filling the bushveld complex magma chamber lateral expansion roof and floor interaction magmatic unconformities and the formation of giant chromitite pge and ti v magnetitite deposits his mind was like a soup dish wide and shallow irving stone on william jennings bryan a compilation of the sr isotopic stratigraphy of the bushveld complex shows that the evolution of the magma chamber occurred in two major stages during the lower open system integration stage lower critical and lower main zone there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing crystallisation and deposition of cumulates larger influxes correspond to the boundaries of the zones and sub zones and are marked by sustained isotopic shifts major changes in mineral assemblages and development of unconformities during the upper closed system differentiation stage upper main zone and upper zone there were no major magma additions other than that which initiated the upper zone and the thick magma layers evolved by fractional crystallisation the lower and lower critical zones are restricted to a belt that runs from steelpoort and burgersfort in the northeast to rustenburg and northam in the west and an outlier of the lower and lower critical zone up to the lg4 chromitite layer in the far western extension north of zeerust it is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the lower critical zone occur these chromitites include the economically important c 1 m thick lg6 and mg1 layers exposed around both the eastern and western lobes of the bushveld complex the upper critical zone has a greater lateral extent than the lower critical zone and overlies but also onlaps the floor rocks to the south of the steelpoort area the source of the magmas also appears to have been towards the south as the mg chromitite layers degrade and thin northward whereas the lg layers are very well represented in the north and degrade southward sr and os isotope data indicate that the major chromitite layers including the lg6 mg1 and ug2 originated in a similar way extremely abrupt and stratigraphically restricted increases in the sr isotope ratio imply that there was massive contamination of intruding melt which hit the roof of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite kruger 1999 kinnaird et al 2002 therefore each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor nevertheless this was achieved by in situ contamination by roof rock melt of the intruding critical zone liquids that had an orthopyroxenitic to noritic lineage the main zone is present in the eastern and western lobes of the bushveld complex where it overlies the critical zone and onlaps the floor rocks to the south and the north where it is also the basal zone in the northern lobe the new magma first intruded the northern lobe north of the thabazimbi murchison lineament interacted with the floor rocks incorporated sulphur and precipitated the platreef along the floor rock contact before flowing south into the main chamber this exceptionally large influx of new magma then eroded an unconformity on the critical zone cumulate pile and initiated the main zone in the main chamber by precipitating the merensky reef on the unconformity the upper zone magma flowed into the chamber from the southern bethal lobe as well as the tml this gigantic influx eroded the main zone rocks and caused very large scale unconformable relationships clearly evident as the gap areas in the western bushveld complex the base of this influx which is also coincident with the pyroxenite marker and a troctolitic layer in the northern lobe is the petrological and stratigraphic base of the upper zone sr isotope data show that all the pge rich ores including chromitites are related to influxes of magma and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion with associated transgressive disconformities onto the floor rocks coincident with major zone changes these positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped the outcrop patterns and the concordance of geochemical isotopic and mineralogical stratigraphy indicate that during crystallisation the bushveld complex was a wide and shallow lobate sill like sheet and the rock strata and mineral deposits are quasi continuous over the whole intrusion

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

on the accuracy of glacier outlines derived from remote sensing data deriving glacier outlines from satellite data has become increasingly popular in the past decade in particular when glacier outlines are used as a base for change assessment it is important to know how accurate they are calculating the accuracy correctly is challenging as appropriate reference data e g from higher resolution sensors are seldom available moreover after the required manual correction of the raw outlines e g for debris cover such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied here we compare outlines for clean and debris covered glaciers as derived from single and multiple digitizing by different or the same analysts on very high 1 m and medium resolution 30 m remote sensing data against each other and to glacier outlines derived from automated classification of landsat thematic mapper data results show a high variability in the interpretation of debris covered glacier parts largely independent of the spatial resolution area differences were up to 30 and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain differences 5 the differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts based on these results we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts e g debris cover shadow

a new surface accumulation map for western dronning maud land antarctica from interpolation of point measurements as a result of intensive field activities carried out by several nations over the past 15 years a set of accumulation measurements for western dronning maud land antarctica was collected based on firn core drilling and snow pit sampling this new information was supplemented by earlier data taken from the literature resulting in 111 accumulation values using geographical information systems software a first region wide mean annual snow accumulation field was derived in order to define suitable interpolation criteria the accumulation records were analyzed with respect to their spatial autocorrelation and statistical properties the resulting accumulation pattern resembles well known characteristics such as a relatively wet coastal area with a sharp transition to the dry interior but also reveals complex topographic effects furthermore this work identifies new high return shallow drilling sites by uncovering areas of insufficient sampling density

cold surface layer thinning on storglaciaren sweden observed by repeated ground penetrating radar surveys 1 a characteristic feature of ground penetrating radar gpr surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface cts hence providing a possible tool for mapping thermal structure with high accuracy comparison of detailed temperature measurements in bore holes and gpr profiles at 345 mhz and 800 mhz center frequencies on storglaciaren sweden show that the cts can be detected and mapped with an accuracy of about 1 m at both frequencies a comparison between comprehensive gpr surveys of the cold surface layer separated by 12 years 1989 2001 shows a substantial and complex thinning of the cold layer an overall decrease of 8 3 m 22 of average thickness of the cts depth is much larger than uncertainties in cts depth determinations the stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of cts there is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning however small increase in average winter air temperature a limiting factor for the temperature gradient through the cold surface layer may provide a partial explanation the weaker temperature gradient reduces the transport of latent heat from the cts thus slowing down its downward migration

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

re and os distribution and os isotope composition of the platreef at the sandsloot mogolakwena mine bushveld complex south africa abstract rhenium and os concentrations and os isotopic compositions were determined for a suite of previously characterized samples from a traverse across the platreef at the sandsloot mogolakwena mine of the northern limb of the bushveld complex the samples comprise five pyroxenites and five parapyroxenites contact rocks representing variable mixtures of calc silicate country rocks and magmatic rocks the isotopic data from the pyroxenites define a re os regression line with an age 2011 51 ma that agrees within uncertainty with the accepted age for the bushveld complex whereas the parapyroxenite data scatter about this trend the initial 187os 188os ratios of the pyroxenites 0 1820 0 1848 are similar to but slightly more radiogenic than previously published values for the merensky reef our preferred interpretation is that this section of the platreef formed from a well mixed crustally contaminated magma genetically related to that which gave rise to the merensky reef the platreef parental magma may also have experienced minor additional contamination by wall rock interaction during emplacement

petrology and mineralisation of the southern platreef northern limb of the bushveld complex south africa the platreef the putative local analogue of the merensky reef forms the floor to the mafic succession in the northern limb of the bushveld complex we define the platreef as the lithologically variable unit dominated by pyroxenite which is irregularly mineralised with pge cu and ni between the transvaal metasedimentary footwall or archaean basement and the overlying main zone gabbronorite we define the mineralisation around calcsilicate xenoliths within the main zone in the far north of the limb as a platreef style mineralisation the platreef ss has a strike extent of 30 km whereas platreef style mineralisation occurs over a strike length of 110 km the platreef varies from 400 m thick in the s to 30 modal in some intersections these are dominated by pyrrhotite with lesser pentlandite and chalcopyrite minor pyrite and traces of a wide compositional range of sulphides in the southern sector mineralised zones have cu grades of 0 1 0 25 and ni 0 15 0 36 massive sulphides are localised commonly but not exclusively towards the contact with footwall metasedimentary rocks magmatic sulphides are disseminated or net textured ranging from a few microns to 2 cm grains of pyrrhotite and pentlandite with chalcopyrite and minor pyrite much of the sulphide is associated with intergranular plagioclase or quartz feldspar symplectites along the margins of rounded cumulus orthopyroxenes the pges in the southern sector occur as tellurides bismuthides arsenides antimonides bismuthoantimonides and complex bismuthotellurides pgm are rarely included in the sulphides but occur as micron sized satellite grains around interstitial sulphides and within alteration assemblages in serpentinised zones the pt pd ratio 1 and pge grade may be decoupled from s and base metal abundance

differentiation and compaction in the skaergaard intrusion igneous differentiation processes are constrained from bulk compositions densities and mineral modes of 116 cumulate gabbro samples in a new reference profile through the layered series of the skaergaard intrusion east greenland the stratigraphic distribution of p u and rb in cumulates and residual magma modeled by rayleigh fractionation constrains the final porosities or trapped liquid contents to 30 52 in lza troctolites decreasing to 4 12 at the top of lzb olivine gabbros and remaining low 1 13 4 middle dot 6 on average in the oxide gabbros of lzc mz and uz local variations in trapped liquid content are associated with modal layering leucocratic low density rocks have higher proportions of trapped melt than adjacent melanocratic high density rocks these observations are explained by varying degrees of compaction compaction was most important after the onset of fe ti oxide crystallization because of the high densities of the crystal matrix here computed rates of compaction exceed the rate of crystal accumulation in layers that are metres to a few tens of metres thick in the basal section lza the crystal pile was too thin and the density of the crystal matrix too low to drive the rate of compaction above the high rate of crystal accumulation promoted by initial cooling through the intrusion floor in the overlying section lzb the efficiency of compaction gradually increased as a result of thickening of the crystal pile and lowering of the rate of crystal accumulation the modeling constrains the p2o5 content of the residual magma to 1 middle dot 7 wt at the level of apatite in suggesting that the magma contained 49 wt sio2 and followed a trend of iron enrichment compaction of the uppermost metres to tens of metres of crystal mush at the top of the cumulate pile was an efficient means of differentiation and resulted in layers with variable final porosities and trace element contents depending on the mineralogy and density of the crystal matrix

determination of total ice volume and ice thickness distribution of two glaciers in the hohe tauern region eastern alps from gpr data global warming is causing an apparent rapid retreat of many glaciers worldwide in addition to mass balance investigation the determination and monitoring of total glacial ice volume and ice thickness distribution are important parameters for understanding the interactions between climate and the complex glacier system because of spatially irregular and sparse datasets scaling of volume and ice thickness distribution is often a challenging problem this study focuses on two small 100 m were identified in the data the acquired gpr data are irregularly distributed and the spatial density is too low to calculate reasonable bedrock topography with standard interpolation approaches thus one main focus of this study was to develop an appropriate interpolation technique eventually kriging technique and a glacial mechanically based interpolation parameter were used mean calculated ice thicknesses for the two investigated glaciers are 40 50 m with a maximum of 150 165 m no direct validation data are available so different considerations support the computed bedrock topography

crustally contaminated komatiite primary source of the chromitites and marginal lower and critical zone magmas in a staging chamber beneath the bushveld complex in the lowermost rocks of the rustenburg layered suite bushveld complex levels of total cr 2 o 3 are up to ten times higher than its putative solubility 0 16 cr 2 o 3 in the magmas that many investigators have accepted as parental to the dunites harzburgites pyroxenites and norites of the lower lower critical and upper critical zones various existing models fail to explain this chromium paradox in so far as they may explain why chromite is precipitated but do not account for its abundance in many cumulates simple mixing calculations and quantitative adiabat 1ph runs support our model in which a heterogeneous liquid crystals system was evolved in a staging chamber beneath the complex by mixing of komatiitic melts with 20 to 30 of crustal melts at depths appropriate to pressures between 10 and 4 5 kbars we contend that crystal settling and the effects of elutriation during magma ascent had generated a high sio 2 cap with modal olivine orthopyroxene and chromite increasing with depth in the staging chamber the magma from the high sio 2 cap of the staging chamber was first injected into the largely sedimentary transvaal supergroup generating what is now termed the marginal zone slurries of crystals plus liquid from the spasmodically rejuvenated main body of the staging chamber were then injected into the shallower bushveld chamber to form the lower and critical zones chromite within the slurries introduced in this way could account for their high gross cr content frequent reversals of normal evolutionary trends evident in the cumulates are attributable to the episodic nature of the influxes from the staging chamber the lithologically diverse nature of the floors upon which the chromitite layers accumulated peridotites pyroxenites norites and anorthosites was therefore more a function of the timing of emplacement of the cr rich slurries generated in the deeper reservoir than of specific evolutionary processes within the bushveld chamber itself

on the errors involved in ice thickness estimates iii error in volume this paper is the third paper iii in a set of studies of the errors involved in the estimate of ice thickness and ice volume here we present a methodology to estimate the error in the calculation of the volume of an ice mass from an ice thickness dem we consider the two main error sources the ice thickness error at each dem grid point and the uncertainty in the boundary delineation to accurately estimate the volume error due to the error in thickness of the dem it is crucial to determine the degree of correlation among the ice thickness errors at the grid points we find that the two dimensional integral range which represents the equivalent area of influence of each independent value allows estimation of the equivalent number of independent values of error within the dem hence it provides an easy way to obtain the volume error resulting from the uncertainty in ice thickness of a dem we show that the volume error arising from the uncertainty in boundary delineation often neglected in the literature can be of the same order of magnitude as the volume error resulting from ice thickness errors we illustrate our methodology through the case study of werenskioldbreen svalbard

geochemistry and mineralogy of the platreef and critical zone of the northern lobe of the bushveld complex south africa implications for bushveld stratigraphy and the development of pge mineralisation the northern lobe of the bushveld complex is currently a highly active area for platinum group element pge exploration this lobe hosts the platreef a 10 300 m thick package of pge rich pyroxenites and gabbros that crops out along the base of the lobe to the north of mokopane formerly potgietersrus and is amenable to large scale open pit mining along some portions of its strike an early account of the geology of the deposit was produced by percy wagner where he suggested that the platreef was an equivalent pge rich layer to the merensky reef that had already been traced throughout the eastern and western lobes of the bushveld complex wagner s opinion remains widely held and is central to current orthodoxy on the stratigraphy of the northern lobe this correlates the platreef and an associated cumulate sequence that includes a chromitite layer known as the grasvally norite pyroxenite anorthosite gnpa member directly with the sequence between the ug2 chromitite and the merensky reef as it is developed in the upper critical zone of the eastern and western bushveld implicit in this view of the magmatic stratigraphy is that similar critical zone magma was present in all three lobes prior to the development of the merensky reef and the platreef however when this assumed correlation is examined in detail it is obvious that there are significant differences in lithologies mineral textures and chemistries mg of orthopyroxene and olivine and the geochemistry of both rare earth elements ree and pge between the two sequences this suggests that the prevailing interpretation of the stratigraphy of the northern lobe is not correct the critical zone of the northern lobe cannot be correlated with the critical zone in the rest of the complex and the simplest explanation is that the gnpa platreef sequence formed from a separate magma or mixture of magmas chilled margins of the gnpa member match the estimated initial composition of tholeiitic main zone type magma rather than a critical zone magma composition where the gnpa member is developed over the ultramafic lower zone hybrid rocks preserve evidence for mixing between new tholeiitic magma and existing ultramafic liquid this style of interaction and the resulting rock sequences are unique to the northern lobe the gnpa member contains at least seven sulphide rich horizons with elevated pge concentrations some of these are hosted by pyroxenites with similar mineralogy crystallisation sequences and pd rich pge signatures to the platreef chill zones are preserved in the lowest main zone rocks above the gnpa member and the platreef and this suggests that both units were terminated by a new influx of main zone magma this opens the possibility that the platreef and gnpa member merge laterally into one another and that both formed in a series of mixing quenching events involving tholeiitic and ultramafic magmas prior to the main influx of tholeiitic magma that formed the main zone

mapping subglacial surfaces of temperate valley glaciers by two pass migration of a radio echo sounding survey high resolution maps of the glacier bed are developed through a pseudo three dimensional migration of dense array of radio echo sounding profiles resolution of three dimensional maps of subglacial surfaces is determined by the radio echo sounding wavelength data spacing in the field and migration based on synthetic radio echo sounding profile experiments the maximum resolution of the final map cannot exceed one half wavelength a methodology of field and processing techniques is outlined to develop a maximum resolution map of the glacier bed the field and processing techniques are used to develop a map of the glacier bed below part of worthington glacier a temperate valley glacier in south central alaska the field techniques and the processing steps used on the glacier result in a map of 20 m 20 m resolution

origin of anorthosite and magnetitite layers in the bushveld complex constrained by major element compositions of plagioclase the bushveld complex a layered mafic intrusion in south africa shows extreme vertical differentiation in terms of mineral compositions and modal proportions from dunite to ferrodiorite in a continuous borehole core drilled through the uppermost 2 8k m of the intrusion typical rocks range upwards from troctolite through gabbronorite and ferrogabbronorite to ferrodiorite with extreme examples of anorthosite magnetitite and feldspathic pyroxenite the an content of plagioclase has previously been determined for 420 samples and decreases upward from an78 to an36 with six minor slow reversals variations in modal proportions of plagioclase have been calculated based on 2200 density determinations on whole rocks forty five anorthosite layers have been identified ranging from 1 to 23 m thick none of these layers is associated with the abovementioned reversals in an content in plagioclase and nearly all have leucocratic rocks below and above with more than the likely cotectic proportions of plagioclase these observations argue against an origin for anorthosite related to magma addition or to supersaturation and oscillatory nucleation rhythmically pulsed crystallization possibly associated with pressure changes followed by crystal settling and sorting of minerals of different densities is a hypothesis consistent with all the observations twenty layers of magnetitite have been identified there is a significant reversal in an content in the overlying plagioclase compared with the underlying sample across only one such layer again this observation challenges hypotheses that such layers result from magma addition but is consistent with a pressure change hypothesis for triggering magnetite crystallization the upper contacts of magnetitite layers that grade into anorthosite over many centimetres possibly also reflect settling and sorting rocks forming the uppermost 100 m of the intrusion contain the most sodic plagioclase compositions demonstrating that there is no downward crystallizing roof facies furthermore this uppermost 100 m section is depleted in plagioclase relative to its cotectic proportions hence we find no evidence supporting flotation or prolonged suspension of plagioclase

ground penetrating radar measurements of 64 austrian glaciers between 1995 and 2010 the ongoing retreat of mountain glaciers necessitates the development of future scenarios of glacier runoff these scenarios are not only governed by future climate scenarios influencing glacier mass balance but also by the glacier volumes which are subject to melt ground penetrating radar gpr is a valuable tool for measuring the thickness of mountain glaciers although ground based measurements are labour intensive so not all glaciers can be surveyed this study presents the results of gpr surveys on 64 alpine glaciers carried out between 1995 and 2010 the glacier areas range from 0 001 to 18 4 km 2 and their ice thickness was surveyed with an average density of 36 points km 2 t he point measurements were extrapolated manually to derive volume maps the mean ice thickness varies between 10 and 92 m the maximum ice thickness is about three times the mean thickness according to the glacier state recorded in the second glacier inventory the 64 glaciers cover an area of 223 3 3 6 km 2 with a mean thickness of 50 3 m and a glacier volume of 11 9 1 1 km 3 the mean maximum ice thickness is 119 5m

mercury in the bushveld complex south africa and the skaergaard intrusion greenland abstract we present mercury concentrations for layered mafic rocks of the bushveld complex the skaergaard intrusion morb and a karoo dolerite sill as determined by combustion atomic absorption spectroscopy combustion aas with gold amalgamation pre concentration mercury in the bushveld complex and the skaergaard intrusion is generally low with about 1 1 and 0 8 ppb hg on average respectively the karoo dolerite sill chill margins and morb have average hg concentrations of 2 5 and 6 4 ppb respectively the reason for the low whole rock hg concentrations in layered mafic intrusions is that the element is incompatible with respect to the cumulus mineral assemblages our results show far lower hg concentrations for the skaergaard cumulates than previous measurements and we find no evidence for preferential enrichment in plagioclase rich rocks as previously reported we attribute this difference to inaccurate analytical methodology of the early measurements there are hg enrichments in distinct levels in both intrusions mercury enrichments in the bushveld complex are observed near the top of the lower zone 2 4 ppb in the merensky reef at 8 6 ppb the platreef at 3 ppb average and in the upper zone near the main magnetitite layer 4 7 ppb these enrichments are due to the concentration of hg by sulfides as suggested by a positive correlation between cu and hg there is no upward increase in hg with stratigraphic height or positive correlation between hg and zr in the bushveld complex as would be expected if hg acted as an immobile incompatible element the lack of correlation is explained by periodic degassing of the bushveld magma chamber in which volatile elements including hg and s escaped in contrast the skaergaard intrusion probably did not degas and there is hg enrichment in the sandwich horizon 53 ppb because of the combination of the incompatibility and the presence of sulfides

precession driven monsoonal activity controlled the development of the early albian paquier oceanic anoxic event oae1b evidence from the vocontian basin se france abstract in the vocontian basin in southeastern france the aptian albian boundary is marked by the occurrence of four laminated black shales jacob kilian paquier leenhardt corresponding to oceanic anoxic event 1b oae1b equivalents of one or more of these intervals are also known from different regions in the tethys atlantic and pacific and correspond in time to major climatic and evolutionary perturbations here we performed an integrated multi proxy high resolution study on the section at l arboudeysse in the northwestern part of the vocontian basin including mineralogical whole rock and clay minerals and geochemical carbon and oxygen isotopes organic matter major and trace elements mercury contents analyses the aim of this study is to reconstruct the level of productivity and related state of oxygenation in addition to the weathering coditions on the adjacent continent during the paquier event modest enrichments in redox sensitive trace elements rste mo as v u ni associated with moderate total organic carbon contents between 0 57 and 5 52 wt indicate the development of suboxic anoxic conditions during deposition of the paquier level the strong enrichment of mo 10 229 relative to other rste

landsat based inventory of glaciers in western canada 1985 2005 abstract we report on a glacier inventory for the canadian cordillera south of 60 n across the two western provinces of british columbia and alberta containing 30 000 km2 of glacierized terrain our semi automated method extracted glacier extents from landsat thematic mapper tm scenes for 2005 and 2000 using a band ratio tm3 tm5 we compared these extents with glacier cover for the mid 1980s from high altitude aerial photography for british columbia and from landsat tm imagery for alberta a 25 m digital elevation model dem helped to identify debris covered ice and to split the glaciers into their respective drainage basins the estimated mapping errors are 3 4 and arise primarily from seasonal snow cover glaciers in british columbia and alberta respectively lost 10 8 3 8 and 25 4 4 1 of their area over the period 1985 2005 the region wide annual shrinkage rate of 0 55 a 1 is comparable to rates reported for other mountain ranges in the late twentieth century least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover the highest relative ice loss in british columbia 24 0 4 6 occurred in the northern interior ranges while glaciers in the northern coast mountains declined least 7 7 3 4

radio echo sounding and ice volume estimates of western nordenskiold land glaciers svalbard as part of ongoing work to obtain a reliable estimate of the total ice volume of svalbard glaciers and their potential contribution to sea level rise we present here volume calculations with detailed error estimates for ten glaciers on western nordenskiold land central spitsbergen svalbard the volume estimates are based upon a dense net of gpr retrieved ice thickness data collected over several field campaigns spanning the period 1999 2012 the total area and volume of the ensemble are 116 06 4 53 km 2 and 10 439 0 373 km 3 respectively while the individual areas volumes and average ice thickness lie within 2 6 50 4 km 2 0 08 5 54 km 3 and 29 108 m respectively volume area scaling relationships overestimate the total volume of these glaciers by up to 35 with respect to our calculation on the basis of the pattern of scattering in the radargrams we also analyse the hydrothermal structure of these glaciers nine of the ten are polythermal while only one is entirely cold

effect of intense weathering and postdepositional degradation of organic matter on hg toc proxy in organic rich sediments and its implicationsfor deep time investigations

mercury anomalies volcanic pulses and drowning episodes along the northern tethyan margin during the latest hauterivian earliest aptian abstract the latest hauterivian earliest aptian time interval includes three episodes of significant environmental change faraoni late early barremian and taxy episodes this time interval appears to partially overlap with large scale volcanic activity related to the tristan da cunha plume along the rio grande rise high arctic large igneous province volcanism and the early phase in the formation of the greater ontong java lip in the pacific the establishment of exact temporal relationships between volcanic activity and environmental change remains however a major challenge due to the scarcity of numerical ages for the early cretaceous we report mercury hg contents in uppermost hauterivian lowermost aptian marl limestone alternations from seven sections along a n s transect in the western tethys the hg contents in marl samples display rather scattered records which are generally well correlated with the total organic carbon toc records in associated limestone beds five distinct spikes in hg concentrations occur in three intervals latest hauterivian early barremian and latest barremian the small amounts of organic matter

a three dimensional calving model numerical experiments on johnsons glacier livingston island antarctica calving from tidewater glaciers and ice shelves accounts for around half the mass loss from both polar ice sheets yet the process is not well represented in prognostic models of ice dynamics benn and others proposed a calving criterion appropriate for both grounded and floating glacier tongues or ice shelves based on the penetration depth of transverse crevasses near the calving front computed using nye s formula the criterion is readily incorporated into glacier and ice sheet models but has not been fully validated with observations we apply a three dimensional extension of benn and others criterion incorporated into a full stokes model of glacier dynamics to estimate the current position of the calving front of johnsons glacier antarctica we find that two improvements to the original model are necessary to accurately reproduce the observed calving front 1 computation of the tensile deviatoric stress opening the crevasse using the full stress solution and 2 consideration of such a tensile stress as a function of depth our modelling results also suggest that johnsons glacier has a polythermal structure rather than the temperate structure suggested by earlier studies

cyclicity in the main and upper zones of the bushveld complex south africa crystallization from a zoned magma sheet the major element composition of plagioclase pyroxene olivine and magnetite and whole rock sr sr data are presented for the uppermost 2 1 km of the layered mafic rocks upper main zone and upper zone at bierkraal in the western bushveld complex initial sr sr ratios are near constant 0 7073 0 0001 for 24 samples and imply crystallization from a homogeneous magma sheet without major magma recharge or assimilation the 2125 m thick section investigated in drill core comprises 26 magnetitite and six nelsonite magnetite ilmenite apatite layers and changes up section from gabbronorite an72 plagioclase mg 74 clinopyroxene to magnetite ilmenite apatite fayalite ferrodiorite an43 mg 5 clinopyroxene fo1 olivine the overall fractionation trend is however interrupted by reversals characterized by higher an of plagioclase higher mg of pyroxene and olivine and higher v2o5 of magnetite in the upper half of the succession there is also the intermittent presence of cumulus olivine and apatite these reversals in normal fractionation trends define the bases of at least nine major cycles we have calculated a plausible composition for the magma from which this entire succession formed forward fractional crystallization modeling of this composition predicts an initial increase in total iron near constant sio2 and an increasing density of the residual magma before magnetite crystallizes after magnetite begins to crystallize the residual magma shows a nearconstant total iron an increase in sio2 and decrease in density we explain the observed cyclicity by bottom crystallization initially magma stratification developed during crystallization of the basal gabbronorites once magnetite began to crystallize periodic density inversion led to mixing with the overlying magma layer producing mineralogical breaks between fractionation cycles the magnetitite and nelsonite layers mainly occur within fractionation cycles not at their bases in at least two cases crystallization of thick magnetitite layers may have lowered the density of the basal layer of melt dramatically and triggered the proposed density inversion resulting in close but not perfect coincidence of mineralogical breaks and packages of magnetitite layers

correlation between chromite composition and pge mineralization in the critical zone of the western bushveld complex detailed mineralogical investigations of chromite in the lower and critical zones in the northwestern sector of the bushveld complex have revealed significant compositional variations with regard to modal proportions host rock lithology and stratigraphic height superimposed on these variations are long range systematic trends in the composition of chromite in the massive layers these long range trends are closely linked with the evolution of the silicate cumulates the massive chromitite layers are divided into two types type 1 comprises the chromitites hosted entirely within ultramafic cumulates while type 2 chromitites are within cyclic units in which plagioclase cumulates occur the types are also distinguishable by their respective contents of platinum group elements pges and distribution patterns thereof viz the ratios between ru os ir and pt pd rh or relative element proportions both of which display a systematic change with height in accordance with chromite composition the relation between silicate geochemistry chromite composition and pge tenor leads to the development of a model explaining the formation of pge mineralized sulphide poor chromitite layers in the critical zone of the bushveld complex

a mass conservation approach for mapping glacier ice thickness the traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging while this approach provides continuous maps of ice thickness it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations we apply this approach to the case of nioghalvfjerdsfjorden 79north glacier a major outlet glacier in northeast greenland that has been relatively stable in recent decades the results show that our mass conserving method removes the anomalies in mass flux divergence yields interpolated data that are within about 5 of the original data and produces thickness maps that are directly usable in high spatial resolution high order ice flow models we discuss the application of this method to the broad and detailed radar surveys of ice sheet and glacier thickness copyright 2011 by the american geophysical union

incompatible trace element behavior in the bushveld complex borehole core from the uppermost 500 m of the rustenburg layered suite of the bushveld complex has been analyzed for rb sr zr y and nb plots of absolute trace element abundance and trace element ratios against stratigraphic height are presented these are used to test for multiple injection of magma and postcumulus migration of residual liquid these and previously published data are used to support the hypotheses that there was a new injection of magma above the merensky reef and that large scale infiltration metasomatism did not occur no evidence from incompatible element data exists for an addition of magma near the pyroxenite marker where a distinct reversal in cumulus mineral composition occurs however this may be the result of relatively small degrees of fractionation of the host magma prior to the addition of new magma the ability to recognize the entry of new magma may be restricted by the analytical precision the uppermost 500 m of the layered sequence appears to behave as a single broadly homogeneous magma in showing a systematic predictable upward increase in incompatible element abundances consistent with a model assuming 10 to 30 percent trapped liquid in the cumulate deviations from the predicted trends for zr y and nb are attributed to these elements being compatible in magnetite for zr and apatite for y and nb which are present in the uppermost rocks

high resolution bed topography mapping of russell glacier greenland inferred from operation icebridge data detailed maps of bed elevation and ice thickness are essential for understanding and projecting the evolution of the ice sheets such maps are traditionally obtained using airborne radarsounding profiler data interpolated onto regular grids using geostatistical tools such as kriging here we compare three mapping techniques applied to a dense radar survey of russell glacier west greenland by nasa operation icebridge 1 radar tomography rt processing of the radar data to map the bed elevation 2 interpolation of radar derived thickness by ordinary kriging kr and 3 reconstruction of ice thickness based on the principles of mass conservation mc combining radar sounding profiler and ice motion data rt eliminates ambiguities caused by off nadir reflections but is spatially limited kr yields a standard error in bed elevation of 35 m but large errors 300m a 1 in flux divergence when combined with ice motion data mc yields a comparable performance in bed elevation mapping and errors smaller than 1m a 1 in flux divergence when the number of radar sounding tracks is reduced the performance of kr decreases more rapidly than for mc our study site shows that mc is capable of maintaining precision levels of 60m at 400m posting with flight tracks separated by 5 km 2014 publishing technology

pressure fluctuations and the formation of the pge rich merensky and chromitite reefs bushveld complex the merensky reef and the underlying upper group 2 chromitite layer in the critical zone of the bushveld complex host much of the world s platinum group element pge mineralization the genesis is still debated a number of features of the merensky reef are not consistent with the hypotheses involving mixing of magmas uniform mixing between two magmas over an area of 150 by 300 km and a thickness of 3 30 km seems implausible the merensky reef occurs at the interval where main zone magma is added but the relative proportions of the pge in the merensky reef are comparable to those of the critical zone magma mineral and isotopic evidence in certain profiles through the merensky unit suggest either mixing of minerals not magmas and in one case the lack of any chemical evidence for the presence of the second magma the absence of cumulus sulphides immediately above the merensky reef is not predicted by this model an alternative model is proposed here that depends upon pressure changes not chemical processes to produce the mineralization in chromite rich and sulphide rich reefs magma was added at these levels but did not mix this addition caused a temporary increase in the pressure in the extant critical zone magma immiscible sulphide liquid and or chromite formed sinking sulphide liquid and or chromite scavenged pge as clusters nanoparticles or platinum group minerals from the magma and accumulated at the floor rupturing of the roof resulted in a pressure decrease and a return to sulphur undersaturation of the magma

mercury anomaly deccan volcanism and the end cretaceous mass extinction reply the contribution of the deccan traps west central india volcanism in the cretaceous paleogene kpg crisis is still a matter of debate recent u pb dating of zircons interbedded within the deccan lava flows indicate that the main eruptive phase 1 1 106 km3 of basalts initiated 250 k y before and ended 500 k y after the kpg boundary however the global geochemical effects of deccan volcanism in the marine sedimentary record are still poorly resolved here we investigate the mercury hg content of the bidart france section where an interval of low magnetic susceptibility ms located just below the kpg boundary was hypothesized to result from paleoenvironmental perturbations linked to the paroxysmal deccan phase 2 results show hg concentrations 2 orders of magnitude higher from 80 cm below to 50 cm above the kpg boundary maximum 46 6 ppb and coincident with the low ms interval increase in hg contents shows no correlation with clay or total organic carbon contents suggesting that the hg anomalies resulted from higher input of atmospheric hg species into the marine realm rather than organic matter scavenging and or increased runoff the hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera suggesting correlative changes in marine biodiversity this discovery represents an unprecedented piece of evidence of the nature and importance of the deccan related environmental changes at the onset of the kpg mass extinction

assessment of multispectral glacier mapping methods and derivation of glacier area changes 1978 2002 in the central southern alps new zealand from aster satellite data field survey and existing inventory data we have measured the glacier area changes in the central southern alps new zealand between 1978 and 2002 and have compiled the 2002 glacier outlines using an image scene from the advanced spaceborne thermal emission and reflection radiometer aster three automated classification methods were tested 1 band ratio 2 normalized difference snow index and 3 supervised classification the results were compared with the glacier outlines photo interpreted from the aster data and were further validated using gps aided field mapping of selected test glaciers the aster 3 4 band ratio provided the best results however all the classification methods failed to extract extensive debris covered parts of the glaciers therefore the photo interpreted 2002 outlines were used when comparing with the existing 1978 glacier inventory derived from aerial photographs our results show a 17 reduction of glacier area mainly driven by the retreat of the large valley glaciers despite the large climatic gradient from west to east glaciers on both sides of the main divide lost similar percentages of area except franz josef and fox glaciers which advanced smaller glaciers were found to have changed very little in the study period

ground penetrating radar measurements of debris thickness on lirung glacier nepal m m is funded by nerc dtp grant number ne l002507 1 receives case funding from reynolds international ltd and was provided travel support by the jesus college doctoral research fund i w was funded by the bb roberts fund university travel fund and st catharine s college research fund equipment gpr and dgps was provided under nerc geophysical equipment facility grant number 1014

the randolph glacier inventory a globally complete inventory of glaciers the randolph glacier inventory rgi is a globally complete collection of digital outlines of glaciers excluding the ice sheets developed to meet the needs of the fifth assessment of the intergovernmental panel on climate change for estimates of past and future mass balance the rgi was created with limited resources in a short period priority was given to completeness of coverage but a limited uniform set of attributes is attached to each of the 198 000 glaciers in its latest version 3 2 satellite imagery from 1999 2010 provided most of the outlines their total extent is estimated as 726 800 34 000 km 2 the uncertainty about 5 is derived from careful single glacier and basin scale uncertainty estimates and comparisons with inventories that were not sources for the rgi the main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover these errors appear not to be normally distributed and quantifying them reliably is an unsolved problem combined with digital elevation models the rgi glacier outlines yield hypsometries that can be com bined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers the rgi has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume and thus actual and potential contributions to sea level rise

platinum group element distribution in the main zone and upper zone of the bushveld complex south africa abstract the platinum group element pge contents of the upper portions of the bushveld complex were investigated with three questions in mind a in natural systems does magnetite concentrate os ir ru and rh ipge as has been observed in experimental systems b is there a au pd enriched layer present such as observed in the upper parts of the skaergaard intrusion c can changes in metal ratios be used for prospecting for pge deposits in the sulfide poor main magnetite layer of the eastern bushveld ir and rh are enriched relative to pt pd and au and this could be because magnetite preferentially concentrated ir and rh over pt pd and au however in most other magnetite layers no enrichment was observed this could be because most magnetite layers contain approximately 1 sulfides and the pge budget is dominated by the sulfides these sulfides obscured the effects of magnetite collecting ipge because sulfides collect all the pge and the partition coefficients for the pge into a sulfide liquid are much greater than the partition coefficient for ipge into magnetite the weighted average of the platinum group elements pge and au over the 2000 m of sampled stratigraphy is au 2 1 ppb pd 1 7 ppb pt 1 7 ppb rh 0 18 ppb ru comparison of the composition of the marginal rocks of the bushveld with a weighted average for the complete 6 km of the bushveld cumulates shows that the cumulate pile is much richer in compatible elements ir rh cr and poorer in incompatible elements sm and hf than the marginal rocks two possible solutions to this are a the magma emplaced into the chamber was a crystal mush and thus more mafic than marginal rocks to the intrusion or b fractionated magma has been removed from the cumulate sequence and either irrupted or intruded the country rocks as granites and granophyres

noble metal enrichment processes in the merensky reef bushveld complex we have analysed sulphides silicates and chromites of the merensky introduction reef for platinum group elements pges re and au using laser the enrichment of noble metals in layered gabbroic ablation inductively coupled plasma mass spectrometry and synthetic intrusions to form stratiform merensky type ore horizons pyrrhotite standards annealed with known quantities of noble metals is an extremely efficient yet poorly understood process os ir and ru reside in solid solution in pyrrhotite and pentlandite metal enrichment must be related to the formation of rh and part of the reef s pd in pentlandite whereas pt au re magmatic layering as the ore horizons form an integral and some pd form discrete phases olivine and chromite often part of the magmatic stratigraphies of their host insuspected to carry os ir and ru are pge free all phases analysed trusions metal concentration is also related to the prescontain noble metals as discrete micro inclusions with diameters ence of magmatic sulphides because the noble metals are either dissolved in base metal sulphides or occur as typically 100 nm inclusions in sulphides commonly have the discrete noble mineral phases intergrown with sulphides element combinations os ir pt and pt pd au inclusions in vermaak hendriks 1976 ballhaus ryan 1995 olivine and chromite are dominated by pt au pd few inclusion ballhaus ulmer 1995 spectra can be related to discrete noble metal phases and few there is considerable controversy as to where the inclusions have formed by sub solidus exsolution rather some metals came from and how metal enrichment worked pge inclusions notably those in olivine and chromite are earlyfor a stratiform platinum group element pge deposit magmatic nuggets trapped when their host phases crystallized we inside the magmatic stratigraphy of a layered intrusion suggest that the silicate melt layer that preceded the merensky reef there are two possibilities either the metals were derived was pge oversaturated at early cumulus times experiments from the melt column above the ore horizon or they came combined with available sulphide silicate partition coefficients sugfrom the magma equivalent to the cumulate package gest that a silicate melt in equilibrium with a sulphide melt underlying the ore owing to the large density contrast containing the pge spectrum of the merensky ore would indeed be between silicate and sulphide melt a popular view is that oversaturated with respect to the least soluble noble metals sulphide the metals were enriched by gravitational settling of melt apparently played little role in enriching the noble metals in sulphide melt i e out of the magma column above the the merensky reef rather its role was to immobilize a pre existing ore campbell et al 1983 barnes naldrett 1985 in situ stratiform pge anomaly in the liquid stratified magma naldrett et al 1987 on the other hand it is well chamber established that gravitational crystal settling plays little role in producing magmatic layering and magmatic stratigraphies mcbirney noyes 1979 morse 1986 campbell 1987 and this cannot remain without consequence for stratiform noble metal deposits a third alternative is noble metal enrichment by late

a method to estimate the ice volume and ice thickness distribution of alpine glaciers sound knowledge of the ice volume and ice thickness distribution of a glacier is essential for many glaciological applications however direct measurements of ice thickness are laborious not feasible everywhere and necessarily restricted to a small number of glaciers in this paper we present a method to estimate the ice thickness distribution and the total ice volume of alpine glaciers this method is based on glacier mass turnover and principles of ice flow mechanics the required input data are the glacier surface topography the glacier outline and a set of borders delineating different ice flow catchments three parameters describe the distribution of the apparent mass balance which is defined as the difference between the glacier surface mass balance and the rate of ice thickness change and two parameters define the ice flow dynamics the method was developed and validated on four alpine glaciers located in switzerland for which the bedrock topography is partially known from radio echo soundings the ice thickness along 82 cross profiles can be reproduced with an average deviation of about 25 between the calculated and the measured ice thickness the cross sectional areas differ by less than 20 on average this shows the potential of the method for estimating the ice thickness distribution of alpine glaciers without the use of direct measurements

cr and sr keys to parental magmas and processes in the bushveld complex south africa abstract large layered intrusions are almost certainly periodically replenished during their protracted cooling and crystallization the exact composition s of the replenishing magma s in the case of the bushveld complex south africa has been debated mainly on the basis of major element composition and likely crystallization sequences the intrusion is dominated by orthopyroxene and plagioclase and so their cr and sr contents and likely partition coefficient values can be used to re investigate the appropriateness of the various proposed parental magmas one magma type with about 12 mgo 1000 ppm cr and 180 ppm sr can explain the genesis of the entire lower and critical zones a number of other magma compositions proposed to produce the critical zone fail to match these trace element constraints by being too poor in cr a fundamentally different magma type was added at the base of the main zone but none of the proposed compositions is consistent with the trace element requirements specifically the cr contents are higher than predicted from pyroxene compositions a further geological constraint is demonstrated from a consideration of the cr budget at this level there is an abrupt decrease from about 0 4 to 0 1 cr 2 o 3 in orthopyroxene across this critical zone main zone transition no realistic proportions of mixing between the residual magma at the top of the critical zone and any proposed added magma composition can have produced a composition that could have crystallized these low cr orthopyroxenes instead it is suggested that the resident magma from the upper critical zone was expelled from the chamber possibly as sills into the country rocks during influx of a dense differentiated magma near the level of the pyroxenite marker in the main zone there is further addition of a ferrobasaltic magma with 6 mgo 111 ppm cr and 350 ppm sr that is consistent with the geochemical requirements

an overview of the pge concentrations in the shetland ophiolite complex extremely anomalous platinum group element pge concentrations are known at one site cliff in the shetland ophiolite complex systematic pge analysis of all the mafic and ultramafic igneous and alteration lithologies in the ophiolite has revealed many lower grade anomalous pge occurrences throughout the cumulate ultramafic sequence and their distribution is described here more sites with pge enrichments as anomalous as those at cliff have not been found at cliff the anomalous values of over 60 ppm pt pd are restricted to a chromite rich sulphide bearing dunite forming a small part of a 200 m dunite lens in mantle harzburgite close to the basal thrust of the ophiolite lower values of up to 6 4 ppm pt pd occur in chromite poor sulphide rich dunites also within this dunite lens the only other chromite rich dunite lens in the cliff area also has detected pt and pd but with low pt pd values of 200 ppb in contrast harzburgites metasediments underlying the basal thrust serpentinites from the basal thrust and internal faults are all barren of pt and pd detection limit 20 ppb in the cliff area therefore detected pge values are restricted to magmatic chromite rich dunite lenses pge analyses of drill core from beneath the disused chromite quarries at cliff are low 227 ppb pt pd indicating that the extremely anomalous pge values are very restricted this supports the idea that pge concentrated magmatically within the dunite lens at cliff may have been remobilized locally to produce extremely anomalous pge values in an alteration zone only a few metres in diameter elsewhere in the ophiolite anomalous pt pd values of up to 4 ppm occur in chromite rich sulphide bearing dunite within the dunite unit which stratigraphically overlies the harzburgite pt pd concentrations of up to 1 ppm are present in the pyroxenites and wehrlites of the upper part of the ultramafic sequences high level wehrlites and pyroxenites within the gabbro unit representing late ultramafic differentiates contain lower levels of pge of up to 310 ppb pt pd the gabbros all have less than 20 ppb pt and pd this distribution indicates that the pge concentrations occur in specific primary magmatic lithologies and pathfinder analysis shows that they are associated with ni cu au and cr pge have not been found above detection limits in fault zones away from primary pge mineralization sites and it is concluded that pge are not significantly hydrothermally reconcentrated at cliff remobilization may have occurred over short distances of only a few metres at most

calculation of glacier volume from sparse ice thickness data applied to schaufelferner austria in order to develop and evaluate a method for the determination of glacier volume from ice thickness data the volume of schaufelferner austria is calculated 1 by manual interpolation of ground penetrating radar gpr data based on measurements at 36 locations in 1995 2 by manual interpolation of 144 gpr measurements acquired for a higher resolution estimate in 2003 and 2006 3 by multiplying the mean of the measured ice thickness data by the glacier area 4 by automatic kriging of the 1995 gpr data and 5 by application of area volume scaling algorithms to the austrian glacier inventory data of 1969 1997 and 2006 the so determined glacier volumes are compared with the ice volume changes calculated from digital elevation models dems of the austrian glacier inventories the manually interpolated volumes based on the 1995 and 2003 06 gpr data yielded a volume loss only slightly different from volume loss calculated from the glacier inventories of 1997 and 2007 other methods were not able to reproduce the volume losses of the glacier inventory dems to assess the accuracy of deriving ice thickness changes with gpr repeated ice thickness measurements at the same locations were carried out between 2005 and 2008

synchronous acceleration of ice loss and glacial erosion glaciar marinelli chilean tierra del fuego to contribute to the understanding of the influence of climate on glacial erosion and on orogenic processes we report contemporary glacial erosion rates from a calving glacier in the southern andes and elucidate the influence of ice dynamics on erosion using seismic profiles of sediments collected in a proglacial fjord and a documented history of retreat we determine the time varying sediment flux of glaciar marinelli as a measure of basin wide erosion rates and compare these rates with the annual ice budget reconstructed using ncep ncar reanalysis climate data from 1950 to 2005 the rate of erosion of the largest tidewater glacier in tierra del fuego averaged 39 16 mm a 1 during the latter half of the 20th century with an annual maximum approaching 130 mm a 1 following a decade of rapid retreat a strong correlation emerges between the variable rate of ice delivery to the terminus and the erosion rate providing quantitative insight into the relationship between ice fluxes and glacial erosion rates for glaciar marinelli as for other calving glaciers for which suitable data exist the marked retreat and thinning over the past 50 years have resulted in a period of accelerated basal sliding and unusually rapid erosion

are bushveld u type parent magmas boninites or contaminated komatiites three distinct categories of magmas bushveld u type parent magmas boninites and siliceous high magnesium basalts from archaean greenstone belts share the distictive geochemical characteristics of high mgo 9 19 low tio2 less than 1 and high sio2 greater than 52 boninites are generally thought to form by hydrous melting of metasomatized previously depleted upper mantle while siliceous high magnesium basalts shmb in greenstone belts have recently been recognized as the products of combined fractionation and crustal contamination of komatiites both these mechanisms can apparently give rise to similar end products and both mechanisms have been proposed for the petrogenesis of bushveld u type magmas

trace element and platinum group element distributions and the genesis of the merensky reef western bushveld complex south africa the merensky reef of the bushveld complex is one of the world s largest resources of platinum group elements pge however mechanisms for its formation remain poorly understood and many contradictory theories have been proposed we present precise compositional data major elements trace elements and platinum group elements pge for 370 samples from four borehole core sections of the merensky reef in one area of the western bushveld complex trace element patterns incompatible elements and rare earth elements exhibit systematic variations including small scale cyclic changes indicative of the presence of cumulus crystals and intercumulus liquid derived from different magmas ratios of highly incompatible elements for the different sections are intermediate to those of the proposed parental magmas critical zone and main zone types that gave rise to the bushveld complex mingling but not complete mixing of different magmas is suggested to have occurred during the formation of the merensky reef the trace element patterns are indicative of transient associations between distinct magma layers the porosity of the cumulates is shown to affect significantly the distribution of sulphides and pge a genetic link is made between the thickness of the merensky pyroxenite the total pge and sulphide content petrological and textural features and the trace element signatures in the sections studied the rare earth elements reveal the important role of plagioclase in the formation of the merensky pyroxenite and the distribution of sulphide

postmagmatic sulphur loss in the skaergaard intrusion implications for the formation of the platinova reef abstract the stratabound platinova au pd reef in the skaergaard intrusion is intimately linked to cu fe sulphide minerals and occurs at a level that shows changes in the sulphur concentration and the cu s ratio these features suggest that the reef is related to silicate sulphide liquid immiscibility in the skaergaard magma however although the evidence is strong present day sulphur concentrations are too low to support such a model the detailed knowledge of the shape volume and compositional relations of the skaergaard lithologies allows for numerical modeling of sulphur and copper concentrations during fractionation of the magma these data can be evaluated with the current models for sulphur saturation in iron rich mafic magmas to assess the original sulphur concentrations the extent of fractionation the composition of sulphide liquids and the extent of postmagmatic sulphur loss mass balance modeling yields initial copper and sulphur concentrations of 250 and 894 ppm for the parental magma to the lower zone a prior to sulphur saturation cu behaves as an incompatible element with a bulk partition coefficient in the cumulus material dcumuluscu of 0 13 indicating some incorporation of cu into mafic silicates probably augite sulphur can be assumed to be perfectly incompatible in the cumulus minerals although it will be included as a component of the interstitial liquid these values yield sulphur saturation at around 635 ppm cu and 2607 ppm s assuming the sulphur to originally be present as a mixture of monosulphide mss and intermediate solid solution sulphide iss the primary sulphides in the cumulates would amount to 0 07 modal through lower and middle zones and 0 53 modal on average through upper zone the expected weight proportion of primary chalcopyrite pyrrhotite evolves from 30 70 at the base of lza through 26 74 at the level of the platinova reef to 18 82 at the sandwich horizon the present day bornite magnetite mineral assemblage is likely to have been derived from a primary pyrrhotite chalcopyrite assemblage through reequilibration and postmagmatic oxidation significant sulphur appears to have been lost from the lower and middle parts of the layered series lower zone a to upper zone b whereas the sulphides of the upper zone c can be explained in the context of a sulphur gain local scale reequilibration of cu from mafic silicates into sulphides may have contributed to the sulphide mineralogy of the lower and middle zones the structure of the platinova reef probably formed from an original single stratabound reef sulphur loss through oxidation in upward migrating deuteric or hydrothermal fluids could have caused dissolution and reprecipitation of pd and au in a cumulate with several stratiform redox barriers this process can thus explain the successive pd peaks of the reef as well as the variable stratigraphic offset of pd and au across the intrusion

the platinum group element and gold contents of the marginal rocks and sills of the bushveld complex previous work has defined three suites of sills and marginal rocks adjacent to and below the rustenburg layered suite of the bushveld complex namely an ultramafic mgo approximately 30 a magnesian basaltic mgo approximately 12 and a tholeiitic suite mgo approximately 7 these three suites are thought to represent magmas which have intruded and been incorporated into the rustenburg layered suite at various times during its formation the elements ir ru rh pd pt and au have been analyzed in 17 samples representative of the three suites the ultramafic sills have the highest total noble metal content 46 ppb followed by the magnesian basaltic suite 37 ppb and the tholeiitic suite 21 ppb the ultramafic sills are characterized by a relatively fiat chondrite normalized platinum group element pattern with an average pt ir ratio of 3 52 and a pronounced rh anomaly the magnesian basaltic and tholeiitic suites both have steep positive chondrite normalized patterns with average pt ir ratios of 16 14 and 40 5 respectively and no rh anomaly modeling done using incompatible trace elements and petrographic mixing suggests the ultramafic sills represent crystal mushes of cumulate olivine and chromite that were intruded into the floor during the crystallization of the lower portion of the rustenburg layered suite the enrichment of ir ru and rh in the ultramafic sills appears to be associated with the cumulate enrichment of olivine or chromite in these sills the chondrite normalized patterns found for the merensky reef and the platreef are similar to those of the magnesian basaltic magma the pattern found for the ug 2 is much flatter and in some respects very similar to that found for the ultramafic sills on a worldwide basis the platinum group element contents of the magnesian basaltic and tholeiitic magmas generally fall in the range of basalts and chill zones of other layered suites the magnesian basaltic magma does have one of the highest pt contents measured for a magma

emplacement and crystallization time for the bushveld complex the bushveld complex formed by the crystallization of successive basaltic magmatism may be of the order of several million years for example the columbia river basalts hooper injections of magma which were sufficiently closely spaced in time that each previous magma had not cooled and differentiated 1988 were erupted in the period 17 12 ma with minor eruptions for a further 5 my although most outpouring significantly before the addition of the next one to constrain the emplacement and crystallization times a thermal model is presented occurred within the first 2 my it is now recognized that large intrusions were not emplaced in a single pulse but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition and subresult from multiple magma injection the question is how rapidly were magma chambers such as the bc traction such modelling indicates that magmas injected into the bushveld complex were emplaced within 75 000 years at that filled and how much magma was involved answers are relevant to the dynamics of melt production storage and time injection into the complex ceased the volume of rock in the eastern and western limbs is 370 000 600 000 km however transport in the mantle and crust this paper describes a thermal modelling technique not previously applied a quantitative evaluation of the cr budget in the formation of chromitite layers indicates that large volumes of magma cannot be to magma chambers which can be used to analyse this process and to obtain an estimate of the emplacement accounted for in the preserved rock sequence similarly an evaluation of the incompatible trace element abundances such as those for zr time to present this model it is necessary to discuss the stratigraphy size and connectivity of the different limbs and k suggests that the chamber was open and that large volumes of differentiated magma escaped the volume of magma therefore of the bushveld complex and to consider the extent of tapping of the magma chamber as well as its filling greatly exceeded the preserved volume of cumulate rocks giving an estimated magma volume of over 1 10 km an average the term bushveld complex has been given several meanings in the literature and according to the south emplacement rate of 13 km year is indicated by these calculations african commission on stratigraphy 1980 includes not only the ultramafic mafic layered rocks but also the sills beneath the intrusion volcanic rocks which pre date the

the cosmochemical behavior of mercury abstract we review long standing reports of both the hg paradox that hg abundances in meteorites are inconsistent with its volatile behavior and the anomalous 196 hg 202 hg ratios in all types of extraterrestrial material a careful study of the literature suggests that both results may be due to overestimation of 202 hg abundances from neutron activation analysis we reevaluate hg condensation in the solar nebula using both volatility trends for chondritic meteorites and thermodynamic calculations the extent of hg depletion in allende indicates a 50 condensation temperature of 350 k thermodynamic calculations show that hg condenses into various metal alloys at 300 k or lower at lower temperatures hg can be incorporated into fe ni sulfides as a trace element we investigate chemisorption as a method for incorporating hg into solid material in the solar nebula a large fraction of hg can chemisorb on metal surfaces at temperatures as high as 515 k depending on the grain size

the bedrock topography of starbuck glacier antarctic peninsula as determined by radio echo soundings and flow modeling a glacier wide ice thickness distribution and bedrock topography is presented for starbuck glacier antarctic peninsula the results are based on 90 km of ground based radio echo sounding lines collected during the 2012 13 field season cross validation with ice thickness measurements provided by nasa s icebridge project reveals excellent agreement glacier wide estimates are derived using a model that calculates distributed ice thickness calibrated with the radio echo soundings additional constraints are obtained from in situ ice flow speed measurements and the surface topography the results indicate a reverse sloped bed extending from a riegel occurring similar to 5 km upstream of the current grounding line the deepest parts of the glacier are as much as 500 m below sea level the calculated total volume of 80 7 7 2 km 3 corresponds to an average ice thickness of 312 30 m

ultramafic rocks in the centre of the vredefort structure south africa possible exposure of the upper mantle abstract the rocks in the central region of the vredefort structure are interpreted as lower crust that has undergone uplift of 36 km during the vredefort cryptoexplosion event 2 0 ga ago the outcrops in this central region are mainly high grade leucogranulites interbanded with mafic granulites and supracrustals rocks from a borehole located near the centre of the structure indicate that the core region is underlain by ultramafic rocks which probably represent the upper mantle beneath this region of the kaapvaal craton the main lithologies sampled by the borehole are serpentinized hornblende bearing harzburgite with minor bands of pyroxenite and glimmerite the major and trace element chemistry of these ultramafic rocks is similar to that of fertile oceanic lithosphere mineral chemistry and petrographic data suggest that the vredefort ultramafics are metamorphic rocks which have undergone a complex tectonic and metamorphic history sm nd and rb sr isotopic data together with the field relationships provide some evidence that these rocks are archaean but also that they have been chemically and isotopically altered similar hydrated and chemically altered ultramafic rocks occur in the jamestown ophiolite complex in the barberton greenstone belt accordingly we speculate that the crust mantle transition zone in the kaapvaal craton consists of a zone of hydrated archaean oceanic lithosphere

glacier dynamics near the calving front of bowdoin glacier northwestern greenland to better understand recent rapid recession of marine terminating glaciers in greenland we performed satellite and field observations near the calving front of bowdoin glacier a 3 km wide outlet glacier in northwestern greenland satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for 20 years ice radar measurements showed that the glacier front is grounded but very close to the floating condition these results in combination with the results of ocean depth soundings suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat presumably glacier thinning due to atmospheric and or ocean warming triggered the initial retreat in situ measurements showed complex short term ice speed variations which were correlated with air temperature precipitation and ocean tides ice speed quickly responded to temperature rise and a heavy rain event indicating rapid drainage of surface water to the bed semi diurnal speed peaks coincided with low tides suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance these observations demonstrate that the dynamics of bowdoin glacier are sensitive to small perturbations occurring near the calving front