shallow seismic reflection profiling over the brevard zone south carolina shallow reflection profiles over crystalline rocks of the brevard zone show events that correlate with projections of mapped lithologic contacts in spite of strong attenuation and statics effects associated with a zone of severe chemical weathering saprolite the profiles which were collected in western south carolina about 5 km from appalachian ultra deep core hole adcoh regional lines 1 and 3 straddle the contact between the brevard fault zone and the wider brevard mylonitic shear zone to the southeast the principal goal of these experiments was to test the feasibility of using a hammer source and 24 channel seismograph to image near surface brittle and ductile structures to a depth of several hundred meters we recorded two dip lines and one strike line with a total common midpoint cmp coverage of 1 km processing focused on eliminating static shifts and separating reflections from overlapping refracted s waves a statics approach based on the alignment of first arrivals on common offset gath

mineralogical characterization of a unique material having heavy oxygen isotope anomaly in matrix of the primitive carbonaceous chondrite acfer 094 abstract we report the mineral compositions and micro texture of the isotopically anomalous 17 18osmow 180 fe s ni o material recently discovered in matrix of the primitive carbonaceous chondrite acfer 094 sakamoto n seto y itoh s kuramoto k fujino k nagashima k krot a n and yurimoto h 2007 oxygen isotope evidence for remnants of the early solar system primordial water science 317 231 233 synchrotron radiation x ray diffraction and transmission electron microscopy studies indicate that this material consists of the symplectitically intergrown magnetite fe3o4 and pentlandite fe5 7ni3 3s8 with magnetite pentlandite volume ratio of 2 3 magnetite forms column shaped grains 10 30 nm in diameter and 100 200 nm in length pentlandite occurs as worm shaped grains or aggregates of grains 100 300 nm in size between magnetite crystals although both the x ray diffraction and electron energy loss spectra support identification of iron oxide as magnetite the electron diffraction patterns show that magnetite has a weak 3 fold superstructure possibly due to ordering of vacancies we infer that the isotopically anomalous symplectite formed by sulfurization and oxidization of metal grains either in the solar nebula or on an icy planetesimal the intersite cation distribution of pentlandite suggests that timescale of oxidation was no longer than 1000 years

crustal structure measurements near fram ii in the pole abyssal plain abstract an extensive refraction profiling program was carried out during the fram ii experiment march may 1980 in the eastern arctic ocean two structural areas were covered north of the ice camp 86 n 24 w into the basin of the pole abyssal plain and south onto the flanks of the morris jesup rise digital multichannel data on an 800 by 800 m 24 channel hydrophone array and a single 2 component ocean bottom seismometer obs were recorded for offsets from 2 5 to 100 km arrival times amplitudes and phase velocities of the seismic signals recieved on the hydrophone array were determined using high resolution array processing from these measurements and the obs data preliminary velocity structural models of the crust have been derived for the purposes of this paper 2 refraction lines have been analyzed a 40 km line on a flat region of the pole abyssal plain and an 86 km line on a slightly dipping region taken as the drifting ice camp shoaled on the morris jesup rise these preliminary analyses yield a sedimentary layer with a gradually increasing velocity 1 5 2 km thick this cover overlays a crust with a thin layer 2 and yields a total ocean bottom to mantle thickness of 4 7 km

nature of the eastern boundary of the rio grande rift from cocorp surveys in the albuquerque basin new mexico reprocessing and synthetic seismic modeling of cocorp profiles across the eastern margin of the rio grande rift at abo pass new mexico suggest that synthetic and antithetic cenozoic normal faults sole into or are truncated by a northwest dipping listric master fault which bounds the eastern side of the basin and reaches a depth of at least 10 km beneath the southern albuquerque basin this fault appears to project toward the surface position of the los pinos cenozoic normal fault which lies basinward of and trends parallel to a mapped laramide duplex thrust zone the los pinos fault may sole into the older thrust reactivating this preexisting compressional structure at depth a lateral change in reflection amplitude and frequency is conspicuous across the eastern rift margin analysis demonstrates that source coupling is the main cause of a much deteriorated signal below the rift basin although complex ray paths and attenuation by the graben fill may contribute

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

wave field processing of data from a large aperture seismic experiment in southwestern oklahoma data from a wide aperture survey performed in january 1985 in southwestern oklahoma have been processed using prestack imaging and the images are interpreted to reveal a new picture of the crustal structure in the wichita uplift and the anadarko basin as the data were in recording apertures of approximately 90 km it was necessary to develop new processing concepts and software a complete new imaging system based on common source gathers was conceived implemented tested and applied to these data the heart of the system consists of velocity estimation by slant stacking and acoustic prestack reverse time finite difference migration the migration produces reflectivity images in regions of 50 km 100 km has no dip restrictions and operates in an arbitrarily complicated two dimensional velocity distribution for comparison the data were also processed using standard common midpoint processing but this is a less valid approach for wide aperture data the main ambiguities and limitations in processing and interpretation are a consequence of the small number of shots processing and interpretation of the data provide a new picture of the subsurface structure of southwestern oklahoma the environment is clearly compressive with thrust faulting as the main accommodating mechanism in the upper and central crust beneath a possible detachment zone at 30 km depth the lower crust has responded to the compression by thickening by 50 the moho is interpreted to be 45 km in depth beneath the thrust zone shallowing to 40 km beneath the wichita uplift and the anadarko basin

observing system simulation experiments in geomagnetic data assimilation 1 observing system simulation experiments osses have been carried out for a geomagnetic data assimilation system the purpose of these experiments is to demonstrate how new algorithms for assimilating geomagnetic observations into a geodynamo model can be evaluated a nature run is carried out to establish a true evolution of the earth s core state from which synthetic surface geomagnetic field observations are created these observations are then assimilated into the geodynamo model using an optimal interpolation oi scheme model error is simulated by using a different rayleigh number in the nature and model runs because the true core state evolution is known completely the assimilation results can be evaluated in terms of any state variable and at any point in the computational domain in this work we focus on the poloidal observed and toroidal unobserved components of the magnetic field throughout the outer core experiments are carried out using observations of different degrees and varying forecast error correlation length scales we also investigate the impact of model error on the assimilation and on the accuracy of geomagnetic forecasts assimilation runs lasting about 90 of the magnetic free decay time show a positive impact on both components of magnetic field deep within the outer core forecasts of the surface magnetic field show much lower error growth indicating that the initial condition used for the forecasts has been substantially improved through assimilation

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

a 2 d ray based depth migration method for deep seismic reflections summary although accurate depth migration is essential for the correct geometrical interpretation of deep reflection data migration by the standard numerical methods has generally not been satisfactory the alternative method presented in this paper provides an efficient migration for deep reflection profiles in the form of a digitized line drawing assuming a general 2 d velocity structure migration of a digitized line drawing reduces the effects of low signal noise ratios the calculation is rapid allowing migrations to be calculated for a large number of alternative velocity structures and iterative improvement of the velocity structure the migration has been applied to 3 d structures observed on intersecting profiles collected by birps british institutes reflection profiling syndicate

deep structure of the u s atlantic continental margin offshore south carolina from coincident ocean bottom and multichannel seismic data we present the results of a combined multichannel seismic reflection mcs and wide angle ocean bottom seismic profile collected in 1988 across the carolina trough on the u s atlantic continental margin inversion of vertical incidence and wide angle travel time data has produced a velocity model of the entire crust across the continent ocean transition the margin consists of three structural elements 1 rifted continental crust comprising 1 4 km of post rift sedimentary rocks overlying a 30 34 km thick subsedimentary crust 2 transitional crust a 70 to 80 km wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10 to 24 km thick subsedimentary crust and 3 oceanic crust comprising 8 km of sedimentary rocks overlying an 8 km thick crystalline crust the boundary between rifted continental and transitional crust marked by the brunswick magnetic anomaly represents an abrupt change in physical properties with strong lateral increases in seismic velocity density and magnetic susceptibility the transitional crust contains mid crustal seaward dipping reflections observed on the mcs section and has seismic velocities of 6 5 6 9 km s in the midcrust and 7 2 7 5 km s in the lower crust modeling of potential field data shows that transitional crust also produces the prominent margin parallel gravity anomaly and the brunswick and east coast magnetic anomalies these observations support the interpretation that the transitional crust was formed by magmatism during continental breakup the prodigious thickness up to 24 km of igneous material rivals that interpreted on continental margins of the north atlantic e g hatton bank and voring plateau which formed in the vicinity of the iceland hotspot these observations when combined with other transects across the margin confirm previous suggestions that the u s atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long lived mantle plume

late formation of a comet wild 2 crystalline silicate particle pyxie inferred from al mg chronology of plagioclase we examined the al mg isotope systematics of plagioclase in a feo poor ferromagnesian wild 2 particle c2092 7 81 1 0 named pyxie using a 2 m spot three analyses show average 27al 24mg ratio of 65 and excess 26mg value of 0 1 4 5 0 1 4 5 2 indicating no resolvable 26mg excess in the particle the inferred initial 26al 27al 0 ratio of plagioclase in pyxie is estimated as 0 6 4 5 10 6 0 6 4 5 10 6 with an upper limit of 4 10 64 10 6 the result is very similar to that of the feo rich ferromagnesian particle iris ogliore et al 2012 assuming homogeneous distribution of 26al in the early solar system pyxie formed at least 2 6 ma after the oldest ca al rich inclusions this minimum formation age is marginally younger than formation ages of most chondrules in type 3 0 chondrites but comparable with those of mg 98 chondrules in cr3 chondrites considered in conjunction with similar oxygen isotope ratios between pyxie and iris and mg 98 chondrules in cr3 chondrites it is inferred that the ferromagnesian wild 2 particles and mg 98 chondrules in cr3 chondrites formed late in local disk environments that had similar oxygen isotope ratios and redox states

oxygen isotopic composition of coarse and fine grained material from comet 81p wild 2 abstract individual particles from comet 81p wild 2 collected by nasa s stardust mission vary in size from small sub m fragments found in the walls of the aerogel tracks to large fragments up to tens of m in size found towards the termini of tracks the comet in an orbit beyond neptune since its formation retains an intact a record of early solar system processes that was compromised in asteroidal samples by heating and aqueous alteration we measured the o isotopic composition of seven stardust fragments larger than 2 m extracted from five different stardust aerogel tracks and 63 particles smaller than 2 m from the wall of a stardust track the larger particles show a relatively narrow range of o isotopic compositions that is consistent with 16 o poor phases commonly seen in meteorites many of the larger stardust fragments studied so far have chondrule like mineralogy which is consistent with formation in the inner solar system the fine grained material shows a very broad range of o isotopic compositions 70 17 o

depth migration and interpretation of the cocorp wind river wyoming seismic reflection data to better understand laramide deformation deep seismic reflection data have been depth migrated focused or imaged in order to more clearly reveal structural features associated with the wind river thrust wyoming major structural features displayed in the migrated data are the wind river fault zone and the pacific creek anticline the wind river fault zone is seen to a depth of at least 25 km and interpretively to 32 km it is a complex zone that includes numerous splays flattening with depth the wind river range was tilted along these arcuate splays as it was compressionally thrust up the pacific creek anticline is asymmetric and thrust cored with the top of basement offset 600 m the pacific creek thrust is viewed as an embryonic wind river thrust

seismic images and evolution of the iberian crust in the pyrenees abstract crustal images of the pyrenean range based on coincident wide angle and vertical deep seismic profiles are presented in this study wide angle experiments in the thickened iberian crust along strike lines have provided no evidence for reflections from interfaces between layers of different velocities in the middle or lower crust in contrast reversed sounding on a line across the pyrenean range shows wide angle reflectivity its unusual reflectivity pattern points to widespread impedance contrasts of localized continuity embedded in the crust this observation is consistent with a new image of vertical incidence reflectivity obtained by coherency weighted migration of the coincident ecors traverse this profile shows numerous discontinuous and dipping reflections from the middle to the base of the crust the reflections dip towards the axis of the range the upper limit and the attitude of the reflective zones are so strongly variable that the crust can hardly be envisaged as the simple continuous three layered model previously used for geodynamical reconstructions the reflective zones cannot be brought back to the horizontal image of a layered lower crust of proposed extensional origin by plate unbending to the pre alpine stage the dipping reflections may result from compressional deformation as the south pyrenean deep crustal domain has undergone both hercynian and alpine orogenic deformation if part of the present reflectivity pattern was due to alpine remobilization the corresponding lower crustal deformation would have spread out thereby accomodating convergence by thickening even outside the axial zone where the upper crustal deformation appears to be concentrated

crustal thickness variations across the blue ridge mountains southern appalachians an alternative procedure for migrating wide angle reflection data abstract migration of wide angle reflections generated by quarry blasts suggests that crustal thickness increases from 38 km beneath the carolina terrane to 47 51 km along the southeastern flank of the blue ridge the migration algorithm developed for generating single fold images from explosions and earthquakes recorded with isolated short aperture arrays uses the localized slant stack as an intermediate data set in contrast with other methods it includes an interpretive step that is based on the assumption that all coherent p wave energy consists of reflections from planar interfaces each sample in the slant stack is mapped into a planar dipping segment with a length that is determined by the recording aperture migrated sections from within the blue ridge show increases in reflectivity at depths of 20 and 40 km high apparent reflectivity from 40 to 50 55 km suggests a layered zone in the lower crust that is similar to models proposed for the cumberland plateau in tennessee and the adirondacks the migration results are consistent with regional gravity data and with the occurrence of crustal roots beneath the urals another paleozoic orogen

migration of wide aperture onshore offshore seismic data central california seismic images of late stage subduction we conducted a high shot and receiver density onshore offshore seismic experiment in 1986 across the central california transform margin as part of the pacific gas and electric edge deep crustal geophysical survey the data set consists of land recordings of 406 marine air gun shots fired along a 70 km track across the santa maria basin the seismic vessel s track was collinear with 154 land seismic recorders deployed over 50 km across the sur obispo terrane and part of the salinian block the source receiver offsets range from 2 5 km to 120 km the unique recording geometry and high shot and receiver density permit imaging the deeper crustal structure of the california transform margin but pose serious challenges for conventional seismic imaging methods consequently we developed a unified approach to wide angle imaging which incorporates a tomography technique for obtaining initial migration velocity models and a prestack kirchhoff depth migration with depth focusing of the main reflectors for velocity model refinement and imaging this approach retains the velocity and dip information in the data and allows user control over the imaging process we applied this processing to subsets of the onshore offshore data to obtain an upper crustal velocity model and a 32 km long wide angle depth migrated image of the lower crust in the coastal region under the santa maria basin and the sur obispo terrane the migration image shows a part of an underplated oceanic crustal layer interpreted as the monterey plate meltzer and levander 1991 miller et al 1992 which dips coastward at depths of 18 to 28 km the plate appears to be kinked or imbricated beneath the coastline the image correlates well with existing wide angle seismic interpretations based on ray tracing walter and sharpless 1987 putzig 1988 howie et al 1993 the migrated lower crustal image has more structural information than is apparent in conventional ray based interpretations along the same crossing and adjacent profiles the crustal image demonstrates that automated imaging techniques applied to wide angle data can provide images of crustal structure comparable in fidelity to conventionally processed and migrated near vertical incidence data

the extension of grenville basement beneath the northern appalachians results from the quebec maine seismic reflection and refraction surveys from 1983 to 1984 the united states geological survey and the geological survey of canada undertook a series of seismic experiments to determine the crustal structure of the appalachian mountain belt in maine and southeast quebec these experiments included four deep crustal seismic reflection profiles perpendicular to the strike of regional geological trends and several high resolution refraction wide angle reflection profiles both parallel and perpendicular to strike here the data recorded in quebec and the northwest part of maine are interpreted in conjunction with existing reflection profiles from quebec synthetic seismogram calculations in laterally varying media are used to model the refraction wide angle reflection data while reprocessing migration and attribute plotting are used in the interpretation of the reflection data a major zone of reflections extending over a distance exceeding 200 km can be traced from shallow depths beneath the st lawrence lowlands southeast to about 25 km depth beneath the southeast edge of the chain lakes massif this zone of reflections is interpreted as a master decollement separating autochthonous grenville basement from overlying allochthonous rocks of the appalachian orogen including foreshortened miogeoclinal rocks the remnants of one or more magmatic arcs the connecticut valley gaspe synclinorium and the chain lakes massif in the vicinity of the chain lakes massif extension has caused grenville basement to be thinned by as much as 40 reflections from the decollement show strong layering and evidence for basement faulting associated with the guadeloupe and other faults normal incidence and wide angle reflections are observed to be almost continuous beneath the baie verte brompton line and connecticut valley gaspe synclinorium indicating that the baie verte brompton line is confined to the upper crust the connecticut valley gaspe synclinorium is characterized by p wave velocities of about 5 3 km s 1 and is shown to be a shallow structure with a maximum depth of about 3 km rock velocities immediately below the connecticut valley gaspe synclinorium are typical of chain lakes material 6 1 km s 1 a new model for the tectonic development of the region is proposed in which all pre silurian units between the baie verte brompton line and the southeastern edge of the chain lakes massif are allochthonous and confined to the upper crust we infer that the chain lakes massif volcanics of the ascot weedon formation and associated deeper crustal rocks were thrust over grenvillian basement as a composite unit and may now underlie parts of the connecticut valley gaspe synclinorium

dip moveout by fourier transform the conventional normal moveout nmo and common midpoint cmp stacking process enhances reflections having a particular moveout velocity while attenuating events such as multiple reflections having different moveout velocities unfortunately this process also acts as a dip filter applied to the cmp stack in other words nmo and stacking enhances reflections having a particular slope in the cmp stack while attenuating reflections having different slopes nmo and stacking like any dip filter degrades lateral resolution fortunately this dip filtering action can be suppressed by applying in addition to nmo a prestack process known variously as devilish prestack partial migration and dip moveout as the latter term implies this process is a dip dependent moveout correction that enables reflections from both horizontal and dipping reflectors to be stacked with the same nmo velocity stated another way nmo velocities estimated from dip moveout corrected seismograms are independent of the dips o

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

focusing in prestack isochrone migration using instantaneous slowness information prestack migration finds increasing application in processing crustal seismic data however less effort has been made to incorporate slowness information in the imaging process the combination of slowness information with migration leads to an improved image in the depth domain especially by reducing migration artefacts and noise a slowness driven isochrone migration scheme is introduced for migration of 2 d seismic data instantaneous slowness information p x t is extracted from the data using correlation analysis in moving time and space windows slowness values resulting from spatial coherent energy signal and incoherent background noise are distinguished by the simultaneous evaluation of an instantaneous coherence criterion g x t in slowness driven isochrone migration this information is used for locally weighting the amplitude a x t smearing on the isochrone surface in particular slowness p and coherence criterion g determine position and sharpness of a gaussian weighting function the method is demonstrated using two synthetic data examples and is subsequently applied to two deep crustal data sets one wide angle along dekorp4 and one steep angle reflection seismic observation ktb8506 both data sets were collected in the surroundings of the ktb drill site oberpfalz as part of the german dekorp project

wide angle reflection migration technique with an example from the polar profile northern scandinavia abstract the 440 km long polar profile runs approximately sw to ne across the baltic shield from the karelian province through the lapland granulite belt and the kola peninsula province in northern finland and northern norway the migration method developed by v n pilipenko physics of the earth n1 1983 36 42 was applied to the wide angle reflection data obtained along the profile to prepare the data for the migration p and s waves were analysed with more attention to the distribution of real reflectors in the crust and on the relation between the p and s wave velocities depth migrated images of the crustal structure were obtained for both the p and s wave fields this new analysis revealed structural features of the crust which had not before been imaged the most impressive features are several inclined boundaries in the upper crust dipping northeast beneath the lapland granulite belt another newly found element is a lower crustal boundary at a depth of 35 km in the karelian province which is well traced in the p wave migration image but is not observed in the s wave image this boundary corresponds to a strong change in the v p v s ratio in the lower crust which may be interpreted in terms of mafic crustal composition we have found that this migration technique can be applied to deep seismic sounding data resulting in new opportunities for deep crustal seismic studies nevertheless more and denser observations are necessary to continue the improvement of the resolution and the reliability of the structure images

enhanced crustal reflection continuity by estimation of staitcs from coherence filtered sections coherency filtered seismic sections provide excellent models for estimating residual statics especially for deep crustal data with low signal to noise a second coherency filter pass following residual statics collections provides even better structural clarity than is seen on sections with only a single coherency filter pass benefits of the technique include increased lateral extent of individual reflections resulting in fewer isolated events uniform wavelet shape throughout the section and an increase in the number of detected events over line drawings this processing flow results in appealing visual displays and may provide new information on structural complexities not recognized in line drawings based on the input data alone

aqueous alteration in the matrix of the vigarano cv3 carbonaceous chondrite the matrix of vigarano a meteorite which belongs to the reduced subgroup of the cv3 chondrites contains small amounts 10 of ferrihydrite and smectite these hydrous minerals occur together as fine fibrous intergrowths between anhydrous silicate and oxide grains coarser crystals of ferrihydrite fill fractures that cut matrix minerals and smectite also lines narrow channels within olivine grains these channels may have formed by preferential alteration of olivines along 100 parallel defects formation of ferrihydrite and smectite in the matrix of vigarano was the result of mild aqueous alteration in a low temperature 150 c oxidising parent body environment partial equilibration of matrix olivines indicates that alteration was followed by thermal metamorphism with a peak temperature of 400 500 c mineralogically similar alteration products which also were formed by parent body processes have previously been described from the matrices of four cv meteorites bali grosnaja kaba and mokoia all of which belong to the oxidised subgroup this discovery of the products of oxidative aqueous alteration in vigarano has important consequences for understanding the chemical and thermal history of the cv class of meteorites

constraints on the formation environment of two chondrule like igneous particles from comet 81p wild 2 using chemical and petrologic evidence and modeling we deduce that two chondrule like particles named iris and callie from stardust cometary track c2052 12 74 formed in an environment very similar to that seen for type ii chondrules in meteorites iris was heated near liquidus equilibrated and cooled at 100 c hr and within 2 log units of the iw buffer with a high partial pressure of na such as would be present with dust enrichments of 103 there was no detectable metamorphic nebular or aqueous alteration in previous work ogliore et al 2012 reported that iris formed late 3 myr after cais assuming 26al was homogenously distributed and was rich in heavy oxygen iris may be similar to assemblages found only in interplanetary dust particles and stardust cometary samples called kool particles callie is chemically and isotopically very similar but not identical to iris

slowness weighted diffraction stack for migrating wide angle seismic data in laterally varying media wide angle prestack depth migration is an important tool for studying the nature of reflecting boundaries in the earth s crust the slowness weighted diffraction stack swds method has been used to incorporate both two way traveltime constraints and slowness information in the migration for this purpose traveltimes and apparent slownesses of reflected arrivals must be calculated in the image space earlier applications of swds required a 1d or gently varying seismic velocity structure to obtain these quantities by ray tracing in the image space i show that the apparent slownesses can also be derived directly from one way traveltime maps using fermat s principle the sdws is applied to an existing onshore offshore wide angle data set and the example shows that the method can be used to image detailed reflectivity structure at great depths

deep crustal features of the celtic sea from complementary processing on the swat data complementary processing develop by bano 1989 including automatic extraction of reflections and migration of deep seismic data are applied to the swat south west approaches traverse deep seismic profiles in the celtic sea the automatic extraction of reflection gives a more reliable definition of the basement under the deep celtic sea basins using migration we derive a more accurate geometry of these basins

decomposition and inversion of seismic data an instantaneous slowness approach interpretation techniques are presented that aim at the estimation of seismic velocities the application of localized slant stacks weighted by coherency produces a decomposition of multichannel seismic data into single trace instantaneous slowness rho chi t components color displays support the interpretation of seismic data relevant to the near surface velocity structure since rho chi t is directly related to stacking velocities and the depth of reflection or bottoming points in the subsurface this data transformation provides a powerful tool for the inversion of reflection and refraction data

a quantitative approach to bedrock velocity resolution and precision the lithoprobe vancouver island experiment bedrock velocities obtained from the inversion of first break picks of multichannel seismic reflection data have been used to aid the interpretation of shallow reflectors the trade off between resolution and stability of inversion results has been examined models have been optimized by minimizing the variability of static corrections and a monte carlo method has been used to estimate their precision a velocity of 4 6 0 4 km s for the leech river complex lrc compares with velocities of 5 9 0 6 and 5 8 0 3 km s for the neighboring geological units velocity contrasts associated with the change in lithologies may therefore be a contributing factor for generating reflections from the faults that bound the lrc velocities of 5 5 0 4 and 4 6 0 6 km s on either side of the san juan fault suggest that an event identified on several shot gathers may be a reflection from a steeply dipping fault

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

seismic reflection imaging of the subducting juan de fuca plate mckenzie and parker s early suggestion1 that the juan de fuca plate is underthrusting north america has since been confirmed by numerous studies evidence for plate convergence along this junction includes a sediment filled trench2 7 intense compressional deformation of the continental slope and shelf sediments2 7 seafloor magnetic anomalies that extend beneath the continental slope2 4 inland andesitic volcanoes8 paired low high heat flow and gravity anomalies9 10 active onshore deformation11 12 onshore crustal earthquakes with compressional axes parallel to the direction of plate convergence13 sinistral strike slip earthquakes along the nootka fault fig 1 14 and a well defined benioff wadati zone6 15 16 here we report the results of a seismic reflection survey that has delineated two slabs of oceanic lithosphere underlying vancouver island one that is currently being subducted and one that is underplated these findings lead us to speculate that successive underplating of oceanic lithosphere may be an important process in the evolution and growth of continents

refractory materials in comet samples transmission electron microscope examination of more than 250 fragments 1 m from comet wild 2 and a giant cluster interplanetary dust particle gcp of probable cometary origin has revealed four new calcium aluminum rich inclusions cais an amoeboid olivine aggregate aoa and an additional aoa or al rich chondrule arc object all of the cais have concentric mineral structures and are composed of spinel anorthite cores surrounded by al ti clinopyroxenes and are similar to two previous cais discovered in wild 2 all of the cometary refractory objects are of moderate refractory character the mineral assemblages textures and bulk compositions of the comet cais are similar to nodules in fine grained spinel rich inclusions fgis found in primitive chondrites and like the nodules may be nebular condensates that were altered via solid gas reactions in the solar nebula oxygen isotopes collected on one wild 2 cai also match fgis the lack of the most refractory inclusions in the comet samples may reflect the higher abundances of small moderately refractory cai nodules that were produced in the nebula and the small sample sizes collected in the comet samples approximately 2 3 of all fragments larger than 1 m by number are cais and nearly 50 of all bulbous stardust tracks contain at least one cai we estimate that 0 5 volume of wild 2 material and 1 volume of gcp is in the form of cais arcs and aoas account for 1 of the wild 2 and gcp grains by number

origin of crystalline silicates from comet 81p wild 2 combined study on their oxygen isotopes and mineral chemistry in order to explore the link between comet 81p wild 2 and materials in primitive meteorites seven particles 5 to 15 m in diameter from comet 81p wild 2 have been analyzed for their oxygen isotope ratios using a secondary ion mass spectrometer most particles are single minerals consisting of olivine or pyroxene with mg higher than 85 which are relatively minor in 81p wild 2 particles 1 3 of the 16o poor cluster four particles extracted from track 149 are 16o poor and show 17o 17o 0 52 18o values from 2 0 to 1 0 similar to previous studies while one enstatite en99 particle shows lower 17o value of 7 4 o 2 this compositional range has not been reported among 16o poor particles in 81p wild 2 but is commonly observed among chondrules in carbonaceous chondrites and in particular in cr chondrites the distribution in 17o indicates that 16o poor 81p wild 2 particles are most similar to chondrules and their fragments in the cr chondrites and tagish lake like wis91600 chondrite chondrule silicate grains which indicates that they likely come from a reservoir with similar dust ice ratios as cr chondrites and wis91600 however differences in the mg distribution imply that the 81p wild 2 reservoir was comparatively more oxidized with a higher dust enrichment two nearly pure enstatite grains from track 172 are significantly enriched in 16o with 18o values of 51 2 1 5 0 2 and 43 0 1 3 2 respectively and 17o values of 22 3 1 9 2 and 21 3 2 3 0 2 respectively they are the first 16o rich pyroxenes found among 81p wild 2 particles with similar 17o values to those of 16o rich low iron manganese enriched lime olivine and cai calcium and aluminum rich inclusions like particles from 81p wild 2 the major element and oxygen isotopic compositions of the pyroxenes are similar to those of enstatite in amoeboid olivine aggregates aoas in primitive chondrites in which 16o rich pyroxenes have previously been found and thus suggest a condensation origin

radiation and receiver pattern of shear and compressional waves as a function of poisson s ratio shear s wave studies in addition to compressional p wave surveys have revealed that s wave velocities are much more variable than p wave velocities this strongly affects poisson s ratio especially in young sediments it is shown that has a great influence on the directivity pattern i e on the radiation and receiving characteristic of horizontal sources and receivers for their calculation well known surface boundary conditions and white s statement of the reciprocity relation white 1965 are used they also form the basis for the combination of source and receiver patterns essential for practical field work the various combinations of horizontally and vertically arranged sources and receivers are investigated with regard to their directivity pattern their amplitude ratio and in general to their usefulness in seismic prospecting

lithoprobe seismic reflection profiling across vancouver island results from reprocessing summary multichannel seismic reflection sections recorded across vancouver island have revealed two extensive zones of deep seismic reflections that dip gently to the northeast and a number of moderate northeasterly dipping reflections that can be traced to the surface where major faults are exposed based on an integrated interpretation of these data with information from gravity heat flow seismicity seismic refraction magnetotelluric and geological studies it is concluded that the lower zone of gently dipping reflections is due to underplated oceanic sediments and igneous rocks associated with the current subduction of the juan de fuca plate and that the upper zone represents a similar sequence of accreted rocks associated with an earlier episode of subduction the high densitylhigh velocity material between the two reflection zones is either an underplated slab of oceanic lithosphere or an imbricated package of mafic rocks reprocessing of data from two of the seismic lines has produced a remarkable image of the terrane bounding leech river fault with its dip undulating from 60 near the surface to 20 at 3 km depth and 38 at 6 km depth

slowness driven gaussian beam prestack depth migration for low fold seismic data subsurface images based on low fold seismic reflection data or data with geometry acquisition limitations such as obtained from ocean bottom seismography obs are often corrupted by migration swing artifacts incorporating prestack instantaneous slowness information into the imaging condition can significantly reduce these migration swing artifacts and improve image quality especially for areas with poor illumination we combine the horizontal surface slowness information of observed seismic data with gaussian beam depth migration to implement a new slowness driven gaussian beam prestack depth migration whereby fresnel weighting is combined naturally with beam summation the prestack instantaneous slowness information is extracted from the original obs or shot gathers using local slant stacks and is combined with a local semblance analysis during migration we propagate the seismic energy downward knowing its instantaneous slowness information at each image location the beam summation is localized in a resolution dependent fresnel zone the instantaneous slowness information controls the beam summation synthetic and real data examples confirm that slowness driven gaussian beam migration can suppress most noise from inadequate stacking and give a clearer migration result

migration of noisy crustal seismic data a slowness weighted diffraction stack algorithm is used to migrate crustal seismic reflection data slowness information is extracted from the data using a slant stack beam forming process the main purpose of beam forming is to improve the signal to noise ratio over a given range of slowness values localized slant stacks are used to design a coherency weighted slowness filter in the time distance domain through migration the subsurface structure and the observed seismic data are tied via slownessselective diffraction curves a combination of nonlinear slowness filtering with migration gives excellent noise rejection and leads to an improved image in the depth domain the method which is particularly effective for migrating moderate to steep dipping events with low signal to noise ratio is applied to various poststack and prestack synthetic data examples and to a deep crustal data set collected on vancouver island as part of the canadian lithoprobe project

migration of the 3 d deep seismic reflection survey at the ktb location oberpfalz germany abstract a near vertical deep 3 d seismic survey covering an area of approximately 17 85 19 1 km has been carried out across the german continental deep borehole ktb site this survey is the first of this kind to investigate complicated crystalline crust two major problems were encountered during the post stack 3 d migration of these data first the survey region includes areas with strong lateral velocity gradients which are difficult to treat with many migration algorithms velocities in the sedimentary rocks are 3000 m s and in the crystalline rocks 5500 m s secondly the data are sparsely sampled 50 50 m binning but include steeply dipping events with true dips up to 60 to determine the optimum 3 d migration approach three different algorithms have been tested summation modified kirchhoff finite difference and phase shift results of the various tests suggest that one pass 3 d migration algorithms produce noticeably superior results to the much faster two pass methods the combination of steep dips and sparsely sampled data was a problem for the finite difference migration whereas shallow dipping features were imaged well by this technique although the adopted phase shift migration algorithm could not handle lateral velocity gradients it produced excellent results for both shallow and steeply dipping structures both of these migration algorithms are relatively fast by comparison the summation migration algorithm produced overall good results for regions containing steep dips and strong lateral velocity variations but it requires a lot of computing time

comprehensive examination of large mineral and rock fragments in stardust tracks mineralogy analogous extraterrestrial materials and source regions abstract transmission electron microscopy examination of 87 large fragments from 16 carrot shaped and bulbous stardust sd tracks was performed to study the range and diversity of materials present in comet wild 2 olivines and low ca pyroxenes represent the largest proportions of fragments observed however a wide range of minerals and rocks were found including probable ferromagnesian al rich and si rich chondrule fragments a refractory inclusion possible matrix mineral lithic clasts and probable condensate minerals these materials combined with fine grained components in the tracks are analogous to components in unequilibrated chondrite meteorites and cluster interplanetary dust particles idps two unusual lithologies in the bulbous tracks are only observed in chondritic porous idps and may have direct links to idps the absence of phyllosilicates indicates that comet wild 2 may be a dry comet that did not accrete or form significant amounts of hydrated phases some large mineral fragments in the sd tracks are analogous to large mineral idps the large variations of the coarse grained components within and between all 16 tracks show that comet wild 2 is mineralogically diverse and unequilibrated on nearly all scales and must have accreted materials from diverse source regions that were widely dispersed throughout the solar nebula

migration of wide angle seismic reflection data from the grenville front in lake huron under the auspices of the great lakes international multidisciplinary program on crustal evolution glimpce coincident steep and wide angle seismic reflection data sets were acquired in lake huron the wide angle data were recorded at stationary onshore receivers during the shooting and recording of the conventional marine steep angle survey to extract information from the wide angle data a variety of processing techniques including automatic trace editing amplitude balancing f k filtering static corrections and predictive deconvolution were applied to the wide aperture common receiver gather before migration the application of a slowness weighted depth migration algorithm which was first tested on synthetic data and which included a slowness filter resulted in an image of the grenville front tectonic zone gftz remarkably similar to that observed in the multichannel steep angle section the migrated wide angle data suggest that prominent bands of east dipping seismic reflections observed across the gftz extend unattenuated to depths of at least 45 km

a refractory inclusion returned by stardust from comet 81p wild 2 among the samples returned from comet 81p wild 2 by the stardust spacecraft is a suite of particles from one impact track track 25 that are ca al rich and feo free we studied three particles from this track that range in size from 5 3 x 3 2 m to 15 x 10 m scanning and transmission electron microscopy show that they consist of very fine grained typically from 0 5 to 2 m al rich ti bearing and ti free clinopyroxene mg al spinel and anorthite with trace amounts of fine perovskite feni metal and osbornite tin grains in addition to these phases the terminal particle named inti also contains melilite all of these phases with the exception of osbornite are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition osbornite though very rare has also been found in meteoritic refractory inclusions and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition compositions of ti pyroxene in inti are similar but not identical to those of fassaite from allende inclusions electron energy loss spectroscopy shows that ti rich pyroxene in inti has ti3 ti4 within the range of typical meteoritic fassaite consistent with formation under reducing conditions comparable to those of a system of solar composition inti is 16o rich with 18o 17o 40 like unaltered phases in refractory inclusions and refractory idps with grain sizes mineralogy mineral chemistry and an oxygen isotopic composition like those of refractory inclusions we conclude that inti is a refractory inclusion that formed in the inner solar nebula identification of a particle that formed in the inner solar system among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula probably either in a bipolar outflow or by turbulence

migration of common shot gathers three depth migration methods which operate on common shot data are presented the first migration method maps digitized horizons from the x t domain to the x z domain because this method is based on ray tracing its computation time is short it is suggested for iterative velocity analysis the other two migration methods map the entire common shot gather into a depth section the common shot migration requires calculation of the arrival time of the direct wave from the source to all the depth points and is done through a direct solution of the eikonal equation all three methods are suitable for areas with both lateral and vertical velocity variation

improved structural characterization of the earth s crust at the german continental deep drilling site using advanced seismic imaging techniques this paper describes the principles of three novel seismic imaging techniques and their application to two deep seismic reflection data sets from the vicinity of the german continental deep drilling site ktb these imaging techniques are based on kirchhoff prestack depth migration and use an inherent restriction of the migration operator to focus the wavefield to its actual reflection point for fresnel volume migration the emergent angle at the receivers is estimated and then used to propagate the wavefield back into the subsurface along which the fresnel volume is determined the migration operator is restricted to this volume thereby focusing the image to the part of the isochrone which physically contributes to the reflection for coherency migration the coherency of the wavefield at neighboring traces is calculated and used as a weighting factor within the migration integral leading to a comparable focusing to the reflection point for coherency based fresnel volume migration both approaches are combined resulting in an even more focused seismic image with significantly increased image quality we applied these methods to two seismic data sets from the area around the ktb a survey with standard split spread geometry ktb8502 and a sparse data set with a small number of source points in combination with short receiver lines instruct93 the focusing approaches yield major improvements in the final images for both data sets incoherent noise and migration artifacts are reduced and the visibility of crustal structures is strongly enhanced allowing for an improved geologic and tectonic characterization

mineralogy and petrology of stardust particles encased in the bulb of track 80 tem investigation of the wild 2 fine grained material abstract we have characterized by transmission electron microscopy the mineralogy of samples extracted from the walls of the stardust track 80 more than 500 fragments were studied using conventional imaging electron diffraction and edx microanalysis two categories of particles are distinguishable in equal proportions wt the first one is comprised of relatively large crystalline grains 1 m on average dominated by silicates olivine and pyroxene they display a wide range of compositions and microstructures comparable to those found in terminal particles minor phases including magnetite and apatite are also present their occurrence suggests that the wild 2 material underwent aqueous alteration to some extent the second type of particle called gems like material is made of silica rich glassy clumps embedding iron sulfide beads and vesicles their microstructure is characteristic of thermally modified particles that have suffered strong interaction with the silica aerogel during the hypervelocity impact this melted material may form by shedding of melted and vaporized material but given the shape of the impact track and high diversity of surviving mineral compositions much of it originated from fine grained aggregates that disaggregated during the collection chemical mapping at the nano scale allowed the localization of individual components within the silica rich glass they are dominated by mg rich components with a size less than 300 nm the average composition of this thermally modified material is close to the solar abundance for the major elements fe mg and s the fine grained material has probably not been chemically fractionated in the protoplanetary disk before its incorporation in comet wild 2 unlike the sulfur depleted matrix of chondrites from these two categories of particles we deduce that wild 2 is likely made of an assemblage of relatively large evolved grains first category cemented by a fine grained material with primitive chemistry second category the pre impact configuration of the incident material deduced from this study seems comparable to the matrix of the most primitive chondrites 3 0 or to chondritic porous interplanetary dust particles

radiation patterns of a shear wave vibrator in near surface shale two shallow surface to borehole field tests were conducted to investigate the radiation patterns of a shear wave vibrator in near surface shale in the in line direction for which baseplate motion is transverse to the source geophone raypath the vibrator produces a broadband high amplitude signal of the sh type and virtually no signal of the sv or p types the amplitude of the sh radiation is approximately constant as a function of polar angle but it falls off as the cosine of the azimuthal angle measured with respect to the in line direction in the broadside direction the vibrator produces a strong uncontaminated signal of the sv type the radiation pattern of the sv signature is lobate in the polar plane and peaks at an incident angle of 30 to 35 degrees in the horizontal plane the sv radiation varies as the sine of the azimuthal angle measured with respect to the in line direction the field tests were conducted on a permian shale in oklahoma and an eocene shale in east texas comparison between sh and sv wave surfaces indicates that both shales behave approximately like transversely isotropic solids with a vertical axis of symmetry theoretical wave surfaces are fit to the observed data by using elastic moduli determined from the field measurements and by making the assumption that the near surface shale at each field site is a single homogeneous inherently transversely isotropic material the analyses indicate that horizontal sh group velocity is about 30 percent greater than horizontal sv group velocity in the permian shale and about 25 percent greater in the eocene shale

heavily metamorphosed clasts from the cv chondrite breccias mokoia and yamato 86009 metamorphosed clasts in the cv carbonaceous chondrite breccias mokoia and yamato 86009 y 86009 are coarse grained granular polymineralic rocks composed of ca bearing up to 0 6 wt cao ferroan olivine fa34 39 ferroan al diopside fs9 13wo47 50 approximately 2 7 wt al2o3 plagioclase an37 84ab63 17 cr spinel cr cr al 0 19 0 45 fe fe mg 0 60 0 79 nepheline pyrrhotite pentlandite ca phosphate and rare grains of ni rich taenite low ca pyroxene is absent most clasts have triple junctions between silicate grains indicative of prolonged thermal annealing based on the olivine spinel and pyroxene thermometry the estimated metamorphic temperature recorded by the clasts is approximately 1100 k few clasts experienced thermal metamorphism to a lower degree and preserved chondrule like textures the mokoia and y 86009 clasts are mineralogically unique and different from metamorphosed chondrites of known groups h l ll r eh el co ck and primitive achondrites acapulcoites brachinites lodranites on a three isotope oxygen diagram compositions of olivine in the clasts plot along carbonaceous chondrite anhydrous mineral line and the allende mass fractionation line and overlap with those of the cv chondrule olivines the 17o values of the clasts range from about 4 3 to 3 0 we suggest that the clasts represent fragments of the cv like material that experienced metasomatic alteration high temperature metamorphism and possibly melting in the interior of the cv parent asteroid the lack of low ca pyroxene in the clasts could be due to its replacement by ferroan olivine during iron alkali metasomatic alteration or by high ca ferroan pyroxene during melting under oxidizing conditions

petrology and mineralogy of type ii feo rich chondrules in semarkona ll3 0 origin by closed system fractional crystallization with evidence for supercooling abstract the petrology of type ii porphyritic olivine chondrules in semarkona ll3 0 has been studied in detail olivines in these chondrules are euhedral fe richand are strongly zoned from cores to rims of grains in feo fa10 30 cr2o3 0 2 0 6 wt mno 0 2 0 7 wt and cao 0 1 0 4 wt interstitial mesostasis is rich in si aland ca and is glassy with abundant microcrystallites minor minerals include troilite fe ni metaland chromite some olivine grains contain euhedral fayalite rich cores that are probably produced during initial supercooling of the chondrule melt rare relict grains of forsteritic olivine have compositions very similar to olivines in type ia chondrules in semarkona and may result from disaggregation of such chondrules apart from these relics all properties of type ii chondrules can be described by closed system fractional crystallization of droplets which were essentially entirely molten the chondrules did not originate as aggregates of large olivine grains and are unlikely to be fragments of precursor igneous rocks cooling rates of the order of 1000 c h are indicated from peak temperatures of around 1600 c the chondrules show considerable evidence for supercooling and large departures from equilibrium during crystallization there is no evidence for chondrule nebula exchange either during or after crystallization or any secondary processes such as aqueous alteration or thermal metamorphism bulk composition data suggest that precursor material included a refractory ca al ti rich component similar to one of the precursor components of type ia chondrulesand a non refractory fe and si rich component type ia chondrules may have formed from type ii chondrules by loss of fe and volatiles alternatively the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different fe mg ratios

constraints on the formation age of cometary material from the nasa stardust mission we measured the 26 al 26 mg isotope systematics of a 5 m refractory particle coki returned from comet 81p wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts the data show no evidence of radiogenic 26 mg and define an upper limit to the abundance of 26 al at the time of particle formation of 26 al 27 al 5 the absence of 26 al indicates coki formed 1 7 ma after the oldest solar system solids ca al rich inclusions cais the data presented here suggest that high temperature inner solar system material formed was subsequently transferred to the kuiper belt and incorporated into comets several million years following cai formation

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

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data

the primitive matrix components of the unique carbonaceous chondrite acfer 094 a tem study the mineralogical and chemical characteristics of the fine grained matrix 53 m of the unique primitive carbonaceous chondrite acfer 094 have been investigated in detail by scanning electron microscopy sem and analytical transmission electron microscopy atem generally the fine grained matrix represents a highly unequilibrated assemblage of an amorphous material small forsteritic olivines 200 300 nm low ca pyroxenes 300 400 nm and fe ni sulfides 100 300 nm the matrix is basically unaffected by secondary processes only minor amounts of serpentine and ferrihydrite as products of hydrous alteration are present texturally the amorphous material acts as a groundmass to olivines pyroxenes and sulfides mostly exhibiting rounded or elongated morphologies only very few clastic mineral grains have been found the texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment as such the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites the non clastic matrix olivines fo98 99 and pyroxenes en97 100 are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material the formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons rapid cooling caused the observed intergrowths of clino orthoenstatite in the mg rich matrix pyroxenes although some similarities exist comparing the fine grained matrix of acfer 094 with the matrices of the unequilibrated c03 chondrite alha77307 and the unique type 3 chondrite kakangari acfer 094 remains unique since it contains the highest measured concentrations of circumstellar sic and the second highest of diamond highest is orgueil it seems reasonable to suggested that at least parts of the amorphous material in the fine grained matrix may be of circumstellar origin

tectonic processes at the collision of the d entrecasteaux zone and the new hebrides island arc the d entrecasteaux zone dez a large submarine mountain chain composed of two east trending subparallel ridges collides with the north trending new hebrides island arc the direction of convergence of the oceanic plate and arc suggests that the dez is being subducted at a slightly oblique angle 10 15 so that the dez creeps slowly north parallel to the trench one possible consequence of this northward creep is that slope strata south of the dez should bear a structural overprint caused by ridge collision whereas strata north of the dez may show no such overprint migrated multichannel seismic data presented in this report reveal the probable form of this overprint within the collision zone strata forming the arc s accretionary wedge dip toward the trench possibly recording progradation of slope rocks across the ocean floor and neither outer arc ridge nor slope basin is present seismic data from south of the dez however show no evidence for this overprint because both an outer arc ridge and slope basin are present and the structure of slope strata on opposite sides of the dez appears broadly similar involving a nearly invariant stratal dip toward the arc nevertheless the slope s morphology shows that collision has modified the structure of rocks below the arc s slope and that the arc responded differently to collision of the dez s two ridges the north ridge is nearly flat topped and mid ocean ridge basalt has been dredged from its flanks isobaths of the slope bulge westward where the ridge is being subducted suggesting that the slope has been uplifted by the ridge in contrast the south ridge shows sharp relief and is made up of stratified possibly sedimentary rocks and the bougainville spur a sharp peak projects above the arc s lowermost slope along the trend of this ridge the spur may be a peak similar to one of those surmounting the south ridge that rammed the arc s slope