formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

preeruption conditions and timing of dacite andesite magma mixing in the 2 2 ka eruption at mount rainier analytical field and experimental evidence demonstrate that the mount rainier tephra layer c 2 2 ka preserves a magma mixing event between an andesitic magma whole rock sio 2 content of 57 60 wt and a dacitic magma whole rock sio 2 content of 65 1 wt the end member andesite a mix of an injected and chamber andesite and dacite can be characterized on the basis of the homogeneity of the matrix glass and phenocryst rim compositions many pumices however contain mixtures of the end members the end member dacite contains a microlite free matrix glass with 74 77 wt sio 2 orthopyroxene rims of mg 57 64 clinopyroxene rims of mg 66 74 and plagioclase rim anorthite contents of an 45 65 the temperature and oxygen fugacity from fe ti oxide compositions are 930 10 c and 0 5 0 75 log units above nno the mixed andesite contains mg 73 84 orthopyroxene rims mg 73 78 clinopyroxene rims an 78 84 plagioclase rims and mg 67 74 amphibole rims the temperature from fe ti oxides hornblendeplagioclase and two pyroxene geothermometry is 1060 15 c and the oxygen fugacity is approximately one log unit above nno for the injected andesite the chamber andesite is estimated to be a magma with a 64 65 wt sio 2 melt at 980 c and a nno oxygen fugacity we conclude that the andesitic and dacitic magmas are from separate magma storage regions at 7 km and 2 4 km due to differences in the bimodal whole rock matrix glass and phenocryst compositions and the presence or absence of stable hornblende the time involved from the mixing event through the eruption is limited to a period of 4 5 days based on fe ti oxide reequilibration phenocryst growth rates and hornblende breakdown the eruption sequence is interpreted as having been initiated by an injection of the 1060 15 c andesitic magma into the 980 c 7 km andesite storage region the mixed andesitic magma then intersected a shallow 2 4 km dacitic storage system on its way toward the surface the eruption became more dacitic over time and the final products some show evidence of partial reequilibration between the andesite and dacite

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

frequent eruptions of mount rainier over the last 2 600 years field geochronologic and geochemical evidence from proximal fine grained tephras and from limited exposures of holocene lava flows and a small pyroclastic flow document ten 12 eruptions of mount rainier over the last 2 600 years contrasting with previously published evidence for only 11 12 eruptions of the volcano for all of the holocene except for the pumiceous subplinian c event of 2 200 cal year bp the late holocene eruptions were weakly explosive involving lava effusions and at least two block and ash pyroclastic flows eruptions were clustered from 2 600 to 2 200 cal year bp an interval referred to as the summerland eruptive period that includes the youngest lava effusion from the volcano thin fine grained tephras are the only known primary volcanic products from eruptions near 1 500 and 1 000 cal year bp but these and earlier eruptions were penecontemporaneous with far traveled lahars probably created from newly erupted materials melting snow and glacial ice the most recent magmatic eruption of mount rainier documented geochemically was the 1 000 cal year bp event products from a proposed eruption of mount rainier between ad 1820 and 1854 x tephra of mullineaux us geol surv bull 1326 1 83 1974 are redeposited c tephra probably transported onto young moraines by snow avalanches and do not record a nineteenth century eruption we found no conclusive evidence for an eruption associated with the clay rich electron mudflow of 500 cal year bp and though rare non eruptive collapse of unstable edifice flanks remains as a potential hazard from mount rainier

dark inclusions in co3 chondrites new indicators of parent body processes abstract a petrographic and scanning electron microscopic study of the four co3 chondrites kainsaz ornans lance and warrenton reveals for the first time that dark inclusions dis occur in all the meteorites dis are mostly smaller in size than those reported from cv3 chondrites they show evidence suggesting that they were formed by aqueous alteration and subsequent dehydration of a chondritic precursor and so probably have a formation history similar to that of dis in cv3 chondrites dis in the co3 chondrites consist mostly of fine grained fe rich olivine and can be divided into two types on the basis of texture type i dis contain rounded porous aggregates of fine grains in a fine grained matrix and have textures suggesting that they are fragments of chondrule pseudomorphs veins filled with fe rich olivine are common in type i dis providing evidence that they experienced aqueous alteration on the parent body type ii dis lack rounded porous aggregates and have a matrix like featureless texture bulk chemical compositions of dis and mineralogical characteristics of olivine grains in dis suggest that these two types of dis have a close genetic relationship the dis are probably clasts that have undergone aqueous alteration and subsequent dehydration at a location different from the present location in the meteorites the major element compositions the mineralogy of metallic phases and the widely dispersed nature of the dis suggest that their precursor was co chondrite material the co parent body has been commonly regarded to have been dry homogeneous and unprocessed however the dis suggest that the co parent body was a heterogeneous conglomerate consisting of water bearing regions and water free regions and that during asteroidal heating the water bearing regions were aqueously altered and subsequently dehydrated brecciation may also have been active in the parent body the dis and the matrices are similarly affected by thermal metamorphism in their own host co3 chondrites petrologic subtypes 3 1 to 3 6 but the degree of the secondary processing aqueous alteration and subsequent dehydration of the dis has no apparent correlation with the petrologic grades of the host chondrites these observations suggest that the dis had been incorporated into the host chondrites before the thermal metamorphism took place and that the secondary processes that affected the dis largely occurred before the thermal metamorphism

some numerical considerations in the geochemical analysis of distal microtephra abstract the use of late quaternary tephra horizons as isochronous markers for high resolution correlation between records is of growing importance in a number of scientific fields particular advancements have been made through the identification of microtephra deposits very distal deposits of volcanic ash invisible to the naked eye the successful correlation of ash layers and volcanic eruptions depends on the acquisition of the major element chemistries of a tephra layer derived from microprobe analyses of individual glass shards this is particularly important for microtephras where aeolian fractionation has removed much of the mineral phase of the ash deposit which often aids tephra discrimination there are however difficulties in distinguishing precisely between different eruptions of the same volcano using major element composition and this may not always be resolved by the use of trace elements given the potential of tephrochronology as a correlative tool in many disciplines it is important to resolve this difficulty one way forward is to perform more robust statistical analyses on the geochemical data as in general analyses are confined to a series of bi plots of major elements here the authors explore some of the problems associated with dealing with microprobe data generated for individual tephras and pay particular attention to the unit sum problem using a subset of data generated as part of a eurodelta project on tephra distribution in the adriatic the authors demonstrate that this problem is detectable in major element data from tephras and have consequently applied the logratio method before further analyses of the data it is demonstrated that the use of logratios combined with discriminant functions analysis provides a more robust assessment of likely chemical correlations between tephras and are superior to the use of bi plots alone and obviate the need for any data normalization a particular point of contention between tephrochronologists

petrography and oxygen isotopic compositions in refractory inclusions from co chondrites fine grained ca al rich inclusions fgis in yamato 81020 co3 0 and kainsaz co3 1 co3 2 chondrites have been studied by secondary ion mass spectrometry the fgis from yamato 81020 consist of aggregates of hibonite spinel melilite anorthite diopside and olivine grains with no petrographic evidence of alteration in contrast the fgis from kainsaz commonly contain alteration products such as nepheline from replacement textures and chemical compositions of altered and unaltered fgis we conclude that the alteration products formed by decomposition of melilite and anorthite all phases in the yamato 81020 fgis are enriched in 16o with 17 18o 40 except for one fgi that experienced melting oxygen isotopic compositions of melilite anorthite some spinel and diopside in kainsaz fgis changed from 17 18o 40 toward 0 by aqueous alteration alteration products in fgis are depleted in 16o relative to primary phases with 17 18o 0 these results show that fgis in co chondrites commonly had 16o rich compositions in the solar nebula the original 16o rich fgis were modified to 16o poor compositions during aqueous alteration in the parent body

petrogenesis of mount rainier andesite magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern washington cascades quaternary mount rainier washington usa of the cascades magmatic arc consists of porphyritic calc alkaline andesites and subordinate dacites with common evidence for mingling and mixing with less evolved magmas encompassing andesites basaltic andesites and rarely basalts basaltic andesites and amphibole andesites spessartites that erupted from vents at the north foot of the volcano represent some of mount rainier s immediate parents and overlap in composition with regional basalts and basaltic andesites geochemical major and trace elements and isotopic sr nd pb o compositions of mount rainier andesites and dacites are consistent with modest assimilation typically 20 wt of evolved sediment or sediment partial melt sandstones and shales of the eocene puget group derived from the continental interior are exposed in regional anticlines flanking the volcano and probably underlie it in the middle to lower crust accounting for their assimilation mesozoic and cenozoic igneous basement rocks are unsuitable as assimilants due to their high 143 nd 144 nd diverse 206 pb 204 pb and generally high 18 o the dominant cause of magmatic evolution at mount rainier however is inferred to be a version of in situ crystallization differentiation and mixing langmuir 1989 wherein small magma batches stall as crustal intrusions and solidify extensively yielding silicic residual liquids with trace element concentrations influenced by accessory mineral saturation subsequent magmas ascending through the intrusive plexus entrain and mix with the residual liquids and low degree re melts of those antecedent intrusions producing hybrid andesites and dacites mount st helens volcanic rocks have geochemical similarities to those at mount rainier and may also result from in situ differentiation and mixing due to low and intermittent long term magma supply accompanied by modest crustal assimilation andesites and dacites of mount adams isotopically overlap the least contaminated mount rainier magmas and derive from similar parental magma types but have trace element variations more consistent with progressive crystallization differentiation probably due to higher magma fluxes leading to slower crystallization of large magma batches allowing time for progressive separation of minerals from melt mount adams also sits atop the southern projection of a regional anticlinorium so eocene sediments are absent or are at shallow crustal levels and so are cold and difficult to assimilate differences between southwest washington stratovolcanoes highlight some ways that crustal geology and magma flux are primary factors in andesite generation

holocene tephrostratigraphy and glacial fluctuations in waterton lakes and glacier national parks alberta and montana waterton lakes national park in alberta and glacier national park in montana lie along adjacent sections of the continental divide in the rocky mountains in cirques or near divides there is evidence for two ages of glacial deposits younger deposits are generally well preserved poorly vegetated and bear no tephra and no or very small lichens older deposits are more poorly preserved better vegetated bear rhizocarpon sp lichens at least up to 92 mm in diameter and bear tephra the tephra often occurs in two different coloured horizons but both are compositionally equivalent to mazama tephra the older advance has a minimum age of about 6800 14c years bp and a probable maximum age of about 12 000 14c years bp it is correlated with the pre mazama crowfoot advance of the canadian rockies deposits of the younger advance are probably not too much older than mid 19th century because some glaciers began retreating from the deposits about then the younger advance is correlated to the cavell advance of t

major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america keuhn s c froese d g carrara p e foit jr f f pearce n j g rotheisler p 2009 major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america quaternary research 71 2 201 216 sponsorship nserc discovery grant alberta ingenuity new faculty award to duane froese

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

evidence for successive episodes of condensation at high temperature in a part of the solar nebula abstract a centimeter sized ca al rich inclusion cai 3643 in the allende meteorite has preserved a record of its multiple stages of growth by condensation at high temperature it consists of three distinct concentric layers core mantle and crust the open textured core is composed of hibonite laths interstitial melilite and voids grains of alumina and osir metal nuggets in the inner core that are complementary in composition to rupt rich nuggets in the outer core the core formed out of rapidly aggregated crystals from two episodes of condensation in the same gaseous reservoir mo and w depletions in the nuggets indicate condensation from a relatively oxidizing gas with 60 times higher h 2 oh 2 than solar gas the compact mantle of coarse melilite contains perovskite inclusions and rare nife metal and sulfide grains the compact fine grained crust consists of melilite hibonite spinel perovskite and opaques similar to those in the mantle neither mantle nor crust has been molten each grew by condensation of solids directly onto the surface of the cai the formed cai experienced some metamorphic recrystallization of melilite and volatile alteration producing grossular feldspathoids and hercynite trace element analyses of perovskites and a bulk sample show the mantle and crust to be depleted in refractory elements i e group ii and complementary to the ultra refractory core despite differences in texture and composition the core mantle and crust display a continuity in their modal mineralogical compositions their extreme al 2 o 3 enrichments 53 69 cf 25 45 for other cai s and their trace element complementarity this implies that all the layers of 3643 formed from the same cooling gaseous reservoir within a limited interval of time and space consistent with an origin in a local transient heating event in the cv chondrite formation region of the nebula

