the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

carbonates in cm2 chondrites constraints on alteration conditions from oxygen isotopic compositions and petrographic observations high precision measurements of the oxygen isotopic compositions of carbonates calcite and dolomite from five cm2 chondrites are presented and put into context of the previously determined mineralogic alteration index mai which places these meteorites into an alteration sequence the carbonate oxygen isotopic compositions range from 20 0 to 35 7 for 18o 8 0 to 17 7 for 17o and 0 7 to 2 7 for 17o carbonate 17o values are inversely correlated with mai and track the evolution of fluid composition from higher to lower 17o values with increasing alteration on the cm parent body similar 17o values for calcite and dolomite fractions from the same splits of the same meteorites indicate that calcite and dolomite in each split precipitated from a single fluid reservoir however reversed calcite dolomite fractionations 18odol 18occ indicate that the fluid was subject to processes such as freeze thaw or evaporation that fractionated isotopes in a mass dependent way consideration of the carbonate isotopic data in the context of previously proposed models for aqueous alteration of carbonaceous chondrites has provided important insights into both the evolving alteration conditions and the utility of the models themselves the data as a whole indicate that the isotopic evolution of the fluid was similar to that predicted by the closed system two reservoir models but that a slightly larger matrix water fractionation factor may apply in the context of this model more altered samples largely reflect greater reaction progress and thus probably indicate more extended times of fluid exposure petrographic observations of carbonates reveal a trend of variable carbonate morphology correlated with alteration that is also consistent with changes in the duration of fluid rock interaction the data can also be reconciled with fluid flow models in a restricted region of the parent body which is consistent with assertions that the different types of carbonaceous chondrites derive from different regions of their parent bodies in this case the model results for a 9 km radius body and our data place the location of the cm chondrite formation in a 100 m thick zone 1 km from the surface the size of this zone could be increased if the model parameters were adjusted

oxygen and magnesium isotope compositions of calcium aluminum rich inclusions from cr2 carbonaceous chondrites abstract we report both oxygen and magnesium isotope compositions measured in situ using a cameca ims 1280 ion microprobe in 20 of 166 cais identified in 47 polished sections of 15 cr2 renazzo type carbonaceous chondrites two additional cais were measured for oxygen isotopes only most cr2 cais are mineralogically pristine only few contain secondary phyllosilicates sodalite and carbonates most likely products of aqueous alteration on the cr2 chondrite parent asteroid spinel hibonite grossite anorthite and melilite in 18 cais have 16o rich 17o 23 3 1 9 2 error compositions and show no evidence for postcrystallization isotopic exchange commonly observed in cais from metamorphosed cv carbonaceous chondrites the inferred initial 26al 27al ratios 26al 27al 0 in 15 of 16 16o rich cais measured are consistent with the canonical value of 4 5 5 10 5 and a short duration 0 9 2 2 0 7 my eight of the 166 cr2 cais identified are associated with chondrule materials indicating that they experienced late stage incomplete melting during chondrule formation three of these cais show large variations in oxygen isotope compositions 17o ranges from 23 5 to 1 7 suggesting dilution by 16o depleted chondrule material and possibly exchange with an 16o poor 17o 5 nebular gas the low inferred 26al 27al 0 ratios of these cais 2 my after crystallization of cais with the canonical 26al 27al 0 and suggest evolution of the oxygen isotope composition of the inner solar nebula on a similar or a shorter timescale because cais in cr2 and cv chondrites appear to have originated in a similarly 16o rich reservoir and only a small number of cr2 and cv cais were affected by chondrule melting events in an 16o poor gaseous reservoir the commonly observed oxygen isotope heterogeneity in cais from metamorphosed cv chondrites is most likely due to fluid solid isotope exchange on the cv asteroidal body rather than gas melt exchange this conclusion does not preclude that some cv cais experienced oxygen isotope exchange during remelting instead it implies that such remelting is unlikely to be the dominant process responsible for oxygen isotope heterogeneity in cv cais the mineralogy oxygen and magnesium isotope compositions of cais in cr2 chondrites are different from those in the metal rich ch and cb carbonaceous chondrites providing no justification for grouping cr ch and cb chondrites into the cr clan

oxygen isotope compositions of chondrule phenocrysts and matrix grains in kakangari k grouplet chondrite implication to a chondrule matrix genetic relationship abstract to investigate a possible relationship between chondrules and matrix we studied mineralogy mineral chemistry and in situ o isotope compositions of chondrules clastic matrix grains and amoeboid olivine aggregates aoas in the kakangari k grouplet chondrite most olivines and low ca pyroxenes in the kakangari chondrules matrix and aoas have similar magnesium rich compositions fo 95 97 0 3 0 5 wt mno and en 90 96 respectively these rather uniform chemical compositions of the different chondritic components are likely due to partial fe mg mn equilibration during thermal metamorphism experienced by the host meteorite oxygen isotope compositions of olivine and low ca pyroxene grains in chondrules and matrix plot along a slope 1 line on a three o isotope diagram and show a range from 16 o enriched composition similar to that of the sun to 16 o depleted composition similar to the terrestrial o isotope composition most olivines and low ca pyroxenes in chondrules are 16 o poor and plot on or close to the terrestrial mass fractionation line mean 17 o values 2 standard deviations 0 0 0 8 and 0 2 0 9 for olivine and pyroxene respectively consistent with the previously reported compositions of bulk chondrules 17 o 0 16 0 70 in addition to these 16 o poor grains a coarse grained igneous rim surrounding a porphyritic chondrule contains abundant 16 o rich relict olivines 17 o 24 oxygen isotope compositions of olivines and low ca pyroxenes in matrix show a bimodal distribution 12 out of 13 olivine and 4 out of 17 pyroxene grains measured are similarly 16 o rich 17 o 23 5 2 9 others are similarly 16 o poor 17 o 0 1 1 7 due to slow oxygen self diffusion olivines and low ca pyroxenes largely retained their original oxygen isotope compositions the nearly identical o isotope compositions between the chondrule phenocrysts and the 16 o poor matrix grains suggest both chondrules and matrix of kakangari sampled isotopically the same reservoirs in addition the presence of abundant 16 o rich grains in matrix and the chondrule igneous rim suggests both components acquired similar precursor inventories these observations imply that chondrules and matrix in kakangari are genetically related in the sense that material that formed matrix was one of the precursors of chondrules and chondrules and some fraction of matrix experienced the same thermal processing event the 16 o enriched bulk matrix value compared to the bulk chondrules reported previously is likely due to presence of abundant 16 o rich grains in the kakangari matrix

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

temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the cm chondrites aqueous alteration of primitive meteorites was among the earliest geological processes during the evolution of our solar system clumped isotope thermometry of carbonates in the cm chondrites cold bokkeveld murray and murchison demonstrates that they underwent aqueous alteration at 20 71 c from a fluid with 18 o vsmow of 2 0 to 8 1 and 17 o vsmow of 0 1 to 3 0 the 13 c vpdb values of these carbonates exhibit a negative correlation with the 18 o vsmow of their formation waters consistent with formation and escape of 13 c depleted ch 4 during aqueous alteration methane generation under these conditions implies that the alteration fluid was characterized by an eh 0 67 and ph 12 5 or lower at the highest alteration temperatures our findings suggest that methane generation may have been a widespread consequence of planetesimal and planetary aqueous alteration perhaps explaining the occurrence of methane on titan triton pluto and other kuiper belt objects

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

the vertical propagation of disturbances triggered by seismic waves of the 11 march 2011 m9 0 tohoku earthquake over taiwan in this paper concurrent colocated measurements of seismometers infrasonic systems magnetometers hf cw high frequency continuous wave doppler sounding systems and gps receivers are employed to detect disturbances triggered by seismic waves of the 11 march 2011 m9 0 tohoku earthquake no time delay between colocated infrasonic i e super long acoustic waves and seismic waves indicates that the triggered acoustic and or gravity waves in the atmosphere or seismo traveling atmospheric disturbances stads near the earth s surface can be immediately activated by vertical ground motions the circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves the speed of about 3 3 km s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves i e stads are mainly induced by the rayleigh waves the agreements in the travel time at various heights between the observation and theoretical calculation suggest that the stads triggered by the vertical motion of ground surface caused by the tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over taiwan

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

oxygen carbon and u series isotopes of aragonites from vestfold hills antarctica clues to geochemical processes in subglacial environments aragonites occurring in situ on the gneissic bedrock at vestfold hills an ice free coastal antarctic oasis possess morphologic and petrographic characteristics typical of subglacial carbonate precipitates the sup 14 c chronology of the samples is invalidated by modern carbon contamination and a sup 14 c sup 12 c reservoir correction of unknown magnitude in contrast u and th isotope analyses suggest that the subglacial deposits can be treated as closed datable systems if allowance is made for the excess sup 230 th derived from the small and variable detrital silicate fraction coexisting with the aragonites the mean sup 230 th depositional age of 35 000 plus minus 2 000 yrs correlates with late isotope stage 3 of deep sea glacial chronology and represents the time when the vestfold hills were partially or completely buried under the advancing east antarctic ice sheet the survival of the aragonites following the ice sheet retreat during the holocene is attributed to the extreme arid climate of the area the aragonites are anomalously depleted in sup 18 o and slightly depleted in sup 13 c relative to smow and pdb standards respectively delta sup 18 o 15 7 plus minus 0 9 per thousand delta sup 13 c minus 3 6 plus minus 0 4 per thousand the melt water with which the aragonitesmore would have equilibrated at 0 degree c is about 7 to 9 per thousand more depleted in sup 18 o relative to the extant basal ice source delta sup 18 o minus 41 per thousand part of this enhanced sup 18 o deficiency i e 4 to 6 per thousand is ascribed to temporal shifts in delta sup 18 o of the antarctic ice the rest to isotope effects of the subglacial hydrology a model of subglacial aragonite precipitation is proposed on the basis of water flow between warm melting zones and cold freezing zones at the ice sheet sole less

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

minor and trace element concentrations in carbonates of carbonaceous chondrites and implications for the compositions of coexisting fluids abstract abundances of fe mg mn sr na b and ba in meteoritic calcites and dolomites have been determined using the ion microprobe the compositions of these carbonates are consistent with their precipitation from or recrystallization in equilibrium with aqueous solutions at low temperatures coexisting calcites and dolomites in cm chondrites are not in equilibrium and presumably formed in distinct events calculated molar element ca ratios for fluids in equilibrium with these carbonates suggest that dolomites in cm and cl chondrites formed from compositionally similar brines calcite solutions were also saline but lower in mg fe and mn calculations suggest that these solutions became more like dolomite solutions with increasing alteration of the host cm meteorite reflecting progressive evolution of solution compositions asteroid brines may have formed by membrane nitration after the formation of compacted phyllosilicates lowered permeability by addition of components to fluids during phyllosilicate forming reactions or through low pressure boiling occurrences of vein filling calcite followed by dolomite and later by sulfates in carbonaceous chondrites represent the final stages of a protracted aqueous alteration sequence

the formation and alteration of the renazzo like carbonaceous chondrites i implications of bulk oxygen isotopic composition abstract to better understand the role of aqueous alteration on the cr chondrite parent asteroid a whole rock oxygen isotopic study of 20 meteorites classified as renazzo like carbonaceous chondrites cr was conducted the cr chondrites analyzed for their oxygen isotopes were dhofar 1432 elephant moraine eet 87770 eet 92042 eet 96259 gao guenie b graves nunataks gra 95229 gra 06100 grosvenor mountains gro 95577 gro 03116 lapaz ice field lap 02342 lap 04720 meteorite hills met 00426 north west africa nwa 801 pecora escarpment pca 91082 queen alexandra range que 94603 que 99177 and yamato 793495 y 793495 three of the meteorites asuka 881595 a 881595 gra 98025 and met 01017 were found not to be cr chondrites the remaining samples concur petrographically and with the well established oxygen isotope mixing line for the cr chondrites their position along this mixing line is controlled both by the primary oxygen isotopic composition of their individual components and their relative degree of aqueous alteration combined with literature data and that of this study we recommend the slope for the cr mixing line to be 0 70 0 04 2 with a 17 o intercept of 2 23 0 14 2 thin sections of al rais shisr 033 renazzo and all but 3 samples analyzed for oxygen isotopes were studied petrographically the abundance of individual components is heterogeneous among the cr chondrites but feo poor chondrules and matrix are the most abundant constituents and therefore dominate the whole rock isotopic composition the potential accreted ice abundance physico chemical conditions of aqueous alteration e g temperature and composition of the fluid and its duration control the degree of alteration of individual cr chondrites combined with literature data we suggest that lap 02342 was exposed to lower temperature fluid during alteration than gra 95229 with only two falls terrestrial alteration of the cr chondrites complicates the interpretation of their whole rock isotopic composition particularly in the most aqueously altered samples and those with relatively higher matrix abundances we report that que 99177 is the isotopically lightest whole rock cr chondrite known 18 o 2 29 17 o 4 08 possibly due to isotopically light unaltered matrix which shows that the anhydrous component of the cr chondrites is isotopically lighter than previously thought although it experienced aqueous alteration que 99177 provides the best approximation of the pristine cr chondrite parent body s oxygen isotopic composition before aqueous alteration took place using this value as a new upper limit on the anhydrous component of the cr chondrites water rock ratios were recalculated and found to be higher than previously thought ratios now range from 0 281 to 1 157 we also find that according to their oxygen isotopes a large number of cr chondrites appear to be minimally aqueously altered although sample heterogeneity complicates this interpretation

oxygen isotope compositions of chondrules in cr chondrites abstract we report in situ ion microprobe analyses of oxygen isotopic compositions of olivine low ca pyroxene high ca pyroxene anorthitic plagioclase glassy mesostasis and spinel in five aluminum rich chondrules and nine ferromagnesian chondrules from the cr carbonaceous chondrites eet92042 gra95229 and mac87320 ferromagnesian chondrules are isotopically homogeneous within 2 in 17 o the interchondrule variations in 17 o range from 0 to 5 small oxygen isotopic heterogeneities found in two ferromagnesian chondrules are due to the presence of relict olivine grains in contrast two out of five aluminum rich chondrules are isotopically heterogeneous with 17 o values ranging from 6 to 15 and from 2 to 11 respectively this isotopic heterogeneity is due to the presence of 16 o enriched spinel and anorthite 17 o 10 to 15 which are relict phases of ca al rich inclusions cais incorporated into chondrule precursors and incompletely melted during chondrule formation these observations and the high abundance of relict cais in the aluminum rich chondrules suggest a close genetic relationship between these objects aluminum rich chondrules formed by melting of spinel anorthite pyroxene cais mixed with ferromagnesian precursors compositionally similar to magnesium rich type i chondrules the aluminum rich chondrules without relict cais have oxygen isotopic compositions 17 o 2 to 8 similar to those of ferromagnesian chondrules in contrast to the aluminum rich chondrules from ordinary chondrites those from crs plot on a three oxygen isotope diagram along the carbonaceous chondrite anhydrous mineral line and form a continuum with amoeboid olivine aggregates and cais from crs we conclude that oxygen isotope compositions of chondrules resulted from two processes homogenization of isotopically heterogeneous materials during chondrule melting and oxygen isotopic exchange between chondrule melt and 16 o poor nebular gas

oxygen isotopes in magnetite and fayalite in cv chondrites kaba and mokoia we report in situ measurements of o isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized cv chondrites kaba and mokoia in both meteorites the magnetite and the secondary olivine fayalite fa90 100 have o isotopic compositions near the terrestrial fractionation tf line the mean 17o 17o 0 52 18o value is about 1 in contrast the compositions of nearby primary chondrule low feo olivines fa1 2 are well below the tf line 17o values range from 3 to 9 krot et al 1998 summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting the compositions of magnetite and fayalite in kaba and mokoia imply that the o isotopic composition of the oxidant was near or somewhat above the tf line in mokoia the fayalite and magnetite differ in 18o by 20 whereas these same materials in kaba have virtually identical compositions the difference between mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water rich environment at low temperatures 300 k in contrast the similar compositions of these phases in kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment with the o coming entirely from the precursor magnetite and silica the 17o of the oxidant incorporated into the cv parent body as phyllosilicates or h2o appears to have been much 7 8 lower than that in that incorporated into the ll parent body choi et al 1998 which suggests that the o isotopic composition of the nebular gas was spatially or temporally variable

terrestrial weathering of antarctic stone meteorites formation of mg carbonates on ordinary chondrites abstract white efflorescences of weathering origin occur superposed on fusion crusts or along fractures in the interiors of approximately 5 of all meteorites in the us antarctic collection efflorescences from equilibrated ordinary chondrites consist of the hydrous mg carbonates nesquehonite hydromagnesite x ray diffraction and scanning electron microscope studies of efflorescences from lew 85320 h5 show abundant elongate prismatic crystals of nesquehonite idiomorphic not pseudomorphous after lansfordite with minor local encrustations of hydromagnesite abundances of na k ca and rb in efflorescences from lew 85320 suggest that the observed contents of these elements would require only modest fractionation of chondritic composition whereas extensive fractionation would be required to derive the observed cation ratios from terrestrial sea salts therefore cations in evaporite minerals on antarctic meteorites are most likely not products of contamination by terrestrial marine salts the mg in the efflorescences probably originated from weathering of meteoritic olivine other cations in the efflorescences are also of meteoritic provenance thermodynamic analysis of the reaction forsterite water carbon dioxide nesquehonite silica at antarctic temperatures and pco 2 indicates spontaneity for all water activities greater than 0 65 compatible with the presence of liquid water as brines and or thin films

the formation and alteration of the renazzo like carbonaceous chondrites ii linking o isotope composition and oxidation state of chondrule olivine abstract to better understand the formation conditions of type i and type ii chondrules in the renazzo like carbonaceous cr chondrites an in situ major and minor element and o isotope study was conducted twenty one ferromagnesian chondrules from three cr chondrites gra 95229 gra 06100 and que 99177 were analyzed to establish an internally consistent data set from this study we infer that type ii chondrule precursors contained enhanced s bearing dust and ice abundances relative to type i chondrules there is a relationship between the o isotope composition and oxidation state of olivine which may be related to the amount of 16 o poor ice and reduced carbon accreted by chondrule precursors before melting type ii chondrules formed under h 2 o h 2 ratios of 230 740 times solar in contrast type i chondrules formed under more reducing conditions with lower h 2 o h 2 ratios of 10 100 times solar we find a relationship between type ii chondrule petrology relict free vs relict grain bearing and o isotope composition which is due to degree of melting and exchange with a 16 o poor gas reservoir the 16 o poor gas that interacted with both type i and type ii chondrules is estimated to have an isotopic composition between 18 o g 13 27 and 17 o g 10 22 different from the o isotope composition of the water accreted by the cr chondrite parent body due to partial melting type i chondrules and relict grain bearing type ii chondrules exchanged with the 16 o poor gas to a lower degree than relict free type ii chondrules

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in acfer 094 carbonaceous chondrite abstract highly precise and accurate ion microprobe analyses of oxygen three isotope ratios in chondrules from the acfer 094 one of the most primitive carbonaceous chondrites show that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule forming regions of the solar nebula identical 17 o values in most minerals and glass within each chondrule indicate that the oxygen isotope ratio in chondrule melt did not change during or after crystallization nearly half of the chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same chondrule most chondrules in acfer 094 can be classified into two oxygen isotope groups 17 o 2 and 17 o 5 indicating that the final melting of chondrules occurred within two distinct oxygen isotope reservoirs probably representing the local protoplanetary disk immediately before planetesimal formation one of these reservoirs 17 o 2 is observed from chondrules in other carbonaceous chondrites and from crystalline silicates in comet wild 2 suggesting that crystalline silicates formed in an oxygen isotope reservoir of 17 o 2 were widely distributed in the outer asteroid belt and throughout the outer solar nebula oxygen three isotope ratios of minerals in chondrules from acfer 094 are distributed along a newly defined primitive chondrule minerals pcm line which has slope 1 17 o 0 987 0 013 18 o 2 70 0 11 and intersects the terrestrial fractionation line at 18 o 5 8 0 4 these data are distinct from and plot between the ccam and young and russell lines the pcm line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the earth

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

calculation of oxygen isotope fractionation in metal oxides abstract a theoretical model calculating the thermodynamic isotope factors of oxygen in metal oxides of geochemical interest is presented for temperatures between 0 and 1200 c on the basis of the modified increment method the following order of 18o enrichment is obtained cassiterite rutile magnetite ilmenite ulvospinel hematite uraninite chromite corundum spinel the results are expressed as 103 in a 106 t2 b 103 t c which compare well with existing theoretical experimental and empirical calibrations on quartz oxides and oxides water systems the present calculations enable not only estimation of the oxygen isotope composition of fluids from which the metal oxides were precipitated when independent temperature information is available but can also be applied as oxygen isotope geothermometers to igneous and metamorphic rocks

low frequency acoustic gravity waves from coseismic vertical deformation associated with the 2004 sumatra andaman earthquake mw 9 2 1 atmospheric pressure perturbations from the 2004 sumatra andaman earthquake mw 9 2 were observed by sensitive microbarographs at several global stations among these observations very low frequency acoustic gravity waves 1 4 2 8 mhz with a group velocity around 300 314 m s and amplitudes ranging between 1 and 12 pa can be clearly identified through data processing at four stations on the japanese islands and also at four international monitoring system ims stations around the indian ocean assuming several seismic source parameters for this great thrust earthquake we produce synthetic barograms using a realistic thermal structure in the atmosphere up to an altitude of 220 km for this modeling we incorporate the source dimensions in different zones the expanding velocity of the source region the vertical displacements of uplift and subsidence and their time constants combinations of these source parameters provide synthetic waveforms consistent with the general features of the observed low frequency records the results clearly indicate that the recorded waves may have been generated by large scale coseismic uplift and subsidence of the sea bottom and associated swelling and depression of the sea surface over the source region extending for 1500 km the uplift in the south central zone of the andaman nicobar regions may be substantially larger than in the other zones the time constant of the coseimic vertical deformation is found to be in the range of 1 0 1 5 min which may correspond to the time elapsed shortly before the generation of tsunami waves

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

progressive aqueous alteration of cm carbonaceous chondrites abstract cm chondrites are aqueously altered rocks that contain 9 wt h 2 o i e indigenous water bound in phyllosilicates also present are clumps of serpentine tochilinite intergrowths previously called poorly characterized phases or pcp pentlandite and ni bearing pyrrhotite we studied 11 cm chondrites that span the known range from least altered to most altered we used various petrologic properties many previously identified that provide information regarding the degree of aqueous alteration there are no known unaltered or slightly altered cm chondrites e g rocks containing numerous chondrules with primary igneous glass some cm properties result from processes associated with early and intermediate stages of the alteration sequence i e hydration of matrix alteration of chondrule glass and production of large pcp clumps other petrologic properties reflect processes active throughout the alteration sequence these include oxidation of metallic fe ni alteration of chondrule phenocrysts changes in pcp composition reflecting an increase in the phyllosilicate sulfide ratio and changes in carbonate mineralogy reflecting the development of dolomite and complex carbonates at the expense of ca carbonate on the basis of these parameters we propose a numerical alteration sequence for cm chondrites because there are no known cm samples that display only incipient alteration the least altered sample was arbitrarily assigned to subtype 2 6 the most altered cm chondrites currently classified cm1 are assigned to subtype 2 0 these highly altered rocks have essentially no mafic silicates they contain chondrule pseudomorphs composed mainly of phyllosilicate however their bulk compositions are cm like and they are closer in texture to other c2 chondrites than to ci1 chondrites which lack chondrule pseudomorphs using several diagnostic criteria we assigned petrologic subtypes 0 1 to every cm chondrite in our study que 97990 cm2 6 murchison cm2 5 kivesvaara cm2 5 murray cm2 4 2 5 y 791198 cm2 4 que 99355 cm2 3 nogoya cm2 2 cold bokkeveld cm2 2 que 93005 cm2 1 lap 02277 cm2 0 met 01070 cm2 0 the proposed cm numerical alteration sequence improves upon the existing scheme of browning et al 1996 in that it does not require a complicated algorithm applied to electron microprobe data to determine the average matrix phyllosilicate composition the new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values new neutron activation analyses of que 97990 que 93005 met 01070 murchison and crescent together with literature data confirm the compositional uniformity of the cm group different degrees of alteration among cm chondrites do not lead to resolvable bulk compositional differences this suggests that the textural differences among individual cm chondrites reflect progressive alteration of similar hypothetical cm3 0 starting materials in different regions of the same parent body with minimal aqueous transport of materials over appreciable e g meters distances

additional attenuation of natural vlf electromagnetic waves observed by the demeter spacecraft resulting from preseismic activity 1 we use vlf electromagnetic wave data measured by the demeter detection of electro magnetic emissions transmitted from earthquake regions satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity due to signals from lightning related to preseismic activity all the relevant data acquired by demeter during almost 6 5 years of the mission have been analyzed using a robust two step data processing schema this enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole demeter mission and to evaluate the statistical significance of the observed effects we confirm previously reported results of a small but statistically significant decrease of the wave intensity by 2 db at frequencies of about 1 7 khz the effect is observed for a few hours before the times of the main shocks it occurs during the night the effect is stronger between march and august at higher latitudes and for the positions of hypocenters below the sea we suggest an explanation based on changed properties of the lower boundary of the ionosphere which leads to a decrease of the intensity of lightning generated whistlers observed at the spacecraft altitude this effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the earth s surface prior to earthquakes

crystal orientation effects in δ18o for magnetite and hematite by sims abstract in situ high precision analysis of oxygen isotope ratios 18 o by secondary ion mass spectrometry sims reveals that instrumental bias in 18 o for magnetite varies due to crystal orientation effects multiple analyses of 18 o have an average precision of 0 4 2sd in single grains of magnetite close to 0 3 that obtained for multiple grains of uwq 1 a homogeneous quartz standard in contrast the average precision is five to ten times worse 2 3 2sd from grain to grain of magnetite due to variation in instrumental bias with crystal orientation electron backscatter diffraction shows that individual grains of magnetite are single crystals and that crystal orientation varies randomly from grain to grain the crystal orientation for each magnetite grain is plotted relative to the incident angle of the sims primary cs beam high values of 18 o are measured when the cs beam is parallel to uv 0 from 110 to 100 preferred channeling and focusing directions for magnetite routine 18 o analysis at wiscsims utilizes a gaussian focused cs primary beam deep pit mode at primary and secondary voltages of 10 kv and 10 kv respectively total impact energy 20 kev four analytical experiments were conducted in attempts to improve the grain to grain precision in measured 18 o for magnetite 1 applying an energy offset of 50 ev 2 using a kohler illuminated beam shallow pit mode 3 reducing the total impact energy and 4 varying the primary and secondary accelerating voltages the best results were obtained in experiment 4 at primary secondary accelerating voltages of 3 kv 10 kv respectively with an incident cs beam angle of 14 the grain to grain precision in measured 18 o for magnetite improves from 2 9 to 0 8 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 4 for both instrumental bias in 18 o also varies with crystal orientation for hematite at similar levels as is seen for magnetite the grain to grain precision in measured 18 o for hematite improves from 2 1 to 1 0 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 3 2sd for both importantly crystal orientation effects have not been identified at levels of 0 3 for 18 o in silicates or other minerals analyzed by wiscsims though many minerals remain to be examined

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

two mode long distance propagation of coseismic ionosphere disturbances 1 using gps total electron content tec measurements we analyzed ionosphere response to the great kurile earthquake of 4 october 1994 high spatial resolution of the japanese dense array of gps receivers geonet provided us the unique opportunity to observe the evolution of coseismic ionospheric disturbances cid which propagated for more than 1800 km away from the epicenter plotting a traveltime diagram for the cid and using an array processing technique within the approximation of a spherical cid wavefront we observed a phenomenon of cid separation into two modes and we found that characteristics of the cid depend on the distance from the epicenter the maximum of the cid amplitude was observed at 500 km from the epicenter within the first 600 700 km the cid propagation velocity was about 1 km s which is equal to the sound speed at the height of the ionospheric f layer starting from 600 to 700 km out from the epicenter the disturbance seems to divide into two separate perturbations with each propagating at a different velocity about 3 km s for the one and about 600 m s for the other apparently the tec response in the far field of the cid source is a mixture of signals that further splits into two modes because of the difference in their velocities our observations are in good agreement with the results of space time data processing in the approximation of a spherical wavefront of cid propagation

why is it so difficult to classify renazzo type cr carbonaceous chondrites implications from tem observations of matrices for the sequences of aqueous alteration abstract a number of different classifications have been proposed for the cr chondrites this study aims at reconciling these different schemes mineralogy based classification has proved particularly challenging for weakly to moderately altered crs because incipient mineral replacement and elemental mobilization arising from aqueous alteration only affected the most susceptible primary phases which are generally located in the matrix secondary matrix phases are extremely fine grained generally sub micron and heterogeneously mixed with primary nebular materials compositional and isotopic classification parameters are fraught with confounding factors such as terrestrial weathering impact processes and variable abundance of clasts from different regions of the cr parent body or from altogether different planetary bodies here detailed tem observations from eighteen fib sections retrieved from the matrices of nine antarctic cr chondrites eet 96259 gra 95229 gro 95577 gro 03116 lap 02342 lap 04516 lap 04720 mil 07525 and mil 090001 are presented representing a range of petrologic types amorphous fe mg silicates are found to be the dominant phase in all but the most altered cr chondrite matrices which still retain significant amounts of these amorphous materials amorphous fe mg silicates are mixed with phyllosilicates at the nanometer scale the ratio of amorphous fe mg silicates to phyllosilicates decreases as 1 the size of phyllosilicates 2 abundance of magnetite and 3 replacement of fe ni sulfides increase carbonates are only abundant in the most altered cr chondrite gro 95577 nanophase fe ni metal and tochilinite are present small abundances in most cr matrices based on the presence abundance and size of phyllosilicates with respect to amorphous fe mg silicates the sub micron features of cr chondrites have been linked to existing classification sequences and possible reasons for inconsistencies among classification schemes are discussed

low temperature aqueous alteration on the cr chondrite parent body implications from in situ oxygen isotope analyses the presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early solar system however the process of aqueous alteration is still poorly understood renazzo like carbonaceous cr chondrites are particularly well suited for the study of aqueous alteration samples range from being nearly anhydrous to fully altered essentially representing snapshots of the alteration process through time we studied oxygen isotopes in secondary minerals from six cr chondrites of varying hydration states to determine how aqueous fluid conditions including composition and temperature evolved on the parent body secondary minerals analyzed included calcite dolomite and magnetite the o isotope composition of calcites ranged from 18o 9 to 35 dolomites from 18o 23 to 27 and magnetites from 18o 18 to 5 calcite in less altered samples showed more evidence of fluid evolution compared to heavily altered samples likely reflecting lower water rock ratios most magnetite plotted on a single trend with the exception of grains from the extensively hydrated chondrite mil 090292 the mil 090292 magnetite diverges from this trend possibly indicating an anomalous origin for the meteorite if magnetite and calcite formed in equilibrium then the relative 18o fractionation between them can be used to extract the temperature of co precipitation isotopic fractionation in al rais carbonate magnetite assemblages revealed low precipitation temperatures 60 c assuming that the cr parent body experienced closed system alteration a similar exercise for parallel calcite and magnetite o isotope arrays yields global alteration temperatures of 55 to 88 c these secondary mineral arrays indicate that the o isotopic composition of the altering fluid evolved upon progressive alteration beginning near the al rais water composition of 17o 1 and 18o 10 and becoming increasingly 16o enriched toward a final fluid composition of 17o 1 2 and 18o 15

distribution of 26 al in the cr chondrite chondrule forming region of the protoplanetary disk we report on the mineralogy petrography and in situ measured oxygen and magnesium isotope compositions of eight porphyritic chondrules seven feo poor and one feo rich from the renazzo like carbonaceous cr chondrites graves nunataks 95229 grosvenor mountains 03116 pecora escarpment 91082 and queen alexandra range 99177 which experienced minor aqueous alteration and very mild thermal metamorphism we find no evidence that these processes modified the oxygen or al mg isotope systematics of chondrules in these meteorites olivine low ca pyroxene and plagioclase within an individual chondrule have similar o isotope compositions suggesting crystallization from isotopically uniform melts the only exceptions are relict grains in two of the chondrules these grains are 16o enriched relative to phenocrysts of the host chondrules only the feo rich chondrule shows a resolvable excesses of 26mg corresponding to an inferred initial 26al 27al ratio 26al 27al 0 of 2 5 1 6 10 6 2se combining these results with the previously reported al mg isotope systematics of cr chondrules nagashima et al 2014 geochem j 48 561 7 of 22 chondrules 32 measured show resolvable excesses of 26mg the presence of excess 26mg does not correlate with the feo content of chondrule silicates in contrast virtually all chondrules in weakly metamorphosed petrologic type 3 0 3 1 unequilibrated ordinary chondrites uocs ornans like carbonaceous co chondrites and the ungrouped carbonaceous chondrite acfer 094 show resolvable excesses of 26mg the inferred 26al 27al 0 in cr chondrules with resolvable excesses of 26mg range from 1 0 0 4 10 6 to 6 3 0 9 10 6 which is typically lower than 26al 27al 0 in the majority of chondrules from uocs cos and acfer 094 based on the inferred 26al 27al 0 three populations of cr chondrules are recognized the population characterized by low 26al 27al 0 4 0 0 3 0 5 ma after the formation of cais with the canonical 26al 27al ratio although rapid accretion after formation of the major population of cr chondrules is not required by our data

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

giant ionospheric disturbances excited by the m9 3 sumatra earthquake of 26 december 2004 1 an mw 9 3 earthquake originated in the indian ocean off the western coast of northern sumatra at 00 58 53 universal time ut on 26 december 2004 two giant ionospheric disturbances at 01 19 and 04 10 ut are observed by a network of digital doppler sounders in taiwan the first disturbance excited mainly by rayleigh waves which consists of a packet of short period doppler shift variations results in vertical ionospheric fluctuations with a maximum velocity of about 70 m s and displacement of about 200 m the second disturbance in a w shaped pulse propagating at a horizontal speed of 360 70 m s is attributable to coupling of the atmospheric gravity waves agw excited by broad crustal uplift together with the following big tsunami waves around the earthquake source zone the accompanying ionosonde data suggest that the agw in the atmosphere may have caused the ionosphere to move up and down by about 40 km

oxygen isotope constraints on the alteration temperatures of cm chondrites abstract we report a systematic oxygen isotopic survey of ca carbonates in nine different cm chondrites characterized by different degrees of alteration from the least altered known to date paris 2 7 2 8 to the most altered alh 88045 cm1 our data define a continuous trend that crosses the terrestrial fractionation line tfl with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk o isotopic compositions of cm chondrites this bulk matrix carbonate bmc trend does not correspond to a mass dependent fractionation i e slope 0 52 as it would be expected during fluid circulation along a temperature gradient it is instead a direct proxy of the degree of o isotopic equilibration between 17 18 o rich fluids and 16 o rich anhydrous minerals our o isotopic survey revealed that for a given cm no carbonate is in o isotopic equilibrium with its respective surrounding matrix this precludes direct calculation of the temperature of carbonate precipitation however the o isotopic compositions of alteration water in different cms inferred from isotopic mass balance calculation and direct measurements define another trend cmw for cm water parallel to bmc but with a different intercept the distance between the bmc and cmw trends is directly related to the temperature of cm alteration and corresponds to average carbonates and serpentine formation temperatures of 110 c and 75 c respectively however carbonate o isotopic variations around the bmc trend indicate that they formed at various temperatures ranging between 50 and 300 c with 50 of the carbonates studied here showing precipitation temperature higher than 100 c the average 17 o and the average carbonate precipitation temperature per chondrite are correlated revealing that all cms underwent similar maximum temperature peaks but that altered cms experienced protracted carbonate precipitation event s at lower temperatures than the least altered cms our data suggest that the 17 o value of ca carbonates could be a reliable proxy of the degree of alteration experienced by cm chondrites

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

observation of tsunami generated ionospheric signatures over hawaii caused by the 16 september 2015 illapel earthquake tsunamis generate internal gravity waves igws that propagate vertically into the atmosphere and can create detectable signatures in the ionosphere these signatures have consistently been observed in the presence of a tsunami for over a decade in the total electron content and for over five years in the 630 0 nm airglow here we show perturbations appearing in filtered gps derived total electron content tec and 630 0 nm airglow above hawaii during the passing of the tsunami induced by the 16 september 2015 earthquake in illapel chile we report measurements of igw parameters from both observation methodologies using a combination of prior methods and a newly developed method that uses a gabor filter bank a previously developed geometric model that takes into account the assumed posture of tsunami induced igws in the geomagnetic field and the observation geometry is shown to predict fairly well the expected location of the observation in the sky results of the gabor filtering technique are also compared to previously published results for the 11 march 2011 tohoku event an overall comparison between all of the tsunami induced signatures that have appeared in both the 630 0 nm airglow and tec above hawaii to date is provided

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

variations in the o isotope composition of gas during the formation of chondrules from the cr chondrites to better understand the environment of chondrule formation and constrain the o isotope composition of the ambient gas in the renazzo like carbonaceous cr chondrite chondrule forming region we studied the mineralogy petrology and in situ o isotope compositions of olivine in 11 barred olivine bo chondrules and pyroxene and silica in three type i porphyritic chondrules from the cr chondrites gao guenie b graves nunataks gra 95229 pecora escarpment pca 91082 and shisr 033 bo chondrules experienced a higher degree of melting than porphyritic chondrules and therefore it has been hypothesized that they more accurately recorded the o isotope composition of the gas in chondrule forming regions we studied the o isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas bo chondrules constitute 4 of the total cr chondrule population by volume on a three isotope oxygen diagram 17o vs 18o olivine phenocrysts in type i and type ii bo chondrules plot along slope 1 line with the exception of a type ii bo chondrule that plots along slope 0 5 line olivine phenocrysts in type i and type ii bo chondrules have similar but more restricted ranges of 17o values 3 8 to 1 3 and 0 8 to 1 4 respectively than those in type i and type ii porphyritic chondrules 4 6 to 0 3 and 1 8 to 0 9 respectively the observation that olivine grains in type i bo chondrules have similar chemical and o isotope compositions to those of olivine in their porphyritic counterparts argues against the hypothesis that olivine grains in type i porphyritic chondrules are xenocrysts and represent relict fragments of early formed planetesimals the compositional and o isotope data suggest that bo chondrules experienced more extensive but incomplete exchange with the ambient gas than porphyritic chondrules we suggest that cr chondrules formed from relatively 16o enriched solids in the presence of relatively 16o depleted gaseous h2o the o isotope compositions of chondrule olivine likely result from differences in the o isotope composition of both the chondrule precursors and the ambient gas during chondrule formation the inferred o isotope composition of this gas 17o ranges from 3 to 3 is inconsistent with a high abundance of water from the outer solar system which has been predicted to be isotopically heavy

extreme 18 o depletion in calcite and chert clasts from the elephant moraine on the east antarctic ice sheet two large morain es are presently forming near the margin of the east antarctic ice sheet west of victoria land where the flow of the ice sheet is disturbed by subglacial bedrock ridges of the transantarctic mountains fig 1 during the 1983 84 search for meteorites in this area several clasts composed of black acicular calcite crystals were collected from the elephant moraine 76 17 35 s and 157 20 05 e where they are ablating out of the ice1 3 additional samples of this calcite were later collected from the elephant moraine during the 1984 85 and 1986 87 field seasons but none were found at the reckling moraine at 76 15 s and 158 40 e4 6 the calcite clasts are strongly depleted in 18o 18o 20 5 0 4 with reference to standard mean ocean water smow and in 13c s13c 22 6 0 1 with reference to the pdb standard in addition to being enriched in radiogenic 87sr 87sr 86sr 0 71417 0 00002 relative to sea water these results suggest that the calcite precipitated from aqueous solutions discharged by hotsprings under the east antarctic ice sheet

aqueous alteration without a pronounced oxygen isotopic shift implications for the asteroidal processing of chondritic materials primitive meteorites exhibit certain features that are consistent with aqueous and thermal alteration on asteroids but o isotopic analyses show only a modest heavy isotope shift interpreted as indicating modification in the nebula to understand the isotopic effects of asteroidal alteration we take the l group ordinary chondrites weathered in antarctica as an analogue the data show that alteration is a two stage process with an initial phase producing only a negligible isotopic effect although surprising a possible explanation is found when we consider the alteration of terrestrial silicates numerous studies report pervasive development of channels a few to a few tens of nanometer wide in the incipient alteration of silicates we observe a similar texture alteration involves a restructuring of clay minerals along these narrow channels in which access of water is restricted the clay shows a topotactic relationship to the primary grain which suggests either epitaxial growth of the clay using the silicate as a substrate or inheritance of the original o structure by the clay our data suggests the latter with extensive inheritance of structural polymers by the weathering product the bulk o isotopic composition is comparatively unaffected this offers an explanation for the lack of an isotopic effect in the weathering of the l chondrites if substantial modification of chondritic materials may occur without a pronounced isotopic effect it also reconciles existing o analyses of cv chondrites with an asteroidal model of aqueous alteration

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

the formation and alteration of the renazzo like carbonaceous chondrites iii toward understanding the genesis of ferromagnesian chondrules to better understand the formation conditions of ferromagnesian chondrules from the renazzo like carbonaceous cr chondrites a systematic study of 210 chondrules from 15 cr chondrites was conducted the texture and composition of silicate and opaque minerals from each observed feo rich type ii chondrule and a representative number of feo poor type i chondrules were studied to build a substantial and self consistent data set the average abundances and standard deviations of cr2o3 in feo rich olivine phenocrysts are consistent with previous work that the cr chondrites are among the least thermally altered samples from the early solar system type ii chondrules from the cr chondrites formed under highly variable conditions e g precursor composition redox conditions cooling rate with each chondrule recording a distinct igneous history the opaque minerals within type ii chondrules are consistent with formation during chondrule melting and cooling starting as s and ni rich liquids at 988 1350 c then cooling to form monosulfide solid solution mss that crystallized around olivine pyroxene phenocrysts during cooling fe ni metal crystallized from the s and ni rich liquid and upon further cooling mss decomposed into pentlandite and pyrrhotite with pentlandite exsolving from mss at 400 600 c the composition texture and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration however some opaque minerals fe ni metal versus magnetite and panethite present in type ii chondrules are a proxy for the degree of whole rock aqueous alteration the texture and composition of sulfide bearing opaque minerals in graves nunataks 06100 and grosvenor mountains 03116 suggest that they are the most thermally altered cr chondrites

cm chondrites exhibit the complete petrologic range from type 2 to 1 we have characterized the most phyllosilicate rich members of the cm chondrite group based upon petrographic and compositional factors we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical cms the lack of anhydrous silicates cai and except as relicts chondrules merits the classification of type cmi for three meteorites eet 83334 alh 88045 and one kaidun lithology still other cms notably alh 83100 eet 90047 and yamato 82042 are clearly intermediate between types 1 and 2 brecciated cm chondrites like cold bokkeveld contain all of these varied lithologies the cm chondrites thus exhibit the complete petrologic range from 2 through 1 our results show that progressive aqueous alteration on the parent cm asteroid s was locally accompanied by significant increases in temperature to a peak of 450 c for the kaidun lithology fo2 and locally degree of chemical leaching all well beyond the conditions recorded by typical cm2s the most altered cms also are commonly deformed displaying a distinct lineation probably due to static rather than dynamic forces

atmospheric gravity waves due to the tohoku oki tsunami observed in the thermosphere by goce oceanic tsunami waves couple with atmospheric gravity waves as previously observed through ionospheric and airglow perturbations aerodynamic velocities and density variations are computed from gravity field and steady state ocean circulation explorer goce accelerometer and thruster data during tohoku oki tsunami propagation high frequency perturbations of these parameters are observed during three expected crossings of the tsunami generated gravity waves by the goce satellite from theoretical relations between air density and vertical and horizontal velocities inside the gravity wave we demonstrate that the measured perturbations are consistent with a gravity wave generated by the tsunami and provide a way to estimate the propagation azimuth of the gravity wave moreover because goce measurements can constrain the wave polarization a marker noted c3 of any gravity wave crossing by the goce satellite is constructed from correlation coefficients between the observed atmospheric state parameters these observations validate a new observation tool of thermospheric gravity waves generated by tsunamis above the open ocean

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

compositional evolution of the protoplanetary disk oxygen isotopes of type ii chondrules from cr2 chondrites chondrules are the dominant component of chondritic meteorites and attest to high temperature transient heating events within the protoplanetary disk they provide valuable constraint on the disk environments in which they formed and potentially the evolution of primitive planetary materials in the disk the oxygen isotopic composition of cr2 chondrite type ii chondrules was investigated our data show significant variation in the isotopic compositions of the chondrules with no petrographic or geochemical means to identify what chondrule will plot where on a three isotope diagram although we cannot rule out that these chondrules may have come from another chondrite forming region we argue in context of type i chondrules from cr2 chondrites that cr2 type ii chondrules record changes in solid and gas composition during formation due to the vaporization of icy bodies in localized regions of the inner disk

oxygen isotope and chemical compositions of magnetite and olivine in the anomalous ck3 watson 002 and ungrouped asuka 881595 carbonaceous chondrites effects of parent body metamorphism we report in situ o isotope and chemical compositions of magnetite and olivine in chondrules of the carbonaceous chondrites watson 002 anomalous ck3 and asuka a 881595 ungrouped c3 magnetite in watson 002 occurs as inclusion free subhedral grains and rounded inclusion bearing porous grains replacing fe ni metal in a 881595 magnetite is almost entirely inclusion free and coexists with ni rich sulfide and less abundant ni poor metal oxygen isotope compositions of chondrule olivine in both meteorites plot along carbonaceous chondrite anhydrous mineral ccam line with a slope of approximately 1 and show a range of 17o values from approximately 3 to 6 one chondrule from each sample was found to contain o isotopically heterogeneous olivine probably relict grains oxygen isotope compositions of magnetite in a 881595 plot along a mass dependent fractionation line with a slope of 0 5 and show a range of 17o values from 2 4 to 1 1 oxygen isotope compositions of magnetite in watson 002 cluster near the ccam line and a 17o value of 4 0 to 2 9 these observations indicate that magnetite and chondrule olivine are in o isotope disequilibrium and therefore not cogenetic we infer that magnetite in ck chondrites formed by the oxidation of pre existing metal grains by an aqueous fluid during parent body alteration in agreement with previous studies the differences in 17o values of magnetite between watson 002 and a 881595 can be attributed to their different thermal histories the former experienced a higher degree of thermal metamorphism that led to the o isotope exchange between magnetite and adjacent silicates

53 mn 53 cr radiometric dating of secondary carbonates in cr chondrites timescales for parent body aqueous alteration abstract we present 53mn 53cr ages of secondary carbonates in renazzo like cr chondrites determined by secondary ion mass spectrometry the timing of aqueous alteration in cr chondrites has been unconstrained in the literature we measured 53mn 53cr isotope systematics in carbonates from three different cr chondrite lithologies calcite in the interchondrule matrix of renazzo calcite in the matrix of gro 95577 and dolomite in a dark inclusion of renazzo all show excesses in 53cr interpreted as the daughter product from the decay of 53mn the renazzo calcite yields an initial ratio of 53mn 55mn 0 3 6 2 7 10 6 and the renazzo dark inclusion dolomite ranges from 53mn 55mn 0 3 1 1 4 10 6 corrected to the rsf of a calcite standard to 3 7 1 7 10 6 corrected to an inferred dolomite rsf when anchored to the d orbigny angrite the renazzo carbonates yield ages between 4563 6 and 4562 6 ma or 4 3 5 3 myr after the formation of cv cais calcite measured in the heavily altered specimen gro 95577 yields a shallower slope of 53mn 55mn 0 7 9 2 8 10 7 corresponding to a much younger age of 4555 4 ma or 12 6 myr after cai formation the two renazzo ages are contemporaneous with mn cr ages of carbonates in tagish lake ci and cm chondrites but the gro 95577 age is uniquely young these findings suggest that early aqueous alteration on chondritic parent bodies was a common occurrence likely driven by internal heating from 26al decay after accretion the young carbonate ages of gro 95577 suggest that either the cr parent body was sufficiently large to sustain heating from 26al for 8 myr or that late stage impact events supplied heat to the region where gro 95577 originated

evidence for low temperature growth of fayalite and hedenbergite in macalpine hills 88107 an ungrouped carbonaceous chondrite related to the cm co clan the carbonaceous chondrite macalpine hills mac 88107 has bulk composition and mineralogy that are intermediate between those of co and cm chondrites this meteorite experienced minor alteration and a low degree of thermal metamorphism petrologic type 3 1 and escaped post accretional brecciation the alteration resulted in the formation of fayalite fa90 100 al free hedenbergite fs50wo50 phyllosilicates saponite serpentine intergrowths magnetite and ni bearing sulfides pyrrhotite and pentlandite fayalite and hedenbergite typically occur as veins which start at the opaque nodules in the chondrule peripheries crosscut fine grained rims and either terminate at the boundaries with the neighboring fine grained rims or continue as layers between these rims these observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine grained rims fayalite also overgrows isolated forsteritic fa1 5 and fayalitic fa20 40 olivine grains without any evidence for fe mg interdiffusion it also replaces massive magnetite sulfide grains the initial 53mn 55mn ratio of 1 58 0 26 10 6 in the mac 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in allende of either 9 or 18 ma depending upon the value of the solar system initial abundance of 53mn used in age calculations formation of secondary fayalite and hedenbergite requires mobilization and transport of ca si and fe either through a high temperature gaseous phase hua and buseck 1995 or low temperature aqueous solution krot et al 1998a b the high temperature nebular model for the origin of fayalite hua and buseck 1995 fails to explain a formation of fayalite hedenbergite assemblages after accretion of fine grained rims that lack any evidence for high temperature processing b extreme fractionation of refractory lithophile elements of similar volatility ca and al in hedenbergite and c absence of fe mg interdiffusion along fayalite forsterite boundaries we conclude that fayalite and hedenbergite in mac 88107 formed during late stage low temperature approximately 150 200 c aqueous alteration the data for mac 88107 extend the evidence for an early onset of aqueous activity on chondrite parent bodies and reinforce the conclusion that liquid water played an important role in the chemical and mineralogical evolution of the first chondritic planetesimals

origin of magnetite in oxidized cv chondrites in situ measurement of oxygen isotope compositions of allende magnetite and olivine magnetite in the oxidized cv chondrite allende mainly occurs as spherical nodules in porphyritic olivine po chondrules where it is associated with ni rich metal and or sulfides to help constrain the origin of the magnetite we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in po chondrules of allende by an in situ ion microprobe technique five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18o values from 4 8 to 7 1 and delta 17o values from 2 9 to 6 3 seven coexisting olivine grains have oxygen isotopic compositions from 0 9 to 6 3 in delta 18o and from 4 6 to 7 9 in delta 17o the delta 17o values of the magnetite and coexisting olivine do not overlap they range from 0 4 to 2 6 and from 4 0 to 5 7 respectively thus the magnetite is not in isotopic equilibrium with the olivine in po chondrules implying that it formed after the chondrule formation the delta 17o of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas we infer that the magnetite formed on the parent asteroid by oxidation of metal by h2o which had previously experienced minor o isotope exchange with fine grained silicates

tsunamigenic ionospheric hole 1 traveling ionospheric disturbances generated by an epicentral ground sea surface motion ionospheric disturbances associated with rayleigh waves as well as post seismic 4 minute monoperiodic atmospheric resonances and other period atmospheric oscillations have been observed in large earthquakes in addition a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content tec in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area the tsunamigenic ionospheric hole detected by the tec measurement with global position system gps was found in the 2011 m9 0 off the pacific coast of tohoku the 2010 m8 8 chile and the 2004 m9 1 sumatra earthquakes this occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter scale downwelling of sea surface at the tsunami source area and is highly depleted due to the chemical processes

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

climate and rock weathering a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions abstract ordinary chondrites oc recovered from the desert areas of roosevelt county new mexico the nullarbor region of western australia and the algerian and libyan sahara for which 14c terrestrial ages have been determined were examined by 57fe mossbauer spectroscopy oc were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry normative mineralogy and isotopic composition define a known pre weathering starting composition given that terrestrial ages are known it is possible to compare initially very similar samples that have been subsequently weathered in a range of climatic regimes from the present day to 44 ka bp in addition recently fallen equilibrated oc contain iron only as fe0 and fe2 thus the abundance of ferric iron is directly related to the level of terrestrial weathering mossbauer spectroscopy identifies two broad types of ferric alteration paramagnetic phases akaganeite lepidocrocite and goethite and magnetically ordered principally magnetite and maghemite oc finds show a range in the percentage of total fe existing as fe3 from zero to over 80 however oxidation is comparable between fragments of the same oc separated since their time of fall i e paired meteorites our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site 1 saharan samples are overall less weathered than non saharan samples which may be related to the relatively recent age ca 20 ka of the saharan accumulation surface 2 broad differences between sites in the rate of weathering arising from regional differences in climate 3 consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides 4 one region the nullarbor that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of australia for the last 30 ka points 3 and 4 may be related to the identification of a rapid initial weathering phase the majority of weathering occurs in the first few hundred years after fall followed by passivation of weathering by porosity reduction porosity reduction and the associated restriction in the ability of water to penetrate the sample appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample

aqueous alteration of opaque assemblages in the ningqiang carbonaceous chondrite evidence from oxygen isotopes chondrules and matrix of the ningqiang carbonaceous chondrite contain numerous opaque assemblages oas these oas are mainly composed of ni rich metal magnetite sulfides phosphates with minor amounts of silicates and trace amounts of pt metal grains their mineral assemblage is very similar to that of oas found in allende refractory inclusions in this study we performed in situ analyses of o isotopic compositions of magnetite and whitlockite in oas and of olivine adjacent to oas from ningqiang o isotopic compositions of magnetite vary by 16 parts per thousand in 618 0 and fall on a regression line with a slope of 0 51 and a mean delta 17o of 2 9 0 3 1 sigma parts per thousand in the three o isotope diagram magnetite grains have consistently higher delta o 17 values than their adjacent olivine grains the mineral chemistry and o isotopic compositions of oas in ningqiang chondrules and matrix are most consistent with the formation of magnetites and whitlockite by aqueous alteration of preexisting metal alloys within a planetary body formation of magnetites and phosphates in oas thus do not constrain processes in the early solar nebula but rather provide information on metamorphism in a planetary environment c 2006 elsevier b v all rights reserved

organic thermometry for chondritic parent bodies abstract a unique spectroscopic feature has been identified in a study of twenty five different samples of meteoritic insoluble organic matter iom spanning multiple chemical classes groups and petrologic types using carbon x ray absorption near edge structure xanes spectroscopy the intensity of this feature a 1s exciton appears to provide a precise measure of parent body metamorphism the intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13c nmr experiments reveal that upon heating primitive iom is transformed into material that is indistinguishable from that in thermally processed chondrites including the development of the 1s exciton a thermo kinetic expression is derived from the experimental data that allows the intensity of the 1s exciton to be used to estimated the effective temperature integrated over time a good correlation is observed between the intensity of the 1s exciton and previously published microraman spectral data these data provide a self consistent organic derived temperature scale for the purpose of calibrating raman based thermometric expressions

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

terrestrial alteration of carbonate in a suite of antarctic cm chondrites evidence from oxygen and carbon isotopes the oxygen 18o 17o and carbon 13c fmod14c the fraction of modern 14c isotopic compositions of carbonate were measured for a set of paired antarctic cm chondrites eet 96006 eet 96016 eet 96017 and eet 96019 while the oxygen isotopic compositions do not plot on the terrestrial fractionation line and indicate that a component of the carbonate minerals has an extraterrestrial origin they also do not fall on the array defined for carbonates by cm falls and are thus consistent with the presence of a terrestrial carbonate component the 13c and fmod14c measurements of carbonate suggest the presence of at least two carbon sources carbonate derived from atmospheric co2 that is inferred to have been produced as a result of silicate weathering reactions and carbonate derived from another carbon source that is either old or non atmospheric the relationships between oxygen and carbon isotope data provide additional constraints on the weathering process and allow the possibility that rock dominated weathering of the meteorite caused the oxygen isotopic composition of antarctic water added to the meteorite to evolve away from the terrestrial mass fractionation array leading to formation of low temperature terrestrial alteration products that do not lie on the terrestrial fractionation line

mineralogy and oxygen isotope systematics of magnetite grains and a magnetite dolomite assemblage in hydrated fine grained antarctic micrometeorites

normal modes modelling of post seismic ionospheric oscillations since 1960 several experiments have shown strong perturbations of the ionosphere after earthquakes for the biggest quakes doppler ionospheric soundings have revealed displacements of several tens of meter of the ionized layers e and f an accurate modelling of these phenomena was however never described we present here synthetic displacements of such oscillations and compare it with experimental data realistic models of the atmosphere including viscosity are used as well as realistic earth and seismic source model these ionospheric oscillations are computed by normal modes summation taking explicitly into account the coupling between the solid earth and the open atmosphere they are associated to the rayleigh fundamental surface waves we obtain a good agreement between synthetics and observations so it should be possible to use this method to study the ionospheric post seismic perturbations and possibly the high altitude profile of the density and the viscosity of the atmosphere

the gro 95577 cr1 chondrite and hydration of the cr parent body we carried out a petrologic and instrumental neutron activation analysis inaa whole chondrite compositional study of grosvenor mountains gro 95577 gro 95577 has many petrological similarities to the cr chondrites although the inaa data show patterns indicative of terrestrial weathering some of the elemental abundances are consistent with a relationship to cr chondrites the oxygen isotopic composition of gro 95577 plots close to the renazzo cr chondrite on the three isotope diagram however gro 95577 is remarkable in that the chondrules are completely hydrated consisting almost entirely of phyllosilicates magnetite and sulfides although gro 95577 is completely hydrated the initial chondrule textures are perfectly preserved the chondrules are in sharp contact with the matrix their fine grained rims are clearly visible and the boundaries of the dark inclusions can be easily discerned many chondrules in gro 95577 have textures suggestive of type i chondrules but the phenocrysts have undergone perfect pseudomorphic replacement by yellow to brownish serpentine rich phyllosilicate with sharp original crystal outlines preserved the chondrule mesostasis is a green aluminous chlorite rich material most likely a hydration product of the feldspathic mesostasis commonly found in anhydrous type i chondrules some chondrules contain magnetite spheres most likely formed by oxidation of metal we propose that gro 95577 be classified as a cr1 chondrite making it the first known cr1 chondrite and expanding the range of alteration conditions on the cr parent body