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

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

oxygen isotopic evolution of amoeboid olivine aggregates in the reduced cv3 chondrites efremovka vigarano and leoville amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka vigarano and leoville consist of forsteritic olivine feni metal and a refractory component composed of spinel al diopside anorthite secondary ferrous olivine and alkali rich minerals nepheline and sodalite commonly observed in the oxidized cvs are rare mineralogy and chemical compositions of aoas are similar to those predicted by equilibrium thermodynamic condensation models suggesting that aoas formed primarily by gas solid condensation over a narrow temperature range slightly below the temperatures over which most ca al rich inclusions cais formed aoas in the reduced cvs preserve a 1st generation 16o rich signal 17 18o 40 similar to that observed in many cais suggesting that these refractory objects originated from a common source in the solar nebula in fact aoas and many fine grained cais may have formed by the same processes but at slightly different temperatures and can be considered a single class of refractory objects alteration of the aoas is manifested by differing extents of 16o depletion in original aoa minerals feo enrichment in olivine and formation of interstitial very fine grained na bearing phases from the six aoas and one fine grained melilite pyroxene rich cai examined in this study five distinct patterns of alteration were identified 1 one unaltered aoa from vigarano is characterized by 16o rich forsterite without feo rich rims and interstitial na bearing phases 2 weak alteration in the melilite pyroxene rich cai is characterized by incomplete 16o depletion in some melilite and precipitation of na bearing phases near the cai rim 3 oxygen isotopic composition and mineralogy are correlated in two aoas from leoville with 16o rich olivine 16o poor anorthite and a range of intermediate compositions in al diopside this pattern is consistent with model diffusion between original grains and a 16o poor reservoir during a relatively short term 60 yr high temperature 900 1100 c event 4 original forsterite has been enriched in feo but remained 16o rich in one aoa from vigarano this result is consistent with the slower rate of diffusion of o than fe and mg in olivine at least some interstitial phases are 16o rich and na bearing phases are abundant in this aoa 5 in contrast oxygen isotopic composition and fo content are correlated in two aoas from efremovka the olivine in these aoas tends to have forsteritic 16o rich cores and feo rich 16o depleted rims the general correlation between oxygen isotopic composition and fo content is difficult to model by diffusion and may have formed instead by aqueous dissolution and precipitation along the margins of preexisting olivine grains independent evidence for aqueous alteration of the efremovka aoas is provided by oh rich signals detected during ion beam sputtering of some of the 16o poor olivine elevated 16oh count rates and order of magnitude increases in 16oh detected during single analyses reflect trapping of an aqueous phase in 16o depleted olivine an elevated 16oh signal was also detected in one analysis of relatively 16o poor melilite in the melilite pyroxene cai from vigarano suggesting that this object also was altered by aqueous fluid

the heterogeneous upper mantle low velocity zone abstract the upper mantle low velocity zone lvz is a depth interval with slightly reduced seismic velocity compared to the surrounding depth intervals the zone is present below a relatively constant depth of 100 km in most continental parts of the world both in cratonic areas with high average velocity and tectonically active areas with low average velocity evidence for the low velocity zone arises from controlled and natural source seismology including studies of surface waves and of primary and multiple reflections of body waves from the bounding interfaces calculations of receiver functions and absolute velocity tomography the available data indicates a more pronounced reduction in seismic velocity and q value for s waves than p waves as well as high electrical conductivity in the lvz seismic waves are strongly scattered by the zone which demonstrates the existence of small scale heterogeneity the depth to the base of the lvz is systematically shallower in cold stable cratonic areas than in hot active regions of the world because of its global occurrence below a relative constant depth of 100 km the lvz cannot be explained by metamorphic or compositional variation and rheological changes calculated upper mantle temperatures indicate that the rocks are close to the solidus in an interval with variable thickness below 100 km depth provided that the rocks contain water and carbon dioxide the presence of even small amounts of such fluids in the mantle rocks will lower the solidus by several hundred degrees and introduce a characteristic kink on the solidus curve around 80 100 km depth the seismic velocities and q values are significantly reduced of rocks which are close to the solidus or contain small amounts of partial melt hence the lvz may be explained by upper mantle temperatures being close to the solidus in a depth interval below 100 km assuming that the rocks contain only limited amounts of fluids this mechanism may explain the low velocities q values and resistivity as well as the intrinsic scattering and the characteristic variation in thickness of the low velocity zone

upper mantle seismic shear discontinuities of the pacific 1 shear wave impedance discontinuities are inventoried for eight paths connecting circum pacific earthquakes with seismic stations on hawaii and oahu in addition to the transition zone discontinuities we observe a consistent impedance decrease at a depth of 80 km that marks the transition from the fast seismic lid to the low velocity zone the interval over which this transition occurs is less than 30 km the requisite impedance decrease ascribed almost entirely to diminished velocities in the low velocity zone exceeds predictions for peridotite chemistries of appropriate lithospheric age in all cases the transition is better matched by lithosphere of roughly half of the true age four paths show clear evidence of the x discontinuity an impedance increase of 3 8 near 300 km depth the only viable explanations would require extensive eclogite or basalt depleted mantle in the upper mantle of the western pacific the impedance contrast of the 410 km discontinuity which depends on the modal fraction of mantle olivine does not signal the presence of either although a mixture of the two remains a possibility we find no evidence of a low velocity layer atop of the 410 km discontinuity if present it is either consistently thin 15 km highly variable in thickness topography in excess of 60 km or has little impedance contrast 2 3 with overlying mantle the apparent absence of melt atop the 410 km discontinuity an intermittent and weak 520 km discontinuity and a thinned transition zone are consistent with relatively dry conditions in the deep upper mantle of the central pacific

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

2d model of the crust and uppermost mantle along rift profile siberian craton abstract a two dimensional model of the crust and uppermost mantle for the western siberian craton and the adjoining areas of the pur gedan basin to the north and baikal rift zone to the south is determined from travel time data from recordings of 30 chemical explosions and three nuclear explosions along the rift deep seismic sounding profile this velocity model shows strong lateral variations in the crust and sub moho structure both within the craton and between the craton and the surrounding region the pur gedan basin has a 15 km thick low velocity sediment layer overlying a 25 km thick high velocity crystalline crustal layer a paleo rift zone with a graben like structure in the basement and a high velocity crustal intrusion or mantle upward exists beneath the southern part of the pur gedan basin the sedimentary layer is thin or non existent and there is a velocity reversal in the upper crust beneath the yenisey zone the siberian craton has nearly uniform crustal thickness of 40 43 km but the average velocity in the lower crust in the north is higher 6 8 6 9 km s than in the south 6 6 km s the crust beneath the baikal rift zone is 35 km thick and has an average crustal velocity similar to that observed beneath the southern part of craton the uppermost mantle velocity varies from 8 0 to 8 1 km s beneath the young west siberian platform and baikal rift zone to 8 1 8 5 km s beneath the siberian craton anomalous high pn velocities 8 4 8 5 km s are observed beneath the western tunguss basin in the northern part of the craton and beneath the southern part of the siberian craton but lower pn velocities 8 1 km s are observed beneath the low angara basin in the central part of the craton at about 100 km depth beneath the craton there is a velocity inversion with a strong reflecting interface at its base some reflectors are also distinguished within the upper mantle at depth between 230 and 350 km

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

evidence for a compositional boundary within the lithospheric mantle beneath the kalahari craton from s receiver functions abstract s and p receiver functions from the southern african seismic experiment are analyzed for lithospheric discontinuities beneath the kalahari craton besides the moho the most prominent feature is a discontinuous reduction in seismic velocity of about 4 5 at approximately 150 km depth the discontinuity appears to have a width of about 10 km termed the k discontinuity this feature is restricted to the northern half of the array extending from the zimbabwe craton south to the tml thabazimbi murchison lineament and in the west from botswana to the edge of the kalahari craton in the east it spans several archean sutures and is thus unlikely related to archean tectonics it does however appear to be related to subsequent magmatic episodes the strongest anomaly is coincident with the most intense karoo volcanism and it extends to the northern edge of the bushveld intrusion from mantle xenoliths and xenocrysts the entire lithosphere in this region appears to have experienced a long term infiltration of basaltic melt and metasomatic fluids we propose that the k discontinuity reflects the influence of this melt metasomatic infiltration which has over time intruded and refertilized the lithosphere based on kimberlites pipes that show obvious signs of melt metasomatism and likely karoo influence the observed reduction in seismic velocity is plausibly consistent with the observed major element and volatile enrichment at 150 km depth in such kimberlites if this interpretation is correct then the high temperature kimberlite nodules that most clearly reflect this perturbation likely represent the general state of the lower lithosphere rather than only reflecting local mantle properties in the immediate vicinity of the kimberlite eruption

26al 26mg systematics of ca al rich inclusions amoeboid olivine aggregates and chondrules from the ungrouped carbonaceous chondrite acfer 094 we report in situ magnesium isotope measurements of 7 porphyritic magnesium rich type i chondrules 1 aluminum rich chondrule and 16 refractory inclusions 14 ca al rich inclusions cais and 2 amoeboid olivine aggregates aoas from the ungrouped carbonaceous chondrite acfer 094 using a cameca ims 6f ion microprobe both aoas and 9 cais show radiogenic 26mg excesses corresponding to initial 26al 27al ratios between 5 x 10 5 and 7 x 10 5 suggesting that formation of the acfer 094 cais may have lasted for 300 000 years four cais show no evidence for radiogenic 26mg three of these inclusions a corundum rich a grossite rich and a pyroxene hibonite spherule cai are very refractory objects and show deficits in 26mg suggesting that they probably never contained 26al the fourth object without evidence for radiogenic 26mg is an anorthite rich igneous type c cai that could have experienced late stage melting that reset its al mg systematics significant excesses in 26mg were observed in two chondrules the inferred 26al 27al ratios in these two chondrules are 10 3 7 4 10 6 and 6 0 3 8 10 6 errors are 2 suggesting formation and myr after cais with the canonical 26al 27al ratio of 5 10 5 these age differences are consistent with the inferred age differences between cais and chondrules in primitive ordinary ll3 0 ll3 1 and carbonaceous co3 0 chondrites

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

deposition of sand by suspension currents experimental and theoretical studies abstract flume experients with heterogeneous sediment mixtures show that all the grain sizes present in suspension are involved in the process of formation of a bed when the flow velocity is decreased the size distribution deposited closely reflects the one present in suspension this finding is contradictory to the common belief that the coarser grains are the first to be discarded at decreasing current velocity the existing equations after rouse 1938 and hunt 1969 also tend to overestimate depletion of the coarser grains a mathematical model for deposition based on the idea that the process of depletion of the coarser grains is actually dampened in nature has been developed in this work this model gives results which compare well particularly for low velocities with the observed values comprising wide range of grain sizes using the model it should be possible to estimate the grain size distribution of the deposited material given the size distribution present in suspension at a higher velocity since the size distribution of the deposits closely reflects that present in suspension it should also be possible to work out paleoflow velocities of suspension currents from grain size parameters of ancient deposits following the relationship established earlier between mean grain size in suspension and the shear velocity ghosh and mazumder 1981

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

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

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

the rapid drift of the indian tectonic plate the breakup of the supercontinent gondwanaland into africa antarctica australia and india about 140 million years ago and consequently the opening of the indian ocean is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the marion kerguelen and reunion plumes plate reconstructions based on palaeomagnetic data suggest that the indian plate attained a very high speed 18 20 cm yr 1 during the late cretaceous period subsequent to its breakup from gondwanaland and then slowed to approximately 5 cm yr 1 after the continental collision with asia approximately 50 myr ago the australian and african plates moved comparatively less distance and at much lower speeds of 2 4 cm yr 1 refs 3 5 antarctica remained almost stationary this mobility makes india unique among the fragments of gondwanaland here we propose that when the fragments of gondwanaland were separated by the plume the penetration of their lithospheric roots into the asthenosphere were important in determining their speed we estimated the thickness of the lithospheric plates of the different fragments of gondwanaland around the indian ocean by using the shear wave receiver function technique we found that the fragment of gondwanaland with clearly the thinnest lithosphere is india the lithospheric roots in south africa australia and antarctica are between 180 and 300 km deep whereas the indian lithosphere extends only about 100 km deep we infer that the plume that partitioned gondwanaland may have also melted the lower half of the indian lithosphere thus permitting faster motion due to ridge push or slab pull

scattered wave imaging of the lithosphere asthenosphere boundary several recent studies have imaged discontinuities interpreted as the lithosphere asthenosphere boundary using receiver function methods these are exciting results since this boundary is fundamental and yet relatively elusive its location is not well imaged nor are its properties well understood the receiver function method provides high depth resolution and the multitude of studies using this method have increased lateral resolution a better global understanding of the location and nature of the boundary is developing which ultimately will have implications for mantle dynamics and planetary evolution however these new results do not all form a clear and consistent picture and in some cases introduce new complexities and questions some apparent contradictions may represent unmodeled earth structure overall interpretation and synthesis requires careful consideration of the approaches and sensitivities of individual studies

thermochemical stability of low iron manganese enriched olivine in astrophysical environments low iron manganese enriched lime olivine grains are found in cometary samples returned by the stardust mission from comet 81p wild 2 similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix lime olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar but enrichment of solar composition vapor in a dust of chondritic composition causes the feo mno ratio of olivine to increase the compositions of lime olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition the compositional zoning of lime olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine without re equilibration at lower temperatures a similar history is likely for lime olivines found in comet samples and in interplanetary dust particles lime olivine is not likely to persist in nebular conditions in which silicate liquids are stable

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

the teleseismic signature of fossil subduction northwestern canada 1 between june 2003 and september 2005 20 broadband three component seismometers were deployed along the mackenzie liard highway in canada s northwest territories as part of the joint lithoprobe iris canada northwest experiment canoe these stations traverse a paleo proterozoic suture and subduction zone that has been previously documented to mantle depths using seismic reflection profiling teleseismic receiver functions computed from 250 earthquakes clearly reveal the response of the ancient subduction zone on the radial component the suture is evident as a direct conversion from the moho the depth of which increases from 30 km to 50 km over a horizontal distance of 70 km before its signature disappears the structure is still better defined on the transverse component where the moho appears as the upper boundary of a 10 km thick layer of anisotropy that can be traced from 30 km to at least 90 km depth the seismic response of this layer is characterized by a frequency dependence that can be modeled by upper and lower boundaries that are discontinuous in material properties and their gradients respectively anisotropy can be characterized by a 5 variation in shear velocity and hexagonal symmetry with a fast axis that plunges at an oblique angle to the subduction plane the identification of this structure provides an unambiguous connection between fossil subduction and fine scale anisotropic mantle layering previous documentation of similar layering below the adjacent slave province and from a range of precambrian terranes across the globe provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction

lithospheric and upper mantle structure of the indian shield from teleseismic receiver functions receiver functions derived from teleseismic p waveforms of 297 earthquakes recorded at broadband station hyderabad hyb are analysed to investigate the lithospheric and upper mantle structure in the vicinity of the station located in the northeastern part of the archaean dharwar craton the internal structure of the 33 2 km thick crust is simple it can be approximated by a single layer with s velocity linearly increasing with depth from 3 4 to 4 0 km s the average being 3 7 0 2 km s the crustal poisson s ratio is 0 25 0 01 a seismic discontinuity at 90 km depth is inferred from a signal particularly prominent on the sh component and possibly indicative of a layer of depth localized anisotropy in the lithospheric mantle the two principal mantle discontinuities are at depths of 406 and 659 km which are close to the global averages

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

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

petrology and origin of amoeboid olivine aggregates in cr chondrites amoeboid olivine aggregates aoas are irregularly shaped fine grained aggregates of olivine and ca al rich minerals and are important primitive components of cr chondrites the aoas in cr chondrites contain feni metal and some aoas contain mn rich forsterite with up to 0 7 mno and mn fe ratios greater than one additionally aoas in the cr chondrites do not contain secondary phases nepheline and fayalitic olivine that are found in aoas in some cv chondrites the aoas in cr chondrites record a complex petrogenetic history that included nebular gas solid condensation reaction of minerals with the nebular gas small degrees of melting and sintering of the assemblage a condensation origin for the mn rich forsterite is proposed the mn rich forsterite found in idps unequilibrated ordinary chondrite matrix and aoas in cr chondrites may have had a similar origin a type a calcium aluminum rich inclusion cai with an aoa attached to its wark lovering rim is also described this discovery reveals a temporal relationship between aoas and type a inclusions additionally a thin layer of forsterite is present as part of the wark lovering rim revealing the crystallization of olivine at the end stages of the wark lovering rim formation the ca al rich nodules in the aoas may be petrogenetically related to the ca al rich minerals in wark lovering rims on type a cais aoas are chondrite components that condensed during the final stage of wark lovering rim formation but in general were temporally spatially or kinetically isolated from reacting with the nebula vapor during condensation of the lower temperature minerals that were commonly present as chondrule precursors

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

converted waves reveal a thick and layered tectosphere beneath the kalahari super craton abstract thick and high velocity roots are generally observed beneath the archean cratons inside these high velocity keels velocity contrasts are detected neither by surface nor by body waves tomographies we present here evidences based on the s to p and p to s converted waves for the existence of an irregularly stratified and thick keel beneath the kalahari super craton to satisfy surface wave data and s to p conversions the velocity model should have beneath the moho a 160 km thick anisotropic structure with vertical slow axis and decreasing anisotropic parameters with depth such a structure may stem from the preferred orientation of olivine 100 axis in the horizontal plane under shearing deformation this structure together with the 100 km thick layer underlying it forms a 300 km thick continental root beneath the cratons inside this root the p and s velocities should be higher on average respectively by an amount of 6 and 4 than the ak135 velocity model beneath 300 350 km depth a low velocity zone is clearly detected that may be either the remainder of large magma reservoirs related to cratonic flood basalts or a melted silicate layer created by the transformation just above the 410 km deep discontinuity of wadsleyite assembly to olivine assembly

lithosphere and asthenosphere of the tien shan imaged by s receiver functions 1 the s receiver function technique was applied to the recordings from 36 broad band stations in the tien shan the results reveal a pronounced difference in the properties of the lithosphere asthenosphere of the tien shan and those of the neighboring platforms beneath the tien shan an upper mantle lid with an s velocity of about 4 5 km s is underlain at a depth of about 90 km by a low velocity zone where the s velocity drops to 4 1 4 2 km s trends of p and s travel time residuals are consistent with the presence of melt or other liquids in this zone there is no evidence of any similar layer beneath the platforms the crust is 55 65 km thick beneath most of the tien shan and 45 km below the platforms although it thins to about 45 km near the naryn basin in the central tien shan

contrasts in lithospheric structure within the australian craton insights from surface wave tomography abstract contrasts in the seismic structure of the lithosphere within and between elements of the australian craton are imaged using surface wave tomography new data from the wacraton and tigger experiments are integrated with re processed data from previous temporary deployments of broad band seismometers and permanent seismic stations the much improved path coverage in critical regions allows an interpretation of structures in the west of australia and a detailed comparison between different cratonic regions improvements to the waveform inversion procedure and a new multi scale tomographic method increase the reliability of the tomographic images in the shallowest part of the model 75 km a region of lowered velocity is imaged beneath central australia and confirmed by the delayed arrival times of body waves for short paths within the cratonic lithosphere there is clearly structure at scale lengths of a few hundred kilometres resolution tests indicate that path coverage within the continent is sufficient to reveal features of this size in the upper part of our model in western australia differences are seen beneath and within the archaean cratons at depths greater than 150 km faster velocities are imaged beneath the yilgarn craton than beneath the pilbara craton in the complex north australian craton a fast wavespeed anomaly continuing to at least 250 km is observed below parts of the craton suggesting the possibility of archaean lithosphere underlying areas of dominantly proterozoic surface geology

upper mantle seismic wave velocity effects of realistic partial melt geometries we investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle the amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations the geometries of the inclusions are taken directly from laboratory experiments of mantle melting with finite element meshes constructed to conform to these shapes the shear and bulk moduli of the composite material are found for both the unrelaxed isolated inclusions and relaxed pressure equalized inclusions cases by assigning appropriate material properties to the fluid modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction the three dimensional response is estimated from two dimensional distributions of the melt phase by determining the mode ii and mode iii components of elastic modulus reduction separately and summing their effects in general cuspate and naturally organized melt inclusions cause greater velocity reduction it is shown that v and vs reduction per percent partial melt are at least 3 6 and 7 9 respectively even higher values for velocity reduction are possible above 1 melt fraction if melt exists only in tubules below 1 melt fraction the lower more conservative values of velocity reduction are 070 greater for vp and 84 greater for vs than the analytically determined values for ellipsoidal inclusions somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

constraints on upper mantle discontinuities from observations of long period reflected and converted phases stacked images combining over 5 years of long period global digital seismograph network data reveal many phases associated with reflections and conversions from upper mantle discontinuities these images show travel time and amplitude relative to a reference phase which is aligned and normalized on all seismograms prior to stacking results obtained for p s ss and pp reference arrivals resolve numerous phases from discontinuities near 410 and 660 km while some of the stacks also show evidence for a weaker discontinuity near 520 km phases of particular interest include p and sh multiples resulting from topside reflections precursors to ss from underside reflections and p to sv converted phases these phases can be clearly seen both in the waveform stacks and in cross correlation analysis of individual seismograms travel times for these arrivals are converted to discontinuity depths relative to velocities in the preliminary reference earth model and empirical corrections are applied for the effects of lateral velocity variations in the upper mantle average apparent depths to the discontinuities for the different phases agree to within 3 km for the 410 km discontinuity to within 4 km for the 520 km discontinuity and to within 8 km for the 660 km discontinuity the best global averages are obtained from the ss precursor data which indicate discontinuities at 415 519 and 659 km discontinuity depths obtained from the p to sv converted phases at over 35 individual seismic stations exhibit variations of less than 20 km apparent depths to the 660 km discontinuity consistently show greater variability than depths to the 410 km discontinuity supporting recent laboratory results which indicate that the clapeyron slope for the 660 km discontinuity is significantly larger in magnitude than the slope for the 410 km discontinuity precursors to ss seen between 110 and 180 are particularly useful for mapping possible lateral variations in discontinuity depths since each arrival can be associated with a single underside reflection point apparent discontinuity depths computed from ss precursors for different tectonic regions agree to within about 5 km the ss precursors have especially good coverage near the subducting slabs in the northwest pacific analysis of apparent discontinuity depths in this area suggests the presence of a broad 1000 to 1500 km wide region near the slab in which the 660 km discontinuity is depressed by about 20 km measuring absolute amplitudes for these phases is difficult due to the large corrections required to compensate for the effects of incoherent stacking relative amplitude analysis suggests that the p and s wave impedance changes at 410 km are about 0 8 1 1 times the size of the changes at 660 km and that the contrasts at 520 km are between 0 3 and 0 6 of the changes at 410 km

deep structure of the continental lithosphere in an unextended orogen an explosive source seismic reflection profile in the urals urals seismic experiment and integrated studies urseis 1995 explosive source near vertical seismic reflection data from the urals seismic experiment and integrated studies urseis profile displays an image of orogenic lithosphere to depths of 225 km the reflective crustal section is characterized by dipping crustal scale shear zones and a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late paleozoic collision toward the east the uralian crustal root is composed of a partially subducted volcanic arc while to the west it has affinity with the east european platform the reflection character of the moho varies across tectonic strike and implies that the moho 1 acted as a structural detachment beneath the trans uralian zone 2 forms a tectonic boundary between terranes beneath the east uralian zone 3 consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root 4 is a 3 9 km thick reflective zone beneath the fold and thrust belt and 5 is a boundary 200 m thick in the west mantle reflections at 80 100 km depth 22 24 s may represent a continuation of the main uralian fault into the subcrustal lithosphere alternatively these reflectors may signify paleozoic or younger mantle shear zones or the top of a zone of partial melting in the upper mantle deeper mantle reflections at 140 160 km 35 45 s and 225 km 55 s may image mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle

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

fe ni metal in primitive chondrites indicators of classification and metamorphic conditions for ordinary and co chondrites we report the results of our petrological and mineralogical study of fe ni metal in type 3 ordinary and co chondrites and the ungrouped carbonaceous chondrite acfer 094 fe ni metal in ordinary and co chondrites occurs in chondrule interiors on chondrule surfaces and as isolated grains in the matrix isolated ni rich metal in chondrites of petrologic type lower than type 3 10 is enriched in co relative to the kamacite in chondrules however ni rich metal in type 3 15 3 9 chondrites always contains less co than does kamacite fe ni metal grains in chondrules in semarkona typically show plessitic intergrowths consisting of submicrometer kamacite and ni rich regions metal in other type 3 chondrites is composed of fine to coarse grained aggregates of kamacite and ni rich metal resulting from metamorphism in the parent body we found that the number density of ni rich grains in metal number of ni rich grains per unit area of metal in chondrules systematically decreases with increasing petrologic type thus fe ni metal is a highly sensitive recorder of metamorphism in ordinary and carbonaceous chondrites and can be used to distinguish petrologic type and identify the least thermally metamorphosed chondrites among the known ordinary and co chondrites semarkona is the most primitive the range of metamorphic temperatures were similar for type 3 ordinary and co chondrites despite them having different parent bodies most fe ni metal in acfer 094 is martensite and it preserves primary features the degree of metamorphism is lower in acfer 094 a true type 3 00 chondrite than in semarkona which should be reclassified as type 3 01

europe mediterranean tomography high correlation between new seismic data and independent geophysical observables 1 to improve the fidelity of european tomographic images we implement variable resolution parameterization finite frequency and ray theory and improved data coverage in new tomographic inversions we supplement an existing high quality database of global teleseismic phase velocity observations of both love and rayleigh waves with a set of new phase delay observations recorded by a dense array of stations in the region we invert these data to find global phase velocity maps characterized by a more densely parameterized europe and mediterranean we compare our seismic images with laterally variable independent geophysical observables including crustal thickness gravity and heat flow and find correlations between 0 25 and 0 6 while at most periods finite frequency and ray theory yield almost coincident results we find some possibly significant differences in the phase velocity of 150s rayleigh waves our results represent significant progress toward high resolution modeling of upper mantle s velocity structure with the possibility of also constraining seismic anisotropy

crystal chemical effects on the partitioning of trace elements between mineral and melt an experimental study of melilite with applications to refractory inclusions from carbonaceous chondrites the partitioning behavior of the trace elements be sc ba la ce and tm between melilite and liquid has been determined using stepwise integration of a rayleigh fractionation equation for ion microprobe analyses of synthetic zoned melilite crystals distribution coefficients between melilite and liquid d mel l i were determined over the entire range of melilite spinel crystallization for one bulk composition corresponding to that of an average type b inclusion from the allende c3v carbonaceous chondrite beryllium is incompatible in gehlenitic meliliters e g d mel l b e 0 5 for x ak 0 3 but compatible in akermanitic melilites e g d mel l b e 1 9 for x ak 0 75 barium d mel l b a 0 04 0 05 sc d mel l s c 0 01 0 02 la d mel l l 0 07 0 29 ce d mel l c e 0 05 0 21 and tm d mel l t m 0 03 0 14 are all incompatible in melilites in the range ak25 ak75 variations in d mel l i as a function of x ak are explicable in terms of a simple thermodynamic treatment of trace element partitioning based on crystal chemical considerations characteristic trace element zoning patterns are predicted for early crystallizing melilite from meliliterich type b inclusions for example concentrations of the rees in melilite should continually decrease with increasing degrees of crystallization opposite the behavior normally expected of an incompatible element concentrations of be should rise with increasing degrees of crystallization even when the element is compatible again opposite the behavior normally expected of compatible elements in general zoning patterns of trace elements in melilite from type b inclusions are consistent with those predicted for fractional crystallization from a melt in a closed system trace element zoning patterns in meteoritic melilite crystals constrain the origin and thermal histories of ca al rich inclusions from carbonaceous chondrites

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

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

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

super deep low velocity layer beneath the arabian plate 1 s and p receiver functions reveal indications of a low s velocity layer at 350 410 km depths beneath the arabian plate a similar layer was previously found beneath the kaapvaal craton in southern africa and tunguska basin of the siberian platform we hypothesize that the boundary at 350 km depth may separate dry mantle root of the arabian plate from the underlying wet mantle layer this boundary is not found beneath the gulf of aden where the root is destroyed by sea floor spreading

crystallization sequences of ca al rich inclusions from allende an experimental study the equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of type b ca al rich inclusions from the allende meteorite is spinel 1550 c melilite 1400 c ak22 anorthite 1260 c ti al rich clinopyroxene 1230 c ti fassaite the melilite becomes increasingly akermanitic with decreasing temperature the pyroxene is similar in composition to fassaites from type b inclusions preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron wustite buffer the results of these experiments have been integrated with available phase equilibrium data in the system cao mgo al 2o 3 sio 2tio 2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse grained ca al rich inclusions has been developed available bulk compositions of coarse grained inclusions form a well defined trend in terms of major elements extending from type a and bl inclusions near the spinel melilite join to more pyroxene rich type b2 inclusions the trend deviates from the expected sequence of solid condensates from a nebular gas at p 10 3 atm if pure diopside is assumed to be the clinopyroxene that condenses the type a b1 end of the trend is similar in composition to calculated equilibrium condensates at 1202 1227 c and the trend as a whole parallels the sequence of condensates expected from diopside condensation at 1170 c the trend is consistent to first order with the condensation of solid ti rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense partially molten condensates may be likely in this case or if the nebular pressure is higher than 10 3 atm

lithospheric boundaries and upper mantle heterogeneity beneath russian eurasia evidence from the dss profile quartz abstract a combined interpretation of seismic data from the 3850 km long russian seismic profile quartz using chemical and nuclear explosions reveals complex structure of the lithosphere related to the regional tectonics our analysis is focused on the structure of the uppermost mantle and based on 2d ray tracing and inversion of the data from all 51 shots along the profile on 2d attenuation measurements and on the results of an analysis of the long range pn phase three groups of reflectors within the lithosphere are associated with regional to global boundaries previously recognized in stable continental environments one almost continuous upper mantle boundary occurs at 65 to 80 km depth and another with an approximately 40 km thick low velocity zone lvz occurs at 120 140 km depth the shallow upper mantle blocks and the extensive interfaces indicate strong upper mantle heterogeneity imaged by this unique profile the thickness of the lithosphere varies from 220 km under the baltic shield to about 120 130 km under the tectonically active himalayan altay sayan fold belt within the lower part of the lithosphere a zone of lower velocity increased attenuation and varying thickness might be related to hydration and partial melting large structural differences related to tectonic ages and histories are characteristic for the entire lithosphere and extend 200 400 km into the asthenosphere analysis of quartz data gives confident indication of seismic heterogeneity from crustal to regional mantle scales indicating strong involvement of the mantle in tectonic processes

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

oxygen and magnesium isotopic compositions of amoeboid olivine aggregates from the semarkona ll3 0 chondrite amoeboid olivine aggregates aoas in the ll3 0 semarkona chondrite have been studied by secondary ion mass spectrometry the aoas mainly consist of aggregates of olivine grains with interstitial al ti rich diopside and anorthite oxygen isotopic compositions of all phases are consistently enriched in 16o with 17 18o 50 the initial 26al 27al ratios are calculated to be 5 6 0 9 2 10 5 these values are equivalent to those of aoas and fine grained calciumaluminum rich inclusions fgis from pristine carbonaceous chondrites this suggests that aoas in ordinary chondrites formed in the same 16o rich calcium aluminum rich inclusion cai forming region of the solar nebula as aoas and fgis in carbonaceous chondrites and subsequently moved to the accretion region of the ordinary chondrite parent body in the solar nebula

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

subcratonic low velocity layer and flood basalts 1 teleseismic recordings of several seismograph stations are processed with the aid of the s receiver function technique farra and vinnik 2000 the data provide evidence of a strong reduction of s velocity at a depth around 360 km station bosa and 280 300 km station lbtb in the east of southern africa a similar feature is found in the tunguska basin of the siberian platform from the recordings of station nril in both regions large volumes of flood basalts have been erupted 190 180 ma and 250 ma ago respectively the coincidence suggests a causal relation between the two phenomena this relation implies that the low velocity anomalies migrate with the plates

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

imaging ruptured lithosphere beneath the red sea and arabian peninsula abstract the red sea rift an archetype of a newly formed ocean basin is an ideal environment in which to study the controversial processes associated with continental rifting different models have been proposed to explain how rifting in the red sea evolved however accurate constraints on lithospheric structure have not been available to discriminate rifting models we use the s wave receiver function technique to produce the first images of the lithosphere asthenosphere boundary lab structure along the red sea and throughout the arabian peninsula lithospheric thickness varies considerably with thin lithosphere centered on the rift axis thickening toward the arabian interior gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium requiring dynamic compensation for its support while our derived structure is consistent with active rifting processes previous studies demonstrated that the red sea initiated as a passive rift therefore our results suggest a two stage rifting history where extension and erosion by flow in the underlying asthenosphere are responsible for variations in lab depth lab topography guides asthenospheric flow beneath western arabia and the red sea demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments

p and s wave delays beneath intraplate volcanic ridges and gravity lineations near the east pacific rise the gravity lineations intraplate melting petrology and seismic expedition glimpse explored the origin of two intraplate non hot spot ridge systems associated with gravity lineations in the south central pacific using the 11 month ocean bottom seismometer obs deployment of the glimpse experiment we determined the average p and s station delays for the region across the array station delays varied by 1 22 s for p waves and 2 13 s for s waves the presence of ultraslow shear velocity

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

ghosts of lithospheres past imaging an evolving lithospheric mantle in southern africa group ii 143 117 ma and group i kimberlites 108 74 ma intrude across the southwest boundary of the kaapvaal craton sampling the same volume of the subcontinental lithospheric mantle sclm in two time slices major and trace element analyses of 3699 peridotitic garnet xenocrysts were used to construct paleogeotherms for 17 kimberlite localities and to place each garnet at its depth of origin the ti contents of each garnet and the calculated x mg of its coexisting olivine were projected onto a southwest northeast section across the craton boundary and splines were used to interpolate between the virtual boreholes in each age group the sections show that the cratonic sclm extends at least 75 km southwest of the mapped craton boundary suggesting a dipping contact marked differences between the time slice sections show that between 117 and 108 ma the sclm on both sides of the craton boundary was heated and chemically refertilized by infiltrating asthenosphere derived melts thinning the depleted layer by 40 km the thermal and geochemical changes record a significant tectonothermal event that may be related to changes in the stress field associated with opening of the south atlantic or with mantle upwelling

trans pacific upper mantle shear velocity structure 1 we use 50 tonga fiji events recorded at the broadband trinet array southern california to develop a pure path upper mantle shear velocity model across the pacific at the epicentral distances of 70 95 multibounce s waves up to s5 are observed including their triplicated branches which become particularly clear after stacking since these s wave multiples turn at various depths simultaneously modeling their differential traveltimes and waveforms provides strong constraints on the radial velocity structure we parameterize the velocity model according to a priori information from the previous oceanic models so that we can take a grid search approach to fully investigate possible interdependencies among the model parameters we construct synthetics with a reflectivity code and study both the sh and sv components by modeling the whole recordings from events at different depths with different mechanisms we are able to separate shallow low velocity zone lvz features from deeper structure our preferred model pac06 contains a fast lid vsh 4 78 km s 1 vsv 4 58 km s 1 with a thickness of 60 km the underlying lvz is prominent with the lowest velocities vsh 4 34 km s 1 and vsv 4 22 km s 1 occurring at a depth of 160 km these velocities are below the estimates of solid state lvz suggesting the presence of partial melt the anisotropy vsv vsh of pac06 extends to 300 km depth which is constrained by s5 turning at this depth besides the 406 km and 651 km discontinuities pac06 also has a small 1 velocity jump at 516 km we consider these main features of pac06 to be well determined since pac06 explains a large data set from various events therefore it is ideally suited for comparing with mineralogical models

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

upper mantle discontinuity structure beneath east anatolian plateau turkey from receiver functions abstract imaging of seismic velocity discontinuities with receiver functions suggests a complex mantle structure beneath the east anatolian plateau by stacking all the receiver functions as a function of ray parameter we examined the moveout characteristics of the data set and tested different velocity models to fit the arrival times of converted phases from the moho and the lithosphere asthenosphere boundary and their multiples the best fitting model shows anomalously thin crust 40 km and lithosphere 65 km and low uppermost mantle velocities causing systematic delays on later discontinuity arrivals these findings are consistent with the high plateau supported by partially molten and buoyant asthenosphere the upper mantle discontinuities are all visible in different frequencies 0 15 and 0 4 hz especially the 410 km discontinuity does not show frequency dependence in amplitude and suggests a sharpness of 10 km or less spatial variations of the 410 and 660 km discontinuities reveal anticorrelated topography and distinct zones of diminished amplitude associated with a detached slab and delaminated fragments of lithospheric mantle in the south the slab becomes deeper and horizontally deflected towards the east suggesting westward migration of slab detachment and resistance to slab penetration at the 660 km discontinuity in the north the mantle transition zone is characterized by two spatially limited lithospheric fragments with complex geometry at the center of the study area the transition zone is thin 230 km suggesting excess temperature of 120 c this warm mantle anomaly most likely is due to hot material trapped within the upper mantle between slab in the south and delaminated fragments in the north

rheological stratification of the lithosphere a direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the north american continent 1 a sequence of new analyses of the process of glacial isostatic adjustment gia is described the focus is upon the resolution of a recognized flaw in the currently prevalent model of this process that denoted ice 5g vm2 the flaw concerns a previously noted inability of the model to simultaneously reconcile the vlbi and gps measured rates of vertical and horizontal motion in the region of the north american continent that lay outboard and to the south of the laurentide ice sheet lis at last glacial maximum this characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity it is demonstrated herein that on the contrary this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere an influence not previously accounted for in global models of the gia process but which must exist on a priori grounds

stacked uppermost mantle layers within the slave craton of nw canada as defined by anisotropic seismic discontinuities 1 a 20 station seismic array in nw canada recorded 336 teleseismic events with distribution in back azimuth and epicentral distance sufficient to characterize uppermost mantle discontinuities between depths typical of the mohorovicic and lehman discontinuities following wavefield decomposition groups of seismograms were source normalized through simultaneous deconvolution to estimate the near receiver impulse response and thus detect major discontinuities beneath each seismic station stations within the lac de gras kimberlite field display an unusually strong negative impulse on the radial component within the nw quadrant and two moderate impulses on the transverse component forward modeling of these impulses suggests a mantle layer dipping at 22 to the southeast with a mildly anisotropic 2 upper discontinuity at 120 135 km depth and another mildly anisotropic 2 discontinuity at about 170 km depth superimposed on these layers is another stronger anisotropic 4 layer between 110 and 180 km depths that dips to the west stations outside of the lac de gras field but within the southeastern slave craton display more numerous but weaker impulses the most prominent of these occurs at about 150 km depth on the transverse component and has opposite polarity to that observed farther north the prominent negative impulse observed on the radial component is interpreted to arise from structural preferred orientation in the form of a stockwork of wehrlite dykes beneath the lac de gras field interpretation of the other layers in the context of known surface geology as well as xenolith petrology and garnet geochemistry of diamondiferous kimberlites favors previous suggestions that they represent 4000 2900 ma depleted harzburgite and eclogite layers underthrust from the northwest at 2600 or 1880 ma the layer beneath the se slave craton has a similar but distinct tectonic history of nw verging underthrusting associated with the 2635 2615 ma defeat suite of plutonism taken together these interpretations indicate that the slave craton was assembled from at least four lithospheric blocks prior to its cratonization about 2580 ma each block is 90 120 km thick and all four blocks abut across a steep suture boundary beneath mackay lake in the central slave craton significant amounts of carbon and eclogites could have become incorporated into the central slave mantle within the diamond stability field during the proposed underthrusting of lithosphere to explain their relatively common occurrence in kimberlite eruptions within the slave craton

upper mantle structure beneath the hawaiian swell constraints from the ocean seismic network pilot experiment 1 data from two broadband ocean bottom seismographic stations deployed 225 km southwest of oahu hawaii during the ocean seismic network pilot experiment provide constraints on upper mantle structure beneath the hawaiian swell receiver functions show that the mantle transition zone is thinned by 50 km relative to reference model pa5 which in the absence of compositional changes implies excess temperatures of 350 k in the transition zone the combination of the measurements reported here and the thickness variations reported by li et al 2000 imply that the transition zone is thinned by 30 15 km over an along swell dimension of at least 700 km at 80 km depth p to s converted phases are identified from the gutenberg discontinuity marking the lid of the oceanic low velocity zone and the base of the lithosphere shear wave splitting measurements imply that fast polarization azimuths are intermediate between the absolute plate motion vector and the fossil spreading direction multi event stacked values of o and t are 80 and 1 5 s respectively

amoeboid olivine aggregates from ch carbonaceous chondrites amoeboid olivine aggregates aoas in ch carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups they show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite fa 3 in wt cao 0 1 0 8 cr2o3 0 04 0 48 mno 0 5 anorthite al diopside in wt al2o3 0 7 8 1 tio2 1 fe ni metal spinel and occasionally low ca pyroxene fs1wo2 3 and calcium aluminum rich inclusions cais the cais inside aoas are composed of hibonite grossite melilite ak13 44 spinel perovskite al ti diopside in wt al2o3 up to 19 6 tio2 up to 13 9 and anorthite the ch aoas including cais within aoas have isotopically uniform 16o rich compositions average 17o 23 4 2 3 2sd and on a three isotope oxygen diagram plot along slope 1 line the only exception is a low ca pyroxene bearing aoa 1 103 that shows a range of 17o values from 24 to 13 melilite grossite and hibonite in four cais within aoas show no evidence for radiogenic 26mg excess 26mg in contrast anorthite in five out of six aoas measured has 26mg corresponding to the inferred initial 26al 27al ratio of 4 3 0 7 10 5 4 2 0 6 10 5 4 0 0 3 10 5 1 7 0 2 10 5 and 3 0 2 6 10 6 anorthite in another aoa shows no resolvable 26mg excess an upper limit on the initial 26al 27al ratio is 5 10 6 we infer that ch aoas formed by gas solid condensation and aggregation of the solar nebula condensates forsterite and fe ni metal mixed with the previously formed cais subsequently they experienced thermal annealing and possibly melting to a small degree in a 16o rich gaseous reservoir during a brief epoch of cai formation the low ca pyroxene bearing aoa 1 103 may have experienced incomplete melting and isotope exchange in an 16o poor gaseous reservoir the lack of resolvable 26mg excess in melilite grossite and hibonite in cais within aoas reflects heterogeneous distribution of 26al in the solar nebula during this epoch the observed variations of the inferred initial 26al 27al ratios in anorthite of the mineralogically pristine and uniformly 16o rich ch aoas could have recorded i admixing of 26al in the protoplanetary disk during the earliest stages of its evolution and or ii closed system mg isotope exchange between anorthite and mg rich minerals spinel forsterite and al diopside during subsequent prolonged days to weeks thermal annealing at high temperature 1100 c and slow cooling rates 0 01 k h 1 that has not affected their o isotope systematics the proposed thermal annealing may have occurred in an impact generated plume invoked for the origin of non porphyritic magnesian chondrules and fe ni metal grains in ch and cb carbonaceous chondrites about 5 myr after formation of cv cais

the origin and significance of reverse zoning in melilite from allende type b inclusions in many type b allende inclusions melilite is reversely zoned over restricted portions of each crystal textural relationships and the results of dynamic crystallization experiments suggest that the reverselyzoned intervals in these type melilites result from the co precipitation of melilite with clinopyroxene from a melt prior to the onset of anorthite precipitation when clinopyroxene begins to precipitate the al mg ratio of the melt rises causing the crystallizing melilite to become more gehlenitic an effect which is negated by crystallization of anorthite because the equilibrium crystallization sequence in these liquids is anorthite before pyroxene melilite reverse zoning can occur only when anorthite nucleation is suppressed relative to pyroxene this has been achieved in our experiments at cooling rates as low as 0 5 c hour our experiments further indicate however that reverse zoning does not form at cooling rates 50 c hour probably because the clinopyroxene becomes too al rich to drive up the al mg ratio of the liquid type inclusions with reversely zoned melilites must have cooled at rates greater than those at which anorthite begins to crystallize before clinopyroxene but 50 c hour such rates are far too slow for the type droplets to have cooled by radiation into a nebular gas but are much faster than the cooling rate of the solar nebula itself one possibility is that type b s formed in local hot regions within the nebula where their cooling rate was equal to that of their surrounding gas other possibilities are that their cooling rates reflect their movement along nebular temperature gradients or the influence of a heat source the sun or viscous drag on inclusions as they moved through the nebular gas are potential candidates for such heat sources

strong along arc variations in attenuation in the mantle wedge beneath costa rica and nicaragua attenuation structure in the central american subduction zone was imaged using local events recorded by the tomography under costa rica and nicaragua array a 20 month long deployment july 2004 until march 2006 of 48 seismometers that spanned the fore arc arc and back arc regions of nicaragua and costa rica p and s waveforms were inverted separately for the corner frequency and moment of each event and for the path averaged attenuation operator t of each event station pair assuming attenuation is slightly frequency dependent 0 27 then tomographic inversions were performed for s and p attenuation q s 1 and q p 1 since p wave amplitudes reflect both shear and the bulk moduli tomographic inversions were also performed to determine shear and bulk attenuation q s 1 and q 1 the loss of energy per cycle owing to shearing and uniform compression respectively damping and other inversion tomographic parameters were systematically varied as is typical in subduction zone attenuation studies a less attenuating slab upper plate and wedge corner and a more attenuating mantle wedge were imaged in addition first order differences between the mantles beneath nicaragua and costa rica were observed the slab in nicaragua is more attenuating than the slab in costa rica a larger zone of higher shear attenuation also characterizes the nicaraguan mantle wedge within the wedge maximum attenuation values at 1 hz correspond to qs 38 73 beneath nicaragua and qs 62 84 beneath costa rica and average values are qs 76 78 and qs 84 88 respectively attenuation variations correlate with along arc trends in geochemical indicators that suggest that melting beneath nicaragua occurs at more hydrated conditions and possibly to greater extents and depths relative to northern costa rica shear attenuation dominates over bulk attenuation in the well resolved regions of the wedge the more extensive zones of greater shear attenuation observed in the nicaraguan wedge could be explained by higher temperatures and or greater hydration but comparison with petrological data suggests that hydration variations play a larger role average wedge attenuation values are comparable to estimates for the andes and japan greater than those for alaska and less than those for tonga lau