evolution of protoplanetary disk inferred from 26 al chronology of individual chondrules abstract we review the 26al ages of chondrules in various type 3 0 chondrites the 26al ages of chondrules are 1 3 myr after calcium aluminum rich inclusion cai for ll3 0 co3 0 and acfer 094 ungrouped c 3 0 available data for chondrules in cr chondrites indicate that many chondrules are relatively younger 3 myr although data from chondrules in cr3 0 are not yet available to confirm their younger ages the total ranges for the 26al ages of chondrules in a single chondrite group are more than 0 5 1 myr however most chondrules show relatively narrow range of ages in a single chondrite group 0 2 0 4 myr 1 sd which might be short enough to preserve the group specific chemical and isotope signatures against radial diffusion of solid in the disk distinct oxygen isotope reservoirs might exist in the protoplanetary disk simultaneously which could be spatially separated

a systematic for oxygen isotopic variation in meteoritic chondrules primitive meteorites are characteristically formed from an aggregation of sub millimeter silicate spherules called chondrules chondrules are known to present large three isotope oxygen variations much larger than shown by any planetary body we show here that the systematic of these oxygen isotopic variations results from open system gas melt exchanges during the formation of chondrules a conclusion that has not been fully assessed up to now we have considered mg rich porphyritic chondrules and have modeled the oxygen isotopic effects that would result from high temperature interactions in the disk between precursor silicate dust and a gas enriched in sio during the partial melting and evaporation of this dust this formation process predicts i a range of oxygen isotopic composition for bulk chondrules in agreement with that observed in mg rich porphyritic chondrules and ii variable oxygen isotopic disequilibrium between chondrule pyroxene and olivine which can be used as a proxy of the dust enrichment in the chondrule forming region s such enrichments are expected during shock waves that produce transient evaporation of dust concentrated in the mid plane of the accretion disk or in the impact plumes generated during collisions between planetesimals according to the present model gas melt interactions under high psio gas left strong imprints on the major petrographic chemical and isotopic characteristics of mg rich porphyritic chondrules

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

a model for planetesimal meltdown by 26al and its implications for meteorite parent bodies the melting of planetesimals heated by 26 al has been modelled using a new finite difference method that incorporates convection as an example we consider a planetesimal with a radius of 64 km which accretes instantaneously at t 0 75 myr after the formation of calcium aluminum rich inclusions from cold 250 k nebular dust with 50 porosity at t 0 9 myr t 700 k the planetesimal shrinks to a radius of 50 km due to sintering at t 1 2 myr t 1425 k the fully insulated interior deeper than a few kilometers starts to melt and at t 1 5 myr t 1725 k with 50 melting convection starts by t 2 myr the planetesimal is a globe of molten convecting slurry inside a thin residual crust from about t 2 5 myr the crust thickens rapidly as the power of 26 al fades planetesimals probably melt in this manner when they accrete before t 1 3 myr and are large enough to insulate themselves r 20 km for accretion at t 0 rising to 80 km at t 1 3 myr melting behavior will also be affected by the level of 60 fe in nebular dust by the extent of devolatilization reactions and basalt segregation during heating and by gradual accretion the model suggests that a the parent bodies of differentiated meteorites had accreted before about t 1 5 to 2 myr and before most chondritic parent bodies had formed and b that molten planetesimals may be a source for chondrule melt droplets

analysis of the first gigantic jet recorded over continental north america 1 two low light cameras near marfa texas recorded a gigantic jet over northern mexico on 13 may 2005 at approximately 0423 50 utc assuming that the farthest of two candidate storm systems was its source the bright lower channel ended in a fork at around 50 59 km height with the very dim upper branches extended to 69 80 km altitude during the time window containing the jet extremely low frequency magnetic field recordings show that there was no fast charge moment change larger than 50 coulomb times kilometers c km but there was a larger and slower charge moment change of 520 c km over 70 ms the likely parent thunderstorm was a high precipitation supercell cluster containing a persistent mesocyclone with radar echo tops of at least 17 km however photogrammetric analysis suggests that the gigantic jet occurred over the forward flank downdraft region with echo tops of 14 km this part of the supercell may have had an inverted polarity charge configuration as evidenced by positive cloud to ground lightning flashes cg dominating over negative flashes cg while cgs occurred under the downwind anvil four minutes before the gigantic jet cg activity practically ceased in this area while cg rates increased culminating during the 20 s leading up to the gigantic jet with four national lightning detection network detected cgs a relative lull in lightning activity of both polarities was observed for up to 1 5 min after the gigantic jet the maturing storm subsequently produced 30 sprites between 0454 and 0820 utc some associated with extremely large impulse charge moment change values

high precision oxygen three isotope analyses of anhydrous chondritic interplanetary dust particles abstract oxygen three isotope ratios of three anhydrous chondritic interplanetary dust particles idps were analyzed using an ion microprobe with a 2 m small beam the three anhydrous idps show 17o values ranging from 5 to 1 which overlap with those of ferromagnesian silicate particles from comet wild 2 and anhydrous porous idps for the first time internal oxygen isotope heterogeneity was resolved in two idps at the level of a few per mil in 17o values anhydrous idps are loose aggregates of fine grained silicates 3 m in this study with only a few coarse grained silicates 2 20 m in this study on the other hand wild 2 particles analyzed so far show relatively coarse grained few m igneous textures if anhydrous idps represent fine grained particles from comets the similar 17o values between anhydrous idps and wild 2 particles may imply that oxygen isotope ratios in cometary crystalline silicates are similar independent of crystal sizes and their textures the range of 17o values of the three anhydrous idps overlaps also with that of chondrules in carbonaceous chondrites suggesting a genetic link between cometary dust particles wild 2 particles and most anhydrous idps and carbonaceous chondrite chondrules

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

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

refractory forsterite in primitive meteorites condensates from the solar nebula all groups of chondritic meteorites contain discrete grains of forsteritic olivine with feo contents below 1 wt and high concentrations of refractory elements such as ca al and ti ten such grains 52 to 754 g with minor amounts of adhering matrix were separated from the allende meteorite after bulk chemical analysis by instrumental neutron activation analysis inaa some samples were analyzed with an electron microprobe and some with an ion microprobe matrix that accreted to the forsterite grains has a well defined unique composition different from average allende matrix in having higher cr and lower ni and co contents which implies limited mixing of allende matrix all samples have approximately chondritic relative abundances of refractory elements ca al sc and rare earth elements ree although some of these elements such as al do not quantitatively reside in forsterite whereas others e g ca are intrinsic to forsterite the chondritic refractory element ratios in bulk samples the generally high abundance level of refractory elements and the presence of ca al ti rich glass inclusions suggest a genetic relationship of refractory condensates with forsteritic olivine the ca al ti rich glasses may have acted as nuclei for forsterite condensation arguments are presented that exclude an origin of refractory forsterite by crystallization from melts with compositions characteristic of allende chondrules a all forsterite grains have cao contents between 0 5 and 0 7 wt with no apparent zoning requiring voluminous parental melts with 18 to 20 wt cao far above the average cao content of allende chondrules similar arguments apply to al contents b the low feo content of refractory forsterite of 0 2 0 4 wt imposes an upper limit of 1 wt of feo on the parental melt too low for ordinary and carbonaceous chondrule melts c the mn contents of refractory forsterites are between 30 to 40 ppm this is at least one order of magnitude below the mn content of chondrule olivines in all classes of meteorites the observed mn contents of refractory forsterite are much too low for equilibrium between olivine and melts of chondrule composition d as shown earlier refractory forsterites have o isotopic compositions different from chondrules weinbruch et al 1993a refractory olivines in carbonaceous chondrites are found in matrix and in chondrules the compositional similarity of both types was taken to indicate that all refractory forsterites formed inside chondrules e g jones 1992 as refractory forsterite cannot have formed by crystallization from chondrule melts we conclude that refractory forsterite from chondrules are relic grains that survived chondrule melting and probably formed in the same way as refractory forsterite enclosed in matrix we favor an origin of refractory forsterite by condensation from an oxidized nebular gas

direct detection of projectile relics from the end of the lunar basin forming epoch the lunar surface a key proxy for the early earth contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the earth moon system in ancient 3 4 billion years ago ga regolith breccias from the apollo 16 landing site we located mineral and lithologic relics of magnesian chondrules from chondritic impactors these ancient impactor fragments are not nearly as diverse as those found in younger 3 4 ga to today regolith breccias and soils from the moon or that presently fall as meteorites to earth this suggests that primitive chondritic asteroids originating from a similar source region were common earth moon crossing impactors during the latter stages of the basin forming epoch

on the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite alha77307 abstract the origin of isolated olivine grains in carbonaceous chondrites has been suggested to be either by direct condensation or by fragmentation of chondrules in an attempt to resolve this debate isolated olivine grains in the carbonaceous chondrite alha77307 have been studied in detail zoning characteristics and minor element compositions of olivines from all isolated and chondrule occurrences are described the data show that a strong relationship exists between isolated olivines and the chondrule population chondrule olivine compositions and zoning properties are consistent with olivine crystallization from the molten chondrules because properties of isolated grains are very similar to chondrule olivines an igneous origin for most if not all isolated grains is proposed large isolated forsterite grains may be derived from fragmentation of macroporphyritic type i chondrules which contain one or very few large olivine grains relic forsterite grains in type ii chondrules and complex isolated olivine grains with forsteritic cores and fayalite rich rims provide evidence that fragmentation and recycling of chondrules and their components was a common and efficient process in the chondrule forming region

coordinated observations of sprites and in cloud lightning flash structure 1 the temporal and spatial development of sprite producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system mcs on 29 june 2011 near the oklahoma lightning mapping array lma sprites produced by a total of 26 lightning flashes were observed simultaneously on video from bennett colorado and hawley texas enabling a triangulation of sprites in comparison with temporal development of parent lightning in particular negatively charged stepped leaders in three dimensional space in general prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced typically 30 km however both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant lma sources with affinity to negative stepped leaders during the prior 100 ms interval multiple sprites appearing as dancing jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash by a single stroke through a series of current surges superposed on an intense continuing current or by both our observations imply that sprites elongated in one direction are sometimes linked to in cloud leader structure with the same elongation and sprites that were more symmetric were produced above the progression of multiple negative leaders this suggests that the large scale structure of sprites could be affected by the in cloud geometry of positive charge removal based on an expanded dataset of 39 sprite parent flashes by including more sprites recorded by one single camera over the same mcs the altitude above mean sea level msl of positively charged cloud region tapped by sprite producing strokes declined gradually from 10 km msl 35 c to around 6 km msl 10 c as the mcs evolved through the mature stage on average the positive charge removal by causative strokes of sprites observed on 29 june is centered at 3 6 km above the freezing level or at 7 9 km above ground level

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

grain growth in partially molten olivine aggregates grain growth rates in partially molten olivine aggregates were determined experimentally at a pressure of 1 gpa the aim of the experiments with fine grained starting material solution gelation derived fo90 olivine with a grain size of 1 m with 2 and 4 wt added basaltic glass was to determine growth rates during steady state grain growth a series of experiments was conducted at a fixed temperature of 1 350 c for durations from 2 to 700 h and a second series at fixed duration 168 h at temperatures from 1 250 to 1 450 c the resulting activation energy e 390 kj mol and growth exponent n 4 3 are comparable to melt free results nichols and mackwell 1991 the observed grain size distributions are broader than those predicted for normal grain growth or ostwald ripening and most similar to the log normal distribution the observed melt distribution is influenced by the continuous rearrangement of neighboring grains during growth the relatively large growth exponent observed in this study and by nichols and mackwell 1991 where secondary phases are present suggests that grain growth in the upper mantle is slower than predicted by karato 1989

relict olivine chondrule recycling and the evolution of nebular oxygen reservoirs chondrules often contain relict olivine grains that did not crystallize in situ providing opportunities to decipher how chondrule components evolved we studied olivine in the sahara 97210 ll3 2 wells ll3 3 and chainpur ll3 4 chondrites using sem empa and sims techniques oxygen isotopes were analyzed in 16 objects from all three meteorites and trace elements were analyzed in sahara 97210 and chainpur two groups of olivine are identified based on oxygen isotope compositions one group is enriched in 16 o 17 o 8t o 4 and falls close to the ccam mixing line it includes forsterite and mg rich olivine present as relict grains in type ii ferrous chondrules and the forsteritic cores of some isolated grains these low 17 o grains are poor in mno 0 2 wt and are usually enriched in cao 0 3 0 65 wt the other group is less enriched in 16 o 17 o 3t o 4 it includes normal non relict ferrous olivine in type ii chondrules normal non relict mg rich olivine in type i magnesian chondrules dusty olivine relict grains in type i chondrules and mg rich olivine relicts in a type ii and a type i chondrule these high 17 o grains have variable cao 0 0 95 wt and mno 0 0 45 wt contents with the more calcic and mn poor compositions associated with forsteritic olivine trace element data show that forsteritic olivine grains in both oxygen groups are similarly enriched in refractory elements al sc y ca ti v and depleted in volatile elements cr mn p rb sometimes k and na compared to normal ferrous olivine suggesting that variations in chemical composition reflect the extent of thermal processing greater for magnesian olivine the data are consistent with a model in which nebular reservoirs became less enriched in 16 o with time an earlier episode of chondrule formation produced type i chondrules and isolated forsterites in carbonaceous chondrites and forsteritic grains that were incorporated into ordinary chondrites as relict grains in chondrules and as isolated grains later episodes of chondrule formation produced both type i and type ii chondrules in ordinary chondrites under a variety of thermal and redox conditions 2007 elsevier b v all rights reserved

relationships between type i and type ii chondrules implications on chondrule formation processes in unequilibrated chondrites the ferromagnesian silicates in chondrules exhibit wide ranges of mg mg mg fe allowing to sub divide porphyritic chondrules into either type i mg 0 9 or type ii mg 0 9 although both chondrule types formed under oxidizing conditions relative to the canonical solar nebula it is generally inferred that type ii chondrules formed in more oxidizing conditions than type i in order to check whether this redox difference was established during chondrule formation or reflects differences in their precursors we have undertaken a set of experiments aimed at heating type i olivine rich a chondrule proxy i e forsterite fe metal ca mg si al glass mixtures under oxidizing conditions we show that high temperature isothermal oxidation of type ia like assemblages is a very efficient and rapid process e g few tens of minutes to form textures similar to type iia chondrules due to the rapid dissolution of fe metal blebs a feo increase in the melt and in combination with the dissolution of magnesian olivine allows the melt to reach ferroan olivine saturation crystallization of ferroan olivine occurs either as new crystal in the mesostasis or as overgrowths on the remaining unresorbed forsterite grains relicts interruption of this process at any time before its completion by rapid cooling allows to reproduce the whole range of textures and chemical diversity observed in type a chondrules i e from type i to type ii several implications on chondrule formation processes can be inferred from the presented experiments type i chondrules or fragments of type i chondrules are very likely the main precursor material involved in the formation of most type ii chondrules formation of porphyritic olivine type ii chondrules is very likely the result of processes generating crystal growth by chemical disequilibrium at high temperature rather than processes generating crystallization only by cooling rates this questions the reliability of chondrule thermal history e g cooling rate values hitherto inferred for producing porphyritic textures from dynamical cooling rate experiments only type a chondrule formation can be a very fast process after periods of sub isothermal heating or slow cooling 103 104 k h in order to preserve their glassy mesostasis such inferred thermal history being at odds with nebular shock models we thus advocate that impacts on planetesimals causing rapid melting and vaporization may provide the high density and highly volatile enriched gaseous environments required to form chondrules in this scenario chondrules and their diversity should result from various degrees of interaction of the ejected fragments with the impact vapor plume the most oxidizing conditions recorded in type iia chondrules being very likely the closest to those imposed by the impact vapor plume

three years of lightning impulse charge moment change measurements in the united states 1 we report and analyze 3 years of lightning impulse charge moment change icmc measurements obtained from an automated real time lightning charge moment change network cmcn the cmcn combines u s national lightning detection network nldn lightning event geolocations with extremely low frequency 1 khz data from two stations to provide icmc measurements across the entire united states almost 14 million lightning events were measured in the 3 year period we present the statistical distributions of icmc versus polarity and nldn measured peak current including corrections for the detection efficiency of the cmcn versus peak current we find a broad distribution of icmc for a given peak current implying that these parameters are at best only weakly correlated curiously the mean icmc does not monotonically increase with peak current and in fact drops for positive cg strokes above 150 ka for all positive strokes there is a boundary near 20 c km that separates seemingly distinct populations of high and low icmc strokes we also explore the geographic distribution of high icmc lightning strokes high icmc positive strokes occur predominantly in the northern midwest portion of the u s with a secondary peak over the gulf stream region just off the u s east coast high icmc negative strokes are also clustered in the midwest although somewhat south of most of the high icmc positive strokes this is a region far from the locations of maximum occurrence of high peak current negative strokes based on assumed icmc thresholds for sprite production we estimate that approximately 35 000 positive polarity and 350 negative polarity sprites occur per year over the u s land and near coastal areas among other applications this network is useful for the nowcasting of sprite producing storms and storm regions

ph control on oxygen isotopic composition of symbiotic corals abstract boron carbon and oxygen isotopic compositions were determined at the micrometre scale by high resolution ion microprobe in a sample of modern coral massive hermatypic coral porites lutea the ion probe data show for b and o much larger isotopic variations at the micrometre scale than those measured at the millimetre scale by conventional techniques 18opdb values range from 10 6 0 9 to 0 2 0 5 and 11b values range from 18 6 1 5 to 30 6 1 6 by contrast 13c values show the same range of variations from 4 6 0 65 to 2 2 0 67 at the micrometre and millimetre scales the range of 11b values indicates that significant ph variations from 7 1 to 9 0 are present at the sites of calcification the largest 18o variations correspond to the highest 11b values i e to the highest phs this measurement of ph allows modelling the oxygen isotopic fractionation occurring during aragonite precipitation taking into account the rate of o isotopic equilibrium between dissolved carbonate species h2co3 hco3 and co32 and water via the two reactions of hydration and hydroxylation the full range of 18o values measured at the micrometre scale can be modelled for residence times of dissolved carbonates in the calcifying fluid ranging between 1 h and at maximum 12 h the ph controls the 18o of the growing carbonate through the relative fractions of dissolved carbonate species and through the kinetics of their isotopic equilibration with water via hydration and hydroxylation the so called vital effect systematically observed for 18o in corals can thus be understood as representing an average of rapid ph variations due to coral biology during coral growth selectively measuring 18o values in the zones of coral skeletons that have low 11b values i e formed at low ph should significantly improve the quality of palaeoclimatic reconstructions based on 18o values

global distributions and occurrence rates of transient luminous events 1 we report the global transient luminous event tle distributions and rates based on the imager of sprites and upper atmospheric lightning isual experiment onboard the formosat 2 satellite isual observations cover 45 s to 25 n latitude during the northern summer and 25 s to 45 n latitude during the northern winter from july 2004 to june 2007 isual recorded 5 434 elves 633 sprites 657 halos and 13 gigantic jets surprisingly elve is the dominant type of tles while sprites halos are a distant second elve occurrence rate jumps as the sea surface temperature exceeds 26 degrees celsius manifesting an ocean atmosphere ionosphere coupling in the isual survey elves concentrate over the caribbean sea south china sea east indian ocean central pacific ocean west atlantic ocean and southwest pacific ocean while sprites congregate over central africa japan sea and west atlantic ocean the isual experiment observed global rates of 3 23 0 50 0 39 and 0 01 events per minute for elves sprites halos and gigantic jets respectively taking the instrumental detection sensitivity and the restricted survey area into account the corrected global occurrence rates for sprites and elves likely are a factor of two and an order of magnitude higher respectively isual observations also indicate that the relative frequency of high peak current lightning 80 ka is 10 times higher over the oceans than over the land on the basis of the corrected isual elve global occurrence rate the total electron content at the lower ionosphere above elve hot zones was computed to be elevated by more than 5

formation of unequilibrated r chondrite chondrules and opaque phases abstract sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules these assemblages are widely hypothesized to form through pre accretionary corrosion of metal by h2s gas or through parent body processes we report here on two unequilibrated r chondrite samples that contain large chondrule sized sulfide nodules in the matrix both samples are from mount prestrud pre 95404 chemical maps and spot and broad beam electron microprobe analyses empa were used to assess the distribution stoichiometry and bulk composition of sulfide nodules and silicate chondrules in the clasts oxygen isotope data were collected via secondary ion mass spectrometry sims to assess the relationship of chondrules to other chondrite groups scanning electron microscopy sem focused ion beam fib and transmission electron microscopy tem analyses were used to assess fine scale features and identify crystal structures in sulfide assemblages thermodynamic models were used to assess the temperature sulfur fugacity fs2 total pressure dust to gas ratio and oxygen fugacity fo2 conditions during sulfide nodule and chondrule formation the unequilibrated clasts include a mixture of type i and type ii chondrules as well as non porphyritic chondrules chondrule oxygen isotopes overlap with ordinary chondrite chondrules sulfide nodules average 200 m in diameter have rounded shapes and are primarily composed of pyrrhotite pentlandite and magnetite some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules both nodules and sulfides in chondrules include phosphate inclusions and cu rich lamellae which suggests a genetic relationship between sulfides in chondrules and in the matrix ni co ratios for matrix and chondrule sulfides are solar while fe and ni are non solar and inversely related we hypothesize that sulfide nodules formed via pre accretionary melt processes during chondrule formation precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets which separated and cooled to form si rich chondrules and s rich nodules sulfide melt was stabilized by a high total pressure 1 atm in a dust or ice enriched environment heating of this material contributed to a high fs2 2 10 3 atm at 1138 c and high fo2 iw 1 to iw 4 in an environment with peak temperatures between 1539 c and 1750 c oxygen isotopic compositions in this region were similar to those recorded by the ll chondrite chondrules

multiple rind structure in pillow lava as an indicator of shallow water multiple rind structure is common among shallow water pillows with diameters larger than about 1 m in oamaru new zealand on the columbia plateau usa and elsewhere a rind consists of sideromelane tachylyte and tachylytic basalt a multiple rind is a concentric set of repeated rinds in various forms e g a portion of a broken rind thrust under another part a series of short and detached subparallel rinds or a pouch shaped depression transitions and combinations of these three forms are common multiple rind structure develops at any part of the pillow perimeter but does not cover the pillow completely it is always accompanied by a rupture in the outermost rind up to 13 rinds have been observed but two to four rinds are most common the multiple rind structure is formed by implosion resulting from condensation of exsolved h2o when h2o condenses a pressure difference between the interior and exterior of a pillow is created above a certain threshold pressure difference the outer skin of a pillow is torn at weak points such as radial joints and thrusts under the neighboring skin buckles to form a pouch shaped depression or produces some variation of these one set of multiple rinds is thus formed further exsolution and condensation of h2o in solidifying pillows may cause development of additional rinds h2o exsolution and condensation and subsequent implosion are limited to low pressure environments so that multiple rind structure is characteristic of shallow water pillow lava

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

granoblastic olivine aggregates in magnesian chondrules planetesimal fragments or thermally annealed solar nebula condensates abstract granoblastic olivine aggregates goa have been discovered in some type i magnesian chondrules within carbonaceous chondrites by libourel and krot libourel g krot a n 2007 evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin earth planet sci lett 254 1 8 who proposed an origin from pre existing planetesimals amoeboid olivine aggregates aoa generally considered as aggregates of solar nebula condensates and found within similar carbonaceous chondrites display similar equilibrium texture though on a finer scale for these reasons we conducted experiments to determine if annealing of olivine required time scales appropriate to planetesimal or nebular heating pressed 88 4 was isothermally heated at temperatures ranging from 1350 1550 c for 1 100 h the 100 h runs yield olivine aggregates with well developed granoblastic texture at all temperatures manifest as a network of randomly oriented and sutured olivine grains with 120 triple junctions individual olivine grains are 4 6 sided and polygonal by 1450 c and equigranular texture is developed at high temperature 1500 1550 c melting of olivine commences at 1450 1500 c and aids in ripening and suturing grain coarsening and grain boundary migration textural equilibrium is clearly met at 1550 c a planetesimal origin cannot be ruled out however the experimental evidence reveals that granoblastic texture can be reproduced in an interval not inconsistent with heating times for nebular objects goa may have experienced higher degrees of thermal processing than the finer grained aoa if the precursors were the same grain coarsening would have to be accompanied by modification to bulk and isotopic compositions however the precursors could have been olivine condensates formed later than aoa annealing may have been a widespread process operating in the primordial solar nebula responsible for thermal processing and formation of goa prior to their incorporation into chondrules

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

numerical simulations of the differentiation of accreting planetesimals with 26al and 60fe as the heat sources numerical simulations have been performed for the differentiation of planetesimals undergoing linear accretion growth with 26al and 60fe as the heat sources planetesimal accretion was started at chosen times up to 3 ma after ca al rich inclusions cais were formed and was continued for periods of 0 001 1 ma the planetesimals were initially porous unconsolidated bodies at 250 k but became sintered at around 700 k ending up as compact bodies whose final radii were 20 50 100 or 270 km with further heating the planetesimals underwent melting and igneous differentiation two approaches to core segregation were tried in the first labelled a the core grew gradually before silicate began to melt and in the second labelled b the core segregated once the silicate had become 40 molten in a when the silicate had become 20 molten the basaltic melt fraction began migrating upward to the surface carrying 26al with it the 60fe partitioned between core and mantle the results show that the rate and timing of core and crust formation depend mainly on the time after cais when planetesimal accretion started they imply significant melting where accretion was complete before 2 ma and a little melting in the deep interiors of planetesimals that accreted as late as 3 ma the latest melting would have occurred at 10 ma the effect on core and crust formation of the planetesimals final size the duration of accretion and the choice of 60fe 56fe initial were also found to be important particularly where accretion was late the results are consistent with the isotopic ages of differentiated meteorites and they suggest that the accretion of chondritic parent bodies began more than 2 or 3 ma after cais

emplacement of pillow lavas from the 2 8 ga chitradurga greenstone belt south india a physical volcanological morphometric and geochemical perspective abstract the physical volcanology and morphometric analyses of pillowed lava flows from the chitradurga basin of chitradurga greenstone belt south india have been undertaken in the chitradurga hills individual pillowed flows alternate with massive submarine sheet flows the pillows from such flows are separated by chert and occur as spheroidal elongated or reniform units that are devoid of vesicles vesicle bands or pipe vesicles the mardihalli flow is exposed as a small elongated mound in the basin and consists of a massive core that is draped by pillows along the flow crest and flanks the pillows from mardihalli occur as spheroidal to elongate units with smooth spalled or wrinkled surfaces with vesicular interiors repeated budding of larger pillows have produced a series of interconnected pillow units indicating fluid lava that was emplaced on steeply dipping flanks based on the morphological features the pillowed flows from the chitradurga basin were emplaced at low effusion rates 5 m3 s pillows in these flows formed from low viscosity lavas that underwent negligible to moderate inflation due to rapid chilling sporadic occurrences of pillow breccias hyaloclastite and chert breccias in the pillowed flow fields indicate disruption of pillows due to lava surges and slumping it is envisaged that the chitradurga basin witnessed distinct episodes of submarine tholeiite eruptions that produced pillowed lavas that variably interacted with sea water to produce geochemistries the field and stratigraphic relationships of the volcanics and associated clastic sediments suggest that the pillow lavas were emplaced in a shallow marine marginal inter back arc basin

outward migration of chondrule fragments in the early solar system o isotopic evidence for rocky material crossing the jupiter gap abstract determining the origins of chondrule precursors is key to constraining how material migrated in the early solar system chondrules that were only partially melted during their formation retain portions of their solid precursors termed relict grains by measuring the chemical and o isotopic compositions of relict grains in chondrules from an unequilibrated ordinary chondrite uoc and renazzo like carbonaceous cr and mighei like carbonaceous cm chondrites we constrain their origins and discuss implications for disk transport within the first 4 million years of the solar system for all three chondrite groups the chemical and o isotopic compositions of dusty olivine grains are sometimes consistent with the reduction of type i feo poor and or type ii feo rich chondrules from the same meteorite group however other dusty olivine grains from the cm chondrites and the uoc are found to be xenocrysts that require an origin from a source distinct from the host meteorite this material plausibly originated as fragments of earlier formed chondrules from another chondrite group or of partially or fully differentiated planetesimals that migrated into an active chondrule forming region multiple cm chondrite dusty olivine chondrules have o isotope compositions that match those of uoc chondrule olivine 17o 0 suggesting an origin from an uoc source this implies that uoc chondrules and or chondrule fragments migrated from the inner solar system outwards to cm chondrite chondrule forming region likely beyond the orbit of jupiter these uoc chondrules or chondrule fragments could have migrated outwards in the protoplanetary disk before the formation of the jupiter gap or

evidence for refilling of previously emptied basaltic pillows in the hooggenoeg complex barberton greenstone belt some large metabasaltic pillows in the uppermost part of the palaeoarchaean hooggenoeg complex in the barberton greenstone belt south africa exhibit flow banded margins and homogeneous cores that have a different texture and compositional variation the margins consist of millimetre to several centimetre thick alternating bands of pale green spherulitic and darker conspicuously variolitic varieties of non vesicular and aphyric metabasalt previously inferred to be due to mingling of two different types of lava the dark cores have sharp aphanitic contacts with the flow banded carapaces they lack flow banding have coarse grained interiors and exhibit well preserved primary textures with pseudomorphs after prismatic pyroxene set in a groundmass containing skeletal plagioclase the compositional range of samples from these cores is unlike that of the flow banded metabasalt but is similar to a 19 m thick lobate metabasalt flow 150 m stratigraphically further up at the local top of the hooggenoeg volcanic sequence the pillow cores are inferred to result from the later refilling of drained hollow pillows

oxygen isotope characteristics of chondrules from the yamato 82094 ungrouped carbonaceous chondrite further evidence for common o isotope environments sampled among carbonaceous chondrites high precision secondary ion mass spectrometry sims was employed to investigate oxygen three isotopes of phenocrysts in 35 chondrules from the yamato y 82094 ungrouped 3 2 carbonaceous chondrite twenty one of 21 chondrules have multiple homogeneous pyroxene data 17o 3sd analytical uncertainty 0 7 17 of 17 chondrules have multiple homogeneous pyroxene and plagioclase data twenty one of 25 chondrules have one or more olivine data matching coexisting pyroxene data such homogeneous phenocrysts 1 are interpreted to have crystallized from the final chondrule melt defining host o isotope ratios and 2 suggest efficient o isotope exchange between ambient gas and chondrule melt during formation host values plot within 0 7 of the primitive chondrule mineral pcm line seventeen chondrules have relict olivine and or spinel with some 17o and 18o values approaching 40 similar to cai or aoa like precursors regarding host chondrule data 22 of 34 have mg s of 98 8 99 5 and 17o of 3 9 to 6 1 consistent with most acfer 094 co cr and cv chondrite chondrules and suggesting a common reduced o isotope reservoir devoid of 16o poor h2o six y 82094 chondrules have 17o near 2 5 with mg s of 64 97 consistent with lower mg chondrules from acfer 094 co cr and cv chondrites their signatures suggest precursors consisting of those forming mg 99 17o 5 1 chondrules plus 16o poor h2o at high dust enrichments three type ii chondrules plot slightly above the pcm line near the terrestrial fractionation line 17o 0 1 their o isotopes and olivine chemistry are like ll3 type ii chondrules suggesting they sampled ordinary chondrite like chondrule precursors finally three mg 99 chondrules have 17o of 6 7 to 8 1 potentially due to 16o rich refractory precursor components the predominance of mg 99 17o 5 1 chondrules and a high chondrule to matrix ratio suggests bulk y 82094 characteristics are closely related to anhydrous dust sampled by most carbonaceous chondrite chondrules

chondrules born in plasma simulation of gas grain interaction using plasma arcs with applications to chondrule and cosmic spherule formation we are investigating chondrule formation by nebular shock waves using hot plasma as an analog of the heated gas produced by a shock wave as it passes through the protoplanetary environment precursor material mainly silicates plus metal and sulfide was dropped through the plasma in a basic experimental set up designed to simulate gasgrain collisions in an unconstrained spatial environment i e no interaction with furnace walls during formation these experiments were undertaken in air at atmospheric pressure to act as a proof of principlecould chondrules or chondrule analog objects cao be formed by gasgrain interaction initiated by shock fronts our results showed that if accelerating material through a fixed plasma field is a valid simulation of a supersonic shock wave traveling through a cloud of gas and dust then cao certainly could be formed by this process melting of and mixing between starting materials occurred indicating temperatures of at least 1266 c the olivine feldspar eutectic the production of cao with mixed mineralogy from monomineralic starting materials also shows that collisions between particles are an important mechanism within the chondrule formation process such that dust aggregates are not necessarily required as chondrule precursors not surprisingly there were significant differences between the synthetic cao and natural chondrules presumably mainly because of the oxidizing conditions of the experiment results also show similarity to features of micrometeorites like cosmic spherules particularly the dendritic pattern of iron oxide crystallites produced on micrometeorites by oxidation during atmospheric entry and the formation of vesicles by evaporation of sulfides

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

partitioning of ca and al between forsterite and silicate melt in dynamic systems with implications for the origin of ca al rich forsterites in primitive meteorites we report the results of dynamic crystallization experiments that were specifically designed to study the dependence of ca and al partitioning between forsterite and melt in rapidly cooling ca and al rich melts the partitioning of ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1 5 to 1000 c hr and at cao contents of up to 25 wt within analytical uncertainty our data plot on the equilibrium partitioning curve obtained by libourel 1999 the partitioning behavior of al at high cooling rates is more complex aluminum is much more heterogenously distributed in the olivine and the co existing melt than ca but no systematic trend of al partition coefficient with cooling rate is observed we apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of ca and al although these forsterites are found frequently inside chondrules the ca contents of their host chondrules are far too low to crystallize these high ca forsterites this is also true for very rapid cooling of chondrule melts the parental melt of these forsterites requires cao contents above 20 wt

oxygen isotope systematics of chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs high precision oxygen three isotope measurements of olivine and pyroxene were performed on 33 chondrules in the yamato 81020 co3 0 chondrite by secondary ion mass spectrometry in chondrules where oxygen isotopes were measured in both olivine and pyroxene the majority of grains have similar values indicating co magmatic crystallization however many chondrules contain relict grains with unique oxygen isotope ratios a striking feature of yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios as those with mg 97 phenocrysts range in 17o from 4 8 to 6 5 5 5 group and those with mg 96 36 phenocrysts have 17o values of 2 1 to 3 0 2 5 group a single mg 99 6 barred olivine chondrule has a 17o of 3 3 we discuss that 17o 5 5 chondrules are derivative of a reservoir with limited dust enrichment 100 solar system which yielded a relatively reduced chondrule forming environment in contrast the 17o 2 5 chondrules may have been influenced by 16o poor h2o ice that sublimed and then homogenized with precursor material the addition of h2o when combined with high dust enrichment 1000 solar system and greater bulk fe content could have induced an oxidized environment at high temperatures forming mg 96 36 chondrules among the 33 chondrules studied the al mg relative ages of 20 had been obtained previously comparing the oxygen isotope ratios and the 26al ages of these chondrules it is likely that the 5 5 and 2 5 oxygen isotope reservoirs existed contemporaneously this implies that the snow line was spatially fixed during chondrule formation and separated the co chondrite accretion region into two distinct volumes of precursors

relict olivine grains chondrule recycling and implications for the chemical thermal and mechanical processing of nebular materials chondrules and isolated forsterites in five low subtype ordinary chondrites nwa 3127 ll3 1 sahara 97210 ll3 2 wells ll3 3 chainpur ll3 4 and sahara 98175 ll3 5 were studied using petrographic empa and sims techniques to better constrain the origin of chondrules and the olivine grains within them our results imply that igneous crystallization vapor fractionation redox e ects and open system behavior were important processes all olivine grains including normal relict and isolated forsterite grains show evidence for igneous fractionation under disequilibrium conditions with olivine crystallizing during rapid cooling closer to 2000 c h than to 100 c h vapor fractionation is manifested by anti correlated abundances between refractory elements al sc y ti ca v and volatile elements cr mn p rb fe in olivine redox e ects are evidenced in various ways and imply that fe co ni and p were partitioned more into metal and v was partitioned more into olivine under reducing conditions in the most feo poor melts there is no obvious evidence for systematic variations in olivine composition according to meteorite subtype but shock melting in sahara 97210 resulted in the injection of glass derived melt into olivine resulting in artificially high abundances of ba sr na ti and some other incompatible elements in olivine terrestrial weathering in a hot desert environment may have mobilized ba and sr in some glasses our data suggest that chondrules in ordinary chondrites experienced repeated thermal chemical and mechanical processing during a recycling process over an extended time period which involved multiple episodes of melting under fluctuating redox and heating conditions and multiple episodes of chondrule break up in some cases forsterite grains including normal grains in forsterite bearing type i chondrules the cores of isolated forsterites and relict forsterite in type ii chondrules all crystallized from similar refractory melts under reducing conditions relict mg olivine and isolated forsterite grains were thus derived from type i chondrules olivine in type ii chondrules including normal grains and ferroan overgrowths on relict mgolivine crystallized from more volatile rich oxidized and relatively unfractionated melts relict dusty olivine grains in type i chondrules were derived from type ii chondrules during incomplete melting episodes involving reduction and some vaporization with clear non dusty grains in dusty olivine bearing chondrules crystallizing from the reduced and partly vaporized melts melt compositions parental to normal olivine grains in type i and ii chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions implying that chondrules often experienced open system exchange with more volatile rich surroundings after some olivine had crystallized possibly while the chondrules were still partly molten type ii chondrules could have been derived from type i chondrules by the addition of relatively volatile rich material followed by re melting and little evaporation under oxidizing conditions in contrast type i chondrules could have been derived from type ii chondrules by re melting involving more or less evaporation under reducing conditions chemical oxygen

role of gas melt interaction during chondrule formation abstract it is generally believed that most chondrules formed in the protoplanetary disk by melting of fine grained solid precursor materials and that during these melting events chondrules behaved as closed systems both chemically and isotopically i e the observed range in chondrule bulk chemistry and modal mineralogy was entirely inherited from solid precursors that experienced melting to varying degrees followed by igneous crystallization accompanied by very limited if any evaporation recondensation our mineralogical and chemical study of magnesium rich porphyritic type i chondrules in primitive ordinary and carbonaceous chondrites revealed that chondrule glasses are not located on the subtraction lines of olivine or low ca pyroxene in appropriate phase diagrams indicating that type i chondrules do not obey closed system crystallization we suggest that gas melt interaction played a major role in evolution of mineralogy bulk chemical and isotopic compositions of type i chondrules chondrules are thus complex objects composed of an inherited solid component and a melt component that equilibrated with nebular gas suggesting that chondrules formed in regions with high ambient gas partial pressures as a result chondrule glasses melts are therefore thermochemical and isotopic sensors of the surrounding nebular gas in the chondrule forming regions of the protoplanetary disk and can be used for evaluating its physico chemical conditions

oxygen isotopes in crystalline silicates of comet wild 2 a comparison of oxygen isotope systematics between wild 2 particles and chondritic materials abstract oxygen three isotope ratios of nine crystalline silicate particles from comet wild 2 were measured to investigate oxygen isotope systematics of cometary materials we are able to analyze particles as small as 4 m using an ion microprobe with a 1 2 m beam by locating the analysis spots with an accuracy of 0 4 m three particles of mn rich forsterite known as low iron manganese enriched lime olivine showed extremely 16 o rich signatures 18 o 17 o 50 similar to refractory inclusions in chondrites the three mn rich forsterite particles may have formed by condensation from an 16 o rich solar nebula gas other particles consist of olivine and or pyroxene with a wide range of mg molar mgo feo mgo from 60 to 96 their oxygen isotope ratios plot nearly along the carbonaceous chondrite anhydrous mineral ccam and young and russell lines with 17 o 17 o 0 52 18 o values of 3 0 to 2 5 these data are similar to the range observed from previous analyses of wild 2 crystalline silicates and those of chondrules in carbonaceous chondrites six particles extracted from stardust track 77 show diverse chemical compositions and isotope ratios two mn rich forsterites feo poor pigeonite and three feo rich olivines with a wide range of 17 o values from 24 to 1 6 these results confirmed that the original projectile that formed track 77 was an aggregate 6 m of silicate particles that formed in various environments the 17 o values of ferromagnesian wild 2 particles including data from previous studies increase from 23 to 2 5 with decreasing mg 17 o values of mn rich forsterite particles mg 98 99 8 cluster at 23 those of feo poor particles mg 95 97 cluster at 2 and those of feo rich particles mg 90 scatter mainly from 1 5 to 2 5 compared to chondrules in primitive chondrites the systematic trend between mg and 17 o among the wild 2 particles is most similar to that reported for cr chondrite chondrules we argue that cr chondrites and some cometary materials share multiple common chemical and isotope characteristics we suggest that many of the crystalline silicate particles formed in the outer regions of the asteroid belt or regions that share the common properties and were transported to comet forming regions and accreted into comet wild 2

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

oxygen isotopes in chondrule olivine and isolated olivine grains from the co3 chondrite allan hills a77307 we have measured o isotopic ratios in a variety of olivine grains in the co3 chondrite allan hills alh a77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites oxygen isotopic ratios of olivines in this chondrite are variable from delta 17 o 15 5 to 4 5 parts per thousand and delta 18 o 11 5 to 3 9 parts per thousand with delta 17 o varying from 10 4 to 3 5 parts per thousand forsteritic olivines fa 1 are enriched in o 16 relative to the bulk chondrite whereas more feo rich olivines are more depleted in o 16 most ratios lie close to the carbonaceous chondrite anhydrous minerals ccam line with negative values of delta 17 o although one grain of composition fa 4 has a mean delta 17 o of 1 6 parts per thousand marked o isotopic heterogeneity within one feo rich chondrule is the result of incorporation of relic o 16 rich mg rich grains into a more o 16 depleted host isolated olivine grains including isolated forsterites have similar o isotopic ratios to olivine in chondrules of corresponding chemical composition this is consistent with derivation of isolated olivine from chondrules as well as the possibility that isolated grains are chondrule precursors the high o 16 in forsteritic olivine is similar to that observed in forsterite in cv and ci chondrites and the ordinary chondrite julesburg and suggests nebula wide processes for the origin of forsterite that appears to be a primitive nebular component

morphology and distribution of lava flows on mid ocean ridges a review abstract both pillow lavas and sheet flows are important features of oceanic volcanism at mid ocean ridges submersible surveys of the neovolcanic zone and off axis areas of these complex seafloor volcanic terrains conducted during the past two decades have uncovered a wide array of basaltic surface forms with pillow basalts displaying bulbous spherical and elongate tubular patterns and sheet flows exhibiting smooth lobate rippled wrinkled ropy whorly hackly and jumbled configurations the genesis of pillow lavas and sheet flows appears to be coupled to variations of spreading rates within the plate boundary zone while pillow lavas predominate at slow spreading centers i e mid atlantic ridge sheet flows prevail along the active volcanic zones at intermediate i e galapagos rift and juan de fuca ridge fast and superfast i e east pacific rise spreading centers yet both types of flows are present at each setting the distribution of pillow lavas and sheet flows along a ridge segment is related to the topographic gradient of the ridge axis hence the formation of sheet flows tends to be favored by the development of topographic highs between ridge segment boundaries where the crustal lid is thinnest and rifting directly taps the underlying magma chamber fissure eruptions here release copious amounts of surface fed fluid lavas which decrease in volume down the topographic gradient away from the bathymetric high of the ridge segment lava flows become more distal and channelized thereby fostering greater concentrations of tube fed pillow flows toward the segment boundaries the type of lava flow morphologies encountered at any specific site on the seafloor is contingent upon the effusion rate cooling rate and slope as demonstrated by laboratory simulations

magnesium isotopes constraints on the origin of mg rich olivines from the allende chondrite nebular versus planetary abstract high precision mg isotope measurements by multi collector ion microprobe show that refractory olivines from the allende chondrite either olivines isolated in the matrix 2 samples studied or olivines in type i chondrules 6 samples studied have variable 26mg enrichments and deficits calculated in permil as the 26mg deviation from the instrumental mass fractionation line relative to the earth most average 26mg noted 26mg av values between 10 and 20 analyses per chondrule are negative but the total range is from 0 029 0 010 2 sigma errors to 0 011 0 011 with an exception of one olivine at 0 043 0 023 these variations in 26mg av reflect the formation of the olivines from reservoirs enriched in various amounts of 26mg by the decay of short lived 26al t1 2 0 73 ma similarly 30 analyses of olivines from the eagle station pallasite show a 26mg av value of 0 033 0 008 as negative as some olivines from allende chondrules and the solar system initial 26mg value of 0 038 0 004 defined at the time of formation of type b ca al rich inclusions cais when 26al 27al 5 23 10 5 jacobsen et al 2008 because olivines are al poor and because their mg isotopic compositions are not reset during the chondrule forming events their 26mg av can be used to calculate model crystallization ages relative to various theoretical mg isotope growth curves the two end member scenarios considered are i a nebular growth in which the al mg ratio remains chondritic and ii a planetary growth in which a significant increase of the al mg ratio can be due to for instance olivine magmatic fractionation the low 26mg av value of olivines from the eagle station pallasite demonstrate that metal silicate differentiation occurred as early as 0 15 0 23 0 29 ma after cais in either of the growth scenarios similarly the variable 26mg av values of refractory olivines can be understood if they were formed in planetesimals which started to differentiate as early as the eagle station parent body accretion of these planetesimals must have been coeval to the formation of cais and their disruption could explain why their fragments mg rich olivines were distributed in the chondrule forming regions of the disk

oxygen isotopic constraints on the origin of magnesian chondrules and on the gaseous reservoirs in the early solar system abstract we report in situ ion microprobe analyses of the oxygen isotopic composition of the major silicate phases olivine low ca pyroxene silica and mesostasis of 37 magnesian porphyritic type i chondrules from cv vigarano usnm 477 2 vigarano uh5 mokoia and efremovka and cr eet 92042 eet 92147 eet 87770 el djouf 001 mac 87320 and gra 95229 carbonaceous chondrites in spite of significant variations of the modal proportions of major mineral phases in cr and cv chondrules the same isotopic characteristics are observed i olivines are isotopically homogeneous at the level within a chondrule although they may vary significantly from one chondrule to another ii low ca pyroxenes are also isotopically homogeneous but systematically 16o depleted relative to olivines of the same chondrule and iii all chondrule minerals analyzed show 16o enrichments relative to the terrestrial mass fractionation line enrichments that decrease from olivine spinel to low ca pyroxene and to silica and mesostasis the observation that in most of the type i chondrules studied the coexisting olivine and pyroxene crystals and glassy mesostasis have different oxygen isotopic compositions implies that the olivine and pyroxene grains are not co magmatic and that the glassy mesostasis is not the parent liquid of the olivine the 18o and 17o values of pyroxene and olivine appear to be strongly correlated for all the studied cr and cv chondrules according to 18 o pyroxene 0 72 0 16 0 13 18 o olivine 1 21 0 54 0 79 17 o pyroxene 0 81 0 15 0 13 17 o olivine 0 60 1 00 0 95 these correlations are consistent with mass balance of oxygen isotopes calculated in the case of chondrule formation according to the following gas melt mineral reactions mg 2 sio 4 olivine sio 2 melt mg 2 si 2 o 6 pyroxene sio 2 melt sio gas 1 2 o 2 gas these equations imply that 2 3 of the oxygen incorporated by low ca pyroxene during its crystallization in the melt is derived from the dissolution of precursor olivine and 1 3 from the addition of chemical components such as sio from the nebular gas the composition of the nebular gaseous reservoir in which type i cr and cv chondrules formed is determined from the present data set to be 18o gas 3 6 1 and 17o gas 1 8 1 this isotopic composition is in excellent agreement with that of the gaseous reservoir previously inferred from the oxygen isotope systematics of bulk chondrules from various chondrite groups i e cv cr unequilibrated ordinary and eh thus the oxygen isotopic systematic strongly supports the idea that most of the olivines in type i chondrules are relict grains and that gas melt interaction played a major role in the formation of type i chondrules

gas melt interactions and their bearing on chondrule formation interactions between nebular gas and molten silicates or oxides could have played a major role in the formation and differentiation of the first solids formed in the solar system in order to simulate such interactions we set up a new experimental device in which isothermal condensation experiments have been conducted partially molten chondrule like samples have been exposed to high sio g partial pressures for intervals between 80 and 300 s and at temperatures ranging from 1600 to 1750 k results show that silica entering from the gas phase could be responsible for several textural and mineralogical features observed in natural chondrules for instance these experiments reproduce not only the mineralogical zonation of porphyritic olivine pyroxene chondrules with the peripheral location of pyroxenes but also olivine resorption textures and the common poikilitical enclosure of olivines in pyroxenes in the light of these similarities we advocate that gas melt interactions through condensation are viable mechanisms for chondrule formation and hence may place severe constraints on the history of these primitive objects in the nebula high sio g partial pressures could have been established by the volatilization of regions with high dust gas ratio a possible scenario for this stochastic thermal activity is the intense activity of the protosun in its young stellar object phase

origin of chondritic forsterite grains abstract iron poor and refractory lithophile element rle rich forsterite grains occur in all major types of unequilibrated chondrites in our laser ablation inductively coupled mass spectrometry la icpms minor and trace element study we show that refractory forsterites rf from carbonaceous cc unequilibrated ordinary uoc and a rumuruti chondrite rc have similar chemical compositions with high rle concentrations and low concentrations of mn fe co and ni fractionation of rles and rare earth elements rees is in agreement with formation by crystallization from a rle rich silicate melt low concentrations and the fractionation of moderately siderophile elements fe co ni in rfs suggests formation at low oxygen fugacity possibly in equilibrium with primitive fe ni metal condensates in a gas of solar composition anomalously high ti in the parental melt can be explained by ti3 ti4 1 5 supporting formation of rf in highly reducing conditions low mn concentrations indicate formation at high temperatures 1160 k the model of formation of rfs and the accompanying physico chemical conditions during their formation as well as their relation to non refractory olivine are discussed

a few remarks on the kinetics of static grain growth in rocks static grain growth is a relatively simple transformation in which grain size increases under driving forces caused by grain and interphase boundary curvature given the relative simplicity of the protocol for grain growth experiments measurements of grain boundary mobility show surprising variations boundary mobilities during grain growth are affected by solute and impurity chemistry chemical fugacity of trace and major elements pore size and number pore fluid chemistry the presence of melts and the presence of solid second phases as well as temperature and pressure all of these factors may exert influence on grain growth of rocks in natural situations and many are also present during the laboratory experiments provided that the necessary kinetics parameters are known bounds may be placed on the interface mobility when pores partial melts or solutes are present to predict the rate of grain growth in natural situations will require improved laboratory data and careful consideration of the thermodynamic conditions likely to be encountered in nature

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

mg isotope heterogeneity in the allende meteorite measured by uv laser ablation mc icpms and comparisons with o isotopes first results from a new uv laser ablation mc icpms method for measuring mg isotope ratios in situ in meteoritical materials show that there are mass dependent variations in 25 mg and 26 mg up to 1 5 per amu in chondrules and 0 3 per amu in a cai from the allende meteorite in both cases the mass dependent fractionation is associated with alteration comparisons with laser ablation o isotope data indicate that incorporation of pre existing grains of forsterite with distinct mg and o isotopic compositions and post formation alteration both contributed to the variability in mg isotope ratios in the chondrules resulting in a correlation between high 25 mg and low 17 o the laser ablation analyses of the cai show that high precision determinations of both 25 mg and 26 mg can be used to discriminate features of the 26 al 26 mg isotope system that are relevant to chronology from those that result from element mobility copyright 2002 elsevier science ltd

widespread magma oceans on asteroidal bodies in the early solar system our solar system formed about 4 6 billion years ago and within 4 million years small planetary bodies had formed some melting to form volcanic and related rocks two families of meteorites the heds and angrites are thought to have originated from asteroids that melted at this time new oxygen isotope measurements confirm that these meteorites are from two distinct asteroids that underwent large scale melting in the early solar system these new results show that early global scale melting was a feature of all the differentiated planets earth moon and mars and asteroids so far sampled immediately following the formation of the solar system small planetary bodies accreted1 some of which melted to produce igneous rocks2 3 over a longer timescale 15 33 myr the inner planets grew by incorporation of these smaller objects4 5 through collisions processes operating on such asteroids strongly influenced the final composition of these planets4 including earth5 currently there is little agreement about the nature of asteroidal igneous activity proposals range from small scale melting to near total fusion and the formation of deep magma oceans2 here we report a study of oxygen isotopes in two basaltic meteorite suites the heds howardites eucrites and diogenites which are thought to sample the asteroid 4 vesta6 and the angrites from an unidentified asteroidal source our results demonstrate that these meteorite suites formed during early global scale melting 50 per cent events we show that magma oceans were present on all the differentiated solar system bodies so far sampled magma oceans produced compositionally layered planetesimals the modification of such bodies before incorporation into larger objects can explain some anomalous planetary features such as earth s high mg si ratio

granoblastic olivine aggregates as precursors of type i chondrules an experimental test abstract chondrule formation models involving precursors of granoblastic olivine aggregates goa of either planetesimal or nebular origin have recently been proposed we have therefore conducted chondrule simulation experiments using mixtures of 100 h thermally annealed goa and an en to test the viability of goa as predecessors of porphyritic olivine po chondrules isothermal runs of less than 5 min at 1350 1550 c result in goa disaggregation and fe mg exchange runs of 0 5 4 h show textures superficially similar to granular and po chondrules but with reversely zoned olivine charges isothermally heated at 1550 c for 1 and 4 h before being cooled at 10 and 100 c h undergo olivine crystallization and yield classical po textures although most evidence of origin from goa is erased the cores of normally zoned euhedral crystals are relict as phenocrysts in type i chondrules can be relict such chondrules could have experienced similar peak temperatures to those of type ii chondrules chondrules containing goa with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 c and type i chondrules with subhedral to anhedral olivine plus goa relicts resemble charges heated at the same temperatures but for longer duration type i chondrules with a mass of granular olivine or irregular anhedral olivine grains in the center and much glass nearer the margin on the other hand require limited heating at high temperature 1550 c while type i chondrules with euhedral olivines resemble charges heated at 1550 c for 4 h the majority of type i chondrules in cv chondrites display evidence of derivation from goa many finer grained chondrules in cr and uoc on the other hand could not have been derived from such coarse grained precursors but could have formed from fine grained dustballs as stipulated in the standard paradigm thus both goa and dustballs represent viable chondrule precursors of coarser and finer grained type i po chondrules respectively

the early archaean nondweni greenstone belt southern kaapvaal craton south africa part ii characteristics of the volcanic rocks and constraints on magma genesis the early archaean nondweni greenstone belt is dominated by mafic volcanic rocks which have a wide range in compositions primary volcanic structures and compositional characteristics point to this succession being unique in archaean geology and an important indicator of controls of magma formation and environment of deposition compositionally the nondweni lavas are broadly similar to those of the barberton sequence high values for cao al2o3 ti y and low al2o3 tio2 they are also distinctly different in that sio2 content is markedly higher and incompatible trace element ratios are also different the high silica content has promoted the subdivision of komatiitic and basaltic rocks into the following categories komatiite komatiitic andesite komatiitic basalt basalt and basaltic andesite the recognition of the distinct suite of komatiitic andesites is aided by the lower zr ti ratios than those lithologies of equivalent mgo content reported from other greenstone belts and sio2 contents as high as 58 these characteristics suggest similarity to recent high mg andesites none of the lava compositions exceed 23 mgo anhydrous and pyroxene rather than olivine dominates the crystallization assemblage olivine spinifex textures are entirely absent in the nondweni greenstone belt and instead pyroxene or amphibole after pyroxene spinifex is abundantly developed and is characterised by spectacular radial conical structures which have their apices towards the tops of the flow units some of the spinifex cone structures attain heights of up to 6 m branching pyroxene crystals and feathery textured plagioclase typify the spinifex textures of the komatiitic andesites the common occurrence of coned and branching spinifex textures in a wide range of magma compositions indicates that these were controlled by thermal characteristics and depositional environment for the flow units rather than solely by composition this may have been facilitated by emplacement in shallow water rather than in deep water as envisaged for the onverwacht group of the barberton sequence shallow water depositional environments in the nondweni group are supported by sedimentary lithofacies well preserved pillow structures also show a wide range in textural forms sizes of pillows degree of welding of pillow margins development of hyaloclastite and formation of shelf structures formed by repeated filling of lava tubes are related to both compositional type as well as physical controls such as extrusion rate and nature of the substrate komatiites seldom form pillows and very large pillow formation is restricted to the komatiitic andesite lava type komatiite flow successions are typified by spinifex textured units as well as by massive and highly brecciated aphyric flow units unaltered pyroxene and plagioclase characterise some of the massive flow units and pillowed basalts of the witkop formation the present paper is the second part of a series on the nondweni greenstone belt part i wilson and versfeld 1994 describes the stratigraphy sedimentology mineralization and depositional environment there are strong of kaapvaal craton may have been different to that of the barberton greenstone belt a present day analogue to the nondweni tectonic setting may be an ensialic back arc basin adjacent to a continental margin

compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites several percent of the olivine in the c2 c3 and unequilibrated ordinary chondrites uoc can be distinguished by blue cathodoluminescence cl and an unusual composition for forsterite this olivine has the following textural features 1 1 forms cores in single olivine grains 2 2 shows subhedral to euhedral boundaries against rim olivine 3 3 rarely contains inclusions 4 4 has embayments containing olivine like that of the rim 5 5 occurs within chondrules especially in uoc meteorites the blue olivine is always fe poor 0 25 feo 1 0 and shows the following average and maximum values al2o3 0 25 0 5 tio2 0 05 0 09 cao 0 5 0 8 cr2o3 0 15 0 5 and mno 0 02 0 15 vanadium is present within a single olivine and within all blue olivines al ca and ti are strongly positively correlated as are mn fe and cr in olivine surrounding the blue the blue cores are not zoned but each element shows a marked change at the boundary of the blue with al showing the most rapid change these are interpreted as diffusion profiles between rim and core olivine textures suggest initial free growth probably from a gas and later addition of olivine by liquid crystallization to form single crystals or chondrules the unusual olivine composition indicates high temperature growth from a refractory rich reservoir with al entering olivine in tetrahedral coordination vapor growth is suggested as the process allowing the high minor element levels the occurrence of blue olivine in all primitive meteorites indicates that it is relic material which was widespread prior to chondrule and hence meteorite formation similarities in composition exist between this relic olivine and olivine of cosmic dust and deep sea particles pointing to this olivine being a common component in all primitive extraterrestrial material

evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin abstract chondrules are the major high temperature components of chondritic meteorites which are conventionally viewed as the samples from the very first generation of undifferentiated planetesimals growing evidences from long and short lived radionuclide chronologies indicate however that chondrite parent asteroids accreted after or contemporaneously with igneous activities on differentiated asteroids questioning the pristine nature of chondrites here we report a discovery of metal bearing olivine aggregates with granoblastic textures inside magnesian porphyritic type i chondrules from the cv carbonaceous chondrite vigarano formation of the granoblastic textures requires sintering and prolonged high temperature 1000 c annealing conditions which are not expected in the solar nebula during chondrule formation but could have been achieved on parent bodies of olivine rich differentiated or thermally metamorphosed meteorites the mineralogy and petrography of the metal olivine aggregates thus indicate that they are relict dunite like lithic fragments which resulted from fragmentation of such bodies the very old pb pb absolute ages and al mg relative model ages of bulk cv chondrules suggest that such planetesimals may have formed as early as the currently accepted age of the solar system 4567 2 0 6 ma

radar and lightning analyses of gigantic jet producing storms 1 an analysis of thunderstorm environment structure and evolution associated with six gigantic jets five negative polarity one positive was conducted three of these gigantic jets were observed within detection range of very high frequency lightning mapping networks all six were within range of operational radars and two dimensional lightning network coverage five within the national lightning detection network and one within the global lightning detection gld360 network most of the storms producing the jets formed in moist tropical or tropical like environments precipitable water ranged from 37 to 62 kg m 2 and 0 6 km shear from 3 5 to 24 8 m s 1 featuring high convective available potential energy 1200 3500 j kg 1 and low lifted indices 2 8 to 6 4 the storms had maximum radar reflectivity factors of 54 to 62 dbz and 10 dbz echo contours reached 14 17 km storms covered by three dimensional lightning mappers were near peak altitude of lightning activity modes of the vertical distributions of radio sources were at altitudes colder than 50 c and vertical reflectivity intensity with overshooting echo tops around the times of their jets two of the other three jet producing storms produced their jet around the time of a convective surge as indicated by radar data and likely featured overshooting tops the observations suggest a link between convective surges overshooting tops and the occurrence of gigantic jets similar to prior modeling studies

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

chondrule formation by repeated evaporative melting and condensation in collisional debris clouds around planetesimals a synthesis of previous work leads to a model of chondrule formation that involves periodic melting of dispersed dust in debris clouds that were generated by collisions between chondritic planetesimals i suggest that chondrules formed by the passage of nebular shock waves through these dust clumps which temporarily surrounded disrupted planetesimals type i chondrules formed by more intense evaporative heating of fewer particles in tenuous clumps or at the edges of dense clumps and type ii chondrules formed by less intense evaporative heating of more particles deeper within dense clumps chondrules reaccreted by self gravity into the planetesimals mixing with less heated dust and rock this process of disruption melting and reaccretion could have repeated many times in this way chondrite components of various origins and thermal histories could remain preserved in planetesimals as a distinctive mix of materials for extended periods of time while still allowing for a repetitive melting process that converted some of the planetesimal debris into chondrules i also suggest that during chondrule formation the inner solar nebula gas was evolving by the gradual incorporation and heating of icy bodies depleted in 16 o causing a general increase in gaseous d 17 o with time in most places especially close to the snow line in this model early formed type i chondrules in c chondrites with lower d 17 o values were produced inside the snow line and later formed type i and type ii chondrules in c and o chondrites with higher d 17 o values were created nearer the snow line after it had moved closer to the young sun

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

subglacial to emergent basaltic volcanism at hloðufell south west iceland a history of ice confinement abstract hlo ufell is a familiar 1186 m high landmark located about 80 km northeast of reykjavik and 9 km south of the langkjokull ice cap in south west iceland this is the first detailed study of this well exposed and easily accessible subglacial to emergent basaltic volcano eight coherent and eleven volcaniclastic lithofacies are described and interpreted and its evolution subdivided into four growth stages i iv on the basis of facies architecture vents for stages i ii and iv lie along the same fissure zone which trends parallel to the dominant nne ssw volcano tectonic axis of the western volcanic zone in this part of iceland but the stage iii vent lies to the north and is probably responsible for the present n s elongation of the volcano the basal stage i is dominated by subglacially erupted lava mounds and ridges which are of 240 m maximum thickness were fed from short fissures and locally display lava tubes some of the stage i lavas preserve laterally extensive flat to bulbous steep glassy surfaces that are interpreted to have formed by direct contact with surrounding ice and are termed ice contact lava confinement surfaces these surfaces preserve several distinctive structures such as lava shelves pillows that have one flat surface and mini pillow

lightning development associated with two negative gigantic jets 1 we report observations of two negative polarity gigantic jets sufficiently near very high frequency vhf lightning mapping networks that the associated lightning characteristics and charge transfer could be investigated in both cases the gigantic jet producing flash began as ordinary intracloud lightning with upper level channels attempting to exit the cloud and then produced the upward gigantic jet neither flash had developed channels to ground confirming that the major charge transfer during gigantic jets occurred between the cloud and ionosphere the leader progression of one event was detected at altitudes above 20 km demonstrating the possibility of detecting and tracking the propagation of negative jets above the cloud with vhf techniques citation lu g et al 2011 lightning development associated with two negative gigantic jets geophys res lett 38 l12801

oxygen isotopic diversity of chondrule precursors and the nebular origin of chondrules feo poor type i porphyritic chondrules formed by incomplete melting of solid dust precursors via a yet elusive mechanism two settings are generally considered for their formation i a nebular setting where primordial solids were melted e g by shock waves propagating through the gas and ii a collisional planetary setting here we report a method combining high current electron microprobe x ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from chondrule precursors we find that these olivine crystals are ca al ti poor relative to host olivine crystals their variable 17o even in individual chondrule is inconsistent with derivation from planetary interiors as previously argued from 120 triple junctions also exhibited by the chondrules studied herein this indicates that chondrule precursors correspond to solid nebular condensates formed under changing physical conditions we propose that porphyritic chondrules formed during gas assisted melting of nebular condensates comprising relict olivine grains with varying 17o values and ca al ti rich minerals such as those observed within amoeboid olivine aggregates incomplete melting of chondrule precursors produced ca al ti rich melts cat melts allowing subsequent crystallization of ca al ti rich host olivine crystals via epitaxial growth on relict olivine grains incoming mgo and sio from the gas phase induced i the dilution of cat melts as attested by the positive al ti correlation observed in chondrule olivine crystals and ii buffering of the o isotope compositions of chondrules as recorded by the constant 17o values of host olivine grains the o isotopic compositions of host olivine grains are chondrule specific suggesting that chondrules formed in an array of environments of the protoplanetary disk with different 17o values possibly due to variable solid gas mixing ratios

oxygen isotope systematics of chondrules in the allende cv3 chondrite high precision ion microprobe studies the oxygen three isotope systematics of 36 chondrules from the allende cv3 chondrite are reported using high precision secondary ion mass spectrometer cameca ims 1280 twenty six chondrules have shown internally homogenous 17 o values among olivine pyroxene and spinel within a single chondrule the average 17 o values of 19 feo poor chondrules 13 porphyritic chondrules 2 barred olivine chondrules and 4 chondrule fragments show a peak at 5 3 0 6 2sd another 5 porphyritic chondrules including both feo poor and feo rich ones show average 17 o values between 3 and 2 and 2 other feo poor barred olivine chondrules show average 17 o values of 3 6 and 0 these results are similar to those for acfer 094 chondrules showing bimodal 17 o values at 5 and 2 nine porphyritic chondrules contain olivine grains with heterogeneous 17 o values as low as 18 indicating that they are relict olivine grains and some of them were derived from precursors related to refractory inclusions however most relict olivine grains show oxygen isotope ratios that overlap with those in homogeneous chondrules the 17 o values of four barred olivine chondrules range from 5 to 0 indicating that not all bo chondrules plot near the terrestrial fractionation line as suggested by previous bulk chondrule analyses based on these data we suggest the presence of multiple oxygen isotope reservoirs in local dust rich protoplanetary disk from which the cv3 parent asteroid formed a compilation of 225 olivine and low ca pyroxene isotopic data from 36 chondrules analyzed in the present study lie between ccam carbonaceous chondrite anhydrous mineral and young and russell lines these data define a correlation line of 17 o 0 982 0 019 18 o 2 91 0 10 which is similar to those defined by chondrules in cv3 chondrites and acfer 094 in previous studies plagioclase analyses in two chondrules plot slightly below the ccam line with 17 o values of 2 6 which might be the result of oxygen isotope exchange between chondrule mesostasis and aqueous fluid in the cv parent body

the complex facies architecture and emplacement sequence of a miocene submarine mega pillow lava flow system muriwai north island new zealand the early miocene waiatarua formation at maori bay muriwai north island new zealand consists of a complex association of basaltic andesite volcanic facies including entablature jointed thick massive facies colonnade jointed thin massive sheet facies mega pillow facies normal pillow facies and minor associated fragmental facies including vitric sandstone and breccia interpreted as hyaloclastite and peperite field observations suggest that the facies which form the waiatarua formation lava were emplaced as multiple flow lobes in a single lava flow from one sustained eruption magma discharge rate at the vent was high however magma supply rate to the more distal and lateral portions of the flow as its surface area increased varied considerably higher magma supply rates produced thick massive and thin sheet facies whereas mega pillow facies and normal pillow facies were produced contemporaneously with the thick and thin massive sheet facies but were restricted to portions of the distal flow subjected to lower magma supply rates the evolution of the waiatarua formation lava flow at maori bay has been reconstructed from the complex facies architecture this suggests that the propagation of the lava involved 7 discrete lobes that were emplaced successively

a magmatic origin for silica rich glass inclusions hosted in porphyritic magnesian olivines in chondrules an experimental study rare silica rich glass inclusions 69 sio2 82 wt are described within magnesian olivines of porphyritic type ia chondrules these glass inclusion compositions are clearly out of equilibrium with their host mg olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases we performed dynamic crystallisation experiments that demonstrate that these si rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a ci i e solar composition their silica rich compositions are the consequence of the small volumes of inclusions which inhibit the nucleation of secondary crystalline phase ca poor pyroxene but allow olivine to continue to crystallize metastably on the walls of the inclusions we suggest that si rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system exhibiting a ci i e non fractionated composition

chondrules precursors and interactions with the nebular gas chondrule compositions suggest either ferroan precursors and evaporation or magnesian precursors and condensation type i chondrule precursors include granoblastic olivine aggregates planetary or nebular and fine grained dustball precursors in carbonaceous chondrites type i chondrule precursors were s free while type ii chondrules have higher fe mn than in ordinary chondrites many type ii chondrules contain diverse forsteritic relicts consistent with polymict dustball precursors the relationship between finer and coarser grained type i chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules fe metal in type i and na and s in type ii chondrules indicate high partial pressures in ambient gas as they are rapidly evaporated at canonical conditions the occurrence of metal sulfide or low ca pyroxene on chondrule rims suggests re condensation in semarkona type ii chondrules na rich olivine cores na poor melt inclusions and na rich mesostases suggest evaporation followed by recondensation type ii chondrules have correlated feo and mno consistent with condensation onto forsteritic precursors but with different ratios in carbonaceous chondrites and ordinary chondrites indicating different redox history the high partial pressures of lithophile elements require large dense clouds either clumps in the protoplanetary disk impact plumes or bow shocks around protoplanets in ordinary chondrites clusters of type i and type ii chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together in carbonaceous chondrites the much less abundant type ii chondrules were probably added late to batches of type i chondrules from different o isotopic reservoirs

multi instrumental observations of a positive gigantic jet produced by a winter thunderstorm in europe 1 at 2336 56 utc on 12 december 2009 a bright gigantic jet gj was recorded by an observer in italy forty nine additional sprites elves halos and two cases of upward lightning were observed that night the location of the gj corresponded to a distinct cloud top 34 c west of ajaccio corsica the gj reached approximately 91 km altitude with a trailing jet reaching 49 59 km matching with earlier reported gjs the duration was short at 120 160 ms this is the first documented gj which emerged from a maritime winter thunderstorm only 6 5 km tall showing high cloud tops are not required for initiation of gjs in the presence of strong vertical wind shear the meteorological situation was different from typical outbreaks of fall and winter thunderstorms in the mediterranean during the trailing jet phase of the gj a sprite with halo triggered by a nearby cloud to ground lightning flash occurred at a relatively low altitude 72 km at the same time the trailing jet and beads were reilluminated electromagnetic waveforms from hungary poland and the usa revealed this gj is the first reported to transfer negative charge approximately 136 c from the ionosphere to the positively charged origins in the cloud i e a positive cloud to ionosphere discharge ci with a large total charge moment change of 11600 c km and a maximum current of 3 3 ka early vlf transmitter amplitude perturbations detected concurrently with the gj confirm the production of large conductivity changes due to electron density enhancements in the d region of the ionosphere

gigantic jets produced by an isolated tropical thunderstorm near reunion island five gigantic jets gjs have been recorded with video and photograph cameras on 7 march 2010 above an isolated tropical storm east of reunion island three of them were produced before the storm reached its coldest cloud top temperature approximately 81 c and two others occurred during the cloud extension thanks to the close distance of observation 50 km the luminosity within the cloud was recorded and the events are analyzed in unprecedented detail the tops of the gjs are estimated between 80 and 90 km all these gjs are accompanied by long continuous cloud illumination and they are preceded and followed by intermittent optical flashes from the cloud most of time without any cloud to ground cg flash simultaneously detected which suggests they originated mainly as intracloud discharges and without any charge transfer to earth the cg lightning activity is observed to cease a few tens of seconds before the jets according to elf data recorded at nagycenk hungary the five gjs serve to raise negative charge their duration ranges from 333 to 850 ms the leading jet has the most variable duration 33 167 ms and propagates faster at higher altitudes the trailing jet exhibits a continuous decrease of luminosity in different parts of the jet lower channel transition zone and for most events carrot sprite like top and in the cloud with possible rebrightening the lower channels 20 40 km altitude produce blue luminosity which decreases with altitude and become more and more diffuse with time the transition zone around 40 65 km consists of bright red luminous beads slowly going up 104 m s 1 retracing the initial leading jet channels

magnesium isotopic fractionation in chondrules from the murchison and murray cm2 carbonaceous chondrites we present high precision measurements of the mg isotopic compositions of a suite of types i and ii chondrules separated from the murchison and murray cm2 carbonaceous chondrites these chondrules are olivine and pyroxene rich and have low 27 al 24 mg ratios 0 012 0 316 the mg isotopic compositions of murray chondrules are on average lighter d 26 mg ranging from 0 95 to 0 15 relative to the dsm 3 standard than those of murchison d 26 mg ranging from 1 27 to 0 77 taken together the cm2 chondrules exhibit a narrower range of mg isotopic compositions than those from cv and cb chondrites studied previously the least altered cm2 chondrules are on average lighter average d 26 mg 0 39 0 30 2se than the moderately to heavily altered cm2 chondrules average d 26 mg 0 11 0 21 2se the compositions of cm2 chondrules are consistent with isotopic fractionation toward heavy mg being associated with the formation of secondary silicate phases on the cm2 parent body but were also probably affected by volatilization and recondensation processes involved in their original formation the low al cm2 chondrules analyzed here do not exhibit any mass independent variations in 26 mg from the decay of 26 al with the exception of two chondrules that show only small variations just outside of the analytical error in the case of the chondrule with the highest al mg ratio a type iab chondrule from murchison the lack of resolvable 26 mg excess suggests that it either formed 1 ma after calcium aluminum rich inclusions or that its al mg isotope systematics were reset by secondary alteration processes on the cm2 chondrite parent body after the decay of 26 al

the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites high precision oxygen isotopic compositions of eighteen large cosmic spherules 500 mu m diameter from the atacama desert chile were determined using ir laser fluorination isotope ratio mass spectrometry the four discrete isotopic groups defined in a previous study on cosmic spherules from the transantarctic mountains suavet et al 2010 were identified confirming their global distribution approximately 50 of the studied cosmic spherules are related to carbonaceous chondrites 38 to ordinary chondrites and 12 to unknown parent bodies approximately 90 of barred olivine bo cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites similarly similar to 90 porphyritic olivine po cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites other textures are related to all potential parent bodies the data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters we propose that the po texture may essentially be formed from a coarse grained precursor having an ordinary chondritic mineralogy and chemistry coarse grained precursors related to carbonaceous chondrites i e chondrules are likely to either survive atmospheric entry heating or form v type cosmic spherules due to the limited number of submicron nucleation sites after total melting ordinary chondrite related coarse grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline cc textures instead of bo textures conversely the bo textures would be mostly related to the fine grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases allowing the preservation of submicron nucleation sites independently of the nature of the precursors increasing peak temperatures form glassy textures

evolution of a subglacial basaltic lava flow field tennena volcanic center mount edziza volcanic complex british columbia canada abstract studies of terrestrial glaciovolcanic deposits have elucidated the utility of these deposits as tools to constrain ice conditions at the time of their emplacement very few studies however have documented the emplacement of effusion dominated basaltic glaciovolcanic eruptions the tennena volcanic center tvc located at 57 40 57 705 n 130 39 43 138 w on the western flank of mount edziza volcanic complex mevc in northwestern british columbia canada preserves a detailed record of interactions between coherent basaltic lavas and a local regional ice sheet inferred to be associated with the last glacial maximum lgm here we describe the field characteristics of five primary volcanic lithofacies and five associated glaciogenic lithofacies and discuss their spatial distribution within the volcanic center we find that 1 the distribution of primary hydrovolcanic clastic deposits tuff breccias and lapilli tuffs is confined to tennena cone 2 pillow lavas are present throughout the extent of the surrounding lava field with morphologies that include distinctive structures comprising vertically oriented distended pillows 3 multiple lobes of massive non pillowed lavas that represent high initial magma discharge rates are confined to medial distances from the cone and 4 associated glaciogenic facies that underlie or onlap the tvc lavas indicate a variable sediment water ratio during subglacial meltwater drainage at the time of the eruption or shortly afterwards analyses of h 2 o co 2 in pillow rim samples give broad constraints for emplacement pressures equivalent to 500 1400 m of overlying ice no subaerial lava morphologies are found on the cone or in the proximal medial and distal lithofacies and the sequence is interpreted as documenting an eruption of basaltic lava flows beneath either the lgm cordilleran ice sheet or a younger dryas expansion of the still extant edziza ice cap the tvc lavas especially medial and distal ones display excellent examples of textures and morphologies that can be used to 1 help identify other terrestrial and martian basaltic lava flows emplaced beneath ice and 2 further our understanding on how sub ice lava flows are emplaced

ultrathin lava layers exposed near san luis obispo bay california sequences of extraordinarily thin 1 5 cm thick lava layers resembling individual lava flows are interbedded with jurassic and cretaceous pillowed lava flows near san luis obispo bay on the california coast such layers are formed inside submarine pillowed lava pipes or flow lobes as the lava surface in a pillow pipe falls to a lower level owing to diminished supply entering the pipe water enters the upper compartment through cracks in the outer crust and chills a new crust on top of the lava stream repeated lowerings of the lava level in the pipe create a series of discrete lava shelves each of which represents the upper crust of the lava stream flowing within the pipe these crusts are supported at different levels on their edges at the side of the pipe the weight of subsequent overlying lava flows collapses the partly hollow tube creating a stacked sequence of ultrathin lava layers progressively younger downward

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

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity