the hans tausen drill design performance further developments and some lessons learned in the mid 1990s excellent results from the grip and gisp2 deep drilling projects in greenland opened up funding for continued ice coring efforts in antarctica epica and greenland northgrip the glaciology group of the niels bohr institute university of copenhagen was assigned the task of providing drilling capability for these projects as it had done for the grip project the group decided to further simplify existing deep drill designs for better reliability and ease of handling the drill design decided upon was successfully tested on hans tausen ice cap peary land greenland in 1995 the 5 0 m long hans tausen ht drill was a prototype for the 11 m long epica and northgrip versions of the drill which were mechanically identical to the ht drill except for a much longer core barrel and chips chamber these drills could deliver up to 4 m long ice cores after some design improvements had been introduced the berkner island antarctica drill is also an extended ht drill capable of drilling 2 m long cores the success of the mechanical design of the ht drill is manifested by over 12 km of good quality ice cores drilled by the ht drill and its derivatives since 1995

luhf geochronology applied to dating cenozoic events affecting lower crustal xenoliths from kilbourne hole new mexico abstract melt extraction or crystal accumulation events that affected garnet bearing granulite xenoliths from kilbourne hole new mexico have been dated using the lu hf isotope system two garnet bearing granulites from kilbourne hole have extreme 176 lu 177 hf ratios of 0 95 and 1 3 lu hf 28 and 39 chondritic but relatively normal hf values 5 and 12 necessitating either garnet accumulation or melt extraction from a garnet bearing protolith in the cenozoic hf isotope evolution curves for these two samples intersect those of depleted mantle and proterozoic crust at high angles and at similar times demonstrating the potential of hf isotope model ages to yield true age significance even if the initial hf isotope composition is not well constrained a third garnet granulite xenolith ckh63 176 lu 177 hf 0 025 contains zircon which buffered this sample against changes in lu hf during the cenozoic differentiation event the three garnet granulites lie closely about a 25 ma lu hf reference line demonstrating the potential of the lu hf system for detecting garnet controlled differentiation events in the cenozoic given the range in lu hf ratios measured events as young as 5 ma may be detected using the lu hf system conventional u pb zircon data from sample ckh63 reveal both a ca 1 4 ga inherited component and a component of recent pb loss or new zircon growth supporting the cenozoic event documented by hf isotope model ages

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

pre 4 0 billion year weathering on mars constrained by rb sr geochronology on meteorite alh84001 abstract the timing and nature of aqueous alteration of meteorite alh84001 has important implications for the history of water on early mars the evolution of the martian atmosphere and the potential for early mars habitability rubidium sr isotope analyses of mineral separates from igneous textured and carbonate rich aliquots of martian meteorite alh84001 constrain the age of alteration and the source of fluids the carbonate rich aliquot defines a precise rb sr isochron between maskelynite orthopyroxene and chromite of 3952 22 ma and this is interpreted to represent a shock resetting event that was broadly coeval with carbonate precipitation carbonate bulk rock and multi mineral separates all have high 87 sr 86 sr ratios that can only have been produced by alteration via a fluid derived through interaction with high rb sr phyllosilicates that were produced prior to 3950 ma these data confirm that the source of sr in the fluids was previously altered crustal rock consistent with fluids that underwent low temperature water rock interaction eiler et al 2002 halvey et al 2011 these results therefore provide evidence for wet clay rich conditions on the surface of mars prior to 4 2 ga

constraints on martian differentiation processes from rbsr and smnd isotopic analyses of the basaltic shergottite que 94201 isotopic analyses of mineral leachate and whole rock fractions from the martian shergottite meteorite que 94201 yield rb sr and sm nd crystallization ages of 327 12 and 327 19 ma respectively these ages are concordant although the isochrons are defined by different fractions within the meteorite comparison of isotope dilution sm and nd data for the various que 94201 fractions with in situ ion microprobe data for que 94201 minerals from the literature demonstrate the presence of a leachable crustal component in the meteorite this component is likely to have been added to que 94201 by secondary alteration processes on mars and can affect the isochrons by selectively altering the isotopic systematics of the leachates and some of the mineral fractions initial 87sr 86sr of 0 701298 14 nd143 of 47 6 1 7 and whole rock nd142 of 0 92 0 11 indicate that que 94201 was derived from a source that was strongly depleted in 87rb 86sr and enriched in 147sm 144nd early in its history modeling demonstrates that the sm nd isotopic compositions of que 94201 can be produced by either four episodes of melting at 327 ma of cumulates crystallized from a magma ocean at 4 525 ga or five episodes of melting of an initially solid mars at 4 525 ga and 327 ma the neodymium isotopic systematics of que 94201 are not consistent with significant melting between 4 525 ga and 327 ma the estimated timing of these events is based on initial neodymium isotopic ratios and is independent of differentiation of the que 94201 parental magma rb sr based partial melting models are unable to reproduce the composition of que 94201 using the same model parameters employed in the sm nd based models implying a decoupling of rb sr and sm nd isotopic systems the initial decoupling of the two isotopic systems can be attributed to either cumulate or crust formation processes which are able to more efficiently fractionate rb from sr compared to sm from nd the fact that all martian meteorites analyzed so far define a rb sr whole rock isochron age of 4 5 ga suggests that virtually all rb was partitioned out of their mantle source regions and into either fractionated residual liquids trapped in the cumulate pile or into the crust at that time thus the martian mantle cumulates and restites are not expected to evolve past 87sr86sr of 0 700 and could not have been significantly enriched in incompatible elements by crustal recycling processes all martian meteorites have initial 87sr86sr values that are higher than 0 700 and are therefore likely to be produced by mixing between evolved crustal like and depleted mantle reservoirs the absence of crustal recycling processes on mars may preserve the geochemical evidence for decoupling of the rb sr and sm nd isotopic systems underscoring one of the fundamental differences between geologic processes on mars and the earth

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

chronology and petrogenesis of young achondrites shergotty zagami and alha77005 late magmatism on a geologically active planet a study was undertaken to determine the chronology petrogenesis and relationships among the shergottites shergotty and zagami and the unique achondrite alha77005 these meteorites are the product of a variety of complex processes petrogenesis chondrite normalized abundance patterns of shergotty and zagami are very similar and show pronounced depletions of both the light ree la nd and heavy ree dy lu relative to sm gd these characteristic depletions are even more pronounced for alha77005 the light ree depletion is qualitatively consistent with the presence of cumulus pyroxene and or olivine in these meteorites but trace element models show that the parental magmas of all three meteorites were probably also light ree depleted both trace element model calculations and combined rb sr and sm nd isotopic systematics show that the meteorites could not have been co magmatic nor can alha77005 be representative of the source material of the shergottites light ree depletion of the parental magmas also implies light ree depletion of the source material the sm nd systematics of the shergottites require a time averaged sub chondritic light ree enriched sm nd ratio since 4 6 ae ago the sm nd systematics of alha77005 permit a time averaged super chondritic light ree depleted sm nd ratio if its crystallization age is less than tice 0 72 ae chronology rb sr internal isochrons for all three meteorites and a sm nd internal isochron for zagami are concordant at 180 myr 39ar 40ar plateau ages of shergotty and zagami maskelynite are 250 260 myr these ages apparently reflect resetting of these isotopic systems by shock metamorphism which converted the feldspar to maskelynite the concordance of these ages suggests a single shock event during which the meteorites were in close physical proximity the time of this event is most precisely given by the rb sr age of 180 4 myr for zagami the crystallization ages of the meteorites were not precisely determined extreme upper limits are determined by sm nd model ages relative to an eucrite initial 143nd144nd 0 505835 at 4 6 ae ago these model ages for shergotty zagami and alha77005 are 3600 3500 and 2850 myr respectively the sm nd whole rock age of 1340 60 myr for the three meteorites gives the crystallization age if the sm nd ratios of the precursor materials were always the same we consider this 1340 myr age as a best estimate upper limit best estimate lower limits for shergotty and zagami are taken from the average 39ar 40ar ages of 1200 and 900 myr of pyroxene separates the average 39ar 40ar age of a whole rock sample of alha77005 was 1600 myr and can be partitioned between a low temperature feldspar phase and a high temperature olivine pyroxene inclusions phase the average apparent 39ar 40ar age of the low temperature phase is 1050 myr which is chosen as the best estimate lower limit to the age the crystallization ages of shergotty zagami and alha77005 probably lie within the ranges of 1200 1300 900 1300 and 1000 1300 myr respectively the rb sr whole rock age of 4400 400 myr and single stage babi model ages of 4800 5100 myr are interpreted as reflecting differentiation of the parent body at 4600 myr ago the complex geochemical and isotopic evolution recorded by these meteorites suggests a geologically active parent body capable of sustaining melting at two or more epochs in its history

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

the early differentiation history of mars from 182w 142nd isotope systematics in the snc meteorites we report here the results of an investigation of w and nd isotopes in the snc shergottite nakhlite chassignite martian meteorites we have determined that 182 w values in the nakhlites are uniform within analytical uncertainties and have an average value of 3 also while 182 w values in the shergottites have a limited range from 0 3 0 7 their 142 nd values vary considerably from 0 2 0 9 there appears to be no correlation between 182 w and 142 nd in the nakhlites and shergottites these results shed new light on early differentiation processes on mars particularly on the timing and nature of fraction ation in silicate reservoirs assuming a two stage model the metallic core is estimated to have formed at 12 myr after the beginning of the solar system major silicate differentiation established the nakhlite source reservoir before 4542 ma and the shergottite source reservoirs at 4525 19 ma these ages imply that within the uncertainties afforded by the 182 hf 182 w and 146 sm 142 nd chronometers the silicate differentiation events that established the source reservoirs of the nakhlites and shergottites may have occurred contempo raneously possibly during crystallization of a global magma ocean the distinct 182 w 142 nd isotope systematics in the nakhlites and the shergottites imply the presence of at least three isotopically distinct silicate reservoirs on mars two of which are depleted in incompatible lithophile elements relative to chondrites and the third is enriched the two depleted silicate reservoirs most likely reside in the martian mantle while the enriched reservoir could be either in the crust or the mantle therefore the 182 w 142 nd isotope systematics indicate that the nakhlites and the shergottites originated from distinct source reservoirs and cannot be petrogenetically related a further implication is that the source reservoirs of the nakhlites and shergottites on mars have been isolated since their establishment before 4 5 ga therefore there has been no giant impact or efficient global mantle convection to thoroughly homogenize the martian mantle following the establish ment of the snc source reservoirs copyright 2005 elsevier ltd

