mineralogy petrology and trace element geochemistry of the johnstown meteorite a brecciated orthopyroxenite with siderophile and ree rich components the johnstown meteorite is a brecciated orthopyroxenite diogenite containing coarsegrained centimeter sized clasts of cumulate origin that have undergone subsolidus recrystallization the brecciated portion is dominated by subangular fragments of orthopyroxene wo2 3en72 74fs23 25 in a variably comminuted matrix of the same material minor and accessory phases include plagioclase an82 90ab10 18or0 1 diopside wo44 45en46 47fs9 10 olivine fo71 72 tridymite troilite metallic ni fe 3 ni and chromite cm71 80hc1 8sp11 19mt2 4uv1 3 the clastic component is parental to the brecciated matrix which contains no foreign lithic or mineralogic components siderophile trace element studies however reveal the presence of meteoritic chondritic contamination in the brecciated portion using unbrecciated clasts for indigenous values rare earth element abundances show a wide range of values for the light ree in different samples although all samples exhibit a strong negative eu anomaly indicative of earlier plagioclase fractionation two pairs of adjacent brecciated and unbrecciated samples from different portions of the meteorite show respectively the most enriched and the most depleted light ree patterns the variability in la content is over a factor of 100 however in each case the ree pattern for the brecciated portion is very similar to that of the unbrecciated portion these differences are attributed to sampling of variable amounts of residual ree enriched trapped liquid the most representative ree pattern for the bulk meteorite has an intermediate composition and was obtained from the largest sample the data presented here indicate that johnstown is a monomict breccia in contrast to several other diogenites which may be considered to be polymict on the basis of their mineral compositions and or clast populations

well to seismic tie method in complex imaging areas examples in the deep offshore subsalt angola domain recently imaging capabilities have allowed a major step forward in subsalt exploration in particular new psdm algorithms have appeared on the market that account for complex wave propagation through salt canopies to produce better images these improvements have allowed the drilling of numerous subsalt exploration wells but at the time of appraisal and development questions arise on the reliability of these seismic cubes to accurately predict geometries this issue is crucial in the offshore deepwater blocks of angola where reflectors often have high dips and subsalt seismic visibility is not optimal furthermore velocity models used for subsalt imaging are seldom as accurate as one could want and significant discrepancies can often be observed between seismic and well depth of geological markers these discrepancies can have several origins such as neglecting to account for anisotropy as discussed by shumaker et al 2007 the lack of accuracy of velocity models can also be due to the limitati

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

igneous lithologies on asteroid 4 vesta mapped using gamma ray and neutron data abstract we use data collected by the dawn gamma ray and neutron detector grand at vesta to map compositions corresponding to nearly pure igneous lithologies in the howardite eucrite diogenite hed meteorite clan samples likely from vesta at the 300 km spatial scale of grand measurements basaltic eucrite occurs on only 3 of the surface whereas cumulate eucrite and orthopyroxenitic diogenite are not detected the basaltic eucrite region is generally coincident with an area of the surface with thick regolith elevated h and moderate crater density and may represent the best compositional sample of primordial vestan crust we observe an absence of pure orthopyroxenitic diogenite terrains in the rheasilvia basin and its ejecta an observation corroborated by vir 0 1 which suggests the south polar crust was a polymict mixture of igneous lithologies howardite at the time of the rheasilvia impact or was a thick basaltic eucrite crust with heterogeneously distributed orthopyroxenitic diogenite plutons the most dominant igneous composition detected 11 of the surface corresponds to one of the least abundant igneous lithologies in the hed meteorite collection the yamato type b diogenites plagioclase bearing pyroxenites the distribution of type b diogenite is spatially correlated with post rheasilvia craters in the north polar region that are in close proximity to the rheasilvia basin antipode this suggests that north polar type b plutonism may have been associated with the rheasilvia impact event we propose that this was either through 1 uplift of pre existing plutons at the antipode through focusing of rheasilvia impact stress or 2 rheasilvia impact antipodal crustal melting creating magmas that underwent fractionation to produce type b plutons

mineralogical records of early planetary processes on the howardite eucrite diogenite parent body with reference to vesta abstract mineralogical information recovered from the howardite eucrite diogenite hed meteorites was employed to reconstruct the history of the parent body and relate it to 4 vesta these interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto planet 4 vesta the original crustal materials of the hed parent body were preserved as mineral grains and lithic clasts but in many eucrites fe mg ratios in pyroxenes were homogenized by diffusion after crystallization the crystallization trend of the protocrust has been deciphered by 1 examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends and by 2 reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites mineral components are identical both in the individual hed and in polymict breccias and no remnants of primitive materials were preserved in the polymict breccias a layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava like eucrites that have been brecciated and metamorphosed diogenite mantle and cumulate eucrites of varying thickness between them this model can be used to explain the surface geological features of vesta observed from the hubble space telescope a large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model the old terrain of eucritic surface materials of vesta can be howardites polymict eucrites or regolith like eucrites produced from eucrites extruded and impacted on the surface partial melting models of eucrites seem to be favored by the rare earth element ree chemistry and experimental studies unfortunately partial melting models have not demonstrated how the hed parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust the origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid discovery of basaltic materials with na rich plagioclase and augite in iron meteorites which are the products of partial melting suggests that eucrites may be unique to a body that underwent large scale differentiation and metamorphism

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

low gradient outlet glaciers ice streams drained the laurentide ice sheet observations of geomorphic features dated with cosmogenic nuclides are used to determine the configuration of glaciation in cumberland sound baffin island during the last glacial maximum cumberland sound which was a major drainage of the laurentide ice sheet at its northeastern arctic canada margin contained low gradient ice with a surface slope of 0 038 and a driving stress between 2 and 7 kpa these values are similar to those observed for the ice streams that dominate the dynamics of the west antarctic ice sheet today the presence of low gradient ice in cumberland sound and other major outlets may similarly have influenced laurentide ice sheet behavior and would account for the iceberg discharge episodes that produced the heinrich event debris layers observed in north atlantic ocean sediments

holocene delevelling of devon island arctic canada implications for ice sheet geometry and crustal response the raised beaches and deltas of devon island contain an abundance of dateable materials a large set of radiocarbon dates 228 154 of which are new are used to construct relative sea level curves and isobase maps for the island the best materials for this purpose are driftwood logs 61 dates and bowhead whale bones 74 dates from raised beaches and mollusc shells from marine limit deltas 20 dates or from altitudes close to marine limit 14 dates during the last glacial maximum the island is thought to have lain beneath the southeastern flank of the innuitian ice sheet the relative sea level history is congruent with that inferred ice configuration the island spans half the ice sheet width relative sea level curves are of simple exponential form except near the glacial limit where an early holocene emergence proceeded to a middle holocene lowstand below present sea level which was followed by submergence attending the passage of the crustal forebulge the response times of relative sea lev

glacier expansion on baffin island during early holocene cold reversals abstract the north atlantic was a key locus for circulation driven abrupt climate change in the past and could play a similar role in the future abrupt cold reversals including the 8 2 ka event punctuated the otherwise warm early holocene in the north atlantic region and serve as useful paleo examples of rapid climate change in this work we assess the cryospheric response to early holocene climate history on baffin island arctic canada using cosmogenic radionuclide dating of moraines we present 39 new 10be ages from four sets of multi crested early holocene moraines deposited by cirque glaciers and ice cap outlet glaciers as well as erratic boulders along adjacent fiords to constrain the timing of regional deglaciation the age of one moraine is additionally constrained by in situ 14c measurements which confirm 10be inheritance in some samples all four moraines were deposited between 9 2 and 8 0 ka and their average ages coincide with abrupt coolings at 9 3 and 8 2 ka that are recorded in greenland ice cores freshwater delivery to the north atlantic that reduced the flux of warm atlantic water into baffin bay may explain brief intervals of glacier advance although moraine formation cannot be definitively tied to centennial scale cold reversals we thus explore other possible contributing factors including ice dynamics related to retreat of laurentide ice sheet outlet glaciers using a numerical glacier model we show that the debuttressing effect of trunk valley deglaciation may have contributed to these moraine building events these new age constraints and process insights highlight the complex behavior of the cryosphere during regional deglaciation and suggest that multiple abrupt cold reversals as well as deglacial ice dynamics likely played a role in early holocene moraine formation on baffin island

composition and origin of nuevo laredo trend eucrites new bulk rock analyses are reported for the eucritic meteorites alha81001 lakangaon and nuevo laredo alha81001 resembles ibitira as both have far lower concentrations of na than any other eucrite lakangaon and nuevo laredo are the two most ferroan low mgfe of all eucrites monomict eucrites have previously been divided into three geochemical classes a main group and the nuevo laredo and stannern trends the nuevo laredo trend which is characterized by limited variations of incompatible element contents despite considerable variations in mg mg fe ratio and v content clearly formed out of melt s undergoing fractional crystallization probably as partial cumulates the less distinctive main group eucrites are often assumed to be primary basalts geochemically but one step equilibrium partial melting removed from the bulk composition of the eucrite parent asteroid this partial melting model seems more appropriate for the stannern trend which is characterized by moderate high mg mg fe despite moderate high incompatible element contents our new data and a review of literature data suggest that most of the so called main group eucrites actually belong to the nuevo laredo trend while few if any belong to the stannern trend or any other partial melting trend the nuevo laredo trend may be part of a series of fractional crystallization products that began with orthopyroxenite cumulates diogenites the bulk mgo mgo feo ratio of the eucrite parent asteroid is generally estimated at 0 67 by assuming that typical eucrites are primary basalts but if typical eucrites are diogenite comagmatic fractional crystallization products the bulk mgo mgo feo of the parent asteroid must be considerably higher probably about 0 81

numerical modelling of the laurentide ice sheet in the baffin island region the role of a cumberland sound ice stream a numerical model reconstruction was made of the northeastern laurentide ice sheet in the baffin island foxe basin region using geophysical terrestrial and marine geologic evidence for initial

a new fully integrated method for seismic geohazard prediction ahead of the bit while drilling geohazards have a direct impact on the drilling and completion of wells they present safety risks and are costly they can be caused by formation properties such as overpressure and can be associated with geological structures such as faults and salt bodies critical to drilling success seismic data provide information used to construct an earth model consisting of 3d structural depth images showing geological targets or hazards and formation properties relevant to drilling such as pore pressure however predrill estimates of structural depth images and formation pressures typically have large uncertainties which elevate safety concerns and drilling risks and could increase the cost of wells this risk is especially problematic in challenging environments such as deep water where rig rates are high and continue to increase

mineralogy of yamato 791073 with reference to crystal fractionation of the howardite parent body shock textures and mineral chemistry indicate that yamato 791073 is a type of meteorite intermediate between diogenite and cumulate eucrite and is similar to the yamato 75032 type achondrites the presence of vesicles in shock melt glass and swirly glasses of plagioclase composition as in the suevite in the matrix indicates that it is the most intensely shocked sample among this group of achondrites pyroxene compositions in y791073 fall in a limited range from mg mg fe 0 7 to 0 6 and are compatible with the continuum of rock types produced presumably by differentiation on the howardite parent body the chemical variation of pyroxene is wider than that of the monomict y75032 group in addition to fe rich diogenite like pyroxene ca2mg66fe31 common in y75032 y791073 contains clasts of pyroxene texturally like those in moore county the plagioclase glass with an89 may originally have been associated with this pyroxene as a cumulate eucrite such clasts are uncommon in the y75032 type achondrites y791073 also contains a very differentiated si and k rich clast y791073 shows a more polymict nature than other y75032 type achondrites but the lithic variation more limited than normal howardites suggests that it sampled two or three layers of the layered crust or pluton produced by the crystal fractionation

comparisons of antarctic and non antarctic achondrites and possible origin of the differences abstract in order to discuss differences between antarctic and non antarctic achondrites we investigated pairing of mainly the yamato achondrites by mineralogical techniques in addition to five paired specimens of the y74159 type polymict eucrites three new groups distinct from the y74159 type have been recognized one group y791960 of howarditic polymict eucrites is similar to those of non antarctic origin some antarctic monomict eucrites differ in texture and chemistry from the non antarctic specimens more than 50 diogenite specimens recovered from the yamato bare ice field can be grouped into two falls of separate locations compared with 8 from the usa collection and 9 from the non antarctic groups thirty antarctic ureilites are separate falls 2 pairings and their individual masses are small these observations suggest that discussion of differences between the antarctic and non antarctic achondrites largely depends on detection of pairings of the antarctic specimens the pairings of the specimens from victoria land have not been as well characterized as those of the yamato mountains comparisons with non antarctic meteorites show that the antarctic heds and ureilites differ from non antarctic specimens by the following criteria 1 1 polymict eucrites excluding those with howarditic affinity have not been found in the non antarctic collections 2 2 magnesian ureilites and augite bearing ureilites were found only in antarctica the differences may not be attributed to just one factor the above evidence of two unique diogenite falls preserved on the restricted ice fields suggests that the yamato diogenites may represent falls on restricted areas in the distant past the discovery of many small unique eucrites and ureilites suggests that within the large number of small specimens on a bare ice field there is a higher chance of finding unique varieties

deglaciation of the greenland and laurentide ice sheets interrupted by glacier advance during abrupt coolings abstract understanding patterns of ice sheet deglaciation is key for predicting the rate of future ice sheet melt yet the processes underlying deglaciation remain elusive the early holocene 11 7 ka to 8 2 ka greenlandian stage represents the most recent period when the laurentide and greenland ice sheets underwent large scale recession moreover this ice sheet recession occurred under the backdrop of regional temperatures that were similar to or warmer than today and comparable to those projected for the upcoming centuries reconstructing laurentide and greenland ice sheet behavior during the early holocene and elucidating the mechanisms dictating this behavior may serve as a partial analog for future greenland ice sheet change in a warming world here we present 123 new 10be surface exposure ages from two sites on baffin island and southwestern greenland that constrain the behavior of the laurentide and greenland ice sheets and an independent alpine glacier during the early holocene on baffin island we focus on a unique area where moraines deposited by the laurentide ice sheet rest directly adjacent to moraines deposited by an independent alpine glacier sixty one 10be ages reveal that advances and or stillstands of the laurentide ice sheet and an alpine glacier occurred in unison around 11 8 ka 10 3 ka and 9 2 ka sixty two 10be ages from southwestern greenland indicate that the greenland ice sheet margin experienced re advances or stillstands around 11 6 ka 10 4 ka 9 1 ka 8 1 ka and 7 3 ka our results reveal that ice sheets respond to climate perturbations on the same centennial timescale as small alpine glaciers we hypothesize that during the warming climate of the early holocene freshening of the north atlantic ocean induced by ice sheet melt resulted in regional cooling and brief periods of ice sheet stabilization superimposed on net glacier recession these observations point to a negative feedback mechanism inherent to melting ice sheets in the baffin bay region that slows ice sheet recession during intervals of otherwise rapid deglaciation

geochemical relationships between anorthosite and associated iron rich rocks laramie range wyoming rocks enriched in iron oxide and mafic silicates are commonly present as minor volumes of proterozoic anorthosite complexes in the laramie range wyoming anorthositic rocks gabbros and iron oxide ore have been chemically analyzed to determine if the spatial association is a result of genetic relationships between the rock types variations in abundances of ree th sc and sr in whole rock and in mineral separates from anorthositic rocks provide evidence for the presence of trapped intercumulus liquid initial 87sr 86sr ratios in apatites separated from iron oxide ore 0 70535 0 00004 are analogous to initial 87sr 86sr ratios in laramie range anorthosite 0 70531 and 0 70537 in addition ree abundances in calculated parental liquids for both anorthositic rocks and iron ore are similar providing further evidence for a comagmatic relationship trace element and textural characteristics of spatially associated laramie range gabbros indicate that they are not mixtures of the trapped liquid and cumulus components which formed anorthositic rocks it is suggested that gabbros are early differentiation products of a high al gabbroic magma which subsequently crystallized large volumes of plagioclase to produce the anorthosite massif

10be measurements in bedrock constrain erosion beneath the greenland ice sheet margin glacial erosion is a key process driving landscape evolution but it remains unclear what factors dictate the rate and which subglacial erosion occurs and moreover measurements of subglacial erosion that do not rely on sediment flux measurements are rare here we present in situ 10be measurements from bedrock surfaces in western greenland with well constrained ice cover histories to quantify the erosion rate beneath the greenland ice sheet margin during historical times we calculate an abrasion rate of 0 72 0 35 mm yr 1 and a likely total basin wide erosion rate abrasion quarrying of 1 1 8 mm yr 1 which are at least 1 order of magnitude higher than typical subglacial erosion rates in other polar landscapes a compilation of published 10be data suggest that the southwestern greenland ice sheet acts as a particularly effective erosional agent within the broader baffin bay greenland region over millennial to glacial interglacial timescales suggestive of a basal ice sheet thermal regime controlled by regional climate

the polymict eucrites elephant moraine a79004 and a79011 and the regolith history of a basaltic achondrite parent body the achondrites elephant moraine a79004 and a79011 are closely related polymicteucrites of a type previously unrecognized in antarctica they contain an early metamorphically homogenized breccia containing clasts of great textural diversity very similar to those in howardites and a late injected mafic clast component that contains a suite of basalts that may in part be the result of impact melting rather than internal igneous processes the basaltic achondrite parent body bap of which they are regolith samples had a complex igneous history of 1 early igneous activity 2 brecciation to form polymict breccias 3 localized metamorphism resulting in partial homogenization of areas of the regolith 4 late igneous activity resulting from internal igneous or impact melting processes and 5 further brecciation and mixing of late formed mafic rocks with early breccias

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

grosvenor mountains 95 howardite pairing group insights into the surface regolith of asteroid 4 vesta regolithic howardites are analogs for the surface materials of asteroid 4 vesta recently mapped by the dawn spacecraft rigorously evaluating pairing of howardites recovered in 1995 in the grosvenor mountains gro 95 antarctica enables an examination of a larger more representative regolith sample previous work on two of the howardites studied here concluded that gro 95602 and gro 95535 are solar wind rich surface regolith samples and that they are not paired with each other leading to uncertainty regarding pairing relationships between the other gro 95 howardites based on petrology cosmic ray exposure history and terrestrial age four gro 95 howardites are paired the paired howardites gro 95534 95535 95574 95581 were from a meteoroid with radius of 10 15 cm a preatmospheric size comparable to that of kapoeta the largest known regolithic howardite the paired gro 95 howardites contain clasts of at least 18 separate hed lithologies providing evidence they were assembled from diverse source materials the total eucrite diogenite mixing ratio ratio of all eucrite lithologies to all diogenite lithologies in the paired gro 95 howardites is 2 1 petrographically determined basaltic eucrite cumulate eucrite ratios in regolithic howardites studied here and previously vary more widely than total eucrite diogenite ratios relative to eucritic pyroxene plagioclase is depleted in these howardites which provides evidence that plagioclase is preferentially comminuted in the vestan regolith the extent of plagioclase depletion could be an indicator of regolith maturity

multiphase inclusions in plagioclase from anorthosites in the stillwater complex montana implications for the origin of the anorthosites multiphase inclusions consisting of clinopyroxene ilmenite apatite occur within cumulus plagioclase grains from anorthosites in the stillwater complex montana and in other rocks from the middle banded series of the intrusion the textures and constant modal mineralogy of the inclusions indicate that they were incorporated in the plagioclase as liquid droplets that later crystallized rather than as solid aggregates their unusual assemblage including a distinctive manganiferous ilmenite and the presence of baddeleyite zro2 indicates formation from an unusual liquid a process involving silicater liquid immiscibility is proposed whereby small globules of a liquid enriched in mg fe ca ti p ree zr and mn exsolved from the main liquid that gave rise to the anorthosites became trapped in the plagioclase and later crystallized to form the inclusions the immiscibility could have occurred locally within compositional boundaries around crystallizing plagioclase grains or it could have occurred pervasively throughout the liquid it is proposed that the two immiscible liquids were analogous n terms of their melt structures to immiscible liquid pairs reported in the literature both in experiments and in natural basalts for the previously reported pairs immiscibility is between a highly polymerized liquid typically granitic in composition and a depolymerized liquid typically ferrobasaltic in composition in the case of the anorthosites the depolymerized liquid is represented by the inclusions and the other liquid was a highly polymerized aluminosilicate melt with a high normative plagioclase content from which the bulk of the anorthosites crystallized crystallization of the anorthosites from this highly polymerized liquid accounts for various distinctive textural and chemical features of the anorthosites compared to other rocks in the stillwater complex a lack of correlation between p contents and chondrite normalized rare earth element ree ratios of plagioclase separates indicates that the amount of apatite in the inclusions is too low to affect the ree signature of the plagioclase separates nevertheless workers should use caution when attempting ree modelling studies of cumulates having low ree contents because apatite bearing inclusions can potentially cause problems

improved moraine age interpretations through explicit matching of geomorphic process models to cosmogenic nuclide measurements from single landforms abstract the statistical distributions of cosmogenic nuclide measurements from moraine boulders contain previously unused information on moraine ages and they help determine whether moraine degradation or inheritance is more important on individual moraines here we present a method for extracting this information by fitting geomorphic process models to observed exposure ages from single moraines we also apply this method to 94 10 be apparent exposure ages from 11 moraines reported in four published studies our models represent 10 be accumulation in boulders that are exhumed over time by slope processes moraine degradation and the delivery of boulders with preexisting 10 be inventories to moraines inheritance for now we neglect boulder erosion and snow cover which are likely second order processes given a highly scattered data set we establish which model yields the better fit to the data and estimate the age of the moraine from the better model fit the process represented by the better fitting model is probably responsible for most of the scatter among the apparent ages our methods should help resolve controversies in exposure dating we reexamine the conclusions from two published studies based on our model fits

geochemistry and oxygen isotope composition of main group pallasites and olivine rich clasts in mesosiderites implications for the great dunite shortage and hed mesosiderite connection evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in solar system history these bodies should have had welldeveloped olivine rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites which they are not to investigate this great dunite shortage we have undertaken a geochemical and oxygen isotope study of main group pallasites and dunitic rocks from mesosiderites oxygen isotope analysis of 24 main group pallasites 103 replicates yielded a mean 17o value of 0 187 0 016 2 which is fully resolved from the hed 17o value of 0 246 0 014 2 obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies our results show no evidence for 17o bimodality within the main group pallasites as suggested by a number of previous studies olivine rich materials from the vaca muerta mount padbury and lamont mesosiderites and from two related dunites nwa 2968 and nwa 3329 have 17o values within error of the mesosiderite average this indicates that these olivine rich materials are co genetic with other mesosiderite clasts and are not fragments from an isotopically distinct pallasite like impactor despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to 17o a feature best explained by an early phase of large scale melting magma ocean followed by prolonged igneous differentiation based on the results of magma ocean modeling studies we infer that mg rich olivines in mesosiderites formed as cumulates in high level chambers and do not represent samples of the underlying mantle by analogy recently documented mg rich olivines in howardites may have a similar origin although the dawn mission did not detect mesosiderite like material on vesta evidence linking the mesosiderites and heds includes i their nearly identical oxygen isotope compositions ii the presence in both of coarse grained mg rich olivines iii both have synchronous lu hf and mn cr ages iv there are compositional similarities between the metal in both and v mesosiderite like material has been identified in a howardite breccia the source of the mesosiderites remains an outstanding question in meteorite science the underrepresentation of olivine rich materials amongst both asteroids and meteorites results from a range of factors however evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early catastrophic destruction of planetesimals in the terrestrial planet forming region and the subsequent preferential loss of their olivine rich mantles

stillwater anorthosites a lunar analog samples of anorthosite from stillwater complex units an i and an ii terminology of mccallum et al 1980 were analyzed by instrumental neutron activation analysis inaa for feo cao na2o ree and other trace elements no compositional trend with stratigraphic position was observed mean concentrations for most elements are about the same for three traverses two for an ii but cao feo and sr concentrations are slightly different for the three traverses the elements are not normally or lognormally distributed among samples from a single traverse strong interelement correlations can be understood in terms of sample mineralogy little evidence for compositional evolution of minerals during precipitation of the entire middle banded zone is apparent as in lunar anorthosites the component of trapped residual liquid is relatively insignificant less than 5 in addition to plagioclase which makes up on average 90 of the anorthosites the rocks contain interstitial pyroxene augite and inverted pigeonite and in some cases quartz titano magnetite sulfides and rare apatite and allanite there is an inverse relationship between the amounts of pyroxene and quartz general compositional trends exemplified by la sc systematics indicate that the bulk of the poikilitic pyroxene appears to be cumulus adcumulus presumably formed at the crystallization front from a magma saturated in plagioclase and pyroxene a small fraction of the pyroxene and plagioclase plus all the quartz and other trace minerals formed from the minor trapped liquid component the irregular distribution of pyroxene oikocrysts indicates that interstitial melt migrated substantially prior to final consolidation of the rock

late glacial flow patterns deglaciation and postglacial emergence of south central baffin island and the north central coast of hudson strait eastern canadian arctic new georaorphic sedimentologic and chronologic data are used to reconstruct late quaternary ice sheet flow patterns deglaciation and isostatic uplift along the largest marine trough connecting the laurentide ice sheet with the north atlantic ocean the lake harbour region was targeted for study given its potential to record flow from several ice dispersal centers striations and sediment provenance indicators define flow patterns thirty four radiocarbon dates constrain a chronology of events centuries or millennia before deglaciation a southeast flowing ice stream impinged on southernmost big island as recorded by a single striation site and delimited in extent by geomorphic evidence of cold based ice during the cockburn substagc 9000 8000 bp the region was scoured by southward to southwestward flow from an ice cap on meta incognita peninsula as recorded by 60 striation sites along 200 km of coastline carbonate erratics are uncommon in till above the marine limit where present they sugg

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

petrogenesis of the labrieville alkalic anorthosite massif grenville province quebec the labrieville massif 1010 ma is an eroded dome consisting mineral plagioclase feldspar the circumstances whereby such nearly monomineralic plutons can be produced of three zones 1 a foliated inner core of pink anorthosite an30or13 2100 ppm sr 1300 ppm ba with minor have puzzled geologists for more than a century and massif anorthosites remain petrologic enigmas in adleuconorite 2 a foliated outer core of pink anorthosite an35or10 1900 ppm sr 850 ppm ba with more abundant leuconorite dition to this fundamental aspect of the anorthosite problem see bowen 1917 scoates 2000 the petro 3 a border of foliated to massive green leucogabbro antiperthitic plagioclase orthopyroxene hemoilmenite and small amounts of genesis of massif anorthosites was apparently restricted in time and space specifically virtually all of the world s biotite are present in all rocks the border zone contains additional clinopyroxene magnetite and apatite labrieville is more alkalic supply of massif anorthosite was formed during the proterozoic and much of it is found in the grenville and srand ba rich than almost all other massif anorthosites the widespread presence of biotite and the high hematite content of province of quebec and labrador kranck 1961 anderson 1969 ashwal 1993 hemoilmenite suggest crystallization from a relatively oxidizing and water bearing magma collectively these features imply that despite their similar plagioclase rich nature it is now apparent that massif anorthosites worldwide are minlabrieville originated from a magma that differed considerably from typical tholeiitic liquids majorand trace element variations suggest eralogically and compositionally diverse see xue that all rock types represent mixtures of cumulus minerals with morse 1993 implying involvement of a wide range of negligible trapped melt the compositionally distinct zones imply parental magma compositions or petrogenetic processes differentiation during crystallization although plagioclase comin their formation however comprehensive studies on positions become more evolved inward other indicators e g xmg individual anorthosite complexes that can elucidate their in pyroxene suggest differentiation outward from core to border we petrogenesis combining field and petrographic obfavor the latter interpretation and suggest that the increase in servations with mineral chemical data and with complete plagioclase an content reflects a decline in pressure during crysmajorand trace element data on a wide range of rock tallization types are few in number admittedly the immense size of certain massifs e g lac st jean complex woussen et al 1988 and the remote or inhospitable locations of

genesis of compositional characteristics of stillwater an i and an ii thick anorthosite units a single 10 m 10 m outcrop of stillwater anorthosite unit an ii was mapped for pyroxene mode on a decimeter scale and samples from each range of pyroxene proportion were analyzed for major and trace elements distinct one to several square meter regions of different pyroxene mode were observed samples from regions with 10 pyroxene showed strong elemental correlations and anticorrelations with mgo concentrations that can be interpreted in terms of the following scheme for development of the stillwater anorthosites aggregates containing 50 to 80 cumulus plagioclase average 67 formed stable frameworks in a crystal mush of complexly zoned plagioclase the interstices among the plagioclase grains in these frameworks filled in part with pyroxene and plagioclase that were produced in equilibrium with the bulk melt and in part with pyroxene and plagioclase derived by crystallization of trapped intercumulus liquid the proportions of these three types of materials were mutually constrained in a manner that gave rise to lines instead of fields on two element variation diagrams samples richest in cumulus plagioclase are also richest in intercumulus plagioclase and pyroxene regions of the outcrop with 10 original pyroxene underwent substantial alteration by hydrous fluids that produced variations in fe2o3 tio2 loi and most incompatible trace elements

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

the stillwater complex integrating zircon geochronological and geochemical constraints on the age emplacement history and crystallization of a large open system layered intrusion a reply to the comment by rais latypov on wall et al j petrology 59 153 190 2018

posteucritic magmatism on vesta evidence from the petrology and thermal history of diogenites we report on the petrology and the thermal histories of 13 diogenites in order to constrain the formation processes of the vestan crust we classify diogenites into unequilibrated and equilibrated diogenites in a scheme similar to that for basaltic eucrites pyroxenes in unequilibrated diogenites are chemically zoned indicating that they crystallized rapidly from melts and escaped from global crustal metamorphism the presence of unequilibrated diogenites casts doubt on the fact that all the diogenites formed at depth in the parent body as commonly thought some diogenites probably crystallized in shallow intrusions or were extruded on the surface these facts strengthen the geochemical evidence that diogenites and eucrites are not directly cogenetic and suggest that at least some diogenites have intruded the early formed eucritic crust thus diogenites are certainly not the products of the crystallization of the magma ocean that triggered the differentiation of vesta but are more likely cumulates associated with a later stage of magmatism furthermore the intrusion of diogenites could have significantly thickened the early formed crust making it difficult to excavate deep seated olivine mantle by moderate impact events

cogenetic rock fragments from a lunar soil evidence of a ferroan noritic anorthosite pluton on the moon abstract the impact that produced north ray crater apollo 16 landing site exhumed rocks that include relatively mafic members of the lunar ferroan anorthositic suite bulk and mineral compositions indicate that a majority of 2 4 mm lithic fragments from sample 67513 including impact breccias and monomict igneous rocks are related to a common noritic anorthosite precursor compositions and geochemical trends of these lithic fragments and of related samples collected along the rim of north ray crater suggest that these rocks derived from a single igneous body this body developed as an orthocumulate from a mixture of cumulus plagioclase and mafic intercumulus melt after the plagioclase had separated from any cogenetic mafic minerals and had become concentrated into a crystal mush 70 wt plagioclase 30 wt intercumulus melt we present a model for the crystallization of the igneous system wherein system is defined as cumulus plagioclase and intercumulus melt the initial accumulation of plagioclase is analogous to the formation of thick anorthosites of the terrestrial stillwater complex however a second stage of formation is indicated involving migration of the cumulus plagioclase intercumulus melt system to a higher crustal level analogous to the emplacement of terrestrial massif anorthosites compositional variations of the lithic fragments from sample 67513 are consistent with dominantly equilibrium crystallization of intercumulus melt the highly calcic nature of orthocumulus pyroxene and plagioclase suggests some reaction between the intercumulus melt and cumulus plagioclase perhaps facilitated by some recrystallization of cumulus plagioclase bulk compositions and mineral assemblages of individual rock fragments also require that most of the mafic minerals formed in close contact with cumulus plagioclase not as separate layers the distribution of compositions and by inference modes has a narrow peak at anorthosite and a broader larger peak at noritic anorthosite characteristics of the samples and their geochemical trends imply an origin in a system that was large relative to the unknown size of the impact that produced the brecccas of ferroan noritic anorthosite composition that were excavated later by the formation of north ray crater and they appear to be consistent with an origin of the suite within a perched plagioclase cumulate if the moon s crust formed by accumulation of plagioclase in a magma ocean ferroan noritic anorthosite formed as an orthocumulate is an alternative to extensive adcumulus formation of ferroan anorthosite 90 vol plagioclase this provides a relatively mafic ferroan anorthositic component 15 vol mafics which is required by mass balance models of compositions of polymict lunar crustal materials the inferred bulk composition of the system of cumulus plagioclase and intercumulus melt is similar to that of ferroan regolith breccia macalpine hills 88104 5 a lunar highland meteorite and may represent a common and widespread component of the moon s early highland crust

early holocene delevelling and deglaciation of the cumberland sound region baffin island arctic canada radiocarbon cosmogenic surface exposure and relative sea level data are used to examine deglaciation and glacioisostatic adjustment of cumberland sound and cumberland peninsula and southeastern baffin island in the context of a new model for the glacial history of the eastern canadian arctic over the last decade a multidisciplinary effort on easternmost baffin island has documented far greater ice expansion during the last glacial maximum than previously believed including low gradient glaciation in marine embayments coexisting with ice free or thin cold based ice on adjacent upland crystalline terrain this study documents that the cumberland sound region underwent about twice as much glacioisostatic movement during the last glacial maximum as shown in previous reconstructions however the loading impact of the laurentide ice sheet and local glaciation on adjacent cumberland peninsula was limited the mapped zero isoline on emergence shows that postglacial eustatic rise exceeded glacial isostatic uplift for much of the eastern peninsula a finding that is consistent with that of prior studies the center of loading and the major source of glacial ice for the entire cumberland sound region were foxe basin and western baffin island strandlines dated 10 500 and 8500 1 4 c yr b p show that slow deglaciation of cumberland sound was punctuated by at least two periods of faster grounding line retreat coastal southeastern cumberland peninsula was deglaciated before 9400 1 4 c yr b p and other areas surrounding cumberland sound were deglaciated after ca 9000 1 4 c yr b p these land areas experienced relatively slow glacial retreat and restrained rebound cosmogenic surface exposure ages on glacially scoured bedrock support the 1 4 c based inferred timing for deglaciation of the sound although inheritance of nuclides from prior exposure is evident in samples indicating limited bedrock erosion in many areas for central cumberland sound a rapid rise of relative sea level of 4 5 m 100 1 4 c yr 4 6 m 100 yr and a half life for crustal response of 720 1 4 c yr 1400 yr are consistent with those values obtained in other studies of isostatic adjustment around the edges of the former northern hemisphere ice sheets where lithospheric influences were relatively dominant

cosmogenic 10be and 26al ages for the last glacial maximum eastern baffin island arctic canada a chronology for the last glacial maximum based on cosmogenic exposure dating in the pangnirtung fjord area eastern baffin island arctic canada is at odds with many decades of land based glacial stratigraphic research most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late wisconsinan ca 24 8 ka in contrast by directly dating glacial features we conclude that late wisconsinan ice was far more extensive than previously believed there are 36 gneissic boulders and 8 samples of ice molded gneissic bedrock that yield late wisconsinan 10 be and 26 al exposure ages for the last glaciation of pangnirtung fjord the prominent duval moraines which were previously interpreted to represent a significant early wisconsinan 100 60 ka ice advance on southern cumberland peninsula were actually deposited between 24 and 9 ka two boulders from a raised glaciomarine delta stratigraphically related to the duval moraines date to about 10 ka two recessional moraines and striated bedrock along pangnirtung fjord as well as erratics on the floor of the kolik river valley a tributary to pangnirtung fjord indicate that deglaciation began between 12 and 9 ka in situ produced 10 be and 26 al abundances indicate that ice filled pangnirtung fjord for about 15 k y either continuously or intermittently prior to 10 ka which is compatible with 14 c chronologies for adjacent cumberland sound thus our data support other recent studies that suggest the northern and southern margins of the laurentide ice sheet were generally in phase during the latest wisconsinan contrary to earlier interpretations

wisconsinan refugia and the glacial history of eastern baffin island arctic canada coupled evidence from cosmogenic isotopes and lake sediments new data constrain the timing and character of glaciation of eastern baffin island arctic canada lake sediments radiocarbon dated to between 14 and 52 ka coupled to 10 be and 26 al exposure ages 35 ka from adjacent moraines and bedrock demonstrate that some coastal uplands remained above the limits of continental glaciation throughout oxygen isotope stage 2 at lower elevations exposure ages from a flight of distinct lateral moraines range from 10 to 35 ka and imply that low gradient outlet glaciers reached the outer coast during the late wisconsinan collectively these results reconcile terrestrial evidence for the presence of ice free refugia through the late wisconsinan with marine evidence for extensive outlet glaciers in the major fiords and bays of eastern baffin island

the case for a melt matrix in plagioclase poik mesosiderites the plagioclase poik mesosiderites bondoc budulan and mincy have poikilitic matrix textures exactly like igneous rocks including the olivine zone of the palisades sill and apollo 17 mare basalts they contain olivine grains with embayed margins characteristic of resorption in liquid rather than coronas formed during solid state reactions there is a nonrandom i e nonmetamorphic arrangement of pyroxene phases in the matrix orthopyroxene is enclosed poikilitically by plagioclase but inverted pigeonite is interstitial and locally subophitic to plagioclase as in an igneous crystallization sequence these mesosiderites are therefore reclassified from subgroup 3b highly recrystallized matrix to 4b igneous matrix the 4a mesosiderites have fine grained intergranular textures because they are richer in plagioclase than subgroup 4b so that plagioclase crystallized earlier than in 4b but also because they contained abundant nuclei associated with relict plagioclase clasts the only 4a melt rock mesosiderite pinnaroo with an intergranular poikilitic matrix texture transitional between 4a and 4b mesosiderites contains very few plagioclase clasts over half the mesosiderites contain melt matrix or melt rock clasts the heterogeneity within mesosiderites as a whole and within specific mesosiderites e g estherville may be due to variations in the proportions of hot melt and cold clasts incorporated

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

rapid early holocene retreat of a laurentide outlet glacier through an arctic fjord marine terminating outlet glaciers control the stability of ice sheets exposure ages and radiocarbon dates show that an arctic outlet glacier of the laurentide ice sheet rapidly retreated about 9 500 years ago and imply strong feedbacks between bathymetry and ice movement

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

petrology of the polymict eucrite petersburg abstract the polymict eucrite petersburg contains eucritic and diogenitic materials which span a broad range of compositions the present study focuses on four eucritic clasts for which bulk compositions and mineralogical data were acquired the broad compositional range of these clasts documents the diversity of the parent regolith clast a is ree rich 26 chondrite and magnesian mg 48 7 composition of this clast can best be explained by partial melting of a source region distinctly different from that of other noncumulate eucrites composition of eucritic clast b is similar to compositions of cumulate eucrites in ree and sr abundances but it has a much lower mg than moore county clasts c and d are similar in texture mineralogy and composition to main group eucrites the presence of anomalous clast a in the same polymict breccia as typical eucrite clasts c and d emphasizes the variability of source materials from which eucritic melts were derived on the hed parent body ies after final accretion this breccia apparently was exposed to a minor episode of thermal metamorphism causing 30 m wide alteration rims around larger pyroxene fragments and causing alteration of pyroxenes at the edges of eucritic clasts this metamorphism completely altered the mg of smaller matrix pyroxenes less than 40 60 m in size to values closer to the bulk mg of the meteorite

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

mid wisconsin laurentide ice sheet growth and decay implications for heinrich events 3 and 4 a close look at the sedimentology of heinrich event 4 from the northwest labrador sea indicates that an extended ice margin perhaps greater than before heinrich events 1 or 2 h 1 and h 2 existed in the hudson strait region pre heinrich event 4 h 4 and that on the basis of characteristics of the sediment unit heinrich event 4 was different than heinrich events 1 or 2 i e larger ice sheet collapse longer duration dirtier icebergs other data from across the southern and eastern margin of the laurentide ice sheet as well as greenland and the north atlantic support this interpretation possibly indicating a relative mid wisconsin glacial maximum pre heinrich event 4 many of these data also indicate that heinrich event 4 35 ka resulted in serious climatic and oceanographic reorganizations we suggest that heinrich event 4 gutted the hudson strait leaving it devoid of ice for heinrich event 3 we further hypothesize that heinrich event 3 did not originate from axial ice transport along the hudson strait thus heinrich event 3 may be more analogous to the proposed northward advancing ice from ungava bay during heinrich event 0 than to the more typical down the strait flow during h 1 h 2 and h 4 consequently the climatic and oceanographic impacts resulting from heinrich events are highly susceptible to the type origin and magnitude of ice sheet collapse something which varied per heinrich event during the last glacial period

the diogenite eucrite links and the crystallization history of a crust of their parent body aspects of the crystallization history of the primitive crust of the hed howardites eucrites diogenites achondrite parent body have been deciphered from the microtextures and chemical compositions of pyroxene and plagioclase in some antarctic hed achondrites intermediate to diogenite and eucrite five new specimens related to yamato 75032 and three eucritic clasts in y791186 and y791208 have been investigated by electron microprobe analytical transmission electron microscope and x ray diffraction techniques their pyroxene compositions cover the entire range from fe rich diogenite to eucrite the pyroxene textures of the y75032 type achondrites indicate that many of them crystallized as low ca pigeonite and some as orthopyroxene later shock events modified the original inversion and exsolution textures the chemical compositions and the interstitial occurrence of plagioclase crystals in pyroxene indicate crystallization from intercumulus trapped liquid the pyroxene crystallization and the relation between the anorthite content an of plagioclase and the mg mg fe number of the coexisting pyroxene in these specimens reveal two crystallization trends one trend is intermediate to that of the mg rich suites of the lunar highland crust and that of ferroan anorthosite and the other is a trend with a steep decrease in the an content while the mg mg fe of the pyroxene remains effectively constant a model involving crystal fractionation in a shallow magma ocean or intrusion in the parent body has been proposed

antarctic polymict eucrite yamato 792769 and the cratering record on the hed parent body yamato y792769 is a polymict breccia containing pyroxenes of a limited range in chemical compositions compared to most other yamato polymict eucrites y792769 includes fewer and smaller eucritic clasts with homogenized pyroxenes its fine grained matrix is shock compacted and sintered the time of the last thermal event which produced this texture and formed the breccia is determined by the well defined 39ar 40ar age of 3 99 0 04ga the complete resetting of the 39ar 40ar age is consistent with the texture of y792769 as viewed in the transmission electron microscope tem which suggests shock compaction converted part of the matrix plagioclase to maskelynite sm nd data define an apparent isochron corresponding to an age of 4 23 0 12ga this apparent age probably reflects partial resetting of the sm nd system during breccia formation but similar ages recorded in the highest temperature argon releases and in the rb sr model age of relict plagioclases lend some support to its reality sm nd data for relict pyroxenes fall on a 4 56 ga sm nd reference isochron and on or above a 4 56 ga rb sr reference isochron suggesting slight loss of rubidium during breccia formation the pyroxene data are most suggestive of a conventional 4 56 ga age for the protolith rocks the 3 99 ga39ar 40ar age predates the accepted age of formation of the lunar imbrium and serenitatis basins but probably reflects a period of intense meteoroid bombardment that affected the entire inner solar system

diachronous evolution of sea surface conditions in the labrador sea and baffin bay since the last deglaciation assessing changes in sea surface conditions due to the effects of past freshwater outflow through baffin bay and davis strait to the labrador sea hereafter referred to as the baffin bay corridor

the plagioclase magma density paradox re examined and the crystallization of proterozoic anorthosites intermediate composition plagioclase an40 60 is typically less dense than the relatively evolved basaltic magmas from which it crystallizes and the crystallization of plagioclase produces a dens residual liquid thus plagioclase should have a tendency to float in these magmatic systems there is however little direct evidence for plagioclase flotation cumulates either in layered intrusions or in proterozoic anorthosite complexes the layered series of the poe mountain anorthosite southeast wyoming contains numerous anorthosite leucogabbro blocks that constrain density relations during differentiation all blocks are more mafic than their hosting anorthositic cumulates their plagioclase compositions are more calcic and each block is in strong sr isotopic disequilibrium with its host cumulate associated structures disrupted and deformed layering indicate that 1 a floor was present during crystallization and that plagioclase was accumulating and or crystallizing on the floor 2 compositional layering and plagioclase lamination formed directly at the magma crystal pile interface and 3 the upper portions of the crystal pile contained significant amounts of interstitial melt liquid densities are calculated for proposed high al olivine gabbroic parental magmas and fe enriched ferrodioritic and monzodioritic residual magmas of the anorthosites taking into account pressure oxygen fugacity p2o5 estimated volatile contents and variable temperatures of crystallization for all reasonable conditions calculated block densities are greater than those of the associated melt the liquid densities however are greater than those for an40 60 plagioclase which cannot have settled to the floor plagioclase must either have been carried to the floor in relatively dense packets of cooled liquid plus crystals or have crystallized in situ a sloping floor possibly produced by diapiric ascent of relatively light plagioclase rich cumulates is required to allow for draining and removal of the dense interstitial liquid produced in the crystal pile and may be a characteristic feature during the crystallization of many proterozoic anorthosites and layered intrusions

mantle viscosity and ice age ice sheet topography ice age paleotopography and mantle viscosity can both be inferred from observations of earth s response to the most recent deglaciation event of the current ice age this procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ice 4g model the accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process thus resolving a fundamental issue concerning mantle rheology the combined model also explains postglacial sea level histories for the east coast of the united states

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

glacial history and landscape evolution of southern cumberland peninsula baffin island canada constrained by cosmogenic 10be and 26al since the first application of cosmogenic nuclides to the study of glacial history and processes in 1990 increasing numbers of studies have used a variety of cosmogenic isotopes to quantify the exposure age and erosion rate of glaciated landscapes however obtaining chronological data from glaciated landscapes once covered by cold based nonerosive ice is challenging because these surfaces violate assumptions associated with simple cosmogenic exposure dating nonerosive glacial ice fails to completely remove nuclides produced during previous periods of exposure leaving behind rock surfaces with complex multigenetic nuclide inventories here we constrain the glacial history landscape evolution and efficiency of subglacial erosion in the pangnirtung fiord region of southern baffin island using over 300 paired analyses of in situ cosmogenic 10be and 26al simple exposure ages are 6 3 160 ka for 10be n 152 and 4 3 124 ka for 26al n 153 paired bedrock boulder samples have discordant ages simple exposure ages generally increase with elevation 10be and 26al ages for the same sample disagree and both boulders and bedrock yield multimodal age distributions all patterns suggestive of limited subglacial erosion measured 26al 10be ratios indicate that about one third of the samples in the data set experienced at least one period of pre holocene exposure followed by burial with limited erosion modeled two isotope minimum limiting exposure durations are as high as hundreds of thousands of years and minimum limiting burial durations range up to millions of years implying that parts of southern baffin island have been preserved beneath nonerosive glacial ice for much if not all of the quaternary a subset of the samples contains few nuclides inherited from prior periods of exposure and is thus useful for constraining the chronology of the most recent deglaciation using these samples we infer that deglaciation of most of the landscape occurred ca 11 7 ka and that the duval moraines a prominent feature of the last deglaciation formed ca 11 2 ka

the goldilocks dilemma big ice little ice or just right ice in the eastern canadian arctic our conceptions of the ne sector of the laurentide ice sheet lis at the last glacial maximum lgm have evolved through three major paradigms over the past 50 years until the late 1960s the conventional view was that the eastern canadian arctic preserved only a simple deglacial sequence from a lis margin everywhere at the continental shelf edge flint paradigm glacial geologic field studies began in earnest in this region in the early 1960s and within the first decade field evidence documenting undisturbed deposits predating the lgm led a pendulum swing to a consensus view that large coastal stretches of the eastern canadian arctic remained free of actively eroding glacial ice at the lgm and that the most extensive ice margins occurred early in the last glacial cycle this minimalist paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated lgm ice at least locally reached the continental shelf within the past decade the marine data coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the eastern canadian arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence collectively these lines of evidence indicate that all of southern baffin island was glaciated at the lgm but that some coastal uplands north of cumberland sound remained above the limit of actively eroding glacial ice even though outlet glaciers reached the continental shelf in front of most fiords and sounds the most plausible explanation for the observed glacial limits is that low gradient relatively fast moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain slow moving ice frozen to its bed would have had steeper surface gradients hence would have terminated inland from the coast this scenario is consistent with observations indicating high elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf lgm summer temperatures were apparently much lower than present as lakes in the ice free regions were permanently frozen

adcumulus growth of anorthosite at the base of the lunar crust unzoned plagioclase crystals imply isothermal adcumulus solidification and cannot result from reactive equilibrium crystallization in dry magma extraction of latent heat upward through lunar crust results only in chilled or cotectic mesocumulate rocks not anorthosite or adcumulates adcumulus growth of anorthosite requires exchange of refractory for incompatible components between the site of crystal growth and nearby fresh magma and the extraction of calories from growing crystals to the flowing supercooled magma supercooling can be acquired at remote sites like upwellings and then be carried by convective flow beneath crust which is accreting plagioclase by flotation or in situ nucleation and growth if transport distances are larger than the scale of rockbergs cotectic norites and troctolites may result impact induced upwellings tend to promote growth of buoyant rather than mafic crust hence impacts are not solely destructive

rare earth elements in minerals of the alha77005 shergottite and implications for its parent magma and crystallization history abstract rare earth element ree and selected trace element abundances were measured in individual grains of pyroxenes whitlockite maskelynite and olivine of the alha77005 shergottite minor 1 whitlockite which displays a negative eu anomaly indicative of co crystallization with plagioclase dominates the bulk rock ree pattern detectable ce anomalies in 20 of the pyroxene grains analyzed appear to be the result of weathering in the antarctic environment and indicate that pyroxene is particularly susceptible to element remobilization mineral compositions and textural observations suggest that alha77005 is a cumulate with 50 cumulus material olivine chromite olivine re equilibrated with intercumulus liquid on cooling the intercumulus liquid then crystallized as a closed system to form successively poikilitic low ca and high ca pyroxene followed by interstitial pyroxenes plagioclase whitlockite and other minor phases and reacted with cumulus crystals to form rims of different composition this crystallization sequence provides a constraint on the shergottite source region composition the alha77005 and shergotty intercumulus liquids had similar ree compositions however as opposed to shergotty if alha77005 was formed during the last 0 72 ga its parent melt was not contaminated by lree enriched material

unmelted meteoritic debris collected from eltanin ejecta in polarstern cores from expedition ant xii 4 abstract a total of 1 7 g of unmelted meteorite particles have been recovered from fs polarstern piston cores collected on expedition ant xii 4 that contain ejecta from the eltanin impact event most of the mass 1 2 g is a large single specimen that is a polymict breccia similar in mineralogy and chemistry to howardites or the silicate fraction of mesosiderites most of the remaining mass is in several large individual pieces 20 75 mg each that are polymict breccias fragments dominated by pyroxene and an igneous rock fragment the latter has highly fractionated ree similar to those reported in mafic clasts from mesosiderites other types of specimens identified include fragments dominated by maskelynite or olivine these pieces of the projectile probably survived impact by being blown off the back surface of the eltanin asteroid during its impact into the bellingshausen sea

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic radiocarbon dates from marine piston cores and from onshore raised marine stratigraphic sections in the hudson strait region were used to reconstruct deglacial isochrons for 9900 9500 8800 8500 and 8000 bp at the culmination of the gold cove readvance 9900 bp labrador ungava ice flowed northeastward across hudson strait and outer frobisher bay and stood for the last time on the baffin island continental shelf subsequent retreat by calving was rapid and profound opening the entire hudson strait marine trough by 9500 bp at this time ice dispersal from foxe basin labrador ungava and local ice on meta incognita peninsula supported tidewater margins along much of the coastline with the exception of northernmost ungava peninsula where the ice margin stabilized onshore this onshore margin remained in place throughout the cockburn substage while a major northeastward readvance of ungava bay ice the noble inlet readvance from 8800 to 8500 bp crossed outer hudson strait grounding on the hudson st

using hed meteorites to interpret neutron and gamma ray data from asteroid 4 vesta here we construct a comprehensive howardite eucrite and diogenite hed bulk chemistry data set to compare with dawn data using the bulk chemistry data set we determine four gamma ray neutron parameters in the heds 1 relative fast neutron counts fast counts 2 macroscopic thermal neutron absorption cross section absorption 3 a high energy gamma ray compositional parameter cp and 4 fe abundance these correspond to the four measurements of vesta made by dawn s gamma ray and neutron detector grand that can be used to discern hed lithologic variability on the vestan surface we investigate covariance between fast counts and average atomic mass in the meteorite data set where a strong correlation r2 0 99 is observed and we demonstrate that systematic offsets from the fast count trend are linked to changes in fe and ni concentrations to compare the meteorite and grand data we investigate and report covariance among fast counts absorption cp and fe abundance in the hed meteorite data set we identify several grand measurement spaces where the yamato type b diogenites are distinct from all other hed lithologies including polymict mixtures the type b s are diogenites that are enriched in fe pigeonite diopside plagioclase relative to typical orthopyroxenitic diogenites we then compare these results to grand data and demonstrate that regions north of 70 n latitude on vesta including the north pole are consistent with type b diogenites we propose two models to explain type b diogenite compositions in the north 1 deposition as rheasilvia ejecta or 2 type b plutons that were emplaced at shallow depths in the north polar region and sampled by local impacts lastly using principal component pc analysis we identify unique pc spaces for all hed lithologies indicating that the corresponding grand measurables may be used to produce comprehensive lithologic maps for vesta

thermal and deformational histories of diogenites as inferred from their microtextures of orthopyroxene abstract orthopyroxenes of bronzite composition from three diogenites johnstown ibbenburen and allan hills alpha 77256 were examined by transmission electron microscopy to find microtextures suggestive of their origin subboundaries decorated with thick augite lamellae up to 100 m in length were found in all three orthopyroxenes and suggest either dislocation recovery processes during mild deformation or annealing at high subsolidus temperature the ibbenburen orthopyroxene has augite exsolution lamellae up to 0 4 m wide with the 100 plane in common the augite is semicoherent with the host as was found in those of the terrestrial layered intrusions of bushveld both textures are consistent with a deep seated origin in their parent body the johnstown orthopyroxene with the bulk chemical compositions ca 3 4 mg 71 0 fe 25 6 is similar to ibbenburen and contains coherent 100 augite lamellae only several unit cell wide and abundant guinier preston zones in addition the presence of untwinned pigeonite lamellae up to 0 1 m in width with remnant antiphase boundaries which are interpreted to have been produced by stress induced transformation at high temperature suggest shock deformation processes due to meteoritic impacts and excavation of its parental mass resulting in rapid cooling at high temperature

two stage models for lunar and terrestrial anorthosites petrogenesis without a magma ocean two stage diapiric models for lunar ferroan anorthosites and terrestrial massif anorthosites are examined the lunar model is developed to explain early lunar differentiation in the absence of a magma ocean if correct the terrestrial model serves as an analog for the development of lunar anorthositic diapirs there is field and textural evidence of transport of mostly crystalline anorthositic material within the terrestrial complexes this evidence combined with the absence of anorthositic lavas and phase equilibrium constraints inhibiting the production of hyperaluminous magmas is consistent with the detachment of plagioclase rich crystalline mushes from large uppermost mantle plutons and multiple diapiric intrusion of these mushes into the upper sialic crust with attendant anatexis rudimentary dynamical calculations suggest that a simple single layer source for the diapirs is improbable either there were several parental magma chambers or there was a single large chamber that was repeatedly replenished the lunar model is a development of wetherill s 1975 suggestion that following accretion the outer portion of the moon consisted of a stack of overlapping layered intrusions and that reheating of these intrusions mobilized their anorthositic layers which intruded upwards to produce the anorthositic lunar crust dynamical calculations show that gravitational instabilities in anorthositic layers 1 km thick could develop into diapirs on a reasonable time scale 50 100 m y only if the outer portion of the moon was partially remelted we suggest that partial melting of the interior due to the decay of long lived radionuclides with the subsequent onset of global convection heated the stack of intrusions from below thus causing melting and allowing the anorthositic diapirs to grow and ascend fairly rapidly as the convecting zone thickened a mass expulsion of anorthositic material out of the lunar interior may have occurred

the formation of eucrites constraints from metal silicate partition coefficients this study explores the controls of oxygen fugacity and temperature on the solubilities of fe ni co mo and w in natural eucritic liquids to better constrain the formation of eucritic melts the solubilities of all five elements in molten silicate in equilibrium with fenico femo and fewalloys increase with increasingly oxidizing conditions and decrease with decreasing temperatures in applying these data to formation scenarios of the eucrite parent body we find that the siderophile element abundances in eucrites meteoritic basalts cannot be explained by a single step partialmelting process from a chondritic metal containing source the ni content of the partial melt is too high and the w and mo contents are too low compared to the abundances in eucritic meteorites but fe ni and co concentrations in eucrites can be modeled by metal silicate equilibrium during more or less complete melting of the eucrite parent body with subsequent fractional crystallization of olivine and orthopyroxene however the computed values of mo are still too low and those of w too high when compared with mo and w abundances in eucritic meteorites one possibility is that the mo and w partition coefficients strongly depend on pressure although the howardite eucrite diogenite hed parent body only had a minimal pressure gradient maximum interior pressure 0 1 gpa alternatively sulfides may have played some role in establishing mo abundances

wisconsinan and early holocene glacial dynamics of cumberland peninsula baffin island arctic canada abstract three glacier systems an ice sheet with a large marine based ice stream an ice cap and an alpine glacier complex coalesced on cumberland peninsula during the late wisconsinan we combine high resolution mapping of glacial deposits with new cosmogenic nuclide and radiocarbon age determinations to constrain the history and dynamics of each system during the middle wisconsinan oxygen isotope stage 3 ois 3 the cumberland sound ice stream of the laurentide ice sheet retreated well back into cumberland sound and the alpine ice retreated at least to fiord head positions a more significant recession than previously documented the advance to maximal ois 2 ice positions beyond the mouth of cumberland sound and beyond most stretches of coastline remains undated partial preservation of an over ridden ois 3 glaciomarine delta in a fiord side position suggests that even fiord ice was weakly erosive in places moraines formed during deglaciation represent stillstands and re advances during three major cold events h 1 14 6 ka younger dryas 12 9 11 7 ka and cockburn 9 5 ka distinctly different responses of the three glacial systems are evident with the alpine system responding most sensitively to bolling allerod warming whereas the larger systems retreated mainly during pre boreal warming while the larger ice masses were mainly influenced by internal dynamics the smaller alpine glacier system responded sensitively to local climate effects asymmetrical recession of the alpine glacier complex indicates topoclimatic control on deglaciation and perhaps migration of the accumulation area toward moisture source

depth calibrating seismic data in the presence of allochthonous salt seismic depth errors can be significant in psdm processed seismic data the purpose of this paper is to discuss best practice techniques for depth calibrating seismic volumes particularly in the presence of allochthonous salt where lateral and vertical velocity heterogeneity is great we will present the concepts of apparent seismic depth and true seismic depth propose anisotropy as a first order mechanism for seismic depth error discuss the implications of depth error as it pertains to well planning and resource estimation and present different corrective measures and discuss their implementation our paper will be supported by two case studies one from the deepwater gulf of mexico and another from offshore west africa

magnesium oxide iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites according to a currently popular model for petrogenesis on the howardite eucrite and diogenite hed parent asteroid the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite dominated plutons this model can be tested for consistency with mass balance for mgo and feo assuming the overall diogenite diogenite eucrite ratio d of the parent asteroid is at least comparable to the average d for the eucrite diogenite dominated howardite regolith breccias average mg mgo mgo feo is much lower for eucrites especially noncumulate eucrites than for diogenites unless the diogenite parent magmas eventually produced a large proportion of low mg residual basalt and gabbro rbg the implied initial magma s mg is vastly higher than that of any noncumulate eucrite starting from a source previously depleted by putative primary eucrite genesis melt mg can be estimated as a function of the exchange reaction kd and degree of melting using several very conservative assumptions e g assuming that the total mgo feo concentration is nearly the same in the nascent melt as in the residual solids the degree of melting required to yield a melt with mg high enough to satisfy mass balance without implying an rbg component that accounts for 50 of all eucrites is an implausibly high 60 80 wt the separate orthopyroxenitic plutons sop model also seems inconsistent with the uniform density of melts across the diogenite eucrite compositional spectrum 2 77 2 82 g cm3 which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas this difficulty cannot be reduced by simply assuming that later formed magmas were systematically both more plutonic and more mgo rich than earlier ones because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg than noncumulate eucrites conceivably the bulk mg of the asteroid s silicate system was increased between primary melt eucrite genesis and sop diogenite genesis by graphite fueled reduction of feo however the graphite oxidation process generates a huge proportion of gas which would have enhanced the buoyancy of the nascent diogenite parent magmas thus exacerbating the difficulty of achieving the implied high degrees of partial melting to avoid these difficulties but still form most eucrites as rapidly cooled extrusives i propose the nerd noncumulate eucrites as extruded residua of diogenites model in this model the diogenites form as early cumulates from a large magma system probably a global magma ocean that yields a large proportion of eucritic melt as residuum this residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions dikes and sills of rapidly cooled noncumulate eucrites slight 5 10 porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone the common thermal metamorphism of noncumulate eucrites results from baking by superjacent flows during the episodic venting of the melt zone the nerd model s greatest advantage is that it does not require implausibly high degrees of localized melting in the mature stages of igneous evolution of the hed asteroid

oxygen isotopic constraints on the origin and parent bodies of eucrites diogenites and howardites abstract a few eucrites have anomalous oxygen isotopic compositions to help understand their origin and identify additional samples we have analyzed the oxygen isotopic compositions of 18 eucrites and four diogenites except for five eucrites these meteorites have 17o values that lie within 2 of their mean value viz 0 242 0 016 consistent with igneous isotopic homogenization of vesta the five exceptional eucrites nwa 1240 pasamonte both clast and matrix samples pca 91007 a 881394 and ibitira have 17o values that lie respectively 4 5 5 15 and 21 away from this mean value nwa 1240 has a 18o value that is 5 below the mean eucrite value four of the five outliers are unbrecciated and unshocked basaltic eucrites like nwa 011 the first eucrite found to have an anomalous oxygen isotopic composition the fifth outlier pasamonte is composed almost entirely of unequilibrated basaltic clasts published chemical data for the six eucrites with anomalous oxygen isotopic compositions including nwa 011 exclude contamination by chondritic projectiles as a source of the oxygen anomalies only nwa 011 has an anomalous fe mn ratio but several anomalous eucrites have exceptional na ti or cr concentrations we infer that the six anomalous eucrites are probably derived from five distinct vesta like parent bodies pasamonte and pca 91007 could come from one body these anomalous eucrites like the isotopically normal unbrecciated eucrites with 4 48 gyr ar ar ages are probably deficient in brecciation and shock effects because they were sequestered in small asteroids 10 km diameter during the late heavy bombardment following ejection from vesta like bodies the preservation of vesta s crust and the lack of deeply buried samples from the hypothesized vesta like bodies are consistent with the removal of these bodies from the asteroid belt by gravitational perturbations from planets and protoplanets rather than by collisional grinding

ice sheet dynamics and glacial history of southeasternmost baffin island and outermost hudson strait southeasternmost baffin island is mantled by hudson strait drift it contains abundant limestone erratics and 20 to 50 carbonate in the matrix to the northwest it is replaced by drift dominated by locally derived rock of the canadian shield the sense and orientation of ice erosional features demonstrate that hudson strait drift is associated with northeasterly ice flow that crossed the tip of meta incognita peninsula local drift associated with ice flow s10 w along the hudson strait coast was derived from a dispersal center on the peninsula erratic lithologies contained in the hudson strait drift indicate a labradorean provenance large scale bedrock molding and the distribution of cirques indicate ne flowing ice has been dominant throughout the middle and late quaternary radiocarbon dates of in situ shells confirm that deglaciation began more than 11 000 yr ago with the frobisher bay coast becoming ice free by 9300 yr ago five dates from hudson strait suggest that the strait was deglaciated before 9000 yr bp however ice from the labradorean sector recrossed hudson strait during the cockburn substage about 8500 yr ago damming drainage from the west final retreat of labradorean ice from baffin island was complete by 8000 yr ago at which time the sea was able to penetrate hudson bay

heinrich event 0 dc 0 in sediment cores from the northwest labrador sea recording events in cumberland sound layers of ice rafted limestone debris rich sediment were deposited in the northwest labrador sea and the north atlantic during the last glacial period 10 80 ka these sediments were deposited by heinrich events h events which record catastrophic collapses of the laurentide ice sheet in the region of the hudson strait these intervals of detrital carbonate rich sediments are referred to as detrital carbonate layers dc in the northwest labrador sea accelerator mass spectrometry ams 14c dates provide a strong constraint on the timing for these events h 1 dc 1 and h 2 dc 2 dc 0 also known as h 0 correlative to the younger dryas cooling event is not as distinct a sediment unit in the northwest labrador sea as dc 1 and dc 2 an analysis of sediments from two cores hu75009 iv 055 and hu75009 iv 056 off the mouth of the hudson strait in the northwest labrador sea basin sheds new light on the missing dc 0 sediment unit timing for the dc 0 event in cores 055 and 056 is bracketed between 11

summer melt rates on penny ice cap baffin island past and recent trends and implications for regional climate 1 at latitude 67 n penny ice cap on baffin island is the southernmost large ice cap in the canadian arctic yet its past and recent evolution is poorly documented here we present a synthesis of climatological observations mass balance measurements and proxy climate data from cores drilled on the ice cap over the past six decades 1953 to 2011 we find that starting in the 1980s penny ice cap entered a phase of enhanced melt rates related to rising summer and winter air temperatures across the eastern arctic presently 70 to 100 volume of the annual accumulation at the ice cap summit is in the form of refrozen meltwater recent surface melt rates are found to be comparable to those last experienced more than 3000 years ago enhanced surface melt water percolation and refreezing have led to a downward transfer of latent heat that raised the subsurface firn temperature by 10 c at 10 m depth since the mid 1990s this process may accelerate further mass loss of the ice cap by pre conditioning the firn for the ensuing melt season recent warming in the baffin region has been larger in winter but more regular in summer and observations on penny ice cap suggest that it was relatively uniform over the 2000 m altitude range of the ice cap our findings are consistent with trends in glacier mass loss in the canadian high arctic and regional sea ice cover reduction reinforcing the view that the arctic appears to be reverting back to a thermal state not seen in millennia

cosmogenic exposure dating in arctic glacial landscapes implications for the glacial history of northeastern baffin island arctic canada cosmogenic exposure dating and detailed glacial terrain mapping from the clyde foreland baffin island arctic canada reveal new information about the extent and dynamics of the northeastern sector of the laurentide ice sheet lis during the last glacial maximum lgm the clyde foreland is composed of two distinct landscape zones 1 glacially scoured terrain proximal to the major sources of laurentide ice that flowed onto the foreland and 2 ice distal unscoured sectors of the foreland both zones are draped with erratics and dissected by meltwater channels indicating past ice cover we interpret the two landscape classes in terms of ice sheet erosive ability linked with basal thermal regime glacially scoured terrain was occupied by erosive warm based ice and unscoured terrain was last occupied by non erosive cold based ice cosmogenic exposure ages from 100 erratics from the two landscape types have different age distributions cosmogenic exposure ages from the glacially scoured areas suggest ice cover during the lgm followed by deglaciation between 15 and 12 ka in the unscoured lowlands the cosmogenic exposure ages have multiple modes ranging between 12 and 50 ka suggesting multiple periods of cold based ice cover during the last glacial cycle in landscapes covered by cold based ice large numbers of cosmogenic exposure ages are required for elucidating glacial histories

late holocene fluctuations of qori kalis outlet glacier quelccaya ice cap peruvian andes geology v 42 p 347 350 1 doi 10 1130 g35245 1 there was an error in determining the number of 10be atoms per gram of quartz for samples js 09 20 24 14 and 15 and thus the calculated 10be ages all usage of these samples and their ages has been corrected in the gsa data repository

cosmogenic nuclide age estimate for laurentide ice sheet recession from the terminal moraine new jersey usa and constraints on latest pleistocene ice sheet history

forms response times and variability of relative sea level curves glaciated north america abstract relative sea level curves from glaciated north america reveal coherent spatial patterns of response times in the laurentide ice sheet area curve half lives range from 1 2 1 4 ka at the uplift centre to 1 7 2 ka in a ridge of high values inboard of the glacial limit half lives decline from this ridge to less than 1 ka along the margin in the innuitian ice sheet area half lives are about 2 ka at the uplift centre and decline to less than 1 ka at the margin the central laurentide response times are about half those of central fennoscandia this accords with the theoretical expectation that central response times are inversely proportional to ice sheet radius for ice loads large enough that rebound at the centre is insensitive to lithospheric thickness the innuitian central response time indicates that rebound at the centre of this ice sheet which is much smaller than the fennoscandian ice sheet remains sensitive to lithospheric thickness radial gradients in response times reflect the increasing influence of the lithosphere at sites increasingly closer to the margin along this gradient rebound progresses as though at the centres of smaller and smaller ice sheets that is the effective spatial scale of the ice load decreases toward the margin near the glacial limit postglacial isostatic adjustment is complicated by forebulge migration and collapse this is seen most strongly in the relative sea level record of atlantic canada which has subsided during the holocene more than 20 m more than the adjacent american seaboard the relative sea level history of some areas notably the st lawrence estuary is complicated by tectonic processes

kiglapait geochemistry vii yttrium and the rare earth elements abstract based on 51 wholerock analyses by xrf and summation over the layered group the kiglapait intrusion contains 4 7 1 6 1 2 ppm y which resides principally in augite and apatite using liquid compositions calculated by summation the partition coefficient daug ly is 0 95 0 12 from 84 to 97 pcs percent solidified and 1 5 0 4 above 97 pcs for feldspar the most likely value for d is 0 028 0 02 n 6 ree analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs pcs summations over the rocks of the layered group gave la 2 5 ce 5 8 nd 3 9 sm 1 0 eu 0 8 tb 0 17 yb 0 37 and lu 0 06 ppm with 2 s d errors near 30 all these elements are highly incompatible until the arrival of augite which affects chiefly the hree and apatite which affects all but more strongly the lree the net result is that after apatite arrival at 94 pcs the liquid compositions are nearly constant hence dwr lree 1 0 these results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar olivine augite apatite and fe ti oxide minerals for pre apatite liquids dfsp lree vary regularly with the normative di content of the liquid and change by an order of magnitude hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids the eu anomaly at first decreases in kiglapait liquids due to plagioclase fractionation but then increases due to removal of augite and apatite with negative eu anomalies the features dominantly responsible for eu partitioning are liquid structure and for monoclinic ternary feldspars crystal structure the former is best monitored by the augite or diopside content of the liquid and the latter by the k content of the feldspar the chondrite normalized ree pattern for the intrusion has lan 7 4 lun 1 6 ce yb n 3 6 and eu eu 2 4 indicating its feldspar rich nature the chilled margin of the nearby hettasch intrusion has a similar but more evolved pattern corresponding roughly to the kiglapait liquid at 70 pcs as with other data those for the ree suggest source differences for the two intrusions rather than a relationship due to fractionation

chronology geochemistry and petrology of a ferroan noritic anorthosite clast from descartes breccia 67215 clues to the age origin structure and impact history of the lunar crust the petrology major and trace element geochemistry and nd ar sr isotopic compositions of a ferroan noritic anorthosite clast from lunar breccia 67215 have been studied in order to improve our understanding of the composition age structure and impact history of the lunar crust the clast designated 67215c has an unusually well preserved igneous texture mineral compositions are consistent with classification of 67215c as a member of the ferroan anorthositic suite of lunar highlands rocks but the texture and mineralogy show that it cooled more rapidly and at shallower depths than did more typical ferroan anorthosites fans incompatible trace element concentrations are enriched in 67215c relative to typical fans but diagnostic signatures such as ti sm sc sm plagiophile element ratios and the lack of zr hf and nb ta fractionation show that this cannot be due to the addition of kreep alternatively 67215c may contain a greater fraction of trapped liquid than is commonly present in lunar fans 147sm 143nd isotopic compositions of mineral separates from 67215c define an isochron age of 4 40 0 11 gyr with a near chondritic initial 143nd of 0 85 0 53 the 40ar 39ar composition of plagioclase from this clast records a post crystallization thermal event at 3 93 0 08 gyr with the greatest contribution to the uncertainty in this age deriving from a poorly constrained correction for lunar atmosphere 40ar rb sr isotopic compositions are disturbed probably by the same event recorded by the ar isotopic compositions trace element compositions of fans are consistent with crystallization from a moderately evolved magma ocean and do not support a highly depleted source composition such as that implied by the positive initial 143nd of the ferroan noritic anorthosite 62236 alternatively the nd isotopic systematics of lunar fans may have been subject to variable degrees of modification by impact metamorphism with the plagioclase fraction being more strongly affected than the mafic phases 147sm 143nd isotopic compositions of mafic fractions from the 4 ferroan noritic anorthosites for which isotopic data exist 60025 62236 67016c 67215c define an age of 4 46 0 04 gyr which may provide a robust estimate for the crystallization age of lunar ferroan anorthosites

geomorphological evidence and cosmogenic 10be 26al exposure ages for the last glacial maximum and deglaciation of the antarctic peninsula ice sheet this paper presents the first systematic attempt to map the last glacial maximum lgm configuration of the southern and central parts of the antarctic peninsula ice sheet and to determine the timing of onshore ice sheet retreat geomorphologic evidence shows that the lgm ice sheet expanded to form two ice domes in palmer land and merged with an expanded and thicker west antarctic ice sheet in the weddell sea ice from the antarctic peninsula merged with alexander island ice in george vi sound cosmogenic 10 be and 26 al data from 29 erratics on nunataks yield model ages between 7 2 ka and older than 1 ma the data set contains a high proportion of erratics with evidence of nuclide inheritance once these ages have been excluded the cosmogenic ages suggest that thinning of the west side of the antarctic peninsula ice sheet to near present configuration was almost complete by the early holocene these data combined with previously published 14 c data exclude the possibility that the west side of the antarctic peninsula ice sheet has been thinning throughout the holocene as has been demonstrated for some other sectors of the west antarctic ice sheet on the east side of the antarctic peninsula ice sheet thinning was under way prior to the early holocene but our data do not constrain the ice sheet behavior more recently than 7 2 ka

rare earth element selenochemistry of immiscible liquids and zircon at apollo 14 an ion probe study of evolved rocks on the moon abstract secondary ion mass spectrometry sims analyses of trace elements in two zircons from 14001 7003 are similar in most respects to one reported recently hinton and meyer 1991 hinton and upton 1991 the major difference being the lack of a positive ce anomaly in the zircon ree pattern reported here which obviates an oxidizing environment for lunar zircon using recently published ree partition coefficients all three lunar zircons indicate separation from a primitive magma with a large negative eu anomaly which is slightly lree enriched and contains rees 10 30 cl chondrites however this calculated liquid has a ree pattern which is unlike the host material or any lunar granite it is postulated that these lunar zircons were precipitated in the upper crust of the moon from late stage gabbroic to anorthositic magmas which have undergone extensive fractionation the exact nature of these evolved magmas remains uncertain evidence for suspected immiscible liquids has been found as glasses in fragments from sample 14001 7003 though the granitic complement to this immiscible pair is a viable immiscible liquid composition the mafic complement has likely undergone some post immiscibility modification however the original liquid liquid element partitioning has not been grossly affected by the post immiscibility modification analyses of the glasses by sims yields a set of partitioning data for the ree in actual rocks from the moon for the most part the partitioning of the rees between the glasses is consistent with that determined experimentally and indicates the importance of liquid immiscibility in late stage lunar igneous processes

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites