undrained response of clays to varying strain rate the undrained stress deformation behavior of clays is significantly affected by the loading rate based on the observed experimental response it is possible to model the strain rate response of clays as an apparent overconsolidated clay response in this work we have quantitatively determined the change in the overconsolidation ratio ocr due to a change in the strain rate our results show that the shear strength response and the excess pore water pressure response at the peak stress provide quantitatively similar magnitudes of change in the ocr with increasing strain rate this finding holds true for both normally and overconsolidated clays this suggests that the relationship between strain rate and change in the ocr can be considered as an inherent material characteristic and is quantifiable a relationship between the change in the ocr and change in the strain rate is described

chemical studies of h chondrites i mobile trace elements and gas retention ages abstract trends for 16 trace elements ag as au bi cd co cs ga in k rb sb se te tl and zn chosen to span a broad geochemical and thermal response range in 44 h4 6 chondrites differ widely from those in l4 6 chondrites in particular h chondrites classified as heavily shocked petrologically do not necessarily exhibit 40 ar loss and vice versa the clear cut causal relationship between siderophile and mobile element loss with increasing late shock seen in l chondrites is not generally evident in the h group h chondrite parent material experienced an early high temperature genetic episode that mobilized a substantial proportion of these trace elements so that later thermal episodes resulted in more subtle collateral fraction ations mildly shocked l chondrites escaped this early high temperature event indicating that the two most numerous meteorite groups differ fundamentally in genetic history

an igneous textured clast in the peace river meteorite insights into accretion and metamorphism of asteroids in the early solar system the mineralogy petrology and geochemistry of an igneous textured clast in the peace river l6 chondrite meteorite was examined to determine the roles of nebular processes accretion and parent body metamorphism in its origin the centimetre scale clast is grey and fine grained and is in sharp contact with the host chondrite two sub millimetre veins cut across both the clast and host indicating that the clast formed prior to the impact shock event s that produced the numerous veins present in the peace river meteorite the clast and host are indistinguishable in terms of mineral compositions in contrast there are differences in modal mineralogy texture as well as trace element and oxygen isotope composition between the clast and host these differences strongly suggest that the clast was formed by impact melting of ll group chondritic material involving loss of fe fes and phosphate components followed by relatively rapid cooling and incorporation into the peace river host meteorite subsequent metamorphism on the peace river parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host shock metamorphism including formation of shock melt veins occurred post metamorphism during fragmentation of the l chondrite parent body the results suggest that the formation of the peace river parent asteroid included the incorporation of material from other asteroids and that the pre metamorphic protolith was a breccia accordingly we propose that the peace river meteorite be reclassified as a polymict breccia

extensive impact melting on the h chondrite parent asteroid during the cataclysmic bombardment of the early solar system evidence from the achondritic meteorite dar al gani 896 dag 896 is an olivine rich microporphyritic rock of komatiitic composition both the olivine composition fa 17 5 2 1 mn mg 0 0061 and the bulk oxygen isotopic composition delta 17 o 2 55 delta 18 o 3 50 indicate that dag 896 is a sample of the h chondrite parent body the bulk chemistry shows an h chondritic distribution of lithophile elements whereas chalcophile and siderophile elements are strongly depleted indicating formation through whole rock melting or nearly so of h chondrite material nearly complete loss of the metal plus sulfide component and crystallization without significant igneous fractionation superheated severely shocked chondritic relics similar to10 vol typically in the form of corroded lithic fragments 100 mum in size intimately distributed within the igneous lithology indicate that melting was triggered by a highly energetic impact which possibly induced shock pressures of similar to80 100 gpa the relatively young 3 704 0 035 ga ar 40 ar 39 crystallization age is consistent with the impact melting origin as magmatism in the asteroid belt was active only in the first hundred million years of solar system history 1ased on textural data and thermodynamic crystallization modelling we infer that dag 896 crystallized from a liquidus temperature of similar to1630degreesc under relatively slow cooling rates similar to10degreesc h 1 to 1300degreesc before quenching the two stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor metal silicate fractionation may have been accomplished at least at the centimeter scale of the studied meteorite sample through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism alternatively dag 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid for metal particles 1 to 10 mm in size typically observed in partially differentiated impact melt rocks stokes law indicates a settling velocity 1 in h 1 during the first few hours of crystallization on asteroidal bodies of 25 kin radius the similar to3 7 ga age of dag 896 nearly overlaps with the slightly older resetting ages of h chondrites all impact melts available from the literature indicating that the h chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system such an age overlap may also indicate early disruption of the initial h chondrite parent asteroid the close similarity between the bulk composition and degassing age of dag 896 and silicate inclusions in he iron meteorites is further evidence in support of a common origin by impact melting and metal silicate segregation on the h chondrite parent asteroid our new high precision oxygen isotopic measurements of h chondrites delta 17 o 0 77 0 04 should be extended to iies to verify this possible petrogenetic link

meteomod a numerical model for the calculation of melting crystallization relationships in meteoritic igneous systems the meteomod model is a computer program designed to calculate melting crystallization relationships in igneous systems compositionally similar to ordinary chondrites and basaltic achondrites the core of meteomod is a set of empirically calibrated equations called geothermometers which describe equilibria between silicate melt and minerals such as olivine orthopyroxene pigeonite augite plagioclase and metallic fe in terms of pressure temperature and liquid compositions the silicate mineral geothermometers are calibrated from a database containing the compositions of melts and minerals produced in melting experiments on 113 meteoritic and 141 synthetic systems the metallic iron silicate melt geothermometer is calibrated from a database of 396 melting experiments the meteorite melting model or meteomod calculates crystallization temperatures and contents of major end members in mineral solid solutions with accuracies of 10 15 c and 1 2 mol respectively input parameters for the program are 1 increment in crystallization degree 2 one of 12fo2 buffers routinely used in petrology 3 shift from the buffer in log units if any 4 a choice of equilibrium or fractional crystallization trajectory 5 terminal crystallization degree 6 contents of ten major elements in wt 7 a set of minor and trace elements in parts per million 8 the number of initial compositions to be modeled in a single computation run the output consists of a series of tables that list equilibrium temperatures o fugacities and proportions of melt and minerals and their compositions as a function of the degree of crystallization the results of application of meteomod to modeling of melting crystallization of the st severin ll chondrite are compared with the experimental data of jurewicz et al 1995

shear strength characteristics of an unsaturated expansive clay the shear strength characteristics of an expansive clay from china were studied by performing suction controlled direct shear tests on both natural and compacted specimens the tested soil was a silty clay with intermedi ate plasticity and medium expansion potential a modified direct shear apparatus with a newly developed water volume indicator was used for this laboratory study the experimental results clearly show that the dilatancy of the expansive clay increases with an increase in the applied suction for both the natural and compacted specimens matric suction contributes to the shear strength of the expansive clay via two different mechanisms the contribution of capillary force to interparticle normal stress and the effect of suction on soil dilatancy as a result of the second mechanism the con tribution of suction to peak shear strength for the clay is more significant than that to post failure shear strength par ticularly at a high suction range the contribution of suction to post failure shear strength for the natural specimen is basically consistent with that for the compacted specimen the higher peak shear strength and dilatancy for the natural specimen are related to the cementation effect of the iron and manganese oxides the contribution of suction to shear strength for the compacted expansive clay is more significant than that for a compacted kaolin at suctions less than 100 kpa

a survey of clasts and large chondrules in ordinary chondrites we report the results of a survey of clasts and large 5 mm chondrules macrochondrules within the 833 ordinary chondrites of the natural history museum collection thirty six macrochondrules and 24 clasts were identified and studied macrochondrules have textures and mineral assemblages like normal chondrules and so share a common origin clasts show evidence for fracturing from larger bodies and can be classified as either 1 chemically fractionated if they have major and trace element compositions differing substantially from most chondrules and clasts 2 impact melt clasts if they have microporphyritic textures and signs that indicate they are derived from shock melted chondritic material 3 microporhyritic clasts if they are similar to the last category but lack evidence for derivation through shock melting or 4 indeterminate clasts forming a diverse class that includes all those clasts that do not fit into the other categories

strain rate dependent stress strain behavior of overconsolidated hong kong marine clay a total number of 24 consolidated undrained triaxial shear tests on reconsolidated saturated hong kong marine clay hkmc have been performed in both compression and extension shear states the specimens were prepared in four different overconsolidation ratios ocrs and sheared at three different axial strain rates the strain rate dependency of undrained shear strength pore water pressure stress path and secant young s modulus are investigated the influence of ocr on the stress strain strength behavior of hkmc is also examined the results of all tests are presented and interpreted the interpreted results are compared with the results in the literature for the hkmc with ocr varying from 1 to 8 the average value of the strain rate parameter 0 15 is 5 5 for compression tests and 8 4 for extension tests most interpreted results are conclusive and consistent with the published results whereas some results are not conclusive a new parameter for describing the strain rate dependency of undrained

chemical studies of l chondrites iii mobile trace elements and ar 40 ar 39 ages abstract we report data for trace elements ag au bi cd co cs ga in rb se te tl and zn determined by radiochemical neutron activation analysis in l4 6 chondrites with undisturbed 40 ar release patterns or with patterns showing some disturbance in the 4 4 4 6 gyr plateau indicating shock induced loss mean concentrations are lower many significantly so in 16 chondrites with disturbed patterns than in 4 with undisturbed ones consistent with shock induced mobilization similar trends were noted earlier in l4 6 chondrites having mineralogically observable shock indicators mean concentrations are lower in strongly shocked i e 22 gpa than in mildly shocked 40 ar release patterns are mildly shocked but chondrites with disturbed patterns are more strongly heated on average than those of shock facies d f i e 22 to 57 gpa pooling these populations significantly lower mean concentrations of nearly all trace elements in 26 strongly shocked l4 6 chondrites than in 14 mildly shocked ones indicate loss in shock formed fes fe eutectic and or by vaporization during cooling of shock heated collisional debris two element correlations and the pattern of them i e correlation profiles are also consistent with this picture trace elements can act as thermometers for collisional episodes in l4 6 chondrites but not for earlier thermal fractionations unless compensation can be made for late shock heating

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

formation conditions of igneous regions in ordinary chondrites chico rose city and other heavily shocked h and l chondrites we report microprobe and radiochemical neutron activation analysis rnaa data for hosts and igneous inclusions in the heavily shocked ordinary chondrites rose city h5 yanzhuang h6 farmington l5 malakal l5 chantonnay l6 chico l6 and tuan tuc l6 based on these analytical results equilibrium crystallization calculations ghiorso and sack 1995 phase equilibrium analysis e g sack and ghiorso 1994a b sack et al 1994 and experimental cooling rate studies e g walker et al 1976 we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites we infer that 1 unfractionated chondritic liquids were intruded to depths 0 1 km in the parent asteroid of rose city 2 early chondritic liquids experiencing 5 10 olivine fractionation were erupted onto the surface of the parent asteroid s of yanzhuang and chantonnay and 3 near surface crystallization is also indicated for the liquids in tuan tue and farmington with chico and malakal crystallizing at slightly greater depths in all but chantonnay liquids appear to have derived from melting of chondrite types corresponding to their hosts in the l chondrite chantonnay the intrusive liquids derive from melting an h chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts heating effects are also reflected in the trace element contents of the chondrites our rnaa data for rose city seem to reflect only the siderophile lithophile fractionation evident in the metal distribution the yanzhuang rnaa data are generally similar to those of other h chondrites severe shock not involving phase transport seems to leave h chondrites unaffected compositionally contents of the four most mobile elements cd bi t1 in and cs in chico indicate loss so that this assemblage experienced extended low temperature cooling after injection of dike material into the chico host rnaa data for the other four l chondrites examined indicate more rapid cooling

core formation in asteroids chemical arguments based on the s concentrations in the metallic magmas that formed magmatic iron meteorites and on the lack of pyroxene in pallasites suggest that core formation in asteroids was accompanied by 40 melting of the associated silicates the existence of plagioclase free residues from partial melting such as lodranite meteorites indicates that metal did not segregate from silicates when the amount of partial melting was only 15 thus core formation in asteroids requires substantial melting of an asteroid high interfacial energies between metallic melts and silicates require that metallic spherules sink through partially molten silicates to form cores in asteroids and planetesimals the globule sinking mechanism is not very efficient because silicate crystal liquid mixtures have high yield strengths making it difficult for the globules to sink calculations suggest that the melt fraction must reach 50 before globules can sink alternatively porous flow of molten metal is possible when the amount of metal is high enough to form an interconnected network about 50 this can be achieved by high initial abundances of metal or by gradual removal of silicate melt thereby enriching the residue in the metal sulfide assemblage this also requires removal of 50 silicate partial melt though not necessarily all at once such high amounts of melting were not always attained in asteroids so many asteroids probably consist of partially differentiated silicates and metallic masses that did not segregate to a core s asteroids might represent such partially differentiated bodies

influence of suction on the strength and stiffness of compacted sand bentonite this paper examines the constitutive behaviour of unsaturated mixtures of compacted sand bentonite material two different techniques have been used to modify soil suction in laboratory specimens to examine the influence of suction on the behaviour of compacted materials the two methods generated inherent differences in material fabric and therefore in stress strain behaviour the difference in microstructure generated by these two preparation techniques created different properties for the two series of specimens this paper compares the behaviour of the two series of specimens and relates the observed mechanical behaviour to the initial soil fabric created by the two different preparation techniques specimens of similar compacted material were taken from two full scale in ground experiments conducted at atomic energy of canada limited s underground research laboratory at lac du bonnet manitoba and sheared using the same triaxial equipment the results are compared to the results of shearing laborator

chemical studies of l chondrites ii shock induced trace element mobilization abstract previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock heated collisional debris indicate that au co se ga rb cs te bi in ag zn tl and cd progress in mobility we report data for these 13 trace elements in 14 l4 6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier trace element contents vary with petrologic type s fe sub group and shock history the last dominating strongly absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock loading i e residual temperatures established from mineralogic petrologic study a tertiary process shock heating previously known to have affected radiogenic 40 ar and or 4 he in meteorites but not other elements apparently was at least as effective as other open system processes secondary parent body and primary nebular and or accretionary episodes in establishing mobile trace element contents of l chondrites and probably others if conditions during early genetic episodes are to be deduced from compositional information shocked meteorites should be avoided or effects of later processes should be compensated for

igneous inclusions from ordinary chondrites high temperature cumulates and a shock melt we report microprobe instrumental neutron activation analysis and radiochemical neutron activation analysis data for three large igneous inclusions in the yamato y 75097 y 793241 and y 794046 ordinary chondrites the inclusions in the first two chondrites are troctolitic cumulates that have undergone appreciable reactions with their hosts either during emplacement and or cooling olivine spinel fe mg exchange pairs in these two inclusions record equilibration temperatures of about 710 c and these temperatures are similar to those exhibited by mineral pairs in the y 75097 and y 793241 hosts the inclusion in y 794046 is texturally unique consisting of fine grained randomly distributed olivines coarse 2 mm fascicular pyroxene laths and angular pockets of maskelynite plagioclase feldspar the phase compositions are readily interpreted as having resulted from extremely rapid essentially isochemical cooling to temperatures 1670 c we suggest that this igneous inclusion formed in situ by shock

behavior of unsaturated weathered residual granite soil with initial water contents abstract there is a significant difference between the swccs response for drying and wetting curves in unsaturated state in other words the initial water content condition can influence the behavior of unsaturated soils to find this out a series of triaxial compression tests was performed on samples of compacted granite soils in a modified triaxial cell that can separately control pore air pressure u a and pore water pressure u w unsaturated granite soil samples were prepared with different initial water contents dry wet and optimum moisture by compaction in a mould these samples were tested at different suction and confining stresses the volume change of an unsaturated soil during shearing is more sensitive to the confining pressure compared to the initial water content and the matric suction the volume expands during shearing and the volumetric strain is much larger at the smaller confining pressure and at the higher matric suction the variation of the internal frictional angle with the initial water content and the matric suction is negligible but the effective cohesion increases with matric suction

the relationship of the unsaturated soil shear strength to the soil water characteristic curve the measurement of soil parameters such as the permeability and shear strength functions used to describe unsaturate soil behaviour can be expensive difficult and often impractical to obtain this paper proposes a model for predicting the shear strength versus matric suction function of unsaturated soils the prediction model uses the soil water characteristic curve and the shear strength parameters of the saturated soil i e effective cohesion and effective angle of internal friction once a reasonable estimate of the soil water characteristic curve is obtained satisfactory predictions of the shear strength function can be made for the unsaturated soil closed form solutions for the shear strength function of unsaturated soils are obtained for cases where a simple soil water characteristic equation is used in the prediction model key words soil suction soil water characteristic curve shear strength function unsaturated soil

shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil shear strength and dilative characteristics of a re compacted completely decomposed granite cdg soil are studied by performing a series of single stage consolidated drained direct shear tests under different matric suctions and net normal stresses the axis translation technique is applied to control the pore water and pore air pressures a soil water retention curve swrc is obtained for the cdg soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus shear strength increases with matric suction and net normal stress and the failure envelope is observed to be linear the apparent angle of internal friction and cohesion intercept increase with matric suction a greater dilation angle is found at higher suctions with lower net normal stresses while lower or zero dilation angles are observed under higher net normal stresses with lower suctions also at a saturated condition experimental shear strength

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

prediction of the unconfined compressive strength of compacted granular soils by using inference systems adaptive neuro fuzzy inference system anfis and artificial neural network ann models have been extensively used to predict different soil properties in geotechnical applications in this study it was aimed to develop anfis and ann models to predict the unconfined compressive strength ucs of compacted soils for this purpose 84 soil samples with different grain size distribution compacted at optimum water content were subjected to the unconfined compressive tests to determine their ucs values many of the test results for 64 samples were used to train the anfis and the ann models and the rest of the experimental results for 20 samples were used to predict the ucs of compacted samples to train these models the clay content fine silt content coarse silt content fine sand content middle sand content coarse sand content and gravel content of the total soil mass were used as input data for these models the ucs values of compacted soils were output data in these models the anfis model results were compared with those of the ann model and it was seen that the anfis model results were very encouraging consequently the results of this study have important findings indicating reliable and simple prediction tools for the ucs of compacted soils

behavior of a compacted completely decomposed granite soil from suction controlled direct shear tests a series of single staged consolidated drained direct shear tests are carried out on recompacted completely decomposed granite cdg soil a typical residual soil in hong kong under different matric suctions and net normal stresses matric suction is controlled by applying air pressure in the pressure chamber and water pressure at the bottom of the high air entry ceramic disk the experimental results show that the contribution of suction to shear strength is significant shear strength of cdg soil increases with the increase of matric suction net normal stress has a remarkable influence on the shear strength of unsaturated cdg soil the increase in shear strength due to an increase in matric suction suction envelope is observed as nonlinear i e b value varies with matric suction no soil dilatancy is observed for zero matric suction saturated case but as the suction value is increased higher soil dilatancy is obvious in lower net normal stresses the rate of increase of soil dilatancy is greater

shear strength characteristics of statically compacted unsaturated kaolin the shear strength characteristics of statically compacted unsaturated soil specimens of commercial kaolin ip 15 were determined using conventional triaxial shear testing apparatus extending total stress analysis the testing program consists of two different types of confined compression shear strength tests on unsaturated soil specimens in the first series of tests the specimens were sheared immediately after the application of the confining pressure under undrained loading conditions in the second series of tests the specimens were first allowed to come to equilibrium with respect to volume change and suction value under the applied confining pressure and sheared at two different rates of strain a psychrometer was used for measuring suction values in addition conventional consolidated undrained tests were also conducted on specimens that were saturated using the back pressure technique before shearing comparisons with respect to the shear strength behavior are provided for both saturated a

a relationship describing the shear strength of unsaturated soils a relationship describing the shear strength profile of a desiccating soil deposit is essential for the purpose of analysis especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation dependent shear strength value the matric suction profile of a desiccating soil deposit is nonlinear up to the air entry value an increase in matric suction is associated with a linear increase in shear strength beyond air entry as the soil starts to desaturate a nonlinear increase in shear strength occurs the soil water characteristic curve is stress dependent as is the shear strength gain as matric suction increases in this paper a three dimensional nonlinear regression analysis showed that a power additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction the proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength

shear strength characteristics of a residual soil shallow landslides in natural residual soils slopes are common all over the world the slip surfaces associated with these landslides are often situated above the groundwater table therefore it i

shear strength of a compacted residual soil from consolidated drained and constant water content triaxial tests rainfall induced landslides in unsaturated residual soils can occur slowly under drained conditions or rapidly under undrained conditions consolidated drained cd and constant water content cw

chemical studies of h chondrites ii weathering effects in the victoria land antarctic population and comparison of two antarctic populations with non antarctic falls abstract we report rnaa data for 14 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in sb se te tl u zn in interior portions of 45 different h4 6 chondrites 49 samples from victoria land antarctica and 5 h5 chondrites from the yamato mts antarctica relative to h5 chondrites of weathering types a and b all elements are depleted 10 at statistically significant levels in extensively weathered types b c and c samples probably by leaching on the ice sheet surface contents of 8 elements in extensively weathered samples may provide a qualitative ranking for terrestrial surface residence chondrites of weathering types a and b seem compositionally uncompromised and as useful as contemporary falls for trace element studies when data distributions for these 14 trace elements in non antarctic h chondrite falls and unpaired samples from victoria land and from the yamato mts queen maud land are compared statistically numerous significant differences are apparent concentrations of 8 elements differ significantly in the victoria land and non antarctic h5 chondrite populations essentially the same compositional differences and 53 mn content and shock history differences appear when h4 6 populations are compared contents of 8 elements differ when queen maud land and victoria land populations are compared and 5 for the queen maud land non antarctic comparison these and other differences give ample cause to doubt that the various sample populations derive from the same parent population the observed differences do not reflect weathering chance or other trivial causes a preterrestrial source must be responsible the least unlikely of these involves a temporal variation in the source regions from which meteoroids derive

determination of the shear strength parameters of an unsaturated soil using the direct shear test multistage direct shear tests have been performed on saturated and unsaturated specimens of a compacted glacial till a conventional direct shear apparatus was modified in order to use the axis tra

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

late paleozoic serpentinites and mafic schists from the coast range accretionary complex central chile their relation to aeromagnetic anomalies regional structural trends within the poorly exposed metamorphic basement complex of central chile between 39 30 and 41 30 s latitudes are evident on total intensity aeromagnetic maps field and laboratory measurements of magnetic susceptibility indicate that anomalies are related to relic magnetite and rare ilmenite phase concentrations in serpentinites and lower greenschist facies mafic schists

a planetary h group pebble in the barwell l6 unshocked chondritic meteorite abstract one stone of the barwell l6 shower contains an igneous inclusion with the oxygen isotopic signature of h group chondrites the inclusion is composed dominantly of olivine with a composition fo 75 5 identical with that of its host other phases are only partially equilibrated with the host the inclusion has a fractionated rare earth element pattern showing depletion in the heavy rare earth elements and a positive eu anomaly it is depleted in siderophile elements inclusion and host have ar ar ages 4 44 and 4 51 ga respectively and 129 xe r i ratios identical within experimental error we conclude that melting occurred very early on an h group chondritic body two objects from a single meteorite have different oxygen isotopic ratios but identical 129 xe r 127 i ratios which may indicate that the i xe systematics reflect chronological differences in closure to xe rather than isotopically heterogeneous iodine the inclusion and its host cooled to xe closure temperature contemporaneously with chondrules from unequilibrated ordinary chondrites

metallogenic and tectonic characteristics of the paleozoic ophiolitic belt of the southern chile coastal cordillera the comparison of the tectonic geochemical and metallogenic information of the crystalline paleozoic basement of the south coast range of chile with those classical ophiolites complexes like cyprus oman the apennines magellean etc allows to find many similarities between them ultramafic rocks mainly wherlites harzburgites and dunites with strong serpentinization and rodingites tholeiitic basalts with pillow structures volcano clastic sediments green schists of tholeiitic composition and meta pelites grey schists

a transmission electron microscopy tem investigation of opaque phases in shocked chondrites shock defects in the most common silicate minerals of chondrites olivine pyroxenes and feldspars have been investigated in detail but there have been almost no studies of the shock defects in other components like metal and sulfide this probably stems from the fact that these latter phases are opaque in the optical microscope the same reason explains why veins and melt pockets which are constituted of microcrystalline or glassy phases i e isotropic are also poorly documented we have investigated such phases by analytical transmission electron microscopy atem in two shocked chondrites tenham l6 and gaines county h5 we have characterized shock defects in troilite very similar to those occurring in silicates i e a mosaic texture and sets of straight and very narrow 10 nm lamellae of amorphized fes there are many small regions in shocked chondrites that are composed of very fine grained 1 m mixtures of metal and sulfide or of various silicates they must result from local melting followed by a rapid cooling that prevented grain growth we have determined the chemical compositions and the volume proportions of the tiny grains in these veins and melt pockets which has allowed their temperature and pressure t p history to be partially deciphered finally we have observed a dense network of very narrow fractures down to 10 nm in the olivine and enstatite grains these fractures are systematically filled with an amorphous or cryptocrystalline material that stems from the melt pockets and was injected when the fractures were opened by the rarefaction wave this material was then quenched at the contact with the colder crystalline rims

shear strength characteristics of two saprolitic soils the saturated and unsaturated shear strength behavior of an undisturbed completely decomposed fine ash tuff and an undisturbed completely decomposed granite from hong kong were studied using direct shear and triaxial tests the completely decomposed fine ash tuff is a fine to medium grained saprolite the completely decomposed granite is a coarse grained saprolite results show that matric suction increases the shear strength of both soils the extent of the increase is the shear strength with matric suction is related to the soil water characteristic curve for the soil and to the amount of dilation during shear the effect of matric suction on the shear strength was more pronounced for the fine to medium grained completely decomposed fine ash tuff than for the coarse grained completely decomposed granite these studies on the saprolitic soils provide insight into the understanding of the shear strength of unsaturated coarse grained soils key words saprolites shear strength matric suction triaxi

impact cratering on the h chondrite parent asteroid 1 this paper reports petrological data for lapaz icefield 02240 03922 031125 031173 031308 04462 and 04751 which are meteoritic samples of clast rich impact melt rocks from the h chondrite parent asteroid the size distribution and metallographic characteristics of fe ni metal in the melts indicate very rapid 1 to 40 c s cooling in the temperature range between 1500 and 950 c when the clast melt mixtures were thermally equilibrating cooling slowed to values between 10 3 and 10 2 c s in the temperature range between 700 and 400 c when the melt rocks were cooling to their surroundings these data suggest that the rocks cooled near the surface of the h chondrite asteroid within suevitic impact deposits integrating these data with the petrologic characteristics of other h chondrite melt rocks and their radioisotopic ages indicates that the h chondrite asteroid suffered at least one large impact event while still cooling from endogenous metamorphism at 4500 ma this impact must have degraded the asteroid s integrity but did not cause shattering impact events in the era between 4100 and 3600 ma produced melt volumes large enough to allow segregation of metal and troilite from silicate melts possibly within continuous impact melt sheets contained in craters the impact record after 3600 ma does not display such assemblages which suggests a decrease in the rate of large impact events or a catastrophic size reduction of the h chondrite parent asteroid at around this time

experimental evaluation of mechanical behavior of unsaturated silty sand under constant water content condition abstract there are very few experimental data on the mechanical behavior of unsaturated soils particularly in constant water content condition because of the technical difficulties and time consuming nature of measuring suction and deformation this paper presents the results of a series of constant water constant triaxial tests on the specimens of an unsaturated silty sand constant water content tests correspond to a field condition where the rate of loading is much quicker than the rate at which the pore water is able to drain out of the unsaturated soil the axis translation technique and a double walled triaxial cell have been used to measure the soil matric suction and variation of pore air volume respectively test specimens were prepared at two different compaction conditions prior to testing to achieve different initial density it is found that the mechanical behavior of the soil mainly depends on the initial density the mean net stress and the initial matric suction also the volume and pore water pressure changes are significantly different in specimens with different initial condition the results of tests indicated that the shearing strength of silty sand increases non linearly with matric suction

chemical studies of l chondrites iv antarctic non antarctic comparisons abstract we report shock facies and rnaa data for 13 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in rb se te tl zn in interior portions of 19 different l3 6 chondrites from victoria land antartica comparison of these data for essentially unweathered antarctic samples with those previously published for 39 l4 6 chondrite falls indicate substantial differences the victoria land population lacks the most heavily shocked 35 gpa representatives found in the non antarctic population while contents of nearly all trace elements studied are lower at statistically significant levels in strongly shocked 22 gpa falls than in mildly shocked 22 gpa ones this is not true for the victoria land population contents of most trace elements vary with petrologic type of heavily shocked facies d 22 35 gpa l chondrites from victoria land such a variation is not observed for non antarctic falls or mildly shocked samples of either population l4 6 chondrites from victoria land contain significantly lesser amounts of nearly every trace element than do falls these differences are reflected in correlations between elements including the putative cosmothermometric trace elements bi in and tl while antarctic weathering could account for the compositional differences between antarctic and non antarctic l chondrites such processes cannot be responsible for the shock differences observed physical and chemical differences between other sorts of antarctic and non antarctic meteorites suggest rather that the l chondrite differences are preterrestrial in origin if so the parent region s for the victoria land samples that fell to earth 0 1 to 1 myr ago generally formed and or evolved under higher temperature conditions than those regions yielding contemporary falls the dominant influence of late shock that altered mobile trace element contents of l chondrites falls is not evident in samples from victoria land

asteroid 6 hebe the probable parent body of the h type ordinary chondrites and the iie iron meteorites the s iv type asteroid 6 hebe is identified as the probable parent body of the h type ordinary chondrites and of the iie iron meteorites the ordinary chondrites are the most common type of meteorites falling to earth but prior to the present study no large mainbelt source bodies have been confirmed hebe is located adjacent to both the v6 and 3 1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface the silicate portion of the surface assemblage of hebe is consistent both in overall average and in its range of variation with the silicate components in the suite of h type chondrites the high albedo of hebe rules out a lunar style space weathering process to produce the weakened absorption features and reddish spectral slope in the s type spectrum of hebe linear unmixing models show that a typical ni fe metal spectrum is consistent with the component that modifies an h chondrite spectrum to produce the s type spectrum of hebe on the basis of the association between the h chondrites and the he iron meteorites our model suggests that large impacts onto the relatively metal rich h chondrite target produced melt bodies sheets or pods that differentiated to form thin laterally extensive near surface layers of ni fe metal fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in h chondrite breccias alternately masses of metal could have been deposited on the surface of hebe by the impact of a core or core fragment from a differentiated parent body of h chondrite composition subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of hebe in this interpretation the nonmagmatic iie iron meteorites are samples of the ni fe metal masses on the surface of hebe whereas the h chondrites are samples from between and or beneath the metal masses

petrology and geochemistry of patuxent range 91501 a clast poor impact melt from the l chondrite parent body and lewis cliff 88663 an l7 chondrite we have performed petrologic and geochemical studies of patuxent range pat 91501 and lewis cliff lew 88663 pat 91501 originally classified as an l7 chondrite is rather a unique near total impact melt from the l chondrite parent body lewis cliff 88663 was originally classified as an achondrite but we find that it is a very weakly shocked l7 chondrite pat 91501 is an unshocked homogeneous igneous textured ultramafic rock composed of euhedral to subhedral olivine low ca pyroxene augite and chrome rich spinels with interstitial albitic plagioclase and minor silica alumina alkali rich glass only 10 relic chondritic material is present olivine grains are homogeneous fa25 2 26 8 low ca pyroxene wo1 9 7 2en71 9 78 2fs19 9 20 9 and augite wo29 8 39 0en49 2 55 3fs11 8 14 9 display a strong linear tio2 al2o3 correlation resulting from igneous fractionation plagioclase is variable in composition or3 0 7 7ab79 8 84 1an8 2 17 2 chrome rich spinels are variable in composition and zoned from cr rich cores to ti al rich rims some have evolved compositions with up to 7 9 wt tio2 pat 91501 bulk silicate has an l chondrite lithophile element composition except for depletions in zn and br siderophile and chalcophile elements are highly depleted due to sequestration in centimeter size metal troilite nodules the minerals in lew 88663 are more uniform in composition than those in pat 91501 olivine grains have low cao and cr2o3 contents similar to those in l5 6 chondrites pyroxenes have high tio2 contents with only a diffuse tio2 al2o3 correlation low ca pyroxenes are less calcic wo1 6 3 1en76 5 77 0fs20 4 21 4 while augites wo39 5 45 6en46 8 51 1fs7 6 9 4 and plagioclases or2 6 5 7ab74 1 83 1an11 2 23 3 are more calcic spinels are homogeneous and compositionally similar to those in l6 chondrites lew 88663 has an l chondrite bulk composition for lithophile elements and only slight depletions in siderophile and chalcophile elements that are plausibly due to weathering and or sample heterogeneity