surface based polarimetric c band scatterometer for field measurements of sea ice a portable surface based polarimetric c band scatterometer for field deployment over sea ice is presented the scatterometer system its calibration signal processing and near field correction are described the near field correction is shown to be effective for both linear polarized and polarimetric backscatter field methods for the scatterometer are described sample linear polarized and polarimetric backscatter results are presented for snow covered first year sea ice fyi multiyear hummock ice and rough melt pond water on fyi the magnitude of backscatter signature variability due to system effects is presented providing the necessary basis for quantitative analysis of field data

the yavapai mazatzal boundary a long lived tectonic element in the lithosphere of southwestern north america a seismic reflection profile crossing the jemez lineament in north central new mexico images oppositely dipping zones of reflections that converge in the deep crust we interpret these data as a paleoproterozoic bivergent orogen centered on the jemez lineament that formed during original proterozoic crustal assembly by collision of mazatzal island arcs with yavapai proto north american continent at ca 1 68 1 65 ga the two major sets of reflections within the yavapai mazatzal transition boundary dip at 15 20 and we interpret them as part of a south dipping thrust system and as a north dipping crustal scale duplex that formed synchronously with the thrust system the upper crust shows structures recording a succession of tectonic and magmatic events from the paleoproterozoic to the holocene notable among these structures is a system of nappes that formed during development of the bivergent orogen elements of the nappe system are exposed in rocky mountain uplifts and have been dated as having formed at 1 68 ga at depths of 10 km and at temperatures of 500 c we also see continuous bright reflections in the upper part of the middle crust that we associate with basaltic sills that postdate accretion the data show that the yavapai mazatzal suture is low angle 20 an observation that explains why the boundary between the provinces has previously been so hard to define in the surface geology the jemez lineament overlies the root of this bivergent orogen that we also suggest is a paleoproterozoic zone of weakness that has subsequently acted as a conduit for magmas and a locus of tectonism

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

the petrology and geochemistry of the ocate volcanic field north central new mexico the ocate volcanic field in north central new mexico is on the eastern flank of the sangre de cristo mountains it is a suite of pliocene pleistocene basaltic and intermediate lavas which were erupted in five pulses over a period of 7 m y 8 3 0 8 m y b p during rejuvenation of the rio grande rift geochemical and petrographic criteria are used to define five major rock types alkali olivine basalt aob transitional olivine basalt tob xenocrystic basaltic andesite xba olivine andesites oa and dacite the timing and eruptive volumes of these five lava types define a complex temporal sequence in which the transitional basalts and intermediate rocks are closely associated during the maximum in basaltic activity 4 5 2 0 m y b p the alkali olivine basalts have higher incompatible and compatible trace element abundances and higher normative nepheline 2 than do the tob lavas the two basalt types apparently were derived from physically discrete or heterogeneous source regions the aob lavas could be the products of smaller degrees of melting from similar sources source heterogeneity and or melting at greater depth the intermediate lavas were generated from basaltic parent magmas by varying degrees of fractionation assimilation of crustal material and mixing with silicic melts derived by crustal anatexis the xba lavas and dacites are characterized by disequilibrium phase assemblages which include olivine coexisting with biotite and quartz melt inclusions of k and si rich glass and a bimodal distribution of plagioclase phenocryst compositions with modes at an60 and an25 the high concentration of mg ni and cr in the intermediate lavas is inconsistent with simple fractionation of basaltic parent magmas the linear trends defined on variation diagrams are consistent with mixing mafic and silicic end members the lack of continuity between two hybrid types may be a reflection of contrasting subvolcanic environments in which the hybridization took place the olivine andesites show little petrographic evidence for mixing chemical variations within this group define highly nonlinear trends more consistent with extensive crystal fractionation calculated liquid lines of descent from available mafic parent magmas assuming perfect fractional crystallization do not satisfactorily produce the observed intermediate compositions if assimilation of a silicic crystal component is paired with crystal fractionation such that the mass of crustal material is approximately equal to 50 of the fractionated solids the major and trace element characteristics of the olivine andesites can be successfully modeled

seismic tomography of the colorado rocky mountains upper mantle from crest lithosphere asthenosphere interactions and mantle support of topography abstract the crest experiment colorado rocky mountains experiment and seismic transects integrated the earthscope usarray transportable array with portable and permanent stations to provide detailed seismic imaging of crust and mantle properties beneath the highest topography region of the rocky mountains inverting approximately 14 600 p and 3600 s wave arrival times recorded at 160 stations for upper mantle v p and v s structure we find that large v p perturbations relative to ak135 of 7 and v s variations of 8 take place over very short approaching tens of kilometers lateral distances highest heterogeneity is observed in the upper 300 km of the mantle but well resolved low velocity features extend to the top of the transition zone in portions of these images the previously noted low velocity upper mantle aspen anomaly is resolved into multiple features the lowest v p and v s velocities in the region are found beneath the san juan mountains which is clearly distinguished from other low velocity features of the northern rio grande rift taos latir region aspen region and below the never summer mountains we suggest that the san juan anomaly and a similar feature below the taos latir region of northern new mexico are related to delamination and remnant heat and melt beneath these sites of extraordinarily voluminous middle cenozoic volcanism we interpret a northeast southwest grain in velocity structure that parallels the colorado mineral belt to depths near 150 km as being reflective of control by uppermost mantle proterozoic accretionary lithospheric architecture further to the north and west the wyoming province and northern colorado plateau show high velocity features indicative of thick 150 km preserved archean and proterozoic lithosphere respectively overall we interpret the highly heterogeneous uppermost mantle velocity structure beneath the southern rocky mountains as reflecting interfingered chemical proterozoic lithosphere that has been is currently being replaced and modified by upwelling asthenosphere low velocity features resolved here indicate that this process may be sourced as deeply as the top of the mantle transition zone at 410 km one driving mechanism for this is upper mantle interaction between upwelling hydration induced partial melt and destabilized downwelling lithosphere in the deeper upper mantle tomographic imaging of mantle seismic velocity and crustal thickness results and modeling from the crest experiment indicate that the highest elevations of the colorado rocky mountains are substantially supported by the mantle and strong correlations between low velocity mantle and thin crust high topography are noted across the region this along with rich upper mantle seismic heterogeneity suggests that mantle buoyancy and dynamics are central to present day topographic support and recent geomorphic evolution of the region

application of high resolution x ray computed tomography to mineral deposit origin evaluation and processing abstract high resolution x ray computed tomography ct is the industrial equivalent of medical cat scanning and provides a mechanism for non destructive studies of the three dimensional nature of geological materials hrxct produces two dimensional images slices that reveal the interior of an object as if it had been sliced open along the image plane for viewing a ct image is generated by differences in x ray attenuation that arise from differences in density and composition within the object by acquiring a contiguous set of slices volumetric data for all or part of a sample can be obtained allowing three dimensional inspection and measurement of features of interest ct is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials available software can produce grain shape size and orientation data from the scanned volume which can be particularly useful for oriented samples ct is particularly useful for studies of gold and other precious metal bearing minerals that typically have significant contrast even with common metallic mineral phases ct precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other forms of data collected e g isotope or trace element geochemistry another area of application is fluid inclusions which can be discerned even in opaque phases and fluid and vapor volumes measured for sufficiently large occurrences we summarize ct principles and review available instrumentation as well as scanning and data reduction protocols that provide unique three dimensional information for diverse ore types and applications in mineral deposits geology ct applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three dimensional relationships particularly for fine grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast

evidence for late middle proterozoic extension in the precambrian basement beneath the permian basin through an integrated interpretation of gravity magnetic seismic reflection and well data we are able to define the geometry lateral extent and tectonic setting of late middle proterozoic mafic rocks the pecos mafic intrusive suite in the basement of the permian basin of west texas and eastern new mexico in this region seismic reflection data are characterized by subhorizontal layered reflectivity within basement that can be tied to compositional variation in a layered mafic intrusion through well cuttings and a synthetic seismogram in places the intrusion forms a sill and the base of the sill is imaged in the reflection data integration of the seismic interpretation with gravity models shows that the pecos mafic intrusive suite is 3 10 km thick and 50 100 km wide the overall structure of the suite is that of a sill with a locally dikelike keel north south trending gravity and magnetic anomalies associated with the pecos mafic intrusive suite suggest that it is composed of four large intrusive centers which cover a minimum area of 9200 km2 making it one seventh the size of the bushveld complex and one of the largest layered mafic intrusions in the world we interpret this massive intrusion to be associated with collisional rifting in the foreland of the grenville orogeny

squaw peak arizona paleoproterozoic precursor to the laramide porphyry copper province re os dating of two molybdenite samples from the squaw peak porphyry copper molybdenum prospect in central arizona returned essentially identical ages of 1 729 7 and 1 738 7 ma therefore the prospect is not a component of the laramide late cretaceous early tertiary porphyry copper province of southwestern north america as previously presumed these paleoproterozoic ages are similar to that of 1 740 15 ma for the i type magnetite series cherry batholith within which the squaw peak porphyry stock and associated mineralization are located squaw peak cannot be more than a few million years younger than volcanogenic massive sulfide vms copper deposits in the nearby jerome district which are part of the yavapai supergroup host to the cherry batholith these volcanic and intrusive rocks and their associated copper mineralization were formed in a juvenile island arc setting and are now part of the yavapai province which was assembled and accreted to the archean nucleus of north america by 1 68 ga the paleoproterozoic age for squaw peak in conjunction with the existence of the slightly older vms deposits shows that the laramide province of southwestern north america first developed its copper metallogenic signature 1 700 m y ago the presence of this paleoproterozoic copper mineralization may be taken as further support for recently proposed metasomatism of the mantle lithosphere during paleoproterozoic subduction as a precursor to formation of at least part of the laramide porphyry copper province similar spatial associations between inferred metal sources in proterozoic mantle lithosphere and lowermost crust relatively minor copper and or molybdenum mineralization in proterozoic magmatic arcs and important post paleozoic porphyry copper and or molybdenum provinces have recently been documented elsewhere particularly in eastern china and could prove to be of more general exploration significance

modeling and measurement of c band radar backscatter from snow covered first year sea ice in this paper we present model and measurement results for c band hh and vv normalized radar cross sections nrcs from winter snow covered first year sea ice with average snow thicknesses of 16 4 and 3 cm the brine content in snow pack was low in all three case studies which is typical for cold winter conditions we used the first order approximation of the small perturbation theory accounting for surface scattering from the air snow and snow ice rough interfaces and continuously layered snow and sea ice the experimental data were collected during the circumpolar flaw lead system study in the winter of 2008 in the southern beaufort sea from the research icebreaker amundsen good agreement between the model and experimental data were observed for all three case studies the model results revealed that the scattering at the snow ice rough interface is usually stronger than that at the air snow interface furthermore both model and experimental nrcs values at vv and hh polarizations were considerably higher for thin snow cover compared with the thick snow cover case we associate this effect with the lower attenuation of the propagated wave within the thin snow pack in comparison to the thick snow pack we also demonstrated that different brine volume contents in snow with close thicknesses of 4 and 3 cm did not affect the backscattering coefficients at certain incidence angles and polarization our findings provide the physical basis for winter snow thickness retrieval and suggest that such retrievals may be possible from radar observations under particular scattering conditions

parameterization of centimeter scale sea ice surface roughness using terrestrial lidar microwave scattering from sea ice is partially controlled by the ice surface roughness in this paper we propose a technique for calculating 2 d centimeter scale surface roughness parameters including the rms height correlation length and form of autocorrelation function from 3 d terrestrial light detection and ranging data we demonstrate that a single scale of roughness can be extracted from complex sea ice surfaces incorporating multiple scales of topography after sophisticated 2 d detrending and calculate roughness parameters for a wide range of artificial and natural sea ice surface types the 2 d technique is shown to be considerably more precise than standard 1 d profiling techniques and can therefore characterize surface roughness as a stationary single scale process which a 1 d technique typically cannot do sea ice surfaces are generally found to have strongly anisotropic correlation lengths indicating that microwave scattering models for sea ice should include surface spectra that vary as a function of the azimuthal angle of incident radiation however our results demonstrate that there is no fundamental relationship between the rms height and correlation length for sea ice surfaces if the sampling area is above a threshold minimum size

evaluating scattering contributions to c band radar backscatter from snow covered first year sea ice at the winter spring transition through measurement and modeling in this paper we present model and measurement results for time series angular dependencies of c band hh and vv normalized radar cross sections nrcs over first year snow covered sea ice during a winter spring transition period experimental scatterometer and physical data were collected near cambridge bay nunavut canada between may 20 and may 28 2014 covering a severe storm event on may 25 we use the small perturbation scattering theory to model small scale surface scattering the mie scattering theory to estimate the level of volume scattering in snow and the kirchhoff physical optics model to compute the large scale surface scattering component we observed good agreement between the model and experimental hh and vv nrcs before the storm r 2 between model and experimental nrcs was 0 88 and 0 82 for vv and hh respectively after the storm r 2 was 0 81 and 0 78 for vv and hh respectively our model results suggest an overall increase in surface roughness after the storm event supported by lidar measurements of the snow surface topography before the storm the large scale and small scale surface scattering from the air snow interface as well as volume scattering components dominated after the storm the large and small scale scattering contributions increased while the volume scattering component considerably dropped we attribute these effects to the increase in surface roughness and snow moisture content during the poststorm period our results could aid in interpretation of time series synthetic aperture radar images with respect to physical properties of snow and ice during the winter spring transition period

ocean surface wind speed retrieval from c band sar images without wind direction input two new models for wind speed retrieval from c band synthetic aperture radar sar data have been developed based on a large body of statistics on buoy observations collocated and coinciding with radarsat 1 and 2 scansar images the first model s independent variables are co polarization hh normalized radar cross section nrcs and antenna beam incidence angle the second model s predictors are hh nrcs cross polarization hv nrcs instrument noise floor and incidence angle the latter model has better accuracy than the first because of using an additional hv variable furthermore we found that the proposed models without wind direction input demonstrated a better accuracy than cmod ifr2 and cmod5 n models in combination with the sad hh co polarization ratio vv hh which require wind direction input these results were confirmed on a large independent subset of collected data the developed wind speed retrieval models in conjunction with our previously developed ice motion tracking algorithm can be a useful tool for studying sea ice dynamics processes in the marginal ice zone the developed models have been integrated into a quasi operational system at the meteorological service of canada

experiments and models bearing on the role of chromite as a collector of platinum group minerals by local reduction chromite is widely recognized to act as a collector for platinum group elements pge which tend to be observed as discrete grains of platinum group minerals included within magmatic chromite grains in the course of experiments involving the re equilibration or growth of chromite and cr spinel in molten silicate we observe that platinum group minerals pgm including metal alloys and laurite form at the mineral melt interface the formation of pgm to the extent observed requires a mechanism involving sustained transport of pge from a source within the experiment to the site of deposition we propose that the driving force for this process is a redox gradient developed in response to mineral growth or re equilibration with the surrounding melt the mechanism is local reduction within the mineral melt interfacial region as a consequence of the selective uptake of trivalent cr and fe from the melt by spinel relative to the divalent species we have modeled the transient perturbation of fo2 in a compositional boundary layer melt around spinel for both crystal growth and diffusive re equilibration of mineral and melt we find that metal solubilities decrease by several per cent in the silicate melt at the melt crystal interface during crystal growth providing the driving force for pgm formation in magmas that are saturated with pgm as a result of falling temperature and oxygen fugacity during spinel crystallization nucleation of pgm will be impeded by interfacial tension everywhere except in the reduced boundary layer around spinel crystals the resulting concentration and trapping of alloy particles in the growing chromite crystals can produce apparent bulk chromite melt partition coefficients exceeding 20 even if there is no solid solution of pge in the chromite the introduction of spinel grains initially equilibrated with a mafic magma into a more primitive magma with higher cr al would lead to disequilibrium between chromite and melt the perturbation of fo2 in the compositional boundary layer surrounding a chromite xenocryst would exceed 0 1 log unit leading to local reduction of alloy solubility of the order of 13 18 a small number of spinel xenocrysts could serve as collection sites for all of the excess pge in the magma leading to the eventual observation that a few chromite crystals contain many pgm inclusions whereas the rest of the chromite population may be relatively free of pgm

field observations and model calculations of dielectric properties of arctic sea ice in the microwave c band the complex dielectric constant of first year and multiyear sea ice was measured during the seasonal ice monitoring and modeling simms field experiments conducted in the arctic in the spring of 1992 1993 and 1995 the dielectric constant was also computed based on an established dielectric mixing model by using different assumptions about inclusion shape computations were based on detailed measurements and observations of ice physical properties and crystalline structure comparison between measurements and model results was conducted to identify working models for first year and multiyear ice for first year ice models that employ the assumption of vertically oriented brine pockets are applicable to columnar ice and those with the assumption of randomly oriented brine pockets are applicable to frazil ice the validity of the models are established only for ice temperatures less than 8 spl deg c for multiyear ice there is no need to account for air bubble shape the coexistence of brine and air inclusions in multiyear pond ice makes it characteristically different from hummock ice best results for pond ice were obtained from a simple model that accounts only for volume fractions of inclusions rather than their shape physical parameters that can be retrieved directly from the dielectric constant are salinity of first year ice at temperatures below 15 spl deg c and density of multiyear hummock ice detailed measurements of permittivity and loss of first year and multiyear ice are presented along with some insight into interactions between the dielectric constant and physical parameters

chromite in komatiites 3d morphologies with implications for crystallization mechanisms high resolution x ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies chromite contents and degrees of alteration and metamorphism to reveal the wide range of sizes shapes and degrees of clustering that chromite grains display as a function of cooling history dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops at slower cooling rates in the interiors of thick flows chromite forms predominantly euhedral grains large clusters up to a dozen of grains are characteristic of liquidus chromite whereas fine dustings of mostly individual 20 m grains form by in situ crystallization from trapped intercumulus liquid chromite in coarse grained olivine cumulates from komatiitic dunite bodies occurs in two forms as clusters or chains of euhedral crystals developing into chicken wire texture where chromite is present in supra cotectic proportions and as strongly dendritic semi poikilitic grains these dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite in some cases this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs this texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures our 3d textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks

petroleum geology of pennsylvanian and lower permian strata tucumcari basin east central new mexico abstract the tucumcari basin of east central new mexico is a structural depression that existed as a depositional basin from strawn middle pennsylvanian until late wolfcampian early permian time depth to precambrian ranges from 6500 ft to more than 9000 ft high angle faults form the north east and west edges of the basin no major structural discontinuities separate the basin from a shallow shelf to the south faults cut pennsylvanian and wolfcampain strata but generally do not offset post wolfcampian strata faults and regional structure control facies and thickness patterns within the pennsylvanian and wolfcampian coarse arkosic sands in the pennsylvanian and wolfcampian are good reservoirs those sands were deposited in northern and western parts of the basin and were derived from highlands of precambrian granitic rocks that formed the northern and western margins of the basin high energy limestones are possible reservoirs in the southern part of the basin porous wolfcampian dolostones cover the frio uplift on the east side of the basin pennsylvanian and wolfcampian marine shales and micritic limestones are source rocks within the tucumcari basin post wolfcampian strata are thermally immature two presently noncommercial pools of oil and gas the latigo ranch pool and the t 4 ranch pool have been discoveredmore in strawn sands in the northern part of the tucumcari basin oil generated in the upper paleozoic has migrated vertically into the triassic two oil accumulations the santa rosa tar sands and the newkirk oil pool are in triassic sandstones and have combined reserves of 153 million bbls of oil less

late holocene hydroclimatic change at cienega amarilla west central new mexico usa a late holocene carbonate spring mound and associated wetland deposits at cienega amarilla new mexico contain a 4000 yr record of geomorphic paleoenvironmental and hydroclimatic change on the southern colorado plateau forty four 14c dates support a century scale chronostratigraphic framework pollen plant macrofossil mollusk ostracode and soil analyses indicate rapid spring mound growth and wetland expansion beginning 2300 cal yr bp followed by a pronounced decline in groundwater discharge gwd between 1500 and 1000 cal yr bp the isotopic composition of cienega amarilla springwater suggests gwd is driven primarily by winter precipitation historical climate data indicate that el nino and warm pacific decadal oscillation pdo conditions foster wetter than average winters in the cienega amarilla area whereas dry winters are associated with la nina conditions regardless of pdo phase the 2300 1500 cal yr bp cienega amarilla pluvial appears to represent an interval of peak late holocene cool season precipitation that implies unusually strong or persistent el nino like and warm pdo like conditions in the pacific other southwestern paleoenvironmental records corroborate atypically wet conditions during this interval and pluvial conditions related to increased winter precipitation likely fostered significant prehistoric cultural changes throughout the region including increased sedentism population and dependence on agriculture

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

terminal pleistocene to early holocene volcanic eruptions at zuni salt lake west central new mexico usa zuni salt lake zsl is a large maar in the red hill quemado volcanic field located in west central new mexico in the southwestern usa stratigraphic analysis of sections in and around the maar coupled with optically stimulated luminescence osl and accelerator mass spectrometry ams 14c dating indicate that zsl volcanic activity occurred between 13 4 and 9 9 ka and was most likely confined to a 500 year interval sometime between 12 3 and 11 0 ka the basal volcanic unit consists of locally widespread basaltic ash fallout interpreted to represent a violent or wind aided strombolian eruption tentatively attributed to cerro pomo a scoria cone 10 km south of zsl subsequent eruptions emanated from vents near or within the present day zsl maar crater strombolian eruptions of multiple spatter and scoria cones produced basaltic lava and scoria lapilli fallout next a phreatomagmatic eruption created the maar crater and surrounding tephra rim and apron zsl eruptions ended with strombolian eruptions that formed three scoria cones on the crater floor the revised age range of zsl is younger and more precise than the 190 24 ka 2 sigma age range derived from previous argon dating this implies that other morphologically youthful argon dated volcanoes on the southern margin of the colorado plateau might be substantially younger than previously reported

