subgrain boundaries in antarctic ice quantified by x ray laue diffraction ice in polar ice sheets undergoes deformation during its flow towards the coast deformation and recrystallization microstructures such as subgrain boundaries can be observed and recorded using high resolution light microscopy of sublimation edged sample surfaces microstructure mapping subgrain boundaries observed by microstructure mapping reveal characteristic shapes and arrangements as these arrangements are related to the basal plane orientation full crystallographic orientation measurements are needed for further characterization and interpretation of the subgrain boundary types x ray laue diffraction measurements validate the sensitivity of different boundary types with sublimation used by microstructure mapping for the classification x ray laue diffraction provides misorientation values of all four crystal axes line scans across a subgrain boundary pre located by microstructure mapping can determine the rotation axis and angle together with the orientation of the subgrain boundary this yields information on the dislocation types tilt and twist boundaries composed of dislocations lying in the basal plane and tilt boundaries composed of nonbasal dislocations were found a statistical analysis shows that nonbasal dislocations play a significant role in the formation of all subgrain boundaries

ice microstructure and fabric an up to date approach for measuring textures automatic c axes analyzers have been developed over the past few years leading to a large improvement in the data available for analysis of ice crystal texture such an increase in the quality and quantity of data allows for stricter statistical estimates the current textural parameters i e fabric crystallographic orientations and microstructure grain boundary networks are presented these parameters define the state of the polycrystal and give information about the deformation undergone by the ice to reflect the findings from automatic measurements some parameter definitions are updated and new parameters are proposed moreover a matlab toolbox has been developed to extract all the textural parameters this toolbox which can be downloaded online is briefly described

quaternary stratigraphy of the buried valleys of the lower red deer river alberta canada the quaternary fills of the buried valleys of southern alberta and saskatchewan have provided a wealth of information for the reconstruction of the glacial interglacial record of the western plains of canada and this paper reports on the previously unstudied stratigraphy of the buried calgary valley and its former tributaries in the lower red deer river area we attempt to differentiate empress group sediments which potentially relate to pre glacial interglacial interstadial and post glacial lake and river deposition using sedimentology stratigraphy and palaeoecology twenty nine stratigraphical logs indicate that empress group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the calgary valley located 15 km to the north of dinosaur provincial park radiocarbon dates of 52 4 ka 27 4 ka and 42 4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid wisconsinan in age however outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials interstadials and that older even pre glacial sediments could have survived subglacial channels recognisable on air photographs largely coincide with buried valley positions due to the preferential excavation of the quaternary sediment by meltwater and are filled with post glacial lake sediment from which a radiocarbon date of 16 ka bp was obtained pre glacial and glacial post glacial empress group sediments are lithologically indistinct but cover a large time span in southern alberta

kreep glass and the exotic provenance and formation of polymict breccia 66055 polymict breccia 66055 from the apollo 16 site is unique in that it contains abundant brown kreep glass 0 3 0 4 k2o and related brown glassy breccias which have fluid forms during assembly it consisted of hot and cold debris which flowed together most of the rock consists of clasts of poikiloblastic breccia granulitic impactite and mesostasis rich impact melt vha basalt both of which predate the assembly of 66055 in contrast the kreep glass was created in the impact which produced the rock kreep compositions are sparse among glasses in soils and other breccias at the apollo 16 site and the rock would not have formed locally it must be exotic terrains in which 66055 might have formed exist to the west of the landing site suitable igneous target materials for the kreep glass have not positively been identified in 66055 so the petrogenesis of apollo 16 kreep remains enigmatic although the presence of a granitic glass fragment embedded in kreep glass suggests that it is igneous a local volcanic origin is more consistent with the spatial relationships as deduced from orbital geochemical data than is a basin ejecta deposit

siderophile lithophile and mobile trace elements in the lunar meteorite allan hills 81005 contents of siderophilic as au co ga and sb volatile mobile ag bi cd in se te tl and zn and lithophilic cs rb and u determined by radiochemical neutron activation analysis in alh a81005 are similar to those of lunar highlands samples returned by apollo missions indicating this meteorite s lunar origin five elements co ga and lithophiles reflect lunar crustal processes while the remaining 11 siderophile and mobile elements including the most mobile ones indicate 1 4 0 5 micrometeorite cl equivalent admixture or enrichment by thermal redistribution on the moon thus in contrast to l chondrites where severe shock caused trace element loss impact launching of alh a81005 to earth was free of substantial 20 gpa shock loading in this light a martian origin for severely shocked snc meteorites is plausible

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

relation between neighbouring grains in the upper part of the northgrip ice core implications for rotation recrystallization abstract we propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the northgrip ice core this method shows unexpected correlations between neighbours in the so called normal grain growth regime questioning the classical view on the onset of rotation recrystallization in ice sheets moreover the fractionation rate associated to the rotation recrystallization appears constant through time finally grains with low angle boundaries do not present a special distribution pattern of their c axes this suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain

fabric and texture at siple dome antarctica preferred c axis orientations are present in the firn at siple dome west antarctica and recrystallization begins as shallow as 200 m depth in ice below 20 c based on digital analysis of c axis fabrics grain sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer long siple dome ice core the shallowest section analyzed from 22 m shows clustering of c axes toward the vertical by 200 m depth girdle fabric and other features of recrystallized ice are evident in layers or regions separated by layers regions of typically finer grained ice lacking evidence of recrystallization ice from about 700 780m depth which was deposited during the last ice age is especially fine grained with strongly vertical c axes but deeper ice shows much larger crystals and strong evidence of recrystallization azimuthal asymmetry of some c axis fabrics trends in grain size and other indicators reveal additional information on processes and history of ice flow at siple dome

impeding effect of air bubbles on normal grain growth of ice abstract normal grain growth experiments were performed using polycrystalline ice samples with and without air bubbles the bubble free polycrystalline ice was prepared by a special sample preparation technique that employed a phase change method the ice samples with air bubbles were prepared from a mixture of ice powder and pure distilled water using conventional methods the temperature dependencies of the rate of grain growth were measured in artificial polycrystalline ice samples with and without air bubbles the average grain growth exponent n of the ice with bubbles was much greater than the theoretical value of 2 while that of bubble free ice was close to 2 the activation energy for the grain boundary migration of bubble free ice was 110 120 kj mol 1 whereas that of the ice with bubbles was between 40 and 70 kj mol 1 the observation of the microscopic images of samples and analyses of the evolution of bubble size distribution and location during grain growth revealed that small air bubbles are caught and swept by moving grain boundaries and a coalescence of bubbles occurs this indicates that the slow grain boundary migration of ice with bubbles is controlled by the migration of air bubbles dragged by grain boundary migration

elephant moraine 87521 the first lunar meteorite composed of predominantly mare material abstract the trace element chemistry and detailed petrography of brecciated antarctic meteorite eet87521 reveal that it is not as originally classified a eucrite its fe mn ratio and bulk co content are far higher than expected for a eucrite an affiliation with the snc meteorites appears almost equally improbable on the basis of far lower ga al and na ca ratios in eet87521 only one known type of extraterrestrial material resembles eet87521 in all important respects for which constraints exist very low ti vlt lunar mare basalts even compared to vlt basalts eet87521 is enriched in ree however other varieties of high alumina low ti mare basalt are known that contain ree at even higher concentrations than eet87521 several clasts in eet87521 preserve clear vestiges of coarse grained igneous possibly orthocumulate textures mineralogically these coarse grained clasts are diverse e g olivine ranges from fo15 in one to fo67in another one clast with an anomalously fine grained texture is anor thositic and contains exceptionally mg rich pyroxene and na poor plagioclase along with the only feni metal in the thin section this clast is probably an impact melt breccia from the lunar highlands its feni metals have compositions typical of metals incorporated into lunar soils and polymict breccias as debris from metal rich meteorites however the low ni and ir contents of our bulk rock analysis imply that the proportion of impact projectile matter in our chip sample is probably small the moderate degree of lithologic diversity among the lithic clasts and the bulk composition in general indicate that eet87521 is dominated by a single rock type vlt mare basalt the fundamental distinction between mare and nonmare lunar materials has traditionally been based primarily on ti content and secondarily on such characteristics as ca al ratio and ree pattern however eet87521 recent studies of apollo 12 and apollo 14 rocks and the many apparent vlt basalts reported earlier as clasts in lunar highlands meteorites all tend to indicate that the dichotomy of lunar magmatism into distinct nonmare and mare styles may have been less abrupt than commonly envisaged

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

a ferroan region of the lunar highlands as recorded in meteorites mac88104 and mac88105 macalpine hills 88104 and 88105 mac88104 5 are paired meteorites of noritic anorthosite composition from the lunar highlands mac88105 is a breccia composed mainly of melt breccia clasts in a fine grained fragmental and partly glassy matrix the most abundant melt lithologies are feldspathic and are similar in composition to the bulk meteorite other melt lithologies include feldspathic melt rocks mafic melt breccias and a rare melt breccia relatively enriched in incompatible trace elements subordinate lithic clasts are granulitic breccias and ferroan relatively low mg mg fe igneous lithologies including troctolitic anorthosite anorthositic norite gabbronorite and anorthosite igneous clasts having mafic mineral compositions more magnesian than fo55 and en60 were not observed rare fragments of glass spheres and shards as well as glass clasts indicate that the meteorite was derived from an immature regolith the bulk composition of mac88105 is characterized by a molar mg mg fe ratio of 0 62 at the extreme low end of the range for meteorites from the lunar highlands its low concentrations of incompatible trace elements and feldspathic bulk composition 29 al2o3 suggest that it like the other lunar meteorites formed at a site far removed from the areas sampled by the apollo missions similarities in mineral compositions among the different lithologies of the breccia melt breccia clasts granulitic breccias igneous fragments and the distribution of mineral fragments suggest that most components of the meteorite were derived from a crustal section dominated by material with a noritic anorthosite composition and an affinity to the ferroan suite of plutonic rocks the mafic melt breccias have roughly peritectic melt compositions similar to many low k fra mauro melt breccias in the apollo collection but much more ferroan and represent a source material distinct from the noritic anorthosite moderate ce anomalies both positive and negative occur in some separated clasts and to a lesser extent in some small chips dominated by matrix but not in powder prepared from 20 g of bulk meteorite these anomalies are almost certainly terrestrial weathering effects one granulitic breccia clast is rich in siderophile elements as a result of a large amount of fe ni metal the auir ratio of the clast 0 64 ci normalized is distinctly different from that of metal rich impact melts from apollo 16 3 ci normalized the compositional range observed among the nonmare lunar meteorites alha81005 y791197 y82192 3 y86032 and mac88104 5 is equivalent to that observed among representative samples of 1 mm fines from apollo 16 thus compositional data provide little constraint on the number of impacts required to eject these meteorites from the moon

evidence of dynamic recrystallization in polar firn 1 microstructural analyses have been performed on polar firn from the european project for ice coring in antarctica drilling site in dronning maud land antarctica the results derived from images of the firn structure in microscopic resolution indicate that dynamic recrystallization is active in firn at all depths and it dominates the evolution of the microstructure when the firn density exceeds a critical value of 730 kg m3 overburden snow load 0 2 mpa at the firn ice transition density 820 kg m3 the microstructure is characterized by many small grains and bulged or irregularly shaped grain boundaries more than half of all grains show subgrain boundaries thus strain induced boundary migration is an essential feature to describe the irregular grain structure in agreement with previous studies significant grain growth has been observed with depth for the largest grains in the samples however our microscopic analysis reveals that the grain growth with depth in fact vanishes if all grains larger than 65 m in diameter are taken into account this result reflects the fact that the growth of the largest grains is counteracted by grain size reduction by shrinking and subdivision of old grains as well as production of new grains consequently previous conclusions that grain growth in polar firn is essentially analogous to normal grain growth in metallic and ceramic sinters and that the stored strain energy is small in comparison with grain boundary energy can no longer be supported additionally our observations show that the incipience of dynamic recrystallization in polar ice sheets is not as sensitive to temperature as supposed so far a discussion of the change of the mean grain size due to the measuring technique is imperative

competition between grain growth and grain size reduction in polar ice static or normal grain growth i e grain boundary migration driven solely by grain boundary energy is considered to be an important process in polar ice many ice core studies report a continual increase in average grain size with depth in the upper hundreds of metres of ice sheets while at deeper levels grain size appears to reach a steady state as a consequence of a balance between grain growth and grain size reduction by dynamic recrystallization the growth factor k in the normal grain growth law is important for any process where grain growth plays a role and it is normally assumed to be a temperature dependent material property here we show using numerical simulations with the program elle that the factor k also incorporates the effect of the microstructure on grain growth for example a change in grain size distribution from normal to log normal in a thin section is found to correspond to an increase in k by a factor of 3 5

geochemistry and petrography of the macalpine hills lunar meteorites abstract macalpine hills 88104 and 88105 are anorthositic lunar meteorites recovered from the same area in antarctica which are demonstrated to be paired samples of the same fall petrographic studies of matrix and clasts show that mac88104 5 is a polymict breccia dominated by impact melt clasts it contains a small amount of highland impact glass and very few regolith glass spherules it is better classified as a fragmental breccia than a regolith breccia the bulk composition is ferroan mg 63 and highly aluminous al 2 o 3 28 ree and other incompatible element concentrations are very low compositions of anorthositic granulitic and impact melt breccia clasts are very similar to but distinct from matrix composition mac88104 5 is very similar in composition to the other anorthositic lunar meteorites but each of the meteorites is distinct the anorthositic lunar meteorites especially mac88104 5 and y82192 3 86032 are very similar to north ray crater feldspathic fragmental breccias in compositon and petrography these fragmental lunar meteorites may have been ancient deeply buried breccias from the megaregolith comparisons of chemical petrographic features and exposure histories suggest that the twelve lunar meteorites were derived from two to nine but probably four to seven impacts onto the lunar surface discrepancies between the proportions of lunar meteorites and results of apollo missions may be due to unrepresentative sampling lunar meteorites provide valuable new information on the nature of the lunar crust

stuck at the bar larger than average grain lag deposits and the spectrum of particle mobility larger than average grain deposits in gravel bed rivers potentially exert a distinctive influence upon fluvial morphodynamics and flow resistance they are products of historical contingency sourced from rare events that supply atypically coarse material larger than average grain lag deposits are emblematic attributes of the tongariro river new zealand they are deposited on bar edges and heads derived from lahar valley floor deposits that subsequently became terraces these materials are less likely to be reworked across a range of flows compared to other bar material conceptual models that consider channel configuration and incorporate distributions of particle mobility and flood flows are necessary to assess the role of larger than average grain deposits on river morphodynamics

multiscale modeling of ice deformation behavior understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change the flow of ice has hitherto received relatively little attention from the structural geological community this paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale and beyond to the scale of polar ice sheets all through these scales various models have been developed to understand describe and predict the processes that operate during deformation of ice with the aim to correctly represent ice rheology and self induced anisotropy most of the modeling tools presented in this paper originate from the material science community and are currently used and further developed for other materials and environments we will show that this community has deeply integrated ice as a very useful model material to develop and validate approaches in conditions of a highly anisotropic behavior this review by no means exhaustive aims at providing an overview of methods at different scales and levels of complexity

a model of crystal size evolution in polar ice masses in the deep ice cores drilled at the grip ngrip and gisp2 sites in greenland and at byrd station and the summit of law dome in antarctica the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth this behaviour has been attributed to the competition between grain boundary migration driven crystal growth and crystal polygonization but the effects of changing crystal dislocation density and non equiaxed crystal shape in this competition are uncertain we study these effects with a simple model it describes how the mean height and width of crystals evolve as they flatten under vertical compression and as crystal growth and polygonization compete the polygonization rate is assumed to be proportional to the mean dislocation density across crystals migration recrystallization which can affect crystal growth via strain induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present is not accounted for when applied to the five ice core sites the model simulates the observed crystal size profiles well down to the bottom of their steady regions although the match for law dome is less satisfactory polygonization rate factors retrieved for the sites range from 10 5 to 10 2 a 1 we conclude that since crystal size and dislocation density evolve in a strongly coupled manner consistent modelling requires multiple differential equations to track both of these variables future ice core analysis should also determine crystal size in all three principal directions

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

mapping c axis fabrics to study physical processes in ice mapping the spatial distribution of c axis orientations in ice thin sections is not much more difficult than preparing c axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice distributions of angles between c axes of neighboring grains from the byrd station west antarctica ice core suggest that polygonization causes average grain size to stabilize below 400 m depth

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

history of the paired lunar meteorites mac88104 and mac88105 derived from noble gas isotopes radionuclides and some chemical abundances abstract noble gas isotopes radionuclides and chemical abundances were studied in the lunar meteorites mac88104 and mac88105 collected in the macalpine hills area of antarctica the concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical proving that the two meteorites are paired from 40k 40ar dating we obtain a gas retention age of 3550 400 ma typical for lunar surface material probably before breccia compaction the mac88104 5 material resided for 630 200 ma at an average shielding depth of 85 g cm 2 that is about 50 cm below the lunar surface in the lunar regolith as judged from the concentration of cosmic ray produced kr and xe isotopes although this duration of lunar regolith residence is relatively long mac88104 5 represent immature regolith material the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil the reason for that might be the relatively high average shielding the 40 ar 36ar ratio of the trapped component is 5 7 1 0 indicating an intermediate antiquity of the material we estimate that the solar wind and lunar atmospheric particles were implanted about 2000 ma ago the radionuclide activities allow us to derive the exposure history of the mac88104 5 material the duration of the moon earth transfer was 0 24 ma production of the radionuclides on the lunar surface immediately before ejection is possible but duration and shielding depth for such an exposure cannot be determined from our data we obtain a terrestrial age of 0 1 tterr 0 6 ma and an ejection time of mac88104 5 from the moon of 0 1 tejection 0 8 ma the exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the moon our first noble gas results for lunar meteorite yamato 793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gases and a duration of several hundred million years of exposure to cosmic rays

dynamics of crystal formation in the greenland northgrip ice core the north greenland icecore project northgrip ice core provides palaeoclimatic information back to about 120 kyr bp the size distributions of ice crystals in the upper 880 m of the northgrip ice core which cover a time span of approximately 5300 years have been obtained previously the distributions evolve towards a universal curve indicating a common underlying physical process in the formation of crystals we identify this process as an interplay between fragmentation of the crystals and diffusion of their grain boundaries the process is described by a two parameter differential equation to which we obtain the exact solution the solution is in excellent agreement with the measured distributions

rate controlling processes in the creep of polar ice influence of grain boundary migration associated with recrystallization abstract information on the deformation modes and recrystallization processes in polar ice sheets was obtained thanks to the analysis of the ice structure along two deep ice cores from greenland and antarctica it is shown that the deformation of polar ice at low stresses is produced by intracrystalline slip accommodated by grain boundary migration gbm a deformation model based on an equilibrium between work hardening and recovery processes has been developed the decrease in dislocation density is due to both gbm associated with grain growth and the formation of boundaries by recrystallization the value of the dislocation density along the byrd and grip ice cores obtained thanks to the model is about 1 10 11 m 2 this value is in agreement with data from synchrotron x ray diffraction on samples taken along the core this deformation model can account for the deformation of polar ice at low stresses it is shown that the flow law with a stress exponent lower than 2 can be related to the efficiency of gbm as a recovery process

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

macalpine hills 88104 and 88105 lunar highland meteorites general description and consortium overview abstract macalpine hills 88104 and 88105 are new lunar meteorites returned from antarctica by the 1988 1989 us meteorite collection team the two specimens were found in nearby locations and based on field and laboratory evidence are thought to be pieces of the same meteorite mac88105 is the largest lunar meteorite yet found 662g mac88104 5 is an anorthositic breccia consisting of numerous small clasts in a glassy matrix an origin on the moon is supported by the mineral bulk and oxygen isotope compositions a consortium of twenty research groups has studied these meteorites samples were prepared at the nasa johnson space center meteorite processing laboratory details of consortium plans and allocations are documented herein a summary list of lunar meteorites and an overview of consortium research is presented discussions in this and the following consortium papers involve the issue of paired meteorites and paired ejecta and what new information about the nature and evolution of the lunar crust is provided by the lunar meteorites

lunar granulites and their precursor anorthositic norites of the early lunar crust lunar granulites are breccias with metamorphic textures they are not pristine having been contaminated with meteoritic siderophiles nonetheless they constitute an abundant class of highlands rocks that are important because they are ancient and kreep free they may represent our best samples of the early lunar crust the granulites can be divided into ferroan and magnesian groups and each group can be subdivided on the basis of mineral composition and ree concentrations textural and compositional data show that some of the granulites especially 67215 and 67415 may be derived from distinct anorthositic norite precursors while some other granulites 79215 78155 are clearly polymict even the polymict granulites probably had anorthositic norites as their dominant precursors and not anorthosites norites or troctolites the granulites have compositions similar to those of the two lunar meteorites one of which yamato 791197 is ferroan the other alha81005 magnesian these meteorites are soil breccias from an unknown location distant from the apollo landing sites and contain anorthositic norites as abundant clasts compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands as determined by remote sensing than do those of any other returned lunar samples the predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from apollo missions

the athabasca fluting field alberta canada implications for the formation of large scale fluting erosional lineations abstract current drumlin and fluting hypotheses centred on processes of formation erosion and deposition by subglacial deformation accretion by lodgement glacial erosion and meltwater erosion and deposition rarely receive comprehensive field testing this paper documents the morphology internal structure and landscape associations of the athabasca fluting field alberta and discusses how well these characteristics are explained by postulated fluting forming processes fluting hypotheses are comprehensively tested by this approach and their rejection or acceptance are firmly based on field observation and knowledge of processes using multiple criteria fluting is shown to be erosional and not to be a product of pervasive subglacial deformation or accretion by lodgement morphology landscape associations bed truncation plus glaciofluvial lags and gravel on fluting ridges are inferred to support erosion by meltwater intact primary bedding synsedimentary faults and injection structures very close to the landsurface showing no sign of shear deformation are used to reject erosion by subglacial deformation fluting is shown to be closely associated with tunnel channels and indicates that these channels were overtopped by broad floods that formed the fluting field and eroded anabranching tracts over the length of the alberta plains prior to fluting formation sequences with melt out and lodgement till conduit sediment and boulder lags record net deposition over an extended time period diapirism prior to fluting formation marks a period of extreme pressure gradients which are related to bed separation following fluting formation there was only minimal landscape modification dominated by glaciofluvial and glaciolacustrine deposition not glacial processes this progression is presented as evidence for two very different glacial regimes separated by a short period with diapirism and extensive landscape modification by meltwater erosion we note that the study area was glaciated only once during the late wisconsinian and it follows that glacial sedimentation and landscape modification were confirmed to this single glacial episode

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

composition and evolution of the lunar crust in the descartes highlands apollo 16 samples from the north ray crater ejecta blanket apollo 16 were investigated by petrographic microscope electron microprobe instrumental neutron activation and xray fluorescence analyses and 40ar 39ar and rb sr dating techniques nine major groups of monomict and polymict breccias were defined on the basis of microscopic texture and these were further subdivided into chemical subgroups on the basis of characteristic elements such as al mg fe cr ree ni and co the polymict breccias fragmental breccias granulitic breccias and impact melt breccias are the result of multiple impact induced mechanical mixing and melting and of thermal and impact metamorphism of rock and mineral clasts derived from primordial igneous crustal rocks for calculations of mixing models it was found that end members consisting of the pristine igneous rock components present as discrete samples at the apollo 16 site and supplemented by kreep dunite and a meteoritic component yield the best fits for the composition of polymict breccias the end member rocks a re ferroan anorthosite various magnesian gabbronorites including sodic ferrogabbro and feldspathic lherzolite and spinei troctolite the following model is proposed for the composition and stratigraphy of the target for north ray crater the lower section of the stratigraphy is composed of a megabreccia with clasts of highly feldspathic polymict breccias kreep free old eastern highland rock suite interpreted as nectaris ejecta descartes formation the top section contains kreep bearing polymict breccias kreep bearing young western highland rock suite and appears to be similar to the lithologies found in the cayley plains this material interpreted as cayley formation may be a distant facies of imbrium basin ejecta deposits of the imbrium basin the petrographic differences between these two major selenographic units the descartes and the cayley formations in the apollo 16 area are more distinct than the chemical differences the petrographic and chemical composition of the primordial igneous upper crust in the regions of the nectaris and imbrium basins has been calculated by subtraction of the kreep and meteoritic components from the bulk composition of the descartes and cayley materials the nectaris crust which is better constrained consists of 86 87 a northosite 4 sodic ferrogabbro 0 5 1 3 feldspathic lherzolite 6 8 regular magnesian gabbronorite 1 8 2 8 dunite and 0 1 spinel troctolite a model for the evolution of the upper lunar crust in the descartes highlands is proposed on the basis of isotope ages and clast matrix relationships of polymict breccias essential features of this model in sequenial order are 1 development of multiple layers of kreep free early feldspathic fragmental megabreccias and impact melt sheets on the primordial crust in the time period from 4 4 aeons to the time of the nectaris impact which could have occurred as late as 3 85 aeons ago 2 excavation of these megabreccias by the nectaris event and deposition of a nectarian feldspathic fragmental megabreccia in the descartes area 3 introduction of kreep basaltic material into the upper crust mainly west and northwest of the descartes site and formation of kreepy impact melt sheets most probably from 4 05 to 3 80 aeons ago 4 imbrium impact at 3 8 aeons ago and deposition of kreep bearing imbrian feldspathic fragmental breccias at the descartes site which form the cayley formation and 5 redeposition mixing and melting of all preexisting breccias yielding kreep bearing and kreep poor post cayley fragmental breccias and melt ejecta glass bombs as the result of small impacts craters 1 5 km in diameter in the cayley plains and the descartes mountains respectively

antarctic meteorite alha81005 not just another lunar anorthositic norite seven subsamples of meteorite alha81005 a regolith breccia from the lunar highlands were analyzed by inaa for 32 elements four of them were also studied petrographically in bulk composition the rock corresponds to anorthositic norite with a very small component of kreep and is very similar to estimates of average lunar highlands surface compositions of the white clasts and the dark matrix are similar but the clasts are more magnesian and 30 50 as rich in kreep related elements the white clasts have fine grained granulitic textures and are generally similar to apollo 16 and 17 granulitic anorthositic norites but are more magnesian and only 20 as rich in kreep related elements some granulitic clasts are dominated by a magnesian anorthositic norite component not represented among the pristine apollo samples

age depth correlation grain growth and dislocation density evolution for three ice cores two previous theoretical analyses of data from the grip vostok and byrd ice cores presenting age depth correlations grain growth and dislocation density evolution are re examined it is found that the age depth correlations are inconsistent with the idealized flow with unchanging history adopted but that good correlations can be obtained by relaxing those restrictions a modified grain growth relation is proposed consistent with the distinct growth profiles of the vostok and other two cores which can be solved simultaneously with the given dislocation density evolution equation these are solved for all three cores with the given parameters and the depth profiles of grain diameter and dislocation density at the present time are determined with the new age depth correlation and with that shown empirically in the papers the varying flow history influences the age depth correlation and hence the depth profiles which is important both for the interpretation of core data and for the determination of constitutive variables at each depth at the present time

lunar basalt breccia identified among antarctic meteorites the antarctic meteorite elephant moraine eet 87521 is a lunar mare basalt breccia this 30 7 g meteorite was originally identified as a brecciated eucrite1 but new petrographic evidence from a more representative thin section fig 1 indicates that it is a breccia of mainly very low titanium vlt basalt and should be reclassified as a lunar meteorite the four or five antarctic lunar meteorites collected previously at allan hills yamato mountains and macalpine hills alha81005 y79117 y793274 y82192 82193 y86032 and mac88104 88105 have all sampled only the plagioclase rich lunar highlands2 3 which dominate the surface of the moon eet87521 extends the lunar meteorite collections to include the less abundant basaltic provinces the maria of the lunar crust

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

holocene geomorphology and stratigraphy of the lower falcon valley dinosaur provincial park alberta canada a tributary of the red deer river in dinosaur provincial park southern alberta contains evidence of a sequence of valley cutting and the deposition of three alluvial fills and one eolian deposit with the exception of the eolian deposit and minor amounts of shield and cordilleran rocks the sediments are derived from local bedrock incision of the bedrock valley occurred in the early postglacial period about 14 000 12 000 bp by rapid drainage of proglacial lakes and meltwaters the valley was subsequently partly infilled as locally fed stream discharges declined during the early to middle holocene by 6000 5000 bp alluvial fans had formed along the base of the valley walls fan development was followed by two phases of stream entrenchment and alluvial deposition including the most recent phase of cutting and filling that began approximately 800 bp the erosional and depositional events may reflect climatic changes as inferred in lacustrine deposits in southern alberta and in valleys elsewhere in the

syndeformational grain growth microstructures and kinetics abstract grain growth can be an important high temperature process in fine grained polycrystalline materials we studied its effect on texture during deformation using a two dimensional computer model and a see through experiment with octachloropropane syndeformational grain growth in geological materials can slow down the development of a grain shape preferred orientation or even obliterate it important processes are preferentially oriented deformation induced neighbour switches the presence of a grain shape preferred orientation slows down the increase in grain size due to grain growth

impurity influence on normal grain growth in the gisp2 ice core greenland intercept analysis of approximately bi yearly vertical thin sections from the upper part of the gisp2 ice core central greenland shows that grain size ranges increase with increasing age this demonstrates that something in the ice affects grain growth rates and that grain size cannot be used directly in paleothermometry as has been proposed correlation of grain growth rates to chemical and isotopic data indicates slower growth in ice with higher impurity concentrations and especially slow growth in forest fire layers containing abundant ammonium however the impurity grain growth relations are quite noisy little correlation is found between growth rate and isotopic composition of ice

the microstructure of polar ice part ii state of the art an important feature of natural ice in addition to the obvious relevance of glaciers and ice sheets for climate related issues is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point without losing its polycrystalline character this fact together with its strong mechanical anisotropy and other notable properties makes natural ice an interesting model material for studying the high temperature creep and recrystallization of rocks in earth s interior after having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in part i of this work faria et al 2014 here in part ii we present an up todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them in particular we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure also known as the three stage model cf part i these results prove that grain growth in ice sheets is dynamic in the sense that it occurs during deformation and is markedly affected by the stored strain energy as well as by air inclusions and other impurities the strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal which demand large amounts of strain accommodation from the microstructural analyses of ice cores we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice additionally in fine grained high impurity ice layers e g cloudy bands strain may sometimes be accommodated by diffusional flow at low temperatures and stresses or microscopic grain boundary sliding via microshear in anisotropic ice sheared at high temperatures grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets evidence of nucleation of new grains is also observed at various depths provided that the local concentration of strain energy is high enough which is not seldom the case as a substitute for the tripartite paradigm we propose a novel dynamic recrystallization diagram in the three dimensional state space of strain rate temperature and mean grain size which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure dedicated to sepp kipfstuhl on occasion of his 60th birthday

electrical conductivity method ecm stratigraphic dating of the byrd station ice core antarctica a continuous ecm profile strong acid concentration has been measured along the 2191 m of ice core recovered at byrd station antarctica in 1968 the ecm profile reveals continuous and systematic seasonal changes which are used for dating the ice core back to 50 000 bp hammer and others ecm stratigraphic dating of byrd station ice core antarctica

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

ferromagnetic resonance and magnetic properties of alha81005 seven chips of primarily matrix material from the antarctic meteorite alha81005 were analyzed by ferromagnetic resonance fmr and magnetic hysteresis techniques the fmr spectra of two chips have a resonance at g 2 1 that resembles the g 2 1 resonance that is characteristic of lunar soils thus the fmr spectra are consistent with the lunar regolith being a progenitor for the matrix material for the two chips is feo 5 units which is equivalent to a value for an immature lunar soil the total concentration of metallic iron is on the order of 0 11 equivalent wt which is within the observed range for apollo 16 rocks and soils

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

exposure histories of lunar meteorites alha81005 mac88104 mac88105 and y791197 the cosmogenic radionuclides sup 41 ca sup 36 cl sup 26 al and sup 10 be in the allan hills 81005 macalpine hills 88104 macalpine hills 88105 and yamato 791197 meteorites were measured by accelerator mass spectrometry ams sup 53 mn in allan hills 81005 and yamato 791197 was measured by activation these four lunar meteorites experienced similar histories they were ejected from near the surface of the moon ranging in depth down to 400 g cm sup 2 and had very short transition times less than 0 1 ma from the moon to the earth a comparison of the cosmogenic nuclide concentrations in macalpine hills 88104 and macalpine hills 88105 clearly indicates that they are a pair from the same fall

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

mac88105 a regolith breccia from the lunar highlands mineralogical petrological and geochemical studies abstract the new large lunar meteorite mac88105 is a dense breccia with lithic and mineral clasts and fragments set into a welded matrix it is a regolith breccia which shows some recrystallization and evidence for a late shock event during which anorthositic glass veins were formed shock effects most probably due to the impact ejection from the moon are present throughout the sample and require a shock pressure of about 25 30 gpa in agreement with observations made on other lunar meteorites some components of mac88105 have been subjected to a shock pressure of about 40 45 gpa as evident from melt pockets in a clast the population of lithic clasts in mac88105 is similar to other lunar highland breccias vitric breccias are more abundant than granulitic breccias and plutonic rock fragments the presence of devitrified glass spheres and shards supports a regolith origin most common are metameltbreccias consisting of abundant anorthitic plagioclase clasts and a dense fine grained matrix some fine grained hornfelsic to granulitic metabreccias are also present lithic clast compositions are predominantly anorthositic noritic or noritic anorthositic and anorthositic troctolitic spinel bearing rocks are present but do not belong to the spinel troctolite group a spinel bearing clast in mac88105 consists of anorthite pigeonite spinel and indicates a different heritage possibly similar to spinel cataclasites described from apollo 17 the pyroxenes in mac88105 have somewhat unusual compositions orthopyroxenes and augites appear to be rare most lithologies breccias and igneous rocks contain solely pigeonite we have found one igneous mafic rock a gabbro which has a low mg number and is possibly of mare origin a metal grain of a composition similar to metal in h chondrites supports the interpretation of mac88105 as a regolith breccia the bulk composition of mac88105 is similar to the other lunar highland meteorites the ree contents are slightly higher than for the other anorthositic meteorites with a smaller positive eu anomaly this is in agreement with a possible kreep contribution possibly introduced from glasses macs 8105 is a mixture of rocks with a predominant contribution from the anorthosite suite and small admixtures from other rock types mare basalt mg suite which becomes obvious in plots of molar mg or sm content vs the ti sm ratio the siderophile element abundances in mac88105 are similar to other highland meteorites and show the characteristic co excess and a au ir ratio similar to the other anorthositic meteorites and lower than the hyperchondritic ratio in apollo 16 rocks thus support the notion that the lunar meteorites are a more representative sample of the lunar highlands than the apollo samples the chemistry and mineralogy of mac88105 is different from that of the other lunar meteorites and suggests a different source which is supported by cosmic ray and noble gas data at this time it seems likely that about four individual impact events have been responsible for delivering the seven highland meteorites mac88105 and other lunar meteorites are important as they are probably random samples from the lunar surface and may thus be more representative than the apollo and luna rocks which come from only a small area of the moon

geochemical studies of feldspathic fragmental breccias and the nature of north ray crater ejecta major and trace element analyses of clasts and matrix from feldspathic fragmental breccias show that these breccias are not all alike but vary widely in their bulk compositions and clast assemblages these studies together with analyses of other north ray crater large rocks reveal the major components to be anorthosites ferroan anorthositic norites magnesian granulites feldspathic melt rocks and vha impact melts the ferroan anorthositic norites are important lunar crustal rocks identified here for the first time the kreepy vha melts are found to be much more important in north ray crater ejecta than was previously assumed sodic ferrogabbro is an important minor component the compositional characteristics of bulk breccias and feldspathic melt rocks are modeled quantitatively as mixtures of two to five components anorthosites ferroan anorthositic norites magnesian granulites sodic ferrogabbros and vha melt rocks breccia 67455 is unique in consisting wholly of ferroan kreep free components

dynamic recrystallization and texture development in ice as revealed by the study of deep ice cores in antarctica and greenland the preferred c axis orientation of ice from polar ice sheets develops essentially as a result of intracrystalline slip but dynamic recrystallization appears to alter the kinetics of the development of deformation textures and is at high temperature at the origin of recrystallization textures the purpose of this work is to obtain a better understanding of recrystallization processes that occur in polar ice sheets and to clarify the relationship between dynamic recrystallization and textures the study was based on two deep ice cores from greenland and antarctica the greenland ice core project grip and vostok ice cores the structure along the grip core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and migration recrystallization near the bottom only grain growth and rotation recrystallization appear to occur in the vostok ice core the transition between these recrystallization regimes was studied estimating for interglacial ice the evolution with depth of the dislocation density this calculation has shown the efficiency of grain boundary migration for the absorption of dislocations at vostok the highest value of the dislocation density is found at a depth of about 1000 m and the continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate it is shown that the driving force required to initiate migration recrystallization is not reached in interglacial ice at vostok the observed textures were compared with those predicted by the self consistent approach recrystallization textures are interpreted by assuming that the less stressed grains i e the best oriented for basal slip are favored by the size advantage of subgrains the recrystallization textures are compared with those of other materials

petrology and geochemistry of lunar dimict breccia 61015 dimict breccia 61015 consists dominantly of granulated anorthosite and impact melt rock of vha very high alumina basalt composition the anorthosite is a typical apollo 16 ferroan anorthosite except that it is slightly more augite rich than most other ferroan anorthosites the breccia probably formed in the floor of an expanding crater cavity by the following process impact melt generated within the cavity was injected into underlying anorthositic bedrock and solidified rapidly and the anorthosite and melt rock were then fragmented by deformation in the later stages of the impact all the apollo 16 dimict breccias except perhaps 61016 appear to have formed in the same impact the source crater cannot yet be identified but it may be an intermediate sized 50 150 km diameter crater within a few hundred kilometers of the apollo 16 site in the direction of the imbrium basin of either pre nectarian or post nectarian pre imbrian age the breccia has been affected by at least one and perhaps as many as four recent small impacts the most recent was probably the south ray impact the recent impact s produced internal shock induced melting of the breccia and injected and coated the rock with externally derived impact melts the coating glass is heterogeneous its average composition is similar to the compositions of other apollo 16 coating glasses except that its tio2 content is lower the vein glass is unusually mafic and has very low tio2 for its al2o3 content the tio2 contents of these glasses establish that they cannot be melted soils their compositions require a mafic low tio2 protolith component that has not yet been identified among the large rock samples perhaps a very mafic member of the ferroan anorthosite suite

microstructure mapping a new method for imaging deformation induced microstructural features of ice on the grain scale this work presents a method of mapping deformation related sublimation patterns formed on the surface of ice specimens at microscopic resolution 3 4 mm pixel 1 the method is based on the systematic sublimation of a microtomed piece of ice prepared either as a thick or a thin section the mapping system consists of an optical microscope a ccd video camera and a computer controlled xy stage about 1500 images are needed to build a high resolution mosaic map of a 4 5 9 cm section mosaics and single images are used to derive a variety of statistical data about air inclusions air bubbles and air clathrate hydrates texture grain size shape and orientation and deformation related features subgrain boundaries slip bands subgrain islands and loops pinned and bulged grain boundaries the most common sublimation patterns are described and their relevance for the deformation of polar ice is briefly discussed

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

exposure histories of the lunar meteorites mac88104 mac88105 y791197 and y86032 four lunar meteorites macalpine hills mac 88104 macalpine hills 88105 yamato y 791197 and yamato 86032 were analyzed for the cosmogenic radionuclides 10be 26al 36cl and 41ca from these and published data histories of exposure to cosmic rays were modelled in terms of two stage irradiations each with a long first stage on the moon lasting a time t2 5 ma at a burial depth d2 gcm2 followed by a second stage in space i e the transit time between the moon and the earth lasting a time t4 ma in a body of typical meteoroidal size the terrestrial age tt ma gives the time elapsed between meteorite fall and recovery in antarctica the following sets of parameters were obtained mac88104 5 390 d2 500 0 04 t4 0 11 0 10 tt 0 19 y791197 d2 1000 t4 10 2 0 08 tt 0 12 from the number and exposure histories of lunar meteorites we infer a production rate on the order of 5 ma 1 and an arrival rate worldwide of about 3 106 meteorites ma 1 these results suggest that each impact event large enough to produce lunar meteorites sends a large number of them to the earth

a potpourri of regolith breccias new samples from the apollo 14 16 and 17 landing sites forty suspected regolith breccias from the apollo 14 16 and 17 landing sites were studied as part of a search for regolith samples exotic to the small traverse areas associated with these missions as well as a general effort to constrain the nature and origins of regolith breccias of these 40 samples 31 are indeed regolith breccias regolith breccias from apollo 14 exhibit much greater compositional diversity than their soil sensu stricto counterparts 14004 55 displays incompatible element concentrations about 1 4 those found in typical apollo 14 regolith while 14315 is radically different in many respects higher al lower mg and fe lower incompatible elements from all other apollo 14 regolith materials and hence probably exotic to the apollo 14 traverse area application of mixing models to apollo 14 regolith materials suggests that whereas normal apollo 14 regolith contains only slightly more ferroan anorthosite fa than alkali anorthosite aa and far more kreep than fa and aa combined 14315 contains more fa than kreep and roughly 10 times more fa than aa three new regolith breccias from apollo 16 bring to 20 the total number of regolith breccias that have been analyzed for mg and fe from the site the molar mg mg fe or mg ratios of lunar regolith breccias are of great interest because lunar meteorite alha81005 has a much higher mg than two other lunar meteoritic regolith breccias y791197 and y82192 3 even though these three samples are remarkably similar in all other compositional respects a bimodality in mg among apollo 16 regolith breccias may result from 1 statistical scattering among the small number of samples 2 a tendency for older regolith breccias from this site to be compositionally distinct from their younger counterparts or 3 differences between the cayley and descartes formations among 10 samples from apollo 17 all but one proved to be typical apollo 17 regolith breccias however 72504 10 is 99 pure pyroclastic glass compositionally identical to the apollo 17 orange glass 74220 even though 72504 10 was obtained at a location over 4 km from shorty crater where 74220 was obtained the nearly pure concentration of 74220 identical glass spherules in 72504 10 attests to the widespread distribution of these distinctive deposits

a gravel diamicton lag on the south albertan prairies canada evidence of bed armoring in early deglacial sheet flood spillway courses a clast supported massive diamicton to poorly sorted massive gravel gm dcm bed in the area around dinosaur provincial park southern alberta canada provides a means of identifying early deglacial flood courses this is especially useful where flood and spillway courses have very subtle geomorphic definition and are difficult to map from aerial photographs the gm dcm bed conformably overlies a brown late wisconsinan till and rarely overlies bedrock and lacustrine sediments the geographic distribution of the bed is restricted to flat to gently undulating prairie on either side of the red deer river where shallow floods and spillway melt waters were concentrated upon deglaciation the bed has also been observed along the banks of the south saskatchewan river at medicine hat 90 km to the south and is therefore regionally extensive because the gm dcm bed has none of the attributes of supraglacial sediment and possesses a clast fabric and sphericity very similar to those of underlying till it is interpreted as a winnowed gravel diamicton lag which was produced by low competence melt water floods along shallow depressions in the prairie surface after the drainage of local proglacial lakes after enough of the fine grained matrix of the late wisconsinan till was removed to create a lag

the macalpine hills lunar meteorite and implications of the lunar meteorites collectively for the composition and origin of the moon the mac88104 mac88105 meteorite is a lunar highlands regolith breccia even more anorthositic than previously available samples of highlands regolith clasts studied include two unusual pristine rocks one a 2 5 mm slightly granulitic clast rated as probably pristine contains extraordinarily fe rich fo40 olivine the other a 5 mm clast with clear vestiges of a poikilitic cumulate texture has silicate compositions that extend the range of the mg suite in the direction of the high mg end of the ferroan anorthositic suite the pyroxene of the latter clast is relatively ca rich and poorly equilibrated by lunar cumulate standards suggesting that it may have formed in an uncommonly shallow intrusion the four lunar highlands meteorites are all regolith breccias or in one case a marginal type between regolith breccia and ordinary polymict breccia and they probably represent three to four separate lunar source craters the proportion of regolith breccias is higher among lunar highlands meteorites than among rock samples from the classic highlands site apollo 16 9 regolith breccias for the majorelement composition of the crust the highlands meteorites confirm that the two low th central nearside sites luna 20 and especially apollo 16 are approximately representative the consistently high al2o3 composition indicated for the upper crust supports the magmasphere hypothesis for the trace element composition of the crust the highlands meteorites indicate that the central nearside apollo and luna sites are in several respects grossly unrepresentative concentrations of siderophile elements are far lower in highlands meteoritic regolith breccias than in their central nearside counterparts the high overall siderophile levels and hyperchondritic niir and auir ratios characteristic of highlands materials from apollo 16 and apollo 14 are evidently idiosyncracies of the central nearside concentrations of incompatible elements including k th and u are far lower in the highlands meteorites than in regolith samples from the central nearside this trend implies that certain lower limits on the bulk moon content of u and associated refractory lithophile elements should be relaxed models of lunar origin implying large enrichments of refractory lithophile elements are not favored by the new constraints from these meteorites

depth and time dependent vertical strain rates at siple dome antarctica as part of a project to investigate the flow of ice at low effective stress two independent strain gauge systems were used to measure vertical strain rate as a function of depth and time at siple dome antarctica the measurements were made from january 1998 until january 2002 at the ice divide and a site 7 km to the northeast on the flank the strain rate profiles place constraints on the rheology of ice at low stress show the expected differences between divide and flank flow with some structure due to firn compaction and probably ice stratigraphy and suggest that the flow of the ice sheet has not changed much in the last 8 6 kyr the strain rates show an unexpected time dependence on scales ranging from several months to hours including discrete summer events at the divide time dependence in strain rate water pressure seismicity velocity and possibly basal motion has been seen previously on the siple coast ice streams but it is especially surprising on siple dome because the bed is cold

subgrain boundaries and related microstructural features in edml antarctica deep ice core subgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization statistical data obtained from the epica dronning maud land edml deep ice core drilled in east antarctica cannot detect a depth region of increased subgrain boundary formation grain boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths the data do not support the classical view of a change of dominating recrystallization regimes with depth three major types of subgrain boundaries reflecting high mechanical anisotropy are specified in combination with crystal orientation analysis

antarctic meteorite alha 81005 a piece from the ancient lunar crust a 128 mg sample of the antarctic meteorite alha 81005 was analysed for major and trace elements by instrumental neutron activation techniques the meteorite or at least its major components may be older than 4 billion years and represent a piece of the ancient lunar crust before the formation of the large basins on the front side of the moon the evidence is derived from the low absolute content of incompatible elements and their slightly different fractionation pattern from kreep the dominant source for these elements on the front side the basically chondritic pattern of siderophile elements ni co ir au is clearly distinguished from younger basin related meteoritic components