early magnetic field and magmatic activity on mars from magma ocean cumulate overturn abstract significant and perhaps complete melting of the young terrestrial planets is expected from their heat of accretion and core formation the process of subsequent magma ocean fractional solidification creates a cumulate mantle unstable to gravitational overturn overturn should be fast 1 to 10 ma and result in increasing mantle density with depth this stable stratification inhibits later thermal convection preserving geochemical heterogeneities overturn places cold cumulates against the core mantle boundary which creates sufficient heat flux to drive a core dynamo producing a brief strong magnetic field during overturn hot cumulates rise from depth and melt adiabatically creating an early crust to record this field and leaving behind mantle reservoirs with isotopic fractionations dating from the early evolution of the planet

density profile of an snc model martian interior and the moment of inertia factor of mars the density profile of an snc model martian interior is calculated from the results of previous experimental work that determined the modal mineralogy of the model mantle up to martian core mantle boundary pressures the moment of inertia factor of mars is calculated as a function of core composition and crustal thickness using the snc model mantle density profile as a constraint two sets of calculations are performed in the first the bulk composition of the planet is not constrained to a c1 chondrite composition assuming a martian crust density of 2 7 3 0 g cm3 a crust thickness of 25 150 km and the core composition proposed by dreibus and wanke fe 14 wt s the calculated moment of inertia factor ranges from 0 367 to 0 357 these models include a perovskite bearing zone in the martian interior considering core compositions ranging from pure fe to pure fes changes the moment of inertia factor by only 0 001 but at higher s abundances core size increases such that the depth of the core mantle boundary is shallower than the depth of perovskite stability in the second set of calculations the bulk composition of the planet is constrained to a c1 composition requiring a crust thickness of 180 320 km assuming a crust density of 2 7 3 0 g cm3 the calculated moment of inertia factor is 0 354 and a perovskite bearing layer is absent from the martian interior as it is unlikely that the thickness of the martian crust is greater than 100 km the bulk composition of mars cannot be constrained to a c1 chondrite composition as proposed by the dreibus and wanke model g dreibus h wanke meteoritics 20 1985 367 382 in order to determine if the martian mantle is more iron rich than the earth s mantle we may need not only an improved estimate of the moment of inertia factor of mars but also tighter constraints on martian crust thickness and density the absolute degree of iron enrichment however cannot be specified without also knowing the size of the martian core a moment of inertia factor of less than 0 342 is not geochemically feasible because it requires that the mantle of mars contains no iron

re os isotopic evidence for early differentiation of the martian mantle variations in the short lived systems of 182hf 182w and 146sm 142nd in the snc meteorites indicate an early isolation of and subsequent inefficient mixing between mantle reservoirs in mars correlations of ew and e142nd with initial os are consistent with the re os isotopic systematics of these meteorites being set during the earliest differentiation history of mars contamination by a juvenile martian crust may have affected zagami os isotopic systematics but successful contamination models combining nd and os systematics are inconsistent with such a process affecting the isotopic compositions of the shergottite lherzolites eeta 77005 lew 88516 y 793605 at least two long lived mantle reservoirs and possibly three are required to explain the observed systematics one mantle reservoir nc group represented by nakhla and chassigny has a projected present day os of 5 4 2 6 another mantle reservoir represented by the shergottite lherzolites and possibly zagami has a present day os of about 4 this represents a 2 to 3 enrichment in re os relative to the primitive mantle estimated for the earth 1 6 a third mantle reservoir may be represented by dag 476 having a nearly chondritic os coupled with very high e143nd of around 40 the isotopic systematics of these reservoirs may be linked to development of cumulate crystal piles in a martian magma ocean and variable amounts of late stage intercumulus melt following borg et al 1997 in this model fractional crystallization of olivine and possibly other phases with slightly subchondritic re os from a solidifying magma ocean resulted in a lower re os ratio in the nc group source cumulates and a resultant low os later cumulates or evolved melts crystallized with higher re os ratios to produce the shergottite mantle reservoir s and hence consequent higher os crystallization of the martian magma ocean followed earliest core formation as indicated by the correlation of ew with e142nd and initial os

petrogenesis of shergottite meteorites inferred from minor and trace element microdistributions abstract as an extension of our previous work on the lherzolitic shergottites alha77005 and lew88516 ion microprobe measurements of rees and other selected trace and minor elements were made in individual minerals of the basaltic shergottites shergotty zagami and eeta79001 whole rock ree abundances in these achondrites are dominated by whitlockite which is usually present only in trace amounts one of the most significant features is the extensive zoning of trace and minor elements in pyroxenes this zonation which provides information on the crystallization histories of these meteorites is of primary magmatic origin and not the result of secondary processes such as diffusive reequilibration and or metasomatic infiltration coherent trends in element element plots for low ca pyroxenes indicate that each shergottite formed essentially by progressive closed system fractional crystallization the calculated ree patterns of the parent melts of all shergottites are lree depleted and parallel to their whole rock ree patterns also indicative of closed system fractional crystallization on the basis of observations reported in this study as well as previously determined petrologic and geochemical including isotopic characteristics we present a model that suggests possible relationships among all five known shergottites

accretion timescale and impact history of mars deduced from the isotopic systematics of martian meteorites abstract high precision sm nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on mars associated with the formation of their mantle sources these data are used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic ages determined from the sm nd isotopic systematics of individual samples are strongly dependent on the assumed nd isotopic composition of the bulk planet this assumption is problematic given differences observed between the nd isotopic composition of earth and chondritic meteorites and the fact that these materials are both commonly used to represent bulk planetary nd isotopic compositions ages determined from the slope of 146sm 142nd whole rock isochrons are not dependent on the assumed 142nd 144nd ratio of the planet but require the sample suite to be derived from complementary contemporaneously formed reservoirs in this work we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a 143nd 142nd whole rock isochron and is also independent of any a priori assumptions regarding the bulk isotopic composition of the planet this expression is also applicable to mineral isochrons and has been used to successfully calculate 143nd 142nd model crystallization ages of early refractory solids as well as lunar samples this permits ages to be obtained using only nd isotopic measurements without the need for 147sm 144nd isotope dilution determinations when used in conjunction with high precision nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504 6 ma because the sm nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the solar system recent thermal models however suggest that mars sized bodies cool rapidly in less than 5 ma after accretion ceases even in the presence of a thick atmosphere assuming these models are correct an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504 ma late accretional heating of mars could either be associated with protracted accretion occurring at a quasi steady state or alternatively be associated with a late giant impact if this scenario is correct then accretion of mars sized bodies takes up to 60 ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation this further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed

a discussion of isotopic systematics and mineral zoning in the shergottites evidence for a 180 m y igneous crystallization age abstract proposed igneous and metamorphic ages of the shergottites a suite of achondritic basaltic meteorites are examined in terms of the shergottites petrography and mineral chemistry no metamorphic or hydrothermal event appears capable of resetting the refractory sr and nd isotopic systems of the shergottites since the time of their igneous crystallization the approximately concordant rb sr 180 20 m y and u th pb 190 30 m y internal isochrons are thus interpreted as representing the time of igneous crystallization the sm nd internal isochrons which yield older apparent ages also show large scatter and are regarded as artifacts of the shergottites complex igneous history rubidium sr sm nd and pb pb wholerock isochrons are interpreted as mixing lines and are reasonably attributed to igneous processes such as wall rock assimilation and magma mixing if the shergottites are indeed less than 200 m y old they represent the youngest known extraterrestrial basalts this conclusion is supportive of the hypothesis that the snc meteorites are samples of the planet mars

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

constraints on the petrogenesis of martian meteorites from the rb sr and sm nd isotopic systematics of the lherzolitic shergottites alh77005 and lew88516 abstract detailed rb sr and sm nd isotopic analyses have been completed on the lherzolitic shergottites alh77005 and lew88516 alh77005 yields a rb sr age of 185 11 ma and a sm nd age of 173 6 ma whereas the rb sr and sm nd ages of lew88516 are 183 10 and 166 16 ma respectively the initial sr isotopic composition of alh77005 is 0 71026 4 and the initial end value is 11 1 0 2 these values are distinct from those of lew88516 which has an initial sr isotopic composition of 0 71052 4 and an initial end value of 8 2 0 6 several of the mineral and whole rock leachates lie off the rb sr and sm nd isochrons indicating that the isotopic systematics of the meteorites have been disturbed the sm nd isotopic compositions of the leachates appear to be mixtures of primary igneous phosphates and an alteration component with a low 143nd 144nd ratio that was probably added to the meteorites on mars tie lines between leachate residue pairs from lew88516 mineral fractions and whole rocks have nearly identical slopes that correspond to rb sr ages of 90 1 ma this age may record a major shock event that fractionated rb sr from lattice sites located on mineral grain boundaries on the other hand the leachates could contain secondary alteration products and the parallel slopes of the tie lines could be coincidental nearly identical mineral modes compositions and ages suggest that these meteorites are very closely related nevertheless their initial sr and nd isotopic compositions differ outside analytical uncertainty requiring derivation from unique sources assimilation fractional crystallization models indicate that these two lherzolitic meteorites can only be related to a common parental magma if the assimilant has a sr nd ratio near 1 and a radiogenic sr isotopic composition further constraints placed on the evolved component by the geochemical and isotopic systematics of the shergottite meteorite suite suggest that it a formed at 4 5 ga b has a high la yb ratio c is an oxidant and d is basaltic in composition or is strongly enriched in incompatible elements the composition and isotopic systematics of the evolved component are unlike any evolved lunar or terrestrial igneous rocks its unusual geochemical and isotopic characteristics could reflect hydrous alteration of an evolved martian crustal component or hydrous metasomatism within the martian mantle

meteoritic evidence for a previously unrecognized hydrogen reservoir on mars abstract fluvial landforms on mars suggest that it was once warm enough to maintain persistent liquid water on its surface the transition to the present cold and dry mars is closely linked to the history of surface water yet the evolution of surficial water is poorly constrained based on in situ hydrogen isotope d h analyses of quenched and impact glasses in martian meteorites we provide evidence for the existence of a distinct but ubiquitous water ice reservoir d h 2 3 times earth s ocean water that lasted from at least the time when the meteorites crystallized 173 472 million years ago to the time they were ejected by impacts 0 7 3 3 million years ago but possibly much longer the origin of this reservoir appears to predate the current martian atmospheric water d h 5 6 times earth s ocean water and is unlikely to be a simple mixture of atmospheric and primordial water retained in the martian mantle d h earth s ocean water this reservoir could represent hydrated crust and or ground ice interbedded within sediments our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of mars

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

sr and nd isotopic systematics of shergotty meteorite abstract strontium and neodymium isotopic measurements are reported on mineral separates whole rock samples and their leachates and residues of shergotty meteorite a very large variation of the sm nd ratio in the phosphates of shergotty is observed two sources of nd are observed which are not mixed completely within shergotty resulting in two ages 1 an apparent age of 147 20 m y from the whole rock leachateresidue nd trend and 2 360 16 m y from a well defined nd isochron of minerals and their leachates and residues about 60 of the sr in the rock resides in the plagioclase and mesostasis and this was reset at 167 m y for the pyroxenes this resetting event had a more complex but also a more localized effect from the general pattern of this resetting a shock event at this time seems possible the 360 m y whole rock leachate residue age in the rb sr isotopic system coincides with the sm nd isochron age we think that the 360 m y age represents the crystallization of shergotty the apparently younger nd age of the phosphates which are indicated by the leaching experiments might be caused by late or post magmatic contamination of the whitlockites with radiogenic nd this same contamination process must also have affected the sr isotopic system the 360 m y crystallization age implies that the plagioclase and phosphates behaved as an open system to the contaminant after the crystallization of the pyroxenes the sr of the contaminant affected both the plagioclase and whitlockite but nd influenced only the whitlockites reflecting the partitioning of sr and nd between these phases the general chemical pattern of this contamination process is different from contamination patterns observed in terrestrial rocks this pattern may represent the finger print of localized fluid rock interaction on mars since a similar trend is observed in other snc meteorites it could indicate that a potassium phase could be a mantle mineral on mars this would have important effects on the chemical evolution of a planet especially in respect to isotopic tracers like ar pb sr

mineralogy of the martian interior up to core mantle boundary pressures in order to determine the mineralogy of the martian interior along a high temperature areotherm multianvil experiments have been performed with a model martian mantle composition up to 23 5 gpa the dreibus and wanke 19851 martian mantle composition yields an upper mantle that consists of olivine clinopyroxene orthopyroxene garnet at pressures up to 9 gpa above 9 gpa orthopyroxene is no longer present the transition zone is marked by the appearance of spinel at 13 5 gpa up to 15 gpa clinopyroxene and majorite coexists with phase and or spinel by 17 gpa clinopyroxene is entirely replaced by majorite and the modal abundance of spinel increases at the expense of phase the dominant assemblage throughout most of the transition zone is spinel majorite two experiments completed in the perovskite stability field indicate that the lower mantle consists of mg fe silicate perovskite magnesiowustite and majorite casio 3 perovskite is not present in these experiments both the presence of a martian lower mantle i e an mg fe silicate perovskite bearing zone and the phase assemblage stable in the martian lower mantle are very sensitive to the temperature profile of the interior a low temperature profile may stabilize stishovite in the lower mantle or it may lead to the absence of the lower mantle because of the higher transition pressure required for forming perovskite at lower temperatures regardless of the temperature profile assumed the martian upper mantle and transition zone will account for a larger proportion of the planet s interior than is the case for the earth s interior because of the smaller size of mars

176lu 176hf and 147sm 143nd ages of the martian shergottites evaluation of the shock resetting hypothesis through diffusion kinetic experiments and modeling and petrological observations abstract we address the age controversy of the shergottite suite of martian meteorites 200 ma dates determined by 176lu 176hf 147sm 143nd and various other decay systems as opposed to a 4 ga whole rock pb pb date by calculating the timescales needed to reset hf and nd isotopes in clinopyroxene which is the primary host of rare earth elements amongst the minerals used to compose the 176lu 176hf and 147sm 143nd isochrons at the peak and post shock p t conditions likely to have been experienced by the shergottites it is concluded that impact heating is highly unlikely to have significantly reset the 176lu 176hf and or 147sm 143nd mineral isochrons of these meteorites this conclusion is bolstered by the nature of measured concentration profiles of cr and fe across olivine maskelynite boundaries and ti profiles across clinopyroxene maskelynite melt interfaces in the shergottite rbt 04262 the lack of any evidence of diffusion in the measured concentration profiles coupled with the qualitative incompatibility of the measured crystal melt fractionation trends at these interfaces with the nature of fractionation expected from equilibrium partitioning provides strong evidence that no substantial chemical exchange took place between the solid and melt phases during peak shock p t conditions furthermore we find that the compositional profiles of major elements in coexisting augite and pigeonite are homogenous and reflect a magmatic temperature of 1143 9 c we argue that the pyroxene compositions and consequently the 176lu 176hf and 147sm 143nd geochronometers were highly unlikely to have been reset by the thermal effect of a shock event x ray mapping of a selected section of rbt 04262 shows no evidence of enhanced grain boundary diffusion we thus conclude that the 200 ma dates recorded by the 176lu 176hf and 147sm 143nd geochronometers most likely record the crystallization age of the shergottites

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

experimental study of polybaric ree partitioning between olivine pyroxene and melt of the yamato 980459 composition insights into the petrogenesis of depleted shergottites abstract a synthetic composition representing the yamato 980459 martian basalt shergottite has been used to carry out phase relation and rare earth element ree olivine and pyroxene partitioning experiments yamato 980459 is a sample of primitive basalt derived from a reduced end member among martian mantle sources experiments carried out between 1 2 gpa and 1350 1650 c simulate the estimated pressure temperature conditions of basaltic melt generation in the martian mantle olivine melt and orthopyroxene melt partition coefficients for la nd sm eu gd and yb d ree values were determined by la icpms and are similar to the published values for terrestrial basaltic systems we have not detected significant variation in d values with pressure over the range investigated and by comparison with previous studies carried out at lower pressure we apply the experimentally obtained olivine melt and orthopyroxene melt d ree values to fractional crystallization and partial melting models to develop a three stage geochemical model for the evolution of martian meteorites in our model we propose two ancient 4 535 ga sources the nakhlite source located in the shallow mantle and the deep mantle source located close to the martian core mantle boundary these two sources evolved distinctly on the e 143 nd evolution curve due to their different sm nd ratios by partially melting the nakhlite source at 1 3 ga we are able to produce a slightly depleted residue nakhlite residue the nakhlite residue is left undisturbed until 500 ma at which point the depleted deep mantle source is brought up by a plume mechanism carrying with it high heat flow melts and isotopic signatures of the deep mantle e g e 182 w e 142 nd etc the plume derived deep mantle source combines with the nakhlite residue producing a mixture that becomes a mantle source herein referred to as the y98 source for yamato 980459 and the other depleted shergottites with the characteristic range of sm nd ratios of these meteorites the same hot plume provides a heat source for the formation of enriched and intermediate shergottites our model reproduces the ree patterns of nakhlites and depleted shergottites and can explain high e 143 nd in depleted shergottites furthermore the model results can be used to interpret whole rock rb sr and sm nd ages of shergottites

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

importance of the lu hf isotopic system in studies of planetary chronology and chemical evolution the 176lu 176hf isotope method and its applications in earth sciences are discussed greater fractionation of lu hf than sm nd in planetary magmatic processes makes 176hf177hf a powerful geochemical tracer in general proportional variations of 176hf177hf exceed those of 143ndl44nd by factors of 1 5 3 in terrestrial and lunar materials lu hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time and this is the principal importance of lu hf new data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in 176hf177hf 87sr86sr and 143ndl44nd 87sr86sr diagrams 176hf177hf and 143nd144nd display a single linear isotopic variation in the suboceanic mantle these discordant 87sr86sr relationships may allow with the acquisition of further hf nd sr isotopic data a distinction between processes such as mantle metasomatism influence of seawater altered material in the magma source or recycling of sediments into the mantle in order to evaluate the hf nd isotopic correlation in terms of mantle fractionation history there is a need for measurements of hf distribution coefficients between silicate minerals and liquids and specifically for a knowledge of hf behavior in relation to rareearth elements for studying ancient terrestrial hf isotopic variations the best quality hf isotope data are obtained from granitoid rocks or zircons new data show that very u pb discordant zircons may have upwardly biased 176hf177hf but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial 176hf177hf until the controls on addition of radiogenic hf to zircon are understood combined zircon whole rock studies are recommended lu hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples but because it offers little advantage over existing methods is unlikely to find wide application in pure chronological studies

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

accretion and core formation on mars molybdenum contents of melt inclusion glasses in three snc meteorites abstract molybdenum cerium barium yttrium and rubidium contents of glasses in melt inclusions in three snc meteorites lew 88516 governador valadares and chassigny have been measured by ion microprobe ratios of mo ba and mo ce have been used to estimate the mo content of the primitive martian mantle 120 60 ppb abundances of five moderately siderophile elements ni co mo w and p and re in the martian mantle are consistent with metal silicate equilibrium between s bearing metallic liquid in a core 22 wt of the planet and peridotite melt at 75 kb 1620 c and oxygen fugacity 1 4 logfo2 units below the iw buffer this homogeneous accretion scenario is different than many heterogeneous accretion models for the earth but similar to recent studies suggesting homogeneous accretion in the presence of a deep terrestrial magma ocean

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

hydrogen isotopic composition of the martian mantle inferred from the newest martian meteorite fall tissint the hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets the sources of water and the hydrological evolution of mars may be inferred from the hydrogen isotopic compositions of mineral phases in martian meteorites which are currently the only samples of mars available for earth based laboratory investigations previous studies have shown that d values in minerals in the martian meteorites span a large range of 250 to 6000 the highest hydrogen isotope ratios likely represent a martian atmospheric component either interaction with a reservoir in equilibrium with the martian atmosphere such as crustal water or direct incorporation of the martian atmosphere due to shock processes the lowest d values may represent those of the martian mantle but it has also been suggested that these values may represent terrestrial contamination in martian meteorites here we report the hydrogen isotopic compositions and water contents of a variety of phases merrillites maskelynites olivines and an olivine hosted melt inclusion in tissint the latest martian meteorite fall that was minimally exposed to the terrestrial environment we compared traditional sample preparation techniques with anhydrous sample preparation methods to evaluate their effects on hydrogen isotopes and find that for severely shocked meteorites like tissint the traditional sample preparation techniques increase water content and alter the d h ratios toward more terrestrial like values in the anhydrously prepared tissint sample we see a large range of d values most likely resulting from a combination of processes including magmatic degassing secondary alteration by crustal fluids shock related fractionation and implantation of martian atmosphere based on these data our best estimate of the d value for the martian depleted mantle is 116 94 which is the lowest value measured in a phase in the anhydrously prepared section of tissint this value is similar to that of the terrestrial upper mantle suggesting that water on mars and earth was derived from similar sources the water contents of phases in tissint are highly variable and have been affected by secondary processes considering the h2o abundances reported here in the driest phases most likely representing primary igneous compositions and appropriate partition coefficients we estimate the h2o content of the tissint parent magma to be 0 2 wt

lu hf and sm nd isotopic systematics in chondrites and their constraints on the lu hf properties of the earth sm nd and lu hf isotopic data are presented for 19 chondritic meteorites six carbonaceous chondrites five l chondrites seven h chondrites and a single enstatite chondrite the primary goal of the study is to better define the bulk silicate earth bse reference values for hf isotopes except for one sample with lower sm nd the sm nd data define a cluster around the accepted reference values for chondrites and terrestrial planets giving a mean 147sm 144nd of 0 1960 0 0005 and a mean 143nd 144nd of 0 512631 0 000010 uncertainties are two standard errors it seems appropriate to retain the presently accepted sm nd reference parameters 147sm 144nd 0 1966 and 143nd 144nd 0 512638 when fractionation corrected to 146nd 144nd 0 7219 lu hf isotopic data are not clustered but spread along an approximate 4 5 ga isochron trend with a range of 176lu 177hf from 0 0301 to 0 0354 the data are similar to many of the samples of chondrites presented by bizzarro et al nature 421 2003 931 but lack the range to lower lu hf shown by those authors our chondrite data define a regression line of 4 44 0 34 ga when 1 867 10 11 year 1 is used for the decay constant of 176lu science 293 2001 683 earth planet sci lett 219 2004 311 324 combining our data with the main population of analyses from bizzarro et al nature 421 2003 931 yields 4 51 0 24 ga unless samples of eucrite meteorites and deviating replicates of chondrites with 176lu 177hf less than 0 030 are employed no combination of the main population of chondrite lu hf data yields a regression with sufficiently low error to constrain the decay constant of 176lu sample heterogeneity seems to hinder the acquisition of reproducible lu hf analyses from small manually ground pieces of chondrites and we suggest that analysis of powders prepared from large volumes of meteorite will be needed to adequately characterize the lu hf isotope systematics of chondritic reservoirs and of bse our results for carbonaceous chondrites show higher average 176lu 177hf and 176hf 177hf than ordinary chondrites and the mean of carbonaceous chondrites also coincides with replicate analyses of a powder representing a large volume of meteorite the allende powder from the smithsonian institution use of the carbonaceous chondrite mean for bse lu hf characteristics results in a bse hf nd point that lies well within the array of terrestrial compositions and leads to plausible initial ehf values for precambrian rocks an improved objective resolution of meteorite data and of meteoritic models for the earth needs to occur before bse can be established for lu hf

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

geochemical diversity in first rocks examined by the curiosity rover in gale crater evidence for and significance of an alkali and volatile rich igneous source the first four rocks examined by the mars science laboratory alpha particle x ray spectrometer indicate that curiosity landed in a lithologically diverse region of mars these rocks collectively dubbed the bradbury assemblage were studied along an eastward traverse sols 46 102 compositions range from na and al rich mugearite jake matijevic to fe mg and zn rich alkali rich basalt hawaiite bathurst inlet and span nearly the entire range in feo and mno of the data sets from previous martian missions and martian meteorites the bradbury assemblage is also enriched in k and moderately volatile metals zn and ge these elements do not correlate with cl or s suggesting that they are associated with the rocks themselves and not with salt rich coatings three out of the four bradbury rocks plot along a line in elemental variation diagrams suggesting mixing between al rich and fe rich components chemcam analyses give insight to their degree of chemical heterogeneity and grain size variations in trace elements detected by chemcam suggest chemical weathering li and concentration in mineral phases e g rb and sr in feldspars we interpret the bradbury assemblage to be broadly volcanic and or volcaniclastic derived either from near the gale crater rim and transported by the peace vallis fan network or from a local volcanic source within gale crater high fe and fe mn in et then likely reflect secondary precipitation of fe 3 oxides as a cement or rind the k rich signature of the bradbury assemblage if igneous in origin may have formed by small degrees of partial melting of metasomatized mantle

large shield volcanoes on the moon 1 the volcanic style of the moon has long been understood to consist almost exclusively of flood basalts erupted from fissures along with minor pyroclastic activity large central vent shield volcanoes that characterize basaltic volcanism on the other terrestrial planets appeared to be absent small few kilometers diameter central vent constructs have long been recognized in the lunar maria and often are found clustered in fields throughout the lunar maria new global topographic data from the lola and lroc instruments on lro reveal that almost all of these volcanic complexes on the moon occur on large regional topographic rises in the lunar maria tens to hundreds of kilometers in extent and between several hundred to several thousand meters high we propose that these topographic swells are shield volcanoes and are the lunar equivalents of the large basaltic shields found on the earth venus and mars the newly recognized lunar shields are found peripheral to the large deeply flooded impact basins imbrium and serenitatis suggesting a genetic relation to those features loading of the lithosphere by these basalt filled basins may be responsible for inducing a combination of flexural and membrane stress inducing a pressure distribution on vertically oriented dikes favorable to magma ascent this condition would occur in a zone annular to the large circular loads produced by the basins where the shield volcanoes occur

a chemical model for generating the sources of mare basalts combined equilibrium and fractional crystallization of the lunar magmasphere abstract it is generally considered that mare basalts were generated by the melting of a cumulate mantle formed in an early moon wide magma ocean or magmasphere however the nature and chemistry of this cumulate mantle and the logistics of its origin have remained elusive extensive studies of terrestrial layered mafic intrusions over the past sixty years have emphasized the imperfection of fractional crystallization and attendant crystal crystal and crystal liquid separation in a convecting magma chamber crystal liquid and crystal crystal separations were similarly inefficient during evolution of the lunar magma ocean lmo allowing for the trapping of interstitial liquid and entrainment of a small proportion of less dense plagioclase into the denser mafic cumulate mush indeed petrography of lunar highlands samples demonstrates this for anorthosites with 1 10 olivine the residual liquid after 80 90 crystallization was very evolved in fact kreepy and even in small proportions 1 5 would have a noticeable effect on the trace element chemistry of melts generated from these cumulates this trapped residual liquid would elevate total ree abundances in the cumulate pile while synchronously deepening the already negative eu anomaly essentially this trapped liquid will make the cumulate more fertile for melting to generate both kreep basalt and mare basalt magmas plagioclase entrained in the mafic cumulate pile adds an essential al component to the high ti basalt source and will moderate the requisite negative eu anomaly in the cumulate early in the evolution of the lunar mantle when the lmo still was largely liquid it is likely that vigorous convection was an important factor in crystallization such convection would allow crystals to remain suspended and in equilibrium with the lmo liquid for relatively long periods of time this extended period of equilibrium crystallization would then have been followed by fractional crystallization once plagioclase became a liquidus phase and began to float to form the lunar highlands crust previous authors have proposed a three component model for the evolution of high ti mare basalt source regions this model includes kreep early olivine rich high mg cumulates and late ilmeniterich low mg cumulates in various proportions however we propose a model for high ti basalt parent magmas which is in accord with studies of terrestrial layered intrusions this model for the high ti source includes trapped instantaneous residual liquid tirl 1 3 and entrainment of a small 2 5 proportion of plagioclase into the late stage cumulate pile in order to account for both the observed al compositions and trace element characteristics of high ti mare basalts melting of this relatively shallow ilmenite and clinopyroxene bearing late stage cumulate can generate high ti mare basalt magmas furthermore we are in agreement with other workers that only through a process of nonmodal melting will the high ti values for the parent magmas be realized large scale convective overturn of the cumulate pile and mixing of kreep with early and late stage cumulates is not required however localized overturn of the upper tenth of the cumulate pile is likely and in fact required to achieve an appropriate major element balance for the high ti mare basalt source region

distinct chlorine isotopic reservoirs on mars implications for character extent and relative timing of crustal interactions with mantle derived magmas evolution of the martian atmosphere and the building blocks of an early mars the style magnitude timing and mixing components involved in the interaction between mantle derived martian magmas and martian crust have long been a point of debate understanding this process is fundamental to deciphering the composition of the martian crust and its interaction with the atmosphere the compositional diversity and oxygen fugacity variations in the martian mantle the bulk composition of mars and the materials from which it accreted and the noble gas composition of mars and the sun recent studies of the chlorine isotopic composition of martian meteorites imply that although the variation in delta sup 37 cl is limited total range of approximately14 per mille there appears to be distinct signatures for the martian crust and mantle however there are potential issues with this interpretation new cl isotope data from the sam sample analysis at mars instrument on the mars science lab indicate a very wide range of cl isotopic compositions on the martian surface recent measurements by 10 duplicated the results of 7 8 but placed them within the context of sam surface data in addition martian meteorite chassigny contains trapped noble gases with isotopic ratios similar to solar abundance and has long been considered a pristine mantle derived sample however previous studies of apatite in chassigny indicate that crustal fluids have interacted with regions interstitial to the cumulus olivine the initial cl isotope measurements of apatite in chassigny suggest an addition of crustal component to this lithology apparently contradicting the rare gas data here we examine the cl isotopic composition of multiple generations and textures of apatite in chassigny to extricate the crustal and mantle components in this meteorite and to reveal the style and timing of the addition of crustal components to mantle derived magmas these data reveal distinct martian cl sources whose signatures have their origins linked to both the early solar system and the evolving martian atmosphere