nepheline and sodalite in the matrix of the ningqiang carbonaceous chondrite implications for formation through parent body processes abstract ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles cv3 chondrites the matrix of ningqiang shows much higher abundances of na k and al by factors of 4 4 2 7 and 1 6 respectively than in cv3 chondrites our scanning and transmission electron microscope observations and synchrotron radiation x ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite rietveld refinement of x ray diffraction data shows that the feldspathoids constitute 7 7 vol of all crystalline phases in the matrix nepheline and sodalite occur mostly as discrete equidimensional grains 2 5 m in diameter that are dispersed homogeneously in the matrix most of the grains contain inclusions of fe rich olivine and minor ca pyroxene magnetite troilite and pentlandite despite the high abundances of na k and al in the matrix of ningqiang the bulk meteorite abundances of these elements are comparable to those of the cv group e g rubin et al 1988 this means that the chondrules which constitute a major proportion of the volume other than the matrix in ningqiang are depleted in na k and al in fact our analyses and observations show that the chondrules in ningqiang overall contain very small amounts of these elements our interpretation of these findings suggests that nepheline and sodalite in the ningqiang matrix were originally formed by na metasomatism of the chondrules and ca al rich inclusions in the meteorite parent body afterward they were likely disaggregated and scattered into the matrix however it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite hence we suggest that the ningqiang meteorite underwent these processes before final lithification

anorthite spinel rich inclusions in the ningqiang carbonaceous chondrite genetic links with type a and c inclusions many ca al rich inclusions cais were molten once and the question of what their precursors consisted of is controversial in this paper we report a new type of anorthite spinel rich inclusion asi in the ningqiang carbonaceous chondrite the modal and bulk compositions of the asis are similar to those of type c inclusions but with nonmolten textures the asis are proposed to be the precursors of type c inclusions the asis show alteration textures with melilite being replaced by anorthite and ca pyroxene furthermore compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the asis are close to those of the spinel rich type a inclusions in the ningqiang meteorite which suggests that asis formed by alteration of the latter in the solar nebula petrography and mineral chemistry of one type c inclusion in ningqiang are also reported

olivine rich rims surrounding chondrules in the mokoia cv3 carbonaceous chondrite further evidence for parent body processes abstract fine grained rims surrounding chondrules and inclusions in the mokoia cv3 carbonaceous chondrite can be divided into phyllosilicate rich and olivine rich types we present a petrographic and electron microscopic study of the olivine rich rims and their host objects referred to as chondrules olivine rich rims the olivine rich rims consist mainly of fe rich olivine and very minor phyllosilicate saponite their host chondrules contain minor saponite and phlogopite which resulted from aqueous alteration of anhydrous silicates mineralogical and compositional characteristics of the chondrules olivine rich rims suggest that they experienced mild thermal metamorphic effects the rims commonly contain veins of coarse grained fe rich olivine magnetite and fe ni sulfides the chondrules show abundant evidence of alteration along their peripheries and the alteration textures suggest a mechanism for rim formation by replacement of the chondrules initially enstatite and opaque nodules preferentially reacted to form coarse platy fe rich olivine crystals which were subsequently divided into finer grains forsterite was also replaced by fe rich olivine as the alteration advanced these fe rich olivines were disaggregated mixed with simultaneously produced saponite and formed rims in contrast the surrounding matrix shows no evidence of such alteration and metamorphism these observations indicate that the chondrules olivine rich rims did not experience these secondary processes in their present setting the results suggest that the chondrules olivine rich rims experienced extensive replacement reactions in an environment in which aqueous fluids existed but only in minor amounts they have probably also undergone simultaneous and or subsequent mild thermal metamorphism we suggest that the chondrules olivine rich rims are actually clasts transported from a relatively dry region in the parent body that was different from the region where mokoia was finally lithified

comparison of wind measurements between yamagawa mf radar and the mu radar a new mf radar was installed at yamagawa 31 20 n 130 62 e japan in august 1994 by the communications research laboratory and the first comparison of wind measurements taken with the yamagawa mf radar and meteor wind measurements with the mu radar at shigaraki 34 85 n 136 10 e are carried out in spite of their spatial separation of approximately 650 km reasonable agreement between wind velocities by the two radars at 80 92 km in altitude is confirmed except for small scale perturbations that are probably due to gravity waves enhanced for the period from 17 h lt on september 13 to 7 h lt on september 14 1994 it is found that the winds of the mf radar above 92 km tend to be smaller than the winds obtained with the mu radar receiver saturation and interference are possible causes of the reduced wind velocities observed with the mf radar the height structures of semidiurnal tides are also compared the amplitude and phase of zonal components agree at most heights between the two radars for the meridional component the amplitudes fluctuate above 88 km with a significant difference and the phase from the mu radar leads that of the mf radar by less than several hours at 86 km to 92 km an enhanced gravity wave seems to pass over the mu radar almost from north to south resulting in a contamination of the meridional wind component of the semidiurnal variation

late quaternary volcanism in new zealand towards an integrated record using distal airfall tephras in lakes and bogs studies on distal airfall tephra layers preserved in lake sediments and peats in northern new zealand have documented the stratigraphic chronologic and compositional relationships of 46 eruptives aged c 17000 700yr bp which originated from six north island volcanic centres taupo 9 tephras okataina 8 maroa 1 rhyolitic mayor island 2 peralkaline tongariro 11 egmont 15 andesitic sources were distinguished by mineralogy and composition field relations and 14c chronology all known rhyolitic tephra producing eruptions from taupo okataina and maroa volcanoes since c 17000yr bp are represented but only a small proportion of the known tephras erupted from tongariro egmont or mayor island volcanoes is recorded the distal tephras from these latter volcanic centres may thus reflect atypically powerful or oblique eruptions or dispersal by strong winds an improved record of volcanism for the tongariro egmont and mayor island centres might be obtainable from suitable lakes or bogs more proximal to them

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

correlated petrologic and geochemical characteristics of co3 chondrites many properties of co3 chondrites have been shown previously to have resulted from thermal metamorphism petrologic subtypes 3 0 3 7 have been assigned to members of the group additional properties that correlate with the metamorphic sequence but seem to have resulted from hydrothermal alteration include the modal abundance of amoeboid olivine inclusions aoi chondrule size the types of refractory inclusions and whole rock o isotopic composition the percentage of rimmed aoi increases with petrologic subtype the rims most likely formed during hydrothermal alteration the previously reported correlation between aoi abundance and chondrite subtype is probably an artifact due to the difficulty in recognizing small unrimmed aoi in the least metamorphosed co3 chondrites because large 200 micron size porphyritic chondrules have nearly the same mean size in all co3 chondrites it seems likely that the correlation between chondrule size and subtype is due to alteration of the smallest chondrules to the point of unrecognizability as complete objects in the more metamorphosed co3 chondrites the previously reported decrease in the proportion of melilite rich refractory inclusions with increasing petrologic subtype may have resulted from more extensive hydrothermal alteration in co3 4 3 7 chondrites that converted primary melilite into ca pyroxene andradite and nepheline alteration probably caused the preferential occurrence of o 16 poor oxygen isotopes in the more metamorphosed whole rock samples

ubiquitous anorthitic plagioclase in type i chondrules in co3 chondrites implications for chondrule formation and parent body metamorphism

western canadian glaciers advance in concert with climate change circa 4 2 ka 1 disparate climate proxies from the northern hemisphere record a climate event at 4 2 3 8 ka here we show that glaciers throughout the mountain ranges of western canada advanced at about this time this conclusion is based on 1 new and previously reported radiocarbon ages on in situ stumps logs branches and soils exposed by recent retreat in glacier forefields and 2 clastic rich sediment intervals in cores retrieved from four montane lakes these glacier and lacustrine data indicate a period of several decades to century length when climate conditions cool summers wet winters or both favoured glacier nourishment and advance across western canada

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

mineralogy and petrography of amoeboid olivine aggregates from the reduced cv3 chondrites efremovka leoville and vigarano products of nebular condensation accretion and annealing amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka leoville and vigarano are irregularly shaped objects up to 5 mm in size composed of forsteritic olivine fa 50 melting we infer that aoas are aggregates of high temperature nebular condensates which formed in cai forming regions and that they were absent from chondrule forming regions at the time of chondrule formation the absence of low ca pyroxene and depletion in moderately volatile elements mn cr na k suggest that aoas were either removed from cai forming regions prior to condensation of these elements and low ca pyroxene or gas solid condensation of low ca pyroxene was kinetically inhibited

fluffy type a ca al rich inclusions in the allende meteorite abstract allende fluffy type a s fta s are a distinct sub group of ca al rich inclusions whose primary mineral assemblage consists of al rich melilite ak 0 33 spinel that is commonly very v rich perovskite and frequently hibonite some contain relatively coarse grained melilite up to 1 5 mm that is intensely kink banded and commonly reversely zoned hibonite and v rich spinel others contain much finer grained and strain free melilite 50 m and have not been found to contain hibonite or v rich spinel some fta s contain both coarser and finer grained melilite and textural relationships indicate that the latter is replacing the former fta s are characterized by extremely irregular shapes and 60 75 volume per cent of fine grained secondary alteration products many are aggregates of innumerable nodules each of which is surrounded by a wark lovering type rim sequence these nodules are frequently separated from one another by matrix like clastic rim material other fta s do not have nodular structure structural and mineralogical characteristics of their wark lovering rims suggest that fta s did not achieve their shapes by deformation of a liquid or a hot plastic solid in contrast to those in type b inclusions formation of reverse zoning in the coarser grained melilite crystals in fta s cannot be understood in terms of crystallization from a liquid but are readily explainable by condensation from a solar nebular gas during a period of falling pressure further evidence against a liquid origin is the wide range of spinel compositions within individual coarser grained fta s the fact that the reversely zoned melilite crystals cannot have been produced in any kind of sublimation or distillation process precludes formation of these inclusions as volatilization residues fta s are aggregates in some of which are preserved vapor solid condensate grains that formed at high temperature in the solar nebula

tephra geochemistry a discussion of some persistent analytical problems distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation this quantitation can involve difficulties not often encountered in more conventional petrology solving these problems is of particular importance in the holocene and late quaternary of northwest europe where numerous tephra layers of icelandic origin have been detected in peat bogs and lake and marine sediments electron probe microanalysis epma has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis standard epma techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature in many previous studies geochemical data of avoidably low quality have been produced and little attention appears to have been directed to modification of epma methods it is suggested that the black box approach to geochemical analysis should be avoided by the consideration of several factors these include

holocene and latest pleistocene fluctuations of stutfield glacier canadian rockies the holocene and late glacial history of fluctuations of stutfield glacier are reconstructed using moraine stratigraphy tephrochronology and dendroglaciology stratigraphic sections in the lateral moraines contain tills from at least three glacier advances separated by volcanic tephras and paleosols the oldest pre mazama till is correlated with the crowfoot advance dated elsewhere to be younger dryas equivalent a neoglacial till is found between the mazama tephra and a paleosol developed on the bridge river tephra a log dating 2400 bp from the upper part of this till indicates that this glacier advance correlated with the peyto advance culminated shortly before deposition of the bridge river tephra radiocarbon and tree ring dates from overridden trees exposed in moraine sections indicate that the initial cavell little ice age lia advance overrode this paleosol and trees after a d 1271 three subsequent phases of the cavell advance were dated by dendrochronology the maximum glacier extent occurred in the mid 18th century predating 1743 on the southern lateral although ice still occupied and tilted a tree on the north lateral in 1758 subsequent glacier advances occurred ca 1800 1816 and in the late 19th century the relative extent of the lia advances at stutfield differs from that of other major eastward flowing outlets of the columbia icefield which have maxima in the mid late 19th century this is the first study from the canadian rockies to demonstrate that the large morphologically simple lateral moraines defining the lia glacier limits are actually composite features built up pro gressively but discontinuously over the holocene and contain evidence of multiple holocene and crowfoot age gla cier advances resume la stratigraphie des moraines la tephrochronologie et la dendroglaciologie des moraines ont servi a recons truire les fluctuations a l holocene et au cours de l histoire glaciaire tardive du glacier stutfield les sections stratigra phiques dans les moraines laterales contiennent des tills d au moins trois avancees glaciaires separees par des tephras volcaniques et des paleosols le plus ancien le till pre mazama est correle a l avancee crowfoot dont on a determine l ge ailleurs comme etant un equivalent du dryas recent un till de l epoque neo glaciaire se retrouve entre le tephra mazama et un paleosol developpe sur le tephra de bridge river un billot date 2400 bp provenant de la partie supe rieure de ce till indique que cette avancee glaciaire correlee a l avancee de peyto a culmine peu de temps avant la deposition du tephra de bridge river des datations au 14 c et des series chronlogiques provenant d arbres recouverts puis exposes dans des sections de moraine indiquent que l avancee cavell initiale petit ge glaciaire a chevauche ce paleosol et les arbres apres l an 1271 la dendrochronologie a permis la datation de trois phases subsequentes de l avancee cavell l etendue glaciaire maximale eut lieu au milieu du 18e siecle avant 1743 sur le cote sud bien que la glace fut encore presente sur le cote nord et y ait bascule un arbre en 1758 des avancees glaciaires subsequentes ont eu lieu vers 1800 1816 et vers la fin du 19e siecle l etendue relative des avancees du petit ge glaciaire a stutfield differe de celles d autres glaciers majeurs du champ de glace columbia s ecoulant vers l est et qui ont eu leur maxi mum dans la deuxieme moitie du 19e siecle cette etude est la premiere provenant des rocheuses canadiennes a de monter que les grandes moraines laterales morphologiquement simples definissant les limites du glacier au petit ge glaciaire sont en fait des elements composites developpes progressivement mais de facon discontinue tout au cours de l holocene et qu elles contiennent des evidences d avancees glaciaires multiples d ge holocene et crowfoot

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

oxygen isotopic distribution in an amoeboid olivine aggregate from the allende cv chondrite primary and secondary processes the oxygen isotopic distribution in an amoeboid olivine aggregate aoa tta1 02 from the allende cv3 chondrite has been determined by secondary ion mass spectrometry the irregular shaped tta1 02 5 3mm consists mostly of olivine grains of ca 5 m in diameter olivine grains of mg rich fo95 and fe rich fo60 composition are in direct contact with each other with a sharp compositional boundary oxygen isotopic compositions of fe rich olivine grains are 16o poor 17o 5 whereas mg rich olivine is 16o rich 17o 25 several al rich inclusions ca 500 m in diameter are enclosed by olivine grains in the aoa oxygen isotopic compositions of spinel and fassaite in al rich inclusions are 16o rich 17o 20 whereas those of anorthite nepheline and phyllosilicate are 16o poor 17o 5 we propose the following sequence of events during the formation of aoas in the allende meteorite 1 formation of al rich inclusions with 16o rich oxygen isotopic composition 2 accretion of mg rich olivine grains with 16o rich oxygen isotopic composition around al rich inclusions 3 accretion into parent body and 4 aqueous alteration in the parent body which led to crystallization of 16o poor minerals fe rich olivine anorthite nepheline and phyllosilicate this is reflecting reactions among primary 16o rich aoa minerals and aqueous fluid having 16o poor oxygen isotopic composition fe rich olivine grains precipitated from aqueous fluids which partially dissolved pre existing mg rich olivine grains sintering and mg fe diffusion occurred during thermal metamorphism anorthite nepheline and phyllosilicate in al rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage

a high precision age estimate of the holocene plinian eruption of mount mazama oregon usa the climactic eruption of mount mazama in oregon north america resulted in the deposition of the most widespread holocene tephra deposit in the conterminous united states and south western canada the tephra forms an isochronous marker horizon for palaeoenvironmental sedimentary and archaeological reconstructions despite the current lack of a precise age estimate for the source eruption previous radiocarbon age estimates for the eruption have varied and greenland ice core ages are in disagreement for the mazama tephra to be fully utilised in tephrochronology and palaeoenvironmental research a refined precise and accurate age for the eruption is required here we apply a meta analysis of all previously published radiocarbon age estimations n 81 and perform bayesian statistical modelling to this data set to provide a refined age of 7682 7584 cal yr bp 95 4 probability range although the depositional histories of the published ages vary this estimate is consistent with that estimated from the gisp2 ice core of 7627 150 yr bp zdanowicz et al 1999

variation in cascade volcanism with margin orientation the orientation of the convergent margin of the juan de fuca subduction zone changes from north south off oregon to northwest southeast off british columbia because of this change the effective ratio of overriding plate velocity to roll back velocity of the subducting plate increases by at least 20 from oregon to british columbia this appears to alter the tectonic regime from slightly extensional in oregon to slightly compressional in washington and british columbia and thus may account for the lesser amount of volcanism at the northern end of the cascade volcanic chain the variation in margin geometry may also explain other tectonic features such as initiation of the nootka fault zone and the quaternary change of the volcanic pattern in british columbia

indicators of parent body processes hydrated chondrules and fine grained rims in the mokoia cv3 carbonaceous chondrite abstract a petrographic and electron microscopic study of the mokoia cv3 carbonaceous chondrite shows that all of the chondrules and inclusions 400 m in diameter and most of their fine grained rims studied referred to as chondrules rims contain various amounts of hydrous phyllosilicates mostly saponite formed by aqueous alteration of anhydrous silicates the rims mainly consist of fine grained olivine and saponite in varying proportions and contain crosscutting veins of fe rich olivine the boundaries between the chondrules and their rims are irregular and show abundant evidence of aqueous alteration interactions between them in contrast the host matrix contains very minor amounts of saponite and shows no evidence of such extensive aqueous alteration the boundaries between the chondrules rims and the matrix are sharp and show no traces of the matrix having been involved in the alteration of the chondrules rims these observations indicate that the aqueous alteration in the chondrules rims did not occur in the present setting we suggest that the chondrules rims are actually clasts transported from a location on the meteorite parent body different from where the mokoia meteorite was from the aqueous alteration of the chondrules rims probably occurred there the veins in the rims were originally fractures produced in an interchondrule matrix by impacts these were later filled by fe rich olivine during aqueous activity this location was then involved in impact brecciation and individual chondrules were ejected as clasts with remnants of the matrix surrounding them during the continuing brecciation those chondrule rim clasts were transported mixed with anhydrous matrix grains and finally lithified to the present meteorite therefore the rims are fragmented remnants of a former matrix textures characterized by fine grained rims surrounding chondrules in chondrites have been widely thought to have formed in the solar nebula before they accreted into their parent bodies however our results suggest that some textures may not be explained by such an accretionary model instead the multi stage parent body process modeled for the mokoia rim formation may be a more plausible explanation

petrology and mineralogy of the ningqiang carbonaceous chondrite we report detailed chemical petrological and mineralogical studies on the ningqiang carbonaceous chondrite ningqiang is a unique ungrouped type 3 carbonaceous chondrite its bulk composition is similar to that of cv and ck chondrites but refractory lithophile elements 1 01 x ci are distinctly depleted relative to cv 1 29 x ci and ck 1 20 x ci chondrites ningqiang consists of 47 5 vol chondrules 2 0 vol ca al rich inclusions cals 4 5 vol amoeboid olivine aggregates aoas and 46 0 vol matrix most chondrules 95 in ningqiang are mg rich the abundances of fe rich and al rich chondrules are very low al rich chondrules arcs in ningqiang are composed mainly of olivine plagioclase spinel and pyroxenes in arcs spinel and plagioclase are enriched in moderately volatile elements cr mn and na and low ca pyroxenes are enriched in refractory elements al and ti the petrology and mineralogy of arcs in ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes we found 294 cals 55 0 type a 39 5 spinel pyroxene rich 4 4 hibonite rich and several type c and anorthite spinel rich inclusions and 73 aoas in 15 ningqiang sections equivalent to 20 cm 2 surface area this is the first report of hibonite rich inclusions in ningqiang they are texturally similar to those in cm ch and cb chondrites and exhibit three textural forms aggregates of euhedral hibonite single crystals fine grained aggregates of subhedral hibonite with minor spinel and hibonite al ti diopside spinel spherules evidence of secondary alteration is ubiquitous in ningqiang opaque assemblages formed by secondary alteration of pre existing alloys on the parent body are widespread in chondrules and matrix on the other hand nepheline and socialite existing in all chondritic components formed by alkali halogen metasomatism in the solar nebula

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

alteration of al rich inclusions inside amoeboid olivine aggregates in the allende meteorite lightly altered al rich inclusions in amoeboid olivine aggregates have cores containing primary melilite fassaite spinel perovskite and no secondary alteration products in moderately altered inclusions whose cores now contain only fassaite spinel perovskite melilite was replaced by a fine grained mixture of grossular anorthite feldspathoids and perovskite was partially replaced by ilmenite in heavily altered inclusions fassaite has been replaced by a mixture of phyllosilicates ilmenite and the remaining primary phases are spinel perovskite in very heavily altered inclusions no primary phases remain the spinel having reacted to form either phyllosilicates or a mixture of olivine feldspathoids this sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures during alteration sio2 na2o k2o feo cr2o3 h2o and cl were introduced into the inclusions and cao was lost mgo may have been lost during the melilite reaction and added during formation of phyllosilicates electron microprobe analyses indicate that the phyllosilicates are a mixture of na rich phlogopite and chlorite or alrich serpentine thermodynamic calculations suggest that at a solar nebular water fugacity of 10 6 na rich phlogopite could have formed from fassaite at 470 k and chlorite from na rich phlogopite at 328 k olivine mantling al rich inclusions is not serpentinized suggesting that these objects stopped equilibrating with the nebular gas above 274 k

effects of tephra addition on soil processes in spodosols in the cascade range washington u s a abstract a study was conducted in the cascade range of washington state u s a to examine the effects of tephra additions on soil processes occurring in spodosols unleached tephra from the 18 may 1980 mt st helens eruption was applied in 5 or 15 cm depths to soils that had escaped airfall tephra deposition in 1980 but had received periodic additions of tephra during the holocene soil solutions were collected from the major genetic horizons of tephra treated and non treated profiles interpretation of soil solution composition provided an instantaneous record of the response of soil processes to the added tephra soluble salts composed of basic cations ca2 na mg2 k and so42 were initially leached from the tephra basic cations in the leachate displaced h and al3 from the exchange sites in the original upper horizons the soluble salts and al3 migrated through the soil profile where their concentrations were greatly attenuated by interaction with the solid phase calcium k al3 and so42 were strongly retained in the b horizons whereas na mg2 and cl showed little affinity for the solid phase biological uptake anion adsorption exchange reactions and neoformation of minerals may all be responsible for the differential movement of solutes through the soil profile no enhancement of elemental leaching was measured from the c horizon during the first four months of monitoring podzolization the prevailing process in these mountains was relatively unaffected by the addition of tephra

defining the potential source region of volcanic ash in northwest europe during the mid to late holocene abstract far travelled volcanic ash fine grained tephra clouds pose economic and societal risks largely through their potential impact on the aviation industry a long view of ash clouds extending over northwest europe assembled from the study and geochemical characterisation of cryptotephra i e tephra invisible to the naked eye in sedimentary records can help inform the understanding of the frequency of such events and the nature of eruptions that generate them here we review the records of cryptotephra deposition in northwest europe during the mid to late holocene the last eight millennia to gain insights into the sources of volcanic ash reaching this region we consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from ireland to latvia and on the basis of their major element geochemical composition we identify 90 unique ash horizons and their likely provenance the majority 72 of the cryptotephras derive from icelandic eruptions but a large proportion 24 originates from other volcanic regions including alaska the cascades kamchatka mexico the azores and possibly the mediterranean although moderate magnitude eruptions in iceland may potentially disperse ash clouds over europe it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed nevertheless the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid to high latitudes particularly those to the west of europe as well as in tropical north america have the potential to extend to northwest europe volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by icelandic eruptions but also by any large magnitude eruptions in north america or the north pacific area

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

al mg isotopic evidence for episodic alteration of ca al rich inclusions from allende textures mineral assemblages and al mg isotope systematics indicate a protracted episodic secondary mineralization history for allende ca al rich inclusions cais detailed observations from one type b1 cai one b2 one compact type a cta and one fluffy type a fta indicate that these diverse types of cais are characterized by two distinct textural and mineralogic types of secondary mineralization 1 grossular rich domains concentrated along melilite grain boundaries in cai interiors and 2 feldspathoid bearing domains confined mostly to cai margins just interior to the wark lovering rim sequence the al mg isotopic compositions of most secondary minerals in the type b1 cai and some secondary minerals in the other cais show no resolvable excesses of 26mg whereas the primary cai phases mostly yield correlated excesses of 26mg with increasing al mg corresponding to canonical initial 26al 27al 4 55 10 5 these secondary minerals formed at least 3 ma after the primary cai minerals all but two analyses of secondary minerals from the fluffy type a cai define a correlated increase in 26mg 24mg with increasing al mg yielding 26al 27al 0 4 9 2 8 10 6 the secondary minerals in this cai formed 1 8 3 2 ma after the primary cai minerals in both cases the timing of secondary alteration is consistent with but does not necessarily require alteration in an asteroidal setting one grossular from the type b2 cai and several grossular and secondary feldspar analyses from the compact type a cai have excesses of 26mg consistent with initial 26al 27al 4 5 10 5 especially in the compact type a cai where 26mg 24mg in grossular correlates with increasing al mg these 26mg excesses are almost certainly due to in situ decay of 26al they indicate a nebular setting for formation of the grossular the preservation of these diverse isotopic patterns indicates that heating on the allende parent body was not pervasive enough to reset isotopic systematics of fine grained secondary minerals secondary mineralization clearly was not restricted to a short time interval and at least some alteration occurred coincident with cai formation and melting events chondrule formation in the nebula this observation supports the possibility that alteration followed by melting affected the compositional evolution of cais

redistribution of chondrules in a carbonaceous chondrite parent body a model abstract carbonaceous chondrites mainly consist of chondrules and inclusions embedded in a fine grained matrix this texture is widely believed to have formed primarily by direct accretion of solar nebular materials although it may have been modified to various extents by subsequent parent body processes recently we studied all chondrules and inclusions larger than 400 m in diameter and their rims referred to as chondrules rims in the mokoia cv3 carbonaceous chondrite using a scanning electron microscope and found that the chondrules rims experienced various degrees of aqueous alteration and that some also exhibit evidence of thermal metamorphism the mineralogical and petrographic characteristics of the chondrules rims suggest that the alteration and metamorphism occurred within the meteorite parent body in contrast however the surrounding matrix does not show evidence of such alteration and metamorphism these findings indicate that the alteration and metamorphism of the chondrules rims did not occur in situ based on these results we proposed a model that the chondrules rims are actually clasts transported from regions in the parent body different from the location where the host meteorite was finally lithified if it can be assumed that the chondrules and inclusions studied are representative of all chondrules and inclusions in mokoia the results and interpretation pose a fundamental challenge regarding the formation of the whole mokoia lithology that is it cannot be explained by either direct accretion of the solar nebula or conventional parent body brecciation we propose a model for the development of the mokoia lithology through formation of chondrules rims and fine matrix grains by fragmentation in different regions in the parent body followed by transportation mixing and accumulation in a fluid state and finally lithification of those objects these processes may have been repeated cyclically within the parent body

sodium metasomatism in chondrules in co3 chondrites relationship to parent body thermal metamorphism we have studied the mineralogy and petrology of mesostases of 783 type i chondrules in seven co3 chondrites that range in petrologic subtype from 3 0 to 3 7 chondrule mesostases in the co chondrite of subtype 3 0 consist mainly of primary glass and plagioclase while chondrule mesostases in the co chondrites of higher subtypes 3 2 3 7 contain various amounts of nepheline in addition to glass and plagioclase nepheline has replaced glass and plagioclase forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase the nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites nepheline also has a tendency to increase in grain size with increasing petrologic subtype we conclude that nepheline in chondrules in the co3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body we suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids the degree of hydrothermal activity must have increased with increasing degree of heating and thus chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline the results imply that co3 chondrites have gone through lowgrade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body

hydrous and anhydrous alterations of chondrules in kaba and mokoia cv chondrites chondrules in the bali like cv chondrite kaba and the allende like portion of the mokoia breccia have been studied to explore the relationship between hydrous alteration to form phyllosilicates and anhydrous alteration resulting in secondary olivine zonation replacement of enstatite by ferroan olivine and formation of feldspathoids nepheline and sodalite all kaba chondrules experienced extensive hydrous alteration whereas anhydrous alteration was minor and resulted only in the olivine zonation on the other hand all of the mokoia chondrules experienced both extensive anhydrous and hydrous alteration bronzite rims formed between relic enstatite grains and phyllosilicates in both kaba and mokoia during the hydrous alteration petrographic observations indicate that phyllosilicates in mokoia postdate formation of the secondary ferroan olivine and feldspathoids we conclude that anhydrous alteration in kaba and mokoia predated hydrous alteration and took place before accretion of chondrules into the cv parent asteroid

an inter laboratory comparison of the electron probe microanalysis of glass geochemistry abstract tephrochronology commonly relies upon grain discrete analysis of glass shards to reveal the subtle geochemical differences between tephras from past explosive volcanic eruptions the use of electron probe microanalysis for this purpose is widely accepted by tephrochronologists it is widely recognised that both precision and accuracy must be maximised and that rigorous standardisation procedures must be followed in this paper the performances of seven northern european electron microprobe centres are compared using a geochemically homogeneous obsidian secondary standard the results reveal that a number of tephra oriented probe centres could benefit from exercises similar to the programme outlined within in particular it is evident that a number of these centres undertaking tephrochronological investigations have generated geochemical data that may be inadequate in terms of distinguishing between tephras inaccuracy in the determination of sodium is seen to be the main difficulty in recent years the application of distal tephrochronology to stratigraphical problems in the northern european quaternary record has become increasingly common geochemical standardisation is essential at an early stage in the development of a regional tephrochronological framework and we hope exercises such as presented here will encourage the production of reliable tephra geochemical data

geochemical characterization and dating of r tephra a postglacial marker bed in mount rainier national park washington usa the oldest postglacial lapilli ash tephra recognized in sedimentary records surrounding mount rainier washington state usa is r tephra a very early holocene deposit that acts as an important stratigraphic and geochronologic marker bed this multidisciplinary study incorporates tephrostratigraphy radiocarbon dating petrography and electron microprobe analysis to characterize r tephra tephra samples were collected from tipsoo lake and a stream cut exposure in the cowlitz divide area of mount rainier national park field evidence from 25 new sites suggests that r tephra locally contains internal bedding and has a wider distribution than previously reported herein we provide the first robust suite of geochemical data that characterize the tephra glass compositions are heterogeneous predominantly ranging from andesite to rhyolite in ash to lapilli sized clasts the mineral assemblage consists of plagioclase orthopyroxene clinopyroxene and magnetite with trace apatite and ilmenite subaerial r t

secondary calcium iron rich minerals in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions we have characterized ca fe rich silicates salite hedenbergite pyroxenes fs10 50wo45 50 andradite ca3fe2si3o12 kirschsteinite cafesio4 and wollastonite ca3si3o9 in the type i chondrules and matrices in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions in type i chondrules in the bali like cv3 chondrites metal is oxidized to magnetite magnetite sulfide nodules are replaced by ca fe rich pyroxenes with minor andradite and pure fayalite we infer that ca fe rich pyroxenes andradite fayalite magnetite and phyllosilicates which occur in mesostases formed at relatively low temperatures 300 c in the presence of aqueous solutions thermodynamic analysis of phase relations in the si fe ca o h system and large o isotopic fractionation of the coexisting magnetite and fayalite 20 krot et al 1998 are consistent with this interpretation in type i chondrules in the allende like cv3 chondrites and dark inclusions magnetite sulfide nodules are replaced by ca fe rich pyroxenes and ferrous olivine low ca pyroxene and forsterite phenocrysts are rimmed and veined by ferrous olivine it appear that the ca fe rich pyroxenes predate formation of ferrous olivine the latter postdates formation of talc and biopyriboles brearley 1997 the allende dark inclusions are crosscut by ca fe pyroxene andradite veins and surrounded by ca rich rims that consist of ca fe rich pyroxenes andradite wollastonite and kirschsteinite calcium rich veins and rims formed after aggregation and lithification of the dark inclusions the rimmed dark inclusions show zoned depletion in ca which is due to a lower abundance of ca fe rich pyroxenes close to the rim calcium was probably leached from the inclusions and redeposited along their edges we infer that the allende like chondrites and dark inclusions experienced similar aqueous alteration to the bali like chondrites and were metamorphosed subsequently which resulted in loss of aqueous solutions and dehydration of phyllosilicates we conclude that ca fe rich silicates in the oxidized cv3 chondrites and allende dark inclusions are secondary and resulted from aqueous fluid rock interactions during progressive metamorphism of a heterogeneous mixture of hydrous ices and anhydrous materials the latter were possibly mineralogically similar to the reduced cv3 chondrites

early holocene glacier advance southern coast mountains british columbia canada abstract terrestrial and lake sediment records from several sites in the southern coast mountains british columbia provide evidence for an advance of alpine glaciers during the early holocene silty intervals within organic sediments recovered from two proglacial lakes are bracketed by ams 14 c dated terrestrial macrofossils and mazama tephra to 8780 6730 and 7940 6730 14 c yr bp 10 150 7510 and 8990 7510 cal yr bp radiocarbon ages ranging from 7720 to 7380 14 c yr bp 8630 8020 cal yr bp were obtained from detrital wood in recently deglaciated forefields of sphinx and sentinel glaciers these data together with previously published data from proglacial lakes in the canadian rockies imply that glaciers in western canada advanced during the early holocene the advance coincides with the well documented 8200 yr cold event identified in climate proxy data sets in the north atlantic region and elsewhere

field weathering rates of mt st helens tephra the initial stages of chemical weathering in tephra were examined under field conditions in a cool and humid forest ecosystem in the cascade mountains of washington unleached tephra from the 1980 eruption of mt st helens was applied in 5 cm and 15 cm depths to simulate natural tephra deposition leachate solutions from the tephra were then collected and analyzed over a 4 year period concentrations of dissolved elements were combined with the water fluxes to determine elemental fluxes from tephra and to estimate chemical weathering rates solutions leached from the tephra layer indicate incongruent dissolution resulting in formation of a cation depleted silica rich leached layer on glass and mineral surfaces measured weathering rates were 1 3 orders of magnitude less than comparable rates reported in the literature for laboratory dissolution studies but considerably greater than those measured for entire watersheds in field studies dissociation of carbonic acid originating primarily from upward transport of carbon dioxide from the buried soil was the dominant source of protons for weathering reactions weathering rates in the 5 cm treatment were approximately twice those of the 15 cm treatment a greater flux of co2 per unit volume of tephra in the 5 cm treatment is believed to be responsible for the differential weathering rates

nepheline and sodalite in chondrules of the ningqiang carbonaceous chondrite implications for a genetic relationship with those in the matrix abstract ningqiang is an ungrouped carbonaceous chondrite that has a chemical and mineralogical affinity to cv3 chondrites the ningqiang matrix has distinctly higher abundances of na k and al than cv3 matrices a recent study by matsumoto et al 2014 revealed that the major proportions of these elements can be attributed to the presence of nepheline and sodalite scanning electron microscopy revealed that all of the ningqiang chondrules studied show abundant evidence of extensive na fe metasomatism only a small proportion of the chondrules contain primary mesostases in their cores but the mesostases in their mantles were replaced by fine grains of nepheline sodalite fe rich olivine and hedenbergite the mesostases in the majority of the chondrules were completely replaced by fine grains of the same secondary minerals most opaque nodules were also largely replaced by various fine grained secondary minerals nepheline sodalite form veins penetrating the primary mesostases providing evidence that aqueous fluids were involved in the alteration reactions the nepheline sodalite in the mesostases contain various amounts of inclusions of fe rich olivine diopside hedenbergite fe sulfides and magnetite the mineralogical features of the nepheline sodalite in the mesostases are almost identical to those in the meteorite matrix these results suggest that a significant fraction of the nepheline sodalite grains in the ningqiang matrix originated from the nepheline sodalite produced in chondrules and refractory inclusions and that they were disaggregated and mixed into the matrix these processes can be explained consistently by the model of the dynamic formation of chondrite lithology in a parent body proposed by tomeoka and ohnishi 2015 we suggest that after a ningqiang precursor with a cv3 like lithology was metasomatized it was fragmented causing the disaggregation of the fine grained host matrix and the fine grained altered mesostases including nepheline sodalite and opaque nodules in the chondrules the chondrules were thereby separated into multiple fragments subsequently during transportation in a fluidized state all these materials were homogenously mixed together and later underwent accumulation and lithification

extent timing and climatic implications of glacier advances mount rainier washington u s a at the pleistocene holocene transition abstract the north atlantic younger dryas climatic reversal did not cause a glacier advance on mount rainier the glaciers on mount rainier seem to have advanced in response to regional or local shifts in climate however the younger dryas climatic reversal may have affected the mount rainier area causing a cold but dry climate unfavorable to glacier advances glaciers in the vicinity of mount rainier advanced twice during late glacial early holocene time radiocarbon dates obtained from lake sediments adjacent to the corresponding moraines are concordant indicating that the ages for the advances are closely limiting the first advance occurred before 11 300 14c yr bp 13 200 cal yr bp during the north atlantic younger dryas event between 11 000 and 10 000 14c yr bp 12 900 and 11 600 cal yr bp glaciers retreated on mount rainier probably due to a lack of available moisture but conditions may have remained cold the onset of warmer conditions on mount rainier occurred around 10 000 14c yr bp 11 600 cal yr bp organic sedimentation lasted for at least 700 years before glaciers readvanced between 9800 and 8950 14c yr bp 10 900 and 9950 cal yr bp

mineralogy and weathering processes in recent and holocene tephra deposits of the pacific northwest usa abstract weathering and evolution of minerals in tephra deposits in the cascade range of washington state usa are influenced by climate vegetation time microtopography and in the vicinity of mt st helens naturally acidic precipitation we have observed the interaction of these factors in spodosols developed on holocene tephra in the central cascades and in entisols formed on the 1980 pyroclastic flow of mt st helens weathering regimens in these tephritic soils can be qualitatively characterized by the soil solution composition weathering reactions in the spodosol are driven by organic acids in the upper soil horizons and by carbonic acid in the lower b and c horizons the mineral assemblage in the spodosol reflects in part the chemical regimen dictated by each proton donor the presence of smectite in the highly acidic e horizon ph