metal troilite magnetite assemblage in shock veins of sixiangkou meteorite the first natural occurrence of metal troilite magnetite assemblage composed of fe ni metal and magnetite dendrites and a groundmass of troilite was identified in the shock veins of the sixiangkou l6 chondrite which contain abundant high pressure minerals this assemblage suggests a liquid miscibility among metal fes and iron oxide and subsequently quenching under pressure components of magnetite could be in origin related to chromite that was embedded and dissolved in an fe ni s liquid cr2o3 dissociated from chromite was mainly incorporated into garnet and magnesiowustite in the fine grained matrix of shock veins in which chromium behaves as a lithophile element at the p t conditions experienced by the shock veins the occurrence of metal troilite magnetite assemblage suggests that the shock veins were still under pressure at temperatures from 900 to 950degreesc during solidification of fe ni s or fe ni s o liquid hence indicating a long duration of high pressure in the shock veins copyright c 2002 elsevier science ltd

comparison of geodetic and glaciological mass balance techniques gulkana glacier alaska u s a the net mass balance on gulkana glacier alaska u s a has been measured since 1966 by the glaciological method in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier systematic errors can accumulate linearly with time in this method therefore the geodetic balance in which errors are less time dependent was calculated for comparison with the glaciological method digital elevation models of the glacier in 1974 1993 and 1999 were prepared using aerial photographs and geodetic balances were computed giving 6 0 0 7 m w e from 1974 to 1993 and 11 8 0 7 m w e from 1974 to 1999 these balances are compared with the glaciological balances over the same intervals which were 5 8 0 9 and 11 2 1 0 m w e respectively both balances show that the thinning rate tripled in the 1990s these cumulative balances differ by 6 for this close agreement the glaciologically measured mass balance of gulkana glacier must be largely free of systematic errors and be based on a time variable area altitude distribution and the photography used in the geodetic method must have enough contrast to enable accurate photogrammetry

on the characterization of glacier response by a single time scale glacier response to climate can be characterized by a single time scale when the glacier changes sufficiently slowly then the derivative of volume with respect to area defines a thickness scale similar to that of johannesson and others and the time scale follows from it our version of the time scale is different from theirs because it explicitly includes the effect of surface elevation on mass balance rate which can cause a major increase in the time scale or even lead to unstable response the time constant has a dual role controlling both the rate and magnitude of response to a given climate change data from south cascade glacier washington u s a illustrate the ideas some of the difficulty in obtaining accurate values for the thickness and time scales and the susceptibility of all response models to potentially large errors

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

the compositions of incipient shock melts in l6 chondrites abstract microprobe analyses of 33 melt pocket glasses in five l6d and l6e chondrites show them to be chemically varied but typically enriched in the constituents of plagioclase relative to the host meteorites this enrichment appears to increase with the degree of melting 0 6 5 vol but other chemical variations among the glasses sodium depletion reduction of ferrous iron appear to be unrelated to shock intensity and melt abundance chemical trends for melt pocket glasses differ sharply from those reported for chondrules in ordinary chondrites thus partial shock melting of chondritic material is an inadequate explanation for the chemical properties of chondrules

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

implications for the dynamic health of a glacier from comparison of conventional and reference surface balances conventional and reference surface mass balance data from gulkana and wolverine glaciers alaska usa are used to address the questions of how rapidly these glaciers are adjusting or responding to climate whether their responses are stable and whether the glaciers are likely to survive in today s climate instability means that a glacier will eventually vanish or at least become greatly reduced in volume if the climate stabilizes at its present state a simple non linear theory of response is presented for the analysis the response of gulkana glacier is characterized by a timescale of several decades but its stability and therefore its survival in today s climate are uncertain wolverine seems to be responding to climate more slowly on the timescale of one to several centuries its stability is also uncertain but a slower response time would make it more susceptible to climate changes

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

reanalysis of the us geological survey benchmark glaciers long term insight into climate forcing of glacier mass balance mountain glaciers integrate climate processes to provide an unmatched signal of regional climate forcing however extracting the climate signal via intercomparison of regional glacier mass balance records can be problematic when methods for extrapolating and calibrating direct glaciological measurements are mixed or inconsistent to address this problem we reanalyzed and compared long term mass balance records from the us geological survey benchmark glaciers these five glaciers span maritime and continental climate regimes of the western united states and alaska each glacier exhibits cumulative mass loss since the mid 20th century with average rates ranging from 0 58 to 0 30 m w e a 1 we produced a set of solutions using different extrapolation and calibration methods to inform uncertainty estimates which range from 0 22 to 0 44 m w e a 1 mass losses are primarily driven by increasing summer warming continentality exerts a stronger control on mass loss than latitude similar to elevation topographic shading snow redistribution and glacier surface features often exert important mass balance controls the reanalysis underscores the value of geodetic calibration to resolve mass balance magnitude as well as the irreplaceable value of direct measurements in contributing to the process based understanding of glacier mass balance

the halite bearing zag and monahans 1998 meteorite breccias shock metamorphism thermal metamorphism and aqueous alteration on the h chondrite parent body zag and monahans 1998 are h chondrite regolith breccias comprised mainly of light colored metamorphosed clasts dark clasts that exhibit extensive silicate darkening and a halite bearing clastic matrix these meteorites reflect a complex set of modification processes that occurred on the h chondrite parent body the light colored clasts are thermally metamorphosed h5 and h6 rocks that were fragmented and deposited in the regolith the dark clasts formed from light colored clasts during shock events that melted and mobilized a significant fraction of their metallic fe ni and troilite grains the clastic matrices of these meteorites are rich in solar wind gases parent body water was required to cause leaching of chondritic minerals and chondrule glass the fluids became enriched in na k cl br al ca mg and fe evaporation of the fluids caused them to become brines as halides and alkalies became supersaturated grains of halite and in the case of monahans 1998 halite with sylvite inclusions precipitated at low temperatures 100 c in the porous regolith in both meteorites fluid inclusions were trapped inside the halite crystals primary fluid inclusions were trapped in the growing crystals secondary inclusions formed subsequently from fluid trapped within healed fractures

post shock annealing of miller range 99301 ll6 implications for impact heating of ordinary chondrites mil 99301 is an ll chondrite that has experienced successive episodes of thermal metamorphism shock metamorphism and annealing the first recognizable petrogenetic episode resulted in thermal metamorphism of the rock to petrologic type 6 as indicated by homogeneous olivine compositions significant textural recrystallization and the presence of coarse grains of plagioclase metallic fe ni and troilite the source of heat for this thermal episode is not identified the rock also experienced shock metamorphism to shock stage s4 as indicated by extensive silicate darkening caused by the dispersion within silicate grains of thin chromite melt veins and trails of metallic fe ni and troilite blebs polycrystalline troilite myrmekitic plessite a relatively high occurrence abundance oa of metallic cu 3 6 the presence of numerous chromite plagioclase assemblages and coarse grains of low ca clinopyroxene with polysynthetic twinning the shock event responsible for these effects must have occurred after the epoch of thermal metamorphism to type 6 levels otherwise the polycrystallinity of the troilite would have disappeared and the low ca clinopyroxene would have transformed into orthopyroxene despite abundant evidence of strong shock olivine and plagioclase in mil 99301 exhibit sharp optical extinction consistent with shock stage s1 and characteristic of an unshocked rock this implies that an episode of post shock annealing healed the damaged olivine and plagioclase crystal lattices and thereby changed undulose extinction into sharp extinction the rock was probably annealed to metamorphic levels approximating petrologic type 4 more significant heating would have transformed the low ca clinopyroxene into orthopyroxene it is not plausible that an episode of annealing occurring after the epoch of thermal metamorphism could have been caused by the decay of 26al because this isotope would have decayed away by that time impact heating is a more plausible source of post metamorphic annealing of rocks in the vicinity of impact craters on low density high porosity asteroids with rubble pile structures

39ar40ar age and petrology of chico large scale impact melting on the l chondrite parent body our studies of the 105 kg chico l chondrite show that it contains 60 impact melt and the largest volume of impact melt recognized in stony meteorites we suggest that it is part of a much larger dike complex that formed when chondritic impact melt was intruded into host chondrite during a large if not catastrophic impact on the l chondrite parent body at about 0 5 ga petrologic and 39ar 40ar dating studies were made on several lithologies including the massive melt zone host chondrite and melt chondrite boundaries for the purpose of studying the melting and thermal histories associated with impacts on small bodies and their effects on the k ar chronometer the chondritic host is shocked to stage s6 and contains pockets and veins of melt there are no unmelted clasts in the interior of the melt coalesced metal troilite nodules reach up to 2 cm in size melt near the contact with the host chondrite contains numerous clasts and quenched more rapidly metal troilite textures suggest cooling rates of 0 1 c s in the interior of the melt dike during crystallization secondary kamacite rims indicate cooling at 0 01 1 c y over the range of 700 500 c consistent with an impact heated volume of up to a kilometer in thickness compositions of olivines and pyroxenes are generally similar in melt and chondritic host reflecting rapid crystallization not metamorphic equilibration the interior melt shows an overall depletion in k whereas the melt near the boundary is enriched in k the 39ar 40ar release spectra during stepwise heating of both melt and chondrite samples can be divided into two parts based on ar diffusion properties and k ca ratios the low temperature high k ca phase of both melt and host chondrite show ages of 0 54 0 78 ga ages of the high temperature low k ca phase of the melt are comparable or higher 0 61 1 35 ga whereas those of the host chondrite are even higher 0 87 1 86 ga due to lesser degrees of degassing isochron plots for several melt samples suggest an age of 0 53 ga and the presence of variable amounts of excess 40ar not completely degassed by the impact even this age however is significantly higher than the previously reported rb sr isochron age of 0 467 015 ga the apparent retention of radiogenic 40ar in the chico impact melt in spite of its relatively large size absence of clasts and moderately slow cooling rate below 700 c raises questions as to the reliability of using melts for 39ar 40ar dating of meteoritic impact events

reevaluation of formation of metal nodules in ordinary chondrites compositions of four metal nodules from two ordinary chondrites wis91627 h3 7 and juin h5 were determined by instrumental and radiochemical neutron activation analyses compared with bulk metal fractions the metal nodules are characterized by strong and variable depletion of the refractory siderophile elements re os ir ru pt and rh but normal w and mo some fractionation of co from ni and low cu concentrations these characteristics are difficult to explain by shock induced vaporization followed by fractional condensation a mechanism suggested by widom et al 1986 we propose formation of metal nodules during metamorphism in the parent body refractory siderophile elements such as ir os rh etc are partly locked up in noble metal nuggets and cannot participate in kamacite formation the occurrence of metal nodules in both equilibrated and unequilibrated ordinary chondrites suggests that diffusion along grain boundaries was important in the development of kamacite and taenite in ordinary chondrites

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

brecciation among 2280 ordinary chondrites constraints on the evolution of their parent bodies abstract after accretion of meteorite parent bodies larger and smaller collisions have led to significant modifications of these bodies involved processes include excavation of material thermal metamorphism melting mixing of different materials re accretion and re lithification all these processes can be repeated several times in this study polished thin sections pts of 2280 chondrites 1193 h 947 l and 140 ll chondrites were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites in addition we have determined the abundance and characteristics of shock vein bearing h l and ll chondrites and of impact melt rock clasts we also recognized xenolithic components based on o isotope studies noble gas data were considered in order to detect regolith breccias and to discuss late impact histories the investigation of 2280 samples shows that 23 276 of 1193 of the h chondrites 23 220 of 947 of the l chondrites and 79 110 of 140 of the ll chondrites are brecciated considering the heavily brecciated ll chondrites in 63 of the 140 chondrites 45 shock veins were clearly detected 57 of these 63 chondrites are brecciated rocks the investigation of the h and l chondrites has shown that about 26 310 of 1193 of the h chondrites and 40 379 of 947 of the l chondrites contain shock veins in our data set 20 of the h chondrites and 8 3 of the ll chondrites but only 3 0 of the l chondrites contain solar noble gases remarkably about 62 of all brecciated h chondrites with noble gases analyzed contain solar noble gases compared to only around 11 and 10 of the brecciated l and ll chondrites respectively the identification of xenolithic clasts e g ci cm and ureilite like lithologies in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules these clasts must have been formed early within the first 2 ma on subsequently destroyed precursor first generation parent bodies the formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage although the onion shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint petrologic types 3 6 subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble pile structure are required to explain certain features discussed in this work however distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 ma were responsible to deliver the majority of the ordinary chondritic meteoroids to earth yet this certainly does not tell anything about the number of last generation parent bodies that exist in the asteroid belt since s type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites

glacier mass balance fluctuations in the pacific northwest and alaska usa the more than 40 year record of net and seasonal mass balance records from measurements made by the u s geological survey on south cascade glacier washington and wolverine and gulkana glaciers alaska show annual and interannual fluctuations that reflect changes in the controlling climatic conditions at regional and global scales as the mass balance record grows in length it is revealing significant changes in previously described glacier mass balance behavior and both inter glacier and glacier climate relationships south cascade and wolverine glaciers are strongly affected by the warm and wet maritime climate of the northeast pacific ocean their net balances have generally been controlled by winter accumulation with fluctuations that are strongly related to the pacific decadal oscillations pdo recently warm dry summers have begun to dominate the net balance of the two maritime glaciers with a weakening of the correlation between the winter balance fluctuations and the pdo non synchronous periods of positive and negative net balance for each glacier prior to 1989 were followed by a 1989 to 2004 period of synchronous and almost exclusively negative net balances that averaged 0 8 m for the three glaciers

south cascade glacier mass balance 1935 2006 a simple model uses daily observations of precipitation and temperature at a nearby weather station to estimate glacier average seasonal mass balance components at south cascade glacier washington usa from 1935 24 years before measurements began at the glacier this is 13 years earlier than measurements that can be derived using the ncep ncar reanalysis database begins 1 january 1948 although the model s error in estimating winter balance and summer balance over 1959 2006 is greater than that of a model using the reanalysis database its error in estimating net balance is comparable the model uses an empirically determined precipita tion ratio between the station and the glacier and a seasonally varying temperature lapse rate de termined from 9 years of measurements at the glacier temperature is used with a degree day for mulation to estimate ablation and to partition precipitation between rain and snow for estimating accumulation both processes are assumed to exist throughout the year and model results are compared seasonally with adjusted observations of winter and summer balances the published mass balance series is adjusted to a constant topography 1970 series in an attempt to remove the influence of changing topography on the glacier s response to climate the reconstructed values prior to 1959 are also with respect to the 1970 glacier topography because precipitation is measured at the weather station rather than being inferred from other meteorological variables it enables us to distinguish more accurately between wet day and dry day conditions including vertical lapse rates of temperature

landslide characteristics in the loess plateau northern china abstract landslides play an important role in landscape evolution of the loess plateau northern china but they have not been systematically analysed across the region the contribution to regional rates of erosion and sediment budgets is poorly known as a consequence co seismic landslides are a significant natural hazard and exacerbate the threat posed by active faults in the region but this aspect of the landslides is also poorly quantified this paper presents inventories for 80 000 landslides in the loess plateau and analyses the distributions and extents four study areas focus on the epicentres of major m 7 historical earthquakes from 1303 ce hongdong 1556 huaxian 1718 tongwei and 1920 haiyuan which are likely to have been major triggers for landslides in these regions a fifth study area focuses on landslides in the aftermath of localised storms in 2010 in the tianshui region to allow comparison of landslides clearly triggered by rainfall with landslides in the regional inventories landslides predominantly resulted from failure of the regional loess blanket that gives the region its name or the soil profile developed above it rainfall generated landslides are dominantly surficial soil landslides landslides preserved in the four epicentral areas are larger and deeper and resemble global bedrock landslides in the dimensions total volume of landslide in each of the four epicentral areas are on the order of 3 7 km3 these volumes are likely to be the cumulative totals of repeated earthquakes in the same regions with each event reactivating landslide scarps on hillsides comparison of landslide distributions and modern settlement patterns suggests that future m 7 earthquakes striking the loess plateau may trigger landslides that could directly hit 30 50 of the communities

transmission electron microscopy of l group chondrites 1 natural shock effects abstract high voltage and analytical transmission electron microscopy are used to characterize fine scale deformational and thermal effects of shock in l group chondrites belonging to shock facies d and e of dodd and jarosewich 1 in facies d olivine showing optical mosaicism has a dislocation substructure exactly like that produced in shock experiments thermal effects become pervasive in olivine of facies e with recovery of dislocation distributions and local recrystallization analogous to that in facies f but less coarse orthopyroxene has behaved more inhomogeneously than in shock experiments no single deformation mechanism being predominant in any specimen twinned clinopyroxene in facies e is attributed to the sequence of inversions ortho proto clino due to heating and rapid cooling in diopside as well as the 100 twinning previously described from less intensely shocked meteorites there is 001 twinning produced by a distinctive mechanism plagioclase is converted to glass maskelynite in lamellae and patches an intimate association of chromite with glass of plagioclase composition is interpreted as a melting phenomenon the characteristic melt pockets of facies d consist of glass with metal and sulphide globules the glass is derived from more than one mineral giving it a mixed silicate composition in facies e crystallization of silicate melts occurred and metal grains crystallized from the same melts volatilization accompanying melting is indicated by vesiculation of melt pockets and thin 1 m veins with high si mg are interpreted as vapour deposition products or melts modified by vapour transport of volatile elements

shock compaction heating and collisional processes in the production of type 3 ordinary chondrites lessons from the nearly unique l3 chondrite melt breccia northwest africa 8709

the gao guenie impact melt breccia sampling a rapidly cooled impact melt dike on an h chondrite asteroid the gao guenie h5 chondrite that fell on burkina faso march 1960 has portions that were impact melted on an h chondrite asteroid at 300 ma and through later impact events in space sent into an earth crossing orbit this article presents a petrographic and electron microprobe analysis of a representative sample of the gao guenie impact melt breccia consisting of a chondritic clast domain quenched melt in contact with chondritic clasts and an igneous textured impact melt domain olivine is predominantly fo80 82 the clast domain contains low ca pyroxene impact melt grown pyroxene is commonly zoned from low ca pyroxene in cores to pigeonite and augite in rims metal troilite orbs in the impact melt domain measure up to 2 mm across the cores of metal orbs in the impact melt domain contain 7 9 wt of ni and are typically surrounded by taenite and ni rich troilite the metallography of metal troilite droplets suggest a stage i cooling rate of order 10 c s 1 for the superheated impact melt the subsolidus stage ii cooling rate for the impact melt breccia could not be determined directly but was presumably fast an analogy between the ni rim gradients in metal of the gao guenie impact melt breccia and the impact melted h6 chondrite orvinio suggests similar cooling rates probably on the order of 5000 40 000 c yr 1 a simple model of conductive heat transfer shows that the gao guenie impact melt breccia may have formed in a melt injection dike 0 5 5 m in width generated during a sizeable impact event on the h chondrite parent asteroid

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

petrogenesis of miller range 07273 a new type of anomalous melt breccia implications for impact effects on the h chondrite asteroid miller range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine grained 3 gpa possibly to 15 19 gpa and temperature 1350 c possibly to 2000 c the higher pressures and temperatures would have involved back reaction of high pressure polymorphs to pyroxene and olivine upon cooling silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration

accretion dispersal and reaccumulation of the bishunpur ll3 1 brecciated chondrite evidence from troilite silicate metal inclusions and chondrule rims abstract a set of troilite silicate metal tsm inclusions and chondrule rims in the bishunpur ll3 1 chondrite provide information regarding impact brecciation of small bodies in the early solar system the tsm inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite feni metal also occurs in the troilite matrix the silicates include olivine fo55 98 low ca pyroxene en78 98 and high ca pyroxene en48 68wo11 32 al and si rich glass coexists with the silicates relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type 3 chondrites troilite fills all available cracks and pores in the silicate grains some of the tsm inclusions and rims are themselves surrounded by fine grained silicate rich rims fgr the tsm inclusions and rims texturally resemble the troilite rich regions in the smyer h chondrite breccia they probably formed by shock induced mobilization of troilite during an impact event on a primitive asteroidal body because silicates in the tsm inclusions and rims have highly unequilibrated compositions their precursor was presumably type 3 chondritic material like bishunpur itself the tsm inclusions and the chondrules with the tsm rims were fragmented and dispersed after the impact induced compaction then reaccreted onto the bishunpur parent body fgr probably formed around the tsm inclusions and rims as well as around some chondrules during the reaccumulation process components of most type 2 and 3 chondrites probably experienced similar processing i e dispersal of unconsolidated materials and subsequent reaccumulation

the portales valley meteorite breccia evidence for impact induced melting and metamorphism of an ordinary chondrite abstract the portales valley h chondrite fall is an annealed impact melt breccia with coarse metal interstitial to angular and subrounded silicate clasts the large metal rich regions exhibit a widmanstatten structure and contain very little troilite we were able to examine a 16 5 kg metal rich specimen of portales valley silicates contain numerous flecks of metallic cu and curvilinear trails of tiny metallic fe ni blebs characteristic of shocked and annealed chondrites one silicate clast appears to have experienced little

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

tree ring based reconstructions of north american glacier mass balance through the little ice age contemporary warming transition abstract glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer term context in western north america mass balance records span four to five decades and capture a relatively narrow window of glacial behavior over an interval that was dominated by warming and ablation we use temperature and moisture sensitive tree ring series to reconstruct annual mass balance for six glaciers in the pacific northwest and alaska mass balance models rely on the climatic sensitivity of tree ring chronologies and teleconnection patterns in the north pacific the reconstructions extend through the mid to latter portions of the little ice age lia and explore the role of climate variability in forcing mass balance across multiple environmental gradients synchronous positive mass balance intervals coincide with regional moraine building and solar minima whereas differences in lia glacier behavior are related to synoptic climate forcing secular warming in the late 19th century to present corresponds with the only multi decadal intervals of negative mass balance in all glacier reconstructions this suggests that contemporary retreat in western north america is unique with respect to the last several centuries and that regional patterns of glacier variability are now dominated by global climate forcing

shock features in iron nickel metal and troilite of l group ordinary chondrites shock metamorphic features in opaque minerals feni metal and troilite of 22 l chondrites have been studied petrographically and geochemically in an attempt to establish a connection between the present silicate based shock classification scheme stoffler et al 1991 and the peak shock and postshock thermal history recorded in these minerals unshocked to weakly shocked s1 s3 l chondrites contain feni metal and troilite that display textures related to normal slow cooling they may also contain rare disequilibrium shock features which suggest localized departures from equilibrium shock conditions above shock stage s3 selected melting of feni metal and troilite produces melt droplets whose composition and abundance correspond to the maximum equilibrium shock state achieved by the sample at these higher shock levels the abundance of other shock induced features such as polycrystalline kamacite sheared and fizzed troilite coarse grained pearlitic plessite polycrystalline troilite and polymineralic melt veins serve as textural criteria that can be used to establish peak shock conditions minimum postshock temperatures obtained from analyses of plessite components show a systematic increase in temperature with an increase in shock stage thereby providing additional information about the postshock thermal histories of l chondrites at the highest shock levels recorded in l chondrites s6 and above melting and chemical homogenization of feni metal produces flattened ni profiles that may partially to completely obscure any evidence for an earlier slow cooling history all of these features serve as aids for shock classifying l chondrites as well as for quantifying minimum peak temperatures that resulted during shock metamorphism

whole edifice ice volume change a d 1970 to 2007 2008 at mount rainier washington based on lidar surveying net changes in thickness and volume of glacial ice and perennial snow at mount rainier washington state have been mapped over the entire edifice by differencing between a high resolution lidar light detection and ranging topographic survey of september october 2007 2008 and the 10 m lateral resolution u s geological survey digital elevation model derived from september 1970 aerial photography excepting the large emmons and winthrop glaciers all of mount rainier9s glaciers thinned and retreated in their terminal regions with substantial thinning mainly at elevations

analog experimental insights into the formation of magmatic sulfide deposits abstract magmatic sulfide deposits result from transport and settling of dense sulfide liquid droplets in basic magma to model these processes we carried out analog experiments in which dense silicone oil droplets were transported in a viscous aqueous polymer solution the results of the experiments indicate that sulfide droplets can be carried in suspension by magma flowing at typical velocities due to the large surface tension of sulfide droplets coalescence does not occur during transport transport ceases when upward magma velocity decreases because of conduit enlargement or change from vertical to horizontal flow coalescence of droplets is controlled by magma viscosity and the presence of crystals

sulfur isotope composition of putative primary troilite in chondrules from bishunpur and semarkona the sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules 10 feo poor and 5 feo rich chondrules in the least metamorphosed ordinary chondrites bishunpur and semarkona have been measured by ion microprobe some troilite grains are located inside metal spherules within chondrules since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies those troilites are most likely primary having survived chondrule forming high temperature events if they are primary they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass dependent isotopic fractionations however the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations 104 106 k h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors this heating rate may provide a new constraint on the chondrule formation processes

cat mountain a meteoritic sample of an impact melted asteroid regolith cat mountain is a new ordinary chondrite impact melt breccia that contains several shocked chondrule bearing clasts of l5 material these clasts are surrounded by a total impact melt of similar composition material which appears to have cooled over a period of a few thousand years probably within a melt breccia lens in the bottom of a large 1 km diameter crater on an l chondrite asteroid noble gas isotopes indicate that the sample was involved in at least two different impact events approximately 880 and 20 myr ago following the 4 55 ga accretion of primitive chondritic material the 880 ma event is responsible for the impact breccia texture of the sample and the 20 ma event reduced the sample to a meter sized object we also infer that another impact occurred between 880 and 20 ma possibly the 500 ma event recorded in many other l chondrites to jettison the material from the asteroid belt into an orbit that evolved into an earth crossing trajectory the shock metamorphic processes that occurred at 880 ma redistributed the opaque phases in the meteorite and altered the crystalline characteristics of silicate phases this reduced the reflectance of the l5 material and decreased the amplitude of its spectral absorption features these characteristics are consistent with the spectral characteristics of some c class asteroids and suggest that some dark asteroids that appear to belong to the c class could be covered with shocked ordinary chondrite material if one assumes that cat mountain came from the same asteroid as other l chondrites with the same cosmic ray exposure age then the juxtaposition of these different materials suggests asteroids are rubble piles which are heterogeneous on a scale less than 100 m furthermore the structural integrity of cat mountain and other l chondrites suggests the strengths of asteroid rubble piles are limited by fractures and contrasting material properties and are thus inherently weak in a ram pressure regime produced when they enter a planetary atmosphere however in a regime where the asteroid is the target of impact fragmentation rather than the projectile the added porosity of a rubble pile structure will compensate for the presence of fractures and absorb a large amount of the impact energy in this case the structural integrity of the asteroid may appear to be the same as a previously unshocked chondritic material

redistribution of elements in the heavily shocked yanzhuang chondrite compositions of metal sulfide olivine pyroxene and plagioclase plagioclase glass were studied for the melted and unmelted parts of the heavily shocked h6 s6 chondrite yanzhuang we found that the partitioning of some trace elements significantly changed between the 2 parts compared with the corresponding minerals in the unmelted part ga is enriched in the metal co cr and zn are enriched in the sulfide cr is enriched in olivine and pyroxene and ti is enriched in the plagioclase glass of the melt pocket these detailed studies of the mineral phases put constraints on 3 important parameters temperature pressure and duration associated with the post shock melting process the coexistence of melted and unmelted olivine in the melt pocket of yanzhuang implies a peak temperature after shock that approaches the melting point of olivine the lack of ni in the olivine crystallized from a melt suggests crystallization of olivine at pressures below 10 kbar the resetting of ga partitioning between metal and silicate in the melt pocket indicates that the interval from the peak temperature after shock to the crystallization of metal sulfide and plagioclase glass in the melted part of yanzhuang is longer than 500 sec

origin of rapidly solidified metal troilite grains in chondrites and iron meteorites inclusions of troilite and metallic fe ni 0 2 4 mm in size with a dendritic or cellular texture were observed in 12 ordinary chondrites cooling rates in the interval 1400 950 c calculated from the spacing of secondary dendrite arms or cell widths and published experimental data range from 10 7 to 104 c sec in 8 of these chondrites which are breccias containing some normal slow cooled metal grains the inclusions solidified before they were incorporated into the breccias their cooling rates of 1 300 c sec indicate cooling by radiation or by conduction in contact with cold silicate or hot silicate volumes only 6 40 mm in size this is quantitative evidence that these inclusions and their associated clasts were melted on the surface of a parent body by impact and were not formed at depth from an internally derived melt in ramsdorf rose city and shaw which show extensive reheating to 1000 c fe fes textures in melted areas are coarser and indicate cooling rates of 10 1 to 10 4 c sec during solidification this metal may have solidified inside hot silicate volumes that were 10 300 cm in size as shaw and rose city are breccias of unmelted and melted material their melted metal did not necessarily cool through 1000 c within a few m of the surface shock melted fine grained irregular intergrowths of metal and troilite formed in situ in many irons and some chondrites by rapid solidification at cooling rates of 105 c sec their kamacite and taenite compositions may result from annealing at 250 c of metallic glass or exceedingly fine grained quench products

glass veins in the unequilibrated eucrite yamato 82202 the unequilibrated eucrite yamato 82202 y82202 contains a network of relatively thick up to 1 mm in width glass veins the host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized 4 3 ga ago as a lava flow on the surface of 4 vesta the veins formed 3 90 0 04 ga ago probably as a result of frictional melting associated with impact under conditions of low effective oxygen fugacity and higher sulfur fugacity the glass contains disordered structural elements characteristic of pyroxene and feldspar reminiscent of the eucritic target lithology the unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava hence it was not affected by regional metamorphism caused by burial to a significant depth or by long term contact metamorphism associated with a thick lava flow large intrusion or hot layer of impact ejecta the meteorite resided at a shallow depth though not at the surface on 4 vesta or on one of the vestoids until it was ejected and traveled to earth probably with other hed materials that have 36ar exposure ages of 13 ma these data suggest that the surface of the asteroid 4 vesta has significant though probably small proportions of glass as well as unequilibrated volcanic rock

glacier change 1958 1998 in the north cascades national park complex washington usa the spatial characteristics for all glaciers in the north cascades national park complex usa were estimated in 1958 and again in 1998 the total glacier area in 1958 was 117 3 1 1 km 2 by 1998 the glacier area had decreased to 109 1 1 1 km 2 a reduction of 8 2 0 1 km 2 7 estimated volume loss during the 40 year period was 0 8 0 1 km 3 of ice this volume loss contributes up to 6 of the august september stream flow and equals 16 of the august september precipitation no significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation aspect or slope however the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers most of the well studied alpine glaciers are much larger than the population median so global estimates of glacier shrinkage based on these well studied glaciers probably underestimate the true magnitude of regional glacier change

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

a macroscopic approach to glacier dynamics a simple approach to glacier dynamics is explored in which there is postulated to be a relationship between area and volume with three parameters the time for area to respond to changes in volume a thickness scale and an area characterizing the condition of the initial stale this approach gives a good fit to the measurements of cumulative balance and area on south cascade glacier from 1970 97 the area time scale is roughly 8 years the thickness scale about 123 m and the 1970 area roughly 4 larger than required for adjustment with volume combining this relationship with a version of mass continuity expressed in terms of area and volume produces a theory of glacier area and volume response to climate in which another time constant the volume time scale appears area and volume both respond like a damped spring and mass system the damping of the south cascade response is approximately critical and the volume time scale is roughly 48 vexes six times the area time scale the critically damped spring and mass analogy reproduces the time dependence predicted by the more complicated traditional theory of nyc

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

mineralogical comparison and cooling history of lunar and chondritic vesicular melt breccias lunar vesicular melt breccia 77135 was mineralogically compared with ll chondritic analog yamato 790964 to elucidate impact melting processes microprobe analyses were made of pyroxenes plagioclases and olivines and of bulk compositions of the glasses which appear to be solidified from impact melts notable similarities between the lunar and chondritic melt breccias are 1 abundant vesicles 2 similar pyroxene chemical zoning trends 3 presence of variable amounts of clastic material and 4 similar chemical compositions except for k and na contents of the glass and mesostasis some constraints on the cooling history are estimated from mg fe diffusion profiles in olivine and pyroxene the burial depth of lunar sample 77135 during cooling was not large 0 2 100 m for the chondrite the burial depth during cooling is probably smaller than that of the lunar analog even if the size of the chondrite parent body is small it is probable that impact melts were produced and a layer of ejecta debris was produced which was sufficiently thick to homogenize mg fe chemical zoning of olivines

spatial variations of sr nd isotopic ratios mineralogical and elemental compositions of cryoconite in an alaskan glacier to understand the geological origins of minerals in cryoconite and the nutrients sources for microbes on glaciers we analyzed the sr nd isotopic ratios of the four mineral fractions in cryoconites including saline carbonate phosphate silicate and the organic fraction obtained from gulkana glacier in alaska the isotopes in the silicate mineral fraction exhibited spatial variation within the glacier 87sr 86sr 0 704533 0 709563 end 0 16 0 to 0 5 which can be explained by the different mixing ratios of the two distinct sources one of the sources is lateral and terminal moraines or soil and the other is the medial moraine of the glacier the minerals in the cryoconite at the lower sites in the glacier are likely derived from the former source whereas those at the upper sites are from latter sources the mineralogical and elemental compositions also support mixing of the silicate minerals from the two local sources the sr isotopic ratios of the organic fraction also showed spatial variation on the glacier in the middle sites a trend similar to those of the phosphate fraction the results suggest that the organic matter is mostly the byproducts of microbes using the phosphate minerals as a nutrient source

the formation and chronology of the pat 91501 impact melt l chondrite with vesicle metal sulfide assemblages the l chondrite patuxent range pat 91501 is an 8 5 kg unshocked homogeneous igneous textured impact melt that cooled slowly compared to other meteoritic impact melts in a crater floor melt sheet or sub crater dike mittlefehldt d w and lindstrom m m 2001 petrology and geochemistry of patuxent range 91501 and lewis cliff 88663 meteoritics planet sci 36 439 457 we conducted mineralogical and tomographic studies of previously unstudied mm to cm sized metal sulfide vesicle assemblages and chronologic studies of the silicate host metal sulfide clasts constitute about 1 vol comprise zoned taenite troilite and pentlandite and exhibit a consistent orientation between metal and sulfide and of metal sulfide contacts vesicles make up 2 vol and exhibit a similar orientation of long axes 39ar 40ar measurements probably date the time of impact at 4 461 0 008 gyr b p cosmogenic noble gases and 10be and 26al activities suggest a pre atmospheric radius of 40 60 cm and a cosmic ray exposure age of 25 29 myr similar to ages of a cluster of l chondrites pat 91501 dates the oldest known impact on the l chondrite parent body the dominant vesicle forming gas was s2 15 20 ppm which formed in equilibrium with impact melted sulfides the meteorite formed in an impact melt dike beneath a crater as did other impact melted l chondrites such as chico cooling and solidification occurred over 2 h during this time 90 of metal and sulfide segregated from the local melt remaining metal and sulfide grains oriented themselves in the local gravitational field a feature nearly unique among meteorites many of these metal sulfide grains adhered to vesicles to form aggregates that may have been close to neutrally buoyant these aggregates would have been carried upward with the residual melt inhibiting further buoyancy driven segregation although similar processes operated individually in other chondritic impact melts their interaction produced the unique assemblage observed in pat 91501

formation of large metal nodules in ordinary chondrites literature data show that many large 2 30 mm metallic fe ni nodules in ordinary chondrites are depleted in refractory siderophiles e g re os ir ru pt and rh and cu relative to fine grained metal but are not depleted in normally refractory w and mo common siderophiles e g ni and co and volatile siderophiles e g au as and sb it was recently proposed that metamorphic diffusion could form the metal nodules and that partitioning of siderophile elements between kamacite and taenite could account for the nodules unusual compositions however the nodules have the same compositional trends as metal nodules and veins in shocked meteorites that clearly formed by impact related processes if large metal nodules formed during metamorphism type 6 chondrites should contain abundant large nodules instead the mean metal grain size in h6 chondrites is 0 12 0 15 mm far smaller than any of the nodules it seems likely that the metal nodules formed by impact vaporization oxidation of w and mo to form volatile oxides concomitant partial oxidation of re and os rapid fractional condensation of refractory siderophiles transport of the residual vapor condensation of cu s and se into vugs and fractures to form sulfide and condensation of the remaining siderophiles to form metal nodules and veins during vapor cooling and condensation or during subsequent parent body annealing w mo re and os oxides were reduced

smyer h chondrite impact melt breccia and evidence for sulfur vaporization smyer is an h chondrite impact melt breccia containing 20 vol 0 5 to 13 mm thick silicate rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension at the interface between some of the melt veins and chondritic clasts there are troilite rich regions consisting of unmelted crushed 0 2 to 140 m size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins troilite fills every available fracture in the silicates including some as thin as 0 1 m little metallic fe ni is present in these regions the fes fe modal ratio ranges from 25 1 to 500 1 far higher than the eutectic weight ratio of 7 5 1 the texture of these regions indicates that the sulfide formed from a fluid of very low viscosity the moderately high viscosity 0 2 poise and large surface tension of liquid fes its inability to wet silicate grain surfaces at low oxygen fugacities and the supereutectic fes fe ratios in the troilite rich regions indicate that the fluid was a vapor it seems likely that during the shock event that melted smyer many silicates adjacent to the melt veins were crushed upon release of shock pressure some of the troilite evaporated and dissociated molecules of s2 were transported and condensed into fractures and around tiny silicate grains there they combined with fe from small adjacent metallic fe ni grains to form troilite the ni content at the edges of some of these metal grains increased significantly co from these ni rich grains diffused into nearby kamacite impact induced s volatilization may have played a major role in depleting the surface of 433 eros and other chondritic asteroids in s

chromite plagioclase assemblages as a new shock indicator implications for the shock and thermal histories of ordinary chondrites abstract chromite in ordinary chondrites oc can be used as a shock indicator a survey of 76 equilibrated h l and ll chondrites shows that unshocked chromite grains occur in equant subhedral and rounded morphologies surrounded by silicate or intergrown with metallic fe ni and or troilite some unmelted chromite grains are fractured or crushed during whole rock brecciation others are transected by opaque veins the veins form when impacts cause localized heating of metal troilite intergrowths above the fe fes eutectic 988 c mobilization of metal troilite melts and penetration of the melt into fractures in chromite grains chromite plagioclase assemblages occur in nearly every shock stage s3 s6 oc the assemblages range in size from 20 300 m and consist of 0 2 20 m size euhedral subhedral anhedral and rounded chromite grains surrounded by plagioclase or glass of plagioclase composition plagioclase has a low impedance to shock compression heat from shock melted plagioclase caused adjacent chromite grains to melt chromite grains crystallized from this melt those chromite grains in the assemblages that are completely surrounded by plagioclase are generally richer in al 2 o 3 than unmelted matrix chromite grains in the same meteorite chromite veinlets typically 0 5 2 m thick and 10 300 m long occur typically in the vicinity of chromite plagioclase assemblages the veinlets formed from chromite plagioclase melts that were injected into fractures in neighboring silicate grains chromite crystallized in the fractures and the residual plagioclase rich melt continued to flow eventually pooling to form plagioclase rich melt pockets chromite rich chondrules consisting mainly of olivine plagioclase normative mesostasis and 5 15 vol chromite occur in many shocked oc and oc regolith breccias but they are absent from primitive type 3 oc they may have formed by impact melting chromite plagioclase and adjacent mafic silicates during higher energy shock events the melt was jetted from the impact site and formed droplets due to surface tension crystallization of these droplets may have commenced in flight prior to landing on the parent body surface chromite plagioclase assemblages and chromite veinlets occur in 25 out of 25 shock stage s1 oc of petrologic type 5 and 6 that i examined although these rocks contain unstrained olivine with sharp optical extinction most possess other shock indicators such as extensive silicate darkening numerous occurrences of metallic cu polycrystalline troilite and opaque veins it seems likely that these rocks were shocked to levels at least as high as shock stage s3 and then annealed by heat generated during the shock event during annealing the olivine crystal lattices healed but other shock indicators survived published ar ar age data for some s1 oc indicate that many shock and annealing events occurred very early in the history of the parent asteroids the common occurrence of shocked and annealed oc is consistent with collisions being a major mechanism responsible for metamorphosing oc

impact melt products of chondritic material a large variety of objects in chondritic meteorites formed as a result of impact melting shock veins metal troilite mixtures metal and sulfide nodules melt pockets vugs agglutinates glassy and crystalline spherules and numerous types of melt rock clasts the type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock impact melting has also affected large portions of several chondrite breccias many of these contain vugs and patches of silicate glass some workers have suggested that various iron meteorites including groups iab iiicd and iie as well as several ungrouped irons were formed from individual impact melt pools in chondritic regoliths the eagle station trio pallasites and several ungrouped meteorites bencubbin weatherford enon acapulco and allan hills a77081 may have formed from impact melted chondritic material it is also possible that the parent magmas of ureilites were derived from impact melted metal rich carbonaceous chondrite material

estimating south cascade glacier washington u s a mass balance from a distant radiosonde and comparison with blue glacier a simple flux model using twice daily measurements of wind humid ity and temperature from standard upper air levels in a distant radiosonde estimated winter balance of south cascade glacier over 1959 98 with error 0 24 m w e correla tion between net and winter balance is strong the model estimates net balance with error 0 53 m w e over the past 40 years average net balance of south cascade glacier has been strongly negative 0 46 m w e and it has been shrinking steadily in com parison 200 km wsw at blue glacier the average balance has been less negative 0 13 m w e that glacier has undergone little change over the 40 years balance histories of the two glaciers are positively correlated r 0 54 and south cascade has been more out of balance than blue presumably because it is still adjusting to climate change since the little ice age recent warming and drying has made the net balance of both glaciers strongly negative since 1976 0 84 m w e at south cascade 0 56 m w e at blue if south cascade glacier were in balance with the 1986 1998 climate it would be about 1 4 of its present area if conditions persist retreat of both glaciers is inevitable

high frequency observations of melt effects on snowpack stratigraphy kahiltna glacier central alaska range with an increased volume of melt on many of the world s glaciers study of how meltwater affects the properties of glacial snowpack becomes essential to our understanding of how glaciers will respond to climate change we address this problem by studying how snow properties changed on sub daily timescales on the kahiltna glacier alaska between may 26 and june 10 2010 during this period we dug 1 8 m deep snow pits twice daily to record the stratigraphy of melt layers snow hardness grain size and density and sampled for hydrogen isotopic composition d on four occasions from these data we show that 65 of the melted surface snow infiltrates and refreezes in the snowpack this leads to a densification of the snow a 729 increase in volume of melt layers and a homogenization of isotopic and physical snow properties from visual and stratigraphic observations we show that meltwater flow within the snowpack is conducted primarily along lenses and pipes where melt layers later form but that more homogeneous capillary based flow is also important finally we show using isotope ratios that post depositional alteration is exacerbated with increased melt extent using the d profile below a volcanic ash layer as a case study in the future similar studies would benefit from this high frequency monitoring approach to assessing snowpack evolution as it allows for a greater understanding of short duration processes new directions for study would include longer term monitoring efforts over a wider spatial snow pit network copyright 2012 john wiley sons ltd

composition and formation of metal nodules and veins in ordinary chondrites abstract five large metal nodules a composite sample of five small metal nodules one troilite nodule and two metal veins from five ordinary chondrites were analyzed by electron microprobe and neutron activation analysis metal nodules and veins in h chondrites generally consist of large single crystals of kamacite whereas l nodules contain significant taenite most nodules and veins are depleted by large factors ranging up to 240 in refractory siderophiles re os ir pt tungsten normally a refractory siderophile and au as and ga volatile siderophiles have abundance ratios similar to those of the common siderophiles fe co and ni we propose that the metal with extremely low refractory element contents was produced by shock induced vaporization of chondritic material the refractory elements condensed near the point of vaporization and were not transported with the vapor because the shock generated gas was mildly oxidizing w formed volatile oxides the low ni fe ratio and the resulting high kamacite contents may reflect dilution by fe from dissociated fes subsequent condensation of the refractory depleted vapor into fractures and voids formed the metal veins and nodules

temporal and spatial variations in spectral reflectance and characteristics of surface dust on gulkana glacier alaska range spectral reflectances in the visible to near infrared wavelength range 350 1050 nm were measured on the surface of gulkana glacier alaska range alaska usa at six different elevations from may to september 2001 the measurements showed variable spectral reflectances on the glacier surface and the spectra changed over time and elevation the spectra in may were those of a typical wet snow surface the reflectance ranged approximately from 0 4 to 0 8 and generally decreased as the wavelength increased as snowmelt proceeded the reflectance gradually fell and specific absorptions appeared in the spectrum at wavelength ranges of 400 600 and 670 680 nm corresponding to a red snow surface due to snow algal bloom as the ice surface was exposed the spectrum finally shifted to a lower 0 1 0 4 and flat reflectance curve typical of an ice surface contaminated with dust analyses of the dust on the glacier surface showed that its quantity and characteristics changed spatially and seasonally and were correlated with spectral albedo the results showed that the temporal and spatial variations in spectral reflectance on this glacier are due not only to physical properties of the glacier surface but also to biogenic materials on the surface e g red colored snow algal cells and cryoconite

a shock metamorphic model for silicate darkening and compositionally variable plagioclase in ck and ordinary chondrites abstract silicate darkening in ordinary chondrites oc is caused by tiny grains of metallic fe ni and troilite occurring mainly within curvilinear trails that traverse silicate interiors and decorate or in some cases cut across silicate grain boundaries highly shocked oc characterized by olivine grains with undulose to mosaic extinction tend to have greater degrees of silicate darkening than lightly shocked oc this indicates that silicate darkening is probably a result of shock metamorphism the low fe fes eutectic temperature 988 c renders metal and troilite susceptible to melting and mobilization during shock heating a few oc also contain thin melt veins of chromite this implies that localized shock temperatures reached 1635 c in these meteorites silicate darkening is also evident in ck carbonaceous chondrites where magnetite and pentlandite grains form analogous curvilinear trails it is possible that magnetite and pentlandite in ck chondrites were mobilized during shock metamorphism and dispersed through silicate interiors alternatively metal and troilite may have been dispersed and then transformed into magnetite and pentlandite during subsequent oxidation of these chondrites unshocked oc tend to have plagioclase with uniform compositions shocked oc tend to have plagioclase with more variable albeit still stoichiometric compositions the low impedance of plagioclase to shock compression makes it particularly susceptible to melting and mobilization this is consistent with the molten appearance of plagioclase in highly shocked oc e g rose city and paragould ck chondrites also have compositionally variable plagioclase the common association of silicate darkening with compositionally variable plagioclase is consistent with the hypothesis that both are products of shock metamorphism some ck and oc chondrites exhibit light shock effects in olivine that are consistent with equilibrium peak shock pressures that are too low to account for the silicate darkening or opaque shock veins in these meteorites therefore the olivine in these chondrites may have been annealed after intense shock produced these effects a few ck chondrites that contain olivine with undulose or mosaic extinction e g lew87009 and eet83311 may have been shocked again after annealing

a ab complex iron meteorite containing low ca clinopyroxene abstract northwest africa 468 nwa 468 is a new ungrouped silicate rich member of the iab complex of nonmagmatic iron meteorites the silicates contain relatively coarse 300 m grains of low ca clinopyroxene with polysynthetic twinning and inclined extinction low ca clinopyroxene is indicative of quenching from high temperatures either from protoenstatite in a few seconds or high temperature clinoenstatite in a few hours it seems likely that nwa 468 formed by impact melting followed by rapid cooling to 660 c after the loss of a metal sulfide melt from the silicates sulfide was reintroduced either from impact mobilized fes or as an s 2 vapor that combined with metallic fe to produce fes the o isotopic composition 17 o 1 39 indicates that the precursor material of nwa 468 was a metal rich e g cr carbonaceous chondrite lodranites are similar in bulk chemical and o isotopic composition to the silicates in nwa 468 the mac 88177 lodranite which also contains low ca clinopyroxene is close in bulk chemical composition both nwa 468 and mac 88177 have relatively low abundances of rare earth and plagiophile elements siderophiles in the metal rich areas of nwa 468 are similar to those in the mac 88177 whole rock both samples contain low ir and relatively high fe cu and se most unweathered lodranites contain 20 to 38 wt metallic fe ni these rocks may have formed in an analogous manner to nwa 468 i e by impact melting of metal rich carbonaceous chondrite precursors but with less separation of metal rich melts from silicates

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

troilite in the chondrules of type 3 ordinary chondrites implications for chondrule formation abstract the presence of primary troilite in chondrules requires that nebular temperatures were 1170 k but much less ni at lower temperatures because this is far higher than the metamorphic temperature inferred for semarkona 670 k the troilite must be primary primary troilite fitting the three criteria occurs in a smaller fraction of low feo feo feo mgo in olivine and or low ca pyroxene not greater than 0 075 than high feo porphyritic chondrules in semarkona 9 vs 33 coarse grained low feo porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size we found a few troilite free metallic fe ni bearing low feo chondrules that contain na2o bearing augite and na2o and k2o rich mesostasis these chondrules were probably formed after ambient nebular temperatures cooled below 910 k the 50 condensation temperature of na and before they reached 650 k literature reports of rare fayalitic microchondrules in the rims around a few normal size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 k secondary troilite occurs in a few percent of semarkona chondrules as thin veins mobilized by shock troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite carbide ni rich sulfide awaruite and co rich kamacite produced by parent body hydrothermal alteration

glacier status and contribution to streamflow in the olympic mountains washington usa the olympic peninsula washington usa currently holds 184 alpine glaciers larger than 0 01 km 2 and their combined area is 30 2 0 95 km 2 only four glaciers are 1 km 2 and 120 of the others are 2 this represents a loss of 82 glaciers and a 34 decrease in combined area since 1980 with the most pronounced losses occurring on south facing aspects and in the more arid northeastern part of the range annual rate of loss in glacier area for seven of the largest glaciers accelerated from 0 26 km 2 a 1 1900 80 to 0 54 km 2 a 1 1980 2009 thinning rates on four of the largest glaciers averaged nearly 1 ma 1 from 1987 to 2010 resulting in estimated volume losses of 17 24 combined glacial snow firn and ice melt in the hoh watershed is in the range 63 79 7 10 6 m 3 or 9 15 of total may september streamflow in the critical august september period the glacial fraction of total basin runoff increases to 18 30 with one third of the water directly from glacial ice i e not snow and firn glaciers in the elwha basin produce 12 15 1 3 10 6 m 3 2 5 4 0 while those in the dungeness basin contribute 2 5 3 1 0 28 10 6 m 3 3 0 3 8

mineralogy petrology chronology and exposure history of the chelyabinsk meteorite and parent body three masses of the chelyabinsk meteorite have been studied with a wide range of analytical techniques to understand the mineralogical variation and thermal history of the chelyabinsk parent body the samples exhibit little to no postentry oxidation via mossbauer and raman spectroscopy indicating their fresh character but despite the rapid collection and care of handling some low levels of terrestrial contamination did nonetheless result detailed studies show three distinct lithologies indicative of a genomict breccia a light colored lithology is ll5 material that has experienced thermal metamorphism and subsequent shock at levels near s4 the second lithology is a shock darkened ll5 material in which the darkening is caused by melt and metal troilite veins along grain boundaries the third lithology is an impact melt breccia that formed at high temperatures 1600 c and it experienced rapid cooling and degassing of s2 gas portions of light and dark lithologies from chel 101 and the impact melt breccias chel 102 and chel 103 were prepared and analyzed for rb sr sm nd and ar ar dating when combined with results from other studies and chronometers at least eight impact events e g 4 53 ga 4 45 ga 3 73 ga 2 81 ga 1 46 ga 852 ma 312 ma and 27 ma are clearly identified for chelyabinsk indicating a complex history of impacts and heating events finally noble gases yield young cosmic ray exposure ages near 1 ma these young ages together with the absence of measurable cosmogenic derived sm and cr indicate that chelyabinsk may have been derived from a recent breakup event on an neo of ll chondrite composition

shock melted material in the krymka ll3 1 chondrite behavior of the opaque minerals six large millimeter to centimeter size regions of one specimen of the krymka ll3 1 ordinary chondrite show evidence of having been completely or nearly completely shock melted in situ a phenomenon rarely observed in primitive chondrites the shock pressure nominally in the range of 75 90 gpa could only have been 30 35 gpa in a porous material like fine grained matrix the melted regions have an igneous texture and their silicates are zoned and unequilibrated large metal troilite intergrowths formed in these regions the metal has a nickel content corresponding to martensite and the troilite contains up to 4 2 wt nickel melting must have been very short and cooling very fast 100 c h at high temperature the metal contains up to 0 7 wt phosphorus abundant chromite crystals and sodium iron phosphate glass globules are found in troilite the differences in composition between the opaque phases found in the melted regions and those generally observed in unmetamorphosed chondrules are assigned to melting under closed system conditions surprisingly high co concentrations up to 13 wt were found in some metal grains in or at the periphery of melted regions they likely resulted from sulfurization of metal by sulfur vapor produced during the shock after solidification at least one other shock led to mechanical effects in the melted regions

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

first finding of impact melt in the iie netschaevo meteorite about half of the iie nonmagmatic iron meteorites contain silicate inclusions with a primitive to differentiated nature the presence of preserved chondrules has been reported for two iie meteorites so far netschaevo and mont dieu which represent the most primitive silicate material within this group in this study silicate inclusions from two samples of netschaevo were examined both silicate inclusions are characterized by a porphyritic texture dominated by clusters of coarse grained olivine and pyroxene set in a fine grained groundmass that consists of new crystals of olivine and a glassy appearing matrix this texture does not correspond to the description of the previously examined pieces of netschaevo which consist of primitive chondrule bearing angular clasts detailed petrographic observations and geochemical analyses suggest that the investigated samples of netschaevo consist of quenched impact melt this implies that netschaevo is a breccia containing metamorphosed and impact melt rock imr clasts and that collisions played a major role in the formation of the iie group