a compositional classification scheme for meteoritic chondrules a taxonomic scheme is proposed for the main component of the primitive chondrite meteorites the chondrules the scheme provides insight into the variety of chondrules originally produced in the primordial solar nebula and the effects on them of secondary processes on meteorite parent bodies it may also contribute to understanding the origin of compositional diversity in the chondrites

comment on temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw 7 1 hector mine earthquake by su et al 2013 we review the recent paper by su et al 2013 using global position system and global ionospheric maps data su et al claimed to have found ionospheric precursors a few days before the 16 october 1999 hector mine california earthquake they proposed that this type of analysis of ionospheric data may be useful for locating forthcoming large earthquakes in this comment we reexamine these data and show that ionospheric anomalies reported by su et al were not precursors to the hector mine earthquake therefore their proposed analysis is not useful in the context of earthquake prediction

empirical predictive models for earthquake induced sliding displacements of slopes earthquake induced sliding displacement is the parameter most often used to assess the seismic stability of slopes the expected displacement can be predicted as a function of the characteristics of the slope yield acceleration and the ground motion e g peak ground acceleration yet there is significant aleatory variability associated with the displacement prediction using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2 000 acceleration time histories and four values of yield acceleration these empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement with the goal of minimizing the standard deviation of the displacement prediction the combination of peak ground acceleration and peak ground velocity is the tw

seismic damage and behavior analysis of earth dams during the 2008 wenchuan earthquake china abstract the may 12 2008 ms 8 0 wenchuan great earthquake china caused earthquake damages of 2666 earth dams these damaged dams are in medium and small scale located in 8 provinces or municipalities of which 69 dams were at dam break risk and 331 were at high risk there were 1996 damaged dams located in sichuan province including all the 69 at dam break risk and 310 at high risk through a detailed scientific investigation earthquake damage and emergency data were collected and the isoseismal map of wenchuan earthquake with damaged dams marked on it was given also distribution feature of the above 69 dams along the fault zones were discussed typical damage types of earth dams were analyzed and the action of rare great earthquake poor quality of dam construction adverse running state of earth dams before earthquake and frequent aftershocks were concluded as four main reasons of dam damages taking 147 dams with complete geometric parameters as statistical samples some empirical graphic formulas were proposed to make rapid evaluation of damage degree finally some useful practical measures were provided to serve the post earthquake emergency danger removal also it may improve the seismic performance of dams in view of the insufficiency of local geology site effect and soil property data of damaged dams application of the qualitative results and empirical relationships to other sites should be very prudent

composition of chondrule silicates in ll3 5 chondrites and implications for their nebular history and parent body metamorphism our petrologic studies of 75 type ia and type ii porphyritic olivine chondrules in nine selected ll group chondrites of type 3 3 to type 5 and comparisons with published studies of chondrules in semarkona ll3 0 show that compositions of silicates and bulk chondrules but not overall chondrule textures vary systematically with the petrologic type of the chondrite these compositional trends are due to diffusive exchange between chondrule silicates and other phases e g matrix such as those now preserved in semarkona during which olivines in both chondrule types gained fe2 and mn2 and lost mg2 cr3 and ca2 in a given ll4 5 chondrite the olivines from the two chondrule types are identical in composition enrichments of fe2 in olivine are particularly noticeable in type ia chondrules from type 3 3 3 6 chondrites especially near grain edges chondrule rims grain boundaries and what appear to be annealed cracks compositional changes in low ca pyroxene lag behind those in coexisting olivine consistent with its lower diffusion rates with increasing petrologic type low ca pyroxenes in type ia chondrules become enriched in fe2 and mn2 and depleted in mg2 cr3 and a13 these compositional changes are entirely consistent with mineral equilibration in chondritic material during metamorphism from these compositional data alone we cannot exclude the possibility that chondritic material was metamorphosed to some degree in the nebula but we see no evidence favoring nebula over asteroidal metamorphism nor evidence that the chondrule reacted with nebular gases after crystallization modelling of the equilibration of chondrule olivines suggests that heterogeneous feo concentrations in olivine could be preserved after cooling from 600 c at rates of 1 10 c ma for at least tens to hundreds of millions of years this is consistent with published estimates for the maximum metamorphic temperatures in type 3 chondrites thermal histories derived from metallographic and fission track cooling rates and 4 4 ga 40ar 39ar ages for ordinary chondrites since the lifetime of the solar nebula was not more than 106 years and there is abundant evidence that meteorite parent bodies were heated some even above their melting point we confidently conclude that the formation of type 3 3 5 ordinary chondrites from type 3 0 material by metamorphism occurred in parental asteroids not the solar nebula

dynamic crystallization of chondrule melts of porphyritic and radial pyroxene composition abstract dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures without preexisting nuclei too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial in the near total absence of nuclei radial textures can form at cooling rates as slow as 5 c hr in this study by varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable analogs to most of the recognized chondrule textures can be produced in a single melt composition olivine inclusions in pyroxene can form readily during an experiment from a starting material which did not initially contain olivine crystals thus care must be taken in the assumption that olivine inclusions in pyroxene represent preexisting crystals

ionospheric electron enhancement preceding the 2011 tohoku oki earthquake 1 the 2011 march 11 tohoku oki earthquake mw9 0 caused vast damages to the country large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics and here i report one such finding the japanese dense network of global positioning system gps detected clear precursory positive anomaly of ionospheric total electron content tec around the focal region it started 40 minutes before the earthquake and reached nearly ten percent of the background tec it lasted until atmospheric waves arrived at the ionosphere similar preseismic tec anomalies with amplitudes dependent on magnitudes were seen in the 2010 chile earthquake mw8 8 and possibly in the 2004 sumatra andaman mw9 2 and the 1994 hokkaido toho oki mw8 3 earthquakes but not in smaller earthquakes

a statistical investigation of preearthquake ionospheric anomaly 1 empirical evidence of the preearthquake ionospheric anomalies peias is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric f2 peak fof2 and 184 earthquakes with magnitude m 5 0 during 1994 1999 in the taiwan area the peia defined as the abnormal decrease more than about 25 in the ionospheric fof2 during the afternoon period 1200 1800 lt significantly occurs within 5 days before the earthquakes moreover the odds of earthquakes with peia increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station these results indicate that the peia is energy related

origin of a unique impact melt rock the l chondrite ramsdorf we have studied a unique impact melt rock the ramsdorf l chondrite using optical and scanning microscopy and electron microprobe analysis ramsdorf contains not only clast poor impact melt begemann and wlotzka 1969 but also a chondritic portion 60 g with what appears at low magnification to be a normal well defined chondritic texture however detailed studies at high magnification show that 90 vol of the crystals in the chondritic portion were largely melted by the impact the chondrules lack normal microtextures and are ghosts of the original features the only relics from the precursor chondrules are olivine crystals which have the highest melting temperature 1620 c pyroxene rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine rich melts fine grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts probably because pyroxene rich melts are significantly more viscous complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of ramsdorf formed directly from petrologic type 3 4 material by strong shock we infer that ramsdorf was largely melted by shock pressures of 75 90 gpa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture

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

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

ubiquitous high feo silicates in enstatite chondrites our electron microprobe studies of four type 3 enstatite chondrites show that olivines and low ca pyroxenes with more than 3 wt feo are more abundant than previously recognized 4 8 of clear pyroxene grains and a higher proportion of dusty pyroxenes have fs 5 20 from scanning electron microscope and electron probe surveys of these four eh3 chondrites we discovered 542 objects that contain silicates very largely pyroxene with 3 wt feo 18 chondrules 381 rimmed or unrimmed grains and 143 mineral aggregates with fs 5 27 pyroxene or fa 3 14 olivine aggregates and grains may have been derived from chondrules by comminution rims of enstatite with fs 0 3 on many grains formed by reduction or growth in the nebula or parent body in two eh4 5 chondrites we identified 89 feo rich objects that are all enstatite grains with fs 1 10 having feo poor enstatite rims which grew during planetary metamorphism two of the 18 feo rich chondrules in eh3 chondrites have textures and mineral compositions that are consistent with crystallization of feo rich melts in others these textures are modified by nebula or planetary reduction along cracks and grain edges that formed low feo silicates and metallic fe ni however several feo rich chondrules contain crystals of both high and low feo silicates that appear to have igneous origins but could not have formed by closed system crystallization of chondrule melts these probably reflect either reduction of chondrule melts by the nebula during crystallization or collisions of partly molten chondrules having very different feo concentrations an origin involving partial melting of chondrule precursor grains seems less plausible

reply to comment by f masci and j n thomas on temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw7 1 hector mine earthquake

cooling history of pyroxene chondrules in the yamato 74191 chondrite l3 an electron microscopic study abstract fine textures of clinopyroxene in an excentroradial pyroxene chondrule epc and a comb like pyroxene chondrule cpc in the yamato 74191 chondrite l3 have been studied by analytical electron microscopy both pyroxenes consist of three regions different in composition and texture core mantle and marginal regions though the pyroxenes of the cpc are more fe rich than those of the epc the core region is the most mg rich with no ca component and commonly shows polysynthetic 100 twins the mantle region is slightly calcic and the marginal region shows a rapid increase of ca outward the polysynthetic twins cracks and subgrain boundaries in the core in the epc and cpc must have formed during the transition from proto type to clino type pyroxenes the exsolution textures in the mantle and marginal regions indicate initial crystallization of pigeonite c followed by decomposition into pigeonite p and augite the decomposition must have taken place by nucleation growth in the mantle region and by spinodal decomposition in the marginal region the periodicity of 15 20 nm in the spinodal decomposition textures indicates that the cooling rate of the pyroxenes when passing through about 1000 c was of the order of a few tens to several degrees centigrade per hour the cooling history of the chondrules has been explained by a monotonous cooling controlled by the cooling rate of the surrounding medium

petrology of feo poor porphyritic pyroxene chondrules in the semarkona chondrite abstract the mineralogy and petrology of feo poor porphyritic pyroxene and olivine rich chondrules in the semarkona ll3 0 chondrite are described in detail in an extension of the textural classification scheme these chondrules are designated types iab and ib in type iab chondrules the proportion of olivine phenocrysts is between 20 80 and in type ib chondrules olivine constitutes

a correlation for permanent earthquake induced deformation of earth embankments abstract seismic design of earth dams and embankments is mainly controlled by the permanent deformation that may be induced directly or indirectly because of the design earthquake simple design charts such as those developed by yegian et al yegian m k marciano e a and ghahraman v g 1991 earthquake induced permanent deformations probabilistic approach j geotech eng 117 35 50 hynes griffin and franklin hynes griffin m e and franklin a g 1984 rationalizing the seismic coefficient method miscellaneous paper gl 84 13 us army corps of engineers waterways experiment station vicksburg mississippi makdisi and seed makdisi f i and seed h b 1978 simplified procedure for estimating dam and embankment earthquake induced deformations j geotech eng 104 849 867 and sarma sarma s k 1975 seismic stability of earth dams and embankments geotechnique 25 743 761 are often used to obtain a preliminary estimate of the permanent earthquake induced deformation of earth dams and embankments comparison of permanent deformations estimated from these procedures with observations from 122 published case histories on performance of earth dams and embankments during past earthquakes indicate that the estimated permanent earthquake induced deformations were in general smaller than the observed deformations however the observed permanent deformation davg was found to relate to the ratio of yield acceleration ay and the peak horizontal ground acceleration amax the scatter in the observational data upon which the davg ay amax relationship is based can be partly explained by the variations in the ratio of the fundamental elastic period of the earth structure td and the predominant period of the earthquake ground motion tp and the magnitude of the earthquake mw

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

the motion and active deformation of india measurements of surface displacements using gps constrain the motion and deformation of india and india eurasia plate boundary deformation along the himalaya the gps velocities of plate interior sites constrain the pole of the angular velocity vector of india with respect to eurasia to lie at 25 6 1 0 n 11 1 9 0 e approximately 6 west of the nuvel 1a pole of 3 ma plate motion the angular rotation rate of 0 44 0 03 myr 1 is 14 slower than the long term rate of 0 51 myr 1 insignificant velocities between plate interior sites indicate that the exposed indian plate is stable to within 7 10 9 yr 1 the observed contraction vector across the himalaya 20 mm yr veers from n20 e in the northwest himalaya to n25 w in east nepal consistent with east west extension of southern tibet

on the reported ionospheric precursor of the 1999 hector mine california earthquake 1 using global positioning system gps data from sites near the 16 oct 1999 hector mine california earthquake pulinets et al 2007 identified anomalous changes in the ionospheric total electron content tec starting one week prior to the earthquake pulinets 2007 suggested that precursory phenomena of this type could be useful for predicting earthquakes on the other hand and in a separate analysis afraimovich et al 2004 concluded that tec variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake in an investigation of these very different results we examine tec time series of long duration from gps stations near and far from the epicenter of the hector mine earthquake and long before and long after the earthquake while we can reproduce the essential time series results of pulinets et al we find that the signal they identified as being anomalous is not actually anomalous instead it is just part of normal global scale tec variation we conclude that the tec anomaly reported by pulinets et al is unrelated to the hector mine earthquake

the ionospheric anomalies prior to the m9 0 tohoku oki earthquake the gps total electron content tec data were used to investigate the ionospheric abnormal behaviors prior to the 2011 tohoku oki earthquake the observations show a significant enhancement in tec on march 8 2011 and during the same period the solar activity also has a large increase both an empirical model and a theoretical model were used to check whether the tec anomalies were entirely contributed by the increase in solar radiation the comparison between the observations and the simulation results shows that only the solar radiation enhancement was not enough to produce the observed significant tec enhancement it means that some additional mechanisms such as the per earthquake ionospheric disturbance or the geomagnetic activities may play a significant role in the significant tec enhancement on march 8 the temporal spatial distribution of the extreme tec enhancement within 30 days before the earthquake was particularly pursued it is found that the extreme enhancement was persistently located in the region adjacent to the epicenter and the magnetic conjugate point for a long time of 16 h in addition a geomagnetic disturbance with kp 4 occurred on march 7 therefore the significant tec enhancement on march 8 might be related to the m9 0 tohoku oki earthquake and the geomagnetic disturbance

observations and simulations of seismoionospheric gps total electron content anomalies before the 12 january 2010 m7 haiti earthquake 1 in this paper the total electron content tec of the global ionosphere map gim is used to detect seismoionospheric anomalies associated with the 12 january 2010 m7 haiti earthquake and an ionospheric model is applied to simulate the detected anomalies the gim temporal variation shows that the tec over the epicenter significantly enhances on 11 january 2010 1 day before the earthquake the latitude time tec ltt plots reveal three anomalies 1 the northern crest of equatorial ionization anomaly eia moves poleward 2 the tecs at the epicenter and its conjugate increase and 3 the tecs at two dense bands in the midlatitude ionosphere of 35 n and 60 s further enhance the spatial analysis demonstrates that the tec enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area the simulation well reproduces the three gim tec anomalies which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period

the study of ionospheric anomalies in japan area during 1998 2010 by kon et al an inaccurate claim of earthquake related signatures abstract the problem of identifying precursory signals of earthquakes in the hope of mitigate the seismic hazard is a very important topic but inaccurate documentations of precursory signatures decrease the credibility of this field of research the statistical analysis by kon et al 2011 shows that there is tendency of positive total electron content tec anomalies to occur 1 5 days before 52 m 6 earthquakes which struck japan during 1998 2010 kon et al 2011 also report in detail three selected case studies claiming the occurrence of tec anomalies possibly related to large and destructive earthquakes this paper casts doubts on the possibility that in the three cases the tec disturbances were caused by seismic events suggesting that these tec changes could be induced by normal variations of the global geomagnetic activity as a consequence also the results of the superimposed epoch analysis performed by kon et al 2011 could be seriously influenced by global magnetospheric signals

aqueous alteration of chondrules in the cm carbonaceous chondrite allan hills 81002 implications for parent body alteration abstract alh 81002 is a cm carbonaceous chondrite that has petrographic characteristics suggesting that it experienced a high degree of aqueous alteration but has entirely escaped parent body brecciation in this study we report the results of a systematic investigation of the alteration of more than 35 chondrules in alh 81002 that belong to specific well defined chondrule types our results show that the extent of chondrule alteration is almost exclusively controlled by the properties of the chondrule phases although these chondrules taken as a group show highly variable degrees of alteration no evidence for differences in the alteration histories of chondrules has been found instead the widely varying rates of alteration of chondrule phases such as forsteritic and fayalitic olivine clinoenstatite orthopyroxene and augite are sufficient to explain the diversity of chondrule alteration in alh 81002 chondrules with similar primary textural and mineralogical characteristics e g type ia type iia etc show remarkably similar degrees of alteration detailed studies of the alteration products of chondrules show that they retain a detailed record of the alteration history of the chondrules from the earliest to last stages and provide strong evidence for the compositional evolution of the altering fluid contrary to what might be expected the fluid composition appears to be the dominant controlling factor on the composition of serpentines that replace olivines pyroxenes and mesostasis the consistent degree of alteration observed in chondrules of the same type in alh 81002 indicates that they were altered under the same conditions for similar lengths of time such conditions are most consistent with alteration in a parent body environment in addition the compositional and textural uniformity of rim material chondrule alteration phases and vein fillings in chondrule components throughout alh 81002 also argue strongly that alteration occurred after accretion several observations on alh 81002 provide additional constraints and modifications on existing models of in situ parent body alteration for example inferences on the degree of alteration of cm chondrites based on the extent of brecciation as a parameter of the alteration degree appear to be compromised in addition models which suggest that tochilinite serpentine pcp rich objects have resulted from the break up of chondrules during brecciation are also inconsistent with our observations on alh 81002

fayalite silica association in unequilibrated ordinary chondrites evidence for aqueous alteration on a parent body we report ten occurrences of high fayalite fa56 99 mol four with fa 82 mol olivine in association with silica in type 3 ordinary chondrites pyroxene with high fs contents is much less common fs contents do not exceed 66 mol and most maxima are 50 mol in those cases where the amount of fayalite is minor relative to that of silica the fayalite forms a layer on the silica and shows textural evidence of formation by reaction of silica with oxidized fe the latter seems to have resulted from reaction of metallic fe ni with an oxidant most likely h2o vapor the fayalite is generally in contact with pyroxene and in one case olivine having much lower fe fe mg ratios indicating that lattice diffusion has been minimal formation of fayalite from sio2 explains the low mg content of this olivine the mg was sequestered inside the lattices of mafic minerals and was thus inaccessible in contrast the moderately high mn contents of the fayalite indicate that an appreciable fraction of the mn in the precursor assemblage was accessible it was probably sited in the matrix in the form of tiny poorly crystallized oxide grains produced by nebular condensation at temperatures too low to permit diffusion into forsterite or enstatite the reaction of sio2 with feo produced by oxidation during metamorphism of fe ni can also account for fayalitic olivine associated with sio2 microspherules in the fine grained matrices of type 3 ordinary chondrites and because matrix is sio2 normative for other occurrences of fayalite in matrix the presence of mn in the fayalitic rims on the olivine of carbonaceous chondrites does not require a nebular origin

oscillatory zoning in meteoritic forsterite some isolated forsterite grains in allende c3v and alha 76004 ll3 show oscillatory zoning when viewed with cathodoluminescence concentration profiles for these grains show that the oscillations correspond to cyclic variations in al and ti and by inference with known correlations v and sc other elements including mg fe ca and cr show only monotonic changes across the oscillatory zoned area under reducing conditions assumed present during forsterite growth the varying elements should be trivalent or higher in charge whereas the mg fe ca cr group would be divalent substitution into the olivine structure is considered to be two trivalent elements dominated by ai for mg si which represents a small substitution of the spinel component into forsterite this same type of substitution is proposed for similar terrestrial oscillatory zoned olivines in which no fe or mg variation is found by analogy with terrestrial and lunar oscillatory zoned minerals crystallization of the forsterite from a liquid is probable currently no such source material is known although crystallization of porphyritic chondrules may produce grains of equivalent size with zoning although no oscillatory zoned forsterite has been observed in chondrules their recognition may be confirmation of the source of isolated forsterite grains alternatively the source of these forsterite grains has not yet been recognized

oscillatory zoning of mn in solution grown calcite crystals abstract oscillatory zoning of mn in calcite was produced in free drift solution growth experiments the repetitive mn doped subzones imaged using cathodoluminescence microscopy are not correlated with external controls or perturbations and they generally cannot be correlated between crystals the fluctuations causing the oscillatory zoning form autonomously in a system far from equilibrium and represent an example of self organization

characteristics of deformation and past seismicity associated with the 1819 kutch earthquake northwestern india the 1819 earthquake in kutch northwestern india is one of the most significant events to have occurred in a plate interior setting despite being the second largest among the stable continental region scr earthquakes this event has not been analyzed within the context of present day understanding of earthquake seismology coseismic changes related to this earthquake include massive ground deformation in a wide low lying tidal flat area although detailed historic accounts of this earthquake exist many questions regarding the mode of deformation and the seismic history of the region remain unresolved we explored the region nearly 180 years after the earthquake and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone a 90 km long tract of elevated land with a peak height of 4 3 m is the most visible surface expression of this earthquake we surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region the scarp morphology is suggestive of a growing fold related to a buried north dipping thrust rather than a discrete fault that could have resulted from a surface rupture the extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history age data of liquefaction features suggest that a previous event of comparable size must have occurred 800 1000 years ago seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north south compression

chondrules as products of dust collisions with totally molten droplets within a dust rich nebular environment an experimental investigation abstract chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting if barred olivine bo chondrules formed by nearly total melting at their respective liquidi i e over a wide temperature range it is surprising that there are so few totally glassy chondrules the occurrence of fine grained accretionary rims on chondrules suggests mineral dust in the chondrule forming environment which might have collided with totally molten droplets to produce chondrule textures we have therefore conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500 c h and cause nucleation our experiments reproduce the majority of common chondrule textures the production of textures in our experiments is a function of the temperature at which dust is encountered the number of dust grains encountered and to a lesser extent the mineralogy of the encountered mineral grains crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters we have produced some less commonly discussed types of chondrule textures e g barred olivine porphyritic olivine pyroxene bo pop by dust seeding that have not been reproduced by the incomplete melting of starting materials the reproduction of bo pop and excentroradial textures by dust collisions and the scarcity of natural totally glassy chondrules suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures e g feo rich chondrules from these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs however we have reproduced the very fine grained microporphyritic textures characteristic of type ia chondrules only by incomplete melting such chondrules could not have reached average internal temperatures above their liquidus temperatures the conclusion that at least some chondrules formed from total melts that collided with mineral dust during cooling indicates that chondrule formation occurred within a region of the nebula rich in mineral dust

preseismic ionospheric electron enhancements revisited 1 possible enhancement of ionospheric total electron content tec immediately before the 2011 tohoku oki earthquake mw9 0 has been reported by heki 2011 critical responses to it often come in two stages they first doubt the enhancement itself and attribute it to an artifact second when they accept the enhancement they doubt the significance of the enhancement among natural variability of space weather origin for example kamogawa and kakinami 2013 attributed the enhancement to an artifact falsely detected by the combined effect of the highly variable tec under active geomagnetic condition and the occurrence of a tsunamigenic ionospheric hole here we closely examine the time series of vertical tec before and after the 2011 tohoku oki earthquake we first demonstrate that the tsunami did not make an ionospheric hole and next confirm the reality of the enhancement using data of two other sensors ionosonde and magnetometers the amplitude of the preseismic tec enhancement is within the natural variability and its snapshot resembles to large scale traveling ionospheric disturbances however distinction could be made by examining their propagation properties similar tec anomalies occurred before all the m 8 5 earthquakes in this century suggesting their seismic origin

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

trace element geochemistry of ordinary chondrite chondrules the type i type ii chondrule dichotomy we report trace element concentrations of silicate phases in chondrules from ll3 ordinary chondrites bishunpur and semarkona results are similar to previously reported data for carbonaceous chondrites with rare earth element ree concentrations increasing in the sequence olivine 10 k h than type i chondrules appreciable na concentrations 3 221 ppm are measured in olivine from both chondrule types type ii chondrules seem to have behaved as closed systems which may require chondrule formation in the vicinity of protoplanets or planetesimals at any rate higher solid concentrations in type ii chondrule forming regions may explain the higher oxygen fugacities they record compared to type i chondrules type i and type ii chondrules formed in different environments and the correlation between high solid concentrations and or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for

is an unusual large enhancement of ionospheric electron density linked with the 2008 great wenchuan earthquake 1 on 12 may 2008 at 0628 ut a major earthquake ms 8 0 struck wenchuan county 31 0 n 103 4 e in southwest china the maximum ionospheric electron density at f2 peak nmf2 recorded an unusual large enhancement during the afternoon sunset sector by the chinese ionosondes over wuhan 30 5 n 114 4 e and xiamen 24 4 n 123 9 e which are close to the earthquake epicenter an averaged increase at these two stations is about 2 times on a geomagnetic quiet day 9 may kp 2 3 days prior to the earthquake relative to the median value of 1 12 may whereas the increase was much less significant over yamagawa 31 2 n 130 6 e and okinawa 26 7 n 128 2 e in japan combining the data from the network of 58 global positioning system receivers around china and the global ionospheric map the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90 130 e our results suggest that this abnormal enhancement is most possibly a seismo ionospheric signature

chondrules and other components in c o and e chondrites similarities in their properties and origins we describe three types of chondrules that are common to h3 ll3 cm2 co3 and cv3 chondrites low and high feo porphyritic olivine chondrules contain olivine with fa0 3 8 and fa5 50 respectively and can easily be distinguished petrographically poikilitic pyroxene chondrules have 1 20 vol olivine fa0 2 8 enclosed by low ca pyroxene fs0 5 7 and also occur in e chondrites these three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups metallic fe ni grains containing 0 1 1 cr si and p are present in low feo olivine chondrules from all type 2 and least metamorphosed type 3 chondrites metal compositions reflect reduction during chondrule formation in the nebula not nebular condensation opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy and probably have related origins we conclude that chondrules in all known chondrite groups share similar nebular origins

strong ground motion estimation during the kutch india earthquake in the absence of strong motion records ground motion during the 26th january 2001 kutch india earthquake has been estimated by analytical methods a contour map of peak ground acceleration pga values in the near source region is provided these results are validated by comparing them with spectral response recorder data and field observations it is found that very near the epicenter pga would have exceeded 0 6 g a set of three aftershock records have been used as empirical green s functions to simulate ground acceleration time history and 5 damped response spectrum at bhuj city it is found that at bhuj pga would have been 0 31 g 0 37 g it is demonstrated that source mechanism models can be effectively used to understand spatial variability of large scale ground movements near urban areas due to the rupture of active faults

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

gradual reduction in ionospheric f 2 region before the 2013 lushan earthquake contributed to the forthcoming earthquake or solar activity ionospheric anomalies before earthquakes during geomagnetic quiet conditions have been extensively discussed due to the importance of earthquake prediction however because of the high variability of ionosphere a real caution should be adopted before attributing the observations to seismo ionospheric precursors sips in an investigation of contradictory results in ionospheric variation before 2013 lushan earthquake we examine the ionospheric variation versus solar activity in order to assess the influence of solar activity of 27 day periodicity on ionospheric variation a quadratic regression model is developed by using the data of f2 layer critical frequency fof2 in april of 2008 2014 using the model ionospheric variation before the 2013 lushan earthquake is analyzed the results show that fof2 was strongly correlated with solar activity index f10 7 and had a low correlation with the remaining by eliminating the contribution of solar radiation which indicates that the gradual reduction in fof2 before the earthquake was contributed to the variation of solar radiation rather than the forthcoming earthquake

seismo ionospheric signatures prior to m 6 0 taiwan earthquakes this paper examines variations of the greatest plasma frequency in the ionosphere fof2 recorded by the chung li ionosonde 25 0 n 121 1 e before m 6 0 earthquakes during 1994 1999 the 15 day running median and the associated inter quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric fof2 variations for finding seismo ionospheric signatures precursors of the earthquakes it is found that precursors in the form of the recorded fof2 falling below its associated lower bound around 1200 1700 lt appear 1 6 days prior to these earthquakes on september 20 1999 ut september 21 taiwan local time a large mw 7 7 earthquake struck central taiwan near the small town of chi chi we analyzed the fof2 and found three clear precursors 1 3 and 4 days prior to the chi chi earthquake

formation conditions of pyroxene olivine and magnesian olivine chondrules abstract dynamic crystallization experiments performed on a type i and an intermediate type ii iii composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei this factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time glassy and excentroradial textures form from superheated melts with no nuclei and barred textures form with initial temperatures near the olivine disappearance temperature porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000 c h whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000 c h texture composition relationships suggest chondrules experienced initial temperatures below 1750 c these observations are consistent with the idea that chondrules formed by transient heating in dust rich regions i e in the midplane of the solar nebula

is an ionospheric electron enhancement preceding the 2011 tohoku oki earthquake a precursor 1 heki 2011 reported that the tec gradually enhanced from 40 minutes before the 2011 m9 0 off the pacific coast of tohoku earthquake tohoku eq to the time when the co seismic acoustic wave reached the ionosphere and the tec immediately recovered at the normal state this paper shows an alternative interpretation of total electron content tec variation in the ionosphere associated with the tohoku eq our interpretation is that a tsunamigenic ionospheric hole a wide depletion of the tec occurred after the co seismic acoustic wave reached the ionosphere and gradually recovered at the normal state with several tens of minutes kakinami et al 2012 the difference between heki 2011 and kakinami et al 2012 is attributed to the reference curves of the tec to extract the ionospheric variations the former is given by the least squares fitting curve of the eq day data excluding an expected precursor period while the latter is given by the data of the similar orbit of global positioning system gps satellite on another day the results suggest that variation of slant tec is explained by the depletion of tec due to tsunami rather than the precursory enhancement

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

chondrule formation metamorphism brecciation an important new primary chondrule group and the classification of chondrules abstract the recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases olivine or pyroxene and the mesostasis both of which are genetically important the scheme is here applied to discussions of three topics the petrographic classification of roosevelt county 075 the least metamorphosed h chondrite known brecciation an extremely important and ubiquitous process probably experienced by 40 of all unequilibrated ordinary chondrites and the group a5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed equilibrated chondrites since composition provides insights into both primary formation properties of the chondrules and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of rc075 as 3 1 with unique certainty similarly the new scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite which makes it especially suitable for studying breccias finally the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important like group a1 and a2 chondrules but unlike group b1 chondrules the primitive group a5 chondrules did not supercool during formation but unlike group a1 and a2 chondrules and like group b1 chondrules they did not suffer volatile loss and reduction during formation it is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes

feo rich porphyritic pyroxene chondrules in unequilibrated ordinary chondrites abstract a suite of feo rich type ii porphyritic olivine pyroxene pop chondrules has been studied in detail data for ten chondrules from semarkona ll3 0 are emphasized and one chondrule from chainpur ll3 4 and two from parnallee ll3 6 are included as further examples of certain properties the chondrules contain phenocrysts of pyroxene and olivine in varying proportions and have fe fe mg 10 mol in the silicate minerals four pyroxene minerals are present clinoenstatite orthorhombic enstatite pigeonite and augite pyroxene phenocrysts may consist of all four minerals with progressive overgrowths in order of increasing wo content enstatite may occur independently of clinoenstatite but ca rich pyroxenes pigeonite and augite always nucleate on low ca pyroxene phenocrysts pyroxene and olivine phenocrysts may be independent of each other or may be intergrown and commonly show hopper morphologies indicative of rapid growth pyroxenes and olivines are commonly strongly zoned as a result of fractional crystallization of the chondrules in addition low ca pyroxene may contain ghost regions of slightly more feo and minor element rich material in the cores of grains these regions are partially resorbed and appear to be derived from previous crystallization of essentially the same chondrule oscillatory zoning is observed in enstatite in two chondrules and is believed to be the result of disquilibrium kinetic effects relict grains including a forsterite relict and a partially reduced feo rich relict in the same chondrule and clinoenstatite cores of pyroxene phenocrysts in another chondrule are evidence for recycling and mixing of chondrule material all of the chondrules are highly disequilibrium assemblages they appear to have cooled from essentially molten droplets with little volatile loss or recondensation occurring during the heating event peak temperatures were probably close to liquidus temperatures 1500 1700 c and cooling rates were probably of the order of hundreds of degrees per hour this description will serve as a basis for future interpretation of the effects of metamorphism on porphyritic pyroxene rich chondrules

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

cooling rates of porphyritic olivine chondrules in the semarkona ll3 00 ordinary chondrite a model for diffusional equilibration of olivine during fractional crystallization cooling rates of chondrules provide important constraints on the formation process of chondrite components at high temperatures although many dynamic crystallization experiments have been performed to obtain the cooling rate of chondrules these only provide a possible range of cooling rates rather than providing actual measured values from natural chondrules we have developed a new model to calculate chondrule cooling rates by using the fe mg chemical zoning profile of olivine considering diffusional modification of zoning profiles as crystals grow by fractional crystallization from a chondrule melt the model was successfully verified by reproducing the fe mg zoning profiles obtained in dynamic crystallization experiments on analogs for type ii chondrules in semarkona we applied the model to calculating cooling rates for olivine grains of type ii porphyritic olivine chondrules in the semarkona ll3 00 ordinary chondrite calculated cooling rates show a wide range from 0 7 c h to 2400 c h and are broadly consistent with those obtained by dynamic crystallization experiments 10 1000 c h variations in cooling rates in individual chondrules can be attributed to the fact that we modeled grains with different core fa compositions that are more fe rich either because of sectioning effects or because of delayed nucleation variations in cooling rates among chondrules suggest that each chondrule formed in different conditions for example in regions with varying gas density and assembled in the semarkona parent body after chondrule formation

secondary melting events in semarkona chondrules revealed by compositional zoning in low ca pyroxene abstract it is well established that many chondrules contain relict grains formed in previous generations of chondrules we here describe evidence that chondrules experienced multiple mesostasis melting events while remaining closed systems spheroidal chondrule shapes resulted from surface tension effects following a primary heating event that caused substantial melting 40 of the precursor assemblages in some high feo chondrules in ll3 00 semarkona low ca pyroxene phenocrysts show multiple overgrowth layers produced by secondary melting events we characterized these layers with the electron microprobe in terms of fe ca and cr in two semarkona chondrules the first low ca pyroxene overgrowth that forms after a minor heating melting event has low ca and fe concentrations of these incompatibles gradually increase over the next 8 4 m until falling temperatures and slowing diffusion caused growth to stop the next melting event remelts and mixes the local mesostasis cooling causes growth of a normal igneously zoned layer in the simplest cases the ca concentrations at the minima gradually increase towards the edge of the phenocryst heat deposition during heating events varied over a wide range the weakest events produced recognizable changes in slopes that we call inflections rather than minima large fractions of the individual phenocrysts were formed by the process that produced the overgrowth layers it appears that overgrowth formation stopped when the ca content of the mesostasis became high enough to make high ca pyroxene a liquidus phase both semarkona chondrules include olivine phenocrysts similar in size and modal abundance to the low ca pyroxene phenocrysts olivine compositional profiles show symmetrical apparently normal zoning except for asymmetries attributable to the presence of relict grains surface compositions of different olivine phenocrysts in the same chondrule are very similar to one another consistent with growth from mesostasis in the present chondrule hence these olivines must have experienced the same heating events as the pyroxenes with overgrowths as argued in earlier papers the fraction of chondrules heated to low temperatures sufficient to melt only mesostasis during nebular heating and melting processes is much larger than the fraction heated sufficiently to melt half or more of the mafic minerals melting is expected to result from flash heating in which heat is transported into the chondrule by radiation

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

total risk rating and stability analysis of embankment dams in the kachchh region gujarat india a method for total risk analysis of embankment dams under earthquake conditions is discussed and applied to the selected embankment dams i e chang tapar rudramata and kaswati located in the kachchh region of gujarat india to obtain the seismic hazard rating of the dam site and the risk rating of the structures based on the results of the total risk analysis of the dams coupled non linear dynamic numerical analyses of the dam sections are performed using acceleration time history record of the bhuj india earthquake as well as five other major earthquakes recorded worldwide the objective of doing so is to perform the numerical analysis of the dams for the range of amplitude frequency content and time duration of input motions the deformations calculated from the numerical analyses are also compared with other approaches available in literature viz makdisi and seed 1978 approach jansen s approach 1990 swaisgood s method 1995 bureau s method 1997 singh et al approach 2007 and saygili and rathje approach 2008 and the results are utilized to foresee the stability of dams in future earthquake scenario c 2010 elsevier b v all rights reserved