of 98 of terrestrial pb relative to the solar system bulk composition by the end of the moon forming process implies that the current inventory of earth s most volatile elements including water arrived during post impact veneering by volatile rich bodies

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

uranium lead isotope systematics of mars inferred from the basaltic shergottite que 94201 abstract uranium lead ratios commonly represented as 238u 204pb calculated for the sources of martian basalts preserve a record of petrogenetic processes that were active during early planetary differentiation and formation of martian geochemical reservoirs to better define the range of values represented by the source regions of martian basalts we completed u pb elemental and isotopic analyses on whole rock mineral and leachate fractions from the martian meteorite queen alexandra range 94201 que 94201 the whole rock and silicate mineral fractions have unradiogenic pb isotopic compositions that define a narrow range 206pb 204pb 11 16 11 61 in contrast the pb isotopic compositions of weak hcl leachates are more variable and radiogenic the intersection of the que 94201 data array with terrestrial pb in 206pb 204pb 207pb 204pb 208pb 204pb compositional space is consistent with varying amounts of terrestrial contamination in these fractions we calculate that only 1 7 contamination is present in the purified silicate mineral and whole rock fractions whereas the hcl leachates contain up to 86 terrestrial pb this terrestrial pb contamination generated a 206pb 207pb array in the que fractions that appears to represent an ancient age which contrasts with a much younger crystallization age of 327 10 ma derived from rb sr and sm nd isochrons borg l e nyquist l e taylor l a wiesmann h and shih c y 1997 constraints on martian differentiation processes from rb sr and sm nd isotopic analyses of the basaltic shergottite que 94201 geochim cosmochim acta 61 4915 4931 despite the contamination and accepting 327 10 ma as the crystallization age we use the u pb data to determine the initial 206pb 204pb of que 94201 to be 11 086 0 008 and to calculate the value of its mantle source to be 1 82 0 01 the value calculated for the que 94201 source is the lowest determined for any martian basalt source and when compared to the highest values determined for martian basalt sources indicates that values in martian source reservoirs vary by at least a factor of two additionally the range of source values indicates that the value of bulk silicate mars is approximately three the amount of variation in the values of the mantle sources 2 4 is greater than can be explained by igneous processes involving silicate phases alone we suggest the possibility that a small amount of sulfide crystallization may generate greater extents of u pb fractionation during formation of the mantle sources of martian basalts

hadean age for a post magma ocean zircon confirmed by atom probe tomography the only physical evidence from the earliest phases of earth s evolution comes from zircons ancient mineral grains that can be dated using the u th pb geochronometer 1 oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established 2 3 chemical homogenization of earth s crust and the existence of a magma ocean have not been dated directly but must have occurred earlier 4 however the accuracy of the u pbzirconagescanplausiblybebiasedbypoorlyunderstood processes of intracrystalline pb mobility 5 7 here we use atomprobe tomography 8 to identify and map individual atoms in the oldest concordant grain from earth a 4 4 gyr old hadean zircon with a high temperature overgrowth that formed about 1gyrafterthemineral score isolatednanoclusters measuring about 10nm and spaced 10 50nm apart are enriched in incompatible elements including radiogenic pb with unusually high 207 pb 206 pbratios wedemonstratethatthelengthscales of these clusters make u pb age biasing impossible and that they formed during the later reheating event our tomography data thereby confirm that any mixing event of the silicate earth must have occurred before 4 4gyr ago consistent with

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

new constraints on early solar system chronology from al mg and u pb isotope systematics in the unique basaltic achondrite northwest africa 2976 abstract we report elemental abundances and the isotopic systematics of the short lived 26 al 26 mg half life of 0 73 ma and long lived u pb radiochronometers in the ungrouped basaltic meteorite northwest africa nwa 2976 the bulk geochemical composition of nwa 2976 is clearly distinct from that of the eucrites and angrites but shows broad similarities to that of the paired nwa 001 and 2400 ungrouped achondrites indicating that it is likely to also be paired with these two samples the major and trace element abundances in nwa 2976 further indicate that it formed by extensive melting and magmatic fractionation processes on its parent body the al mg and pb pb isotope systematics indicate that this meteorite represents the earliest stages of crust formation on a differentiated parent body in the early solar system the absolute pb pb internal isochron age of nwa 2976 obtained from acid leaching residues of three whole rock samples and two pyroxene separates is 4562 89 0 59 ma mswd 0 02 this pb pb age is calculated using the measured 238 u 235 u ratio of a nwa 2976 whole rock of 137 751 0 018 2 which was determined relative to the recently revised value of 137 840 0 008 for the srm 950a u isotope standard the al mg systematics reveal the presence of 26 mg isotopic anomalies produced by the decay of 26 al with an 26 al 27 al 0 of 3 94 0 16 10 7 and indicate a time of formation of 0 26 0 18 ma after the d orbigny angrite using the revised pb pb age of 4563 36 0 34 ma for the d orbigny anchor corrected for its u isotopic composition we deduce an al mg model age of 4563 10 0 38 ma for nwa 2976 which is consistent with its pb pb internal isochron age the concordance of the pb pb and al mg chronometers when taking into account the differences in the u isotopic compositions of the d orbigny and nwa 2976 achondrites whose parent bodies likely formed in distinct regions of early solar system as indicated by their different oxygen isotopic compositions implies that 26 al was homogeneously distributed in the early solar system it also suggests that igneous processes on planetesimals as represented by the formation of various basaltic meteorite groups that likely originated on distinct parent bodies e g eucrites and angrites as well as ungrouped achondrites were widespread throughout the protoplanetary disk within the first 5 ma of the history of the solar system