the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

joint deconvolution of building and downhole strong motion recordings evidence for the seismic wavefield being radiated back into the shallow geological layers in this study the strong motion recordings collected by a vertical array of borehole sensors and a network of accelerometers installed in a nearby building distance between borehole and building 10 m are innovatively jointly analyzed through wavefield deconvolution analysis the analysis shows complicated patterns in the deconvolved wavefield of the borehole sensors that are interpreted by taking advantage of synthetic seismograms generated considering vertically propagating plane waves in the soil and building using a constrained deconvolution approach we show that it is possible to separate the different components of the wavefield and in particular to retrieve the input ground motion and the wavefield radiated back by the building at different levels in the borehole without a priori information about the attenuation structure and velocity of the building and soil this therefore allows the energy radiated back by the structure at different depth to be estimated which in the case of the bottom of the borehole at 145 m is of the order of 10 of the energy of the input wavefield in the 1 10 hz frequency band

rare earth elements and the petrogenesis of aubrites ree measurements in the bishopville aubrite confirm that oldhamite cas is the dominant ree carrier while most other phases including the major silicates are extremely ree depleted in oldhamite a variety of ree patterns are observed which could not have been produced during crystallization from a single fractionating magma although the aubrites have clearly undergone igneous processing oldhamite which is highly refractory may be a relict phase in this case whole rock ree data cannot provide information on the igneous evolution of these meteorites

39ar 40ar chronology of the enstatite chondrite parent bodies ar ar isochron ages of el chondrites suggest closure of the k ar system at 4 49 0 01 ga for el5 and 6 chondrites and 4 45 0 01 ga for el3 mac 88136 the high temperature release regimes contain a mixture of radiogenic 40ar and trapped primordial argon solar or q type with 40ar 36artr 0 which does not affect the 40ar budget the low temperature extractions show evidence of an excess 40ar component the 40ar 36ar is 180 270 it is defined by intercept values of isochron regression excess 40ar is only detectable in petrologic types 4 5 these lost most of their primordial 36ar from low temperature phases during metamorphism and retrapped excess 40ar the origin of this excess 40ar component is probably related to metamorphic ar mobilization homogenization of primordial and in situ radiogenic ar and trapping of ar by distinct low temperature phases ar ar ages of eh chondrites are more variable and show clear evidence of a major impact induced partial resetting at about 2 2 ga ago or alternatively prolonged metamorphic decomposition of major k carrier phases eh impact melt lap 02225 displayed the highest ar ar isochron age of 4 53 0 01 ga this age sets a limit of about 25 45 ma for the age bias between the k ar and u pb decay systems

amplification of seismic ground motion in the tunis basin numerical bem simulations vs experimental evidences this paper aims at the analysis of seismic wave amplification in a deep alluvial basin in the city of tunis in tunisia this sedimentary basin is 3000m wide and 350m deep since the seismic hazard is significant in this area the depth of the basin and the strong impedance ratio raise the need for an accurate estimation of seismic motion amplification various experimental investigations were performed in previous studies to characterize site effects the boundary element method is considered herein to assess the parameter sensitivity of the amplification process and analyse the prevailing phenomena the various frequencies of maximum amplification are correctly estimated by the bem simulations the maximum amplification level observed in the field is also well retrieved by the numerical simulations but due to the sensitivity of the location of maximum amplification in space the overall maximum amplification has to be considered the influence of the wave field incidence and material damping is also discussed

magnitude determination using strong ground motion attenuation in earthquake early warning 1 we use 1661 strong motion accelerograms with peak ground acceleration pga larger than 80 gal 1 gal 1 0 cm s2 from 77 earthquakes recorded by the taiwan strong motion instrumentation program tsmip stations to derive a strong motion attenuation relationship this relationship can be used to dynamically define a mpga magnitude for earthquakes using earthquake locations determined by earthquake early warning process the mpga magnitude using this strong motion attenuation relationship corresponds well with mw given a sufficient number of pga readings mems micro electro mechanical systems acceleration sensor could be widely used for ground motion monitoring purposes thus we propose that once a large earthquake has begun that we might be able to use strong near field tens of kilometers pga values to quickly estimate the earthquake s magnitude which would improve earthquake early warning

soil basin and soil building soil interaction effects on motions of mexico city during seven earthquakes starting with the destructive 1985 michoacan mw 8 0 earthquake the lake zone of mexico city has been experiencing ground motions bearing the effects of strong soil amplification at specific site d

large effects of moho reflections sms on peak ground motion in northwestern taiwan abstract a total of 336 three component strong motion recordings from the m w 6 35 niu dou earthquake of 25 june 1995 at a focal depth of 39 9 km in northern taiwan are used to study the effects on strong ground motion due to moho reflection of s waves the residuals of both horizontal peak ground acceleration pga and peak ground velocity pgv recorded from the earthquake are analyzed the results confirm that many class e soft soil stations in the taipei basin and the ilan plain had the expected large amplification of about 1 7 and 1 5 times respectively the predicted median pga values surprisingly a large group of class c or d dense and stiff soil sites in taoyuan tcu007 lungtan tcu013 guanshi tcu021 hsinchu tcu095 and miaoli tcu047 areas in northwestern taiwan had unusually large amplification of about 3 4 8 1 and 1 7 3 3 times the predicted median pga and pgv values respectively they are interpreted in terms of focusing and interference between sms waves reflected from the horizontal and inclined portions of an east dipping moho discontinuity in this area this interpretation is supported by the close agreement between the expected amplitudes and arrival times of the largest shear waves with the observed data our results suggest that when a damaging earthquake occurs near an inclined moho boundary the reflected sms waves can result in significantly amplified ground motions at distances beginning about 50 km the exact distance range will depend on the thickness of the crust and the dip angle of the moho boundary

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

enstatite chondrites el3 as building blocks for the earth the debate over the 146 sm 142 nd systematics the 146sm 142nd extinct decay scheme 146sm half life of 103 my is a powerful tool to trace early earth silicate differentiation differences in 142nd abundance measured between different chondrite meteorite groups and the modern earth challenges the interpretation of the 142nd isotopic variations found in terrestrial samples because the origin of the earth and the nature of its building blocks is still an ongoing debate as bulk meteorites the enstatite chondrites ec have isotope signatures that are the closest to the earth value with an average small deficit of 10 ppm in 142nd relative to modern terrestrial samples here we review all the nd isotope data measured on ec so far and present the first measurements on an observed meteorite fall almahata sitta containing pristine fragments of an unmetamorphosed enstatite chondrite belonging to the el3 subgroup once 142nd 144nd ratios are normalized to a common chondritic evolution samples from the ec group both el and eh have a deficit in 142nd but the dispersion is important 142 nd 10 12 2sd ppm this scatter reflects their unique mineralogy associated to their formation in reduced conditions low fo2 or high c o rare earth elements are mainly carried by the sulfide phase oldhamite cas that is more easily altered than silicates by weathering since most of the ec meteorites are desert finds the el6 have fractionated rare earth element patterns with depletion in the most incompatible elements deviations in nd mass independent stable isotope ratios in enstatite chondrites relative to terrestrial standard are not resolved with the level of analytical precision achieved by modern mass spectrometry techniques here we show that enstatite chondrites from the el3 and el6 subgroups may come from different parent bodies samples from the el3 subgroup have nd 142nd 0 8 7 0 2sd and ru isotope ratios undistinguishable from that of the bulk silicate earth el3 samples have never been analyzed for mo isotopes because these enstatite chondrites are relatively small in size and number they are usually not available for destructive isotopic measurements average values based on the measurement of el6 samples should not be considered as representative of the whole el group because of melting and thermal metamorphism events affecting the sm nd ratios and prolonged open system history the el3 chondrites are the best candidates as the earth s building blocks these new results remove the need to change the composition of refractory incompatible elements early in earth s history

mineralogical and spectroscopic investigation of enstatite chondrites by x ray diffraction and infrared reflectance spectroscopy 1 the mineralogy and infrared reflectance spectra of 13 enstatite e chondrite meteorite finds spanning the full range of textural alteration grades in both el and eh classes have been investigated rietveld refinement of high resolution powder x ray diffraction xrd data was used to determine quantitative major mineral abundances sample correlated mid infrared 2 0 to 25 0 m 4500 cm 1 to 400 cm 1 reflectance infrared spectra were collected for each meteorite spectral features due to the fundamental lattice vibrations of the silicates primarily enstatite dominate the spectra of these meteorites over most of the spectral range investigated the spectral features related to primary i e pre terrestrial mineralogy include fundamental stretching and bending lattice modes 8 3 25 0 m 1200 400 cm 1 overtones and combinations of the fundamental modes 4 5 6 1 m 2200 1650 cm 1 and the principle christensen feature 8 3 m 1200 cm 1 terrestrial weathering products including fe oxyhydroxides gypsum and carbonates occur in most of these meteorites and contribute to some spectral features particularly an asymmetric feature near 2 6 to 3 8 m 3800 to 2600 cm 1 attributed to adsorbed hydrogen bonded and or structural oh and h 2 o and a feature near 6 2 m 1625 cm 1 attributed to adsorbed hydrogen bonded and or structural h 2 o modal mineral abundances determined by rietveld refinement have been used to calculate model grain densities for each meteorite bulk magnetic susceptibility measurements combined with modal mineralogy and grain densities reveal a trend toward lower grain density and lower bulk susceptibility with increased terrestrial weathering

three dimensional density structures of taiwan and tectonic implications based on the analysis of gravity data abstract taiwan is located in a collision and subduction area and has a complex tectonic history to better understand the complicated structure beneath taiwan gravity studies in addition to seismic and geological studies provide useful geophysical information for studying shallow depths previous gravity studies of taiwan in the last 30 years focused on local regionalized explanations and 2 d profile modeling this study is the first to complete a 3 d gravity inversion of taiwan and it provides a more comprehensive and large scale tectonic analysis following 3 d gravity inversion using the least squares method we sliced horizontal and vertical profiles from the 3 d density model to visualize tectonic changes the low bouguer anomaly was caused by thick sediment and crust layers the high density layers are located in special tectonic areas such as the peikang and kuanying basement highs the deepest moho depth beneath the middle of the central range is 45 50 km the high gradient changes of the eastern section of the moho relief are shown by the complex mechanism of plate collision the geometry of plate subduction is apparent in northeastern taiwan and the oceanic crust is observable under eastern taiwan showing arc collision boundaries our 3 d density model when combined with updated gravity data and seismic tomography offers better resolution for deep structures than the previous 2 d forward results and serves as a physical property reference to better understand the tectonic structure beneath taiwan

the lithophile trace elements in enstatite chondrites we report on the abundances of a selected set of lithophile trace elements namely rees y rb ba sr zr hf nb th u in a comprehensive suite of enstatite chondrites ec 13 eh and 11 el eh3 and el3 display only minor deviations from chondritic distributions for these elements in most metamorphosed ec a wide range of compositions is observed and suggests a mobility of many of the elements studied during the history of these rocks for example el6 chondrites exhibit light ree and nb depletions negative eu anomalies and positive y anomalies more important trace element fractionations are observed in metamorphosed eh like st marks rb depletion lap 02225 rb nb zr eu light ree depletions and galim b which displays large ba sr eu nb and light ree depletions leaching experiments were undertaken to investigate the contributions of sulfides in the whole rock budgets these phases control not only the ree budget but also important fractions of the other elements we studied these fractions strongly depend on the type of the rock eh or el and metamorphic grade for many elements the sulfide contributions increase with the metamorphic grades the trace element abundances of silicate residues are extremely variable negative sm and yb anomalies are observed in el3 and eh3 residues and are certainly the results of early nebular processes such anomalies are lacking in residues obtained with most metamorphosed ec underlining the importance of trace element redistributions during metamorphism in addition el6 residues display distinctive positive y anomalies that could be potentially ascribed to a less chalcophile behavior than ho in the conditions that prevailed during el metamorphism

the compositional classification of chondrites ii the enstatite chondrite groups we present new data from a neutron activation analysis of four enstatite chondrites including the taxonomically important st sauveur and discuss the classification of enstatite chondrites the enstatite chondrites can be divided into two compositionally distinct sets in one set abundances of nonrefractory siderophiles and moderately volatile chalcophiles and alkalis are 1 5 2 0 higher than in the other a well resolved compositional hiatus separates these two sets the differences in composition are as great as those between the groups of ordinary chondrites and therefore it appears best to treat these sets as separate groups by analogy with the symbols used for ordinary chondrites we propose to designate the high fe high siderophile group eh and the low fe low siderophile group el known members of the eh group belong to petrologic types 4 and 5 whereas all el members are petrologic type 6 within the eh group no correlation is observed between petrologic type and abundance of nonrefractory siderophiles or moderately volatiles or alkalis two physical properties show only modest overlap between the eh and el groups cosmic ray ages for eh chondrites are 0 5 7 ma while those for el chondrites are 4 18 ma relative to bjurbole i xe formation intervals are 1 3 0 6 ma for eh chondrites and 2 9 0 5 ma for el chondrites the weight of the chemical and physical evidence indicates that the eh and el groups formed separate bodies at similar distances from the sun the available evidence for shallowater and happy canyon two strongly recrystallized silicate rich meteorites containing 40 mg g fe ni indicates that the former is an enstatite clan chondrite altered by loss of sulfide and plagioclase rich melts whereas the latter is intermediate in composition between el chondrites and the chondritic silicates in the pine river iab anomalous meteorite

site city interaction theoretical numerical and experimental crossed analysis the collective excitation of city structures by a seismic wavefield and the subsequent multiple structure soil structure interactions sssis between the buildings are usually disregarded in conventional seismology and earthquake engineering practice the objective here is to qualify and quantify these complex multiple sssis through the design of an elementary study case which serves as a benchmark for theoretical numerical and experimental crossed analysis the experimental specimen consists of an idealized site city setup with up to 37 anisotropic resonant structures arranged at the top surface of an elastic layer and in co resonance with it the experimental data from shaking table measurements is compared with the theoretical and numerical results provided respectively by an equivalent city impedance model derived analytically from homogenization in the long wavelength approximation and a model based on boundary elements the signatures of the site city interactions are identified in the frequency time and space domain and in particular consist of a frequency dependent free rigid switch in the surface condition at the city resonance beatings in the records and the depolarization of the wavefield a parametric study on the city density shows that multiple sssis among the city structures five are sufficient can have significant effects on both the seismic response of its implantation site and that of the buildings key parameters are provided to assess site city interactions in the low seismic frequency range they involve the mass and rigidity of the city compared to those of the soil and the damping of the building

experimental and numerical evidence of the clustering effect of structures on their response during an earthquake a case study of three identical towers in the city of grenoble france in this article interpretation of an equivalent to a macroseismic intensity survey performed in three identical stand alone buildings located in grenoble france after an m l 4 1 earthquake reveals a clustering effect resulting in different levels of perception of seismic loading by inhabitants the clustering effect is confirmed using numerical simulation the variation of the seismic response of the building in the middle of the cluster depends on the azimuth of the seismic source relative to the building cluster the major effect is the splitting of its resonance frequency accompanied by a decrease in vibration amplitude we conclude that clustering has an impact on urban effects calling into question the validity of seismic design which considers buildings in urban areas as stand alone constructions and the interpretation of macroseismic intensity surveys conducted in dense urban areas

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

site city seismic interaction in mexico city like environments an analytical study recent destructive earthquakes have confirmed the importance of hazard and vulnerability studies to predict and prevent the impact of large seisms most seismic risk analysis considers the buildings as a passive constituent integrated into the vulnerability analysis this approach neglects the possible contribution of the building vibration to the free field this article describes an analysis of site city effects that is the seismic interaction of the city with soft soil layers an analytic method derived from soil structure interaction studies is described and applied to the roma norte zone of mexico city the building parameters are derived from detailed studies of the ja and pc buildings the soil city system is subjected to the mexican m w 7 3 14 september 1995 earthquake the simulated ground surface motions which incorporate the wave field radiated from the buildings of roma norte district are compared to seismic records from this zone analytical procedures reproduce the long time duration and beating of the observed ground motion in mexico city parametric analysis are also performed to identify the predominant factors e g urbanization density soil to city stiffness ratio that favor the site city interaction effects a simple relation is proposed to estimate the expected efficiency of the site city interaction effects for any city

neighbourhood inversion of teleseismic ps conversions for anisotropy and layer dip summary the inversion of teleseismic receiver functions for lithospheric structure is difficult due to the non linearity of the problem which is greatly increased in the presence of dipping interfaces and layer anisotropy given an efficient ray theoretical tool for forward modelling teleseismic seismograms we perform a directed monte carlo search technique using the neighbourhood algorithm of sambridge enabling us to search 20 30 parameters in a reasonable amount of computer time tests on synthetic data reveal inherent velocity depth trade offs in typical data sets due to the limited moveout present in teleseismic ps the azimuth of the anisotropic symmetry axis and the strike of a dipping interface prove to be well resolved given adequate backazimuthal coverage we apply this technique to two single station data sets the first from permanent station pgc vancouver island british columbia displays dipping low velocity sediment layers in the mid crust the second from a station at the northern end of the tibetan plateau operating in 1991 and 1992 requires a sequence of thick crustal anisotropic layers to explain the observed pattern of receiver function arrivals

constraints on average taiwan reference moho discontinuity model receiver function analysis using bats data summary by analysing teleseismic waveform data we propose a large scale taiwan reference moho discontinuity model trmdm through coherent stacking and h analysis of receiver functions rfs tectonic structural features are determined from accurate crustal thickness h and reliable vp vs ratio consequently poisson s ratio estimations for taiwan the best estimated regional average moho depth is 33 5 2 9 km noted is a westward crustal thinning from 39 3 0 km in eastern taiwan to 30 1 5 km in southeastern china the averaged moho depth is 23 0 2 5 km in northern taiwan and increases to 33 5 2 0 km in the south the markedly thin crust and high vp vs ratio in northern taiwan are mainly associated with backarc opening and magmatic activities based on h estimations and associated seismicity patterns beneath suang long sslb and adjacent four stations we propose two moho reference models that exhibit distinctive crustal thickening in central taiwan the spatial variations of crustal thickness models show strong lateral change in the moho topography the thick crust in the south thin crust in the north and transition in central taiwan mark the different tectonic units between the subduction wedge and the collision prism onshore in view of the following list of constraints thicker crust in the south than in the north eastward crust thickening significant moho depth changes clear 9 11 s subcrustal boundaries from five stations the compelling thickening of crust and upper mantle beneath the central mountain belt seismicity patterns with the absence of mantle earthquake in the wadatibenioff zone regional geological features the occurrence of the inland chi chi earthquake the compelling low at yulb 1 58 0 13 that may extend to central taiwan at sslb 1 59 0 23 relatively thick crust at yulb 39 5 1 6 km and sslb 40 5 1 3 km or 52 5 1 5 km and finally the apparent horizontal offset between highest yu shan mountain and the deepest moho at sslb we are able to suggest that the initial subduction of the eurasian plate occurred in southern taiwan and most likely extended to the transition zone in central taiwan although the current rf study is limited by large interstation distance our analysis provides more notable constraints than previous studies to explicitly determine the characteristic features of moho discontinuity this detailed approach means that rather than treating the tectonic framework as a whole heterogeneous lithospheric feature clear moho boundary geometry variations indicate that active orogenic processes and differential tectonic stress loading create separate and complex crustal and subcrustal to upper mantle structural features caused by the arc continent collision

the origin of oldhamite in unequilibrated enstatite chondrites abstract we report the results of an ion probe study of rare earth elements rees in six unequilibrated enstatite chondrites oldhamite is confirmed as the major but not the only ree carrier in these meteorites data are also provided for other minerals enstatite niningerite and alabandite that carry detectable amounts of rees although the variety of ree patterns in oldhamite is not as extreme as in hibonite there are seven distinct ree patterns four of which form a continuum that characterize most oldhamite grains from e chondrites two of these patterns f and g were each found in only one weathered grain there is no correlation between ree pattern and oldhamite petrologic setting our trace element data are used to evaluate earlier work and a number of elements zr y sc rees sr se and probably sb and cs including both refractory and volatile species under oxidizing conditions are found enriched in oldhamite a comparison of ree patterns with the results of equilibrium condensation calculations indicates that nebular processes were important in determining the composition of the oldhamite precursors whereas metamorphic processes also affected oldhamite compositions enrichments of chalcophiles are not necessarily due to interaction of oldhamite with nebular gas at low temperatures as previously suggested oldhamite like hibonite was formed from melts whose trace element compositions were determined by high temperature transient events in the solar nebula

samarium neodymium chronology and rubidium strontium systematics of an allende calcium aluminum rich inclusion with implications for 146sm half life abstract calcium aluminum rich inclusions cais are primitive objects that formed within the protoplanetary disk surrounding the young sun recent pb pb chronologic studies have demonstrated that cais are the oldest solar system solids crystallizing 4567 ma ago amelin et al 2002 connelly et al 2012 the isotope systematics of cais therefore provide critical insight into the earliest history of the solar system although sm nd and rb sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early solar system previous studies of cais have revealed evidence for isotopically disturbed systems here we report new age data for allende cai al3s4 derived from both the long lived 147sm 143nd and short lived 146sm 142nd isotopic systems the 147sm 143nd chronometer yields an age of 4560 34 ma that is concordant with 207pb 206pb ages for cais and indicates that the sm nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes the slope of the 146sm 142nd isochron defines the solar system initial 146sm 144sm of 0 00828 0 00044 this value is significantly different from the value of 0 0094 determined by kinoshita et al 2012 ages recalculated from all published 146sm 142nd isochron data using the traditional 103 ma half life and the initial 146sm 144sm value determined here closely match pb pb and 147sm 143nd ages determined on the same samples in contrast ages recalculated using the 68 ma half life determined by kinoshita et al 2012 and either of the initial 146sm 144sm values are often anomalously old this is particularly true for the youngest samples with 146sm 142nd isochron ages that are most sensitive to the choice of 146sm half life used in the age calculation in contrast to the sm nd isotope system the rb sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 110 ma although the rb sr system in cais appears to be disturbed the initial 87sr 86sr value determined from the isochron is 0 698942 0 000008 and closely approximates estimates of the initial solar system value although this isochron may be a mixing line it might also record alteration on the allende parent body in which rb was added to the al3s4 cai that was initially largely devoid of rb

moho depth variation in taiwan from teleseismic receiver functions we determine lateral variation of moho discontinuity crustal thickness and vp vs ratios in the vicinity of taiwan by analyzing all the available teleseismic waveform data collected by the broadband array in taiwan for seismology network from 1998 to 2004 the crustal thickness and the average crustal vp vs ratio beneath each station are obtained by stacking ps ppps and ppss psps phases coherently the best estimated crustal thickness of taiwan from 27 broadband stations is 30 km on average the thinnest crust 11 15 km is found east of the longitude valley suture zone as part of the oceanic crust of the philippine sea plate in other places the crustal thickness varies from 17 19 km in northern taiwan to 32 39 km in the southwestern island the deepest moho is found to be 53 km beneath station sslb in central taiwan the average crustal vp vs ratio in taiwan is 1 74 with higher values of 1 74 1 99 in the north and lower values of 1 60 1 74 in the south the crustal thickness variation is supported by gravity measurements in taiwan and indicates that the collision between the philippine sea plate and eurasian plate in taiwan involves the whole crust the thin crust and high vp vs ratios in northern taiwan are believed to be related to the volcanism in tatun and keelung located in the southwestern extent of the okinawa trough

possible impact induced refractory lithophile fractionations in el chondrites abstract literature data show that refractory lithophile elements in most chondrite groups are unfractionated relative to ci chondrites the principal exception is the el chondrite group whose observed falls all of which are type 6 are depleted in ca and light ree in contrast literature data and our new inaa data on el3 pca 91020 el3 mac 88136 and el4 grein 002 show that some replicates of these samples have nearly flat ree patterns unlike those of el6 chondrites other replicates exhibit fractionated ree patterns similar to those of el6 chondrites petrographic examination shows that many el6 and some el3 and el4 chondrites are impact melt breccias or contain impact melted portions we suggest that the same impact processes that formed these breccias and produced melt are responsible for the observed bulk compositional fractionations in refractory lithophile elements i e el6 chondrites were produced from initially unequilibrated el3 material when large amounts of impact heat were deposited plagioclase and or oldhamite cas the major ree carriers in enstatite chondrites may have been melted and then transported appreciable 10 cm distances el6 chondrites represent the residuum that is depleted in ree particularly in lree and ca unlike the case for el chondrites our new inaa data on alh 84170 eet 87746 and sah 97096 all eh3 show some scatter but are consistent with the eh group having uniform refractory lithophile abundances

heterogeneous ree patterns in oldhamite from aubrites their nature and origin abstract a comprehensive study of the rees in oldhamite from three aubrites confirms that heterogeneous ree patterns are a general feature of cas in these meteorites ten distinct patterns have been observed in 109 grains analyzed four patterns are directly comparable to ree patterns seen in oldhamite from the unequilibrated e3 4 enstatite chondrites and many of these exhibit positive eu and or yb anomalies that are best understood in terms of condensation from the solar nebula other ree patterns however show evidence of igneous fractionation more than one process is thus required to explain the variety of ree patterns seen in oldhamite from the aubrites it is proposed that oldhamite was close to the liquidus under the conditions of aubrite formation and that some grains melted while others did not thus some oldhamites have ree patterns that reflect the fractionations of igneous processing while others have retained ree characteristics established during formation in the solar nebula in contrast to oldhamite from the aubrites and e3 4 chondrites cas from two equilibrated el6 enstatite chondrites shows high and uniform ree abundances that result from equilibration of the rees with neighboring phases during a prolonged metamorphic episode

asteroid 2008 tc 3 almahata sitta a spectacular breccia containing many different ureilitic and chondritic lithologies abstract asteroid 2008 tc3 impacted earth in northern sudan on october 7 2008 the meteorite named almahata sitta was classified as a polymict ureilite in this study 40 small pieces from different fragments collected in the almahata sitta strewn field were investigated and a large number of different lithologies were found some of these fragments are ureilitic in origin whereas others are clearly chondritic as all are relatively fresh w0 w0 1 and as short lived cosmogenic radioisotopes were detected within two of the chondritic fragments there is strong evidence that most if not all belong to the almahata sitta meteorite fall the fragments can roughly be subdivided into achondritic ureilitic 23 samples and chondritic lithologies 17 samples among the ureilitic rocks are at least 10 different lithologies a similar number of different chondritic lithologies also exist most chondritic fragments belong to at least seven different e chondrite rock types eh3 el3 4 el6 el breccias several different types of el and eh impact melt rocks and impact melt breccias some of the latter are shock darkened in addition two h group ordinary chondrite lithologies were identified and one sample of a chondrite type that is so far unique the latter has some affinities to r chondrites oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the almahata sitta meteorite based on the findings presented in this study the reflectance spectrum of asteroid 2008 tc3 has to be evaluated in a new light

influence of lateral heterogeneities on strong motion shear strains simulations in the historical center of rome italy abstract the influence of lateral heterogeneities on alluvial deposits is a topic of particular interest in the field of urban planning and engineering design of structures and infrastructures this work focuses on the effects of such heterogeneities on the shear strains produced within the recent alluvial deposits of the tiber river in the historical center of rome in case of the worst expected earthquake scenario to this aim a 3d engineering geology model of the subsoil is used to derive four geological sections across the tiber river valley as well as 48 soil columns to perform numerical simulations various models are considered a viscoelastic equivalent linear rheology in a 1d finite difference model for one component horizontal input a nonlinear elastoplastic model in a 1d finite element scheme for three component input and a nonlinear viscoelasto plastic rheology in a 2d finite difference model under one component horizontal input after comparing these different simulations results have shown that lateral heterogeneities play a key role with respect to the expected shear strains within multilayered soils to this aim some specific indexes are introduced to estimate the maximum shear strain mss concentration within the soil layers as well as to highlight their effect due to the stratigraphic position of the layers within the soil column independently from its depth a final differential index leads to the evaluation of the lateral heterogeneity effect on the estimated mss demonstrating their prevalent role with respect to the bedrock shape i e the angle of inclination of the buried valley slopes from these results an mss zoning map is obtained for the historical center of rome showing that the local seismic response should be modeled by assuming 1d or 2d conditions depending on the location considered

seismic wave propagation in alluvial basins and influence of site city interaction the geometrical and mechanical features of alluvial deposits have a major influence on seismic wave propagation and amplification however for alluvial basins located in densely urbanized areas the surface structures such as buildings could influence seismic wave propagation near the free surface in this article the influence of surface structures on seismic wave propagation is analyzed numerically in the case of an actual two dimensional 2d shallow basin at a local scale the vibration of a surface structure can induce a seismic wave field in the surficial soil layers at the scale of an alluvial basin the site city models considered herein show that the city effect can lead to a significant seismic wave field modification when compared to the free field case the coincidence between the fundamental frequencies of the soil layers and eigenfrequencies of the surface structures is a key parameter to investigate site city interaction when comparing simplified sitecity models kham et al 2006 to the basin city model the influence of the lateral heterogeneities on the site city interaction is found to be significant indeed the seismic wave field radiated by the city appears to be trapped within the alluvial basin and specific directivity features are found for this wave field the influence of site city interaction on the free field seismic hazard may then be significant the effects of the site city interaction are beneficial in some parts of the city or detrimental in other parts especially city boundaries these effects strongly depend on the urban configuration city heterogeneity building density etc finally the full characterization of the seismic wave field in densely urbanized areas could often raise the need for investigating site city interaction and consider such parameters as basin and city fundamental frequencies building density and city arrangement as well as basin effects combined with the seismic wave field radiated by the city

evaluation of soil building resonance effect in the urban area of the city of matera italy abstract this study discusses the effect of buildings vibrations in the urban field in the context of local seismic response studies in order to evaluate the possible occurrence of double resonance effects during strong motions the aim is to recognise the interaction effect between near surface geology and all overlying buildings in the urban area of the city of matera southern italy single station seismic ambient noise measurements 230 were performed on the main lythologies 134 and on the principal building typologies 96 soil and building measurements allowed estimating the main frequencies and relative amplitudes of the soil fundamental peaks as well as the first vibrational frequency of buildings the period height linear relationship derived by experimental results made it possible estimating the fundamental frequency for all the matera s buildings having also estimated the frequencies at each point of the urban soil it was thus possible to obtain a soil building resonance map in the linear elastic domain matera represents an important case study because the first vibration frequency for most of the buildings is quite close to those of the foundation soils about 21 of buildings show high probability of occurrence of soil building resonance effect about 63 of the buildings are characterised by a medium resonance level while about 16 are at zero or very low level the proposed approach makes it also possible to identify the areas of the city characterised by these different probabilities of resonance levels

seismic site city interaction main governing phenomena through simplified numerical models this work focuses on the analysis of the multiple interactions between soil layers and civil engineering structures in dense urban areas submitted to a seismic wave to investigate such phenomena called site city interaction sci herein two simplified site city configurations are considered a homogeneous periodically spaced city and a heterogeneous nonperiodically spaced city both on a constant depth basin model these 2d boundary element method models are subjected to a vertically incident plane sh ricker wavelet a parametric study of the city parameters density of buildings and their natural frequencies and the thickness of the basin is carried out to characterize the sci and to investigate its sensitivity to some governing parameters the following parameters are analyzed building vibrations induced ground motion ground motion perturbations inside and outside the city spatial coherency and kinetic energy of the urban wave field a so called site city resonance is reached when the soil fundamental frequency and structure eigenfrequencies coincide building vibrations and ground motion are then significantly decreased and the spatial coherency of the urban field is also strongly modified building density and city configuration play a crucial role in the energy distribution inside the city

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

a comparative study of opaque phases in qingzhen eh3 and macalpine hills 88136 el3 representatives of eh and el parent bodies opaque minerals in the qingzhen eh3 and macalpine hills mac 88136 el3 enstatite chondrites were studied and compared with other eh and el chondrites all opaque minerals usually occur in multi sulfide metal clasts and nodules in the matrix between chondrules el goresy et al 1988 the higher abundance of opaque minerals the occurrence of niningerite and various alkali sulfides e g caswellsilverite phases a and b djerfisherite are diagnostic criteria for eh chondrites while alabandite is characteristic for el chondrites in addition eh chondrites are characterized by enrichments of si in both kamacite and perryite and alkali elements in sphalerite and chalcopyrite the mn contents of daubreelite and sphalerite are lower in eh than in el chondrites these are consistent with lower oxygen fugacity and higher h2s fugacity of eh than el chondrites in contrast the discovery of sphalerite and zn rich daubreelite in mac 88136 indicates that their absence in el6 chondrites is probably related to thermal metamorphism in the parent body schreibersite microspherules are commonly enclosed in most sulfides in qingzhen but are absent in mac 88136 they were once molten and probably predated all sulfide host phases the petrographic setting and chemical compositions of the sulfide hosts of the schreibersite microspherules in eh3 chondrites are consistent with formation by condensation the earliest sulfide condensates oldhamite and niningerite occupy the interiors of the clasts and nodules whereas the rims consist of troilite and djerfisherite in addition in qingzhen some other troilite djerfisherite and sphalerite assemblages coexist with perryite they were produced by sulfurization of metallic fe ni in the nebula in mac 88136 sulfurization of si bearing fe ni metal is less pronounced and it produced troilite schreibersite and less abundant perryite two kinds of normal zoning and a reverse zoning trends of niningerite and both normal and reverse zoning of sphalerite were found in clasts and nodules in qingzhen the coexistence of normal and reverse zoning profiles in niningerite grains in the same meteorite strongly suggests that they formed before accretion in the parent body because an asteroidal metamorphic or an impact event in the parent body would have erased these contrasting profiles and destroyed the textural settings in contrast alabandite in mac 88136 shows only normal zoning with the fes content decreasing to 9 3 mol toward troilite indicating very slow cooling at low temperature

array analysis of the large aperture array of the 1988 89 passcal basin and range passive source seismic experiment summary the 1988 89 passcal basin and range passive source seismic experiment consisted of two array deployments the large and small aperture arrays the large aperture array consisted of seven stations with three component mid period seismometers and independently triggered prototype passcal data recorders with goes clocks the array spatial distribution and the synchronized data have permitted us to employ simple beamforming operations to improve receiver function estimation from single teleseismic events the beamforming reinforces the coherent teleseismic p wave and the deterministic portions of the p wave coda primarily generated by interactions at major lithospheric interfaces microseismic background noise is incoherent across the array and is attenuated by beamforming beamforming also diminishes those portions of the coda due to scattering by inhomogeneities that appear random on the scale of the array aperture the enhanced signal to noise ratio of the teleseismic recording dramatically improves the single event receiver function deconvolution results

petrography mineral chemistry and origin of type i enstatite chondrites abstract optical and cathodoluminescence petrography were coupled with electron microprobe analysis to relate the textures and chemical compositions of minerals in the chondrules and matrix of the indarch kota kota adhi kot and abee type i enstatite chondrites clinoenstatites fall into two distinct chemical groups with characteristic red or blue luminescence red crystals are higher in ti al cr mn and ca and lower in na than blue ones rare forsterites in indarch and kota kota show distinct compositions associated with orange or blue luminescence the chemical ranges are indistinguishable for each color type in chondrules of all textural types and the presence of both color types in a single chondrule or a metal fragment requires mechanical aggregation of both crystals and liquids of both color types porphyritic chondrules are ascribed mainly to aggregation of existing crystals because both types of pyroxene and olivine occur in the same chondrule large crystals of one color type are surrounded by fine grained crystals of another type in some barred and radiating chondrules all types of chondrules are surrounded by fine grained rims rich in sulfide the matrix contains many broken chondrules and individual silicate grains but is rich in sulfide and metal analyses are given of albite minor elements and luminescence color vary between chondrites kamacite schreibersite oldhamite and niningerite although the mineral assemblages do not fit theoretical condensation sequences in detail the red pyroxene and orange olivine might result ultimately from near equilibrium crystallization in which early reduced condensates reacted with a gas while the blue crystals might result from fractional condensation in which early condensates were removed mechanically from a gas subsequent episodes involving mixing melting crystallization condensation fracturing and mechanical aggregation would be needed to produce the complex textures

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

seismicity and tectonics of a continent island arc collision zone at the island of taiwan a collision between the eurasian plate continental margin and a volcanic island arc on the philippine sea plate about 4 m y ago uplifted the island of taiwan many lines of geological and geophysical evidence suggest that the collision is still active today and is currently propagating southward due to plate interaction geological and tectonic settings have become more complicated since the onset of the collision the collision suture is along the longitudinal valley lv in eastern taiwan seismic studies including earthquake monitoring and seismic refraction lines conducted in 1985 in eastern taiwan and its offshore area using land seismic stations and ocean bottom seismographs have generated results that better constrain the present day plate interaction both the crustal velocity structure and earthquake hypocenter distribution suggest that the subduction of the philippine sea plate along the ryukyu trench extends to the east coast of taiwan near about 23 5 n very high seismicity with dominant right lateral strike slip faulting is found in the back arc region behind the ryukyu trench this seismic activity is interpreted as a result of plate convergence and back arc wrenching due to the relative motion between the okinawa platelet and the eurasian plate the region close to the lv in eastern taiwan showed only shallow and a relatively low level of seismicity during this experiment with higher seismicity to the east of the lv the lack of intermediate depth events suggests that subduction is no longer active along the collision zone and the difference in seismicity between the regions east and west of the lv reflects the difference in strength of the adjacent continental and island arc crusts to the south of the lv seismicity continued southward with intermediate depth events distributed mainly to the east of taiwan along a nearly vertical benioff zone this supports the argument that convergence and collision are still active south of taiwan

crustal structure beneath taiwan using frequency band inversion of receiver function waveforms receiver function analysis is used to determine local crustal structure beneath taiwan we have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality receiver function analysis is then applied to data from the taiwan seismic network to obtain radial and transverse receiver functions due to the limited azimuthal coverage only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station in order to improve convergence of the receiver function inversion frequency band inversion fbi is implemented in which an iterative inversion procedure with sequentially higher low pass corner frequencies is used to stabilize the waveform inversion frequency band inversion is applied to receiver functions at six stations of the taiwan seismic network initial 20 layer crustal models are inverted for using prior tomographic results for the initial models the resulting 20 1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency band inversion for the six stations investigated the resulting simplified models provide an average estimate of 38 km for the moho thickness surrounding the central range of taiwan also the individual station estimates compare well with the recent tomographic model of and the refraction results of rau and wu 1995 and the refraction results of ma and song 1997

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

nature of volatile depletion and genetic relationships in enstatite chondrites and aubrites inferred from zn isotopes enstatite meteorites include the undifferentiated enstatite chondrites and the differentiated enstatite achondrites aubrites they are the most reduced group of all meteorites the oxygen isotope compositions of both enstatite chondrites and aubrites plot along the terrestrial mass fractionation line which suggests some genetic links between these meteorites and the earth as well for this study we measured the zn isotopic composition of 25 samples from the following groups aubrites main group and shallowater el chondrites eh chondrites and happy canyon impact melt breccia we also analyzed the zn isotopic composition and elemental abundance in separated phases metal silicates and sulfides of the eh4 el3 and el6 chondrites the different groups of meteorites are isotopically distinct and give the following values parts per thousand aubrite main group 7 08 delta zn 66 0 37 eh3 chondrites 0 15 delta zn 66 0 31 eh4 chondrites 0 15 delta zn 66 0 27 eh5 chondrites delta zn 66 0 27 0 09 n 1 el3 chondrites 0 01 delta zn 66 0 63 the shallowater aubrite 1 48 delta zn 66 2 36 el6 chondrites 2 26 delta zn 66 7 35 and the impact melt enstatite chondrite happy canyon delta zn 66 0 37 the aubrite pena blanca spring delta zn 66 7 0 parts per thousand and the el6 north west forrest delta zn 66 7 35 are the isotopically lightest and heaviest samples respectively known so far in the solar system in comparison the range of zn isotopic composition of chondrites and terrestrial samples 1 5 delta zn 66 1 parts per thousand is much smaller luck et al 2005 herzog et al 2009 eh and el3 chondrites have the same zn isotopic composition as the earth which is another example of the isotopic similarity between earth and enstatite chondrites the zn isotopic composition and abundance strongly support that the origin of the volatile element depletion between el3 and el6 chondrites is due to volatilization probably during thermal metamorphism aubrites show strong elemental depletion in zn compared to both eh and el chondrites and they are enriched in light isotopes delta zn 66 down to 7 04 parts per thousand this is the opposite of what would be expected if zn elemental depletion was due to evaporation assuming the aubrites started with an enstatite chondrite like zn isotopic composition evaporation is therefore not responsible for volatile loss from aubrites on earth zn isotopes fractionate very little during igneous processes while differentiated meteorites show only minimal zn isotopic variability it is therefore very unlikely that igneous processes can account for the large isotopic fractionation of zn in aubrites condensation of an isotopically light vapor best explains zn depletion and isotopically light zn in these puzzling rocks mass balance suggests that this isotopically light vapor carries zn lost by the el6 parent body during thermal metamorphism and that aubritcs evolved from an el6 like parent body finally zn isotopes suggest that shallowater and aubrites originate from distinct parent bodies

ree and actinide microdistribution in sahara 97072 and alha77295 eh3 chondrites a combined cosmochemical and petrologic investigation abstract we report the results of rare earth elements rees and u th inventory of individual minerals oldhamite enstatite and niningerite in two of the most unequilibrated and primitive eh3 known so far alha77295 and sahara 97072 under the highly reducing condition that prevailed during the formation of enstatite chondrites rees are mainly chalcophile and concentrated in oldhamite the study is guided by detailed petrographic investigations of the individual minerals in chondrules complex sulfide metal clasts and enstatite dominated matrices we developed two textural parameters in order to resolve the evolution of oldhamite condensates and their residence in the solar gas prior to their accretion in the individual objects or in matrices and relate these textural features to the measured ree patterns of the individual oldhamite crystals these textural parameters are the crystal habit of oldhamite grains idiomorphic or anhedral and their host assemblages ree concentrations were measured by sims and la icpms oldhamite grains display ree enrichments 10 100 ci four types of ree patterns are encountered in oldhamite in alha77295 in general the ree distributions cannot be assigned to a specific oldhamite bearing assemblage the most represented ree pattern is characterized by both slight to large positive eu and yb anomalies and is enriched in light rees relative to heavy rees this pattern is present in 97 of oldhamite in sahara 97072 suggesting a different source region in the reduced part of the nebula or different parental eh asteroids for the two eh3 chondrites different parental asteroids are also supported by mgs fes zoning profiles in niningerite grains adjacent to troilite revealing both normal and reverse zoning trends and different mns contents the observed homogeneity of ree distribution in oldhamite grains in sahara 97072 is not related to the mild metamorphic event identified in this meteorite that caused breakdown of the major k and rb bearing sulfide djerfisherite ree concentrations in enstatite range between 0 2 and 8 ci hence enstatite is an important ree host next to oldhamite most patterns are characterized by negative eu and yb anomalies niningerites are negligible contributors to bulk eh3 ree inventory average positive eu and yb anomalies observed in most oldhamite are complimentary to the negative ones in enstatite thus explaining the flat patterns of the bulk meteorites the condensation calculations based on cosmic abundances predict that the first oldhamite condensates should have flat ree patterns with eu and yb depletions since eu and yb condense at lower temperature than other ree however this pattern is seen in enstatite our findings are at odds with the predicted negative eu and yb anomalies in oldhamite earliest condensates from a closed system in a reduced solar source our petrographic mineral chemistry and ree abundances of oldhamite enstatite and niningerite discards an origin of oldhamite by impact melting rubin et al 2009 our results do not support in first order the scenario of the incorporation of ree in the earth s core to explain 142nd excess in terrestrial samples relative to chondrites because oldhamite is the major ree carrier phase and has super chondritic sm nd ratios

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny