on the imbalance and response time of glaciers in the european alps glaciers in the european alps rapidly lose mass to adapt to changes in climate conditions here we investigate the relationship and lag between climate forcing and geometric glacier response with a regional glacier evolution model accounting for ice dynamics the volume loss occurring as a result of the glacier climate imbalance increased over the early 21st century from about 35 in 2001 to 44 in 2010 this committed loss reduced to 40 by 2018 indicating that temperature increase was outweighing glacier retreat in the early 2000s but that the fast retreat effectively somewhat diminished glacier imbalances we analyze the lag in glacier response for each individual glacier and find mean response times of 50 28 years our findings indicate that the response time is primarily controlled by glacier slope and secondarily by elevation range and mass balance gradient rather than by glacier size

a geochemical study of the winonaites evidence for limited partial melting and constraints on the precursor composition abstract the winonaites are primitive achondrites which are associated with the iab iron meteorites textural evidence implies heating to at least the fe ni fes cotectic but previous geochemical studies are ambiguous about the extent of silicate melting in these samples oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites here we analysed a suite of winonaites for modal mineralogy and bulk major and trace element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite iab parent asteroid modal mineralogy and geochemical data are presented for eight winonaites textural analysis reveals that for our sub set of samples all except the most primitive winonaite northwest africa 1463 reached the fe ni fes cotectic however only one tierra blanca shows geochemical evidence for silicate melting processes tierra blanca is interpreted as a residue of small degree silicate melting our sample of winona shows geochemical evidence for extensive terrestrial weathering all other winonaites studied here fortuna queen alexander range 94535 hammadah al hamra 193 pontlyfni and nwa 1463 have chondritic major element ratios and flat ci normalised bulk rare earth element patterns suggesting that most of the winonaites did not reach the silicate melting temperature the majority of winonaites were therefore heated to a narrow temperature range of between 1220 the fe ni fes cotectic temperature and 1370 k the basaltic partial melting temperature silicate inclusions in the iab irons demonstrate partial melting did occur in some parts of the parent body ruzicka and hutson 2010 thereby implying heterogeneous heat distribution within this asteroid together this indicates that melting was the result of internal heating by short lived radionuclides the brecciated nature of the winonaites suggests that the parent body was later disrupted by a catastrophic impact which allowed the preservation of the largely unmelted winonaites despite major element similarities to both ordinary and enstatite chondrites trace element analysis suggests the winonaite parent body had a carbonaceous chondrite like precursor composition the parent body of the winonaites was volatile depleted relative to ci but enriched compared to the other carbonaceous classes the closest match are the cm chondrites however the specific precursor is not sampled in current meteorite collections

characterizing cosmochemical materials with genetic affinities to the earth genetic and chronological diversity within the iab iron meteorite complex abstract the iab iron meteorite complex consists of a main group mg and five chemical subgroups sll slm slh shl and shh here mass independent mo and radiogenic 182 w isotope compositions are reported for iab complex meteorites to evaluate the genetics and chronology respectively of the mg and subgroups osmium isotopes are used to correct for cosmic ray exposure effects on isotopes of mo and w the mg and three subgroups i e sll slm and slh characterized by low au abundances have the same mo isotopic compositions within analytical uncertainty consistent with a common genetic origin these meteorites together with winonaites are the only cosmochemical materials yet identified with mo isotopic compositions that are identical to earth the mo isotopic compositions of two subgroups characterized by higher au abundances shl and shh are identical to one another within uncertainty but differ from the low au subgroups indicating derivation from genetically distinct materials the mg has a 182 w post calcium aluminum inclusion cai formation model age of 3 4 0 7 ma one of the low au subgroups slm is 1 7 ma younger whereas the high au subgroups are 1 5 3 ma older the new mo w data coupled with chemical data indicate that the mg and the low au subgroups formed in different impact generated melts some of which evidently formed on a chemically disparate but genetically identical parent body the high au subgroups likely formed via core formation processes on separate internally heated parent bodies from other iab subgroups the iab complex meteorites fall on a linear trend defined by 94 mo 96 mo vs 95 mo 96 mo along with most other iron meteorite groups variation along this line was caused by mixing between at least two nebular components one component was likely a pure s process enriched nucleosynthetic carrier and the other a homogenized nebular component sombrerete currently classified as an shl iron has a mo isotopic composition that is distinct from all iab complex meteorites analyzed here along with group ivb iron meteorites and some ungrouped iron meteorites it falls on a separate line from other meteorites which may reflect addition of an r process enriched component and it should no longer be classified as a iab iron

hf w chronology of ordinary chondrites abstract fifteen h l and ll ordinary chondrites of petrologic types 4 6 have been analyzed for hf w isotope systematics to constrain the chronology internal structure and thermal history of their parent bodies for most samples coarse grained metals plot below the isochrons defined by silicate dominated fractions which consist of variable mixtures of silicate minerals with tiny metal inclusions this offset results from an earlier hf w closure in the large metal grains and provides a new means for simultaneously determining cooling rates and hf w closure ages for individual samples for most type 5 and 6 samples cooling rates and hf w ages are inversely correlated indicating that these samples derive from concentrically zoned bodies in which more strongly metamorphosed samples derive from greater depth these data therefore provide strong evidence for a common onion shell structure for the h l and ll chondrite parent bodies the cooling rates and hf w ages of some type 5 and 6 chondrites overlap indicating that the hf w systematics provide a more robust measure of the thermal history and burial depth of a given sample than the simple petrographic distinction between types 5 and 6 two type 6 samples deviate from the correlation between cooling rates and hf w ages and cooled much faster than expected for their hf w age these samples likely were excavated by impacts that occurred during high temperature metamorphism and prior to complete closure of the hf w system at 10 ma after cai formation as these impacts would have disturbed the asteroid s cooling history these samples likely derive from different bodies than samples with undisturbed cooling histories implying that ordinary chondrites derive from more than just three parent bodies the hf w data reveal that metal silicate fractionation among the h l and ll groups occurred between 2 and 2 7 ma after cai formation and hence was about coeval to chondrule formation as both metal silicate fractionation and chondrule formation occurred prior to chondrite parent body accretion there should be no ordinary chondrite chondrules that are younger than 2 7 ma finally ordinary chondrite precursors had lower hf w ratios than carbonaceous chondrites suggesting that inner and outer solar system materials respectively were chemically distinct even for refractory elements

origin of isotopic heterogeneity in the solar nebula by thermal processing and mixing of nebular dust we have investigated mo and w isotope compositions in acid leachates and an insoluble residue from the murchison carbonaceous chondrite the new data reveal variable enrichments of s and r process isotopes and demonstrate that several isotopically diverse presolar components are present in murchison the insoluble residue is enriched in s process mo and w evidently due to the enrichment of presolar sic grains in contrast mo and w released by leaching with weak acids are depleted in s process isotopes most likely reflecting the isotope composition of the homogenized portion of the protosolar nebula the mo and w isotope compositions of the different leach steps are broadly correlated as expected from s process nucleosynthesis theory indicating that mo and w are presumably hosted in the same carriers however at the bulk meteorite scale no nucleosynthetic w isotope anomalies have been identified except for ivb iron meteorites in spite of large mo isotope heterogeneities among the same samples this decoupling of mo and w isotopes in bulk meteorites may reflect physical mixing of varying proportions of isotopically diverse presolar components with a normal solar nebula component due to the high w mo ratio and near terrestrial w isotope composition of the latter such mixing has no measurable effect on w isotopes but results in large mo isotope variations alternatively thermal processes within the solar nebula imparted mo isotope heterogeneity on an initially homogeneous mixture of presolar dust while w was not affected removal of volatile mo oxides during the thermal destruction of fragile presolar components would have created isotopically heterogeneous reservoirs of nebular dust accretion of meteorite parent bodies from such variably processed dust would thus result in mo isotope heterogeneities at the bulk meteorite scale other elements such as os and w were not or only slightly affected because they were more refractory during thermal processing and therefore remained isotopically homogeneous thermal processing of presolar dust within the solar nebula can thus account for both isotope heterogeneities observed for some elements and the lack of such isotopic heterogeneity for other elements

nucleosynthetic molybdenum isotope anomalies in iron meteorites new evidence for thermal processing of solar nebula material abstract we have investigated nucleosynthetic mo isotope anomalies in 38 different bulk iron meteorites from 11 groups to produce by far the largest and most precise dataset available to date for such samples all magmatic iron groups were found to display deficits in s process mo isotopes with essentially constant anomalies within but significant variations between groups only meteorites of the non magmatic iab iiicd complex revealed terrestrial mo isotopic compositions the improved analytical precision achieved in this study enables two isotopically distinct suites of iron meteorites to be identified of these the r p suite encompasses the ic iiab iie iiiab iiie and iva groups and exhibits relatively modest but pure s process deficits relative to earth the second r p suite includes groups iic iiif and ivb these iron meteorites show larger s process deficits than the r p suite coupled with an excess of r process relative to p process components comparison of the results with data for other elements e g cr ni ru ti zr suggests that the mo isotope variability is most likely produced by thermal processing and selective destruction of unstable presolar phases an updated model is proposed which relates the iron meteorite suites to different extents of thermal processing in the solar nebula as governed by heliocentric distance in detail the r p suite of iron meteorite parent bodies is inferred to have formed closer to the sun where the extent of thermal processing was similar to that experienced by terrestrial material so that the meteorites exhibit only small s process deficits relative to earth in contrast the r p suite formed at greater heliocentric distance where more subtle thermal processing removed a smaller proportion of r and p process host phases thereby generating larger s process deficits relative to the terrestrial composition in addition the thermal conditions enabled selective destruction of p versus r isotope carrier phases to produce the observed divergence of r and p process mo isotope abundances

neutron capture on pt isotopes in iron meteorites and the hf w chronology of core formation in planetesimals the short lived 182hf 182w isotope system can provide powerful constraints on the timescales of planetary core formation but its application to iron meteorites is hampered by neutron capture reactions on w isotopes resulting from exposure to galactic cosmic rays here we show that pt isotopes in magmatic iron meteorites are also affected by capture of epi thermal neutrons and that the pt isotope variations are correlated with variations in 182w 184w this makes pt isotopes a sensitive neutron dosimeter for correcting cosmic ray induced w isotope shifts the pre exposure 182w 184w derived from the pt w isotope correlations of the iid iva and ivb iron meteorites are higher than most previous estimates and are more radiogenic than the initial 182w 184w of ca al rich inclusions cai the hf w model ages for core formation range from 1 6 1 0 million years ma for the iva irons to 2 7 1 3 ma after cai formation for the iid irons indicating that there was a time gap of at least 1 ma between cai formation and metal segregation in the parent bodies of some iron meteorites from the hf w ages a time limit of 1 5 2 ma after cai formation can be inferred for the accretion of the iid iva and ivb iron meteorite parent bodies consistent with earlier conclusions that the accretion of differentiated planetesimals predated that of most chondrite parent bodies

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

40ar 39ar dating of plagioclase grain size separates from silicate inclusions in iab iron meteorites and implications for the thermochronological evolution of the iab parent body abstract in order to better constrain the thermochronological evolution of the iab parent body we performed a 40ar 39ar age study on individual silicate inclusions of the iab irons caddo county campo del cielo landes and ocotillo in contrast to earlier studies several plagioclase separates of different grain sizes and quality grades were extracted from each inclusion to reduce the complexity of the age spectra and study the influence of these parameters on the ar ar ages in nearly all inclusions we found significantly different ar ar ages among the separates caddo county 4 472 0 02 4 562 0 02 ga campo del cielo 2 4 362 0 04 4 442 0 03 ga landes 2 4 412 0 05 4 522 0 04 ga ocotillo 4 382 0 04 4 462 0 03 ga these ages were calculated using the new 40k decay constant published by mundil r renne p r min k and ludwig k r 2006 resolvable miscalibration of the 40ar 39ar geochronometer eos trans agu 87 fall meet suppl abstract v21a 0543 the ages did not systematically correlate with the respective grain size of the separate as expected i e smaller grains did not necessarily show younger ages due to later closure to ar diffusion or easier re opening of the system in the course of a reheating event compared to larger grains based on the large range of ar ar ages we suggest that the individual inclusions are composed of silicate grains from different locations within the iab parent body while some grains remained in a hot deep environment that allowed ar diffusion over an extended time period in some cases combined with grain coarsening others cooled significantly earlier near surface through the k ar blocking temperature these different grains where brought together during an impact followed by mixing and reassembly of the debris as proposed by benedix et al benedix g k mccoy t j keil k and love s g 2000 a petrologic study of the iab iron meteorites constraints on the formation of the iab winonaite parent body meteorit planet sci 35 1127 1141 due to rapid cooling after the impact some of the age differences among the grains could be preserved based mainly on our caddo county ar ar age information the iab parent body was destroyed by impact and reassembled between 4 5 and 4 47 ga however iab silicate ar ar ages should depend much more on the pre and post impact cooling rate and burial depth than on the time of the actual impact this is supported by a compilation of our and literature iab and winonaite ar ar ages ranging smoothly from the time of accretion of the chondritic iab parent body down to the time of its final cooling through the k ar blocking temperature after impact and reassembly instead of showing a peak in ar ar ages at the time of the destructive impact

nucleosynthetic w isotope anomalies and the hf w chronometry of ca al rich inclusions abstract ca al rich inclusions cai are the oldest dated objects formed in the solar system and are pivotal reference points in early solar system chronology knowledge of their initial 182hf 180hf and 182w 184w is essential not only for obtaining precise hf w ages relative to the start of the solar system but also to assess the distribution of short lived radionuclides in the early solar nebula however the interpretation of hf w data for cai is complicated by nucleosynthetic w isotope variations to explore their extent and nature and to better quantify the initial hf and w isotope compositions of the solar system we obtained hf w data for several fine and coarse grained cai from three cv3 chondrites the fine grained cai exhibit large and variable anomalies in e183w e i w equals 0 01 deviation from terrestrial values extending to much larger anomalies than previously observed in cai and reflecting variable abundances of s and r process w isotopes conversely the coarse grained mostly type b inclusions show only small if any nucleosynthetic w isotope anomalies the investigated cai define a precise correlation between initial e182w and e183w providing a direct empirical means to correct the e182w of any cai for nucleosynthetic isotope anomalies using their measured e183w after correction for nucleosynthetic w isotope variations the cai data define an initial 182hf 180hf of 1 018 0 043 10 4 and an initial e182w of 3 49 0 07 the hf w formation intervals of the angrites d orbigny and sahara 99555 relative to this cai initial is 4 8 0 6 ma in good agreement with al mg ages of these two angrites this renders a grossly heterogeneous distribution of 26al in the inner solar system unlikely at least in the region were cai and angrites formed

the cosmic molybdenum ruthenium isotope correlation dauphas et al astrophys j 565 2002 640 644 reported molybdenum isotopic anomalies in differentiated and bulk primitive meteorites it is shown here that these isotopic anomalies correlate with one another in exactly the way expected from nucleosynthesis theory if different regions of the nebula received different contributions of s process matter synthesized in lowmass agb stars furthermore when bulk measurements are grouped by meteorite class the molybdenum isotopic anomalies correlate with the ruthenium isotopic anomalies recently reported by chen et al lunar planet sci xxxiv 2003 1789 again indicating a heterogeneous distribution of s process matter as molybdenum is only moderately siderophile most of the molybdenum presently in the mantle was delivered before the completion of core formation in contrast because ruthenium is highly siderophile nearly all of the mantle ruthenium was delivered by a late veneer after the end of core formation thus the fact the silicate earth lies on the mo ru cosmic correlation supports the idea that the earth accreted homogeneously stated otherwise the feeding zone of the earth did not change drastically with time as both the bulk of the earth and the late veneer accreted from material from the same mo ru isotopic reservoir d 2004 elsevier b v all rights reserved

hf w thermochronometry ii accretion and thermal history of the acapulcoite lodranite parent body article acapulcoites and lodranites are highly metamorphosed to partially molten meteorites with mineral and bulk compositions similar to those of ordinary chondrites these properties place the acapulcoites and lodranites between the unmelted chondrites and the differentiated meteorites and as such acapulcoites lodranites are of special interest for understanding the initial stages of asteroid differentiation as well as the role of 26 al heating in the thermal history of asteroids to constrain the accretion timescale and thermal history of the acapulcoite lodranite parent body and to compare these results to the thermal histories of other meteorite parent bodies the hf w system was applied to several acapulcoites and lodranites acapulcoites dhofar 125 and nwa 2775 and lodranite nwa 2627 have indistinguishable hf w ages of tcai 5 2 0 9 ma and tcai 5 7 1 0 ma corresponding to absolute ages of 4563 1 0 8 ma and 4562 6 0 9 ma closure temperatures for the hf w system for acapulcoites and lodranites estimated from numerical simulations of w diffusion in high ca pyroxene are 975 50 c and 1025 50 c respectively owing to these high closure temperatures the hf w ages provide information on the earliest high temperature evolution and combined with thermal modeling indicate that the acapulcoite lodranite parent body accreted 1 5 2 ma after cai formation was internally heated by 26

contribution of neutron capture reactions to observed tungsten isotopic ratios to study whether tungsten isotopic ratios observed in terrestrial samples relative to w ratios in an iron meteorite could be made by neutron capture reactions in the iron meteorite the fluxes of thermal and epithermal neutrons in a large iron meteoroid toluca were calculated using monte carlo particle production and transport codes peak neutron capture rates on w isotopes were calculated to occur at depths of 30 34 cm the calculated changes in the 182w 183w due to neutrons are much less than those observed in terrestrial samples relative to iron meteorites indicating a non cosmogenic origin of the observed w isotopic ratios

coupled w os pt isotope systematics in ivb iron meteorites in situ neutron dosimetry for w isotope chronology tungsten isotope compositions of magmatic iron meteorites yield ages of differentiation that are within 2 ma of the formation of cais with the exception of ivb irons that plot to systematically less radiogenic compositions yielding erroneously old ages secondary neutron capture due to galactic cosmic ray gcr irradiation is known to lower the e182w of iron meteorites adequate correction of which requires a measure of neutron dosage which has not been available thus far the w os and pt isotope systematics of 12 of the 13 known ivb iron meteorites were determined by mc icp ms w os pt and tims os on the same dissolutions that yield precise e182w stable os and pt isotopes were determined as in situ neutron dosimeters for empirical correction of the ubiquitous cosmic ray induced burn out of 182w in iron meteorites the w isotope data reveal a main cluster with e182w of 3 6 but a much larger range than observed in previous studies including irons weaver mountains and warburton range that show essentially no cosmogenic effect on their e182w the ivb data exhibits resolvable negative anomalies in e189os 0 6e and complementary e190os anomalies 0 4e in tlacotepec due to neutron capture on 189os which has approximately the same neutron capture cross section as 182w and captures neutrons to produce 190os the least irradiated ivb iron warburton range has e189os and e190os identical to terrestrial values similarly pt isotopes which are presented as e192pt e194pt and e196pt range from 4 4e to 53e 1 54e to 0 32e and 0 73e to 0 20e respectively also identify tlacotepec and dumont as the most gcr damaged samples in w os and w pt isotope space the correlated isotope data back project toward a 0 epsilon value of e192pt e189os and e190os from which a pre gcr irradiation e182w of 3 42 0 09 2 is derived this pre gcr irradiation e182w is within uncertainty of the currently accepted cai initial e182w the pt and os isotope correlations in the ivb irons are in good agreement with a nuclear model for spherical irons undergoing gcr spallation although this model over predicts the change of e182w by 2 indicating a need for better w neutron capture cross section determinations a nucleosynthetic effect in e184w in these irons of 0 14 0 08 is confirmed consistent with the presence of mo and ru isotope anomalies in ivb irons the lack of a non gcr os isotope anomaly in these irons requires more complex explanations for the production of w ru and mo anomalies than nebular heterogeneity in the distribution of s process to r process nuclides

hf w chronometry of the iab iron meteorite parent body abstract the iab iron meteorites are unusual in having abundant silicate inclusions but the relationship of metal and silicates is not well understood in order to study the sequence and the timing of events that led to the observed structure of iab iron meteorites the hf w isotope system was applied to metal and silicate separates from seven iab iron meteorites a major metal segregation event on the iab parent body is dated by the average 182 w 184 w ratio of the iab metal phases 3 1 0 2 e 182 w units corresponding to a time of 1 8 2 3 2 0 ma after the formation of ca al rich inclusions cais the 182 hf 182 w data for three bulk inclusions from landes copiapo and el taco define a linear trend interpreted as an isochron corresponding to an age of 2 5 2 3 2 0 ma after cai formation this age most likely dates silicate differentiation on the iab parent body and is within analytical uncertainty indistinguishable from the major metal segregation event several silicate inclusions are displaced from the iab silicate isochron towards less radiogenic w compositions most likely reflecting thermal events on the parent body metal segregation and silicate differentiation occurred early enough so that these processes could have at least partially been triggered by an internal heat source e g 26 al basaltic inclusions of the caddo county specimen define an age of 4 6 0 7 0 6 ma most likely dating a partial melting event on the iab parent body three silicate separates from another el taco inclusion yield an age that postdates cai formation by 10 8 2 4 2 0 ma and the iab silicate isochron by 8 3 ma this prolonged interval of local thermal events on the iab parent body are best explained by collisional heat sources i e impacts the hf w ages for thermal events on the iab parent body are within the range of previously reported 129 i 129 xe ages but are significantly older than published 87 rb 87 sr 147 sm 143 nd and most 40 k 40 ar ages most likely these chronometers were reset during later thermal events that had only a minor effect on the 182 hf 182 w and 129 i 129 xe systems

post impact thermal evolution of porous planetesimals abstract impacts between planetesimals have largely been ruled out as a heat source in the early solar system by calculations that show them to be an inefficient heat source and unlikely to cause global heating however the long term localized thermal effects of impacts on planetesimals have never been fully quantified here we simulate a range of impact scenarios between planetesimals to determine the post impact thermal histories of the parent bodies and hence the importance of impact heating in the thermal evolution of planetesimals we find on a local scale that heating material to petrologic type 6 is achievable for a range of impact velocities and initial porosities and impact melting is possible in porous material at a velocity of 4 km s burial of heated impactor material beneath the impact crater is common insulating that material and allowing the parent body to retain the heat for extended periods millions of years cooling rates at 773 k are typically 1 1000 k ma matching a wide range of measurements of metallographic cooling rates from chondritic materials while the heating presented here is localized to the impact site multiple impacts over the lifetime of a parent body are likely to have occurred moreover as most meteorite samples are on the centimeter to meter scale the localized effects of impact heating cannot be ignored

a petrologic study of the iab iron meteorites constraints on the formation of the iab winonaite parent body abstract we have studied iab iron meteorites and their silicate bearing inclusions to elucidate the origin of their parent body we have divided iab irons into five categories which best describe the inclusions and other properties of the irons these are 1 sulfide rich irons such as mundrabilla that contain a significant volume fraction of troilite with or without associated silicates 2 irons with non chondritic silicate inclusions such as basaltic inclusions in caddo county 3 irons with rounded troilite and or graphite inclusions sometimes containing embedded angular silicate inclusions 4 irons with angular silicate inclusions similar to those of the winonaites where silicates may comprise up to 40 vol of the rock and 5 irons with phosphate bearing inclusions such as the brianite bearing iab san cristobal similarities in mineralogy mineral and oxygen isotopic compositions suggest that iab irons and winonaites are almost certainly from a common parent body iiicd irons may also have originated on this parent body although evidence supporting this suggestion is less convincing previous models for the origin of iab irons propose that they are either products of selective impact melting in the megaregoliths of a chondritic asteroid or products of partial melting and fractional crystallization during formation of a sulfur rich core the former model suffers from the fact that impact is incapable of causing preferential melting of metal and sulfide on a large scale and pooling of these selective melts into sizable bodies the latter model does not readily explain the occurrence of often fragmentary angular silicate clasts in a metallic fe ni host we propose a new model for the origin of iab irons that incorporates aspects of both previous models we suggest that a chondritic possibly heterogeneous parent body was heated by a non collisional heat source which caused partial but not complete melting of the body after peak temperatures were reached and cooling and crystallization had begun a major impact catastrophically fragmented this body and the debris gravitationally reassembled scrambling the parent body lithologies we suggest that the impact caused extensive mixing of molten metallic fe ni and solid silicate material resulting in the formation of iab irons with silicate inclusions whereas winonaites represent metamorphosed rocks and partial melt residues of the precursor silicate lithologies high temperatures of some of the reassembled debris and deep burial resulted in continued fractionation and formation of the 2

new implications for the origin of the iab main group iron meteorites and the isotopic evolution of the noncarbonaceous nc reservoir abstract the origin of the iab main group mg iron meteorites is explored through consideration of 182w isotopic compositions thermal modeling of 26al decay and mass independent nucleosynthetic mo isotopic compositions of planetesimals formed in the noncarbonaceous nc protosolar isotopic reservoir a refined 182w model age for the meteorites campo del cielo canyon diablo and nantan suggests that the iab mg parent body underwent some form of metal silicate segregation as early as 5 3 0 4 myr after calcium aluminum rich inclusion cai formation or as late as 13 8 1 4 myr after cai formation if melting of the iab mg occurred prior to 7 myr after cai formation it was likely driven by 26al decay for a parent body radius 40 km otherwise additional heat from impact is required for melting metal this late in solar system history if melting was partially or wholly the result of internal heating a thermal model of 26al decay heat production constrains the accretion age of the iab mg parent body to 1 7 0 4 myr after cai formation if melting was instead dominantly caused by impact heating thermal modeling suggests the parent body accreted more than 2 myr after cai formation comparison of mo mass independent isotopic compositions of the iab mg to other nc bodies with constrained accretion ages suggests that the mo isotopic composition of the nc reservoir changed with time and that the iab mg parent body accreted between 2 to 3 myr after cai formation thus requiring an origin by impact the relationship between nucleosynthetic mo isotopic compositions and accretion ages of planetesimals from the nc reservoir suggests that isotopic heterogeneity developed from either addition of s process material to or removal of coupled r p process material from the nc reservoir

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

evidence for homogeneous distribution of osmium in the protosolar nebula separate s r and possibly p process enriched and depleted components have been shown to host os in low metamorphic grade chondrites although no measureable os isotopic anomalies have yet been discovered for bulk chondrites here iron meteorites from groups iab iiab iiiab iva and ivb as well as the main group pallasites are examined many of these meteorites show well resolved anomalies in e190os e189os and e186osi the anomalies however differ from those observed in chemically extracted components from chondrites and are interpreted to reflect long term exposure of the meteorites to cosmic rays rather than nucleosynthetic effects a neutron capture model is presented that can well account for observed isotopic variations in 190os and 189os the same model predicts greater enrichment in 186osi than is observed for at least one iron suggesting as yet unaccounted for effects or failings of the model despite the variable anomalies resulting from cosmic ray exposure each of the major meteorite groups examined contains at one member with normal os isotopic compositions that are unresolved from chondritic compositions this indicates that some domains within these meteorites were little affected by cosmic rays these domains are excellent candidates for application of the 182hf 182w system for dating metal silicate segregation on their parent bodies the normal os also implies that os was homogeneously distributed throughout the protosolar nebula on the scale of planetesimal accretion within the current level of analytical resolution the homogeneity in os contrasts with isotopic heterogeneity present for other siderophile elements including mo ru and w the contrast in the scale of anomalies may reflect a late stage injection of s and p process rich material into the coalescing nebula alternately nebular thermal processing and destruction of some presolar host phases of mo ru and w may also be responsible

siderophile element systematics of iab complex iron meteorites new insights into the formation of an enigmatic group siderophile trace element abundances and the 187re 187os isotopic systematics of the metal phases of 58 iab complex iron meteorites were determined in order to investigate formation processes and how meteorites within chemical subgroups may be related close adherence of 187re 187os isotopic data of most iab iron meteorites to a primordial isochron indicates that the siderophile elements of most members of the complex remained closed to elemental disturbance soon after formation minor presumably late stage open system behavior however is observed in some members of the slm slh shl and shh subgroups the new siderophile element abundance data are consistent with the findings of prior studies suggesting that the iab subgroups cannot be related to one another by any known crystallization process equilibrium crystallization coupled with crystal segregation solid liquid mixing and subsequent fractional crystallization can account for the siderophile element variations among meteorites within the iab main group mg the data for the slm subgroup are consistent with equilibrium crystallization combined with crystal segregation and mixing by contrast the limited fractionation of siderophile elements within the sll subgroup is consistent with metal extraction from a chondritic source with little subsequent processing the limited data for the other subgroups were insufficient to draw robust conclusions about crystallization processes involved in their formation collectively multiple formational processes are represented in the iab complex and modeling results suggest that fractional crystallization within the mg may have been a more significant process than has been previously recognized

molybdenum isotopic evidence for the origin of chondrules and a distinct genetic heritage of carbonaceous and non carbonaceous meteorites abstract nucleosynthetic isotope anomalies are powerful tracers to determine the provenance of meteorites and their components and to identify genetic links between these materials here we show that chondrules and matrix separated from the allende cv3 chondrite have complementary nucleosynthetic mo isotope anomalies these anomalies result from the enrichment of a presolar carrier enriched in s process mo into the matrix and the corresponding depletion of this carrier in the chondrules this carrier most likely is a metal and so the uneven distribution of presolar material probably results from metal silicate fractionation during chondrule formation the mo isotope anomalies correlate with those reported for w isotopes on the same samples in an earlier study suggesting that the isotope variations for both mo and w are caused by the heterogeneous distribution of the same carrier the isotopic complementary of chondrules and matrix indicates that both components are genetically linked and formed together from one common reservoir of solar nebula dust as such the isotopic data require that most chondrules formed in the solar nebula and are not a product of protoplanetary impacts allende chondrules and matrix together with bulk carbonaceous chondrites and some iron meteorites groups iid iiif and ivb show uniform excesses in 92 mo 95 mo and 97 mo that result from the addition of supernova material to the solar nebula region in which these carbonaceous meteorites formed non carbonaceous meteorites enstatite and ordinary chondrites as well as most iron meteorites do not contain this material demonstrating that two distinct mo isotope reservoirs co existed in the early solar nebula that remained spatially separated for several million years this separation was most likely achieved through the formation of the gas giants which cleared the disk between the inner and outer solar system regions parental to the non carbonaceous and carbonaceous meteorites the mo isotope dichotomy of meteorites provides a new means to determine the provenance of meteoritic and planetary materials and to assess genetic links between chondrites and differentiated meteorites

the evolution of partially differentiated planetesimals evidence from iron meteorite groups iab and iiicd group iab irons probably come from a parent body that partially differentiated into a sulfur rich molten core and a primitive silicate outer layer in which only minor or localized melting occurred although the complexity of meteorites from this parent body or bodies irons with and without massive silicate inclusions stony meteorites like winona sulfide rich meteorites like mundrabilla etc implies a complicated history the partial differentiation model is consistent with most properties of these meteorites the behavior of five model parent bodies of different composition during heating to 1400 k the temperature recorded in many i ab silicates shows that meteorites like iab irons can form by this process sulfide rich parent bodies differentiate into a liquid s rich core and a primitive metal bearing mantle around 1230 k but in parent bodies lower in sulfide abundance this process may be delayed until minor melting of silicates occurs 1370 30 k in most cases any silicate melt that may have formed resolidified in situ the sulfide melt fractionally crystallized along the fe ni fes cotectic some melt was injected into silicates to form copiapo type breccias considerations of graphite metal silicate equilibrium and the retention of noble gases suggest that brecciated iabs formed at depth inside a moderately large a few tens to a hundred kilometers parent body the correlation of i xe ages with ni content is interpreted as the result of an excess 129xe component associated with the s rich melt which increases with melt evolution

palladium silver chronology of iab iron meteorites abstract the extinct 107pd 107ag decay system half life 6 5 ma is a useful chronometer to constrain the thermal evolution of the iab parent body to this end pd ag concentrations and the ag isotope compositions of metals separated from 6 different iab iron meteorites were determined the samples show e107ag variations between 0 1 and 15 8 with 108pd 109ag ratios between 38 and 200 the data can be divided into two groups based on their petrology each defining an isochron a graphite and troilite rich inclusion bearing group a with the iab meteorites toluca odessa and canyon diablo and a more silicate rich group b which includes campo del cielo caddo county and goose lake using the initial abundance of 107pd derived from carbonaceous chondrites the corresponding age for the group a is 18 7 3 6 5 0 ma after the start of the solar system and 14 9 2 5 4 9 ma for the group b this suggests that the last thermal event to reach high enough temperatures to melt metal on the iab parent body occurred within the first 15 ma of our solar system

new insights into mo and ru isotope variation in the nebula and terrestrial planet accretionary genetics abstract when corrected for the effects of cosmic ray exposure mo and ru nucleosynthetic isotope anomalies in iron meteorites from at least nine different parent bodies are strongly correlated in a manner consistent with variable depletion in s process nucleosynthetic components in contrast to prior studies the new results show no significant deviations from a single correlation trend in the refined mo ru cosmic correlation a distinction between the non carbonaceous nc group and carbonaceous chondrite cc group is evident members of the nc group are characterized by isotope compositions reflective of variable s process depletion members of the cc group analyzed here plot in a tight cluster and have the most s process depleted mo and ru isotopic compositions with mo isotopes also slightly enriched in r and possibly p process contributions this indicates that the nebular feeding zone of the nc group parent bodies was characterized by mo and ru with variable s process contributions but with the two elements always mixed in the same proportions the cc parent bodies sampled here by contrast were derived from a nebular feeding zone that had been mixed to a uniform s process depleted mo ru isotopic composition six molybdenite samples four glacial diamictites and two ocean island basalts were analyzed to provide a preliminary constraint on the average mo isotope composition of the bulk silicate earth bse combined results yield an average 97mo value of 3 6 this value coupled with a previously reported 100ru value of 1 7 for the bse indicates that the isotopic composition of the bse falls precisely on the refined mo ru cosmic correlation the overlap of the bse with the correlation implies that there was homogeneous accretion of siderophile elements for the final accretion of 10 to 20 wt of earth s mass the only known cosmochemical materials with an isotopic match to the bse with regard to mo and ru are some members of the iab iron meteorite complex and enstatite chondrites

the hemlo gold deposit ontario an example of melting and mobilization of a precious metal sulfosalt assemblage during amphibolite facies metamorphism and deformation the timing of mineralization at the hemlo gold deposit has long been a controversial issue we present arguments that use partial melting of the ore assemblage to explain the mechanism of ore mobilization and resolve problems with the model of premetamorphic mineralization the results have implications for mine exploitation and exploration strategies we show that the ore mineral assemblage underwent partial melting during middle amphibolite facies metamorphism 600 650 c 6 7 kbars primarily through breakdown of stibnite and arsenopyrite in a high s2 environment concurrent deformation led to segregation of the resulting sb and as rich sulfosalt melt interaction between this melt and a range of unmelted sulfides led to further melting and incorporation of other elements into the melt the gold bearing melt was mobilized from compressional high strain sites into dilational domains such as boudin necks and extensional fractures developed in competent lithologies ore minerals that did not melt significantly pyrite molybdenite pyrrhotite and sphalerite were not extensively mobilized and largely remained within high strain compressional domains this segregation of melt from residue thus resulted in the observed heterogeneous distribution of ore minerals within the deposit crystallization of the sulfosalt melt produced a diverse suite of ore minerals dominated by stibnite and realgar and containing an array of rare sulfosalts native elements intermetallic compounds and tellurides some sulfosalt melt persisted to low temperature 300 c allowing continued small scale localized mobilization during late deformation although gold occurs at moderate concentrations within the compressional high strain domains it is particularly concentrated in the dilational domains a consequence of its mobilization within a sulfosalt melt our model of partial melting of the ore mineral assemblage with consequent mobilization explains how ore minerals that are unstable even at greenschist facies conditions came to be hosted in structures that formed at or near the peak of amphibolite facies metamorphism

antimony in iron meteorites abstract antimony concentrations determined by radiochemical neutron activation analysis in 60 iron meteorites range from 0 2 ng g to 36 g g the meteorites with the highest sb concentrations are those of the non magmatic groups iab and iiicd while the lowest sb concentrations are found in groups iva and ivb the groups with the lowest concentrations of the other most volatile siderophiles ge and ga in all groups sb is positively correlated with ni in each of the magmatic groups slopes on log sb vs log ni plots decrease with increasing ni this decrease may reflect an increasing tendency to avoid schreibersite during the analysis of high ni meteorites because sb partitions strongly into schreibersite schreibersite from new westville is enriched in cr ni ge as sb and au and depleted in fe co and ir the content of sb in schreibersite is 540 higher than the bulk metal value the sb abundances of the iron meteorite groups are as expected from volatility trends with the exception of iab and iiab in which abundances appear depleted the most likely explanation for this and the decreasing slope in the magmatic groups is that one or more sb rich phases were not sampled during metal analyses

the iab iron meteorite complex a group five subgroups numerous grouplets closely related mainly formed by crystal segregation in rapidly cooling melts abstract we present new data for iron meteorites that are members of group iab or are closely related to this large group and we have also reevaluated some of our earlier data for these irons in the past it was not possible to distinguish iab and iiicd irons on the basis of their positions on element ni diagrams but we now show that plotting the new and revised data yields six sets of compact fields on element au diagrams each set corresponding to a compositional group the largest set includes the majority 70 of irons previously designated ia we christened this set the iab main group the remaining five sets we designate subgroups within the iab complex three of these subgroups have au contents similar to the main group and form parallel trends on most element ni diagrams the groups originally designated iiic and iiid are two of these subgroups they are now well resolved from each other and from the main group the other low au subgroup has ni contents just above the main group two other iab subgroups have appreciably higher au contents than the main group and show weaker compositional links to it we have named these five subgroups on the basis of their au and ni contents the three subgroups having au contents similar to the main group are the low au l subgroups the two others the high au h subgroups the ni contents are designated high h medium m or low l thus the old group iiid is now the slh subgroup the old group iiic is the slm subgroup in addition eight irons assigned to two grouplets plot between sll and slm on most element au diagrams a large number 27 of related irons plot outside these compact fields but nonetheless appear to be sufficiently related to also be included in the iab complex many of these irons contain coarse silicates having similar properties most are roughly chondritic in composition the mafic silicates show evidence of reduction during metamorphism in each case the silicate o isotopic composition is within the carbonaceous chondrite range 17o 0 3 in all but four cases these are within the so called iab range 0 30 17o 0 68 fine silicates appear to be ubiquitous in the main group and low au subgroups this requires that viscosities in the parental melt reached high values before buoyancy could separate these the well defined main group trends on element au diagrams provide constraints for evaluating possible models we find the evidence to be most consistent with a crystal segregation model in which solid and melt are essentially at equilibrium the main arguments against the main group having formed by fractional crystallization are a the small range in ir and b the evidence for rapid crystallization and a high cooling rate through the iron stability field the evidence for the latter are the small sizes of the iron crystals parental to the widmanstatten pattern and the limited thermal effects recorded in the silicates including retention of albitic plagioclase and abundant primordial rare gases in contrast crystal segregation in a cooling metallic melt and related processes such as incomplete melting and melt migration can produce the observed trends in the main group we infer that this melt was formed by impact heating on a porous chondritic body and that the melt was initially hotter than the combined mix of silicates and metal in the local region the melt cooled rapidly by heat conduction into the cooler surroundings mainly silicates we suggest that the close compositional relationships between the main group and the low au subgroups are the result of similar processes instigated by independent impact events that occurred either at separate locations on the same asteroid or on separate but compositionally similar asteroids

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous