sea ice leads in the arctic ocean model assessment interannual variability and trends sea ice leads in the arctic are important features that give rise to strong localized atmospheric heating they provide the opportunity for vigorous biological primary production and predicting leads may be of relevance for arctic shipping it is commonly believed that traditional sea ice models that employ elastic viscous plastic evp rheologies are not capable of properly simulating sea ice deformation including lead formation and thus new formulations for sea ice rheologies have been suggested here we show that classical sea ice models have skill in simulating the spatial and temporal variation of lead area fraction in the arctic when horizontal resolution is increased here 4 5 km in the arctic and when numerical convergence in sea ice solvers is considered which is frequently neglected the model results are consistent with satellite remote sensing data and discussed in terms of variability and trends of arctic sea ice leads it is found for example that wintertime lead area fraction during the last three decades has not undergone significant trends

a sea ice lead detection algorithm for use with high resolution airborne visible imagery the detection of leads or cracks in sea ice is critical for the derivation of sea ice freeboard from altimetric measurements of sea ice elevation we present an approach for lead detection in sea ice using high resolution visible imagery from airborne platforms we develop a new algorithm i e the sea ice lead detection algorithm using minimal signal sildams that detects clouds extracts leads and classifies ice types within leads from airborne visible imagery cloud detection is based on an assessment of local variances of pixel brightness across image scenes and where available coincident altimetric measurements are used to confirm suspected cloudy scenes the lead extraction step computes affine time frequency distributions minimal signal for the red green and blue channels of each image the transformed outputs are combined to take advantage of three channels simultaneously finally lead pixel geolocations are extracted using a set of uniform thresholds for ice typing including open water thin ice and gray ice within leads along each flight line sildams was tested using data from the digital mapping system dms dms digital photographs represent the highest resolution 10 cm visible imagery available over sea ice and were collected during nasa operation icebridge sea ice flights in the antarctic and the arctic in 2009 and 2010 respectively we demonstrate that sildams has a high lead detection capability of 99

discovery of the large scale huangtian scheelite deposit and implications for the structural control of tungsten mineralization in southeastern yunnan south china abstract the large scale huangtian scheelite deposit represents one of the most important such deposits discovered recently in southeastern yunnan china results of the geological metallotectonic and geochemical investigations indicate that this deposit formed in a magmatic hydrothermal system during the yanshanian period its deposition is controlled by the ore hosted structure of a secondary fold and by interlayer faults f0 1 and f0 2 which are linked to the ore guided structure of a secondary oblique strike slip fault f7 associated to the regional maguan deep fault and to an ew trending tectonic zone that represents the main metallogenic tectonic system the oblique strike slip structure and the tianchong granitic porphyries located along the southern margin of the laojunshan granite body are primary ore controlling structures which directly controlled the movement of the ore bearing fluid and its subsequent precipitation within the huangtian scheelite deposit the distribution of the orebodies is controlled by a group of metallogenic structural surfaces the fold and fault systems as well as a silicon calcium surface silicification fluoritization and calcitization are the main hydrothermal alterations observed and exhibited a distinct alteration zonation the hydrothermal mineralization process can be divided into three stages the quartz fluorite scheelite tourmaline stage the scheelite quartz calcite fluorite stage and the calcite pyrite quartz scheelite stage the evolution of the mineralizing fluid proceeded as follows medium temperature and low salinity fluid medium to low temperature and low salinity fluid low temperature and low salinity fluid the results concerning oxygen and hydrogen isotopic compositions demonstrate that the ore forming fluids derived from a magmatic fluid mixed with a small amount of meteoric water overall these features indicate that the huangtian scheelite deposit represents a medium to low temperature magmatic hydrothermal deposit that is obviously controlled by the ew trending tectonic zone this study demonstrates the significance of such mineral exploration in similar geological regions

barents sea seasonal ice zone features and processes from ers 1 synthetic aperture radar seasonal ice zone experiment 1992 sea ice features and processes in the barents sea were studied during the seasonal ice zone experiment 1992 sizex92 a dedicated ers 1 satellite synthetic aperture radar sar field campaign carried out in march 1992 sizex92 was based around the research vessels polarsyssel and hakon mosby in situ oceanographic meteorological and ice measurements were made coordinated with low altitude aerial observations and ers 1 sar data acquired in near real time fifty eight low and full resolution sar scenes were obtained during sizex92 which provided a validation data set for ers 1 sar backscatter under winter conditions in the barents sea analysis of sizex92 data has provided geophysical insights including a better understanding of barents sea ice edge freezing processes and ice edge development in response to atmospheric forcings in particular areas of new ice formation were found to be related to bathymetric features through their influence on the circulation of arctic and atlantic water masses ers 1 sar image sequences revealed rapid mesoscale variations in new ice areas and the ice edge in response to wind conditions in addition to geophysical insight sizex92 demonstrated some of the technical capabilities and limitations of ers 1 sar to identify new ice areas the ice edge ice floes and ice types mapping new ice areas using satellite sar data may be considered the most promising new application the limitations of ers 1 sar derived ice classification and ice motion estimates in the marginal ice zone are identified

analyzing lead information from sar images leads are relatively linear features in the sea ice cover which are composed of open water or new thin ice because of their composition leads impact the ocean air heat exchange automated analysis of leads from sea ice imagery may provide a means of gathering important information about the sea ice cover and its climatic influence this paper describes 1 a method for extracting and analyzing leads from ers 1 synthetic aperture radar sar images classified by ice type and 2 the results of using this method on images of the beaufort sea the methodology consists of identifying potential lead features in the image and measuring their characteristics both before and after using a thinning or skeletonization technique on the features the measurements obtained using this method include lead area average width number of leads in an area amount of branching and linearity of the lead these measurements were analyzed with respect to the time of year and the latitude of the images results indicate that the measurements produced by the methodology are consistent with lead measurement distributions that others have found the results of the study suggest that the methodology is appropriate to study lead characteristics on a large scale

chemical studies of h chondrites i mobile trace elements and gas retention ages abstract trends for 16 trace elements ag as au bi cd co cs ga in k rb sb se te tl and zn chosen to span a broad geochemical and thermal response range in 44 h4 6 chondrites differ widely from those in l4 6 chondrites in particular h chondrites classified as heavily shocked petrologically do not necessarily exhibit 40 ar loss and vice versa the clear cut causal relationship between siderophile and mobile element loss with increasing late shock seen in l chondrites is not generally evident in the h group h chondrite parent material experienced an early high temperature genetic episode that mobilized a substantial proportion of these trace elements so that later thermal episodes resulted in more subtle collateral fraction ations mildly shocked l chondrites escaped this early high temperature event indicating that the two most numerous meteorite groups differ fundamentally in genetic history

alkali feldspathic material entrained in fe s rich veins in a monomict ureilite the elephant moraine eet 96001 ureilite contains a remarkable diversity of feldspars which occur as tiny no more than 60 m maximum dimension grains within a few fe s rich now weathered to mostly fe oxide veins molar s fe ratio in the veins averages 0 08 0 02 the veins meander and feature large fluctuations in apparent width they appear to have entered this monomict breccia by a gentle percolative process not by violent impact injection the feldspars are accompanied by a diverse suite of k rich and generally also ti rich feldspathic glasses and also major proportions of silica and pyroxene which is largely fassaitic a rhnite like phase is also found and as inclusions in one of the fassaites a cr poor spinel like phase the feldspars mostly feature remarkably high k na compared to feldspars of comparable an from polymict ureilites the eet 96001 feldspathic component was probably once part of a thin basaltic crust on a ureilite asteroid the spinel included in one of the fassaites formed at remarkably high fo2 apparent oxidation state of iron 41 atom fe3 suggesting that the parent magma possibly assimilated near surface water however the fe3 was not directly measured and has conceivably been affected by terrestrial weathering also there is no assurance that this fassaite originated together with the typical feldspar we speculate that the feldspathic component was mixed into the dense fe s rich vein material and very soon thereafter the fe s rich vein material was emplaced adjacent to the eet 96001 host ureilite at an advanced stage in a chaotic catastrophic disruption and partial reassembly process that affected all ureilites the high k nature of the eet 96001 feldspathic component including the feldspathic glasses suggests that fractional fusion may not have been as common during ureilite anatexis as has been inferred from recent studies of clast assemblages in polymict ureilites

an igneous textured clast in the peace river meteorite insights into accretion and metamorphism of asteroids in the early solar system the mineralogy petrology and geochemistry of an igneous textured clast in the peace river l6 chondrite meteorite was examined to determine the roles of nebular processes accretion and parent body metamorphism in its origin the centimetre scale clast is grey and fine grained and is in sharp contact with the host chondrite two sub millimetre veins cut across both the clast and host indicating that the clast formed prior to the impact shock event s that produced the numerous veins present in the peace river meteorite the clast and host are indistinguishable in terms of mineral compositions in contrast there are differences in modal mineralogy texture as well as trace element and oxygen isotope composition between the clast and host these differences strongly suggest that the clast was formed by impact melting of ll group chondritic material involving loss of fe fes and phosphate components followed by relatively rapid cooling and incorporation into the peace river host meteorite subsequent metamorphism on the peace river parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host shock metamorphism including formation of shock melt veins occurred post metamorphism during fragmentation of the l chondrite parent body the results suggest that the formation of the peace river parent asteroid included the incorporation of material from other asteroids and that the pre metamorphic protolith was a breccia accordingly we propose that the peace river meteorite be reclassified as a polymict breccia

multifrequency polarimetric synthetic aperture radar observations of sea ice the first known fully polarimetric airborne synthetic aperture radar sar data set of sea ice is introduced images were acquired in the beaufort bering and chukchi seas in march 1988 during a campaign for validation of defense meteorological satellite program special sensor microwave imager radiometer ice products statistics of the magnitude phase and polarization of complex backscattered signals recorded by the jet propulsion laboratory three frequency sar are examined in detail for various scenes with different ice characteristics the full stokes matrix information generated from c l and p band data characterize the scattering behavior of different ice types polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency fixed polarization micro wave radar a specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ers 1 5 3ghz vv polarization sar data such findings are consistent with theoretical model simulations of scattering characteristics of sea ice overall these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods

extensive impact melting on the h chondrite parent asteroid during the cataclysmic bombardment of the early solar system evidence from the achondritic meteorite dar al gani 896 dag 896 is an olivine rich microporphyritic rock of komatiitic composition both the olivine composition fa 17 5 2 1 mn mg 0 0061 and the bulk oxygen isotopic composition delta 17 o 2 55 delta 18 o 3 50 indicate that dag 896 is a sample of the h chondrite parent body the bulk chemistry shows an h chondritic distribution of lithophile elements whereas chalcophile and siderophile elements are strongly depleted indicating formation through whole rock melting or nearly so of h chondrite material nearly complete loss of the metal plus sulfide component and crystallization without significant igneous fractionation superheated severely shocked chondritic relics similar to10 vol typically in the form of corroded lithic fragments 100 mum in size intimately distributed within the igneous lithology indicate that melting was triggered by a highly energetic impact which possibly induced shock pressures of similar to80 100 gpa the relatively young 3 704 0 035 ga ar 40 ar 39 crystallization age is consistent with the impact melting origin as magmatism in the asteroid belt was active only in the first hundred million years of solar system history 1ased on textural data and thermodynamic crystallization modelling we infer that dag 896 crystallized from a liquidus temperature of similar to1630degreesc under relatively slow cooling rates similar to10degreesc h 1 to 1300degreesc before quenching the two stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor metal silicate fractionation may have been accomplished at least at the centimeter scale of the studied meteorite sample through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism alternatively dag 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid for metal particles 1 to 10 mm in size typically observed in partially differentiated impact melt rocks stokes law indicates a settling velocity 1 in h 1 during the first few hours of crystallization on asteroidal bodies of 25 kin radius the similar to3 7 ga age of dag 896 nearly overlaps with the slightly older resetting ages of h chondrites all impact melts available from the literature indicating that the h chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system such an age overlap may also indicate early disruption of the initial h chondrite parent asteroid the close similarity between the bulk composition and degassing age of dag 896 and silicate inclusions in he iron meteorites is further evidence in support of a common origin by impact melting and metal silicate segregation on the h chondrite parent asteroid our new high precision oxygen isotopic measurements of h chondrites delta 17 o 0 77 0 04 should be extended to iies to verify this possible petrogenetic link

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

a survey of clasts and large chondrules in ordinary chondrites we report the results of a survey of clasts and large 5 mm chondrules macrochondrules within the 833 ordinary chondrites of the natural history museum collection thirty six macrochondrules and 24 clasts were identified and studied macrochondrules have textures and mineral assemblages like normal chondrules and so share a common origin clasts show evidence for fracturing from larger bodies and can be classified as either 1 chemically fractionated if they have major and trace element compositions differing substantially from most chondrules and clasts 2 impact melt clasts if they have microporphyritic textures and signs that indicate they are derived from shock melted chondritic material 3 microporhyritic clasts if they are similar to the last category but lack evidence for derivation through shock melting or 4 indeterminate clasts forming a diverse class that includes all those clasts that do not fit into the other categories

contrasts in sea ice deformation and production in the arctic seasonal and perennial ice zones 1 four years 1997 2000 of radarsat geophysical processor system rgps data are used to contrast the sea ice deformation and production regionally and in the seasonal siz and perennial piz ice zones ice production is of seasonal ice in openings during the winter three day estimates of these quantities are provided within lagrangian elements initially 10 km on a side a distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter regional divergence over the winter could be up to 30 spatially the highest deformation is seen in the siz north of coastal alaska both ice deformation and production are higher in the siz deformation related ice production in the siz 0 5 m is 1 5 2 3 times that of the piz 0 3 m this is connected to ice strength and thickness atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability seasonal ice growth in ice fractures accounts for 25 40 of the total ice production of the arctic ocean uncertainties in these estimates are discussed by itself this deformation ice production relationship could be considered a negative feedback when thickness is perturbed however the overall effect on ice production in the face of increasing seasonal and thinner weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones

large silica rich igneous textured inclusions in the buzzard coulee chondrite condensates differentiates or impact melts we studied three large 2 4 mm diameter igneous textured inclusions in the buzzard coulee h4 chondrite using microanalytical techniques olm sem empa sims to better elucidate the origins of igneous inclusions in ordinary chondrites the inclusions are clasts that come in two varieties 1 white inclusions bz 1 and bz 2 represent a nearly holocrystalline assemblage of low ca and high ca pyroxene 63 66 area and cristobalite 33 36 and 2 tan inclusion bz 3 is glass rich approximately 60 with low ca and high ca pyroxene phenocrysts the bulk compositions of the inclusions determined by modal reconstruction are all sio2 rich approximately 67 wt for bz 1 and bz 2 approximately 62 for bz 3 but bz 3 is enriched in incompatible elements e g ree approximately 4 5 ci abundances whereas bz 2 and bz 1 are depleted in those elements that are most incompatible in pyroxene e g la ho approximately 0 15 0 4 ci abundances these bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor and show no evidence for overall volatility control we infer that the inclusions originated through igneous differentiation and feo reduction with bz 3 forming as an andesitic partial melt approximately 30 40 partial melting of an h chondrite precursor and bz 1 and bz 2 forming as pyroxene cristobalite cumulates from an si rich melt we suggest that both types of melts experienced a period of transit through a cold low pressure space environment in which cooling feo reduction and interaction with a vapor occurred melts may have been lofted into space by excavation or splashing during collisions or by pyroclastic volcanism our results indicate intriguing similarities between the inclusions in buzzard coulee and the silicates in some iron iie type and stony iron iva type meteorites suggesting a genetic relationship

pan arctic lead detection from modis thermal infrared imagery polynyas and leads are key elements of the wintertime arctic sea ice cover they play a crucial role in surface heat loss potential ice formation and consequently in the seasonal sea ice budget while polynyas are generally sufficiently large to be observed with passive microwave satellite sensors the monitoring of narrow leads requires the use of data at a higher spatial resolution we apply and evaluate different lead segmentation techniques based on sea ice surface temperatures as measured by the moderate resolution imaging spectroradiometer modis daily lead composite maps indicate the presence of cloud artifacts that arise from ambiguities in the segmentation process and shortcomings in the modis cloud mask a fuzzy cloud artifact filter is hence implemented to mitigate these effects and the associated potential misclassification of leads the filter is adjusted with reference data from thermal infrared image sequences and applied to daily modis data from january to april 2008 the daily lead product can be used to deduct the structure and dynamics of wintertime sea ice leads and to assess seasonal divergence patterns of the arctic ocean

evaluation of high resolution sea ice models on the basis of statistical and scaling properties of arctic sea ice drift and deformation sea ice drift and deformation from models are evaluated on the basis of statistical and scaling properties these properties are derived from two observation data sets the radarsat geophysical processor system rgps and buoy trajectories from the international arctic buoy program iabp two simulations obtained with the louvain la neuve ice model lim coupled to a high resolution ocean model and a simulation obtained with the los alamos sea ice model cice were analyzed model ice drift compares well with observations in terms of large scale velocity field and distributions of velocity fluctuations although a significant bias on the mean ice speed is noted on the other hand the statistical properties of ice deformation are not well simulated by the models 1 the distributions of strain rates are incorrect rgps distributions of strain rates are power law tailed i e exhibit wild randomness whereas models distributions remain in the gaussian attraction basin i e exhibit mild randomness 2 the models are unable to reproduce the spatial and temporal correlations of the deformation fields in the observations ice deformation follows spatial and temporal scaling laws that express the heterogeneity and the intermittency of deformation these relations do not appear in simulated ice deformation mean deformation in models is almost scale independent the statistical properties of ice deformation are a signature of the ice mechanical behavior the present work therefore suggests that the mechanical framework currently used by models is inappropriate a different modeling framework based on elastic interactions could improve the representation of the statistical and scaling properties of ice deformation

exposure history of the regolithic chondrite fayetteville ii solar gas free light inclusions abstract noble gases and cosmic ray tracks were determined on light solar gas free inclusions of the solar gas rich h4 chondrite fayetteville 10 be 26 a1 major and trace element concentrations as well as oxygen isotope ratios complete the data set one exceptional inclusion is an l chondrite xenolith identified by its oxygen isotope signature and the concentration of metallic fe ni oxidized fe of this inclusion equilibrated with the host early in the history of fayetteville s parent body track density variations indicate that the majority of fayetteville s inclusions were irradiated as pebbles in the parent body by solar flare particles for about 10 4 10 6 years the l chondritic inclusion contains an unequivocal excess of gcr produced he and ne relative to the remaining inclusions this clast as well as two more solar gas free samples suffered a gcr exposure on the parent body lasting some 10 million years or longer this exposure is comparable in length to the residence times of solar gas rich matrix samples in the gcr active zone of the fayetteville parent regolith probably the other inclusions also were irradiated by gcr during at least several million years prior to the separation of the meteoroid from the parent body

declassified high resolution visible imagery for arctic sea ice investigations an overview abstract since 2009 subsets of declassified satellite images of arctic sea ice have been released as literal image derived products lidps with one meter resolution for scientific use the collections include imagery acquired over six fixed locations in the arctic basin since 1999 targeted acquisitions over drifting ice parcels from 2009 on provide an added dimension to the lidp archive this mode of acquisition is especially useful for capturing time varying processes during the melt season in this paper we describe the characteristics of lidps the extent of the current archive and highlight their uses for arctic sea ice science at this writing the archive of lidps is still quite limited and thus this paper illustrates the potential utility of the imagery we provide an overview of the retrieval of five sea ice parameters that would benefit significantly from the surface details afforded by the higher resolution lidps they include melt pond coverage open water fraction ridge height floe size and openings and closings two other uses are suggested measurement of lateral melt and the interpretation of radar backscatter the intent is to motivate geophysical uses of the lidp and future acquisitions results here suggest that the effective observations of sea ice parameters and especially their changes require more focused sampling strategies to address specific spatial and temporal sampling needs presently acquisitions of this type of imagery at fixed locations and drifting sites are being continued and lidps are added to the archive as they are released

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

derivation of a heterogeneous lithic fragment in the bovedy l group chondrite from impact melted porphyritic chondrules the bovedy l group chondrite contains a light colored poikilitic lithic fragment with olivine low ca pyroxene and kamacite compositions characteristic of porphyritic chondrules from unequilibrated ordinary chondrites its texture compositional similarities to porphyritic chondrules and low na2o k2o and p2o5 content indicate that the fragment represents a solidified slightly fractionated impact melt formed from a source that was rich in porphyritic chondrules the fragment is heterogeneous with a progressive increase in the bulk mgofeo ratio and in mgo content of olivines and low ca pyroxenes across its length 39ar40ar analyses of the fragment and host indicate that the meteorite experienced extensive degassing due to reheating the approximate age of 0 5 0 94 byr dates the reheating event and not the formation of the lithic fragment or the bovedy breccia this reheating event renders the fragment s and host s metallographic cooling rate of 5 c myr through 500 c imprecise however the absence of martensite and the presence of kamacite zoned taenite and tetrataenite in the fragment and host are consistent with such slow cooling through 500 c this cooling rate must have resulted from burial of the fragment host assemblage beneath insulating material on the bovedy parent body if the thermal diffusivity of this overburden was approximately comparable to that of the lunar regolith 10 4cm2 sec then the fragment was buried at a depth 6 5 km if k 10 2 cm2 sec similar to chondritic material then the fragment was buried at a depth 65 km

formation conditions of igneous regions in ordinary chondrites chico rose city and other heavily shocked h and l chondrites we report microprobe and radiochemical neutron activation analysis rnaa data for hosts and igneous inclusions in the heavily shocked ordinary chondrites rose city h5 yanzhuang h6 farmington l5 malakal l5 chantonnay l6 chico l6 and tuan tuc l6 based on these analytical results equilibrium crystallization calculations ghiorso and sack 1995 phase equilibrium analysis e g sack and ghiorso 1994a b sack et al 1994 and experimental cooling rate studies e g walker et al 1976 we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites we infer that 1 unfractionated chondritic liquids were intruded to depths 0 1 km in the parent asteroid of rose city 2 early chondritic liquids experiencing 5 10 olivine fractionation were erupted onto the surface of the parent asteroid s of yanzhuang and chantonnay and 3 near surface crystallization is also indicated for the liquids in tuan tue and farmington with chico and malakal crystallizing at slightly greater depths in all but chantonnay liquids appear to have derived from melting of chondrite types corresponding to their hosts in the l chondrite chantonnay the intrusive liquids derive from melting an h chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts heating effects are also reflected in the trace element contents of the chondrites our rnaa data for rose city seem to reflect only the siderophile lithophile fractionation evident in the metal distribution the yanzhuang rnaa data are generally similar to those of other h chondrites severe shock not involving phase transport seems to leave h chondrites unaffected compositionally contents of the four most mobile elements cd bi t1 in and cs in chico indicate loss so that this assemblage experienced extended low temperature cooling after injection of dike material into the chico host rnaa data for the other four l chondrites examined indicate more rapid cooling

open water production in arctic sea ice satellite measurements and model parameterizations sequential synthetic aperture radar sar images from the ers 1 spacecraft were routinely used as input to the geophysical processor system at the alaska sar facility from 1992 through 1994 to produce sea ice displacement vectors on a 5 km grid we have combined some 5000 of these products consisting of nearly 700 000 displacement vectors into a set of 914 strips or mosaics of ice motion that span mostly 3 day intervals for each strip we compute the opening and closing of leads based on the change in area of the 5 km grid cells we also compute the area averaged deformation or strain invariants of the motion the small scale several kilometer lead activity can be parameterized fairly well in terms of the large scale several hundred kilometer strain invariants sea ice models implicitly contain such a parameterization through their constitutive equations the well known model of hibler 1979 that uses a viscous plastic rheology and an elliptical yield curve is in good agreement with our data the variance in the data about this theoretical relationship is less than that suggested by a random model of sea ice motion the data also indicate that shearing deformation contributes to the opening and closing of leads models with two categories or levels of ice thickness generally do not take shearing deformation into account in the evolution of the ice concentration nor do they redistribute ice as a result of ridging we show how to add these features to two level models however we argue that three level models consisting of open water thin ice and thick ice are much better suited to the proper treatment of open water production and we present such a model

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

igneous inclusions from ordinary chondrites high temperature cumulates and a shock melt we report microprobe instrumental neutron activation analysis and radiochemical neutron activation analysis data for three large igneous inclusions in the yamato y 75097 y 793241 and y 794046 ordinary chondrites the inclusions in the first two chondrites are troctolitic cumulates that have undergone appreciable reactions with their hosts either during emplacement and or cooling olivine spinel fe mg exchange pairs in these two inclusions record equilibration temperatures of about 710 c and these temperatures are similar to those exhibited by mineral pairs in the y 75097 and y 793241 hosts the inclusion in y 794046 is texturally unique consisting of fine grained randomly distributed olivines coarse 2 mm fascicular pyroxene laths and angular pockets of maskelynite plagioclase feldspar the phase compositions are readily interpreted as having resulted from extremely rapid essentially isochemical cooling to temperatures 1670 c we suggest that this igneous inclusion formed in situ by shock

a search for h chondritic chromite grains in sediments that formed immediately after the breakup of the l chondrite parent body 470 ma ago abstract a large abundance of l chondritic material mainly in the form of fossil meteorites and chromite grains from micrometeorites has been found in mid ordovician 470 ma old sediments globally the material has been determined to be ejecta from the l chondrite parent body breakup event a major collision in the asteroid belt 470 ma ago in this study we search the same sediments for h chondritic chromite grains in order to improve our understanding of the extraterrestrial flux to earth after the asteroid breakup event we have used sims in conjunction with quantitative sem eds to determine the three oxygen isotopic and elemental compositions respectively of a total of 120 randomly selected sediment dispersed extraterrestrial chromite grains mainly representing micrometeorites from 470 ma old post breakup limestone from the thorsberg quarry in sweden and the lynna river site in russia we show that 99 or more of the grains are l chondritic whereas the h chondritic fraction is 1 or less the l h chondrite ratio after the breakup thus was 99 compared to 1 1 in today s meteoritic flux this represents independent evidence in agreement with previous estimates based on sediment dispersed extraterrestrial chromite grain abundances and sedimentation rates of a two orders of magnitude higher post breakup flux of l chondritic material in the micrometeorite fraction finally we confirm the usefulness of three oxygen isotopic sims analyses of individual extraterrestrial chromite grains for classification of equilibrated ordinary chondrites the h and l chondritic chromites differ both in their three oxygen isotopic and elemental compositions but there is some overlap between the groups in chromite tio 2 is the oxide most resistant to diagenesis and the combined application of tio 2 and oxygen three isotope analysis can resolve uncertainties arising from the compositional overlaps

zircon u pb dating of granites in gejiu superlarge tin polymetallic orefield and its significance lots of igneous rocks are distributed in the gejiu tin polymetallic orefield of yunnan province and granites here are considered to have some original connection with the ore deposits shrimp and la icp ms zircon u pb dating yielded some age data the longchahe porphyritic granite is 81 2 1 4 83 2 1 4 ma the porphyritic granite in malage songshujia area is 82 8 1 7 ma the porphyritic granite in laochang area is 83 3 1 6 ma and the baishachong equigranular granite is 77 4 2 5 ma based on these data together with some new data obtained in this study the authors hold that southeast yunnan and west guangxi belonged to the same geotectonic setting in late yanshanian period but were obviously different from the south tibet three river tin belt

sea ice motion tracking from sequential dual polarization radarsat 2 images a new sea ice motion tracking algorithm that operates with two sequential synthetic aperture radar sar radarsat 2 scansar images is presented the feature tracking approach is based on the combination of the phase correlation and cross correlation methods an algorithm for selecting control points a matching technique an approach for filtering out error vectors and a confidence levels setting for output drift vectors were specifically developed in order to increase the system s robustness and accuracy we evaluated ice motion tracking results derived from hh and hv channels of radarsat 2 scansar imagery and formulated a condition where the hv channel is more reliable than the hh channel for ice tracking furthermore we found that the ice motion tracking from the hv channel is not affected by noise floor stripes which are prominent in the cross polarization radarsat 2 scansar images the developed sea ice tracking technology was implemented at the canadian ice service environment canada for operational use the system was successfully run to provide operational support of field work in the arctic ocean in compliance with the united nations convention on the law of the sea in the spring of 2010

the 40ar 39ar dating of biotite in ore veins and zircon u pb dating of porphyrtic granite dyke in the nanyangtian tungsten deposit in se yunnan china abstract the nanyangtian tungsten deposit is located in the laojunshan sn w polymetallic metallogenic province in se yunnan china tectonically it is located in the conjunction of the cathaysia and indochina blocks the orebodies primarily hosted within the stratiform like skarn and marble in the paleoproterozoic nanyangtian formation three ore forming stages have been identified based on mineral assemblages and on the intercalated relationships between the veins they include skarn scheelite stage quartz scheelite vein stage and carbonate scheelite vein stage in this paper we present 40ar 39ar laser incremental heating analyses of hydrothermal biotite intergrowth with scheelite from quartz scheelite vein with two yielded well defined 40ar 39ar plateau ages of 97 49 0 97 ma and 99 48 0 97 ma and two isochronal ages of 97 01 1 39 ma and 99 58 0 98 ma respectively representing the age of second mineralization stage of the nanyangtian tungsten deposit the ages are well consistent with the emplacement age of the laojunshan granite 96 ma to 117 ma u pb geochronological data for magmatic zircons separated from porphyritic granite dyke in the mine pit indicate that the granite body was emplaced in the post ore stage 89 88 0 53 ma integrated with previously high resolution diagenetic and metallogenic geochronological data two significant magmatic mineralization events are presented in se yunnan china and north vietnam the first event took place from 97 ma to 124 ma which is closely related to the tungsten mineralization the second event occurred from 75 ma to 95 ma which is closely related to the sn cu ag zn mineralization according to the exhibited data we preliminarily conclude that the late cretaceous magmatic mineralization activity in se yunnan and north vietnam is the product of post collision of the cathaysia and indochina blocks and should have formed under a same geodynamic setting

earliest planetary melting the view from meteorites abstract the eucrite basaltic meteorites and iron meteorites from the cores of asteroids have ages that testify to planetary formation and differentiation 4 55 4 60 ga ago these ages are indistinguishable from those of the ordinary chondrites mixtures of silicate sulphide and metal that did not melt after their formation rare inclusions in the ordinary chondrites have textures and or fractionated rare earth element patterns indicating that they are the products of basaltic melts thus some basaltic rocks predate the accretion of the ordinary chondrites four inclusions are briefly described one contains evidence for the former presence of live 26al another exhibits an ophitic texture extreme fe enrichment in the pyroxenes and an abnormally high mno feo ratio this inclusion is from a differentiated body of which we have identified no other sample

constraining ultrahigh pressure uhp metamorphism and titanium ore formation from an infrared microthermometric study of fluid inclusions in rutile from donghai uhp eclogites eastern china eclogites in the donghai area of the sulu ultrahigh pressure uhp metamorphic belt in eastern china contain both disseminated rutile and rutile deposits the rutile occurs as small inclusions in garnet omphacite phengite and quartz as larger euhedral to subhedral grains in equilibrium with garnet omphacite phengite and kyanite and as discrete veinlets aggregates and megacrysts in cracks and along grain boundaries to investigate the processes of rutile mineralization and its relationship to the evolution of the sulu uhp metamorphic belt we sampled the exposed maobei deposit at donghai and drill core between 100 and 2000 m in the nearby chinese continental scientific drilling project ccsd main hole to carry out a detailed infrared microthermometric fluid inclusion study three types of fluid inclusions were identified aqueous type i co 2 h 2 o type ii and ch 4 type iii type i and type ii inclusions are the most common primary and pseudosecondary type i inclusions which were trapped during recrystallization of the eclogite or early amphibolite facies retrograde metamorphism have a narrow range of homogenization temperatures but a wide range of salinities in contrast secondary type i inclusions which formed entirely during retrograde amphibolite facies metamorphism associated with exhumation of the uhp rocks have higher and more varied homogenization temperatures but medium to low salinities type ii inclusions formed contemporaneously with the type i variety and are characterized by having small amounts of co 2 and n 2 in addition to h 2 o in addition some of the rutile grains contain sparse inclusions composed of ch 4 type iii our results combined with those of previous studies suggest a great diversity of fluid composition in the peak metamorphic to early retrograde stages implying very limited fluid rock interaction during syn to post peak high pressure hp and uhp metamorphism this study shows that infrared microthermometric investigation of fluid inclusions can provide information not only on the composition of titanium ore forming fluids but also on the relationship between mineralization and the evolution of uhp metamorphic belt

the iodine xenon system in clasts and chondrules from ordinary chondrites implications for early solar system chronology abstract we have studied the i xe system in chondrules and clasts from ordinary chondrites cristobalite bearing clasts from parnallee ll3 6 closed to xe loss 1 4 ma after bjurbole feline a feldspar and nepheline rich clast also from parnallee closed at 7 04 0 15 ma two out of three chondrules from parnallee that yielded well defined initial i ratios gave ages identical to bjurbole s within error a clast from barwell l6 has a well defined initial i ratio corresponding to closure 3 62 0 60 ma before bjurbole partial disturbance and complete obliteration of the i xe system by shock are revealed in clasts from julesburg l3 6 and quenggouk h4 respectively partial disturbance by shock is capable of generating anomalously high initial i ratios in some cases these could be misinterpreted yielding erroneous ages a macrochondrule from isoulane n amahar contains concentrations of i similar to ordinary chondrules but unlike most ordinary chondrules contains no radiogenic 129xe this requires resetting 50 ma or more later than most chondrules the earliest chondrule ages in the i xe mn cr and al mg systems are in reasonable agreement this and the frequent lack of evidence for metamorphism capable of resetting the i xe chronometer leads us to conclude that at least the earliest chondrule i xe ages represent formation if so chondrule formation took place at a time when sizeable parent bodies were present in the solar system

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

phosphate minerals in the h group of ordinary chondrites and fluid activity recorded by apatite heterogeneity in the zag h3 6 regolith breccia phosphate minerals in ordinary chondrites provide a record of fluids that were present during metamorphic heating of the chondrite parent asteroids we have carried out a petrographic study of the phosphate minerals merrillite and apatite in metamorphosed h group ordinary chondrites of petrologic type 4 6 to understand development of phosphate minerals and associated fluid evolution during metamorphism in unbrecciated chondrites apatite is cl rich and shows textural evolution from fine grained apatite merrillite assemblages in type 4 toward larger uniform grains in type 6 the cl f ratio in apatite shows a similar degree of heterogeneity in all petrologic types and no systematic change in compositions with metamorphic grade which suggests that compositions in each meteorite are dictated by localized conditions possibly because of a limited fluid rock ratio the development of phosphate minerals in h chondrites is similar to that of l and ll chondrites despite the fact that feldspar equilibration resulting from albitization is complete in h4 chondrites but not in l4 or ll4 chondrites this suggests that albitization took place during an earlier period of the metamorphic history than that recorded by preserved apatite compositions and chemical equilibrium was not achieved throughout the h chondrite parent body or bodies during the late stages of metamorphism a relict igneous clast in the h5 chondrite oro grande has apatite rims on relict phenocrysts of possibly diopside that have equilibrated with the host chondrite apatite in the zag h3 6 regolith breccia records a complex fluid history which is likely related to the presence of halite in this meteorite the porous dark h4 matrix of zag where halite is observed has a high apatite merrillite ratio and apatite is extremely cl rich one light h6 clast contains similarly cl rich apatite in a second light h6 clast apatite compositions are very heterogeneous and more f rich apatites in both h4 matrix and h6 clasts have very low h 2o contents heterogeneous apatite compositions in zag record multiple stages of regolith processing and shock at the surface of the h chondrite parent body and apatite records either the passage of fluids of variable compositions resulting from different impact related processes or the passage of a single fluid whose composition evolved as it interacted with the chondrite regolith unraveling the history of apatite can potentially help to interpret the internal structure of chondrite parent bodies with implications for physical and mechanical properties of chondritic asteroids the behavior of halogens recorded by apatite is important for understanding the behavior of volatile elements in general if impact melt materials close to the surface of a chondritic asteroid are readily degassed the volatile inventories of terrestrial planets could be considerably more depleted than the ci carbonaceous chondrite abundances that are commonly assumed

shock and thermal history of northwest africa 4859 an annealed impact melt breccia of ll chondrite parentage containing unusual igneous features and pentlandite abstract northwest africa 4859 nwa 4859 is a meteorite of ll chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite the most obvious unusual feature is a high proportion of large 3 cm diameter igneous textured enclaves lites interpreted as shock melts that were intruded into an ll chondrite host one such lite appears to have been produced by whole rock melting of ll chondrite initial rapid partial crystallization and subsequent slow cooling of the residual melt in the host to produce a differentiated object other unusual features include mm sized overgrowth objects fine grained plagioclase rich bands and coarse troilite 7 mm across grains all these features are interpreted as having crystallized from melts produced by a single transient shock event followed by slow cooling a subsequent shock event of moderate s3 intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype pentlandite together with associated troilite in nwa 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature 230 c following the second shock event nwa 4859 is interpreted to be an unusual impact melt breccia that contains shock melt which crystallized in different forms at depth within the parent body

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

a new modeling framework for sea ice mechanics based on elasto brittle rheology we present a new modeling framework for sea ice mechanics based on elasto brittle eb behavior the eb framework considers sea ice as a continuous elastic plate encountering progressive damage simulating the opening of cracks and leads as a result of long range elastic interactions the stress relaxation following a damage event can induce an avalanche of damage damage propagates in narrow linear features resulting in a very heterogeneous strain field idealized simulations of the arctic sea ice cover are analyzed in terms of ice strain rates and contrasted to observations and simulations performed with the classical viscous plastic vp rheology the statistical and scaling properties of ice strain rates are used as the evaluation metric we show that eb simulations give a good representation of the shear faulting mechanism that accommodates most sea ice deformation the distributions of strain rates and the scaling laws of ice deformation are well captured by the eb framework which is not the case for vp simulations these results suggest that the properties of ice deformation emerge from elasto brittle ice mechanical behavior and motivate the implementation of the eb framework in a global sea ice model

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

fe ni and co variations in the metals of some antarctic chondrites abstract nearly 4 000 fe ni and co analyses have been carried out on the metal phases of 12 antarctic chondritic meteorites by means of the electron microprobe h group chondrites show relatively simple patterns of variation for these elements but l and ll group members show much more scatter in both ni and co concentrations a single member of the co3 group investigated shows some scatter in the concentrations and also much higher co concentrations in the high ni awaruite phase 1 25 2 than in the coexisting kamacite 0 2 0 5 thus analysis of the metal phases can provide not only a means of identifying the group to which a meteorite belongs but also the possibility of distinguishing between individual chondrites from the same group the overall concentrations of co in the metal particles in the different groups are considered to be related inversely to the abundance of metal grains in meteorites of these groups while the scatter is interpreted as reflecting characteristics inherited at the time of accretion the absence of homogenisation of the concentrations of fe ni and co in the metal particles even in so called equilibrated chondrites provides further evidence against the widely held notion that these meteorites have been involved in a high temperature prograde metamorphism

geochronology geochemistry and hf isotopic composition of late cretaceous laojunshan granites in the western cathaysia block of south china and their metallogenic and tectonic implications abstract sn in and w rich granites are identified in laojunshan area in the western cathaysia block south china including coarse grained two mica monzogranite cmg and fine grained two mica monzogranite fmg laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of cmg and fmg are from 85 6 0 8 ma to 90 37 0 7 ma and 89 9 1 4 ma respectively all samples have relatively high total alkalis contents 5 74 wt to 9 73 wt and al saturation indices 0 95 to 1 79 indicating that most of granites belong to the strongly peraluminous granites the granites are enriched in p rb cs sn li be and u and are depleted in ti mg co ni sr ba zr and hf the fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations while rare earth elements were fractionated by accessory minerals such as apatite monazite or ilmenite these geochemical features suggest that most of rocks are highly fractionated s type granites the ehf t values of the zircon samples from cmg and fmg range from 12 88 to 1 19 with the two stage hf model ages ranging from 1 2 ga to 1 9 ga the geochemical and isotopic data show that the laojunshan granites are derived from a crystalline basement that has metamorphosed pelitic rocks from the mes paleoproterozoic continental crust the upwelling of the asthenosphere caused by a strong lithospheric extension led to the partial melting of the metamorphosed pelitic rocks to form widespread late cretaceous s type granites in the laojunshan area lithospheric extension and cretaceous magma in se yunnan are probably related to the palaeo tethys ocean crustal delamination which subducted beneath the indochina block

extracting sea ice data from satellite sar imagery with the prospect of operational satellite sar s by the end of the decade there is a clear need to develop automated algorithms for the extraction of geophysical data about sea ice from highresolution radar imagery to this end we have developed techniques for distinguishing ice from open water and for resolving the details of deformation within areas 100 km square imaged by seasat sar the classification of ice and open water is based on the creation of a second band of image data consisting of the local variance of the original brightness the first band being a local average brightness in the space of these two variables ice and open water are separated into two distinct clusters the deformation is found on a 3 4 km mesh by local cross correlations of the brightness the strategy is to find a coarse displacement field with a highly averaged image and to proceed through a hierarchy of images with increasing resolution improving the accuracy of the displacements at each step comparison with manually determined displacement shows room for improvement in regions of high deformation by using smaller areas for cross correlation the concentration and deformation data are used together to determine localized regions of the scene where open water is produced or lost

ore forming fluids and metallogenesis of nanyangtian tungsten deposit in laojunshan southeastern yunnan province the nanyangtian tungsten deposit is located in the tungsten tin polymetallic ore forming area in laojunshan southeastern yunnan province ore bodies fairly simple in shape are largely concordant with the bedding of the strata and the distribution of the ore bodies is spatially related to skarn the formation of tungsten deposit experienced a period composed of skarn phase and quartz sulfide phase the skarn phase is divided into skarn stage and retrogressive alteration stage whereas the quartz sulfide phase consists of two stages called respectively quartz sulfide stage and calcite sulfide stage tungsten mineralization probably occurred at the retrogressive alteration stage there are three dominant types of fluid inclusions as evidenced by petrographic characteristics of fluid inclusions of garnet epidote quartz fluorite and calcite formed at different oreforming stages in the nanyangtian tungsten deposit they are liquid rich inclusions gas rich two phase inclusions and daughter minerals bearing polyphase inclusions systemmatic measurement of homogeneous and freezing temperatures as well as salinities and laser raman spectroscopic analysis of fluid inclusions were conducted the gas compositions of ore forming fluids in the nanyangtian tungsten deposit are mostly h2o ch4 and n2 with a small amount of co2 whereas the liquid composition is primarily h2o fluid inclusions in the skarn phase show homogenization temperatures and salinities w nacleq from 260 to 420 and from 6 45 to 53 26 respectively with the densities ranging from 0 83 g cm3 to 1 15 g cm3 homogenization temperatures and salinities w nacleq of fluid inclusions in the quartz sulfide phase mainly vary from 160 to 300 and from 4 to 8 respectively and the densities of the fluids are 0 67 0 96 g cm3 which are obviously lower than the data of the fluid inclusions in the skarn phase the 18osmow values of garnet quartz and calcite range from 3 78 to 16 23 with the corresponding 18oh2o values between 4 52 and 10 28 and d values of fluid inclusions between 83 and 59 the combined isotopic data imply that the ore forming fluids in the nanyangtian tungsten deposit were mainly derived from magmatic fluids the 34s values of pyrite from the nanyangtian tungsten deposit vary in a narrow range of 4 2 8 1 reflecting the derivation of sulfur from deep magma source tungsten mineralization in the nanyangtian ore deposit took place in late triassic with its metallogenesis related to the magmatic activity during the indosinian period

a planetary h group pebble in the barwell l6 unshocked chondritic meteorite abstract one stone of the barwell l6 shower contains an igneous inclusion with the oxygen isotopic signature of h group chondrites the inclusion is composed dominantly of olivine with a composition fo 75 5 identical with that of its host other phases are only partially equilibrated with the host the inclusion has a fractionated rare earth element pattern showing depletion in the heavy rare earth elements and a positive eu anomaly it is depleted in siderophile elements inclusion and host have ar ar ages 4 44 and 4 51 ga respectively and 129 xe r i ratios identical within experimental error we conclude that melting occurred very early on an h group chondritic body two objects from a single meteorite have different oxygen isotopic ratios but identical 129 xe r 127 i ratios which may indicate that the i xe systematics reflect chronological differences in closure to xe rather than isotopically heterogeneous iodine the inclusion and its host cooled to xe closure temperature contemporaneously with chondrules from unequilibrated ordinary chondrites

chemical studies of h chondrites iii regolith evolution of the fayetteville chondrite parent abstract data for ag au bi cd co cs ga in rb sb se te tl and zn in consortium samples of solar gas and track rich dark matrix and dark and light clasts in the fayetteville h chondrite regolith breccia were determined by radiochemical neutron activation analysis the matrix proved chemically homogeneous at a level never before observed in an ordinary chondrite most dark clasts had similar mean trace element concentrations as matrix but were compositionally much more heterogeneous two clasts were unusual one having apparently formed from impact melted soil the other representing a mixture of 90 matrix 10 c2m chondrite the single light clast proved compositionally similar to h4 6 chondrite falls except for its higher contents of labile bi cd in and tl relative to matrix all other samples seemed cs deficient other h chondrite regolith breccias studied in the past had shown peculiar cs and or rb contents so that these alkalis seem diagnostic of such breccias dark portions of such breccias apparently represent compacted regolith soil produced by isochemical comminution of normal dark and light clasts the dark clasts in turn likely represent primordial nebular condensate although it is possible that they represent planetary cold traps that garnered labile elements generated elsewhere in the parent body

iodine xenon dating of chondrules from the qingzhen and kota kota enstatite chondrites abstract initial 129 i 127 i values i xe ages have been obtained for individual mineralogically characterized chondrules and interchondrule matrix from the enstatite chondrites qingzhen eh3 and kota kota eh3 in view of the absence of aqueous alteration and the low peak metamorphic temperatures experienced by these meteorites we suggest that the i xe ages for the chondrules record the event in which they were formed these ages are within the range recorded for chondrules from ordinary chondrites demonstrating that chondrules formed during the same time interval in the source regions of both ordinary chondrites and enstatite chondrites the timing of this chondrule forming episode or episodes brackets the i xe closure age of planetesimal bodies such as the shallowater aubrite parent body although chondrule formation need not have occurred close to planetesimals the existence of planetesimals at the same time as chondrule formation provides constraints on models of this process whichever mechanisms are proposed to form and transport chondrules they must be compatible with models of the protosolar nebula which predict the formation of differentiated bodies on the same timescale at the same heliocentric distance

old formation ages of igneous clasts on the l chondrite parent body reflect an early generation of planetesimals or chondrule formation abstract the barwell meteorite contains large abundant clasts that are igneous in nature we report iodine xenon ages of five clasts and one sample of host chondrite material the fragment of host chondrite material yielded the oldest age determined 4567 8 1 2 ma two clasts produced old well defined ages of 4564 96 0 33 ma and 4565 60 0 33 ma these and a third clast having a less precise old age of 4566 0 3 2 ma are interpreted as recording the timing of crystallisation of the samples they were incorporated into the barwell parent body before it underwent thermal metamorphism but the i xe ages survived secondary processing on the parent body and were not reset by metamorphism metasomatism or shock two further clasts record younger ages of 4560 96 0 45 ma and 4554 22 0 38 ma these samples contain a high abundance of albitic mesostasis and the most likely explanation of the ages is that they record the timing of metasomatism on the parent body we also analysed four host chondrite samples that do not give i xe ages in these samples the system appears to have been disturbed by shock it has been suggested previously that the igneous clasts are derived from an early generation of partially melted asteroids we do not have direct evidence that the clasts we examined were necessarily derived from a partially differentiated body only that they were derived from cooling of a silicate melt the clasts could thus be the products of any one of several proposed models for chondrule formation our results indicate that processes akin to chondrule formation in that they involve rapid cooling of a silicate melt were ongoing at the same time as cai formation lending support to the suggestion that al mg chondrule ages indicate either heterogeneous distribution of 26 al or resetting of the al mg system after chondrule formation

sea ice tracking by nested correlations spatial differences in sea ice displacement affect ice stress ice production and the mass balance of the ice cover our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution and does so fully automatically many small areas of ice common to two images are identified by correlating the two images the strategy is to acquire a crude displacement field first from highly averaged images and to refine this field with images of successively higher resolution the median discrepancy between automatically and manually measured displacements is three pixels 0 075 km the algorithm operates successfully on compact ice with large floes and modest rotation rates we believe it will prove applicable to most of the arctic ice cover throughout the year