indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

fluid evolution in cm carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates the oxygen isotopic compositions of calcite grains in four cm carbonaceous chondrites have been determined by nanosims and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration two types of calcite were identified in murchison mighei cold bokkeveld and lapaz icefield 031166 by differences in their petrographic properties and oxygen isotope values type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration on average the type 1 grains have a 18o of 32 36 vsmow and 17o of between 2 and 1 most grains of type 2 calcite precipitated after type 1 they contain micropores and inclusions and have replaced ferromagnesian silicate minerals type 2 calcite has an average 18o of 21 24 vsmow and a 17o of between 1 and 3 such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose 18o and 17o values had changed by reaction with parent body silicates as predicted by the closed system model for aqueous alteration temperatures are likely to have increased over the timespan of calcite precipitation possibly owing to exothermic serpentinisation the most highly altered cm chondrites commonly contain dolomite in addition to calcite dolomite grains in two previously studied cm chondrites have a narrow range in 18o 25 29 vsmow with 17o 1 to 3 these grains are likely to have precipitated between types 1 and 2 calcite and in response to a transient heating event and or a brief increase in fluid magnesium calcium ratios in spite of this evidence for localised excursions in temperature and or solution chemistry the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions the cm carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or more probably a single c type asteroid

aragonite breunnerite calcite and dolomite in the cm carbonaceous chondrites high fidelity recorders of progressive parent body aqueous alteration abstract carbonate minerals in cm carbonaceous chondrite meteorites along with the silicates and sulphides with which they are intergrown provide a detailed record of the nature and evolution of parent body porosity and permeability and the chemical composition temperature and longevity of aqueous solutions fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered cm2 5 to completely hydrated cm2 0 all of them contain calcite whereas aragonite occurs only in the cm2 5 cm2 2 meteorites and dolomite in the cm2 2 cm2 0 all of the aragonite crystals and most of the calcite and dolomite grains formed during early stages of parent body aqueous alteration by cementation of pores produced by the melting of tens of micrometre size particles of h2o rich ice aragonite was the first carbonate to precipitate in the cm2 5 to cm2 2 meteorites and grew from magnesium rich solutions in the least altered of these meteorites the aragonite crystals formed in clusters owing to physical restriction of aqueous fluids within the low permeability matrix the strong correlation between the petrologic subtype of a meteorite the abundance of its aragonite crystals and the proportion of them that have preserved crystal faces is because aragonite was dissolved in the more altered meteorites on account of their higher permeability and or greater longevity of the aqueous solutions dolomite and breunnerite formed instead of aragonite in some of the cm2 1 and cm2 2 meteorites owing to higher parent body temperatures the pore spaces that remained after precipitation of aragonite dolomite and breunnerite cements were occluded by calcite following completion of cementation the carbonates were partially replaced by phyllosilicates and sulphides calcite in the cm2 5 cm2 2 meteorites was replaced by fe rich serpentine and tochilinite followed by mg rich serpentine in the cm2 1 and cm2 0 meteorites dolomite breunnerite and calcite were replaced by fe rich serpentine and fe ni sulphide again followed by mg rich serpentine the difference between meteorites in the mineralogy of their replacive sulphides may again reflect greater temperatures in the parent body regions from where the more highly altered cms were derived this transition from fe rich to mg rich carbonate replacement products mirrors the chemical evolution of parent body solutions in response to consumption of fe rich primary minerals followed by the more resistant mg rich anhydrous silicates almost all of the cms examined contain a second generation of calcite that formed after the sulphides and phyllosilicates and by replacement of remaining anhydrous silicates and dolomite dedolomitization the ca and co2 required for this replacive calcite is likely to have been sourced by dissolution of earlier formed carbonates and ions may have been transported over metre plus distances through high permeability conduits that were created by impact fracturing

late quaternary paleoenvironments and growth of intrusive ice in eastern beringia eagle river valley northern yukon canada in this study the sediments exposed in a fluvial terrace and in the headwall of a thaw slump in the eagle river valley northern yukon provide new data about the timing of flooding of glacial lake old crow the formation of massive ground ice bodies and the vegetation and the fauna in eastern beringia during the late quaternary the stratigraphy and radiocarbon ages establish the following chronology of events 1 a gravel fluvial terrace was deposited by an overflow from glacial lake hughes into glacial lake old crow 2 a carbonate silty clay was deposited during the maximum level of glacial lake old crow at 15 120 14c year bp 3 permafrost and large intrusive ice bodies aggraded through the glaciolacustrine and underlying sediments following the drainage of glacial lake old crow from the site 4 at 11 290 14c year bp a shrub sedge tundra colonized an uneven surface deformed by the bodies of ground ice 5 a thaw lake drained at 6730 14c year bp after flooding the site 6 during the early h

alteration of mesostasis in chondrules and aggregates from three c2 carbonaceous chondrites abstract microprobe analyses of mesostasis glass and phyllosilicate spinach in a variety of chondrules and aggregates from the c2 chondrites murchison essebi and renazzo suggest that a two stage alteration process acted on glass to produce the current range of spinach compositions the first stage was short but active coinciding both with a period of vigorous gardening of the c2 parent regolith and with the pervasive alteration that modified the proportion of matrix phyllosilicates in c2 meteorites during this stage mesostasis glass was hydrated and was mg enriched by limited reaction with chondrule and aggregate phenocrysts the second alteration stage involved slow but extensive reactions between mesostasis material and altered matrix resulting in a field of fe enriched spinach compositions that is distinctive for each meteorite

aqueous alteration in carbonaceous chondrites mass balance constraints on matrix mineralogy abstract bulk chemical compositions of matrix material in antarctic cm chondrites and other non antarctic cm and ci chondrites have been determined using microprobe defocused beam techniques these are used along with the results of previously published mineralogical studies to provide mass balance constraints on the relative proportions of intergrown and intermixed phyllosilicate phases in carbonaceous chondrite matrices results of these calculations indicate differing amounts of pcp a mixture of approximately 25 tochilinite and 75 cronstedtite and serpentines mg rich and fe rich varieties in varying proportions or intermediate compositional varieties additional sulfide phases are also probably necessary to account for excess ni and s fe si ratios for matrices of individual meteorites range from 1 21 to 2 77 corresponding to pcp pcp serf ratios of 0 16 to 0 58 progressive aqueous alteration of matrix appears to have occurred by formation of tochilinite then cronstedtite and mg rich serpentine and finally fe rich serpentine and sulfides cm matrix clearly did not behave as an isolated system during alteration ci chondrite matrices appear to contain little if any pcp this may be a natural consequence of the absence of chondrule associated metal from which pcp forms in the unaltered precursor material these data provide a more quantitative picture of low temperature aqueous alteration processes in carbonaceous chondrite parent bodies than has heretofore been possible from tem studies alone

segregated intrusive ice of subglacial meltwater origin in retrogressive thaw flow headwalls richardson mountains nwt canada abstract extensive beds of icy sediments are exposed in the headwalls of active retrogressive thaw flows which developed on the aklavik plateau richardson mountains nwt sedimentary and isotopic characteristics defined two units debris rich ice overlain by icy diamicton these units originated from the same glacial sediment deposited during the late wisconsin westward expansion of the laurentide ice sheet the icy diamicton is a result of the development of thaw flows and mass movement processes during the early holocene warm interval which reworked the sediments the ice in the diamicton is characterized by average 18o and d values of 22 6 1 8 and 181 15 respectively which are similar to the modern isotropic composition of precipitation for that area the debris rich ice is more depleted in 18o and d with 18o ranging from 30 to 27 and d ranging from 230 to 210 air bubbles enclosed in the ice have 13c values ranging between 24 and 19 and a co2 concentration nine times higher than the expected concentration of air entrapped in modern glacier ice but similar to that of soil co2 both physical and isotopic properties of the debris rich ice suggest that it is segregated intrusive ice that formed after the retreat of the laurentide ice sheet during permafrost aggradation as sediment laden subglacial meltwater moved through a proglacial talik this article discusses the mechanism involved in the formation of massive segregated intrusive ice and how it differs from both buried glacier ice and holocene massive intrasedimental ice

nitrogen isotopic composition of a gas rich ordinary chondrite alha 77216 abstract nitrogen abundance and isotopic composition in a gas rich chondrite alha 77216 l3 or h3 was measured in order to obtain an independent estimate of the average nitrogen isotopic composition of the solar system nitrogen ne and ar were extracted by a stepped combustion method and measured using a static mass spectrometer the cosmic ray exposure age based on the 21 ne abundance is about 35 3 1 1 million yr isotopically heavy nitrogen is observed at 700 1100 c the abundance in a bulk sample is 1 38 ppm with 0 61 ppb excess 15 n of which 0 17 ppb could be due to cosmogenic nitrogen heavy nitrogen is enriched in the metal phases compared with silicates a 15 n value as large as 174 was observed for a the 800 c step of a magnetic separate the abundance ratio of nitrogen to solar type rare gases in this meteorite is higher than those in lunar samples we suggest that the isotopically heavy nitrogen is of solar origin but other possibilities presolar and indigenous nitrogen cannot be completely ruled out

irradiation of olivine by 4 kev he simulation of space weathering by the solar wind 1 we have studied the effects of 4 kev he ion irradiation on olivine while measuring in situ changes in the near infrared nir reflectance and in the chemical composition of the surface the observed changes in reflectance are reddening and the attenuation of the fe 3d absorption bands in the nir spectral reddening of irradiated olivine powder 45 m correlates with the amount of metallic iron formed by ion impact consistent with the idea that space weathering effects in the reflectance of olivine bearing s type asteroids are due to the formation of metallic iron the metallization rate of the powder is about half that of a sectioned rock of olivine which we propose is a consequence of redeposition of sputtered material the nir spectral changes observed in ion irradiation experiments are similar to those observed in our previous experiments on vapor redeposition indicating that different space weathering mechanisms can lead to similar final effects on reflectance finally we estimate that at 1 au the spectral reddening caused by the solar wind saturates approximately 2 orders of magnitude faster than comparable reddening caused by micrometeorite impacts

occlusion of noble gases he ne ar kr xe into synthetic magnetite at 500 1300 c abstract the trapping mechanism of noble gases during growth of magnetite is investigated by oxidizing fe with water vapor at temperatures ranging from 500 to 1300 c an apparent negative correlation between the concentration of argon and synthetic temperatures suggests that gases are trapped by adsorption the fixation of adsorbed gas atoms is probably due to crystal growth the elemental fractionation pattern of noble gases resembles so called planetary type patterns with enrichments in heavier noble gases at high trapping temperatures however at lower temperatures significant fractionation is not observed reflecting a smaller absolute value of the negative heat of adsorption for lighter noble gases the amount of argon in chondritic magnetite orgueil ci can be explained by adsorptive trapping of ambient noble gases at the suggested condensation temperature of magnetite in the solar nebular 400 k solar type helium neon and argon elemental ratios observed for the orgueil magnetite are also qualitatively consistent with the results of the present experiments comparison experiments which synthesize magnetite with aqueous water are necessary for further discussion on the origin of the chondritic magnetite and its noble gases

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

fine grained rims in the allan hills 81002 and lewis cliff 90500 cm2 meteorites their origin and modification antarctic cm meteorites allan hills alh 81002 and lewis cliff lew 90500 contain abundant fine grained rims fgrs that surround a variety of coarse grained objects fgrs from both meteorites have similar compositions and petrographic features independent of their enclosed objects the fgrs are chemically homogeneous at the 10 m scale for major and minor elements and at the 25 m scale for trace elements they display accretionary features and contain large amounts of volatiles presumably water they are depleted in ca mn and s but enriched in p all fgrs show a slightly fractionated rare earth element ree pattern with enrichments of gd and yb and depletion of er gd is twice as abundant as er our results indicate that those fgrs are not genetically related to their enclosed cores they were sampled from a reservoir of homogeneously mixed dust prior to accretion to their parent body the rim materials subsequently experienced aqueous alteration under identical conditions based on their mineral textural and especially chemical similarities we conclude that alh 81002 and lew 90500 likely have a similar or identical source

ci chondrite like clasts in the nilpena polymict ureilite implications for aqueous alteration processes in ci chondrites abstract we have carried out a detailed petrographic and mineralogical study of carbonaceous chondrite matrix clasts in the nilpena polymict ureilite the bulk compositions of a number of clasts determined by electron microprobe show that they have close affinities to ci chondrite matrix and differ substantially from cm matrix material transmission electron microscopy studies show that the mineralogy of the clasts is also consistent with ci chondrite matrix indicated by the presence of saponitic smectite clays serpentine magnetite pentlandite pyrrhotite and ferrihydrite phases such as tochilinite and cronstedtite diagnostic of cm matrix are absent based on the oxygen isotopic composition of the matrix the phase chemistry and the bulk clast chemistry we suggest that the matrix clasts in nilpena represent material which is less altered than orgueil the difference in oxygen isotopic composition of the nilpena matrix clasts from ci chondrites may be because the clasts underwent alteration at a lower water rock ratio increased alteration of nilpena type material should result in the oxidation of fe bearing saponite and sulfides to produce ferrihydrite and more mg rich saponite such as that in orgueil matrix although the presence of ci like matrix clasts in the polymict ureilites suggests that ci matrix may have been a precursor to the ureilites in detail this seems highly unlikely the trace element and carbon isotopic compositions of ureilites are incompatible with a significant ci chondrite precursor we suggest that the ci like matrix clasts in nilpena represent a component of a late accreting veneer on the ureilite parent body

fault slip and seismic moment of the 1700 cascadia earthquake inferred from japanese tsunami descriptions 1 the 1700 cascadia earthquake attained moment magnitude 9 according to new estimates based on effects of its tsunami in japan computed coseismic seafloor deformation for hypothetical ruptures in cascadia and tsunami modeling in the pacific ocean reports of damage and flooding show that the 1700 cascadia tsunami reached 1 5 m heights at seven shoreline sites in japan three sets of estimated heights express uncertainty about location and depth of reported flooding landward decline in tsunami heights from shorelines and post 1700 land level changes we compare each set with tsunami heights computed from six cascadia sources each source is vertical seafloor displacement calculated with a three dimensional elastic dislocation model for three sources the rupture extends the 1100 km length of the subduction zone and differs in width and shallow dip for the other sources ruptures of ordinary width extend 360 670 km to compute tsunami waveforms we use a linear long wave approximation with a finite difference method and we employ modern bathymetry with nearshore grid spacing as small as 0 4 km the various combinations of japanese tsunami heights and cascadia sources give seismic moment of 1 9 1022 n m equivalent to moment magnitude 8 7 9 2 this range excludes several unquantified uncertainties the most likely earthquake of moment magnitude 9 0 has 19 m of coseismic slip on an offshore full slip zone 1100 km long with linearly decreasing slip on a downdip partial slip zone the shorter rupture models require up to 40 m offshore slip and predict land level changes inconsistent with coastal paleoseismological evidence

ground motion attenuation source and site effects for the 26 september 2003 m 8 1 tokachi oki earthquake sequence abstract on 26 september 2003 a megathrust earthquake of m 8 1 occurred at the kurile trench northern japan we used accelerograms recorded on more than 300 k net stations ranging in distance from 40 to 500 km to determine source attenuation and site effects for the mainshock and four aftershocks with m 7 3 6 4 5 9 and 5 5 the analyses are based on linear regression applied to the fourier spectra data of each event the ground motion attenuation for all the events can be modeled using an assumed geometric spreading coefficient b 1 1 0 with an associated anelastic attenuation model given by an apparent q 135 f 0 76 by using dummy variables in the regression site amplifications relative to national earthquake hazard reduction program nehrp c sites are determined for d and e sites nonlinear site amplification was investigated for the m 8 1 data but was not significant in determining the overall amplification factors fourier spectra data were corrected to a reference near source distance and site condition hard rock the source spectrum for each event was compared to that of the theoretical brune model spectrum in order to compute seismic moment and stress drop seismic moments obtained in this manner agree with those of other studies stress drops range from 100 to 200 bars with no apparent dependence on magnitude the mainshock stress drop was 120 bars a similar value 100 bars was calculated for an interface aftershock events with the highest stress drops near 200 bars may have been in slab events

holocene migration of lodgepole pine pinus contorta var latifolia in southern yukon canada a palynological reconstruction n 25 profiles suggests that the northern extent of lodgepole pine pinus contorta var latifolia engelmann ex s watson occurred between 59 and 60 n latitude in

tracking hydrological responses of a thermokarst lake in the old crow flats yukon territory canada to recent climate variability using aerial photographs and paleolimnological methods recent studies using remote sensing analysis of lake rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming however images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice free season duration here we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the old crow flats ocf canada and to identify their causes images show that the water level in lake ocf 48 declined markedly sometime between 1972 and 2001 in a sediment core from ocf 48 complacent stratigraphic profiles of several physical geochemical and biological parameters from 1874 1967 indicate hydro limnological conditions were relatively stable from 1967 1989 declines in organic matter content organic carbon isotope values and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment and subsequent decline in aquatic productivity caused by increased thermo erosion of shoreline soils lake expansion was likely caused by increased summer rainfall as recorded by increased cellulose inferred lake water oxygen isotope compositions stratigraphic trends defining the lake expansion phase terminated at 1989 which likely marks the year when the lake drained above average precipitation during the previous year probably raised the lake level and promoted further thermo erosion of the shoreline soils that caused the lake to drain these are meteorological conditions that have led to other recent lake drainage events in the ocf thus the decline in lake level evident in the aerial photograph from 2001 is unlikely to have been caused by evaporation but rather is a remnant of a drainage event that took place more than a decade earlier after drainage the lake began to refill and most paleolimnological parameters approach levels that are similar to those during the stable phase these findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes copyright 2011 john wiley sons ltd

constraints on the flux of meteoritic and cometary water on the moon from volatile element n ar analyses of single lunar soil grains luna 24 core abstract we report new nitrogen and argon isotope and abundance results for single breccia clasts and agglutinates from four different sections of the luna 24 drill core in order to re evaluate the provenance of n trapped in lunar regolith and to place limits on the flux of planetary material to the moon s surface single luna 24 grains with 40ar 36ar ratios 10 1126 science 188 4184 162 is no longer apparent when the luna and apollo data are combined instead the n isotope signatures corrected for cosmogenic 15n are consistent with binary mixing between isotopically light solar wind sw n and a planetary n component with a 15n value of 100 to 160 the lower 15n values of luna 24 grains compared to apollo samples reflect a higher relative proportion of solar n resulting from the higher sw fluence in the region of mare crisium compared to the central near side of the moon carbonaceous chondrite like micro impactors match well the required isotope characteristics of the non solar n component trapped in low antiquity lunar regolith in contrast a possible cometary contribution to the non solar n flux is constrained to be 3 13 based on the mixing ratio of sw to planetary n obtained for recently exposed lunar soils we estimate the flux of micro impactors to be 2 2 5 7 103 tons yr 1 at the surface of the moon our estimate for luna 24 agrees well with that for young apollo regolith indicating that the supply of planetary material does not depend on lunar location thus the continuous influx of water bearing cosmic dust may have represented an important source of water for the lunar surface over the past 1 ga provided that water removal rates i e by meteorite impacts photodissociation and sputtering do not exceed accumulation rates

predicted ground motions for great interface earthquakes in the cascadia subduction zone ground motions for earthquakes of moment magnitude m 7 5 9 0 on the cascadia subduction zone interface are simulated based on a stochastic finite fault model and used to estimate average response spectra for firm site conditions in vancouver victoria and seattle we also express the response spectra as ground motion prediction equations gmpes for cascadia events the simulations are calibrated by modeling the wealth of ground motion data from the m 8 1 tokachi oki earthquake sequence of japan adjustments to the calibrated model are made to consider average source attenuation and site parameters for the cascadia region we perform best estimate simulations for a preferred set of input parameters typical results suggest mean values of 5 damped pseudoacceleration in the range from about 100 to 200 cm sec2 at frequencies from 1 to 4 hz for firm ground conditions in vancouver victoria and seattle uncertainty in stress drop causes uncertainty in simulated response spectra of about 50 uncertainties in the attenuation model produce even larger uncertainties in response spectral amplitudes a factor of about 2 at 100 km becoming even larger at greater distances it is thus important to establish the regional attenuation model for ground motion simulations furthermore combining data from regions with different attenuation characteristics in particular japan and mexico into a global subduction zone database for development of global empirical gmpes may not be a sound practice time histories of acceleration for the stochastically simulated motions are provided for reference sites in vancouver victoria and seattle an alternative set of motions based on lightly modifying real recordings from the tokachi oki earthquake to match expected conditions for cascadia cities are also provided these alternative records have similar spectral content to the simulated motions but contain additional complexity and more realistic phasing the provision of alternative record sets allows users to conduct studies to determine the importance of these effects for structural response

hydrothermal experiments on alteration of ca al rich inclusions cais in carbonaceous chondrites implication for aqueous alteration in parent asteroids carbonaceous chondrites contain ca al rich inclusions cais which consist mainly of refractory minerals including gehlenite spinel perovskite and hibonite which are predicted to be the first phases formed from early solar nebula on the basis of thermodynamic calculations however many cais contain secondary minerals such as nepheline calcite and phyllosilicates the formation process of secondary minerals in cais is still controversial whether they were produced by the reaction with solar nebula or by aqueous alteration in parent asteroids we performed hydrothermal experiments on gehlenite spinel and diopside which are common in cais in carbonaceous chondrites to study aqueous alteration in parent asteroids mixtures of gehlenite with sio2 and or al2o3 and those of sio2 with al2o3 were also employed to study products of these systems which have a close relationship to crystallization of secondary minerals in cais in fluid in parent asteroids hydrogrossular calcite and amorphous al si were obtained from gehlenite by hydrothermal experiments whereas both spinel and diopside escaped alteration suggesting that gehlenite is the weakest mineral among these refractory minerals against alteration this result is consistent with observation of cais analcime nepheline hydrate and tobermorite were obtained from the runs for mixtures of gehlenite with sio2 whereas the products from mixtures of al2o3 with sio2 were analcime nepheline hydrate and hydrosodalite these results suggest that the alteration process of gehlenite is as follows 1 gehlenite was dissolved by fluid in chondrite parent asteroids to release ca al and si from the surface 2 co32 in fluid reacted with ca to crystallize calcite 3 na al and si in fluid crystallized nepheline hydrate hydrosodalite and or analcime 4 ca al and si in fluid crystallized hydrogrossular without co32 and excess ca and si crystallized ca si hydrate such as tobermorite heating experiments on several minerals obtained through hydrothermal experiments were also performed to study thermal metamorphism in parent asteroids hydrogrossular was converted into hydrogrossular with a lower h2o content and analcime and nepheline hydrate were converted into nepheline tobermorite is known to be converted into wollastonite with increasing temperature the results of experimental studies suggest that most secondary minerals found in cais in carbonaceous chondrites were produced from gehlenite by aqueous alteration and the subsequent thermal metamorphism in parent asteroids

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

helium ion implantation into minerals abstract we implanted rock forming minerals olivine magnetite ilmenite and rutile with a 3 6 kev helium ion beam which simulates solar wind particles and analyzed implanted helium a total fusion experiment shows that nearly 100 of impinging helium ions is trapped in a target at smaller doses while the concentration of trapped helium tends to be saturated above a helium ion dose of 10 16 ions cm 2 there is no appreciable difference in the concentration of trapped helium among minerals a stepwise heating experiment shows that implanted helium is retained more firmly in magnetite and rutile than in olivine on the basis of the experimental results a high degree of loss of implanted helium out of idps is suggested this may be attributed to decomposition of helium bearing minerals in idps during their entry into the earth s atmosphere

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

alluvial history of the porcupine river alaska role of glacial lake overflow from northwest canada the stratigraphy and morphology of alluvial terraces in the lower porcupine valley permit the definition of twelve river stages each marked by distinctive surface characteristics sediment composition and regional gradient terraces that exhibit characteristics suggestive of extremely high discharge such as coarse bouldery braided gravel surfaces and intense scouring formed at times when the porcupine river at the ramparts acted as an overflow outlet for glacial lakes in northern yukon territory which had been impounded by the lauren tide ice sheet terraces capped by sediment suggestive of relatively low discharge meandering streams and which were strongly affected by coleen river drainage probably formed when glacial lake overflow did not occur ten radiocarbon dates on alluvial sediments from the lower porcupine river range from greater than 35 000 to 2 350 55 yr b p when combined with geomorphologic interpretations on terraces in alaska and with radiocarbon dates from northern yukon territory these dates suggest repeated glaciolacustrine innundations of the old crow and bluefish basins during wisconsinan time

palaeohydrology of the southwest yukon territory canada based on multiproxy analyses of lake sediment cores from a depth transect lake level variations at marcella lake a small hydrologically closed lake in the southwestern yukon territory document changes in effective moisture since the early holocene former water levels driven by regional palaeohydrology were reconstructed by multiproxy analyses of sediment cores from four sites spanning shallow to deep water marcella lake today is thermally stratified being protected from wind by its position in a depression it is alkaline and undergoes bio induced calcification relative accumulations of calcium carbonate and organic matter at the sediment water interface depend on the location of the depositional site relative to the thermocline we relate lake level fluctuations to down core stratigraphic variations in composition geochemistry sedimentary structures and to the occurrence of unconformities in four cores based on observations of modern limnology and sedimentation processes twenty four ams radiocarbon dates on macrofossils and pollen provide the lake level chronology prior to 10 000 cal bp water levels were low but then they rose to 3 to 4 m below modern levels between 7500 and 5000 cal bp water levels were 5 to 6 m below modern but rose by 4000 cal bp between 4000 and 2000 cal bp they were higher than modern during the last 2000 years water levels were either near or 1 to 2 m below modern levels marcella lake water level fluctuations correspond with previously documented palaeoenvironmental and palaeoclimatic changes and provide new independent effective moisture information the improved geochronology and quantitative water level estimates are a framework for more detailed studies in the southwest yukon

cliff top eolian deposits and associated molluscan assemblages as indicators of late pleistocene and holocene environments in beringia abstract northern yukon cliff top eolian deposits are indicators of past climates and environments the deposits are located along the ramparts of the porcupine river near the international boundary these eolian deposits resulted from southwest wind regimes that operated at about 14 860 bp and more certainly at 11 640 8200 bp and from 4600 bp to present palynological analysis indicates that these three periods were marked by different vegetation covers the earliest one being dominated with cyperaceae the intermediate one by shepherdia canadiensis and the most recent one by spruce picea molluscs are particularly numerous and diversified which suggests that the cliff top deposits were important refuges for these animals molluscan assemblages indicate that the climate was wetter at about 14 860 bp than between 11 640 bp and 8200 bp the xeric regime that marked the latter period is also indicated by gypsum concretions it is suggested that the molluscs could have been introduced by migratory birds that in turn would also have been able to use the snail shells from the eolian deposits as an important dietary element it is also suggested that the molluscs are relicts of endemic fauna

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

inelastic seismic demand of real versus simulated ground motion records for cascadia subduction earthquakes nonlinear dynamic analysis of structures requires strong ground motion time histories accelerograms as input the inherent scarcity of recorded ground motions for specific conditions magnitude distance region and site makes utilization of alternatives unavoidable such alternatives include simulated records and modified real records there are many simulation methods available but there is often a preference to using stochastic simulation methods if justifiable due to the ease with which many records can be simulated in a generic way however there are concerns that such simulated records may not produce similar nonlinear response in structures as real records or modified real records due to the lack of realistic phasing and other record characteristics including peaks and troughs effects and response spectral shape effects this study investigates peak nonlinear responses of inelastic single degree of freedom systems with different hysteretic characteristics subjected to sets of stochastically simulated records lightly modified real records and scaled real records the former two of which were proposed by atkinson and macias 2009 as representative of expected ground motions for cascadia subduction earthquakes of m 8 5 at vancouver victoria and seattle we conclude that 1 the peak nonlinear responses due to the modified records and the scaled real records are similar if the peaks and troughs effects and response spectral shape effects are taken into account adequately in the choice of scaling factors for the real records and 2 the peak nonlinear responses due to the simulated and modified records are similar these findings though obtained based on limited sets of ground motion records are in agreement with previous studies and highlight the need for judicious choices in cases involving the scaling of records the results also suggest that stochastically simulated records may be an appropriate way to capture overall response potential for both linear and nonlinear structural systems at least over a range of periods from 0 1 to 2 sec

analyses of nitrogen and argon in single lunar grains towards a quantification of the asteroidal contribution to planetary surfaces abstract we performed nitrogen and argon isotopic analyses in single 200 m sized ilmenite grains of lunar regolith samples 71501 79035 and 79135 cosmogenic and trapped components were discriminated using stepwise heating with a power controlled co 2 laser cosmogenic 15 n and 38 ar correlate among different ilmenite grains yielding a mean 15 n c 38 ar c production ratio of 14 4 1 0 atoms atom this yields a 15 n production rate in bulk lunar samples of 3 8 5 6 pg g rock 1 ma 1 which agrees well with previous estimates the trapped 15 n values show large variations up to 300 among different grains of a given soil reflecting complex histories of mixing between different end members the 36 ar 14 n ratio which is expected to increase with increasing contribution of solar ions varies from 0 007 to 0 44 times the solar abundance ratio the trapped 15 n values correlate roughly with the 36 ar 14 n ratios from a non solar end member characterized by a 36 ar 14 n ratio close to 0 and variable but generally positive 15 n values to lower 15 n values accompanied by increasing 36 ar 14 n ratios supporting the claim of hashizume et al 2000 that solar nitrogen is largely depleted in 15 n relative to meteoritic or terrestrial nitrogen nevertheless the 36 ar 14 n ratio of the 15 n depleted solar end member is lower than the solar abundance ratio by a factor of 2 5 5 we explain this by a reprocessing of implanted solar wind atoms during which part of the chemically inert rare gases were lost we estimate that the flux of non solar n necessary to account for the observed 15 n values is comparable to the flux of micrometeorites and interplanetary dust particles estimated for the earth hence we propose that the variations in 15 n values observed in lunar regolith can be simply explained by mixing between solar wind contributions and micrometeoritic ones infalling on the moon temporal variations of 15 n values among samples of different antiquities could be due to changes in the micrometeoritic flux through time in which case such flux has increased by up to an order of magnitude during the last 0 5 ga

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

late quaternary sequence stratigraphy of the mackenzie delta the late wisconsinan and holocene sequence stratigraphy of the mackenzie delta provides insights into the glacial history of the region the base of the described succession is a hummocky regional reflector interpreted to be a flooding surface formed immediately after retreat of glacial ice from the mackenzie trough above this flooding surface two progradational parasequences are present the first assigned to the transgressive systems tract is correlated with the tutsieta lake readvance of the ice sheet at approximately 13 000 bp a flooding surface forming the upper boundary of this parasequence extends inland to at least inuvik developing as a response to glacial retreat and early holocene relative sea level rise the second parasequence of holocene deltaic deposits is assigned to the highstand systems tract and is characterized by progressive progradation of the delta into the mackenzie trough to a position seaward of the present delta coastline a distinct reduction in gradient of the most recen

late wisconsinan erosion and eolian deposition summer island area pleistocene mackenzie delta northwest territories optical dating and implications for glacial chronology the summer island area of the pleistocene mackenzie delta western canadian arctic is thought to have been last glaciated during the early wisconsinan 35 ka with a suggested late wisconsinan 13 ka glacial limit located 80 100 km to the south cryostratigraphic observations in the summer island area identify eolian and fluvial sediments overlying an erosion surface on summer island eolian sand occurs within sand wedges the tops of which are contiguous with an eolian sand sheet deposited on a formerly bare ice surface this paleo ice surface is attributed to fluvial erosion and that in turn is attributed to proglacial meltwater activity the age of erosion is inferred to be shortly before 14 ka determined by optical dating using infrared stimulation of luminescence from feldspar of the eolian sand wedges this 14 ka meltwater erosion is significantly north of the generally accepted limit of late wisconsinan glaciation in this coastal area suggesting that ice last covered the whole of rich

response of the porcupine and old crow rivers in northern yukon canada to holocene climatic change a major aggradation took place from 8000 bp to 4000 bp in the porcupine and old crow rivers northern yukon the aggradation was a consequence of an increase in flow and the result of a perturbation of the permafrost active layer following the early holocene climatic warming of northwestern canada these findings are useful for improving our understanding of how natural landscapes and river systems evolved in regions that experienced a permafrost history and more particurlarly an increase in climatic warming this article also contributes to an improved understanding of natural landscape evolution along the porcupine and old crow rivers in eastern beringia where there has been much interest in questions related to animal and human migration and adaptation

experiments on thermal release of implanted noble gases from minerals and their implications for noble gases in lunar soil grains abstract experiments on ion implantation were performed in order to study the release mechanisms of solar particles from lunar soil grains helium neon and argon ions were implanted into olivine and ilmenite the release temperatures of noble gases were investigated by heating samples stepwise the results show that they depend on irradiation energy and dose we conclude that the release temperature is related to the size of bubbles in which noble gases are trapped noble gases in small and large bubbles are released at 400 600 c and 800 1200 c respectively in ne and ar implantation experiments into olivine a component was released during recrystallization of amorphized surfaces based on these experimental results we suggest that components released from lunar ilmenite grains at different temperatures would correspond to solar particles of different energies we also suggest that he and ne of solar wind energy about 1 kev amu should be retained in lunar ilmenite grains while they should be lost from olivine grains

dune stabilization in central and southern yukon in relation to early holocene environmental change northwestern north america abstract eolian deposits of central and southern yukon northwestern canada consist of loess mantles small areas of active dunes and larger stabilized dune fields dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation infrared stimulation luminescence irsl dating in central and southern yukon reveals that these dune fields stabilized as late as 9 8 5 ka well after the retreat of cordilleran glaciers these findings are comparable to other valley setting dune fields and loess from central alaska which record activity during the period from the lateglacial to the holocene thermal maximum htm and reduced or altered activity after 9 8 ka post glacial dune activity was most likely related to warm dry conditions during the htm under predominantly shrub tundra vegetation early holocene stabilization of these dunes probably occurred in response to cooler moister conditions and replacement of predominantly tundra by boreal forest cover dominated by spruce stabilization of dune fields in southern yukon and alaska most likely represented an extension of the time transgressive stabilization of dune fields that occurred across northwestern north america with the post glacial expansion of the boreal forest

multiple precursors of secondary mineralogical assemblages in cm chondrites we report a petrographic and mineralogical survey of tochilinite cronstedtite intergrowths tcis in paris a new cm chondrite considered to be the least altered cm identified to date our results indicate that type i tcis consist of compact tochilinite cronstedtite rims surrounding fe ni metal beads thus confirming kamacite as the precursor of type i tcis in contrast type ii tcis are characterized by complex compositional zoning composed of three different fe bearing secondary minerals from the outside inwards tochilinite cronstedtite and amakinite type ii tcis present well developed faces that allow a detailed morphological analysis to be performed in order to identify the precursors the results demonstrate that type ii tcis formed by pseudomorphism of the anhydrous silicates olivine and pyroxene hence there is no apparent genetic relationship between type i and type ii tcis in addition the complex chemical zoning observed within type ii tcis suggests that the alteration conditions evolved dramatically over time at least three stages of alteration can be proposed characterized by alteration fluids with varying compositions 1 fe and s rich fluids 2 s poor and fe and si rich fluids and 3 s and si poor fe rich fluids the presence of unaltered silicates in close association with euhedral type ii tcis suggests the existence of microenvironments during the first alteration stages of cm chondrites in addition the absence of mg bearing secondary minerals in paris tcis suggests that the mg content increases during the course of alteration

the paradox between low shock stage and evidence for compaction in cm carbonaceous chondrites explained by multiple low intensity impacts abstract petrographic analysis of eight cm carbonaceous chondrites eet 96029 lap 031166 lon 94101 met 01072 murchison murray sco 06043 que 93005 by electron imaging and diffraction and x ray computed tomography reveals that six of them have a petrofabric defined by shock flattened chondrules with the exception of murchison those cms that have a strong petrofabric also contain open or mineralized fractures indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix the cms studied span a wide range of petrologic subtypes and in common with rubin 2012 we find that the strength of their petrofabrics increases with their degree of aqueous alteration this correspondence suggests that impacts were responsible for enhancing alteration probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body two meteorites that do not fit this pattern are met 01072 and murchison both have a strong petrofabric but are relatively unaltered in the case of met 01072 impact deformation is likely to have postdated parent body aqueous activity the same may also be true for murchison but as this meteorite also lacks fractures and veins its chondrules were most likely flattened by multiple low intensity impacts multiphase deformation of murchison is also revealed by the microstructures of calcite grains and chondrule defined petrofabrics as revealed by x ray computed tomography the contradiction between the commonplace evidence for impact deformation of cms and their low shock stages most belong to s1 can be explained by most if not all having been exposed to multiple low intensity i e

partition of noble gases between olivine and basalt melt abstract the distribution coefficients ki of noble gases were determined for synthesized olivine basalt melt pairs seven samples bh series were synthesized at 1370 1300 c under a one atmospheric pressure 105 pa noble gas mixture and four samples hpp and hpg series at 1360 1050 c at high pressures 0 2 1 5 gpa the two different experiments gave consistent results with each other some bh series olivine samples were apparently contaminated with gas rich inclusions or the glass phase and the effects of such interferences on the calculated distribution coefficients were evaluated the possible ranges of the distribution coefficients of noble gases thus obtained are khe 0 07 kne 0 006 0 08 kar 0 05 0 15 kkr 0 15 and kxe 0 3 these show remarkable features compared to solid element distribution coefficients the distribution coefficients of noble gases are rather insensitive to or even positively correlated with the atomic size of noble gases the striking contrast between the partition of noble gases and that of solid elements may be attributed to the electrical neutrality of noble gases and the increasing electronic polarizability from he to xe

assessment of simulated ground motions in earthquake engineering practice a case study for duzce turkey simulated ground motions can be used in structural and earthquake engineering practice as an alternative to or to augment the real ground motion data sets common engineering applications of simulated motions are linear and nonlinear time history analyses of building structures where full acceleration records are necessary before using simulated ground motions in such applications it is important to assess those in terms of their frequency and amplitude content as well as their match with the corresponding real records in this study a framework is outlined for assessment of simulated ground motions in terms of their use in structural engineering misfit criteria are determined for both ground motion parameters and structural response by comparing the simulated values against the corresponding real values for this purpose as a case study the 12 november 1999 duzce earthquake is simulated using stochastic finite fault methodology simulated records are employed for time history analyses of frame models of typical residential buildings next the relationships between ground motion misfits and structural response misfits are studied results show that the seismological misfits around the fundamental period of selected buildings determine the accuracy of the simulated responses in terms of their agreement with the observed responses

bulk mineralogy of individual micrometeorites determined by x ray diffraction analysis and transmission electron microscopy abstract bulk mineralogy of individual fine grained micrometeorites from 50 to 200 m in diameter was determined on the basis of the powder x ray diffraction patterns and the observation of internal textures by a transmission electron microscope tem x ray diffraction analysis of 56 micrometeorites indicated that 42 11 and 3 samples are olivine rich pyroxene rich and phyllosilicate rich micrometeorites respectively among the phyllosilicate rich micrometeorites one contains saponite and other two contain serpentine no samples contain both saponite and serpentine we found that saponite rich micrometeorite was weakly heated which results in shrinkage of 001 basal spacing of saponite down to 9 7 a and that cronstedtite which is commonly contained in cm chondrites occurs in serpentine rich micrometeorites micrometeorites that consist entirely of anhydrous minerals and amorphous phases are predominant in the samples studied the major phases of such micrometeorites are olivine low ca pyroxene magnetite and fe sulfide and the average abundances are 65 17 11 and 7 wt respectively when the total abundance of the four minerals are normalized to 100 wt the relative mineral abundance varies greatly between samples low ca pyroxene olivine ratios range from 0 to 3 5 with a mean of 0 3 tem observations of inner portions of some micrometeorites revealed that they are aggregates of very small equigranular grains 100 nm of olivine magnetite or low ca pyroxene olivine magnesiowustite the textures are very similar to those of hydrous carbonaceous chondrite that was experimentally heated to temperature below melting point thus suggesting that the micrometeorites had been hydrous particles but were decomposed by the brief heating upon atmospheric entry it is newly found that magnesiowustite was formed in micrometeorites instead of magnetite as a product of phyllosilicate decomposition under low oxygen fugacity the decomposed hydrous micrometeorites gave two types of characteristic x ray diffraction patterns 1 broad olivine and magnetite reflections or 2 variable intensities of magnesiowustite reflections together with magnetite low ca pyroxene and olivine reflections twenty nine olivine or pyroxene rich micrometeorites showed such diffraction patterns thus suggesting that more than half of micrometeorites investigated must be decomposed hydrous particles the results confirmed that hydrous dust particles are much more abundant in the interplanetary space than in the micrometeorites recovered on the earth

brecciation and chemical heterogeneities of ci chondrites abstract fragments in the size range from 40 m to several hundred m in the ci chondrites orgueil ivuna alais and tonk show a wide range of chemical compositions with variations in major elements such as iron 10 4 42 4 wt feo silicon 12 7 42 2 wt sio 2 and sulfur 1 01 15 8 wt so 3 but also important minor elements such as phosphorous up to 5 2 wt p 2 o 5 or calcium up to 6 6 wt cao these variations are the result of the varying mineralogical compositions of these fragments the distribution of phyllosilicates magnetites and possibly ferrihydrite in particular control the abundances of these elements high ree contents up to 150 times the solar abundances were observed in phosphates while matrix and sulfates are ree depleted the studied 113 fragments were subdivided into eight lithologies with similar mineralogical and thus chemical properties the most common is the cga lithology consisting of a groundmass of mg rich coarse grained phyllosilicates and varying abundances of inclusions such as magnetite the second most abundant lithology is the fga lithology consisting of a groundmass of fine grained fe rich phyllosilicates a rare but important lithology consists of fragments with high contents of phosphates and other minerals the proposed model for the evolution of these lithologies is based on a closed system alteration where mineralogical differences in the lithologies reflect heterogeneities in the starting material comparison of our results with literature data indicates a general similarity of the four ci chondrites analyzed further comparison of bulk analyses suggests that the mass threshold for chemical heterogeneities in ci chondrite samples is smaller than 1 2 g

magnitude scaling rate in ground motion prediction equations for response spectra from large subduction interface earthquakes in japan magnitude scaling rates msrs the rates of increase in predicted response spectra with increasing moment magnitude are evaluated for three ground motion prediction equations for response spectra from subduction interface earthquakes including two empirical models developed for data from japan and a model based on synthetic records generated by using a stochastic finite fault model msrs vary significantly among the three models and the difference between the two empirical models is unacceptably large a set of 2100 strong motion records from subduction interface events with a magnitude of 6 5 or larger from japan including the 11 march 2011 magnitude 9 earthquake were compiled the earthquakes were grouped according to magnitude so that the magnitude spread in each group is less than 0 2 magnitude units each earthquake group was treated as a single event with magnitude equal to the average magnitude for the group a simple attenuation model was fitted to the normalized and grouped data the model has a constant term for each earthquake group to represent the effect of magnitude three separate functions of magnitude a linear model for events with a magnitude greater than 7 a bilinear model and a curved model were then fitted to the constants and msrs were derived from these functions at short periods the derived msrs are only a fraction of those from two of the three attenuation models at spectral periods greater than 0 5 s the derived msrs are between about 1 3 and 1 2 of those of the two empirical models but are closer to those based on a set of synthetic records

late holocene sea level changes and paleoclimate recorded in lake lungue southern mozambique abstract we report on late holocene paleoenvironmental and sea level changes in southern mozambique based on analysis of diatom stratigraphy mineral magnetic susceptibility saturation isothermal remnant magnetization sirm and organic carbon content in a sediment core from lake lungue located ca 30 km north of xai xai city in the limpopo river floodplain eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age depth model high content of brackish marine taxa especially diploneis suborbicularis and navicula yarrensis suggests that the lake lungue basin was part of the indian ocean coastal zone between ca 740 and 910 ce suggesting higher relative sea level during this phase a similar diatom distribution in older parts of the sequence of unknown age indicates that the site was connected to the indian ocean also at some stage prior to 740 ce between ca 910 and 1130 ce the basin was under a combined effect of sporadic marine water influx and limpopo river actions a freshwater lake was established sometime between 1130 and 1360 ce when the basin became less affected by marine influences due to lower sea levels instead the lake system was more influenced by limpopo river meandering dynamics and flooding events and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources during this phase high abundance of freshwater planktonic species i e aulacoseira granulata and a ambigua indicates high lake levels and wetter conditions dated to ca 1360 1560 ce from 1560 ce until present the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels reported by a decline in freshwater planktonic taxa and increase in brackish taxa e g amphora robusta

nanometer scale measurements of iron oxidation states of cronstedtite from primitive meteorites we report the first nanometer scale measurements of the iron iii to total iron fe 3 fe ratios from primitive meteorites these ratios from the matrices and fine grained rims fgrs of the murchison murray and cold bokkeveld cm chondrites fall within a tight range from 0 45 to 0 54 0 02 the measurements were made using electron energy loss spectroscopy eels on cronstedtite which is a product of aqueous alteration early in the history of the solar system the results indicate that the alteration of these meteorites which display a broad range of alteration intensity occurred under similar redox conditions and further that alteration likely occurred in situ on asteroidal bodies rather than in the solar nebula

matrix mineralogy of the lance co3 carbonaceous chondrite a transmission electron microscope study the lance co3 carbonaceous chondrite cc is less altered than the ci and cm chondrites and so provides a view of the mineralogy and textures resulting from the earliest stages of aqueous alteration of ccs matrix olivine in lance has been partly altered to fine grained fe bearing serpentine and poorly crystalline fe3 oxide a process that required both hydration and oxidation serpentine occurs as discrete packets separated from the olivine surfaces by the fe3 oxide the fe released during the dissolution of olivine was partly incorporated into the serpentine the remainder was oxidized to form fe3 oxide matrix metal was also altered to produce fe oxides leaving the residual metal enriched in ni olivine grains in lance matrix contain channels along their 100 and 001 directions the formation and convergence of such channels resulted in a grain size reduction of the olivine the alteration was pervasive but incomplete suggesting a limited availability of fluid a brief study of two other co chondrites kainsaz and warrenton shows that these meteorites do not contain phyllosilicates in their matrices although both contain fe3 oxide between olivine grains prior to its alteration lance probably resembled kainsaz an unaltered co3 chondrite the alteration assemblage in lance is only slightly different from that in mokoia and essentially the same as that in c3 xenoliths from murchison alteration products in lance show greater similarities to ci than to cm chondrites