the climatology of zonal wave numbers 1 and 2 planetary wave structure in the mlt using a chain of northern hemisphere superdarn radars the zonal wave components 1 and 2 were extracted from the meridional wind along the latitude band of 51 66 n for the years 2000 2008 using eight super dual auroral radar network superdarn radars spanning longitudes from 25 e to 150 w each extracted zonal component represents the superposition of all temporal periods with that zonal structure and indicates the total planetary wave energy available with that wave number the hovmoller diagrams show stationary as well as eastward and westward traveling planetary waves propagating in the background wind the method used to detect the zonal planetary wave components in the superdarn data are detailed and validated using uk meteorological office data which allows the evolution of s1 and s2 planetary wave energy between the stratosphere and mesosphere to be assessed the climatology of zonal wave number 1 and 2 planetary wave activity in the mesosphere lower thermosphere mlt is presented and compared to the activity in the stratosphere the mlt climatology of the mean wind anomalies shows stronger planetary wave activity during winter and weaker activity during summer with enhancement around midsummer and autumn equinox the climatology of the mean wind displays similar amplitudes apart from very strong s1 planetary wave amplitudes during summer in addition planetary wave activity during winters with major and minor stratospheric warming events are examined and contrasted

inclusions of phlogopite and phlogopite hydrates in chromite from the hongguleleng ophiolite in xinjiang northwest china

stratigraphic and textural variations in the chromite composition of the ophiolitic sakhakot qila complex pakistan the deposits and their host rocks compare well with podiform ores hosted by alpine type peridotites of ophiolites unlike most alpine type complexes predominant stratigraphic variations in the chemical composition of chromite exist the chromite deposits fall in two major zones the first consisting of three subzones regular compositional correlations between the accessory chromites of the host rocks and the associated segregated chromites are drawn indicating relatively later crystallization of the former relict cumulate chromitite textures cover the podiform range and are examined in the light of compositional data the inequigranular textural varieties probably developed by crystallization of successive crops from magmatic fractionation with their coarser grained massive chromite components always being slightly higher in mg mg fe super 2 than the associated finer grained chromite components the mg fe super 2 exchange between chromite and silicates seems to start during the cumulus stage and continues during the postcumulus stage but is reduced to a very small intensity during the subsolidus stage until it ends at about 700 degrees c modified journal abstract

a new superdarn meteor wind measurement raw time series analysis method and its application to mesopause region dynamics 1 superdarn meteor wind measurements in the mesopause region using the standard analysis of acfs constructed from the multi pulse sequence have several shortcomings to overcome them we have developed a new method to enable raw time series analysis without degrading normal superdarn acf observations the unevenly sampled raw time series is processed to detect only underdense meteor echoes to deduce line of sight neutral wind velocities and decay time constants we installed this new code at the sensu syowa radar in antarctica distributions of underdense meteor echoes show clear and expected dependency on distance from the radar local time and diffusion coefficient by using diffusion coefficients as height information we successfully obtained the structure of a downward phase propagating semi diurnal tide which has not previously been achieved by analysing normal superdarn acf data

controls on platinum group elemental distributions of podiform chromitites a case study of high cr and high al chromitites from chinese orogenic belts abstract a study of podiform chromite deposits from the asiatic orogenic belt and the qilian qiangling kunlun himalaya tectonic domain provides new insights into the geochemistry of the pges in podiform chromite deposits and the genesis of the deposits themselves the bulk of deposits which occur in mantle peridotites of ophiolites have typical ophiolitic pge patterns that are depleted in pt and pd relative to the average upper mantle and have negatively sloping distributions on mantle normalized diagrams type i high cr chromitites have higher os ir ru and rh contents than type ii high al chromitites although both have similar pd and pt most of the type i and ii chromite deposits have lower pd and pt contents than the upper mantle peridotites in which they occur podiform chromitites are essentially products of melt rock interaction in the upper mantle their cr and pges were contributed by not only the invading magmas but also by the upper mantle host the chromite deposits are in part metasomatic replacement bodies the type i high cr chromitite pge patterns were produced by interaction between s undersaturated boninitic magmas and depleted harzburgites whereas the type ii high al chromitite pge patterns were formed by interaction between initially s saturated tholeiitic magmas and depleted harzburgites the low to very low pd and pt contents of both type i and type ii chromitites require that the mantle assemblage in which the chromite deposits were formed had lost their sulfides and hence pd and pt prior to formation of the chromite deposits in addition no or little pd and pt were deposited by the invading magma which either remained s undersaturated boninite or became morb s undersaturated due to interaction with the s depleted harzburgitic mantle it is suggested that the very low ir os and ru contents of boninites in general might be due to loss of ir during the formation of podiform chromitites it is suggested that podiform chromitites with type i pge patterns were formed in an island arc environment whereas those with type ii pge patterns were formed in a back arc setting

compositional variations in the mesoarchean chromites of the nuggihalli schist belt western dharwar craton india potential parental melts and implications for tectonic setting the chromite deposits in the archean nuggihalli schist belt are part of a layered ultramafic mafic sequence within the western dharwar craton of the indian shield the 3 1 ga ultramafic mafic units occur as sill like intrusions within the volcano sedimentary sequences of the nuggihalli greenstone belt that are surrounded by the tonalite trondhjemite granodiorite ttg suite of rocks the entire succession is exposed in the tagdur mining district the succession has been divided into the lower and the upper ultramafic units separated by a middle gabbro unit the ultramafic units comprise of deformed massive chromitite bodies that are hosted within chromite bearing serpentinites the chromitite bodies occur in the form of pods and elongated lenses 60 500 m by 15 m detailed electron microprobe studies reveal intense compositional variability of the chromite grains in silicate rich chromitite 50 modal chromite and serpentinite 2 modal chromite throughout the entire ultramafic sequence however the primary composition of chromite is preserved in the massive chromitites 60 75 modal chromite from the byrapur and the bhaktarhalli mining district of the nuggihalli schist belt these are characterized by high cr ratios cr cr al 0 78 0 86 and moderate mg ratios mg mg fe2 0 38 0 58 the compositional variability occurs due to sub solidus re equilibration in the accessory chromite in the serpentinite mg ratio 0 01 0 38 cr ratio 0 02 0 99 and in silicate rich chromitite mg ratio 0 06 0 48 cr ratio 0 60 0 99 in the massive chromitites the sub solidus re equilibration for chromite is less or absent however the re equilibration is prominent in the co existing interstitial and included olivine fo96 98 and pyroxene grains mg numbers 97 99 compositional variability on the scale of a single chromite grain occurs in the form of zoning and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite in the zoned grains the composition of the core is modified and the rim is ferritchromit in general ferritchromit occurs as irregular patches along the grain boundaries and fractures of the zoned grains in this case ferritchromit formation is not very extensive this indicates a secondary low temperature hydrothermal origin of ferritchromit during serpentinization in some occurrences the ferritchromit rim is very well developed and only a small relict core appears to remain in the chromite grain however complete alteration of the chromite grains to ferritchromit without any remnant core is also present the regular well developed and continuous occurrence of ferritchromit rims around the chromite grain boundaries the complete alteration of the chromite grains and the modification of the core composition indicate the alteration in the nuggihalli schist belt to be intense pervasive and affected by later low grade metamorphism the primary composition of chromite has been used to compute the nature of the parental melt the parental melt calculations indicate derivation from a high mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the western dharwar craton tectonic discrimination diagrams using the primary composition of chromites indicate a supra subduction zone setting ssz for the archean chromitites of nuggihalli and derivation from a boninitic magma the composition of the komatiitic basalts resembles those of boninites that occur in subduction zones and back arc rift settings formation of the massive chromitites in nuggihalli may be due to magma mixing process involving hydrous high mg magmas or may be related to intrusions of chromite crystal laden magma however there is little scope to test these models because the host rocks are highly altered serpentinized and deformed the present configurations of the chromitite bodies are related to the multistage deformation processes that are common in archean greenstone belts

magnetic data processing for hydrocarbon exploration in the pannonian basin yugoslavia because magnetic minerals may directly indicate the presence of oil and gas deposits magnetic methods are applied to hydrocarbon exploration in oil bearing sedimentary basins the basic problem in applying these methods is the isolation of weak magnetic anomalies sourced by low concentrations of the magnetic minerals present these weak anomalies are often masked by much stronger magnetic anomalies caused by underlying magnetic rocks and or by rocks in the basin sediments weak local anomalies can efficiently be isolated by applying selective 1 d digital frequency filters the method of filtering has been checked by data obtained using simple models of magnetic sources and using a model representative of the local geology in our study area in the southern pannonian basin yugoslavia the magnetic field frequency content was analyzed by applying the power spectral density estimation using the maximum entropy method the digital filters were designed using the window function method the best results were

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

chromitite and ultramafic rock compositional zoning through a paleotransform fault poum new caledonia the major mylonitic shear zone of the northern part of the ophiolitic peridotite sheet of new caledonia has been described as a paleotransform fault secher 1981 located along this structure the poum ultramafic massif shows a wide spectrum of peridotite compositions ranging from plagioclase lherzolite to dunite across a 2 km thick transition zone the mylonitized plagioclase lherzolite contains abundant pyroxenite and mafic veins the poum ultramafic massif includes more than 30 chromitite orebodies their composition vanes according to the nature of the host peridotite al rich in the plagioclase lherzolite zone 31 43 al 2 o 3 and 25 36 cr 2 o 3 cr rich 39 60 cr 2 o 3 in the spinel lherzolite and clinopyroxene harzburgite zones and still richer in the harzburgite dunite zone 49 64 cr 2 o 3 in peridotites the accessory cr spinel also displays a cr enrichment from lherzolite to dunite segregations of cr rich chromite 50 60 cr 2 o 3 are present in orthopyroxenite veins displaying boninitic affinities the poum chromitites display low platinum group element pge contents and pd ir ratios as do the chromitite segregations of the orthopyroxenite veins suggesting a common parent magma or and common fractionation processes the compositional zoning of the poum massif can be explained by the contrasting behavior of ultramafic rocks and upwelling mafic melts away from the axis of the transform fault using the current ideas about the genesis of boninitic melts and the formation of dunite and harzburgite by magma rock interactions during melt percolation nicolas and prinzhofer 1983 kelemen 1990 kelemen et al 1992 takazawa et al 1992 in the lithospheric lherzolite zone that was cooled and mylonitized along the older wall of the transform fault melts were channeled along fractures leaving al rich chromitite pods by contrast pervasive percolation along the lithosphere asthenosphere boundary allowed important melt rock interactions resulting in the progressive formation of harzburgite and dunite and generating mg cr rich melts from which precipitated cr rich chromitites

irarsite hollingworthite solid solution series and other associated ru os ir and rh bearing pgm s from the shetland ophiolite complex pure end and intermediate members of the irarsite hollingworthite solid solution series occur in the shetland ophiolite complex hollingworthite frequently rims irarsite their compositions are unusually pt poor compared with analyses of these minerals from elswhere suggesting the existence of a pt poor environment during their formation ir sb s and rh sb s have been identified as inclusions within irarsite ir sb s and rh sb s together with rh ni sb are thought to be new platinum group minerals pgm s in ophiolite complexes two types of laurite are present an os rich up to 22 os variety is entirely enclosed by chromite whereas an os free variety is located in the silicate matrix interstitial to the chromite laurites in the rims of chromite grains are os free but contain tiny inclusions of native osmium it is suggested that either the availability of os decreased during crystallisation of the laurites or that os has been removed from laurites not totally enclosed by chromite in a few cases laurite is surrounded by a ruthenian pentlandite containing up to 12 ru

high rossby wave activity in austral winter 2002 modulation of the general circulation of the mlt during the macwave midas northern summer program 1 the seasonally and zonally averaged effects of the anomalously strong rossby wave activity in austral winter 2002 are estimated by a sensitivity experiment using an idealized general circulation model the approach focuses on the modulation of gravity wave saturation via the altered mean winds in the mesosphere and mlt in the northern summer mlt the effects consist of increased vertical gradients of the mean zonal wind and temperature as well as downward shifts of the residual circulation and the gravity wave induced frictional heating all these signals agree reasonably with observations obtained during the macwave midas program 2002

the genesis of archaean chromitites from the nuasahi and sukinda massifs in the singhbhum craton india abstract the chromitite deposits of the nuasahi and sukinda massifs are part of layered ultramafic bodies which occur within archaean low grade metamorphic rocks of the iron ore group iog in the singhbhum craton of the indian shield the chromitite seams are interlayered with dunite and associated with orthopyroxenite detailed electron microprobe study reveals very high mg numbers 0 66 0 82 and cr numbers 0 75 0 87 for chromite in massive chromitite from the seams high fo content fo 92 95 for olivine in dunite and high en content en 89 94 for orthopyroxene in orthopyroxenite our study suggests that the original igneous compositions for these minerals are preserved in the respective monomineralic rocks and can be used to evaluate the primary magmatic petrogenesis of the rocks the primitive compositions of the minerals in monomineralic rocks suggest high degree of partial melting of the source mantle during the mesoarchaean the parental magma from which the massive chromitites crystallized was of siliceous high mg basaltic or boninitic compositions similar to the compositions of spatially associated chromite bearing siliceous high mg basalts of the iron ore group the parental magma may have generated due to the interaction of a depleted mantle with a fluid enriched melt possibly derived in response to the dehydration of a subducting slab monomineralic chromitite layers formed either in response to mixing of magmas or due to the suppression of silicate mineral crystallization in response to elevated h 2 o concentrations in the parent magmas the parental magmas that produced chromitites may have intruded into the volcano sedimentary greenstone belts of a supra subduction zone setting

precious metals in magmatic fe ni cu sulfides from the potosi chromitite deposit eastern cuba abstract the moa baracoa ophiolite in eastern cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform chromite ores hosted in the mantle crust transition these sulfide ores chiefly consist of fe ni cu sulfides namely pyrrhotite pentlandite chalcopyrite and cubanite partly altered to valleriite the sulfide mineralization is located along the contact between the podiform like chromite ores and intruding pegmatitic gabroic dykes the detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation icp ms analysis reveals that this sulfide mineralization show contents of the precious metals os ir ru pt re au ag and other semi metals co ni cu se te bi pb as sb comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust the results obtained from this study confirm that fe ni cu sulfides at potosi are magmatic in origin and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre existing chromitite at the mantle crust transition zone of the ophiolite the immiscibility of sulfide melt was achieved as a result of a progressive increase of fs2 very likely triggered by a set of circumstances including the progressive fractionation of the intruding mafic melt leading to increase of asio2 and accumulation of volatiles as well as the crystallization of oxides two main generations of pentlandite were observed one generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution mss during low temperature cooling the second type of pentlandite resulted from the reaction of mss with coexisting droplets of cu and ni rich sulfide melt la icp ms analysis reveals that most precious metals ru os ir re au ag were concentrated along with the base metal sulfides bms although their distribution among the different bms pyrrhotite pentlandite chalcopyrite and cubanite does not strictly follow the expected distribution according to the known melt solid and solid solid partition coefficients unlike the other analyzed pges pt was not preferentially concentrated in bms but as discrete micrometer sized sperrylite grains the crystallization of sperrylite took place before and contemporaneous to sulfide segregation and pt as nanoparticles probably played an important role in the pt uptake as nucleation seeds for the formation of micron sized sperrylite grains these observations highlight the open system nature of the ore forming system as well as the important role of arsenic in concentrating pge in high temperature silicate and sulfide melts

a search for direct hydrocarbon indicators in the formby area it has been proposed that the high frequency low amplitude magnetic anomalies found over some hydrocarbon deposits are due to long term microseepage of hydrocarbons into iron rich sedimentary roof rocks with subsequent precipitation of diagenetic magnetite or pyrrhotite at or near the water table aerogeophysical data sets comprising both magnetic and gamma ray spectrometer measurements over the formby oil field lancashire u k have been analysed for hydrocarbon related anomalies detailed ground magnetic traverses were also made to investigate some of the aeromagnetic anomalies no hydrocarbon induced magnetic anomalies were detected the majority of the high frequency events occurring in the aeromagnetic data correlated with cultural features others were attributed to artefacts of the data processing in particular there were no extensive areas of high frequency low amplitude anomalies as might be expected from authigenic magnetic minerals borehole chippings from inside and outside the oil field were examined high magnetic susceptibilities were due to contamination during drilling magnetite which was identified by mineralogical analysis was found to be of detrital origin if any diagenetic magnetic material was present it was in such small quantities as to be insignificant the oil field did not possess a characteristic gamma ray spectrometric signature anomalies were found to be related to hydrological conditions and to the distribution of surficial deposits attempts to suppress the influence of the drift geology had only limited success it is concluded that the effectiveness of high resolution aeromagnetic onshore surveys for direct hydrocarbon detection has yet to be established in particular the anomaly found over the formby oil field was caused by the cumulative effect of borehole casing similar cultural contamination by oil field equipment may explain some of the anomalies discovered over hydrocarbon deposits in north america it is also unlikely that the spectrometric method can be applied diagnostically in any but the most simple and drift free geological environments

zircon ages and geochemical compositions of the manlay ophiolite and coeval island arc implications for the tectonic evolution of south mongolia abstract numerous small dismembered ophiolite fragments occur in south mongolia but they are very poorly studied the lack of age data and geochemical analysis hampers our understanding of the paleozoic tectonic evolution of the region we conducted detailed studies on the manlay ophiolitic complex and huree volcanic rocks south of the main mongolian lineament mml to provide some constraints on these rocks the manlay ophiolite consists of dunite harzburgite pyroxenite gabbro plagiogranite basalt and chert locally with chromite mineralization in dunite the gabbro and plagiogranite yielded shrimp zircon weighted mean 206 pb 238 u ages of 509 5 ma and 482 4 ma respectively the basalt and dolerite samples of this complex show enrichment in lree and lile and negative nb ta and ti anomalies and the chrome spinel from the chromitite lens in the dunite is characterized by high cr and low tio 2 contents these features suggest a supra subduction zone ssz origin for the ophiolitic complex the huree volcanic rocks ranging from basalt to dacite display enrichment in lree and lile weak eu anomalies and distinctly negative nb ta and ti anomalies consistent with those of typical magmas in a subduction environment an andesite sample from this arc yielded a shrimp 206 pb 238 u zircon age of 487 5 ma which is the oldest reliable age for an island arc in south mongolia recognition of an early paleozoic ophiolitic complex and a coeval island arc indicates that south mongolia underwent a period of active volcanism during late cambrian to ordovician additionally the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have shrimp zircon u pb ages of 391 5 ma and 304 4 ma respectively combining the available data we propose that the early paleozoic subduction accretionary complexes likely constitute the basement of the late paleozoic arc formations and correlate with the lake zone in western mongolia

chromite typology and composition characterized through multispectral specular reflectance abstract determination of multispectral specular reflectance is an important tool for ore identification in reflected light microscopy and may be used for automated characterization of ores however reflectance values can be affected by compositional variations in a way that is seldom understood the aim of the present work is to investigate this problem in chromite an ore whose composition may show typically large natural variations as member of the spinel family and whose relatively high reflectance variations are apparently unpredictable for this research eighteen samples of chromian spinel covering a large range of compositions in the base of the hagerthy prism were selected for microprobe analysis and reflectance measure on polished sections the samples belong to a variety of deposits and types ultramafic massif ophiolitic and metamorphosed types ojen and ronda massifs spain mayari moa baracoa camaguey and sagua de tanamo cuba golyamo kemenyane avren and yakovitsa bulgaria the specular reflectances are characterized as multispectral values measured at thirteen intervals 50 nm each in the vnir region visible and near infrared 400 1000 nm using the automated cameva system the relationship between compositional and reflectance values is studied by multivariate analysis and subsequently tested on independent samples for this purpose the samples have been grouped in two sets a larger population of fifteen samples constitutes the initial data set for mathematical processing while a selection of three samples of widely differing compositions is used to test the resulting functions so as to gain a critical appraisal of their validity the results obtained show that the specular reflectance of chromite depends on composition and can be used to estimate compositional parameters as cr cr cr al or mg mg mg fe2 but this relationship is complex and does not allow simple direct determinations due to the multiplicity of possible changes and coupled substitutions e g al cr fe3 or mg fe2 ni zn ti in the chromian spinel family on the other hand the relationship of chromite composition with deposit type is also detectable through the reflectance values but with a higher uncertainty reflectance increases with increasing cr and fe3 contents in all cases but the relationship of reflectance with mg seems to be specific of the deposit type while reflectance increases with increasing mg in the ojen chromites it shows the opposite behaviour in podiform chromites although these results should be regarded as preliminary until further studies on larger sample populations can be achieved they are suggestive of possible practical applications for exploration e g to approach cr spinel compositions or chromite deposit typology early in an exploration campaign by inexpensive reflected light determination of specular reflectance in a few samples

observed relation of soil magnetic susceptibility and soil gas hydrocarbon analyses to subsurface hydrocarbon accumulations magnetic susceptibility ms studies on soils over 19 oil and gas fields showed anomalously large amounts of diagenetic magnetic minerals in shallow depth samples in about 89 of the cases tested soil ms anomalies were compared with soil gas hydrocarbon ghc anomalies over 12 oil and gas fields including several stratigraphic traps and one gas storage reservoir samples were collected along the same profiles six examples are presented with detailed data listings our goal is to test the utility of soil magnetic susceptibility and soil gas hydrocarbons as petroleum prospecting methods we emphasize statistical evaluation of anomalies and their empirical correlation with producing areas and leads identified by other geochemical geological or geophysical data for direct comparison of anomaly strengths data are expressed statistically in terms of the appropriate background mean and standard deviation soil ms and soil ghc data complement each other providing better guidance to productive areas than either data set alone when used in an integrated exploration program their combined positive evidence of hydrocarbon presence under prospects could result in fewer dry holes than when drilling with structural information only

distribution of aluminum rich and chromium rich chromite pods in ophiolite peridotites detailed study of the acoje and the coto districts zambales philippines and comparison with new caledonia the troodos massif and other ophiolites cr rich pods are located near the lherzolite harzburgite transition zone whereas the al rich pods are distributed along the harzburgite dunite transition zone the chromite pods have probably been generated from different sources during the upwelling of mantle peridotites modified journal abstract

properties of the quasi 16 day wave derived from eos mls observations 1 this paper describes the use of eos microwave limb sounder mls data to observe the field of traveling planetary waves with quasi 16 day periods this study utilizes mls v2 2 temperature and geopotential data between 1 january 2005 and 31 december 2008 in the range 316 hpa to 0 001 hpa approximately 8 to 97 km to examine these waves analysis demonstrates that the quasi 16 day wavefield is made up of a number of components with westward and eastward propagating s 1 and s 2 waves generally dominant in the northern hemisphere the westward and eastward propagating s 1 waves have similar magnitudes and are larger than the other modes while in the southern hemisphere the eastward propagating s 1 and s 2 waves are larger than the westward propagating wave modes all of the modes examined display strong seasonal patterns in the temperature amplitude significant variability in the wave activity from year to year and the presence of strong pulse like patterns in the activity all of the modes also display large median temperature amplitudes poleward of 40 degrees in both hemispheres our analysis also demonstrates that the variability in winter from year to year is larger in the northern hemisphere than the southern hemisphere detailed study also suggests that the exclusion of waves from regions of negative refractive index squared likely forms much of the seasonal pattern observed thus regions of strong westward wind speeds effectively exclude vertically propagating waves as expected from theory the reflection and absorption of waves associated with critical lines is also likely to explain the frequent occurrence of standing wave patterns in the eos mls temperature observations this study highlights the potential of mls observations for observing waves from the upper troposphere to the lower mesosphere

september 2019 antarctic sudden stratospheric warming quasi 6 day wave burst and ionospheric effects an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming ssw in the southern hemisphere in september 2019 ionospheric data from esa s swarm

podiform chromitites of the tari misaka ultramafic complex southwestern japan as mantle melt interaction products petrological and geochemical data for chromian spinel from the tari misaka ultramafic complex southwest japan are discussed in this complex the spinels form a chromitite pod coated by a dunite envelope and are collectively enclosed by clinopyroxene bearing harzburgite chromitite and its dunite envelope are distinctly different from the surrounding harzburgite in terms of the chromian spinel chemistry the ti content is five to ten times higher in spinels of the enveloped chromitite than in those of the harzburgite although the cr ratio cr cr al the atomic ratio for both is almost constant or varies only slightly 0 4 0 5 this eliminates a comagmatic origin for the harzburgite dunite chromitite association spinel chemistry for both major and trace elements is almost the same in the chromitite and its dunite envelope except for the mg ratio and the co and mn contents which have a changed subsolidus as a function of the spinel mode thus the dunite and chromitite could be comagmatic but fractional crystallization of the dunite after or before chromitite deposition is not possible the chemistry of the chromian spinel and the mode of occurrence of the dunite chromitite association are consistent with an origin by interaction of an exotic melt with wall rock harzburgite the dunite may be of replacive origin the exotic melt would react with the harzburgite at the new contact to form dunite and a secondary si rich melt the melt thus formed could mix with a successive inflow of a more primitive melt the mixed melt would be expected to have chromite chromian spinel as the only liquidus phase precipitating chromitite next to the replacive dunite the dunite envelope podiform chromitite is most commonly formed in the mantle beneath island arcs the spread in cr ratios of spinel in podiform chromitites is almost comparable with that of spinel in primitive arc related magmas the presence of chromitite in the upper mantle beneath the japan arcs is consistent with this interpretation

a comparison of northern hemisphere winds using superdarn meteor trail and mf radar wind measurements the main purpose of the super dual auroral radar network super darn is to use paired radars to deduce the f region convection from doppler measurements of backscatter seen at large ranges typically beyond 900 km nearer to each hf radar the nearest ranges at 165 400 km are dominated by meteor trail echoes once formed the motion of these meteor trails is normally controlled by neutral winds in the 80 110 km altitude range by combining the line of sight velocities from all 16 receiver beams 52 in azimuth of a given superdarn radar it is possible to determine the full horizontal wind vector field over the meteor trail height range elevation angles are also measured using an interferometer mode and as such height information can in principle be obtained from the combined range and elevation angle data a comparison with neutral wind measurements from a colocated saskatoon canada mf wind radar indicates good agreement between the two radar systems at heights of 95 km based on these detailed comparisons a simple common method for determining two dimensional winds for all superdarn radars which have extensive longitudinal coverage was developed comparisons with other systems used for dynamical studies of tides and planetary waves are desirable and prove to be essential to obtain a good superdarn neutral wind motion analysis the mf radars at saskatoon and tromso norway are located near the western and eastern ends of the northern hemisphere network of six superdarn radars comparisons between the two types of radars for two seasonal intervals september and december show that the superdarn radars provide good longitudinal coverage of tides in support of the more detailed mf radar data the two systems complement each other effectively

formation of podiform chromitites by melt rock interaction in the upper mantle high cr and high al podiform chromitites are derived from melts formed by high and low degrees of partial melting in the upper mantle respectively the close association of the chromitites regardless of compositions with dunites and harzburgites can be explained by interaction between melts and harzburgites or depleted lherzolites in the upper mantle continuous reaction between melt and wallrock modifies the compositions of the magmas towards the precipitation of chromite alone under upper mantle conditions the modified magmas would have higher silica and lower magnesia and would be extracted into the crust or erupted leaving chromite pods in situ with dunite rinds that grade to harzburgites or lherzolites

os isotope heterogeneity of the upper mantle evidence from the mayari baracoa ophiolite belt in eastern cuba in an attempt to quantify the extent of geochemical heterogeneity within a restricted and well dated portion of the upper mantle 27 chromite separates from the 90 my old chromite deposits in the mayari baracoa ophiolite belt in eastern cuba have been investigated for platinum group element pge concentrations and re os isotopic systematics the samples are characterized by systematically subchondritic initial 187 os 188 os ratios and substantial heterogeneity the initial 187 os 188 os ratios vary with chromite chemistry and with geographical distribution reflecting differences in the os isotopic evolution for the different upper mantle sections represented by the ophiolite accordingly the os isotope data might be divided into three groups in the moa baracoa district where the chromite bodies are located in the mantle crust transition zone the calculated initial gos values average 0 97f0 69 n 13 in the sagua de tanamo district where chromite chemistry is highly variable and their location in relation the mantle sequence is less clear the initial gos values are intermediate with an average of 1 77f0 80 n 7 in the mayari district where the chromite bodies are located in the lower part of the mantle sequence initial gos values average 2 66f0 29 n 7 these subchondritic i e negative initial gos values are most simply explained by re depletion during ancient partial melting and or melt percolation events the os isotope heterogeneity documented here indicates a high degree of geochemical complexity on small to intermediate length scales in the upper mantle our results in combination with data on chromites from the literature show that an baverage present day os isotopic compositionq for the hypothetical depleted morb mantle dmm reservoir cannot be precisely established beyond the statement that it is bbroadly chondriticq indeed the upper mantle cannot be considered a sufficiently homogeneous geochemical breservoirq to serve meaningfully as a baseline against which geochemical banomaliesq are evaluated on the other hand our findings are consistent with the bstatistical upper mantle assemblageq or bsumaq concept according to which a high level of geochemical heterogeneity is maintained in the upper mantle at all relevant length scales as a result of the plate tectonic cycle and intra mantle processes such as melt migration and metasomatism d 2005 elsevier b v all rights reserved

high pge contents and extremely abundant pge minerals hosted in chromitites from the veria ophiolite complex northern greece abstract more than 100 small isolated chromite occurrences form elongated lenses that follow the nw se trend of the host serpentinized dunite within a 60 km 2 area 15 km se of veria northern greece they occur only within mylonite shear zones characterized by a strong overprint of late brittle deformation detailed investigation of chromitites by scanning electron microscope with energy dispersive x ray analysis shows that chromite is dominantly of high cr composition with the atomic cr cr al ratio ranging from 0 55 to 0 84 and an average value of 0 7 interstitial primary silicates in chromitites have been replaced by secondary phases consisting of mostly cr andradite cr chlorite and serpentine flakes in lesser amounts the most salient feature is the high total platinum group element pge content up to 25 ppm coupled with the presence of extremely abundant solitary platinum group element minerals pgm within massive chromite samples located along a shear zone these pgm fragments are angular rarely corroded grains or fine grained aggregates and occur in a matrix of cr garnet they are mostly os ru ir fe alloys containing small amounts of cr co mn followed by irarsite laurite rus 2 with variable os and ir contents occurs as remnants surrounding by ru os ir oxides of varying composition available geological mineralogical and geochemical data indicate a prolonged multistage evolution at least four stages for the pge mineralization the relatively high ipge enrichment in chromitites seems to be related to post magmatic processes encompassing a long period of deformation episodes beginning with plastic deformation in the asthenospheric mantle and culminating with brittle deformation in the crust metasomatic fluids have during a process of rodingitization and serpentinization at a low state of sulfidation substantially modified the composition of primary laurite towards fe cr co and mn bearing fe os ir ru alloys and oxides the most prospective locations for chromitite pgm targets seem to exclusively be small chromite occurrences that are found along shear zones within ophiolite complexes these shear zones post date the initial magmatic deposition of the host chromitites

composition and textures of chromite and platinum group minerals in chromitites of the western ophiolitic belt from pampean ranges of cordoba argentina abstract chromitite bodies hosted in the neoproterozoic western ophiolitic belt of pampean ranges of cordoba argentina were studied at los congos and los guanacos ultramafic bodies with regard to the composition and textures of the chromite and platinum group minerals primary chromite composition is only preserved in some massive chromitites from the los guanacos ultramafic body and is similar to al rich ophiolitic chromitites suggesting that they crystallized from melts with back arc basin basalts babb affinity in the suprasubduction mantle subsequently these chromitites underwent a prograde metamorphism chromites from chromitites and associated metamorphosed ultramafic rocks show complex replacement and exsolution textures mineral chemistry and texture indicate that the chromite composition records two main metamorphic trends a first trend defined by chromite from massive chromitite in which there is an enrichment in fe3 and fe2 cr remain relatively constant and slightly depleted in al mg a second trend is defined by chromite from disseminated chromitite and metamorphosed dunite and harzburgite in which a fe rich phase is replacing the al rich chromite this alteration trend is characterized by enrichment in the total iron content fe3 fe2 and a strong depletion in al and mg the chemical composition of all analyzed spinels from los guanacos and los congos as plotted on the ternary fe3 cr al diagram correlates well with the cr spinels from the upper amphibolite to granulite facies metamorphism platinum group minerals pgm identified include native osmium laurite erlichmanite irarsite platinum and a number of inadequately identified phases such as an oxide or hydroxide of ru pt and ir ru pt telluride ir ru as se and ir ru ti compounds native osmium was the only pgm which remained unaltered other pgm underwent mineralogical reworking during metamorphism although it is difficult to establish the extent of platinum group element mobilization based on mineralogical observation our results suggest that the ru os ir pgm in the los guanacos and los congos chromitites were modified in situ producing re distribution of these pge on a small scale the presence of rare pt and pge as se minerals was possibly related to remobilization of pt as and se by fluids during the alteration processes

petrological characteristics of podiform chromitites and associated peridotites of the pan african proterozoic ophiolite complexes of egypt mafic ultramafic fragments of a dismembered ophiolite complex are abundant in the late precambrian pan african belt of the eastern desert of egypt and north east sudan the ultramafic bodies in the eastern desert of egypt are mostly characterised by the harzburgite dunite chromitite association because of their severe metamorphism almost all primary silicates were converted to secondary minerals and we use the chrome spinel as a reliable petrogenetic indicator the podiform chromitite deposits are common as small and irregularly shaped masses in the central and southern parts of the eastern desert they strongly vary in texture degree of alteration and chemical composition of chrome spinel the podiform chromitites exhibit a wide range of composition from high cr to high al varieties the cr of chrome spinel ranges from 0 65 to 0 85 in dunite quite similar in the high cr chromitite whereas it is around 0 5 in harzburgite primary hydrous mineral inclusions amphibole and phlogopite in chrome spinel are reported for the first time from the pan african proterozoic podiform chromitites the petrological characteristics of pan african podiform chromitites and associated peridotites of egypt are similar to those of phanerozoic ophiolites the proterozoic podiform chromitites may have formed in the same way as the phanerozoic ones namely by melt harzburgite reaction and subsequent melt mixing the similarity of the mantle section of the late proterozoic and the phanerozoic ophiolites suggests that the thermal conditions controlling genesis of the crust mantle system basically have not changed since the late proterozoic era the pan african harzburgite is very similar to abyssal peridotite at fast spreading ridges and the high cr low ti character of spinel in chromitite and dunite indicates a genetic link with a supra subduction zone setting the late proterozoic ophiolites of egypt are possibly a fragment of oceanic lithosphere modified by arc related magmatic rocks or a fragment of back arc basin lithosphere

significance of melt wall rock reaction a comparative anatomy of three ophiolites the ascent of basaltic melts through the upper mantle results in chemical disequilibrium between the melts and the pyroxene and plagioclase of the wall rock peridotite phase and cryptic variations in ophiolitic peridotites demonstrate that the resulting reactions deplete the mantle in magmatophile components and enrich ascending melts in ca na al and incompatible trace elements while buffering their mg mg fe ratios at primitive values 0 6 a comparative anatomy of the trinity oman and darb zubaydah ophiolites illustrates both the significance of this process in shaping the composition of the shallow lithospheric mantle and how the integrated effects may reflect tectonic setting a first order correlation between crustal thickness and degree of mantle depletion exists but multiple rifting events may remove part of the crustal record so that melt rock ratios are difficult to quantify most impressive in ophiolitic peridotites is the abundance of melt crystallization and reaction products in zone

systematics of chromitite occurrences in central palawan philippines the chromitite occurrences in the central palawan ophiolite can be classified into four groups based on their chemistry and geological relationships group i chromites from a deep tectonite level of the ophiolite complex show cr cr al values of between 0 78 and 0 90 whereas group ii from a shallower level gives values of 0 64 0 78 and group iii from the immediate gabbro lower contact dunite cumulates and diapirs show values of 0 5 0 64 group iv chromites from the gabbro zone have ratios around 0 38 0 5 larger orebodies type a representing a first stage of partial melting of a primordial mantle show cr fe ratios between 2 5 and 4 5 whilst those of small chromitite bodies with a thin dunite envelope type b lie below 2 5 these small bodies belong to a second stage of magma generation for both types the cr fe ratio increases with the chromite silicate ratio within individual occurrences an additional method which may help to subdivide these chromitites involves their silicate and ore inclusions the platinum group minerals for example occur mainly in chromites of group ii type a the intensive tertiary tectonic activity to which the ophiolite was subjected during and after emplacement disturbs the regular pattern of the ophiolite stratigraphy and its chromitite occurrences

compositions of chromite associated minerals and parental magmas of podiform chromite deposits the role of slab contamination of asthenospheric melts in suprasubduction zone environments abstract podiform chromitites in the mantle sections of ophiolites belong to either high cr metallurgical or high al refractory varieties their highly variable compositions are reflected by different cr s 100cr cr al and cr2o3 and al2o3 contents of the chromite falling in the boninitic and morb fields respectively parental magmas of high cr chromitites have higher sc mn co and ni and lower ti v zn and ga concentrations than morb melts their trace element patterns are similar to those of boninites except for ni and zn in contrast high al chromitites have parental magmas characterized by generally flat morb normalized patterns showing slight enrichments in v mn and co and depletion in ni and zn regardless of their compositions both types of chromitites have chondrite normalized platinum group element pge patterns showing enrichment in ipge and depletion in ppge a variety of platinum group minerals are typically present in both types occurring either as euhedral inclusions or along fractures in chromite grains these minerals have a wide span of re os isotopic compositions reflecting a variety of origins there is a diversity of unusual minerals and mineral inclusions associated with podiform chromitites the presence of these minerals suggest that grains of amphibolite plagioclase amphibole and zircon and eclogite coesite kyanite and garnet were present in the magmas from which chromite crystallized multiphase mineral inclusions demonstrate that podiform chromitites form from hydrous mafic magmas in suprasubduction zone environments ssz we propose a new model in which chromitite formation was involved in intra oceanic subduction zones initiated in closing oceanic basins continued subduction carries oceanic and possibly continental crustal materials to deep levels where they are metamorphosed under greenschist amphibolite and eclogite facies conditions the tearing and breakoff of the subducted slab possibly along the transitional contact between amphibolites and eclogites create a slab window through which the underlying asthenosphere rises and melts to generate cr rich mafic magmas these upward migrating magmas pass through the subduction zone and assimilate the subducted slab as a result of slab contamination these magmas become more siliceous more oxidized and more hydrous rapidly triggering chromite crystallization minute grains of chromite are suspended in the upward moving magmas as they migrate through the overlying metasomatized mantle wedge such chromite bearing magmas eventually deposit chromite in magma conduits in the uppermost mantle close to the moho where the upward flow changes from vertical to subhorizontal and velocity is greatly reduced highly reduced and ultrahigh pressure minerals including diamonds are reported in literature both in podiform chromitites and host peridotites of ophiolites some of these minerals in association with host peridotites may have been brought by the uprising asthenosphere at mid oceanic ridges due to the mantle convection it is also possible that some diamonds may have formed in the subducted slab below about 150 km some minerals of subducted slabs are preserved because they are encapsulated in chromite grains where they are protected from the ssz melts some of these ssz mantle wedges are emplaced on land to become podiform chromitite bearing ophiolites

the giant chromite deposits at kempirsai urals constraints from trace element pge ree and isotope data the investigation of stable and radiogenic isotopes and of platinum group pge and rare earth elements ree in chromitites and associated ultramafic rocks of the kempirsai massif southern urals gives strong evidence for a multistage formation of giant ophiolitic podiform chromite deposits present in the southeastern part of the massif the kempirsai ophiolite massif is divided by a shear zone into two parts in the northwestern area small bodies of al rich chromite formed from basaltic melts between 420 to 400 ma according to sm nd mineral isochrons of harzburgite pyroxenite websterite and gabbro harzburgites and pyroxenites in this area are enriched in light ree and have nd 400 6 and sr 400 5 chromitites have scattered pge distributions pd ir 0 4 7 0 being partly enriched in pd and pt os 400 of one chromitite is 4 4 the southeastern part of the kempirsai massif well known for its world class deposits of podiform low al magnesiochromite is characterized by harzburgite and dunite enriched in light ree with very low nd 400 4 3 to 17 1 and positive sr 400 10 values chromitites are strongly enriched in ir os and ru and depleted in pd and pt os 400 of three chromitites is uniform and approaches c1 and dmm compositions in veins and pods postdating crystallization of massive chromite pargasitic amphibole formed in equilibrium with fluid inclusion bearing chromite at temperatures close to 1000 c these amphiboles give 40ar 39ar stepwise heating ages of 365 to 385 ma and are characterized by low nd 400 0 6 to 4 6 and general enrichment in ree the cooling ages correspond to a 379 3 1 6 ma rb sr mineral isochron produced from amphibole and phlogopite of a pyroxenite vein in the western part of the massif from these data it is concluded that parts of the kempirsai massif have been pervasively metasomatized by large amounts of fluids and melts derived from a subducted slab composed of oceanic crust and sediments subduction occurred at least 15 35 ma after a melting event that produced a typical ophiolitic sequence in the paleozoic sakmara zone we conclude that large chromite orebodies formed from second stage high mg melts that interacted with depleted mantle and fluids on their way upward in a suprasubduction zone regime and in a fore arc position to the magnitogorsk island arc

unexpectedly high pge chromitite from the deeper mantle section of the northern oman ophiolite and its tectonic implications unusually high platinum group element pge enrichments are reported for the first time in a podiform chromitite of the northern oman ophiolite the chromitite contains 1 5 ppm of total pge being highly enriched in the ipge subgroup ir os and ru and strongly depleted in the ppge subgroup rh pt and pd its platinum group minerals pgms are classified into three types arranged in order of abundance 1 sulphides os rich laurite laurite erlishmanite solid solution and an unnamed ir sulphide 2 alloys os ir alloy and ir rh alloy and 3 sulpharsenides irarsite and hollingworthite the high pge concentrations are observed only in a discordant chromitite deep in the mantle section which has high cr 0 7 spinel with an olivine matrix all the other types of chromitite in the moho transition zone mtz and concordant pods in the deeper mantle section are poor in pges and tend to have spinels with lower cr up to 0 6 this diversity of chromitite types suggests two stages of magmatic activity were responsible for the chromitite genesis in response to a switch of tectonic setting the first is residual from lower degree partial melting of peridotite which produced low cr pge poor chromitites at the moho transition zone and to a lesser extent within the mantle possibly beneath a fast spreading mid ocean ridge the second chromitite forming event involves higher degree partial melting which produced high cr pge rich discordant chromitite in the upper mantle possibly in a supra subduction zone setting

distribution of platinum group elements and gold within the vourinos chromitite ores greece a geochemical study of chromite ores and host rocks of the vourinos ophiolite complex leads to the distinction of three geotectonic units corresponding to the north vourinos south vourinos and kissavos geographic areas this is based on the range and variability of cr cr al pt pd os ir ru and pd ir ratios and the relative abundance of compatible platinum group elements pge os ir and ru within the three blocks the platinum group element and gold contents are low average concentrations in ppb are os 23 ir 19 ru 58 rh 12 pt 5 9 pd 3 3 and au 2 7 however a few pge enriched chromite samples up to 3 030 ppb were also found the south vourinos area differs from north vourinos as far as its remarkably constant chemical composition major and trace elements its lower pd ir and pt pd os ir ru ratios its greater abundance of the os ir sum relative to ru and its absence of pge enriched chromite ores there is no significant correlation between chromite composition and pge data throughout the complex the only exception is the kissavos area where the pge content is higher and the pd ir ratio lower in cr rich ores than in al rich ones showing a strong negative correlation between the cr cr al and pd ir ratios r 0 8 the low pge content in the majority of the vourinos chromite ores may reflect a lack of sulfur saturation during an early stage of their crystallization whereas pge enrichment may suggest a mixing of primitive and partially fractionated magmas assuming that the vourinos complex formed in a suprasubduction zone environment it seems likely that south vourinos chromitites formed directly above the spreading center whereas the north vourinos chromitites formed at a distance from the spreading center in addition the strong depletion of pge in the kissavos cr rich ores particularly os ir and ru may suggest that these chromitites were crystallized from magmas derived by partial melting of an already depleted mantle source the geochemical trend throughout the vourinos complex seems to provide valuable confirmation of a stratigraphic orientation in the mantle sequence of the complex

relations among hydrocarbon reservoirs epigenetic sulfidization and rock magnetization examples from the south texas coastal plain this paper focuses on the association between concentrations of iron disulfide fes2 minerals in the shallow subsurface and underlying hydrocarbon accumulations such fes2 concentrations are the result of migration of either h2s or organic constituents from the underlying hydrocarbons the h2s from reservoirs is produced inorganically from sulfate in the reservoir rocks at high temperature 90 c and migrates to shallower beds to react inorganically with iron to form fes2 organic constituents from reservoirs in contrast provide nourishment for sulfate reducing bacteria in shallow relatively cool 90 c beds sandstone in the ray point uranium district in live oak county texas contains abundant fes2 which formed both from deep seated h2s and from h2s produced in the shallow subsurface by bacteria that utilized organic materials from depth deep petroleum reservoirs were physically connected to near surface 100 m beds containing epigenetic fes2 by the oakville fault epigenetic iron sulfide format

magnetic forward models of cement oil field oklahoma based on rock magnetic geochemical and petrologic constraints magnetic forward models of the cement oil field oklahoma were generated to assess the possibility that ferrimagnetic pyrrhotite related to hydrocarbon seepage in the upper 1 km of permian strata contributes to aeromagnetic anomalies at cement six bodies having different magnetizations were constructed for the magnetic models based on geology and on petrologic and geochemical results supplemented by rock magnetic measurements of shallow core and outcrop samples the column of rock through which hydrocarbons have passed is divided into three sulfide zones on the basis of pyrrhotite content and the column is capped by a 30 m thick zone that contains ferric oxide minerals formed mainly from oxidized pyrite red beds unaffected by sulfidization as well as a zone of rock depleted in hematite but lacking sulfide surround sulfidic zones the synthetic magnetic profiles are controlled mainly by pyrrhotite bearing strata at depths of 200 500 m the magnetizations of these bodies are calculated from 1 pet

empirical observations relating near surface magnetic anomalies to high frequency seismic data and landsat data in eastern sheridan county montana our empirical synergistic correlations of aeromagnetic and seismic data and a landsat lineament interpretation revealed lineations on the magnetic map that have expression on seismic sections we observed a conjugate set of northwest southeast and northeast southwest trending magnetic lineaments zones which offset and truncate near surface magnetic anomalies we believe these ozs offset zones represent lateral faults in a wrench fault system lateral offsets appear to be 100s of meters to a few kilometers fractions of a mile to a few miles we observed a direct correlation between ozs and vertical faults in seismic data faults on seismic sections extend from near the surface to near the seismic basement the faults are most pronounced in the upper cretaceous reflectors and seem to disappear with depth fault throws are inconsistent reversing throw across faults ozs trend northeast southwest in the north half of the study area and both northeast southwest and northwest southeast in the south half

planetary waves and intraseasonal oscillations at davis antarctica from undersampled time series 1 nine years 1997 to 2005 of nighttime hydroxyl 6 2 band rotational temperatures were measured with a scanning spectrometer over davis station antarctica 68 6 s 78 0 e a novel time series analysis technique is employed to create continuous long term time series and local spectral analysis of these temperature time series was performed to search for planetary wave and intraseasonal oscillations many significant wave signatures were observed coincident observations are found in a comparison between these temperature wave signatures and horizontal wind measurements made from a collocated mf radar several very long term wave signatures 30 to 50 days are seen in the oh temperatures which are absent from the mf radar winds an increase in wave activity is seen in the late winter season interannual variations are also shown indicating a peak in 2002 the year of the southern hemisphere stratospheric warming event

syngenetic magnetic anomaly sources three examples aeromagnetic anomalies encountered in three areas two in the western united states and one in central america are shown to arise from magnetic sedimentary formations these examples are selected from a larger number of similar areas surveyed by applied geophysics inc in various places in the u s midcontinent and rocky mountain regions the first area discussed is the northwest corner of nebraska where the miocene arikaree formation comprised of magnetic airfall and windblown tuffs causes anomalies in areas of incised topography the second area is located in south central utah where the upper cretaceous kaiparowits sandstones contain detrital magnetite that causes large anomalies in tilted structures and over incised topography the third area treated covers over half of southern belize in central america including much of the offshore portion here the toledo formation of paleocene eocene age contains a thick section of clastic detritus rich in lithic grains of volcanic rocks that produce magne

super dual auroral radar network observations of meteor echoes radar echoes from ranges less than 500 km are routinely observed by the super dual auroral radar network superdarn on most days many of these echoes have properties which are markedly different from what one would expect from e or f region irregularities we show that these unusual short range hf echoes are due to scattering off meteor trails this explains why among other things the doppler shift from the short range echoes taken from the superdarn saskatoon antenna are consistent with the mesospheric winds observed by the saskatoon mf radar this means that the superdarn radars can be used to study neutral winds at meteor heights a result which is especially interesting since it opens up the capability for a global coverage of mesospheric winds using the worldwide distribution of superdarn radars

chromite and pge geochemistry of the elekdag ophiolite kastamonu northern turkey implications for deep magmatic processes in a supra subduction zone setting abstract the geochemistry of chromium spinel and platinum group elements pge provides significant information about conditions in the mantle during the emplacement and genesis of ophiolitic complexes the elekdag ophiolite is a greenschist to amphibolite facies ophiolite that was emplaced onto the sakarya zone in the central part of the pontides of northern turkey nw se trending elekdag ophiolite hosts small scale chromitite occurrences in serpentinized harzburgite and dunite and have maximum resource of several thousands t cr2o3 the chromitites the elekdag ophiolite can be divided in to high cr and high al types the calculated melt composition of the high cr chromitites is 9 4 13 2 wt al2o3 0 2 0 4 wt tio2 with feo mgo ratios of 0 4 1 9 which are indicative of boninitic compositions however the high al chromitites have 14 7 17 3 wt al2o3 and 0 3 0 8 wt tio2 with feo mgo ratios of between 0 3 and 0 8 which are consistent with morb like tholeiitic affinities the total pge content of the chromitites range between 82 and 1466 ppb and the average pge content of the high cr and high al chromitites are 267 ppb and 195 ppb respectively the chromitites are characterized by low pd ir ratios of 0 02 0 20 that is characteristic of non fractionated chromitites the chondrite normalized pge pattern of the chromitites resemble those of mantle derived cr rich chromitites in ophiolites of the supra subduction zone ssz elsewhere mineral and bulk rock pge data for the elekdag chromitites indicate that high cr chromitites formed from cr rich and al and ti poor boninitic melts most probably in the fore arc setting in the deeper part of the mantle this was succeeded by the mineralization of high al chromitites from a differentiated boninitic melt at shallow depths close to the moho discontinuity

quasi biennial oscillation influence on long period planetary waves in the antarctic upper mesosphere 1 long period planetary wave data derived from meteor wind observations recorded over a 12 year period with the superdarn radar at halley antarctica are presented and compared with the phase of the quasi biennial oscillation qbo throughout the equatorial stratosphere enhanced planetary wave activity in the antarctic upper mesosphere is found during the summer months when the qbo in the equatorial upper stratosphere is westerly and during the late winter when the qbo in the upper stratosphere is easterly these quasi biennial enhancements in planetary wave activity coincide with a reduction in strength by up to 30 of the late winter eastward winds in the antarctic upper mesosphere in addition when the qbo is in the correct phase for enhanced planetary wave activity in the upper mesosphere above halley planetary wave activity measured in the upper mesosphere of the high latitude northern hemisphere is reduced and vice versa these results clearly indicate significant interhemispheric propagation of planetary waves from the winter to summer hemispheres observational evidence that the stratospheric qbo induces a strong enough qbo in the equatorial upper mesosphere to act as a gate to the interhemispheric propagation of these long period waves is discussed in light of these results

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

mesospheric planetary waves over antarctica during 2002 1 wind measurements from a series of atmospheric radars located around antarctica have been used to characterize the mesospheric planetary wave field during the winter of 2002 combining winds from the medium frequency mf radar at rothera 68 s 68 w and the superdarn high frequency meteor wind radars at halley 76 s 27 w sanae 72 s 3 w and syowa 69 s 40 e stations we have been able to measure the period wavenumber and propagation direction of the most prominent planetary waves the results show that the planetary wave field before the unusual stratospheric warming in 2002 was dominated by a very long period 43 days westward and upward propagating zonal planetary wavenumber 1 however after the stratospheric warming events began in late winter the character of the wave field changed and a shorter period 14 days westward zonal wavenumber 1 became established it would appear that the previously reported oscillations of the mesospheric hydroxyl airglow temperatures at rothera and halley which were strongly anti correlated to the meridional wind were the result of these planetary waves

nanoscale constraints on the in situ transformation of ru os ir sulfides to alloys at low temperature abstract we report new results of a combined focused ion beam high resolution transmission electron microscopy fib hrtem investigation of two grains of platinum group minerals pgm corresponding to the laurite rus2 erlichmanite oss2 solid solution series the grains are included within unaltered chromite and the serpentine dominant matrix of the mantle hosted chromitite body of monte bueno in eastern cuba at the micron scale the grain hosted in unaltered chromite preserves magmatic features including a complex oscillatory zoning defined by a core of erlichmanite surrounded by alternating bands of os rich os poor laurite revealed by conventional field emission scanning electron microscopy fe sem and x ray mapping by electron microprobe analyzer epma combining high magnification hmem high angle annular dark field haadf images and the corresponding energy dispersive spectra eds the elemental mappings acquired using hrtem showed that the oscillatory zoning occurs at both the micron and nano scales a specific feature highlighted by hrtem observations is the rather complex structure of the erlichmanite core consisting of an aggregation of much smaller cores

stabilities of laurite rus2 and monosulfide liquid solution at magmatic temperature we have reversed the equilibria ru s2 rus2 and 2feo s2 2fes o2 under controlled temperature oxygen fugacity fo2 and sulfur fugacity fs2 at 1 atm to test if the platinum group mineral laurite rus2 has a stability field at magmatic temperature outside that of magmatic monosulfide liquid the fs2 in equilibrium with ru and rus2 is given by log fs2 6 9 12190 t 1173 to 1673 k whereas the fs2 at sulfide saturation of a basaltic melt may be approximated from log fs2 6 7 12800 t 2 log xfeo log fo2 1473 to 1673 k our experiments support the notion that the sulfide mineral laurite can crystallize directly out of a sulfur bearing sulfide undersaturated silicate melt as implied by laurite chromite intergrowth textures in natural chromite ore

platinum group element distribution in chromite ores from ophiolite complexes implications for their exploration abstract compilation of some new data on ophiolites for greece and yugoslavia and published data from previous studies indicate that platinum group element pge and gold concentrations in chromite ores are generally low ranging from less than 100 ppb to a few hundred ppb however samples from several ophiolite complexes exhibit an enrichment of a few ppm a only in os ir and ru b only in pt and or pd or c in all pge this enrichment up to 10s ppm is mainly related with chromitites hosted in supra moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local independent of the chromitite major element composition and the chromite potential of the ophiolite complexes the contents of pge combined with less chalcophile elements ni co cu the ratios of incompatible compatible elements and pge patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas although they have a similar major element composition thus they can be used for a stratigraphic orientation in the mantle sequence and therefore for exploration targets moreover pge data offer valuable information for the evaluation of the chromite potential in ophiolite complexes the most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type the other type being only in small proportion of limited compositional variation in both major elements and pge low ratios of pd ir while pge enriched chromitites in the mantle sequence are only occasionally present in contrast ophiolites which contain both high cr and al chromitites and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores although they are related with a ssz environment

long term observations of the wind field in the antarctic and arctic mesosphere and lower thermosphere at conjugate latitudes 1 mean winds semidiurnal and diurnal tides and trends and long period oscillations spanning a solar cycle from early 1999 through june 2010 measured by medium frequency mf radars at conjugate antarctic and arctic latitudes syowa antarctica 69 s 39 6 e and andenes norway 69 3 n 16 e are described and compared zonal mean winds are stronger and more uniform from year to year over the antarctic with a stronger eastward winter jet spanning the range of altitudes presented 70 to 96 km the summer westward jet is also stronger and maximizes at higher altitudes over the antarctic than over the arctic the eastward winter jet over the arctic while generally weaker exhibits a localized maximum in late winter at 2 to 3 year intervals meridional mean winds likewise achieve somewhat stronger maxima at higher altitudes over the antarctic than over the arctic semidiurnal tide amplitudes are typically somewhat larger over the antarctic and similar in the two components with maxima at 85 km or above and narrow responses that tend to cluster from february to may and september to november over the antarctic and from december to february and june to september over the arctic zonal diurnal tide amplitudes are quite similar between the sites with maxima extending from 70 to 90 km and slightly stronger over the antarctic meridional diurnal amplitudes display more significant growth with altitude achieve stronger maxima at the highest altitudes presented and typically exhibit a single and narrow maximum during december to february over the antarctic and double maxima from may to september over the arctic also discussed are trends and long period oscillations over a solar cycle observed in these mean and tidal wind fields

solid inclusions in chrome spinels and platinum group element concentrations from the hochgrossen and kraubath ultramafic massifs austria a great variety of platinum group mineral sulfide and silicate inclusions in chrome spinel from hochgrossen and kraubath ultramafic massifs and platinum group element contents of three different rock types have been investigated both ultramafic massifs are tectonically isolated bodies variably serpentinized and metamorphosed greenschist to lower amphibolite facies and show ophiolitic geochemical affinities the chromite from massive chromitites and disseminated in serpentinized dunites and serpentinites exhibits compositional zonation as the result of alteration during serpentinization and metamorphism three distinctive alteration stages are indicated in the chrome spinels from the hochgrossen whereas alteration is less significant in chromites from kraubath the core of chrome spinel represents the least altered part surrounded by an inner rim characterized by slight compositional differences in cr mn fe2 and al with respect to the core the outer rim is formed by ferritchromite with a sharp boundary to the inner rim and shows a significant decrease of al mg cr and increase of fe2 fe3 and ni compared to the core two different groups of inclusions in chrome spinel are present the first group occurs within the chromite core and comprises olivine orthopyroxene amphibole sulfides and platinum group minerals i e dominated by ru os ir sulfides the second group is formed by chlorite serpentine galena pyrite arsenopyrite pt pd rh dominated sulfarsenides and sperrylite in particular the abundance of pt pd rh sulfarsenides and arsenides is typical of both ultramafic massifs and is very unusual for chromitites from ophiolites morphology paragenesis and chemical composition indicate a different origin for these two groups of inclusions the first group is intimately related to the crystallisation of the chromite host the second group of inclusions clearly displays a secondary formation during serpentinization and metamorphism closely related to the alteration of chrome spinel and the development of ferritchromite the distribution patterns of the platinum group elements from massive chromitites disseminated chrome spinel bearing serpentinites and serpentinites exhibit variable enrichment of rh pt and pd rh pt for the hochgrossen and kraubath massifs respectively these results are in accordance with the occurrence and distribution of platinum group mineral phases a remobilisation of pt pd and rh together with ni cu and possibly fe as bisulfide and or hydroxide complexes and deposition of metals by the reaction of the metal bearing hydrothermal fluid with chromite is proposed

large scale rossby normal modes during some recent northern hemisphere winters abstractlarge scale rossby normal modes are studied for the northern hemisphere winters of 2005 2006 2008 and 2009 using global observational meteorological analyses spanning the 0 92 km altitude range spectral analysis of geopotential height fields shows pronounced peaks at westward propagating zonal wavenumber 1 near the theoretical locations of the free rossby waves at 25 16 10 and 5 days that in some cases have amplitudes significantly larger than the estimated background spectrum evidence is also found for a wavenumber 2 free mode near 4 days a coherence analysis is used to extract the amplitude and phase of the waves and to isolate those regions of the latitude altitude plane where the signals are statistically significant although the spectral location temporal evolution and vertical structure of several of these waves are suggestive of the presence of rossby normal modes this study shows that in the real atmosphere the waves only occasionally have the global properties of classical

origin of podiform chromite deposits by magma mingling abstract i have oversaturated the immiscible system sio2 al2o3 feo k2o with fecr2o4 to study the fractionation of chromite between conjugate siliceous and fayalitic melts although both melts are oversaturated with chromite chromite only nucleates in the fayalite rich melt where the crystal melt interfacial energy sl is lowest in less than three days at 1150 c all excess chromium in the bulk composition is concentrated as cumulus chromite in the fayalitic melt pools producing nodular cumulate textures as observed in podiform chromite ore when these results are applied to the lithospheric mantle podiform chromite deposits may form when droplets of olivine normative high pressure low viscosity melt mingle with siliceous low pressure more viscous melt in shallow magma conduits it is inferred from the experimental analogue that chromite only nucleates in the melt where sl is lowest which in the mantle would be the high pressure melt the low pressure melt only serves as the diffusive chromium reservoir the richest chromite ores form when the volume ratio of the melt nucleating chromite is small relative to the ambient melt

metallogeny of the chrome ores of the xerolivado skoumtsa mine vourinos ophiolite greece implications on the genesis of ipge bearing high cr chromitites within a heterogeneously depleted mantle section abstract chrome ore deposits comprise less than 1 of the volume of a pervasively serpentinized dunite body 3 5 km 3 that constitutes the xerolivado skoumtsa mine of the vourinos ophiolite in northwestern greece ores have been examined to aid determination of their geological mode of occurrence their mineralogy and mineral chemistry cr spinel and olivine and platinum group element pge geochemistry the ore bodies are highly deformed and of the schlieren type where cr spinel rich and serpentine after olivine rich layers 1 20 cm thick alternate the cr spinel displays a limited range in cr 100 cr cr al atomic ratio 77 85 and tio 2 content 0 05 0 22 wt the mg 100 mg mg fe 2 of cr spinel shows a wider variation 52 74 indicating that subsolidus mg sp fe 2 ol re equilibration occurred remnant fresh olivine in the serpentine rich layers is typical forsterite fo 100 mg mg fe 2 93 95 the cr rich chromitite ores have total pge and au abundances that range between 74 3 and 205 ppb they show a general enrichment in ir and ru over ppge rh pt and pd resulting mostly in a negatively sloping c1 chondrite normalized pge profile with a quite strong ru peak field observations indicate that the schlieren banding of the deformed ore bodies is a tectonometamorphic feature acquired within ductile deformation of the ophiolitic slab geochemical calculations demonstrate that the parental melts of the xerolivado skoumtsa high cr chromitites were boninitic their high ru content and variation in cr sp values indicate a polygenetic origin from geochemically similar but spatially distinct melt inputs these melts originated within a hydrated mantle wedge beneath a forearc basin within an evolving lithospheric slab we emphasize that the pge budget of the xerolivado skoumtsa chromitites was not inherited from interactions of the migrating melts with their parental harzburgites but it is an intrinsic feature of the deep seated and heterogeneously depleted mantle source of these magmas

pge rich podiform chromitites in the al ays ophiolite complex saudi arabia an example of critical mantle melting to extract and concentrate pge the al ays ophiolite complex in saudi arabia is an example of an ophiolite that contains anomalous concentrations of all six platinum group elements pge in podiform chromitite with maximum values of 2 570 ppb pt 6 870 ppb pd 840 ppb rh 5 800 ppb ru 6 200 ppb ir and 3 300 ppb os smooth chondrite normalized pge profiles indicate igneous pge ratios these suggest that in situ alteration of the pgm caused only minor mobility of pge during secondary modification of the mineralogy thus the geochemistry of the igneous concentration processes can be examined despite the mineralogical changes caused by subsequent alteration three main types of pge mineralization are observed that are defined by their relative abundances of individual pge type 1 has ru both pt and pd with negative slope chondrite normalized profiles type 2 has ru either pt or pd pt pd ir ratios of 1 to 5 and convex upward chondrite normalized profiles type 3 has ru either pt or pd pt pd ir ratios of 5 to 60 positive slope chondrite normalized profiles and is associated with elevated cu and ni concentrations the unaltered centers of chromite grains in the chromitite within this complex have an unusually large range of composition for example cr2o3 varies from 39 to 69 wt percent pge mineralization types 1 2 and 3 are related to the composition of the chromite type 1 occurs across the range of chromitite compositions from 39 to 69 wt percent cr2o3 type 2 occurs in chromitite having a range of 53 to 61 wt percent cr2o3 and type 3 occurs in chromitite having a range of 39 to 51 wt percent cr2o3 the pge form a great variety of platinum group minerals pgm and they differ among the three types of pge mineralization type 1 is characterized by euhedral os ir and ru ipge alloys and laurite both commonly enclosed in chromite as well as members of the irarsite hollingworthite solid solution series and pt ipge bearing pgm both commonly interstitial to the chromite grains type 2 pge enrichment is characterized by ipge pt and rh bearing pgm type 3 pge enrichment hosts predominantly pd and pt bearing pgm associated with ni and cu bearing minerals where exposed to the serpentinization process the pgm are altered to alloys arsenides antimonides and oxides that form irregular shapes or may form pseudomorphs of former pgm they are commonly associated with ni and cu bearing minerals including ruthanian pentlandite millerite arsenides and pge bearing awaruite mantle melting and subsequent crystallization were at an optimum to concentrate pge in the al ays ophiolite complex crystallization of ipge commonly prior to chromite crystallization and latterly with some pt and rh occurred across the range of chromitite composition crystallization of pd with some remaining pt occurred during sulfur saturation in chromitite formed from a more evolved magma we propose that this crystallization was from a magma that was enriched in pge because the degree of mantle melting was just sufficient to extract the pge but not dilute them in a melt that includes further mantle melting this feature is likely to be common to other pge rich ophiolite complexes such as in shetland in the united kingdom leka in norway thetford in canada pindos in greece tropoja in albania and in new caledonia if equilibrium partial melting had continued in al ays then the magma would have been diluted by subsequent pge poor melt this would have prevented sulfur saturation until much higher in the sequence producing pt and pd bearing base metal sulfides in the crustal wehrlite and gabbro as has occurred in the cyprus and oman ophiolites

chemical composition and origin of platinum group minerals from placers of the aunik river buryatia russia abstract platinum group minerals pgms are occasionally encountered in gold placers around the world most research related to the gold placer deposits focuses on the origin migration and concentration of gold the primary commercial mineral in the placers both origin and fate of pgm are rarely studied the present study of pgm grains reveals complex relationships between the mineral phases within the grains conforms to the published results on immiscibility within certain pgm solid solutions presents evidence of alteration of pgms and shows the presence of unusual secondary minerals within the grains the studied pgm grains are os ir ru alloys and can be divided into two types based on their chemical composition the first type is solid solutions enriched in os and ru bearing inclusions of silicates such as olivine pyroxene and amphibole the second type is enriched in ir and pt with inclusions of sulfides tellurides and selenides such as cuproiridsite iridisite malanite cooperite laurite erlichmanite and tolovkite these two types of pgm have been described in other regions and the first type was attributed to ophiolitic origin of the mineralization the authors confirm this theory and find that the pgm of the aunik river placers likely originated from ophiolites of the shamanskaya spreading zone with a possible contribution from ultrabasic rocks of ural alaskan type the secondary mineralization of the pgm especially prominent in the peripheral parts of many studied samples is most likely the result of post magmatic metasomatic alteration interestingly an unnamed new mineral phase ir os se2 was detected in a hydrothermally altered grain

distribution of platinum group elements and os isotopes in chromite ores from mayari baracoa ophiolitic belt eastern cuba the mayari baracoa ophiolitic belt in eastern cuba hosts abundant chromite deposits of historical economic importance among these deposits the chemistry of chromite ore is very variable ranging from high al cr 0 43 0 55 to high cr cr 0 60 0 83 compositions platinum group element pge contents are also variable from 33 ppb to 1 88 ppm and corre late positively with the cr of the ore bulk pge abundances correlate negatively with the pd ir ratio showing that chromite concentrates mainly os ir and ru which gives rise to the characteristic negatively sloped chrondrite normalized pge patterns in many chromitites this is consistent with the mineralogy of pges which is dominated by members of the laurite erlichmanite solid solution series rus2 oss2 with minor amounts of irarsite irass os ir alloys ru os ir fe ni alloys ni rh as and sulfides of ir os rh cu ni and or pd measured 187 os 188 os ratios from 0 1304 to 0 1230 are among the lower values reported for podiform chromitites the 187 os 188 os ratios de crease with increasing whole rock pge contents and cr of chromite furthermore cos values of all but one of the chromitite samples are negative indicating a subchondiritc mantle source cos decrease with increasing bulk os content and decreasing 187 re 188 os ratios these mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying in composition from back arc basalts al rich chromite to boninites cr rich chromite in a su prasubduction zone setting chromite crystallization occurs as a consequence of magma mixing and assimi lation of preexisting gabbro sills at the mantle crust transition zone cr pge abundances and bulk os isotopic composition of chromitites are determined by the combined effects of mantle source heterogeneity the degree of partial melting the extent of melt rock inter actions and the local sulfur fugacity small scale l mt o cm chemical and isotopic heterogeneities in the plati num group minerals are controlled by the mechanism s of chromite crystallization in a heterogeneous environ ment created by the turbulent regime generated by suc cessive inputs of different batches of melt

planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 1 the vertical coupling of the stratosphere mesosphere system through quasi stationary and traveling planetary waves during the major sudden stratospheric warming ssw in the arctic winter of 2003 2004 has been studied using three types of data the uk met office ukmo assimilated data set was used to examine the features of the global scale planetary disturbances present in the winter stratosphere of the northern hemisphere sounding the atmosphere using broadband emission radiometry saber satellite measurements were used as well for extracting the stationary planetary waves in the zonal and meridional winds of the stratosphere and mesosphere radar measurements at eight stations four of them situated at high latitudes 63 69n and the other four at midlatitudes 52 55n were used to determine planetary waves in the mesosphere lower thermosphere mlt the basic results show that prior to the ssw the stratospheremesosphere system was dominated by an upward and westward propagating 16 day wave detected simultaneously in the ukmo and mlt zonal and meridional wind data after the onset of the ssw longer period 22 24 days oscillations were observed in the zonal and meridional mlt winds these likely include the upward propagation of stationary planetary waves from below and in situ generation of disturbances by the dissipation and breaking of gravity waves filtered by stratospheric winds citation pancheva d et al 2008 planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 j geophys res 113 d12105 doi 10 1029 2007jd009011

platinum group minerals in alpine chromitites from southwestern oregon electron microprobe and scanning electron microscopy the platinum group minerals found in the chromitites are laurite porous ru rich alloys os ir and pt rich alloys with highly variable compositions an ir cu rich sulfide a pt arsenide and three relatively rare platinum group sulfides the platinum group minerals are 1 to 30 mu m in diameter and occur as inclusions in chromite grains some of these inclusions also contain silicates and millerite base metal alloys largely ni fe occur in cracks in the chromitites along with magnetite ferritchromite chromian chlorite and serpentine the primary platinum group mineral assemblage is interpreted to have formed before or during crystallization of the chromite grains and not as a result of exsolution from the chromite modified journal abstract

the chromite deposits of the troodos complex cyprus evidence for the role of a fluid phase accompanying chromite formation the troodos ophiolite of cyprus hosts chromite deposits both as podiform bodies within the basal harzburgite and as lesser layers and schlieren within the overlying dunites and clinopyroxene dunites of the metacumulate sequence all chromitite types have been studied from both field and mineralogical aspects with particular emphasis on the chemistry of the ubiquitous silicate inclusions within chromite grains two distinct inclusion assemblages have been documented chromites from podiform bodies contain abundant hornblende serpentine ortho and clinopyroxene and lesser olivine while those from the metacumulates host pargasite albite serpentine and rare pyroxenes this implies that no single silicate inclusion assemblage in chromite can be considered typically ophiolitic the presence of an alkalirich fluid phase during chromite crystallization as evidenced by the unusual mineralogy of these inclusions has already been widely discussed in the literature however the marked stratigraphic control of inclusion types in chromite as reported here enables more complete modelling of the evolution of this phase to be made

high cr and high al chromitites from the sagua de tanamo district mayari cristal ophiolitic massif eastern cuba constraints on their origin from mineralogy and geochemistry of chromian spinel and platinum group elements article i nfo several chromitite bodies of variable sizes are hosted in dunite harzburgite of the small b3 km mining district of sagua de tanamo in the mayari cristal ophiolitic massif eastern of cuba the chromian spinel in these bodies displays a large range in cr cr cr al atomic ratio from 0 74 to 0 45 in high cr chromitites cr and ti contents increase from harzburgite to dunite to chromitite a roughly opposite trend of variation in cr is observed in high al chromitites although in this case ti distributes randomly the differences in the type of chromian spinel i e high cr or high al in the chromitite coincide with a different behavior of the platinum group elements pge whereas high cr chromitites are rich in pge and contain abundant grains of platinum group minerals pgm high al chromitites are systematically poor in pge and in pgm the calculated melts in equilibrium with chromian spinel of high cr chromitite are island arc thoeliites iat with boninitic affinity whereas those in equilibrium with chromian spinel of high al chromitites are back arc basin basalts babb the formation of high cr chromitites is interpreted as a result of the extensive reaction of harzburgite with migrating island arc tholeiite melts of boninitic affinity melt rock reaction produces boninitic melts with variable composition and porous dunitic channels in which the mixing mingling of melts promotes crystallization of mononomineralic high cr chromian spinel in contrast high al chromitites formed by the mixing mingling of babb melts within conduits not in equilibrium with dunite percolation of primitive babb melts through pre existing dunite dissolved olivine producing melt conduits in which babb melts mixed and formed high al chromian spinel the higher pge and pgm in high cr chromitites is not only a function of the degree of partial melting but is linked to interaction between the migrating melt and mantle harzburgite during the formation of the chromitite the coexistence of both types of chromitites in one small mining district reflects the temporal and or spatial variations of separate melt intrusions emplaced in different subarc mantle domains during the opening of a back arc basin in a supra subduction zone environment

spinel compositions of mantle hosted chromitite from the eastern anatolian ophiolite body turkey implications for deep and shallow magmatic processes abstract the eastern anatolian accretionary complex includes several ophiolitic megablocks and or tectonic slivers within a 150 180 km long east west trending complex formed during the late cretaceous tertiary in eastern turkey the alabayir mollatopuz yukaribalcikli and mehmetalan ophiolites are megablocks or tectonic slivers containing locally massive nodular or schlieren banded chromitite layers these podiform chromitites formed in mantle sequences and are classified as high cr chromitites cr 0 63 0 88 mg 0 50 0 64 0 01 0 5 wt tio 2 5 7 18 8 wt al 2 o 3 calculated parental melt compositions of these chromitites indicate boninite magma characteristics 8 2 13 4 wt al 2 o 3 0 64 1 50 feo mgo the pge patterns also support the view that they crystallized from a boninitic melt the total pge contents of chromitites vary between 79 and 390 ppb pd ir ratios of chromitites vary from 0 07 to 0 28 and are consistent with an ipge fractionated nature the examined chromitites were divided into two groups in terms of their mineral chemistry group i alabayir mollatopuz yukaribalcikli and mehmetalan i chromitites group ii mehmetalan ii chromitites mineral chemistry of these chromitites and their parental melt composition indicate that group i chromitites were probably formed at shallow mantle depths and that group ii chromitites formed in deeper parts of the mantle mineral chemistry of these eastern anatolia high cr chromitites indicate that they formed not only in the deeper mantle but also in shallower parts of the moho transition zone