detection of lower mantle scatterers northeast of the marianna subduction zone using short period array data short period university of washington northern california and southern california seismic array records of a sequence of deep mariana subduction zone earthquakes show unexpected clear arrivals nearly 90 and 105 s following p we measure slowness arrival time and arrival azimuth of these phases relative to p using array techniques to find where they emanate in the mantle by combining slowness and back azimuth deviations and the move out with depth of the arrivals from different earthquakes we find their most probable origin is through s to p conversion at point scatterers in the mid to lower mantle at 25 7 n 148 2 e 1590 km and 25 5 n 151 0 e 1850 km respectively separated by 300 km these features indicate elastically distinct material in the middle of the lower mantle which if fragments of subducted slabs are not related to contemporary subduction they may represent upwelling convective material from the deep mantle or d but they are not purely thermal in nature as chemically distinct bodies they may represent potential reservoirs of the isotopic and trace element components recognized geochemically

an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

a waveform migration for the investigation of p wave structure at the top of d beneath northern siberia we present the first waveform migration for the lower mantle focusing on the lowermost 400 km of the mantle beneath northern siberia we migrate vertical component p wave seismograms recorded in western europe for earthquakes located in the kuril islands region we focus on the time window between the direct p wave and the pcp wave reflected at the core mantle boundary and we investigate the origin of pcp precursors the data selected for their good signal to noise ratio are deconvolved by the source time function determined by the beam of the p wave we observe the signature of a finite size scattering object located around 75 n 85 e at an apparent depth of 2650 km with respect to the iasp91 model its scale length is probably of the order of 100 km this object is characterized by an anisotropic scattering diagram and may be related to the presence of an ancient subducted plate near the core mantle boundary

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

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

formation conditions of aluminum rich chondrules abstract we have studied the formation conditions of al rich chondrules by doing isothermal and dynamic crystallization experiments at one atmosphere on four different chondrule analogue compositions within the pure cao mgo al2o3 sio2 system for the dynamic crystallization experiments we cooled from both liquidus and subliquidus peak temperatures tmax at cooling rates from 5 1000 c h the starting compositions include two with anorthite and two with forsterite as the dominant liquidus phases all at or near spinel saturation one of each pair evolves towards diopside crystallization and the others cordierite or enstatite crystallization giving a total of four completely different crystallization sequences analogous to the four basic varieties of al rich chondrule recently proposed bulk composition is the main controlling factor both in terms of mineralogy and texture the textures of the anorthite rich compositions are more sensitive to tmax than they are to cooling rate whereas the textures of the forsterite rich compositions are more sensitive to cooling rate comparisons of natural al rich chondrules having similar compositions to our synthetic analogues indicate that the natural objects reflect a range of peak heating temperatures 1400 1500 c and cooling rates of 10 500 c h for porphyritic chondrules and possibly higher 1000 c h for barred chondrules these conditions are consistent with the conditions inferred for ferromagnesian chondrules but differ from those inferred for some calcium aluminum rich inclusions

plagioclase rich chondrules in the reduced cv chondrites evidence for complex formation history and genetic links between calcium aluminum rich inclusions and ferromagnesian chondrules plagioclase rich chondrules prcs in the reduced cv chondrites efremovka leoville vigarano and grosvenor mountains gro 94329 consist of magnesian low ca pyroxene al ti cr rich pigeonite and augite forsterite anorthitic plagioclase feni metal sulfide nodules and crystalline mesostasis composed of silica anorthitic plagioclase and al ti cr rich augite the silica grains in the mesostases of the cv prcs are typically replaced by hedenbergitic pyroxenes whereas anorthitic plagioclase is replaced by feldspathoids nepheline and minor sodalite some of the prcs contain regions that are texturally and mineralogically similar to type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules several prcs are surrounded by igneous rims or form independent compound objects twelve prcs contain relic calcium aluminum rich inclusions cais composed of anorthite spinel high ca pyroxene forsterite and al rich low ca pyroxene anorthite of these cais is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules this suggests that either the alteration predated formation of the prcs or that anorthite of the relic cais was more susceptible to the alteration than anorthitic plagioclase of the host chondrules these observations and the presence of igneous rims around prcs and independent compound prcs suggest that the cv prcs may have had a complex multistage formation history compared to a more simple formation history of the cr prcs relatively high abundances of moderately volatile elements such as cr mn and si in the prcs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only we infer instead that prcs in carbonaceous chondrites formed by melting of the reduced chondrule precursors magnesian olivine and pyroxene feni metal mixed with refractory materials relic cais composed of anorthite spinel high ca pyroxene and forsterite the mineralogical chemical and textural similarities of the prcs in several carbonaceous chondrite groups cv co ch cr and common presence of relic cais in these chondrules suggest that prcs may have formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated

mineralogy and petrology of chondrules and inclusions in the mokoia cv3 chondrite all objects 100 m in apparent diameter in five polished thin sections of the mokoia cv3 chondrite were studied and classified number and volume percentages and mean apparent size of each type of chondrule and inclusion were determined three major types of olivine chondrules were observed igneous chondrules recrystallized chondrules and chondrules that appear to be accretional aggregates coarse grained cai s have igneous textures and mineral parageneses while fine grained cai s are aggregates containing varying proportions of al rich concentric objects ca rich chaotic material and inclusion matrix chondrules and refractory inclusions in mokoia and allende are broadly similar in texture and mineral chemistry but mokoia refractory inclusions contain phyllosilicates rather than feldspathoids and melilite rich cai s are more abundant in allende we think that most cai s formed during the metamorphism partial melting and incomplete distillation of primitive dust aggregates when they were heated in the solar nebula in the process ca rich melt appears to have been physically separated from al rich residues producing the observed fractionation of ca from al into distinct constituents of cai s some cai s may be aggregates of devitrified amorphous metastable condensates inclusion matrix may have condensed from silicate rich vapors produced during distillation mokoia inclusion matrix contains phyllosilicates that are probably primitive nebular material

evidence of a laterally variable lower mantle structure from p and s waves summary examples of grafenberg array data showing anomalous p waves which typically arrive 3 5s after the direct p wave and which have a slowness 0 7 0 8 sdeg smaller than direct p are presented this additional phase is most frequently observed for events located in the ne portion of the southern kurile island subduction zone 73 80 from grafenberg but systematically disappears for events in the sw portion of this zone because of the magnitude of the slowness difference these observations cannot be attributed to a complex source rupture process nor to multipathing through the descending slab likewise they may not be accounted for by near receiver structure because these phases are not seen for all kurile events if present they appear at all stations of the array but they follow direct p too closely to be a multiple from the moho therefore we conclude they are very likely caused by lower mantle velocity structure the most likely explanation is the presence of a p velocity jump of about 3 per cent approximately 290 km above the core mantle boundary since such a reflector in the lowermost mantle not only gives a good fit of traveltimes and slowness but is also able to model the waveform and the amplitudes of this additional p phase the distribution of bounce points on this reflector for the kurile events indicates a lateral extension of this velocity anomaly under northern siberia of about 150 km by at least 200 km the best fitting s wave model has a reflector in the same depth but the velocity contrast seems to be only about 2 per cent suggesting a different behaviour of the p and s velocity in d few events from other regions in this distance range are suitable for a definitive analysis of this kind from among this group some observations indicate a lower mantle anomaly under the lomonosow ridge and under northern greenland but since the lower mantle under western siberia northern novaya zemlya the azores islands region and the ussr afghanistan border region does not produce an additional phase in the grafenberg recordings it is very unlikely that such a velocity anomaly in the lowermost mantle is a global feature

the mineral chemistry and origin of inclusion matrix and meteorite matrix in the allende cv3 chondrite the two textural varieties of olivine rich allende inclusions rimmed and unrimmed olivine aggregates consist primarily of a porous fine grained mafic constituent inclusion matrix that differs from the opaque meteorite matrix of cv3 chondrites by being relatively depleted in sulfides metal grains and perhaps carbonaceous material olivine is the most abundant mineral in allende inclusion matrix clinopyroxene nepheline sodalite and ti al pyroxene occur in lesser amounts olivine in unrimmed olivine aggregates type 1a inclusions is ferrous and has a narrow compositional range fo50 65 olivine in rimmed olivine aggregates type 1b inclusions is on average more magnesian with a wider compositional range fo53 96 olivine grains in the granular rims of type 1b inclusions are zoned with magnesian cores fo 80 and ferrous rinds fo 70 ferrous olivines fo 65 in both varieties of inclusions commonly contain significant amounts of al2o3 as much as 0 7 wt cao as much as 0 4 wt and tio2 as much as 0 2 wt refractory elements that probably occur in submicroscopic inclusions of ca al ti rich glass rather than in the olivine crystal structure defocussed beam analyses of allende matrix materials demonstrate that 1 inclusion matrix in type 1a inclusions is more enriched in olivine and feo than inclusion matrix in the cores of type 1b inclusions 2 opaque matrix materials are depleted in feldspathoids and enriched in sulfides and metal grains relative to inclusion matrix 3 the bulk compositions of type 1a and type 1b inclusions overlap and 4 excluding sulfides and metal the bulk compositions of allende matrix materials cluster in a complementary pattern around the bulk composition of c1 chondrites inclusion matrix and meteorite matrix in allende and other cv3 chondrites are probably relatively primitive nebular material but a careful evaluation of the equilibrium condensation model suggests that these matrix materials do not consist of crystalline phases that formed under equilibrium conditions in a relatively cool gas of solar composition allende inclusion matrix is interpreted as an aggregate of condensates that formed under relatively oxidizing non equilibrium conditions from supercooled supersaturated vapors produced during the vaporization of interstellar dust by aerodynamic drag heating in the solar nebula cv3 meteorite matrix contains in addition a proportion of interstellar material that was heated but not vaporized in the nebula granular olivine in rimmed olivine aggregates may have formed during the recrystallization and incipient melting of aggregates of inclusion matrix in the nebula the mineral chemistry of matrix olivine in allende seems to have been established by three different processes non equilibrium vapor solid condensation recrystallization and partial melting in the nebula and femg equilibration without textural homogenization in the meteorite parent body

evolution of a warm core ring in the gulf of mexico lagrangian observations during 1985 and 1986 a gulf of mexico ring shed by the loop current was observed to migrate toward the western gulf of mexico this movement across the gulf was well documented by observations that included drifter data within and outside the ring sea surface temperature at weekly intervals expendable bathythermograph surveys at various times one major hydrographic cruise when the ring was in the northwestern gulf and currents from moorings over which the ring passed the drifter data were used to infer the movement of the ring center as well as the eccentricity and orientation of the major axes the data from the drifters bridge the gaps between detailed surveys to the extent that a daily history of the position and shape of the ring can be constructed the synthesis of these diverse but complimentary data sources provides a detailed description of how the ring interacted with the bathymetry of the northern gulf of mexico as well as with previously and subsequently shed rings

bulk mg isotopic compositions of ca al rich inclusions and amoeboid olivine aggregates high precision mg isotopic compositions of ca al rich inclusions cais from both ningqiang ungrouped and allende cv3 carbonaceous chondrites and amoeboid olivine aggregations aoas from allende were analyzed by multicollector inductively coupled plasma mass spectrometry mc icp ms the cais from allende plot on a line with an inferred initial 26al 27al ratio of 4 77 0 39 10 5 close to the canonical value this indicates a relatively closed al mg system in the cais and no significant mg isotope exchange with ambient materials although two of the cais are severely altered the aoas contain excess 26mg and plot close to the cai regression line which is suggestive of their contemporary formation the cais from ningqiang define a different line with a lower inferred 26al 27al 0 ratio of 3 56 0 08 10 5 none of the cais and aoas studied in this work shows significant mass fractionation with enrichment of the heavier mg isotopes arguing against an evaporation origin

microstructural constraints on complex thermal histories of refractory cai like objects in an amoeboid olivine aggregate from the alha77307 co3 0 chondrite abstract we have carried out a fib tem study of refractory cai like objects in one aoa from the alha77307 co3 0 chondrite the cai like objects in the aoa consist of a zoned sequence with a spinel rich core through an intergrowth layer of spinel and al ti rich diopside to a diopside rim the spinel rich core consists of polycrystalline aggregates of spinel and minor melilite showing equilibrated grain boundary textures the intergrowth layer contains fine grained diopside and spinel with minor anorthite with highly curved and embayed grain boundaries the diopside rim consists of polycrystalline aggregates of diopside the compositions of pyroxene change significantly outward from al ti rich diopside in contact with the spinel rich core to al ti poor diopside next to the surrounding olivine of the aoa overall microstructural and chemical characteristics suggest that the spinel rich core formed under equilibrium conditions whereas the intergrowth layer is the result of reactions that occurred under conditions that departed significantly from equilibrium the remarkable changes in formation conditions of the cai like objects may have been achieved by transport and injection of refractory objects into a region of a partially condensed ca ti saturated gas which reacted with spinel and melilite to form al ti rich diopside crystallographically oriented tio2 nanoparticles decorate the grain boundaries between spinel grains and between spinel and al ti rich diopside grains during the disequilibrium back reaction of spinel with a partially condensed ca ti saturated gas metastable tio2 nanoparticles may have condensed by an epitaxial nucleation mechanism and grown on the surface of spinel these tio2 nanoparticles are disordered intergrowths of the two tio2 polymorphs anatase and rutile these nanoparticles are inferred to have nucleated as anatase that underwent partial transformation into rutile the local presence of the tio2 nanoparticles and intergrowth of anatase and rutile imply that the disequilibrium back reaction of spinel with the gas occurred on a short timescale i e minutes to hours at maximum

a broadband seismic study of the lowermost mantle beneath mexico constraints on ultralow velocity zone elasticity and density broadband seismic stacking is performed for pcp waves sampling the lowermost mantle and core mantle boundary beneath central mexico and the western gulf of mexico the data contain evidence of a loto 20 km thick ultralow velocity zone on the western edge of the study area tapering or vanishing to the east to less than 5 km thickness over a horizontal distance of 200 km epicentral distance varies from 20 to 60 a range over which the amplitude of reflections from the top of the ultralow velocity zone responds strongly to changes in the ratio of shear to compressional velocity reduction r ln v s in v p and to density within the zone where the zone is present and thick enough to separate pcp and the precursory reflection our modeling is consistent with a value of r near 3 and ln v p near 10 assuming only a minor density increase 1 to 2 the value of r is reduced to 2 for a 14 density increase but ln v p remains large 7 very low amplitude multiply converted phases are synthetically well reproduced with extreme attenuation within the zone suggesting the presence of a melt component

refractory calcium aluminum rich inclusions and aluminum diopside rich chondrules in the metal rich chondrites hammadah al hamra 237 and queen alexandra range 94411 the metal rich chondrites hammadah al hamra hh 237 and queen alexandra range que 94411 paired with que 94627 contain relatively rare 1 vol calcium aluminum rich inclusions cais and al diopside rich chondrules forty cais and cai fragments and seven al diopside rich chondrules were identified in hh 237 and que 94411 94627 the cais 50 400 mum in apparent diameter include a 22 56 pyroxene spinel melilite forsterite rim b 11 28 forsterite bearing pyroxene spinel melilite anorthite forsterite rim c 2 5 grossite rich spinel melilite pyroxene rim d 2 5 hibonite melilite spinel pyroxene forsterite rim e 1 2 hibonite bearing spinel perovskite melilite pyroxene rim f 1 2 spinel melilite pyroxene anorthite and g 1 2 amoeboid olivine aggregate each type of cai is known to exist in other chondrite groups but the high abundance of pyroxene spinel melilite cais with igneous textures and surrounded by a forsterite rim are unique features of hh 237 and que 94411 94627 additionally oxygen isotopes consistently show relatively heavy compositions with delta o 17 ranging from 6 parts per thousand to 10 parts per thousand 1 sigma 1 3 parts per thousand for all analyzed cai minerals grossite hibonite melilite pyroxene spinel this suggests that the cais formed in a reservoir isotopically distinct from the reservoir s where normal o 16 rich delta o 17 20 cais in most other chondritic meteorites formed

anorthite rich chondrules in cr and ch carbonaceous chondrites genetic link between ca al rich inclusions and ferromagnesian chondrules anorthite rich chondrules in cr and ch carbonaceous chondrites consist of magnesian low ca pyroxene and forsterite phenocrysts feni metal nodules interstitial anorthite al ti cr rich low ca and high ca pyroxenes and crystalline mesostasis composed of silica anorthite and high ca pyroxene three anorthite rich chondrules contain relic ca al rich inclusions composed of anorthite spinel al diopside and forsterite a few chondrules contain regions which are texturally and mineralogically similar to magnesian type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules anorthite rich chondrules in cr and ch chondrites are mineralogically similar to those in cv and co carbonaceous chondrites but contain no secondary nepheline sodalite or ferrosilite relatively high abundances of moderately volatile elements such as cr mn and si in the anorthite rich chondrules suggest that these chondrules could not have been produced by volatilization of the ferromagnesian chondrule precursors or by melting of the refractory materials only we infer instead that anorthite rich chondrules in carbonaceous chondrites formed by melting of the reduced chondrule precursors olivine pyroxenes feni metal mixed with the refractory materials including relic cais composed of anorthite spinel high ca pyroxene and forsterite the observed mineralogical and textural similarities of the anorthite rich chondrules in several carbonaceous chondrite groups cv co ch cr may indicate that these chondrules formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated this may explain the relative enrichment of anorthite rich chondrules in 16o compared to typical ferromagnesian chondrules russell et al 2000

fine scale topography of the d discontinuity and its correlation to volumetric velocity fluctuations we constrained the correlation of the topography of the d discontinuity to volumetric velocity fluctuations we used data obtained from hi net tiltmeters deployed by the national research institute for earth science and disaster prevention japan and conducted stacking and migration to map the discontinuity beneath the southwestern pacific we compared the obtained map with the distribution of scs s travel time residuals an index of volumetric velocity fluctuations in the lowermost mantle we detected the fine scale of the order of a few hundred kilometers topography of the d discontinuity as well as fine scale volumetric velocity fluctuations regions with relatively higher velocities generally have a discontinuity with shallower depths and those with relatively lower velocities generally have a discontinuity with deeper depths the scattering plot between the observed depths of the discontinuity and the observed scs s residuals appears to exhibit a nonlinear trend these results may suggest the existence of both thermal and chemical anomalies such as those seen in thermochemical plumes

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

mineralogy and petrology of amoeboid olivine inclusions in co3 chondrites relationship to parent body aqueous alteration petrographic and mineralogic studies of amoeboid olivine inclusions aois in co3 carbonaceous chondrites reveal that they are sensitive indicators of parent body aqueous and thermal alteration as the petrologic subtype increases from 3 0 to 3 8 forsteritic olivine fa0 1 is systematically converted into ferroan olivine fa60 75 we infer that the fe si and o entered the assemblage along grain boundaries forming ferroan olivine that filled fractures and voids as temperatures increased fe 2 from the new olivine exchanged with mg 2 from the original aoi to form diffusive haloes around low feo cores cations of mn 2 ca 2 and cr 3 were also mobilized the systematic changes in aoi textures and olivine compositional distributions can be used to refine the classification of co3 chondrites into subtypes in subtype 3 0 olivine occurs as small forsterite grains fa0 1 free of ferroan olivine in petrologic subtype 3 2 narrow veins of feo rich olivine have formed at forsterite grain boundaries with increasing alteration these veins thicken to form zones of ferroan olivine at the outside aoi margin and within the aoi interior by subtype 3 7 there is a fairly broad olivine compositional distribution in the range fa63 70 and by subtype 3 8 no forsterite remains and the high fa peak has narrowed fa64 67 even at this stage there is incomplete equilibration in the chondrite as a whole e g data for coarse olivine grains in isna co3 8 chondrules and lithic clasts show a peak at fa39 we infer that the mineral changes in aoi identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes 3 3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids

short wavelength lateral variation of a d p wave reflector beneath the southwestern pacific the short period vertical component data from the fiji is earthquakes recorded by three seismological networks in japan are analysed to investigate short wavelength lateral heterogeneities in d layer a double array stacking method which allows us to combine event and receiver arrays is applied to the records of each network three regions in the d layer sampled by the three networks are located at horizontal intervals of a few hundred kilometers in all three regions the d reflectors are detected the height of the d reflector above the cmb which is estimated by the differential travel time between pdp d reflection and p changes from 270 km to 170 km this result may suggest that some strong short wavelength lateral heterogeneities exist in the d layer beneath the southwestern pacific

anorthite spinel rich inclusions in the ningqiang carbonaceous chondrite genetic links with type a and c inclusions many ca al rich inclusions cais were molten once and the question of what their precursors consisted of is controversial in this paper we report a new type of anorthite spinel rich inclusion asi in the ningqiang carbonaceous chondrite the modal and bulk compositions of the asis are similar to those of type c inclusions but with nonmolten textures the asis are proposed to be the precursors of type c inclusions the asis show alteration textures with melilite being replaced by anorthite and ca pyroxene furthermore compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the asis are close to those of the spinel rich type a inclusions in the ningqiang meteorite which suggests that asis formed by alteration of the latter in the solar nebula petrography and mineral chemistry of one type c inclusion in ningqiang are also reported

origin of plagioclase olivine inclusions in carbonaceous chondrites plagioclase olivine inclusions pois are an abundant group of chondrule like objects with igneous textures found in carbonaceous chondrites pois consist of plagioclase olivine pyroxene and spinel and cover a wide range of compositions between type c ca al rich inclusions cais and ferromagnesian chondrules pois are distinguished from cais by the absence of melilite lack of refractory siderophile rich opaque assemblages more sodic plagioclase and abundance of olivine and aluminousenstatite rare accessory minerals including armalcolite zirconolite rutile and sapphirine are found in several pois the petrographie and chemical properties of pois indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre existing solids seven of fourteen pois contain isotopically fractionated mg and despite their textures these pois are not isotopically homogeneous spinel is the major carrier of fractionated mg in six pois the magnitude of mg isotopic fractionation fmg of spinel ranges from 8 to 11 amu among the pois but f mg is always either positive or negative within an individual pol within a single inclusion f mg of coexisting spinel is not constant but varies by up to 7 amu isotopic fractionation of mg in silicates is less common and always positive f mg 0 pyroxenes in two pois and plagioclase in a third contain isotopically heavy mg radiogenic 26 mg is rare in pois as only two inclusions show evidence of excess 26 mg with 26 mg 27 al 4 10 6 the preservation of isotopic heterogeneity in objects whose igneous textures suggest crystallization from a homogeneous melt implies that melting was incomplete allowing survival of relict phases a comparison of the essential characteristics of pois and cais suggests that the major processes leading to formation of pois including condensation dust gas fractionation aggregation of chemically and isotopically disparate materials and partial melting are common to most cais and chondrules we present a scenario for the formation of these objects and conclude that the homogeneity of the final assemblage cai poi or chondrule is primarily a reflection of the thermal history rather than the nature of precursor materials

lateral variations in d thickness from long period shear wave data we explore global variations in d shear wave structure by examining 12 years of long period global digital seismograph network gdsn data to identify reflected phases from the d layer in the lowermost mantle we restrict our search to epicentral distances between 63 and 74 where a precritical d reflection will lie between the s and scs arrivals with gdsn long period records a d signal at these ranges is generally obscured by the stronger neighboring phases so to isolate the d reflections we develop a technique for stripping away the interfering s and scs waveforms we interpret travel time variations in the observed sds phases in terms of variations in d thickness and generate maps of inferred d thickness for areas of good seismic coverage the regions of observed d reflections are beneath australasia north central asia the arctic alaska and central america we find considerable variation in d structure in these regions a result consistent with previous studies which have found evidence for lateral heterogeneity in d on average the estimated d thickness is 260 km but there is a fairly uniform distribution of thicknesses between 150 km and 350 km a possible correlation is observed between d thickness and regions of predicted strong horizontal mantle flow

laterally varying reflector at the top of d beneath northern siberia summary we analyse p wave data from the french laboratoire de dctection et gcophysique l d g network of digital short period seismic stations whereas our previous paper houard nataf 1992 showed a few promising kurd events and depicted the methods we proposed to apply an extensive analysis of 32 earthquakes from the kurivkamchatka region has now been carried out by using the deconvolution technique previously described houard nataf 1992 clear and quantitative evidence of intermediate arrivals between the p and pcp waves is shown in the 75 82 distance range our approach is complementary to previous studies in the same region which used broad band data recorded at a dense narrow aperture array weber davis 1990 weber 1993 or long period data recorded at the wwssn stations gaherty lay 1992 for each station record sections of deconvolved signals from different earthquakes are built and lead us to eliminate crustal reverberations beneath l d g stations as a major explanation for these secondary arrivals a compilation of the most conclusive signals has been made it is perhaps one of the most complete pdp wave record sections since the move out with distance can be followed clearly with a good sampling over more than 5 the move out with distance of this extra pdp arrival its residual slowness value eliminates source complexities diffraction or multipathing through the kuril subduction slab as possible explanations the extra arrivals indicate the existence of a lower mantle reflector the structure of the lay discontinuity is investigated using tpdp tp residual traveltimes two different residual time versus distance tendencies are found which correlate to different geographical bounce point regions indicating the existence of lateral variations of the structure the d region is also sampled further south at distances well beyond the theoretical triplication cross over by analysing events from the honshu ryukyu islands region but only one p wave branch is observed the hodochrones and p a curves of the first p arrival are used as a complementary analysis the global prem model dziewonski anderson 1981 predicts correct p wave slownesses though its smooth lower mantle structure does not account for pdp observations this may be an indication that the lay discontinuity is a global feature however the hodochrones of the first p arrival do not allow us to test the existence of the discontinuity in the 82 85 cross over distance range

an experimental study of enstatite formation reaction between forsterite and si rich gas experiments on the reaction between forsterite and si rich gas were carried out in a vacuum furnace using a newly designed double capsule technique a thin layer of enstatite was formed on the surface of the forsterite by the reaction the thickness of the enstatite layer changes in proportion to the square root of time parabolic rate law indicating that the rate is controlled by diffusion in the enstatite layer the activation energy and the logarithm of the pre exponential term of the parabolic rate constant were obtained at505 188 kj mol and3 6 5 6 cm2 s respectively it is difficult to definitely determine the mechanism of the reaction from these values but consideration of strain generation due to volume change during the reaction may suggest that the counter diffusion of silicon and magnesium takes place along the grain boundary in the enstatite layer the degree of the reaction of forsterite with si rich residual gas in the primordial solar nebula is discussed based upon the measured reaction rate and it is suggested that very little enstatite was formed by this reaction in the cooling nebula if the grain size of the forsterite crystals was controlled by homogeneous nucleation theory

correlated petrologic and geochemical characteristics of co3 chondrites many properties of co3 chondrites have been shown previously to have resulted from thermal metamorphism petrologic subtypes 3 0 3 7 have been assigned to members of the group additional properties that correlate with the metamorphic sequence but seem to have resulted from hydrothermal alteration include the modal abundance of amoeboid olivine inclusions aoi chondrule size the types of refractory inclusions and whole rock o isotopic composition the percentage of rimmed aoi increases with petrologic subtype the rims most likely formed during hydrothermal alteration the previously reported correlation between aoi abundance and chondrite subtype is probably an artifact due to the difficulty in recognizing small unrimmed aoi in the least metamorphosed co3 chondrites because large 200 micron size porphyritic chondrules have nearly the same mean size in all co3 chondrites it seems likely that the correlation between chondrule size and subtype is due to alteration of the smallest chondrules to the point of unrecognizability as complete objects in the more metamorphosed co3 chondrites the previously reported decrease in the proportion of melilite rich refractory inclusions with increasing petrologic subtype may have resulted from more extensive hydrothermal alteration in co3 4 3 7 chondrites that converted primary melilite into ca pyroxene andradite and nepheline alteration probably caused the preferential occurrence of o 16 poor oxygen isotopes in the more metamorphosed whole rock samples

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

observed and simulated kinematic properties of loop current rings two rings shed by the loop current in 1980 and 1982 were observed for several months by satellite tracked drifters to migrate across the gulf of mexico the drifter path data have been inverted to obtain estimates of the paths of the centers of the two rings ring shape and the swirl velocities three drifters were deployed in the 1980 ring and the analysis of that data set establishes the variability of the above kinematic estimates for one ring a comparison of the analysis of data from both rings provides some idea on inter ring variability both rings impacted the mexican continental slope at about 22 8 n 95 5 w after a brief adjustment period both rings reestablished and maintained a vortex character for several months in the slope region while migrating slowly to the north the paths of the centers of the two rings along the slope are virtually identical the same analysis routine was applied to some simulated drifter data obtained from the hurlburt and thompson 1980 gulf of mexico primitive equation model in the midgulf the agreement between the observed rings and the simulated ring is good although the former showed stronger interaction with the continental slope topography and or circulation than was seen in the latter along the slope the model ring kinematic characteristics were in extraordinary agreement with the observations

ca al rich inclusions amoeboid olivine aggregates and al rich chondrules from the unique carbonaceous chondrite acfer 094 i mineralogy and petrology based on their mineralogy and petrography 200 refractory inclusions studied in the unique carbonaceous chondrite acfer 094 can be divided into corundum rich 0 5 hibonite rich 1 1 grossite rich 8 5 compact and fluffy type a spinel melilite rich 50 3 pyroxene anorthite rich 7 4 and type c pyroxene anorthite rich with igneous textures 1 6 ca al rich inclusions cais pyroxene hibonite spherules 0 5 and amoeboid olivine aggregates aoas 30 2 melilite in some cais is replaced by spinel and al diopside and or by anorthite whereas spinel pyroxene assemblages in cais and aoas appear to be replaced by anorthite forsterite grains in several aoas are replaced by low ca pyroxene none of the cais or aoas show evidence for fe alkali metasomatic or aqueous alteration the mineralogy textures and bulk chemistry of most acfer 094 refractory inclusions are consistent with their origin by gas solid condensation and may reflect continuous interaction with sio and mg of the cooling nebula gas it appears that only a few cais experienced subsequent melting the al rich chondrules arcs 10 wt bulk al2o3 consist of forsteritic olivine and low ca pyroxene phenocrysts pigeonite augite anorthitic plagioclase spinel feni metal and crystalline mesostasis composed of plagioclase augite and a silica phase most arcs are spherical and mineralogically uniform but some are irregular in shape and heterogeneous in mineralogy with distinct ferromagnesian and aluminous domains the ferromagnesian domains tend to form chondrule mantles and are dominated by low ca pyroxene and forsteritic olivine anorthitic mesostasis and fe ni metal nodules the aluminous domains are dominated by anorthite high ca pyroxene and spinel occasionally with inclusions of perovskite have no or little feni metal and tend to form cores of the heterogeneous chondrules the cores are enriched in bulk ca and al and apparently formed from melting of cai like precursor material that did not mix completely with adjacent ferromagnesian melt the inferred presence of cai like material among precursors for al rich chondrules is in apparent conflict with lack of evidence for melting of cais that occur outside chondrules suggesting that these cais were largely absent from chondrule forming region s at the time of chondrule formation this may imply that there are several populations of cais in acfer 094 and that mixing of normal cais that occur outside chondrules and chondrules that accreted into the acfer 094 parent asteroid took place after chondrule formation alternatively there may have been an overlap in the cai and chondrule forming regions where the least refractory cais were mixed with fe mg chondrule precursors this hypothesis is difficult to reconcile with the lack of evidence of melting of aoas which represent aggregates of the least refractory cais and forsterite grains

late accretion and lithification of chondritic parent bodies mg isotope studies on fragments from primitive chondrites and chondritic breccias recent results of isotopic dating studies 182hf 182w 26al 26mg and the increasing number of observed igneous and metamorphosed fragments in primitive chondrites provide strong evidence that accretion of differentiated planetesimals predates that of primitive chondrite parent bodies the primitive chondrites adrar 003 and acfer 094 contain some unusual fragments that seem to have undergone recrystallization magnesium isotope analyses reveal no detectable radiogenic 26mg in any of the studied fragments the possibility that evidence for 26al was destroyed by parent body metamorphism after formation is not likely because several other constituents of these chondrites do not show any metamorphic features since final accretion of a planetesimal must have occurred after formation of its youngest components formation of these parent bodies must thus have been relatively late i e after most 26al had decayed al mg isotope data for some igneous textured clasts granitoids and andesitic fragments within the two chondrite regolith breccias adzhi bogdo and study butte reveal also no evidence for radiogenic 26mg as calculated from the upper limits the formation of these igneous clasts the incorporation into the parent body regolith and the lithification must have occurred at least 3 8 myr andesite in study butte and 4 7 myr granitoids in adzhi bogdo after calciumaluminum rich inclusions cai formation the absence of 26mg excess in the igneous inclusions does not exclude 26al from being a heat source for planetary melting in large early formed planetesimals cooling below the closure temperature of the al mg system may be too late for any evidence for live 26al in the form of 26mg excess to be preserved thus growing evidence exists that chondritic meteorites represent the products of a complex multi stage history of accretion parent body modification disruption and re accretion

complex scattering within d observed on the very dense los angeles region seismic experiment passive array several seismic phases that scattered within a few hundred kilometers of the base of the mantle are observed in a very dense seismic section the los angeles region seismic experiment passive phase array was composed of 88 seismometers placed along a 175 km profile records from two deep earthquakes in tonga and one earthquake near honshu japan show a secondary arrival between clear p and pcp arrivals modeling with layered structures shows that the tonga and honshu seismic sections are consistent with an increase in seismic velocity 140 and 240 km above the core mantle boundary respectively and a 10 km thick low velocity zone at the base of the mantle beneath a region in the mid pacific several of these arrivals are not coherent enough to appear in higher resolution stacks from the much larger southern california seismic network this experiment illustrates that fine scale passive array data can reveal small scale deep earth structure invisible to larger scale seismic networks

deep mantle seismic modeling and imaging detailed seismic modeling and imaging of earth s deep interior is providing key information about lower mantle structures and processes including heat flow across the core mantle boundary the configuration of mantle upwellings and downwellings phase equilibria and transport properties of deep mantle materials and mechanisms of core mantle coupling multichannel seismic wave analysis methods that provide the highest resolution deep mantle structural information include network waveform modeling and stacking array processing and 3d migrations of p and s wave seismograms these methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography some methods are adapted from oil exploration seismology but all are constrained by the source and receiver distributions long travel paths and strong attenuation experienced by seismic waves that penetrate to the deep mantle large and small scale structures with velocity variations ranging from a fraction of a percent to tens of percent have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution

mineralogy and petrography of amoeboid olivine aggregates from the reduced cv3 chondrites efremovka leoville and vigarano products of nebular condensation accretion and annealing amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka leoville and vigarano are irregularly shaped objects up to 5 mm in size composed of forsteritic olivine fa 50 melting we infer that aoas are aggregates of high temperature nebular condensates which formed in cai forming regions and that they were absent from chondrule forming regions at the time of chondrule formation the absence of low ca pyroxene and depletion in moderately volatile elements mn cr na k suggest that aoas were either removed from cai forming regions prior to condensation of these elements and low ca pyroxene or gas solid condensation of low ca pyroxene was kinetically inhibited

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

localized double array stacking analysis of pcp d and ulvz structure beneath the cocos plate mexico central pacific and north pacific abstract a large high quality p wave data set comprising short period and broadband signals sampling four separate regions in the lowermost mantle beneath the cocos plate mexico the central pacific and the north pacific is analyzed using regional one dimensional double array stacking and modelling with reflectivity synthetics a data screening criterion retains only events with stable pcp energy in the final data stacks used for modelling and interpretation this significantly improves the signal stacks relative to including unscreened observations allows confident alignment on the pcp arrival and allows tight bounds to be placed on p wave velocity structure above the core mantle boundary cmb the pcp reflections under the cocos plate are well modelled without any ultra low velocity zone from 5 to 20 n at latitudes from 15 to 20 n we find evidence for two p wave velocity discontinuities in the d region the first is 182 km above the cmb with a ln vp of 1 5 near the same depth as a weaker discontinuity

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

heterogeneities in d beneath the southwestern pacific inferred from scattered and reflected p waves we investigate the fine structure of the d layer beneath the southwestern pacific using short period data from 7 deep events in the fiji tonga region recorded at the j array in japan we use a double array migration method which integrates source array beamforming with receiver array beamforming the phase weighted stacking technique which reduces incoherent noise by employing complex trace analysis is also applied this combination greatly enhances small phases common to the source and receiver beams we present coherent phases originating from the lowermost mantle using these new array techniques the results indicate that seismic energy is reflected at two negative discontinuities near 2550 and 2650 km the migration shows only weak evidence for scattering objects which may be an indication that scattering in the d layer beneath the southwestern pacific is weak

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

detection of p wave reflector in d beneath the south western pacific using double array stacking the double array event and receiver array stacking is applied to the p wave data from 6 fiji is events recorded by a local network of short period seismographs in japan to investigate vp structure in the lowermost mantle a signal which may be interpreted as the reflection from a discontinuity at 170 km above the cmb core mantle boundary is observed between p and pcp in the stacked record as compared with the receiver array stacking with a small number of stations applied to a single event the double array stacking is effective to detect the weak signal of pdp

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

coexisting shear and compressional wave seismic velocity discontinuities beneath the central pacific stacking of broadband shear waves s and short period compressional waves p provides compelling evidence for the existence of a localized discontinuous increase in both s and p wave velocity 230 km above the core mantle boundary cmb beneath the central pacific modelling indicates a 1 7 increase in s velocity v s and a 0 75 increase in p velocity vp similar features have been detected intermittently on a global basis but seldom with s and p structure being resolved in the same location previous evidence for anisotropy near the cmb beneath the central pacific suggests that the discontinuity may be related to anisotropic fabrics induced by flow in the thermal boundary layer above the core

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

oxygen isotopic distribution in an amoeboid olivine aggregate from the allende cv chondrite primary and secondary processes the oxygen isotopic distribution in an amoeboid olivine aggregate aoa tta1 02 from the allende cv3 chondrite has been determined by secondary ion mass spectrometry the irregular shaped tta1 02 5 3mm consists mostly of olivine grains of ca 5 m in diameter olivine grains of mg rich fo95 and fe rich fo60 composition are in direct contact with each other with a sharp compositional boundary oxygen isotopic compositions of fe rich olivine grains are 16o poor 17o 5 whereas mg rich olivine is 16o rich 17o 25 several al rich inclusions ca 500 m in diameter are enclosed by olivine grains in the aoa oxygen isotopic compositions of spinel and fassaite in al rich inclusions are 16o rich 17o 20 whereas those of anorthite nepheline and phyllosilicate are 16o poor 17o 5 we propose the following sequence of events during the formation of aoas in the allende meteorite 1 formation of al rich inclusions with 16o rich oxygen isotopic composition 2 accretion of mg rich olivine grains with 16o rich oxygen isotopic composition around al rich inclusions 3 accretion into parent body and 4 aqueous alteration in the parent body which led to crystallization of 16o poor minerals fe rich olivine anorthite nepheline and phyllosilicate this is reflecting reactions among primary 16o rich aoa minerals and aqueous fluid having 16o poor oxygen isotopic composition fe rich olivine grains precipitated from aqueous fluids which partially dissolved pre existing mg rich olivine grains sintering and mg fe diffusion occurred during thermal metamorphism anorthite nepheline and phyllosilicate in al rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage

a hibonite corundum inclusion from murchison a first generation condensate from the solar nebula through freeze thaw disaggregation of the murchison cm carbonaceous chondrite we have recovered a 90 x 75 m refractory inclusion that consists of corundum and hibonite with minor perovskite corundum occurs as small 10 m rounded grains enclosed in hibonite laths 10 m wide and 30 40 m long throughout the inclusion perovskite predominantly occurs near the edge of the inclusion the crystallization sequence inferred petrographically corundum followed by hibonite followed by perovskite is that predicted for the first phases to form by equilibrium condensation from a solar gas for ptot 5 x 10 3 atm in addition the texture of the inclusion with angular voids between subhedral hibonite laths and plates is also consistent with formation of the inclusion by condensation hibonite has heavy rare earth element ree abundances of 40 x ci chondrites light ree abundances 20 x ci chondrites and negative eu anomalies the chondrite normalized abundance patterns especially one for a hibonite perovskite spot are quite similar to the patterns of calculated solid gas partition coefficients for hibonite and perovskite at 10 3 atm and are not consistent with formation of the inclusion by closed system fractional crystallization in contrast with the features that are consistent with a condensation origin there are problems with any model for the formation of this inclusion that includes a molten stage relic grains or volatilization if thermodynamic models of equilibrium condensation are correct then this inclusion formed at pressures 5 x 10 3 atm possibly with enrichments 1000x in ci dust relative to gas at low pressures below 10 4 atm both hibonite and corundum have 17o 18o 50 indicating formation from an 16o rich source the inclusion does not contain radiogenic 26mg and apparently did not contain live 26al when it formed if the short lived radionuclides were formed in a supernova and injected into the early solar nebula models of this process suggest that 26al free refractory inclusions such as this one formed within the first 6 x 10 5 years of nebular collapse

the p wave velocity structure near the base of the mantle travel times from 16 events recorded at two temporary networks of short period seismometers deployed across australia have been used to study the p wave velocity structure of the mantle below depths of 1700 km the slowness distance curve derived from these times shows small deviations from the slownesses predicted from the preliminary reference earth model of dziewonski and anderson 1981 that may be significant the most important feature is a rapid decrease of more than 0 5 s degree between distances of 85 and 88 velocity filtering of seismograms from 5 nuclear explosions in kazakh recorded at these australian networks indicates the presence of two arrival branches at distances between 83 and 91 whose slownesses differ by 0 40 to 0 55 s degree and which intersect at a distance of 87 processed p wave seismograms from the yellowknife array in canada also indicate the presence of a similar phenomenon in the same distance range in two separate regions the results can be explained by a widespread rapid or sharp increase in velocity of 2 5 to 3 0 about 200 km above the core mantle boundary

mapping the core mantle boundary louise h kellogg deep within earth lies a boundary between the solid iron core and the mantle where seismologists see an abrupt change in seismic wave velocity as kellogg discusses in her perspective new studies are revealing many details about this core mantle boundary including two reports in the same issue revenaugh and meyer report studies of the core mantle boundary beneath tonga japan and central america suggesting that it is partially molten earle and shearer use new data processing methods to reveal details of the fine structure of the core mantle boundary

origin of low ca pyroxene in amoeboid olivine aggregates evidence from oxygen isotopic compositions amoeboid olivine aggregates aoas in primitive carbonaceous chondrites consist of forsterite fa 50 objects is texturally and mineralogically intermediate between aoas and al rich chondrules it consists of euhedral forsterite grains pigeonite augite anorthitic mesostasis abundant anhedral spinel grains and minor fe ni metal it is surrounded by a coarse grained igneous rim largely composed of low ca pyroxene with abundant fe ni metal sulfide nodules the mineralogical observations suggest that only spinel grains in this igneous object were not melted the spinel is 16o rich 17o 22 whereas the neighboring plagioclase mesostasis is 16o depleted 17o 11 we conclude that aoas are aggregates of solar nebular condensates forsterite fe ni metal and cais composed of al diopside anorthite spinel and melilite formed in an 16o rich gaseous reservoir probably cai forming region s solid or incipiently melted forsterite in some aoas reacted with gaseous sio in the same nebular region to form low ca pyroxene some other aoas appear to have accreted 16o poor pyroxene normative dust and experienced varying degrees of melting most likely in chondrule forming region s the most extensively melted aoas experienced oxygen isotope exchange with 16o poor nebular gas and may have been transformed into chondrules the original 16o rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains

calcium aluminum rich inclusions and amoeboid olivine aggregates from the cr carbonaceous chondrites calcium aluminum rich refractory inclusions cais in cr chondrites are rare 1 vol fairly small 500 m and irregularly shaped and most of them are fragmented based on the mineralogy and petrography they can be divided into grossite hibonite rich melilite rich and pyroxene anorthite rich cais other types of refractory objects include fine grained spinel melilite pyroxene aggregates and amoeboid olivine aggregates aoas some of the pyroxene anorthite rich cais have igneous textures and most melilite rich cais share similarities to both the fluffy and compact type a cais found in cv chondrites one major difference between these cais and those in cv cm and co chondrites is that secondary mineral phases are rare in situ ion microprobe analyses of oxygen isotopic compositions of 27 cais and aoas from seven cr chondrites demonstrate that most of the cais are 16o rich 17o of hibonite melilite spinel pyroxene and anorthite 22 and isotopically homogeneous within 3 4 likewise forsterite spinel anorthite and pyroxene in aoas have nearly identical 16o rich compositions 24 17o 20 deg in contrast objects which show petrographic evidence for extensive melting are not as 16o rich 17o less than 18 o secondary alteration minerals replacing 16o rich melilite in melilite rich cais plot along the terrestrial fractionation line most cr cais and aoas are mineralogically pristine objects that largely escaped thermal metamorphism and secondary alteration processes which is reflected in their relatively homogeneous 16o rich compositions it is likely that these objects or their precursors condensed in an 16o rich gaseous reservoir in the solar nebula in contrast several igneous cais are not very enriched in 16o probably as a result of their having melted in the presence of a relatively 16o poor nebular gas if the precursors of these cais were as 16o rich as other cr cais this implies either temporal excursions in the isotopic composition of the gas in the cai forming regions and or radial transport of some cai precursors into an 16o poor gas the absence of oxygen isotope heterogeneity in the primary minerals of melilite rich cais containing alteration products suggests that mineralogical alteration in cr chondrites did not affect oxygen isotopic compositions of their cais

simultaneous inversion of steep angle observations of pcp and scp in europe what can we learn about the core mantle boundary summary at epicentral distances less than 30 the steep angle reflections pcp and scp from the core mantle boundary cmb are normally difficult to identify and rarely reported the reason is that the reflection coefficient at the cmb for these phases is relatively small and pcp and scp onsets are often disturbed by interference with other more prominent phases however the absolute traveltimes of pcp and scp in the steep angle range are the most sensitive seismic phases for depth undulations of the cmb and in addition of all cmb reflections these phases are influenced least by lateral heterogeneities along their ray paths during this study a set of more than 200 such reflections from the earth s core observed at european stations with reflection points below europe was collected and analysed starting from observations at the geres array in germany pcp and scp could also be identified at other european seismic stations the stations used for this study were the fennoscandian arrays norsar nores and fines the grafenberg array in germany and the stations of the german regional seismic network grsn with the combined investigation of pcp and scp a map of reflection points of the cmb below europe could be constructed to reduce the influence of location and other errors traveltime differences were measured between the onsets of p or pn pcp and scp these traveltime differences show positive and negative deviations from theoretical values of up to several seconds cmb undulations of up to 6 km as discussed in the literature change the absolute traveltimes of pcp or scp only by about 0 9 or 1 2 s for an epicentral distance of 20 the observed residuals can be explained by several factors still unresolved location errors lateral heterogeneities along the whole ray paths of all investigated phases or undulations of the depth of the cmb all observed traveltime effects must be known at least one order of magnitude better than the expected effects to resolve statistically reliable cmb undulations inverting the residuals for possible cmb undulations shows that if there is any cmb signal in the data it is very small most of the observed residuals can easily be explained by smaller changes in event depth lateral heterogeneities in the source region and along the whole ray paths and or station corrections but the observations do not require any cmb topography if such undulations of up to 6 km exist all other traveltime effects will mask them coming to this disillusioning result by using the most sensitive data to resolve a cmb topography can only lead to this conclusion all models of cmb undulations derived from traveltime data must be taken as very unsure and any far reaching interpretations of such models should be avoided

seismological mapping of fine structure near the base of the earth s mantle the earth s core mantle boundary cmb juxtaposes liquid iron and crystalline silicates and is a region of large vertical thermal gradients the d region which extends up to 200 300 km above the cmb often has elevated shear wave velocity and suggestions of lateral variations in structure1 recent improvements in our ability to assemble and analyse records from regional seismic networks have allowed us to examine long profiles of travel times amplitudes and waveforms from more than a thousand short period seismometers2 we observe across canada and the united states p waves that have grazed the cmb from the powerful nuclear test in lop nor china on 21 may 1992 first arrival travel times and large secondary arrivals are consistent with a 1 5 compressional velocity increase with depth 130 km above the cmb about half the thickness of d in this locality3 our observations together with evidence for the absence of such a thin fast layer in neighbouring regions suggest the presence of lateral heterogeneity in composition or phase at the base of the mantle

an experimental study of chondrule formation from chondritic precursors via evaporation and condensation in knudsen cell shock heating model of dust aggregates abstract chondrules igneous objects of 1 mm in diameter formed in the earliest solar system via a transient heating event are divided into two types main type i feo poor and minor type ii feo rich using various chondritic materials for different redox conditions and grain sizes chondrule reproduction experiments were carried out at iw 2 to iw 3 8 with cooling rates mainly 100 c h with peak temperatures mainly at 1450 c and mainly at 100 pa in a knudsen cell providing near chemical equilibrium between the charge and the surrounding gas at the peak temperatures vapor pressures in the capsule were controlled using solid buffers after and during the significant evaporation of the iron component from the metallic iron poor starting materials in near equilibrium crystallization occurred this resulted in the formation of a product similar to the type i chondrules dusty olivine grains occurred in charges that had precursor type ii chondrules containing coarse ferroan olivine but such grains are not common in type i chondrules therefore fine grained ferroan matrices rather than type ii chondrules are main precursor for type i chondrules the type i chondrules would have evolved via evaporation and condensation in the similar conditions to the present experimental system residual gas which escaped in experiments could have condensed to form matrices leading to complementary compositions clusters of matrices and primordial chondrules could have been recycled to form main generation chondrules originated from the shock heating

p and s wave reflections from anomalies in the lowermost mantle summary seismic p and s waves recorded at the grf array in germany are used to study the inhomogeneous structure of the boundary layer d at the base of the mantle the use of the seismic array allows the detection of small scale anomalies in the lowermost mantle the lateral resolution attainable is about 100 to 400 km i e more than 10 times better than with tomographic methods the analysis of 13 years of grf broad band array data yields 255 events with high signal to noise ratio which are used to map the lowermost mantle 74 of these events show anomalous p waves pdp which arrive 3 6 s after the direct p wave and have a slowness 0 7 0 8 s smaller than the slowness of direct p other events close to the events with pdp do not have such an anomalous phase using slowness traveltime amplitude and waveform information it is demonstrated that pdp is caused by an anomalous lower mantle velocity structure below the turning point of the p wave if the pp phase i e a p wave first reflected at the free surface near the source is used together with the p phase distinct and well sepaarted p velocity anomalies can be determined under the nansen basin the kara sea and northern siberia the areas of the bounce points of pdp in the lower mantle have a lateral extension of about 100 by 200 km but this is not the size of the anomaly since the resolution of p waves at 1 hz in this depth is 130 km by 260 km fresnel zone the accuracy to which the depth of the reflector 2612 km under the nansen basin and 2605 km under northern siberia respectively can be determined for 1 d models is 10 to 20 km the velocity contrast at the lower mantle discontinuity is about 3 per cent 1 to 1 5 per cent areas which have velocity fluctuations smaller than about 1 per cent can not be detected as anomalous areas 2 d models of the anomalies reveal the range of adequate models and possible trade offs if the lateral extension of the anomaly is about 7 the reflector has to be 40 km deeper than in the 1 d model if the dip of the reflector in the lowermost mantle is only about 1 5 it is difficult to resolve if the reflector is tilted towards the source or towards the receiver for the anomaly under the nansen basin deviations from the great circle path are observed for pdp indicating 3 d effects below the three anomalies the core mantle boundary cmb can be located by pcp with a depth in agreement with standard earth models under northern siberia has a region where p and s velocity anomalies coincide but also a region where only an s velocity anomaly but no p velocity anomaly is observed this results in changes of the poisson ratio from 5 9 per cent to 4 8 per cent 1 5 per cent across the discontinuity in the lowermost mantle for the regions studied the analysis of the s waves s sds and scs reveals two s velocity anomalies in the lowermost mantle under northern siberia the first anomaly coincides with the p velocity anomaly under northern siberia and can be explained by a 1 d model with a reflector depth of 2610 km 15 km and a velocity contrast of 2 3 per cent the second s velocity anomaly is in an area where no p velocity anomaly can be detected the corresponding 1 d s velocity model has a reflector depth of 2575 km 15 km and an s velocity contrast of 2 6 per cent the smallest structures that can be resolved with the s waves in this depth are about twice as large as for the p waves i e 230 km by 460 km fresnel zone the joint analysis of p and s waves therefore shows a region with a p velocity anomaly together with weak indications for an s velocity anomaly nansen basin and a second region with a p but no s anomaly kara sea the lowermost mantle

scale lengths of shear velocity heterogeneity at the base of the mantle from s wave differential travel times resolving the seismic velocity heterogeneity in the lowermost mantle is essential for understanding the chemical and dynamical processes operating in the boundary layer between the core and the mantle several regions of the lowermost mantle appear to have abrupt increases in shear velocity several hundred kilometers above the core mantle boundary at the top of the d sup prime prime layer this structure is revealed by seismic wave energy refracted by the velocity increase resulting in an extra arrival scd in teleseismic s wavetrains at distances from 65 to 95 degree anomalies in differential travel times of the extra arrival relative to direct s which turns at shallower depths in the midmantle or scs which reflects from the core mantle boundary below the velocity increase provide probes of the velocity heterogeneity in the lowermost mantle with better vertical resolution than provided by conventional scs s measurements we explore the spatial patterns in scd s scs scd and scs s differential time residuals for paths through the lower mantle beneath alaska eurasia and india all being regions with coherent scd phases to place constraints on the strength and scale lengths of shear velocity heterogeneity and or variable topography of the lower mantle discontinuity in these regions the observed patterns are poorlymore predicted by existing global tomographic models significant small scale heterogeneity with lateral length scales of 200 endash 500 km or less exists even within regions that display a relatively uniform d sup prime prime discontinuity structure over scale lengths of 1500 endash 2000 km the strongest travel time variations are associated with structure above the d sup prime prime region in contrast to common assumptions rapid lateral fluctuations in scs scd differential times suggest that the anomalies accumulate within a relatively thin zone less than the overall thickness of d sup prime prime abstract truncated less

short period p wave constraints on d reflectivity we present evidence of a p wave reflector in d beneath the central and eastern equatorial pacific obtained from nearly 7000 short period seismic recordings of earthquakes in the tonga fiji and south america subduction complexes both regions overlap previous observations of an s wave triplication at similar depths double array waveform stacking places the reflector 190 20 km above the core mantle boundary and allows for a velocity transition zone no thicker than 50 km the data admit a wide range of compressional v p and shear wave velocities v s the 2 3 increase in v s suggested by earlier long period s wave studies however necessitates only a 0 5 0 6 increase in v p the data stacks represent spatial averages over large areas of the lower mantle such that reflector intermittence and topography decrease stack amplitude and lower the apparent v p jump our results constrain these processes to act over length scales of 10 100 km

alteration of al rich inclusions inside amoeboid olivine aggregates in the allende meteorite lightly altered al rich inclusions in amoeboid olivine aggregates have cores containing primary melilite fassaite spinel perovskite and no secondary alteration products in moderately altered inclusions whose cores now contain only fassaite spinel perovskite melilite was replaced by a fine grained mixture of grossular anorthite feldspathoids and perovskite was partially replaced by ilmenite in heavily altered inclusions fassaite has been replaced by a mixture of phyllosilicates ilmenite and the remaining primary phases are spinel perovskite in very heavily altered inclusions no primary phases remain the spinel having reacted to form either phyllosilicates or a mixture of olivine feldspathoids this sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures during alteration sio2 na2o k2o feo cr2o3 h2o and cl were introduced into the inclusions and cao was lost mgo may have been lost during the melilite reaction and added during formation of phyllosilicates electron microprobe analyses indicate that the phyllosilicates are a mixture of na rich phlogopite and chlorite or alrich serpentine thermodynamic calculations suggest that at a solar nebular water fugacity of 10 6 na rich phlogopite could have formed from fassaite at 470 k and chlorite from na rich phlogopite at 328 k olivine mantling al rich inclusions is not serpentinized suggesting that these objects stopped equilibrating with the nebular gas above 274 k

oxygen isotopic zoning of reversely zoned melilite crystals in a fluffy type a ca al rich inclusions from the vigarano meteorite the oxygen isotopic microdistributions within melilite measured using in situ secondary ion mass spectrometry correspond to the chemical zoning profiles in single melilite crystals of a fluffy type a ca al rich inclusions cais of reduced cv3 vigarano meteorite the melilite crystals show chemical reverse zoning within an individual single crystal from the akermanite rich core to the akermanite poor rim the composition changes continuously with the crystal growth the zoning structures suggest that the melilite grew in a hot nebular gas by condensation with decreasing pressure the oxygen isotopic composition of melilite also changes continuously from 16o poor to 16o rich with the crystal growth these observations suggest that the melilite condensation proceeded with change consistent with an astrophysical setting around the inner edge of a protoplanetary disk where both 16o rich solar coronal gas and 16o poor dense protoplanetary disk gas could coexist fluffy type a cais could have been formed around the inner edge of the protoplanetary disk surrounding the early sun

amoeboid olivine aggregates with low ca pyroxenes a genetic link between refractory inclusions and chondrules amoeboid olivine aggregates aoas in primitive unmetamorphosed and unaltered carbona ceous chondrites are uniformly 16 o enriched 17 o 20 and consist of forsterite fa2 feni metal and a refractory component individual cais and fine grained minerals interspersed with forsterite grains composed of al diopside anorthite spinel and exceptionally rare melilite a u k15 some cais in aoas have compact igneous textures melilite in aoas is replaced by a fine grained mixture of spinel al diopside and anorthite spinel is corroded by anorthite or by al diopside in 10 of 500 aoas studied in the cr cv cm co ch cb and ungrouped carbonaceous chondrites acfer 094 adelaide and lew85332 forsterite is replaced to a various degree by low ca pyroxene there are three major textural occurrences of low ca pyroxene in aoas i thin 10 m discontinuous layers around forsterite grains or along forsterite grain boundaries in aoa peripheries ii haloes and subhedral grains around feni metal nodules in aoa peripheries and iii thick up to 70 m continuous layers with abundant tiny inclusions of feni metal grains around aoas aoas with low ca pyroxene appear to have experienced melting of various degrees in the most extensively melted aoa in the cv chondrite leoville only spinel grains are relict forsterite anorthite and al diopside were melted this aoa has an igneous rim of low ca pyroxene with abundant feni metal nodules and is texturally similar to type i chondrules based on these observations and thermodynamic analysis we conclude that aoas are aggregates of relatively low temperature solar nebular condensates originated in 16 o rich gaseous reservoir s probably cai forming region s some of the cais were melted before aggregation into aoas many aoas must have also experienced melting but of a much smaller degree than chondrules before and possibly after aggregation melilite and spinel reacted with the gaseous sio and mg to form ca tschermakite caal2sio6 diopside camgsi2o6 solid solution and anorthite solid or incipiently melted olivine in some aoas reacted with gaseous sio in the cai or chondrule forming regions to form low ca pyroxene mg2sio4 sio g h2o g mg2si2o6 h2 g some low ca pyroxenes in aoas may have formed by oxidation of si bearing feni metal mg2sio4 si in feni 2h2o g mg2si2o6 2h2 g and by direct gas solid condensation mg g sio g h2o g mg2si2o6 s h2 g from fractionated mg si ratio solar nebular gas although bulk compositions of aoas are rather similar to those of type i chondrules on the projection from spinel onto the plane ca2sio4 mg2sio4 al2o3 these objects plot on different sides of the anorthite forsterite thermal divide suggesting that type i chondrules cannot be produced from aoas by an igneous fractionation formation of low ca pyroxene by reaction of aoas with gaseous sio and by melting of silica rich dust accreted around aoas moves bulk compositions of the aoas towards chondrules and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors the rare occurrences of low ca pyroxene in aoas may indicate that either aoas were isolated from the hot nebular gas before condensation of low ca pyroxene or that condensation of low ca pyroxene by reaction between forsterite and gaseous sio was kinetically inhibited if the latter is correct then the common occurrences of pyroxene rich type i chondrules may require either direct condensation of low ca pyroxenes or sio2 from fractionated nebular gas or condensation of gaseous sio into chondrule melts copyright 2004 elsevier ltd

ca al rich inclusions from the ningqiang meteorite continuous assemblages of nebular condensates and genetic link to type b inclusions the petrography and mineral chemistry of 110 ca al rich inclusions cais and 9 ca and or al rich amoeboid olivine aggregates aoas from the ningqiang carbonaceous chondrite are reported these cais are referred to as hibonite bearing and hibonite free melilite spinel rich type a and spinel pyroxene inclusions melilite is more gehlenitic in the hibonite bearing type as than in the other two types and all of them vary within a range of ak0 30 modal compositions of the three types of cais overlap with each other and make up a continuum with wide ranges of melilite spinel diopside the diopside occurs as rims on the cais or their individual concentric objects the 9 aoas contain spinel diopside anorthite in the centers of the aggregates the spinel grains rimmed by diopside in the centers are similar to the spinel pyroxene inclusions bulk compositions of these cais vary along the condensation trajectory with the hibonite bearing type as plotting at the beginning followed by hibonite free type as then by spinel pyroxene inclusions as temperature decreases bulk compositions of the aoas are close to the lowest temperature condensation trajectory except for a few with compact textures most of the type as and spinel pyroxene inclusions are fluffy aggregates probably pristine vapor solid condensates of the nebula the bulk compositions of the type as appear to overlap with the range of most melilite ti al clinopyroxene rich type b inclusions hence crystallization of liquids produced by melting the type as can form type b inclusions without significant evaporative loss of mgo or sio2 a few type bs have bulk compositions deviating from the range of their proposed precursors and may have suffered significant evaporation as suggested in previous studies

amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites a record of condensate evolution in the solar nebula abstract amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution spinel rich nodules and ribbons in aoas often show group ii trace element patterns and formed either by fractional condensation or by condensation following partial vaporization the dominant olivine component in aoas can be explained as a condensate produced in the same way but with fractionation occurring at a lower temperature other spinel rich material in aoas appears to be a vaporization residue ca rich pyroxene anorthite patches in aoas show chemical signatures similar to those observed for spinel or melilite bearing regions but with lower refractory element and higher mg and si contents supporting the idea that the patches formed by reaction between cai like material and mg si rich gas different trace element patterns group ii and non group ii refractory are sometimes found for al rich regions ca pyroxene anorthite or melilite bearing in a given aoa suggesting that aoas agglomerated from materials that formed under different conditions and that they did not subsequently homogenize aoas appear to have originated in a system with near canonical solar composition and a low pressure gas 10 6 10 4 bar over a range of temperatures mainly 1200 1384 k under somewhat non equilibrium conditions relative to predicted equilibrium condensates most aoas show an apparent paucity of metal possibly reflecting differential density dependent sorting between olivine and metal grains during aggregate formation trace element data are consistent with a simple model involving melting and igneous fractionation of aoa like olivine to produce type i chondrule olivine but other data suggest that open system melting of chondrules occurred in a different gaseous environment than that which produced aoas

nebular history of amoeboid olivine aggregates minor element ca cr and mn concentrations in amoeboid olivine aggregates aoas from primitive chondrites were measured and compared with those predicted by equilibrium condensation in the solar nebula cao concentrations in forsterite are low particularly in porous aggregates a plausible explanation appears that an equilibrium ca activity was not maintained during the olivine condensation cao and mno in forsterite are negatively correlated with cao being higher in compact aggregates this suggests that the compact aggregates formed either by a prolonged reheating of the porous aggregates or by condensation and aggregation of forsterite during a very slow cooling in the nebula

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

microstructural evidence for complex formation histories of amoeboid olivine aggregates from the alha77307 co3 0 chondrite the microstructures and compositions of olivine and refractory components in six amoeboid olivine aggregates aoas in the allan hills a77307 co3 0 chondrite have been characterized in detail using the focused ion beam sample preparation technique with transmission electron microscopy in the aoas refractory components perovskite melilite spinel anorthite and al ti bearing diopside provide evidence of a high degree of textural and compositional heterogeneity suggesting that these phases have formed by disequilibrium gas solid condensation at high temperatures under highly dynamic conditions we infer different possible reactions of early condensed solid minerals perovskite and spinel with a nebular gas forming diopside with wide ranges of al and ti contents and or anorthite the progressive incomplete consumption of spinel in these reactions may have resulted in the cr enrichment in the remaining unreacted spinel in the aoas in contrast to the refractory components olivines in the aoas have equilibrated textures with 120 triple junctions indicating that the aoas were subjected to high temperature annealing after agglomeration of olivine and refractory components because the aoas consist of fine grained olivine grains with numerous pores the annealing is constrained by experimental data to have occurred for a short duration of the order of a few hours to tens of hours depending on the annealing temperature in comparison the effects of annealing on the refractory components are minimal probably due to pinning of grain boundaries in the multiphase assemblages that inhibited grain growth

mineralogical anatomy and implications of a ti sc rich ultrarefractory inclusion from sayh al uhaymir 290 ch3 chondrite titanium rich minerals are common in ca al rich inclusions from primitive chondrites they are important not only for testing the condensation models for a gas with a solar composition but also for constraining the redox conditions of the early solar nebula in this study we report the detailed mineralogical features and its oxygen isotope compositions of a ti sc rich ultrarefractory inclusion a0031 from a ch3 chondrite sayh al uhaymir 290 the a0031 inclusion has a compact and layered texture with the interior consisting of panguite sc rich anosovite ti rich davisite and anorthite a few hexaferrum perovskite and spinel crystals are present as inclusions in these minerals outside of ti rich davisite are a layer of al ti rich diopside and two grains of enstatite this texture strongly suggests that a0031 has a condensation origin panguite is its third occurrence in nature and similar in composition to the type panguite from the allende meteorite sc rich anosovite in a0031 has a chemical formula of ti 4 ti 3 mg sc al 3o 5 with the pseudobrookite structure this is the second report of ti 3o 5 in nature but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase the discovery of sc rich anosovite in a0031 reveals the stability of ti 3o 5 in the early solar nebula and supports the prediction of previous equilibrium condensation calculations the panguite sc rich anosovite and ti rich davisite in a0031 show a large variation in ti 3 ti tot the primitive nature of a0031 implies that the variations in ti 3 ti tot among different ti rich minerals are primary features we propose that the distribution of ti 3 and ti 4 could be controlled mainly by their various competition abilities of incorporating into these ti sc al rich minerals similarity of ti 3 ti tot value between ti rich davisite from a0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings the 16 o depleted isotope compositions of a0031 confirm the existence of diverse oxygen reservoirs for ch ca al rich inclusions in the solar nebula

a search for anomalies in the lowermost mantle using seismic bulletins abstract for deep events and epicentral distances around 75 the bulletins of the international seismological centre bisc contain many secondary arrivals between p and pcp the reflection from the core mantle boundary cmb which cannot be explained by current spherical symmetric earth models assuming that these arrivals in the p coda are reflections from p velocity anomalies in the lower mantle we calculate the associated reflection points geographical coordinates and distance from the cmb and map both strength relative density of reflection points in bins in the lower mantle and distance of the reflectors from the cmb on a global scale the regions with these anomalous bins cover 3 of the 50 of the lowermost mantle that can be analysed with this data set the most significant regions with anomalous bins values in parentheses give a preliminary estimate of the distance of the reflector from the cmb are under the north atlantic ridge 250 km northern central siberia 230 km japan 180 km the central mid atlantic ridge 310 and 260 km and off the coast of ecuador 340 km the presence of reflectors in one of these regions has already been confirmed by detailed seismic studies using waveform data from arrays and networks a slight 2 3 p velocity contrast is sufficient to produce measurable reflection amplitudes in the distance range of 70 80 ten percent of the lower mantle sampled by this study is covered by bins with no or very few secondary arrivals in the p coda the most significant regions with such a normal lower mantle are under central america the caroline and marshall islands in the eastern pacific the area of hawaii and the easter islands and the northern atlantic identification of the regions with anomalous bins serves to locate the areas of the lowermost mantle which should be analysed further by using the full information content of seismograms the study of the travel time the amplitude and the form of the wavefield recorded preferably at seismic arrays dense networks will allow the determination of the anomalous velocity structure of the core mantle transition zone in more detail the most promising areas for such a study are given here but further anomalies are likely to exist

genesis of a gulf of mexico ring as determined from kinematic analyses the kinematics of the loop current are studied using trajectories of drifters in the gulf of mexico during mid june through september 1985 one of the drifters was in the loop current proper while other drifters were in two recently shed loop current rings the drifter in the loop current showed strong anticyclonic motion during the study period this loop current anticyclone first began off the northwest coast of cuba it rapidly moved northward into the gulf of mexico as a ring pinched off from the loop current analysis of the loop current drifter motion showed that the anticyclone became an integral part of the loop current taking on many of the characteristics of the most recently shed ring the results of the analysis suggest a process by which loop current rings can be generated apparently this mechanism can cause the loop current to become reconfigured in 2 3 months for beginning the process of ring separation

remelting of refractory inclusions in the chondrule forming regions evidence from chondrule bearing type c calcium aluminum rich inclusions from allende we describe the mineralogy petrology oxygen and magnesium isotope compositions of three coarse grained igneous anorthite rich type c ca al rich inclusions cais abc ts26 and 93 that are associated with ferromagnesian chondrule like silicate materials from the cv carbonaceous chondrite allende the cais consist of lath shaped anorthite an99 cr bearing al ti diopside al and ti contents are highly variable spinel and highly akermanitic and na rich melilite ak63 74 0 4 0 6 wt na2o ts26 and 93 lack wark lovering rim layers abc is a cai fragment missing the outermost part the peripheral portions of ts26 and abc are enriched in sio2 and depleted in tio2 and al2o3 compared to their cores and contain relict ferromagnesian chondrule fragments composed of forsteritic olivine fa6 8 and low ca pyroxene pigeonite fs1wo 1 9 the relict grains are corroded by al ti diopside of the host cais and surrounded by haloes of augite fs0 5wo 30 42 the outer portion of cai 93 enriched in spinel is overgrown by coarse grained pigeonite fs0 5 2wo 5 17 augite fs0 5wo 38 42 and anorthitic plagioclase an84 relict olivine and low ca pyroxene pigeonite in abc and ts26 and the pigeonite augite rim around 93 are 16 o poor 17 o 1 to 8 spinel and al ti diopside in cores of cais abc ts26 and 93 are 16 o enriched 17 o down to 20 whereas al ti diopside in the outer zones as well as melilite and anorthite are 16 o depleted to various degrees 17 o 11 to 2 in contrast to typical allende cais that have the canonical initial 26 al 27 al ratio of 5 10 5 abc 93 and ts26 are 26 al poor with 26 al 27 al 0 ratios of 4 7 1 4 10 6 1 5 1 8 10 6 and 1 2 10 6 respectively we conclude that abc ts26 and 93 experienced remelting with addition of ferromagnesian chondrule silicates and incomplete oxygen isotopic exchange in an 16 o poor gaseous reservoir probably in the chondrule forming region this melting episode could have reset the 26 al 26 mg systematics of the host cais suggesting it occurred 2 myr after formation of most cais these observations and the common presence of relict cais inside chondrules suggest that cais predated formation of chondrules

seismic heterogeneous structure in the lowermost mantle beneath the southwestern pacific 1 the p and s wave velocity structure of the d layer beneath the southwestern pacific was investigated by using short period data from 12 deep events in the tonga fiji region recorded by the j array and the hi net two large aperture seismic arrays in japan reflected wave beam forming rwb and a migration method were used to extract weak signals originating from heterogeneities in the lowermost mantle in order to acquire high resolution a double array method was applied to the data the results of the rwb method indicate that seismic energy is reflected at discontinuities near the depths of 2520 and 2650 km which have a negative p wave velocity contrast of 1 at the most in addition there is a positive seismic discontinuity at a depth of 2800 km in the case of the s wave reflected energy is produced almost at the same depth 2550 km depth an apparent depth shift 50 km of the discontinuity at the depth of 2850 km may indicate that the s wave velocity reduction in the lowermost mantle is 2 3 times stronger than that of p a two dimensional cross section constructed with the rwb method suggests that the observed discontinuities can be characterized as intermittent lateral heterogeneities whose lateral extent is a few hundred kilometers the migration shows weak evidence of scattering objects which belong to the seismic discontinuities detected by the rwb method these anomalous structures may represent a part of hot plume generated beneath the southwestern pacific in the lowermost mantle

refractory inclusions in the murchison meteorite mineralogical and petrographic studies of a wide variety of refractory objects from the murchison c2 chondrite have revealed for the first time melilite rich and feldspathoid bearing inclusions in this meteorite but none of these is identical to any inclusion yet found in allende blue spinel hibonite spherules have textures indicating that they were once molten and thus their sio2 poor bulk composition requires that they were exposed to higher temperatures 1550 c than those deduced so far from any allende inclusion melilite rich inclusions are similar to allende compact type a s but are more al ti rich one inclusion much 1 consists of a delicate radial aggregate of hibonite crystals surrounded by alteration products and probably originated by direct condensation of hibonite from the solar nebular vapor the sinuous nodular and layered structures of another group of inclusions spinel pyroxene aggregates suggest that these also originated by direct condensation from the solar nebular gas each type of inclusion is characterized by a different suite of alteration products and or rim layers from all the other types indicating modification of the inclusions in a wide range of different physico chemical environments after their primary crystallization all of these inclusions contain some iron free rim phases these could not have formed by reaction of the inclusions with fluids in the murchison parent body because the latter would presumably have been very rich in oxidized iron other rim phases and alteration products could have formed at relatively low temperatures in the parent body but some inclusions were not in the locations in which they were discovered when this took place some of these inclusions are too fragile to have been transported from one region to another in the parent body indicating that low temperature alteration of these may have occurred in the solar nebula

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

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

petrography and classification of ca al rich and olivine rich inclusions in the allende cv3 chondrite a detailed systematic petrographic survey of all 189 ca al rich and olivine rich inclusions larger than 0 2 mm in diameter in 17 thin sections of allende was performed by optical and scanning electron microscopy most of these inclusions are aggregates containing varying proportions of three distinct constituents termed concentric objects chaotic material and inclusion matrix a new classification system for allende inclusions is proposed olivine rich inclusions occur in two textural varieties unrimmed olivine aggregates type 1a inclusions and rimmed olivine aggregates type 1b inclusions we classify ca al rich inclusions cai s on the basis of the size and abundance of their constituent concentric objects rather than their grain size into unrimmed complex cai s type 2 inclusions rimmed complex cai s type 3 inclusions and simple cai s type 4 inclusions several of the inclusion classes grade into each other some fundamental relationships among various types of allende inclusions are discussed we suggest that the term coarse grained even if used only in a relative sense is too restrictive for some members of one class of inclusion simple cai s and is inappropriate for most members of another class melilite rich complex cai s