chondrules in h3 chondrites textures compositions and origins major and minor element bulk compositions of 90 individual chondrules and 16 compound chondrule sets in unequilibrated type 3 h group chondrites were determined in polished thin sections by broad beam electron probe analysis and the chondrules were classified petrographically into six textural types barred olivine porphyritic olivine porphyritic pyroxene barred pyroxene radiating pyroxene fine grained although analyses of individual chondrules scatter widely the mean composition of each textural type except barred pyroxene is rather distinct as verified by discriminant function analysis al2o3 tio2 and na3o are correlated in chondrules but al2o3 and cao do not correlate compound chondrule sets were found to consist almost entirely of chondrules or partial chondrules of similar texture and composition the data suggest that composition played a conspicuous role in producing the observed textures of chondrules though other factors such as cooling rates and degrees of supercooling prior to nucleation were also important if compound chondrules formed and joined when they were still molten or plastic then the data suggest that chondrules of each textural type could have formed together in space or time the correlation of al2o3 and tio2 with na2o and not with cao appears to rule out formation of chondrules by direct equilibrium condensation from the nebula we conclude that the most reasonable model for formation of the majority of chondrules is that they originated from mixtures of differing fractions of high intermediate and low temperature nebular condensates that underwent melting in space a small percentage of chondrules might have formed by impacts in meteorite parent body regoliths

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

olivine in terminal particles of stardust aerogel tracks and analogous grains in chondrite matrix abstract the dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the wild 2 samples we present 68 analyses of olivine fa 0 97 in the coarse grained terminal particles of stardust aerogel tracks and a comprehensive dataset 10 3 analyses of analogous olivine grains 5 30 m isolated in ci cm cr ch co cv3 oxidized cv3 reduced c3 ungrouped acfer 094 and ningqiang l ll 3 0 4 eh3 and kakangari chondrite matrix these compositions reveal that wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite forming regions the wild 2 olivine includes amoeboid olivine aggregates aoas refractory forsterite type i and type ii chondrule fragments and or microchondrules and rare relict grain compositions in addition we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low temperature aqueous processing in the kuiper belt the generally low cr content of feo rich olivine in the stardust samples indicates that they underwent mild thermal metamorphism akin to a petrologic grade of 3 05 3 15

large silica rich igneous textured inclusions in the buzzard coulee chondrite condensates differentiates or impact melts we studied three large 2 4 mm diameter igneous textured inclusions in the buzzard coulee h4 chondrite using microanalytical techniques olm sem empa sims to better elucidate the origins of igneous inclusions in ordinary chondrites the inclusions are clasts that come in two varieties 1 white inclusions bz 1 and bz 2 represent a nearly holocrystalline assemblage of low ca and high ca pyroxene 63 66 area and cristobalite 33 36 and 2 tan inclusion bz 3 is glass rich approximately 60 with low ca and high ca pyroxene phenocrysts the bulk compositions of the inclusions determined by modal reconstruction are all sio2 rich approximately 67 wt for bz 1 and bz 2 approximately 62 for bz 3 but bz 3 is enriched in incompatible elements e g ree approximately 4 5 ci abundances whereas bz 2 and bz 1 are depleted in those elements that are most incompatible in pyroxene e g la ho approximately 0 15 0 4 ci abundances these bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor and show no evidence for overall volatility control we infer that the inclusions originated through igneous differentiation and feo reduction with bz 3 forming as an andesitic partial melt approximately 30 40 partial melting of an h chondrite precursor and bz 1 and bz 2 forming as pyroxene cristobalite cumulates from an si rich melt we suggest that both types of melts experienced a period of transit through a cold low pressure space environment in which cooling feo reduction and interaction with a vapor occurred melts may have been lofted into space by excavation or splashing during collisions or by pyroclastic volcanism our results indicate intriguing similarities between the inclusions in buzzard coulee and the silicates in some iron iie type and stony iron iva type meteorites suggesting a genetic relationship

acoustic inversions for measuring boundary layer suspended sediment processes although sound has been applied to the study of sediment transport processes for a number of years it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters in particular when the attenuation due to the suspension becomes significant the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension to study this attenuation propagation problem numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters the results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters which become increasingly erroneous with range as the sound propagates through the suspension to address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion this approach is not subject to the accumulation of errors and has an explicit solution here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion

turbidity currents and submarine channel formation in rupert inlet british columbia 1 surge observations acoustic backscatter images obtained at 107 and 200 khz of surge type turbidity currents resulting from mine tailing discharge are presented excess densities in the head of the order of 100 kg m 3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom reflected signal these excess densities are comparable to estimates based on surge height and speed the speed being determined by assuming a universal head shape unlike gravity current surges from an impulsively started steady source the surge type turbidity flows consist of a high concentration slug of short duration followed by a longer lived wake in which sediment concentrations are lower by 2 3 orders of magnitude the profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments discrete scatterers probably fish are observed to avoid the surges

new kind of type 3 chondrite with a graphite magnetite matrix abstract we have discovered four clasts in three ordinary chondrite regolith breccias which are a new kind of type 3 chondrite like ordinary and carbonaceous type 3 chondrites they have distinct chondrules some of which contain glass highly heterogeneous olivines and pyroxenes and predominantly monoclinic low ca pyroxenes but instead of the usual fine grained fe rich silicate matrix the clasts have a matrix composed largely of aggregates of micron and submicron sized graphite and magnetite the bulk compositions of the clasts as well as the types of chondrules largely porphyritic are typical of type 3 ordinary chondrites although chondrules in the clasts are somewhat smaller 0 1 0 5 mm a close relationship with ordinary chondrites is also indicated by the presence of similar graphite magnetite aggregates in seven type 3 ordinary chondrites this new kind of chondrite is probably the source of the abundant graphite magnetite inclusions in ordinary chondrite regolith breccias and may be more common than indicated by the absence of whole meteorites made of chondrules and graphite magnetite

the behavior of actinides phosphorus and rare earth elements during chondrite metamorphism new data on the u pu and p distributions in less metamorphosed h chondrites type 3 5 coupled with literature results permit a provisional picture to be assembled of the chemistry of these elements and for the rare earth elements in ordinary chondrites and the changes brought about by chondritic metamorphism preferential associations of phosphates with metals and or sulndes in all chondrites strongly indicate an initially siderophile or conceivably chalcophile character for p in ordinary chondrite precursor materials with phosphate subsequently formed by oxidation this oxidation occurred prior to or during chondritic metal silicate fractionation uranium is initially concentrated in chondrule glass at 100 ppb levels with phosphates primarily merrillite in h 3 chondrites being essentially u free 20 ppb as chondrule glass devitrified during metamorphism u migrated into phosphates reaching 50 ppb in nadiabondi h 5 merrillite and 200 300 ppb in merrillite from equilibrated chondrites but froze out before total concentration in phosphates occurred relative 244 pu fission track densities in the outer 5 m of olivine and pyroxene grains in contact with merrillite and with chondrule mesostasis in bremervorde h 3 give pu mesostasis pu merrillite 0 01 implying total concentration of pu in phosphates similarly no detectable pu 0 1 ppb was found in chondrule mesostasis in tieschitz and sharps whereas direct measurements of tracks in phosphates in h 3 chondrites are consistent with high 10 ppb pu concentrations thus a strong pu p correlation is indicated for ordinary chondrites there is variable pu u fractionation in all chondritic phosphates reaching an extreme degree in the unequilibrated chondrites therefore the pu u ratio in phosphates appears relatively useless for relative meteorite chronology literature data indicate that the ree are located in chondrules in unequilibrated chondrites most likely in glass thus there may also be strong pu nd fractionation within these meteorites like u the ree migrate into phosphates during metamorphism but unlike u appear to be quantitatively concentrated in phosphates in equilibrated chondrites thus relative ages based on pu nd may be possible for equilibrated chondrites but the same chronological conclusions are probably obtainable from pu concentrations in phosphates i e on the pu p ratio however pu p chronology is possible only for ordinary chondrites so there appears to be no universal reference element to cancel the effects of pu chemical fractionation in all meteorites available data are consistent with but certainly do not prove that variations in pu p represent age differences but if these age differences do not exist then it is conceivable that the solar system 244 pu 238 u ratio important for cosmochronology is still lower than the presently accepted value of 0 007

characterization of mason gully h5 the second recovered fall from the desert fireball network mason gully the second meteorite recovered using the desert fireball network dfn is characterized using petrography mineralogy oxygen isotopes bulk chemistry and physical properties geochemical data are consistent with its classification as an h5 ordinary chondrite several properties distinguish it from most other h chondrites its 10 7 porosity is predominantly macroscopic present as intergranular void spaces rather than microscopic cracks modal mineralogy determined via ps xrd element mapping via energy dispersive spectroscopy eds and x ray tomography for sulfide metal and porosity volume fractions consistently gives an unusually low olivine orthopyroxene ratio 0 67 0 76 for mason gully versus 1 3 for typical h5 ordinary chondrites widespread silicate darkening is observed in addition it contains a bright green crystalline object at the surface of the recovered stone diameter 1 5 mm which has a tridymite core with minor quartz and a rim of both low and high ca pyroxene the mineralogy allows the calculation of the temperatures and o2 characterizing thermal metamorphism on the parent body using both the two pyroxene and the olivine chromite geo oxybarometers these indicate that mg experienced a peak metamorphic temperature of 900 c and had a similar o2 to kernouve h6 that was buffered by the reaction between olivine metal and pyroxene there is no evidence for shock consistent with the observed porosity structure thus while mason gully has some unique properties its geochemistry indicates a similar thermal evolution to other h chondrites the presence of tridymite while rare is seen in other ocs and likely exogenous however the green object itself may result from metamorphism

the adhi kot breccia and implications for the origin of chondrules and silica rich clasts in enstatite chondrites abstract the adhi kot eh4 enstatite chondrite breccia consists of silica rich clasts 12 mn 5 vol chondrule rich clasts 55 mn 10 vol and matrix 35 mn 10 vol the silica rich clasts are a new kind of enstatite chondritic material which contains more cristobalite 18 28 wt than enstatite 12 14 wt as well as abundant niningerite and troilite the bulk atomic mg si ratios of the clasts 0 22 0 40 are much lower than the average for enstatite chondrites 0 79 kamacite and martensite with 8 11 wt ni and a martensitic structure occur in all three breccia components the clasts have kamacite rich rims and kamacite rich aggregates occur in the matrix a unidirectional change in the ambient ps2 po2 ratio in the region of the solar nebula where adhi kot agglomerated can explain many of the breccia s petrologic features if this region initially had a very high ps2 po2 ratio in a gas of non cosmic composition sulfurization of enstatite and metallic fe e g mgsio3 2fe c 3h2s mgs sio2 2fes h2o ch4 may have occurred producing abundant niningerite free silica and troilite at the expense of enstatite and metallic fe the ni content of the residual metal would have increased perhaps to 8 10 wt the silica rich clasts agglomerated under these conditions a significant fraction of the originally produced niningerite was lost perhaps by aerodynamic size sorting processes lowering the clasts bulk mg si ratios the ps2 po2 ratio then decreased perhaps because of infusion of additional h2o and sulfurization of metallic fe and enstatite ceased the chondrule rich clasts agglomerated under these conditions acquiring little free silica and niningerite an episode of chondrule formation occurred at this time by melting millimeter sized agglomerates of this relatively silica poor enstatite chondrite material and concomitant fractionation of an immiscible liquid of metallic fe ni and sulfide the chondrule rich clasts agglomerated many such chondrules subsequently the matrix agglomerated acquiring the few remaining chondrules kamacite rich aggregates formed after the cessation of metal sulfurization and agglomerated with the matrix the kamacite rich clast rims were acquired at this time the components of adhi kot accreted to the eh chondrite parent body where the breccia was assembled buried beneath additional accreting material and metamorphosed at temperatures of 700 c impact excavation of the breccia and deposition onto the surface caused the formation of martensite from taenite inside the clasts and the matrix at the surface impact melting produced an albite glass spherule which was incorporated into the matrix however the absence of solar wind implanted rare gases in bulk adhi kot indicates that the breccia spent little time in a regolith

cristobalite pyroxene in an l6 chondrite implications for metamorphism crispy is a cristobalite pyroxene assemblage in the l6 chondrite alha 76003 it was formed by reaction of a very siliceous inclusion with the surrounding olivine rich rock oxygen isotopes show that the inclusion was derived from a source with non chondritic isotopic composition the isotopes also show that the oxygen of the pyroxene reaction product was derived by simple mixing of oxygen from the inclusion and its immediately adjacent surroundings with exchange with the bulk meteorite limited to a distance of about a millimeter the persistence of cristobalite in close proximity to olivine and the lack of isotopic equilibration show that the metamorphic processes that form petrographic grade 6 chondrites involve transport of major elements over distances only on the order of millimeters

acoustic imaging of reservoir structure from a horizontal well recent advances in well placement technology now allow a borehole to be steered with considerable precision inside the reservoir with modern completion technology the subsequent flow of hydrocarbons within the reservoir can be controlled to a greater extent than ever before these developments have further emphasized the need for an improved ability to image structures such as caprock stringers faults fractures and pore fluid contacts on the reservoir scale

processing array acoustic logging data to image near borehole geologic structures imaging near borehole structures using acoustic logging data depends on the data processing method used we demonstrate that extracting the up and downgoing reflections from the data and using those separately for the imaging can significantly improve the image quality a parametric wave separation is first applied to array data to separate direct and reflection waves in particular we use a transmitter array gathered from successive source positions to extract the upgoing reflection reflection data can also be enhanced by stacking data along the reflection moveout in array using approximate structural dip information implementation of this method to acoustic logging data processing improves imaging quality making it possible to image near borehole geologic structures using conventional array acoustic logging a potentially important application of drilling steering is using logging while drilling acoustic measurements

characteristics of waveforms recorded by azimuthally spaced hydrophones of sonic logging tool for incident plane waves abstractthe borehole acoustic reflection survey bars is a method for imaging near borehole structures using waveforms acquired by a sonic logging tool signals from a monopole or dipole source are reflected from geologic interfaces and recorded by arrays of the hydrophones of the same tool due to the nearly 1d configuration of the source and hydrophones bars provides only 2d images in which the dimensions are the axis of the well and the distance from the center of the well we have developed methods for identifying the azimuthal direction of the reflector which is not given by the bars image by using the differences of the signals recorded by hydrophones at varying azimuths we have conducted a theoretical analysis for incident plane waves as follows analytic solutions in the frequency domain are numerically computed at discrete frequencies and converted to time domain synthetics using the fast fourier transform for a newly derived model that includes the effect of the tool in the fluid filled bo

fayalite in the kaba and mokoia carbonaceous chondrites abstract the olivines in the kaba and mokoia cv3 carbonaceous chondrites range from almost pure forsterite fo99 6 to almost pure fayalite fa99 9 individual grains of fayalite of such high purity have not previously been reported from meteorites they can reach 100 m in diameter and occur in the matrix chondrules forsterite enstatite aggregates and rims around ca al rich inclusions chondrules and aggregates the fayalite is three to nine times richer in mn than in bulk ci chondrites many grains are associated with magnetite troilite and pentlandite an assemblage that suggests relatively oxidizing conditions we propose that the fayalite formed through reaction of sio g released by decomposition of enstatite with magnetite and sulfide the lower thermal limit for fayalite formation is determined by the above reaction whereas the upper thermal limit is controlled by magnetite stability thermodynamic calculations indicate that fayalite coexisting with magnetite and sulfides could have formed in a nebular environment that had a h 2 o h 2 ratio substantially greater than the canonical solar nebula coexisting olivines having endmember compositions indicate that they experienced little or no thermal metamorphism

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

determining the extinction cross section of aggregating fish when fish are aggregated over a flat bottom and fish and bottom echoes can be distinguished it is possible to determine the fish extinction cross section by a simple application of the echo integration method the theory for this is developed measurements at 38 khz are presented for aggregations of the same 1983 year class of herring over flat bottomed fjord areas in 1988 1990 and 1991 the ratio of extinction and backscattering cross sections is found to lie in the approximate range from 1 2 2 3 depending on fish size and time of day

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

silica bearing chondrules and clasts in ordinary chondrites unusual silica bearing chondrules and clasts have been observed in several unequilibrated ordinary chondrites there appear to be two distinct types i silica low ca pyroxene assemblages and ii silica fayalite intergrowths coexisting with low ca pyroxene only the former types are chondrules the bulk compositions of most of these objects can be expressed in terms of three components mgo feo and sio 2 since ca al and na are essentially trace elements secondary alteration has probably perturbed the fe mg ratios in most objects and produced ca rich pyroxenes in some type ii clasts but the silica low ca pyroxene and fayalite are hard to understand as other than primary phases such silica rich bulk compositions can be understood as an intermediate temperature condensate of a solar gas formed by the loss of refractory solid material by gas solid separation before the complete condensation of silicon alternatively the silicarich bulk compositions could have been formed by extreme reduction of normal chondritic olivine and orthopyroxene however the observed ca al depletion and the lack of ni poor metals are not explained by this model the fayalite bearing clasts can be explained by a relatively complex two stage process involving reduction followed by oxidation partial reduction of olivine in the presence of s produces mg rich pyroxene silica and fefes oxidation of metal and sulfide followed by reaction with silica forms fayalite an alternative is that the fayalite bearing clasts result from the decomposition of ferrosilite but this requires the production of metastable ferrosilite during shock or some other high pressure event the simplest unflawed alternative is that the fayalite bearing clasts result from the mixing of a partially molten silica fayalite liquid with mg rich pyroxene