nucleosynthetic osmium isotope anomalies in acid leachates of the murchison meteorite abstract we present osmium isotopic results obtained by sequential leaching of the murchison meteorite which reveal the existence of very large internal anomalies of nucleosynthetic origin e 184 os from 108 to 460 e 186 os from 14 1 to 12 6 e 188 os from 2 6 to 1 6 e 190 os from 1 7 to 1 1 despite these large variations the isotopic composition of the total leachable osmium weighted average of the leachates is close to that of bulk chondrites this is consistent with efficient large scale mixing of os isotopic anomalies in the protosolar nebula the os isotopic anomalies are correlated and can be explained by the variable contributions of components derived from the s r and p processes of nucleosynthesis surprisingly much of the s process rich osmium is released by relatively mild leaching suggesting the existence of an easily leachable s process rich presolar phase or alternatively of a chemically resistant r process rich phase taken together with previous evidence for a highly insoluble s process rich carrier such as sic these results argue for the presence of several presolar phases with anomalous nucleosynthetic compositions in the murchison meteorite the s process composition of os released by mild leaching diverges slightly from that released by aggressive digestion techniques perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments the correlation between e 190 os and e 188 os can be used to constrain the s process 190 os 188 os ratio to be 1 275 0 043 such a ratio can be reproduced in a nuclear reaction network for a macs value for 190 os of 200 22 mbarn at 30 kev more generally these results can help refine predictions of the s process in the os mass region which can be used in turn to constrain the amount of cosmoradiogenic 187 os in the solar system and hence the age of the galaxy we also present evidence for extensive internal variation of 184 os abundances in the murchison meteorite a steep anti correlation is observed between e 184 os and e 188 os since 184 os is formed uniquely by the p process this anti correlation cannot be explained by variable addition or subtraction of s process os to average solar system material instead this suggests that p process rich presolar grains e g supernova condensates may be present in meteorites in sufficient quantities to influence the os isotopic compositions of the leachates nevertheless 184 os is a low abundance isotope and we cannot exclude the possibility that the measured anomalies for this isotope reflect unappreciated analytical artifacts

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

low temperature alteration of dredged volcanics from the southern chile ridge additional information about early stages of seafloor weathering abstract a suite of submarine volcanic rocks from the southern chile ridge has been examined in order to investigate the early stages of low temperature alteration alteration in these samples proceeded as follows 1 fe staining on sample surface and along fractures 2 filling of vesicles with secondary material 3 breakdown of glassy matrix 4 breakdown of microcrystalline matrix and 5 breakdown and replacement of olivine plagioclase and pyroxene were sometimes found to be slightly altered along internal fissures secondary or alteration phases generally showed high k 3 5 wt fe 30 70 wt and low al rb k during initial stages of alteration the behavior of some trace elements such as rare earth elements ree ba zr hf ta nb and mo are solely controlled by the precipitation of mn rich fe oxyhydroxides the preferred incorporation of ce into mn rich fe oxyhydroxides may be a principal factor explaining the ce depletion in seawater we conclude that the earliest stages of submarine weathering are controlled by eh and ph gradients between the rock and seawater in the absence of a buffer oxidation of ferrous iron causes a decrease in solution ph

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

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

osmium isotopic homogeneity in the ck carbonaceous chondrites abstract variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements e g ca ti cr ni sr zr mo ru pd ba nd and sm in both bulk chondrites and achondrites however although large os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites bulk chondrites of various groups iron meteorites and pallasites exhibit os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites this study reports high precision os isotopic compositions and highly siderophile element hse concentrations for ten ck chondrites the isotope dilution concentration data for hse and high precision os isotope ratios were determined on the same digestion aliquots to precisely correct for radiogenic contributions to 186os and 187os while acid leached bulk unequilibrated carbonaceous chondrites show deficits of s process os components to the same extent as revealed by unequilibrated enstatite ordinary and rumuruti chondrites equilibrated bulk ck chondrites exhibit no resolvable os isotopic anomalies these observations support the idea that acid resistant carbon rich presolar grains such as silicon carbide sic or graphite are major carriers for nucleosynthetic isotopic anomalies of os the destruction of these presolar grains which are omnipresent in unequilibrated meteorites must have occurred during aqueous alteration and thermal metamorphism early in the ck chondrite parent body history the dispersal of ck chondrites along the iiiab iron meteorite isochron on a 187os 188os versus 187re 188os diagram with re os ratios from 0 032 to 0 083 in combination with the observed redistribution of other hse e g pt pd highlights the influence of parent body processes overprinted by effects of recent terrestrial alteration under the oxidizing conditions prevalent on the ck parent body evident from high abundances of magnetite and limited fe ni metal in ck chondrites these parent body processes made all isotopically anomalous os originally hosted in reduced presolar grains accessible the absence of os isotopic anomalies in ordinary enstatite and now also carbonaceous chondrites implies that the carriers of s and r process os must have been effectively homogenized across the region of chondrite formation and possibly even the entire solar protoplanetary nebula as suggested by the os isotopic compositions of iron meteorites and non anomalous ureilites except for a limited number of ureilites the relative proportions of presolar s and r process carriers of os and other elements such as w in chondrites and most other planetary bodies must have remained constant during all subsequent nebular and planetary processes which appears not to have been the case for other siderophile elements including mo ru and pd the existence of mo ru pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements e g volatility their host phase s e g sic graphite metal sulfides and the nature of the nebular or planetary processes experienced in the early solar system

the distribution of trace elements in carbonaceous chondrites 12 carbonaceous chondrites amongst them representatives of nearly all known petrologic types were analyzed for twenty trace elements by spark source mass spectrography combined with the isotope dilution method data on different element groups refractory moderately volatile and volatile show that the distribution of the trace elements in the carbonaceous chondrites with the exception of renazzo can be well explained by anders two component model this is also valid for the highly metamorphosed cv5 chondrite karoonda furthermore it is observed that the zrhf ratios in the carbonaceous chondrites increase with increasing petrologic type which is interpreted as the result of mixing two components with different zrhf ratios

nucleosynthetic isotope variations of siderophile and chalcophile elements in the solar system numerous investigations have been devoted to understanding how the materials that contributed to the solar system formed were incorporated into the precursor molecular cloud and the protoplanetary disk and ultimately evolved into the building blocks of planetesimals and planets chemical and isotopic analyses of extraterrestrial materials have played a central role in decoding the signatures of individual processes that led to their formation among the elements studied the siderophile and chalcophile elements are crucial for considering a range of formational and evolutionary processes consequently over the past 60 years considerable effort has been focused on the development of abundance and isotopic analyses of these elements in terrestrial and extraterrestrial materials e g shirey and walker 1995 birck et al 1997 reisberg and meisel 2002 meisel and horan 2016 this volume in this review we consider nucleosynthetic isotopic variability of siderophile and chalcophile elements in meteorites chapter 4 provides a review for siderophile and chalcophile elements in planetary materials in general day et al 2016 this volume in many cases such variability is denoted as an isotopic anomaly however the term can be ambiguous because several pre and post solar system formation processes can lead to variability of isotopic compositions as recorded in meteorites here we strictly define the term isotopic anomaly as referring to an isotopic deviation from the terrestrial composition resulting from the incorporation of varying proportions of elements with diverse nucleosynthetic origins into a meteorite component or parent body the term will not be used here to refer to isotopic variations that result from mass dependent isotopic fractionation radioactive decay in the solar system or spallation effects based on astronomical observations and physical modelling the formation of the solar system has generally been thought to have initiated by the collapse of a dense molecular cloud

source rock evaluation of devonian lacustrine carbonates northern scotland a rock eval pyrolysis data set from devonian lacustrine rocks from scotland shows that the hydrocarbon yields per unit weight of organic matter hydrogen indices are greater from carbonate rich rocks than from mudrocks higher yields are recorded from both primary carbonate laminites and from rocks in which the carbonate is a diagenetic precipitate the distinction in yield between carbonates and mudrocks is related to both type of organic matter and lithological differences the carbonate laminites deposits of a stratified lake contain a higher proportion of type i kerogen than the mudrocks deposits of shallower water oxidation of kerogen was not important in either rock type samples of both rock types represent a similar range of thermal maturities and this is not an overriding control on the pyrolytic yield the transformation indices for the mudrocks are higher than for the carbonate rocks indicating that the mudrocks contain a greater proportion of migrated bitumen both primary and diagenetic carbonates are relatively impermeable and lack migrated bitumen after solvent extraction mudrock samples yield hydrogen indices more comparable with those from the carbonates the carbonate rocks also have higher total organic carbon toc contents than the mudrocks consequently their pyrolytic yields s 2 are much higher

shear rate dependent strength control on the dynamics of rainfall triggered landslides tokushima prefecture japan a typhoon typhoon no 10 attacked shikoku island and the tyugoku area of japan in 2004 this typhoon produced a new daily precipitation record of 1317 mm on shikoku island and triggered hundreds of landslides in tokushima prefecture one catastrophic landslide was triggered in the shiraishi area of kisawa village and destroyed more than 10 houses while also leaving an unstable block high on the slope the unstable block kept moving after the event showing accelerating and decelerating movement during and after rainfall and reaching a displacement of several meters before countermeasures were put into place to examine the mechanism for this landsliding characteristic samples weathered serpentinite were taken from the field and their shear behaviours examined using ring shear tests the test results revealed that the residual shear strength of the samples is positively dependent on the shear rate which may provide an explanation for the continuous accelerating decelerating process of the landsliding the roughness of the shear surface and the microstructure of the shear zone were measured and observed by laser microscope and sem techniques in an attempt to clarify the mechanism of shear rate effect on the residual shear strength copyright 2010 john wiley sons ltd

variation in residual shear strength of the soil with the salinity of pore fluid slope stabilization procedures for seven landslides in the niigata prefecture of japan had provided an excellent and rare opportunity to examine the composition of ground water and residual shear strength of the sliding surface soil as well as unsheared mudstone ring shear tests were conducted on the soil samples collected from sliding surface soil revealed during the installation of 3 m diameter drainage galleries shear strength and index properties of the soil were measured by mixing the soil with distilled water and sea water and after leaching the nacl from the pore water the residual shear strength of the soil sample with distilled water was 3 5 lower than that with the sea water the residual shear strength of the intact rock powder after leaching the dissolved salt was close to that of the soil from sliding surface and the residual shear strength of the soil from sliding surface after mixing with sea water was close to that of the intact rock powder the increase in residual shear strength

the hydrology of carbonaceous chondrite parent bodies and the evolution of planet progenitors oxygen isotope ratio data from carbonaceous chondrites are explained if aqueous fluids flowed from high to low temperatures within the parent objects of these primitive meteorites recognition of ancient hydrological activity on primitive asteroid precursors affords a new class of constraints on the heat sources ages and sizes of planet precursors in the early solar system based on the geological evolution of planetesimals

microscale oxygen isotopic exchange and magnetite formation in the ningqiang anomalous carbonaceous chondrite we report in situ measurements of o isotopic compositions of magnetite olivine and pyroxene in chondrules of the ningqiang anomalous carbonaceous chondrite the petrographic setting of ningqiang magnetite is similar to those in oxidized cv chondrites such as allende where magnetite is found together with ni rich metal and sulfide in opaque assemblages in chondrules both magnetite and silicate oxygen data fall close to the carbonaceous chondrite anhydrous mineral line with relatively large ranges in 18o in magnetite 4 9 to 4 2 and in silicates 15 2 to 4 5 magnetite and silicates are not in o isotopic equilibrium the weighted average 17o 17o 0 52 18o values of magnetite are 1 7 to 3 6 higher than those of the silicates in the same chondrules the petrological characteristics and o isotopic disequilibrium between magnetite and silicates suggest the formation of ningqiang magnetite by the oxidation of preexisting metal grains by an aqueous fluid during parent body alteration the weighted average 17o of 3 3 0 3 is the lowest magnetite value measured in unequilibrated chondrites and there is a positive correlation between 17o values of magnetite and silicates in each chondrule these observations indicate that during aqueous alteration in the ningqiang parent asteroid the water rock ratio was relatively low and o isotopic exchange between the fluid and chondrule silicates occurred on the scale of individual chondrules

sandstone chert and laminated chert black shale couplets cretaceous uhangri formation southwest korea depositional events in alkaline lake environments abstract the cretaceous uhangri formation southwest korea is a lacustrine sequence surrounded by acidic volcanic terrain and comprises sandstone chert and laminated chert black shale couplets in the upper part in both cases the uhangri chert is composed mainly of sio 2 74 81 al 2 o 3 10 12 and k 2 o 6 7 its impure nature is largely due to the presence of feldspar grains and clays within a microcrystalline quartz matrix the uhangri chert is characterized by common soft sediment deformation in situ brecciation slumping and no organic traces which collectively indicate its inorganic origin the sandstone chert couplets are alternations of massive graded crudely stratified rippled or ripple cross laminated sandstone layers and generally homogeneous chert layers the laminated chert black shale couplets consist of alternating light and dark coloured laminae of chert and overlying black shale these couplets were most likely deposited by episodic riverine inflows into a silica rich alkaline lake the freshwater input could trigger direct inorganic silica precipitation through an abrupt decrease in lake water ph the sandstone chert couplets would be deposited by high density underflows whereas the laminated chert black shale couplets by fine sediment dominant overflows

recognising the taghanic crisis in the devonian terrestrial environment and its implications for understanding land sea interactions the late mid devonian eday marl formation from the orcadian basin scotland is a terrestrial equivalent of the marine devonian taghanic crisis the eday marl from orkney contains a high resolution archive of climatic change controlled by the relative strength of the seasonal insolation this includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites bedded evaporites marginal sheet flood sands and marine influenced bioturbated sheet sands these flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall recognition of these basin flooding events has enabled the definition of three new units the wha taing roeberry and berstane members the eday marl formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation an environmental hydrological and climatic interpretation is given for the different events recognised in the eday marl this sequence of events when combined with the palynological age dates enables a detailed correlation to be made with the marine tully formation of new york state this suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the tully formation in what is otherwise a clastic depositional system comparison with the pelagic marine record shows that the latter as yet gives only limited resolution of the taghanic crisis recognising the taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm

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

syneruptive and intereruptive lithofacies in lacustrine environments the cretaceous beolkeum member wido island korea abstract the cretaceous beolkeum member was deposited in a lacustrine environment affected by explosive volcanism and a number of syneruptive lithofacies are intercalated with lacustrine mudstones the syneruptive lithofacies were formed by primary volcanic processes and resedimented depositional processes during and after eruptions and exhibit unique depositional features which can be grouped into four syneruptive lithofacies assemblages sla 1 to sla 4 from bottom to top primary syneruptive lithofacies are represented by welded massive lapilli tuff in sla 1 and a normally graded lapilli tuff in sla 2 in sla 1 sustained pyroclastic density currents were able to displace lake water and rarely interacted with lake water resulting in the formation of a welded texture and columnar joints in sla 2 unsteady pyroclastic density currents rapidly disintegrated mixed with ambient water and transformed into high density turbidity currents depositing thick normally graded lapilli tuff resedimented syneruptive lithofacies were primarily controlled by volcaniclastic sediment supply after eruptions when volcaniclastic sediments were continuously supplied into the lake by debris flows a volcaniclastic fan can be formed sla 1 resulting in a coarsening upward trend and progradational geometry in case of relatively small amounts of volcaniclastic sediment supply turbidity currents would be a main depositional process depositing a series of normally graded tuff on the primary syneruptive lithofacies sla 2 showing a fining upward trend in sla 3 and sla 4 there are only a few cm thick normally graded tuff reflecting minor volcaniclastic sediment supply however overlying normally graded sandstones in sla 3 showing a coarsening upward trend and a thick normally graded sandstone in sla 4 suggest favorable conditions for the generation of the sediment gravity flows probably due to an increase in volcaniclastic sediment supply after eruptions

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

presolar diamond sic and graphite in primitive chondrites abundances as a function of meteorite class and petrologic type abstract acid resistant residues were prepared for eighteen meteorites from seven chondrite classes using improved procedures designed to minimize loss of presolar grains noble gases were measured by stepped pyrolysis and the abundances of five exotic noble gas components were used to determine abundances of diamond sic and graphite diamond separates were prepared to check diamond abundances determined from noble gases diamond and sic were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in orgued ci and ll3 0 3 1 chondrites our data and noble gas and stable isotope data in the literature show that presolar grains were incorporated into all chondrite classes the grains are sited in the fine grained matrix and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite the pattern of metamorphic destruction differs from class to class in unequilibrated ordinary chondrites uocs graphite is most easily destroyed followed by sic and then diamond no presolar grains remain in uocs of petrologic type 3 8 whose matrices have been completely recrystallized in eh chondrites diamond and sic survive much more severe metamorphism than in uocs with sic apparently more stable than diamond presolar graphite was not detected in cv3 and c03 chondrites diamond appears to be more stable than sic and graphite again is missing inferred premetamorphic diamond abundances matrix normalized vary by a factor of 2 2 between classes with eh cv and co chondrites having higher initial abundances than orgueil similar diamond sic ratios are observed in most classes and differences in the ratio can be tied to secondary processing suggesting that all chondrite classes sampled the same solar system wide reservoir of presolar grains differences in initial abundances between classes appear to correlate with chemical and physical properties of the host meteorites these bulk properties and variations in presolar grain abundances both may be the result of thermal processing of presolar dust in the accretion disk

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

petrologic evidence for collisional heating of chondritic asteroids abstract the identification of the mechanism s responsible for heating asteroids is among the major problems in planetary science because of difficulties with models of electromagnetic induction and the decay of short lived radionuclides it is worthwhile to evaluate the evidence for collisional heating localized impact heating is responsible for forming shock veins melt pockets metal sulfide mixtures vugs agglutinates and a wide variety of melt rock clasts new evidence for localized impact heating comes from the high proportion of relict type 6 material among impact melt bearing ordinary chondrites oc this relict material was probably metamorphosed by residual heat within large craters olivine aggregates composed of faceted crystals with 120 triple junctions occur within the melted regions of the chico and rose city oc melt rocks the olivine aggregates formed from shocked mosaicized olivine grains that underwent contact metamorphism large scale collisional heating is supported by the correlation in oc between petrologic type and shock stage no other heating mechanism can readily account for this correlation the occurrence of impact melt rock clasts in oc that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism such impact events occurring during or shortly after accretion are probably responsible for substantially melting 0 5 of oc these events most have heated a larger percentage of oc to subsolidus temperatures sufficient to have caused significant metamorphism if collisional heating is viable then oc parent asteroids must have been large large oc asteroids in the main belt may include those of the s iv spectral subtype collisional heating is inconsistent with layered onion shell structures in oc asteroids wherein the degree of metamorphism increases with depth but the evidence for such structures is weak it seems likely that collisional heating played an important role in metamorphosing chondritic asteroids

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

a new method for the correlation of residual shear strength of the soil with mineralogical composition mineralogical composition measured with x ray diffraction for soil specimens collected from more than 80 natural disaster areas show smectite kaolinite mica feldspar and quartz as major constituent minerals based on the results of more than 35 mixtures of smectite kaolinite and quartz in different proportions a new correlation method was proposed for estimation of the residual friction angle r with the proportion of the minerals the mineralogical compositions of the natural samples were used to estimate the r based on the proposed triangular model the estimation method resulted in values as close as 90 to the measured r and as close as 80 to the case of 53 samples tested by other researchers the paper incorporates the correlation of r with the liquid limit the plasticity index the clay fraction the specific surface area and the proportion of smectite various ranges are proposed according to the influence of the constituent clay minerals in addition the applicable range

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

rhenium osmium systematics of calcium aluminium rich inclusions in carbonaceous chondrites the re os isotopic systematics of calcium aluminium rich inclusions cais in chondrites were investigated in order to shed light on the behavior of the re os system in bulk chondrites and to constrain the timing of chemical fractionation in primitive chondrites cais with relatively unfractionated rare earth element ree patterns groups i iii v vi define a narrow range of 187 re 188 os 0 3764 0 4443 and 187 os 188 os 0 12599 0 12717 and high but variable re and os abundances 3209 41 820 ppb os in contrast cais that show depletions in highly refractory elements and strongly fractionated ree patterns group ii also show a much larger range in 187 re 188 os 0 409 0 535 and 187 os 188 os 0 12695 0 13770 and greater than an order of magnitude lower re and os abundances than other groups e g 75 7 680 2 ppb os sixteen bulk cais and cai splits plot within analytical uncertainty of a 4558 ga reference isochron as is expected for materials of this antiquity eight samples however plot off the isochron several possible reasons for these deviations are discussed data for multiple splits of one cai indicate that the nonisochronous behavior for at least this cai is the result of re os reequilibration at approximately 1 6 ga thus the most likely explanation for the deviations of most of the nonisochronous cais is late stage open system behavior of re and os in the asteroidal environment the 187 os 188 os os systematics of cais are consistent with previous models that indicate group ii cais are mixtures of components that lost the bulk of their highly refractory elements in a previous condensation event and a minor second component that provided refractory elements at chondritic relative proportions the high re os of group ii cais relative to other cais and chondrite bulk rocks may have been caused by variable mobilization of re and os during medium to low temperature parent body alteration 4 5 ga ago this model is favored over nebular models which pose several difficulties the narrow range of 187 os 188 os in group i iii v and vi bulk cais and the agreement with 187 os 188 os of whole rock carbonaceous chondrites suggest that on a bulk inclusion scale secondary alteration only modestly fractionated re os in these cais the average of 187 os 188 os for group i iii v and vi cais is indistinguishable from average ci chondrites indicating a modern solar system value for 187 os 188 os of 0 12650 corresponding to a 187 re 188 os of 0 3964 copyright 2001 elsevier science ltd

conditions for pore water convection within carbonaceous chondrite parent bodies implications for planetesimal size and heat production abstract the critical rayleigh number for convective flow of pore water through a permeable spherical body is derived the result affords constraints on carbonaceous chondrite planetesimal sizes and rates of heat production if the chemical compositions of carbonaceous chondrites are taken as evidence against flow of pore water then the present calculations suggest that the parent bodies were less than 80 km in diameter the maximum diameter for absence of flow depends in part on the high permeabilities required by estimates of high water rock ratios in altered carbonaceous chondrites pore water would have flowed through parent bodies larger than 120 km in diameter with typical rock like permeabilities convective flow and isochemical alteration are not compatible and our calculations can be used to identify the combinations of parent body size and heat generation consistent with one or the other

osmium isotope systematics of ureilites abstract the 187 os 188 os for 22 ureilite whole rock samples including monomict augite bearing and polymict lithologies were examined in order to constrain the provenance and subsequent magmatic processing of the ureilite parent body or bodies the re os ratios of most ureilites show evidence for a recent disturbance probably related to re mobility during weathering and no meaningful chronological information can be extracted from the present data set the ureilite 187 os 188 os ratios span a range from 0 11739 to 0 13018 with an average of 0 1258 0 0023 1 similar to typical carbonaceous chondrites and distinct from ordinary or enstatite chondrites the similar mean of 187 os 188 os measured for the ureilites and carbonaceous chondrites suggests that the ureilite parent body probably formed within the same region of the solar nebula as carbonaceous chondrites from the narrow range of the 187 os 188 os distribution in ureilite meteorites it is further concluded that re was not significantly fractionated from os during planetary differentiation and was not lost along with the missing ureilitic melt component the lack of large re os fractionations requires that re os partitioning was controlled by a metal phase and thus metal had to be stable throughout the interval of magmatic processing on the ureilite parent body

on the nature of the ni rich component in splash form australasian tektites abstract the australasian tektite strewn field is exceptional not only as the largest and most recent but also as the only strewn field without an identified source impact crater therefore scenarios without the formation of an impact crater such as a low altitude cometary airburst have proven hard to discard here new geochemical evidence is presented for mixing of projectile and target material which implies the formation of an australasian tektite related impact crater first ninety two australasian tektites were grouped according to their cr co and ni concentrations based on this data australasian tektites with the highest ni contents 200 g g occur more than 1500 km south southeast sse of the northern indochina region with the highest concentration of ni rich tektites in south vietnam the islands of borneo belitung and java and reports in literature for ni rich tektites in central australia the tektites with the highest cr and ni abundances often also show highly siderophile element hse enrichments of up to 4 ng g ir the most ni rich samples exhibit broadly chondrite relative hse proportions however a chondritic impactor contribution appears to be inconsistent with the observed ni cr ni co and cr co ratios a previously suggested significant terrestrial mantle contribution can also not explain the siderophile element enrichments in combination with relatively low feo tot

objective oriented multistage ring shear test for shear strength of landslide soil ring shear tests were conducted on five samples of different nature with a modified imperial college type ring shear machine the three different testing methods used 1 individual sample testing for each normal stress 2 increasing load multistage ring shear test and 3 reducing load multistage ring shear test all showed similar effective residual internal friction angle for the samples irrespective of testing method however effective residual shear intercept was different according to the testing methodology the internal friction angle did not vary particularly after the first minimum point in the stress displacement curve although the residual shear intercept decreased with increase in the displacement the thickness of the shearing zone increased along with the displacement the remolded peak shear strength for saturated conditions at field dry density varied with the consolidation history measurement of remolded peak shear strength was possible in a single sample using the increasing load multistage ring shear test at normal consolidation the equilibrium water content of the sample after the ring shear test was nearly equal to the plastic limit

highly siderophile elements and 187re 187os isotopic systematics of the allende meteorite evidence for primary nebular processes and late stage alteration abstract the abundances of highly siderophile elements hse re os ir ru pt and pd as well as 187 re 187 os isotopic systematics were determined for calcium aluminum rich inclusions cais chondrules and matrix separated from the cv3 carbonaceous chondrite allende consistent with prior studies cais are characterized by significant depletions in pd relative to the other hse while the other hse are in generally bulk chondritic relative abundances the depletions in pd can be linked with initial formation of cais via condensation or subsequent processing by evaporative processes chondrules generally have relative hse patterns similar to cais although they have lower absolute abundances palladium depletions in chondrules may reflect solid metal liquid metal fractionation at the time of formation or alternatively be the result of processes that acted on precursor materials matrix samples have nearly chondritic absolute abundances of all hse measured consequently matrix is the only major chondritic component examined here that shows no relative depletion in pd mass balance suggests the existence of an unidentified pd rich carrier although it is possible that the dataset presented here is too limited to represent typical hse abundances of some chondritic components e g chondrules the 187 re 187 os isotopic systematics of only six out of twenty four allende chondritic components analyzed plot within uncertainties of a 4568 ma primordial reference isochron the deviations from the expected isochron most likely reflect late stage open system behavior within the last 2 billion years and in some cases could even have resulted from terrestrial alteration the open system behavior is most readily observed in small millimeter size sub samples of allende consistent with re and or os mobility on that scale

precipitation of silica and formation of chert mudstone peat association in miocene coastal environments at the opening of the sea of japan abstract a sedimentary sequence of layered chert alternating with mudstone and associated peat is present at yachi japan these deposits were accumulated in a local lacustrine to brackish water environment along a coastal setting during the early to middle miocene the basement of the sedimentary sequence is rhyolite erupted just before the chert precipitation and its weathered derivatives the chert and the mudstone lack coarse detrital grains on the other hand associated peat contains abundant plant leaves and debris that are compressed and deformed post depositionally uncompressed leaf fragments and broken twiggy trunks in the chert suggest rapid chert precipitation and early lithification four quartz fabrics are recognized chalcedony microquartz megaquartz and euhedral quartz these types vary from colorless to pale brown microscopic sem and xrd observations reveal a paragenetic sequence of silica crystallization chalcedony microquartz and megaquartz was precipitated and consolidated rapidly then euhedral quartz was crystallized in voids there is neither evidence indicating opal a and opal ct precursors of these quartz nor evidence showing that the chert is a post depositional silicification product of volcanic ashes petrographic observation indicates that the initial silica mineral phase was quartz and chalcedony silica was interpreted to have precipitated as a result of influx of low ph water and mixing with silica concentrated solution in the coastal depressions the petrography and depositional environment of the chert are compared with those of other chert types the chert mudstone peat association found at the yachi seems to represent brackish water sediments deposited during continental rifting of the sea of japan type

cherts with moganite in continental mg clay deposits an example of false magadi type cherts madrid basin spain abstract during the miocene the madrid basin was a closed basin in which a succession of alluvial and lake deposits were replaced by different types of crusts mainly calcretes dolocretes and silcretes in a geographically restricted area to the south mg clay deposits were precipitated in ponds on the sand flats a discontinuous nodular and stratiform mg rich chert appears at the top of the mg clay deposits and displays visual mineralogical and petrological characteristics that are very different from the other silcretes of the madrid basin as revealed by x ray diffraction the cherts consist mainly of quartz and moganite which are commonly found in magadi type cherts the petrological characteristics reveal that the chert consists of a groundmass crossed by several networks of quartz veins the groundmass is formed by mosaic quartz with different sizes of crystals usually less than 20 m and length slow chalcedony the presence of gridwork extinction patterns the differentiation of silica flakes and the preservation of the micromorphological characteristics of the mg clay deposits indicate an early replacement by quartz and moganite the quartz networks show veins of different shapes rectilinear irregular branched and v shaped sizes from a few microns to several millimeters and textures mainly megaquartz microquartz and length slow chalcedony the v shaped veins and some irregular and branched veins are considered to be a consequence of the silicification of cracks in the host rocks the other veins represent silica filling cracks that formed by shrinkage during the various stages of chert formation many macroscopic attributes e g some kinds of cracks mineralogical features the presence of moganite and petrological characteristics e g rectilinear or gridwork orientation of quartz crystals are similar to those of magadi type cherts in spite of this the origin and the environment of formation of this mg rich chert which crystallized by silicification of mg clays during deposition of silcrete are very different from those of the typical pleistocene magadi cherts of african lakes a pronounced shrinkage during silicification in a zone just below the water table and the presence of the moganite are the two factors that caused these mg rich cherts to appear similar to magadi type cherts

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

stable isotopes and the noncarbonaceous derivation of ureilites in common with nearly all differentiated planetary materials abstract the abundant diverse ureilite meteorites are peridotitic asteroidal mantle restites that have remarkably high bulk carbon contents average 3 wt and have long been linked to the so called carbonaceous chondrites although this term is potentially misleading because the high petrologic type carbonaceous chondrites are if anything c poor compared to ordinary chondrites ureilite oxygen isotopic compositions i e diversely negative ccam like 17o viewed in isolation have long been viewed as confirming the carbonaceous chondritic derivation hypothesis however a very different picture emerges through analysis of a compilation of recently published high precision isotopic data for chromium titanium and nickel for ureilites and various other planetary materials ureilites have lower e62ni and far lower e50ti and e54cr than any known variety of carbonaceous chondrite on a plot of e50ti vs e54cr and similarly 17o vs e54cr ureilite compositions cluster far from and in a direction approximately orthogonal to a trend internal to the carbonaceous chondrites and the carbonaceous chondrites are separated by a wide margin from all other planetary materials i conclude that notwithstanding the impressive resemblance to carbonaceous chondrites in terms of diversely negative 17o the ureilite precursors accreted from preponderantly noncarbonaceous sensu stricto materials despite total depletion of basaltic matter the ureilites retain moderate pyroxene olivine ratios which is an expected outcome from simple partial melting of moderate sio2 feo mgo noncarbonaceous chondritic material but would imply an additional process of major reduction of feo if the precursor material were carbonaceous chondritic the striking bimodality of planetary materials on the e50ti vs e54cr and 17o vs e54cr diagrams may be an extreme manifestation of the effects of episodic accretion of early solids in the protoplanetary nebula however an alternative admittedly speculative explanation is that the bimodality corresponds to a division between materials that originally accreted in the outer solar system carbonaceous and materials that accreted in the inner solar system noncarbonaceous including the ureilites

siderophile element anomalies in ck carbonaceous chondrites implications for parent body aqueous alteration and terrestrial weathering of sulfides abstract ck chondrites constitute the most oxidized anhydrous carbonaceous chondrite group most of the fe occurs in magnetite and in feo rich mafic silicates the two observed ck falls karoonda and kobe along with thirteen relatively unweathered ck finds have unfractionated siderophile element abundance patterns in contrast a sizable fraction of ck finds 9 of 24 investigated shows fractionated siderophile abundance patterns including low abundances of ni co se and au the most extreme depletions are in ni 0 24 of normal ck and au 0 14 of normal ck this depletion pattern has not been found in other chondrite groups out of the 74 ck chondrites listed in the meteoritical bulletin database 2006 excluded considerably paired specimens see http tin er usgs gov meteor metbull php we analyzed 24 and subclassified the ck chondrites in terms of their chemical composition and sulfide mineralogy sl siderophiles low six samples for large depletions in ni co se and au 50 of sulfides lost sm siderophiles medium two cks for moderately low ni and co abundances sulfides are highly altered or partly lost sh siderophiles high one specimen for enrichments in ni co se and au normal for unfractionated samples 13 samples the sole sh sample may have obtained additional sulfide from impact redistribution in the parent asteroid we infer that these elements became incorporated into sulfides after asteroidal aqueous processes oxidized nebular metal thermal metamorphism probably also played a role in their mineral siting the siderophile losses in the sl and sm samples are mainly the result of oxidation of pentlandite pyrite and violarite by terrestrial alteration followed by leaching of the resulting phases some antarctic ck chondrites have lost most of their sulfides but retained ni co se and au presumably as insoluble weathering products

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

s process os isotope enrichment in ureilites by planetary processing abstract ubiquitous nucleosynthetic isotope anomalies relative to the terrestrial isotopic composition in mo ru and other elements are known from both bulk chondrites and differentiated meteorites but os isotope ratios reported from such meteorites have been found to be indistinguishable from the terrestrial value the carriers of s and r process os must thus have been homogeneously distributed in the solar nebula as large os isotope anomalies are known from acid leachates and residues of primitive chondrites the constant relative proportions of presolar s and r process carriers in such chondrites must have been maintained during nebular processes it has long been assumed that partial melting of primitive chondrites would homogenize the isotopic heterogeneity carried by presolar grains here ureilites carbon rich ultramafic achondrites dominantly composed of olivine and low ca pyroxene are shown to be the first differentiated bulk solar system materials for which nucleosynthetic os isotope anomalies have been identified these anomalies consist of enrichment in s process os heterogeneously distributed in different ureilites given the observed homogeneity of os isotopes in all types of primitive chondrites this os isotope variability among ureilites must have been caused by selective removal of s process poor os host phases probably metal during rapid localized melting on the ureilite parent body while mo and ru isotope anomalies for all meteorites measured so far exhibit s process deficits relative to the earth the opposite holds for the os isotope anomalies in ureilites reported here this might indicate that the earth preferentially accreted olivine rich restites and inherited a s process excess relative to smaller meteorite bodies consistent with earth s high mg si ratio and enrichment of s process nuclides in mo ru and nd isotopes our new os isotope results imply that caution must be used when applying nucleosynthetic isotope anomalies as provenance indicators between different classes of meteorites

chondrules in ck carbonaceous chondrites and thermal history of the cv ck parent body ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 it is commonly reported than 15 vol of ck4 6 samples are composed of chondrules the modal abundance of chondrules estimated here for 18 ck3 6 including 5 ck3s ranges from zero totally recrystallized to 50 5 although almost all chemically re equilibrated with the host matrix we recognized in ck3s and tanezrouft tnz 057 ck4 up to 85 of chondrules as former type i chondrules mean diameters of chondrules range from 0 22 to 1 05 mm for karoonda ck4 and tnz 057 ck4 respectively up to 60 of chondrules in ck3 4 are surrounded by igneous rims from 20 m to 2 mm width zoned olivines were found in unequilibrated chondrules from dag 431 ck3 an nwa 4724 ck3 8 nwa 4423 ck3 9 and tnz 057 ck4 we modeled fe mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the ck parent body metamorphism and proposed a two stage diffusion process in order to account for the position of inflection points situated within chondrules time scales inferred from fe mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred of thousand years from 50 to 70 000 years for peak metamorphic temperatures of 1140 and 920 k respectively these durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay using the concept of a continuous cv ck metamorphic series which is reinforced by this study we estimated peak metamorphic temperatures 850 k for cv 850 920 k for ck3 and 920 1140 k for ck4 6 chondrites considering a duration of 70 000 years

study of preexisting shear surfaces of reactivated landslides from a strength recovery perspective abstract residual shear strength is generally considered in the design of preventive measures for slopes consisting of preexisting shear surfaces of large scale landslides recent research suggests that the preexisting shear surface of a reactivated landslide can regain strength with the passage of time which might also be considered in designing the slope stability measures in this study three reactivated landslide soils were tested in a ring shear apparatus for the discontinued shear periods of 1 3 7 15 and 30 days with the following main objectives i to understand the strength recovery behavior of landslide soils in a residual state of shear after as long as 30 days of discontinued shear ii to understand the comparative pattern of strength recovery in highly plastic and less plastic soils and iii to understand the mechanism involved in strength recovery at a residual state of shear the results indicate that recovered strength measured in the laboratory is hardly noticeable after a rest period of 3 days but recovered strength is lost after a small shear displacement this paper primarily focuses on the effect of strength recovery from residual strength on preexisting shear surface soils and the mechanisms behind it

comparison of residual shear strengths from back analysis and ring shear tests on undisturbed and remolded specimens slope stabilization procedures for six landslides in the niigata prefecture in japan afforded an excellent opportunity to examine the residual drained shear strength of weathered mudstones installation of 3 m diameter drainage galleries allowed undisturbed block samples to be collected which contained the slickenside surface of the failure plane ring shear tests were conducted on undisturbed samples and remolded samples of the same material in addition to the laboratory testing back analysis was performed to calculate the residual shear strength parameters of the slopes good agreement was found between the residual friction angles determined from back analysis tests on undisturbed samples and tests on remolded specimens many of the landslide materials exhibited a small cohesion at low values of effective normal stress but the secant friction angle achieved a constant value at higher normal stresses

climatic and eustatic controls on the development of a late triassic source rock in the jameson land basin east greenland complex environmental controls have influenced deposition of the graklint beds a prospective oil and gas prone late triassic mid carnian source rock in the jameson land basin east greenland the identification of a late triassic source rock is significant for hydrocarbon exploration in the north atlantic region detailed sedimentological analysis biostratigraphy and geochemical analysis provide insights into the controls on source rock development and have wider implications for palaeoclimatic trends and palaeogeographical reconstructions of the north atlantic at this time the graklint beds were deposited in a predominantly lacustrine setting during a phase of climatic cooling that can be ascribed to the mid carnian pluvial event this further extends the evidence for the global effect of such climatic perturbations and furthermore highlights the potential for the use of climatic events for global and regional correlation between varying environmental settings evidence is also recorded for marine ingression which resulted in the precipitation of magadiite nasi 7 oh 3 3h 2 o and the brief influx of a marine fauna this provides the most southerly record of marine influence from the boreal ocean at this time and has important implications for palaeoenvironmental reconstructions and correlation in the region

osmium isotope anomalies in chondrites results for acid residues and related leachates abstract we have investigated os isotope anomalies in acid residues enriched in insoluble organic matter iom extracted from ten primitive chondrites acid leachates and residues of these fractions as well as acid leachates of bulk chondrites osmium isotopic compositions of bulk carbonaceous ordinary and enstatite chondrites are also reported consistent with prior results bulk chondrites have homogeneous os isotope compositions for s r and p process nuclides that are indistinguishable from terrestrial at the current level of resolution in contrast nearly all the iom rich residues are enriched in s process os evidently due to the preferential incorporation of s process enriched presolar grains most likely presolar sic presolar silicate grains that formed in red giant branch rgb or asymptotic giant branch agb stars are also likely hosts of additional s process os in chondrites consistent with one prior study os released by weak acid leaching of bulk chondrites is slightly to strongly enriched in r process nuclides of which the carrier may be fine grained presolar silicates formed in supernovae or unidentified solar phases collectively the different chemically concentrated components in these meteorites are variably enriched in s r and possibly p process os of which the individual carriers must have been produced in multiple stellar environments the lack of evidence for os isotopic heterogeneity among bulk chondrites contrasts with evidence for isotopic heterogeneities for various other elements at approximately the same levels of resolution e g cr mo ru ba sm and nd one possible explanation for this is that the heterogeneities for some elements in bulk materials reflect selective removal of some types of presolar grains as a result of nebular processes and that because of the strong chemical differences between os and the other elements the os was not significantly affected another possible explanation is that late stage injection of isotopically distinct materials into the nebula led to heterogeneous distribution of some elements osmium may not have been affected because of a lack of isotopic contrast with the pre injection well mixed nebula

fast shearing of pre existing shear zones in soil the paper presents results from a laboratory investigation into the influence of fast rates of displacement on the residual strength of soil this influence was studied in the ring shear apparatus shear zones were formed by slow drained shearing and then tested at alternately fast and slow rates of displacement results from a wide range of natural soils are presented all soils show initially an increase in strength when resheared at fast rates of displacement the strength then tends to decrease with fast displacement to a minimum value the fast residual strength three types of rate effects on the residual strength are identified a positive rate effect in soils showing a fast residual strength higher than the slow residual a neutral rate effect in soils showing a constant fast residual strength equal to the slow residual irrespective of rate of displacement and a negative rate effect in soils showing a significant drop in fast residual strength below the slow residual when sheared at rates higher

devonian magadi type cherts in the orcadian basin scotland abstract magadi type cherts occur in lacustrine rocks of the middle devonian middle old red sandstone orcadian basin scotland chert nodules are replacive within organic rich laminites the deposits of a stratified lake they exhibit soft sediment deformation including sediment injection along shrinkage fractures within the nodules the thefts preserve stellate quartz pseudomorphs after an evaporite mineral which may have been a sodium carbonate mineral trona these are features common to other documented occurrences of magadi type cherts nodules were nucleated about vertical cracks in the host sediment and show polygonal or parallel aligned patterns precipitation of the magadiite precursor occurred from alkaline groundwaters rather than in the lake water column

the relationship between ck and cv chondrites ck chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of fe ni metal although the group is predominately composed of equilibrated meteorites types 4 6 in recent years a significant number of new samples have been classified as being either ck3 or ck3 anomalous these unequilibrated cks often display a close affinity with members of the cv oxidized subgroup cks and cvs oxidized subgroup may therefore form a continuum and by implication could be derived from a single common parent body to investigate the relationship between these two groups a detailed study of the oxygen isotope composition opaque mineralogy and major and trace element geochemistry of a suite of cv and ck chondrites has been undertaken the results of oxygen isotope analysis confirm the close affinity between cv and ck chondrites while excluding the possibility of a linkage between the co and ck groups magnetites in both cv and ck chondrites show significant compositional similarities but high ti contents are a diagnostic feature of the latter group the results of major and trace element analysis demonstrate that both cv and ck chondrites show overlapping variation supporting evidence for a single common source for both groups comes from their similar cosmic ray exposure age distributions recent reflectance spectral analysis is consistent with both the cvs and cks being derived from eos family asteroids which are believed to have formed by the catastrophic disruption of a single large asteroid thus a range of evidence appears to be consistent with cv and ck chondrites representing samples from a single thermally stratified parent body in view of the close similarity between cv and ck chondrites some modification of the present classification scheme may be warranted possibly involving integration of the two groups one means of achieving this would be to reassigned ck chondrites to a subgroup of the oxidized cvs it is recognized that a full evaluation of this proposal may require further study of the still poorly understood ck3 chondrites

compositional and petrographic similarities of cv and ck chondrites a single group with variations in textures and volatile concentrations attributable to impact heating crushing and oxidation abstract greenwood et al 2010 gathered data on o isotopic and elemental compositions and reevaluated literature data for cv and ck chondrites they concluded that these two chondrite groups originated on the same parent asteroid with ck chondrites being metamorphosed cv chondrites which are otherwise missing types 4 through 6 to test this interpretation we have gathered new instrumental neutron activation analysis inaa data for cv and ck chondrites and reexamined their petrographic features the new inaa data like the older data show scatter attributable to weathering effects but we conclude that the refractory lithophile abundances are the same in cv and ck in agreement with the greenwood et al interpretation several volatile elements are significantly lower in ck than in cv chondrites among the elements we determine the greatest difference between cv and ck is found for br for which the cv ck ratio is 4 as and sb are about 20 lower in ck than cv and smaller differences are observed for zn ga and se it seems likely that volatiles were lost during impact heating events that also provided the heat responsible for metamorphic recrystallization within statistical uncertainty chondrules in cv and ck chondrites are the same size and have similar textural distributions a significant petrographic difference between ck and cv chondrites cited by kallemeyn et al 1991 was the much higher percentage of igneous rims around cv chondrules however we now recognize that many chondrules in ck3 8 nwa 1559 have igneous rims and in ck4 chondrites igneous rims are recognizable by their associated sulfide rich rings there are no quantifiable cv ck differences in igneous rim abundances we used ca and al maps to show that ck chondrites have cai abundances similar to those of cv chondrites it thus appears that there are no resolvable pre metamorphic petrographic differences between cv and ck chondrites we recommend that the ck designation be abandoned and that the cv group be acknowledged as spanning the range of petrologic types 3 6 we suggest that ck3 chondrites be designated cv3oxk most ck4 chondrites are highly fragmental collisional crushing appears to be much more common than in cv chondrites it seems likely that ck chondrites formed from reduced cv3 materials after the latter was impacted buried aqueously altered and annealed

nucleosynthetic strontium isotope anomalies in carbonaceous chondrites abstract precise sr isotopic compositions in samples from sequential acid leaching experiments have been determined for three carbonaceous chondrites allende murchison and tagish lake together with those in the bulk aliquots of these meteorites the chondritic acid leachates and residues were characterized by sr isotope anomalies with variable 84sr values 106 relative deviation from a standard material ranging from 120 to 4700 ppm documenting multiple nucleosynthetic sources within a single meteorite in addition the 84sr patterns across leaching samples for individual chondrites differed from one another the highest 84sr values were observed for leaching step 3 hcl h2o 75 c for allende and murchison likely because of the incorporation of calcium and aluminum rich inclusions cais in contrast extremely low 84sr values were observed in the later fractions steps 6 and 7 for murchison and tagish lake suggesting the existence of s process enriched presolar sic grains derived from agb stars a 84sr 54cr diagram was prepared with the cais and bulk aliquots of carbonaceous chondrites and other meteorites noncarbonaceous that were plotted separately however they still formed a global positive correlation cais presented the highest 84sr and 54cr values whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowest 84sr and 54cr values respectively the positive trend was interpreted as resulting from global thermal processing in which sublimation of high 84sr and 54cr carriers generated the excess 84sr and 54cr signatures in cais while noncarbonaceous planetesimals accreted from materials that underwent significant thermal processing and thus had relatively low 84sr and 54cr values apart from the global trend the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations e g 54cr 50ti 54cr 17o a plausible scenario for creation of the intrinsic variations involves local thermal processing e g flash heating for chondrule formation caused by additional selective destruction of presolar grains differently than that caused by global thermal processing the existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing material transportation and mixing in the protoplanetary disk prior to planetesimal formation

a shear constitutive model for describing the full process of the deformation and failure of slip zone soil abstract the shear mechanical behaviour of slip zone soil is of great significance for the stability analysis of landslides based on the shear deformation failure characteristics of slip zone soil and the statistical damage theory a shear constitutive model is proposed to describe the shear stress displacement relation of slip zone soil parameters in the proposed model have clear physical mechanical meaning and can be easily obtained by shear tests the shear constitutive model is verified by comparing model results with ring shear test results on the slip zone soil from the huangtupo landslide in the three gorges reservoir area of china it reveals that the model is capable of capturing the salient behaviour of the slip zone soil such as the pre peak and post peak deformation characteristics moreover utilizing limited ring shear test data under given normal stresses shear stresses at various shear displacements under untested normal stress are available by this model finally a dynamic evaluation method of landslide stability which incorporates the landslide displacement by presented constitutive model is proposed and applied to analyze the stability of the riverside slump ii of the huangtupo landslide

metamorphosed calcium aluminum rich inclusions in ck carbonaceous chondrites ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 although cks are described as calcium aluminum rich inclusion cai poor objects the abundance of cais in the 18 ck3 6 we analyzed ranges from zero to approximately 16 4 during thermal metamorphism some of the fine grained cais recrystallized as irregular assemblages of plagioclase ca rich pyroxene olivine ca poor pyroxene magnetite coarse grained cais display zoned spinel fassaite destabilization and secondary grossular and spinel secondary anorthite grossular ca rich pyroxene and spinel derive from the destabilization of melilite which is lacking in all cais investigated the al mg isotopic systematics measured in fine and coarsegrained cais from tanezrouft tnz 057 was affected by mg redistribution the partial equilibration of al mg isotopic signatures obtained in the core of a coarse grained cai cg1 cai in tnz 057 may indicate a lower peak temperature for mg diffusion of approximately 540 580 c while grossular present in the core of this cai indicates a higher temperature of around 800 c for the metamorphic event on the parent body of tnz 057 excluding metamorphic features the similarity in nature and abundance of cais in ck and cv chondrites confirms that cvs and cks form a continuous metamorphic series from type 3 to 6

assessment of the 187re decay constant by cross calibration of re os molybdenite and u pb zircon chronometers in magmatic ore systems the past decade has seen renewed interest in 187re 187os geochronology using a variety of matrices including sulfide minerals shales and meteorites the most widely used value of the 187re decay constant 187re is 1 666 0 005 10 11 a 1 0 31 which is based on cross calibration of re os and pb pb chronometers for certain meteorites smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 however other recent studies have yielded alternate values of 187re based upon either direct counting experiments or analysis of meteorites here we provide an independent assessment of 187re using methodology sample materials and preparation of os standard solutions different from those of smoliar et al 1996 combining re os age data for molybdenite formed in magmatic ore deposits with the u pb zircon age of the magmatic rocks a refined 187re value is determined by averaging 11 individual cross calibration experiments spanning ca 2700 ma of earth history using the u decay constants of jaffey jaffey a h flynn k f glendenin l e bentley w c and essling a m 1971 precision measurement of half lives and specific activities of 235u and 238u phys rev 4 1889 1906 a value for 187re of 1 6668 0 0034 10 11 a 1 is determined using the 238u value of jaffey et al 1971 and 235u value of schoene schoene b crowley j l condon d j schmitz m d and bowring s a 2006 reassessing the uranium decay constants for geochronology using id tims u pb data geochim cosmochim acta 70 426 445 a value for 187re of 1 6689 0 0031 10 11 a 1 is determined these values are nominally higher ca 0 1 and ca 0 2 than the value determined by smoliar et al smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 but within calculated uncertainty further refinement of 187re by cross calibrating the molybdenite and u pb zircon chronometers should be possible by utilizing high precision single grain chemical abrasion zircon u pb analyses

some fluidized landslides triggered by the 2011 tohoku earthquake mw 9 0 japan abstract the 2011 tohoku earthquake off the pacific coast of japan generated a large tsunami and many landslides resulting in a great number of casualties although almost all casualties resulted from the tsunami some long travel fluidized small scale landslides also killed 13 people after the earthquake we surveyed seven of these catastrophic landslides triggered by the earthquake we found that most of them have nearly identical geological features with slopes consisting of pyroclastic deposits formed at different times and with a palaeosol layer that outcropped in most cases after the landslide above the palaeosol there are layers of pumice and scoria the palaeosol had a natural moisture content of 160 and the pumice and scoria had a moisture content of 145 from field observations we concluded that the sliding surface originated in the very upper part of palaeosol and liquefaction occurred in both layers resulting in the fluidization of displaced landslides to examine the trigger and movement mechanism of these landslides we monitored the ground motion of one landslide area during the many aftershocks and compared the results with records obtained by a national seismic station nearby we inferred that strong seismic motion occurred in the landslide area during the main shock we sampled the palaeosol and pyroclastic deposits and performed undrained static cyclic shear tests on the materials both in a saturated state and at natural moisture content the results indicate that high pore water pressure was generated resulting in decreased shear strength even in samples with the natural moisture content the shear strength of the palaeosol lowered to a very small value with continuous increase of shear rate enabling the high mobility of the displaced landslide materials

chemical compositions of siderophile element rich opaque assemblages in an allende inclusion abstract ten opaque assemblages or fremdlinge weighing 0 17 19 g from an allende type b ca al rich coarse grained inclusion were analyzed by inaa for ca na mn sc ta ti v cr fe ni co w re os ir mo ru pt rh au as sb and se refractory siderophiles are usually enriched by factors of 103 104 relative to cl chondrites but not uniformly from sample to sample c1 chondrite normalized re os ir pt os ru and pt rh ratios vary from 0 81 1 03 0 70 2 25 0 67 3 32 and 0 45 1 43 respectively attempts to model the abundances of refractory siderophiles by condensation from the solar nebula into a single phase assuming ideal solution fail to match the observed combination of subchondritic re os and ir pt ratios even allowing for fractionation of the highest temperature condensates a different model in which all metals whose high temperature crystal structures are hcp condense into one alloy bcc into another and fcc into a third is capable of matching virtually all refractory siderophile fractionations in these fremdlinge in this model all isostructural metals are assumed to form ideal solutions with one another and metals of different structure are assumed to be insoluble in one another after fractionation of high temperature hcp and fcc alloys individual proto fremdlinge formed by mixing of high and low temperature varieties of each of the three alloys either in the nebula before and during cai accretion or during later partial melting of the silicate oxide and metal components of cais

silica diagenesis origin of inorganic and replacement cherts abstract silicification of originally non siliceous sediments affects a wide variety of rock types and materials and ranges from minor to pervasive partial and minor chertification occur mostly in phanerozoic carbonates carbonate bearing sandstones evaporites and fossil wood the source of the silica is predominantly biogenic in petrified wood the silicification mechanism is a permeation or void filling process not a replacement in this example the sequence of silica phase transformation is the same as that in deep sea siliceous sediments in many silicified rocks particularly in certain carbonates the transformation sequence is different from that in radiolarites or diatomites the chemical environment and conditions of early diagenetic chert formation in shallow water carbonates are delineated by the general mixing model of knauth 1979 but remain unknown for most other types an exception are the flint nodules and bands of the english chalk a detailed geochemical study of the paramoudra flint structures by clayton 1986 provided remarkable insight into the replacement process seven different recurring silica fabrics have been recognized in chert replaced carbonates including equigranular microcrystalline quartz or microquartz and megaquartz and fibrous types chalcedony quartzine or length slow chalcedony lutecite zebraic chalcedony and microflamboyant quartz among the latter quartzine and microflamboyant quartz are common in but by no means restricted to chert replaced evaporites for which milliken 1979 recognized a sequence of seven quartz fabrics as a single criterion only anhydrite inclusions in megaquartz quartzine or microflamboyant quartz provide unequivocal evidence for an evaporite precursor the relative timing between silicification and well established diagenetic carbonate reactions shows that virtually all theoretically possible sequences occur chertification of carbonate host sediment thus may take place during early intermediate or late diagenesis and even during anchimetamorphism pervasive to complete silicification has been described in lacustrine pedogenic and hydrothermal volcanogenic rocks and occurs on the scale of individual beds members or entire formations it may affect some of the aforementioned rock types too for example carbonates the source of the silica is predominantly inorganic chert formation in these environments includes direct chemical silica precipitation from solution through a gel stage magadi type cherts result from the conversion of the hydrous sodium silicate magadiite into microcrystalline quartz which has occurred in east african rift valley lakes such as lake magadi in late pleistocene time they are closely related to directly precipitated inorganic cherts which have been observed in alkaline environments of playa lakes silcretes originate from weathering and soil forming processes under climatic and environmental conditions conducive to the formation of duricrusts and laterites in more humid climates however non weathering profile silcretes occur which have been distinguished from weathering profile silcretes four to five different silcrete fabric types have been established including the 1 grain supported or quartzitic 2 floating terrazzo 3 matrix albertinia and opaline and 4 conglomeratic types in volcanic edifices silicification related to hydrothermal activity occurs 1 along the ascent routes of the fluids vents within the volcanic complexes 2 in isolated ponds and depressions on the sea floor where the fluids discharge mostly in the median rift valley of mid ocean ridges and 3 in geothermal areas on land associated with spreading lineaments volcanic islands arcs transform faults or continental hot spots attention has focussed on the associated base metal concentrations and less on the silicification and accompanying iron enrichment processes the precambrian banded iron formations may be indirectly or directly related to hydrothermal volcanic processes the origin of these cherty iron formations certainly requires more than one genetic model and at present remains a major unresolved problem despite massive efforts to tackle it

ree and hf distribution among mineral phases in the cv ck clan a way to explain present day hf isotopic variations in chondrites chondrites are among the most primitive objects in the solar system and constitute the main building blocks of telluric planets among the radiochronometers currently used for dating geological events sm nd and lu hf are both composed of refractory lithophile element they are thought to behave similarly as the parent elements sm and lu are generally less incompatible than the daughter elements nd and hf during geological processes as such their respective average isotopic compositions for the solar system should be well defined by the average of chondrites called chondritic uniform reservoir chur however while the sm nd isotopic system shows an actual spread of less than 4 in the average chondritic record the lu hf system shows a larger variation range of 28 bouvier a vervoort j d and patchett p j 2008 the lu hf and sm nd isotopic composition of chur constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets earth planet sci lett 273 48 57 to better understand the contrast between sm nd and lu hf systems the ree and hf distribution among mineral phases during metamorphism of karoonda ck and vigarano type cv carbonaceous chondrites has been examined mineral modes were determined from elemental mapping on a set of five ck chondrites from types 3 6 and one cv3 chondrite trace element patterns are obtained for the first time in all the chondrite forming minerals of a given class ck chondrites as well as one cv3 sample this study reveals that ree are distributed among both phosphates and silicates only 30 50 of sm and nd are stored in phosphates at least in chondrites types 3 5 as such they are not mobilized during early stages of metamorphism the remaining fraction of sm and nd is distributed among the same mineral phases these elements are therefore not decoupled during metamorphism of the whole rock total of lu the fraction held in phosphate decreases significantly as the degree of metamorphism increases 30 for types 3 and 4 less than 5 in type 6 in contrast to lu hf is mainly hosted by silicates with little contribution from phosphates throughout the ck metamorphic sequence a significant part of sm and nd are stored in phosphates in types 3 5 and these elements behave similarly during ck chondrite metamorphism that explains the robustness of the sm nd ratios in chondrites through metamorphism and the slight discrepancies observed in the present day isotopic nd values in chondrites on the contrary lu and hf are borne by several different minerals and consequently they are redistributed during metamorphism induced recrystallization the lu hf ratios are therefore significantly disturbed during chondrites metamorphism leading to the high discrepancies observed in present day hf isotopic values in chondrites

the compositional classification of chondrites vii the r chondrite group bulk compositional and petrographic data clearly define the new r rumuruti group of chondrites consisting of rumuruti the only fall alh85151 acfer 217 carlisle lakes dar al gani 013 pca91002 pca91241 y 75302 y 793575 and y 82002 compositional petrographic rare gas and 0 isotopic data strongly suggest that pca91002 and pca91241 are paired the yamato specimens are probably not paired the matrices of the known r chondrites have experienced similar minor degrees of metamorphism petrographic types are 3 8 3 9 with the exception of alh85151 3 6 all except carlisle lakes contain equilibrated r5 r6 clasts petrographically the r chondrites are characterized by a low chondrule matrix modal abundance ratio high states of oxidation reflected by abundant nio bearing olivine with fa37 40 relatively small chondrules mean apparent diameters of 400 abundant up to 11 wt sulfides mainly pyrrhotite and pentlandite and negligible amounts of metallic fe ni refractory lithophile abundances are 0 95 x cl intermediate between those in ordinary chondrites oc and ci chondrites abundances of the volatile elements se and zn are greatly enhanced relative to oc the r chondrites are clearly distinguished from other chondrite groups on the basis of al mn and zn mn abundance ratios the oxygen isotopic data plot roughly along a slope 12 line with whole rock 17o values higher than for any other chondrite group rumuruti acfer 217 alh85151 pca91002 and pca91241 have light dark structures and solar wind implanted rare gases indicating that they are regolith breccias the yamato specimens also have light dark structures and are inferred to be regolith breccias carlisle lakes lacks solar rare gases and is unbrecciated based on similarities in refractory lithophile abundances 00 95 x ci oxygen isotope compositions 17o 0 and refractory inclusion abundances 0 1 vol none have been reported the r chondrites probably belong to a noncarbonaceous superclan of chondrites that also includes ordinary and enstatite chondrites the high oxidation state high matrix chondrule modal abundance ratio relatively low abundance of droplet chondrules and high 17o composition suggest that the r chondrites formed at greater heliocentric distances than the oc

non nucleosynthetic heterogeneity in non radiogenic stable hf isotopes implications for early solar system chronology abstract nucleosynthetic heterogeneity and secondary neutron capture reactions may have important implications for 176 lu 176 hf chronology and modelling of early planetary evolution so far the relevance of these phenomena for the lu hf system has not been explored we therefore have analyzed the non radiogenic stable hf isotope composition 177 hf 178 hf 179 hf and 180 hf of meteorites meteorite components and terrestrial rock samples to identify nucleosynthetic or neutron capture induced variations all analyzed chondrites have uniform 178 hf 177 hf and 180 hf 177 hf values that cannot be resolved from the average terrestrial composition thus there is no evidence for nucleosynthetic heterogeneity in chondrites or earth and these data support the use of a chondritic reference value for the hf isotope composition of the bulk silicate earth this homogeneity contrasts with nucleosynthetic heterogeneities found in lighter elements and provides evidence for a separate synthesis of light and heavy r process nuclei various mesosiderite samples and one lunar meteorite display coupled 178 hf 177 hf and 180 hf 177 hf anomalies that are associated with neutron capture induced deviations in 149 sm 154 sm and 150 sm 154 sm however the analyzed chondrites and an aubrite show only sm isotope anomalies and these are the result of neutron capture the hf isotope anomalies require substantial capture of epithermal neutrons whereas sm anomalies result primarily from thermal neutron capture the non radiogenic stable isotope composition of hf is thus a suitable monitor for epithermal neutron capture reactions the data reveal distinct neutron energy spectra mesosiderites are characterized by high epithermal to thermal neutron fluence ratios whereas the remaining samples show low epithermal to thermal ratios secondary neutron capture may significantly increase the measured 176 hf 177 hf in whole rock meteorite samples without causing a resolvable shift in 176 lu 177 hf thus it could potentially induce scatter in lu hf whole rock isochrons and produce spurious initial 176 hf 177 hf values however the slopes of internal i e mineral isochrons cannot be increased significantly by secondary neutron capture this process therefore cannot account for the unrealistically old 176 lu 176 hf ages e g 4 75 ga of some meteorites

chondrites as samples of differentiated planetesimals abstract chondritic meteorites are unmelted and variably metamorphosed aggregates of the earliest solids of the solar system the variety of metamorphic textures in chondrites motivated the onion shell model in which chondrites originated at varying depths within a parent body heated primarily by the short lived radioisotope 26 al with the highest metamorphic grade originating nearest the center allende and a few other chondrites possess a unidirectional magnetization that can be best explained by a core dynamo on their parent body indicating internal melting and differentiation here we show that a parent body that accreted to 200 km in radius by 1 5 ma after the formation of calcium aluminum rich inclusions cais would have a differentiated interior and ongoing accretion would add a solid undifferentiated crust overlying a differentiated interior consistent with formational and evolutionary constraints inferred for the cv parent body this body could have produced a magnetic field lasting more than 10 ma this hypothesis represents a new model for the origin of some chondrites presenting them as the unprocessed crusts of internally differentiated early planetesimals such bodies may exist in the asteroid belt today the shapes and masses of the two largest asteroids 1 ceres and 2 pallas can be consistent with differentiated interiors conceivably with small iron cores with hydrated silicate or ice silicate mantles covered with undifferentiated crusts

long runout mechanism and landsliding behaviour of large catastrophic landslide triggered by heavy rainfall in guanling guizhou china a large catastrophic landslide was triggered by a heavy rainfall on 28 june 2010 in guanling guizhou china the landslide buried two villages and killed 99 people along the runout path the lands

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

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

oxidation during metamorphism of the ordinary chondrites subtle but progressive changes in the compositions and relative abundances of olivine pyroxene and metal with increasing metamorphic grade in equilibrated types 4 6 ordinary chondrites indicate that these meteorites experienced oxidation of metallic fe during heating oxygen fugacities calculated from these mineral assemblages increase with petrologic type the hypothesis of oxidation during chondrite metamorphism differs from a commonly accepted idea that chondritic fe was reduced by graphite the mineralogies of unequilibrated type 3 chondrites do not conform to the progressions in equilibrated chondrites allowing the possibility that fe may first have been reduced through reaction with graphite at the onset of metamorphism although there are conflicting observations supporting both oxidation and reduction in these meteorites as temperatures increased to levels appropriate for types 4 6 chondrites the activity of graphite may have been lowered by its dissolution in taenite and in any case oxygen fugacities appear to have been well within the stability field of graphite precluding its reaction at these temperatures oxidation state was largely controlled by equilibrium between ferromagnesian silicates and metal oxygen fugacities calculated from chondrite mineral equilibria are 2 3 log units below previously reported intrinsic o2 measurements we propose that progressive oxidation during metamorphism was promoted by interaction with small amounts of an oxidizing vapor derived by heating ices originally accreted into the parent asteroids assuming that this vapor was pure h2o the watenrock weight ratio required to account for the observed oxidation of fe in h and l chondrites is very modest less than several per mil progressive oxidation in the metamorphic sequence resulted from different degrees of reaction with such a fluid possibly caused by temperature variations or evolution of the composition of the fluid as it permeated through the body the presence of even minor amounts of a vapor phase during metamorphism affects interpretations of the volatile trace element and oxygen isotopic fractionations observed in ordinary chondrites and inferred to have formed by nebular or parent body processes

platinum group element fractionation in a komatiitic basalt lava lake precise pge os ir ru pt pd abundance data for bulk rock samples and mineral separates from a deep differentiated komatiitic basalt lava lake in the vetreny belt baltic shield were obtained using an icp ms id technique the composition of the erupted liquid mgo 5 15 is characterized by a highly fractionated pge pattern pd os n 5 48 with subchondritic os ir n 5 0 43 analysis of separated olivine and chromite revealed that ru os and ir were slightly compatible to moderately incompatible in olivine d 5 1 7 0 8 and were compatible with chromite d 5 100 150 platinum and pd were highly incompatible with olivine d 5 0 08 0 03 and moderately compatible with chromite d 5 1 6 3 3 bulk solid liquid partition coefficients for pges ni cr and cu estimated from the whole rock regressions were os 7 9 ir 6 6 ru 4 5 pt 0 53 pd 0 09 ni 6 2 cr 4 4 and cu 0 01 the highly incompatible behavior of cu and pd indicates that there was no separation of fenicu immiscible sulfide liquid during the differentiation of the lava lake comparison of the bulk partition coefficients with those calculated from the olivine and chromite compositions implies that the fractionating mineral assemblage included 10 2561 mass fraction of pyrrhotite the data obtained provide new constraints on the effects of fractional crystallization on the pge compositions of mafic ultramafic magmas copyright 2001 elsevier science ltd