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

the santa rita nickel sulfide deposit in the fazenda mirabela intrusion bahia brazil geology sulfide geochemistry and genesis the santa rita ore zone within the fazenda mirabela intrusion is an unusual example of high tonnage magmatic ni cu pge sulfide mineralization developed as a stratiform layer within the main cumulus sequence of a layered intrusion the intrusion as a whole is about 4 2 5 km in outcrop dimensions and at least 3 km in original maximum stratigraphic thickness with an original boat shaped morphology the ore zone comprises a 50 to 200 m thick interval containing up to 5 wt percent disseminated sulfides within a sequence of mostly unaltered harzburgites and orthopyroxenites this orthopyroxene dominated sequence lies between the dominantly olivine rich cumulates that comprise the lower half of the intrusion and the gabbroic cumulates that make up the upper half sulfide tenor variations and silicate host rock compositions have been derived from a very large database of continuous assays of more than 500 diamond drill cores consistent patterns of sulfide tenor gradually decreasing ni from over 20 to about 10 wt percent near constant cu and gradually decreasing pges with cyclically varying pt pd ratios are found within the santa rita ore zone across the entire intrusion and display relatively little lateral variability the position of the sulfide mineralization envelope within the harzburgite orthopyroxenite package migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene bearing cumulates asymmetrically disposed toward the southern margin of the intrusion nickel tenors of the sulfides range from 15 to 25 wt percent exceptionally high for rocks with relatively low values of mgo mgo feo and are closer to the typical values observed in komatiite hosted deposits although cu tenors typically 5 8 wt are much higher than komatiite values sulfide pge tenors range from less than 100 ppb to greater than 10 ppm of both pt and pd with maximum values in s poor rocks at the base of the sulfide bearing interval pges become significantly more depleted toward the top of the santa rita zone we attribute these features along with the localization of the sulfide bearing interval at the contact between ultramafic and mafic cumulates to mixing of an initially s undersaturated moderately ni enriched resident magma with a relatively low ni pge depleted significantly lower temperature replenishing magma charged with suspended sulfide liquid droplets

the application of high resolution x ray computed tomography on naturally deformed rock salt multi scale investigations of the structural inventory abstract x ray computed tomography ct represents a useful technique providing new perspectives and insights for the structural investigation of naturally deformed rock salt several samples of permian rock salt from gorleben asse and teutschenthal germany were investigated by exploiting the non destructive nature of ct and nct techniques particularly for salt rocks ct imaging enabled the visualization and quantification of anhydrite impurities pore space and fluid phases located along grain boundaries or trapped as intracrystalline inclusions disseminated grains and aggregates of anhydrite in rock salt of the gorleben salt dome have been visualized and quantified by ct for the first time in order to portray their spatial occurrence the visualization of anhydrite aggregates and pore space shows no correlation between their spatial distributions this independence excludes the anhydrite to be responsible for elevated porosity 0 87 0 07 vol high resolution nct scans 1 m voxel size of single intracrystalline and grain boundary fluid inclusions from gorleben and asse rock salt allowed the visualization and quantification of their various phase components a major achievement is the detailed description of the morphology and shape of the fluid inclusions and of their phase components which has not been conducted in rock salt research by high resolution x ray ct imaging before

modeling the merensky reef bushveld complex republic of south africa the merensky pegmatoid normal reef in the western bushveld complex is commonly characterized as a pyroxene rich pegmatoidal unit with a base that is enriched in chromite and platinum group element bearing sulfides overlying a leuconorite footwall models for its formation have ranged from those that view it as entirely a magmatic cumulate succession to those that have suggested that it is a zone of volatile induced remelting the consequences of the latter interpretation are investigated using the numerical modeling program iridium which links diffusive and advective mass and heat transport with a phase equilibration routine based on the melts program the initial system consists of a simple stratigraphic succession of a partially molten leuconorite overlain by a partially molten pyroxenite both initially at 1 190 c and 2 kbar 2 wt of a volatile fluid composed of 75 mol h2o 20 mol co2 and 5 mol h2s is then added to the lower 20 cm of the pyroxenite the system is then allowed to evolve under conditions of chemical diffusion in the liquid the addition of the volatile components results in a modest increase in the amount of melt in the pyroxenite however chemical diffusion across the leuconorite pyroxenite boundary leads to more extensive melting at and below the boundary with preferential loss of opx from the underlying leuconorite preferential re precipitation of sulfide and chromite and concentration of the pge at this boundary these results mimic actual mineral and compositional profiles across the merensky pegmatoid and illustrate that long term diffusion process can effectively produce mineralogical and compositional layering not present in the original assemblage

comparisons between sar backscattering coefficient and results of a thermodynamic snow ice model for the baltic sea land fast sea ice we have compared the time series of c band hh polarization backscattering coefficients sigmadeg of the baltic sea land fast level ice with results from a 1 d high resolution thermodynamic snow ice model hightsi the sigmadeg time series were obtained from envisat synthetic aperture radar sar images the study period was from the middle of the winter to the early melt season february 3 april 7 2004 due to the large incidence angle range of the sar images the sigmadeg values were divided into three subseries in general the hightsi results greatly helped to interpret the sigmadeg behavior with changing ice and weather conditions the modeled snow surface temperature cases of snow melting and evolution of snow and ice thickness were related to the changes in sigmadeg equally useful information could not be obtained solely on the basis of large scale atmospheric models realistic forcing data for hightsi were available in the form of coastal weather observations and model results of the european centre of medium range weather forecasts ecmwf the latter make it possible to apply hightsi in the interpretation of sar data from all ice covered seas there were some cases where detailed ground truth combined with theoretical sigmadeg modeling would have been needed for interpretation of the sigmadeg trends a very interesting observation was the large variation of level ice sigmadeg with changing weather conditions which complicates automatic classification of the sar images and thus the algorithms must be tuned for different ice conditions the hightsi model could act as an indicator of various ice conditions for algorithm development

surface roughness of baltic sea ice small medium and large scale measurements of sea ice surface roughness were carried out in the baltic sea over a 3 year period a clear relationship was found between the rms height and correlation length of baltic sea ice in most cases the surface correlation function was close to exponential the logarithm of rms height showed a linear dependence on that of measured distance similarly the correlation length was in many cases linearly dependent on the measured distance this dependence on length suggests that ice surface roughness could be characterized as a fractal

growth stabilization and reactivation of proterozoic lithosphere in the southwestern united states growth of proterozoic continental lithosphere in the southwestern united states involved assembly of tectonostratigraphic terranes during several pulses of convergent tectonism ca 1 74 1 70 and 1 65 1 60 ga prograde metamorphism accompanied orogenic assembly and peak metamorphic conditions outlasted deformation regions now characterized by the highest metamorphic grades underwent slow isobaric cooling and were not uplifted until more than 200 m y after assembly regions of low metamorphic grade were not uplifted substantially after assembly we suggest that 1 relatively thin lithospheric fragments were assembled into isostatically stable normal thickness continental lithosphere 2 assembly did not erase lithospheric scale heterogeneities 3 the present juxtaposition of different crustal levels reflects differential uplift related to 1 4 1 1 ga tectonomagmatic activity and 4 the boundaries between different lithospheric blocks were repeatedly reactivated from precambrian through tertiary time

concentration of platinum group elements by magmatic fluids in layered intrusions evidence leading to a model which supports the formation of pt pd reefs in a layered intrusion by the action of magmatic fluids is presented as well as some of the constraints imposed on such a model the stillwater complex is used as an example of this model within the stillwater complex no laterally continuous sulfide enriched cumulates occur above the lowermost parts of the ultramafic series until one reaches the platiniferous j m reef this sulfide poor stratigraphic interval beneath the j m reef is characterized by unusually cl rich apatite although reported sulfide modes and whole rock sulfur contents in the cumulates below the j m reef are approximately an order of magnitude lower than that expected for a sulfide saturated magma sulfide saturation prior to the formation of the j m reef is suggested by relatively high pd and pt concentrations reported in the cumulates below the j m reef as well as by the presence of sulfide as inclusions in silicate and oxide cumulus minerals hence it is suggested that the footwall cumulates to the j m reef were originally sulfide saturated but later lost sulfur to a fluid phase exsolving from inter cumulus liquid sporadic sulfide bearing pegmatoids in some of these rocks are additional evidence for late loss of sulfur these observations as well as the association of the j m reef at the first significant stratigraphic break in the cl cl f ratio of apatite and the relatively high solubility of pt and pd as aqueous cl complexes are consistent with the formation of the j m reef by exsolution of cl and volatile rich fluids from footwall intercumulus liquids which leached and transported ore components both the pge and s upward to the level of the reef using published whole rock platinum group element pge concentrations for the ultramafic and lower banded series the cumulates below the j m reef must have been enriched by a factor of at most 1 24 for pt and 1 75 for pd if these rocks were to be the source for the metals in the j m reef model raleigh fractionation calculations suggest that the cumulates beneath the j m reef could have had the required metal concentrations if during the crystallization of a parent magma containing no more than 15 ppb of either metal the average bulk solid liquid distribution coefficients for pt and pd were no more than 5 these values are consistent with assumption of sulfide saturation prior to the formation of the j m reef during solidification of intercumulus liquid the separation and loss of a cl rich fluid will deplete the residual assemblage of s and pge if 0 1 to 0 5 wt percent fluid containing 5 percent s evolved during solidification of the footwall cumulates the amount of fluid expected to be exsolved by the crystallization of approximately 2 to 10 percent fluid saturated intercumulus liquid the fluid liquid distribution coefficients for pt and pd would need to be almost as large as the sulfide liquid silicate liquid distribution coefficients to remove significant amounts of pt and pd much smaller distribution coefficients are needed if sulfide is completely lost to fluid during degassing the latter possibility is consistent with the low s contents of the footwall cumulates beneath the j m reef numerical models of the degassing of intercumulus liquids suggest that thick cumulus sequences can act as chromatographic columns to separate the pge and s during the degassing of intercumulus silicate liquids the pge being enriched at a sulfide dissolution front as upward migrating sulfide undersaturated fluids resorb cumulus sulfides zones of pge and s enrichment can occur where degassing fronts encounter stratigraphic physical chemical discontinuities such as changes in the fluid saturation temperature of the intercumulus silicate liquids

geophysical and geochronological constraints on the extent and age of mafic intrusions in the basement of west texas and eastern new mexico a deep drill hole recently completed on the central basin platform of west texas provides a rare look at almost 5 km of basement rocks most of the crystalline rocks encountered were basic and ultrabasic in composition a variety of geophysical data is available from the bore hole and vicinity the petrographic and geophysical data suggest that a large layered basic intrusion was penetrated by the well geochronologic u pb data indicate an age of about 1 1 ga for this intrusion this date has significant tectonic implications because it indicates that commonly accepted analogies with the southern oklahoma aulacogen 550 ma rifting are not valid however it is interesting to note that this feature formed during another widespread period of rifting keweenawan

primary cumulus platinum minerals in the monts de cristal complex gabon magmatic microenvironments inferred from high definition x ray fluorescence microscopy an unusual occurrence of pt enriched pyroxenites in the monts de cristal igneous complex is characterized by unusually high ratios of pt to other platinum group elements pges and very low cu and sulfide contents synchrotron x ray fluorescence microscopy was used to identify over a hundred discrete grains of platinum minerals and relate their occurrence to textural associations in the host heteradcumulate orthopyroxenites element associations backed up by fib sem and pixe probe observations indicate that most of the pt is associated with either as or trace cu ni rich sulfides or both some of the pt as grains can be identified as sperrylite and most are likely to be pt fe alloy the relative abundances and volumes of pt minerals to sulfide minerals are very large compared with typical magmatic sulfides almost all of the grains observed lie at or within a few tens of m of cumulus orthopyroxene grain boundaries and there is no significant difference between the populations of grains located inside or outside plagioclase oikocrysts these oikocrysts are inferred to have crystallized either at the cumulus stage or very shortly thereafter on the basis of their relationship to ti enrichment in the margins of pyroxene grains not enclosed in oikocrysts this relationship precludes a significant role of trapped intercumulus liquid in pt deposition or mobilization and also allows a confident inference that pt rich and pt as enriched phases precipitated directly from the magma at the cumulus stage these observations lead to the conclusion that fractionation of pt from other pges in this magmatic system is a consequence of a solubility limit for solid pt metal and or pt arsenide

the formation of pt ir alloys and cu pd rich sulfide melts by partial desulfurization of fe ni cu sulfides results of experiments and implications for natural systems abstract we propose a model of high temperature formation of platinum group element pge alloys from base metal sulfides subjected to decreasing sulfur fugacity f s 2 for this purpose we experimentally investigated the effect of partial desulfurization of monosulfide solid solution mss with variable ni and cu contents on the distribution behaviour of pt ir and pd at 1000 c we partially removed sulfur from the pge bearing mss using the tube in tube technique and pyrrhotite as an f s 2 buffer we found that mss undergoing s loss can produce 1 pt and ir exsolution from the mss matrix in the form of pge bearing alloys 2 partial melting of the cu ni bearing mss to form fe rich mss cu ni pd rich sulfide liquid and fe ir pt alloy both of these processes are geologically important the partial melting of the s depleted sulfides could explain the presence of two types of sulfides found in the mantle mss dominated sulfides and s poor sulfides consisting mainly of pentlandite and chalcopyrite we also suggest that the cu ni pd rich liquid formed by partial melting of the sulfides could migrate away from the mss and fe ir pt alloys thus spatially decoupling ir pt and cu pd as observed in reefs and mantle nodules in addition the formation of pge alloys in response to the desulfurization processes potentially could occur 1 after pressure falls during transport of the basalt magma with entrained sulfide droplets 2 after sulfur removal by s undersaturated melts or fluids from pge enriched sulfide proto ore 3 after degassing of the sulfide droplets occurring in a sub volcanic chamber and 4 as a result of sulfide interaction with chromite

preservation of proterozoic terrane boundaries within the colorado plateau and implications for its tectonic evolution abstract during the proterozoic the north american continent grew by the accretion of arcs onto the archean craton subsequent tectonic events affected much of the lithosphere of western north american resulting in the destruction of many of the features that reflect continental growth the colorado plateau which is centrally located within the tectonically active western portion of north america experienced only minor amounts of volcanism during subsequent magmatic events and has undergone comparatively little internal deformation during the remainder of the precambrian and phanerozic despite the occurrence of some significant tectonic events because the lithosphere of the plateau has not been significantly reworked by tectonic events it may have retained structures since accretion that give insight into processes of continental growth the crust of the southeastern portion of the colorado plateau revealed here through seismic data recorded by the temporary spe and la ristra arrays is greater than 40 km thick and possesses distinct changes in intercrustal layering and the character of the moho the moho appears quite dim towards the center of the plateau and much brighter along its southeastern margins connecting changes in crustal features that are common between the two arrays indicates a northeastern structural trend that matches the pattern of gravity anomalies in the region differences in crustal structures between terranes extend across much of the crust suggesting that entire distinct crustal columns align with terrane boundaries it is unlikely that extensive crustal flow as required by some models of plateau evolution could have traversed across the entire colorado plateau without producing features that cross cut these boundaries

seismic identification of basement reflectors the bagdad reflection sequence in the basin and range province colorado plateau transition zone arizona although seismic reflection profiling has contributed greatly to our knowledge of the crust and upper mantle it is often difficult to unambiguously identify the geologic origin of reflections this is particularly true of intrabasement reflectors whose geometry and origin we need to know in order to understand tectonic processes operating in the crust we present synthetic seismogram modeling of recently collected p and s wave seismic reflection data which suggests that the intrabasement bagdad reflectors in west central arizona are intrusive mafic sheets the identification is based on the determination of the phase positive polarity and amplitudes of the reflected arrivals if the bagdad reflectors are cenozoic age mafic sheets they may be the product of rapid intrusion into an area of weak extension where the principal stresses are approximately equal

paleoproterozoic rocks of central colorado accreted arcs or extended older crust paleoproterozoic 1770 1735 ma bimodal volcanic rocks in central colorado have been considered to represent southward growth of laurentia by arc accretion although the bimodality of these rocks suggests an extensional continental setting rather than continental or oceanic arcs there has been little evidence for pre 1800 ma crust south of the wyoming craton other than the 1840 1 ma elves chasm pluton in the upper granite gorge of the grand canyon arizona we report shrimp u pb ages of inherited zircons from metarhyolites and plutons in central colorado that are latest archean earliest proterozoic 2520 2000 ma and trans hudson penokean 1878 1814 ma associated quartzites contain detrital zircons with mean ages of 1735 ma indicating only local derivation a meta arkose however contains detrital zircons of trans hudson penokean and archean ages we believe it likely that the 1900 1800 ma trans hudson penokean orogens including archean enclaves extended farther south and west than is currently thought and were the source of the bimodal volcanic rocks and associated plutons during the period 1770 1700 ma

tectonics of the jemez lineament in the jemez mountains and rio grande rift the jemez lineament is a ne trending crustal flaw that controlled volcanism and tectonism in the jemez mountains and the rio grande rift zone the fault system associated with the lineament in the rift zone includes from west to east the jemez fault zone southwest of the valles toledo caldera complex a series of ne trending faults on the resurgent dome in the valles caldera a structural discontinuity with a high fracture intensity in the ne jemez mountains and the embudo fault zone in the espanola basin the active western boundary faulting of the espanola basin may have been restricted to the south side of the lineament since the mid miocene the faulting apparently began on the sierrita fault on the east side of the nacimiento mountains in the late oligocene and stepped eastward in the early miocene to the canada de cochiti fault zone at the end of the miocene about 5 ma the active boundary faulting again stepped eastward to the pajarito fault zone on the east side of the jemez mountains the north end of the pajarito fault terminates against the jemez lineament at a point where it changes from a structural discontinuity zone of high fracture intensity on the west to the embudo fault zone on the east major transcurrent movement occurred on the embudo fault zone during the pliocene and has continued at a much slower rate since then the relative sense of displacement changes from right slip on the western part of the fault zone to left slip on the east the kinematics of this faulting probably reflect the combined effects of faster spreading in the espanola basin than the area north of the lineament abiquiu embayment and san luis basin the right step in the rift that juxtaposes the san luis basin against the picuris mountains and counterclockwise rotation of various crustal blocks within the rift zone no strike slip displacements have occurred on the lineament in the central and eastern jemez mountains since at least the mid miocene although movements on the still active jemez fault zone in the western jemez mountains may have a significant strike slip component basaltic volcanism was occurring in the jemez mountains at four discrete vent areas on the lineament between about 15 ma and 10 ma and possibly as late as 7 ma indicating that it was being extended during that time

winagami reflection sequence seismic evidence for postcollisional magmatism in the proterozoic of western canada a recent lithoprobe seismic reflection transect in the peace river arch region of the western canada sedimentary basin traverses continental crust that was assembled in a series of magmatic and collisional events during the interval 2 0 1 9 ga the seismic data reveal panels of dipping reflectivity at tectonic domain boundaries but they are otherwise dominated by prominent subhorizontal reflections that occur between 3 5 and 18 5 km depth over an area of at least 120 000 km 2 these reflections here named the winagami reflection sequence overlap several tectonic domains and are comparable in geometry depth and areal distribution to sills and discordant intrusive sheets imaged by previous seismic profiling in the baltic shield and the basin and range province of the western united states as many as five distinct reflections are present some of which can be traced for more than 100 km contrasting reflection character in adjacent tectonic domains suggests an intrusive geometry controlled partly by the mechanical properties of the host rocks seismic modeling indicates that observed waveforms are consistent with reflections from tabular mafic bodies 70 m thick the winagami reflection sequence crosscuts the collisional fabric ca 1890 ma but the sequence is offset by a brittle fault with an estimated age of 1760 ma these timing constraints suggest that the winagami reflection sequence is a previously unknown component of a regional magmatic event emplaced during a period of brittle indentation of the western canadian shield by the slave province

image analysis and composition of platinum group minerals in the j m reef stillwater complex detailed imaging bulk geochemical analyses and laser ablation icp ms analyses were conducted on mineralized samples from the platinum group element pge bearing j m reef stillwater complex montana the aims of the study were to determine which phases are the main hosts of the pge to examine the textural relationships of the pge bearing minerals and the associated base metal sulfides silicates and secondary magnetites the platinum group minerals pgm observed in the studied samples consist of pd or pt sulfides pt fe alloy isoferroplatinum pd or pt tellurides and pd cu alloy skaergaardite with minor native pd ru ir os s sub 2 laurite and au pd ag alloy palladian electrum these minerals account for all the pt half the pd ru and ir and a smaller proportion of the os in whole rocks the balance being found in the base metal sulfide most of these pgm are closely associated with base metal sulfides either included in the base metal sulfide or located at the contact between the base metal sulfide and the silicate or oxide minerals the textures of the pgm within and at the margins of the base metal sulfide suggest that they exsolved from the sulfides we suggest that the pge ni cu and te partitioned into a magmatic sulfide liquid that crystallized into base metal sulfide the pt fe alloys and some of the pd sulfides exsolved from the base metal sulfide during desulfurization at fairly high temperatures in contrast the skaergaardite and some pd sulfides are found in association with secondary magnetite and probably formed at relatively low temperatures approximately 250 degrees 465 degrees c during a second fluid migration event the pd pt ratio of the reef approximately 3 3 is higher than most mafic magmas and the pd pt ratio of the footwall is lower 0 3 0 7 it is possible that some of the pd in the reef was leached from the underlying rocks and deposited in the reef as pgm associated with secondary magnetite

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

comparative isotopic and chemical geochronometry of monazite with implications for u th pb dating by electron microprobe an example from metamorphic rocks of the eastern wyoming craton u s a polygenetic monazite grains in diverse precambrian crystalline rocks from the black hills south dakota have been analyzed in situ by ion and electron microprobe methods shrimp and emp to evaluate the accuracy and precision of emp ages determined using a new analytical protocol that incorporates improved background acquisition and interference corrections parallel evaluations were conducted by comparing emp chemical and shrimp isotopic ages at regional rock and grainscales the monazite data set includes 354 emp chemical analyses from 26 grains in six metamorphic rocks which resolve into 54 age composition domains and 31 shrimp isotopic ages from 13 grains in one of the rocks with six grains microanalyzed in common by the two methods the data set also includes monazite bearing garnets in two of the rocks whose isotopic compositions were analyzed using pb stepwise leaching pbsl methods both the emp and shrimp data sets reveal a continuum of apparent monazite ages spanning a 1790 1680 ma timeframe with a relatively high probability of ages at 1755 and 1715 ma that correspond spatially to core and rim domains pbsl ages of 1742 and 1734 ma obtained from monazite bearing garnet in two rocks are intermediate compared to the corresponding emp ages and are thereby interpreted as mixed ages emp data for two grains in the structurally deepest of the six rocks record 1785 and 1755 ma ages in the cores and higher y and lower th rims respectively and these results are duplicated by shrimp ages in these and or other grains from the same rock overall the emp shrimp and pbsl ages are internally consistent at the various scales of observation which serves to validate emp chemical dating as an accurate and precise method of discerning monazite age populations in polymetamorphic terrains the emp data set is interpreted geologically as res ecting multiple episodes of monazite growth that are provisionally related to known metamorphic events in the black hills taking the most precise emp data at face value it is possible to resolve the timing of the two older events at 1784 4 ma or 1786 6 ma and 1756 3 ma or 1753 4 ma with 95 con dence these events are considered to be related to sequential episodes of n directed thrusting and e w compression associated with paleoproterozoic crustal assembly in the mid continent a younger metamorphism related to granite intrusion known to have occurred at 1715 3 ma is dated independently at 1717 2 ma from the emp monazite ages

shear wave splitting and mantle flow beneath the colorado plateau and its boundary with the great basin shear wave splitting measurements from sks and skks phases show fast polarization azimuths that are subparallel to north american absolute plate motion within the central rio grande rift rgr and colorado plateau cp through to the western rim of the cp with anisotropy beneath the cp and central rgr showing a remarkably consistent pattern with a mean fast azimuth of 40 6 e of n approaching the rim from the southeast fast anisotropic directions become north northeast south southwest nne ssw rotate counter clockwise to north south in the cp gb transition and then to nnw sse in the western great basin gb this change is coincident with uppermost mantle s wave velocity perturbations that vary from 4 beneath the western cp and the eastern edge of the marysvale volcanic field to about 8 beneath the gb corresponding delay times average 1 5 sec beneath the central cp decrease to approximately 0 8 sec near the cp gb transition and increase to about 1 2 sec beneath the gb for the central cp we suggest anisotropy predominantly controlled by north american plate motion above the asthenosphere the observed pattern of westward rotating anisotropy from the western cp through the cp gb transition may be influenced to asthenospheric flow around a cp lithospheric keel and or by vertical flow arising from edge driven small scale convection the anisotropic transition from the cp to the gb thus marks a first order change from absolute plate motion dominated lithosphere asthenosphere shear to a new regime controlled by regional flow processes the nnw sse anisotropic fast directions of split sks waves in the eastern gb area are part of a broad circular pattern of seismic anisotropic fast direction in the central gb that has recently been hypothesized to be due to toroidal flow around the sinking juan de fuca gorda slab

platinum ore in three dimensions insights from high resolution x ray computed tomography platinum group elements referred to as pge comprising pt pd rh ru ir and os are strategic metals with a wide variety of industrial applications most of the world s pge production is mined from large mafic ultramafic intrusions such as the bushveld complex in south africa which currently provides 75 of the world s pt production the pge mineralization is found within distinctive layers tens to hundred of centimeters thick but extending laterally for many tens of kilometers where the pge occur at low parts per million levels as platinum group minerals pgm and in solid solution within disseminated base metal sulfides there is still heated debate at the most fundamental level about the mode of formation of this class of deposit genetic models range from primary magmatic sulfide collection to concentration by migrating halogen rich fluids a crucial line of evidence is the spatial relationship between the pgm which are the most important pge bearing phases and the base metal sulfide aggregates or blebs so far all observations have been carried out using two dimensional mineralogical studies where textural relationships with other minerals are ambiguous and with statistical limitations owing to sampling of trace phases intersecting random surfaces we present the first detailed three dimensional in situ analysis of the pgm at the sample scale using high resolution x ray computed tomography coupled with conventional microscopic and mineralogical study we find a striking and highly consistent relationship of pgm grains with the edges of complex shaped magmatic sulfide blebs and the intersection of these blebs with chromite silicate grain boundaries these new three dimensional observations strongly support an orthomagmatic model coupled with nucleation and growth of pgm at the margins of sulfide liquid droplets

morphology and microstructure of chromite crystals in chromitites from the merensky reef bushveld complex south africa the merensky reef of the bushveld complex consists of two chromitite layers separated by coarse grained melanorite microstructural analysis of the chromitite layers using electron backscatter diffraction analysis ebsd high resolution x ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals fine grained idiomorphic and large silicate inclusion bearing crystals the lower chromitite layer contains both populations whereas the upper contains only fine idiomorphic grains most of the inclusion bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre existing smaller idiomorphic crystals two possible mechanisms have been proposed for sintering of chromite crystals 1 amalgamation of a cluster of grains with the same original crystallographic orientation and 2 sintering of randomly orientated crystals followed by annealing into a single grain the ebsd data show no evidence for clusters of similarly oriented grains among the idiomorphic population nor for earlier presence of idiomorphic subgrains spatially related to inclusions and therefore are evidence against both of the proposed sintering mechanisms electron backscatter diffraction analysis maps show deformation related misorientations and curved subgrain boundaries within the large amoeboidal crystals and absence of such features in the fine grained population microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation an alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during the magma influx that formed the merensky reef the upper chromite layer formed from a subsequent magma influx and hence lacked a mechanism to form dendritic chromite this accounts for the difference between the two layers

interpretation of reflections from the central part of the siljan ring impact structure based on results from the stenberg 1 borehole abstract in 1984 1985 and 1990 several multichannel seismic reflection profiles were shot over the siljan ring a meteorite impact structure believed to have been formed approximately 360 ma ago the bedrock of the area consists mainly of gneisses and granites and the ring itself of palaeozoic sedimentary rocks lying on top of granites dolerite dikes of different age and orientation have been mapped in the area the existence of dolerite intrusions at depth has been verified through the drilling of two deep boreholes gravberg 1 and stenberg 1 interpretation of seismic data and borehole data from the gravberg 1 borehole showed a strong correlation between high amplitude subhorizontal reflections and dolerite sills geophysical and geological well logging in the stenberg 1 borehole showed the occurrence of dolerites in the borehole profile 4 running e w across the borehole has been reprocessed in order to improve the seismic image several thick dolerites below 5 7 km in the borehole correlate with high amplitude reflectors on the seismic section both the logging data and the seismic interpretation suggest that these intrusions are subhorizontal and laterally continuous above 5 7 km in the borehole the dolerites are thinner and are in some cases associated with fracture zones on the seismic section at these depths there is a complex system of weaker dipping reflectors some of these dipping reflectors correlate with either fracture zones thin dolerites or a combination of both

electron probe ultrachron microchronometry of metamorphic monazite unraveling the timing of polyphase thermotectonism in the easternmost wyoming craton black hills south dakota a metapelite from the easternmost wyoming craton black hills south dakota has been analyzed by microstructural methods to unravel polyphase deformational history associated with 1800 1700 ma assembly of southern laurentia three deformational fabrics are recognized in oriented thin sections an ene trending s 1 fabric preserved as oblique inclusion trails in garnet porphyroblasts a nnw trending s 2 fabric preserved as microlithons in the rock matrix and a flattening fabric s 3 which transposed s 1 s 2 and dominates the matrix a complex monazite porphyroblast has been analyzed in situ with the electron microprobe ultrachron to constrain the timing of s 1 s 3 fabric formation associated with monazite growth the core of this grain uniquely preserves the s 1 s 2 fabrics as sigmoidal inclusion trails the mean total pb age of this domain is 1750 10 ma all dates reported at 95 confidence n 39 spots which is equivalent to the published 2 0 7 pb 2 0 6 pb age for the same domain these results validate the total pb dating method in general and the ultrachron in particular for reliable age determination in low th monazite and are interpreted as 1750 ma minimum ages for the s 1 s 2 fabrics and sequential d 1 d 2 collisional events that imposed them n directed arc accretion and e w continental collision respectively a higher th y rim of this same rosetta grain truncates the s 1 s 2 sigmoid and is associated with resorption textures in garnet porphyroblasts coupled release of y and an s 3 fabric that pervasively overprinted s 1 s 2 in the rock matrix the mean ultrachron date of this domain is 1692 5 ma n 17 spots which is slightly younger that the published isotopic age for all monazite rims combined these results support a 1715 1690 ma timeframe for localized doming d 3 related to granite magmatism the onset of which has been dated independently at 1715 3 ma the timing of post d 3 cooling through 350 and 300 c is constrained by 4 0 ar 3 9 ar dates of 1610 and 1480 ma obtained for separates of d 3 matrix muscovite and biotite respectively which are interpreted as closure ages this study shows that fabrics in poly deformed rocks can be dated by linking monazite spot ages to key microtextures further the results of this micrometer scale study enhance previous knowledge of local thermotectonism black hills and regional terrane assembly laurentia

regional trends in the platinum group mineralogy of the critical zone of the bushveld complex south africa a wealth of quantitative data on the types volume distribution and mode of occurrence of the platinum group minerals residing in the merensky reef the ug 2 chromitite layer and platreef has been obtained over a twelve year period with the result that general platinum group mineral types for unexplored areas can perhaps now be predicted the platinum group minerals of the ug 2 and overlying merensky layers although locally different in composition mode of occurrence and size show close ties when viewed on a regional scale especially with regard to their pt pd sulfide and pt fe alloy contents thus if in one particular area the merensky reef contains pt pd sulfides as the predominant platinum group minerals then it can be safely inferred that pt pd sulfides will be a significant component of the ug 2 layer in that area the occurrence of pt fe alloy also follows this principle the distribution of pt fe alloy is in fact a major factor in differentiating the ores in the vicinity north and south of the pilansberg alkaline complex from those of the same layers farther along the arcuate strike northeastern and southeastern horns of the western bushveld and has led to an overall concept relating platinum group mineral types to postulated centers of increased volatile activity or perhaps feeder sites of the complex the mineralogy of reef disturbances such as potholes is discussed the mode of occurrence of the platinum group minerals varies between base metal sulfide silicate and chromite associations and the size of platinum group minerals in the various reefs is given solid solution or lattice substitutions of platinum group elements in the base metal sulfides account for the very important latent fraction of the total platinum group elements as distinct from platinum group minerals of the bushveld complex rhodium in the merensky reef occurs almost wholly in solid solution within pentlandite whereas rh minerals occur in the ug 2 layer chromite tends to host microscopic to submicroscopic inclusions of laurite and does not appear to take ru into the crystal lattice the probability of solid solution of platinum group elements in silicate and other oxide phases is discussed

u pb geochronologic constraints on the paleoproterozoic crustal evolution of the upper granite gorge grand canyon arizona new field observations and u pb zircon and monazite ages are used to outline a geologic history of paleoproterozoic rocks beneath the colorado plateau in the grand canyon of northern arizona the upper granite gorge of the grand canyon exposes three lithotectonic units including supracrustal rocks mafic to intermediate composition plutons and peraluminous granite dikes that are variably deformed and metamorphosed new u pb ages indicate that layered supracrustal rocks were deposited or erupted over at least 8 m y between 1750 2 and 1741 1 ma mafic to intermediate composition plutons intruded the supracrustal rocks at 1741 1 ma zoroaster granite 1737 1 ma grapevine camp granite 1730 3 ma trinity granodiorite 1717 1 ma ruby granodiorite and 1713 2 ma horn diorite both supracrustal and plutonic rocks are intruded by 1698 1662 ma peraluminous granite and pegmatite dikes that locally form 50 of the rock volume u pb ages of foliated plutonic rocks and crosscutting granite dikes bracket the timing of fabric development for three groups of fabrics group 1 fabrics formed between 1730 3 and 1698 1 ma group 2 fabrics formed between 1713 2 and 1685 1 ma the timing of group 3 fabric formation is poorly constrained although the 1662 ma phantom pluton contains shear bands that offset pegmatitic dikes that crosscut the pluton metamorphic grade varies across the transect from lower amphibolite facies to lower granulite facies we suggest that single crystal u pb ages 1706 1697 of metamorphic monazite from a 1741 ma supracrustal rock directly date the timing of lower granulite facies metamorphism in the eastern upper gorge u pb ages 1685 1680 ma of granite dikes that postdate the development of leucosomal pegmatite pods in migmatitic supracrustal rocks in the eastern upper gorge are consistent with this suggestion the paleoproterozoic geologic history of the upper granite gorge is similar to that of the yavapai province in central arizona however unlike the juvenile crust that characterizes the yavapai province rocks in the western upper gorge preserve evidence for pre 1 8 ga crust first the 1840 1 ma elves chasm pluton the oldest known rock from the southwestern united states has a pb isotopic signature similar to that of rocks in the mojave province second the tuna creek granodiorite a member of the 1710 1750 ma arc related plutonic suite contains inherited zircons with minimum ages of 1998 and 2178 ma and exhibits whole rock pb isotopic signatures similar to rocks of the mojave province these data indicate that pre 1 8 ga crustal components participated at least locally in the development of the 1740 1710 ma arc related magmatic suite and suggest that a boundary between reworked crust and juvenile crust may be present in the western upper gorge

detection of melt onset over the northern canadian arctic archipelago sea ice from radarsat 1997 2014 abstract we present an algorithm to detect melt onset over arctic sea ice using high resolution synthetic aperture radar sar images from radarsat the algorithm is based on the temporal evolution of the sar backscatter coefficient using an ice type specific threshold approach that also corrects for incidence angle variation using 4457 radarsat images the algorithm was applied over sea ice in the northern canadian arctic archipelago that low spatial resolution microwave sensors have difficulty resolving thus generating a new time series of melt onset from 1997 to 2014 over the 1997 2014 period the mean annual average melt onset date in the northern caa was on year day 164 mid june with a standard deviation of 4 days no significant trend for melt onset date was found over the 18 year period an earlier later melt onset was associated with increased decreased solar energy absorption r 0 64 significant at 95 confidence and subsequently associated in lighter heavier september sea ice coverage in the northern caa r 0 62 significant at 95 confidence radarsat estimates of melt onset were found to be in good agreement but more robust compared to passive microwave and scatterometer estimates over the northern caa

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

tectonic evolution of proterozoic rocks in the cimarron mountains northern new mexico usa abstract portions of three proterozoic tectonostratigraphic sequences are exposed in the cimarron mountains of new mexico the cimarron river tectonic unit has affinities to a convergent margin plutonic volcanic complex igneous hornblende from a quartz diorite stock records an emplacement pressure of 2 2 6 kbar rocks within this unit were subsequently deformed during a greenschist facies regional metamorphism at 4 5 kbar and 330 50 c the tolby meadow tectonic unit consists of quartzite and schist mineral assemblages are indicative of regional metamorphism at pressures near 4 kbar and temperatures of 520 20 c a low angle ductile shear zone separates this succession from gneisses of the structurally underlying eagle nest tectonic unit gneissic granite yields hornblende pressures of 6 8 kbar pelitic gneiss records regional metamorphic conditions of 6 7 kbar and 705 15 c overprinted by retrogression at 4 kbar and 530 10 c comparison of metamorphic and retrograde conditions indicates a p t path dominated by decompression and cooling the low angle ductile shear zone represents an extensional structure which was active during metamorphism this extension juxtaposed the tolby meadow and eagle nest units at 4 kbar and 520 c both units were later overprinted by folding and low grade metamorphism and then were emplaced against the cimarron river tectonic unit by right slip movement along the steeply dipping fowler pass shear zone an argon isotope correlation age obtained from igneous hornblende dates plutonism in the cimarron river unit at 1678 ma muscovite associated with the greenschist facies metamorphic overprint yields a 40 ar 39 ar plateau age of 1350 ma by contrast rocks within the tolby meadow and eagle nest units yield significantly younger argon cooling ages hornblende isotope correlation ages of 1394 1398 ma are interpreted to date cooling during middle proterozoic extension muscovite plateau ages of 1267 1257 ma appear to date cooling from the low grade metamorphic overprint the latest ductile movement along the fowler pass shear zone post dated these cooling ages argon released from muscovites of the eagle nest tolby meadow composite unit at low experimental temperatures yields apparent ages of c 1100 ma similar ages are not obtained north east of the fowler pass shear zone suggesting movement more recently than 1100 ma

limex 87 ice surface characteristics implications for c band sar backscatter signatures ice surface characterization data collected in 1987 during the labrador ice margin experiment are analyzed to estimate the changes in snow and ice properties at the onset of melt surface measurements were made from an ice research vessel on several days some of which had coincident remote sensing flights at a number of locations in the marginal ice zone these data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon c band scattering signatures

pge tenor and metal ratios within and below the merensky reef bushveld complex implications for its genesis the merensky reef is the consequence of several major influxes of magma into the bushveld magma chamber that gave rise to at least two cyclic units including the pre merensky and merensky cyclic units analysis of the s ni cu platinum group element pge and au contents of 1140 samples from 24 profiles through the rocks forming these units and two profiles extending downward from the reef to close to the ug 2 horizon of the western bushveld complex provide important petrogenetic constraints on the origin of the reef particular attention is paid to variations in the calculated pge tenors and cu pd ratios of sulfides both vertically and laterally all of the profiles show a decrease in pt tenor and concomitant increase in cu pd ratio upward across the pyroxenite of the merensky unit and laterally away from certain centres that are interpreted as feeder zones the data also document that more mafic horizons within the merensky to ug 2 interval of the southwestern bushveld are characterized by much lower cu pd 100 400 than the ambient ratio 4000 this is interpreted as demonstrating that these horizons are the consequence of incursions of magma whose composition has been modified in a staging chamber by reaction with sulfide resident there the favoured interpretation for the merensky reef is that the bushveld chamber s was occupied by a resident magma crystallizing orthopyroxene and plagioclase pre merensky and subsequently merensky magmas entered the chamber s intermittently from localized feeder structures mixing or mingling with the resident magma and giving rise to the more mafic cumulates at specific horizons including the merensky reef the mixing or mingling caused sulfide immiscibility in these cases as the new magma pulses flowed laterally away from the entry zones they deposited sulfide becoming depleted in pge on coming to rest the magma continued to segregate sulfide and crystallize pyroxene so that the sulfides became progressively depleted in pge and acquired a higher cu pd upward through the pyroxenite this model requires that the merensky magmas could dissolve up to two orders of magnitude more pge than current measurements on dry diopside anorthite melts have indicated it is suggested that very pge rich magmas can develop as a result of sulfide unsaturated magma reacting with early formed sulfide in a staging chamber dissolving fes and enriching the remaining sulfide in pge later magmas equilibrating with this enriched sulfide will themselves become highly enriched in pge

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

a monte carlo method for simulating scattering from sea ice using fvtd a scattering model based on a monte carlo method and the finite volume time domain fvtd method has been created for sea ice scattering simulations statistical methods were used to generate a gaussian distributed randomly rough surface the polder van santen de loor pvd model was used to estimate the sea ice dielectric values with inputs based upon actual measured physical variables obtained during field based experiments and well known parameterizations scattering simulations were performed through an application of the scattered field sf formulation invoked in an fvtd computational engine simulated sfs were compared with c band scatterometer measurements and showed good agreement for copolarized signals in a series of case studies the developed simulation method has the potential to be used for a variety of sea ice types under different physical conditions

numerical and experimental evaluation of terrestrial lidar for parameterizing centimeter scale sea ice surface roughness terrestrial light detection and ranging lidar offers significant advantages over conventional techniques for measuring the centimeter scale surface roughness of natural surfaces such as sea ice however the laser scanning technique is inherently limited principally by the following 1 the high inclination scanning angle of the sensor with respect to nadir 2 the precision of the laser ranging estimate and 3 the beam divergence of the laser in this paper we introduce a numerical model that has been designed to simulate the acquisition of lidar data over a regular rough surface results from the model compare well r 2 0 97 with lidar observations collected over two experimental surfaces of known roughness that were constructed from medium density fibreboard using a computer numerical control three axis router the model demonstrates that surface roughness parameters are not sensitive to minor variations in the lidar sensor s range and laser beam divergence but are slightly sensitive to the precision of the ranging estimate the model also demonstrates that surface roughness parameters are particularly sensitive to the inclination angle of the lidar sensor the surface rms height is underestimated and the correlation length is overestimated as either the inclination angle of the sensor or the true roughness of the surface increases an isotropic surface is also increasingly observed as an anisotropic surface as either the inclination angle or the true surface roughness increases based on the model results we propose a set of calibration functions that can be used to correct in situ lidar measurements of surface roughness

age provenance and tectonic setting of paleoproterozoic quartzite successions in the southwestern united states new field studies combined with u pb zircon geochronology constrain the ages of deposition and sedimentary provenance of paleoproterozoic quartzite successions exposed in the southwestern united states orthoquartzites were deposited in short lived basins at two times ca 1 70 and 1 65 ga during crustal assembly of southern laurentia the more voluminous ca 1 70 ga successions occur in southern colorado northern new mexico and central arizona and are interpreted here to be time correlative though not necessarily deposited in the same basins detrital zircon from quartzites and metaconglomerates exposed in southern colorado and northern new mexico is characterized by a single population with a relatively narrow range of ages 1 80 1 70 ga and minimal archean input 5 of grains analyzed peak detrital zircon ages 1 76 1 70 ga vary slightly from location to location and mimic the age of underlying basement unimodal detrital populations suggest local sources and a first cycle origin of the orthoquartzites within a short time interval 1 70 1 68 ga during unroofing of local underlying basement the maximum age of quartzite exposed at blue ridge colorado is constrained by the 1705 1698 ma coarse grained granitoid basement on which quartzite was deposited unconformably the minimum age of ortega formation quartzite new mexico is constrained by ca 1680 1670 ma metamorphic monazite overgrowths these dates agree with direct ages on the lower mazatzal group arizona and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca 1 70 ga yavapai orogeny regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca 1 66 1 60 ga mazatzal orogeny thus making them important time markers separating the yavapai and mazatzal orogenic events our model for syntectonic deposition involves extensional basin development followed by thrust closure possibly due to opening and closing of slab rollback basins related to outboard subduction the first cycle origin of orthoquartzites near the end of the arc collisions of the yavapai orogeny seems to contrast sharply with their extreme compositional maturity this can be explained in terms of protracted extreme diagenesis and or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the proterozoic similarities among quartzites exposed throughout the southwestern united states and along the laurentian margin suggest that they represent a widespread regional and perhaps global episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions a combination that might make these units a signature lithology for paleoproterozoic time

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation a common model for the paleoproterozoic crustal evolution of southern laurentia involves southerly accretion of successively younger island arcs from 1780 to 1650 ma this model may be oversimplified however for although andesite and basaltic andesite major components of modern island arcs occur they are relatively rare and large volumes of rocks are dominantly bimodal metavolcanic assemblages and related granitoids ophiolites occur but they are also rare and only one accretionary melange has been described inherited zircons and common pb and nd isotopic data indicate involvement of older crust in ca 1750 ma rocks of the mojave province of southeastern california and western arizona and the bimodal assemblages of central colorado these data suggest that the bimodal volcanic rocks were derived from pre existing continental crust likely of ca 1850 ma trans hudson penokean age during extension and partial melting associated with the development of transpressional crustal scale shear zones the occurrence of the 1840 1 ma elves chasm pluton in the grand canyon demonstrates that rocks of trans hudson penokean age are present in southwestern laurentia

epeirogenic controls on canadian river incision and landscape evolution great plains of northeastern new mexico abstract the canadian river has carved a deep bedrock canyon into the great plains of northeastern new mexico in response to a complex interaction of post laramide epeirogenic rock uplift processes along the jemez lineament and downstream baselevel fall caused by late tertiary and quaternary evaporite dissolution broad slow bulging along the jemez lineament a lithospheric scale structure with prolific late cenozoic volcanism along its trend helps drive incision in the canyon canadian river canyon fluvial terraces mapped and correlated according to soils elevation and rock type criteria reveal longitudinal profiles that appear broadly warped across the jemez lineament and converge to the modern channel profile both upstream and downstream of the canyon similarly the modern channel long profile is distinctly and broadly convex through its great plains reach a unique feature among major rivers draining the eastern flank of the southern rocky mountain front radiocarbon dated charcoal from terrac

fractional crystallization induced variations in sulfides from the noril sk talnakh mining district polar siberia russia abstract the distribution of platinum group elements pge within zoned magmatic ore bodies has been extensively studied and appears to be controlled by the partitioning behavior of the pge during fractional crystallization of magmatic sulfide liquids however other chalcophile elements especially tabs te as bi sb and sn have been neglected despite their critical role in forming platinum group minerals pgm tabs are volatile trace elements that are considered to be mobile so investigating their primary distribution may be challenging in magmatic ore bodies that have been somewhat altered magmatic sulfide ore bodies from the noril sk talnakh mining district polar siberia russia offer an exceptional opportunity to investigate the behavior of tabs during fractional crystallization of sulfide liquids and pgm formation as the primary features of the ore bodies have been relatively well preserved in this study new petrographic 2d and 3d and whole rock geochemical data from cu poor to cu rich sulfide ores of the noril sk talnakh mining district are integrated with published data to consider the role of fractional crystallization in generating mineralogical and geochemical variations across the different ore types disseminated to massive despite textural variations in cu rich massive sulfides lenses veins and breccias these sulfides have similar chemical compositions which suggests that cu rich veins and breccias formed from fractionated sulfide liquids that were injected into the surrounding rocks numerical modeling using the median disseminated sulfide composition as the initial sulfide liquid composition and recent dmss liq and diss liq predicts the compositional variations observed in the massive sulfides especially in terms of pt pd and tabs therefore distribution of these elements in the massive sulfides was likely controlled by their partitioning behavior during sulfide liquid fractional crystallization prior to pgm formation our observations indicate that in the cu poor massive sulfides the pgm formed as the result of exsolution from sulfide minerals whereas in the cu rich massive sulfides the pgm formed by crystallization from late stage fractionated sulfide liquids we suggest that the significant amount of sn bearing pgm may be related to crustal contamination from granodiorite whereas as bi te and sb were likely added to the magma along with s from sedimentary rocks large pgm that are scarce and randomly distributed may account for most of the whole rock pt budget based on our results we propose a holistic genetic model for the formation of the magmatic sulfide ore bodies of the noril sk talnakh mining district

new constraints on the origin of the skaergaard intrusion cu pd au mineralization insights from high resolution x ray computed tomography abstract this contribution presents the first detailed three dimensional 3d in situ analysis of samples from the platinova reef using high resolution x ray computed tomography hrxct and 3d image processing and quantification coupled with microscopic and mineralogical investigations our hrxct analyses reveal the complex textural relationships between cu rich sulfides bulk composition close to bornite skaergaardite pdcu au rich phases silicates and fe ti oxides and provide unequivocal textural evidences not observed previously the association in 3d between cu rich sulfide globules pdcu alloy and ilmenite is inconsistent with a hydrothermal origin of the cu pd mineralization in contrast our results combined with phase diagrams strongly support a primary magmatic origin for the cu pd mineralization where cu and pd rich fe poor sulfide liquid represents a cumulus phase that forms by in situ nucleation these sulfide droplets and attached skaergaardite grains were trapped during the formation and crystallization of the fe ti oxides subsequent post cumulus processes led to the partial to total dissolution of the sulfide not entirely enclosed by the fe ti oxides i e not protected from reaction leading to the observed variability in cu and pd composition at the aggregate sulfide pdcu scale and to the occurrence of free pdcu alloys in contrast to the pdcu alloy gold bearing minerals are never observed entirely enclosed within the fe ti oxide two hypotheses can be envisaged for the formation of the gold enriched layer in the upper part of the section gold may have either precipitated from high temperature late magmatic cl rich fluids alternatively gold may have been enriched during fractional crystallization after sulfide had been suppressed from the liquidus after the pd layer crystallized and then deposited along redox barriers

platinum group elements in sulphide minerals platinum group minerals and whole rocks of the merensky reef bushveld complex south africa implications for the formation of the reef the concentrations of platinum group elements pge co re au and ag have been determined in the base metal sulphide bms of a section of the merensky reef in addition we performed detailed image analysis of the platinum group minerals pgm the aims of the study were to establish 1 whether the bms are the principal host of these elements 2 whether individual elements preferentially partition into a specific bms 3 whether the concentration of the elements varies with stratigraphy or lithology 4 what is the proportion of pge hosted by pgm 5 whether the pgm and the pge found in bms could account for the complete pge budget of the whole rocks in all lithologies most of the pge 65 up to 85 are hosted by pgm essentially pt fe alloy pt pd sulphide pt pd bismuthotelluride lesser amounts of pge occur in solid solution within the bms in most cases the pgm occur at the contact between the bms and silicates or oxides or are included within the bms pentlandite is the principal bms host of all of the pge except pt and contains up to 600 ppm combined pge it is preferentially enriched in pd rh and co pyrrhotite contains rh os ir and ru but excludes both pt and pd chalcopyrite contains very little of the pge but does concentrate ag and cd platinum and au do not partition into any of the bms instead they occur in the form of pgm and electrum in the chromitite layers the whole rock concentrations of all the pge except pd are enriched by a factor of five relative to s ni cu and au this enrichment could be attributed to bms in these layers being richer in pge than the bms in the silicate layers however the pge content in the bms varies only slightly as a function of the stratigraphy the bms in the chromitites contain twice as much pge as the bms in the silicate rocks but this is not sufficient to explain the strong enrichment of pge in the chromitites in the light of our results we propose that the collection of the pge occurred in two steps in the chromitites some pgm formed before sulphide saturation during chromitite layer formation the remaining pge were collected by an immiscible sulphide liquid that percolated downward until it encountered the chromitite layers in the silicate rocks pge were collected by only the sulphide liquid

c band polarimetric backscattering signatures of newly formed sea ice during fall freeze up a study of the polarimetric backscattering response of newly formed sea ice types under a large assortment of surface coverage was conducted using a ship based c band polarimetric radar system polarimetric backscattering results and physical data for 40 stations during the fall freeze up of 2003 2006 and 2007 are presented analysis of the copolarized correlation coefficient showed its sensitivity to both sea ice thickness and surface coverage and resulted in a statistically significant separation of ice thickness into two regimes ice less than 6 cm thick and ice greater than 8 cm thick a case study quantified the backscatter of a layer of snow infiltrated frost flowers on new sea ice showing that the presence of the old frost flowers can enhance the backscatter by more than 6 db finally a statistical analysis of a series of temporal spatial measurements over a visually homogeneous frost flower covered ice floe identified temperature as a significant but not exclusive factor in the backscattering measurements

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

filling the north american proterozoic tectonic gap 1 60 1 59 ga deformation and orogenesis in southern wyoming usa abstract structural and thermochronologic studies in the sierra madre southern wyoming indicate that parts of the 1 78 1 75 ga cheyenne belt an archean proterozoic suture were reactivated at ca 1 6 ga new shear zones notably the brittle battle lake thrust tear fault zone also formed at this time the battle lake fault zone blfz which displaced parts of the cheyenne belt at least 30 km to the north corresponds to the surface expression of a south dipping reflector imaged by regional seismic studies continental dynamics of the rocky mountains experiment 40ar 39ar and u pb data define age patterns in the sierra madre that are delineated by discrete structures north of the 1 78 ga divide peak mylonite zone a foreland structure associated with the medicine bow orogeny 40ar 39ar biotite dates suggest cooling below 300 c by 2 0 ga south of the divide peak mylonite zone but north of the blfz hornblendes yield apparent 40ar 39ar ages of ca 1 80 1 78 ga that may record tectonic burial and cooli

architecture of a 1 38 1 34 ga granite rhyolite complex as revealed by geochronology and isotopic and elemental geochemistry of subsurface samples from west texas usa abstract during the evolution of laurentia a mesoproterozoic felsic igneous belt extended from fennoscandia through canada to the southwestern united states this belt referred to as the granite rhyolite province in north america forms much of the west texas and eastern new mexico basement we present data from 41 closely spaced wells in west texas that penetrated several hundred meters into the southern granite rhyolite province and provide the first opportunity to develop a three dimensional view of the basement from subsurface samples the felsic rock types include hornblende bearing quartz monzonite ignimbritic rhyolite and comagmatic granite with eutectic textures these rocks plot in the high k to ultra high k field quartz syenite which plots exclusively in the ultra high k field is the final felsic phase of magmatism all of the felsic magmas were variably oxidizing based on biotite compositions u pb chronology supports the intrusive relations established by petrography the quartz monzonite is oldest 1380 ma and is followed by the granite rhyolite sequence 1360 ma and the quartz syenite 1340 ma nd model ages range from 1520 to 1740 ma indicating involvement of older proterozoic crust in many wells thick mafic sills intrude the granite rhyolite sequence nd model ages for the mafic rocks range from 1560 to 1440 ma implying that they are mesoproterozoic in age the mafic rocks include an alkaline oib like suite which is not supportive of a subduction origin u pb ages are also reported for the mescalero well 1 in eastern new mexico in this well metasedimentary and metavolcanic rocks of the debaca sequence unconformably overlie a quartz syenite similar to the quartz syenite from the west texas wells detrital zircons from the basal meta arkose of the sequence are 1690 and 1320 ma indicating a maximum age of 1300 ma for this sequence

geometry and folding history of the baraboo syncline implications for the mazatzal orogeny in the north central u s abstract the baraboo syncline in south central wisconsin formed during the mazatzal orogeny it is a doubly plunging asymmetric syncline internal structures such as chocolate tablet style boudinage and tension gashes indicate stretching parallel to the fold axis and preclude folding by plane strain models both the fold geometry and the internal deformation within the fold limbs suggest a history of 1 buckling that varied along the fold axis resulting in doubly plunging folds and stretching along the fold axis followed by 2 continued buckling combined with top to the south simple shearing that may have varied along the fold axis the second stage of deformation could be the result of the onset of an overriding thrust package the deformation history is consistent with a typical south verging fold forming in a fold and thrust belt that inherited its geometry from a north dipping subduction zone

paragenesis of multiple platinum group mineral populations in shetland ophiolite chromitite 3d x ray tomography and in situ os isotopes abstract chromitite from the harold s grave locality in the mantle section of the shetland ophiolite complex is extremely enriched in ru os and ir at g g concentrations high resolution x ray computed tomography on micro cores from these chromitites was used to determine the location size distribution and morphology of the platinum group minerals pgm there are five generations of pgm in these chromitites small average 5 m in equivalent sphere diameter esd euhedral laurites often with os ir alloys are totally enclosed in the chromite and are likely to have formed first by direct crystallisation from the magma as the chromite crystallised also within the chromitite there are clusters of larger 50 m esd aligned elongate crystals of pt rh ir os and ru bearing pgm that have different orientations in different chromite crystals these may have formed either by exsolution or by preferential nucleation of pgms in boundary layers around particular growing chromite grains thirdly there is a generation of large 100 m esd composite os ir ru rich pgm that are all interstitial to the chromite grains and sometimes form in clusters it is proposed that os ir and ru in this generation were concentrated in base metal sulfide droplets that were then re dissolved into a later sulfide undersaturated magma leaving pgm interstitial to the chromite grains fourthly there is a group of almost spherical large 80 m esd laurites hosting minor os ir ru rich pgm that form on the edge or enclosed in chromite grains occurring in a sheet crosscutting a chromitite layer these may be hosted in an annealed late syn or post magmatic fracture finally a few of the pgm have been deformed in localised shear zones through the chromitites the vast majority of the pgm including small pgm enclosed within chromite larger interstitial pgm and elongate aligned pgm have os isotope compositions that give re depletion model ages approximately equal to the age of the ophiolite at 492 ma a number of other pgm not confined to a single textural group fall to more or less radiogenic values with four pgm giving anomalously unradiogenic os corresponding to an older age of 1050 ma the 187 os 188 os isotopic ratios for pgm from cliff and quoys from the same ophiolite section are somewhat more radiogenic than those at harold s grave this may be due to a distinct mantle source history or possibly the assimilation of radiogenic crustal os

crustal structure beneath the sub himalayan fold thrust belt kangra recess northwest india from seismic reflection profiling implications for late paleoproterozoic orogenesis and modern earthquake hazard abstract most compressional orogens include salients and recesses along their strike the age and origin of which can be hard to ascertain in the kangra recess in the trace of the main boundary thrust mbt the largest such recess within the active himalayan orogen the sub himalayan sedimentary fold thrust belt increases in width to as much as 90 km the kangra basin but narrows to as little as 10 km in the adjoining nahan salient of the mbt the subathu basin to the southeast new seismic reflection profiling places the himalayan decollement at 6 8 km depth above thin but reflective meso to neoproterozoic vindhyan lesser himalayan series equivalent strata these data show that the vindhyan sedimentary rocks are thinner in the kangra recess than further southeast allowing the hypothesis that the width of the lesser himalayan thrust belt and the existence of the kangra recess could be related to the pre deformation basin thickness this hypothesis obviates the need for control of the kangra recess by a lateral ramp in the main himalayan thrust so making it more likely that the kangra segment could rupture as part of an earthquake far larger than the devastating 1905 m 7 8 kangra earthquake below the proterozoic sedimentary rocks our reflection data show a west southwest dipping reflective fabric spanning a 30 km crustal thickness which we infer corresponds to a widespread ulleri wangtu orogenic event at c 1850 ma affecting a pre tethyan indian continental margin thickening the basement by c 20 the deepest 10 km of this 50 km thick crust shows a more horizontal arguably younger reflectivity though the moho is not clearly marked by strong reflectors

a scattering model for snow covered sea ice the special properties of a robust radiative transfer model for scattering from layers of inhomogeneous rough boundary slabs are presented the model is applied to backscattering from saline and desalinated ice comparisons are made at single and multiple frequencies with some of the most complete sets of measurement data available using measured physical and electrical characteristics of the ice as inputs to the model where possible the results show close agreement for example for the saline ice backscatter data set which consisted of measurements at two like and two cross polarizations at 5 and 13 9 ghz the agreement with model predictions is within 2 db except at 13 9 ghz cross polarization backscattering from 15 cm thick saline ice is generally dominated by scattering from the top surface while backscattering from

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

the role of snow on the thermal dependence of microwave backscatter over sea ice our understanding of snow distribution in the polar regions is severely restricted owing to the heterogeneity both in space and time of this solid precipitate processes such as vapor and mass fluxes across the interface are to a large extent controlled by the presence and geophysical state of the snow cover on sea ice numerous studies have shown the importance of snow cover in ecosystem processes and particularly in photosynthetically active radiation extinction researchers are currently exploiting developments in electromagnetic interaction theory in an attempt to measure snow thickness distributions remotely in this paper we investigate the dependence of radar backscatter on snow thickness over smooth first year ice we use data from the seasonal sea ice monitoring and modeling site located in the canadian archipelago results show that the thermodynamics of the snow cover affect wave propagation attenuation and scattering through the control that brine volume exerts on interfacial characteristics of the snow and ice layers the effect is subtle and specific to certain ranges of salinity surface roughness and thickness of sea ice we describe the phenomenon responsible for this effect using a microwave model consistently for both complex effective permittivities and backscatter coefficients coupled to a one dimensional model we validate the physical principles using in situ field data we then discuss the potential of synthetic aperture radar in estimating snow thickness distributions under these specific conditions using both observed and modeled microwave scattering

microscale data to macroscale processes a review of microcharacterization applied to mineral systems microanalysis can provide rapid quantitative characterization of mineral systems that complements the field and core scale observations traditionally made in ore deposits we review recent innovations in microanalytical procedures and their application to studies of ore deposits case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems synchrotron x ray fluorescence shows centimetre scale chemical variations associated with proximity to mineralization in samples from sunrise dam gold mine western australia pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid driven brecciation with very little shearing both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization a second case study of sulphide mineralogy at the mt keith nickel sulphide deposit western australia demonstrates how x ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems large scale interaction between silicate and sulphide melts shown by homogenous palladium enrichment in pentlandite leads to a large proportion of globular ores with a high nickel content increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro and macroscale datasets

first year sea ice spring melt transitions in the canadian arctic archipelago from time series synthetic aperture radar data 1992 2002 this paper synthesizes 10 years worth of interannual time series space borne ers 1 and radarsat 1 synthetic aperture radar sar data collected coincident with daily measurement of snow covered land fast first year sea ice fyi geophysical and surface radiation data collected from the seasonal sea ice monitoring and modeling site collaborative interdisciplinary cryospheric experiment and 1998 north water polynya study over the period 1992 to 2002 the objectives are to investigate the seasonal co relationship of the sar time series dataset with selected surface mass bulk snow thickness and climate state variables surface temperature and albedo measured in situ for the purpose of measuring the interannual variability of sea ice spring melt transitions and validating a time series sar methodology for sea ice surface mass and climate state parameter estimation we begin with a review of the salient processes required for our interpretation of time series microwave backscatter from land fast fyi our results suggest that time series sar data can reliably measure the timing and duration of surface albedo transitions at daily to weekly time scales and at a spatial scales that are on the order of hundreds of metres snow thickness on fyi immediately prior to melt onset explains a statistically significant portion of the variability in timing of sar detected melt onset to pond onset for sar time series that are made up of more than 25 images our results also show that the funicular regime of snowmelt resolved in time series sar data at a temporal resolution of approximately 2 5 images per week is not detectable for snow covers less than 25 cm in thickness copyright 2007 john wiley sons ltd

solubility of pt in sulphide mattes implications for the genesis of pge rich horizons in layered intrusions the partitioning of pt in sulphide melt matte has been studied as a function of fs2 and fo2 at 1200 and 1300 c the results show that the solubility of pt in mattes increases strongly with increasing fs2 and decreases weakly with increasing fo2 the increase in pt solubility with increasing fs2 is attributed to pt dissolving in the melt as a sulphide species and the weak inverse dependence of pt solubility on fo2 to the diluting effect of increasing o in the melt at high fo2 these results coupled with measurements of pt solubility in silicate melts taken from the literature allow the calculation of pt matte silicate melt partition coefficients d pt matte sil for a range of conditions pertinent to the formation of pt rich horizons in layered intrusions the calculated values range between 107 and 1011 depending on fo2 and fs2 several orders of magnitude higher than previously published values our preferred value for d pt matte sil for conditions appropriate to the merensky reef is 107 and for the stillwater pt rich horizon 108 the new results are consistent with the magmatic hypothesis for pt rich horizons in layered intrusions

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied